JPS6249846B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a polyester film. More specifically, the present invention relates to a method for producing a uniform high Young's modulus polyester film. It has been known that polyester, which has the property of forming an optically anisotropic melt, exhibits unique behavior when formed into fibers. That is, by simply melt-spinning this polymer, the polyester molecules are highly oriented in the fiber axis direction, resulting in a fiber with a high Young's modulus. On the other hand, when this polyester is formed into a film by the melting method, it is presumed from the above behavior that molecular orientation occurs in the extrusion direction when passing through the die slit.
A film is obtained that is highly oriented in the machine axis direction. For example, a film produced by extrusion using a T-die using a conventional method exhibits extremely high strength (e.g., 30 Kg/mm ² or more) and high Young's modulus (e.g., 700 Kg/mm ² or more) in the machine axis direction. However, in the width direction perpendicular to this, both the strength (for example, 2 Kg/mm ² ) and Young's modulus (for example, 100 Kg/mm ² ) are extremely low. As a result, such polyester films are either not practical, or even if they are, this property is a major hindrance to practical use. If an attempt is made to stretch the film in the width direction, some parts will stretch and some will not stretch, resulting in a film with extremely uneven thickness and poor practical use. As a result of repeated research into a method for producing a uniform biaxially oriented polyester film that does not have such drawbacks, the present inventor has found that The optical anisotropy of polyester is affected by temperature,
For example, the inventors discovered that the optical anisotropy characteristic becomes weaker as the temperature increases, and that the above-mentioned problems can be improved by utilizing this characteristic, and the present invention was achieved based on this finding. That is, in manufacturing a film by melt-extruding polyester that has the property of forming an optically anisotropic melt through a slit, the present invention involves extruding the polyester within the melt passage of the slit and slightly inside the tip (lip) on the discharge side. A plate-shaped porous body having a large number of slits is provided, and at least the discharge side surface of the plate-shaped porous body is heated so that the melt passing through a certain slit and the adjacent slit are heated.
This method of producing a polyester film is characterized in that the molten material that has passed through the slit is rejoined within the slit to form a continuous layer in the width direction of the slit, and then melt extruded. In the present invention, a polyester having the property of forming an optically anisotropic melt refers to a polyester having the property of allowing polarized light to pass through an optical system in which a polymer in a molten state is provided with a 90-crossed polarizer. Examples of such polyesters include (1) terephthalic acid, diphenyl ether-4,
Such as 4'-dicarboxylic acid, diphenyl-4,4'-dicarboxylic acid, diphenooxyethane-4,4'-dicarboxylic acid, naphthalene-2,6-dicarboxylic acid, transcyclohexane-1,4-dicarboxylic acid, etc. Symmetric aromatic dicarboxylic acid or symmetric alicyclic dicarboxylic acid; methyl terephthalic acid,
Methoxyterephthalic acid, chlorterephthalic acid, bromoterephthalic acid, diphenyl ether-2,2'-dimethyl-4,4'-dicarboxylic acid,
Diphenooxyethane-2,2-dichloro-
