JPS61102234A - Manufacture of polyester film - Google Patents

Abstract

PURPOSE:To manufacture isotropically well balanced biaxially oriented film, even in the width direction of which the mechanical properties and dimensional stability are also excellent, by a method wherein film is manufactured so that the ratio of the draw ratio in the width direction normal to the pulling-off direction to that in the bulling-off direction is made so as to be the specified value. CONSTITUTION:When the manufacturing of biaxially oriented film is intended by inflation method out of polyester, which forms optically anisotropic melt, the film is manufactured so that the ratio of the draw ratio in the width direction normal to the pulling-off direction to that in the pulling-off direction is 2.5 or more. In the range of the temperature, under which the polyester is fluid, or under molten state, the polyester has a property that light transmits in the optical system equipped with polarizers, the principal planes of which are arranged at right angles. When amorphous polyester is molded by inflation method, any desired optical state can be given to the resultant film by controlling the temperature change and pulling-off speed of the polyester film leaving a die.

Description

DETAILED DESCRIPTION OF THE INVENTION The invention relates to a method for producing polyester films, more specifically, an inflation film from polyester to form an optically anisotropic melt. The present invention relates to a method for producing an equidirectionally balanced biaxially oriented film having excellent mechanical properties and dimensional stability not only in the take-up direction but also in the width direction.

Conventional Technology Conventionally, among the film manufacturing methods, the inflation method has been applied to various plastic films as a method for manufacturing simultaneous biaxially oriented films because biaxially oriented films can be obtained with relatively simple equipment. There is.

By the way, from polyester that forms an optically anisotropic melt called liquid crystal polyester, fibers, resin molded products, and films with excellent mechanical properties can be obtained through a relatively easy manufacturing process due to its liquid crystal orientation. It is also known that these have relatively good heat resistance.

As a method for producing a film from such liquid crystal polyester, the above-mentioned inflation method is used, with a stretching ratio in the take-off direction of 2 to 50 times and a width direction O stretching ratio (expansion rate) perpendicular to the take-off direction of 1.2 to 20 times. A method for obtaining a biaxially oriented film has been proposed (JP-A-56-46728).
Publication No.).

However, since the liquid crystal polyester exhibits optical anisotropy in the molten state, under such film forming conditions,
Satisfactory results are not always obtained. For example, under the conditions used in the above-mentioned method, where the stretching ratio and expansion rate in the take-off direction are approximately equal, the orientation in the take-off direction is significantly stronger than the orientation in the width direction, resulting in good mechanical properties in the take-off direction. Despite having good and dimensional stability, these products have the disadvantage that they yield films that are significantly inferior in the width direction compared to the take-up direction.

Problems to be Solved by the Invention The purpose of the invention is to overcome these drawbacks and create a machine that is excellent not only in the drawing direction but also in the width direction by using an inflation method from polyester that forms an optically anisotropic melt. It is an object of the present invention to provide a method for producing an isodirectionally balanced biaxially oriented film having dimensional properties and dimensional stability.

Means to Solve the Problem As a result of intensive research by the inventors, the inventors developed a film so that the ratio of the stretching ratio in the width direction perpendicular to the pulling direction to the stretching ratio in the pulling direction was a specific value. The inventors have discovered that the above object can be achieved by doing so, and have completed the invention based on this knowledge.

That is, in producing a biaxially oriented film using the inflation method from a polyester that forms an anisotropic melt, the stretching ratio in the width direction perpendicular to the drawing direction is the same as the stretching ratio in the drawing direction. The present invention provides a method for producing a polyester film in which the film is formed at a magnification of 2.5 times or more with a ratio of 11%.

