JP2012251102A - Curable surface coating composition, laminated polyester resin film and solar cell back sheet - Google Patents

Abstract

Provided is a curable surface coating composition in which a laminated polyester resin film having better weather resistance can be obtained more easily than in the past. A polyester resin, an organic polyisocyanate compound, and an antioxidant are provided. And / or a polyester resin having a glass transition temperature of 30 to 90 ° C. in a differential scanning calorimetry method (DSC method) as a polyester resin in a curable surface coating composition containing a light stabilizer. A curable surface coating composition, a laminated polyester resin film in which a cured film of the curable surface coating composition is laminated on a polyester resin film, and a solar battery backsheet having a multilayer structure.
[Selection] Figure 1

Description

  The present invention relates to a curable surface coating composition, a laminated polyester resin film, and a solar battery back sheet.

  The present invention is, for example, an overlay film for the purpose of surface protection, improvement in gloss, prevention of discoloration / deterioration of a marking film used on a surface of a railway vehicle, automobile, vending machine, etc. The present invention relates to a highly weather-resistant film / sheet used mainly for the purpose of protection and prevention of discoloration, such as a surface protection film for plastic windows and exterior signs, a liquid crystal display reflection sheet, and a solar cell backsheet.

  The above-mentioned high weather resistance films and sheets are commonly intended to shield and protect objects from harsh external environments, such as exposure to ultraviolet rays from direct sunlight, large temperature changes, and exposure to wind and rain. Even if there is an environmental change, it is necessary to be able to reliably protect an object without being broken for a long time.

  For example, a solar cell back sheet is a sheet intended to shield and protect a solar cell body from a severe external environment. Since solar panels are installed outdoors, they need to operate stably over a long period of time, even if they are exposed to ultraviolet rays from direct sunlight, large temperature changes, or environmental changes such as exposure to wind and rain. It is. Of course, the back sheet itself is also required to have transparency and weather resistance so that the solar cell can be visually recognized.

  In order to satisfy the above-mentioned stringent quality, the polyester resin film applied to such a solar battery backsheet is an additive such as an ultraviolet absorber or a light stabilizer in a polyester resin such as polyethylene terephthalate or polyethylene naphthalate. Has been conventionally produced by adding, kneading, and melt-extrusion molding to a required thickness.

  However, the production method as described above has a drawback that although a polyester resin film having a certain degree of transparency and weather resistance can be obtained, the production process is multi-step and cannot be obtained easily.

  In order to eliminate such defects, recently, a resin coating for providing a durable resin film on a conventional polyester resin film to which additives such as an ultraviolet absorber and a light stabilizer are not added. It has been attempted to obtain a polyester resin film excellent in transparency and weather resistance.

  As the surface coating agent for the outermost layer of the base material and the interlayer adhesive for bonding a plurality of layers, various two-component types such as a combination of a polyester polyol and a polyisocyanate compound, a combination of a polyurethane polyol and a polyisocyanate compound, etc. Although the composition is used, the required performance differs between the surface coating agent and the interlayer adhesive. For example, a simple conversion such as the use of a known interlayer adhesive for the surface coating agent has the expected performance. It is common that it is not obtained.

  Patent Document 1 describes a polyurethane-based curable surface coating composition comprising a hydroxyl group-containing acrylic resin and an organic polyisocyanate compound, to which an ultraviolet absorber and / or a hindered amine light stabilizer is added. The obtained highly weather-resistant polyester film is suggested to be applied to a solar battery back sheet, which has sufficient weather resistance even under the influence of heat, light and water, and excellent film adhesion. ing.

  Patent Document 2 describes a polyurethane-based curable surface coating composition obtained by combining an organic polyisocyanate compound and an epoxy resin with respect to an ionomer-type polyurethane resin. A solar cell backsheet coated and cured with the coating composition is also described.

  However, the cured film obtained from the curable surface coating composition as described in Patent Documents 1 and 2 described above is still in reality, although the weather resistance is not yet sufficient.

JP 2005-15557 A JP 2010-16286 A

An object of this invention is to provide the curable surface coating composition from which the laminated polyester resin film which has the more outstanding weather resistance is obtained more simply than before.
Therefore, it aims at providing the solar cell back sheet of a multilayer structure which contains at least the laminated polyester resin film more excellent in weather resistance, and the laminated polyester resin film more excellent in weather resistance.

  As a result of intensive studies in view of the above circumstances, the present inventors have found that in a curable surface coating composition containing a polyester resin, an organic polyisocyanate compound, an antioxidant and / or a light stabilizer, a polyester resin As a result, it was found that the weather resistance of the cured film can be remarkably improved by using a polyester resin having a glass transition temperature of 30 to 90 ° C., and the present invention has been completed.

  That is, the present invention relates to a curable surface coating composition comprising a polyester resin, an organic polyisocyanate compound, an antioxidant and / or a light stabilizer, and a polyester resin having a glass transition temperature of 30 to 90 ° C. as a polyester resin. A curable surface coating composition is provided.

  The present invention also provides a laminated polyester resin film in which a cured film of the curable surface coating composition is laminated on a polyester resin film. Hereinafter, the cured film is abbreviated as a cured film.

  Furthermore, this invention provides the solar cell backsheet of a multilayer structure containing at least the said laminated polyester resin film.

