JP5930106B2 - Hydrolysis resistant polyester film - Google Patents

Description

  The present invention relates to a hydrolysis resistant polyester film. More specifically, the present invention relates to a weather-resistant polyester film for electrical insulation such as for solar cell backsheets, motor insulation, and capacitors. In particular, it is a hydrolysis-resistant polyester film suitably used for a solar battery backsheet.

  Polyester films are excellent in mechanical properties and chemical properties, and are used in a wide range of fields such as packaging, magnetic tape, electronic parts, electrical insulation, and protective sheets. In particular, in solar cell field backsheet applications, motor insulation applications, and capacitor applications, since they are exposed to harsh usage environments for a long period of time, higher durability is required. However, when a polyester film is used in a high-temperature and high-humidity environment, there is a problem in that hydrolysis of an ester bond site in a molecular chain occurs and mechanical properties deteriorate. Therefore, various studies have been made on improving the hydrolysis resistance of polyester films.

  For example, Patent Document 1 discloses a technique for improving hydrolysis resistance by lowering the acid value of a resin. Patent Documents 2 to 4 disclose techniques for improving the weather resistance by increasing the molecular weight of the resin.

  Patent Documents 5 to 7 disclose techniques for adding a carboxylic acid end-capping agent such as an epoxy compound, an oxazoline compound, and an isocyanate compound in order to improve the hydrolysis resistance of a polyester film. These are used in combination with a hindered phenol acid value stabilizer as an additive for preventing the end-capping agent from being deactivated or preventing gelation. Further, Patent Documents 8 to 10 disclose techniques for improving weather resistance and various physical properties by uniformly mixing and blending polyester and other resins. In addition, a hindered phenol compound is also used as an additive in order to prevent decomposition and coloring of the resin to be blended. As for hindered phenol compounds, conventionally, in the field of engineering plastics such as injection molding, a technique for preventing thermal aging of molded articles by adding them as antioxidants is widely known (Patent Document 11).

JP 2007-150084 A JP 2002-134770 A JP 2005-11923 A JP 2002-26354 A JP 2007-302878 A JP 2007-276478 A JP 2007-99971 A JP 2003-268111 A JP 2000-119417 A JP 2004-250485 A JP-A-6-107923

  However, in Patent Documents 1 to 4, since the intrinsic viscosity of the resin is increased and shearing heat is likely to be generated, and the acid value is increased by decomposition instead of melt molding, a film having a sufficiently low acid value cannot be obtained. Moreover, the method of patent documents 5-10 does not improve the weather resistance of the film which consists essentially of polyester. On the other hand, the method of adding a hindered phenol-based compound as an antioxidant as in Patent Document 11 has a large amount of addition because the purpose is to prevent the molded product from being deteriorated even when it is exposed to high temperatures. Therefore, when applied to a film, the periphery of the lip of the die, rolls such as a chill roll and a stretching roll may be contaminated during film formation, and stable film formation for a long time may be difficult. In addition, the stabilizer may bleed out, causing problems such as delamination of laminated solar cell backsheets.

  The present invention has been made against the background of such prior art problems. That is, the object of the present invention is to suppress an increase in the acid value during film molding and to obtain a low acid value hydrolysis-resistant polyester film. When this is used for a back sheet of a solar cell, it is conventional. It is an object of the present invention to provide a polyester film excellent in hydrolysis resistance that can achieve excellent weather resistance that is not present.

The present inventors diligently studied a high hydrolysis resistance film and clarified the following.
Even if the acid value is lowered at the resin raw material stage as in the prior art, degradation of the polyester proceeds and the acid value slightly increases due to the thermal history applied in the extruder during film formation. In particular, this tendency is remarkable for resin raw materials having a large molecular weight and a high intrinsic viscosity. Even if the increase in the acid value occurring during melt extrusion is slight, the degradation of the polyester main chain is catalyzed by the acid, so that the degradation proceeds in a self-propagating manner due to such catalytic action. Therefore, as a result, the weather resistance is lowered in long-term use. Thus, it was found that a slight increase in the acid value generated during melt molding of the resin raw material has a great influence on long-term durability.

  Therefore, as a result of intensive studies to suppress an increase in the acid value in the extruder of the resin raw material, by adding a very small amount of a hindered phenol compound compared to the conventionally applied amount, An unexpected result was obtained that the increase in the acid value was suppressed, and as a result, the long-term durability was remarkably improved. The added amount of the hindered phenol compound that is effective here is not a large amount (several thousand ppm or more) used in engineering plastics or the like, but a large effect is exhibited even if it is a small amount of several hundred ppm or less.

  The present invention is based on finding a new effect of a hindered phenol compound. That is, the present invention includes 0.03 to 6.7 equivalent / ton of hindered phenol structural units in the polyester resin composition constituting the film, the acid value of the polyester constituting the film is less than 25 equivalent / ton, and the intrinsic viscosity. Is a polyester film characterized by having an excess specific gravity of 0.64 dL / g and 0.90 dL / g or less, and an apparent specific gravity of 0.7 to 1.3.

  In the above, it is preferable that the film contains 5 to 20% by mass of white fine particles.

  In the above, the film has a three-layer structure of a skin layer composed of a polyester layer containing white fine particles and a core layer composed of a polyester layer containing many cavities derived from a thermoplastic resin incompatible with polyester. preferable.

  In the above, the polyester contains at least one of terephthalic acid or naphthalenedicarboxylic acid as the acid component, and the total amount of terephthalic acid or naphthalenedicarboxylic acid is 90 mol% or more based on the total acid component, and ethylene as the glycol component It is preferable that the total amount of ethylene glycol and diethylene glycol including glycol and diethylene glycol is 90 mol% or more based on the total glycol component.

In the above, it is preferable that the polyester resin composition does not substantially contain a compound having a substituent that reacts with these (OH group or carboxyl group) in addition to the OH group and carboxyl group.

  In the above, it is preferable that polyester is contained exceeding 90 mass% in the polyester resin composition.

  In the above, the heat-resistant oxidative decomposition parameter (TOD) of the polyester resin composition constituting the film is preferably 0.25 or less.

  In the above, it is preferable that polyester is polymerized using a calcium compound, an antimony compound, a lithium compound, and a phosphorus compound as a catalyst.

  Moreover, the heat-resistant oxidative decomposition parameter (TOD) of the polyester resin composition constituting the film is 0.25 or less, the acid value of the polyester constituting the film is less than 25 equivalents / ton, and the intrinsic viscosity exceeds 0.64 dL / g. It is a hydrolysis-resistant polyester film characterized by being 90 dL / g or less.

  The film is preferably one of solar cell backsheet, solar cell frontsheet, and electrical insulation.

  Furthermore, the present invention is a solar cell characterized in that the polyester film described above is laminated on at least one of the light receiving surface or the side opposite to the light receiving surface.

  Although the hydrolysis-resistant polyester film of the present invention is substantially composed of a polyester resin, it has good hydrolysis resistance. Therefore, it can be suitably used for applications requiring durability such as solar cell backsheet applications and electrical insulation applications.

  In the present invention, the polyester means the polycondensed polyester itself as a raw material, and the polyester resin composition further maintains the function as a polyester such as a stabilizer, a terminal blocking agent, and other resins compatible with the polyester. Or a resin added with a substance for modifying the polyester, and the film resin composition indicates a material added to give a function as a film such as a colorant, a lubricant, a filler, or a cavity developing material. . Various stabilizers, particles and fillers may be added at the time of polycondensation regardless of the necessity for polycondensation, but when they are labeled as a polyester resin composition or film resin composition, they are added during polymerization. We shall also include things.

  In this invention, the hindered phenol structure is contained in the polyester resin composition which comprises a film. The lower limit of the hindered phenol structure content in the polyester composition is preferably 0.03 equivalent / ton, more preferably 0.1 equivalent / ton, further preferably 0.17 equivalent / ton, especially The amount is preferably 0.2 equivalent / ton, and most preferably 0.22 equivalent / ton. If the hindered phenol structure content in the polyester composition is less than the above, sufficient weather resistance improvement effect may not be obtained.

  On the other hand, the upper limit of the hindered phenol structure content is preferably 6.7 equivalent / ton, more preferably 3.4 equivalent / ton, still more preferably 3.35 equivalent / ton, and even more preferably 1.69 equivalent / ton. Tons, particularly preferably 1.5 equivalents / ton, and most preferably 1.4 equivalents / ton. If the above is exceeded, the effect is saturated and economically disadvantageous, and die lip dirt, chill roll dirt, conveyance and stretching roll dirt are likely to occur during film formation, and frequent cleaning is required, making stable production difficult. There is. Furthermore, if the above is exceeded, the hindered phenol compound bleeds out and the adhesiveness is lowered, the adhesion between the polyester film and the functional layer is lowered, for example, a moisture-proof layer such as an aluminum foil, a decrease in adhesion to the light reflecting layer, ethylene In some cases, delamination may occur with a sealing material such as a vinyl acetate polymer.

In addition, the hindered phenol structure which becomes object here is a thing (semi-hindered phenol) in which one side is a t-butyl group and the other is a methyl group (semi-hindered phenol), and one side is t-butyl group. -Includes all butyl groups with the other being hydrogen (resindered phenol).
In addition, when a hindered phenol compound is added during polymerization, the hindered phenol compound may be incorporated into the polyester, and the hindered phenol structure part incorporated into the polyester molecular chain is also included. And

  A polyester resin composition containing a hindered phenol structure can be obtained by adding a hindered phenol compound to a polyester. Generally, commercially available hindered phenol compounds have a molecular weight per hindered phenol structural unit of 250. It is about -300. Therefore, the lower limit of the amount of hindered phenol compound added to the polyester resin composition is preferably 10 ppm, more preferably 30 ppm, still more preferably 50 ppm, particularly preferably 60 ppm, and most preferably 65 ppm. is there. The upper limit is preferably less than 2000 ppm, more preferably less than 1000 ppm, still more preferably less than 800 ppm, even more preferably less than 500 ppm, particularly preferably less than 450 ppm, and most preferably less than 400 ppm.

