JP2015192123A - Seal-material sheet for solar battery modules, and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a seal-material sheet for solar battery modules, which is composed of a seal-material sheet primarily made of a polyethylene-based resin subjected to a crosslink processing by exposure to ionizing radiation, and which enables the effective utilization of ultraviolet light of UVA region, and is superior in durability against adhesion with glass.SOLUTION: A method for manufacturing a seal-material sheet for solar battery modules comprises: a sheet-forming step for melting and molding a seal-material composition including a base resin consisting of a polyethylene-based resin having a density of 0.870-0.940 g/cm, and not A-wave UV absorber, but a low-wavelength wave UV absorber having a maximum absorption wavelength in a wavelength region of 280-250 nm, of which the absorbance in a UVA wavelength region of 315-400 nm is 0 into an uncrosslinked seal-material sheet; and a crosslinking step for performing a crosslinking process on the uncrosslinked seal-material sheet by exposure to ionizing radiation to obtain a crosslinked seal-material sheet.

Description

  The present invention relates to a sealing material sheet for a solar cell module and a method for producing the same. More specifically, it is a sealing material sheet for a solar cell module mainly composed of a polyethylene-based resin that has been subjected to a crosslinking treatment by irradiation with ionizing radiation, and can be used to improve the power generation efficiency of the solar cell module. The present invention relates to a stopping material sheet and a manufacturing method thereof.

  In recent years, solar cells as a clean energy source have attracted attention due to the growing awareness of environmental issues. The solar cell module constituting the solar cell includes a solar cell element, and this solar cell element plays a role of converting light energy such as sunlight into electric energy.

  Solar cell elements are often manufactured using a single crystal silicon substrate or a polycrystalline silicon substrate. For this reason, the solar cell element is vulnerable to physical impact, and it is necessary to protect the solar cell element from rain when the solar cell module is mounted outdoors. Moreover, since the electrical output generated by one solar cell element is small, it is necessary to connect a plurality of solar cell elements in series and parallel so that a practical electrical output can be taken out. For this reason, a solar cell module is usually manufactured by connecting a plurality of solar cell elements and enclosing them with a transparent substrate and a sealing material layer. Generally, a solar cell module is manufactured by a lamination method or the like in which a transparent front substrate, a sealing material sheet, a solar cell element, a sealing material sheet, a back surface protection sheet, and the like are sequentially laminated, and these are vacuum-sucked and heat-pressed. .

  The sealing material sheet for solar cell modules usually contains an ultraviolet absorber for preventing deterioration of the resin due to ultraviolet rays. While this ultraviolet absorber prevents deterioration of the resin, it naturally absorbs ultraviolet rays in the UVA region from about 315 nm to about 400 nm that the solar cell element can use for power generation. For this reason, the sealing material sheet | seat for solar cell modules which does not contain the A wave ultraviolet absorber which absorbs the ultraviolet-ray of this UVA area | region was examined (refer patent document 1).

  However, in the case of a polyethylene-based encapsulant sheet mainly composed of a polyethylene-based resin, there is a separate problem that the adhesive strength to glass is reduced due to the deterioration of the resin simply by not including the A-wave ultraviolet absorber. For this reason, especially in the polyethylene-type sealing material sheet | seat for solar cell modules, the specification which can utilize the ultraviolet-ray of a UVA area | region effectively for electric power generation was desired.

  In response to this problem, a polyethylene resin contains a larger amount of light stabilizer (HALS) than before, and by limiting the molecular weight, ultraviolet rays in the UVA region can be used effectively, and glass and There has been proposed a polyethylene-based sealing material sheet that is also excellent in adhesive strength (Patent Document 2).

  On the other hand, in recent years, for polyethylene-based sealing material sheets, the demand for sealing material sheets subjected to crosslinking treatment by irradiation with ionizing radiation has been increasing. According to the cross-linking treatment by irradiation with ionizing radiation, it is possible to combine a polyethylene-based sealing material sheet with a high level of heat resistance and flexibility, and at the time of film formation and module integration. This is because it is also possible to improve productivity by being released from restrictions on temperature conditions (see Patent Documents 3 and 4).

US Pat. No. 6,093,757 JP 2013-65610 A JP 2011-77357 A JP2013-115212A

  However, as a result of research by the present inventors, in the polyethylene-based sealing material sheet subjected to the above-described crosslinking treatment by irradiation with ionizing radiation, an A-wave ultraviolet absorber is not included in pursuit of improvement in power generation efficiency. It was found that the problem cannot be solved by the means described in Patent Document 2. That is, in the polyethylene-based sealing material sheet subjected to the crosslinking treatment by irradiation with ionizing radiation, as in the manufacturing method of the sealing material sheet described in Patent Document 2, an A-wave ultraviolet absorber is not added, instead. When a general-purpose high molecular weight type light stabilizer (HALS) is added, in many cases, the problem of decrease in adhesion due to resin deterioration still occurs. According to the knowledge of the present inventors, this resin deterioration is formed due to the low molecular weight of the resin occurring at a depth of 1 to 2 μm from the surface of the encapsulant sheet and the accompanying decrease in mechanical strength. It is presumed to be due to cohesive failure resulting from the growth of lamellar crystals.

  In the encapsulant sheet for solar cell modules that are required to contribute to the improvement of power generation efficiency, it is especially a polyethylene encapsulant sheet that has undergone crosslinking treatment by irradiation with ionizing radiation, and is effective in the UVA region. The specifications that can be used for power generation were desired.

  The present invention has been made in view of the above situation, and is a polyethylene-based resin-based sealing material sheet subjected to crosslinking treatment by irradiation with ionizing radiation, and can effectively use ultraviolet rays in the UVA region, and Another object of the present invention is to provide a sealing material sheet for a solar cell module that is excellent in durability against adhesion to glass.

