JP2012008324A - Reflection sheet having film of curable resin composition - Google Patents

Abstract

Provided is a reflective sheet provided with a reflective film having excellent properties such as weather resistance and heat resistance, and having flexibility, low warpage and adhesion.
A reflective sheet having a reflective film formed of a curable resin composition, wherein the curable resin composition has (A-1) (meth) acrylic acid and a hydroxyl group at a terminal ( A carboxyl group-containing copolymer resin obtained by reacting a (meth) acrylate compound (a1), or (A-2) a (meth) acrylate compound (a1) having a hydroxyl group at the terminal and a carboxyl at the terminal Carboxyl group-containing copolymer resin obtained by reacting a (meth) acrylic acid ester compound (a2) having a group, (B) a compound having a quaternary alkylphosphonium cation, (C) a compound having an epoxy group, and (D ) An anti-curable resin composition containing an inorganic white pigment.
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Description

  The present invention relates to a reflective sheet provided with a cured product of a curable resin composition as a reflective film, 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. In view of this, a solar battery back sheet having an adhesive coating layer made of a polyacrylic acid resin colored with a white pigment mainly composed of titanium oxide is proposed on the innermost surface to be bonded to the sealing layer constituting the solar battery module. (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. In addition, the solar cell back sheet is required to have low warpage from the viewpoint of improving power conversion efficiency by being in close contact with the back surface of the solar cell module, and more flexible from the viewpoint of preventing damage during transportation and installation work. It is also required to have adhesion from the viewpoint of preventing peeling of the reflective film during use.

JP 2010-109240 A JP2008-211036

  In view of the above circumstances, an object of the present invention is to provide a reflective sheet including a reflective film having excellent properties such as weather resistance and heat resistance, and having flexibility, low warpage, and adhesion.

  A first aspect of the present invention is a reflective sheet having a reflective coating formed of a curable resin composition, wherein the curable resin composition is (A-1) general formula (i).

(Wherein R ¹ represents a hydrogen atom or a methyl group) and a general formula (ii)

(Wherein R ² represents a hydrogen atom or a methyl group, n1 is an integer of 2 to 4, n2 is an integer of 3 to 6, and m1 is an integer of 1 to 5). Or a carboxyl group-containing copolymer resin obtained by (A-2) general formula (ii)

In the formula, R ² represents a hydrogen atom or a methyl group, n1 is an integer of 2 to 4, n2 is an integer of 3 to 6, and m1 is an integer of 1 to 5; Formula (iii)

(Wherein R ³ represents a hydrogen atom or a methyl group, n3 is an integer of 2 to 6, and m2 is an integer of 1 to 5). Resin, (B) general formula (iv)

(In the formula, R ⁴ , R ⁵ , R ⁶ and R ⁷ are the same or different and are each a linear or branched alkyl group having 1 to 8 carbon atoms or a monovalent alicyclic group having 3 to 8 carbon atoms. A hydrocarbon group, which may have a hydroxyl group or an alkoxy group having 1 to 3 carbon atoms as a substituent.) And a compound having a quaternary alkylphosphonium cation represented by (C) an epoxy group A reflective sheet comprising a compound and (D) an inorganic white pigment.

  The cured product of the curable resin composition described above is used for the reflective film of the reflective sheet according to this embodiment. And in the said curable resin composition, (A) As a copolymer resin, (A-1) The polymerizable monomer represented by the said general formula (i), and the polymerizable monomer represented by the said general formula (ii) Or (A-2) a polymerizable monomer represented by the above general formula (ii) and a polymerizable monomer represented by the above general formula (iii). A carboxyl group-containing copolymer resin is used.

  A second aspect of the present invention is a reflective sheet having a reflective coating formed of a curable resin composition, wherein the curable resin composition is (A-3) general formula (i).

(Wherein R ¹ represents a hydrogen atom or a methyl group) and a general formula (ii)

In the formula, R ² represents a hydrogen atom or a methyl group, n1 is an integer of 2 to 4, n2 is an integer of 3 to 6, and m1 is an integer of 1 to 5; Formula (v)

(Wherein R ⁸ represents a hydrogen atom or a methyl group, R ⁹ represents a phenyl group, an α-cumyl group, an alkoxy group having 1 to 10 carbon atoms, an acyl group having 1 to 10 carbon atoms in an alkyl group, and t-butyl. A group, an adamantyl group or a trifluoromethyl group, A represents a C2-C10 alkylene group or a C3-C10 hydroxyalkylene group containing a linear or cyclic skeleton, and m3 is 0 or 1-3. An integer, p is an integer of 1 to 5.) or a carboxyl group-containing copolymer resin obtained by reacting a compound represented by (A-4) general formula (ii)

In the formula, R ² represents a hydrogen atom or a methyl group, n1 is an integer of 2 to 4, n2 is an integer of 3 to 6, and m1 is an integer of 1 to 5; Formula (iii)

(Wherein R ³ represents a hydrogen atom or a methyl group, n3 is an integer of 2 to 6, and m2 is an integer of 1 to 5), and the general formula (v)

(Wherein R ⁸ represents a hydrogen atom or a methyl group, R ⁹ represents a phenyl group, an α-cumyl group, an alkoxy group having 1 to 10 carbon atoms, an acyl group having 1 to 10 carbon atoms in an alkyl group, and t-butyl. A group, an adamantyl group or a trifluoromethyl group, A represents a C2-C10 alkylene group or a C3-C10 hydroxyalkylene group containing a linear or cyclic skeleton, and m3 is 0 or 1-3. An integer, p is an integer of 1 to 5.), a carboxyl group-containing copolymer resin obtained by reacting a compound represented by (B) general formula (iv)

(In the formula, R ⁴ , R ⁵ , R ⁶ and R ⁷ are the same or different and are each a linear or branched alkyl group having 1 to 8 carbon atoms or a monovalent alicyclic group having 3 to 8 carbon atoms. A hydrocarbon group, which may have a hydroxyl group or an alkoxy group having 1 to 3 carbon atoms as a substituent.) And a compound having a quaternary alkylphosphonium cation represented by (C) an epoxy group A reflective sheet comprising a compound and (D) an inorganic white pigment.

