JP5403679B2 - Polyester film for solar cell backside sealing - Google Patents

Description

  The present invention relates to a polyester film for sealing a back surface of a solar cell, and particularly to a polyester film having excellent heat resistance and moldability and improved hydrolysis resistance under high temperature conditions.

  In recent years, as global warming has been highlighted as an environmental issue, solar cells have been attracting attention as the next generation energy source from the viewpoints of carbon dioxide suppression and fossil fuel escape. Its development and effective use are being advanced to the construction field such as houses. Among these, solar cells used outdoors are required to have high durability against the natural environment, and the demand for the back surface sealing film which is one of the components of the solar cells is particularly strong.

  Conventionally, as a solar cell back surface sealing film, a fluorine resin film, a polyethylene resin film, a polyester resin film, and the like are widely used. Among these, the fluororesin is excellent in heat resistance and hydrolysis resistance, and can be said to be desirable in terms of durability against the natural environment. However, the fluororesin film has a drawback that it has poor gas barrier properties, particularly water vapor barrier properties, and is not sufficient in terms of mechanical strength. In addition, the processing of the resin is difficult, it is difficult to form into a film, and the cost is also high. Moreover, although the polyethylene-type resin film is comparatively cheap and easy to shape | mold, there existed difficulty in the point of the heat resistance especially when exposed to high temperature (for example, 100-120 degreeC).

  On the other hand, since the polyester resin film has good heat resistance and mechanical properties and is relatively easy to mold, for example, biaxially stretched polyethylene colored white for the purpose of improving the conversion efficiency by reflected light. A terephthalate (PET) film, a PET film colored in black for decoration purposes, and the like are sold as back surface sealing films for solar cells. However, even in these polyester resin films, when used as a back surface sealing film for solar cells, the resin may undergo hydrolysis, particularly when it is exposed to high temperatures for a long time. There was a problem of being low.

  To make a resin film with more desirable characteristics as a backside sealing film for solar cells, change the resin monomer composition, add additives to the resin, combine various resins with different characteristics, or Although various studies have been made such as forming a resin film or a vapor deposition layer on the film (see, for example, Patent Documents 1 to 6), the polyester resin film alone has durability against the natural environment, particularly hydrolysis resistance. We have not yet obtained a satisfactory result.

JP 2009-43979 A JP 2008-227203 A JP 2008-85270 A International Publication No. WO07 / 105306 JP 2007-7885 A JP 2006-335853 A

  The present invention has been made in view of the background of the prior art, and has a polyester for sealing a back surface of a solar cell, which has excellent heat resistance and moldability and has improved hydrolysis resistance under high temperature conditions. The problem to be solved is to provide a film.

  As a result of intensive investigations in view of the above problems, the present inventors have found that the polyester resin (A) is mainly composed of a terephthalic acid component and an ethylene glycol component, and the terephthalic acid component and 1,4-cyclohexene. By using a polyester resin mixture obtained by mixing 95 to 55 parts by mass of a polyester resin composed of a samdiethanol component, it has excellent heat resistance and moldability and improved hydrolysis resistance under high temperature conditions. The obtained polyester film was obtained and found to be very suitable for use as a solar cell back surface sealing film, and the present invention was completed.

That is, the solar cell backside sealing polyester film according to the present invention comprises a dicarboxylic acid component containing 80 mol% or more of terephthalic acid or an ester-forming derivative thereof and a glycol component containing 80 mol% or more of ethylene glycol. 5 to 45 parts by mass of the polyester resin (A), a dicarboxylic acid component containing 80 mol% or more of terephthalic acid or an ester-forming derivative thereof, and a glycol component containing 60 mol% or more of 1,4-cyclohexanedimethanol A polyester resin mixture formed by mixing 95 to 55 parts by mass of the polyester resin (B) consisting of the polyester resin (A) and the polyester resin (B) so that the total amount becomes 100 parts by mass. To do.
Moreover, as for the said polyester film for solar cell backside sealing, it is suitable that the glycol component of a polyester resin (B) contains 1, 4- cyclohexane dimethanol 80 mol% or more.

Moreover, it is suitable for the said polyester film for solar cell backside sealing that the tensile fracture elongation retention rate after processing with 120 degreeC and a hot water for 72 hours is 60% or more.
Moreover, it is suitable for the said polyester film for solar cell backside sealing that content of the phosphorus element in a polyester resin mixture is 10-300 ppm.

Moreover, it is suitable for the said polyester film for solar cell backside sealing that the amount of terminal carboxyl groups in a polyester resin mixture is 30 equivalent / tons or less.
Moreover, it is suitable for the said polyester film for solar cell backside sealing that the glass transition temperature Tg is 80 degreeC or more.

  The polyester film for sealing a back surface of a solar cell of the present invention has excellent hydrolysis resistance as well as excellent heat resistance and moldability. In particular, when the solar cell backside sealing polyester film of the present invention is used for a solar cell used outdoors, it has a high durability against the natural environment, so that the performance of the solar cell can be improved for a long time. Can be exerted over.

Hereinafter, the present invention will be described in more detail.
The solar cell as used in the present invention refers to a system that takes in sunlight or the like, converts it into electricity, and stores the electricity. Usually, for example, it is installed on the roof of a house, or is incorporated into an electric or electronic component. Used. As a part which comprises a solar cell, there exist a transparent surface protection member which permeate | transmits sunlight, a solar cell element, a filling resin layer, the film for back surface sealing, etc. normally. And the film for solar cell backside sealing concerning this invention is affixed on the back surface (opposite surface of a sunlight incident surface) of a solar cell, and plays the role of protecting a solar cell element from external environment.

  The solar cell back surface sealing film according to the present invention is a polyester obtained by mixing 5 to 45 parts by mass of the polyester resin (A) having the following specific composition and 95 to 55 parts by mass of the polyester resin (B) having the following specific composition. It consists of a resin mixture.

Polyester resin (A)
The polyester resin (A) used in the present invention is a known method comprising a dicarboxylic acid component containing 80 mol% or more of terephthalic acid or an ester-forming derivative thereof and a glycol component containing 80 mol% or more of ethylene glycol. Is a polyester resin obtained by polycondensation.

  The proportion of terephthalic acid in the dicarboxylic acid component of the polyester resin (A) needs to be 80 mol% or more, preferably 90 mol% or more, more preferably 95 mol% or more with respect to the total amount of the dicarboxylic acid component. Further, the ethylene glycol ratio in the glycol component is required to be 80 mol% or more, preferably 90 mol% or more, more preferably 95 mol% or more with respect to the total amount of the glycol component. For example, polyethylene terephthalate in which both terephthalic acid and ethylene glycol are 100 mol% is suitably used as the polyester resin (A).

  Examples of dicarboxylic acid components other than terephthalic acid include, for example, isophthalic acid, naphthalenedicarboxylic acid, succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, fumaric acid, maleic acid, itaconic acid, 1,4-cyclohexane-dicarboxylic acid. An acid, a dimer acid, etc. are mentioned, These dicarboxylic acid components may be contained in less than 20 mol%. In particular, isophthalic acid and naphthalenedicarboxylic acid, which are aromatic dicarboxylic acids, can be suitably used in the present invention.

