JP5351630B2 - Solar cell sealing film and solar cell using the same - Google Patents

Description

  The present invention relates to a solar cell sealing film mainly composed of an ethylene-unsaturated ester copolymer and a solar cell using the sealing film, and particularly to a solar cell sealing film excellent in transparency and yellowing prevention.

  In recent years, solar cells that convert sunlight into electrical energy have attracted attention and are being developed from the viewpoint of effective use of resources and prevention of environmental pollution.

  As shown in FIG. 1, a solar cell generally includes a light receiving surface side transparent protective member 11 made of a glass substrate or the like, a light receiving surface side sealing film 13A, a power generation element 14 made of silicon, a back surface side sealing film 13B, and The back side protection member (back cover) 12 is laminated in this order, degassed under reduced pressure, and then heated and pressurized to crosslink and cure the light receiving side sealing film 13A and the back side sealing film 13B to bond and integrate. It is manufactured by. In a conventional solar cell, a plurality of power generation elements 14 are connected and used in order to obtain a high electric output. Therefore, the power generating element is sealed using the insulating sealing films 13A and 13B. Thereby, it is possible to prevent electricity leakage inside the solar cell and reliably extract the generated electricity via the wiring.

  In order to produce such a solar cell, the light receiving surface side transparent protective member, the light receiving surface side sealing film, the power generation element, the back surface side sealing film, and the back surface side protective member (back cover) are laminated in this order, A method of crosslinking and curing the light-receiving surface side sealing film and the back surface side sealing film is used by pressurizing and heating the obtained laminate. Thus, each member of the laminated body is bonded and integrated by crosslinking and curing the light-receiving surface side sealing film and the back surface side sealing film.

  In order to improve the power generation efficiency of the solar cell, it is necessary to make light enter the cell as efficiently as possible and collect it on the power generation element. For this purpose, the sealing film is required to have high transparency. From such a viewpoint, as a sealing film for solar cells, a film made of an ethylene-unsaturated ester copolymer such as an ethylene-vinyl acetate copolymer (EVA) or an ethylene-ethyl acrylate copolymer (EEA) is used. It is used. Patent Document 1 discloses that the transparency of the sealing film can be improved by using an alkyleneoxy group-containing compound such as tetraethylene glycol di (meth) acrylate.

JP 2008-053379 A

  The surface temperature of the solar cell is as high as 70 ° C. or higher when outdoors in summer. When a solar cell is used for a long period of time in such a high temperature environment, the sealing film may turn yellow, leading to a decrease in sunlight transmittance and poor appearance.

  Therefore, an object of this invention is to provide the sealing film for solar cells which has the outstanding transparency and the yellowing by the influence of heat was suppressed.

  The present invention relates to an ethylene-unsaturated ester copolymer, a crosslinking agent, and the following general formula (I):

(Wherein, R ¹ and R ^2, which may be the same or different and is a hydrogen atom or a methyl group, R ³ and R ^4, Ri ethylene der, R ⁵ and R ^6, methyl der is, and n and m represents an average molar number of addition of alkylene oxide, characterized in that it comprises a 2 ≦ n + m ≦ 20 is a number satisfying) di (meth) acrylate compound represented by The said subject is solved with the sealing film for solar cells.

  In this invention, the sealing film excellent in heat-resistant yellowing can be provided by using the di (meth) acrylate compound represented by the said general formula (I). Therefore, even if such a sealing film is used over a long period of time in an environment where the surface temperature of the solar cell is 70 ° C. or higher, such as in summer, yellowing is suppressed, and the appearance of the solar cell is poor. There is no risk of reducing power generation efficiency. Furthermore, the di (meth) acrylate compound inhibits crystallization of the ethylene-unsaturated ester copolymer that causes light scattering (decrease in transparency) during heating and pressurization in the sealing step of the solar cell, and is excellent. It is also possible to provide a sealing film having high transparency.

It is explanatory drawing of a solar cell.

  The sealing film for solar cells of this invention contains an ethylene-unsaturated ester copolymer, a crosslinking agent, and a Hiji (meth) acrylate compound. In the present invention, (meth) acrylate means acrylate or methacrylate.

