JP2014065882A - Polyester film, and solar battery back sheet and solar battery using the film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film having sufficient moisture-heat resistance and hue while containing no heavy metal element, and to provide a solar battery back sheet having high durability by using a film for a solar battery back sheet, and a solar battery using the back sheet.SOLUTION: A biaxially oriented polyester film is provided, which contains at last one metal element selected from a calcium element, a manganese element and an aluminum element. A polyester constituting the polyester film has 5 ppm or less content of a calcium element and of divalent metal elements excluding a manganese element, has 1 ppm or more and 20 ppm or less content of a titanium element excluding a titanium element derived from titanium oxide, 5 ppm or more and 100 ppm or less content of phosphorus element, and 3 ppm or more and 100 ppm or less content of alkali metal elements. When the titanium element content, the phosphorus element and the alkali metal element content with respect to the polyester are denoted by T (mol/ton), P (mol/ton), and M1 (mol/ton), respectively, these contents satisfy expressions (i):0.13≤T/P≤0.85 and (ii):T/M1≥0.1.

Description

  The present invention particularly relates to a polyester film that can be suitably used as a solar battery back sheet, and also relates to a solar battery back sheet and a solar battery using the film.

  Polyester (especially polyethylene terephthalate, polyethylene-2, 6-naphthalenedicarboxylate, etc.) resins are excellent in mechanical properties, thermal properties, chemical resistance and electrical properties and are used in various applications. The polyester film made from the polyester, especially the biaxially oriented polyester film, is a copper-laminated laminate, solar battery backsheet, adhesive tape, flexible printed circuit board, membrane switch, planar heating element, due to its mechanical and electrical properties. It is also used as various industrial materials such as electrical insulation materials such as flat cables, magnetic recording materials, capacitor materials, packaging materials, automotive materials, building materials, photographic applications, graphic applications, thermal transfer applications.

  Of these uses, solar battery backsheets used outdoors are often used in harsh environments over long periods of temperature and humidity. Therefore, if a general-purpose polyester is used as the resin constituting the solar battery back sheet, the molecular weight is reduced by hydrolysis, and the embrittlement progresses and the mechanical properties and the like are lowered. There is a need for improved thermal properties. In addition, if a heavy metal element is contained in the resin constituting the solar cell backsheet, the heavy metal element contained in the resin constituting the solar cell backsheet is used in the process of using the solar cell for many years or in the process of discarding the solar cell. There is a concern of being discharged into the environment. Therefore, in recent years, from the viewpoint of environmental protection, it is also required to reduce the amount of heavy metal elements contained in the resin constituting the solar cell backsheet. In general, hydrolysis of a polyester in a moist and hot atmosphere proceeds using the terminal carboxyl group of the polyester as an autocatalyst, and as a result of hydrolysis of the polyester, the amount of terminal carboxyl groups further increases and hydrolysis proceeds further. Therefore, in order to improve wet heat resistance, it is necessary to suppress an increase in the amount of terminal carboxyl groups in a wet heat atmosphere. In patent document 1, the technique which adds polycarbodiimide and improves heat-and-moisture resistance is examined. Patent Document 2 discusses a solar battery backsheet composed of a polyester resin that does not contain a heavy metal element using a titanium compound as a polymerization catalyst. In Patent Documents 3, 4, and 5, by adding phosphoric acid and alkali metal phosphate, the increase in the amount of terminal carboxyl groups of the polyester in a moist heat atmosphere is suppressed, and the heat and moisture resistance of the film comprising the polyester composition is reduced. Techniques to improve are being studied. In Patent Documents 6, 7, 8, and 9, the ratio of the content of the phosphorus compound and the content of the metal compound is adjusted to suppress an increase in the amount of terminal carboxyl groups of the polyester in a humid heat atmosphere, thereby improving the durability of the polyester. Technology to make it happen is being studied.

Japanese National Patent Publication No. 11-506487 JP 2007-204538 A JP 2010-248492 A International Publication No. 2010/103945 International Publication No. 2011/052290 JP 2003-306536 A JP 2008-81533 A JP 2006-265792 A JP 2000-309649 A

  However, in Patent Document 1, although the effect of improving the heat and moisture resistance is high, the compound produced by the reaction of polycarbodiimide and polyester has low heat resistance, and therefore, a decomposition gas harmful to the human body is generated during melt molding. There is a problem. In Patent Document 2, there is a problem that the amount of terminal carboxyl group increased in a humid heat atmosphere increases, and the resulting polyester film is yellowish and inferior in color tone due to the high catalytic activity of the titanium compound used as a polymerization catalyst. is there. In Patent Documents 3 to 8, the heat and humidity resistance of the polyester film is not sufficient, and when a titanium compound is used as the polymerization catalyst, the resulting polyester film is inferior in color tone. In Patent Document 9, the effect of improving the heat and moisture resistance of the phosphorus compound contained in the polyester is not sufficient, and the heat and heat resistance of the resulting polyester film is not sufficient. Moreover, when a titanium compound is used as a polymerization catalyst, the color tone is inferior.

  As described above, the conventional technique does not contain a heavy metal element, has no problem in safety and color tone, and has not been able to sufficiently suppress an increase in the amount of terminal carboxyl groups in a humid heat atmosphere. For this reason, there is a problem in that the mechanical properties cannot be maintained because the hydrolysis reaction of the polyester film proceeds during long-term use.

  Therefore, the problem of the present invention is that no heavy metal element such as an antimony compound is used, or the amount used is small, and even when a titanium compound is used as a polymerization catalyst, yellowness can be suppressed and the color tone is excellent, and An object of the present invention is to provide a polyester film that can suppress an increase in the amount of terminal carboxyl groups in a moist heat atmosphere, and that exhibits excellent moist heat resistance.

In order to solve the above problems, the present invention has the following configuration.
(1) The polyester constituting the polyester film contains at least one metal element of calcium element, manganese element, and aluminum element, and the amount of divalent metal elements other than calcium element and manganese element contained in the polyester is 5 ppm or less for each of the polyesters, the amount of titanium element excluding titanium element derived from titanium oxide is 1 ppm or more and 20 ppm or less, the amount of phosphorus element is 5 ppm or more and 100 ppm or less, and the alkali metal element content is 3 ppm or more and 100 ppm or less,
When the titanium element content with respect to the polyester is T (mol / ton), the phosphorus element content is P (mol / ton), and the alkali metal element content is M1 (mol / ton), the following formula (i) The biaxially oriented polyester film characterized by satisfying the formula (ii).
(I) 0.13 ≦ T / P ≦ 0.85
(Ii) T / M1 ≧ 0.1
(2) The biaxially oriented polyester film as described in (1), wherein the sum of the contents of calcium element, manganese element and aluminum element with respect to the polyester is 5 ppm or more and 150 ppm or less.
(3) The alkali metal element content with respect to the polyester is M1 (mol / ton), the sum of the calcium element content and the manganese element content is M2 (mol / ton), and the aluminum element content is M3 (mol / ton). The metal content Ma (mol / ton) and the phosphorus element content P (mol / ton) in the polyester, which are obtained by the following formula (iii), satisfy the following formula (iv): The biaxially oriented polyester film according to (1) or (2).
(Iii) Ma = M1 / 2 + M2 + 3 × M3 / 2
(Iv) 0.75 ≦ Ma / P ≦ 3.0
(4) The biaxially oriented polyester film according to (1), which contains at least one metal element of calcium element and manganese element.
(5) The biaxially oriented polyester film according to (4), wherein the total content of calcium element and manganese element is 5 ppm or more and 150 ppm or less with respect to the polyester.
(6) When the alkali metal element content with respect to the polyester is M1 (mol / ton) and the sum of the calcium element content and the manganese element content is M2 (mol / ton), the following formula (v) is obtained. The metal content Mb (mol / ton) and the phosphorus element content P (mol / ton) in the polyester satisfy the following formula (vi), (2) according to (4) or (5) Axial-oriented polyester film.
(V) Mb = M1 / 2 + M2
(Vi) 0.75 ≦ Mb / P ≦ 3.0
(7) The biaxially oriented polyester film according to any one of (1) to (6), wherein the alkali metal element contained in the polyester is at least one of potassium element and sodium element.
(8) The biaxially oriented polyester film according to any one of (1) to (7), wherein the polyester is obtained by adding phosphoric acid and an alkali metal phosphate.
(9) The polyester is obtained by adding a titanium compound (excluding titanium oxide) having at least one substituent selected from the group consisting of an alkoxy group, a phenoxy group, an acylate group, an amino group, and a hydroxyl group. The biaxially oriented polyester film according to any one of (1) to (8).
(10) The biaxially oriented polyester film according to any one of (1) to (9), which is used for a solar battery backsheet.
(11) A solar battery back sheet using the biaxially oriented polyester film according to any one of (1) to (10).
(12) A solar cell using the solar cell back sheet according to (11).

  ADVANTAGE OF THE INVENTION According to this invention, the polyester film which does not contain a heavy metal element or has little content of a heavy metal element and satisfies moisture-heat resistance and color tone can be provided. Furthermore, by using such a polyester film, a high-performance solar battery backsheet and a solar battery using the same can be provided.

