JP2001342243A - Aromatic liquid crystal polyester film and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a film having low-temperature processability, capable of being formed into a thin film, especially excellent in oxygen barrier and steam barrier properties and composed of an aromatic liquid crystal polyester. SOLUTION: This film is obtained by melting and extruding the aromatic liquid crystal polyester comprising 65-25 mol% repeating unit (A) and 35-75 mol%; repeating unit (B) based on the whole repeating units, and having <=300 deg.C fluidization temperature, >=4.0 dl/g logarithm viscosity and 0.20-0.80 value of the ratio (viscosity 2/viscosity 1) of the melt viscosity (viscosity 2) measured at the temperature 20 deg.C higher than the fluidization temperature at a shear rate of 100 sec-1 or 1,000 sec-1 to the melt viscosity (viscosity 1) measured at the fluidization temperature at the sear rate same as that at the measurement of the viscosity 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aromatic liquid crystalline polyester film excellent in film formability (film forming property) and oxygen / water vapor barrier properties, and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, films made from various polymers have become indispensable in daily life. For example, various films such as a high strength film, a high elasticity film, an oxygen barrier film, a conductive film, a heat resistant film, and a light barrier film have been developed. Above all, films having an oxygen barrier property or a water vapor barrier property are permeating our lives as packaging materials regardless of whether they are for industrial use or for consumer use.

Conventionally, in this field, stretched films of polyolefins such as polyethylene and polypropylene, stretched films of polyethylene terephthalate (hereinafter abbreviated as PET), polyvinylidene chloride (hereinafter abbreviated as PVDC) films, saponified ethylene -A vinyl acetate copolymer (hereinafter abbreviated as EVOH) film or the like has been developed and used as a single layer or a multilayer film having two or more layers depending on the purpose and application. In many cases, multilayering is essential to maintain gas barrier properties, which is one of the factors that increase the manufacturing cost. In recent years, in the field of food packaging such as retort pouches, there is a tendency to perform high-temperature and short-time treatment for efficient sterilization, and a packaging material having high heat resistance is required. PET films and the like on which silica, alumina, and the like have been deposited have been developed, but there are still problems in the waste separation and incineration methods in the future. Polyethylene naphthalate (hereinafter referred to as PE) with improved heat resistance and oxygen barrier properties of PET film
Abbreviated as N. ) Based packaging development of materials (container) have been made, but high gas barrier property (oxygen permeability 1cc / m ² · 24
Gas barrier properties are still insufficient for applications (e.g., hr · atm or less) (for example, Japanese Patent Application Laid-Open Nos. 8-113363 and 8-92467). In addition, for EVOH, which is excellent in oxygen barrier property, but inferior in steam barrier property, the problem of steam barrier property is being solved by forming a multilayer film laminated with polyolefin or the like having excellent steam barrier property, Problems remain in heat resistance.

[0004] These fields are inexpensive and heat resistant,
Assuming future room temperature distribution, a resin material for films (high gas barrier material) having both high water vapor barrier properties and high oxygen barrier properties is desired. As a resin material having an oxygen barrier property and a water vapor barrier property, a liquid crystal polymer, particularly a thermotropic liquid crystal polyester (hereinafter, may be abbreviated as LCP) has been attracting attention, and a film formation thereof has been studied. For example, PET / having an aliphatic chain in the main chain
Liquid crystalline copolyester resin composed of p-hydroxybenzoic acid (hereinafter sometimes abbreviated as POB) (Japanese Patent Publication No. 8-2974) and other semi-aromatic liquid crystalline polyesters (Japanese Patent Publication No. 6-53383). Film and wholly aromatic liquid crystalline polyester (JP-A-7-323506)
And JP-A-7-251438).

[0005] However, in these, molecular orientation occurs in the flow direction (MD), which is a characteristic of LCP, and mechanical anisotropy occurs in the direction (TD) perpendicular to the molecular orientation.
It was difficult to make the film thinner, and it was difficult to obtain a thin film having a practical LCP film thickness of 50 μm or less. Some of the PET / POB copolyesters,
Except for polyesters (for example, Vectra series) obtained by copolymerizing different aromatic hydroxycarboxylic acids, the processing temperature of wholly aromatic LCP often exceeds 300 ° C., and the deflection temperature under load (TDUL) is 250. Liquid crystalline wholly aromatic polyesters having heat resistance exceeding ℃
In some cases, a higher processing temperature of 350 ° C. or higher was required, and an expensive processing machine with special specifications was required.

Further, for practical use as, for example, a gas barrier film, it is desired that it can be easily compounded (multi-layered) with another thermoplastic resin film. For that purpose, it has been desired that the thin film is excellent in low-temperature processability as well as has a positive heat shrinkage like other thermoplastic resin films.

A method for forming a film from a wholly aromatic polyester resin which forms an optically anisotropic melt upon melting is described in, for example, Japanese Patent Publication No. 62-58378 and Japanese Patent Publication No. 63-33450. Although a film forming method using a die is described, all require a processing temperature of 340 ° C. or more, and there is still room for improvement in terms of the processing temperature. Further, a film forming method using a rotary die or the like is disclosed in US Pat.
Nos. 5312 and WO9015706, all of which show a method of relaxing anisotropy peculiar to liquid crystal polyester by a special molding method.
A wholly aromatic liquid crystalline polyester obtained by copolymerizing different kinds of aromatic hydroxycarboxylic acids which can be molded at a low temperature (320 ° C. or lower) is described in JP-B-63-3888. Japanese Patent Application Laid-Open No. 2-3430 discloses a method for forming an inflation film at a high shear rate of 500 sec ^-1 or more using the melt strength measured under a certain condition as a technical factor as an index on film formation. And a film of 16 μm to 22 μm is exemplified. However, these films have 250
The heat shrinkage at ℃ is 1% or less in both the machine axis direction (MD direction) and the direction perpendicular to it (TD direction), which is extremely excellent in dimensional stability. If the difference in shrinkage is too large to be used as a multilayer film, it is considered to cause warpage and wrinkles. In addition, there remains a problem of further thinning.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide an aromatic liquid crystalline polyester which has a low-temperature processability, can be formed into a thin film, and is particularly excellent in gas barrier properties (oxygen barrier properties, water vapor barrier properties). An object of the present invention is to provide a film and a method for producing the film.

