DESCRIPTION
OPTICAL FILM AND ITS PRODUCTION METHOD,
POLARIZER AND LIQUID CRYSTAL DISPLAY DEVICE
TECHNICAL FIELD
The present invention relates to an optical film and its
production method, a polarizer and a liquid crystal display
device .
BACKGROUND ART
As capable of saving power energy consumption and capable
of being thin-walled, liquid crystal display devices are widely
employed as image display devices such as TVs, personal
computers, etc. The liquid crystal display device comprises
a polarizer arranged on both sides of the liquid crystal cell
therein, in which the polarizer comprises a polarizing film
having iodine or dye adsorbed and aligned therein and sandwiched
between transparent resin layers put on both sides thereof. In
this, the transparent resin layers act to protect the polarizing
element, for which a cellulose ester film is well used.
With the recent popularization of such liquid crystal
display devices, much desired are further thin-walled,
large-sized and high-performance devices.
A cellulose ester film has a high transmittance, and by
dipping in an aqueous alkali solution, its surface is saponified
and hydrophilicated to thereby realize excellent adhesiveness
to a polarizing element. However, the film has a problem of
dimensional change through moisture absorption and water
removal in environmental temperature/humidity change.
Another problem is that, when the cellulose ester film is
incorporated in a liquid crystal display device and when the
other constitutive parts of the device that have been deformed
through aging degradation or the like therein are kept in
contact with the film, display fluctuation often occurs; and
the problem has become considered serious with the recent
tendency toward advanced demand for body thickness reduction.
For solving the problems, there has been proposed an
acrylic resin film having a small moisture absorption and having
a small photoelastic coefficient, as a film that could be
substitutable for the cellulose ester film; however, it could
not be said that the adhesiveness of the film of the type to
a polarizing element could be sufficient, and therefore there
still remains a problem in that an acrylic single-layer film
could hardly be adhered to a polarizing element.
In that situation, there has been proposed a technique
of laminating these different types of films to solve the
problems with the individual films (see JP-A 2001-215331) .
JP-A 2001-215331 discloses a technique of producing a
cellulose triacetate/acrylic resin laminate film according to
a co-casting method. For example, in Examples in the patent
publication, described is a configuration of cellulose
triacetate film/acrylic resin film/cellulose triacetate film.
However, the acrylic resin used in Examples in the patent
publication is not specifically identified as a material.
On the other hand, as the acrylic resin, one having a
molecular weight of 100,000 or so is generally used for film
formation. Precisely, it is naturally impossible to form a
high-molecular-weight acrylic resin film according to a melt
casting method. An acrylic resin film may be formed according
to a solution casting method, but in such a case, a dope having
a viscosity suitable for solution casting must be prepared.
Heretofore, an acrylic resin having a molecular weight of
300, 000 or so can form a dope highly suitable for casting film
formation, and the acrylic resin of the type has heretofore been
used in film formation.
SUMMARY OF THE INVENTION
The dope composition in Examples in JP-A 2001-215331 is
merely such that, when an acrylic resin having a molecular
weight of 300,000 or so therein, the composition could have a
good aptitude for ordinary solution casting film formation; and
the present inventors have tried the method described in JP-A
2001-215331, using the above-mentioned ordinary acrylic resin,
but have found that there occurs another problem in point o f
the film surface condition, especially in that the laminate film
surface is roughened.
A n object o f the invention is to provide an optical film
comprising a cellulose ester film, which, when the optical film
is incorporated in a liquid crystal display device and when the
other constitutive parts in the device are kept in contact with
the cellulose ester film, hardly causes display unevenness and
which is therefore easy to adhere to a polarizing element and
has a good film surface condition.
For solving the above-mentioned problem, the inventors
have assiduously studied and, as a result, have found that, in
case where an acrylic resin and a cellulose ester resin are
co-cast to form an acrylic resin/cellulose ester resin laminate
film, when the combination between the concentration and the
viscosity o f the dope is suitably defined, then the surface
condition o f the laminate film can b e dramatically improved.
The inventors have further found that, for suitably defining
the relationship between the dope concentration and viscosity,
an acrylic resin having a much higher molecular weight than the
ordinary acrylic resin generally used in formation o f optical
film must b e indispensably used. Based on these findings, the
inventors have completed the present invention.
The following constitution can solve the above-mentioned
problem.
[1] A n optical film having an acrylic resin layer containing
an acrylic resin, and, a s formed on the surface of the acrylic
resin layer, at least one cellulose acylate layer containing
a cellulose acylate, wherein the weight-average molecular
weight o f the acrylic resin used a s the main ingredient in the
acrylic resin layer is from 600,000 to 4,000,000.
[2] The optical film o f [1], wherein the weight-average
molecular weight o f the cellulose acylate used as the main
ingredient in the cellulose acylate layer is from 50,000 to
500,000.
[3] The optical film o f [1] or [2], wherein the thickness o f
the acrylic resin layer is from 20 to 60 , and the thickness
o f every cellulose acylate layer is from 1 to 10 urn.
[4] The optical film o f any one o f [1] to [3], wherein the
proportion of the total thickness of the cellulose acylate layer
to the overall film thickness is at most 40%.
[5] The optical film of any one of [1] to [4], wherein the
degree of substitution with the acyl group in the cellulose
acylate is from 1.2 to 3.0.
[6] The optical film of any one of [1] to [5], wherein the
weight-average molecular weight of the acrylic resin used as
the main ingredient in the acrylic resin layer is from 1 ,000, 000
to 1,800,000.
[7] The optical film of any one of [1] to [6], which has a
photoelastic coefficient of from -5.0 to 5.0 x 10 12 Pa-1 .
[8] The optical film of any one of [1] to [7], wherein the
in-plane retardation Re defined by the following formula (I)
and the thickness-direction retardation Rth defined by the
following formula (II) satisfy the following formula (III) and
the following formula (IV) in an environment at 25°C and at a
relative humidity of 60%, and wherein the absolute value o f the
difference between the value Rth measured in an environment at
25°C and at a relative humidity of 10% and the value Rth measured
in an environment at 25°C and at a relative humidity o f 80% is
at most 10 nm:
(I) Re = (nx - ny) x d
(ID Rth = { (nx + ny) 2 - nz} x d
(III) |Re| < 10 nm
(IV) |Rth| < 25 nm
wherein nx means the in-plane refractive index of the film in
the slow axis direction; ny means the in-plane refractive index
of the film in the fast axis direction; n z means the refractive
index of the film in the thickness direction; d means the film
thickness (nm) .
[9] The optical film of any one of [1] to [8], wherein the
cellulose acylate layer is provided on both surfaces of the
acrylic resin layer.
[10] A method for producing an optical film comprising casting
at least two types of dopes (A) and (B) each containing a
thermoplastic resin and an organic solvent onto a casting
substrate simultaneously or successively in the order of
(A) - (B) - (A) from the casting substrate side, and removing the
organic solvent, wherein the dope (A) contains a cellulose
acylate and the dope (B) contains an acrylic resin having a
weight-average molecular weight of from 600,000 to 4,000,000.
[11] The method for producing an optical film of [10] , wherein
the weight-average molecular weight of the cellulose acylate
contained in the dope (A) is from 50,000 to 500,000.
[12] The method for producing an optical film of [10] or [11],
wherein the solid concentration of the dope (A) and the dope
(B) each is from 16 to 30% by mass.
[13] The method for producing an optical film of any one of
[10] to [12], wherein the absolute value of the difference
between the solid concentration of the dope (A) and that of the
dope (B) is at most 10% by mass.
[14] The method for producing an optical film of any one of
[10] to [13] , wherein the complex viscosity of the dope (A) and
the dope (B) each is from 10 to 80 Pa-s and the complex viscosity
of the dope (B) is larger than the complex viscosity of the dope
(A) .
[15] The method for producing an optical film of any one of
[10] to [14], wherein in the organic solvent contained in the
dope (A) and the dope (B) , the proportion of methanol to the
entire organic solvent in the dope is from 20 to 35% by mass.
[16] An optical film produced according to the optical film
production method of any one of [10] to [15] .
[17] A polarizer comprising a polarizing element and the
optical film of any one of [1] to [9] and [16],
[18] A liquid crystal display device comprising the optical
film of any one of [1] to [9] and [16] or the polarizer of [17] .
According to the invention, there can be provided an
optical film comprising a cellulose ester film, which, when the
optical film is incorporated in a liquid crystal display device
and when the other constitutive parts in the device are kept
in contact with the cellulose ester film, hardly causes display
unevenness and which is therefore easy to adhere to a polarizing
element and has a good film surface condition; and a method for
producing the optical film.
BRIEF DESCRIPTION OF DRAWING
Fig. 1 is a graphical view showing one example of a drum
casting apparatus. In Fig. 1 , 101 is casting apparatus, 102
is drum, 14 is casting die, 12 is dope, PS is casting start point,
105 is condenser plate, 53 is liquid receiver, 56 is collector
tank, 36 is film and 37 is peeling roller.
MODES FOR CARRYING OUT THE INVENTION
Embodiments of carrying out the invention are described
in detail hereinunder, however, the invention should not be
limited to these. In this description, when a numerical value
indicates a physical value, a characteristic value or the like,
the numerical range expressed by the wording " (numerical value
1 ) to (numerical value 2 )" means the range that falls "from the
(numerical value 1 ) or more to the (numerical value 2 ) or less".
(Meth)acryl means methacryl or acryl; and (meth) acryloyl means
methacryloyl or acryloyl. In this description, the wording "as
the main ingredient" means that the amount of the ingredient
is at least 50% by mass. For example, the main ingredient of
the cellulose acylate contained in the cellulose acylate layer
means the cellulose acylate that accounts for at least 50% by
mass of the cellulose acylate contained in the cellulose acylate
layer.
[Optical Film]
The optical film of the invention (hereinafter this may
be referred to as the film of the invention) has an acrylic resin
layer containing an acrylic resin, and, as formed on the surface
of the acrylic resin layer, at least one cellulose acylate layer
containing a cellulose acylate, wherein the weight-average
molecular weight of the acrylic resin used as the main
ingredient in the acrylic resin layer is from 600,000 to
4 ,000, 000.
In the film of the invention, such an acrylic resin having
a molecular weight of from 600,000 to 4,000,000, which is much
larger than that of the acrylic resin heretofore used in the
field of optical film, is used, and therefore the film surface
condition of the laminate film can be greatly improved.
In addition, the cellulose acylate layer may be formed
on one surface of the acrylic layer, but preferably formed on
both surfaces thereof for the purpose of well controlling the
physical properties and the behavior to environmental change
of the film.
Preferred embodiments of the film of the invention are
described below.

