JP2010260903A - Polyester film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyester film having long-term thermal stability and extremely high hydrolysis resistance. <P>SOLUTION: The polyester film includes not more than 5 eq/ton of carboxy terminals with respect to polyester, and not more than 150 ppm content of all metal elements with respect to the polyester. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a polyester film excellent in heat resistance and hydrolysis resistance. In detail, it is related with the polyester film excellent in the weather resistance suitable for a solar cell backside sealing sheet or an electrical insulation sheet.

  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. However, in applications where higher heat resistance and hydrolysis resistance are required, it is common to use materials that are more durable than polyester, such as fluorine-based films. However, with the recent cost reduction, there is a demand for replacement of these materials with cheaper polyester films.

  For example, constituent members such as a solar cell back surface sealing sheet and a surface protective sheet for sealing the back surface of the solar cell module are used for the solar cell module, and a base film is used for these constituent members. Since solar cells used outdoors are used for a long time, these components are also required to have high durability against the natural environment. Therefore, it has been carried out that a fluorine-based film is used as such a constituent member. However, it has been pointed out that the fluorine-based film itself is high in cost and has a high environmental load depending on the disposal / treatment method, and is not suitable for a solar cell module intended to reduce the environmental load.

  Furthermore, even in applications that have been used as conventional polyester films, higher durability is required as performance is improved. For example, with the improvement in performance of electrical equipment, the amount of heat generated by electrical equipment is increasing, and the operating temperature range of polyester films used for electrical insulation is expanding. Furthermore, electric devices are becoming smaller and lighter, and high weather resistance that can withstand long-term use outdoors has been demanded.

  As a polyester film used for such an application, as disclosed in Patent Documents 1 to 4, those having a reduced carboxy terminal amount and improved hydrolysis resistance have been proposed.

JP 2000-129007 A JP 2007-150084 A JP 2007-204538 A JP 2008-4839 A

  Conventionally, as a measure for improving the durability of a polyester film, improvement of hydrolysis by reducing the amount of carboxy terminals has been proposed as in the above-mentioned patent document. However, solar cell modules, for example, have been developed from solar roof installations to installations in large-scale solar power plants such as desert areas. In such an environment, the sunshine time is long, and it is exposed to high temperatures for a long time. In addition, there is an increasing demand for long-term thermal stability that can withstand high-level and long-term heat generation by improving the output of electronic devices and solar cell modules. Therefore, it was thought that sufficient durability could not be achieved only by the improvement by the conventional hydrolysis resistance. Furthermore, the environment in which solar cell modules and electrical equipment are used is more severe, and the polyester film used for solar cell backside sealing and electrical insulation is proposed in the above patent document. In some cases, sufficient hydrolysis resistance may not provide sufficient durability.

  In view of the above problems, an object of the present invention is to provide a polyester film having long-term thermal stability and extremely high hydrolysis resistance.

  As a result of intensive studies to solve the above problems, the inventor of the present application has sensed that the residual metal element of the polyester has an effect on the thermal deterioration, and has reduced the amount of the residual metal element to an extremely low concentration. By reducing the terminal amount, the present inventors have found an effect of exhibiting excellent long-term heat resistance and high hydrolyzability for solar cell back surface sealing or electrical insulation, and have led to the present invention.

1st invention of this application is a biaxially-oriented polyester film, Comprising: It is a polyester film which satisfy | fills the following requirements (1) and (2).
(1) The carboxy terminal amount is 5 eq / ton or less with respect to the polyester (2) The total metal element content is 150 ppm or less with respect to the polyester (here, the total metal element content is an alkali metal, (The total amount of transition metals and typical element metals excluding alkaline earth metals and titanium.)
The second invention of the present application is the polyester film that further satisfies the following requirements (3) and (4).
(3) Phosphorus element content is 100 ppm or less with respect to polyester (4) TODΔ carboxy terminal amount represented by the following formula is 20 eq / ton or less (TODΔ carboxy terminal amount) = (thermal oxidation by the following) Carboxy terminal amount after test)-(Carboxy terminal amount before thermal oxidation test)
(Thermal oxidation test)
The polyester film sample is freeze-pulverized and then made into a powder of 100 mesh or less and vacuum dried at 130 ° C. for 12 hours. 0.3 g of this is weighed, put into a glass test tube, vacuum-dried at 70 ° C. for 12 hours, and then heat-treated at 230 ° C. for 15 minutes in air. The amount of carboxy terminus is measured for the sample before and after the heat treatment and the sample before the heat treatment.
3rd invention of this application is the said polyester film which satisfy | fills the following requirements (5) further.
(5) HSΔ carboxy terminal amount represented by the following formula is 10 eq / ton or less (HSΔ carboxy terminal amount) = (carboxy terminal amount after hydrolysis test) − (carboxy terminal amount before hydrolysis test) )
(Hydrolysis test)
The polyester film is cut into 1 cm × 1 cm pieces and vacuum-dried at 130 ° C. for 12 hours, and 1 g is weighed and put into 100 ml of pure water. This is sealed and heated for 6 hours at 130 ° C. under pressure. The amount of carboxy terminal is measured for the sample before and after the hydrolysis treatment and the sample before the hydrolysis treatment.
4th invention of this application is the said polyester film formed by adding a reactive terminal blocker in polyester.
5th invention of this application is the polyester film for solar cell backside sealing which consists of said polyester film.
6th invention of this application is the polyester film for electrical insulation which consists of the said polyester film.

  The polyester film for solar cells of the present invention is excellent in hydrolysis resistance and long-term thermal stability. Therefore, it is useful as a solar cell member used outdoors, for example, a base film for solar cell back surface sealing. Moreover, the manufacturing method of the polyester film for solar cells of this invention can provide the polyester for solar cells which has high durability with favorable productivity.

  The polyester film of the present invention is characterized in that the total metal element content which is the total amount of transition metal excluding alkali metal, alkaline earth metal, titanium and typical element metal is 150 ppm or less based on the polyester.

  Here, the alkali metal is Li, Na, K, Rb, Cs, and Fr, and the alkaline earth metal is Be, Mg, Ca, Sr, Ba, and Ra.

  The transition metals excluding titanium are Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, La, Hf, Ta, W, Re, Os, Ir, Pt, and Au are periodic table group 3 to group 11 metal elements, and typical element metals are Zn, Cd, Hg, Al, Ga, In, Tl, Ge, Sn, Pb, Sb, and Bi are represented.

  When a metal element other than the above elements is contained in the polyester, it can be a factor that promotes the thermal decomposition reaction of the polyester at a high temperature and causes thermal degradation of the polyester. Therefore, in the present invention, the content of metal elements excluding the above elements is set to 150 ppm or less from the viewpoint of maintaining the long-term thermal stability of the polyester film. Furthermore, the content of the metal element is preferably 100 ppm or less, more preferably 80 ppm or less, and further preferably 50 ppm or less. From the viewpoint of reducing the thermal degradation of the polyester, the content of the metal element is preferably small, but in order to promote the polymerization reaction during the production of the polyester, a transition metal or a typical metal element is used as a catalyst within the concentration range. It is desirable to add. Therefore, the lower limit of the content of the metal element is preferably 1 ppm or more, more preferably 5 ppm or more, and further preferably 10 ppm or more. From the viewpoint of polyester productivity, it is desirable to select an appropriate catalyst type as described later in order to achieve sufficient catalytic activity while being within the above-mentioned content range.

  Alkali metals and alkaline earth metals can be used as constituent elements of the catalyst or co-catalyst in the polymerization of polyester. Preferred element types and concentrations to be used in this case will be described later.

  Polyester polymerization methods include a transesterification method using a diester carboxylic acid component and a glycol component as starting materials, and a direct esterification method using a dicarboxylic acid component and a glycol component as starting materials. In the transesterification method, in order to ensure productivity, a catalyst such as Zn, Ca, Mg, etc. is added at the time of transesterification, so the concentration range may not be satisfied. Therefore, the polyester polymerization method in the present invention is a direct esterification method. preferable.

  The polymerization catalyst for polymerizing the polyester of the present invention is preferably not a heavy metal from the viewpoint of environmental burden, and more preferably aluminum and / or an aluminum compound from the viewpoint of polymerization activity and physical properties of the polyester.

  As the aluminum and / or aluminum compound, known aluminum compounds can be used in addition to metal aluminum.

  Specific examples of aluminum compounds include carboxylates such as aluminum formate, aluminum acetate, basic aluminum acetate, aluminum propionate, and aluminum oxalate; inorganic acid salts such as aluminum chloride, aluminum hydroxide, and aluminum hydroxide chloride; Aluminum alkoxides such as aluminum methoxide, aluminum ethoxide, aluminum iso-propoxide, aluminum n-butoxide, aluminum t-butoxide, aluminum chelate compounds such as aluminum acetylacetonate, aluminum acetylacetate, trimethylaluminum, triethylaluminum, etc. Examples thereof include organoaluminum compounds and partial hydrolysates thereof, and aluminum oxide. Of these, carboxylates, inorganic acid salts and chelate compounds are preferred, and among these, aluminum acetate, aluminum chloride, aluminum hydroxide, aluminum hydroxide chloride and aluminum acetylacetonate are particularly preferred.

  However, aluminum alone has a low polymerization activity, and in order to ensure productivity, it is necessary to add 150 ppm or more to all constituent units of carboxylic acid components such as polyester dicarboxylic acid and polycarboxylic acid. Therefore, in order to control the total metal element content to 150 ppm or less with respect to the polyester, it is preferable to add a phosphorus compound as a promoter for the purpose of increasing the polymerization activity.

  In this invention, it is preferable that the density | concentration of the phosphorus compound which should be used as said promoter is 100 ppm or less with respect to polyester as phosphorus element content. When the phosphorus element content with respect to the polyester exceeds the above range, the phosphorus compound may be incorporated into the main chain of the polyester in the polyester polymerization reaction, and the durability of the polyester may be lowered. The phosphorus element content relative to the polyester is more preferably 95 ppm or less, and even more preferably 90 ppm or less. When used as the cocatalyst, the polyester element content is preferably 1 ppm or more and more preferably 3 ppm or more for the purpose of increasing the polymerization activity. In addition, although the kind and the addition amount of the preferable phosphorus compound which should be used in this invention are mentioned later, it displays as an addition amount with respect to all the structural units of a carboxylic acid component as the addition amount of a phosphorus compound in that case. This is the amount added in anticipation of the amount disappearing during the polymerization reaction, and the phosphorus element content relative to the polyester after forming as a film is preferably within the above range.

  The phosphorus compound used as the co-catalyst is not particularly limited, but it is preferable to use one or two or more compounds selected from the group consisting of phosphonic acid compounds and phosphinic acid compounds because the effect of improving catalytic activity is great. Among these, when one or two or more phosphonic acid compounds are used, the effect of improving the catalytic activity is particularly large and preferable. Especially, the phosphorus compound which has a phenol part in the same molecule from the point of improving the thermal oxidation stability of polyester is especially preferable.

  The phosphonic acid compound and the phosphinic acid compound are compounds having structures represented by the following formulas (1) and (2), respectively.