  As a result of intensive studies, the inventors of the present invention, in the production of a polyethylene-based sealing material sheet subjected to a crosslinking treatment by irradiation with ionizing radiation, in a sealing material composition having a polyethylene-based resin as a base resin, The inventors have found that the above problems can be solved by adding an ultraviolet absorber having a maximum absorption wavelength on the shorter wavelength side than the A-wave ultraviolet region to be added to the encapsulant composition, and the present invention has been completed. More specifically, the present invention provides the following.

(1) a density 0.870 g / cm ³ or more 0.940 g / cm ³ or less of the polyethylene resin as a base resin, does not contain A wave ultraviolet absorber having a maximum absorption wavelength from wavelength 280nm to 250nm region A sheet forming step of obtaining an uncrosslinked encapsulant sheet by melt-molding an encapsulant composition containing a low-wavelength ultraviolet absorber having an absorbance of 0 in the UVA region from 315 nm to 400 nm; A method for producing a sealing material sheet for a solar cell module, comprising: a crosslinking step of crosslinking the sealing material sheet by irradiation with ionizing radiation to obtain a crosslinked sealing material sheet.

  (2) The manufacturing method of the sealing material sheet as described in (1) whose said low wavelength wave ultraviolet absorber is a benzoate type ultraviolet absorber.

(3) A sealing material sheet for a solar cell module crosslinking treatment is performed by irradiation with ionizing radiation, the base resin consisting of a density 0.870 g / cm ³ or more 0.940 g / cm ³ or less of the polyethylene resin And a low-wavelength ultraviolet absorber having a maximum absorption wavelength in the wavelength range of 280 nm to 250 nm and an absorbance in the UVA range of 315 nm to 400 nm of 0, and containing no A-wave ultraviolet absorber .

  (4) The encapsulant sheet according to (3), wherein the light transmittance at a wavelength of 300 nm is 50% or more when measured at a thickness of 460 μm.

  (5) The encapsulant sheet according to (3) or (4), wherein the low wavelength wave ultraviolet absorber is a benzoate ultraviolet absorber.

  (6) The encapsulant sheet for a solar cell module according to any one of (3) to (5), wherein the polyethylene resin is a metallocene linear low-density polyethylene.

  (7) The polyethylene-based resin contains a silane copolymer obtained by copolymerizing at least an α-olefin and an ethylenically unsaturated silane compound as a comonomer, and any one of (3) to (6) A sealing material sheet for a solar cell module according to claim 1.

  (8) The sealing according to any one of (3) to (7), wherein a glass adhesion strength maintenance rate after a dump heat durability test (JIS C8917) under conditions of 85 ° C., 85%, and 1000 hours is 80% or more. Material sheet.

  (9) A solar cell module provided with the light-receiving surface side sealing material layer which consists of a sealing material sheet for solar cell modules in any one of (3) to (8).

  According to the present invention, it is a polyethylene resin-based sealing material sheet subjected to crosslinking treatment by irradiation with ionizing radiation, and can effectively use ultraviolet rays in the UVA region, and is excellent in adhesion strength with glass. A sealing material sheet for a solar cell module can be provided.

It is sectional drawing which shows an example of the laminated constitution of the solar cell module of this invention.

<Encapsulant composition>
The encapsulant composition for producing the encapsulant sheet for the solar cell module of the present invention (hereinafter also simply referred to as “encapsulant composition”) is a UVA that can contribute to improving the power generation efficiency of the solar cell module. It does not contain A-wave ultraviolet absorbers that cut off the ultraviolet rays in the region. Then, density of 0.870 g / cm ³ or more 0.940 g / cm ³ or less, preferably, the low-wavelength waves having a density of 870 g / cm ³ or more 0.900 g / cm ³ or less of the polyethylene resin, a predetermined absorbance characteristics It contains an ultraviolet absorber. In the present specification, an ultraviolet absorber having a maximum absorption wavelength in the wavelength range of 280 nm to 250 nm and having an absorbance of 0 in the UVA range of wavelengths 315 nm to 400 nm is referred to as “low wavelength wave ultraviolet absorber”. It shall be said.

  The encapsulant sheet for the solar cell module of the present invention is a single layer film made of this encapsulant composition or a multilayer sheet made by laminating a single layer film made of this encapsulant composition. When the encapsulant sheet for the solar cell module is a multilayer sheet, the encapsulant composition for forming each layer is a resin composition containing 90% or more of a polyethylene resin in the above density range. Those having different compositions and component ratios can be used for each layer.

[Polyethylene resin]
As the base resin, the density in the present invention is 0.870 g / cm ³ or more 0.940 g / cm ³ or less of the polyethylene resin, preferably, the density 0.900 g / cm ³ or less of low density polyethylene (LDPE), more preferably Uses linear low density polyethylene (LLDPE). The linear low density polyethylene is a copolymer of ethylene and α-olefin, and in the present invention, the density is 0.900 g / cm ³ or less, preferably 0.870 to 0.890 g / cm ³ . is there. If it is this range, favorable transparency and heat resistance can be provided, maintaining sheet workability.

  In the present invention, it is preferable to use a metallocene linear low density polyethylene. Metallocene linear low density polyethylene is synthesized using a metallocene catalyst which is a single site catalyst. Such polyethylene has few side chain branches and a uniform distribution of comonomer. For this reason, molecular weight distribution is narrow and it is possible to make it the above ultra-low density. In addition, since the crystallinity distribution is narrow and the crystal sizes are uniform, not only a large crystal size does not exist, but also the crystallinity itself is low due to the low density. For this reason, it is excellent in transparency when processed into a sheet shape. Therefore, even if the sealing material for solar cell modules comprising the sealing material composition of the present invention is disposed between the transparent front substrate and the solar cell element, the power generation efficiency hardly decreases.

  As the α-olefin of the linear low density polyethylene, an α-olefin having no branch is preferably used. Among these, 1-hexene and 1-heptene which are α-olefins having 6 to 8 carbon atoms are preferable. Or 1-octene is particularly preferably used. When the α-olefin has 6 to 8 carbon atoms, the solar cell module sealing material can be provided with good flexibility and good strength. As a result, the adhesiveness between the solar cell module sealing material and the base material is increased, and moisture can be prevented from entering between the solar cell module sealing material and the base material.