  The cured product of the curable resin composition described above is used for the reflective film of the reflective sheet according to this embodiment. And in the said curable resin composition, (A) As copolymer resin, (A-3) The polymerizable monomer represented by the said general formula (i) and the polymerizable monomer represented by the said general formula (ii) And a carboxyl group-containing copolymer resin obtained by reacting the polymerizable monomer represented by the general formula (v), or (A-4) the polymerizable monomer represented by the general formula (ii) and the general formula ( A carboxyl group-containing copolymer resin obtained by reacting the polymerizable monomer represented by iii) with the polymerizable monomer represented by the general formula (v) is used.

  A third aspect of the present invention is a reflective sheet, wherein the compound represented by the general formula (ii) has a polycaprolactone skeleton. According to a fourth aspect of the present invention, there is provided a reflective sheet, wherein the compound represented by the general formula (iii) has a polycaprolactone skeleton.

  A fifth aspect of the present invention is the reflective sheet, wherein the compound (B) having a quaternary alkylphosphonium cation is a quaternary alkylphosphonium hydroxide. A sixth aspect of the present invention is a reflective sheet, wherein the compound (C) having an epoxy group has two or more epoxy groups in one molecule. According to a seventh aspect of the present invention, there is provided a reflective sheet characterized by further comprising (E) a phosphorus-based flame retardant. An eighth aspect of the present invention is the reflective sheet, wherein the phosphorus flame retardant is a metal salt of an alkyl phosphinic acid. 9th aspect of this invention is a solar cell module provided with the reflective sheet of the said aspect.

  According to the first aspect of the present invention, (meth) acrylic acid or a (meth) acrylic acid derivative having a carboxyl group and (meth) acrylate are used as components of the copolymer, and the carboxyl group of the copolymer resin is ( By specifying the structure derived from (meth) acrylic acid or a (meth) acrylic acid derivative having a carboxyl group, and using the compound having the quaternary alkylphosphonium cation as a curing catalyst, the diffuse reflection of the reflective film over time and heat The rate drop can be suppressed. Therefore, the reflective sheet provided with the reflective film excellent in heat resistance and weather resistance can be obtained. Moreover, since the softness | flexibility of a reflective sheet improves by the said structure, the failure | damage of the reflective film at the time of transportation and installation work can be prevented. Furthermore, since the adhesion of the reflective film is improved, it is possible to prevent the reflective film from being peeled off from the surface of the underlying sheet when the reflective sheet is used. Since a reflective sheet having low warpage can be obtained, for example, when the reflective sheet is used as a back sheet of a solar cell, adhesion with the solar cell module is ensured. According to the second aspect of the present invention, by adding the (meth) acrylate having an aromatic ring represented by the general formula (v) described above, the side chain α of the aromatic hydrocarbon skeleton is obtained after polymerization. A compound having no hydrogen atom at the position is a component of the copolymer resin, that is, for a compound having no hydrogen atom at the α-position of the side chain relative to the aromatic hydrocarbon skeleton or the aromatic hydrocarbon skeleton Thus, since the compound in which the α-position hydrogen atom is present in the main chain is a constituent element of the copolymer resin, it is possible to more reliably suppress a decrease in the diffuse reflectance of the reflective film due to heat and aging.

  According to the third and fourth aspects of the present invention, a polycaprolactone skeleton is included in the constituent elements of the copolymer, so that it is possible to further suppress a decrease in the diffuse reflectance of the reflective film due to aging and thermal history, and to have more heat resistance And the reflective sheet provided with the reflective film excellent in weather resistance is obtained. According to the fifth aspect of the present invention, since the compound having a quaternary alkylphosphonium cation is a quaternary alkylphosphonium hydroxide and having a hydroxyl group as a counter anion, a small amount is formed in forming a salt with the carboxyl group of the copolymer. It can be easily volatilized at the time of drying and curing. Therefore, the production process of the reflective sheet can be simplified. In addition, when a quaternary alkylphosphonium hydroxide is used as compared with the case where the counter anion has chlorine ions and bromine ions, inorganic ionic impurities that adversely affect weather resistance do not remain in the reflective film. Furthermore, since the counter anion forms a salt with a carboxyl group of the copolymer having a relatively high molecular weight, the quaternary alkylphosphonium cation component is less likely to volatilize when the thin film is applied and dried and cured. It prevents the remaining of components that sufficiently contribute to the curing of the coating film and inhibit the degree of crosslinking of the coating film. In addition, in order to avoid a trace amount of water residue, it is also possible to mix the copolymer and quaternary phosphonium hydroxide in advance to form a salt, and then volatilize the water before blending. According to the 6th aspect of this invention, since the compound which has an epoxy group has two or more epoxy groups in 1 molecule, hardening of a curable resin composition speeds up and the production efficiency of a reflective sheet improves. . According to the seventh and eighth aspects of the present invention, since the phosphor-based flame retardant is further included, the flame retardancy of the reflective sheet is improved.

