JP2011204841A - Polyester film for solar cell back sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film with excellent durability, specifically, a back sheet for a solar cell which is hardly deteriorated by an environmental change and is excellent in hydrolysis resistance, weather resistance, heat resistance, and bleeding-out property when used as the back sheet for the solar cell.SOLUTION: The polyester film for the solar cell back sheet is a film where a loss tangent (tan δ) peak temperature is 120-180°C and an amount of increase (a Δb value) of yellowness (a b value) after 48-hour irradiation of ultraviolet light of 295-450 nm in wavelength at 100 mW by using a metal halide lamp is 0-15.

Description

  The present invention relates to a polyester film for a solar battery back sheet, which is excellent in hydrolysis resistance, heat resistance, weather resistance, and bleed-out property.

  Polyester film is used for magnetic recording media, for electrical insulation, for solar cells, for capacitors, for packaging, and for various industrial applications, utilizing its excellent properties such as mechanical properties, thermal properties, electrical properties, surface properties and heat resistance. It is used for various applications such as materials. In these high quality applications, for example, in recent years, the demand for solar cells that are clean energy as a next-generation energy source that is semi-permanent and non-polluting has been increasing. There is an increasing demand for improving the durability (hydrolysis resistance, heat resistance, weather resistance) of the backsheet. In the midst of this, various studies have been conducted on improving durability. Specifically, techniques for adding a carbodiimide compound to improve the hydrolysis resistance of the polyester resin have been proposed (Patent Document 1 and Patent Document 2). However, in these proposals, there is no detailed description of the film, and the improvement of the hydrolysis resistance of the resin does not directly become the hydrolysis resistance of the film. In addition, it is difficult to achieve the required characteristics without obtaining other improvements in heat resistance and weather resistance. Furthermore, a technique for controlling the intrinsic viscosity (hereinafter sometimes abbreviated as IV) and the plane orientation coefficient (hereinafter sometimes abbreviated as fn) of a film has been proposed (Patent Document 3).

  However, the demand for the next generation is further increasing, and it is difficult to achieve the required characteristics with this proposal. In order to improve the weather resistance of the polyester film, it is necessary to suppress UV deterioration due to the UV absorber, and a method of blending the UV absorber with the biaxially oriented polyester film has been proposed (Patent Documents 4 and 5). . However, there are problems such as sublimation and bleed-out due to heat in the production process of the polyester film, resulting in contamination of the film-forming machine and surface contamination, and deterioration of adhesion to other members. In addition, it is difficult to achieve the required characteristics because hydrolysis resistance and heat resistance cannot be improved. Moreover, the technique which adds a polyimide and a carbodiimide compound and improves the hydrolysis resistance and heat resistance of a polyester film is proposed (patent document 6).

  However, since the polyester in the blend chip at the time of mixing with polyimide is once heated, deterioration due to ultraviolet rays is likely to occur, and weather resistance is deteriorated. In addition, carbodiimide compounds undergo thermal decomposition under the extrusion conditions of polyester, and there are problems such as generation of decomposition gas and bleeding out. Therefore, as a result of intensive studies, the present inventors have found that in order to improve the durability of the polyester film, the loss tangent (hereinafter sometimes abbreviated as tan δ) peak temperature and the yellowness after ultraviolet irradiation (hereinafter referred to as the b value) It has been found that it is important to control the amount of increase (hereinafter may be abbreviated as Δb).

JP 11-34048 A Japanese National Patent Publication No. 11-506487 JP 2007-70430 A JP 2009-188105 A JP 2004-161800 A JP 2003-160718 A

  The object of the present invention is to solve the above-mentioned problems and to provide a polyester film which is less deteriorated due to environmental changes when used as a solar cell backsheet and is excellent in hydrolysis resistance, weather resistance and heat resistance.

The present invention for solving the above-described problems is characterized by the following (1) to (8).
(1) Loss tangent (tan δ) peak temperature is 120 to 180 ° C., and the amount of increase (Δb value) in yellowness (b value) after irradiation with 295 to 450 nm ultraviolet rays at 100 mW for 48 hours using a metal halide lamp It is 0-15, The polyester film for solar cell backsheets characterized by the above-mentioned.
(2) The polyester film for solar battery backsheet as described in (1) above, which is a polyester film using polyester (A) and polyimide (B).
(3) The polyester film for solar battery backsheet according to (1) to (2) above, wherein the content of the polyimide (B) is 2% by mass to 30% by mass with respect to the entire film. .
(4) Content of ultraviolet absorber is 0.01 mass% or less with respect to the whole film, The polyester for solar cell backsheets in any one of said (1)-(3) characterized by the above-mentioned. the film.
(5) The polyester film for solar cell backsheet according to any one of the above (1) to (4), wherein the plane orientation coefficient fn is 0.140 to 0.280.
(6) The solar cell bag according to any one of the above (1) to (5), wherein the retention rate of elongation at break in at least one direction after heat treatment at 200 ° C. is 10 to 100%. Polyester film for sheet.
(7) The solar cell according to any one of the above (1) to (6), wherein the retention of fracture elongation in at least one direction after 72 hours at 125 ° C. and 100% RH is 10 to 100%. Polyester film for back sheet.
(8) The polyester film for solar cell backsheet according to any one of (1) to (7) above, wherein the light transmittance at a wavelength of 360 nm is 0 to 20%.
(9) The process for producing a polyester film for a solar battery backsheet according to any one of the above (1) to (8), wherein the following steps 1 to 3 are performed in that order.
Step 1: A step of obtaining a compound raw material (AB) by melt-kneading polyester (A) and polyimide (B) so that the mass fraction (A / B) is 70/30 to 30/70.
Process 2: The process of obtaining the heat-processed compound raw material (ABH) by heat-processing the compound raw material (AB) at the temperature of 210-250 degreeC under the reduced pressure of 0.1 kPa or less for 1 to 100 hours.
Step 3: The polyester (A ′) and the heat-treated compound raw material (ABH) are mixed, melt-extruded to obtain an unstretched sheet, and the unstretched sheet is biaxially stretched to obtain a biaxially oriented polyester film. Process.

  The present invention can provide a polyester film that is less deteriorated due to environmental changes when used as a solar cell backsheet, and that is excellent in hydrolysis resistance, weather resistance, and heat resistance.

  In the present invention, the polyester film is composed of, for example, a polymer (polyester) having an acid component such as aromatic dicarboxylic acid, alicyclic dicarboxylic acid, or aliphatic dicarboxylic acid and a diol component as constituent units (polymerization units). Is.

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

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

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

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

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

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

  As the polyester (A) of the present invention, polyethylene terephthalate and polyethylene naphthalate are preferably used. The polyester may be a copolymer or a modified product thereof. From the viewpoint of crystallinity, polyethylene terephthalate and polyethylene naphthalate are preferably the main components, and particularly preferably 90% or more is polyethylene terephthalate and polyethylene naphthalate. Further, it may be a polymer alloy with another thermoplastic resin. The polymer alloy here refers to a polymer multi-component compound, which may be a block copolymer by copolymerization or a polymer blend by mixing.

  The polyester film of the present invention particularly preferably contains polyester (A) and polyimide (B) from the viewpoint of improving hydrolysis resistance, heat resistance, and weather resistance. Polyimide (B) improves the heat resistance of the polyester and absorbs ultraviolet rays, thereby improving the weather resistance of the polyester.

