WO2012096215A1

WO2012096215A1 - Solar-cell back-side protective sheet

Info

Publication number: WO2012096215A1
Application number: PCT/JP2012/050100
Authority: WO
Inventors: 市村　茂樹; 武俊岩佐; 高橋　章; 榮一杉本
Original assignee: 日本発條株式会社
Priority date: 2011-01-14
Filing date: 2012-01-05
Publication date: 2012-07-19
Also published as: JP2012151150A; TW201235422A

Abstract

This solar-cell back-side protective sheet is characterized by comprising: a base film comprising at least one layer; a coating layer that is formed on one surface of the base film and comprises at least one layer; and a highly-adhesive film formed on the other surface of the base film. This solar-cell back-side protective sheet is further characterized in that the aforementioned coating layer is a ternary-copolymer layer obtained by curing a liquid film that has a resin component comprising: a metal alkoxide that has a reactive functional group (Y); an acrylic monomer that has a reactive functional group (X) that reacts with the aforementioned reactive functional group (Y); and an acrylic monomer that does not have said reactive functional group (X).

Description

Back protection sheet for solar cells

The present invention has an excellent weather resistance, an excellent water vapor barrier property, and a water vapor gas barrier even if there is some bending associated with assembly by hot press molding or vacuum / pressure air molding when manufacturing a solar cell panel. For solar cells having flexibility without impairing the properties, and having good adhesion to a sealing agent interposed between the back protective sheet and the light-receiving side transparent base material to seal the solar cells It is related with a back surface protection sheet.

Conventionally, several configurations have been proposed as back surface protection sheets constituting solar cell modules. As these sheets, as a device for imparting a gas barrier property such as water vapor and oxygen gas to the sheet, a sheet in which films having different characteristics are laminated with an adhesive and multilayered is mainly used.

For example, Patent Document 1 discloses a configuration using an aluminum foil in order to ensure gas barrier properties. Further, Patent Document 2 discloses a configuration in which a film with an oxide vapor deposition film added to the surface is bonded with an adhesive to ensure gas barrier properties. Furthermore, Patent Document 3 discloses a multilayer structure in which an oxide vapor deposition film and a coating layer made of a composite of a hydrolysis product of a metal alkoxide and a water-soluble polymer are combined.

In the sheet using the aluminum foil as disclosed in Patent Document 1 above, the aluminum foil is extremely excellent in gas barrier properties, but by the heat of a hot press at about 150 ° C. applied to the sheet when manufacturing a solar cell module. The resin film constituting the sheet is softened, and the protrusion of the solar cell element electrode part may penetrate the softened resin film layer. In that case, the electrode part is short-circuited to the aluminum foil, and the battery performance Adversely affect.

In the sheet using the inorganic oxide vapor deposition film as disclosed in Patent Document 2, the inorganic oxide vapor deposition film has a glassy film structure, so that the film is inferior in bending resistance, and the film has cracks due to mechanical stress. There is a problem that the gas barrier property of the sheet is remarkably deteriorated. In addition, in such a sheet, if a thin film is deposited in order to give a certain degree of flexibility, a defect occurs in the film, which causes a problem that the gas barrier property is lowered.

In the sheet disclosed in Patent Document 3, a coating layer made of a composite composed of a water-soluble polymer such as polyvinyl alcohol (PVA) and at least one metal alkoxide and / or a hydrolyzate thereof is used as an inorganic oxide vapor deposition film. By providing it on top, gas barrier properties are secured. However, in such a sheet, the polymer such as PVA does not have sufficient water vapor gas barrier properties and the main chain CC bond is easily broken by ultraviolet rays, so deterioration is unavoidable. Without the configuration, problems arise in the long-term reliability of the gas barrier property and weather resistance of the single unit. Further, in such a sheet, in order to form an oxide vapor deposition film on the surface of the base film, a large-scale vacuum system is required. Further, after the oxide vapor deposition film is formed, a water-soluble polymer and a metal alkoxide and / or Since a process of coating the composite composed of the hydrolyzate is required, the number of manufacturing processes increases. As a result, such a sheet has a problem that the manufacturing cost increases.

In any of the above sheets, in order to impart weather resistance, a resin film having weather resistance, such as a fluorine-based resin or an olefin-based resin, is bonded to one or both surfaces of the above-described gas barrier layer (base film). Etc. are pasted together. In any of these resin films, since the C—C bond that is the main chain of the resin component is easily cut by ultraviolet rays, the deterioration of the resin film is unavoidable, and the gas barrier property is also deteriorated along with the deterioration of the weather-resistant resin film by ultraviolet rays. To do. As the gas barrier property deteriorates, water vapor enters the back surface protection sheet from the outside, and the adhesive of the adhesive layer adhered to the base film is hydrolyzed and deteriorated. There is a problem that peeling of the weather resistant resin film occurs.

In order to seal the solar cell element, a sealant is provided between the light-receiving side transparent base material and the back surface protective sheet, but peeling is also likely to occur at the interface between the sealant layer and the back surface protective sheet. There is a case.

In a conventional solar cell module, a sheet molded from an EVA resin composition is used as a sealant sheet for sealing a solar cell element. There are various types of this EVA resin, and the fact is that the EVA resin used by the sealant manufacturer is different. And even if what is classified into the same EVA resin, depending on a kind, there exists a thing with low adhesiveness of the above-mentioned back surface protection sheet. In order to cope with this, the composition of the material used for the sealant bonding surface of the back surface protection sheet must be changed. Such a problem has been pointed out as one of the reasons why the manufacturing cost of the back surface protection sheet cannot be reduced.

