Surface protection film for solar cells, surface protection material for solar cells, solar cell module, and manufacturing method of solar cell module

Abstract

To provide a surface protection film for solar cells and surface protection material for solar cells with excellent durability while keeping good adhesion to the sealing member.SOLUTION: A surface protection film for solar cells consists of one or more layers. The outermost surface layer of the surface protection film for solar cells contains (1) (meth)acrylic resin emulsion and (2) blocked polyisocyanate. The (1) (meth)acrylic resin emulsion is a resin having a hydroxyl value of 3 mg / g-KOH or more and 150 mg / g-KOH or less, or a resin having an amino value of 3 mgKOH / g or more and 150 mgKOH / g or less. The (2) blocked polyisocyanate has at least one isocyanate compound selected from the group consisting of aliphatic isocyanates and alicyclic isocyanates as the backbone.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a surface protective film for a solar cell, a surface protective material for a solar cell, a solar cell module, and a method for manufacturing a solar cell module. [Background technology]

[0002] In recent years, solar cells have been attracting attention as an energy source that does not emit carbon dioxide when generating electricity, with the aim of achieving so-called carbon neutrality. The solar cell module that makes up a solar cell is generally constructed by laminating, in order from the light-receiving side, a surface protection material, a surface sealing material, a solar cell, a back sealing material, and a back protection sheet (back sheet), and electricity is generated when sunlight enters the solar cell.

[0003] Solar modules are used outdoors for decades, so the components that make up the solar module must be durable enough to withstand the harsh outdoor environment, with surface protection materials in particular being required to be highly durable.

[0004] Surface protection materials must be highly durable, so conventional solar cell modules have used glass substrates as surface protection materials to ensure weather resistance. However, in applications where weight is limited, such as in-vehicle applications, solar cell modules must be lightweight. For this reason, efforts have been made in recent years to replace glass substrates with transparent resin substrates or films, with replacement with transparent resin films in particular attracting attention.

[0005] Patent Document 1 discloses a polyester film as a surface protection film. Patent Document 2 discloses an embodiment in which a fluorine-based coating layer is used on a polyethylene terephthalate (PET) film. In Patent Document 3, weather resistance is ensured by using a fluorine-based resin film as a surface protection film. Patent Document 4 discloses a polyethylene terephthalate (PET) film laminated with a siloxane-based coating layer. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 5776541 [Patent Document 2] Japanese Patent Application Publication No. 2017-98483 [Patent Document 3] International Publication No. 2012 / 002416 [Patent Document 4] Patent No. 6790236 Summary of the Invention [Problem to be solved by the invention]

[0007] There is a concern that the surface protection film disclosed in Patent Document 1 may not be able to exhibit the high durability required for solar cell modules. As in Patent Documents 2 and 3, there is a concern that fluorine materials may not be able to exhibit sufficient adhesion to the underlying surface sealing material or sufficient scratch resistance. When the laminate disclosed in Patent Document 4 is used outdoors, the reaction in the siloxane-based coating layer may progress, leading to breakage or cracks in the surface layer.

[0008] By using the techniques described in Patent Documents 1 and 4, it is possible to obtain a surface protective material for solar cells that has adhesion to the encapsulant, but it is difficult to achieve this while also achieving high durability. Furthermore, by using the techniques described in Patent Documents 2 and 3, it is possible to obtain a highly durable surface protective material for solar cells, but it is difficult to achieve a high level of adhesion to the encapsulant.

[0009] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a surface protective film for solar cells and a surface protective material for solar cells that have excellent durability while maintaining good adhesion to an encapsulant. A further object of the present invention is to provide a solar cell module using the solar cell surface protective film and solar cell surface protective material, and a method for manufacturing the solar cell module. In this specification, "durability" means weather resistance, acid resistance, base resistance, and solvent resistance. [Means for solving the problem]

[0010] That is, the present invention includes the following aspects. [1] A surface protection film for solar cells which is composed of one or more layers, wherein the outermost layer of the surface protection film for solar cells contains (1) a (meth)acrylic resin emulsion and (2) a blocked polyisocyanate, wherein the (1) (meth)acrylic resin emulsion is a resin having a hydroxyl value of 3 mg / g-KOH or more and 150 mg / g-KOH or less, or a resin having an amino value of 3 mgKOH / g or more and 150 mgKOH / g or less, and the (2) blocked polyisocyanate is a blocked polyisocyanate having, as a skeleton, at least one isocyanate compound selected from the group consisting of aliphatic isocyanates and alicyclic isocyanates. [2] The surface protective film for a solar cell according to [1], wherein the (meth)acrylic resin emulsion (1) has a glass transition temperature of −20° C. or higher and 120° C. or lower. [3] The surface protective film for solar cells according to [1] or [2], wherein the glass transition temperature of the surface protective film for solar cells is −40° C. or higher and 140° C. or lower. [4] The surface protective film for a solar cell according to any one of [1] to [3], wherein the (meth)acrylic resin emulsion (1) has a number average molecular weight of 1,000 or more and 2,000,000 or less. [5] The surface protective film for solar cells according to any one of [1] to [4], wherein the monomer units constituting the (1) (meth)acrylic resin emulsion include a monomer having a carboxyl group. [6] The surface protection film for solar cells according to any one of [1] to [6], wherein the weight fraction of the (1) (meth)acrylic resin emulsion is 50% or more and 99% or less, and the weight fraction of the (2) blocked polyisocyanate is 1% or more and 50% or less. [7] The surface protective film for solar cells according to any one of [1] to [6], wherein the molar ratio (NCO groups / OH groups) of the blocked isocyanate groups contained in the (2) blocked polyisocyanate to the hydroxyl groups contained in the (1) (meth)acrylic resin emulsion is 0.05 to 3.0. [8] The surface protective film for a solar cell according to any one of [1] to [7], further comprising a surfactant. [9] The surface protective film for solar cells according to any one of [1] to [8], wherein the weight fraction of the surfactant relative to the weight of the surface protective film for solar cells is 0.01 mass % or more and 10 mass % or less.

[10] A surface protective film for a solar cell comprising two or more layers, wherein, when the glass transition temperature of the outermost layer is Tgu and the glass transition temperature of the bottom layer is Tgl, the Tgu is higher than the Tgl.

[11] A surface protective laminate for solar cells, comprising at least two layers selected from the group consisting of a surface layer, a base layer, a pressure-sensitive adhesive layer, and a release layer, wherein the surface layer is the surface protective film for solar cells according to any one of [1] to

[10] .

[12] The surface protective material for solar cells according to

[11] , which has a film thickness of 5 μm or more and 1000 μm or less.

[13] A solar cell module protected by the surface protective film for solar cells according to any one of [1] to

[10] .

[14] A solar cell module protected by the solar cell surface protective material according to

[11] or

[12] .

[15]

[13] A method for manufacturing a solar cell module according to the present invention, comprising the steps of stacking a surface protective film, a surface sealing material, a solar cell, a back sealing material, and a back protective material in this order, and integrally molding the same by either or both of heating and pressure bonding, wherein the heating temperature during the integral molding is 50°C or higher and 180°C or lower.

[16]

[14] A method for manufacturing a solar cell module according to the above, comprising the steps of stacking a surface protective material, a surface sealing material, a solar cell, a back sealing material, and a back protective material in this order, and integrally molding them by either or both of heating and pressure bonding treatment, wherein the heating temperature during the integral molding is 50°C or higher and 180°C or lower. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a surface protective film for solar cells and a surface protective material for solar cells that are excellent in durability while maintaining good adhesion to an encapsulant. Furthermore, it is possible to provide a solar cell module using the solar cell surface protective film and solar cell surface protective material, and a method for manufacturing the solar cell module. The solar cell module of the present invention includes a surface protective film for solar cells or a surface protective material for solar cells, and therefore has excellent durability while maintaining adhesion between the encapsulant and the surface protective film. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail. The following embodiments are merely examples for explaining the present invention, and are not intended to limit the present invention to the following contents. The present invention can be implemented by appropriately modifying it within the scope of its gist.

[0013] In this specification, the term "polyisocyanate" refers to a polymer in which a plurality of monomers having one or more isocyanate groups (-NCO) are bonded together. In addition, in this specification, the term "polyol" refers to a compound having two or more hydroxyl (-OH) groups. Unless otherwise specified, "(meth)acrylic" includes methacrylic and acrylic.

[0014] <Surface protection film for solar cells> The surface protective film for a solar cell of this embodiment is composed of one or more layers. Hereinafter, the "surface protective film for a solar cell" of this embodiment may be referred to as a "surface protective film." In one embodiment of the present invention, the surface protection film is a single-layer film composed of one layer. In one embodiment of the present invention, the surface protection film is a multi-layer film composed of two or more layers.

[0015] The outermost layer of the surface protection film of this embodiment contains (1) a (meth)acrylic resin emulsion and (2) a blocked polyisocyanate. Here, the "outermost layer" refers to the layer that comes into contact with the outside air. (1) The emulsion containing the (meth)acrylic copolymer is a resin having a hydroxyl value of 3 mg / g-KOH or more and 150 mg / g-KOH or less, or an amino value of 3 mgKOH / g or more and 150 mgKOH / g or less. The surface protection film of this embodiment contains (1) and (2) as essential components, and therefore has high durability and adhesion to the sealing material. Hereinafter, each component constituting the surface protection film of this embodiment will be described.

[0016] [(1) (Meth)acrylic resin emulsion] (1) (Meth)acrylic resin emulsion The (1) (meth)acrylic resin emulsion constituting the surface protection film of this embodiment is a resin having a hydroxyl value of 3 mg / g-KOH or more and 150 mg / g-KOH or less, or a resin having an amino value of 3 mgKOH / g or more and 150 mgKOH / g or less.

[0017] (1) The hydroxyl value of the (meth)acrylic resin emulsion can be measured by, for example, a known titration method such as that described in JIS K1557-1. 13 It can be determined by C-NMR measurement. From the viewpoint of achieving both adhesion to the sealing material and high durability, the hydroxyl value of the (1) (meth)acrylic resin emulsion is more preferably 5 mg / g-KOH or more and 120 mg / g-KOH or less, even more preferably 10 mg / g-KOH or more and 110 mg / g-KOH or less, and particularly preferably 15 mg / g-KOH or more and 100 mg / g-KOH or less.

[0018] (1) The amino value of the (meth)acrylic resin emulsion can be measured by a known titration method such as that described in JIS K1557-1. 13 It can be determined by C-NMR measurement. From the viewpoint of achieving both adhesion to the sealing material and high durability, the amino value of the (1) (meth)acrylic resin emulsion is more preferably 5 mg / g-KOH or more and 120 mg / g-KOH or less, even more preferably 10 mg / g-KOH or more and 110 mg / g-KOH or less, and particularly preferably 15 mg / g-KOH or more and 100 mg / g-KOH or less.

[0019] The surface protection film of this embodiment can be obtained by applying the aqueous film-forming composition described below to a substrate or the like and drying the composition at room temperature or by heating. Specifically, the water and film-forming aids contained in the aqueous film-forming composition evaporate and dry the composition, thereby forming a film.

[0020] At this time, (2) by drying under temperature conditions that maintain the blocking of the isocyanate groups of the blocked polyisocyanate, good adhesion to the sealing material when manufacturing a solar cell module is achieved.

[0021] Generally, when manufacturing solar cell modules, a heat lamination process is performed in a vacuum. During this process, the blocking agent bonded to the isocyanate group dissociates, and the hydroxyl or amino groups contained in the (1) (meth)acrylic resin emulsion react with the isocyanate group, forming crosslinks. This crosslinking improves the crosslink density of the film, resulting in a solar cell surface protection material that exhibits durability such as weather resistance and chemical resistance.