[0009]

Means for Solving the Problems The present inventors have studied diligently about the formation of a film of an aromatic liquid crystalline polyester comprising two or more aromatic hydroxycarboxylic acid units, and have found that a composition having a relatively high ratio of naphthalene nuclei. In this case, the inventors have found that a film which can be formed into a thin film and has particularly excellent gas barrier properties (oxygen barrier properties and water vapor barrier properties) can be obtained, and the present invention has been completed.

That is, the present invention relates to [1] an aromatic liquid crystalline polyester comprising two or more aromatic hydroxycarboxylic acid units, wherein the following repeating unit (A) is 65 to 25 mol% of the entire repeating unit, (B) 35
Wherein 75 mol%, the flow temperature is at 300 ° C. or less, a logarithmic viscosity of 4.0 dl / g or more, and the melt viscosity measured at a shear rate of 100 sec ^-1 or of 1,000 sec ^-1 at the flow temperature (viscosity 1), The value of the ratio (viscosity 2 / viscosity 1) of the viscosity 1 to the melt viscosity (viscosity 2) measured at the same shear rate at a temperature 20 ° C. higher than the flow temperature is 0.20.
The present invention relates to a film which is melt-extruded from an aromatic liquid crystalline polyester having a molecular weight of about 0.80.

Embedded image

Embedded image Here, the flow temperature is measured by a capillary rheometer, and the resin heated and melted at a heating rate of 4 ° C./min is subjected to a load of 100 kgf / cm ² and an inner diameter of 1 mm and a length of 10 mm.
mm when extruded from a nozzle having a melt viscosity of 48,
A temperature (° C.) indicating 000 poise.

The present invention further provides [2] an aromatic liquid crystalline polyester comprising two or more aromatic hydroxycarboxylic acid units, wherein the repeating unit (A) described in [1] is used in an amount of 65 to 25 mol% of the entire repeating unit. Containing 35 to 75 mol% of the repeating unit (B), having a flow temperature of 300 ° C. or lower, a melt tension measured at a temperature 25 ° C. or higher than the flow temperature of 3.0 g or more, and winding at the time of cutting. The present invention relates to a film melt-extruded from an aromatic liquid crystalline polyester having a speed of 10 m / min or more.

Further, the present invention relates to [3] mixing a compound represented by the following formula (I) at a ratio of 65 to 25 mol% and a compound represented by the following formula (II) at a ratio of 35 to 75 mol%. Into a reaction vessel to cause a polycondensation reaction at 270 ° C. to 350 ° C.
Flow temperature is 200 ° C or more and 30 ° C from polycondensation reaction temperature
The above-mentioned aromatic liquid crystalline polyester having a low temperature is produced, the aromatic liquid crystalline polyester, which is the content of the reaction vessel, is recovered in a molten state and solidified, and then pulverized into particles having a particle size of 3 mm or less. 200 ° C under an inert gas atmosphere in the phase state
The present invention relates to the film according to [1] or [2], which is melt-extruded from an aromatic liquid crystalline polyester heat-treated at a temperature of from about 300 ° C.

Embedded image (However, R ¹ represents a hydrogen atom, a formyl group, an acetyl group, a propionyl group or a benzoyl group, and R ² represents a hydrogen atom, a methyl group, an ethyl group, a propyl group, a benzyl group or a phenyl group.)

Embedded image (However, the definitions of R ¹ and R ² are the same as the respective definitions in formula (I). R in formulas (I) and (II)
¹ may be the same or different from each other, and R ² in the formula (I) and the formula (II) may be the same or different from each other. )

Further, the present invention provides [4] the above [1] to [1].
The present invention relates to a method for producing an aromatic liquid crystalline polyester film, wherein the aromatic liquid crystalline polyester according to any one of [3] is formed into an inflation film at a temperature of 60 ° C. or higher than a flowing temperature.

Further, the present invention provides the above [5] [1] to [1].
The aromatic liquid crystalline polyester according to any one of [3] is blown (TD stretching ratio) 1.5 to 15, draw ratio (MD stretching ratio) 1.5 to 60, and 500 sec ^{− The present} invention relates to a method for producing an aromatic liquid crystalline polyester film for inflation film formation at a shear rate of ¹ or less.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The aromatic liquid crystalline polyester used in the present invention comprises two or more aromatic hydroxycarboxylic acid units, and the repeating unit (A) is 65 to 25 mol% of the entire repeating unit. It preferably contains 60 to 30 mol%, and contains 35 to 75 mol%, preferably 40 to 70 mol% of the repeating unit (B), exhibits optical anisotropy (liquid crystallinity) when melted, and has melt moldability, chemical resistance, It has the feature of excellent mechanical properties.

In the aromatic liquid crystalline polyester used in the present invention, if the repeating unit (A) is less than 25 mol% of the total repeating units constituting the polymer, the processing temperature may exceed 300 ° C. This is not preferred. On the other hand, if it is more than 65 mol%, the oxygen permeability of the aromatic liquid crystalline polyester film may be relatively large, which is not preferable. Within the above range, molding (film formation) at a lower temperature becomes possible, and in particular, it becomes possible to obtain a thin film having excellent oxygen barrier properties and water vapor barrier properties of 25 μm or less. Shows good physical properties and workability.

The aromatic liquid crystalline polyester used in the present invention has a flow temperature of 300 ° C. or lower, preferably 23 ° C. or less.
The temperature is 0 to 295 ° C, more preferably 235 to 290 ° C. If the flow temperature exceeds 300 ° C., the film forming temperature may exceed 350 ° C., which is not preferable.

Here, the flow temperature (hereinafter sometimes abbreviated as FT) is measured by a capillary rheometer.
The resin heated and melted at a heating rate of 4 ° C./min is loaded with a load of 10
Under 0kgf / cm ² , inner diameter 1mm, length 10mm
Melted when extruded from a nozzle of 48,000
A temperature (° C.) indicating poise (corresponding to 4800 Pa · S).