  As the di (meth) acrylate compound, specifically, the following general formula (I)

(In the formula, R ¹ and R ² may be the same or different, and are a hydrogen atom or a methyl group, R ³ and R ⁴ are ethylene groups, and R ⁵ and R ⁶ are methyl. a group, and n and m represents an average molar number of addition of alkylene oxide, a compound represented by the number a is) satisfying 2 ≦ n + m ≦ 20 is used. R ³ and R ⁴ are ethylene groups because a sealing film excellent in heat-resistant yellowing can be obtained, and R ⁵ and R ⁶ can provide a sealing film having more excellent transparency and heat-resistant yellowing. Therefore, it is a methyl group.

R ¹ and R ² are a hydrogen atom or a methyl group. Especially, since the sealing film which has the more outstanding transparency and heat-resistant yellowing is obtained, a methyl group is preferable.

  m and n show the average addition mole number of alkylene oxide. m and n are each independently a positive number selected such that n + m is 2 to 20, preferably 2 to 10. When n + m exceeds 20, the above-described effects due to the di (meth) acrylate compound may not be sufficiently obtained. Preferably, m and n are each a positive number from 1 to 10, in particular from 1 to 5.

  The content of the di (meth) acrylate compound is preferably 0.05 to 3.0 parts by mass, particularly preferably 0.1 to 2.0 parts with respect to 100 parts by mass of the ethylene-unsaturated ester copolymer. If the content is less than 0.05 parts by mass, a sufficient effect of the di (meth) acrylate compound may not be obtained, and if it exceeds 3.0 parts by mass, the di (meth) acrylate compound can be finely dispersed. In addition, the transparency of the sealing film may be reduced.

  The sealing film of the present invention contains an ethylene-unsaturated ester copolymer in addition to the di (meth) acrylate compound. The unsaturated ester monomer of the ethylene-unsaturated ester copolymer includes methyl acrylate, ethyl acrylate, isobutyl acrylate, n-butyl acrylate, isooctyl acrylate, methyl methacrylate, isobutyl methacrylate, maleic acid Examples thereof include unsaturated carboxylic acid esters such as dimethyl and diethyl maleate, vinyl esters such as vinyl acetate and vinyl propionate, and the like. Among these, it is preferable to use an ethylene-vinyl acetate copolymer as the ethylene-unsaturated ester copolymer because a sealing film having excellent transparency can be obtained.

  The vinyl acetate content of the ethylene-vinyl acetate copolymer is preferably 20 to 35 parts by mass, more preferably 20 to 30 parts by mass, particularly preferably 24 to 100 parts by mass of the ethylene-vinyl acetate copolymer. 28 parts by mass. Thereby, the sealing film which has the outstanding transparency is obtained.

  The sealing film further contains an organic peroxide as a crosslinking agent. Any organic peroxide may be used as long as it decomposes at a temperature of 100 ° C. or higher and generates radicals. The organic peroxide is generally selected in consideration of the film formation temperature, the adjustment conditions of the composition, the curing temperature, the heat resistance of the adherend, and the storage stability. In particular, a decomposition temperature of a half-life of 10 hours is preferably 70 ° C. or higher, particularly 80 to 120 ° C.

  Examples of the organic peroxide include 2,5-dimethylhexane-2,5-dihydroperoxide; 2,5-dimethyl-2, from the viewpoint of compatibility with the ethylene-unsaturated ester copolymer. 5-di (tert-butylperoxy) hexane; 3-di-tert-butyl peroxide; tert-dicumyl peroxide; 2,5-dimethyl-2,5-bis (tert-butylperoxy) hexane; 2 , 5-dimethyl-2,5-di (tert-butylperoxy) hexyne; dicumyl peroxide; tert-butylcumyl peroxide; α, α'-bis (tert-butylperoxyisopropyl) benzene; α, α '-Bis (tert-butylperoxy) diisopropylbenzene; n-butyl-4,4-bis (tert-butylperoxy) Oxy) butane; 2,2-bis (tert-butylperoxy) butane; 1,1-bis (tert-butylperoxy) cyclohexane; 1,1-bis (tert-butylperoxy) 3, 3,5- Preferable examples include trimethylcyclohexane; tert-butyl peroxybenzoate; benzoyl peroxide. These may be used individually by 1 type, and 2 or more types may be mixed and used for them.

