JP5858210B2 - Inorganic thin film forming substrate polyester film for solar cells - Google Patents

Description

  TECHNICAL FIELD The present invention relates to an inorganic thin film-forming substrate polyester film for solar cells suitable for long-term moisture resistance maintenance when used in a solar cell protective sheet, a barrier polyester film using the same, and a solar cell 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. In recent years, a protective sheet called a front sheet formed by laminating a polymer resin film instead of glass has been used from the viewpoint of weight reduction.

  As a method for producing 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. Place the upper transparent material or Freon sheet, and cover the back sheet on the opposite filler sheet, then preheat at 40-50 ° C for about 5 minutes, and further from both sides at about 150 ° C for about 30 minutes It is made by hot pressing and fusing and integrating the back sheet for solar cells.

  Solar cell protective sheets such as a solar cell back sheet and a solar cell front sheet are required to have various functions such as light resistance, weather resistance, hydrolysis resistance, heat resistance, light reflection characteristics, light transmission characteristics, and barrier properties. Therefore, it has the structure which the several functional film which has various functions laminated | stacked on the multilayer. For example, a solar cell backsheet having a laminated structure such as a barrier layer (moisture-proof layer) / adhesive / high durability film (outermost layer) by a polyester film / inorganic thin film layer is proposed from the solar cell element side. ing. Further, as a solar cell front sheet, a solar cell front sheet having a laminated structure such as an antifouling layer / cured resin layer / polyester film / inorganic thin film layer from the incident light side / adhesive layer has been proposed. .

In Patent Document 1 and Patent Document 2, a polyester resin used as a raw material for a polyester film used for a solar cell protective sheet is a polyester resin that has been subjected to treatment such as solid phase polymerization for improving durability at the stage of a pellet-shaped resin. It has been. 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 produced using a polyethylene terephthalate resin that has been further oligomer-reduced using a polymerization catalyst comprising an aluminum compound and a phosphorus compound, and the cyclic trimer concentration in the polyester film is disclosed. A laminated film in which the amount of cyclic trimer on the film surface is from 0.1 mg / m ² to 0.11 mg / m ² is exemplified.

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 cell protective 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 amount of the cyclic trimer can be obtained by performing the solid phase polymerization treatment or the like.

  As described above, the solar cell module is required to have a high barrier property (moisture resistance) for preventing insulation and preventing deterioration of the power generation element. However, when the use period of the solar cell module is set as 20 years or more, the above-described polyester film may not be able to be said to have a sufficiently low long-term moisture-proof maintenance.

  In view of the above problems, an object of the present invention is to provide an inorganic thin film-forming substrate polyester film for solar cells capable of maintaining moisture resistance for a long period of time.

  As a result of earnest study on the long-term moisture-proof maintenance of the solar cell protective sheet, the present inventor has performed heat press when there are innumerable protrusions due to the crystalline product of the cyclic trimer on the surface of the inorganic thin film forming substrate polyester film used for the protective sheet. It has been found that scratches and numerous dents are sometimes generated in a highly durable moisture-proof layer such as a metal or metal oxide 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 has been found that when a polyester film having a large amount is used, even if the deterioration of the solar cell element due to the occasional decrease in moisture-proof property is slight, the performance of the solar cell is greatly affected when used for more than 20 years.

The above-described problem can be achieved by the following solution means.
The first invention has a coating layer on at least one surface of a polyester film, and the coating layer includes a resin having an oxazoline group, and an aqueous acrylic resin containing a carboxylic acid group or an aqueous polyester resin containing a carboxylic acid group. The proportion of the aqueous acrylic resin containing a carboxylic acid group other than the resin having an oxazoline group or the aqueous polyester resin containing a carboxylic acid group is 5 to 60% by weight, and the cyclic trimer content in the polyester film Is an inorganic thin film-forming base material polyester film for solar cells in which the amount of the cyclic trimer on the surface of the polyester film is 50 μg / m ² or less.
2nd invention is the said inorganic thin film formation base-material 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.
In a third aspect of the invention, 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 substantially does not contain particles. It is a base polyester film.
The fourth invention is the ratio (P1 / P2) of the peak intensity (P1) of 1655 cm ^{−1 and} the peak intensity (P2) of 1580 cm ⁻¹ in the total reflection infrared absorption spectrum of the coating layer, and the film thickness D of the coating layer. [Nm] is the above-mentioned inorganic thin film forming substrate polyester film for solar cells that satisfies the following formula [1].
0.05≤ (P1 / P2) /D≤0.25 ... [1]
5th invention is a barrier polyester film for solar cells formed by laminating | stacking an inorganic thin film layer on the coating layer surface of the said inorganic thin film formation base material polyester film for solar cells.
6th invention is a solar cell protective sheet which uses the said barrier polyester film for solar cells as a structural member.
7th invention is the method of manufacturing the inorganic thin film formation base-material polyester film for solar cells in any one of 1st-4th, Comprising: The following (1)-(5) means is formed during film forming. It is a manufacturing method of the inorganic thin film formation base material polyester film for solar cells characterized by selecting or combining.
(1) the transverse stretching and / or wind speed control (2) in the heat setting step thermal solid funnel of control of the cooling rate (3) adjustment of the furnace the air in the transverse stretching and / or heat fixing step (4) melting step (5) Removal of surface cyclic trimer by touch roll

The inorganic thin film forming substrate polyester film for solar cells of the present invention has a small amount of cyclic trimer present on the surface. Therefore, there are few protrusions which consist of cyclic trimers which inhibit long-term moisture-proof property, and it is suitable for long-term moisture-proof maintenance as an inorganic thin film formation base polyester film for solar cells.
Furthermore, in the preferable aspect of this invention, since it has a coating layer on the film surface, it is suitable for long-term moisture-proof maintenance.

