JP2011256254A - Polyester film and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a blend film of polyester and polyimide, decreasing a moisture content in the film, improving breaking strength, and having excellent hydrolysis resistance while maintaining the excellent dimensional stability and gas barrier property.SOLUTION: A biaxially oriented polyester film contains 70-99 pts.mass of polyester (A) and 1-30 pts.mass of polyimide (B), wherein an imidization rate of the polyimide (B) is ≥95%, and a water content of the polyester film after 24 hours at 25°C and at a relative humidity of 60% is ≤0.7 wt.%.

Description

  The present invention relates to a polyester film and a method for producing the same.

Conventionally, polyester and polyimide blend films have been studied (Patent Documents 1 and 2). This is because these films are excellent in dimensional stability and gas barrier properties. However, such a film does not necessarily have sufficient hydrolysis resistance. Therefore, when such a film is used for an element that has been placed outdoors for many years, such as a solar cell element, there is a problem that hydrolysis of the film proceeds and the breaking strength of the film is significantly deteriorated. In addition, if the amount of water remaining in the film when it is formed is large, there is also a problem that the water causes hydrolysis to proceed.
That is, in a blend film of polyester and polyimide, a technique for suppressing hydrolysis and improving breaking strength is required.

JP 2009-212278 A International Publication WO2007 / 040039 Pamphlet

  The present invention aims to solve the above problems, and in a blend film of polyester and polyimide, while maintaining excellent dimensional stability and gas barrier properties, the moisture content in the film is reduced, and the breaking strength is increased. The purpose is to improve.

Under such circumstances, as a result of intensive studies by the present inventors, it has been found that polyamicoic acid contained in polyimide deteriorates the hydrolysis resistance of polyester as an acid catalyst. And this inventor solved this problem by imidating polyamicoic acid and making it cyclic | annular skeleton, and came to complete this invention. Specifically, the above problem has been achieved by the following means.
(1) A biaxially oriented polyester film containing 70 to 99 parts by mass of polyester (A) and 1 to 30 parts by mass of polyimide (B), wherein the imidization ratio of the polyimide (B) is 95% or more, A polyester film in which the polyester film has a moisture content of 0.7% by weight or less at 25 ° C., a relative humidity of 60%, and after 24 hours.
(2) The polyester film as described in (1) whose imidation ratio is 97% or more.
(3) The polyester film as described in (1) whose imidation ratio is 99% or more.
(4) The polyester film according to any one of (1) to (3), wherein the polyimide (B) is a polyetherimide.
(5) In any one of (1) to (4), 70 to 99% by weight of the resin constituting the polyester film is polyester (A) and 1 to 30% by weight is polyimide (B). The polyester film as described.
(6) In any one of (1) to (4), 80 to 99% by weight of the resin constituting the polyester film is polyester (A) and 1 to 20% by weight is polyimide (B). The polyester film as described.
(7) The polyester (A) contains at least one polymer selected from the group consisting of polyethylene terephthalate, polyethylene naphthalate, and modified products thereof, and copolymers thereof. The polyester film according to any one of 6).
(8) The polyester film according to any one of (1) to (7), wherein the terminal COOH concentration of the polyester (A) is 25 (eq / ton) or less.
(9) The polyester film according to any one of (1) to (8), wherein the polyester film has a moisture content of 259 ° C., a relative humidity of 60%, and a water content after 24 hours of 0.59% by weight or less.
(10) The polyester film according to any one of (1) to (9), wherein the polyimide (B) pellets are heated to 180 ° C. to 240 ° C. for 10 hours or longer to form an imidized film. .
(11) When stored in an atmosphere at a temperature of 85 ° C. and a relative humidity of 85%, the storage time at which the breaking elongation after storage is 50% of the breaking elongation before storage is 3500 hours or more. The polyester film according to any one of (1) to (10), wherein:
(12) The polyester film according to any one of (1) to (11), which is a polyester film for solar cells.
(13) A sealing film having a gas barrier layer on the surface of the polyester film according to any one of (1) to (12).
(14) A solar cell module comprising the polyester film according to any one of (1) to (12) or the sealing film according to (13).
(15) In the method for producing a biaxially oriented polyester film containing 70 to 99 parts by mass of polyester (A) and 1 to 30 parts by mass of polyimide (B), the polyimide (B) is 180 ° C to 240 ° C. The manufacturing method of the polyester film including heat processing for 10 to 50 hours at ° C.

  According to the present invention, it is possible to obtain a polyester / polyimide blend film having a low moisture content and excellent elongation at break.

FIG. 1 shows the basic configuration of the solar cell module of the present invention.

  Hereinafter, the contents of the present invention will be described in detail. In the present specification, “to” is used to mean that the numerical values described before and after it are included as a lower limit value and an upper limit value.

The polyester film of the present invention is a biaxially oriented polyester film containing 70 to 99 parts by mass of polyester (A) and 1 to 30 parts by mass of polyimide (B), and the imidization ratio of the polyimide (B) is 95%. Thus, the polyester film is characterized in that the moisture content after 24 hours at 25 ° C., 60% relative humidity is 0.7% by weight or less.
Conventionally, a biaxially oriented polyester film containing 70 to 99 parts by mass of polyester (A) and 1 to 30 parts by mass of polyimide (B) is known to have excellent dimensional stability and gas barrier properties. Such a film has a problem of poor hydrolysis resistance. However, in the present invention, the imidation ratio of the polyimide (B) is 95% or more, and the moisture content of the polyester film after 25 ° C., relative humidity 60% and 24 hours is 0.7% by weight or less. This solves this problem.

  In the present invention, the polyester (A) is composed of, for example, a polymer having an acid component such as aromatic dicarboxylic acid, alicyclic dicarboxylic acid or aliphatic dicarboxylic acid or a diol component as a structural unit (polymerization unit). Can be used.

  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, and 4,4′-diphenyldicarboxylic acid. Acid, 4,4′-diphenyl ether dicarboxylic acid, 4,4′-diphenylsulfone dicarboxylic acid, and the like can be used. Among them, terephthalic acid, phthalic acid, and 2,6-naphthalenedicarboxylic acid can be preferably used. . 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.

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

  Polyester (A) may be copolymerized with a monofunctional compound such as lauryl alcohol or phenyl isocyanate, trimellitic acid, pyromellitic acid, glycerol, pentaerythritol, 2,4-dioxybenzoic acid, etc. These trifunctional compounds 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, the present invention includes aromatic hydroxycarboxylic acids such as p-hydroxybenzoic acid, m-hydroxybenzoic acid, and 2,6-hydroxynaphthoic acid, p-aminophenol, and p-aminobenzoic acid. As long as the effect is not impaired, the copolymerization can be further carried out.

  Polyester (A) is preferably polyethylene terephthalate or polyethylene naphthalate (particularly polyethylene-2,6-naphthalate). Further, these copolymers and modified products may be used, and polymer alloys with other thermoplastic resins may be used. The polymer alloy here refers to a polymer multi-component system, which may be a block copolymer by copolymerization or a polymer blend by mixing. In this invention, it is preferable that at least 1 sort (s) of these polymers is included.

