JPH06104729B2 - Adhesive sheet for solar cell module - Google Patents

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an adhesive sheet material used for protecting a solar cell module made of a semiconductor such as amorphous silicon from external impact and moisture permeation.

[0002]

2. Description of the Related Art Solar cells utilizing inexhaustible sunlight are
It is rapidly becoming popular in recent years. A solar cell consists of an element that converts light energy into electrical energy.Since this element, for example, a silicon semiconductor, deteriorates in its function when exposed directly to the outside air, the outer surface of the cell is covered with glass to protect it from the outside air. A polyvinyl fluoride (PVF) or polyvinylidene fluoride (PVDF) film is laid on the bottom surface to prevent moisture permeation, and an ethylene-vinyl acetate copolymer (EV
A) is used as a hermetic filler. The most required performance of the adhesive sheet for a solar cell module is that it has good sunlight receiving properties, that is, excellent transparency, in order to store energy in the module more efficiently.

Conventionally, polyvinyl butyral (PVB) has been used as an adhesive sheet material, but since an anti-adhesive agent (specifically, sodium hydrogencarbonate) is applied to the surface thereof, Wash away,
It has the drawback that it must be dried and that the material price is higher than that of a general-purpose thermoplastic resin. Among general-purpose thermoplastic resins, ethylene-vinyl acetate copolymer is relatively inexpensive and has excellent transparency.
Although it can be expected to be used as an adhesive sheet material, its performance, especially heat resistance and durability, deteriorates when it is used for a long time in a natural environment. There is a drawback that the adhesiveness to vinyl or vinylidene film is not sufficient.

For the improvement, a technique of adding a coupling agent and an organic peroxide to an ethylene-vinyl acetate copolymer to improve adhesiveness, heat resistance and durability (Japanese Patent Publication No. 62-14111). ), A technique for improving adhesiveness, heat resistance and durability by adding an organic peroxide to an ethylene-vinyl acetate copolymer graft-modified with an organic silane compound (Japanese Patent Publication No. 62-9232). However, as far as the present inventors know, they are not always satisfactory. That is,
The former has a drawback in that after the adhesive sheet is formed, the coupling agent is volatilized from the surface of the sheet, and the adhesiveness is not stable at the time of adhering to a glass, an element, a polyvinyl fluoride film or the like which constitutes a solar cell module. The adhesive sheet formed by the latter method has a stable adhesive property when adhered to glass, an element, a polyvinyl fluoride or vinylidene film constituting a solar cell module, but has a crosslinking reaction when the adhesive sheet is formed. However, there is a drawback in that it is impossible to carry out molding, and so-called molding stability is not preferable.

The cause of the drawbacks seen in this latter technique is that
Perhaps it is difficult to completely react the organosilane compound when graft-modifying the ethylene-vinyl acetate copolymer with the organosilane compound, and several% to several tens% of the unreacted organosilane is present in the modified copolymer. It is considered that this is because the compound remains and the unreacted organic silane compound reacts with the organic peroxide added for the purpose of obtaining a crosslinked sheet during the formation of the adhesive sheet to induce crosslinking.

[Outline of Invention]

DISCLOSURE OF THE INVENTION The present invention aims to provide an adhesive sheet for a solar cell module, which is excellent in transparency, adhesiveness, crosslinkability and stability during sheet forming, and uses a specific material. By doing so, the problem is solved.

[0007]

[Means for Solving the Problems]

<Summary> The adhesive sheet for a solar cell module according to the present invention is formed by molding a composition containing 95 to 99.9 wt% of the following component (A) and 0.1 to 5 wt% of the component (B). It is characterized by being a thing.

(A) Ethylene 84.9 to 55% by weight,
An ethylenically unsaturated silane compound represented by the general formula RSiR ' _n Y _3-n (wherein R is an ethylenically unsaturated hydrocarbyl or hydrocarbyloxy group or a (meth) acryloyloxyalkyl group, R ′ Is an aliphatic saturated or aromatic hydrocarbyl or hydrocarbyloxy group, Y is an aliphatic saturated or aromatic hydrocarbyl or hydrocarbyloxy group, or an aliphatic acyloxy group, and n is 0 or 1 or 2. Represent)
0.1 to 5% by weight, and an ethylenically unsaturated carboxylic acid ester 15 to 40% by weight.

