JP6314396B2 - Sealant sheet for solar cell module - Google Patents

Description

  The present invention relates to a sealing material sheet for a solar cell module.

  The solar cell module is always exposed to a harsh environment such as strong ultraviolet rays, heat rays, wind and rain, etc. for a long period of time. For this reason, a high degree of weather resistance and durability are calculated | required by the solar cell module. Therefore, high adhesion is required between the members constituting the solar cell module.

  As a sealing material sheet filled in the solar cell module and used to protect the solar cell element from external impacts and prevent moisture from entering the solar cell module, ethylene-vinyl acetate copolymer Combined resins (EVA) have been used as the most common. However, in recent years, as a solution to the problem of deterioration of water vapor barrier properties in long-term use, which is a drawback of EVA resin, sealing for solar cell modules using low-density polyethylene resin instead of EVA resin Material sheets have been proposed.

  However, since polyethylene resin does not have a polar group in the main chain like EVA, for example, it has adhesion to a base material that is a constituent member of a solar cell module, such as glass that is a material of a transparent front substrate of a solar cell module. There was a problem of being insufficient.

  Conventionally, a silane coupling agent has been widely used as an adhesion improving component added to the sealing material composition in order to improve the adhesiveness of the sealing material sheet. In recent years, there has also been proposed a sealing material sheet in which the adhesion between a metal or glass constituting each member of a solar cell module is improved by adding a specific silane coupling agent (Patent Document 1). reference).

  Further, a sealing sheet that is a multilayer sheet in which thermoplastic resin sheets are laminated and is manufactured by adding a silane coupling agent only to a surface layer that contributes to adhesion has also been proposed (see Patent Document 2).

  In addition, a silane-modified polyethylene resin (hereinafter also simply referred to as “silane-modified polyethylene resin”) obtained by graft-polymerizing an ethylenically unsaturated silane compound on linear low density polyethylene in advance is a part of the raw material of the sealing material composition. As a sealing material sheet for a solar cell module with improved adhesion to a glass substrate or the like has been proposed (see Patent Document 3).

  Also, a thermoplastic encapsulant sheet has been proposed in which transparency and flexibility are improved in a balanced manner by using a combination of a plurality of low density polyethylene resins in a specific density range (patent) Reference 4). And when this encapsulant sheet has a multi-layer structure, the use of an expensive silane-modified polyethylene resin by making the silane-modified polyethylene resin unevenly distributed in the outermost layer portion where special adhesion is required. It is also disclosed that the adhesiveness of the encapsulant sheet can be improved while suppressing the amount.

JP 2012-195561 A JP 2013-176899 A Japanese Patent Laid-Open No. 2002-235048 JP 2011-37883 A

  The addition of the silane coupling agent in the encapsulant sheet described in Patent Document 1 contributes to the improvement of the adhesion of the encapsulant sheet, but on the other hand, a decrease in the adhesion improving function due to so-called bleed out becomes a problem. There is a case. This problem is particularly noticeable when a silane coupling agent is added to a polyethylene resin having poor compatibility with the silane coupling agent.

  Moreover, the sealing material sheet of patent document 2 is a thermoplastic sealing material sheet, Comprising: In the manufacturing stage as a sealing material composition, a silane coupling agent is included only in the surface layer which contributes to adhesion. I am going to do that. However, a part of the silane coupling agent that is a monomer component always moves to the intermediate layer. Therefore, in the completion stage of the encapsulant sheet, there cannot be a multilayer sheet in which all the added silane coupling agents are unevenly distributed only in the surface layer.

  Here, by using the silane-modified polyethylene resin described in Patent Document 3, the problem of bleeding out of the silane coupling agent can be avoided. Furthermore, by using a silane-modified resin that has been grafted to the base resin in advance for the adhesion improving component only in the surface layer, all the components for improving the adhesion are unevenly distributed only in the surface layer. It is also possible to maximize the cost performance of the adhesive component when paying attention to the adhesiveness.

  However, for example, in a multi-layer encapsulant sheet using a thermoplastic resin, such as the encapsulant sheet described in Patent Document 4, the surface does not contain any adhesion component in the intermediate layer. On the other hand, there arises a problem that the adhesion strength between the layers at the interface between the layer and the intermediate layer becomes insufficient and the risk of delamination at the interface increases. Therefore, in the multilayer sealing material sheet made of the thermoplastic polyethylene-based resin described in Patent Document 4, in order to prevent delamination, the intermediate layer that actually does not contribute to the close contact with the other base material to some extent. It is essential to add the adhesive component.

  As can be seen from the above, in the encapsulant sheet for solar cell modules based on low-density polyethylene, in order to further improve cost performance, the method of improving adhesion by adding an adhesion improving component to the base resin There was room for improvement.

  The present invention has been made in view of the above circumstances, and in a sealing material sheet for a solar cell module using low density polyethylene as a base resin, on the other hand, transparency, flexibility, heat resistance, durability, etc. While maintaining various physical properties at a sufficiently favorable level, the adhesiveness of the encapsulant sheet was sufficiently improved while minimizing the amount of expensive resin grafted with adhesive components such as silane-modified polyethylene resin. It aims at providing the sealing material sheet for solar cell modules.

  When the base resin for constituting each layer of the multilayer encapsulant sheet is a heat-crosslinking type low density polyethylene, the crosslinking reaction proceeds between the layers of the multilayer sheet. Thus, the inventors have conceived that the risk of delamination described above can be greatly reduced. Further, in the multilayer sheet using such heat-crosslinking type low-density polyethylene, a structure in which the resin grafted with the adhesion improving component in advance is substantially unevenly distributed only on the surface layer contributing to adhesion. By grafting the adhesion component to be added to improve adhesion while maintaining the transparency, flexibility, heat resistance and durability required for the solar cell module sealing material sheet at a sufficiently preferable level. It has been found that the adhesiveness of the encapsulant sheet can be sufficiently improved while minimizing the amount of resin used, and the present invention has been completed. More specifically, the present invention provides the following.

