JP5423106B2 - Biaxially oriented polyester film - Google Patents

Description

  The present invention relates to a biaxially oriented polyester film excellent in hydrolysis resistance, a solar cell backsheet using the same, and an electrical insulating film.

  Polyester film is used for magnetic recording media, for electrical insulation, for solar cells, for capacitors, for packaging, and for various industrial applications, utilizing its excellent properties such as mechanical properties, thermal properties, electrical properties, surface properties and heat resistance. It is used for various applications such as materials. In these high quality applications, for example, in recent years, the demand for solar cells that are clean energy as a next-generation energy source that is semi-permanent and non-polluting has been increasing. There is an increasing demand for improving the durability (hydrolysis resistance) of backsheets. In addition, electrical insulation films for electric car air conditioners that use next-generation refrigerants are also required to have improved hydrolysis resistance.

  Various studies have been conducted on improving hydrolysis resistance. Specifically, a technique for adding a carbodiimide compound to improve the hydrolysis resistance of a polyester resin has been proposed (see Patent Document 1 and Patent Document 2). However, in these proposals, there is no detailed description about the film, and the improvement of the hydrolysis resistance of the resin does not become the hydrolysis resistance of the film as it is. Therefore, even if the resin composition of Patent Documents 1 and 2 is made into a film, It is difficult to achieve the required characteristics.

  Moreover, the technique which controls the intrinsic viscosity (IV) of a film and a plane orientation coefficient (fn) is proposed (refer patent document 3). However, the demand for the next generation is further increasing, and it is difficult to achieve the required characteristics with this proposal.

  Moreover, the technique which adds a carbodiimide compound and improves the hydrolysis resistance of a polyester film is proposed (refer patent document 4 and patent document 5). However, in these proposals, it is difficult to form a stable film because it is a film with high intrinsic viscosity or contains polyimide. Furthermore, the carbodiimide compound causes thermal decomposition under the extrusion conditions of polyester and generates decomposition gas. Therefore, there is a problem in productivity. In addition, due to the recent increase in required characteristics, further improvement in hydrolysis resistance is required, making it difficult to achieve the required characteristics.

  Therefore, as a result of intensive studies, the present inventors have found that in order to improve the hydrolysis resistance of the polyester film, it is important that the intrinsic viscosity and the carboxyl terminal amount are difficult to crystallize (the crystallization parameter ΔTcg is large). I found out. Polyester is reduced in elongation by wet heat treatment. It was found that embrittlement was promoted because crystallization occurred not only at the molecular chain breakage due to moisture but also at the same time. Thus, it has been found that the hydrolysis resistance is drastically improved by setting the crystallization parameter within a certain range.

JP 11-34048 A Japanese National Patent Publication No. 11-506487 JP 2007-70430 A Japanese Patent Laid-Open No. 9-7423 JP 2003-160718 A

  An object of the present invention is to solve the above problems and provide a biaxially oriented polyester film having excellent hydrolysis resistance. Specifically, the object of the present invention is to provide a solar cell backsheet that is less deteriorated due to environmental changes when used as a solar cell backsheet and has excellent durability, and is used under severe conditions when used as an electrical insulation film. However, it is to provide a film for electrical insulation that does not deteriorate and has excellent durability.

The present invention for solving the above-described problems is characterized by the following (1) to (8).
(1) The crystallization parameter ΔTcg by differential scanning calorimetry (DSC) is 70 to 110 ° C., the carboxyl end amount is 0.1 to 10 equivalent / ton, and the intrinsic viscosity is 0.50 to 0.90 dl / g. Biaxially oriented polyester film (2) characterized in that the retention of the elongation at break in at least one direction after 72 hours at a temperature of 125 ° C. and a humidity of 100% RH is 10 to 100% The biaxially oriented polyester film according to (1) above.
(3) The biaxially oriented polyester film as described in (1) or (2) above, wherein the amount of thermal decomposition weight loss for 30 minutes at a temperature of 300 ° C. is 0 to 0.2% by weight.
(4) The biaxially oriented polyester according to any one of (1) to (3) above, wherein the amount of isocyanate-based gas generated at 300 ° C. for 30 minutes is 0 to 0.05% by weight. the film.
(5) The biaxially oriented polyester film as described in any one of (1) to (4) above, containing 0.1 to 5% by weight of a terminal blocking agent.
(6) The biaxially oriented polyester film as described in (5) above, wherein the terminal blocking agent is a carbodiimide compound.
(7) The biaxially oriented polyester film according to any one of (1) to (6) above, wherein the plane orientation coefficient fn is 0.155 to 0.180.
(8) A solar cell backsheet using the biaxially oriented polyester film according to any one of (1) to (7).
(9) An electrically insulating film using the biaxially oriented polyester film according to any one of (1) to (7).

  According to the present invention, a biaxially oriented polyester film having excellent hydrolysis resistance, and more specifically, a solar cell back that is less deteriorated due to environmental changes and has excellent durability when used as a solar cell backsheet. When a sheet is provided and used as an electrical insulation film, an electrical insulation film excellent in durability can be obtained without being deteriorated even in a severe environment.

  In the present invention, the biaxially oriented polyester film is, for example, a polymer (polyester) having an acid component such as aromatic dicarboxylic acid, alicyclic dicarboxylic acid or aliphatic dicarboxylic acid or a diol component as a structural unit (polymerization unit). It is configured.

  Examples of the aromatic dicarboxylic acid component include terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 6,6 ′-(alkyl). Rangeoxy) di-2-naphthoic acid, 4,4′-diphenyldicarboxylic acid, 4,4′-diphenyletherdicarboxylic acid, 4,4′-diphenylsulfonedicarboxylic acid, and the like. Acid, phthalic acid and 2,6-naphthalenedicarboxylic acid can be used.

  The 6,6 ′-(alkylenedioxy) di-2-naphthoic acid component is preferably an alkylene having 2 to 10 carbon atoms, and more specifically 6,6 ′-(ethylenedioxy) di-2- Examples thereof include naphthoic acid, 6,6 ′-(trimethylenedioxy) di-2-naphthoic acid, and 6,6 ′-(butyleneoxy) di-2-naphthoic acid.

  As the alicyclic dicarboxylic acid component, for example, cyclohexane dicarboxylic acid or the like can be used. As the aliphatic dicarboxylic acid component, for example, adipic acid, suberic acid, sebacic acid, dodecanedioic acid and the like can be used. These acid components may be used alone or in combination of two or more.

  The 6,6 '-(alkylenedioxy) di-2-naphthoic acid component can be used as a main component, but is preferably copolymerized with other aromatic polyester components. The preferable copolymerization amount of the 6,6 ′-(alkylenedioxy) di-2-naphthoic acid component is 5 to 50 mol%, more preferably 10 to 40 mol%, still more preferably 15 to 30 mol%. is there.

  Examples of the diol component include ethylene glycol, 1,2-propanediol, 1,3-propanediol, neopentyl glycol, 1,3-butanediol, 1,4-butanediol, and 1,5-pentanediol. 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, diethylene glycol, triethylene glycol, polyalkylene glycol and 2,2′-bis (4 '-Β-hydroxyethoxyphenyl) propane and the like can be used, and among them, ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, diethylene glycol and the like can be preferably used, and particularly preferably Echile It can be used glycol. These diol components may be used alone or in combination of two or more.

  The polyester may be copolymerized with a monofunctional compound such as lauryl alcohol or phenyl isocyanate, or a trifunctional compound such as trimellitic acid, pyromellitic acid, glycerol, pentaerythritol and 2,4-dioxybenzoic acid. May be copolymerized within a range in which the polymer is substantially linear without excessive branching or crosslinking. Furthermore, in addition to the acid component and the diol component, aromatic hydroxycarboxylic acids such as p-hydroxybenzoic acid, m-hydroxybenzoic acid and 2,6-hydroxynaphthoic acid, and p-aminophenol and p-aminobenzoic acid, The copolymer can be further copolymerized as long as the effect of the present invention is not impaired. The copolymerization ratio of the polymer can be examined by using an NMR method (nuclear magnetic resonance method) or a microscopic FT-IR method (Fourier transform microinfrared spectroscopy).

  As the polyester, polyethylene terephthalate and polyethylene naphthalate are preferably used. Further, the polyester may be a polymer alloy with these copolymers, modified products and other thermoplastic resins. The polymer alloy here refers to a polymer multi-component compound, which may be a block copolymer by copolymerization or a polymer blend by mixing. From the viewpoint of crystallinity, polyethylene terephthalate and polyethylene naphthalate are preferably the main components, and particularly preferably 90% or more is polyethylene terephthalate and polyethylene naphthalate.

