JP2012158769A - Polyester film for solar cell, and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film for a solar cell, excellent in hydrolysis resistance and long term thermal stability.SOLUTION: The polyester film for a solar cell is a polyester film which includes a polyester produced by polymerization using a polycondensation catalyst containing aluminum and/or a compound thereof and a phosphorus-based compound with an aromatic group in the molecule as a main component, wherein concentration of a carboxy terminal is 25 eq/ton or less with respect to the polyester, and intrinsic viscosity (IV) of the film is 0.60-0.90 dl/g.

Description

  TECHNICAL FIELD The present invention relates to a solar cell polyester film suitable for a solar cell constituent material such as a solar cell backside sealing sheet and a solar cell protective sheet, and more specifically, a solar cell polyester film excellent in hydrolysis resistance and long-term thermal stability. About.

  In recent years, solar cells have attracted attention as a next-generation clean energy source. In the solar cell module, 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, and a base film is used for these constituent members. Since solar cells used outdoors are used for a long period of time, these components are also required to have durability against the natural environment. As such a component, for example, a base film for sealing the back surface of a solar cell, a fluorine-based film, a polyethylene-based film, or a polyester-based film is used. (Patent Documents 1 and 2)

  Among these, polyester films having various durability improvements have been proposed. (Patent Documents 3, 4, 5, 6, 7, 8, 9)

JP-A-11-261085 JP 2000-114565 A JP 2002-134770 A JP 2002-26354 A JP 2006-270025 A JP 2007-150084 A JP 2007-204538 A JP 2008-31680 A JP 2007-7885 A

  Conventionally, as durability of the polyester film for solar cells, hydrolysis resistance has been improved. For example, the above-mentioned proposal has provided a polyester film for solar cells with improved hydrolysis resistance. In recent years, however, solar cells have evolved from conventional rooftops to installation 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. Furthermore, the solar cell module has been increased in size and output, and a temperature increase due to the increase in size and a temperature increase in the electrode / connector part due to the increase in output have occurred. In such a situation where long-term thermal stability is increasingly required, it has been considered that sufficient durability cannot be achieved only by improvement by conventional hydrolysis resistance.

  On the other hand, in the above proposal, in order to increase the hydrolysis resistance of polyester, the carboxyl terminal concentration (acid value) of the film resin is kept low (Patent Documents 6 and 7). In addition, polyesters having relatively high molecular weight (IV is comparatively high) are used in order not to greatly reduce the physical properties even if the deterioration has progressed to some extent (Patent Documents 3, 4, 5, and 8). In order to keep the carboxyl terminal concentration of the film resin low, it is desirable not only to lower the carboxyl terminal concentration of the resin as a raw material but also to suppress the increase of the carboxyl terminal concentration during the film production process. One factor for the increase in the carboxyl end concentration that occurs during the film production process is thermal decomposition in the melting step. However, when a high molecular weight resin is used, shear heat generation may occur in the extruder and the melting temperature may increase. In addition, if the melting temperature is set low in order to suppress thermal decomposition, the discharge amount may be lowered particularly in the case of a resin having a high molecular weight, and productivity may be lowered. Therefore, a method for producing a film having a low carboxyl terminal concentration (acid value) and a relatively high molecular weight while maintaining high productivity has been desired.

  In view of the above problems, an object of the present invention is to provide a solar cell polyester film having hydrolysis resistance and long-term thermal stability. Moreover, the objective of this invention provides the manufacturing method of the polyester film for solar cells with high productivity.

  As a result of intensive studies to solve the above problems, the present inventor senses that the catalyst type of the polyester has an effect on the thermal degradation, and uses the polyester polymerized by a specific polymerization catalyst, so that the solar cell As a polyester film for solar cells, it has the surprising effect that it can produce a polyester film for solar cells that exhibits excellent hydrolysis resistance and outstanding long-term thermal stability, while maintaining high productivity. The headline and the present invention have been achieved.

  That is, the present invention is a polyester film mainly comprising polyester polymerized using a polycondensation catalyst containing aluminum and / or a compound thereof and a phosphorus compound having an aromatic group in the molecule, It is a polyester film for solar cells, having a carboxyl end concentration of 25 eq / ton or less with respect to polyester and an intrinsic viscosity (IV) of the film of 0.60 to 0.90 dl / g.

  The polyester film is mainly composed of polyester polymerized using a polycondensation catalyst containing an aluminum salt of a phosphorus compound, and the carboxyl end concentration is 25 eq / ton or less of the polyester, and the intrinsic viscosity of the film (IV) is a polyester film for solar cells, characterized in that it is 0.60 to 0.90 dl / g.

  The polyester film mainly comprises polyester polymerized using a polycondensation catalyst containing at least one selected from the compounds represented by the general formula (5), wherein the film is a carboxyl film. The polyester film for solar cells, wherein the terminal concentration is 25 eq / ton or less with respect to the polyester, and the intrinsic viscosity (IV) of the film is 0.60 to 0.90 dl / g.

  Furthermore, a melting step of melting the polyester chip in an extruder, a film forming step of forming an unstretched film by extruding a molten resin from the extruder, a stretching step of stretching in at least one direction of the unstretched film, and a stretched In the method for producing a solar cell polyester film including a heat setting step of heat-treating the film, the maximum temperature of the polyester resin in the melting step is 280 ° C. or higher, and the carboxyl end concentration of the polyester chip and the polyester film for solar cell The method for producing a polyester film for solar cells according to any one of the above, wherein the difference from the carboxyl terminal concentration is 6 eq / ton or less.