In the present invention, a polyester that forms an optically anisotropic melt means a polyester that has the property of transmitting light in an optical system equipped with polarizers crossed at 90° in a flowable temperature range, that is, in a molten state. . Such polyesters include (1) one or more units of aromatic dicarboxylic acids and alicyclic dicarboxylic acids, and one or more units of aromatic diols, alicyclic diols, and aliphatic diols.
(2) one or more units of aromatic oxycarboxylic acid; (3)
An example is one consisting of a unit (1) and a unit (2). Here, the aromatic dicarboxylic acids include terephthalic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-triphenyldicarboxylic acid, 2,6-naphthalene dicarboxylic acid, diphenyl ether-4,4'-dicarboxylic acid,
Diphenoxyethane-4,4'-dicarboxylic acid, diphenoxybutane-4+4'-dicarboxylic acid, diphenylethane-4,4'-dicarboxylic acid, isophthalic acid, diphenyl ether-3,3'-dicarboxylic acid, diphenoxyethane- 3,3'-dicarboxylic acid, diphenylethane
Aromatic dicarboxylic acids such as a, a'-dicarboxylic acid, naphthalene-1,6-dicarboxylic acid, and c) chlorterephthalic acid, dichloroterephthalic acid 114!2, bromoterephthalic acid, methylterephthalic acid.

Examples include alkyl, alkoxy, or halogen substituted products of the aromatic dicarboxylic acids such as dimethyl terephthalic acid, ethyl terephthalic acid, methoxyterephthalic acid, and ethoxyterephthalic acid.

Examples of alicyclic dicarboxylic acids include alicyclic dicarboxylic acids such as trans-1,4-cyclohexanedicarboxylic acid, cis-1,4-cyclohexanedicarboxylic acid, and 1,3-cyclohexanedicarboxylic acid, or trans-1,4-( 1
-methyl)cyclohexanedicarboxylic acid, trans-1
, 4-(1-chloro)cyclohexanedicarboxylic acid, and the like, alkyl, alkoxy, or halogen-substituted alicyclic dicarboxylic acids.

Aromatic diols include hydroquinone, resorcinol,
4.4'-dioxydiphenyl, 4.4'-dioxytriphenyl, 2.6-naphthalenediol, 4.4'
-dioxydiphenyl ether, bis(4-oxyphenoxy)ethane, 3.3'-dioxydiphenyl,
Aromatic diols such as 3.3'-dioxydiphenyl ether, 1.6-naphthalenediol, 2,2-bis(4-hydroxyphenyl)furopane, 2.2-bis(4-hydroxyphenyl)methane, or chlorohydroquinone , methylhydroquinone, t-butylhydroquinone, phenylhydroquinone, methoxyhydroquinone, phenoxyhydroquinone, 4-chlorresorcinol, 4-methylresorcinol, and other alkyl, alkoxy, or halogen-substituted aromatic diols.

Examples of aliphatic group diols include trans-1,4-cyclohexanediol, cis-1,4-cyclohexanediol, trans-1,4-cyclohexane dimetatool, cis-1,4-cyclohexane dimetatool, and trans-1,4-cyclohexanediol. 1,3-cyclohexanediol, cis-1,2
-Alicyclic diols such as cyclohexanediol, trans-1,3-cyclohexane dimetatool, or trans-1,4-(1-methyl)cyclohexanediol, trans-1,4-(1-chloro)cyclohexanediol Examples include alkyl, alkoxy or halogen substituted products of the alicyclic diols.

Examples of aliphatic diols include ethylene glycol, ],
3-7'ropanediol, 1,4-butanediol,
Mention may be made of linear or branched aliphatic diols such as neopentyl glycol.

Aromatic oxycarboxylic acids include p-hydroxybenzoic acid, 1m-hydroxybenzoic acid, 6-hydroxy-2-
Aromatic oxycarboxylic acids such as naphthoic acid, 6-hydroxy-1-naphthoic acid, 3-methyl-4-hydroxybenzoic acid, 3-chloro-4-hydroxybenzoic acid, 3
Examples of the -methoxy-4-hydroxybenzoic acid include alkyl, alkoxy or hahalogen substituted products of the aromatic oxycarboxylic acids.

Polyesters composed of one unit of each of the monomers (1) to (3) above may or may not form an optically anisotropic melt depending on the constituent units, the composition ratio in the polymer, and sea fence distribution. However, among the polyesters mentioned above, the polyesters used in the present invention are limited to those that completely form an optically anisotropic melt.