  The biaxially oriented polyester film of the present invention needs to have a crystallization parameter ΔTcg of 70 to 110 ° C. by differential scanning calorimetry (DSC). If the crystallization parameter ΔTcg is less than 70 ° C., the crystallization rate of the polyester is too high, crystallization by wet heat treatment is promoted, and hydrolysis resistance deteriorates. In addition, when the crystallization parameter ΔTcg exceeds 110 ° C. or more, the crystallization rate is too slow, so the crystallization degree of the polyester film tends to be low, mechanical properties and heat resistance are low, and oriented crystallization occurs in the stretching process. Difficult to hydrolyze. A preferred lower limit of the crystallization parameter ΔTcg is 75 ° C., and a more preferred lower limit is 80 ° C. Further, a preferable upper limit value of the crystallization parameter ΔTcg is 105 ° C., and a more preferable upper limit value is 100 ° C. A preferable range of the crystallization parameter ΔTcg is 75 to 105 ° C, and a more preferable range is 80 to 100 ° C.

  The crystallization parameter is an index representing the crystallization speed of polyester, and becomes larger if the molecular structure is difficult to crystallize, and becomes smaller if the molecular structure is easy to crystallize. Furthermore, the intrinsic viscosity of the film also affects, and the higher the intrinsic viscosity of the film, the larger the crystallization parameter, and the lower the intrinsic viscosity of the film, the smaller. In addition, when an end-capping agent is added, the end-capping agent is bonded to the end of the molecular chain, so that crystallization is difficult and crystallization parameters are increased.

  The biaxially oriented polyester film of the present invention is required to have a carboxyl end amount of 0.1 to 10 equivalent / t. Since the carboxyl terminal dissociates protons and acts as a catalyst for hydrolysis, hydrolysis resistance deteriorates when the carboxyl terminal amount is larger than 10 equivalents. On the other hand, it is difficult to obtain a polyester having a carboxyl end amount of less than 0.1 equivalent / t. In order to improve the hydrolysis resistance, the carboxyl end amount is preferably as small as possible. A preferable upper limit of the carboxyl end amount is 7 equivalent / t, and a more preferable upper limit is 5 equivalent / t. A preferable range of the carboxyl end amount is 0.1 to 7 equivalent / t, and a more preferable range is 0.1 to 5 equivalent / t.

  As for the carboxyl end amount, when an end-capping agent is added to the polyester, the carboxyl end of the polyester and the end-capping agent are bonded, and the carboxyl end amount decreases. The amount of carboxyl terminal can be controlled by the amount of terminal blocking agent added. Moreover, since the reactivity with a carboxyl terminal changes with kinds of terminal blocker, the amount of carboxyl terminals changes. Moreover, although the amount of carboxyl ends varies depending on many factors, the intrinsic viscosity of the master chip has a great influence. The higher the intrinsic viscosity of the master chip, the smaller the carboxyl end amount.

  The biaxially oriented polyester film of the present invention needs to have an intrinsic viscosity of 0.50 to 0.90 dl / g. When the intrinsic viscosity is less than 0.50 dl / g, the hydrolysis resistance is deteriorated because the molecular chain is short and once hydrolysis occurs, the hydrolysis is accelerated. On the other hand, if the intrinsic viscosity is greater than 0.90 dl / g, the viscosity is high in the molten state, and a load is applied to the extruder during film formation, making it difficult to stably discharge. In addition, since it is difficult to achieve orientation due to stretching, it is necessary to increase the stretching ratio.

  A preferable lower limit of the intrinsic viscosity is 0.60 dl / g, and a more preferable lower limit is 0.70 dl / g. Moreover, the upper limit of a preferable intrinsic viscosity is 0.85 dl / g, and a more preferable upper limit is 0.80 dl / g. A preferable range of the intrinsic viscosity is 0.60 to 0.85 dl / g, and a more preferable range is 0.70 to 0.80 dl / g.

  The intrinsic viscosity of the film is particularly affected by the intrinsic viscosity of the raw material. The intrinsic viscosity of the film becomes higher as the intrinsic viscosity of the raw material and the intrinsic viscosity of the master pellet are higher. Moreover, since intrinsic viscosity may fall by thermal decomposition etc. when the temperature of an extruder is high, the fall of intrinsic viscosity can be prevented by extruding as low temperature as possible.

  The biaxially oriented polyester film of the present invention preferably has a retention rate of elongation at break in at least one direction after 72 hours at a temperature of 125 ° C. and a humidity of 100% RH of 10 to 100%. When the retention of the breaking elongation is less than 10%, the durability tends to deteriorate when the back sheet for solar cells or the film for electrical insulation is used. Moreover, the retention rate of breaking elongation being 100% represents the fact that it does not change in a treatment for 72 hours at a temperature of 125 ° C. and a humidity of 100% RH, and is the most preferred embodiment. If the retention of breaking elongation is greater than 100%, the polyester film is likely to be relaxed in orientation, so that the mechanical properties are low and handling is difficult. A more preferable lower limit of the retention of elongation at break is 20%, and a more preferable lower limit is 30%. A more preferable range of the retention of breaking elongation is 20 to 100%, and a more preferable range is 30 to 100%.

  Under an environment of a temperature of 125 ° C. and a humidity of 100% RH, the polyester film undergoes hydrolysis and thermal crystallization, and the elongation at break decreases. In order to increase the retention rate of breaking elongation, it is necessary to suppress hydrolysis and thermal crystallization. To suppress hydrolysis, the amount of carboxyl ends is reduced, and to suppress thermal crystallization, the crystallization parameter is increased. It is preferable.

  The biaxially oriented polyester film of the present invention preferably has a thermal decomposition weight loss of 0 to 0.2% by weight for 30 minutes at a temperature of 300 ° C. If the amount of weight loss by thermal decomposition is more than 0.2% by weight, it means that thermal decomposition is likely to occur, and thermal decomposition occurs during film formation, which tends to cause defects or to tear the film. Moreover, that the thermal decomposition weight loss amount is smaller than 0% by weight means that the reaction is performed at a temperature of 300 ° C. for 30 minutes. A more preferred upper limit is 0.15% by weight, and a still more preferred upper limit is 0.1% by weight. A more preferable range of weight loss by thermal decomposition is 0 to 0.15% by weight, and a further preferable range is 0 to 0.1% by weight.

  The amount of decrease in pyrolysis weight varies depending on the generation of gas as the added end-capping agent is decomposed. In particular, polycarbodiimide, which has different heat resistance depending on the type of end-capping agent and changes the amount of pyrolysis weight loss, has high heat resistance and a small amount of pyrolysis weight reduction. Among polymers and monomers, the polymer has a smaller amount of weight loss due to pyrolysis. In the case of the same type of additive, the smaller the amount added, the smaller the pyrolysis weight loss.

  In the biaxially oriented polyester film of the present invention, the amount of isocyanate-based gas generated at a temperature of 300 ° C. for 30 minutes is preferably 0 to 0.02% by weight. Isocyanate-based gas is a gas having an isocyanate group, for example, diisopropylphenyl isocyanate, 1,3,5-triisopropylphenyl diisocyanate, 2-amino-1,3,5-triisopropylphenyl-6-isocyanate, 4, Examples thereof include 4′-dicyclohexylmethane diisocyanate, isophorone diisocyanate, and cyclohexyl isocyanate.

  If the amount of isocyanate-based gas generated is greater than 0.02% by weight, problems such as deterioration of the operator's physical condition may occur due to the generation of isocyanate-based gas during film formation. The amount of isocyanate gas generated is most preferably 0% by weight. A more preferred upper limit is 0.015% by weight, and a still more preferred upper limit is 0.01% by weight. A more preferable range of the amount of the isocyanate-based gas generated is 0 to 0.015% by weight, and a further preferable range is 0 to 0.1% by weight.

  The amount of isocyanate-based gas generated varies depending on the generation of gas as the added end-capping agent is decomposed. In particular, the heat resistance varies depending on the type of end-capping agent, and the amount of isocyanate-based gas generated changes. In the case of the same type of additive, the smaller the amount added, the smaller the amount of isocyanate-based gas generated.

