JP2012006188A - Reflection sheet having coating of white hardenable resin composition for spray coating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflection sheet having a reflective film which has e.g. excellent resistances to weather, heat and light and whose sagging, orange peel and yellowing caused by a thermal history are controlled.SOLUTION: In the reflection sheet having a reflective film formed with a white hardenable resin composition for spray coating, the white hardenable resin composition for spray coating comprises (A) a carboxyl-containing photosensitive resin, (B) the powder of a silicon dioxide and/or a metal oxide prepared by pyrolysis, (C) a photopolymerization initiator, (D) a diluent, (E) an epoxy compound, (F) a titanium oxide and (G) a solvent.

Description

  The present invention relates to a reflective sheet having a reflective coating of a white curable resin composition composition for spray coating, and particularly to a reflective sheet that can be used as a back sheet of a solar cell module.

Carbon dioxide increases and global warming due to the generated during fossil energy sources combustion, NO _X, measures for environmental destruction such as air pollution due to the release of SO _X has become an urgent task. Therefore, in recent years, solar cells that can directly obtain electricity from sunlight have attracted attention as a new energy source having no environmental load. A solar cell is a combination of a plurality of photovoltaic elements, and has a structure in which several to several tens of photovoltaic elements are wired in series and in parallel. Moreover, since a solar cell is installed in a natural environment for a long period of time, it is used as a solar cell module packaged with a cover material in order to protect the photovoltaic element.

  Specifically, the solar cell module is composed of an upper transparent material made of glass, transparent plastic, and the like, and a sealing layer made of a thermoplastic resin such as an ethylene vinyl acetate copolymer, in order from the side on which the sunlight hits. A plurality of photovoltaic cells in which photovoltaic elements are wired in series and in parallel, a sealing layer (a layer similar to the sealing layer), and a solar battery backsheet are laminated.

  The back sheet of the solar cell is installed as a protective member on the back surface side, and generally, a material excellent in impact resistance is used. In addition, the back sheet is required to have a white color tone having high reflectivity in order to effectively use the incident light to the solar cell module and increase the power conversion efficiency. On the other hand, since the solar cell module is installed in the natural environment for a long time as described above, the solar cell backsheet has good adhesion to the sealing layer and has various properties such as weather resistance and moisture resistance. There is a demand for excellence. Therefore, a solar cell backsheet provided with an adhesive coating layer made of a polyacrylic acid resin colored with a white pigment mainly composed of titanium oxide on the innermost surface bonded to the sealing layer constituting the solar cell module. It has been proposed (Patent Document 1).

  However, in the above conventional solar cell backsheet, the solar cell module is exposed to a harsh natural environment, so that the light reflectivity gradually deteriorates due to the influence of solar radiation, solar heat, moisture, etc. over a long period of time. There was a problem of going.

  On the other hand, when using a photocurable resin composition as a white paint for a solar battery backsheet, discoloration may occur when the coating is heated and cured, resulting in a decrease in light reflectance. It was. Therefore, as a photo-curable resin composition for suppressing discoloration and reflectivity decrease due to ultraviolet rays or heat, it is obtained from (A) an alicyclic skeleton epoxy resin and has at least two ethylenically unsaturated bonds in one molecule. Contains an active energy ray curable resin, (B) a thiol compound, (C) a photopolymerization initiator, (D) a diluent, (E) a rutile titanium oxide, and (F) an epoxy thermosetting compound. A photosensitive resin composition is known (Patent Document 2).

  However, the photosensitive resin composition of Patent Document 2 still has a problem that the surface of the coating film changes to yellow and the reflectance decreases. Furthermore, in the photosensitive resin composition of Patent Document 2, a conventional coating method such as a screen printing method is used, but in order to further improve the production efficiency, the time for coating on a sheet or the like is shortened, The demand for labor saving is also increasing.

  Therefore, in recent years, spray coating has also been studied. However, spray coating has a problem that the amount of solvent used is increased and a large load is placed on the environment, and the cured coating film is dulled or damaged, resulting in a poor finished appearance.

JP 2010-109240 A JP2008-211036

  In view of the above circumstances, the present invention provides a reflective sheet having a reflective film that is excellent in various properties such as weather resistance, heat resistance, and light resistance, and that suppresses yellowing due to sagging, crushed skin, and thermal history. Objective.

  A first aspect of the present invention is a reflective sheet having a reflective coating formed of a white curable resin composition for spray coating, wherein the white curable resin composition for spray coating contains (A) a carboxyl group-containing Photosensitive resin, (B) silicon dioxide powder and / or metal oxide powder produced by pyrolysis, (C) photopolymerization initiator, (D) diluent, (E) epoxy compound, (F) titanium oxide And (G) a reflective sheet comprising a solvent.

  In the present invention, a cured product of the above-described white curable resin composition for spray coating is used for the reflective coating of the reflective sheet. And by adjusting the viscosity and thixotropy (thixo ratio) of the white curable resin composition, the reflectance is lowered by using (B) silicon dioxide powder and / or metal oxide powder produced by the thermal decomposition method. It is possible to obtain a reflection sheet that suppresses yellowing and prevents yellowing. Moreover, the viscosity characteristic suitable for spray coating can be obtained while reducing the environmental load by reducing the solvent content.