The aromatic liquid crystalline polyester of the present invention has a logarithmic viscosity (ηinh) defined by the following formula of 4.0 dl.
/ G or more, more preferably 6.0 dl / g or more, still more preferably 8.0 d, from the viewpoint of mechanical properties and moldability.
1 / g or more. Further, ηinh is preferably 20 dl / g or less, more preferably 15 d / g from the viewpoint of moldability.
1 / g or less. When ηinh is less than 4.0 dl / g, the melt tension is small and there is a problem in film formability and mechanical strength. ηinh = (ln (ηrel)) / C (where ηrel is called the relative viscosity and is the ratio of the polymer solution and the time it takes to fall between certain marked lines in the capillary (polymer solution / solvent). Is the concentration of the polymer solution, the unit is g / dl In the present invention, 3,5-bis (trifluoromethyl) phenol is used as a solvent, the polymer concentration is 0.1 g / dl, and the temperature is 60 ° C. Is the value measured with an Ubbelohde viscometer.)

Examples of the aromatic liquid crystalline polyester in the present invention, the melt viscosity measured at a shear rate of 100 sec ^-1 or of 1,000 sec ^-1 at the flow temperature (viscosity 1)
And the melt viscosity (viscosity 2) measured at the same shear rate as viscosity 1 at a temperature 20 ° C. higher than the flow temperature (viscosity 2)
The value of / viscosity 1) is from 0.20 to 0.80, preferably from 0.25 to 0.70. The value of (viscosity 2 / viscosity 1) of the conventional aromatic liquid crystalline polyester was 0.10 or less, but the aromatic liquid crystalline polyester in the present invention preferably has a larger value than the conventional one. It is considered that such an aromatic liquid crystalline polyester has a small temperature dependency of the melt viscosity and tends to improve the molding stability during processing.

The aromatic liquid crystalline polyester used in the present invention has a capillary inner diameter of 2.1 mm, a length of 8 mm, and a piston speed of 5 mm / 25 ° C. or higher than the flowing temperature.
The melt tension (hereinafter sometimes abbreviated as MT) measured under the conditions of minutes is 3.0 g or more, preferably 4.5 g or more, more preferably 6.0 or more.
g or more. MT is preferably 30.0 g or less, more preferably 25.0 g or less. The winding speed measured at the time of cutting is preferably 10 m / min, more preferably 10 to 100 m / min, and still more preferably 20 m / min.
８０80 m / min. Although it depends on the composition of the aromatic liquid crystalline polyester, when the MT value is less than 3.0 g, the inflation film forming temperature range may be narrow. From the viewpoint of film forming properties, those having a small temperature dependency of MT are preferable.

In the conventional so-called one-stage depressurization polymerization, problems such as adhesion to a pipe at the time of removal and thickening at the time of retention occur, so that it may be difficult to take out with a sufficient molecular weight suitable for film formation. It is estimated that the melt tension mentioned in the present invention cannot always be achieved. After the melt polycondensation (pre-polymerization), the melt is drawn out, and the solid phase polymerization is performed in combination with the pulverized powder, the melt tension can be stably increased to a desired melt tension, which is preferable in film formation.

The preferred aromatic liquid crystalline polyester in the present invention is, for example, 65 to 25 mol% of the compound represented by the formula (I) and 35 to 75 mol% of the compound represented by the formula (II). Mixed in a proportion and charged to the reaction tank, 2
The polycondensation reaction is carried out at 70 ° C.
An aromatic liquid crystalline polyester having a temperature of at least 0 ° C., more preferably at least 210 ° C., and at least 30 ° C. lower than the polycondensation reaction temperature is produced, and the aromatic liquid crystalline polyester which is the content of the reaction vessel is recovered in a molten state. 3mm after solidifying
Pulverized into particles of the following particle size, 200 ° C. in the solid state
It can be obtained by heat-treating at ~ 300 ° C, preferably by subjecting it to a heat treatment in an inert gas atmosphere for 1 to 24 hours and granulating it into a pellet under heating and melting.

In the formulas (I) and (II) in the present invention, those in which a benzene nucleus or a naphthalene nucleus is substituted with a halogen, an alkyl group or the like are also included. Examples of the compound represented by the formula (I) include 4-hydroxybenzoic acid, 4-formoxybenzoic acid, 4-acetoxybenzoic acid, 4-propionyloxybenzoic acid, methyl 4-hydroxybenzoate, and 4-hydroxybenzoic acid. Propyl benzoate, phenyl 4-hydroxybenzoate, benzyl 4-hydroxybenzoate, methyl 4-acetoxybenzoate, 4
Phenyl acetoxybenzoate;
-Hydroxybenzoic acid or 4-acetoxybenzoic acid is preferred.

Examples of the nuclear-substituted compound represented by the above formula (I) include 3-chloro-4-hydroxybenzoic acid, 2-chloro-4-hydroxybenzoic acid, and 2,3-dichloro-4-hydroxy Benzoic acid, 3,5-dichloro-
Examples thereof include 4-hydroxybenzoic acid, 2,5-dichloro-4-hydroxybenzoic acid, 3-bromo-4-hydroxybenzoic acid and acetylated products thereof, and they can be used in combination for the purpose of improving gas barrier properties.

Examples of the compound represented by the formula (II) include 6-hydroxy-2-naphthoic acid, 6-acetoxy-2-naphthoic acid, methyl 6-hydroxy-2-naphthoate, and 6-hydroxy-naphthoic acid. Examples thereof include phenyl 2-naphthoate and methyl 6-acetoxy-2-naphthoate, and particularly preferably 6-hydroxy-2-naphthoic acid and 6-acetoxy-2-naphthoic acid.

Examples of the nuclear-substituted compound represented by the formula (II) include 6-hydroxy-5-chloro-2-naphthoic acid, 6-hydroxy-7-chloro-2-naphthoic acid,
Examples thereof include 6-hydroxy-4,7-dichloro-2-naphthoic acid and acetylated products thereof, and they can be used in combination for the purpose of improving gas barrier properties.

In the present invention, 3-hydroxybenzoic acid, 3-formoxybenzoic acid, and 3-acetoxy acid are used within a range that does not significantly affect the physical properties and processability (film-forming properties) of the resulting aromatic liquid crystalline polyester. Benzoic acid, 3-propionyloxybenzoic acid, methyl 3-hydroxybenzoate,
Propyl 3-hydroxybenzoate, phenyl 3-hydroxybenzoate, benzyl 3-hydroxybenzoate, 3-
Methyl acetoxybenzoate, 4'-hydroxybiphenyl-4-carboxylic acid, 4'-acetoxybiphenyl-4
-Carboxylic acids and the like can be used in combination.