(Ratio of Cellulose Acylate Layer and Acrylic Resin Layer)
In the film of the invention, preferably, the thickness
of the acrylic resin layer is from 20 to 60 , and the thickness
of every cellulose acylate layer is from 1 to 10 um.
Also preferably, the thickness of one cellulose acylate
layer is from 1 to 10 um, more preferably from 1 to 8 , even
more preferably from 1 to 5 . Also preferably, the thickness
of the acrylic resin layer is from 20 to 60 , more preferably
from 25 to 50 um, even more preferably from 25 to 40 um.
The overall thickness of the entire optical film as a
laminate is preferably from 11 to 240 um, more preferably from
15 to 150 um, most preferably from 20 to 100 um, still more
preferably from 20 to 50 um.
Also preferably, the proportion of the total thickness
of the cellulose acylate layer to the overall film thickness
of the film is at most 40%, more preferably from 1 to 30%, even
more preferably from 5 to 20%. The total thickness of the
cellulose acylate layer as referred to herein means the total
thickness of two cellulose acylate layers, if any, in the film.
When these requirements are satisfied, the surface
condition of the cast film may be more bettered. In addition,
the interfacial adhesiveness and the curling resistance of the
optical film may be bettered and the water absorption thereof
may be lowered.
(Film Surface Condition)
The film of the invention is characterized in that the
maximum difference between the largest thickness and the
smallest thickness thereof (P-V value) is small.
The maximum difference between the largest thickness and
the smallest thickness of the film (P-V value) may be measured
according to a known method, for example, using a fringe
analyzer, a laser displacement meter, a contact film thickness
gauge, etc.
In the method of using a fringe analyzer, for example,
a fringe analyzer, FUJINON FX-03 can be used for the measurement.
In the other method than the method of using a fringe analyzer,
for example, the film thickness within a range of a circle drawn
around a center point in the film and having a diameter of 60
mm may be measured using a laser displacement meter, a contact
film thickness gauge or the like, and from the found data, the
maximum difference between the largest thickness and the
smallest thickness of the film may be computed.
Preferably, the maximum difference between the largest
thickness and the smallest thickness (P-V value) of the film
of the invention is at most 3.0 um, more preferably at most 1.1
, even more preferably at most 0.9 um.
(Retardation)
In this description, Re () and Rth ( ) each mean the
in-plane retardation and the thickness-direction retardation
of the film at a wavelength of . In this description, the
wavelength is 550 nm unless otherwise specifically indicated.
Re () is measured by applying a light having a wavelength of
nm in the normal direction of the film, using KOBRA-21ADH or
WR (by 0ji Scientific Instruments). In selecting the
measurement wavelength nm, a wavelength selection filter may
be exchanged by manual, or the measured data may be converted
according to the corresponding program or the like.
When the film to be analyzed is represented by a monoaxial
or biaxial index ellipsoid, then its Rth^) may be computed
according to the method mentioned below.
Rth ( ) is determined as follows: With the in-plane slow
axis (determined by KOBRA 21ADH or WR) taken as the tilt axis
(rotation axis) of the film (in case where the film has no slow
axis, the rotation axis of the film may be in any in-plane
direction of the film) , Re () of the film is measured at 6 points
in all thereof, from the normal direction of the film up to 50
degrees on one side relative to the normal direction thereof
at intervals of 10°, by applying a light having a wavelength
of nm from the tilted direction of the film. Based on the
thus-determined retardation data of Re (), the assumptive mean
refractive index and the inputted film thickness, Rth^) of the
film is computed with KOBRA 21ADH or WR.
In the above, with the in-plane slow axis from the normal
direction taken as the rotation axis thereof, when the film has
a zero retardation value at a certain tilt angle, then the symbol
of the retardation value of the film at a tilt angle larger than
that tilt angle is changed to a negative one, and then applied
to KOBRA 21ADH or WR for computation.
With the slow axis taken as the tilt axis (rotation axis)
(in case where the film has no slow axis, the rotation axis of
the film may be in any in-plane direction of the film) , the
retardation values of the film are measured in any tilted two
directions; and based on the data, the assumptive mean
refractive index and the inputted film thickness, Rth may be
computed according to the following formulae (11) and (12):
wherein Re(0) means the retardation value of the film in the
direction titled by an angle from the normal direction.
In the formula (11) , nx means the in-plane refractive
index of the film in the slow axis direction; ny means the
in-plane refractive index of the film in the direction vertical
to nx; nz means the refractive index of the film vertical to
nx and ny; and d means the film thickness.
(12) Rth = ((nx + ny) /2 - nz) d .
When the film to be analyzed could not be represented by
a monoaxial or biaxial index ellipsoid, or that is, when the
film does not have an optical axis, then its Rth ( ) may be
computed according to the method mentioned below.
With the in-plane slow axis (determined by KOBRA 21ADH
or WR) taken as the tilt axis (rotation axis) of the film, Re ( )
of the film is measured at 11 points in all thereof, from -50°
to +50° relative to the normal direction of the film at intervals
of 10°, by applying a light having a wavelength of nm from
the tilted direction of the film. Based on the thus-determined
retardation data R ( ) , the assumptive mean refractive index
and the inputted film thickness, Rth^) of the film is computed
with KOBRA 21ADH or WR.
In this, for the assumptive mean refractive index,
referred to are the data in Polymer Handbook (John Wiley & Sons,
Inc.) or the data in the catalogues of various optical films.
Films of which the mean refractive index is unknown may b e
analyzed with an Abbe's ref ractiometer to measure the mean
refractive index thereof. Data of the mean refractive index
of some typical optical films are mentioned below. Cellulose
acylate (1.48), cycloolefin polymer (1.52), polycarbonate
(1.59), polymethyl methacrylate (1.49), polystyrene (1.59).
With the assumptive mean refractive index and the film thickness
inputted thereinto, Kobra 21ADH or WR can compute nx, ny and
nz. From the thus-computed data nx, ny and nz, N z = (nx - nz) / (nx
- ny) is induced.
Preferably in the film of the invention, the in-plane
retardation Re defined b y the following formula (I) and the
thickness-direction retardation Rth defined b y the following
formula (II) satisfy the following formula (III) and the
following formula (IV) in an environment at 25°C and at a
relative humidity of 60%, and the absolute value of the
difference between the value Rth measured in an environment at
25°C and at a relative humidity of 10% and the value Rth measured
in an environment at 25°C and at a relative humidity of 80% is
at most 10 nm:
(I) Re = (nx - ny) x d
(II) Rth = { (nx + ny) 12 - nz} x d
(III) |Re| < 10 nm
(IV) |Rth| < 25 nm
wherein nx means the in-plane refractive index of the film in
the slow axis direction; ny means the in-plane refractive index
of the film in the fast axis direction; n z means the refractive
index of the film in the thickness direction; d means the film
thickness (nm) .
Preferably, the film of the invention satisfies |Re| < 10
nm, more preferably |Re| < 5 nm, even more preferably |Re| < 2
nm.
Also preferably, the film of the invention satisfies |Rth|
< 25 nm, more preferably |Rth| < 15 nm, even more preferably |Rth|
(Humidity Dependence of Rth)
In the film of the invention, the humidity dependence of
Rth (ARth = Rth(10%) - Rth(80%)) is preferably at most 10 nm,
more preferably less than 8 nm, even more preferably less than
5 nm, still more preferably less than 3 nm.
In the invention, the humidity dependence of Re (ARe) and
the humidity dependence of Rth (ARth) are computed according
to the following formulae, based on the in-plane and
thickness-direction retardation values at a relative humidity
of H (unit, %), Re (H% ) and Rth(H%):
ARe = Re (10%) - Re (80%) [nm]
ARth = Rth (10%) - Rth (80%) [nm]
Re (H% ) and Rth (H%) are the retardation values o f the film
that has been conditioned at 25°C and at a relative humidity
of H% for 24 hours, and the values thereof are measured and
computed according to the same methods as above, at 25°C and
at a relative humidity of H % and at a measurement wavelength
of 590 nm. A mere expression Re with no indication relating to
the relative humidity means the value of retardation measured
at a relative humidity of 60%.
More preferably, the retardation values of the optical
film as measured at different humidity satisfy the following
relational formulae.
|ARe| < 8 nm, and |ARth| < 8 nm;
even more preferably,
|ARe| < 5 nm, and |ARth| < 5 nm;
still more preferably,
|ARe| < 3 nm, and |ARth| < 3 nm.
Controlling the retardation values of the film at
different humidity in the manner a s above makes it possible to
reduce the retardation change of the film in varying external
environments and therefore makes it possible to provide
high-reliability liquid crystal display devices comprising the
film.
Reducing the ARth of the optical film of the invention
may bring about a favorable effect that, when the film is
incorporated in a liquid crystal display device, a problem of
circular color unevenness (display unevenness ) that may be seen
in watching the device obliquely on the display panel thereof
under a specific condition could be solved.
(Photoelastic Coefficient)
Preferably, the absolute value of the photoelastic
coefficient of the film of the invention is at most 5.0 x 10~12
Pa-1, more preferably at most 3 x 10~12 Pa 1, even more preferably
at most 1 x 10 12 Pa-1 . The photoelastic coefficient is the
property inherent in a substance; and rather few substances
could express the photoelastic coefficient thereof. For
example, most polymer resins express birefringence owing to
external stress or thermal stress given thereto. The sign of
the photoelastic coefficient may be defined in relation to the
direction of the applied stress. Specifically, in case where
a tensile stress is given to a medium (polymer resin) , the sign
of the photoelastic coefficient of the medium can be expressed
as plus or minus of the photoelastic coefficient c represented
by the following formula (1) , relative to the refractive index
P ara to the polarized light having a polarization plane in the
direction parallel to the tensile stress, and the refractive
index nper p to the polarized light having a polarization plane
in the direction perpendicular to that parallel direction,
c = / = (n para - nperp )/ (1)
In other words, in case where npara is larger than nperp
the photoelastic coefficient is plus, but in case where the
former is smaller than the latter, the photoelastic coefficient
is minus. When the photoelastic coefficient of the film of the
invention falls within a range of from -5.0 x 10~12 to 5.0 x 10~12
Pa-1, it is favorable since the liquid crystal display device
comprising the film may be free from a problem of display
unevenness. In particular, in case where the film of the
invention is stretched and then incorporated in a liquid crystal
display device, it is especially desirable that the
photoelastic coefficient of the film falls within the above
range .
(Film Width)
Preferably, the width of the film of the invention is from
400 to 2500 mm, more preferably at least 1000 mm, even more
preferably at least 1500 mm, still more preferably at least 1800
mm.

