JP2012056158A - Polyester film and solar cell using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film excellent in wet heat resistance and thermal dimensional stability, a solar cell back sheet, and a solar cell.SOLUTION: A method for producing the polyester film which is produced by the following processes (1)-(3). In a biaxially stretching process (1), a film is biaxially stretched at least 13.5 times in area magnification in the longitudinal direction (MD) and the width direction (TD) of the film at a temperature T1n satisfying formula (a): Tg≤T1n≤Tg+40°C (Tg: the glass transition temperature of the film (°C)). In the first heat treatment process (2), both ends in the width direction of the film are gripped while the dislocation in the gravity direction of the central part of the film is ≥1 and ≤50 mm to a straight line connecting both ends in the width direction of the film, and heat treatment is executed at a heat treatment temperature Th1 satisfying formula (b): Tm-90°C≤Th1≤Tm-45°C [Tm: the melting point of the film (°C)]. In the second heat treatment process (3), MD and TD are contracted 1-10% under the condition of a heat treatment temperature Th2 satisfying formula (c): 150°C≤Th2≤Th1.

Description

  The present invention relates to a polyester film having good heat and humidity resistance and thermal dimensional stability.

  Polyester (especially polyethylene terephthalate, polyethylene-2, 6-naphthalenedicarboxylate, etc.) resins are excellent in mechanical properties, thermal properties, chemical resistance, electrical properties, and moldability, and are used in various applications. Polyester film made from the polyester resin, especially biaxially oriented polyester film, from its mechanical properties, electrical properties, etc., copper-clad laminate, solar cell backsheet, adhesive tape, flexible printed circuit board, flexible display substrate, Various industrial materials such as membrane switches, sheet heating elements, or electrical insulation materials such as flat cables, magnetic recording materials, capacitor materials, packaging materials, automotive materials, building materials, photographic applications, graphic applications, thermal transfer applications, etc. It is used as

  Of these applications, electrical insulation materials used outdoors (for example, solar battery back sheets), automotive materials, and building materials are often used in harsh environments for a long period of time, and polyester resins are hydrolyzed. Due to the decrease in molecular weight due to the decrease in the molecular weight, mechanical properties and the like decrease, so when used in a harsh environment for a long period of time, or in applications where it is used in a damp state, it has high heat and heat resistance. Is required. In addition, when used in a harsh environment for a long period of time, the film dimensions change due to heat and cause damage to the apparatus, so high thermal dimensional stability is required. In addition, a flexible display substrate (for example, an organic EL display substrate) requires many heating processes such as vapor deposition of a transparent conductive layer and application of an organic EL element, and thus high thermal dimensional stability is required. . For example, in solar cell backsheet applications, in order to improve the service life of solar cells and reduce power generation costs, it is required to improve the moisture and heat resistance and thermal dimensional stability of polyester films.

  Therefore, various studies have been made to suppress hydrolysis of the polyester resin and improve thermal dimensional stability. For example, a technique has been studied in which an epoxy compound (Patent Document 1) or polycarbodiimide (Patent Document 2) is added to improve the moisture and heat resistance of the polyester resin itself. In addition, with regard to the biaxially oriented polyester film, studies have been made to improve the moisture and heat resistance by setting the film to a high IV (high intrinsic viscosity) and controlling the degree of plane orientation (Patent Document 3). In addition, studies have been made to reduce the heat shrinkage rate by reducing the tension of the amorphous chain by setting the heat treatment temperature after stretching near the melting point of the resin (Patent Document 4).

Japanese Patent Laid-Open No. 2007-302878 Japanese National Patent Publication No. 11-506487 JP 2007-70430 A JP-A-9-29833

  In the technique of the above-mentioned Patent Document 1, there is a high possibility that gelation occurs during melt molding, resulting in poor molding or foreign matter, and it is necessary to remove the foreign matter. In addition, the effect of improving heat and humidity resistance is insufficient. In Patent Document 2, although the effect of improving heat and humidity resistance is high, the compound produced by the reaction of polycarbodiimide with the polyester resin has low heat resistance, and therefore, a decomposition gas harmful to the human body is generated during melt molding. Problems and explosion-proof measures are necessary. In addition, the technique of Patent Document 3 is not sufficient in improving the heat and moisture resistance, and the thermal dimensional stability is not sufficient. Further, the technique of Patent Document 4 has a problem that although the thermal shrinkage rate is reduced, the thermal expansion rate of the film is increased because the tension of the amorphous chain is relaxed. Therefore, improvement in heat and humidity resistance and thermal dimensional stability has been demanded.

  The present invention provides a polyester film excellent in wet heat resistance and thermal dimensional stability, and a sheet containing a crystalline polyester layer whose main constituents are a dicarboxylic acid constituent and a diol constituent, and specific stretching conditions and heat treatment conditions. It is the manufacturing method of the polyester film characterized by adopting and forming into a film.

  The polyester film of the present invention is mainly composed of a layer (P layer: described later) that provides excellent heat and moisture resistance and thermal dimensional stability to the polyester film. In the polyester film of the present invention, the P layer may be the film itself, or may be laminated with other layers. Moreover, when manufacturing the polyester film by which P layer was laminated | stacked with the other layer, when it exists in a lamination | stacking state before the biaxial stretching of a process (1), the other layer is simultaneously applied to the manufacturing method of this invention. Including the case, the layer that becomes the P layer in the polyester film of the present invention is referred to as a P layer forming layer.

In order to solve the above problems, the present invention has the following configuration. That is,
1. Forming a sheet containing a crystalline polyester layer (P layer forming layer) whose main components are a dicarboxylic acid component and a diol component by a method including the following steps (1) to (3) in this order. A process for producing a polyester film characterized by
(1) At a temperature T1n that satisfies the following formula (a) (n represents the n-th stage temperature in this step), the area magnification is 13.5 in the film longitudinal direction (MD) and the film width direction (TD). Step of biaxial stretching more than double Tg ≦ T1n ≦ Tg + 40 ° C. (a)
Tg: Glass transition temperature (° C.) of the crystalline polyester obtained by differential scanning calorimetry
(2) Gripping both ends of the film in the width direction with respect to a straight line connecting both ends of the film in the width direction so that the shift in the center of the film in the gravitational direction is 1 mm or more and 50 mm or less. First heat treatment step for performing heat treatment at a heat treatment temperature Th1 satisfying Tm−90 ° C. ≦ Th1 ≦ Tm−45 ° C. (b)
Tm: Melting point (° C.) of the crystalline polyester obtained by differential scanning calorimetry
(3) Under the condition of the heat treatment temperature Th2 satisfying the following formula (c), both MD and TD contract by 1% to 10% by the following processing method (3-1) or (3-2), Heat treatment step 150 ° C. ≦ Th2 ≦ Th1 (c)
(3-1) Cut out the film into sheets and paste it in a state where both MD and TD are loosened in a rectangular metal frame (3-2) Film installed between the winding roll and the winding roll 1. Continuous treatment in a state where the tension due to the dimensional change of the MD shrinkage of the film is relaxed by the difference in speed between the unwinding roll and the winding roll using an oven having an inlet and an outlet. A sheet containing a crystalline polyester layer (P layer forming layer) whose main constituents are a dicarboxylic acid constituent and a diol constituent is formed by a method including the following steps (4) and (5) in this order. A method for producing a polyester film.
(4) At a temperature T1n satisfying the following formula (d) (n represents the temperature at the n-th stage in this step), the area magnification is 13.5 in the longitudinal direction (MD) of the film and the width direction (TD) of the film. Step of biaxial stretching more than double Tg ≦ T1n ≦ Tg + 40 ° C. (d)
Tg: Glass transition temperature (° C.) of the crystalline polyester obtained by differential scanning calorimetry
(5) Grasp both ends of the film width direction with respect to a straight line connecting both ends of the film width direction so that the shift in the gravity direction of the film center portion is 1 mm or more and 50 mm or less. An integrated heat treatment step for shrinking from 1.0% to 10% in the MD and TD directions at the heat treatment temperature Th3 to be satisfied.

Tm−90 ° C. ≦ Th3 ≦ Tm−45 ° C. (e)
Tm: Melting point (° C.) of the crystalline polyester obtained by differential scanning calorimetry
3. The crystalline polyester of the P layer forming layer contains phosphoric acid and alkali metal phosphate, the content of alkali metal phosphate is 0.5 mol / t or more, and the content of phosphoric acid is alkali metal phosphate The manufacturing method of the polyester film of 1 or 2 which is the molar ratio of 0.25 times or more and 1.5 times or less with respect to this.
4). The crystalline polyester of the P layer forming layer contains a component having three or more carboxylic acid groups and / or hydroxyl groups as a copolymerization component in an amount of 0.005 mol% to 1.5 mol% based on the total components. The manufacturing method of the polyester film in any one of -3.
5. The crystalline polyester of the P-layer forming layer contains a hydrolysis-resistant agent, and the content of the hydrolysis-resistant agent is 0.01% by mass or more with respect to the P-layer forming layer. Of manufacturing polyester film.
6). The plane orientation coefficient R in the Raman band spectrum method determined by the following formula is 5.0 or more and 10.0 or less, and after heat treatment at 150 ° C. for 30 minutes in the longitudinal direction (MD) of the film and the width direction (TD) of the film. The average thermal expansion rate is 0.8% or less, and the average linear expansion coefficient α of the linear expansion coefficient α (MD) of MD and TD from 50 ° C. to 150 ° C. is 22 ppm / The polyester film manufactured by the method in any one of 1-5 containing the crystalline polyester layer (P layer) whose main structural component which is below degrees C is a dicarboxylic acid structural component and a diol structural component.

R = (R (MD) + R (TD)) / 2
R (MD) = I (MD) / I (ND)
R (TD) = I (TD) / I (ND)
(Here, I (ND), I (MD), and I (TD) are respectively the intensities in the polarization arrangement perpendicular to the film plane direction of the Raman band spectrum of 1615 cm ⁻¹ in laser Raman spectroscopy (I (ND)), intensity in a polarization arrangement parallel to the longitudinal direction of the film plane (I (MD)), and intensity in a polarization arrangement parallel to the width direction of the film plane (I (TD))
A solar cell backsheet using the polyester film according to 7.6.
A solar cell using the solar cell backsheet described in 8.7.
A flexible substrate using the polyester film described in 9.6.
Is the main point.

  ADVANTAGE OF THE INVENTION According to this invention, the polyester film excellent in heat-and-moisture resistance and thermal dimensional stability can be provided. Such polyester films include copper-clad laminates, solar battery back sheets, adhesive tapes, flexible printed boards, flexible display boards, membrane switches, planar heating elements, flat cables, and other electrically insulating materials, capacitor materials, and automotive materials. In addition, it can be suitably used for applications in which moisture and heat resistance and thermal dimensional stability are important, including building materials.

It is sectional drawing which shows typically an example of a structure of the solar cell using the polyester film of this invention.

The present invention is a method comprising the following steps (1) to (3) in this order for a sheet containing a crystalline polyester layer (P layer forming layer) whose main constituent components are a dicarboxylic acid constituent component and a diol constituent component: This is a method of forming a film.
(1) At a temperature T1n that satisfies the following formula (a) (n represents the n-th stage temperature in this step), the area magnification is 13.5 in the film longitudinal direction (MD) and the film width direction (TD). Step of biaxial stretching more than double Tg ≦ T1n ≦ Tg + 40 ° C. (a)
Tg: Glass transition temperature (° C.) of the crystalline polyester obtained by differential scanning calorimetry
(2) Gripping both ends of the film in the width direction with respect to a straight line connecting both ends of the film in the width direction so that the shift in the center of the film in the gravitational direction is 1 mm or more and 50 mm or less. First heat treatment step for performing heat treatment at a heat treatment temperature Th1 satisfying Tm−90 ° C. ≦ Th1 ≦ Tm−45 ° C. (b)
Tm: Melting point (° C.) of the crystalline polyester obtained by differential scanning calorimetry
(3) Under the condition of the heat treatment temperature Th2 satisfying the following formula (c), both MD and TD contract by 1% to 10% by the following processing method (3-1) or (3-2), Heat treatment step 150 ° C. ≦ Th2 ≦ Th1 (c)
(3-1) Cut out the film into sheets and paste it in a state where both MD and TD are loosened in a rectangular metal frame (3-2) Film installed between the winding roll and the winding roll Using an oven having an inlet and an outlet, continuous treatment is performed in a state in which the tension due to the dimensional change of the shrinkage of the MD of the film is relaxed due to the difference in speed between the winding roll and the winding roll.
Although the polyester film obtained by the above manufacturing method has high heat-and-moisture resistance, it can also have favorable thermal dimensional stability, but the mechanism is considered as follows. In general, in a polyester film produced from a crystalline polyester (including a crystalline polyester layer when a crystalline polyester layer is exposed on either surface as a layer), a crystalline portion and an amorphous portion of the polyester are included. Part of the polyester film obtained by biaxial stretching of the crystalline polyester, and a portion where the polyester is crystallized by orientation of the molecular chain in the stretching direction (hereinafter referred to as an oriented crystal part) There are a portion crystallized without orientation (hereinafter simply referred to as a crystal portion) and an amorphous portion. The amorphous part is considered to be in a state where the density is lower than that of the crystal part and the oriented crystal part and the average intermolecular distance is large.