  In the second aspect of the present invention, the silicon dioxide powder and / or metal oxide powder produced by the thermal decomposition method (B) is 2 to 100 parts by weight of (A) the carboxyl group-containing photosensitive resin. It is a reflective sheet characterized by containing 20 mass parts. A third aspect of the present invention is the reflective sheet, wherein the solvent (G) contains propylene glycol monomethyl ether.

  The 4th aspect of this invention is a solar cell module provided with the above-mentioned reflection sheet.

  According to the first aspect of the present invention, (B) silicon dioxide powder and / or metal oxide powder produced by a thermal decomposition method is used for adjustment of viscosity and thixo ratio, so that after ultraviolet (UV) irradiation. Moreover, the fall of each reflectance after heating and after humidification heating and yellowing by a heat history are suppressed. Therefore, a reflective sheet having a reflective coating excellent in various properties such as weather resistance, heat resistance, light resistance and discoloration resistance can be obtained. Moreover, since generation | occurrence | production of sagging can be suppressed, the reflective sheet which has a reflective film excellent in the designability can be obtained. In forming the reflective film, the environmental load can be suppressed by reducing the content of the solvent (G). Furthermore, since the viscosity suitable for spray coating is obtained, the production efficiency of the reflective sheet is improved.

  According to the second aspect of the present invention, (B) the silicon dioxide powder and / or metal oxide powder produced by the pyrolysis method is 2 (A) per 100 parts by mass of the carboxyl group-containing photosensitive resin. Since the reflective coating is formed using a white curable resin composition having a viscosity and a thixo ratio more suitable for spray coating by containing ˜20 parts by mass, the design of the reflective sheet is further improved. According to the 3rd aspect of this invention, when the (G) solvent contains propylene glycol monomethyl ether, the sagging property of a reflective film is suppressed more and the design property of a reflective sheet improves further.

  According to the fourth aspect of the present invention, the solar cell module has a power generation efficiency over a long period of time because it includes a reflective sheet having a reflective coating excellent in various properties such as weather resistance, heat resistance, light resistance and discoloration resistance. Can be improved.

  Next, each component of the white curable resin composition for spray coating used for the reflective film of the reflective sheet of the present invention will be described. The white curable resin composition for spray coating used for the formation of the reflective film of the reflective sheet is composed of (A) a carboxyl group-containing photosensitive resin, (B) a silicon dioxide powder and / or a metal oxide powder produced by a thermal decomposition method. , (C) a photopolymerization initiator, (D) a diluent, (E) an epoxy compound, (F) titanium oxide, and (G) a solvent, wherein the above components are as follows.

(A) Carboxyl group-containing photosensitive resin No particular limitation as long as it is a photosensitive resin containing a carboxyl group, for example, a photosensitive carboxyl group-containing resin having one or more photosensitive unsaturated double bonds, photosensitive property And a carboxyl group-containing resin having no unsaturated double bond. As an example of the component (A), a radical polymerizable unsaturated monocarboxylic acid such as acrylic acid or methacrylic acid is reacted with at least a part of the epoxy group of the alicyclic epoxy resin having two or more epoxy groups in the molecule. Subsequently, a product obtained by reacting the produced hydroxyl group with a saturated or unsaturated polybasic acid or polybasic acid anhydride can be exemplified.

  The alicyclic epoxy resin is a resin having an alicyclic skeleton, and the skeleton is an epoxy resin formed by a chain of aliphatic cyclic compounds. Although there is no restriction | limiting in particular of an epoxy equivalent, Usually, 1000 or less, Preferably the thing of 100-500 is used.

  As the alicyclic skeleton epoxy resin, for example, “EHPE-3150” manufactured by Daicel Chemical Industries, Ltd. (1,2-epoxy-4- (2-oxiranyl) of 2,2-bis (hydroxymethyl) -1-butanol) Cyclohexene adduct).

  When these epoxy resins are reacted with radically polymerizable unsaturated monocarboxylic acid, the epoxy group is cleaved by the reaction of the epoxy group and the carboxyl group to form a hydroxyl group and an ester bond.

  The radically polymerizable unsaturated monocarboxylic acid to be used is not particularly limited, and examples thereof include acrylic acid, methacrylic acid, crotonic acid, and cinnamic acid. However, at least one of acrylic acid and methacrylic acid (hereinafter referred to as (meth) acrylic). It is sometimes referred to as an acid.), And acrylic acid is particularly preferable.

  Moreover, the reaction method of an epoxy resin and radically polymerizable unsaturated monocarboxylic acid is not specifically limited, For example, it can be made to react by heating an epoxy resin and acrylic acid in a suitable diluent. Examples of the diluent include ketones such as methyl ethyl ketone and cyclohexanone, aromatic hydrocarbons such as toluene and xylene, alcohols such as methanol, isopropanol and cyclohexanol, and alicyclic hydrocarbons such as cyclohexane and methylcyclohexane. Petroleum solvents such as petroleum ether and petroleum naphtha, cellosolves such as cellosolve and butylcellosolve, carbitols such as carbitol and butylcarbitol, ethyl acetate, butyl acetate, cellosolve acetate, butyl cellosolve acetate, carbitol acetate, butyl Examples include acetates such as carbitol acetate. Examples of the catalyst include amines such as triethylamine and tributylamine, and phosphorus compounds such as triphenylphosphine and triphenylphosphate.

