JP2011032421A - Polyester film for solar cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laminated polyester film for a solar cell suitable for a solar cell module suitable for maintenance of a moisture-proofing property for a long period of time and an adhesion property with a moisture-proofing layer. <P>SOLUTION: In the polyester film for the solar cell, the content of a cyclic trimer in the polyester film is 5,000 ppm or less based on the amount of polyester film, the amount of cyclic trimer on a film surface on at least one surface of the polyester film is 50 μg/m<SP>2</SP>or less, and the amount of a linear oligomer on the film surface is 20-100 μg/m<SP>2</SP>. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a solar cell polyester film suitable for a solar cell module suitable for long-term moisture resistance maintenance when used in a solar cell backsheet.

  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.

  As a method for manufacturing a solar cell module, specifically, a solar cell element is sandwiched between two filler sheets made of ethylene / vinyl acetate copolymer resin, and then a tempered glass plate is placed on one filler sheet. The upper transparent material is placed, and the back sheet is placed on the opposite side of the filler sheet, and then preheated at 40 to 50 ° C. for about 5 minutes, and then the whole is hot-pressed at about 150 ° C. for about 30 minutes from both sides. Thus, the solar cell backsheet is fused and integrated.

  As the solar cell backsheet, for example, from the solar cell element side, a moisture barrier layer / adhesive such as polyester film / adhesive / polyester high durability moisture barrier film (outermost layer), polyester film / metal or metal oxide thin film layer, etc. / Polyester-based highly durable moisture-proof film (outermost layer) and other laminated structures are on the market. For example, the followings have been proposed as polyester-based high durability moisture-proof films used here.

In Patent Document 1 and Patent Document 2, as a raw material for a polyester-based high durability moisture-proof film used for a back sheet, a polyester resin is a polyester resin that has been subjected to treatment such as solid phase polymerization in order to improve durability at the stage of a pellet-shaped resin. It is used. Patent Document 3 exemplifies a polyester film for solar cells prepared using a polyester resin having a cyclic trimer concentration of 0.5% or less. Patent Document 4 discloses a laminated film manufactured using a polyethylene terephthalate resin subjected to oligomer reduction treatment using a polycondensation catalyst composed of an aluminum compound and a phosphorus compound, and the concentration of cyclic trimer in the polyester film is disclosed. Is a laminated film having a cyclic trimer content on the film surface of from 0.1 mg / m ² to 0.11 mg / m ² .

JP 2007-70430 A JP 2008-31680 A JP 2002-134770 A JP 2008-30370 A

  As described above, the polyester resin used for the solar battery back sheet is generally subjected to solid phase polymerization for the purpose of improving durability, and the carboxyl terminal concentration in the film resin is generally kept low. Furthermore, the effect of reducing the production | generation of an oligomer is acquired by performing the said solid-phase polymerization process.

  As described above, a high degree of moisture resistance is maintained in the solar cell module by providing a moisture-proof layer via an adhesive layer in order to prevent insulation and deterioration of the power generation element. From the viewpoint of the environment, a water-based adhesive may be used for the adhesive layer. However, in the case of the above-described polyester film, when the usage period of the solar cell module is set as 20 years or more, there are cases where it is still insufficient to maintain moisture resistance over a long period of time.

  In view of the above problems, an object of the present invention is to provide a solar cell polyester film that can maintain moisture resistance for a long period of time and has excellent adhesion to a moisture barrier layer.

  As a result of diligent study on long-term moisture-proof maintenance of the solar battery back sheet, the present inventor found that there are innumerable protrusions due to the crystal of the cyclic trimer on the surface of the polyester film used for the back sheet. It has been discovered that scratches and numerous dents may occur in a highly durable moisture-proof layer such as a physical thin film layer, which reduces moisture resistance. That is, the cyclic trimer deposited on the film surface may grow into a crystal having a size of 1 μm or more, sometimes 5 μm or more. It was found that there is a problem in maintaining moisture resistance for a long time when using a polyester film with a large amount of the polyester film.

  Furthermore, as a result of intensive studies on the adhesion between the solar cell polyester film and the adhesive (especially the water-based adhesive), the present inventor has found that minute repellings generated on the film surface when the adhesive is applied are adhered over a long period of time. It was found that it was a factor of sex decline. Furthermore, the present inventor has found that minute repellency generated on the film surface is suppressed by the linear oligomer on the film surface.