(1) A sealing material sheet for a solar cell module, wherein the sealing material sheet is a multilayer sheet having an intermediate layer and an outermost layer, and the intermediate layer has a density of 0.870 g / cm ³ or more and 0. A base resin composed of low density polyethylene of 910 g / cm ³ or less, and a crosslinking agent, and the outermost layer is composed of the base resin composed of the low density polyethylene, and the low density polyethylene and other adhesiveness. An adhesive copolymer resin obtained by copolymerizing a resin as a comonomer, and a crosslinking agent, the intermediate layer does not contain the adhesive copolymer resin, and the outermost layer is Content of the said adhesive copolymer resin in 100 mass parts of resin components which consist of the said base resin and the said adhesive copolymer resin is 8 mass parts or more, The said intermediate | middle layer and the said outermost layer are the said resin component. 100 parts by weight Encapsulant sheet content of the crosslinking agent is less than 2.0 parts by mass or more 0.3 part by weight against.

  (2) The encapsulant sheet according to (1), wherein the adhesive copolymer resin is a copolymer obtained by copolymerizing an α-olefin and an ethylenically unsaturated silane compound as a comonomer.

  (3) The encapsulant sheet according to (1) or (2), wherein the gel fraction of the intermediate layer and the outermost layer are both 0%.

  (4) The encapsulant sheet according to any one of (1) to (3), wherein the multilayer sheet has a three-layer structure in which outermost layers are laminated on both surfaces of an intermediate layer.

  (5) A solar cell module comprising the solar cell module sealing material sheet according to any one of (1) to (4) as a sealing material layer.

  (6) The solar cell module according to (5), wherein the outermost layer of the sealing material sheet is in close contact with the glass surface.

  (7) The solar cell module according to (5) or (6), wherein the gel fraction of the sealing material layer is 20% or more and 80% or less.

  According to the solar cell module sealing material sheet of the present invention and the manufacturing method thereof, low density polyethylene is used as a base resin, and the crosslinking treatment is performed in any step up to modularization. It is a thermosetting type sealing material sheet that becomes a sealing material sheet excellent in both properties and heat resistance, and can provide a sealing material sheet for a solar cell module that is also excellent in adhesion between substrates. .

It is sectional drawing which shows typically an example of the laminated constitution of the sealing material sheet of this invention. It is sectional drawing which shows typically an example of the layer structure about the solar cell module using the sealing material sheet of this invention.

  Hereinafter, a sealing material composition for solar cell modules according to the present invention (hereinafter also simply referred to as “sealing material composition”), a sealing material sheet for solar cell modules (hereinafter simply referred to as “sealing material sheet”). And the manufacturing method thereof, the solar cell module and the manufacturing method thereof will be described in detail in this order.

<Encapsulant composition>
Encapsulant composition used in the present invention contains a density 0.870 g / cm ³ or more 0.910 g / cm ³ or less of low density polyethylene, a crosslinking agent, as essential components. The encapsulant sheet of the present invention is a multilayer sheet including an intermediate layer and an outermost layer, as will be described in detail later. The encapsulant composition forming the outermost layer is further composed of low-density polyethylene and In addition, an adhesive copolymer resin obtained by copolymerization with other adhesive resin as a comonomer (hereinafter also simply referred to as “adhesive copolymer resin”) is contained as an essential component. On the other hand, the sealing material composition forming the intermediate layer does not contain an adhesive copolymer resin.

[Base resin]
In the sealing material composition of the present invention, as a base resin, a density 0.870 g / cm ³ or more 0.910 g / cm ³ or less of low density polyethylene (LDPE). By setting the density of the low density polyethylene within the above range, it is possible to impart good flexibility and transparency to the encapsulant sheet while maintaining the sheet processability of the encapsulant sheet.

(Low density polyethylene)
The low density polyethylene (LDPE) is preferably linear low density polyethylene (LLDPE), and more preferably metallocene linear low density polyethylene (M-LLDPE). 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 comonomer distribution. For this reason, molecular weight distribution is narrow, it is easy to make it a desired low density, and a softness | flexibility can be provided to a sealing material sheet. As a result of the flexibility, adhesion between the encapsulant sheet and the base material such as adhesion between the encapsulant sheet and the transparent front substrate and adhesion between the encapsulant sheet and the back surface protective sheet is increased.

  In addition, since the metallocene linear low density polyethylene has a narrow crystallinity distribution and a uniform crystal size, 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 sheet which consists of a sealing material composition of this invention is arrange | positioned between a transparent front substrate and a solar cell element, power generation efficiency hardly falls.

  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 number of carbon atoms of the α-olefin is 6 or more and 8 or less, the sealing material sheet can be given good flexibility and good strength. As a result, the adhesion between the encapsulant sheet and the other base material constituting the solar cell module is further enhanced.

  The melt mass flow rate (MFR) of low density polyethylene is MFR at 190 ° C. and a load of 2.16 kg measured according to JIS-K6922-2 (in this specification, unless otherwise specified, this measurement condition is used) The measured value is referred to as “MFR”.) Is preferably 0.5 g / 10 min or more and 40 g / 10 min or less, and more preferably 6 g / 10 min or more and 40 g / 10 min or less.

  The encapsulant sheet of the present invention is a so-called thermosetting encapsulant sheet on the premise that a curing process by thermal crosslinking is performed. For this reason, the excessive fluidity | liquidity at the time of the high temperature of the low density polyethylene used as a base can fully be suppressed. For this reason, even if it is high MFR like the said range, it can be used conveniently.

  In addition, although the sealing material sheet of this invention is a multilayer sheet comprised by two or more layers, there is no special limitation about the difference in the base resin which forms each layer. The base resin that forms the outermost layer may be a resin having a lower density than the base resin that forms the intermediate layer, or the same type of polyethylene resin may be used as the base resin. These may be determined flexibly within the above range in consideration of various physical properties and cost problems desired for the sealing material sheet.

