JP5644456B2 - Solar cell back surface protection sheet, method for producing the sheet, and solar cell module - Google Patents

Description

  The present invention relates to a back surface protective sheet for solar cells, and more particularly to a back surface protective sheet for solar cells provided with a function of trapping acetic acid generated from a sealing layer constituting a solar cell module.

  In recent years, solar cells have been attracting attention as a clean energy source free from environmental pollution due to an increase in awareness of environmental problems, and earnestly researched and put into practical use from the viewpoint of using solar energy as a useful energy resource.

  There are various types of solar cell elements, and typical examples thereof include a crystalline silicon solar cell element, a polycrystalline silicon solar cell element, an amorphous silicon solar cell element, a copper indium selenide solar cell element, and a compound semiconductor solar. Battery elements and the like are known. Among these, thin-film crystal solar cell elements, amorphous silicon solar cell elements, and compound semiconductor solar cell elements are relatively low cost and can be increased in area, and therefore are actively researched and developed in various fields. ing. Among these solar cell elements, thin film solar cell elements represented by amorphous silicon solar cell elements in which silicon is laminated on a conductive metal substrate and a transparent conductive layer is further formed thereon are lightweight, Since it is rich in impact resistance and flexibility, it is considered promising as a future form of solar cells.

  A simple one of the solar cell modules has a configuration in which a sealing layer and a glass plate are sequentially laminated on both sides of the solar cell element. A glass plate is still generally used as a protective material on the light receiving surface side of the sun because it is excellent in transparency, weather resistance, and scratch resistance. However, on the non-light-receiving surface side that does not require transparency, a back surface protection sheet for solar cells (hereinafter referred to as a back surface protection sheet) other than the glass plate has been developed by each company in terms of cost, safety, and workability. Is being replaced.

As the back surface protection sheet, a monolayer film such as a polyester film, a polyester film provided with a metal oxide or non-metal oxide vapor deposition layer, a polyester film, a fluorine-based film, an olefin film, an aluminum foil, etc. The multilayer film which laminated | stacked the film is mentioned.
The back surface protective sheet having a multilayer structure can impart various performances depending on the multilayer structure. For example, insulating properties can be imparted by using a polyester film, weather resistance can be imparted by using a fluorine-based film, and water vapor barrier properties can be imparted by using an aluminum foil.
What kind of back surface protection sheet is used can be appropriately selected depending on the product and application in which the solar cell module is used.

By the way, as a sealing layer which is a component of the solar cell module, a film-like ethylene-vinyl acetate copolymer (EVA) is generally used from the viewpoints of transparency and cost.
However, since EVA film contains vinyl acetate as its constituent component, EVA tends to hydrolyze and produce acetic acid from moisture or water permeation at high temperatures. Therefore, the solar cell module using the EVA film has a problem that the power generation performance deteriorates with time (Patent Documents 1 and 2).

  Moreover, the solar cell module using an EVA film as a sealing layer also has a problem that the back surface protection sheet is easily peeled off from the sealing layer. In this regard, Patent Document 3 [0031] and [0033] contain at least one of ethylene-acrylic acid ester copolymer, ethylene-methacrylic acid ester copolymer and EVA as a main component, and an epoxy compound. A protective sheet for sealing, that is, a back protective sheet, is formed by laminating a heat-fusible layer further blended with an oxazoline compound or a carbodiimide compound on a heat-resistant film, optionally via a urethane adhesive layer. Is described. Further, [0027] and [0030] of Patent Document 3 also describe a solar cell module in which this back surface protection sheet is bonded to an EVA film.

  In Patent Document 3, a heat-fusible layer formed by blending an ethylene-ethyl acrylate copolymer with a carbodiimide compound in Table 1 and [0113] is used as a heat-resistant film without using a urethane-based adhesive layer. When the back surface protection sheet is constituted by laminating on the back surface and this back surface protection sheet is heat-sealed to the EVA film, it is heat resistant at the initial stage, that is, before being subjected to a deterioration promotion test in a high temperature and high humidity environment. It is described that delamination occurs between the film and the heat-fusible layer. Further, in Table 1 and [0112], the heat-fusible layer is made of only an ethylene-ethyl acrylate copolymer, and this heat-fusible layer is placed on the heat-resistant film via the urethane-based adhesive layer. When a back protective sheet similar to the above except that it is laminated is bonded to an EVA film, sufficient adhesive strength can be achieved in the initial stage, but the strength is reduced by a deterioration promotion test in a high temperature and high humidity environment. It is noted that it is remarkable. From the description such as [0020] in Patent Document 3, this is because the hydrolysis of the urethane-based adhesive layer located in the inner layer of the back surface protection sheet was promoted by acetic acid generated from the EVA film during the deterioration promotion test. It is estimated to be.

Japanese Patent Laying-Open No. 2005-29588 (paragraph [0007]) Japanese Patent Laying-Open No. 2007-329404 (paragraph [0005]) JP 2008-108948 A

  The subject of this invention is providing the back surface protection sheet for solar cells which provided the function which traps the acetic acid which arises from a sealing layer by hydrolysis and becomes a factor of the power generation performance deterioration of a solar cell.

  The present invention comprises an adhesive layer (1 ′) as an outermost surface containing an epoxy resin (A), and a plastic film (2) having one main surface supporting the adhesive layer (1 ′). The adhesive layer (1 ′) further contains a resin (B) other than an epoxy resin having a hydroxyl group and substantially not having a carboxyl group, and a polyisocyanate compound (C), The resin (B) relates to a solar cell back surface protective sheet (V ′) selected from the group consisting of a polyester resin (B1), an acrylic resin, and a urethane resin. Further comprising at least one of a metal foil and a vapor deposition layer made of a metal oxide or a non-metal inorganic oxide on the back side of the main surface supporting the adhesive layer (1 ′) of the plastic film (2). Is preferred.

In the solar cell back surface protective sheet (V ′), the amount of epoxy groups in the adhesive layer (1 ′) as the outermost surface is preferably 0.01 to 2.5 mmol / g.
Moreover, it is preferable that the epoxy equivalent of an epoxy resin (A) is 5000 g / eq or less.
Moreover, as resin (B) other than an epoxy resin which has a hydroxyl group and does not have a carboxyl group substantially, it is more preferable that it is a polyester-type resin (B1),
Furthermore, the ratio of the epoxy resin (A) in the total amount of the epoxy resin (A) and the polyester resin (B1) is preferably in the range of 1 to 50% by weight.
Furthermore, the glass transition temperature of the polyester resin (B1) is preferably in the range of 20 to 100 ° C.
In the solar cell back surface protective sheet (V ′), the polyisocyanate compound (C) is preferably a blocked polyisocyanate compound (C1).

  Furthermore, the present invention provides an epoxy resin (A), a hydroxyl group-free resin (B) other than an epoxy resin, and a polyisocyanate on one main surface of the plastic film (2). Coating the adhesive containing the compound (C) and forming the adhesive layer (1 ′) as the outermost surface, wherein the resin (B) comprises a polyester resin (B1), an acrylic resin, and It is related with the manufacturing method of the back surface protection sheet (V ') for solar cells chosen from the group which consists of urethane type resin.

The present invention also includes a surface protection material (I), a solar cell element (III) having a light receiving surface and a non-light receiving surface, the light receiving surface facing the surface protection material (I), and the solar cell. The sealing layer (IV), which is located on the non-light-receiving surface side of the element (III) and contains an ethylene-vinyl acetate copolymer system, and the solar cell back surface protective sheet (V ′) are bonded to the adhesive layer (1 It is related with the solar cell module which comprised the back surface protection sheet (V) for solar cells affixed on the said sealing layer (IV) so that ') and the said sealing layer (IV) may contact.
The solar cell module may further include a sealing layer (II) containing an ethylene-vinyl acetate copolymer between the surface protective material (I) and the solar cell element (III). .

  Even if acetic acid is generated from the sealing layer by hydrolysis, the acetic acid is supported on the outermost surface of the plastic film (2), is in contact with the sealing layer, and contains the epoxy resin (A). Trapped by Therefore, it can suppress that power generation performance deteriorates due to the acetic acid produced from a sealing layer by hydrolysis.

  The solar cell back surface protective sheet (V ′) of the present invention has the plastic film (2) as an essential constituent layer, and should be a bonding interface with EVA as the sealing layer (IV). And a plastic film (2) carrying an adhesive layer (1 ′) as the outermost surface containing the epoxy resin (A). That is, the back surface protective sheet (V ′) is attached to the sealing layer (IV) of the solar cell module described later so that the adhesive layer (1 ′) and the sealing layer (IV) containing EVA are in contact with each other. Attached.

The adhesive layer (1 ′) as the outermost surface constituting the solar cell back surface protective sheet of the present invention will be described.
The adhesive layer (1 ′) as the outermost surface in the present invention is a resin layer provided in order to improve the adhesion between the plastic film (2) and EVA.

In the solar cell module, the adhesive layer (1) corresponding to the adhesive layer (1 ′) traps acetic acid generated by hydrolysis in the sealing layer (IV). Specifically, the epoxy resin (A) contained in the adhesive layer (1) traps at least a part of acetic acid generated from EVA.
The adhesive layer (1 ′) includes an epoxy resin (A), a resin (B) other than an epoxy resin having a hydroxyl group and having substantially no carboxyl group, and a polyisocyanate compound (C). Is an essential component.