  Examples of the phosphonic acid compounds include dimethyl methylphosphonate, diphenyl methylphosphonate, dimethyl phenylphosphonate, diethyl phenylphosphonate, diphenyl phenylphosphonate, dimethyl benzylphosphonate, diethyl benzylphosphonate, and the like.

  Examples of the phosphinic acid-based compound include diphenylphosphinic acid, methyl diphenylphosphinate, phenyl diphenylphosphinate, phenylphosphinic acid, methyl phenylphosphinate, and phenylphenylphosphinate.

  As the phosphinic acid compound, compounds represented by the following formulas (3) and (4) are preferably used.

  In the cocatalyst, among the phosphorus compounds, it is preferable to use a compound having an aromatic ring structure in the molecule in order to obtain sufficient catalytic activity.

  Moreover, as a phosphorus compound which comprises a promoter, when the compound represented by following General formula (5), (6) is used, especially the improvement effect of a catalyst activity is large and preferable.

(In the formulas (5) and (6), R ¹ and R ⁴ are each independently hydrogen, a hydrocarbon group having 1 to 50 carbon atoms, a hydroxyl group, a halogen group, an alkoxyl group, or an amino group and having 1 to 50 carbon atoms. R ² and R ³ each independently represent hydrogen, a hydrocarbon group having 1 to 50 carbon atoms, a hydrocarbon group having 1 to 50 carbon atoms including a hydroxyl group or an alkoxyl group, provided that each hydrocarbon group is a hydrocarbon group; May contain an alicyclic structure such as cyclohexyl or an aromatic ring structure such as phenyl or naphthyl.)

As the phosphorus compound constituting the promoter, a compound in which R ¹ and R ⁴ are groups having an aromatic ring structure in the above formulas (5) and (6) is particularly preferable.

  Examples of the phosphorus compound constituting the polycondensation catalyst include, for example, dimethyl methylphosphonate, diphenyl methylphosphonate, dimethyl phenylphosphonate, diethyl phenylphosphonate, diphenyl phenylphosphonate, dimethyl phosphophosphonate, diethyl benzylphosphonate, and diphenylphosphine. Examples include acid, methyl diphenylphosphinate, phenyl diphenylphosphinate, phenylphosphinic acid, methyl phenylphosphinate, and phenylphenylphosphinate. Of these, dimethyl phenylphosphonate and diethyl benzylphosphonate are particularly preferred.

  The addition amount as the phosphorus element is preferably 1 to 120 ppm, more preferably 3 to 100 ppm with respect to all constituent units of the carboxylic acid component such as dicarboxylic acid or polycarboxylic acid.

  As described above, the phosphorus compound as a cocatalyst particularly preferably has a phenol part in the same molecule from the viewpoint of improving the thermal oxidation stability of the polyester. The phosphorus compound having a phenol moiety constituting the promoter in the same molecule is not particularly limited as long as it is a phosphorus compound having a phenol structure, but is a phosphonic acid compound or phosphinic acid compound having a phenol moiety in the same molecule. When one or two or more compounds selected from the group consisting of compounds are used, the effect of improving the catalytic activity is greatly preferred. Among these, when a phosphonic acid compound having one or two or more phenol moieties in the same molecule is used, the effect of improving the catalytic activity is particularly large and preferable.

  Moreover, as a phosphorus compound which has the phenol part which comprises a promoter in the same molecule, the compound etc. which are represented by following General formula (7), (8) are mentioned. Among these, it is particularly preferable to use the following formula because catalytic activity is improved.

(In the formulas (7) and (8), R1 is a hydrocarbon group having 1 to 50 carbon atoms including a phenol part, a substituent such as a hydroxyl group, a halogen group, an alkoxyl group or an amino group, and 1 to 1 carbon atoms including a phenol part. Each represents a hydrocarbon group having 50. R ⁴ independently represents hydrogen, a hydrocarbon group having 1 to 50 carbon atoms, a hydrocarbon group having 1 to 50 carbon atoms containing a substituent such as a hydroxyl group, a halogen group, an alkoxyl group, or an amino group. R ² and R ³ each independently represents hydrogen, a hydrocarbon group having 1 to 50 carbon atoms, a hydrocarbon group having 1 to 50 carbon atoms including a substituent such as a hydroxyl group or an alkoxyl group. The hydrogen group may have a branched structure or the ends of cyclo R ² and R ⁴ may be bonded to each other.)

  Examples of the phosphorus compound having the phenol moiety in the same molecule include p-hydroxyphenylphosphonic acid, dimethyl p-hydroxyphenylphosphonate, diethyl p-hydroxyphenylphosphonate, diphenyl p-hydroxyphenylphosphonate, bis ( p-hydroxyphenyl) phosphinic acid, methyl bis (p-hydroxyphenyl) phosphinate, phenyl bis (p-hydroxyphenyl) phosphinate, p-hydroxyphenylphenylphosphinic acid, methyl p-hydroxyphenylphenylphosphinate, p-hydroxy Phenylphenylphosphinic acid phenyl, p-hydroxyphenylphosphinic acid, p-hydroxyphenylphosphinic acid methyl, p-hydroxyphenylphosphinic acid phenyl and the following formulas (9) to (12 Such a compound represented by the like. Among these, a compound represented by the following formula (11) and dimethyl p-hydroxyphenylphosphonate are particularly preferable.

  As the compound represented by the above formula (11), for example, SANKO-220 (manufactured by Sanko Co., Ltd.) can be used.

  By adding a phosphorus compound having these phenol moieties in the same molecule during the polymerization of the polyester, the catalytic activity of the aluminum compound is improved and the thermal stability of the polymerized polyester is also improved.

  The addition amount of the phosphorus compound having the phenol part in the same molecule is preferably 1 to 120 ppm, more preferably 3 to 100 ppm, based on all constituent units of the carboxylic acid component such as dicarboxylic acid or polycarboxylic acid. is there.

  Moreover, it is preferable to use a metal salt compound of phosphorus as the phosphorus compound. The phosphorus metal salt compound is not particularly limited as long as it is a metal salt of a phosphorus compound. However, it is preferable to use a metal salt of a phosphonic acid compound because of its large effect of improving the catalytic activity. Examples of the metal salt of the phosphorus compound include a monometal salt, a dimetal salt, and a trimetal salt.

  Further, among the above phosphorus compounds, when the metal part of the metal salt is selected from Li, Na, K, Be, Mg, Sr, Ba, Mn, Ni, Cu, Zn, the catalytic activity is improved. The effect is large and preferable. Of these, Li, Na, and Mg are particularly preferable.

  When at least one selected from the compounds represented by the following general formula (13) is used as the phosphorus metal salt compound, the effect of improving the catalytic activity is greatly preferred.

(In formula (13), R ¹ represents hydrogen, a hydrocarbon group having 1 to 50 carbon atoms, a hydroxyl group, a halogen group, an alkoxyl group, or an amino group, and a hydrocarbon group having 1 to 50 carbon atoms. R ² represents Represents hydrogen, a hydrocarbon group having 1 to 50 carbon atoms, a hydroxyl group or an alkoxyl group, and a hydrocarbon group having 1 to 50 carbon atoms, wherein R ³ represents hydrogen, a hydrocarbon group having 1 to 50 carbon atoms, a hydroxyl group or an alkoxyl group; Or a hydrocarbon group having 1 to 50 carbon atoms including carbonyl, l is an integer of 1 or more, m is 0 or an integer of 1 or more, (l + m) is 4 or less, and M is a (l + m) valence. Represents a metal cation, n represents an integer of 1 or more, and the hydrocarbon group may contain an alicyclic structure such as cyclohexyl, a branched structure, or an aromatic ring structure such as phenyl or naphthyl.

Examples of R ¹ include phenyl, 1-naphthyl, 2-naphthyl, 9-anthryl, 4-biphenyl, 2-biphenyl, and the like. Examples of R ² include hydrogen, methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group, long-chain aliphatic group, phenyl group, naphthyl group, Examples thereof include a substituted phenyl group, a naphthyl group, and a group represented by —CH ₂ CH ₂ OH. Examples of R ³ O ⁻ include hydroxide ions, alcoholate ions, acetate ions, and acetylacetone ions.

  Among the compounds represented by the general formula (13), it is preferable to use at least one selected from the compounds represented by the following general formula (14).

(In Formula (14), R ¹ represents hydrogen, a hydrocarbon group having 1 to 50 carbon atoms, a hydroxyl group, a halogen group, an alkoxyl group, or an amino group, and a hydrocarbon group having 1 to 50 carbon atoms. R ³ represents Hydrogen, a hydrocarbon group having 1 to 50 carbon atoms, a hydroxyl group or an alkoxyl group, or a hydrocarbon group having 1 to 50 carbon atoms including carbonyl, l is an integer of 1 or more, m is 0 or an integer of 1 or more, (L + m) is 4 or less, M represents a (l + m) -valent metal cation, and the hydrocarbon group may contain an alicyclic structure such as cyclohexyl, a branched structure, or an aromatic ring structure such as phenyl or naphthyl. )

Examples of R ¹ include phenyl, 1-naphthyl, 2-naphthyl, 9-anthryl, 4-biphenyl, 2-biphenyl, and the like. Examples of R ³ O ⁻ include hydroxide ions, alcoholate ions, acetate ions, and acetylacetone ions.

  Among the above phosphorus compounds, the use of a compound having an aromatic ring structure is preferable because the effect of improving the catalytic activity is great.

  Among the above formulas (14), it is preferable that M is selected from Li, Na, K, Be, Mg, Sr, Ba, Mn, Ni, Cu, and Zn because the effect of improving the catalytic activity is large. Of these, Li, Na, and Mg are particularly preferable.

  Examples of the metal salt compound of phosphorus include lithium [ethyl (1-naphthyl) methylphosphonate], sodium [ethyl (1-naphthyl) methylphosphonate], magnesium bis [ethyl (1-naphthyl) methylphosphonate], potassium [( 2-naphthyl) methyl phosphonate], magnesium bis [(2-naphthyl) methyl phosphonate], lithium [benzyl phosphonate], sodium [benzyl phosphonate], magnesium bis [benzyl phosphonate], beryllium bis [ Benzyl phosphonate], strontium bis [benzyl phosphonate], manganese bis [benzyl phosphonate], sodium benzyl phosphonate, magnesium bis [benzyl phosphonate], sodium [(9-anthry ) Ethyl methylphosphonate], magnesium bis [(9-anthryl) methylphosphonate ethyl], sodium [ethyl 4-hydroxybenzylphosphonate], magnesium bis [4-hydroxybenzylphosphonate ethyl], sodium [4-chlorobenzylphosphonic acid] Phenyl], magnesium bis [ethyl 4-chlorobenzylphosphonate], sodium [methyl 4-aminobenzylphosphonate], magnesium bis [methyl 4-aminobenzylphosphonate], sodium phenylphosphonate, magnesium bis [ethyl phenylphosphonate] ], Zinc bis [ethyl phenylphosphonate] and the like.