  The hindered phenol compound may be added during the polymerization of the polyester or may be added during the film formation. When adding at the time of film forming, the method of creating and adding a masterbatch is preferable.

Examples of the hindered phenol compound include triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate], 1,6-hexanediol-bis [3- (3,5- Di-t-butyl-4-hydroxyphenyl) propionate], 2,4-bis- (n-octylthio) -6- (4-hydroxy-3,5-di-t-butylanilino) -1,3,5- Triazine, pentaerythrityl tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], 2,2-thio-diethylenebis [3- (3,5-di-t-butyl) -4-hydroxyphenyl) propionate], octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, N, N'-hex Methylenebis (3,5-di-tert-butyl-4-hydroxy-hydrocinnamamide), 3,5-di-tert-butyl-4-hydroxybenzylphosphonate-diethyl ester, 1,3,5-trimethyl -2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, bis (3,5-di-t-butyl-4-hydroxybenzylphosphonate ethyl) calcium, tris- (3,5-di-t-butyl-4-hydroxybenzyl) -isocyanurate, isooctyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, and the like. Is commercially available as Irganox®. Among these, the vapor pressure at 20 ° C. is 1.0 × 10 ⁻⁵ Pa or less, more preferably 1.0 × 10 ⁻⁶ Pa or less, and particularly 1.0 × 10 ⁻⁷ Pa or less at the time of film formation. It is preferable for reducing volatilization. Moreover, when adding at the time of superposition | polymerization, it is preferable that it is 1.0 * 10 <^-10> Pa or less in order to prevent the distillation by polycondensation.

  Furthermore, the polyester resin composition constituting the film may contain a phosphorus stabilizer. The lower limit of the content of the phosphorus stabilizer is preferably 10 ppm, more preferably 30 ppm, still more preferably 50 ppm, and particularly preferably 60 ppm. If it is less than the above, sufficient effects may not be obtained. The upper limit of the phosphorus stabilizer content is preferably 1000 ppm, more preferably 700 ppm, still more preferably 500 ppm, particularly preferably 400 ppm, and most preferably 300 ppm. When the above is exceeded, die lip stains, chill roll stains, conveyance and stretch roll stains are likely to occur during film formation, and frequent cleaning is required, which may make stable production difficult. In addition, phosphorus stabilizers may bleed out and adhesion may be reduced, causing adhesion to moisture-proof layers such as aluminum foil, light reflecting layers, and delamination from sealing materials such as ethylene vinyl acetate polymers. .

  Examples of phosphorus stabilizers include tris (2,4-di-t-butylphenyl) phosphite (Irgafos (R) 168), tetrakis (2,4-di-t-butylphenyl) 4,4′-biphenylenediene. Phosphite (Sandostab® P-EPQ), tetrakis (2,4-di-t-butyl-5-methylphenyl) [1,1-biphenyl] -4,4′-diylbisphosphonite (Osaki Kogyo Co., Ltd.) Manufactured GSY-P101).

  The intrinsic viscosity of the polyester of the film is preferably more than 0.64 dL / g (exceeds not exceeding, the same applies hereinafter), more preferably more than 0.65 dL / g, and still more preferably more than 0.66 dL / g. Particularly preferably more than 0.67 dL / g, most preferably more than 0.68 dL / g. If it is not more than the above, sufficient weather resistance may not be obtained. The upper limit of IV is preferably 0.90 dL / g, more preferably 0.85 dL / g, still more preferably 0.82 dL / g, particularly preferably 0.80 dL / g, most preferably 0.78 dL / g. Exceeding the above makes it difficult at the time of molding with the film forming machine currently widely used, or the high temperature during film forming causes the polyester to decompose, so that the inhibitory effect by the hindered phenol compound is relatively lowered, and the acid value is high. May be.

  In order to make the intrinsic viscosity of the polyester of the film within the above range, the intrinsic viscosity of the raw material polyester is preferably more than 0.66 dL / g, more preferably more than 0.67 dL / g, and still more preferably 0.68 dL. / G, particularly preferably more than 0.69 dL / g, most preferably more than 0.7 dL / g. The upper limit of the intrinsic viscosity of the raw material polyester is preferably 0.92 dL / g, more preferably 0.88 dL / g, still more preferably 0.84 dL / g, and particularly preferably 0.82 dL / g. Most preferably, it is 0.80 dL / g.

  The acid value of the polyester of the film is preferably less than 25 equivalents / ton, more preferably less than 22 equivalents / ton, even more preferably less than 20 equivalents / ton, and particularly preferably less than 18 equivalents / ton. When these values are exceeded, even if a hindered phenol compound is contained, the effect cannot be fully utilized. In other words, the hindered phenolic compound has a relatively low acid value suppression effect when the resin is melted, and the higher the absolute acid value of the polyester, the lower the relative effect. descend. Since the lower limit of the acid value is preferable, it is not particularly defined. However, actually, it is preferably 0 equivalent / ton or more, more preferably 1 equivalent / ton or more, more preferably 2 equivalent / ton from the viewpoint of productivity. Tons or more, particularly preferably 3 equivalents / ton or more.

  When the film is required to have particularly high weather resistance, such as for solar cell backsheets and electrical insulation applications, the acid value of the polyester of the film is preferably less than 15 equivalents / ton, more preferably 13 equivalents / tonne. Less than 12 tons, more preferably less than 12 equivalents / ton, particularly preferably less than 11 equivalents / ton, and most preferably less than 10 equivalents / ton. If the above is exceeded, high hydrolysis resistance may not be obtained.

When such weather resistance with a low acid value is required, it is preferable that the film does not contain a large amount of coloring pigments, void forming agents, and the like. When adding many of these, it becomes difficult to add during polymerization, and it is necessary to add during molding. It is necessary to strengthen the melt-kneading conditions during film formation for uniform dispersion, and the acid value increase during film formation is large. May be. In this case, the addition amount of the color pigment and the cavity forming agent is preferably 5% by mass or less, more preferably 3.0% by mass or less, and particularly preferably 2.5% by mass or less. If this range is exceeded, the amount of masterbatch may increase, and pigments may be difficult to add during polymerization, which may be disadvantageous for lowering the acid value.

  In order to make the acid value of the polyester of the film within the above range, the acid value of the raw material polyester is preferably 10 equivalent / ton or less, more preferably 9 equivalent / ton or less, and further preferably 8 equivalent / ton or less. And particularly preferably 7 equivalents / ton or less. If the above is exceeded, the acid value of the polyester of the film may not be lowered as intended. The lower limit of the acid value of the raw material polyester is preferably low, and is not particularly defined, but is practically about -3. In addition, according to the method of an Example, when an acid value is lowered to the limit, a negative value may be obtained. Further, in order to lower the acid value of the raw material polyester, solid phase polymerization is performed. However, when the acid value is lowered, the solid phase polymerization rate is lowered. Therefore, considering the productivity, the lower limit of the acid value of the raw material polyester is preferably 0, more preferably 1, and still more preferably 2.

  The lower limit of the cyclic trimer (CT) in the polyester of the film is preferably 0.20% by mass, more preferably 0.25% by mass, still more preferably 0.28% by mass, particularly preferably. 0.30% by mass. If it is less than the above, the solid phase polymerization will take a long time and the productivity will be poor. The upper limit of CT is preferably 0.60% by mass, more preferably 0.55% by mass, and still more preferably 0.50% by mass. If the above is exceeded, roll stains and die lip stains may occur. Further, CT may precipitate on the surface and cause film whitening, or when a gas barrier layer is deposited on the film surface, it may cause pinholes in the gas barrier layer. The amount of CT can be reduced by solid phase polymerization.

  The acetaldehyde content in the polyester composition constituting the film is preferably 50 ppm or less. More preferably, it is 40 ppm or less, Most preferably, it is 30 ppm or less. Acetaldehyde easily causes a condensation reaction between acetaldehydes, and water is produced as a side reaction product, and the water may cause hydrolysis of the polyester. The lower limit of the acetaldehyde content is practically about 1 ppm. In order to keep the amount of acetaldehyde within the above range, keep the oxygen concentration in each step such as melt polymerization and solid phase polymerization during resin production, keep oxygen concentration during resin storage and drying, and extrude during film production It is possible to adopt a method such as lowering the heat history applied to the resin by a machine, melt piping, die or the like, or preventing a strong shear from being applied locally by the screw configuration of the extruder at the time of melting.

  The polyester is preferably a polyester comprising an aromatic dicarboxylic acid and a diol. The aromatic dicarboxylic acid is preferably terephthalic acid or naphthalenedicarboxylic acid. Other aromatic dicarboxylic acids and aliphatic dicarboxylic acids may be copolymerized, and examples of dicarboxylic acids include isophthalic acid, orthophthalic acid, biphenyldicarboxylic acid, adipic acid, sebacic acid, and cyclohexanedicarboxylic acid.

