JPH0665703B2 - Impact modifier for thermoplastics - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an impact resistance modifier for a thermoplastic resin, which can impart high impact resistance and good moldability, and also has good weather resistance.

Thermoplastic resins, especially vinyl chloride resins (hereinafter abbreviated as PVC) are widely used as general-purpose resins,
Its mechanical properties are not always satisfactory. That is, PVC is inferior in impact strength, especially impact strength with notches,
Various modifiers have been proposed for the purpose of improving such impact strength.

The most effective method among these proposals is the so-called MBS resin in which a conjugated diene elastic body is graft-polymerized with an alkyl methacrylate and an aromatic vinyl compound, and the ABS resin in which a conjugated diene elastic body is graft-polymerized with a vinyl cyan compound and an aromatic vinyl compound. Is known to be blended with PVC. However, since these MBS resins and ABS resins contain many double bonds in the main chain of the elastic component, when used outdoors for a long time, they tend to cause thioking phenomenon, impact strength reduction, etc. and are not suitable for outdoor applications. .

Also proposed is a method of using an elastic body in which a saturated dialkyl alkyl ester is partially replaced by a conjugated diene. In this case, a high impact strength improving effect is exhibited, but the weather resistance is MB.
Even if it is not as good as S resin or ABS resin, it still has the drawback of being bad.

We also proposed various resin compositions that use saturated polyacrylic acid alkyl ester as the elastic body and blended with PVC a copolymer obtained by graft-polymerizing alkyl methacrylate, aromatic vinyl compound and vinyl cyan compound with PVC. Has been done.

However, these copolymers show a considerable impact strength improving effect under well kneading conditions (hereinafter referred to as low lubricity conditions), even though they are not as good as MBS resin, but when a large amount of lubricant is used, Alternatively, under the condition that the mixing is not difficult (hereinafter referred to as high slip condition) such as when processed at a relatively low temperature, almost no effect of improving impact strength is exhibited.

The inventors of the present invention have made extensive studies in view of the present situation, and have found that evenly dispersing a multilayer graft copolymer using an alkyl acrylate elastomer in PVC greatly contributes to impact strength development. Surprisingly, the glass transition temperature (hereinafter abbreviated as Tg) of the outermost layer is 0 ° C. as compared with the conventionally well-known multilayer graft copolymer in which a resin component having good compatibility with PVC is graft-polymerized to an elastic body. Below, the multi-layered graft copolymer having a multi-layered structure consisting of at least three layers in which the Tg of the second layer from the outermost layer is 60 ° C or higher and the Tg of the third layer from the outermost layer is 0 ° C or lower is higher. Even when the shear stress is low under slipping conditions, the multi-layered graft copolymer easily melts quickly, the PVC resin composition accelerates gelation, and the dispersed state becomes extremely good. Molding condition Oite it is possible to exhibit high impact strength, a and workability good, excellent surface gloss, and reached the present invention further is weatherability good.

That is, the gist of the present invention is that the outermost layer (A) is composed of a monomer selected from the group of monomers consisting of alkyl acrylates, methacrylic acid alkyl esters, aromatic vinyl compounds and vinyl cyan compounds. The Tg of the polymer constituting the polymer is 0 ° C or lower, the Tg of the polymer constituting the second layer (B) from the outermost layer (A) is 60 ° C or higher, the outermost layer (A).
Has a multi-layer structure consisting of at least three layers of layers (A), (B) and (C) in which the polymer constituting the third layer (C) has a Tg of 0 ° C. or less, and each layer has each layer On the other hand, it is an impact modifier for a thermoplastic resin having good weather resistance, which is composed of a multi-layered graft copolymer containing 0.1 to 5% by weight of a polyfunctional crosslinking agent.

It is essential for the impact modifier of the present invention to have a multilayer structure of three or more layers obtained by polymerizing in at least three stages, and the fourth layer counted from the outermost layer has its single weight. Even if it is a four-layer graft copolymer consisting of a polymer having a Tg of 60 ° C or higher, the fifth layer counted from the outermost layer is a polymer whose Tg of the homopolymer is 0 ° C or lower. It may be a multi-layer graft copolymer such as the following five-layer graft copolymer, and in such a case, the impact resistance improving effect is similarly shown.

Monomers constituting the impact modifier of the present invention include acrylic acid alkyl ester, methacrylic acid alkyl ester,
It is composed of an aromatic vinyl compound and a vinyl cyan compound.