(Polyester film)
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 polymerization catalyst used during 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 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.

  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. 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 a solar cell component. is there.

  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 deteriorates, and a cyclic trimer is likely to be deposited on the film surface. When a moisture-proof layer composed of an inorganic thin film layer is laminated, a through-hole is generated in the moisture-proof layer. It is not preferable because it causes an adverse effect.

  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 as in 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 surface of the film exceeds 50 μg / m ² , protrusions due to the amount of the cyclic trimer increase, and the probability of causing scratches and dents in the moisture-proof layer composed of the inorganic thin film layer increases. 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 by the moisture-proof layer can be suppressed.

  In this invention, if the cyclic | annular trimer amount of the film surface in the at least one surface of a polyester film is the said range, long-term moisture-proof property can be suitably maintained by providing a moisture-proof layer in the surface concerned. Moreover, if the surface cyclic | annular trimer amount on both surfaces of a film is the said range, a moisture-proof layer can be suitably provided in both surfaces.

  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) the transverse stretching and / or wind speed control (2) in the heat setting step thermal solid funnel of control of the cooling rate (3) adjustment of the furnace the air in the transverse stretching and / or heat fixing step (4) melting step (5) Removal of surface cyclic trimer by touch roll

  The polyester film of the present invention may be a single-layer polyester film or a laminated polyester film having at least three layers 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. Moreover, by taking this structure, a highly transparent film can be obtained, and it is also suitable for fields where transparency is required, such as a front sheet.

  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 10 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 30 μm, more preferably 50 μm, still 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.

(Coating layer)
In view of maintaining the moisture-proof function of the inorganic thin film layer for a long period of time, it is desirable to provide a coating layer on at least one surface of the polyester film as an intermediate layer with the inorganic thin film layer. Thereby, since the adhesiveness of an inorganic thin film layer improves, it is suitable for long-term maintenance of a moisture-proof function.

  The components constituting the coating layer include (1) metal oxides composed of oxides such as Al, Si, Ti, (2) polyester resin, polyurethane resin, acrylic resin, polyvinyl alcohol, polyvinyl pyrrolidone, starch, methyl cellulose, carboxy Polymer resin such as methyl cellulose (3) Metal alkoxide and hydrolyzate thereof, silane coupling agent, cross-linked compound such as methylol melamine compound, oxazoline compound, and combinations thereof, for example, polymer resin described in (2) above Can be used which is crosslinked with the crosslinking compound described in (3) above. In particular, it is preferable to use a polymer resin alone or in combination in terms of adhesion to a polyester film.

  In order to prevent deterioration of the inorganic thin film layer due to oligomer precipitation from the base film, a method of providing a coating layer made of a mixture of various aqueous acrylic resins and an oxazoline group-containing water-soluble polymer is known. In this case, crosslinking the coating layer with an oxazoline group is suitable for improving water resistance. In particular, in order to improve the water resistance of the coating layer under wet heat, a method of providing a coating layer composed of various aqueous polyurethane and / or aqueous polyester resins and an oxazoline group-containing water-soluble polymer is preferable.

  Furthermore, by using a resin having an oxazoline group for the polyester film coating layer and reacting / remaining the oxazoline group in a specific range, the moisture resistance of the laminate formed with the inorganic thin film layer after high temperature and high humidity over time It can be further improved. Residual oxazoline groups in the coating layer have a high affinity with inorganic thin films such as metal oxides due to their polarities, and good adhesion with metal oxides during the formation of inorganic thin film layers and after aging under high temperature and high humidity. It is considered that the adhesion between the polyester film and the coating layer is improved.

  Examples of the resin having an oxazoline group include a polymer having an oxazoline group, for example, a polymerizable unsaturated monomer having an oxazoline group, and other polymerizable unsaturated monomers as required, and a conventionally known method (for example, solution polymerization). And a polymer obtained by copolymerization by emulsion polymerization or the like.

  Examples of the polymerizable unsaturated monomer having an oxazoline group include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2- Examples thereof include isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, and 2-isopropenyl-5-ethyl-2-oxazoline.

