TWI577721B - Polyester film and method for manufacturing the same - Google Patents

Description

Polyester film and method of producing the same

The present invention relates to a biaxially oriented polyester film which is particularly excellent in thermal dimensional stability in a high temperature range. The biaxially oriented polyester film of the present invention can be suitably used for a base film for a flexible member or the like. The biaxially oriented polyester film of the present invention, in particular, a substrate film which is an organic electroluminescence (hereinafter sometimes abbreviated as EL) display, an electronic paper, an organic EL illumination, an organic solar cell, and a dye-sensitized solar cell. In this case, a substrate film having small dimensional changes in various steps, small curl, and good processing suitability can be obtained.

In recent years, various electronic components have been used in applications such as light weight, thin film formation, and freedom of shape, and the flexibility has been attracting attention. For the flexibility of electronic components, instead of the glass which is a conventional substrate, there is a method of using a plastic film. However, the plastic film has a large thermal expansion coefficient or thermal shrinkage, and is inferior in thermal dimensional stability, and is liable to cause curling.

Biaxially oriented polyester film, which utilizes its excellent thermal properties, dimensional stability, mechanical properties, electrical properties, heat resistance and surface properties, is widely used as magnetic recording materials, packaging materials, electrical insulating materials, various photo materials, graphic arts. a variety of materials or optical display materials, etc. The substrate used for the purpose. However, the substrate film for a flexible member needs to further enhance physical properties. In order to improve the properties of the polyester film, a method of blending a polyester with another thermoplastic resin (Patent Document 1) and a method of reducing the coefficient of thermal expansion by adding particles at a high concentration have been disclosed (Patent Document 2). A method of relaxing and annealing treatment in order to reduce the heat shrinkage rate (Patent Document 3).

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2003-101166

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2004-35720

[Patent Document 3] Japanese Patent Laid-Open No. 3-67627

However, in the method of blending a thermoplastic resin described in Patent Document 1, since the polyester is difficult to be aligned, the thermal expansion coefficient cannot be sufficiently lowered. Further, in the method disclosed in Patent Document 2, since the stretchability is deteriorated when the particles are added at a high concentration, the thermal expansion coefficient cannot be sufficiently lowered. Further, the technique described in Patent Document 3 does not reduce the coefficient of thermal expansion for the purpose of reducing the heat shrinkage rate.

As described above, it is difficult to have both low thermal expansion and low thermal shrinkage.

The object of the present invention is to solve the aforementioned problems, in particular to obtain a biaxially oriented polyester film having excellent thermal dimensional stability in a high temperature range, and to provide a biaxially oriented polyester film having small curl and good processing suitability, particularly Reduced in various steps when using a substrate film for flexible components The size of the step changes.

The present invention has the following features in order to achieve the aforementioned objects.

(1) A polyester film obtained by using a polyester having a crystallization index (?Tcg) of 10 ° C or more and 60 ° C or less, and having a surface alignment coefficient (fn) of 0.15 or more and 0.28 or less and crystallization The degree (Xc (%)) is 35% or less, and the heat shrinkage ratio of 180 ° C in the longitudinal direction and the transverse direction of the film is 0% to 1.5%, respectively.

(2) The polyester film according to (1), wherein a value (fn/Xc) obtained by dividing a surface alignment coefficient (fn) by a degree of crystallinity (Xc) is 0.50 or more.

(3) The polyester film according to (1) or (2), wherein the film has a haze value of from 0 to 3%.

(4) The polyester film according to any one of (1) to (3), wherein the polyester contains a nucleating agent, and the content of the nucleating agent is 0.01 parts by mass or more based on 100 parts by mass of the polyester. 2 parts by mass or less.

(5) The polyester film according to any one of (1) to (4) wherein the polyester is polyethylene terephthalate.

(6) A film for an organic EL substrate, which is obtained by using the polyester film according to any one of (1) to (5).

(7) A film for a flexible solar cell substrate, which is obtained by using the polyester film according to any one of (1) to (5).

(8) The method for producing a polyester film according to any one of (1) to (5), wherein the polyester resin is melt-extruded and cooled and solidified to form an unstretched film, and then, The unstretched film biaxial stretching Thereafter, after heat setting at a heat setting temperature Ths (° C.) of 180 to 220° C., the film is cooled at a temperature of 35° C. or lower, and then subjected to a relaxation annealing treatment, wherein the polyester resin contains at least one nucleating agent. The relaxation annealing treatment is performed at a temperature (Ths-25) to (Ths-5) °C.

According to the present invention, a polyester film excellent in thermal dimensional stability in a high temperature range can be obtained. When it is used as a base material film for a flexible element, it can be reduced in dimensional change in various steps, and in particular, a polyester film excellent in flatness of curling during annealing can be obtained.

[Formation of the Invention]

In order to satisfy the thermal dimensional stability in the high temperature range, the polyester film of the present invention is important in that the crystallization index (hereinafter referred to as ΔTcg) is 10° C. or more and 60° C. or less. When ΔTcg is in the above range, the thermal dimensional stability at a high temperature is improved in the polyester film by promoting the formation of microcrystals. In particular, the high-temperature heat shrinkage before the relaxation annealing step (the step of annealing treatment while relaxing) is small, and as a result, the planarity of the film is improved in the relaxation annealing step. When ΔTcg is less than 10 ° C, the crystallinity becomes too high, and the deterioration of the stretchability is accompanied by the difficulty in film formation. Further, when ΔTcg exceeds 60 ° C, high-temperature heat shrinkage increases, and thermal dimensional stability at high temperatures may be insufficient. ΔTcg is more preferably 30 to 50 °C. As a method of making ΔTcg into the above range, at least one or more nucleating agents are contained in the polyester, and nucleation is used. It is preferred that the effect of the agent is adjusted so that the crystallization rate becomes faster. The nucleating agent can also be used as a compound for use as a transesterification catalyst or a polymerization catalyst. For example, a method in which lithium acetate, magnesium acetate, potassium acetate, phosphorous acid, phosphonic acid, phosphinic acid or the like, cerium oxide or cerium oxide is present during transesterification or polymerization is effective. A particularly preferred combination is magnesium acetate and phosphonic acid (or a derivative thereof) and cerium oxide. Examples of the phosphonic acid (or a derivative thereof) include phenylphosphonic acid and dimethylphenyl phosphate.

Further, a method of increasing the crystallization rate by adding a nucleating agent other than the above compound to the polyester is also effective. The nucleating agent is preferably selected from the group consisting of talc, an aliphatic carboxylic acid decylamine, an aliphatic carboxylic acid salt, an aliphatic alcohol, an aliphatic carboxylic acid ester, an aliphatic/aromatic carboxylic acid hydrazine, and a sorbitol system. A group of compounds, organophosphorus oxides. The polyester of the present invention is particularly preferably a nucleating agent containing at least one selected from the group consisting of aliphatic carboxylic acid amides, aliphatic carboxylic acid salts, and sorbitol compounds. Here, the preferable content of the nucleating agent is such that the polyester is used as 100 parts by mass, and the nucleating agent is 0.01 parts by mass or more and 2 parts by mass or less, more preferably 0.1 part by mass or more and 2 parts by mass or more of the nucleating agent. the following. When the content of the nucleating agent is less than 0.01 parts by mass, the effect may not be sufficiently exhibited, and when the nucleating agent is contained in an amount exceeding 2 parts by mass, the transparency may be impaired.