(B) 10-hour half-life temperature is 90 to 170
Organic peroxide that is ° C.

<Effect> The above object is achieved by improving the transparency, adhesiveness, crosslinkability during the production of an adhesive sheet for a solar cell module, and stability during sheet formation.

[Detailed Description of the Invention] <Material for Adhesive Sheet> The material constituting the sheet of the present invention includes a copolymer and an organic peroxide containing ethylene, an ethylenically unsaturated silane compound and an unsaturated carboxylic acid ester. A formulation comprising an oxide.

(1) Copolymer (i) Outline The copolymer (A) used in the present invention comprises ethylene, an ethylenically unsaturated silane compound and an ethylenically unsaturated carboxylic acid ester. . Here, "comprising" means, in addition to the three types of monomers listed above,
Unless the object of the present invention is impaired, it is meant to include a small amount (for example, up to about 10% by weight, preferably up to 5% by weight, based on the essential monomer) of the copolymerizable monomer. . Such monomers include, for example, vinyl esters such as vinyl acetate and vinyl propionate, and ethylenically unsaturated carboxylic acids such as acrylic acid and methacrylic acid.

(Ii) Ethylenically Unsaturated Silane Compound As a component which introduces characteristics derived from silicon atoms into this copolymer to impart adhesiveness or affinity to, for example, a silicon semiconductor element and / or coated glass, an ethylenic unsaturated silane compound is used. The unsaturated silane compound is one of the essential components in the copolymer (A), but the copolymer according to the present invention contains the ethylenically unsaturated silane compound in an amount of 0.1 to 5% by weight, preferably 0.2. .About.3% by weight. If the silane compound content is less than 0.1% by weight, the adhesiveness will be poor, and if it exceeds 5% by weight, crosslinking tends to occur during sheet molding,
Molding stability deteriorates.

The ethylenically unsaturated silane compound used as a constituent of the copolymer of the component (A) of the present invention has the general formula RSiR ' _n Y _3-n (where R is ethylenically unsaturated hydrocarbyl. Group or ethylenically unsaturated hydrocarbyloxy group or (meth) acryloyloxyalkyl group, R'is an aliphatic saturated or aromatic hydrocarbyl group, or an aliphatic saturated or aromatic hydrocarbyloxy group, Y is a fat Group saturated or aromatic hydrocarbyl group, aliphatic saturated or aromatic hydrocarbyloxy group, or aliphatic acyloxy group, and n represents 0 or 1 or 2).

The hydrocarbyl group of the ethylenically unsaturated hydrocarbyl group or hydrocarbyloxy group of R is an aliphatic group (including cycloaliphatic group), that is, an alkenyl group or a cycloalkenyl group. Are preferred, and particularly those having about 2 to 8 carbon atoms, especially lower alkenyl groups are suitable. “(Meth) acryloyl” when R is a (meth) acryloyloxyalkyl group means either an acryloyl or a methacryloyl group, and an alkyl bonded to this unsaturated acyl group via an oxygen atom. The group (if only this is taken out, an alkylene group) preferably has about 1 to 6 carbon atoms.

R'has about 1 to 5 carbon atoms, preferably 1
To about 3 or about 6 to 10 carbon atoms,
Aryl (including an alkaryl group) of about 6 to 7, preferably aliphatic ones are preferable.

Y is an aliphatic saturated or aromatic hydrocarbyloxy group, particularly about 1 to 5 carbon atoms, preferably 1
.About.3, especially aliphatic ones, or aliphatic acyloxy groups, preferably about 1 to 5 carbon atoms, especially 2 to
About 3 is suitable.

Specific examples of such unsaturated silane compounds include those in which R is vinyl, allyl, isopropenyl,
Butenyl, cyclohexenyl, γ- (meth) acryloyloxypropyl, R ′ is methyl, ethyl, propyl,
Decyl, phenyl, Y is methoxy, ethoxy, formyloxy, acetoxy, propionyloxy. Particularly preferred is CH ₂ = CHSi (OA).
₃ (wherein A is an aliphatic saturated hydrocarbyl group or an aliphatic saturated acyl group having 1 to 8 carbon atoms), preferably the hydrocarbyl or acyl group has about 1 to 3 carbon atoms Of these, specifically, vinyltrimethoxysilane, vinyltriethoxysilane, and vinyltriacetoxysilane.