  Examples of glycol components other than ethylene glycol include diethylene glycol, propylene glycol, 1,3-propanediol, 2,4-dimethyl-2-ethylhexane-1,3-diol, and 2,2-dimethyl-1, 3-propanediol, 2-ethyl-2-butyl-1,3-propanediol, 2-ethyl-2-isobutyl-1,3-propanediol, 1,3-butanediol, 1,4-butanediol, neo Pentyl glycol, 1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, 2,2,4-trimethyl-1,6-hexanediol, thiodiethanol, 2,2,4,4- Examples include tetramethyl-1,3-cyclobutanediol, and various high molecular weight polyethylene glycols. , These glycol components may be contained in an amount of less than 20 mol%.

Polyester resin (B)
The polyester resin (B) used in the present invention includes a dicarboxylic acid component containing 80 mol% or more of terephthalic acid or an ester-forming derivative thereof, and a glycol containing 60 mol% or more of 1,4-cyclohexanedimethanol. It is a polyester resin obtained by polycondensing components with a known method.

  The proportion of terephthalic acid in the dicarboxylic acid component of the polyester resin (B) needs to be 80 mol% or more, preferably 90 mol% or more, more preferably 95 mol% or more with respect to the total amount of the dicarboxylic acid component. Moreover, the 1, 4- cyclohexane dimethanol ratio in a glycol component needs 60 mol% or more with respect to the glycol component whole quantity, Preferably it is 80 mol% or more, More preferably, it is 90 mol% or more. For example, a polyester resin (PCTA 13319: Eastman Chemical Co.) containing 95 mol% terephthalic acid, 5 mol% isophthalic acid, and 100 mol% 1,4-cyclohexanedimethanol is preferably used as the polyester resin (B).

  As the dicarboxylic acid component other than terephthalic acid, the same compounds as listed in the polyester resin (A) can be used, and may be contained in a range of less than 20 mol%. In addition, as a dicarboxylic acid component other than terephthalic acid, it is preferable that a slight amount of aromatic dicarboxylic acid such as isophthalic acid or naphthalenedicarboxylic acid is contained in terms of hydrolysis resistance and high glass transition temperature Tg.

  Examples of diol components other than 1,4-cyclohexanedimethanol include 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, ethylene glycol, diethylene glycol, propylene glycol, 1,3-propanediol, , 4-dimethyl-2-ethylhexane-1,3-diol, 2,2-dimethyl-1,3-propanediol, 2-ethyl-2-butyl-1,3-propanediol, 2-ethyl-2- Isobutyl-1,3-propanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, 2, 2,4-trimethyl-1,6-hexanediol, thiodiethanol, 2,2,4, - tetramethyl-1,3-cyclobutanediol, and various high molecular weight polyethylene glycols and the like of, these glycol components may be contained in an amount of less than 40 mol%. In particular, 1,2-cyclohexanedimethanol and 1,3-cyclohexanedimethanol, which are alicyclic glycols, can be suitably used in the present invention.

  In addition, in the polyester resin (B) used for this invention, it is necessary to contain 60 mol% or more of 1, 4- cyclohexane dimethanol in glycol component whole quantity, Preferably it is 80 mol% or more, More preferably Is a polyester containing 90 mol% or more. When the content ratio of 1,4-cyclohexanedimethanol is less than this, the hydrolysis resistance, particularly the hydrolysis resistance at high temperature, is inferior, and a higher glass transition temperature Tg may not be obtained.

  The polyester resin mixture used for the solar cell backside sealing polyester film of the present invention is obtained by mixing 5 to 45 parts by mass of the polyester resin (A) and 95 to 55 parts by mass of the polyester resin (B). The resin mixture is included. When the amount of the polyester resin (A) is less than 5 parts by mass, the polyester resin (A) is easily broken during film formation, and the breakage may occur. That is, the strength and moldability of the film can be improved by blending 5 parts by mass or more of the polyester resin (A). On the other hand, when the polyester resin (A) exceeds 45 parts by mass, the heat resistance is lowered and the hydrolysis resistance is also lowered. That is, by blending 55 parts by mass or more of the polyester resin (B), it has good heat resistance and can improve hydrolysis resistance.

  The polyester film for solar cell backside sealing concerning this invention uses the resin mixture which mixed the said polyester resin (A) and the said polyester resin (B) by specific amount ratio, for example, 120 degreeC, 72 The tensile elongation at break after treatment with hot water for a period of time can be set to 60% or more, and the hydrolysis resistance is particularly excellent when exposed to a high temperature for a long time. For this reason, for example, it has sufficient performance as a polyester film for sealing the back surface of a solar cell for outdoor installation used in a harsh environment.

  In the polyester resin mixture used in the present invention, the content of phosphorus element is not particularly limited, but is preferably 10 to 300 ppm, more preferably 10 to 200 ppm, and further preferably 10 to 100 ppm. . The amount of the phosphorus element in the polyester resin is desirably adjusted in relation to the content of the catalyst-derived metal element. That is, the metal element derived from the catalyst is inactivated by the phosphorus element, and the hydrolysis reaction and thermal decomposition reaction of the polyester resin are suppressed. For this reason, when there is too little content of this phosphorus P element, it will become a catalyst which accelerates | stimulates the hydrolysis and thermal decomposition of the polyester resin by the catalytic metal element in the polyester resin, and is extremely inferior in heat resistance and hydrolysis resistance. It may become polyester.

  The amount of phosphorus element is preferably 10 ppm or more in the polyester resin mixture from the viewpoint of inactivation of the metal element. On the other hand, if the amount of phosphorus element is too large, gelation occurs in the resin, resulting in foreign matter. Since it may cause the quality of a film to deteriorate, it is not preferable. For this reason, it is preferable that phosphorus element content in a polyester film is 300 ppm or less, More preferably, it is 200 ppm or less, More preferably, it is 10-100 ppm or less.

  In addition, examples of the metal element derived from the catalyst include antimony, germanium, titanium, aluminum, and metal elements used as a transesterification catalyst, calcium, manganese, magnesium, lithium, cobalt, and the like. In the present invention, it is desirable that the metal element does not particularly contain antimony from the viewpoint of hydrolysis resistance of the film. The titanium element content is desirably 100 ppm or less. If the titanium element content is too high, a decomposition reaction is likely to occur during film production, the molecular weight of the polyester is lowered, resulting in inferior strength and heat resistance, and handling in the processing process is deteriorated. In some cases, hydrolysis resistance when used as a member of a solar cell may be inferior. Similarly, it is desirable that manganese element is 75 ppm or less, zinc element is 150 ppm or less, and germanium element is 200 ppm or less. However, if the metal element content in the catalyst is reduced too much, the productivity at the time of production of the polyester raw material is inferior, and not only the polyester raw material reaching the desired degree of polymerization can be obtained, but also the polycondensation reaction rate becomes slow, resulting in There is a problem that the terminal carboxyl group concentration of the obtained polyester resin becomes high and the hydrolysis resistance is poor. In addition, it is desirable that the content ratio (mass ratio) of the phosphorus element P with respect to the metal element M is P / M = 0.05 to 2.0.