The polyester film of the present invention is a biaxially oriented polyester film. In general, a biaxially oriented polyester film can be obtained by stretching an unstretched polyester sheet in the sheet longitudinal direction and width direction, followed by heat treatment to complete crystal orientation. In the present invention, the polyester constituting the biaxially oriented polyester film needs to satisfy the following requirements (I) to (V).
(I) It contains at least one metal element of calcium element, manganese element, and aluminum element, and the content of divalent metal elements other than calcium element and manganese element is 5 ppm or less with respect to the polyester.
(II) The titanium element content excluding the titanium element derived from titanium oxide is 1 ppm or more and 20 ppm or less with respect to the polyester.
(III) The phosphorus element content is 5 ppm or more and 100 ppm or less with respect to the polyester.
(IV) The alkali metal element content is 3 ppm or more and 100 ppm or less with respect to the polyester.
(V) When the titanium element content with respect to the polyester is T (mol / ton), the phosphorus element content is P (mol / ton), and the alkali metal element content is M1 (mol / ton), the following (i) Satisfy equation (ii).
(I) 0.13 ≦ T / P ≦ 0.85
(Ii) T / M1 ≧ 0.1
Hereinafter, the present invention will be described in detail with specific examples.

  As for the polyester film of this invention, polyester needs to comprise a film. The term “polyester constitutes a film” here means that the resin constituting the film contains 80% by weight or more of polyester. The content of polyester in the resin constituting the film is preferably 90% by weight or more, more preferably 95% by weight or more, and particularly preferably 98% by weight or more.

  The polyester referred to in the present invention has a dicarboxylic acid component and a diol component. In addition, in this specification, a structural component shows the minimum unit which can be obtained by hydrolyzing polyester.

  Examples of the dicarboxylic acid component constituting the polyester include, but are not limited to, dicarboxylic acids such as aliphatic dicarboxylic acids, alicyclic dicarboxylic acids, and aromatic dicarboxylic acids, and ester derivatives thereof. . Examples of the aliphatic dicarboxylic acids include malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, dimer acid, eicosandioic acid, pimelic acid, azelaic acid, methylmalonic acid, ethyl And malonic acid. Examples of the alicyclic dicarboxylic acids include adamantane dicarboxylic acid, norbornene dicarboxylic acid, cyclohexane dicarboxylic acid, decalin dicarboxylic acid, and the like. Examples of the aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and 1,8-naphthalenedicarboxylic acid. Acid, 4,4′-diphenyl dicarboxylic acid, 4,4′-diphenyl ether dicarboxylic acid, 5-sodium sulfoisophthalic acid, phenyl endandicarboxylic acid, anthracene dicarboxylic acid, phenanthrene dicarboxylic acid, 9,9′-bis (4-carboxyl) Phenyl) fluoric acid and the like.

  Examples of the diol component constituting the polyester include diols such as aliphatic diols, alicyclic diols, and aromatic diols, and those in which a plurality of such diols are linked. It is not limited to these. Examples of the aliphatic diols include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, 1,3-butanediol, and the like. . Examples of the alicyclic diols include cyclohexanedimethanol, spiroglycol, and isosorbide. Examples of aromatic diols include bisphenol A, 1,3-benzenedimethanol, 1,4-benzenedimethanol, 9,9'-bis (4-hydroxyphenyl) fluorene, and the like.

  The polyester constituting the polyester film of the present invention is a polyester mainly composed of terephthalic acid and / or 2,6-naphthalenedicarboxylic acid and ethylene glycol from the viewpoint of mechanical properties, crystallinity, and heat and humidity resistance. Is preferred. The polyester mainly composed of terephthalic acid and / or 2,6-naphthalenedicarboxylic acid and ethylene glycol has a ratio of terephthalic acid and / or 2,6-naphthalenedicarboxylic acid component in all dicarboxylic acid components. It refers to a polyester having 90 mol% or more and the proportion of ethylene glycol constituents in all diol constituents being 90 mol% or more. By making the ratio of the constituents of terephthalic acid and / or 2,6-naphthalenedicarboxylic acid in all dicarboxylic acid constituents, and the ratio of ethylene glycol constituents in all diol constituents within the above ranges, mechanical properties, Crystallinity and wet heat resistance can be improved.

  The polyester constituting the polyester film of the present invention has a constituent component having three or more carboxylic acid groups and / or hydroxyl groups as a copolymerization component, and is 0.025 mol% or more and 1.5 mol% or less with respect to all the constituent components of the polyester. It is preferable to contain.

  The component having 3 or more carboxylic acid groups and / or hydroxyl groups herein refers to one having 3 or more carboxylic acid groups and / or hydroxyl groups in one molecule.

  When a component having three or more carboxylic acid groups and / or hydroxyl groups is copolymerized, molecular chains are cross-linked at the polyfunctional compound component. As a result of crosslinking, the molecular mobility of the molecular chain is lowered, and the progress of hydrolysis is further suppressed, which is preferable. Trimerization of trimellitic acid, cyclohexanetricarboxylic acid, biphenyltetracarboxylic acid, pyromellitic acid, butanetetracarboxylic acid, and long-chain aliphatic carboxylic acid as components having 3 or more carboxylic acid groups and / or hydroxyl groups Polycarboxylic acids such as trimer acid and anhydrides and esters thereof, glycerin, pentaerythritol, dipentaerythritol, trimethylolpropane, ditrimethylolpropane, trihydroxybenzene, trihydroxyhexane and other polyhydric alcohols, citric acid, dihydroxy Examples thereof include polyvalent hydroxycarboxylic acids such as benzenecarboxylic acid and dihydroxynaphthalenecarboxylic acid, and anhydrides and esters thereof. In particular, a component having three carboxylic acid groups and / or three hydroxyl groups is preferred from the viewpoint of heat and humidity resistance and film moldability.

  The polyester constituting the polyester film of the present invention contains at least one metal element of calcium element and manganese element, and the content of divalent metal elements other than calcium element and manganese element is relative to the polyester, respectively. And 5 ppm or less. The reason for this will be described later.

  Here, the metal element contained in the polyester includes not only atoms but also those existing in the polyester in an ionic state. In general, the metal element exists in an ionic state in the polyester. The divalent metal element is an alkaline earth metal element up to the 3rd period of the chemical periodic table, an element from the 1st group to the 12th group after the 5th period, and a 4th period transition excluding Ti. Refers to a metal element. The valence of the metal element in the present invention is the total number of electrons existing in the outermost shell or the s orbital closest to the outermost shell among the electron orbits of the metal atoms.

  In the polyester constituting the polyester film of the present invention, the titanium element content excluding the titanium element derived from titanium oxide needs to be 1 ppm or more and 20 ppm or less with respect to the polyester. Here, a titanium compound containing a titanium element excluding a titanium element derived from titanium oxide has a polymerization catalyst ability and functions as a polymerization catalyst. If the titanium element content excluding titanium element derived from titanium oxide is less than 1 ppm with respect to the polyester, the polymerization activity is not sufficiently obtained, the polymerization time is delayed, and the thermal history received is increased, The resulting polyester is colored yellow and inferior in color tone, or has an increased amount of terminal carboxyl groups, and is inferior in heat and moisture resistance. When the content of titanium element excluding titanium element derived from titanium oxide exceeds 20 ppm with respect to the polyester, the resulting polyester is colored yellow or the polymerization activity is too high, so gelation or bumping occurs during the polymerization. The polyester cannot be obtained, or even if the polyester is obtained, the heat and moisture resistance is poor. The titanium element content excluding the titanium element derived from titanium oxide is preferably 8 ppm or more and 16 ppm or less with respect to the polyester from the viewpoints of polymerization reactivity, color tone, and heat and humidity resistance.

  The polyester constituting the polyester film of the present invention needs to have a phosphorus element content of 5 ppm to 100 ppm with respect to the polyester. When the phosphorus element content is less than 5 ppm, the heat resistance of the polyester is deteriorated, the thermal history received during film molding and extrusion, the deterioration of the polyester proceeds, and the amount of terminal carboxyl groups of the polyester constituting the resulting polyester film is Larger and inferior in heat and humidity resistance. When the phosphorus element content exceeds 100 ppm, the phosphorus compound containing the phosphorus element deactivates the polymerization activity of the titanium compound that acts as a polymerization catalyst, so that the polymerization activity cannot be sufficiently obtained and the polymerization time is delayed. Or polyester having a sufficient degree of polymerization cannot be obtained.

  The polyester constituting the polyester film of the present invention needs to have an alkali metal element content of 3 ppm or more and 100 ppm or less in terms of alkali metal element with respect to the polyester. If the alkali metal element content is less than 3 ppm, the color tone of the resulting polyester film is inferior, and if it exceeds 100 ppm, there is a concern about the formation of foreign matter, and the resulting polyester film is inferior in the heat and moisture resistance.

