JP2012084719A - Laminate polyester film for solar cell surface protective sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminate polyester film for solar cell surface protective sheets which excels in durability, transparency, and workability.SOLUTION: The laminate polyester film for solar cell surface protective sheets is a three-layered laminate polyester film having an outermost layer and a central layer, consisting of polyester which is polymerized using a polycondensation catalyst containing aluminum and/or its compound and a phenol based compound. The outermost layer contains particles, while the central layer does not essentially contain particles, where the haze is 5% or less, the total light transmittance is 85% or more, carboxyl terminal concentration with respect to polyester is 25 eq/ton or less, and the intrinsic viscosity is 0.60 to 0.90 dl/g. On the surface of the laminate polyester film, the number of protrusions in height of 1 μm or more is 10 pcs. to 100 pcs. per 1000 cm, both ends inclusive.

Description

  The present invention relates to a laminated polyester film for a solar cell surface protective sheet having excellent processability and having excellent transparency and durability when used in a solar cell surface protective sheet.

  In recent years, solar cells have attracted attention as an energy means to replace petroleum energy that causes global warming, and the demand for solar cells has increased. A solar cell is a solar power generation system that directly converts solar energy into electricity, and the heart of the solar cell is made of a semiconductor. As a structure thereof, a single solar cell element is not used as it is, and generally several to several tens of solar cell elements are wired in series and in parallel, for a long time (about 20 years or more). In order to protect the device, various parsing is performed and unitized. The unit incorporated in this package is called a solar cell module. Generally, the surface that is exposed to sunlight is covered with glass, the gap is filled with a filler made of a thermoplastic resin, and the back surface is backed with a heat-resistant or weather-resistant plastic material. It is the structure protected by the protective sheet which has a some layer structure called a sheet | seat.

  Conventionally, it has been common to use glass as a surface protection member of a solar cell module. In recent years, interest has increased in plastic films such as polyester having flexibility in terms of impact resistance and weight reduction (Patent Documents 1, 2, and 3). However, since it is difficult to maintain performance corresponding to glass with only a plastic film, it has been proposed to stack functional layers such as a moisture-proof layer, a durable layer, and an ultraviolet absorption layer by metal deposition.

JP 2010-186932 A JP 2007-253463 A JP 2006-261287 A

  In order to improve the conversion efficiency of the solar cell, it is advantageous that the amount of light reaching the solar cell element is large. Therefore, it is desirable for the surface protection sheet to maintain high transparency. However, in order to cope with a high line speed from the viewpoint of productivity, it is necessary to add lubricant particles in the film to achieve a predetermined slip property. Therefore, it is calculated | required to make these highly compatible as a film for solar cell surface protection sheets.

  Moreover, when it is used outdoors as a solar cell surface protection sheet for a long period of time, the hydrolysis of the polyester tends to proceed. Conventionally, a durable layer such as a fluororesin layer has been laminated. However, it has been difficult to maintain high transparency in order to maintain the conversion efficiency of the solar cell.

  Furthermore, the solar cell surface protective sheet film may be provided with various functional layers, for example, a barrier layer such as a metal vapor-deposited layer. It is necessary to control the shape. That is, if the polyester film used for the backsheet has a protrusion having a height of 1 μm or more, the metal thin film layer and the durable layer are scratched or dented. Therefore, it turned out that moisture resistance falls locally and has a big influence on the lifetime of a solar cell.

  That is, this invention makes it a subject to provide the polyester film which is excellent in workability and has the transparency and durability which were excellent when it used for the solar cell surface protection sheet.

The above-described problem can be achieved by the following solution means.
1st invention of this invention is a laminated polyester film which consists of 3 layers which have an outermost layer and a center layer, and the said laminated polyester film uses the polycondensation catalyst containing aluminum and / or its compound, and a phenol type compound. The outermost layer contains particles, the central layer is substantially free of particles, the haze is 5% or less, the total light transmittance is 85% or more, and the carboxyl end concentration is It is 25 eq / ton or less with respect to the polyester, the intrinsic viscosity is 0.60 to 0.90 dl / g, and the number of protrusions having a height of 1 μm or more is 10 to 100 per 1000 cm ² on the surface of the laminated polyester film. It is the laminated polyester film for solar cell surface protection sheets which is not more than one.
In a second aspect of the present invention, the particles contained in the outermost layer are at least one inorganic particle selected from calcium phosphate, titanium oxide, silica, alumina, calcium carbonate, and barium sulfate, and the average particle diameter of the particles Is 0.1 to 3.0 μm, and the content of particles in the outermost layer is 0.01 to 0.20% by mass.
A third invention of the present invention is the laminated polyester film for a solar cell surface protective sheet, wherein the particles are porous silica.
4th invention of this invention is a laminated polyester film for the said solar cell surface protection sheet which contains a ultraviolet absorber in the said center layer.
According to a fifth aspect of the present invention, there is provided a coating having a coating layer comprising at least one of a copolyester resin, an acrylic resin, and a polyurethane resin as a main component on at least one surface of the laminated polyester film for solar cells. It is the laminated polyester film for solar cell surface protection sheets with a layer.

The laminated polyester film for solar cell surface protective sheet of the present invention is excellent in durability, transparency, and workability, and has projections having a height of 1 μm or more of 100 pieces / 1000 cm ² or less, and is used for a solar cell surface protective sheet. Effective in maintaining moisture resistance.

On the surface of the laminated polyester film of the present invention, the number of protrusions having a height of 1 μm or more is 100 or less per 1000 cm ² . When the number of the protrusions exceeds 100, when a functional layer such as a moisture-proof layer is laminated and used for the solar cell surface protective sheet, the moisture-proof property may deteriorate due to long-term use. The upper limit of the number of protrusions is preferably smaller, more preferably 95 or less, still more preferably 80 or less, and still more preferably 70 or less. The lower limit of the protrusions is preferably 10. If the number is less than 10, suitable slipperiness cannot be obtained, and it may be difficult to cope with a line speed suitable for high productivity.

  In order to control the projection height on the film surface, it is desirable to set the addition amount of the inert particles and the average particle diameter in the film within a predetermined range as described later, but other than that, the height is 1 μm or more. As a result of examining the formation factors of the protrusions, the present inventor has obtained the following knowledge.

  Conventionally, antimony trioxide has been widely used as a polyester polymerization catalyst used during polycondensation of polyester. Antimony trioxide is an inexpensive catalyst having excellent catalytic activity. However, when it is used in an amount of a main component of the polycondensation catalyst, that is, a practical polymerization rate, it is heavy. At the time of condensation, antimony trioxide is reduced to produce metal antimony particles of 10 μm or less. And in the melt extrusion process at the time of film manufacture, metal antimony particles aggregate and come to exist in a film as a foreign material of 20-50 micrometers, and this may become a processus | protrusion with a height of 1 micrometer or more. In particular, metal antimony tends to become a crystal nucleus of polyester and easily forms aggregates that are difficult to deform, and this tendency is remarkable.