  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 polycondensation catalyst used when polymerizing the polyester which is the main constituent of the polyester film for solar cells of the present invention is a catalyst containing aluminum and / or a compound thereof and a phosphorus compound having an aromatic group in the molecule, A catalyst containing an aluminum salt of a phosphorus compound, or a catalyst containing at least one selected from the compounds represented by the general formula (5).

  As said aluminum and / or an aluminum compound, a well-known aluminum compound other than metallic aluminum can be used without limitation.

  Specific examples of 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 alkoxide 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.

  The addition amount of the aluminum and / or aluminum compound is preferably 0.001 to 0.05 mol% with respect to the number of moles of all constituent units of the carboxylic acid component such as dicarboxylic acid or polycarboxylic acid of the obtained polyester. More preferably, it is 0.005-0.02 mol%. If the addition amount is less than 0.001 mol%, the catalytic activity may not be sufficiently exerted. If the addition amount is 0.05 mol% or more, the thermal stability or thermal oxidation stability is deteriorated, resulting from aluminum. Occurrence of foreign matters or increased coloring may be a problem. As described above, the polymerization catalyst of the present invention has a great feature in that it exhibits a sufficient catalytic activity even when the addition amount of the aluminum component is small. As a result, thermal stability and thermal oxidation stability are excellent, and foreign matters and coloring caused by aluminum can be reduced.

  Although it does not specifically limit as a phosphorus compound which comprises the said polycondensation catalyst, When the 1 type, or 2 or more types of compound chosen from the group which consists of a phosphonic acid type compound and a phosphinic acid type compound is used, the improvement effect of a catalyst activity is large and preferable. . Among these, when one or two or more phosphonic acid compounds are used, the effect of improving the catalytic activity is particularly large and preferable.

  The phosphonic acid-based compound and the phosphinic acid-based compound are compounds having structures represented by the following formulas (6) and (7), 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 (8) and (9) are preferably used.

  In the polycondensation catalyst of the present invention, among the above phosphorus compounds, it is necessary 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 the said polycondensation catalyst, when the compound represented by following General formula (10)-(11) is used, especially the improvement effect of a catalyst activity is large and preferable.

(In formulas (10) to (11), 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 a phosphorus compound which comprises the said polycondensation catalyst, the compound whose R < ¹ >, R < ⁴ > is group which has an aromatic ring structure in said formula (10)-(11) is especially 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 amount of the phosphorus compound added is preferably 5 × 10 ^{−7 to} 0.01 mol based on the number of moles of all constituent units of the carboxylic acid component such as dicarboxylic acid and polyvalent carboxylic acid of the polyester obtained. Preferably it is 1 * 10 < ^-6 > -0.005 mol.

  The phosphorus compound having a phenol part constituting the polycondensation catalyst in the same molecule is not particularly limited as long as it is a phosphorus compound having a phenol structure, but a phosphonic acid compound having a phenol part in the same molecule, When one or two or more compounds selected from the group consisting of phosphinic acid 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 the said polycondensation catalyst in the same molecule, the compound etc. which are represented with following General formula (12), (13) are mentioned. Among these, it is particularly preferable to use the following formula because catalytic activity is improved.

(In the formulas (12) to (13), R1 is a hydrocarbon group having 1 to 50 carbon atoms containing a phenol part, a substituent such as a hydroxyl group, a halogen group, an alkoxyl group or an amino group, and a carbon number 1 to 1 containing 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 (14) to (1) A compound represented by), and the like. Among these, a compound represented by the following formula (16) and dimethyl p-hydroxyphenylphosphonate are particularly preferable.

  As the compound represented by the above formula (16), 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.

As the addition amount of the phosphorus compound having the phenol part in the same molecule, 5 × 10 ⁻⁷ to the number of moles of all constituent units of the carboxylic acid component such as dicarboxylic acid and polycarboxylic acid of the obtained polyester 0.01 mol is preferable, and more preferably 1 × 10 ^{−6 to} 0.005 mol.

  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 (18) is used as the phosphorus metal salt compound, the effect of improving the catalytic activity is greatly preferred.

(In formula (18), 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 (18), it is preferable to use at least one selected from the compounds represented by the following general formula (19).

(In formula (19), 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 (19), 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 greatly preferred. 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) methylphosphonic acid ethyl], magnesium bis [(2-naphthyl) methylphosphonic acid ethyl], lithium [benzylphosphonic acid ethyl], sodium [benzylphosphonic acid ethyl], magnesium bis [benzylphosphonic acid ethyl], 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 the compounds represented by the following general formula (20).

(In Formula (20), 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. 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 (21).

(In formula (21), M ^{n +} represents an n-valent metal cation. N represents 1, 2, 3 or 4.)

  Among the above formulas (20) or (21), when M is selected from Li, Na, K, Be, Mg, Sr, Ba, Mn, Ni, Cu, 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 (34) is preferably used because the effect of improving the catalytic activity is great.

(In formula (22), 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 (23). The aluminum salt of the phosphorus compound may be used in combination with other aluminum compounds, phosphorus compounds, phenolic compounds, and the like.

(In formula (23), 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 (24).

(In the formula (24), 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 the phosphorus compound having at least one P—OH bond constituting the polycondensation catalyst is at least one selected from compounds represented by the following general formula (25), the effect of improving the catalytic activity is greatly preferred. .

(In formula (25), 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) ethyl methylphosphonate, ethyl 4-hydroxybenzylphosphonate, ethyl 2-methylbenzylphosphonate, phenyl 4-chlorobenzylphosphonate, methyl 4-aminobenzylphosphonate, ethyl 4-methoxybenzylphosphonate, 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 (26). To do.