The alkyl acrylate preferably has an alkyl group having 2 to 10 carbon atoms, for example, ethyl acrylate, propyl acrylate, n-butyl acrylate, isobutyl acrylate, hexyl acrylate, octyl acrylate and acrylic acid. 2 ethyl-hexyl etc. are mentioned.

As the methacrylic acid alkyl ester, one having an alkyl group having 1 to 4 carbon atoms is preferable, for example, methyl methacrylate, ethyl methacrylate, propyl methacrylate,
Isopropyl methacrylate, n-butyl methacrylate,
Examples thereof include isobutyl methacrylate and tert-butyl methacrylate. Considering compatibility with PVC, methyl methacrylate is particularly preferable.

Examples of the aromatic vinyl compound include styrene, α-substituted styrene, nucleus-substituted styrene and its derivatives such as α
-Methylstyrene, chlorostyrene, vinyltoluene and the like.

Further, as a vinyl cyanide compound, acrylonitrile,
Methacrylonitrile and the like can be mentioned.

The component of the outermost layer (A) constituting the impact modifier of the present invention is selected from the above monomer group so that the Tg of the outermost layer (A) itself is 0 ° C or less. The composition ratio of the monomer in the outermost layer (A) is 60 to 100 for alkyl acrylate.
% By weight, 0 to 40% by weight of methacrylic acid alkyl ester,
The aromatic vinyl compound can be used in the range of 0 to 40% by weight and the vinyl cyan compound in the range of 0 to 20% by weight. When the Tg of the outermost layer (A) itself exceeds 0 ° C, if the modifier finally obtained is blended with PVC and molded, the (A) layer part will melt slowly and the desired impact resistance improvement effect Is difficult to obtain.

The proportion of the outermost layer (A) in the total amount of the multi-layered graft copolymer is preferably 10 to 50% by weight, the impact resistance improving effect is small when the proportion is less than 10% by weight, and PVC when the proportion exceeds 50% by weight. It is not preferable because the molding processability during blending and molding deteriorates.

The components of the outermost layer (A) to the second layer (B) are selected from the above monomer group so that the Tg of the layer (B) itself is 60 ° C or higher. The composition ratio of the above-mentioned monomers in the layer (B) is 0 to 100% by weight of methacrylic acid alkyl ester, 0 to 100% by weight of aromatic vinyl compound, and 0 to 3 of vinylcyanide compound.
It can be used in the range of 0% by weight and 0 to 20% by weight of alkyl acrylate. When the Tg of the layer (B) itself is less than 60 ° C, it is difficult to obtain a multilayer graft polymer as a good powder. As the component of the layer (B), when blended with PVC, alkyl methacrylate is preferable, and methyl methacrylate is particularly preferable. Aromatic vinyl compounds improve their fluidity when blended with PVC, but when used in large amounts the compatibility deteriorates and impact resistance decreases. A vinyl cyan compound is preferable because it promotes gelation at the time of blending with PVC, but if used in a large amount, it tends to cause coloration during molding and also deteriorates processability.

The ratio of the layer (B) in the total amount of the multilayer graft copolymer is
20 to 60% by weight is preferable, and a ratio of less than 20% by weight is not preferable because the molding processability in molding by blending with PVC is poor. On the other hand, if it exceeds 60% by weight, the amount of the elastic component in the entire multilayer graft copolymer is reduced, and the impact resistance improving effect is small, which is not preferable.

Further, the components of the outermost layer (A) to the third layer (C) are selected from the above monomer group so that the Tg of the layer (C) itself is 0 ° C. or lower. The composition ratio of the monomer in the layer (C) is as follows: acrylic acid alkyl ester 60 to 100% by weight, methacrylic acid alkyl ester 0 to 40% by weight, aromatic vinyl compound 0 to 40% by weight, vinyl cyanide compound 0 to 20% by weight. It can be used in the range of weight%. When the Tg of the layer (C) itself exceeds 0 ° C., the elastic properties of the layer (C) itself are impaired, and it is difficult to obtain the desired impact resistance improving effect.

The ratio of the layer (C) in the total amount of the multilayer graft copolymer is
10 to 60% by weight is preferable, less than 10% by weight has a small impact resistance improving effect, and more than 60% by weight.
Molding workability when blending with PVC and molding is inferior, which is not preferable.