(Iii) Ethylenically Unsaturated Carboxylic Acid Ester The unsaturated carboxylic acid ester used as the other component of the copolymer of the component (A) of the present invention is 15 to 40 in the copolymer of the present invention. % By weight, preferably 20-35% by weight,
Contained. When the ester content is less than 15% by weight,
Since the transparency of the sheet is inferior, the light transmittance is lowered, and when it exceeds 40% by weight, the stickiness of the sheet becomes large and blocking occurs.

The unsaturated carboxylic acid ester is typically an ester of an ethylenically unsaturated monovalent carboxylic acid with an aliphatic saturated monohydric alcohol, and the carboxylic acid is acrylic acid or methacrylic acid, and the alcohol is Is preferably one having about 1 to 10 carbon atoms, particularly about 1 to 4 carbon atoms.

Specific ethylenically unsaturated carboxylic acid esters include methyl acrylate, ethyl acrylate,
Acrylic acid esters or methacrylic acid esters such as butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate are preferably used.

(IV) Others The melt flow rate (MFR) of the copolymer of the present invention is
It is usually 0.1 to 500 g / 10 minutes, preferably 1 to 100 g / 10 minutes.

Such a copolymer may be prepared by mixing the predetermined monomers (including the above-mentioned fourth monomer when used) individually or in a mixture, temporarily or stepwise. It can be produced by subjecting it to polymerization conditions.
Due to the presence of polar monomers such as silane compounds or unsaturated carboxylic acid esters, high-pressure radical polymerization is more suitable for polymerization than using Ziegler type catalysts. Homopolymerization and copolymerization of ethylene by high-pressure radical polymerization are well known, and suitable methods can be adopted in the present invention. Radical polymerization is usually carried out using oxygen or peroxide catalysts.

(2) Organic peroxide The organic peroxide used as the component (B) in the present invention is
Any material may be used as long as it has a function of decomposing when the sheet of the present invention is laminated on the external protective material of the solar cell module to crosslink the copolymer of the present invention. The 10-hour half-life temperature is 90 to 170 ° C., preferably 100 to 160
It is assumed that an organic peroxide of ℃ is used.

Typical examples of such organic peroxides are as follows. (1) 1,1-bis (tertiary butylperoxy) 3,3,5
-Trimethylcyclohexane (10-hour half-life temperature (hereinafter the same): 90 ° C), (2) 1,1-bis (tertiary butylperoxy) cyclohexane (91 ° C), (3) Tertiary butylperoxymaleic acid (96 ° C), (4) Tertiary butylperoxylaurate (96 ° C), (5) Tertiary butylperoxy-3,5,5-trimethylhexanoate (97
℃),

(6) Cyclohexanone peroxide (9
7 ° C), (7) tert-butylperoxyallyl carbonate (97 ° C), (8) tert-butylperoxyisopropyl carbonate (98 ° C), (9) 2,5-dimethyl-2,5
-Di (benzoylperoxy) hexane (100 ° C),
(10) 2,2-bis (tertiary butylperoxy) octane (101 ° C),

(11) Tertiary butyl peroxyacetate (1
02 ℃), (12) 2,2-bis (tertiary butylperoxy)
Butane (103 ° C), (13) tertiary butyl peroxybenzoate (104 ° C), (14) n-butyl-4,4-bis (tertiary butylperoxy) valerate (105 ° C), (1
5) Di-tert-butyl peroxyisophthalate (107
℃),

(16) Methyl ethyl ketone peroxide (109 ° C.), (17) dicumyl peroxide (117
℃), (18) 2,5-Dimethyl-2,5-di (tertiary butylperoxy) hexane (118 ℃), (19) α, α'-bis (tertiary butylperoxy-m-isopropyl) Benzene (119 ° C), (20) tert-butylcumyl peroxide (120 ° C),

(21) Diisopropylbenzene hydroperoxide (122 ° C.), (22) di-tert-butyl peroxide (124 ° C.), (23) p-menthane hydroperoxide (133 ° C.), (24) 2, 5-dimethyl-2,5
-Di (tertiary butylperoxy) hexyne-3 (135
° C), (25) 1,1,3,3-tetramethylbutyl hydroperoxide (153 ° C), (26) 2,5-dimethylhexane-2,5-dihydroperoxide (154
℃), (27) cumene hydroperoxide (158
℃), (28) Tertiary butyl hydroperoxide (167
℃) and so on.

