JP2014019007A - Solar cell back sealing material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solar cell back sealing material having excellent partial discharge voltage property, including a coating layer having excellent adhesiveness and hydrolysis resistance with an ethylene-vinyl acetate copolymer at least on one side thereof, made of a transparent polyester having excellent ultraviolet light resistance and hydrolysis resistance.SOLUTION: A solar cell back sealing material has, at least on one side of a substrate film, a coating layer obtained through coating with a coating liquid including: polyurethane having at least one of a polycarbonate skeleton and a polyether skeleton; and a crosslinking agent. In the substrate film, an ultraviolet light absorber content is 0.6-3.5 wt%, intrinsic viscosity (IV) is 0.64 (dl/g) or more, a terminal carboxyl group amount (AV) is 26 eq./ton or less, and thickness of the entire film is 250 μm or more.

Description

  The present invention has an application layer having an adhesive property excellent in hydrolysis resistance with an ethylene vinyl acetate copolymer (hereinafter sometimes abbreviated as EVA) on the side to be bonded to EVA, and the outermost layer (mainly Further, the present invention relates to a solar cell back surface sealing material having a good partial discharge voltage, which has a polyester layer excellent in ultraviolet resistance and hydrolysis resistance on the side not adhered to EVA.

  Photovoltaic power generation that converts light energy into electrical energy using the photoelectric conversion effect is widely performed as a means for obtaining clean energy. And with the improvement of the photoelectric conversion efficiency of a photovoltaic cell, the photovoltaic power generation system has come to be provided also in many private houses. In order to use such a solar power generation system as an actual energy source, a solar cell module having a configuration in which a plurality of solar cells are electrically connected in series is used.

  The solar cell module includes a solar cell front sheet (mainly glass) / a sealing material (mainly EVA) / a photoelectric conversion layer (called a cell portion) / a sealing material (mainly EVA) / a solar cell back surface sealing material, Is a typical configuration example. As a solar cell back surface sealing material, for example, a technique using a fluorine-based film as disclosed in Patent Document 1 is disclosed. However, since the fluorine-based film is expensive, there is a problem that the price of the solar cell back surface sealing material is also expensive.

  Patent Document 2 describes an invention relating to a solar cell back surface sealing material comprising a hydrolysis-resistant resin film, a metal oxide-coated resin film, and a white resin film. Since the said invention has provided the film with low hydrolysis resistance inside, a metal oxide coating resin film is required. Therefore, it is necessary to bond three films via an adhesive, which is not preferable because of high cost.

Japanese Patent Laid-Open No. 11-186575 Japanese Patent Laid-Open No. 2002-100788

  The present invention has been made in view of the above circumstances, and the problem to be solved is an application having adhesiveness excellent in hydrolysis resistance with an ethylene vinyl acetate copolymer (hereinafter sometimes referred to as EVA). An object of the present invention is to provide a solar cell back surface sealing material having a partial discharge voltage and having a layer on at least one side and made of a transparent polyester excellent in ultraviolet resistance and hydrolysis resistance.

  As a result of intensive studies in view of the above circumstances, the present inventors have found that the above-mentioned problems can be solved by using a polyester film having a specific configuration, and have completed the present invention.

  That is, the gist of the present invention has a coating layer obtained by applying a coating solution containing a polyurethane having at least one of a polycarbonate skeleton or a polyether skeleton and a crosslinking agent on at least one surface of the base film, The ultraviolet absorber content of the base film is 0.6 to 3.5 weight, the intrinsic viscosity (IV) is 0.64 dl / g or more, and the terminal carboxyl group amount (AV) is 26 equivalents / t or less. And the thickness of the entire film is 250 μm or more.

  According to the present invention, the coating layer having an adhesive property excellent in hydrolysis resistance with an ethylene vinyl acetate copolymer (hereinafter sometimes referred to as EVA) is provided on at least one side, and has ultraviolet resistance and water resistance. It is possible to provide a solar cell back surface sealing material that is made of transparent polyester excellent in decomposability and has good partial discharge characteristics. The industrial value of the present invention is high.

  The polyester film referred to in the present invention is a film stretched after cooling a molten polyester sheet extruded by a so-called extrusion method, which is melt-extruded from an extrusion die.

  In the present invention, the polyester used for the polyester film refers to a polyester obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol. Examples of the aromatic dicarboxylic acid include terephthalic acid and 2,6-naphthalenedicarboxylic acid. Examples of the aliphatic glycol include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol. Representative polyesters include polyethylene terephthalate (PET), polyethylene-2,6-naphthalenedicarboxylate (PEN), and the like. Among these, polyethylene terephthalate (PET) is preferable.

  As for the amount of the compound in the polyester film of the present invention, it is desirable that titanium element and phosphorus element are detected by analysis using a fluorescent X-ray analyzer, and that the content of magnesium element content is in a specific range.

  The titanium element content in the polyester film of the present invention is preferably 2 ppm or more. When the titanium element is less than 2 ppm, the productivity at the time of producing the polyester raw material is inferior, and the polyester raw material reaching the target degree of polymerization cannot be obtained. On the other hand, the upper limit of the titanium element content in the polyester film is not particularly limited, but a preferred range is 20 ppm or less, a more preferred range is 15 ppm or less, and a particularly preferred range is 9 ppm or less. When there is too much content of a titanium compound, an oligomer will be easy to byproduce in the process of melt-extruding polyester, and it will become a polyester film which the oligomer precipitated on the surface. The surface oligomer of the polyester film becomes a causative substance such as the roll is contaminated by transferring the oligomer to the roll used at the time of film formation, and the generation of film foreign matter is caused.

  The phosphorus element in the polyester film of the present invention is usually derived from a phosphoric acid compound, and is added during the production of the polyester. The phosphorus element content in the polyester film of the present invention is preferably 3 ppm or more. When the phosphorus element is less than 3 ppm, the productivity at the time of production of the polyester raw material is inferior, and the polyester raw material reaching the target degree of polymerization cannot be obtained. On the other hand, the upper limit of the phosphorus element content in the polyester film is not particularly limited, but a preferred range is 170 ppm or less, a more preferred range is 100 ppm or less, and a particularly preferred range is 50 ppm or less. If the amount of phosphorus element is too large, gelation may occur during film formation, resulting in a foreign matter, which may cause deterioration in film quality.