  The biaxially oriented polyester film of the present invention preferably contains 0.1 to 5% by weight of an end-capping agent. When the end-capping agent is less than 0.1% by weight, the effect of sealing the carboxyl group is small and the hydrolysis resistance is deteriorated. On the other hand, when the end-capping agent is larger than 5% by weight, a large amount of foreign matter is generated during film formation or decomposition gas is generated, which affects productivity. A more preferable upper limit of the content of the end-capping agent is 4% by weight, and a more preferable upper limit is 2% by weight. A more preferable lower limit of the content of the end-capping agent is 0.3% by weight, and a more preferable lower limit is 0.5% by weight. A more preferable range of the content of the terminal blocking agent is 0.3 to 4% by weight, and a further preferable range is 0.5 to 2% by weight.

  The end-capping agent is an additive that reacts with the carboxyl group at the end of the polyester to reduce the amount of carboxyl end of the polyester, and is preferably a compound having a carbodiimide group, an epoxy group, and an oxazoline group.

  The carbodiimide compound having a carbodiimide group includes a monofunctional carbodiimide and a polyfunctional carbodiimide. Examples of the monofunctional carbodiimide include dicyclohexylcarbodiimide, diisopropylcarbodiimide, dimethylcarbodiimide, diisobutylcarbodiimide, dioctylcarbodiimide, t-butylisopropylcarbodiimide, and diphenylcarbodiimide. , Di-t-butylcarbodiimide, di-β-naphthylcarbodiimide, and the like. Particularly preferred are dicyclohexylcarbodiimide and diisopropylcarbodiimide.

  As the polyfunctional carbodiimide, carbodiimide having a polymerization degree of 3 to 15 is preferably used. Specifically, 1,5-naphthalene carbodiimide, 4,4′-diphenylmethane carbodiimide, 4,4′-diphenyldimethylmethane carbodiimide, 1,3-phenylene carbodiimide, 1,4-phenylene diisocyanate, 2,4-tolylene Carbodiimide, 2,6-tolylene carbodiimide, mixture of 2,4-tolylene carbodiimide and 2,6-tolylene carbodiimide, hexamethylene carbodiimide, cyclohexane-1,4-carbodiimide, xylylene carbodiimide, isophorone carbodiimide, isophorone carbodiimide, Dicyclohexylmethane-4,4′-carbodiimide, methylcyclohexanecarbodiimide, tetramethylxylylene carbodiimide, 2,6-diisopropylphenylcarbodiimide and , And the like can be exemplified 3,5-triisopropyl-2,4-carbodiimide.

  The carbodiimide compound is preferably a carbodiimide compound having high heat resistance because an isocyanate gas is generated by thermal decomposition. In order to improve heat resistance, it is preferable that the molecular weight (degree of polymerization) is high, and it is more preferable that the terminal of the carbodiimide compound has a structure with high heat resistance. Further, once thermal decomposition occurs, further thermal decomposition is likely to occur. Therefore, it is necessary to devise measures such as setting the extrusion temperature of the polyester as low as possible.

  Preferred examples of the epoxy compound include glycidyl ester compounds and glycidyl ether compounds.

  Specific examples of the glycidyl ester compound include benzoic acid glycidyl ester, t-Bu-benzoic acid glycidyl ester, P-toluic acid glycidyl ester, cyclohexanecarboxylic acid glycidyl ester, pelargonic acid glycidyl ester, stearic acid glycidyl ester, and lauric acid glycidyl ester. , Glycidyl palmitate, glycidyl behenate, glycidyl versatate, glycidyl oleate, glycidyl linoleate, glycidyl linolein, glycidyl behenol, glycidyl stearol, diglycidyl terephthalate, isophthalic acid Diglycidyl ester, phthalic acid diglycidyl ester, naphthalenedicarboxylic acid diglycidyl ester Ter, methylterephthalic acid diglycidyl ester, hexahydrophthalic acid diglycidyl ester, tetrahydrophthalic acid diglycidyl ester, cyclohexanedicarboxylic acid diglycidyl ester, adipic acid diglycidyl ester, succinic acid diglycidyl ester, sebacic acid diglycidyl ester, dodecane Examples thereof include diglycidyl diacid, octadecanedicarboxylic acid diglycidyl ester, trimellitic acid triglycidyl ester, and pyromellitic acid tetraglycidyl ester. These may be used alone or in combination of two or more.

  Specific examples of the glycidyl ether compound include phenyl glycidyl ether, O-phenyl glycidyl ether, 1,4-bis (β, γ-epoxypropoxy) butane, 1,6-bis (β, γ- Epoxypropoxy) hexane, 1,4-bis (β, γ-epoxypropoxy) benzene, 1- (β, γ-epoxypropoxy) -2-ethoxyethane, 1- (β, γ-epoxypropoxy) -2-benzyl Oxyethane, 2,2-bis- [р- (β, γ-epoxypropoxy) phenyl] propane and 2,2-bis- (4-hydroxyphenyl) propane and 2,2-bis- (4-hydroxyphenyl) Examples thereof include bisglycidyl polyether obtained by reaction of bisphenol such as methane and epichlorohydrin, and these use one kind or two or more kinds. Door can be.

  The oxazoline compound is preferably a bisoxazoline compound, specifically 2,2,2′-bis (2-oxazoline), 2,2′-bis (4-methyl-2-oxazoline), 2,2 ′. -Bis (4,4-dimethyl-2-oxazoline), 2,2'-bis (4-ethyl-2-oxazoline), 2,2'-bis (4,4'-diethyl-2-oxazoline), 2 , 2′-bis (4-propyl-2-oxazoline), 2,2′-bis (4-butyl-2-oxazoline), 2,2′-bis (4-hexyl-2-oxazoline), 2,2 '-Bis (4-phenyl-2-oxazoline), 2,2'-bis (4-cyclohexyl-2-oxazoline), 2,2'-bis (4-benzyl-2-oxazoline), 2,2'- p-Phenylenebis (2-oxa Phosphorus), 2,2'-m-phenylenebis (2-oxazoline), 2,2'-o-phenylenebis (2-oxazoline), 2,2'-p-phenylenebis (4-methyl-2-oxazoline) ), 2,2′-p-phenylenebis (4,4-dimethyl-2-oxazoline), 2,2′-m-phenylenebis (4-methyl-2-oxazoline), 2,2′-m-phenylene Bis (4,4-dimethyl-2-oxazoline), 2,2′-ethylenebis (2-oxazoline), 2,2′-tetramethylenebis (2-oxazoline), 2,2′-hexamethylenebis (2 -Oxazoline), 2,2'-octamethylenebis (2-oxazoline), 2,2'-decamethylenebis (2-oxazoline), 2,2'-ethylenebis (4-methyl-2-oxazoline) 2,2′-tetramethylenebis (4,4-dimethyl-2-oxazoline), 2,2′-9,9′-diphenoxyethanebis (2-oxazoline), 2,2′-cyclohexylenebis (2 -Oxazoline) and 2,2'-diphenylenebis (2-oxazoline) and the like. Among these, 2,2'-bis (2-oxazoline) is most preferably used from the viewpoint of reactivity with polyester. Furthermore, as long as the objective of this invention is achieved, the bisoxazoline compound mentioned above may be used individually by 1 type, or may use 2 or more types together.

  The biaxially oriented polyester film of the present invention preferably has a plane orientation coefficient of 0.155 to 0.300. The plane orientation coefficient is more preferably 0.155 to 0.180 when the polyester is polyethylene terephthalate, and 0.180 to 0.300 when the polyester is polyethylene naphthalate. In the case of polyethylene terephthalate, when the plane orientation coefficient is smaller than 0.155, the molecular chain orientation is small and mechanical properties and hydrolysis resistance tend to be lowered. In addition, since a film having a plane orientation coefficient larger than 0.180 needs to be extremely oriented, film tearing frequently occurs at the time of film formation, which may deteriorate the film forming property. A more preferable lower limit value of the plane orientation coefficient is 0.157, and a more preferable lower limit value is 0.160. A more preferred upper limit is 0.175, and a more preferred upper limit is 0.170. A more preferred range is 0.157 to 0.175, and a further preferred range is 0.160 to 0.170.

  In the case of polyethylene naphthalate, if the plane orientation coefficient is smaller than 0.180, the molecular chain orientation is small and the hydrolysis resistance tends to be lowered. In addition, since a film having a plane orientation coefficient larger than 0.300 needs to be extremely oriented, film tearing frequently occurs at the time of film formation, which may deteriorate the film forming property. A more preferable lower limit value of the plane orientation coefficient is 0.200, and a more preferable lower limit value is 0.220. A more preferable upper limit value of the plane orientation coefficient is 0.290, and a more preferable upper limit value is 0.280. A more preferable range of the plane orientation coefficient is 0.200 to 0.290, and a further preferable range is 0.220 to 0.280.