The polyfunctional crosslinking agent of the present invention not only facilitates the graft cross-linking in producing the impact modifier of the present invention, but also significantly improves the coagulation property of the emulsion polymer latex. . Examples of the polyfunctional crosslinking agent include divinylbenzene, diacrylic acid ester or dimethacrylic acid ester which is an ester of acrylic acid or methacrylic acid and polyhydric alcohol, or triallyl cyanurate, triallyl isocyanurate, allyl acrylate, allyl methacrylate. , Diallyl itaconate, diallyl phthalate and the like. From the viewpoint of graft crossing property, a cross-linking agent having an allyl group is preferable.

The ratio of the polyfunctional crosslinking agent in each layer is 0.1 to 5% by weight.
Is. When it is used in an amount exceeding 5% by weight, the outermost layer (A) or layer (C), which is an elastic layer, too impairs the elastic properties. Further, since the compatibility of the resin layer (B) with PVC is deteriorated, the impact resistance improving effect is deteriorated, which is not preferable. The proportion of the polyfunctional cross-linking agent in each layer is 0.1 to 3% by weight in consideration of the coagulation property of the emulsion polymer latex during the production of the multilayer graft copolymer and the impact resistance improving effect of the obtained multilayer graft copolymer. % Range is preferred.

The multi-layered graft copolymer as the impact resistance modifier of the present invention is preferably produced by a usual emulsion polymerization method.

Emulsifiers include fatty acid salts, alkyl sulfate salts,
Anionic surfactants such as alkylbenzene sulphonates, alkyl phosphates, dialkyl sulphosuccinates and nonionics such as polyoxyethylene alkyl ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid esters and glycerin fatty acid esters Surfactants and further cationic surfactants such as alkylamine salts can be used. These surfactants can be used alone or in combination. In addition, depending on the type of emulsifier, when the pH of the polymerization system is on the alkaline side, an appropriate pH adjusting agent can be used to prevent hydrolysis of the alkyl acrylate.

As the polymerization initiator, an ordinary inorganic initiator such as persulfate, an organic peroxide, an azo compound or the like may be used alone, or the above compound and a sulfite, a hydrogen sulfite, a thiosulfate, a first metal may be used. It can also be used as a redox type initiator in combination with a salt, sodium formaldehyde sulfoxylate or the like. Preferred persulfates as initiators are sodium persulfate, potassium persulfate, ammonium persulfate and the like, and organic peroxides include t-butyl hydroperoxide, cumene hydroperoxide, benzoyl peroxide, lauroyl peroxide and the like. is there.

A chain transfer agent may be used to control the molecular weight of the polymer, and an alkylmercaptan having 5 to 20 carbon atoms can be used.

Polymerization is carried out at a temperature equal to or higher than the decomposition temperature of the initiator under ordinary emulsion polymerization conditions, and at least the outermost layer (A) and the outermost layer (A) to 2
The second layer (B) and the outermost layer (A) to the third layer (C) can be formed to have the structure as described above. At this time, the polymerization in each of the steps can be carried out while adding the whole amount of each monomer or the mixture of the monomers at once, or continuously adding the whole amount or a part thereof.
However, from the viewpoints of stability of polymerization, removal of heat of polymerization reaction, etc., it is preferable to carry out polymerization while adding the whole amount or a part thereof.

The particle size of the multilayer graft copolymer has a great influence on the impact strength of the PVC resin composition. If the particle size is too small, the impact strength improving effect is small, and the particle size is preferably as large as possible so as not to impair the stability of the latex. The particle size of the graft copolymer should be in the range of 0.15 to 0.40μ, and it may be adjusted with an appropriate emulsifier type and amount, or at the appropriate polymerization stage using a thickening agent such as an acid or an inorganic salt. it can.

When recovering the multi-layered graft copolymer from the obtained latex, it can be recovered by salting out or acidifying and coagulating and then collecting in powder form after filtration and washing with water, or by spray drying, freeze drying and the like.

Further, it can be recovered by the method described in JP-A-57-187322.

