JP3510646B2 - Adhesive sheet for solar cells - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an adhesive sheet for solar cells. More specifically, the present invention relates to an adhesive sheet for solar cells, which is excellent in yellowing resistance and is capable of obtaining a durable solar cell module.

[0002]

2. Description of the Related Art Solar cells, which are expected to be used as clean energy, have been studied to reduce power generation cost and use them for electric power, but there are still some problems to be solved. One of them is to improve the weather resistance of the solar cell module so that a stable output can be obtained even when it is used outdoors for a long period of time. That is, in the current solar cell module, the cross-linked sheet of the ethylene-vinyl acetate copolymer used for adhesion between the surface glass and the silicon power generation element is colored yellow with time to reduce the transmittance of sunlight. However, there is a problem that the power generation efficiency is reduced.

[0003]

SUMMARY OF THE INVENTION Therefore, the present inventors have investigated factors for yellowing, and have made earnest studies to find a prescription for preventing yellowing. The ethylene-vinyl acetate copolymer used for the conventional adhesive sheet contains a cross-linking agent, an ultraviolet absorber, an antioxidant, etc., but as a result of the study, the mechanism of yellowing has not been clarified yet, but a cross-linking agent is used. Found that he was deeply involved in yellowing. Conventionally, an organic peroxide is usually used as a crosslinking agent for such an adhesive sheet, and many are known (for example, Japanese Patent Publication No. 2-40709),
It has not been known that it has a decomposition temperature and a crosslinking ability that are convenient for the production of solar cells, and that it has excellent resistance to yellowing. As a result of investigations, the present inventors have found that by using a peroxide described below, yellowing resistance is improved, a decrease in light transmittance is small even in long-term use, and an adhesive sheet having desired properties can be obtained. .

[0004]

That is, the present invention relates to an adhesive sheet for a solar cell comprising an ethylene copolymer containing alkyl-3,3-di (tert-butylperoxy) butyrate. The present invention also relates to a solar cell module manufactured using such an adhesive sheet.

In general, a solar cell module is formed by connecting wafers of silicon semiconductor elements or selenium semiconductor elements, which have a function of generating an electric current when irradiated with light, in series or in parallel using an interconnector, and glass, polyacrylate, It is packaged by protecting it with an upper transparent protective material such as polycarbonate and a lower substrate protective material such as glass, stainless steel, aluminum, or plastic. An adhesive sheet is used between the semiconductor element and each of these protective materials. Are joined together. The present invention uses such an adhesive sheet an ethylene copolymer in which alkyl-3,3-di (tert-butylperoxy) butyrate is blended.

The ethylene copolymer has a light transmittance of about 80% or more, preferably about 90% or more, and an elastic modulus of about 1 to 30 MPa, preferably about 3 to 12.
The thing of MPa is used as a suitable copolymer. Specifically, for example, copolymers of ethylene and vinyl acetate, vinyl propionate and other vinyl esters, ethylene and ethyl acrylate, butyl acrylate, methyl methacrylate and other unsaturated fatty acid ester copolymers, ethylene And propylene, butene-1,4-methylpentene-1
And copolymers with α-olefin, such as ethylene-
A vinyl ester-unsaturated fatty acid terpolymer, an ethylene-unsaturated fatty acid ester-unsaturated fatty acid terpolymer, or a metal salt thereof is used.

Among these ethylene copolymers, the ethylene-vinyl acetate copolymer or the ethylene-unsaturated fatty acid ester copolymer is preferable, and the ethylene content in the copolymer is 60 to 80% by weight. , Especially 60-7
5% by weight is particularly preferable because it has a high light transmittance and is excellent in flexibility and extrusion moldability.

In the present invention, alkyl-3,3 is used in order to improve heat resistance or further improve adhesion by crosslinking such an ethylene copolymer.
Blend with di (tert-butylperoxy) butyrate. More specifically, methyl-3,3-di (tert
-Butylperoxy) butyrate, ethyl-3,3-di (tert-butylperoxy) butyrate, n-butyl-3,3-di (tert-butylperoxy) butyrate and the like. As shown in Examples and Comparative Examples below,
By using such a peroxide, the coloring tendency over time can be significantly reduced.

The peroxide may be blended in such an amount that the ethylene copolymer can be crosslinked to a desired degree. Generally, it is 0.1 to 5 parts by weight based on 100 parts by weight of the ethylene copolymer.
Particularly, it is 0.5 to 3 parts by weight.