[Adhesive copolymer resin]
Among the sealing material compositions of the present invention, the sealing material composition for forming the outermost layer contains an adhesive copolymer resin typified by a silane-modified polyethylene resin. The adhesive copolymer resin in the present invention is not necessarily limited to the silane-modified polyethylene resin as long as the adhesion improving component is a resin that has been polymerized in advance. Other epoxy-modified, polyethylene-based resins modified with unsaturated carboxylic acid or derivatives thereof may be used. Examples of unsaturated carboxylic acids include maleic acid, itaconic acid, and fumaric acid. Examples of derivatives thereof include maleic acid monoester, maleic acid diester, maleic anhydride, itaconic acid monoester, itaconic acid. Examples thereof include esters and anhydrides such as diester, itaconic anhydride, fumaric acid monoester, fumaric acid diester, and fumaric anhydride. However, a silane-modified polyethylene resin can be particularly preferably used from the viewpoints of compatibility with the base resin and adhesion with other solar cell module components such as a glass substrate. Hereinafter, the case where the adhesive copolymer resin is a silane-modified polyethylene resin will be described in detail as a specific example of a preferred embodiment of the present invention.

(Silane-modified polyethylene resin)
The silane-modified polyethylene resin is a resin obtained by graft polymerizing low-density polyethylene as a main chain, preferably linear low-density polyethylene, with an ethylenically unsaturated silane compound as a side chain. Since such a graft copolymer has a high degree of freedom of silanol groups that contribute to the adhesive force, it can improve the adhesion of the sealing material sheet to other members in the solar cell module. The silane-modified polyethylene resin in the present specification refers to, for example, a silane-modified polyethylene resin that can be produced by the following production method, and at least a part of a linear low-density polyethylene resin that becomes a main chain. Is a concept indicating a resin obtained by graft polymerization with an ethylenically unsaturated silane compound. The resin as a main chain of the above, similar to the base resin of the sealing material composition is preferably a density 0.870 g / cm ³ or more 0.910 g / cm ³ or less of the polyethylene resin.

The silane-modified polyethylene resin can be produced by the following method, for example, as described in JP-A-2003-46105. For example, one or more α-olefins, one or more ethylenically unsaturated silane compounds, and, if necessary, one or more other unsaturated monomers are desired. reactions using the container, for example, a pressure 500~4000Kg / cm ^2-position, preferably, 1000~4000Kg / cm ^2-position, temperature, 100 to 400 ° C.-position, preferably under the conditions of 150 to 350 ° C.-position, Part of the silane compound constituting the random copolymer which is produced by random copolymerization simultaneously or stepwise in the presence of a radical polymerization initiator and, if necessary, a chain transfer agent. Can be modified or condensed to produce a silane-modified polyethylene resin.

  As the polyethylene-based resin of the main chain, it is preferable to use linear low-density polyethylene that is an ethylene-α-olefin copolymer, and it is more preferable to use metallocene-based 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 comonomer distribution. For this reason, molecular weight distribution is narrow, it is possible to make it the above ultra-low density, and a softness | flexibility can be provided with respect to a sealing material sheet. As a result of the flexibility imparted to the sealing material sheet, the adhesion between the sealing material sheet and a transparent front substrate such as glass can be enhanced.

  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 number of carbon atoms of the α-olefin is 6 or more and 8 or less, the sealing material sheet can be given good flexibility and good strength. As a result, the adhesion between the encapsulant sheet and a transparent front substrate such as glass is further enhanced.

  Examples of ethylenically unsaturated silane compounds to be graft polymerized with linear low density polyethylene include, for example, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltripropoxysilane, vinyltriisopropoxysilane, vinyltributoxysilane, vinyltripentyloxysilane , One or more selected from vinyltriphenoxysilane, vinyltribenzyloxysilane, vinyltrimethylenedioxysilane, vinyltriethylenedioxysilane, vinylpropionyloxysilane, vinyltriacetoxysilane, and vinyltricarboxysilane be able to.

Moreover, the silane modified polyethylene resin used for the sealing material composition of the present invention is a graft copolymer of linear low density polyethylene and an ethylenically unsaturated silane compound as described above. The graft ratio of the ethylenically unsaturated silane compound was measured by the ATR method of JASCO FT / IR 610 after cutting the pelletized resin to be measured flat. Peak of SiC, ^{1090 cm} -1, the peak of the CH ₂ was the intensity ratio using the 1465cm ^-1. In the sealing material composition of the present invention, the graft ratio calculated in this way, that is, the peak intensity ratio (SiC peak value / CH ₂ peak value) between the SiC peak and the CH ₂ peak of the silane-modified polyethylene resin is 0. .15 or more and 0.85 or less, and preferably 0.2 or more and 0.65 or less. As described above, the ethylenically unsaturated silane compound is previously unsaturated before being molded as a sealing material sheet in order to graft-copolymerize the ethylenically unsaturated silane compound to the above value in the stage before molding as a sealing material sheet. Compared with graft copolymerization of a silane compound, there are merits such as reduction of the crosslinking agent and improvement of durability.

  The graft amount, which is the content of the ethylenically unsaturated silane compound in the silane-modified polyethylene resin, is 0.001 to 15% by mass, preferably 0.01 to 5% by mass in the base resin of the silane-modified polyethylene resin. %, Particularly preferably 0.05 to 2% by mass. In the present invention, when the content of the ethylenically unsaturated silane compound is large, the mechanical strength and heat resistance are excellent. However, when the content is excessive, the tensile elongation and heat-fusibility tend to be inferior.

