JPH04259537A - Manufacture of polyester film - Google Patents

Abstract

PURPOSE:To obtain polyester film having excellent biaxial orientation effect and uniform thickness. CONSTITUTION:This manufacturing method is to manufacture polyester film using inflation molding technique. A three-layer laminated product consisting of a polyester resin which forms a thermotropic liquid crystal as an intermediate layer and a thermoplastic resin having a higher shear viscosity than said polyester resin and capable of being peeled off said intermediate layer after molding an inner and an outer layer extruded together from an annular die. Then after inflation molding, the inner and outer layers are peeled apart.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a method for producing polyester films using an inflation molding method.

0002

[Prior Art] Resins that form liquid crystals in a molten state (hereinafter referred to as
Thermotropic liquid crystal resin (thermotropic liquid crystal resin) has excellent mechanical properties, dimensional stability, heat resistance, chemical stability, and gas barrier properties, as well as good electrical properties, so it can be used to create films that meet various performance requirements. It has attracted attention as a raw material, and various application developments are being carried out in various fields.

[0003] However, this thermotropic liquid crystal resin is extremely difficult to melt-extrude because the strength of the film in the width direction is extremely weak due to the high degree of orientation of its molecular chains. In particular, inflation molding is difficult because the melt-extruded bubbles become unstable.

[0004] That is, thermotropic liquid crystal resin is
While flowing in the die, there is a very strong tendency for the material to be oriented in the take-up direction, and on the contrary, there is a strong tendency for the orientation in the width direction to be very small. For this reason, in inflation molding, in order to achieve the so-called biaxial orientation effect, in which the mechanical properties in both directions are balanced by biaxial orientation in the take-up direction and the width direction, the tubular bubble extruded from the die is When inflating the material, it is necessary to increase the expansion rate, that is, the blow ratio defined by the following equation, to produce an orientation effect in the width direction. Blow ratio=Folding width of tubular film x 2/Aperture diameter of annular die slit x π The larger the blow ratio, the greater the biaxial orientation effect.

However, thermotropic liquid crystal resin
If the melt viscosity is small and it is inflation molded in a single layer, the maximum blow ratio that can be molded is small at around 5. If the blow ratio is higher than this, the bubbles will oscillate and become unstable, so stable molding is required. It becomes difficult to continue. Therefore, the thickness of the obtained liquid crystal resin film was non-uniform and the biaxial orientation was poor.

[0006] In order to improve these problems, various inflation molding methods have been studied up to now. For example, a method of increasing the blow ratio to improve the biaxial orientation effect (JP-A-56-48728, JP-A-6
1-102234), a method of rotating a ring die to apply shear stress in a direction perpendicular to the film take-up direction (JP-A-56-2127, JP-A-63-1736)
20), a method of laminating formed anisotropic films (JP-A-52-109578, JP-A-58-31718, JP-A-61-89816, JP-A-62-95213)
(No.), and a method of increasing the shear rate of the fluidized resin at the exit of a molding die (Japanese Patent Application Laid-open No. 2-3430).

On the other hand, although it is a T-die film molding method,
Using a three-layer coextrusion die, the middle layer is a thermotropic liquid crystal resin, and the outer layer is a thermotropic liquid crystal resin and a non-adhesive thermoplastic resin (polycarbonate, polyolefin).
A method has been proposed (Japanese Unexamined Patent Publication No. 31729/1983) in which a film is molded with two types and three layers, and then the outer layer is peeled off to take out the intermediate layer thermotropic liquid crystal resin film.

[0008]

[Problems to be Solved by the Invention] However, even with the various inflation molding methods described above, it has not yet been possible to obtain a thermotropic liquid crystal resin film with uniform thickness and excellent biaxial alignment effects.

[0009] Furthermore, in the T-die film forming method,
Due to the characteristics of the molding method, the film is highly oriented in the take-off direction, has relatively low strength in the width direction, and therefore has only a poor biaxial orientation effect.

[0010] The present invention was made in view of these conventional problems, and an object of the present invention is to provide a method for producing a polyester film having an excellent biaxial orientation effect and having a uniform thickness. .

[0011]

[Means for Solving the Problems] The method for manufacturing a polyester film provided by the present invention is a method for manufacturing a polyester film by inflation molding, in which a polyester resin that forms a thermotropic liquid crystal is used as an intermediate layer, and a polyester resin is used as an intermediate layer during molding. Among them, a thermoplastic resin whose shear viscosity at a shear rate of 100 per second at a molten resin temperature is higher than that of the polyester resin and which can be easily peeled off from the intermediate polyester resin layer after forming a laminated film.
In this method, the three-layer laminate that serves as the outer layer is coextruded from an annular die, formed into a inflation film, and then the inner and outer thermoplastic resin layers are peeled off.