In order to improve the weather resistance of the adhesive sheet, it is preferable to use one or more additives such as a light resistance stabilizer, an ultraviolet absorber and an antioxidant. Examples of such additives include hindered amine-based light stabilizers, hindered phenol-based and phosphite-based antioxidants, 2-hydroxy-4-methoxybenzophenone, 2,2-dihydroxy-4-methoxybenzophenone, 2 -Hydroxy-4-methoxy-2'-carboxybenzophenone,
Benzophenone-based compounds such as 2-hydroxy-4-n-octoxybenzophenone, 2- (2'-hydroxy-
3 ', 5'-di-tert-butylphenyl) benzotriazole, 2- (2'-hydroxy-5-methylphenyl) benzotriazole, 2- (2'-hydroxy-5-tertiary
Examples thereof include ultraviolet absorbers such as benzotriazoles such as octylphenyl) benzotriazole, salicylates such as phenylsalicylate, p-octylphenylsalicylate, and the like.

An adhesive aid may be added to the adhesive sheet for the purpose of increasing the adhesive strength with the upper protective material and the lower protective material. Examples of such an adhesion aid include coupling materials such as silane coupling and titanate coupling, and acid-modified resins.

The thickness of the adhesive sheet is not particularly limited, but is usually about 0.1 to 1 mm.

The solar cell module can be manufactured, for example, as follows. When the solar cell element is composed of a semiconductor wafer of silicon or selenium, these solar cell elements are sandwiched between at least two adhesive sheets, and if necessary, a protective material preliminarily treated on both sides thereof, that is, After the upper transparent protective material and the lower substrate protective material are superposed and deaerated by applying a vacuum, or simultaneously with this, heating and then pressurization are performed to adhere and bond them. At this time, the solar cell element may be previously laminated with at least two filler sheets made of an ethylene copolymer containing an organic peroxide, and then bonded to the upper transparent protective material and the lower substrate protective material. In addition, the lower substrate protective material, the filler sheet, the solar cell element, the adhesive sheet, and the upper transparent protective material, which have been appropriately treated with a primer, may be sequentially laminated or arranged and bonded. It is desirable that the heating is finally performed until the organic peroxide added to the adhesive sheet is almost completely decomposed. By this heat treatment, the adhesive sheet is cross-linked and the adhesive sheet and each protective material are firmly adhered to each other, and the solar cell element is laminated with two adhesive sheets, which are the upper transparent protective material and the lower substrate protective material. A solar cell module firmly bonded to and is formed there.

The heat treatment performed here is preferably performed in two stages. That is, under the conditions where the organic peroxide is not completely decomposed and the module adheres slowly, for example, in the case of an organic peroxide having a decomposition temperature of 140 ° C,
A step of temporarily adhering in a vacuum laminator at 140 ° C. for about 0.1 to 5 minutes, and a condition of almost completely decomposing this peroxide, for example, a step of heating at 140 ° C. at room temperature for about 60 to 200 minutes. It is industrially advantageous to carry out in separate steps.

When the solar cell element is formed on a protective material such as glass, plastic, ceramic or stainless steel, an adhesive sheet preliminarily treated with a primer is used as an intermediate layer to protect either one of them. An upper transparent protective material and a lower substrate protective material having solar cell elements formed on the inner peripheral surface (contact surface of the filler sheet) of the material are stacked on the upper and lower sides of the intermediate layer adhesive sheet, specifically, the upper surface of the lower substrate protective material. The filler sheet and the upper transparent protective material are formed on the solar cell element formed on, or the adhesive sheet and the lower substrate protective material are sequentially laminated under the solar cell element formed on the lower surface of the upper transparent protective material. As in the case described above, when heat-bonding in a vacuum in two steps, one protective material on which the solar cell element is formed, the adhesive sheet, and the other protective material are firmly bonded to each other. Battery module is formed therein.

In the adhesive sheet layer of the solar cell module thus produced, the gelation rate of the ethylene copolymer (1 g of the sheet is dipped in 100 ml of xylene,
After heating at 110 ° C. for 24 hours, it is filtered by gold steel, the insoluble matter is collected, dried, and weighed) to 70 to 9
It is desirable to be 8%, preferably 80 to 95%.

[0017]

According to the present invention, since an adhesive sheet excellent in yellowing resistance can be provided, a solar cell module manufactured using this adhesive sheet is less likely to have a decrease in light transmittance over time, and therefore has a higher power generation efficiency. The decrease can be prevented.