  In the present invention, the terminal COOH concentration of the polyester (A) is preferably 25 (eq / ton) or less, more preferably 20 (eq / ton) or less, and 17 (eq / ton) or less. More preferably, it is particularly preferably 12 (eq / ton) or less. By setting it as such a range, the hydrolysis resistance of polyester improves.

  In particular, the polymer alloy of the polyester resin and the polyimide resin is preferable because the heat resistance (glass transition temperature) can be controlled by the mixing ratio, and the polymer can be designed according to the use conditions. The mixing ratio of the polymer can be examined using a micro FT-IR method (Fourier transform micro infrared spectroscopy).

For example, in the case of polyester and polyimide, it is dissolved in a mixed solution of 70 parts by mass of hexafluoroisopropanol (HFIP) / 30 parts by mass of deuterated chloroform, and the NMR spectrum of ¹ H nucleus is measured. In the obtained spectrum, the peak area intensity of absorption specific to polyester and polyimide (for example, aromatic proton of terephthalic acid if polyester is polyethylene terephthalate, aromatic proton of bisphenol A if polyimide is polyetherimide) The molar ratio of the blend is calculated from the ratio and the number of protons. Further, the mass ratio is calculated from the formula amount corresponding to the unit unit of the polymer. In this way, the mixing ratio of the polyester component and the polyimide component can be specified.

In the present invention, the imidization ratio of polyimide is adjusted to 95% or higher, and the imidization ratio in the present invention is preferably 97% or higher, and more preferably 99% or higher. As the imidization rate improves, the effects of the present invention are more effectively exhibited.
As the polyimide, 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

などの脂肪族炭化水素基、脂環族炭化水素基、芳香族炭化水素基から選ばれた一種もしくは二種以上の基を表している。

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. The polyetherimide (B) is a resin containing an ether bond in a polyimide constituent component composed of an imide group, and is represented by the following general formula.

（ただし、上記式中Ｒ³は、６〜３０個の炭素原子を有する２価の芳香族または脂肪族残基、Ｒ⁴は６〜３０個の炭素原子を有する２価の芳香族残基、２〜２０個の炭素原子を有するアルキレン基、２〜２０個の炭素原子を有するシクロアルキレン基、および２〜８個の炭素原子を有するアルキレン基で連鎖停止されたポリジオルガノシロキサン基からなる群より選択された２価の有機基である。）
上記Ｒ³、Ｒ⁴としては、例えば、下記式群に示される芳香族残基を挙げることができる。

(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.)
Examples of R ³ and R ⁴ include aromatic residues represented by the following formula group.

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

（ｎは２以上の整数、好ましくは２０〜５０の整数）
このポリエーテルイミドは、"ウルテム"（登録商標）の商品名で、ＳＡＢＩＣイノベーティブプラスチック社より入手可能であり、「Ｕｌｔｅｍ１０００」、「Ｕｌｔｅｍ１０１０」、「Ｕｌｔｅｍ１０４０」、「Ｕｌｔｅｍ５０００」、「Ｕｌｔｅｍ６０００」および「ＵｌｔｅｍＸＨ６０５０」シリーズや「Ｅｘｔｅｍ ＸＨ」および「Ｅｘｔｅｍ ＵＨ」の登録商標名等で知られているものである。

(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), and is "Ultem 1000", "Ultem 1010", "Ultem 1040", "Ultem 5000", "Ultem 6000" and "Ultem XH6050". ”Series,“ Extreme XH ”, and“ Extreme UH ”registered trademark names.

  The film of the present invention contains polyester (A) and polyimide (B), and the total amount of polyester (A) and polyimide (B) is 70 to 99% by mass of polyester (A) and polyimide (B). It is preferable to contain 1-30 mass%. The more preferable content of the polyester (A) is 80 to 99% by mass, and the particularly preferable range is 85 to 99% by mass. Moreover, the more preferable content of a polyimide (B) is 1-20 mass%, and especially preferable content is 1-15 mass%. When the content of the polyimide (B) is 1% by mass or more, the glass transition temperature of the film is sufficiently increased, and a film excellent in heat resistance, moist heat resistance and dimensional stability can be obtained. Moreover, the film formability of a film improves by setting it as 30 mass% or less, and the average dispersion diameter of the polyimide (B) in polyester (A) is in the preferable range of this invention as described below. It becomes easy to control. Furthermore, in the film of the present invention, 99% of the resin is preferably made of the polyester (A) and the polyimide (B).

  In the biaxially oriented polyester film of the present invention, polyimide (B) forms a dispersed phase in polyester (A). The average dispersion diameter of the polyimide (B) in the polyester (A) is preferably in the range of 1 to 50 nm. When the average dispersion diameter of the polyimide (B) is less than the above range or larger than the above range, the glass transition temperature (Tg) of the polyester film of the present invention cannot be sufficiently increased, and the film has excellent heat resistance and moisture resistance. Thermal properties may not be imparted. The average dispersion diameter of the polyimide (B) is more preferably 40 nm or less. More preferably, it is 30 nm or less. Most preferably, it is 20 nm or less. The average dispersion diameter of the polyimide (B) is more preferably 3 nm or more. More preferably, it is 5 nm or more. Most preferably, it is 8 nm or more. The average dispersion diameter of the polyimide (B) is more preferably 3 to 40 nm. More preferably, it is 5-30 nm. Most preferably, it is 8-20 nm. When the average dispersion diameter of the polyimide (B) is within the above range, the film forming property may be more stable.

  Here, the average dispersion diameter is an average equivalent circle diameter obtained on a plurality of observation surfaces.

  The average dispersion diameter of the polyimide (B) in the polyester (A) is as follows. First, the cut surface of the film is observed using a transmission electron microscope under a condition of a pressurized voltage of 100 kV, and a photograph is taken at a magnification of 20,000 times. . Next, the obtained photograph is taken into an image analyzer as an image, 100 arbitrary dispersed phases are selected, image processing is performed as necessary, the dispersion diameter is obtained, and the average dispersion is obtained with the number average. The diameter.

  More specifically, the average dispersion diameter is determined as follows. Cut the film in (a) a direction parallel to the longitudinal direction and perpendicular to the film surface, (b) a direction parallel to the width direction and perpendicular to the film surface, and (c) a direction parallel to the film surface. Prepare by thin section method. In order to clarify the contrast of the dispersed phase, it may be stained with osmic acid or ruthenic acid. The cut surface is observed using a transmission electron microscope (Hitachi H-7100FA type) under a condition of a pressurization voltage of 100 kV, and a photograph is taken at a magnification of 20,000 times. The obtained photograph is taken into an image analyzer as an image, 100 arbitrary dispersed phases are selected, and image processing is performed as necessary, thereby obtaining the size of the dispersed phase as shown below. . The maximum thickness (la) and the maximum length (lb) in the film thickness direction of each dispersed phase appearing on the cut surface of (a), and the maximum thickness (lb) in the longitudinal direction of each disperse phase appearing on the cut surface of (a). The maximum length (lc), the maximum length (ld) in the width direction, the maximum length (le) in the film longitudinal direction and the maximum length (lf) in the width direction of each dispersed phase appearing on the cut surface of (c). Ask. Next, the shape index I of the dispersed phase I = (number average value of lb + number average value of le) / 2, shape index J = (number average value of ld + number average value of lf) / 2, shape index K = (of la Number average value + number average value of lc) / 2, and the average dispersion diameter of the dispersed phase is (I + J + K) / 3. Further, from I, J, and K, the maximum value is determined as the average major axis L, and the minimum value is determined as the average minor axis D.