  In addition, when a germanium compound is used as a polycondensation catalyst at the time of manufacture of the polyester which is the raw material of the film, it is expensive and is not preferable for production on an industrial scale. Further, when a titanium compound is used, since the heat resistance is poor, it may be difficult to obtain a film having high transparency suitable for the surface protection sheet because it is yellowed during the solid phase polymerization described later.

  Furthermore, in order to impart slipperiness to the polyester film, for example, a lubricant having a particle size of about 0.1 to 10 μm is added. However, since these lubricants easily form aggregates, the addition of the lubricant causes a height of 1 μm. It is easy to form the above protrusions.

  Therefore, the present inventor has intensively studied to suppress aggregation of metal antimony particles due to antimony oxide and aggregation of lubricant, which are factors of surface protrusions. As a result, the inventors have found that surface projections can be suppressed within a suitable range by using polyester polymerized by a specific catalyst as described below, and further having a specific layer structure. Then, the aspect of this invention is explained in full detail below.

  The polycondensation catalyst used when polymerizing the polyester which is the main component of the film of the present invention contains a catalyst containing aluminum and / or its compound and a phenol compound, and contains aluminum and / or its compound and a phosphorus compound. The catalyst is a catalyst containing an aluminum salt of a phosphorus compound.

  As said aluminum and / or an aluminum compound, a well-known aluminum compound other than metallic aluminum can be used without limitation.

  Specific examples of the aluminum compound include aluminum formate, aluminum acetate, basic aluminum acetate, aluminum propionate, aluminum oxalate, aluminum acrylate, aluminum laurate, aluminum stearate, aluminum benzoate, aluminum trichloroacetate, and aluminum lactate. , Carboxylates such as aluminum citrate, aluminum salicylate, inorganic acid salts such as aluminum chloride, aluminum hydroxide, aluminum hydroxide chloride, aluminum carbonate, aluminum phosphate, aluminum phosphonate, aluminum methoxide, aluminum ethoxide, aluminum Aluminum such as n-propoxide, aluminum iso-propoxide, aluminum n-butoxide, aluminum t-butoxide Aluminum alkoxide, aluminum acetylacetonate, aluminum acetylacetate, aluminum ethylacetoacetate, aluminum ethyl acetoacetate diiso-propoxide, organoaluminum compounds such as trimethylaluminum, triethylaluminum and their partial hydrolysates And aluminum oxide. Of these, carboxylates, inorganic acid salts and chelate compounds are preferred, and among these, aluminum acetate, aluminum chloride, aluminum hydroxide, aluminum hydroxide chloride and aluminum acetylacetonate are particularly preferred.

  The addition amount of the aluminum and / or aluminum compound is preferably 0.001 to 0.05 mol% with respect to the number of moles of all constituent units of the carboxylic acid component such as dicarboxylic acid or polycarboxylic acid of the obtained polyester. More preferably, it is 0.005-0.02 mol%. If the addition amount is less than 0.001 mol%, the catalytic activity may not be sufficiently exhibited. If the addition amount is 0.05 mol% or more, the thermal stability or thermal oxidation stability is deteriorated, resulting from the catalyst. Occurrence of foreign matters or increased coloring may be a problem. As described above, the polymerization catalyst of the present invention has a great feature in that it exhibits a sufficient catalytic activity even when the addition amount of the aluminum component is small. As a result, the thermal stability and thermal oxidation stability are excellent, and foreign matters and coloring caused by the catalyst can be reduced. In particular, in order to maintain hydrolysis resistance, the polyester may be subjected to solid phase polymerization, but the polyester polymerized by the above catalyst has high thermal stability and is not easily yellowed, so that high transparency is maintained. It is suitable.

  The phenol compound constituting the polycondensation catalyst is not particularly limited as long as it is a compound having a phenol structure. For example, 2,6-di-tert-butyl-4-methylphenol, 2,6-di- tert-butyl-4-ethylphenol, 2,6-dicyclohexyl-4-methylphenol, 2,6-diisopropyl-4-ethylphenol, 2,6-di-tert-amyl-4-methylphenol, 2,6- Di-tert-octyl-4-n-propylphenol, 2,6-dicyclohexyl-4-n-octylphenol, 2-isopropyl-4-methyl-6-tert-butylphenol, 2-tert-butyl-2-ethyl-6 -tert-octylphenol, 2-isobutyl-4-ethyl-6-tert-hexylphenol, 2-cyclohexyl-4-n-butyl-6-isopropylphenol, 1,1,1-tris (4-hydroxyphenyl) ethane, 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, tri Ethylene glycol-bis [3- (3-tert-butyl-5-methyl-4-hydroxyphenyl) propionate], 1,6-hexanediol-bis [3- (3,5-di-tert-butyl-4- Hydroxyphenyl) propionate], 2,2-thiodiethylenebis [3- (3,5-di-tert-butyl-4,4-hydroxyphenyl) propionate], N, N′-hexamethylenebis (3,5- Di-tert-butyl-4-hydroxy-hydrocinnamide), 1,3,5-tris (2,6-dimethyl-3-hydroxy-4-tert-butylbenzyl) isocyanurate, 1,3,5-tris (3 , 5-Di-tert-butyl-4-hydroxybenzyl) isocyanurate, 1,3,5-tris [(3,5-di-tert-butyl-4-hydroxyphenyl) propionyloxyethyl] isocyanurate, tris ( 4-tert-butyl-2,6-dimethyl-3-hydroxybenzyl) isocyanurate, 2,4-bis (n-octylthio) -6- (4- Droxy-3,5-di-tert-butylanilino) -1,3,5-triazine, tetrakis [methylene (3,5-di-tert-butyl-4-hydroxy) hydrocinnamate] methane, bis [(3, 3-bis (3-tert-butyl-4-hydroxyphenyl) butyric acid) glycol ester, N, N'-bis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionyl] hydrazine 2,2′-ogizamide bis [ethyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], bis [2-tert-butyl-4-methyl-6- (3-tert- Butyl-5-methyl-2-hydroxybenzyl) phenyl] terephthalate, 1,3,5-trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-hydroxybenzyl) benzene, 3, 9-bis [1,1-dimethyl-2- {β- (3-tert-butyl-4-hydroxy-5-methylphenyl) propionyloxy} ethyl] -2,4,8,10-tetraoxaspir [5,5] undecane, 2,2-bis [4- (2- (3,5-di-tert-butyl-4-hydroxycinnamoyloxy)) ethoxyphenyl] propane, β- (3,5-di -tert-butyl-4-hydroxyphenyl) propionic acid alkyl ester, tetrakis- [methyl-3- (3 ', 5'-di-tert-butyl-4-hydroxyphenyl) propionate] methane, octadecyl-3- (3 , 5-Di-tert-butyl-4-hydroxyphenyl) propionate, 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, thiodiethylene-bis [3- (3 , 5-di-tert-butyl-4-hydroxyphenyl) propionate], ethylenebis (oxyethylene) bis [3- (5-tert-butyl-4-hydroxy-m-tolyl) propionate], hexamethylenebis [3 -(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, triethylene glycol-bis-[-3- (3'-tert-butyl-4-hydro Xyl-5-methylphenyl)] propionate, 1,1,3-tris [2-methyl-4- [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionyloxy] -5-tert -Butylphenyl] butane.