  When the polyester film is exposed to a moist heat atmosphere, moisture (water vapor) enters the interior through the molecular chains of the amorphous part having a low density, and plasticizes the amorphous part to increase the mobility of the molecular chain. . Polyester has a carboxyl group terminal derived from its raw material, but moisture that has entered the inside hydrolyzes the amorphous part with relatively high molecular chain mobility using the proton at the carboxyl group terminal as a reaction catalyst. To do. By hydrolyzing in this way, the mobility of the molecular chain is further increased as the molecular weight is lowered in the amorphous part, and the crystallization of the polyester having the lowered molecular weight is advanced in the amorphous part. Thus, it is considered that the amorphous part having high toughness has a low molecular weight and is changed to the crystalline part. As a result, the embrittlement of the film progresses, and finally, even a slight impact results in a state of breaking.

  In this invention, as process (1), it is temperature T1n which satisfies following formula (a) (n represents the temperature of the nth step | paragraph in this process), The longitudinal direction (MD) of a film, and the width direction (TD) of a film ) Is biaxially stretched to an area magnification of 13.5 times or more.

Tg ≦ T1n ≦ Tg + 40 ° C. (a)
Tg: Glass transition temperature (° C.) of crystalline polyester in the P layer forming layer obtained by differential scanning calorimetry
Subsequently, as the step (2), the both ends of the film in the width direction are gripped so that the deviation in the gravity direction of the center of the film is 1 mm or more and 50 mm or less with respect to the straight line connecting the both ends in the width direction of the film. Then, heat treatment is performed at a heat treatment temperature Th1 that satisfies the following formula (b) (first heat treatment step).

45 ° C. ≦ Tm−Th1 ≦ 90 ° C. (b)
Tm: Melting point (° C) of crystalline polyester in P layer forming layer obtained by differential scanning calorimetry
Thus, biaxial stretching under the above conditions and heat treatment can increase the proportion of oriented crystal parts having a higher density than amorphous parts, and prevent moisture from entering the film. it can. Moreover, when the ratio of the oriented crystal part is increased, the rigidity of the film is increased and the film is hardly thermally expanded. On the other hand, when the number of oriented crystal parts increases, the distortion of the amorphous part increases in the orientation direction of the oriented crystal parts. This strain is released when heat is applied to the film and the film shrinks irreversibly. In order to remove this distortion and suppress thermal shrinkage of the film, the following (3-1) or (3-2) treatment method is performed as a step (3) under the condition of a heat treatment temperature Th2 that satisfies the following formula (c): Thus, both the longitudinal direction (MD) of the film and the width direction (TD) of the film are contracted by 1% to 10% (second heat treatment step).

150 ° C. ≦ Th2 ≦ Th1 (c)
(3-1) Cut out the film into sheets and paste it in a state where both MD and TD are loosened in a rectangular metal frame (3-2) Film installed between the winding roll and the winding roll Continuous treatment in a state where the tension due to the dimensional change of the MD shrinkage of the film is relaxed by the difference in speed between unwinding and winding rolls using an oven having an inlet and an outlet of the crystalline polyester layer (P layer forming layer) By forming the sheet containing the film by the method including the steps (1) to (3) in this order, a polyester film having excellent heat and heat resistance and good thermal dimensional stability can be obtained.

  Hereinafter, the present invention will be described in detail with specific examples.

  In the present invention, the crystalline polyester of the P layer forming layer and the P layer (hereinafter simply referred to as “P layer forming layer”) in the polyester film obtained by the production method of the present invention includes a dicarboxylic acid component and a diol component. It is a crystalline polyester comprising In addition, in this specification, a structural component shows the minimum unit which can be obtained by hydrolyzing polyester.

  Examples of the dicarboxylic acid component constituting the crystalline polyester include malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, dimer acid, eicosandioic acid, pimelic acid, azelaic acid, Aliphatic dicarboxylic acids such as methyl malonic acid and ethyl malonic acid, adamantane dicarboxylic acid, norbornene dicarboxylic acid, isosorbide, cyclohexane dicarboxylic acid, decalin dicarboxylic acid, terephthalic acid, isophthalic acid, phthalic acid, 1 , 4-Naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 4,4′-diphenyldicarboxylic acid, 4,4′-diphenyletherdicarboxylic acid, 5 -Sodium sul Isophthalic acid, phenyl ene boys carboxylic acid, anthracene dicarboxylic acid, phenanthrene carboxylic acid, 9,9'-bis (4-carboxyphenyl) there may be mentioned dicarboxylic acids such as fluorene acids and aromatic dicarboxylic acids are not limited thereto. Moreover, even if these are individual, multiple types may be contained as needed.

  Examples of the diol component constituting the crystalline polyester of the P layer forming layer include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, Aliphatic diols such as 1,3-butanediol, cycloaliphatic diols such as cyclohexanedimethanol, spiroglycol and isosorbide, bisphenol A, 1,3-benzenedimethanol, 1,4-benzenedimethanol, 9, Examples include, but are not limited to, 9′-bis (4-hydroxyphenyl) fluorene, diols such as aromatic diols, and those in which a plurality of the above diols are linked. Moreover, even if these are individual, multiple types may be contained as needed.

  A crystalline polyester having a structure in which the above-mentioned compounds are appropriately combined and polycondensed can be used as the P layer forming layer (and the P layer).

  In the present invention, the dicarboxylic acid constituent component in the crystalline polyester in the P layer forming layer is preferably an aromatic dicarboxylic acid as the main constituent component, and the total dicarboxylic acid constituent in the crystalline polyester in the P layer forming layer The ratio of the aromatic dicarboxylic acid constituent component in the component is more preferably 90 mol% or more and 100 mol% or less. More preferably, it is 95 mol% or more and 100 mol%. More preferably, it is 98 mol% or more and 100 mol% or less, particularly preferably 99 mol% or more and 100 mol% or less, and most preferably 100 mol%, that is, all of the dicarboxylic acid components should be aromatic carboxylic acid components. If it is less than 90 mol%, the heat and moisture resistance and heat resistance may decrease. In the polyester film of the present invention, the ratio of the aromatic dicarboxylic acid component in the total dicarboxylic acid component in the crystalline polyester in the P layer forming layer is 90 mol% or more and 100 mol% or less, so It becomes possible to achieve both heat resistance.

  In the present invention, the main repeating unit consisting of a dicarboxylic acid component and a diol component, mainly composed of the crystalline polyester in the P layer forming layer, is ethylene terephthalate, ethylene-2,6-naphthalenedicarboxylate, propylene terephthalate. , Butylene terephthalate, 1,4-cyclohexylenedimethylene terephthalate, ethylene-2,6-naphthalenedicarboxylate and mixtures thereof are preferably used. The main repeating unit referred to here is more preferably 70 mol% or more of all repeating units in the case where the total of the above repeating units is a crystalline polyester contained in the crystalline polyester layer (P layer forming layer). Means 80 mol% or more, more preferably 90 mol% or more.

  Furthermore, it is preferable that ethylene terephthalate, ethylene-2,6-naphthalenedicarboxylate, and a mixture thereof are main constituents in that they can be easily polymerized at low cost and have excellent heat resistance. . In this case, when more ethylene terephthalate is used as a structural unit, a cheap and versatile film having heat and heat resistance can be obtained, and more ethylene-2,6-naphthalenedicarboxylate is used as a structural unit. When used, the film can be made more excellent in heat and moisture resistance.

  In the present invention, the number of carboxylic acid terminal groups of the crystalline polyester constituting the crystalline polyester layer (P layer forming layer) is preferably 20 equivalents / t or less. More preferably, it is 18 equivalents / t or less, more preferably 16 equivalents / t or less. When it exceeds 20 equivalents / t, the catalytic action by protons of the carboxylic acid end groups is strong, hydrolysis is accelerated, and deterioration tends to proceed. In order to set the number of carboxylic acid end groups to 20 equivalents / t or less, 1) an esterification reaction between a dicarboxylic acid component and a diol component is performed, and when a predetermined melt viscosity is obtained by melt polymerization, A method of solid-phase polymerization after stranding, cutting and chipping, 2) From the end of the ester exchange reaction or esterification reaction to the initial stage of the polycondensation reaction (intrinsic viscosity is less than 0.3). It can be obtained by a combination of methods of adding, and the like. Moreover, it can obtain also by adding a buffering agent and terminal blocker at the time of shaping | molding.

  In the polyester film of the present invention, the intrinsic viscosity (IV) of the crystalline polyester resin constituting the crystalline polyester layer (P layer forming layer) is preferably 0.65 or more. More preferably, it is 0.68 or more, More preferably, it is 0.7 or more, Most preferably, it is 0.72 or more. If the IV is less than 0.65, the molecular weight is too low to obtain sufficient heat-and-moisture resistance and mechanical properties, or the entanglement between molecules becomes too small, and the rate of thermal crystallization after hydrolysis increases. , May become brittle. In the polyester film of the present invention, when the crystalline polyester resin constituting the crystalline polyester layer (P layer forming layer) has an IV of 0.65 or more, high heat and heat resistance and high mechanical properties can be obtained. Although the upper limit of IV is not particularly determined, it is preferably 1.0 or less, more preferably 0.9 from the viewpoint that the polymerization time is long, which is disadvantageous in cost and difficult to melt extrusion. It is as follows.

  In order to obtain the above-mentioned intrinsic viscosity, when a predetermined melt viscosity is obtained by melt polymerization, a chip is formed by discharging, forming a strand, and cutting, and a chip is formed once at an intrinsic viscosity lower than the target, and then solidified. There is a method of performing phase polymerization. Of these, it is preferable to form chips once with an intrinsic viscosity lower than the target, and then perform solid-phase polymerization in that thermal deterioration can be suppressed and the number of carboxylic acid end groups can be reduced.

  In the present invention, the crystalline polyester constituting the P layer forming layer is a crystalline resin. Specifically, a crystalline resin means that the resin is heated from 25 ° C. to 300 ° C. at a temperature rising rate of 20 ° C./min (1stRUN) according to JIS K7122 (1999). ), 2ndRUN differential scanning calorimetry chart obtained by holding in that state for 5 minutes, then rapidly cooling to 25 ° C. or less, and again raising the temperature from room temperature to 300 ° C. at a rate of 20 ° C./min. The heat of crystal fusion ΔHm obtained from the peak area of the melting peak is 15 J / g or more. It is preferable to use a resin having a heat of crystal melting of 20 J / g or more, more preferably 25 J / g or more, and even more preferably 30 J / g or more. By using a crystalline polyester resin as the resin constituting the P layer forming layer, it becomes possible to cause orientational crystallization by stretching and heat treatment. As a result, the polyester is excellent in mechanical strength, heat and humidity resistance, and thermal dimensional stability. It can be a film.

  In the polyester film of the present invention, the crystalline polyester constituting the crystalline polyester layer (P layer forming layer) preferably has a melting point Tm of 250 ° C to 280 ° C. The melting point Tm here is the melting point Tm in the temperature rising process (temperature rising rate: 20 ° C./min) obtained by DSC, and 25 ° C. by the method based on JIS K-7121 (1999) as described above. Heat from 1 to 300 ° C. at a rate of temperature increase of 20 ° C./min (1st RUN), hold in that state for 5 minutes, then rapidly cool to below 25 ° C. The melting point Tm of the crystalline polyester is determined by the temperature at the peak top of the 2ndRun crystal melting peak obtained by raising the temperature to 2 m. More preferably, melting | fusing point Tm is 247-275 degreeC, More preferably, it is 250-265 degreeC. If the melting point Tm is less than 245 ° C, the heat resistance of the film may be inferior, and it is not preferable. If the melting point Tm exceeds 280 ° C, extrusion may be difficult, which is not preferable. In this invention, it can be set as the polyester film which made heat resistance and workability compatible by making melting | fusing point Tm of crystalline polyester which comprises the layer (P layer formation layer) of crystalline polyester into 250-280 degreeC.

  In the step (1) of the present invention, the sheet including the P layer forming layer is a temperature satisfying the following formula (a) A temperature T1n satisfying the following formula (a) (n is a temperature of the nth stage in this step) 2) is biaxially stretched to an area magnification of 13.5 times or more in the longitudinal direction (MD) of the film and the width direction (TD) of the film.

