JPS624742A - Covering film for highly bright reflective material - Google Patents

Abstract

PURPOSE:To provide the titled film having excellent transparency, weather resistance, tensile strength and tear strength, by blending a thermoplastic polymer with a multi-layer structural polymer. CONSTITUTION:A thermoplastic polymer (A) composed of a 1-4C alkyl methacrylate and other ethylenically unsaturated monomer copolymerizable there with is blended with a multi-layer structural polymer (B) composed of the innermost polymer (B1) having a glass transition point (Tg) of 10 deg.C or above, consisting of a 4C or lower alkyl methacrylate (a). other monomer (b) contg. a copolymerizable double bond, a polyfunctional monomer (c) and a grafting crosslinking gent (d), a central polymer layer (B2) having a Tg of 0 deg.C or below, consisting of components (b)-(d) and an 8C or lower alkyl acrylate (e), wherein the outermost polymer layer (B3) has a Tg of 50 deg.C or above, consisting of components (a) and (b) and an intermediate layer (B4) consisting of component (a) and components (c)-(e). The resulting thermoplastic resin compsn. having a gel content of from 10wt% to less than 50wt% is molded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a surface protection film used in a retroactive high-brightness reflective material that has improved weather resistance and processability.

[Prior Art] A retroreflective sheet is well known, in which spherical glass beads are embedded in a transparent resin layer with good weather resistance, and an aluminum vapor-deposited layer with high reflection efficiency is provided on the surface. As a further improvement on this, a spherical glass bead layer exists between the base sheet and the covering film, with some of the glass beads being exposed, and an air layer between the base sheet and the covering film. U.S. Patent No. 4190.1 discloses a high-brightness reflective material in which a base film and a covering film are partially bonded in a cellular manner.
No. 78 and 4.025°159.

The performance required of the coating film used for this high-brightness reflective material is excellent transparency and weather resistance. This is because it is used outdoors as a road sign. For this purpose, a film made of polymethyl methacrylate, a polycarbonate film, a polyethylene terephthalate film, etc. can be used as the covering film.

Among these, films made of polymethyl methacrylate are often used due to their excellent transparency and weather resistance.

[Problems to be Solved by the Invention] However, the high-brightness reflective material has a base sheet layer and a covering film of 1 to 2 cP! Since each I is connected in a cell shape and an air layer is provided, if a crack occurs on the covering film, it is desirable that the crack end only within one cell. For this purpose, a strong film that is resistant to cracking is required.

Tsu'! Relatively strong tensile strength (350 kg at 20°C)
There is a need for a film material with high tear strength (150 f or more) and high tear strength (150 f or more).

Furthermore, since high-brightness reflective materials are often used outdoors, the coating film is required to have durability at low temperatures (film elongation of 5% or more at C° C.).

However, coating films made of polymethyl methacrylate lack durability against temperature changes, and the elongation at break of the film is too small, making it difficult to manufacture films, especially films for high-brightness reflective materials. . Furthermore, polycarbonate films, polyethylene terephthalate films, etc. do not have good weather resistance, so they are not suitable for practical use.

Therefore, various methods of improving workability and durability by adding a rubber component to polymethyl methacrylate resin have been investigated, and the use of a multistage polymer in which a resin component is graft-polymerized onto an elastic body was proposed in 1983. -1694, JP-A-57-1
40161, JP-A-52-33991, JP-A-55-2
7576, etc., but when a film using the rubber-containing multistage polymer obtained by the invention alone is used as a coating film for a high-brightness reflective material, the yield strength of the film is relatively small and the elongation at break is low. Due to its large size, the coating film easily cracks, making it unsuitable.

Therefore, in order to add elasticity to the high-brightness reflective material film and optimize its durability and film strength against temperature changes,
As a result of studying the method of blending a multistage polymer obtained by graft polymerizing a resin component onto a rubber elastic body with a resin component, paying special attention to the transparency of the film, we found that a blend of thermoplastic polymers as described below could be used. It has been found that if used, a film for high-brightness reflective materials with excellent weather resistance and processability can be obtained.