  The alkali metal element, manganese element, and calcium element contained in the polyester constituting the polyester film of the present invention are chemically bonded to a phosphorus element-containing compound or a terminal carboxyl group of the polyester, thereby deactivating the polymerization catalyst by the phosphorus compound. It has the effect of suppressing or inhibiting hydrolysis by suppressing the autocatalytic action of the terminal carboxyl group. The alkali metal element is effective in suppressing the deactivation of the polymerization catalyst, and the manganese element and calcium element are effective in suppressing the deactivation of the polymerization catalyst and the hydrolysis by suppressing the autocatalytic action of the terminal carboxyl group.

  Furthermore, when using a titanium compound as a polymerization catalyst when synthesizing the polyester constituting the polyester film, if an alkali metal element is contained in the polyester, the polyester has a color tone improving effect that suppresses yellowing of the polyester. At present, the detailed mechanism to achieve this effect is not known, but the deterioration of the color tone of the polyester by using the titanium compound as a polymerization catalyst is caused by the coordination of the titanium compound to the carbonyl oxygen of the ester group of the polyester. The alkali metal element is presumed to have an effect of improving the color tone by suppressing the coordination of the ester group of the titanium compound to the carbonyl oxygen.

  In general, metal ions contained in polyester chemically bond with oxygen of a carbonyl group including a terminal carboxyl group. In particular, when the metal ion is chemically bonded to oxygen of the carbonyl group of the terminal carboxyl group, the presence of water molecules causes the autocatalytic action of the terminal carboxyl group, thereby causing hydrolysis and deterioration of the polyester. In order to suppress this hydrolysis, it is effective to stabilize the metal ion chemically bonded to the terminal carboxyl group and the water molecule. That is, it is effective to hydrate metal ions and water molecules. As an index of this effect, the product of the hydration enthalpy of the metal ion and the radius of the metal ion can be used. Examples of metal elements having a large product value include calcium ions, manganese ions, and aluminum ions. Polyesters containing these metal ions can effectively stabilize water molecules, and as a result, the moisture and heat resistance of the polyester can be improved. That is, the polyester constituting the polyester film of the present invention needs to contain at least one metal element of calcium element, manganese element, and aluminum element. Compared with calcium and manganese elements, which are trivalent metal ions, the aluminum element, which is a trivalent metal ion, is more coordinated with the oxygen of the ester group in the polyester than calcium elements and manganese elements. It happens strongly. Therefore, a positive charge is more induced in the carbon of the ester group, and water molecules are likely to approach the vicinity of the ester group. As a result, the effect of improving heat and moisture resistance is relatively small compared to calcium and manganese elements. Therefore, it is preferable that the polyester constituting the polyester film of the present invention contains at least one metal element of calcium element and manganese element. On the other hand, in the polyester constituting the polyester film of the present invention, when the content of any divalent metal element other than manganese element or calcium element exceeds 5 ppm with respect to the polyester, manganese element, calcium element, aluminum The effect of improving moisture and heat resistance by elements cannot be obtained.

The polyester constituting the polyester film of the present invention has a titanium element content of T (mol / ton), a phosphorus element content of P (mol / ton), and an alkali metal element content of M1 (mol / ton). , It is necessary to satisfy the following equations (i) and (ii).
(I) 0.13 ≦ T / P ≦ 0.85
(Ii) T / M1 ≧ 0.1
When T / P is less than 0.13, the polymerization activity of the titanium compound acting as a polymerization catalyst is deactivated, so that the polymerization activity is not sufficiently obtained, the polymerization time is delayed, and the resulting polyester is yellow. It has a taste and is inferior in color tone, or has an increased amount of terminal carboxyl groups and is inferior in moisture and heat resistance. When T / P exceeds 0.85, the heat resistance of the polyester is deteriorated. Therefore, the deterioration of the polyester proceeds due to the thermal history received during film forming and extrusion, and the amount of terminal carboxyl groups of the resulting polyester film increases. Inferior to heat and humidity resistance. Preferably, the range of T / P is 0.4 or more and 0.6 or less.

  Further, if T / M1 is less than 0.1, foreign matter is generated and the heat and moisture resistance is poor. In general, under a moist heat atmosphere, polyester undergoes a hydrolysis reaction to lower the molecular weight, increase the mobility of the molecular chain, and facilitate crystallization. As crystallization progresses, the film becomes brittle, and when an impact is applied, the stress is insufficiently distributed, so that even a slight impact is applied, it will be in a state of breaking, resulting in poor moisture and heat resistance. It will be a thing. When a foreign substance is generated in the polyester film, crystallization with the foreign substance as a nucleus progresses further, and it becomes easy to form an enlarged crystal, so that the heat resistance of the resulting polyester film is lowered. Therefore, it is preferable that there are few foreign materials from a heat-and-moisture resistant viewpoint. The upper limit of T / M1 is not particularly provided, but is preferably 1.0 or less from the viewpoint of color tone. More preferably, it is 0.7 or less, more preferably 0.3 or less, even more preferably 0.2 or less, and most preferably 0.15 or less.

  In the polyester constituting the polyester film of the present invention, the sum of the contents of calcium element, manganese element and aluminum element is preferably 5 ppm or more and 150 ppm or less. If the sum of the contents of calcium element, manganese element, and aluminum element is less than 5 ppm, the above-described effects of inhibiting the deactivation of the polymerization catalyst by the manganese element, calcium element, and aluminum element and the effect of inhibiting the self-catalyst of the terminal carboxyl group are not sufficient. For this reason, the heat and humidity resistance may decrease. When the sum of the contents of calcium element, manganese element, and aluminum element exceeds 150 ppm, there is a concern of foreign matters and a decrease in wet heat resistance. As described above, calcium element and manganese element have a higher effect of improving heat and humidity resistance than aluminum element. Therefore, the polyester constituting the polyester film of the present invention has a total content of calcium element and manganese element of 5 ppm or more and 150 ppm or less. It is preferable that The sum of the contents of calcium element and manganese element is more preferably 5 ppm or more and 100 ppm or less, and further preferably 5 ppm or more and 50 ppm or less.

  The polyester constituting the polyester film of the present invention preferably has a metal element content of true specific gravity of 5.0 or more of 50 ppm or less. By controlling the content of the true specific gravity of 5.0 or more in the polyester to 50 ppm or less, it is possible to suppress the discharge of heavy metal elements into the environment when the polyester film of the present invention is used as a solar battery back sheet. it can. The true specific gravity in the present invention refers to a specific gravity that does not include voids, and the specific gravity refers to the ratio of the mass of a substance in the same volume to the standard substance (water at 4 ° C.). Specific examples of the metal element having a true specific gravity of 5.0 or more include an antimony element, a germanium element, a cobalt element, a tin element, a zinc element, a manganese element, a lead element, and a cadmium element. The content of the metal element having a true specific gravity of 5.0 or more is more preferably 30 ppm or less.

In the polyester film of the present invention, in the polyester constituting the polyester film, the alkali metal element content with respect to the polyester is M1 (mol / ton), and the sum of the calcium element content and the manganese element content is M2 (mol / ton). ), When the aluminum element content is M3 (mol / ton), the metal content Ma (mol / ton) and the phosphorus element content P (mol / ton) in the polyester obtained by the following formula (iii): However, it is preferable that the following formula (iv) is satisfied.
(Iii) Ma = M1 / 2 + M2 + 3 × M3 / 2
(Iv) 0.75 ≦ Mb / P ≦ 3.0
Ma in this formula represents the content of ions of metal elements that are chemically bonded to anions derived from phosphorus compounds in the polyester. However, since the anion derived from the phosphorus compound in the polyester is divalent, it interacts 1: 1 with the cation of the divalent metal element. For this reason, the content M1 of the metal element that becomes a monovalent cation in the polyester needs to be multiplied by a coefficient of 0.5. Further, the content M3 of the metal element that becomes a trivalent cation in the polyester needs to be multiplied by a factor of 1.5.

  Therefore, when Ma / P is too small, the amount of the metal element relative to the amount of the phosphorus compound is too small to suppress the deactivation of the polymerization catalyst by the phosphorus compound or the suppression of the autocatalytic action of the terminal carboxyl group of the polyester composition, The progress of the hydrolysis reaction under a moist heat atmosphere cannot be suppressed, and there is a risk that the heat and moist heat resistance is lowered. Moreover, when Ma / P is too large, the compound containing a metal element becomes excessive, and there is a possibility that it becomes a foreign substance. For this reason, Ma / P is preferably within the range of the above formula (iv). More preferably, it is 0.9 or more and 2.0 or less, and further preferably 1.0 or more and 1.5 or less. Most preferably, it is 1.2 or more and 1.3 or less.