  Examples of the other polymerizable unsaturated monomers include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and cyclohexyl (meta ) Acrylate, lauryl (meth) acrylate, isobornyl (meth) acrylate and other (meth) acrylic acid alkyl or cycloalkyl esters having 1 to 24 carbon atoms; 2-hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate (Meth) acrylic acid hydroxyalkyl esters such as (meth) acrylic acid, etc .; vinyl aromatic compounds such as styrene and vinyltoluene; (meth) acrylamide, dimethylaminopropyl (meth) acrylamide, dimethylaminoethyl Addition product of meth) acrylate, glycidyl (meth) acrylate and amines; polyethylene glycol (meth) acrylate; N-vinylpyrrolidone, ethylene, butadiene, chloroprene, vinyl propionate, vinyl acetate, (meth) acrylonitrile, etc. . These may be selected singly or in appropriate combination of two or more.

  The composition molar ratio of the copolymer of the polymerizable unsaturated monomer having an oxazoline group and another polymerizable unsaturated monomer is such that the polymerizable unsaturated monomer having an oxazoline group is 30 to 70 mol%. It is preferable that it is 40 to 65 mol%.

  The resin having an oxazoline group is preferably a water-soluble resin because it improves compatibility with other resins, improves wettability, improves the crosslinking reaction efficiency, and the transparency of the coating layer. In order to make the resin having an oxazoline group water-soluble, it is preferable to contain a hydrophilic monomer as another polymerizable unsaturated monomer. As the hydrophilic monomer, a monomer having a polyethylene glycol chain such as 2-hydroxyethyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, a monoester compound of (meth) acrylic acid and polyethylene glycol, (Meth) acrylic acid 2-aminoethyl and its salts, (meth) acrylamide, N-methylol (meth) acrylamide, N- (2-hydroxyethyl) (meth) acrylamide, (meth) acrylonitrile, sodium styrenesulfonate, etc. Can be mentioned. Especially, it is preferable to contain the monomer which has polyethyleneglycol chains, such as (meth) acrylic-acid methoxypolyethylene glycol with high solubility to water, and the monoester compound of (meth) acrylic acid and polyethyleneglycol. The molecular weight of the polyethylene glycol chain to be introduced is preferably 200 to 900, more preferably 300 to 700.

  Further, the oxazoline value of the compound having an oxazoline group is not particularly limited, but specifically, for example, 1000 g-solid / eq. Or less, more preferably 500 g-solid / eq. Hereinafter, even more preferably, 300 g-solid / eq. It is as follows. When the oxazoline value exceeds the upper limit, the interaction with the carboxylic acid group and the like contained in the inorganic thin film layer, the base film and the coating layer is not expressed, and the durability and water resistance may not be obtained satisfactorily. . The oxazoline value (g-solid / eq.) Is assumed to be a polymer weight per 1 mol of the oxazoline group. Therefore, the smaller the value of the oxazoline value, the larger the amount of oxazoline groups in the polymer, and the larger the value, the smaller the amount of oxazoline groups in the polymer.

  The resin having oxazoline is preferably contained as a main component in the coating layer, preferably 50% by mass or more, more preferably 70% by mass or more, and further preferably 80% by mass or more.

Furthermore, as the coating layer, the ratio (P1 / P2) of the peak intensity (P1) of 1655 cm ^{−1 and} the peak intensity (P2) of 1580 cm ⁻¹ in the total reflection infrared absorption spectrum and the film thickness D [nm] of the coating layer Preferably satisfies the following formula [1]. Here, the peak at 1655 cm ⁻¹ is the absorbance derived from the oxazoline group, and the peak at 1580 cm ⁻¹ is the absorbance derived from the polyester. The range of the above formula [1] is preferably 0.055 ≦ (P1 / P2) /D≦0.22, more preferably 0.06 ≦ (P1 / P2) /D≦0.20.
0.05≤ (P1 / P2) /D≤0.25 ... [1]

  Conventionally, it has been considered desirable to actively introduce a crosslinked structure in order to maintain the moisture resistance of the coating layer, that is, moisture resistance in a high temperature and high humidity state. However, the barrier property can be more suitably maintained for a long period of time by configuring the coating layer as described above. Conventionally, if the adhesion between the inorganic thin film layer and the laminated film provided with the base film or the coating layer is insufficient, the laminated body formed with the inorganic thin film layer has water between the layers when used for a long time in a humid heat environment. It is considered that peeling occurs at the interface with the inorganic thin film layer. As a result of the peeling portion being used as a trigger, the inorganic thin film layer is cracked or floated, resulting in a decrease in barrier strength. Also, delamination can occur between the base film and the coating layer. That is, in a high temperature and high humidity state, the polyester resin constituting the base film or the resin in the coating layer is hydrolyzed and the bonds are broken. As a result, poor adhesion between the base film and the coating layer occurs, which can cause the barrier strength to decrease as described above. Therefore, the unreacted oxazoline group present in the coating layer as described above reacts with the carboxylic acid terminal generated by hydrolysis of the base film and the coating layer to form a crosslink. In other words, a decrease in adhesion with the inorganic thin film layer due to hydrolysis can be prevented by self-healing. Moreover, the unreacted oxazoline group has a high affinity with an inorganic thin film such as a metal oxide because of its polarity, and can exhibit strong adhesion with the metal oxide when forming the inorganic thin film layer. The coating layer may contain other resin that reacts with the oxazoline group within the range satisfying the above formula [1]. However, the unreacted oxazoline group is present in the coating layer so that the unreacted oxazoline group is present in the coating layer. The group is considered to act on the self-healing of the coating layer and the adhesion with the inorganic thin film layer.