  In the present invention, the content of the phosphorus element in the polyester resin mixture can be adjusted by adding a phosphorus compound to the resin. As the phosphorus compound, known phosphorus compounds such as phosphoric acid, phosphorous acid or ester phosphonic acid compounds, phosphinic acid compounds, phosphonous acid compounds, and phosphinic acid compounds can be used. Specific examples of phosphorus compounds include orthophosphoric acid, dimethyl phosphate, trimethyl phosphate, diethyl phosphate, diethyl phosphate, triethyl phosphate, dipropyl phosphate, tripropyl phosphate, dibutyl phosphate, tributyl phosphate, Diamyl phosphate, triamyl phosphate, dihexyl phosphate, trihexyl phosphate, diphenyl phosphate, triphenyl phosphate, ethyl acid phosphate, dimethyl phosphite, trimethyl phosphite, diethyl phosphate, triethyl phosphate, etc. Phosphate compounds, dipropyl phosphite, tripropyl phosphite, dibutyl phosphite, tributyl phosphite Phosphite compounds such as diphenyl phosphite, triphenyl phosphite, diamyl phosphite, triamyl phosphite, dihexyl phosphite, trihexyl phosphite, phenylphosphonite, 2-carboxyphenylphosphonite, 3- Carboxyphenyl phosphonite, 4-carboxyphenyl phosphonite, 2,3-dicarboxyphenyl phosphonite, 2,4-dicarboxyphenyl phosphonite, 2,5-dicarboxyphenyl phosphonite, 2,6-dicarboxyphenyl phosphonite Knight, 3,4-dicarboxyphenylphosphonite, 3,5-dicarboxyphenylphosphonite, 2,3,4-tricarboxyphenylphosphonite, 2,3,5-tricarboxyphenylphosphonite, , 3,6-tricarboxyphenylphosphonite, 2,4,5-tricarboxyphenylphosphonite, 2,4,6-tricarboxyphenylphosphonite, phenylphosphonite dimethyl, phenylphosphonite diethyl, phenylphosphonite diphenyl, Phosphonous compounds such as phenylphosphonite dibenzyl, 2,4-di-t-butylphenylphosphonite diethyl, 2,4-di-t-butyl-5-methylphenylphosphonite diethyl, phenylphosphonate, 2- Carboxyphenyl phosphonate, 3-carboxyphenyl phosphonate, 4-carboxyphenyl phosphonate, 2,3-dicarboxyphenyl phosphonate, 2,4-dicarboxyphenyl phosphonate, 2,5-dicarboxyphenyl phosphonate, 2, 6-dicarboxyphenylphosphonate, 3,4-dicarboxyphenylphosphonate, 3,5-dicarboxyphenylphosphonate, 2,3,4-tricarboxyphenylphosphonate, 2,3,5-tricarboxyphenylphosphonate, 2,3 , 6-tricarboxyphenylphosphonate, 2,4,5-tricarboxyphenylphosphonate, 2,4,6-tricarboxyphenylphosphonate, phenylphosphonate dimethyl, phenylphosphonate diethyl, phenylphosphonate diphenyl, phenylphosphonate dibenzyl, 2,4 Phosphonic acid compounds such as diethyl di-t-butylphenylphosphonate diethyl and 2,4-di-t-butyl-5-methylphenylphosphonate diethyl, dimethyl [1,1-biphenyl] -4-ylphospho Phonite, diethyl [1,1-biphenyl] -4-ylphosphonite, dibutyl [1,1-biphenyl] -4-ylphosphonite, dihexyl [1,1-biphenyl] -4-ylphosphonite, dioctyl [1 , 1-biphenyl] -4-ylphosphonite, dibenzyl [1,1-biphenyl] -4-ylphosphonite, di-t-butyl [1,1-biphenyl] -4-ylphosphonite, diphenyl [1, 1-biphenyl] -4-ylphosphonite, bis (2,4-di-t-butylphenyl) [1,1-biphenyl] -4-ylphosphonite, bis (2,4-di-t-butyl- 5-methylphenyl) [1,1-biphenyl] -4-ylphosphonite and other phosphonous compounds, dimethyl [1,1-biphenyl] -4-ylphosphonate, die [1,1-biphenyl] -4-ylphosphonate, dibutyl [1,1-biphenyl] -4-ylphosphonate, dihexyl [1,1-biphenyl] -4-ylphosphonate, dioctyl [1,1-biphenyl] -4-ylphosphonate, dibenzyl [1,1-biphenyl] -4-ylphosphonate, di-t-butyl [1,1-biphenyl] -4-ylphosphonate, diphenyl [1,1-biphenyl] -4-yl Phosphonate, bis (2,4-di-t-butylphenyl) [1,1-biphenyl] -4-ylphosphonate, bis (2,4-di-t-butyl-5-methylphenyl) [1,1- Phosphonic acid compounds such as biphenyl] -4-ylphosphonate, tetramethyl [1,1-biphenyl] -4,4′-diylbisphosphonite, tetrae Tyl [1,1-biphenyl] -4,4′-diylbisphosphonite, tetrabutyl [1,1-biphenyl] -4,4′-diylbisphosphonite, tetrahexyl [1,1-biphenyl] -4, 4′-diylbisphosphonite, tetraoctyl [1,1-biphenyl] -4,4′-diylbisphosphonite, tetrabenzyl [1,1-biphenyl] -4,4′-diylbisphosphonite, tetra- phosphonous compounds such as t-butyl [1,1-biphenyl] -4,4′-diylbisphosphonite, tetraphenyl [1,1-biphenyl] -4,4′-diylbisphosphonite, tetramethyl [1,1-biphenyl] -4,4′-diyl bisphosphonate, tetraethyl [1,1-biphenyl] -4,4′-diyl bisphosphonate, tetra Tyl [1,1-biphenyl] -4,4′-diylbisphosphonate, tetrahexyl [1,1-biphenyl] -4,4′-diylbisphosphonate, tetraoctyl [1,1-biphenyl] -4,4′- Diyl bisphosphonate, tetradodecyl [1,1-biphenyl] -4,4'-diyl bisphosphonate, tetrabenzyl [1,1-biphenyl] -4,4'-diyl bisphosphonate, tetra-t-butyl [1,1-biphenyl ] -4,4'-diylbisphosphonate, tetraphenyl [1,1-biphenyl] -4,4'-diylbisphosphonate, and the like. In addition, tetrakis (2,4-di-t-butylphenyl) [1,1-biphenyl] -4,4′-diylbisphosphonite, tetrakis (2,4-di-t-) are preferable phosphorus compounds. Butyl-5-methylphenyl) [1,1-biphenyl] -4,4′-diylbisphosphonite, these compounds are IRGAFOS P-EPQ (Ciba Specialty Chemicals), Sandostab P-EPQ ( Clariant Japan Co., Ltd.) and GSY-P101 (Osaki Kogyo Co., Ltd.).

