JPS62121032A - Biaxially oriented fluorine stretched film and its manufacture - Google Patents

Abstract

PURPOSE:To contrive an improvement in strength and heat resistance, by containing an ethylene chlorotrifluoroethylene copolymer at more than a specific rate. CONSTITUTION:After a film is produced by cooling thermoplastic resin containing more than 80mol% ethylene chlorotrifluoroethylene copolymer, whose mol ratio between ethylene and chlorotrifluoroethylene is 20:80-80:20, at a temperature range of (the fusion point -10 deg.C) - (the fusion point -100 deg.C) and a cooling rate of more than 80 deg.C/sec by extruding the same through a die by heating and fusing, the film is stretched biaxially more than two times as long as the same in each of a longitudinal and lateral directions at a time at the temperature range of more than 50 deg.C and less than 180 deg.C. Crystallization characteristic value DELTAT of a biaxially oriented fluorine stretched film obtained in this manner is more than 20 deg.C and less than 70 deg.C, tensile strength which has been only about 4kg/mm<2> on an unstretched film improves up to more than 13kg/mm<2>, and tensile modulus which has been about 120kg/mm<2> up to 180kg/mm<2>.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a biaxially oriented fluororesin film and a method for producing the same. For more information, see Ethylene
The present invention relates to a biaxially stretched film made of a chlorotrifluoroethylene copolymer and a method for producing the same.

(Prior art) Fluorine resins include polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, fluorinated ethylene, and propylene copolymers.

There are perfluoroalkyl ethers, etc., and some are used in film form, but with the exception of polyvinyl fluoride, most of them are used in an unstretched state, and their strength is weak and their heat resistance is insufficient. There were many. Fluorine resins have excellent weather resistance, chemical resistance, electrical properties, mold release properties, etc., and are used for a wide variety of purposes. However, when used in film form, they have poor strength and thermal stability, and In many cases, it cannot be used because it is in the form of a thin film, so its applications are limited.

(Problems and Means to be Solved by the Invention) As a result of extensive research into these problems, the present inventors came to invent the following method for producing a fluorine-based stretched film. That is, it is a biaxially oriented fluorine-based stretched film containing 80 mol% or more of an ethylene/chlorotrifluoroethylene copolymer, and a method for producing the same. When an unstretched film containing 80 mol% or more of ethylene/chlorotrifluoroethylene copolymer is stretched at least twice in each direction and horizontally, the tensile strength of the unstretched film increases to 4 Kg/mm", which was only about 4 kg/mm". +13Kg/mm2 or more. Also, the tensile modulus is 120Kg/m-
The average weight was improved to over 180 kg/mm2.

(Function) The ethylene/chlorotrifluoroethylene copolymer resin used in the present invention has a molar ratio of ethylene to chlorotrifluoroethylene of 20:80 to 80:20, preferably 40:60 to 60:40. is film formable.

This is suitable from the viewpoint of stretchability and the like. Furthermore, it is effective to provide a fluorine-based side chain in order to suppress crystallinity.

Further, it is also possible to add to this resin an ultraviolet shielding agent such as titanium oxide powder or carbon powder, an ultraviolet absorber such as anthraquinone or anthracene, or a slip property improver such as silica or kaolin. Ethylene/chlorotrifluoroethylene copolymer resin has a fast crystallization rate, and crystallization progresses too much at a normal film forming cooling rate, making uniform stretching impossible.

The difference between melting point and cooling crystallization temperature as an indicator of crystallization rate,
That is, the temperature difference between melting and crystallization is generally used, and the larger this temperature difference is, the slower the crystallization rate is and the more difficult it is for crystallization to proceed. The faster the temperature decrease rate from the melting point, the higher the crystallization temperature, and the difference between the melting point and the decrease crystallization temperature tends to become smaller, so when using this index, the temperature decrease rate must be specified.

The inventors of the present invention determined the cooling rate after melting to be 80°C/min, and conducted experiments while determining the difference between the melting point and the cooling crystallization temperature using a differential calorimeter (DSC). It has been found that stretching can be performed satisfactorily at a temperature of 20° C. or higher, preferably 30° C. or higher, and 70° C. or lower, preferably 55° C. or lower, and that a uniform stretched film can be produced.

If this temperature difference is less than 20°C, crystallization progresses too much, making uniform stretching difficult and making it difficult to obtain a film with uniform physical properties.

Moreover, when it exceeds 70°C, the degree of crystallinity is too low and the heat resistance is insufficient.

The melting point is the melting peak temperature when the temperature is raised at a temperature increase rate of 20 °C/min by OSC. The crystallization peak temperature is defined as the cooling crystallization temperature.

In order to suppress crystallization during film formation, it is necessary to cool the resin extruded from the die.

As a result of repeated studies on the cooling rate during film formation, the inventors found that the film can be formed at a temperature range of (melting point -10°C) to (melting point -100°C) and at a cooling rate of 80°C/sec or more. It has been found that crystallization can be suppressed and uniform stretching becomes possible.

The method for biaxially stretching a film involves pre-stretching it uniaxially, and then
Furthermore, there is a so-called sequential biaxial stretching method in which stretching is performed in the perpendicular direction, and a simultaneous biaxial stretching method in which stretching is performed in the perpendicular direction at the same time. It is difficult to stretch at high magnification. This is thought to be because the molecular chains are highly uniaxially oriented by -axial stretching, and the subsequent lateral stretching makes it easier to tear along the orientation axis.