In the two-pack type curable surface coating composition of the present invention, since the polyester resin contained therein has a glass transition temperature of 30 to 90 ° C., a polyester resin film having superior weather resistance compared to the conventional one can be obtained. It has a particularly remarkable technical effect.
In addition, the laminated polyester resin film of the present invention is a polyester resin film having superior weather resistance compared to the conventional one because the cured film of the curable surface coating composition is laminated on the polyester resin film. It is possible to obtain a particularly remarkable technical effect.
Furthermore, since the solar cell backsheet of the present invention includes at least the laminated polyester resin film having excellent weather resistance as described above, it is a particularly remarkable technical that a solar cell backsheet having a multilayer structure having more excellent weather resistance can be obtained. There is an effect.

It is a figure which shows the one aspect | mode of the layer structure of the solar cell backsheet using the curable surface coating composition of this invention. It is a figure which shows the one aspect | mode of the layer structure of the solar cell backsheet using the curable surface coating composition of this invention. It is a figure which shows the one aspect | mode of the layer structure of the solar cell backsheet using the curable surface coating composition of this invention.

  In the two-component curable surface coating composition of the present invention, the polyester resin contained therein is a polyester resin having a glass transition temperature of 30 to 90 ° C. in a differential scanning calorimetry method (DSC method). It is characterized by being. Hereinafter, the glass transition temperature may be referred to as Tg.

  The polyester resin can be obtained, for example, by polycondensing various glycols and dibasic acids as essential raw material components. The polyester resin thus obtained is a linear (linear) polyester resin. It can also be obtained by using an ester-forming derivative such as a dibasic acid anhydride or a dibasic acid lower alkyl ester in place of the dibasic acid.

  Examples of polyester resins include aliphatic glycols such as ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, heptanediol, decanediol, and cyclohexanedimethanol, and succinic acid, adipic acid, sebacic acid, fumaric acid, and the like. Aliphatic polyester resins obtained by reacting aliphatic dibasic acids such as suberic acid, azelaic acid, 1,10-decamethylenedicarboxylic acid, and cyclohexanedicarboxylic acid as essential raw material components, such as ethylene glycol, propylene glycol, and butanediol An aromatic polyester resin obtained by reacting an aliphatic glycol with an aromatic dibasic acid such as terephthalic acid, isophthalic acid or naphthalenedicarboxylic acid as an essential raw material component may be mentioned.

  Examples of the polyester resin include “Byron” series manufactured by Toyobo Co., Ltd. and “Eritel” series manufactured by Unitika Ltd.

  The above-mentioned polyester resin tends to have a higher Tg by containing more benzene rings and naphthalene rings in the main chain. For example, the target substrate to be coated is PET (polyethylene terephthalate) or PBT ( Since affinity with polybutylene terephthalate) or PEN (polyethylene naphthalate) is increased, it is preferable to use an aromatic polyester resin rather than an aliphatic aliphatic polyester resin in the present invention. However, on the other hand, when more benzene rings and naphthalene rings are contained in the main chain, the crystallinity, the melting point, etc. tend to be increased, and the fluidity and applicability tend to be lowered.

  Therefore, in the present invention, it is more preferable to use an aromatic polyester resin having a Tg of 30 to 90 ° C. In the present invention, Tg of 30 to 55 ° C. obtained using 25 mol% or more of aliphatic glycol having 2 to 4 carbon atoms in all alcohols and 30 mol% or more of aromatic dibasic acid in all polybasic acids. It is preferable to use an aromatic polyester resin.

  In addition, since the polyester resin used by this invention is used in combination with an organic polyisocyanate compound in preparation of a surface coating agent so that it may mention later, it is preferable that it is a polyester resin containing the hydroxyl group which can act as a crosslinking point. . The polyester resin containing a hydroxyl group is a polyester resin having a hydroxyl value of 1 to 10 mgKOH / g. When crosslinked with an organic polyisocyanate compound described later, an unreacted hydroxyl group hardly remains on the surface of the cured product and is free. It is preferable in that the polyester resin in the cured product is not easily decomposed with time by radicals starting from the hydroxyl group of this group, and the excellent characteristics of the used polyester resin are easily exhibited.

  Such a hydroxyl group-containing polyester resin can be easily obtained by carrying out the reaction so that the equivalent amount of the hydroxyl group of the raw material glycol component and the equivalent amount of the acid group of the raw material dibasic acid component are excessive. Can be obtained.

  In addition to the above-mentioned essential raw material components, the polyester resin may be a tribasic or higher polybasic acid such as trimellitic acid, pyromellitic acid or an anhydride thereof, or an ester-forming derivative thereof, or trimethylolpropane. By using a small amount of a trifunctional or higher functional polyol such as pentaerythritol, a polyester resin partially having a branched structure can be obtained within a range that does not significantly impair the linear properties. In the present invention, a polyester resin partially having a branched structure can be used as long as the above Tg is satisfied.

