JP3117627B2 - Composition for protective sheet for solar cell module and protective sheet for solar cell module - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a composition for a protective sheet for a solar cell module and a protective sheet for a solar cell module obtained by molding the composition.
An object of the present invention is to provide a protective sheet which is excellent in weather resistance, transparency, adhesiveness, etc., and is effective for improving the performance and extending the life of a solar cell module.

[0002]

BACKGROUND OF THE INVENTION In recent years, sunlight has received widespread attention as a clean energy source due to environmental problems, and a device for directly converting this sunlight into electric power, ie, a solar cell, has been actively developed. ing. Solar cells are expected to play a major role in conventional solar energy utilization, and research and development are being continued with a focus on improving efficiency and reducing costs. Conventionally,
A solar cell module used for photovoltaic power generation was composed of glass as a substrate, an ethylene-vinyl acetate copolymer (EVA) sheet as a protective sheet, silicon power generation electrons as a photoelectric conversion element, a fluororesin for a back cover, and the like. A method using EVA as a protective sheet is disclosed in JP-B-62-14111, JP-B-62-9232, and JP-A-4-311732.
, JP-A-6-177412 and JP-A-6-334207. Japanese Patent Publication No. 6-104729 also proposes a copolymer of ethylene and an ethylenically unsaturated carboxylic acid ester. These protective sheets are often used indoors like electric desk calculators,
It has been used without major problems. However, recently, solar cells have been used for large-capacity power generation installed on the roof of a house, and there is a problem with the weather resistance of EVA and the like. However, problems such as a decrease in transparency and peeling of an adhered portion have occurred. In addition, EVA and the like are thermoplastic,
As can be seen from the molecular structure having a large amount of carbon and hydrogen, it has a high flammability, and there is a problem that it may flow out in the event of a fire in a house or a neighborhood or cause an increase in fire due to combustion. It can be easily inferred that the above problem can be solved by using silicone rubber for this protective sheet.
JP-A-60-194253, JP-A-3-185769, JP-B-6-5773, JP-A-6-85306, JP-A-6-338627
And Japanese Unexamined Patent Application Publication No. 6-350117 and Japanese Utility Model Publication No. 6-10703. However, the silicone rubber exemplified here is a liquid silicone rubber, and when a large-sized solar cell module is made, it protrudes outside the system,
The workability was inferior, such as infiltration of air. Further, the use of a millable silicone rubber improves the workability, but has a problem in that the transparency is reduced. Also, in the case of a millable silicone rubber, transparency can be improved by substituting 7 to 30 mol% of organic groups bonded to silicon with a phenyl group.
In the case of forming a sheet having a thickness of about 5 mm, there is a problem that the workability is inferior due to sticking to a forming roll, and a problem that yellowing tends to occur in a long term as the amount of phenyl group increases. In Japanese Patent Publication No. 21622/1985, there is an example of a heat-vulcanizable silicone rubber composition which does not easily yellow, but the fine powder silica used here has no limitation on the particle size, and is generally used. When using the finely divided silica that is used, a completely colorless and transparent composition cannot be obtained, and there is no problem with milky white ones in the conventionally used rubber bottle caps and food vending machine parts. However, when used as a solar cell protective cover, it cannot be used as it is because the light transmittance is greatly reduced.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a protective sheet for a solar cell module having excellent transparency, flame retardancy, weather resistance, and moldability.

[0004]

The present inventors have conducted intensive studies to achieve the above object, and as a result, have found that a specific silicone rubber composition is effective for a protective sheet for a solar cell module, thereby completing the present invention. Reached. That is, the present invention relates to (A) a degree of polymerization of from 3,000 to 3, in which at least 93 mol% of organic groups bonded to silicon atoms is a methyl group and 0.01 to 2 mol% is a vinyl group.
(B) 40-130 parts by weight of finely divided silica having a primary particle size of 0.1-10 nm, surface-treated with hexamethyldisilazane, based on 100 parts by weight of 20000 polyorganosiloxane (C) 0.05-15 parts by weight of organic peroxide And a protective sheet for a solar cell module obtained by molding the composition to a thickness of 0.1 to 5 mm.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The component (A) constituting the composition of the present invention has a degree of polymerization of 30.
Of polyorganosiloxanes having a molecular weight of 00 to 20000, and it is necessary that 93 mol% or more of the organic groups bonded to silicon atoms are methyl groups. If the degree of polymerization is less than 3000, the viscosity is too low to allow the sheet to be discharged, and if it is more than 20,000, the flowability is poor at the time of mounting on a solar cell, which causes the formation of air pockets. Preferably, the degree of polymerization is from 4000 to 10,000. As the organic group bonded to the silicon atom, it is necessary that at least 93 mol% of the organic group is a methyl group from the viewpoint of heat resistance and roll processability, but part of the organic group is an alkyl group such as an ethyl group, a propyl group, and a butyl group. Alkenyl groups such as vinyl group, allyl group, butaniel group, aryl groups such as phenyl group and tolyl group, or part or all of the hydrogen atoms bonded to carbon atoms of these groups are replaced with halogen atoms, cyano groups, etc. Chloromethyl group, chloropropyl group, 3,3,3
It may be replaced by the same or different unsubstituted or substituted monovalent hydrocarbon group selected from -trifluoropropyl group, 2-cyanoethyl group and the like. Further, in order to cure and bond the composition on a solar cell, 0.01 to 2 mol%
Needs to be a vinyl group. If the vinyl group content is less than 0.01% by mole, the curing is insufficient, and if it exceeds 2% by mole, the cured product becomes brittle or the composition yellows. Preferably it is 0.03-1.5 mol%. This polyorganosiloxane may be linear or branched, but is preferably linear in consideration of roll processability.