  Examples of phosphoric acid compounds include known ones such as phosphoric acid, phosphorous acid or ester phosphonic acid compounds, phosphinic acid compounds, phosphonous acid compounds, phosphinic acid compounds, and specific examples include regular phosphoric acid. , Dimethyl phosphate, trimethyl phosphate, diethyl phosphate, triethyl phosphate, dipropyl phosphate, tripropyl phosphate, dibutyl phosphate, tributyl phosphate, diamyl phosphate, triamyl phosphate, dihexyl phosphate, tri Examples include hexyl phosphate, diphenyl phosphate, triphenyl phosphate, and ethyl acid phosphate.

  Further, it is preferable not to contain as much as possible a metal compound that can act as a catalyst in order to suppress thermal decomposition and hydrolysis, but in order to reduce the volume resistivity value at the time of melting in order to improve the productivity of the polyester film, Metals such as calcium, lithium and manganese are contained in the film. Among these, magnesium element is particularly preferable, and the magnesium element content is 9 to 40 ppm, preferably 10 to 30 ppm. When the elemental magnesium content is less than 9 ppm, the volume specific resistance value obtained by the method described later of the polyester film is high, and thus when the film production speed during film production is high, a sheet extruded from a die called a pinning bubble A phenomenon of poor adhesion with the casting drum is likely to occur, and it becomes difficult to obtain a homogeneous film that is completely adhered and rapidly cooled. On the other hand, if the magnesium element content is 40 ppm or more, the amount of foreign matter (magnesium salt) insoluble in the polyester increases, which is not preferable.

  The above-mentioned volume resistivity value is preferably less than 40 Ω · cm, more preferably less than 35 Ω · cm, and particularly preferably less than 30 Ω · cm. When the volume resistivity is 40 Ω · cm or more, when the film production speed is high during film production, the adhesion phenomenon between the sheet extruded from a die called a pinning bubble and the casting drum is likely to occur, and the adhesion is rapidly quenched. It may be difficult to obtain a uniform film. Although there is no particular lower limit, it is practically about 3 Ω · cm.

  The method for adding the magnesium element to the polyester film is not particularly limited. (B) a method using a polyester raw material added with a magnesium compound as a catalyst during polymerization, (b) a method using a polyester raw material with a low magnesium content, and a polyester raw material added with a magnesium compound as a catalyst during polymerization; ) A method using a polyester raw material with a low magnesium content and a polyester raw material obtained by masterbatching a magnesium compound into a polyester raw material with a low magnesium content by a kneading method, and (2) producing a film with a polyester raw material with a low magnesium content. A method of adding a magnesium compound directly from an extruder at the time of film formation is exemplified, but it is not particularly limited.

  The intrinsic viscosity (IV) of the polyester is 0.64 dl / g or more, preferably 0.66 dl / g or more. When the intrinsic viscosity of the polyester is 0.64 dl / g or more, a polyester film having good long-term durability and hydrolysis resistance after wet heat treatment can be obtained. On the other hand, although there is no upper limit of the intrinsic viscosity of the polyester, it is about 0.90 dl / g from the viewpoint of the efficiency of the polycondensation reaction and the prevention of pressure increase in the melt extrusion process.

  The terminal carboxyl group amount (AV) of the polyester is 26 equivalent / t or less, preferably 23 equivalent / t or less, more preferably 20 equivalent / t or less. When the amount of terminal carboxyl groups of the polyester is 26 equivalents / t or less, a polyester film having good long-term durability and hydrolysis resistance after wet heat treatment can be obtained. On the other hand, there is no lower limit of the amount of terminal carboxyl groups of the polyester, but it is usually about 5 equivalents / t in terms of the efficiency of the polycondensation reaction, thermal decomposition in the melt extrusion process, and the like.

  In order to improve workability in the film winding process, coating process, vapor deposition process, and the like, it is desirable that the polyester film in the present invention contains fine particles. The fine particles include inorganic particles such as silica, calcium carbonate, magnesium carbonate, calcium sulfate, barium sulfate, lithium phosphate, magnesium phosphate, calcium phosphate, lithium fluoride, aluminum oxide, and kaolin, and organic particles such as acrylic resin and guanamine resin. In addition, there can be mentioned, but not limited to, precipitated particles in which the catalyst residual is made into particles. Among these particles, porous silica particles that are aggregate particles of temporary particles are particularly preferable. Since the porous silica particles are less likely to generate voids around the film when the film is stretched, the porous silica particles have the feature of improving the transparency of the film.

  The average particle diameter of primary particles constituting the porous silica particles is preferably in the range of 0.001 to 0.1 μm. If the average particle size of the primary particles is less than 0.001 μm, ultrafine particles are generated by crushing at the slurry stage, which may form aggregates and increase the number of foreign matters. On the other hand, if the average particle size of the primary particles exceeds 0.1 μm, the porosity of the particles may be lost, and as a result, the feature of generating less voids may be lost.

  Furthermore, the pore volume of the agglomerated particles is preferably in the range of 0.5 ml / g to 2.0 ml / g, preferably 0.6 ml / g to 1.8 ml / g. When the pore volume is less than 0.5 ml / g, the porosity of the particles is lost, voids are easily generated, and the transparency of the film tends to be lowered. When the pore volume is larger than 2.0 ml / g, crushing and aggregation are likely to occur, and it may be difficult to adjust the particle size.

  The method for adding particles to the polyester film in the present invention is not particularly limited, and a known method can be adopted. For example, it can be added at any stage for producing the polyester, but it is preferably added as a slurry dispersed in ethylene glycol or the like at the stage of esterification or before the start of the polycondensation reaction after completion of the transesterification reaction. The condensation reaction may proceed. Also, a method of blending a slurry of particles dispersed in ethylene glycol or water with a vented kneading extruder and a polyester raw material, or a blending of dried particles and a polyester raw material using a kneading extruder. It is done by methods.

  As the ultraviolet absorber used in the present invention, it is desirable to use an ultraviolet absorber having excellent heat resistance, good compatibility with the above-mentioned polyester, uniform dispersion, and little coloration that does not adversely affect the resin. In particular, a film having a weight loss temperature of 5% by weight or more, which is a measure of heat resistance, of 250 ° C. or more is suitable in terms of film forming properties and film characteristics.