  Among the organic peroxides, 2,5-dimethyl-2,5-bis (tert-butylperoxy) hexane is used because a solar cell sealing film having excellent transparency can be obtained. Particularly preferred.

  The content of the organic peroxide in the sealing film is preferably 0.1 to 1.5 parts by mass, more preferably 0.1 to 1 part by mass with respect to 100 parts by mass of the ethylene-unsaturated ester copolymer. 0 parts by mass. By using the crosslinking agent in such an amount, the heat-resistant yellowing of the sealing film can be further improved.

  Furthermore, the sealing film may contain a crosslinking aid as necessary. The cross-linking aid can improve the gel fraction of the ethylene-unsaturated ester copolymer and improve heat-resistant yellowing.

  Examples of the crosslinking aid (compound having a radical polymerizable group as a functional group) include trifunctional crosslinking aids such as triallyl cyanurate and triallyl isocyanurate, and (meth) acrylic esters (eg, NK ester) ) Monofunctional or bifunctional crosslinking aids. Of these, triallyl cyanurate and triallyl isocyanurate are preferable, and triallyl isocyanurate is particularly preferable.

  The crosslinking aid is preferably used in an amount of 0.1 to 3.0 parts by mass, more preferably 0.1 to 2.5 parts by mass with respect to 100 parts by mass of the ethylene-unsaturated ester copolymer.

  The sealing film preferably has an excellent adhesive force in consideration of the sealing performance inside the solar cell. Therefore, the sealing film preferably further contains an adhesion improver.

  As the adhesion improver, a silane coupling agent can be used. Thereby, it becomes possible to form the sealing film for solar cells which has the outstanding adhesive force. Examples of the silane coupling agent include γ-chloropropylmethoxysilane, vinylethoxysilane, vinyltris (β-methoxyethoxy) silane, γ-methacryloxypropyltrimethoxysilane, vinyltriacetoxysilane, and γ-glycidoxypropyltrimethoxy. Silane, γ-glycidoxypropyltriethoxysilane, β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, vinyltrichlorosilane, γ-mercaptopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-β Mention may be made of-(aminoethyl) -γ-aminopropyltrimethoxysilane. These silane coupling agents may be used alone or in combination of two or more. Of these, γ-methacryloxypropyltrimethoxysilane is particularly preferred.

  The content of the silane coupling agent is preferably 0.1 to 0.7 parts by mass, more preferably 0.3 to 0.65 parts by mass with respect to 100 parts by mass of the ethylene-unsaturated ester copolymer. .

  The sealing film is a plasticizer or epoxy as necessary to improve or adjust various physical properties of the film (optical properties such as mechanical strength and transparency, heat resistance, light resistance, crosslinking speed, etc.). Various additives such as a group-containing compound may be further included.

  The plasticizer is not particularly limited, but polybasic acid esters and polyhydric alcohol esters are generally used. Examples thereof include dioctyl phthalate, dihexyl adipate, triethylene glycol-di-2-ethylbutyrate, butyl sebacate, tetraethylene glycol diheptanoate, and triethylene glycol dipelargonate. One type of plasticizer may be used, or two or more types may be used in combination. The content of the plasticizer is preferably in the range of 5 parts by mass or less with respect to 100 parts by mass of the ethylene-unsaturated ester copolymer.

Examples of the epoxy-containing compound include triglycidyl tris (2-hydroxyethyl) isocyanurate, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, allyl glycidyl ether, 2-ethylhexyl glycidyl ether, phenyl glycidyl ether, Examples include phenol (ethyleneoxy) ₅ glycidyl ether, pt-butylphenyl glycidyl ether, adipic acid diglycidyl ester, phthalic acid diglycidyl ester, glycidyl methacrylate, and butyl glycidyl ether.