In producing the aromatic liquid crystalline polyester of the present invention, first, the above formulas (I) and (II)
Is subjected to a polycondensation reaction in a reaction tank, and these compounds may be charged into a polymerization tank either in a batch system or in a batch system. The reaction can be carried out at normal pressure, reduced pressure, or a combination thereof under an atmosphere of an inert gas such as nitrogen, and the process can be batch, continuous, or a combination thereof.

When a compound having a phenolic hydroxyl group is used as the formula (I) or (II), a reaction for converting the compound into a compound which is more liable to polycondensation reaction, for example, an acid anhydride such as acetic anhydride is used. It is preferable that the transesterification reaction is carried out in a different or the same reaction vessel from the one in which the polycondensation reaction is carried out prior to the polycondensation reaction, and then the polycondensation reaction is carried out. Formula (I) or (II)
When a compound having a phenolic hydroxyl group is used, an acid anhydride of a lower aliphatic acid such as acetic anhydride in an amount equal to or more than the equivalent of the phenolic hydroxyl group, more preferably 1.1 to 1.3 equivalents, is used. , Together with a mixture comprising the compound represented by the above formula (I) or (II) into a reaction vessel,
After performing the esterification reaction, it is more preferable to carry out the polycondensation reaction. At that time, SUS3
16. Corrosion-resistant materials such as titanium and Hastelloy can be used. When the aromatic liquid crystalline polyester requires a high color tone (L value), it is preferable to use a glass-lined reaction tank or the like.

The temperature of the polycondensation reaction in the present invention is 27
0-350 ° C is preferred, and more preferably 280-33 ° C.
0 ° C. If the temperature is lower than 270 ° C., the progress of the reaction is slow, and if it exceeds 350 ° C., side reactions such as decomposition are likely to occur.
A multi-stage reaction temperature may be employed, or an aromatic liquid crystalline polyester, which is a reaction product, may be extracted in a molten state and recovered during the reaction or as soon as the maximum temperature is reached.

The melt polycondensation reaction usually proceeds sufficiently without a catalyst. However, if necessary, Ge, Sn, T
Oxides such as i, Sb, Co, and Mn, and compounds such as acetic acid can also be used. When used for a film for food packaging, it may be necessary to remove a catalyst component or the like, and a non-catalyst is preferred.

As the shape of the reaction tank, known ones can be used. In the case of a vertical reaction tank, multi-stage paddle blades, turbine blades, Monte blades, and double helical blades are preferable. In the case of a horizontal reaction tank, blades of various shapes perpendicular to one or two stirring axes, for example, A lens wing, a spectacle wing, a multi-circular flat wing, and the like are preferably provided. Further, the blade may be twisted to improve the stirring performance and the feed mechanism.

The reaction tank is heated by a heating medium, a gas, or an electric heater, but it is preferable to heat the stirring shaft, blades, baffles, etc. for the purpose of uniform heating.

When the reaction tank is divided into multiple stages or partitioned, the reaction temperature of the final part is the polycondensation reaction temperature in the present invention. The time for the polycondensation reaction should be appropriately determined depending on the reaction conditions and the like, but is preferably 0.5 to 5 hours at the reaction temperature.

In the method for producing an aromatic liquid crystalline polyester, it is important that the flow temperature of the aromatic liquid crystalline polyester obtained by the polycondensation reaction is 200 ° C. or higher and 30 ° C. or lower than the polycondensation reaction temperature. It is. More preferably, the flow temperature of the obtained aromatic liquid crystalline polyester is 210 ° C. or higher and 35 ° C. or lower than the polycondensation temperature.
It is preferable that the temperature is lower by at least C. If the flowing temperature is not higher than 200 ° C., the molecular weight of the aromatic liquid crystalline polyester is not sufficient, and there is a problem in processing and physical properties. Even if post-treatment such as solid phase polymerization is performed, fusion between aromatic liquid crystalline polyesters and a large amount of by-products occur, which is not economically preferable. If the fluidization temperature is close to the polycondensation reaction temperature, the viscosity of the polyester will increase, making it difficult to recover, and also worsening the stirring and mixing properties, which will affect the thermal stability of the polymer due to uneven heating. There is. Further, industrially, in a batch polymerization system, washing the polymerization tank increases the cost, so that continuous use of the polymerization tank is advantageous, and the conditions for melting and extracting are particularly important. As a method for cleaning the reaction kettle, the applicant of the present invention disclosed in JP-A-5-29592 and JP-A-5-29593.
The washing method using glycols and / or amines proposed in Japanese Patent Application Laid-Open No. H10-260,086.

When the aromatic liquid crystalline polyester is taken out in a molten state, it is preferably carried out in an inert gas atmosphere, for example, in a nitrogen atmosphere in view of the color tone of the obtained polymer. good.

As a mechanism for taking out the aromatic liquid crystalline polyester of the present invention in a molten state, a known extruder and a gear pump may be mentioned, but a simple valve may be used. The removed material usually solidifies after a while, and can be cut or crushed by a strand cutter or a sheet cutter according to the purpose. As means for processing a large amount and in a short time, the present applicant has disclosed in Japanese Patent Application Laid-Open No. 6-25648.
A method of cooling with a double belt cooler via a fixed-quantity supply device proposed in Japanese Patent Application Publication No. 5 (1993) -175 is cited.

The aromatic liquid crystalline polyester recovered in a molten state is preferably subjected to solid-phase polymerization from the viewpoint of removing unreacted raw materials and increasing the molecular weight to increase physical properties.
When the molecular weight is increased by using the reduced pressure polymerization method in combination, the desired M
If the molecular weight is increased until T is reached, it may be difficult to continuously recover the polymer, or there may be a problem that the polymer retained in the polymerization vessel or the discharge port becomes contaminated due to high temperature treatment.

The obtained aromatic liquid crystalline polyester is pulverized by a known pulverizer, and is 3 mm or less, preferably 0.5 mm or less.
Hereinafter, more preferably, particles (powder) having an average particle diameter (Rosin-Rammar method) of 0.1 to 0.4 mm.
It is preferable to carry out solid-state polymerization in which heat treatment is performed in an inert gas atmosphere in a solid state.

If the particle size exceeds 3 mm, the polymerization rate and the diffusion time of by-products generated as a result of the reaction of the unreacted raw materials differ between the surface layer and the inside. Since kimono cannot be sufficiently removed, foaming and gas generation may be caused.