  The plane orientation coefficient can be controlled by the stretching conditions of the polyester film. In particular, since the polyester film of the present invention has a large ΔTcg, it is difficult to increase the plane orientation coefficient. In order to make the plane orientation coefficient within the above range, it is preferable to perform two-stage MD stretching in which MD stretching is first performed at a low temperature, and then the temperature is increased and MD stretching is performed. The plane orientation coefficient increases as the draw ratio increases, but if the ratio is too high, the film-forming property is deteriorated, and therefore there is an optimum draw ratio.

  In this invention, although the thickness as a biaxially-oriented polyester film can be suitably determined according to a use, 25-250 micrometers is preferable in a solar cell backsheet or an electrical insulation film use. When this thickness is smaller than 25 μm, there is a problem that the film is not elastic and is difficult to convey. On the other hand, when this thickness is larger than 250 μm, the film may be too thick to be excellent in workability. The lower limit of the thickness is more preferably 30 μm, still more preferably 40 μm. Further, the upper limit value of the thickness is more preferably 220 μm, still more preferably 200 μm. A more preferable range of the thickness is 30 to 220 μm, and a more preferable range is 40 to 200 μm.

  The biaxially oriented polyester film of the present invention as described above is produced, for example, as follows. First, a polyester film constituting a biaxially oriented polyester film is manufactured. In order to produce a polyester film, for example, polyester pellets are melted using an extruder, discharged from a die, cooled and solidified, and formed into a sheet. At this time, in order to remove the unmelted material in the polymer, it is preferable to filter the polymer with a fiber sintered stainless metal filter.

  In addition, inorganic and organic particles such as clay, mica, titanium oxide, calcium carbonate, carion, talc, wet silica, dry type are used to impart easy slipping, abrasion resistance and scratch resistance to the surface of the polyester film. Inorganic particles such as silica, colloidal silica, calcium phosphate, barium sulfate, alumina and zirconia, organic particles containing acrylic acids, styrene resins, thermosetting resins, silicones and imide compounds, and polyester polymerization reaction It is also a preferred embodiment to add particles (so-called internal particles) that are precipitated by the catalyst or the like.

  Furthermore, various additives such as compatibilizers, plasticizers, weathering agents, antioxidants, thermal stabilizers, lubricants, antistatic agents, whitening agents, coloring, as long as the effects of the present invention are not impaired. Agents, conductive agents, ultraviolet absorbers, flame retardants, flame retardant aids, pigments and dyes may be added.

  Subsequently, the sheet-like material obtained as described above is heat-treated after being stretched biaxially in the longitudinal direction and the width direction. As the stretching method, a sequential biaxial stretching method such as stretching in the width direction after stretching in the longitudinal direction, a simultaneous biaxial stretching method in which the longitudinal direction and the width direction are simultaneously stretched using a simultaneous biaxial tenter, etc. A method combining a sequential biaxial stretching method and a simultaneous biaxial stretching method is included.

  Next, the production method of the biaxially oriented polyester film of the present invention will be described as an example in which polyethylene terephthalate (PET) is used as polyester. Of course, the present invention is not limited to a biaxially oriented polyester film using a PET film, and may be one using another polymer. For example, when a polyester film is formed using polyethylene-2,6-naphthalenedicarboxylate having a high glass transition temperature or a high melting point, it may be extruded or stretched at a temperature higher than the following temperature.

  First, polyethylene terephthalate is prepared. Polyethylene terephthalate is manufactured by one of the following processes. (1) Using terephthalic acid and ethylene glycol as raw materials, a low molecular weight polyethylene terephthalate or oligomer is obtained by direct esterification reaction, and then a polymer is obtained by polycondensation reaction using antimony trioxide or titanium compound as a catalyst. And (2) a process in which dimethyl terephthalate and ethylene glycol are used as raw materials, a low molecular weight product is obtained by a transesterification reaction, and a polymer is obtained by a subsequent polycondensation reaction using antimony trioxide or a titanium compound as a catalyst. Here, the reaction proceeds even without a catalyst, but in the transesterification reaction, the esterification usually proceeds using a compound such as manganese, calcium, magnesium, zinc, lithium and titanium as a catalyst. After the exchange reaction is substantially completed, a phosphorus compound may be added for the purpose of inactivating the catalyst used in the reaction. The obtained PET pellet is preferably heat-treated at a temperature of 225 ° C. for 35 hours under a reduced pressure of 1 mmHg using a rotary vacuum polymerization apparatus to increase the intrinsic viscosity.

  When the terminal blocker is contained in the polyester constituting the film, the end blocker is directly mixed with the PET pellets, and heated to a temperature of 270 to 275 ° C. using a vented twin-screw kneading extruder. A method of kneading into a high-concentration master pellet is effective. In this case, the intrinsic viscosity IV of PET is higher than usual, and preferably 0.7 to 1.6. The intrinsic viscosity IV is more preferably 1.2 to 1.4. When the intrinsic viscosity IV is less than 0.7, the amount of carboxyl ends of the master pellet is increased, and the reaction with the end-capping agent occurs when the master pellet is formed. May become smaller, and the amount of carboxyl ends may not be reduced. On the other hand, if the intrinsic viscosity IV is greater than 1.6, the melt viscosity becomes too high, and the extrusion may not be stable and master pellets may not be produced. If the temperature of the extruder is raised to lower the melt viscosity, the end-capping agent may be thermally decomposed and the effect may not appear.

  Next, the obtained PET pellets are dried under reduced pressure for 3 hours or more at a temperature of 180 ° C., and then under a nitrogen stream or under reduced pressure so that the intrinsic viscosity does not decrease, more preferably 270 to 280 ° C. It supplies to the extruder heated to the temperature of 275 degreeC, it extrudes from a slit-shaped die | dye, it cools on a casting roll, and an unstretched film is obtained. At this time, it is preferable to use various types of filters, for example, filters made of materials such as sintered metal, porous ceramic, sand and wire mesh, in order to remove foreign substances and denatured polymers. Moreover, you may provide a gear pump as needed in order to improve fixed_quantity | feed_rate supply property. When laminating films, a plurality of different polymers are melt laminated using two or more extruders and manifolds or merging blocks.

  Next, the unstretched film thus obtained is stretched in the machine direction using the difference in peripheral speed of the roll (MD stretching) using a longitudinal stretching machine in which several rolls are arranged, and subsequently A biaxial stretching method in which transverse stretching is performed using a stenter (TD stretching) will be described.

  First, the unstretched film is MD stretched. Since the biaxially oriented polyester film of the present invention has a crystallization parameter ΔTcg larger than that of ordinary polyester, orientation crystallization hardly occurs. Therefore, in MD stretching, first, stretching is performed at a low temperature, and then the temperature is raised, and two-stage stretching is performed, whereby orientation crystallization occurs and the orientation can be increased. The first low-temperature stretching (MD1 stretching) is performed by a heating roll group in the range of (Tg-20) to (Tg + 10) ° C., more preferably in the range of (Tg-10) to (Tg + 5) ° C., and the longitudinal direction. Preferably, the film is stretched 1.1 to 3.0 times, more preferably 1.2 to 2.5 times, still more preferably 1.5 to 2.0 times, and then higher than the MD stretching 1 temperature (Tg + 10). MD stretching 2 is performed at ~ (Tg + 50). A more preferable temperature is (Tg + 15) (˜Tg + 30). The preferable draw ratio of MD drawing 2 is 1.2 to 4.0 times, more preferably 1.5 to 3.0 times. The MD stretching ratio of MD stretching 1 and MD stretching 2 is preferably 2.0 to 6.0 times, more preferably 3.0 to 5.5 times, and even more preferably 3.5 to 5 times. .0 times. It is preferable to cool with the cooling roll group of the temperature of 20-50 degreeC after extending | stretching.

  Next, stretching in the width direction is performed using a stenter. The draw ratio is preferably 2.0 to 6.0 times, more preferably 3.0 to 5.5 times, and still more preferably 3.5 to 5.0 times. The temperature is preferably in the range of (Tg) to (Tg + 50) ° C., more preferably in the range of (Tg) to (Tg + 30) ° C. (TD stretching). Although heat setting is performed after TD stretching, it is preferable to perform heat treatment at a lower temperature than usual in order to suppress orientation relaxation of the film. In the heat setting treatment, the film is heat-treated at a temperature of 150 to 190 ° C., more preferably 165 to 185 ° C., and even more preferably 160 to 180 ° C. while relaxing the film under tension or in the width direction. The heat treatment time is preferably in the range of 0.5 to 10 seconds. Then, after cooling to 25 ° C., the film edge can be removed to obtain the biaxially stretched polyester film of the present invention.

