JP2958177B2 - Acrylic resin composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acrylic resin composition which is excellent in weather resistance and impact resistance and has good adhesion to thermosetting resins such as melamine resin and phenol resin.

[0002]

2. Description of the Related Art Melamine resins and phenol resins are used as interior wall materials and flooring materials, etc., taking advantage of their characteristics such as surface hardness and solvent resistance. However, they have poor weather resistance and are subject to discoloration and deterioration due to long-term use. There is. On the other hand, the acrylic resin can suppress the deterioration of the weather resistance of the substrate by bonding or laminating due to its good weather resistance.
Acrylic resin films containing methyl methacrylate as a main component and made of a multi-layer polymer having a tapered structure as described in JP-A-129449 and JP-A-52-56150 are laminated, and the weather resistance of the substrate is laminated. In addition to suppressing deterioration, it has excellent impact resistance, water whitening resistance, solvent resistance, stress whitening resistance, and has the function of giving design to the base material, but it has a thermosetting property like melamine resin and phenol resin There is a problem that the adhesiveness to the resin is poor, and sufficient adhesive strength cannot be obtained by thermal bonding.

[0003]

The object of the present invention is to provide excellent weather resistance, impact resistance, solvent resistance, water whitening resistance, and stress whitening resistance, and to the thermosetting properties of melamine resins and phenol resins. An object of the present invention is to provide an acrylic resin composition having excellent adhesion to a resin.

[0004]

The gist of the present invention is as follows. The innermost layer polymer (A), crosslinked elastic layer polymer (B), outermost layer polymer (C) and intermediate layer polymer (D) )
And an acrylic resin composition having a multilayer polymer having a gel content of at least 50% and a residual metal content of 500 ppm or less. Innermost layer polymer (A) 80 to 100 parts by weight of alkyl acrylate having an alkyl group having 1 to 8 carbon atoms and / or alkyl methacrylate having an alkyl group having 1 to 4 carbon atoms (A ₁ ) 0 to 20 parts by weight of Copolymerizable monomer having a double bond (A ₂ ) 0 to 10 parts by weight of polyfunctional monomer (A ₃ ) (A ₁ ) to (A ₃ ). .1 to
Polymer present in the core obtained from the composition of 5 parts by weight of graft-linking agent (A ₄ ) Crosslinked elastic layer polymer (B) 80 to 100 parts by weight Alkyl acrylate having an alkyl group having 1 to 8 carbon atoms (B ₁₎ a monomer having a copolymerizable double bond 0-20 parts by weight (B ₂₎ a polyfunctional monomer of 0 parts by weight _{(B 3) (B 1)} ~ (B 3 ) For 100 parts by weight of the total amount
A polymer which is obtained from the composition of 5 parts by weight of the graft-linking agent (B ₄ ) and is present outside the innermost layer polymer (A). The outermost layer polymer (C) 51 to 100 parts by weight having 1 to 4 carbon atoms. Alkyl methacrylate (C ₁ ) 0.1 to 40 parts by weight of hydroxyalkyl (meth) acrylate (C ₂ ) having an alkyl group of 1 to 8 carbon atoms 0 to 49 parts by weight of a monomer having a copolymerizable double bond obtained from the composition of the body (C _3), a polymer intermediate layer polymer present on the outer surface (D) 10 to 90 parts by weight of alkyl acrylate having an alkyl group having 1 to 8 carbon atoms (D ₁₎ 90 to 10 0 to 20 parts by weight of a copolymerizable double bond-containing monomer (D ₃ ) 0 to 10 parts by weight of polyfunctionality of 0 to 10 parts by weight of alkyl methacrylate (D ₂ ) having 1 to 4 carbon atoms monomer _{(D 4) (D 1)} ~ (D 4) 0.1 weight per 100 parts by weight
It is obtained from the composition of ₅ parts by weight of the graft crossing agent (D ₅ ), is present between the crosslinked elastic layer polymer (B) and the outermost layer polymer (C), and has an alkyl acrylate (D ₁ ) amount of the crosslinked elasticity. Polymer adjusted so as to decrease monotonously from layer polymer (B) to outermost layer polymer (C)