  Among these, lithium [ethyl (1-naphthyl) methylphosphonate], sodium [ethyl (1-naphthyl) methylphosphonate], magnesium bis [ethyl (1-naphthyl) methylphosphonate], lithium [ethyl benzylphosphonate], Sodium [ethyl benzylphosphonate], magnesium bis [ethyl benzylphosphonate], sodium benzylphosphonate, magnesium bis [benzylphosphonic acid] are particularly preferred.

  The metal salt compound of phosphorus which is another preferable phosphorus compound constituting the polycondensation catalyst is composed of at least one selected from compounds represented by the following general formula (15).

(In the formula ^{(15), R 1, R} 2 are each independently hydrogen, .R ³ representing a hydrocarbon group having 1 to 30 carbon atoms, hydrogen, a hydrocarbon group having 1 to 50 carbon atoms, a hydroxyl group or an alkoxyl group R ⁴ represents a hydrocarbon group having 1 to 50 carbon atoms, including hydrogen, a hydrocarbon group having 1 to 50 carbon atoms, a hydroxyl group, an alkoxyl group, or a carbonyl group. Examples of R ⁴ O ⁻ include hydroxide ion, alcoholate ion, acetate ion, acetylacetone ion, etc. l represents an integer of 1 or more, m represents 0 or an integer of 1 or more, and (l + m) represents 4 or less. M represents a (l + m) -valent metal cation, n represents an integer of 1 or more, and the hydrocarbon group contains an alicyclic structure such as cyclohexyl, a branched structure, or an aromatic ring structure such as phenyl or naphthyl. Moyo .)

  Among these, it is preferable to use at least one selected from compounds represented by the following general formula (16).

(In the formula (16), M ^{n +} represents an n-valent metal cation. N represents 1, 2, 3 or 4.)

  Among the above formulas (15) or (16), when M is selected from Li, Na, K, Be, Mg, Sr, Ba, Mn, Ni, Cu, and Zn, the effect of improving the catalytic activity is obtained. Largely preferred. Of these, Li, Na, and Mg are particularly preferable.

  Examples of the metal salt compound of the specific phosphorus include lithium [ethyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate], sodium [3,5-di-tert-butyl-4-hydroxybenzylphosphone]. Ethyl], sodium [3,5-di-tert-butyl-4-hydroxybenzylphosphonic acid], potassium [ethyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonic acid], magnesium bis [3, 5-di-tert-butyl-4-hydroxybenzylphosphonic acid ethyl], magnesium bis [3,5-di-tert-butyl-4-hydroxybenzylphosphonic acid], beryllium bis [3,5-di-tert-butyl -Methyl 4-hydroxybenzylphosphonate], strontium bis [3,5-di-tert-butyl-4-hydroxybenzylphosphonate ethyl], barium bis [3,5-di-tert-butyl] -Phenyl-4-hydroxybenzylphosphonate], manganese bis [3,5-di-tert-butyl-4-hydroxybenzylphosphonate ethyl], nickel bis [3,5-di-tert-butyl-4-hydroxybenzylphosphone] Ethyl acrylate], copper bis [ethyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate], zinc bis [ethyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate] and the like. It is done. Among these, lithium [ethyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate], sodium [ethyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate], magnesium bis [ Ethyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate] is particularly preferred.

  Another embodiment of the present invention is a polyester polymerization catalyst comprising at least one selected from aluminum salts of phosphorus compounds. You may use combining the aluminum salt of a phosphorus compound with another aluminum compound, a phosphorus compound, a phenol type compound, etc.

  The aluminum salt of the phosphorus compound, which is a preferred component constituting the polycondensation catalyst, is not particularly limited as long as it is a phosphorus compound having an aluminum part, but the use of an aluminum salt of a phosphonic acid compound improves the catalytic activity. Is preferable. Examples of the aluminum salt of the phosphorus compound include a monoaluminum salt, a dialuminum salt, and a trialuminum salt.

  Among the aluminum salts of the phosphorus compounds, the use of a compound having an aromatic ring structure is preferable because the effect of improving the catalytic activity is great.

  As the aluminum salt of the phosphorus compound constituting the polymerization catalyst, at least one selected from the compounds represented by the following general formula (17) is preferably used because the effect of improving the catalytic activity is great.

(In Formula (17), R ¹ represents hydrogen, a hydrocarbon group having 1 to 50 carbon atoms, a hydroxyl group, a halogen group, an alkoxyl group, or an amino group, and a hydrocarbon group having 1 to 50 carbon atoms. R ² represents Represents hydrogen, a hydrocarbon group having 1 to 50 carbon atoms, a hydroxyl group or an alkoxyl group, and a hydrocarbon group having 1 to 50 carbon atoms, wherein R ³ represents hydrogen, a hydrocarbon group having 1 to 50 carbon atoms, a hydroxyl group or an alkoxyl group; Or it represents a C1-C50 hydrocarbon group containing carbonyl, l represents an integer of 1 or more, m represents 0 or an integer of 1 or more, and (l + m) represents 3. n represents an integer of 1 or more. The hydrocarbon group may contain an alicyclic structure such as cyclohexyl, a branched structure, or an aromatic ring structure such as phenyl or naphthyl.)

Examples of R ¹ include phenyl, 1-naphthyl, 2-naphthyl, 9-anthryl, 4-biphenyl, 2-biphenyl, and the like. Examples of R ² include hydrogen, methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group, long-chain aliphatic group, phenyl group, naphthyl group, Examples thereof include a substituted phenyl group, a naphthyl group, and a group represented by —CH ₂ CH ₂ OH. Examples of R ³ O ⁻ include hydroxide ions, alcoholate ions, ethylene glycolate ions, acetate ions, and acetylacetone ions.

  Examples of the aluminum salt of the phosphorus compound include an aluminum salt of ethyl (1-naphthyl) methylphosphonate, an aluminum salt of (1-naphthyl) methylphosphonic acid, an aluminum salt of ethyl (2-naphthyl) methylphosphonate, and an ethyl benzylphosphonate. Aluminum salt, Aluminum salt of benzylphosphonic acid, Aluminum salt of ethyl (9-anthryl) methylphosphonate, Aluminum salt of ethyl 4-hydroxybenzylphosphonate, Aluminum salt of ethyl 2-methylbenzylphosphonate, 4-Chlorobenzylphosphonic acid Examples thereof include an aluminum salt of phenyl, an aluminum salt of methyl 4-aminobenzylphosphonate, an aluminum salt of ethyl 4-methoxybenzylphosphonate, and an aluminum salt of ethyl phenylphosphonate.

  Among these, an aluminum salt of ethyl (1-naphthyl) methylphosphonate and an aluminum salt of ethyl benzylphosphonate are particularly preferable.

  Another embodiment is a polyester polymerization catalyst comprising at least one selected from aluminum salts of phosphorus compounds represented by the following general formula (18). The aluminum salt of the phosphorus compound may be used in combination with other aluminum compounds, phosphorus compounds, phenolic compounds, and the like.

(In the formula (18), R ¹ and R ² each independently represent hydrogen and a hydrocarbon group having 1 to 30 carbon atoms. R ³ represents hydrogen, a hydrocarbon group having 1 to 50 carbon atoms, a hydroxyl group or an alkoxyl group. R ⁴ represents a hydrocarbon group having 1 to 50 carbon atoms, including hydrogen, a hydrocarbon group having 1 to 50 carbon atoms, a hydroxyl group, an alkoxyl group, or a carbonyl group. l represents an integer of 1 or more, m represents 0 or an integer of 1 or more, and (l + m) represents 3. n represents an integer of 1 or more, and the hydrocarbon group is an alicyclic structure such as cyclohexyl, a branched structure, or phenyl. Or may contain an aromatic ring structure such as naphthyl.)

  Among these, it is preferable to use at least one selected from compounds represented by the following general formula (19).

(In formula (19), R ³ represents hydrogen, a hydrocarbon group having 1 to 50 carbon atoms, a hydrocarbon group having 1 to 50 carbon atoms including a hydroxyl group or an alkoxyl group. R ⁴ represents hydrogen and 1 carbon atom. Represents a hydrocarbon group having 1 to 50 carbon atoms, including 1 to 50 hydrocarbon group, hydroxyl group or alkoxyl group, or carbonyl, l represents an integer of 1 or more, m represents 0 or an integer of 1 or more, and (l + m) represents 3 The hydrocarbon group may contain an alicyclic structure such as cyclohexyl, a branched structure, or an aromatic ring structure such as phenyl or naphthyl.)

Examples of R ³ include hydrogen, methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group, long-chain aliphatic group, phenyl group, and naphthyl group. A substituted phenyl group, a naphthyl group, a group represented by —CH ₂ CH ₂ OH, and the like. Examples of R ⁴ O ⁻ include hydroxide ions, alcoholate ions, ethylene glycolate ions, acetate ions, and acetylacetone ions.

  Examples of the aluminum salt of the phosphorus compound include aluminum salt of ethyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate, aluminum of methyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate. Salt, aluminum salt of isopropyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate, aluminum salt of phenyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate, 3,5-di- Examples thereof include an aluminum salt of tert-butyl-4-hydroxybenzylphosphonic acid.

  Among these, an aluminum salt of ethyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate and an aluminum salt of methyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate are particularly preferable.

  Moreover, it is preferable to use a phosphorus compound having at least one P—OH bond as the phosphorus compound. The phosphorus compound having at least one P—OH bond is not particularly limited as long as it is a phosphorus compound having at least one P—OH in the molecule. Among these phosphorus compounds, the use of a phosphonic acid compound having at least one P—OH bond is preferable because the effect of improving the catalytic activity is great.

  Among the above phosphorus compounds, the use of a compound having an aromatic ring structure is preferable because the effect of improving the catalytic activity is great.

  When at least one selected from the compounds represented by the following general formula (20) is used as the phosphorus compound having at least one P-OH bond constituting the polycondensation catalyst, the effect of improving the catalytic activity is greatly preferred. .

(In Formula (20), R ¹ represents hydrogen, a hydrocarbon group having 1 to 50 carbon atoms, a hydroxyl group, a halogen group, an alkoxyl group, or an amino group, and a hydrocarbon group having 1 to 50 carbon atoms. R ² represents Represents a hydrocarbon group having 1 to 50 carbon atoms including hydrogen, a hydrocarbon group having 1 to 50 carbon atoms, a hydroxyl group or an alkoxyl group, n represents an integer of 1 or more, and the hydrocarbon group represents an alicyclic structure such as cyclohexyl, It may contain a branched structure or an aromatic ring structure such as phenyl or naphthyl.)

Examples of R ¹ include phenyl, 1-naphthyl, 2-naphthyl, 9-anthryl, 4-biphenyl, 2-biphenyl, and the like. Examples of R ² include hydrogen, methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group, long-chain aliphatic group, phenyl group, naphthyl group, Examples thereof include a substituted phenyl group, a naphthyl group, and a group represented by —CH ₂ CH ₂ OH.

  Among the above phosphorus compounds, the use of a compound having an aromatic ring structure is preferable because the effect of improving the catalytic activity is great.

