JP2002190610A - Solar battery sealing material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain solar battery sealing material, the main component of which is ethylene-vinyl acetate copolymer with high volume resistivity. SOLUTION: In this solar battery sealing material, 1,1-bis(t-butylperoxy)-3,3,5- trimethylcyclohexane as organic peroxide, wherein half-life at 140 deg.C is at most 30 minutes, and triallylisocyanurate(TAIC) as crosslinking auxiliary agent are added in ethylene-vinyl acetate copolymer, wherein the content of vinyl acetate is 26-30 wt.%, and heating and crosslinking are performed. The volume resistivity, after crosslinked, is at least 3.0×1015 Ωcm. Insulating property of a solar battery module is improved in the case that the sealing material is used as a thin layer, so that leakage current from a solar battery is restrained effectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for producing ethylene-
The present invention relates to a solar cell encapsulant made of a vinyl acetate copolymer.

[0002]

2. Description of the Related Art In recent years, the depletion of fossil fuels such as petroleum and coal has been threatened, and there is an urgent need for development to secure alternative energy to the energy obtained from these fossil fuels. For this reason, nuclear power, hydropower,
Various methods such as wind power generation and photovoltaic power generation have been studied, and have been extended to practical use. However, waste nuclear power has always been associated with waste problems and concerns about adverse effects on the environment, and hydropower and wind power are inferior in terms of energy conversion efficiency. On the other hand, the photovoltaic power generation system has remarkably improved the price / performance ratio when actually used, and the expectations as a clean energy source are also very high.

In photovoltaic power generation, solar energy is directly converted into electric energy by using a semiconductor such as silicon. However, the function of the semiconductor used here is reduced when it comes into direct contact with the outside air, so that a solar cell module is used. It is necessary to provide a protective film or a sealing material on the surface. Furthermore, in order to stabilize the function of the solar cell, it is necessary to improve the insulation performance in addition to the withstand voltage performance of the sealing material, and to prevent leakage of current in the semiconductor as much as possible. That is, an increase in the volume resistivity of the sealing material is an important point for improving the performance of the photovoltaic power generation system.

At present, crosslinked ethylene-vinyl acetate (EVA) is generally considered promising as a sealing material that comes into direct contact with the power generating element from the viewpoint of cost reduction and the like, and its practical use is progressing. For example, a sealing material obtained by adding an organic peroxide such as 2,5-dimethyl-2,5-di (t-butylperoxy) hexane to EVA as a crosslinking agent is used.

[0005]

As described above, in photovoltaic power generation, research and development for cost reduction from various parts and performance improvement are being carried out. There is a need to improve energy conversion efficiency and reduce and reduce material costs. In other words, it is considered that improving the members and methods used when modularizing the power generating element other than the power generating element itself leads to improvement in performance, cost reduction, and compactness, and also improves the entire system. Can be

[0006] While promoting such a rationalization,
The low volume resistivity of EVA as a sealing material is cited as a problem. That is, when the conventional EVA is used, the thickness is increased to satisfy the withstand voltage performance of the module. However, such a use method not only increases the cost of materials but also increases the volume of the entire module. This is considered to be a factor inhibiting the spread of solar cells and solar power generation.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a solar cell encapsulant containing ethylene-vinyl acetate copolymer as a main component and having a sufficient volume resistivity. is there.

[0008]

In order to achieve the above object, the ethylene-vinyl acetate copolymer of the present invention having a vinyl acetate content of 26 to 30% by mass has a half-life at 140 ° C. of 30 minutes or less. 1,1-bis (t) as an organic peroxide of
-Butylperoxy) -3,3,5-trimethylcyclohexane, and triallyl isocyanurate (TAIC) as a crosslinking aid, and heat-crosslinking, resulting in a volume resistivity of 3.0 × 10 ¹⁵ Ωcm or more after crosslinking. When a solar cell encapsulant is used, it is possible to enclose the solar power generation element with a small amount of the encapsulant, and to keep the energy conversion efficiency high.

At the time of production, an organic peroxide having a half-life at 140 ° C. of 30 minutes or less is added to EVA. If necessary, a silane coupling agent, a crosslinking assistant, a stabilizer, a coloring agent, an ultraviolet ray It is also possible to add an absorbent, an antioxidant, a discoloration inhibitor and the like. These components are mixed using a mixer to obtain the solar cell sealing material of the present invention.

