JPS62255113A - Manufacture of film of liquid crystal - Google Patents

Abstract

PURPOSE:To reduce neck-in effect or the variability in thickness and obtain a monoaxially orientated film smoothly by a method wherein the film is contacted closely to a rotary cooling drum by employing the method of static electricity impressing cooling. CONSTITUTION:Liquid crystal polymer is extruded out of an extruder so as to obtain the shape of a film and a film, orientated into the flow direction of the polymer, is obtained by employing static electricity impressing cooling method. In this case, a rotary cooling drum, provided with a mirror surface, is arranged immediately below a slit and an air gap is provided. On the other hand, a positive electrode or a tungsten wire, for example, is suspended on the upper surface of the rotary cooling drum orthogonally to the direction of the flow of the film in order to impress an electrostatic charge and, then, a DC voltage is impressed. The amount of extrusion is controlled and the speed of the rotary cooling drum is increased gradually whereby the film is obtained by melting orientation. In this case, the specific resistance of the liquid crystal polymer upon melting is 5X10<8>OMEGA.cm or less and the sectional area of the film after the melting orientation is 1/3-1/100 as compared with the same before the melting orientation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for obtaining films from liquid crystal polymers. More specifically, the present invention relates to a method for efficiently obtaining a film made of a substantially uniaxially oriented liquid crystal polymer having excellent mechanical strength and flatness.

[Conventional technology]

BACKGROUND ART Polymers exhibiting melt anisotropy, ie, liquid crystal polymers, have been known as materials for producing resin molded products with high strength and high Young's modulus. For example, JP-A-Sho Dub-Cuco 3 De No. 3 Public 1,
[Kokai 36-ko/Koku No. Publication, JP-A-Sho,! T? It has been shown that the polymers described in Japanese Patent No. 3-JA Co., Ltd. and the like have fluidity and exhibit optical anisotropy, that is, liquid crystal properties, above a certain temperature.

It is also disclosed that these polymers have so-called self-reinforcing properties and can be used as films in addition to being useful as fibers or molded articles.

One of the simplest methods for obtaining films from such liquid crystal polymers is, for example, disclosed in JP-A-Sho! This is a method of melt-extruding a polymer into a thin film through a die slit of an extruder as described in Japanese Patent Application No. g-3/ri/l. .

Although this method is simple and can be easily implemented industrially, the present inventors have developed a method for stretching the molten polymer by applying tension in the flow direction of the molten polymer in order to increase the mechanical strength of the film obtained by this method. It has been found that a major problem arises when attempting to perform melt-stretching.

That is, when performing such an operation, a rotating cooling drum is usually placed below or to the side of the die slit, and the melt-stretched film is cooled and solidified on the rotating cooling drum. The point at which the stretched film is fixed to the drum becomes unstable and the so-called neck-in effect becomes noticeable. Moreover, the thickness unevenness of the obtained stretched film also becomes large.

This neck-in effect is also observed when forming films from ordinary thermoplastic resins such as polyethylene terephthalate, but attempts have been made to obtain highly uniaxially oriented films by melt stretching to improve mechanical properties using liquid crystal polymers as starting materials. In this case, the extrudate shrinks in the width direction, which is particularly noticeable, and the thickness of the end region increases.

As a method for cooling and solidifying liquid crystal polymers that have conventionally been highly melted and stretched, JP-A-Sho! Although cooling rolls, air blowing, water cooling, etc. are known as described in Publication No. RG-, 3/7/LJ, no specific means for reducing the neck-in effect is disclosed at all. Not yet.

[Problem that the invention seeks to solve]

Therefore, an object of the present invention is to provide a method for ensuring sufficient fixation of the stretched film to a rotating cooling drum and reducing neck-in when obtaining a highly uniaxially oriented film using a melt stretching method using a liquid crystal polymer. It is in.

[Means for solving problems]

According to the invention, this problem can be solved by applying a so-called electrostatic cooling method.

That is, the gist of the present invention is to melt-stretch a melt-extruded liquid crystal polymer between a die slit and a rotating cooling drum to obtain a film that is highly oriented in the flow direction of the polymer, and to apply an electrostatic cooling method to the film. The present invention relates to a method for forming a film of a liquid crystal polymer, which is characterized in that the film is formed in close contact with a rotating cooling drum using a liquid crystal polymer.

The present invention will be explained in more detail below.

The liquid crystal polymer used in the present invention refers to a polymer that has the property of forming an optically anisotropic melt, such as fully aromatic polyester, aromatic-aliphatic polyester, aromatic polyazomethine, aromatic polyester/carbonate, and aromatic polyester/carbonate. A part of polyesteramide falls under this category.