4,4'-dicarboxylic acid, transcyclohexane-1-methyl-1,4-dicarboxylic acid, etc., the symmetrical aromatic dicarboxylic acids or alicyclic dicarboxylic acids mainly substituted with lower alkyl, lower alkoxy or halogen nuclei, etc. As an acid component, symmetrical dioxyaromatic compounds such as hydroquinone, 4,4'-dioxydiphenyl, 4,4'-dioxydiphenyl ether, bis(4-oxyphenooxy)ethane, etc.; chlorohydroquinone, Bromohydroquinone, methylhydroquinone, ethylhydroquinone, tertiary butylhydroquinone, tertiary amylhydroquinone, phenylhydroquinone, 2,2'-dimethyl-4,4'-dioxydiphenyl, 3,
Lower alkyl, lower alkoxy, aryl or halogen nucleus of the symmetrical dioxyaromatic compound such as 3'-dimethoxy-4,4'-dioxydiphenyl ether, bis(2-chloro-4-oxyphenooxy)ethane, etc. Homopolyester or copolyester (hereinafter referred to as polyester) containing a substituent as the main diol component, (2) p-oxybenzoic acid, 4-oxydiphenyl-4'-carboxylic acid, 3-chloro-4-oxybenzoic acid, 3-methoxy-4-oxybenzoic acid, 3-ethoxy-4-oxybenzoic acid, 2
-Methyl-4-oxybenzoic acid, 3-methyl-
Copolyesters containing aromatic oxycarboxylic acids such as 4-oxybenzoic acid, 2-chloro-4-oxydiphenyl-4'-carboxylic acid, etc. and/or lower alkyl, lower alkoxy or halogen substituted products thereof as main components ( (hereinafter referred to as polyester). In addition to the oxycarboxylic acids that are the main components of the polyester, the acid components that can be copolymerized with the polyester include isophthalic acid, diphenyl ether-3,3'-dicarboxylic acid, and diphenooxyethane-3,3'-dicarboxylic acid. Acid, naphthalene-1,6-dicarboxylic acid, m-oxybenzoic acid, 5-methylisophthalic acid, 5-chloroisophthalic acid, 4-methylisophthalic acid, 5-tertiary butyl isophthalic acid, diphenyl ether-4,
4'-dichloro-3,3'-dicarboxylic acid, diphenyl-3,4'-dimethyl-4,3'-dicarboxylic acid,
diphenooxyethane-2,2'-dibrome-3,
3'-dicarboxylic acid, naphthalene-2,7-dichloro-1,6-dicarboxylic acid, 4-ethoxy-3
-Oxybenzoic acid, carbonic acid, cyclohexane-1,
Examples include aromatic dicarboxylic acids such as 3-dicarboxylic acids, aromatic oxycarboxylic acids, and alicyclic dicarboxylic acids. On the other hand, the acid component copolymerized into the polyester is the main acid component of the polyester or the acid component that becomes a copolymerization component. In addition, diol components that can be copolymerized with polyester include resorcinol, 3,3'-dioxydiphenyl, 3,3'-dioxydiphenyl ether,
1,6-dioxynaphthalene, bis(3-hydroxyphenoxy)ethane, 2,2-bis(4-
hydroxyphenyl)propane, 1,1-bis(4-hydroxyphenyl)cyclohexane, 4
-chlorresorcin, 4-ethoxyresorcin, 4-bromoresorcin, 4,4'-dimethoxy-3,3'-dioxydiphenyl, 4,4'-dimethyl-3,3'-dioxydiphenyl, 4 , 4'-dimethoxy-3,3'-dioxydiphenyl ether, 2,4'-dichloro-3,3'-dioxydiphenyl ether, 2,5-dichloro-1,6-dihydroxynaphthalene, 2, 2′-dibrome-3,
Aromatic dioxy compounds such as 3'-dioxydiphenooxyethane or lower alkyl thereof,
Examples include lower alkoxy or halogen-substituted products. Next, the diol component to be copolymerized with the polyester is the main diol component of the polyester or the diol component that becomes a copolymerization component. Specific examples of preferred polyesters in the present invention include (1) p-oxybenzoic acid, terephthalic acid, isophthalic acid, diphenooxyethane-4,4'-dicarboxylic acid, diphenyl ether-4,4'-dicarboxylic acid; , naphthalene-2,6-dicarboxylic acid, naphthalene-2,7-dicarboxylic acid, and one or more selected from the group consisting of hydroquinone, resorcinol, chlorohydroquinone, methylhydroquinone, tertiary butylhydroquinone, tertiary amyl hydroquinone,
A copolyester composed of an ester with one or more dioxyaromatic compounds selected from the group consisting of 4,4'-dioxydiphenyl and 4,4'-dioxydiphenyl ether; (2 ) Terephthalic acid, diphenyl ether-4,
One or more selected from the group consisting of 4'-dicarboxylic acid, diphenyl-4,4'-dicarboxylic acid, diphenooxyethane-4,4'-dicarboxylic acid, and naphthalene-2,6-dicarboxylic acid. and hydroquinone, chlorhydroquinone,