That is, the said subject can be achieved by the following solution means.
In the first invention of the present application, the cyclic trimer content in the polyester film is 5000 ppm or less per the polyester film, and the cyclic trimer content on the film surface on at least one side of the polyester film is 50 μg / m ^2. It is a polyester film for solar cells which is below and the amount of linear oligomers on the film surface is 20 μg / m ² or more and 100 μg / m ² or less.
2nd invention of this application is the said polyester film for solar cells which consists of a polyester resin polymerized using the polycondensation catalyst containing aluminum and / or its compound, and a phenol type compound.
According to a third invention of the present application, the polyester film has at least three layers of an outermost layer and a center layer, the outermost layer contains particles, and the center layer contains substantially no particles. It is a film.

  The polyester film for solar cells of the present invention has a small amount of cyclic trimer present on the surface and exhibits excellent adhesion. Therefore, it is excellent in long-term moisture-proof maintenance and adhesiveness with a moisture-proof layer as a polyester film for solar cells.

  The polyester film of the present invention is a film composed of a polyester resin, and mainly contains at least one of polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate as a constituent component.

  Polyester used by this invention can be performed by a conventionally well-known manufacturing method. For example, when producing polyethylene terephthalate (PET), a method in which terephthalic acid and ethylene glycol are esterified and then polycondensed, or an ester exchange reaction between terephthalic acid alkyl ester such as dimethyl terephthalate and ethylene glycol Any of the methods of polycondensation after carrying out can be carried out. The polymerization apparatus may be a batch type or a continuous type.

  The polyester polycondensation catalyst used in the polycondensation of the polyester is not particularly limited, but antimony trioxide is suitable because it is inexpensive and has excellent catalytic activity. A known method can be used to obtain a polyester resin using antimony trioxide as a catalyst. For example, the polyester resin mentioned in patent 4023220 gazette can be illustrated.

  In addition to the above, it is also preferable to use a germanium compound or a titanium compound as the polycondensation catalyst. More preferable polycondensation catalysts include a catalyst containing aluminum and / or its compound and a phenol compound, a catalyst containing aluminum and / or its compound and a phosphorus compound, and a catalyst containing an aluminum salt of a phosphorus compound. By using a catalyst containing aluminum and / or a compound thereof and a phosphorus compound, a polyester resin polymerized using an antimony trioxide catalyst is used. In the extruder during the film forming process, in the stretching process, and heat setting. It is because the production | generation of the cyclic trimer in a process can be reduced. Although it is not clear about this reason, it is guessed that the catalyst containing aluminum and / or its compound and a phosphorus compound has the effect | action which suppresses the thermal deterioration of a polyester resin.

  Hereinafter, the catalyst containing aluminum and / or a compound thereof and a phosphorus compound that can be used in the present invention will be described in detail, but the present invention is not limited to this.

  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 aluminum compounds 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 partial hydrolysates thereof 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. Thus, even if the addition amount of the aluminum component is small, the polycondensation catalyst of the present invention has a great feature in that it exhibits sufficient catalytic activity. As a result, the thermal stability and thermal oxidation stability are excellent, and foreign matters and coloring caused by the catalyst can be reduced.

  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 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. Further, the catalyst has catalytic activity not only in melt polymerization but also in solid phase polymerization or solution polymerization, and any method can produce a polyester resin suitable for production of a polyester film for solar cells. Is possible.

  The cyclic trimer content in the polyester film of the present invention is required to be 5000 ppm or less, preferably 4000 ppm or less, and more preferably 3500 ppm or less. Exceeding 5000 ppm is not preferable because durability decreases, and a cyclic trimer is likely to be deposited on the film surface. When a moisture-proof layer such as a metal or metal oxide thin film layer is laminated, a through-hole is formed in the moisture-proof layer. This is not preferable because it causes adverse effects such as generation.

  The durability mentioned in the present invention can be evaluated by the elongation at break at 192 hours under 105 ° C., 100% RH, 0.03 MPa. This breaking elongation retention is preferably 65% or more, more preferably 70% or more. By being in such a range, the polyester film for solar cells of the present invention can exhibit high hydrolysis resistance that can withstand long-term use outdoors.

  In order to bring the content of the cyclic trimer of the polyester film into the above range, it is preferable to use a polyester resin subjected to oligomer reduction treatment by a solid phase polymerization method as a raw material.

  The solid phase polymerization method referred to in the present invention is a method in which a polyester resin is heated in a solid phase under reduced pressure or in an inert gas stream as described above to further proceed polycondensation. You may combine the method of heating under reduced pressure in a solid-phase state, and the method of heat-processing in inert gas stream. The solid phase polymerization reaction can be carried out by a batch type apparatus or a continuous type apparatus, similarly to the melt polycondensation reaction. Melt polycondensation and solid phase polycondensation may be carried out continuously or separately. In addition, there is no restriction on taking measures such as removing oligomers such as cyclic trimers and by-products such as acetaldehyde contained in the polyester resin. Furthermore, for example, it is possible to incorporate a treatment such as purifying a polyester resin by an extraction method such as a supercritical pressure extraction method to remove impurities such as the by-products.