  Two or more of these can be used in combination. Of these, 1,3,5-trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-hydroxybenzyl) benzene, tetrakis- [methyl-3- (3 ', 5' -Di-tert-butyl-4-hydroxyphenyl) propionate] methane, thiodiethylene-bis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate] are preferred.

  By adding these phenol compounds at the time of polymerization of the polyester, the catalytic activity of the aluminum compound is improved and the thermal stability of the polymerized polyester is also improved.

The amount of the phenolic compound added is preferably 5 × 10 ^{−7 to} 0.01 mol relative to the number of moles of all constituent units of the carboxylic acid component such as dicarboxylic acid and polyvalent carboxylic acid of the polyester obtained. Preferably it is 1 * 10 < ^-6 > -0.005 mol. In the present invention, a phosphorus compound may be used together with the phenol compound.

  Although it does not specifically limit as a phosphorus compound which comprises the said polycondensation catalyst, The group which consists of a phosphonic acid type compound, a phosphinic acid type compound, a phosphine oxide type compound, a phosphonous acid type compound, a phosphinic acid type compound, a phosphine type compound The use of one or two or more selected compounds is preferable because the effect of improving the catalytic activity is great. Among these, when one or two or more phosphonic acid compounds are used, the effect of improving the catalytic activity is particularly large and preferable.

  The phosphorus compound constituting the polycondensation catalyst is particularly preferably a compound that is a group having an aromatic ring structure.

  Examples of the phosphorus compound constituting the polycondensation catalyst include, for example, dimethyl methylphosphonate, diphenyl methylphosphonate, dimethyl phenylphosphonate, diethyl phenylphosphonate, diphenyl phenylphosphonate, dimethyl phosphophosphonate, diethyl benzylphosphonate, and diphenylphosphine. Examples include acids, methyl diphenylphosphinate, phenyl diphenylphosphinate, phenylphosphinic acid, methyl phenylphosphinate, phenylphenylphosphinate, diphenylphosphine oxide, methyldiphenylphosphine oxide, and triphenylphosphine oxide. Of these, dimethyl phenylphosphonate and diethyl benzylphosphonate are particularly preferred.

The amount of the phosphorus compound added is preferably 5 × 10 ^{−7 to} 0.01 mol based on the number of moles of all constituent units of the carboxylic acid component such as dicarboxylic acid and polyvalent carboxylic acid of the polyester obtained. Preferably it is 1 * 10 < ^-6 > -0.005 mol.

  The phosphorus compound having a phenol part constituting the polycondensation catalyst in the same molecule is not particularly limited as long as it is a phosphorus compound having a phenol structure, but a phosphonic acid compound having a phenol part in the same molecule, The use of one or two or more compounds selected from the group consisting of phosphinic acid compounds, phosphine oxide compounds, phosphonous acid compounds, phosphinic acid compounds, and phosphine compounds is preferable because the effect of improving the catalytic activity is great. Among these, when a phosphonic acid compound having one or two or more phenol moieties in the same molecule is used, the effect of improving the catalytic activity is particularly large and preferable.

  The polyester used in the present invention can be produced by a conventionally known production method except that the specific catalyst is used as a polyester polymerization catalyst. For example, in the case of producing PET, a method in which terephthalic acid and ethylene glycol are esterified and then polycondensed, or after transesterification of an alkyl ester of terephthalic acid such as dimethyl terephthalate with ethylene glycol is performed. Any method of polycondensation can be used. The polymerization apparatus may be a batch type or a continuous type.

  The polyester catalyst used in the present invention has catalytic activity not only in the polymerization reaction but also in the esterification reaction and transesterification reaction. For example, polymerization by an ester exchange reaction between an alkyl ester of a dicarboxylic acid such as dimethyl terephthalate and a glycol such as ethylene glycol is usually carried out in the presence of an ester exchange catalyst such as a titanium compound or a zinc compound. Instead, the catalyst described in the claims of the present invention can be used together with these catalysts. The catalyst has catalytic activity not only in melt polymerization but also in solid phase polymerization or solution polymerization, and it is possible to produce a polyester suitable for producing a polyester film by any method.

  The polyester thus obtained does not contain a metal antimony aggregate and is suitable as a raw material for producing a laminated polyester film for solar cells.

  In order to obtain high hydrolysis resistance as a member for a solar cell, the polyester film of the present invention preferably has a carboxyl terminal concentration of 25 eq / ton or less with respect to the polyester. The polyester film preferably has a carboxyl terminal concentration of 20 eq / ton or less, more preferably 18 eq / ton or less, still more preferably 15 eq / ton or less, and 13 eq / ton or less. It is particularly preferable that it is 10 eq / ton or less. When this value is larger than 25 eq / ton, the hydrolytic property is lowered, and the durability as a solar cell surface protective sheet can be exhibited, and early deterioration tends to occur. In addition, the measurement of the carboxyl terminal density | concentration of polyester can be measured by the titration method mentioned later or NMR method.

  In particular, since the polyester of the present invention uses a specific catalyst species, the carboxyl terminal of the polyester can be more suitably reduced. Conventionally, an antimony compound or the like used as a polymerization catalyst for polyester has a high catalytic ability for a polymerization reaction, but shows little activity for an esterification reaction. However, the aluminum compound used in the present invention has high catalytic ability for the polymerization reaction and also has high activity for the esterification reaction. Therefore, consumption of the carboxyl terminal is remarkable due to the ester bond, and the carboxyl terminal concentration can be suitably reduced.

  In order to obtain high heat resistance and hydrolysis resistance, the polyester film of the present invention preferably has an intrinsic viscosity of 0.60 to 0.90 dl / g, and more preferably 0.62 to 0.40. It is 85 dl / g, More preferably, it is 0.65-0.8 dl / g. When the intrinsic viscosity is lower than 0.60 dl / g, the hydrolysis resistance and heat resistance are not sufficient, and when it is higher than 0.90 dl / g, the back pressure in the melting process is increased. This is not preferable because the thermal deterioration is promoted due to the deterioration of the heat resistance and shear heat generation.

  Since the polyester terminal concentration and intrinsic viscosity of the polyester film of the present invention are in the above ranges, it is not necessary to separately provide a durable layer such as a fluororesin layer, which is suitable for maintaining high transparency. In order to set the carboxyl terminal concentration and the intrinsic viscosity within the above ranges, it can be carried out by appropriately selecting the polymerization conditions of the resin. For example, production equipment factors such as the structure of the esterification reaction apparatus, composition ratio of dicarboxylic acid and glycol in the slurry supplied to the esterification reaction tank, esterification reaction temperature, esterification reaction pressure, esterification reaction time, etc. What is necessary is just to set reaction conditions or solid layer polymerization conditions etc. suitably. In particular, it is preferable to use a polyester having a high molecular weight and a low acid value by solid phase polymerization. Furthermore, it is also preferable to block the carboxyl terminal of the polyester with an epoxy compound or a carbodiimide compound.