The polyester used in the invention has a softening point of 130 to 400.
It is preferably in the range of 180 to 350°C, more preferably in the range of 180 to 350°C.

Preferred polyesters used in the invention include (1) units selected from the following: terephthalic acid, diphenyl ether-4,4'-dicarboxylic acid, diphenoxyethane-4,4'-dicarboxylic acid, and 2,6-naphthalene dicarboxylic acid; and at least one unit selected from hydroquinone, chlorohydroquinone, methylhydroquinone, methoxyhydroquinone, phenylhydroquinone, and phenoxyhydroquinone, (2) at least one unit selected from terephthalic acid, diphenyl ether-4,4'-dicarboxylic acid, dienoxyethane-4,4'-dicarboxylic acid, and 2,6-naphthalene dicarboxylic acid; and hydroquinone. , chlorhydroquinone,
A copolyester composed of at least one unit selected from methylhydroquinone, methoxyhydroquinone, phenylhydroquinone, and phenoxyhydroquinone units and p-hydroxybenzoic acid units, (3)
At least one unit selected from terephthalic acid, diphenyl ether-4,4'-dicarboxylic acid, diphenoxyethane-4,4'-dicarboxylic acid, and 2,6-naphthalene dicarboxylic acid units, and ethylene glycol. (4) Terephthalic acid, diphenyl ether-4,4'-dicarboxylic acid, dienoxyethane-
At least 41 units selected from 4,4'-dicarboxylic acid and 2,6-naphthalene dicarboxylic acid units, and each of hydroquinone, chlorohydroquinone, methylhydroquinone, methoxyhydroquinone, phenylhydroquinone, and phenoxyhydroquinone. Copolyester composed of at least one unit selected from among units and ethylene glycol unit, (5) prephthalic acid, diphenyl ether-4,4'-dicarboxylic acid, dienoxyethane-4,4' - at least one unit selected from each unit of dicarboxylic acid and 2,6-naphthalene dicarboxylic acid, and hydroquinone, chlorohydroquinone,
Examples include device esters composed of at least one unit selected from methylhydroquinone, methoxyhydroquinone, phenylhydroquinone, and phenoxyhydroquinone units, an ethylene glycol unit, and a p-hydroxybenzoic acid unit.

The polyester used in the invention can be produced by a known method from dicarboxylic acids, diols, oxycarboxylic acids, and derivatives thereof corresponding to the above-mentioned structural units. For example, (1) at least one selected from aromatic dicarboxylic acids and alicyclic dicarboxylic acids;
A method of mixing at least one selected from aromatic diols and acetate esters of alicyclic diols and performing an acetic acid depolycondensation reaction while heating and stirring; (2) aromatic dicarboxylic acid and alicyclic dicarboxylic acid; At least one selected from acids, at least one selected from acetic esters of aromatic diols and alicyclic diols, and acetic esters of aromatic oxycarboxylic acids are mixed, heated,
A method of performing acetic acid depolycondensation reaction while stirring, (3) at least one selected from phenyl esters of aromatic dicarboxylic acids and alicyclic dicarboxylic acids, and aromatic diols and alicyclic diols. At least one selected
(4) At least one selected from phenyl esters of aromatic dicarboxylic acids and alicyclic dicarboxylic acids, aromatic diol and A method of mixing at least one selected from alicyclic diols and a phenyl ester of an aromatic oxycarboxylic acid and carrying out a dephenol-depolycondensation reaction while heating and stirring, (5) an aromatic dicarboxylic acid and polyesters obtained by conventional melt polycondensation from at least one selected from alicyclic carboxylic acids and aliphatic diols, such as polyethylene terephthalate and polybutylene terephthalate.

