JPH0733836A - Production of graft copolymer and thermoplastic resin composition - Google Patents

Abstract

PURPOSE:To obtain a graft copolymer capable of manifesting excellent impact resistance and a thermoplastic resin using the graft copolymer. CONSTITUTION:This method for producing a graft copolymer comprises impregnating substantially uncross, linked polyorganosiloxane particles in a latex state with an alkyl (meth)acrylate component composed of an alkyl (meth) acrylate and a polyfunctional alkyl (meth)acrylate, providing a complex latex, then polymerizing the alkyl (meth)acrylate component in the complex latex, affording a complex rubber and further carrying out the graft copolymerization of one or more vinylic monomers with the complex rubber. Furthermore, this thermoplastic resin composition is composed of (A) the graft copolymer obtained by the method for production thereof and (B) a thermoplastic resin.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a graft copolymer excellent in impact resistance and economical efficiency, and a thermoplastic resin composition comprising the resulting graft copolymer and another thermoplastic resin.

[0002]

2. Description of the Related Art Various efforts have been made so far to improve the performance of impact resistant resins. For example, JP-A-60-25261
In Japanese Patent Publication No. 3, attention is paid to a decrease in Tg and elastic modulus of the rubber layer, and it is considered to use a polyorganosiloxane rubber having both a low Tg and a low elastic modulus as a rubber source of an impact resistant resin. . However, this method cannot improve the matte appearance of the surface derived from polyorganosiloxane rubber.

JP-A-63-69859, JP-A-1-279954 and JP-A-3-231907 disclose a polyaorganosiloxane component and a polyalkyl (polyalkylorganosiloxane) component in order to improve the surface appearance of a resin molded product. It is disclosed that a graft copolymer of a composite rubber composed of a (meth) acrylate component is mixed. These composite rubbers are produced by impregnating polyorganosiloxane rubber particles with an alkyl (meth) acrylate component and polymerizing an acrylic (meth) acrylate component.

[0004]

However, since the polyorganosiloxane component used in the production of this composite rubber is a polyorganosiloxane rubber particle crosslinked with a crosslinking agent and has a crosslinked structure, the alkyl ( The impregnation efficiency of the (meth) acrylate component is insufficient. Therefore, a significant portion of the alkyl (meth) acrylate component added to the polymerization system forms free particles without being impregnated with polyorganosiloxane particles, and a large amount of polyalkyl (meth) acrylate rubber is generated during the polymerization process. Had the problem of being generated.

This is apparent from the example of Japanese Patent Laid-Open No. 3-231907. This prior art proposes a composite rubber having an apparent silicone content of 1 to 10% by weight, but substantially, a composite rubber having a silicone content of about 10% by weight or more and a by-product poly rubber. It discloses only a mixture with an acrylic (meth) acrylate rubber in which the proportion of the silicone component in the total rubber when viewed as an aggregate of the mixture is from 1 to 10% by weight. That is, the average particle size of the polyorganosiloxane rubber of Example 1 of JP-A-3-231907 is 0.24 μm, while the average particle size of the composite rubber is 0.26 μm. The increase in the particle size of the composite rubber relative to the average particle size is extremely small. If a substantially homogeneous composite rubber is produced, the average particle size of the composite rubber expected from the charging ratio of the polyorganosiloxane rubber component and the alkyl (meth) acrylate component is 0.6.
It is about 5 μm.

As described above, according to the conventional method using polyorganosiloxane rubber particles as the polyorganosiloxane component, a large amount of polyalkyl (meth) is produced during the production of the composite rubber.
A by-product of acrylate rubber was unavoidable. The graft composite rubber obtained from the composite rubber containing a large amount of (meth) acrylate rubber as an impurity has insufficient performance as an impact resistance improver for various thermoplastic resins. Therefore, it has been desired to develop an inexpensive graft copolymer capable of solving such a problem, exhibiting good impact strength, and containing a small amount of polyorganosiloxane.

[0007]

The present inventors have found that in a polyorganosiloxane-polyalkyl (meth) acrylate composite rubber graft copolymer, the composite efficiency of the polyorganosiloxane component and the polyalkyl (meth) acrylate component is improved. As a result of extensive studies on good composite rubbers, it was found that when a composite rubber is produced by using a non-crosslinked polyorganosiloxane latex, the graft copolymer obtained from this composite rubber exhibits excellent impact resistance. The invention was reached.