(In formula (26), 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 (27).

(In formula (27), 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 (28).

(In the formula (28), 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 (28) 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 (35).

(In the above formula (35), R ¹ and R ² each independently represent hydrogen and a hydrocarbon group having 1 to 30 carbon atoms. R ³ and R ⁴ are each independently hydrogen and 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 (35), it is preferable to use at least one selected from the compounds represented by the following general formula (36) because the effect of improving the catalytic activity is high.

(In said formula (36), 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 the compounds represented by chemical formula (37) and chemical formula (38).

  As the compound represented by the chemical formula (37), 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 (38).

  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 of the phosphorus compound is preferably 0.0001 to 0.1 mol%, preferably 0.005 to 0.05 mol%, based on the number of moles of all the structural units of the dicarboxylic acid component constituting the polyester. More preferably. When the addition amount of the phosphorus compound is less than 0.0001 mol%, the addition effect may not be exhibited. On the other hand, if added over 0.1 mol%, 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 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. When such a known catalyst is used, a polyester having excellent thermal stability can be obtained. However, when a known catalyst using an alkali metal compound or an alkaline earth metal compound is used to obtain a practical catalytic activity, the amount of catalyst added Need to be more.

  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 is added, the addition amount M (mol%) is 1 × 10 ⁻⁶ or more and 0 with respect to the number of moles of all polycarboxylic acid units constituting the polyester. It is preferably less than 1 mol%, more preferably 5 × 10 ^{−6 to} 0.05 mol%, still more preferably 1 × 10 ^{−5 to} 0.03 mol%, and particularly preferably 1 * 10 < ^-5 > -0.01 mol%.

  That is, since the amount of alkali metal or alkaline earth metal added is small, the reaction rate can be increased without causing problems such as a decrease in thermal stability, generation of foreign matter, and coloring. In addition, problems such as degradation of hydrolysis resistance do not occur.

When the added amount M of an alkali metal, alkaline earth metal, or compound thereof is 0.1 mol% or more, there are problems in product processing such as a decrease in thermal stability, an increase in foreign matter generation and coloring, and a decrease in hydrolysis resistance. The case that becomes. If M is less than 1 × 10 ⁻⁶ mol%, the effect is not clear even if it is added.

  The alkali metal or alkaline earth metal constituting the second metal-containing component preferably used in addition to the aluminum or a compound thereof includes Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba Is preferably at least one selected from the group consisting of alkali metals and compounds thereof.

  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 substances 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.

The polyester which is the main constituent of the polyester film of the present invention preferably has a thermal stability parameter (TS) satisfying the following formula, more preferably 0.20 or less, and particularly preferably 0.18 or less. By using a polyester having a TS of less than 0.25, it is possible to obtain a polyester film having excellent thermal stability in the melting step at the time of producing a film and less coloring and foreign matter. Further, the lower limit of TS is preferably 0.01 or more, more preferably 0.05 or more, and further preferably 0.07 or more from the viewpoint of productivity.
(1) TS <0.25

TS is calculated by the following method. 1 g of polyester is placed in a glass test tube and vacuum dried at 130 ° C. for 12 hours. Subsequently, after maintaining in a molten state at 300 ° C. for 2 hours under a non-circulating nitrogen atmosphere, the sample is taken out and frozen and ground. After it is vacuum dried, the intrinsic viscosity ([IV] _f ) is measured. For example, when the polyester is polyethylene terephthalate, it can be calculated by the following formula.
TS = 0.245 {[IV] _f ^-1.47- [IV] _i ^-1.47 }

  The non-circulating nitrogen atmosphere means a non-circulating nitrogen atmosphere. For example, a glass test tube containing a resin chip is connected to a vacuum line, and after repeating depressurization and nitrogen filling five or more times, nitrogen is added so that the pressure becomes 100 Torr. It is in a sealed and sealed state.

Moreover, it is preferable that the polyester which is a main component of the polyester film of the present invention has a thermal oxidation stability parameter (TOS) satisfying the following formula (2), more preferably 0.10 or less, and still more preferably 0.07. Hereinafter, it is more preferably 0.05 or less. Further, TOS is preferably low, but 0.0001 is considered to be the lower limit.
(2) TOS <0.20

TOS is calculated by the following method. The polyester resin is frozen and ground to a powder of 20 mesh or less. The powder is vacuum dried at 130 ° C. for 12 hours and 0.3 g is placed in a glass test tube. Next, after vacuum drying at 70 ° C. for 12 hours and further heating at 230 ° C. for 15 minutes under air dried with silica gel, the intrinsic viscosity ([IV] _f1 ) is measured. For example, when the polyester is polyethylene terephthalate, it can be calculated by the following formula.
TOS = 0.245 {[IV] _f1 ^-1.47- [IV] _i ^-1.47 }
In the above formula, [IV] _i and [IV] _f1 indicate IV (dl / g) before and after the heating test, respectively.

  Examples of the method of heating in air dried with silica gel include a method of connecting a drying tube containing silica gel to the upper part of a glass test tube and heating in dry air.