In addition, when an EVA resin is basically used for a long period of time, it tends to be deteriorated and deteriorated such as yellowing, cracking and foaming. When the sealant is deteriorated or altered, corrosion of the solar cell element is induced accordingly. When the corrosion of the solar cell element starts, the power generation capacity of the solar cell module is rapidly reduced. Further, such deterioration and alteration phenomenon are likely to occur when the use environment conditions change in a more severe direction. Insufficient resistance to the environment of use is a cause of limited applications of conventional solar cells.

It is speculated that the reason why the EVA resin sheet deteriorates and changes with time is due to problems in the composition of the EVA resin composition as a material and the molecular structure of the resin component. That is, high hydrolyzable ester structure, cross-linking agents such as organic peroxides and polyfunctional vinyl compounds added for thermal cross-linking, cross-linking agent residues, reaction products, high-grade carbon and reaction end of EVA cross-linking point, etc. Has become an active point, and it is presumed that this active point gradually causes deterioration and alteration of the resin sheet.

In order to solve such problems, an adhesive sheet made of an ethylene-based resin having an excellent sealing performance equivalent to that of an EVA-based resin and less prone to deterioration and deterioration of the resin sheet is used as a sealing agent. Has been proposed (for example, Patent Document 4). This sealant sheet is interposed between the back surface protection sheet (back sheet) and the glass plate or transparent resin sheet that is the light receiving side transparent base material so as to sandwich the solar cell element. The laminated body obtained by interposing the sealant sheet is vacuum-pressure molded while being heated (hereinafter, sometimes referred to as heated vacuum-pressure molding), thereby sealing the solar cell element.

As described above, in order to impart weather resistance, the conventional back surface protection sheet uses a fluorine-based resin having weather resistance or weather-resistant PET (polyethylene terephthalate) on one or both surfaces of a base material. It is the structure which stuck together. Therefore, when the sealant made of the above-described polyethylene resin is used as the sealant, the polyethylene resin layer is in close contact with the fluororesin layer or the weather resistant PET layer that is the surface layer of the back protective sheet. . Since the polyethylene resin is less polar than the EVA resin, the adhesive property of the sealant layer made of the polyethylene resin to the fluorine resin layer or the weather resistant PET layer is the sealant layer made of the EVA resin. It becomes low compared with the adhesiveness to the fluororesin layer or weather-resistant PET layer. According to the study by the present inventors, the adhesive property of the sealant layer made of polyethylene resin to the fluorine resin layer or weather resistant PET layer is to maintain the sealing property of the solar cell module at a practical level. It was found that this was insufficient and peeling might occur over time.

Japanese Utility Model Publication 2-44995 JP 2002-134771 A JP 2006-253264 A Japanese Patent Laid-Open No. 2002-235048

The present invention has been made in view of the above problems of the prior art, and its purpose is to satisfy weather resistance, gas barrier properties and flexibility at the same time, and to be used in combination with a sealant made of any material. Is providing the back surface protection sheet for solar cells with the favorable adhesiveness to a sealing agent.

In order to solve the above-described problems, the present invention provides a back surface protection sheet for solar cells that employs the following configuration.

[1] A base film composed of at least one layer, a coat layer composed of at least one layer formed on one side of the base film, and an easy adhesion formed on the other side of the base film And having an adhesive film,
The coating layer includes a metal alkoxide having a reactive functional group (Y), an acrylic monomer having a reactive functional group (X) that reacts with the reactive functional group (Y), and a reactive functional group ( A solar cell back surface protective sheet, which is a ternary copolymer layer obtained by curing a liquid coating film having a resin component comprising an acrylic monomer having no X).
[2] The metal alkoxide has a general formula: YM (OR) _3- , YRM (OR) ₂ , YR ₂ M (OR) (wherein M is a metal, R is an alkyl group, and Y is reactive) The back surface protection sheet for solar cells according to the above [1], which is a compound represented by the formula:
[3] The solar cell back surface protective sheet according to [1], wherein the easy-adhesive film is a linear low-density polyethylene film.

The solar cell back surface protective sheet according to the present invention satisfies weather resistance, gas barrier properties, and flexibility at the same time, and even when used in combination with a sealant made of any material, has good adhesion to the sealant. It is a solar cell back surface protective sheet excellent in practicality.

FIG. 1 is a cross-sectional configuration diagram illustrating an example of a solar cell back surface protective sheet according to the present invention. FIG. 2 is a schematic diagram for explaining the characteristics of the ternary copolymer constituting the coat layer of the solar cell back surface protective sheet according to the present invention. FIG. 3 is a schematic diagram for explaining the characteristics of the polymer constituting the composite coat layer of the conventional back protective sheet for solar cells. FIG. 4 is a schematic diagram for explaining the self-healing characteristics of the ternary copolymer constituting the coat layer of the solar cell back surface protective sheet according to the present invention. FIG. 5 is a diagram showing an infrared total reflection absorption spectrum of a dry coating film of a commercially available emulsion main ingredient used as a liquid material used in the present invention.

The back surface protection sheet for solar cells according to the present invention includes a base film composed of at least one layer, a coat layer composed of at least one layer formed on one surface side of the base film, and the other of the base film. And an adhesive film formed on the surface side of the substrate, and the coat layer has a reactive property that reacts with the metal alkoxide having a reactive functional group (Y) and the reactive functional group (Y). A ternary copolymer layer obtained by curing a liquid film having a resin component comprising an acrylic monomer having a functional group (X) and an acrylic monomer having no reactive functional group (X) It is characterized by being.