[0022] When the (1) (meth)acrylic resin emulsion having a hydroxyl value or amino value within the above range is used, the crosslinking reaction with the isocyanate group easily proceeds, and a surface protection film exhibiting durability such as weather resistance, blocking resistance, and chemical resistance can be obtained.

[0023] The (1) (meth)acrylic resin emulsion in this embodiment is obtained from emulsion particles produced by polymerizing a vinyl monomer in the presence of an aqueous medium and an emulsifier. The average particle size of the emulsion particles in this embodiment can be determined from the size of the particles observed by cross-sectional SEM or dynamic light scattering.

[0024] The average particle size of the emulsion particles is not particularly limited, but from the viewpoint of improving the transparency of the (1) (meth)acrylic resin obtained and the storage stability of the aqueous film-forming composition, it is preferably from 10 nm to 500 nm, more preferably from 20 nm to 400 nm, even more preferably from 30 nm to 300 nm, and particularly preferably from 40 nm to 250 nm. The average particle size of the emulsion particles can be measured by the method described in the Examples below.

[0025] The vinyl monomer is not particularly limited, but examples thereof include (meth)acrylic acid esters, aromatic vinyl compounds, and vinyl cyanide compounds, as well as monomers containing functional groups such as carboxyl group-containing vinyl monomers, hydroxyl group-containing vinyl monomers, epoxy group-containing vinyl monomers, carbonyl group-containing vinyl monomers, amino group-containing vinyl monomers, and vinyl monomers having secondary and / or tertiary amide groups.

[0026] The (meth)acrylic acid ester is not particularly limited, but examples thereof include (meth)acrylic acid alkyl esters having 1 to 50 carbon atoms in the alkyl portion, (poly)oxyethylene di(meth)acrylates having 1 to 100 ethylene oxide groups, (meth)acrylic acid cycloalkyl esters having 1 to 20 carbon atoms in the cycloalkyl portion, and (meth)acrylic acid oxyalkyl esters having 1 to 50 carbon atoms in the alkyl portion.

[0027] The (meth)acrylic acid alkyl ester is not particularly limited, but examples thereof include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, hexyl (meth)acrylate, n-octyl (meth)acrylate, isobutyl (meth)acrylate, isononyl (meth)acrylate, isodecyl (meth)acrylate, hexadecyl (meth)acrylate, t-butyl (meth)acrylate, lauryl (meth)acrylate, dodecyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, nonyl (meth)acrylate, and docosyl (meth)acrylate.

[0028] The (poly)oxyethylene di(meth)acrylate is not particularly limited, but examples thereof include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, diethylene glycol methoxy(meth)acrylate, and tetraethylene glycol di(meth)acrylate. The (meth)acrylic acid cycloalkyl ester is not particularly limited, but examples thereof include methylcyclohexyl (meth)acrylate, cyclohexyl (meth)acrylate, ethylcyclohexyl (meth)acrylate, isobornyl (meth)acrylate, γ-butyrolactone (meth)acrylate, dicyclopentanyl (meth)acrylate, (3,4-epoxycyclohexyl)methyl acrylate, 1-ethylcyclopentyl (meth)acrylate, 2-isopropyl-2-adamantyl methacrylate, and 2-methyl-2-adamantyl methacrylate.

[0029] The (meth)acrylic acid oxyalkyl ester is not particularly limited, but examples thereof include carbitol (meth)acrylate, ethyl carbitol (meth)acrylate, 2-methoxyethyl (meth)acrylate, polyethylene glycol monomethyl ether (meth)acrylate, 2-(acetoacetyloxy)ethyl (meth)acrylate, glycidyl (meth)acrylate, and 2-ethoxyethyl (meth)acrylate.

[0030] The aromatic vinyl compound is not particularly limited, but examples thereof include styrene and 4-vinyltoluene. The vinyl cyanide compound is not particularly limited, but examples thereof include acrylonitrile and methacrylonitrile.

[0031] The carboxy group-containing vinyl monomer is not particularly limited, but examples thereof include (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, maleic anhydride, or half esters of dibasic acids such as itaconic acid, maleic acid, and fumaric acid, and carboxy group-containing (meth)acrylic acid esters such as 2-acryloyloxyethyl succinate and 2-acryloyloxyethyl phthalate.

[0032] The hydroxyl group-containing vinyl monomer is not particularly limited, but examples thereof include hydroxyalkyl esters of (meth)acrylic acid such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 3-hydroxy-1-adamantane (meth)acrylate; hydroxyalkyl esters of fumaric acid such as di-2-hydroxyethyl fumarate and mono-2-hydroxyethyl monobutyl fumarate; allyl alcohol; (poly)oxyethylene mono(meth)acrylate having 1 to 100 ethylene oxide groups; (poly)oxypropylene mono(meth)acrylate having 1 to 100 propylene oxide groups; and further, "Placcel FM, FA Monomer" (trade name of a caprolactone addition monomer manufactured by Daicel Corporation) and other hydroxyalkyl esters of α,β-ethylenically unsaturated carboxylic acids.

[0033] The (poly)oxyethylene (meth)acrylate is not particularly limited, but examples thereof include ethylene glycol (meth)acrylate, ethylene glycol methoxy(meth)acrylate, diethylene glycol (meth)acrylate, diethylene glycol methoxy(meth)acrylate, tetraethylene glycol (meth)acrylate, and tetraethylene glycol methoxy(meth)acrylate.

[0034] The (poly)oxypropylene (meth)acrylate is not particularly limited, but examples thereof include propylene glycol (meth)acrylate, propylene glycol methoxy(meth)acrylate, dipropylene glycol (meth)acrylate, dipropylene glycol methoxy(meth)acrylate, tetrapropylene glycol (meth)acrylate, and tetrapropylene glycol methoxy(meth)acrylate.

[0035] The epoxy group-containing vinyl monomer is not particularly limited, but examples thereof include glycidyl group-containing vinyl monomers, etc. The glycidyl group-containing vinyl monomer is not particularly limited, but examples thereof include glycidyl (meth)acrylate, allyl glycidyl ether, allyl dimethyl glycidyl ether, etc.

[0036] The carbonyl-containing vinyl monomer is not particularly limited, but examples thereof include diacetone acrylamide.

[0037] The amino group-containing (meth)acrylic acid ester is not particularly limited, but examples thereof include aminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, and butylaminoethyl (meth)acrylate.

[0038] Specific examples of vinyl monomers other than those mentioned above include, but are not limited to, olefins such as ethylene, propylene, and isobutylene; dienes such as butadiene; haloolefins such as vinyl chloride, vinylidene chloride vinyl fluoride, tetrafluoroethylene, and chlorotrifluoroethylene; vinyl carboxylic acid esters such as vinyl acetate, vinyl propionate, vinyl n-butyrate, vinyl benzoate, vinyl pt-butylbenzoate, vinyl pivalate, vinyl 2-ethylhexanoate, vinyl versatate, and vinyl laurate; isopropenyl carboxylic acid esters such as isopropenyl acetate and isopropenyl propionate; ethyl vinyl ether; Examples of suitable acrylates include vinyl ethers such as methyl vinyl ether and cyclohexyl vinyl ether, allyl esters such as allyl acetate and allyl benzoate, allyl ethers such as allyl ethyl ether and allyl phenyl ether, 4-(meth)acryloyloxy-2,2,6,6-tetramethylpiperidine, 4-(meth)acryloyloxy-1,2,2,6,6-pentamethylpiperidine, perfluoromethyl (meth)acrylate, perfluoropropyl (meth)acrylate, perfluoropropylmethyl (meth)acrylate, vinylpyrrolidone, trimethylolpropane tri(meth)acrylate, allyl (meth)acrylate, and combinations thereof.

[0039] The vinyl monomer having either or both of a secondary and a tertiary amide group is not particularly limited, and examples thereof include N-alkyl or N-alkylene substituted (meth)acrylamides, etc. Specific examples include N-methylacrylamide, N-methylmethacrylamide, N-ethylacrylamide, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N,N-diethylacrylamide, N-ethylmethacrylamide, N-methyl-N-ethylacrylamide, N-methyl-N-ethylmethacrylamide, N-isopropylacrylamide, Nn-propylacrylamide, N-isopropylmethacrylamide, Nn-propylmethacrylamide, N-methyl-Nn-propylacrylamide, N-methyl-N-iso ... Examples of the vinyl acrylate copolymer include N-vinyl amide, N-acryloylpyrrolidine, N-methacryloylpyrrolidine, N-acryloylpiperidine, N-methacryloylpiperidine, N-acryloylhexahydroazepine, N-acryloylmorpholine, N-methacryloylmorpholine, N-vinylpyrrolidone, N-vinylcaprolactam, N,N'-methylenebisacrylamide, N,N'-methylenebismethacrylamide, N-vinylacetamide, diacetone acrylamide, diacetone methacrylamide, N-methylolacrylamide, and N-methylol methacrylamide.

[0040] (1) The (meth)acrylic resin emulsion may contain a surfactant. Examples of the surfactant include, but are not limited to, acidic emulsifiers such as alkylbenzenesulfonic acid, alkylsulfonic acid, alkylsulfosuccinic acid, polyoxyethylene alkylsulfuric acid, polyoxyethylene alkylarylsulfuric acid, and polyoxyethylene distyrylphenyl ether sulfonic acid; anionic surfactants such as alkali metal (Li, Na, K, etc.) salts of acidic emulsifiers, ammonium salts of acidic emulsifiers, and fatty acid soaps; cationic surfactants of the quaternary ammonium salt, pyridinium salt, or imidazolinium salt type such as alkyltrimethylammonium bromide, alkylpyridinium bromide, and imidazolinium laurate; nonionic surfactants such as polyoxyethylene alkylaryl ether, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene oxypropylene block copolymer, and polyoxyethylene distyrylphenyl ether; and reactive emulsifiers having a radically polymerizable double bond.

[0041] The reactive surfactant having a radically polymerizable double bond is not particularly limited, and examples thereof include Eleminol JS-2 (trade name, manufactured by Sanyo Chemical Industries, Ltd.), Latemul S-120, S-180A, and S-180 (trade name, manufactured by Kao Corporation), Aqualon HS-10, KH-1025, RN-10, RN-20, RN30, and RN50 (trade names, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), Adeka Reasop SE1025, SR-1025, NE-20, NE-30, and NE-40 (trade names, manufactured by ADEKA Corporation), ammonium salt of p-styrenesulfonic acid, sodium salt of p-styrenesulfonic acid, potassium salt of p-styrenesulfonic acid, alkylsulfonic acid (meth)acrylates such as 2-sulfoethyl acrylate, methylpropanesulfonic acid (meth)acrylamide, ammonium salt of allylsulfonic acid, sodium salt of allylsulfonic acid, and potassium salt of allylsulfonic acid.

[0042] From the viewpoint of enhancing the stability of the resulting emulsion particles, it is preferable to use an anionic surfactant or a nonionic surfactant as the surfactant.

[0043] The glass transition temperature (Tg) of the (1) (meth)acrylic resin emulsion in this embodiment is preferably −20° C. or higher and 120° C. or lower, more preferably 0° C. or higher and 90° C. or lower, even more preferably 10° C. or higher and 80° C. or lower, and particularly preferably 20° C. or higher and 70° C. or lower. By setting the glass transition temperature to −20° C. or higher, it is possible to further improve durability. On the other hand, by setting the glass transition temperature to 120° C. or lower, it is possible to further improve the film formability of the film to be formed. The glass transition temperature can be determined by a known thermal analysis method such as differential scanning calorimetry (DSC).