Further, the polyester used in the present invention preferably has a hydrolysis resistance parameter (HS) satisfying the following formula (3), more preferably 0.06 or less, and particularly preferably 0.055 or less. Further, HS is preferably low, but 0.0005 is considered to be the lower limit.
(3) HS <0.07

HS is calculated by the following method. The polyester resin is frozen and ground to a powder of 20 mesh or less. After vacuum drying at 130 ° C. for 12 hours, 1 g thereof is put into a beaker with 100 ml of pure water. The mixture is stirred for 6 hours under a heated and pressurized condition at 130 ° C., and then the intrinsic viscosity ([IV] _f2 ) is measured. For example, when the polyester is polyethylene terephthalate, it can be calculated by the following formula.
HS = 0.245 × {[IV] _f2 ^-1.47 − [IV] _i ^−1.47 }

  As the beaker used for the measurement of HS, a beaker having no acid or alkali elution is used. Specifically, it is preferable to use a stainless beaker or a quartz beaker.

  The polyester used in the present invention can be produced by a conventionally known production method except that the specific catalyst is used as a polyester polymerization catalyst. For example, in the case of producing PET, a method in which terephthalic acid and ethylene glycol are esterified and then polycondensed, or after transesterification of an alkyl ester of terephthalic acid such as dimethyl terephthalate with ethylene glycol is performed. Any method of polycondensation can be used. The polymerization apparatus may be a batch type or a continuous type.

  The polyester catalyst used in the present invention has catalytic activity not only in the polymerization reaction but also in the esterification reaction and transesterification reaction. For example, polymerization by an ester exchange reaction between an alkyl ester of a dicarboxylic acid such as dimethyl terephthalate and a glycol such as ethylene glycol is usually carried out in the presence of an ester exchange catalyst such as a titanium compound or a zinc compound. Instead, the catalyst described in the claims of the present invention can be used together with these catalysts. The catalyst has catalytic activity not only in melt polymerization but also in solid phase polymerization or solution polymerization, and it is possible to produce a polyester suitable for producing a polyester film by any method. In particular, in the present invention, it is preferable to use a polyester having an intrinsic viscosity of more than 0.60 dl / g in order to impart durability of the polyester film. However, in order to adjust the intrinsic viscosity, it is desirable to perform solid-phase polymerization after polymerization. .

  The polyester polymerization catalyst used in the present invention can be added to the reaction system at any stage of the polymerization reaction. For example, it can be added to the reaction system at any stage before and during the esterification reaction or transesterification reaction, immediately before the start of the polycondensation reaction, or at any stage during the polycondensation reaction. In particular, aluminum or a compound thereof is preferably added immediately before the start of the polycondensation reaction.

  The method for adding the polyester polycondensation catalyst used in the present invention is not particularly limited, but it may be added in the form of powder or neat, or in the form of a slurry or solution of a solvent such as ethylene glycol. May be. Further, aluminum metal or a compound thereof and other components, preferably those obtained by mixing the phenolic compound or phosphorus compound of the present invention in advance may be added, or these may be added separately. In addition, aluminum metal or a compound thereof and other components, preferably a phenolic compound or a phosphorus compound, may be added to the polymerization system at the same addition time, or may be added at different addition times.

  The polyester polycondensation catalyst used in the present invention preferably does not use other polymerization catalysts such as an antimony compound, a titanium compound, a germanium compound, and a tin compound, but there are problems in the properties, workability, and color tone of the polyester. An appropriate amount may be allowed to coexist within a range that does not occur.

  Specifically, the addition amount of the antimony compound is preferably 50 ppm or less in terms of antimony atoms, more preferably 30 ppm or less, with respect to the polyester obtained by polymerization. When the amount converted to antimony exceeds 50 ppm, metal antimony is precipitated, and the polyester becomes blackish, which is not preferable in appearance. Moreover, the foreign material resulting from a metal antimony increases and it is unpreferable especially in the use with a severe request | requirement with respect to a fault.

  The addition amount of the titanium compound is preferably 10 ppm or less, more preferably 5 ppm or less, still more preferably 2 ppm or less, and particularly preferably 1 ppm or less, in terms of titanium atom with respect to the polyester obtained by polymerization. If the titanium atom equivalent exceeds 10 ppm, the thermal stability of the resulting resin is significantly reduced.

  The addition amount of the germanium compound is preferably 20 ppm or less, more preferably 10 ppm or less, in terms of germanium atom, based on the polyester obtained by polymerization. If the germanium atom equivalent exceeds 20 ppm, it is not preferable because it is disadvantageous in terms of cost.

  The kind of the antimony compound, titanium compound, germanium compound and tin compound is not particularly limited.

  Specifically, examples of the antimony compound include antimony trioxide, antimony pentoxide, antimony acetate, and antimony glycoloxide. Of these, antimony trioxide is preferable.

  Examples of titanium compounds include tetra-n-propyl titanate, tetraisopropyl titanate, tetra-n-butyl titanate, tetraisobutyl titanate, tetra-tert-butyl titanate, tetracyclohexyl titanate, tetraphenyl titanate, and titanium oxalate. Of these, tetra-n-butoxy titanate is preferred.

  Furthermore, examples of the germanium compound include germanium dioxide, germanium tetrachloride, etc. Among these, germanium dioxide is preferable.

  As tin compounds, dibutyltin oxide, methylphenyltin oxide, tetraethyltin, hexaethylditin oxide, triethyltin hydroxide, monobutylhydroxytin oxide, triisobutyltin adduct, diphenyltin dilaurate, monobutyltin trichloride, dibutyltin sulfide, Examples thereof include dibutylhydroxytin oxide, methylstannoic acid, and ethylstannic acid, and the use of monobutylhydroxytin oxide is particularly preferable.

  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.

  Further, after polymerizing the polyester, the thermal stability of the polyester can be further enhanced by removing the catalyst from the obtained polyester or deactivating the catalyst by adding a phosphorus compound or the like.