  In general, the epoxy group-containing compound is preferably contained in an amount of 0.5 to 5.0 parts by weight, particularly 1.0 to 4.0 parts by weight, based on 100 parts by weight of the ethylene-unsaturated ester copolymer.

  Furthermore, the sealing film may contain an ultraviolet absorber, a light stabilizer and an anti-aging agent.

  By including the ultraviolet absorber in the sealing film, it is possible to prevent the ethylene-unsaturated ester copolymer from being deteriorated and yellowing due to the influence of irradiated light or the like. The ultraviolet absorber is not particularly limited, but 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-n-dodecyloxybenzophenone, 2,4-dihydroxybenzophenone, 2,2′-dihydroxy-4- Preferred examples include benzophenone-based ultraviolet absorbers such as methoxybenzophenone and 2-hydroxy-4-n-octoxybenzophenone. In addition, it is preferable that the compounding quantity of the said benzophenone series ultraviolet absorber is 0.01-5 mass parts with respect to 100 mass parts of ethylene-unsaturated ester copolymers.

  Even when the sealing film contains a light stabilizer, it is possible to suppress deterioration of the ethylene-unsaturated ester copolymer and yellowing of the solar battery sealing film due to the influence of irradiated light or the like. . As the light stabilizer, a light stabilizer called a hindered amine type is preferably used. For example, LA-52, LA-57, LA-62, LA-63LA-63p, LA-67, LA-68 (all ( ADEKA), Tinuvin 744, Tinuvin 770, Tinuvin 765, Tinuvin 144, Tinuvin 622LD, CHIMASORB 944LD (all manufactured by Ciba Specialty Chemicals), UV-3034 (BF Goodrich) Can be mentioned. In addition, the said light stabilizer may be used individually or may be used in combination of 2 or more types, and the compounding quantity is 0.01-5 mass with respect to 100 mass parts of ethylene-unsaturated ester copolymers. Part.

  Examples of the antioxidant include hindered phenol antioxidants such as N, N′-hexane-1,6-diylbis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionamide]. , Phosphorus heat stabilizers, lactone heat stabilizers, vitamin E heat stabilizers, sulfur heat stabilizers, and the like.

  What is necessary is just to carry out according to a well-known method in order to produce the sealing film of this invention. For example, it can be produced by a method for obtaining a sheet-like material by molding by ordinary extrusion molding, calendar molding (calendering) or the like. Alternatively, a sheet-like material can be obtained by dissolving the composition in a solvent and coating the solution on a suitable support with a suitable coating machine (coater) and drying to form a coating film. The heating temperature during film formation is preferably a temperature at which the crosslinking agent does not react or hardly reacts. For example, it is preferably 50 to 90 ° C, particularly 40 to 80 ° C. Thereafter, the sealing film for solar cell may be crosslinked and cured for sealing according to a conventional method such as heating and pressurization.

  Although the thickness in particular of the sealing film for solar cells is not restrict | limited, What is necessary is just the range of 50 micrometers-2 mm.

  The solar cell sealing film of the present invention has high total light transmittance and is excellent in transparency. Specifically, the total light transmittance of the solar cell sealing film after the gel fraction is cured to 80 to 95% is 80% or more, particularly 81% or more. Generally, in a solar cell, the sealing film is cured until the gel fraction is about 80 to 95% in order to seal the power generation element. The solar cell sealing film of the present invention has excellent transparency even after such curing. In the present invention, the total light beam means a light beam in the wavelength region of sunlight, and is usually a light beam having a wavelength in the range of 300 nm to 1200 nm.

  In addition, the sealing film for solar cells is excellent in heat-resistant yellowing, and even if it is installed over a long period of time in a high-temperature environment where the surface temperature of the solar cell is 70 ° C. or higher, it has excellent transparency. Can be maintained. Therefore, a solar cell using such a solar cell sealing film has a high transmittance of light incident from the outside, can be efficiently condensed on a power generation element, and exhibits a high output voltage over a long period of time. It becomes possible to do.