  In the polyester used in the present invention, other arbitrary polycondensates, antistatic agents, antifoaming agents, dyeing improvers, dyes, pigments, matting agents, fluorescent whitening agents, stabilizers, antioxidants Agents and other additives may be contained. As antioxidants, aromatic amine-based and phenol-based antioxidants can be used, and as stabilizers, phosphoric acid and phosphate ester-based phosphorus-based, sulfur-based, amine-based stabilizers, etc. Can be used.

  The solid phase polymerization is desirably performed at a temperature of 180 ° C. or higher and lower than the melting point, and particularly preferably 195 to 235 ° C. Above the melting point, the polyester resin melts and is not practical, and below 180 ° C., the rate of reduction of the cyclic trimer is extremely slow, which is not preferable. Furthermore, the solid phase polymerization needs to be performed under an inert gas flow or under reduced pressure. This inert gas means a gas that does not cause deterioration of the polyester resin obtained after solid-phase polymerization, and it is generally preferable to use inexpensive nitrogen. The amount of water in the inert gas may be in a range where the intrinsic viscosity of the polyester resin does not decrease during solid phase polymerization, and is usually 500 ppm or less. When solid-phase polymerization is performed under reduced pressure, the degree of vacuum is usually 0.1 KPa or less, more preferably 0.05 KPa or less.

  The solid-phase polymerization apparatus uniformly heats pellet resins such as a rotary solid-phase polymerization apparatus, a tower-type stationary solid-state polymerization apparatus, a fluidized-bed solid-phase polymerization apparatus, and a solid-phase polymerization apparatus having various stirring blades. What can be done is preferred.

  From the viewpoint of durability of the polyester film, it is also preferable to use polyester having a high molecular weight by solid phase polymerization or low acid value polyester. Thereby, the hydrolysis resistance of the polyester film can be further improved. When the polyester is made to have a high molecular weight by solid phase polymerization, the intrinsic viscosity is preferably 0.65 to 0.80 dl / g in order to obtain high heat resistance and hydrolysis resistance, and more preferably 0.70. ~ 0.75 dl / g. The intrinsic viscosity of polyester can be measured by dissolving polyester in a mixed solvent of parachlorophenol (6 parts by mass) and 1,1,2,2-tetrachloroethane (4 parts by mass) and measuring at 30 ° C. it can.

In the present invention, the amount of cyclic mer on the film surface on at least one surface is 50 μg / m ² or less, preferably 40 μg / m ² or less, particularly preferably 30 μg / m ² or less. When the amount of the cyclic trimer on the film surface exceeds 50 μg / m ² , protrusions due to the amount of the cyclic trimer increase, and there is a high probability that a moisture-proof layer such as a metal or metal oxide thin film layer will be scratched or dented. Become. The influence of the cyclic trimer on the moisture-proof layer can be evaluated by the number of dent defects generated when the moisture-proof film is pressed on the film surface. Specifically, the cyclic trimer amount on the film surface is 50 μg / m. ^In the case of ² or less, the number of dents measured by the following measurement method can be set to 200 or less per 1 mm ² , and deterioration of the moisture-proof function due to the moisture-proof layer can be suppressed.

  Thus, in maintaining the long-term moisture-proof property of the solar cell, by controlling the amount of surface cyclic trimer present on the film surface within a specific range, it is possible to suppress protrusions that cause scratches on the moisture-proof layer. The finding is an important point of the present invention. In order to bring the amount of the cyclic trimer on the film surface into the above range, it is not sufficient to simply reduce the cyclic trimer content of the polyester resin as in the prior art. This is because even if the cyclic trimer content of the polyester resin as a raw material is reduced, the cyclic trimer is deposited on the film surface due to the thermal history in film formation. Therefore, in addition to controlling the cyclic trimer content contained in the polyester film within the aforementioned range, it is desirable to perform a surface cyclic trimer reduction treatment during film formation.

