JP2006253565A - Surface protection film for solar cell, and solar cell laminated body composed by using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a film suitable as a surface protection film for a solar cell which has environment-resistant characteristics excellent in the shielding performance of ultraviolet rays and water vapor, and excellent in adhesion with an EVA resin. <P>SOLUTION: In the surface protection film for a solar cell, a polyester film is used as a base material film. The film has a layer with ultraviolet-ray absorbency and a layer with water vapor shielding performance. At least one uppermost surface layer is made as an easy adhesion layer including at least one kind of a cross-linker of an epoxy resin or a polymer including an oxazoline group. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a surface protection film for solar cells that is lightweight and excellent in handleability. More specifically, the present invention relates to a solar cell surface protective film suitable as a protective film for a silicon solar cell, which has excellent ultraviolet shielding properties and water vapor shielding properties and has excellent durability when used outdoors, and a solar cell laminate using the same. It is.

  In recent years, a solar power generation system has been spreading as one of power generation means using clean energy. For example, as disclosed in Patent Document 1, a solar cell module generally has a plurality of plate-like solar cell elements sandwiched between a light receiving side glass substrate and a back surface side protective film. The internal gap is filled with sealing resin. Here, ethylene-vinyl acetate copolymer resin (EVA resin) is used as the sealing resin because it is highly transparent and excellent in moisture resistance.

  As the protective film on the back side, for example, Patent Document 2 discloses that a sheet of polyethylene resin or polyester resin, a fluororesin film, or the like is used. However, such a protective film does not necessarily have sufficient adhesiveness with the EVA resin and remains uneasy about long-term durability.

  For example, polyester films, especially biaxially stretched films of polyethylene terephthalate and polyethylene naphthalate, have excellent mechanical properties, heat resistance and moisture resistance, so magnetic tape, ferromagnetic thin film tape, photographic film, packaging film, electronic parts It is widely used as a film for electrical use, an electrical insulating film, a film for laminating metal plates, a film for display members, etc., and has excellent performance as a solar cell back surface protective film. However, a polyester film, in particular, a polyester film that has been biaxially stretched and highly oriented and crystallized, has extremely poor adhesion to the EVA resin because its surface is inactive.

  In order to improve the adhesiveness between such a polyester film and EVA resin, Patent Document 3 proposes to laminate a thermal adhesive layer made of a styrene / olefin copolymer resin.

  Furthermore, in order to prevent alteration due to oxygen, water vapor, etc. entering from the outside, a high gas barrier property is required. Therefore, a film coated with a gas barrier resin such as polyvinyl alcohol (PVA), ethylene / vinyl alcohol copolymer (EVOH), polyvinylidene chloride (PVDC), or a film made of these resins is laminated for the purpose of imparting gas barrier properties. Laminated films have been used.

  However, these protective films for silicon solar cells are difficult to use outdoors for a long time because they are easily deteriorated by ultraviolet rays in sunlight, and the water vapor barrier property that affects the performance of silicon solar cells is not sufficient. There wasn't.

Japanese Utility Model Publication No. 6-38264 JP-A-11-261085 JP 2003-60218 A

  The present invention has been made in view of the above-mentioned background art. The object of the present invention is for solar cells having environmental resistance characteristics excellent in ultraviolet and water vapor shielding properties and excellent adhesion to EVA resins. The object is to provide a surface protective film and a solar cell laminate using the same.

  According to the inventor's research, the above-mentioned problem is “a laminated film having a polyester film as a base film and having a layer having ultraviolet absorptivity and a layer having water vapor shielding properties, and at least one of the laminated films. The outermost layer is an easy-adhesion layer containing at least one crosslinking agent of an epoxy resin or an oxazoline group-containing polymer. The surface protective film for solar cells, which can be achieved by the present invention, It has been found that this can be achieved by "a solar cell laminate in which a silicon solar cell is sandwiched between the surface protective films via an ethylene-vinyl acetate copolymer resin."

  The surface protective film of the present invention is a base film made of polyester that has excellent water vapor shielding properties and ultraviolet light shielding properties and excellent adhesion to EVA resin, and also has good mechanical properties, heat resistance and moisture resistance. Therefore, it is extremely useful as a surface protective film for improving the durability of the solar cell.