The film of the invention has an acrylic resin layer
containing an acrylic resin, in which the weight-average
molecular weight of the acrylic resin to be used as the main
ingredient of the acrylic resin layer is from 600,000 to
4 ,000, 000.
(Acrylic Resin)
The acrylic resin for use in the invention includes a
methacrylic resin, for which well known are
acrylate/methacrylate derivatives, especially
acrylate/methacrylate (co) polymers . Not specif ically defined,
the acrylic resin preferably comprises from 50 to 99% by mass
of a methyl methacrylate unit and from 1 to 50% by mass of any
other monomer unit copolymerizable with the methyl methacrylate
unit, from the viewpoint of obtaining a film having a small
photoelastic coefficient.
In the acrylic resin, the other copolymerizable monomer
includes alkyl methacrylates in which the alkyl group has from
2 to 18 carbon atoms, alkyl acrylates in which the alkyl group
has from 1 to 18 carbon atoms; a ,-unsaturated acids such as
acrylic acid, methacrylic acid, etc.; unsaturated
group-containing dicarboxylic acids such as maleic acid,
fumaric acid, itaconic acid, etc.; aromatic vinyl compounds
such as styrene, a-methylstyrene, etc.; a ,-unsaturated
nitriles such as acrylonitrile, methacrylonitrile, etc.;
maleic anhydride, maleimide, N-substituted maleimides,
glutaric anhydride, etc. One alone or two or more of these
monomers may be used as the copolymerization component, either
singly or as combined.
Of those, preferred are methyl acrylate, ethyl acrylate,
n-propyl acrylate, n-butyl acrylate, s-butyl acrylate,
2-ethylhexyl acrylate, etc., from the viewpoint of the thermal
decomposition resistance and the flowability of the copolymers;
and more preferred are methyl acrylate and n-butyl acrylate.
As the resin capable of forming an optical film, of which
the performance change is small even in high-temperature and
high-humidity environments and which is highly transparent,
preferred is an acrylic resin preferably has an alicyclic alkyl
group as the copolymerization component thereof, or an acrylic
resin of which the main chain of the molecule has a cyclic
structure formed through intramolecular cyclization. One
preferred embodiment of the acrylic resin of which the main
chain of the molecule has a cyclic structure formed through
intramolecular cyclization is an acrylic thermoplastic resin
including a lactone ring-containing polymer; and the preferred
resin composition and the preferred production method are
described in JP-A 2006-171464. Another preferred embodiment
is a resin containing glutaric anhydride as the
copolymerization component thereof; and the copolymerization
component and the concrete production method are described in
JP-A 2004-070296.
(Weight-Average Molecular Weight of Acrylic Resin)
In the film of the invention, the weight-average
molecular weight of the acrylic resin used as the main
ingredient in the acrylic resin layer is from 600,000 to
4,000,000, preferably from 800,000 to 3,000,000, more
preferably from 1,000,000 to 1,800,000.
The weight-average molecular weight of the acrylic resin
may be measured through gel permeation chromatography.
Preferably, the molecular weight of the acrylic resin
does not lower during the process of producing the film of the
invention. For example, in the process of producing the film
of the invention, the film may be heated in the step of drying
the film for removing the solvent therefrom. In this step, the
acrylic resin may be thermally decomposed and the molecular
weight thereof may be lowered. Concretely, in case where the
molecular weight of the acrylic resin before film formation is
100, it is desirable that the molecular weight of the acrylic
resin in the film of the invention after film formation is larger
than 60, more preferably larger than 75, even more preferably
larger than 90.
The production method for the acrylic resin is not
specifically defined, for which is employable any known method
of suspension polymerization, emulsion polymerization, bulk
polymerization, solution polymerization or the like.
Two or more different types of acrylic resins may be used
here as combined.
(Other Thermoplastic Resin Capable of Being Combined with
Acrylic Resin)
The acrylic resin may contain any other thermoplastic
resin. The thermoplastic resin usable in the invention is
preferably one having a glass transition temperature of not
lower than 100°C and a total light transmittance of at least
85%, as capable of enhancing the heat resistance and the
mechanical strength of the film formed of it combined with the
acrylic resin.
Regarding the content of the acrylic resin and the other
thermoplastic resin in the acrylic resin layer, the ratio by
mass of [acrylic resin/ (total thermoplastic resin)] x 100 is
preferably from 30 to 99% by mass, more preferably from 50 to
97% by mass, even more preferably from 60 to 95% by mass. When
the content of the acrylic resin in the acrylic resin layer is
at least 30% by mass, it is favorable since the resin can
sufficiently exhibit heat resistance.
The other thermoplastic resin includes, for example,
olefinic polymers such as polyethylene, polypropylene,
ethylene/propylene copolymer, poly (4-methyl-l-pentene) ,
etc.; halogenopolymers such as polyvinyl chloride, vinyl
chloride resin, etc.; styrenic polymers such as polystyrene,
styrene-methyl methacrylate copolymer, styrene/acrylonitrile
copolymer, acrylonitrile/butadiene/styrene block copolymer,
etc.; polyesters such as polyethylene terephthalate,
polybutylene terephthalate, polyethylene naphthalate, etc.;
polyamides such as nylon 6 , nylon 66, nylon 610, etc.;
polyacetals; polycarbonates; polyphenylene oxides;
polyphenylene sulfides; polyether ether ketones;
polysulf ones ; polyether sulfones; polyoxybenzylenes ;
polyamidimides ; rubbery polymers such as ABS resins or ASA
resins mixed with polybutadiene rubber, acrylic rubber, etc.
The rubbery polymer preferably has a graft moiety having a
composition miscible with the cyclic polymer in the invention,
in the surface thereof, and more preferably the mean particle
size of the rubbery polymer is at most 100 nm, even more
preferably at most 70 nm from the viewpoint of increasing the
transparency of the formed film.
Preferably, the other thermoplastic resin is
thermodynamically miscible with the acrylic resin. A s the
other thermoplastic resin of the type, preferred are an
acrylonitrile/styrene copolymer having a vinyl cyanide monomer
unit and an aromatic vinyl monomer unit, and a polyvinyl
chloride resin, etc. Of those, more preferred is an
acrylonitrile/styrene copolymer as capable of readily
producing an optical film having a glass transition temperature
of not lower than 120°C, an in-plane retardation per 100 of
at most 20 n and a total light transmittance of at least 85%.
As the acrylonitrile/styrene copolymer, concretely, one
having a copolymerization ratio by mol of from 1/10 to 10/1 is
advantageously used here.
(Cellulose Acylate Layer>
The film of the invention has at least one cellulose
acylate layer containing a cellulose acylate, as formed on the
surface of the above-mentioned acrylic layer therein.
(Type of Cellulose Acylate)
The cellulose acylate for use in the invention is not
specifically defined. The starting cellulose includes cotton
linter and wood pulp (hardwood pulp, softwood pulp) , etc. ; and
any cellulose acylate obtained from any starting cellulose can
be used herein. As the case may be, different starting
celluloses may be mixed for use herein. The starting cellulose
materials are described in detail, for example, in Marusawa &
Uda's "Plastic Material Lecture (17), Cellulosic Resin" (by
Nikkan Kogyo Shinbun, 1970) , and in Hatsumei Kyokai Disclosure
Bulletin No. 2001-1745, pp. 7-8.
(Degree of Acyl Substitution of Cellulose Acylate)
Preferably, the cellulose acylate for use in the
invention has a total degree of substitution with acyl group
of from 1.2 to 3.0.
Preferably, the cellulose acylate for use in the
invention satisfies the following conditions where TA-Total
means the total degree of substitution with acyl group, TA2
means the degree of substitution with acyl group having 2 carbon
atoms, and TA3 means the degree of substitution with acyl group
having from 3 to 7 carbon atoms. Satisfying the following
conditions, there can be obtained an optical film excellent in
point of the adhesiveness thereof to neighboring layers, the
drum releasability thereof, and the curling resistance thereof.
2.2 < TA-Total < 3.0
1.5 < TA2 < 3.0
0.0 < TA3 < 0.7
More preferably, the cellulose acylate satisfies the
following conditions:
2.5 < TA-Total < 3.0
2.4 < TA2 < 3.0
0.0 < TA3 < 0.1
Especially preferably, the cellulose acylate for use in
the invention is at least one selected from cellulose acetate,
cellulose acetate propionate, cellulose acetate butyrate,
cellulose acetate benzoate, cellulose propionate, cellulose
butyrate. Of those, more preferred as the cellulose acylate
are cellulose acetate and cellulose acetate propionate; and
even more preferred is triacetyl cellulose.
The degree of substitution with acetyl group and the
degree of substitution with other acyl group may be determined
according to the method defined in ASTM-D817-96.
(Weight-Average Molecular Weight of Cellulose Acylate)
Regarding the weight-average molecular weight (Mw) of the
cellulose acylate for use in the invention, the weight-average
molecular weight of the cellulose acylate for use as the main
ingredient in the cellulose acylate layer is preferably from
50,000 to 500,000 from the viewpoint of bettering the film
surface condition, more preferably from 80, 000 to 400, 000, even
more preferably from 100,000 to 300,000.
On the other hand, the weight-average molecular weight
of the cellulose acylate for use in the invention is more
preferably from 75,000 to 300,000 from the viewpoint of the
adhesiveness thereof to acrylic resin, even more preferably
from 100,000 to 240,000, still more preferably from 160,000 to
240, 000. When the weight-average molecular weight (Mw) of the
cellulose acylate is at least 75, 000, then it is favorable since
the self-film formability of the cellulose acylate layer is
bettered and the layer can exhibit improved adhesiveness. In
the invention, two or more different types of cellulose acylates
may be combined and used.