The above-mentioned “metal alkoxide having a reactive functional group (Y), an acrylic monomer having a reactive functional group (X) that reacts with the reactive functional group (Y), and a reactive functional group (X)” "Liquid having a resin component composed of an acrylic monomer not having a water content" means an aqueous emulsion containing a resin component composed of only the above three monomers at a predetermined concentration (preferably a concentration of 50% by weight in the end). And a resin solution obtained by dissolving a resin component consisting of only the three monomers in a non-aqueous solvent.

The base film may have a single layer structure or a multilayer structure of two or more layers. The coating layer includes a metal alkoxide having a reactive functional group (Y), an acrylic monomer having a reactive functional group (X) that reacts with the reactive functional group (Y), and a reactive functional group (X ) Is a ternary copolymer layer obtained by polymerizing and curing a liquid coating film having a resin component composed of an acrylic monomer having no. The coating film may be formed in one layer or in multiple layers.

When making the said base film into a multilayer structure, it is preferable to interpose a silane adhesive layer between each base film.
Moreover, it is preferable that at least 1 layer of the said base film which consists of at least 1 layer shall be a film with an inorganic oxide vapor deposition film. That is, when a base film consists of 1 layer, it is preferable that the 1 layer film is a film with an inorganic oxide vapor deposition film. And when making a base film into a multilayer structure, it is preferable to make at least 1 layer of them into a film with an inorganic oxide vapor deposition film | membrane, In that case, silane-type adhesives are interposed between each layer, and each layer is put. Glue.

FIG. 1 is a cross-sectional structure showing an embodiment of the solar battery backsheet of the present invention. In FIG. 1, the base film 1 has a single-layer structure, a coat layer 2 is formed on one surface side of the base film, and an easy-adhesive film 3 is bonded to the other surface side of the base film 1. The case of the laminated structure formed through the agent layer 4 is shown. Hereinafter, each component will be described with reference to the drawings.

(Process for preparing a base film)
As the base film 1, a resin film that can be molded and processed within a range that does not melt and soften while being appropriately adjusted within a predetermined heating time because it is heated in a hot press when forming a solar cell module is used. it can. Examples of the material of the base film include at least one selected from polyester resins, polyolefin resins, polystyrene resins, polyamide resins, polycarbonate resins, and polyacrylonitrile resins. In other words, examples of the base film 1 include polyester films such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), polyolefin films such as polyethylene and polypropylene, polystyrene films, polyamide films, and polycarbonate. Engineering plastic films such as films, polyacrylonitrile films, and polyimide films are used.
The thickness of the base film 1 is in the range of 3 to 300 μm.

It is preferable that the surface of the film is oxidized by irradiation treatment or flame treatment using oxygen plasma or corona discharge. By oxidizing the surface, many functional groups are present on the surface. A film rich in surface functional groups tends to have better adhesion with a silane-based adhesive. Therefore, it is preferable to use a film that has been appropriately surface-treated as the base film 1.

Moreover, although the said base film 1 is the illustration in the case of 1 layer structure, the film used as this 1 layer structure base film 1 may vapor-deposit the inorganic oxide on the surface. In the present invention, when the base film has a multilayer structure, at least one of them is a film with an inorganic oxide vapor deposition film, and the number of layers of the film with a vapor deposition film is determined according to the required degree of gas barrier properties. Can be incorporated. Moreover, when bonding a film with a vapor deposition film, it is preferable to bond a vapor deposition surface to the PET surface which does not have a vapor deposition film.

As the inorganic oxide for vapor deposition, silicon oxide, aluminum oxide, zinc oxide, or the like can be used, and the vapor deposition thickness is preferably 1 nm to 100 nm.

As adhesives used to bond films together, urethane, acrylic, epoxy, and silicon adhesives have been used in the past. Deterioration was a problem. On the other hand, in the present invention, a silane-based adhesive having excellent adhesive performance even at high temperature and high humidity is used for bonding the films constituting the base film 1 having a multilayer structure.

The silane-based adhesive here is an alkoxysilane which is a kind of metal alkoxide-based compound contained in a conventional silane coupling agent or a resin component (ternary monomer) used for forming a coating layer in the present invention. A mixture containing can be used.

In the silane-based adhesive, the alkoxy group of alkoxysilane is hydrolyzed to produce a silanol group (Si—OH), and this silanol group is oxidized by oxygen plasma or corona discharge on the film surface. Since it reacts and binds, the adhesiveness between films is good. Further, since hydrolysis does not occur even under high temperature and high humidity, it has excellent weather resistance because of good adhesive properties and a strong silanol bond against UV energy.

When the base film 1 is composed of two or more layers bonded with a silane-based adhesive, the combination structure includes the same types of films, different types of films, In addition, a combination of the same films with an inorganic oxide deposited on one side or a combination of different films with an inorganic oxide deposited on one side may be used.

(Process for preparing liquid material)
A coating layer 2 is formed on one surface side of the base film 1 in a thickness range of 5 to 300 μm. The coating layer 2 is a resin component comprising a metal alkoxide having a reactive functional group (Y), an acrylic monomer having a reactive functional group (X), and an acrylic monomer having no reactive functional group (X). It is the ternary copolymer layer which hardened the coating film of the liquid body which has this. The liquid here means a metal alkoxide having a reactive functional group (Y), an acrylic monomer having a reactive functional group (X) that reacts with the reactive functional group (Y), and a reactive monomer. It is an aqueous emulsion containing a resin component consisting of only three types of monomers with an acrylic monomer having no functional group (X) at a predetermined concentration (preferably a final concentration of 50% by weight), or the above three types The resin solution which melt | dissolved the resin component which consists only of said monomer in the non-aqueous solvent.