[Means for Solving the Invention] The present invention provides at least one alkyl methacrylate having a weight ratio of 50 to 100 having an alkyl group having 1 to 4 carbon atoms and another monoethylenically unsaturated monomer copolymerizable therewith. Building 0
Thermoplastic polymer [
1] 20 to 80 parts by weight (hereinafter abbreviated as "parts") and 180 to 20 parts of the following multilayer structure polymer [I], and a thermoplastic having a gel content of 10% by weight or more and less than 50% by weight. This relates to a high-brightness reflective material coating film composed of a resin composition, and the multilayer structure polymer [I] 1 contains (4) an alkyl group having 4 or less carbon atoms? 51 to 100 parts of an alkyl methacrylate having a copolymerizable double bond, 0 to 49 parts of another monomer having a copolymerizable double bond, 0 to 10 parts of a polyfunctional monomer, and 5 parts of a grafting agent [I]. An innermost layer polymer which has a glass transition temperature (hereinafter abbreviated as Tg) obtained by polymerization of at least 10°C or higher, and which accounts for 2 to 35% by weight in the multilayer structure polymer [I] 1, ( E) 80 to 100 parts of an alkyl acrylate having an alkyl group having 8 or less carbon atoms, 0 to 20 parts of another monomer having a copolymerizable double bond, 0 to 10 parts of a polyfunctional monomer, and a graft. A central layer polymer having a TE obtained by polymerizing 1 to 5 parts of a cross-agent α and having a TE of 0° C. or less and an amount of 5 to 60 parts by weight in the polymer [I] 1, and (C) carbon. The Tg obtained by polymerizing 51 to 100 parts of an alkyl methacrylate having an alkyl group of number 4 or less and 0 to 49 parts of another monomer having a copolymerizable double bond is 50°C or higher, and the polymer [n] Outermost layer polymer having an amount of 20 to 80% by weight 17, as the basic structural unit, between layer (4) and layer (B) or between layer (4) and layer (C) As an intermediate layer, an alkyl methacrylate having an alkyl group having 4 or less carbon atoms 10 to 90
90 to 10 parts of an alkyl methacrylate having an alkyl group having 8 or less carbon atoms, 0 to 10 parts of a polyfunctional monomer, and 0.1 to 5 parts of a grafting agent. It is a multilayer structure polymer having zero or one or more layers (the intermediate layer may be omitted).

The purpose of the present invention is to maintain the excellent transparency and weather resistance that are characteristic of acrylic resins, while maintaining durability against temperature changes, by using a specific acrylic polymer for coating films of high-intensity reflective materials. The aim is to provide a film that is expensive and has good processability. In order to maintain the strong tensile strength inherent to acrylic resin, the amount of rubber component added must be limited. The rubber component can be measured as gel content, but if this amount exceeds 50% of the molded film, the tensile strength and tear strength of the molded film will decrease, making it unsuitable as a coating film for high-brightness reflective materials.

If the amount of rubber component added is less than 10% in terms of gel content, the elongation at low temperatures will decrease, making it unsuitable as a coating film for high-brightness reflective materials that are often used outdoors. As described above, the amount of the rubber component added, which is indicated by the gel content, should be strictly controlled. As a method of adjusting the amount of the rubber component added, a thermoplastic composition is formed by blending the resin of the polymer [I] whose main component is alkyl methacrylate and the multilayer structure polymers C and I []. If a high-brightness reflective material film is made only from the multilayer structure polymer [I], it will be difficult to balance fluidity and film strength during film molding, and a good coating film will not be obtained.

Therefore, two types of polymers must be blended. Here, the blend ratio of the polymer [I] and the multilayer structure polymer [II] should be adjusted so that the gel content of the blend composition is 10% by weight or more and less than 50% by weight, and the gel content of the polymer [1]
] is required to be 20 parts or more and 80 parts or less, and multilayer structure polymer Ell] is required to be 80 parts or less and 20 parts or more. If the amount of polymer [I] is less than 20 parts, the gel content will be 50% or more and the strength of the film molded product will be weakened, which is unsuitable. Furthermore, if 80 parts or more of the polymer is used, the gel content of the film molded product will be less than 10 parts by weight, which is inappropriate.

In the present invention, the thermoplastic polymer [l] has 1 to 1 carbon atoms.
It is a polymer obtained by polymerizing a monomer containing at least 50% by weight of alkyl methacrylate having an alkyl group of No. 4, and may be appropriately selected depending on the type of multilayer structure polymer so as to satisfy the above characteristics.