[Methods for measuring physical properties and methods for evaluating effects]
(1) Intrinsic viscosity Calculated based on the following equation from solution viscosity measured at a temperature of 25 ° C in orthochlorophenol.
ηsp / C = [η] + K [η] ² × C
Here, ηsp = (solution viscosity / solvent viscosity) −1, C is the dissolved polymer weight per 100 ml of solvent (g / 100 ml, usually 1.2), and K is a Huggins constant (assuming 0.343) It is. The solution viscosity and solvent viscosity are measured using an Ostwald viscometer.

(2) Carboxyl terminal quantity The carboxyl terminal quantity was measured by the method of Malice. (Reference M. J. Malice, F. Huizinga. Anal. Chim. Acta, 22 363 (1960)).

(3) Crystallization parameters {Glass transition temperature Tg, crystallization temperature Tc, melting point Tm, crystallization parameter ΔTcg}
Using a differential scanning calorimeter DSCII type manufactured by Seiko Instrument Co., Ltd., 5 mg of the sample was heated at a rate of 20 ° C./min to comply with JIS-K7121 (1987), the glass transition temperature (Tg), The crystallization temperature (Tc) and melting point (Tm) were measured. Specific measurement methods are described below.
1) JIS-K7121 (1987) 3. (1) and 3. The state of the sample is adjusted based on the method described in (3). 3. In the state adjustment in (3), the temperature is raised from 25 ° C. to 300 ° C. at a rate of temperature rise of 20 ° C./min and then rapidly cooled to 25 ° C.
2) Next, using the sample conditioned in 1), based on JIS-K7121 (1987) and the above conditions, the glass transition temperature (Tg), the crystallization temperature at the time of temperature rise (Tc), and the melting point (Tm) Measure. The measurement is performed by increasing the temperature from 25 ° C. to 300 ° C. at a temperature increase rate of 20 ° C./min. In addition, let the temperature obtained based on the measuring method of the midpoint glass transition temperature of JIS-K7121 (1987) be glass transition temperature (Tg). Moreover, let the temperature obtained based on the measuring method of the crystallization peak temperature described in JIS-K7121 (1987) be the crystallization temperature (Tc). Moreover, let the temperature obtained based on the measuring method of the melting peak temperature described in JIS-K7121 (1987) be a melting point (Tm).
3) The crystallization parameter ΔTcg is obtained from the following equation.
ΔTcg = Tc−Tg.

(4) Elongation retention The breaking elongation is the elongation at break when a sample is cut into a size of 1 cm × 20 cm based on ASTM-D882 (1999) and pulled at a chucking distance of 5 cm and a pulling speed of 300 mm / min. The degree was measured. The measurement was performed on five samples, and the elongation at break was defined as the average value. In addition, the elongation retention is obtained by cutting a sample into the shape of a measurement piece (1 cm × 20 cm) and then using a pressure cooker manufactured by Tabai Espec Co., Ltd. under conditions of a temperature of 125 ° C., a humidity of 100%, and a pressure of 1.5 atm. After the treatment for 72 hours, the breaking elongation of the sample after the treatment was measured based on ASTM-D882 (1999), when the breaking elongation was 5 cm between chucks and pulled at a pulling speed of 300 mm / min. The measurement was performed on five samples, and the elongation at break was defined as the average value. Using the obtained breaking elongations E0 and E1, the elongation retention was calculated according to the following formula.
Elongation retention rate (%) = E1 / E0 × 100.

(5) Thermal decomposition reduction amount The thermal decomposition reduction amount was evaluated by the weight reduction rate during heating using the following thermogravimetric analyzer.
・ Device: TGA7 manufactured by PerkinElmer
・ Measurement atmosphere: under nitrogen flow ・ Sample preparation weight: approx. 10mg
·Measurement condition:
(A) Hold for 1 minute at a program temperature of 50 ° C. (b) Sample weight when a temperature of 100 ° C. is reached when thermogravimetric analysis is performed from a program temperature of 50 ° C. to 300 ° C. at a heating rate of 20 ° C./min (W1) after reaching a temperature of 300 ° C. relative to the, from the sample weight (W2) when the hold 30 minutes, determine the [Delta] W _{300 ° C.} according to the following equation defines the [Delta] W _{300 ° C.} and the pyrolysis decrease, calculated did.
ΔW _{300 ° C.} = (W1−W2) / W1 × 100 (%).

(6) Isocyanate gas generation amount The generated isocyanate gas was collected by an adsorption tube (Tenax-GR), and set in the next GC / MS apparatus for analysis.
[Gas sampling conditions]
・ Heating temperature: 300 ℃
・ Heating time: 30 minutes ・ Purge gas: Nitrogen 100 mL / min ・ Sample amount: 1 mg
[GS / MS analysis]
・ Thermal desorption device: TDS-A + CIS-4 (manufactured by Gerstel)
・ Thermal desorption temperature: 20 ° C. (2 minutes hold) → 280 ° C. (heating rate 60 ° C./min)
Hold at 280 ° C. for 15 minutes. GC / MS equipment: GC6890 + MSD5973N (manufactured by Agilent)
-Separation column: SPB-1Sulfur
(Length 30m ID 0.32mm ID Liquid phase film thickness 4.0μm
・ Oven condition: 40 ° C → 300 ° C
Carrier gas: Helium 1.5 mL / min Split ratio: 33: 1
・ Inlet temperature: -150 ° C during cold trap, 300 ° C during introduction
・ GC / MS transfer line: 280 ℃
・ Ion source: EI
-Ion source temperature: 230 ° C
Scan range: m / z 29-600
Calibration curve: Analyzing toluene under the same conditions to prepare a calibration curve Compounds having isocyanate groups (2,6-diisopropylphenyl isocyanate (Mw: 203), 1,3,5-triisopropylphenyl diisocyanate (Mw: 286) ) And 2-amino-1,3,5-triisopropylphenyl-6-isocyanate (Mw: 260)) is defined as an isocyanate gas generation amount.

(7) Plane orientation coefficient A plane orientation coefficient is measured based on JIS-K7142 (1996). The refractive index in the MD, TD and ZD directions was measured using an Abbe refractometer using sodium D line as a light source. The mount solution was methylene iodide, and measurement was performed under conditions of a temperature of 25 ° C. and a humidity of 65% RH.
・ Sample width: 25mm
・ Sample length: 30 mm
・ Measurement device: Abbe refractometer NAR-1T manufactured by Atago Co., Ltd. ・ Mount solution: methylene iodide (in the case of polyethylene naphthalate, sulfur methylene iodide)
Measurement environment: temperature 23 ° C., humidity 65% RH.
・ Calculation formula:
Plane orientation coefficient fn = (nMD + nTD) / 2-nZD.

(8) Hydrolysis resistance Biaxially oriented polyester film was used as the first layer, and 90 parts by weight of “Takelac” (registered trademark) A310 (manufactured by Mitsui Takeda Chemical Co., Ltd.) and “Takenate” (registered trademark) as the adhesive layer. A3 (manufactured by Mitsui Takeda Chemical Co., Ltd.) was applied, and a 125 μm thick biaxially stretched polyester film “Lumirror” (registered trademark) S10 (manufactured by Toray Industries, Inc.) was laminated thereon as the second layer. The above-mentioned adhesive layer is applied onto the above-mentioned second layer, and the barrier layer “HGTS” (registered trademark) having a thickness of 12 μm (alumina-deposited PET film manufactured by Toray Film Processing Co., Ltd.) is used as the second layer. And a back sheet having a thickness of 188 μm was formed.

  Based on ASTM-D882 (1999), the sample was cut into a size of 1 cm × 20 cm, and the elongation at break was measured when the sample was pulled at a chuck distance of 5 cm and a pulling speed of 300 mm / min. The measurement was performed on five samples, and the elongation at break was defined as the average value.

  In addition, the elongation retention is obtained by cutting a sample into the shape of a measurement piece (1 cm × 20 cm) and then using a constant temperature and humidity chamber (Espec Corp. constant temperature and humidity chamber KH-60A) at a temperature of 85 ° C. After leaving for 3000 hours in an atmosphere with a humidity of 85% RH, the breaking elongation of the sample after the treatment was measured based on ASTM-D882 (1999), when the tensile strength was 5 cm between chucks and the tensile speed was 300 mm / min. Was measured. The measurement was performed on five samples, and the elongation at break was defined as the average value.