  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 adjusting the amount of diethylene glycol within the above range, the heat resistance stability can be increased, and the increase in the carboxyl end concentration 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.

  The content of the aluminum-based foreign matter insoluble in the polyester is preferably 3500 ppm or less. More preferably, it is 2500 ppm or less, More preferably, it is 1500 ppm or less, Most preferably, it is 1000 ppm or less. When the above range is exceeded, the insulation resistance may deteriorate. In addition, the aluminum-type foreign material insoluble in polyester is measured by the following method.

  30 g of a film cut to about 1 cm square and 300 ml of a parachlorophenol / tetrachloroethane (3/1: weight ratio) mixed solution were put into a round bottom flask equipped with a stirrer, and stirred and dissolved at 100 to 105 ° C. for 2 hours. The solution was allowed to cool to room temperature, and a polytetrafluoroethylene membrane filter (Advantec PTFE membrane filter, product name: T100A047A) having a diameter of 47 mm / pore size of 1.0 μm was used, and the total amount was under a pressure of 0.15 MPa. The foreign matter was filtered off with The effective filtration diameter was 37.5 mm. After completion of the filtration, the product was subsequently washed with 300 ml of chloroform, and then dried under reduced pressure at 30 ° C. overnight. The amount of aluminum element was quantified on the filtration surface of the membrane filter with a scanning fluorescent X-ray analyzer (manufactured by RIGAKU, ZSX100e, Rh line sphere 4.0 kW). The quantification was performed on a portion having a diameter of 30 mm at the center of the membrane filter. The calibration curve of the X-ray fluorescence analysis was determined using a polyethylene terephthalate resin having a known aluminum element content, and the apparent aluminum element amount was expressed in ppm. The measurement was carried out by measuring the intensity of Al-Kα rays under the conditions of PHA (wave height analyzer) 100-300 using X-ray output 50 kV-70 mA and using pentaerythritol as a spectroscopic crystal and PC (proportional counter) as a detector. . The amount of aluminum element in the PET resin for the calibration curve was quantified by high frequency inductively coupled plasma emission spectrometry.

  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 antioxidants, aromatic amines, phenols and other antioxidants can be used, and 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 preferably an oriented polyester film from the viewpoint of durability and mechanical strength, and more preferably a biaxially oriented polyester film. In the case of an oriented polyester film, a melting step of melting a polyester chip polymerized using the specific catalyst in an extruder, a film forming step of forming an unstretched film by extruding a molten resin from the extruder, It is desirable to produce the film through a stretching process of stretching in at least one direction and a heat setting process of heat-treating the stretched film. Next, the manufacturing method of the oriented polyester film of this invention is demonstrated in detail.

  In the melting step, the 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 carboxyl end concentration 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 carboxyl terminal concentration of the polyester increases, and the hydrolysis resistance may decrease.

  The polyester polymerized using the specific catalyst used in the present invention has high thermal oxidation stability, and suppresses a decrease in carboxyl end concentration during film production even when the maximum temperature in the extruder is within the above range. be able to. The difference (variation amount) between the carboxyl terminal concentration of the polyester chip used as the raw material resin and the carboxyl terminal concentration 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 0.60 dl / g is used, an 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.

  Moreover, in the case of the manufacturing method of this invention, the fall of the intrinsic viscosity in the film manufacture by heat deterioration can also be suppressed. The difference (variation) between the intrinsic viscosity (IV) of the polyester chip used as the raw material resin and the intrinsic viscosity (IV) of the polyester film after film formation is preferably 0.07 dl / g or less, and 0.06 dl / g More preferably, it is g or less. The lower limit of the fluctuation amount is considered to be 0.001 dl / g from the viewpoint of productivity.

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

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

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

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

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

  It is preferable that the thickness of the obtained polyester film for solar cells is 10-500 micrometers, More preferably, it is 15-400 micrometers, More preferably, it is 20-250 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 abrasion resistance, the surface of the polyester film for solar cells 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.

  Moreover, it is preferable that the polyester film for solar cells of the present invention 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.

  It is important for the polyester film for solar cells of the present invention that the carboxyl end concentration is 25 eq / ton or less with respect to the polyester to obtain high hydrolysis resistance as a member for solar cells. The polyester film for solar cell preferably has a carboxyl end concentration of 20 eq / ton or less, more preferably 18 eq / ton or less, still more preferably 15 eq / ton or less, and 13 eq / ton relative to the polyester. It is particularly preferably not more than ton, and particularly preferably not more than 10 eq / ton. When this value is larger than 25 eq / ton, the hydrolytic property is lowered, and the durability as a solar cell member can be exhibited, and early deterioration tends to occur. In addition, the measurement of the carboxyl terminal density | concentration of polyester can be measured by the titration method mentioned later or NMR method.

  In order to make the carboxyl end concentration of the polyester film within the above range, it is preferable that the carboxyl end concentration of the polyester chip used as the raw material resin is less than 25 eq / ton. The polyester terminal concentration of the polyester chip used is more preferably less than 20 eq / ton, more preferably less than 13 eq / ton, even more preferably less than 10 eq / ton, and less than 8 eq / ton. Is particularly preferred, and it is particularly preferred that it is less than 5 eq / ton. Setting the carboxyl terminal concentration of the polyester chip within the above range can be performed by appropriately selecting the polymerization conditions of the resin. For example, production equipment factors such as the structure of the esterification reaction apparatus, composition ratio of dicarboxylic acid and glycol in the slurry supplied to the esterification reaction tank, esterification reaction temperature, esterification reaction pressure, esterification reaction time, etc. What is necessary is just to set reaction conditions or solid layer polymerization conditions etc. suitably. Furthermore, as described above, it is preferable to control the moisture content of the polyester chip or to control the resin temperature in the melting step. It is also a preferred method to block the carboxyl terminal of the polyester with an epoxy compound or a carbodiimide compound. In addition, although the one where the carboxyl terminal density | concentration of a polyester film is smaller is preferable, it considers that 0.5eg / ton is a minimum from the point of productivity.