  Next, the curable resin composition used for the reflective film of the reflective sheet according to the present invention will be described. The curable resin composition used for forming the reflective film of the reflective sheet is (A) a copolymer resin (A-1), (A-2), (A-3) or (A-4); B) A compound having a quaternary alkylphosphonium cation represented by the general formula (iv), (C) a compound having an epoxy group, and (D) an inorganic white pigment.

(A) Copolymer resin: Among the copolymer resins (A) of (A-1), (A-2), (A-3) and (A-4) , among the copolymer resins (A-), (A- The copolymer resin 1) is obtained by copolymerizing acrylic acid or methacrylic acid represented by the general formula (i) and a (meth) acrylate having a hydroxyl group represented by the general formula (ii). The copolymer resin (A-2) is obtained by copolymerizing a (meth) acrylate having a hydroxyl group represented by the general formula (ii) and a (meth) acrylate having a carboxyl group represented by the general formula (iii). Obtained. The copolymer resin of (A-3) is represented by the general formula (v) and (meth) acrylate having the acrylic acid or methacrylic acid represented by the general formula (i) and the hydroxyl group represented by the general formula (ii). It is obtained by copolymerizing (meth) acrylate having an aromatic ring. The copolymer resin (A-4) includes a (meth) acrylate having a hydroxyl group represented by the general formula (ii), a (meth) acrylate having a carboxyl group represented by the general formula (iii), and the general formula (v ) And a (meth) acrylate having an aromatic ring.

  Examples of the (meth) acrylate having a hydroxyl group represented by the general formula (ii) include a lactone adduct of 2-hydroxyethyl (meth) acrylate, a lactone adduct of propylene glycol mono (meth) acrylate, butanediol mono ( And lactone adducts of (meth) acrylate. Of these, an ε-caprolactone adduct of 2-hydroxyethyl (meth) acrylate is preferable from the viewpoint of ensuring the heat resistance and flexibility of the reflective coating. These compounds may be used alone or in combination of two or more.

  Examples of the (meth) acrylate having a carboxyl group represented by the general formula (iii) include a caprolactone adduct of (meth) acrylic acid and β-carboxyethyl (meth) acrylate. Of these, ε-caprolactone adduct of acrylic acid and ε-caprolactone adduct of methacrylic acid are preferable from the viewpoint of ensuring the heat resistance and flexibility of the reflective film. These compounds may be used alone or in combination of two or more.

  Examples of the (meth) acrylate having an aromatic ring represented by the general formula (v) include phenoxy polyethylene glycol (meth) such as phenoxyethyl (meth) acrylate and 2- (2-phenoxyethoxy) ethyl (meth) acrylate. 4-, such as phenoxypolypropylene glycol (meth) acrylate such as acrylate, phenoxypropyl (meth) acrylate and 2-phenoxypropyl (meth) acrylate, phenylglycidyl ether (meth) acrylate, 4-α-cumylphenoxyethyl (meth) acrylate, etc. Examples include α-cumylphenoxypolyethylene glycol (meth) acrylate and 2-phenylphenoxypolyethylene glycol (meth) acrylate such as 2-phenylphenoxyethyl (meth) acrylate. Can. These compounds may be used alone or in combination of two or more.

  The copolymer resin (A-1), the copolymer resin (A-2), the copolymer resin (A-3) and the copolymer resin (A-4) are all synthesized by a known solution polymerization method. can do. The solvent used is not particularly limited as long as it is inert to radical polymerization. Examples thereof include ethylene glycol monoalkyl ether acetates such as ethyl acetate, isopropyl acetate, cellosolve acetate and butyl cellosolve acetate; diethylene glycol monoalkyl ether acetates such as diethylene glycol monomethyl ether acetate, carbitol acetate and butyl carbitol acetate; propylene glycol Acetic esters such as monoalkyl ether acetates and dipropylene glycol monoalkyl ether acetates; Diethylene glycol dialkyl ethers, diethylene glycol dialkyl ethers such as methyl carbitol, ethyl carbitol, and butyl carbitol; Triethylene glycol dialkyl ethers; Propylene glycol dialkyl ether Dipropylene glycol dialkyl ethers; dipropylene glycol monoalkyl ethers; ethers such as 1,4-dioxane and tetrahydrofuran; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; benzene, toluene, xylene, octane, Hydrocarbons such as decane; petroleum solvents such as petroleum ether, petroleum naphtha, hydrogenated petroleum naphtha and solvent naphtha; lactic esters such as methyl lactate, ethyl lactate and butyl lactate; dimethylformamide, N-methylpyrrolidone and the like It is done. These solvents may be used alone or in combination of two or more. The compounding quantity of a solvent is 30-1000 mass parts with respect to 100 mass parts of copolymer resins, Preferably it is 50-800 mass parts.

  The radical polymerization initiator used in the solution polymerization method is not particularly limited, and for example, an organic peroxide or an azo compound can be used. Specific examples include benzoyl peroxide, dicumyl peroxide, diisopropyl peroxide, di-t-butyl peroxide, t-butyl peroxybenzoate, t-hexyl peroxybenzoate, t-butylperoxy-2-ethylhexa Noate, t-hexylperoxy-2-ethylhexanoate, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-bis ( t-butylperoxy) hexyl-3,3-isopropyl hydroperoxide, t-butyl hydroperoxide, dicumyl peroxide, dicumyl hydroperoxide, acetyl peroxide, bis (4-t-butylcyclohexyl) peroxy Dicarbonate, diisopropyl par Xidicarbonate, isobutyl peroxide, 3,3,5-trimethylhexanoyl peroxide, lauryl peroxide, 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane, 1,1-bis (T-Hexylperoxy) 3,3,5-trimethylcyclohexane, azobisisobutyronitrile, azobiscarbonamide and the like can be used. A radical polymerization initiator having an appropriate half-life is appropriately selected according to the polymerization temperature. The compounding quantity of a radical polymerization initiator is 0.2-20 mass parts with respect to a total of 100 mass parts of a radically polymerizable unsaturated compound, Preferably it is 0.3-10 mass parts.