  The structure of the solar cell using the solar cell sealing film according to the present invention is not particularly limited, but the power generation element is interposed between the front surface side transparent protective member and the back surface side protective member via the solar cell sealing film. A structure in which is sealed. In the present invention, the light receiving surface side with respect to the power generation element is referred to as “front surface side”, and the surface opposite to the light receiving surface of the solar battery cell is referred to as “back surface side”.

  In the solar cell, in order to sufficiently seal the power generation element, as shown in FIG. 1, the front surface side transparent protective member 11, the front surface side sealing film 13A, the power generation element 14, the back surface side sealing film 13B, and the back surface side protection. The member 12 may be laminated and the sealing film may be cross-linked and cured according to a conventional method such as heat and pressure.

For the heating and pressurization, for example, the laminate is heated with a vacuum laminator at a temperature of 135 to 180 ° C., further 140 to 170 ° C., particularly 145 to 165 ° C., a degassing time of 0.1 to 7 minutes, and a press pressure of 0.1. What is necessary is just to heat-press in about 1.5 kg / cm < ² > and press time 5-15 minutes. By crosslinking the ethylene-unsaturated ester copolymer contained in the front-side sealing film 13A and the back-side sealing film 13B during the heating and pressurization, the front-side sealing film 13A and the back-side sealing film 13B are Thus, the power generation element 14 can be sealed by integrating the front surface side transparent protection member 11, the back surface side transparent member 12, and the power generation element 14.

  The surface side transparent protective member used for the solar cell of the present invention is usually a glass substrate such as silicate glass. As for the thickness of a glass substrate, 0.1-10 mm is common, and 0.3-5 mm is preferable. The glass substrate may generally be chemically or thermally strengthened.

  In addition, the back side protection member is a plastic film such as PET, but in consideration of heat resistance and moist heat resistance, a fluorinated polyethylene film or a plastic film surface on which a vapor deposition film made of silver is formed, particularly a fluorinated polyethylene film. A film in which / Al / fluorinated polyethylene films are laminated in this order is preferable.

  In addition, the solar cell of this invention has the characteristics in the sealing film used for the surface side and a back surface side as above-mentioned. Therefore, members other than the sealing film, such as the front-side transparent protective member, the back-side protective member, and the power generation element, are not particularly limited as long as they have the same configuration as a conventionally known solar cell.

  The present invention will be described below with reference to examples. The present invention is not limited by the following examples.

Example 1
Each material was supplied to a roll mill with the composition shown below and kneaded at 70 ° C. The obtained composition was calendered at 70 ° C, allowed to cool, and then a solar cell sealing film (thickness 1.0 mm) was formed. Obtained.

Sealing film composition:
EVA (vinyl acetate content 26 parts by mass with respect to EVA 100 parts by mass) 100 parts by mass,
1.2 parts by mass of a crosslinking agent (2,5-dimethyl-2,5-di (tert-butylperoxy) hexane),
1.5 parts by mass of a crosslinking aid (triallyl isocyanurate), and ethylene oxide (EO) modified bisphenol A di (meth) acrylate 1 (in formula (I), R ¹ and R ² are methyl groups, R ³ and R ⁴ is an ethylene group, R ⁵ and R ⁶ are methyl groups, m + n is 2.6; Light Ester BP-2EMK manufactured by Kyoei Chemical Co., Ltd.) 0.1 parts by mass.

(Examples 2 to 11)
As shown in Table 1, a solar cell sealing film was produced in the same manner as in Example 1 except that the type and / or addition amount of EO-modified bisphenol A di (meth) acrylate was changed. Details of the EO-modified bisphenol A di (meth) acrylates 2 to 5 are described below.