[0005] The acrylic resin composition of the present invention comprises a crosslinked elastic layer polymer containing alkyl acrylate as a main component in the presence of an innermost polymer (A) containing a specific alkyl acrylate and / or alkyl methacrylate as a main component. B) is polymerized, and an outermost layer polymer (C) containing an alkyl methacrylate as a main component and a specific hydroxyl group-containing monomer component is disposed as the outermost layer, and the polymer (B) layer and the polymer (C) are arranged. An intermediate layer polymer (D) layer adjusted so that the amount of the alkyl acrylate as a monomer component monotonously decreases from the polymer (B) layer toward the polymer (C) layer. It is a multi-layer polymer with intervening layers. Moreover, this multilayer structure polymer has a gel content and a residual metal content of the final polymer composition of a specific amount by using a specific range of the amount of the grafting agent in each polymer layer other than the outermost layer polymer (C). It is specified.

Acrylic rubbers generally have better weather resistance than diene rubbers, but have a property of slow elastic recovery, large deformation under stress, and low rubber efficiency. That is, in order to provide various properties such as solvent resistance and water whitening resistance while maintaining excellent weather resistance, there is a limit in the conventional elastic structure consisting of only one layer. In the present invention, in order to solve such a drawback, the innermost layer polymer (A) is present in the core of the crosslinked elastic layer polymer (B). That is, when stress is applied, the stress concentrated in the crosslinked elastic layer polymer (B) layer is dispersed and relieved by the presence of the innermost layer polymer (A), and as a result, the generation rate of microvoids also increases. Thus, it is considered that excellent impact resistance is exhibited even without apparent stress whitening.

Hereinafter, each layer of the resin composition having a multilayer structure of the present invention will be described. First, the innermost layer polymer (A) will be described. The alkyl acrylate (A ₁ ) having an alkyl group having 1 to 8 carbon atoms constituting the innermost layer polymer (A) may be linear or branched, and may be methyl acrylate, ethyl acrylate, propyl acrylate, or 2-ethylhexyl. Acrylate, n-octyl acrylate and the like are used alone or in combination, but those having a low glass transition point Tg are more preferable. The alkyl methacrylate (A ₁ ) having an alkyl group having 1 to 4 carbon atoms may be linear or branched, and methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, or the like may be used alone or as a mixture. Can be Further, these alkyl acrylates and alkyl methacrylates may be used as a mixture. These alkyl (meth) acrylates (A
₁ ) is used in the range of 80 to 100 parts by weight. Also,
It is preferable that these alkyl (meth) acrylates (A ₁ ) are subsequently used in all the multi-layers (A) to (D), but in any of (A) to (D), depending on the final purpose, 2 More than one kind of monomer may be mixed, or another kind of acrylate may be used.

A monomer having a copolymerizable double bond (A)
₂ ) Examples include lower alkyl acrylate, lower alkoxy acrylate, cyanoethyl acrylate, acrylic monomers such as acrylamide, acrylic acid and methacrylic acid, aromatic vinyl monomers such as styrene and alkyl-substituted styrene, acrylonitrile, methacrylonitrile and the like. And used in the range of 0 to 20 parts by weight.

The polyfunctional monomer (A ₃ ) includes alkylene glycol dimethacrylate such as ethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, 1,4-butylene glycol dimethacrylate and propylene glycol dimethacrylate. Preferably, polyvinylbenzene such as divinylbenzene and trivinylbenzene, and alkylene glycol diacrylate can be used. Even if the polyfunctional monomer (A ₃ ) is not used at all, a fairly stable multilayered polymer can be obtained as long as the graft-linking agent (A ₄ ) is present, but the hot strength is strictly required. It is preferable to add them to the composition, for example, in the range of 0 to 10 parts by weight.

The graft-linking agent (A ₄ ) refers to a compound having two or more unsaturated groups having addition polymerizability and having a large difference in the polymerization reactivity of each unsaturated group. Allyl, methallyl or crotyl esters of .beta.-unsaturated carboxylic acids or dicarboxylic acids, preferably allyl esters of acrylic acid, methacrylic acid, maleic acid and fumaric acid are used, and allyl methacrylate in particular has an excellent effect. Other triallyl cyanurate,
Triallyl isocyanurate is also effective. These may be used alone or as a mixture. Such graft-crosslinkers primarily react conjugated unsaturated bonds of the ester much more rapidly than allyl, methallyl or crotyl groups and chemically bond. During this time, a substantial portion of the allyl, methallyl or crotyl groups work effectively during the polymerization of the next layer of crosslinked elastic layer polymer (B) to provide a graft bond between two adjacent layers.