That is, the gist of the present invention is to provide a substantially non-crosslinked polyorganosiloxane particle in a latex state with an alkyl (meth) acrylate composed of an alkyl (meth) acrylate and a polyfunctional alkyl (meth) acrylate.
An acrylate component is impregnated into a composite latex, and then an alkyl (meth) acrylate component in the composite latex is polymerized into a composite rubber, and one or more vinyl monomers are grafted onto the composite rubber. A method for producing a graft copolymer to be polymerized, and a thermoplastic resin composition comprising the graft copolymer (A) and the thermoplastic resin (B) obtained by the above production method.

In the present invention, as a raw material of the polyorganosiloxane, for example, diorganosiloxane or a mixture of the same and a siloxane-based graft crossing agent is used. A latex obtained by emulsifying this raw material with an emulsifier and water is atomized using a homomixer that atomizes it with shearing force by high-speed rotation or a homogenizer that atomizes it with the jetting force of a high-pressure generator. A polyorganosiloxane can be obtained by dropping the solution into an aqueous solution of benzenesulfonic acid at a constant rate for polymerization and then neutralizing dodecylbenzenesulfonic acid with an alkaline substance.

The size of the polyorganosiloxane is not particularly limited, but the number average particle size is preferably smaller. For example, when polyorganosiloxane particles having a number average particle diameter of 0.01 to 0.06 μm are used, the alkyl (meth) acrylate component is more easily impregnated, so that a substantially uniform composite rubber can be obtained.

Such a polyorganosiloxane having a small size can be obtained by dropping a finely divided latex into an aqueous solution of an acid catalyst such as dodecylbenzenesulfonic acid having a low concentration of 50 ° C. or higher at a very small speed to polymerize the latex. it can.

Examples of the organosiloxane that constitutes the organosiloxane mixture include various organosiloxane cyclic compounds having three or more membered rings, and those having 3 to 6 membered rings are preferable. Specifically, hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, dodecamethylcyclohexasiloxane, trimethyltriphenylcyclotrisiloxane, tetramethyltetraphenylcyclotetrasiloxane, octaphenylcyclotetrasiloxane, etc. These may be used alone or in admixture of two or more.

As the siloxane-based graft crossing agent, compounds capable of forming a unit represented by the following formula are used.

[0014]

[Chemical 1]

In the above formula, R ¹ is a methyl group, an ethyl group, a propyl group or a phenyl group, R ² is a hydrogen atom or a methyl group, n is 0, 1 or 2, and p is a number from 1 to 6. .

A unit of formula (I-1) may be formed (meta).
Acryloyloxysiloxane has a high grafting efficiency and thus can form an effective graft chain, and is advantageous in that it exhibits impact resistance.

Methacryloyloxysiloxane is particularly preferred as the unit capable of forming the unit of the formula (I-1). Specific examples of methacryloyloxysiloxane include β-methacryloyloxyethyldimethoxymethylsilane, γ-methacryloyloxypropylmethoxydimethylsilane, γ-methacryloyloxypropyldimethoxymethylsilane, γ-methacryloyloxypropyltrimethoxysilane, γ-methacryloyloxypropyl. Examples thereof include ethoxydiethylsilane, γ-methacryloyloxypropyldiethoxymethylsilane, and δ-methacryloyloxybutyldiethoxymethylsilane.

Vinyl siloxanes can be mentioned as those capable of forming the unit of the formula (I-2), and specific examples thereof include tetramethyltetravinylcyclotetrasiloxane. Examples of the unit capable of forming the unit of the formula (I-3) include p-vinylphenyldimethoxymethylsilane. Further, as a unit capable of forming the unit of formula (I-4), γ-
Examples thereof include mercaptopropyldimethoxymethylsilane, γ-mercaptopropylmethoxydimethylsilane and γ-mercaptopropyldiethoxymethylsilane.

The amount of the graft crossing agent used in the organosiloxane mixture is 10% by weight or less, preferably 0.5 to 5% by weight.

As the emulsifier, anionic emulsifiers are preferable, and sodium alkylbenzene sulfonate, sodium lauryl sulfonate, sodium sulfosuccinate,
An emulsifier selected from sodium polyoxyethylene nonylphenyl ether sulfate and the like is used. Particularly, sulfonic acid-based emulsifiers such as sodium alkylbenzene sulfonate and sodium lauryl sulfonate are preferable.