  A method for performing image analysis will be described. Transmission electron micrographs of each sample were taken into a computer with a scanner. Thereafter, image analysis was performed with dedicated software (Image Pro Plus Ver. 4.0, manufactured by Planetron). By manipulating the tone curve, brightness and contrast are adjusted, and then 100 points of the equivalent circle diameter of the high contrast component of the image obtained using a Gaussian filter are randomly observed, and the average value is taken as the average dispersion diameter. did. Here, when using a negative photograph of a transmission electron microscope photograph, Leafscan 45 Plug-In manufactured by Nippon Cytex Co., Ltd. is used as the scanner, and when using a positive transmission electron microscope, the scanner is used as the scanner. GT-7600S manufactured by Seiko Epson is used, and any of them can obtain an equivalent value.

Image processing procedures and parameters:
Flattening once contrast +30
Gauss once contrast +30, brightness -10
Gaussian flattening filter: background (black), object width (20 pix)
Gaussian filter: size (7), strength (10)
Further, among the dispersed domains formed in the polyester, nitrogen atoms (N) are formed by energy dispersive X-ray spectroscopy using a field emission electron microscope (TEM-EDX method). The detected domain is defined as a polyimide (B) domain.

  The melt crystallization peak temperature of the biaxially oriented polyester film of the present invention is 200 to 240 ° C. Preferably, it is 205-240 degreeC, More preferably, it is 210-230 degreeC. When the melt crystallization peak temperature is less than 200 ° C., the high Young's modulus, which is the effect of the present application, and the temperature expansion coefficient and the humidity expansion coefficient may be drastically reduced, making it difficult to control the dimensional stability. Sometimes. In addition, when the melt crystallization peak temperature exceeds 240 ° C., crystallization may proceed in the melt extrusion process of the film, and the filtration pressure may increase and coarse foreign matter may be generated or the film may be broken. is there. For example, when used for a magnetic recording medium, electromagnetic conversion characteristics may be poor. The melt crystallization peak temperature is an index of ease of crystallization in sheeting cooled from the molten state of the polyester.

  In order to control the preferable melt crystallization peak temperature of the present invention, it is preferable to contain 0.2 to 1% by mass of a crystal nucleating agent. A more preferable content is 0.2 to 0.7% by mass, and a more preferable content is 0.3 to 0.5% by mass. If the content of the crystal nucleating agent is less than 0.1% by mass, it is not sufficient to control the melt crystallization peak. On the other hand, if it exceeds 1% by mass, crystallization proceeds excessively and the film stretchability is poor. And surface characteristics may be poor. Here, the crystal nucleating agent is an additive having an effect of promoting crystallization from a molten state by increasing the temperature of the melt crystallization peak of the resin composition used for the polyester film.

  Examples of the crystal nucleating agent include alkali metal salts and alkaline earth metal salts of montanic acid. In addition, 4-carboxylic acid metal salts such as 4-tert-butylbenzoic acid aluminum salt and sodium adipate, sodium bis (4-tert-butylphenyl) phosphate, sodium-2,2′-methylenebis (4,6-ditertiary Preferred examples include acidic phosphate metal salts such as butylphenyl) phosphate, polyhydric alcohol derivatives such as dibenzylsorbitol, bis (4-methylbenzylidene) sorbide, and the like. When applied to the polyester of the present invention, among them, an alkali metal salt or alkaline earth metal salt of montanic acid is preferable, and sodium montanate is particularly preferable in terms of achieving compatibility and the effects of the present invention.

  Polyesters that do not contain polyimide are susceptible to melt crystallization in the unstretched sheeting process due to the inclusion of the crystal nucleating agent, and orientation crystallization also occurs in the stretching process. There are cases where film breakage occurs, and it is difficult to increase the Young's modulus and improve the dimensional stability by stretching at a high magnification. In the biaxially oriented polyester film of the present invention, the crystal nucleating agent has the effect of effectively suppressing molecular crystallization and enhancing the molecular chain orientation in the stretching step. That is, in the polyester containing the polyimide of the present invention, the degree of crystallinity tends to be high in a low-magnification region from an unstretched sheet to a stretch ratio of about 2 times, but no polyimide is added in a higher-magnification stretch region. Compared to the case, orientation crystallization in stretching tends to be suppressed. Therefore, it is easy to increase the tension of the amorphous molecular chain while suppressing the progress of orientation crystallization, and it is possible to control the characteristics depending on the molecular chain tension such as the temperature expansion coefficient and the humidity expansion coefficient.

The polyester film of the present invention has a moisture content of 25 wt. C., a relative humidity of 60% and a moisture content after 24 hours of 0.7 wt% or less, preferably 0.59 wt% or less. By setting it as such a range, hydrolysis resistance can be improved more.
In the present invention, a known method can be adopted as a method for reducing the moisture content of the polyester film. For example, increasing the imidization rate, orienting molecular chains by performing biaxial stretching, copolymerizing a hydrophobic monomer during synthesis of polyimide, adding a hydrophobic low molecular weight agent, and the like. Among these, it is preferable from the viewpoint of cost to increase the imidization rate and / or to perform molecular biaxial orientation by biaxial stretching.

When the polyester film of the present invention is stored in an atmosphere at a temperature of 85 ° C. and a relative humidity of 85%, the storage time when the breaking elongation after storage is 50% of the breaking elongation before storage is 3500 hours. The above is preferable. By setting it as such a range, when it uses as a sheet | seat for solar cells, sufficient effect is exhibited.
The thickness of the polyester film of the present invention is preferably 50 to 300 μm after biaxial stretching.

  The polyester film of the present invention preferably has a visible light total light transmittance of 80% or more, more preferably 85% or more. In order to control the total light transmittance of visible light of the polyester film of the present invention to 80% or more, it is preferable that the amount of the additive added is less than 5% by mass.

  If the total light transmittance of the visible light is less than 80%, the rate of converting sunlight into electricity (hereinafter sometimes referred to as “conversion efficiency”) tends to decrease, which is not preferable. Visible light as used herein refers to electromagnetic waves felt by the human eye, and is a light beam having a wavelength of approximately 350 to 800 nm, and is the most important light beam for the conversion efficiency of the solar cell module. The “total light transmittance of visible light” in the present invention is a transmittance of light having a wavelength of 550 nm and is a value measured based on JIS K7105-1981.

  The polyester film according to the present invention may have a structure in which two or more of the same or different polymer layers are laminated. Moreover, it is preferable that an ultraviolet absorber, a hydrolysis inhibitor, or the like is applied, laminated, or added.