The amount of the grafting agent (A ₄ ) used is extremely important, and is 0.1 to 5 parts by weight, preferably 0.5 part by weight, based on 100 parts by weight of the total of the components (A ₁ ) to (A ₃ ). It is used in the range of ~ 2 parts by weight. When the amount is less than 0.1 part by weight, the effective amount of the graft bond is small, and when it exceeds 5 parts by weight, the reaction amount with the crosslinked elastic layer polymer (B) formed by polymerization in the second stage becomes large, and the feature of the present invention is obtained. In this case, the elasticity of the two-layer crosslinked rubber elastic body having the two-layer elastic structure is reduced.

The Tg of the innermost layer polymer (A) is appropriately set according to the required physical properties of the final polymer. In general, the higher the crosslink density is the same as or rather higher than that of the crosslinked elastic layer polymer (B), the better in terms of quality. The innermost layer polymer (A) and the crosslinked elastic layer polymer (B) may have the same composition, but in such a case, instead of being temporarily charged, the two-layered elastic body structure by the two-stage polymerization is merely used. It is important that the amount of the catalyst, the crosslink density and the like be set higher for the polymer (A). Considering the initial polymerizability, the presence of the innermost layer polymer (A) is extremely important for obtaining a stable multilayer structure polymer, and it is generally preferred that the catalyst amount is the largest in each polymer layer.

The use of the grafting agent (A ₄ ) is intended to effectively synthesize a two-layer elastic structure chemically bonded to the crosslinked elastic layer polymer (B) formed in the second stage. Required. Without this graft bond, the two-layer elastic structure easily undergoes phase breakage during melt formation, lowering the rubber efficiency and not exhibiting the intended purpose of excellent weather resistance, solvent resistance, water whitening resistance, etc. . The content of the innermost layer polymer (A) in the multilayer structure polymer is 5 to 35% by weight, and more preferably 5 to 35% by weight.
It is preferably 15% by weight, and is preferably lower than the content of the crosslinked elastic layer polymer (B).

Next, the crosslinked elastic layer polymer (B) will be described. The crosslinked elastic layer polymer (B) is a main component that gives rubber elasticity to the multilayer structure polymer, and constitutes this component (B
_For ( ₁ ) to (B ₄ ), (A ₁ ) to (A ₄ ) used in the innermost layer polymer (A) described above are used, respectively. (B ₁ )
The component is 80 to 100 parts by weight, the component (B ₂ ) is 0 to 20 parts by weight, the component (B ₃ ) is 0 to 10 parts by weight, and the component (B ₄ ) is the total amount of (B ₁ ) to (B ₃ ). 0.1 to 5 for 100 parts
Each is used in the range of parts by weight. Tg of the crosslinked elastic layer polymer (B) alone is preferably 0 ° C or lower, more preferably -30 ° C or lower.

The content of the crosslinked elastic layer polymer (B) in the multilayer polymer is preferably in the range of 10 to 45% by weight.
Further, the content is preferably higher than the content of the innermost layer polymer (A). By having a double-layer crosslinked rubber elastic body having a double-layer elastic body structure in which the innermost layer polymer (A) and the crosslinked elastic layer polymer (B) are graft-polymerized as described above, a conventional single rubber can be achieved. Various properties that could not be satisfied can be satisfied simultaneously. This two-layer crosslinked rubber elastic body had a gel content of 85% or more and a swelling degree of 3 or more determined by the following measurement method.
It is preferable to set in the range of from 13 to 13 to obtain excellent solvent resistance and water whitening resistance.

(Method for measuring gel content and swelling degree) JIS K
Take a predetermined amount of a two-layer crosslinked rubber elastic body according to -6388,
Immersion and swelling in methyl ethyl ketone (hereinafter referred to as MEK) at 25 ° C. for 48 hours, pulling up, wiping off the attached MEK, measuring its weight, and then MEK in a vacuum dryer
Is dried and removed to obtain a constant weight, and the absolute dry weight is read and calculated by the following equation. Swelling degree = (weight after swelling MEK-absolute dry weight) / absolute dry weight Gel content (%) = (absolute dry weight / weight of collected sample)
× 100

Generally, if the degree of polymerization of the crosslinked elastic layer polymer (B) is as high as possible, a high impact strength is imparted to the final polymer. On the other hand, the innermost layer polymer (A) as the core is not limited to this. Rather, a large amount of catalyst is used to stabilize the desired polymerization including particle formation, and a large amount of the graft activator is used. The better the performance as a two-layer crosslinked rubber elastic body is, the better. Such a combined effect cannot be obtained with a conventional single layer rubber polymer system.