[0044] From the viewpoint of improving the toughness of the film itself and providing the aqueous film-forming composition with a viscosity that facilitates application, the number average molecular weight of the (1) (meth)acrylic resin emulsion in this embodiment is preferably 1,000 or more and 2,000,000 or less, more preferably 12,000 or more and 450,000 or less, and particularly preferably 15,000 or more and 400,000 or less.

[0045] The monomers constituting the (1) (meth)acrylic resin emulsion in this embodiment preferably contain a carboxyl group-containing vinyl monomer. By including the carboxyl group-containing vinyl monomer in the (1) (meth)acrylic resin emulsion, carboxyl groups can be introduced into the (meth)acrylic resin emulsion, and the electrostatic repulsion between particles improves the stability of the emulsion.

[0046] For example, resistance to external dispersion disruption, such as aggregation during stirring, tends to be improved. Furthermore, it has the effect of thickening the emulsion, making it easier to adjust the viscosity of the aqueous film-forming composition. To further improve the electrostatic repulsion, the introduced carboxyl groups can be partially or completely neutralized with ammonia, amines such as triethylamine or dimethylethanolamine, or bases such as NaOH or KOH. Furthermore, the presence of carboxyl groups is expected to improve adhesion to sealing materials.

[0047] In the present embodiment, the proportion of the carboxyl group-containing vinyl monomer among the monomers constituting the (1) (meth)acrylic resin emulsion is preferably 0.1% by mass or more and 10% by mass or less, more preferably 0.5% by mass or more and 7% by mass or less, even more preferably 0.8% by mass or more and 5.0% by mass or less, and particularly preferably 1.0% by mass or more and 4.5% by mass or less. By setting the proportion of the carboxyl group-containing vinyl monomer to 0.1% by mass or more, the stability of the emulsion can be sufficiently ensured, while by setting the proportion of the carboxyl group-containing vinyl monomer to 10% by mass or more, the durability of the solar cell surface protective film can be sufficiently ensured.

[0048] In the surface protection film of this embodiment, the weight fraction of the (1) (meth)acrylic resin emulsion relative to the film weight is preferably 50% to 99%, more preferably 55% to 95%, and particularly preferably 60% to 90%. (1) By setting the weight fraction of the (meth)acrylic resin emulsion to the above lower limit or more, durability can be ensured when the surface protection film is formed. (1) By setting the weight fraction of the (meth)acrylic resin emulsion to the above upper limit or less, adhesion to the sealing material can be ensured when the surface protection film is formed.

[0049] [(2) Blocked polyisocyanate] The surface protective film of this embodiment and the outermost layer of the solar cell surface protective material described below contain a blocked polyisocyanate, which has at least one isocyanate compound selected from the group consisting of aliphatic isocyanates and alicyclic isocyanates as its skeleton.

[0050] The blocked polyisocyanate in this embodiment is configured such that all of the isocyanate groups in one molecule of polyisocyanate are blocked with a blocking agent. The average number of isocyanate groups blocked with a blocking agent per molecule of polyisocyanate contained in the blocked polyisocyanate in this embodiment (hereinafter, sometimes abbreviated as "average number of functional groups") is preferably 2 or more and 20 or less, more preferably 2.3 or more and 15 or less, and particularly preferably 2.5 or more and 10 or less.

[0051] When the average number of functional groups is 2 or more, crosslinking is further improved, and a film having better blocking resistance and solvent resistance can be obtained. On the other hand, when the total average number of isocyanate groups is equal to or less than the upper limit, excessive crosslinking can be more effectively suppressed, and the stretchability of the obtained film can be maintained better.

[0052] The average number of functional groups can be calculated using the following formula: In the formula, "Mn" is the number-average molecular weight of the blocked polyisocyanate contained in the aqueous film-forming composition, measured after dissociating the blocking agent by heating or other means. "NCO content" is the content of isocyanate groups present relative to the total mass of the blocked polyisocyanate contained in the aqueous film-forming composition, measured after dissociating the blocking agent by heating or other means. The NCO content is multiplied by "0.01" to convert it from a percentage to a decimal. "42" is the formula weight of the isocyanate.

[0053] Total average number of isocyanate groups (total average number of NCO groups) = (Mn × NCO content × 0.01) / 42 The number average molecular weight (Mn) can be calculated, for example, by measuring the blocked polyisocyanate used in the aqueous film-forming composition or the aqueous film-forming composition by gel permeation chromatography (GPC). The NCO content can be calculated, for example, by titration using the blocked polyisocyanate used in the aqueous film-forming composition or the aqueous film-forming composition as a sample, in which the blocking agent has been dissociated by heating or the like.

[0054] Alternatively, a blocked polyisocyanate used in the aqueous film-forming composition or an aqueous film-forming composition is used as a sample. 13 The total average number of isocyanate groups can also be calculated by C-NMR measurement.

[0055] Examples of polyisocyanates include isocyanurate polyisocyanates obtained by trimerizing diisocyanates, biuret polyisocyanates formed by the reaction of three isocyanate group molecules with one water molecule, and allophanate polyisocyanates formed by the reaction of two isocyanate group molecules with one alcohol hydroxyl group molecule. Among these, from the viewpoint of weather resistance, isocyanurate polyisocyanates are preferred as polyisocyanates having a total average number of isocyanate groups within the above range.

[0056] [Polyisocyanate] The polyisocyanate, which is a raw material for the blocked polyisocyanate, is derived from at least one isocyanate compound selected from the group consisting of aliphatic isocyanates and alicyclic isocyanates and has the skeleton of the isocyanate compound. The polyisocyanate may contain an isocyanurate group, a biuret group, an allophanate group, an oxadiazinetrione group, a urea group, or a urethane group, and preferably has an isocyanurate group. The isocyanate compound that forms the skeleton of the polyisocyanate is not particularly limited, but specifically, one that does not contain an aromatic ring such as a benzene ring in its structure is preferred.

[0057] (Aliphatic isocyanate) The aliphatic isocyanate is not particularly limited, but specific examples thereof include aliphatic monoisocyanates, aliphatic diisocyanates, lysine triisocyanate, 4-isocyanatomethyl-1,8-octamethylene diisocyanate (trimer triisocyanate), etc. Among these, aliphatic diisocyanates are preferred.

[0058] The aliphatic diisocyanate is not particularly limited, but specifically, one having 4 to 30 carbon atoms is preferred, such as tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate (hereinafter referred to as "HDI"), 2,2,4-trimethyl-1,6-diisocyanatohexane, and lysine diisocyanate. Among these, HDI is preferred because of its ease of industrial availability. One type of aliphatic diisocyanate may be used alone, or two or more types may be used in combination.

[0059] (alicyclic isocyanate) The alicyclic isocyanate is not particularly limited, but specific examples include alicyclic monoisocyanates, alicyclic diisocyanates, etc. Among these, alicyclic diisocyanates are preferred. The alicyclic diisocyanate is not particularly limited, but specifically, those having 8 to 30 carbon atoms are preferred, such as isophorone diisocyanate (hereinafter referred to as "IPDI"), 1,3-bis(isocyanatomethyl)-cyclohexane, 4,4'-dicyclohexylmethane diisocyanate, norbornene diisocyanate, and hydrogenated xylylene diisocyanate. Of these, IPDI is preferred from the viewpoints of weather resistance and ease of industrial availability. One type of alicyclic diisocyanate may be used alone, or two or more types may be used in combination.

[0060] The polyisocyanate derived from the above-mentioned aliphatic diisocyanate is not limited to the following, but examples thereof include polyisocyanates having a uretdione structure obtained by cyclodimerizing two isocyanate groups, polyisocyanates having an isocyanurate structure obtained by cyclotrimerizing three isocyanate groups, polyisocyanates having an iminooxadiazinedione structure obtained by cyclotrimerizing three isocyanate groups, polyisocyanates having a biuret structure obtained by reacting three isocyanate groups with one water molecule, and polyisocyanates having a methyl group obtained by reacting two isocyanate groups with one water molecule. Examples of suitable polyisocyanates include polyisocyanates having an oxadiazinetrione structure obtained by reacting one isocyanate group with one hydroxyl group, polyisocyanates having a urethane group obtained by reacting two isocyanate groups with one hydroxyl group, polyisocyanates having an allophanate structure obtained by reacting two isocyanate groups with one hydroxyl group, polyisocyanates having an acylurea group obtained by reacting one isocyanate group with one carboxyl group, and polyisocyanates having a urea structure obtained by reacting one isocyanate group with one primary or secondary amine. These polyisocyanates may be used alone or in combination of two or more. The term "polyisocyanate" as used herein includes not only polyisocyanates derived solely from the above-mentioned aliphatic diisocyanates, but also polyisocyanates obtained by reacting the above-mentioned aliphatic diisocyanates with compounds other than diisocyanates (e.g., alcohols such as monoalcohols, water, amines).

[0061] [Blocking agent] The blocking agent is not particularly limited, but specifically includes a compound having one active hydrogen in the molecule.Such blocking agent is not particularly limited, but specifically includes alcohol-based compounds, alkylphenol-based compounds, phenol-based compounds, active methylene-based compounds, mercaptan-based compounds, acid amide-based compounds, acid imide-based compounds, imidazole-based compounds, urea-based compounds, oxime-based compounds, amine-based compounds, imine-based compounds, pyrazole-based compounds, and triazole-based compounds.These blocking agents may be used alone or in combination of two or more.More specific examples of blocking agents are shown below.

[0062] The alcohol-based compound is not particularly limited, but specific examples include methanol, ethanol, 2-propanol, n-butanol, sec-butanol, 2-ethyl-1-hexanol, 2-methoxyethanol, 2-ethoxyethanol, and 2-butoxyethanol.

[0063] The alkylphenol compound is not particularly limited, but specific examples include mono- and di-alkylphenols having an alkyl group having 3 to 12 carbon atoms as a substituent. Examples of mono-alkylphenols include n-propylphenol, iso-propylphenol, n-butylphenol, sec-butylphenol, tert-butylphenol, n-hexylphenol, 2-ethylhexylphenol, n-octylphenol, and n-nonylphenol. Examples of di-alkylphenols include di-n-propylphenol, diisopropylphenol, isopropyl cresol, di-n-butylphenol, di-tert-butylphenol, di-sec-butylphenol, di-n-octylphenol, di-2-ethylhexylphenol, and di-n-nonylphenol.

[0064] The phenolic compound is not particularly limited, but specific examples include phenol, cresol, ethylphenol, styrenated phenol, and hydroxybenzoic acid esters. The active methylene compound is not particularly limited, but specific examples include dimethyl malonate, diethyl malonate, diisopropyl malonate, methyl acetoacetate, ethyl acetoacetate, acetylacetone, ethyl isobutanoylacetate, and the like.

[0065] The mercaptan compound is not particularly limited, but specific examples include butyl mercaptan, dodecyl mercaptan, and the like. The acid amide compound is not particularly limited, but specific examples include acetanilide, acetic acid amide, ε-caprolactam, δ-valerolactam, γ-butyrolactam, and the like. The acid imide compound is not particularly limited, but specific examples include succinimide and maleimide.

[0066] The imidazole-based compound is not particularly limited, but specific examples include imidazole, 2-methylimidazole, and the like. The urea-based compound is not particularly limited, but specific examples include urea, thiourea, and ethylene urea. The oxime compound is not particularly limited, but specific examples include formaldoxime, acetaldoxime, acetoxime, methyl ethyl ketoxime, cyclohexanone oxime, and the like.

[0067] The amine compound is not particularly limited, but specific examples include diphenylamine, aniline, carbazole, di-n-propylamine, diisopropylamine, and isopropylethylamine. The imine compound is not particularly limited, but specific examples include ethyleneimine, polyethyleneimine, and the like.