  In the present invention, it is important that the thermal shrinkage rate at 150 ° C. in the longitudinal direction and the width direction of the polyester film is within (0 ± 2)%, preferably (0 ± 1.7)%. Less, more preferably within (0 ± 1.5)%, and the difference in heat shrinkage value at 150 ° C. between the longitudinal direction and the width direction is 2% or less, preferably 1.5% or less. It is important to use.

  Here, “difference (%) in heat shrinkage value at 150 ° C. in the longitudinal direction and width direction” means a difference in heat shrinkage rate value (%) at 150 ° C. in the longitudinal direction and width direction, It is a value indicated by its absolute value.

  That is, the polyester film of the present invention, which is the object of the present invention, is used for a long time by reducing the heat shrinkage of the polyester film as much as possible and using the one that balances the heat shrinkage rate in the longitudinal direction and the width direction as much as possible. It is possible to suppress the deterioration of the gas barrier property of the solar cell module and to improve the output decrease over time of the solar cell module.

  Here, the thermal shrinkage rate is a value obtained by performing a shrinkage treatment at 150 ° C. for 30 minutes measured based on JIS C2151-1990, and represents the shrinkage direction as a plus and the expansion direction as a minus. .

If either the longitudinal or width direction thermal shrinkage value is out of the range of (0 ± 2)%, the gas barrier performance is greatly degraded, and the output of the solar cell module over time is outside the allowable range. It becomes difficult to obtain the effect of the present invention as desired. If any one of the thermal shrinkage values at 150 ° C. in the longitudinal direction and the width direction of the polyester film is within (0 ± 2)%, a coating layer such as a gas barrier layer, a solar cell The polyester film between the filling adhesive resin layers filling and fixing the element repeatedly undergoes large dimensional changes such as shrinkage and expansion due to temperature changes in the installation environment, and the hard metal such as the above-mentioned metal that gave gas barrier performance to the entire sealing film A large stress is repeatedly applied to the coating layer. As a result, it is considered that cracks, peeling, and the like occur in the coating layer such as the gas barrier layer and the barrier property of water vapor is lowered.
Furthermore, even when a polyester film having a difference in heat shrinkage value between the longitudinal direction and the width direction exceeding 2% is used, the same problem occurs, and the desired effect of the present invention cannot be obtained. . Therefore, satisfying these two requirements simultaneously is an important requirement in the present invention.
The above-mentioned gas barrier performance possessed by the polyester film of the present invention is realized by a coating layer such as a gas barrier layer.

Polyester film of the present invention, preferably, by application of the gas barrier layer, the numerical entire polyester film of the main invention, gas barrier properties having the following moisture vapor transmission rate 2.0g / m ² /24hr/0.1mm Can be realized. That is, if the gas barrier layer is removed from the polyester film of the present invention, the water vapor permeability value is several to several tens times larger than the above value, and cannot function as a sealing film. . Incidentally, according to various findings of the present inventors, in the general polyester film provided with no coating layer, such as metal, usually, water vapor transmission rate 7.2g / m ² /24hr/0.1mm about It is.

And the value of the water vapor transmission rate of the polyester film of the present invention described above is shown by the initial performance before the forced aging treatment, so this performance is further improved by the polyester film of the present invention. Even after being subjected to a specific aging treatment to be described later, it is maintained at a high water vapor transmission rate value.
The mechanism is brought about by using a specific polyester film as described above.

Specific performance polyester film of the present invention, preferably, after being subjected to the aging process to be described later, after the excellent aging of showing water vapor permeability 5.0 g / m ² less than /24hr/0.1mm It has gas barrier performance.

  The gas barrier performance in the polyester film of the present invention is a performance corresponding to the oxygen permeation performance and the water vapor permeation performance, but the most important among them is the water vapor barrier performance. It is optimal to evaluate the polyester film. The water vapor transmission rate described above is an initial value (value before aging) of the water vapor transmission rate measured based on JIS Z0208-11973, and a value obtained by performing the same measurement after the aging treatment. However, it is optimal because it can know both the initial performance level and the level of change in performance over time.

The biaxially oriented polyester film of the present invention as described above is produced, for example, as follows.
In the present invention, polyimide is imidized before mixing polyester and polyimide. As the imidization method, a method of imidizing by heating polyimide at 180 ° C. to 240 ° C. for 10 hours or more is preferably employed. Usually, polyimide is heated in a pellet state to imidize. The temperature for imidization is preferably 190 ° C to 240 ° C, and more preferably 195 to 220 ° C. The heating time is preferably 15 hours or more, more preferably 20 hours or more, further preferably 30 hours or more, and particularly preferably 45 hours or more. The upper limit is not particularly defined, but is usually 100 hours or less, more preferably 70 hours or less.
Polyimidation is preferably carried out in a vacuum or under a nitrogen stream.

In the present invention, usually, polyimide may be imidized and then mixed with polyester, or may be mixed with polyester and then polyimideized.
In the present invention, for example, as a method of mixing polyester and polyimide, before melt extrusion, a mixture of polyester and polyimide is pre-melted and kneaded (pelletized) into a master chip, or mixed and melted during melt extrusion. There is a method of kneading. Of these, a method of pre-kneading into a master chip using a high-shear mixer with high shear stress such as a twin screw extruder is preferably exemplified. In that case, the mixed master chip raw material may be put into an ordinary single-screw extruder to form a melt film, or may be directly sheeted without forming a master chip in a state where high shear is applied. When mixing with a twin screw extruder, from the viewpoint of reducing poor dispersion, a screw equipped with a triple twin screw type or a double twin screw type is preferable. Moreover, when mixing polyester and a polyimide, since there exists a difference in melt viscosity, it is preferable to produce the master chip which mixed the polyimide resin in high concentration.

In the kneading part, the temperature range of the melting point of the polyester resin +10 to 65 ° C. is preferable. A more preferable temperature range is the melting point of the polyester resin +15 to 55 ° C., and a more preferable temperature range is the melting point of the polyester resin +20 to 45 ° C. Setting the temperature range of the kneading part to a preferable range facilitates increasing the shear stress and contributes to the reduction of defective dispersion. The residence time at that time is preferably in the range of 1 to 5 minutes. Moreover, it is preferable that screw rotation speed shall be 100-500 rotation / min, More preferably, it is the range of 200-400 rotation / min. Even when the screw rotation speed is set within a preferable range, high shear stress is easily applied, and defective dispersion is easily reduced. Further, the ratio of (screw shaft length / screw shaft diameter) of the twin screw extruder is preferably in the range of 20 to 60, more preferably in the range of 30 to 50.
Further, in the twin screw, in order to increase the kneading force, it is preferable to provide a kneading part by a kneading paddle or the like, and the kneading part is preferably formed in a screw shape having two or more, more preferably three or more. At this time, the mixing order of the raw materials is not particularly limited, and a method in which all raw materials are blended and then melt-kneaded by the above method, a part of the raw materials are blended and then melt-kneaded by the above method, and the remaining raw materials are blended. Any method such as a method of melt kneading or a method of mixing a part of raw materials and mixing the remaining raw materials using a side feeder during melt kneading by a single-screw or biaxial extruder may be used. Further, a method using a supercritical fluid described in Journal of Plastics Processing Society of Japan, “Molding”, Vol. 15, No. 6, pp. 382 to 385 (2003) can be preferably exemplified.