As the organic peroxide used in the present invention, any organic peroxide having a half-life at 140 ° C. or more of 30 minutes or less can be used. Examples of this are 2,5-
Dimethylhexane-2,5-dihydroperoxide, di-t-butyl peroxide, t-dicumyl peroxide, dicumyl peroxide, α, α'-bis (t-butylperoxyisopropyl) benzene, n-
Butyl-4,4-bis (t-butylperoxy) butane, 2,2-bis (t-butylperoxy) butane,
1,1-bis (t-butylperoxy) cyclohexane, 1,1-bis (t-butylsiloxy) 3,3,5
-Trimethylcyclohexane, t-butylperoxybenzate, benzoyl peroxide and the like can be used. It is sufficient that the amount of these organic peroxides is 5 parts by mass or less based on 100 parts by mass of EVA.

When 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane is particularly added to the above organic peroxide and EVA has a crosslinked structure by thermal decomposition, The reduction of the volume resistivity of the EVA is small and effective.

As the EVA used in the present invention, those having a vinyl acetate content of 50% by mass or less can be used. In particular, considering the volume resistivity of the EVA itself, the vinyl acetate content is 30% by mass or less. Are preferred.

Further, in order to further improve the performance of the EVA as a sealing material and mainly the adhesion to the solar cell lower substrate or the power generating element, a silane coupling agent such as γ-chloropropyltrimethoxysilane, vinyl Trichlorosilane, vinyltriethoxysilane, vinyl-tris (β
-Methoxyethoxy) silane, γ-methacryloxypropyltrimethoxysilane, β- (3,4-ethoxycyclohexyl) ethyl-trimethoxysilane, γ-glycidoxypropyltrimethoxysilane, vinyltriacetoxysilane, γ-mercaptopropyl Trimethoxysilane, γ-aminopropyltrimethoxysilane, N-β-
And (aminoethyl) -γ-aminopropyltrimethoxysilane. The compounding amount of these silane coupling agents is 5 parts by mass or less, preferably 0.02 parts by mass or less based on 100 parts by mass of EVA.

In order to further improve the volume resistivity of the solar cell encapsulant of the present invention, a silane coupling agent having a functional group of 4 or less carbon atoms directly bonded to a silicon atom, particularly preferably Vinyl trimethoxysilane to E
It is also effective to add it to VA.

In the present invention, a silane coupling agent having a functional group having 5 or more carbon atoms directly bonded to a silicon atom, such as γ-methacryloxypropyltrimethoxysilane, has an EVA of 100 mass%. If the amount added to the parts is 0.02 parts by mass or less, the volume resistivity of the EVA can be improved.

In the present invention, it is also possible to add a photosensitizer to EVA in advance, decompose the photosensitizer by light irradiation, and give EVA a crosslinked structure. The photosensitizer used in the present invention may be any photosensitizer that generates a radical upon irradiation with light, such as benzoin, benzomethyl ether, benzoin isoethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, dibenzoyl, Nitriacenaphthene, hexachlorocyclopentadiene, paranitrodiphenyl, paranitroaniline, 2,4,6-trinitroaniline, 1,2-
And benzanthraquinone. These photosensitizers are E
It is generally used in an amount of 10 parts by mass or less based on 100 parts by mass of VA.

Further, since the EVA sealing material is used for a long period of time and is expected to be exposed to wind and rain, durability is also important. In order to improve the durability, it is also possible to add a crosslinking agent to EVA to improve the gel fraction. Examples of the cross-linking auxiliary used for this purpose include monofunctional cross-linking auxiliary in addition to trifunctional cross-linking auxiliary such as triallyl isocyanurate or triallyl isocyanate. These crosslinking assistants are used at a ratio of 10 parts by mass or less based on 100 parts by mass of EVA.

Further, in the present invention, hydroquinone, hydroquinone monomethyl ether,
EVA1 with P-benzoquinone, methylhydroquinone, etc.
5 parts by mass or less can be added to 00 parts by mass.

Further, in addition to the above, a coloring agent, an ultraviolet absorber,
Additives such as anti-aging agents and anti-tarnish agents can be used.