  Examples of phosphorus compounds having at least one P—OH bond include ethyl (1-naphthyl) methylphosphonate, (1-naphthyl) methylphosphonic acid, ethyl (2-naphthyl) methylphosphonate, ethyl benzylphosphonate, benzylphosphonic acid, 9-anthryl) methylphosphonic acid ethyl, 4-hydroxybenzylphosphonic acid ethyl, 2-methylbenzylphosphonic acid ethyl, 4-chlorobenzylphosphonic acid phenyl, 4-aminobenzylphosphonic acid methyl, 4-methoxybenzylphosphonic acid ethyl etc. It is done. Of these, ethyl (1-naphthyl) methylphosphonate and ethyl benzylphosphonate are particularly preferred.

  A preferable phosphorus compound includes a specific phosphorus compound having at least one P-OH bond. The specific phosphorus compound having at least one P—OH bond, which is a preferable phosphorus compound constituting the polycondensation catalyst, means at least one compound selected from the compounds represented by the following general formula (21). To do.

(In formula (21), R ¹ and R ² each independently represent hydrogen and a hydrocarbon group having 1 to 30 carbon atoms. R ³ represents hydrogen, a hydrocarbon group having 1 to 50 carbon atoms, a hydroxyl group or an alkoxyl group. And n represents an integer of 1 or more, even if the hydrocarbon group contains an alicyclic structure such as cyclohexyl, a branched structure, or an aromatic ring structure such as phenyl or naphthyl. Good.)

  Among these, it is preferable to use at least one selected from compounds represented by the following general formula (22).

(In the formula (22), R ³ represents hydrogen, a hydrocarbon group having 1 to 50 carbon atoms, a hydrocarbon group having 1 to 50 carbon atoms including a hydroxyl group or an alkoxyl group. The hydrocarbon group is an alicyclic ring such as cyclohexyl. It may contain a structure, a branched structure, or an aromatic ring structure such as phenyl or naphthyl.)

Examples of R ³ include hydrogen, methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group, long-chain aliphatic group, phenyl group, and naphthyl group. A substituted phenyl group, a naphthyl group, a group represented by —CH ₂ CH ₂ OH, and the like.

  Specific phosphorus compounds having at least one P—OH bond include ethyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate, 3,5-di-tert-butyl-4-hydroxybenzyl. Methyl phosphonate, isopropyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate, phenyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate, 3,5-di-tert-butyl- Examples include octadecyl 4-hydroxybenzylphosphonate, 3,5-di-tert-butyl-4-hydroxybenzylphosphonic acid, and the like. Of these, ethyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate and methyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate are particularly preferred.

  A preferable phosphorus compound includes a phosphorus compound represented by the chemical formula (23).

(In the formula (23), R ¹ represents a hydrocarbon group having ¹ to 49 carbon atoms, or a hydrocarbon group having ¹ to 49 carbon atoms including a hydroxyl group, a halogen group, an alkoxyl group, or an amino group, and R ² , R ³ Each independently represents a hydrocarbon group having 1 to 50 carbon atoms including hydrogen, a hydrocarbon group having 1 to 50 carbon atoms, a hydroxyl group or an alkoxyl group, and the hydrocarbon group includes an alicyclic structure, a branched structure or an aromatic ring structure. You may go out.)

More preferably, at least one of R ¹ , R ² and R ^{3 in} the chemical formula (23) is a compound containing an aromatic ring structure.

  Specific examples of the phosphorus compound are shown below.

  The phosphorus compound having a large molecular weight is more preferable because it is less likely to be distilled off during polymerization.

  Another phosphorus compound that is preferably used as the polycondensation catalyst is at least one phosphorus compound selected from compounds represented by the following general formula (30).

(In the above formula (30), R ¹ and R ² each independently represent hydrogen and a hydrocarbon group having 1 to 30 carbon atoms. R ³ and R ⁴ each independently represent hydrogen and a hydrocarbon having 1 to 50 carbon atoms. Represents a hydrocarbon group having 1 to 50 carbon atoms including a group, a hydroxyl group or an alkoxyl group, n represents an integer of 1 or more, and the hydrocarbon group represents an alicyclic structure such as cyclohexyl, a branched structure, or an aromatic ring such as phenyl or naphthyl. May contain structure.)

  Among the general formula (30), it is preferable to use at least one selected from the compounds represented by the following general formula (31) because the effect of improving the catalytic activity is high.

(In said formula (31), R < ³ >, R < ⁴ > represents a C1-C50 hydrocarbon group containing hydrogen, a C1-C50 hydrocarbon group, a hydroxyl group, or an alkoxyl group each independently. Hydrocarbon group. May contain an alicyclic structure such as cyclohexyl, a branched structure, or an aromatic ring structure such as phenyl or naphthyl.)

Examples of R ³ and R ⁴ include short chain aliphatic groups such as hydrogen, methyl and butyl groups, long chain aliphatic groups such as octadecyl, phenyl groups, naphthyl groups, substituted phenyl groups and naphthyl groups. An aromatic group such as a group, a group represented by —CH ₂ CH ₂ OH, and the like.

  Examples of the specific phosphorus compound include diisopropyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate, di-n-butyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate, 3 , 5-di-tert-butyl-4-hydroxybenzylphosphonate dioctadecyl, 3,5-di-tert-butyl-4-hydroxybenzylphosphonate diphenyl, and the like.

  Of these, dioctadecyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate and diphenyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate are particularly preferred.

  Another phosphorus compound that is preferably used as the polycondensation catalyst is at least one phosphorus compound selected from compounds represented by chemical formula (32) and chemical formula (33).

  As the compound represented by the chemical formula (32), Irganox 1222 (manufactured by Ciba Specialty Chemicals) is commercially available. Moreover, Irganox1425 (made by Ciba Specialty Chemicals) is marketed as a compound shown by Chemical formula (33).

  Phosphorus compounds are generally well known as antioxidants, but it is not known that melt polymerization is greatly promoted when these phosphorus compounds are used in combination with conventional metal-containing polyester polymerization catalysts. Actually, even when a phosphorus compound is added to melt-polymerize polyester using a polymerization catalyst of an antimony compound, titanium compound, tin compound or germanium compound, which is a typical catalyst for polyester polymerization, to a substantially useful level. It is not observed that polymerization is accelerated.

  That is, by using the phosphorus compound in combination, a sufficient catalytic effect can be exhibited even if the content of aluminum in the polyester polymerization catalyst is small.

  The addition amount as the phosphorus element is preferably 1 to 120 ppm, and more preferably 3 to 100 ppm, based on the number of moles of all constituent units of the dicarboxylic acid component. When the addition amount of the phosphorus compound is 1 ppm, the addition effect may not be exhibited. On the other hand, if it exceeds 120 ppm, the catalytic activity as a polyester polymerization catalyst may be reduced. Further, the tendency of the change varies depending on the amount of aluminum added.

  By using aluminum compound as the main catalyst component without using a phosphorus compound, reducing the amount of aluminum compound added, and adding a cobalt compound, coloring due to a decrease in thermal stability when using an aluminum compound as the main catalyst Although it has been studied to prevent the thermal stability, the addition of the cobalt compound to the extent that it has sufficient catalytic activity also reduces the thermal stability. Therefore, it is difficult to make both compatible with this technique.

  By using the phosphorus compound having the above specific chemical structure, polycondensation does not cause problems such as deterioration of thermal stability and generation of foreign matter, and has a sufficient catalytic effect even if the addition amount of the metal-containing component as aluminum is small. A catalyst is obtained, and the thermal oxidation stability of the polyester film after melt molding is improved by using the polyester polymerized by the polycondensation catalyst.

  Moreover, even if it replaces with the said phosphorus compound and phosphoric acid esters, such as phosphoric acid and a trimethyl phosphoric acid, are added, the said addition effect is not seen. Furthermore, even if the above phosphorus compound is used in combination with a metal-containing polyester polycondensation catalyst such as a conventional antimony compound, titanium compound, tin compound, and germanium compound within the range of the preferable addition amount, the melt polymerization reaction is promoted. The effect is not recognized.

  On the other hand, in the present invention, in addition to aluminum or its compound, a small amount of alkali metal, alkaline earth metal and at least one selected from the compound may coexist as the second metal-containing component. The coexistence of such a second metal-containing component in the catalyst system is effective in improving productivity by obtaining a catalyst component having an increased reaction rate in addition to an effect of suppressing the formation of diethylene glycol, and thus a higher reaction rate. .

  A technique of adding an alkali metal compound or an alkaline earth metal compound to an aluminum compound to obtain a catalyst having sufficient catalytic activity is known. A known catalyst using an alkali metal compound or an alkaline earth metal compound is required to increase the amount of catalyst added to obtain a practical catalytic activity, and thus the hydrolyzability and thermal stability required in the present invention. Can not be compatible.

  When an alkali metal compound is used in combination, the amount of foreign matters resulting therefrom increases, and the frequency of filter replacement tends to be shortened or film defects tend to increase in the melt extrusion process during film production.

  In addition, when an alkaline earth metal compound is used in combination, when the practical activity is obtained, the thermal stability and thermal oxidation stability of the obtained polyester is lowered, coloring due to heating is large, and foreign matter is generated. The amount also increases.

  When an alkali metal, an alkaline earth metal, or a compound thereof coexisting as the second metal-containing component is added, the addition amount thereof is 1 ppm or more and 50 ppm or less with respect to all carboxylic acid units constituting the polyester. It is preferably 1 ppm to 40 ppm, more preferably 1 ppm to 30 ppm, and particularly preferably 1 to 25 ppm.

  Within the above range, the addition amount of alkali metal or alkaline earth metal is small, so the reaction rate can be increased without causing problems such as thermal stability degradation, generation of foreign matter, and coloring. is there. In addition, problems such as degradation of hydrolysis resistance do not occur.

  When the added amount of alkali metal, alkaline earth metal, or compound thereof is 50 ppm or more with respect to all carboxylic acid units constituting the polyester, thermal stability decreases, foreign matter generation and coloring increase, and hydrolysis resistance decreases. May cause problems in product processing. If the amount of alkali metal, alkaline earth metal, or compound thereof added is less than 1 ppm with respect to all carboxylic acid units constituting the polyester, the effect is not clear even if added.

  The alkali metal or alkaline earth metal constituting the second metal-containing component preferably used in addition to aluminum as a catalyst or a compound thereof includes Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr. And at least one selected from Ba, and the use of an alkali metal or a compound thereof is more preferable.

  When an alkali metal or a compound thereof is used, Li, Na, and K are particularly preferable as the alkali metal. Examples of the alkali metal and alkaline earth metal compounds include saturated aliphatic carboxylates such as formic acid, acetic acid, propionic acid, butyric acid, and succinic acid, and unsaturated aliphatic carboxylates such as acrylic acid and methacrylic acid. , Aromatic carboxylates such as benzoic acid, halogen-containing carboxylates such as trichloroacetic acid, hydroxycarboxylates such as lactic acid, citric acid and salicylic acid, carbonic acid, sulfuric acid, nitric acid, phosphoric acid, phosphonic acid, hydrogen carbonate, phosphorus Inorganic acid salts such as acid hydrogen, hydrogen sulfide, sulfurous acid, thiosulfuric acid, hydrochloric acid, hydrobromic acid, chloric acid and bromic acid, and organic sulfonates such as 1-propanesulfonic acid, 1-pentanesulfonic acid and naphthalenesulfonic acid , Organic sulfates such as lauryl sulfate, methoxy, ethoxy, n-propoxy, iso-propoxy, n-butoxy, tert-butyl Alkoxides such as alkoxy, chelate compounds and the like acetylacetonate, hydrides, oxides, and hydroxides and the like.