Here, as the aliphatic carboxylic acid amide, for example, decyl laurate, decyl palmitate, decyl oleate, decylamine stearate, decyl citrate, decyl phthalate, ricinoleic acid can be used. An aliphatic monocarboxylic acid amide such as guanamine or hydroxystearic acid amide; for example, N-oleyl palmitate, N-oleyl oleate, N-oleyl stearate, N-stearyl oleate, N-stearyl stearate, N-stearyl erucamide, hydroxymethyl stearin An N-substituted aliphatic monocarboxylic acid amide such as decylamine or hydroxymethyl behenyl phthalate; for example, decyl methylene bis-stearate, decyl ammonium bis-laurate, ethyl Bisuccinic acid decylamine, ethyl bis-oleic acid decylamine, ethyl bis-stearate decylamine, ethyl erucic acid decylamine, ethyl bis-docosic acid amide, ethylene ethyl Isohexyl isostearate, decylamine ethyl hydroxystearate, decyl butyl bis-stearate, decyl hexamethylene bisoleate, decyl hexamethylene bis-stearate, six Methylenebis-docosic acid decylamine, hexamethylene bishydroxystearate decylamine, m-xylylene bis-stearate decylamine, m-xylylene bis-12-hydroxystearic acid decylamine Aliphatic dicarboxylic acid amides such as N,N'-dioleyl sebacate, N,N'-dioleyl adipate, N,N'-distearyl Ammonium adipate, N,N'-distearoyl sebacate, N,N'-distearylisophthalate, N,N'-distearate terephthalic acid N-substituted aliphatic carboxylic acid bis-amines such as guanamine; such as N-butyl-N'-stearyl urea, N-propyl-N'-stearyl urea, N-stear -N'-stearyl urea, N-phenyl-N'-stearyl urea, benzyl dimethyl stearyl urea, stilbene double stearyl urea, hexamethylene double N-substituted ureas such as stearyl urea, diphenylmethane bis-stearyl urea, diphenylmethane dilauryl urea. These may also be one type or a mixture of two or more types. Among them, aliphatic monocarboxylic acid decylamines, N-substituted aliphatic monocarboxylic acid decylamines, and aliphatic dicarboxylic acid decylamines are particularly suitable, and in particular, palmitic acid amide, stearic acid decylamine and mustard are suitable. Acid amide, decyl octadecylamine, ricinoleic acid decylamine, hydroxystearic acid amide, N-oleyl palmitate, N-stearyl erucamide, ethyl bis-stearic acid Indoleamine, ethyl bis-oleic acid decylamine, ethyl bis-laurate decylamine, ethyl erucic acid decylamine, m-xylylene bis-stearate decylamine, m-xylylene bis -12-hydroxystearic acid decylamine.

As a specific example of the aliphatic carboxylate, an acetate such as sodium acetate, potassium acetate, magnesium acetate or calcium acetate; sodium laurate, potassium laurate, potassium hydrogen laurate, magnesium laurate, calcium laurate, and laurel may be used. a laurate of zinc citrate or silver laurate; a meat of lithium myristate, sodium myristate, potassium hydrogen myristate, magnesium myristate, calcium myristate, zinc myristate, silver myristate, etc. Myristic acid salt; palmitate of lithium palmitate, potassium palmitate, magnesium palmitate, calcium palmitate, zinc palmitate, copper palmitate, lead palmitate, barium palmitate, cobalt palmitate, etc.; sodium oleate, oil Acid acid potassium salt, magnesium oleate, calcium oleate, zinc oleate, lead oleate, barium oleate, copper oleate, nickel oleate, etc.; sodium stearate, lithium stearate, magnesium stearate , stearic acid calcium, barium stearate, aluminum stearate, barium stearate, lead stearate, nickel stearate, barium stearate, etc.; sodium isostearate, iso-hard Potassium oleate, magnesium isostearate, calcium isostearate, barium isostearate, aluminum isostearate, zinc isostearate, nickel isostearate, etc.; Twenty-two of sodium diperate, potassium behenate, magnesium behenate, calcium behenate, barium behenate, aluminum behenate, zinc behenate, nickel behenate Acid salt; sodium montanic acid, potassium montanate, magnesium montanate, calcium montanate, barium montanate, aluminum montanate, zinc montanate, nickel montanate, etc. These may also be one type or a mixture of two or more types. In particular, salts of stearic acid or salts of montanic acid are particularly suitable, and sodium stearate, potassium stearate, zinc stearate, barium stearate, sodium montanate, and the like are particularly suitable.

As a specific example of the aliphatic alcohol, pentadecyl alcohol, cetyl alcohol, heptadecyl alcohol, stearyl alcohol, nonadecanol, eicosyl alcohol, wax alcohol, thirty An aliphatic monool such as an alcohol; 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-nonanediol, etc. Aliphatic polyols; cyclic alcohols such as cyclopentane-1,2-diol, cyclohexane-1,2-diol, cyclohexane-1,4-diol, and the like. These may also be one type or a mixture of two or more types. It is especially suitable for aliphatic monoalcohols, especially stearyl alcohol.

Specific examples of the aliphatic carboxylic acid esters include cetyl laurate, benzammonium laurate, cetyl myristate, benzammonium myristate, isopropylidene palmitate, palm. Dodecyl acid ester, tetradecyl palmitate, pentadecyl palmitate, octadecyl palmitate, cetyl palmitate, phenyl palmitate, benzammonium palmitate, cetyl stearate, An aliphatic monocarboxylic acid ester such as ethyl laurate; a monoester of ethylene glycol such as monolauric acid diol, monopalmitic acid diol or monostearic acid diol; dilauric acid diol; a diester of ethylene glycol such as dipalmitic acid diol or distearic acid diol; glycerin such as glycerol monolaurate, glyceryl monomyristate, glycerol monopalmitate or glyceryl monostearate Monoesters; diesters of glycerol such as dilauric acid glyceride, dimyristate, dipalmitate, glyceryl distearate; glycerol trilaurate, glyceryl trimyristate , tripalmitin, tristearate, glyceryl dioleate palmitolate, glyceryl distearate palmitoleate, glycerol Stearate triesters of glycerol oleate and the like. These may also be one type or a mixture of two or more types.

As a specific example of the aliphatic/aromatic carboxylic acid cerium, ceric acid dibenzoic acid cerium can be used. As a specific example of the melamine-based compound, melamine cyanurate or melamine polyphosphate can be used as the phenylphosphonic acid metal salt. Specific examples, zinc phenylphosphonate, phenylphosphonic acid can be used. Calcium salt, magnesium phenylphosphonate, magnesium phenylphosphonate, and the like.

Examples of the sorbitol-based compound include 1,3-bis(P-methylbenzylidene)sorbitol and 2,4-di(P-methylbenzylidene)sorbitol; 3-dibenzylidene sorbitol, 2,4-dibenzylidene sorbitol, 1,3-bis(P-ethyldiphenylmethylene)sorbitol, 2,4-di ( P-ethyldibenzylidene) sorbitol or the like.