Tg ≦ T1n ≦ Tg + 40 ° C. (a)
If the area magnification is 13.5 times or more, it may be stretched twice or more MD and / or TD within the above temperature range. The order of stretching may be from either MD or TD, but it is preferable to stretch from MD in order to efficiently perform the subsequent heat treatment step. One each time the MD and TD, when extending from MD leads to a roll group heated to a temperature T1 ₁ satisfying the above formula (a), performs stretching in the MD, then the both ends of the film with clips the grasped while stretched biaxial th needs to be performed in the TD at a temperature T1 ₂ satisfying the following formula (a).

  If T1n is lower than Tg, stretching cannot be performed. Moreover, when T1n is higher than Tg + 40 ° C., it is not preferable because the alignment is difficult to be achieved. The upper limit of T1n is more preferably Tg + 30 ° C. or less, and further preferably Tg + 20 ° C. or less.

  When the area magnification is less than 13.5, the orientation of the resulting film is low and the heat and humidity resistance is poor, which is not preferable. On the other hand, if the area stretch ratio exceeds 18 times, tearing tends to occur at the time of stretching, and the heat-and-moisture resistance tends to decrease.

In the present invention, it is preferable that the ratio _M MD _{/ M TD} draw ratio _{M TD} draw ratio _{M MD} and TD of the MD and 0.7 to 0.95. If it is in a range other than this, the orientation is biased in either direction and the heat and moisture resistance tends to be poor.

  In the step (2) in the present invention, in order to complete the crystal orientation of the obtained biaxially stretched film and to impart flatness, the film in the middle part of the film with respect to the straight line connecting both ends in the width direction of the film. The both ends in the width direction of the film are gripped so that the shift in the direction of gravity is 1 mm or more and 50 mm or less, and heat treatment is performed at a heat treatment temperature Th1 that satisfies the following formula (b) (first heat treatment step).

45 ° C. ≦ Tm−Th1 ≦ 90 ° C. (b)
Tm: Melting point (° C) of crystalline polyester in P layer forming layer obtained by differential scanning calorimetry
If the heat treatment temperature is out of the above range and becomes too high, the orientation of the molecular chain in the stretching direction is relaxed. As a result, the orientation of the oriented crystal part is also relaxed, and part of it becomes an amorphous part with high molecular mobility. Some are considered to be crystal parts that do not undergo orientation by heat treatment at high temperature. As a result of the increase in the amorphous part and the crystal part, it is not preferable because the crystal part is likely to increase after hydrolysis and the embrittlement easily proceeds in a wet heat atmosphere. Further, if the heat treatment temperature is out of the above range and becomes too low, the formation of oriented crystal parts becomes insufficient, the flatness is poor, and further, crystallization after hydrolysis is promoted in a humid heat atmosphere, and embrittlement tends to proceed. This is not preferable. Moreover, it is preferable that the heat processing time is 1 second or more and 60 seconds or less.

  In the step (3) of the present invention, after winding the obtained biaxially stretched film on a roll, in order to impart thermal dimensional stability, the following heat treatment temperature Th2 satisfying the following formula (d) is satisfied: By the processing method of (3-1) or (3-2), both the longitudinal direction (MD) of the film and the width direction (TD) of the film are contracted by 1% to 10% (second heat treatment step).

150 ° C. ≦ Th2 ≦ Th1 (c)
(3-1) A batch process in which a film is cut into a single sheet and MD and TD are both loosened in a rectangular metal frame. The amount by which the film is loosened during the treatment is preferably 5 mm or more and 50 mm or less in the direction of gravity with respect to the metal frame plane in a state where the metal frame plane is arranged substantially horizontally. Outside the above range, film flatness after heat treatment is impaired, which is not preferable.
(3-2) Dimensional change in shrinkage of the film MD due to the difference in speed between the unwinding roll and the winding roll using an oven having an entrance and an exit of the film installed between the unwinding roll and the winding roll. Continuous treatment with relaxed tension. During such treatment, the tension in the MD direction is preferably 10 N / m to 100 N / m. Outside the above range, the flatness of the film deteriorates or the film is torn, which is not preferable.
When Th2 is lower than 150 ° C., the shrinkage during the heat treatment step cannot be sufficiently performed, and the thermal shrinkage rate is deteriorated or the flatness of the film is deteriorated. On the other hand, if Th2 is higher than Th1, the orientation of the oriented crystal part obtained in the stretching step and the first heat treatment step is relaxed, and the moist heat resistance is deteriorated. The heat treatment time of the second heat treatment step in the present invention is preferably 30 seconds or longer and 120 seconds or shorter.

  When the film shrinkage amount in the second heat treatment step in the present invention is outside the above range, the thermal dimensional stability is deteriorated or the flatness is deteriorated, which is not preferable.

  In the present invention, the first heat treatment step that completes the crystal orientation of the biaxially stretched film in the step (2) and imparts flatness, and the second heat treatment that imparts thermal dimensional stability in the step (3). It is also possible to integrate processes. That is, as step (4) (same as step (1)), the temperature T1n satisfying the following formula (d) is satisfied for the sheet including the crystalline polyester layer (P layer forming layer) (n is n steps in this step). In the step (2) and the step (3), the film is biaxially stretched to an area magnification of 13.5 times or more in the film longitudinal direction (MD) and the film width direction (TD). Instead, as a step (5), with respect to a straight line connecting both end portions in the width direction of the film, gripping both ends in the film width direction in a state where the shift in the gravity direction of the center portion of the film is 1 mm or more and 50 mm or less, It is also possible to shrink 1.0% to 10% (integrated heat treatment) in the longitudinal direction (MD direction) and the orthogonal direction (TD direction) of the film at a heat treatment temperature Th3 satisfying the following formula (e). .

Tg ≦ T1n ≦ Tg + 40 ° C. (d)
Tm−90 ° C. ≦ Th3 ≦ Tm−45 ° C. (e)
Tg: Glass transition temperature (° C.) of the crystalline polyester obtained by differential scanning calorimetry
Tm: Melting point (° C.) of the crystalline polyester obtained by differential scanning calorimetry
Also by adopting such a production method, it is possible to obtain a polyester film excellent in heat and moisture resistance and thermal dimensional stability.

  In the polyester film obtained by the production method of the present invention, the plane orientation coefficient R in the Raman band spectrum method determined by the following formula is 5.0 or more and 10.0 or less, and the longitudinal direction (MD) of the film and the width direction of the film. (TD) The average thermal contraction rate after heat treatment at 150 ° C. for 30 minutes is 0.8% or less, and the linear expansion coefficient α (MD) in the MD direction from 50 ° C. to 150 ° C. and the linear expansion in the TD direction A main constituent component having an average linear expansion coefficient α of a coefficient α (TD) of 22 ppm / ° C. or less includes a dicarboxylic acid constituent component and a crystalline polyester layer (P layer) which is a diol constituent component.

R = (R (MD) + R (TD)) / 2
R (MD) = I (MD) / I (ND)
R (TD) = I (TD) / I (ND)
(Here, I (ND), I (MD), and I (TD) are respectively the intensities in the polarization arrangement perpendicular to the film plane direction of the Raman band spectrum of 1615 cm ⁻¹ in laser Raman spectroscopy (I (ND)), intensity in a polarization arrangement parallel to the longitudinal direction of the film plane (I (MD)), and intensity in a polarization arrangement parallel to the width direction of the film plane (I (TD))
When the plane orientation coefficient is less than 5.0, since there are few oriented crystal parts in the film, there is no tension in the amorphous part and the mobility is high. This is not preferred because it tends to occur. Further, when the plane orientation coefficient R is greater than 10.0, the ratio of the oriented crystal part is large, and when the amorphous part is crystallized in a moist heat atmosphere, the amount of the amorphous part becomes extremely small, and the film becomes brittle. It is not preferable because it easily occurs. When the thermal shrinkage rate exceeds 0.8% or the linear expansion coefficient exceeds 23 ppm / ° C., the thermal dimensional stability of the film is deteriorated and workability is deteriorated, which is not preferable.

  The P layer forming layer of the polyester film of the present invention contains phosphoric acid and an alkali metal phosphate, the content of alkali metal phosphate is 0.5 mol / t or more, and the content of phosphoric acid is alkali phosphate. The molar ratio must be 0.25 times or more and 1.5 times or less with respect to the metal salt. By including phosphoric acid and an alkali metal phosphate in the P layer forming layer of the polyester film of the present invention, the initial carboxyl group terminal number can be further reduced, and in the polyester film obtained by the production method of the present invention The hydrolysis reaction of the P layer in a moist heat environment can be suppressed. Moreover, the neutralization of protons acting as a catalyst for the hydrolysis reaction at the end of the carboxyl group newly generated by the hydrolysis reaction can further suppress the hydrolysis reaction, thereby further suppressing the wet heat degradation of the polyester film. It becomes possible.

The alkali metal phosphate used in the present invention is preferably the one represented by the following formula from the viewpoint of polymerization reactivity of the crystalline polyester resin and heat resistance during melt molding, and the alkali metal is sodium, And / or potassium is preferable from the viewpoint of polymerization reactivity, heat resistance, and heat-and-moisture resistance, and phosphoric acid and sodium and / or potassium metal salts are particularly preferable from the viewpoint of polymerization reactivity and heat-and-heat resistance.
POxHyMz (I)
(Here, x is an integer of 2 to 4, y is 1 or 2, z is 1 or 2, and M is an alkali metal.)
Specific examples of the alkali metal phosphate include alkali metal salts with compounds such as phosphoric acid, phosphorous acid, and hypophosphorous acid. As the alkali metal element, potassium and sodium are preferable from the point that precipitates due to catalyst residues are difficult to be generated. Specifically, potassium hydrogen phthalate, sodium dihydrogen citrate, disodium hydrogen citrate, citric acid Potassium dihydrogen, dipotassium citrate, sodium carbonate, sodium tartrate, potassium tartrate, sodium lactate, potassium lactate, sodium bicarbonate, disodium hydrogen phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, diphosphate phosphate Examples thereof include sodium hydrogen, sodium hydrogen phosphite, potassium hydrogen phosphite, sodium hypophosphite, potassium hypophosphite, and sodium polyacrylate.

  In the polyester film of the present invention, the crystalline polyester of the P layer forming layer preferably contains 0.5 mol / t or more of an alkali metal phosphate. More preferably, it is 1 mol / t or more. If the content of the alkali metal phosphate is less than 0.5 mol / t, the hydrolysis resistance is reduced, and the obtained polyester film may not have sufficient wet heat resistance. In the polyester film of the present invention, the alkali metal phosphate of the crystalline polyester of the P layer is 0.5 mol / t or more, and high moisture and heat resistance can be expressed without deteriorating the quality of the film. Become. In addition, the upper limit of the content of alkali metal phosphate is preferably 3 mol / t or less, more preferably 2.5 mol, from the viewpoint that excessive alkali metal phosphate may precipitate and become foreign matters. / T or less.

  In the polyester film of the present invention, the crystalline polyester of the P layer preferably contains phosphoric acid in a molar ratio of 0.25 to 1.5 times with respect to the alkali metal phosphate. More preferably, it is 0.3 times or more and 1.25 times or less. If it is less than 0.25 times, the buffering action is difficult to be exhibited, the hydrolysis resistance is reduced, and the obtained polyester film may not have sufficient wet heat resistance. If the ratio exceeds 1.5 times, excess phosphoric acid reacts with the polyester during the polymerization reaction, and the phosphate ester skeleton is formed in the molecular chain, which accelerates the hydrolysis reaction. May decrease. In the polyester film of the present invention, the polyester obtained by containing phosphoric acid in the crystalline polyester of the P layer forming layer in a molar ratio of 0.25 to 1.5 times with respect to the alkali metal phosphate. It becomes possible to make the film exhibit high heat and heat resistance.

  Phosphoric acid and alkali metal phosphate may be added at the time of polymerization of the crystalline polyester constituting the P layer forming layer, or may be added at the time of melt molding. It is preferable to add at the time of polymerization from the viewpoint of uniform dispersion therein. In the case of adding at the time of polymerization, the timing of addition is arbitrary as long as it is from the end of the esterification reaction or the transesterification reaction at the time of polymerization of the crystalline polyester to the initial stage of the polycondensation reaction (inherent viscosity is less than 0.3). Can be added at the time. As a method for adding phosphoric acid and alkali metal phosphate, either adding powder directly or adjusting and adding a solution dissolved in a diol component such as ethylene glycol may be used. It is preferably added as a solution dissolved in the diol component. In this case, when the solution concentration is diluted to 10% by mass or less and added, there is little adhesion of phosphoric acid and alkali metal phosphate to the vicinity of the addition port, and the error of the addition amount becomes small, and the reactivity This is preferable.