Specific examples of the surface cyclic trimer reduction process during film formation include the following means. It is preferable to control the amount of cyclic trimer on the surface of the film within the aforementioned range by appropriately selecting or combining these means.
(1) Wind speed control in transverse stretching step and / or heat setting step (2) Control of cooling rate after thermal identification (3) Adjustment of furnace air in transverse stretching step and / or heat setting step (4) Melting step (5) Removal of surface cyclic trimer by touch roll

Furthermore, in the present invention, the amount of linear oligomer on the film surface on at least one of the surfaces is 20 μg / m ² or more and 100 μg / m ² or less, preferably 30 μg / m ² or more and 80 μg / m ² or less. When the linear oligomer on the film surface is 20 μg / μg / m ² or more, it is preferable because the number of minute repellency when an adhesive is applied to the film surface is suppressed. Here, the fine repellency is a fine repellency of 1 mm or more measured by the measurement method described later, and by generating the amount of linear oligomer on the film surface within the above range, the occurrence of fine repellency is 3 or less per 10 cm ^2. Preferably it can be zero. Moreover, when there is much oligomer amount which exists in the film surface, the layer of a linear oligomer may be formed and adhesiveness may be inhibited. Therefore, the amount of linear oligomer on the film surface is desirably 100 μg / m ² or less.

  Here, the amount of linear oligomer refers to the total amount of a linear dimer, a linear trimer, and a linear tetramer derived from a polyester resin used as a film raw material. For example, in the case of a polyester having ethylene terephthalate as the main repeating unit and starting from terephthalic acid and ethylene glycol, the linear dimer has two terephthalic acid units in one molecule and has a carboxylic acid terminal or a hydroxyl terminal. Means an oligomer having Similarly, a linear trimer means one having three terephthalic acid units in one molecule and having the same end groups as the linear dimer except that it has four linear tetramers. To do.

  The present invention has found that the fine repellency of the adhesive on the film surface, which causes a decrease in long-term adhesion between the solar cell polyester film and the moisture-proof layer, is reduced by the presence of the linear oligomer present on the film surface. This is also an important point. It is not clear how the linear oligomer present on the film surface reduces the fine repellency of the adhesive, but the presence of the linear oligomer improves the hydrophilicity of the film surface, and the adhesive (especially aqueous adhesives) Is likely to be uniformly applied to the film surface.

  Conventionally, as a polyester film for solar cells, a polyester film having a reduced cyclic trimer was used from the viewpoint of durability, but in such a polyester film, the content of linear oligomers is also reduced. It is counterproductive to the suppression of minute repellency. In order to achieve the durability suitable for solar cell applications, the present invention reduces the cyclic trimer content in the above range, and makes the amount of linear oligomer present on the film surface in the above range. It is desirable to perform a surface linear oligomer formation treatment on the membrane.

Specific examples of the surface linear oligomer generation process during film formation include the following means. It is preferable to control the surface linear oligomer amount on the surface of the film within the aforementioned range by appropriately selecting or combining these means.
(1) Surface treatment after heat treatment step and cooling step (2) Adjustment of surface treatment strength (3) Air humidity adjustment after heat treatment step and cooling step (3) Control of residence time in melting step (4) Thermal identification After cooling rate control

  In the present invention, if the amount of the cyclic trimer and the amount of linear oligomer on the film surface on at least one surface of the polyester film are in the above ranges, long-term moisture resistance and adhesion can be suitably provided by providing a moisture-proof layer on the surface. Can be maintained. Further, if the surface cyclic trimer amount and the linear oligomer amount on both sides of the film are in the above ranges, the moisture-proof layer can be suitably provided on both sides.

Next, the film forming method of the present invention will be described.
The polyester film of the present invention may be a single layer polyester film or a laminated polyester film having at least three layers and having an outermost layer and a center layer. In particular, it is preferable to have a three-layer structure of an outermost layer and a central layer from the viewpoint of productivity. As the layer structure in the three-layer structure, the outermost layers on the front and back may be the same composition or different compositions, but the two types and three layers (A layer / B layer / A layer) are flat. To preferred.

  In the case of the three-layer structure in the present invention, particles are contained in the outermost layer (A layer in the case of the above-mentioned two types and three layers), and particles are substantially contained in the central layer (B layer in the case of the above two types and three layers). It is preferable not to contain. The reason why particles are included in the A layer is that the metal or metal oxide-based thin film layer or coating layer is laminated with a moisture-proof layer such as laminating a handling property in a post-processing step and increasing the surface area so as to adhere to the moisture-proof layer. This is to improve the performance. When particles are added to the outermost layer, sufficient handling properties suitable for processability can be obtained. 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 it is preferable that the B layer substantially does not contain particles is to reduce the probability of formation of protrusions due to aggregates of lubricant particles, particularly inorganic particles. Further, by adopting such a configuration, a highly transparent film can be obtained, which is suitable for a field requiring transparency, such as a see-through solar cell.

  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.

  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.

  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. When it exceeds 3.5 μm, coarse protrusions are likely to be generated.

  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 generate coarse protrusions.

  The content of inorganic particles in the outermost layer is preferably 0.01 to 0.20 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, coarse protrusions are likely to be generated.