The epoxy resin (A) will be described.
The epoxy resin (A) has a function of trapping acetic acid generated from EVA.
In addition to the epoxy resin (A), as a component having a function of trapping acetic acid generated from EVA, there is a carbodiimide compound as disclosed in Patent Document 3.
However, since the carbodiimide group is more reactive with water than the epoxy group, the trap function is less likely to be sustained due to the influence of water. And if a trap function does not continue, the output fall as a solar cell module will be caused.

  Examples of the epoxy resin (A) used in the present invention include bisphenol type epoxy resin, novolac type epoxy resin, biphenol type epoxy resin, bixylenol type epoxy resin, trihydroxyphenylmethane type epoxy resin, tetraphenylolethane type epoxy resin, and the like. Is mentioned.

Examples of the bisphenol type epoxy resin include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, brominated bisphenol A type epoxy resin, and hydrogenated bisphenol A type epoxy resin.
In the present invention, a bisphenol A type epoxy resin can be preferably used from the viewpoint of cost and solvent solubility.

  Examples of the novolak type epoxy resin include phenol novolak type epoxy resin, cresol novolak type epoxy resin, brominated phenol novolak type epoxy resin, naphthalene skeleton containing phenol novolak type epoxy resin, dicyclopentadiene skeleton containing phenol novolak type epoxy resin, and the like. .

In addition, in the present invention,
An alicyclic epoxy resin such as EHPE-3150 manufactured by Daicel Chemical Industries,
Heterocyclic epoxy resins such as triglycidyl isocyanurate,
A copolymer of glycidylamines such as N, N, N ′, N′-tetraglycidylmetaxylenediamine, glycidyl (meth) acrylate and a compound having an ethylenically unsaturated double bond,
An epoxy compound obtained by glycidyl etherification of a hydroxyl group of glycol or polyol can also be used as the epoxy resin (A).
These may be used alone or in combination of two or more.

The adhesive layer (1 ′) as the outermost surface containing the epoxy resin (A) can be provided by various methods. For example,
An adhesive containing an epoxy resin (A), a resin (B) other than the epoxy resin described later, and a polyisocyanate compound (C) is applied to the plastic film (2), and the coating layer (1′-a) is applied. Once formed, the coating layer (1′-a) can be the outermost adhesive layer (1 ′).
Alternatively, an adhesive containing an epoxy resin (A), a resin (B) other than the epoxy resin described later, and a polyisocyanate compound (C) is applied to the peelable film, dried, and then coated with a coating layer (1′-a ) And transferring the coating layer (1′-a) onto the polyester film (2) via an interlayer adhesive or directly, and then peeling off the peelable film to remove the coating layer ( 1'-a) can be the outermost adhesive layer (1 ').

  In the present invention, in order to define the amount of epoxy group contained in the adhesive layer (1 ') as the outermost surface, the amount of the epoxy group is defined in units of X [mmol / g]. This indicates that X mmol of an epoxy group is contained per 1 g of the solid content in the adhesive layer (1 ') as the outermost surface.

For example, the amount of the epoxy group in the adhesive layer (1 ′) as the outermost surface is preferably 0.01 to 2.5 [mmol / g], more preferably 0.01 to 2 [mmol / g. ], More preferably 0.03 to 1.5 [mmol / g].
When the amount of the epoxy group is less than 0.01 [mmol / g], the trapping effect of acetic acid is reduced. On the other hand, when the amount of the epoxy group is larger than 2.5 [mmol / g], the sealing layer included in the adhesive layer (1 ′) as the outermost surface and the adhesive layer (1) as the outermost surface; Since the content of the component for ensuring the adhesive performance of the resin is relatively reduced, there is a possibility that the adhesive force with the sealing layer is reduced.

  In the present invention, the quantity of epoxy equivalent Y [g / eq] is used as an index representing the amount of epoxy group contained in the epoxy resin (A). This indicates that 1 mol of an epoxy group is contained in the epoxy resin (A) Yg, and the smaller this value, the more the epoxy group is contained in the molecule.

For example, the epoxy resin (A) preferably has an epoxy equivalent of 5000 (g / eq) or less, and more preferably 2000 (g / eq) or less.
If the epoxy equivalent of the epoxy resin (A) is larger than 5000 (g / eq), the number average molecular weight of the epoxy resin is necessarily larger than 5000. Thereby, compatibility with other components is deteriorated, and it becomes difficult to uniformly contain the epoxy resin in the adhesive layer (1 ′) as the outermost surface.
Even if the value of the epoxy equivalent is small, no particular inconvenience has been found.

Moreover, in this invention, the epoxy resin (A) whose number average molecular weight (Mn) is 500-5000 is preferable, and the thing of 500-2000 is more preferable.
When the number average molecular weight of the epoxy resin (A) is less than 500, tackiness may occur on the surface of the adhesive layer (1 ′) as the outermost surface. In an industrial level, the back surface protection sheet (IV) of the present invention has a form in which a long sheet (web) is wound into a roll. Since it is wound up in a roll shape, the surface of the adhesive layer (1 ′) as the outermost surface is in contact with the opposite side of the plastic film (2), or when the back protective sheet (IV) has a multilayer structure. Since it is in contact with various layers provided on the opposite side of the plastic film (2), if tack occurs on the surface of the adhesive layer (1 ') as the outermost surface, it adheres to these contacting layers (blocking) ). Moreover, the durability of a solar cell module may fall that the number average molecular weight of an epoxy resin (A) is less than 500.
When the number average molecular weight of the epoxy resin (A) is larger than 5000, the compatibility with other components deteriorates as described above, which is not preferable.

Next, a resin (B) other than an epoxy resin that has a hydroxyl group and does not substantially have a carboxyl group will be described.
It is important that the resin (B) other than the epoxy resin has substantially no carboxyl group. If the resin (B) other than the epoxy resin has a carboxyl group, the carboxyl group and the epoxy resin (A) react with each other, and the acetic acid trapping effect of the adhesive layer (1) as the outermost surface is reduced. Therefore, it is not preferable.

  Specifically, the acid value of the resin (B) other than the epoxy resin is preferably 3 [mg KOH / g] or less, and more preferably 2 [mg KOH / g] or less. If the acid value of the resin (B) other than the epoxy resin is larger than 3 [mgKOH / g], the resin (B) other than the epoxy resin and the epoxy resin (A) that reacts with the carboxyl group react with each other. The acetic acid trapping effect of the adhesive layer (1) as the surface is reduced.

  The hydroxyl value of the resin (B) other than the epoxy resin is preferably 0.1 to 50 [mg KOH / g], and more preferably 0.5 to 30 [mg KOH / g]. When the hydroxyl value is less than 0.1, the number of reaction points with the polyisocyanate compound (C) decreases, the crosslinking density decreases, and the heat and humidity resistance deteriorates. On the other hand, when the hydroxyl value is larger than 50, the crosslinking density increases, and the adhesive layer (1) after curing becomes too hard, so that the adhesive force with the sealing layer is lowered.

  Moreover, as resin (B) other than an epoxy resin, that whose glass transition temperature (Tg) is 20-100 degreeC is preferable. When the glass transition temperature is lower than 20 ° C., the surface of the adhesive layer (1 ′) as the outermost surface is tucked to be easily blocked and the durability is lowered. When it is higher than 100 ° C., the solution viscosity of the adhesion is increased, and the coating property is lowered.

  Examples of the resin (B) other than the epoxy resin include a polyester resin (B1), a urethane resin, and an acrylic resin, and these can be used alone or in combination of two or more. Further, a composite of these resins can be used.

  The polyester resin (B1) referred to in the present invention is a polyester resin obtained by reacting a carboxylic acid component and a hydroxyl component (esterification reaction, transesterification reaction), and further reacting an isocyanate compound with a polyester resin having a hydroxyl group. And polyester polyurethane polyurea resin obtained by reacting a diamine component.

  As the carboxylic acid component constituting the polyester resin (B1), benzoic acid, p-tert-butylbenzoic acid, phthalic anhydride, isophthalic acid, terephthalic acid, succinic anhydride, adipic acid, azelaic acid, tetrahydrophthalic anhydride , Hexahydrophthalic anhydride, maleic anhydride, fumaric acid, itaconic acid, tetrachlorophthalic anhydride, 1,4-cyclohexanedicarboxylic acid, trimellitic anhydride, methylcyclohexeric carboxylic anhydride, pyromellitic anhydride, ε-caprolactone, A fatty acid can be illustrated. Examples of the carboxylic acid component include methyl esterified products of these carboxylic acid components and lower alcohols such as methanol.

  Examples of the hydroxyl group component constituting the polyester resin (B1) include ethylene glycol, propylene glycol, 1,3-butylene glycol, 1,6-hexanediol, diethylene glycol, dipropylene glycol, neopentyl glycol, triethylene glycol, 3-ethylene glycol, In addition to diol components such as methylpentanediol and 1,4-cyclohexanedimethanol, polyfunctional alcohols such as glycerin, trimethylolethane, trimethylolpropane, trishydroxymethylaminomethane, pentaerythritol, and dipentaerythritol can be exemplified.