  The content in the outermost layer of the silane-modified polyethylene resin used in the sealing material composition for forming the outermost layer of the sealing material sheet of the present invention is the base resin and adhesive copolymer resin of the sealing material composition It is preferable that content in 100 mass parts of resin components of the sealing material sheet which consists of 8 mass parts or more and 20 mass parts or less. In the present invention, if the content of the silane-modified polyethylene resin is 8 parts by mass or more, it is excellent in mechanical strength and heat resistance, but if the content is excessive, it tends to be inferior in tensile elongation and heat-fusibility. It is in. In the present specification, the resin component of the encapsulant sheet is a resin component composed of the base resin of the encapsulant composition and the adhesive copolymer resin as described above.

  By using the silane-modified polyethylene resin described above as a component of a sealing material composition for solar cell modules, it has excellent adhesion, strength, durability, etc., and weather resistance, heat resistance, water resistance, light resistance , Wind pressure resistance, yield resistance, and other various properties can be obtained. Various effects can be obtained in this way by using a silane-modified polyethylene resin, but it is extremely excellent in a sealing material sheet without being affected by manufacturing conditions such as thermocompression bonding for manufacturing a solar cell module. In addition, the greatest advantage is that it can impart excellent heat adhesion to the glass substrate constituting the solar cell module.

  However, since the silane-modified polyethylene resin is more expensive than other base resins and the like, if the amount used is excessive, the cost performance of the sealing material sheet production may be deteriorated. The sealing material sheet of the present invention focuses on the above-mentioned adhesion improving effect, and seals by making the adhesive copolymer resin represented by the silane-modified polyethylene resin unevenly distributed only in the outermost layer of the multilayer sheet. It is characterized by greatly improving the cost performance of the material sheet manufacturing.

  The content of the resin component comprising the base resin and the adhesive copolymer resin contained in the sealing material composition for the present invention is preferably 10% by mass or more and 99% by mass in all components of the sealing material composition. % Or less, more preferably 50% by mass or more and 99% by mass or less, and further preferably 90% by mass or more and 99% by mass or less. Other resins may be included within a range not departing from the above composition range. These may be used, for example, as an additive resin, or may be used for masterbatching other components described later. However, as described above, the sealing material composition for the intermediate layer does not include a resin made of an adhesive copolymer resin.

[Crosslinking agent]
A well-known thing can be used for a crosslinking agent, It does not specifically limit, For example, a well-known radical polymerization initiator can be used. Examples of radical polymerization initiators include hydroperoxides such as diisopropylbenzene hydroperoxide and 2,5-dimethyl-2,5-di (hydroperoxy) hexane; di-t-butyl peroxide, t-butyl Cumyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, 2,5-dimethyl-2,5-di (t-peroxy) hexyne-3, etc. Dialkyl peroxides; diacyl peroxides such as bis-3,5,5-trimethylhexanoyl peroxide, octanoyl peroxide, benzoyl peroxide, o-methylbenzoyl peroxide, 2,4-dichlorobenzoyl peroxide; t-butyl peroxyacetate, t-butyl pero Ci-2-ethylhexanoate, t-butyl peroxypivalate, t-butyl peroxyoctoate, t-butyl peroxyisopropyl carbonate, t-butyl peroxybenzoate, di-t-butyl peroxyphthalate, 2 , 5-dimethyl-2,5-di (benzoylperoxy) hexane, 2,5-dimethyl-2,5-di (benzoylperoxy) hexyne-3, t-butylperoxy-2-ethylhexyl carbonate Oxyesters; organic peroxides such as methyl peroxides such as methyl ethyl ketone peroxide and cyclohexanone peroxide, or azo compounds such as azobisisobutyronitrile and azobis (2,4-dimethylvaleronitrile), dibutyltin Diacetate, dibutyltin dilaurate It can be mentioned dibutyltin dioctoate, dioctyltin dilaurate, dicumyl peroxide, such a silanol condensation catalyst.

  The content of the crosslinking agent in the intermediate layer and the outermost layer is such that the content of the encapsulant sheet in each layer with respect to 100 parts by mass of the resin component is in the range of 0.3 to 2.0 parts by mass. It is preferable that it is in a range of 0.5 parts by mass or more and 1.5 parts by mass or less. By setting the content of the crosslinking agent to 0.3 parts by mass or more, sufficient heat resistance can be imparted to the low-density polyethylene resin used in the sealing material sheet of the present invention. When the content of the crosslinking agent is less than 0.3 parts by mass, the heat resistance is insufficiently improved. On the other hand, when the content of the crosslinking agent exceeds 1.5 parts by mass, the crosslinking proceeds in the crosslinking step. Becomes excessive, and the followability to the unevenness of other members at the time of modularization becomes insufficient, which is not preferable.

[Crosslinking aid]
In the present invention, a polyfunctional monomer having a carbon-carbon double bond and / or an epoxy group can be used as a crosslinking aid. More preferably, the functional group of the polyfunctional monomer is an allyl group, a (meth) acrylate group, or a vinyl group. As a result, an appropriate crosslinking reaction is promoted to reduce the gel fraction to 80% or less, and in the present invention, this crosslinking aid reduces the crystallinity of the linear low density polyethylene and maintains transparency. As a result, it is possible to obtain a sealing material sheet that is more excellent in transparency and low-temperature flexibility, and specifically, it is possible to obtain transparency and low-temperature flexibility equivalent to those of EVA.

  Specifically, polyallyl compounds such as triallyl isocyanurate (TAIC), triallyl cyanurate, diallyl phthalate, diallyl fumarate, diallyl maleate, trimethylolpropane trimethacrylate (TMPT), trimethylolpropane triacrylate (TMPTA) , Poly (meth) acryloxy compounds such as ethylene glycol diacrylate, ethylene glycol dimethacrylate, 1,4-butanediol diacrylate, 1,9-nonanediol diacrylate, glycidyl methacrylate containing a double bond and an epoxy group, 4- Hydroxybutyl acrylate glycidyl ether and 1,6-hexanediol diglycidyl ether and 1,4-butanediol diglycidyl ether containing two or more epoxy groups Cyclohexanedimethanol diglycidyl ether, and epoxy compounds such as trimethylolpropane polyglycidyl ether. These may be used alone or in combination of two or more. Among these, TAIC is preferably used from the viewpoint of good compatibility with low density polyethylene, promoting a crosslinking reaction, reducing crystallinity, maintaining transparency, and imparting flexibility at low temperature.