  In the reaction between the epoxy resin and the radically polymerizable unsaturated monocarboxylic acid, 0.7 to 1.2 equivalents of the radically polymerizable unsaturated monocarboxylic acid are reacted per 1 equivalent of epoxy group of the epoxy resin. When at least one of acrylic acid or methacrylic acid is used, it is preferable to carry out a reaction of 0.8 to 1.0 equivalent per equivalent of epoxy group of the epoxy resin. The reaction between the epoxy resin and the radically polymerizable unsaturated monocarboxylic acid is preferably performed in a heated state, and the reaction temperature is particularly preferably 80 to 140 ° C. If the reaction temperature exceeds 140 ° C., the radically polymerizable unsaturated monocarboxylic acid may undergo thermal polymerization and may be difficult to synthesize. If the reaction temperature is less than 80 ° C., the reaction rate becomes slow and the production efficiency decreases. .

  In the reaction of the epoxy resin and the radically polymerizable unsaturated monocarboxylic acid in the diluent, the blending amount of the diluent is preferably 20 to 50% with respect to the total weight of the reaction system. The reaction product of the epoxy resin and the radically polymerizable unsaturated monocarboxylic acid can be subjected to the reaction with the following polybasic acids, if necessary, in the form of a diluent solution without isolation.

  The polybasic acid or polybasic acid anhydride reacts with a hydroxyl group generated by a reaction between an epoxy resin and a radically polymerizable unsaturated monocarboxylic acid to give the resin a free carboxyl group. The polybasic acid or its anhydride is not particularly limited, and either saturated or unsaturated can be used. Examples of the polybasic acid include succinic acid, maleic acid, adipic acid, citric acid, phthalic acid, tetrahydrophthalic acid, 3-methyltetrahydrophthalic acid, 4-methyltetrahydrophthalic acid, 3-ethyltetrahydrophthalic acid, 4- Ethyltetrahydrophthalic acid, hexahydrophthalic acid, 3-methylhexahydrophthalic acid, 4-methylhexahydrophthalic acid, 3-ethylhexahydrophthalic acid, 4-ethylhexahydrophthalic acid, methyltetrahydrophthalic acid, methylhexahydro Examples include phthalic acid, endomethylenetetrahydrophthalic acid, methylendomethylenetetrahydrophthalic acid, trimellitic acid, pyromellitic acid, and diglycolic acid. Examples of polybasic acid anhydrides include these anhydrides. These compounds may be used alone or in combination of two or more.

  The amount of the polybasic acid or polybasic acid anhydride to be reacted is 0.3 to 1.0 mol with respect to 1 mol of the hydroxyl group of the reaction product of the epoxy resin and the radically polymerizable unsaturated monocarboxylic acid. From the point that a highly sensitive resin film can be obtained at the time of exposure, it is preferably 0.4 to 1.0 mol, more preferably 0.6 to 1.0 mol. When the pattern is formed on the reflection sheet when the amount is less than 0.3 mol, a residue is generated after development. When the amount exceeds 1.0 mol, various properties (for example, weather resistance) of the finally obtained cured coating film are obtained. May decrease.

  The polybasic acid is preferably added to the unsaturated monocarboxylic oxide epoxy resin and subjected to a dehydration condensation reaction. The water produced during the reaction is preferably removed continuously from the reaction system, but the reaction is preferably carried out in a heated state. The reaction temperature is preferably 70 to 130 ° C. When the reaction temperature exceeds 130 ° C., those bonded to an epoxy resin and radically polymerizable unsaturated groups of unreacted monomers may easily cause thermal polymerization, making synthesis difficult. The speed is slow, which may be undesirable in actual manufacturing.

  The acid value of the polybasic acid-modified unsaturated monocarboxylic oxide epoxy resin, which is a reaction product of the polybasic acid or polybasic acid anhydride and the unsaturated monocarboxylic oxide epoxy resin, is preferably 60 to 300 mgKOH / g. The acid value of the reaction product can be adjusted by the amount of the polybasic acid to be reacted.

  In the present invention, the polybasic acid-modified unsaturated monocarboxylic oxide epoxy resin can also be used as a photosensitive resin, but one or more radical polymerizations are carried out on the carboxyl group of the polybasic acid-modified unsaturated monocarboxylic oxide epoxy resin. By reacting a glycidyl compound having a polymerizable unsaturated group and an epoxy group, a radical polymerizable unsaturated group may be further introduced to further improve the photosensitivity of the carboxyl group-containing photosensitive resin.

  In this carboxyl group-containing photosensitive resin with improved photosensitivity, the radically polymerizable unsaturated group is bonded to the side chain of the polymer skeleton of the precursor photosensitive resin by the reaction of the last glycidyl compound. High photopolymerization reactivity and excellent photosensitivity. Examples of the compound having one or more radically polymerizable unsaturated groups and an epoxy group include glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether, pentaerythritol triacrylate monoglycidyl ether, and the like. In addition, you may have multiple glycidyl groups in 1 molecule. These compounds may be used alone or in combination of two or more.

  The glycidyl compound is added to and reacted with the polybasic acid-modified unsaturated monocarboxylic oxide epoxy resin solution, but at a ratio of 0.05 to 0.5 mol with respect to 1 mol of the carboxyl group introduced into the resin. It is preferable to make it react and to make it react in the ratio of 0.1-0.5 mol. The reaction temperature is preferably 80 to 120 ° C. The photosensitive resin comprising the glycidyl compound-added polybasic acid-modified unsaturated monocarboxylic oxide epoxy resin obtained as described above preferably has an acid value of 45 to 250 mg KOH / g.