One or two selected from the group consisting of methyl hydroquinone, tertiary butyl hydroquinone, tertiary amyl hydroquinone, phenyl hydroquinone, 4,4'-dioxydiphenyl, and 4,4'-dioxydiphenyl ether (3) selected from the group consisting of terephthalic acid and isophthalic acid and chlorohydroquinone, methylhydroquinone, tertiary butylhydroquinone, tertiary amylhydroquinone, and phenylhydroquinone; Examples include copolyesters composed of one or more esters. Particularly preferred polyesters in the present invention are polyesters consisting essentially of repeating units represented by the following formulas (A), (B) and (C). [However, in the formula, x:y and x:z are both 80:
20 to 50:50, y:z is 10:15 to 15:10, n is 0 or 1, the carbonyl groups of formula (B) are in a meta or (and) para position relationship with each other, and the carbonyl groups of formula (C )
The oxy groups of are in a meta or (and) para position to each other when n=0, and in a para or (and) position to the diphenyl group when n=1. The repeating unit represented by formula (A) is a p-oxybenzoic acid residue, and the repeating unit represented by formula (B) is a residue of terephthalic acid or isophthalic acid, and the repeating unit represented by formula (C) is a p-oxybenzoic acid residue. The repeating unit used is the residue of an aromatic diol such as hydroquinone, resorcinol, 4,4'-dioxydiphenyl, 3,3'-dioxydiphenyl, 3,4'-dioxydiphenyl. In the present invention, particularly preferred specific examples of polyesters include (1-1) polyesters containing p-oxybenzoic acid, isophthalic acid, and hydroquinone as main components; (1-2) p-oxybenzoic acid, terephthalic acid, and resorcinol; (1-3) Polyesters containing p-oxybenzoic acid, isophthalic acid, and 4,4'-dioxydiphenyl as main components. Among the polyesters of the present invention, the most preferred polyester is the polyester (1-1). The polyester of the present invention can be produced by a conventionally known method. For example, (i) an aromatic dicarboxylic acid and/or an alicyclic dicarboxylic acid and a lower aliphatic ester of a dioxyaromatic compound (such as acetic acid ester) are optionally combined with a lower fatty acid ester of an aromatic oxycarboxylic acid (such as acetic acid ester). (for example, acetic acid ester, etc.); (ii) The aryl ester (for example, phenyl ester, etc.) of an aromatic dicarboxylic acid and/or alicyclic dicarboxylic acid and a dioxyaromatic compound are polymerized with aromatic oxy- The method includes heating together with an aryl ester (for example, phenyl ester, etc.) of a carboxylic acid and/or a diaryl carbonate (for example, diphenyl carbonate, etc.). In the present invention, polyesters substantially composed of repeating units represented by the formulas (A), (B), and (C) include the following formulas (A'), (B'), and (C'). )
It can be obtained by heating and polymerizing p-hydroxybenzoic acid and/or its derivatives, benzenedicarboxylic acid and/or its derivatives, and dioxybenzene and/or dioxydiphenyl and/or their derivatives, each represented by the following. In the above formula, R ₁ , R ₅ and R ₆ are each independently selected from the group consisting of a hydrogen atom, a lower alkanoyl group having 7 or less carbon atoms, and a benzoyl group, and R ₂ , R ₃ and R ₄ are a hydrogen atom, a carbon Each of them is independently selected from the group consisting of an aryl group having 6 to 12 carbon atoms and a lower alkyl group having 6 or less carbon atoms. The polyester of the present invention can be produced by a conventionally known method, but these raw materials are melt-polymerized (preferably under reduced pressure) at a polymerization temperature lower than, for example, 320°C, and then the obtained polyester is melt-polymerized (preferably under reduced pressure). It is preferable to use a method in which a prepolymer is solid-phase polymerized. By such a method, the apparent melt viscosity is