  The film of the present invention preferably has a total light transmittance of 85% or more, more preferably 86% or more, and further preferably 87% or more. Further, the haze of the film of the present invention is preferably 5% or less, more preferably 4% or less, and even more preferably 3% or less. Thus, since it has high transparency, also when it uses as a solar cell surface protection sheet, the utilization factor of light can be made high.

  The laminated polyester film of the present invention is a laminated polyester film composed of three layers having an outermost layer and a center layer. As the layer structure in the three-layer structure, the outermost layer on the front and back layers may have the same composition or different compositions, but two types and three layers (A layer / B layer / A layer) are the points of productivity. To preferred.

In order to achieve both high transparency and processing characteristics, in the present invention, particles are contained in the outermost layer (A layer in the case of the above-mentioned 2 types and 3 layers), and in the central layer (B layer in the case of the above 2 types and 3 layers). Is substantially free of particles. The reason why particles are contained in the A layer is to provide workability that can correspond to a high line speed by setting the number to 10 or more per 1000 cm ² . The handling property of the laminated film of the present invention can be evaluated by the coefficient of dynamic friction (μd) between the laminated film surfaces. In this case, the dynamic friction coefficient (μd) is preferably 0.7 or less from the viewpoint of workability.

The reason why the layer B does not substantially contain particles is to maintain high transparency. Further, it is also suitable for controlling the generation probability of protrusions of 1 μm or more due to lubricant particles, particularly inorganic particle aggregates, to 10 or less per 1000 cm ² .

  Note that “substantially free of inert particles” means, for example, in the case of inorganic particles, when the element derived from the particles is quantitatively analyzed by fluorescent X-ray analysis, it is less than 50 ppm, preferably less than 10 ppm. Preferably, the content is below the detection limit. This means that even if particles are not actively added to the base film, contaminants derived from foreign substances and raw material resin or dirt adhering to the line or equipment in the film manufacturing process will be peeled off and mixed into the film. It is because there is a case to do.

  The type and content of the particles contained in the outermost layer may be inorganic particles or organic particles, and are not particularly limited, but include metal oxidation such as silica, titanium dioxide, talc, and kaolinite. Examples thereof include inorganic particles that are inert to polyesters such as products, calcium carbonate, calcium phosphate, and barium sulfate. Any one of these inert inorganic particles may be used alone, or two or more thereof may be used in combination.

  The particles preferably have an average particle size of 0.1 to 3.5 μm. The lower limit of the average particle diameter is more preferably 0.5 μm, further preferably 0.8 μm, and still more preferably 1.0 μm. Further, the upper limit of the average particle is more preferably 3.0 μm, still more preferably 2.8 μm. If the average particle size is less than 0.1 μm, sufficient handling properties cannot be obtained. If it exceeds 3.5 μm, the transparency may decrease.

  These particles are preferably porous particles, particularly porous silica. This is because the porous particles are easily deformed into a flat shape at the time of stretching in the film forming process, and it is difficult to form protrusions having a height of 1 μm or more.

  The content of inorganic particles in the outermost layer is preferably 0.01 to 0.20% by mass with respect to the polyester constituting the outermost layer. The lower limit of the concentration is more preferably 0.02% by mass, and further preferably 0.03% by mass. Further, the upper limit of the concentration is more preferably 0.15% by mass, and further preferably 0.10% by mass. If it is less than 0.01% by mass, sufficient handling properties cannot be obtained. If it exceeds 0.2% by mass, the transparency may be lowered.

The average particle diameter of the particles can be measured by the following method.
The particles are photographed with an electron microscope or an optical microscope, and the maximum diameter of 300-500 particles (in the case of porous silica, the aggregate size) is such that the size of one smallest particle is 2-5 mm. Particle diameter) is measured, and the average value is taken as the average particle diameter. Moreover, when calculating | requiring the average particle diameter of the particle | grains in the coating layer of a laminated film, the cross section of a laminated film is image | photographed by 120,000 times magnification using a transmission electron microscope (TEM), and it exists in the cross section of a coating layer. The maximum diameter of the particles can be determined.

  A known method can be adopted as a method of blending the above-mentioned particles with polyester. 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 after the end of the ester exchange reaction and before the start of the polycondensation reaction. The polycondensation 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 method of blending dried particles and a polyester raw material using a kneading extruder It can be carried out.

  Among them, in the present invention, after the aggregated inorganic particles are homogeneously dispersed in the monomer liquid that is part of the polyester raw material, the filtered material is the polyester raw material before the esterification reaction, during the esterification reaction, or after the esterification reaction. The method of adding to the remainder of is preferable. According to this method, since the monomer liquid has a low viscosity, homogeneous dispersion of particles and high-accuracy filtration of the slurry can be easily performed, and when added to the remainder of the raw material, the dispersibility of the particles is good and new aggregation is achieved. Aggregation is unlikely to occur. From this point of view, it is particularly preferable to add to the remainder of the raw material in a low temperature state before the esterification reaction. In addition, after obtaining a polyester containing particles in advance, the aggregate of the lubricant can be further reduced by a method (master batch method) in which the pellet and the pellet not containing the particle are kneaded and extruded. Since the number can be reduced, it is preferable.

  These layers may contain various additives in the polyester as necessary. Examples of the additive include an antioxidant, a light resistance agent, an antigelling agent, an organic wetting agent, an antistatic agent, an ultraviolet absorber, and a surfactant.

  In particular, it is preferable to add an ultraviolet absorber to the center layer in order to prevent deterioration against ultraviolet rays. Thereby, it is not necessary to separately provide an ultraviolet absorbing layer, and high transparency can be easily maintained.

  In order to provide weather resistance, the light transmittance at a wavelength of 380 nm of the film is preferably 20% or less, more preferably 15% or less, further preferably 10% or less, and further more preferably 5% or less. preferable. In addition, the transmittance | permeability in this invention is measured by the perpendicular | vertical method with respect to the plane of a film, and can be measured using a spectrophotometer (for example, Hitachi U-3500 type). In order to achieve weather resistance, it is preferable that the light transmittance at a wavelength of 380 nm is low. However, when a large amount of an ultraviolet absorber is added, the ultraviolet absorber may bleed out on the film surface. Therefore, the lower limit of the light transmittance at a wavelength of 380 nm is considered to be 0.001%.

  The ultraviolet absorber used in the present invention is a known substance. Examples of the ultraviolet absorber include an organic ultraviolet absorber and an inorganic ultraviolet absorber, and an organic ultraviolet absorber is preferable from the viewpoint of transparency. Examples of the organic ultraviolet absorber include benzotoazole, benzophenone, cyclic imino ester, and combinations thereof, but are not particularly limited as long as the absorbance is within the range defined by the present invention. From the viewpoint of durability, benzotoazole and cyclic imino ester are particularly preferable. When two or more kinds of ultraviolet absorbers are used in combination, ultraviolet rays having different wavelengths can be absorbed simultaneously, so that the ultraviolet absorption effect can be further improved.