  The melt mass flow rate (MFR) of the polyethylene resin is preferably 1.0 g / 10 min or more and 40 g / 10 min or less at 190 ° C. and a load of 2.16 kg, preferably 2 g / 10 min or more and 40 g / 10 min or less. More preferably it is. When the MFR is in the above range, the processability during film formation is excellent. In addition, about MFR after the crosslinking process by irradiation of ionizing radiation, it is preferable that it is 0.1 g / 10min or more and 5.0 g / 10min or less.

Here, MFR in the present specification is a value obtained by the following method unless otherwise specified.
MFR (g / 10 min): Measured according to JIS K7210. Specifically, the synthetic resin was heated and pressurized at 190 ° C. in a cylindrical container heated by a heater, and the amount of resin extruded per 10 minutes from an opening (nozzle) provided at the bottom of the container was measured. . The test machine used was an extrusion plastometer, and the extrusion load was 2.16 kg.
In addition, about the sealing material sheet | seat which is a multilayer sheet, with the multilayer state in which all the layers were laminated | stacked integrally, the measurement by the said process was performed, and the obtained measured value was taken as the value of MFR of the said multilayer sealing material sheet | seat. did.

  The “polyethylene resin” in the present invention includes not only ordinary polyethylene obtained by polymerizing ethylene, but also a resin obtained by polymerizing a compound having an ethylenically unsaturated bond such as α-olefin. Examples include resins obtained by copolymerizing a plurality of different compounds having an ethylenically unsaturated bond, and modified resins obtained by grafting different chemical species to these resins.

  Among these, a silane copolymer obtained by copolymerizing at least an α-olefin and an ethylenically unsaturated silane compound as a comonomer can be preferably used. By using such a resin, adhesiveness between a member such as a transparent front substrate or a solar cell element and a solar cell module sealing material can be obtained. In particular, in a resin sheet having a polyethylene-based resin as a base resin like the encapsulant sheet of the present invention, it is possible to use a composition containing this silane copolymer rather than by external addition of a silane coupling agent. It is more effective in improving adhesion and adhesion durability.

  The silane copolymer is described in, for example, JP-A-2003-46105. By using the copolymer as a component of the solar cell module sealing material composition, it is excellent in strength, durability, etc., and weather resistance, heat resistance, water resistance, light resistance, wind pressure resistance, yield resistance In addition, it has excellent other characteristics, and has extremely excellent heat-sealability without being affected by manufacturing conditions such as thermocompression bonding for manufacturing solar cell modules. A solar cell module suitable for the above can be manufactured.

  The silane copolymer is a copolymer obtained by copolymerizing at least an α-olefin and an ethylenically unsaturated silane compound as a comonomer and, if necessary, further using another unsaturated monomer as a comonomer. The modified product or condensate is also included.

Specifically, for example, one or more of α-olefins, one or more of ethylenically unsaturated silane compounds, and, if necessary, one or more of other unsaturated monomers. Using a desired reaction vessel, for example, pressure 500-4000 Kg / cm ² position, preferably, 1000-4000 Kg / cm ² position, temperature 100-400 ° C., preferably 150-350 ° C. In the presence of a radical polymerization initiator and, if necessary, a chain transfer agent, random copolymerization is performed simultaneously or stepwise, and if necessary, a random copolymer formed by the copolymerization is formed. A silane compound portion can be modified or condensed to produce a copolymer of an α-olefin and an ethylenically unsaturated silane compound, or a modified or condensed product thereof.

  Examples of the copolymer of an α-olefin and an ethylenically unsaturated silane compound or a modified or condensate thereof include, for example, one or more α-olefins and, if necessary, other unsaturated monomers. One or two or more kinds are polymerized simultaneously or stepwise in the presence of a radical polymerization initiator and, if necessary, a chain transfer agent, using a desired reaction vessel, and then the polymerization. 1 to 2 or more types of ethylenically unsaturated silane compounds are graft-copolymerized to the polyolefin-based polymer produced by the above, and further, if necessary, a graft copolymer produced by the copolymer is constituted. A silane compound portion can be modified or condensed to produce a copolymer of an α-olefin and an ethylenically unsaturated silane compound or a modified or condensed product thereof. .

  Examples of the α-olefin include ethylene, propylene, 1-butene, isobutylene, 1-pentene, 2-methyl-1-butene, 3-methyl-1-butene, 1-hexene, 1-heptene, 1-octene, One or more selected from 1-nonene and 1-decene can be used.

  Examples of the ethylenically unsaturated silane compound include vinyl trimethoxy silane, vinyl triethoxy silane, vinyl tripropoxy silane, vinyl triisopropoxy silane, vinyl tributoxy silane, vinyl tripentyloxy silane, vinyl triphenoxy silane, vinyl tri One or more selected from benzyloxysilane, vinyltrimethylenedioxysilane, vinyltriethylenedioxysilane, vinylpropionyloxysilane, vinyltriacetoxysilane, and vinyltricarboxysilane can be used.

  As the other unsaturated monomer, for example, one or more selected from vinyl acetate, acrylic acid, methacrylic acid, methyl acrylate, methyl methacrylate, ethyl acrylate, and vinyl alcohol can be used.

  Examples of radical polymerization initiators include organic peroxides such as lauroyl peroxide, dipropionyl peroxide, benzoyl peroxide, di-t-butyl peroxide, t-butyl hydroperoxide, and t-butyl peroxyisobutyrate. Products, molecular oxygen, azo compounds such as azobisisobutyronitrile azoisobutylvaleronitrile, and the like can be used.

  Examples of the chain transfer agent include paraffinic hydrocarbons such as methane, ethane, propane, butane and pentane, α-olefins such as propylene, 1-butene and 1-hexene, and aldehydes such as formaldehyde, acetaldehyde and n-butyraldehyde. Further, ketones such as acetone, methyl ethyl ketone, and cyclohexanone, aromatic hydrocarbons, chlorinated hydrocarbons, and the like can be used.