  When forming into a film, the mixed master chip raw material may be put into a normal single-screw extruder to form a melt, or may be directly sheeted without being converted into a master chip in a state where high shear is applied. Good.

  In order to produce a biaxially oriented polyester film, for example, polyester pellets are melted using an extruder, discharged from a die, cooled and solidified, and formed into a sheet. At this time, it is preferable to filter the polymer with a fiber-sintered stainless metal filter in order to remove unmelted material in the polymer.

  The polyester film of the present invention preferably contains a light stabilizer. By containing the light stabilizer, it is possible to prevent ultraviolet degradation. Examples of the light stabilizer include a compound that absorbs light such as ultraviolet rays and converts it into thermal energy, a material that absorbs light and decomposes when the film or the like absorbs light, and a material that suppresses the decomposition chain reaction. .

  The light stabilizer is preferably a compound that absorbs light such as ultraviolet rays and converts it into heat energy. By including such a light stabilizer in the film, it becomes possible to keep the effect of improving the partial discharge voltage by the film high for a long time even if the film is irradiated with ultraviolet rays continuously for a long time. Changes in color tone, strength deterioration, and the like due to UV rays. For example, if an ultraviolet absorber is a range in which other properties of the polyester are not impaired, any of organic ultraviolet absorbers, inorganic ultraviolet absorbers, and combinations thereof are preferably used without particular limitation. Can do. On the other hand, it is desired that the ultraviolet absorber is excellent in moisture and heat resistance and can be uniformly dispersed in the film.

Examples of the ultraviolet absorber include salicylic acid-based, benzophenone-based, benzotriazole-based, cyanoacrylate-based ultraviolet absorbers, hindered amine-based ultraviolet stabilizers, and the like as organic ultraviolet absorbers. Specifically, for example, salicylic acid-based p-tert-butylphenyl salicylate, p-octylphenyl salicylate, benzophenone-based 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy -5-sulfobenzophenone, 2,2 ', 4,4'-tetrahydroxybenzophenone, bis (2-methoxy-4-hydroxy-5-benzoylphenyl) methane, benzotriazole 2- (2'-hydroxy-5) '-Methylphenyl) benzotriazole, 2- (2'-hydroxy-5'-methylphenyl) benzotriazole, 2,2'-methylenebis [4- (1,1,3,3-tetramethylbutyl) -6 (2H benzotriazol-2-yl) phenol], cyanoacrylate Ethyl-2-cyano-3,3′-diphenyl acrylate) and 2- (4,6-diphenyl-1,3,5-triazin-2-yl) -5-[(hexyl) oxy as triazine ] -Phenol, hindered amine bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, dimethyl succinate 1- (2-hydroxyethyl) -4-hydroxy-2,2,6,6 -Tetramethylpiperidine polycondensate, in addition, nickel bis (octylphenyl) sulfide, 2,4-di-tert-butylphenyl-3 ', 5'-di-tert-butyl-4'-hydroxybenzoate, etc. Is mentioned.
Of these ultraviolet absorbers, triazine-based ultraviolet absorbers are more preferable in that they have high resistance to repeated ultraviolet absorption. In addition, these ultraviolet absorbers may be added to the above-mentioned ultraviolet absorber alone, or a form in which an organic conductive material or a water-insoluble resin is copolymerized with a monomer having an ultraviolet absorber ability. May be introduced.

  The content of the light stabilizer in the polyester film is preferably 0.1% by mass or more and 10% by mass or less, and more preferably 0.3% by mass or more and 7% by mass or less with respect to the total mass of the polyester film. More preferably, it is 0.7 mass% or more and 4 mass% or less. Thereby, the molecular weight fall of the polyester by the photodegradation over a long time can be suppressed, and the adhesive force fall resulting from the cohesive failure in the film which arises as a result can be suppressed.

  In addition to the light stabilizer, the polyester film of the present invention includes, for example, a lubricant (fine particles), an ultraviolet absorber, a colorant, a heat stabilizer, a nucleating agent (crystallization agent), and a flame retardant. Etc. can be contained as additives.

  Subsequently, the sheet is stretched biaxially in the longitudinal direction and the width direction and heat-treated. The stretching process is preferably divided into two or more stages in each direction. That is, the method of performing re-longitudinal and re-lateral stretching is preferable because a high-strength film optimum for a magnetic tape for high-density recording can be easily obtained.

  As the stretching method, a sequential biaxial stretching method such as stretching in the width direction after stretching in the longitudinal direction, a simultaneous biaxial stretching method in which the longitudinal direction and the width direction are simultaneously stretched using a simultaneous biaxial tenter, etc. Further, a method of combining a sequential biaxial stretching method and a simultaneous biaxial stretching method is included.

  In the present invention, it is particularly preferable to use the simultaneous biaxial stretching method. In the present invention, in an unstretched film composed of a polyester-polyimide composition containing a crystal nucleating agent, crystallization is enhanced as compared with a normal polyester film. Therefore, in sequential biaxial stretching, in the first longitudinal direction or transverse direction stretching. Crystallization is likely to proceed, and stretching in the subsequent stretching step, and as a result, it may be difficult to achieve high magnification and high orientation as a total stretching ratio. Simultaneous biaxial stretching is preferred because it facilitates orientation crystallization and molecular orientation at once in the longitudinal and width directions. Furthermore, compared with the sequential biaxial stretching method, in the simultaneous biaxial stretching method, crystals are uniformly grown in the longitudinal direction and the width direction in the film forming process, and therefore, it is easy to stably stretch at a high magnification. Here, the simultaneous biaxial stretching is a stretching method including a step in which stretching in the longitudinal direction and the width direction is performed simultaneously. The longitudinal direction and the width direction do not necessarily have to be stretched at the same time in all sections, the longitudinal stretching starts first, and the stretching is performed in the width direction from the middle (simultaneous stretching). A method may be adopted in which the process is terminated first and the rest is stretched only in the width direction. As the stretching apparatus, for example, a simultaneous biaxial stretching tenter is preferably exemplified, and among them, a linear motor driven simultaneous biaxial tenter is particularly preferable as a method of stretching a film without breaking.

  The heat treatment after the stretching process may be carried out in one stage, but it is effective to control the temperature expansion coefficient and humidity expansion coefficient within the scope of the present invention without causing relaxation of molecular chain orientation by excessive heat treatment. Therefore, it is preferable to carry out the heat treatment in multiple stages by controlling the heat treatment temperature. Multi-stage means that the heat treatment temperature is changed and the process is carried out in two or more stages.

  The heat treatment temperature can be determined based on the melting point of the polyester. The heat treatment temperature is preferably [melting point of polyester (A) (Tm) -100] to (Tm-50) ° C., and the heat treatment time is preferably in the range of 0.5 to 10 seconds. In particular, the heat treatment temperature for the first stage is preferably set to (Tm-75) to (Tm-50) ° C., more preferably (Tm-75) to (Tm-60) ° C. May be set to a lower temperature than the first stage. Preferably it is set to (Tm-100)-(Tm-75) degreeC, More preferably, it is set to (Tm-100)-(Tm-85) degreeC. Further, it is more preferable to perform a relaxation treatment at a relaxation rate of 1 to 5% in the width direction in the first-stage and / or second-stage heat treatment step.

