DESCRIPTION
Title of Invention
FIBER-RIEXNFORCED COMPOSITE MATERIAL
Technical Field
The present invention relates to a fiber-reinforced composite material constituted by
reinforcing fibers and a thermoplastic resin, and which is thin-walled and excellent in
mechanical properties and may provide an isotropic shaped product.
Background Art
A fiber-reinforced composite material in which carbon fibers, aramid fibers, glass
fibers or the like are used as reinforcing fibers has been widely utilized for structural materials
of aircrafts, vehicles or the like, or in general industries and sports such as a tennis racket, a
golf club shaft and a fishing rod by utilizing high specific strength and high specific elasticity
thereof. The forms of reinforcing fibers used therein may include a woven fabric made by
using continuous fibers, a UD sheet in which fibers are pulled and aligned unidirectionally, a
random sheet made by using cut fibers, a non-woven fabric and the Iike.
Generally, in case of the fabric made from continuous fibers or the UD sheet and the
Iike. complicated layering steps such as layering at various angles of, for example, 0/+451-
45/90, because of anisotropy of the fibers, or and fiather plane-symmetrical layering for
preventing warpage of a shaped product. This is one of factors that increase the cost for the
fiber-reinforced composite material.
Thus, by using m isotropic random mat in advance, a relatively inexpensive fiberreinforced
composite material may be obtained. The random mat may be obtained by a
spray-up method (dry production method) wherein spraying cut reinforcing fibers alone or
spraying the cut fibers together with a thermosetting resin are performed at the same time into
a mold. or a paper-manufacturing method (wet method) of adding previously cut reinforcing
fibers into an aqueous slurry containing a binder, followed by paper-making. The dry
manufacturing method requires a relatively small device and thus allows the random mat to be
obtained at a lower cost.
In the dry production method, a method of cutting continuous fibers and
simultaneously spraying the cut fibers is frequently used, and a rotary cutter is used mostly,
However, when an interval between blades of the cutter is widened in order to increase a fiber
length, the cut frequency is decreased and thus results in discontinuous discharge of the fibers
from the cutter. For this reason, unevenness in fiber areal weight of the fibers in the mat
locally occurs. Especially, when a mat with a low fiber areal weight of fibers is made, there
is a problem in that unevenness in thickness becomes significant and thus surface appearance
is deteriorated.
Meanwhile, another factor that increases the cost for the fiber-reinforced composite
material is that a long time is required for molding. In general, the fiber-reinforced
composite material is obtained by heating and pressurizing a material called a prepreg by an
autoclave for 2 hours or more, in which the prepreg is obtained by impregnating a reinforcing
fiber base material with a thermosetting resin in advance. There has recently been suggested
an RTM molding method in which a reinforcing fiber base material not impregnated with a
resin is set in a mold, and a thermosetting resin is poured thereto. This significantly shortens
a time for molding. However, even though the RTM molding method is adopted, a time
required for rnoIding one part is 10 minutes or more.
Therefore, a composite material employing a thermoplastic resin as a matrix, in place
of conventional thermosetting resin, has been spotlighted. However, the tbermopliistic resin
generally has a higher viscosity than the thermosetting resin, and thus has a problem in that a
time far impregnating a fiber base material with the molten resin is long, and as a result, a tact
time until molding is prolonged. .
As a method for solving the foregoing problems, there is suggested a method called
therrnoplastic stamping molding (TP-SMC). This is a molding method in which chopped
fibers impregnated with a thermoplastic resin in advance are heated up to a melting point or
more or a flowable temperature or more of the resin, and me put into a part of a mold, and
immediately, the mold is closed. In the method, the fibers and the resin are allowed to flow
in the mold so as to form a product shape, followed by cooling to form a shaped product. In
the method, since the fibers impregnated with the resin in advance are used, it is possible to
mold in a short time of about I minute. A methad of manufacturing a chopped fiber bundle
and a molding material is disclosed in Patent Documents 1 and 2. However, the disclosed
method empioys a molding material called an SMC or a stampable sheet. In such
thermoplastic stamping molding, fibers and a resin are largely flowed within a mold, and thus
fiber orientation is disturbed. In a case of a random mat employing cut fibers, lack of
isotropy is caused due to unidirectional fiber orientation. As a result, a development rate of
physical property of an isotropic composite material is lowered by unidirectiona1 orientation
caused by the flow of the resin and the reinforcing fibers. Also, in the molding within the
mold accompanying the flow of the reinforcing fibers and the matrix resin, especially, a mold
temperature or a mold structure has to be investigated in order to secure stability in a thickness
direction and a planar dimension of a shaped product. Thus, there is a problem in that it is
difficult to adjust manufacturing conditions in mass production, and also it is difficult to make
a thin-walled product. Meanwhile, fox the composite material employing the thermoplastic
resin as a matrix, there is suggested a technique in which a long-fiber pellet that contains
reinforcing fibers is injection-molded. However, the long-fiber pellet dso has a limitation on
the length of the pellet. Further, there is a problem in that the reinforcing fibers in the
thermoplastic resin are cut by kneading and thus the length of the reinforcing fibers may not
be kept. Also, the molding method through such injection molding has a problem in that the
reinforcing fibers are oriented, and thus isotropy may not be achieved.
Also, as a means for a thin-walled product without flow of fibers, there is suggested a
method of manufacturing a prepreg in which a thin sheet is manufactured from reinforcing
fibers through a paper-making method, and then the thin sheet is impregnated with a resin
(Patent Document 3). In the paper-making method, since reinforcing fibers are uniformIy
dispersed in a dispersion liquid, the reinforcing fibers are in single fiber form.
(Patent Document 1) Japanese Patent Laid-Open Publication No. 2009-1 1461 1
(Patent Document 2) Japanese Patent Laid-Open Publication No. 2009- 1 146 12
(Patent Document 3) Japanese Patent Laid-Open Publication No. 20 10-235779
Summary of Invention
Problems to be solved
An object of the present invention is to provide a fiber-reinforced composite material
constituted by reinforcing fibers and a thermoplastic resin, which is thin-walled and excellent
in mechanical properties and may provide an isotropic shaped product. Further, in the fiberreinforced
composite material of the present invention, the fiber-reinforced composite material
has a particular viscodastic characteristic, and thus the reinforcing fibers and the matrix resin
may be flowed at a predetermined level within a mold so that a shaped product may be
dimensionally accurately obtained.
Means for solving the Problems
In order to obtain an isotropic shaped product which is thin-wdled and excellent in
mechanical properties, extensive studies have been made. As a result, it has been found that
when a fiber-reinforced composite material has a particular viscoelastic characteristic, a
thermoplastic matrix resin may be easily impregnated, and the matrix resin and reinforcing
fibers are allowed to be flowed at a predetermined level so that unidirectional orientation of
the reinforcing fibers may be suppressed during molding. The present invention has been
made based on these findings. That is, the fiber-reinforced composite material of the present
invention constituted by reinforcing fibers with an average fiber length of 5 mm to 100 mm
and a thermoplastic resin, in which in tad' that exhibits a viscoelastic characteristic as defmed
by following formulas (1) and (21, an average value of tan6' in a range of -2S°C of the melting
point of a matrix resin to +2S°C of the melting point of a matrix resin satisfies following
formula (3).
tanS= G/G' (1)
tan6'=Vfx tan6/(1OO-Vf) (2)
0.015tmG'~0 .2 (3)
(wherein, G' represents a storage modulus (Pa) of the fiber-reinfbrced composite
material, G" represents a loss modulus (Pa) of the fiber-reinforced composite material, and Vf
represents a volume fiaction (%) of the reinforcing fibers in the fiber-reinforced composite
material)
The fiber-reinforced composite material may be preferably obtained by mol&ng a
random mat in which reinforcing fibers included in the composite material have a specific
opening degree. In the random mat that has the reinforcing fibers having a specific opening
degree, a ratio of reinforcing fiber bundles (A) constihlted by the reinforcing fibers of a critical
single fiber number or more defined by formula (4) with respect to a total amout of the
reinforcing fibers in the mat is 20 VoI% or more and less than 90 Vol%, and an average
number of fibers (N) in the reinforcing fiber bundles (A) satisfies following formula (5).
Critical single fiber number=600/D (4)
Q.~~~o~/1xD10~5 /D< 2N < (5)
(wherein D represents an average fiber diameter (pm) of single reinforcing frbers)
Effect of Invention
Through the fiber-reinforced composite material of the present invention, a shaped
product excellent in a surface appearance may be provided with high dimensional accuracy.
Here, high dimensional accuracy indicates that the shaped product may be formed with a
required thickness, and the shaped article may be produced according to a mold shape.
Especially, the thickness dimension of the shaped product is highly influential on material
properties such as tensile strength or bending strength, and finally becomes a critical factor
that determines whether the shaped product as a structure body may allow a product in
accordance with designed values to be manufactured. Thus, an effect that a shaped product
in accordance with designed valued may be obtained by using the fiber-reinforced composite
material of the present invention is large.
Also, when the fiber-reinforced composite material of the present invention is used for
molding, a shaped article may be thinned and isotropic, and shape follow-up property into a
complicated three-dimensional shape may be secured. The fiber-reinforced composite
material of the present invention may be used as a preform for various kinds of structural
members, for example, an inner plate, an outer plate, and constructional elements of a vehicle,
various electrical products, a frame or a housing of a machine.
Brief Description of Drawings
FIG. 1 is a schematic view illustrating a step for cutting a fiber bundle.
FIG. 2 is a schematic view illustrating a front side and a cross-section of a rotary spiral
cutter.
FIG. 3 is a schematic view illustrating a fiont side and a cross-section of a rotary fiber
separating cutter.
FIG. 4 shows measurement results of tan6' in a fiber-rexorced composite material of
Example 1.
FIG. 5 shows measurement results of tad' in a fiber-reinforced composite material of
Example 2.
FIG. 6 shows measurement results of tad' in a fiber-reinforced composite material of
Comparative Example 1.
Best Mode for Carrying Out the Invention
Hereinafter, the exemplary embodiments of the present invention will be sequentially
described.
[Fiber-reinforced composite material]
A fiber-reinforced composite material of the present invention is constituted by
reinforcing fibers with an average fiber length of 5 mm to 100 - and a ~ e m o p l=dsi n,
in which an elastic component is substantially dominant in the deformation characteristic of
the composite material.
The fiber-reinforced composite rnaterial of the present invention is characterized in that
in tanSY that exhibits a viscoelastic characteristic as defined by following formulas (1) and (2),
an average value of tang' in a range of -25°C of the melting point of a matrix resin to +25*C of
the melting point of the matrix resin satisfies formula (3).
tanG=G/G' (1)
tan6'=Vfxtanti/(lOO-Vf) (2)
0.0 1 Ltan6'10.2 (3)
(wherein G' represents a storage modulus (Pa) of the fiber-reinforced composite
material, G" represents a loss modulus (Pa) of the fiber-reinforced composite material, and Vf
represents a volume fiaction (5%) of reinforcing fibers in the fiber-reinforced composite
material)
Here, "the elastic component is substantially dominant in the deformation
characteristic of the composite material" indicates that in the thermal deformation of the
composite rnaterial, a dimensionless value of GN/G' by a volume fiaction of the reinforcing
fibers included in the composite material is not greater than 0.2, in which G" indicates a
viscous component dominating a flow characteristic of a material, that is, a loss modulus of
the composite material, and 0' indicates a component dominating a shape retention
characteristic of a material, that is, a storage modulus of the composite material.
[Reinforcing fibers in fiber-reinforced composite material]
The fiber-reinforced composite material of the present invention is characterized in that
it includes reinforcing fibers which are long to some extent, and thus may exhibit st reinforchg
function. The fiber length of the reinforcing fibers is represented by an average fiber length
which is obtained by measuring a fiber length of the reinforcing fibers in the fiber-reinforced
composite material. There may be a method of measwing the average fiber length, in which
after a resin is removed within a furnace at 500°C for about 1 hour, fiber lengths of randomly
extracted 100 fibers are measured to a unit of 1 rnm by using a vernier caliper or a loupe, and
the average thereof is obtained.
In the fiber-reinforced composite rnaterial of the present invention, the average fiber
length of the reinforcing fibers ranges from 5 mm to 100 mm, preferably ffom 10 rnm to 100
mm, more preferably from 15 mm to 100 rnm, and further more preferably from I5 mm to 80
mm. Further, a range fiom 20 mrn to 60 mm is preferred.
In a preferred example of manufh3uring the composite material as described later,
when the reinforcing fibers are cut into a fixed length to manufacture a random mat, the
average fiber length of the reinforcing fibers in the random mat and the composite material is
almost the same as the cut fiber length.
The composite material is useful as a prepreg for molding, and its density may be
variously selected according to a required shaped product. The fiber areal weight of the
reinforcing fibers in the composite material preferably ranges fiom 25 g/m2 to 4500 g/rn2.
Preferably, in the reinforcing fibers in the fiber-reinforced composite material, there
exist reinforcing fiber bundles (A) constituted by the reinforcing fibers of a critical single fiber
number or more defined by formuIa (4), reinforcing fibers in the single form, and fiber bundles
having a single fiber number less than the critical single fiber number.
CriticaI single fiber nurnber=6oO/D (4)
(wherein D represents an average fiber diameter (pm) of single reinforcing fibers)
In the reinforcing fibers in the fiber-reinforced composite material, the ratio of the
reinforcing fiber bundles (A) with respect to the total amount of fibers in the fiber-reinforced
composite material is preferably 20 Vol% or more and less than 90 Val%. The ratio is more
preferably 30 Vol% or more and less than 90 Vol%.
In the reinforcing fibers in the fiber-reinforced composite material, the average number
of fibers (N) in the reinforcing fiber bundles (A) preferably satisfies the following formula (5).
4 2 0.7~10/D < N< 1x105 / D 2 (5)
(wherein D represents an average fiber diameter (p)of single reinforcing fibers)
Specifically, the average number of fibers (N) in the reinforcing fiber bundles (A)
constituted by the reinforcing fibers of the critical single fiber number or more is preferably
less than 6x104 / D2 .
The fiber-reinforced composite material may be preferably manufactured by pressmolding
a random mat that includes reinforcing fibers and a thermoplastic resin. The
opening degree of the reinforcing fibers in the fiber-reinforced composite material is
substantially maintained in the random mat. In the reinforcing fibers in the fiber-reinforced
composite material, the ratio of the reinforcing fiber bundles (A), and the average number of
fibers (N) in the reinforcing fiber bundles (A) may be preferably adjusted to be withih the
foregoing range by controlling the ratio of the reinforcing fiber bundles (A) in the random mat,
and the average number of fibers (N) in the reinforcing fiber bundles (A) in the random mat.
A prefemed method of controlling the ratio of the reinforcing fiber bundles (A) in the random
mat, and the average number of fibers will be described later.
The reinforcing fiber that constitutes the fiber-reinforced composite material is
pretkrably at least one kind selected from the group consisting of a carbon fiber, an m i d
fiber and a glass fiber. They may be used in combination, Among them, the carbon fiber is
preferred from the viewpoint of providing a composite material that is lightweight and
excellent in strength. In a case of the carbon fiber, the average fiber diameter preferably
ranges from 3 pm to 12 p, and more preferably from 5 pn to 7 pm.
As for the reinforcing fibers, fibers added with a sizing agent are preferably used.
The sizing agent is preferably used in an amount of greater than 0 parts to 10 parts by weight
based on 100 parts by weight of the reinforcing fibers.
[Thermoplastic resin in fiber-reinforced composite material]
There is no specific limitation on the kind of the thermoplastic resin that constitutes the
fiber-reinforced composite material, and examples thereof may include a vinyl chloride resin,
a vinyiidene chloride resin, a vinyl acetate resin, a polyvinyl alcohol resin, a polystyrene resin,
an acrylonitrile-styrene resin (AS resin), an acrylonitrile-butadiene-stpene resin (mS resin),
an acrylic resin, a methacrylc resin, a polyethylene resin, a polypropylene resin, a polyamide
6 resin, a polyamide 1 I resin, a polyamide 12 resin, a polyamide 46 resin, a poiyamide 66
resin, a polyamide 610 resin, a polyacetal resin, a polyearbonate resin, a polyethylene
terephthalate resin, a polyethylene naphthalate resin, a polybutylene terephthalate resin, a
polybutylene naphthalate resin, a polyarylate resin, a polyphenylene ether resin, a
polyphenylene sulfide resin, a polysulfonc resin, a polyethersulfone resin, a polyetherefher
kerone resin, a polylactic resin and so on. Among them, at least one kind selected &om the
group consisting of a polyamide 6 resin, and a polypropylene resin is preferred. These
thermopIastic resins may be used alone or in combination of two or more thereof.
The thermoplastic resin exists in the fiber-reinforced composite material in an amount
of preferably 50 parts to 1,000 parts by weight based on 100 parts by weight of the reinforcing
fibers. More preferably, the thermoplastic resin exists in an amount of 55 parts to 500 parts
by weight based on 100 parts by weight of the reinforcing fibers, and M e r more preferably,
the thermoplastic resin exists in an amount of 60 parts to 300 parts by weight based on I00
parts by weight of the reinforcing fibers.
In the fiber-reidorced composite material, the reinforcing fiber volume fraction (Vf)
defined by the following formula (7) preferably ranges from 5% to 80%.
Reinforcing fiber volume fraction (Vf) = 100 x volume of reinforcing fiber/(volume of
reinforcing fibers + volume of thermoplastic resin) (7)
The reinforcing fiber volume fraction (V£) represents a composition of the reinforcing
fibers and the thermoplastic resin included in the fiber-reinforced composite material, that is, a
shaped product formed by the fiber-reinforced composite material. When the reinforcing
fiber volume fraction is lower than 4%, a reinforcing effect may not be sufficiently exhibited.
Also, when the content is greater an 8094, there is a possibility that a void may be easily
generated in the fiber-reinforced composite material, and the physical property of the shaped
product may be deteriorated. It is more preferred fiat the reinforcing fiber volume fraction
ranges from 20% to 60%.
In an example of a specific method of calculating the forgoing reinforcing fiber volume
fraction (Vf), mass values of reinforcing fibers and a thermoplastic resin are obtained by
removing the thermoplastic resin fkom a specimen of a shaped product, and converted into
volumes by using densities of the respective components, and the volume values are
substituted in the formula above.
As for a method of removing the thermoplastic resin from the shaped product specimen,
a method using combustion (thermal decomposition) removal may be simply and preferably
used when the reinforcing fibers are inorganic fibers such as carbon fibers or glass fibers. In
this case, a mass af a sufficiently dried specimen of a shaped product is weighed, and then is
treated using an electric furnace or the like at 500°C to 700°C for 5 to 60 minutes so as to
combust the thermoplastic resin component. The remaining reinforcing fibers after the
combustion are left cool in a dry atmosphere, and weighed so as to calculate masses of the
respective components.
As for a method of removing the thermoplastic resin fiam the shaped product specimen,
there is another preferred method in which a chemical material capable of easily decomposing
or dissolving the thermoplastic resin is used so that the thermoplastic resin may be removed
through decomposition or dissolution. Specifically, the mass of a shaped product specimen
formed into a thin piece having an area of l cm' to 10 cm2 is weighed, and then a chemical
material capable of dissolving or decomposing the thermoplastic resin may be used to extract a
component dissolved therein, Then, the residue is washed and dried, and then weighed so as
to calculate masses of respective c~mponmts. For example, in a case where the
thermoplastic resin is polypropylene, rhe polypropylene may be dissolved using heated toluene
or xylene. In a case where the thermoplastic resin is polyamide, the polyamide may be
decomposed using heated formic acid. When the resin is polycarbonate, the polycarbonate
may be dissolved using heated chlorinated hydrocarbon.
When the fiber-reinforced composite material is obtained form a random mat, the ratio
of the supply amount (based on mass) ofthe reinforcing fiber content to the resin content in
manufacturing the random mat may be considered as the mass ratio of the reinforcing fiber
content to the resin content in the random mat.
[Other agents]
The fiber-reinforced composite material of the present invention may include various
kinds of fibrous or non-fibrous fillers made kern an organic fiber or an inorganic fiber, or
additives such as a flame retardant, an anti-W agent, a pigment, a releasing agent, a softening
agent, a plasticizer or a surfactant within a limitation that does not impair the object of the
present invention.
[Flow characteristic of fiber-reinforced composite material]
In a heating step within a mold at the time of molding, restraint of a material within a
flow range at a predetermined level has a preferable influence on retaining the development
rate of physical property of reinforcing-fiber of anisotropic material and the product dimension
accuracy. The fiber-reinforced composite material of the present invention is characterized
in which in tan6' that exhibits a viscoelastic characteristic as defined by formulas (1) and (2),
an average value of tans' in a range of -25°C of the melting point of a matrix resin to +2S°C of
the melting point of a matrix resin satisfies the following formula (3).
tanS= G"fG' (1)
tan8'=VfxtanG/(1 OO-Vf) (2)
(wherein G' represents a storage modulus (Pa) of the fiber-reinforced composite
material, G" represents a loss modulus (Pa) of the fiber-reinforced composite material, and Vf
represents a volume fraction (%) of the reinforcing fibers in the fiber-reinforced composite
material.)
0.0 1 ~tan6'50.2 (3)
Here, G' represents an elastic component of a material, and 0" represents a viscous
component. In material properties having both of the viscous component and the elastic
component, tan6 represents a behavior when a material is deformed by a strain, and represents
which one of the viscous component and the elastic component appears as a dominant
behavior, as a ratio of the viscous component and the elastic component. As the viscous
effect is larger, tan6 has a larger value. The fiber-reinforced composite material of the
present invention is characterized in that in a range of -25OC of the melting point of a
resin to +25OC of the melting point of the matrix resin, tad' that exhibits a viscoelastic
characteristic is substantially fixed. Further, the fiber-reinforced composite rnaterial of the
present invention preferably satisfies the formula (3) even in a range of -25°C of the melting
point of a matrix resin to +35OC of the melting point of the matrix resin.
When tan6' is less than 0.01, the storage modulus G' of the fiber-reinforced composite
material is relatively higher with respect to the loss modulus G", and the material becomes a
rigid material in which the reinforcing fibers and the matrix resin never flow at the time of
heating. Thus, at the time af heating in a press-molding step, follow-up property in mold of
the material is impaired, and thus it is dificult to obtain a predetermined product shape.
Meanwhile, when EanG' is a value greater than 0.2, fie effect of the storage modulus G' is
relatively lowered with respect to the loss modulus G", and the material allows the reinforcing
fibers and the matrix resin to easily flow at the time of heating. Thus, a significant
unidirectional orientation of the reinforcing fibers is generated. When the value of tad'
ranges from 0.01 to 0.2, it is possible to secure shape follow-up propem into a complicated
three-dimensional shape by slightly flowing the material in a range capable of securing a
product dimension in accordance with a find shape of a composite material product.
The average value of tan6' in a range of -25°C of the melting point of a matrix resin to
-t25"C of the melting point of the matrix resin more preferably ranges fiom 0.02 to 0.15.
FIGS. 4 and 5 show measurement results of tad' exhibiting a viscoelastic
characteristic in an example of fhe fiber-reinforced composite material of the present invention,
in which the fiber-reidorced composite material includes polyamide as a matrix, and carbon
fibers as reinforcing fibers, and a volume fraction of the carbon fibers is 30%. FIG. 4 shows
measurement results of the viscoelastic characteristic (that is, tan6') of a fiber-reinforced
composite material obtained from a random mat in which the ratio of reinforcing fiber bundles
(A) constituted by the reinforcing fibers of a critical single fiber number or more defined by
formula (4) is 30 Vol% or more with respect to tbe total amount of fibers in the mat. FIG. 5
shows measurement results of the viscoelastic characteristic (tan8') of a fiber-reinforced
composite material obtained forrn a random mat in which the ratio of reinforcing fiber bundles
(A) is 70%. The horizontal axis indicates the range of a heating temperature around the
melting point (Tm) of the matrix resin (in this example, the melting point of the matrix resin is
225"C, and the measurement temperature ranges from 200°C to 260°C). The vertical axis
indicates the values of tad' of the fiber-reinforced composite material. As can be seen from
this. when the ratio of the reinforcing fiber bundles (A) constituted by the reinforcing fibers of
the critical single fiber number or more is 30% or 70%, the fiber-reinforced composite
material obtained from the random mat including the reinforcing fiber bundles (A) exhibits
substantially stable values of tan6' in a range of -25°C of the melting point of a matrix resin to
+25"C of the melting point of the matrix resin, or in the range of -25OC of the melting point of
a matrix resin to 4-35'C of the melting point of the matrix resin. That is, the fiber-reinforced
composite material in the present invention exhibits a substantially stable viscoeki.stic
characteristic in a wide temperature range which is the range of -25°C of the melting point of a
matrix resin to +35"C of the meIting point of the matrix resin, or the range of -2S°C ~f the
melting point of a matrix resin to +35OC of the melting point of the matrix resin, and indicates
that the material has a property capable of maintaining material moldability and dimensional
accuracy irrespective of the temperature condition within a mold at the time of molding.
Specifically, the viscoelastic characteristic may be controlled by selecting the ratio of
the reinforcing fiber bundles (A) in the random mat as a starting material of the fiberreinforced
composite material, or in the fiber-reinforced composite material. Especially,
when the ratio of the reinforcing fiber bundles (A) ranges fiom 20% to 40%, more specifically
from 30% to 40%, the material has a relatively high effect of a storage modulus G' with
respect to a loss modulus G , and thus it is assumed that at the time of heating the material
within a mold, the reinforcing fibers and the matrix resin are required to be slightly flowed to
secure formability.
Meanwhile, when the ratio of the reinforcing fiber bundles (A) ranges fiom 70% or
more and less than 90%, the materia1 has a relatively low effect of a storage modulus G' with
respect to a loss modulus G", and thus it is assumed that at the time of heating the material
within a mold, the reinforcing fibers and the matfix resin are required to be flowed at a
predetermined level to suppress unidirectional orientation of the reinforcing fibers, such that
the formability into a complicated shape may be secured only while maintaining the isotropy.
[Random Mat]
The fiber-reinforced composite material of the present invention which satisfies a
particular viscoeIastic characteristic and is constituted by reinforcing fibers and a
thermoplastic resin and may be preferably obtained by molding a random mat in which the
reinforcing fibers satisfies a specific opening degree. The random mat in which the
reinforcing fibers exist at a specific opening degree, specifically includes reinforcing fibers
with an average fiber length of 5 mm to 100 mm and a thermoplastic resin, in which the fiber
areal wei@t of the reinforcing fibers ranges from 25 g/m2 to 3,000 g/m2, the reinforcing fiber
bundles (A) constituted by the reinforcing fiber of a critical single fiber number or more
defined by the following formula (4) is included in the ratio of 20 Vol% or more and less than
90 Vol% with respect to the total amount of fibers in the mat, and the average number of fibers
(N) in the reinforcing fiber bundles (A) satisfies the following formula (5).
Critical single fiber number=600/D (4)
0.7~140J D2 +I< 1x105/DZ (5)
(wherein D represents an average fiber diameter (pm) of single reinforcing f i r s )
Within a plane of the random mat, the reinforcing fibers are not oriented in a specific
direction, but are dispersed and arranged in random directions,
The composite material of the present invention is an in-plane isotropic material. In
the shaped product employing the present invention, the ratio of modulus in two perpendicular
directions may be obtained to quantitatively evaluate the isotropy of the shaped product.
When a ratio obtained by dividing the larger one by the smaller one among modulus values in
the two directions of the shaped product is not greater than 2, the product is considered to be
isotropic. When the ratio is not greater than 1.3, the product is considered to be excellent in
isotropy.
In the random mat, the fiber areal weight of the reinforcing fibers ranges from 25
to 3,000 g/rn2. The fiber-reinforced composite material of the present invention obtained
from the random mat is useful as a prepreg, and its fiber areal weight may be variously
selected according to a required molding.
The random mat that may preferably provide the fiber-reinforced composite material of
the present invention includes, as reinforcing fibers, reinforcing fiber bundles (A) constituted
by the reinforcing fiber of a critical single fiber number or more defined by formula (4).
Critical single fiber numbe~600/D (4)
(wherein D represents an average fiber diameter (p)of single reinforcing fibers)
In the random mat, besides the reinforcing fiber bundles (A), as the reinforcing fibers,
reinforcing fibers in a single form and fiber bundles having a single fiber number less than the
critical single fiber number are contained.
The ratio of the reinforcing fiber bundles (A) with respect to the total amount of fibers
in the mat is preferably 20 Vol% or more and less than 90 Vol%. The lower limit of the
existing amount of the reinforcing fiber bundles is preferably 30 Vol%. In order that the
existing amount of the reinforcing fiber bundles is 20 Vol% or more and less than 90 Vol%, in
the following preferred manufacturing method, for example, the control may be performed by
the pressure or the like of air blown in a fiber opening step. Also, the control may be
performed by adjusting the size of fiber bundles to be subjected to a cutting step, for example,
the bundle width or the number of fibers per width. Specifically, there is a method of
widening the width of fiber bundles through extending means or the like and subjecting the
fiber bundles to a cutting step, or a method of providing a slitting step before a cutting step.
Otherwise, there is a method of cutting fiber bundles by using a so-called fiber separating
knife having a pludity of arranged short blades, or a method of simuitaneously performing
cut and slit. Preferred conditions will be described in the section about the opening step.
Further, in the random mat that may preferably provide the fiber-reinforced composite
material of the present invention, the average number of fibers (N) in the reinforcing fiber
bundles (A) constituted by the reinforcing fibers of the critical single fiber number or more
preferably satisfies the following formula (5).
0.7~140 / D2< N<~x~o'/D' (5)
(wherein D represents an average fiber diameter (pm) of single reinforcing fibers)
Specifically, the average number of fibers (N) in the reinforcing fiber bundles (A)
constituted by the reinforcing fibers of the critical single fiber number or more is preferably
less than 6 x1 04 L D 2 .
In order that the average number of fibers (N) in the reinforcing fiber bundles (A) is
within the foregoing range, in the following preferred manufacturing method, the control may
be performed by adjusting the size of fiber bundles to be subjected to a cueing step, for
example, the bundle width or the number of fibers per width. Specifically, there may be a
method of widening the width of fiber bundles through extending means or the like and
subjecting the fiber bundles to a cutting step, or a method of providing a slitting step before a
cutting step. Otherwise, the fiber bundles may be cut and slit at once.
Also, the average number of fibers (N) in the reinforcing fiber bundles (A) may be
controlled by adjusting the degree of opening of the cut fiber bundles through the pressure or
the like of air blown in the opening step. Preferred conditions will be described in the
sections about the opening step and the cutting step.
Specifically, when the average fiber diameter of the carbon fibers that constitute the
random mat ranges from 5 pm to 7 p, the critical single fiber number ranges from 86 to 120,
and when the average fiber diameter of the carbon fibers is 5 pm, the average number of fibers
in the fiber bundles is greater than 280 and less than 4,000, and preferably ranges from 600 to
2,500, and more preferably fiom 600 to 1,600. When the average fiber diameter of the
carbon fibers is 7 p, the average number of fibers in the fiber bundles is greater than 142 and
less than 2,040, and preferably ranges from 300 to 1,500, and more preferably from 300 to 800.
The random mat constituted by the reinforcing fibers and the thermoplastic resin as
described above, in which the thermoplastic resin exists in a solid phase, and the random mat
serves as a preform to obtain the fiber-reinforced composite material of the present invention.
The kinds of the thermoplastic resin are as described above. In the random mat, the
thermoplastic resin preferably exists in a fibrous and/or particulate form. When the
reinforcing fibers mixed with the thermoplastic resin in the fibrous andor particulate form
exist. there is a characteristic that the fibers and the resin are not required to be flowed within a
mold, and the thermoplastic resin may be easily impregnated within the reinforcing fiber
bundles and between single fibers of the reinforcing fibers at the time of molding. Two or
more kinds of thermoplastic resins may be used, and the fibrous form and the particulate form
may be used in combination.
In the case of the fibrous form, the fineness ranges fiom 100 dtex to 5,000 dtex, and
more preferably from 1,000 dtex to 2,000 dtex. The average fiber length preferably ranges
from 0.5 mm to 50 mm, and more preferably from 1 mrn to 10 mm.
The particulate form may preferably employ a spherical, strip or cylindrical (e.g.,
pellet) shape. The spherical shape may preferably employ a rotating body of a circle or an
ellipse, or an egg-like shape. The spherical shape preferably has an average particle diameter
ranging from 0.01 prn to 1,000 p.m. The average particle diameter more preferably ranges
fiom 0.1 pm to 900 pm, and further more preferably from I prn to 800 pm. There is no
particular limitation on the distribution of the particle diameter, but for the purpose of
obtaining a thinner shaped product, a sharp distribution is more preferred. Meanwhile, by an
operation such as classification, a desired particle size distribution may be achieved.
The strip form may employ, as a preferred shape, a cylindrical (e.g., pellet), prismatic
or scaly-piece shape, and also may preferably employ a film cut into a recmgular form. In
this case, the aspect ratio to some extent may be employed, but the preferred length may be
almost the same as that in the fibrous form.
The random mat may include various kinds of fibrous or non-fibrous fillers of an
organic fiber, or additives such as a flame retardant, an anti-W agent, a pigmcnt, a releasing
agent, a softening agent, a plasticizer or a surfactant within a limitation that does not impair
the object of the present invention.
[Method of manufacturing fiber-reinforced composite material]
Hereinafter, a preferred method of obtaining the fiber-reinforced composite material of
the present invention will be described. The fiber-reinforced composite material of the
present invention may be preferably manufactured by press-molding a random mat constituted
by reinforcing fibers and a thermoplastic resin.
That is, the fiber-reinforced composite material of the present invention is preferably
manufactured by the following steps (I) to (5):
(1 ) step of cutting reinforcing fiber bundles;
(2) step of introducing the cut reinforcing fiber bundles into a tube, and opening a fiber
bundle by blowing air thereto;
(3) application step of spreading the opened reinforcing fibers and at the same time
while suctioning the fibers together with a thermoplastic resin in the fibrous or particdate
form to spray the reinforcing fibers and the thermoplastic resin;
(4) step of fixing the applied reinforcing fibers and the applied thermoplastic resin to
obtain a random mat; and
(5) step of press-molding the obtained random mat.
Hereinafter, each step will be described in detail.
[Cutting step]
In the method of the present invention, a method of cutting the reinforcing fiber
specifically includes a step of cutting the reinforcing fiber bundles by using a knife. As for
the knife used for the cutting, a rotary cutter or the like is preferred. As for the rotary cutter,
a spiral knife, or a so-called fiber separating knife having a plurality of short blades manged is
preferably provided. FIG. 1 illustrates a specific schematic view illustrating the cutting step.
FIG. 2 illustrates an example of the rotary cutter having the spiral knife, and FIG. 3 illustrates
an example of the rotary cutter having the fiber separating knife.
In order that the average number of fibers CN) in the reinforcing fiber bundles (A) is
within the preferred range of the present invention, the control may be performed by adjusting
the size of fiber bundles to be subjected to the cutting step, for example, the bundle width or
the number of fibers per width.
As the fiber bundle providing to the cutting step, the reinforcing fiber bundle
previously having a fiber number within the range of the formula (5) is preferably used.
However, in general, as the number of fiber bundles is fewer, the price of the fiber becomes
expensive. Therefore, when a reinforcing fiber bundle having a large fiber number which is
available at a low cost is used, the width of the fiber bundles to be subjected to the cutting step
or the number of fibers per width is preferably adjusted before subjecting the fiber bundles to
the cutting step. Specifically, there may be a method of thinly spreading fiber bundles by
extending or the like to widen the width of the fiber bundles and then subjecting the fiber
bundles to a cutting step, or a method of providing a slit step prior to a cutting step. In the
method of providing the slit step, the fiber bundles are thinned in advance, and then are
subjected to the cutting step. Thus, as a cutter, a conventional flat blade or spiral blade with
no special mechanism may be used.
Also, there may be a method of cutting fiber bundles by using a fiber separating knife,
or a method of simultaneously peflorming cut and slit by using a cutter having a slit function.
In the case of using the fiber separating knife, the average number of fibers (N) may be
decreased by using a knife with narrow width thereof, and on the other hand, the average
number of fibers (N) may be increased by using a knife with wide width thereof.
Also, as the cutter having the slit function, a fiber separating cutter that has a blade
perpendicular to the fiber direction together with a slit-functional blade parallel to the fiber
direction may be used.
In obtaining a thermoplastic resin-reinforcing random mat having a good surface
appearance, the unevenness in fiber ma1 weight is highly influential. In a rotary cutter
having arranged conventional flat blades, the cutting of fibers is discontinuous. Then, when
such cut fibers are subjected to the application step, the unevenness in fiber areal weight
occurs. Meanwhile, when knives at a predetermined angle are used to continuously cut the
fibers without discontinuance, application with only small unevenness in fiber areal weight
may be made. That is, for the purpose of continuously cutting the reinfbrcing fibers, it is
preferred that the knives are regularly arranged at a predetermined angle on the rotary cutter.
Also the cutting is preferably made such that the angle of the arranging direction of the blade
with respect to the circumferential direction satisfies the following formula (6).
Pitch of blades = reinforcing fiber strand width x tm(90-8) (6)
(wherein 0 represents an angle of the arranging direction of a knife with respect to the
circumferential direction)
The pitch of blades in the circumferential direction is, as it is, reflected in the fiber
length of the reinforcing fibers.
FIGS. 2 and 3 are examples of a knife at a predetermined angle as described above.
In the examples of the cutter, the angle (8) of the arranging direction of the knife with respect
to the circumferential direction is illustrated in the drawings.
[Fiber opening step]
The opening step is a step of introducing the cut reinforcing fiber bundles into a tube,
and blowing air to the fibers so as to open fiber bundles. The degree of opening, the existing
amount of the reinforcing fiber bundles (A), and the average number of fibers (N) in the
reinforcing fiber bundies (A) may be appropriately controlled by pressure of air, or the like.
In the opening step, air may be directly blown to the fiber bundles fiom compressed air
blowing holes, preferably at a wind speed of 1 rn/sec to 1,000 dsec so as to open the
reinfbrcing fibers. More preferably, the wind speed ranges from 5 m/sec to 500 m/sec.
Specifically, a plurality of holes with a size of about Dl mrn to 2 mm are formed within the
tube through which the reinforcing fibers pass, and from the outside, a pressure ranging fiom
0.01 MPa to 1.0 MPa, and more preferably from 0.2 MPa to 0.8 MPa is applied so as to
directly blow the compressed air to the fiber bundles. By lowering the wind speed, it is
possible to leave more fiber bundles, while by increasing the wind speed, it is possible to open
the fiber bundles up to a single fiber form.
[Application step]
The application step is a step of spreading the opened reinforcing fibers and at the
same time, suctioning the fiber together with the thennoplastic resin in the fibrous or
particulate form to spray the reinforcing fibers and the thermoplastic resin. The opened
reinforcing fibers and the thermoplastic resin in the fibrous or particulate form are, preferably
at the same time, applied on a sheet, specifically on a breathable sheet provided below an
opening device.
In the application step, the supply amount of the thermoplastic resin preferably ranges
from 50 parts to 1,000 parts by weight based on 100 parts by weight of the reinforcing fibers.
The amount of the thermoplastic resin more preferably ranges from 55 parts to 500 parts by
weight based on 100 parts by weight of the reinforcing fibers, and Wher more preferably
from 60 parts to 300 parts by weight based on 100 parts by weight of the reinforcing fibers.
Here, the reinforcing fibers and the thermopl~tsticr esin in the fibrous or particulate
form are preferably sprayed to be two-dimensionally oriented. In order that the opened fibers
are applied to be two-dimensionally oriented, the application method and the following fixing
method are important. In the application method of the reinforcing fibers, a tapered tube
such as a cone is preferably used. Within the tube of a cone or the like, air is diffused and
thus the flow velocity within the tube is decreased, and a rotational force is applied to the
reinforcing fibers- BY using the Vem.ui effect, the opened reinforcing fibers may be
preferably spread and sprayed.
~ l s ot,h e following fixing step and the application step may be performed at the same
time. hat is, the fibers may be fixed while being applied and deposited. It is preferred that
the reinforcing fibers and the themoplastic resin are sprayed on a movable breathable sheet
having a suction mechanism, are deposited in a mat shape and are futed as it is. Here, when
the breathable sheet is provided as a conveyor constituted by a net, and is continuously moved
in unidirection to allow the fibers and the resin to be deposited thereon, a random mat may be
continuously formed. Also, by moving the breathable sheet back and forth and around,
uniform deposition may be achieved. Further, it is preferable that a leading edge of the
application (spray) unit of the reinforcing fibers and the therm~plasticr esin is reciprocated in
the direction perpendicular to the moving direction of the continuously moving breathable
support so as to continuously perform application and fixation. Here, it is preferable that the
reinforcing fibers and the thermoplmtic resin are uniformly sprayed in the random mat without
unevenness.
[Fixing step]
The fixing step is a step of fixing the applied reinforcing fibers and the applied
themoplastic resin. Preferably, the fibers are fixed by suctioning air from the bottom of the
breathable sheet. Also, the thermoplastic resin that is sprayed together with the reinforcing
tibers is mixed, and then fixed by air suction in a case of the fibrous form or together with the
reinforcing fibers even in a case of the particulate form.
By suctioning fkom the bottom through the breathable sheet, a highly twodimensionally
oriented mat may be obtained. Also, the thermoplastic resin in the particulate
or fibrous form may be suctioned by using generated negative pressure, and then easily mixed
with the reinforcing fibers by the diffiion flow generated within the tube. In the obtained
reinforced base material, the thennopiastic resin exists in the vicinity of the reinforcing fibers,
and thus the moving distance of the resin in the impregnating step is short, and the
impregnation of the resin into the mat for a relatively short time is possible. Also, a
breathable non-woven fabric made of the same material as that of the matrix resin to be used
may be set on a fixing unit in advance, and the reinforcing fibers and partides may be sprayed
on the non-woven fabric.
Through the foregoing preferred method of manufacturing the random mat, a random
mat made of fibers orientated two-dimensionally and containing few fibers whose long axes
are three-dimensionally oriented may be obtained.
Also, when a random mat is industrially produced, it is prefemd that application and
fixation are performed whik continuously moving the breathable support.
[Press]
Then, the obtained random mat may be press-molded to obtain the fiber-reidorced
composite material of the present invention. Here, a plurality of sheets of random mat may
be stacked to a required thickness or fiber areal weight and pressed. There is no specific
limitation on the method and condition of press-molding, but, specifically, it is preferred that
the thermoplastic resin in the random mat is molten under pressure, and is impregnated into
the reinforcing fiber bundles and between single fibers of the reinforcing fibers, followed by
cooling and molding. Especially, heat-press is preferably performed under a condition of
from the melting point to the melting point + 80°C of the matrix thermoplastic resin, or the
decomposition temperature or Iess of the matrix thermoplastic resin, The pressure of press
and the time for press may be appropriately selected.
[Fiber-reinforced composite material]
By molding the fiber-reinforced composite material of the present invention, a shaped
product which is thin-walled and isotropic, and is excellent in mechanical properties may be
obtained. Unlike in conventional stamping molding, in molding of the fiber-reinforced
composite material of the present invention, it is not necessary to largely flow fibers and a
resin within a mold in a heating step. This suppresses the orientation of the reinforcing fibers
in one direction, which improves the mechanical properties and allows a product with a high
dimensional accuracy to be produced. Meanwhile, in molding of a complicated threedimensional
shape, especially, a vertical plane existing within a mold is problematic. That is,
there is a problem in that when a material is set on a vertical plane within a mold, the material
may be slipped down. Also, there is a problem in that in a case where a materid is set on a
vertical portion in advance, when an upper mold is slid toward a lower mold, the material on
the vertical portion quickly comes in contact with the mold as compared to a material set on a
flat portion, and thus the material on the flat portion may not be sufficiently pressurized.
Especially, when the height of the vertical plane is large, the probIem becomes significant.
Thus, in order to manufacture a shaped product in a complicated shape, it is necessary to flow
a material at a predetermined level. The fiber-reinforced composite material of the present
invention has a particular viscoelastic characteristic, and thus it is possible to flow the
reinforcing fibers and the matrix resin at a predetermined level. Thus, there is a characteristic
in that even after flowing, isotropy of the obtained shaped product of the fiber-reinforced
composite material is maintained, and thus a product with a high mechanicd property may be
dimensionally accurately obtained. Further, by flowing the reinforcing fibers and the matrix
resin within a mold, a thin-walled matter may be preferably molded.
In this manaer, for example, a plate-like fiber-reinf'orced composite material may be
efficiently obtained in a short time. The plate-like fiber-reinforced composite material is also
useful as a prepreg for three-dimensional molding, especially, a prepreg for press-molding.
Specifically, a shaped product may be obtained by a so-called cold press, in which the platelike
fiber-reinforced composite material is heated up to a melting point of the resin or more or
a glass transition point of the resin or more, and the heated material as a single sheet or a
plurality of stacked sheets in accordance with the shape of a required shaped product is
introduced into a mold kept at a temperature of Iess than a melting point of the resin or less
than a glass transition point of the resin, pressurized, and cooled.
Otherwise, a shaped product may be obtained by a so-called hot press, in which a
plate-like fiber-reinforced composite material is introduced into a mold, and heated up to a
melting point of the resin or more or a glass transition point of the resin or more, while being
subjected to press-molding, and subsequently, the mold is cooled to Iess than a melting point
of the resin or less than a glass transition temperature of the resin.