In the polyester film of the present invention, in the polyester constituting the polyester film, the alkali metal element content with respect to the polyester is M1 (mol / ton), and the sum of the calcium element content and the manganese element content is M2 (mol / ton). , It is preferable that the metal content Mb (mol / ton) and the phosphorus element content P (mol / ton) in the polyester determined by the following formula (v) satisfy the following formula (vi).
(V) Mb = M1 / 2 + M2
(Vi) 0.75 ≦ Mb / P ≦ 3.0
In general, since phosphorus compounds exist as anions in polyester, they chemically bond with metal elements present in an ionic state in polyester. When the anion derived from the phosphorus compound is chemically bonded to the metal element ion derived from the polymerization catalyst, the polymerization catalyst is deactivated. The presence of ions of metal elements other than the metal element derived from the polymerization catalyst in the polyester can suppress the chemical bond between the metal element ion derived from the polymerization catalyst and the anion derived from the phosphorus compound, and polymerization. Deactivation of the catalyst can be suppressed. Here, Mb / P represented by the above formula (vi) serves as an index for suppressing the deactivation of the polymerization catalyst by the phosphorus compound or suppressing the autocatalysis of the terminal carboxyl group of the polyester. Mb in this formula represents the content of metal element ions that are chemically bonded to anions derived from phosphorus compounds in the polyester. However, since the anion derived from the phosphorus compound in the polyester is divalent, it interacts 1: 1 with the cation of the divalent metal element. For this reason, the content M1 of the metal element that becomes a monovalent cation in the polyester needs to be multiplied by a coefficient of 0.5.

  Therefore, when Mb / P is too small, the amount of the metal element relative to the amount of the phosphorus compound is too small to suppress the deactivation of the polymerization catalyst by the phosphorus compound or the suppression of the autocatalysis of the terminal carboxyl group of the polyester composition, The progress of the hydrolysis reaction under a moist heat atmosphere cannot be suppressed, and there is a risk that the heat and moist heat resistance is lowered. Moreover, when Mb / P is too large, the compound containing a metal element becomes excessive, and there is a possibility that it becomes a foreign substance. For this reason, it is preferable that Mb / P be in the range of the above formula (vi). More preferably, it is 0.9 or more and 2.0 or less, and further preferably 1.0 or more and 1.5 or less. Most preferably, it is 1.2 or more and 1.3 or less.

  The alkali metal element contained in the polyester constituting the polyester film of the present invention is not particularly limited, but is preferably at least one of potassium element and sodium element from the viewpoint of long-term moist heat resistance.

  The polyester constituting the polyester film of the present invention is preferably obtained by adding phosphoric acid and an alkali metal phosphate as a phosphorus compound. According to such a configuration, the activity of the terminal carboxyl group of the polyester is reduced by the buffering action, and as a result of suppressing the progress of hydrolysis under a moist heat atmosphere, it becomes possible to improve the moist heat resistance. Examples of the alkali metal phosphate include sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, lithium dihydrogen phosphate, Examples include dilithium hydrogen phosphate and trilithium phosphate. Preferred are alkali metal dihydrogen phosphate and dialkali metal hydrogen phosphate. In addition, alkali metal phosphates whose alkali metal elements are sodium and potassium are preferred from the viewpoint of long-term moist heat resistance. Particularly preferred are sodium dihydrogen phosphate and potassium dihydrogen phosphate.

  The polyester constituting the polyester film of the present invention is added with a titanium compound (excluding titanium oxide) having at least one substituent selected from the group consisting of alkoxy groups, phenoxy groups, acylate groups, amino groups and hydroxyl groups. Is preferably obtained. Specific alkoxy groups include tetraethoxide, tetrapropoxide, tetraisopropoxide, tetrabutoxide, titanium tetraalkoxide such as tetra-2-ethylhexoxide, β-diketone functional groups such as acetylacetone, lactic acid, Examples include hydroxy polyvalent carboxylic acid functional groups such as malic acid, tartaric acid, salicylic acid, citric acid, and ketoester functional groups such as methyl acetoacetate and ethyl acetoacetate, with aliphatic alkoxy groups being particularly preferred. Examples of the phenoxy group include phenoxy and cresylate. The acylate groups include tetraacylate groups such as lactate and stearate, phthalic acid, trimellitic acid, trimesic acid, hemimellitic acid, pyromellitic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid , Functional groups of polycarboxylic acids such as sebacic acid, maleic acid, fumaric acid, cyclohexanedicarboxylic acid or their anhydrides, ethylenediaminetetraacetic acid, nitrilotripropionic acid, carboxyiminodiacetic acid, carboxymethyliminodipropionic acid, diethylenetria Nitrogenous polyvalent carboxylic acid functional groups such as minopentaacetic acid, triethylenetetraminohexaacetic acid, iminodiacetic acid, iminodipropionic acid, hydroxyethyliminodiacetic acid, hydroxyethyliminodipropionic acid, methoxyethyliminodiacetic acid Especially aliphatic asylum Group is preferred. Examples of the amino group include aniline, phenylamine, diphenylamine and the like. Moreover, the diisopropoxy bis acetylacetone and the triethanolaminato isopropoxide group which contain 2 types of these substituents are mentioned.

  In the polyester film of the present invention, the polyester constituting the film is not particularly limited as long as it is a thermoplastic resin capable of forming a film by melt extrusion. Among them, polyethylene terephthalate, polyethylene-2,6-naphthalene dicarboxylate, Polypropylene terephthalate, polybutylene terephthalate, poly-1,4-cyclohexylene dimethylene terephthalate and mixtures thereof are preferably used, and more preferably polyethylene terephthalate, polyethylene-2, 6-Naphthalenedicarboxylate is preferred.

  The polyester constituting the polyester film of the present invention preferably has an intrinsic viscosity of 0.6 dl / g or more and 1.0 dl / g or less from the viewpoint of mechanical properties and heat resistance. Therefore, the intrinsic viscosity of the polyester constituting the polyester film is preferably 0.6 dl / g or more and 1.1 dl / g or less. More preferably, it is 0.7 dl / g or more and 0.9 dl / g or less.

  The polyester constituting the polyester film of the present invention has a terminal carboxyl group content of 15 eq. / T (equivalent / ton) or less is preferable from the viewpoint of heat and humidity resistance. Therefore, the polyester constituting the polyester film has a terminal carboxyl group content of 17 eq. / T (equivalent / ton) or less is preferable from the viewpoint of heat and humidity resistance. More preferably, 14 eq. / T or less. The terminal carboxyl group amount is 17 eq. / T or less polyester is, for example, a method in which an alkali metal phosphate is added between the end of the transesterification or esterification reaction and the beginning of the polymerization reaction (inherent viscosity is less than 0.3), or by the above method The obtained polyester can be obtained by a method of further solid-phase polymerization. The solid phase polymerization is preferably carried out after the melt polymerization is finished at an intrinsic viscosity of 0.5 dl / g or more and 0.6 dl / g or less to make chips once. The solid phase polymerization temperature is preferably at a melting point of polyester Tm-60 ° C. or higher and Tm-30 ° C. or lower and a vacuum degree of 0.3 Torr or lower because the amount of terminal carboxyl groups can be reduced.

  In the polyester film of the present invention, as long as the effects of the present invention are not impaired, a heat stabilizer, an oxidation stabilizer, an ultraviolet absorber, an ultraviolet stabilizer, an organic / inorganic lubricant, an organic / inorganic Additives such as fine particles (including color pigments), fillers, nucleating agents, dyes, dispersants, coupling agents and the like may be blended.

When the said color pigment is a white pigment, it is preferable that content of this pigment is 1 to 20 weight% with respect to the polyester which comprises a polyester film.
As the white pigment, barium sulfate, titanium oxide, and the like are preferable from the viewpoint of stability to ultraviolet rays (UV resistance), but rutile type titanium oxide is particularly preferable from the viewpoints of UV resistance and wet heat resistance. If the content is less than 1% by weight, the UV resistance is not sufficiently exhibited. If the content exceeds 20% by weight, the heat and humidity resistance may decrease.

  Moreover, when the said color pigment is a black pigment, it is preferable that content of this pigment is 0.5 to 5 weight% with respect to the polyester which comprises a polyester film. The black pigment is preferably carbon black from the viewpoint of UV resistance and wet heat resistance. If the content is less than 0.5% by weight, the UV resistance is not sufficient, and if it exceeds 5% by weight, the heat and humidity resistance may be lowered.

  The thickness of the polyester film of the present invention is preferably 10 μm or more and 300 μm or less, more preferably 20 μm or more and 200 μm or less, and most preferably 30 μm or more and 150 μm or less. When the thickness of the polyester film is less than 10 μm, the flatness of the film is deteriorated, or when it is thicker than 300 μm, for example, when used as a solar battery back sheet, the entire thickness of the solar battery cell becomes too thick, which is not preferable.

  Next, a method for producing a biaxially stretched (biaxially oriented) polyester film of the present invention will be described.

  The raw material supplied to the extruder is melted in the extruder, and extruded from the die onto a cast drum cooled to obtain an unstretched (non-oriented) polyester sheet. At this time, it is preferable to use a wire-like, tape-like, needle-like, or knife-like electrode, which is brought into close contact with a cooling body such as a cast drum by electrostatic force and rapidly solidified. In addition, when performing melt extrusion with an extruder, it is better that the time of extrusion from the chip supply to the extruder until the die is melted in a nitrogen atmosphere is 30 minutes or less, more preferably 15 hours. From the viewpoint of inhibiting the increase in terminal carboxyl groups, it is preferable to set it to 5 minutes or less, more preferably 5 minutes or less.