Hereinafter, the configuration of the present invention will be described in detail.
[Polyester film]
First, examples of the polyester constituting the polyester film used in the base film of the present invention include aromatic dicarboxylic acid components such as terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, and 4,4'-diphenyldicarboxylic acid. And, for example, an aromatic polyester composed of glycol components such as ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, 1,6-hexanediol, and the like, There may be. Among these, polyethylene terephthalate and polyethylene-2,6-naphthalene dicarboxylate are preferable. Particularly, polyethylene-2,6-naphthalene dicarboxylate is excellent in water vapor shielding performance, and the base film itself is a layer having water vapor shielding properties. This is preferable because it can play a role.

  In order to improve the rollability of the film at the time of film formation and the transportability of the film in the processing step of the surface protection film for solar cells, such polyester has a transparency and surface shape as long as it is not impaired. Organic or inorganic fine particles as a lubricant can be contained. Examples of such fine particles include calcium carbonate, calcium oxide, aluminum oxide, kaolin, silicon oxide, zinc oxide, crosslinked acrylic resin particles, crosslinked polystyrene resin particles, urea resin particles, melamine resin particles, and crosslinked silicone resin particles. In addition to fine particles, other resins such as colorants, antistatic agents, antioxidants, ultraviolet absorbers, lubricants, catalysts, polyethylene, polypropylene, ethylene / propylene copolymers, olefinic ionomers, etc. It can contain arbitrarily in the range which does not impair film characteristics, such as intensity | strength.

［式中、Ｒは１価の炭化水素残基を示す。］
で表わされる環状イミノエステル基を含有する環状イミノエステル系紫外線吸収剤を用いると、ポリエステル中に添加しても昇華物が殆ど生じないので、製膜でダイ周辺を汚すことが少なく、また、紫外線から３８０ｎｍ付近の光線を吸収するのでフィルムの着色がなく、後述する紫外線吸収性を有する層としての役割を果たすと共に、基材フィルム自体の劣化を防止する特性にも優れているので好ましい。 Especially as UV absorber, the following formula

[Wherein R represents a monovalent hydrocarbon residue. ]
When a cyclic iminoester-based ultraviolet absorber containing a cyclic iminoester group represented by the formula (1) is used, there is little sublimation even if it is added to the polyester. Since the film absorbs light in the vicinity of 380 nm to 380 nm, the film is not colored, serves as a layer having ultraviolet absorbability described later, and is excellent in the property of preventing deterioration of the base film itself.

  The amount of the cyclic imino ester UV absorber added is preferably in the range of 0.1 to 5.0% by weight, particularly preferably in the range of 0.2 to 3.0% by weight, and less than 0.1% by weight based on the polyester. In this case, the effect of preventing deterioration due to ultraviolet rays is reduced. On the other hand, if it exceeds 5.0% by weight, the film forming characteristics of the polyester are lowered.

  The method of adding the ultraviolet absorber to the polyester is not particularly limited, and examples thereof include a polyester polymerization step, kneading into a polymer in a melting step before film formation, impregnation into a biaxially stretched film, and the like. In particular, kneading into the polymer in the melting step before film formation is also preferred in order to prevent a decrease in the degree of polymerization of the polyester. At that time, the kneading of the ultraviolet absorber can be performed by a direct addition method of a compound powder, a master batch method or the like.

[Water vapor shielding layer]
It is important that the surface protective film for solar cells has water vapor shielding properties because the permeation of moisture through the film may reduce the adhesion durability of the solar cell structure. In addition, silicon solar cells that are currently in practical use include single crystal silicon, polycrystalline silicon, and amorphous silicon solar cells. In particular, in the case of amorphous silicon, the unstable structure makes it impossible to Performance may be degraded. Therefore, the surface protection film for solar cells of the present invention needs to be provided with a layer having a water vapor shielding function. The water vapor shielding function herein has a water vapor transmission rate measured in accordance with JIS K7129 of 1.0 g / (m ² · 24 h) or less, preferably 0.3 g / (m ² · 24 h) or less. That means.

  Such a layer having a water vapor shielding property may be composed of an organic resin, may be composed of an inorganic material, and further, as described above, as a layer having a water vapor shielding property on the base film itself. It may have a function. Examples of the organic resin include polyvinylidene chloride resin and polyvinylidene fluoride resin. On the other hand, examples of the inorganic substance include metal oxides, nitrides, and carbon nitride thin layers. Or nitride is preferable. As a metal element of such a compound, indium, magnesium, zinc, tin, silicon, aluminum, titanium, and zirconium are preferable. When such a metal compound is used, it is preferable to reduce the film thickness in order to maintain transparency, flexibility, and productivity, and it is preferable that the film thickness be less than 500 nm, particularly 150 nm or less. On the other hand, if the film thickness becomes too thin, the water vapor shielding property is lowered, so that it is preferably 50 nm or more, particularly 75 nm or more.