These polymers in a molten state have the property of passing polarized light in an optical system equipped with crossed polarizers. A typical example is a copolymer, but the invention is not limited thereto.

The greatest feature of the present invention is that an electrostatic cooling method is used to reduce the neck-in effect that inevitably occurs when a highly substantially uniaxially oriented film is obtained from liquid crystalline polyester by a melt-stretching method. .

Such an electrostatic application cooling method is, for example, disclosed in Japanese Patent Publication No. 37-41'I.
As described in Japanese Patent Application No. 11, this is a method in which a film-like molten polymer extruded from a die is given an electrostatic charge and brought into close contact with a rotating cooling drum to solidify it.

This electrostatic application cooling method has already been widely applied to polyethylene terephthalate, which is optically isotropic when melted, but when it is optically anisotropic and oriented, it is electromagnetically However, there is no known example in which a liquid crystal polymer exhibiting anisotropy has been investigated.

The present inventors have conducted intensive studies on a method for fixing a film made of a highly oriented liquid crystal polymer in a molten state to a rotating cooling drum. As a result, the electrostatic application cooling method, which has not been tried before, has an excellent effect. We have discovered that this effect can be exhibited and that this effect is extremely remarkable under certain specific conditions, leading to the present invention.

That is, according to the present invention, the neck-in effect can be reduced and the flatness of the obtained film can be improved, but this effect is only possible when the specific resistance of the liquid crystal polymer when melted is 3 x 10"Ω. It becomes particularly noticeable when the resistance is less than m, especially less than /×10 8 Ω·m.

Conventionally, when manufacturing liquid crystal polymers, consideration has not been given to specific resistance during melting, but the present inventors have taken this point into consideration and have found that the present invention is particularly effective in melt-stretching. It is.

In the present invention, in order to reduce the specific resistance of the liquid crystal polymer when it is melted, it is necessary to make solubilized ions exist in the liquid crystal polymer, and for this purpose, for example, the following method is preferably employed. That is, one of them is a method of blending approximately 0.00 to 3% by weight of one or more alkali metal compounds and/or alkaline earth metal compounds during the production of the liquid crystal polymer, and at least a part of it is solubilized in the liquid crystal polymer. It is. Examples of such metal compounds include lithium acetate, calcium acetate, magnesium acetate, manganese acetate, zinc acetate, lithium chloride, calcium chloride, calcium benzoate, barium benzoate, and the like.

Alternatively, after producing the liquid crystal polymer, one or more of the above metal compounds may be blended and used for film formation. When this method is adopted, metal compounds having a melting point Sθ°C to 3.20°C, such as zinc sebacate, lead sebacate, calcium sebacate, magnesium sebacate, manganese sebacate, tin sebacate, cadmivalmitic acid sebacate, etc. Magnesium, zinc stearate, magnesium stearate, sodium oleate, potassium oleate, magnesium oleate, etc. can be used as particularly preferred compounds. The method of the present invention is particularly effective for highly uniaxially aligned liquid crystal polymers. This is the case when we obtain

In other words, the more severe the melt-stretching conditions, the more the cross-sectional area of the film after melt-stretching becomes 1/~ to that before melt-stretching.
1/, particularly 1/~''10.0, the neck-in effect becomes noticeable and the flatness of the film deteriorates, and it is not possible to obtain a film of a satisfactory level using methods such as air blowing. However, the present inventors have revealed for the first time that the electrostatic cooling method is particularly useful in such a region, and that the specific resistance of the liquid crystal polymer when melted is 5×
/θ8Ω·m or less, the effect becomes even more remarkable.

There are no particular restrictions on the method of imparting an electrostatic charge to the melt-extruded liquid crystal polymer, but it is usually
As described in Publication No. 7-A/4'J, a method of arranging a linear electrode on the upper surface of the film in a direction perpendicular to the flow of the film is preferably used, but the method is of course not limited to this method. For example, regarding the shape of the electrodes, in addition to linear electrodes, pin-shaped electrodes, brush-shaped electrodes, etc. may be used, and a plurality of electrodes may be used. Regarding the applied voltage, in addition to positive and negative DC voltages, alternating current voltages may also be used. Further, any position of the electrode can be adopted. In any case, the method is not particularly limited as long as it does not impair the spirit of the present invention.

〔Effect of the invention〕

As detailed above, according to the present invention, the neck-in effect and thickness unevenness, which have been serious obstacles when melting and stretching a liquid crystal polymer in a trench to obtain a film that is highly oriented in the direction of polymer flow, can be solved. By reducing this, it is possible to obtain a uniaxially stretched film extremely smoothly.

It has been found that this effect is remarkable when the specific resistance of the liquid crystal polymer during melting is below a certain value, and that it is particularly effective in areas where melt-stretching conditions are severe, and this is of great significance.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples.
The present invention is not limited to the following examples without exceeding the gist thereof.