  The phosphorus compound may be added alone in the production of the polyester resin, or may be added after being dissolved or dispersed in a glycol component such as ethylene glycol. Further, a polyester resin containing a predetermined amount of a phosphorus compound may be produced as a master batch and mixed with other polyesters. As a method for producing a master batch of a phosphorus compound, there are a method of polymerizing using a germanium catalyst or a titanium catalyst, a method of directly adding in a melt extrusion step of polyester, and the like.

  In the polyester film of the present invention, the amount of terminal carboxyl groups in the polyester resin mixture is preferably 30 equivalent / ton or less, more preferably 20 equivalent / ton or less, and further preferably, from the viewpoint of improving hydrolysis resistance. Is 10 equivalents / ton or less. In order to make the amount of terminal carboxyl groups in a film into the above-mentioned specific range, it is necessary to make the amount of terminal carboxyl groups smaller than that of a normal polyester resin. For this reason, for example, the phosphorus P element content in the polyester film is set to a specific ratio with the polymerization catalyst-derived metal M, and / or the melting temperature is set to 320 ° C. or less in the melt extrusion step under a nitrogen stream. Thus, a polyester resin having a small amount of terminal carboxyl groups can be obtained. The conditions are such that the amount of catalyst is too small or the pressure reduction in the polycondensation reaction step is insufficient and the polymerization time becomes too long. When polycondensation is performed under the condition, it becomes impossible to obtain a polyester resin having a terminal carboxyl group amount in the specific range. In addition, when a recycled polyester resin raw material that has undergone a melting step is blended during film production, the amount of terminal carboxyl groups in the resin increases. Therefore, in the present invention, it is desirable not to blend a recycled polyester raw material. Is preferably 20% by mass or less based on the total amount of the resin.

  Moreover, it is preferable that the glass transition temperature Tg of the polyester resin mixture used for this invention is 80 degreeC or more, More preferably, it is 85 degreeC or more. By setting it as a higher glass transition temperature, it becomes a polyester film excellent in heat resistance and hydrolysis resistance.

  As the polyester film for sealing the back surface of the solar cell according to the present invention, the polyester resin mixture obtained above may be used alone, but the respective characteristics such as hydrolysis resistance, heat resistance and moldability are not significantly reduced. Within the range, other polymers may be blended. In addition, the mixing amount of the other polymer is 40 parts by mass or less, preferably 20 parts by mass or less with respect to the total amount of the polyester resin mixture.

  You may mix | blend particle | grains with the polyester film for solar cell backside sealing of this invention for the purpose of providing the slipperiness of a film. The kind of the particle to be blended is not particularly limited as long as it is a particle capable of imparting slipperiness. Specific examples thereof include silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, and phosphoric acid. Examples of the particles include magnesium silicon oxide, kaolin, and aluminum oxide. Furthermore, precipitated particles in which a part of a metal compound such as a catalyst is precipitated and finely dispersed during the production process of the polyester resin can also be used.

  The shape of the particles to be blended in the polyester film of the present invention is not particularly limited, and any of a spherical shape, a block shape, a rod shape, a flat shape, and the like may be used. Moreover, there is no restriction | limiting in particular also about the hardness, specific gravity, a color, etc. Two or more kinds of these particles may be used in combination as required. The average particle size of the particles is usually preferably 0.01 to 10 μm. When the average particle size is less than 0.01 μm, the effect of imparting easy slipperiness to the film is insufficient. On the other hand, when the thickness exceeds 10 μm, breakage frequently occurs at the time of film forming, and productivity may be lowered.

  Furthermore, the content of the particles in the polyester film is usually in the range of 0.0003 to 2 mass%, preferably 0.0005 to 1 mass%, based on the total amount of polyester constituting the film. When the particle content is less than 0.0003 mass%, the slipperiness of the film may be insufficient. On the other hand, when the content exceeds 2 mass%, the particle size is too large. The film productivity may be insufficient. In addition, in this invention, when it contains the titanium oxide particle | grains mentioned later, a barium sulfate particle | grain, and a carbon black particle | grain, it may not be necessary to mix | blend other particles.

  The method for adding particles to the polyester film is not particularly limited, and a conventionally known method can be adopted. For example, particles can be added at any stage of producing the polyester resin. Alternatively, a method of blending a slurry of particles dispersed in ethylene glycol, 1,4-cyclohexanedimethanol, water or the like and a polyester raw material, or a method of blending dry particles and a polyester raw material using a kneading extruder with a vent and so on.

  The solar cell backside sealing polyester film of the present invention may be colored by blending a coating, dye, or pigment in the film. In particular, in order to obtain weather resistance or concealment, is it a high haze film? It is preferably colored white. In order to obtain a white film, titanium oxide particles having an average particle size of 1 μm or less or barium sulfate particles having an average particle size of 3 μm or less are contained in an amount of 2 to 30% by mass, preferably 10 to 20% by mass. desirable. Moreover, in order to improve the concealability inside the solar cell, it is desirable that the optical density of the polyester film is 0.4 or more, preferably 0.6 or more. When the content of the titanium oxide particles or the barium sulfate particles is less than 2% by mass, good weather resistance and concealment improving effect cannot be obtained. On the other hand, when the content of titanium oxide particles or barium sulfate particles exceeds 30% by mass, or when the average particle size exceeds a predetermined range, the effect of improving weather resistance and concealment may not be obtained. In addition, there may be a problem in that the film production process frequently causes film breakage and the productivity is greatly reduced. Alternatively, as a method for improving the concealability of the film and improving the weather resistance, there is a method of containing 0.5 to 30% by mass of carbon black particles in the film. Moreover, it is effective in improving the reflectivity from the back surface of a sunlight ray and improving the conversion efficiency as a solar cell by raising the reflectivity of a film. As an additive for this purpose, it is necessary to contain barium sulfate in a large amount of 10 to 30% by mass. Further, 10-20% by mass of a polymer that is incompatible with the polyester, such as methylpentene polymer, may be biaxially stretched to generate a large number of voids and increase the reflectivity by a layered structure. .

  In addition to the above particles, the polyester film for sealing the back surface of the solar cell of the present invention may include conventionally known antioxidants, thermal stabilizers, lubricants, antistatic agents, fluorescent whitening agents, dyes as necessary. , Pigments and the like can be added. Further, for the purpose of improving the weather resistance, an ultraviolet absorber, particularly a benzoxazinone-based ultraviolet absorber or the like can be contained in the range of 0.01 to 5% by mass with respect to the total amount of the polyester resin.

  Although it will not specifically limit if the thickness of the polyester film for solar cell backside sealing of this invention is a range which can be formed into a film, Usually, it is the range of 12-250 micrometers, Preferably it is the range of 25-200 micrometers.

  Hereinafter, although it demonstrates concretely regarding the manufacturing method of the polyester film for solar cell backside sealing of this invention, this invention is not specifically limited to the following illustrations.