  Examples of the method of modifying or condensing the silane compound portion constituting the random copolymer, or the method of modifying or condensing the silane compound portion constituting the graft copolymer include, for example, tin, zinc, iron, lead, Using α-olefin and ethylenically unsaturated silane using metal carboxylate such as cobalt, organometallic compound such as titanate and chelate, organic base, inorganic acid, silanol condensation catalyst such as organic acid, etc. Modification of copolymer of α-olefin and ethylenically unsaturated silane compound by performing dehydration condensation reaction between silanols of the silane compound part constituting the random copolymer or graft copolymer with the compound The method of manufacturing a condensate is mentioned.

  As the silane copolymer, any of a random copolymer, an alternating copolymer, a block copolymer, and a graft copolymer can be preferably used. However, the silane copolymer is more preferably a graft copolymer. A graft copolymer obtained by polymerizing polyethylene for polymerization as a main chain and an ethylenically unsaturated silane compound as a side chain is more preferable. Since such a graft copolymer has a high degree of freedom of silanol groups that contribute to the adhesive force, the adhesion of the solar cell module sealing material to other members in the solar cell module can be improved.

  The content of the ethylenically unsaturated silane compound when constituting the copolymer of the α-olefin and the ethylenically unsaturated silane compound is, for example, about 0.001 to 15% by mass relative to the total copolymer mass. Preferably, about 0.01 to 5 mass%, particularly preferably about 0.05 to 2 mass% is desirable. In the present invention, when the content of the ethylenically unsaturated silane compound constituting the copolymer of the α-olefin and the ethylenically unsaturated silane compound is large, the mechanical strength and heat resistance are excellent, but the content is excessive. When it becomes, it exists in the tendency which is inferior to tensile elongation, heat-fusibility, etc.

Content of said polyethylene-type resin contained in a sealing material composition should just be 90 mass% or more in a sealing material composition, and it is preferable that it is 99.9% or more. Within that range, other resins may be included. Examples of other resins include other polyethylene resins exceeding 0.940 g / cm ³ . These may be used, for example, as an additive resin, and can be used for masterbatching other components described later.

[Ultraviolet absorber]
The sealing material composition according to the present invention does not contain an A-wave ultraviolet absorber. Here, the A-wave ultraviolet absorber is an ultraviolet absorber that absorbs ultraviolet rays in the UVA region in the vicinity of 315 nm to 400 nm. By not incorporating the A-wave ultraviolet absorber, the ultraviolet rays in the UVA region can be effectively used. The surface can be irradiated and the power generation efficiency can be improved. The A-wave ultraviolet absorber can be an organic ultraviolet absorber and is not particularly limited. For example, benzophenone-based ultraviolet absorbers represented by KEMISORB 12 (manufactured by Chemipro Chemical Co., Ltd.) and CHIMASORB 81 (manufactured by BASF) can be exemplified. In addition, even if the trace amount ultraviolet absorber of the grade which does not show an A wave ultraviolet-ray absorption effect is contained in an impurity, it is in the scope of the present invention. The trace amount is, for example, less than 0.01% by mass in the composition.

  The sealing material composition according to the present invention has an ultraviolet absorber having a maximum absorption wavelength in a wavelength range of 280 nm to 250 nm and an absorbance of 0 in a UVA range of wavelengths 315 nm to 400 nm, that is, low wavelength wave ultraviolet absorption. Contains agents. Usually, ultraviolet rays in a wavelength region lower than the UVA region can be sufficiently cut by the transparent glass laminated on the light receiving surface side in a general solar cell module configuration. Therefore, basically, it is not always required to provide the sealing material sheet for a solar cell module with the physical property of cutting ultraviolet rays in this wavelength band. However, surprisingly, as will be shown later in the Examples, ionizing radiation is intentionally added by adding a low-wavelength ultraviolet absorber having such an absorbance property that cuts ultraviolet rays in the low-wavelength band to the encapsulant composition. The present inventors have found that the above-described decrease in adhesiveness can be sufficiently suppressed even in a sealing material sheet obtained by performing a crosslinking treatment by irradiation. This is because such a low-wavelength ultraviolet absorber has a previously unknown action different from the original action of ultraviolet absorption, i.e., any adhesion improving component in the sealing material composition is destroyed by irradiation with ionizing radiation. This is considered to be due to the fact that it can also exert the action of suppressing the phenomenon. On the other hand, since this low-wavelength ultraviolet absorber does not cut the rays in the UVA region that can contribute to the improvement of power generation efficiency of the solar cell module, by using this, the adhesion as a sealing material sheet can be improved. It can contribute to the improvement of the power generation efficiency of the solar cell module while being held.

  As such a low wavelength wave ultraviolet absorber, for example, 2,4-di-tert-butylphenyl-3,5-di-tert-butyl-4-hydroxybenzoate (TINUVIN120 (manufactured by BASF) A benzoate-based ultraviolet absorber represented by ()) is commercially available and can be exemplified as a specific example of an ultraviolet absorber that can be preferably used.

  The content of the low-wavelength ultraviolet absorber in the sealing material composition is 0.10% by mass to 0.40% by mass, preferably 0.20% by mass to 0.30% by mass. is there. If it is less than 0.10% by mass, the glass adhesion strength is lowered, which is not preferable, and if it exceeds 0.40% by mass, bleeding out occurs, which is not preferable because the glass adhesion strength is reduced.

[Light stabilizer (HALS)]
It is preferable that the sealing material composition according to the present invention further contains a high molecular weight type hindered amine light stabilizer (HALS) having a molecular weight of 2000 or more. Specific examples of the high molecular weight type HALS that can be preferably used in the sealing material composition according to the present invention include KEMISTAB 62 (softening point 50 to 70 ° C., molecular weight 3100 to 4000). The content of the high molecular weight type HALS is 0.1% by mass or more and 0.5% by mass or less, and preferably 0.20% by mass or more and 0.30% by mass or less in the sealing material composition. If it is less than 0.1% by mass, the glass adhesion strength decreases, which is not preferable. On the other hand, if it exceeds 0.5% by mass, HALS bleed out may occur.