  Among these alkali metals, alkaline earth metals or their compounds, when using strongly alkaline ones such as hydroxides, these tend to be difficult to dissolve in diols such as ethylene glycol or organic solvents such as alcohols. However, it must be added to the polymerization system in an aqueous solution, which may cause a problem in the polymerization process.

  Furthermore, when using strongly alkaline substances such as hydroxides, the polyester is liable to undergo side reactions such as hydrolysis during polymerization, and the polymerized polyester tends to be colored, and the hydrolysis resistance also decreases. Tend to.

  Accordingly, the alkali metal or the compound thereof, the alkaline earth metal or the compound thereof is preferably a saturated aliphatic carboxylate, unsaturated aliphatic carboxylate or aromatic carboxylate of the alkali metal or alkaline earth metal. , Halogen-containing carboxylate, hydroxycarboxylate, sulfuric acid, nitric acid, phosphoric acid, phosphonic acid, hydrogen phosphate, hydrogen sulfide, sulfurous acid, thiosulfuric acid, hydrochloric acid, hydrobromic acid, chloric acid, bromic acid Acid salts, organic sulfonates, organic sulfates, chelate compounds, and oxides. Among these, from the viewpoint of ease of handling, availability, and the like, it is preferable to use an alkali metal or alkaline earth metal saturated aliphatic carboxylate, particularly acetate.

Since the polyester which is the main constituent of the polyester film of the present invention can be suitably obtained using the above-mentioned catalyst species, the total amount of metal elements relative to the polyester can be made 150 ppm or less. Therefore, the polyester film of the present invention is excellent in thermal oxidation stability and can exhibit long-term thermal stability. The polyester used in the polyester film of the present invention preferably has a TODΔ carboxy terminal amount represented by the following formula, which is an index of thermal oxidation stability, of 20 eq / ton or less.
(TODΔ carboxy terminal amount) = (carboxy terminal amount after thermal oxidation test by the following) − (carboxy terminal amount before thermal oxidation test)
(Thermal oxidation test)
The polyester film sample is freeze-pulverized and then made into a powder of 100 mesh or less and vacuum dried at 130 ° C. for 12 hours. 0.3 g of this is weighed, put into a glass test tube, vacuum-dried at 70 ° C. for 12 hours, and then heat-treated at 230 ° C. for 15 minutes in air. The carboxy terminal amount is measured for the sample before and after the heat treatment and the sample before the heat treatment.

  The amount of the TODΔ carboxy terminal is more preferably 15 or less, still more preferably 10 or less, and still more preferably 5 or less. The lower the total metal content, the more advantageous the thermal oxidation stability. However, when the metal content is small, that is, the catalyst amount is small, it is disadvantageous in terms of productivity. Therefore, it is preferable to use a small amount of aluminum and a phosphorus compound as a cocatalyst to ensure polymerization activity. Further, the phosphorus compound preferably has a phenol moiety. Furthermore, a phosphorus moiety-containing phosphorus compound is particularly preferable because it has an effect of suppressing polyester degradation that decomposes under a radical mechanism under oxygen. In order to enhance this function, it is preferable that the phenol moiety has a hindered phenol skeleton that is sterically and electronically stabilized and expresses more radical trapping ability. In addition, although the one where the said TOD (DELTA) carboxy terminal amount is smaller is preferable, about 0.1 is considered to be a minimum.

  Polyester, which is the main constituent of the film of the present invention, can also use titanium as a catalyst. Even when titanium is used as a catalyst, productivity can be ensured with a small addition amount of 150 ppm or less. However, since titanium has high catalytic activity, thermal oxidation deterioration of the polyester tends to occur under heating, and long-term thermal stability is obtained. It may not be possible. Therefore, in the present invention, it is preferable to use the above-mentioned catalyst species other than titanium as the polyester catalyst species. In addition, it is also preferable to add a titanium oxide to the film of this invention in order to provide easy slipperiness or concealment property so that it may mention later. In this case, unlike the amount of titanium added used as a catalyst, the amount of titanium element is preferably 300 ppm or more, more preferably 400 ppm or more for imparting slipperiness, and the amount of titanium element is preferably 10,000 ppm for imparting concealment. The above titanium oxide is added. Whether titanium is used as a catalyst or used for other purposes can be distinguished by the amount of titanium added.

  The polyester constituting the polyester film of the present invention is characterized in that the carboxy terminal amount is 5 eq / ton or less with respect to the polyester. Thus, the film of this invention can show high hydrolysis resistance by making carboxy terminal amount into such minimum density | concentration. When the amount of the carboxy terminal exceeds the above range, the carboxy terminal becomes a proton source and self-acts and hydrolysis resistance decreases, so that sufficient durability cannot be obtained for solar cell back surface sealing or electrical insulation. There is.

  The upper limit of the carboxy terminal amount is preferably 4 eq / ton or less, more preferably 3 eq / ton or less, and still more preferably 2 eq / ton or less. A smaller amount of the carboxy terminus is preferable, but from the viewpoint of productivity, 0.1 eq / ton is considered to be the lower limit.

  The means for setting the carboxy terminal amount of the polyester in the above range is not particularly limited, but (1) a method for obtaining a polyester having a high degree of polymerization by appropriately selecting conditions such as the time and temperature of the polymerization reaction, and (2) a solid phase. A method of performing polymerization, (3) a method of reducing the moisture content of the polyester, (4) a method of modifying the carboxy terminal of the polyester with a reactive terminal blocking agent, and the like can be appropriately selected and combined. It is possible to reduce the amount of carboxy terminals by increasing the degree of polymerization of polyester, but the inherent viscosity of polyester also increases, so high stress is required during film formation, and heat is generated in the melt extruder. Thermal degradation may occur. Therefore, in order to prevent the intrinsic viscosity from being increased and the carboxy terminal amount to be in the above range, it is preferable to modify the carboxy terminal of the polyester with a reactive terminal blocking agent.

  The reactive end-capping agent is a compound that reacts with a carboxy end group of a polyester to modify the carboxy group. The reactive end-capping agent is not particularly limited as long as it has the effect, but from the viewpoint of high reactivity and ease of handling, a compound selected from the group consisting of carbodiimide compounds, oxazoline compounds and epoxy compounds Can be suitably used.

  Specific examples of the carbodiimide compound include di-o-toluyl-carbodiimide, di- (2,4-diisopropyl) phenyl-carbodiimide, p-phenylene-bis- (2,6-xylyl-carbodiimide), p-phenylene-bis. -(T-butyl-carbodiimide), tetramethylene-bis- (t-butyl-carbodiimide), cyclohexane-1,4-bis- (methylene-t-butyl-carbodiimide), ortho-2,4-toluyl-carbodiimide, Examples include Carbodilite (LA-1) manufactured by Nisshinbo Chemical Co., Ltd., Stabuzol manufactured by Rhein Chemie, Stabuzol P, Stabuzol P100, Stabuzol P400, Stabuzol KE7646, etc., but are limited to these in the present invention. It is not a thing.

  Specific examples of the oxazoline compound include, for example, 2-methoxy-2-oxazoline, 2-ethoxy-2-oxazoline, 2-propoxy-2-oxazoline, 2-butoxy-2-oxazoline, 2-pentyloxy-2-oxazoline. 2-hexyloxy-2-oxazoline, 2-heptyloxy-2-oxazoline, 2-octyloxy-2-oxazoline, 2-nonyloxy-2-oxazoline, 2-decyloxy-2-oxazoline, 2-cyclopentyloxy-2 -Oxazoline, 2-cyclohexyloxy-2-oxazoline, 2-allyloxy-2-oxazoline, 2-methallyloxy-2-oxazoline, 2-crotyloxy-2-oxazoline, 2-phenoxy-2-oxazoline, 2-cresyl- 2-oxazoline, -O-ethylphenoxy-2-oxazoline, 2-o-propylphenoxy-2-oxazoline, 2-o-phenylphenoxy-2-oxazoline, 2-m-ethylphenoxy-2-oxazoline, 2-m-propylphenoxy- 2-oxazoline, 2-p-phenylphenoxy-2-oxazoline, 2-methyl-2-oxazoline, 2-ethyl-2-oxazoline, 2-propyl-2-oxazoline, 2-butyl-2-oxazoline, 2-pentyl 2-oxazoline, 2-hexyl-2-oxazoline, 2-heptyl-2-oxazoline, 2-octyl-2-oxazoline, 2-nonyl-2-oxazoline, 2-decyl-2-oxazoline, 2-cyclopentyl-2 -Oxazoline, 2-cyclohexyl-2-oxazoline, 2-ali -2-oxazoline, 2-methallyl-2-oxazoline, 2-crotyl-2-oxazoline, 2-phenyl-2-oxazoline, 2-o-ethylphenyl-2-oxazoline, 2-o-propylphenyl-2-oxazoline , 2-o-phenylphenyl-2-oxazoline, 2-m-ethylphenyl-2-oxazoline, 2-m-propylphenyl-2-oxazoline, 2-p-phenylphenyl-2-oxazoline, and the like. Are 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-oxazoline) ), 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 Screw (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'-tetramethylene Bis (4,4′-dimethyl-2-oxazoline), 2,2′-9,9′-diphenoxyethanebis (2-oxazoline), 2,2′-cyclohexylenebis (2-oxazoline), 2, Examples thereof include 2′-diphenylenebis (2-oxazoline), Nippon Shokubai Epochros Co., Ltd. and the like. Furthermore, a polyoxazoline compound containing the above-described compound as a monomer unit, such as a styrene-2-isopropenyl-2-oxazoline copolymer, may be mentioned, but the invention is not limited thereto.

  Specific examples of the epoxy compound include diallyl monoglycidyl isocyanuric acid, monoallyl diglycidyl isocyanuric acid, sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, diglycerol polyglycidyl ether, glycerol polyglycidyl ether, Methylolpropane polyglycidyl ether, resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, hydrogenated bisphenol-A-diglycidyl ether, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, Propylene glycol diglycidyl ether, polypropylene glycol Diglycidyl ether, allyl glycidyl ether, 2-ethylhexyl glycidyl ether, phenyl glycidyl ether, phenol glycidyl ether, p-tert-butylphenyl glycidyl ether, lauryl alcohol glycidyl ether, polybutadiene diglycidyl ether, diglycidyl-o-phthalate, hydroquinone di Glycidyl ether, diglycidyl terephthalate, N-glycidyl phthalimide, dibromophenyl glycidyl ether, dibromoneopentyl glycol diglycidyl ether, resorcin diglycidyl ether, acrylic glycidyl ether, sorbitan polyglycidyl ether, bisphenol-A-diglycidyl ester, bisphenol-S -Diglycidyl ether, dimer Diglycidyl ester, p- hydroxy benzoic acid glycidyl ester ether and the like, but not limited to the present invention. Further, when adding the epoxy compound, it is preferable to add a catalyst such as triphenylphosphine.