The heating rate and the maximum processing temperature during the solid phase polymerization are as follows:
It is necessary to select so as not to fuse the aromatic liquid crystalline polyester particles. If fusion occurs, the surface area will decrease,
The polycondensation reaction and the removal of low boiling components are undesirably slow. The maximum treatment temperature of the solid-state polymerization is in the range of 200 to 300 ° C., more preferably 230 to 300 ° C. without fusing.
It is effective to perform the treatment in an inert gas atmosphere at a temperature of 295 ° C. At temperatures below this range, the reaction is slow and
The processing time is uneconomical, and if the temperature is 310 ° C. or higher, the powder particles are undesirably fused or melted, so that the solid phase cannot be maintained.

The inert gas is preferably selected from nitrogen, helium, argon and carbon dioxide, more preferably nitrogen. In the presence of air, especially oxygen,
The liquid crystalline aromatic polyester resin is oxidized at a high temperature, and tends to cause deterioration in physical properties and coloring, which is not preferable.

As the solid-phase polymerization apparatus, known dryers, reactors, mixers, electric furnaces and the like can be used, but in view of the above-mentioned point, a gas-flow-type apparatus having a high airtightness is preferable.

The aromatic liquid crystalline polyester used in the present invention is usually used in a molding process in the form of pellets (granulated pellets) obtained by pelletizing under heat and melting with a powder or a twin-screw extruder or the like. But more preferably,
Granulated pellets. The flow temperature (FT1) of the pellets after granulation of the aromatic liquid crystalline polyester of the present invention tends to be lower than the flow temperature (FT0) in the powder stage. This tendency is greatly reduced as compared with the conventional aromatic liquid crystalline polyester using the solid phase polymerization method. The difference may be attributed to the difference in crystallinity due to the difference in solid-state polymerization conditions, but the details are unknown.

As a method of granulating the aromatic liquid crystalline polyester into a pellet while heating and melting, a known method can be used. There is also a method in which a molten state is supplied from a polymerization tank to a parallel roller with grooves, shaped into a strand shape (string shape), and cut by a strand cutter or the like. As a method of producing pellets by granulating an aromatic liquid crystalline polyester powder, melt kneading using a commonly used single-screw or twin-screw extruder, air-cooled or water-cooled if necessary, usually used. The pellets are formed with a pelletizer (strand cutter). The purpose is to homogenize the melt and shape, but with the same composition, a high FT which is considered to be high molecular weight
In the case of an advanced polymer having a high kneader, a high kneader may be required. At the time of melt-kneading, the cylinder set temperature (die head temperature) of the kneading device is preferably in the range of 200 to 350 ° C, more preferably 230 to 330 ° C, and still more preferably 240 to 320 ° C.

The aromatic liquid crystalline polyester used in the present invention may optionally contain an inorganic filler. Such inorganic fillers include calcium carbonate,
Examples include talc, clay, silica, magnesium carbonate, barium sulfate, titanium oxide, alumina, montmorillonite, gypsum, glass flake, glass fiber, carbon fiber, alumina fiber, silica alumina fiber, aluminum borate whisker, potassium titanate fiber and the like. You. These inorganic fillers can be used in a range that does not significantly impair the transparency and mechanical strength of the film.

The aromatic liquid crystalline polyester used in the present invention may further contain, if necessary, an organic filler, an antioxidant, a heat stabilizer, a light stabilizer, a flame retardant, a lubricant, an antistatic agent,
Various additives such as inorganic or organic colorants, rust inhibitors, cross-linking agents, foaming agents, fluorescent agents, surface smoothing agents, surface gloss improvers, release improvers such as fluororesins, etc. during or after the manufacturing process It can be added in the processing step.

The method of forming a film comprising an aromatic liquid crystalline polyester in the present invention is not particularly limited, and can be carried out by a known method. For example, a film can be obtained by an inflation film forming method in which a molten resin is extruded from a T die and wound up, a molten resin is extruded into a cylindrical shape from an extruder provided with an annular die, and cooled and wound up. A film obtained by further uniaxially stretching a sheet obtained by an injection molding method or an extrusion method can also be obtained.

A more preferred method of forming (forming a film) the aromatic liquid crystalline polyester film includes inflation film forming. That is, the aromatic liquid crystalline polyester is supplied to a melt-kneading extruder equipped with an annular slit die, and the cylinder set temperature is 200 to 320 ° C, preferably 210 to 310 ° C, more preferably 220 to 300 ° C.
And the extruder extrudes the cylindrical film upward or downward from the annular slit. The interval between the annular slits is 0.25 to 2 mm, preferably 0.5 to 1.5 m
m, the diameter of the annular slit is usually 20 to 1000 mm, preferably 25 to 600 mm.

A draft is applied to the melt-extruded cylindrical molten resin film in the longitudinal direction (MD), and air or an inert gas, for example, nitrogen gas or the like is blown from the inside of the cylindrical film into the longitudinal direction. The film is expanded and stretched in the transverse direction (TD) at right angles.

In the inflation film formation of the aromatic liquid crystalline polyester film in the present invention, a preferable T
The D stretching ratio, that is, the blow ratio is 1.5 to 15, and more preferably 2.5 to 15. Also, preferred MD
The stretching ratio, that is, the draw ratio is 1.5 to 60, and more preferably 2.5 to 50. Further, it is preferable that the value of the blow ratio / draw ratio is 1.2 or less. here,
The blow ratio is determined by (diameter of cylindrical film) / (diameter of die), and the draw ratio is determined by (area of annular slit) / (cross-sectional area of film). If the setting conditions during the inflation film formation are out of the above range, it is difficult to obtain an aromatic liquid crystalline polyester film having a uniform thickness and no wrinkles, which is not preferable. The shear rate during film formation is known (for example, see JP-A-2-34).
No. 30 publication), preferably 50 to
500 sec ^-1 , more preferably 60 to 400 sec
c ⁻¹ , and more preferably 70 to 300 sec ⁻¹ .

The expanded film is usually cooled with air or an inert gas such as nitrogen gas, and then pulled through a nip roll. In inflation film formation, conditions can be selected according to the composition of the aromatic liquid crystalline polyester such that the cylindrical molten film expands to a uniform thickness and a smooth surface.

The thickness of the aromatic liquid crystalline polyester layer in the present invention is not particularly limited, but is preferably from 1 to 500.
μm, more preferably 5 to 200 μm, particularly preferably 5 to 50 μm, and is characterized in that it can be formed into a thin film of 25 μm or less.