  Polyester chips of the polyester resin (A) and the polyester resin (B) are prepared, and a polyester chip dried by vacuum or hot air at a temperature of less than 180 ° C. by a known method, or an undried polyester chip is uniaxially or preferably Is supplied to a twin-screw extruder and heated to a temperature not lower than the melting point of each polyester resin and lower than 320 ° C. to melt. Here, the mixing ratio of each polyester resin is adjusted to be 5 to 45 parts by mass of the polyester resin (A) and 95 to 55 parts by mass of the polyester resin (B). Alternatively, other types of polymer chips may be mixed in an appropriate amount as necessary. Next, the molten polymer is extruded from a die, brought into close contact with a rotary cooling drum, and rapidly cooled and solidified to a temperature not higher than the glass transition temperature to obtain a substantially amorphous unoriented sheet. At this time, in order to improve the flatness of the sheet, it is preferable to improve the adhesion between the sheet and the rotary cooling drum, and it is desirable to employ an electrostatic application adhesion method and / or a liquid application adhesion method. In the melt extrusion process, the amount of terminal carboxyl groups increases depending on the conditions, so shorten the residence time of the polyester in the extruder in the extrusion process. Is sufficiently dried so as to be 100 ppm or less, preferably 50 ppm or less. When a twin screw extruder is used, a vent port is provided, and a reduced pressure of 40 hectopascals, preferably 30 hectopascals or less, more preferably 20 hectopascals or less. It is desirable to maintain. Immediately after melting, in order to prevent decomposition of the polyester, to prevent an increase in the number of carboxyl terminal groups, to prevent a decrease in molecular weight, or to prevent coloring, it is supercooled to near or below the melting point of the polyester resin. For this purpose, it is preferable to use a twin screw extruder, or cooling may be performed in the second stage of the tandem extruder.

  Moreover, the method of extending | stretching the sheet | seat obtained by making it above into a biaxial direction, and making it into a film is preferable at the point of hydrolysis resistance or a mechanical characteristic. As the biaxial stretching method, there are a sequential biaxial stretching method and a simultaneous biaxial stretching method. In consideration of productivity, the sequential biaxial stretching method is more preferable. Specifically describing the sequential biaxial stretching conditions, the unstretched sheet is preferably in the machine direction, a temperature not lower than the glass transition temperature Tg of the polyester resin and not higher than the cold crystallization start temperature Tcc, specifically 80 to 130 ° C. In a stretch ratio of 2 to 6 times and a longitudinal uniaxially stretched film, the film is stretched 2 to 6 times, preferably 3 to 4 times at 90 to 160 ° C. above the glass transition temperature Tg of the transverse polyester resin. Heat treatment is preferably performed at 180 to 260 ° C. for 1 to 600 seconds. Further, at this time, a method of relaxing 0.5 to 10% in the longitudinal direction and / or the transverse direction in the maximum temperature zone of the heat treatment and / or the cooling zone at the outlet of the heat treatment is preferable. Further, it is possible to add re-longitudinal stretching and re-lateral stretching as necessary. As the degree of orientation of the polyester film obtained as described above is higher in hydrolysis resistance, it is desirable to raise the degree of orientation as much as possible.

Alternatively, two or three or more polyester resin melt extruders can be used to form a laminated film of two layers or three or more layers by a so-called coextrusion method. It is desirable to laminate the polyester resin mixture (C) layer of the present invention and another polyester resin (E) layer from the viewpoint of hydrolysis resistance, mechanical properties, productivity, and the like. Specifically, by [C / E / C] 3 layers or [C / blend layer (C + E) / C] 3 layers, hydrolysis resistance at high temperature in the surface layer and mechanical properties in the intermediate layer Therefore, it is possible to achieve both. As the resin used for the other polyester resin (E) layer, a general-purpose polyester resin such as polyethylene terephthalate or polyethylene naphthalate is preferable. As the lamination ratio, a range in which the ratio of the total thickness of both surface layers to the total film thickness is about 10 to 50% is effective. The order of the three layers is not limited to the above, and may be a reverse layer structure such as [E / C / E] or [E / blend layer (C + E) / E]. If necessary, the number of layers n may be super multi-layer stacking of 8 or more as represented by [E / C] _n .

  Moreover, in the polyester film of this invention, in order to improve water vapor | steam barrier property, you may provide the vapor deposition layer etc. of a metal or a metal oxide on the film surface. Also, improving the suitability and adhesiveness when forming these vapor-deposited layers, or improving the adhesiveness with the adhesive layer when used by adhering to a film having a barrier property, the process of processing the film For the purpose of providing antistatic properties for preventing contamination during use, a coating layer as an undercoat layer can be provided on the film. In forming the coating layer on the film, the method of forming the film, particularly after stretching in the longitudinal direction and before stretching in the transverse direction, can form a very thin coating layer, drying the coating solution Or the curing reaction can be carried out during the film forming process. The coating layer is preferably composed of a combination of a crosslinking agent and various binder resins. The binder resin is usually polyester, acrylic polymer, polyurethane, ionomer resin, or a derivative thereof from the viewpoint of adhesiveness. A polymer selected from is used. In addition, a derivative here means the polymer which made the reactive compound react with the copolymer with another polymer, and a functional group. Moreover, after manufacturing the film, if necessary, one or both sides thereof may be coated with an off-line coat. As a coating material, either an aqueous system or a solvent system may be used in the case of off-line coating, but in the case of in-line coating, an aqueous system or an aqueous dispersion system is preferable.

  Among the polyesters, acrylic polymers, and polyurethanes used as the binder resin for the coating layer, particularly preferred polymers have a glass transition temperature Tg of 0 ° C. or higher, more preferably 40 ° C. or higher. This is a polymer having a carboxylic acid residue, at least a part of which is made aqueous with an amine or ammonia. As the crosslinking agent resin, melamine-based, epoxy-based, and oxazoline-based resins are generally used, but melamine-based resins are particularly preferable from the viewpoints of coatability and durable adhesiveness. The melamine-based resin may be either a monomer, a condensate composed of a dimer or higher multimer, or a mixture thereof.

  In addition, in order to further improve the slipperiness, adhesiveness, etc., it is preferable to contain inorganic particles or organic particles in the coating layer. The compounding quantity of the particle | grains in an application layer is 0.5-10 mass% normally, Preferably it is 1-5 mass%. When the blending amount is less than 0.5% by mass, the blocking resistance may be insufficient. When the blending amount exceeds 10% by mass, the transparency of the film is hindered and the image sharpness tends to be lowered. Examples of the inorganic particles include silicon dioxide, alumina, zirconium oxide, kaolin, talc, calcium carbonate, titanium oxide, barium oxide, carbon black, molybdenum sulfide, and antimony oxide. Among these, silicon dioxide is easy to use because it is inexpensive and has various particle sizes. On the other hand, examples of the organic particles include polystyrene or polyacrylate polymethacrylate in which a crosslinked structure is achieved by a compound containing two or more carbon-carbon double bonds in one molecule (for example, divinylbenzene).

  The above inorganic particles and organic particles may be surface-treated. Examples of the surface treatment agent include a surfactant, a polymer as a dispersant, a silane coupling agent, a titanium coupling agent, and the like. The content of particles in the coating layer is usually preferably 10% by mass or less, and more preferably 5% by mass or less. In addition to the above particles, the coating layer may contain an antistatic agent, an antifoaming agent, a coating property improving agent, a thickener, an antioxidant, an ultraviolet absorber, a foaming agent, a dye, a pigment, and the like. Good.