In this way, physical properties suitable as a coating film for high-intensity reflective materials can only be obtained by blending the multilayer structure polymer [■] with the alkyl methacrylate polymer El. Eft] will be explained in detail.

Multilayer structure polymer [I]] contains 51 to 10 parts of alkyl methacrylate having 4 or less carbon atoms, 0 to 49 parts of other monomers having copolymerizable double bonds, and 0 to 10 parts of polyfunctional monomers. and 0.1 to 5 parts of the grafting agent, Tg is 10°C or higher, and the amount in the polymer [I[] is 2 to 5 parts.
35 parts by weight of the innermost layer polymer (4), 80 to 100 parts of alkyl acrylate having 8 or less carbon atoms, 0 to 20 parts of other monomers having copolymerizable double bonds, and polyfunctional monomers. A central layer polymer comprising 0 to 10 parts of polymer, and 0.1 to 5 parts of a grafting agent, having a υ, Tg of 0°C or less, and an amount of 5 to 60 parts by weight in the polymer [I]] (B), 51 to 100 parts of an alkyl methacrylate having 4 or less carbon atoms, and 0 to 49 parts of another monomer having a copolymerizable double bond, and has a Tg of 50°C or more, and is a polymer. El
l] The outermost layer polymer (C) which accounts for 20 to 80 parts by weight in the basic structural unit, and further contains 10 to 90 parts of alkyl methacrylate having 4 or less carbon atoms, and alkyl acrylate having 8 or less carbon atoms. ) 90 to 10 parts, 0 to 100% polyfunctional monomer
10 parts, and 1 to 5 parts of the grafting agent CL.
Or, one or more intermediate layers include the central polymer (B) and the innermost layer (
A) or the multilayer structure polymer [n] existing between the outermost layer (C).

As the alkyl methacrylate having 4 or less carbon atoms used in the innermost layer (A), at least one of butyl methacrylate, propyl methacrylate, ethyl methacrylate, and methyl methacrylate is used. Gives an excellent composition.

As the monomer having a copolymerizable double bond, acrylic acid derivatives such as lower alkyl acrylate, lower alkoxy acrylate, cyanethyl acrylate, acrylamide, acrylic acid, and methacrylic acid are preferred, as well as styrene and alkyl-substituted styrene. , acrylonitrile, methacrylonitrile, and other alkyl methacrylates.

As the grafting agent, α1 to 5 parts of copolymerizable α, β unsaturated monocarboxylic acid or dicarboxylic acid allyl, metaallyl, crotyl ester, triallyl isocyanurate, triallyl cyanurate are used.

Allyl esters include acrylic acid, methacrylic acid,
Allyl esters such as maleic acid, fumaric acid, and itaconic acid, and allyl methacrylate in particular has excellent effects.

A polyfunctional monomer has a double bond conjugated with a carboxyl group, etc., and generally reacts much faster to form a chemical bond than a non-conjugated allyl group, metaallyl group, or crotyl group. On the other hand, since the reaction rate of allyl, meta-allyl, and crotyl groups is slow, the Kana 9 part remains even after the polymerization reaction of the layer is completed, and works effectively during the formation reaction of the next layer, forming a tight bond between the two layers. It works effectively.

ftfl[L of the graft cross-agent used is used in the range of 1 to 5 parts, preferably α5 to 2 parts. If it is less than 0.1 part, the effective amount of graft bonding is too small, so even if many intermediate layers are arranged, layer destruction will easily occur during melt-kneading during molding, and the desired transparency / stress whitening resistance will not be achieved. An excessive amount exceeding 0 or 5 parts, which does not result in a film with good properties, is undesirable because it particularly reduces the elasticity of the film and impairs its mechanical properties, including impact strength.

As a copolymerizable polyfunctional monomer, ethylene! +)-1
-dimethacrylate, 1,3-phthylene gelicol dimethacrylate, 1,4-butylene glycol dimethacrylate, propylene glycol dimethacrylate, etc. are preferred, and divinylbenzene, alkylene glycol diacrylate, etc. can also be used. These monomers effectively work to crosslink the layer itself in which they are included, and do not work at all on bonding between layers with other layers.