[0018]

【Example】

"Example 1" Ethylene-vinyl acetate copolymer (Mitsui DuPont Polychemical Co., Ltd. "Evaflex 150"
P "(vinyl acetate content 33% by weight, MFR 30 dg / m
in) 100 parts by weight of ethyl-3,3-di (t-
Butyl peroxy) butyrate 1.5 parts by weight, γ-methacryloxypropyltrimethoxysilane 1.0 parts by weight, 2-hydroxy-4-n-octylbenzophenone 0.3 parts by weight, bis (2,2,6,6) -Tetramethyl-
A mixture of 0.1 part by weight of 4-piperidyl) sebacate and 0.2 part by weight of tris (nonylphenyl) phosphite was used at a resin temperature of 100 using a T-die sheet.
It was extruded at 0 ° C into a sheet having a thickness of 0.6 mm. Using this sheet, yellowing resistance was evaluated by the following test method in the state of a laminated product having a configuration used in a solar cell. No yellowing of the copolymer sheet in the laminate was observed either in the weather resistance test or after 16 hours in the heat resistance test. The results are shown in Table 1.

(1) Weather resistance (weatherometer test) A transparent glass plate which is an upper transparent protective material for a solar cell and a polyvinyl fluoride (a product of DuPont) which is a lower substrate protective material.
The extruded sheet is sandwiched with the sheet, and melt-bonding (temporary adhesion) at a heating temperature of 110 ° C. using a vacuum laminator
I went. This temporary adhesive laminate is further heated under normal pressure at 150 ° C. for 30 minutes on a hot plate to decompose the organic peroxide, crosslink the T-die sheet and firmly adhere to the transparent glass plate and the polyvinyl fluoride sheet. A laminated product was prepared. This laminated product was continuously irradiated with ultraviolet rays for 1600 hours from the transparent glass surface with a sunshine weatherometer under the conditions of black panel 83 ° C. and spraying for 12 minutes / 60 minutes, and the degree of yellowing was visually observed to evaluate the weather resistance. .

(2) Heat resistance Further, regarding the laminated product prepared under the above-mentioned bonding conditions,
The heat resistance was evaluated by visually observing the degree of yellowing after heating for 2 hours and 16 hours in an oven at 0 ° C.

Comparative Example 1 Ethyl-3,3-of Example 1
In place of di (t-butylperoxy) butyrate, 2-
5-dimethyl-2,5-bis (t-butylperoxy)
An extruded sheet of the ethylene-vinyl acetate copolymer composition was prepared in the same manner as in Example 1 except that hexane was used, and the yellowing resistance of the extruded sheet was evaluated. The results are shown in Table 1.

Comparative Example 2 In place of the ethyl-3,3-di (t-butylperoxy) butyrate of Example 1, n-butyl 4'4-bis (t) was used.
- except using butyl peroxy) bus Rereto creates an extruded sheet in the same manner as in Example 1 to evaluate yellowing resistance of the extruded sheet. The results are shown in Table 1.

Comparative Example 3 Ethyl-3,3-of Example 1
Instead of di (t-butylperoxy) butyrate, 1,
An extruded sheet was prepared in the same manner as in Example 1 except that 1-bis (t-butylperoxy) cyclohexane was used.
The yellowing resistance of the extruded sheet was evaluated. The results are shown in Table 1.

Comparative Example 4 Ethyl-3,3-of Example 1
Extruded sheets were prepared in the same manner as in Example 1 except that dicumyl peroxide was used instead of di (t-butylperoxy) butyrate, and the yellowing resistance of the extruded sheets was evaluated. The results are shown in Table 1.

Example 2 An ethylene-ethyl acrylate copolymer ( ethyl acrylate content 25% by weight, MFR 5 dg / min) was used in place of the ethylene-vinyl acetate copolymer of Example 1. Except for the above, an extruded sheet was prepared in the same manner as in Example 1, and the yellowing resistance of the extruded sheet of the ethylene-ethyl acrylate copolymer composition was evaluated. The results are shown in Table 1.

[0026]

[Table 1]

─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Masatoshi Hayashi 33-2, Inaoka-cho, Inage-ku, Chiba-shi, Chiba (56) References JP-A-58-79850 (JP, A) JP-A-59-22978 (JP, A) JP 61-246279 (JP, A) JP 5-186610 (JP, A) JP 6-299125 (JP, A) JP2-40709 (JP, B2) (58) Survey Areas (Int.Cl. ⁷ , DB name) C09J 4/00-201/10 H01L 31/04-31/058 C08F 8/00-8/08 C08J 3/24

Claims (2)

(57) [Claims] 1. An adhesive sheet for a solar cell, which comprises an ethylene copolymer containing alkyl-3,3-di (tert-butylperoxy) butyrate. 2. A solar cell module having an ethylene copolymer adhesive sheet layer crosslinked with alkyl-3,3-di (tert-butylperoxy) butyrate.