  Moreover, the lower limit of the weight average molecular weight of the carboxyl group-containing photosensitive resin as the component (A) is 3000, preferably 5000, from the viewpoint of the toughness of the cured product, that is, the reflective film, and the dryness to the touch. On the other hand, the upper limit of the weight average molecular weight is 200,000, preferably 50,000 from the viewpoint of compatibility with the diluent (D) as a component.

(B) The silicon dioxide powder produced by the thermal decomposition method and / or the silicon dioxide powder produced by the metal oxide powder thermal decomposition method includes, for example, fumed silica. By adding fumed silica, the white curable resin composition used for the formation of the reflective coating of the reflective sheet is imparted with thixotropy to suppress sagging of the reflective coating, while the yellowing due to the thermal history of the reflective coating, etc. Discoloration and reduction in reflectance can be suppressed. Although the fumed silica which can be used by this invention is not specifically limited, For example, what is obtained by hydrolyzing silicon chloride as a raw material at high temperature can be mentioned.

Although the characteristics of fumed silica such as specific surface area, primary particle diameter and surface treatment are not particularly limited, fumed silica having a specific surface area of 50 to ²⁰⁰ m ² / g is preferable from the viewpoint of leveling properties after coating. Examples of the fumed silica include AEROSIL (R) 90, AEROSIL (R) 130, AEROSIL (R) 150, AEROSIL (R) 200, AEROSIL (R) manufactured by Nippon Aerosil Co., Ltd. ) 300, AEROSIL (R) 380, AEROSIL (R) OX50, AEROSIL (R) EG50, AEROSIL (R) TT600, Leorosil QS-09, QS-10L, QS-10, QS-102, manufactured by Tokuyama Corporation CP-102, QS-20L, QS-20, QS-25C, QS-30, QS-30C, QS-40, etc. are mentioned. As the hydrophobic fumed silica, AEROSIL® R972, AEROSIL® R974, AEROSIL® R104, AEROSIL® R106, AEROSIL® R106, AEROSIL® R202, AEROSIL (R) manufactured by Nippon Aerosil Co., Ltd. ) R805, AEROSIL (R) R812, AEROSIL (R) R816, AEROSIL (R) R7200, AEROSIL (R) R8200, AEROSIL (R) R9200, AEROSIL (R) RY50, AEROSIL (R) NY50, AEROSIL (R) RY200 , AEROSIL (R) RY200S, AEROSIL (R) RX50, AEROSIL (R) NAX50, AEROSIL (R) RX200, AEROSIL (R) RX300, AEROSIL (R) R504, AEROSIL (R) DT4, Toroyama Co., Ltd. MT-10, MT-10C, DM-10, DM-10C, DM-20S, DM-30, DM-30S, KS-20S, KS-20SC, HM-20L, HM-30S, PM-20L, etc. It is done. These may be used alone or in combination of two or more.

  Examples of the metal oxide powder produced by the pyrolysis method include fumed metal oxide. By adding a fumed metal oxide, like the fumed silica, the white curable resin composition used for the formation of the reflective coating of the reflective sheet is imparted with thixotropy to prevent the reflective coating from sagging. Discoloration such as yellowing due to the thermal history of the film and a decrease in reflectance can be suppressed. Although the fumed silica which can be used by this invention is not specifically limited, For example, what is obtained by hydrolyzing a metal chloride as a raw material at high temperature can be mentioned.

The characteristics of the fumed metal oxide such as the specific surface area, the primary particle diameter, and the surface treatment are not particularly limited, but a fumed metal oxide having a specific surface area of 50 to ²⁰⁰ m ² / g is preferable in terms of leveling properties after coating. Examples of the fumed metal oxide include AEROXIDE® Alu, AEROXIDE® TiO ₂ , AEROXIDE® TiO ₂ P25S, VP AEROPERL® P25 / 20, VP Zirconium Oxide 3 manufactured by Nippon Aerosil Co., Ltd. -YSZ, VP Zirconium Oxide PH, AEROXIDE® TiO ₂ T805, AEROXIDE® AluC805 and the like. These compounds may be used alone or in combination of two or more. In particular, titanium oxide can improve white hiding power, and can be used as a white pigment.

  Further, two or more of the above fumed oxides may be mixed, but from the viewpoint of workability, silicon dioxide (for example, new silica) powder produced by pyrolysis and metal oxidation produced by pyrolysis A material (for example, fumed metal oxide) powder previously mixed may be used. Examples of the mixture of fumed silica and fumed metal oxide include AEROSIL (R) MOX80, AEROSIL (R) MOX170, and AEROSIL (R) COK84 manufactured by Nippon Aerosil Co., Ltd.

  The blending amount of the silicon dioxide powder and / or metal oxide powder produced by the pyrolysis method can be appropriately selected in consideration of the finished appearance of the reflective film, the reflectance, and the like. For example, with respect to 100 parts by mass of the carboxyl group-containing photosensitive resin, the lower limit is preferably 2 parts by mass from the viewpoint of increasing thixotropy and preventing sagging of the reflective coating, and particularly from the point of reliably preventing sagging. The amount is preferably 7 parts by mass. The upper limit is preferably 20 parts by mass from the viewpoint of maintaining the smoothness of the reflective film and preventing the skin from becoming ugly, and particularly preferably 17 parts by mass from the viewpoint of reliably maintaining the smoothness of the reflective film. It is.