  As content of a crosslinking adjuvant, it is preferable that content in the resin component of a sealing material sheet is contained about 0.01 mass%-3 mass%. If it is in this range, a sufficient crosslinking resistance can be imparted at the same time while promoting an appropriate crosslinking reaction and maintaining a preferable flexibility in the sealing material layer after modularization.

[Radical absorbent]
In the present invention, by using the above-mentioned crosslinking aid serving as a radical polymerization initiator in combination with the radical absorbent that quenches it, the degree of crosslinking is adjusted and the gel content of the encapsulant sheet after crosslinking treatment The rate can be finely adjusted. Examples of such radical absorbents include hindered phenol-based antioxidants, hindered amine-based weather resistance stabilization, and the like. A hindered phenol-based radical absorbent having a high radical absorbing ability near the crosslinking temperature is preferred. It is preferable that the usage-amount of a radical absorbent is 0.01 mass part-3 mass parts with respect to 100 mass parts of resin components, More preferably, it is the range of 0.05 mass part-2.0 mass parts. . If it exists in this range, a crosslinking reaction can be suppressed moderately and a gel fraction can be controlled to 80% or less, and the preferable softness | flexibility of a sealing material sheet can be hold | maintained.

[Other ingredients]
The sealing material composition may further contain other components. For example, components such as a weather resistance masterbatch for imparting weather resistance to a sealing material sheet produced from the sealing material composition of the present invention, various fillers, a light stabilizer, an ultraviolet absorber, and a heat stabilizer Illustrated. These contents vary depending on the particle shape, density, and the like, but are preferably in the range of 0.001 to 5 parts by mass with respect to 100 parts by mass of the resin component. By including these additives, it is possible to impart a mechanical strength that is stable over a long period of time, an effect of preventing yellowing, cracking, and the like to the encapsulant composition.

  A weatherproof masterbatch is obtained by dispersing a light stabilizer, an ultraviolet absorber, a heat stabilizer and the above-mentioned antioxidant in a resin such as polyethylene, and adding this to a sealing material composition. Thus, good weather resistance can be imparted to the encapsulant sheet. The weatherproof masterbatch may be prepared and used as appropriate, or a commercially available product may be used. The resin used in the weatherproof masterbatch may be a linear low density polyethylene used in the present invention, or other resins described above. These light stabilizers, ultraviolet absorbers, heat stabilizers and antioxidants can be used alone or in combination of two or more.

<Sealing material sheet>
The encapsulant sheet of the present invention is an encapsulant composition for forming an intermediate layer that does not contain an adhesive copolymer resin, and an encapsulant for forming an outermost layer that contains an adhesive copolymer resin with a predetermined content. The material composition is obtained as a raw material for each layer, and is formed by a conventionally known multilayer sheet forming method. That is, the sealing material sheet of the present invention is a multilayer sealing composed of a plurality of layers including an intermediate layer and at least one of the intermediate layers, preferably the outermost layer disposed on the outermost surface of both. It is a material sheet. Hereinafter, as a preferred embodiment of the present invention, a sealing material sheet 1 having a three-layer structure including two outermost layers in total, one layer above and below a single intermediate layer, will be described with reference to FIG. . However, the present invention is not limited to this embodiment.

  The sealing material sheet 1 has an intermediate layer 11, and the outermost layer 12 is disposed on both surfaces of the intermediate layer 11. However, for example, a sealing material sheet having a two-layer structure in which the outermost layer is disposed only on one side of the intermediate layer, or a seal in which the intermediate layer has a multilayer structure and other functional layers are disposed in the intermediate layer. Even if it is a sealing material sheet, it is within the scope of the present invention as long as it is an encapsulant sheet having an intermediate layer and an outermost layer having the constituent elements of the present invention and having other constituent elements of the present invention.

  The intermediate layer 11 is a layer constituting a main part as a substrate layer in the encapsulant sheet 1. The intermediate layer 11 is given sufficient heat resistance by sufficiently proceeding with cross-linking, whereby the durability of the solar cell module can be improved.

  The outermost layer 12 is a layer that is disposed on the outermost surface of the sealing material sheet in the sealing material sheet 1 and constitutes a subordinate portion as a surface material. The outermost layer 12 is provided with a preferable adhesion due to the adhesion improvement effect by blending the adhesive copolymer resin, thereby improving molding characteristics and substrate adhesion during the integration process as a solar cell module. Can be made.

  In general, when the encapsulant sheet is a multilayer sheet formed by laminating thermoplastic polyethylene resin sheets, in order to ensure sufficient adhesion at the interface between the layers, for example, with other base materials As described above, it is necessary to add the minimum necessary adhesion component to the intermediate layer not involved in the adhesion. On the other hand, since the sealing material sheet 1 of the present invention comprises the intermediate layer 11 and the outermost layer 12 with a thermosetting polyethylene resin containing a crosslinking agent, the adhesion at the interface between the above-mentioned respective layers. As a result of the cross-linking reaction that finally proceeds at the interface between the layers, the adhesion component to the intermediate layer 11 is added to ensure the adhesion of the interface between the layers. There is no need to do. Therefore, it is possible to make an adhesion component unevenly distributed only in the outermost layer 12 that directly contributes to adhesion, and this can greatly improve the cost performance of manufacturing the sealing material sheet.

  The total thickness of the encapsulant sheet 1 including the intermediate layer 11 and both outermost layers 12 is preferably 200 μm or more and 800 μm or less. If it is less than 200 μm, the impact cannot be sufficiently mitigated, and if it exceeds 800 μm, no further effect can be obtained, which is uneconomical.