  And the polyester film manufactured in this way is wound up by a roll. Furthermore, in order to improve the dimensional stability and storage stability which are the effects of the present invention, it is also preferable to heat-treat the wound film together with the rolls under a certain temperature condition. “Constant temperature condition” means that the film is placed together with a roll in a hot air oven or zone set to a certain temperature condition. By heat-treating the film while being in a roll, distortion of the internal structure of the film is easily removed, and dimensional stability such as creep characteristics is easily improved. For example, when the film is wound and stored, when it is used for a magnetic recording medium such as a magnetic tape, the film is stored in a wound state, or when the tape is run and used, the length of the film Although tension is applied in the direction and creep deformation may occur in the longitudinal direction, storage stability is likely to be significantly improved if dimensional stability such as creep characteristics is improved.

In the present invention, the polyester film and the polyester film are optionally subjected to any processing such as heat treatment, microwave heating, molding, surface treatment, lamination, coating, printing, embossing, etching, etc. Also good.
In addition, the description of paragraph number 0075-0088 of Unexamined-Japanese-Patent No. 2009-212278 is employable for the detail of the manufacturing method of the polyester film of this invention.

  The polyester film of the present invention can be preferably used as a sealing film for solar cell modules. The solar cell module in the present invention refers to a system for converting sunlight into electricity, and an example of the module structure is shown in FIG. That is, FIG. 1 is a schematic cross-sectional view showing an example of the basic configuration of the solar cell module of the present invention, wherein 1 is present on the sunlight incident side (surface) and is made of the polyester film of the present invention. A front sheet layer, 2 is a filling adhesive resin layer, 3 is a solar cell element, 4 is a back sheet layer which is present on the non-incident side (back surface) of sunlight and is made of the polyester film of the present invention. Thus, the front sheet layer 1, the filling adhesive resin layer 2 (front side), the solar cell element 3, the filling adhesive resin layer 2 (back side), and the back sheet layer 4 are the basic configuration from the side on which sunlight is incident. A solar cell module is used by being incorporated in a roof of a house, or installed in a building or a fence or used for an electronic component. In addition, the solar cell module transmits light called a daylighting type or a see-through type, and is also used for soundproof walls such as windows, highways, and railways. A flexible type has also been put into practical use.

Here, the front sheet layer 1 is a layer provided for the purpose of allowing sunlight to enter efficiently and protecting the solar cell element inside. The filling adhesive resin layer is a layer for the purpose of adhesion and filling for storing and sealing the solar cell element between the front sheet and the back sheet, weather resistance, water resistance (hydrolysis resistance), transparency, Adhesiveness is required. Preferable examples include ethylene vinyl acetate copolymer resin (hereinafter sometimes abbreviated as EVA), polyvinyl butyral, ethylene vinyl acetate partial oxide, silicon resin, ester resin, olefin resin, and the like. EVA is the most common. Further, the back sheet layer is used for the purpose of protecting the solar cell element on the back side of the solar cell module, has a water vapor blocking property and an insulating property, and further requires good mechanical properties and the like. . In addition, the white type that reflects sunlight that is incident from the front seat side and reuses the sunlight, and is colored such as black in consideration of design, etc., and transparent that allows sunlight to enter from the back seat side. Although there are types, the present invention can be used for all of them. Here, in the transparent type, the total light transmittance is preferably 80% or more, more preferably 85% or more, so that the amount of incident sunlight can be increased, and the daylighting type or see-through type solar cell is obtained. It is preferable in adopting.
The gas barrier layer to be applied to the sealing film is preferably provided on at least one side of the previously produced polyester film according to the present invention. The gas barrier layer may be composed of only an inorganic layer, but it is preferable to provide an organic / inorganic laminated gas barrier layer in which organic layers and inorganic layers are alternately laminated. For the organic-inorganic laminated gas barrier layer, for example, the description in JP-A-2009-076436, particularly the descriptions in paragraph numbers 0015 to 0040 can be referred to.

  Moreover, as another embodiment of the sealing film concerning this invention, a fluorine-type film is laminated | stacked as a weather resistant film, for example on the at least single side | surface (at least sunlight incident surface) of the sealing film manufactured above. As the lamination method, a method similar to the method of providing a gas barrier layer on the above-mentioned another film and laminating it on the polyester film according to the present invention can be used. That is, a weather-resistant film can be laminated on at least one surface of the polyester film according to the present invention via an adhesive. In this case, the adhesive preferably contains an ultraviolet absorber and is highly transparent. As the adhesive, urethane, acrylic, epoxy, ester, fluorine and the like can be used. The thickness of the adhesive layer is preferably in the range of 1 to 30 μm from the viewpoint of adhesive strength and transparency. It is rather preferable that the fluorine-based film is subjected to an easy adhesion treatment.

  Next, the manufacturing method of the solar cell module concerning this invention is demonstrated. For example, the system is configured with the configuration shown in FIG. For example, a transparent plate glass is prepared for the front sheet layer 1, and the sealing film obtained above is prepared for the back sheet layer 4. The front sheet layer 1 and the sealing film (preferably, a coating layer (gas barrier layer) such as metal) are provided on both sides of the solar cell element 3 through an adhesive resin layer 2 (for example, EVA having a thickness of 100 to 1000 μm). On the adhesive side).

  In the present invention, for the purpose of weight reduction, a sealing film can be used for the front layer in the above-described configuration.

  Here, various known methods can be used as the laminating method, but vacuum laminating is preferable because defects such as wrinkles and bubbles are hardly generated and can be laminated uniformly. The laminating temperature is usually in the range of 100 to 180 ° C.

  Furthermore, a solar cell module can be manufactured by providing a lead wire that can take out electricity and fixing it with an exterior material.

  The present invention will be described more specifically with reference to the following examples. The materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below.

  194 parts by mass of dimethyl terephthalate and 124 parts by mass of ethylene glycol were charged into a transesterification reactor, and the contents were heated to 140 ° C. and dissolved. Thereafter, 0.3 parts by mass of magnesium acetate tetrahydrate and 0.05 parts by mass of antimony trioxide were added while stirring the contents, and a transesterification reaction was performed while distilling methanol at 140 to 230 ° C. Next, 1 part by mass of a 5% by mass ethylene glycol solution of trimethyl phosphate (0.05 parts by mass as trimethyl phosphate) was added.

  Addition of trimethyl phosphoric acid in ethylene glycol reduces the temperature of the reaction contents. Therefore, stirring was continued until the temperature of the reaction contents returned to 230 ° C. while distilling excess ethylene glycol. In this way, after the temperature of the reaction contents in the transesterification reactor reached 230 ° C., the reaction contents were transferred to the polymerization apparatus.