[Other additives]
In any of the sealing material compositions, the following additives can be appropriately contained as necessary.

(Crosslinking agent)
The sealing material composition may contain a necessary minimum amount of a crosslinking agent, but more preferably does not contain a crosslinking agent. By adding a crosslinking aid described later, adequate crosslinking can proceed sufficiently. On the other hand, when a crosslinking agent such as an organic peroxide is added separately, for integration with the solar cell module. This is because there is an increased risk of problems such as foaming due to degas during the heat laminating process. When adding a crosslinking agent in a suitable amount range, a well-known thing can be used and it does not specifically limit, For example, a well-known radical polymerization initiator can be used.

  When the crosslinking agent is added, the content is preferably 0 part by mass or more and 0.5 parts by mass or less with respect to 100 parts by mass in total of all the resin components in the encapsulant composition. More preferably, it is in the range of 0.02 parts by mass or more and 0.5 parts by mass or less. When the addition amount of the cross-linking agent exceeds 0.5 parts by mass, the progress of cross-linking in the cross-linking step becomes excessive, and molding characteristics become insufficient, which is not preferable.

(Crosslinking aid)
In addition to the base resin, it is preferable that the sealing material composition contains a crosslinking aid. As a crosslinking aid, a polyfunctional monomer having a carbon-carbon double bond and / or an epoxy group can be preferably used. More preferably, the cross-linking aid is one in which the functional group of the polyfunctional monomer is an allyl group, a (meth) acrylate group, or a vinyl group. By adding such a crosslinking aid, the crystallinity of the low density polyethylene can be reduced, and a crosslinked encapsulant sheet excellent in low temperature flexibility can be obtained.

  Specifically, polyallyl compounds such as triallyl isocyanurate (TAIC), triallyl cyanurate, diallyl phthalate, diallyl fumarate, diallyl maleate, trimethylolpropane trimethacrylate (TMPT), trimethylolpropane triacrylate (TMPTA) , Ethylene glycol diacrylate, ethylene glycol dimethacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, 1,9-nonanediol diacrylate, tricyclodecane dimethanol diacrylate, etc. ) An acryloxy compound, a glycidyl methacrylate containing a double bond and an epoxy group, 4-hydroxybutyl acrylate glycidyl ether and 1, containing two or more epoxy groups - hexanediol diglycidyl ether, and 1,4-butanediol diglycidyl ether, cyclohexanedimethanol diglycidyl ether, an epoxy-based compounds such as trimethylolpropane polyglycidyl ether. These may be used alone or in combination of two or more.

(Adhesion improver)
In any of the encapsulant compositions according to the present invention, adhesion durability with other base materials can be further increased by appropriately adding an adhesion improver. As the adhesion improver, a known silane coupling agent can be used. The silane coupling agent is not particularly limited. For example, vinyl-based silane coupling agents such as vinyltrichlorosilane, vinyltrimethoxysilane, and vinyltriethoxysilane, 3-methacryloxypropyltrimethoxysilane, and 3-methacryloxypropyldiethoxy. A methacryloxy-based silane coupling agent such as silane or 3-methacryloxypropyltriethoxysilane can be preferably used. In addition, these can also be used individually or in mixture of 2 or more types.

  When adding a silane coupling agent as an adhesion improver, the content is 0.1 parts by mass or more and 10.0 parts by mass or less with respect to 100 parts by mass in total of all resin components of the sealing material composition. Yes, and the upper limit is preferably 5.0 parts by mass or less. When the content of the silane coupling agent is in the above range, and the polyolefin resin constituting the encapsulant composition contains an appropriate amount of the ethylenically unsaturated silane compound, the adhesion is more preferable. And improve. In addition, when it exceeds this range, the film-forming property is deteriorated, or so-called bleed-out in which the silane coupling agent aggregates and solidifies with time and is pulverized on the surface of the sealing material sheet is not preferable.

  Furthermore, as other components used in the encapsulant composition, in addition to the above, radical absorbents such as antioxidants for further fine-tuning the degree of crosslinking, and in addition, nucleating agents, dispersing agents, leveling agents, A plasticizer, an antifoamer, a flame retardant, etc. can be mentioned.

<Sealing material sheet>
The encapsulant sheet for the solar cell module of the present invention (hereinafter also simply referred to as “encapsulant sheet”) is obtained by molding the above encapsulant composition by a conventionally known method. A single layer or multilayer sheet or film. In addition, the sheet form in this invention means the film form, and there is no difference in both.

  The sealing material sheet is formed into a sheet by various molding methods such as injection molding, extrusion molding, hollow molding, compression molding, and rotational molding, which are usually used in ordinary thermoplastic resins. In addition, as an example of the sheet forming method when the encapsulant sheet is a multilayer sheet, a method of forming by co-extrusion using two or more types of melt-kneading extruders can be given.

  The encapsulant sheet preferably has a gel fraction of 0% at the intermediate stage when it is formed into a sheet from the encapsulant composition. Further, the gel fraction in the finished product stage at the time when it is completed as a sealing material sheet through crosslinking treatment by irradiation with ionizing radiation is 25% or less, preferably 10% or less, more preferably 0%. Including 1% or less. Further, the encapsulant sheet may be of a type in which cross-linking further proceeds during thermal lamination treatment for integration as a solar cell module. In that case, it is preferable that the gel fraction of the sealing material sheet after integration as an integrated solar cell module is about 30% to 80%.

  Here, the gel fraction (%) means that 0.1 g of a sealing material sheet is put in a resin mesh, extracted with 60 ° C. toluene for 4 hours, taken out together with the resin mesh, weighed after drying, and mass before and after extraction. Comparison is made and the mass% of the remaining insoluble matter is measured, and this is used as the gel fraction.