The blending amount of these organic peroxides (B) is 0.1 to 100 parts by weight based on the total amount of 100 parts by weight of the copolymer (A).
5 parts by weight, preferably 0.3 to 3 parts by weight, that is, component (A) is 95 to 9 based on component (A) + component (B).
9.9% by weight and component (B) is 0.1 to 5% by weight. By satisfying this blending amount, a sheet having an appropriate degree of cross-linking can be obtained, and the transparency can be maintained and high adhesiveness can be maintained.

(3) Blend The blend used in the present invention is the above-mentioned ethylene / ethylenically unsaturated silane compound / ethylenically unsaturated carboxylic acid ester copolymer (component (A)) and organic oxide. It is basically composed of (component (B)), but a part of the copolymer is blended with a compatible or fusible thermoplastic polymer (C) within a range that does not impair the effects of the present invention. It doesn't matter. Specifically, 3 of the copolymer of the component (A)
Polymer (C) can be added in an amount up to 0% by weight. In other words, regarding the component (A) + the component (C), the contents of the unsaturated silane compound and the ethylenically unsaturated carboxylic acid ester should not be below the respective lower limits defined for the component (A).

Thermoplastic polymers suitable for blending are ethylene-based copolymers, such as ethylene-vinyl acetate copolymers and ethylene- (meth) acryl, because of their compatibility with the component (A). Copolymers with unsaturated carboxylic acid esters such as methyl acidate, ethyl (meth) acrylate and butyl (meth) acrylate, copolymers of ethylene and propylene, α-olefins such as butene-1, ethylene-acetic acid A terpolymer such as a vinyl-unsaturated carboxylic acid ester is preferably used.

The formulations of the present invention include various stabilizers, colorants,
If necessary, an anti-blocking agent, a lubricant, an anti-UV deterioration agent and the like can be added.

(4) Adhesive Sheet for Solar Cell Module To mold the composition of the present invention into a sheet, a method adopted for molding polyolefin materials such as ordinary polyethylene, ethylene-vinyl acetate copolymer, polypropylene and the like is used. Similar methods can be used. For example, using a T-die extruder, a temperature not higher than the decomposition temperature of the organic peroxide, eg, 9
A sheet having a thickness of about 0.1 to 1.0 mm can be obtained by molding at a temperature of 0 to 170 ° C.

The sheet thus obtained is used by being laminated on the external protective material of the solar cell module, such as glass or PVDF.

The solar cell is modularized in the following manner. A silicon semiconductor or selenium semiconductor wafer is used as a solar cell element, and these elements are sandwiched by two adhesive sheets. Then, for example, an upper transparent protective material such as glass and a back protective sheet such as PVF or PVDF sheet are superposed on both sides thereof, and in this state, they are degassed in vacuum and heat-bonded to form glass / adhesive sheet / sun. Battery element / Adhesive sheet / PVF or PV
Stick with DF composition. At this time, it is preferable to carry out heating until the organic peroxide contained in the adhesive sheet is completely decomposed, because this leads to improvement in heat resistance of the sheet. In this way, the solar cell element is completely protected by the two adhesive sheets, and the strongly adhered solar cell module is completed by heat-bonding the external protective materials and the adhesive sheet.

[0037]

EXAMPLES The following examples serve to explain the present invention more specifically.

Example 1 Using a stirred autoclave type continuous reactor, vinyltrimethoxysilane dissolved in ethylene and normal hexane, methyl acrylate, and tertiary butyl peroxyneodecanate dissolved in normal hexane as a catalyst. Is continuously supplied, and the polymerization pressure is 2000 kg / c.
Copolymerized at m ² and a polymerization temperature of 190 ° C. to give an ethylene / vinyltrimethoxysilane / methyl acrylate terpolymer (vinyltrimethoxysilane content 2% by weight, methyl acrylate content 27% by weight, melt flow rate 12 g /
10 minutes) was obtained. The terpolymer was subjected to methanol extraction, and the unreacted vinyltrimethoxysilane content was measured by gas chromatography to find that it was 0.01% by weight.