The finely divided silica having a primary particle diameter of 0.1 to 10 nm, which has been surface-treated with component (B) hexamethyldisilazane,
It is effective to increase the light transmittance while maintaining the strength and processability of the composition. The primary particle size needs to be 10 nm or less. If it is larger than 10 nm, the light transmittance will decrease. More preferably, it is 6 nm or less. On the other hand, if it is smaller than 0.1 nm, the compounding becomes difficult. Here, the primary particle diameter is a basic unit before the particles are aggregated, and means an average diameter of the particles measured by an electron microscope. In order to improve the processability and the light transmittance of the composition filled with the fine silica powder, it is necessary to treat the fine silica powder with hexamethyldisilazane. Either a method of treating fine powder silica with hexamethyldisilazane or a method of performing surface treatment of fine powder silica during the compounding step may be used. When the fine silica powder is previously treated with hexamethyldisilazane, the amount of hexamethyldisilazane is preferably 5 to 30% by weight based on the fine silica powder. As a treatment method, it is common to put fine powdered silica and hexamethyldisilazane in a closed container, stir at room temperature or higher, and then remove decomposition products at a temperature of 100 ° C or higher. In some cases, water is simultaneously added for the purpose of accelerating the reaction. As a method of performing the surface treatment of the fine powder silica in the compounding process of, a polyorganosiloxane, fine powder silica, hexamethyldisilazane, and in some cases, water are compounded in a kneader or a Banbury mixer, and room temperature or higher. After kneading at a temperature, the decomposition products are removed at a temperature of 100 ° C or higher. Similarly, the amount of hexamethyldisilazane used in this case is preferably 5 to 30% based on the fine silica powder. Further, instead of treating untreated fine powder silica with hexamethyldisilazane, fine powder silica previously treated with silane or siloxane may be treated with hexamethyldisilazane, or silane, siloxane, hexamethyldisilazane may be used. At the same time, and in this case, there is an effect that the amount of hexamethyldisilazane used can be reduced to 0.5 to 15% by weight based on the fine powder silica.

The amount of this silica is also characteristic of the present invention, and is 40 to 130 parts by weight per 100 parts by weight of the component (A).
Parts by weight. If the amount is less than 40 parts by weight, sufficient light transmittance and workability cannot be obtained, and if it exceeds 130 parts by weight, the workability is greatly reduced. Preferably it is 55 to 80 parts by weight.

The organic peroxide as the component (C) is necessary when the composition is cured and adhered to a solar cell. Specifically, dicumyl peroxide, cumyl-t-butyl peroxide, 2,5-dimethyl-2,5-di-t-butylperoxyhexane, di-t-butyl peroxide, benzoyl peroxide, 2,4-dichlorobenzoyl Various organic peroxides such as peroxides are used. The amount of the organic peroxide is determined by the amount of the polyorganosiloxane (A).
The range of 0.05 to 15 parts by weight per 100 parts by weight is preferred. If the compounding amount of the organic peroxide is less than 0.05 part by weight, curing cannot be sufficiently performed, and if the compounding amount exceeds 15 parts by weight, not only does not have any further special effect but also the physical properties of the obtained silicone rubber. This is because it may have an adverse effect.

On the other hand, although silicone rubber is excellent in weather resistance and heat resistance, when it is left outdoors for several decades, some yellowing may be observed. In this case, the following formula R ¹ _{a Hb} SiO _{(4-ab) / 2} (wherein R ¹ is a substituted or unsubstituted monovalent hydrocarbon group, a =
1-2, b = 0.1-1.2, a + b = 1.8-2.2) The organohydrogenpolysiloxane represented by the formula (A)
It can be prevented by adding 0.1 to 5 parts by weight to 100 parts by weight.