The outermost layer polymer (C) should contribute to the adhesiveness, moldability, mechanical properties, etc., of the multilayer structure polymer, and (C ₁ ) constitutes the (A ₁ ) component, (C ₃₎
The components used for the component (A ₂ ) are used. Also, hydroxyalkyl having an alkyl group having 1 to 8 carbon atoms (meth) acrylate (C ₃₎ The linear, branched either well hydroxymethyl acrylate, hydroxyethyl acrylate, 4-hydroxybutyl acrylate, hydroxymethyl Methacrylate, hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate and the like are used alone or in combination.

In the present invention, 0.1 to 40 parts by weight, preferably 0.5 to 40 parts by weight of the outermost layer polymer (C) is used.
The desired object described above can be achieved by copolymerizing 20 parts by weight of a hydroxyalkyl (meth) acrylate having 1 to 8 carbon atoms. The content of the outermost layer polymer (C) in the multilayer structure polymer is preferably 10 to 80% by weight, more preferably 40 to 60% by weight.

The multilayer structure polymer of the present invention comprises the above innermost layer polymer (A), crosslinked elastic layer polymer (B) and outermost layer polymer (C) as basic constituent units, and further comprises a crosslinked elastic layer polymer ( An intermediate polymer (D) exists between the layer (B) and the outermost polymer (C). This intermediate layer polymer (D) is 10 to 9
0 parts by weight of an alkyl acrylate having an alkyl group having 1 to 8 carbon atoms (D ₁ );
Alkyl methacrylate having an alkyl group of 4 (D ₂ ), 0 to 20 parts by weight of a monomer having a copolymerizable double bond (D ₃ ), 0 to 10 parts by weight of a polyfunctional monomer (D ₄ ), and the total amount of these (D ₁ ) to (D ₄ ) is 10
Composed of the composition of 0.1 to 5 parts by weight of the grafting agent (D ₅₎ with respect to 0 parts by weight. In the intermediate polymer layer (D), the amount of the alkyl acrylate component in the intermediate polymer layer (D) decreases monotonously from the crosslinked elastic polymer layer (B) to the outermost polymer layer (C). At least one layer.

Here, (D ₁ ) can be an alkyl acrylate usable for (A ₁ ), (D ₂ ) can be an alkyl methacrylate usable for (A ₁ ), and (D ₃ )
As each component of (D ₅ ), each component which can be used in the above (A ₂ ) to (A ₄ ) can be used. The graft crossing agent (D ₅ ) used in the intermediate layer (D) is essential for tightly bonding the polymer layers and obtaining excellent properties. Since the (B) layer and the (C) layer have different refractive indices, the (D) layer is provided to provide a gradient of the refractive index. In the layer (D), the amount of the acrylate component must necessarily decrease monotonically, but the distribution of the acrylate component can be controlled by changing the supply amount of the acrylate. The content of the intermediate layer (D) in the multilayer polymer is preferably from 5 to 35% by weight, and if it is less than 5% by weight, the function as the intermediate layer is not sufficient. There is a risk of breaking.

The multi-layered polymer has the above-mentioned (A), (B),
It is composed of the polymer layers of (C) and (D), and the gel content must be at least 50% in order to obtain more excellent solvent resistance and water whitening resistance. This is one of the major features of the present invention. In this case, the gel content of the two-layer crosslinked rubber elastic body (consisting of the innermost layer polymer (A) and the crosslinked elastic layer polymer (B)) itself, the intermediate layer polymer (D) and the outermost layer polymer (C ) In addition to the graft component to the crosslinked rubber elastic body,
Here, the definition of the gel content is the same as described above. The component is the added weight of the two-layer crosslinked rubber elastic body and the graft chain and can be replaced by the graft ratio.However, in the present invention, since the multilayer structure polymer has a special structure, it has a gel content and has a graft amount. As a guide. From the viewpoint of solvent resistance, the larger the gel content, the more advantageous. However, from the viewpoint of easy moldability, the upper limit of the gel content is preferably about 80% because the presence of a free polymer is required.