  In the polymerization method, the unsaturated monomer and the radical polymerization initiator may be added dropwise to a heated solvent, followed by stirring. The unsaturated monomer and the radical polymerization initiator are dissolved in the solvent, and the temperature is increased while stirring. May be performed. Moreover, you may add an unsaturated monomer dropwise while adding a radical polymerization initiator in a solvent and heating up.

  About the weight average molecular weight of each copolymer resin of (A-1), (A-2), (A-3), (A-4), the lower limit is the toughness of the reflective coating which is a cured coating, and the finger It is 3000 from the point of touch drying property, Preferably it is 5000. On the other hand, the upper limit is 200000 from the point of a softness | flexibility and low curvature property, Preferably it is 50000.

(B) Compound having quaternary alkylphosphonium cation The compound having quaternary alkylphosphonium cation is a compound having a carboxyl group contained in the curable resin composition and a compound having an epoxy group as component (C) described later. A catalyst for accelerating the curing reaction, that is, a curing accelerator. Examples of the compound having a quaternary alkylphosphonium cation include tetraethylphosphonium hydroxide, tetrabutylphosphonium hydroxide, tetrabutylphosphonium acetate, tributylmethylphosphonium hydroxide, tetrapentylphosphonium hydroxide, trioctylmethylphosphonium hydroxide, and the like. be able to. Of the above compounds, tetrabutylphosphonium hydroxide whose counter anion is hydroxide is preferred. These compounds may be used alone or in combination of two or more. About the compounding quantity of the compound which has a quaternary alkyl phosphonium cation, an upper limit is 10 mass parts at the point which prevents the fall of the physical property by remaining in a reflective film with respect to 100 mass parts of copolymer resins, Preferably 5 parts by mass. Moreover, a lower limit is 0.1 mass part at the point which shows a curing reaction with respect to 100 mass parts of copolymer resins, and 0.5 mass part is preferable at the point which speeds up a curing reaction.

(C) Compound having an epoxy group The compound having an epoxy group is for obtaining a reflective film in which the crosslinking density of the cured coating film is increased and the decrease in diffuse reflectance is suppressed in the curable resin composition. For example, an epoxy resin can be mentioned. Examples of the epoxy resin include bisphenol A type epoxy resin (bisphenol A type liquid epoxy resin, bisphenol A type modified flexible epoxy resin, nuclear hydrogenated bisphenol A type liquid epoxy resin, etc.), novolac type epoxy resin (phenol novolac type epoxy). Resin, o-cresol novolak type epoxy resin, p-tert-butylphenol novolak type, etc.), bisphenol F type and bisphenol S type epoxy resin obtained by reacting bisphenol F and bisphenol S with epichlorohydrin, cyclohexene oxide group, tri Cycloaliphatic epoxy resin having cyclodecane oxide group, cyclopentene oxide group, tris (2,3-epoxypropyl) isocyanurate, triglycidyl tris (2-hydro Shiechiru) triglycidyl isocyanurate having a triazine ring such as isocyanurate, dicyclopentadiene type epoxy resins, adamantane 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 copolymer resins from the point which obtains sufficient film-curing property and diffuse reflectance, and the balance of film-curing property and a softness | flexibility. The point is preferably 10 to 50 parts by mass.

(D) Inorganic white pigment An inorganic white pigment is for whitening a coating film, and can mention an anatase type titanium oxide and a rutile type titanium oxide, for example. Anatase-type titanium oxide has a higher whiteness than rutile-type titanium oxide, but has photocatalytic activity and may cause discoloration of the resin in the curable resin composition. On the other hand, rutile titanium oxide is preferable in that it has almost no photocatalytic activity and can prevent discoloration of the reflective film. The average particle size of the rutile-type titanium oxide particles is not particularly limited, but is usually 0.01 to 1 μm. Further, the surface treating agent for rutile type titanium oxide particles is not particularly limited. 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”, “JR-1000”, “JR-805”, “JR-806” manufactured by Teika Co., Ltd. can be used. The compounding quantity of a rutile type titanium oxide is 30-800 mass parts with respect to 100 mass parts of copolymer resins, Preferably it is 50-500 mass parts.

  In the curable resin composition used for forming the reflective film of the reflective sheet of the present invention, the following components can be blended as required in addition to the above components.