  According to a conventional method, those obtained by polymerizing these carboxylic acid component and hydroxyl group component into a predetermined polyester resin can be used in the present invention.

  The urethane-based resin is obtained by reacting a hydroxyl group component other than a polyester resin having a hydroxyl group with an isocyanate compound.

  Examples of the hydroxyl component include polyethylene glycol, polypropylene glycol, polymer polyol such as polyether polyol added with ethylene oxide or propylene oxide, polycarbonate polyol, acrylic polyol, and polybutadiene polyol.

  As an isocyanate compound, the thing similar to the polyisocyanate compound (C) mentioned later can be illustrated. Trimethylene diisocyanate (TDI), hexamethylene diisocyanate (HDI), methylene bis (4,1-phenylene) = diisocyanate (MDI), 3-isocyanate methyl-3,5,5-trimethylcyclohexyl isocyanate (IPDI), xylylene diisocyanate ( XDI), trimethylolpropane adducts of these diisocyanates, isocyanurates that are trimers of these diisocyanates, burette conjugates of these diisocyanates, polymeric diisocyanates, and the like.

In the present invention, a urethane urea resin obtained by further reacting the urethane resin thus polymerized with a diamine component can also be used as a kind of the resin (B) other than the epoxy resin.
As the diamine component, those commonly used when producing a urethane urea-based resin can be used.

  The acrylic resin can be obtained by polymerizing various conventionally known acrylic monomers. As the acrylic monomer, for example, a monomer having no hydroxyl group, glycidyl group or carboxyl group and having a (meth) acrylic monomer having an alkyl group, a (meth) acrylic monomer having a hydroxyl group, or a glycidyl group ( And (meth) acrylic monomers. In addition to these acrylic monomers, vinyl acetate, maleic anhydride, vinyl ether, vinyl propionate, styrene, etc. may be used as the copolymerization monomer.

  Monomers having no hydroxyl group, glycidyl group or carboxyl group and having an alkyl group include (meth) acrylic monomers such as methyl (meth) acrylate, ethyl (meth) acrylate, normal butyl (meth) acrylate, 2-ethylhexyl. (Meth) acrylate, octyl (meth) acrylate, etc. are mentioned.

  Examples of the (meth) acrylic monomer having a hydroxyl group include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, and 4-hydroxybutyl (meth) acrylate.

  Examples of the (meth) acrylic monomer having a glycidyl group include glycidyl acrylate, glycidyl methacrylate, and 4-hydroxybutyl acrylate glycidyl ether.

  In the present invention, unless otherwise specified, “acrylic” means “(meth) acrylic”, and “(meth) acrylic” and “(meth) acrylate” Abbreviations for “acrylic and / or methacrylic” and “acrylate and / or methacrylate”.

  For polymerization of the above acrylic monomer, ordinary radical polymerization can be used. There is no limitation on the reaction method, and it can be carried out by a known polymerization method such as solution polymerization, bulk polymerization, emulsion polymerization, etc., but solution polymerization is preferable because the control of the reaction is easy and the next operation can be directly performed. .

  The solvent is not particularly limited as long as the resin can be dissolved in the present invention, such as methyl ethyl ketone, methyl isobutyl ketone, toluene, cellosolve, ethyl acetate, butyl acetate, and a single solvent or a plurality of solvents may be mixed. Also known as polymerization initiators used in the polymerization reaction are organic peroxides such as benzoyl peroxide, acetyl peroxide, methyl ethyl ketone peroxide, lauroyl peroxide, and azo initiators such as azobisisobutyronitrile. There is no particular limitation.

  Among these resins (B) other than the epoxy resin, the resin (B) other than the epoxy resin is preferably a polyester resin (B1) from the viewpoint of adhesion to the plastic film (2) and the sealing layer. .

  In the present invention, when the adhesive layer (1 ′) as the outermost surface is formed using the adhesive containing the epoxy resin (A) and the polyester resin (B1), the content of the epoxy resin (A) is The total amount of both is preferably 1 to 50% by weight, more preferably 10 to 40% by weight. When the content is less than 1% by weight, the durability is lowered, and the adhesive strength with EVA after wet heat is lowered. On the other hand, if it is more than 50% by weight, the adhesive layer (1) constituting the solar cell module becomes hard and the adhesive force with the initial sealing layer is lowered.

The polyisocyanate compound (C) will be described.
The isocyanate group reacts with a hydroxyl group in the resin (B) other than the epoxy resin, imparts moisture and heat resistance to the cured adhesive layer (1) in contact with the sealing layer (IV), and constitutes a back protective sheet. Adhesiveness with a plastic film (2) or a sealing layer can be improved. Therefore, it is important for the isocyanate compound to have two or more isocyanate groups in one molecule, and examples thereof include aromatic polyisocyanates, chain aliphatic polyisocyanates, and alicyclic polyisocyanates.

  Aromatic polyisocyanates include 1,3-phenylene diisocyanate, 4,4'-diphenyl diisocyanate, 1,4-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4-tolylene diisocyanate, 2,6-triylene diisocyanate. Range isocyanate, 4,4'-toluidine diisocyanate, 2,4,6-triisocyanatetoluene, 1,3,5-triisocyanatebenzene, dianisidine diisocyanate, 4,4'-diphenyl ether diisocyanate, 4,4 ', 4 " -Triphenylmethane triisocyanate etc. can be mentioned.

  Examples of chain aliphatic polyisocyanates include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (HDI), pentamethylene diisocyanate, 1,2-propylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, and dodeca. Examples include methylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate and the like.

  Examples of alicyclic polyisocyanates include 3-isocyanate methyl-3,5,5-trimethylcyclohexyl isocyanate (IPDI), 1,3-cyclopentane diisocyanate, 1,3-cyclohexane diisocyanate, 1,4-cyclohexane diisocyanate, methyl- 2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 4,4′-methylenebis (cyclohexyl isocyanate), 1,4-bis (isocyanatomethyl) cyclohexane, and the like.

  In addition to the polyisocyanate, an adduct of the polyisocyanate and a polyol compound such as trimethylolpropane, a burette or isocyanurate of the polyisocyanate, and further, the polyisocyanate and a known polyether polyol or polyester polyol, Examples thereof include adducts with acrylic polyol, polybutadiene polyol, polyisoprene polyol and the like.

  Among these polyisocyanate compounds (C), a low yellowing type aliphatic or alicyclic polyisocyanate is preferable from the viewpoint that the color hardly changes, and an isocyanurate body is preferable from the viewpoint of heat and moisture resistance. More specifically, hexamethylene diisocyanate (HDI) isocyanurate and 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (IPDI) isocyanurate are preferred.

  Furthermore, the blocked polyisocyanate compound (C1) can be obtained by reacting almost all of the isocyanate groups of the polyisocyanate compound (C) with the blocking agent. The adhesive layer (1 ′) as the outermost surface in the present invention is preferably uncrosslinked until a solar cell module is produced by laminating with a sealant, and therefore the polyisocyanate compound (C) is a block. It is preferable that it is a generalized polyisocyanate compound (C1).

  Examples of the blocking agent include phenols such as phenol, thiophenol, methylthiophenol, xylenol, cresol, resorcinol, nitrophenol, chlorophenol, oximes such as acetone oxime, methyl ethyl ketone oxime, cyclohexanone oxime, methanol, ethanol, n- Alcohols such as propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, t-butyl alcohol, t-pentanol, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, benzyl alcohol Pyrazo such as 3,5-dimethylpyrazole, 1,2-pyrazole , Triazoles such as 1,2,4-triazole, halogen substituted alcohols such as ethylene chlorohydrin, 1,3-dichloro-2-propanol, ε-caprolactam, δ-valerolactam, γ-butyrolactam, β- Examples include lactams such as propyl lactam, and active methylene compounds such as methyl acetoacetate, ethyl acetoacetate, acetylacetone, methyl malonate, and ethyl malonate. Other examples include amines, imides, mercaptans, imines, ureas, and diaryls.

  Among these blocking agents, those having a dissociation temperature of 80 to 150 ° C. are preferable. When the dissociation temperature is less than 80 ° C., when the adhesive as the outermost surface is applied and the solvent is volatilized, the curing reaction proceeds and the adhesion with the sealing layer may be reduced. When the dissociation temperature exceeds 150 ° C., the curing reaction does not sufficiently proceed in the vacuum thermocompression bonding step when the solar cell module is configured, and the adhesion with the sealing layer is lowered.

  Examples of the blocking agent having a dissociation temperature of 80 ° C. to 150 ° C. include methyl ethyl ketone oxime (dissociation temperature: 140 ° C., the same applies hereinafter), 3,5-dimethylpyrazole (120 ° C.), diisopropylamine (120 ° C.), and the like.