The metal alkoxide having a reactive functional group (Y) is a general formula: YM (OR) ₃ , YRM (OR) ₂ , YR ₂ M (OR) (wherein M is a metal, R is an alkyl group, Y Represents a functional group having reactivity).

Examples of the metal alkoxide having such a reactive functional group (Y) include α, β-ethylenically unsaturated monomers containing silane, such as vinyltrimethoxyxysilane, vinyltriisopropoxysilane, allyltrimethoxysilane, diallyl. Dimethylsilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-mercaptopropyltriethoxysilane, 3-octainoylthio-1-propyltriethoxy Silane, 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, N- (2-aminoethyl) -3-aminopropylmethyldimethoxysilane, N- (2-aminoethyl) -3-aminopropyltrimethoxy Mention one or a mixture selected from α, β-ethylenically unsaturated monomers such as lan, 3-ureidopropyltriethoxysilane, 3-isocyanatopropyltriethoxysilane, 3-isocyanatepropyltrimethoxysilane Can do.

In addition to the metal alkoxide having the reactive functional group (Y), tetraalkoxysilane, trialkoxyaluminum, tetraalkoxytitanium and the like may be added.

In addition, when the reactive functional group (Y) of the metal alkoxide has an isocyanate group, it is reactive for the purpose of suppressing the direct reaction with water and effectively promoting the reaction with the reactive functional group (X). A capping agent (also called a blocking agent or a protective agent) is used for the functional group (Y). Any suitable aliphatic, alicyclic, or aromatic alkyl monoalcohol or phenolic compound can be used as the capping agent.

Examples of the aliphatic, alicyclic, or aromatic alkyl monoalcohol include lower aliphatic groups such as methanol, ethanol, and n-butanol, 2-methyl-2-propanol, and 2-methyl-1-propanol. Mention may be made of alcohols; alicyclic alcohols such as cyclohexanol; aromatic-alkyl alcohols such as phenyl carbinol and methyl phenyl carbinol.

The phenolic compound includes phenolic compounds such as phenol itself and substituted phenols such as cresol and nitrophenol (the substituent does not affect the coating operation).

In addition, glycol ether can also be used as the capping material. Suitable glycol ethers include ethylene glycol butyl ether, diethylene glycol butyl ether, ethylene glycol methyl ether and propylene glycol methyl ether. Of the glycol ethers, diethylene glycol butyl ether is preferred.

Furthermore, other capping agents include oximes such as methyl ethyl ketoxime, acetone oxime and cyclohexanone oxime, lactams such as ε-caprolactam, and amines such as dibutylamine.

When using an appropriate capping, it is possible to select and use one suitable for drying the coating and reaction temperature.

In the reaction, the capping agent modified with an isocyanate group is coated in the emulsion and then volatilized (azeotropically) with moisture by heat drying or decomposed by heating, whereby a reactive functional group (isocyanate) The polymerization starts. The desorption reaction of the capping agent is caused by heating to 80 ° C. or higher. However, when the temperature exceeds 120 ° C., the polymerization of the monomer proceeds rapidly. Therefore, the heating for desorption of the capping agent is performed at 80 ° C. It is preferable to carry out at a temperature in the range of ˜120 ° C. This capping agent desorption reaction is usually realized simultaneously in the coating film drying step.

In addition, the reactive functional group (X) has a property of reacting with and binding to the reactive functional group (Y) of the metal alkoxide such as an ester group, an epoxy group, a ketone group, an amino group, and a hydroxyl group. It is a functional group having.

Examples of the acrylic monomer having such a reactive functional group (X) include α, β-ethylenically unsaturated monomers such as hydroxyethyl acrylate, hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate. , Hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, methacryl alcohol, 4-hydroxybutyl acrylate glycidyl (epoxy) ether, hydroxyethyl acrylate or hydroxyethyl methacrylate and ε-caprolactone And α, β-ethylenically unsaturated monomers having a hydroxyl group such as the above-mentioned compounds.

Further, “having no reactive functional group (X)” means having no functional group that reacts with the metal alkoxide having the reactive functional group (Y).
Examples of the acrylic monomer having no reactive functional group (X) include α, β-ethylenically unsaturated monomers such as acrylic acid esters or methacrylic acid esters [for example, methyl acrylate, methyl methacrylate, ethyl acrylate. , Ethyl methacrylate, n-propyl acrylate, n-propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, n-butyl acrylate, n-butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, t-butyl acrylate T-butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, phenyl acrylate, isobornyl acrylate, isobornyl methacrylate, cyclohexyl methacrylate, t-butyl acrylate Chloroyl, tert-butylcyclohexyl methacrylate, dicyclopentadienyl (meth) acrylate, dihydrodicyclopentadienyl acrylate, dihydrodicyclopentadienyl methacrylate, and the like.

A ternary copolymer layer obtained by polymerizing and curing a liquid coating film having the above three types of monomers as resin components may be obtained by simultaneously polymerizing the three types of monomers. "Acrylic monomer having reactive functional group (X)" and "acrylic monomer having no reactive functional group (X)", "acrylic monomer having reactive functional group (X)" and "reactive functional group (Y ) "Metal alkoxide", "reactive functional group (Y) -containing metal alkoxide)" and "reactive functional group (X) -free acrylic monomer" in combination with two types of monomers in advance. Alternatively, the polymerization may be partially advanced and semi-polymerized, and then the remaining monomer components may be mixed and polymerized. Among these polymerization processes, two types of monomers, “acrylic monomer having reactive functional group (X)” and “acrylic monomer not having reactive functional group (X)”, are mixed or partially polymerized. It is preferable to employ a process in which the remaining “metal alkoxide having a reactive functional group (Y)” is mixed and polymerized after semi-polymerization.