  The inorganic thin film forming method is not particularly limited, and can be formed by a conventionally known method, but a shielding layer having a dense film structure can be formed by a vapor phase method such as a vapor deposition method or a sputtering method. preferable. On the other hand, the method for forming the layer made of the organic resin is not particularly limited. For example, the layer may be formed by a conventionally known coating method.

[UV absorbing layer]
The surface protective film for a solar cell of the present invention needs to have a layer having ultraviolet absorptivity together with the layer having the water vapor shielding performance. Such a layer may be formed by containing an ultraviolet absorber in the base film as described above, or may be a layer in which a resin layer having ultraviolet absorptivity is separately formed on the film surface. Good.

  In addition, in order to form the resin layer which has an ultraviolet absorptivity, you may mix | blend an ultraviolet absorber in suitable resin, and you may use resin which has group which has an ultraviolet absorptivity in a side chain. Of these, polyester resins, melamine resins, acrylic resins, urethane resins and the like having a benzophenone skeleton or a benzotriazole skeleton in the side chain are preferable, and acrylic resins are particularly preferable. The molecular weight is preferably 5000 or more, particularly 10,000 or more. It is desirable that the film thickness of the resin layer having ultraviolet absorptivity is such that the transmittance of the finally obtained laminated film at a wavelength of 380 nm is less than 40%, preferably less than 20%, usually 3 to 15 μm. The range is appropriate. If it is too thin, it will be difficult to absorb the ultraviolet rays sufficiently, and conversely, productivity will be reduced when the resin layer is formed too thick.

  In the present invention, the order of stacking the layer having the ultraviolet absorbing property and the layer having water vapor shielding properties on the base film need not be particularly limited, and the layer may be stacked only on one side of the base film. Even if laminated on both sides, or both laminated on both sides, the base film also functions as a layer having ultraviolet absorptivity and water vapor shielding as described above. It may be a thing given. Moreover, you may provide an adhesive layer for the purpose of improving the adhesiveness between each layer as needed. In particular, it is preferable that the polyester film is provided with the same easy-adhesion layer as will be described later, a layer having a water vapor shielding property is laminated thereon, and then a layer having an ultraviolet absorptive layer is laminated if necessary. .

  Further, the layer having ultraviolet absorptivity and the layer having water vapor shielding properties in the present invention do not need to be separate layers, and one layer may be used as long as it has both functions.

[Easily adhesive layer]
In the surface protective film of the present invention, in addition to the above-described structure, at least one outermost layer thereof is composed of an easy-adhesion layer containing at least one crosslinking agent of an epoxy resin or an oxazoline group-containing polymer. is required.

  Examples of the oxazoline group-containing polymer include polymers described in JP-B 63-48884, JP-A-2-60941, JP-A-2-99537, and the like. Specific examples include a polymer obtained by copolymerizing an addition-polymerizable oxazoline represented by the following formula and, if necessary, other monomers.

式中のＲ^１、Ｒ^２、Ｒ^３およびＲ^４は、それぞれ、水素、ハロゲン、アルキル基、アラルキル基、フェニル基および置換フェニル基から選ばれる置換基を示し、Ｒ^５は付加重合性不飽和結合基を有する非環状有機基を示す。

R ¹ , R ² , R ³ and R ⁴ in the formula each represent a substituent selected from hydrogen, halogen, alkyl group, aralkyl group, phenyl group and substituted phenyl group, and R ⁵ is addition polymerizable unsaturated An acyclic organic group having a linking group is shown.