  As an ultraviolet absorber, various adaptations, such as a benzoxazine type or a triazine type, are possible, for example. In the case of benzoxazine, 2,2 ′-(1,4-phenylene) bis [4H-3,1-benzoxazin-4-one]: a compound represented by CAS Number 18600-59-4 (for example, Cytec's CYASORB UV-3638F), if triazine, 2- [4,6-bis (2,4-dimethylphenyl) 1,3,5-triazin-2-yl] -5- (octyloxy) phenol: CAS Number 2725- Compounds represented by 22-6 (for example, Cytec's CYASORB UV-1164) and 2- (4,6-diphenyl-1,3,5 triazin-2-yl) -5-[(hexyl) oxy] -phenol : CAS Number 147315-50-2 (for example, BASF Tinuvin 1577FF) can be used.

  The ultraviolet absorber is not particularly limited, and may be used alone or in combination of two or more in some cases.

  The content of the ultraviolet absorber in the polyester is preferably 0.6% by weight or more, more preferably 1.2% by weight or more, and particularly preferably 1.7% by weight or more. When the ultraviolet absorber content is less than 0.6% by weight, the ultraviolet resistance is not satisfied. The upper limit is preferably 3.5% by weight or less, more preferably 3.0% by weight or less, and particularly preferably 2.5% by weight or less. When the UV absorber content exceeds 3.5% by weight, an increase in film haze accompanying bleeding out of the UV absorber is observed when exposed to the external environment for a long time, which is not preferable.

  In addition to the above-mentioned particles, conventionally known antioxidants, heat stabilizers, lubricants, antistatic agents, and dyes can be added to the polyester film of the present invention as necessary.

  The thickness of the polyester film of the present invention is 250 μm or more, preferably 275 μm or more. When the thickness is less than 250 μm, the partial discharge voltage is low, which is not preferable as a solar cell back surface sealing material. On the other hand, although the upper limit of the thickness is not particularly provided, it is preferably 350 μm or less from the viewpoint of handling when passing the roll during film formation.

  In the polyester film of the present invention, improved wet heat resistance with sealing materials such as EVA and polyvinyl acetal resin (hereinafter sometimes abbreviated as PVB) which are generally used as solar cell sealing materials It is preferable to provide the coating layer to be provided on at least one side of the polyester film.

  The coating liquid component for forming the coating layer preferably contains a polyurethane having at least one of a polycarbonate skeleton or a polyether skeleton, and a crosslinking agent. The polyurethane having a polycarbonate skeleton or a polyether skeleton is obtained by using a compound having a polycarbonate skeleton or a polyether skeleton as a polyol. In addition, you may have a polycarbonate frame | skeleton and a polyether frame | skeleton simultaneously.

  The polycarbonate polyol used for the polyurethane in the coating solution component for forming the coating layer can be obtained, for example, by reaction of diphenyl carbonate, dialkyl carbonate, ethylene carbonate or phosgene with a diol. Examples of the diol include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, , 6-hexanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, neo Examples include pentyl glycol, 3-methyl-1,5-pentanediol, 3,3-dimethylol heptane and the like. Among these, a polycarbonate polyol using 1,6-hexanediol is preferable because it is easily available industrially, is excellent in terms of improving adhesiveness, and is also excellent in hydrolysis resistance.

  The polycarbonate polyol has a polystyrene-equivalent number average molecular weight by gel permeation chromatography (GPC) and is preferably 300 to 5,000.

  Polyether polyols used in the coating liquid component polyurethane for forming the coating layer include polyoxyethylene polyol (polyethylene glycol, etc.), polyoxypropylene polyol (polypropylene glycol, etc.), polyoxytetramethylene polyol (polytetramethylene ether glycol, etc.) ), Copolymer polyether polyols (block copolymers and random copolymers such as polyoxyethylene glycol and polyoxypropylene glycol), and the like. Among these, polyoxytetramethylene glycol is preferable because it is excellent in terms of improving adhesiveness and also has good hydrolysis resistance.

  The polyether polyol has a number average molecular weight in terms of polyethylene glycol determined by gel permeation chromatography (GPC) and is preferably 300 to 5,000.

  The polyurethane using the above-described polycarbonate polyol or polyether polyol has better resistance to hydrolysis than the polyurethane using polyester polyol, which is another general-purpose polyol.

  Each of these polycarbonate polyols or polyether polyols may be used alone or in combination of two or more. As described above, these polycarbonate polyols and polyether polyols can be used in combination.

  Examples of the polyisocyanate used in the polyurethane as a coating solution component for forming a coating layer include known aliphatic, alicyclic, aromatic and other polyisocyanates.

  Specific examples of the aliphatic polyisocyanate include, for example, tetramethylene diisocyanate, dodecamethylene diisocyanate, hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, 2-methylpentane- Examples include 1,5-diisocyanate and 3-methylpentane-1,5-diisocyanate.

  Specific examples of the alicyclic polyisocyanate include, for example, isophorone diisocyanate, hydrogenated xylylene diisocyanate, hydrogenated diphenylmethane-4,4′-diisocyanate, hydrogenated biphenyl-4,4′-diisocyanate, 1,4-cyclohexane diisocyanate. , Hydrogenated tolylene diisocyanate, 1,3-bis (isocyanatemethyl) cyclohexane, 1,4-bis (isocyanatemethyl) cyclohexane, and the like.

  Specific examples of the aromatic polyisocyanate include, for example, tolylene diisocyanate, 2,2′-diphenylmethane diisocyanate, 2,4′-diphenylmethane diisocyanate, 4,4′-diphenylmethane diisocyanate, 4,4′-diphenyldimethylmethane diisocyanate, 4,4'-dibenzyl diisocyanate, 1,5-naphthalene diisocyanate, xylylene diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate and the like can be mentioned. These polyisocyanates may be used alone or in combination of two or more.

  Examples of chain extenders include ethylene glycol, propylene glycol, butanediol, diethylene glycol, neopentyl glycol, trimethylolpropane, hydrazine, ethylenediamine, diethylenetriamine, isophoronediamine, 4,4′-diaminodiphenylmethane, 4,4 ′. -Diaminodicyclohexylmethane, water, etc.

  The polyurethane having at least one of a polycarbonate structure and a polyether structure used as a coating solution component for forming a coating layer may be one using an organic solvent as a medium, but preferably one containing water as a medium. . In order to disperse or dissolve polyurethane in water, there are a forced emulsification type using an emulsifier, a self-emulsification type in which a hydrophilic group is introduced into a polyurethane resin, and a water-soluble type. In particular, a self-emulsification type in which an ionic group is introduced into the skeleton of a polyurethane resin to form an ionomer is preferable because of excellent storage stability of the liquid and water resistance, transparency and adhesiveness of the resulting coating layer.