When a solar cell is installed as a roof material for a house, it is necessary to make the roof material non-combustible in case of a fire. In this case, it is effective to mix a platinum compound in an amount of 1 to 1000 ppm in terms of platinum with respect to the component (A). Specific examples of the platinum compound include chloroplatinic acid, a platinum olefin complex, a platinum vinyl siloxane complex, platinum black, and a platinum triphenylphosphine complex.

[0011] The composition and sheet are used for solar cells and glass,
To cure and adhere to a fluorine film, etc.,
This can be done by applying an adhesive primer or corona treatment in advance, but in order to easily obtain a strong adhesive force,
0.1 to 10 parts by weight of a compound having at least one (R ² O) ₃ Si group (R ² is hydrogen or a monovalent hydrocarbon group) in one molecule per 100 parts by weight of the component (A) Is valid.

In order to obtain a protective sheet for a solar cell module, the protective sheet is rolled by a calender roll or the like.
Since it is necessary to dispense to a thickness of 0.1 to 5 mm, the viscosity of the composition needs to be high to some extent, but in order to obtain a solar cell module, this composition is It is necessary to flow, in which case the viscosity needs to be low. EVA used conventionally
Since it is a thermoplastic resin, it has excellent processability such that it has high viscosity at room temperature and low viscosity at high temperature.
In the case of silicone rubber, the temperature dependency of viscosity is rather small, which is an unfavorable feature for use in a protective sheet for a solar cell module. In order to improve this point, a (CH ₃ CH ₂ O) (CH ₃ ) ₂ Si group or (CH ₃ O) (C
It is effective to blend 1 to 30 parts by weight of a polyorganosiloxane oil having a degree of polymerization of 2 to 100 having an H ₃ ) ₂ Si group with respect to 100 parts by weight of the component (A). In this case, if the degree of polymerization is larger than 100, the desired thermoplasticity cannot be obtained. If the amount is less than 1 part by weight, thermoplasticity cannot be obtained, and if it exceeds 30 parts by weight, the strength is greatly reduced.

The method for producing the composition for a protective sheet for a solar cell module can be obtained by blending and kneading with a kneader, a Banbury mixer, a two-roll mill or the like. The composition may be formed into a thickness of 0.1 mm to 5 mm by rolling with a calender roll or the like, extruding into a sheet with an extruder, sandwiching with a polyethylene sheet, or a fluororesin sheet to be finally used. It can be obtained by a method of putting on top.

[0014]

The protective sheet for a solar cell module obtained by the present invention has transparency, adhesiveness, processability, weather resistance,
It is excellent in flame retardancy, and can generate stable power for a long time even when using a solar cell module in a severe environment.

[0015]

EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples. In the following examples, parts are parts by weight. Example 1 A primary particle diameter of 5 nm was determined with respect to 100 parts of an organopolysiloxane having a degree of polymerization of 6000, comprising 99.8 mol% of dimethylsiloxane units and 0.2 mol% of methylvinylsiloxane units each having a molecular chain terminal capped with a dimethylvinylsilyl group. After mixing 60 parts of fumed silica having a specific surface area of 400 m ² / g, 12 parts of hexamethyldisilazane and 6 parts of water and kneading at room temperature for 1 hour, the temperature was raised to 150 ° C. and kneaded for 2 hours to remove decomposition residues. . Thereafter, the temperature was lowered to room temperature, and 1.6 parts of dicumyl peroxide was added. With respect to this composition, the sheeting property was evaluated using two rolls, and the thickness of the sheet that could be separated was measured. To evaluate thermoplasticity,
The plasticity at 120 ° C. was measured. From this composition, 170 ° C
A 3 mm sheet was prepared by hot pressing with a mold for 10 minutes, and the oxygen index was measured to evaluate the flame retardancy. In addition, the light transmittance immediately after this sheet and the light transmittance after 1000 hours at 100 ° C. were measured. Further, in order to evaluate the adhesive property, the adhesive property was evaluated by thermocompression bonding at 170 ° C. for 10 minutes to three kinds of base materials, a fluororesin whose surface was corona-treated, glass, and a glass treated with an adhesive primer. When the rubber breaks when peeling, ○, when peeled between the rubber and the substrate ×,
Those that partially destroyed rubber were expressed as △. The results are shown in Table 1.

Example 2 A sample was prepared and evaluated in the same manner as in Example 1, except that the fine silica powder was changed to a powder having a primary particle diameter of 7 nm (AEROSIL 380, manufactured by Nippon Aerosil Co., Ltd.).