  The epoxy resin may be a polyepoxy compound having two or more epoxy groups in the molecule or a monoepoxy compound, but preferably contains a polyepoxy compound. Examples of the polyepoxy compound include sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, diglycerol polyglycidyl ether, triglycidyl tris (2-hydroxyethyl) isocyanate, glycerol polyglycidyl ether, trimethylolpropane poly Glycidyl ether, N, N, N ′, N′-tetraglycidylmetaxylylenediamine, N, N, N ′, N′-tetraglycidyl-4,4′-diaminodiphenylmethane, N, N, N ′, N ′ A tri- or higher functional polyepoxy compound such as tetraglycidyl-1,3-bisaminomethylcyclohexane, and, for example, neopentyl glycol diglycidyl ether, 1,6-hexanediol jig Ethers, resorcin diglycidyl ether, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and diepoxy compounds of polytetramethylene glycol diglycidyl ether. On the other hand, examples of the monoepoxy compound include allyl glycidyl ether, 2-ethylhexyl glycidyl ether, and phenyl glycidyl ether. Among these, N, N, N ′, N′-tetraglycidylmetaxylylenediamine, N, N, N ′, N′-tetraglycidyl-4,4′-diaminodiphenylmethane, N, N, N ′, N '-Tetraglycidyl-1,3-bisaminomethylcyclohexane is preferred.

  Said crosslinking agent may be individual, or may use 2 or more types together as needed. In particular, an oxazoline group-containing polymer is preferable because it exhibits excellent adhesiveness.

  In addition, content of a crosslinking agent should just be the range of 10 to 100 weight% on the basis of solid content weight in the coating liquid for forming this easily bonding layer, and it contains suitably according to the kind of crosslinking agent especially. It is preferable to change the amount. In the case of an oxazoline group-containing polymer, it is preferably in the range of 10 to 100% by weight, and in the case of an epoxy resin, it is preferably in the range of 10 to 50% by weight. When the content of the cross-linking agent is less than 10% by weight, the cohesive force of the easy-adhesion layer is lowered and the adhesion durability particularly under high humidity tends to be lowered.

  The easy-adhesion layer of the present invention preferably contains, in addition to the above-mentioned crosslinking agent, a resin component composed of a polyester resin or acrylic resin having a glass transition point in the range of 20 to 100 ° C., particularly a polyester resin. In particular, the glass transition point of the resin is preferably in the range of 30 to 90 ° C. When the glass transition point is less than 20 ° C., blocking between the films may occur. On the other hand, when the glass transition point exceeds 100 ° C., the easy-adhesion layer may become brittle and adhesion may not be maintained.

  Such a polyester resin having a glass transition point in the range of 20 to 100 ° C. is formed from the following polybasic acid or an ester-forming derivative thereof and a polyol or an ester-forming derivative thereof. That is, as the polybasic acid component, terephthalic acid, isophthalic acid, phthalic acid, phthalic anhydride, 2,6-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, adipic acid, sebacic acid, trimellitic acid, pyromellitic acid , Dimer acid, 5-sodium sulfoisophthalic acid and the like. A copolymer polyester resin is synthesized using preferably two or more of these acid components. Further, if it is a slight amount, an unsaturated polybasic acid component such as maleic acid, itaconic acid, or hydroxycarboxylic acid such as p-hydroxybenzoic acid can be used in combination. The polyol component includes ethylene glycol, 1,4-butanediol, diethylene glycol, dipropylene glycol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, xylene glycol, dimethylolpropane, and poly (ethylene oxide) glycol. , Poly (tetramethylene oxide) glycol and the like.

  On the other hand, examples of the acrylic resin having a glass transition point in the range of 20 to 100 ° C. include acrylic resins obtained by polymerizing acrylic monomers as exemplified below. Examples of the acrylic monomer include alkyl acrylate and alkyl methacrylate (the alkyl group includes methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, 2-ethylhexyl group, cyclohexyl group). Groups); hydroxyl group-containing monomers such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate and 2-hydroxypropyl methacrylate; epoxy group-containing monomers such as glycidyl acrylate, glycidyl methacrylate and allyl glycidyl ether; Acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, styrene sulfonic acid and its salts (sodium salt, potassium salt, ammonium salt, tertiary amine salt, etc.) A monomer containing a carboxy group, a sulfoxy group or a salt thereof; acrylamide, methacrylamide, N-alkylacrylamide, N-alkylmethacrylamide, N, N-dialkylacrylamide, N, N-dialkylmethacrylamide (as alkyl groups, Methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, 2-ethylhexyl group, cyclohexyl group, etc.), N-alkoxyacrylamide, N-alkoxymethacrylamide, N, N-dialkoxyacrylamide, N, N-dialkoxymethacrylamide (alkoxy groups include methoxy, ethoxy, butoxy, isobutoxy, etc.), acryloylmorpholine, N-methylolacrylamide, N-methylol Monomers containing amide groups such as chloramide, N-phenylacrylamide, N-phenylmethacrylamide; monomers of acid anhydrides such as maleic anhydride and itaconic anhydride; vinyl isocyanate, allyl isocyanate, styrene, α-methylstyrene, vinyl Methyl ether, vinyl ethyl ether, vinyl trialkoxy silane, alkyl maleic acid monoester, alkyl fumaric acid mono ester, alkyl itaconic acid mono ester, acrylonitrile, methacrylonitrile, vinylidene chloride, ethylene, propylene, vinyl chloride, vinyl acetate, butadiene And the like.