When producing a multilayer polymer, an aqueous dispersion polymerization method is preferred, and the dispersion particle diameter of the final polymer is not particularly limited, but a range of about 800 to 2,000 angstroms provides the most balanced structure. Can be In addition,
There are no particular restrictions on the surfactants, catalysts and the like used in the production, and if necessary, additives such as antioxidants and lubricants can be added for salting out. Here, in the case of salting out using a metal salt, it is extremely important to keep the residual metal content in the final product at 500 ppm or less, which is one of the great features of the present invention. In particular, when using a metal salt with high affinity for water such as magnesium and sodium as a salting-out agent, whitening decreases when the final polymer is immersed in boiling water unless the residual metal content is reduced as much as possible. This is a serious problem in practical use. In addition, calcium-based,
Sulfuric acid-based coagulation shows a relatively good tendency, but in any case, it is necessary to reduce the residual metal content to 500 ppm or less by washing the polymer or the like in order to give excellent water whitening resistance. And the smaller the residual metal, the better. As a method for producing a multilayer structure polymer, a sequential multi-stage polymerization method by emulsion polymerization is the most suitable polymerization method, but is not limited to this. For example, after the emulsion polymerization, the polymerization of the outermost layer polymer (C) may be replaced by a suspension polymerization system. The conversion can also be carried out by an emulsion suspension polymerization method.

The acrylic resin composition of the present invention can be used alone, but can also be used by blending with a homopolymer or copolymer of an alkyl (meth) acrylate having 1 to 8 carbon atoms. is there. In order to adhere the acrylic resin composition of the present invention to a thermosetting resin substrate such as a melamine resin or a phenol resin, a method of forming the acrylic resin composition into a film or a sheet and then thermally bonding the substrate to the substrate. And a method in which the acrylic resin composition is dissolved in an appropriate organic solvent, applied to a substrate, and dried, and may be arbitrarily selected depending on the purpose. When formed into a film or sheet using the acrylic resin composition of the present invention, either a single layer or a bilayer may be used, and in the case of a bilayer, the present acrylic resin composition is disposed at least in an adhesive layer with a substrate. I just want to.

[0025]

The present invention will be described in more detail with reference to the following examples. In the examples, “parts” means “parts by weight”. Examples 1 to 7 (Production of acrylic resin composition) In a polymerization vessel equipped with a cooler, 250 parts of ion-exchanged water, 2 parts of ester soda salt of sulfosuccinic acid, Rongalit (S
FS), and stirred under nitrogen. After stirring under nitrogen, 1.6 parts of methyl methacrylate (MMA), 8 parts of butyl acrylate (BuA), 0.4 part of 1,3-butylene glycol dimethacrylate (BD), allyl methacrylate (A
MA) 0.1 part and cumene hydroperoxide (C
(HP) 0.04 parts of a mixture were charged. After the temperature was raised to 70 ° C., the reaction was continued for 60 minutes to complete the polymerization of the innermost layer polymer (A). Subsequently, 1.5 parts of MMA and 22.5 BuA
, 1.0 part of BD and 0.25 part of AMA, a monomer mixture for forming a crosslinked elastic layer polymer (B) is added for 60 minutes and polymerized, whereby the innermost layer polymer (A) is crosslinked elastic layer weight. A two-layer crosslinked rubber elastic body covered with the union (B) was obtained. In this case, CH used for forming the crosslinked elastic layer polymer (B) was used.
The amount of P was 0.05% by weight based on the monomer mixture.

The degree of swelling and the gel content of the obtained two-layer crosslinked rubber elastic body were determined to be 10.0% and 90%, respectively. Subsequently, MM was used to form the interlayer polymer (D).
A mixture of 5 parts of A, 5 parts of BuA, 5 parts of BD and 0.1 part of AMA was reacted, and finally, the one shown in Table 1 was used as a monomer mixture for forming the outermost layer polymer (C),
Various acrylic resin compositions were obtained. The resulting polymer emulsion was subjected to salting out using 5 parts of calcium chloride with respect to 100 parts of the solid content of the polymer, washed and dried, and after adding a stabilizer,
Various evaluations were made by shaping. Table 1 shows the residual amount of calcium and the gel content in the obtained final polymer.