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.

  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.

  The thickness of the 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 a 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 sequentially biaxially stretched in a biaxial direction. Alternatively, a biaxially oriented polyester film that is simultaneously biaxially stretched and heat-set is suitable.

  When the film of the present invention is produced, it is preferable to remove foreign matters contained in the raw material polyester, which cause protrusions. 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 be reduced by performing high-precision filtration of molten resin using a filter medium with a filtration particle size (initial filtration efficiency: 95%) of 25 μm or less, but it is important to obtain a film with few protrusions. is there. The residence time of the molten resin in the extruder is preferably as short as possible from the viewpoint of cyclic trimer formation. When forming a relatively thin film, the residence time may be longer because the discharge amount of the molten resin may be reduced, but in order to suppress an increase in the amount of cyclic trimer in the film, Even in that case, it is preferable to be within 20 minutes. More preferably, it is within 15 minutes, More preferably, it is within 10 minutes.

  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 at 220 to 240 ° C., heat setting treatment and cooling are 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.

The heat setting process will be described more specifically.
As described above, in the present invention, the conditions of the transverse stretching step, the heat setting step, and the cooling step are important for reducing the amount of the cyclic trimer on the film surface. In general, the transverse stretching process, the heat setting process, and the cooling process are performed by blowing hot or cold air whose temperature is controlled in each adjacent zone. In the present invention, the wind speed is preferably 10 m / second or more in the transverse stretching step and the heat setting step in order to quickly remove the cyclic trimer deposited on the surface. More preferably, it is 20 m / sec or more. If the wind speed is less than 10 m / sec, the cyclic trimer tends to remain on the surface.

  Further, the cooling rate can be controlled by appropriately adjusting the temperature and speed of the cooling air. For example, the wind speed in the cooling step is preferably 5 m / second or more, and more preferably 10 m / second or more. In the cooling step, if the time from the maximum temperature in the heat setting step to 60 ° C. or less is too short, the cyclic trimer is likely to precipitate on the surface, which is not preferable. Therefore, the wind speed in the cooling step is preferably 30 m / second or less, and more preferably 20 m / second or less.

  Furthermore, in order to prevent re-adhesion of the cyclic trimer, it is preferable that the furnace air is exhausted out of the system or filtered through a filter having a filtration accuracy of 1 μm or less and then recirculated in the furnace. The heat setting temperature is preferably 220 ° C to 250 ° C. If it is less than 220 ° C., the amount of the cyclic trimer deposited may not be sufficiently removed, and the heat shrinkage rate of the film is further increased. If it exceeds 250 ° C., the amount of cyclic trimer precipitated may increase, which is not preferable. In addition, the wind speed said by this invention means the wind speed in the film surface which faced the hot air blowing nozzle exit, and is the value measured using the thermal-type anemometer (Nippon Kanomax make, Anemomaster model 6161).

  In order to reduce fine repellency of the polyester film of the present invention with respect to the adhesive, it is desirable to perform a linear oligomer generation treatment on the film surface after the film forming process, particularly the heat treatment process and the cooling process. Even if a linear oligomer is formed before the heat treatment step and the cooling step, it is not preferable because it decreases in the heat treatment step. The surface treatment method for imparting the linear oligomer is not particularly limited, and examples thereof include corona discharge treatment, glow discharge treatment, flame treatment, ultraviolet irradiation treatment, electron beam irradiation treatment, and ozone treatment. Among these, the corona discharge treatment is particularly preferable because it can be relatively easily performed.

  When performing a corona discharge treatment, the watt density is 3 to 30 w / m / min, preferably 5 to 20 w / m / min. If the watt density is less than 3 w / m / min, a sufficient linear oligomer may not be produced. On the other hand, if it exceeds 30 w / m / min, the cyclic trimer on the film surface may increase. When the amount of the cyclic trimer on the film surface increases, surface protrusions are formed, and long-term moisture-proof maintenance when the moisture-proof layer is laminated may be lowered.

  Furthermore, in a corona treatment environment, it is preferable that the temperature is 20 to 35 ° C. and the relative humidity is 50 to 80%. By maintaining the relative humidity relatively high, linear oligomers can be generated moderately while keeping the cyclic trimer formation on the film surface low. This is presumed to be due to the fact that linear oligomers are likely to react with moisture in the air. In general, the humidity during the film forming process is often kept at a relatively low humidity in order to reduce the corrosion of the equipment, but in the present invention, it is preferable to keep the relative humidity within the above range. A relative humidity of 80% or more is not preferable from the viewpoint of condensation and equipment corrosion.