  As the ionic group to be introduced, examples of the anionic group include a carboxylate group, a sulfonate group, a phosphate group, and a phosphonate group, and examples of the cationic group include quaternary ammonium. For example, carboxylic acid group as an anionic group is exemplified by dimethylolpropionic acid, dimethylolbutanoic acid, bis- (2-hydroxyethyl) propionic acid, bis- (2-hydroxyethyl) butanoic acid, trimellitic acid- Ammonium salts such as bis (ethylene glycol) ester, lower amine salts, and the like can be preferably used. Moreover, about the quaternary ammonium of a cationic group, quaternization products, such as N-alkyl dialkanolamines, such as N-methyldiethanolamine and N-ethyldiethanolamine, can be used preferably. Among these ionic groups, when the carboxylate is a base and the counter ion is an organic amine having a boiling point of 150 ° C. or lower such as ammonia or triethylamine, an oxazoline-based crosslinking agent or a carbodiimide-based crosslinking agent described later It is particularly preferable in that it has a high reactivity with and increases the crosslink density of the coating layer.

  As a method for introducing an ionic group into the urethane resin in the coating solution component for forming the coating layer, various methods can be taken in each stage of the polymerization reaction. For example, at the time of prepolymer synthesis, a resin having an ionic group can be used as a copolymerization component, or a component having an ionic group can be used as one component such as a polyol or a chain extender.

  In the coating liquid component for forming the coating layer, in addition to the above-described polyurethane, it is necessary to use a crosslinking agent together in order to impart heat resistance, heat-resistant adhesiveness, moisture resistance, and blocking resistance to the coating layer. This cross-linking agent is preferably water-soluble or water-dispersible. Specifically, in addition to melamine compounds, benzoguanamine compounds, urea compounds, acrylamide compounds, which are methylolated or alkoxymethylolated, epoxy compounds It is preferable to contain at least one selected from an isocyanate compound, a carbodiimide compound, an oxazoline compound, a silane coupling agent compound, a titanium coupling agent compound, and the like. Among these crosslinking agents, an oxazoline-based compound or a carbodiimide-based compound, which is a polymer itself, is particularly preferable because the heat and moisture resistance adhesion of the coating layer is greatly improved. Such an oxazoline-based cross-linking agent is commercially available, for example, under the trade name Epocross (registered trademark) of Nippon Shokubai Co., Ltd., and a carbodiimide-based cross-linking agent is commercially available, for example, under the trade name Carbodilite (registered trademark) of Nisshinbo Chemical Co., Ltd. . Moreover, the addition amount of these crosslinking agents is 10: 90-90: 10 by the weight ratio with respect to the polyurethane in the coating liquid component for coating layer formation, Preferably it is used in the ratio of 20: 80-80: 20. Is preferred.

  In the coating solution component for forming the coating layer, the total of the polyurethane and the crosslinking agent component described above is preferably present in an amount of 50% by weight or more, and more preferably 75% by weight or more. In addition to these resin components, other resins can be additionally added. Examples of the resin component that can be additionally added include polyester resins, acrylic resins, polyvinyl resins, and polyester polyurethane resins. However, polyester resins and polyester polyurethane resins are often poor in hydrolysis resistance, and these resins are preferably not added to the coating layer, or even if added, the added amount is preferably less than 10% by weight.

  In addition, in order to prevent blocking of the coating layer and to impart slipperiness, it is also possible to add fine particles to the coating solution component for forming the coating layer. As fine particles, for example, inorganic particles such as silica, alumina, and metal oxide, or organic particles such as crosslinked polymer particles can be used. The size of the fine particles is 150 nm or less, preferably 100 nm or less, and the addition amount in the coating layer is preferably selected in the range of 0.5 to 10% by weight.

  In addition, components other than those described above can be included in the coating solution component for forming the coating layer, if necessary. For example, surfactants, antifoaming agents, coatability improvers, thickeners, antioxidants, antistatic agents, foaming agents, dyes, pigments and the like. These additives may be used alone or in combination of two or more.

  The coating layer is preferably formed by coating on a polyester film as a coating solution mainly using water as a medium. The polyester film to be applied may be biaxially stretched in advance, but it is preferable to use a so-called in-line coating method in which the polyester film is stretched in at least one direction after being applied and further heat-set.

  Any known method can be applied as a method of applying the coating solution to the polyester film as the substrate. Specifically, roll coating method, gravure coating method, micro gravure coating method, reverse coating method, bar coating method, roll brush method, spray coating method, air knife coating method, impregnation method, curtain coating method, die coating method, etc. It can be applied alone or in combination.

Next, a method for forming the coating layer will be described.
The coating layer in the present invention has a coating amount of 0.005 to 1.0 g as a final dry film after being dried and solidified or after being biaxially stretched or heat-set. / M ² , more preferably 0.01 to 0.5 g / m ² . In the coating amount is less than 0.005 g / m ^2, there is a tendency that adhesion becomes insufficient, when it exceeds 1.0 g / m ² is no longer the adhesive is saturated, such as blocking the reverse There is a tendency that the adverse effects of are likely to occur.

  Analysis of the components in the coating layer can be performed by surface analysis such as TOF-SIMS.

  In the present invention, the drying and curing conditions for forming the coating layer on the polyester film are not particularly limited. For example, when the coating layer is provided by off-line coating, it is usually 3 to 40 at 80 to 200 ° C. The heat treatment may be performed for 2 seconds, preferably 100 to 180 ° C. for 3 to 40 seconds.

  On the other hand, when the coating layer is provided by in-line coating, heat treatment is usually performed at 70 to 280 ° C. for 3 to 200 seconds as a guide.

  Further, irrespective of off-line coating or in-line coating, heat treatment and active energy ray irradiation such as ultraviolet irradiation may be used in combination as required. The polyester film constituting the laminated polyester film in the present invention may be subjected to surface treatment such as corona treatment or plasma treatment in advance.

  The polyester film used as the solar cell back surface sealing material of the present invention may be a single-layer film using one polyester melt extruder, or two layers by so-called coextrusion using two or three or more. It is good also as the above laminated film.

  Hereinafter, although the manufacturing method of the polyester film of this invention is demonstrated concretely, as long as the summary of this invention is satisfied, this invention is not specifically limited to the following illustrations.