  In order to obtain high heat resistance and hydrolysis resistance, the polyester film for solar cell of the present invention preferably has an intrinsic viscosity (IV) value of 0.60 to 0.90 dl / g, more preferably It is 0.62-0.85 dl / g, More preferably, it is 0.65-0.8 dl / g. When the IV value is lower than 0.60 dl / g, the hydrolysis resistance and heat resistance are not sufficient, and when it is higher than 0.90 dl / g, the back pressure in the melting process becomes high, resulting in high productivity. Is not preferable, and thermal deterioration is promoted by shearing heat generation.

  The polyester film for solar cells of the present invention has a breaking elongation retention half-life in a heat resistance test at 160 ° C. of 700 hours or more, more preferably 800 hours or more. By being in such a range, the polyester film for solar cell of the present invention can exhibit long-term thermal stability that can withstand long-term use even with a large-sized and high-output solar cell.

  The polyester film for solar cells of the present invention has an elongation retention rate of 192 hours at 105 ° C., 100% RH, 0.03 MPa, which is an evaluation of hydrolysis resistance, preferably 65% or more, more preferably 70% or more. It is. By being in such a range, the polyester film for solar cells of the present invention can exhibit high hydrolysis resistance that can withstand long-term use outdoors.

The polyester film for solar cells of the present invention preferably has a density of 1.38 to 1.41 g / cm ³ , more preferably 1.39 to 1.40 g / cm ³ . When the density of the film is lower than 1.38 g / cm ³ , the dimensional stability at high temperature of the film may be deteriorated. Moreover, when the density of a film is higher than 1.41 g / cm < ³ >, the elongation retention in heat resistance evaluation may fall. As a method of controlling the film density within the above range, it can be carried out by appropriately controlling the stretching ratio in the stretching step.

  The polyester film for solar cell of the present invention preferably has a thermal shrinkage rate at 150 ° C. of −0.5% to 2.0% in both the longitudinal direction (longitudinal direction) and the width direction (lateral direction). More preferably, it is 5% to 1.8%. In addition, for example, when a more severe heat shrinkage rate is required as a solar cell such as use at a high temperature or high temperature processing, the heat shrinkage rate at 150 ° C. is both in the longitudinal direction (longitudinal direction) and the width direction (lateral direction). -0.5% to 0.5% is preferable. Thereby, the generation | occurrence | production of the curl at the time of heat processing, such as adhesion layer formation, and a lamination | stacking state can be suppressed. As a method of setting the heat shrinkage rate at 150 ° C. in the above range, it can be carried out by controlling stretching conditions or performing longitudinal relaxation treatment and transverse relaxation treatment in the heat setting step.

  In order to maintain the elongation at break, it is preferable to balance the orientation of the film in the vertical and horizontal directions. The MOR value (MOR-C) when the film thickness of the polyester film for solar cells of the present invention is converted to 50 μm is preferably 1.0 to 2.0, and preferably 1.3 to 1.8. Is more preferable. As a result, the balance between the vertical and horizontal films is adjusted, which is effective in maintaining the mechanical strength and durability. In addition, the occurrence of curling at the time of stacking can be suppressed, which is effective in improving adhesion. As a method for bringing MOR-C into the above range, it can be carried out by controlling the ratio of the longitudinal and lateral stretching ratios in the stretching step.

  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.

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

(2) 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.

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

(4) Method for measuring carboxyl terminal concentration 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 carboxyl terminal concentration Using the titration amounts XA, XB and XC for each dissolution time, the titration amount V (ml) at a dissolution time of 0 minutes is determined by the least square method. Similarly, titration volume V0 (ml) is obtained using Xa, Xb, and Xc. Subsequently, the carboxyl terminal concentration was calculated | required according to following Formula.
Carboxyl terminal concentration (eq / ton) = [(V−V0) × 0.04 × NF × 1000] / W
NF: factor of 0.04 mol / l potassium hydroxide solution W: sample weight (g)

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

(6) Thermal stability parameter (TS)
The film was pulverized to a side of 1 mm or less, 1 g of the obtained film sample (before melting test; [IV] _i ) was placed in a glass test tube having an inner diameter of about 14 mm and vacuum-dried at 130 ° C. for 12 hours. It connected to the vacuum line, and after repeating pressure reduction and nitrogen filling 5 times or more, nitrogen was sealed so as to be 100 Torr and sealed. This test tube is immersed in a salt bath at 300 ° C. and maintained in a molten state for 2 hours, and then a sample is taken out, freeze-ground by the above method, vacuum dried, and then IV (after the melt test; [IV] _f2 ) It was measured. From this [IV] _f2 , TS was determined using the following formula.
TS = 0.245 {[IV] _f2 ^-1.47- [IV] _i ^-1.47 }

(7) Moisture content of polyester chip Using a moisture content measuring instrument (VA-05 type, manufactured by Mitsubishi Kasei), heat treatment was performed on chips 1 to 2 g at 230 ° C. for 10 minutes, and moisture contained in the chip. Is evaporated and the moisture content is measured.