  In the polyester film for solar cells of the present invention, it is desirable to provide a moisture-proof layer for the purpose of imparting water vapor barrier properties. As the moisture-proof layer, a coating or film having a water vapor barrier property, an inorganic oxide layer, an aluminum foil, or the like can be laminated.

  The coating layer can be applied by coating a fluororesin solution such as a polyvinyl fluoride solution. Moreover, as a barrier film, a polyvinylidene fluoride coat film, a silicon oxide vapor deposition film, an aluminum oxide vapor deposition film, an aluminum vapor deposition film, etc. can be used. The inorganic oxide layer is a layer made of an inorganic oxide such as aluminum oxide, silicon oxide, tin oxide, magnesium oxide, or a mixture thereof, and is a vacuum deposition method, a sputtering method, an ion plating method, a plasma vapor phase growth method. It can be laminated by a method (CVD) or the like. These can be directly laminated on the polyester film for solar cell of the present invention, or preferably used in a form of sandwich structure through an adhesive layer.

  The adhesive layer is not particularly limited, but urethane, polyester, acrylic polyol, isocyanate, silane coupling agent, and the like can be used. In particular, it is preferable from the environmental viewpoint to use a water-based adhesive. The adhesive layer is formed by using an adhesive solution by using a known printing method such as an offset printing method, a gravure printing method, a silk screen printing method, or a known coating method such as a roll coating, a knife edge coating, or a gravure coating. It forms by apply | coating to the polyester film for solar cells of this, and drying after that.

  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.

1. Content of cyclic trimer in polyester film The content of cyclic trimer in the polyester film was measured by the following method. 100 mg of the pulverized film sample is precisely weighed and dissolved in 3 ml of a hexafluoroisopropanol / chloroform mixed solution (volume ratio = 2/3), and further diluted with 20 ml of chloroform. To this is added 10 ml of methanol to precipitate the polymer, followed by filtration. The filtrate was evaporated to dryness and made up to volume with 10 ml of dimethylformamide. Subsequently, the cyclic trimer was quantified by the following high performance liquid chromatography method.

(Measurement condition)
Device: L-7000 (manufactured by Hitachi, Ltd.)
Column: μ-Bondasphere C18 5μ 100 Å 3.9 mm × 15 cm (manufactured by Waters)
Solvent: eluent A: 2% acetic acid / water (v / v)
Eluent B: Acetonitrile Gradient B%: 10 → 100% (0 → 55 min)
Flow rate: 0.8 ml / min Temperature: 30 ° C
Detector: UV-259nm

2. Amount of cyclic trimer and amount of linear oligomer on film surface Faces to be extracted of two films faced each other, and a 25.2 cm × 12.4 cm area per sheet was fixed to a frame with a spacer. 30 ml of ethanol was injected between the extraction surfaces, and cyclic trimers and linear oligomers on the film surface were extracted at 25 ° C. for 3 minutes. After evaporating the extract to dryness, the dry residue of the resulting extract was made up to 200 μl of dimethylformamide. Subsequently, the cyclic trimer and the linear oligomer were quantified from a calibration curve obtained in advance by the following method using high performance liquid chromatography. In addition, the linear oligomer was taken as the total value of a dimer, a trimer, and a tetramer.

(Measurement condition)
Apparatus: ACQUITY UPLC (manufactured by Waters)
Column: BEH-C18 2.1 × 150 mm (manufactured by Waters)
Mobile phase: Eluent A: 0.1% formic acid (v / v)
Eluent B: Acetonitrile Gradient B%: 10 → 98 → 98% (0 → 25 → 30 minutes)
Flow rate: 0.2 ml / min Column temperature: 40 ° C
Detector: UV-258nm

3. Average particle diameter 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.

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

5). Number of dents generated after pressing The sample film and the vapor-deposited surface of a film obtained by vapor-depositing aluminum on a polyethylene terephthalate film having a thickness of 50 μm were superimposed and pressed at a pressure of 0.1 MPa for 5 minutes. Next, the aluminum vapor-deposited film was peeled off, and unevenness data was collected on the pressed surface of the sample film using a non-contact surface shape measurement system (VertScan R5500H-M100).

(Measurement condition)
・ Measurement mode: PHASE mode ・ Objective lens: 50 × ・ 1 × Tube lens ・ Measurement area: 92 × 70 μm
Next, in the contour line display mode, an image in which the measurement surface was color-coded according to the height was displayed. At this time, surface correction (quaternary function correction) was performed to remove the waviness of the surface shape. In the contour line display mode, the average height in the measurement range is set to 0 nm, the maximum height value is set to 5 nm, the minimum height value is set to -5 nm, and the recessed portion having a depth of 2 nm or more is displayed from blue to blue-violet. It was displayed as follows. This operation was repeated, and the number of dents per 1 mm ² was determined.