[0012] The above-mentioned die is of a type in which three layers of molten resin merge in the die on the way to the die exit, and the gap width of the annular slit at the die exit is 0, which is generally used for polyolefin resins. Any material in the range of .5 to 3 mm is applicable.

The above polyester resin forms an anisotropic melt and is well known as a so-called thermotropic liquid crystal resin. Confirmation of an anisotropic melt can be carried out by observing a sample in a molten state using a polarized light microscope. If it is an anisotropic melt, it is recognized that light is transmitted due to optical anisotropy under the orthogonal conditions of a polarizer and an analyzer.

The general structure of the thermotropic liquid crystal resin is a semi-aromatic polyester consisting of an aliphatic diol, an aromatic dicarboxylic acid, and an aromatic hydroxycarboxylic acid, and an aromatic diol and an aromatic dicarboxylic acid, or an aromatic diol and an aromatic dicarboxylic acid. A wholly aromatic polyester consisting of an aromatic dicarboxylic acid and an aromatic hydroxycarboxylic acid, or only an aromatic hydroxycarboxylic acid is known.

Here, examples of the aliphatic diol include aromatic diols such as ethylene glycol, 1,3-propylene glycol, 1,4-butene glycol, 1,6-hexene glycol, and 1,12-dodecamethylene glycol. Examples include 1,4- or 1,3-dihydroxybenzene, 4,4'- or 3,3'-dihydroxydiphenyl, 2,2-bis(4'-hydroxyphenyl)propane, 4,4'-dihydroxy Aromatic dicarboxylic acids such as diphenyl ether, 4.4'-dihydroxydiphenylsulfone, 4.4'-dihydroxydiphenylsulfide, 1.4-dihydroxynaphthalene, 2.6-dihydroxynaphthalene, 1.6-dihydroxynaphthalene, etc. Terephthalic acid, isophthalic acid, diphenyl-4,4'-dicarboxylic acid, naphthalene-1,4-dicarboxylic acid, naphthalene-2,6-dicarboxylic acid, diphenylsulfone-4,4'-dicarboxylic acid, diphenyl ether-4. Aromatic hydroxycarboxylic acids such as 4'-dicarboxylic acid include 4-hydroxybenzoic acid, 4-hydroxydiphenyl-4'-carboxylic acid, 2-hydroxy-6-naphthoic acid, 1-hydroxy-4-naphthoic acid, etc. can be mentioned. Note that the benzene ring and naphthalene ring may be substituted with a lower alkyl group, an aryl group, or a halogen group.

Specific examples of thermotropic liquid crystal resins include polyesters consisting of ethylene glycol, terephthalic acid and 4-hydroxybenzoic acid, polyesters consisting of 1,4-dihydroxybenzene, terephthalic acid and 4-hydroxybenzoic acid, and 4-hydroxybenzoic acid. - Polyester consisting of 4'-dihydroxydiphenyl, terephthalic acid and 4-hydroxybenzoic acid, polyester consisting of 4-4'-dihydroxydiphenyl, isophthalic acid and 4-hydroxybenzoic acid, 2-hydroxy-6-naphthoic acid and Typical examples include polyester consisting of 4-hydroxybenzoic acid. these are,
For example, "X-7G" from Eastman, "Novaculate" from Mitsubishi Chemical, "Rodrun" from Unitika, "Idemitsu LCP" from Idemitsu Petrochemical, Dartco,
It is commercially available under the trade names ``Zyder'' from Nippon Petrochemicals, ``Econol'' from Sumitomo Chemical, ``Vectra'' from Hoechst Celanese and Polyplastics, and ``Victrex'' from ICI Japan. There is.

It is essential that the shear viscosity of the thermoplastic resin is greater than that of the polyester resin, and it is desirable to provide a difference of 10% or more. As such a thermoplastic resin, polyolefin resins such as linear low-density polyester, high-density polyethylene, and polypropylene are most suitable.

The extrusion temperature of the polyester resin is in the range of 5°C to 30°C above the transition temperature to liquid crystal measured at the endothermic peak temperature using a differential scanning calorimeter, preferably in the range of 10°C to 20°C above the transition temperature. It is. The extrusion temperature for thermoplastic resins is the same as for polyester resins.

[0019]

[Function] Since the shear viscosity of the thermoplastic resin at the molten resin temperature is higher than that of the polyester resin, the inflation moldability is good. Moreover, even if the blow ratio is increased to 5 or more, the tubular bubble remains stable without being shaken.

[0020] Therefore, when polyester resin is extruded between a tubular bubble of thermoplastic resin consisting of two inner and outer layers, the resin is held (sandwiched) between the inner and outer thermoplastic resin layers. (inflated).