  Among these, monomers containing a hydroxyl group such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, N-methylol acrylamide, N-methylol methacrylamide and the like are 2-20. It is preferably contained in a mol%, preferably 4 to 15 mol%.

  In addition, in order to improve the handleability of the surface protection film obtained and to prevent blocking between films, an inert fine particle can be added to the easily bonding layer of this invention. Such fine particles are preferably organic or inorganic inert fine particles as long as they do not affect transparency. For example, calcium carbonate, calcium oxide, aluminum oxide, kaolin, silicon oxide, zinc oxide, crosslinked acrylic resin particles, crosslinked polystyrene resin particles, melamine Examples thereof include resin particles and crosslinked silicone resin particles.

  Furthermore, a wax can be added for the purpose of obtaining better slipperiness. Specific examples of the wax preferably used include carnauba wax, candelilla wax, rice wax, wood wax, jojoba oil, palm wax, rosin-modified wax, olicuric wax, sugar cane wax, esparto wax, and bark wax. Animal waxes such as plant wax, beeswax, lanolin, whale wax, ibota wax, shellac wax, mineral waxes such as montan wax, ozokerite, ceresin wax, petroleum waxes such as paraffin wax, microcrystalline wax, petrolactam, and fisher Examples include synthetic hydrocarbon waxes such as tropush wax, polyethylene wax, oxidized polyethylene wax, polypropylene wax and oxidized polypropylene wax. That. Of these, carnauba wax, paraffin wax, and polyethylene wax are preferred because they are easy to adhere to hard coats and pressure-sensitive adhesives and have good lubricity. In view of ease of handling of the coating liquid and environmental problems, the coating liquid is preferably aqueous, so that an aqueous dispersion is preferably used.

  In addition to the above components, an antistatic agent, a colorant, a surfactant, an ultraviolet absorber and the like may be used for the easy-adhesion layer of the present invention.

  The surface protective film of the present invention only needs to have at least one outermost layer formed of the above-mentioned easy-adhesion layer. For example, the ultraviolet protective layer and the water vapor shielding layer are formed on one side of the base film. The easy adhesion layer may be formed on the other surface, or the easy adhesion layer may be formed on the upper surface on which the ultraviolet ray absorbing layer and the water vapor shielding layer are formed. Of course, you may form the outermost layer of both surfaces with this easily bonding layer.

  Among these, it is particularly preferable to provide an easy-adhesion layer on both sides of the polyester film, then provide a layer having water vapor shielding properties on one side, and further provide an ultraviolet absorbing layer on the layer if necessary.

  When forming the said easily bonding layer on both surfaces of a polyester film, this film may be an unstretched film, and what was uniaxially stretched or biaxially stretched may be sufficient as it. In particular, the method of applying a coating solution to an unstretched film and then simultaneously biaxially stretching, or applying a coating solution to a uniaxial vertical stretched film and then stretching it horizontally and then heat-treating the adhesive layer and the film are bonded. This is preferable because of improved properties. The coating liquid is preferably an aqueous coating liquid (aqueous dispersion or emulsion) from the viewpoint of handleability and working environment, and its solid content concentration is in the range of 2 to 30% by weight, particularly 5 to 10% by weight. Is appropriate.

  Further, as a pretreatment for improving the coating property of the aqueous coating liquid, the film surface is subjected to physical treatment such as corona surface treatment, flame treatment, plasma treatment, or chemically inactive with the above components in the coating liquid. It is preferable to use a surfactant in combination.

  Examples of the surfactant preferably used include polyoxyethylene alkylphenyl ether, polyoxyethylene-fatty acid ester, sorbitan fatty acid ester, glycerin fatty acid ester, fatty acid metal soap, alkyl sulfate, alkyl sulfonate, alkyl sulfosuccinate, and the like. And anionic and nonionic surfactants. It is preferable that 1 to 10 weight% of surfactant is contained on the basis of the component which forms a coating film. If it is this range, the surface tension of a coating liquid can be 40 mN / m or less, and it will become possible to apply | coat uniformly.