Next, a mixture of 100 parts by weight of this terpolymer and 2 parts by weight of dicumyl peroxide (10-hour half-life temperature of 117 ° C.) as an organic peroxide was mixed with a screw diameter of 65 mm and L / D26. , Die effective width 1000mm
T-die extruder at a temperature of 120 ° C. and a thickness of 0.6
It was formed into a sheet of mm. The sheet was molded for 5 hours, and the molding stability was good throughout.

Using the sheet thus obtained,
Glass / adhesive sheet / solar cell element / adhesive sheet / polyvinyl fluoride sheet (“Tedlar” film made by DuPont, USA) are laminated in this order and melt-bonded at a heating temperature of 120 ° C. with a vacuum laminator, then 150 ℃
Was heated for 10 minutes to decompose the organic peroxide, and at the same time when the copolymer sheet was crosslinked, an external protective material was adhered to form a module.

The performance of the solar cell module is 450 mμ
The light transmittance, the peel strength from the external protective material (sample width 10 mm, tensile speed 50 mm / min) and the degree of crosslinking (the amount of undissolved by xylene 10 hours boiling point extraction) were measured. The results are shown in Table 1.

Example 2 A mixture of 100 parts by weight of the same terpolymer as in Example 1 and 0.5 parts by weight of ditertiary butyl peroxide (10-hour half-life temperature 124 ° C.) as an organic peroxide was used. A 0.6 mm-thick sheet was formed in the same manner as in Example 1 except that the above was used. The sheet was molded for 5 hours, and the molding stability was good throughout.

A module was prepared in the same manner as in Example 1 and its performance was measured. The results are shown in Table 1.

Example 3 An ethylene / vinyltrimethoxysilane / methyl methacrylate terpolymer (vinyltrimethoxysilane content 0.5% by weight, methyl methacrylate content 30% by weight) was prepared by the same production method as in Example 1. , Melt flow rate 15g / 10
Min). This terpolymer was subjected to extraction with methanol, and the unreacted vinyltrimethoxysilane content was measured by gas chromatography to find that it was 0.005% by weight.

A sheet having a thickness of 0.6 mm was formed in the same manner as in Example 1 except that this terpolymer was used. The sheet was molded for 5 hours, and the molding stability was good throughout.

A module was prepared in the same manner as in Example 1 and its performance was measured. The results are shown in Table 1.

Example 4 By the same production method as in Example 1, an ethylene / vinyltrimethoxysilane / ethyl acrylate terpolymer (vinyltrimethoxysilane content 5% by weight, ethyl acrylate content 30% by weight, melt A flow rate of 25 g / 10 min) was obtained. This terpolymer was subjected to extraction with methanol, and the unreacted vinyltrimethoxysilane content was measured by gas chromatography and found to be 0.03% by weight.

A sheet having a thickness of 0.6 mm was formed in the same manner as in Example 1 except that this terpolymer was used. The sheet was molded for 5 hours, and the molding stability was good throughout.

A module was prepared in the same manner as in Example 1 and its performance was measured. The results are shown in Table 1.

Comparative Example 1 An ethylene / vinyltrimethoxysilane / vinyl acetate terpolymer (vinyltrimethoxysilane content 2% by weight, vinyl acetate content 27% by weight) was prepared by the same production method as in Example 1.
Polymerization was carried out in an attempt to obtain a melt flow rate of 12 g / 10 minutes), but a terpolymer which could be molded could not be obtained due to a crosslinking reaction in the polymerization stage.

Comparative Example 2 By the same production method as in Example 1, an ethylene / vinyltrimethoxysilane / acrylic acid terpolymer (vinyltrimethoxysilane content 2% by weight, acrylic acid content 27% by weight,
Polymerization was carried out to obtain a melt flow rate of 12 g / 10 min), but a crosslinking reaction occurred in the polymerization stage as in Comparative Example 1, and a moldable terpolymer could not be obtained.

Comparative Example 3 Ethylene / methyl acrylate copolymer (methyl acrylate content 27% by weight, melt flow rate 20 g / 10
Min) 100 parts by weight of vinyltrimethoxysilane 2.5 parts by weight and tertiary butylperoxy 2-
After adding 0.3 parts by weight of ethyl hexanoate and mixing with a Henschel mixer, this mixture was extruded with an L / D24 extruder set at a temperature of 160 ° C. for an average residence time of 2 minutes to graft silane. Copolymer pellets were obtained. When this copolymer was subjected to extraction with methanol and the unreacted vinyltrimethoxysilane content was measured by gas chromatography, it was 0.5% by weight. Also,
Undecomposed tertiary butyl peroxy-2-ethylhexanoate was extracted with methanol, and the content of the content was analyzed by gas chromatography. The result was 0.05% by weight or less.