In the aromatic liquid crystalline polyester film of the present invention, the heat shrinkage at 200 ° C. is in the machine axis direction (MD direction) and the direction perpendicular thereto (TD direction).
Is preferably at least 0%, more preferably at least 0.2%, particularly preferably at least 1.0%. More preferably, each of the heat shrinkage rates is 0.2% or more. If the heat shrinkage is less than 0%, it may cause warpage or wrinkles during the formation of a multilayered film with another film or during heating. The upper limit of the heat shrinkage is preferably 50%,
More preferably, it is 40%. If you shrink any more,
In some cases, the shape cannot be maintained, and practicality may be lacking.

[0056]

The present invention will be described in detail with reference to the following examples, which should not be construed as limiting the scope of the present invention. In addition, each physical property was measured by the method shown below. [Measurement Method of Physical Properties] Fluid temperature (FT): an index indicating the melt fluidity, which is measured by a capillary rheometer (Kokazu flow tester CFT500, manufactured by Shimadzu Corporation).
When a sample resin (about 2 g) heated and melted at a heating rate of 4 ° C./min is extruded from a nozzle having an inner diameter of 1 mm and a length of 10 mm under a load of 100 kg / cm ² , the melt viscosity becomes 48,000 poise ( (Corresponding to 4800 Pa · S).

Optical anisotropy: The optical anisotropy of the sample resin in the molten state was determined by measuring the particle size of 25
The sample resin powder having a particle size of 0 μm or less was heated under polarized light at a rate of 25 ° C./min, and visually observed or the amount of transmitted light was recorded on an XY recorder.

Melt viscosity: Using a Capillograph 1B (manufactured by Toyo Seiki Seisaku-sho, Ltd.), the inner diameter of the capillary was 0.5
A sample having a length of 10 mm and a length of 10 mm was charged with about 10 g of a sample, and a predetermined shear rate (100 sec.
The melt viscosity was measured at c ^-1 , 1000 sec ^-1 ).

Melt tension test: About 10 g of a sample was charged using a Capillograph 1B (manufactured by Toyo Seiki Seisaku-sho, Ltd.), and the inside diameter of the capillary was 2.095 m.
m, length 8.0 mm, piston extrusion speed 5.0
The sample was pulled up into a thread while being automatically accelerated by a variable speed winder at a rate of mm / min, and the tension (melt tension) and the winding speed when the sample was cut were measured.

Oxygen permeability: OX-TRAN 2/20 type (Model) according to JIS K7126 B method
n Control), at a temperature of 23.5 ° C.,
The measurement was performed under the condition of a relative humidity of 60%. The unit is cc / m ²
24 hr.atm.

Water vapor permeability (moisture permeability): JIS Z02
08 (cup method), temperature 40 ° C, relative humidity 90
%. The unit is g / m ² · 24 hr.

Heat shrinkage rate: A mark of a certain length was placed in the MD and TD directions of the sample, and after leaving it in a TABAI hot air dryer set at 200 ° C. and 250 ° C. under no load for 30 minutes, before and after heat treatment The variation in length was measured. Specifically, it was calculated by the following equation. Here, LB indicates the length between the marks before the heat treatment, and LA indicates the length between the marks after the heat treatment. (LB-LA) / LB × 100%

Example 1 ((A) / (B) in repeating structural unit = 30/70)
(Mol%). (1) Melt polymerization A three-liter four-tube having a Dimroth cooling tube, a nitrogen-introducing tube, a G-type connecting tube equipped with a thermocouple for measuring the internal temperature, and a squirrel-type stirring blade, and a thermocouple also provided on the outside of the flask. Using a mouth-separable flask, 428.8 g (3.10 mol) of 4-hydroxybenzoic acid, 1359.7 g (7.20 mol) of 6-hydroxy-2-naphthoic acid, and 1159. 7 g (11.4 mol) was charged, and after acetylation (150 ° C., about 3 hours under reflux), 1 ° C.
/ Min and maintained at 320 ° C. to perform melt polycondensation.
During this time, acetic acid produced as a by-product of the polycondensation reaction was continuously distilled off. 45 minutes after the temperature reached 320 ° C. during the polymerization, the stirring was stopped, and the polymer could be easily removed in a molten state. There was almost no adhesion to the polymerization tank and the stirring blade. The obtained polyester solidified after a while. Yield 1557g
(97.2% of theoretical yield). Repeat the same operation three times, the obtained polyester 3-5cm
After making into the size of a square, using a crusher, average particle size 1m
m, and after measuring the flow temperature (FT),
236 ° C. This polymer (prepolymer) exhibited optical anisotropy when melted.

(2) Solid-phase polymerization This prepolymer was put in an aluminum tray, charged in a nitrogen atmosphere furnace, and heated from room temperature to 208 ° C. under a nitrogen atmosphere.
The temperature was raised to 260 ° C. over 8 hours and 40 minutes, kept at the same temperature for 5 hours, allowed to cool, and then taken out.
A powder of an aromatic liquid crystalline polyester (advanced polymer) having a T of 281 ° C. was obtained. The weight loss here is
It was about 1.1%.

(3) Granulation The obtained advanced polymer was prepared by using Ikekai Kihan Co., Ltd.
Using a CM-30 twin screw extruder, set the die head temperature to 310 ° C.
, And melt-kneading was performed at a screw rotation speed of 150 rpm to obtain aromatic liquid crystalline polyester pellets having an FT of 260 ° C. 290 ° C (FT + 3
0 ° C.) is 4.7 g;
The winding speed at this time was 19.7 m / min. 60
The logarithmic viscosity (ηinh) measured at ° C. was 4.4 dl / g. The melt viscosity is shown in Table 1.

(4) Inflation Film Formation A 30 mmφ twin screw extruder was installed on the obtained aromatic liquid crystalline polyester pellets in a Labo Plast Mill (manufactured by Toyo Seiki Seisaku-sho, Ltd.).
A 75 mm inflation die was attached, and a film was formed at a cylinder setting temperature of 260 to 300 ° C., a screw rotation speed of the cylinder of 100, a die head setting temperature of 320 ° C., and a take-up speed of 15 m / min to obtain a film having a folding width of 205 mm. The bubbles were also stable, the film thickness was about 15 to 25 μm, and the film appearance was relatively good. The calculated blow ratio, draw ratio, TD / MD, discharge rate and shear rate are shown in Table 2.