  When the aqueous liquid is applied to a polyester film, when it is carried out in a normal coating process, that is, a process in which the polyester film that has been biaxially stretched and heat-fixed is separated from the manufacturing process of the film, dust, dust, etc. are involved. Since it is easy, application in a cleaner atmosphere, that is, application in a film manufacturing process is preferable.

As the coating method, any known coating method can be applied. For example, a roll coating method, a gravure coating method, a roll brush method, a spray coating method, an air knife coating method, an impregnation method, and a curtain coating method can be used alone or in combination. The coating amount is suitably 0.5 to 20 g / m ² , particularly 1 to 10 g / m ² . In addition, you may form this easily bonding layer only in the single side | surface of a film as needed as above-mentioned.

  After drying, the polyester film coated with the coating liquid is led to a stretching heat treatment step as necessary, but such treatment can be performed under conditions accumulated in the industry. As preferable conditions, for example, the drying conditions are 90 to 130 ° C. × 2 to 10 seconds, the stretching temperature is 90 to 150 ° C., the stretching ratio is 3 to 5 times in the machine direction, and 3 to 5 times in the transverse direction. It is 1 to 3 times in the vertical direction, and 180 to 250 ° C. × 2 to 60 seconds when heat-fixed.

  The thickness of the biaxially oriented polyester film after such treatment is preferably 50 to 250 μm, and the thickness of the easy adhesion layer is preferably 0.01 to 1 μm.

[Production of surface protective film]
The surface protective film of the present invention is preferably at least one side of a polyester film provided with an easy-adhesion layer as described above (preferably one side (the opposite side when the easy-adhesion layer is provided only on one side)) In addition, the ultraviolet ray absorbing layer and the water vapor shielding layer are formed by a conventionally known method, or a water vapor shielding layer is applied to at least one surface of the polyester film containing the ultraviolet absorber. Can be manufactured. In addition, what is necessary is just to form an easily bonding layer in at least one surface again, when the outermost layer of the laminated | multilayer film obtained becomes a thing different from the said easily bonding layer.

  The surface protective film of the present invention having such a structure desirably has a total light transmittance of 60% or more, preferably 70% or more, particularly preferably 80% or more. When the transmittance is less than 60%, the solar energy does not sufficiently reach the surface of the silicone solar cell, and the conversion efficiency to electric energy is reduced.

[Solar cell laminate]
The solar cell laminate having a structure in which a silicon solar cell is sandwiched via an EVA resin in the surface protective film of the present invention described above has superior durability compared to the conventional one.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. In addition, each evaluation in an Example followed the following method.

(1) Water vapor permeability Measured according to JIS K7129.

(2) Ultraviolet shielding properties At wavelengths in the ultraviolet region, transmittance was measured using a Shimadzu UV-3101PC type, and the ultraviolet transmittance at a wavelength of 380 nm was defined as shielding properties.
T _{380 nm} is less than 20.0%: ○
20.0% or more and less than 40.0: △
40.0% or more: ×

(3) Adhesiveness with EVA Two surface protection films cut to 20 mm width x 100 mm length, EVA sheet (High Sheet Industry Co., Ltd. SOLAR EVA SC4) cut to 20 mm width x 50 mm length Prepare one each. Heat sealer (TPA manufactured by Tester Sangyo Co., Ltd.) is placed in the order of film / EVA sheet / film so that the EVA sheet is located at the approximate center of the film, and the surface to be evaluated for easy adhesion of the film is on the EVA side. Press at -701-B). The pressure bonding conditions are 120 ° C. and 0.02 MPa for 5 minutes, then heated to 150 ° C., the press pressure is increased to 0.1 MPa, and the pressure is bonded for 25 minutes. The thermobonded sample was subjected to 23 ° C. and 50% RH atmosphere in accordance with JIS Z0237, with the unadhered film sandwiched between the upper and lower clips, and the adhesive strength was measured at a peel angle of 180 ° and a pulling speed of 100 mm / min. .
A: 20 N / 20 mm or more: Adhesiveness is very good B: 10 N / 20 mm or more, less than 20 N / 20 mm ... Adhesiveness is good Δ: 5 N / 20 mm or more, less than 10 N / 20 mm ... Adhesiveness is slightly good × : Less than 5N / 20mm ... poor adhesion

(4) Weather resistance The sample prepared in the above (3) was used with a sunshine weather meter (Suga Test Instruments Co., Ltd., WEL-SUN-HCL type) for 1000 hours (exposed outdoors) according to JIS K6783b. (Equivalent to one year) After performing an outdoor exposure promotion test by irradiation, the adhesiveness was measured in the same manner as in (3) above, and the evaluation was made in comparison with the adhesiveness before the test.
◎: Adhesion retention rate 75% or more: very good weather resistance ○: Adhesion retention rate 50% or more, less than 75% ... Weather resistance good Δ: Adhesion retention rate 25% or more, less than 50% ..Slightly good weather resistance x: Adhesiveness retention rate of less than 25%: poor weather resistance

(5) Weight reduction Weight ratio (W) = Laminate weight when using surface protective film / Laminate weight when using glass ○: Less than 0.3 Δ: 0.3 or more and less than 0.6 ×: 0.6 or more

(6) Flexibility A force was applied to the sample sheet prepared in the procedure for creating the adhesion evaluation method with EVA, and the evaluation was performed with a curvature radius r at which cracking or peeling of the laminated portion occurred.
○: Less than 300 mm Δ: 300 mm or more and less than 500 mm x: 500 mm

[Example 1]
Preparation of surface protective film A Polyethylene terephthalate (inherent viscosity: 0.62) was melt-extruded on a rotating cooling drum maintained at 20 ° C. to obtain an unstretched film. Next, the film was stretched 3.3 times in the longitudinal direction at 100 ° C., and then the following easy-adhesion layer coating solution (8% concentration aqueous coating solution) was uniformly applied on both sides thereof with a roll coater.

Oxazoline composed of 30% by mole of methyl methacrylate / 2% by mole of 2-isopropenyl-2-oxazoline / 10% by mole of polyethylene oxide (n = 10) methacrylate / 30% by mole of acrylamide as a cross-linking agent Polymer having a group (Tg = 50 ° C.) As other resin components, acid component is 80 mol% terephthalic acid / isophthalic acid 15 mol% / 5-sodium sulfoisophthalic acid 5 mol%, glycol component is 60 mol of ethylene glycol % / Copolymerized polyester composed of 40 mol% of diethylene glycol (Tg = 43 ° C.), silica particles having an average particle diameter of 60 nm as filler, polyoxyethylene (n = 7) lauryl ether as wetting agent, Mixing ratio is set to crosslinking agent / other resin / filler / wetting agent = 15 layers The amount was 75% by weight / 4% by weight / 6% by weight.

  The coated film is dried at 95 ° C., then stretched 3.6 times in the transverse direction at 110 ° C., and then thermally fixed by shrinking 3% in the width direction at 220 ° C. Got. The thickness of the coating film was 0.05 μm.

  On one side of the obtained film, a paint having ultraviolet absorptivity (UV-G101 manufactured by Nippon Shokubai Co., Ltd .: acrylic resin having a benzotriazole skeleton) was applied by roll coating so that the coating thickness was 10 μm. Further, a silicon oxide film having a thickness of 100 nm was formed on the layer having ultraviolet absorptivity as a layer having water vapor shielding properties by a normal sputtering method to obtain a surface protective film. The evaluation results of the obtained film are shown in Table 1.

[Example 2]
Preparation of surface protective film B Unstretched by melt-extruding polyethylene terephthalate (inherent viscosity: 0.62) containing 1% by weight of an ultraviolet absorber represented by the following formula (Chemical Formula 3) on a rotating cooling drum maintained at 20 ° C. A film was obtained.

  Next, the film was stretched 3.3 times in the longitudinal direction at 100 ° C., and then the same aqueous coating liquid for easy-adhesion layer (concentration: 8% by weight) as used in Example 1 was uniformly applied to both sides with a roll coater. The polyester film was dried at 100 ° C., stretched 3.6 times in the transverse direction at 110 ° C., shrunk 3% in the width direction at 220 ° C., and heat-set to obtain a polyester film having a thickness of 100 μm. Note that the thickness of each easy-adhesion layer was 0.05 μm.

  Next, in the same manner as in Example 1, a water-blocking layer composed of a 100 nm thick silicon oxide film was formed by a normal sputtering method to obtain a surface protective film. The evaluation results of the obtained film are shown in Table 1.

[Example 3]
Preparation of surface protective film C Polyethylene-2,6-naphthalene dicarboxylate (intrinsic viscosity: 0.61) was melt-extruded on a rotating cooling drum maintained at 60 ° C. to obtain an unstretched film. Next, the film was stretched 3.1 times in the longitudinal direction at 120 ° C., and then the same aqueous coating liquid for an easy-adhesion layer as used in Example 1 was uniformly applied on both sides thereof with a roll coater.

  Next, after drying at 120 ° C., the film was stretched 3.2 times in the transverse direction at 145 ° C. and heat-set at 240 ° C. for 30 seconds to obtain a polyester film having a thickness of 100 μm. The thickness of the coating film was 0.05 μm.

  On one side of the obtained film, a paint having ultraviolet absorptivity (UV-G101 manufactured by Nippon Shokubai Co., Ltd .: acrylic resin having a benzotriazole skeleton) was applied by roll coating so that the coating thickness was 10 μm. The evaluation results of the obtained film are shown in Table 1.

[Example 4]
Preparation of surface protective film D Rotation of polyethylene-2,6-naphthalenedicarboxylate (inherent viscosity: 0.61) containing 1% by weight of the ultraviolet absorber represented by the formula (Formula 3) maintained at 60 ° C. It was melt-extruded on a cooling drum to obtain an unstretched film. Next, the film was stretched 3.1 times in the longitudinal direction at 120 ° C., and then the same aqueous coating liquid for an easy-adhesion layer as used in Example 1 was uniformly applied on both sides thereof with a roll coater.

  Next, after drying at 120 ° C., the film was stretched 3.2 times in the transverse direction at 145 ° C. and heat-set at 240 ° C. for 30 seconds to obtain a polyester film having a thickness of 100 μm. The thickness of the coating film was 0.05 μm. The evaluation results of the obtained film are shown in Table 1.

  As is clear from the results in Table 1, the surface protective film of the present invention is excellent in adhesiveness with EVA, and is excellent in ultraviolet shielding property and water vapor shielding property, so that the durability of the solar cell is improved. It can be seen that it is useful as a surface protective film.

[Example 5]
Using the surface protective film obtained in Examples 1 to 4, through an EVA sheet (SOLAR EVA SC4 manufactured by Hisheet Kogyo Co., Ltd.), a silicon solar cell element (generally used from a commercially available silicon solar cell module) ) Was sandwiched between the combinations shown in Table 2 to form a laminated body corresponding to a solar cell. As shown in Table 2, the obtained laminate corresponding to the solar cell is superior in lightness and flexibility as compared with those using a conventional glass surface protective material, has good handleability, and is durable. The property was also good.

  The surface protective film of the present invention described above is excellent in ultraviolet shielding property and water vapor shielding property, and also has good adhesion to EVA resin, so that the protective film for obtaining a solar cell laminate excellent in durability. As extremely useful.

Claims (7)

  A laminated film comprising a polyester film as a base film and having an ultraviolet absorbing layer and a water vapor shielding layer, wherein at least one outermost layer of the laminated film is made of an epoxy resin or an oxazoline group-containing polymer. A surface protective film for solar cells, which is an easy-adhesion layer containing at least one crosslinking agent.   The surface protective film for a solar cell according to claim 1, wherein the base film is made of a polyester film containing a cyclic imino ester-based ultraviolet absorber, and the base film is a layer having ultraviolet absorptivity.   The surface protection film for solar cells of Claim 1 or 2 by which the easily bonding layer containing the at least 1 sort (s) of crosslinking agent of an epoxy resin or an oxazoline group containing polymer is laminated | stacked on both surfaces of the polyester film.   The solar cell surface protective film according to claim 1 or 3, wherein the layer having ultraviolet absorptivity is a layer containing an acrylic resin having a benzophenone skeleton or a benzotriazole skeleton in a side chain. The surface protection film for solar cells according to any one of claims 1 to 4, wherein the water vapor permeation amount of the layer having water vapor shielding properties is 1.0 g / (m ² · 24 h) or less.   The surface protection film for solar cells according to any one of claims 1 to 5, wherein the layer having water vapor shielding properties is formed from a metal oxide, and the film thickness thereof is 50 nm or more and less than 500 nm.   The solar cell laminated body formed by pinching | interposing a silicon solar cell with the surface protection film in any one of Claims 1-6 through ethylene-vinyl acetate copolymer resin.