On the other hand, in the case of simultaneous biaxial stretching, since stretching is carried out simultaneously in the longitudinal and lateral directions, a well-balanced orientation in the longitudinal and lateral directions can be obtained, and high-magnification stretching is possible without cutting. The stretching ratio is 1. Judging from the stretching effect such as improved strength, the stretching ratio is 2.
0 times or more, preferably 2.5 times or more is required. The method of simultaneous biaxial stretching is not particularly limited, and either a tenter method or a tubular method may be used. Further, as described in the comparative examples, it is necessary to select an appropriate stretching temperature within a range of 50° C. or higher and 160° C. or lower, preferably 70° C. or higher and 150° C. or lower. When the temperature is less than 50°C, the stretching stress is very large and it is easy to break at a stretching ratio of 2 times or more, but when the temperature exceeds 50°C, the stretching stress decreases rapidly and it is possible to stretch without difficulty. Further increase the stretching temperature to 180
If the temperature exceeds .degree. C., crystallization will proceed more than necessary, and a stretching phenomenon will occur during stretching, making it impossible to obtain a uniform stretched film.

Stretched films have poor thermal stability as they are;
Since it cannot withstand use at high temperatures, it must be heat-set when used at high temperatures. Good results can be obtained by heat-setting at temperatures above 160°C and below the melting point, preferably above 190°C and below 220°C. . Heat setting is preferably carried out under limited shrinkage or elongation or constant length within 20%.

The following will be described in more detail with reference to comparative examples and examples.

Comparative Examples 1 to 19 and Examples 1 to 8 Ethylene/chlorotrifluoroethylene copolymers with various molar ratios of ethylene and chlorotrifluoroethylene were melted at 280"C using an axle extruder.

Extruded from T-die (melting point -10℃) to (melting point -100℃)
An unstretched film with a thickness of 100 μm was prepared while changing the cooling rate (°C). These unstretched films were biaxially stretched using a test stretching machine under different conditions.

The results are shown in Table 1, but in the case of sequential biaxial stretching, stretching is difficult, and even in the case of simultaneous biaxial stretching, necking occurs depending on the crystallization property value of the resin, cooling conditions, or stretching conditions. Uniform stretching was sometimes difficult.

Example 9 The same unstretched film as in Examples 4 to 8 was stretched at a stretching temperature of 1) 0°C using a tenter set of continuous and simultaneous biaxial stretching machine.

Under the conditions of stretching speed 500mm for 7 seconds, length and width 3. OX3.
Biaxial stretching was carried out at zero tension, followed by heat setting at 205° C. while relaxing 2% in the transverse direction.

The performance of the stretched film was measured.

As shown in Table 2, it was dramatically improved compared to the unstretched film.

(Effect of the invention) The biaxially oriented fluorine-based stretched film produced by the method of the present invention has a strength approximately three times or more that of an unstretched film, and also has excellent heat resistance by heat setting. Therefore, it can be used in fields where it was previously difficult to use.

Biaxial stretching allows for thinning of the film.

Applications can be expanded to new fields. Further, when used as a shrink film, the purpose can be achieved by using it as it is without heat setting.

A stretched film produced by the method of the present invention.

This is an exterior protective film that has excellent mechanical properties compared to conventional unstretched films, can be manufactured in thicknesses from 500μ to 2μ, and takes advantage of its weather resistance.

Solar films, solar cell base and exterior films, soundproof wall exterior films, electrical insulation films that take advantage of electrical properties and heat resistance, and electrical insulation tapes.

It can be used for capacitors, interior protective films that take advantage of chemical resistance and mold release properties, mold release films, anticorrosion tapes, etc. Moreover, when heat setting is not performed, it is useful as a weather-resistant exterior shrink film.

Claims (7)

[Claims] (1) A biaxially oriented fluorine-based stretched film containing 80 mol% or more of an ethylene/chlorotrifluoroethylene copolymer. (2) The biaxially oriented fluorine-based stretched film according to claim 1, wherein the stretched film is stretched at least twice in both length and width. (3) The tensile strength and tensile modulus of the stretched film in the longitudinal and transverse directions are 13 Kg/mm^2 or more and 180 Kg/m, respectively.
Claim 1 characterized in that it is m^2 or more
The biaxially oriented fluorine-based stretched film described in 2. (4) The biaxially oriented fluorinated stretched film according to claim 1, wherein the copolymer has a molar ratio of ethylene and chlorotrifluoroethylene of 20:80 to 80:20. (5) The biaxially oriented fluorine-based stretched film according to claim 1, characterized in that the following crystallization characteristic value ΔT is 20°C or more and 70°C or less. △T=Tm-Tc Tm (melting point): 20℃/ by differential calorimetry (DSC)
Melting peak temperature (°C) when temperature is increased at a heating rate of
) at a cooling rate of 80°C/min. Crystallization peak temperature (°C) (6) A thermoplastic resin containing 80 mol% or more of ethylene/chlorotrifluoroethylene copolymer is heated and melted and extruded through a die (melting point -10°C) to (melting point -100°C)
Biaxial orientation characterized by forming a film by cooling at a temperature range of 80° C./sec or more, and then simultaneously biaxially stretching the length and width by at least twice as much in a temperature range of 50° C. or more and 180° C. or less. A method for producing a fluorine-based stretched film. (7) After biaxial stretching, 2
6. The method for producing a biaxially oriented fluorine-based stretched film according to claim 5, characterized in that the film is heat-set under limited shrinkage of 0% or less, elongation, or constant length.