[0068] The pyrazole-based compound is not particularly limited, but specific examples include pyrazole, 3-methylpyrazole, 3,5-dimethylpyrazole, and the like. The triazole-based compound is not particularly limited, but specific examples include 1,2,4-triazole and 1,2,3-triazole.

[0069] Among these, acid amide compounds, oxime compounds, active methylene compounds, and pyrazole compounds are preferred in terms of availability, the viscosity of the resulting blocked polyisocyanate, the curing temperature, and the curing time. Specifically, methyl ethyl ketoxime, ε-caprolactam, diethyl malonate, 3-methylpyrazole, and 3,5-dimethylpyrazole are preferred, methyl ethyl ketoxime, diethyl malonate, 3-methylpyrazole, and 3,5-dimethylpyrazole are more preferred, and 3-methylpyrazole and 3,5-dimethylpyrazole are particularly preferred.

[0070] From the viewpoint of water dispersibility, the isocyanate compound is preferably a water-dispersible isocyanate compound obtained by reacting the above-mentioned polyisocyanate compound having two or more isocyanate groups per molecule with a hydroxyl group-containing hydrophilic compound having a nonionic and / or ionic hydrophilic group at an isocyanate group / hydroxyl group equivalent ratio in the range of 1.05 to 1000. More preferably, the equivalent ratio is 2 to 200, and even more preferably, 4 to 100. An equivalent ratio of 1.05 or more ensures that the isocyanate group content in the hydrophilic polyisocyanate is at a predetermined level or higher, thereby increasing the number of crosslinking points in the crosslinkable aqueous coating composition, which leads to an increased curing rate and improved strength of the coating, such as a coating film. An equivalent ratio of 1000 or less is preferred because hydrophilicity is exhibited. Such water-dispersible isocyanate compounds are not particularly limited, and commercially available products can also be used. For example, WS50-30W manufactured by Asahi Kasei Corporation and WM44-L70G manufactured by Asahi Kasei Corporation are preferably used as they have the above-mentioned characteristics.

[0071] The water-dispersible isocyanate compound is not particularly limited as long as it has a hydrophilic group introduced therein by a conventionally known method. For example, a compound represented by the general formula R 1 O(R 2 O)nH(where R 1represents an alkyl group having 1 to 30 carbon atoms or a group containing two or more aromatic rings, and R 2 represents an alkylene group having 1 to 5 carbon atoms, and n is an integer of 2 to 250) with a polyisocyanate compound, a reaction product of a vinyl polymer having a hydrophilic group and a hydroxyl group with a polyisocyanate compound, and a reaction product of an emulsifier obtained by reacting an alkoxypolyalkylene glycol with a dialkanolamine with a polyisocyanate compound. Among these, the reaction product of compound (m) with a polyisocyanate compound and the reaction product of a vinyl polymer having a hydrophilic group and a hydroxyl group with a polyisocyanate compound are particularly preferred because of their excellent water dispersibility.

[0072] Examples of compound (m) include alkoxypolyalkylene glycols such as polymethylene glycol monomethyl ether, polyethylene glycol monomethyl ether, polyethylene glycol monoethyl ether, polyethylene glycol monopropyl ether, polyethylene glycol monolauryl ether, polyoxyethylene-oxypropylene (random and / or block) glycol monomethyl ether, polyoxyethylene-oxytetramethylene (random and / or block) glycol polybutylene glycol monomethyl ether, and nonionic surfactants having a group containing two or more aromatic rings such as (mono- to penta)styrenated phenyl groups, mono- (or di-, tri-)styrylmethyl-phenyl groups, tribenzylphenyl groups, and β-naphthyl groups. Among these, polyethylene glycol monomethyl ether and nonionic surfactants having (mono- to penta)styrenated phenyl groups are preferred in terms of self-emulsifying ability and pot life.

[0073] As these compounds (m), those having a molecular weight in the range of preferably 100 to 10,000, more preferably 300 to 5,000 can be suitably used. The hydrophilic group of the vinyl polymer having a hydrophilic group and a hydroxyl group may be any of various known anionic, cationic, and nonionic groups, with a nonionic group being preferred. The nonionic group significantly extends the pot life of the coating composition and reduces the particle size of the polyisocyanate oil droplets, which tends to further improve the water resistance of the coating film formed.

[0074] Specific examples of vinyl polymers having a hydrophilic group and a hydroxyl group include acrylic polymers, fluoroolefin polymers, vinyl ester polymers, aromatic vinyl polymers, polyolefin polymers, etc. Among these, acrylic polymers are preferred from the viewpoint of the weather resistance of the coating film to be formed. The polymerization method for obtaining an acrylic polymer suitable as a vinyl polymer having a hydrophilic group and a hydroxyl group is not particularly limited, and examples thereof include suspension polymerization, emulsion polymerization, and solution polymerization.Preferably, the acrylic polymer is obtained by solution polymerization of an ethylenically unsaturated monomer (i) having a hydrophilic group and an ethylenically unsaturated monomer (ii) having a hydroxyl group, and if necessary, another ethylenically unsaturated monomer (iii) copolymerizable with these can also be used.

[0075] Examples of the ethylenically unsaturated monomer (i) having a hydrophilic group include alkoxypolyalkylene glycol (meth)acrylates such as methoxypolyethylene glycol (meth)acrylate, ethoxypolyethylene glycol (meth)acrylate, and butoxypolyethylene glycol (meth)acrylate, polyalkylene glycol di(meth)acrylates such as polyethylene glycol di(meth)acrylate, as well as (meth)acrylamide monomers and anionic vinyl monomers. Furthermore, ethylenically unsaturated monomers having both a hydrophilic group and a hydroxyl group in the molecule, such as polyalkylene glycol (meth)acrylates, can also be used. These may be used alone or in combination of two or more.

[0076] Examples of other ethylenically unsaturated monomers (iii) copolymerizable therewith include (meth)acrylic acid esters, aromatic vinyl compounds, vinyl cyanides, carbonyl group-containing vinyl monomers, olefins, dienes, haloolefins, vinyl ethers, allyl esters, etc. These may be used alone or in combination of two or more.

[0077] The vinyl polymer containing a hydrophilic group and a hydroxyl group preferably has a weight average molecular weight (polystyrene equivalent GPC method) in the range of 2,000 to 100,000, more preferably 3,000 to 50,000.

[0078] The viscosity of the aqueous film-forming composition is preferably 1 to 50,000 mPa·s (20°C), more preferably 1 to 20,000 mPa·s (20°C), and even more preferably 10 to 10,000 mPa·s (20°C). The viscosity of the isocyanate compound (C) may be 10 to 50,000 mPa·s (20°C), 10 to 20,000 mPa·s (20°C), or 10 to 10,000 mPa·s (20°C). The viscosity of the polyisocyanate compound (M) is preferably 50,000 mPa·s or less, as this facilitates dispersion in water.

[0079] The viscosity here can be measured using a general E-type viscometer or B-type viscometer. The isocyanate compound is not particularly limited, and commercially available products can be used. For example, WS50-30W manufactured by Asahi Kasei Corporation and WM44-L70G manufactured by Asahi Kasei Corporation are preferably used as they have the above-mentioned characteristics.

[0080] [NCO / OH] In the surface protection film of this embodiment, the molar ratio (NCO / OH) of the blocked isocyanate groups contained in (2) the blocked isocyanate to the hydroxyl groups contained in (1) the (meth)acrylic resin emulsion is preferably 0.05 or more and 3.0 or less, more preferably 0.1 or more and 1.5 or less, even more preferably 0.2 or more and 1.3 or less, and particularly preferably 0.3 or more and 1.2 or less.

[0081] NCO / OH can be determined by, for example, known titration methods or 13 It can be determined by measuring the content of blocked isocyanate groups and hydroxyl groups contained in the film by C-NMR measurement. When the NCO / OH ratio is equal to or greater than the lower limit, the adhesion between the surface protection film and the sealing material can be ensured. When the NCO / OH ratio is equal to or less than the upper limit, the durability of the surface protection film can be ensured.

[0082] In the surface protection film of this embodiment, the weight fraction of (2) the blocked polyisocyanate relative to the weight of the surface protection film is preferably 1% or more and 50% or less, more preferably 5% or more and 40% or less, even more preferably 10% or more and 35% or less, and particularly preferably 15% or more and 30% or less.

[0083] (2) When the weight fraction of the blocked polyisocyanate is equal to or greater than the lower limit, durability with the surface protective film can be ensured, and when the weight fraction of the blocked polyisocyanate is equal to or less than the upper limit, adhesion between the surface protective film and the sealing material can be ensured.

[0084] [Surfactants] The surface protection film of the present embodiment may further contain a surfactant. The surfactant is an anionic surfactant or a nonionic surfactant. The inclusion of a surfactant can improve the stability of the aqueous film-forming composition and the stability during the formation of the surface protection film.

[0085] Examples of anionic surfactants include, but are not limited to, acidic emulsifiers such as alkylbenzenesulfonic acid, alkylsulfonic acid, alkylsulfosuccinic acid, polyoxyethylene alkylsulfuric acid, polyoxyethylene alkylarylsulfuric acid, and polyoxyethylene distyrylphenyl ether sulfonic acid; alkali metal (Li, Na, K, etc.) salts of acidic emulsifiers, ammonium salts of acidic emulsifiers, and fatty acid soaps.

[0086] The nonionic surfactant is not particularly limited, but examples thereof include polyoxyethylene alkylaryl ether, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene oxypropylene block copolymer, polyoxyethylene distyrylphenyl ether, and the like.

[0087] In the surface protection film of this embodiment, the weight fraction of the surfactant relative to the film weight is not particularly limited, but is preferably 0.01% or more and 10% or less, more preferably 0.1% or more and 8.0% or less, even more preferably 0.5% or more and 5.0% or less, and particularly preferably 1.0% or more and 3.0% or less.

[0088] When the weight fraction of the surfactant is equal to or greater than the lower limit, the stability of the aqueous film-forming composition for forming the surface protective film and the stability when forming the surface protective film can be ensured.

[0089] Furthermore, by ensuring that the weight fraction of the surfactant is equal to or less than the upper limit, durability can be ensured when the surface protection film is formed.

[0090] Alternatively, a method may be used in which a reactive surfactant having a radically polymerizable double bond is added during the production of a (meth)acrylic resin emulsion, and then the surfactant is further added to bind to the (meth)acrylic resin.

[0091] The reactive anionic surfactant having a radically polymerizable double bond is not particularly limited, and examples thereof include Eleminol JS-2 (trade name, manufactured by Sanyo Chemical Industries, Ltd.), Latemul PD-104, PD-105, S-120, S-180A, and S-180 (trade name, manufactured by Kao Corporation), Aqualon HS-10, KH-1025, RN-10, RN-20, RN30, and RN50 (trade names, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), Adeka Reasop SE-1025 and SR-1025 (trade names, manufactured by ADEKA Corporation), ammonium salt of p-styrenesulfonic acid, sodium salt of p-styrenesulfonic acid, potassium salt of p-styrenesulfonic acid, alkylsulfonic acid (meth)acrylates such as 2-sulfoethyl acrylate, methylpropanesulfonic acid (meth)acrylamide, ammonium salt of allylsulfonic acid, sodium salt of allylsulfonic acid, and potassium salt of allylsulfonic acid.

[0092] The reactive anionic surfactant having a radically polymerizable double bond is not particularly limited, but examples thereof include Latemul PD-420, PD-430, and PD-450 (trade names, manufactured by Kao Corporation), and Adeka Reasop NE-10, NE-20, NE-30, ER-10, ER-20, ER-30, and ER-40 (trade names, manufactured by ADEKA Corporation).

[0093] [Other additives] The surface protection film of the present embodiment can contain various additives, such as previously unmentioned compounds and polymers, ultraviolet absorbers, light stabilizers, curing-accelerating catalysts, antioxidants, leveling agents, plasticizers, crosslinking agents, tackifiers, pigments, dyes, luster materials, fillers, antioxidants, conductive materials, release adjusters, softeners, flame retardants, antioxidants, etc. These additives can be used alone or in appropriate combinations of two or more.

[0094] The ultraviolet absorber is not particularly limited, but examples thereof include benzotriazole-based compounds, triazine-based compounds, benzophenone-based compounds, and cyanoacrylate-based compounds.

[0095] The benzotriazole compound is not particularly limited, but examples thereof include Tinuvin P·PS·99-2·213·234·326·329·360·384-2·571·900·928·970·1130 (manufactured by BASF Japan Ltd.), ADK STAB LA-24·29·31RG·31G·32·36·36RG·F70 (manufactured by ADEKA Corporation), and EVERSORB 70·71·72·73·74·75·76·77·78·79·80·81·82·88·89·109·234 (manufactured by Taiwan Yongkoh Chemical Industry Co., Ltd.).

[0096] The triazine-based compound is not particularly limited, but examples thereof include Tinuvin 400, 400-DW, 405, 460, 477, 479, 479-DW, 1577ED, and 1600 (manufactured by BASF Japan Ltd.), and EVERSORB 40, 41FD, and 45 (manufactured by Taiwan Yongkoh Chemical Industry Co., Ltd.).

[0097] The benzophenone compound is not particularly limited, but examples thereof include Chimassorb 81 and 81FL (manufactured by BASF Japan Ltd.), Uvinul 3049 and 3050 (manufactured by BASF Japan Ltd.), Adekastab 1413 (manufactured by ADEKA Corporation), and EVERSORB 10, 11, 12, 51, and 52 (manufactured by Taiwan Yongkou Chemical Industry Co., Ltd.).

[0098] The cyanoacrylate compound is not particularly limited, but examples thereof include Uvinul 3030FF, 3035, and 3039 (manufactured by BASF Japan Ltd.).

[0099] From the viewpoint of maintaining weather resistance over a long period of time, benzotriazole-based compounds, triazine-based compounds, and benzophenone-based compounds are preferred, and benzotriazole-based compounds and triazine-based compounds are more preferred. The light stabilizer is not particularly limited, but specific examples thereof include hindered amine compounds.

[0100] The hindered amine compound is not particularly limited, but examples thereof include Tinuvin 111FDL, 123, 123-DW, PA144, 152, 249, 292, and 783FDL (manufactured by BASF Japan Ltd.), ADK STAB LA-52, 57, 63P, 68, 72, 77Y, 77G, 81, and 402AF (manufactured by ADEKA Corporation), and EVERSORB 60, 61, 90, 91FD, 93, 94FD, 95, 765, and S02 (manufactured by Taiwan Yongkoh Chemical Industry Co., Ltd.).

[0101] The curing accelerator catalyst is not particularly limited, but examples thereof include tin compounds, zinc compounds, titanium compounds, cobalt compounds, bismuth compounds, zirconium compounds, and amine compounds. Examples of tin compounds include dibutyltin dilaurate, dibutyltin diacetate, dioctyltin dilaurate, dimethyltin dineodecanoate, and tin bis(2-ethylhexanoate). Examples of zinc compounds include zinc 2-ethylhexanoate and zinc naphthenate. Examples of titanium compounds include titanium 2-ethylhexanoate and titanium diisopropoxybis(ethylacetonate). Examples of cobalt compounds include cobalt 2-ethylhexanoate and cobalt naphthenate. Examples of bismuth compounds include bismuth 2-ethylhexanoate and bismuth naphthenate. Examples of zirconium compounds include zirconium tetraacetylacetonate, zirconyl 2-ethylhexanoate, and zirconyl naphthenate.

[0102] The pigment is not particularly limited, but examples thereof include titanium oxide, carbon black, indigo, pearl mica, and aluminum.

[0103] The leveling agent is not particularly limited, but examples thereof include silicone oil.

[0104] The plasticizer is not particularly limited, but examples thereof include phthalate esters, phosphoric acid compounds, and polyester compounds.

[0105] The crosslinking agent is not particularly limited, but examples thereof include epoxy-based crosslinking agents, carbodiimide-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, amine-based crosslinking agents, peroxide-based crosslinking agents, melamine-based crosslinking agents, urea-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, and metal salt-based crosslinking agents. The antioxidant is not particularly limited, but examples thereof include phenolic compounds, amine compounds, phosphorus compounds, and sulfur compounds.

[0106] The surface protection film of this embodiment may contain other components, such as compounds, polymers, and additives not previously mentioned. These other components may be used alone or in appropriate combinations of two or more. Examples of such other components include, but are not limited to, thermoplastic resins, thermosetting resins, and rubber / elastomers. Among these, acrylic resins, acrylic urethane resins, urethane resins, and silicone resins are preferred.

[0107] Furthermore, the surface protective film of this embodiment may contain an active hydrogen compound other than the (meth)acrylic resin, as long as the effects of the present invention are achieved.

[0108] The active hydrogen-containing compound is not particularly limited, but specifically, a compound having two or more active hydrogens bonded in the molecule is preferred. Preferred active hydrogen-containing compounds include, for example, polyol compounds, polyamine compounds, alkanolamine compounds, and polythiol compounds.

[0109] These active hydrogen-containing compounds may be used alone or in combination of two or more. From the viewpoint of improving the dispersion stability of the aqueous film-forming composition for forming the surface protective film of the present embodiment, the active hydrogen compound is preferably a water-dispersible or water-soluble compound.

[0110] The glass transition temperature (Tg) of the surface protection film of this embodiment is preferably −40° C. or higher and 140° C. or lower, more preferably −10° C. or higher and 100° C. or lower, even more preferably 0° C. or higher and 90° C. or lower, and particularly preferably 10° C. or higher and 80° C. or lower. By setting the glass transition temperature to −10° C. or higher, it is possible to further improve durability. On the other hand, by setting the glass transition temperature to 120° C. or lower, the surface protection film is sufficiently softened during vacuum lamination, and adhesion to the sealing material can be further improved.

[0111] The glass transition temperature can be determined by a known thermal analysis method such as differential scanning calorimetry (DSC).

[0112] In one embodiment of the present invention, the surface protection film is a multilayer film having two or more layers. When the surface protection film is a multilayer film, when the glass transition temperature of the outermost layer is Tgu and the glass transition temperature of the bottom layer is Tgl, it is preferable that Tgu is higher than Tgl. The outermost layer is the layer in contact with the outside air, and the bottom layer is the layer in contact with the sealing material.

[0113] By making the Tg of the bottom layer that comes into contact with the encapsulant lower than that of the outermost layer, the film becomes more susceptible to softening during vacuum lamination, further improving adhesion to the encapsulant. On the other hand, by making the Tg of the outermost layer that is exposed to the outdoor environment higher than that of the bottom layer, durability and scratch resistance can be further improved.

[0114] In one embodiment of the present invention, the difference between Tgu and Tgl is, for example, 5°C or more and 60°C or less, 6°C or more and 45°C or less, or 10°C or more and 40°C or less.

[0115] <Surface protection film manufacturing method> The surface protection film of this embodiment can be obtained by applying an aqueous film-forming composition, which is prepared by dispersing (1) a (meth)acrylic resin emulsion and (2) a blocked polyisocyanate, which are components of the surface protection film of this embodiment, in an aqueous medium, to a substrate or the like, and drying the composition at room temperature or by heating. Specifically, the film is formed by evaporation of water, film-forming aids, and the like contained in the aqueous film-forming composition.

[0116] Examples of the coating method include known methods such as reverse roll coating, gravure coating, kiss coating, die coater, roll brush, spray coating, air knife coating, wire bar coating, pipe doctor coating, impregnation coating, curtain coating, roll coating, curtain flow coating, spray coating, bell coating, and electrostatic coating.

[0117] The thickness of the surface protection film is not particularly limited, but is preferably from 0.2 μm to 500 μm, more preferably from 1 μm to 500 μm, even more preferably from 5 μm to 300 μm, and particularly preferably from 5 μm to 100 μm.

[0118] <Film-forming aqueous composition> The aqueous film-forming composition contains (1) a (meth)acrylic resin emulsion and (2) a blocked polyisocyanate, which are components of the surface protection film of this embodiment. The aqueous film-forming composition refers to a composition in which water accounts for the largest proportion of the solvent components in the composition. In the aqueous film-forming composition, the water content is preferably 50% or more, more preferably 60% or more, and even more preferably 70% or more, based on 100% by mass of the solvent. By setting the mass ratio of water in the solvent to the above-mentioned lower limit or more, this contributes to stabilization of the emulsion particles and blocked polyisocyanate in the aqueous coating composition and tends to reduce the environmental load.

[0119] (Film-forming aid) The aqueous film-forming composition may contain a film-forming aid depending on the purpose and application, as long as the effects of the present invention are achieved.

[0120] The film-forming aid swells the emulsion particles, thereby lowering the temperature at which they dry to form a continuous film, thereby accelerating film formation.

[0121] The film-forming aid is not particularly limited, but it is preferable that it does not have a functional group that reacts with a hydroxyl group or an isocyanate group, and that it is sufficiently compatible with the (meth)acrylic resin emulsion and the blocked polyisocyanate.

[0122] The film-forming aid having the above-described characteristics is not particularly limited, but examples thereof include glycol ether-based compounds, ether-based compounds, ketone-based compounds, ester-based compounds, nitrile-based compounds, amine-based compounds, and sulfoxide-based compounds, and may also be organic compounds that are not generally used as film-forming aids.

[0123] The glycol ether compound is not particularly limited, but examples thereof include ethylene glycol monoethyl ether acetate, diethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, butyl carbitol acetate, propylene glycol methyl ether acetate, dipropylene glycol dimethyl ether, propylene glycol monomethyl ether propionate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, diethylene glycol dibutyl ether, propylene glycol dimethyl ether, diethylene glycol butyl methyl ether, methylene glycol diethyl ether, ethylene glycol monomethyl ether acetate, and ethylene glycol dibutyl ether.

[0124] Examples of ether compounds include, but are not limited to, diisopropyl ether, triethylene glycol butyl methyl ether, tetrahydrofuran, tert-butyl methyl ether, polyethylene glycol dimethyl ether, 4-methyltetrahydropyran, cyclopentyl methyl ether, dibutyl ether, tetrahydropyran, and 2-methyltetrahydrofuran.

[0125] The ketone compound is not particularly limited, but examples thereof include isoamyl methyl ketone, isopropyl methyl ketone, isophorone, diisobutyl ketone, methoxyacetone, 3-pentanone, 2-pentanone, methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, cyclohexanone, 2-heptanone, γ-butyrolactone, and acetone.

[0126] Examples of ester compounds include, but are not limited to, sec-butyl acetate, butyl acetate, 2-ethoxyethyl isobutyrate, 2-ethylhexyl acetate, ethyl acetate, dimethyl glutarate, isobutyl isobutyrate, tert-butyl acetoacetate, isopropyl acetate, isobutyl acetate, ethyl 3-ethoxypropionate, isoamyl acetate, propyl acetate, and butyl propionate.

[0127] The nitrile compounds are not particularly limited, but include benzonitrile, propionitrile, butyronitrile, acetonitrile, and the like.

[0128] The amine compound is not particularly limited, but examples thereof include N-methyl-2-pyrrolidone, N,N-dimethylformamide, and dimethylacetamide.

[0129] The sulfoxide compound is not particularly limited, but examples thereof include dimethyl sulfoxide.

[0130] The film-forming aid preferably remains in the surface protection film of this embodiment during film formation and in the early stages of drying, and preferably volatilizes from the surface protection film in the later stages of drying after the surface protection film has been formed.

[0131] The above-mentioned characteristics can be achieved by adjusting the boiling point of the film-forming aid to an appropriate range. The boiling point range of the film-forming aid is preferably from 140°C to 350°C, more preferably from 140°C to 300°C, and particularly preferably from 150°C to 250°C.

[0132] The film-forming aid satisfying the above-mentioned boiling point range is not particularly limited, but examples thereof include ethylene glycol monoethyl ether acetate, diethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, butyl carbitol acetate, propylene glycol methyl ether acetate, dipropylene glycol dimethyl ether, propylene glycol monomethyl ether propionate, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dimethyl ether, Examples of suitable solvents include ethylene glycol methyl ethyl ether, diethylene glycol dibutyl ether, ethylene glycol monomethyl ether acetate, ethylene glycol dibutyl ether, dibutyl ether, isoamyl methyl ketone, isophorone, diisobutyl ketone, 2-heptanone, cyclohexanone, γ-butyrolactone, 2-ethylhexyl acetate, isobutyl isobutyrate, tert-butyl acetoacetate, ethyl 3-ethoxypropionate, butyl propionate, benzonitrile, N-methyl-2-pyrrolidone, N,N-dimethylformamide, dimethylacetamide, and dimethyl sulfoxide.

[0133] In order to swell the emulsion particles with the film-forming aid, the film-forming aid contained in the aqueous film-forming composition must be absorbed into the emulsion particles. From the above viewpoint, the solubility of the film-forming aid in water is preferably 0.01% to 60%, more preferably 0.1% to 55%, even more preferably 0.5% to 50%, and particularly preferably 3% to 40%.

[0134] By setting the solubility of the film-forming aid in water to the above lower limit or more, the stability of the emulsion particles, which are hydrophilic substances, in the aqueous coating composition can be appropriately maintained, and the film-forming aid can be stably present in the aqueous film-forming composition without separation or sedimentation in the composition. Furthermore, by setting the solubility of the film-forming aid in water to the above upper limit or less, the film-forming aid can be efficiently absorbed into the emulsion particles.

[0135] Examples of the film-forming aid satisfying the above characteristics include, but are not limited to, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, butyl carbitol acetate, propylene glycol methyl ether acetate, dipropylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dibutyl ether, ethylene glycol dibutyl ether, diisopropyl ether, tert-butyl methyl ether, cyclopentyl methyl ether, dibutyl ether, tetrahydropyran, isoamyl methyl ketone, isopropyl methyl ketone, isophorone, diisobutyl ketone, methoxyacetone, 3-pentanone, 2-pentanone, methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, cyclohexanone, 2-heptanone, sec-butyl acetate, butyl acetate, ethyl acetate, dimethyl glutarate, isopropyl acetate, isobutyl acetate, isoamyl acetate, propyl acetate, propionitrile, and butyronitrile.

[0136] Compounds having both the above-mentioned boiling point range and solubility in water are particularly preferred as film-forming aids. As long as the compound has the above characteristics, it is not particularly limited, but examples thereof include ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, butyl carbitol acetate, propylene glycol methyl ether acetate, dipropylene glycol dimethyl ether, diethylene glycol dibutyl ether, ethylene glycol dibutyl ether, dibutyl ether, isoamyl methyl ketone, isophorone, diisobutyl ketone, 3-pentanone, 2-heptanone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, dimethyl glutarate, and isoamyl acetate.

[0137] The amount of the film-forming aid added is preferably 0.1% to 20% by weight of the aqueous film-forming composition, more preferably 0.5% to 15% by weight, even more preferably 1.0% to 12% by weight, and particularly preferably 3.0% to 10% by weight. By adding the film-forming aid in an amount equal to or greater than the lower limit, a film can be formed more efficiently. Furthermore, by adding the film-forming aid in an amount equal to or less than the upper limit, the amount of film-forming aid remaining in the film can be reduced, leading to a reduction in the environmental impact during film production.

[0138] (organic solvent) The aqueous film-forming composition of the present embodiment is aqueous-based, but an organic solvent may be added depending on the purpose and application.

[0139] The organic solvent preferably does not have a functional group that reacts with a hydroxyl group or an isocyanate group, and preferably has sufficient compatibility with (1) the (meth)acrylic resin emulsion and (2) the blocked polyisocyanate. Such organic solvents are not particularly limited, but may be, for example, solvents generally used as solvents for paints, such as ester compounds, ether compounds, ketone compounds, aromatic compounds, ethylene glycol dialkyl ether compounds, polyethylene glycol dicarboxylate compounds, and hydrocarbon solvents.

[0140] When an organic solvent is added to the aqueous film-forming composition of the present embodiment, the concentration of the organic solvent contained in the aqueous film-forming composition is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less.

[0141] <Properties of the aqueous film-forming composition> From the viewpoint of improving coatability, the viscosity of the aqueous film-forming composition at 25° C. is preferably 1 to 100,000 mPa·s, more preferably 10 to 10,000 mPa·s, and particularly preferably 100 to 5,000 mPa·s. In this specification, viscosity can be measured using a general B-type viscometer or E-type viscometer.

[0142] From the viewpoint of improving coating and drying properties, the concentration of solids contained in the aqueous film-forming composition is preferably 1 to 75 mass %, more preferably 5 to 70 mass %, and particularly preferably 10 to 60 mass %.

[0143] <Method for producing aqueous film-forming composition> The method for producing the aqueous film-forming composition is not particularly limited, but for example, (2) blocked polyisocyanate is added to (1) (meth)acrylic resin emulsion, and the mixture is forcibly stirred with a stirring device. The method for adding the surfactant is not particularly limited, but examples thereof include a method of adding the surfactant during the production of a (meth)acrylic resin emulsion, a method of adding the surfactant during the production of a blocked polyisocyanate, and a method of adding the surfactant during the production of an aqueous film-forming composition, and two or more of the above methods may be used in combination.

[0144] Next, a film-forming auxiliary is added, and the mixture is forcibly stirred with a stirring device, and then allowed to stand to swell the (meth)acrylic resin emulsion. Thereafter, additives such as the active hydrogen-containing compound, other resins, catalysts, pigments, leveling agents, antioxidants, UV absorbers, light stabilizers, plasticizers, and surfactants are added as needed. Water and solvents are further added as needed to adjust the viscosity. The resulting mixture is then forcibly stirred with a stirring device to obtain an aqueous film-forming composition.

[0145] <Solar cell surface protection material> The surface protective material for a solar cell of this embodiment includes at least two layers selected from the group consisting of a surface layer, a substrate layer, an adhesive layer, and a release layer. Hereinafter, the "solar cell surface protective material" may be referred to as the "surface protective material."

[0146] Of the layers constituting the surface protective material of this embodiment, at least the surface layer contains the surface protective film of this embodiment. One type of layer constituting the surface protective material may contain one layer (single layer) of the above film, or two or more layers. The surface protective material of this embodiment has excellent adhesion to the sealing material and durability.

[0147] The thickness of the surface protective material is not particularly limited, but is preferably from 5 μm to 1000 μm, more preferably from 15 μm to 800 μm, even more preferably from 20 μm to 500 μm, and particularly preferably from 25 μm to 300 μm.

[0148] [Surface layer] The surface layer is the layer that is placed on the outermost surface of a solar cell covered with a surface protective material when in use, and is the layer that comes into contact with the outside air. The surface layer plays a role in protecting the base layer, adhesive layer, solar cell module encapsulant, solar cell cells, etc. from ultraviolet rays, chemicals, etc.

[0149] The surface layer includes the surface protection film of the present embodiment described above. The surface layer may be a multi-layer structure of two or more layers, and may be laminated with a layer different from the surface protection film of the present embodiment described above, as long as the effects of the present invention are not impaired. When different layers are laminated, there are no particular limitations, but examples thereof include (meth)acrylic resins, urethane resins, silicone-based resins, melamine resins, epoxy resins, unsaturated polyester resins, and fluorine-based resins.

[0150] The thickness of the surface layer is not particularly limited, but is preferably 0.2 μm to 500 μm, more preferably 1 μm to 500 μm, even more preferably 5 μm to 300 μm, and particularly preferably 5 μm to 100 μm. Note that the "thickness of the surface layer" here means the thickness of the entire surface layer, and for example, the thickness of a surface layer consisting of multiple layers means the total thickness of all layers that make up the surface layer.

[0151] [Base material layer] The substrate layer serves as a support layer for the surface layer, and can also function as a protective layer that more effectively protects the structure from external punctures, impacts, etc. The substrate layer may consist of one layer (single layer), or may consist of two or more layers. When the substrate layer consists of multiple layers, the compositions, shapes, and thicknesses of these multiple layers may be the same or different from one another, and the combination of these multiple layers is not particularly limited as long as it does not impair the effects of the present invention.

[0152] The substrate layer is not particularly limited, and examples thereof include layers formed from materials such as resins. Examples of resins include acrylic resins including polymethyl methacrylate, polyurethane, polyvinyl chloride, polycarbonate, polyolefins, polyesters, acrylonitrile-butadiene-styrene copolymers, ethylene-acrylic acid copolymers, ethylene-ethyl acrylate copolymers, and ethylene-vinyl acetate copolymers. Examples of polyolefins include polyethylene and polypropylene. Examples of polyesters include polyethylene terephthalate and polyethylene naphthalate.

[0153] The surface protection film of the present embodiment described above may also be used as the substrate layer.

[0154] The thickness of the substrate layer is not particularly limited, but from the viewpoint of imparting the functions of the substrate layer to the film, it is preferably 2 μm or more and 500 μm or less, and more preferably 5 μm or more and 300 μm or less. Note that the "thickness of the substrate layer" here means the thickness of the entire substrate layer, and for example, the thickness of a substrate layer consisting of multiple layers means the total thickness of all layers constituting the substrate layer.

[0155] [Adhesive layer] The surface protective material of this embodiment may further include an adhesive layer between each of the surface layer, base layer, adhesive layer, and release layer, or between these layers when each layer is composed of multiple layers. The adhesive layer may consist of one layer (single layer), or may consist of multiple layers of two or more. When the adhesive layer consists of multiple layers, the compositions, shapes, and thicknesses of these multiple layers may be the same or different, and the combination of these multiple layers is not particularly limited as long as it does not impair the effects of the present invention.

[0156] The adhesive contained in the adhesive layer is not particularly limited, but may be any adhesive that is commonly used, and specific examples thereof include solvent-based, emulsion-based, pressure-sensitive, heat-sensitive, thermosetting, or ultraviolet-curing adhesives, such as acrylic-based, polyolefin-based, polyurethane-based, polyester-based, and rubber-based adhesives. The aqueous film-forming composition of the present embodiment may also be used as the adhesive. Furthermore, the sheet-like pressure-sensitive adhesive may be directly laminated to each layer, or the surface protection film of this embodiment may be used.

[0157] The thickness of the adhesive layer is not particularly limited, but is preferably 2 μm or more and 200 μm or less, more preferably 5 μm or more and 100 μm or less, from the viewpoint of not adversely affecting the formability of the decorative layer and imparting the functions of the above-mentioned base layer to the film. Note that the "thickness of the adhesive layer" here means the thickness of the entire adhesive layer, and for example, the thickness of an adhesive layer consisting of multiple layers means the total thickness of all layers that make up the adhesive layer.

[0158] [Peeling layer] The release layer is provided for the purposes of preventing scratches on the film surface and protecting the adhesive layer, making it easier to handle the surface protection material before use. Therefore, the release layer is peeled off during thermal lamination of the surface protection material or before using the photovoltaic module formed by thermal lamination.

[0159] The release layer may consist of one layer (single layer) or two or more layers. When the release layer consists of multiple layers, the compositions, shapes, and thicknesses of these multiple layers may be the same or different from one another, and the combination of these multiple layers is not particularly limited as long as it does not impair the effects of the present invention.

[0160] The release layer is not particularly limited, but examples thereof include resins such as acrylic resins, soluble nitrocellulose resins, polyurethane resins, chlorinated rubber resins, vinyl chloride-vinyl acetate copolymer resins, polyamide resins, polyester resins, epoxy resins, polycarbonate resins, olefin resins, and acrylonitrile-butadiene-styrene resins, as well as paper.

[0161] Furthermore, when a release layer is provided for the purpose of protecting the adhesive layer, it is preferable that the release layer can be easily peeled off from the adhesive layer. Therefore, in order to ensure releasability, a release agent may be applied to the surface of the resin, paper, etc.

[0162] The release agent is not particularly limited, but examples thereof include silicone-based release agents, fluororesin-based release agents, polyolefin-based release agents, melamine resin-based release agents, cellulose resin-based release agents, urea resin-based release agents, paraffin-based release agents, acrylic resin-based release agents, and composite release agents thereof.

[0163] Furthermore, the surface protection film of the present embodiment described above may be coated with the release agent and used as the release layer.

[0164] <Solar cell module> This embodiment is a solar cell module protected by the surface protective film of the embodiment or the surface protective material of the embodiment.

[0165] A solar cell module is constructed by laminating, in order from the light-receiving surface side, a surface protection material, a surface sealing material, a solar cell element, a back sealing material, and a back protection sheet (back sheet). The surface protection material is placed on the outermost surface of the solar cell module, and therefore it is essential that it has long-term durability.

[0166] [Solar cell element] Conventionally known solar cell elements can be used. Examples include silicon-based solar cells, compound-based solar cells, and organic solar cells. Silicon-based solar cells include, but are not limited to, crystalline silicon solar cells such as single-crystalline silicon solar cells, polycrystalline silicon solar cells, multi-junction solar cells, and heterojunction solar cells, as well as amorphous silicon solar cells with single junction or tandem structures. Compound-based solar cells include, but are not limited to, III-V group compound semiconductor solar cells such as gallium arsenide (GaAs) and indium phosphide (InP), II-VI group compound semiconductor solar cells such as cadmium telluride (CdTe) and copper indium selenide (CuInSe), and copper indium gallium selenide solar cells. Organic solar cells include, but are not limited to, dye-sensitized solar cells, perovskite-based solar cells, and organic semiconductor solar cells.

[0167] [Sealing material] The sealing material can be any known material and is not particularly limited, but examples include ionomer-based sealing materials, polyolefin-based sealing materials, ethylene vinyl acetate copolymer (EVA)-based sealing materials, polyvinyl butyral (PVB)-based sealing materials, silicone-based sealing materials, polyurethane-based sealing materials, and polycarbonate-based sealing materials.

[0168] [Back seat] The back sheet may be a conventionally known one, and is not particularly limited, but may be a polyvinyl fluoride (PVF)-based back sheet, a polyethylene terephthalate (PET)-based back sheet, Inorganic and the like.

[0169] <Solar cell module manufacturing method> A solar cell module can be manufactured, for example, by stacking a surface protection film, a surface sealing material, a solar cell element, a back sealing material, and a back protection sheet (back sheet) in that order from the light-receiving surface side, and then performing either or both of heating and pressure bonding treatments using a vacuum thermal lamination method or the like to form the module into a single unit. For example, in the vacuum thermal lamination method, the lamination temperature is preferably within the range of 50° C. to 180° C., and the time for either or both of the heating and pressure bonding treatment is preferably within the range of 5 to 90 minutes.

[0170] A solar cell module can be manufactured, for example, by stacking a surface protective material, a surface sealing material, a solar cell element, a back sealing material, and a back protective sheet (back sheet) in that order from the light-receiving surface side, and then performing either or both of heating and pressure bonding treatments using a vacuum thermal lamination method or the like to form the module into a single unit. For example, in the vacuum thermal lamination method, the lamination temperature is preferably within the range of 50° C. to 180° C., and the time for either or both of the heating and pressure bonding treatment is preferably within the range of 5 to 90 minutes. [Example]

[0171] The present embodiment will be described in more detail below based on examples and comparative examples, but the present embodiment is not limited to the following examples. Unless otherwise specified, "%" and "parts" in the text all refer to those based on mass.

[0172] <Production example> [(Production Example A1) Production of aqueous dispersion of (meth)acrylic resin emulsion particles] A reactor equipped with a reflux condenser, a dropping tank, a thermometer, and a stirrer was charged with 172.5 parts of distilled water and 4.2 parts of a 15% aqueous solution of sodium dodecylbenzenesulfonate, an anionic surfactant. The temperature in the reactor was raised to 80°C, and then 1.9 parts of a 25% aqueous solution of Adeka Reasoap SR-1025, a nonionic surfactant, and 12.1 parts of a 2% aqueous solution of ammonium persulfate were charged, followed by stirring for 5 minutes.

[0173] Next, a monomer mixture of 239.2 parts of methyl methacrylate, 146.7 parts of butyl methacrylate, 49.4 parts of butyl acrylate, 34.2 parts of 2-hydroxyethyl methacrylate, 19.6 parts of methacrylic acid, 12.4 parts of a 25% aqueous solution of Adeka Reasoap SR-1025, 67.9 parts of a 2% aqueous solution of ammonium persulfate, 33.2 parts of a 15% aqueous solution of sodium dodecylbenzenesulfonate, and 183.6 parts of distilled water was added to the reaction vessel over 2.5 hours from a dropping tank. After completion of the addition, the temperature in the reaction vessel was kept at 80°C for 0.5 hours.

[0174] Next, 22.6 parts of a 2% aqueous solution of ammonium persulfate was added. After the addition, the temperature in the reaction vessel was raised to 80°C and maintained for 2.0 hours. Thereafter, the reaction vessel was cooled to room temperature, and a 25% aqueous ammonia solution was added to adjust the pH to 8.5. The mixture was then filtered through a 400-mesh wire screen to obtain an aqueous dispersion of (meth)acrylic resin emulsion particles with a solid content of 49.7% and an average particle size of 95 nm.

[0175] [(Manufacturing examples A2~A8)] A water dispersion of (meth)acrylic resin emulsion particles having the solid content and average particle size shown in Table 1 was obtained by the same production method as in Production Example 1, except that the composition of the monomer mixture was as shown in Table 1.

[0176] <Methods for measuring and evaluating physical properties> [Physical properties 1-1] Number average molecular weight The number average molecular weight is a number average molecular weight based on polystyrene measured by gel permeation chromatography (GPC) using the following equipment. A (meth)acrylic resin emulsion was used as the sample. The measurement conditions are shown below.

[0177] (Measurement conditions) Equipment: Tosoh Corporation, HLC-802A Column: Tosoh Corporation, G1000HXL x 1 G2000HXL x 1 G3000HXL x 1 Carrier: dimethylformamide Detection method: differential refractometer

[0178] [Table 1]

[0179] In Table 1, each symbol represents the following material. SR-1025: A 25% aqueous solution of the nonionic surfactant Adeka Reasoap SR-1025 (trade name, manufactured by ADEKA Corporation) DBS-Na: 15% aqueous solution of sodium dodecylbenzenesulfonate APS: Ammonium persulfate BMA: butyl methacrylate MMA: methyl methacrylate BA: butyl acrylate HEMA: 2-hydroxyethyl methacrylate MAA: methacrylic acid

[0180] [(Production Example B1) Preparation of aqueous film-forming composition] To 58.4 parts of the aqueous dispersion of (meth)acrylic resin emulsion particles from Production Example A1, 25.3 parts of a water-dispersible blocked polyisocyanate (WS50-30W (trade name) manufactured by Asahi Kasei Corporation) as a blocked polyisocyanate and 5.3 parts of distilled water for adjusting the solids content were added and mixed at room temperature. Furthermore, 5.8 parts of butyl carbitol acetate as a film-forming aid were added at room temperature, stirred for 3 hours, and then allowed to stand for 24 hours. Furthermore, 3.7 parts of Tinuvin® 479-DW (trade name, manufactured by BASF Japan Ltd.) as an ultraviolet absorber and 1.5 parts of Tinuvin® 123-DW (trade name, manufactured by BASF Japan Ltd.) as a light stabilizer were added and mixed at room temperature to obtain an aqueous film-forming composition of Production Example B1.

[0181] The solids concentration of the aqueous film-forming composition of Production Example B1 was 39.0%, and the amount of film-forming aid contained in the aqueous film-forming composition of Production Example B1 was 5.8%. The molar ratio NCO / OH of the blocked isocyanate groups contained in the blocked polyisocyanate to the hydroxy groups in the (meth)acrylic resin was 0.75, and the mass fraction of the (meth)acrylic resin in the solids content of the aqueous film-forming composition of Production Example B1 (i.e., in the film resin) was 74.9%, and the mass fraction of the blocked polyisocyanate resin was 19.4%.

[0182] [(Production Examples B2 to B15) Preparation of aqueous film-forming compositions] The aqueous film-forming compositions of Production Examples B2 to B15 were obtained in the same manner as in the above [(Production Example B1) Preparation of aqueous film-forming composition-1], except that the (meth)acrylic resin emulsions, blocked polyisocyanates, film-forming aids, UV absorbers, light stabilizers, and distilled water shown in Tables 2 and 3 were used in the amounts shown in Table 2.

[0183] Comparative Production Example 1: Preparation of aqueous film-forming composition Except for not adding the blocked polyisocyanate resin, an aqueous film-forming composition of Comparative Production Example 1 was obtained in the same manner as in Example 1. The solids concentration of the aqueous film-forming composition of Comparative Production Example 1 was 39.0 mass%. The mass fraction of the (meth)acrylic resin in the solids of the aqueous film-forming composition (i.e., in the film resin) was 94.3%, and the mass fraction of the blocked polyisocyanate resin was 0%.

[0184] [Table 2]

[0185] [Table 3]

[0186] In Tables 2 and 3, the symbols represent the following materials. WS50-30W: Water-dispersible blocked polyisocyanate manufactured by Asahi Kasei Corporation BCA: butyl carbitol acetate Tinuvin 479-DW: UV absorber manufactured by BASF Japan Ltd. Tinuvin 123-DW: Light stabilizer manufactured by BASF Japan Ltd.

[0187] <Example> [Examples 1 to 15: Preparation of surface protection films for solar cells] As shown in Tables 4 and 5, each aqueous film-forming composition obtained in each production example was applied to a polyethylene terephthalate (PET) film that had been subjected to a release treatment using an applicator to a resin film thickness of 50 μm. After application, the film was dried at room temperature for 30 minutes and then heated and dried at 90°C for 30 minutes. The film was then peeled off from the PET film to obtain a pre-cured film.

[0188] [Cure film preparation] The film obtained in the above [Film Preparation] was further heat-cured at 140° C. for 30 minutes, and then peeled off from the PET film to obtain a surface protection film.