A high degree of polymerization polyester having a shear rate of 100 sec ^-1 (film forming temperature) of 5000 poise or more, preferably 1000 poise or more, particularly preferably 20000 poise or more is obtained. If the degree of polymerization of the polyester is too low, not only the strength of the obtained film will be insufficient, but also the film will become fibrillated when the desired film is formed by melt extrusion, for example, which is undesirable. In addition, the polyester of the present invention has a softening point of 150 to 380°C, preferably
Choose one with a temperature of 200-350℃. In the present invention, a film is produced by extruding the polyester melt through a slit in which a plate-like porous body having a large number of pores is provided at least on the discharge side. It is necessary to re-bond the molten material that has passed through each slit while heating the slit to form a continuous layer in the width direction of the slit, and then melt-extrude it. More specifically, the plate-like porous body preferably has a diameter of 2 mm to less than 5 mm so that the discharge side surface is located slightly inside the slit tip (lip) of a film die that is normally used. disposed internally in the melt passageway of the die. As a result, the molten material divided at each strip is rejoined to form a continuous layer before being extruded from the die lip. The plate-shaped porous body is made of metal or other materials, and is wire mesh or wire mesh-like, or a plate-shaped body in which a large number of microspheres are densely packed or arranged at least in the surface layer and fixed by sintering, etc. For example, a plate-shaped body made of metal or the like with a large number of pores formed therein. Each slit of the plate-like porous body may be independent within the plate-like porous body, and the interior may have a structure that allows molten polymer to pass between adjacent slits. In some cases, it may be preferable to have a structure that allows access. The porosity of plate-shaped porous material is 15-70%, especially 20-50%
It is preferable that the thickness is 0.01 to 5
mm, particularly preferably 0.1 to 1 mm. Furthermore, the average distance between adjacent narrow gaps is preferably 0.03 to 2 mm, particularly 0.06 to 1 mm. The width of the slit can be selected appropriately depending on the desired thickness of the film, but is usually 0.01~
10 mm, preferably in the range of 0.1 to 2 mm. In the present invention, melt extrusion is performed at a temperature higher than the softening point of the polyester, preferably at least 20°C higher than the softening point, particularly preferably at a temperature higher than 40°C higher than the softening point, at least on the discharge side of the plate-shaped porous body. It is necessary to heat the surface. As the heating method, the method described below is preferable. In order to heat the discharge side surface of a plate-shaped porous body, it is necessary to supply energy to the discharge side surface. Examples of methods for this include (i) a method of causing the plate-shaped porous body surface to self-heat; (ii) method of heating by heat transfer,
(iii) There is a method of using both together. Furthermore, as a method of causing a plate-shaped porous body to generate self-heating as described in (i) above, the plate-shaped porous body surface is configured with an electric conductor, and this is connected to a DC or AC power source to supply electricity to the plate-shaped porous body surface. A method that utilizes the Joule heat generated in the process (hereinafter referred to as the energization heating method); the surface of a plate-shaped porous body is made of a conductor, and an induced magnetic field of a suitable frequency is applied to it.