(8) Density of polyester film It measured at 25 degreeC using the density gradient tube according to JISK7112.

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

(10) Thermal contraction rate of film at 150 ° C. (HS150)
The film was cut into a size of 10 mm in width and 250 mm in length along the direction in which the long side (250 mm) coincided with the longitudinal direction and the width direction, marked at intervals of 200 mm, and the interval A was measured with a constant tension of 5 g. . Subsequently, it was left in an oven at 150 ° C. for 30 minutes with no load. After the film was taken out of the oven and cooled to room temperature, the mark interval B was determined under a constant tension of 5 g, and the thermal shrinkage rate was determined by the following equation. In addition, the heat shrinkage rate at 150 ° C. of the film is measured at 100 mm intervals in the film width direction, the average value of three samples is rounded off to the third decimal place, and rounded to the second decimal place. The values in the direction with larger values in the longitudinal direction and the width direction were used.
Thermal contraction rate (%) = [(A−B) / A] × 100

(11) MOR-C
The obtained film was divided into 5 equal parts in the width direction, 100 mm square samples were taken in the longitudinal direction and the width direction at each position, and a microwave transmission type molecular orientation meter (Oji Scientific Instruments MOA-6004) was used. And measured. The thickness correction was 50 μm, MOR-C was determined, and an average value of 5 points was used.

Example 1
(1) Preparation of polycondensation catalyst solution (preparation of ethylene glycol solution of phosphorus compound)
After adding 2.0 liters of ethylene glycol to a flask equipped with a nitrogen introduction tube and a cooling tube at room temperature and normal pressure, while stirring at 200 rpm in a nitrogen atmosphere, Irganox 1222 (Ciba 39) represented by -200 g of Specialty Chemicals) 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.

(2) Esterification reaction and polycondensation A high-speed stirrer is provided in the transfer line from the third esterification reaction tank to the first polycondensation reaction tank, comprising three continuous esterification reaction tanks and three polycondensation reaction tanks. 0.75 parts by mass of ethylene glycol with respect to 1 part by mass of high-purity terephthalic acid was continuously supplied to a slurry preparation tank. The prepared slurry is continuously supplied, the first esterification tank has a reaction temperature of 250 ° C. and 110 kPa, the second esterification reaction tank has 260 ° C. and 105 kPa, the third esterification reaction tank has 260 ° C. and 105 kPa, and the second ester A polyester oligomer was obtained by continuously adding 0.025 parts by mass of ethylene glycol to the chemical reaction tank. The oligomer is continuously transferred to a continuous polycondensation apparatus comprising three reaction tanks, and the ethylene glycol solution of the aluminum compound and the ethylene glycol solution of the phosphorus compound prepared by the above method in an in-line mixer installed in the transfer line. Are continuously added while stirring with an agitating mixer so as to be 0.015 mol% and 0.036 mol% as aluminum atoms and phosphorus atoms with respect to the acid component in the polyester, respectively. Is 265 ° C., 9 kPa, medium-term polycondensation reaction tank is 265-268 ° C., 0.7 kPa, final polycondensation reaction tank is 273 ° C., 13.3 Pa, and polycondensation is IV 0.620 dl / g, carboxyl end concentration is 12.5 eq / Ton PET was obtained.

  The obtained PET resin was subjected to solid phase polymerization at a reduced pressure of 0.5 mmHg at 220 ° C. under a reduced pressure of 0.5 mmHg using a rotary type vacuum polymerization apparatus, and polyester chips having various IV values and carboxyl terminal concentrations as shown in Table 1. It was created.

(3) 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. , Dried at 135 ° C. for 10 hours under reduced pressure (1 Torr), and then supplied to the extruder. The maximum resin temperature up to the melter, kneader, polymer tube, gear pump and filter of the extruder is 290 ° C. The temperature was set to 0 ° C., and the sheet was extruded from a die. Each of these polymers was filtered using a stainless steel sintered filter medium (nominal filtration accuracy 20 μm particles 95% cut). Further, the resin temperature of the flat die was set to 285 ° C. 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)
Example 1 except that a PET chip with an IV of 0.85 dl / g was used, and the maximum resin temperature up to the melter, kneading part, polymer tube, gear pump, and filter of the extruder was 295 ° C., and the subsequent polymer tube was 290 ° C. Film formation was carried out in the same manner as above to obtain a biaxially stretched PET film having a thickness of 50 μm. The properties of the obtained PET film are shown in Table 1.

(Example 3)
Except that the thickness of the unstretched film was adjusted by adjusting the casting speed, a film was formed in the same manner as in Example 1 to obtain a biaxially stretched PET film having a thickness of 350 μm. The properties of the obtained PET film are shown in Table 1.

Example 4
Use a tenter clip with a structure that can relax 3.0% in the vertical direction. After heat setting, perform a relaxation treatment in the width direction at 200 ° C, and at the same time narrow the gap between the clips and 3.0% in the longitudinal direction. Except for relaxation, a film was formed in the same manner as in Example 1 to obtain a biaxially stretched PET film having a thickness of 50 μm. The properties of the obtained PET film are shown in Table 1.

(Example 5)
The same method as in Example 1 except that the thickness of the unstretched film was adjusted by adjusting the casting speed, the stretching ratio in the longitudinal direction was 3.5 times, and the stretching ratio in the width direction was 4.2 times. A biaxially stretched PET film having a thickness of 50 μm was obtained. The properties of the obtained PET film are shown in Table 1.