  When the encapsulant sheet is a multi-layer sheet, it is more preferable to use an encapsulant sheet in which MFR, gel fraction, molecular weight, etc. are separately optimized for each layer. As will be described later, in the solar cell module, the sealing material sheet is generally used with one surface being in close contact with the electrode surface of the solar cell element. In that case, the encapsulant sheet is required to have high adhesion regardless of the unevenness of the electrode surface. Even when the encapsulant sheet of the present invention is a single-layer encapsulant sheet, the encapsulant sheet has preferable adhesion. It is more preferable that it is excellent in molding characteristics. For example, by disposing a layer having a high MFR in the outermost layer on the side to be used in close contact with the electrode surface of the solar cell element, while maintaining preferable heat resistance and the like as a sealing material sheet for a solar cell module, The molding characteristics in the contact surface with the battery element can be further enhanced.

  For example, in the encapsulant sheet that is a multilayer sheet composed of three or more layers, the thickness of the outermost layer is 30 μm or more and 120 μm or less, and the intermediate layer and the outermost layer composed of all layers other than the outermost layer The thickness ratio is preferably in the range of outermost layer: intermediate layer: outermost layer = 1: 3: 1 to 1: 8: 1. By doing in this way, while maintaining the preferable heat resistance as a sealing material, the preferable molding characteristic in an outermost layer can be provided, and also manufacturing cost can be suppressed low.

  And when the light transmittance of the sealing material sheet of this invention is measured by thickness 450 micrometers, it is preferable that the light transmittance in wavelength 300nm is 50% or more. Thereby, it can contribute significantly to the power generation efficiency improvement of a solar cell module by the effective utilization of the light ray of a UVA area | region. The light transmittance is a value measured with a conventionally known spectrophotometer. Here, as for the power generation efficiency of the solar cell module, a fierce development competition of about 0.1% unit is performed all over the world, for example, by comparing Pmax values. As will be shown later in the examples, the improvement rate of the power generation efficiency of the solar cell module by the use of the sealing material sheet of the present invention reaches about + 2% in terms of the Pmax value. It leads to improvement.

  Moreover, the sealing material sheet of the present invention is characterized in that the glass adhesion, particularly the maintenance rate of the glass adhesion strength, is extremely excellent. Specifically, the glass adhesion strength maintenance rate after a dump heat durability test (JIS C8917) under the conditions of 85 ° C., 85%, and 1000 hours is 80% or more. In the present specification, the “glass adhesion strength maintenance ratio” specifically refers to the adhesion strength maintenance ratio that can be obtained by the test method described in <Evaluation Example 2> in the following Examples.

<Method for producing sealing material sheet>
The sealing material sheet of the present invention can be manufactured by a manufacturing method including at least a sheet forming step and a crosslinking step described below using the above-described sealing material composition having a unique composition according to the present invention. it can.

[Sheet making process]
The melt molding of each composition for the intermediate layer and the outermost layer, each of which has been described in detail above, is a molding method usually used in ordinary thermoplastic resins, that is, injection molding, extrusion molding, hollow molding, compression molding, It is performed by various molding methods such as rotational molding. As an example of the forming method as the multilayer sheet, a method of forming by co-extrusion with two or more melt-kneading extruders can be given.

  The lower limit of the molding temperature during molding may be any temperature that exceeds the melting point of the encapsulant composition. The upper limit of the molding temperature is the temperature at which crosslinking does not start during film formation, that is, the temperature at which the gel fraction of the encapsulant composition can be maintained at 0%, depending on the 1 minute half-life temperature of the crosslinking agent used. Good. Here, in the method for producing a sealing material sheet of the present invention, a crosslinking agent is not essential in the sealing material composition, and even when a crosslinking agent is added, its content is less than 0.5% by mass. It is limited to. For this reason, under a normal low density polyethylene resin molding temperature, for example, a heating condition of about 120 ° C., the gel fraction does not change, and the crosslinking that substantially affects the physical properties of the resin does not proceed. In addition, as described above, it is possible to use a cross-linking agent having a half-life temperature higher than that of the conventional one by solving from the limitation of the heating conditions in the modularization process. Therefore, even if the molding temperature is set higher than before, the gel fraction of the encapsulant composition can be maintained at 0%. According to the production method of the present invention that maintains the gel fraction of the encapsulant composition during film formation at 0%, the load on the extruder and the like during film formation is reduced, and the productivity of the encapsulant sheet is increased. It is possible.

[Crosslinking process]
A cross-linking step of performing a cross-linking process by ionizing radiation on the uncross-linked encapsulant sheet after the sheet forming step is integrated with the other members after the completion of the sheet forming step. Performed before the start of the solar cell module integration step. By this crosslinking treatment, the gel fraction of the encapsulant sheet is 0% or more and 25% or less, preferably 10% or less, more preferably 1% or less including 0%. The cross-linking treatment may be performed continuously in-line following the sheet forming step, or may be performed off-line.

  Regarding the crosslinking treatment by irradiation with ionizing radiation, the individual crosslinking conditions are not particularly limited. What is necessary is just to set suitably so that the gel fraction of the sealing material sheet | seat after bridge | crosslinking processing may become a desired range according to the density of a base resin, sheet thickness, and other conditions. Specifically, the crosslinking treatment can be performed by ionizing radiation such as electron beam (EB), α-ray, β-ray, γ-ray, neutron beam, etc. Among them, it is preferable to use an electron beam. Further, the ionizing radiation may be irradiated from either one side or both sides.

  When ionizing radiation is applied by single-sided irradiation, the acceleration voltage is determined by the thickness of the sheet that is the object to be irradiated, and a thicker sheet requires a larger acceleration voltage. For example, in the case of a sheet having a thickness of 0.6 mm, irradiation is performed at 200 kV to 1000 kV, preferably 250 kV to 1000 kV. When the acceleration voltage is less than 200 kV, electrons do not pass through to the outermost layer on the non-irradiated surface side, and the heat resistance of the encapsulant sheet becomes insufficient. The irradiation dose is in the range of 5 kGy to 800 kGy, preferably 10 kGy to 50 kGy. Irradiation may be in an air atmosphere or a nitrogen atmosphere.