  In the present invention, the crystalline polyester of the P layer forming layer has 0.005 mol% or more and 1.5 mol% of the structural component having three or more carboxylic acid groups and / or hydroxyl groups as a copolymerization component with respect to all the structural components. It is preferable to include the following. Here, the structural component having 3 or more carboxylic acid groups and / or hydroxyl groups refers to the following components.

  Examples of carboxylic acid components having three or more carboxylic acid groups include trifunctional aromatic carboxylic acid components such as trimesic acid, trimellitic acid, pyromellitic acid, naphthalenetricarboxylic acid, and anthracentricarboxylic acid. Examples of aromatic carboxylic acid constituents include methanetricarboxylic acid, ethanetricarboxylic acid, propanetricarboxylic acid, butanetricarboxylic acid, and tetrafunctional aromatic carboxylic acid constituents such as benzenetetracarboxylic acid, benzophenonetetracarboxylic acid, naphthalenetetracarboxylic acid, Anthracene tetracarboxylic acid, berylene tetracarboxylic acid, etc. are tetrafunctional aliphatic carboxylic acid constituents such as ethanetetracarboxylic acid, ethylenetetracarboxylic acid, butanetetracarboxylic acid, cyclopentanetetracarboxylic acid, Hexanetetracarboxylic acid, adamantanetetracarboxylic acid, etc. are pentafunctional or higher functional aromatic carboxylic acid constituents such as benzenepentacarboxylic acid, benzenehexacarboxylic acid, naphthalenepentacarboxylic acid, naphthalenehexacarboxylic acid, naphthaleneheptacarboxylic acid, naphthalene. Octacarboxylic acid, anthracenepentacarboxylic acid, anthracenehexacarboxylic acid, anthraceneheptacarboxylic acid, anthraceneoctacarboxylic acid, etc. are penta- or higher functional aliphatic carboxylic acid constituents such as ethanepentacarboxylic acid, ethaneheptacarboxylic acid, butanepentapenta Carboxylic acid, butaneheptacarboxylic acid, cyclopentanepentacarboxylic acid, cyclohexanepentacarboxylic acid, cyclohexanehexacarboxylic acid, adamantanepentacarboxylic acid, adama Tan hexacarboxylic acid and the, and the like These ester derivatives and acid anhydrides thereof as examples without limitation. Also preferred are those obtained by adding oxyacids such as l-lactide, d-lactide, hydroxybenzoic acid and the like, or a combination of a plurality of the oxyacids to the carboxy terminal of the carboxylic acid component. Used. Moreover, these may be used independently or may be used in multiple types as needed.

  Examples of components having 3 or more hydroxyl groups include trifunctional aromatic components such as trihydroxybenzene, trihydroxynaphthalene, trihydroxyanthracene, trihydroxychalcone, trihydroxyflavone, trihydroxycoumarin, and trifunctional fat. As an aliphatic alcohol constituent, glycerin, trimethylolpropane, propanetriol, a tetrafunctional aliphatic alcohol constituent, a compound such as pentaerythritol, and a constituent obtained by adding a diol to the hydroxyl terminal of the above compound are also preferable. Used. Moreover, these may be used independently or may be used in multiple types as needed.

  The component having three or more carboxylic acid groups and hydroxyl groups is an oxyacid having both a hydroxyl group and a carboxylic acid group in one molecule, and the total of the number of carboxylic acid groups and the number of hydroxyl groups is 3 or more. Specific examples include hydroxyisophthalic acid, hydroxyterephthalic acid, dihydroxyterephthalic acid, dihydroxyterephthalic acid, and the like.

In addition, the above-described constituent components may be used alone, or a plurality of types may be used as necessary.
In this invention, content of this structural component is 0.005 mol% or more and 1.5 mol% or less with respect to all the structural components in a P layer formation layer in P layer formation layer. More preferably, it is 0.020 or more and 1 or less, More preferably, it is 0.025 or more and 1.0 or less, More preferably, it is 0.035 or more and 0.5 or less. Moisture resistance of the P layer in the polyester film obtained by the production method of the present invention when the content of the constituent component of the P layer forming layer is 0.005 mol% or less with respect to all the constituent components in the P layer forming layer. The thermal improvement effect may be insufficient, and if it exceeds 1.5 mol%, the resin may gel and melt extrusion may be difficult. In such a case, the gel exists as a foreign substance, and the film In some cases, the biaxial stretchability may be reduced, or the film obtained by stretching may have a large number of foreign matter defects. In the polyester film of the present invention, the content of the constituent component in the P layer forming layer is 0.005 mol% or more and 1.5 mol% with respect to all the constituent components in the P layer, so that melt extrudability is achieved. It is possible to improve the heat and humidity resistance while maintaining the above, and it is possible to maintain the stretchability during biaxial stretching and the quality of the obtained film.

  In the present invention, the P layer forming layer preferably contains 0.01% by mass or more of the hydrolysis resistance agent. Here, the hydrolysis-resistant agent is a compound that reacts with and bonds to the COOH end group of the polyester to eliminate the catalytic activity of the proton of the COOH group, and specifically includes an oxazoline group, an epoxy group, a carbodiimide group. And the like.

  The carbodiimide compound having a carbodiimide group includes a monofunctional carbodiimide and a polyfunctional carbodiimide. As the monofunctional carbodiimide, dicyclohexylcarbodiimide, diisopropylcarbodiimide, dimethylcarbodiimide, diisobutylcarbodiimide, dioctylcarbodiimide, t-butylisopropylcarbodiimide, diphenylcarbodiimide, Examples thereof include di-t-butylcarbodiimide and di-β-naphthylcarbodiimide. Particularly preferred are dicyclohexylcarbodiimide and diisopropylcarbodiimide. As the polyfunctional carbodiimide, carbodiimide having a polymerization degree of 3 to 15 is preferable. Specifically, 1,5-naphthalene carbodiimide, 4,4′-diphenylmethane carbodiimide, 4,4′-diphenyldimethylmethane carbodiimide, 1,3-phenylene carbodiimide, 1,4-phenylene diisocyanate, 2,4-tolylene Carbodiimide, 2,6-tolylene carbodiimide, mixture of 2,4-tolylene carbodiimide and 2,6-tolylene carbodiimide, hexamethylene carbodiimide, cyclohexane-1,4-carbodiimide, xylylene carbodiimide, isophorone carbodiimide, isophorone carbodiimide, Dicyclohexylmethane-4,4′-carbodiimide, methylcyclohexanecarbodiimide, tetramethylxylylene carbodiimide, 2,6-diisopropylphenylcarbodiimide, 1, , And the like can be exemplified 5- triisopropylbenzene-2,4-carbodiimide.

  Since a carbodiimide compound generates an isocyanate gas by thermal decomposition, a carbodiimide compound having high heat resistance is preferable. In order to improve heat resistance, it is preferable that the molecular weight (degree of polymerization) is high, and it is more preferable that the terminal of the carbodiimide compound has a structure having high heat resistance. Further, once thermal decomposition occurs, further thermal decomposition is likely to occur. Therefore, in the method for producing a polyester film of the present invention, it is preferable to devise such as making the extrusion temperature as low as possible.

  Preferred examples of the epoxy compound include glycidyl ester compounds and glycidyl ether compounds. Specific examples of glycidyl ester compounds include benzoic acid glycidyl ester, t-Bu-benzoic acid glycidyl ester, p-toluic acid glycidyl ester, cyclohexanecarboxylic acid glycidyl ester, pelargonic acid glycidyl ester, stearic acid glycidyl ester, and lauric acid glycidyl ester. , Glycidyl palmitate, glycidyl behenate, glycidyl versatate, glycidyl oleate, glycidyl linoleate, glycidyl linolein, glycidyl behenol, glycidyl stearol, diglycidyl terephthalate, isophthalic acid Diglycidyl ester, phthalic acid diglycidyl ester, naphthalenedicarboxylic acid diglycidyl ester Ter, methylterephthalic acid diglycidyl ester, hexahydrophthalic acid diglycidyl ester, tetrahydrophthalic acid diglycidyl ester, cyclohexanedicarboxylic acid diglycidyl ester, adipic acid diglycidyl ester, succinic acid diglycidyl ester, sebacic acid diglycidyl ester, dodecane Examples include diionic diglycidyl ester, octadecanedicarboxylic acid diglycidyl ester, trimellitic acid triglycidyl ester, and pyromellitic acid tetraglycidyl ester. These may be used alone or in combination of two or more. Specific examples of the glycidyl ether compound include phenyl glycidyl ether, O-phenyl glycidyl ether, 1,4-bis (β, γ-epoxypropoxy) butane, 1,6-bis (β, γ-epoxypropoxy). ) Hexane, 1,4-bis (β, γ-epoxypropoxy) benzene, 1- (β, γ-epoxypropoxy) -2-ethoxyethane, 1- (β, γ-epoxypropoxy) -2-benzyloxyethane 2,2-bis- [р- (β, γ-epoxypropoxy) phenyl] propane, 2,2-bis- (4-hydroxyphenyl) propane, 2,2-bis- (4-hydroxyphenyl) methane, etc. Bisglycidyl polyether obtained by the reaction of bisphenol and epichlorohydrin, and the like, and these may be used alone or in combination of two or more. Kill. A polyfunctional epoxy compound having a glycidyl ester group or a glycidyl ether group in the polymer side chain is also preferably used.

  The oxazoline compound is preferably a bisoxazoline compound or a polyfunctional oxazoline. Specific examples of the bisoxazoline or the compound include 2,2′-bis (2-oxazoline), 2,2′-bis (4-methyl). -2-oxazoline), 2,2′-bis (4,4-dimethyl-2-oxazoline), 2,2′-bis (4-ethyl-2-oxazoline), 2,2′-bis (4,4 '-Diethyl-2-oxazoline), 2,2'-bis (4-propyl-2-oxazoline), 2,2'-bis (4-butyl-2-oxazoline), 2,2'-bis (4- (Hexyl-2-oxazoline), 2,2′-bis (4-phenyl-2-oxazoline), 2,2′-bis (4-cyclohexyl-2-oxazoline), 2,2′-bis (4-benzyl-) 2-Oki Zoline), 2,2'-p-phenylenebis (2-oxazoline), 2,2'-m-phenylenebis (2-oxazoline), 2,2'-o-phenylenebis (2-oxazoline), 2, 2'-p-phenylenebis (4-methyl-2-oxazoline), 2,2'-p-phenylenebis (4,4-dimethyl-2-oxazoline), 2,2'-m-phenylenebis (4- Methyl-2-oxazoline), 2,2′-m-phenylenebis (4,4-dimethyl-2-oxazoline), 2,2′-ethylenebis (2-oxazoline), 2,2′-tetramethylenebis ( 2-oxazoline), 2,2′-hexamethylene bis (2-oxazoline), 2,2′-octamethylene bis (2-oxazoline), 2,2′-decamethylene bis (2-oxazoline), 2 2′-ethylenebis (4-methyl-2-oxazoline), 2,2′-tetramethylenebis (4,4-dimethyl-2-oxazoline), 2,2′-9,9′-diphenoxyethanebis ( 2-oxazoline), 2,2′-cyclohexylenebis (2-oxazoline), 2,2′-diphenylenebis (2-oxazoline) and the like. Among these, 2,2′- Bis (2-oxazoline) is most preferred from the viewpoint of reactivity with polyester. Examples of the polyfunctional oxazoline compound include compounds having a plurality of oxazoline-based substituents on the side chain of the polymer. Furthermore, the bisoxazoline compounds listed above may be used singly or in combination of two or more as long as the object of the present invention is achieved.

  These compounds are preferably low in volatility, and therefore, higher molecular weight is preferable. By using a high molecular weight type hydrolysis-resistant agent, the volatility can be lowered. As a result, the flame retardancy of the resulting polyester film can be further increased. In the polyester film of the present invention, the hydrolysis-resistant agent is preferably a compound having a carbodiimide group, and more preferably a polycarbodiimide compound having a high degree of polymerization, because the catalytic activity disappearance effect of the proton of the COOH group of the polyester is high. Is good.

  If the amount of the hydrolysis-resistant agent in the P layer forming layer is less than 0.01% by mass, the improvement of the heat and moisture resistance by the addition of the hydrolysis-resistant agent may not be observed. In addition, the upper limit of the content of the hydrolysis-resistant agent is preferably 2% by mass or less, more preferably 1% by mass or less from the viewpoint that an excessive hydrolysis-resistant agent may reduce flame retardancy.