  At this time, the concentration of the UV absorber in the master batch is preferably 1 to 30% by mass in order to uniformly disperse the UV absorber and economically mix it. Is preferably low. As a condition for producing the master batch, it is preferable to use a kneading extruder and to extrude it at a temperature not lower than the melting point of the polyester raw material and not higher than 290 ° C. for 1 to 15 minutes. Above 290 ° C, the weight loss of the UV absorber is large, and the viscosity of the master batch is greatly reduced. When the extrusion temperature is 1 minute or less, uniform mixing of the UV absorber becomes difficult. At this time, if necessary, a stabilizer, a color tone adjusting agent, and an antistatic agent may be added.

  The thickness of the laminated film used in the present invention is not particularly limited, but can be arbitrarily determined in the range of 30 to 300 μm according to the standard to be used. The upper limit of the thickness of the base film is preferably 250 μm, particularly preferably 200 μm. On the other hand, the lower limit of the film thickness is preferably 50 μm, more preferably 75 μm, and particularly preferably 100 μm. When the film thickness is less than 30 μm, rigidity and mechanical strength tend to be insufficient. On the other hand, when the film thickness exceeds 300 μm, the cost increases.

  As the laminated film used in the present invention, an unoriented sheet obtained by melt extrusion or solution extrusion of the polyester is stretched in a uniaxial direction in the longitudinal direction or the width direction as necessary, or biaxially sequentially biaxially. A biaxially oriented polyester film that has been stretched or simultaneously biaxially stretched and heat-set is suitable.

  After sufficiently drying the polyester pellets in vacuum, each polyester constituting the outermost layer and the central layer is supplied to a co-extrusion machine, melt-extruded into a sheet at 270 to 295 ° C., cooled and solidified, and an unoriented cast film Get. The obtained cast film is stretched 2.5 to 5.0 times in the longitudinal direction with a roll heated to 80 to 120 ° C. to obtain a uniaxially oriented polyester film.

  Thereafter, both ends of the film are gripped with clips, guided to a hot air zone heated to 80 to 180 ° C., and stretched 2.5 to 5.0 times in the width direction after drying. Subsequently, it is guided to a heat treatment zone of 220 to 240 ° C., and heat treatment is performed to complete crystal orientation. In this heat treatment step, a relaxation treatment of 1 to 12% may be performed in the width direction or the longitudinal direction as necessary.

  Moreover, when manufacturing the film of this invention, in order to maintain high transparency, it is preferable to remove the foreign material contained in the raw material polyester. In order to remove foreign substances in the polyester, high-precision filtration is performed at an arbitrary place where the molten resin is maintained at about 280 ° C. during melt extrusion. The filter medium used for high-precision filtration of the molten resin is not particularly limited, but agglomerates mainly composed of Si, Ti, Sb, Ge, and Cu and high-melting-point organic substances in the case of a stainless steel sintered filter medium are removed. Excellent performance and suitable.

  The filtration particle size (initial filtration efficiency: 95%) of the filter medium used for high-precision filtration of the molten resin is preferably 25 μm or less. When the filter particle size of the filter medium exceeds 25 μm, removal of foreign matters of 20 μm or more tends to be insufficient. Productivity may decrease due to high-precision filtration of molten resin using filter media with a filtration particle size (initial filtration efficiency: 95%) of 25 μm or less, but extremely important to obtain a film with few protrusions It is.

  In addition, the laminated film is a surface activation treatment such as a corona discharge treatment, a glow discharge treatment, a flame treatment, an ultraviolet irradiation treatment, an electron beam irradiation treatment, an ozone treatment, etc., as long as the object of the present invention is not impaired May be applied.

  In the present invention, at least one surface of the laminated film is a copolyester-based polyester in order to improve adhesion to various functional layers laminated on one side or both sides of the laminated film of the present invention and an encapsulant of solar cell elements such as ethylene vinyl alcohol. You may form the coating layer which has at least 1 sort (s) as a main component among resin, an acrylic resin, and a polyurethane-type resin. The step of forming the coating layer may be on an unstretched sheet, a uniaxially stretched film, or a biaxially stretched film. Here, the “main component” means a component that occupies 50% by mass or more of the solid component in the non-multilayer.

The coating liquid used when forming the coating layer is preferably an aqueous coating liquid containing at least one of water-soluble or water-dispersible copolymerized polyester resins, acrylic resins, and polyurethane resins. Examples of these coating solutions include water-soluble or water-dispersible copolyester solutions, acrylic solutions, polyurethane solutions and the like disclosed in Japanese Patent No. 3567927, Japanese Patent No. 3589232, Japanese Patent No. 3589233, and the like. . The coating layer can be obtained by coating these coating liquids on one or both sides of a uniaxially stretched polyester film in the longitudinal direction, drying at 100 to 150 ° C., and stretching in the lateral direction. The final coating amount of the coating layer is preferably controlled to 0.05 to 0.20 g / m ² . When the coating amount is less than 0.05 g / m ² , the adhesion between the obtained laminated film and the functional layer may be insufficient. On the other hand, when the coating amount exceeds 0.20 g / m ² , blocking resistance may be lowered. When coating layers are provided on both sides of the base film, the coating amount of the coating layers on both sides may be the same or different, and is independently set within the above range depending on the use of the laminated film can do. It is preferable to add fine particles to the coating layer in order to impart easy slipperiness. It is preferable to use particles having an average particle size of 0.1 μm or less. When the average particle diameter of the particles exceeds 0.1 μm, not only the particles easily fall off from the coating layer, but also aggregates are generated and protrusions having a height of 1 μm or more are likely to be generated.

  The particles to be included in the coating layer include calcium carbonate, calcium phosphate, amorphous silica, crystalline glass filler, kaolin, talc, titanium dioxide, alumina, silica-alumina composite oxide, barium sulfate, calcium fluoride, and fluoride. Inorganic particles such as lithium, zeolite, molybdenum sulfide and mica, crosslinked polystyrene particles, crosslinked acrylic resin particles, crosslinked methyl methacrylate resin particles, benzoguanamine / formaldehyde condensate particles, melamine / formaldehyde condensate particles, polytetrafluoroethylene particles And heat resistant polymer particles. Among these particles, silica particles are preferred because the resin component of the coating layer is relatively close in refractive index and a film having high transparency can be easily obtained. Moreover, a well-known method can be used as a method of apply | coating a coating liquid. For example, reverse roll coating method, gravure coating method, kiss coating method, roll brush method, spray coating method, air knife coating method, wire bar coating method, pipe doctor method, etc. can be mentioned. Or it can carry out in combination.

  The solar cell referred to in the present invention refers to a system that takes in incident light such as sunlight and room light, converts it into electricity, and stores the electricity. Surface protection sheet, high light transmission material, solar cell module, filler layer And a back sheet. There are flexible properties depending on the application.

  As a solar cell surface protective sheet, a composite layer in which the above laminated polyester film is provided with a hard coat layer made of an acrylic resin, a barrier layer made of a metal deposition layer, or a functional layer such as a thermal adhesive layer, a flame retardant layer, or an antireflection layer. It is preferable to use a sheet. The solar cell surface protective sheet is in contact with an encapsulant such as ethylene vinyl alcohol in which the solar cell element is encapsulated, and is attached by pressing or the like. At this time, more suitable adhesion can be obtained by performing the above-described easy adhesion treatment on the surface in contact with the encapsulant.

  EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these Examples from the first. In addition, the evaluation method used in each Example and the comparative example is demonstrated below.

(Detection of protrusion)
A 10 m portion was removed from the surface layer of the product film roll having a width of 1 m of the laminated film obtained in the examples and comparative examples, and a film having a length of 1 m or more was extracted and hung in the vertical direction. Next, a three-wavelength daylight fluorescent lamp (FL20SS EX-N / 18P: manufactured by National Corporation) is placed on the back of the film, and it shines in comparison with the surroundings while changing the angle from the front to the film surface in the range of about 10 ° to 45 °. A point, a point that looks whitish, or a point that looks blackish was marked.

(Measurement of protrusion height)
The marked sample was measured under the following conditions using a non-contact surface shape measurement system (VertScan R550H-M100), and the maximum height of the protrusion was obtained from the cross-sectional profile mode. In addition, the protrusion derived from dust adhesion was excluded.
In the case of a sample having a coating layer, the portion marked with Kimwipe (WIPRS S200: manufactured by Crecia) impregnated with a solvent (methyl ethyl ketone) is rubbed so as not to be scratched, the coating layer is removed, and the protrusion Sought height. (The solvent in this case is not particularly limited as long as it can dissolve the coating layer.)

(Measurement condition)
・ Measurement mode: WAVE mode ・ Objective lens: 10 times ・ 0.5 × Tube lens ・ Measurement area: 938 × 696 μm
The measurement was performed on both sides of the sample. As for the protrusion of the marking portion, the higher one was counted as the protrusion on the surface based on the height measured on both surfaces. Thus, the number of protrusions per 1000 cm ^{2 of} the film surface was determined.

(Handling properties)
Sample films were prepared by cutting out from the laminated films obtained in Examples and Comparative Examples into an area of 8 cm × 5 cm. A laminated film was fixed to the bottom of a metal rectangular parallelepiped having a weight of 4.4 kg and a bottom having a size of 6 cm × 5 cm. At this time, the 5 cm width direction of the sample film and the 5 cm width direction of the metal cuboid were matched, one side in the longitudinal direction of the sample film was bent, and fixed to the side surface of the metal cuboid with an adhesive tape.
Next, a sample film was cut out in an area of 20 cm × 10 cm from the same laminated film, and the end in the longitudinal direction was fixed on a flat metal plate with an adhesive tape. The measurement surface of the metal rectangular parallelepiped with the sample film attached thereto was placed in contact, and the dynamic friction coefficient (μd) was measured under the conditions of a pulling speed of 200 mm / min, 23 ° C., and 65% RH. For the measurement, RTM-100 manufactured by Toyo BALDWIN was used, and the dynamic friction coefficient (μd) was calculated and determined in accordance with JIS K-7125.
When the dynamic friction coefficient (μd) is 0.7 or less, the handling property is good, and when it exceeds 0.7, the handling property is bad.

(Average particle size)
The inert particles were observed with a scanning electron microscope (S-51O type, manufactured by Hitachi, Ltd.), the magnification was appropriately changed according to the size of the particles, and the photographed photographs were enlarged and copied. Next, the outer circumference of each particle was traced for at least 300 particles selected at random, the equivalent circle diameter of the particles was measured from these trace images with an image analyzer, and the average of these was taken as the average particle diameter.

(Intrinsic viscosity of polyester)
The polyester was dissolved using a 6/4 (weight ratio) mixed solvent of phenol / 1,1,2,2-tetrachloroethane and measured at a temperature of 30 ° C.

(Carboxyl terminal concentration)
A. Preparation of sample The polyester is pulverized, vacuum dried at 70 ° C. for 24 hours, and then weighed in a range of 0.20 ± 0.0005 g using a balance. The weight at that time is defined as W (g). A sample weighed with 10 ml of benzyl alcohol is added to a test tube, the test tube is immersed in a benzyl alcohol bath heated to 205 ° C., and the sample is dissolved while stirring with a glass rod. Samples with dissolution times of 3 minutes, 5 minutes, and 7 minutes are designated as A, B, and C, respectively. Next, a new test tube is prepared, and only benzyl alcohol is added and processed in the same procedure, and samples when the dissolution time is 3 minutes, 5 minutes, and 7 minutes are designated as a, b, and c, respectively.
B. Titration Titration is performed using a 0.04 mol / l potassium hydroxide solution (ethanol solution) whose factor is known in advance. Phenol red is used as the indicator, and the titration (ml) of the potassium hydroxide solution is determined with the end point being changed from yellowish green to light red. Samples A, B, and C are titrated as XA, XB, and XC (ml). The titration amounts of samples a, b, and c are Xa, Xb, and Xc (ml).
C. Calculation of carboxyl terminal concentration Using the titration amounts XA, XB and XC for each dissolution time, the titration amount V (ml) at a dissolution time of 0 minutes is determined by the least square method. Similarly, titration volume V0 (ml) is obtained using Xa, Xb, and Xc. Subsequently, the carboxyl terminal concentration was calculated | required according to following Formula.
Carboxyl terminal concentration (eq / ton) = [(V−V0) × 0.04 × NF × 1000] / W
NF: factor of 0.04 mol / l potassium hydroxide solution W: sample weight (g)

(Haze, total light transmittance)
The haze (cloudiness value) and total light transmittance of the laminated film test piece were measured according to JIS K 7105 “Testing method for optical properties of plastics”. The film test piece was installed with the longitudinal direction of the film set in the vertical direction and directed toward the light source, and measured using an NDH-300A turbidimeter manufactured by Nippon Denshoku Industries Co., Ltd.

(Hydrolysis resistance)
As the hydrolysis resistance evaluation, HAST (Highly Accelerated Temperature and Humidity Stress Test) standardized in JIS-60068-2-66 was performed. The equipment was EHS-221 manufactured by ESPEC CORP. Under the conditions of 105 ° C., 100% RH, and 0.03 MPa.
The laminated film was cut into 70 mm × 190 mm, and the film was installed using a jig. Each film was placed at a distance where it did not touch. The treatment was performed for 192 hours under the conditions of 105 ° C., 100% RH, and 0.03 MPa. Before and after the treatment, the elongation at break was measured according to JIS-C-2318-1997 5.3.31 (tensile strength and elongation), and the elongation at break was calculated according to the following formula. % Or more was marked with ○, and less than 70% was marked with ×.
Breaking elongation retention ratio (%) = [(breaking elongation after treatment (MPa)) / (breaking elongation before treatment (MPa))] × 100

(Light transmittance at a wavelength of 380 nm or less)
Using a spectrophotometer (U-3500, manufactured by Hitachi, Ltd.), the light transmittance in the wavelength region of 300 to 500 nm was measured using the air layer as a standard, and the transmittance at a wavelength of 380 nm was determined.