100 parts by weight of the pellets were treated with an organic peroxide of dicumyl peroxide (10-hour half-life temperature 1
(17 ° C.) 2 parts by weight of the mixture were mixed with the same T-die extruder having a die effective width of 1000 mm as in Example 1 to obtain 120.
It was formed into a sheet having a thickness of 0.6 mm at a temperature of ° C. Thirty minutes after the start of sheet forming, the resin caused a cross-linking reaction at the die ears, making sheet forming difficult.

As a reference, a module was prepared in the same manner as in Example 1 using the sheet when the molding was good, and its performance was measured. The results are shown in Table 1.

Comparative Example 4 2.5 parts by weight of vinyltrimethoxysilane and dicumyl peroxide were added to 100 parts by weight of an ethylene / vinyl acetate copolymer (vinyl acetate content 28% by weight, melt flow rate 22 g / 10 minutes). After adding 0.5 parts by weight and mixing with a Henschel mixer, the mixture was heated to a temperature of 16
Average residence time 2 with L / D24 extruder set at 0 ° C
Extrusion in minutes gave pellets of silane-grafted copolymer.

The copolymer was subjected to extraction with methanol and the unreacted vinyltrimethoxysilane content was measured by gas chromatography to find that it was 0.6% by weight. In addition, undegraded tertiary butyl peroxy-2-
Ethyl hexanoate was extracted with methanol, and the content was analyzed by gas chromatography. As a result, it was 0.05% by weight or less.

A mixture of 100 parts by weight of the pellets and 2 parts by weight of dicumyl peroxide as an organic peroxide was prepared at a temperature of 120 ° C. using the same T-die extruder having a die width of 1000 mm as in Example 1. A sheet having a size of 0.6 mm was formed. Twenty-five minutes after the start of sheet formation, the resin caused a cross-linking reaction at the die ears, making sheet formation difficult.

As a reference, a module was prepared in the same manner as in Example 1 using the sheet when the molding was good, and its performance was measured. The results are shown in Table 1.

Table 1 _{Molding stability Light transmittance Peel strength (kg / cm} 2 _{) Crosslinking degree} (%) Glass PVF (%) Example 1 Good 87 5.4 5.0 85 Example 2 Good 87 5.2 5.2 4.7 78 Example 3 Good 90 3.8 3.5 83 Example 4 Good 91 8.3 7.9 85 Comparative Example 1 −−−−− Comparative Example 2 −−−−− Comparative Example 3 Bad 86 3.7 3.3 82 Comparative Example 4 Bad 88 4.0 4.0 83 PVF: Polyvinyl fluoride film

[0060]

EFFECTS OF THE INVENTION The solar cell module adhesive sheet of the present invention is superior in transparency, adhesiveness and cross-linking property to conventional ones, and is also excellent in stability during sheet formation and has practical performance. The further improvement is as described above in the section "Summary of the Invention".

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Claims (1)

[Claims] 1. A sheet is formed from a composition containing 95 to 99.9% by weight of the following component (A) and 0.1 to 5% by weight of the component (B). Adhesive sheet for solar cell module. (A) Ethylene 84.9 to 55% by weight, general formula RSi
An ethylenically unsaturated silane compound represented by R ′ _n Y _3-n (wherein R is an ethylenically unsaturated hydrocarbyl or hydrocarbyloxy group or a (meth) acryloyloxyalkyl group, and R ′ is An aliphatic saturated or aromatic hydrocarbyl or hydrocarbyloxy group, Y is an aliphatic saturated or aromatic hydrocarbyl or hydrocarbyloxy group, or an aliphatic acyloxy group, and n is 0, 1 or 2. ) 0.1
A copolymer comprising 5% by weight and 15 to 40% by weight of an ethylenically unsaturated carboxylic acid ester. (B) An organic peroxide having a 10-hour half-life temperature of 90 to 170 ° C.