  The polyester resin having a Tg of 30 to 90 ° C. used in the present invention is a polyester resin satisfying a number average molecular weight of 16,000 to 4,000 in the vapor pressure osmometry method (VaporPressure Osmometry method; VPO method). A polyester resin satisfying an average molecular weight of 18,000 to 4,000 is more preferable from the viewpoint of excellent weather resistance of the cured film. The above-mentioned molecular weight polyester resin is in a higher molecular weight range than the polyester polyol used in the prior art, but for example, when dissolved in an organic solvent and the polyester polyol is used without significantly impairing the fluidity of the solution It exhibits outstanding weather resistance not found in In addition, the present invention relates to a surface coating agent for a substrate, and can also solve the flame retardancy, which is a technical problem inherent in the surface coating use, which cannot be found only from application with an interlayer adhesive. Conventionally, it has been necessary to make the base material itself flame-retardant in order to make the outermost layer film flame-retardant. Specifically, the flame retardancy of a polyester film substrate includes a method of copolymerizing a flame retardant monomer during the production of the polyester resin itself of the substrate, and a method of mixing a flame retardant with a polyester resin. Although a method of melt-mixing a phosphorus compound and an inorganic compound, for example, aluminum hydroxide, as a flame retardant has been proposed, a polyester resin having a higher molecular weight range is used to some extent without adopting such a method. With the cured film of the curable surface coating agent using the above, it is possible to express outstanding flame retardancy that is not possible when an acrylic resin containing a hydroxyl group is used without performing the above-mentioned special flame retardancy. .

  As a commercially available product (trade name) of a polyester resin satisfying a Tg of 30 to 90 ° C. and a number average molecular weight of 16,000 to 2,000 suitable for the present invention, for example, Elitel UE-3210 and XA-0611 manufactured by Unitika Ltd. Can be mentioned.

  In the present invention, an organic polyisocyanate compound is used in combination in order to crosslink the above-described polyester resin. Examples of the organic polyisocyanate compound include organic compounds having at least two isocyanate groups in the molecule. Examples of the organic polyisocyanate compound include tolylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, 1,6-hexamethylene diisocyanate, isophorone diisocyanate, 4,4′-methylenebis (cyclohexyl isocyanate), lysine diisocyanate, trimethylhexamethylene diisocyanate, Polyisocyanates such as 1,3- (isocyanatomethyl) cyclohexane, 1,5-naphthalene diisocyanate, triphenylmethane triisocyanate; derivatives of polyisocyanates such as adducts, burettes and isocyanurates of these polyisocyanates (modified) Etc.).

  The organic polyisocyanate compound may be appropriately selected depending on the application to be used. However, an aromatic system such as tolylene diisocyanate may turn yellow, and if more excellent weather resistance is required, It is preferable to use alicyclic. It is not preferable that the cured coating film is colored on a transparent substrate such as a polyester resin film and the transparency is lowered in view of deterioration of visibility. Therefore, preferred in the present invention are aliphatic or cycloaliphatic organic polyisocyanates, such as hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), adducts, burettes, isocyanurates of these polyisocyanates, etc. It is preferable to use a polyisocyanate derivative (modified product).

  As such an organic polyisocyanate compound, for example, manufactured by Sumika Bayer Urethane Co., Ltd., trade name: Sumidur N3200, N3300, BL3175, N3400, N3600, VPLS2102; Asahi Kasei Kogyo Co., Ltd., Product name: Duranate E-402-90T etc. are mentioned.

  The mass ratio of the polyester resin as the main agent and the organic polyisocyanate compound as the curing agent cannot be determined unconditionally because it varies depending on the type of the main agent and the curing agent used, the content of each functional group, etc. When the sum of both in terms of mass is 100%, the proportion of use in the curing agent is usually 0.1 to 30%, particularly 1 to 10%, from the viewpoints of adhesion of the cured coating film and hydrolysis resistance. It is preferable.

  Although only an organic polyisocyanate compound may be sufficient as a hardening | curing agent, a high hydrolysis resistance can be provided with a cured coating film by using together an organic polyisocyanate compound and an epoxy resin positively.

  Examples of the epoxy resin used in the present invention include bisphenol type epoxy resins such as bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, bisphenol AD type epoxy resin, etc .; orthocresol novolac type epoxy resin, phenol Novolac epoxy resin, naphthol novolac epoxy resin, bisphenol A novolac epoxy resin, brominated phenol phenol novolac epoxy resin, alkylphenol novolac epoxy resin, bisphenol S novolac epoxy resin, alkoxy group-containing novolac epoxy resin, brominated Novolak type epoxy resins such as phenol novolac type epoxy resins; other phenol aralkyl type epoxy resins (commonly known as The Epoxidized products of lock resin), diglycidyl ether of resorcin, diglycidyl ether of hydroquinone, diglycidyl ether of catechol, biphenyl type epoxy resin, tetramethylbiphenyl type epoxy resin, sulfur-containing epoxy resin, stilbene type epoxy resin, etc. Type epoxy resin, triglycidyl isocyanurate, triphenylmethane type epoxy resin, tetraphenylethane type epoxy resin, dicyclopentadiene-phenol addition reaction type epoxy resin, biphenyl modified novolak type epoxy resin (phenol nucleus is linked by bismethylene group) Epoxidized polyhydric phenol resin), alkoxy group-containing novolac type epoxy resin, alkoxy group-containing phenol aralkyl resin, tetrabromobisphenol A type epoxy resin Resins, such as brominated phenol novolak type epoxy resins. Moreover, the said epoxy resin may be used independently and may mix 2 or more types.