  This crosslinking treatment may be performed continuously in-line following the sheet forming step, or may be performed off-line. Further, when the crosslinking treatment is a general heat treatment, generally, the content of the crosslinking agent is 0.5 parts by mass or more and 1.5 parts by mass or less with respect to 100 parts by mass of all components of the sealing material sheet. However, in the sealing material sheet of the present invention, the content of the crosslinking agent may be 0, and even if it is contained, it is preferably less than 0.5 parts by mass. Thereby, the risk of the productivity fall by gelatinization of the sealing material composition in the sheeting process of a sealing material composition can be reduced.

<Solar cell module>
Next, an example of the solar cell module of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing an example of the layer structure of the solar cell module of the present invention. In the solar cell module 1 of the present invention, a transparent front substrate 2, a front sealing material layer 3, a solar cell element 4, a back sealing material layer 5, and a back surface protection sheet 6 are sequentially laminated from the incident light receiving surface side. ing. The solar cell module 1 of the present invention uses the encapsulant sheet of the present invention as the front encapsulant layer 3 serving as at least the light-receiving surface side encapsulant layer. In addition, about the back surface sealing material layer 5, although the sealing material sheet of this invention can also be used, you may use the white sealing material sheet etc. which have reflection performance, for example. Further, in the case of a double-sided lighting type module, the sealing material sheet of the present invention can be preferably used for both the front sealing material layer 3 and the back sealing material layer 5.

  The solar cell module 1 includes, for example, the transparent front substrate 2, the encapsulant sheet that forms the front encapsulant layer 3, the encapsulant sheet that forms the solar cell element 4, the back encapsulant layer 5, and the back surface. The members made of the protective sheet 6 can be sequentially laminated and then integrated by vacuum suction or the like, and then the above-mentioned members can be manufactured by thermocompression forming as an integrally formed body by a molding method such as a lamination method.

  Further, the solar cell module 1 is formed on the front side and the back side of the solar cell element 4 by a molding method usually used in ordinary thermoplastic resins, for example, T-die extrusion molding. In order to form the back surface sealing material layer 5, the sealing material composition according to the present invention is melt-laminated, the solar cell element 4 is sanded, and then the transparent front substrate 2 and the back surface protective sheet 6 are sequentially laminated, Then, they may be manufactured by a method in which these are integrated by vacuum suction or the like and heat-pressed.

  In the solar cell module 1 of the present invention, the transparent front substrate 2, the solar cell element 4 and the back surface protection sheet 6 which are members other than the front sealing material layer 3 and the back sealing material layer 5 are made of conventionally known materials. It can be used without particular limitation. Moreover, the solar cell module 1 of this invention may also contain members other than the said member. The sealing material sheet of the present invention is not limited to a general single crystal type solar cell element, but includes all other solar cell elements such as a thin film type solar electronic element or a back contact type solar electronic element. It can be used for a solar cell module to be mounted.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited to a following example.

<Manufacture of sealing material for solar cell module>
Using the sealing material composition having the composition (unit mass part) shown in Table 1, the sealing material sheets of Examples and Comparative Examples were molded. First, the sealing material composition was formed into a sheet at an extrusion temperature of 210 ° C. and a take-off speed of 1.5 m / min using a φ30 mm extruder and a film molding machine having a 200-mm width T die, respectively. The layer thickness of these resin sheets was 450 μm.

The following raw materials were used as the sealing material composition raw material.
Base resin: Metallocene linear low density polyethylene (M-LLDPE) having a density of 0.880 g / cm ³ , a melting point of 60 ° C., and an MFR at 190 ° C. of 3.5 g / 10 min. 85 parts by mass of this base resin was added to the encapsulant composition used for molding the encapsulant sheets of all Examples and Comparative Examples.
Silane-modified polyethylene resin: 100 parts by mass of a metallocene linear low density polyethylene having a density of 0.880 g / cm ³ and an MFR of 20 g / 10 min, 2 parts by mass of vinyltrimethoxysilane, and a radical generator ( Silane-modified polyethylene resin obtained by mixing 0.15 parts by mass of dicumyl peroxide as a reaction catalyst), melting and kneading at 200 ° C. Density 0.880 g / cm ³ , MFR 1.0 g / 10 min. Melting point 60 ° C. 15 parts by mass of this silane-modified polyethylene resin was added to the encapsulant compositions used for molding the encapsulant sheets of all Examples and Comparative Examples.
Low wavelength ultraviolet absorber (indicated as “UVL” in Table 1, the same applies hereinafter): TINUVIN 120, maximum absorption wavelength 270 nm
A wave ultraviolet absorber 1 ("UVA1"): KEMISORB12
A wave ultraviolet absorber 2 ("UVA2"): KEMISORB 79
Hindered amine light stabilizer: KEMISTAB62, molecular weight 3100-4000, softening point 50-70 ° C. 0.2 parts by mass of this hindered amine light stabilizer was added to the encapsulant composition used for molding the encapsulant sheets of all Examples and Comparative Examples.

  In addition, the light absorbency in the wavelength 240nm -420nm area | region of said low wavelength wave ultraviolet absorber (UVL) (TINUVIN120) used for the Example was computed from the change of the spectral transmittance. The results are shown in Table 2. Each spectral transmittance was measured using a spectrophotometer (manufactured by Shimadzu Corporation: UV-3600).

  Next, using the electron beam irradiation apparatus (product name EC250 / 15 / 180L, manufactured by Iwasaki Electric Co., Ltd.) on the molded sealing material sheets of Examples and Comparative Examples 1 and 2, an acceleration voltage of 200 kV, irradiation intensity Was irradiated with ionizing radiation from both sides at 50 kGy to obtain a crosslinked encapsulant sheet.