  As long as water is the main medium, the coating agent may contain a small amount of an organic solvent for the purpose of improving dispersion in water or improving the film-forming performance. It is necessary to use the organic solvent as long as it is soluble in water. Examples of the organic solvent include aliphatic or alicyclic alcohols such as n-butyl alcohol, n-propyl alcohol, isopropyl alcohol, ethyl alcohol, and methyl alcohol, glycols such as propylene glycol, ethylene glycol, and diethylene glycol, n-butyl cellosolve, Glycol derivatives such as ethyl cellosolve, methyl cellosolve, propylene glycol monomethyl ether, ethers such as dioxane and tetrahydrofuran, esters such as ethyl acetate and amyl acetate, ketones such as methyl ethyl ketone and acetone, amides such as N-methylpyrrolidone Can be mentioned. These organic solvents may be used in combination of two or more as required.

  As a coating method of the coating agent, a reverse roll coater, a gravure coater, a rod coater, an air doctor coater, or a coating apparatus other than these can be used. The coating layer may be formed only on one side of the polyester film, or may be formed on both sides. When formed only on one side, other characteristics can be imparted by forming a coating layer different from the above-mentioned coating layer on the opposite surface as necessary. In addition, in order to improve the applicability | paintability and adhesiveness to the film of a coating agent, you may give a chemical process and an electrical discharge process to a film before application | coating. Further, in order to further improve the surface characteristics, a discharge treatment may be performed after the coating layer is formed.

  The thickness of the coating layer is usually 0.01 to 0.5 μm, preferably 0.015 to 0.3 μm as the final dry thickness. When the thickness of the coating layer is less than 0.01 μm, the effect of the coating layer may not be sufficiently exhibited. When the thickness of the coating layer exceeds 0.5 μm, the films tend to stick to each other, and particularly when the coated film is re-stretched to increase the strength of the film, it adheres to the roll in the process. There is a tendency to become easy. The problem of sticking appears particularly when the same coating layer is formed on both sides of the film.

  In the solar cell back surface sealing film, a film provided with a water vapor barrier layer is usually used in order to block the entry of water vapor from the outside that adversely affects the solar cell element. In order to impart gas barrier properties, a gas barrier layer can be provided on the surface of the film by a known method such as vacuum deposition or sputtering of a metal such as aluminum or a metal oxide such as silicon or aluminum. Its thickness is usually in the range of 100 to 3000 angstroms. It is possible to use a method in which a film having a thickness of about 12 μm with a separate gas barrier layer is adhered and laminated on the polyester film surface, or a method in which a gas barrier layer is directly provided on the polyester film surface. Moreover, the method of adhere | attaching and laminating | stacking metal foil (for example, a general thing aluminum foil) on the polyester film surface can also be used. In this case, the thickness of the metal foil is preferably in the range of 10 to 50 μm from the viewpoint of workability and gas barrier properties. There is also a method of providing a vinylidene chloride-based coating layer, but it may be insufficient in terms of weather resistance and the like. Moreover, the gas barrier layer does not necessarily have to be on the surface of the film, and may be sandwiched between two layers of films, for example.

  A solar cell is produced by the structure shown below, for example. That is, a base material (glass, film, etc.) having a high light transmittance is used as a surface layer, and a silicon-based solar cell element is provided with a lead wire that can take out electricity, and is filled with a resin such as ethylene vinyl acetate resin. The film is fixed, and a back surface sealing film is provided on the back side (back surface) and fixed with an exterior material. In the back surface sealing film, the side closest to the solar cell element usually uses a high degree of reflectivity, for example, a white polyester film or the like to reflect sunlight and increase the conversion efficiency. . And it is set as the laminated structure of the structure which pinched | interposed and adhered the film or metal foil which has water vapor | steam barrier property between this white polyester film and the polyester film of this invention, and uses it as a film for back surface sealing of a solar cell. Can do. When the polyester film of the present invention is used as a film disposed on the outer layer side of the back surface sealing film in this way, it exhibits an excellent effect in terms of durability against the external environment, particularly hydrolysis resistance. .

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example. The measurement method used in the present invention is as follows.

(1) Measurement of intrinsic viscosity IV of polyester [η] [dl / g]
0.5 g of the sample was precisely weighed, dissolved in 50 ml of a mixed solvent of phenol / tetrachloroethane = 60/40 (mass ratio), and measured at 20 ° C. using an Ostwald viscometer. In addition, the measurement was performed 3 times and the average value was calculated | required.

(2) Determination of elements in film (ppm)
For metal M, 2 g of polyester was ignited in air at 700 ° C. for 2 hours to ash the polymer, and then dissolved in hydrochloric acid, and the equivalent of the metal was determined by atomic absorption according to a conventional method. Phosphorus P was wet ashed in the presence of sulfuric acid and perchloric acid, and then developed with ammonium molybdate in an acidic sulfuric acid solution. The absorbance at 845 μm was measured and quantified using a calibration curve.

(3) Amount of terminal carboxyl group (equivalent / ton)
The amount of terminal carboxyl groups was measured by a titration method. That is, polyester was dissolved in benzyl alcohol, phenol red indicator was added, and titrated with a water / methanol / benzyl alcohol solution of sodium hydroxide.

(4) Hydrolysis resistance at high temperature The film was treated for 72 hours at 120 ° C. in hot water, and the elongation at break was measured using a tensile tester (Orientec, UCT-500). The retention rate (%) of the breaking elongation before and after the treatment was calculated by the following formula and judged according to the following criteria.
Breaking elongation retention rate = (breaking elongation after treatment) ÷ (breaking elongation before treatment) × 100
A: Retention ratio is 80% or more B: Retention ratio is 60 to less than 80% B: Retention ratio is 40% to less than 60% X: Retention ratio is less than 40%

(5) Glass transition temperature Tg, melting point Tm of resin
A differential scanning calorimeter (Perkin Elmer Co., Ltd., DSC8), 10 mg of a sample was filled in an aluminum pan, heated to 290 ° C. at a temperature increase rate of 20 ° C./min in a nitrogen atmosphere, and at the same temperature. After holding for 3 minutes, the aluminum pan was poured into liquid nitrogen and quenched. The rapidly cooled aluminum pan was set on the differential scanning calorimeter again, and the glass transition temperature Tg and melting point Tm (endothermic peak peak temperature) were determined from the chart when the temperature was raised at a rate of 10 ° C./min. .

(6) Degree of plane orientation Using a sodium D line (wavelength 589 nm) as a light source and using an Abbe refractometer (manufactured by ATAGO, DR-M2), the refractive index (Nz) in the longitudinal direction of the film and the refractive index in the width direction ( Ny), the refractive index (Nz) in the thickness direction was measured, and the degree of plane orientation (ΔP) was calculated from the following formula.
ΔP = ((Nx + Ny) / 2) −Nz

(7) Film-forming property About the generation | occurrence | production state of the fracture | rupture at the time of using for film forming (stretching process), it determined by the following reference | standard.
○: No breakage occurred.
Δ: Occasional breakage.
X: Breaking occurred frequently.