Examples of the organophosphorus compound include sodium bis(4-t-butylphenyl) phosphate and sodium-2,2'-methylenebis(4,6-di-t-butylphenyl)phosphate. a mixture of a cyclic organophosphate basic polyvalent metal salt and one selected from the group consisting of an alkali metal carboxylate, an alkali metal β-diketone salt, and an alkali metal β-keto acetate salt; .

In the above, an aliphatic carboxylic acid decylamine, an aliphatic carboxylic acid salt, or a sorbitol-based compound is particularly preferably used from the viewpoint of transparency and heat resistance.

In the polyester film of the present invention, it is important that the film has a surface alignment coefficient (fn) of 0.15 or more and 0.28 or less. When the surface alignment coefficient (fn) is less than 0.15, the alignment property is lowered, and there is a case where sufficient low thermal expansion cannot be achieved. When the surface alignment coefficient (fn) exceeds 0.28, the film formation property is deteriorated due to excessively high alignment, and it is difficult to form a film. In the present invention, it is important to have both low thermal expansion and low thermal shrinkage. In order to achieve low thermal expansion, it is necessary to make the film highly aligned, but it is less desirable to reduce the heat shrinkage rate by highly aligning the film. Therefore, it is necessary to adjust ΔTcg as described above to lower the heat shrinkage rate. The surface alignment coefficient (fn) can be controlled by the film forming conditions, but in particular, the conditions of the heat treatment step and the stretching ratio are greatly affected. When the heat treatment temperature becomes high, because Since the thermal crystallization is promoted, there is a tendency that the surface alignment coefficient (fn) increases. Further, since the alignment in the plane is increased by increasing the stretching ratio, the surface alignment coefficient (fn) tends to increase. In particular, when the polyester is polyethylene terephthalate, the surface alignment coefficient (fn) is preferably 0.155 or more and 0.175 or less, more preferably 0.160 or more and 0.175 or less.

The polyester film of the present invention is important in that the degree of crystallization (Xc (%)) is 35% or less. When it is more than 35%, the crystal orientation is increased, and the alignment in the in-plane direction is lowered, and sufficient low thermal expansion cannot be achieved. In particular, the degree of crystallization (Xc (%)) is preferably 30% or less. The degree of crystallization (Xc (%)), which is greatly affected by the conditions of ΔTcg and the heat treatment step and the relaxation annealing step. For example, the degree of crystallization can be lowered by lowering the heat setting temperature in the heat treatment step.

The polyester film of the present invention has a heat shrinkage ratio of from 0 to 1.5%, preferably from 0 to 1.2%, more preferably from 0 to 1.0%, particularly preferably from 0 to 0.7%, in the longitudinal direction and the transverse direction at 180 ° C. It is 0~0.4%. When the heat shrinkage ratio of 180 ° C in the longitudinal direction and the transverse direction is within the above range, the curl caused by heat of various steps at the time of forming the element layer can be reduced, and since the dimensional change becomes small, peeling from the element layer can be suppressed, and thus, More ideal.

The heat shrinkage rate of 180 ° C in the longitudinal direction and the transverse direction can be controlled by a predetermined film forming condition to be described later, but it is particularly preferable to control the conditions of the relaxation annealing step. When the heat shrinkage rate of the film before the annealing step is large, the heat shrinkage rate of the film of the present invention becomes large. In order to make the heat shrinkage rate 1.5% or less, the heat shrinkage ratio of 180 ° C of the film before the annealing step is preferably 0 to 8.0%. When the heat shrinkage rate of the film at 180 ° C before the annealing step exceeds 8.0%, the heat shrinkage rate becomes too large, so even after relaxation In the annealing treatment step, there is also a case where the heat shrinkage rate cannot be reduced to the range specified in the present case. Further, in the relaxation annealing step in which the thermal dimensional stability in the high temperature region is insufficient, there is a case where the shrinkage becomes large, wrinkles, undulations, curls, and flatness are deteriorated. The heat shrinkage ratio at 180 ° C of the film before the relaxation annealing is preferably 0 to 7.0%, more preferably 0 to 5.0%. The heat shrinkage rate of the film before the annealing step is affected by the stretching ratio or the heat treatment step, but by setting ΔTcg to a predetermined range, the heat shrinkage of the film before the relaxation annealing step can be reduced even when the alignment is high. The rate is such that the heat shrinkage rate at 180 ° C is 0 to 1.5%, and the planarity in the relaxation annealing step can be maintained.

The polyester film of the present invention preferably has a thermal expansion coefficient of from 0 to 25 ppm/°C in a longitudinal direction and a transverse direction at a temperature of from 50 to 150 °C. When the thermal expansion coefficient of the longitudinal direction and the transverse direction of the temperature of 50 to 150 ° C is within the foregoing range, the dimensional change in the relaxation annealing step can be reduced and the planarity can be maintained, and the element layer can be suppressed at the time of forming the element layer. It is preferable to peel off and deform by deformation. The thermal expansion coefficient of the longitudinal direction and the transverse direction at 50 to 150 ° C is preferably 0 to 22 ppm / ° C, and is particularly preferably 0 to 18 ppm / ° C. It has been found that the coefficient of thermal expansion is related to the surface alignment coefficient or the degree of crystallization, and the coefficient of thermal expansion of the present invention can be obtained by the film forming conditions described later, and can be obtained, in particular, by controlling the stretching ratio and the heat treatment conditions.

The polyester used in the present invention is a polymer containing 80% by mass of a polymer obtained by polycondensation of a diol and a dicarboxylic acid. The dicarboxylic acid here is represented by terephthalic acid, isophthalic acid, phthalic acid, naphthalene dicarboxylic acid, adipic acid, sebacic acid, etc. The alcohol is represented by ethylene glycol, trimethyl glycol, tetramethyl glycol, cyclohexane dimethanol or the like.

As a specific polymer, for example, polytrimethylene terephthalate, polyethylene terephthalate, polytrimethylene terephthalate, polyethylene isophthalate, polytetramethylene can be used. Terephthalic acid ester, poly-p-oxybenzoic acid ester, poly-1,4-cyclobutylene terephthalate dimethyl ester, poly 2,6-naphthalenedicarboxylate, and the like.

It is obvious that the resins may be homopolymers or copolymers. In the case of a copolymer, as a copolymerization component, for example, diethylene glycol, neopentyl glycol, polyolefin-based diol, etc. may be contained. a diol component; a dicarboxylic acid component such as adipic acid, sebacic acid, phthalic acid, isophthalic acid or 2,6-naphthalenedicarboxylic acid; hydroxybenzoic acid, 6-hydroxy-2 naphthoic acid, etc. a hydroxycarboxylic acid component.