(C) Photopolymerization initiator The photopolymerization initiator is not particularly limited as long as it is a commonly used photopolymerization initiator. Butyl ether, benzoin isobutyl ether, acetophenone, dimethylaminoacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2,2-diethoxy-2-phenylacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one 1-hydroxycyclohexyl phenyl ketone, 2-methyl-1- [4- (methylthio) phenyl] -2-morpholino-propan-1-one, 4- (2-hydroxyethoxy) phenyl-2- (hydroxy-2- Propyl) ketone Benzophenone, p-phenylbenzophenone, 4,4'-diethylaminobenzophenone, dichlorobenzophenone, 2-methylanthraquinone, 2-ethylanthraquinone, 2-tertiarybutylanthraquinone, 2-aminoanthraquinone, 2-methylthioxanthone, 2-ethylthioxanthone Examples include 2-chlorothioxanthone, 2,4-dimethylthioxanthone, 2,4 diethylthioxanthone, benzyl dimethyl ketal, acetophenone dimethyl ketal, and P-dimethylaminobenzoic acid ethyl ester. These photopolymerization initiators may be used alone or in combination of two or more. The compounding quantity of a photoinitiator is 1-30 mass parts with respect to 100 mass parts of carboxyl group-containing photosensitive resin, Preferably it is 5-20 mass parts.

(D) The diluent diluent is, for example, a photopolymerizable monomer that is a reactive diluent, and is used to obtain a reflective film having sufficient heat resistance and the like by sufficiently photocuring the carboxyl group-containing photosensitive resin. To do. Examples of the photopolymerizable monomer include 1,4-butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, Neopentyl glycol adipate di (meth) acrylate, hydroxypivalic acid neopentyl glycol di (meth) acrylate, dicyclopentanyl di (meth) acrylate, caprolactone modified dicyclopentenyl di (meth) acrylate, ethylene oxide modified di (meth) phosphate ) Acrylate, allylated cyclohexyl di (meth) acrylate, isocyanurate di (meth) acrylate, trimethylolpropane tri (meth) acrylate, dipentaerythritol tri (meth) acrylate Rate, propionic acid modified dipentaerythritol tri (meth) acrylate, pentaerythritol tri (meth) acrylate, propylene oxide modified trimethylolpropane tri (meth) acrylate, tris (acryloxyethyl) isocyanurate, propionic acid modified dipentaerythritol penta Examples include reactive diluents such as (meth) acrylate, dipentaerythritol hexa (meth) acrylate, and caprolactone-modified dipentaerythritol hexa (meth) acrylate. These may be used alone or in combination of two or more. The compounding quantity of the said diluent is 20-300 mass parts with respect to 100 mass parts of carboxyl group-containing photosensitive resin, Preferably it is 2.0-40 mass parts.

(E) Epoxy compound In the white photosensitive resin composition, the epoxy compound is added to increase the crosslink density of the reflective film, prevent discoloration due to the thermal history of the reflective film, and further suppress the decrease in reflectance. For example, an epoxy resin can be mentioned. Examples of the epoxy resin include bisphenol A type epoxy resin, novolak type epoxy resin (phenol novolak type epoxy resin, o-cresol novolak type epoxy resin, p-tert-butylphenol novolak type, etc.), bisphenol F and bisphenol S with epichlorohydrin. Bisphenol F-type and bisphenol S-type epoxy resins obtained by reaction, alicyclic epoxy resins having cyclohexene oxide groups, tricyclodecane oxide groups, cyclopentene oxide groups, and the like, tris (2,3-epoxypropyl) isocyanurate , Triglycidyl isocyanurate having a triazine ring such as triglycidyl tris (2-hydroxyethyl) isocyanurate, dicyclopentadiene type epoxy resin, Adama It can be exemplified Tan type epoxy resin. These compounds may be used alone or in combination of two or more.

  The compounding quantity of an epoxy compound is 1-75 mass parts with respect to 100 mass parts of carboxyl group-containing photosensitive resin from the point which obtains a sufficient coating film after hardening, and 20-60 mass parts is preferable.

(F) Titanium oxide Titanium oxide is blended to whiten the coating film, and examples include anatase-type titanium oxide and rutile-type titanium oxide having a rutile crystal structure. Among these, rutile type titanium oxide is preferable in terms of whiteness. Examples of rutile titanium oxide include “TR-600”, “TR-700”, “TR-750”, “TR-840” manufactured by Fuji Titanium Industry Co., Ltd., and “R-550” manufactured by Ishihara Sangyo Co., Ltd. ”,“ R-580 ”,“ R-630 ”,“ R-820 ”,“ CR-50 ”,“ CR-60 ”,“ CR-90 ”,“ CR-93 ”, manufactured by Titanium Industry Co., Ltd. “KR-270”, “KR-310”, “KR-380” and the like can be mentioned. The compounding quantity of a rutile type titanium oxide is 30-200 mass parts with respect to 100 mass parts of carboxyl group-containing photosensitive resin, Preferably it is 50-150 mass parts.