Using the obtained breaking elongations E0 and E1, the elongation retention was calculated according to the following formula.
・ Elongation retention (%) = E1 / E0 × 100
The elongation retention was determined according to the following criteria, and the hydrolysis resistance was evaluated.
◎: Elongation retention is 70% or more ◯: Elongation retention is 50% or more and less than 70% △: Elongation retention is 30% or more and less than 50% ×: Elongation retention is less than 30% A degree retention of 30% or more was accepted and less than 30% was rejected.

(9) Mechanical strength Mechanical strength is measured according to ASTM-D882 (1997). The following Instron type tensile tester is used for the apparatus, and the conditions are as follows.
・ Measuring device: Automatic measuring device for film strength at Orientec Co., Ltd.
“Tensilon AMF / RTA-100”
・ Sample size: width 10mm x sample length 100mm
・ Tensile speed: 200 mm / min ・ Measurement environment: Temperature 23 ° C., humidity 65% RH
-Number of measurements: measured 5 times and calculated from the average value The sum of the Young's modulus of MD and TD (total Young's modulus) was calculated and evaluated according to the following criteria.
◎: Total Young's modulus is 6.5 GPa or more ○: Total Young's modulus is 6.2 GPa or more and less than 6.5 GPa Δ: Total Young's modulus is 6.0 GPa or more and less than 6.2 GPa x: Total Young's modulus is less than 6.0 GPa The total Young's modulus of 6.0 GPa or more was accepted and less than 6.0 GPa was rejected. In addition, it can be used more suitably for the use (solar cell backsheet or electrical insulation film) in which mechanical characteristics are required when it is either ◯ or ◎. And it is most preferable that it is (double-circle).

(10) Film-forming stability The film-forming property of the film was evaluated according to the following criteria.
○: Stable film formation is possible with almost no film tearing.
(Triangle | delta): Film tearing generate | occur | produces occasionally and film forming stability is a little low.
X: Many film breaks occur and the film formation stability is low.

  Judgment made ○ and △ pass, and made x fail.

(11) Low thermal decomposition generated gas The odor around the extruder during film formation was collected, and the amount of isocyanate gas generated was analyzed by the method of (6) above, and the low thermal decomposition generated gas was evaluated according to the following criteria.
○: less than the amount of generated gas is 0.015mg / ^{m 3} △: amount of generated gas is 0.015 mg / ^{m 3} or higher 0.035 mg / ^{m 3} less ×: the determination amount generated gas is 0.035 mg / ^{m 3} or more, generation A gas amount of less than 0.035 mg / m ³ was accepted, and a generated gas amount of 0.035 mg / m ³ or more was rejected.

(Reference Example 1)
100 parts by mass of dimethyl terephthalate and 64 parts by mass of ethylene glycol were charged into a transesterification reaction apparatus, and the contents were heated to a temperature of 140 ° C. and dissolved. Thereafter, 0.09 parts by mass of calcium acetate and 0.03 parts by mass of antimony trioxide were added while stirring the contents, and a transesterification reaction was performed while distilling methanol at a temperature of 140 to 230 ° C. Next, 0.18 parts by mass of lithium acetate and 4.8 parts by mass of a 5% ethylene glycol solution of trimethyl phosphate (0.24 parts by mass as trimethyl phosphate) were added.

  When the ethylene glycol solution of trimethyl phosphoric acid is added, the temperature of the reaction contents decreases. Therefore, stirring was continued until the temperature of the reaction contents returned to 230 ° C. while distilling excess ethylene glycol. When the temperature of the reaction contents in the transesterification reactor thus reached 230 ° C., the reaction contents were transferred to the polymerization apparatus.

  After the reaction contents were transferred to the polymerization apparatus, the reaction system was gradually heated from 230 ° C. to 290 ° C. and the pressure was reduced to 0.1 kPa. The time to reach a final temperature of 290 ° C. and a final pressure of 0.1 kPa was both 60 minutes. After reaching the final temperature and final pressure, the reaction was carried out for 2 hours (3 hours after the start of polymerization), and the stirring torque of the polymerization apparatus was a predetermined value (the specific value differs depending on the specifications of the polymerization apparatus, but this polymerization apparatus The value indicated by polyethylene terephthalate having an intrinsic viscosity of 0.55 was a predetermined value). Therefore, the reaction system was purged with nitrogen and returned to normal pressure to stop the polycondensation reaction, discharged into cold water in a strand form, and immediately cut to obtain PET pellet X (3 mm cubic) of polyethylene terephthalate having an intrinsic viscosity of 0.55. Obtained.

(Reference Example 2)
Using a rotary vacuum polymerization apparatus, the PET pellet X obtained in the above Reference Example 1 was heat-treated at a temperature of 230 ° C. under a reduced pressure of 0.1 kPa for a long time to carry out solid phase polymerization. The longer the heat treatment time, the higher the intrinsic viscosity. Intrinsic viscosity is 0.60 at processing time of 1 hour, intrinsic viscosity is 0.70 at 5 hours, intrinsic viscosity is 0.80 at 15 hours, intrinsic viscosity is 0.85 at 25 hours, and intrinsic viscosity is 0 at 40 hours The intrinsic viscosity is 1.0 at 90 and 100 hours.

(Reference Example 3)
Bent-type twin-screw kneading extruder of the same direction rotation type provided with one kneading paddle kneading section heated to a temperature of 275 ° C. (manufactured by Nippon Steel Works, screw diameter 30 mm, screw length / screw diameter = 45.5) 90 parts by mass of 1.4 pellets having an intrinsic viscosity of 1.4 PET obtained in Reference Example 2 above and 10 parts by mass of the polycarbodiimide prepared in Reference Example 4 were melt extruded at a screw speed of 200 revolutions / minute to form a strand. Then, after cooling with water at a temperature of 25 ° C., it was immediately cut to produce a blend chip (I).

(Reference Example 4)
29,0 g (1.03 mol) of 2,4,6-triisopropylphenyl 1,3-diisocyanate having an NCO content of 29.5% by weight are added to 1-methylphospholene 1-oxide in 200 ml of anhydrous xylene. It was heated to a temperature of 100 ° C. in the presence of 2% by weight (0.59 g) and condensed at this temperature under the release of carbon dioxide. After an NCO content of 5.0% by weight in the reaction mixture was achieved (reaction time about 11 hours), the solvent, residual monomer and catalyst residue were distilled off in vacuo. As a result, 270.2 g of an oligomer polycarbodiimide mixture having an NCO content of 7.0% by mass and a carbodiimide content of 12.6% by mass was obtained.

  85 g of the obtained oligomeric polycarbodiimide was homogenized in 100 ml of anhydrous toluene at a temperature of 60 ° C. under nitrogen. Then 16.3 g (0.14 mol) of powdered 2,2-bis (4-hydroxyphenyl) propane was added batchwise followed by 1.5 g of catalyst, 33% of triethylenediamine in dipropylene glycol. The solution was added. The mixture was boiled under reflux for 12 hours. The solvent was then removed in vacuo. As a result, 93 g of polycarbodiimide having an NCO content of 0% by mass, a carbodiimide content of 10.6% by mass, a glass transition point of 75.2 ° C., and an average molecular weight of 5300 g / mol was obtained.

Example 1
In an extruder E heated to a temperature of 275 ° C., 90 parts by mass of PET pellets having an intrinsic viscosity of 0.85 obtained in Reference Example 2 and 10 parts by mass of Blend Chip (I) obtained in Reference Example 3 were added. After drying under reduced pressure at a temperature of 180 ° C. for 3 hours, the solution was supplied and introduced into a T die die under a nitrogen atmosphere. Next, from the inside of the T die die, it was extruded into a sheet shape to obtain a molten single layer sheet, which was closely cooled and solidified by an electrostatic application method on a drum maintained at a surface temperature of 25 ° C. to obtain an unstretched single layer film.

  Subsequently, after preheating the obtained unstretched monolayer film with a heated roll group, 1.8 times MD stretching 1 is performed at a temperature of 80 ° C., and 2.3 times MD stretching 2 is further performed at a temperature of 95 ° C. went. The film was stretched 4.1 times in the longitudinal direction (MD direction) in total, and then cooled with a roll group having a temperature of 25 ° C. to obtain a uniaxially stretched film. While holding both ends of the obtained uniaxially stretched film with clips, it is led to a preheating zone at a temperature of 95 ° C. in the tenter, and continuously in the heating zone at a temperature of 100 ° C. in the width direction (TD direction) perpendicular to the longitudinal direction. The film was stretched 4.0 times. Subsequently, a heat treatment was performed at a temperature of 170 ° C. for 10 seconds in a heat treatment zone in the tenter, and further a relaxation treatment was performed in the 4% width direction at a temperature of 170 ° C. Then, after gradually cooling uniformly, it was wound up to obtain a biaxially stretched film having a thickness of 50 μm.