  Although terephthalic acid and naphthalenedicarboxylic acid may be used in any ratio, the lower limit of the total amount of terephthalic acid and naphthalenedicarboxylic acid is preferably 95 mol%, more preferably 97 mol%, still more preferably 99 mol%. Yes, particularly preferably 100 mol%. If it is less than the above, the physical properties and weather resistance may be lowered. The upper limit of the amount of terephthalic acid and naphthalenedicarboxylic acid is 100 mol%. Most preferably, it is 95 mol% or more of terephthalic acid, More preferably, it is 97 mol% or more, More preferably, it is 99 mol% or more, Most preferably, it is 100 mol%.

  The diol is preferably ethylene glycol. A part of ethylene glycol becomes diethylene glycol during polymerization and is incorporated into the polyester, but the lower limit of the amount of ethylene glycol + diethylene glycol is preferably 90 mol%, more preferably 95 mol%, still more preferably 98 mol%, Especially preferably, it is 100 mol%. If it is less than the above, physical properties and weather resistance may be lowered (aliphatic). The upper limit is 100 mol%.

  Other diol components include propylene glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, cyclohexanedimethanol, bisphenol A-EO adduct, bisphenol A-PO adduct, polytetramethylene glycol Etc.

  Most preferred polyesters are homopolyethylene terephthalate, homopolyethylene naphthalate, and homopolybutylene terephthalate. The homo here may be a product obtained by copolymerizing by-products such as diethylene glycol generated during the polymerization.

The lower limit of the diethylene glycol content (in the glycol component) in the polyester is preferably 0.5 mol%, more preferably 0.8 mol%, and even more preferably 1 mol%. Less than the above may be difficult to achieve in practice. The upper limit of the diethylene glycol content is preferably 3 mol%, more preferably 2.6 mol%, still more preferably 2.4 mol%, and particularly preferably 2.2 mol%. If the above is exceeded, the weather resistance may be lowered. The amount of diethylene glycol can be suppressed by adding an alkali component during the esterification reaction.
The configuration of the present invention will be described below.

1. Raw Material Polyester The raw material polyester preferably used in the present invention is an ester exchange reaction (ester exchange method or DMT) in which a dicarboxylic acid and a diol component are esterified (esterification method) or a dimethyl ester of a dicarboxylic acid is reacted with a diol component. And then polycondensed under reduced pressure.

  Any of the commonly used polycondensation catalysts for polymerizing the polyester may be used, and examples thereof include Al compounds, Sb compounds, Ge compounds, and Ti compounds. Of these, Al compounds, Sb compounds, and Ti compounds are preferable from the viewpoint of economic efficiency, and Al compounds, Sb compounds, and Ge compounds are preferable from the viewpoint of heat resistance stability. In terms of obtaining a commercially stable catalyst, Sb compounds are preferred. Ge compounds and Ti compounds are preferred, and Sb compounds are most preferred when these points are combined.

The Al compound has low activity by itself, and preferably has increased catalytic activity in combination with other metals. Al / Co, Al / Li, Al / Na, Al / Mg, etc. are preferably used. Also preferred are those in which the catalytic activity is further improved by combining a phosphorus compound in combination with Al or another metal (except for phosphorus compounds having a hindered phenol structure in the molecule), and particularly preferred phosphorus compounds. Is a phosphonic acid having an aromatic group in its molecule represented by Ar—CH ₂ —P (═O) (OH) ₂ (Ar represents an aryl group, but excluding those having a hindered phenol structure). These alkyl esters and salt compounds are also included.

  Examples of germanium compounds include germanium dioxide and germanium tetrachloride. Among these, germanium dioxide is preferred. The addition amount of the germanium compound is ppm as Ge atoms, and the lower limit is preferably 10 ppm, more preferably 20 ppm, and even more preferably 30 ppm. If it is less than the above, the polycondensation reaction may be delayed, resulting in poor productivity. The upper limit is preferably 200 ppm, more preferably 150 ppm, and even more preferably 100 ppm. A germanium compound is expensive and exceeding the above is not economically preferable. In the case of using a germanium compound, it is also preferable to deactivate the catalyst by treating the polyester chip with hot water after the production of the polyester.

  Titanium compounds include tetra-n-propyl titanate, tetraisopropyl titanate, tetra-n-butyl titanate, tetraisobutyl titanate, tetra-tert-butyl titanate, tetracyclohexyl titanate, tetraphenyl titanate, titanium oxalate, phthalate titanate, tri Mellitic acid titanate, pyromellitic acid titanate and the like can be mentioned, and among these, tetra-n-butoxy titanate and trimellitic acid titanate are preferable. In particular, trimellitic titanate is preferable in terms of yellowing resistance and heat stability. The lower limit of the amount of Ti compound added as Ti atoms is preferably 1 ppm, more preferably 2 ppm, and even more preferably 3 ppm. If it is less than the above, the polycondensation reaction may be delayed, resulting in poor productivity. The upper limit is preferably 30 ppm, more preferably 25 ppm, and even more preferably 20 ppm. When the above is exceeded, the thermal decomposition during film formation becomes severe and the weather resistance may be inferior. When a titanium compound is used, it is preferable to adjust the activity of the catalyst by adding a phosphorus compound during polymerization. In addition, after completion of the polymerization, it is also preferable to deactivate the titanium catalyst by adding a phosphorus compound at the time of film formation, for example. Examples of the phosphorus compound include phosphoric acid, phosphorous acid, and phosphonic acids described later.

  Examples of the antimony compound include antimony trioxide, antimony pentoxide, antimony acetate, and antimony glycoloxide. Of these, antimony trioxide is preferable. In the case of an Sb compound, the lower limit of the addition amount of Sb atoms is preferably 50 ppm, more preferably 70 ppm, and even more preferably 100 ppm. If it is less than the above, the polycondensation reaction may be delayed, resulting in poor productivity. The upper limit is preferably 400 ppm, more preferably 350 ppm, and even more preferably 300 ppm. If the above is exceeded, the amount of foreign matter may increase.

  When polymerizing polyester, an esterification catalyst or a transesterification catalyst may be used separately from the polycondensation catalyst. Examples of the transesterification catalyst include fatty acid salts such as Zn, Cd, Mg, Mn, Co, Ca, and Ba, carbonates, Pb, Zn, Sb, and Ge oxides.

  In particular, when an Sb catalyst is used for polycondensation, it is preferable to use a Ca compound as the transesterification catalyst. By using a Ca compound, thermal degradation during film formation can be reduced. In addition, after the transesterification reaction, the Ca catalyst is deactivated with a phosphorus compound to further generate calcium phosphate particles, which can be used as a lubricant during film formation. The lower limit of the amount of Ca compound added as Ca atoms is preferably 50 ppm, more preferably 70 ppm, and even more preferably 100 ppm. If it is less than the above, the transesterification reaction may be delayed, or the amount of calcium phosphate particles to be deposited later may be reduced, resulting in poor slipping properties during film winding. The upper limit of the Ca content is preferably 400 ppm, more preferably 350 ppm, and even more preferably 300 ppm. When the above is exceeded, not only the effect is saturated but also foreign matter may increase.

  The lower limit of the amount of phosphorus compound added after the transesterification reaction is preferably 100 ppm, more preferably 150 ppm, and even more preferably 200 ppm as a P atom. If the amount is less than the above, the amount of calcium phosphate particles to be precipitated may be reduced and the slipping property during film winding may be inferior. The upper limit of the amount of P is preferably 1000 ppm, more preferably 800 ppm, and still more preferably 700 ppm. If the above is exceeded, the polycondensation reaction may be delayed. As a preferable phosphorus compound, one or more phosphorus compounds selected from phosphoric acid, phosphorous acid, phosphonic acid and lower alkyl esters and phenyl esters of these phosphoric acids can be used. Specifically, phosphoric acid, trimethyl phosphate, triethyl phosphate, triphenyl phosphate, phosphoric acid ester such as acidic phosphoric acid methyl ester, phosphorous acid such as phosphorous acid, trimethyl phosphite, triethyl phosphite Mention may be made of phosphonic acid esters such as esters, methylphosphonic acid, phenylphosphonic acid, benzylphosphonic acid, and methylphosphonic acid methyl ester, phenylphosphonic acid ethyl ester, benzylphosphonic acid phenyl ester.

  Furthermore, it is also preferable to add a lithium compound. By adding a lithium compound, calcium phosphate particles having a size excellent in slipping can be efficiently precipitated, and hydrolysis resistance can be improved. The lower limit of the amount of lithium compound added as lithium atoms is preferably 20 ppm, more preferably 30 ppm, still more preferably 40 ppm, and particularly preferably 50 ppm. The upper limit is preferably 300 ppm, more preferably 250 ppm, and even more preferably 200 ppm. A high effect is achieved by setting it as the said range. Examples of lithium compounds include lithium chloride, lithium hydride, and lithium acetate.

  In particular, by using the above-described Sb / Ca / Li / P-based catalyst and using the DMT method, it is possible to obtain a high effect on hydrolysis resistance and slipperiness as a film.

  As a method for obtaining a low acid value polyester, it is effective to increase the esterification rate of the esterified product and lower the acid value after entering the polycondensation step after the esterification when using the esterification method. It is. As a method for increasing the esterification rate, methods such as adjusting the acid / glycol ratio, adjusting conditions such as the temperature and time of the esterification reaction, and the like can be employed. In the DMT method, it is preferable to reduce the moisture content of the raw material dicarboxylic acid dimethyl ester or glycol by drying or purification.

  In the polycondensation step, acid is generated by oxidation with oxygen or moisture. It is preferable to set the temperature of the polycondensation reaction lower, lower the oxygen concentration of the reaction system, increase the degree of vacuum, increase the stirring efficiency, and the like.