  That is, a dried or undried polyester chip (polyester component) by a known method is supplied to a kneading extruder, heated to a temperature equal to or higher than the melting point of the polyester component, and melted. Next, the melted polyester is extruded from a die, and rapidly cooled and solidified on a rotary cooling drum so that the temperature is equal to or lower than the glass transition temperature, thereby obtaining a substantially amorphous unoriented sheet. In this case, in order to improve the flatness of the sheet, it is preferable to improve the adhesion between the sheet and the rotary cooling drum. In the present invention, the electrostatic application adhesion method and / or the liquid application adhesion method are preferably employed. Even in the melt extrusion process, the amount of terminal carboxyl groups increases depending on the conditions. Therefore, in the present invention, it is necessary to shorten the residence time of the polyester in the extruder in the extrusion process. Dry sufficiently so that the amount is 50 ppm or less, preferably 30 ppm or less. When a twin screw extruder is used, a vent port is provided, and a reduced pressure of 40 hectopascals, preferably 30 hectopascals, more preferably 20 hectopascals or less. A method such as maintaining the above is adopted.

  In the present invention, the sheet thus obtained is stretched biaxially to form a film. Specifically describing the stretching conditions, the unstretched sheet is preferably stretched 2 to 6 times at 70 to 145 ° C. in the machine direction to form a uniaxially stretched film, and then 90 to 160 ° C. in the transverse direction. Then, the film is stretched 2 to 6 times and moved to a heat setting step at 180 to 245 ° C.

  In the present invention, the polyester film can be obtained by shortening the residence time of the polyester component in the extruder in the extrusion process of the polyester chip, for example, in order to set the terminal carboxyl group amount of the polyester component in the polyester film in a specific range. . Moreover, you may obtain the polyester film whose terminal carboxyl group amount is a specific range by forming the polyester chip of low terminal carboxyl group amount into a film. In film production, if a recycled material that has undergone a melting step is blended, the amount of terminal carboxyl groups of the polyester component tends to increase outside a specific range. Therefore, it is preferable not to blend such a recycled material in the present invention. Moreover, even if it mix | blends a reproduction | regeneration raw material, it is preferable to use the flakes obtained by grind | pulverizing the film obtained by itself as it is, and about 40 weight% or less about an amount, More preferably, it is 20 weight% or less.

  In the present invention, a coating layer is formed on one side or both sides of the film in order to impart adhesiveness, antistatic property, slipperiness, releasability, etc. to the film in or after the stretching step, or corona treatment. It is also possible to perform a discharge treatment such as.

  The solar cell back surface sealing material comprising the polyester film of the present invention requires that the coating layer on the polyester film is provided on at least one side. If there is no coating layer, EVA and the solar cell back surface sealing material which consists of the polyester film of this invention will not adhere | attach.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples unless it exceeds the gist of the present invention. In addition, the measurement and evaluation method of various physical properties of a film are shown below.

<Intrinsic viscosity dl / g>
When sampling polyester chips, grind them. When sampling a polyester film, the necessary amount is appropriately cut in advance with a cutter or scissors.
The obtained sample is precisely weighed and added to phenol / tetrachloroethane = 50/50 (weight ratio) to 1.0 (g / dl). After dissolving at 120 ° C. for 10 minutes, the mixture was gradually cooled to room temperature. Using a capillary viscometer, the flow time of the solution and the flow time of the solvent alone were measured, and the intrinsic viscosity was calculated from the time ratio using the Huggins equation. At that time, the Huggins constant was assumed to be 0.33.

<Terminal carboxyl group equivalent / t>
When sampling polyester chips, grind them. When sampling a polyester film, the necessary amount is appropriately cut in advance with a cutter or scissors.
Once the sample is obtained, it is dried for 15 minutes at 140 ° C. in a hot air dryer, 1.0 g from the sample cooled to room temperature in a desiccator is accurately weighed and collected in a test tube, and 30 ml of benzyl alcohol is added and dried. The solution was dissolved at 195 ° C. for 3 minutes while blowing nitrogen gas, and then 50 ml of chloroform was gradually added and cooled to room temperature.
Add 1-2 drops of phenol red indicator to the resulting solution and titrate with 0.1 (N) benzyl alcohol solution of caustic soda while blowing dry nitrogen gas, and finish when it turns from yellow to red It was. It is assumed that 1.0 g of the polyester raw material is contained in the supernatant. Further, as a blank, the same operation was carried out without a polyester resin sample, and the acid value was calculated by the following formula.
Acid value equivalent / t = (A−B) × 0.1 × f / W
[Where A is the amount of benzyl alcohol solution of 0.1N caustic soda required for titration (μl), B is the amount of benzyl alcohol solution of 0.1N caustic soda required for titration with a blank (μl) , W is the amount (g) of the polyester resin sample, and f is the titer of the benzyl alcohol solution of caustic soda of 0.1 (N). ]

The titer (f) of a 0.1 (N) caustic soda benzyl alcohol solution was obtained by collecting 5 ml of methanol in a test tube, adding 1 to 2 drops of phenol red ethanol solution as an indicator, and adding 0.1 (N ) Titration with 0.4 ml of a benzyl alcohol solution of caustic soda, and then adding 0.2 ml of 0.1 (N) aqueous hydrochloric acid solution having a known titer as a standard solution, and adding 0.1 (N) again. N) The solution was titrated with the benzyl alcohol solution of caustic soda to the discoloration point (the above operation was performed under blowing of dry nitrogen gas). The titer (f) was calculated by the following formula.
Titer of aqueous solution of hydrochloric acid with titer (f) = 0.1 (N) × amount of collected aqueous solution of hydrochloric acid with 0.1 (N) (μl) / titration of benzyl alcohol solution of caustic soda with 0.1 (N) (Μl)