  After the transition, 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 the final temperature and final pressure was both 60 minutes. After reaching the final temperature and the final pressure, the reaction was carried out for 2 hours (3 hours after the start of polymerization), and the agitation torque of the polymerization apparatus was a predetermined value (specific values differ depending on the specifications of the polymerization apparatus. The value indicated by polyethylene terephthalate having an intrinsic viscosity of 0.62 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 polyethylene terephthalate PET pellets (X) having an intrinsic viscosity of 0.62.

  The pellets of polyetherimide “Ultem1010” manufactured by SABIC Innovative Plastics were subjected to heat treatment under vacuum for the times shown in the following table.

  Bent-type twin-screw kneading extruder of the same direction rotation type provided with three kneading paddle kneading parts heated to 290 ° C (manufactured by Nippon Steel, screw diameter 30 mm, screw length / screw diameter = 45.5) Then, the obtained PET pellets (X) and the polyetherimide pellets subjected to the above heat treatment are supplied at the blending ratio shown in Table 1, and melt-extruded at a screw rotation speed of 300 rotations / minute and discharged into a strand shape. After cooling with water at a temperature of 25 ° C., it was immediately cut to produce a blend chip (I).

  Using an extruder heated to 295 ° C., the blend chip (I) was dried at 180 ° C. under reduced pressure for 3 hours and then supplied. In addition, the glass transition temperature (Tg) of the unstretched film was 90 degreeC.

  This unstretched film was biaxially stretched using a simultaneous biaxial tenter having a linear motor clip. Simultaneously in the longitudinal direction and the width direction, the film was stretched 3.1 times by 3.1 times at a temperature of 105 ° C. and a stretching speed of 6,000% / min, and cooled to 70 ° C. Subsequently, the film was redrawn at a temperature of 180 ° C. in the longitudinal direction and the width direction simultaneously by 1.4 × 1.7 times. Thereafter, after heat treatment at 200 ° C. for 5 seconds, a relaxation treatment of 2% in the width direction was performed at 160 ° C. to produce a biaxially oriented polyester film having a thickness of 5 μm. The biaxially stretched film had a glass transition temperature (Tg) of 115 ° C. and a melting point (Tm) of 255 ° C.

  A film was formed in the same manner as in Example 5 except that the polyimide was changed from Ultem 1010 to Mitsui Chemicals' thermoplastic polyimide, Aurum PL450C (Example 13).

  About the obtained film, the imidation ratio, polyester terminal COOH concentration, water content, half life of elongation at break, and storage stability were measured, respectively.

(Measurement method of polyimide ratio in film)
The imidization rate was measured by proton NMR as follows. 20 mg of a sample was put in an NMR sample tube, and 0.53 ml of deuterated dimethyl sulfoxide (DMSO-d ₆ , 0.05% TMS mixture) was added and completely dissolved. This solution was measured for proton NMR at 500 MHz with a JEOL NMR measuring instrument (ECA500). The imidation rate determines the protons that come to the structure that does not change before and after imidation, the peak integrated value of this proton, and the proton peak integrated value derived from the NH group of the amic acid that appears near 9.5-10.0 ppm And obtained from the ratio.
The unit is shown in mol%.

(Method of measuring polyester terminal COOH concentration in film)
The polyester terminal COOH concentration was measured by proton NMR in consideration of the method of JP-A-2001-201471.
The unit is shown in eq / ton.

(Method for measuring moisture content of film)
The moisture content of the film was measured by holding a film cut to a size of 7 mm × 35 mm for 24 hours or more in an atmosphere of a temperature of 25 ° C. and a humidity of 60% RH. Measurement was performed by a Karl Fischer method using a sample drying apparatus (CA-03, VA-05, both Mitsubishi Chemical Corporation), and the water content (g) was divided by the sample mass (g).
The unit is expressed in wt%.

(Measurement method of half life of elongation at break of film)
The breaking elongation retention half-life is obtained by subjecting the obtained polyester film to a storage treatment (heating treatment) under conditions of 85 ° C. and a relative humidity of 85%, and the elongation at break [%] exhibited by the polyester film after storage. However, it evaluated by measuring the storage time (breaking elongation retention time) which becomes 50% with respect to breaking elongation [%] which the polyester film before storage shows.
The elongation at break (%) was obtained by cutting a sample piece having a size of 1 cm × 20 cm from the polyester film and pulling the sample piece at a rate of 5 cm between chucks and 20% / min.
It shows that it is excellent in the hydrolysis resistance of a polyester resin composition and the polyester film obtained using this, so that a break elongation retention half-life is long.
The unit is shown in hours.

(Dimensional stability)
The width dimension (l _C , l _D ) was measured under the following two conditions, and the dimensional change rate was calculated by the following formula. The dimensional stability was evaluated according to the following criteria. After 24 hours at 23 ° C. and 65% RH, 1 _C is measured. After storing the cartridge for 10 days in an environment of 40 ° C. and 20% RH, 1 _D is measured after 24 hours at 23 ° C. and 65% RH. Three points were measured: a sample cut from a 30 m point from the longitudinal end of the film, a sample cut from a 100 m point, and a sample cut from a 170 m point. X is rejected.

Width change rate (ppm) = 10 ⁶ × (| l _C −l _D | / l _C )
○: The maximum value of the width dimension change rate is less than 100 (ppm) Δ: The maximum value of the width dimension change rate is 100 (ppm) or more and less than 150 (ppm) ×: The maximum value of the width dimension change rate is 150 (ppm) or more

  These results are shown in the table below.

  As is apparent from the above results, a polyester film containing polyester and polyimide, which has an imidization rate of 95% or more, is a polyester film having a long half-life of elongation at break in addition to excellent dimensional stability. It turns out that it is obtained. In particular, the half life of the elongation at break is 2500 hours when the imidization rate is 94% (Comparative Example 2), whereas when the imidization rate becomes 95% (Example 1), 3500 hours, 1000 hours longer. This is extremely useful when used for an element used outdoors for a long time such as a solar cell. Further, it was found that even when the imidization ratio was 95% or more, when the compounding ratio of polyimide and polyester was outside the scope of the present invention (Comparative Example 4), the half life of elongation at break was inferior at 2500 hours. Furthermore, as apparent from the results of Example 13, it was confirmed that the effects of the present invention were exhibited regardless of the type of polyimide.

Manufacture of Solar Cell Module One side of the polyester film obtained above was subjected to a corona discharge treatment of 6000 J / m ² . On the other hand, 12 μm thick PET-BO (“Lumirror” P11 manufactured by Toray Industries, Inc.) was prepared, and aluminum oxide was formed on one side of the film to a thickness of 600 Å by sputtering.