A method that uses so-called induction heating, which generates eddy currents and generates heat; A method that utilizes so-called dielectric heating, in which the surface of a plate-shaped porous body is made of a dielectric, and an electric field of a suitable frequency is applied thereto to generate dielectric loss and generate heat. etc. In addition, as for the method (ii) of heating the surface of a plate-shaped porous body by heat transfer, the surface of the plate-shaped porous body itself or the vicinity thereof is formed into an organization composed of thin tubes, and a heating medium is flowed through the thin tubes. There is a method of heating a plate-shaped porous body (hereinafter referred to as a thermal fluid heating method). Materials that can be used in the current heating method and induction heating method include platinum, gold, silver, copper, titanium, vanadium, tungsten, iridium, molybdenum, palladium, iron, nickel, chrome, cobalt,
Single metals such as lead, zinc, bismuth, tin, and aluminum; Alloys such as stainless steel, nichrome, tantalum, silver, phosphor bronze, and duralumin; graphite, silicone, germanium, selenium,
Inorganic compounds that mainly exhibit semiconductor properties such as tin oxide, indium oxide, iron oxide, and nickel oxide; Organic compounds that exhibit semiconductor properties such as polyacetylene and polyphenylene; Substances that have a specific resistance of about 10 ^-7 to ^{10 9} Ωcm. The plate-shaped porous body described above is advantageously used. Furthermore, in addition to the above-mentioned conductive materials, there are also structures in which the surfaces of glass beads are coated with silver and brought into pressure contact to make them conductive; conductive metals such as aluminum are evaporated onto ceramic fibers such as alumina and zirconium, and the Examples include a pressure-formed conductive plate-like porous body; a conductive plate-like porous body structure in which a porous ceramic plate is immersed in a graphite particle dispersion and deposited, and other heatable structures can also be used. When heating the above-mentioned conductive plate-like porous body with electricity,
Usually, an electric field of 0.1 to several hundred V/cm, a current of 0.1 to several hundred amperes, and a watt density of 0.1 to several thousand W/cm ² are used. These values can vary depending on the purpose of use, and desired properties can be obtained by selecting the material of the porous plate and designing the structure of the porous plate. The plate-shaped porous body of the electric heating method is attached to the lip of the die slit or in the middle of the slit, but the insulating material between the plate-shaped porous body and the die body depends on the temperature to which the plate-shaped porous body is heated. However, heat-resistant organic materials such as aromatic polyimide and fluororesin, and combinations of ceramic plates and inorganic adhesives such as silica, alumina, and zirconia can be used. On the other hand, when heating the surface of a conductive porous plate by induction heating, a coil is generally placed approximately parallel to the surface of the porous plate, and a magnetic field approximately perpendicular to the porous plate is applied. Eddy currents are generated on the surface of the porous body, generating Joule heat. If the heating frequency is selected to be high, the penetration of eddy current will be shallow due to the skin effect, allowing local heating of only the surface. Depending on the thermal properties of the polyester to be molded and the material and shape of the apparatus, the optimum conditions can be obtained by appropriately combining the arrangement of the coils, the strength and frequency of the magnetic field. In addition, the surface material of the plate-shaped porous body that can be used in the dielectric heating method is generally a substance that causes dielectric loss, and depending on the frequency of the applied electric field and the properties of the polyester to be molded, ceramics with polar groups can be used. etc. can be exemplified. It is possible to create a local temperature distribution by configuring the surface of a plate-shaped porous body with materials having different dielectric properties and applying an electric field of a predetermined frequency. When heating the surface of such a dielectric porous plate by a dielectric heating method, an electrode is usually placed parallel or perpendicular to the surface of the porous plate. An alternating electric field parallel or perpendicular to the surface of the plate-shaped porous body is applied, causing dielectric loss and generating heat. The thin tubes used in the thermal fluid heating method are preferably of high thermal conductivity, such as aluminum, stainless steel, iron, copper, copper, silica, nickel, inconel, tungsten, tantalum, molybdenum, rhenium, titanium. , niobium, and other materials are used. The heat medium is selected to be compatible with the operating temperature and thin tube, such as water, ammonia, methanol, acetone, Freon 11, Freon 21, Freon 113, C ₆ F ₆ , n-butane, n-pentane, n