<UV resistance>
(1) Ultraviolet irradiation device Super Xenon weather meter made by Suga Test Instruments: SX75
(2) Ultraviolet irradiation equipment conditions Irradiance: 180 W / m2 (in the range of 300-400 nm)
Filter: Inner / Outer = Quartz / # 275
Black panel temperature: spraying / non-spraying = non-control / 63 ° C
Test bath temperature: spraying / non-spraying = 28 ° C./non-control Test bath humidity: spraying / non-spraying = 95% RH / 50% RH
Cycle time: spraying / non-spraying = 18 minutes / 102 minutes (3) Evaluation method Using a super xenon weather meter: SX75 (manufactured by Suga Test Instruments), the polyester film is treated under the above-mentioned conditions. With Autograph AG-I (manufactured by Shimadzu Corp.), the tensile elongation at break as a mechanical property of the film was measured at a speed of 200 mm / min with respect to the direction (TD) perpendicular to the film forming direction of the obtained film. Measure and obtain the tensile elongation at break rate. The tensile breaking elongation retention rate is obtained from the following formula, that is, the quotient of the tensile breaking elongation before and after ultraviolet irradiation.
Tensile elongation at break [%] = “tensile elongation at break after super xenon weather meter treatment” ÷ “tensile elongation at break before super xenon weather meter treatment” × 100
The tensile fracture elongation retention rate after 300 hours of ultraviolet radiation was evaluated according to the following criteria.
◎: 60% or more ○: 40% or more and less than 60% △: 20% or more and less than 60% ×: less than 20%

<Hydrolysis resistance test>
Using a personal pressure cooker (manufactured by Hirayama Seisakusho), the polyester film is treated in an atmosphere of 120 ° C.-100% RH. With Autograph AG-I (manufactured by Shimadzu Corporation), the tensile breaking elongation as a mechanical property of the film is measured at a speed of 200 mm / min with respect to the film forming direction (MD) in the same direction as the film forming direction. Measure and obtain the tensile elongation at break rate. The tensile breaking elongation maintenance ratio is obtained from the following formula, that is, the quotient of the tensile breaking elongation before and after the personal pressure cooker treatment.
Tensile rupture elongation retention rate [%] = “tensile rupture elongation after personal pressure cooker treatment” ÷ “tensile rupture elongation before personal pressure cooker treatment” × 100
From the time when the tensile elongation at break maintenance rate reached less than 10%, the following criteria were used for evaluation.
A: Time at which the tensile fracture elongation maintenance ratio reached less than 10%: 84 hr or more O: Time at which the tensile fracture elongation maintenance ratio reached less than 10%: 72 hr or more and less than 84 hr Δ: Tensile fracture elongation maintenance ratio of 10 Time when it reached less than%: 60 hr or more and less than 72 hr x: Time when the tensile fracture elongation retention rate reached less than 10%: less than 60 hr

<EVA adhesiveness>
Two pieces of polyester film having a length of 300 mm and a width of 25 mm were cut out so that the longitudinal direction was MD. On the other hand, one piece of the EVA film having a length of 50 mm and a width of 25 mm was cut out and stacked so that the EVA film was sandwiched between the application layer surfaces of the two pieces of the polyester film. This was laminated using a heat seal device (TP-701-B manufactured by Tester Sangyo Co., Ltd.). The EVA film used was 485 (standard curing type, thickness 0.5 mm) manufactured by Etimex, Germany, and the heat seal conditions were a temperature of 150 ° C. and a pressure of 0.13 MPa for 20 minutes. In order to measure the adhesive strength with EVA, first, a sample having a length of 300 mm and a width of 15 mm is cut out from a polyester film / EVA film laminate piece having a width of 25 mm. The non-laminated end of this 15 mm wide polyester film piece is mounted in a tensile / bending tester (EZGraph manufactured by Shimadzu Corporation). Subsequently, the force (adhesive strength) required to separate the polyester film / EVA film laminate at an angle of 180 ° and a speed of 100 mm / min was measured for 10 samples, and the average values were classified as follows. did.
◎: Adhesive strength is 50 N / 15 mm width or more ○: Adhesive strength is 30 N / 15 mm width to less than 50 N / 15 mm width Δ: Adhesive strength is 10 N / 15 mm width to less than 30 N / 15 mm width ×: Adhesive strength is less than 10 N / 15 mm width

<Heat and heat resistant EVA easy adhesion>
Using the polyester film / EVA film laminate 25 mm wide test piece prepared above, a polyester film was prepared in an atmosphere of 120 ° C.-100% RH using a personal pressure cooker device (manufactured by Hirayama Seisakusho). Wet heat treatment for hours. Next, after adjusting the temperature and humidity at 23 ° C. × 50% RH for 24 hours, a measurement sample having a width of 15 mm is cut out from the sample, and the force (adhesion) required for separating the polyester film / EVA film laminate is cut in the same manner as described above. The average value of (strength) was determined.
From this value and the adhesive strength before the wet heat treatment, the adhesive strength retention was calculated by the following formula and judged according to the following criteria.
Adhesive strength retention rate (%) = (Adhesive strength after wet heat treatment) / (Adhesive strength before wet heat treatment)
A: Retention ratio is 70% or more B: Retention ratio is 50 to less than 70% B: Retention ratio is 30 to less than 50% X: Retention ratio is less than 30% Next, the polyester raw material used in the following examples will be described.

<Partial discharge voltage>
Partial discharge tester: Using KPD2050 (manufactured by Kikusui Electronics Co., Ltd.), the partial discharge start voltage defined in IEC61730-2 was measured according to IEC60664-1. Specific test conditions were as follows: maximum applied voltage: 1.6 kV, maximum applied voltage time: 5 seconds, threshold: starting voltage 10 pc. Evaluation is based on the following criteria.
○: 1000 V or more Δ: 900 V or more and less than 1000 V ×: less than 900 V

<Bleed resistance of UV absorber>
The film sample was held in an 85 ° C./85% RH environment and treated for 1500 hours. Evaluation is based on the difference in haze between film samples before and after the environmental treatment test.
◎: Less than 2.0 ○: 2.0 or more and less than 5.0 Δ: 5.0 or more and less than 6.0 ×: 6.0 or more

<Evaluation method of haze>
The haze of a film sample is measured with a haze meter (Nippon Denshoku NDH-300A) on the polyester film.