A two-component urethane adhesive (“ADCOAT” 76P1: manufactured by Toyo Morton Co., Ltd.) was applied to the sputtering surface of this sputtering film and laminated on the corona-treated surface of PET-BO-1. Here, the adhesive was mixed at a ratio of 1 part by mass of the curing agent with respect to 100 parts by mass of the main agent, and adjusted to a 20% by mass solution with ethyl acetate. The coating method used was a gravure roll method, and the coating thickness was adjusted to 3 μm. The drying temperature was 100 ° C. Lamination was performed by a heated press roll method, and the temperature was 60 ° C. and the pressure was 1 kg / cm (linear pressure). Further, the adhesive was cured at 60 ° C. for 3 days. The obtained sealing film had a total light transmittance of 88%. Further, water vapor permeability (non-aged product) was 0.3g / m ² /24hr/0.1mm.
A solar cell module was manufactured using the film. As the front sheet layer, a flat glass generally called white plate glass (made by Asahi Glass: float plate glass) having a thickness of 4 mm was prepared. Electrical lead of 400 μm thick EVA sheet / solar cell element (PIN type solar element bonded by a bonding film) / 400 μm thick EVA sheet / glass plate on the above-mentioned coating layer (gas barrier performance imparting layer) side The wire was taken and thermocompression bonded by a vacuum laminating method. The laminating temperature was 135 ° C.
About the obtained sealing film for solar cell modules and the solar cell module using this sealing film, gas barrier performance (after aging), hydrolysis resistance, and weather resistance were evaluated according to the following methods.

(Water vapor permeability after aging)
Four sides of a 30 cm square sealing film were fixed so as to be sandwiched on both sides by a metal plate having a thickness of 2 mm, and a constant tension was applied to the four sides by applying a weight of 1 kg. In this state, it was aged in an atmosphere of 85 ° C. × 93% RH for 2000 hours. The water vapor transmission rate before and after this aging was measured based on JIS Z0208-1973. The measurement conditions were a temperature of 40 ° C. and a humidity of 90% RH.

The initial water vapor permeability, aluminum hydroxide gas barrier layer, by forming by sputtering so that the thickness of 600 angstroms, when controlled below 0.5g / m ² /24hr/0.1mm, The transmittance after the aging treatment was measured and evaluated. For each example / comparative example, the number of samples was set to 3, and the average value was the water vapor permeability after aging of each example / comparative example.

The evaluation criteria were divided into the following three levels, and in the table, “Excellent” was indicated by “◯”, “Normal” was indicated by “△”, and “Inferior” was indicated by “X”.
- better and (○ mark): water vapor transmission rate of less than 5g / m ² /24hr/0.1mm.
· Normal (△ mark): water vapor transmission rate of 5g / m ^{2 /24hr/0.1mm} above, 6.25 / m less than ^{2 /24hr/0.1mm.}
- poor (× mark): water vapor transmission rate of 6.25g / m ² /24hr/0.1mm more.

(Hydrolysis resistance)
An incision of 10 mm width (150 mm length) was cut in advance in a sealing film having a size of 80 mm × 200 mm so that the tensile strength could be measured. This sealing film was put in a constant temperature and humidity chamber and aged for 2000 hours in an atmosphere of 85 ° C. × 93% RH. The breaking strength before and after the aging was measured based on JIS C2151.
A comparative evaluation was performed using a ratio (retention ratio) when the breaking strength without aging was 100%.
The evaluation criteria were divided into the following three levels, and in the table, “Excellent” was indicated by “◯”, “Normal” was indicated by “△”, and “Inferior” was indicated by “X”.
-Excellent (circle): Retention rate is 30% or more.
-Normal (△ mark): Retention rate is 24% or more and less than 30%.
-Inferior (x mark): Retention rate is less than 24%.

(Weatherability)
Using an accelerated tester iSuper UW tester, the following cycle was repeated 5 times, and the retention rate was determined by the above-described tensile test method for comparative evaluation. 1 cycle: UV irradiation was performed for 8 hours in an atmosphere at a temperature of 60 ° C. and a humidity of 50% RH, and then aged in a dew condensation state (temperature of 35 ° C., humidity of 100% RH) for 4 hours. The evaluation criteria were divided into the following three levels, and in the table, “Excellent” was indicated by “◯”, “Normal” was indicated by “△”, and “Inferior” was indicated by “X”.
-Excellent (circle): Retention rate is 30% or more.
-Normal (△ mark): Retention rate is 24% or more and less than 30%.
-Inferior (x mark): Retention rate is less than 24%.

(Solar cell module output evaluation)
Based on JIS C8917-1998, the environmental test of the solar cell module was performed, the output of the photovoltaic power before and after the test was measured, and the following output reduction rate (%) was shown.
-(Photovoltaic value before test-Photovoltaic value after test) / Photovoltaic value before test x 100 (%)
Evaluation was made into a two-step evaluation of “pass” and “fail”, and an output reduction value of 10% or less was determined as “pass”.

  As is clear from the above results, the sealing film using a polyester film containing polyester and polyimide and having an imidization rate of 95% or more has gas barrier properties (water vapor permeability), hydrolysis resistance, and weather resistance. It was found that it is suitable for use as a solar cell sheet. Moreover, all the output evaluation of the solar cell module using the sealing film of this invention was a pass.

1: Front sheet layer 2: Filling adhesive resin layer 3: Solar cell element 4: Back sheet layer

Claims (15)

It is a biaxially oriented polyester film containing 70 to 99 parts by mass of polyester (A) and 1 to 30 parts by mass of polyimide (B), and the imidation ratio of the polyimide (B) is 95% or more, and the polyester film A polyester film having a water content of 0.7% by weight or less after 25 hours at 25 ° C. and a relative humidity of 60%. The polyester film according to claim 1, wherein the imidization ratio is 97% or more. The polyester film according to claim 1, wherein the imidization ratio is 99% or more. The polyester film according to any one of claims 1 to 3, wherein the polyimide (B) is a polyetherimide. The polyester film according to any one of claims 1 to 4, wherein 70 to 99% by weight of the resin constituting the polyester film is polyester (A) and 1 to 30% by weight is polyimide (B). The polyester film according to any one of claims 1 to 4, wherein 80 to 99% by weight of the resin constituting the polyester film is polyester (A) and 1 to 20% by weight is polyimide (B). The polyester (A) includes at least one polymer selected from the group consisting of polyethylene terephthalate, polyethylene naphthalate, and modified products thereof, and copolymers thereof. The polyester film according to item 1. The polyester film according to any one of claims 1 to 7, wherein a terminal COOH concentration of the polyester (A) is 25 (eq / ton) or less. The polyester film according to any one of claims 1 to 8, wherein the polyester film has a water content of 0.59% by weight or less at 25 ° C, a relative humidity of 60%, and 24 hours later. The polyester film according to any one of claims 1 to 9, wherein the polyimide (B) pellets are heated to 180 ° C to 240 ° C for 10 hours or longer to form an imidized film. When stored in an atmosphere at a temperature of 85 ° C. and a relative humidity of 85%, the storage time at which the breaking elongation after storage is 50% of the breaking elongation before storage is 3500 hours or more. The polyester film according to any one of claims 1 to 10. The polyester film of any one of Claims 1-11 which is a polyester film for solar cells. The sealing film which has a gas barrier layer on the surface of the polyester film of any one of Claims 1-12. The solar cell module provided with the polyester film of any one of Claims 1-12, or the sealing film of Claim 13. In the method for producing a biaxially oriented polyester film containing 70 to 99 parts by mass of polyester (A) and 1 to 30 parts by mass of polyimide (B), the polyimide (B) is added at 180 to 240 ° C., 10 ° C. A method for producing a polyester film comprising heat-treating for 50 hours.

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