  The polyimide (B) referred to in the present invention is a melt moldable polymer containing a cyclic imide group, and is not particularly limited as long as it can be applied to the object of the present invention, but is aliphatic, alicyclic or aromatic. A polyetherimide (hereinafter sometimes abbreviated as PEI) containing an ether unit and a cyclic imide group as a repeating unit is preferred. For example, polyether imides described in U.S. Pat. Nos. 4,141,927, 2,262,678, 2,606,912, 2,606,914, 2,596,865, 2,596,662, and 2,598,478, and 2,598,536. No. 2, Japanese Patent No. 2599171, Japanese Patent Laid-Open No. 9-48852, Japanese Patent No. 2565556, Japanese Patent No. 2564636, Japanese Patent No. 2564537, Japanese Patent No. 2563548, Japanese Patent No. 2563547, Japanese Patent No. 2558341, Japanese Patent No. 2558339 And polymers described in Japanese Patent No. 2833580.

In addition, as long as the effect of the present invention is not impaired, the main chain of polyimide contains a cyclic imide, a structural unit other than an ether unit, for example, an aromatic, aliphatic, alicyclic ester unit, oxycarbonyl unit, etc. May be. Moreover, as long as the effect of the present invention is not impaired, the main chain of the polyetherimide has a cyclic imide, a structural unit other than the ether unit, such as an aromatic, aliphatic, alicyclic ester unit, oxycarbonyl unit, etc. It may be contained.
As the polyimide (B), for example, those containing a structural unit represented by the following general formula are preferable.

However, R ¹ in the formula is

Represents one or two or more groups selected from an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, and an aromatic hydrocarbon group. R ² in the formula is

Represents one or two or more groups selected from an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, and an aromatic hydrocarbon group.

  From the viewpoints of melt moldability and affinity with polyester, a polyetherimide containing an ether bond in the polyimide component as shown by the following general formula is particularly preferred.

(Wherein R ³ is a divalent aromatic or aliphatic residue having 6 to 30 carbon atoms, R ⁴ is a divalent aromatic residue having 6 to 30 carbon atoms, From the group consisting of alkylene groups having 2 to 20 carbon atoms, cycloalkylene groups having 2 to 20 carbon atoms, and polydiorganosiloxane groups chain-terminated with alkylene groups having 2 to 8 carbon atoms Selected divalent organic group.)
As said R < ³ >, R < ⁴ >, the aromatic residue shown by the following formula group can be mentioned, for example.

  In the present invention, 2,2-bis [4- (2,3-dicarboxyphenoxy) phenyl] propane dianhydride and m-phenylenediamine from the viewpoint of affinity with polyester, cost, melt moldability, and the like, or A polymer having a repeating unit represented by the following formula, which is a condensate with p-phenylenediamine, is preferable.

Or

(N is an integer of 2 or more, preferably an integer of 20 to 50)
This polyetherimide is available from SABIC Innovative Plastics under the trade name “Ultem” (registered trademark).

  The content of the polyimide (B) in the polyester film of the present invention is preferably 2 to 30% by mass. If the polyimide (B) is less than 2% by mass, the loss tangent (tan δ) peak temperature becomes low, and it becomes difficult to improve heat resistance and hydrolysis resistance. In addition, since polyimide absorbs ultraviolet rays, the influence on polyester is small and the weather resistance is improved when irradiated with ultraviolet rays. However, if the content of polyimide (B) is less than 2% by mass, the effect is small and the weather resistance is low. Does not improve. Moreover, when polyimide (B) exceeds 30 mass%, the film formability of a film is bad and it becomes difficult to raise a surface orientation coefficient, and it becomes difficult to improve heat resistance and hydrolysis resistance. Moreover, it becomes a problem in cost and processing characteristics. A more preferable lower limit of the content of the polyimide (B) is 5% by mass, and a more preferable lower limit is 7% by mass. A more preferable upper limit value of the content of the polyimide (B) is 20% by mass, and a more preferable upper limit value is 15% by mass.

  The polyester film of the present invention needs to have a loss tangent (tan δ) peak temperature of 120 to 180 ° C. When the loss tangent (tan δ) peak temperature is lower than 120 ° C., the molecular chain of the polyester starts to move at a temperature lower than 120 ° C., so that heat resistance and hydrolysis resistance are greatly reduced. Further, when the loss tangent (tan δ) peak temperature exceeds 180 ° C. or more, there is a problem that stretching is difficult because the molecular mobility is low and the film cannot be highly oriented. A more preferable lower limit value of the loss tangent (tan δ) peak temperature is 130 ° C, and a more preferable lower limit value is 140 ° C. A more preferable upper limit value of the loss tangent (tan δ) peak temperature is 170 ° C., and a more preferable upper limit value is 160 ° C. A more preferable range of the loss tangent (tan δ) peak temperature is 130 to 170 ° C, and a more preferable range is 140 to 160 ° C.

  The loss tangent (tan δ) peak temperature is an index representing molecular chain mobility, and increases as the content of polyimide (B) increases, and decreases as it decreases.

  The polyester film of the present invention needs to have an increase in yellowness (b value) (Δb value) of 0 to 15 after irradiation with ultraviolet rays of 295 to 450 nm at 100 mW for 48 hours using a metal halide lamp. The Δb value is a change in color and indicates the degree of deterioration of the polyester film. A Δb value of 0 is most preferable because there is almost no deterioration due to ultraviolet rays. If the Δb value is greater than 15, the color changes greatly and the weather resistance deteriorates. A more preferable upper limit value of Δb value is 10, and a more preferable upper limit value is 5. A preferable range of the Δb value is 0 to 10, and a more preferable range is 0 to 5.

  The Δb value decreases as the polyimide (B) content increases, and decreases as it decreases. Moreover, it becomes so small that the intrinsic viscosity (IV) of the compound raw material (AB) which consists of polyester (A) and a polyimide (B) is large.

  In the polyester film of the present invention, the content of the ultraviolet absorber needs to be 0.01% or less with respect to the entire film. Examples of the ultraviolet absorber include additives having the following molecular structure (benzophenone series, benzotriazole series, hydroxyphenyltriazine series). Examples of the benzophenone-based additive include 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-n-octoxybenzophenone, 2,2′-dihydroxy-4,4′-dimethoxybenzophenone, and n-hexyl-2- (4-diethylamino-2-hydroxybenzoyl) benzoate and the like. Examples of the benzotriazole-based additive include 2- (2′-hydroxy-5′-methylphenyl) benzotriazole and 2- [2′-hydroxy-5 ′-(1,1,3,3-tetramethylbutyl). Phenyl] benzotriazole, 2- (2′-hydroxy-3′-t-butyl-5′-methylphenyl) -5-chlorobenzotriazole, 2,2′-methylenebis [6- (2H-benzotriazole-2- Yl) -4- (1,1,3,3-tetramethylbutyl) phenol]. Examples of the hydroxyphenyl triazine-based additive include 2-[(2-hydroxy-4-n-hexyloxy) phenyl] -4,6-diphenyltriazine, 2,4- [di [2-hydroxy-4- (2 -Ethylhexyloxy)] phenyl] -6- (4-methoxyphenyl) triazine and the like. When the content of the ultraviolet absorber is more than 0.01% by mass, the adhesiveness with other members deteriorates when bleeding out on the film surface and using it as a solar battery back sheet.

  As long as the effects of the present invention are not impaired, the polyester film of the present invention contains various additives such as compatibilizers, plasticizers, antioxidants, heat stabilizers, lubricants, antistatic agents, Whitening agents, coloring agents, conductive agents, flame retardants, flame retardant aids, pigments and dyes may be added.

  The polyester film of the present invention preferably has a plane orientation coefficient of 0.140 to 0.280. When the plane orientation coefficient is smaller than 0.14, the orientation of the molecular chain is small and the hydrolysis resistance and heat resistance tend to decrease. In addition, since a film having a plane orientation coefficient larger than 0.280 needs to be extremely oriented, film tearing frequently occurs at the time of film formation, and the film cannot be stably formed. A more preferable lower limit value of the plane orientation coefficient is 0.150, and a more preferable lower limit value is 0.155. A more preferable upper limit value of the plane orientation coefficient is 0.180, and a more preferable upper limit value is 0.165. A more preferable range of the plane orientation coefficient is 0.150 to 0.180, and a more preferable range is 0.155 to 0.165.