Next, the obtained multilayer structure polymer was extruded under the following conditions to obtain nine types of films. 40 mmφ (screw diameter) extruder Resin temperature 245 ° C Discharge rate 17 kg / h (for 50 μm thickness) Nine kinds of obtained laminated films and melamine resin-impregnated paper are sandwiched between metal plates and 50 kg / h at 140 ° C and 160 ° C. cm ²
For 30 minutes, and the film layer was cut with a cutter, and the adhesiveness was evaluated by whether or not the film layer could be peeled off by hand. Table 2 shows the results. From the results in Table 2, it is clear that the acrylic resin composition has excellent adhesiveness with a coating agent such as a melamine resin.

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

The acrylic resin composition of the present invention has good weather resistance and extremely excellent adhesiveness with thermosetting resins such as melamine resin and phenol resin, and is therefore formed into a film or sheet. Afterwards, it is possible to obtain excellent adhesive strength very easily by heat bonding, and it is also possible to easily bond the thermosetting resin and the thermoplastic resin such as vinyl chloride resin decorative board by using it as a binder. It becomes possible and its industrial significance is great.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-5-271361 (JP, A) JP-A-2-60903 (JP, A) JP-A-59-124916 (JP, A) JP-A-57- 44641 (JP, A) JP-A-51-129449 (JP, A) JP-A-49-6034 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C08F 251/00-292 / 00 C08L 51/00-51/10

Claims (1)

(57) [Claims] 1. A gel content of at least 50%, comprising the following innermost layer polymer (A), crosslinked elastic layer polymer (B), outermost layer polymer (C) and intermediate layer polymer (D): An acrylic resin composition having a multilayer structure polymer having a metal content of 500 ppm or less. Innermost layer polymer (A) 80 to 100 parts by weight of alkyl acrylate having an alkyl group having 1 to 8 carbon atoms and / or alkyl methacrylate having an alkyl group having 1 to 4 carbon atoms (A ₁ ) 0 to 20 parts by weight of Copolymerizable monomer having a double bond (A ₂ ) 0 to 10 parts by weight of polyfunctional monomer (A ₃ ) (A ₁ ) to (A ₃ ). .1 to
Polymer present in the core obtained from the composition of 5 parts by weight of graft-linking agent (A ₄ ) Crosslinked elastic layer polymer (B) 80 to 100 parts by weight Alkyl acrylate having an alkyl group having 1 to 8 carbon atoms (B ₁₎ a monomer having a copolymerizable double bond 0-20 parts by weight (B ₂₎ a polyfunctional monomer of 0 parts by weight _{(B 3) (B 1)} ~ (B 3 ) For 100 parts by weight of the total amount
A polymer existing outside the innermost layer polymer (A), obtained from the composition of 5 parts by weight of the graft crosslinking agent (B ₄ ). Outermost layer polymer (C) 51 to 100 parts by weight having 1 to 4 carbon atoms Alkyl methacrylate (C ₁ ) 0.1 to 40 parts by weight of hydroxyalkyl (meth) acrylate (C ₂ ) having an alkyl group having 1 to 8 carbon atoms 0 to 49 parts by weight of a monomer having a copolymerizable double bond obtained from the composition of the mer (C _3), a polymer intermediate layer polymer present on the outer surface (D) 10 to 90 parts by weight of alkyl acrylate having an alkyl group having 1 to 8 carbon atoms (D ₁₎ 90 to 10 parts by weight of an alkyl methacrylate having an alkyl group having 1 to 4 carbon atoms (D ₂ ) 0 to 20 parts by weight of a monomer having a copolymerizable double bond (D ₃ ) 0 to 10 parts by weight of a polyfunctional monomer Monomer (D ₄ ) (D ₁ ) to (D ₄ ) For 100 parts by weight of the total amount
It is obtained from the composition of ₅ parts by weight of the graft crosslinking agent (D ₅ ), is present between the crosslinked elastic layer polymer (B) and the outermost layer polymer (C), and the amount of the alkyl acrylate (D ₁ ) is the crosslinked elasticity. Polymer adjusted to decrease monotonously from layer polymer (B) to outermost layer polymer (C)