  In the present invention, the P layer forming layer is made of a heat resistance stabilizer, an oxidation resistance stabilizer, an ultraviolet absorber, an ultraviolet stabilizer, an organic / inorganic type as long as the effects of the present invention are not impaired as necessary. Additives such as lubricants, organic / inorganic fine particles, fillers, nucleating agents, dyes, dispersants, coupling agents, and bubbles may be blended.

  When the polyester film of the present invention is composed of only the P layer, it is preferably used in the case of a laminated structure with other layers (hereinafter, other layers may be abbreviated as P2 layers). In the case of a laminated structure, in order to exhibit the effect of high heat and heat resistance of the crystalline polyester layer, in the produced polyester film, the ratio of the P layer may be 40% or more of the entire polyester film. preferable. More preferably, it is 50% or more, more preferably 70% or more, and particularly preferably 80% or more. If the ratio of the crystalline polyester layer (P layer) is less than 40%, the effect of improving the heat and moisture resistance by the crystalline polyester layer (P layer) may not be exhibited. In the polyester film of the present invention, when the laminated structure is adopted, the moisture and heat resistance higher than that of a conventional polyester film can be obtained by setting the ratio of the crystalline polyester layer (P layer) to 40% or more.

  In the polyester film of the present invention, the thickness of the crystalline polyester layer (P layer) is preferably 10 μm or more and 500 μm or less, and more preferably 20 μm or more and 300 μm or less. More preferably, they are 25 micrometers or more and 200 micrometers or less. When thickness is less than 10 micrometers, the heat-and-moisture resistance of a film may fall too much. On the other hand, when it is thicker than 500 μm, for example, the thickness of the solar cell back sheet using this becomes too thick, and as a result, the thickness of the entire solar cell may become too large.

Moreover, the thickness of the entire polyester film of the present invention is preferably 10 μm or more and 500 μm or less, and more preferably 20 μm or more and 300 μm or less. More preferably, they are 25 micrometers or more and 200 micrometers or less. When the thickness is less than 10 μm, it is difficult to ensure the flatness of the film. On the other hand, when it is thicker than 500 μm, for example, the thickness of the solar cell back sheet using this becomes too thick, and as a result, the thickness of the entire solar cell may become too large.
The polyester film of the present invention preferably has an elongation retention of 40% or more after standing for 72 hours under conditions of a temperature of 125 ° C. and a humidity of 100% Rh. The elongation retention here is measured based on ASTM-D882 (1999), and is 72 hours under the conditions of breaking elongation E0, temperature 125 ° C., and humidity 100% Rh of the film before processing. It is a value obtained by the following formula (f) when the elongation at break after standing is E1.

Elongation retention (%) = E1 / E0 × 100 (f)
Note that E1 is a value measured using a sample that was cut into the shape of a measurement piece and then treated for 72 hours under conditions of a temperature of 125 ° C. and a humidity of 100% Rh. More preferably, the elongation retention determined by the above method is 40% or more, more preferably 50% or more, particularly preferably 60% or more, and most preferably 70% or more. In the polyester film of the present invention, when the elongation retention rate is less than 40%, for example, when used for a solar battery back sheet, the moisture and heat resistance of the back sheet including the film becomes insufficient, and the back sheet is mounted. When a solar cell is used for a long period of time, the backsheet may break when some external impact is applied to the solar cell (for example, when a falling stone hits the solar cell). It is not preferable. In the polyester film of the present invention, by setting the elongation retention rate to 40% or more, for example, when used for a solar battery backsheet, the durability of the backsheet during long-term use can be enhanced.

  Next, although an example is demonstrated about the manufacturing method of the sheet | seat containing the P layer formation layer of this invention, this invention is not limited only to this example. First, the manufacturing method of the raw material which comprises P layer formation layer can be manufactured with the following method. In the method for producing the polyester film of the present invention, the resin used as the raw material is a dicarboxylic acid constituent component, a diol constituent component, a constituent component in which the sum of the number of carboxylic acid groups and the number of hydroxyl groups is 3 or more in a known manner. It can be obtained by polycondensation. Here, as for the dicarboxylic acid component and the component having a total number of carboxylic acid groups and hydroxyl groups of 3 or more, those obtained by esterifying carboxyl groups can reduce the number of carboxyl group terminals and improve heat and heat resistance. It is more preferable in that it can be further enhanced.

  As an example of the polymerization step, it is produced by a first step for performing an esterification reaction or a transesterification reaction, a second step for adding an additive such as a polymerization catalyst or a phosphorus compound, and a third step for performing a polymerization reaction. A fourth step of performing a solid phase polymerization reaction may be added if necessary.

  In the first step, for example, using a dicarboxylic acid component, a diol component, and a component having a tri- or higher functional carboxylic acid group and / or a hydroxyl group as necessary, an esterification reaction by a known method, or A transesterification reaction can be performed. For example, when performing a transesterification reaction, a known transesterification reaction catalyst such as magnesium acetate, calcium acetate, manganese acetate, cobalt acetate, calcium acetate can be used, and antimony trioxide as a polymerization catalyst is added. May be. By adding several ppm of alkali metal such as potassium hydroxide during the esterification reaction, diethylene glycol by-product is suppressed and hydrolysis resistance is improved.

  The second step is a step in which an additive such as a polymerization catalyst or a phosphorus compound is added after the esterification reaction or transesterification reaction is substantially completed until the intrinsic viscosity reaches 0.4. .

  As the polymerization catalyst, an ethylene glycol solution of germanium dioxide, antimony trioxide, titanium alkoxide, a titanium chelate compound, or the like can be used.

  As a phosphorus compound, it is preferable to add 0.5 mol / t or more of an alkali metal phosphate from the viewpoint of hydrolysis resistance. More preferably, it is 1 mol / t or more. When the addition amount of the alkali metal phosphate is less than 0.5 mol / t, the hydrolysis resistance and the molecular chain restraining effect are reduced, and the obtained polyester film may not have sufficient wet heat resistance. . In addition, the upper limit of the addition amount of the alkali metal phosphate is preferably 3 mol / t or less, more preferably 2.5 mol from the viewpoint that excessive alkali metal phosphate may be precipitated and easily become a foreign substance. / T or less.

  In addition, phosphoric acid is added in a molar ratio of 0.25 to 1.5 times with respect to the alkali metal phosphate from the viewpoint of long-term hydrolysis resistance. More preferably, it is 0.3 times or more and 1.25 times or less. If it is less than 0.25 times, the buffering action is difficult to be exhibited, the hydrolysis resistance is reduced, and the obtained polyester film may not have sufficient wet heat resistance. If the ratio exceeds 1.5 times, excess phosphoric acid reacts with the polyester during the polymerization reaction, and the phosphate ester skeleton is formed in the molecular chain, which accelerates the hydrolysis reaction. May decrease.

  As a method for adding phosphoric acid or alkali metal phosphate, it is preferable from the viewpoint of long-term hydrolysis resistance that the phosphoric acid and alkali metal phosphate are previously dissolved in ethylene glycol and mixed. At this time, from the viewpoint of heat resistance and hydrolysis resistance, it is preferable to use the same alkylene glycol as the linear alkylene glycol having 2 to 4 carbon atoms contained in the polyester composition of the present invention. preferable. If different types of alkylene glycol are used, they may be copolymerized and heat resistance may be reduced.

  In particular, it is preferable to adjust the pH of the liquid mixture at this time to an acidity of 2.0 or more and 6.0 or less from the viewpoint of suppressing foreign matter formation. More preferably, it is 4.0 or more and 6.0 or less.

  These phosphorus compounds are preferably added with a polymerization catalyst at an interval of 5 minutes or more from the viewpoint of polymerization reactivity, and may be added after the polymerization catalyst or before the addition.

  Examples of other additives include magnesium acetate for the purpose of imparting electrostatic application characteristics, and calcium acetate as a co-catalyst, and can be added within a range that does not hinder the effects of the present invention. In particular, when an esterification reaction has been performed, the carboxyl group terminal group is added by adding the total diol component so that the total number of diol components is 1.5 to 1.8 times the number of moles of the dicarboxylic acid component. Since the amount can be reduced, it is more preferable in that the hydrolysis resistance can be improved.

  Further, various particles may be added to add film slipperiness, or internal precipitation particles using a catalyst may be included.

  In the third step, the polymerization reaction can be carried out by a known method. In order to reduce the carboxyl group terminal group amount in the range of 20 equivalents / t or less, the polymerization reaction temperature is set to the melting point of the crystalline polyester. It is preferably + 30 ° C. or lower. Further, it is effective in that it is possible to reduce the amount of carboxyl group terminals further by forming chips once with an intrinsic viscosity of 0.5 or more and 0.6 or less and performing solid phase polymerization as the fourth step.

  In the fourth step, it is preferable to carry out the solid phase polymerization reaction at a solid phase polymerization temperature of melting point Tm-30 ° C. or lower of the polyester composition, melting point Tm-60 ° C. or higher, and vacuum degree 0.3 Torr or lower.

  Next, in the production method of the sheet including the P layer forming layer, when the polyester film of the present invention has a single film configuration consisting of only the P layer, the P layer forming layer raw material is heated and melted in an extruder and cooled from the die. A method (melt cast method) of extruding onto a cast drum and processing it into a sheet can be used. As another method, the raw material for the P layer forming layer is dissolved in a solvent, and the solution is extruded from a die onto a support such as a cast drum or an endless belt to form a film, and then the solvent is dried and removed from the film layer. A method of processing into a sheet (solution casting method) or the like can also be used.

  When the P layer forming layer is produced by the melt casting method, the composition containing the dried polyester can be extruded with a normal extruder and a T die and biaxially stretched. At this time, it is better that the time from melting in a nitrogen atmosphere and feeding from the chip to the extruder to extrusion from the T-die is as short as possible. As a guideline, it is 30 minutes or less, more preferably 15 minutes or less, and even more preferably 5 It is preferable to set it to less than or equal to the minute in terms of suppressing increase in the number of carboxyl group terminals.

  Moreover, the manufacturing method in the case of the laminated structure in which the polyester film of this invention contains P layer and another layer (P2 layer) is as follows. When the material of each layer to be laminated is made of thermoplastic resin as the main constituent material, two different materials are put into two extruders, respectively, melted and co-extruded on a cast drum cooled from the die, into a sheet form Method of processing (coextrusion method), method of laminating a coating layer raw material on a sheet made of a single film into an extruder, melting and extruding and extruding from a die (melt laminating method), P2 layer laminated with P layer A method of making each separately, thermocompression bonding with a heated group of rolls (thermal laminating method), a method of bonding with an adhesive (adhesion method), and other materials for P2 layer are dissolved in a solvent, The method (coating method) which apply | coats the solution on the P layer formation layer produced previously, the method which combined these, etc. can be used.

  In addition, when the P2 layer is mainly composed of a material that is not a thermoplastic resin, a P2 layer to be laminated with a P layer forming layer is prepared separately and bonded via an adhesive or the like (adhesion method) In the case of a curable material, a method of curing by applying electromagnetic wave irradiation, heat treatment or the like after coating on the P layer can be used.

  The sheet including the P layer forming layer in the production method of the present invention can be formed by the above-described steps, and the polyester film obtained by the production method of the present invention has high moisture and heat resistance and thermal dimensional stability. is there. The polyester of the present invention takes advantage of its features, such as copper-clad laminates, solar battery back sheets, adhesive tapes, flexible printed circuit boards, flexible display boards, membrane switches, sheet heating elements, flat cables, and other electrically insulating materials, for capacitors It can be suitably used for applications in which flame retardancy is important, including materials, automobile materials, and building materials. In these, it uses suitably as a film for solar cell backsheets.

  The configuration of the solar cell backsheet of the present invention can be any configuration as long as the above-described polyester film is used, and an ethylene-vinyl acetate copolymer (hereinafter referred to as a power generation element) sealed in the polyester film of the present invention. EVA adhesion layer for improving adhesion to the EVA, an anchor layer for increasing adhesion with the EVA adhesion layer, a water vapor barrier layer, an ultraviolet absorption layer for preventing ultraviolet degradation, power generation efficiency The solar battery back sheet of the present invention is formed by forming a light reflecting layer for enhancing, a light absorbing layer for expressing design properties, an adhesive layer for adhering each layer, and the like.

  The EVA adhesion layer is a layer that improves adhesion to the EVA resin that seals the power generation element, and is disposed on the side closest to the power generation element, and contributes to adhesion between the backsheet and the system. The material is not particularly limited as long as adhesion with EVA resin is expressed. For example, EVA, EVA and ethylene-methyl acrylate copolymer (EMA), ethylene-ethyl acrylate copolymer (EEA), ethylene A mixture of butyl acrylate copolymer (EBA), ethylene-methacrylic acid copolymer (EMAA), ionomer resin, polyester resin, urethane resin, acrylic resin, polyethylene resin, polypropylene resin, polyamide resin or the like is preferably used. Moreover, in order to improve the adhesiveness to the back sheet | seat of an EVA contact bonding layer as needed, forming an anchor layer is also performed preferably. The material is not particularly limited as long as adhesion to the EVA adhesion layer is expressed, and for example, a mixture containing a resin as a main constituent such as an acrylic resin or a polyester resin is preferably used.