  Next, the obtained unstretched polyester sheet is biaxially stretched to obtain a biaxially stretched (biaxially oriented) polyester film. The stretching is preferably performed at a temperature equal to or higher than the glass transition temperature (Tg) of the polyester. As the biaxial stretching method, in addition to the sequential biaxial stretching method in which the longitudinal direction and the width direction are separated separately, any of the simultaneous biaxial stretching methods in which the longitudinal direction and the width direction are simultaneously stretched. It doesn't matter.

  In the case of sequential biaxial stretching, it is led to a group of rolls heated to a temperature of Tg ° C. or more and Tg + 15 ° C. or less, more preferably Tg ° C. or more and Tg + 10 ° C. or less of the polyester, and the longitudinal direction (that is, the film traveling direction. The direction is sometimes referred to as “direction”, and the film is stretched 3 to 5 times and cooled with a roll group having a temperature of 20 ° C. or more and 50 ° C. or less. Subsequently, the film is guided to a tenter while holding both ends of the film with clips, and is heated to a temperature of Tg + 5 ° C. or higher and Tg + 30 ° C. or lower, more preferably Tg + 5 ° C. or higher and Tg + 25 ° C. or lower, more preferably Tg + 5 ° C. or higher and Tg + 20 ° C. or lower. Thus, the film is preferably stretched 3 to 5 times in a direction perpendicular to the longitudinal direction (sometimes referred to as “width direction” or “lateral direction”).

  The stretching ratio is 3 times or more and 5 times or less in the longitudinal direction and the width direction in both simultaneous biaxial stretching and sequential biaxial stretching, but the area stretching ratio is 12 times or more, more preferably 13 times or more, and still more preferably 14 times. The film is stretched so as to be at least twice, particularly preferably at least 15 times, most preferably at least 16 times. In particular, it is more preferable that the area stretching ratio is 13 times or more from the viewpoint that the heat and moisture resistance of the obtained film is further improved. When the area magnification is less than 13 times, the heat and humidity resistance of the resulting biaxially stretched film may decrease, which is not preferable. Further, if the area stretching ratio exceeds 20 times, the film tends to be broken during stretching.

  In addition, in order to complete the crystal orientation of the obtained biaxially stretched film and to impart flatness and dimensional stability, heat treatment is performed for 1 second to 30 seconds at a temperature lower than the melting point of the polyester to gradually and uniformly. After cooling, it is preferable to cool to room temperature. In general, when the heat treatment temperature is low, the thermal shrinkage of the film increases, and therefore it is preferable to increase the heat treatment temperature in order to impart high thermal dimensional stability.

  However, if the heat treatment temperature is too high, the amorphous part of the polyester in the film will be relaxed and the molecular mobility will be high, and hydrolysis will occur easily. It is not preferable because the crystallization is promoted and the embrittlement is likely to proceed. Therefore, it is preferable that the value obtained by subtracting the heat treatment temperature from the melting point of the polyester is set to 40 ° C. or more and 90 ° C. or less, more preferably 50 ° C. or more and 80 ° C. or less, and further preferably 55 ° C. or more and 75 ° C. or less. Further, during the heat treatment step, a relaxation treatment of 3 to 12% may be performed in the width direction or the longitudinal direction as necessary. Subsequently, as necessary, the polyester film of the present invention can be obtained by performing corona discharge treatment or the like in order to further improve the adhesion with other members and winding it.

  When laminating other films, a known co-extrusion method, a method in which another thermoplastic resin is melt-extruded on the produced film and laminated while being extruded from a die (melt laminating method), and the polyester film of the present invention A method of thermocompression bonding with a film made of another resin (thermal lamination method), a method of bonding the polyester film of the present invention and a film made of another resin via an adhesive (adhesion method), the polyester film of the present invention A method (coating method) in which another material is applied and laminated on the surface of the film, a method combining these, and the like can be used.

  The polyester film of the present invention does not contain a heavy metal element or has a low heavy metal content, is excellent in moisture and heat resistance and color tone, and should be used in applications where long-term durability is important without concern for discharge of heavy metals to the environment. In particular, it is suitably used as a film for a solar battery backsheet.

  Moreover, in order to make a solar cell backsheet using the polyester film of the present invention, for example, to increase the adhesion of the polyester film of the present invention to the EVA adhesion layer and EVA adhesion layer that improve the adhesion to EVA. An anchor layer, a water vapor barrier layer, an ultraviolet absorbing layer for absorbing ultraviolet rays, a light reflecting layer for improving power generation efficiency, a light absorbing layer for expressing design, an adhesive layer for bonding each layer, etc. In particular, the polyester film of the present invention can be suitably used as an ultraviolet absorbing layer and a light absorbing layer.

  The thickness of the solar battery backsheet using the polyester film of the present invention is preferably 50 μm or more and 500 μm or less, and more preferably 100 μm or more and 300 μm or less. More preferably, it is 125 μm or more and 200 μm or less. When the thickness is less than 10 μm, it is difficult to ensure the flatness of the film. On the other hand, when it is thicker than 500 μm, when it is mounted on a solar cell, the thickness of the entire solar cell may become too large.

The solar cell of the present invention is characterized by using a solar cell back sheet using the polyester film of the present invention. The solar battery backsheet using the polyester film of the present invention does not contain a heavy metal element or has a low heavy metal content and is excellent in moisture and heat resistance and color tone as compared with a conventional backsheet, and particularly contains a heavy metal element. The polyester of the present invention can be applied to solar cell applications that require long-term durability without concern for heavy metal emissions to the environment. By incorporating a solar battery back sheet using a film into a solar battery, it becomes possible to obtain a highly durable solar battery as compared with a conventional solar battery. The solar cell of the present invention can be suitably used for various uses without being concerned about the discharge of heavy metals to the environment, such as solar power generation and power sources for small electronic components, and not limited to outdoor use and indoor use.
(Characteristic evaluation method)
The characteristic evaluation method is described below.
(A) Measurement of elongation at break Based on ASTM-D882 (1999), a polyester film was cut into a size of 1 cm × 20 cm, and the elongation at break when the polyester film was pulled under the following conditions was measured. The measurement was carried out at n = 5, and after measuring for each of the longitudinal direction and the width direction of the film, the elongation at break was determined as an average value thereof.
Distance between chucks: 5cm
Pulling speed: 300mm / min
(B) Moisture and heat resistance The moisture and heat resistance was evaluated based on the elongation retention after the moisture and heat resistance test.

(B-1) Humidity and heat resistance of polyester film The polyester film was treated for 72 hours under the conditions of a temperature cooker of 125 ° C. and a relative humidity of 100% RH in a pressure cooker manufactured by Tabai Espec Co., Ltd. The degree of elongation was measured and set as the breaking elongation E1.
Moreover, also about the film before processing, the breaking elongation E0 is measured according to the above (A), and the elongation retention is calculated by the following equation (1) using the breaking elongations E0 and E1 thus obtained. did.
Elongation retention rate (%) = E1 / E0 × 100 (1) Formula The elongation retention rate obtained was determined as follows.
When the elongation retention is 50% or more: S
When the elongation retention is 45% or more and less than 50%: A
When the elongation retention is 40% or more and less than 45%: B
When the elongation retention is 35% or more and less than 40%: C
When the elongation retention is 30% or more and less than 35%: D
When the elongation retention is less than 30%: E
S to D are good, and S is the best among them.

(B-2) Moisture and heat resistance of the backsheet The moisture and heat resistance of the backsheet was determined in the same manner as in (B-1). That is, the breaking elongation of the backsheet before the treatment is E0 ′, and the breaking elongation of the backsheet after being treated for 72 hours under the conditions of a temperature of 125 ° C. and a relative humidity of 100% RH is the breaking elongation E1 ′. The elongation retention was calculated according to the equation (2).
Elongation retention rate (%) = E1 ′ / E0 ′ × 100 (2) Formula The elongation retention rate obtained was determined as follows.
When the elongation retention is 50% or more: S
When the elongation retention is 45% or more and less than 50%: A
When the elongation retention is 40% or more and less than 45%: B
When the elongation retention is 35% or more and less than 40%: C
When the elongation retention is 30% or more and less than 35%: D
When the elongation retention is less than 30%: E
S to D are good, and S is the best among them.
(C) Color tone For measurement, a spectroscopic color meter SE-2000 manufactured by Nippon Denshoku Industries Co., Ltd. was used. The measurement conditions were a C light source, a viewing angle of 2 °, a reflection measurement mode, and a sample measurement diameter of 30 mmφ. For standard matching, an attached standard white plate (X value, Y value, and Z value in the above-described measurement method is 93.67, 95.54, 113.35) was used. The sample used was a stack of 20 polyester films, and a white film ("Lumirror" (registered trademark) E20F, manufactured by Toray Industries, Inc.) at the position farthest from the light source. It measured according to JIS Z-8722 (2000). The number of samples was n = 5, each b value was measured, the average value was calculated as b0, and the obtained b0 was determined as follows.
When b0 is less than 0: S
When b0 is 0 or more and less than 0.2: A
When b0 is 0.2 or more and less than 0.4: B
When b0 is 0.4 or more and less than 0.6: C
When b0 is 0.6 or more and less than 0.8: D
When b00.8 or more: E
S to D are good, and S is the best among them.
(D) Intrinsic viscosity (IV)
Polyester or polyester film was dissolved in 100 ml of orthochlorophenol (solution concentration C = 1.2 g / ml), and the viscosity of the solution at 25 ° C. was measured using an Ostwald viscometer. Similarly, the viscosity of the solvent was measured. [Η] was calculated by the following equation (3) using the obtained solution viscosity and solvent viscosity, and the obtained [η] value was determined as the intrinsic viscosity (IV).
ηsp / C = [η] + K [η] ² · C (3) (where ηsp = (solution viscosity / solvent viscosity) −1, K is a Huggins constant (assuming 0.343))
(E) Quantification of metal element amount excluding alkali metal element and phosphorus element Measured using a fluorescent X-ray analyzer (model number: 3270) manufactured by Rigaku Corporation.