(Comparative Example 1)
After transesterification using 100 parts by mass of dimethylene terephthalate, 64 parts by mass of ethylene glycol and 0.09 parts by mass of calcium acetate, trimethyl phosphate and antimony trioxide were polymerized at 0.03% by mass, and IV was 0.60 dl / g, PET having a carboxyl terminal concentration of 11 eq / ton was obtained. The obtained PET was subjected to solid phase polymerization in the same manner as in Example 1 to obtain a PET chip having an IV value and a carboxyl terminal concentration as shown in Table 1. Using this PET chip, a film was formed in the same manner as in Example 1 to obtain a biaxially stretched PET film having a thickness of 50 μm. The properties of the obtained PET film are shown in Table 1.

(Comparative Example 2)
The conditions for solid phase polymerization were changed to obtain PET chips having IV values and carboxyl terminal concentrations shown in Table 1. Using this PET chip, a film was formed in the same manner as in Example 1 to obtain a biaxially stretched PET film having a thickness of 50 μm. The properties of the obtained PET film are shown in Table 1.

  The polyester film for solar cells of the present invention has excellent hydrolysis resistance and long-term thermal stability. Therefore, it is useful as a constituent member for a solar cell such as a solar cell back surface sealing sheet, a solar cell surface protective sheet, and a solar cell bonding member having flexibility.

Claims (14)

  A polyester film comprising, as a main component, a polyester polymerized using a polycondensation catalyst containing aluminum and / or a compound thereof and a phosphorus compound having an aromatic group in the molecule, and having a carboxyl terminal concentration in the polyester The polyester film for solar cells, wherein the film is 25 eq / ton or less and the intrinsic viscosity (IV) of the film is 0.60 to 0.90 dl / g.   The polyester film for solar cells according to claim 1, wherein the phosphorus compound is one or more compounds selected from the group consisting of phosphonic acid compounds and phosphinic acid compounds. The solar cell according to claim 1, wherein the phosphorus compound is one or more selected from the group consisting of compounds represented by the following general formulas (1) to (2). Polyester film.
(Formula (1) and (2) in, R ^1, R ⁴ are each independently hydrogen, 1 to 50 carbon atoms hydrocarbon group, a hydroxyl group or 1 to 50 carbon atoms containing a halogen group, an alkoxyl group, or an amino group 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 or an aromatic ring structure.) The polyester film for solar cells according to claim 3, wherein R ¹ and R ^{4 in the} general formulas (1) to (2) are groups having an aromatic ring structure.   The polyester film for solar cells according to claim 1, wherein the phosphorus compound has a phenol part in the same molecule. 6. The phosphorus compound having a phenol moiety in the same molecule is one or more selected from the group consisting of compounds represented by the following general formulas (3) to (4). Polyester film for solar cells.
(In the formulas (3) to (4), R ¹ is a carbon group having 1 to 50 carbon atoms including a phenol part, a hydroxyl group, a halogen group, an alkoxyl group, an amino group and a phenol part. R ⁴ represents 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 a hydrocarbon group having 1 to 50 carbon atoms, R ² , 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 hydroxyl group or an alkoxyl group, provided that the hydrocarbon group represents a branched structure, alicyclic structure or aromatic group. (It may contain a ring structure. The ends of R ² and R ⁴ may be bonded to each other.)   A polyester film comprising, as a main component, a polyester polymerized using a polycondensation catalyst containing an aluminum salt of a phosphorus compound, having a carboxyl terminal concentration of 25 eq / ton or less relative to the polyester, and having an intrinsic viscosity (IV ) Is 0.60 to 0.90 dl / g, a polyester film for solar cells. A polyester film mainly comprising polyester polymerized using a polycondensation catalyst containing at least one selected from compounds represented by the following general formula (5), wherein the film has a carboxyl end concentration Is 25 eq / ton or less with respect to polyester, and the intrinsic viscosity (IV) of a film is 0.60-0.90 dl / g, The polyester film for solar cells characterized by the above-mentioned.
(In formula (7), 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 The hydrocarbon group has an alicyclic structure, a branched structure, or an aromatic ring structure. May be included.)   The biaxially oriented polyester film for sealing a back surface of a solar cell according to any one of claims 1 to 8, wherein a half life of breaking elongation in a heat resistance test at 160 ° C is 700 hours or more. The density of a film is 1.38-1.41 g / cm < ³ >, The polyester film for solar cells in any one of Claims 1-9 characterized by the above-mentioned.   11. The polyester film for solar cells according to claim 1, wherein the film has a thermal shrinkage rate at 150 ° C. of −0.5% or more and 2.0% or less in both the longitudinal direction and the width direction. . 12. The polyester film for solar cells according to claim 1, wherein the film has a thermal shrinkage rate at 150 ° C. of −0.5% or more and 0.5% or less in both the longitudinal direction and the width direction. .   The polyester film for solar cells according to any one of claims 1 to 12, wherein the MOR value (MOR-C) when the film thickness is converted to 50 µm is 1.0 to 2.0. A melting step for melting a polyester chip in an extruder, a film forming step for forming an unstretched film by extruding a molten resin from the extruder, a stretching step for stretching in at least one direction of the unstretched film, and a stretched film In the manufacturing method of the polyester film for solar cells including the heat setting process to heat-treat,
The maximum temperature of the polyester resin in the melting process is 280 ° C. or higher,
The difference of the carboxyl terminal density | concentration of this polyester chip and the carboxyl terminal density | concentration of this polyester film for solar cells is 6 eq / ton or less, The polyester film for solar cells in any one of Claims 1-13 characterized by the above-mentioned. Production method.