In the case of the present invention, polyethylene terephthalate, polyethylene-2,6-naphthalate, and copolymers thereof are preferred, and blends with other polymers, even laminates, may also be used. Such as the complex. In particular, a polyester having polyethylene terephthalate (hereinafter sometimes referred to as PET) as a main component is preferable from the viewpoints of mechanical strength, heat resistance, chemical resistance, durability, and the like. Therefore, PET is preferable in order to improve the effect of the present invention. The polyester may also contain various additives such as an antioxidant, a heat stabilizer, a lubricant, an anti-caking agent, an antistatic agent, inorganic particles, and organic particles. Of course, the film of the present invention may be a single film, or other polymer layers may be laminated thereon, for example, polyester, polyamide, polyvinyl chloride polymer, or the like. Moreover, it is also possible to attach a polyurethane, a polyacrylate, a polyester, a polyamide, etc. to the surface of the film. The coating layer of the resin of the watch is used as a film after surface modification. Further, surface activation treatment such as corona discharge treatment may be performed on the surface of the film.

In the polyester film of the present invention, the value (fn/Xc) of the surface alignment coefficient (fn) divided by the degree of crystallinity (Xc) is preferably 0.50 or more. When the value (fn/Xc) of the surface alignment coefficient (fn) divided by the degree of crystallinity (Xc) is in the above range, the coefficient of thermal expansion can be reduced and the thermal dimensional stability can be improved, which is preferable. The value is more preferably 0.55 or more. (fn/Xc) of the present invention can be obtained by the film forming conditions described later, and can be obtained, in particular, by controlling the stretching ratio, the heat treatment conditions, and the relaxation annealing temperature.

The polyester film of the present invention preferably has a film haze value of from 0 to 5%. When the film haze value exceeds 5%, there is a case where the transparency is low and the performance of the organic EL or thin film solar cell is insufficient. The haze value of the film is preferably from 0 to 3%, particularly preferably from 0 to 1%. When the film haze value is a polyester having a high crystallization index (?Tcg), it may become large. Further, it can be controlled according to the added concentration of the added particles or the average particle diameter. When the average particle diameter of the added particles is from 1 nm to 3,000 nm, it is easy to make the film haze value into the above range, and it is preferable from the viewpoint of transparency of the film. More preferably, it is 1 nm to 2000 nm, and particularly preferably 1 nm to 1500 nm. Further, the particle concentration of the added particles is preferably from 0.0 part by mass to 1.0 part by mass based on 100 parts by mass of the polyester. In addition, as long as the particle diameter and the particle concentration are within the range described above, two or more kinds of particles having different mixed particle diameters may be used.

In the biaxially oriented polyester film of the present invention, the amount of change in the haze value of the film at a temperature of 180 ° C for 30 minutes is preferably 0.0 to 3.0%. When the amount of change in the haze value of the film is within the above range, transparency can be maintained during the formation of the element layer, which is preferable. When the film haze value changes When the amount is more than 3.0%, the transparency is deteriorated during the formation of the element layer, and the power generation efficiency is deteriorated and the luminous efficiency is deteriorated. The amount of change in the haze value of the film is more preferably 0 to 1.5%. When the polyester film is heat-treated at a high temperature, the low molecular weight component is precipitated as an oligomer, and the film haze value is increased. In the biaxially oriented polyester film of the present invention, a polyester resin from which an oligomer component is removed is preferably used as a raw material. As a method of producing the polyester resin from which the oligomer component is removed, for example, the technique disclosed in JP-A-2005-53968 can be employed.

The polyester film of the present invention preferably has a film thickness of 25 to 150 μm. When the thickness is less than 25 μm, the rigidity of the film is lowered, and in the case of an organic EL or a solar cell, folding or wrinkling is likely to occur. When it exceeds 150 μm, the film loses flexibility and the flexibility is impaired. The film thickness is preferably 75 to 125 μm. The film thickness can be controlled according to the film forming conditions.

Hereinafter, the method for producing a film of the present invention will be specifically described. Hereinafter, PET will be described as a specific example, but it is not limited thereto.

First, prepare the PET resin to be used. PET is manufactured by any of the following procedures. That is, (1) terephthalic acid and ethylene glycol are used as raw materials, and low molecular weight PET or oligomer is obtained by direct esterification reaction, and then antimony trioxide or titanium compound is used by a procedure for obtaining a polymer by a polycondensation reaction of a catalyst, or (2) using dimethyl terephthalate and ethylene glycol as a raw material, obtaining a low molecular weight body by transesterification, and then adding antimony trioxide Or a titanium compound is used in a polycondensation reaction of a catalyst to obtain a polymer.

Here, the esterification can be carried out even without a catalyst. However, in the transesterification reaction, a compound such as manganese, calcium, magnesium, zinc, lithium or titanium is usually used for the catalyst to carry out a reaction. Further, after the transesterification reaction is substantially completed, a phosphorus compound may be added for the purpose of inerting the catalyst of the reaction.

In the case of promoting the crystallization of the PET film of the present invention, lithium acetate, magnesium acetate, potassium acetate, phosphorous acid, phosphonic acid, phosphinic acid or derivatives thereof, cerium oxide are present during transesterification and polymerization. , yttrium oxide is preferred. In the case of using a nucleating agent other than the above-mentioned compound, the nucleating agent and the PET resin are previously subjected to a vented biaxial kneading extruder from the viewpoint of handleability and dispersibility, and kneaded into PET and motherd. Granulation is preferred. As a method of setting ΔTcg to a predetermined range, it is preferred to use a PET pellet containing a nucleating agent produced by the above method and a PET resin substantially free of a nucleating agent to adjust the nucleating agent content. method.

In order to impart slipperiness, abrasion resistance, scratch resistance, and the like to the surface of the PET film, it is also preferable to add inorganic particles or organic particles, for example, adding clay, mica, titanium oxide, calcium carbonate, kaolin, talc. Inorganic particles such as wet cerium oxide, dry cerium oxide, colloidal cerium oxide, calcium phosphate, barium sulfate, aluminum oxide, and zirconia; acrylic acid, styrene resin, thermosetting resin, anthrone, and Organic particles as a constituent component such as a quinone imine compound; and particles (so-called internal particles) precipitated by a catalyst or the like added during the PET polymerization reaction.

PET which is a constituent of the PET film of the present invention In the case where the inert particles are contained, it is preferred to disperse the inert particles in the form of a slurry in a predetermined ratio in ethylene glycol, and to add the ethylene glycol at the time of polymerization. When the inert particles are added, for example, when the inert particles are synthesized, the obtained hydrosol or the alcohol sol-state particles are temporarily dried, and the particles have good dispersibility. Further, the aqueous slurry of the inert particles is directly mixed with the PET pellets, and a vented biaxial kneading extruder is used, and kneading is also effective for the method of PET. As a method of adjusting the content of the inert particles, a masterbatch of a high concentration of inert particles is produced by the above method, and is diluted with PET which does not substantially contain inert particles at the time of film formation, and the method of adjusting the content of the inert particles is effective. .

Next, the obtained pellets (PET pellets containing a nucleating agent) and raw PET chips (PET resin chips not containing a nucleating agent) were dried under reduced pressure at a temperature of 180 ° C for 3 hours or more, and then The viscosity is not lowered, and it is supplied to an extruder having a temperature of 270 to 320 ° C under a nitrogen flow or a reduced pressure, and is melt-extruded by a slit type mold. The casting roll was cooled and solidified to obtain an unstretched film. At this time, in order to remove foreign matter or a deteriorated polymer, various filters are preferably used, for example, a filter containing materials such as sintered metal, porous ceramics, sand, and metal mesh. Further, a gear pump may be provided in order to increase the quantitative supply as needed. In the case of laminating a film, a plurality of different polymers are melt-laminated by using two or more extruders and a branch pipe or a junction block. In order to make the intrinsic viscosity of the polyester constituting the film into a preferable range, the inherent viscosity of the PET pellet containing the nucleating agent and the PET resin pellet not containing the nucleating agent is preferably 0.5 to 1.5 dl/g.

Furthermore, as long as it does not hinder the effects of the present invention Various additives may also be added, for example, compatibility reagents, plasticizers, weathering agents, antioxidants, heat stabilizers, lubricants, antistatic agents, brighteners, colorants, conductive agents, ultraviolet absorbers, flame retardants Agents, flame retardant additives, pigments and dyes.

Next, the sheet formed as described above was biaxially stretched. The biaxial stretching is performed in the longitudinal direction and the transverse direction, and heat treatment is performed.

Examples of the stretched form include a secondary biaxial stretching method such as transverse stretching after longitudinal stretching, or a simultaneous biaxial stretching while simultaneously stretching the longitudinal direction and the transverse direction using a simultaneous biaxial tenter. The stretching method is even a method of combining the sequential biaxial stretching method and the simultaneous biaxial stretching method. The heat treatment after the stretching step is controlled to the thermal expansion coefficient or the heat shrinkage ratio within the scope of the present invention, and the molecular chain alignment is not caused by excessive heat treatment, and the heat treatment is preferably carried out efficiently.

In the following, a longitudinal stretching machine in which a plurality of rolls are disposed is used for the unstretched film, and the longitudinal direction is stretched by the circumferential speed difference of the rolls (MD stretching), and then the transverse stretching is performed by a tenter (TD stretching). The biaxial stretching method is further described in detail.

First, the unstretched film was subjected to MD stretching. The stretching temperature is preferably in the range of glass transition temperature (Tg) to (Tg+40) °C, more preferably in the range of (Tg+5) to (Tg+30) °C, and particularly preferably in (Tg+10). The range of ~(Tg+20) °C is heated by the heating roller group, and the stretching is preferably 3.0 to 4.0 times, more preferably 3.2 to 4.0 times, and particularly preferably 3.5 to 4.0 times in the machine direction (MD). After that, it is preferred to cool the cooling roll group at a temperature of 20 to 50 °C. Among them, when it is carried out at 3.2 to 4.0 times, the stretching alignment can be improved, and the stretching can be effectively carried out in the next step.

Next, use a tenter to stretch in the transverse direction (TD). In the invention of the present invention, by forming a plurality of microcrystals by a preheating step before the transverse stretching (TD stretching) and forming them into nodes, the alignment can be effectively improved in the TD stretching, and a predetermined thermal expansion coefficient can be obtained. The point of view is a more ideal form. The specific preheating temperature is preferably from 90 ° C to 110 ° C, more preferably from 95 ° C to 100 ° C. Next, the stretching temperature is in the range of (preheating temperature - 5) - (preheating temperature + 5) ° C, and more preferably stretching at the same temperature as the preheating temperature. The stretching ratio is preferably 3.5 to 6.0 times, more preferably 4.0 to 6.0 times, and particularly preferably 4.5 to 6.0 times.

Next, the stretched film is heat-fixed while being stretched or while being laterally relaxed. The heat setting temperature (hereinafter sometimes abbreviated as Ths) is preferably from 180 to 220 ° C, more preferably from 195 to 210 ° C, and particularly preferably from 200 to 210 ° C. When Ths is less than 180 ° C, the structure is insufficiently fixed, fn becomes large, and the increase in heat shrinkage rate and film formability are deteriorated. When Ths exceeds 220 ° C, the growth of crystals is promoted, the alignment in the plane is alleviated, and the coefficient of thermal expansion is deteriorated. The heat setting time is preferably in the range of 0.5 to 10 seconds. The relaxation rate in the heat setting treatment (hereinafter sometimes abbreviated as Rxhs) is preferably within 3 times of the relaxation rate of the next relaxation annealing treatment (hereinafter sometimes abbreviated as Rxa). The relaxation rate is a ratio of the width before the treatment to the difference between the widths after the treatment. For example, the relaxation rate of 2% indicates a case of 100 mm before the treatment, and 2% of 2 mm is relaxed, and after treatment, it is 98 mm. When the Rxhs of Rxa is more than 3 times, the alignment relaxation is excessively performed and the thermal expansion coefficient is deteriorated. Rxhs is preferably 0 to 9%.

Thereafter, it is preferably 35 ° C or less, more preferably 25 ° C cooling. After the following temperatures, the edges of the film were removed and wound onto the core. Next, in order to improve the thermal dimensional stability, the wound biaxially stretched PET film is preferably handled by applying tension under a certain temperature condition, and is subjected to relaxation annealing in order to remove the distortion of the molecular structure and reduce the heat shrinkage rate. deal with. The relaxation annealing treatment temperature (hereinafter sometimes abbreviated as Ta.) is preferably lower than the heat setting temperature (Ths), and preferably (Ths-25) to (Ths-5) °C, more preferably (Ths-20)~( Ths-10) ° C, particularly preferably (Ths-20) ~ (Ths-10) ° C and is 195 ° C ~ 205 ° C. When Ta exceeds (Ths-5) ° C, the structure fixed by the heat setting treatment is easily relaxed again, and the growth of crystals is promoted, the alignment in the plane is relaxed, and the coefficient of thermal expansion is easily deteriorated. When Ta is not full (Ths-25) ° C, there is a case where the annealing treatment causes the twist of the molecular structure to be incompletely removed and the heat shrinkage cannot be reduced. The relaxation annealing treatment time is preferably from 1 to 120 seconds, more preferably from 5 to 90 seconds, and particularly preferably from 20 to 60 seconds. The relaxation rate (Rxa) in the relaxation annealing treatment is preferably from 0.1 to 3%. When Rxa is less than 0.1%, the effect of relaxation cannot be exhibited, and the distortion of the molecular structure is incompletely removed, and the heat shrinkage cannot be reduced. When Rxa is more than 3%, there is a case where the alignment relaxation is excessively performed and the thermal expansion coefficient is deteriorated. Rxa can be set according to the tensile tension of the relaxed annealing step and the width of the clip. The biaxially stretched PET film of the present invention can be obtained by annealing the film while being conveyed at a speed of 10 to 300 m/min.

In the present invention, the PET film or the PET film roll may be subjected to any processing such as molding, surface treatment, lamination, coating, printing, embossing, and engraving as needed.

On the film obtained as described above, for example, after the chamber is evacuated to 5 × 10 ^-4 Pa before discharge of the plasma, argon and oxygen are introduced into the chamber to bring the pressure to 0.3 Pa (the partial pressure of oxygen is 3.7 mPa), using indium oxide containing 36% by mass of tin oxide (manufactured by Sumitomo Metal Mining Co., Ltd., density 6.9 g/cm ³ ), applying electric power at a power density of ² W/cm ² , and by DC magnetron sputtering A transparent conductive layer containing ITO having a film thickness of 250 nm is formed, and can be used as an organic EL display substrate or an organic EL illumination substrate by forming an organic EL light-emitting layer. Moreover, it can be used as a flexible solar cell substrate by forming a power generation layer.

(Method for measuring physical properties and method for evaluating effects)

The method for measuring the characteristic value and the method for evaluating the effect in the present invention are as follows.

(1) Crystallization index (ΔTcg (°C)), degree of crystallization (Xc (%))

According to JIS K7121-1987, DSC (RDC6220) manufactured by Seiko Instruments Co., Ltd. was used as a differential scanning calorimeter, and a disk station (SSC/5200) manufactured by the same company was used as a data analysis device, and 5 mg of the sample was sealed in an aluminum pan using a disk cover. The temperature was raised from 25 ° C to 300 ° C in a nitrogen atmosphere at a temperature increase rate of 10 ° C / min. Thereafter, the mixture was quenched with liquid nitrogen, and the temperature was raised again at a rate of 10 ° C/min from 20 ° C to 300 ° C in a nitrogen atmosphere.

The crystallization index (ΔTcg) was calculated from the glass transition temperature (Tg) and the cold crystallization temperature (Tcc) in the second temperature rising process using the following formula.

△Tcg=Tcc-Tg

The degree of crystallization (Xc (%)) was calculated by the following formula using the heat of fusion (ΔH _m ) and the heat of cold crystallization (ΔH _c ) in the first heating process.

Xc(%)={(△H _m -ΔH _c )/△H _m ⁰ }×100

Here, ΔH _m ⁰ is the heat of complete crystal melting. For example, in the case of PET, 140.1 J/g is used, and in the case of PEN, 103.3 J/g (reference Wunderlich B "Thermal analysis of Polymeric Materials").

(2) Surface alignment coefficient (fn)

According to JIS-K7142 (2008), the measurement was performed using the following measuring instrument. The sample was cut to a width of 25 mm and a length of 30 mm, and the film longitudinal direction, the film transverse direction, and the film thickness direction were measured, and the average value was taken as the refractive index in each direction. Using the results, the surface alignment coefficient was calculated by the following formula. Further, when the longitudinal direction or the transverse direction of the film is not separated, the direction having the largest refractive index in the film is taken as the longitudinal direction, and the direction perpendicular to the longitudinal direction is taken as the lateral direction. Further, the direction of the maximum refractive index in the film can be determined by measuring the refractive index in all directions of the film by an Abbe refractometer, and can be determined, for example, by a phase difference measuring device (birefringence measuring device) or the like. Determined by the slow axis direction.

‧Device: Abbe refractometer 4T (made by ATAGO Co., Ltd.)

‧Light source: sodium D line

‧Measurement temperature: 25 ° C

‧Measure humidity: 65% RH

‧ Fixative solution: methane iodide (n _D ²⁰ = 1.74), methane iodide (n _D ²⁰ ≒ 1.74~1.78). When the refractive index is high and it cannot be measured using methyl iodide, it is measured using thiomethane iodide.

‧face alignment coefficient (fn)

Fn=(nMD+nTD)/2-nZD

nMD: refractive index of the film in the longitudinal direction

nTD: refractive index of the film in the transverse direction

nZD: refractive index in the thickness direction of the film.

(3) Thermal expansion coefficient

According to JIS K7197 (1991), the sample number 3 was measured for the longitudinal direction and the transverse direction of the film by the following conditions, and the average value was taken as the thermal expansion coefficient in the longitudinal direction and the lateral direction.

‧Measuring device: "TMA/SS6000" manufactured by Seiko Instruments

‧ sample size: width 4mm, length 20mm

‧ Temperature conditions: increase from 30 ° C to 175 ° C at 5 ° C / min for 10 minutes

‧and cool down from 175 ° C to 40 ° C at 5 ° C / min for 20 minutes

‧Load conditions: fixed 29.4mN

Here, the coefficient of thermal expansion coefficient measurement range is 150 ° C to 50 ° C at the time of temperature drop. The coefficient of thermal expansion is calculated by the following formula.

Thermal expansion coefficient [ppm/°C] = 10 ⁶ × {(dimension mm at 150 ° C) - (dimension mm at 50 ° C) / 20 mm} / (150 ° C - 50 ° C).

(4) Thermal shrinkage at a temperature of 180 ° C

The heat shrinkage rate was measured by the following apparatus and conditions.

‧Test length device: universal projector

‧Data size: test length 200m × width 10mm

‧ Heat treatment unit: GEER OVEN

‧ Heat treatment conditions: 180 ° C, 30 minutes

‧Load: 3g

‧ Calculation method

The sample is drawn at 150 mm intervals before the heat treatment, and the measurement is performed. The distance between the lines after the heat treatment was calculated from the change in the distance between the lines before and after the heating, and was used as an index of dimensional stability. For the measurement, 5 samples were applied to each of the films in the longitudinal direction and the transverse direction, and the average value was evaluated.

(5) Directional parameters (fn/Xc)

According to the surface alignment coefficient (fn) and the degree of crystallinity (Xc (%)) obtained by the above calculation formula, the alignment parameter (fn/Xc) can be obtained by the following formula.

Fn/Xc=fn/(Xc(%)/100)

(6) Film haze value

A sample of 10 cm × 10 cm was cut out from the film, and measured by a fully automatic direct reading haze computer HGM-2DP (manufactured by Suga Tester Co., Ltd.) in accordance with JIS K7105 (1985). The sample was randomly measured at 10 points, and the average value thereof was taken as a film haze value.

(7) Film stability

The film formability of the film was evaluated on the basis of the following criteria. Evaluation D was unacceptable.

A: No film breakage occurs, and film formation can be stably performed.

B: The occurrence of film breakage is small, and film formation can be stably performed.

C: Film rupture often occurs and film formation is possible.

D: Film rupture frequently occurs, and it is difficult to continuously form a film.

[Examples]

Embodiments of the present invention will be described based on the embodiments.

(Reference example 1)

194 parts by mass of dimethyl terephthalate and 124 parts by mass of ethylene glycol were added to the transesterification reactor, and the contents were heated to a temperature of 140 ° C. To dissolve. Then, 0.1 parts by mass of magnesium acetate tetrahydrate and 0.03 parts by mass of antimony trioxide were added while stirring the contents, and methanol was distilled off at a temperature of 140 to 230 ° C to carry out a transesterification reaction. Next, 1 part by mass (0.05 parts by weight of trimethyl phosphate) of a 5 mass% ethylene glycol solution of trimethyl phosphate was added. When an ethylene glycol solution of trimethyl phosphate is added, the temperature of the reaction contents is lowered. Therefore, while the remaining ethylene glycol was distilled off, stirring was continued until the temperature of the reaction contents was restored to a temperature of 230 °C. As described above, after the temperature of the reaction contents in the transesterification reactor reached a temperature of 230 ° C, the reaction contents were transferred to a polymerization apparatus. After the transfer, the reaction system was gradually heated from a temperature of 230 ° C to a temperature of 290 ° C while the pressure was lowered to 0.1 kPa. The time until the final temperature and final pressure were reached was set at 60 minutes. After reaching the final temperature and the final pressure, after reacting for 2 hours (starting polymerization for 3 hours), the stirring torque of the polymerization apparatus shows a predetermined value (the specific value varies depending on the specifications of the polymerization apparatus, but the polymerization apparatus is different) The value shown by polyethylene terephthalate having an intrinsic viscosity of 0.65 is shown as a predetermined value). Therefore, the reaction system was purged with nitrogen, returned to normal pressure to stop the polycondensation reaction, and discharged in a strand form in cold water, and immediately cut off to obtain polyethylene terephthalate having an intrinsic viscosity of 0.65. Ester PET pellets X.

(Reference example 2)

0.35 parts by mass of dimethyl phenyl phosphate (DPPO) as a nucleating agent was added in place of trimethyl phosphate, and a transesterification reaction and a polymerization reaction were carried out in the same manner as in Reference Example 1, to obtain an intrinsic viscosity of 0.62. The PET pellet Y after adjusting the crystallization rate.

(Reference Example 3)

The PET pellet obtained in Reference Example 1 was mixed with sodium montanate (manufactured by Nitto Chemical Co., Ltd.) as a nucleating agent at a mass ratio of 90:10, and mixed at 280 ° C using a vented twin-shaft extruder. The steel masterbatch Z containing 10 parts by mass of sodium montanate was obtained.

(Reference example 4)

Addition of 0.3 parts by mass of manganese acetate ‧ hydrate salt to a mixture of 100 parts by mass of dimethyl 2,6-naphthalenedicarboxylate and 60 parts by mass of ethylene glycol, and gradually raising the temperature from 150 ° C to 240 ° C At the temperature, the transesterification reaction is carried out. On the way, 0.024 parts by mass of antimony trioxide was added at a time point when the reaction temperature reached 170 °C. Further, 0.042 parts by mass of a tetrabutylphosphonium 3,5-dicarboxybenzenesulfonate (corresponding to 2 mmol%) was added at a reaction temperature of 220 °C. Thereafter, a transesterification reaction was subsequently carried out, and 0.023 parts by mass of trimethylphosphoric acid was added. Next, the reaction product was transferred to a polymerization apparatus, the temperature was raised to 290 ° C, and the polycondensation reaction was carried out under a reduced pressure of 30 Pa. The stirring torque of the polymerization apparatus showed a predetermined value (depending on the specifications of the polymerization apparatus, specific The numerical value is different, but the value shown by the polyethylene 2,6-naphthalenedicarboxylate having an intrinsic viscosity of 0.65 in the polymerization apparatus is taken as a predetermined value). Therefore, the reaction system was purged with nitrogen, returned to normal pressure to stop the polycondensation reaction, and discharged in a strand form in cold water, and immediately cut off to obtain PEN pellet X having an intrinsic viscosity of 0.65.

(Reference example 5)

The PEN pellet obtained in Reference Example 4 and the sodium montanate as a nucleating agent were mixed at a mass ratio of 90:10, and kneaded at 280 ° C using a vented twin-shaft extruder to obtain sodium montanate 10 Parts by mass of PEN masterbatch Y.

(Example 1)

90 parts by mass of the PET pellet X obtained in Reference Example 1 and 10 parts by mass of the PET pellet Y obtained by adjusting the crystallization rate obtained in Reference Example 2 were subjected to pressure reduction at a temperature of 180 ° C for 3 hours. It was supplied to an extruder heated to a temperature of 280 ° C and introduced into a T-die ferrule under a nitrogen atmosphere. Subsequently, the T-die ferrule was extruded into a sheet shape and used as a melted single-layer sheet, and the film was kept at a surface temperature of 25 ° C by an electrostatic application method to obtain an unstretched single-layer film by electrostatic application. The glass transition temperature (Tg) of the unstretched single layer film was measured to be 78 °C.

Next, the obtained unstretched single-layer film was preheated by the heated roll group, and then subjected to 3.5-fold MD stretching at a temperature of 93 ° C, and cooled at a temperature of 25 ° C to obtain uniaxial stretching. film. The cold crystallization temperature of the obtained uniaxially stretched film was 90 °C. While the two ends of the obtained uniaxially stretched film are clamped by the clip, they are guided to a preheating zone at a temperature of 95 ° C in the tenter, followed by a heating zone continuously at a temperature of 90 ° C, in the longitudinal direction. The lateral direction of the right angle (TD direction) is stretched 4.6 times. Further, a heat treatment for 5 seconds was then carried out at a temperature of 210 ° C in the heat treatment zone in the tenter as a heat setting treatment, and a 2% lateral relaxation treatment was performed at the same temperature. Next, after uniformly cooling at 25 ° C, the film edge was removed and wound up on the core to obtain a biaxially stretched film having a thickness of 100 μm.

Then, the film was subjected to a relaxation annealing treatment at a relaxation rate of 1% for 30 seconds at a film speed of 30 m/min at a temperature of 190 ° C to obtain a polyester film.

The obtained polyester film, as shown in Table 1, has Both thermal dimensional stability and film forming properties are quite excellent.

(Example 2)

The same procedure as in Example 1 was carried out, except that 98 parts by mass of the PET pellets X obtained in Reference Example 1 and 2 parts by mass of the PET pellets Y obtained by adjusting the crystallization rate obtained in Reference Example 2 were mixed. Polyester film. The polyester film obtained was evaluated to have excellent thermal dimensional stability and film forming properties.

(Example 3)

A polyester film was obtained in the same manner as in Example 1 except that 80 parts by mass of the PET pellet X obtained in Reference Example 1 and 20 parts by mass of the PET master batch Z of sodium montanate obtained in Reference Example 3 were mixed. . The obtained polyester film was evaluated to have excellent thermal dimensional stability.

(Example 4)

In addition to mixing 95 parts by mass of the PET pellet X obtained in Reference Example 1 and 5 parts by mass of the PET master batch Z of sodium montanate obtained in Reference Example 3, the MD stretching ratio was changed to 3.0 times, and TD was pulled. A polyester film was obtained in the same manner as in Example 1 except that the draw ratio was changed to 4.2 times. The obtained polyester film was evaluated to have excellent thermal dimensional stability.

(Example 5)

In addition to mixing 95 parts by mass of the PET pellet X obtained in Reference Example 1 and 5 parts by mass of the PET master batch Z of sodium montanate obtained in Reference Example 3, the MD stretching ratio was changed to 3.2 times, and TD was pulled. A polyester film was obtained in the same manner as in Example 1 except that the draw ratio was changed to 4.2 times. The obtained polyester film was evaluated to have excellent thermal dimensional stability.

(Example 6)

In addition to 80 parts by mass of the PET pellet X obtained in Reference Example 1 and 20 parts by mass of the PET masterbatch Z of sodium montanate obtained in Reference Example 3, the MD stretching ratio was changed to 3.2 times, and TD was pulled. A polyester film was obtained in the same manner as in Example 1 except that the draw ratio was changed to 4.2 times. The obtained polyester film was evaluated to have excellent thermal dimensional stability.