<Evaluation Example 1: Spectral transmittance and power generation efficiency>
About the sealing material sheet | seat of an Example and Comparative Examples 1-2, the spectral transmittance in wavelength 200nm, 300nm, and 400nm was measured using the spectrophotometer (Shimadzu Corp. make: UV-3600), respectively.
Moreover, the solar cell module sample for power generation efficiency evaluation was formed using the sealing material sheet | seat of an Example and Comparative Examples 1-2, and the power generation efficiency was measured (calculated) with the following method about each sample. The results are shown in Table 1.
(Solar cell module power generation efficiency test)
A polycrystalline solar cell element of 5 × 5 inch size is formed on a 150 mm square semi-tempered glass, and any one of the sealing material sheets of Examples and Comparative Examples 1 and 2 is further formed on the polycrystalline solar cell element of 150 mm × 150 mm. In this order, the one cut into 150 mm square and the semi-tempered glass of 150 mm square are laminated in this order and pressure-bonded at 150 ° C. for 15 minutes with a vacuum laminator for manufacturing a solar cell module. No. 2 solar cell module samples for power generation efficiency evaluation were used. At this time, sealing with an edge seal or the like was not performed. Then, the Pmax values of these samples were measured, and the relative values when the Pmax value of Comparative Example 2 containing a UVA ultraviolet absorber, which is a sample corresponding to the general mode of the conventional product, was 100%. Was calculated. The Pmax value is the maximum output value at the operating point at which the output of the solar cell is maximum, and the power generation output of the module before and after the environmental test was measured based on JIS-C8935-1995. The results are shown in Table 1.

<Evaluation Example 2: Glass adhesion>
About the sealing material sheet | seat of an Example and Comparative Examples 1-2, glass adhesive strength was evaluated with the following measuring method.
First, each sealing material sheet of Examples and Comparative Examples is brought into close contact with a glass substrate (white plate semi-tempered glass JPT3.2 75 mm × 50 mm × 3.2 mm), and vacuum heating laminator treatment is performed at 150 ° C. for 16 minutes. A sample for evaluation of adhesion was prepared. And in this sample for adhesion evaluation, the sealing material sheet | seat closely_contact | adhered on a glass substrate is cut into 15 mm width, and vertical peeling (50 mm / mm) with a peeling tester (Tensilon universal testing machine RTF-1150-H). min) A test was conducted to measure the glass adhesion strength. The measurement results are shown in Table 1 as “initial adhesion strength”.
Next, the glass adhesion strength maintenance rate after the following dump heat (DH) test was measured for each of the above samples for adhesion evaluation. D. H. The test was based on JIS C8917, and the durability test of the sample for evaluation was performed for 1000 hours under the conditions of 85 ° C. in the test tank and 85% humidity. About the sample for adhesiveness evaluation after a test, the glass adhesive strength was measured again by the same test method as the above, and the maintenance rate (%) of the adhesive strength with respect to the initial glass adhesive strength was calculated. The results are shown in Table 1 as “adhesion strength maintenance ratio”.

  As can be seen from Tables 1 and 2, the examples of the present invention have a high glass adhesion strength maintenance rate and transmit more than 50% of ultraviolet rays at 300 nm in the UVA region, and effectively use ultraviolet rays in the UVA region. As a result, it can be understood that the power generation efficiency is also significantly improved.

DESCRIPTION OF SYMBOLS 1 Solar cell module 2 Transparent front substrate 3 Front sealing material layer (light-receiving surface side sealing material layer)
4 Solar cell element 5 Back surface sealing material layer 6 Back surface protection sheet

Claims (9)

Density 0.870 g / cm ³ or more 0.940 g / cm ³ or less of the polyethylene resin as a base resin, does not contain A wave ultraviolet absorber, a wavelength 315nm has a maximum absorption wavelength from wavelength 280nm to 250nm region A sheet forming step of obtaining a non-crosslinked encapsulant sheet by melt-molding an encapsulant composition containing a low-wavelength ultraviolet absorber having an absorbance in the UVA region of 400 nm of 0;
A crosslinking process for crosslinking the uncrosslinked encapsulant sheet by irradiation with ionizing radiation to obtain a crosslinked encapsulant sheet, and a method for producing a encapsulant sheet for a solar cell module.   The method for producing a sealing material sheet according to claim 1, wherein the low-wavelength ultraviolet absorber is a benzoate-based ultraviolet absorber. A solar cell module sealing material sheet that has been subjected to crosslinking treatment by irradiation with ionizing radiation,
In a base resin consisting of a density 0.870 g / cm ³ or more 0.940 g / cm ³ or less of the polyethylene resin, the absorbance at UVA region of 400nm wavelength 315nm has a maximum absorption wavelength from wavelength 280nm to 250nm region is 0 A sealing material sheet that contains a certain low-wavelength ultraviolet absorber and does not contain an A-wave ultraviolet absorber.   The encapsulant sheet according to claim 3, wherein the light transmittance at a wavelength of 300 nm is 50% or more when measured at a thickness of 460 µm.   The encapsulant sheet according to claim 3 or 4, wherein the low-wavelength ultraviolet absorber is a benzoate ultraviolet absorber.   The encapsulant sheet for a solar cell module according to any one of claims 3 to 5, wherein the polyethylene resin is a metallocene linear low density polyethylene.   The sun according to any one of claims 3 to 6, wherein the polyethylene resin contains a silane copolymer obtained by copolymerizing at least an α-olefin and an ethylenically unsaturated silane compound as a comonomer. Sealant sheet for battery module.   The encapsulant sheet according to any one of claims 3 to 7, wherein a glass adhesion strength maintenance ratio after a dump heat durability test (JIS C8917) under conditions of 85 ° C, 85%, and 1000 hours is 80% or more.   A solar cell module provided with the light-receiving surface side sealing material layer which consists of a sealing material sheet for solar cell modules in any one of Claim 3 to 8.

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