  When the obtained biaxially oriented polyester film was evaluated, as shown in Tables 1 and 2, it had excellent hydrolysis resistance, film-forming properties and mechanical properties.

(Example 2)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that PET pellets having an intrinsic viscosity of 1.0 were used. When the obtained biaxially oriented polyester film was evaluated, as shown in Tables 1 and 2, it had excellent resistance to hydrolysis.

(Example 3)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that PET pellets having an intrinsic viscosity of 0.6 were used. When the obtained biaxially oriented polyester film was evaluated, as shown in Tables 1 and 2, it had excellent film forming properties and mechanical properties.

Example 4
A biaxially oriented polyester film was produced in the same manner as in Example 1 except that the intrinsic viscosity of the PET pellets used in Reference Example 3 was 0.8. When the obtained biaxially oriented polyester film was evaluated, as shown in Tables 1 and 2, it had excellent film forming properties and mechanical properties.

(Example 5)
In an extruder E heated to a temperature of 275 ° C., 70 parts by mass of PET pellets having an intrinsic viscosity of 0.85 obtained in Reference Example 2 and 30 parts by mass of Blend Chip (I) obtained in Reference Example 3 were added at 180 ° C. A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that it was supplied after being dried under reduced pressure at a temperature of 3 hours for 3 hours. When the obtained biaxially oriented polyester film was evaluated, as shown in Tables 1 and 2, the carboxyl end amount was 0.1 equivalent / ton, and the hydrolysis resistance, film forming property, and mechanical properties were excellent. Had characteristics.

(Example 6)
In an extruder E heated to a temperature of 275 ° C., 80 parts by mass of PET pellets having an intrinsic viscosity of 1.0 obtained in Reference Example 2 and 20 parts by mass of Blend Chip (I) obtained in Reference Example 3 were added at 180 ° C. A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that it was supplied after being dried under reduced pressure at a temperature of 3 hours for 3 hours. When the obtained biaxially oriented polyester film was evaluated, as shown in Tables 1 and 2, it had excellent resistance to hydrolysis.

(Example 7)
A biaxially oriented polyester film was obtained in the same manner as in Example 4 except that PET pellets having an intrinsic viscosity of 1.0 obtained in Reference Example 2 were supplied to Extruder E heated to a temperature of 275 ° C. It was. When the obtained biaxially oriented polyester film was evaluated, as shown in Tables 1 and 2, it had excellent mechanical properties.

(Example 8)
A biaxially oriented polyester film was obtained in the same manner as in Example 4 except that the extruder E heated to a temperature of 275 ° C. was supplied with the PET pellets having an intrinsic viscosity of 0.6 obtained in Reference Example 2. It was. When the obtained biaxially oriented polyester film was evaluated, as shown in Tables 1 and 2, it had excellent film forming properties and mechanical properties.

Example 9
In an extruder E heated to a temperature of 275 ° C., 40 parts by mass of PET pellets having an intrinsic viscosity of 0.60 obtained in Reference Example 2 and 60 parts by mass of Blend Chip (I) obtained in Reference Example 3 were added to 180 parts. A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that it was supplied after drying under reduced pressure at a temperature of 3 ° C. for 3 hours. When the obtained biaxially oriented polyester film was evaluated, as shown in Tables 1 and 2, it had excellent hydrolysis resistance and mechanical properties.

(Example 10)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that PET pellets having an intrinsic viscosity of 0.90 were used. When the obtained biaxially oriented polyester film was evaluated, as shown in Tables 1 and 2, it had excellent hydrolysis resistance and mechanical properties.

(Example 11)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that PET pellets having an intrinsic viscosity of 0.80 were used. When the obtained biaxially oriented polyester film was evaluated, as shown in Tables 1 and 2, it had excellent hydrolysis resistance, film-forming properties and mechanical properties.

(Example 12)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that PET pellets having an intrinsic viscosity of 0.95 were used. When the obtained biaxially oriented polyester film was evaluated, as shown in Table 1 and Table 2, it had excellent resistance to hydrolysis and mechanical properties.

(Example 13)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that PET pellets having an intrinsic viscosity of 0.70 were used. When the obtained biaxially oriented polyester film was evaluated, as shown in Tables 1 and 2, even if the intrinsic viscosity was 0.6, it had excellent hydrolysis resistance, film forming properties and mechanical properties. Was.

(Example 14)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the PET raw material used in Reference Example 3 had an intrinsic viscosity of 1.2. When the obtained biaxially oriented polyester film was evaluated, as shown in Tables 1 and 2, even when the carboxyl end amount was 5 equivalents / ton, it was excellent in hydrolysis resistance, film-forming properties and mechanical properties. Had.

(Example 15)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the PET raw material used in Reference Example 3 had an intrinsic viscosity of 1.0. When the obtained biaxially oriented polyester film was evaluated, as shown in Tables 1 and 2, even when the carboxyl end amount was 7 equivalents / ton, it was excellent in hydrolysis resistance, film-forming properties and mechanical properties. Had.

(Example 16)
To a mixture of 100 parts by mass of dimethyl 2,6-naphthalenedicarboxylate and 60 parts by mass of ethylene glycol, 0.03 parts by mass of manganese acetate tetrahydrate salt is added and gradually increased from a temperature of 150 ° C. to a temperature of 240 ° C. The transesterification was carried out while raising the temperature. In the middle, when the reaction temperature reached 170 ° C., 0.024 parts by mass of antimony trioxide was added. When the reaction temperature reached 220 ° C., 0.042 parts by mass of 3,5-dicarboxybenzenesulfonic acid tetrabutylphosphonium salt (corresponding to 2 mmol%) was added. Thereafter, a transesterification reaction was carried out, and 0.023 parts by mass of trimethyl phosphoric acid was added. Next, the reaction product is transferred to a polymerization apparatus, heated to a temperature of 290 ° C., a polycondensation reaction is performed under a high vacuum of 30 Pa, and the stirring torque of the polymerization apparatus is a predetermined value (specifically depending on the specifications of the polymerization apparatus). Although the values are different, the value indicated by polyethylene-2,6-naphthalate having an intrinsic viscosity of 0.65 in this polymerization apparatus is a predetermined value). Therefore, the reaction system was purged with nitrogen and returned to normal pressure to stop the polycondensation reaction, discharged into cold water in a strand form, and immediately cut to obtain polyethylene-2,6-naphthalate pellets X ′ having an intrinsic viscosity of 0.65. Obtained.

  Using a rotary vacuum polymerization apparatus, the PEN pellet X ′ obtained in Reference Example 1 was heat-treated at a temperature of 230 ° C. for a long time under a reduced pressure of 0.1 kPa to perform solid phase polymerization. Intrinsic viscosity is 0.80 in 20 hours.

  Bent-type twin-screw kneading extruder of the same direction rotation type provided with one kneading paddle kneading part heated to a temperature of 300 ° C. (manufactured by Nippon Steel Works, screw diameter 30 mm, screw length / screw diameter = 45.5) 90 parts by mass of the obtained PEN pellet having an intrinsic viscosity of 0.80 and 10 parts by mass of the end sealant “STABACKZOL P400” manufactured by Rhein Chemie, Inc. are melt-extruded at a screw rotational speed of 200 revolutions / minute to obtain a strand. Then, after cooling with water at a temperature of 25 ° C., it was immediately cut to produce a blend chip (II).

  In Extruder E heated to a temperature of 300 ° C., 90 parts by mass of PEN pellets having an intrinsic viscosity of 0.80 obtained by solid phase polymerization and 10 parts by mass of Blend Chip (II) were added at a temperature of 180 ° C. for 3 hours. After drying under reduced pressure, the solution was supplied and introduced into a T die die under a nitrogen atmosphere. Next, from the inside of the T die die, it was extruded into a sheet shape to obtain a molten single layer sheet, which was closely cooled and solidified by an electrostatic application method on a drum maintained at a surface temperature of 25 ° C. to obtain an unstretched single layer film.