  In order to effectively perform the end-capping reaction, the moisture content of the carbodiimide compound, oxazoline compound and epoxy compound added to the polyester is preferably 1000 ppm or less. More preferably, the moisture content of the compound is 800 ppm or less, and particularly preferably 500 ppm or less. Although the moisture content of the carbodiimide compound, the oxazoline compound, and the epoxy compound can be reduced by the drying process, it is desirable that it is a solid from the viewpoint of handling in the drying process.

  Moreover, it is preferable that the addition amount of a reactive terminal blocker is 0.1-10 equivalent with respect to the carboxy terminal amount of polyester in a reactive group unit. When the addition amount is 0.1 equivalent or less, it does not function as a terminal blocking agent and the hydrolyzability cannot be improved. When the addition amount exceeds 10 equivalents, in the case of polyfunctional carbodiimide compounds, oxazoline compounds, and epoxy compounds, gelation may occur and the back pressure during film formation may increase. Even in the case of a compound having only one functional group, there are many unreacted functional groups in the film, which may adversely affect subsequent processes. A more preferable addition amount is 0.2 to 7 equivalents with respect to the carboxy terminal amount of the polyester, and a particularly preferable addition amount is 0.3 to 5 equivalents with respect to the carboxy terminal amount of the polyester.

  In addition to adding a carbodiimide compound, an oxazoline compound and an epoxy compound, it is preferable to add an antioxidant. Antioxidants are effective when used in combination with the above compounds. Although the mechanism is not clarified, it is considered that the hydrolysis resistance and the heat discoloration resistance are improved by the antioxidant suppressing the thermal degradation of the terminal blocker. As the antioxidant of the present invention, a phenol-based antioxidant is preferably used because it has a high decomposition inhibiting effect. Specific examples of the phenolic antioxidant include 2,6-di-tert-butyl-4-methyl-phenol, 4,4-methylenebis (2,6-di-tert-butylphenol), tetrakis [methylene 3- ( 3 ′, 5′-di-tert-butyl-4′-hydroxyphenyl) propionate] -methane, stearyl-3- (3 ′, 5′-di-tert-butyl-4′-hydroxyphenyl) propionate, etc. However, the present invention is not limited to these examples.

  The reaction between the polyester and the reactive end-blocking agent is preferably performed by adding the reactive end-blocking agent in a state where the polyester is melted at 250 ° C. or higher, more preferably 260 ° C. or higher, more preferably 280 ° C. or higher. Can be carried out by stirring for 3 minutes or more, more preferably 5 minutes or more. The reaction with the reactive end-capping agent adds a thermal history to the polyester, but in the present invention, it is possible to achieve high thermal stability by making the total metal element content 150 ppm or less. Thermal oxidative decomposition is less likely to occur in the reaction with the sequestering agent.

  Although the process of mix | blending a reactive terminal blocker with polyester is not specifically limited, For example, the method of mix | blending at the polycondensation process of a polyethylene terephthalate, the method of mix | blending after the polycondensation process of polyester, The film forming process of a biaxially oriented film ( And a method of blending in a polyester raw material melting step). As a blending form, there are a method of directly blending the above compound with polyethylene terephthalate and performing melt kneading, and a method of preparing a masterbatch containing the above compound at a high concentration in advance and blending the masterbatch.

  Moreover, when forming a biaxially oriented film, the part (what is called an ear | edge) which does not become a product of the edge part of a film may be used as a collection | recovery raw material. Reusing the recovered raw material is advantageous in terms of cost because it reduces the basic unit of film. However, since the recovered film may deteriorate hydrolyzability due to an increase in the carboxy terminal due to thermal history, high durability may not be obtained. In this case, it is also effective to add a reactive end-capping agent as a pretreatment when used as a recovered raw material. Although it is possible to reduce the amount of carboxy terminal by solid-phase polymerization of the recovered raw material again, the production cost increases and the merit of using the recovered raw material decreases. Therefore, it is useful to reduce the amount of carboxy terminus by the end capping technique described in the present invention.

  Furthermore, when various additives such as particles and UV absorbers are blended into the polyester, the polyester may take an extra heat history, which may reduce the durability. Even in this case, the reactive endblocker is added. By doing so, the durability of the polyester can be maintained, which is effective.

Since the polyester film of the present invention has a carboxy terminal amount in the above range, it exhibits high hydrolysis resistance. Therefore, the polyester which is the main constituent of the polyester film of the present invention preferably has an HSΔ carboxy terminal amount represented by the following formula, which is an index of hydrolysis resistance, of 10 eq / ton or less.
(HS Δ carboxy terminal amount) = (carboxy terminal amount after hydrolysis test by the following) − (carboxy terminal amount before hydrolysis test)
(Hydrolysis test)
The polyester film is cut into 1 cm × 1 cm pieces and vacuum-dried at 130 ° C. for 12 hours, and 1 g is weighed and put into 100 ml of pure water. This is sealed and heated for 6 hours at 130 ° C. under pressure. The amount of carboxy terminal is measured for the sample before and after the hydrolysis treatment and the sample before the hydrolysis treatment.

  The HSΔ carboxy terminal amount is more preferably 9 eq / ton or less, further preferably 8 eq / ton or less, and further preferably 7 eq / ton or less. In order to make the HSΔ carboxy terminal amount within the above range, it is preferable to reduce the amount of the carboxy terminal of the polyester, but more preferably, by blocking the carboxy terminal of the polyester with a reactive terminal blocking agent, Can be within the above range. The HSΔ carboxy terminal amount is preferably small, but from the viewpoint of productivity, 0.1 eq / ton is considered to be the lower limit.

  The polyester used as a film raw material in the present invention is one or two or more selected from a polyhydric carboxylic acid containing a dicarboxylic acid and one or more of these ester-forming derivatives and a polyhydric alcohol containing a glycol. Or consisting of a hydroxycarboxylic acid and an ester-forming derivative thereof, or consisting of a cyclic ester.

  Preferred polyesters are those in which the main acid component is terephthalic acid or an ester-forming derivative thereof, or naphthalene dicarboxylic acid or an ester-forming derivative thereof, and the main glycol component is alkylene glycol.

  The polyester whose main acid component is terephthalic acid or its ester-forming derivative or naphthalene dicarboxylic acid or its ester-forming derivative is terephthalic acid or its ester-forming derivative and naphthalene dicarboxylic acid or its ester formation with respect to all acid components It is preferable that it is polyester containing 70 mol% or more in total of the functional derivatives, more preferably polyester containing 80 mol% or more, and still more preferably polyester containing 90 mol% or more.

  The polyester whose main glycol component is an alkylene glycol is preferably a polyester containing 70 mol% or more of the total amount of alkylene glycol with respect to all glycol components, more preferably a polyester containing 80 mol% or more, More preferably, it is a polyester containing 90 mol% or more.

  Dicarboxylic acids copolymerizable with terephthalic acid and naphthalenedicarboxylic acid do not reduce hydrolysis resistance, so orthophthalic acid, isophthalic acid, 4,4′-biphenyldicarboxylic acid, 4,4′-biphenylsulfonedicarboxylic acid 4,4′-biphenyl ether dicarboxylic acid, 1,2-bis (phenoxy) ethane-p, p′-dicarboxylic acid, pamoic acid, anthracene dicarboxylic acid and the like, or ester formation thereof Sex derivatives are preferred. Further, a tri- or higher functional carboxylic acid component such as pyromellitic acid or trimellitic acid may be copolymerized.

  Examples of the glycol include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, diethylene glycol, triethylene glycol, 1,2-butylene glycol, 1,3-butylene glycol, 2,3-butylene glycol, 1, 4-butylene glycol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 1,2-cyclohexanediol, 1,3-cyclohexanediol, 1,4-cyclohexanediol, 1,2-cyclohexanedi Alkylene glycol such as methanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, 1,4-cyclohexanediethanol, 1,10-decamethylene glycol, 1,12-dodecanediol, poly Aliphatic glycols exemplified by tylene glycol, polytrimethylene glycol, polytetramethylene glycol, hydroquinone, 4,4′-dihydroxybisphenol, 1,4-bis (β-hydroxyethoxy) benzene, 1,4-bis ( β-hydroxyethoxyphenyl) sulfone, bis (p-hydroxyphenyl) ether, bis (p-hydroxyphenyl) sulfone, bis (p-hydroxyphenyl) methane, 1,2-bis (p-hydroxyphenyl) ethane, bisphenol A , Bisphenol C, 2,5-naphthalenediol, and glycols obtained by adding ethylene oxide to these glycols, and the like.

  Among these glycols, alkylene glycol is preferable, and ethylene glycol, 1,3-propylene glycol, 1,4-butylene glycol, and 1,4-cyclohexanedimethanol are more preferable. The alkylene glycol may contain a substituent or an alicyclic structure in the molecular chain, and two or more kinds may be used at the same time.

  Examples of polyhydric alcohols other than these glycols include trimethylolmethane, trimethylolethane, trimethylolpropane, pentaerythritol, glycerol, hexanetriol and the like.

  Among these, polyesters particularly preferably used in the present invention include polyethylene terephthalate, polybutylene terephthalate, polypropylene terephthalate, poly (1,4-cyclohexanedimethylene terephthalate), polyethylene naphthalate, polybutylene naphthalate, polypropylene naphthalate and these. Of these, polyethylene terephthalate and this copolymer are particularly preferable.

  The intrinsic viscosity (IV) of the polyester film is desirably 0.65 dl / g or more from the viewpoint of strength and durability. The upper limit of the intrinsic viscosity (IV) of the polyester film is not particularly limited, but is preferably 1.20 dl / g or less, more preferably 1.00 dl / g, more preferably 0.80 dl / g from the viewpoint of productivity. Even more preferably. It is preferable to carry out solid phase polymerization in order to achieve 0.65 dl / g or more. Although it is possible to make the intrinsic viscosity (IV) 0.65 dl / g or more by melt polymerization, the reaction time becomes long and the melt viscosity becomes high, so that productivity is deteriorated. If the reaction time is long, a cyclic trimer, diethylene glycol, which deteriorates durability as a side reaction, is generated, which is not suitable for solar cell use or insulation use.

  Although the dialkylene glycol is by-produced during the polymerization of the polyester, the dialkylene glycol reduces the heat resistance. Taking diethylene glycol as an example of typical dialkylene glycol, the amount of diethylene glycol is preferably 2.3 mol% or less. More preferably, it is 2.0 mol% or less, More preferably, it is 1.8 mol% or less. By controlling the amount of diethylene glycol within the above range, the heat resistance stability can be improved, and the increase in the amount of carboxy terminal due to decomposition during drying and molding can be reduced. Furthermore, decomposition by heat that cures the filler when sealing the cell can be suppressed to a low level. Although the amount of diethylene glycol is preferably small, it is produced as a by-product during the esterification reaction of terephthalic acid during the polyester production festival or during the transesterification reaction of dimethyl terephthalate. It is 0 mol%, further 1.2 mol%.

  The acetaldehyde content 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 generated as a side reaction product, which 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 locally applied by a screw configuration of a festival extruder to be melted.