(E) Phosphorus-based flame retardant Phosphorus-based flame retardant is for imparting flame retardancy to the reflective coating. For example, tris (chloroethyl) phosphate, tris (2,3-dichloropropyl) phosphate, tris (2-chloropropyl) phosphate, tris (2,3-bromopropyl) phosphate, tris (bromochloropropyl) phosphate, 2,3-dibromopropyl-2,3-chloropropyl phosphate, tris (tribromophenyl) phosphate, Halogen-containing phosphates such as tris (dibromophenyl) phosphate and tris (tribromoneopentyl) phosphate; non-having such as trimethyl phosphate, triethyl phosphate, tributyl phosphate, trioctyl phosphate, tributoxyethyl phosphate Rogen-based aliphatic phosphate ester; triphenyl phosphate, cresyl diphenyl phosphate, dicresyl phenyl phosphate, tricresyl phosphate, trixylenyl phosphate, xylenyl diphenyl phosphate, tris (isopropylphenyl) phosphate, isopropylphenyl diphenyl phosphate, Non-halogenated aromatic phosphates such as diisopropylphenylphenyl phosphate, tris (trimethylphenyl) phosphate, tris (t-butylphenyl) phosphate, hydroxyphenyldiphenyl phosphate, octyldiphenyl phosphate; aluminum trisdiethylphosphinate, trismethylethylphosphinic acid Aluminum, aluminum trisdiphenylphosphinate, bi Zinc diethylphosphinate, zinc bismethylethylphosphinate, zinc bisdiphenylphosphinate, titanyl bisdiethylphosphinate, titanium tetrakisdiethylphosphinate, titanyl bismethylethylphosphinate, titanium tetrakismethylethylphosphinate, titanyl bisdiphenylphosphinate, Phosphinic acid metal salts such as titanium tetrakisdiphenylphosphinate, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (hereinafter HCA), addition reaction product of HCA and acrylate ester, HCA and epoxy Addition reaction products of resins, HCA modified compounds such as addition reaction products of HCA and hydroquinone, diphenylvinylphosphine oxide, triphenylphosphine oxide, trialkylphosphine Examples thereof include phosphine oxide compounds such as oxide and tris (hydroxyalkyl) phosphine oxide. Of these, non-halogen phosphates, alkylphosphinic acid metal salts, HCA-modified compounds, and phosphine oxide compounds are preferred from the viewpoint of reducing environmental impact. In small amounts, not only flame retardancy but also bleedout resistance Alkylphosphinic acid metal salts are particularly preferred from the viewpoint of excellent properties and discoloration resistance.

  The compounding amount of the phosphorus-based flame retardant is 3 to 30 parts by mass with respect to 100 parts by mass of the copolymer resin. 4-25 mass parts is preferable.

  In the present invention, if necessary, the curable resin composition is further added with various additive components such as antifoaming agent, dispersant, extender pigment, inorganic ion catcher, organic solvent, diluent, photopolymerization start. An agent or the like can be appropriately blended.

  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 the dispersant include silane-based, titanate-based, and alumina-based coupling agents. The extender pigment is for increasing the physical strength of the reflective coating applied to the surface of the base sheet, and examples thereof include silica, barium sulfate, alumina, aluminum hydroxide, talc, and mica. . Examples of inorganic ion catchers include zirconium phosphate compounds.

  The organic solvent is for adjusting the viscosity and drying property of the curable resin composition, for example, ketones such as methyl ethyl ketone and cyclohexane, aromatic hydrocarbons such as toluene and xylene, methanol, isopropanol, and cyclohexanol. Alcohols 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, acetic acid Examples thereof include acetates such as ethyl, butyl acetate, cellosolve acetate, butyl cellosolve acetate, carbitol acetate, and butyl carbitol acetate.

  The diluent is, for example, a photopolymerizable monomer, and when the curable resin composition is photocured to form a reflective film, the curable resin is sufficiently photocured to have acid resistance, heat resistance, and alkali resistance. It is used to obtain a reflective film having 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, Dipentaerythritol hexaacrylate, bisphenol A type EO modified di (meth) acrylate, bisphenol A type PO modified di (meth) acrylate, caprolactone modified dipentaerythritol hexaacrylate, EO modified dipentaerythritol hexaacrylate, for example (meth) acrylic group And a urethane-based acrylic compound obtained by reacting a compound having at least one hydroxy group with a compound having at least one isocyanate group.

  The photopolymerization initiator is added when the curable resin composition is photocured. The photopolymerization initiator is not particularly limited as long as it is generally used. For example, oxime initiator, benzoin, acetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1 -Hydroxycyclohexyl phenyl ketone, benzophenone and the like.

  The method for producing the curable resin composition used for the formation of the reflective film is not limited to a specific method. For example, after blending the above components at a predetermined ratio, they are premixed with a stirrer and mixed with three rolls at room temperature. It can be produced by dispersing.

  Next, an example of a method for producing the reflective sheet of the present invention by applying the above-described curable resin composition to the surface of the sheet-like base film will be described. When the curable resin composition obtained as described above is thermally cured to form a reflective film, for example, after the surface of the sheet-like base film is treated with an acid and washed, the cured product is applied to the washed surface. The conductive resin composition is applied to a desired thickness, for example, 5 to 100 μm, using a screen printing method, a spray coating method, or the like. Next, preliminary drying is performed in a hot air furnace or a far-infrared furnace, and the solvent is volatilized from the 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. 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.

  When the curable resin composition obtained as described above is photocured to form a reflective film, for example, the surface of the sheet-like base film is treated with an acid and washed, and then the curable resin is applied to the washed surface. The composition is applied to a desired thickness, for example, 5 to 100 μm, using a screen printing method, a spray coating method, or the like. Next, in order to volatilize the solvent in the curable resin composition, preliminary drying is performed by heating at a temperature of about 60 to 80 ° C. for about 15 to 60 minutes. Thereafter, the applied curable resin composition is photocured by irradiation with ultraviolet rays. At this time, in the case of forming a predetermined pattern of the reflective film on the reflective sheet, a negative film having a predetermined pattern portion made translucent is brought into close contact with the applied curable resin composition, and ultraviolet rays are irradiated thereon. Then, the non-exposed area corresponding to the predetermined pattern is removed with a dilute alkaline aqueous solution to develop the reflective film having the predetermined pattern. As a developing method, a spray method, a shower method, or the like is used. As a dilute alkali aqueous solution used, a 0.5 to 5% sodium carbonate aqueous solution is generally used, but other alkalis can also be used. Then, a post-cure is performed for 20 to 80 minutes with a hot air circulating dryer or the like at 130 to 170 ° C. to produce a reflective sheet having a target reflective film formed on the sheet-like base film.

  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. Further, the curable resin composition is applied to the surface of the polyethylene terephthalate film so that the film thickness after curing is 20 to 23 μm, for example. Furthermore, it is preferable that the coating part of the 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, sunlight transmitted through the solar cell module without being received by the power generation element of the solar cell module is reflected by the reflective sheet and again from the back side of the solar cell module. Since it returns to the inside of the solar cell module, the power generation efficiency of the solar cell module is improved. In addition, the installation method of the reflective 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.

Synthesis of copolymer resin as component (A) Synthesis Example 1
Add 200 g of dipropylene glycol monomethyl ether (hereinafter referred to as DPM) to a 500 mL four-necked flask equipped with a stirrer, thermometer, and reflux tube, raise the temperature to 100 ° C. in a nitrogen atmosphere, and then add caprolactone of acrylic acid Product (corresponding to general formula (iii)) (addition of 2 mol of caprolactone on average, “Aronix M-5300” manufactured by Toa Gosei Co., Ltd.) 35.0 g (0.12 mol), caprolactone adduct of 2-hydroxyethyl methacrylate (general formula (corresponding to (ii)) (addition of 1 mol of caprolactone average, “Placcel FM1D” manufactured by Daicel Chemical Industries, Ltd.) 132.2 g (0.53 mol), methyl methacrylate (“Light Ester M” manufactured by Kyoeisha Chemical Co., Ltd.) 60 0.1 g (0.60 mol) is added, and 30 g of DPM and dimethyl 2,2′-azobis (2- Chill propionate) (manufactured by Wako Pure Chemical Co. of "V-601") was added dropwise a mixed solution of 0.6g over about 2 hours. Then, the DPM solution which contains about 50 mass% of copolymer resins which have the carboxyl group of the synthesis example 1 by stirring at 100 degreeC for 6 hours was obtained. The copolymer resin having a carboxyl group had a weight average molecular weight of about 100,000 (in terms of polystyrene) and a solid content acid value of 30 mg KOH / g.

Synthesis example 2
A 500 mL four-necked flask equipped with a stirrer, thermometer, and reflux tube was charged with 200 g of dipropylene glycol monomethyl ether (hereinafter referred to as DPM), and the temperature was raised to 120 ° C. in a nitrogen atmosphere. (corresponding to i)) 18.1 g (0.21 mol), 2-hydroxyethyl methacrylate caprolactone adduct (corresponding to general formula (ii)) (caprolactone average 1 mol addition, “Plexel FM1D” manufactured by Daicel Chemical Industries, Ltd.) 112.2 g (0.45 mol), phenoxyethyl methacrylate (corresponding to the general formula (v)) (“SR-340” manufactured by Sartomer Co., Ltd.) 92.8 g (0.45 mol) were added, and 30 g DPM and radical A mixed solution of 1.9 g of dimethyl 2,2′-azobis (2-methylpropionate) (“V-601” manufactured by Wako Pure Chemical Industries, Ltd.), which is a polymerization initiator, for about 1 hour Only and was dropped. Then, the DPM solution which contains about 50 mass% of copolymer resins which have the carboxyl group of the synthesis example 2 by stirring at 120 degreeC for 3 hours was obtained. The copolymer resin having a carboxyl group had a weight average molecular weight of about 120,000 (polystyrene conversion) and a solid content acid value of 53 mgKOH / g.

Synthesis example 3
A 500 mL four-necked flask equipped with a stirrer, thermometer, and reflux tube was charged with 200 g of dipropylene glycol monomethyl ether (hereinafter referred to as DPM), and the temperature was raised to 120 ° C. in a nitrogen atmosphere, followed by the caprolactone adduct of acrylic acid. (Corresponding to the general formula (iii)) (Caprolactone average 2 mol addition, “Aronix M-5300” manufactured by Toa Gosei Co., Ltd.) 35.0 g (0.12 mol), 2-hydroxyethyl methacrylate caprolactone adduct (general formula ( (corresponds to ii)) (average addition of 1 mol of caprolactone, “Placcel FM1D” manufactured by Daicel Chemical Industries, Ltd.) 99.7 g (0.4 mol), phenoxyethyl methacrylate (corresponding to general formula (v)) (Sartomer Co., Ltd.) “SR-340”) 92.8 g (0.45 mol) was added, and 30 g of DPM and dimethyl as a radical polymerization initiator were added. A mixed solution of 2.1 g of 2,2′-azobis (2-methylpropionate) (“V-601” manufactured by Wako Pure Chemical Industries, Ltd.) was added dropwise over about 1 hour. Then, the DPM solution which contains about 50 mass% of copolymer resins which have the carboxyl group of the synthesis example 3 by stirring at 120 degreeC for 3 hours was obtained. The copolymer resin having a carboxyl group had a weight average molecular weight of about 65,000 (in terms of polystyrene) and a solid content acid value of 29 mgKOH / g.

Comparative Synthesis Example 1
Into a 500 mL four-necked flask equipped with a stirrer, a thermometer, and a reflux tube, 110 g of dipropylene glycol monomethyl ether (hereinafter referred to as DPM) was added, heated to 120 ° C. in a nitrogen atmosphere, and then 17.2 g (0 .2 mol), 92.8 g (0.45 mol) of phenoxyethyl methacrylate (Sartomer Co., Ltd. “SR-340”) was added, and 10 g of DPM and dimethyl 2,2′-azobis (2 -Methylpropionate) (4.6 V made by Wako Pure Chemical Industries, Ltd.) was added dropwise over about 1 hour. Then, the DPM solution which contains about 49 mass% of copolymer resins of the comparative synthesis example 1 was obtained by stirring at 120 degreeC for 3 hours. The weight average molecular weight of this copolymer resin was about 25000 (polystyrene conversion), and the solid content acid value was 98 mgKOH / g.