  Furthermore, after pre-crystallization of the polyester obtained by melt polymerization, solid phase polymerization at a temperature lower than the melting point under reduced pressure or under an inert gas flow can increase the molecular weight and reduce the acid value. The solid-state polymerization temperature is preferably 190 to 240 ° C, more preferably 195 to 230 ° C. The solid-state polymerization time is preferably 2 hours or longer, more preferably 3 hours or longer. The longer the time, the higher the molecular weight and the lower the acid value. However, the degree of decrease in the acid value decreases with time. From this aspect, 40 hours or less is preferable. The molecular weight and acid value can be adjusted as appropriate by adjusting the melt polymerization conditions and the solid phase polymerization conditions. Moreover, CT can be reduced by performing solid phase polymerization.

2. Polyester resin composition In the present invention, as described above, a hindered phenol compound is further added to the polyester. In the present invention, a polyester resin composition containing these stabilizers and the like, which maintains a function as a polyester in a state of being compatible with the polyester, or is added with a substance for modifying the polyester is referred to as a polyester resin composition. When adding a hindered phenol compound at the time of superposition | polymerization, it is preferable to add at the time of polycondensation catalyst addition just before polycondensation. Moreover, when adding in the middle of a polycondensation process, it can also add without releasing pressure reduction with a gear pump etc. as a slurry of ethylene glycol.

  Moreover, a hindered phenol compound can also be added at the time of film forming, In this case, adding as a masterbatch is preferable. As the base resin for the masterbatch, it is preferable to use a raw material polyester for the film. The hindered phenol compound concentration in the masterbatch is preferably higher, but practically 1 to 20% by mass is preferable. In addition, since polyester decomposes | disassembles at the time of manufacture of a masterbatch and an acid value increases, it is preferable that raw material polyester is fully dried. The water content is the same as the polyester used in the following film formation. Moreover, it is preferable to knead | mix, degassing using a vented extruder at the time of masterbatch manufacture.

  Furthermore, other stabilizers can be added to the polyester resin composition.

  It is preferable that the polyester resin composition does not substantially contain a compound having a substituent that reacts with these (OH group or COOH group) in addition to the OH group and the COOH group. When a compound having a substituent that reacts with an OH group (hydroxyl group) or COOH group is contained in the polyester, it forms a cross-linked structure with the polyester molecule, causing gelation or increasing the molecular weight of the polyester. Sometimes shearing heat is generated, and the effect of the hindered phenol compound may be reduced.

  Examples of the compound having a substituent that reacts with an OH group (hydroxyl group) and a COOH group include epoxy, carbodiimide, and isocyanate compounds, which are used as end-capping agents and chain extenders. Here, “not substantially contained” means less than 1% by mass in the polyester composition, preferably less than 0.5% by mass, more preferably less than 0.1% by mass, and still more preferably less than 0.01% by mass.

  The polyester resin composition may contain other resins other than polyester such as polyurethane, polyamide, polyimide, and polycarbonate for the purpose of modification, but the polyester in the resin composition is preferably more than 90% by mass. Preferably, it is more than 95% by weight, more preferably more than 98% by weight, particularly preferably more than 99% by weight, most preferably more than 99.5% by weight. Most preferably, it is only polyester.

  The thermal oxidation stability parameter (TOD) of the polyester resin composition constituting the film is preferably 0.25 or less, more preferably 0.2 or less, still more preferably 0.15 or less, particularly preferably. 0.1 or less, and most preferably 0.05 or less. If the above is exceeded, the weather resistance may be lowered. The value of TOD can be adjusted by adding a hindered phenol compound within the above range. The lower limit of TOD is 0 in principle.

3. Film resin composition In addition to the film resin composition constituting the film, UV absorbers, organic and inorganic particles as lubricants, white and black pigments such as titanium oxide, barium sulfate, and carbon black may be added. good.

  In particular, the addition of particles as a film lubricant is a preferred form for catalyst systems that do not produce internal particles. As particles, particles made of organic polymers such as crosslinked polyvinylbenzene, acrylic, crosslinked polystyrene, polyester, polyimide, polyamide, fluororesin, colloidal silica, titanium oxide, aluminum oxide, zirconium oxide, calcium carbonate, carbon black, zeolite, etc. Inorganic particles are exemplified. The average particle size of the particles is preferably 0.05 to 5 μm by the Coulter counter method. Moreover, it is preferable that addition amount is 0.01-2 mass%.

These particles and pigments may be added during the polycondensation step, or may be added as a master batch at the time of film formation. However, when high weather resistance is required, it is preferably added during the polycondensation step.

4, Production of Film The film of the present invention may be any of an unstretched film, a uniaxially stretched film, and a biaxially stretched film, but is particularly a biaxially stretched film from the viewpoint of durability and mechanical strength. Is preferred.

  In the case of an oriented polyester film, a melting step of melting a polyester chip polymerized using the specific catalyst in an extruder, a film forming step of forming an unstretched film by extruding a molten resin from the extruder, It is desirable to produce the film through a stretching process of stretching in at least one direction and a heat setting process of heat-treating the stretched film. Next, the manufacturing method of the oriented polyester film of this invention is demonstrated in detail.

  In the melting step, the raw material is supplied to a melt extruder and heated to a temperature equal to or higher than the polymer melting point to be melted. At this time, in order to suppress an increase in the carboxyl terminal concentration during film production, it is preferable to use a sufficiently dried raw material. The water content of the raw material is preferably 100 ppm or less, more preferably 50 ppm or less, further 30 ppm or less, and particularly preferably 20 ppm or less. As a drying method, a known method such as heating or drying under reduced pressure can be used.

  The maximum temperature of the resin in the extruder is preferably 280 ° C. or higher, preferably 285 ° C. or higher, and more preferably 287 ° C. or higher. By raising the melting temperature, the back pressure at the time of filtration in the extruder is lowered, and good productivity can be achieved. The maximum temperature of the resin in the extruder is preferably 310 ° C. or lower, more preferably 305 ° C. or lower, and particularly preferably 300 ° C. or lower. When the melting temperature is increased, the thermal degradation of the polyester proceeds, the carboxyl terminal concentration of the polyester increases, and the hydrolysis resistance may decrease. Also preferred is a method of extruding while venting using a vented extruder. It is also preferable to design the apparatus so that the time during which the resin is in a molten state (from the extruder to the tip of the die) is as short as possible. The residence time in the molten state is preferably within 30 minutes, more preferably within 20 minutes, and particularly preferably within 15 minutes.

  When the polyester resin composition contains a hindered phenol structure, decomposition due to heat in the extruder can be effectively suppressed, and an increase in acid value can be suppressed. When the hindered phenol is not contained, the increase in the acid value in the extruder depends on the molecular weight of the polyester used, the drying state, and the kneading conditions. For example, in the case of a raw material polyester having an IV of about 0.75 dL / g, sufficient drying is performed. Even if it went, about 6-7 equivalent / ton was increasing, but when it contains a hindered phenol within the scope of the present invention, it is suppressed to about 4 equivalent / ton or less. Although the degree of inhibition looks slight, the hydrolysis of the polyester is catalyzed by the generated acid, and the degradation proceeds exponentially, so the initial acid value can be suppressed to maintain the weather resistance. There is a big effect. Furthermore, not only an increase in acid value but also a decrease in molecular weight (IV decrease) can be suppressed, and a raw material polyester having a lower molecular weight can be used when a film having a target molecular weight is produced. This can lower the resin temperature during film formation and further suppress an increase in acid value due to decomposition. Due to this synergistic effect, a polyester film having excellent weather resistance can be obtained. Such an excellent effect can be obtained even in a range smaller than the amount of hindered phenol that is conventionally used.

  In the film forming step, the melted resin is extruded from a T-die onto a cooling rotating roll and molded into a sheet shape to produce an unstretched film. In this case, for example, by applying the technique described in Japanese Patent Publication No. 6-39521 and Japanese Patent Publication No. 6-45175, high-speed film formation is possible. Moreover, it is good also as a laminated | multilayer film by a co-extrusion method, using a several extruder, assigning various functions to a core layer and a skin layer.

  In the stretching step, the polyester film of the present invention can be obtained by stretching 1.1 to 6 times at least in a uniaxial direction at a temperature not less than the glass transition temperature of the polyester and less than the crystallization temperature using a known method. .

  For example, in the case of producing a biaxially oriented polyester film, a sequential biaxial stretching method in which uniaxial stretching is performed in the longitudinal direction or the transverse direction, and then stretching in the orthogonal direction, and a simultaneous biaxial stretching method in which stretching is performed simultaneously in the longitudinal direction and the transverse direction. Furthermore, a method using a linear motor can be employed as a driving method for simultaneous biaxial stretching.

  Further, after the end of stretching, in order to reduce the thermal shrinkage rate of the film, a heat setting process is performed within 30 seconds, preferably within 10 seconds, at a temperature of (melting point−50 ° C.) to less than the melting point in the heat setting step. It is preferable to perform 5-10% longitudinal relaxation treatment, lateral relaxation treatment, etc.

  When higher thermal dimensional stability is required as a polyester film for solar cells, it is desirable to perform longitudinal relaxation treatment. As a method of the longitudinal relaxation processing, a known method can be used. For example, a method of performing longitudinal relaxation processing by gradually narrowing the clip interval of the tenter (Japanese Patent Publication No. 4-028218), Then, a method of performing a relaxation treatment by inserting a razor at the end and avoiding the influence of the clip (Japanese Patent Publication No. 57-54290) can be used.