Poly(ethylene-1,2-bis-diphenoxyethane-
p, p'-dicarboxylate, etc., (a) at least one selected from aromatic dicarboxylic acids and aliphatic dicarboxylic acids, and acetic esters of aromatic diols and alicyclic diols; 1 A method of carrying out acidolysis reaction and deacetic acid polycondensation reaction, (b)
) A method of mixing acetate esters of aromatic oxycarboxylic acids and performing an acidolysis reaction and deacetic acid polycondensation reaction while heating and stirring; (C) at least one selected from aromatic dicarboxylic acids and alicyclic dicarboxylic acids; The seeds, at least one selected from the acetate esters of aromatic diols, alicyclic diols, and group diols, and the acetate ester of aromatic oxycarboxylic acid are mixed, and the mixture undergoes acidolysis reaction and acetic acid depolycondensation while heating and stirring. It can be produced by a reaction method or the like.

These polycondensation reactions are usually carried out in a molten state at a temperature range of 150 to 400°C and a pressure range of normal pressure to 0.01 torr, and in the final stage of the reaction, l Q torr to 0
．． It is carried out under reduced pressure of 01'torr. Furthermore, a polycondensation catalyst such as an antimony or germanium compound, a stabilizer such as a phosphorus compound, a matting agent such as titanium oxide, etc. can be added at any time from the start to the end of the reaction, if necessary. The obtained polyester melt can be extruded as it is from a die to form a film, or it can be used for film formation after being cooled and solidified. It can also be used for film formation after solid phase polymerization in an inert gas or under reduced pressure.

In addition, other meltable polymers such as nylon, polyethylene terephthalate, etc. can be appropriately blended with the polyester used in the invention, if necessary, in an amount that does not satisfy the desired physical properties.

In accordance with the invention, the polyester thus obtained forms an optically anisotropic melt.

A biaxially oriented film is formed by an inflation method. The unique feature of this invention is that in order to obtain a biaxially oriented film that has excellent mechanical properties and dimensional stability not only in the drawing direction but also in the width direction, the stretching ratio in the width direction perpendicular to the drawing direction is increased. The point is that the film is formed so that the stretching ratio in the take-off direction is 2.5 times or more.

Next, to explain a preferred embodiment of the invention, the accompanying drawings are schematic diagrams showing different examples of bubble formation in molten polyester discharged from an inflation die having an annular slit. Figure 1 shows a state in which stretching occurs in the mountain direction immediately after exiting the die.
Figure 3 shows a state in which only stretching occurs in the take-up direction until a certain distance after being discharged from the die, and then stretching in the 1] direction, and Figure 2 shows an intermediate state between these. This shows a state in which stretching in the take-off direction and the width direction occurs simultaneously immediately after exiting the die.

In these figures, the black arrows indicate the flow of polyester.
The white arrow represents the gas flow for expanding the tubular film, the symbol is the annular slit die diameter, d is the diameter of the tubular film after expansion is completed, h is the inside of the annular slit, and L is the length of the annular slit. , 1 is the distance from the die to the starting point of expansion, t is the thickness of the tubular film after expansion is completed,
■ Discharge linear speed (extrusion speed), ■ is winding speed.

In the invention, the film may be formed in any of the states shown in FIGS. 1, 2, and 3, but the state shown in FIG. Revised 6j &d'R
'+t l, Lx, WJL;F'""7 y /L-
(In D-inflation molding, by adjusting the discharge temperature from the die, the temperature change of the polyester flow after discharge from the die, and the take-up speed history, it is possible to achieve any of the conditions shown in Figures 1, 2, and 3. Can be formed into a film.

When inflation occurs in the state shown in Fig. 3, the relationship between the distance t from the die to the inflation start point and the die diameter should be selected so that t/D is in the range of 0.5 to 15. It is preferable to start the expansion rapidly at the expansion start point, since it is easier to control the orientation of the polymer than to start the expansion slowly.