<Polyester A>
A slurry composed of terephthalic acid and 1.02-1.4 (mol / mol) ethylene glycol with respect to terephthalic acid was formed, and an esterification reaction was performed at 250 ° C. When the amount of water generated during esterification reached a predetermined amount, germanium dioxide was added as a polymerization catalyst, and a polycondensation reaction was performed at 280 ° C. for 4 hours under vacuum (40 Pascals) or less. After starting the reaction, the reaction was stopped when the stirring power of the reaction tank reached a predetermined torque, and the polymer was discharged under nitrogen pressure. The intrinsic viscosity of the obtained polyester was 0.58. Using this polyester as a starting material, polyester A was obtained by solid phase polymerization at 220 ° C. under vacuum. The intrinsic viscosity of polyester A was 0.76, and the amount of terminal carboxyl groups of the polymer was 14 equivalents / ton.

<Polyester B>
PCTA 13319 (Essman Chemical Co., Ltd.) was used as polyester B (glycol component: 1,4-cyclohexanedimethanol 100 mol%, dicarboxylic acid component: terephthalic acid 95 mol%, isophthalic acid 5 mol%). As for the physical properties, the intrinsic viscosity IV was 0.96, the glass transition temperature Tg was 92 ° C., and the melting point Tm was 285 ° C.

Comparative Example 1
Polyester B (PCTA13319: manufactured by Eastman Chemical Co., Ltd.) and phosphorus-based heat stabilizer (IRGAFOS38: manufactured by Ciba Japan Co., Ltd.) equivalent to 350 ppm were melted at 300 ° C. with a vented twin screw extruder and extruded from the die. It was cooled and solidified on a cooling roll whose surface temperature was set to 25 ° C. using an application adhesion method, and an unstretched sheet was obtained. Next, the film was stretched 3.0 times in the longitudinal direction at 115 ° C., then led to a tenter, stretched 3.5 times in the transverse direction at 120 ° C., and further heat treated at 240 ° C. to obtain a polyester film having a thickness of 50 μm. .

Example 1
20% by mass of polyester A (polyethylene terephthalate), 80% by mass of polyester B (PCTA13319: manufactured by Eastman Chemical Co., Ltd.), and phosphorus-based heat stabilizer (IRGAFOS38: manufactured by Ciba Japan Co., Ltd.) equivalent to 350 ppm are mixed. In the same manner as above, after being melted at 300 ° C. by a twin screw extruder with a vent, extruded from the die, cooled and solidified on a cooling roll having a surface temperature set to 25 ° C. using an electrostatic application adhesion method, and unstretched sheet Got. Next, the film was stretched 3.0 times in the longitudinal direction at 115 ° C., then led to a tenter, stretched 3.5 times in the transverse direction at 120 ° C., and further heat treated at 240 ° C. to obtain a polyester film having a thickness of 50 μm. .

Example 2
Polyester A (polyethylene terephthalate) 40% by mass, polyester B (PCTA13319: manufactured by Eastman Chemical Co.) 60% by mass, and a phosphorous heat stabilizer (IRGAFOS38: manufactured by Ciba Japan Co., Ltd.) equivalent to 350 ppm were mixed, and Example 1 above was mixed. In the same manner as above, after being melted at 300 ° C. by a twin screw extruder with a vent, extruded from the die, cooled and solidified on a cooling roll having a surface temperature set to 25 ° C. using an electrostatic application adhesion method, and unstretched sheet Got. Next, the film was stretched 3.0 times in the longitudinal direction at 115 ° C., then led to a tenter, stretched 3.5 times in the transverse direction at 120 ° C., and further heat treated at 240 ° C. to obtain a polyester film having a thickness of 50 μm. .

Example 3
20% by mass of polyester A (polyethylene terephthalate), 80% by mass of polyester B (PCTA13319: manufactured by Eastman Chemical Co., Ltd.) and phosphorus-based heat stabilizer (IRGAFOS38: manufactured by Ciba Japan Co., Ltd.) equivalent to 1000 ppm were mixed, In the same manner as in No. 1, after being melted at 300 ° C. by a twin screw extruder with a vent, extruded from the die, cooled and solidified on a cooling roll set at a surface temperature of 25 ° C. using an electrostatic application adhesion method, and unstretched A sheet was obtained. Next, the film was stretched 3.0 times in the longitudinal direction at 115 ° C., then led to a tenter, stretched 3.5 times in the transverse direction at 120 ° C., and further heat treated at 240 ° C. to obtain a polyester film having a thickness of 50 μm. .

Comparative Example 2
Polyester A (polyethylene terephthalate) and phosphorus-based heat stabilizer (IRGAFOS38: manufactured by Ciba Japan Co., Ltd.) equivalent to 350 ppm were melted at 290 ° C. by a twin-screw extruder with a vent in the same manner as in Comparative Example 1, and then from the die. The sheet was extruded and cooled and solidified on a cooling roll whose surface temperature was set to 25 ° C. using an electrostatic application adhesion method, to obtain an unstretched sheet. Next, the film was stretched 3.8 times in the longitudinal direction at 90 ° C., led to a tenter, stretched 4 times in the lateral direction at 95 ° C., and further heat treated at 230 ° C. to obtain a polyester film having a thickness of 50 μm.

Comparative Example 3
50% by mass of polyester A (polyethylene terephthalate), 50% by mass of polyester B (PCTA13319: manufactured by Eastman Chemical Co., Ltd.) and a phosphorus-based heat stabilizer (IRGAFOS38: manufactured by Ciba Japan Co., Ltd.) equivalent to 350 ppm are mixed together. In the same manner as in No. 1, after being melted at 300 ° C. by a twin screw extruder with a vent, extruded from the die, cooled and solidified on a cooling roll set at a surface temperature of 25 ° C. using an electrostatic application adhesion method, and unstretched A sheet was obtained. Next, the film was stretched 3.0 times in the longitudinal direction at 115 ° C., then led to a tenter, stretched 3.5 times in the transverse direction at 120 ° C., and further heat treated at 240 ° C. to obtain a polyester film having a thickness of 50 μm. .

About the polyester film of each Example and comparative example obtained as mentioned above, the physical property and characteristic of various films were evaluated. The results are shown in Table 1 below.

  As shown in Table 1 above, the polyester film of Comparative Example 1 prepared by using polyester B whose glycol component is 1,4-cyclohexanedimethanol alone has good hydrolysis resistance, but the film is stretched. Breakage occurred, which was not sufficient in terms of film formability.

  On the other hand, Examples 1 to 3 prepared using a resin mixture of 80 to 60 parts by mass of polyester B containing 1,4-cyclohexanedimethanol and 20 to 40 parts by mass of polyester A composed of polyethylene phthalate. This polyester film showed good hydrolysis resistance and improved film-forming properties, and it was found that a polyester film having excellent moldability and hydrolysis resistance was obtained. Further, these films showed relatively high numerical values for both the glass transition point and the melting point, and also had good heat resistance. In Example 3 in which the addition amount of the phosphorus compound was increased, the content ratio of the phosphorus element with respect to the metal element in the film was increased as compared with Example 1 in which the other conditions were the same, and as a result, hydrolysis resistance was increased. Was found to be improved further.