<Method for producing polyester (1)>
Continuous polymerization apparatus comprising one slurry preparation tank, a two-stage esterification reaction tank connected in series thereto, and a three-stage melt polycondensation tank connected in series to the second esterification reaction tank And terephthalic acid and ethylene glycol are continuously fed to the slurry preparation tank at a weight ratio of 100: 45, and an ethylene glycol solution of ethyl acid phosphate is contained as a phosphorus atom in the produced polyester resin. A slurry is prepared by continuously adding, stirring and mixing in an amount of 4 ppm by weight, and this slurry is set at 267 ° C., a relative pressure of 100 kPa, and an average residence time of 4 hours under a nitrogen atmosphere. , Continuously fed to the first stage esterification reaction tank where the reaction product exists at a flow rate of 120 kg / hr, and then the first stage esterification The reaction product was continuously transferred to a second stage esterification reaction tank set at 265 ° C., a relative pressure of 5 kPa, and an average residence time of 2 hours under a nitrogen atmosphere, and further esterified. At that time, an amount of 322 mol / ton was continuously supplied to the polyester resin producing ethylene glycol through an upper pipe provided in the second stage esterification reaction tank. In this case, the esterification rate in the second stage esterification reaction tank was 97%.

  The above esterification reaction product was continuously supplied to the first stage polycondensation reaction tank via the transfer pipe. At this time, the discharge pressure of the transfer pump provided in the transfer pipe was 500 kPa. A 0.6 wt% solution of magnesium acetate tetrahydrate in ethylene glycol is continuously added to the esterification reaction product in the transfer pipe in such an amount that the content as magnesium atoms is 7 ppm by weight with respect to the produced polyester resin. Added to. Using an addition pipe, an ethylene glycol solution of tetra-n-butyl titanate was continuously added to the resulting polyester resin in an amount such that the content as titanium atoms was 4 ppm by weight.

  The melt polycondensation reaction conditions were 269 ° C. in the first stage polycondensation reaction tank, absolute pressure 4 kPa, average residence time 1 hour, 274 ° C. in the second stage polycondensation reaction tank, 0.4 kPa absolute pressure, average residence time The time was 0.9 hours, the third stage polycondensation reaction tank was 277 ° C., the absolute pressure was 0.2 kPa, and the average residence time was 1 hour. The melt polycondensation reaction product taken out from the third stage polycondensation reaction tank is extruded from a die into a strand, cooled and solidified, cut with a cutter, and one piece of polyester resin chip having an average particle weight of 24 mg: polyester (1). The intrinsic viscosity of the polyester (1) was 0.64 dl / g, and the amount of terminal carboxyl groups was 14 equivalents / t.

<Method for producing polyester (2)>
Polyester (1) is used as a starting material, and continuously fed in a stirrer crystallizer maintained at about 160 ° C. in a nitrogen atmosphere with the chips not overlapping so that the residence time is about 60 minutes. After crystallizing, the residence time is adjusted so that the intrinsic viscosity of the resulting polyester resin is 0.83 dl / g under a nitrogen atmosphere at 215 ° C. continuously by feeding to a tower-type solid phase polycondensation device. Thus, polyester (2) was obtained by solid phase polycondensation. The amount of terminal carboxyl groups was 6 equivalent / t.

<Method for producing polyester (3)>
100 parts by weight of dimethyl terephthalate and 200 parts by weight of ethylene glycol are used as starting materials, and as a transesterification catalyst, the magnesium content per 1 t of polyester resin from which magnesium acetate tetrahydrate can be obtained is 46 g / resin t. In addition, the reaction start temperature was 150 ° C., and the reaction temperature was gradually increased as methanol was distilled off. After 4 hours, the transesterification reaction was substantially terminated.
The reaction mixture was transferred to a polycondensation tank and the average particle size 2. An ethylene glycol slurry solution composed of a mixture of 5 μm silica particles, ethyl acid phosphate, magnesium acetate tetrahydrate, and tetra-n-butyl titanate was added, and a polycondensation reaction was performed for 4 hours. That is, the temperature was gradually raised from 230 ° C. to 280 ° C. On the other hand, the pressure was gradually reduced from normal pressure, and finally 0.3 mmHg.
The amount of each compound in the ethylene glycol slurry solution is 74 g / resin t as the phosphorus element amount for ethyl acid phosphate so that the silica particles are 3.0% by weight with respect to the content of the obtained polyester. Thus, for magnesium acetate tetrahydrate, the amount of magnesium element is 46 g / resin t (including the magnesium added at the time of transesterification, the total amount of magnesium element is 92 g / resin t). -N-Butyl titanate is adjusted so that the amount of titanium element is 5 g / resin t.

  After the start of the reaction, the reaction was stopped at a time corresponding to an intrinsic viscosity of 0.60 due to a change in stirring power in the reaction tank, and the polymer was discharged under nitrogen pressure to obtain polyester (3). The intrinsic viscosity was 0.60 dl / g, and the amount of terminal carboxyl groups was 21 equivalent / t.

<Method for producing polyester (4)>
100 parts by weight of dimethyl terephthalate and 60 parts by weight of ethylene glycol are used as starting materials, and tetra-n-butyl titanate is obtained as a catalyst. The amount of titanium atoms per 1 ton of polyester resin is 5 g / resin t. In the reactor, the reaction start temperature was 150 ° C., and the reaction temperature was gradually increased as methanol was distilled off. After 4 hours, the transesterification reaction was substantially terminated. This reaction mixture was transferred to a polycondensation tank and subjected to a polycondensation reaction for 4 hours. That is, the temperature was gradually raised from 230 ° C. to 280 ° C. On the other hand, the pressure was gradually reduced from normal pressure, and finally 0.3 mmHg. After the start of the reaction, the reaction was stopped at a time corresponding to an intrinsic viscosity of 0.55 dl / g due to a change in stirring power of the reaction vessel, and the polymer was discharged under nitrogen pressure to obtain a polyester (4) chip. The intrinsic viscosity was 0.55 dl / g, and the amount of terminal carboxyl groups was 35 equivalent / t.

<Method for producing polyester (5)>
Polyester chip (4) was solid-phase polymerized at 220 ° C. under vacuum to obtain polyester (5). The intrinsic viscosity was 0.75 dl / g, and the amount of terminal carboxyl groups was 25 equivalents / t.

<Method for producing polyester (6)>
Starting from 100 parts by weight of dimethyl terephthalate and 60 parts by weight of ethylene glycol, 0.02 part of magnesium acetate tetrahydrate as a catalyst is added to the reactor, the reaction start temperature is set to 150 ° C., and the methanol is gradually distilled off. The reaction temperature was raised to 230 ° C. after 3 hours. After 4 hours, the transesterification reaction was substantially terminated. After adding 0.03 part of ethyl acid phosphate to this reaction mixture, it moved to the polycondensation tank, added 0.04 part of antimony trioxide, and performed polycondensation reaction for 4 hours. That is, the temperature was gradually raised from 230 ° C. to 280 ° C. On the other hand, the pressure was gradually reduced from normal pressure, and finally 0.3 mmHg. After the start of the reaction, the reaction was stopped at a time corresponding to an intrinsic viscosity of 0.64 due to a change in stirring power of the reaction tank, and the polymer was discharged under nitrogen pressure to obtain a polyester (6) chip. This polyester had an intrinsic viscosity of 0.64 dl / g and a terminal carboxyl group content of 45 equivalents / t.