  Among these epoxy resins, bisphenol-type epoxy resins are particularly low in viscosity due to their low viscosity, excellent compatibility with the main agent, and good balance between the heat resistance and strength of cured coatings. Is preferred. As the bisphenol type epoxy resin, bisphenol A is particularly excellent in fluidity at normal temperature when mixed with the main agent, and particularly in the balance between the rigidity of the cured coating film, the hydrolysis resistance, and the heat and humidity resistance. Type epoxy resin is preferred. In addition, the epoxy equivalent of the bisphenol A type epoxy resin is 150 to 700 g / eq. In the range of 150 to 250 g / eq. It is particularly preferable that the range is

  In the present invention, when an epoxy resin is used in combination, 2 to 20 parts, especially 12 to 20 parts of an epoxy resin is used per 100 parts by mass in total of the polyester resin and the organic polyisocyanate compound. It is preferable when combining excellent flexibility, adhesion and hydrolysis resistance.

  The curable surface coating composition of the present invention includes, for example, an antioxidant and a light stabilizer in order to prevent the cured product from being deteriorated by light, heat, water or the like.

  As antioxidant, a phenol type, phosphoric acid type, and a sulfur type are mentioned, for example. Specific phosphoric acid antioxidants include triphenyl phosphite, diphenylisodecyl phosphite, phenylisodecyl phosphite, 4,4′-butylidene-bis (3-methyl-6-tert-butylphenylditridecyl) ) Phosphite, octadecyl phosphite, tris (nonylphenyl) phosphite, tris (mono and / or dinonylphenyl) phosphite, diisodecylpentaerythritol diphosphite, 9,10-dihydro-9-oxa-10-phospha Phenanthrene = 10-oxide, 10- (3,5-di-t-butyl-4-hydroxybenzyl) -9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 10-decyloxy-9 , 10-Dihydro-9-oxa-10-phos Aphenanthrene, tris (2,4-di-t-butylphenyl) phosphite, cyclic neopentanetetraylbis (2,4-di-t-butylphenyl) phosphite, cyclic neopentanetetraylbis (2 , 6-di-t-butyl-4-methylphenyl) phosphite, 2,2-methylenebis (4,6-di-t-butylphenyl) octyl phosphite, tetraphenyltetra (tridecyl) pentaerythritol tetraphosphite, 2,2'-ethylidenebis (4,6-di-t-butylphenol) fluorophosphite, 4,4'-isopropylidene-diphenolalkyl (C12-C15) phosphite, bis (nonylphenyl) pentaerythritol diphos Fight, Dibutyl hydrogen phosphite, Dis Allyl pentaerythritol diphosphite, include phosphorous ester compound.

  Some light stabilizers are used as the above-mentioned antioxidants, and examples include benzotriazole, benzophenone, salicylate, cyanoacrylate, oxalic acid derivative, hindered amine (HALS), hindered phenol, and the like. Be Specific hindered amine light stabilizers include 2- (2′-hydroxy-5′-methylphenyl) benzotriazole, 3 ″, 4 ″, 2- (2′-hydroxy-5′-t-octyl). Phenyl) benzotriazole, 2- (2′-hydroxy-4′-t-octoxyphenyl) benzotriazole, 2- (2′-hydroxy-3 ′, 5′-di-t-butylphenyl) benzotriazole, 2 -(2'-hydroxy-3 ', 5'-di-t-amylphenyl) benzotriazole, 2- (2'-hydroxy-3'-dodecyl-5'-methylphenyl) benzotriazole, 2- (2' -Hydroxy-3 ′, 5′-bis (α, α-dimethylbenzyl) phenylbenzotriazole, 2- [2′-hydroxy-3 ′-(3 ″, 4 ″, 5 ″, 6) '-Tetraphthalimidomethyl) -5'-methylphenyl] benzotriazole, 2- (2'-hydroxy-3'-t-butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2- (2'- Hydroxy-3 ', 5'-di-t-butylphenyl) -5-chlorobenzotriazole, 2,2'-methylenebis [4- (1,1,3,3-tetramethylbutyl) -6- (2H- Condensation with benzotriazol-2-yl) phenol, methyl-3- [3-tert-butyl-5- (2H-benzotriazol-2-yl) -4-hydroxyphenylpropionate-polyethylene glycol (molecular weight about 300) 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-n-octoxybenzof Enone, 2-hydroxy-4-n-dodecyloxybenzophenone, 2-hydroxy-4-benzyloxybenzophenone, 2,2′-dihydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy-2′-carboxybenzophenone, 2-hydroxy-4-methoxy-5-sulfoxybenzophenone, 2,2′-dihydroxy-4,4′-dimethoxybenzophenone, 2,2 ′, 4,4′-tetrahydroxybenzophenone, 2,2′-dihydroxy- Polymer of 4,4′-dimethoxy-5-sodiumsulfoxybenzophenone, bis (5-benzoyl-4-hydroxy-2-methoxyphenyl) methane, 4- (2-acryloyloxyethoxy) -2-hydroxybenzophenone, 2,2'-dihydroxy-4,4'-dimeth A mixture of cibenzophenone and other 4-substituted benzophenones, phenyl salicylate, 2,5-di-t-butyl-4-hydroxybenzoic acid-n-hexadecyl ester, 4-t-butylphenyl salicylate, 4-t-octylphenyl salicylate, 2,4-di-t-butylphenyl-3 ′, 5′-di-t-butyl-4′-hydroxybenzoate, ethyl (β, β-diphenyl) cyanoacrylate, 2-ethylhexyl (β, β-diphenyl) cyanoacrylate, 2-ethoxy-2′-ethylsuccinic acid bisanilide, 2-ethoxy-5-tert-butyl-2′-ethylsuccinic acid bisanilide, succinic acid anilide derivatives, indole, azomethine , Phenyl-4-piperidinyl carbonate, [4- (4-hydroxy-3,5-di-t-butylphenyl Propionyl] -N- (4-hydroxy-3,5-di-t-butylphenyl) methyl-2,2,6,6-tetramethylpiperidine, 1,1 ′-(1,2-ethanediyl) bis (3 , 3,5,5-tetramethylpiperazinone), bis (2,2,6,6-tetramethyl-4-piperidinyl) sebacate, bis- [N-methyl-2,2,6,6-tetramethyl- Piperidinyl sebacate, bis (1,2,2,6,6-pentamethyl-4-piperidyl) -2- (3,5-di-t-butyl-4-hydroxybenzyl) -2-n-butylmalo 1, 2,3,4-butanecarboxylic acid, 2,2,6,6-tetramethyl-4-piperidinol and tridecyl alcohol condensate, 1,2,3,4-butanecarboxylic acid and 1 , 2,2,6,6-pentamethyl- A condensate of piperidinol and tridecyl alcohol, tetrakis (2,2,6,6-tetramethyl-4-piperidyl) -1,2,3,4-butanetetracarboxylate, tetrakis (1,2,2, 6,6-pentamethyl-4-piperidyl) -1,2,3,4-butanetetracarboxylate, poly [[6- (1,1,3,3-tetramethylbutylamino) -1,3,5- Triazine-2,4-diyl] [(2,2,6,6-tetramethylpiperidine) imino] hexamethylene [(2,2,6,6-tetramethylpiperidyl) imino]], poly [6-morpholino- s-triazine-2,4-diyl-2,2,6,6-tetramethylpiperidylimino-hexamethylene] [2,2,6,6-tetramethylpiperidylimino]], 1,2,3,4- Butanteto Carboxylic acid, 2,2,6,6-tetramethyl-4-piperidinol and β, β, β ′, β′-tetramethyl-3,9- (2,4,8,10-tetraoxaspiro [5 5] undecane) condensate with diethanol, 1,6-hexamethylenebis (N, N-dimethylsemicarbazide), 1,1,1 ′, 1′-tetramethyl-4,4 ′-(methylene-di-p -Phenylene) disemicarbazide and the like.

