DESCRIPTION] q ^ . ^ ,
[invention Title]
METHOD FOR PREPARING RUBBER POLYMER AND RUBBERREINFORCED
GRAFT COPOLYMER
5
[Technical Field]
The present invention relates to a method for
preparing a rubber latex. More specifically, the present
invention relates to a method for preparing a rubber latex
10 which includes adding a basic solution to an initial
reaction hydrophilic monomer and a small amount of fatsoluble
monomer when a polymerization conversion ratio is
90% or more to form particles having a small diameter and
superior stability, ionizing an end of the particles to
15 secure stability of the particles and growing the formed
particles, and thereby obtains a stable latex with a large
particle diameter using a minimal amount of emulsifying
agent and minimizes gas generation and heat discoloration
derived from the emulsifying agent.
20
[Background Art]
In general, emulsion polymerization is widely used in
a variety of industrial fields such as materials for
coating, impact resistant materials and materials for
25 medicines due to advantages in that it can easily obtain a
high molecular weight and various spherical particles and
can variably implement particle structures such as coreshell
structures and porous structures, unlike bulk
polymerization and solution polymerization. In particular,
5 rubber-reinforced thermoplastic resins used in fields
requiring impact resistance include materials such as ABS,
MBS, ASA, ATM and the like.
These materials are generally obtained by preparing a
spherical rubber polymer by emulsion polymerization and
10 copolymerizing inside and outside rubber particles with a
different kind of monomer in consideration dispersability of
the prepared rubber polymer with a matrix resin (for
example, SAN, PVC, PET, PC or the like) . Commonly, final
products are manufactured via high-temperature molding
15 processes, so-called, extrusion and injection, with a matrix
resin. In particular, ABS products are applied to fields
requiring superior impact resistance and excellent outer
appearance owing to superior impact resistance, gloss,
coloring properties and the like.
20
[Disclosure]
[Technical Problem!
The preparation of rubber polymers and rubber graft
copolymers by emulsion polymerization entails use of a great
25 amount of emulsifying agent, in order to form particles and
secure polymerization stability during polymerization,
unlike bulk polymerization or solution polymerization. The
emulsifying agent used, in particular, emulsifying agent
remaining in final products, may cause fatal problems upon
5 formation at high temperatures. Representative problems
include gas generation, heat discoloration, and
deterioration in surface gloss upon high-temperature
processing. These problems greatly restrict use of resins
obtained by emulsion polymerization.
10 In academia and industry, a variety of methods have
been attempted in order to overcome these disadvantages of
emulsion polymerization. Examples of the methods broadly
include minimization of an amount of emulsifying agent
remaining in final polymers by reducing a conventional
15 amount of emulsifying agent used, removal of generated gas
by addition of absorbent during processing, reduction of
amount of residual emulsifying agent by reinforcing washing
in the process of solidifying (aggregating and dehydrating)
an emulsion polymerization latex, and reduction of a ratio
20 of gasified emulsifying agent by using a monomer-type
reactive emulsifying agent which is copolymerizable with a
monomer. These methods are effective to some extent, but
the effects are unsatisfactory when considering manufacture
process complexity and additional costs.
25 In particular, as the method for reducing a residual
emulsifying agent by reducing an amount of emulsifying agent
used, selection of polymerization methods minimizing use of
an emulsifying agent and application of alternative
emulsifying agent with superior stability have been
5 considered. However, these methods involve a considerably
limited reduction level of emulsifying agent in order to
secure effective emulsion stability, and have slight
effects. When the reduction level of emulsifying agent
increases, disadvantageously, formation of initial particles
10 is insufficient, the overall reaction rate is deteriorated,
and polymerization yield as well as stability of final
polymer latex is deteriorated. Furthermore, there is a
difficulty in securing emulsion stability using expensive
reactive emulsifying agents utilized in academia and
15 industry, when used alone, due to the disadvantage of
deterioration in emulsion stability upon formation of
initial particles in terms of reduction of amount of
emulsifying agent. In addition, there is a difficulty in
effectively reducing gas generation of final products
20 through unreacted reactive emulsifying agent due to
selectivity of monomers used for polymerization with respect
to copolymerization reaction.
[Technical Solution!
25 Therefore, the present invention has been made in
view of the above problems, and it is one object of the
present invention to provide an emulsion polymerization
method which minimizes an amount of emulsifying agent used
and in particular, a polymerization method which enables
5 easy formation of initial reaction particles in spite of
using a small amount of emulsifying agent and secures
polymerization stability of polymer when a rubber polymer
having a glass transition temperature of 0°C or less is
prepared by emulsion polymerization.
10 It is another object of the present invention to
provide a technical method which minimizes gas generation
and heat discoloration derived from an emulsifying agent
when a rubber-reinforced thermoplastic resin composition is
processed under high-temperature conditions.
15 These objects of the present invention can be
accomplished by the present invention described below.