  The plane orientation coefficient can be controlled by the stretching conditions of the polyester film. In particular, it is difficult for the polyester film of the present invention to increase the plane orientation coefficient when the polyimide content increases. Moreover, since IV of a film will also become high when IV of a raw material is high, it becomes difficult to raise a plane orientation coefficient. In order to make the plane orientation coefficient within the range as described above, first, a two-stage MD stretching is performed in which a machine direction (hereinafter sometimes abbreviated as MD) stretching is performed at a low temperature, and then the temperature is increased and MD stretching is performed. Is preferred. The plane orientation coefficient increases as the draw ratio increases, but if the ratio is too high, the film-forming property is deteriorated, and therefore there is an optimum draw ratio.

  The polyester film of the present invention preferably has a retention rate of elongation at break in at least one direction after heat treatment at 200 ° C. for 72 hours of 10 to 100%. Moreover, it is preferable that the retention of the elongation at break in at least one direction after 72 hours at 125 ° C. and 100% RH is 10 to 100%. When the retention of breaking elongation is less than 10%, the durability tends to deteriorate when used as a solar cell backsheet. Moreover, the retention rate of breaking elongation being 100% represents the fact that it does not change in a treatment for 72 hours at a temperature of 125 ° C. and a humidity of 100% RH, and is the most preferred embodiment. If the retention of breaking elongation is greater than 100%, the polyester film is likely to be relaxed in orientation, so that the mechanical properties are low and handling is difficult. A more preferable lower limit of the retention of breaking elongation is 20%, and a more preferable lower limit is 30%. A more preferable range of the retention of breaking elongation is 20 to 100%, and a more preferable range is 30 to 100%. The retention of breaking elongation becomes better as the plane orientation coefficient of the biaxially oriented polyester film is higher, and the loss tangent (tan δ) is higher, and the higher the film IV is, the better.

  The polyester film of the present invention preferably has a light transmittance of 0 to 20% at a wavelength of 360 nm. If the light transmittance at a wavelength of 360 nm is greater than 20%, the weather resistance tends to deteriorate because the ultraviolet absorptivity is small. Further, the light transmittance at a wavelength of 360 nm being 0% means that it absorbs all and is the most preferable mode. A more preferable range is 0 to 15%, and a further preferable range is 0 to 10%. The light transmittance decreases as the content of polyimide (B) increases.

Next, the method for producing the polyester film of the present invention will be described as an example in which polyethylene terephthalate (PET) is used as polyester. The polyester film of the present invention preferably undergoes the following steps 1 to 3 in that order.
Step 1: A step of obtaining a compound raw material (AB) by melt-kneading polyester (A) and polyimide (B) so that the mass fraction (A / B) is 70/30 to 30/70.
The mass fraction (A / B) of the polyester (A) and the polyimide (B) is preferably 65/35 to 35/65, and more preferably 60/40 to 40/60. When the ratio of the polyester (A) is larger than 70/30, the melt viscosity of the polyimide (B) is too high, so that the polyimide (B) is difficult to disperse in the polyester (A) having a low melt viscosity, resulting in poor dispersion. Occurs. Insufficient dispersion causes extrusion troubles and poor stretching in the polyester film production process, making it difficult to improve heat resistance and hydrolysis resistance. On the other hand, if the ratio of polyimide (B) is larger than 30/70, the overall melt viscosity becomes high, so shear heat is generated during compounding, and polyester (A) is deteriorated. Deterioration of the polyester (A) tends to deteriorate due to poor stretching, heat and humidity in the polyester film production process, and it becomes difficult to improve heat resistance and hydrolysis resistance.
Process 2: The process of obtaining the heat-processed compound raw material (ABH) by heat-processing the compound raw material (AB) at the temperature of 210-250 degreeC under the reduced pressure of 0.1 kPa or less for 1 to 100 hours. The heating temperature is more preferably 215 to 245 ° C, still more preferably 220 to 230 ° C. The time for the heat treatment is more preferably 10 to 80 hours, still more preferably 20 to 50 hours. If step 2 is not carried out, the compound raw material (AB) has a low IV due to the heat during melt extrusion. Therefore, if it is used as it is, the polyester tends to deteriorate and the heat resistance, hydrolysis resistance and weather resistance tend to decrease. In particular, the weather resistance is lowered, and the Δb value is increased by ultraviolet irradiation. When the heat treatment temperature is lower than 210 ° C., solid phase polymerization hardly occurs and the effect of heat treatment cannot be obtained. When the heat treatment temperature is higher than 250 ° C., the polyester melts and a chip shape cannot be obtained, and cannot be used as a raw material for producing a polyester film. When the heat treatment time is shorter than 1 hour, the effect of solid phase polymerization is small, and heat resistance, hydrolysis resistance, and weather resistance are not improved. On the other hand, if the heating time is longer than 100 hours, the IV becomes too high and stretching cannot be performed, making it difficult to improve heat resistance, hydrolysis resistance, and weather resistance.
Step 3: The polyester (A ′) and the heat-treated compound raw material (ABH) are mixed, melt-extruded to obtain an unstretched sheet, and the unstretched sheet is biaxially stretched to obtain a biaxially oriented polyester film. Process.
A polyester film for a solar battery back sheet having both heat resistance, hydrolysis resistance, weather resistance, and low bleed-out property can be obtained through the steps 1 to 3 described above.

  Of course, the present invention is not limited to a polyester film using a PET film, and may be one using another polymer. For example, when a polyester film is formed using polyethylene-2,6-naphthalenedicarboxylate having a high glass transition temperature or a high melting point, extrusion or stretching may be performed at a temperature higher than the temperature shown below.

  First, polyethylene terephthalate is prepared. Polyethylene terephthalate is manufactured by one of the following processes. (1) Using terephthalic acid and ethylene glycol as raw materials, a low molecular weight polyethylene terephthalate or oligomer is obtained by direct esterification reaction, and then a polymer is obtained by polycondensation reaction using antimony trioxide or titanium compound as a catalyst. And (2) a process in which dimethyl terephthalate and ethylene glycol are used as raw materials, a low molecular weight product is obtained by a transesterification reaction, and a polymer is obtained by a subsequent polycondensation reaction using antimony trioxide or a titanium compound as a catalyst. Here, the reaction proceeds even without a catalyst, but in the transesterification reaction, the esterification usually proceeds using a compound such as manganese, calcium, magnesium, zinc, lithium and titanium as a catalyst. After the exchange reaction is substantially completed, a phosphorus compound may be added for the purpose of inactivating the catalyst used in the reaction. The obtained PET pellet is preferably heat-treated at a temperature of 210 to 250 ° C. for 1 to 100 hours under a reduced pressure of 0.1 kPa using a rotary vacuum polymerization apparatus to increase the intrinsic viscosity.