The impact modifier of the present invention is a graft copolymer having a multilayer structure as described above, and imparts high impact resistance, good processability to various thermoplastic resins, and weather resistance of molded articles. The impact modifier of the present invention is added to the thermoplastic resin in an amount of 3 to 50 parts by weight based on 100 parts by weight of the thermoplastic resin.
If the blending ratio is less than 3 parts by weight, the impact resistance improving effect is small, and if it exceeds 50 parts by weight, the mechanical properties inherent in the thermoplastic resin are impaired, which is not preferable. Here, examples of the thermoplastic resin include PVC, polycarbonate resin, polyester resin, acrylonitrile-styrene resin, methyl methacrylate-styrene resin, and the like. PVC is polyvinyl chloride and vinyl chloride 70
A vinyl chloride-based copolymer composed of at least wt% can be used. As the monomer to be copolymerized with vinyl chloride, ethylene, propylene, vinyl bromide, vinylidene chloride, vinyl acetate, acrylic acid ester, methacrylic acid ester and the like are used.

The blending of the impact modifier of the present invention with the thermoplastic resin is preferably in the form of powder, and is carried out, for example, by a ribbon blender, a Henschel mixer or the like, and a known kneader such as a mixing roll, a Banbury mixer, an extruder and an injection machine is used. It is molded by a molding machine or the like. When blending, known stabilizers, plasticizers, lubricants, colorants and the like may be added as required.

The present invention will be specifically described below with reference to examples. In the examples, "part" and "%" are "part by weight" and "% by weight", respectively.
Is meant.

Further, the Tg of the copolymer in each Example and Comparative Example is obtained from the formula of FOX. Example 1 (a) Production of Multilayer Graft Copolymer 190 parts of ion-exchanged water substituted with nitrogen was placed in a reaction vessel. Dissolve 1.2 parts of semi-hardened tallow fatty acid soap and 0.6 part of potassium persulfate, and maintain at 70 ° C while n-butyl acrylate 19.85 parts and triallyl isocyanurate 0.1 as layer (C) components.
A mixture of 5 parts was added dropwise over 1 hour. After completion of the dropping, the temperature was maintained for 1 hour while maintaining the same temperature to complete the polymerization. The polymerization rate was 99.0%.

A mixture of 49.7 parts of methyl methacrylate and 0.3 part of triallyl isocyanurate as a layer (B) component was added dropwise to this polymer latex over 2 hours while maintaining the temperature at 70 ° C., and the mixture was maintained for 1 hour after completion of the addition. , The polymerization was completed. The polymerization rate was 99.5%.

0.2 parts of potassium persulfate was dissolved in 10 parts of water and added to the obtained polymer latex, and acrylic acid n- was added as the layer (A) component.
A mixture of 29.8 parts of butyl and 0.2 parts of triallyl isocyanurate was added dropwise over 90 minutes while maintaining the temperature at 70 ° C.
After completion of dropping, the mixture was maintained for 1 hour to complete the polymerization. The polymerization rate was 99.3%, and the average particle size of the obtained graft copolymer was
It was 0.25μ.

The obtained multi-layered graft copolymer latex was added to a sulfuric acid aqueous solution, coagulated and coagulated, washed, dehydrated and dried to recover the graft copolymer in powder form (Example 1-
1)).

Further, the composition ratios of the layer (C), the layer (B) and the layer (A) were variously changed to obtain a multi-layer graft copolymer obtained by the same polymerization prescription. These are shown in Table 1.

(B) Production of compounded composition with vinyl chloride resin 13 parts of each multilayer graft copolymer obtained in the above (a) and 87 parts of vinyl chloride resin having an average degree of polymerization of 700, totaling 100 parts, and 2.5 parts of dibutyl tin malate. , Butyl stearate 0.8 parts, Lubricant
0.7 part was added and the temperature was raised to 115 ° C in a Hensiel mixer to obtain a uniform mixture. This vinyl chloride resin composition
After kneading with a mixing roll adjusted to 175 ° C. for 3 minutes, the obtained sheet was heated and pressed to prepare a test piece, and its impact strength was measured. The impact strength was tested according to ASTM-D-256 by an Izod impact test with a V-notch. The compounding conditions and molding conditions of this vinyl chloride resin composition are low lubricity conditions.

Further, each multilayer graft copolymer obtained by the above (a)
13 parts and 87 parts of vinyl chloride resin with an average degree of polymerization of 700, 100 parts in total, 2.0 parts of tribasic lead sulfate, 0.3 parts of dibasic lead stearate,
2.0 parts of lead stearate and 0.3 part of stearic acid were added, and the temperature was raised to 115 ° C in a Hensiel mixer to obtain a uniform mixture. This vinyl chloride resin composition was subjected to square bar molding under the following conditions with a 30 mmφ single screw extruder.

The impact strength of the molded product was measured according to ASTM-D-256 except that a test piece with a U-notch having a depth of 2 mm was used. The compounding conditions and molding conditions of this vinyl chloride resin composition are high lubricity conditions.

The results of these measurements are also shown in Table 1.

Table 1 also shows the impact strength of the vinyl chloride resin itself under high-sliding condition and low-sliding condition.

Comparative Example 1 190 parts of ion-exchanged water which had been replaced with nitrogen was placed in a reaction vessel, 1.2 parts of semi-hardened tallow fatty acid soap and 0.4 part of potassium persulfate were dissolved, and while maintaining the temperature at 70 ° C., 59.7 parts of n-butyl acrylate,
3 parts of a mixture consisting of 0.3 parts of triallyl isocyanurate
Dropped over time. After the completion of the dropping, the temperature was maintained for 1 hour to maintain the same temperature to complete the polymerization. The polymerization rate was 99.5%.

To this polymer latex, 0.2 part of potassium persulfate was dissolved in 10 parts of water and added, and a mixture of 39.8 parts of methyl methacrylate and 0.2 part of triallyl isocyanurate was added dropwise over 2 hours while maintaining the temperature at 70 ° C. After the completion of the dropping, the temperature was kept for 1 hour to keep the temperature the same to complete the polymerization. The polymerization rate was 99.7%. The average particle size of the graft polymer was 0.23μ.

The graft copolymer was recovered from this graft polymer latex in the same manner as in Example 1.

A composition prepared by blending this graft copolymer with the same formulation as in (b) of Example 1 was measured for impact strength under the same high slip condition and low slip condition. The results are shown in Table 2.

Comparative Example 2 In Comparative Example 1, the first stage potassium persulfate was changed to 0.2 parts, and a mixture of 39.8 parts of methyl methacrylate and 0.2 parts of triallyl isocyanurate was similarly polymerized.

Furthermore, 0.4 part of potassium persulfate was added to 1 part of water in this polymer latex.
A mixture of 59.7 parts of n-butyl acrylate and 0.3 part of triallyl isocyanurate was dissolved in 0 part of the mixture, polymerization was completed in the same manner as in Comparative Example 1, and the graft copolymer was recovered.

The composition prepared by blending this graft copolymer with the same formulation as in (b) of Example 1 was measured for impact strength under the same high slip condition and low slip condition. The results are also shown in Table 2.

As is clear from the results shown in Tables 1 and 2, it can be seen that the impact resistance modifier of the present invention exhibits a high impact resistance improving effect particularly under high slip conditions.

The abbreviations in Tables 1 and 2 are as follows, and the same applies to the subsequent cases.

BA: n-butyl acrylate MMA: methyl methacrylate MAIC: triallyl isocyanurate Example 2, Comparative Examples 3 to 4 Layer (C) component, layer (B) component and layer (A) component monomer and crosslinking A multilayer graft copolymer obtained by the same operation as in Example 1 except that the type of the agent and the number of parts used were changed as shown in Table 3 was subjected to the same impact strength as in Example 1 (b). Was measured. The results of this are shown in Table 3.

The abbreviations in Table 3 are as follows, and the same applies to the subsequent cases.

2EHA: 2 Ethyl-hexyl acrylate St: Styrene AN: Acrylonitrile AMA: Allyl methacrylate As can be seen from Comparative Examples 3 and 4, the layer (C) component or the layer (A) component having a high Tg has an effect of improving impact resistance. It turns out that is small.

Example 3 180 parts of ion-exchanged water substituted with nitrogen was placed in a reaction vessel, 1.4 parts of sodium lauroylbenzenesulfonate and 0.35 part of sodium phoromaldehyde sulfoxylate were dissolved, and the mixture was kept at 70 ° C. as a layer (C) component. N-octyl acrylate 29.8 parts, triallyl cyanurate 0.2 part,
A mixture of 0.15 parts of cumene hydroperoxide was added dropwise over 1 hour and 30 minutes. After the completion of the dropping, the temperature was maintained for 1 hour to maintain the same temperature to complete the polymerization.