(G) The solvent is appropriately blended to adjust the drying property of the white curable resin composition for spray coating. Examples of the solvent include ketones such as methyl ethyl ketone and cyclohexanone; aromatic hydrocarbons such as toluene, xylene and tetramethylbenzene; methyl cellosolve, ethyl cellosolve, butyl cellosolve, methyl carbitol, butyl carbitol, propylene glycol monomethyl ether, Glycol ethers such as diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, dipropylene glycol monoethyl ether, triethylene glycol monoethyl ether; ethyl acetate, butyl acetate, cellosolve acetate, diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, propylene glycol Monomethyl ether acetate and glyco Esters such as esters of ethers; ethanol, can be mentioned propanol, ethylene glycol, and alcohols such as propylene glycol.

  In the white curable resin composition for spray coating of the present invention, in addition to the above components (A) to (G), various additive components, for example, an antifoaming agent, various additives, and a constitution are used as necessary. A pigment or the like can be contained.

  A well-known thing can be used for an antifoamer, for example, a silicone type, a hydrocarbon type, an acrylic type etc. can be mentioned.

  Examples of various additives include dispersants such as coupling agents such as silane, titanate, and alumina, boron trifluoride-amine complex, dicyandiamide (DICY) and its derivatives, organic acid hydrazide, and diaminomaleonitrile (DAMN). ) And derivatives thereof, guanamine and derivatives thereof, melamine and derivatives thereof, latent curing agents such as amine imide (AI) and polyamine, metal salts of acetylacetone such as acetylacetonate Zn and acetylacetonate Cr, enamine, tin octylate, Examples include quaternary sulfonium salts, triphenylphosphine, imidazole, imidazolium salts, and thermosetting accelerators such as triethanolamine borate.

  The extender is for increasing the physical strength of the coated reflective film, and examples thereof include silica, barium sulfate, alumina, aluminum hydroxide, talc, and mica.

 The manufacturing method of the white curable resin composition for spray coating used for reflective film formation of the above-described reflective sheet of the present invention is not limited to a specific method. For example, the above components (A) to (G) and other components as necessary are blended after mixing at a predetermined ratio, and if necessary, kneading means such as a three roll, ball mill, sand mill, super mixer, planetary or the like. A white curable resin composition for spray coating is obtained by kneading or mixing using a stirring means such as a mixer.

  Next, an example of a method for producing the reflective sheet of the present invention by coating the above-described white curable resin composition on the surface of the sheet-like base film will be described. After the surface of the sheet-like base film is treated with, for example, an acid and washed, the white curable resin composition obtained as described above is spray-coated on the washed surface at a desired thickness, for example, 5 to 100 μm. To do. Examples of spray coating means include an electrostatic spray coating machine, an air spray coating machine, and an airless spray coating machine.

  After spray coating, preliminary drying is performed in a hot air furnace or a far-infrared furnace, and the solvent is volatilized from the white curable resin composition to make the surface of the coating film tack-free. In the preliminary drying, heating is performed at a temperature of about 60 to 80 ° C. for about 15 to 60 minutes.

After preliminary drying, the coating film is photocured by performing exposure by direct laser drawing using LDI (Laser Direct Imaging) or exposure by ultraviolet rays as necessary. In the case of ultraviolet rays, the irradiation amount is 10 to 1000 mJ / cm ² . In addition, when forming the predetermined pattern of a reflective film in a reflective sheet, the negative film which has the said predetermined pattern is closely_contact | adhered on the apply | coated white curable resin composition in the above-mentioned exposure by an ultraviolet-ray. Then, the reflective film having the predetermined pattern is developed by irradiating the negative film with ultraviolet rays and removing the non-exposed areas corresponding to the predetermined pattern with a dilute alkaline aqueous solution. This removal may be any of dissolution, swelling, peeling, etc. of the unexposed part. The dilute alkaline aqueous solution used at this time is generally 0.5 to 5% sodium carbonate aqueous solution, but other alkalis can also be used.

  Next, post-curing is performed by heating for 10 to 80 minutes in a dryer such as a hot-air oven or a far-infrared furnace at 130 to 170 ° C., for example, to thermally cure the coating film on the surface of the base film, and to have a reflective coating Manufacture sheets. In addition, you may post-cure as it is after a preliminary drying, without performing an exposure process.

  The material of the sheet-like base film is not particularly limited. For example, polyimide, polyethylene terephthalate (PET), polyvinyl fluoride (PVF), fluorinated ethylene / propylene copolymer (FEP), polytetrafluoroethylene (PTFE), aramid , Polyamide / imide, epoxy, polyetherimide, polysulfone, polyethylene naphthalate (PEN), liquid crystal polymer (LCP), and the like.

  When manufacturing a reflective sheet for a solar battery back sheet, for example, a polyethylene terephthalate film having a thickness of 40 μm is used as the base film. Moreover, a white curable resin composition is applied to the polyethylene terephthalate film surface so that the film thickness after hardening may be 20-23 micrometers, for example. Furthermore, it is preferable that the coating part of the white curable resin composition is performed on the entire surface or almost the entire surface of the base film surface region facing the back surface of the solar cell module.

  Next, an example of how to use the reflective sheet of the present invention will be described. For example, the reflective sheet of the present invention can be used as a solar battery back sheet by being arranged on the back side of the solar cell module, that is, on the surface opposite to the surface that receives solar radiation. When the reflective sheet of the present invention is used as a solar battery back sheet, solar light transmitted through the solar battery module without being received by the power generation element of the solar battery module is reflected by the reflective film of the solar battery back sheet, and the solar battery module. Since it returns to the inside of the solar cell module again from the back side, the power generation efficiency of the solar cell module is improved. In addition, the installation method of the solar cell back sheet to a solar cell module back surface includes the method of sticking directly on a solar cell module back surface using an adhesive agent or an adhesive tape, for example.