8 g of freeze-pulverized polyester film was used as an analysis sample according to the description of JIS K0119. Quantification was performed according to the description of JIS K0119 (1999) 10.1 d), and the content of each element in the sample was determined.
(F) Determination of the amount of alkali metal element 1 g of polyester film is placed in a platinum dish and completely incinerated at 700 ° C. over 1.5 hours, and then the incinerated product is 0.1 N so that the volume becomes 50 ml. Was dissolved in hydrochloric acid to obtain a solution A. When there was no insoluble matter in the solution A, this was used as a measurement sample.

  On the other hand, when there was an insoluble matter in the solution A, a measurement sample was obtained by the following method. A new polyester film (1 g) was placed in a platinum dish and completely incinerated at 700 ° C. over 1.5 hours. The incinerated product was then dissolved in 5 ml of 6.5 N nitric acid to obtain a solution B. Solution B was heated and the nitric acid was evaporated to give a residue. This residue was dissolved in 0.1N hydrochloric acid so as to have a volume of 50 ml to obtain a solution B. The solution B was used as a measurement sample.

Using the above measurement sample, quantification was performed by atomic absorption spectrometry using a polarized Zeeman atomic absorption spectrophotometer (manufactured by Tadate Corporation, model number: 180-80, frame: acetylene-air).
(G) Terminal carboxyl group amount It was measured by the following method according to the method of Malice (documents MJ Malice, F. Huizinga, Anal. Chim. Acta, 22 363 (1960)). After 0.5 g of polyester or polyester film was dissolved in 10 mL of o-cresol at a temperature of 100 ° C., the mixture was allowed to cool at 25 ° C. for 30 minutes and titrated with a 0.02N NaOH / methanol solution to form terminal carboxyl groups. Measure the concentration, eq. / Indicated by the value of polyester 1t. In addition, the indicator at the time of titration used phenol red, and the place where it changed from yellowish green to light red was set as the end point of titration.
(H) Melting point (Tm) of polyester, glass transition temperature (Tg)
According to JIS K7122 (1999), a differential scanning calorimeter “Robot DSC-RDC220” manufactured by Seiko Denshi Kogyo Co., Ltd., a disk session “SSC / 5200” for data analysis, a polyester melting point Tm, and The glass transition temperature Tg of the polyester was measured. In the measurement, 5 mg of polyester is weighed in a sample pan, the heating rate is 20 ° C./min, and the resin is heated at a heating rate of 20 ° C./min from 25 ° C. to 300 ° C. with 1st RUN, and kept in that state for 5 minutes. Then, the sample was rapidly cooled to 25 ° C. or lower, and the temperature was increased from room temperature to 300 ° C. at a rate of temperature increase of 20 ° C./min. The peak top temperature in the obtained 2ndRun crystal melting peak was defined as the melting point Tm.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated, this invention is not necessarily limited to these.

  First, a method for synthesizing the catalyst will be described.

Reference Example 1 (Method for synthesizing titanium catalyst A and titanium alkoxide compound)
Ethylene glycol (496 g, 8.0 mol) was added from a dropping funnel to titanium tetraisopropoxide (284 g, 1.0 mol) stirred in a 2 L flask equipped with a stirrer, condenser and thermometer. The addition rate was adjusted so that the heat of reaction warmed the flask contents to about 50 ° C. To the reaction flask, 125 g of a 32 wt% aqueous solution of NaOH was slowly added by a dropping funnel to obtain a clear yellow liquid (Ti content 5.2 wt%).

Reference Example 2 (Titanium Catalyst B, Citrate Chelate Titanium Compound Synthesis Method)
Citric acid monohydrate (532 g, 2.52 mol) was dissolved in warm water (371 g) in a 3 L flask equipped with a stirrer, condenser and thermometer. To this stirred solution was slowly added titanium tetraisopropoxide (284 g, 1.0 mol) from the addition funnel. The mixture was heated to reflux for 1 hour to produce a cloudy solution, whereby the isopropanol / water mixture was distilled and distilled under reduced pressure. The product was cooled to a temperature below 70 ° C., and 380 g of a 32 wt% aqueous solution of NaOH was slowly added via a dropping funnel while stirring the solution. The resulting product was filtered and then mixed with ethylene glycol (504 g, 8.1 mol) and heated under vacuum to remove isopropanol / water and a slightly cloudy, pale yellow product (Ti-containing) Amount 3.85% by weight).

Reference Example 3 (Method for synthesizing titanium catalyst C, lactic acid chelate titanium compound)
Ethylene glycol (218 g, 3.51 mol) was added from a dropping funnel to titanium tetraisopropoxide (284 g, 1.0 mol) stirred in a 2 L flask equipped with a stirrer, condenser and thermometer. The addition rate was adjusted so that the heat of reaction warmed the flask contents to about 50 ° C. The reaction mixture was stirred for 15 minutes, and 252 g of an 85 wt% aqueous solution of ammonium lactate was added to the reaction flask to obtain a clear light yellow product (Ti content 6.54 wt%).

Example 1
[Production of biaxially oriented film]
100 parts by weight of dimethyl terephthalate, 57.5 parts by weight of ethylene glycol, 0.0079 parts by weight of manganese acetate (25 ppm in terms of manganese metal element), 0.0043 parts by weight of sodium acetate (12 ppm in terms of sodium metal element), titanium catalyst A0 .0096 part by weight (5 ppm in terms of titanium metal element) was melted at 150 ° C. in a nitrogen atmosphere. While stirring this melt, the temperature was raised to 230 ° C. over 3 hours to distill methanol, and the transesterification reaction was completed. After completion of the transesterification reaction, an ethylene glycol solution in which 0.0026 parts by weight of phosphoric acid (6 ppm in terms of phosphorus metal element) was dissolved in 0.5 parts by weight of ethylene glycol was added. The intrinsic viscosity of the polyester composition at this time was less than 0.2. Thereafter, the polymerization reaction was carried out at a final temperature of 285 ° C. and a degree of vacuum of 0.1 Torr, an intrinsic viscosity of 0.52, a terminal carboxyl group amount of 15 eq. / T polyethylene terephthalate was obtained. The obtained polyethylene terephthalate was dried and crystallized at 160 ° C. for 6 hours. Thereafter, solid state polymerization was performed at 220 ° C. and a vacuum degree of 0.3 Torr for 8 hours, an intrinsic viscosity of 0.85, and a terminal carboxyl group amount of 10.2 eq. / T polyethylene terephthalate was obtained. The obtained polyethylene terephthalate composition had a glass transition temperature of 82 ° C. and a melting point of 255 ° C.

  Polyethylene terephthalate after solid-phase polymerization was vacuum-dried at a temperature of 180 ° C. for 2 hours and then supplied to an extruder under a nitrogen atmosphere. It was discharged from a T die at an extrusion temperature of 280 ° C., quenched with a casting drum (20 ° C.), and formed into a sheet by an electrostatic application method. The sheet was stretched in the longitudinal direction of the film at a stretching temperature of 90 ° C. and a stretching ratio of 3.5 times, and then stretched in the width direction of the film at a stretching temperature of 100 ° C. and a stretching ratio of 4.2 times. Second, a biaxially oriented polyester film having a thickness of 50 μm was obtained.

  Content of titanium element, phosphorus element, sodium element and manganese element in the obtained polyester film, molar ratio T / P, T / M1, Ma / P and Mb / P, terminal carboxyl group content, heat and humidity resistance and color tone The evaluation results are shown in Table 2. As shown in Table 2, the polyester film was excellent in heat and humidity resistance and color tone.

[Preparation of solar cell back sheet]
To the obtained polyester film, an adhesive ("Takelac" (registered trademark) A310 (manufactured by Mitsui Takeda Chemical Co., Ltd.) 90% by weight, "Takenate" (registered trademark) A3 (manufactured by Mitsui Takeda Chemical Co., Ltd.) 10% %) And dried at 150 ° C. for 30 seconds, overlaid with a 100 μm thick polyethylene film and pasted through a laminator heated to 50 ° C. to produce a 155 μm thick solar cell back sheet did. When the obtained back sheet was evaluated for moisture and heat resistance, as shown in Table 2, it was found to have good moisture and heat resistance.

(Examples 2 to 5)
A polyester film was prepared in the same manner as in Example 1 except that titanium catalyst A, phosphoric acid, sodium acetate, and manganese acetate were added as shown in Table 1 for the addition amounts of titanium element, phosphorus element, sodium element, and manganese element. Obtained. Content of titanium element, phosphorus element, sodium element and manganese element in the obtained polyester film, molar ratio T / P, T / M1, Ma / P and Mb / P, terminal carboxyl group content, heat and humidity resistance and color tone The evaluation results are shown in Table 2. As shown in Table 2, in Examples 3-5, the heat-and-moisture resistance higher than Example 1 was shown.

  Moreover, the solar cell back sheet was produced by the method similar to Example 1 using the obtained polyester film. When the obtained back sheet was evaluated for moisture and heat resistance, as shown in Table 2, it was found to have good moisture and heat resistance.

(Examples 6 to 10)
A polyester film was prepared in the same manner as in Example 1 except that titanium catalyst A, phosphoric acid, sodium acetate, and manganese acetate were added as shown in Table 1 for the addition amounts of titanium element, phosphorus element, sodium element, and manganese element. Obtained. Content of titanium element, phosphorus element, sodium element and manganese element in the obtained polyester film, molar ratio T / P, T / M1, Ma / P and Mb / P, terminal carboxyl group content, heat and humidity resistance and color tone The evaluation results are shown in Table 2. As shown in Table 2, T / M1 was smaller than that of Example 1, the color tone was superior to that of Example 1, and both were polyester films having good wet heat resistance. In particular, Example 7 had higher heat and humidity resistance than Example 1.

  Moreover, the solar cell back sheet was produced by the method similar to Example 1 using the obtained polyester film. When the obtained back sheet was evaluated for moisture and heat resistance, as shown in Table 2, it was found to have good moisture and heat resistance.

(Examples 11 to 24)
A polyester film was prepared in the same manner as in Example 1 except that titanium catalyst A, phosphoric acid, sodium acetate, and manganese acetate were added as shown in Table 1 for the addition amounts of titanium element, phosphorus element, sodium element, and manganese element. Obtained. Content of titanium element, phosphorus element, sodium element and manganese element in the obtained polyester film, molar ratio T / P, T / M1, Ma / P and Mb / P, terminal carboxyl group content, heat and humidity resistance and color tone The evaluation results are shown in Table 2. As shown in Table 2, T / M1 was larger than that of Example 1, and although it was inferior to that of Example 1, it had an excellent color tone, and both were polyester films having good wet heat resistance. In particular, Examples 14, 17, 18, 20, and 21 had high wet heat resistance.

  Moreover, the solar cell back sheet was produced by the method similar to Example 1 using the obtained polyester film. When the obtained back sheet was evaluated for moisture and heat resistance, as shown in Table 2, it was found to have good moisture and heat resistance.

(Example 25)
A polyester film was obtained in the same manner as in Example 1 except that calcium acetate was added as shown in Table 1 instead of adding manganese acetate. Content of titanium element, phosphorus element, sodium element and calcium element in the obtained polyester film, molar ratio T / P, T / M1, Ma / P and Mb / P, terminal carboxyl group amount, wet heat resistance and color tone The evaluation results are shown in Table 2. Example 25 was a polyester film having excellent moisture and heat resistance and color tone.

  Moreover, the solar cell back sheet was produced by the method similar to Example 1 using the obtained polyester film. When the obtained back sheet was evaluated for moisture and heat resistance, as shown in Table 2, it was found to have good moisture and heat resistance.

(Example 26)
A polyester film was obtained in the same manner as in Example 1, except that potassium acetate was added as shown in Table 1 instead of adding sodium acetate. Content of titanium element, phosphorus element, potassium element and manganese element in the obtained polyester film, molar ratio T / P, T / M1, Ma / P and Mb / P, terminal carboxyl group content, heat and humidity resistance and color tone The evaluation results are shown in Table 2. As shown in Table 2, Example 26 was a polyester film having excellent wet heat resistance and color tone.

  Moreover, the solar cell back sheet was produced by the method similar to Example 1 using the obtained polyester film. When the obtained back sheet was evaluated for moisture and heat resistance, as shown in Table 2, it was found to have good moisture and heat resistance.

(Example 27)
A polyester film was obtained in the same manner as in Example 1 except that lithium acetate was added as shown in Table 1 instead of adding sodium acetate. Content of titanium element, phosphorus element, lithium element and manganese element, molar ratio T / P, T / M1, Ma / P and Mb / P, terminal carboxyl group content, moisture and heat resistance and color tone in the obtained polyester film The evaluation results are shown in Table 2. As shown in Table 2, Example 27 was a polyester film excellent in moisture and heat resistance and color tone, although the moisture and heat resistance was slightly lowered.

  Moreover, the solar cell back sheet was produced by the method similar to Example 1 using the obtained polyester film. When the obtained back sheet was evaluated for moisture and heat resistance, as shown in Table 2, it was found to have good moisture and heat resistance.

(Examples 28 to 30)
Instead of adding sodium acetate and phosphoric acid, Examples were carried out except that phosphoric acid and sodium dihydrogen phosphate were added after the transesterification reaction so that the contents of phosphorus element and sodium element were as shown in Table 1. In the same manner as in Example 1, a polyester film was obtained. Content of titanium element, phosphorus element, sodium metal element, and manganese metal element in the obtained polyester film, molar ratio T / P, T / M1, Ma / P and Mb / P, terminal carboxyl group amount, wet heat resistance Table 2 shows the evaluation results of the color tone. As shown in Table 2, the moisture and heat resistance is higher than that of the examples having the same M / P (Example 14 in Example 28, Example 17 in Example 29, and Example 18 in Example 30). And a polyester film having the same excellent color tone.

  Moreover, the solar cell back sheet was produced by the method similar to Example 1 using the obtained polyester film. When the obtained back sheet was evaluated for moisture and heat resistance, as shown in Table 2, it was found to have good moisture and heat resistance.

(Examples 31-32)
Instead of adding the titanium catalyst A, a polyester film was obtained in the same manner as in Example 1 except that the titanium catalyst B or the titanium catalyst C was added so that the addition amount of the titanium element was as shown in Table 1. Content of titanium element, phosphorus element, sodium metal element, and manganese metal element in the obtained polyester film, molar ratio T / P, T / M1, Ma / P and Mb / P, terminal carboxyl group amount, wet heat resistance Table 2 shows the evaluation results of the color tone. As shown in Table 2, the polyester film had excellent moisture and heat resistance and color tone equivalent to those of Example 14 in which the content of elements in the polyester film was the same.

Moreover, the solar cell back sheet was produced by the method similar to Example 1 using the obtained polyester film. When the obtained back sheet was evaluated for moisture and heat resistance, as shown in Table 2, it was found to have good moisture and heat resistance.
(Examples 33 to 34)
Instead of adding manganese acetate, aluminum acetate was added, and the polyester film was prepared in the same manner as in Example 1 except that the addition amounts of titanium element, phosphorus element, sodium element and aluminum element were as shown in Table 1. Obtained. Content of titanium element, phosphorus element, sodium element, and aluminum element in the obtained polyester film, molar ratio T / P, T / M1, Ma / P and Mb / P, terminal carboxyl group amount, moisture and heat resistance and color tone The evaluation results are shown in Table 2. As shown in Table 2, it had excellent wet heat resistance. Moreover, the solar cell back sheet was produced by the method similar to Example 1 using the obtained polyester film. When the obtained back sheet was evaluated for moisture and heat resistance, as shown in Table 2, it was found to have good moisture and heat resistance.
(Example 35)
Instead of adding manganese acetate, manganese acetate and aluminum acetate were added, and the addition amounts of titanium element, phosphorus element, sodium element, manganese element, and aluminum element were as shown in Table 1, and the same as in Example 1 Thus, a polyester film was obtained. Content of titanium element, phosphorus element, sodium element, manganese element, and aluminum element, molar ratio T / P, T / M1, Ma / P and Mb / P, terminal carboxyl group amount, moisture resistance in the obtained polyester film Table 2 shows the evaluation results of thermal properties and color tone. As shown in Table 2, it had excellent wet heat resistance and color tone. In particular, it had higher heat and humidity resistance than Example 12.

  Moreover, the solar cell back sheet was produced by the method similar to Example 1 using the obtained polyester film. When the obtained back sheet was evaluated for moisture and heat resistance, as shown in Table 2, it was found to have good moisture and heat resistance.

(Comparative Example 1)
A polyester film was obtained in the same manner as in Example 1 except that titanium catalyst A, phosphoric acid, and sodium acetate were added as shown in Table 3 for the addition amounts of titanium element, phosphorus element and sodium element. Content of titanium element, phosphorus element, sodium element and manganese element in the obtained polyester film, molar ratio T / P, T / M1, Ma / P and Mb / P, terminal carboxyl group content, heat and humidity resistance and color tone Table 4 shows the evaluation results. As shown in Table 4, since the content of titanium element in the polyester film is small, T / P and T / M1 are inappropriate, the amount of terminal carboxyl groups is large, the heat and heat resistance is poor, and the color tone is also poor. Met.