(Example 7)

In addition to mixing 98 parts by mass of the PET pellet X obtained in Reference Example 1 and 2 parts by mass of the PET pellet Y obtained by adjusting the crystallization rate obtained in Reference Example 2, the MD stretching ratio was changed to 3.0 times. A polyester film was obtained in the same manner as in Example 1 except that the TD stretching ratio was changed to 4.2 times. The polyester film obtained was evaluated to have excellent thermal dimensional stability and film forming properties.

(Example 8)

A polyester film was obtained in the same manner as in Example 1 except that the heat-fixing temperature Ths was changed to 190 ° C and the relaxation annealing temperature Ta was changed to 170 ° C. The obtained polyester film was evaluated to have excellent thermal dimensional stability.

(Example 9)

A polyester film was obtained in the same manner as in Example 1 except that the relaxation annealing temperature Ta was changed to 200 °C. The polyester film obtained was evaluated to have excellent thermal dimensional stability and film forming properties.

(Embodiment 10)

In addition to mixing 95 parts by mass of the PEN pellet X obtained in Reference Example 4 and 5 parts by mass of the PEN masterbatch Y of sodium montanate obtained in Reference Example 5 and A polyester film was obtained in the same manner as in Example 1 except for use. The obtained polyester film was evaluated to have excellent thermal dimensional stability.

(Example 11)

In the same manner as in the first embodiment, the TD stretching ratio was changed to 3.7 times, the TD stretching ratio was changed to 3.7 times, the heat setting temperature Ths was changed to 215 ° C, and the relaxation annealing temperature Ta was changed to 205 ° C. The method yielded a polyester film. The polyester film obtained was evaluated to have excellent thermal dimensional stability and film forming properties.

(Comparative Example 1)

A polyester film was obtained in the same manner as in Example 1 except that the PET pellets X obtained in Reference Example 1 were used. The polyester film obtained was evaluated to have a large heat shrinkage ratio and a poor thermal dimensional stability.

(Comparative Example 2)

A polyester film was obtained in the same manner as in Example 1 except that the PET pellets X obtained in Reference Example 1 were used, and the MD stretching ratio was changed to 3.0 times and the TD stretching ratio was changed to 4.2 times. The polyester film obtained was evaluated to have a large heat shrinkage ratio and a poor thermal dimensional stability.

(Comparative Example 3)

As shown in Table 1, a polyester film was obtained in the same manner as in Example 1 except that the relaxation annealing step was not carried out. The polyester film obtained was evaluated to have a large heat shrinkage rate and poor thermal dimensional stability.

(Comparative Example 4)

In addition to changing the MD stretching ratio to 3.0 times, and the TD stretching ratio A polyester film was obtained in the same manner as in Example 1 except that the amount was changed to 3.35 times. The polyester film obtained by the evaluation has a characteristic that the thermal expansion coefficient is deteriorated due to a small surface alignment coefficient, and the thermal dimensional stability is poor.

(Comparative Example 5)

As described in Table 1, except that 75 parts by mass of the PET pellet X obtained in Reference Example 1 and 25 parts by mass of the PET master batch Z of sodium montanate obtained in Reference Example 3 were mixed, the MD stretching ratio was changed to A polyester film was obtained in the same manner as in Example 1 except that the TD stretching ratio was changed to 4.2 times and the relaxation annealing treatment was not performed. The crystallization index (ΔTcg) is small, and the film formation stability is deteriorated, and continuous film formation is difficult.

(Comparative Example 6)

A polyester film was obtained in the same manner as in Example 1 except that the heat setting temperature Ths was changed to 175 ° C and the relaxation annealing temperature Ta was changed to 160 ° C. The polyester film obtained was evaluated to have a large heat shrinkage rate and poor thermal dimensional stability.

(Comparative Example 7)

A polyester film was obtained in the same manner as in Example 1 except that the heat setting temperature Ths was changed to 230 ° C and the relaxation annealing temperature Ta was changed to 210 ° C. The polyester film obtained by the evaluation has a characteristic that the thermal expansion coefficient is deteriorated due to the increase in the degree of crystallization, and the thermal dimensional stability is poor.

(Comparative Example 8)

A polyester film was obtained in the same manner as in Example 1 except that the relaxation annealing temperature Ta was changed to 180 °C. The polyester film obtained was evaluated to have a large heat shrinkage rate and poor thermal dimensional stability.

(Comparative Example 9)

A polyester film was obtained in the same manner as in Example 1 except that the relaxation annealing temperature Ta was changed to 210 °C. The polyester film obtained by the evaluation has a characteristic that the thermal expansion coefficient is deteriorated due to the increase in the degree of crystallization, and the thermal dimensional stability is poor.

(Comparative Example 10)

As shown in Table 1, except that 95 parts by mass of the PEN pellet X obtained in Reference Example 4 and 5 parts by mass of the PEN masterbatch Y of sodium montanate obtained in Reference Example 5 were mixed, the MD stretching ratio was changed to A polyester film was obtained in the same manner as in Example 1 except that the TD stretching ratio was changed to 4.2 times and the relaxation annealing treatment was not performed. The polyester film obtained by the evaluation had a large surface alignment coefficient (fn) and deteriorated film formation stability, and it was difficult to continuously form a film.

[Industrial availability]

The polyester film of the present invention can be applied to a base film for a flexible member which is excellent in both thermal dimensional stability and crimpability. Therefore, it can be used to obtain an organic EL display, an electronic paper, an organic EL illumination, an organic solar cell, and a dye-sensitized solar cell.

Claims (8)

A polyester film obtained by using a polyester having a crystallization index (ΔTcg) of 10° C. or more and 60° C. or less, and a surface alignment coefficient (fn) of 0.15 or more and 0.28 or less, and a degree of crystallization (Xc) (%)) is 35% or less, and the heat shrinkage ratio of 180 ° C in the longitudinal direction and the transverse direction of the film is 0% to 1.5%, respectively. The polyester film of claim 1, wherein the surface alignment coefficient (fn) divided by the degree of crystallinity (Xc) (fn/Xc) is 0.50 or more. For example, the polyester film of claim 1 or 2, wherein the film has a haze value of 0 to 3%. The polyester film according to claim 1 or 2, wherein the polyester contains a nucleating agent, and the content of the nucleating agent is 0.01 parts by mass or more and 2 parts by mass or less based on 100 parts by mass of the polyester. A polyester film according to claim 1 or 2, wherein the polyester is polyethylene terephthalate. A film for an organic EL substrate, which is obtained by using the polyester film according to any one of claims 1 to 5. A film for a flexible solar cell substrate, which is obtained by using the polyester film according to any one of claims 1 to 5. The method for producing a polyester film according to any one of claims 1 to 5, wherein the polyester resin is melt-extruded while being cooled and solidified to form an unstretched film, and then the unstretched film is obtained. After the film is biaxially stretched, it is heat-fixed at a heat setting temperature of Ths (°C) of 180 to 220 ° C, and then cooled at a temperature of 35° C. or lower, followed by relaxation annealing treatment, which is characterized by The polyester resin contains at least one nucleating agent and is subjected to a relaxation annealing treatment at a temperature (Ths-25) to (Ths-5) °C.