  It is preferable that the thickness of the obtained polyester film for solar cells is 10-500 micrometers, More preferably, it is 15-400 micrometers, More preferably, it is 20-300 micrometers. If it is less than 10 μm, there is no waist and it is difficult to handle. On the other hand, if it exceeds 500 μm, the handling property is lowered and the handling becomes difficult.

  Moreover, in order to provide various functions such as adhesiveness, insulation, and scratch resistance, the surface of the polyester film may be coated with a polymer resin by a coating method. Moreover, it is good also as a slippery polyester film by containing inorganic and / or organic particle | grains only in a coating layer. Furthermore, an inorganic vapor deposition layer or an aluminum layer can be provided to provide a water vapor barrier function.

  The polyester film is preferably formed with irregularities on the film surface in order to improve handling properties such as slipping property, running property, wear resistance, and winding property. In order to give unevenness to the film surface, in addition to the method of using the particles described above, a method of embossing with a roll etc. with an unevenness on the surface of the thin film layer, a method of patterning the surface unevenness with a laser beam, etc. Is mentioned.

  Further, a method in which the layered structure is used and the central polyester layer does not contain inert particles and only the surface layer contains particles is also an extremely effective method for reducing haze.

5, Production of void-containing white film It is also preferable to use a white film when high light reflectivity is imparted to the film. In that case, a material containing a large number of fine cavities inside is preferable because it has a high reflectance up to the near infrared region. In that case, the apparent specific gravity is 0.7 or more and 1.3 or less, preferably 0.9 or more and 1.3 or less, more preferably 1.05 or more and 1.2 or less. If it is less than 0.7, the film is not elastic and processing at the time of producing the solar cell module becomes difficult. Even if the film exceeds 1.3, it is within the range of the film of the present invention. However, if the film exceeds 1.3, the film weight is so large that it may become an obstacle when considering the reduction in weight of solar cells. There is.

  The fine cavities can be formed from a thermoplastic resin that is incompatible with the fine particles and / or polyester described below. The term “cavity derived from a thermoplastic resin that is incompatible with fine particles or polyester” means that a void exists around the fine particle or the thermoplastic resin, and is confirmed by, for example, a cross-sectional photograph of the film using an electron microscope. Can do.

  The plastic resin incompatible with polyester is not particularly limited. Specific examples include polystyrene resins, polyolefin resins, polyacrylic resins, polycarbonate resins, polysulfone resins, and cellulose resins. In particular, polyolefin resins such as polystyrene resins, cyclic polyolefin resins, polymethylpentene, and polypropylene are preferably used.

  The mixing amount of these void forming agents, that is, thermoplastic resins incompatible with the polyester, with respect to the polyester composition varies depending on the amount of the intended void, but is in the range of 3 to 20% by mass with respect to the entire film. It is preferably 5 to 18% by mass. And if it is less than 3 mass%, there exists a limit in increasing the production amount of a cavity. On the other hand, if it is 20% by mass or more, the stretchability of the film is remarkably impaired, and the heat resistance, strength, and waist strength are impaired.

  The void-containing white film may have a single layer or a laminated structure composed of two or more layers. The laminated structure includes a skin layer made of a polyester layer containing white fine particles having an average particle diameter of 0.1 to 3 μm, and a core made of a polyester layer containing many cavities derived from a thermoplastic resin incompatible with polyester. Having a layer is also a preferred embodiment of the present invention. Although the manufacturing method is arbitrary and is not particularly limited, for example, it can be manufactured as follows. First, as a method of joining the skin layer to the film surface, after supplying the polyester resin of the skin layer containing fine particles and the polyester resin of the core layer containing an incompatible thermoplastic resin to separate extruders, It is most preferable to employ a coextrusion method in which layers are laminated in a molten state and extruded from the same die.

  Examples of the white fine particles include calcium carbonate, titanium oxide, zinc oxide, lead carbonate, and barium sulfate, and titanium oxide and barium sulfate are particularly preferable. Since the white fine particles are added in an amount of 5 to 20% by mass with respect to the polyester composition, it is preferable to add them as a master batch.

  Each raw material is mixed, put into an extruder, melted, extruded from a T-die, and adhered to a cooling roll to obtain an unstretched sheet. The unstretched sheet is further expanded by stretching between rolls having a speed difference (roll stretching), stretching by gripping and expanding by a clip (tenter stretching), stretching by expanding with air pressure (inflation stretching), and the like. Axial orientation treatment. By performing the orientation treatment, interfacial peeling occurs between the polyester / incompatible thermoplastic resin and between the polyester / fine particles, and many fine cavities appear. Therefore, the conditions for stretching / orienting the unstretched sheet are closely related to the formation of cavities.

  First, the first-stage longitudinal stretching process is the most important process for forming many fine cavities in the film. In the longitudinal stretching, stretching is performed between two or many rolls having different peripheral speeds. As a heating means at this time, a method using a heating roll or a method using a non-contact heating method may be used, or they may be used in combination. Among these, the most preferable stretching method is a method using both roll heating and non-contact heating. In this case, first, the film is preheated to a temperature not higher than 50 ° C. to a glass transition point of polyester using a heating roll, and then heated with an infrared heater.

  Next, the uniaxially stretched film thus obtained is introduced into a tenter and stretched 2.5 to 5 times in the width direction. A preferable stretching temperature at this time is 100 ° C to 200 ° C. The biaxially stretched film thus obtained is subjected to heat treatment as necessary. The heat treatment is preferably performed in a tenter, and is preferably performed in the range of the melting point Tm-50 ° C. to Tm of the polyester.

  Thus, the obtained film has a whiteness of 50 or more, preferably 60 or more, more preferably 70 or more.

  In the case of such a void-containing film or a film containing 5% by mass or more of pigment, it is necessary to increase the kneading conditions or use a large amount of masterbatch, etc., so that the acid value of the polyester of the film is high in weather resistance. However, it may be difficult to achieve the same level as that of a film that is required. In such a case, the acid value of the polyester of the film is preferably less than 25 equivalents / ton, more preferably less than 22 equivalents / ton, even more preferably less than 20 equivalents / ton, and particularly preferably 18 equivalents / ton. Less than tons.

  When a film such as a white film or the like that requires high heat resistance is used as a coextruded laminated film as described above, a layer composed of a polyester composition containing a hindered phenol structure is 50 in thickness relative to the total thickness of the film. % Or more is preferable. Further, it is preferably 65% or more, particularly 70% or more. Most preferably, the entire layer is a layer made of a polyester composition containing a hindered phenol structure. If the layer containing the hindered phenol structure is less than the above, the layer not having the hindered phenol structure deteriorates when elongation is applied, and the layer having the hindered phenol structure is dragged when cracks occur. May break. In addition, a layer having no hindered phenol structure may be finely cracked and whitened to deteriorate the appearance.

  The polyester film of the present invention has high weather resistance and can be used for various applications that require weather resistance, particularly hydrolysis resistance. Specific applications include solar cell front sheet (light-receiving surface) and back sheet (opposite to the light-receiving surface), motor insulation, condenser, etc., especially suitable for solar cell back sheet It is done.

  When used for a back sheet of a solar cell, for example, a back sheet is formed by laminating with a gas barrier layer and a light reflection layer. A laminate adhesive such as urethane can be used for lamination. It is preferable to perform an easy adhesion coating on the surface of the film of the present invention.

  Moreover, aluminum vapor deposition and inorganic oxide vapor deposition can be performed to the polyester film of this invention, and it can also be used as a weather-resistant gas barrier film. Further, when a white or void-containing film is used, it can be used as a weather-resistant light reflective film. In these cases, the number of stacked back sheets can be reduced, and the cost and weight of the solar cell can be reduced.

  Thus, the solar battery backsheet created by laminating the film of the present invention packs an electromotive force cell such as silicon between the transparent surface base material via a filler such as an ethylene vinyl acetate copolymer, It can be set as a solar cell module.

  When the film of the present invention is used for a front sheet of a solar cell, it is also a preferred form to provide an antireflection layer or a hard coat layer.

  Moreover, the polyester film for electrical insulation is a single layer or multilayer laminated film or sheet used for insulation of electronic members. Since the polyester film of the present invention has high durability and heat resistance, it is suitable as a base film for, for example, the interior and exterior of a capacitor, or an electric insulation band for a motor, a flexible printed wiring board, a transformer, a cable, and a generator. is there.

(1) Content of hindered phenol structure in film composition In Examples, the hindered phenol structure was calculated from the amount of hindered phenol added during polymerization or in a master batch.
For example, when Irganox (R) 1330 is added at the start of polycondensation in an amount of 200 ppm based on the resin mass after polymerization, 200 / 775.2 (molecular weight of Irganox (R) 1330) × 3 ((Irganox ( R) Number of hindered phenol structures per molecule of 1330) = 0.77.

(2) Intrinsic viscosity of polyester (IV)
The sample was pulverized and dried, and then dissolved in a 6/4 (weight ratio) mixed solvent of phenol / 1,1,2,2-tetrachloroethane. The solution was centrifuged to remove inorganic particles and unnecessary substances (cavity forming agent in the case of a cavity-containing film), and then measured at a temperature of 30 ° C. using an Ubbelohde viscometer. Moreover, the part other than the polyester was subtracted from the weight of the sample, and the weight of the polyester alone was calculated.

(3) Diethylene glycol content (DEG)
After 0.1 g of polyester was thermally decomposed at 250 ° C. in 2 ml of methanol, it was quantitatively determined by gas chromatography.