In addition, the ternary copolymer is finally obtained by coating on a base film as a ternary copolymer layer. The timing of mixing, coating and polymerization of each monomer is mixed → polymerization. (Semi-polymerization) → Coating (after additional mixing if there are remaining monomers) → Polymerization (drying), or Mixing → Coating → Polymerization (drying).

(Method for preparing emulsion with aqueous solvent)
As the aqueous solvent, ion exchange water or the like is used. If necessary, a conventional dispersant may be added to an aqueous medium containing an organic solvent such as alcohol to improve the dispersibility. Then, using a conventional homogenizer (for example, trade name “NR-300”, manufactured by Microtech Nichion Co., Ltd.) with respect to the aqueous solvent, the mixture is uniformly dispersed, and three kinds of the above combinations are combined under heating and stirring. Or it can superpose | polymerize by dripping a monomer and a polymerization initiator beforehand by 2 types of combinations. The concentration of the resin component is preferably 30 to 60% by weight.

By the above method, the dispersion of the resin component constituting the emulsion from the desired particle size is reduced, and resin component particles having a preferable particle size range can be obtained.

Examples of the polymerization initiator include azo oily compounds [for example, azobisisobutyronitrile, 2,2′-azobis (2-methylbutyronitrile), 2,2′-azobis (2- (2-imidazoline) -2-yl) propane) and 2,2′-azobis (2,4-dimethylvaleronitrile), etc.]; aqueous compounds [eg anionic 4,4′-azobis (4-cyanovaleric acid), 2, 2-azobis (N- (2-carboxyethyl) -2-methylpropionamidine) and

cationic

2,2′-azobis (2-methylpropionamidine)]; redox oily peroxides (eg, benzoyl peroxide) Oxides, parachlorobenzoyl peroxide, lauroyl peroxide and t-butyl perbenzoate); and aqueous peroxides (eg If, like potassium persulfate and ammonium persulfate) and the like.

In addition to the above dispersants, those commonly used by those skilled in the art and emulsifiers such as Antox MS-60 (trade name: manufactured by Nippon Emulsifier Co., Ltd.), Eleminol JS-2 (trade name: Sanyo) Kasei Kogyo Co., Ltd.), ADEKA rear soap NE-20 (trade name: manufactured by Asahi Denka Co., Ltd.) and Aqualon HS-10 (trade name: manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) may be used in combination.

The blending ratio of the conventional dispersant and the resin component composed of the three types of monomers may be adjusted to a conventional ratio when preparing an emulsion. For example, the solid content may be adjusted to a range of 5/95 to 20/80. When the ratio is less than 5/95, the dispersed particles aggregate to form a lump and the smoothness of the coating film tends to be impaired. When the ratio exceeds 20/80, the film thickness tends to be difficult to control.

In order to adjust the molecular weight, a mercaptan such as lauryl mercaptan and a chain transfer agent such as α-methylstyrene dimer may be used as necessary.

The polymerization reaction temperature of the mixed monomer is determined by the initiator. For example, it is preferably 60 to 90 ° C. when an azo initiator is used, and preferably 30 to 70 ° C. when a redox initiator is used. When the initiator is used, the blending amount is generally 0.1 to 5% by mass, preferably 0.2 to 2% by mass, based on the total amount of the emulsion.

As described above, the monomer polymerization process includes two types of monomers, “an acrylic monomer having a reactive functional group (X)” and “an acrylic monomer having no reactive functional group (X)”. It is preferable to employ a process in which mixing or polymerization is partially advanced and semi-polymerization is performed, and then the remaining “metal alkoxide having a reactive functional group (Y)” is mixed and polymerized.

The polymerization in the case of reacting two kinds of monomers in advance is performed in 1 to 8 hours.

Obtained by partially polymerizing (semi-polymerizing) two types of monomers, “acrylic monomer having reactive functional group (X)” and “acrylic monomer not having reactive functional group (X)”. The average particle diameter of the obtained two-component semipolymer resin particles is preferably in the range of 0.05 to 0.30 μm. If the particle diameter is less than 0.05 μm, the effect of improving workability is small, and if it exceeds 0.30 μm, the appearance of the resulting coating film may be deteriorated. The particle diameter can be adjusted, for example, by adjusting the composition of the two monomer mixtures and the emulsion polymerization conditions.

The mass average molecular weight of the two-component semipolymer resin particles is preferably 6000 to 12000. If it is less than 6000, the control of the film thickness tends to be difficult, and if it exceeds 12,000, the smoothness of the coating film tends to decrease.

In the emulsion having the above composition, the resin solid content is preferably 3 to 20% by mass. When the resin solid content is less than 3% by mass, control of the film thickness tends to be difficult, and when it exceeds 20% by mass, the smoothness of the coating film tends to decrease.

(Method for preparing resin solution using non-aqueous solvent)
As the non-aqueous solvent, an organic solvent such as toluene or ethyl acetate is used. As the non-aqueous solvent, xylene, N-methylpyrrolidone, butyl acetate, aliphatic and / or aromatics having a relatively high boiling point, butyl diglycol acetate, acetone, and the like can be used as appropriate.

Further, as the polymerization initiator, an initiator (azo-based or peroxide-based) that generates radicals by heat is used.

In the non-aqueous solvent, the above-described three kinds or two kinds of combinations of monomers and a polymerization initiator are dissolved to obtain a resin solution for polymerization or partial polymerization (semi-polymerization). The concentration of the resin component in the resin solution is preferably 30 to 60% by weight, more preferably 50% by weight.