A mixture of 34.7 parts of methyl methacrylate, 5 parts of acrylonitrile, 0.3 parts of triallyl cyanurate, and 0.2 parts of cumene hydroperoxide was added dropwise to this polymer latex as a component (B) for 2 hours while maintaining the temperature at 70 ° C. . After completion of dropping, the mixture was maintained for 1 hour to complete the polymerization.

To the obtained polymer latex, 0.6 part of sodium lauroyl benzenesulfonate and 0.15 part of sodium formaldehyde sulfoxylate were dissolved in 20 parts of water and added.
A mixture of 29.8 parts of n-octyl acrylate, 0.2 part of triallyl cyanurate and 0.15 part of cumene hydroperoxide was added dropwise as a component of the layer (A) over 1 hour and 30 minutes while maintaining the temperature at 70 ° C. After completion of the dropping, the temperature was maintained for 1 hour while maintaining the same temperature to complete the polymerization. The average particle size of the obtained graft copolymer was 0.22μ.

Example 1 was obtained from the resulting multi-layered graft copolymer latex.
The graft copolymer was recovered in the same manner as in (a) above, and a PVC resin composition was obtained in the same manner as in (b) of Example 1. The impact strength of this was measured in the same manner as in Example 1 (b). The results are shown in Table 4.

Table 4 also shows the results when the composition ratios of the layer (C), the layer (B) and the layer (A) were changed.

The abbreviations in Table 4 are as follows.

OA: n-octyl acrylate TAC: triallyl cyanurate As shown in Table 4, when the amount of the cross-linking agent in each component is large, the impact resistance improving effect is small.

Example 4 A PVC resin composition prepared by using a commercially available PVC resin modifier, methyl methacrylate-butadiene-styrene resin (MBS resin) and chlorinated polyethylene (ClPE) under the high lubricity condition of Example 1 (b). And the first embodiment (a) of the present invention
(B) of Example 1 using the multi-layered graft copolymer obtained in
Table 5 shows the weather resistance of the PVC resin composition under the condition of high lubricity. Weather resistance is weatherometer (WE-II series manufactured by Toyo Rika)
Izod impact strength and degree of coloring after accelerated exposure treatment by.

The indication of the degree of coloring in Table 5 is as follows.

◯: Almost no coloration and good.

Δ: Slightly colored, which is not very preferable.

X: Colored and defective.

From the results shown in Table 5, it can be seen that the modifier according to the present invention has very good weather resistance (initial impact retention rate, coloration) compared to commercially available MBC and ClPE.

Claims (2)

[Claims] 1. A polymer comprising a monomer selected from the group of monomers consisting of alkyl acrylates, methacrylic acid alkyl esters, aromatic vinyl compounds and vinyl cyan compounds and constituting the outermost layer (A). Has a glass transition temperature of 0 ° C or lower, the glass transition temperature of the polymer constituting the second layer (B) from the outermost layer (A) is 60 ° C or higher, and the third layer (C) from the outermost layer (A) is Layers (A), (B) and (C) in which the glass transition temperature of the constituent polymer is 0 ° C. or lower
0.1 to 5% by weight of a polyfunctional crosslinking agent for each layer having a multilayer structure consisting of at least three layers
Impact modifier for thermoplastic resin having good weather resistance, which comprises a multi-layered graft copolymer containing 2. The outermost layer (A) according to claim 1, wherein at least one selected from the group of monomers such that the polymer constituting the layer (A) has a glass transition temperature of 0 ° C. or lower. Monomer of
A polymer composed of 95 to 100% by weight and a polyfunctional crosslinking agent of 0.1 to 5% by weight, and its proportion in the multilayer graft copolymer is 10 to 50% by weight, the second layer from the outermost layer (A). (B)
95% to 100% by weight of at least one monomer selected so that the polymer constituting the layer (B) has a glass transition temperature of 60 ° C. or higher from the group of monomers, and a polyfunctional crosslinking agent. 0.1 to 5% by weight of the polymer, the proportion of which in the multilayer graft copolymer is 20 to 60% by weight, the outermost layer (A) to the third layer (C) is in the monomer group. From 95 to 100% by weight of at least one monomer selected so that the glass transition temperature of the polymer constituting the layer (C) is 0 ° C. or less, and 0.1 to 5% by weight of a polyfunctional crosslinking agent. An impact modifier for a thermoplastic resin, which is a polymer and accounts for 10 to 60% by weight in the multilayer graft copolymer.