Component (A) accounts for 2 to 35% by weight, preferably 3 to 10% by weight in the polymer [1]. The central rubber layer (B) component is a polymer [80 to 100 parts of an alkyl acrylate having an alkyl group of 8 or less carbon atoms, which occupies 5 to 60 double bonds in the polymer, and other components having a copolymerizable double bond. It consists of 0 to 20 parts of a monomer and 0.1 to 10 parts of a polyfunctional monomer, and the Tg measured for the (B) component polymer alone is 0°C or less, preferably,
It is necessary that the temperature is -30°C or lower.

Examples of the alkyl acrylate having 8 or less carbon atoms include methyl acrylate, ethyl acrylate, butyl acrylate, propyl acrylate, and 2-ethylhexyl acrylate.

The lower the Tg of these homopolymers, the more advantageous they are.

Regarding the monomer having a copolymerizable double bond, the graft cross-agent, and the polyfunctional monomer, the same ones as those described in (A) a are used.

The outermost layer (C) consists of 51 to 100 parts of an alkyl methacrylate having an alkyl group having 4 or less carbon atoms, and 0 to 49 parts of another monomer having a copolymerizable double bond.
) The Tg of the layer itself is required to be at least 50°C or higher. In the polymerization of layer (C), it is preferable to adjust the degree of polymerization using a chain transfer agent, etc., and the viscosity average molecular weight is 5.
It is preferably between 0.000 and 1,000.000.

The alkyl methacrylate having 4 or less carbon atoms and the monomer having a copolymerizable double bond used in layer (C) are the same as those in layer (g). The layer (C) occupies 20 to 80% by weight in the polymer [I]. If the amount is less than 2 parts, a stable polymer cannot be obtained from the viewpoint of production such as polymerization and coagulation. 8
If it exceeds 0%, the rubber content will be too small, and the impact strength of the blend will be significantly reduced.

The intermediate layer is made of alkyl methacrylate having 4 or less carbon atoms from 10 to
90 parts, alkyl acrylate having 8 or less carbon atoms 90-1
0 parts, 0 to 10 parts of polyfunctional monomer, grafting agent [I
]～5 parts, respectively (A), (B), (
Monomers similar to those used in layer C) are used.

In the multilayer structure polymer of the present invention, each layer is efficiently grafted together by a grafting agent, and such a multilayer structure is resistant to stress even though a considerable amount of rubber components are present in block form. No whitening occurs when applied, and it has excellent transparency.

The characteristic of the present invention is that the multilayer structure polymer [II] blended in this way is transparent and has no stress whitening property. By blending it with a resin such as Polymer C1], thermoplastic polymers having various properties can be obtained.

Multilayer Structure Polymer C1l] h It can be easily obtained by a sequential multistage polymerization method using ordinary emulsion polymerization. That is, the aforementioned component (4) is first subjected to emulsion polymerization, and after the polymerization, the next intermediate layer is polymerized in the presence of component (, k).

In this case, it is important not to add an emulsifier, and it is necessary to take measures to prevent the formation of new polymer particles during polymerization. Continuing in the same manner, component (B) is polymerized in the presence of the above polymer, and then the intermediate layer and component (C) are polymerized to complete the sequential emulsion polymerization. There are no particular restrictions on the emulsifier, catalyst, coagulant, etc. to be used, but since this is an ester polymerization, it is preferable to perform the polymerization at an acidic pH.

Further, when producing the rubber-containing polymer of the present invention, there is no particular restriction on the emulsion particle size of the final polymer, but it is about 800 to 2000^, preferably 1000 to 2000^.
A range of 1600X provides the most balanced structure.

Furthermore, in the present invention, a synthesis method by suspension polymerization is also possible. In this case, the best physical properties are obtained by carrying out suspension polymerization of only the final stage of the multilayer polymer and emulsion polymerization for the rest.

In addition to the above, if a so-called multilayer polymer can be synthesized stably, there are no particular restrictions on the polymerization method.

All the usual blending methods can be used to blend the multilayer structure polymer [I] 1 into the polymer CD,
Antioxidants, ultraviolet absorbers, fillers, pigments, etc. are added as necessary.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to Examples.

Abbreviations used in the examples are as follows.