  If the amount is less than the lower limit, the amount of oxazoline groups is small or the thickness of the coating layer is too thick, so that sufficient gas barrier strength may not be maintained. Above the above upper limit, the film thickness becomes too thin with respect to the amount of the oxazoline group, and sufficient interlayer adhesion may not be obtained.

  The thickness of the coating layer is preferably 5 to 100 nm. Thereby, the thickness of a coating layer can be made more uniform and an inorganic thin film layer can be deposited densely. Moreover, since the cohesion force of coating layer itself improves and the adhesive force between an inorganic thin film layer-coating layer-base film becomes dense, the water resistance of a coating film can be improved.

  When the thickness of the coating layer exceeds 100 nm, the cohesive force of the coating layer becomes insufficient due to the presence of a large amount of oxazoline groups, and the uniformity of the coating layer also decreases, so the barrier property may not be sufficiently maintained. . Moreover, not only the gas barrier property is lowered, but the production cost may be increased, and the economy may be deteriorated. On the other hand, if it is less than 5 nm, sufficient interlayer adhesion with the substrate may not be obtained.

In the present invention, a resin other than a resin having an oxazoline group is contained in order to improve the water resistance of the coating layer within a range where a large amount of the oxazoline group is not consumed, that is, within the range of the above formula [1]. It is suitable to make it. Examples of the resin to be included in the coating layer include an aqueous acrylic resin, an aqueous polyester resin, and an aqueous urethane resin. Preferably, it contains a carboxylic acid group. When the carboxylic acid group is contained, the cohesive force of the coating layer is improved by partially crosslinking with the oxazoline group, and the water resistance can be further improved. Here, when coexisting resin which has a carboxylic acid group, it is preferable to add so that carboxylic acid group amount [mmol] with respect to the oxazoline group amount [mmol] in a coating liquid may be 0-20 mmol%. More preferably, it is 0-15 mmol%. When the amount is 20 mmol% or more, the cross-linking reaction proceeds excessively at the time of forming the coating layer, so that a large amount of oxazoline groups are consumed. Sexual maintenance may not be sufficient. Examples of those containing carboxylic acid groups include aqueous acrylic resins and aqueous polyester resins.

  The blending ratio of the resin other than the resin having an oxazoline group is usually 5 to 60% by weight, preferably 10 to 55% by weight, more preferably 15 to 50% by weight. When the blending ratio of the resin is less than 5% by weight, the effect of water resistance tends not to be sufficiently exhibited. When the resin content exceeds 60% by weight, the coating layer becomes too hard. There is a tendency that the stress load increases.

  The method for providing the coating layer on at least one surface of the base film is not particularly limited, and for example, a coating method can be employed. Among the coating methods, preferred examples include an off-line coating method and an in-line coating method. For example, in the case of an in-line coating method performed in the process of producing a base film, the drying and heat treatment conditions during coating are the coating thickness, Although it depends on the conditions of the apparatus, it is preferable that the film is sent to a stretching process in a right angle direction immediately after coating and dried in a preheating zone or a stretching zone of the stretching process. In such a case, it is normally performed at about 50 to 250 ° C. The base film may be subjected to corona discharge treatment or other surface activation treatment. The coating layer may be formed after film formation or during the film production process.

If necessary, in the coating layer, antistatic agents and slip agents, is optional so long as it does not inhibit the object of the present invention is a known inorganic, this contains an organic various additives such as antiblocking agent .

(Inorganic thin film forming substrate polyester film manufacturing method for solar cells)
Hereinafter, although the manufacturing method of a film is illustrated, it is not specifically limited to this.
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.

  Moreover, when manufacturing the film of this invention, it is preferable to remove the foreign material contained in the raw material polyester which becomes a cause of protrusion. 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. In the case of the in-line coating method, the coating layer is formed by applying the coating solution to an unstretched or uniaxially stretched PET film, drying it, stretching it at least in a uniaxial direction, and then performing a heat treatment.

  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).

(Barrier polyester film)
The barrier polyester film of the present invention is preferably a laminate in which an inorganic thin film layer is further laminated on the coating layer of the polyester film. For the inorganic thin film layer, an inorganic oxide such as silica, alumina, or a mixture of alumina and silica is used. In particular, it is preferable to use a composite oxide of alumina and silica from the viewpoint that both flexibility and denseness of the thin film layer can be achieved. The mixing ratio of alumina and silica is a weight ratio of metal, and Al is preferably in the range of 20 to 70%.

  In the laminate of the present invention, the thickness of the inorganic thin film layer is usually 1 to 800 nm, preferably 5 to 500 nm. If the film thickness is less than 1 nm, it is difficult to obtain satisfactory barrier properties. Even if the film thickness exceeds 800 nm, the manufacturing cost is disadvantageous.