<Production Method of Polyester (7): Triazine Compound MB>
2- (4,6-diphenyl-1,3,5triazin-2-yl) -5- [, which is a triazine-based ultraviolet absorber, while melt-kneading the polyester (2) in a vented twin-screw extruder. (Hexyl) oxy] -phenol was added to 40 wt%. A polyester (7) was obtained by extruding into a strand form from a die, solidifying by cooling, and cutting with a cutter. For the polyester component, the intrinsic viscosity was 0.47 dl / g, and the amount of terminal carboxyl groups was 40 equivalent / t.

<Production method of polyester (8): benzoxazine compound MB>
2,2 ′-(1,4-phenylene) bis [4H-3,1-benzoxazine-4, which is a benzoxazine-based UV absorber, while melt-kneading polyester (2) in a vented twin-screw extruder -ON] was added to 40 wt%. A polyester (8) was obtained by extruding into a strand form from a die, solidifying by cooling, and cutting with a cutter. For the polyester component, the intrinsic viscosity was 0.48 dl / g, and the amount of terminal carboxyl groups was 42 equivalents / t.

<Production method of polyester (9): production reference example>
In the production method of polyester (1), an attempt was made to produce a polyester by the same method except that ethyl acid phosphate was not added. At that time, the esterification rate was not increased, the polycondensation activity was low, the intrinsic viscosity of the obtained polyester resin was not increased, and the polyester was not suitable for film use.

<Production method of polyester (10): production reference example>
In the production method of polyester (1), an attempt was made to produce polyester by the same method except that tetra-n-butyl titanate was not added. At that time, the intrinsic viscosity did not increase, and the polyester was not suitable for film use.

Examples of compounds constituting the coating layer are as follows.
(Example compounds)
-Urethane U1: Polyurethane water dispersion which is polyurethane (counter ion of carboxylic acid is ammonia) composed of polytetramethylene glycol having a number average molecular weight of about 1000, dimethylolpropionic acid and isophorone diisocyanate U2: polycarbonate polyol of hexamethylenediol (number Aqueous dispersion of polyurethane (average counter weight of triethylamine) consisting of dimethylolpropionic acid and hydrogenated diphenylmethane-4,4'-diisocyanate (average molecular weight about 1000) U3: polyester of aromatic polyester and aliphatic diisocyanate DIC Corporation trade name Hydran (registered trademark) AP-40F, which is an aqueous polyurethane dispersion.

Polyester E1: DIC Corporation trade name Finetech (registered trademark) ES-670, which is an aqueous dispersion of an aromatic polyester

・ Oxazoline X1: Oxazoline-based water-soluble resin cross-linking agent Nippon Shokubai Co., Ltd. Brand name Epocross (registered trademark) WS-500
X2: Carbodiimide water-soluble resin crosslinking agent Nisshinbo Chemical Co., Ltd. Trade name Carbodilite (registered trademark) V-02-L2
X3: Water-soluble epoxy-based cross-linking agent Nagase ChemteX Corporation Brand name Denacol (registered trademark) EX-521

Silica D1: Silica fine particle aqueous dispersion (average particle diameter 60 nm)

(Example of coating solution)
A coating solution for the coating layer was prepared as shown in Table 1 below.

Example 1:
The polyester mixture obtained by mixing the polyester (2), polyester (3) and polyester (7) at a ratio of 92: 4: 4 was charged into a vented twin screw extruder. The internal diameter D of the vented twin-screw extruder was 90 mm, the discharge amount Q was 450 kg / hr, the screw rotation speed N was 100 rpm, and the pressure reduction degree of the vent hole was 5 mmHg.
The raw material is melt-kneaded at 290 ° C. in a twin-screw extruder, and the obtained melt is extruded into a slit shape. An unstretched single layer sheet was obtained by quenching and solidifying on a casting drum whose surface temperature was set to 30 ° C. using an electrostatic application adhesion method. The obtained sheet was stretched 3.3 times in the longitudinal direction at 83 ° C., and then the coating liquid 1 shown in Table 1 was applied to the lower surface of the longitudinally stretched film to preheat / laterally stretch / heat fix 1 / heat fix 2 / Film formation was carried out by guiding the temperature [° C.] in each zone of heat setting 3 / cooling to 115/135/180/215/180/125 ° C. A 300 μm thick polyester film having a coating amount (after drying) of 0.03 g / m ² was obtained. The properties and evaluation results of the obtained film are shown in Table 2 below.

Examples 2-11:
In Example 1, the polyester raw material and the coating material in the mixture were changed to the contents shown in Table 2, and the same method as in Example 1 except that the film forming speed was changed to adjust the thickness as necessary. A film was obtained. The properties and evaluation results of the obtained film are shown in Table 2.

Comparative Example 1 to Comparative Example 10:
In Example 1, the polyester raw material and the coating material in the mixture were changed to the contents shown in Table 2, and the same method as in Example 1 except that the film forming speed was changed to adjust the thickness as necessary. A film was obtained. Table 3 shows the properties and evaluation results of the obtained film.

  The solar cell back surface sealing material of this invention can be utilized suitably as a member of a solar cell.

Claims (3)

A coating layer obtained by coating a coating solution containing a polyurethane having at least one of a polycarbonate skeleton or a polyether skeleton and a crosslinking agent is provided on at least one side of the base film, and the ultraviolet absorber of the base film The content is 0.6 to 3.5 weight, the intrinsic viscosity (IV) is 0.64 (dl / g) or more, the terminal carboxyl group amount (AV) is 26 equivalents / t or less, and the whole film The solar cell back surface sealing material characterized by having a thickness of 250 μm or more. The solar cell back surface sealing material according to claim 1, wherein the ultraviolet absorber is a compound selected from a benzoxazine-based or triazine-based ultraviolet absorber. The solar cell back surface sealing material according to claim 1 or 2, wherein the crosslinking agent is a crosslinking agent comprising a polymer containing an oxazoline group or a carbodiimide group.