-Heptane, benzene, toluene, Dowsum A,
Dowsome B, DC200, DC209, Monsanto CP-
9, pyridine, Monsanto CP-34, lithium,
Sodium, potassium, cesium, mercury, lead, indium, tin, etc. are used in liquid or gas form. By heating the plate-shaped porous body in this manner, the temperature in the vicinity of the plate-shaped porous body generally becomes higher than the temperature in a certain range surrounding the vicinity. When a polyester melt passes through such a plate-like porous body at a high temperature, the flow of the polyester is disturbed, or the polyester becomes hotter, and the optical anisotropic properties are weakened or, in some cases, eliminated. , the following effects are produced. That is, the polyester used in the present invention is subjected to film-forming stretching in the order of extrusion, cooling, heating stretching, cooling, second axis stretching, heat treatment, etc., as in the film-forming stretching of polyalkylene terephthalate and polyalkylene naphthalene dicarboxylate. It is extremely difficult to apply. For example, if the film is cooled once and then reheated and stretched, it may not be possible to stretch uniformly or the stretching may not be smooth, the stretching orientation will be low, and it will be difficult to increase Young's modulus as a film. Become. If an attempt is made to stretch the film by increasing the Young's modulus, stretching irregularities and even film breakage are likely to occur, and irregularities are likely to occur in mechanical properties and thickness. However, the film extruded by the above method can be uniformly stretched even if it is once cooled and then reheated and stretched, and the film can have high strength and Young's modulus. The polyester immediately after being extruded from the slit is somewhat oriented in the direction in which the molten polyester was extruded (hereinafter referred to as the machine axis direction), but since the orientation is insufficient as it is, it is necessary to stretch it. The film of the present invention can be simultaneously stretched in the mechanical direction and in a direction perpendicular thereto, or sequentially biaxially stretched. Conventionally known techniques can be applied to this stretching method. For example, after the film exiting the slit is taken off by a take-off machine, it is first stretched in the direction of the machine axis, and then in a direction perpendicular to the machine axis. Further, the film coming out of the slit is taken up by a take-up machine (through a cooling drum, etc.) and stretched so as to orient the molecules in the direction of the machine axis. The film is then clamped at both ends with metal fittings and can be stretched in a direction perpendicular to the machine axis. In addition, the inflation method, for example, where both ends of the film extruded from a slit are held between metal fittings, the metal fittings move in a direction perpendicular to the machine axis, and the distance between the metal fittings extends in the machine axis direction, so that the film is stretched in the machine axis direction as well. It is also possible to use a so-called simultaneous biaxial stretching method. In this way, a uniform film with high strength and Young's modulus is obtained. In the present invention, the stretching ratio in the direction perpendicular to the machine axis direction is preferably 1.2 times or more, particularly preferably in the range of 1.5 to 10 times. The polyester film obtained according to the present invention has a high Young's modulus, high strength, excellent film thickness uniformity and dimensional stability. Furthermore, in order to improve dimensional stability and mechanical strength,
The film is heated at an appropriate temperature below the softening point of polyester (e.g. 180-300°C, preferably 250-300°C).
℃). At this time, 0.01~
Young's modulus, strength, dimensional stability, etc. can be improved by heat treating under tension and/or relaxation for 10 minutes or by treating the polyester film under solid state polymerization conditions of polyester. According to the method of the present invention, polyester having the property of forming an optically anisotropic melt is used to form a film using a melt film forming method, which provides excellent film properties not only in the direction of the mechanical axis of the film but also in the direction perpendicular to the mechanical axis. A polyester film with uniform mechanical properties is obtained. In addition, in the present invention, the softening point of polyester is determined by charging approximately 1 g of polyester into a Koka type flow tester equipped with a nozzle of 1 mm in diameter and 5 mm in length.