  The typical manufacturing method for forming the inorganic thin film layer is explained by the formation of a silicon oxide / aluminum oxide thin film. Examples of the inorganic thin film forming method by vapor deposition include physical vapor deposition such as vacuum vapor deposition, sputtering, and ion plating. Or CVD method (chemical vapor deposition method) etc. are used suitably.

For example, when the vacuum deposition method is employed, a mixture of SiO ₂ and Al ₂ O ₃ or a mixture of SiO ₂ and Al is used as a deposition material. For heating, resistance heating, high-frequency induction heating, electron beam heating, etc. can be adopted, oxygen, nitrogen, hydrogen, argon, carbon dioxide gas, water vapor, etc. are introduced as reaction gases, ozone addition, ion assist It is also possible to employ reactive vapor deposition using such means. Furthermore, the film forming conditions can be arbitrarily changed, such as applying a bias to the laminated film, heating or cooling the laminated film. The vapor deposition material, reaction gas, substrate bias, heating / cooling, and the like can be similarly changed when a sputtering method or a CVD method is employed.

(Solar cell protection sheet)
The solar cell protective sheet is used on the light incident surface, the opposite surface, or both surfaces of the solar cell module, and is a sheet having a single layer structure or a laminated structure of two or more layers. This is called a sheet. The solar cell protective sheet is preferably a laminate of a plurality of resin sheets having respective functions. Since the solar cell element is deteriorated by humidity, these protective sheets usually have a moisture-proof function (barrier function). The barrier polyester film of the present invention is suitable as a constituent member of a solar cell protective sheet in that the barrier property can be maintained for a long time.

  As a solar cell protective sheet, for example, as a solar cell front sheet, a configuration of polyester film / adhesive / barrier polyester film of the present invention / adhesive / hard coat layer is exemplified.

  It is also a preferred embodiment that an ultraviolet absorber is added to the hard coat layer in order to improve the weather resistance. In addition, providing an antifouling layer, an antireflection layer, or the like as the outermost layer is a preferable embodiment for increasing the amount of light incident on the solar cell element and improving the photoelectric conversion efficiency.

  As a solar cell protective sheet, for example, as a solar cell back sheet, for example, a configuration such as polyester film / adhesive / barrier polyester film of the present invention / adhesive / polyvinyl fluoride film or polyester high durability moisture-proof film is exemplified. Is done.

EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these Examples from the first. The descriptions of Examples 1 to 10, 20 and 21 below are read as Reference Examples 1 to 10, 20 and 21. Moreover , the evaluation method used in each Example , reference example, and comparative example is demonstrated below.

(1) Intrinsic viscosity Based on JIS K7367-5, it measured at 30 degreeC, using the mixed solvent of phenol (60 mass%) and 1,1,2,2-tetrachloroethane (40 mass%) as a solvent.

(2) Reduced viscosity It measured at 30 degreeC using 25 mL of mixed solvents of phenol (60 mass%) and 1,1,2,2-tetrachloroethane (40 mass%) as a solvent with respect to 0.1 g of resin.

(3) Glass transition temperature In accordance with JIS K7121, using a differential scanning calorimeter (Seiko Instruments, DSC6200), 10 mg of a resin sample was heated at a rate of 20 ° C / min over a temperature range of 25 to 300 ° C. The extrapolated glass transition start temperature obtained from the curve was defined as the glass transition temperature.

(4) Number average molecular weight 0.03 g of a resin was dissolved in 10 ml of tetrahydrofuran, and a GPC-LALLS apparatus low angle light scattering photometer LS-8000 (manufactured by Tosoh Corporation, tetrahydrofuran solvent, reference: polystyrene) was used. The number average molecular weight was measured using a flow rate of 1 ml / min and a column (showex KF-802, 804, 806 manufactured by Showa Denko KK).

(5) Resin composition The resin is dissolved in deuterated chloroform, and ¹ H-NMR analysis is performed using a nuclear magnetic resonance analyzer (NMR) Gemini-200 manufactured by Varian, and the mol% ratio of each composition is determined from the integral ratio. Were determined.

(6) Oxazoline value A resin containing oxazoline is freeze-dried and analyzed by ¹ H-NMR, and the oxazoline value is calculated from the absorption peak intensity derived from the oxazoline group and the absorption peak intensity derived from other monomers. did.

(7) 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-258nm

(8) Amount of cyclic trimer on the film surface Faces to be extracted (non-coated layer surfaces) of two films face each other, and a 25.2 cm x 12.4 cm area can be extracted for each sheet with a spacer in a frame Fixed. 30 ml of ethanol was injected between the extraction surfaces, and the cyclic trimer on the film surface was 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 was quantified from a calibration curve obtained in advance by the following method using high performance liquid chromatography.

(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

(9) Average particle diameter Inert particles were observed with a scanning electron microscope (manufactured by Hitachi, Ltd., S-51O type), 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.