  The adhesive layer (1 ′) as the outermost surface used in the present invention has an equivalent ratio of isocyanate groups in the polyisocyanate compound (C) with respect to the total number of hydroxyl groups of the resin (B) other than the epoxy resin. It is preferable to mix | blend so that it may become 1.0-15.0, and it is more preferable to mix | blend so that it may become 1.5-10.0. When there are few polyisocyanate compounds (C), since reaction with resin (B) other than an epoxy resin hardly progresses, the heat-and-moisture resistance of the adhesive bond layer (1) which contact | connects sealing layer (IV) falls. If the polyisocyanate compound (C) is increased, the adhesive layer (1) in contact with the sealing layer (IV) becomes too hard, so that the initial adhesive force with the sealing layer (IV) is reduced.

  The adhesive layer (1 ') as the outermost surface used in the present invention can further contain organic particles or inorganic particles described later. By containing these particles, the tack of the surface of the adhesive layer (1 ') as the outermost surface can be reduced. In particular, organic particles having a melting point or softening point of 150 ° C. or higher can be preferably used. When the melting point or softening point of the organic particles is lower than 150 ° C., the particles may be softened in the vacuum thermocompression bonding process when the solar cell module is formed, and the adhesion with EVA may be hindered.

  Specific examples of organic particles include polymer particles such as polymethyl methacrylate resin, polystyrene resin, nylon resin, melamine resin, guanamine resin, phenol resin, urea resin, silicon resin, methacrylate resin, acrylate resin, or cellulose powder. Nitrocellulose powder, wood powder, waste paper powder, rice husk powder, starch and the like.

  The polymer particles can be obtained by a polymerization method such as an emulsion polymerization method, a suspension polymerization method, a dispersion polymerization method, a soap-free polymerization method, a seed polymerization method, or a microsuspension polymerization method. The organic particles may contain impurities to the extent that the characteristics are not impaired. The shape of the particles may be any shape such as powder, granule, granule, flat plate, and fiber.

  Specific examples of inorganic particles include magnesium, calcium, barium, zinc, zirconium, molybdenum, silicon, antimony, titanium, and other metal oxides, hydroxides, sulfates, carbonates, silicates, etc. Inorganic particles to be used. Further specific examples include silica gel, aluminum oxide, calcium hydroxide, calcium carbonate, magnesium oxide, magnesium hydroxide, magnesium carbonate, zinc oxide, lead oxide, diatomaceous earth, zeolite, aluminosilicate, talc, white carbon, mica , Glass fiber, glass powder, glass beads, clay, wollastonite, iron oxide, antimony oxide, titanium oxide, lithopone, pumice powder, aluminum sulfate, zirconium silicate, barium carbonate, dolomite, molybdenum disulfide, iron sand, carbon black, etc. Inorganic particles containing s.

  Moreover, the said inorganic type particle | grain may contain the impurity to such an extent that the characteristic is not impaired. The shape of the particles may be any shape such as powder, granule, granule, flat plate, and fiber.

  The adhesive layer (1 ′) as the outermost surface used in the present invention is a mixture of the above various particles from 0.01 to 100 parts by weight with respect to a total of 100 parts by weight of the epoxy resin (A) and the resin (B) other than epoxy resin. It is preferable to contain 30 parts by weight, and more preferably 0.1 to 10 parts by weight. When there are few said various particles, the tack | tuck of the adhesive bond layer (1 ') surface as an outermost surface cannot fully be reduced. On the other hand, when the amount of the various particles increases, the adhesion between the adhesive layer (1 ') as the outermost surface and the filler may be hindered, resulting in a decrease in adhesive strength.

  A cross-linking accelerator may be added to the adhesive layer (1 ') as the outermost surface in the present invention as long as the effect of the present invention is not hindered. The crosslinking accelerator plays a role as a catalyst for promoting the urethane bonding reaction by the hydroxyl group of the resin (B) other than the epoxy resin and the isocyanate of the polyisocyanate compound (C). Examples of the crosslinking accelerator include tin compounds, metal salts, bases and the like. Specifically, tin octylate, dibutyltin diacetate, dibutyltin dilaurate, dioctyltin dilaurate, tin chloride, iron octylate, cobalt octylate, and naphthenic acid. Zinc, triethylamine, triethylenediamine and the like can be mentioned.

  Further, in the adhesive layer (1 ′) as the outermost surface in the present invention, a thixotropy-imparting agent, an anti-aging agent, an antioxidant, an antistatic agent, as long as the effects of the present invention are not hindered, if necessary. Flame retardants, thermal conductivity improvers, plasticizers, anti-sagging agents, antifouling agents, antiseptics, bactericides, antifoaming agents, leveling agents, curing agents, thickeners, pigment dispersants, silane coupling agents, etc. Various additives may be added.

  Next, the plastic film (2) which comprises the back surface protection sheet for solar cells of this invention is demonstrated.

Examples of the plastic film (2) include polyester resin films such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, olefin films such as polyethylene, polypropylene, and polycyclopentadiene, polyvinyl fluoride, polyvinylidene fluoride film, and polytetra Fluoro-based films such as fluoroethylene films and ethylene-tetrafluoroethylene copolymer films, acrylic films, and triacetyl cellulose films can be used. A polyester resin film is preferable from the viewpoint of film rigidity and cost, and a polyethylene terephthalate film is preferable.
Further, these films may have a single layer or a multilayer structure of two or more layers.

Examples of the metal oxide or non-metal inorganic oxide to be deposited include oxides such as silicon, aluminum, magnesium, calcium, potassium, tin, sodium, boron, titanium, lead, zirconium, and yttrium. Alkali metal and alkaline earth metal fluorides can also be used, and these can be used alone or in combination.
These metal oxides or non-metal inorganic oxides can be deposited using a conventionally known PVD method such as vacuum deposition, ion plating, sputtering, or the like, or a CVD method such as plasma CVD or microwave CVD.

  These plastic films (2) may be colorless or may contain coloring components such as pigments or dyes. Examples of the method of containing the coloring component include a method of kneading the coloring component in advance at the time of film formation, a method of printing the coloring component on a colorless transparent film substrate, and the like. Further, a colored film and a colorless transparent film may be bonded together.

The back surface protection sheet for solar cells of the present invention is further provided with a metal foil (3) on the side not carrying the adhesive layer (1 ′) as the outermost surface of the plastic film (2) in order to further impart water vapor barrier properties. Or a vapor-deposited layer (4) of a metal oxide or a nonmetal inorganic oxide.

As the metal foil (3), aluminum foil, iron foil, zinc plywood and the like can be used. Among these, an aluminum foil is preferable from the viewpoint of corrosion resistance, and the thickness is preferably 10 μm to 100 μm. More preferably, the thickness is 20 μm to 50 μm.
For the lamination of the metal foil (3), various conventionally known interlayer adhesives can be used.

The vapor deposition layer (4) of a metal oxide or a nonmetal inorganic oxide is provided on one surface of the plastic film (2).
Examples of the metal oxide or non-metal inorganic oxide to be deposited include oxides such as silicon, aluminum, magnesium, calcium, potassium, tin, sodium, boron, titanium, lead, zirconium, and yttrium. Alkali metal and alkaline earth metal fluorides can also be used, and these can be used alone or in combination.

  These metal oxides or non-metal inorganic oxides can be deposited using a conventionally known PVD method such as vacuum deposition, ion plating, sputtering, or the like, or a CVD method such as plasma CVD or microwave CVD.

The back surface protection sheet for solar cells of this invention can further comprise a weather resistant resin layer (5) for imparting weather resistance. The weather resistant resin layer (5) can be located on the outer side of the metal foil (3) or the like responsible for the water vapor barrier property imparting function, that is, on the side opposite to the side where the plastic film (2) is provided. .
The metal foil (3) and the weather-resistant resin layer (5) are preferably provided on the polyester film (2) prior to the formation of the adhesive layer (1 ′) as the epoxy resin-containing outermost surface.

  Examples of the weather resistant resin layer (5) include those obtained by laminating polyester resin films such as polyvinylidene fluoride film, polyethylene terephthalate, polybutylene terephthalate, polynaphthalene terephthalate using various conventionally known interlayer adhesives, Asahi Glass ( A coating layer formed by applying a highly weather-resistant paint such as Lumiflon Co., Ltd. can be used.

Next, a method for forming the adhesive layer (1 ′) as the outermost surface containing the epoxy resin (A) on the plastic film (2) by a coating method will be described.
One main surface of the plastic film (2) is a group consisting of an epoxy resin (A), a polyester resin (B1), an acrylic resin and a urethane resin having a hydroxyl group and substantially no carboxyl group. Apply an adhesive containing a resin (B) other than an epoxy resin and a polyisocyanate compound (C), and volatilize and dry a volatile product such as an organic solvent to obtain an epoxy resin (A). The back surface protection sheet for solar cells of this invention can be obtained by forming the adhesive layer (1 ′) as the outermost surface to be contained.

In the present invention, a conventionally known method can be used as a method of applying the adhesive as the outermost surface to the plastic film (2), specifically, comma coating, gravure coating, reverse coating, roll coating, lip Examples thereof include coating and spray coating. In this invention, the process of apply | coating the adhesive agent as the outermost surface by these methods, and volatilizing a solvent by heat drying is called coating.
The thickness of the formed adhesive layer (1 ′) as the outermost surface is preferably 0.01 to 30 μm, and more preferably 0.1 to 10 μm.