(1) Polymerization of polyester (A) 13 g / l ethylene chloride of aluminum chloride as a polycondensation catalyst for a mixture of bis (2-hydroxyethyl) terephthalate and oligomer produced according to a conventional method from high-purity terephthalic acid and ethylene glycol 0.015 mol% of the solution as an aluminum atom with respect to the acid component in the polyester and 10 g / l ethylene glycol solution of Irganox 1425 (manufactured by Ciba Specialty Chemicals) as 0.02 mol% as the Irganox 1425 with respect to the acid component In addition, the mixture was stirred at 245 ° C. for 10 minutes under a nitrogen atmosphere at normal pressure. Next, the temperature of the reaction system is gradually lowered while raising the temperature to 275 ° C. over 50 minutes to 13.3 Pa (1 Torr) until the intrinsic viscosity reaches 0.65 dl / g at 275 ° C. and 13.3 Pa. A polycondensation reaction was performed. Polyethylene terephthalate obtained by polycondensation was chipped according to a conventional method to obtain polyester (A). At this time, the molten resin was kept at about 275 ° C., and the filtration particle size (initial filtration efficiency 95%) was subjected to high-precision filtration with a 20 μm stainless sintered filter to remove foreign substances contained in the resin.
The obtained polyester was subjected to solid phase polymerization using a rotary vacuum polymerization apparatus under a reduced pressure of 0.5 mmHg and changing the time at 220 ° C. to obtain a polyester (A) having an intrinsic viscosity of 0.75 dl / g.

(2) Polymerization of polyester (B) Porous silica particles having an average particle diameter of 2.5 μm are charged into ethylene glycol, and further filtered through a viscose rayon filter having a 95% cut diameter of 30 μm. An ethylene glycol slurry of particles was obtained.
For a mixture of bis (2-hydroxyethyl) terephthalate and oligomer prepared according to a conventional method from high-purity terephthalic acid and ethylene glycol, a 13 g / l ethylene glycol solution of aluminum chloride as a polycondensation catalyst was used for the acid component in the polyester. 0.015 mol% as an aluminum atom and 10 g / l ethylene glycol solution of Irganox 1425 (manufactured by Ciba Specialty Chemicals) as an acid component, 0.02 mol% as Irganox 1425 with respect to the acid component and an ethylene glycol slurry of the silica particles, It added so that it might become 2000 ppm with respect to production | generation PET. Subsequently, it stirred at 245 degreeC for 10 minutes by the normal pressure in nitrogen atmosphere. Next, the temperature of the reaction system is gradually lowered while raising the temperature to 275 ° C. over 50 minutes to 13.3 Pa (1 Torr) until the intrinsic viscosity reaches 0.65 dl / g at 275 ° C. and 13.3 Pa. A polycondensation reaction was performed. Polyethylene terephthalate obtained by polycondensation was chipped according to a conventional method to obtain polyester. At this time, the molten resin was maintained at about 275 ° C., and the filtration particle size (initial filtration efficiency: 95%) was filtered with a 20 μm stainless sintered body filter to remove foreign substances contained in the resin.
The obtained polyester was subjected to solid phase polymerization using a rotary vacuum polymerization apparatus under a reduced pressure of 0.5 mmHg and changing the time at 220 ° C. to obtain a polyester (B) having an intrinsic viscosity of 0.75 dl / g.

(3) Polymerization of polyester (C) When the temperature of the esterification reactor reached 200 ° C, a slurry consisting of 86.4 parts by mass of high-purity terephthalic acid and 64.4 parts by mass of ethylene glycol was charged. While stirring, 0.03 parts by mass of antimony trioxide and 0.16 parts by mass of triethylamine were added as catalysts. Next, the pressure esterification reaction was carried out under the conditions of a pressure increase in temperature and a gauge pressure of 3.5 kg / cm ² and 240 ° C. Thereafter, the inside of the esterification reaction can was returned to normal pressure.
After 15 minutes, the resulting esterification reaction product was transferred to a polycondensation reaction can and subjected to a polycondensation reaction under reduced pressure at 280 ° C. until the intrinsic viscosity reached 0.65 dl / g.
Polyethylene terephthalate obtained by polycondensation was chipped according to a conventional method to obtain polyester. At this time, the molten resin was kept at about 275 ° C., and the filtration particle size (initial filtration efficiency: 95%) was filtered with high accuracy in order to remove foreign substances contained in the resin with a 5 μm stainless sintered filter.
The obtained polyester was subjected to solid phase polymerization using a rotary vacuum polymerization apparatus under a reduced pressure of 0.5 mmHg and changing the time at 220 ° C. to obtain a polyester (C) having an intrinsic viscosity of 0.75 dl / g.

(4) Polymerization of polyester (D) When the temperature of the esterification reactor was reached and reached 200 ° C, a slurry consisting of 86.4 parts by mass of high-purity terephthalic acid and 64.4 parts by mass of ethylene glycol was charged. While stirring, 0.03 parts by mass of antimony trioxide as a catalyst, 0.16 parts by mass of triethylamine and an ethylene glycol slurry of the porous silica particles were added to 2000 ppm with respect to the generated PET. Next, the pressure esterification reaction was carried out under the conditions of a pressure increase in temperature and a gauge pressure of 3.5 kg / cm ² and 240 ° C. Thereafter, the inside of the esterification reaction can was returned to normal pressure.
After 15 minutes, the resulting esterification reaction product was transferred to a polycondensation reaction can and subjected to a polycondensation reaction under reduced pressure at 280 ° C. until the intrinsic viscosity reached 0.65 dl / g.
Polyethylene terephthalate obtained by polycondensation was chipped according to a conventional method to obtain polyester. At this time, the molten resin was maintained at about 275 ° C., and the filtration particle size (initial filtration efficiency: 95%) was filtered with a 20 μm stainless sintered body filter to remove foreign substances contained in the resin.
The obtained polyester was subjected to solid phase polymerization using a rotary vacuum polymerization apparatus under reduced pressure of 0.5 mmHg and changing the time at 220 ° C. to obtain a polyester (D) having an intrinsic viscosity of 0.75 dl / g.

(5) Polymerization of polyester (E) Polyester in the same manner as polyester (B) except that calcium carbonate particles having an average particle diameter of 1.8 μm were used instead of porous silica particles having an average particle diameter of 2.5 μm. (E) was obtained.

(6) Polymerization of polyester (F) Polyester (F) was obtained by the same method as polyester (A) except that the solid-phase polymerization conditions were changed to an intrinsic viscosity of 0.85 dl / g.

(7) Polymerization of Polyester (G) One UV absorber (2,2 ′-(1,4-phenylene) bis (4H-3,1-benzoxazinon-4-one) is added to polyester (A). Mass% was added to obtain a polyester (G).

(8) Polymerization of polyester (H) UV absorber 2- (5-chloro (2H) -benzotriazol-2-yl) -4-methyl-6- (tert-butyl) phenol (for polyester (A)) 1% by mass of TINUVIN 326) manufactured by Ciba Specialty Chemicals was added to obtain polyester (H).