(10) Number of dents generated after pressing The deposited sample film and a polyethylene terephthalate film having a thickness of 50 μm were superimposed on each other and pressed at a pressure of 0.1 MPa for 5 minutes. Next, height data of the pressed surface of the sample film was collected 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.

(11) Barrier maintenance ability The deposited film was treated at 121 ° C. and 100% RH for 30 minutes and then dried at 40 ° C. for 1 day. For the sample before and after the wet heat treatment, according to JIS K7129 B method, using a water vapor transmission rate measuring device (PERMATRAN-W3 / 33MG MOCOM Co., Ltd.), water vapor in an atmosphere at a temperature of 40 ° C. and a humidity of 100% RH. The transmittance was measured. In addition, humidity control to the barrier film was performed in a direction in which water vapor permeated from the base material layer side to the inorganic thin film layer side. The maintenance rate of the water vapor permeability after the treatment when the water vapor permeability before the treatment was 100% was evaluated according to the following rank.
◎: Barrier maintenance rate is 90% or more ○: Barrier maintenance rate is 80% or more △: Barrier maintenance rate is 70% or more ×: Barrier maintenance rate is less than 70%

(12) Measurement of total reflection infrared absorption spectrum in coating layer About the coating layer surfaces obtained in the examples and comparative examples, the total reflection absorption infrared spectroscopy was used to measure the absorbance specifically obtained from the base film. As a control, an intensity ratio (P1 / P2) of absorbance derived from oxazoline (peak (P1) at 1655 cm ⁻¹ ) and absorbance derived from polyethylene terephthalate (peak intensity (P2) at 1580 cm ⁻¹ ) was determined.
That is, measured by total reflection absorption infrared spectroscopy under the conditions shown below, the absorbance derived from the oxazoline group is the value of the height of the absorption peak having an absorption maximum in the region of 1655 ± 10 cm ⁻¹ , and the absorbance derived from PET is The height of the absorption peak having an absorption maximum in the region of 1580 ± 10 cm ⁻¹ was used. The peak of 1655 cm ^-1, since the peak is in the shoulder, the baseline was line connecting the 1600 cm ^-1 and 1800 cm ^-1. On the other hand, the baseline of the peak at 1580 cm ⁻¹ was a line connecting the sleeves on both sides of the peak.

(Measurement condition)
Apparatus: FTS-60A / 896 manufactured by Varian
Single reflection ATR attachment: Silver Gate manufactured by SPECTRA TECH
Optical crystal: Ge
Incident angle: 45 °
Resolution: 4cm ^-1
Accumulation count: 128 times If the coating layer is thin and sufficient sensitivity cannot be obtained, use a one-time reflection attachment with a larger incident angle (65 degrees) (for example, ST Japan Instead of VeeMax), the measurement may be performed.

(13) Measurement of average thickness of coating layer The sample was cut obliquely, and the film thickness was measured by measuring the height of the coating layer / substrate film interface from the surface of the coating layer with SPM.

  Diagonal cutting was carried out using SAICAS NN04 manufactured by Daipla Wintes. A diamond knife was used as the cutting edge, and oblique cutting was performed at a horizontal speed of 500 nm / s and a vertical speed of 20 nm / s. (The cutting speed is not limited to this condition because optimum conditions are selected depending on the sample.) The coating layer / base film interface has different physical properties of the coating layer and the base film, so that the cutting angle changes at the interface, It can be easily recognized from the fact that the contrast is changed between the coat layer and the substrate in the phase image by SPM, and the uneven state of the cutting surface is changed between the coating layer and the substrate film.

  The oblique cut surface was observed using a scanning probe microscope SPM. SPM used SPA300 (Nanoavi probe station) made by SII Nano Technology. The cantilever used DF3 or DF20 provided by the company, and the observation mode used DFM mode. Observation was performed such that the surface of the coating layer and the oblique cutting surface were within one field of view, and the inclination of the observed image was corrected by performing a flattening process on the surface of the coating layer. For the flattening process, manual tilt correction, which is a function of the software attached to the SPM, was used, and tilt correction in the X and Y directions was performed. The coating layer / substrate film interface was determined by the method described in the section of the cutting method from an image obtained by performing flattening processing (secondary tilt correction, which is a software function) on the entire observation field.

  Using the data of the infrared absorbance ratio (P1 / P2) and the thickness (D) of the coating layer obtained from the above measurement, (P1 / P2) / D of the laminated film obtained in each Example and Comparative Example The value was determined.

(Polymerization of polyester resin (a))
When the temperature of the esterification reactor was raised to 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, and antimony trioxide as a catalyst while stirring. 0.03 part by mass and 0.16 part by mass of triethylamine were added. 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.

(Polymerization of polyester resin (b))
When the temperature of the esterification reactor was raised to 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, and antimony trioxide as a catalyst while stirring. 0.03 part by mass, 0.16 part by mass of triethylamine, and an ethylene glycol slurry of silica particles having an average particle diameter of 2.5 μm 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.