  The content of acetaldehyde was determined by placing the frozen crushed film / distilled water = 1 g / 2 ml into a glass ampoule purged with nitrogen, sealing the top, performing an extraction treatment at 160 ° C. for 2 hours, and after cooling, acetaldehyde in the extract Is a value measured by high-sensitivity gas chromatography.

  The acetic acid content is preferably 1 ppm or less. More preferably, it is 0.5 ppm or less, Most preferably, it is 0.3 ppm or less. When the above range is exceeded, the hydrolysis of the polyester may be accelerated. In order to make acetic acid content into the said range, the policy for making the said acetaldehyde content low can be employ | adopted.

  The acetic acid content was determined by placing 2 g of frozen and ground film in a glass container, pouring 500 ml of boiled ion-exchanged water, allowing to stand for 10 minutes after sealing, cooling to room temperature, leaving for 7 days, and then using 1 ml of this solution for ionization. It is a value quantified by a chromatographic method.

  In the polyester used in the present invention, inactive particles such as inorganic particles, heat-resistant polymer particles, and crosslinked polymer particles, fluorescent whitening agents, ultraviolet light-inhibiting agents, infrared-absorbing dyes, thermal stability, depending on the purpose of use. 1 type, or 2 or more types of various additives, such as an agent, surfactant, and antioxidant, can be contained. As the antioxidant, antioxidants such as aromatic amines and phenols can be used. As stabilizers, phosphoric acid and phosphoric acid ester-based phosphorous, sulfur-based, amine-based stabilizers, etc. Can be used.

  The polyester film of the present invention is a biaxially oriented polyester film from the viewpoint of durability and mechanical strength. In the case of a biaxially oriented polyester film, a melting process in which polymerized polyester chips are melted in an extruder, a film forming process in which an unstretched film is formed by extruding a molten resin from the extruder, and stretching in at least one direction of the unstretched film It is desirable that the film is manufactured through a stretching process and a heat setting process in which the stretched film is heat-treated.

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

  The maximum temperature of the polyester resin in the extruder is preferably 280 ° C. or higher, preferably 285 ° C. or higher, and more preferably 290 ° 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. Moreover, the maximum temperature of the polyester resin in the extruder is preferably 320 ° C. or less, and more preferably 310 ° C. or less. When the melting temperature is increased, the thermal degradation of the polyester proceeds, the carboxy terminal amount of the polyester increases, and the hydrolysis resistance may decrease.

  Polyester polymerized with a small amount of metal catalyst used in the present invention has high thermal oxidation stability, and even if the maximum temperature in the extruder is within the above range, it suppresses the decrease in the amount of carboxy terminal during film production. Can do. The difference (variation amount) between the carboxy terminal amount of the polyester chip used as the raw material resin and the carboxy terminal amount of the polyester film after film formation is preferably 6 eq / ton or less, and more preferably 5 eq / ton or less. . Within the above range, even if a polyester chip having an intrinsic viscosity of more than 0.65 dl / g is used, the increase in the carboxyl end concentration during film production is suppressed, and a highly durable polyester film is maintained with high productivity. Can be manufactured as is. Note that the lower limit of the fluctuation amount is considered to be 0.5 eq / ton from the viewpoint of productivity.

  In the film forming step, a polyester resin polymerized with a small amount of metal catalyst is melt-extruded and formed into a sheet shape on a cooling rotating roll from a T-die to create 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 in the longitudinal direction and the transverse direction simultaneously 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, 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 is 10-500 micrometers, More preferably, it is 15-400 micrometers, More preferably, it is 20-250 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.

  In addition, the polyester film of the present invention preferably has irregularities formed on the film surface in order to improve handling characteristics such as slipperiness, running performance, wear resistance, and winding property. In order to give unevenness to the film surface, an external particle addition method in which inorganic and / or heat-resistant polymer resin particles are added in the polyester polymerization process, the catalyst residue reacts with the polyester constituents in the polymerization process and is insoluble. An inner particle method for precipitating particles, a method for containing the particles in the coating layer, a method for embossing with a roll having irregularities on the surface of the thin film layer, a method for patterning surface irregularities with a laser beam, etc. It is done.

  The kind and content of inert particles added to the polyester for imparting slipperiness are not particularly limited, but include metal oxides such as silica, titanium dioxide, talc, and kaolinite, calcium carbonate, calcium phosphate, Examples thereof include particles inert to the polyester resin, such as metal salts such as barium sulfate or heat-resistant polymer particles. Any one of these inert particles may be used alone, or two or more thereof may be used in combination.

  In order to reduce the haze, the inert particles to be included in the polyester are preferably silica, glass filler, and alumina-silica composite oxide particles having a refractive index close to that of the polyester, and a particle diameter smaller than the wavelength of visible light. The particle | grains which have are preferable and the one where content is low is good. Moreover, since the void generated around the particles increases as the stretching tension increases, the stretching conditions are optimized so that the stretching tension is lowered, that is, the stretching temperature is increased or the stretching ratio is decreased. There is a need. 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.

  The inert particles preferably have an average particle size of 0.01 to 3.5 μm, and the particle size variation degree (ratio between standard deviation and average particle size) is preferably 25% or less. Moreover, it is preferable that the shape of particle | grains contains 1 or more types of particle | grains whose area shape factor is 60% or more. It is preferable to contain 0.005-2.0 mass% of inert particles which have such a characteristic with respect to a polyester resin, Most preferably, it is 1.0 mass% or less.

  Moreover, it is good also as a structure which makes a film a laminated structure and adds an inorganic and / or heat resistant polymer resin particle only to the outermost layer.

  The polyester film of the present invention has high long-term thermal stability, and the half life of elongation at break in a heat resistance test at 160 ° C., which is an index of thermal stability, is 700 hours or more, more preferably 800 hours or more. . By being in such a range, it can be suitably used even under conditions exposed to high temperatures for a long period of time as a solar cell application or an electrical insulation application.

  Further, the polyester film of the present invention has high hydrolysis resistance, and the elongation retention at 192 hours under 105 ° C., 100% RH, 0.03 MPa, which is an index of hydrolysis resistance, is preferably 65%. More preferably, it is 70% or more, more preferably 80% or more, still more preferably 85% or more, and particularly preferably 90% or more. By being in such a range, it can be suitably used even under conditions exposed to the outdoors for a long period of time as a solar cell application or an electrical insulation application.

  The solar cell referred to in the present invention refers to a system that takes in incident light such as sunlight and room light, converts it into electricity, and stores the electricity. Surface protection sheet, high light transmission material, solar cell module, filler layer And a back surface sealing sheet. There are flexible properties depending on the application.

  The polyester film for solar cells of the present invention can be used as a base film (base film) for the surface protective sheet, the back surface sealing sheet, and the bonding material for flexible electronic members. In particular, it is suitable as a base film for a solar cell backside sealing sheet that requires high durability and long-term thermal stability. The solar cell back surface sealing sheet protects the solar cell module on the back side of the solar cell.

  The polyester film for solar cells of the present invention can be used as a solar cell back surface sealing sheet alone or in combination of two or more. The polyester film for solar cells of the present invention can be laminated with a film having water vapor barrier properties, an aluminum foil, or the like for the purpose of imparting water vapor barrier properties. As the barrier film, a polyvinylidene fluoride coating film, a silicon oxide vapor deposition film, an aluminum oxide vapor deposition film, an aluminum vapor deposition film, or the like can be used. These can be used for the solar cell polyester film of the present invention through an adhesive layer, directly laminated, or in a form having a sandwich structure.

  Moreover, in order to improve the adhesiveness of a solar cell sealing sheet and a filler layer, it is also preferable to provide an easily bonding layer in the solar cell polyester film of this invention by offline coating or / and in-line coating.

  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.

  EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these Examples from the first. In addition, the evaluation method used in each Example and the comparative example is demonstrated below.

(1) Content of all metal elements in polyester film (ppm), phosphorus element content The polyester film was obtained by ashing / dissolving acid and then by high-frequency plasma emission analysis and atomic absorption analysis.

(2) Measuring method of carboxy terminal amount Preparation of sample The polyester is pulverized, 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 carboxy terminal amount 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 amount of carboxy terminal was calculated | required according to following Formula.
Carboxy terminal amount (eq / ton) = [(V−V0) × 0.04 × NF × 1000] / W
NF: factor of 0.04 mol / l potassium hydroxide solution W: sample weight (g)

(3) Measuring method of TODΔ carboxy terminal amount A film sample (before thermal oxidation test) was frozen and pulverized and dried in vacuum at 130 ° C. for 12 hours as a powder of 100 mesh or less. 0.3 g was put in a glass test tube at 70 ° C. After vacuum-drying for 12 hours, it was heated at 230 ° C. for 15 minutes under air dried on silica gel. The amount of carboxy terminal of the sample before and after the thermal oxidation treatment was measured by the method (2). From the obtained measurement results, (TODΔcarboxy terminal amount) = (carboxy terminal amount after thermal oxidation test) − (carboxy terminal amount before thermal oxidation test).

(4) Method for measuring the amount of HSΔ carboxy terminal The film (before hydrolysis test) was cut into 1 cm × 1 cm pieces and vacuum-dried at 130 ° C. for 12 hours, and then 1 g was put in 100 ml of pure water to form a sealed system at 130 ° C. The mixture was stirred for 6 hours under heated and pressurized conditions. The amount of carboxy terminal of the sample before and after the hydrolysis test was measured by the method (2). From the measurement results obtained, calculation was performed by (HSΔ carboxy terminal amount) = (carboxy terminal amount after hydrolysis test) − (carboxy terminal amount before hydrolysis test).

(5) Hydrolysis resistance retention of elongation at break As a hydrolysis resistance evaluation, HAST (Highly Accelerated Temperature and Humidity Stress Test) standardized in JIS-60068-2-66 was performed. The equipment was EHS-221 manufactured by ESPEC CORP. Under the conditions of 105 ° C., 100% RH, and 0.03 MPa.
The film was cut into 70 mm × 190 mm, and the film was placed using a jig. Each film was placed at a distance where it did not touch. The treatment was performed for 192 hours under the conditions of 105 ° C., 100% RH, and 0.03 MPa. The breaking elongation before and after the treatment was measured according to JIS-C-2318-1997 5.3.31 (tensile strength and elongation), and the breaking elongation retention was calculated according to the following formula.
Breaking elongation retention (%) = [(breaking elongation after treatment (MPa)) / (breaking elongation before treatment (MPa))] × 100

(6) 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 JIS K-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.

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

(Preparation of polycondensation catalyst solution)
(Preparation of ethylene glycol solution of phosphorus compound)
Irganox 1222 (manufactured by Ciba Specialty Chemicals) was added as a phosphorus compound while stirring at 200 rpm under a nitrogen atmosphere after adding 2.0 liters of ethylene glycol to a flask equipped with a nitrogen introduction tube and a cooling tube. 200 g was added. Further, 2.0 liters of ethylene glycol was added, the temperature was raised by changing the jacket temperature setting to 196 ° C., and the mixture was stirred under reflux for 60 minutes from the time when the internal temperature reached 185 ° C. or higher. Thereafter, the heating was stopped, the solution was immediately removed from the heat source, and the solution was cooled to 120 ° C. or less within 30 minutes while maintaining the nitrogen atmosphere. The mole fraction of Irganox 1222 in the obtained solution was 40%, and the mole fraction of the compound whose structure changed from Irganox 1222 was 60%.