Next, the polyethylene terephthalate pellets and polyetherimide pellets obtained from SABIC Innovative Plastics Co., Ltd. are mixed at a predetermined ratio and supplied to a vent type twin-screw kneading extruder heated to 270 to 300 ° C. And melt extrusion. The shear rate at this time is preferably 50 to 300 sec ⁻¹ , more preferably 100 to 200 sec ⁻¹ , and the residence time is preferably 0.5 to 10 minutes, more preferably 1 to 5 minutes. Furthermore, when the above-mentioned kneading conditions do not make them compatible, the obtained chips may be put into the twin screw extruder again and kneading extrusion may be repeated until they are compatible. Since the obtained PET / PEI blend chip has IV decreased due to heat during melt extrusion, if used as it is, polyethylene terephthalate tends to deteriorate, and heat resistance, hydrolysis resistance, and weather resistance tend to decrease. In particular, the weather resistance is lowered, and the Δb value is increased by ultraviolet irradiation. Therefore, it is preferable to heat-treat the obtained PET / PEI blend chip using a rotary vacuum polymerization apparatus under a reduced pressure of 0.1 kPa at a temperature of 210 to 250 ° C. for 1 to 100 hours to increase the intrinsic viscosity. Preferred intrinsic viscosity IV is 0.6 to 1.2, more preferably 0.7 to 1.1, and still more preferably 0.8 to 1.0.

  Next, the obtained PET pellets and the PET / PEI blend chip are mixed in a desired ratio, dried under reduced pressure at 180 ° C. for 3 hours or more, and then under a nitrogen stream or under reduced pressure so that the intrinsic viscosity does not decrease. , Supplied to an extruder heated to a temperature of 265 to 280 ° C., extruded from a slit-shaped die, and cooled on a casting roll to obtain an unstretched film. At this time, it is preferable to use various types of filters, for example, filters made of materials such as sintered metal, porous ceramic, sand and wire mesh, in order to remove foreign substances and denatured polymers. Moreover, you may provide a gear pump as needed in order to improve fixed_quantity | feed_rate supply property. When laminating films, a plurality of different polymers are melt laminated using two or more extruders and manifolds or merging blocks.

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

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

  Next, stretching in the width direction is performed using a stenter (TD stretching). The draw ratio is preferably 2.0 to 6.0 times, more preferably 3.0 to 5.5 times, and still more preferably 3.5 to 5.0 times. The temperature is preferably in the range of (Tg) to (Tg + 50) ° C., more preferably in the range of (Tg) to (Tg + 30) ° C. After TD stretching, heat setting is performed. In the heat setting treatment, the film is relaxed under tension or in the width direction (relaxation rate 0 to 10%), preferably at a temperature of (Tm-70) to (Tm) ° C., more preferably (Tm-50) to (Tm -10) Heat treatment is performed at a temperature of ° C, more preferably in the range of (Tm-40) to (Tm-20) ° C. The heat treatment time is preferably in the range of 0.5 to 20 seconds. Then, after cooling to 25 ° C., the film edge can be removed to obtain the polyester film of the present invention.

[Methods for measuring physical properties and methods for evaluating effects]
(1) Loss tangent (tan δ) peak temperature Using a dynamic viscoelastic device DMS6100 manufactured by SII Nano Technology, the loss tangent (tan δ) is measured under the following conditions, and the temperature at the maximum height of the peak is measured. The tan δ peak temperature was used. When there are multiple peaks or shoulders, the highest peak is evaluated. Sample and measurement device settings are as follows.
Sample length: 20mm
Sample width: 10mm
Temperature range: 25-200 ° C
Temperature increase rate: 2 ° C./min Strain amplitude: 10 mN
Compression force gain: 1.5
Initial value of force amplitude: 100 mN.

(2) Increase in yellowness (b value) (Δb value)
Tristimulus values X, Y, and Z were measured by a transmission method according to JIS-K-7105 (1981) using a spectroscopic color difference meter CM-3600d (manufactured by KONICA-MINOLTA). From there, the yellowness (b value) of the Hunter Lab color system was calculated according to the following formula.
b value = 7.0 × (Y−0.847 × Z) / Y ^1/2
Further, the Δb value was calculated by the following formula. For ultraviolet irradiation, an ultraviolet deterioration accelerating tester (SUV-W131: manufactured by Iwasaki Electric Co., Ltd., UV illuminance: 100 mW / cm ² , UV wavelength: 295 nm to 450 nm, lamp type: metal halide, temperature and humidity: 60 ° C. × 50% RH) Used.
Δb value = (b value after irradiation for 48 hours of ultraviolet rays) − (initial b value before irradiation).

(3) Measurement of resin content in film After weighing the film, it is dissolved in a mixed solvent of hexafluoroisopropanol (HFIP) / chloroform (mass ratio 50/50). When there is an insoluble component, the insoluble component is separated by centrifugation, then the mass is measured, and the structure and mass fraction of the component are measured by elemental analysis, FT-IR, and NMR methods. If the supernatant component is analyzed in the same manner, the mass fraction and structure of the polyester component and other components can be specified. Specifically, after the solvent is distilled off from the supernatant component and dissolved in a mixed solvent of HFIP / deuterated chloroform (mass ratio 50/50), the NMR spectrum of ¹ H nucleus is measured. In the obtained spectrum, the peak area intensity of absorption peculiar to each component (for example, aromatic proton of terephthalic acid for PET, aromatic proton of bisphenol A for PEI) is determined, and the ratio and number of protons are obtained. The blend molar ratio is calculated. Further, the mass ratio is calculated from the formula amount corresponding to the unit unit of the polymer. In this way, the mass fraction and structure of each component can be specified.

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

(5) Elongation retention (temperature 200 ° C., 72 hours)
The breaking elongation E0 was determined by measuring the breaking elongation when a sample was cut into a size of 1 cm × 20 cm and pulled at a chucking speed of 5 cm and a pulling speed of 300 mm / min based on ASTM-D882 (1997). The measurement was performed on five samples, and the elongation at break was defined as the average value. Next, after cutting the sample into the shape of a measurement piece (1 cm × 20 cm), the sample was treated with STPH-102 manufactured by Espec Co., Ltd. for 72 hours at a temperature of 200 ° C., and then the fracture elongation of the sample after the treatment. Was measured according to ASTM-D882 (1997) at a chuck distance of 5 cm and a pulling speed of 300 mm / min. The measurement was performed on five samples, and the average value was defined as the elongation at break E1. Using the obtained elongation at break E0 and E1, the elongation retention (temperature 200 ° C., 72 hours) was calculated according to the following formula.
Elongation retention rate (temperature 200 ° C., 72 hours) (%) = (E1 / E0) × 100.

(6) Elongation retention (temperature 125 ° C., humidity 100% RH, 72 hours)
The breaking elongation E0 is obtained in the same manner as (5) above. Next, after the sample was cut into the shape of the measurement piece (1 cm × 20 cm), it was treated for 72 hours under the conditions of a temperature cooker PC304R8D manufactured by Hirayama Seisakusho at a temperature of 125 ° C. and a humidity of 100% RH. Based on ASTM-D882 (1997), the breaking elongation of the sample after the treatment was measured at a chuck distance of 5 cm and a pulling speed of 300 mm / min. The measurement was performed on five samples, and the average value was defined as the elongation at break E2. Using the obtained elongation at break E0 and E2, the elongation retention (temperature 125 ° C., humidity 100% RH, 72 hours) was calculated according to the following formula.
Elongation retention (temperature 125 ° C., humidity 100% RH, 72 hours) (%) = (E2 / E0) × 100.

(7) Light transmittance measurement The light transmittance was measured with a spectrophotometer (U-4100 Spectrophotometer) manufactured by Hitachi, Ltd. The light wavelength range was 240 to 800 nm, and the transmittance at 360 nm was evaluated.

(8) Intrinsic viscosity (IV)
Calculation is made based on the following formula from the solution viscosity measured at a temperature of 25 ° C. in orthochlorophenol.
ηsp / C = [η] + K [η] ² × C
Here, ηsp = (solution viscosity / solvent viscosity) −1, C is the dissolved polymer mass per 100 ml of solvent (g / 100 ml, usually 1.2), and K is the Huggins constant (assuming 0.343). It is. The solution viscosity and solvent viscosity are measured using an Ostwald viscometer.