(Polymerization of polyester resin (c))
For a mixture of bis (2-hydroxyethyl) terephthalate and oligomer produced 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. Add 0.012 mol% as an aluminum atom and 10 g / l ethylene glycol solution of Irganox 1425 (manufactured by Ciba Specialty Chemicals) as Irganox 1425 to the acid component, and add atmospheric pressure under nitrogen atmosphere. And stirred at 245 ° C. 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.

(Polymerization of polyester (d) resin)
Porous silica particles having an average particle diameter of 2.5 μm were charged into ethylene glycol, and further filtered through a viscose rayon filter having a 95% cut diameter of 30 μm to obtain an ethylene glycol slurry of porous silica particles.
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.

(Synthesis of Resin (A-1) Having Oxazoline Group)
A flask equipped with a stirrer, a reflux condenser, a nitrogen inlet tube and a thermometer was charged with 460.6 parts of isopropyl alcohol and heated to 80 ° C. while gently flowing nitrogen gas. A monomer mixture consisting of 126 parts of methyl methacrylate, 210 parts of 2-isopropenyl-2-oxazoline and 84 parts of methoxypolyethylene glycol acrylate prepared in advance, and ABN-E (manufactured by Nippon Hydrazine Kogyo Co., Ltd.) Polymerization initiator: An initiator solution consisting of 21 parts of 2,2′-azobis (2-methylbutyronitrile) and 189 parts of isopropyl alcohol was added dropwise over 2 hours using a dropping funnel. During the reaction, nitrogen gas was kept flowing, and the temperature in the flask was kept at 80 ± 1 ° C. After the completion of dropping, the temperature was kept at the same temperature for 5 hours, followed by cooling to obtain a resin (A-1) having an oxazoline group. The obtained resin (A-1) having an oxazoline group has an oxazoline value of 220 g-solid / eq. Met.

(Synthesis of Resin (A-2) Having Oxazoline Group)
A resin (A-2) having an oxazoline group having a different composition was obtained in the same manner as (A-1). The obtained resin (A-2) having an oxazoline group has an oxazoline value of 130 g-solid / eq. Met.

(Polyester resin polymerization)
In a stainless steel autoclave equipped with a stirrer, a thermometer, and a partial reflux condenser, 194.2 parts by weight of dimethyl terephthalate, 184.5 parts by weight of dimethyl isophthalate, 14.8 parts by weight of dimethyl-5-sodium sulfoisophthalate, The mixture was charged with 229.1 parts by mass of neopentyl glycol, 136.6 parts by mass of ethylene glycol, and 0.2 parts by mass of tetra-n-butyl titanate, and subjected to a transesterification reaction from 160 ° C. to 220 ° C. over 4 hours. Next, the temperature was raised to 255 ° C., the pressure of the reaction system was gradually reduced, and the mixture was reacted for 1 hour 30 minutes under a reduced pressure of 30 Pa to obtain a copolymerized polyester resin (B-1). The obtained copolyester resin (B-1) was light yellow and transparent. It was 0.55 dl / g when the reduced viscosity of the obtained copolyester resin (B-1) was measured. The glass transition temperature by DSC was 65 ° C.

In the same manner, copolymer polyester resins (B-2) and (B-3) having different compositions were obtained. Table 1 shows the composition (mole% ratio) and other characteristics measured by ¹ H-NMR for these copolymer polyester resins.

(Adjustment of polyester aqueous dispersion)
30 parts by mass of polyester resin (B-1) and 15 parts by mass of ethylene glycol n-butyl ether were put into a reactor equipped with a stirrer, a thermometer and a reflux device, and heated and stirred at 110 ° C. to dissolve the resin. After the resin was completely dissolved, 55 parts by mass of water was gradually added to the polyester solution while stirring. After the addition, the solution was cooled to room temperature while stirring to prepare a milky white polyester aqueous dispersion (C-1) having a solid content of 30% by mass. Similarly, using the polyester resins (B-2) and (B-3) instead of the polyester resin (B-1), water dispersions were prepared, and the water dispersions (C-2) and (C- 3).

(Acrylic resin polymerization)
A flask equipped with a stirrer, a reflux condenser, a nitrogen inlet tube and a thermometer was charged with 405 parts of 2-butanone and 210 parts of isopropyl alcohol, and heated to 80 ° C. while gently flowing nitrogen gas. A monomer mixture composed of 282 parts of methyl acrylate and 18 parts of acrylic acid, an initiator solution comprising 15 parts of 2,2′-azobisisobutyronitrile and 85 parts of 2-butanone. Were added dropwise by a dropping funnel over 2 hours. During the reaction, nitrogen gas was kept flowing, and the temperature in the flask was kept at 80 ± 1 ° C. After maintaining the same temperature for 5 hours after completion of dropping, 94 parts of 5% aqueous ammonia and 606 parts of water are added, and the flask is further heated to distill off 2-butanone and isopropyl alcohol to obtain an acrylic resin solution having a solid content of 27%. (D-1) was obtained.