  About the ratio of the thickness of each layer in the sealing material sheet 1, the outermost layer 12: the intermediate layer 11: the outermost layer 12 and the n thickness ratio may be in the range of 1: 2: 1 to 1: 30: 1. preferable. By setting the thickness ratio of each layer within this range, both the heat resistance and adhesion of the encapsulant sheet 1 can be maintained within a favorable range.

<Method for producing sealing material sheet>
The encapsulant sheet of the present invention obtains an uncrosslinked encapsulant sheet by a sheet forming process in which the above-described encapsulant composition is melt-molded at a temperature exceeding the melting point, and then integrated as a solar cell module. At any stage up to here, a crosslinking treatment is performed, and finally a crosslinked sheet-like or film-like sealing material sheet is obtained. In addition, the sheet form in this invention means the film form, and there is no difference in both.

[Sheet making process]
The melt molding of the sealing material composition is carried out 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. At that time, the lower limit of the molding temperature may be a temperature exceeding the melting point of the encapsulant composition, and the upper limit is a temperature at which crosslinking does not start during extrusion film formation, depending on the 1-minute half-life temperature of the crosslinking agent used. There is no particular limitation as long as it is within these ranges.

  The encapsulant sheet in the present invention refers to an uncrosslinked encapsulant sheet obtained by this sheeting step. The gel fraction of this sealing material sheet is 0%. However, the encapsulant sheet of the present invention is obtained by crosslinking the uncrosslinked encapsulant sheet at any stage up to the integration step as a solar cell module, and the gel fraction in the final use form Is assumed to be 20% or more and 80% or less. Therefore, if the gel fraction after the crosslinking treatment is 20% or more and 80% or less and the other requirements are included in the constitutional requirements of the present invention, it is naturally within the scope of the present invention. In addition, by making the gel fraction in the stage which comprises the sealing material layer of the solar cell module which is the final usage form into 20% or more and 80% or less, the sealing material layer of a solar cell module is used for a sealing material sheet. Sufficient heat resistance and preferable flexibility can be imparted.

[Crosslinking process]
An integration step as a solar cell module that integrates the sealing material sheet with the other members after the completion of the sheeting step, the crosslinking treatment step for crosslinking the sealing material sheet after the sheeting step. Before starting or in an integration step as a solar cell module. As described above, the gel fraction of the sealing material sheet is finally 20% to 80% by this crosslinking step.

  The crosslinking method is preferably by heat treatment. The crosslinking conditions are not particularly limited. When crosslinking is performed by heat treatment, the gel fraction may be appropriately set as the total treatment result within the range of general crosslinking treatment conditions.

  The crosslinking treatment can also be performed by irradiation with ionizing radiation. Even when the crosslinking treatment is performed by irradiation with ionizing radiation, the individual crosslinking conditions are not particularly limited, and may be set as appropriate so that the gel fraction is the total treatment result. Specifically, it 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. The acceleration voltage in electron beam irradiation is determined by the thickness of the sheet that is the object to be irradiated, and the thicker the sheet, the larger the acceleration voltage is required. For example, a 0.5 mm-thick sheet is irradiated with 100 kV or more, preferably 200 kV or more. If the acceleration voltage is lower than this, the crosslinking is not sufficiently performed. The irradiation dose is in the range of 10 kGy to 1000 kGy, preferably 10 to 300 kGy. When the irradiation dose is less than 10 kGy, sufficient crosslinking is not performed, and when it exceeds 1000 kGy, there is a concern about deformation or coloring of the sheet due to generated heat. In addition, you may irradiate from both sides. Irradiation may be in an air atmosphere or a nitrogen atmosphere.

  By passing through said bridge | crosslinking process, the gel fraction of a sealing material sheet will be 20% or more and 80% or less finally. The gel fraction of the crosslinked encapsulant sheet is more preferably 30% or more and 80% or less. By setting the gel fraction of the crosslinked encapsulant sheet within the above range, the encapsulant sheet can be provided with sufficient heat resistance and preferable flexibility required for the encapsulant layer of the solar cell module. .

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

<Solar cell module>
FIG. 2 is a cross-sectional view showing an example of the layer structure of the solar cell module using the sealing material sheet of the present invention. In the solar cell module 10 of the present invention, the transparent front substrate 2, the front sealing material layer 3, the solar cell element 4, the back sealing material layer 5, and the back surface protection sheet 6 are laminated in order from the incident light receiving surface side. ing. The solar cell module 10 of the present invention uses the encapsulant sheet 1 of the present invention for at least one of the front encapsulant layer 3 and the back encapsulant layer 5. In particular, as the front sealing material layer 3 facing the transparent front substrate 2, it is preferable that the outermost layer 12 of the sealing material sheet 1 is disposed in a manner in close contact with the glass surface of the transparent front substrate 2.

<Method for manufacturing solar cell module>
The solar cell module 10 is, for example, vacuum suction after sequentially laminating members composed of the transparent front substrate 2, the front sealing material layer 3, the solar cell element 4, the back sealing material layer 5, and the back surface protection sheet 6. Then, the above-mentioned members can be manufactured by thermocompression molding as an integrally molded body by a molding method such as a lamination method.

  In the solar cell module 10 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 10 of this invention may also contain members other than the said member. In addition, the sealing material sheet of this invention is applicable not only to a single crystal type but to all other solar cell modules.