  Next, examples of the present invention will be described. However, the present invention is not limited to these examples as long as the gist thereof is not exceeded.

Examples 1-17, Comparative Examples 1-2
Each component shown in Table 1 below is blended in the proportions shown in Table 1 below, mixed and dispersed at room temperature using three rolls, and used in Examples 1-17 and Comparative Examples 1-2. A white curable resin composition for coating was prepared. The numbers in the formulation in Table 1 below indicate parts by mass.

The details of each component in Table 1 are as follows.
(A) Carboxyl group-containing photosensitive resin / Synthesis Example 1: Synthesis of resin A-1 270 parts by mass of epoxy resin (manufactured by Daicel Chemical Industries, Ltd., EHPE-3150) in 400 parts by mass of cellosolve acetate 110 parts by weight of acrylic acid (unsaturated group-containing monocarboxylic acid) is added, and the reaction is carried out under a heating and refluxing condition by a conventional method, and 160 parts by weight of tetrahydrophthalic anhydride (polybasic acid anhydride) is reacted by a conventional method. Subsequently, 40 parts by mass of glycidyl methacrylate (ethylenically unsaturated monomer) was reacted by the heating reflux under constant method to obtain a product (resin A-1).
Synthesis Example 2: Resin A-2 Synthetic epoxy resin Cresol novolac type epoxy resin (DIC, N-680) 210 parts by mass in diethylene glycol monoethyl ether acetate 120 parts by mass 72 parts by mass of acrylic acid The reaction product was reacted with 76 parts by mass of tetrahydrophthalic anhydride (polybasic acid anhydride) by a conventional method to obtain a product (resin A-2). .
Cyclomer P (ACA) Z-300: a carboxyl group-containing resin using a resin having an acrylic copolymer structure manufactured by Daicel Chemical Industries, Ltd.
-ZFR-1124: Nippon Kayaku Co., Ltd. product, bisphenol F type epoxy acrylate structure carboxyl group-containing resin.
FLX-2089: Nippon Kayaku Co., Ltd. product, a carboxyl group-containing resin having a urethane-modified epoxy acrylate structure.
(B) Silicon dioxide powder and / or metal oxide powder produced by pyrolysis method. AEROSIL R974: Hydrophobic fumed silica manufactured by Nippon Aerosil Co., Ltd.
AEROSIL 200: manufactured by Nippon Aerosil Co., Ltd., hydrophilic fumed silica.
-AEROXIDE Alu C: Nippon Aerosil Co., Ltd., fumed metal oxide (aluminum oxide).
AEROXIDE TiO ₂ P25: Nippon Aerosil Co., Ltd., fumed metal oxide (titanium dioxide).
(C) Photopolymerization initiator DAROCURE TPO: Ciba Specialty Chemicals Co., Ltd., 2,4,6-trimethylbenzoyldiphenylphosphine oxide.
(D) Diluent M-408: Toa Gosei Co., Ltd., ditrimethylolpropane tetraacrylate.
(E) Epoxy compound EPICRON 860: Dainippon Ink and Chemicals, bisphenol A type epoxy resin.
(F) Titanium oxide CR-80: manufactured by Ishihara Sangyo Co., Ltd., rutile type titanium oxide.

  In addition, the additive DICY-7 is a curing accelerator made by Japan Epoxy Resin Co., Ltd., melamine is a latent curing agent, and BYK-411 used in Comparative Example 3 is a thixotropy imparted by Big Chemie Japan Co., Ltd. It is an agent.

A process for preparing a test piece having a cured coating film (reflection coating) is shown below.
Sheet: Polyethylene terephthalate film, thickness 40μm
Sheet surface treatment: acid treatment (3% sulfuric acid aqueous solution)
Coating: Spray coating. Examples 1 to 16 and Comparative Examples 1 and 2 use an electrostatic spray device, and Example 17 uses an air spray device.
-Coating conditions of the electrostatic spray device: device (TMK manufactured by Fuji Machinery), discharge rate (110 cc / min), conveyor speed (2.3 m / min), disk rotation speed (30000 rpm), applied voltage (-35 KV), The wet film thickness of the white curable resin composition liquid for spray coating is 50 to 60 μm.
・ Coating conditions for air spray equipment: equipment (TSR manufactured by FANUC), discharge rate (110cc / min), conveyor speed (2.3m / min), atomization pressure (0.2-0.3MPa), for spray coating The wet film thickness of the white curable resin composition liquid is 50 to 60 μm.
DRY film thickness: 25-30 μm
Predrying: 70 ° C, 20 minutes (25 minutes in BOX furnace)
Post cure: 150 ° C, 60 minutes (70 minutes in BOX furnace)
In addition, about the test piece of reflectance evaluation, it replaces with a polyethylene terephthalate film in order to remove the influence of deterioration of the polyethylene terephthalate itself accompanying the environment leaving which is an acceleration test, and it is the same as the above on a glass plate (1.2 mm thickness) A cured coating film was formed in the above process to prepare a test piece of a reflective sheet.