In addition, the stretching ratio (expansion ratio) in the width direction perpendicular to the pulling direction
drl and the stretching ratio dr2 in the take-off direction are expressed by the following formula.

drl= d/'D dr2 = vA' = S/s [However, d° bubble diameter, D, die diameter, ■, take-up speed,
■ = Discharge linear velocity, S, area of the annular slit of the die, S:
Cross-sectional area of the film πat, (t film thickness)] In film formation by such an inflation method,
The die temperature is desirably at least the softening point of the polyester, preferably at least 10°C higher than the softening point and at most 400°C, and the preferred apparent viscosity of the polyester is:
Temperature conditions for film formation and shear rate of 100,000
sec, it is lO~2000 poise, more preferably in the range of 20~1000 poise. This apparent viscosity is influenced by the degree of polymerization, temperature, and shear rate of the polyester; if the viscosity is too low, the resulting film will have poor mechanical properties, and if it is too high, the stringability of the melt will decrease and the expansion rate will decrease. Therefore, it is difficult to obtain a uniform 2111 orientation in many cases.

Furthermore, the intrinsic viscosity of the polymer is 0.5 or more, especially 1.0
It is preferable that the intrinsic viscosity is less than or equal to 1. If the intrinsic viscosity is small, the resulting film will have poor mechanical strength and is not suitable. In the inflation method, a tubular film is obtained by extruding a molten polymer through a die having an annular slit.

At this time, the gap between the slits can be appropriately selected depending on the desired thickness of the film. The gap between this slit is usually 0
．． 01-101111-preferably selected in the range of 0.05-2. T, /h (T, length of the slit, h, gap between the slits) of the die is usually selected in the range of 3 to 70, preferably 5 to 50.

In the present invention, the tubular film thus discharged from the die may be forcibly or naturally cooled as it is, or it may be forced or cooled after passing through a high temperature atmosphere such as a heating cylinder or a heat insulating cylinder. Natural cooling may be used. In this way, by appropriately changing the temperature distribution of the atmosphere after being discharged from the die depending on the characteristics of the polyester used, the valve can be made into one of the types shown in Figures 1, 2, and 3 above. It is possible to form a film in a desired state.

The tubular film discharged from the die is expanded by applying an external force, for example, gas pressure from the inner surface, and at the same time is wound up while being stretched or contracted as necessary in the take-up direction to obtain a film. In this case, the stretching ratio in the direction 1] perpendicular to the taking direction is preferably 2 or more, especially in the range of 3 to 50, and the stretching ratio in the taking direction is preferably 0.1 or more, especially 0.2 to 20. Preferably within this range.

In the invention, it is necessary to form a film so that the stretching ratio in the width direction perpendicular to the pulling direction is 2.5 times or more, particularly in the range of 3 to 15 times. It is preferable to form a film so that Only by forming the film under these conditions can the orientation of the polymer in the resulting film be balanced in the drawing direction and the width direction, resulting in excellent mechanical properties not only in the drawing direction but also in the width direction. It has properties and dimensional stability. A transparent film with good heat resistance can be obtained.

The properties of the film thus obtained can be improved, if necessary, by further heat-treating it under tension or relaxation.

Effects of the Invention Conventional methods, for example, the film forming method described in JP-A No. 56-46728, in which the ratio of the stretching ratio in the take-off direction to the expansion ratio is l l, cannot obtain an isotropic film, and In contrast to films that are excessively uniaxially oriented in the direction (or rather split fiber-like), the films obtained by the uninvented method are excellent not only in the drawing direction but also in the width direction. It is an equidirectionally balanced biaxially oriented film with good mechanical properties and dimensional stability (il-w), and also has high strength, high modulus, low moisture content, good heat resistance, and Moisture dimensional stability.

Video tapes, computer tapes, and cassette tapes because they have good weather resistance.

It is preferably used for electrical-related applications such as floppy disks and films for flexible printed wiring boards, and can also be used for packaging and laminating thereof.

EXAMPLES Next, the present invention will be explained in more detail with reference to Examples.0 Note that each physical property and shear rate were measured according to the methods shown below.

(1) Apparent viscosity (melt viscosity) ηa was calculated by the following formula from the discharge amount Q [m1ZSeC] by discharging the polymer under the same temperature conditions as the 5M film using a high shear rate flow tester.

