JPH0334457B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a fluororesin film and a method for stretching the same. More specifically, the present invention relates to a biaxially stretched film made of an ethylene/tetrafluoroethylene copolymer and a method for producing the same. (Prior art) Fluorine resins include polytetrafluoroethylene, polyvinideline fluoride, vinyl fluoride, fluorinated ethylene, propylene copolymer,
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, which has weak strength and insufficient heat resistance. There were many. Fluorocarbon resins have excellent weather resistance, chemical resistance, electrical properties, mold release properties, etc., and are used in a wide variety of applications, but when used in film form, they have poor strength and thermal stability. Moreover, it is often unusable because it is in the form of a thin film, and its applications are limited. (Problems to be Solved by the Present Invention) As a result of extensive research into this problem, the present inventors have discovered that ethylene
A method for producing a fluorine-based stretched film, which comprises simultaneously biaxially stretching a substantially non-oriented film made of a tetrafluoroethylene copolymer by a factor of 2.0 times or more in both length and width at a temperature range of 90°C or higher and 160°C or lower. proposed. (Means for Solving the Problems) The present inventor has conducted further research on the stretchability of ethylene/tetrafluoroethylene copolymers, and as a result, has arrived at the present invention. That is, it is a biaxially oriented film containing 90 mol% or more of an ethylene/tetrafluoroethylene copolymer and having the following crystallization characteristic value ΔT of 15°C or more and 6°C or less. ΔT=Tm−Tc Tm (melting point): 20℃/ by differential calorimetry (DSC)
Melting peak temperature (°C) when the temperature is increased at a heating rate of 100 min Tc (cooling crystallization temperature): According to DSC (melting point + 20°C)
Crystallization peak temperature (°C) when the temperature is lowered at a cooling rate of 80°C/minute However, the present inventors have discovered that those with specific crystallization characteristics have excellent drawability and heat resistance. (Function) The difference between the melting point and the cooling crystallization temperature, that is, the temperature difference from melting to crystallization again, is generally used as an index of crystallization rate. The larger the temperature difference, the slower the crystallization rate. Crystallization is difficult to progress. 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 present inventors 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 15°C or higher, preferably 20°C or higher and 60°C or lower, preferably 55°C or lower, and that a uniform stretched film can be produced. If this temperature difference is less than 15°C, crystallization progresses too much, making uniform stretching difficult and making it difficult to obtain a film with uniform physical properties. Further, if the temperature exceeds 60°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 increased at a rate of 20°C/min by DSC (melting point + 20°C).
The crystallization peak temperature when the temperature is immediately lowered at a cooling rate of 80°C/min after reaching the temperature is defined as the cooling crystallization temperature. Ethylene-tetrafluoroethylene copolymer resins with the above crystallization properties can be used to form films with fairly good stretchability even with normal cooling methods, but by further limiting the cooling conditions, uniform films can be formed. Stretching becomes possible. In other words, as a result of repeated studies on the cooling rate during film formation, the inventors found that the film can be formed at a cooling rate of 70°C/second or higher in the temperature range of (melting point -10°C) to (melting point -100°C). It has been found that crystallization can be suppressed and uniform stretching becomes possible. By keeping the above-mentioned crystallization property values and cooling rate within the appropriate ranges, it becomes possible to perform stretching at low temperatures, which was previously impossible, and it is also possible to perform stretching at high temperatures more uniformly. Biaxial stretching methods for films include the so-called sequential biaxial stretching method, in which uniaxial stretching is performed in advance and then further stretching in the perpendicular direction, and the simultaneous biaxial stretching method, in which stretching is performed in the perpendicular direction at the same time. In the case of a tetrafluoroethylene copolymer, it is difficult to stretch at a high magnification using the sequential biaxial stretching method. This is thought to be because the molecular chains are highly uniaxially oriented by uniaxial stretching, and the subsequent lateral stretching makes them easy 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 preferably 2.0 times or more in each direction, judging from the stretching effect such as improving strength.
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, the stretching temperature needs to be selected within an appropriate range, and is suitably 50°C or more and 160°C or less, preferably 70°C or more and 150°C or less. 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 can be stretched without difficulty. If the stretching temperature is further increased to exceed 160°C, crystallization will proceed more than necessary, and a netting phenomenon will occur during stretching, making it impossible to obtain a uniform stretched film. Stretched films have poor thermal stability and cannot withstand use at high temperatures, so they must be heat-set when used at high temperatures.
Good results can be obtained by heat setting at a temperature of 180°C or higher and below the melting point, preferably 180°C or higher and 240°C or lower. Heat setting is preferably carried out under limited shrinkage or elongation of up to 20% or under constant length. Furthermore, when used as a shrink film, the purpose can be achieved by using it as it is without heat setting. The ethylene/tetrafluoroethylene copolymer resin applied to the present invention has a molar ratio of ethylene to tetrafluoroethylene of 40:60 to 70:30, preferably 45:55 to 60:40, which has good film-forming properties. This is suitable from the viewpoint of stretchability and the like. Furthermore, when a third component is added and copolymerized in order to suppress crystallinity, the stretchability is further improved. Fluoroolefins other than tetrafluoroethylene are effective as the third component. For example, vinyl fluoride, vinylideline fluoride,
Chlorotrifluoroethylene, hexafluoropropylene, trifluoroethylene, difluoroethylene, dichlorodifluoroethylene, chlorofluoroethylene, dichlorodifluoropropylene, trichlorotrifluoropropylene, tetrafluorodichloropropylene, chloropentafluoropropylene, dichlorotrifluoropropylene, chloro There are tetrafluoropropylene, pentafluoropropylene, tetrafluoropropylene, trifluoropropylene, etc., and these fluoroolefins have a fluorine content of 40 to 75 in the resulting copolymer.
It is preferable that it is added in an amount of % by weight. Moreover, the molar ratio of tetrafluoroethylene and fluoroolefin is preferably 1:0.1 to 2. (Example) The following will be described in more detail using comparative examples and examples. Comparative Examples 1 to 19 and Examples 1 to 8 Ethylene/tetrafluoroethylene copolymers with various molar ratios of ethylene and tetrafluoroethylene were melted at 340°C in a single-screw extruder and extruded through a T-die (melting point An unstretched film with a thickness of 100μ was produced while changing the cooling rate from -10°C to (melting point -100°C). These unstretched films were biaxially stretched using a test stretching machine under varying 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, netting may occur depending on the crystallization properties of the resin, cooling conditions, or stretching conditions. In some cases, uniform stretching was difficult.