The fiber-reinforced composite material of the present invention is a material in which
an elastic component is substantially dominant in the deformation characteristic of the
composite material.
Examples
Hereinafter, Examples will be described, but the present invention is not limited
thereto.
1) Analysis of reinforcing fiber bundles in random mat
A random mat is cut into a size of about 100 mm x 100 mm.
From the cut mat, all of fiber bundles are extracted by tweezers, the number of bundles
(I) of reinforcing fiber bundles (A), and the length (Li) and the weight (Wi) of the fiber
bundles are measured and recorded. Some fiber bundles which are too small to be extracted
by the tweezers are lastly weighed in a mass (Wk). For the measurement of the weight, a
balance capable of measuring to lllO0 mg is used. Based on the fiber diameter (D) of
reinforcing fih used for the random mat, a critical single fiber number is calculated, by
which reinforcing fiber bundles (A) constituted by the reinforcing fibers of the critical single
fiber number or more and others are separated from each other. Also, when two or more
kinds of reinforcing fibers are used in combination, the fibers are divided into respective kinds,
and the respective kinds of fibers are separately measured and evaluated.
Hereinafter, the method of obtaining the average number of fibers (N) of the
reinforcing fiber bundles (A) will be described.
The number of fibers (Ni) in each reinforcing fiber bundle may be obtained fiom the
fineness (F) of the reinforcing fibers in use by the following formula.
Ni= Wi/(Lix F)
The average number of fibers (N) in the reinforcing fiber bundles (A) may be obtained
fiom the number of bundles (I) of the reinforcing fiber bundles (A) by the following formula.
N=Z Ni/I
The ratio (VR) of the reinforcing fiber bundles (A) with respect to the total amount of
fibers in the mat may be obtained by the following formula by using the densiw (p) of the
reinforcing fibers.
VR=Z(Wi/p) x 1 OO/((Wk+CWi)/p)
2) AnaIysis of reinforcing fiber bundles in fiber-reinforced composite material
In the fiber-reinforced composite material, after the resin is removed within a furnace
at 500°C for about 1 hour, measurement is performed in the same manner as in the foregoing
random mat.
3) Analysis of average fiber length of reinforcing fibers included in random mat or
composite material
The lengths of 100 reinforcing fibers randomly extracted from the random mat or the
composite material were measured to a unit of 1 mm by using a vernier caliper or a loupe and
recorded. From all of the measured lengths (Li) of the reinforcing fibers, the average fiber
length (La) was obtained by the following formula. In a case of the composite material, after
the resin was removed within a b a c e at 50U°C for about 1 hour, the reinforcing fibers were
extracted.
La-Z Lill 00
4) Analysis of fiber orientation in composite material
In a method of measuring isotropy of fibers after the molding of the composite material,
a tension test is performed based on an arbitrary direction of a molded plate, and its
perpendicular direction to measure a tensile modulus, and then among the measured values of
the tensile modulus, a ratio (EG) obtained by dividing the larger one by the smaller one is
measured. When the ratio of the elastic modulus is close to 1, the material is excellent in
isotropy. In the present Examples, when the ratio of the elastic modulus is 1.3 or less, the
material is evaluated to be excellent in isotropy.
5) Measurement of viscoelastic characteristic
A sample was processed into a diameter of 25 mm, and a thickness of 1 mm. A
dynamic analyzer RDA-ii (TA Instruments Japan) was used to measure a viscoelastic
characteristic, G' and G", according to the response when strain is periodically given to the
sample interposed between two parallel plates. Then, tan6 was obtained by the following
formula.
tan6= G'/G7 (1)
tan6'=Vfxtan6/(1OO-Vf) (2)
(wherein G' represents a storage modulus (Pa) of the fiber-reinforced composite
material, G" represents a Ioss modulus (Pa) of the fiber-reinforced composite material, and Vf
represents a volume fraction (%) of the reinforcing fibers in the fiber-reinforced composite
material)
The measurement order is as follows. By taking the effect of linear expansion of the
device itself into account, at 23O0C (in the middle of measurement temperature ranging from
200°C to 260°C), zero point between parailel plates in distance was adjusted, the sample
provided between the parallel plates was heated up to 260°C, which is a melting point or more,
and then the parallel plates were adhered to the sample (a melting point of nylon 6 is 225°C).
Here, when the clearance is varied, there is a concern that the structure of the carbon fibers
within the parallel plates may be varied. Thus, while the clearance was fixed, the
measurement was performed at a load strain of 0.1%, and a frequency of IHz, by lowering the
temperature from 260°C to 200°C.
Example 1
As reinforcing fibers, carbon fibers "TENAX" (trademark) STS40-24KS (average fiber
diameter: 7 pm, tensile strength: 4,000 MPa, fiber width: 10 mm) manufactured by TOHO
TENAX Co., Ltd were used. As for a cut device, as illustrated in FIG. 2, a rotary cutter with
a diameter of 150 rnrn was used in which spiral knives made of cemented carbide were
disposed on the surface.
Here, in the following formula (6), 8 was 5S0, and the pitch of blades was 20 mm, by
which the reinforcing fibers were cut into a fiber length of 20 m.
Pitch of blades = reinforcing fiber strand width x tan(90-Q) (6)
(wherein 6 represents an angle of the arranging direction of a knife with respect to the
circumferential direction.)
As for an opening device, a double tube was manufactured by welding nipples made of
SUS304 which have different diameters. Smdl holes were provided in the inner tube such
that compressed air was supplied by a compressor between the inner tube and the outer tube.
Here, the wind speed from the small holes was 450 m/sec. This tube was disposed just below
the rotary cutter, and below it, a tapered tube was welded. From the side surface of the
tapered tube, a nylon resin "A1030" (manufactured by Unitika Limited) was supplied as a
matrix resin such that the volume fraction (Vf) of the carbon fibers w-as 30 Vol%.
Then, a table capable of moving in XY directions was provided below the outlet of the
tapered tube, and suction from the bottom of the table was pedorrned by a blower. After the
supply amount of the reinforcing fibers was set to 110 g/min, and the supply mount of the
matrix resin was set to 253 glmin, the device was operated to obtain a random mat including
the reinforcing fibers mixed with the thermoplastic resin. When the form of the reinforcing
fibers on the random mat was observed, the fiber axis of the reinforcing fibers was
substantially parallel to the plane, and randomly dispersed in the plane. In the obtained
random mat, the average fiber length of the reinforcing fibers was 20 mm, the resin was
included in an amount of 230 parts by weight based on 100 parts by weight of carbon fibs,
and the fiber areal weight of the reinforcing fibers was 420 g/m2.
On the obtained random mat, when the ratio of the reinforcing fiber bundles (A), and
the average number of fibers (N) were investigated, the critical single fiber number defined by
formula (1) was 86, the ratio of the reinforcing fiber bundles (A) with respect to the total
amount of the fibers in the mat was 30%, and the average number of fibers (N) in the
reinforcing fiber bundles (A) was 240. Also, nylon powder was dispersed in the reinforcing
fibers without significant unevenness.
The three sheets of obtained random mat were heated at 1 MPa for 3 minutes by a
press device heated up to 260°C so as to obtain a molded plate with a material thickness of 1.0
mm, that is, the fiber-reinforced composite material of the present invention. When the
obtained molded plate was subjected to an ultrasonic detection test, a non-impregnated section
or a void was not detected.
On the obtained molded plate, when the viscoelastic characteristic (G', G" and tans)
was measured, the average value of tang' in a range of -25°C of the melting point of a matrix
resin to +25"C of the melting point of the matrix resin was 0.013. The average value of tan6'
in a mge of -25°C of the melting point of a matrix resin to +35*C of the melting point of the
matrix resin was 0.012. FIG. 4 shows the measurement results of tan6' at a temperature of
200°C to 260°C.
The thickness dimension of the obtained shaped product was 1.05mrn. Thus, it was
possible to obtain the shaped product formed in a thin plate, in which the increase in thickness
was only 5% compared to a predetermined thickness. Also, when tensile modulus in the
directions of 0" and 90°0f the obtained molded plate were measured, the ratio (ES) of moduli
was 1.03. That is, it was possible to obtain a molded plate in which fiber orientation hardly
occurred, and isotropy was maintained. When the molded plate was heated within a furnace
at 500°C for about 1 hour to remove the resin, the average fiber length of the reinforcing fibers
was measured as 20 mm. After the resin was removed fkom the molded plate, the ratio of the
reinforcing fiber bundles (A) and the average number of fibers (N) were investigated. Here,
the ratio of the reinforcing fiber bundles (A) with respect to the total amount of fibers was
30%, the average number of fibers (N) in the reinforcing fiber bundles (A) was 240, and these
measurement results were not different from those in the random mat.
Example 2
A random mat having carbon fibers in a volume fraction (Vf) of 30 Vol% was obtained
in the same manner as in Example 1, except that carbon fibers "TENAX (trademark) STS40-
24KS (fiber diameter: 7 p, tensile strength: 4000 MPa) manufactured by TOHO TENAX Co.,
Ltd were used as reinforcing fibers, and a nylon resin "A1030" (manufac~edb y Unitika
Limited) was used as a matrix resin, and spray was performed at a wind speed of 150 dsec
from small holes of an opening device. When the form of the reinforcing fibers on the
random mat was observed, the fiber axis of the reinforcing fibers was substantially parallel to
the plane, and randomly dispersed in the plane. In the obtained random mat, the average
fiber length of the reinforcing fibers was 20 mm. On the obtained random mat, when the
rtitio of the reinforcing fiber bundles (A), and the average number of fibers (N) were
investigated, the critical single fiber number defined by fonnula (1) was 86, the ratio of the
reinforcing fiber bundles (A) with respect to the total mount of the fibers in the mat was 70%,
and the average number of fibers (N) in the reinforcing fiber bundles (A) was 900.
From the obtained random mat, a molded plate, which is the fiber-reinforced
composite material of the present invention, was obtained in the same manufacturing method
as in Example 1. On the obtained molded plate, when the viscoelastic characteristic (G', G"
and tans) was memured, the average value of tans' in a range of -25OC of the melting point of
a matrix resin to +25'C of the melting point of the matrix resin way 0.1 19. n e average
value of tans' in a range of -25°C of the melting point of a matrix resin to +35"C of the
melting point of the matrix resin was 0.117. FIG. 5 shows the measurement results of tand'
at a temperature of 200DC to 260°C.
The thickness dimension of the obtained shaped product was 1 .OO mrn. That is, it was
possible to obtain a thickness dimension corresponding to a required design value. Also,
when tensile modulus in the directions of 0" and 90°0f the obtained molded plate were
measured, the ratio (E6) of moduli was 1.04. That is, it was possible to obtain a molded plate
in which fiber orientation hardly occurred, and isotropy was maintained. When the molded
plate was heated within a furnace at 500°C for about 1 hour to remove the resin, the average
fiber length of the reinforcing fibers was measured as 20 mm. After the resin was removed
from the molded plate, the ratio of the reinforcing fiber bundles (A) and the average number of
fibers (N) were investigated. Here, the ratio of the reinforcing fiber bundles (A) with respect
to the total amount of fibers was 70%, the average number of fibers (N) in the reinf'orcing fiber
bundles (A) was 900, and these measurement results were not different from those in the
random mat.
Comparative Example 1
A random mat was manufactured in the same manner as in Example 1 except that the
wind speed from smaIl holes was set to 50 m/sec. When the form of the reinforcing fibers on
the random mat was observed, the fiber axis of the reinforcing fibers was substantially pardlel
to the plane, and randomly dispersed in the plane. The average fiber length of the reinforcing
fibers was 20 m. On the obtained random mat, when the ratio of the reinforcing fiber
bundles (A), and the average number of fibers @wIe)re investigated, the critical single fiber
number defined by formula (1) was 86, the ratio of the reinforcing fiber bundles (A) with
respect to the total amount of fibers of the mat was 95%, and the average number of fibers (N)
in the reinforcing fiber bundles (A) was 1500.
In the obtained random mat, the reinforcing fiber bundles were thick. When the
random mat was manufactured into a molded plate in the same mmer as in Example 1, and
the molded plate was subjected to an ultrasonic detection test, a non-imprepated section was
detected. Also, when the molded plate was cut and the cross-section was observed, the
portion within the fiber bundles in which the resin was not impregnated was found.
The obtained random mat was heated at a pressure increased up to 4 MPa for 3 minutes
by a press device heated up to 260°C so as to obtain a molded plate. The obtained molded
plate had a widened area that was about twice the ma of the mat, and had a thickness of about
0.3 mrn that was about half the thickness of the mat. On the obtained molded plate, it was
possible to confirm the flow of fibers wi& eyes. When tensile modulus in a flow direction
and in a direction of 90" to the flow was measured, the ratio [Eb) of moduli was 2.33, and fiber
orientation was confirmed to largely occur, When the molded plate was heated within a
furnace at 500°C for about 1 how to remove the resin, the average fiber length of the
reinforcing fibers was measured as 20 mm. After the resin was removed fiom the molded
plate, the ratio of the reinforcing fiber bundles (A) and the average number of fibers (N) were
investigated. Here, the ratio of the reinforcing fiber bundles (A) with respect to the total
amount of fibers was 95%, the average number of fibers (N) in the reinforcing fiber bundles
(A) was 1500, and these measurement results were not diffment from those in the random mat.
On the obtained molded plate, when the viscoelastic characteristic (G', G" and tan6) was
measured, the average value of tan6' in a range of -25°C of the melting point of a matrix resin
to +25OC of the melting point of the matrix resin was 0.48. The average value of tanb' in a
range of -25°C of the melting point of a matrix resin to +35*C of the melting point of the
matrix resin was 0.46, FIG. 6 shows the measurement results of tang' at a temperature of
200°C to 260°C.
Description of numerals
I : reinforcing fiber
2: pinch roller
3: rubber roller
4: rotary cutter main body
5: blade
6: cut reinforcing fiber
7: pitch of blades
CLAIMS
I. A fiber-reinforced composite material comprising:
reinforcing fibers with a fiber length of 5 mm to 100 mm; and
a thermoplastic 1-esin,
wherein in tan6' that exhibits a viscoelastic characteristic as defined by formulas (1)
and (21, an average value of the tan6' in a range of -25°C to +2S°C of a melting point of a
matrix resin satisfies formula (3):
tanG=GG/G' (1)
tanS'=Vf~tanS/(lOO-Vf) (2)
0.0 1Stan6'50.2 (3)
wherein G' represents a storage modulus (Pa) of the fiber-reinforced composite
material,
G" represents a loss modulus (Pa) of the fiber-reinforced composite materid, and
Vf represents a volume fraction (%) of the reinforcing fibers in the fiber-reinforced
composite material.
2. The fiber-reinforced composite material according to claim 1,
wherein in the reinforcing fibers in the fiber-reinforced composite material, a ratio of a
reinforcing fiber bundle (A) constituted by the reinforcing fibers of a critical single fiber
number or more, the critical single fiber number defined by formula (4), to a total amount of
the reinforcing fibers in the fiber-reinforced composite material is 20 Vol% or more and less
than 90 Vol%, and an average number (N) of the reinforcing fibers in the reinforcing fiber
bundle (A) satisfies formula (5):
Critical single fiber number=60O/D (4)
0.7~10 4 / D2 < N