+7+a = πPr'/8 tQ γa=4Q/πr, where: Nozzle length [, ], r: Nozzle radius [
, ], P Pressure when extruding through the nozzle [+1yne /
ca ] In addition, 'l = 0.05m, r = 0.012
5 cm, p=9.8 X l 07dyne/
Measured under * conditions.

(2) Intrinsic viscosity ηsp/C 125cm of thoroughly dried polyester was added to 25cc of a mixed solvent consisting of 25% by weight of phenol, 35% by weight of tetrachloroethane and 40% by weight of Up-chlorophenol, and heated at 140°C for 1 hour. After heating with stirring to completely dissolve, the mixture is allowed to cool naturally to 20°C. Take out 10 cc of this solution.

Transferred to Ostwald viscosity liquid and soaked in a constant temperature bath at 35℃.
When the solution temperature reaches 35°C, the flow time T [sec
″3'i was measured and calculated using the following formula.

ηop/c-(T/To-1)/c c = 0.125725 However, To: Flow time of only the solvent containing no polymer [sec] Example 1 Methylhydroquinone diacetate 197. ．． 6f(0,
95 mol), terephthalic acid 124.4 f? (0,7
5 mol), p-acetoxybenzoic acid 284.4 f (
1,58 mol), polyethylene terephthalate) 129
．． 69 (0.68 mol) was charged into a polymerization reactor equipped with a stirrer and a vacuum distillation device, and the temperature was raised to 310°C over 60 minutes while stirring in a nitrogen stream, and the pressure was gradually reduced over 5 minutes. The reaction was carried out at 2 torr for 180 minutes. After the reaction was completed, nitrogen was introduced to return the system to normal pressure, the polyester melt was taken out, and the polyester was allowed to cool and solidify naturally.
It was crushed with a crusher.

The melting point of the obtained polyester was 270°C, and it exhibited optical anisotropy in a molten state. The intrinsic viscosity is 1.96,
Melt viscosity at 310°C is 100,0OOsec-
It showed 150 voids at a shear rate of '.

This polyester 'i was produced at 310°C, with a diameter IQi+i, a slit width of 0, and a circular slit die of 25 m.
It is extruded at a speed of crn/min, and nitrogen is pressurized into the hollow part of this tubular film to make the diameter of the tubular film about 1 cm below the die.
After rapidly expanding 5.3 times at m, 70 cm
/ mJ n. At this time, the bottom of the die was heated to about 300° C. with a cylindrical cover, and then cooled with air at room temperature.

The obtained film had a stretching ratio (expansion ratio) in the width direction that was 4.5 times that of the stretching ratio in the take-off direction, and when this film was subjected to a full tensile test, the initial modulus, strength, and elongation in the take-off direction were as follows. 388Kg/ysd each.

11.6Kg/md, 7.3%, initial modulus in the width direction, strong U, stretch tL406, 9/lnd, 1
2.5 Kg/ml 1, 2, 7%, and was a transparent film with almost the same performance in the take-up direction and the width direction. Moreover, the moisture content was in the o and i ratios.

Example 2 Polyester was obtained by polymerizing and pulverizing in the same manner as in Example 1 using the same raw material composition.

The intrinsic viscosity of this polyester is 1.65, and at 300°C, the diameter is 3.5mm, and the slit width is 0°251mm.
The annular film was extruded at a speed of 170 crn/min through a circular slit die of 374 cm, and nitrogen was injected into the hollow part of the annular film to rapidly expand it by 8 times at about 2 m below the die.
It was wound up at a speed of m/min.

The obtained film is transparent with a stretching ratio (expansion ratio) in the width direction of 3.7 times as much as the stretching ratio in the take-off direction,
The initial modulus, strength, and elongation in the pulling direction are each 51.
9/if for 1, 77i+d for 9.3, 4.9%, initial modulus in the width direction, strength, and elongation are each 543 Ky/
m11.8.9Kg/myA, 3.9% T atte, and showed almost the same performance in the take-up direction and width direction.