Methyl methacrylate) MMA butyl acrylate BuA butyl methacrylate
BMA2ethylhexyl acrylate 2EHA
1.3 Butylene dimethacrylate BD allyl methacrylate AMA styrene
St methyl acrylate MA ethyl methacrylate) EMA cumene hydroperoxide CHPn-octyl mercaptan n-08
Method for measuring H gel content: A predetermined amount of thermoplastic polymer was sampled according to rlS K-6388, and methyl ethyl ketone (hereinafter referred to as M
(abbreviated as EK) and swelled, then pulled out.
After wiping off the adhered MEK, measure its weight, then dry it in a vacuum converter to remove the MEK, read the absolute dry weight that has reached a constant weight, and calculate the gel content using the following formula.

Further, the Tg of various polymers used in the text description is calculated using the commonly known FOX formula from the Tg values of each component described in the Polymer Handbook, for example.

Further, the total light transmittance and tear strength of the films in Examples were determined by the following methods.

Total light transmittance: Measured using an integrating sphere haze meter in accordance with ASTM D 1003-61.

Tear strength: Measured by Elmendorf method with incision 2IIIB in accordance with J Engineering SF-8116.

Example 1 (1) Production of multilayer structure polymer [...] 250 parts of ion-exchanged water, 5 parts of sulfosuccinic acid ester sodium salt, and 85 parts of sodium formaldehyde sulfoxylate Q were placed in a reaction vessel equipped with a cooler. After stirring under a nitrogen stream, 7 parts of MMA, 5 parts of BuA, (LO
I prepared 5 parts of AMA. CHP was dissolved in the MMA in an amount of [I] by weight relative to the MMA. All monomers added in subsequent steps also contained 0.1% CHP by weight of each monomer, unless otherwise specified. The temperature of the reaction vessel was raised to 75°C while stirring at a rotational speed of 20 rpm under a nitrogen stream, and the polymerization of layer (A) was completed after stirring for 30 minutes. Next, BuA 2
5 parts, MMA 4.5 parts, AMA (125 parts, BD
Q. Add 5 parts of the mixture over 30 minutes and add 4 parts of the mixture over a period of 30 minutes.
When held for 0 minutes, polymerization of the rubber layer (B) was completed. Further, an outermost layer (C) consisting of 54 parts of MMA, 6 parts of BuA, and 16 parts of n-08Hα was added and polymerized for 60 minutes.
After the addition is complete, maintain the temperature for 50 minutes to remove the outermost layer (
Multilayer structure polymer [I] 1 consisting of 5 layers by polymerizing C)
It was created. This polymer corresponds to the multilayer polymer (Shu) in Table 1. When the sample sample after the polymerization of each layer was observed using an electron microscope, it was found that new particles were generated during the polymerization of layers (B) and (C). It was confirmed that complete seed polymerization had taken place.The resulting emulsion was coagulated, coagulated, and solidified using aluminum chloride, filtered, washed with water, and dried to obtain a dry powder. .

Using exactly the same polymerization method, multilayer structure polymers (B), ((ri), (D), (kuri) as shown in Table 1 were synthesized.

(2) Production of blended resin composition 50 parts of the multilayer structure polymer (4) was mixed with MMA/Mum copolymer (MMA/MA = 99/1 weight ratio, η8./
C=0.60, (c=n, 1ot/dt) ) (
It was blended with 50 parts of Polymer 1) (7) using a Henschel mixer.

The above mixture was shaped into pellets using a vented extruder (screw, L+/D=24). (Resin temperature 2
(50°C) The obtained pellet was dried at 80°C day and night, and then molded into a 0.1 m thick film using a T-die. The results were as shown in the Example 1 column of Table 2. The sheet moldability of the blended polymer in Example 1 was extremely good, and the film had high transparency, high impact strength, and excellent weather resistance.

Similarly, multilayer structure polymers (B), (C), (D)
, (E).

Films of Examples 2 to 5 were produced by blending 50 parts of each with the above polymer (1). All of these films had excellent transparency, weather resistance, and impact resistance.

The gel content of the blend composition and the physical properties of the obtained film were measured, and the results shown in Table 2 were obtained.

The examples all show high values for yield strength, 0°C elongation, and tear strength, but in the case of the methyl methacrylate homopolymer shown in Comparative Example 1, the film elongation at 0°C is low, Lack of durability at low temperatures. Further, in the case of using only the multilayer structure polymer shown in Comparative Example 2, the film has a low yield strength and a low tear strength, and is therefore unsuitable as a high-brightness reflective material film.