EO-modified bisphenol A di (meth) acrylate 2 (in formula (I), R ¹ and R ² are methyl groups, R ³ and R ⁴ are ethylene groups, R ⁵ and R ⁶ are methyl groups, m + n is 4; light ester BP-4EM manufactured by Kyoei Chemical Co., Ltd.)
EO-modified bisphenol A di (meth) acrylate 3 (in formula (I), R ¹ and R ² are methyl groups, R ³ and R ⁴ are ethylene groups, R ⁵ and R ⁶ are methyl groups, m + n is 6; light ester BP-6EM manufactured by Kyoei Chemical Co., Ltd.)
EO-modified bisphenol A di (meth) acrylate 4 (in formula (I), R ¹ and R ² are hydrogen atoms, R ³ and R ⁴ are ethylene groups, R ⁵ and R ⁶ are methyl groups, m + n is 4; light ester BP-4EA manufactured by Kyoei Chemical Co., Ltd.)
EO-modified bisphenol A di (meth) acrylate 5 (in formula (I), R ¹ and R ² are hydrogen atoms, R ³ and R ⁴ are ethylene groups, R ⁵ and R ⁶ are methyl groups, m + n is 4; light ester BP-10EA manufactured by Kyoei Chemical Co., Ltd.)

(Comparative Examples 1-5)
Instead of EO-modified bisphenol A di (meth) acrylate, as shown in Table 2, ethylene glycol dimethacrylate (Light Ester 9EG manufactured by Kyoei Chemical Co., Ltd.) or polyethylene glycol dimethacrylate (Ethylene oxide average added mole number: 14; light ester 14EG-A manufactured by Kyoei Chemical Co., Ltd.) was used in the same manner as in Example 1 to produce a solar cell sealing film.

(Evaluation)
1. Total light transmittance A solar cell sealing film is sandwiched between two glass substrates (thickness: 3.0 mm), and the resulting laminate is pressure-bonded at 100 ° C. for 10 minutes under vacuum with a vacuum laminator. The sealing film for solar cells was crosslinked and cured so as to have a gel fraction of 95% by mass by pressing in an oven at 0 ° C. for 45 minutes.

  Thereafter, the light transmittance spectrum in the thickness direction of the laminate was measured at three locations with a spectrophotometer (U-4000 manufactured by Hitachi, Ltd.), and the average value was calculated. . The results are shown in Tables 1 and 2.

  The gel fraction (mass%) was measured by weighing the solar cell sealing film after crosslinking (Ag), immersing it in xylene at 120 ° C. for 24 hours, and filtering the insoluble matter through a 200-mesh wire mesh. Then, the residue on the wire net is vacuum-dried, and the weight of the dry residue is measured (Bg), which is a value calculated by the formula [B / A × 100].

2. Yellowness A laminate having a crosslinked and cured sealing film was prepared in the same manner as described above, and was placed in a heat-resistant oven at 120 ° C. for 1500 hours. Thereafter, the yellowing degree (YI) of the laminate was measured using a color difference meter (SH color computer; manufactured by Suga Test Instruments Co., Ltd.) in accordance with JIS-K-7105-6 (1981). The results are shown in Tables 1 and 2.

  From the results shown in Table 1, it can be seen that the sealing films of Examples 1 to 11 are not only excellent in transparency but also suppressed yellowing even when installed in a high temperature environment for a long period of time.

11 Light-receiving surface side transparent protective member,
12 Back side protective material,
13A light-receiving surface side sealing film,
13B Back side sealing film,
14 Power generation element.

Claims (5)

Ethylene-unsaturated ester copolymer, crosslinking agent, and the following general formula (I)

(Wherein, R ¹ and R ^2, which may be the same or different and is a hydrogen atom or a methyl group, R ³ and R ^4, Ri ethylene der, R ⁵ and R ^6, methyl der is, and n and m represents an average molar number of addition of alkylene oxide, sealing a solar cell comprising a 2 ≦ n + m ≦ 20 is a number satisfying) di (meth) acrylate compound represented by film. The solar cell sealing film according to claim 1, wherein n and m are numbers satisfying 2 ≦ n + m ≦ 10. The content of the di (meth) acrylate compound, wherein the ethylene - the unsaturated ester copolymer 100 parts by weight, for a solar cell according to claim 1 or 2, 0.05 to 3.0 parts by weight Sealing film. The solar cell sealing film according to any one of claims 1 to 3 , wherein the ethylene-unsaturated ester copolymer is an ethylene-vinyl acetate copolymer. The solar cell using the sealing film for solar cells of any one of Claims 1-4 .

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