The optical film of the invention may contain additives
in the acrylic resin layer and the cellulose ester layer, along
with one or more thermoplastic resins to be the main ingredient
in these layers.
(Plasticizer)
Preferably, a plasticizer is added to the optical film
of the invention for the purpose of imparting softness to the
film, improving the dimensional stability of the film and
improving the moisture resistance thereof.
Preferably, the plasticizer for use in the invention
contains a resin component having a molecular weight of from
500 to 100, 000. For example, there may be mentioned the
above-mentioned acrylic resin, polyester and polyether
described in JP-A 2002-22956, polyester ether, polyester
urethane and polyester described in JP-A 5-197073, copolyester
ether described in JP-A 2-292342, epoxy resin and novolak resin
described in JP-A 2002-146044, etc.
As the plasticizer excellent in evaporation resistance,
bleeding-out resistance and haze reduction, for example,
preferred for use herein are polyester diols having a hydroxyl
group at both terminals, described in JP-A 2009-98674. As the
plasticizer excellent in planarity and the low haze of the
optical film containing it, preferred are sugar ester
derivatives described in WO2009/031464 .
«Polycondensate Ester»
In the invention, a polycondensate ester is preferably
used as the polymer plasticizer.
The polycondensate ester usable in the invention may be
produced from at least one dicarboxylic acid selected from
aliphatic dicarboxylic acids having from 2 to 20 carbon atoms
and aromatic dicarboxylic acids having from 8 to 20 carbon atoms,
and at least one diol selected from aliphatic diols having from
2 to 12 carbon atoms, alkyl ether diols having from 4 to 20 carbon
atoms, and aromatic ring-containing diols having from 6 to 20
carbon atoms. For the production method, employable is any
known method of dehydrating condensation of dicarboxylic acid
and diol, or addition and dehydrating condensation of
dicarboxylic anhydride to diol.
Dicarboxylic acids and diols preferably used in
production of the polycondensate ester for use in the invention
are described below.
As the dicarboxylic acid, any of aliphatic dicarboxylic
acids and aromatic dicarboxylic acids is usable herein.
The aliphatic dicarboxylic acid includes, for example,
oxalic acid, malonic acid, succinic acid, maleic acid, fumaric
acid, glutaric acid, adipic acid, pimelic acid, suberic acid,
sebacic acid, azelaic acid, undecanedicarboxylic acid,
dodecanedicarboxylic acid, 1 ,4-cyclohexanedicarboxylic acid,
etc. Above all, preferred are malonic acid, succinic acid,
maleic acid, fumaric acid, glutaric acid, adipic acid, pimelic
acid, suberic acid, sebacic acid, azelaic acid,
undecanedicarboxylic acid, dodecanedicarboxylic acid, and
1 ,4-cyclohexanedicarboxylic acid.
The aromatic dicarboxylic acid includes phthalic acid,
isophthalic acid, terephthalic acid, 1 ,4-xylylenedicarboxylic
acid, 1 ,5-naphthalenedicarboxylic acid,
1 ,4-naphthalenedicarboxylic acid,
1 ,8-naphthalenedicarboxylic acid,
2 ,8-naphthalenedicarboxylic acid,
2,6-naphthalenedicarboxylic acid, etc.
Of those, more preferred as the aliphatic dicarboxylic
acid are malonic acid, succinic acid, maleic acid, fumaric acid,
glutaric acid, adipic acid, azelaic acid, and
1 ,4-cyclohexanedicarboxylic acid; and more preferred as the
aromatic dicarboxylic acid are phthalic acid, terephthalic acid,
isophthalic acid, 1 ,5-naphthalenedicarboxylic acid, and
1 ,4-naphthalenedicarboxylic acid. Even more preferred as the
aliphatic dicarboxylic acid are succinic acid, glutaric acid,
and adipic acid; and even more preferred as the aromatic
dicarboxylic acid are phthalic acid, terephthalic acid, and
isophthalic acid. Still more preferred are succinic acid and
adipic acid.
Preferably, the aliphatic dicarboxylic acid for use in
the invention has from 3 to 12 carbon atoms, more preferably
from 3 to 8 carbon atoms. Also preferably, the aromatic
dicarboxylic acid has from 8 to 14 carbon atoms, more preferably
8 carbon atoms.
Two or more different types of dicarboxylic acids may be
used in the invention as a mixture thereof. In this case,
preferably, the mean carbon number of the two or more different
types of dicarboxylic acids is from 3 to 14, more preferably
from 3 to 8.
When the carbon number of the dicarboxylic acid falls
within the above range, then it is favorable since the polymer
may be effective for reducing optical unevenness, may be
excellent in miscibility with thermoplastic polymer, and may
hardly bleed out during formation of polymer film and thermal
stretching thereof.
Also preferred is combined use of aliphatic dicarboxylic
acid and aromatic dicarboxylic acid. Concretely, preferred is
combined use of adipic acid and phthalic acid, combined use of
adipic acid and terephthalic acid, combined use of succinic acid
and phthalic acid, or combined use of succinic acid and
terephthalic acid; and more preferred is combined use of
succinic acid and phthalic acid, or combined use of succinic
acid and terephthalic acid. In case where aliphatic
dicarboxylic acid and aromatic dicarboxylic acid are combined
and used here, the blend ratio of the two (by mol) is preferably
from 95/5 to 40/60, more preferably from 55/45 to 45/55.
Preferably, the diol (glycol) is selected from aliphatic
diols having from 2 to 12 carbon atoms, alkyl ether diols having
from 4 to 20 carbon atoms, and aromatic ring-containing diols
having from 6 to 20 carbon atoms.
The aliphatic diol includes alkyl diols or alicyclic
diols, for example, ethanediol (ethylene glycol) ,
3-oxapentane-l, 5-diol (diethylene glycol), 1 ,2-propanediol,
1 .3-propanediol, 1,2-butanediol , 1 ,3-butanediol,
2-methyl-l, 3-propanediol, 1 ,4-butanediol, 1 ,5-pentanediol,
2 ,2-dimethyl-l, 3-propanediol (neopentyl glycol),
2 ,2-diethyl-l, 3-propanediol (3, 3-dimethylolpentane) ,
2-n-butyl-2-ethyl-l, 3-propanediol (3, 3-dimethylolheptane ),
3-methyl-l, 5-pentanediol, 1,4-hexanediol , 1 ,5-hexanediol,
1 ,6-hexanediol, 2,2, 4-trimethyl-l, 3-pentanediol ,
2-ethyl-l, 3-hexanediol, 2-methyl-l ,8-octanediol ,
1,9-nonanediol, 1 ,10-decanediol, 1 ,4-cyclohexanediol,
1 .4-cyclohexanedimethanol, etc. One or more of these glycols
may be used here either singly or as combined as a mixture
thereof .
As the aliphatic diol, preferred are ethanediol
(hereinafter this may be referred to as ethylene glycol) ,
3-oxapentane-l, 5-diol, 1 ,2-propanediol (hereinafter this may
be referred to as propylene glycol), 1 ,3-propanediol,
1 ,2-butanediol, 1 ,3-butanediol, 2-methyl-l, 3-propanediol,
1 ,4-butanediol, 1 ,5-pentanediol,
2.2-dimethyl-l, 3-propanediol, 1 ,4-hexanediol, 1 ,5-hexanediol,
1 ,6-hexanediol, 2-methyl-l, 8-octanediol, 1 ,4-cyclohexanediol,
and 1 ,4-cyclohexanedimethanol; more preferred are ethanediol,
1 ,2-propanediol, 1 ,3-propanediol, 1 ,2-butanediol,
1 .3-butanediol, 1 ,4-butanediol, 1 ,5-pentanediol,
1 ,6-hexanediol, 1 ,4-cyclohexanediol, and
1 .4-cyclohexanedimethanol . Even more preferred are
ethanediol and 1 ,2-propanediol .
As the alkyl ether diol having from 4 to 20 carbon atoms,
preferred are polytetramethylene ether glycol, polyethylene
ether glycol and polypropylene ether glycol, and their
combination. Not specifically defined, the mean degree of
polymerization of the diol is preferably from 2 to 20, more
preferably from 2 to 10, even more preferably from 2 to 5 , still
more preferably from 2 to 4 . A s their examples, there may be
mentioned typically-useful commercially-available polyether
glycols, such as Carbowax Resin, Pluronics Resin and iax Resin .
As the aromatic diol having from 6 to 20 carbon atoms,
there may be mentioned with no limitation, bisphenol A ,
1 ,2-hydroxybenzene, 1 ,3-hydroxybenzene, 1 ,4-hydroxybenzene,
and benzene-1, 4-methanol . Preferred are bisphenol A ,
1 ,4-hydroxybenzene, and benzene-1, 4-dimethanol .
Preferably, the aromatic diol has from 6 to 12 carbon
atoms.
In case where two or more different types of diols are
used here, preferably, the mean carbon number of those two or
more types of diols is from 2 to 12.
When the carbon number of the diol falls within the above
range, then it is favorable since the polymer may be effective
for reducing optical unevenness, may be excellent in
miscibility with thermoplastic polymer, and may hardly bleed
out during formation of polymer film and thermal stretching
thereof .
In the invention, also usable is a mixture of two or more
different types of diols. In this case, preferably, the mean
carbon number of those two or more types of diols is from 2 to
12, more preferably from 2 to 7 .
Concretely, preferred is a combination of ethylene glycol
and propylene glycol. In case where two or more different types
of diols are used as a mixture thereof, the blend ratio of the
two (by mol) is preferably from 95/5 to 5/95, more preferably
from 55/45 to 45/55.
Blocking)
Both terminals of the polyester oligomer in the invention
may be either blocked or unblocked.
In case where both terminals of the polyester oligomer
are unblocked, the oligomer is preferably a polyester polyol.
Also preferably, at least one terminal is blocked, and
the terminal is at least one selected from an aliphatic group
having from 1 to 22 carbon atoms, an aromatic ring-containing
group having from 6 to 20 carbon atoms, an aliphatic carbonyl
group having from 1 to 22 carbon atoms, and an aromatic carbonyl
group having from 6 to 20 carbon atoms.
Further, in case where both terminals of the polyester
oligomer are blocked, preferably, the oligomer is blocked
through reaction with a monoalcohol or a monocarboxylic acid.
In this case, both terminals of the oligomer are monoalcohol
residues or monocarboxylic acid residues. In this, "residue"
means a partial structure of the oligomer, and the partial
structure characterizes the monomer that forms the oligomer.
For example, the monocarboxylic acid residue of a
monocarboxylic acid R-COOH is R-CO- .
The monoalcohol residue is preferably a substituted or
unsubstituted monoalcohol residue having from 1 to 30 carbon
atoms, including aliphatic alcohols such as methanol, ethanol,
propanol, isopropanol, butanol, isobutanol, pentanol,
isopentanol, hexanol, isohexanol, cyclohexyl alcohol, octanol,
isooctanol, 2-ethylhexyl alcohol, nonyl alcohol, isononyl
alcohol, tert-nonyl alcohol, decanol, dodecanol,
dodecahexanol, dodecaoctanol, allyl alcohol, oleyl alcohol,
etc.; substituted alcohols such as benzyl alcohol,
3-phenylpropanol, etc.
As the terminal-blocking alcohol residue preferred for
use herein, there may be mentioned methanol, ethanol, propanol,
isopropanol, butanol, isobutanol, isopentanol, hexanol,
isohexanol, cyclohexyl alcohol, isooctanol, 2-ethylhexyl
alcohol, isononyl alcohol, oleyl alcohol, benzyl alcohol; and
more preferred are methanol, ethanol, propanol, isobutanol,
cyclohexyl alcohol, 2-ethylhexyl alcohol, isononyl alcohol,
benzyl alcohol.
The monocarboxylic acid residue is preferably an
aliphatic monocarboxylic acid residue having from 2 to 22 carbon
atoms, more preferably an aliphatic monocarboxylic acid residue
having from 2 to 3 carbon atoms, even more preferably an
aliphatic monocarboxylic acid residue having 2 carbon atoms.
When the carbon number of the monocarboxylic acid residue
at both terminals of the polyester oligomer is at most 3 , then
the evaporability of the oligomer lowers and the loss on heating
of the oligomer is not large, and the troubles of contamination
in process and surface failure of film may be reduced.
Accordingly, as the monocarboxylic acids for use for terminal
blocking, preferred are aliphatic monocarboxylic acids. More
preferred are aliphatic monocarboxylic acids having from 2 to
22 carbon atoms, even more preferred are aliphatic
monocarboxylic acids having from 2 to 3 carbon atoms, and still
more preferred are aliphatic monocarboxylic acids having 2
carbon atoms.
As preferred aliphatic monocarboxylic acids, there may
be mentioned acetic acid, propionic acid, butanoic acid,
caprylic acid, caproic acid, decanoic acid, dodecanoic acid,
stearic acid, oleic acid. A s aromatic ring-containing
monocarboxylic acids, there may be mentioned, for example,
benzoic acid, p-tert-butylbenzoic acid, p-tert-amylbenzoic
acid, orthotoluic acid, metatoluic acid, paratoluic acid,
dimethylbenzoic acid, ethylbenzoic acid, normal-propylbenzoic
acid, aminobenzoic acid, acetoxybenzoic acid, etc.
Of those, preferred are acetic acid, propionic acid,
butanoic acid, benzoic acid and their derivatives; more
preferred are acetic acid and propionic acid; and most preferred
is acetic acid (to give an acetyl group at the terminal) . Two
or more different types of monocarboxylic acids may be combined
and used for terminal blocking.
In case where both terminals are blocked, the polymer
could hardly be solid at room temperature and its handlability
may be better, and in addition, a polymer film excellent in
moisture stability and polarizer durability may be obtained.
Preferably, the number-average molecular weight of the
polycondensate ester is from 500 to 2000, more preferably from
600 to 1500, even more preferably from 700 to 1200. When the
number-average molecular weight of the polycondensate ester is
at least 600, then the evaporability thereof lowers and the
troubles of film failure and contamination in process owing to
vaporization under high-temperature condition in stretching
cellulose ester film may be prevented. When the molecular
weight is at most 2000, the miscibility of the polymer with
cellulose ester may increase and the trouble of bleeding out
in film formation or stretching under heat may be prevented.
Specific examples of the polycondensate esters usable in
the invention are shown in the following Table 1 and Table 2 ,
to which, however, the invention should not be limited. In the
following Table 1 and Table 2 , PA means phthalic acid, TPA means
terephthalic acid, IPA means isophthalic acid, AA means adipic
acid, SA means succinic acid, 2,6-NPA means
2 ,6-naphthalenedicarboxylic acid.

The polycondensate ester for use in the invention can be
easily produced according to any of a method of thermal melt
condensation through polyesterif ication or
interesterif ication of a diol and a dicarboxylic acid in an
ordinary manner, or a method of interfacial condensation of a
dicarboxylic acid chloride and a glycol. The polycondensate
esters for use in the invention are described in detail in Koichi
Murai, "Plasticizers, Theory and Application Thereof" (by
Miyuski Shobo Publishing, First Edition, No. 1 , published on
March 1 , 1973) . Materials described in JP-A 05-155809,
05-155810, 5-197073, 2006-259494, 07-330670, 2006-342227,
2007-003679 are usable here.
The content of the polycondensate ester in the cellulose
ester layer in the film of the invention is preferably from 5
to 40% by mass relative to the amount of the cellulose ester
therein, more preferably from 8 to 30% by mass, even more
preferably from 10 to 25% by mass.
The content of the starting materials, aliphatic diol,
dicarboxylic ester or diol ester that may be in the
polycondensate used in the invention, in the cellulose ester
layer is preferably less than 1% by mass, more preferably less
than 0.5% by mass. The dicarboxylic ester includes dimethyl
phthalate, di (hydroxyethyl) phthalate, dimethyl
terephthalate, di (hydroxyethyl) terephthalate,
di (hydroxyethyl) adipate, di (hydroxyethyl) succinate, etc.
The diol ester includes ethylene diacetate, propylene diacetate,
etc .
The type and the ratio of the residues, dicarboxylic acid
residue, diol residue and monocarboxylic acid residue contained
in the polycondensate ester for use in the invention may be
determined and measured according to known methods through
H-NMR. In general, heavy chloroform may be used as the solvent .
The number-average molecular weight of the
polycondensate ester may be measured according to ordinary
methods through GPC (gel permeation chromatography), in which,
in general, polystyrene is used as the standard reference
material .
«Acrylic Oligomer or Acrylic Resin»
In the invention, any other acrylic oligomer or acrylic
resin than the thermoplastic resin used as the main ingredient
in the acrylic resin layer and the cellulose acylate layer may
be added to the acrylic resin layer and the cellulose acetate
layer as the plasticizer therein. The proportion of the acrylic
oligomer or the acrylic resin to the acrylic resin or the
cellulose acylate used in the acrylic resin layer or the
cellulose acylate layer as the main ingredient therein is
preferably from 2 to 140% by mass based on the acrylic resin
or the cellulose acylate used in the acrylic resin layer or the
cellulose acylate layer as the main ingredient therein, more
preferably from 4 to 100% by mass, most preferably from 6 to
60% by mass. The molecular weight of the acrylic oligomer or
the acrylic resin is preferably from 500 to 200, 000, more
preferably from 1,000 to 100,000, even more preferably from
1 ,200 to 50, 000, especially more preferably from 1 ,200 to 10, 000 .
When the molecular weight falls within the range, then the
acrylic resin used as the main ingredient in the acrylic resin
layer as well as the cellulose acylate layer could be excellent
in transparency.
The composition of the acrylic oligomer or the acrylic
resin to be used for the purpose preferably contains an
aliphatic (meth) acrylate monomer, an aromatic ring-containing
(meth) acrylate monomer or a cyclohexyl group-having
(meth) acrylate monomer as the main ingredient thereof. The
main ingredient means that the constitutive mass ratio of the
ingredient is higher than that of the other copolymerizable
components in the (co) polymer.
Preferably, the constitutive mass ratio is from 40 to 100%
by mass, more preferably from 0 to 100% by mass, most preferably
from 70 to 100% by mass.
The aliphatic (meth) acrylate monomer includes, for
example, methyl acrylate, ethyl acrylate, (i-, n-) propyl
acrylate, (n-, i-, s-, t-)butyl acrylate, (n-, i-, s-)pentyl
acrylate, (n-, i-) hexyl acrylate, (n-, i-) heptyl acrylate, (n-,
i-)octyl acrylate, (n-, i-)nonyl acrylate, (n-, i-)myristyl
acrylate, (2-ethylhexyl) acrylate, (-caprolactone) acrylate,
(2-hydroxyethyl) acrylate, (2-hydroxypropyl) acrylate,
(3-hydroxypropyl) acrylate, (4-hydroxypropyl) acrylate,
(2-hydroxybutyl) acrylate, (2-methoxyethyl) acrylate,
(2-ethoxyethyl) acrylate, etc.; as well as methacrylates
corresponding to the above-mentioned acrylates. Above all,
preferred are methyl methacrylate, ethyl methacrylate, (i-,
n-) propyl methacrylate, (n-, i-, s-, t-) butyl methacrylate,
methyl acrylate, ethyl acrylate.
The aromatic ring-having (meth) acrylate monomer includes,
for example, phenyl acrylate, phenyl methacrylate, (2 or
4-chlorophenyl) acrylate, (2 or 4-chlorophenyl ) methacrylate,
(2, 3 or 4-ethoxycarbonylphenyl) acrylate, (2, 3 or
4-ethoxycarbonylphenyl) methacrylate, (o or m or p-tolyl)
acrylate, (o or m or p-tolyl) methacrylate, benzyl acrylate,
benzyl methacrylate, phenethyl acrylate, phenethyl
methacrylate, (2-naphthyl) acrylate, etc. Preferred is use of
benzyl acrylate, benzyl methacrylate, phenethyl acrylate,
phenethyl methacrylate.
The cyclohexyl group-having (meth) acrylate monomer
includes, for example, cyclohexyl acrylate, cyclohexyl
methacrylate, (4-methylcyclohexyl ) acrylate,
(4-methylcyclohexyl) methacrylate, (4-ethylcyclohexyl)
acrylate, (4-ethylcyclohexyl) methacrylate, etc. Preferred
is use of cyclohexyl acrylate and cyclohexyl methacrylate.
A s further copolymerizable components in addition to the
above-mentioned monomers, there may be mentioned
a ,-unsaturated acids such as acrylic acid, methacrylic acid,
etc.; unsaturated bond-containing dicarboxylic acids such as
maleic acid, fumaric acid, itaconic acid, etc.; aromatic vinyl
compounds such as styrene, a-methylstyrene, etc.;
a ,-unsaturated nitriles such as acrylonitrile,
methacrylonitrile, etc.; maleic anhydride, maleimide,
N-substituted maleimide, glutaric anhydride, etc. Either
singly or as combined, one alone or two or more of these monomers
may be used as the copolymerization component.
In producing acrylic oligomers or acrylic resins having
a weight-average molecular weight of at most 10,000 through
ordinary polymerization, it is difficult to control the
molecular weight of the produced polymers. For producing the
polymers having such a low molecular weight, there may be
employed a method of using a peroxide polymerization initiator
such as cumeme peroxide or t-butyl hydroperoxide; a method of
using a larger amount of the polymerization initiator than
usual; a method of using a chain transfer agent such as a mercapto
compound, carbon tetrachloride or the like, in addition to the
polymerization initiator; a method of using a polymerization
terminator such as benzoquinone, dinitrobenzene or the like in
addition to the polymerization initiator; a method of bulk
polymerization using, as the polymerization catalyst, a
compound having one thiol group and one secondary hydroxyl group
or a combination of the compound and an organic metal compound
as in JP-A 2000-128911 or 2000-344823, etc. Any of these
methods is favorably employed in the invention; but the method
described in the patent publications is more preferred.
A s the low-molecular to oligomer compounds, for example,
employable here are phosphates, carboxylates, polyol esters,
etc.
Examples of the phosphates include triphenyl phosphate
(TPP) , tricresyl phosphate, cresyl diphenyl phosphate, octyl
diphenyl phosphate, biphenyl diphenyl phosphate, trioctyl
phosphate, tributyl phosphate, etc. Preferred are triphenyl
phosphate, biphenyl diphenyl phosphate.
The carboxylates typically include phthalates and
citrates. Examples of the phthalates include dimethyl
phthalate, diethyl phthalate, dibutyl phthalate, dioctyl
phthalate, diphenyl phthalate, diethylhexyl phthalate, etc.
Examples of the citrates include triethyl O-acetylcitrate,
tributyl O-acetylcitrate, acetyltriethyl citrate,
acetyltributyl citrate, etc.
These preferred plasticizers are liquid at 25°C, except
TPP (having a melting point of about 50°C) , and have a boiling
point of not lower than 250°C.
Examples or the other carboxylates include butyl oleate,
methylacetyl ricinoleate, dibutyl sebacate, various
trimellitates , etc. Examples of the glycolates include
triacetin, tributyrin, butylphthalylbutyl glycolate,
ethylphthalylethyl glycolate, methylphthalylethyl glycolate,
butylphthalylbutyl glycolate, methylphthalylmethyl glycolate,
propylphthalylpropyl glycolate, butylphthalylbutyl glycolate,
octylphthalyloctyl glycolate, etc.
Plasticizers described in JP-A 5-194788,60-250053,
4-227941, 6-16869, 5-271471, 7-286068, 5-5047, 11-80381,
7-20317, 8-57879, 10-152568, 10-120824 are also preferably used
here. These patent publications disclose not only examples of
the plasticizers but also various methods of using them and
characteristics of the plasticizers; and the disclosure may be
favorably referred to in the present invention.
A s plasticizers also favorably usable here are
(di) pentaerythritol esters described in JP-A 11-124445;
glycerol esters described in JP-A 11-246704; diglycerol esters
described in JP-A 2000-63560; citrates described in JP-A
11-92574; substituted phenyl phosphates described in JP-A
11-90946; ester compounds having an aromatic ring and a
cyclohexane ring described in JP-A 2003-165868, etc.
One alone or two or more of these plasticizers may be used
here either singly or as combined. The amount of the
plasticizer to be added may be generally from 2 to 120 parts
by mass relative to 100 parts by mass of the thermoplastic resin
contained in the dope, preferably from 2 to 70 parts by mass,
more preferably from 2 to 30 parts by mass, even more preferably
from 5 to 20 parts by mass. Using the same plasticizer in the
two neighboring layers of the dopes (A) and (B) for use in the
production method of the invention to be mentioned below is
favorable from the viewpoint that the interface between the
dopes in casting can be prevented from being disordered, the
interfacial adhesiveness may be bettered and the curling
resistance of the formed film may be bettered. Especially
preferably, the dopes (A) and (b) contains the same plasticizer .
(Other Additives)
Any other additive than the above-mentioned plasticizer
may be added to the optical film of the invention.
Examples of the additives include UV absorbent,
fluorosurf actant (its preferred amount is from 0.001 to 1% by
mass relative to the thermoplastic resin) , release agent (from
0.0001 to 1% by mass), antioxidant (from 0.0001 to 1% by mass),
optical anisotropy regulator (from 0.01 to 10% by mass), R
absorbent (from 0.001 to 1% by mass), etc.
Preferably, the UV absorbent for use herein is excellent
in the ability to absorb UV rays having a wavelength of at most
370 nm from the viewpoint of preventing the degradation of
liquid crystal, and absorbs a s little as possible the visible
light having a wavelength o f at least 400 nm from the viewpoint
o f securing good image display capability. More preferably,
the UV absorbent has a transmittance at a wavelength o f 370 nm
o f at most 20%, even more preferably at most 10%, still more
preferably at most 5%. The UV absorbent o f the type includes,
for example, oxybenzophenone compounds, benzotriazole
compounds, salicylate compounds, benzophenone compounds,
cyanoacrylate compounds, nickel complex compounds, UV
absorbent group-having polymer UV absorbent compounds such as
those mentioned above, etc., to which, however, the invention
should not b e limited. Two or more different types o f UV
absorbents may b e used here as combined.
The optical film o f the invention may contain a trace o f
particles o f an organic material, an inorganic material o r their
mixture, a s dispersed therein within a range not detracting from
the effect o f the invention. In case where the particles are
used for the purpose o f enhancing the travelability o f film in
film formation (that is, a s a mat agent) , the particle size o f
the particles is preferably from 5 to 3000 nm, and the amount
thereof is preferably at most 1% b y mass.
The particles may b e added for roughening the surface o f
the film o r for making the film have internal light
scatterability, and in such a case, the particle size o f the
particles is preferably from 1 to 20 jam, and the amount thereof
is preferably from 2 to 30% b y mass. Preferably, the difference
in the refractive index between the particles and the polymer
film of the invention is from 0 to 0.5; and for example, in case
where particles o f an inorganic material are used, they may
include particles o f silicon oxide, aluminium oxide, barium
oxide, etc. Examples o f the particles o f an organic material
include acrylic resin, divinylbenzene resin, benzoguanamine
resin, styrene resin, melamine resin, acryl-styrene resin,
polycarbonate resin, polyethylene resin, polyvinyl chloride
resin, etc. In case where the particles act to impart optical
dif fusibility to the optical film, the haze value is, though
not specifically defined, preferably so controlled to fall
within a range within which the backscattering is not too much
increased and the total light transmittance is not lowered too
much. Concretely, the haze is preferably from 1 to 60%, more
preferably from 3 to 50%.

The optical film of the invention may additionally have,
as formed thereon, a curable resin layer having a thickness of
from 0.1 to 15 . In addition, any other
optically-functional layer such as antistatic layer,
high-ref ractivity layer, low-ref ractivity layer or the like may
be further formed on the curable resin layer. A s the case may
be, the curable resin layer may serve also as an antistatic layer
or a high-ref ractivity layer.
The curable resin layer is preferably formed through
crosslinking reaction or polymerization reaction of an ionizing
radiation-curable compound. For example, a coating
composition that contains an ionizing radiation-curable
polyf unctional monomer or polyf unctional oligomer may be
applied onto the light-transmissive substrate, and the
polyf unctional monomer or the polyf unctional oligomer may be
crosslinked or polymerized to form the intended layer.
The functional group of the ionizing radiation-curable
polyf unctional monomer or polyf unctional oligomer is
preferably one capable of polymerizing with light, electron
beams or radiations, more preferably a photopolymerizing
functional group.
The photopolymerizing group includes unsaturated
polymerizing functional groups such as (meth) acryloyl group,
vinyl group, styryl group, allyl group, etc.; and above all,
preferred is a (meth) acryloyl group.
The curable resin layer may contain any known additive
such as leveling agent, antifouling agent, antistatic agent,
refractive index-controlling inorganic filler, scattering
particles, thixotropic agent, etc.
The strength of the optical film having the curable resin
layer formed thereon is preferably at least H in a pencil
hardness test, more preferably at least 2H.
[Method for Producing Optical Film]
The method for producing the optical film of the invention
(hereinafter this may be referred to as the production method
of the invention) comprises a step of casting at least two types
of dopes (A) and (B) each containing a thermoplastic resin and
an organic solvent onto a casting substrate simultaneously or
successively in the order of (A) - (B) - (A) from the casting
substrate side, and a step of removing the organic solvent,
wherein the dope (A) contains a cellulose acylate and the dope
(B) contains an acrylic resin having a weight-average molecular
weight of from 600,000 to 4,000,000.

Regarding the preparation of the solution (dope) of a
thermoplastic resin for use in the optical film of the invention,
the dissolution method includes a room temperature dissolution
method, a cooling dissolution method or a high-temperature
dissolution method, or a combination of any of these methods.
Regarding these, methods for preparing cellulose acylate
solution are described, for example, in JP-A 5-163301,
61-106628, 58-127737, 9-95544, 10-95854, 10-45950, 2000-53784,
11-322946, 11-322947, 2-276830, 2000-273239, 11-71463,
04-259511, 2000-273184, 11-323017, 11-302388, etc. The
techniques of the dissolution methods for cellulose acylate in
organic solvent disclosed in these are applicable to the
thermoplastic resin in the invention. The details of the
methods, especially the non-chlorine solvents for use therein
are described in detail in the above-mentioned Disclosure
Bulletin No. 2001-1745, pp. 22-25. The dope solution of
thermoplastic resin is generally concentrated and filtered,
which is also described in detail in Disclosure Bulletin No.
2001-1745, p . 25. In dissolution at high temperature, the
system is at a temperature not lower than the boiling point of
the organic solvent used in most cases, and in such a case, the
system is kept under pressure.
(Organic Solvent)
The organic solvent (this may be referred to as solvent)
that dissolve the organic solvent to form the dope in the
invention is described. Any known organic solvent may be used
as the organic solvent, and, for example, preferred are those
having a solubility parameter of from 17 to 22. The solubility
parameter is described, for example, in J . Brandrup, E . H . et
al., "Polymer Handbook (4th Edition)", VII/671 to VII/714.
There may be mentioned lower aliphatic hydrocarbon chlorides,
lower aliphatic alcohols, ketones having from 3 to 12 carbon
atoms, esters having from 3 to 12 carbon atoms, ethers having
from 3 to 12 carbon atoms, aliphatic hydrocarbons having from
5 to 8 carbon atoms, aromatic hydrocarbons having from 6 to 12
carbon atoms, fluoroalcohols (e.g., compounds described in JP-A
8-143709, paragraph [0020], 11-60807, paragraph [0037]), etc.
The solvent may be used here singly, but preferred is use
of a mixture of a good solvent and a poor solvent for securing
good surface condition stability of the film. More preferably,
the blend ratio of the good solvent and the poor solvent is such
that the proportion of the good solvent is from 60 to 99% by
mass and that of the poor solvent is from 40 to 1% by mass. In
the invention, the good solvent means a solvent capable of
dissolving the resin for use herein by itself; and the poor
solvent means a solvent that could not swell or dissolve the
resin by itself. The good solvent for use in the invention
includes organic halogen compounds such as methylene chloride,
etc.; and dioxolans. As the poor solvent for use in the
invention, for example, preferred are methanol, ethanol,
n-butanol, cyclohexane, etc.
Preferably, the proportion of the alcohol in the organic
solvent to be contained in the dopes (A) and (B) is from 10 to
50% by mass of the entire organic solvent from the viewpoint
of shortening the drying time on the support (casting substrate)
after film formation to thereby rapidly peel off the formed film
and dry it, more preferably from 15 to 30% by mass.
Further, in the organic solvent contained in the dope (A)
and the dope (B) , preferably, the proportion of methanol to the
entire organic solvent is from 20 to 35% by mass from the
viewpoint of bettering the co-cast interlayer adhesiveness and
bettering the reworkability of the film. The reworkability as
referred to herein means the property of film of such that, when
a polarizer protective film is once stuck to a polarizing
element to produce a polarizer and the polarizer is once stuck
to the glass substrate of a liquid crystal cell, the polarizer
can be well peeled off and can be again stuck to the glass
substrate for the purpose of increasing the production yield
in producing polarizers and liquid crystal display devices.
The proportion of methanol to the entire organic solvent in the
dope is more preferably from 21 to 35% by mass, even more
preferably from 25 to 30% by mass.
Preferably, the material to form the optical film is
dissolved in the organic solvent in a concentration of from 10
to 60% by mass, more preferably from 10 to 50% by mass. In case
where a cellulose acylate resin is the main ingredient, it is
preferably dissolved in an amount of from 10 to 30% by mass,
more preferably from 13 to 27% by mass, even more preferably
from 15 to 25% by mass. Regarding the method of controlling
the concentration, the system may be so controlled as to have
the desired concentration in the dissolution stage, or the
system may be previously so prepared as to have a low
concentration (for example, from 9 to 14% by mass) and then this
may be concentrated to have the predetermined high
concentration in the subsequent concentration step. Further,
a solution of the material to form the light-transmissive
substrate having a high concentration may be previously
prepared, and various additives may be added thereto to thereby
lower the concentration of the solution to a predetermined
level.
(Solid Concentration in Dope)
In the production method of the invention, the solid
concentration in the dope (B) (the concentration of the
component to be solid after drying the dope) may be suitably
selected depending on the molecular weight of the component.
For making the dope have a viscosity suitable for solution
casting film formation, the solid concentration is preferably
from 16 to 30% by mass. Heretofore, for the reason that the
content of the organic solvent can be reduced and the drying
time can be shortened, it has been considered that the solid
concentration is preferably from 30 to 50%; however, in the
invention, the inventors have found that the solid
concentration falling within the above range is preferred from
the viewpoint of attaining the effect of the invention. More
preferably, the solid concentration in the dope (B) is from 16
to 30% by mass, even more preferably from 18 to 25% by mass.
In the production method of the invention, preferably,
the solid concentration in both the dope (A) and the dope (B)
is from 16 to 30% by mass each.
On the other hand, in the production method of the
invention, for obtaining a film having a good surface condition
in co-casting film formation, preferably, the solid
concentration in the dope (B) is on the same level as that of
the solid concentration in the dope (A) . Preferably, the
difference between the dope (B) and the dope (A) in the solid
concentration therein is at most 10% by mass, more preferably
at most 5% by mass.
In particular, even more preferably, the total
concentration of the components to be solid after drying in the
dope (B) is from 16 to 30% by mass, and the difference in the
concentration between the dope (B) and the dope (A) is at most
10% by mass.
(Complex Viscosity of Dope)
In the production method of the invention, preferably,
the complex viscosity of the dope (A) and the dope (B) each is
from 10 to 80 Pa-s. The complex viscosity falling within the
range is favorable since the solution casting aptitude of the
dope is further bettered. The complex viscosity of the dope
in the invention is the viscosity thereof measured with a fluid
shear rheometer.
More preferably, the complex viscosity is from 20 to 80
Pa-s, even more preferably from 25 to 70 Pa-s. The viscosity
was measured as follows: One mL of the sample solution was put
into a rheometer (CLS 500) , and analyzed with Steel Cone having
a diameter of 4 cm/2° (both by TA Instrumennts ).
The sample solution was previously warmed until its
temperature became constant at the measurement start
temperature, and then the measurement was started. The
temperature at the start of the test is not specifically defined
so far as it is the casting temperature. Preferably, the
temperature is from -5 to 70°C, more preferably from -5 to 35°C.
In the production method of the invention, the viscosity
of the dope may differ between the surface layer and the core
layer, and preferably, the viscosity of the surface layer is
smaller than the viscosity of the core layer. However, the
viscosity of the core layer may be smaller than the viscosity
of the surface layer. In the production method of the invention,
above all, it is desirable that the complex viscosity of the
dope (A) and the dope (B) each is from 10 to 80 Pa-s and the
complex viscosity of the dope (B) is larger than the complex
viscosity of the dope (A) from the viewpoint of bettering the
film surface condition after film formation.
(Composition of Thermoplastic Resin of Dope)
Further, from the viewpoint of securing support
releasability, interfacial adhesiveness and curling
resistance of the formed film, preferably, the composition of
the thermoplastic resin in the dopes (A) and (B) satisfies the
following condition. The proportion of the cellulose acylate
resin in the thermoplastic resin in the dope (A) is preferably
from 50 to 100% by mass, more preferably from 70 to 100% by mass,
most preferably from 80 to 100% by mass. The proportion of the
acrylic resin in the thermoplastic resin in the dope (B) is
preferably from 30 to 100% by mass, more preferably from 50 to
100% by mass, most preferably from 70 to 100% by mass.
(Simultaneous or Successive Casting Step)
The production method of the invention includes a step
of casting at least two types of dopes (A) and (B) each containing
a thermoplastic resin and an organic solvent onto a casting
substrate simultaneously or successively in the order of
(A) -(B) -(A) from the casting substrate side.
In the production method for an optical film of the
invention, preferably, at least two types of the dopes (A) and
(B) are cast on the casting substrate in that order from the
casting substrate side.
The dope is cast onto a drum and the solvent is evaporated
away from it to form a film. Preferably, the drum surface is
finished in a mirror state. The casting and drying modes in
a solvent casting method are described in USP 2336310, 2367603,
2492078, 2492977, 2492978, 2607704, 2739069, 2739070; British
Patent 640731, 736892; JP-B 45-4554, 49-5614; JP-A 60-176834,
60-203430, 62-115035.
Fig. 1 is a view showing a casting apparatus having a drum.
Fig. 1 is a schematic view showing the substantial part of the
casting apparatus 101, and is a plane view taken from the side
thereof. In Fig. 1 , a drum 102 is used. The casting dope 12
from the casting die 14 is cast at a relatively lower position
than the top of the drum 102, so that the cast film formed on
the drum 102 could run downward from the casting start point
PS. In this case, preferably, the casting start point PS is
so positioned that the tangent line at the casting start point
on the drum 102 could be identical as much as possible to the
tangent line of the casting curve from the casting die 14.
The drum 102 has a temperature-controlling function.
Outside the cast film, plural condenser plates 105 are arranged,
and the condensed liquid runs along the inclination between the
condenser plates 105 and is led into the external liquid
receiver 53 and is then collected in the collector tank 56. The
cast film running on the drum 102 is peeled by the peeling roller
37 to be a film 36, which is then fed to a drying zone in the
next step. Accordingly, with preventing liquid dripping, the
cast film can be uniformly dried and the solvent can be recovered
at high yield. However, even when the rotating direction of
the drum 102 is reversed and the running direction of the cast
film is made upward from the casting start point PS, uniform
drying of the cast film can be secured and the thickness of the
film 36 can be kept uniform.
Preferably, the dope is cast onto the drum having a
surface temperature of not higher than 5°C. The surface
temperature of the casting substrate (drum) is preferably from
-30 to 5°C, more preferably from -10 to 2°C.
Preferably, the cast film is dried by exposing it to air
for at least 2 seconds after the casting. The formed film is
peeled away from the drum, and may be dried at high-temperature
air of which the temperature is successively changed from 100°C
to 160°C, to thereby evaporate the residual solvent . The method
is described in JP-B 5-17844 . According to the method, the time
from casting to peeling may be shortened. For carrying out the
method, the dope must gel at the surface temperature of the drum
on which it is cast.
In the invention, at least the above-mentioned two types
of dopes are cast on a casting substrate for film formation
thereon. In the film production method of the invention,
nothing is limited other than the above, and any known
co-casting method is employable. For example, the dope
solutions may be individually cast from plural casting mouths
arranged in the metal support running direction at some
intervals and laminated to form a film, and for example, the
methods described in JP-A 61-158414, 1-122419, 11-198285 are
employable. The film may also be formed by casting the dope
solutions from two casting mouths, and for example, the methods
described in JP-B 60-27562, JP-A 61-94724 , 61-947245, 61-104813,
61-158413, 6-134933 are employable.
In the production method of the invention, preferably,
at least two types of the dopes (A) and (B) are simultaneously
co-cast onto the casting substrate in order from the casting
substrate side. More preferably, the dopes (A), (B) and (A)
are simultaneously co-cast onto the support in that order from
the support side. The compositions of the plural (A) s in one
laminate film may be completely the same or different.
In the case of co-casting, dope solutions in which the
concentration of the additives such as the above-mentioned
plasticizer, UV absorbent, mat agent or the like differs may
be co-cast to form a laminate film. For example, the amount
of the mat agent may be larger in the surface layer on the side
of the support, or the mat agent may be only in the surface layer
on the side of the support . The plasticizer and the UV absorbent
may be in a larger amount in the core layer than in the surface
layer, or may be only in the core layer. Between the core layer
and the surface layer, the type of the plasticizer and the UV
absorbent may be changed, and for example, low-volatile
plasticizer and/or UV absorbent may be contained in the surface
layer, and a plasticizer excellent in plasticization or a UV
absorbent excellent in UV absorption may be added to the core
layer.

The production method of the invention includes a step
of removing the organic solvent.
A method of drying the web that has been dried on the drum
and has been peeled away is described. The web that has been
peeled at the peeling position at which just before the drum
goes into a 360-degree roll with the web thereon is then conveyed,
according to a method of conveying it alternately through
zigzag-arranged rolls, a method of contactlessly conveying the
web while both sides of the web are held with clips or the like,
etc. The web (film) may be dried according to a method of
applying air at a predetermined temperature to both surfaces
of the web being conveyed, or a method of heating the web with
a heating means such as microwaves, etc. Too rapid drying is
unfavorable as probably detracting from the surface planarity
of the formed film. Accordingly, it is desirable that, in the
initial stage of drying, the web is dried at a temperature at
which the solvent does not foam, and after dried in some degree,
the web is further dried at a high temperature. In the drying
step after the film has been peeled away from the support, the
film shrinks in the machine direction or in the cross direction
owing to the solvent evaporation. The degree of shrinkage may
be larger when the film is dried at a higher temperature. It
is desirable that the film is dried while its shrinkage is
retarded as much as possible, from the viewpoint of bettering
the surface planarity of the formed film. From this viewpoint,
for example, preferred is a method (tenter method) of drying
the web while both sides of the web are held with clips or pins
in the cross direction thereof so as to hold the width of the
web in the entire drying step or partly in the drying step, as
described in JP-A 62-46625. Preferably, the drying
temperature in the drying step is from 100 to 145°C. The drying
temperature, the drying air flow and the drying time may differ
depending on the solvent to be used, and may be suitably selected
in accordance with the type and the combination of the solvents
to be used.
Preferably, after the multilayer-cast dopes have been
dried, the formed film is peeled away from the support. The
time to be taken after the dopes are cast on the casting substrate
and before the formed film is peeled away, or that is, the time
for which the film is conveyed on the casting substrate is at
most 60 seconds, more preferably at most 30 seconds.

The production method of the invention may include a step
of stretching the formed laminate film, after the film formation
step. For example, in case where the film of the invention is
desired to be further improved in point of the nonbrittleness
thereof, the film may be stretched in a stretching step to reduce
its brittleness. The improvement of the film in point of the
nonbrittleness thereof may be confirmed, for example, according
to the bending test of JIS P8115, in which the bending resistance
of the film tested with an MIT tester is increased. In the test,
the bending frequency before fracture is preferably at least
one, more preferably at least 10, even more preferably at least
30.
In producing the film of the invention, preferably, the
web (film) peeled from the support is stretched while the
residual solvent content in the web is less than 120% by mass.
The residual solvent content may be represented by the
following formula:
Residual Solvent Content (% by mass) = { (M - N)/N} x 100
wherein M means the mass of a web at a given point in time, and
N means the mass of the web, of which M has been measured, after
dried at 110°C for 3 hours. In case where the residual solvent
content in the web is too large, then the stretching would be
ineffective; but when too small, the web may be extremely
difficult to stretch and may be cut. A more preferred range
of the residual solvent in the web is from 10% by mass to 50%
by mass, most preferably from 12% by mass to 35% by mass. When
the draw ratio in stretching is too low, the stretched film could
not obtain sufficient retardation; but when too high, the web
may be difficult to stretch and may be cut.
The draw ratio in stretching may be generally from 5% to
100%, preferably from 15% to 40%. Stretching in one direction
by from 5% to 100% means that the distance between the clips
or pins to hold the film is expanded in a range of from 1.05
to 2.00 times relative to the original distance therebetween
before stretching.
The film may be stretched in the film traveling direction
(machine direction) or in the direction perpendicular to the
film traveling direction (cross direction) , or in both
directions .
In the invention, the film formed in a mode of solution
casting film formation may be stretched even though not heated
at a high temperature so far as the residual solvent content
therein falls within a specific range; however, preferably, the
film is stretched with drying as capable of shortening the
stretching step. In the invention, preferably, the stretching
temperature in the stretching step is from 110 to 190°C, more
preferably from 120 to 150°C. The stretching temperature is
preferably not lower than 120°C from the viewpoint of securing
low haze of the film, and is preferably not higher than 150°C
from the viewpoint of enhancing the optical performance
expressibility thereof (from the viewpoint of thickness
reduction of the film) .
On the other hand, when the temperature of the web is too
high, then the plasticizer therein may evaporate away; and
therefore in case where a volatile low-molecular plasticizer
is used therein, the temperature of the web is preferably within
a range of room temperature (15°C) to 145°C.
Stretching the film in biaxial directions perpendicular
to each other is effective from the viewpoint of enhancing the
optical performance expressibility of the film, especially from
the viewpoint of increasing Rth (retardation) of the film.
In the invention, the film may be stretched
simultaneously in biaxial directions in the stretching step,
or may be stretched successively in biaxial directions. In the
case where the film is stretched successively in biaxial
directions, the stretching temperature may vary in every
stretching in different directions.
In the case of simultaneous biaxial stretching, the film
of the invention can be obtained even when stretched at a
stretching temperature of from 110°C to 190°C; and the
stretching temperature in simultaneous biaxial stretching is
more preferably from 120°C to 150°C, even more preferably from
130°C to 150°C. Simultaneous biaxial stretching may increase
the haze of the film in some degree, but can further enhance
the optical performance expressibility of the film.
On the other hand, in the case of successive biaxial
stretching, preferably, the film is first stretched in the
direction parallel to the film traveling direction and then in
the direction perpendicular to the film traveling direction.
A more preferred range of the stretching temperature in
successive stretching is the same as the preferred stretching
temperature range for the above-mentioned simultaneous biaxial
stretching .

Preferably, the film production method of the invention
includes a heat treatment step after the drying step. The heat
treatment in the heat treatment step may be attained after the
drying step, and the treatment may be attained just after the
stretching/drying step, or may be attained in a different mode
where the film is once wound up after the drying step and then
heat-treated in an additional heat treatment step. In the
invention, preferably, the heat treatment step is additionally
provided after the drying step and after the film has been once
cooled to room temperature to 100°C or lower. This mode is
advantageous in that a film having more excellent thermal
dimension stability can be obtained. For the same reason, also
preferably, the film is dried to have a residual solvent content
of less than 2% by mass, more preferably less than 0.4% by mass
just before the heat treatment step.
The heat treatment may be attained according to a method
of applying air at a predetermined temperature to the film being
conveyed, or a method of using a heating means such as microwaves,
etc .
Preferably, the heat treatment is attained at a
temperature of from 150 to 200°C, more preferably from 160 to
180°C. Also preferably, the heat treatment is attained for from
1 to 20 minutes, more preferably from 5 to 10 minutes.
(Heated Water Vapor Treatment)
The stretched film may be thereafter processed in a step
of applying thereto water vapor heated at 100°C or higher. The
water vapor applying step is preferred since, in the step, the
residual stress of the produced optical film may be relaxed and
the dimensional change thereof may be reduced. Not
specifically defined, the temperature of the water vapor is
100°C or higher; however, in consideration of the heat
resistance of the film, the temperature of the water vapor may
be at most 200°C.

In case where the optical film of the invention is used
as a protective film for polarizer and where the film is stuck
to a polarizing element, preferably, the film is processed
through acid treatment, alkali treatment, plasma treatment,
corona treatment or the like for hydrophilicating the surface
thereof, from the viewpoint of the adhesiveness of the film to
the polarizing element.
[Polarizer]
The optical film of the invention may be used in a
polarizer having a polarizing element and, as arranged on at
least one side thereof, a protective film, as the protective
film therein.
Regarding the configuration of polarizer, in an
embodiment where a protective film is arranged on both surfaces
of the polarizing element therein, the optical film of the
invention may be used as one protective film or the retardation
film therein.
The polarizing element includes a iodine-based
polarizing element, a dichroic dye-containing dye-based
polarizing element and a polyene-type polarizing element. The
iodine-based polarizing element and the dye-based polarizing
element may be produced generally using a polyvinyl alcohol
film.
A s the polarizing element, herein usable is any known
polarizing element, or a polarizing element cut out of a
long-size polarizing element in which the absorption axis
thereof is neither parallel nor vertical to the lengthwise
direction thereof. The long-size polarizing element in which
the absorption axis thereof is neither parallel nor vertical
to the lengthwise direction thereof may be produced according
to the following method.
Specifically, the polarizing element of the type may be
produced according to a stretching method in which a polymer
film such as polyvinyl alcohol film that is fed continuously
is stretched while both sides thereof are held with a holding
means and while tension is applied thereto, whereby the film
is stretched by from 1.1 to 20.0 times in the film width direction,
and in which, while the running speed difference in the machine
direction in the holding unit to hold both sides of the film
is kept at most 3%, the film traveling direction is folded with
both sides of the film being kept held so that the angle between
the film traveling direction at the outlet of the step of holding
both sides of the film and the substantially stretching
direction of the film could tilt by from 20 to 70°. In particular,
in the method, the film is preferably tilted by 45° from the
viewpoint of the producibility .
[Liquid crystal Display Device]
The optical film of the invention is favorably used in
image display devices such as liquid crystal display devices
(LCD), plasma display panels (PDP), electroluminescence
displays (ELD) , and cathode ray tube display devices (CRT) .
The optical film of the invention and the polarizer of
the invention can be advantageously used in image display
devices such as liquid crystal display devices and others, and
is favorably used therein as the outermost layer on the
backlight side.
In general, a liquid crystal display device comprises a
liquid crystal cell and two polarizers arranged on both sides
of the cell, in which the liquid crystal cell carries liquid
crystal between two electrode substrates. Further, one
optically anisotropic layer may be arranged between the liquid
crystal cell and one polarizer, or two optically anisotropic
layers may be arranged between the liquid crystal cell and both
polarizers in the device.
Preferably, the liquid crystal cell is a TN-mode, VA-mode,
OCB-mode, IPS-mode or ECB-mode cell.
EXAMPLES
The characteristics of the invention are described more
concretely with reference to Examples given below.
In the following Examples, the material used, its amount
and ratio, the details of the treatment and the treatment
process may be suitably modified or changed. Accordingly, the
invention should not be limitatively interpreted by the
Examples given below.
Unless otherwise specifically indicated, "part" is by
weight.
[Measurement Methods]

The weight-average molecular weigh was measured through
gel permeation chromatography. The condition for the
measurement is as follows:
Solvent tetrahydrof uran
Apparatus TOSOH HLC-8220GPC
Column Three columns of TOSOH TSKgel
Super HZ -H (4.6 mm x 15 cm) were connected.
Column temperature 25°C
Sample concentration 0.1% by mass
Flow rate 0.35 ml/min
Calibration curve Calibration curves made with 7
samples of TOSOH' s TSK standard polystyrene (Mw = 2800000 to
1050) were used.