(Preparation of aqueous solution of aluminum compound)
After adding 5.0 liters of pure water to a flask equipped with a cooling tube at room temperature and normal pressure, 200 g of basic aluminum acetate was added as a slurry with pure water while stirring at 200 rpm. Further, pure water was added so as to be 10.0 liters as a whole, and the mixture was stirred at room temperature and normal pressure for 12 hours. Thereafter, the jacket temperature was changed to 100.5 ° C., the temperature was raised, and the mixture was stirred under reflux for 3 hours from the time when the internal temperature reached 95 ° C. or higher. Stirring was stopped and the mixture was allowed to cool to room temperature to obtain an aqueous solution.

(Preparation of ethylene glycol mixed solution of aluminum compound)
After adding an equal volume of ethylene glycol to the aqueous aluminum compound solution obtained by the above method and stirring for 30 minutes at room temperature, the internal temperature is controlled to 80 to 90 ° C., and the pressure is gradually reduced to reach 27 hPa while stirring for several hours. Water was distilled off from the system to obtain an ethylene glycol solution of an aluminum compound at 20 g / l. The peak integration value ratio of ²⁷ Al-NMR spectrum of the obtained aluminum solution was 2.2.

(Preparation of ethylene glycol solution of lithium compound)
Lithium acetate was dissolved in ethylene glycol to obtain an ethylene glycol solution of 20 g / l lithium acetate.

(Preparation of calcium glycol solution of ethylene glycol)
Calcium acetate was dissolved in ethylene glycol to obtain a 20 g / l calcium acetate ethylene glycol solution.

(Preparation of ethylene glycol solution of antimony compound)
Antimony trioxide was dissolved in an ethylene glycol solution to obtain an ethylene glycol solution of 14 g / l antimony trioxide.

Example 1
(1) Preparation of polyester pellets A 2-liter stainless steel autoclave with a stirrer was charged with high-purity terephthalic acid and ethylene glycol, and an esterification reaction was performed according to a conventional method to obtain an oligomer mixture. As a polycondensation catalyst, an ethylene glycol solution of an aluminum compound / an ethylene glycol solution of a phosphorus compound was added to the oligomer mixture so that the residual amount of aluminum element was 20 ppm and the residual amount of phosphorus element was 80 ppm. Next, the mixture was stirred at 250 ° C. for 10 minutes under a nitrogen atmosphere at normal pressure. Thereafter, while raising the temperature to 280 ° C. over 60 minutes, the pressure of the reaction system is gradually lowered to 13.3 Pa (0.1 Torr), and the intrinsic viscosity (IV) of the polyester is 0 at 280 ° C. and 13.3 Pa. The polycondensation reaction was carried out until it reached .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, and then cut to have an intrinsic viscosity of a cylinder shape having a length of about 3 mm and a diameter of about 2 mm ( A pellet with IV) of 0.55 and a carboxy terminal amount of 12 eq / ton 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 to obtain polyester pellets having an intrinsic viscosity (IV) of 0.75 dl / g and a carboxy terminal amount of 5 eq / ton. .

(2) Film formation Polyethylene terephthalate pellets and silica particles having an average particle size of 1.0 μm, a particle size variation of 20%, and an area shape factor of 80% are adjusted to 0.06% by mass with respect to PET. After drying at 135 ° C. under reduced pressure (1 Torr) for 10 hours, carbodilite LA-1 (manufactured by Nisshinbo Chemical Co., Ltd.), which is a carbodiimide compound, was supplied to the extruder together with 1 part by mass. The maximum resin temperature up to the melter, kneading part, polymer tube, gear pump, and filter of the extruder was 290 ° C., and then 285 ° C. for the polymer tube, 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. In addition, as a result of measuring the moisture content of the PET pellet extracted at the entrance of the extruder, the moisture content was 18 ppm. The extruded resin was wound around a casting drum having a surface temperature of 30 ° C. by using an electrostatic application casting method, and was 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 properties of the obtained PET film are shown in Table 1.

(Example 2)
Instead of carbodilite LA-1, diallyl monoglycidyl isocyanuric acid (manufactured by Shikoku Kasei Kogyo Co., Ltd.), which is an epoxy compound, was added so that the amount of epoxy was equal to the carboxy terminal of the polyester pellets during film formation. Except for this, a biaxially oriented PET film was obtained in the same manner as in Example 1. The properties of the obtained PET film are shown in Table 1.

(Example 3)
Instead of carbodilite LA-1, it was the same as Example 1 except that 4 parts by mass was added to the polyester pellets obtained from Epocross RPS-1005 (manufactured by Nippon Shokubai Co., Ltd.) which is an oxazoline compound during film formation. A biaxially oriented PET film was obtained. The properties of the obtained PET film are shown in Table 1.

Example 4
As a polycondensation catalyst, a mixture of an ethylene glycol solution of the above aluminum compound / an ethylene glycol solution of a phosphorus compound, an ethylene glycol solution of a lithium compound, the residual amount of aluminum element is 20 ppm, the residual amount of phosphorus element is 80 ppm, the residual amount of lithium element Was added so as to be 20 ppm to obtain polyester pellets. Using the obtained polyester pellets, diallyl monoglycidyl isocyanuric acid (Shikoku Chemicals) which is an epoxy compound so that the epoxy amount becomes equal to the carboxy terminal of the polyester pellet at the time of film formation, instead of carbodilite LA-1. A biaxially oriented PET film was obtained in the same manner as in Example 5 except that Kogyo Kogyo Co., Ltd. was added. The properties of the obtained PET film are shown in Table 1.

(Comparative Example 1)
As a polycondensation catalyst, a polycondensation catalyst was prepared by adding a mixture of the above-mentioned aluminum compound ethylene glycol solution / phosphorus compound ethylene glycol solution so that the residual amount of aluminum element was 160 ppm and the residual amount of phosphorus element was 80 ppm. In addition to carbodilite LA-1, diallyl monoglycidyl isocyanuric acid (manufactured by Shikoku Kasei Kogyo Co., Ltd.) is added so that the amount of epoxy is equal to the carboxy end of the polyester pellet when forming a film instead of carbodilite LA-1. A biaxially oriented PET film was obtained in the same manner as in Example 1 except that. The properties of the obtained PET film are shown in Table 1.

(Comparative Example 2)
Polyester pellets having an intrinsic viscosity (IV) of 0.50 dl / g and a carboxy terminal amount of 34 eq / ton were obtained by melt polymerization, and an intrinsic viscosity (IV) of 0.75 dl / g and a carboxy terminal amount of 16 eq were obtained by solid phase polymerization. A biaxially oriented PET film was obtained in the same manner as in Example 1 except that / ton polyester pellets were used and no reactive endblocker was added. The properties of the obtained PET film are shown in Table 1.

(Comparative Example 3)
(1) Preparation of polyester pellets A 2 liter stainless steel autoclave with a stirrer is charged with dimethyl terephthalic acid, ethylene glycol, and an ethylene glycol solution of a calcium compound so that the residual amount of calcium element is 200 ppm. An oligomer mixture was obtained. Trimethylphosphoric acid was added to the oligomer mixture so that the residual amount of phosphorus element was 400 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 the ethylene glycol solution of the antimony compound / the ethylene glycol solution of the lithium compound was added so that the residual amount of the antimony element was 200 ppm and the residual amount of the lithium element was 100 ppm. Next, the mixture was stirred at 250 ° C. for 10 minutes under a nitrogen atmosphere at normal pressure. Thereafter, while raising the temperature to 280 ° C. over 60 minutes, the pressure of the reaction system is gradually lowered to 13.3 Pa (0.1 Torr), and the intrinsic viscosity (IV) of the polyester is 0 at 280 ° C. and 13.3 Pa. The polycondensation reaction was carried out until it reached .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, and then cut to have an intrinsic viscosity of a cylinder shape having a length of about 3 mm and a diameter of about 2 mm ( A pellet having IV) of 0.55 dl / g and a carboxy terminal amount of 12 eq / ton 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 to obtain polyester pellets having an intrinsic viscosity (IV) of 0.75 dl / g and a carboxy terminal amount of 5 eq / ton. .

(Film casting)
Using the above polyester pellets, diallyl monoglycidyl isocyanuric acid (manufactured by Shikoku Kasei Kogyo Co., Ltd.) was added as a reactive end-blocking agent so that the amount of epoxy was equal to the carboxyl end of the polyester pellets during film formation. Except for this, a biaxially oriented PET film was obtained in the same manner as in Example 1. The properties of the obtained PET film are shown in Table 1.

  The polyester film of the present invention provides a polyester film having long-term thermal stability and extremely high hydrolysis resistance. Therefore, it can be suitably used as a base film for solar cell back surface sealing sheets and electrical insulating sheets.

Claims (6)

A polyester film that is a biaxially oriented polyester film and satisfies the following requirements (1) and (2).
(1) The carboxy terminal amount is 5 eq / ton or less with respect to the polyester (2) The total metal element content is 150 ppm or less with respect to the polyester (here, the total metal element content is an alkali metal, (The total amount of transition metals and typical element metals excluding alkaline earth metals and titanium.) Furthermore, the polyester film of Claim 1 which satisfies the following requirements (3) and (4).
(3) Phosphorus element content is 100 ppm or less with respect to polyester (4) TODΔ carboxy terminal amount represented by the following formula is 20 eq / ton or less (TODΔ carboxy terminal amount) = (thermal oxidation by the following) Carboxy terminal amount after test)-(Carboxy terminal amount before thermal oxidation test)
(Thermal oxidation test)
The polyester film sample is freeze-pulverized and then made into a powder of 100 mesh or less and vacuum dried at 130 ° C. for 12 hours. 0.3 g of this is weighed, put into a glass test tube, vacuum-dried at 70 ° C. for 12 hours, and then heat-treated at 230 ° C. for 15 minutes in air. The amount of carboxy terminus is measured for the sample before and after the heat treatment and the sample before the heat treatment. Furthermore, the polyester film in any one of Claim 1 or 2 which satisfies the following requirements (5).
(5) HSΔ carboxy terminal amount represented by the following formula is 10 eq / ton or less (HSΔ carboxy terminal amount) = (carboxy terminal amount after hydrolysis test) − (carboxy terminal amount before hydrolysis test) )
(Hydrolysis test)
The polyester film is cut into 1 cm × 1 cm pieces and vacuum-dried at 130 ° C. for 12 hours, and 1 g is weighed and put into 100 ml of pure water. This is sealed and heated for 6 hours at 130 ° C. under pressure. The amount of carboxy terminal is measured for the sample before and after the hydrolysis treatment and the sample before the hydrolysis treatment.   The polyester film according to claim 1, wherein a reactive end-blocking agent is added to the polyester.   The polyester film for solar cell backside sealing which consists of a polyester film in any one of Claims 1-4.   The polyester film for electrical insulation which consists of a polyester film in any one of Claims 1-4.