Next, the solar cell module of the present invention will be described.
The solar cell module of the present invention comprises a surface protective material (I),
A solar cell element (III) having a light-receiving surface and a non-light-receiving surface, the light-receiving surface facing the surface protective material (I);
A sealing layer (IV) located on the non-light-receiving surface side of the solar cell element (III) and containing an ethylene-vinyl acetate copolymer system;
The back surface for solar cells, wherein the back surface protection sheet for solar cells (V ′) is attached to the sealing layer (IV) so that the adhesive layer (1 ′) and the sealing layer (IV) are in contact with each other. The protective sheet (V) is an essential constituent layer, and the solar cell back surface protective sheet (V) is in contact with the sealing layer (IV).

  Further, a sealing layer (II) containing an ethylene-vinyl acetate copolymer can be provided between the surface protective material (I) and the solar cell element (III).

On the other hand, when the adhesive layer (1 ′) as the outermost surface constituting the solar cell back surface protective sheet (V ′) of the present invention is thermosetting, the solar cell back surface protective sheet (V ′) is sealed. The adhesive layer (1 ′) as the outermost surface constituting the back protective sheet for solar cells (V ′) by the heat generated when the solar cell element (III) is sealed by being laminated on the layer (IV) is It hardens | cures and becomes an adhesive layer (1), and the back surface protection sheet (V ') for solar cells turns into the back surface protection sheet (V) for solar cells.
The solar cell module of the present invention comprises a surface protective material (I), and optionally a sealing layer (II), a solar cell element (III), a sealing layer (IV), and a back protective sheet for solar cells. (V ′) can be obtained, for example, by bringing them into contact under reduced pressure and then superimposing them under heating and pressure. After returning to the normal pressure, the adhesive layer (1 ′) as the outermost surface can be cured by further placing under a high temperature condition.

In addition, when thermosetting the adhesive layer (1 ′) as the outermost surface using the thermocompression bonding step when forming the solar cell module, the adhesive as the outermost surface that is not thermoset before the thermocompression bonding step. The adhesive layer (1 ′) with the outermost layer as the outermost layer and the thermosetting adhesive layer after the thermocompression bonding step are distinguished as the adhesive layer (1) with the outermost surface.
Similarly, the back surface protection sheet for solar cells before the thermocompression bonding step is distinguished as the back surface protection sheet for solar cells (V ′), and the back surface protection sheet for the solar cell is distinguished as back surface protection sheet for solar cells (V).

  As the solar cell surface protective material (I), a glass plate, a plastic plate of polycarbonate or polyacrylate, and the like can be used, but a glass plate is preferable in terms of transparency, weather resistance, toughness and the like. Furthermore, white glass with high transparency is preferable among the glass plates.

  Located on the light receiving surface side of the solar cell element (III), and a sealing layer (II) containing an ethylene-vinyl acetate copolymer system, and located on the non-light receiving surface side, including an ethylene-vinyl acetate copolymer system As the sealing layer (IV), an ethylene-vinyl acetate copolymer formed into a sheet having a thickness of 0.2 mm to 1.0 mm is mainly used. It may contain an ultraviolet absorber or the like.

  As the solar cell element (III), an electrode is provided on a photoelectric conversion layer such as crystalline silicon, amorphous silicon, a compound semiconductor typified by copper indium selenide, and the like, and these are laminated on a substrate such as glass. Can be exemplified.

  Hereinafter, the present invention will be described in more detail with reference to examples. In the examples, “part” means “part by weight” and “%” means “% by weight”.

<Epoxy resin solution A1>
Polyethylene glycol diglycidyl ether (manufactured by Nagase ChemteX Corp., Denacol EX-821, epoxy equivalent 185) dissolved in ethyl acetate to give a resin solution with a solid content of 50% is designated as epoxy resin solution A1.

<Epoxy resin solution A2>
A cresol novolac type epoxy resin (manufactured by Toto Kasei Co., Ltd., YDCN-704, epoxy equivalent 210) is dissolved in ethyl acetate to obtain a resin solution having a solid content of 50%, which is referred to as an epoxy resin solution A2.

<Epoxy resin solution A3>
A resin solution having a solid content of 50% dissolved in ethyl acetate by dissolving bisphenol A type epoxy resin (manufactured by Japan Epoxy Resin Co., Ltd., JER1001, epoxy equivalent 450) is designated as epoxy resin solution A3.

<Epoxy resin solution A4>
A bisphenol A type epoxy resin (manufactured by Japan Epoxy Resin Co., Ltd., JER1004, epoxy equivalent 900) dissolved in ethyl acetate to give a resin solution with a solid content of 50% is designated as epoxy resin solution A4.

<Epoxy resin solution A5>
An epoxy resin solution A5 is obtained by dissolving a bisphenol A type epoxy resin (manufactured by Japan Epoxy Resin Co., Ltd., JER1007, epoxy equivalent 1900) in ethyl acetate to give a resin solution with a solid content of 50%.

<Epoxy resin solution A6>
A bisphenol A type epoxy resin (manufactured by Japan Epoxy Resin Co., Ltd., JER1009, epoxy equivalent 2800) dissolved in ethyl acetate to give a resin solution with a solid content of 50% is designated as epoxy resin solution A6.

<Epoxy resin solution A7>
A bisphenol A type epoxy resin (manufactured by Japan Epoxy Resin Co., Ltd., JER1010, epoxy equivalent 4800) dissolved in ethyl acetate to give a resin solution with a solid content of 50% is designated as epoxy resin solution A7.

<Epoxy resin solution A8>
A bisphenol A type epoxy resin (manufactured by Japan Epoxy Resin Co., Ltd., JER1256, epoxy equivalent 8000) dissolved in ethyl acetate to give a resin solution with a solid content of 50% is designated as epoxy resin solution A8.

<Epoxy resin solution A9>
A bisphenol A type epoxy resin (manufactured by Japan Epoxy Resin Co., Ltd., JER4275, epoxy equivalent 9000) dissolved in ethyl acetate to give a resin solution with a solid content of 50% is designated as epoxy resin solution A9.

<Polyester resin solution B1>
Charge 99.6 parts of dimethyl terephthalate, 92.2 parts of ethylene glycol, 72.2 parts of neopentyl glycol, and 0.02 part of zinc acetate, and heat to 160-210 ° C. with stirring under a nitrogen stream. A transesterification reaction was carried out. After 97% of the theoretical amount of methanol was distilled, 77.5 parts of isophthalic acid and 166.9 parts of azelaic acid were charged and heated to 160 to 240 ° C. to carry out an esterification reaction. The reaction vessel was gradually reduced in pressure to 1 to 2 Torr, and when the acid value became 0.8 mgKOH / g or less, the reaction under reduced pressure was stopped. The number average molecular weight was 41,000 and the hydroxyl value was 3.2. A polyester polyol having (mgKOH / g), an acid value of 0.7 (mgKOH / g), and a Tg of −10 ° C. was obtained and diluted with ethyl acetate to obtain a polyester resin solution B1 having a solid content of 50%.

  The number average molecular weight, glass transition temperature, acid value, and hydroxyl value were measured as described below.

<Measurement of number average molecular weight (Mn)>
Mn is measured by GPC (gel permeation chromatography), using “Shodex GPC-101” manufactured by Showa Denko KK for the column and “KF-805L” manufactured by Showa Denko KK ”,“ KF-803L ”and“ KF-802 ”were used in a connected manner. GPC is liquid chromatography in which a substance dissolved in a solvent (THF; tetrahydrofuran) is separated and quantified by the difference in molecular size, and the number average molecular weight (Mn) is determined in terms of polystyrene.

<Measurement of glass transition temperature (Tg)>
The glass transition temperature was measured by differential scanning calorimetry (DSC).
About 10 mg of sample was weighed in an aluminum pan and set in a DSC apparatus (reference: the same type of aluminum pan without sample). After heating at 300 ° C. for 5 minutes, using liquid nitrogen − Rapid cooling was performed to 120 ° C. Thereafter, the temperature was raised at 10 ° C./min, and the glass transition temperature (Tg) was calculated from the obtained DSC chart (unit: ° C.).
A sample obtained by drying a small amount of each resin solution at 100 ° C. for 30 minutes was used.

<Measurement of acid value (AV)>
About 1 g of a sample (resin solution: about 50%) is accurately weighed in a stoppered Erlenmeyer flask, and 100 ml of a toluene / ethanol (volume ratio: toluene / ethanol = 2/1) mixed solution is added and dissolved. To this is added phenolphthalein reagent as an indicator and held for 30 seconds. Thereafter, the solution is titrated with a 0.1N alcoholic potassium hydroxide solution until the solution becomes light red.
The acid value was determined by the following formula. The acid value was a numerical value of the dry state of the resin (unit: mgKOH / g).
Acid value (mgKOH / g) = {(5.611 × a × F) / S} / (Nonvolatile content concentration / 100)
Where S: Amount of sample collected (g)
a: Consumption of 0.1N alcoholic potassium hydroxide solution (ml)
F: Potency of 0.1N alcoholic potassium hydroxide solution

<Measurement of hydroxyl value (OHV)>
About 1 g of a sample (resin solution: about 50%) is accurately weighed in a stoppered Erlenmeyer flask, and 100 ml of a toluene / ethanol (volume ratio: toluene / ethanol = 2/1) mixed solution is added and dissolved. Further, exactly 5 ml of an acetylating agent (a solution in which 25 g of acetic anhydride was dissolved in pyridine to make a volume of 100 ml) was added and stirred for about 1 hour. To this, phenolphthalein reagent is added as an indicator and lasts for 30 seconds. Thereafter, the solution is titrated with a 0.1N alcoholic potassium hydroxide solution until the solution becomes light red.
The hydroxyl value was determined by the following formula. The hydroxyl value was a numerical value in the dry state of the resin (unit: mgKOH / g).