In accordance with one aspect of the present
invention, provided is a method for preparing a rubber
polymer having a glass transition temperature of 0°C by
20 emulsion polymerization comprising (a) performing
polymerization in the presence of 5 to 30 parts by weight of
a unsaturated carboxylic acid derivative, 0.1 to 1.0 parts
by weight of an emulsifying agent, 0.05 to 2.5 parts by
weight of a polymerization initiator and 0.1 to 0.5 parts by
25 weight of a molecular weight modifier, with respect to 100
parts by weight of a total monomer, and continuously adding
0.5 to 10 parts by weight of a basic solution thereto to
prepare a seed polymer having a particle diameter of 500 to
1,500A, and (b) continuously adding 5 to 20 parts by weight
5 of the seed polymer, 80 to 95 parts by weight of a monomer,
0.1 to 1.0 parts by weight of a polymerization initiator and
0.1 to 0.5 parts by weight of an emulsifying agent and
performing polymerization to grow the seed polymer into a
particle diameter of 2,500 to 3,50 oA.
10 In accordance with another aspect of the present
invention, provided is a method for preparing a rubberreinforced
graft copolymer comprising preparing a polymer
having a core-shell structure by emulsion-polymerizing a
mixture comprising 50 to 70 parts by weight of the rubber
15 polymer, and 30 to 50 parts by weight of at least one
monomer selected from the group consisting of a vinyl
aromatic compound, a vinyl cyanide compound and a
(meth)acrylic acid ester compound.
[Best Mode]
20 Hereinafter, the present invention will be described
in detail.
In order to accomplish the objects described above,
the present invention provides preparation of a rubber
polymer having a glass transition temperature (Tg) of 0°C
25 or less, and a rubber-reinforced graft copolymer and a
rubber-reinforced thermoplastic resin composition using
the same.
A great deal of research is repeated in order to
secure suitable polymerization stability and
5 polymerization rate in spite of using a small amount of
emulsifying agent. As a result, a method which obtains a
stable latex without deterioration in polymerization rate
even in the presence of a small amount of emulsifying
agent has been developed. This method conforms to the
10 following polymerization method. First, a stable latex
with a large particle diameter can be obtained using a
minimal amount of emulsifying agent via a method including
forming particles having a small diameter in the presence
of an initial reaction hydrophilic monomer and a small
15 amount of fat-soluble monomer, securing stability of
particles through ionization of an end and then growing
the formed particles.
Products developed by this method are characterized
in that an absolute amount of the emulsifying agent
20 contained in final polymers is considerably small. The
product, in particular, a product obtained using this
method for the preparation of a rubber polymer, exhibits
superior polymerization stability and high reaction rate
even in the presence of a small content of emulsifying
25 agent, and .a graft copolymer using a rubber polymer solves
problems associated with outer appearance quality during
processing such as gas generation and heat discoloration
derived from residual emulsifying agent.
The preparation of the rubber polymer having a glass
5 transition temperature (Tg) of 0°C or less, and
configurations of a rubber-reinforced graft copolymer and
a rubber-reinforced thermoplastic resin composition using
the same are given below. Steps provided by the present
invention are only given as an example, polymerization is
10 not necessarily performed in the exact order in which the
respective steps are given and polymerization may be
performed by a continuous polymerization step.
Hereinafter, the present invention will be described
in more detail.
15 A) Preparation of rubber polymer
a) Preparation of seed polymer
Regarding emulsion polymerization, formation of
initial particles is an essential step which determines a
polymerization rate and controls a particle diameter of a
20 final latex and the method for preparing the seed polymer
provided by the present invention will be given below.
First, 100 parts by weight of a monomer, 0.1 to 1.0
parts by weight of an emulsifying agent, 0.05 to 2.5 parts
by weight of a polymerization initiator, 0.1 to 0.5 parts
25 by weight of a molecular weight modifier, 5 to 30 parts by
u
weight of a unsaturated carboxylic acid derivative and 50
to 150 parts by weight of an ion exchange water are
polymerized, and 5 to 10 parts by weight of a basic
solution is continuously added to the polymerization
5 reaction product while stirring, when a polymerization
conversion ratio is 90% or more, to obtain a latex having
a pH of 10 or more. A mean particle diameter of the
obtained polymer is 500 to 1,50 oA and a ratio of the
polymer to a polymerization coagulum is lower than 0.001%,
10 based on total content of solids added.
Examples of useful monomers include diene monomers
such as 1,3-butadiene, isoprene, 2-chloro-l,3-butadiene
and chloroprene, acrylic sacid ester monomers such as
methyl acrylate, ethyl acrylate, butyl acrylate, 2-
15 ethylhexyl acrylate, and aromatic vinyl compound monomers
such as styrene, alpha-methyl styrene, chlorostyrene and
vinyl toluene, vinyl cyanide compound monomers such as
acrylonitrile, methacrylonitrile, malononitrile and the
like. These monomers may be used alone or in combination
20 thereof.
As the monomer, 100 parts by weight of a diene
monomer, or 100% parts by weight of a monomer mixture
comprising 50 to 90% by weight of the diene monomer and 10
to 50% by weight of at least one monomer selected from the
25 group consisting of an acrylic acid ester monomer, an
— ^
aromatic vinyl compound monomer and a vinyl cyanide
compound monomer is preferably subjected to emulsion
polymerization.
Examples of the unsaturated carboxylic acid
5 derivative that can be used in the polymerization step
include acrylic acid, maleic acid, methacrylic acid,
itaconic acid, fumaric acid and the like. The derivative
may be added in a batch manner at an initial reaction
stage, or may be added in a portion-wise manner, that is,
10 40 to 60% by weight of the unsaturated carboxylic acid
derivative is first added at an initial reaction stage and
40 to 60% by weight thereof is further added when a
reaction conversion ratio is 40% to 60%. The present
invention is not greatly limited to the method for adding
15 the monomer at a later reaction stage and the monomer may
be added in a continuous addition manner.
A content of the unsaturated carboxylic acid
derivative added during reaction is preferably 5 to 30
parts by weight, with respect to 100 parts by weight of a
20 total initial monomer. When the content of the unsaturated
carboxylic acid derivative is lower than 5 parts by
weight, it is not easy to secure latex polymerization
stability and storage stability, and when the content
thereof exceeds 30 parts by weight, rubber latex is
25 unsuitable for use as an impact resistant material due to
10
^-->A
excessive increase in Tg and effective growth of particles
is difficult in the process of growing particles of rubber
latex.
The emulsifying agent that can be used for the
5 preparation step may be a generally used sulfuric acid
ester-type emulsifying agent or sulfonate-type emulsifying
agent. Examples of the sulfuric acid ester-type
emulsifying agent include emulsifying agents having a
structure of sodium lauryl sulfate, sodium dodecyl
10 sulfate, sodium lauryl ether sulfate, sodium dodecyl
benzene sulfate, alkyl sulfate, and alkyl ether sulfate or
alkyl phenyl ether sulfate containing a polyoxyethylene
repeat group. Examples of useful sulfonate-type
emulsifying agents include alkyl benzene sulfonate, alkyl
15 sulfonate and dialkyl sulfosuccinate emulsifying agents.
In addition, carboxylate-type emulsifying agents such as
potassium rosinate, potassium fatty acid and potassium
alkenyl dicarboxylate may be used. Furthermore, the
absorbent emulsifying agent may be used alone or in
20 combination with a non-ionic emulsifying agent. When the
absorbent emulsifying agent is used in combination with an
non-ionic emulsifying agent containing an ethylene oxide
group, the non-ionic emulsifying agent is preferably used
in a content of 10 to 20% by weight, with respect to the
25 total content of the emulsifying agent in order to secure
11
latex stability during polymerization reaction.
The basic solution that can be used for the present
invention is preferably a strong basic aqueous solution
such as sodium hydroxide or potassium hydroxide, more
5 preferably, a 0.1 to 30 wt%, 5 to 20 wt% or 5 to 10 wt%
dilute solution of a strong base in ion exchange water.
The addition is not greatly limited, but is preferably a
continuous addition method. The addition of the basic
solution is preferably performed at an ordinary reaction
10 temperature of 60°C to 80°C and is performed when a
polymerization conversion ratio is 90% or more, more
specifically, 90% to 95%. When the polymerization
conversion ratio of addition time is lower than 90%, the
unreacted unsaturated carboxylic acid derivative is
15 saponified in a continuous aqueous phase, polymerization
stability of the seed polymer and copolymerization
properties of unsaturated carboxylic acid may be
deteriorated, and it may be difficult to secure effective
polymerization stability at a later reaction particle
20 growth stage.
The polymerization initiator that can be used for the
present reaction may be a highly hydrophilic persulfatebased
initiator, and specific examples thereof include
pyrolytic initiators such as potassium persulfate,
25 ammonium persulfate and sodium persulfate. Preferably, in
12
a seed polymerization step, a highly hydrophilic
polymerization initiator is used in an amount of 0.05 to
2.5 parts by weight. When the content of the
polymerization initiator is lower than 0.05 parts by
5 weight in a seed polymer preparation step, polymerization
initiation reaction may be delayed and polymerization rate
may be decreased, and when the content of the
polymerization initiator exceeds 2.5 parts by weight, an
initial polymerization rate is excessively high, the
10 number of seeds having a small particle diameter is great
due to heating upon polymerization and polymerization
stability may be thus deteriorated.
Examples of the molecular weight modifier that can be
used for polymerization include mercaptans such as n-
15 dodecyl mercaptan, n-decyl mercaptan, and t-dodecyl
mercaptan and molecular weight modifiers useful for common
emulsion polymerization such as alpha methyl styrene
dimers. An amount of the molecular weight modifier used is
preferably 0.1 to 0.5 parts by weight with respect to 100
20 parts by weight of a total monomer. When the content of
the molecular weight modifier is lower than 0.1 parts by
weight, the polymerization rate is deteriorated, crosslinkage
degree of rubber polymer is increased and impact
strength of an impact resistant material may be
25 deteriorated, and when the content of the molecular weight
13
modifier exceeds 0.5 parts by weight, production
efficiency may be deteriorated due to decrease in reaction
later polymerization rate, and disgusting odor and gas
generation may be derived from residual molecular weight
5 modifier.
b) Particle growth
The particle growth step includes continuously adding
a monomer to initially formed emulsion polymerization
particles to induce growth of particles and thereby obtain
10 a desired particle diameter. In the present step, a
possible addition is given below.
First, the desired particles are obtained by
continuously adding 80 to 95 parts by weight of a monomer,
0.1 to 1.0 parts by weight of a polymerization initiator,
15 0.1 to 0.5 parts by weight of an emulsifying agent, and 50
to 150 parts by weight of an ion exchange water to 5 to 20
parts by weight of the seed latex prepared in the step a)
at a reaction temperature 60 to 80°C. The monomer that can
be used for the polymerization step is the same as the
20 monomer used for seed polymerization. As the
polymerization initiator, a pyrolytic initiator or a
peroxide-based initiator using an oxidation-reduction
catalyst may be used. A highly hydrophobic polymerization
initiator is more preferable than a highly hydrophilic
25 peroxide-based polymerization initiator. The pyrolytic
14
initiator includes succinic peroxide, lauroyl peroxide,
stearoyl peroxide, tertiary hexyl peroxy-2-ethyl
hexanoate, tertiary butyl peroxy-2-ethyl hexanoate,
benzoyl peroxide and the like, which have a 60°C half-life
5 period of less than 100 hours. As the oxidation-reduction
initiator, a hydroperoxide-based initiator such as
diisopropylbenzene hydroperoxide, cumene hydroperoxide or
tertiary butyl hydroperoxide, described regarding seed
polymerization may be used in combination with a commonly
10 used oxidation-reduction catalyst such as ferrous sulfate,
dextrose, sodium pyrophosphate or sodium sulfite.
B) Preparation of rvibber-reinforced graft copolymer
The rubber polymer prepared by the method A) forms a
shell layer by graft copolymerization reaction using
15 emulsion polymerization and a method for preparing a graft
copolymer will be described in detail.
The graft copolymer is generally prepared by
emulsion-polymerizing a monomer comprising 30 to 50 parts
by weight of a vinyl aromatic compound, a vinyl cyanide
20 compound or a (meth)acrylic acid ester compound, with
respect to 50 to 70 parts by weight of the rubber polymer,
and the vinyl cyanide compound or (meth)acrylic acid ester
compound may be used in an amount of 10 to 40% by weight
with respect to 100 parts by weight of the total monomer
25 used for a shell copolymer.
15
Examples of useful vinyl aromatic compounds include
of-methyl styrene, o-ethyl styrene, p-ethyl styrene and
vinyl toluene, and a monomer such as acrylonitrile or
methacrylonitrile may be used as the vinyl cyanide
5 compound. The (meth)acrylic acid ester is methacrylic acid
ester or acrylic acid ester, methyl methacrylate or ethyl
methacrylate may be used as the methacrylic acid ester,
and a monomer such as methyl acrylate, ethyl acrylate or
butyl acrylate may be used as the acrylic acid ester.
10 The method for preparing the graft copolymer by
emulsion polymerization is not particularly limited, but
include generally adding 30 to 50 parts by weight of a
monomer for forming the graft copolymer, with respect to
50 to 70 parts by weight of the rubber polymer, together
15 with an emulsifying agent, a molecular weight modifier, a
grafting aid and an initiator, and then continuing
reaction until a reaction conversion ratio reaches 98 to
99%.
As the emulsifying agent, a carboxylate absorbent
20 emulsifying agent such as potassium rosinate, potassium
fatty acid or potassium alkenyl dicarboxylate, a sulfonate
absorbent emulsifying agent such as sodium lauryl sulfate
or alkyl benzene sulfonate, or a reactive emulsifying
agent may be used alone or in combination thereof.
25 Examples of the molecular weight modifier used for
16
preparation of the graft copolymer include molecular
weight modifiers such as n-dodecyl mercaptan, t-dodecyl
mercaptan and alpha methyl styrene dimer. Preferably,
tertiary dodecyl mercaptan is used in an amount of 0.2 to
5 1.0 parts by weight.
The initiator may be used in an amount of 0.01 to 1
parts by weight, and the initiator that can be used in the
present invention is not particularly limited and is
preferably a combination of a peroxide initiator such as
10 tertiary butyl hydroperoxide, cumene hydroperoxide, or
diisopropylbenzene hydroperoxide, with an oxidationreduction
catalyst in that it is advantageous to secure
impact resistance and latex stability upon graft
copolymerization.
15 The grafting aid may be used in an amount of 0.05 to
0.5 parts by weight and examples thereof include compounds
containing two or more unsaturated double bonds enabling
radical polymerization, such as divinyl benzene, allyl
methacrylate, diallyl phthalate, ethylene glycol
20 diacrylate, triethylene diacrylate, tetraethylene
diacrylate, polyethylene glycol diacrylate, and
polyethylene glycol dimethacrylate. The grafting aid is
preferably used in an amount of 0.1 to 0.3 parts by weight
in order to obtain an effective graft ratio at a high
25 rubber content.
17
Furthermore, the addition method of monomer upon the
preparation of the graft copolymer may be selected from
direct addition of a monomer emulsion, addition of a
monomer mixture, and addition of a monomer emulsion
5 prepared by mixing an emulsifying agent, water and an
initiator. Upon the monomer addition, 0 to 20% by weight
of the monomer may be added in an initial reaction stage
in a batch addition manner and the remaining monomer may
be then added in a continuous addition manner. In
10 addition, the total amount of monomer may be continuously
added or may be batch added three or four times at an
interval.
After generally used anti-oxidant and heat stabilizer
are added to the graft copolymer obtained after reaction
15 completion, the graft copolymer is aggregated by an acid
such as sulfuric acid, hydrochloric acid, phosphoric acid
or acetic acid, or a metal salt such as calcium chloride,
magnesium sulfate or aluminum sulfate to provide a solid,
or the solid is washed, dehydrated and dried to obtain a
20 power. The powdery graft copolymer may be generally used
in combination with a thermoplastic resin copolymer
prepared by solution polymerization.
C) Preparation of rtibber-reinforced thermoplastic
resin composition
25 The graft copolymer prepared by the method described
18
above is commonly melted and mixed with a thermoplastic
resin through an extrusion process and is molded into a
pellet to prepare a final rubber-reinforced thermoplastic
resin. The thermoplastic resin used herein may be an
5 acrylonitrile-styrene copolymer (SAN), an acrylonitrilestyrene-
methyl methacrylate (AMS) resin, a polycarbonate
(PC) resin, a polybutylene terephthalate (PBT) resin, or a
polyvinyl chloride (PVC) resin. There is no great
limitation as to the resin and any resin may be freely
10 used in a case in which impact resistance is required.
Furthermore, when the graft copolymer B) is meltmolded
with the thermoplastic resin by extrusion and
injection processes, a lubricant, a heat stabilizer and
other additives for processes may be added and kinds
15 thereof are not greatly limited.
The rubber-reinforced thermoplastic resin
composition prepared by the method described above
exhibits superior impact resistance unlike a conventional
preparation method, and is excellent in sensible
20 properties such as high-temperature molding heat stability
and gloss, as compared to conventional resins.
Now, preferred examples will be given below for a
better understanding of the present invention. These
examples are provided only to illustrate the present
25 invention and those skilled in the art will appreciate that
19
various alterations and modifications are possible,
without departing from the scope and spirit of the
invention as disclosed in the accompanying claims.
5 [Example]
Example 1
Preparation of rxabber polymer A-1
50 parts by weight of ion exchange water was added to
a nitrogen-substituted pressurized reactor, 0.3 parts by
10 weight of sodium lauryl sulfate, 10 parts by weight of
1,3-butadiene, 0.3 parts by weight of tertiary dodecyl
mercaptan, 1.5 parts by weight of methacrylic acid, and
0.1 parts by weight of potassium persulfate were added
thereto at room temperature, stirring was performed for
15 one hour, reaction was performed at an elevated reaction
temperature of 70°C for 4 hours, and 1.0 parts by weight
of potassium hydroxide (5% solution) was added at a
reactor temperature of 70°C for one hour when a reaction
polymerization conversion ratio reached 95%, to prepare a
20 latex having pH of 10.5 and a particle diameter of 800A.
Then, reaction was performed while further adding 90 parts
by weight of 1,3-butadiene in a continuous addition manner
for 10 hours, and at the same time, further adding an
emulsion comprising 0.2 parts by weight of potassium
25 rosinate, 0.2 parts by weight of benzoyl peroxide and 10
20
parts by weight of ion exchange water at 70°C in a
continuous addition manner for 10 hours. Then, reaction
was continued for 6 hours while further adding 0.0003
parts by weight of ferrous sulfate, 0.05 parts by weight
5 of dextrose, 0.04 parts by weight of sodium pyrophosphate
and 0.3 parts by weight of tertiary butyl hydroperoxide at
80°C, and the reaction was then completed. A
polymerization conversion ratio of the rubber latex thus
obtained was 95% and a particle diameter thereof was
10 3,100A, and details of physical properties are shown in
Table 1.
Preparation of graft copolymer B-1
65 parts by weight of the rubber polymer A-1, 60
parts by weight of ion exchange water, 0.2 parts by weight
15 of potassium alkenyl dicarboxylate (product name: latemul
ASK), 7.5 parts by weight of styrene, 2.5 parts by weight
of acrylonitrile and 0.3 parts by weight of polyethylene
glycol diacrylate were added to a nitrogen-substituted
reactor, stirring was sufficiently performed at 25°C and a
20 reaction temperature was elevated to 50°C. Then, 0.08
parts by weight of tertiary butyl hydroperoxide, 0.003
parts by weight of ferric sulfate, 0.005 parts by weight
of dextrose, 0.025 parts by weight of sodium
pyrophosphate, and 2.5 parts by weight of ion exchange
25 water were added to the reactor, and reaction was
21
performed while elevating the reaction temperature to 65°C
for one hour. Then, an emulsion comprising 0.3 parts by
weight of potassium alkenyl dicarboxylate, 18.75 parts by
weight of styrene, 6.25 parts by weight of acrylonitrile,
5 0.4 parts by weight of tertiary dodecyl mercaptan, 0.1
parts by weight of diisopropylbenzene peroxide, and 20
parts by weight of ion exchange water were continuously
added to the reactor for one hour. Then, 0.05 parts by
weight of cumene hydroperoxide, 0.003 parts by weight of
10 ferrous sulfate, 0.005 parts by weight of dextrose, 0.025
parts by weight of sodium pyrophosphate, and 2.5 parts by
weight of ion exchange water were further added to the
reactor, and reaction was continued at an elevated
polymerization temperature of 80 °C for one hour and was
15 then completed. A final reaction conversion ratio was 98%,
a polymerization coagulum was 0.02%, and details of
physical properties are shown in Table 1.
Preparation of rubber-reinforced thermoplastic resin
C-1
20 With respect to 23 parts by weight of the graft
copolymer B-1 prepared by an aggregation drying process,
76.5 parts by weight of a styrene-acrylonitrile copolymer
resin (92HR-LG CHEM.), 1.5 parts by weight of a lubricant,
and 0.2 parts by weight of a primary heat stabilizer were
25 added to the reactor, the mixture was extruded at a
22
temperature of 200 °C and was then injected at the same
temperature, to prepare a sample for physical property
testing, and physical properties thereof are shown in
Table 1.
5
Example 2
Preparation of rubber polymer A-2
50 parts by weight of ion exchange water was added to
a nitrogen-substituted pressurized reactor, 0.3 parts by
10 weight of sodium lauryl sulfate, 10 parts by weight of
styrene, 0.3 parts by weight of tertiary dodecyl
mercaptan, 1.5 parts by weight of methacrylic acid, and
0.1 parts by weight of potassium persulfate were added
thereto at room temperature, stirring was performed for
15 one hour, reaction was performed at an elevated reaction
temperature of 70°C for 4 hours, 1.0 parts by weight of
potassium hydroxide (5% solution) was added at the
reaction temperature of 70°C for one hour when a reaction
polymerization conversion ratio reached 92%, to prepare a
20 seed latex having pH of 10.5 and a particle diameter of
600A. Then, reaction was performed while further adding 90
parts by weight of 1,3-butadiene in a continuous addition
manner for 10 hours, and at the same time, further adding
an emulsion comprising 0.2 parts by weight of potassium
25 rosinate, 0.2 parts by weight of benzoyl peroxide, and 10
23
parts by weight of ion exchange water at 70°C in a
continuous addition manner for 10 hours. Then, reaction
was continued for 6 hours while further adding 0.0003
parts by weight of ferrous sulfate, 0.05 parts by weight
5 of dextrose, 0.04 parts by weight of sodium pyrophosphate
and 0.3 parts by weight of tertiary butyl hydroperoxide at
80°C, and the reaction was then completed. A
polymerization conversion ratio of the rubber latex thus
obtained was 96%, a particle diameter thereof was 3,300A,
10 and details of physical properties are shown in Table 1.
Preparation of graft copolymer B-2
A graft copolymer was prepared in the same manner as
in Example 1, except that the prepared rubber polymer A-2
was used. Details of physical properties are shown in
15 Table 1.
Preparation of rubber-reinforced thermoplastic resin
C-2
A rubber-reinforced thermoplastic resin was prepared
in the same manner as in Example 1, except that the
20 prepared graft copolymer B-2 was used. Details of physical
properties are shown in Table 1.
Comparative Example 1
Rubber polymer A-3
25 80 parts by weight of ion exchange water was added to
24
a nitrogen-substituted pressurized reactor, 1.0 parts by
weight of potassium fatty acid, 1.5 parts by weight of
potassium rosinate, and 1.0 parts by weight of potassium
carbonate were added at room temperature, stirring was
5 performed, 80 parts by weight of 1,3-butadiene, 0.3 parts
by weight of tertiary dodecyl mercaptan and 0.3 parts by
weight of potassium persulfate were batch-added, a
reaction temperature was elevated to 70°C, reaction was
performed for 8 hours, 20 parts by weight of 1,3-
10 butadiene, 1.0 parts by weight of potassium rosinate and
0.2 parts by weight of potassium persulfate were further
batch-added when a reaction polymerization conversion
ratio reached 70%, and reaction was further performed for
6 hours. Then, 0.5 parts by weight of potassium rosinate,
15 and 0.2 parts by weight of potassium persulfate were batch
added, and polymerization was further performed for 6
hours while elevating a reaction temperature to 80°C.
Then, 4 parts by weight of ion exchange water, 0.5 parts
by weight of potassium rosinate and 0.2 parts by weight of
20 potassium persulfate were added, and reaction was further
performed at 80°C for 4 hours and was then completed. A
polymerization conversion ratio of a diene rubber latex
thus obtained was 92%, a particle diameter thereof was
3,100A, and details of physical properties are shown in
25 Table 1.
25
Preparation of graft copolymer B-3
A graft copolymer was prepared in the same manner as
in Example 1, except that the prepared rubber polymer A-3
was used. Details of physical properties are shown in
5 Table 1.
Preparation of rubber-reinforced -bhermoplastic resin
C-3
A rubber-reinforced thermoplastic resin was prepared
in the same manner as in Example 1, except that the
10 prepared graft copolymer B-3 was used. Details of measured
physical properties are shown in Table 1.
Comparative Example 2
Rtibber polymer A-4
15 80 parts by weight of ion exchange water was added to
a nitrogen-substituted pressurized reactor, 0.5 parts by
weight of potassium fatty acid, 0.7 parts by weight of
potassium rosinate and 1.0 parts by weight of potassium
carbonate were added at room temperature, stirring was
20 performed, 80 parts by weight of 1,3-butadiene, 0.3 parts
by weight of tertiary dodecyl mercaptan and 0.3 parts by
weight of potassium persulfate were batch-added, a
reaction temperature was elevated to 70°C, reaction was
performed for 8 hours, 20 parts by weight of 1,3-
25 butadiene, 0.5 parts by weight of potassium rosinate and
26
0.2 parts by weight of potassium persulfate were further
batch-added when a reaction polymerization conversion
ratio reached 70%, and reaction was further performed for
6 hours. Then, 0.25 parts by weight of potassium rosinate
5 and 0.2 parts by weight of potassium persulfate were batch
added, and. polymerization was further performed for 6
hours while elevating a reaction temperature to 80°C.
Then, 4 parts by weight of ion exchange water, 0.25 parts
by weight of potassium rosinate and 0.2 parts by weight of
10 potassium persulfate were added, and reaction was further
performed at 80°C for 4 hours and was then completed. A
polymerization conversion ratio of a diene rubber latex
thus obtained was 88%, a particle diameter thereof was
3,500A, and details of physical properties are shown in
15 Table 1.
Preparation of graft copolymer B-4
A graft copolymer was prepared in the same manner as
in Example 1, except that the prepared rubber polymer A-4
was used. Details of physical properties are shown in
20 Table 1.
Preparation of rubber-reinforced thermoplastic resin
C-4
A rubber-reinforced thermoplastic resin was prepared
in the same manner as in Example 1, except that the
25 prepared graft copolymer B-4 was used. Details of measured
27
physical properties are shown in Table 1.
[Experimental Example]
Properties of the rubber polymer, the graft copolymer
5 and the rubber-reinforced thermoplastic resin composition
prepared in accordance with the present invention will be
measured by- the following method.
[Physical property measurement method]
* Measurement of latex particle diameter: weight
10 average particle diameter was measured using a Nocomp
apparatus.
* Polymerization coagulum: latex prepared by an
emulsion polymerization method was filtered through a 100
mesh wire net filter, a polymer trapped in the wire net
15 was dried in a 100°C hot air dryer for one hour, and a
ratio of a' theoretical sum of total monomers added and
additives (such as emulsifying agent) to a polymerization
coagulum was calculated.
* Izod impact strength: measured by ASTM D256 (the
20 thickness of a sample: 1/4", unit: kg.cm/cm).
* Gloss: a pellet obtained from an extruder was
injected at 200°C to give a sample and gloss of the sample
was measured with respect to a 20 degree light source.
* Retention discoloration: a pellet obtained from an
25 extruder was retained in an injector for 20 minutes at
28
y ^
270°C to give a glossy sample, L, a and b color values of
the glossy sample were obtained using a suga color
computer and were compared with color values of a glossy
sample injected at 200°C, and discoloration upon retention
was calculated by the following Equation 1.
Equation 1
A5= ^iiL'-LfHo.'-af + ib'-bf
* Retention gloss: A pellet obtained from an extruder
was retained in an injector for 20 minutes at 270°C to
10 give a glossy sample, gloss at 45° was measured using a
gloss meter in accordance with ASTM D528 and a difference
in gloss between the glossy sample and a sample obtained
by injection at 200°C was represented as percentage.
* Flowability: measured by ASTM D1238 under the
15 conditions of 220°C and 10 kg.
* Latex stability: latex stability of rubber polymer
was obtained by filtering 500g of a final polymer latex
using a 100 mesh net, allowing the polymer latex to stand
in a homo-mixer (T.K. Robomics) at 10,000 RPM for 60
20 minutes, and a ratio of a theoretical total solid content
to a coagulum trapped in the 100 mesh net was recorded as
percentage. Furthermore, in a case of the graft copolymer,
a time at which the polymer is coagulated at 15,000 RPM
was measured and recorded, and polymers having a
29
coagulation time longer than 60 minutes were classified
into stable latex.
TABLE 1
Rubber polymer (A)
Graft copolymer (B)
Rubber-reinforced
thermoplastic resin
(C)
Polymerization
conversion ratio (%)
Weight average
particle diameter (A)
Polymerization
coagulum {%)
Latex stability (%)
Polymerization
conversion ratio (%)
Polymerization
coagulum (%)
Latex stability (%)
Impact strength (1/4)
Flowability
Gloss (45 degrees)
Retention
discoloration (A E)
Retention gloss (%)
Ex.1
95
3,100
0.02
<0.01
98
0.03
<0.01
25
21
98
2.1
0.5
Ex.2
96
3,300
0.03
<0.01
98
0.03
<0.01
23
23
100
1.9
0.1
Comp. Ex.
1
92
3,100
0.05
<0.01
97
0.03
<:0.01
24
20
94
4.5
2.0
Comp. Ex.
2
88
3,500
2.5
7.5
97
3.6
10.5
15
18
80
6.4
10
10
As can be seen from Table above, polymerization
coagulum and latex stability were good even at a low
emulsifying, agent content in the preparation of a rubber
latex and a graft copolymer, and a rubber-reinforced
thermoplastic resin composition using the graft copolymer
according to the present invention exhibited superior heat
discoloration stability and retention gloss.
[industrial applicability!
According to the present invention, unlike a
15 conventional method, polymerization coagulum and latex
30
stability were good even at a low emulsifying agent
content in the preparation of a rubber latex and a graft
copolymer, and a rubber-reinforced thermoplastic resin
composition using the graft copolymer according to the
present invention exhibited superior heat discoloration
stability and retention gloss.

IClaim ll
A method for preparing a rubber polymer by emulsion
5 polymerization comprising:
(a) performing polymerization in the presence of a
monomer, a unsaturated carboxylic acid derivative, an
emulsifying agent, a polymerization initiator and a
molecular weight modifier, and continuously adding a basic
10 solution thereto to prepare a seed polymer; and
(b) continuously adding the seed polymer, a monomer, a
polymerization initiator and an emulsifying agent and
performing polymerization to grow the seed polymer.
15 [claim 2] The method according to claim 1, wherein the
basic solution is added in an amount of 0.5 to 10 parts by
weight, with respect to 100 parts by weight of the total
monomer of the step (a).
20 [claim 3l The method according to claim 1, wherein the
basic solution is a 0.1 to 30 wt% basic aqueous solution.
[claim 4l The method according to claim 1, wherein the
basic solution is added when a polymerization conversion
25 ratio is 90% or more.
32
/-A
[claim 5] The method according to claim 1, wherein the
unsaturated carboxylic acid derivative comprises at least
one selected from the group consisting of acrylic acid,
5 maleic acid, methacrylic acid, itaconic acid and fumaric
acid.
[claim 6] The method according to claim 1, wherein the
basic solution is a sodium hydroxide solution or a
10 potassium hydroxide solution.
[claim 7] The method according to claim 1, wherein, as
the emulsifying agent, one selected from the group
consisting of potassium rosinate, potassium fatty acid,
15 potassium alkenyl dicarboxylate, sodium lauryl sulfate,
sodium dodecyl benzene sulfate, alkyl sulfate, alkyl ether
sulfate, alkyl phenyl ether sulfate, alkyl benzene
sulfonate, alkyl sulfonate and dialkyl sulfonate is used
singly, or is used in combination with 10 to 20% by weight
20 of a non-ionic emulsifying agent containing an ethylene
oxide group.
[claim 8l The method according to claim 1, wherein the
unsaturated carboxylic acid derivative comprises at least
25 one selected from the group consisting of acrylic acid.
33
«
maleic acid, methacrylic acid, itaconic acid and fumaric
acid.
[claim 9l The method according to claim 1, wherein the
5 polymerization initiator of the step (a) is potassium
persulfate, ammonium persulfate or sodium persulfate, and
the polymerization initiator of the step (b) is selected
from the group consisting of succinic peroxide, lauroyl
peroxide, stearoyl peroxide, tertiary hexyl peroxy-2-ethyl
10 hexanoate, tertiary butyl peroxy-2-ethyl hexanoate and
benzoyl peroxide.
[claim lOl The method according to claim 1, wherein, as
the monomer of the steps (a) and (b) , 100 parts by weight
15 of a diene monomer, or 100% parts by weight of a monomer
mixture comprising 50 to 90% by weight of the diene
monomer and 10 to 50% by weight of at least one monomer
selected from the group consisting of a acrylic acid ester
monomer, an aromatic vinyl compound monomer and a vinyl
20 cyanide compound monomer is subjected to emulsion
polymerization.
[claim ll] The method according to claim 10, wherein the
diene monomer comprises at least one selected from the
25 group consisting of 1,3-butadiene, isoprene, 2-chloro-l,3-
34
10
butadiene and chloroprene, the acrylic acid ester monomer
comprises at least one selected from the group consisting
of methyl acrylate, ethyl acrylate, butyl acrylate and 2-
ethylhexyl acrylate, the aromatic vinyl compound comprises
at least one selected from the group consisting of
styrene, alpha-methyl styrene, chlorostyrene and vinyl
toluene, and the vinyl cyanide compound comprises at least
one selected from the group consisting of acrylonitrile,
methacrylonitrile and malononitrile.
[claim I2I The method according to claim 1, wherein the
polymerization initiator comprises at least one selected
from the group consisting of succinic peroxide, lauroyl
peroxide, stearoyl peroxide, tertiary hexyl peroxy-2-ethyl
15 hexanoate, tertiary butyl peroxy-2-ethyl hexanoate,
benzoyl peroxide, diisopropylbenzene hydroperoxide, cumene
hydroperoxide and tertiary butyl hydroperoxide.
[claim 13] A method for preparing a rubber-reinforced
20 graft copolymer comprising:
preparing a polymer having a core-shell structure by
emulsion-polymerizing a mixture comprising 50 to 70 parts by
weight of the rubber polymer according to claim 1 and 30 to
50 parts by weight of at least one monomer selected from the
25 group consisting of a vinyl aromatic compound, a vinyl
35
cyanide compound and a (meth)acrylic acid ester compound.
14.The method according to claim 13, wherein the vinyl cyanide compound or the (meth)acrylic
acid ester compound is present in an amount of 10 to 40% by weight, with respect to 100
parts by weight of the total monomer used for the preparation of the rubber-reinforced graft
copolymer.
15. The method according to claim 13, wherein the vinyl aromatic compovmd comprises at least
one selected from the group consisting of a-methyl styrene, o-ethyl styrene, p-ethyl styrene
and vinyl toluene, the vinyl cyanide compound is acrylonitrile or methacrylonitrile, and the
(meth)acrylic acid ester comprises at least one selected from the group consisting of methyl
methacrylate, ethyl methacrylate, methyl acrylate, ethyl acrylate and butyl acrylate.