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

<Manufacture of encapsulant sheet for solar cell module>
The raw materials of the encapsulant composition described below are mixed so that the content ratio in the composition is the ratio (parts by mass) shown in Table 1 below or the quantitative ratios (parts by mass) described below. It was set as the sealing material composition for manufacturing the resin sheet for intermediate | middle layers and the outermost layer of the sealing material of an example and a comparative example. Each sealing material composition was formed into a single layer for an intermediate layer and an outermost layer at an extrusion temperature of 100 ° C. and a take-off speed of 1.1 m / min, using a φ30 mm extruder and a film forming machine having a 200 mm wide T-die. Each resin sheet is produced, each of these resin sheets is laminated, and the sealing material of the three-layer structure of Examples 1 to 4 and Comparative Examples 1 to 12 including the outermost layer disposed in the intermediate layer and both outermost layers A sheet was used. The thickness of each sealing material sheet of an Example and a comparative example was all made into the total thickness of 600 micrometers. Moreover, about the ratio of the thickness of each layer of each sealing material sheet made into 3 layer structure, it was set as the ratio as described in following Table 1, respectively.

The following raw materials were used as the raw material of the sealing material composition for forming each single-layer resin sheet for the sealing material sheets of Examples and Comparative Examples.
Base resin 1 (shown as “PE” in Table 1): polyethylene resin (LLDPE). A metallocene linear low density polyethylene which is a copolymer of ethylene and 1-hexene and has a density of 0.880 g / cm ³ and an MFR of 30 g / 10 min.
Base resin 2 (shown as “EVA” in Table 1): ethylene-vinyl acetate copolymer resin (EVA). Vinyl acetate content 33% (Mitsui DuPont Polychemical, trade name “EVAFLEX / EV150R grade”)
Adhesive copolymer resin (shown as “S-modified resin” in Table 1): Silane-modified polyethylene resin. 2 parts by mass of vinyltrimethoxysilane and 0.1 part by mass of dicumyl peroxide as a radical generator (reaction catalyst) are mixed with 100 parts by mass of the base resin, and melted and kneaded at 200 ° C. A silane-modified polyethylene resin having a density of 0.884 g / cm ³ and an MFR of 24 g / 10 min.
Cross-linking agent (shown as “cross-linking agent” in Table 1): t-butylperoxy-2-ethylhexyl carbonate (manufactured by Arkema Yoshitomi Corporation, trade name “Lupelox TBEC”)
Silane coupling agent (shown as “SC agent” in Table 1): Vinyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., trade name “KBM1003”)
About the following raw materials, it added to each sealing material composition of an Example and a comparative example so that the content ratio (mass part) with respect to 100 mass parts of resin components of a composition may become the quantitative ratio shown below.
Crosslinking aid: triallyl isocyanurate (Nippon Kasei Co., Ltd., trade name “Tyke”). 0.5 parts by mass of each of the sealing material compositions of Examples and Comparative Examples.
UV absorber: manufactured by Chemipro Kasei Co., Ltd., trade name KEMISORB12. 0.3 mass part in each sealing material composition of an Example and a comparative example.
Weathering stabilizer: Ciba Japan Co., Ltd., trade name Tinuvin 770. 0.2 parts by mass of each of the sealing material compositions of Examples and Comparative Examples.
Antioxidant: Ciba Japan Co., Ltd., trade name Irganox 1076. Each of the sealing material compositions of Examples and Comparative Examples is 0.05 parts by mass.

<Evaluation Example 1: Initial adhesion>
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 by vacuuming at 150 ° C. for 5 minutes. And pressed at 100 kPa for 10 minutes. Thereafter, a crosslinking treatment was carried out in an oven at 150 ° C. for 60 minutes to prepare an evaluation sample. In the above sample for evaluation, the sealing material sheet adhered to the glass substrate was cut to a width of 15 mm, and the vertical peeling (50 mm / min) test was conducted with a peeling tester (Tensilon Universal Tester RTF-1150-H). The glass adhesion strength was measured and evaluated. Evaluation was performed according to the following criteria.
A: 50 N / 15 mm or more B: 45 N / 15 mm or more and less than 50 N / 15 mm C: 40 N / 15 mm or more and less than 45 N / 15 mm D: less than 40 N / 15 mm The evaluation results are shown in Table 2 as “initial adhesion”.

<Evaluation Example 2: Adhesion maintenance rate after storage>
About each said sample for evaluation, the adhesiveness after storage for a fixed period was measured and the maintenance rate was verified. After each sample for evaluation was stored for 1 month under the storage conditions of a temperature of 30 ° C. and a humidity of 90% Rh, the glass adhesion strength was re-measured by the same test method as described above, and the adhesion strength maintenance rate relative to the initial glass adhesion strength ( %) Was calculated and evaluated. Evaluation was performed according to the following criteria.
A: 95% or more B: 85% or more and less than 95% C: 80% or more and less than 85% D: Less than 80% The evaluation results are shown in Table 2 as “adhesion maintenance rate after storage”.

<Evaluation Example 3: Weather resistance adhesion maintenance rate>
About each said sample for evaluation, the maintenance factor with respect to the initial glass adhesion strength of the glass adhesion strength after the following dump heat (DH) test was measured. D. H. The test was performed in accordance with JIS C8917, and the durability test of the sample for evaluation was performed for 500 hours under the conditions of a temperature in the test tank of 85 ° C. and a humidity of 85%. About the test sample after the test, the glass adhesion strength was measured again by the same test method as described above, and the maintenance rate (%) of the adhesion strength with respect to the initial glass adhesion strength was calculated and evaluated. Evaluation was performed according to the following criteria.
A: 95% or more B: 85% or more and less than 95% C: 80% or more and less than 85% D: Less than 80% The evaluation results are shown in Table 2 as “weather resistant adhesion maintenance ratio”.

<Evaluation Example 4: MFR maintenance rate after storage>
About each said sample for evaluation, MFR in 100 degreeC and load 2.16kg was measured according to the method of JIS-K6922-2. This measured value was used as the initial MFR value. After that, the MFR after storage for a certain period was measured, and the MFR maintenance rate was verified. After each evaluation sample is stored for 1 month under the storage conditions of temperature 30 ° C. and humidity 90% Rh, the MFR is measured again by the same test method as above, and the MFR maintenance rate (%) with respect to the initial MFR value is calculated. And evaluated. Evaluation was performed according to the following criteria. Evaluation was performed according to the following criteria.
A: 95% or more B: 92% or more and less than 95% C: 89% or more and less than 92% D: Less than 89% The evaluation results are shown in Table 2 as “MFR maintenance rate after storage”.