  As such ultraviolet absorbers, antioxidants, and light stabilizers, phosphoric acid-based antioxidants and / or hindered amine-based light stabilizers are preferable in that a cured film having better weather resistance can be obtained. In comparison with the same amount used, the hindered amine light stabilizer has a higher effect of improving weather resistance than the phosphoric acid antioxidant.

  These additives may be added in consideration of the toughness of the cured coating film itself and the adhesiveness that can follow the flexibility of the substrate to be coated, depending on the target level of weather resistance. It is preferable to use 0.1 to 15%, particularly 1 to 5% with respect to 100 parts by mass of the solid content of the coating film.

  The curable surface coating composition of the present invention can contain a carbodiimide compound. The carbodiimide group present in the carbodiimide compound is generated by hydrolysis of the ester group in either or both of the ester bond in the polyester resin and when the substrate to be coated is a polyester resin such as a PET film. Reacts instantly with carboxyl groups. Carbodiimide groups also react with water. Therefore, the carbodiimide compound contributes not only to the cured coating film but also to the hydrolysis resistance of the substrate itself by utilizing such a reaction mechanism.

  Moreover, although this carbodiimide compound can improve the hydrolysis resistance of a cured coating film by using together with a polyester resin, an organic polyisocyanate compound, and an epoxy resin, the carbodiimide group reacts with an isocyanate group, Or since carbodiimide groups react and form a crosslinked structure, the hydrolysis resistance of a cured coating film can be further improved by considering the isocyanate equivalent and usage-amount of the organic polyisocyanate compound to be used.

  As such a carbodiimide compound, for example, an organic isocyanate compound can be obtained by a decarboxylation reaction in the presence of a carbodiimidization catalyst such as phospholene oxide. Furthermore, monocarbodiimide obtained from organic monoisocyanate, polycarbodiimide obtained by capping a part of organic diisocyanate with monoalcohol or monoamine, polycarbodiimide obtained by combined use of organic monoisocyanate and organic diisocyanate, and the like can be mentioned. Examples of the organic isocyanate compound include organic monoisocyanate compounds such as phenyl isocyanate and tertiary butyl-1-phenyl isocyanate, and known conventional organic polyisocyanate compounds as described above. Specific products include DIPC (Kawaguchi Kagaku), Stabakzol (registered trademark) I (Bayer), Carbodilite (registered trademark) HMV-8CA (Nisshinbo), ELASTOSTAB (elasto stub; registered trademark) H01 (elastomer gran) AG) and the like. In the present invention, considering compatibility with a hydroxyl group-containing (meth) acrylic resin or the like, the carbodiimide compound is preferably a tetramethylxylylene diisocyanate (TMXDI) carbodiimide compound. In the present invention, the carbodiimide compound may be added in consideration of adhesion and hydrolysis resistance that can follow the flexibility of the substrate to be coated, but with respect to 100 parts by mass of the solid content of the cured coating film. 0.1 to 10%, preferably 1 to 5%.