Example 1
After the polyester (A) is dried at 135 ° C. under reduced pressure (1 Torr) for 6 hours as a raw material for the base film intermediate layer, the polyester (A) and the polyester (B) are made porous in the extruder 2 (for the intermediate layer B layer). They were blended so as to have a silica concentration of 0.06% by mass, supplied to the extruder 1 (for outer layer A layer), and melted at 285 ° C. These two polymers are each filtered through a filter material of stainless steel sintered body (nominal filtration accuracy 10 μm particle 95% cut), laminated in a three-layer confluence block, extruded into a sheet form from the die, and then electrostatically applied. It was wound around a casting drum having a surface temperature of 30 ° C. using a casting method, and solidified by cooling to produce an unstretched film. At this time, the discharge amount of each extruder was adjusted so that the thickness ratio of the A layer, the B layer, and the C layer was 1.5: 7: 1.5. Next, this unstretched film was heated to 100 ° C. with a heated roll group and an infrared heater, and then stretched 3.5 times in the longitudinal direction with a roll group having a difference in peripheral speed to obtain a uniaxially oriented PET film.

  Subsequently, while holding the edge of the film with a clip, the film was guided to a hot air zone at a temperature of 120 ° C. and stretched 4.3 times in the width direction. Next, while maintaining the width stretched in the width direction, it is treated in a heat setting zone having a maximum temperature of 230 ° C., 3% relaxation treatment is performed in the width direction, and a laminate for a solar cell surface protective sheet having a film thickness of 50 μm A polyester film was obtained.

(Example 2)
A laminated polyester film for a solar cell surface protective sheet having a film thickness of 50 μm was obtained in the same manner as in Example 1 except that polyester (E) was used instead of polyester (B).

(Example 3)
Lamination for solar cell surface protective sheet having a film thickness of 50 μm in the same manner as in Example 1 except that polyester (A) and polyester (B) were blended so that the porous silica concentration of layer A was 0.1% by mass. A polyester film was obtained.

Example 4
Lamination for solar cell surface protective sheet having a film thickness of 50 μm in the same manner as in Example 1 except that polyester (A) and polyester (B) were blended so that the porous silica concentration of layer A was 0.03% by mass. A polyester film was obtained.

(Example 5)
A uniaxially oriented PET film was obtained in the same manner as Example 1.

Subsequently, the coating liquid shown below was microfiltered with a felt type polypropylene filter medium having a filtration particle size (initial filtration efficiency: 95%) of 10 μm, and applied to one side of a uniaxially oriented PET film by a roll coating method. The wet coating amount of the coating solution was 5 g / m ² . Further, the above coating solution was microfiltered with a felt type polypropylene filter medium having a filtration particle size (initial filtration efficiency: 95%) of 10 μm, and applied to the opposite surface of the uniaxially oriented PET film by a roll coating method. The coating solution was applied so that the coating thickness was 60 nm when dried.

Then, it was dried in a drying furnace having a maximum temperature of 135 ° C. for 6.8 seconds.
Subsequently, a laminated polyester film for a solar cell surface protective sheet having a film thickness of 50 μm having a coating layer was obtained in the same manner as in Example 1.

(Coating solution adjustment)
A transesterification reaction and a polycondensation reaction are carried out by a conventional method, and as a dicarboxylic acid component (based on the whole dicarboxylic acid component) 46 mol% terephthalic acid, 46 mol% isophthalic acid and 8 mol% sodium 5-sulfonatoisophthalate, A water-dispersible sulfonic acid metal base-containing copolymer polyester having a composition of 50 mol% ethylene glycol and 50 mol% neopentyl glycol (relative to the entire glycol component) was prepared as the glycol component. Next, 51.4 parts by mass of water, 38 parts by mass of isopropyl alcohol, 5 parts by mass of n-butyl cellosolve, 0.06 parts by mass of nonionic surfactant were mixed and then heated and stirred. Add 5 parts by weight of water-dispersible sulfonic acid metal group-containing copolymer polyester and continue stirring until the resin is no longer solidified. Cool the resin water dispersion to room temperature to obtain a uniform solid content of 5.0% by weight. A water-dispersible copolyester liquid was obtained. Furthermore, after 3 parts by mass of porous silica particles (average particle diameter 1.1 μm) were dispersed in 50 parts by mass of water, the aqueous dispersion of porous silica particles was added to 99.46 parts by mass of the water-dispersible copolymer polyester liquid. 0.54 parts by mass was added, and 20 parts by mass of water was added with stirring to obtain a coating solution.

(Example 6)
A laminated polyester film for a solar cell surface protective sheet having a film thickness of 50 μm was obtained in the same manner as in Example 1 except that polyester F was used instead of polyester A.

(Example 7)
A laminated polyester film for a solar cell surface protective sheet having a film thickness of 50 μm was obtained in the same manner as in Example 1 except that polyester G was used instead of polyester A.

(Example 8)
A laminated polyester film for a solar cell surface protective sheet having a film thickness of 50 μm was obtained in the same manner as in Example 1 except that polyester H was used instead of polyester A.

(Comparative Example 1)
A polyester film having a film thickness of 50 μm was obtained in the same manner as in Example 1 except that polyester (C) was used instead of polyester (A) and polyester (D) was used instead of polyester (B).

(Comparative Example 2)
Polyester film having a film thickness of 50 μm in the same manner as in Example 1 except that polyester (A) and polyester (B) were blended so as to have a porous silica concentration of 0.06% by mass and supplied to extruders 1 and 2. Got.

(Comparative Example 3)
A polyester film having a film thickness of 50 μm was obtained in the same manner as in Example 1 except that only the polyester (B) was supplied to the extruder 2.

(Comparative Example 4)
A polyester film having a film thickness of 50 μm was obtained in the same manner as in Example 1 except that the polyester (A) was supplied to the extruders 1 and 2.

  The laminated polyester film for solar cell surface protective sheet of the present invention is excellent in durability and excellent in transparency and workability. Therefore, it is useful as a constituent member of the solar cell surface protective sheet.

Claims (5)

It is a laminated polyester film consisting of three layers having an outermost layer and a center layer,
The laminated polyester film is made of polyester polymerized using a polycondensation catalyst containing aluminum and / or a compound thereof and a phenol compound,
The outermost layer contains particles, and the central layer is substantially free of particles;
Haze is 5% or less, total light transmittance is 85% or more,
The carboxyl end concentration is 25 eq / ton or less with respect to the polyester,
Intrinsic viscosity is 0.60-0.90 dl / g,
On the surface of the laminated polyester film, the number of protrusions having a height of 1 μm or more is 10 or more and 100 or less per 1000 cm ² .
Laminated polyester film for solar cell surface protection sheet. The particles contained in the outermost layer are at least one inorganic particle selected from calcium phosphate, titanium oxide, silica, alumina, calcium carbonate, barium sulfate,
The average particle diameter of the particles is 0.1 to 3.0 μm,
The laminated polyester film for a solar cell surface protective sheet according to claim 1, wherein the content of particles in the outermost layer is 0.01 to 0.20 mass%.   The laminated polyester film for a solar cell surface protective sheet according to claim 1 or 2, wherein the particles are porous silica.   The laminated polyester film for solar cell surface protective sheets according to any one of claims 1 to 3, wherein the central layer contains an ultraviolet absorber.   At least one surface of the laminated polyester film for solar cells according to any one of claims 1 to 4 has a coating layer mainly comprising at least one of a copolyester resin, an acrylic resin, and a polyurethane resin. A laminated polyester film for a solar cell surface protective sheet with a coating layer.