In addition, measurements of various objects in the present invention were performed by the following method. In addition, "parts" in the examples indicate "parts by weight."

(1) Specific resistance during melting;
Appl.

Phys,) Volume 77, No. 1/'Ide~//kl1
The method is described on page (/?A 4th year). However, in this case, the temperature at the time of melting the polymer composition is 300° C., and the value immediately after applying DC Jooov is taken as the specific resistance at the time of melting.

(2) Mechanical strength of film: Measured using Toyo Baldwin-Tensilon (UTM-■). The sample was cut into a width of 11 nm and a length of θ, and the Young's modulus of the polymer in the flow direction was measured at a tensile speed of 1 otyrv- with a chuck interval of j (m).

(3) Film thickness unevenness; film longitudinal direction/θm
70 points every 10σ in the width direction for each of the 10 locations,
The film thickness is measured at a total of 700 points.

The film thickness is measured using a micrometer made by Aki Denshi, and 7θ sheets of film around the relevant location are stacked and measured and converted to the thickness of each film.

The maximum value of all measured values is X, naa, the minimum value is X
. in, when the arithmetic mean value is 1′41≦:”mi
Let n, - be the thickness unevenness that represents the flatness of the film, and the smaller this value is, the better, especially O0! The following are preferred.

Example/ (Production of liquid crystal polymer) Polyethylene terephthalate iq with an intrinsic viscosity of 0.63,
Part a, p ~ acetoxybenzoic acid/l, 2 parts, magnesium acetate 0.07 part, and antimony trioxide 0.07 part were mixed and reacted at a temperature of 275°C to form the following composition (t/m
/n = rθ/jθ//θO molar ratio) was produced.

The specific resistance of this polyester when melted is gX/0'
Ω・saw, its melting point is approximately 230℃, and its intrinsic viscosity is 0.
．． It was A10.

(Manufacture of film) The width of the obtained liquid crystal polyester was 230+1 at 30θ℃.
A film was extruded from an extruder having slits of 111 clearance/rum and oriented in the flow direction of the polymer using an electrostatic cooling method.

At this time, a rotating cooling drum having a mirror surface with a diameter of 300 tran was placed directly below the slit to form an air gap of 2θ.

In addition, the following conditions were adopted to apply an electrostatic charge to the molten polymer. That is, a tungsten wire with a diameter of 0.1 m was used as a positive electrode and was stretched on the upper surface of the rotating cooling drum in a direction perpendicular to the flow of the film, and a DC voltage gK'v was applied.

By adjusting the extrusion rate and gradually increasing the speed of the rotating cooling drum, we finally obtained a film with a width of 10 m and a thickness of 60 μm.The cross-sectional area of this film obtained by melt stretching is the cross-sectional area of the exit of the die slit. It was 1/2o, and was locally uniaxially oriented.

The mechanical strength and thickness unevenness of the films obtained are shown in Table 1, and all were sufficiently satisfactory.

Comparative Example/Same as Example/ except that no electrostatic charge was applied, and the thickness was 10.
A film of μ was obtained. The results at this time are shown in Table 1, and the neck-in effect was extremely large, and the homogeneous film was limited only to the area near the center.

Comparative Example In Example 1, a cold air blower (air knife) was used instead of the electrostatic cooling method to fix the molten stretched film to the rotating cooling drum.

In this case, at the part where the molten film contacts the cooling drum, the jet velocity J
It was sprayed at Om/sec.

However, in this case as well, the neck-in effect was insufficiently reduced, and the thickness of the resulting film was extremely uneven.

In place of the liquid crystal polymer in Example/Example/L/m/rr −,
Using liquid crystal polyester with a ratio of 20/0/100,
A uniaxially oriented film was obtained in the same manner as in Example except that the take-up speed was increased.

The shape, physical properties, etc. of the obtained film are shown in Table 1, and all were at a satisfactory level.

Claims (3)

[Claims] (1) When melt-stretching the melt-extruded liquid crystal polymer between a die slit and a rotating cooling drum to obtain a film that is highly oriented in the flow direction of the polymer, the film is rotary cooled using an electrostatic cooling method. A method for forming a liquid crystal polymer film, which is characterized in that it is brought into close contact with a drum. (2) Specific resistance of liquid crystal polymer when melted is 5×10^8Ω
・Claim 1 characterized in that it is less than cm.
A method for forming a film of a liquid crystal polymer as described in . (3) The method for forming a liquid crystal polymer film according to claim 1, wherein the cross-sectional area of the film after melt-stretching is 1/3 to 1/100 of that before melt-stretching.