6). Evaluation of adhesive repellency The following water-based adhesive was applied to the obtained polyester film so as to have a dry thickness of 5 μm, dried at 150 ° C. for 1 minute, and then visually observable per 10 cm ^2. The number of repels having a length (major axis) of 1 mm or more was counted and judged according to the following criteria.
A: No repelling is observed.
○: Number of cisterns 3 or less ×: Number of cisterns 4 or more

(Water-soluble adhesive composition)
Main agent: Polyester resin (Vylonal (registered trademark) MD1200: manufactured by Toyobo Co., Ltd.)
45% by mass
Curing agent: Melamine-based crosslinking agent (Nicalac (registered trademark) MW-22: manufactured by Sanwa Chemical Co., Ltd.)
5% by mass
Isopropyl alcohol 5% by mass
45% by weight of water

7). Breaking elongation retention rate (hydrolysis resistance evaluation)
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 film was cut into 70 mm × 190 mm, and the film was placed 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. The breaking elongation before and after the treatment was measured according to JIS-C-2318-1997 5.3.31 (tensile strength and elongation), and the breaking elongation retention was calculated according to the following formula.
Breaking elongation retention ratio (%) = [(breaking elongation after treatment (MPa)) / (breaking elongation before treatment (MPa))] × 100

(1) Polymerization of polyester resin (a) When the temperature of the esterification reactor is increased to 200 ° C., a slurry comprising 86.4 parts by mass of high-purity terephthalic acid and 64.4 parts by mass of ethylene glycol is prepared. While charging and 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.

(2) Polymerization of polyester resin (b) When the temperature of the esterification reactor was increased to 200 ° C, a slurry composed of 86.4 parts by mass of high-purity terephthalic acid and 64.4 parts by mass of ethylene glycol was prepared. Add ethylene glycol slurry of 0.03 parts by weight of antimony trioxide, 0.16 parts by weight of triethylamine and silica particles with an average particle diameter of 2.5 μm as a catalyst while charging and stirring to 2000 ppm with respect to the generated PET. did. 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.

(3) Polymerization of polyester resin (c) A mixture of bis (2-hydroxyethyl) terephthalate and oligomer produced from high-purity terephthalic acid and ethylene glycol according to a conventional method, and 13 g / l of ethylene chloride as a polycondensation catalyst. 0.015 mol% of the glycol solution as an aluminum atom with respect to the acid component in the polyester and 0.02 mol% of Irganox 1425 (manufactured by Ciba Specialty Chemicals) as a 10 g / l ethylene glycol solution of Irganox 1425 as Irganox 1425 with respect to the acid component And stirred at 245 ° C. under a nitrogen atmosphere for 10 minutes. 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.

(4) Polymerization of polyester (d) resin Porous silica particles having an average particle diameter of 2.5 μm are charged in ethylene glycol, and further filtered through a viscose rayon filter having a 95% cut diameter of 30 μm. An ethylene glycol slurry of silica 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.

Example 1
Polyester resin (A) and polyester resin (b) are each solid-phase polymerized at 220 ° C. under a reduced pressure of 0.5 mmHg using a rotary vacuum polymerization apparatus, and polyester resin (A) having an intrinsic viscosity of 0.75 dl / g. And polyester resin (B) was obtained.

  After drying the polyester resin (A) as a raw material for the intermediate layer of the base film at 135 ° C. for 6 hours under reduced pressure (1 Torr), the polyester resin (A) and the polyester resin (B ) Were blended so that the concentration of silica particles having an average particle size of 2.5 μm was 0.06% by mass, supplied to the extruder 1 (for outer layer A layer), and dissolved at 285 ° C. These two polyester resins are filtered through a filter medium made of a sintered stainless steel (nominal filtration accuracy of 10 μm particles, 95% cut), laminated in a three-layer confluence block, extruded into a sheet form from a die, and then electrostatically The film was wound around a casting drum having a surface temperature of 30 ° C. using an applied 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 ratio of the thickness of A layer / B layer / A layer was 1.5: 7: 1.5. At this time, the residence time of the molten resin in the extruder was 15 minutes. 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 peripheral speed difference 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, heat setting treatment was performed at a maximum temperature of 235 ° C., and 3% relaxation treatment was performed in the width direction in a cooling process at 30 ° C.
In the preheating process, the transverse stretching process, and the heat setting process, the hot air speed in the furnace was 20 m / second, and the cooling air speed in the cooling process was 10 m / second. The hot air and the cooling air were circulated through a filter having a filtration accuracy of 1 μm. Subsequently, both sides of the film were subjected to corona treatment at a watt density of 5 w / m / min, a treatment surface-electrode distance of 2 mm, an air temperature of 20 ° C., and a relative humidity of 55% to obtain a polyester film for solar cells having a film thickness of 50 μm.