<Evaluation Example 5: Gel fraction during solar cell module formation>
Each gel fraction after the film-forming post-crosslinking process of each sealing material sheet of an Example and a comparative example and after the cross-linking process was measured. The conditions for the cross-linking treatment are as follows: 150 ° C., evacuation 4 minutes, vacuum heating laminator treatment under pressure 100 kPa for 6 minutes, pressure-bond each member, put in an oven and hold at 150 ° C. for 60 minutes did. For each encapsulant sheet after film formation before cross-linking treatment and after cross-linking treatment under these conditions, the gel fraction measuring method as described above, that is, 0.1 g of encapsulating material sheet is put in a resin mesh, After extraction with toluene at 60 ° C. for 4 hours, the entire resin mesh was taken out and weighed after drying treatment, and the gel fraction was measured by the method of comparing the mass before and after extraction and measuring the mass% of the remaining insoluble matter. The measurement results are shown in Table 3.

  From Tables 1 and 2, the encapsulant sheet of the present invention has a configuration in which adhesion components are unevenly distributed only in the outermost layer, and also has excellent initial adhesion and adhesion maintenance ratio in a weather resistant environment. It turns out that it is a material sheet. It can also be seen that the expensive adhesive copolymer resin is unevenly distributed in the layer that contributes to adhesion, which is preferable in terms of cost performance during production.

  From Tables 1 and 2, in Comparative Examples 1 to 4 and 7 to 8 in which a monomer adhesion improving component (silane coupling agent) was added as an adhesion improving component, the amount of adhesion component added to the outermost layer was It was confirmed that not only the adhesion strength is insufficient when it is too small, but also the initial adhesion and the weather resistance adhesion maintenance ratio are lowered when the same component is not contained in the intermediate layer. This is due to the lack of adhesion durability at the above-mentioned interlayer interface, and on the other hand, the dispersion of the monomer component to the intermediate layer or the bleed out occurs during the subsequent storage from the time of film formation. However, it is thought that there is.

  In Comparative Examples 5-6 and 9-10, in which the intermediate layer also contains a certain adhesive copolymer resin (silane-modified polyethylene resin), there is no particular problem with respect to the adhesion strength, but the MFR is maintained. It can be seen that the rate cannot maintain the required level. It is also clear that the cost performance of the additive component for improving the adhesion is lower than in the examples.

  Further, even if the adhesion component is unevenly distributed only in the outermost layer, the comparative examples 11 to 12 in which the content of the adhesive copolymer resin has not reached the predetermined content ratio of the present invention are particularly maintained in the weather resistance adhesion maintenance rate. It can be seen that the decrease in the value becomes significant.

  Further, from Table 3, according to the production method of the present invention, the gel fraction at the use stage after the subsequent crosslinking treatment was obtained after undergoing a stable film-forming treatment for the sealing material sheet made of a thermosetting resin. It can be seen that it can be 20% or more and 80% or less. Thereby, sufficient heat resistance and preferable flexibility required for the sealing material layer of the solar cell module can be imparted to the sealing material sheet.

DESCRIPTION OF SYMBOLS 1 Sealing material sheet 11 Middle layer 12 Outermost layer 2 Transparent front substrate 3 Front sealing material layer 4 Solar cell element 5 Back surface sealing material layer 6 Back surface protection sheet 10 Solar cell module

Claims (7)

A sealing material sheet for a solar cell module,
The encapsulant sheet is a multilayer sheet having an intermediate layer and an outermost layer,
The intermediate layer contains a base resin consisting of a density 0.870 g / cm ³ or more 0.910 g / cm ³ or less of low density polyethylene, a crosslinking agent, a
The outermost layer contains a base resin composed of the low density polyethylene, an adhesive copolymer resin obtained by copolymerizing the low density polyethylene and another adhesive resin as a comonomer, and a crosslinking agent. ,
The intermediate layer does not contain the adhesive copolymer resin,
In the outermost layer, the content of the adhesive copolymer resin in 100 parts by mass of the resin component composed of the base resin and the adhesive copolymer resin is 8 parts by mass or more,
It said intermediate layer and said outermost layer, I said der content less 2.0 parts by mass or more 0.3 part by weight of a crosslinking agent for said resin component 100 parts by weight,
The encapsulant sheet having a post-storage MFR maintenance ratio measured by the following post-storage MFR maintenance ratio calculation method of 92% or more .
MFR maintenance rate calculation method after storage: MFR at 100 ° C. and a load of 2.16 kg is measured for the sample according to the method of JIS-K6922-2. This measured value is used as the initial MFR value, and then the MFR after storage for a certain period is measured to verify the MFR maintenance rate. After each sample is stored for 1 month under storage conditions of a temperature of 30 ° C. and a humidity of 90% Rh, the MFR is measured again by the same test method as described above, and the MFR maintenance rate (%) with respect to the initial MFR value is calculated. The encapsulant sheet according to claim 1 , wherein the adhesive copolymer resin is a copolymer obtained by copolymerizing an α-olefin and an ethylenically unsaturated silane compound as a comonomer. The encapsulant sheet according to claim 1 or 2 , wherein the gel fraction of the intermediate layer and the outermost layer is both 0%. The encapsulant sheet according to any one of claims 1 to 3 , wherein the multilayer sheet has a three-layer structure in which outermost layers are laminated on both surfaces of an intermediate layer. A solar cell module provided with the sealing material sheet for solar cell modules in any one of Claim 1 to 4 as a sealing material layer. The solar cell module according to claim 5 , wherein the outermost layer of the sealing material sheet is in close contact with the glass surface. The solar cell module according to claim 5 or 6 , wherein the gel fraction of the sealing material layer is 20% or more and 80% or less.

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