Example 3 A sample was prepared and evaluated in the same manner as in Example 1 except that the fine silica powder was changed to a powder having a primary particle diameter of 7 nm (AEROSIL 300, manufactured by Nippon Aerosil Co., Ltd.).

Comparative Example 1 A sample was prepared and evaluated in the same manner as in Example 1, except that the fine silica powder was changed to a powder having a primary particle diameter of 12 nm (AEROSIL 200, manufactured by Nippon Aerosil Co., Ltd.).

Comparative Example 2 A sample was prepared and evaluated in the same manner as in Example 1 except that the amount of the fine powdered silica was changed to 35 parts.

Example 4 A sample was prepared and evaluated in the same manner as in Example 1, except that 2 parts of methylhydrogenpolysiloxane having a polymerization degree of 50, in which the molecular chain end was blocked with a trimethylsilyl group, was added to the composition of Example 1. Was.

Example 5 A sample was prepared and evaluated in the same manner as in Example 1, except that 0.01 part of chloroplatinic acid was added to the composition of Example 1.

Example 6 In the composition of Example 1, the terminal of the molecular chain was (CH ₃ O) (CH ₃ ) ₂ Si
Dimethylpolysiloxane 10 having a polymerization degree of 10
A sample was prepared and evaluated in the same manner except that the parts by weight were blended.

Example 7 A sample was prepared and evaluated in the same manner as in Example 1, except that 2 parts by weight of γ-methacryloxytrimethoxysilane was added to the composition of Example 1.

Example 8 A sample was prepared and evaluated in the same manner as in Example 1, except that the organopolysiloxane in which 5 mol% of dimethylsiloxane units were replaced by diphenylsiloxane units was used.

Comparative Example 3 A sample was prepared and evaluated in the same manner as in Example 1, except that the organopolysiloxane in which 10 mol% of dimethylsiloxane units were replaced by diphenylsiloxane units was used.

Comparative Example 4 In place of the composition used in Example 1, an ethylene-vinyl acetate copolymer having a melting point of 100 ° C. and having a vinyl acetate content of 6% and one part of dicumyl peroxide was used. Other than the above, a sheet was prepared and evaluated in the same manner. These results are summarized in Table 1.

[0027]

[Table 1]

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI C08L 83/05 C08L 83/05 E04D 3/40 E04D 3/40 V H01L 31/04 H01L 31/04 F (58) Fields surveyed (Int.Cl. ⁷ , DB name) C08L 83/07 C08K 3/36 C08K 5/14 C08K 5/5415 C08K 9/06 C08L 83/05 C08L 83/04

Claims (7)

(57) [Claims] (A) With respect to 100 parts by weight of a polyorganosiloxane having a polymerization degree of 3,000 to 20,000, (A) at least 93 mol% of an organic group bonded to a silicon atom is a methyl group, and 0.01 to 2 mol% is a vinyl group. ) For protection sheet for solar cell module, which contains 40-130 parts by weight of fine powdered silica having a primary particle size of 0.1-10 nm and surface treated with hexamethyldisilazane (C) 0.05-15 parts by weight of organic peroxide Composition. 2. The composition according to claim 1, wherein the component (B) is finely divided silica having a primary particle diameter of 6 nm or less. (3) An organohydrogenpolysiloxane represented by the following formula is added to 0.1 part by weight based on 100 parts by weight of the component (A).
The composition for a protective sheet for a solar cell module according to claim 1, wherein the composition is 1 to 5 parts by weight. R ¹ _{a Hb} SiO _{(4-ab) / 2} (wherein, R ¹ is a substituted or unsubstituted monovalent hydrocarbon group, a =
1-2, b = 0.1-1.2, a + b = 1.8-2.2) 4. The composition for a protective sheet for a solar cell module according to claim 1, further comprising a platinum compound having a platinum amount of 1 to 1000 ppm. 5. A compound having at least one (R ² O) ₃ Si group (where R ² is hydrogen or a monovalent hydrocarbon group) in one molecule.
The composition for a protective sheet for a solar cell module according to any one of claims 1 to 4, wherein 0.1 to 10 parts by weight of (A) component is blended with respect to 100 parts by weight of the component. 6. A polyorganosiloxane oil having a degree of polymerization of 2 to 100 and having a (CH ₃ CH ₂ O) (CH ₃ ) ₂ Si group or a (CH ₃ O) (CH ₃ ) ₂ Si group at a molecular chain terminal. The composition for a protective sheet for a solar cell module according to any one of claims 1 to 5, wherein 1 to 30 parts by weight is blended with respect to 100 parts by weight of the component (A). 7. A protective sheet for a solar cell module obtained by molding the composition according to any one of claims 1 to 6 to a thickness of 0.1 to 5 mm.