  The water vapor barrier layer is a layer for preventing water vapor from entering from the back sheet side in order to prevent water vapor deterioration of the power generation element when the solar cell is configured. It is formed by providing an oxide such as silicon oxide or aluminum oxide or a metal layer such as aluminum on the film surface by a known method such as vacuum deposition or sputtering. The thickness is preferably in the range of usually 100 angstroms or more and 200 angstroms or less. In this case, both the case where the gas barrier layer is directly provided on the polyester film of the present invention and the case where the gas barrier layer is provided on another film and this film is laminated on the film surface of the present invention are preferably used. Moreover, the method of laminating | stacking metal foil (for example, aluminum foil) on the film surface can also be used. In this case, the thickness of the metal foil is preferably in the range of 10 μm to 50 μm from the viewpoint of workability and gas barrier properties.

  The ultraviolet absorbing layer is a layer for blocking ultraviolet rays in order to prevent ultraviolet degradation of the resin in the inner layer, and any layer can be used as long as it has a function of blocking ultraviolet rays of 380 nm or less. The light reflecting layer is a layer that reflects light, and by forming this layer, the inner layer resin is prevented from UV degradation, or the light that reaches the back sheet without being absorbed by the solar cell system is reflected. This layer is used to increase the power generation efficiency by returning to the system side, and is a layer containing white pigments such as titanium oxide and barium sulfate, or bubbles. The light absorbing layer is a layer that absorbs light, and is a layer that is used to prevent UV degradation of the resin in the inner layer or improve the design of the solar cell by forming this layer.

  The solar cell backsheet of the present invention is formed by combining each of the above layers and the polyester film of the present invention. In the solar battery backsheet of the present invention, it is not necessary to form all of the above layers as independent layers, and it is also a preferred form to form a function integration layer having a plurality of functions. Further, when the polyester film of the present invention already has a function, it can be omitted. For example, when the polyester film of the present invention includes a layer containing a white pigment or bubbles and has light reflectivity, the light reflective layer is included, and the structure including a layer including a light absorber has light absorbability. In the case of a structure including an absorbing layer and a layer containing an ultraviolet absorber, the ultraviolet absorbing layer may be omitted.

  Since the polyester film of the present invention is superior in moisture and heat resistance as compared with a conventional polyester film, the solar cell backsheet including this film can have higher moisture and heat resistance than a conventional backsheet. Here, in the solar battery backsheet, in order for the backsheet to exhibit the high moisture and heat resistance effect of the polyester film of the present invention, the volume ratio of the P layer to the entire backsheet is preferably 10% or more. More preferably, it is 20% or more, more preferably 25% or more, still more preferably 30% or more, and particularly preferably 40% or more.

  Moreover, it is preferable that the solar cell backsheet using the polyester film of the present invention has an elongation retention rate of 15% or more after being left for 72 hours under conditions of a temperature of 125 ° C. and a humidity of 100% Rh. The elongation retention here is measured based on ASTM-D882 (1999), and is the condition of the breaking elongation E0 ′ of the backsheet before treatment, temperature 125 ° C., and humidity 100% Rh. This is a value obtained by the following formula (f ′) when the elongation at break after standing for 72 hours is E1 ′.

Elongation retention (%) = E1 ′ / E0 ′ × 100 (f ′)
E1 ′ is a value measured using a sample that was cut into the shape of a measurement piece and then treated for 72 hours under conditions of a temperature of 125 ° C. and a humidity of 100% Rh. More preferably, the elongation retention obtained by the above method is 40% or more, and more preferably 65% or more. In the solar cell backsheet using the polyester film of the present invention, if the elongation retention rate is less than 15%, for example, the deterioration proceeds when a solar cell equipped with the backsheet is used for a long period of time, and some impact is generated from the outside. Is added to the solar cell (for example, when a falling stone or the like hits the solar cell), the backsheet may break, which is not preferable. In the solar cell backsheet of the present invention, the durability of the solar cell during long-term use can be increased by setting the elongation retention rate to 15% or more.

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

  The solar cell of the present invention includes a solar cell backsheet using the polyester film of the present invention. The solar cell backsheet using the polyester film of the present invention can be made more durable or thinner than the conventional solar cell by taking advantage of its higher heat and moisture resistance than the conventional backsheet. An example of the configuration is shown in FIG. A power generating element connected with a lead wire (not shown in FIG. 1) for extracting electricity is sealed with a transparent filler 2 such as EVA resin, and is called a transparent substrate 4 such as glass and a back sheet 1. Although it is configured by bonding a resin sheet, it is not limited to this and can be used for any configuration.

  The power generating element 3 converts light energy of sunlight into electric energy, and is based on crystalline silicon, polycrystalline silicon, microcrystalline silicon, amorphous silicon, copper indium selenide, compound semiconductor, dye enhancement Arbitrary elements such as a sensitive system can be used in series or in parallel according to the desired voltage or current depending on the purpose.

  Since the substrate 4 having translucency is located on the outermost layer of the solar cell, a transparent material having high weather resistance, high contamination resistance, and high mechanical strength characteristics in addition to high transmittance is used. In the solar cell of the present invention, the light-transmitting substrate 4 can be made of any material as long as the above characteristics are satisfied. Examples thereof include glass, tetrafluoroethylene-ethylene copolymer (ETFE), and polyfluoride. Vinyl fluoride resin (PVF), polyvinylidene fluoride resin (PVDF), polytetrafluoroethylene resin (TFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polytrifluoroethylene chloride resin (CTFE) ), Fluorinated resins such as polyvinylidene fluoride resin, olefinic resins, acrylic resins, and mixtures thereof. In the case of glass, it is more preferable to use a tempered glass. Moreover, when using the resin-made translucent base material, what extended | stretched the said resin uniaxially or biaxially from a viewpoint of mechanical strength is used preferably.

  In addition, in order to impart adhesion to the EVA resin that is a sealing material agent for the power generation element, it is preferable to subject the surface to corona treatment, plasma treatment, ozone treatment, and easy adhesion treatment. Is called.

  The resin 2 for sealing the power generation element is formed by covering and fixing the unevenness of the surface of the power generation element with resin, protecting the power generation element from the external environment, and for the purpose of electrical insulation, as well as a transparent substrate or back In order to adhere to the sheet and the power generation element, a material having high transparency, high weather resistance, high adhesion, and high heat resistance is used. Examples thereof include ethylene-vinyl acetate copolymer (EVA), ethylene-methyl acrylate copolymer (EMA), ethylene-ethyl acrylate copolymer (EEA) resin, ethylene-methacrylic acid copolymer (EMAA), Ionomer resins, polyvinyl butyral resins, and mixtures thereof are preferably used. Among these resins, ethylene-vinyl acetate is more preferably used in terms of excellent balance of weather resistance, adhesiveness, filling property, heat resistance, cold resistance, and impact resistance.

  Here, in the solar cell of the present invention, the above-described solar cell backsheet 1 is installed on the back surface of the resin layer 2 in which the power generation element is sealed.

  As described above, by incorporating the solar cell backsheet using the polyester film of the present invention into the solar cell system, it becomes possible to obtain a highly durable solar cell system as compared with conventional solar cells. The solar cell of the present invention can be suitably used for various applications without being limited to outdoor use and indoor use such as a solar power generation system and a power source for small electronic components.

[Characteristic evaluation method]
The characteristics evaluation method is shown below. Those not specifically defined were evaluated by n number 1.

A. Composition analysis of polyester The P layer was hydrolyzed with alkali, each component was analyzed by gas chromatography or high performance liquid chromatography, and the composition ratio was determined from the peak area of each component. An example is shown below.
The dicarboxylic acid component and the component having a carboxylic acid group were measured by high performance liquid chromatography. The measurement conditions can be analyzed by a known method, and an example of the measurement conditions is shown below.

Equipment: Shimadzu LC-10A
Column: YMC-Pack ODS-A 150 × 4.6 mm S-5 μm
120A
Column temperature: 40 ° C
Flow rate: 1.2ml / min
Detector: UV 240nm
The quantification of the diol component and the component having a hydroxyl group can be analyzed by a known method using gas chromatography. An example of measurement conditions is shown below.

Apparatus: Shimadzu 9A (manufactured by Shimadzu Corporation)
Column: SUPELCOWAX-10 capillary column 30m
Column temperature: 140 ° C. to 250 ° C. (heating rate 5 ° C./min)
Flow rate: Nitrogen 25ml / min
Detector: FID
B. Intrinsic viscosity IV
The P layer was dissolved in 100 ml of orthochlorophenol (solution concentration C = 1.2 g / ml), and the viscosity of the solution at 25 ° C. was measured using an Ostwald viscometer. Similarly, the viscosity of the solvent was measured. [Η] was calculated by the following formula (3) using the obtained solution viscosity and solvent viscosity, and the obtained value was used as the intrinsic viscosity (IV).
ηsp / C = [η] + K [η] ² · C (3)
(Where ηsp = (solution viscosity / solvent viscosity) −1, K is the Huggins constant (assuming 0.343))
C. The number of carboxyl groups was measured by the method of Malice. (Reference M. J. Malice, F. Huizinga. Anal. Chim. Acta, 22 363 (1960)).

D. Quantification of alkali metal element content Quantification was performed by atomic absorption spectrometry (manufactured by Hitachi, Ltd .: polarized Zeeman atomic absorption photometer 180-80, frame: acetylene-air).

E. Quantitative determination of phosphorus element content The content was measured using a fluorescent X-ray analyzer (model number: 3270) manufactured by Rigaku Corporation.

F. Plane orientation coefficient R
Using T64000 manufactured by Horiba Jovin Yvon, the laser light source was Ar laser (514.5 nm, laser power 30 mW), the layer was irradiated with laser to the crystalline polyester layer (P layer), and P of 1615 cm ⁻¹ Raman band spectrum The peak intensity at the center of the layer thickness was determined. Intensity in the polarization arrangement in which the laser polarization is perpendicular to the film plane direction (I (ND)), Intensity in the polarization arrangement parallel to the longitudinal direction of the film plane (I (MD)), and parallel to the width direction of the film plane Intensity (I (TD)) in a polarization arrangement is obtained, and then I (MD) and I (TD) are divided by I (ND) to obtain orientation coefficients R (in the longitudinal direction and width direction of the film). MD) and R (TD) were determined. Furthermore, the average of R (MD) and R (TD) was calculated | required and it was set as the orientation coefficient R of the film surface direction.

G. Heat shrinkage rate The film was cut into a rectangle of length 150 mm × width 10 mm in the longitudinal direction (MD) and the width direction (TD) to obtain a sample. Marks were drawn on the sample at intervals of 100 mm, and a heat treatment was performed by placing in a hot air oven heated to 150 ° C. with a 3 g weight suspended for 30 minutes. The distance between the marked lines after the heat treatment was measured, and the thermal contraction rate in each of the film longitudinal direction and the width direction was calculated from the change in the distance between the marked lines before and after heating. For each film, 5 samples were measured in the longitudinal direction and the width direction for each film, and the average value was evaluated. The average value in the longitudinal direction and the width direction was defined as the heat shrinkage rate.

H. Linear expansion coefficient α
A thermomechanical measuring device TMA / SS6100 (manufactured by Seiko Instruments Inc.) was used, and a load of 3 g was applied to a sample having a sample width of 4 mm and a sample length (distance between chucks) of 20 mm. The temperature was raised from room temperature to 170 ° C. at a rate of temperature rise of 10 ° C./min and held for 10 minutes. Thereafter, the temperature was lowered to 20 ° C. at 10 ° C./min. At that time, the coefficient of thermal expansion was determined from the following equation from the amount of dimensional change from 150 ° C. to 50 ° C. in the temperature-decreasing portion. The thermal expansion coefficient was an average value in the film longitudinal direction and the width direction, and the n number was evaluated as 3.

Thermal expansion coefficient α (ppm / ° C.) = {(L150−L50) / L0} / ΔT × 100,000
L0: Length of film at 23 ° C. (mm)
L150: length of the film at 150 ° C. when the temperature is lowered (mm)
L50: Length of film (mm) at 50 ° C. when the temperature is lowered
ΔT: temperature change (150−50 = 100)
I. Glass transition temperature (Tg)
Using a differential scanning calorimeter “Robot DSC-RDC220” manufactured by Seiko Denshi Kogyo Co., Ltd. according to JIS K7122 (1987), a disk session “SSC / 5200” was used for data analysis. Measurement was carried out in the manner described above.

  5 mg of each sample was weighed in a sample pan, and the resin was heated from 25 ° C. to 300 ° C. at a heating rate of 20 ° C./min, held in that state for 5 minutes, and then rapidly cooled to 25 ° C. or lower. Immediately thereafter, the measurement was performed by increasing the temperature from room temperature to 300 ° C. at a temperature increase rate of 20 ° C./min. In the obtained differential scanning calorimetry chart, in the stepwise change portion of the glass transition, a straight line equidistant from the extended straight line of each baseline in the vertical axis direction and a curve of the step change portion of the glass transition It was calculated from the point of intersection.

J. et al. Melting point (Tm)
Using a method based on JIS K-7121 (1999), a differential scanning calorimeter “Robot DSC-RDC220” manufactured by Seiko Denshi Kogyo Co., Ltd. was used for data analysis, and a disk session “SSC / 5200” was used for data analysis. The measurement was carried out as follows.
Samples are weighed 5 mg each in a sample pan, and the resin is heated from 25 ° C. to 300 ° C. at a heating rate of 20 ° C./min (1stRUN), held in that state for 5 minutes, and then rapidly cooled to 25 ° C. or lower. The temperature at the peak top in the crystal melting peak of 2ndRun obtained by raising the temperature again from room temperature to 300 ° C. at a rate of temperature increase of 20 ° C./min was determined.

K. Breaking elongation, elongation retention rate The breaking elongation of the polyester film is based on ASTM-D882 (1999), when a sample is 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. The elongation at break was measured. In addition, the measurement was performed about 5 samples and it was set as the breaking elongation E0 with the average value. In addition, the elongation retention is obtained by cutting a sample into the shape of a measurement piece (1 cm × 20 cm), and then performing a treatment for 72 hours under a condition of 125 ° C. and humidity 100% Rh using a pressure cooker manufactured by Tabay Espec Co., Ltd. Thereafter, the breaking elongation of the sample after the treatment was measured based on ASTM-D882 (1999) when it was pulled at a chucking distance of 5 cm and a pulling speed of 300 mm / min. In addition, the measurement was performed about 5 samples and the average value was made into elongation at break E1. Using the obtained breaking elongations E0 and E1, the elongation retention was calculated by the following formula (2).

Elongation retention (%) = E1 / E0 × 100 (2)
In addition, the measurement was implemented about MD and TD of P layer of a film, respectively, and let the average value of MD and TD be elongation retention.

  Further, the breaking elongation of the backsheet was obtained by obtaining E1 ′ as the breaking elongation after standing for 72 hours under the conditions of breaking elongation E0 ′, temperature 125 ° C., and humidity 100% Rh of the backsheet before treatment in the same manner as described above. Thus, the elongation retention was calculated by the following formula (2 ′).

Elongation retention (%) = E1 ′ / E0 ′ × 100 (2 ′)
In addition, the measurement was performed for MD and TD of the P layer constituting the back sheet, and the average value of MD and TD was used as the elongation retention rate.
The obtained elongation retention was determined as follows.
When the elongation retention is 65% or more: S
When the elongation retention is 40% or more and less than 65%: A
When the elongation retention is 15% or more and less than 40%: B
When elongation retention is less than 15%: C
S to B are good, and S is the best among them.

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

Example 1
As a first step, 100 parts by mass of dimethyl terephthalate, 57.5 parts by mass of ethylene glycol, 0.06 parts by mass of magnesium acetate, 0.03 parts by mass of antimony trioxide are melted at 150 ° C. in a nitrogen atmosphere, and then stirred. The temperature was raised to 230 ° C. over 3 hours, and methanol was distilled off to complete the transesterification reaction.

  In this example, the second step was not applied.

  As a third step, the polymerization reaction was carried out at a final temperature of 285 ° C. and a degree of vacuum of 0.1 Torr to obtain a crystalline polyester having an intrinsic viscosity of 0.54 and a carboxyl group terminal group number of 13 equivalents / t. As a fourth step, the obtained polyethylene terephthalate was dried and crystallized at 160 ° C. for 6 hours, and then subjected to solid-phase polymerization at 220 ° C. and a vacuum degree of 0.3 Torr for 9 hours to obtain an intrinsic viscosity of 0.90 and a carboxyl group. A crystalline polyester having a terminal group number of 15 equivalents / t, a melting point of 255 ° C., and a glass transition temperature of Tg 83 ° C. was obtained.

  The obtained crystalline polyester was vacuum dried at a temperature of 180 ° C. for 3 hours and then supplied to an extruder, melted at a temperature of 280 ° C. in a nitrogen atmosphere, and introduced into a T die die. Next, the molten single layer sheet is extruded from the inside of the T die die into a molten single layer sheet, and the molten single layer sheet is closely cooled and solidified by an electrostatic application method on a drum maintained at a surface temperature of 25 ° C. A layer film was obtained. Subsequently, the unstretched single layer film was preheated with a roll group heated to a temperature of 80 ° C., and then stretched 3.8 times in the longitudinal direction (MD) using a heating roll having a temperature of 85 ° C. A uniaxially stretched film was obtained by cooling with a roll group at a temperature of 5 ° C. The both ends of the obtained uniaxially stretched film are held by clips while being guided to a preheating zone at a temperature of 80 ° C. in the tenter, and continuously 4.5 times in the film width direction (TD) in a heating zone at a temperature of 90 ° C. The film was stretched twice. Subsequently, heat treatment was performed at a temperature of 170 ° C. for 20 seconds in a heat treatment zone in the tenter. Subsequently, after uniform cooling, it was wound up to obtain a biaxially stretched film. Subsequently, the obtained film was cut into 31.5 cm in the MD and 32.4 cm in the TD so that the four sides of the metal frame and the four sides of the film overlapped with a rectangular metal frame with one side of 30 cm. The film was pasted and introduced into an oven heated to 160 ° C., and the film was heat treated for 60 seconds while shrinking 5% in MD and 8% in TD to obtain a film having a thickness of 50 μm equal to the size of the metal frame. The results of evaluating the properties of the obtained film are shown in Table 1-1. It was found that the film was excellent in heat and humidity resistance and thermal dimensional stability. Next, this film was used as the first layer, and as a bonding layer, 90 parts by mass of “Takelac (registered trademark)” A310 (manufactured by Mitsui Takeda Chemical Co., Ltd.), “Takenate (registered trademark)” A3 (Mitsui Takeda Chemical Co., Ltd.) A biaxially stretched polyester film “Lumirror (registered trademark)” S10 (manufactured by Toray Industries, Inc.) having a thickness of 50 μm was laminated thereon as a second layer. Next, the above-mentioned adhesive layer is applied onto the second layer, and a 12 μm-thick barrier locks “HGTS” (alumina-deposited PET film manufactured by Toray Film Processing Co., Ltd.) is placed on the opposite side of the second layer. And a back sheet having a thickness of 113 μm was formed. The obtained back sheet was evaluated for heat and moisture resistance. The results are shown in Table 1-1. It was found that the heat and heat resistance was excellent.

(Examples 3-5, 7-10)
A polyester film having a thickness of 50 μm was obtained in the same manner as in Example 1 except that the film formation conditions in steps (1) to (3) were as shown in Table 1-1. The results of evaluating the properties of the obtained film are shown in Table 1-1. It was found to be excellent in heat and humidity resistance and thermal dimensional stability.

  Moreover, the solar cell back sheet was obtained by the same method as Example 1. The results of evaluating the characteristics of the obtained backsheet are shown in Table 1-1. It was found to be excellent in heat and humidity resistance.

(Example 2)
As the second heat treatment step of step (3), the film unwound from the film roll obtained through steps (1) and (2) is heated to 160 ° C., and an oven having an inlet and an outlet is applied to the film. Except for continuous heat treatment so that the shrinkage of the film is 5% in MD and 8% in TD while winding at the oven outlet so that the tension is 50 N / m, A polyester film having a thickness of 50 μm was obtained. The properties of the obtained film were found to be equivalent to the film obtained in Example 1. Moreover, the solar cell back sheet was obtained by the same method as Example 1. The characteristics of the obtained back sheet were also found to be equivalent to those obtained in Example 1.

(Example 6)
In step (3) (second heat treatment step), the film unwound from the film roll obtained through steps (1) and (2) was heated to 160 ° C., and an oven having an inlet and an outlet was used. The same method as in Example 5 except that the film was continuously heat treated so that the shrinkage of the film was 3% in MD and 3% in TD while winding at the oven outlet so that the tension was 50 N / m. A polyester film having a thickness of 50 μm was obtained. The properties of the obtained film were found to be equivalent to the film obtained in Example 5. Further, a solar cell back sheet was obtained in the same manner as in Example 5. The characteristics of the obtained back sheet were also found to be equivalent to those obtained in Example 5.

(Example 11)
As an integrated heat treatment step in step (5) instead of steps (2) and (3), except that the film was shrunk to 3% in MD and 8% in TD while being heat treated at 170 ° C. in the heat treatment zone in the tenter. In the same manner as in Example 1, after gradually cooling uniformly, it was wound up to obtain a polyester film having a thickness of 50 μm. The result of having evaluated the characteristic of the obtained film is shown in Table 1-2. It was found to be excellent in heat and humidity resistance and thermal dimensional stability. Moreover, the solar cell back sheet was obtained by the same method as Example 1. The result of evaluating the characteristics of the obtained back sheet is shown in Table 1-2. It was found to be excellent in heat and humidity resistance.

(Examples 12 to 18)
A polyester film having a thickness of 50 μm was obtained in the same manner as in Example 11 except that the biaxial stretching step in step (4) and the integrated heat treatment step in step (5) were as shown in Table 1-2. The results of evaluating the properties of the obtained film are shown in the table. It was found to be excellent in heat and humidity resistance and thermal dimensional stability. Moreover, the solar cell back sheet was obtained by the same method as Example 1. The result of evaluating the characteristics of the obtained back sheet is shown in Table 1-2. It was found to be excellent in heat and humidity resistance.

(Example 19)
As the second step of the polymerization, 0.015 parts by mass of phosphoric acid (equivalent to 1.4 mol / t) and 0.031 parts by mass of sodium dihydrogen phosphate dihydrate (1.7 mol / t) after completion of the transesterification reaction. A polyester was obtained in the same manner as in Example 4 except that an ethylene glycol solution (PH5.0) in which 0.5 equivalent part of ethylene glycol was dissolved was added. The results of evaluating the properties of the obtained polyester are shown in Table 2. A polyester film having a thickness of 50 μm was obtained in the same manner as in Example 4 using the obtained polyester. The results of evaluating the properties of the obtained film are shown in Table 2. It was found that the heat resistance was excellent and the heat dimensional stability was excellent. Moreover, the solar cell back sheet was obtained by the same method as Example 1. Table 2 shows the results of evaluating the characteristics of the obtained backsheet. It was found that the heat and moisture resistance is superior.

(Examples 21 and 22)
A polyester film was obtained in the same manner as in Example 19 except that the polyester was polymerized so as to have the composition shown in Table 2. The results of evaluating the properties of the obtained film are shown in Table 2. It was found that the heat resistance was excellent and the heat dimensional stability was excellent. Moreover, the solar cell back sheet was obtained by the same method as Example 1. Table 2 shows the results of evaluating the characteristics of the obtained backsheet. It was found that the heat and moisture resistance is superior.

(Example 20)
As the second heat treatment step of step (3), the film unwound from the film roll obtained through steps (1) and (2) is heated to 170 ° C. and applied to the film using an oven having an inlet and an outlet. In the same manner as in Example 19, except that the film shrinkage was continuously 3% to MD and 4% to TD while winding at the oven outlet so that the tension was 50 N / m. A polyester film having a thickness of 50 μm was obtained. The characteristics of the obtained film were found to be equivalent to the film obtained in Example 19. Moreover, the solar cell back sheet was obtained by the same method as Example 1. The characteristics of the obtained back sheet were also found to be equivalent to those obtained in Example 19.

(Example 23)
A polyester film was obtained in the same manner as in Example 12 except that the polyester was polymerized so as to have the composition shown in Table 2. The results of evaluating the properties of the obtained film are shown in Table 2. It was found that the heat resistance was excellent and the heat dimensional stability was excellent. Moreover, the solar cell back sheet was obtained by the same method as Example 1. Table 2 shows the results of evaluating the characteristics of the obtained backsheet. It was found that the heat and moisture resistance is superior.