Example 2 Using the multilayer polymers (A) and (E) synthesized in Example 1, an MMA/MA copolymer (MMA/MA
=94/6η8p/c=α55 dt/f) at various ratios to obtain resin compositions. The physical properties of the film obtained from this composition and the durability of the high-brightness reflective material when used as a high-brightness reflective material were measured, and the results shown in Table 5 were obtained.

If the multilayer structure polymer (A) has a weight coefficient of less than 20, the elongation at 0° C. is insufficient and the durability at low temperatures is insufficient. On the other hand, if it exceeds 80% by weight, the tear strength decreases, making it impossible to provide the strength required as a coating film for a high-brightness reflective material.

Since the multilayer polymer (K) has undergone refractive index correction, it has extremely excellent transparency in any region and can form a coating film with excellent transparency and weather resistance.

Example 3 A multilayer structure polymer (1') was synthesized in the same manner as the multilayer structure polymer (C) shown in Example 1, using DMA instead of MMA. Also, instead of MMA, IICM
A multilayer structure polymer (G) was synthesized using A.

Similarly, a multilayer structure polymer (8) was synthesized using 2EHA in place of 'B BuA by the same method as in (C).

50 parts by weight each of these multilayer structure polymers (F), (G), (H) and MMA/'MA copolymer (MMA/M
A = 99/1) and 50 parts by weight to obtain a resin composition (Examples 11, 12.13).

α1 films were prepared from these compositions and their film strengths were measured, and the results shown in Table 4 were obtained, indicating that all of them can be used as coating films for high-brightness reflective materials.

Table 4 [Effects of the Invention] As detailed above, the film obtained by the present invention has excellent transparency, strong tensile strength, high tear strength, and excellent durability at low temperatures. By encapsulating the surface of the high-brightness reflective material, a high-brightness reflective material with high performance can be provided.

Claims (1)

[Scope of Claims] Consisting of 20 to 80 parts by weight of the thermoplastic polymer [I] shown below and 80 to 20 parts by weight of the multilayer structure polymer [II], and having a gel content of 10% by weight or more and 50 parts by weight % of a thermoplastic resin composition. Thermoplastic polymer [I] 50 to 100% by weight of alkyl methacrylate having an alkyl group having 1 to 4 carbon atoms and at least one other monoethylenically unsaturated monomer copolymerizable with the same.
Polymer multilayer structure polymer [II] consisting of 0 to 50% by weight of species (A) 51 to 100 parts by weight of alkyl methacrylate having an alkyl group having 4 or less carbon atoms, and other monomers having a copolymerizable double bond 0 to 49 parts by weight of polyfunctional monomer, 0 to 10 parts by weight of polyfunctional monomer, and 0.1 to 5 parts by weight of grafting agent, which has a glass transition temperature of at least 10° C. and is multilayered. An innermost layer polymer that accounts for 2 to 35% by weight in the structural polymer [II], (B) 80 to 100 parts by weight of an alkyl acrylate having an alkyl group having 8 or less carbon atoms, and a copolymerizable double bond. 0 to 20 parts by weight of other monomers, 0 to 10 parts by weight of a polyfunctional monomer, and 0.1 to 5 parts by weight of a grafting agent, the glass transition temperature of which is 0°C or lower. and a central layer polymer which accounts for 5 to 60% by weight in the multilayer structure polymer [II], and (C) 51 to 100 parts by weight of an alkyl methacrylate having an alkyl group having 4 or less carbon atoms. A monomer obtained by polymerizing 0 to 49 parts by weight of another monomer having a polymerizable double bond, which has a glass transition temperature of 50°C or higher, and which accounts for 20 to 49 parts by weight in the multilayer structure polymer [II]. 80% by weight
The outermost layer polymer is a basic unit, and layer (A) and layer (B) or layer (B)
and layer (C) as an intermediate layer, 10 to 90 parts by weight of an alkyl methacrylate having an alkyl group having 4 or less carbon atoms, 90 to 10 parts by weight of an alkyl methacrylate having an alkyl group having 8 or less carbon atoms, polyfunctionality. A multilayer structure polymer having 0 or one or more layers of a copolymer obtained by polymerizing 0 to 10 parts by weight of a monomer and 0.1 to 5 parts by weight of a grafting agent.