The liquid material may be mixed with a resin component and a solvent and, if necessary, an ultraviolet scattering agent and / or an ultraviolet absorber. Examples of the ultraviolet scattering agent include fine powders such as zinc oxide and titanium oxide. Examples of the ultraviolet absorber include a dye having an ultraviolet absorbing ability and an acrylic polymer into which a high concentration benzotriazole group is introduced. By adding a small amount of such an ultraviolet scattering agent and / or an ultraviolet absorber, the weather resistance of the coating layer can be further improved. When the coating layer has a multilayer structure, it is preferable to mix the ultraviolet scattering agent and / or ultraviolet absorber in at least one layer, and the ultraviolet scattering agent and / or ultraviolet absorber is mixed in two or more layers or all layers. May be mixed.

As the liquid material, products having an emulsion composition are commercially available, and it is also possible to use them. Examples of commercially available products include “Cirrus (trade name)” manufactured by Toagosei Co., Ltd. and “Sherastar MK (trade name)” manufactured by Nippon Paint Co., Ltd.

(Process of forming a liquid coating film)
A coating film of the liquid is formed on one side of the base film 1 so that the film thickness after drying is 6 to 350 μm. As a coating method of the liquid material, conventionally known means such as a dipping method, a roll coating method, a screen printing method, a spray method and the like that are generally used can be used. In order to uniformly control the thickness, a plurality of thin coating layers may be laminated to have a predetermined film thickness. In the case of multiple layers, it is repeated that after the previously applied layer is dried, the next layer is applied, the layer is dried, and then the next layer is applied.

(Step of forming a coat layer comprising a terpolymer layer)
This process includes a coating film drying process for drying the coating film, and a dry coating film curing process for finally forming a cured film (ternary copolymer layer) composed of the ternary copolymer after drying. ,included.

(Coating film drying process)
In this coating film drying step, the solvent is vaporized from the liquid coating film to stabilize the shape of the coating film. The drying temperature is preferably 80 ° C to 120 ° C. If it is less than 80 degreeC, vaporization of a solvent will become inadequate, and if it exceeds 100 degreeC, the polymerization reaction of the unreacted monomer in a coating film will be started. Although the drying time depends on the drying temperature, it is preferably 10 to 15 minutes at 100 ° C., for example.

(Dry paint film curing process)
The coating film whose shape has been stabilized by drying is cured by polymerizing the unreacted monomer in the coating film. The polymerization temperature of the unreacted monomer is preferably 80 ° C to 120 ° C. When the temperature is lower than 80 ° C., the polymerization becomes insufficient, and when the temperature exceeds 120 ° C., when the film is formed on the PET, the PET starts to shrink, and the coating film also adversely affects the adhesion and the like. Although the polymerization time depends on the polymerization temperature, it is preferably 10 to 15 minutes at 100 ° C., for example.

(Characteristics of ternary copolymer layer and characteristics of sheet having ternary copolymer layer as coating layer)
Since the coating layer 2 composed of the terpolymer layer has gas barrier properties and weather resistance while maintaining flexibility, the obtained sheet is excellent in long-term reliability as a back surface protection sheet for solar cells. It becomes.

Conventionally, polyvinyl alcohol (PVA) is used in Patent Document 3 as a water-soluble polymer material. PVA has a water vapor permeability of 1100 g / m ² · 24 hr (measurement conditions: 25 ° C., 90% RH, thickness of 25 μm), and has a poor water vapor barrier property but excellent flexibility. In the conventional back surface protection sheet for solar cells, cracks when bent only with an inorganic oxide vapor deposition film as a gas barrier layer cannot be prevented. Therefore, by laminating a flexible polymer film such as PVA, Gas barrier properties are secured while maintaining flexibility. Therefore, the gas barrier property was insufficient without an inorganic oxide vapor deposition film. That is, the number of stacked layers is increased, making it difficult to control the total thickness of the sheets.

In the present invention, an acrylic resin is used as a monomer (monomer) that can be copolymerized with a metal alkoxide in the coat layer that ensures gas barrier properties. In general, polymethyl methacrylate (PMMA), which is an acrylic resin of the polymer, has a water vapor permeability of 41 g / m ² · 24 hr (measurement conditions: 25 ° C., 90% RH, thickness 25 μm), and has a gas barrier higher than that of PVA. It is known that the property is excellent.

The measured values of water vapor permeability of the above polyvinyl alcohol and polymethyl methacrylate were ““ Animal testing methods and evaluation results for plastic materials <5> ”, Takeo Yasuda, p.119, vol.51, No. .6, Plastics ”.

In the present invention, the monomer material of the ternary copolymer layer constituting the coat layer includes an acrylic monomer having a reactive functional group (X), an acrylic monomer having no reactive functional group (X), and It consists of three types of monomers of a metal alkoxide having a reactive functional group (Y) that reacts with the reactive functional group (X). And the liquid body which has these three types of monomers as a resin component is formed, and let the ternary copolymer layer which formed this liquid body into a film into a coating layer.

In the ternary copolymer layer constituting such a coat layer, as shown in FIG. 2, two kinds of acrylic monomers are combined in a chain by radical polymerization reaction, and the formed acrylic polymer chains are more flexible. Sex is maintained. In the chain acrylic polymer, a plurality of functional groups (X) derived from an acrylic monomer having one reactive functional group (X) are scattered at intervals. (X) and the functional group (Y) in the metal alkoxide react and bond. In addition, an MO bond is formed by hydrolysis of metal alkoxides having a reactive functional group (Y), and the ternary copolymer acquires a network structure. With this network structure, flexibility and high water vapor gas barrier properties and weather resistance can be realized. Therefore, even if the sheet of the present invention is bent, cracks do not occur and the gas barrier property does not deteriorate significantly.