(5) Measurement of gas barrier property The oxygen barrier property (oxygen permeability) of the film having a thickness of 25 μm was measured to be 0.35 cc / m ² · 24 hr · at.
m. 0.17 g of water vapor barrier property (moisture permeability)
/ M ² · 24 hr or less.

(6) Measurement of Heat Shrinkage The heat shrinkage at 200 ° C.
The direction D was 0.2%. The heat shrinkage at 250 ° C. was 0.4% in the MD direction and 0.4% in the TD direction.

Example 2 ((A) / (B) = 60/40 in the repeating structural unit)
(Mol%). (1) Melt polymerization In the same manner as in Example 1 (1), 947.0 g (6.86 mol) of 4-hydroxybenzoic acid, 6-hydroxy-2-
860.3 g (4.57 mol) of naphthoic acid and 1283.7 g (12.6 mol) of acetic anhydride were charged, and after acetylation (150 ° C., about 3 hours under reflux), the temperature was raised at 1 ° C./min to 320 C., and the melt polymerization was carried out while acetic acid produced as a by-product was continuously distilled off. 45 minutes after reaching 320 ° C,
The stirring was stopped and the polymer could be easily removed in the molten state. There was almost no adhesion to the polymerization tank and the stirring blade. The obtained polyester solidified after a while.
The yield was 1563 g (97.7% of the theoretical yield). The same operation was repeated three times, and the obtained polyester was reduced to a size of about 3 to 5 cm square, and then pulverized to an average particle diameter of 1 mm or less using a pulverizer.
It was 208 degreeC when T) was measured. This polymer (prepolymer) exhibited optical anisotropy when melted.

(2) Solid-phase polymerization This prepolymer was placed in an aluminum tray, and the solid-phase polymerization was carried out under the following conditions.
The temperature was raised to 240 ° C. over a period of 20 minutes, and the temperature was maintained at that temperature for 5 hours ”, except that the solid phase polymerization was carried out in the same manner as in Example 1 (2). A group III liquid crystalline polyester (advanced polymer) powder was obtained. The weight loss here was 0.9%.

(3) Granulation The obtained advanced polymer was prepared using the same apparatus as in Example 1 (3), and the die head temperature was set at 280 ° C.
Melt kneading at a screw rotation speed of 150 rpm, FT
Was 230 ° C. to obtain aromatic liquid crystalline polyester pellets. The melt tension of the resin pellet at 260 ° C. (FT + 30 ° C.) was 3.0 g, and the winding speed at this time was 22.3 m / min. The logarithmic viscosity (ηinh) measured at 60 ° C. was 4.9 dl / g. The melt viscosity is shown in Table 1.

(4) Inflation film formation A 30 mmφ twin screw extruder was placed on the obtained aromatic liquid crystalline polyester pellets in a Labo Plast Mill (manufactured by Toyo Seiki Seisaku-sho, Ltd.), and the head portion was 25 mmφ with a die gap of 0 mm.
A 75 mm inflation die was attached, a film was formed at a cylinder set temperature of 240 to 280 ° C., a screw rotation speed of the cylinder was 150, a die head set temperature was 280 ° C., and a take-up speed was 15 m / min, to obtain a film having a folded width of 120 mm. The bubble is also stable, the film thickness is about 25 μm,
The film appearance was relatively good. The calculated blow ratio, draw ratio, TD / MD, discharge rate and shear rate are shown in Table 2.

(5) Measurement of Gas Barrier Property The oxygen barrier property (oxygen permeability) of the film having a thickness of 25 μm was measured to be 0.34 cc / m ² · 24 hr · at.
m. Water vapor barrier (moisture permeability) 0.25g
/ M ² · 24 hr or less.

(6) Heat Shrinkage Measurement Heat shrinkage at 200 ° C.
The direction D was 1.0%. At 250 ° C., measurement was impossible because the film melted.

Comparative Example 1 ((A) / (B) in repeating structural unit = 75/25)
(Mol%). (1) Melt polymerization In the same manner as in Example 1 (1), 1250.7 g (9.06 mol) of 4-hydroxybenzoic acid, 6-hydroxy-2
-568.8 g (3.02 mol) of naphthoic acid and 1355.7 g (13.3 mol) of acetic anhydride were charged, and after acetylation (150 ° C, about 3 hours under reflux), the temperature was raised at 1 ° C / min. While maintaining the temperature at 320 ° C., the melt polymerization was carried out while continuously distilling off acetic acid as a by-product. The stirring was stopped 45 minutes after the temperature reached 320 ° C., and the polymer was easily taken out in a molten state. There was almost no adhesion to the polymerization tank and the stirring blade. The obtained polyester solidified after a while. Yield 1586
g (99.2% of theoretical yield). The same operation is repeated three times, and the obtained polyester is
After having a size of about m square, use a pulverizer to
After pulverization to a diameter of less than mm, the flow temperature (FT) was measured and found to be 243 ° C. This polymer (prepolymer)
Showed optical anisotropy at the time of melting.

(2) Solid-phase polymerization Solid-phase polymerization was carried out under the same conditions as in Example 1 (2), and after cooling, the product was taken out to obtain a powder of an aromatic liquid crystalline polyester (advanced polymer) having an FT of 283 ° C. . The weight loss here was about 1.7%.

(3) Granulation The obtained advanced polymer was prepared by using Ikekai Kihan Co., Ltd.
With a CM-30 twin screw extruder, the die head temperature is 320 ° C.
And melt kneading was performed at a screw rotation speed of 150 rpm to obtain aromatic liquid crystalline polyester pellets having an FT of 272 ° C. 312 ° C. (FT + 40)
C), the melt tension was 2.8 g, and the winding speed at this time was 49.7 m / min. 60 ° C
The logarithmic viscosity (ηinh) measured by was 6.4 dl / g. The melt viscosity is shown in Table 1.

(4) Inflation film formation A 30 mmφ twin screw extruder was installed on the obtained aromatic liquid crystalline polyester pellets in a Labo Plastomill (manufactured by Toyo Seiki Seisaku-sho, Ltd.), and the head portion was 25 mmφ and the die gap was 0.1 mm.
A 75 mm inflation die was attached, and a film was formed at a cylinder set temperature of 270 to 320 ° C., a cylinder screw rotation speed of 100, a die head set temperature of 320 ° C., and a take-up speed of 15 m / min to obtain a film with a folded width of 200 mm. The bubble is also stable, the film thickness is about 25 μm,
The film appearance was relatively good. The calculated blow ratio, draw ratio, TD / MD, discharge rate and shear rate are shown in Table 2.