The evaluation / measurement items are as follows.
(1) Viscosity The viscosity of the prepared white curable resin composition for spray coating was measured at a sample temperature of 25 ° C. using a Malcolm spiral viscometer PC-1C type (φ35 rotor).
(2) Thixo ratio About the prepared white curable resin composition for spray coating, using a Brookfield viscometer RVT type, from the ratio of viscosity of spindle speed 5rpm and 50rpm (η5 / η50) at sample temperature 25 ° C The thixo ratio was calculated.
(3) Sag property The sheet which is a test piece was visually evaluated.
○: There is no twist or sag in the cured coating on the sheet surface.
Δ: The cured coating film on the sheet surface is slightly twisted or sagged.
X: The cured coating film on the sheet surface has a twist or sag.
(4) Scratch skin property The sheet which is a test piece was visually evaluated.
○: The cured coating film on the sheet surface is smooth.
Δ: Some unevenness exists on the cured coating film on the sheet surface.
X: The cured coating film on the sheet surface has irregularities.
―: Evaluation is not possible because a sheet that is significantly sag can not be prepared.
(5) Color change evaluation Color change evaluation: After heating at 260 ° C. for 5 minutes, the color change of the cured coating film was visually evaluated.
○: No discoloration.
Δ: Some discoloration is observed.
X: Yellowing.
(6) Reflectance (%)
Initial: About the test piece after the post-cure, the reflectance at 500 nm was measured with a spectrophotometer U-3410 (manufactured by Hitachi, Ltd .: φ 60 mm integrating sphere).
After irradiation: Light resistance is evaluated for the reflectance of the test piece. After the test piece is irradiated with 50 J UV for 2 minutes, the spectrophotometer U-3410 (manufactured by Hitachi, Ltd .: φ60 mm integrating sphere) is used. Then, the reflectance of the test piece at 500 nm was measured.
After heating: The heat resistance is evaluated for the reflectance of the test piece. After heating the test piece at 170 ° C. for 100 hours, the spectrophotometer U-3410 (manufactured by Hitachi, Ltd .: φ60 mm integrating sphere) is used. The reflectance of the test piece at 500 nm was measured.
After humidification and heating: The weather resistance is evaluated for the reflectance of the test piece. After leaving the test piece for 1000 hours at 85 ° C. and 85% RH, the spectrophotometer U-3410 (manufactured by Hitachi, Ltd.) : Φ60 mm integrating sphere), the reflectance of the specimen at 500 nm was measured.
(7) Coating film hardness A pencil of B to 9H, which has been sharpened so that the tip of the core is flattened, is pressed against the cured coating film formed on the sheet at an angle of about 45 °, resulting in peeling of the coating film. Recorded no pencil hardness.

  The measurement results and evaluation results are shown in Table 2.

  As shown in Table 2 above, in Examples 1 to 17, silicon dioxide powder and / or metal oxide produced by a thermal decomposition method was used to adjust the viscosity and thixotropy (thixo ratio) of the white curable resin composition. Since the powder is used, the fall of the reflectance after humidification heating can be suppressed, and it was excellent in the weather resistance. In addition, it was possible to prevent discoloration due to heat history and to suppress the decrease in reflectance after UV irradiation to the initial value to 2% or less, and thus was excellent in heat resistance and light resistance. Furthermore, the coating film hardness was also good. Further, in Examples 1 to 15 and 17 in which 2 to 20 parts by mass of silicon dioxide powder and / or metal oxide powder produced by the thermal decomposition method are blended, a reflection film that suppresses the occurrence of sagging and dirty skin is formed. The finished appearance was particularly good. This is considered because the viscosity and thixotropy ratio at 25 ° C. of the white curable resin composition are in a numerical range suitable for spray coating.

  From the comparison between Examples 1 to 5 and Examples 9 to 10, both silicon dioxide powder produced by the pyrolysis method and metal oxide powder produced by the pyrolysis method were almost equally prevented from dripping. It was possible to suppress the occurrence of skin. In addition, from the comparison between Examples 1 to 5 and Examples 11 to 13, when propylene glycol monomethyl ether was added to the solvent, the drooping property could be further suppressed.

  On the other hand, in Comparative Example 1, the thixo ratio was as low as 1.1, and sagging occurred, making it impossible to create a test piece. In Comparative Example 2 using a conventional thixotropy imparting agent, no sagging occurred and no skin was observed, but the reflectivity after humidification and heating was significantly lowered and the weather resistance was poor. Moreover, in the comparative example 2, the coating-film surface turned yellow after a heating, the fall of the reflectance after UV irradiation with respect to an initial stage also became 4%, and was also inferior to heat resistance and light resistance.

  The reflective sheet of the present invention is highly useful in the field of solar cell backsheets because it suppresses a decrease in reflectivity and can prevent yellowing due to thermal history and is excellent in appearance.

Claims (4)

A reflective sheet having a reflective coating formed of a white curable resin composition for spray coating,
The white curable resin composition for spray coating is
(A) carboxyl group-containing photosensitive resin, (B) silicon dioxide powder and / or metal oxide powder produced by thermal decomposition, (C) photopolymerization initiator, (D) diluent, (E) epoxy compound (F) Titanium oxide and (G) The reflective sheet characterized by the above-mentioned.   The silicon dioxide powder and / or metal oxide powder produced by the thermal decomposition method (B) contains 2 to 20 parts by mass with respect to 100 parts by mass of the (A) carboxyl group-containing photosensitive resin. The reflecting sheet according to claim 1.   The reflective sheet according to claim 1, wherein the solvent (G) contains propylene glycol monomethyl ether.   The solar cell module provided with the reflective sheet of any one of Claims 1 thru | or 3.