[0189] [Examples 16 to 21: Preparation of surface protective films for solar cells] As shown in Table 6, the aqueous composition for forming an upper layer film was applied to a polyethylene terephthalate (PET) film that had been subjected to a release treatment using an applicator to give a resin film thickness of 50 μm. After application, the film was dried at room temperature for 30 minutes, and then heated and dried at 90°C for 30 minutes. On top of this, the aqueous composition for forming a lower layer film shown in Table 3 was applied using an applicator to give a resin film thickness of 50 μm. After application, the film was dried at room temperature for 30 minutes, and then heated and dried at 90°C for 30 minutes. The film was then peeled off from the PET film to give a pre-cured film.

[0190] [Cure film preparation] The films obtained in Examples 16 to 21 above, Preparation of Surface Protection Films for Solar Cells, were further heat-cured for 30 minutes at 140° C. Thereafter, the films were peeled off from the PET film to obtain surface protection films after curing.

[0191] <Comparative Example> Comparative Example 1: Preparation of a surface protection film for solar cells Each aqueous film-forming composition obtained in the comparative production examples was applied to a polyethylene terephthalate (PET) film that had been subjected to a release treatment using an applicator to a resin film thickness of 50 μm. After application, the film was dried at room temperature for 30 minutes and then heated and dried at 90°C for 30 minutes. The film was then peeled off from the PET film to obtain a pre-cured film.

[0192] [Cure film preparation] The film obtained in the above Comparative Example 1: Preparation of a surface protection film for solar cells was further heat-cured for 30 minutes at 140° C. Thereafter, the film was peeled off from the PET film to obtain a surface protection film after curing.

[0193] Comparative Example 2: Preparation of solar cell surface protection film As a transparent resin film, an ethylene-tetrafluoroethylene copolymer resin (ETFE) film with a thickness of 100 μm was used as it was as a surface protection film for a solar cell.

[0194] Comparative Example 3: Preparation of solar cell surface protective film As a transparent resin film, a polyethylene terephthalate resin (PET) film with a thickness of 100 μm was used as it is as a surface protection film for a solar cell.

[0195] [Laminate formation of surface protection film and sealing material] The surface protection film obtained in the examples and comparative examples was stacked on top of an ionomer-based encapsulant, and vacuum laminated using an LM-type sheet-fed vacuum laminating machine (manufactured by NPC Corporation) at 160°C for 60 minutes to bond the solar cell surface protection film and encapsulant together to form an evaluation sample.

[0196] <Methods for measuring and evaluating physical properties> [Physical Properties 2-1] Glass Transition Temperature The glass transition temperatures of the surface protection films obtained in the examples and comparative examples were measured using a differential scanning calorimetry (DSC, Hitachi High-Tech Corporation, DSC7000X) under conditions of a temperature range of -100°C to +200°C and a heating rate of 10°C / min, and the temperature at the inflection point of the baseline shift associated with the glass transition was taken as the glass transition temperature.

[0197] <Evaluation method> [Rating 1] Weather resistance The weather resistance of the surface protection film-sealant laminates obtained in the examples and comparative examples was evaluated using a Super Xenon Weather Meter SX75 (manufactured by Suga Test Instruments Co., Ltd.). The visual appearance and gloss retention of the surface protection film-sealant laminates were measured using a spectrophotometer CM-26dG (manufactured by Konica Minolta, Inc.). The test conditions and evaluation criteria are described below.

[0198] (Test conditions) ·Irradiance: 180W / m 2 (Wavelength of irradiation light: 300-400nm) Operation cycle: Drying / Spraying = 102 / 18 minutes cycle operation Dry: Black panel temperature 63°C, humidity 50% -Temperature inside the tank when spraying: 28℃ Test time: 2000 hours

[0199] (Evaluation criteria) A: Gloss retention is 90% or more, and no roughness or cracks are observed on the surface. B: Gloss retention rate of 85% or more, slight roughness or cracks were observed on the surface, but to a degree that did not interfere with practical use. C: Gloss retention rate of 80% or more, slight roughness or cracks were observed on the surface, but to a degree that did not interfere with practical use. D: Gloss retention is less than 80%, or obvious roughness or cracks are observed on the surface, making it unsuitable for practical use.

[0200] [Evaluation 2] Acid resistance The surface of the surface protection film-sealant laminate was immersed in a 10 wt% aqueous sulfuric acid solution and left to stand at 20°C for 24 hours. After the specified time had passed, the film surface was thoroughly washed with water, and the state of the film surface after drying was visually observed to evaluate acid resistance. The evaluation criteria were as follows:

[0201] (Evaluation criteria) A: No roughness or marks are found on the surface B: Slight marks were observed on the surface, but they were not a practical hindrance. C: Clear roughness or marks are visible on the surface

[0202] [Evaluation 3] Base resistance The surface of the surface protection film-sealant laminate obtained in the Examples and Comparative Examples was immersed in a 10 wt% aqueous solution of sodium hydroxide and left to stand at 23°C for 24 hours. After the predetermined time had passed, the film surface was thoroughly rinsed with water, and the state of the film surface after drying was visually observed to evaluate the base resistance. The evaluation criteria were as follows:

[0203] (Evaluation criteria) A: No roughness or marks are found on the surface B: Slight marks were observed on the surface, but they were not a practical hindrance. C: There are obvious roughness or marks on the surface, making it unsuitable for practical use.

[0204] [Evaluation 4] Solvent resistance 0.1 mL of xylene was dropped onto the surface of the surface protection film-sealant laminate obtained in the Examples and Comparative Examples. After leaving it to stand for 15 minutes, the state of the film was visually observed and the solvent resistance was evaluated. The evaluation criteria were as follows:

[0205] (Evaluation criteria) A: No roughness or marks are found on the surface B: Slight marks were observed on the surface, but they were not a practical hindrance. C: There are obvious roughness or marks on the surface, making it unsuitable for practical use.

[0206] [Rating 5] Scratch resistance The scratch resistance of the surface protection film-sealing material laminates obtained in the examples and comparative examples was evaluated using a scratch hardness tester (Erichsen's "Pencil-type Scratch Hardness Tester 318S"). After curing, the surface of the film was scratched with the tool while changing the applied pressure, and the presence or absence of scratches was visually confirmed. The highest pressure at which no scratches were observed was used as an index of scratch resistance, and it was evaluated according to the following criteria, with a grade of "C" or higher being considered a pass.

[0207] (Evaluation criteria) A: 1.5N or more B: 1.0N or more and less than 1.5N C: 0.5N or more and less than 1.0N D: Less than 0.5N

[0208] [Evaluation 6] Adhesion to sealing material The adhesion of the surface protection film-sealing material laminates obtained in the examples and comparative examples was tested by a cross-cut adhesion test in accordance with JIS K5600-5-6, and the adhesion was evaluated based on the results according to the following criteria.

[0209] (Evaluation criteria) A: The edges of the cut are completely smooth and there is no peeling on any of the grids. B: Although there is small peeling of the coating at the intersections of the cuts, the affected area of ​​the cross-cuts does not exceed 5%, and there is no problem in practical use. C: The coating has peeled slightly along the edges of the cuts and / or at the intersections. The cross-cut area is affected by more than 5% but not more than 15%, and is not a problem for practical use. D: The coating has peeled along the edges of the cuts and / or at the intersections, with more than 15% of the cross-cut area affected, causing practical problems.

[0210] [Table 4]

[0211] [Table 5]

[0212] [Table 6]

[0213] [Table 7]

[0214] As shown in Tables 4 to 6, the surface protection films shown in Examples 1 to 21 achieved both high durability and good adhesion to the sealing material.

[0215] On the other hand, the surface protection film of Comparative Example 1 did not contain a blocked polyisocyanate, and therefore crosslinking was not formed, and a film with excellent durability was not obtained.

[0216] The surface protection film of Comparative Example 2 uses a fluororesin film, and therefore has high weather resistance, but it has poor adhesion to the encapsulant and poor scratch resistance, making it unsuitable for use as a surface protection film for solar cells.

[0217] The surface protective film of Comparative Example 3 also did not have excellent durability and was not suitable for application as a surface protective film for solar cells. [Industrial Applicability]

[0218] The surface protective film for solar cells, the surface protective material for solar cells, and the solar cell module of the present embodiment have high durability and excellent adhesion to the encapsulant, and are therefore useful as a surface protective film for solar cells.

Claims

1. A surface protective film for a solar cell comprising one or more layers, the outermost layer of the surface protective film for a solar cell contains (1) a (meth)acrylic resin emulsion and (2) a blocked polyisocyanate, The (1) (meth)acrylic resin emulsion is a resin having a hydroxyl value of 3 mg / g-KOH or more and 150 mg / g-KOH or less, or a resin having an amino value of 3 mgKOH / g or more and 150 mgKOH / g or less, The surface protective film for a solar cell, wherein the (2) blocked polyisocyanate is a blocked polyisocyanate having, as a skeleton, at least one isocyanate compound selected from the group consisting of aliphatic isocyanates and alicyclic isocyanates.

2. 2. The surface protective film for solar cells according to claim 1, wherein the (meth)acrylic resin emulsion (1) has a glass transition temperature of −20° C. or higher and 120° C. or lower.

3. 3. The surface protective film for solar cells according to claim 1, wherein the glass transition temperature of the surface protective film for solar cells is −40° C. or higher and 140° C. or lower.

4. 3. The surface protective film for solar cells according to claim 1, wherein the number average molecular weight of the (meth)acrylic resin emulsion (1) is 1,000 or more and 2,000,000 or less.

5. 3. The surface protective film for solar cells according to claim 1, wherein the monomer units constituting the (meth)acrylic resin emulsion (1) include a monomer having a carboxyl group.

6. (1) the weight fraction of the (meth)acrylic resin emulsion is 50% or more and 99% or less; 3. The surface protective film for solar cells according to claim 1, wherein the weight fraction of the blocked polyisocyanate (2) is 1% or more and 50% or less.

7. 3. The surface protective film for solar cells according to claim 1, wherein the molar ratio (NCO group / OH group) of the blocked isocyanate groups contained in the (2) blocked polyisocyanate to the hydroxyl groups contained in the (1) (meth)acrylic resin emulsion is 0.05 to 3.

0.

8. The surface protective film for a solar cell according to claim 1 or 2, further comprising a surfactant.

9. 3. The surface protective film for solar cells according to claim 1, wherein a weight fraction of the surfactant relative to the weight of the surface protective film for solar cells is 0.01% by mass or more and 10% by mass or less.

10. A surface protective film for a solar cell comprising two or more layers, The glass transition temperature of the outermost surface layer is Tgu, When the glass transition temperature of the bottom layer is Tgl, The surface protective film for a solar cell according to claim 1 , wherein the Tgu is greater than the Tgl.

11. A surface protective laminate for solar cells, comprising at least two layers selected from the group consisting of a surface layer, a base layer, a pressure-sensitive adhesive layer, and a release layer, wherein the surface layer is the surface protective film for solar cells according to claim 1 or 2.

12. The surface protective material for a solar cell according to claim 11, having a film thickness of 5 μm or more and 1000 μm or less.

13. A solar cell module protected by the surface protective film for solar cells according to claim 1 or 2.

14. A solar cell module protected by the surface protective material for solar cells according to claim 11.

15. 14. A method for manufacturing a solar cell module according to claim 13, comprising a step of stacking a surface protective film, a surface sealing material, a solar cell, a back sealing material, and a back protective material in this order, and integrally molding them by either one or both of heating and pressure bonding treatment, wherein the heating temperature during the integral molding is 50°C or higher and 180°C or lower.

16. 15. The method for manufacturing a solar cell module according to claim 14, comprising a step of stacking a surface protective material, a surface sealing material, a solar cell, a back surface sealing material, and a back surface protective material in this order, and integrally molding them by either one or both of heating and pressure bonding treatment, wherein the heating temperature during the integral molding is 50°C or higher and 180°C or lower.

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