Examples 1-6, Comparative Examples 1-6
Each component shown in the following Table 1 is blended at the blending ratio shown in the following Table 1, and after preliminary mixing with a stirrer, the mixture is dispersed at room temperature using three rolls, and Examples 1 to 6 and Comparative Examples The curable resin composition used in 1-6 was prepared. And the prepared curable resin composition was applied to the film surface using the test piece preparation process mentioned later, and the test pieces of Examples 1-6 and Comparative Examples 1-6 were produced. The blending amounts shown in Table 1 below represent parts by mass.

In Table 1,
ACA-Z250: Resin solution manufactured by Daicel Chemical Industries, Ltd. (having an alicyclic skeleton, no aromatic hydrocarbon skeleton, having a carboxyl group and an acrylic group),
CCR-1159H: acid anhydride-modified resin of cresol novolac type epoxy acrylate manufactured by Nippon Kayaku Co., Ltd.
TBPH-40: Tetrabutylphosphonium hydroxide 40% solution manufactured by Hokuko Chemical Co., Ltd.
DICY: Dicyandiamide manufactured by Japan Epoxy Resin Co., Ltd.
Epicron EXA-840-ss: bisphenol A type liquid epoxy resin (bifunctional) manufactured by DIC Corporation
Epicron EXA-4816: Bisphenol A modified flexible epoxy resin (bifunctional) manufactured by DIC Corporation
Epicoat YX-8034: Nuclear hydrogenated bisphenol A type epoxy resin (bifunctional) manufactured by Japan Epoxy Resin Co., Ltd.
CR-93: Rutile titanium oxide manufactured by Ishihara Sangyo Co., Ltd.
KS-66: A silicone-based antifoaming agent manufactured by Shin-Etsu Silicone Co., Ltd.

Test piece preparation process The curable resin composition was applied to the surface of a sheet-like polyethylene terephthalate film having a thickness of 40 μm by screen printing, and then pre-dried by heating in a BOX furnace at 70 ° C. for 20 minutes. After preliminary drying, post-curing was performed at 150 ° C. for 60 minutes in a BOX furnace to form a cured coating film, and a test piece of a reflective sheet was produced. The thickness of the cured coating film after post-cure was 20 to 23 μm. About the test piece for evaluation of reflectance, in order to remove the influence of deterioration of the polyethylene terephthalate itself due to the environmental standing as an acceleration test, the above-described test was performed on the glass plate (1.2 mm thickness) instead of the sheet-like polyethylene terephthalate film. A cured coating film was formed in the same process as the evaluation of hardness, and a test piece of a reflective sheet was produced.

Performance Evaluation (1) Flexibility By a cylindrical mandrel method, it was bent 180 ° with a predetermined bending radius, and the flexibility of the reflective film was evaluated by visual observation and optical microscope observation of × 200 in the following three stages.
A: No abnormality in the reflective film after bending at a bending radius of 0.1 mm.
○: After bending at a bending radius of 0.5 mm, there is no abnormality in the reflection film, but after bending at a bending radius of 0.1 mm, the reflection film has an abnormality such as cracking or peeling.
X: Abnormalities such as cracks and peeling occurred in the reflective film after bending at a bending radius of 0.5 mm.
(2) Warping property After cutting the test piece into 2 cm x 2.5 cm, place the test piece gently on a horizontal table so that the top is concave, and make sure that no external force is applied. The vertical distance between the corner and the table was measured to a unit of 1 mm with a straight scale, and the maximum value was taken as the amount of warpage, and the evaluation was made in the following three stages.
○: Warpage amount less than 5 mm.
(Triangle | delta): The curvature amount of 5-8 mm.
X: Warpage amount exceeding 8 mm.
(3) Adhesion Adhesion In accordance with JIS K5600-5-6, 100 test pieces (10 × 10) having a 1 mm square grid were provided, and a peeling test (peeling test) with a cellophane tape was conducted. The peeling state of each grid was visually observed and evaluated in the following three stages.
○: No peeling is observed in 90 or more of 100 pieces.
(Triangle | delta): Peeling is not recognized by 50 to less than 90 pieces in 100 pieces.
X: Peeling is not recognized in less than 50 in 100 pieces.
(4) Flammability The test piece was subjected to a vertical combustion test based on the UL94 standard. Based on UL94 standard, it evaluated by VTM-0-0 combustion.
(5) Diffuse reflectance (%)
Initial: With respect to the test piece after the post cure, the reflectance at 450 nm was measured with a spectrophotometer U-3410 (manufactured by Hitachi, Ltd .: φ60 mm integrating sphere).
After heating: heat resistance is evaluated for the reflectance of the reflective sheet. 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 450 nm was measured.
After humidification and heating: The weather resistance is evaluated for the reflectance of the reflective sheet. After leaving the test piece to stand at 85 ° C. and 85% RH for 1000 hours, a spectrophotometer U-3410 (manufactured by Hitachi, Ltd.) : Φ60 mm integrating sphere), the reflectance of the test piece at 450 nm was measured.

  The evaluation results of Examples 1 to 6 and Comparative Examples 1 to 6 are shown in Table 2 below.