(Comparative Example 2)
A polyester film was obtained in the same manner as in Example 1 except that titanium catalyst A, phosphoric acid, and sodium acetate were added as shown in Table 3 for the addition amounts of titanium element, phosphorus element and sodium element. Content of titanium element, phosphorus element, sodium element and manganese element in the obtained polyester film, molar ratio T / P, T / M1, Ma / P and Mb / P, terminal carboxyl group content, heat and humidity resistance and color tone Table 4 shows the evaluation results. As shown in Table 4, the polyester film had a high phosphorus element content, a large amount of terminal carboxyl groups, and was poor in heat and humidity resistance.

(Comparative Examples 3-5)
A polyester film was obtained in the same manner as in Example 1 except that titanium catalyst A, phosphoric acid, and sodium acetate were added as shown in Table 3 for the addition amounts of titanium element, phosphorus element and sodium element. Content of titanium element, phosphorus element, sodium element and manganese element in the obtained polyester film, molar ratio T / P, T / M1, Ma / P and Mb / P, terminal carboxyl group content, heat and humidity resistance and color tone Table 4 shows the evaluation results. As shown in Table 4, since the content of titanium element in the polyester film is large, gelation proceeds during the polymerization, and in Comparative Examples 3 and 4, the T / P is too large and the polyester film is inferior in heat and humidity resistance. there were. In Comparative Example 3, the polyester film was inferior in color tone.

(Comparative Examples 6-7)
A polyester film was obtained in the same manner as in Example 1 except that titanium catalyst A, phosphoric acid, and sodium acetate were added as shown in Table 3 for the addition amounts of titanium element, phosphorus element and sodium element. Content of titanium element, phosphorus element, sodium element and manganese element in the obtained polyester film, molar ratio T / P, T / M1, Ma / P and Mb / P, terminal carboxyl group content, heat and humidity resistance and color tone Table 4 shows the evaluation results. It was a polyester film with low phosphorus element content, too high T / P, and poor moisture and heat resistance.

(Comparative Examples 8 to 13)
A polyester film was obtained in the same manner as in Example 1 except that titanium catalyst A, phosphoric acid, and sodium acetate were added as shown in Table 3 for the addition amounts of titanium element, phosphorus element and sodium element. Content of titanium element, phosphorus element, sodium element and manganese element in the obtained polyester film, molar ratio T / P, T / M1, Ma / P and Mb / P, terminal carboxyl group content, heat and humidity resistance and color tone Table 4 shows the evaluation results. Since the sodium element content was small, the polyester film was inferior in color tone.

(Comparative Examples 14-16)
A polyester film was obtained in the same manner as in Example 1 except that titanium catalyst A, phosphoric acid, and sodium acetate were added as shown in Table 3 for the addition amounts of titanium element, phosphorus element and sodium element. Content of titanium element, phosphorus element, sodium element and manganese element in the obtained polyester film, molar ratio T / P, T / M1, Ma / P and Mb / P, terminal carboxyl group content, heat and humidity resistance and color tone Table 4 shows the evaluation results. T / M1 was too small and it was a polyester film inferior in heat-and-moisture resistance.

(Comparative Examples 17-22)
A polyester film was obtained in the same manner as in Example 1 except that titanium catalyst A, phosphoric acid, and sodium acetate were added as shown in Table 3 for the addition amounts of titanium element, phosphorus element and sodium element. Content of titanium element, phosphorus element, sodium element and manganese element in the obtained polyester film, molar ratio T / P, T / M1, Ma / P and Mb / P, terminal carboxyl group content, heat and humidity resistance and color tone Table 4 shows the evaluation results. In Comparative Examples 17-19, T / P was too small, and in Comparative Examples 20-22, T / P was too large, and the polyester film was inferior in heat-and-moisture resistance.

(Comparative Example 23)
A polyester film was obtained in the same manner as in Example 1 except that titanium catalyst A, phosphoric acid, and sodium acetate were added as shown in Table 3 for the addition amounts of titanium element, phosphorus element, and sodium element. Content of titanium element, phosphorus element, sodium element and manganese element in the obtained polyester film, molar ratio T / P, T / M1, Ma / P and Mb / P, terminal carboxyl group content, heat and humidity resistance and color tone Table 4 shows the evaluation results. The content of sodium element was too large, T / M1 was small, and the polyester film was inferior in heat and humidity resistance.

(Comparative Example 24)
A polyester film was obtained in the same manner as in Example 1 except that manganese acetate and magnesium acetate were added as shown in Table 3 instead of adding manganese acetate. Content of titanium element, phosphorus element, sodium element, manganese element and magnesium element in the obtained polyester film, molar ratio T / P, T / M1, Ma / P and Mb / P, terminal carboxyl group amount, heat and humidity resistance Table 4 shows the evaluation results of the color tone. As shown in Table 4, Comparative Example 24 was a polyester film having poor moisture and heat resistance.

(Comparative Examples 25-26)
A polyester film was obtained in the same manner as in Example 1 except that magnesium acetate and zinc acetate were added as shown in Table 3 instead of adding magnesium acetate. Content of titanium element, phosphorus element, sodium element, magnesium element / zinc element, molar ratio T / P, T / M1, Ma / P and Mb / P, terminal carboxyl group amount, moisture heat resistance in the obtained polyester film Table 4 shows the evaluation results of the color tone. As shown in Table 4, the polyester film was inferior in moisture and heat resistance.

  The polyester of the present invention is a polyester film that does not contain a heavy metal element and is excellent in heat and moisture resistance and color tone. Taking advantage of the polyester film, it is an electrically insulating material such as a solar battery back sheet, a planar heating element, or a flat cable, and a capacitor. It can be suitably used for applications including materials, automobile materials, and building materials.

Claims (12)

A polyester film containing at least one metal element of calcium element, manganese element, and aluminum element, wherein the polyester constituting the polyester film has a content of divalent metal elements other than calcium element and manganese element 5 ppm or less for each of the polyesters, the titanium element content excluding titanium elements derived from titanium oxide is 1 ppm or more and 20 ppm or less, the phosphorus element content is 5 ppm or more and 100 ppm or less, and the alkali metal element content is 3 ppm or more and 100 ppm or less. ,
When the titanium element content with respect to the polyester is T (mol / ton), the phosphorus element content is P (mol / ton), and the alkali metal element content is M1 (mol / ton), the following formula (i) The biaxially oriented polyester film characterized by satisfying the formula (ii).
(I) 0.13 ≦ T / P ≦ 0.85
(Ii) T / M1 ≧ 0.1 2. The biaxially oriented polyester film according to claim 1, wherein the sum of the contents of calcium element, manganese element, and aluminum element with respect to the polyester is 5 ppm or more and 150 ppm or less. When the alkali metal element content with respect to the polyester is M1 (mol / ton), the sum of the calcium element content and the manganese element content is M2 (mol / ton), and the aluminum element content is M3 (mol / ton) The metal content Ma (mol / ton) and phosphorus element content P (mol / ton) in the polyester determined by the following formula (iii) satisfy the following formula (iv): The biaxially oriented polyester film according to 1 or 2.
(Iii) Ma = M1 / 2 + M2 + 3 × M3 / 2
(Iv) 0.75 ≦ Ma / P ≦ 3.0 2. The biaxially oriented polyester film according to claim 1, comprising at least one metal element of calcium element and manganese element. The biaxially oriented polyester film according to claim 4, wherein the sum of the contents of calcium element and manganese element is 5 ppm or more and 150 ppm or less with respect to the polyester. When the alkali metal element content with respect to the polyester is M1 (mol / ton) and the sum of the calcium element content and the manganese element content is M2 (mol / ton), the polyester is obtained by the following formula (v): The biaxially oriented polyester film according to claim 4 or 5, wherein the metal content Mb (mol / ton) and the phosphorus element content P (mol / ton) satisfy the following formula (vi):
(V) Mb = M1 / 2 + M2
(Vi) 0.75 ≦ Mb / P ≦ 3.0 The biaxially oriented polyester film according to claim 1, wherein the alkali metal element contained in the polyester is at least one of potassium element and sodium element. The biaxially oriented polyester film according to any one of claims 1 to 7, wherein the polyester is obtained by adding phosphoric acid and an alkali metal phosphate. The polyester is obtained by adding a titanium compound (excluding titanium oxide) having at least one substituent selected from the group consisting of an alkoxy group, a phenoxy group, an acylate group, an amino group, and a hydroxyl group. The biaxially oriented polyester film according to any one of claims 1 to 8. The biaxially oriented polyester film according to any one of claims 1 to 9, which is used for a solar battery backsheet. The solar cell backsheet using the biaxially-oriented polyester film in any one of Claims 1-10. A solar cell using the solar cell back sheet according to claim 11.