【table】

[Table] Example 9 The same unstretched film as in Examples 4 to 8 was stretched at a stretching temperature of 130°C using a tenter-type continuous simultaneous biaxial stretching machine.
It was simultaneously biaxially stretched 3.0 x 3.0 times in the longitudinal and transverse directions at a stretching speed of 500 mm/sec, and then heat-set at 200°C while relaxing 2% in the transverse direction. When the performance of the stretched film was measured,
As shown in Table 2, it was dramatically improved compared to the unstretched film.

[Table] (Effects of the invention) The biaxially 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 fully used in fields where it was previously difficult to use. By biaxially stretching, it is possible to make the film thinner, and it can be used in new fields. When an unstretched film containing 90 mol% or more of ethylene/tetrafluoroethylene copolymer is stretched by more than twice the length and width, the tensile strength of the unstretched film, which was only 4 Kg/mm ² or more, increases to 13 Kg/mm ² or more. Improve to. Also, the tensile modulus was 60Kg/mm, and ^{the second} place was 100
Improved to Kg/mm ² or more. In addition, the stretched film produced by the method of the present invention has particularly excellent mechanical properties compared to conventional unstretched films, and can be produced in thicknesses from 500μ to 2μ, providing exterior protection that takes advantage of its weather resistance. Films, solar films, solar cell base and exterior films, soundproof wall exterior films, electrical insulation films that take advantage of their electrical properties and heat resistance, electrical insulation tapes, capacitors, interior protection films that take advantage of their chemical resistance and mold releasability, Can be used for release films, anti-corrosion tapes, etc. In addition, when heat setting is not performed, it is useful as a weather-resistant exterior shrink film.

Claims (1)

[Scope of Claims] 1 Contains 90 mol% or more of ethylene/tetrafluoroethylene copolymer and has the following crystallization characteristic value ΔT
A biaxially oriented film characterized in that the temperature is 15°C or more and 60°C or less. ΔT=Tm−Tc Tm (melting point): 20℃/ by differential calorimetry (DSC)
Melting peak temperature (°C) when the temperature is increased at a heating rate of 100 min Tc (cooling crystallization temperature): According to DSC (melting point + 20°C)
Crystallization peak temperature (℃) when the temperature is lowered at a cooling rate of 80℃/min from 2. The biaxially oriented film according to claim 1, wherein the biaxially oriented film is copolymerized in an amount of 40 to 75% by weight. 3 A thermoplastic resin containing 90 mol% or more of ethylene/tetrafluoroethylene copolymer is heated and melted and extruded through a die (melting point -10°C) to (melting point -
100°C) at a cooling rate of 70°C/sec or more to form a film, and then simultaneously biaxially stretched by at least twice in the length and width at a temperature range of 50°C or more and 160°C or less. A method for producing a bare stretched film.