Further, the conventional product is used as a resin film having weather resistance by adhering a fluorine-based resin or the like on the gas barrier layer described above. As shown in the following (Table 1), the C—F bond energy is 116 kcal, which is very strong against the ultraviolet energy of 96 kcal, but the C—C bond energy of the main chain is 85 kcal and weak against ultraviolet rays. Therefore, deterioration of the resin due to ultraviolet rays occurs. Further, as shown in FIG. 3, the metal alkoxide and polymer complex of the gas barrier layer is a complex with a simple polymer that does not have a chemical bond with the hydrolysis product of the metal alkoxide. When the C—C bond that is the main chain of the polymer chain is broken (marked with x in FIG. 3), the polymer portion is deteriorated by ultraviolet rays, and the water vapor gas barrier property is remarkably deteriorated.

On the other hand, in the terpolymer layer used in the coating layer of the sheet according to the present invention, as shown in FIG. 4, the C—C bond (85 kcal) of the acrylic polymer portion is broken by ultraviolet rays. However, the MO bond (106 to 145 kcal) by the metal alkoxide is not broken. Even if the hydrolysis of the metal alkoxide progresses due to moisture in the air or in the polymer, and the C—C bond of the acrylic polymer is broken by the ultraviolet ray, self-healing can be performed by increasing the MO bond. There is almost no deterioration by.

Furthermore, since the ternary copolymer layer adheres to a resin such as PET with a chemical bond, the adhesiveness is very excellent, and between the base film and the ternary copolymer layer (coat layer). There is no worry of peeling. In addition, it is said that the metal alcoside is hydrolyzed by moisture to form a MO bond in a network, and the —CH ₂ —CHR— of the acrylic polymer is generally hardly hydrolyzed. Therefore, the conventional sheet with a structure in which a weather resistant film and a base film with gas barrier properties are bonded with an adhesive as in the past, that is, moisture enters from the outside due to deterioration of the resin film during long-term use. Thus, the problem that the adhesive deteriorates due to hydrolysis and the films peel off does not occur in the sheet of the present invention.

(Easily adhesive film)
On the surface of the base film 1 opposite to the surface on which the coat layer 2 is formed, an easy-adhesive film 3 is laminated via an adhesive layer 4. As the easily adhesive film 3, linear low density polyethylene (LLDE) is preferably used. Specific commercial products of linear low density polyethylene include “HC-E (trade name)” manufactured by Tosero Co., Ltd. and “SE620N (trade name)” manufactured by Tamapoli.
The thickness of the easily adhesive film 3 is preferably 10 μm to 80 μm.

From the above, the sheet according to the present invention is excellent in flexibility, super weather resistance, water vapor gas barrier property, and has good adhesion to the sealant even when used in combination with a sealant made of any material. It can provide as a back surface protection sheet for batteries.

In the following examples, regarding the acrylic resin component A, an acrylic monomer having a metal alkoxide having a reactive functional group (Y) and a reactive functional group (X) that reacts with the reactive functional group (Y). And glycidoxypropyltriethoxysilane (3-glycidoxypropyltriethoxysilane) as a metal alkoxide having a reactive functional group (Y) among the three types of monomers of the acrylic monomer having no reactive functional group (X). Common to Examples 1 and 2) was used. For acrylic monomers having reactive functional groups (X) that react with the remaining reactive functional groups (Y) and acrylic monomers having no reactive functional groups (X), these monomers A commercially available product (main ingredient of “Sherastar MK” from Nippon Paint Co., Ltd.) was used (common to Examples 1 and 2).

Regarding the point that the commercially available product is a mixture of the acrylic monomer having the reactive functional group (X) and the acrylic monomer not having the reactive functional group (X), dry coating of the product is performed. This can be confirmed by the infrared total reflection absorption spectrum of the film surface. This infrared total reflection absorption spectrum is shown in FIG.

As shown in FIG. 5, typical peaks appear at wave numbers 3650 to 3200 (cm ⁻¹ ), 1760 to 1715 (cm ⁻¹ ), and 1150 to 1025 (cm ⁻¹ ). Absorption derived from OH group of unit part including carboxylic acid (COOH group) and hydroxyl group (OH) of acrylic monomer having reactive functional group (X), acrylic system having no reactive functional group (X) Absorption derived from C = O of unit part containing monomer ester (COOR), CO of unit part containing ester (COOR) and ether (COC) of acrylic monomer having no reactive functional group (X) Absorption derived from -C.

In the following examples, a T.U.X L-LDPE film (brand: HC-E 50 μm thick) manufactured by Tosero Co., Ltd. was used as an easily adhesive film.

Example 1
In Example 1 of the present invention, as an acrylic resin component A, an aqueous emulsion A in which 3-glycidoxypropyltriethoxysilane (1 part by weight) is blended with 15 parts by weight of the main component of Shalaster MK: A liquid body was prepared by blending 35 parts by weight of an aqueous emulsion B obtained by blending the ethylene resin component “AQUATECH 909” (45 wt%) as the ethylene resin component B with respect to 100 parts by weight.

As shown in Table 2 below, a polyethylene terephthalate (PET) film (trade name “Ester Film 5000” manufactured by Toyobo Co., Ltd.) having a thickness of 188 μm was used as the base film.

The liquid was applied to one surface of the substrate film, and the coating film was heated at 80 ° C. for 10 minutes to evaporate the aqueous solvent and dried.
The obtained dried coating film is heated at 100 ° C. for 10 minutes to polymerize unreacted monomers constituting the coating film, and a copolymer layer (coat layer) comprising an acrylic copolymer and an ethylene copolymer Got. The thickness of the obtained film was 20 μm.