  The curable surface coating composition of the present invention can contain a polycarbonate resin. Like the carbodiimide compound, the polycarbonate resin can improve the hydrolysis resistance of the cured coating film by using the polyester resin, the organic polyisocyanate compound and the epoxy resin in combination. Polyester resins contain ester bonds and thus have poor hydrolysis resistance. Polyether resins contain ether bonds and therefore have the disadvantage of low weather resistance and low heat resistance. Does not have such a drawback. Due to the high cohesive strength of the polycarbonate group, the cured coating film can be made more excellent in heat resistance, weather resistance, oil resistance, and chemical resistance. In the present invention, the polycarbonate resin may be added in consideration of adhesion that can follow the flexibility of the substrate to be coated and hydrolysis resistance, but with respect to 100 parts by mass of the solid content of the cured coating film. 0.1 to 10%, preferably 1 to 5%.

  As this polycarbonate resin, for example, a polycarbonate resin obtained using only dialkyl carbonate and 1,6-hexanediol can be used, but in terms of lower crystallinity, as the diol, It is preferable to use a polycarbonate diol obtained by copolymerizing 1,4-butanediol, 1,5-pentanediol or 1,4-cyclohexanedimethanol.

  Examples of such a polycarbonate diol include those having a number average molecular weight of 500 to 2000 and a hydroxyl value of 30 to 500 mgKOH / g. Among these, the number average molecular weight is liquid at room temperature and excellent in compatibility with the polyester resin. The thing of 800-1200 and a hydroxyl value of 50-250 mgKOH / g is preferable.

  Examples of the polycarbonate diol include trade names “T5650J”, “T5651”, “T5652”, “T4671”, “T4672”, or Ube Industries, Ltd., which are copolymer polycarbonate diols manufactured by Asahi Kasei Chemicals Corporation. "UM-CARB90 (1/3)", "UM-CARB90 (1/1)" and the like are commercially available.

  The curable surface coating composition of the present invention is usually prepared by preparing a main component premix in which components other than the organic polyisocyanate compound which is a curing agent are blended in advance, and mixing this with the organic polyisocyanate compound. I can do it. Since the carbodiimide compound and the polycarbonate polyol described above may react with an isocyanate group over time or instantaneously, it is preferable to add them to the main agent premix.

  From the viewpoint of adjusting the viscosity, the curable surface coating composition of the present invention, particularly the main agent described above, can contain an organic solvent that does not have reactivity with the raw material included therein and dissolves the raw material. Specifically, for example, hydrocarbon solvents such as toluene and xylene, ketone solvents such as methyl ethyl ketone and methyl isobutyl ketone, ester solvents such as ethyl acetate and butyl acetate, ether solvents such as dioxane and ethylene glycol diethyl ether , Aliphatic hydrocarbons such as pentane, hexane and heptane.

  The curable surface coating composition of the present invention may contain other additives. Examples of the additive include additives generally used in resin compositions that form films and coating films. Examples of additives include leveling agents; inorganic fine particles such as colloidal silica and alumina sol; organic fine particles based on polymethyl methacrylate; antifoaming agents; anti-sagging agents; silane coupling agents; viscosity modifiers; Metal deactivator; Peroxide decomposing agent; Flame retardant; Reinforcing agent; Plasticizer; Lubricant; Rust preventive agent; Fluorescent whitening agent; Inorganic heat absorber; Flameproof agent; Etc.

The curable surface coating composition of the present invention can be applied to a known and commonly used substrate and dried to laminate a cured coating film having adhesion on the substrate. The coating amount on the substrate is not particularly limited, but for example, selecting from the range of 1 to ²⁰ g / m ² , especially 5 to 10 g / m ² can give excellent weather resistance in a small amount. This is preferable. For this coating, for example, a gravure coater, a micro gravure coater, a reverse coater, a bar coater, a roll coater, a die coater or the like can be used.

  Examples of the substrate at this time include paper, a synthetic resin film obtained from an olefin resin or a polyester resin, a copper foil, a metal foil such as an aluminum foil, and the like. The thickness of the base material is not particularly limited, and can be selected from, for example, 10 to 400 μm. However, the curable surface coating composition of the present invention warps the base material with a small amount of application and low temperature and short time drying. It can be applied to a base material having a softening temperature of 180 ° C. or less at 30 to 80 μm because it can provide excellent adhesion without giving any influence, such as cracking and cutting, and can provide excellent weather resistance.

  Due to low temperature and short time drying, there is no inconvenience such as warping of the substrate or peeling of the coating film, and excellent adhesion to the substrate can be obtained and deterioration of the laminate can be prevented more effectively. In this respect, it is preferable to use a polyester resin film as the base material. The laminated polyester resin film in which the cured coating film of the curable surface coating composition of the present invention is laminated on the polyester resin film has the above-described excellent properties.

  Examples of the polyester resin film in this case include PET, PBT, PEN, and a film of a copolymerized polyester resin such as 1,4-cyclohexanedimethanol copolymerized polyethylene terephthalate (PET-G). Moreover, either a stretched film or an unstretched film may be used. The polyester resin film may be white or colored, but when it is prepared by selecting the raw material so that the cured coating film of the curable surface coating composition of the present invention is transparent, transparency is required for use. In this case, it is preferable to select and use a transparent polyester resin film because the laminated polyester resin film can be transparent. Of course, if necessary, as a polyester resin film, a pattern can be applied to the surface before and after lamination of the cured coating film.