(9) Hydrolysis resistance Using the film for solar cell backsheet of the present invention as the first layer, 90 parts by mass of “Takelac” (registered trademark) A310 (manufactured by Mitsui Takeda Chemical Co., Ltd.) and “Takenate” as the adhesive layer (Registered trademark) A3 (manufactured by Mitsui Takeda Chemical Co., Ltd.) is applied, and a biaxially stretched polyester film “Lumirror” (registered trademark) S10 (manufactured by Toray Industries, Inc.) having a thickness of 125 μm is applied as a second layer thereon. Pasted together. Next, the above-mentioned adhesive layer is applied onto the above-mentioned second layer, and the barrier layer “HGTS” (registered trademark) having a thickness of 12 μm (alumina-deposited PET film manufactured by Toray Film Processing Co., Ltd.) A back sheet having a thickness of 188 μm was formed by bonding so as to be opposite to the two layers. The breaking elongation E0 of the obtained back sheet is obtained in the same manner as in the above (5). Next, after cutting the sample into the shape of a measurement piece (1 cm × 20 cm), using a constant temperature and humidity chamber (Espec Co., Ltd. constant temperature and humidity chamber KH-60A), an atmosphere having a temperature of 85 ° C. and a humidity of 85% RH. The sample was allowed to stand for 3,000 hours, and the breaking elongation of the treated sample was measured at 5 cm between chucks and 300 mm / min pulling speed based on ASTM-D882 (1997). The measurement was performed on five samples, and the average value was defined as the elongation at break E3. Using the obtained elongation at break E0 and E3, the elongation retention (temperature 85 ° C., humidity 85% RH, 3000 hours) was calculated according to the following formula.
Elongation retention (temperature 85 ° C., humidity 85% RH, 3000 hours) (%) = (E3 / E0) × 100
The elongation retention was determined according to the following criteria, and the hydrolysis resistance was evaluated.
◎: Elongation retention 70% or more Very good ◯: Elongation retention 50% or more and less than 70% Good △: Elongation retention 30% or more but less than 50% Slightly good X: Elongation retention 30 Less than% Poor.

(10) Heat resistance As in (9), a back sheet was prepared and the elongation at break E0 was measured. Next, after cutting the sample into the shape of a measurement piece (1 cm × 20 cm), using a high temperature thermostat STPH-102 manufactured by Espec Co., Ltd., left for 3000 hours in an atmosphere at a temperature of 150 ° C., and then a sample after treatment Based on ASTM-D882 (1997), the elongation at break was measured at 5 cm between chucks and at a pulling speed of 300 mm / min. The measurement was performed on five samples, and the average value was defined as the elongation at break E4. Using the obtained elongation at break E0 and E4, the elongation retention (temperature 150 ° C., 3000 hours) was calculated according to the following formula.
Elongation retention (temperature 150 ° C., 3000 hours) (%) = (E4 / E0) × 100
The elongation retention was determined according to the following criteria, and the heat resistance was evaluated.
◎: Elongation retention 70% or more Very good ◯: Elongation retention 50% or more and less than 70% Good △: Elongation retention 30% or more but less than 50% Slightly good X: Elongation retention 30 Less than% Poor.

(11) A back sheet was prepared in the same manner as the weather resistance (9), and the elongation at break E0 was measured. Next, after cutting the sample into the shape of a measurement piece (1 cm × 20 cm) and leaving it for 3000 hours in an outdoor exposure test, the fracture elongation of the treated sample was measured between chucks based on ASTM-D882 (1997). The measurement was performed at 5 cm and a pulling speed of 300 mm / min. The measurement was performed on five samples, and the average value was defined as the elongation at break E5. Using the obtained elongation at break E0 and E5, the elongation retention (outdoor, 3000 hours) was calculated according to the following formula.
・ Elongation retention (outdoor, 3000 hours) (%) = (E5 / E0) × 100
The elongation retention was determined according to the following criteria, and the weather resistance was evaluated.
◎: Elongation retention 70% or more Very good ◯: Elongation retention 50% or more and less than 70% Good △: Elongation retention 30% or more but less than 50% Slightly good X: Elongation retention 30 Less than% Poor.

(12) Bleed-out property Using the film for solar cell backsheet of the present invention as the first layer, 90 parts by mass of “Takelac” (registered trademark) A310 (manufactured by Mitsui Takeda Chemical Co., Ltd.) and “Takenate” ( (Registered Trademark) A3 (Mitsui Takeda Chemical Co., Ltd.) is applied, and a 125 μm thick biaxially stretched polyester film “Lumirror” (Registered Trademark) S10 (Toray Industries, Inc.) is applied as a second layer thereon. Combined. In an atmosphere of 23 ° C. and 50% RH, according to JIS-Z0237 (2009), the unbonded part of the film bonded to the upper and lower clips is sandwiched, and the bleed out is measured at a peeling angle of 180 ° and a pulling speed of 100 mm / min. did. When the additive bleeds out, the adhesiveness deteriorates and the adhesive strength decreases.
○: 10N / 20mm or more, less than 20N / 20mm ... adhesiveness good Δ: 5N / 20mm or more, less than 10N / 20mm ... adhesiveness slightly good x: less than 5N / 20mm ... adhesion poor

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

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

  After the reaction contents were transferred to the polymerization apparatus, the reaction system was gradually heated from 230 ° C. to 290 ° C. and the pressure was reduced to 0.1 kPa. The time to reach a final temperature of 290 ° C. and a final pressure of 0.1 kPa was both 60 minutes. After reaching the final temperature and final pressure, the reaction was carried out for 2 hours (3 hours after the start of polymerization), and the stirring torque of the polymerization apparatus was a predetermined value (the specific value differs depending on the specifications of the polymerization apparatus, but this polymerization apparatus The value indicated by polyethylene terephthalate having an intrinsic viscosity of 0.65 was a predetermined value). Therefore, the reaction system was purged with nitrogen and returned to normal pressure to stop the polycondensation reaction, discharged into cold water in a strand form, and immediately cut to obtain PET pellet A (3 mm cubic) of polyethylene terephthalate having an intrinsic viscosity of 0.65. Obtained.

(Reference Example 2)
Using a rotary vacuum polymerization apparatus, the PET pellet A obtained in the above Reference Example 1 was heat-treated at a temperature of 230 ° C. under a reduced pressure of 0.1 kPa for a long time to carry out solid phase polymerization. The longer the heat treatment time, the higher the intrinsic viscosity. The intrinsic viscosity is 0.80 after a treatment time of 20 hours.

(Reference Example 3)
After 50 parts by mass of polyethylene terephthalate (PET) having an intrinsic viscosity of 0.8 obtained in Reference Example 2 and 50 parts by mass of polyetherimide (PEI) “Ultem” 1010 manufactured by SABIC, dehumidifying and drying at 150 ° C. for 5 hours, Heated to 320-290 ° C (screw zone, temperature gradient set at extrusion head), twin-screw, three-stage type screw (PET and PEI kneading plasticization zone / Dalmage kneading zone / Fine dispersion compatibilizing zone by reverse screwing Dalmage ) And a vent type twin screw extruder (L / D = 40, the pressure reduction degree of the vent hole is 200 Pa), melt-extruded in a residence time of 3 minutes, and PET / PET containing 50% by mass of PEI. A PEI blend chip was obtained. This chip was designated as blend chip A.

(Reference Example 4)
Using a rotary vacuum polymerization apparatus, the blend chip A obtained in Reference Example 3 was heat-treated at a temperature of 230 ° C. under a reduced pressure of 0.1 kPa for a long time to perform solid phase polymerization. The longer the heat treatment time, the higher the intrinsic viscosity. The intrinsic viscosity is 0.90 after a treatment time of 40 hours. The intrinsic viscosity is 1.2 at a treatment time of 90 hours. The intrinsic viscosity is 1.3 at a treatment time of 110 hours.