(4) Method for measuring acid value Preparation of sample The sample is pulverized and vacuum-dried at 70 ° C. for 24 hours, and then weighed in a range of 0.20 ± 0.0005 g using a balance. The weight at that time is defined as W (g). A sample weighed with 10 ml of benzyl alcohol is added to a test tube, the test tube is immersed in a benzyl alcohol bath heated to 205 ° C., and the sample is dissolved while stirring with a glass rod. Samples with dissolution times of 3 minutes, 5 minutes, and 7 minutes are designated as A, B, and C, respectively. Next, a new test tube is prepared, and only benzyl alcohol is added and processed in the same procedure, and samples when the dissolution time is 3 minutes, 5 minutes, and 7 minutes are designated as a, b, and c, respectively.

B. Titration Titration is performed using a 0.04 mol / l potassium hydroxide solution (ethanol solution) whose factor is known in advance. Phenol red is used as the indicator, and the titration (ml) of the potassium hydroxide solution is determined with the end point being changed from yellowish green to light red. Samples A, B, and C are titrated as XA, XB, and XC (ml). The titration amounts of samples a, b, and c are Xa, Xb, and Xc (ml).

C. Calculation of Acid Value Using the titration amounts XA, XB, and XC for each dissolution time, the titration amount V (ml) at a dissolution time of 0 minutes is determined by the least square method. Similarly, titration volume V0 (ml) is obtained using Xa, Xb, and Xc. Subsequently, the carboxyl terminal concentration was calculated | required according to following Formula.
Acid value (equivalent / ton) = [(V−V0) × 0.04 × NF × 1000] / W
NF: Factor W of 0.04 mol / l potassium hydroxide solution: Sample weight (g) In addition, when things other than polyester, such as a cavity containing film, are included, it is the weight of polyester only.

(5) Cyclic trimer content (hereinafter referred to as “CT content”)
The sample is dissolved in a hexafluoroisopropanol / chloroform mixture, and further diluted with chloroform. Methanol is added to this to precipitate the polymer, followed by filtration. The filtrate was evaporated to dryness, made constant with dimethylformamide, and a cyclic trimer composed of ethylene terephthalate units was quantified by liquid chromatography.

(6) Acetaldehyde content (hereinafter referred to as “AA content”)
Sample / distilled water = 1 g / 2 cc of glass ampoule substituted with nitrogen was sealed and subjected to extraction treatment at 160 ° C for 2 hours. After cooling, acetaldehyde in the extract was measured by high-sensitivity gas chromatography. The concentration was expressed in ppm.
In addition, AA content of each Example and the comparative example film was the range of 15-23 ppm.

(7) Thermal oxidation stability parameter (TOS)
The film ([IV] i) was frozen and ground to a powder of 20 mesh or less. This powder was vacuum-dried at 130 ° C. for 12 hours, and 300 mg of the powder was placed in a glass test tube having an inner diameter of about 8 mm and a length of about 140 mm and vacuum-dried at 70 ° C. for 12 hours. [IV] _f1 was then measured after a drying tube containing silica gel was attached to the top of the test tube and immersed in a 230 ° C. salt bath and heated for 15 minutes under dry air. TOS was determined as follows. However, [IV] _i and [IV] _f1 indicate IV (dL / g) before and after the heating test, respectively. The freeze pulverization was performed using a freezer mill (Specks Corp., Model 6750). After putting about 2 g of a resin chip or film and a dedicated impactor in a dedicated cell, the cell is set in the apparatus, liquid nitrogen is filled into the apparatus and held for about 10 minutes, and then RATE10 (the impactor is about 1 second per second). Crushed for 5 minutes.
TOS = 0.245 {[IV] _f1 ^-1.47- [IV] _i ^-1.47 }

(8) Moisture content of polyester chip Using a moisture content meter (VA-05 type, manufactured by Mitsubishi Kasei Co., Ltd.), heat was applied to chips 1 to 2 g at 230 ° C. for 10 minutes, and moisture contained in the chip. Is evaporated and the moisture content is measured.

(9) Hydrolysis resistance evaluation (breaking elongation retention)
As the hydrolysis resistance evaluation, HAST (Highly Accelerated Temperature and Humidity Stress Test) standardized in JIS-60068-2-66 was performed. The equipment was EHS-221 manufactured by ESPEC CORP. Under the conditions of 105 ° C., 100% RH, and 0.03 MPa.
The film was cut into 70 mm × 190 mm, and the film was placed using a jig. Each film was placed at a distance where it did not touch. The treatment was performed at 105 ° C., 100% RH, 0.03 MPa for 200 hours and 300 hours. The breaking elongation before and after the treatment was measured according to JIS-C-2318-1997 5.3.31 (tensile strength and elongation), and the breaking elongation retention was calculated according to the following formula.
Breaking elongation retention (%) = [(breaking elongation after treatment (MPa)) / (breaking elongation before treatment (MPa))] × 100

(10) Half-life of elongation at break in heat resistance test at 160 ° C. A strip sample having a length of 200 mm and a width of 10 mm was cut out and used in the longitudinal direction. In accordance with the method defined in JISK-7127, the elongation at break was measured at 25 ° C. and 65% RH using a tensile tester. The distance between the initial pull chucks was 100 mm, and the pull speed was 300 m / min. The measurement was performed 20 times by changing the sample, and the average value (X) of the elongation at break was determined. In addition, a strip-shaped sample having a length of 200 mm and a width of 10 mm was put in a gear oven, left in an atmosphere of 160 ° C., then naturally cooled, and this sample was subjected to a tensile test under the same conditions as described above 20 times. The average value (Y) of elongation was determined. From the average values (X) and (Y) of the obtained elongation at break, the elongation retention was determined by the following equation.
Elongation retention (%) = (Y / X) × 100
The heat treatment time until the elongation retention was 50% or less was determined and defined as the half life of elongation at break.

(11) Content of metal element (ppm), Content of phosphorus element (ppm)
After ashing / dissolving the sample, the sample was obtained by high-frequency plasma emission analysis or atomic absorption analysis.

(12) Apparent specific gravity The film is accurately cut into a 10 cm × 10 cm square, and its thickness is measured at 50 points to determine an average thickness t (unit: μm). Next, the mass of the sample is measured to 0.1 mg and is set to w (unit: g). And the apparent specific gravity was calculated by the following formula.
Apparent specific gravity (−) = (w / t) × 10000

(13) Whiteness Whiteness This was carried out using Nippon Denshoku Industries Co., Ltd. Z-1001DP according to JIS-L1015-1981-B method.

(14) Dirt such as die lip and roll The degree of dirt on the periphery of the die lip after film formation, the cooling roll, the transport roll at each position, and the stretching roll was visually observed.
○: Equivalent to hindered phenol-free polyester.
(Triangle | delta): There exists some deposits increase in the lip periphery, and some cloudiness is recognized by a part of roll.
X: There is a possibility that the operability may be lowered, for example, there is an increase in deposits around the lip or cloudiness is observed on the roll.

Reference Examples 1-3
Magnesium acetate tetrahydrate was added to the polyester in an amount of 120 ppm as Mg atoms in a mixture of terephthalic acid and ethylene glycol, and reacted at a temperature of 255 ° C. at normal pressure. Then, an amount of antimony trioxide as 250 ppm in the polyester as Sb atoms and an amount of trimethyl as 150 ppm in the polyester as cobalt acetate tetrahydrate P atoms as an amount of 30 ppm in the polyester as Co atoms. Phosphate was added and further reacted at 260 ° C.

  Subsequently, the reaction product was transferred to the polycondensation reaction layer, and hindered phenol compounds (Irganox 1330) in the amounts shown in the table and silica particles having an average particle diameter of 1.0 μm were added to the polyester so as to be 800 ppm. Thereafter, the reaction system was gradually depressurized while being heated and heated, and polymerization was performed at 290 ° C. under a reduced pressure of 133 Pa (1 mmHg) to obtain a chip of IV 0.60 dL / g. Subsequently, solid polycondensation was performed at 220 ° C. under a reduced pressure of 67 Pa (0.5 mmHg) using a rotary vacuum polymerization apparatus to obtain a resin composition having an intrinsic viscosity of 0.76 dL / g and an acid value of 5 equivalents / ton. . The cyclic trimer (CT) content was 0.29% by mass.

  The obtained polyester resin composition chips are dried to a moisture content of 17 ppm and supplied to an extruder, and the maximum resin temperature up to the melter, kneader, polymer tube, gear pump and filter of the extruder is 290 ° C., and the subsequent polymer The temperature of the tube was 285 ° C., and the sheet was extruded from a die. Each of these polymers was filtered using a stainless steel sintered filter medium (nominal filtration accuracy 20 μm particles 95% cut). Further, the resin temperature of the flat die was set to 285 ° C. The extruded resin was wound around a casting drum having a surface temperature of 30 ° C. and cooled and solidified to produce an unstretched film.

Next, this unstretched film was heated to 100 ° C. with a heated roll group and an infrared heater, and then stretched 3.3 times in the longitudinal direction with a roll group having a peripheral speed difference to obtain a uniaxially oriented PET film. Subsequently, the film was stretched 4.0 times in the width direction at 130 ° C. with a tenter, heat-set at 235 ° C., and further relaxed in the width direction at 200 ° C., and biaxially oriented with a thickness of 50 μm. A PET film was obtained.
The results are shown in Table 1.