  As shown in Table 2, from Examples 1 to 6 and Comparative Examples 1 to 6, the resins (A), (A-1), (A-2), (A-3), (A- 4) When a carboxyl group-containing copolymer resin and a compound having a quaternary alkylphosphonium cation are used as the curing accelerator as the component (B), the decrease in the diffuse reflectance of the reflective film after heating and after humidification is suppressed. I was able to. Therefore, the reflective sheet excellent in heat resistance and weather resistance could be obtained. Moreover, in Examples 1-6, the reflective sheet excellent in all of a softness | flexibility, low curvature property, and adhesiveness was able to be obtained. Further, from Examples 1 to 6 and Comparative Example 6, when a compound having a quaternary alkylphosphonium cation is used as the curing accelerator, it is possible to suppress a decrease in the diffuse reflectance of the reflective film after heating and after humidification and heating. The obtained reflective sheet was excellent in flexibility and low warpage. Further, from Example 6, when a phosphorus-based flame retardant was further blended, the flame retardancy was improved.

  The present invention provides a reflective sheet coated with a reflective film having excellent reflectivity after heating and after humidification, as well as flexibility, low warpage, and adhesion, and particularly excellent heat resistance and weather resistance. It has high utility value in the field of solar cell module backsheets that require easy handling.

Claims (9)

A reflective sheet having a reflective coating formed of a curable resin composition,
The curable resin composition is
(A-1) General formula (i)

(Wherein R ¹ represents a hydrogen atom or a methyl group);
General formula (ii)

(Wherein R ² represents a hydrogen atom or a methyl group, n1 is an integer of 2 to 4, n2 is an integer of 3 to 6, and m1 is an integer of 1 to 5). Carboxyl group-containing copolymer resin obtained by
Or (A-2) general formula (ii)

(Wherein R ² represents a hydrogen atom or a methyl group, n1 is an integer of 2 to 4, n2 is an integer of 3 to 6, and m1 is an integer of 1 to 5);
General formula (iii)

(Wherein R ³ represents a hydrogen atom or a methyl group, n3 is an integer of 2 to 6, and m2 is an integer of 1 to 5). resin,
(B) General formula (iv)

(In the formula, R ⁴ , R ⁵ , R ⁶ and R ⁷ are the same or different and are each a linear or branched alkyl group having 1 to 8 carbon atoms or a monovalent alicyclic group having 3 to 8 carbon atoms. A hydrocarbon group, which may have a hydroxyl group or an alkoxy group having 1 to 3 carbon atoms as a substituent.) A compound having a quaternary alkylphosphonium cation represented by:
A reflective sheet comprising (C) a compound having an epoxy group and (D) an inorganic white pigment. A reflective sheet having a reflective coating formed of a curable resin composition,
The curable resin composition is
(A-3) General formula (i)

(Wherein R ¹ represents a hydrogen atom or a methyl group);
General formula (ii)

(Wherein R ² represents a hydrogen atom or a methyl group, n1 is an integer of 2 to 4, n2 is an integer of 3 to 6, and m1 is an integer of 1 to 5);
General formula (v)

(Wherein R ⁸ represents a hydrogen atom or a methyl group, R ⁹ represents a phenyl group, an α-cumyl group, an alkoxy group having 1 to 10 carbon atoms, an acyl group having 1 to 10 carbon atoms in an alkyl group, and t-butyl. A group, an adamantyl group or a trifluoromethyl group, A represents a C2-C10 alkylene group or a C3-C10 hydroxyalkylene group containing a linear or cyclic skeleton, and m3 represents 0 or 1-3. An integer, p is an integer of 1 to 5.) A carboxyl group-containing copolymer resin obtained by reacting a compound represented by:
Or (A-4) general formula (ii)

(Wherein R ² represents a hydrogen atom or a methyl group, n1 is an integer of 2 to 4, n2 is an integer of 3 to 6, and m1 is an integer of 1 to 5);
General formula (iii)

(Wherein R ³ represents a hydrogen atom or a methyl group, n3 is an integer of 2 to 6, and m2 is an integer of 1 to 5),
General formula (v)

(Wherein R ⁸ represents a hydrogen atom or a methyl group, R ⁹ represents a phenyl group, an α-cumyl group, an alkoxy group having 1 to 10 carbon atoms, an acyl group having 1 to 10 carbon atoms in an alkyl group, and t-butyl. A group, an adamantyl group or a trifluoromethyl group, A represents a C2-C10 alkylene group or a C3-C10 hydroxyalkylene group containing a linear or cyclic skeleton, and m3 represents 0 or 1-3. An integer, p is an integer of 1 to 5.) A carboxyl group-containing copolymer resin obtained by reacting a compound represented by:
(B) General formula (iv)

(In the formula, R ⁴ , R ⁵ , R ⁶ and R ⁷ are the same or different and are each a linear or branched alkyl group having 1 to 8 carbon atoms or a monovalent alicyclic group having 3 to 8 carbon atoms. A hydrocarbon group, which may have a hydroxyl group or an alkoxy group having 1 to 3 carbon atoms as a substituent.) A compound having a quaternary alkylphosphonium cation represented by:
A reflective sheet comprising (C) a compound having an epoxy group and (D) an inorganic white pigment.   The reflective sheet according to claim 1 or 2, wherein the compound represented by the general formula (II) has a polycaprolactone skeleton.   The reflective sheet according to claim 1 or 2, wherein the compound represented by the general formula (III) has a polycaprolactone skeleton.   The reflective sheet according to claim 1 or 2, wherein the compound (B) having a quaternary alkylphosphonium cation is a quaternary alkylphosphonium hydroxide.   The reflective sheet according to claim 1 or 2, wherein the compound (C) having an epoxy group has two or more epoxy groups in one molecule.   Furthermore, (E) Phosphorus flame retardant is included, The reflective sheet of any one of Claims 1-6 characterized by the above-mentioned.   The reflective sheet according to claim 7, wherein the phosphorus-based flame retardant is an alkylphosphinic acid metal salt.   The solar cell module provided with the reflection sheet of any one of Claims 1-8.