Example 1
In extruder E heated to a temperature of 280 ° C., 80 parts by mass of PET pellets having an intrinsic viscosity of 0.8 obtained in Reference Example 2 and blend chip A20 having an intrinsic viscosity of 0.9 obtained in Reference Example 4 were used. The mass part was supplied after drying under reduced pressure at a temperature of 180 ° C. for 3 hours, and introduced into a T-die die under a nitrogen atmosphere. Next, from the inside of the T die die, it was extruded into a sheet shape to obtain a molten single layer sheet, which was closely cooled and solidified by an electrostatic application method on a drum maintained at a surface temperature of 25 ° C. to obtain an unstretched single layer film.

  Subsequently, after preheating the obtained unstretched monolayer film with a heated roll group, 1.8 times MD stretching 1 is performed at a temperature of 90 ° C., and 2.3 times MD stretching 2 is further performed at a temperature of 110 ° C. went. The film was stretched 4.1 times in the longitudinal direction (MD direction) in total, and then cooled with a roll group having a temperature of 25 ° C. to obtain a uniaxially stretched film. While holding both ends of the obtained uniaxially stretched film with clips, it is led to a preheating zone at a temperature of 95 ° C. in the tenter, and continuously in the heating zone at a temperature of 100 ° C. in the width direction (TD direction) perpendicular to the longitudinal direction The film was stretched 4.0 times. Subsequently, a heat treatment was performed for 10 seconds at a temperature of 220 ° C. in a heat treatment zone in the tenter, and a relaxation treatment was further performed in the 4% width direction at a temperature of 220 ° C. Subsequently, the film was gradually cooled and wound up to obtain a biaxially oriented polyester film having a thickness of 50 μm.

  When the obtained polyester film was evaluated, as shown in Tables 1 and 2, the polyester film had excellent resistance to hydrolysis, heat resistance, weather resistance, and bleed out.

(Example 2)
Use 96 parts by mass of PET pellets having an intrinsic viscosity of 0.8 obtained in Reference Example 2 and 4 parts by mass of blend chip A having an intrinsic viscosity of 0.9 obtained in Reference Example 4; 8 times MD stretching 1 was performed, and 2.3 times MD stretching 2 was further performed at a temperature of 102 ° C. The film was stretched 4.1 times in the longitudinal direction (MD direction) in total, and then cooled with a roll group having a temperature of 25 ° C. to obtain a uniaxially stretched film. While holding both ends of the obtained uniaxially stretched film with clips, the tenter is guided to a preheating zone at a temperature of 87 ° C. in the tenter, and then continuously in the heating zone at a temperature of 92 ° C. in the width direction (TD direction) perpendicular to the longitudinal direction. A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the film was stretched 4.0 times. When the obtained polyester film was evaluated, it had excellent heat resistance, hydrolysis resistance, weather resistance, and bleed-out properties.

(Example 3)
Use 40 parts by mass of PET pellets having an intrinsic viscosity of 0.8 obtained in Reference Example 2 and 60 parts by mass of Blend Chip A having an intrinsic viscosity of 0.9 obtained in Reference Example 4, and at a temperature of 110 ° C. 8 times MD stretching 1 was performed, and 2.3 times MD stretching 2 was further performed at a temperature of 130 ° C. The film was stretched 4.1 times in the longitudinal direction (MD direction) in total, and then cooled with a roll group having a temperature of 25 ° C. to obtain a uniaxially stretched film. While holding both ends of the obtained uniaxially stretched film with clips, it is guided to a preheating zone at a temperature of 115 ° C in the tenter, and then continuously in the heating zone at a temperature of 120 ° C in the width direction (TD direction) perpendicular to the longitudinal direction. A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the film was stretched 4.0 times. When the obtained polyester film was evaluated, it had excellent resistance to hydrolysis, heat resistance, weather resistance, and bleed out.

Example 4
Use 84 parts by mass of PET pellets having an intrinsic viscosity of 0.8 obtained in Reference Example 2 and 16 parts by mass of blend chip A having an intrinsic viscosity of 0.9 obtained in Reference Example 4; 8 times MD stretching 1 was performed, and 2.3 times MD stretching 2 was further performed at a temperature of 108 ° C. The film was stretched 4.1 times in the longitudinal direction (MD direction) in total, and then cooled with a roll group having a temperature of 25 ° C. to obtain a uniaxially stretched film. While holding both ends of the obtained uniaxially stretched film with clips, it is led to a preheating zone at a temperature of 93 ° C. in the tenter, and then continuously in the heating zone at a temperature of 98 ° C. in the width direction (TD direction) perpendicular to the longitudinal direction. A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the film was stretched 4.0 times. When the obtained polyester film was evaluated, it had excellent resistance to hydrolysis, heat resistance, weather resistance, and bleed out.

(Example 5)
Use 60 parts by mass of PET pellets having an intrinsic viscosity of 0.8 obtained in Reference Example 2 and 40 parts by mass of blend chip A having an intrinsic viscosity of 0.9 obtained in Reference Example 4 and at a temperature of 100 ° C. 8 times MD stretching 1 was performed, and further 2.3 times MD stretching 2 was performed at a temperature of 120 ° C. The film was stretched 4.1 times in the longitudinal direction (MD direction) in total, and then cooled with a roll group having a temperature of 25 ° C. to obtain a uniaxially stretched film. While holding both ends of the obtained uniaxially stretched film with clips, it is guided to a preheating zone at a temperature of 105 ° C. in the tenter, and then continuously in a heating zone at a temperature of 110 ° C. in the width direction perpendicular to the longitudinal direction (TD direction). A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the film was stretched 4.0 times. When the obtained polyester film was evaluated, it had excellent resistance to hydrolysis, heat resistance, weather resistance, and bleed out.

(Example 6)
Use 40 parts by mass of PET pellets having an intrinsic viscosity of 0.8 obtained in Reference Example 2 and 60 parts by mass of Blend Chip A having an intrinsic viscosity of 0.59 obtained in Reference Example 3, and at a temperature of 110 ° C. 8 times MD stretching 1 was performed, and 2.3 times MD stretching 2 was further performed at a temperature of 130 ° C. The film was stretched 4.1 times in the longitudinal direction (MD direction) in total, and then cooled with a roll group having a temperature of 25 ° C. to obtain a uniaxially stretched film. While holding both ends of the obtained uniaxially stretched film with clips, it is guided to a preheating zone at a temperature of 115 ° C in the tenter, and then continuously in the heating zone at a temperature of 120 ° C in the width direction (TD direction) perpendicular to the longitudinal direction. A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the film was stretched 4.0 times. When the obtained polyester film was evaluated, it had excellent resistance to hydrolysis, heat resistance and bleed out.

(Example 7)
Using 80 parts by mass of PET pellets having an intrinsic viscosity of 0.8 obtained in Reference Example 2 and a rotary vacuum polymerization apparatus, blend chip A obtained in Reference Example 3 was reduced to 1 at 230 ° C. under a reduced pressure of 0.1 kPa. A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that 20 parts by mass of blend chip A after the time treatment and having an intrinsic viscosity of 0.60 was used. When the obtained polyester film was evaluated, it had excellent hydrolysis resistance, heat resistance, and bleed out properties.

(Example 8)
Except for using 80 parts by mass of PET pellets having an intrinsic viscosity of 0.8 obtained in Reference Example 2 and 20 parts by mass of intrinsic viscosity blend chip A (inherent viscosity 1.2) obtained in Reference Example 4. A biaxially oriented polyester film was obtained in the same manner as in Example 1. When the obtained polyester film was evaluated, it had excellent resistance to hydrolysis, heat resistance, weather resistance, and bleed out.

Example 9
After preheating the unstretched single layer film obtained in Example 1 with a heated roll group, 1.8 times MD stretching 1 is performed at a temperature of 90 ° C., and 2.5 times MD stretching 2 is performed at a temperature of 110 ° C. Went. The film was stretched 4.5 times in the longitudinal direction (MD direction) in total, and then cooled with a roll group at a temperature of 25 ° C. to obtain a uniaxially stretched film. While holding both ends of the obtained uniaxially stretched film with clips, it is led to a preheating zone at a temperature of 95 ° C. in the tenter, and then continuously in the heating zone at a temperature of 100 ° C. in the width direction (TD direction) perpendicular to the longitudinal direction. The film was stretched 4.3 times. Subsequently, heat treatment was carried out in the same manner as in Example 1 except that heat treatment was performed at a temperature of 220 ° C. for 10 seconds in the heat treatment zone in the tenter, and further relaxation treatment was performed in the 2% width direction at a temperature of 220 ° C. An axially oriented polyester film was obtained. When the obtained polyester film was evaluated, it had excellent resistance to hydrolysis, heat resistance, weather resistance, and bleed out.

(Example 10)
After preheating the unstretched monolayer film obtained in Example 1 with a heated roll group, 1.8 times MD stretching 1 is performed at a temperature of 90 ° C., and 2.1 times MD stretching 2 is performed at a temperature of 110 ° C. Went. The film was stretched 3.8 times in the longitudinal direction (MD direction) in total, and then cooled with a roll group at a temperature of 25 ° C. to obtain a uniaxially stretched film. While holding both ends of the obtained uniaxially stretched film with clips, it is led to a preheating zone at a temperature of 95 ° C. in the tenter, and then continuously in the heating zone at a temperature of 100 ° C. in the width direction (TD direction) perpendicular to the longitudinal direction. The film was stretched 3.8 times. Subsequently, heat treatment was performed in the same manner as in Example 1 except that heat treatment was performed at a temperature of 220 ° C. for 10 seconds in the heat treatment zone in the tenter, and further relaxation treatment was performed in the 5% width direction at a temperature of 220 ° C. An axially oriented polyester film was obtained. When the obtained polyester film was evaluated, it had characteristics excellent in weather resistance and bleed-out property.

(Example 11)
Use 90 parts by mass of PET pellets having an intrinsic viscosity of 0.8 obtained in Reference Example 2 and 10 parts by mass of blend chip A having an intrinsic viscosity of 0.9 obtained in Reference Example 4; 8 times MD stretching 1 was performed, and further 2.1 times MD stretching 2 was performed at a temperature of 105 ° C. The film was stretched 3.8 times in the longitudinal direction (MD direction) in total, and then cooled with a roll group at a temperature of 25 ° C. to obtain a uniaxially stretched film. While holding both ends of the obtained uniaxially stretched film with clips, it is guided to a preheating zone at a temperature of 90 ° C. in the tenter, and continuously in the heating zone at a temperature of 95 ° C. in the width direction (TD direction) perpendicular to the longitudinal direction. A biaxially oriented polyester film was obtained in the same manner as in Example 10 except that the film was stretched 3.8 times. When the obtained polyester film was evaluated, it had excellent bleed-out properties.

(Example 12)
Same as Example 10 except that 80 parts by mass of PET pellets having an intrinsic viscosity of 0.65 obtained in Reference Example 1 and 20 parts by mass of blend chip A having an intrinsic viscosity of 0.9 obtained in Reference Example 4 are used. A biaxially oriented polyester film was obtained by this method. When the obtained polyester film was evaluated, it had characteristics excellent in weather resistance and bleed-out property.

(Example 13)
Using 80 parts by mass of PET pellets having an intrinsic viscosity of 0.65 obtained in Reference Example 1 and 20 parts by mass of Blend Chip A having an intrinsic viscosity of 0.59 obtained in Reference Example 3, an ultraviolet absorber (benzophenone-based Adekastab LA A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that 0.02% by mass of -51) was added. When the obtained polyester film was evaluated, it had excellent properties in hydrolysis resistance, weather resistance, and heat resistance.

(Example 14)
To a mixture of 100 parts by mass of dimethyl 2,6-naphthalenedicarboxylate and 60 parts by mass of ethylene glycol, 0.03 parts by mass of manganese acetate tetrahydrate salt is added, and gradually from 150 ° C. to 240 ° C. The transesterification was carried out while raising the temperature. In the middle, when the reaction temperature reached 170 ° C., 0.024 parts by mass of antimony trioxide was added. When the reaction temperature reached 220 ° C., 0.042 parts by mass (corresponding to 2 mmol%) of 3,5-dicarboxybenzenesulfonic acid tetrabutylphosphonium salt was added. Thereafter, a transesterification reaction was carried out, and 0.023 parts by mass of trimethyl phosphoric acid was added. Next, the reaction product is transferred to a polymerization apparatus, heated to a temperature of 290 ° C., and subjected to a polycondensation reaction under a high vacuum of 30 Pa. Although the values were different, the values indicated by polyethylene-2,6-naphthalate having an intrinsic viscosity of 0.65 in this polymerization apparatus were set as predetermined values). Therefore, the reaction system was purged with nitrogen and returned to normal pressure to stop the polycondensation reaction, discharged into cold water in a strand form, and immediately cut to obtain polyethylene-2,6-naphthalate pellets X ′ having an intrinsic viscosity of 0.65. Obtained.

  Using the rotary vacuum polymerization apparatus, the obtained PEN pellet was subjected to solid phase polymerization at a temperature of 250 ° C. under a reduced pressure of 0.1 kPa for 20 hours to obtain a PEN pellet X ″ having an intrinsic viscosity of 0.80. 50 parts by weight of the obtained PEN pellet X having an intrinsic viscosity of 0.80 and polyetherimide (PEI) “Ultem” 1010 made by SABIC were dehumidified and dried at 150 ° C. for 5 hours, and then at 320 to 290 ° C. Vent equipped with heated (screw zone, temperature gradient set at extrusion head), twin-screw, three-stage type screw (PEN and PEI kneading plasticizing zone / Dalmerizing kneading zone / inverted screw Dalmerizing fine dispersion compatibilizing zone) This is fed to a twin screw extruder (L / D = 40, the degree of pressure reduction of the vent hole is 200 Pa), melt extruded with a residence time of 3 minutes, and PEI is 50% by mass To obtain a PEN / PEI blend chips having. This chip was designated as Blend Chip B.

  Further, using a rotary vacuum polymerization apparatus, the blend chip B obtained above was subjected to solid phase polymerization at a temperature of 250 ° C. under a reduced pressure of 0.1 kPa for 40 hours to obtain a blend chip B ′ having an intrinsic viscosity of 0.90. It was.

  In an extruder E heated to a temperature of 300 ° C., 80 parts by mass of PEN pellet X ″ having an intrinsic viscosity of 0.80 obtained by solid phase polymerization and 20 parts by mass of blend chip B ′ having an intrinsic viscosity of 0.9 are added. After drying under reduced pressure at a temperature of 3 ° C. for 3 hours, the mixture was supplied and introduced into a T-die die under a nitrogen atmosphere, and then extruded into a sheet from the T-die die to obtain a molten single-layer sheet, which was maintained at a surface temperature of 25 ° C. An unstretched single-layer film was obtained by tightly cooling and solidifying on a drum by an electrostatic application method.