Reference Examples 4 to 10, Comparative Examples 1 and 2
A resin composition chip of solid phase polymerized polyester having an IV of 0.76 dL / g and an acid value of 5 equivalents / ton was obtained in the same manner as in Reference Example 1 except that no hindered phenol compound was added. The chips were further dried to a moisture content of 15 ppm and then put into a twin screw extruder together with a hindered phenol compound, and melt kneaded while reducing the pressure with a vent to obtain a master batch containing 50000 ppm of the hindered phenol compound.

  The obtained solid-phase-polymerized polyester chip and hindered phenol compound-containing master batch were dried to a moisture content of 17 ppm, and a film was produced in the same manner as in Reference Example 1. The results are shown in Table 2.

  From the results of Reference Examples 4 to 10 and Comparative Examples 1 and 2, it was found that the increase in the hindered phenol structure suppresses deterioration in the film forming process and improves the weather resistance. Further, in Comparative Example 2, there were some deposits on the die lip part, chill roll and the like.

Comparative Example 3
The polycondensation reaction is carried out without adding a hindered phenol compound during the polycondensation, and the polycondensation reaction is carried out in the same manner as in Reference Examples 1 to 3 except that the solid phase polymerization time is lengthened. I got a chip. Further, a PET film was produced in the same manner as in Reference Example 1, but the temperature was adjusted so that the resin pressure in each part of the film forming process was equivalent to that in Reference Example 3. As a result, the extruder melting part, kneading part, polymer tube The maximum resin temperature up to the gear pump and filter was 300 ° C, and the subsequent polymer tube was 290 ° C.

  The results are shown in Table 2. Although the intrinsic viscosity of the film is the same, it was necessary to increase the intrinsic viscosity of the raw material polyester, so that a high temperature was required in the film-forming process, the thermal decomposition progressed, and the acid value of the film increased, resulting in poor weather resistance. It was.

Reference examples 11 and 12
It carried out similarly to the reference example 1 except having changed the hindered phenol compound to add and the addition amount. The results are shown in Table 3.

Reference Example 13
Polyester having an IV of 0.55 dL / g was produced by melt polymerization, and further solid phase polymerization was performed to obtain a resin composition chip of solid phase polymerized polyester having an IV of 0.68 dL / g and an acid value of 6 equivalents / ton. The others were performed in the same manner as in Reference Example 3.

  Further, a PET film was produced in the same manner as in Reference Example 3, but the temperature was adjusted so that the resin pressure in each part of the film forming process was equivalent to that in Reference Example 3. As a result, the extruder melted part, kneading part, polymer tube The maximum resin temperature up to the gear pump and filter was 288 ° C., and the subsequent polymer tube was 285 ° C. Since the molecular weight was low, the weather resistance was inferior to that of Reference Example 3, but it was at a level with no problem at all. The results are shown in Table 3.

Reference Example 14
A polycondensation reaction was carried out in the same manner as in Reference Example 3 except that the solid phase polymerization time was increased to obtain a resin composition chip of solid phase polymerized polyester. Further, a polyester film was produced in the same manner as in Reference Example 3, but the temperature was adjusted so that the resin pressure in each part of the film forming process was equivalent to that in Reference Example 3. As a result, the extruder melting part, kneading part, polymer tube The maximum resin temperature up to the gear pump and filter was 305 ° C., and the subsequent polymer tube was 290 ° C. Although the acid value was slightly higher, the molecular weight was maintained, so the weather resistance was excellent. The results are shown in Table 3.

Comparative Example 4
Polyester having an IV of 0.68 dL / g was produced by melt polymerization, and further solid phase polymerization was performed to obtain a resin composition chip of solid phase polymerized polyester having an IV of 0.76 dL / g and an acid value of 23 equivalents / ton. The others were performed in the same manner as in Reference Example 3.
The results are shown in Table 3. Although a hindered phenol structure was contained, the acid value was high and the weather resistance was poor.

Comparative Example 5
Polyester having an IV of 0.52 dL / g was produced by melt polymerization, and further solid phase polymerization was performed to obtain a resin composition chip of solid phase polymerized polyester having an IV value of 0.64 dL / g and an acid value of 5 equivalents / ton. The others were performed in the same manner as in Reference Example 3.
The results are shown in Table 3. Although a hindered phenol structure was contained, the intrinsic viscosity was low and the weather resistance was insufficient.

Reference Examples 15-18
A master batch was produced from the hindered phenol compounds shown in Table 4, and the same procedure as in Reference Example 4 was conducted except that the amount of hindered phenol compounds added during film production was changed. The same effect was observed even when the hindered phenol compound was changed.

Reference Example 19 and Comparative Example 6
An ethylene glycol solution of calcium acetate was added to a mixture of dimethyl terephthalate and ethylene glycol so that the residual calcium element was 200 ppm, and an ester exchange reaction was performed according to a conventional method to obtain an oligomer mixture. Trimethyl phosphoric acid was added to the oligomer mixture so that the residual amount of phosphorus element was 350 ppm, and the mixture was stirred at 200 ° C. for 10 minutes in a nitrogen atmosphere at normal pressure. Thereafter, as a polycondensation catalyst, a mixture of ethylene glycol solution of antimony trioxide / ethylene glycol solution of lithium acetate was added so that the residual amount of antimony element was 200 ppm and the residual amount of lithium element was 100 ppm. Next, the mixture was stirred at 250 ° C. for 10 minutes under a nitrogen atmosphere at normal pressure. Thereafter, the temperature of the reaction system is gradually decreased to 280 ° C. over 60 minutes to reduce the pressure of the reaction system to 13.3 Pa (0.1 Torr), and a polycondensation reaction is further performed at 280 ° C. and 13.3 Pa. A polyester chip of .58 dL / g was obtained.

The chip obtained by the above melt polymerization was subjected to solid phase polymerization at 220 ° C. under a reduced pressure of 0.5 mmHg using a rotary vacuum polymerization apparatus, and the intrinsic viscosity (IV) was 0.76 dL / g, and the acid value was 5 A resin composition chip of solid-phase-polymerized polyester at an equivalent weight / ton was obtained.
In Reference Example 19, the hindered phenol compound was added simultaneously with the addition of the polycondensation catalyst. A film was produced in the same manner as in Reference Example 1.

The results are shown in Table 5. It was found that the weather resistance can be further improved by introducing a hindered phenol structure even in the Sb / Ca / P / Li catalyst system by the DMT method, which is superior in weather resistance than Reference Example 19 and Comparative Example 6.

Reference Example 20 and Comparative Example 7
A slurry of high-purity terephthalic acid and ethyl glycol is continuously supplied to the first esterification reactor containing the reactants in advance, and is stirred at about 250 ° C. and 150 kPa (0.5 kg / cm ² G). The reaction was carried out with an average residence time of 3 hours. This reaction product was sent to the second esterification reactor, and the reaction was carried out with stirring at about 260 ° C. and 106 kpa (0.05 kg / cm 2 G) to a predetermined reactivity. Further, crystalline germanium dioxide was dissolved in water by heating, and a catalyst solution in which ethylene glycol was added and heat-treated thereto and an ethylene glycol solution of phosphoric acid were separately and continuously supplied to the second esterification reactor. The esterification reaction product is continuously fed to the first polycondensation reactor, with stirring at about 265 ° C., 3300 Pa (25 torr) for 1 hour, then with the second polycondensation reactor with stirring at about 265 ° C., Polycondensation was carried out at 400 Pa (3 torr) for 1 hour and further at about 275 ° C. and 60 to 100 Pa (0.5 to 0.8 torr) with stirring in the final polycondensation reactor. The melt polycondensation reaction product was chipped. Subsequently, the obtained chip was subjected to solid polycondensation at 220 ° C. under a reduced pressure of 67 Pa (0.5 torr) using a rotary vacuum polymerization apparatus, and a polyester chip having an IV of 0.76 dL / g and an acid value of 5 equivalents / ton. Got.

After drying the obtained chips to a moisture content of 15 ppm, a master batch containing 10000 ppm of silica particles was put into a vented twin screw extruder together with silica particles having an average particle diameter of 1.0 μm, melted and kneaded while degassing. Obtained. The obtained solid phase polymerized polyester chip, silica particle masterbatch, and the hindered phenol compound-containing masterbatch used in Reference Example 17 were dried at a moisture content of 17 ppm, and a film was produced in the same manner as in Reference Example 4.
The results are shown in Table 5. It was recognized that a germanium catalyst had the same effect.

Reference Example 21, Comparative Example 8
<Manufacture of polyester (A)>
Trimellitic acid titanate was added to a mixture of dimethyl terephthalate and ethylene glycol so that the residual amount of titanium element was 15 ppm, and a transesterification reaction was performed according to a conventional method to obtain an oligomer mixture. Then, after adding 800 ppm of silica particles having an average particle size of 1.0 μm, the temperature of the reaction system was gradually decreased to 13.3 Pa (0.1 Torr) while raising the temperature to 280 ° C. over 60 minutes, and further to 280 ° C. The polycondensation reaction was carried out at 13.3 Pa until the intrinsic viscosity (IV) of the polyester was 0.55 dL / g. After releasing the pressure, the resin under slight pressure is discharged into cold water in a strand form and rapidly cooled. After that, the resin is held in cold water for 20 seconds. A chip with IV) of 0.55 dL / g was obtained.
The pellets obtained by the above melt polymerization were subjected to solid phase polymerization at 220 ° C. under a reduced pressure of 0.5 mmHg using a rotary vacuum polymerization apparatus. The intrinsic viscosity (IV) was 0.75 dL / g and the acid value was 6 An equivalent / ton solid-state polymerized polyester chip was obtained.