  Subsequently, after preheating the obtained unstretched monolayer film with a heated roll group, 1.8 times MD stretching 1 is performed at a temperature of 1150 ° C., and 2.3 times MD stretching 2 is performed at a temperature of 135 ° C. went. The film was stretched 4.1 times in the longitudinal direction (MD direction) in total, and then cooled with a roll group having a temperature of 25 ° C. to obtain a uniaxially stretched film. While holding both ends of the obtained uniaxially stretched film with clips, it is guided to a preheating zone at a temperature of 135 ° C. in the tenter, and then continuously in the heating zone at a temperature of 145 ° C. in the width direction (TD direction) perpendicular to the longitudinal direction. The film was stretched 4.5 times. Subsequently, a heat treatment for 10 seconds was performed at a temperature of 190 ° C. in a heat treatment zone in the tenter, and a relaxation treatment was further performed in the 4% width direction at a temperature of 190 ° C. Subsequently, after uniform cooling, the film was wound up to obtain a biaxially stretched polyester film having a thickness of 50 μm.

  When the obtained biaxially oriented polyester film was evaluated, as shown in Tables 1 and 2, it had excellent hydrolysis resistance, film-forming properties, and mechanical properties.

(Example 17)
A biaxially oriented polyester is produced in the same manner as in Example 1 except that the polycarbodiimide prepared in Reference Example 4 of Reference Example 3 is changed to “Cardura E10P” (registered trademark) manufactured by Hexion Specialty Chemicals of an epoxy compound. A film was obtained. When the obtained biaxially oriented polyester film was evaluated, as shown in Tables 1 and 2, it had excellent film forming properties and mechanical properties.

(Example 18)
Biaxially oriented polyester in the same manner as in Example 1 except that the polycarbodiimide prepared in Reference Example 4 of Reference Example 3 is changed to “Epocross RPS-1005” (registered trademark) manufactured by Nippon Shokubai Co., Ltd. as an oxazoline compound. A film was obtained. As a result of evaluating the obtained biaxially oriented polyester film, as shown in Tables 1 and 2, it had characteristics excellent in low pyrolysis gas properties.

(Example 19)
A biaxially oriented polyester film was produced in the same manner as in Example 1 except that the polycarbodiimide prepared in Reference Example 4 of Reference Example 3 was changed to “STABACKZOL I” (registered trademark) manufactured by Rhein Chemie, a monocarbodiimide compound. Got. When the obtained biaxially oriented polyester film was evaluated, as shown in Tables 1 and 2, it had excellent hydrolysis resistance and mechanical properties.

(Example 20)
A biaxially oriented polyester film is obtained in the same manner as in Example 1 except that the polycarbodiimide prepared in Reference Example 4 of Reference Example 3 is changed to “Carbodilite LA-1” (registered trademark) manufactured by Nisshinbo Co., Ltd., a carbodiimide compound. It was. When the obtained biaxially oriented polyester film was evaluated, as shown in Tables 1 and 2, the film had excellent film forming properties, mechanical properties, and low thermal decomposition gas properties.

(Example 21)
After pre-heating the unstretched single layer film with a heated roll group, only MD stretching 2 is performed at a temperature of 95 ° C. without performing MD stretching 1, and the total length is 3.4 times in the longitudinal direction (MD direction). A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that stretching was performed. When the obtained biaxially oriented polyester film was evaluated, as shown in Tables 1 and 2, it had excellent film forming properties.

(Example 22)
3. While holding both ends of the uniaxially stretched film with clips, lead to a preheating zone at a temperature of 95 ° C. in the tenter, and then continuously in the heating zone at a temperature of 100 ° C. in the width direction (TD direction) perpendicular to the longitudinal direction. Stretched 0 times. Subsequently, a heat treatment zone in the tenter was subjected to a heat treatment for 10 seconds at a temperature of 195 ° C., and further subjected to a relaxation treatment in the 4% width direction at a temperature of 195 ° C., in the same manner as in Example 1. A biaxially oriented polyester film was obtained. When the obtained biaxially oriented polyester film was evaluated, as shown in Tables 1 and 2, it had excellent film forming properties and mechanical properties.

(Comparative Example 1)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the PET raw material used in Reference Example 3 had an intrinsic viscosity of 0.6. When the obtained biaxially oriented polyester film was evaluated, as shown in Tables 1 and 2, since the carboxyl end amount was 11 equivalents / ton, it was inferior in hydrolysis resistance and the like.

(Comparative Example 2)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that PET pellets having an intrinsic viscosity of 1.1 were used. When the obtained biaxially oriented polyester film was evaluated, as shown in Tables 1 and 2, since the intrinsic viscosity was 0.95, the film-forming properties and mechanical properties were inferior.

(Comparative Example 3)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that solid phase polymerization was not performed and PET pellets X having an intrinsic viscosity of 0.55 were used. When the obtained biaxially oriented polyester film was evaluated, as shown in Tables 1 and 2, the intrinsic viscosity was 0.49, and thus the hydrolysis resistance was poor.

(Comparative Example 4)
In an extruder E heated to a temperature of 275 ° C., 99 parts by mass of PET pellets having an intrinsic viscosity of 1.1 obtained in Reference Example 2 and 1 part by mass of Blend Chip (I) obtained in Reference Example 3 were 180 parts. A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that it was supplied after drying under reduced pressure at a temperature of 3 ° C. for 3 hours. When the obtained biaxially oriented polyester film was evaluated, as shown in Tables 1 and 2, since the intrinsic viscosity is 0.95 and the carboxyl terminal amount is 11 equivalents / ton, hydrolysis resistance and film-forming properties are obtained. Had inferior properties.

(Comparative Example 5)
A biaxially oriented polyester film was obtained in the same manner as in Comparative Example 1 except that the extruder E was heated to a temperature of 285 ° C., solid phase polymerization was not performed, and PET pellets X having an intrinsic viscosity of 0.60 were used. It was. When the obtained biaxially oriented polyester film was evaluated, as shown in Tables 1 and 2, the intrinsic viscosity was 0.49, the carboxyl end amount was 11 equivalents / ton, and the crystal parameter ΔTcg was 60 ° C. The hydrolysis resistance was inferior.

(Comparative Example 6)
In an extruder E heated to a temperature of 275 ° C., 180 parts by mass of PET pellets having an intrinsic viscosity of 1.1 obtained in Reference Example 2 and 40 parts by mass of Blend Chip (I) obtained in Reference Example 3 were added. A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that it was supplied after drying under reduced pressure at a temperature of 3 ° C. for 3 hours. When the obtained biaxially oriented polyester film was evaluated, as shown in Tables 1 and 2, since the intrinsic viscosity was 0.95 and the crystal parameter ΔTcg was 115 ° C., hydrolysis resistance, film-forming property, mechanical The physical properties and low pyrolysis gas generation were inferior.

(Comparative Example 7)
In an extruder E heated to a temperature of 275 ° C., 30 parts by mass of PET pellets having an intrinsic viscosity of 0.55 obtained in Reference Example 2 and 70 parts by mass of Blend Chip (I) obtained in Reference Example 3 were added to 180 parts. A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that it was supplied after drying under reduced pressure at a temperature of 3 ° C. for 3 hours. When the obtained biaxially oriented polyester film was evaluated, as shown in Tables 1 and 2, the intrinsic viscosity was 0.49, and the properties of hydrolysis resistance, film-forming property and low pyrolysis gas generation were inferior. Had.

(Comparative Example 8)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the blend chip (I) was not used. When the obtained biaxially oriented polyester film was evaluated, as shown in Tables 1 and 2, since the carboxyl terminal amount was 15 equivalents / ton and the crystal parameter ΔTcg was 65 ° C., the hydrolysis resistance was poor. Had.

Claims (8)

Crystallization Parameter ΔTcg by differential scanning calorimetry (DSC) is the 70 to 110 ° C., a carboxyl terminus amount from 0.1 to 10 equivalents / ton, an intrinsic viscosity of Ri 0.50～0.90Dl / g Der The biaxially oriented polyester film is characterized in that the plane orientation coefficient fn is 0.155 to 0.300 .   2. The biaxially oriented polyester film according to claim 1, wherein the retention of the elongation at break in at least one direction after 72 hours at a temperature of 125 ° C. and a humidity of 100% RH is 10 to 100%.   3. The biaxially oriented polyester film according to claim 1, wherein a thermal decomposition weight loss amount at a temperature of 300 ° C. for 30 minutes is 0 to 0.2 wt%.   The biaxially oriented polyester film according to any one of claims 1 to 3, wherein the amount of isocyanate-based gas generated at 300 ° C for 30 minutes is 0 to 0.05 wt%.   The biaxially oriented polyester film according to any one of claims 1 to 4, further comprising 0.1 to 5% by weight of a terminal blocking agent.   The biaxially oriented polyester film according to claim 5, wherein the end-capping agent is a carbodiimide compound. The solar cell backsheet using the biaxially-oriented polyester film in any one of Claims 1-6 . The film for electrical insulation using the biaxially oriented polyester film in any one of Claims 1-6 .