Hydroxyl value (mgKOH / g) = [{(ba) × F × 28.25} / S] / (Nonvolatile content concentration / 100) + D
Where S: Amount of sample collected (g)
a: Consumption of 0.1N alcoholic potassium hydroxide solution (ml)
b: Consumption of 0.1N alcoholic potassium hydroxide solution in the empty experiment (ml)
F: Potency of 0.1N alcoholic potassium hydroxide solution D: Acid value (mgKOH / g)

<Polyester resin solution B2>
A polyester resin “Byron 200” (Toyobo Co., Ltd., number average molecular weight 17,000, hydroxyl value 6 (mgKOH / g), acid value 2 (mgKOH / g) or less, Tg: 67 ° C.) was dissolved in methyl ethyl ketone. A polyester resin solution B2 having a solid content of 50% was obtained.

<Polyester resin solution B3>
The polyester resin solution B1 and the polyester resin solution B2 were mixed at a weight ratio of 1: 1 to obtain a polyester resin solution B3 having a solid content of 50% by weight.
The polyester resin in the polyester resin solution B3 had a hydroxyl value of 4.6 (mgKOH / g), an acid value of 0.8 (mgKOH / g), and a Tg of 28 ° C.

<Polyester resin solution B4>
Polyester resin “Elitel UE-3210” (Unitika Ltd., number average molecular weight 20,000, hydroxyl value 4 (mgKOH / g), acid value 1 (mgKOH / g), Tg: 45 ° C.) dissolved in methyl ethyl ketone As a result, a polyester resin solution B4 having a solid content of 50% was obtained.

<Polyester resin solution B5>
117 parts of diethylene glycol, 319 parts of neopentyl glycol, 192 parts of isophthalic acid, 188 parts of terephthalic acid, and 214 parts of adipic acid are charged into a reaction can and heated to 160-240 ° C. with stirring under a nitrogen stream to carry out an esterification reaction. It was. The reaction vessel was gradually reduced in pressure to 1 to 2 Torr, and when the acid value became 1 mgKOH / g or less, the reaction was stopped under reduced pressure, the number average molecular weight was 10,000, and the hydroxyl value was 19 (mgKOH / g ), A polyester resin having an acid value of 0.9 (mg KOH / g) and a Tg of 0 ° C. was obtained and diluted with ethyl acetate to obtain a polyester resin solution B5 having a solid content of 50%.

<Polyester resin solution B6>
Polyester resin “Elitel UE-9900” (Unitika Ltd., number average molecular weight 20,000, hydroxyl value 8 (mgKOH / g), acid value 2 (mgKOH / g), Tg: 101 ° C.) dissolved in methyl ethyl ketone As a result, a polyester resin solution B6 having a solid content of 50% was obtained.

<Polyester resin solution B7>
A polyester resin “Byron 670” (Toyobo Co., Ltd., number average molecular weight 30,000, hydroxyl value less than 2 (mgKOH / g), acid value 2 (mgKOH / g), Tg: 7 ° C.) was dissolved in methyl ethyl ketone. A polyester resin solution B7 having a solid content of 50% was obtained.

<Polyester resin solution B8>
A polyester resin “Byron GK360” (Toyobo Co., Ltd., number average molecular weight 16,000, hydroxyl value 7 or less (mgKOH / g), acid value 5 (mgKOH / g), Tg: 56 ° C.) was dissolved in methyl ethyl ketone. A polyester resin solution B8 having a solid content of 50% was obtained.

<Polyester resin solution B9>
Polyester resin “Elitel XA-0653” (Unitika Ltd., number average molecular weight 5,000, hydroxyl value 2 or less (mgKOH / g), acid value 20 (mgKOH / g), Tg: 56 ° C.) to methyl ethyl ketone It melt | dissolved and the polyester resin solution B9 of 50% of solid content was obtained.

<Acrylic resin solution B10>
In a four-necked flask equipped with a cooling tube, a stirrer, a thermometer, and a nitrogen introduction tube, 40 parts of methyl methacrylate, 30 parts of n-butyl methacrylate, 28 parts of 2-ethylhexyl methacrylate, 2 parts of 2-hydroxyethyl methacrylate, 100 of toluene The temperature was raised to 80 ° C. with stirring in a nitrogen atmosphere, 0.15 parts of azobisisobutyronitrile was added, and the polymerization reaction was carried out for 2 hours. 07 parts were added and the polymerization reaction was further performed for 2 hours, and 0.07 parts of azobisisobutyronitrile was further added and the polymerization reaction was further performed for 2 hours. The number average molecular weight was 25,000, the hydroxyl value was 8.4 ( mgKOH / g), an acid value of 0 (mgKOH / g), Tg of 39 ° C., and an acrylic resin solution B10 having a solid content of 50% were obtained.

<Acrylic resin solution B11>
A four-necked flask equipped with a cooling tube, a stirrer, a thermometer, and a nitrogen introduction tube was charged with 40 parts of methyl methacrylate, 30 parts of n-butyl methacrylate, 30 parts of 2-ethylhexyl methacrylate, and 100 parts of toluene, and under a nitrogen atmosphere. While stirring, the temperature was raised to 80 ° C., 0.15 part of azobisisobutyronitrile was added to conduct a polymerization reaction for 2 hours, and then 0.07 part of azobisisobutyronitrile was added to conduct polymerization for another 2 hours. Then, 0.07 part of azobisisobutyronitrile was added and polymerization reaction was further performed for 2 hours. The number average molecular weight was 24,000, the hydroxyl value was 0 (mgKOH / g), and the acid value was 0 ( mgKOH / g), an acrylic resin solution B11 having a Tg of 36 ° C. and a solid content of 50% was obtained.

<Acrylic resin solution B12>
In a four-necked flask equipped with a cooling tube, a stirrer, a thermometer, and a nitrogen introduction tube, 40 parts of methyl methacrylate, 30 parts of n-butyl methacrylate, 27 parts of 2-ethylhexyl methacrylate, 1 part of 2-hydroxyethyl methacrylate, methacrylic acid 2 parts and 100 parts of toluene were added, the temperature was raised to 80 ° C. with stirring in a nitrogen atmosphere, 0.15 part of azobisisobutyronitrile was added and a polymerization reaction was carried out for 2 hours. 0.07 part of nitrile is added and the polymerization reaction is further performed for 2 hours, and further 0.07 part of azobisisobutyronitrile is added and the polymerization reaction is further performed for 2 hours. The number average molecular weight is 27,000, the hydroxyl value is Was 4.4 (mgKOH / g), the acid value was 15 (mgKOH / g), Tg was 42 ° C., and an acrylic resin solution B12 having a solid content of 50% was obtained.

<Urethane resin solution B13>
140 parts of polycarbonate diol (Ube Industries, Ltd., UC-100, number average molecular weight 1,000), 5 parts of 1,6-hexanediol, and 27 parts of isophorone diisocyanate were charged into a reaction can and stirred under a nitrogen stream. While gradually heating to 140 to 160 ° C., the urethanization reaction was carried out. After reacting at 160 ° C. for 3 hours and confirming that there is no NCO peak by IR measurement, ethyl acetate was added, the number average molecular weight was 35,000, the hydroxyl value was 3.2 (mgKOH / g), the acid value. Was 0 (mg KOH / g), Tg was 30 ° C., and a solid content of 50% urethane resin solution B13 was obtained.

<Urethane resin solution B14>
82 parts of polycarbonate diol (manufactured by Ube Industries, Ltd., UC-100, number average molecular weight 1,000), 18 parts of dimethylolbutanoic acid, and 100 parts of isophorone diisocyanate are charged into a reaction can and stirred under a nitrogen stream. The urethanization reaction was performed by gradually heating to 140 to 160 ° C. After reacting at 160 ° C. for 3 hours and confirming that there is no NCO peak by IR measurement, ethyl acetate was added, the number average molecular weight was 32,000, the hydroxyl value was 3.5 (mgKOH / g), and the acid value. Was 12 (mgKOH / g), Tg was 35 ° C., and a solid content of 50% urethane resin solution B14 was obtained.

<Curing agent solution C>
A trimer of isophorone diisocyanate blocked with MEK oxime and a trimer of hexamethylene diisocyanate blocked with MEK oxime were mixed at a weight ratio of 1: 1 and diluted with ethyl acetate to give a solid content of 50%. The resin solution is used as a curing agent solution.

<Additive D1>
N, N′-dicyclohexylcarbodiimide (functional group equivalent 206) is used as additive D1.