(Example 2)
Solar with a film thickness of 50 μm as in Example 1, except that the wind speed in the furnace in the preheating step, the transverse stretching step, and the heat setting step was 10 m / second, and the corona treatment was performed with a watt density of 10 w / m / min. A battery polyester film was obtained.

(Example 3)
The polyester resin (a) and the polyester resin (b) are respectively replaced with the polyester resin (c) and the polyester resin (d), and each polyester resin is subjected to solid phase polymerization in the same manner as in Example 1 to obtain the polyester resin (C) and A polyester resin (D) was obtained. A polyester film for a solar cell having a film thickness of 50 μm was obtained in the same manner as in Example 2 except that the polyester resin (C) and the polyester resin (D) were used.

Example 4
A polyester film for a solar cell having a film thickness of 50 μm was obtained in the same manner as in Example 3 except that the wind speed in the furnace in the preheating step, the transverse stretching step, and the heat setting step was 20 m / sec.

(Example 5)
A polyester film for a solar cell having a film thickness of 50 μm was obtained in the same manner as in Example 3 except that the wind speed in the furnace in the preheating step, the transverse stretching step, and the heat setting step was changed to 30 m / sec.

(Example 6)
A polyester film for a solar cell having a film thickness of 50 μm was obtained in the same manner as in Example 3 except that the corona treatment was performed in an environment with an air temperature of 20 ° C. and a relative humidity of 75%.

(Example 7)
In the corona treatment, a polyester film for a solar cell with a film thickness of 50 μm was obtained in the same manner as in Example 3 except that the watt density was 20 w / m / min.

(Example 8)
A solar cell polyester film having a film thickness of 50 μm was obtained in the same manner as in Example 3 except that the watt density was 30 w / m / min in the corona treatment.

Example 9
A polyester film for a solar cell was obtained in the same manner as in Example 3 except that the discharge amount of the extruder was adjusted so that the film thickness was 188 μm. The residence time of the molten resin in the extruder at this time was 10 minutes.

(Example 10)
A polyester film for a solar cell having a film thickness of 50 μm was obtained in the same manner as in Example 3 except that the wind speed in the cooling step was changed to 5 m / min second.

(Example 11)
A polyester film for a solar cell having a film thickness of 50 μm was obtained in the same manner as in Example 3 except that the hot air and cold air in the furnace in the preheating step, transverse stretching step, heat setting step, and cooling step were circulated without passing through a filter. .

(Comparative Example 1)
A polyester film for a solar cell having a film thickness of 50 μm was obtained in the same manner as in Example 3 except that the polyester resin (c) and the polyester resin (d) not subjected to solid phase polymerization were used.

(Comparative Example 2)
A polyester film for a solar cell having a film thickness of 50 μm was obtained in the same manner as in Example 2 except that the corona treatment was not performed.

(Comparative Example 3)
A polyester film for a solar cell with a film thickness of 50 μm was obtained in the same manner as in Example 3 except that the hot air velocity in the furnace in the preheating step, the transverse stretching step, and the heat setting step was changed to 5 m / sec.

(Comparative Example 4)
A polyester film for a solar cell having a film thickness of 50 μm was obtained in the same manner as in Example 3 except that the corona treatment was performed in an environment with an air temperature of 20 ° C. and a relative humidity of 35%.

(Comparative Example 5)
In the corona treatment, a polyester film for a solar cell having a film thickness of 50 μm was obtained in the same manner as in Example 3 except that the watt density was 40 w / m / min.

  The laminated polyester film for solar cells of the present invention is suitable for long-term moisture-proof maintenance and adhesion with a moisture-proof layer, and can be suitably used as a constituent member of a solar cell backsheet.

Claims (3)

The cyclic trimer content in the polyester film is 5000 ppm or less per the polyester film,
The solar cell in which the amount of cyclic trimer on the film surface on at least one surface of the polyester film is 50 μg / m ² or less and the amount of linear oligomer on the film surface is 20 μg / m ² or more and 100 μg / m ² or less. Polyester film.   The polyester film for solar cells according to claim 1, comprising a polyester resin polymerized using a polycondensation catalyst containing aluminum and / or a compound thereof and a phenol compound. The polyester film has at least three layers of an outermost layer and a central layer;
The outermost layer contains particles;
The polyester film for solar cells according to claim 1, wherein the central layer does not substantially contain particles.