50 μm thick L-LDPE film (manufactured by Tosero Co., Ltd., product) as an easy-adhesive film via urethane adhesive (trade name “TMOFLEX AD-502” manufactured by Toyo Ink Co., Ltd.) on the other side of the above laminated sheet The name “HC-E”) was laminated.
As described above, a 20 μm thick coat layer (copolymer layer) is laminated on one surface of a 188 μm thick base film, and a 50 μm thick easy-adhesive film is laminated on the other surface ( A solar cell back surface protection sheet) was obtained.

(Example 2)
In Example 2 of the present invention, as shown below (Table 2), as a base film, a polyethylene terephthalate (PET) film having a thickness of 188 μm and a thickness of 12 μm on which several tens of nm of silicon oxide or aluminum oxide were deposited. A multilayer film in which a polyethylene terephthalate (PET) film (trade name “Ecosia VE500”, manufactured by Toyobo Co., Ltd.) is bonded with an alkoxysilane-based adhesive (3-methacryloxypropyltriethoxysilane) layer having a thickness of 5 μm. Was used. As the liquid material, the same liquid material as that used in Example 1 was prepared.

The liquid was applied to one surface of the substrate film, and the coating film was heated at 80 ° C. for 10 minutes to evaporate the aqueous solvent and dried.
The obtained dried coating film was heated at 100 ° C. for 10 minutes to polymerize unreacted monomers constituting the coating film, thereby obtaining a copolymer layer (coat layer). The thickness of the obtained film was 20 μm.
As described above, a sheet was obtained in which a coating layer (copolymer layer) having a thickness of 20 μm was laminated on one surface of a base film having a thickness of 92 μm.

50 μm thick L-LDPE film (manufactured by Tosero Co., Ltd., product) as an easy-adhesive film via a urethane adhesive (trade name “TMOFLEX AD-502” manufactured by Toyo Ink Co., Ltd.) on the other side of the above laminated sheet The name “HC-E”) was laminated.
As described above, a 20 μm thick coat layer (copolymer layer) is laminated on one surface of a 188 μm thick base film, and a 50 μm thick easy-adhesive film is laminated on the other surface ( A solar cell back surface protection sheet) was obtained.

(Comparative Example 1)
In this comparative example, as shown below (Table 2), a polyethylene terephthalate (PET) film having a thickness of 188 μm was used as the base film.

The liquid material was applied to both surfaces of the base film, and the coating film was heated at 80 ° C. for 10 minutes to evaporate the aqueous solvent and dried.
The obtained dried coating film was heated at 100 ° C. for 10 minutes to polymerize unreacted monomers constituting the coating film, thereby obtaining a copolymer layer (coat layer). The thickness of the obtained film was 20 μm.
As described above, a sheet (back surface protection sheet for solar cell module) in which a 20 μm thick coat layer (copolymer layer) was laminated on both surfaces of a 188 μm thick base film was obtained.

(Evaluation)
As performance evaluation of each back surface protection sheet for solar cell modules of Examples 1 and 2 and Comparative Example 1, the amount of water vapor permeation, the peel strength with respect to each of the polyethylene sealant and the EVA sealant were measured. The results are also shown in (Table 2).

The water vapor transmission amount was measured by the cup method under the conditions of a temperature of 40 ° C. and a humidity of 90% RH based on JIS Z0208.

Measurement of peel strength with polyethylene sealant and EVA sealant was performed as follows.
First, as the polyethylene sealant, low-density polyethylene ("Ultzex (trade name)": 1 mm thick sheet) manufactured by Mitsui Chemicals, Inc. is used. As the EVA sealant, "Solar" manufactured by Mitsui Tosero Co., Ltd. is used. Eva SC4 (trade name) "was used.
The back protection sheets for solar cells of Examples 1 and 2 and Comparative Example 1 are laminated on each of the above two types of sealant sheets, and pressed at 150 ° C. for 20 minutes at a pressure of 1 kg / cm for adhesion. did. The peel strength of each sample from the sealant sheet was measured using an Instron 55R4204 type tester manufactured by Instron, in accordance with JISC2151.

As can be seen from (Table 2), it can be seen that the back surface protection sheets of Examples 1 and 2 have high adhesion to both the polyethylene sealant and the EVA sealant.

From the above, according to the present invention, the solar cell is excellent in flexibility, super weather resistance, water vapor gas barrier property, and has good adhesion to the sealant even when used in combination with a sealant made of any material. The back surface protection sheet can be provided.

DESCRIPTION OF SYMBOLS 1 Base film 2 Coat layer 3 Adhesive film 4 Adhesive layer

Claims

A base film composed of at least one layer; a coat layer composed of at least one layer formed on one side of the base film; and an easily adhesive film formed on the other side of the base film; Having
The coating layer includes a metal alkoxide having a reactive functional group (Y), an acrylic monomer having a reactive functional group (X) that reacts with the reactive functional group (Y), and a reactive functional group ( A solar cell back surface protective sheet, which is a ternary copolymer layer obtained by curing a liquid coating film having a resin component comprising an acrylic monomer having no X).
The metal alkoxide has a general formula: YM (OR) 3- , YRM (OR) 2 , YR 2 M (OR) (wherein M is a metal, R is an alkyl group, and Y is a reactive functional group. The back surface protection sheet for solar cells of Claim 1 characterized by the above-mentioned.
The back protective sheet for solar cells according to claim 1, wherein the easily adhesive film is made of a linear low density polyethylene film.