<Additive D2>
Carbodilite V-07 (Nisshinbo Co., Ltd., functional group equivalent 200) is set as additive D2.

<Adhesive adjustment>
Mix the epoxy resin solution (A), the resin solution other than the epoxy resin (B), the curing agent solution (C), the additive (D), and dibutyltin dilaurate so that the solid content ratios shown in Tables 1 and 2 are obtained. Then, adhesives 1 to 39 as outermost surfaces were obtained.

[Reference Examples 1 to 11], [Examples 12 to 15], [Examples 17 to 21], [Reference Examples 22 to 23], [Examples 24 to 25], [Comparative Examples 1 to 14]
Using the adhesives 1 to 39 for the outermost surface, the adhesion between the polyester film and the EVA sheet (initial, after wet heat aging) and the amount of acetic acid generated from the EVA sheet were measured by the method described later.
These results are shown in Table 2.

[Adhesive strength measurement]
Adhesives 1 to 39 as the outermost surface are applied to the corona-treated surface of a polyester film (Toray Co., Ltd., Lumirror X-10S, thickness 50 μm) with a Mayer bar, the solvent is evaporated, and the coating amount is 2 g / m 2. A polyester film with an adhesive layer (1 ′) as the outermost surface was provided.
Two polyester films with an adhesive layer (1 ′) as the outermost surface are prepared, and an adhesive layer as the outermost surface is formed on both sides of an EVA sheet (thickness 450 μ, standard cure type, hereinafter the same) manufactured by Sanvic Co., Ltd. The EVA sheet is sandwiched between two polyester films with an adhesive layer (1 ′) as the outermost surface so that (1 ′) is in contact, the temperature is 150 ° C. with a vacuum laminator, the degassing time is 5 minutes, the press pressure is 1 atm, A press time was 10 minutes and after-curing was performed under pressure at 150 ° C. for 15 minutes to produce a sample for measuring the adhesive force.
A part of the sample for measuring the adhesive force was subjected to a pressure cooker test (hereinafter referred to as a PCT test) for 192 hours under an environmental condition of a temperature of 105 ° C. and a relative humidity of 100% RH.
Those that were not subjected to the PCT test (initial) and those that were tested (after wet heat aging) were each cut into a 15 mm wide rectangle to obtain a test piece. Each test piece was subjected to a T-peeling test using a tensile tester at a load speed of 100 mm / min.
○: 20 N / 15 mm or more Δ: 5 N / 15 mm or more to less than 20 N / 15 mm ×: less than 5 N / 15 mm

[Evaluation method of acetic acid generation amount]
<Preparation of polyester film (2)>
Corona treatment was applied to both sides of a polyester film (Teijin DuPont Films, Tetron S, thickness 188 μm), and an interlayer adhesive “Dyna Leo VA-3020 / HD-701” (manufactured by Toyo Ink Manufacturing Co., Ltd.) A blending ratio of 100/7, the same applies hereinafter) is applied by a gravure coater, the solvent is dried, an application amount: an interlayer adhesive layer of 10 g / square meter is provided, and a vapor deposition surface of the following deposited PET is provided on the interlayer adhesive layer. Superimposed. Thereafter, an aging treatment was performed at 50 ° C. for 4 days to cure the interlayer adhesive layer, thereby obtaining a polyester film (2) for evaluation.
The vapor-deposited PET used was a single-side vapor-deposited polyethylene terephthalate film formed by applying a silicon oxide vapor-deposited layer on one side of the polyethylene terephthalate film and the other side being corona-treated (Tech Barrier LX, thickness 12 μm, manufactured by Mitsubishi Plastics) It is.

<Creation of back surface protection sheets 1-39>
Adhesives 1 to 39 as the outermost surface are applied to the corona-treated surface of the single-side vapor-deposited PET of the polyester film for evaluation (2) with a Mayer bar, the solvent is stripped off, and the coating amount is 2 g / square meter as the outermost surface. An adhesive layer (1 ′) was formed, and back protection sheets 1 to 39 for evaluation were obtained.

<Production of pseudo module for evaluation>
The glass sheet, the same EVA sheet used for preparing the adhesive force measurement sample, and the back surface protection sheets 1 to 39 are stacked so that the EVA sheet and the adhesive layer (1 ′) as the outermost surface are in contact with each other. In addition, a pseudo module for evaluation was manufactured by heating and pressure bonding with a vacuum laminator at a temperature of 150 ° C., a deaeration time of 5 minutes, a press pressure of 1 atm, a press time of 10 minutes, and an after cure of 150 ° C.-15 minutes.

<Acceleration of hydrolysis of EVA sheet>
The pseudo module for evaluation was subjected to a pressure cooker test for 96 hours or 192 hours under an environmental condition of a temperature of 105 ° C. and a relative humidity of 100% RH, thereby promoting hydrolysis of the EVA sheet under each condition.

<Measurement of acetic acid generation amount>
(1) After performing a 96-hour or 192-hour pressure cooker test, the glass plate and the protective sheet were peeled off from the evaluation pseudo module, and the EVA sheet was isolated.
(2) Weigh out the center part (part at least 3 cm away from the peripheral part) of the EVA sheet cut into 1.5 cm square (Xg), and immerse it in about 4 g of water (Yg) to seal it, The mixture was left overnight, and acetic acid generated in the EVA sheet due to acceleration of hydrolysis was extracted into water.
(3) The concentration of acetic acid (Z μg / g) was determined by ion chromatography for the extracted water described in (2) above.
(4) By multiplying the concentration of acetic acid (Z μg / g) determined in (3) above by the amount of immersed water (Yg) and dividing by the weight (Xg) of EVA used for extraction, The amount of acetic acid generated (μg / g) was calculated. This calculation formula is described below.
(Acetic acid generation amount per 1 g of EVA [μg / g]) = Z [μg / g] × Y [g] / X [g]

[Comparative Example 19]
In Example 1, without applying the adhesive 1 as the outermost surface, the evaluation polyester film (2) is used as it is as the back protective sheet 44, and the adhesive strength with the EVA sheet (initial, after wet heat aging), and the EVA sheet The amount of acetic acid generated from was measured. The results are shown in Table 3.

As shown in Table 3, Examples 12 to 15 , 17 to 21 , and 24 to 25 are produced by hydrolysis of EVA, with the adhesive layer (1) as the outermost surface in contact with the EVA sheet containing an epoxy resin. Since acetic acid is trapped, the adhesive layer (1) as the outermost surface is generated from EVA as compared with Comparative Examples 1 to 5 that do not contain an epoxy resin and Comparative Example 19 that does not have an adhesive layer as the outermost surface. Can reduce the amount of acetic acid.

  In Comparative Examples 6 and 9, since the resin (B) other than the epoxy resin does not have a hydroxyl group, Comparative Example 14 does not have the polyisocyanate compound (C). Since it does not adhere to the stopper layer, the amount of acetic acid is greatly increased by bringing water into the sealing layer interface as a result.

  In Comparative Examples 7, 8, 10, and 11, since the resin (B) other than the epoxy resin substantially has a carboxyl group, the glycidyl group of the epoxy resin (A) and the resin other than the epoxy resin (B ) Reacts with the carboxyl group. As a result, the amount of glycidyl groups in the epoxy resin is reduced, so that the amount of acetic acid generated from EVA cannot be trapped, resulting in a significant increase in the amount of acetic acid.

  In Comparative Examples 12 and 13, since carbodiimide that reacts with acetic acid is added to the adhesive layer (1) as the outermost surface, the amount of acetic acid generated after PCT test 105 ° C. × 96 h is the same as in Examples 1 to 25 However, a lot of acetic acid was detected after PCT test 105 ° C. × 192 h. This is because the carbodiimide group is more reactive than the epoxy group, so that the carbodiimide group reacts with moisture during the PCT test, and the trapping effect of acetic acid is reduced.

  In Comparative Examples 15 and 16, the dispersion of the epoxy resin in the adhesive sheets 1 and 2 was non-uniform, so that the portion that exhibits the acid trapping effect by the epoxy resin and the portion that does not exhibit the adhesion and the sealing layer are bonded. Since the part which did not adhere | attach with a part had arisen, the effect of reducing the amount of acetic acid was not acquired as a result. Moreover, since Comparative Examples 17 and 18 have no non-uniform portion as seen in Comparative Examples 15 and 16, the adhesive strength after initial and wet heat was sufficient, but there was no function to trap acetic acid. The amount of acetic acid increased significantly.

In Examples 13 to 15 , since the epoxy equivalent of the epoxy resin (A) is too large, the compatibility with the resin (B) other than the epoxy resin is inferior, so the acid trapping effect is slightly inferior.
In Reference Example 22 , since the amount of epoxy groups in the adhesive solid content is small, the acid trapping effect is slightly inferior.
Since Reference Example 23 has a large amount of epoxy groups in the adhesive solid content, it is slightly inferior in adhesive force with the sealing layer.
In Examples 24 and 25, since the ratio of the epoxy resin (A) in the total amount of the epoxy resin (A) and the resin (B) other than the epoxy resin is large, the adhesive strength with the sealing layer is slightly inferior.
Further, in Examples 17 and 18, since the glass transition temperature of the resin (B) other than the epoxy resin was low, the initial adhesive force can be expressed, but the adhesive force after wet heat is slightly lowered, and Example 19 is a glass transition. Since the temperature was high, the initial adhesive strength was slightly inferior.

[ Reference Example 26 ]
<Creation of solar cell module>
Back surface protection sheet 1 ... Back surface protection sheet using adhesive 1 as the outermost surface (sheet having the same laminated structure as used in the evaluation of the amount of acetic acid generated)
White glass ... Solar cell surface protective material (I)
EVA sheet: Light-receiving surface side sealant layer (II)
Polycrystalline silicon solar cell element ... solar cell element (III)
EVA sheet: EVA non-light-receiving surface side sealant layer (IV)
The above (I)-(IV) and the back surface protective sheet 1 are stacked in order so that the adhesive layer (1 ′) as the outermost surface of the back surface protective sheet 1 is in contact with the EVA non-light-receiving surface side sealant layer (IV). After that, the solar cell module 1 for photoelectric conversion efficiency evaluation of 10 cm × 10 cm square is heated with a vacuum laminator at a temperature of 150 ° C., a deaeration time of 5 minutes, a press pressure of 1 atm, a press time of 15 minutes, and an after cure of 150 ° C. for 30 minutes. Produced.

<Measurement of photoelectric conversion efficiency>
The solar cell output of the obtained solar cell module 1 was measured, and the photoelectric conversion efficiency was measured using a solar simulator (SS-100XIL, manufactured by Eihiro Seiki Co., Ltd.) according to JIS C8912.
Furthermore, the photoelectric conversion efficiency after the wet heat resistance test after leaving still for 1000 hours and 2000 hours under environmental conditions of a temperature of 85 ° C. and a relative humidity of 85% RH was measured in the same manner. The ratio of the decrease in photoelectric conversion efficiency after the wet heat resistance test with respect to the initial photoelectric conversion efficiency was calculated and evaluated as follows.
◎: Output decrease is less than 5% ○: Output decrease is from 5% to less than 10% △: Output decrease is from 10% to less than 20% ×: Output decrease is 20% or more

[Reference Examples 27 to 36], [Examples 37 to 40], [Examples 42 to 46], [Reference Examples 47 to 48], “Reference Examples 49 to 50”, [ Comparative Examples 20 to 38]
In the same manner as in Reference Example 26 , solar cell modules 2 to 44 were prepared using the back surface protective sheets 2 to 44 used in the evaluation of the amount of acetic acid generated, and the photoelectric conversion efficiency (initial, after the wet heat resistance test) was measured. did.

[ Reference Example 51]
Polyester film (manufactured by Teijin DuPont Films, Tetron S, thickness 188 μm
) On one side, the adhesive 6 as the outermost surface is applied to the corona-treated surface with a Mayer bar, the solvent is stripped, and the adhesive layer as the outermost surface with an application amount: 2 g / square meter (
1 ′) was formed, and a back protective sheet 45 for evaluation was obtained. Using this, the solar cell module 45 was produced in the same manner as in Example 26, and the photoelectric conversion efficiency (initial, after the wet heat resistance test) was measured.

[Comparative Example 39]
In Reference Example 51, except that the adhesive 27 as the outermost surface was used instead of the adhesive 1 as the outermost surface, the back surface protective sheet 46 for evaluation was obtained in the same manner as in Reference Example 51, and the solar cell module 46 was produced, and the photoelectric conversion efficiency (initial, after wet heat resistance test) was measured. The above results are shown in Table 3.

As shown in Table 4, Examples 37 to 40 , 42 to 46 , and 49 to 50 are adhesive layers (1) containing the epoxy resin (A) as the outermost surface adhesive layer (1). Since the back surface protection sheet having 1 ′) is used and the acid generated from EVA is trapped, the output reduction of the solar cell module after the wet heat test can be suppressed.

On the other hand, Comparative Examples 20 to 30 and 33 to 39 have no effect of reducing the amount of acetic acid generated, and thus the output of the solar cell module is lowered due to the influence of acid generated from EVA during the wet heat test.
In Reference Example 51, since the epoxy resin (A) in the adhesive layer (1) as the outermost surface has an acid trapping effect, the solar cell module is deteriorated as compared with Comparative Example 39 having no such effect. However, since the back protective sheet has no water vapor barrier property, the output is reduced as compared with Reference Example 31.

  Moreover, since Comparative Examples 31 and 32 contain carbodiimide that reacts with acetic acid in the adhesive layer (1) as the outermost surface, the output degradation of the solar cell module at the initial stage of the wet heat test is suppressed. Since moisture reacts with carbodiimide and the trap effect of acetic acid is weakened, deterioration cannot be suppressed over a long period of time. These results are in agreement with the results of acetic acid generation in Table 2.

  As described above, by using the solar cell protective sheet of the present invention, acetic acid generated from the sealing layer can be trapped and output degradation of the solar cell module can be suppressed.

Claims (11)

An adhesive layer (1 ′) as an outermost surface containing an epoxy resin (A), and a plastic film (2) having one main surface supporting the adhesive layer (1 ′); The layer (1 ′) further contains a resin (B) other than an epoxy resin and a polyisocyanate compound (C),
The resin (B) is a resin selected from the group consisting of an acrylic resin and a urethane resin, and has a hydroxyl group of 0.1 to 50 mgKOH / g and an acid value of 3 mgKOH / g or less.
Solar cell back surface protection sheet (V ').   The back protective sheet (V ') for solar cells according to claim 1, wherein the amount of epoxy groups in the adhesive layer (1') is in the range of 0.01 to 2.5 mmol / g.   The back surface protection sheet (IV ') for solar cells according to claim 1 or 2, wherein an epoxy equivalent of the epoxy resin (A) is 5000 g / eq or less.   The sun according to any one of claims 1 to 3, wherein a ratio of the epoxy resin (A) in a total amount of the epoxy resin (A) and the resin (B) is in a range of 1 to 50% by weight. Battery back surface protection sheet (V ′).   The back surface protection sheet (V ') for solar cells according to any one of claims 1 to 4, wherein a glass transition temperature of the resin (B) is in a range of 20 to 100C.   An adhesive layer (1 ′) as an outermost surface containing an epoxy resin (A), and a plastic film (2) having one main surface supporting the adhesive layer (1 ′); The layer (1 ′) further contains, other than the epoxy resin, a resin (B) having a hydroxyl group of 2 to 50 mgKOH / g and an acid value of 3 mgKOH / g or less, and a polyisocyanate compound (C).
  The resin (B) is a polyester resin (B1).
  Solar cell back surface protection sheet (V ').
(However, the adhesive layer (1 ′) as the outermost surface layer containing the epoxy resin (A) having an epoxy equivalent of 5000 g / eq or less, and one main surface supported the adhesive layer (1 ′). A plastic film (2), and the adhesive layer (1 ′) has a hydroxyl group and substantially does not have a carboxyl group, a resin (B) other than an epoxy resin, and a polyisocyanate compound ( C) and the resin (B) is a polyester resin (B1) having a glass transition temperature in the range of 20 to 100 ° C., and the amount of epoxy groups in the adhesive layer (1 ′) Is in the range of 0.05 to 2 mmol / g, and the ratio of the epoxy resin (A) in the total amount of the epoxy resin (A) and the polyester resin (B1) is in the range of 1 to 50% by mass. Back for solar cell inside Protective sheet (V ') except)   The back protective sheet (V ') for solar cells according to any one of claims 1 to 6, wherein the polyisocyanate compound (C) is a blocked polyisocyanate compound (C1).   At least one of a metal foil and a vapor deposition layer made of a metal oxide or a nonmetal inorganic oxide is further provided on the back side of the main surface supporting the adhesive layer (1 ′) of the plastic film (2). The back surface protection sheet (V ') for solar cells in any one of Claims 1 thru | or 7. On one main surface of the plastic film (2), an adhesive containing an epoxy resin (A) , a resin (B) other than an epoxy resin, and a polyisocyanate compound (C) is applied, and an adhesive layer ( Forming 1 ′) as the outermost surface,
The resin (B) is a resin selected from the group consisting of an acrylic resin and a urethane resin, and has a hydroxyl group of 0.1 to 50 mgKOH / g and an acid value of 3 mgKOH / g or less.
The manufacturing method of the back surface protection sheet (V ') for solar cells. Surface protective material (I),
A solar cell element (III) having a light-receiving surface and a non-light-receiving surface, the light-receiving surface facing the surface protective material (I);
A sealing layer (IV) located on the non-light-receiving surface side of the solar cell element (III) and containing an ethylene-vinyl acetate copolymer system;
The solar cell back surface protective sheet (V ') according to any one of claims 1 to 8 is attached to the adhesive layer (1).
A solar cell module comprising a solar cell back surface protective sheet (V) which is attached to the sealing layer (IV) so that the sealing layer (IV) is in contact with the sealing layer (IV). The solar cell module according to claim 10, further comprising a sealing layer (II) containing an ethylene-vinyl acetate copolymer between the surface protective material (I) and the solar cell element (III).