  Above all, the short-time drying at a relatively low temperature of 160 ° C. or less for 1 minute or less does not cause the above-mentioned disadvantages to the thin film substrate, and the excellent adhesion to the substrate can be obtained and the moisture resistance of the laminate can be obtained. As a base material, it is preferable to use a PET film in that deterioration based on heat resistance and hydrolysis resistance can be more effectively prevented. The laminated polyester resin film in which the cured coating film of the coating composition of the present invention is laminated on a PET film has the above-described excellent properties.

  In order to improve the adhesion between the polyester resin film and the cured coating film, a surface treatment may be performed on the surface on which the cured coating film of the polyester resin film is formed. As this surface treatment, for example, corona treatment, plasma treatment, ozone treatment, flame treatment, radiation treatment and the like can be performed.

  In obtaining the laminated polyester resin film in which the cured coating film of the curable surface coating composition of the present invention is laminated on the polyester resin film, the cured coating film 1 may be provided only on one side of the polyester resin film 2. However, it may be provided on both sides. The layer structure of the laminated polyester resin film in which the cured coating film 1 is provided on one side of the polyester resin film 2 is as shown in FIG. A polyester resin-based or polyurethane resin-based easy-adhesive coating agent 3 is applied to the PET surface 2 opposite to the cured coating film 1 of the surface coating composition of the present invention of the laminated polyester resin film of FIG. A laminated polyester resin film as shown in FIG. 2 that can be bonded to a substrate can also be obtained. For distribution, a release paper (release film) is further laminated on the outside of the easy-adhesive coating agent 3 and, when in use, the laminate polyester resin film can be adhered to the substrate by peeling it off. . These laminated polyester resin films shown in FIGS. 1 and 2 can be used for a solar battery back sheet.

  For applications that receive light, heat, water, and other effects that cause deterioration from only one side, it is generally sufficient to provide a cured coating only on that side of the two surfaces of the polyester resin film. effective. However, when there is a possibility of receiving the action of light, heat or water from both sides, it is desirable to provide both sides.

  A multilayer polyester resin film having a multilayer structure including at least a laminated polyester resin film in which a cured film of the curable surface coating composition of the present invention is laminated on a polyester resin film can also be used as a solar battery backsheet.

  In order to give a further excellent gas barrier property to the solar cell back sheet, it is preferable to provide a thin film of, for example, aluminum, aluminum oxide, silicon oxide, tin oxide or magnesium oxide in the intermediate layer. For example, an adhesive having excellent adhesion between a polyester resin film and an intermediate layer having a gas barrier property on the surface of the polyester resin film 2 opposite to the cured coating film 1 of the coating composition of the present invention of the laminated polyester resin film of FIG. 4, a flexible thin film (intermediate layer) 5 of a metal or metal oxide having a gas barrier property such as a soft aluminum layer is laminated, and a polyester resin film and a gas barrier property are further formed outside the intermediate layer 5. Including a structure in which another polyester resin film 2 is laminated via an adhesive 4 excellent in adhesiveness with a certain intermediate layer so that the gas barrier intermediate layer 5 is sandwiched between the polyester resin films, The polyester resin film surface of was coated with a cured coating film of the coating composition of the present invention, Can be obtained solar cell back sheet (see FIG. 3.).

  In addition, it replaces with the polyester resin film with which the surface is untreated, PET film layer by using two polyester resin films provided with vapor deposition thin films, such as aluminum, aluminum oxide, silicon oxide, tin oxide, and magnesium oxide, on one side No adhesive layer 4 is provided between the intermediate layer 5 and the intermediate layer 5, and a cured coating film of the coating composition of the present invention is laminated on the surface opposite to the surface of the deposited thin film, and the respective deposited thin film sides are bonded to each other It is possible to obtain a solar battery back sheet similar to that shown in FIG.

  EXAMPLES Next, an Example demonstrates this invention in detail. Hereinafter, parts and% are based on mass.

As shown in Table 1 and Table 2 below, a polyester resin, an organic polyisocyanate compound, an epoxy resin, a carbodiimide compound, a polycarbonate resin, an antioxidant, a light stabilizer, a two-component type of a main component and a curing agent component Of the present invention and a conventional curable surface coating composition were prepared.
Each of the obtained curable surface coating compositions was immediately applied to a corona-treated surface of a corona-treated PET film (thickness 50 μm) manufactured by Toyobo Co., Ltd. with a bar coater so that the coating amount was 7 g / m ^2. And dried at 100 ° C. for 30 seconds to obtain each laminated polyester resin film having the layer structure of FIG.

The weather resistance was determined by using the heat and humidity resistance including the influence of hydrolysis resistance as an index. This weather resistance was evaluated using a laminated polyester resin instead of the cured coating film itself. In evaluating weather resistance, each laminated polyester resin film was subjected to a pressure cooker test (PCT) to determine how much the breaking strength and elongation strength of the laminated polyester resin film changed before and after the test. PCT was performed under conditions of a temperature of 121 ° C. × humidity of 100% × 50 hours, and each strength was measured with a Tensilon universal material testing machine manufactured by A & D Corporation.
The strength retention ratios before and after PCT are shown in Tables 1 and 2 below, where 90% or more is ◎, 89 to 70% is ○, 69 to 40% is Δ, and 39% or less is ×.