Example 3 ,-A and F-Ya. , □, 6°, 8□2. . □F23
, 1,6-acetoxy-2-naphthoic acid 107. O
f (0,47 mol), tv7 tkrIR51,4t
(0.31 mol), biphenol diacetate 83.
89 (0.31 mol) was charged into a polymerization reactor equipped with a stirrer and a vacuum distillation device, and the temperature was raised to 330°C over 60 minutes while stirring in a nitrogen stream, and then the pressure was gradually reduced over 10 minutes. The reaction was carried out at 2 torr for 130 minutes. After the reaction was completed, nitrogen was introduced to return the system to normal pressure, the polyester melt was taken out, allowed to cool naturally to solidify, and then pulverized using a crusher. .

The melting point of the obtained polyester was 270°C, and the melt viscosity at 320°C was 50 poise at a shear rate of 16,000 θeC-1.

This polyester'i at 310°C has a diameter of 5111. 56c from annular slit die with slit width 0.25m5+
The annular film was extruded at a speed of 63 cm/min, and nitrogen was injected into the hollow part of the annular film to rapidly expand it by a factor of 5.0 at about 2 saws below the die, and the film was wound up at a speed of 63 cm/min.

The obtained film is a transparent film in which the stretch ratio in the width direction is 4.4 times that in the take-off direction, and the initial modulus, strength, and elongation in the take-off direction are each n381 kg.
/ml, 22.0 to 9/ynd, 34.6%, initial modulus in the width direction, strength, and elongation are each 323 K9
/ll111.18.4Kg/mti, 35.3%
It showed almost the same performance in the take-up direction and the width direction.

Comparative Example 1 The polyester obtained in Example 1 was heated at 310°C and the diameter IQ1
1+, extruded at a speed of 56 cm/min through an annular slit die with a slit width of 0.25111, nitrogen was injected into the hollow part of the tubular film, and the tubular film was rapidly expanded at approximately 1 era below the die. .4 times 1
It was wound up at a speed of 18 m/min.

The obtained film has a stretching ratio in the width direction that is 2.2 times that of the stretching ratio in the take-off direction, and the initial modulus, strength, and elongation in the take-off direction are 1220 K9/rad, respectively.
17.4 K97d, 2.1%, while the initial modulus in the width direction, strength, and elongation were each 59 Kg/
md, 1.2 to 9/myll, 3.2%,
Although it had good mechanical properties in the drawing direction, it was an unbalanced film that was extremely weak in the width direction.

Comparative Example 2 The polyester obtained in Example 2 was heated to 310°C with a diameter of 1
The tubular film is extruded at a speed of 56 cm/mj, n through a 25 mm annular slit die, nitrogen is injected into the hollow part of the tubular film, and the tubular film is rapidly expanded immediately after exiting the die. 5.1 times the diameter of 118
It was wound at a speed of cm/mj, n.

The obtained film has a stretching ratio in the width direction of 2.4 times as much as a stretching ratio in the pulling direction, and the initial modulus, strength, and elongation in the pulling direction are 747 and 9/myl, respectively.
19.8 K9/m1N, 3.0%, while the initial modulus in the width direction, strength, and elongation were each 16
6 Kg/mtfL, 2.6 g/vrtl, 1.
9, the film had unbalanced mechanical performance in the take-up direction and the width direction.

Note that it was confirmed that the polyester melts used in Examples 2 and 3 had optical anisotropy when observed using a polarizing microscope.

[Brief explanation of the drawing]

FIGS. 1, 2, and 3 are schematic diagrams showing different examples of the state in which the molten polyester discharged from the annular slit die forms bubbles in the uninvented method.

Claims (1)

[Claims] 1. When producing a biaxially oriented film by the inflation method from a polyester that forms an optically anisotropic melt, the stretching ratio in the width direction perpendicular to the pulling direction is 2.5 with respect to the stretching ratio in the pulling direction. A method for producing a polyester film, characterized by forming the film so that the film is more than doubled in size.