These emulsifiers are used in the range of 0.05 to 5 parts by weight based on 100 parts by weight of the organosiloxane mixture. When the amount used is small, the dispersion state becomes unstable, and it becomes impossible to maintain the emulsified state with a fine particle size. or,
If the amount used is large, the coloring caused by the emulsifier of the polyorganosiloxane becomes severe, which is inconvenient.

The polyorganosiloxane latex thus produced is impregnated with an alkyl (meth) acrylate component consisting of an alkyl (meth) acrylate and a polyfunctional alkyl (meth) acrylate, and then polymerized to give a composite rubber. Obtainable.

As the alkyl (meth) acrylate,
For example, methyl acrylate, ethyl acrylate, n-
Propyl acrylate, n-butyl acrylate, 2-
Alkyl acrylates such as ethylhexyl acrylate and hexyl methacrylic acid, alkyl methacrylates such as 2-ethylhexyl methacrylic acid, n-lauryl methacrylic acid and the like, and particularly n- The use of butyl acrylate is preferred.

Examples of polyfunctional alkyl (meth) acrylates include allyl methacrylate, ethylene glycol dimethacrylate, propylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate,
1,4-butylene glycol dimethacrylate, triallyl cyanurate, triallyl isocyanurate and the like can be mentioned. The amount of the polyfunctional alkyl (meth) acrylate used is 0.1 to 20 in the alkyl (meth) acrylate component.
%, Preferably 0.5 to 10% by weight.

The alkyl (meth) acrylate and the polyfunctional alkyl (meth) acrylate may be used alone or in combination of two or more.

The above alkyl (meth) acrylate component is added to the latex of the neutralized polyorganosiloxane component, and the usual radical polymerization initiator is allowed to act to polymerize. As the polymerization initiator, a peroxide, an azo initiator, or a redox initiator in which an oxidizing agent and a reducing agent are combined is used. Among these, a redox type initiator is preferable, and a sulfoxylate type initiator in which ferrous sulfate, ethylenediaminetetraacetic acid disodium salt, Rongalite, and hydroperoxide are combined is particularly preferable.

A latex of a composite rubber is obtained in which the polyorganosiloxane component and the polyalkyl (meth) acrylate rubber component cannot be substantially separated from each other as the polymerization proceeds.

In the composite rubber composed of polyorganosiloxane and polyalkyl (meth) acrylate according to the present invention, the polyorganosiloxane component is 0.1-2.
It is about 0% by weight. If it is less than 0.1% by weight, the characteristics of polyorganosiloxane cannot be exhibited and the impact resistance is lowered.

In the practice of the present invention, a polyorganosiloxane rubber obtained by using octamethyltetracyclosiloxane as the dialkylorganosilane and γ-methacryloyloxypropyldimethoxymethylsilane as the siloxane grafting agent is used. It is preferable to use a composite rubber in which a polyalkyl (meth) acrylate rubber component having a main skeleton having a repeating unit of n-butyl acrylate is composited.

The composite rubber thus produced by emulsion polymerization can be graft-copolymerized with a vinyl monomer, and the polyorganosiloxane component and the polyalkyl (meth) acrylate rubber component are different from each other. Since they are so tightly entangled with each other, they cannot be extracted and separated with an ordinary organic solvent such as acetone or toluene.

Further, the composite rubber obtained in the process of the production method of the present invention is characterized in that the composite efficiency of the polyorganosiloxane component and the polyalkyl (meth) acrylate component is good. Therefore, when the volume of the particles calculated as impregnated with all the alkyl (meth) acrylates in the polyorganosiloxane is 100%, the percentage of the volume of the composite rubber particles actually obtained is expressed as a percentage. When the value shown is R, R is 50% in the present invention.
The above is preferable.

The vinyl-based monomer to be graft-polymerized on the composite rubber includes aromatic alkenyl compounds such as styrene, α-methylstyrene and vinyltoluene; methacrylates such as methylmethacrylate and 2-ethylhexylmethacrylate. Acid ester; acrylic acid ester such as methyl acrylate, ethyl acrylate, butyl acrylate;
Vinyl cyanide compounds such as acrylonitrile and methacrylonitrile; epoxy group-containing vinyl compounds such as glycidyl methacrylate; various vinyl-based monomers such as carboxylic acid group-containing vinyl compounds such as methacrylic acid. Are used alone or in combination of two or more.