The raw materials used for the preparation of each coating composition in Table 1 and Table 2 below are as follows.
Elitel UE-3210:
Unitika Ltd. Aromatics containing hydroxyl groups, obtained using 25 mol% or more of aliphatic glycols having 2 to 4 carbon atoms in all alcohols and 30 mol% or more of aromatic dibasic acids in all polybasic acids Polyester resin. Solid content: 100%, Tg by DSC method: 45 ° C., hydroxyl value: 4 mg KOH / g, number average molecular weight by VPO method: 20,000
Elitel XA-0611:
Unitika Ltd. Aromatics containing hydroxyl groups, obtained using 25 mol% or more of aliphatic glycols having 2 to 4 carbon atoms in all alcohols and 30 mol% or more of aromatic dibasic acids in all polybasic acids Polyester resin. Solid content: 100%, Tg by DSC method: 65 ° C., hydroxyl value: 4 mg KOH / g, number average molecular weight by VPO method: 17,000
Elitel UE-9900:
Unitika Polyester resin. Solid content: 100%, Tg by DSC method: 101 ° C., hydroxyl value: 8 mg KOH / g, number average molecular weight by VPO method: 15,000
Elitel UE-3220:
Unitika Polyester resin. Solid content: 100%, Tg by DSC method: 5 ° C., hydroxyl value: 3 mg KOH / g, number average molecular weight by VPO method: 25,000
Epicron 860:
Bisphenol A type epoxy resin (manufactured by DIC Corporation). Solid content: 100%, epoxy equivalent: 240
DURANOL T-5651:
Polycarbonate diol (Asahi Kasei Chemicals Corporation). Solid content: 100%, number average molecular weight: 1000, hydroxyl value: 100-120
IRGAFOS 168:
Phosphoric acid antioxidant (manufactured by BASF Japan Ltd.). Solid content: 100%
Tinuvin 123:
A hindered amine light stabilizer (manufactured by BASF Japan Ltd.). Solid content: 100%
ELASTOSTAB H01:
TMXDI carbodiimide resin (Nisshinbo Chemical Co., Ltd.). Solid content: 100%
Sumijour N3300:
HDI polyisocyanate (manufactured by Sumika Bayer Urethane Co., Ltd.). Solid content: 100%

  As can be seen from the comparison between Example 3 and Comparative Examples 1 and 2, the curable surface coating of the present invention comprising a polyester resin having a Tg of 30 to 90 ° C., an organic polyisocyanate compound, an antioxidant and / or a light stabilizer. The composition has a higher weather resistance than the curable surface coating composition of the present invention comprising a polyester resin having a Tg outside the range specified in the present invention, an organic polyisocyanate compound, an antioxidant and / or a light stabilizer. It is clear that it is excellent in nature.

  Moreover, as can be seen from the comparison between Example 1 and Example 3, the curable surface coating of the present invention comprising a polyester resin having a Tg of 30 to 55 ° C., an organic polyisocyanate compound, an antioxidant and / or a light stabilizer. The composition is more excellent in weather resistance than the curable surface coating composition of the present invention comprising a polyester resin having a Tg of 65 ° C., an organic polyisocyanate compound, an antioxidant and / or a light stabilizer. Is obvious.

Flame retardance:
The test piece (20 × 5 cm) of the laminated polyester resin film obtained in Examples 1 to 3 was wound in a cylindrical shape, attached vertically to a clamp, and subjected to a 3 second indirect flame with a 20 mm flame twice. When the sex classification was determined, both were not found in the laminated polyester resin film obtained in the same way using a hydroxyl group-containing acrylic resin instead of UE-3210 or XA-0611. A laminated polyester resin film having excellent properties was obtained.

  Since the curable surface coating composition of the present invention has more excellent weather resistance, for example, surface protection, gloss improvement, and discoloration of a marking film used on a surface of a railway vehicle, automobile, vending machine, etc.・ Mainly protect and fade discoloration of precision parts such as overlay film for preventing deterioration, surface protection film for plastic windows and exterior signs for vehicles and houses, LCD sheet reflective sheet, solar cell back sheet, etc. It is possible to provide a highly weather resistant film / sheet used for the purpose of prevention.

1 Cured product (cured coating film) of the coating composition of the present invention
2 PET film 3 Adhesive coating agent 4 Adhesive 5 Soft aluminum

Claims (8)

In a curable surface coating composition containing a polyester resin, an organic polyisocyanate compound, an antioxidant and / or a light stabilizer, a differential scanning calorimetry method (DSC method) is used as a polyester resin. A curable surface coating composition comprising a polyester resin having a glass transition temperature of 30 to 90 ° C. The curable surface coating composition according to claim 1, further comprising an epoxy resin. 2. The curable surface coating composition according to claim 1, wherein the polyester resin is a polyester resin that further satisfies a number average molecular weight of 16,000 to 4,000 in a vapor pressure osmometry method (VaporPressure Osmometry method; VPO method). The curable surface coating composition according to any one of claims 1 to 3, wherein the antioxidant and / or the light stabilizer is a phosphorus antioxidant and / or a hindered amine light stabilizer. Furthermore, the curable surface coating composition as described in any one of Claims 1-4 containing a carbodiimide compound. Furthermore, the curable surface coating composition as described in any one of Claims 1-5 containing a polycarbonate resin. The laminated polyester resin film by which the hardened | cured material film of the curable surface coating composition as described in any one of Claims 1-6 was laminated | stacked on the polyester resin film. A solar cell backsheet having a multilayer structure, comprising at least the laminated polyester resin film according to claim 7.

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