The maximum difference between the largest thickness and
the smallest thickness (P-V value) of the film was determined,
using a fringe analyzer, FUJINON FX-03. The test area was
within a range of a circle having a diameter of 60 mm. The
refractive index value inputted here was 1.48, the mean
refractive index of cellulose acylate. The resolution of the
apparatus was 512 x 512.
(Humidity Dependence of Rth (ARth) )
Regarding the change in the retardation value with
humidity change, Rth (Rth(10%)) of the film was measured
according to the same method as in this description except that
the film was conditioned at 25°C and at a relative humidity of
10% for 12 hours, Rth (Rth(80%)) of the film was measured
according to the same method as in this description except that
the film was conditioned at 25°C and at a relative humidity of
80% for 12 hours, and the humidity dependence of Rth, ARth was
computed from the found data. Concretely, ARth = Rth (10%) -
Rth (80%) ; and the obtained results are shown in Table 3 below.
(Photoelastic Coefficient)
A sample of 1 cm x 5 cm was cut out of the formed optical
film, and using a spectroscopic ellipsometer (JASCO's M-220) ,
the in-plane retardation of the sample was measured with
applying stress thereto at 25°C; and from the retardation value
and the inclination of the stress coefficient, the photoelastic
coefficient was computed.
[Example 1 ]

Dopes each having the composition shown in Table 3 below
were prepared.
Acryl 1 to Acryl 5 are all polymethyl methacrylate ; and
their molecular weight is shown in Table 3 below.
Additive Al is an acetate ester of a polycondensate of
adipic acid/ethylene glycol propylene glycol (number-average
molecular weight = 1000, ethylene glycol/propylene glycol ratio
= 50/50) .
Additive A2 is a condensate of terephthalic acid succinic
acid/ethylene glycol (number-average molecular weight = 700,
terephthalic acid/succinic acid ratio = 50/50) .
Additive A3 is methyl acrylate (number-average molecular
weight = 1200) .

The dopes shown in Table 3 were formed into a film in a
mode of solution casting film formation, thereby producing an
optical film having the configuration sown in Table 4 below.
Concretely, through a three-layer co-casting Giesser, the dopes
were co-cast onto a metal support to form thereon a film having
the layer configuration as shown in Table 4 . In this stage,
the dopes were so cast as to form the layer 1 , the layer 2 and
the layer 3 in that order from the metal support surface side.
The film thickness configuration is in terms of the thickness
of each layer that was assumed to be a film having a uniform
thickness, based on each dope flow rate. While on the metal
support, the dope was dried with dry air at 40°C to form a film
thereon, then the film was peeled away, and with both sides of
the film kept held with pins and with the distance between the
pins kept constant, the film was dried with dry air at 105°C
for 5 minutes . After the pins were removed, the film was further
dried at 130°C for 20 minutes.

Each film produced in Examples and Comparative Examples
and Fujitac TD60UL (by FUJIFILM) were dipped in an aqueous, 4.5
mol/L sodium hydroxide solution (saponification liquid)
conditioned at 37°C, for 1 minute, then the films were washed
with water, thereafter dipped in an aqueous 0.05 mol/L sulfuric
acid solution for 30 seconds, and further led to pass through
a water-washing bath. Using an air knife, the films were
dewatered repeatedly three times to thereby remove water, and
then kept in a drying zone at 70°C for 15 seconds and thus dried,
thereby producing saponified films.
According to Example 1 in JP-A 2001-141926, a film was
stretched in the machine direction, between two pairs of nip
rolls having a different peripheral speed to prepare a
polarizing element having a thickness of 20 .
Thus obtained, the polarizing element was sandwiched
between any two of the saponified films, and then stuck together
using an adhesive of an aqueous 3% PVA (Kuraray's PVA-117H)
solution in a roll-to-roll process in such a manner the
polarization direction of the polarizing element could be
perpendicular to the machine direction of the film, thereby
producing a polarizer. In this, one film on the polarizing
element is one selected from the saponified films shown in Table
4 , and the other film thereon is the saponified Fujitac TD60UL.
In Comparative Example 3 , the film readily peeled away
from the polyvinyl alcohol, and therefore did not have a
suitable workability for polarizer production. All the other
films well adhered to polyvinyl alcohol, and therefore had
excellent workability for polarizer production.
(Display Performance Evaluation in IPS-Mode Liquid crystal
Display Device)
The polarizers set to sandwich the liquid crystal cell
were peeled away from a commercially-available liquid crystal
television (IPS-mode slim-type 42-inch liquid crystal
television) , and the previously produced polarizers were
re-adhered to the liquid crystal cell using an adhesive, in such
a manner that the film shown in Table 4 could face the liquid
crystal cell side. Thus reconstructed, the liquid crystal
television was kept in an environment at 50°C and at a relative
humidity of 80% for 3 days, and then transferred into an
environment at 25°C and at a relative humidity of 60%, in which
the television was kept ON in a condition of black level of
display, and after 48 hours, the panel was visually checked for
the presence of absence of display unevenness. The evaluation
results are shown in Table .
(Front Direction Display Unevenness)
The panel was watched in the front direction of the device
and visually checked for the brightness unevenness at the time
of black level of display, and the device was evaluated
according to the following evaluation standards.
A : Little display unevenness was seen in the environment
at an illumination intensity of 100 lx.
B : Some but slight display unevenness was seen in the
environment at an illumination intensity of 100 lx.
C : Definite display unevenness was seen in the
environment at an illumination intensity of 100 lx.
D : Definite display unevenness was seen in the
environment at an illumination intensity of 300 lx.
(Oblique Direction Display Unevenness)
Further, the panel was checked for the brightness
unevenness and color unevenness at the time of black level of
display at an azimuth angle of 45 degrees and a polar angle of
70 degrees from the front direction, and the device was
evaluated according to the following evaluation standards.
A : Little display unevenness was admitted in the
environment at an illumination intensity of 100 lx.
B : Some but slight display unevenness was admitted in the
environment at an illumination intensity of 100 lx.
C : Definite display unevenness was admitted in the
environment at an illumination intensity of 100 lx.
D : Definite display unevenness was admitted in the
environment at an illumination intensity of 300 lx.
(Reworkability)
The produced polarizer of Examples and Comparative
Examples was cut in the direction parallel to the absorption
axis thereof to give a piece having a size of 4 cm square. Using
an adhesive, Soken Chemical's SK-2057, the sample was stuck to
a glass plate. The polarizer was peeled away in the 45-degree
direction relative to the absorption axis thereof, and from the
peeling degree between the polarizing element and the sample
film, the sample was evaluated according to the following
evaluation standards. The rank B and the rank A are on a level
suitable to practical use.
A : No film remained on the glass plate.
B : The area of the film remained on the glass plate is
at most 1/4 of the adhered area.
C : The area of the film remained on the glass plate is
from more than 1/4 to 1/2 the adhered area.
D : The area of the film remained on the glass plate is
more than 1/2 of the adhered area.
The evaluation results are shown in Table 4 below.

From the above, it is known that the films of the invention
are all free from the problem of display unevenness to occur
when the other parts in a liquid crystal display device are kept
in contact with the cellulose ester film moiety thereof, and
can be readily stuck to a polarizing element, and have a good
film surface condition. Further, it is known that the films
of Examples 11, 15 and 16 are especially excellent in
reworkability .
Regarding the dope AD9 not satisfying the range of the
production method of the invention, the ingredients could not
well dissolve, and therefore the dope was not tested for
measurement of the solution viscosity and was not used for film
formation .
While the present invention has been described in detail
and with reference to specific embodiments thereof, it will be
apparent to one skilled in the art that various changes and
modifications can be made therein without departing from the
spirit and scope thereof.
The present disclosure relates to the subject matter
contained in Japanese Patent Application No. 2010-219612 filed
on September 29, 2010 and Japanese Patent Application No.
2011-146320 filed on June 30, 2011, the contents of which are
expressly incorporated herein by reference in their entirety.
All the publications referred to in the present specification
are also expressly incorporated herein by reference in their
entirety.
The foregoing description of preferred embodiments of the
invention has been presented for purposes of illustration and
description, and is not intended to be exhaustive or to limit
the invention to the precise form disclosed. The description
was selected to best explain the principles of the invention
and their practical application to enable others skilled in the
art to best utilize the invention in various embodiments and
various modifications as are suited to the particular use
contemplated. It is intended that the scope of the invention
not be limited by the specification, but be defined claims.
CLAIMS
1 . An optical film having an acrylic resin layer
containing an acrylic resin, and, as formed on the surface of
the acrylic resin layer, at least one cellulose acylate layer
containing a cellulose acylate, wherein the weight-average
molecular weight of the acrylic resin used as the main
ingredient in the acrylic resin layer is from 600,000 to
4 ,000, 000.
2 . The optical film according to Claim 1 , wherein the
weight-average molecular weight of the cellulose acylate used
as the main ingredient in the cellulose acylate layer is from
50,000 to 500,000.
3 . The optical film according to Claim 1 or 2 , wherein
the thickness of the acrylic resin layer is from 20 to 0 ,
and the thickness of every cellulose acylate layer is from 1
to 10 .
4 . The optical film according to any one of Claims 1 to
3 , wherein the proportion of the total thickness of the
cellulose acylate layer to the overall film thickness is at most
40%.
5 . The optical film according to any one of Claims 1 to
4 , wherein the degree of substitution with the acyl group in
the cellulose acylate is from 1.2 to 3.0.
6 . The optical film according to any one of Claims 1 to
5 , wherein the weight-average molecular weight of the acrylic
resin used as the main ingredient in the acrylic resin layer
is from 1,000,000 to 1,800,000.
7 . The optical film according to any one of Claims 1 to
6 , which has a photoelastic coefficient of from -5.0 to 5.0 x
10 12 Pa 1 .
8 . The optical film according to any one of Claims 1 to
7 , wherein the in-plane retardation, Re, defined by the
following formula (I) and the thickness-direction retardation,
Rth, defined by the following formula (II) satisfy the following
formula (III) and the following formula (IV) in an environment
at 25°C and at a relative humidity of 60%, and wherein the
absolute value of the difference between the value Rth measured
in an environment at 25°C and at a relative humidity of 10% and
the value Rth measured in an environment at 25°C and at a relative
humidity of 80% is at most 10 nm:
(I) Re = (nx - ny) x d
(II) Rth = { (nx + ny) /2 - nz} x d
(III) |Re| < 10 nm
(IV) |Rth| < 25 nm
wherein nx means the in-plane refractive index of the film in
the slow axis direction; ny means the in-plane refractive index
of the film in the fast axis direction; n z means the refractive
index of the film in the thickness direction; d means the film
thickness (nm) .
9 . The optical film according to any one of Claims 1 to
8 , wherein the cellulose acylate layer is provided on both
surfaces of the acrylic resin layer.
10. A method for producing an optical film comprising:
casting at least two types of dopes (A) and (B) each
containing a thermoplastic resin and an organic solvent onto
a casting substrate simultaneously or successively in the order
of (A) -(B) -(A) from the casting substrate side, and
removing the organic solvent,
wherein the dope (A) contains a cellulose acylate and the dope
(B) contains an acrylic resin having a weight-average molecular
weight of from 600,000 to 4,000,000.
11. The method for producing an optical film according
to Claim 10, wherein the weight-average molecular weight of the
cellulose acylate contained in the dope (A) is from 50, 000 to
500, 000.
12. The method for producing an optical film according
to Claim 10 or 11, wherein the solid concentration of the dope
(A) and the dope (B) each is from 16 to 30% b y mass.
13. The method for producing an optical film according
to any one o f Claims 10 to 12, wherein the absolute value of
the difference between the solid concentration of the dope (A)
and that of the dope (B) is at most 10% by mass.
14. The method for producing an optical film according
to any one of Claims 10 to 13, wherein the complex viscosity
of the dope (A) and the dope (B) each is from 10 to 80 Pa-s and
the complex viscosity of the dope (B) is larger than the complex
viscosity of the dope (A) .
15. The method for producing an optical film according
to any one of Claims 10 to 14, wherein in the organic solvent
contained in the dope (A) and the dope (B) , the proportion of
methanol to the entire organic solvent in the dope is from 20
to 35% by mass.
16. An optical film produced by the method for producing
an optical film of any one of Claims 10 to 15.
17. A polarizer comprising a polarizing element and the
optical film of any one of Claims 1 to 9 and 16.
18. A liquid crystal display device comprising the
optical film of any one of Claims 1 to 9 and 16 or the polarizer
of Claim 17.