The graft copolymer can be obtained by adding a vinyl-based monomer to the latex of the composite rubber and polymerizing it in a single stage or in multiple stages by radical polymerization technique.

After the graft polymerization is completed, the graft composite rubber can be separated and recovered by introducing the latex into hot water in which a metal salt such as calcium chloride or aluminum sulfate is dissolved, salting out and coagulating. .

The ratio of the composite rubber and the vinyl monomer in obtaining the graft copolymer is 10 to 95% by weight, preferably 20 to 90% by weight, based on the weight of the obtained graft copolymer. , And vinyl monomer are 5 to 90% by weight, preferably 10 to 80% by weight. If the vinyl-based monomer is less than 5% by weight, the dispersion of the graft copolymer component in the resin composition mixed with other resin is not sufficient,
On the other hand, if it exceeds 90% by weight, the impact strength decreases, which is not preferable.

This graft copolymer can be extruded and molded by a commonly known kneading machine. Examples of such a machine include an extruder, an injection molding machine, a blow molding machine, and an inflation molding machine.

The graft copolymer obtained by the production method of the present invention is mixed with various thermoplastic resins,
It can be a resin composition. Examples of various thermoplastic resins include polymers obtained by polymerizing one or more vinyl monomers selected from aromatic alkenyl compounds, vinyl cyanide compounds, methacrylic acid esters, and acrylic acid esters, and polyphenylene ether. Examples thereof include a mixture of resin and polystyrene resin, polyacetal resin, vinyl chloride, polyester resin, polycarbonate resin, polyamide resin, polyphenylene sulfide resin, polymers and copolymers of ethylenically unsaturated monomers. Aromatic alkenyl compounds, vinyl cyanide compounds,
A polymer obtained by polymerizing one or more vinyl monomers selected from methacrylic acid esters and acrylic acid esters is a copolymer obtained by copolymerizing 70% by weight of styrene and 30% by weight of acrylonitrile. Polymers or polymethylmethacrylate are preferred.

If desired, the resin composition of the present invention may contain stabilizers, plasticizers, lubricants, flame retardants, pigments and the like. Specifically, stabilizers such as triphenyl phosphite, lubricants such as polyethylene wax and polypropylene wax, phosphate flame retardants such as triphenyl phosphate and tricresyl phosphate, and brominated flame retardants such as decabromobiphenyl and decabromophenyl ether. Fuel,
Examples thereof include flame retardant aids such as antimony trioxide, pigments such as titanium oxide, zinc sulfide and zinc oxide, fillers such as glass fiber, asbestos, wollastonite, mica and talc.

The present invention will be described below with reference to examples. In the Reference Examples and Examples, "parts" and "%" mean "parts by weight" and "% by weight" unless otherwise specified.

In the reference example, the particle size of the polyorganosiloxane in the latex was measured by the dynamic light scattering method.
This measurement is a method that utilizes the Brownian motion of particles in latex. When the particles in the latex are irradiated with laser light, they show fluctuations according to the particle diameters, so the particle diameters can be calculated by analyzing these fluctuations. The number average particle size and the particle size distribution were determined using a DLS-700 type manufactured by Otsuka Electronics Co., Ltd.

In the examples, the Izod impact strength was measured by the method of ASTM D258.

The R value means the percentage of the volume of the composite rubber particles actually obtained, when the volume of the particles calculated as impregnating all the alkyl (meth) acrylate in the polyorganosiloxane is 100%. Is expressed as a percentage.

[0043]

【Example】

Reference Example 1 Polyorganosiloxane Latex S-
Preparation of 1 0.5 part of γ-methacryloyloxypropyldimethoxymethylsilane (KBM) and 99.5 parts of octamethylcyclotetrasiloxane (DMC) were mixed to obtain 100 parts of a siloxane-based mixture. Distilled water 30 in which 0.67 parts of sodium dodecylbenzenesulfonate was dissolved
After adding 0 part of the mixture and stirring with a homomixer at 10,000 rpm for 2 minutes, it was passed through a homogenizer twice at a pressure of 300 kg / cm ² to obtain a stable premixed organosiloxane latex.

On the other hand, 10 parts of dodecylbenzenesulfonic acid and 90 parts of distilled water were poured into a separable flask equipped with a cooling condenser to prepare a 14% by weight dodecylbenzenesulfonic acid aqueous solution.

With this aqueous solution heated to 85 ° C., the premixed organosiloxane latex was added dropwise over 2 hours, and after the completion of the addition, the temperature was maintained for 3 hours and cooled. The reaction was then kept at room temperature for 12 hours before caustic soaking.
It was neutralized with an aqueous solution of da.

The polyorganosiloxane latex thus obtained was dried at 170 ° C. for 30 minutes to determine the solid content, which was 18.2% by weight. The number average particle diameter measured by the dynamic light scattering method was 0.03 μm.

Reference Examples 2 to 7 Production of Polyorganosiloxane Latex S-2 to 7 A latex was produced in the same manner as in Reference Example 1 except that the concentration of the dodecylbenzenesulfonic acid aqueous solution or the composition of the siloxane mixture was changed. The performance of the obtained latex is shown in Table 1. However, tetraethoxysilane (T
EOS) was used as a crosslinking agent.

Reference Examples 8 to 11 Preparation of Polyorganosiloxane Latex S-8 to 11 To 100 parts of the siloxane mixture shown in Reference Examples 8 and 9 of Table 1, 1 part of sodium dodecylbenzenesulfonate and the amount of dodecyl shown in Table 2 were added. 200 parts of distilled water in which benzenesulfonic acid was dissolved was added, and preliminarily dispersed by a homomixer and emulsified / dispersed by a homogenizer. The premixed organosiloxane latex was heated at 80 ° C. for 5 hours, cooled, and then allowed to stand at 20 ° C. for 48 hours.
The pH was adjusted to 7 with an aqueous sodium hydroxide solution to complete the polymerization, and the polyorganosiloxane latex (S-8 to 1
1) was obtained. The solid content was 29%. The results are shown in Table 2.

Example 1 3.3 parts of the polyorganosiloxane latex obtained in Reference Example 1 was collected in a separable flask and distilled water 28
After adding and mixing 7.3 parts, butyl acrylate 2
A mixture of 8.8 parts, allyl methacrylate 0.6 parts and cumene hydroperoxide 0.12 parts was added.

The atmosphere in the flask was replaced with nitrogen by passing a nitrogen stream through the separable flask.
The temperature was raised to ° C. When the liquid temperature reached 60 ° C, 0.001 part of ferrous sulfate, 0.003 part of ethylenediaminetetraacetic acid disodium salt and 0.25 part of Rongalit were added to 10 parts of distilled water.
An aqueous solution dissolved in each part was added to initiate radical polymerization. This state was maintained for 1 hour to complete the polymerization of the acrylate component to obtain a latex of a composite rubber of polyorganosiloxane and butyl acrylate.

When polyorganosiloxane is impregnated with butyl acrylate to form a composite, the average particle diameter becomes 0.11 μm, and the volume increase rate due to the composite is 48 times as determined by the dynamic light scattering method, and the R value is It was 96%. Then, a mixed solution of 70 parts of styrene and 0.35 part of cumene hydroperoxide was added dropwise over 2 hours for polymerization. After completion of the dropping, the temperature was kept at 60 ° C. for 2 hours to complete the polymerization, and a graft copolymer latex was obtained by graft-polymerizing styrene to a composite rubber composed of polydimethylsiloxane and polybutylacrylate.

Next, 400 parts of an aqueous solution in which aluminum sulfate was dissolved in a proportion of 7.5% by weight was heated to 60 ° C. and stirred. The latex of the composite rubber-based graft copolymer was gradually dropped into this and coagulated. It was separated, washed with water and dried to obtain a graft copolymer (G-1).

This graft copolymer powder was fed to an extruder heated to 240 ° C. and kneaded to obtain pellets. Cylinder temperature 230 ° C, mold temperature 60
Molded into a V-shaped 1/4 "Izod test piece by an injection molding machine set at ℃. Izod impact value is 16 kg · cm / c
It was m.

Examples 2 to 7 The polyorganosiloxane latices (S-2 to 7) obtained in Reference Examples 2 to 7 were subjected to the same composite rubber formation, graft polymerization and evaluation as in Example 1. The volume increase rate and R value of the obtained composite rubber and the graft copolymer (G-
The Izod impact values of 2 to 7) are shown in Table 3. In the case of using a polyorganosiloxane that is not substantially crosslinked, the volume increases due to the formation of a composite and the Izod impact strength shows a high value.

Examples 8 to 9 and Comparative Examples 1 to 3 Polyorganosiloxane latices of Reference Examples 4 and 7 (S
-4, 7), the amounts of the polyorganosiloxane latex, butyl acrylate and allyl methacrylate to be injected into the separable flask are set to the ratios shown in Table 3, and the vinyl monomer used in the graft polymerization has an acrylonitrile / styrene amount ratio of 3 Acrylonitrile / styrene mixture of 7 or methyl methacrylate was used. Other conditions were the same as in Example 1 except that the composite rubber-forming reaction and the graft polymerization were carried out, and the graft copolymer (G-8 to 9, g-1 to 3) were obtained. Furthermore, Example 1
An Izod impact test was conducted in the same manner as in. The results are shown in Table 3. Non-crosslinking is much more complex and the Izod impact strength is higher.

Examples 10 to 12 and Comparative Examples 4 to 6 Regarding the polyorganosiloxane latex (S-8 to 11) of Reference Examples 8 to 11, the polyorganosiloxane latex, butyl acrylate and allyl methacrylate to be injected into a separable flask were prepared. The amounts were set to the ratios shown in Table 4, and the other conditions were the same as in Example 9 to obtain graft copolymers (G-10 to 12, g-4 to 6).
Furthermore, 100 parts of vinyl chloride polymer having a degree of polymerization of 700, 3.5 parts of dibutyl tin malate, 0.8 parts of stearyl alcohol.
Part, a vinyl chloride resin consisting of 0.4 parts of a high molecular lubricant and a graft copolymer (G-10 to 12, g-4 to 6) were blended in a ratio shown in Table 4, and an Izod test piece was extruded in a modified shape. Then, an Izod impact test was conducted. The results are shown in Table 4.

Examples 13 to 19 and Comparative Examples 7 to 13 Graft copolymers G-10 and g-4 were added to the resins shown below in the proportions shown in Table 5 to prepare Izod test pieces, which were then subjected to Izod impact. The test was conducted. The modified polyphenylene ether (mPPE) resin has a reduced viscosity of 0.6.
dl / g poly (2,6-dimethyl-1,4-phenylene)
A mixture of 40 parts of ether and 45 parts of polystyrene having a melt index of 30 g / 10 min at a load of 5 kg and 200 ° C. was used. As the polyacetal (POM) resin, a homotype having a melt index of 18.2 g / 10 min was used. As the polycarbonate (PC) resin, Novalex 7022A (Mitsubishi Kasei Co., Ltd.) was used. Tuffpet PBT: N-1000 was used as the polybutylene terephthalate (PBT) resin. As polyamide (PA) resin, Novamid 1012C
(Mitsubishi Kasei Co., Ltd.) was used. As the polyphenylene sulfide (PPS) resin, Topren T-4 (Toprene Co., Ltd.) was used. As the modified polyolefin which is an ethylenically unsaturated monomer copolymer, MODIC P
-10B (Mitsubishi Petrochemical Co., Ltd.) was used.

[0058]

[Table 1]

[0059]

[Table 2]

[0060]

[Table 3]

[0061]

[Table 4]

[0062]

[Table 5]

[0063]

The production method of the present invention is a polyorganosiloxane-polyalkyl (meth) acrylate composite rubber graft copolymer, which is a composite rubber of a polyorganosiloxane component and a polyacrylic (meth) acrylate component with good composite efficiency. The resin composition of the obtained graft copolymer and various thermoplastic resins can provide a molded article having excellent impact resistance.

Claims (2)

[Claims] 1. A composite latex obtained by impregnating substantially non-crosslinked polyorganosiloxane particles in a latex state with an alkyl (meth) acrylate component composed of an alkyl (meth) acrylate and a polyfunctional alkyl (meth) acrylate. Then, a method for producing a graft copolymer in which an alkyl (meth) acrylate component in the composite latex is polymerized to form a composite rubber, and one or more vinyl monomers are graft-polymerized to the composite rubber . 2. A thermoplastic resin composition comprising the graft copolymer (A) obtained by the production method according to claim 1 and a thermoplastic resin (B).