Examples of the colorant include inorganic pigments such as metal oxides and metal powders, and organic pigments such as azo-based, phthalocyanine-based, achi-based, acidic or basic dye-based lakes.

The ultraviolet absorbers include 2-hydroxy-4-
Benzophenones such as octoxybenzophenone and 2-hydroxy-4-methoxy-5-sulfobenzophenone, benzotriazoles such as 2- (2'-hydroxy-5-methylphenyl) benzotriazole, phenylsalicylate, pt Hindered amines such as -butylphenyl salicylate.

Antiaging agents include amines, phenols, bisphenyls and hindered amines.
For example, di-t-butyl-p-cresol, bis (2,
2,6,6-tetramethyl-4-piperazyl) sebacate.

It is possible to form a three-layered solar cell encapsulant by processing the obtained EVA as a solar cell encapsulant into a plate shape and using two sheets, sandwiching a film other than EVA therebetween. By obtaining such a structure, the volume resistivity can be further improved. Examples of the film other than EVA used here include a polyester film, a polyethylene film, a polypropylene film, a polycarbonate film, and a fluorinated polyethylene.

Among them, the polyester film is particularly excellent in insulating properties and inexpensive, and is practical.

[0025]

EXAMPLES Examples 1 and 2 and Comparative Examples 1 and 2 Each component shown in Table 1 was mixed with a roll mill heated to 80 ° C. to prepare an EVA resin composition. E obtained in this way
Each of the VA resin compositions was formed into a crosslinked sheet having a thickness of 1 mm by using a press at 150 ° C. Each sheet was sandwiched between electrodes from both sides, a voltage was applied, and the volume resistivity was measured.

[0026]

[Table 1] The mixing ratio of each component in the above table is based on parts by mass.

The sheets composed of the compositions obtained in Examples 1 and 2 were compared with the sheets of Comparative Examples 1 and 2 conventionally used.
It can be seen that it has a clearly large volume resistivity.

Examples 3 and 4 and Comparative Examples 3 and 4 Production of sealing materials as laminates and measurement of leakage current EVA compositions according to Examples 1 and 2, and EVA obtained in Comparative Examples 1 and 2 The compositions were each processed into a 0.25 mm thick sheet using a 90 ° C. press. Two EVA each
A sheet was used, and a polyethylene terephthalate (PET) film having a thickness of 100 μm was sandwiched between the sheets, and integrated with a laminator. Thereafter, EVA was heated and cross-linked in an oven at 150 ° C. to obtain each of the laminates of the present invention and comparative laminates (Examples 3, 4, and Comparative Examples 3, 4 respectively).

Each of the above laminates was punched into a 50 mm diameter, a voltage of 1000 V was applied, the current was measured, and the leakage current value was obtained. The results are shown in Table 2 below.

[0030]

[Table 2]

As is clear from Table 2, the leak current obtained for the laminate of the present invention is extremely small as compared with the leak current of the comparative laminate.

[0032]

As described above, the solar cell encapsulant made of the ethylene-vinyl acetate copolymer of the present invention has a high volume resistivity, and is used as a laminate of the encapsulant and other materials. The sealing material can efficiently prevent current leakage from the solar cell. As a result, the solar cell encapsulant of the present invention improves the insulation properties of the solar cell module even when used in a thin layer, thereby achieving a reduction in the size of the solar cell module itself and a reduction in material costs.

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Claims (3)

[Claims] 1. An ethylene-vinyl acetate copolymer having a vinyl acetate content of 26 to 30% by mass is mixed with 1,1-bis (t- in butylperoxy) -3,3,5-trimethylcyclohexane, and the addition of triallyl isocyanurate (TAIC) as a crosslinking agent, heat crosslinking, volume resistivity after crosslinking is 3.0 × ^{10 15} Ωcm or more A solar cell encapsulant, comprising: 2. 100 parts by mass of ethylene-vinyl acetate copolymer, 5 parts by mass or less of 1,1,1-bis (t
The solar cell encapsulant according to claim 1, wherein (-butylperoxy) -3,3,5-trimethylcyclohexane is added. 3. The solar cell encapsulant according to claim 1, wherein 10 parts by mass or less of triallyl isocyanurate is added to 100 parts by mass of the ethylene-vinyl acetate copolymer.