Example 1
(1) Adjustment of coating liquid The following coating agent was mixed and the coating liquid was created.
86.10% by mass of water
Isopropanol 7.50% by mass
Resin having oxazoline group (A-1) 6.40% by mass

(2) Production of polyester base film and coating of coating solution Polyester resin (a) and polyester resin (b) were each solid-phase polymerized at 220 ° C. under a reduced pressure of 0.5 mmHg using a rotary vacuum polymerization apparatus. A polyester resin (A) and a polyester resin (B) having an intrinsic viscosity of 0.75 dl / g were 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.

  The coating solution was coated on one side of the obtained uniaxially oriented PET film by a fountain bar coating method. 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. Thus, a film in which a coating layer was formed on a biaxially stretched polyester film having a thickness of 50 μm was obtained.

(3) Deposition Next, in order to deposit on the coating surface of the film obtained in (2), particulate SiO ₂ (purity 99.9%) and Al ₂ O ₃ (purity) of about 3 mm to 5 mm as a deposition source. 99.9%), a composite inorganic oxide layer of aluminum oxide and silicon dioxide was formed on the obtained coated film by an electron beam evaporation method.

(Example 2)
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 film as in Example 1 except that polyester resin (C) and polyester resin (D) are used as the polyester raw material, and the wind speed in the preheating step, the transverse stretching step, the heat setting step, and the cooling step is set to 10 m / sec. A film with a thickness of 50 μm was obtained.

(Example 3)
A film having a film thickness of 50 μm was obtained in the same manner as in Example 2 except that the wind speed in the preheating step, the transverse stretching step, and the heat setting step was 20 m / sec.

Example 4
A film having a film thickness of 50 μm was obtained in the same manner as in Example 2 except that the wind speed in the preheating step, the transverse stretching step, and the heat setting step was changed to 30 m / sec.

(Example 5)
A film was obtained in the same manner as in Example 2 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 6)
A film with a film thickness of 50 μm was obtained in the same manner as in Example 2 except that the wind speed in the cooling step was 5 m / sec.

(Example 7)
A film having a film thickness of 50 μm was obtained in the same manner as in Example 2 except that the hot air and cold air in the preheating step, transverse stretching step, heat setting step, and cooling step were circulated without passing through the filter.

(Examples 8 to 21)
Samples were prepared and evaluated in the same procedure as in Example 1 except that the coating solution was changed as shown in Table 2.

(Comparative Example 1)
Samples were prepared and evaluated in the same procedure as in Example 1 without coating.

(Comparative Example 2)
A film having a film thickness of 50 μm was obtained in the same manner as in Example 2 except that the polyester resin (c) and polyester resin (d) not subjected to solid phase polymerization were used.

(Comparative Example 3)
A film having a film thickness of 50 μm was obtained in the same manner as in Example 2 except that the velocity of hot air in the preheating step, the transverse stretching step, and the heat setting step was changed to 5 m / sec.

  The inorganic thin film forming substrate polyester film for solar cells of the present invention has few surface protrusions due to the cyclic trimer on the film surface, and is suitable for long-term moisture resistance maintenance. Therefore, it is useful as a constituent member of the solar cell protective sheet.

Claims (7)

Having a coating layer on at least one side of the polyester film;
An aqueous acrylic resin containing a carboxylic acid group other than a resin having an oxazoline group, wherein the coating layer includes a resin having an oxazoline group and an aqueous acrylic resin containing a carboxylic acid group or an aqueous polyester resin containing a carboxylic acid group. Or the compounding ratio of the aqueous polyester resin containing a carboxylic acid group is 5 to 60% by weight,
The cyclic trimer content in the polyester film is 5000 ppm or less per the polyester film,
An inorganic thin film-forming substrate polyester film for solar cells, wherein 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.   The inorganic thin film forming substrate 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 inorganic thin film forming substrate polyester film for solar cell according to claim 1 or 2, wherein the center layer substantially does not contain particles. The ratio (P1 / P2) of the peak intensity (P1) of 1655 cm ^{−1 and} the peak intensity (P2) of 1580 cm ⁻¹ in the total reflection infrared absorption spectrum of the coating layer and the film thickness D [nm] of the coating layer are expressed by the following formula: The inorganic thin film forming substrate polyester film for solar cells according to any one of claims 1 to 3, which satisfies [1].
0.05≤ (P1 / P2) /D≤0.25 ... [1]   The barrier polyester film for solar cells formed by laminating | stacking an inorganic thin film layer on the coating layer surface of the inorganic thin film formation base-material polyester film for solar cells in any one of Claims 1-4.   The solar cell protective sheet which uses the barrier polyester film for solar cells of Claim 5 as a structural member. It is a method of manufacturing the inorganic thin film forming substrate polyester film for solar cells according to any one of claims 1 to 4, wherein the following (1) to (5) means are selected or combined during film formation: The manufacturing method of the inorganic thin film formation base material polyester film for solar cells characterized by the above-mentioned.
(1) the transverse stretching and / or wind speed control (2) in the heat setting step thermal solid funnel of control of the cooling rate (3) adjustment of the furnace the air in the transverse stretching and / or heat fixing step (4) melting step (5) Removal of surface cyclic trimer by touch roll