As a result, the blowing ratio of the polyester resin bubble can be made the same as that of the thermoplastic resin bubble. Therefore, by setting the blowing ratio of the thermoplastic resin bubble to 5 or more, the blowing ratio of the polyester resin bubble can be set to 5 or more, preferably 6 or more, which balances the mechanical strength in the width direction and the take-up direction. can. Furthermore, since the polyester resin bubble is sandwiched between the inner and outer thermoplastic resin layers and does not move, its wall thickness becomes uniform.

[0022]

[Embodiments] Examples of the present invention will be described below. The shear viscosity at a shear rate of 100 per second in the following Examples and Comparative Examples was measured using a Capillograph (manufactured by Toyo Seiki Co., Ltd.) at the extrusion temperature, with a cylinder of 9.55 mmφ x 40 mmL;
This is a value measured with an orifice of 1.0 mmφ x 10 mmL.

(Example 1) From a circular die for two resin three layers with a diameter of 40 mmφ and a slit gap of 1.0 mm, two
The shear viscosity at a shear rate of 100 per second at 90°C is 5
．． 46×103 poise linear low density polyethylene (
"Yukalon NC80" manufactured by Mitsubishi Yuka Co., Ltd., density 0.925g
/cc) was extruded as inner and outer layers at an extrusion temperature of 290°C, and inflation molded while cooling with an air ring. When the tubular bubble was stabilized, the shear viscosity under the above conditions was 3.48 x 103 poise, and the liquid crystal A polyester resin having a transition temperature of 273°C (Vectra A950 manufactured by Polyplastics) was extruded as an intermediate layer at 290°C, and inflation molded at a blow ratio of 8.0.

The average thickness of the intermediate layer polyester film obtained by peeling the inner and outer layers from the obtained three-layer film is:
The fold width of the tubular film was 502 mm, and the thickness deviation in the width direction was ±8%. When the mechanical strength of this polyester film was measured in the take-off direction and the width direction, the strength in the take-off direction was 3800 kgf/cm2, the elongation at break was 4.3%, and the strength in the width direction was 3830 kgf/cm2.
/cm2, and the elongation at break was 4.2%.

(Example 2) The low density polyethylene and polyester resin used in Example 1 were mixed with a slit gap of 2.
．． When inflation molding was performed in the same manner as in Example 1 except that a 5 mm die was used and the inner and outer layers were peeled off, a polyester film with an average thickness of 25 μm was obtained. The thickness deviation in the width direction was ±9%. The strength in the pulling direction is 37
00kgf/cm2, elongation at break is 4.5%, strength in the width direction is 3830kgf/cm2, elongation at break is 4.
．． It was 2%.

(Comparative Example-1) In the same inflation molding as in Example-1, 29
The shear viscosity at a shear rate of 100 per second at 0°C is 2.
03×103 poise branched low-density polyethylene (“Yukalon ZC41” manufactured by Mitsubishi Yuka Co., Ltd., density 0.923 g/
When cc) was used, the inflation formability was poor and stable film formation was impossible.

(Comparative Example-2) Using the same molding apparatus as in Example-1, single-layer inflation molding of only polyester resin was carried out under the same conditions as in Example-1, with a blow ratio of 5.0. The average thickness of the obtained polyester film was 25 μm, and the thickness deviation in the width direction was ±18%. The strength in the take-up direction is 3100 kgf/cm2, the elongation at break is 4.4%, and the strength in the width direction is 1330 kgf
/cm2, and the elongation at break was 3.3%.

(Comparative Example-3) Using the same molding equipment as in Example-1, an attempt was made to carry out single-layer inflation molding of only polyester resin under the same conditions as in Example-1 at a blow ratio of 8.0. However, the stability of the tubular bubble was poor and molding was impossible.

[0029]

As explained above, according to the present invention, polyester resin is sandwiched between thermoplastic resins having good inflation moldability and extruded using a two-resin, three-layer die, and each resin layer is separated after cooling and solidifying. Since it can be peeled off,
A polyester film having an excellent biaxial orientation effect and a uniform thickness can be obtained.

Claims (1)

[Claims] 1. A method for producing a polyester film by inflation molding, wherein a polyester resin forming a thermotropic liquid crystal is used as an intermediate layer, and the shear viscosity at a shear rate of 100 per second at the temperature of the molten resin during molding is such that the shear viscosity of the polyester resin is A three-layer laminate with inner and outer layers made of thermoplastic resin, which is larger than that and can be easily peeled off from the intermediate polyester resin layer after forming a laminate film, is coextruded from an annular die, and after forming into a blown film, the inner and outer layers are A method for producing a polyester film, comprising peeling off a thermoplastic resin layer.