  On the other hand, the polyester film of Comparative Example 2 prepared by using polyester A (polyethylene terephthalate) alone without using polyester B containing 1,4-cyclohexanedimethanol, although there is no problem in terms of film formability, It was considerably inferior in hydrolysis resistance. Furthermore, in the polyester film of Comparative Example 3 using a resin mixture in which polyester A and polyester B are mixed in half amounts, hydrolysis resistance is not improved, and polyester B containing 1,4-cyclohexanedimethanol It has been found that more than half of the mixture needs to be used.

  Subsequently, in order to further examine the suitability as a film for sealing a back surface of a solar cell, a laminated film of polyester A and polyester B, and polyester B ′ containing 80 mol% and 33 mol% of 1,4-cyclohexanedimethanol, respectively. , B ″ were prepared as single film and blend single film, and the physical properties and properties of each film were evaluated in the same manner as in the above test. The results are shown in Table 2 below.

Comparative Example 4
20 parts by mass of polyester A (polyethylene terephthalate) and 80 parts by mass of polyester B (glycol component = 1,4-cyclohexanedimethanol 100 mol%, dicarboxylic acid component = terephthalic acid 95 mol%, isophthalic acid 5 mol%) After drying at 130 ° C. under reduced pressure for 8 hours to reduce the water content to 100 ppm or less, it was supplied to a multilayer extruder having a T-die having a width of 40 cm to obtain a two-layer polyester film having a thickness of 250 μm. The cylinder temperature of the extruder was 280 ° C. on the polyester A side, 290 ° C. on the polyester B side, the temperature of the T die was 290 ° C., and the temperature of the cooling roll was 25 ° C. Next, the film was stretched 3.0 times in the longitudinal direction at 90 ° C., then led to a tenter, stretched 3.5 times in the lateral direction at 95 ° C., and further heat treated at 230 ° C. to obtain a polyester film having a thickness of 50 μm. .

Comparative Example 5
Polyester B ′ (glycol component = 1,4-cyclohexanedimethanol 80 mol%, ethylene glycol 20 mol%, dicarboxylic acid component = terephthalic acid 100 mol%) and phosphorus heat stabilizer (IRGAFOS38: manufactured by Ciba Japan) 350 ppm In the same manner as in Comparative Example 1 above, after being melted at 290 ° C. by a twin screw extruder with a vent, extruded from a die, and on a cooling roll having a surface temperature set to 25 ° C. using an electrostatic application adhesion method. Cooled and solidified to obtain an unstretched sheet. Next, the film was stretched 3.0 times in the longitudinal direction at 90 ° C., then led to a tenter, stretched 3.5 times in the lateral direction at 95 ° C., and further heat treated at 230 ° C. to obtain a polyester film having a thickness of 50 μm. .

Example 4
20 parts by mass of polyester A (polyethylene terephthalate), 80 parts by mass of polyester B ′ (CHDM 80 mol%, EG 20 mol%, TPA 100 mol%), and phosphorus thermal stabilizer (IRGAFOS38: manufactured by Ciba Japan) equivalent to 350 ppm are compared with the above. In the same manner as in Example 1, after being melted at 290 ° C. with a vented twin-screw extruder, it was extruded from the die, cooled and solidified on a cooling roll set at a surface temperature of 25 ° C. using an electrostatic application adhesion method, A stretched sheet was obtained. Subsequently, after stretching 3.0 times and 3.5 times in the vertical and horizontal directions, a polyester film having a thickness of 50 μm was obtained.

Comparative Example 6
20 parts by mass of polyester A (polyethylene terephthalate) and 80 parts by mass of polyester B ″ (glycol component = 1,4-cyclohexanedimethanol 33 mol%, ethylene glycol 67 mol%, dicarboxylic acid component = terephthalic acid 100 mol%) , Phosphorus heat stabilizer (IRGAFOS38: manufactured by Ciba Japan) equivalent to 350 ppm was melted at 280 ° C. with a vented twin-screw extruder in the same manner as in Comparative Example 1 above, and then extruded from the die. It was used to cool and solidify on a cooling roll whose surface temperature was set to 25 ° C. to obtain an unstretched sheet. Subsequently, after stretching 3.0 times and 3.5 times in the vertical and horizontal directions, a polyester film having a thickness of 50 μm was obtained.

  As shown in Table 2 above, the polyester film of Comparative Example 4 in which the polyester A and the polyester B were laminated at a ratio that the CHDM amount in the film was 80% resulted in inferior hydrolysis resistance due to the polyester A layer. It was. Moreover, in Comparative Example 5 using polyester B ′ containing 80 mol% of 1,4-cyclohexanedimethanol alone, although it is excellent in hydrolysis resistance, the crystallinity is low, so that it breaks during stretching. It has occurred. On the other hand, in Example 4 in which 20% by mass of polyester A was blended with polyester B ', good film-forming properties were exhibited while maintaining hydrolysis resistance. On the other hand, in Comparative Example 6 in which polyester B ″ containing 33 mol% of 1,4-cyclohexanedimethanol was used, even when polyester A was blended, the hydrolysis resistance was poor.

  From the above results, various characteristics suitable for a film for sealing a back surface of a solar cell can be obtained by using a polyester resin mixture in which polyester A and polyester B having a specific composition are mixed at a specific ratio as in each of the above examples. It became clear that it was obtained.

Claims (6)

5 to 45 parts by mass of a polyester resin (A) comprising a dicarboxylic acid component containing 80 mol% or more of terephthalic acid or an ester-forming derivative thereof, and a glycol component containing 80 mol% or more of ethylene glycol;
95-55 mass of polyester resin (B) comprising a dicarboxylic acid component containing 80 mol% or more of terephthalic acid or an ester-forming derivative thereof and a glycol component containing 60 mol% or more of 1,4-cyclohexanedimethanol A polyester film for sealing a back surface of a solar cell, comprising a polyester resin mixture obtained by mixing a portion of the polyester resin (A) and the polyester resin (A) so that a total amount of the polyester resin (A) and (B) is 100 parts by mass .   The polyester film for sealing a back surface of a solar cell according to claim 1, wherein the glycol component of the polyester resin (B) contains 80 mol% or more of 1,4-cyclohexanedimethanol.   The polyester film for sealing a back surface of a solar cell according to claim 1 or 2, wherein the tensile breaking elongation retention after treatment with hot water at 120 ° C for 72 hours is 60% or more.   Content of the phosphorus element in a polyester resin mixture is 10-300 ppm, The polyester film for solar cell backside sealing in any one of Claim 1 to 3 characterized by the above-mentioned.   5. The polyester film for sealing a back surface of a solar cell according to claim 1, wherein the amount of terminal carboxyl groups in the polyester resin mixture is 30 equivalents / ton or less.   The glass transition temperature Tg is 80 ° C. or higher, The solar cell back surface sealing polyester film according to claim 1.