  Subsequently, after preheating the obtained unstretched monolayer film with a heated roll group, 1.8 times MD stretching 1 is performed at a temperature of 115 ° C., and 2.3 times MD stretching 2 is performed at a temperature of 135 ° C. went. The film was stretched 4.1 times in the longitudinal direction (MD direction) in total, and then cooled with a roll group having a temperature of 25 ° C. to obtain a uniaxially stretched film. While holding both ends of the obtained uniaxially stretched film with clips, it is guided to a preheating zone at a temperature of 135 ° C. in the tenter, and then continuously in the heating zone at a temperature of 145 ° C. in the width direction (TD direction) perpendicular to the longitudinal direction. The film was stretched 4.5 times. Subsequently, a heat treatment for 10 seconds was performed at a temperature of 230 ° C. in a heat treatment zone in the tenter, and a relaxation treatment was further performed in the 4% width direction at a temperature of 230 ° C. Subsequently, after uniform cooling, the film was wound up to obtain a biaxially oriented polyester film having a thickness of 50 μm.

  When the obtained polyester film was evaluated, it had excellent resistance to hydrolysis, heat resistance, weather resistance, and bleed out.

(Comparative Example 1)
Adding 100% by weight of PET pellets having an intrinsic viscosity of 0.80 obtained in Reference Example 2 and adding 0.1% by weight of an ultraviolet absorber (benzophenone-based Adekastab LA-51) without using the blend chip A, 80 ° C. Then, 1.8 times MD stretching 1 was performed at a temperature of 2.3 ° C., and 2.3 times MD stretching 2 was performed at a temperature of 100 ° C. The film was stretched 4.1 times in the longitudinal direction (MD direction) in total, and then cooled with a roll group having a temperature of 25 ° C. to obtain a uniaxially stretched film. While holding both ends of the obtained uniaxially stretched film with clips, the tenter is guided to a preheating zone at a temperature of 85 ° C. in the tenter, and then continuously in the heating zone at a temperature of 90 ° C. in the width direction (TD direction) perpendicular to the longitudinal direction. A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the film was stretched 4.0 times. When the obtained polyester film was evaluated, the loss tangent (tan δ) was out of the range of the present invention, and therefore, the polyester film had characteristics inferior in hydrolysis resistance, heat resistance, and bleed-out property.

(Comparative Example 2)
Use 20 parts by mass of PET pellets having an intrinsic viscosity of 0.8 obtained in Reference Example 2 and 80 parts by mass of Blend Chip A having an intrinsic viscosity of 0.9 obtained in Reference Example 4, and at a temperature of 120 ° C. 7-fold MD stretching 1 was performed, and 2.1-fold MD stretching 2 was further performed at a temperature of 140 ° C. The film was stretched 3.6 times in the longitudinal direction (MD direction) in total, and then cooled with a roll group having a temperature of 25 ° C. to obtain a uniaxially stretched film. While holding both ends of the obtained uniaxially stretched film with clips, it is led to a preheating zone at a temperature of 125 ° C. in the tenter, and then continuously in the heating zone at a temperature of 130 ° C. in the width direction (TD direction) perpendicular to the longitudinal direction. A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the film was stretched 3.6 times. When the obtained polyester film was evaluated, the loss tangent (tan δ) was out of the range of the present invention, and therefore, the polyester film had characteristics inferior in hydrolysis resistance and heat resistance.

(Comparative Example 3)
Same as Example 1, except that 80 parts by mass of PET pellets having an intrinsic viscosity of 0.8 obtained in Reference Example 2 and 20 parts by mass of blend chip A having an intrinsic viscosity of 0.59 obtained in Reference Example 3 are used. A biaxially oriented polyester film was obtained by this method. When the obtained polyester film was evaluated, the Δb value was outside the range of the present invention, and therefore, the polyester film had characteristics inferior in hydrolysis resistance, heat resistance, and weather resistance.

(Comparative Example 4)
Using 100 parts by mass of PET pellets having an intrinsic viscosity of 0.80 obtained in Reference Example 2, performing 1.8 times MD stretching 1 at a temperature of 80 ° C., and further 2.3 times MD stretching at a temperature of 100 ° C. 2 was performed. The film was stretched 4.1 times in the longitudinal direction (MD direction) in total, and then cooled with a roll group having a temperature of 25 ° C. to obtain a uniaxially stretched film. While holding both ends of the obtained uniaxially stretched film with clips, the tenter is guided to a preheating zone at a temperature of 85 ° C. in the tenter, and then continuously in the heating zone at a temperature of 90 ° C. in the width direction (TD direction) perpendicular to the longitudinal direction. A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the film was stretched 4.0 times. When the obtained polyester film was evaluated, the loss tangent (tan δ) and Δb value were out of the range of the present invention, and therefore, the polyester film had characteristics inferior in hydrolysis resistance, heat resistance, and weather resistance.

(Comparative Example 5)
In the extruder E heated to a temperature of 300 ° C., 100 parts by mass of the PEN pellet X ″ having an intrinsic viscosity of 0.80 obtained in Example 14 was used and the blend chip B was not used, but an ultraviolet absorber (benzophenone series) A biaxially oriented polyester film was obtained in the same manner as in Example 14 except that 0.1% by mass of ADK STAB LA-51) was added, and the obtained polyester film was evaluated. Since it was out of the range, the weather resistance and bleed-out properties were poor.

  The polyester film for a solar battery backsheet of the present invention is less deteriorated due to environmental changes, and can provide a backsheet excellent in hydrolysis resistance, weather resistance, heat resistance, and bleed-out property. Therefore, it may be used to obtain a highly durable solar cell.

Claims (9)

Loss tangent (tan δ) peak temperature is 120 to 180 ° C., and increase in yellowness (b value) (Δb value) is 0 to 15 after irradiation with ultraviolet rays of 295 to 450 nm at 100 mW for 48 hours using a metal halide lamp. A polyester film for a solar battery backsheet. The polyester film for a solar battery back sheet according to claim 1, which is a polyester film containing polyester (A) and polyimide (B). The polyester film for solar battery backsheet according to claim 2, wherein the content of the polyimide (B) is 2% by mass to 30% by mass with respect to the entire film. The polyester film for solar cell backsheet according to any one of claims 1 to 3, wherein the content of the ultraviolet absorber is 0.01% by mass or less based on the whole film. The plane orientation coefficient fn is 0.140-0.280, The polyester film for solar cell backsheets in any one of Claims 1-4. The polyester film for solar cell backsheet according to any one of claims 1 to 5, wherein a retention rate of breaking elongation in at least one direction after 72 hours of heat treatment at 200 ° C is 10 to 100%. The polyester film for a solar battery back sheet according to any one of claims 1 to 6, wherein a retention rate of elongation at break in at least one direction after 72 hours of heat treatment at 125 ° C and 100% RH is 10 to 100%. The polyester film for solar cell backsheet according to any one of claims 1 to 7, wherein the light transmittance at a wavelength of 360 nm is 0 to 20%. It is a manufacturing method of the polyester film for solar cell backsheets in any one of Claims 1-8, Comprising: The following processes 1-3 are passed in that order, The manufacturing method of the polyester film for solar cell backsheets characterized by the above-mentioned. .
Step 1: A step of obtaining a compound raw material (AB) by melt-kneading polyester (A) and polyimide (B) so that the mass fraction (A / B) is 70/30 to 30/70.
Process 2: The process of obtaining the heat-processed compound raw material (ABH) by heat-processing the compound raw material (AB) at the temperature of 210-250 degreeC under the reduced pressure of 0.1 kPa or less for 1 to 100 hours.
Step 3: The polyester (A ′) and the heat-treated compound raw material (ABH) are mixed, melt-extruded to obtain an unstretched sheet, and the unstretched sheet is biaxially stretched to obtain a biaxially oriented polyester film. Process.