<Manufacture of polyester (B)>
Using dimethyl terephthalate and ethylene glycol as starting materials and germanium dioxide as a catalyst, a polyester having an IV of 0.75 dL / g and an acid value of 6 equivalents / ton containing 1000 ppm of normal phosphoric acid was obtained.

In Reference Example 21, the hindered phenol-containing masterbatch used in Polyester (A), Polyester (B), and Reference Example 17 was dried to a moisture content of 17 ppm, and a film was produced in the same manner as in Reference Example 4.
In Comparative Example 8, a film was produced in the same manner as in Reference Example 21 except that the hindered phenol-containing masterbatch was not used.
The results are shown in Table 5. From Reference Example 21 and Comparative Example 8, it was confirmed that there was an effect even when titanium was used as the catalyst.

Example 22
(Preparation of fine particle-containing masterbatch)
50% by mass of rutile titanium dioxide having an average particle size of 0.3 μm (electron microscopic method) was mixed with 50% by mass of the resin composition chip of the solid phase polyester used in Reference Example 2 dried to a moisture content of 17 ppm. The product was supplied to a vent type twin screw extruder, kneaded and extruded at 275 ° C. while degassing to prepare a master batch (MB-I) containing rutile type titanium dioxide fine particles.

(Preparation of cavity forming agent)
As raw materials, 20% by mass of polystyrene with a melt flow rate of 1.5 (manufactured by Nippon Polystyrene Co., Ltd., G797N), 20% by mass of vapor phase polymerization polypropylene with a melt flow rate of 3.0 (F300SP, manufactured by Idemitsu Petrochemical), and melt flow Rate 180 polymethylpentene (manufactured by Mitsui Chemicals: TPX DX-820) 60% by mass pellets were mixed, supplied to a twin screw extruder and kneaded sufficiently to prepare a cavity forming agent (MB-II).

  Resin composition chip of solid phase polyester used in Reference Example 2 Chip: MB-I: MB-II was mixed to 80: 12: 8 (mass%) and dried to a moisture content of 18 ppm in an extruder. The unstretched sheet | seat was injected | thrown-in, mixed and melted at 280 degreeC, and it extruded on the cooling drum adjusted to 30 degreeC using the T-die. The obtained unstretched sheet was uniformly heated to 70 ° C. using a heating roll, and 3.3-fold roll stretching was performed at 90 ° C. The obtained uniaxially stretched film was led to a tenter, heated to 140 ° C. and transversely stretched 3.7 times, fixed in width and subjected to heat treatment at 220 ° C. for 5 seconds, and further at 220 ° C. in the width direction of 4%. By relaxing, a white film with a thickness of 188 μm was obtained.

Example 23
A master batch containing fine particles was produced from the solid phase polymerized polyester resin composition obtained in Reference Example 3 (MB-III), and the resin composition chip of the solid phase polymerized polyester was changed to the one obtained in Reference Example 3. Except that, it carried out similarly to Example 22, and obtained the cavity containing white film.

Comparative Example 9
A fine particle-containing master batch was produced from a solid-state polymerized polyester resin composition chip (containing no hindered phenol compound) produced for Reference Examples 4 to 10 (MB-IV), and used as a polyester resin composition Reference Example 4 10 was carried out in the same manner as in Example 22 except that it was changed to a resin composition chip of solid-phase polymerization polyester produced for 10 to 10 (no hindered phenol compound), to obtain a void-containing white film.

Example 24
A white film was obtained in the same manner as in Example 22 except that 70% by mass of the resin composition chip of solid-phase polymerized polyester obtained in Reference Example 3 and 30% by mass of MB-III were used.

Example 25
The raw material composition of the layer (A) in which 50% by mass of the polyester resin composition chip obtained in Reference Example 3 and 50% by mass of MB-III were mixed, and the raw material composition of the film of Example 23 in the layer (B) The raw materials were put into separate extruders, mixed and melted at 280 ° C., and then the B layer was joined to one side of the A layer in a molten state using a feed block. At this time, the discharge rate ratio of the A layer and the B layer was controlled using a gear pump. Subsequently, it was extruded onto a cooling drum adjusted to 30 ° C. using a T-die, and an unstretched sheet was prepared so as to be an A / B / A layer.

(Preparation of a biaxially stretched film) The obtained unstretched sheet was uniformly heated to 70 ° C using a heating roll, and 3.3-fold roll stretching was performed at 90 ° C. The obtained uniaxially stretched film was led to a tenter, heated to 140 ° C. and transversely stretched 3.7 times, fixed in width and subjected to heat treatment at 220 ° C. for 5 seconds, and further at 220 ° C. in the width direction of 4%. By relaxing, a void-containing white film having a thickness of 188 μm (19/150/19) was obtained.
The results of Examples 22 to 25 are shown in Table 6.

Reference Example 22
The solid phase polymerized polyester resin composition chip produced for Reference Examples 4 to 10 (without hindered phenol compound) was used as the material for the A layer, and the film raw material composition used in Reference Example 7 was used as the material for the B layer. It put into a separate extruder, mixed and melted at 280 ° C., and subsequently, using a feed block, the B layer was joined in a molten state to one side of the A layer. At this time, the discharge rate ratio of the A layer and the B layer was controlled using a gear pump. Subsequently, it was extruded onto a cooling drum adjusted to 30 ° C. using a T-die, and an unstretched sheet was prepared so as to be an A / B / A layer.

(Production of biaxially stretched film)
The obtained unstretched sheet was uniformly heated to 70 ° C. using a heating roll, and 3.3-fold roll stretching was performed at 90 ° C. The obtained uniaxially stretched film was led to a tenter, heated to 140 ° C. and transversely stretched 3.7 times, fixed in width and subjected to heat treatment at 220 ° C. for 5 seconds, and further at 220 ° C. in the width direction of 4%. By relaxing, a film having a thickness of 50 μm (5/40/5) was obtained.
The result of the weather resistance test (105 ° C., 300 hours) was 85%, which was not a problem, but was whitened because the surface was cracked from the beginning of elongation, and the appearance was not excellent.

Reference Example 23
In Reference Example 22, the raw materials of layer A and layer B were exchanged, and a film was obtained in the same manner as in Reference Example 1.
The result of the weather resistance test (105 ° C., 300 hours) was 55%, which was inferior in weather resistance. This is presumably because the core layer, which is the main part of the film, is inferior in weather resistance, so that elongation cannot be achieved with only a thin surface layer.

  From the above results, the polyester films of the examples exhibit much higher hydrolysis resistance than conventionally known low AV and high IV hydrolysis resistant polyester films (for example, Comparative Example 3 and Comparative Example 6).

  In the case of a solar cell backsheet, it is prepared by combining and laminating the film of the example and, if necessary, a barrier film, an electrical insulating film, a light reflective film, and the like. Solar cell cells such as crystalline silicon and amorphous silicon are sealed between the obtained back sheet and a surface member such as glass using a filler such as EVA to obtain a solar cell module. The obtained solar cell can achieve very high durability.

  The polyester film of the present invention has high weather resistance, and is useful for various applications that require weather resistance, particularly hydrolysis resistance. Specific applications include solar cell front sheet (light-receiving surface) and back sheet (opposite to the light-receiving surface), motor insulation, condenser, etc., especially suitable for solar cell back sheet It is done.

Claims (9)

The polyester resin composition constituting the film contains 0.03 to 6.7 equivalents / ton of hindered phenol structural units, the acid value of the polyester constituting the film is less than 25 equivalents / ton, and the intrinsic viscosity is 0.64 dL / g. Exceeding 0.90 dL / g, the apparent specific gravity of the film is 0.7 to 1.3,
The polyester is polymerized using a catalyst of an antimony compound of 70 ppm to 400 ppm as Sb atoms and / or a germanium compound of 30 ppm to 200 ppm as Ge atoms,
Hydrolysis resistant polyester film.   The hydrolysis-resistant polyester film according to claim 1, wherein the film contains 5 to 20% by mass of white fine particles.   The film has a three-layer structure of a skin layer composed of a polyester layer containing white fine particles and a core layer composed of a polyester layer containing many cavities derived from a thermoplastic resin incompatible with polyester. The hydrolysis-resistant polyester film according to claim 1 or 2.   The polyester contains at least one of terephthalic acid and naphthalenedicarboxylic acid as an acid component, and the total amount of terephthalic acid or naphthalenedicarboxylic acid is 90 mol% or more based on the total acid components, and ethylene glycol and diethylene glycol as glycol components 4. The hydrolysis-resistant polyester film according to claim 1, wherein the total amount of ethylene glycol and diethylene glycol is 90 mol% or more based on the total glycol component.   The polyester resin composition does not substantially contain a compound having a substituent that reacts with these (OH group or carboxyl group) in addition to the OH group and carboxyl group. Hydrolysis resistant polyester film.   6. The hydrolysis-resistant polyester film according to claim 1, wherein the polyester resin composition contains 90% by mass of polyester. The hydrolysis-resistant polyester according to any one of claims 1 to 6, wherein the polyester is polymerized using a calcium compound, a lithium compound, and a phosphorus compound as a catalyst in addition to an antimony compound. the film.   The hydrolysis-resistant polyester film according to any one of claims 1 to 7, wherein the hydrolysis-resistant polyester film is any one of a solar cell back sheet, a solar cell front sheet, and an electrical insulator.   A solar cell, wherein the polyester film according to claim 1 is laminated on at least one of a light receiving surface or a side opposite to the light receiving surface.