(5) Measurement of Gas Barrier Property The oxygen barrier property (oxygen permeability) of the film having a thickness of 25 μm was measured and found to be 0.62 cc / m ² · 24 hr · at.
m. 0.47 g of water vapor barrier property (moisture permeability)
/ M ² · 24 hr or less.

(6) Measurement of Heat Shrinkage The heat shrinkage at 200 ° C. was −0.1% in the MD direction.
The TD direction was -0.3%. The heat shrinkage at 250 ° C. is −0.1% in the MD direction and −0.4% in the TD direction.
Met.

[0081]

[Table 1]

[0082]

[Table 2]

[0083]

The aromatic liquid crystalline polyester used in the film of the present invention has a lower temperature dependency of the melt viscosity and a wider processing temperature range than the conventional wholly aromatic liquid crystalline polyester. It is possible to increase the melt tension while suppressing the increase in the temperature, and has low-temperature workability. The film extruded from the aromatic liquid crystalline polyester has good film appearance, can be formed into a thin film, and is particularly excellent in oxygen barrier properties and water vapor barrier properties. The film can be used as a gas barrier layer of a single-layer film or a multilayer film with another thermoplastic resin, and can be used for various packaging applications such as food packaging, medicine packaging, cosmetic packaging, and electronic material packaging.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) C08L 67:04 C08L 67:04 (72) Inventor Shino Moriyama 6 Kitahara, Tsukuba, Ibaraki Sumitomo Chemical Co., Ltd. F-term (reference) 4F071 AA43X AA76X AA88X AF08Y AF12 AF12Y AH04 BA01 BB06 BB09 BC01 4F210 AA27 AC07 AG01 AR06 AR08 QA01 QK01 QK05 4J029 AA02 AB01 AB07 AC02 AD01 AD09 AE03 EB05A03 H01B03H01B

Claims (8)

[Claims] 1. An aromatic liquid crystalline polyester comprising two or more aromatic hydroxycarboxylic acid units, wherein the following repeating unit (A) is 65 to 25 mol% of the entire repeating unit, and the repeating unit (B) is 35 to 35 mol%. Containing 75 mol%, having a flow temperature of 300 ° C. or less, and having an inherent viscosity of 4.0 dl
/ G or more at a flow rate and a shear rate of 100 sec.
The melt viscosity (viscosity 1) measured at c ^-1 or 1000 sec ^-1 and the viscosity 1 at a temperature 20 ° C. higher than the flow temperature
Characterized in that it is melt-extruded from an aromatic liquid crystalline polyester having a ratio (viscosity 2 / viscosity 1) to the melt viscosity (viscosity 2) measured at the same shear rate as that of the above. Film. Embedded image Embedded image Here, the flow temperature is measured by a capillary rheometer, and the resin heated and melted at a heating rate of 4 ° C./min is subjected to a load of 100 kgf / cm ² and an inner diameter of 1 mm and a length of 10 mm.
mm when extruded from a nozzle having a melt viscosity of 48,
A temperature (° C.) indicating 000 poise. 2. An aromatic liquid crystalline polyester comprising two or more aromatic hydroxycarboxylic acid units, wherein the repeating unit (A) according to claim 1 is 65% of the total repeating units.
２５25 mol%, 35 to 75 mol% of the repeating unit (B)
Including, the flow temperature is 300 ° C or less, and the flow temperature is 2
2. Melt tension measured at a temperature higher than 5 ° C.
A film which is melt-extruded from an aromatic liquid crystalline polyester which is 0 g or more and has a winding speed at the time of cutting of 10 m / min or more. 3. The aromatic liquid crystalline polyester further has a melt tension measured at a temperature 25 ° C. or more higher than the flow temperature of 3.0 g or more, and a winding speed at the time of cutting is 10 m / min or more. A film obtained by melt extrusion from the aromatic liquid crystalline polyester according to claim 1. 4. A 25 μm thick, 23 ° C., 60% relative humidity
Oxygen permeability measured at 0.5 cc / m ² · 24 hr · a
tm or less, and 40 ° C., the film according to claim 1, water vapor permeability measured at 90% relative humidity is equal to or less than 0.5g / m ² · 24hr. 5. A compound represented by the following formula (I):
5 mol% of a compound represented by the following formula (II):
The mixture was mixed at a ratio of 5 mol% and charged into the reaction tank, and 270 ° C.
The polycondensation reaction is performed at 350 ° C. to produce an aromatic liquid crystalline polyester having a flow temperature of 200 ° C. or higher and a temperature lower than the polycondensation reaction temperature by 30 ° C. or higher. After being recovered and solidified in a molten state, it is pulverized into particles having a particle size of 3 mm or less, and melt-extruded from an aromatic liquid crystalline polyester obtained by heat treatment at 200 ° C. to 300 ° C. in an inert gas atmosphere in a solid state. The film according to any one of claims 1 to 3, wherein the film is formed. Embedded image (However, R ¹ represents a hydrogen atom, a formyl group, an acetyl group, a propionyl group or a benzoyl group, and R ² represents a hydrogen atom, a methyl group, an ethyl group, a propyl group, a benzyl group or a phenyl group.) ] (However, the definitions of R ¹ and R ² are the same as the respective definitions in formula (I). R in formulas (I) and (II)
¹ may be the same or different from each other, and R ² in the formula (I) and the formula (II) may be the same or different from each other. ) 6. A method for producing an aromatic liquid crystalline polyester film, wherein the aromatic liquid crystalline polyester according to claim 1 is formed into an inflation film at a temperature of 60 ° C. or higher than a flowing temperature. . 7. The aromatic liquid crystalline polyester according to claim 1, wherein the blow ratio (TD stretching ratio) is 1.5.
A method for producing an aromatic liquid crystalline polyester film, wherein inflation film formation is performed at a draw ratio (MD stretching ratio) of 1.5 to 60 and a shear rate of 500 sec ^-1 or less at the exit of a forming die. 8. The method according to claim 6, wherein the blow ratio / draw ratio is 1.2 or less.