(Example 24)
As the first step of the polymerization, 100 parts by mass of dimethyl terephthalate, trimethyl trimellitic acid (added so that the molar ratio of dimethyl terephthalate / trimethyl trimellitic acid = 99.9 / 0.1), ethylene glycol 57.5 A polyester film was obtained in the same manner as in Example 4 except that a transesterification reaction was performed on parts by mass, 0.06 parts by mass of magnesium acetate, and 0.03 parts by mass of antimony trioxide. The results of evaluating the properties of the obtained film are shown in Table 2. It was found that the heat resistance and heat dimensional stability are superior. Moreover, the solar cell back sheet was obtained by the same method as Example 1. Table 2 shows the results of evaluating the characteristics of the obtained backsheet. It was found that the heat and moisture resistance is superior.

(Examples 26 and 27)
A polyester film was obtained in the same manner as in Example 24 except that the polyester was polymerized so as to have the composition shown in Table 2. The results of evaluating the properties of the obtained film are shown in Table 2. It was found that the heat resistance and heat dimensional stability are superior. Moreover, the solar cell back sheet was obtained by the same method as Example 1. Table 2 shows the results of evaluating the characteristics of the obtained backsheet. It was found that the heat and moisture resistance is superior.

(Example 25)
As the second heat treatment step of step (3), the film unwound from the film roll obtained through steps (1) and (2) is heated to 170 ° C. and applied to the film using an oven having an inlet and an outlet. In the same manner as in Example 24, except that the film was continuously heat-treated so that the shrinkage amount of the film was 3% in MD and 4% in TD while winding at the oven outlet so that the tension was 50 N / m. A polyester film having a thickness of 50 μm was obtained. The characteristics of the obtained film were found to be equivalent to the film obtained in Example 24. Moreover, the solar cell back sheet was obtained by the same method as Example 1. The characteristics of the obtained back sheet were also found to be equivalent to those obtained in Example 24.

(Examples 28 and 29)
A polyester film was obtained in the same manner as in Example 4 except that a hydrolysis-resistant agent was added so as to have the composition shown in Table 2. The results of evaluating the properties of the obtained film are shown in Table 2. It was found that the heat resistance was excellent and the heat dimensional stability was excellent. Moreover, the solar cell back sheet was obtained by the same method as Example 1. Table 2 shows the results of evaluating the characteristics of the obtained backsheet. It was found that the heat and moisture resistance is superior.

(Examples 30, 32, 33, 35)
A polyester film was obtained in the same manner as in Example 4 except that the polyester was polymerized to have the composition shown in Table 3. The results of evaluating the properties of the obtained film are shown in Table 3. It was found that the heat-and-moisture resistance was excellent and the thermal dimensional stability was excellent. Moreover, the solar cell back sheet was obtained by the same method as Example 1. Table 3 shows the results of evaluating the characteristics of the obtained backsheet. It was found that the heat and moisture resistance is very excellent.

(Example 31)
As the second heat treatment step of step (3), the film unwound from the film roll obtained through steps (1) and (2) is heated to 170 ° C. and applied to the film using an oven having an inlet and an outlet. Polyester in the same manner as in Example 30 except that the film was continuously heat-treated so that the shrinkage of the film was 3% in MD and 4% in TD while winding at the oven outlet so that the tension was 50 N / m. A film was obtained. The characteristics of the obtained film were found to be equivalent to the film obtained in Example 30. Moreover, the solar cell back sheet was obtained by the same method as Example 1. The characteristics of the obtained back sheet were also found to be equivalent to those obtained in Example 30.

(Examples 34 and 36)
A polyester film was obtained in the same manner as in Example 12 except that the polyester was polymerized to have the composition shown in Table 3. The results of evaluating the properties of the obtained film are shown in Table 3. It was found that the heat and moisture resistance was excellent and the thermal dimensional stability was excellent. Moreover, the solar cell back sheet was obtained by the same method as Example 1. The results of evaluating the characteristics of the obtained backsheet are shown in the table. It was found that the heat and moisture resistance is very excellent.

(Comparative Examples 1 and 2)
A polyester film was obtained in the same manner as in Example 1 except that the film forming conditions shown in Table 4 were used. The results of evaluating the properties of the obtained film are shown in Table 4. It turned out that it is inferior to heat-and-moisture resistance and a thermal dimensional stability table property. Moreover, the solar cell back sheet was obtained by the same method as Example 1. The results of evaluating the characteristics of the obtained backsheet are shown in the table. It was found that the heat and heat resistance was poor.

(Comparative Example 3)
As the second heat treatment step of step (3), the film unwound from the film roll obtained through steps (1) and (2) is heated to 170 ° C. and applied to the film using an oven having an inlet and an outlet. In the same manner as in Comparative Example 2 except that the film shrinkage was continuously 3% to MD and 4% to TD while winding at the oven outlet so that the tension was 50 N / m. A polyester film having a thickness of 50 μm was obtained. It was found that the properties of the obtained film were equivalent to the film obtained in Comparative Example 2. Moreover, the solar cell back sheet was obtained by the same method as Example 1. It was found that the characteristics of the obtained back sheet were equivalent to those obtained in Comparative Example 2.

(Comparative Example 4)
A polyester film was obtained in the same manner as in Example 1 except that the film forming process conditions shown in Table 4 were used. The results of evaluating the properties of the obtained film are shown in Table 4. Although it was excellent in thermal dimensional stability, it turned out that it is inferior to heat-and-moisture resistance. Moreover, the solar cell back sheet was obtained by the same method as Example 1. Table 4 shows the results of evaluating the characteristics of the obtained backsheet. It was found that the heat and heat resistance was poor.

(Comparative Example 5)
A polyester film was obtained in the same manner as in Example 1 except that the film forming process conditions shown in Table 4 were used. The results of evaluating the properties of the obtained film are shown in Table 4. Although it was excellent in heat-and-moisture resistance, it was found to be inferior in heat shrinkage. Moreover, although the solar cell backsheet was produced by the method similar to Example 1, since heat contraction rate was large, bonding was not successful and it was not able to evaluate.

(Comparative Example 6)
A polyester film was obtained in the same manner as in Example 1 except that the film forming process conditions shown in Table 4 were used. The results of evaluating the properties of the obtained film are shown in Table 4. Although it was excellent in thermal dimensional stability, it turned out that it is inferior to heat-and-moisture resistance. Moreover, the solar cell back sheet was obtained by the same method as Example 1. Table 4 shows the results of evaluating the characteristics of the obtained backsheet. It was found that the heat and heat resistance was poor.

(Comparative Example 7)
As the second heat treatment step of step (3), the film unwound from the film roll obtained through steps (1) and (2) is heated to 170 ° C. and applied to the film using an oven having an inlet and an outlet. In the same manner as in Comparative Example 6 except that the film shrinkage was continuously 3% to MD and 4% to TD while winding at the oven outlet so that the tension was 50 N / m. A polyester film having a thickness of 50 μm was obtained. The characteristics of the obtained film were found to be equivalent to the film obtained in Comparative Example 6. Moreover, the solar cell back sheet was obtained by the same method as Example 1. The characteristics of the obtained back sheet were also found to be equivalent to those obtained in Comparative Example 6.

(Comparative Examples 8 and 9)
A polyester film was obtained in the same manner as in Example 1 except that the film forming process conditions shown in Table 4 were used. The results of evaluating the properties of the obtained film are shown in Table 4. It was found that the heat resistance and heat dimensional stability were inferior. Moreover, the solar cell back sheet was obtained by the same method as Example 1. Table 4 shows the results of evaluating the characteristics of the obtained backsheet. It was found that the heat and heat resistance was poor.

  The polyester film of the present invention is made of a copper-clad laminate, a solar battery back sheet, an adhesive tape, a flexible printed circuit board, a membrane switch, a sheet heating element, or a flat cable, an electrically insulating material, a capacitor material, It can be suitably used for applications such as automotive materials and building materials where heat and heat resistance is important. In particular, it can be suitably used for an electrically insulating material (for example, a solar battery back sheet) used outdoors, an automotive material, a building material, and the like.

1: Solar cell backsheet 2: Resin 3 for sealing the power generation element 3: Power generation element 4: Transparent substrate

Claims (9)

Forming a sheet containing a crystalline polyester layer (P layer forming layer) whose main components are a dicarboxylic acid component and a diol component by a method including the following steps (1) to (3) in this order. A process for producing a polyester film characterized by
(1) Biaxial stretching step of biaxial stretching at an area magnification of 13.5 times or more in the longitudinal direction (MD) of the film and the width direction (TD) of the film at a temperature T1n satisfying the following formula (a) Tg ≦ T1n ≦ Tg + 40 ° C (a)
Tg: Glass transition temperature (° C.) of the crystalline polyester obtained by differential scanning calorimetry
(2) Gripping both ends of the film in the width direction with respect to a straight line connecting both ends of the film in the width direction so that the shift in the center of the film in the gravitational direction is 1 mm or more and 50 mm or less. First heat treatment step for performing heat treatment at a heat treatment temperature Th1 satisfying Tm−90 ° C. ≦ Th1 ≦ Tm−45 ° C. (b)
Tm: Melting point (° C.) of the crystalline polyester obtained by differential scanning calorimetry
(3) Under the condition of the heat treatment temperature Th2 satisfying the following formula (c), both MD and TD contract by 1% to 10% by the following processing method (3-1) or (3-2), Heat treatment step 150 ° C. ≦ Th2 ≦ Th1 (c)
(3-1) Cut out the film into sheets and paste it in a state where both MD and TD are loosened in a rectangular metal frame (3-2) Film installed between the winding roll and the winding roll Using an oven having an inlet and an outlet, continuous treatment is performed in a state in which the tension due to the dimensional change of the MD shrinkage of the film is relaxed due to the difference in speed between the unwinding roll and the winding roll. A sheet containing a crystalline polyester layer (P layer forming layer) whose main constituents are a dicarboxylic acid constituent and a diol constituent is formed by a method including the following steps (4) and (5) in this order. A method for producing a polyester film.
(4) Biaxial stretching step of biaxial stretching at an area magnification of 13.5 times or more in the longitudinal direction (MD) and the width direction (TD) of the film at a temperature T1n satisfying the following formula (d) Tg ≦ T1n ≦ Tg + 40 ° C. (d)
Tg: Glass transition temperature (° C.) of the crystalline polyester obtained by differential scanning calorimetry
(5) Grasp both ends of the film width direction with respect to a straight line connecting both ends of the film width direction so that the shift in the gravity direction of the film center portion is 1 mm or more and 50 mm or less. An integrated heat treatment step for shrinking from 1.0% to 10% in the MD and TD directions at the heat treatment temperature Th3 to be satisfied.
Tm−90 ° C. ≦ Th3 ≦ Tm−45 ° C. (e)
Tm: Melting point (° C.) of the crystalline polyester obtained by differential scanning calorimetry The crystalline polyester of the P layer forming layer contains phosphoric acid and alkali metal phosphate, the content of alkali metal phosphate is 0.5 mol / t or more, and the content of phosphoric acid is alkali metal phosphate The method for producing a polyester film according to claim 1, wherein the molar ratio is 0.25 times or more and 1.5 times or less of the ratio. The crystalline polyester of the P layer forming layer contains 0.005 mol% or more and 1.5 mol% or less of a component having a total of three or more carboxylic acid groups and hydroxyl groups as a copolymerization component with respect to all components. The manufacturing method of the polyester film in any one of claim | item 1-3. The crystalline polyester of the P-layer forming layer contains a hydrolysis-resistant agent, and the content of the hydrolysis-resistant agent is 0.01% by mass or more with respect to the P-layer forming layer. The manufacturing method of the polyester film of description. The plane orientation coefficient R in the Raman band spectrum method determined by the following formula is 5.0 or more and 10.0 or less, and after heat treatment at 150 ° C. for 30 minutes in the longitudinal direction (MD) of the film and the width direction (TD) of the film. The average thermal expansion rate is 0.8% or less, and the average linear expansion coefficient α of the linear expansion coefficient α (MD) of MD and TD from 50 ° C. to 150 ° C. is 22 ppm / The polyester film manufactured by the method in any one of Claims 1-5 containing the crystalline polyester layer (P layer) whose main component which is below degrees C is a dicarboxylic acid component and a diol component.
R = (R (MD) + R (TD)) / 2
R (MD) = I (MD) / I (ND)
R (TD) = I (TD) / I (ND)
(Here, I (ND), I (MD), and I (TD) are respectively the intensities in the polarization arrangement perpendicular to the film plane direction of the Raman band spectrum of 1615 cm ⁻¹ in laser Raman spectroscopy (I (ND)), intensity in a polarization arrangement parallel to the longitudinal direction of the film plane (I (MD)), and intensity in a polarization arrangement parallel to the width direction of the film plane (I (TD)) The solar cell backsheet using the polyester film of Claim 6. A solar cell using the solar cell backsheet according to claim 7. A flexible substrate using the polyester film according to claim 6.

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