The temperature is raised from room temperature at a rate of 10°C per minute under a pressure of Kg/cm ² , and this is the temperature at which the polymer softens and starts flowing out from the nozzle, and also the shear rate (γa) and apparent melt viscosity of the polyester. (ηa) is measured at the measurement temperature using the Koka type flow tester as described above, and is calculated by the following formula. γa=4Q/r ³ ηa=pr ⁴ /8lQ [where, Q: discharge amount (cc/sec), r: radius of capillary tube (cm), p: extrusion pressure (dyne/cm ² ), l: radius of capillary tube Length (cm)] Furthermore, the Young's modulus and strength of the film are
It is determined by applying a film with a sample length of 20 mm to an Instron tensile tester and measuring the tensile rate at 100% per minute. The present invention will be explained below with reference to Examples. In the examples, "parts" means parts by weight. Example 1 116 parts of p-oxybenzoate phenyl, 114 parts of diphenyl isophthalate and 42 parts of hydroquinone were reacted at normal pressure for 2 hours at a temperature of 250 to 290°C in the presence of 0.13 parts of stannous acetate, and then the pressure was gradually reduced. At the same time as the transition, the temperature was raised to 320℃ and under a reduced pressure of 20mmHg.
Melt polymerization was carried out for 20 minutes. The obtained melt-polymerized polyester was pulverized at 250°C at 0.3mmHg for 8 hours, and then at 270°C at 0.3mmHg.
Solid state polymerization for 10 hours under Hg, 350℃ shear rate
A highly polymerized polyester having a melt viscosity of 60,000 poise at 100 sec ^-1 was obtained. Made from stainless steel wire with a diameter of approximately 0.2 mm at a position 2.0 mm inward from the lip of a slit with a width of 0.5 mm. Porosity: approximately 31%, number of slits per ¹ cm2.
Attach a 590 plain weave wire mesh and apply approximately 2.4W/ to this wire mesh.
The die was heated to 370° C. by applying power and heating of cm ² . The polyester was extruded through this slit at a linear discharge speed of 0.3 m/min, and the resulting film was once cooled, then both widthwise ends of the film were held between clamps, and stretched three times in a direction perpendicular to the machine axis at 250°C. The mechanical properties and thickness of the obtained film are shown in Table 1. Comparative Example 1 The same polyester used in Example 1 was
The film was extruded at 370° C. through a 0.5 mm slit and once cooled, the resulting film was stretched in the same manner as in Example 1. Table 1 shows the mechanical properties and thickness of the obtained film. Example 2 A level weave 70 mesh wire mesh made of bronze wire with a diameter of 0.2 mm was used, and a wire mesh of 2.7 W/
Extrusion and stretching were carried out in the same manner as in Example 1 except that a power of cm ² was applied and heating was performed. The mechanical properties and thickness of the obtained film are shown in Table 1. 【table】

Claims (1)

[Scope of Claims] 1. When producing a film by melt-extruding a polyester that has the property of forming an optically anisotropic melt through a slit, it is possible to melt and extrude polyester having the property of forming an optically anisotropic melt through a slit, within the melt passage of the slit and slightly from the tip (lip) on the discharge side. A plate-shaped porous body having a large number of slots inside is provided, and at least the discharge side surface of the plate-shaped porous body is heated to separate the melt that has passed through a certain slot and the melt that has passed through an adjacent slot. 1. A method for producing a polyester film, which comprises rejoining the polyester films in a slit to form a continuous layer in the width direction of the slit, and then melt-extruding the film. 2 Polyester consisting of repeating units of the following formulas (A), (B) and (C) [However, in the formula, x:y and x:z are both 80:20
to 50:50, y:z is 10:15 to 15:10, n is 0
or 1, and the carbonyl groups in formula (B) are in a meta- or (and) para-position relationship with each other, and formula (C)
When n=0, the oxy groups are in a meta or (and) para position with each other, and when n=1, they are in a meta or (and) position with respect to the diphenyl group.
It is related to the para position. ] The method for producing a polyester film according to claim 1, characterized in that: