JPS58185226A - Manufacture of thermoplastic film - Google Patents

Abstract

PURPOSE:To obtain the titled film for a food packaging which is stretched uniformly, balanced longitudinally and laterally and has only the small amount of a bowing, by stretching the unstretched film of a poly(4-methylpentene-1) biaxially under heating, then heat setting it. CONSTITUTION:The unstretched film which is obtained by melt extruding a poly(4-methylpentene-1) resin from a die and forming a film, contacting it to a cooling roll below 40 deg.C e.g., by an electrostatic contact method is biaxially stretched both longitudinally and laterally simultaneously by three or more times at a temperature 85-185 deg.C, then heat setting it at the temperature above said stretch temperature and below 230 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing an axially oriented film of poly-4-methylpentene. More specifically, the present invention relates to a method for producing an axially oriented poly(4-methylpentene) film that is uniformly stretched, has a small amount of bowing, and has a well-balanced length and width.

For axially oriented films on poly-4-methylpentene, see British Patent No. 1249322 and British Patent No. 1317.
586, a film formation method using a refrigerant cooling method,
Methods such as stretching at a stretching temperature of 200C or more and 230C or less have been described, but these methods are only laboratory production methods, and it is difficult to achieve uniform stretching, and there are problems with the vertical and horizontal balance and the center of the film. Only films lacking edge uniformity could be obtained. In addition, another method is described in Japanese Patent Publication No. 52-34664, in which a film is formed and stretched by mixing with polyethylene or polystyrene, but the method is manufactured under different conditions and conditions from those used in conventional films, and its purpose is to roughen the surface. belongs to.

The inventors of the present invention have conducted extensive research in order to uniformly stretch an unstretched film of poly-4-me≠-pentene-1, and as a result, they have come up with the following method.

That is, after biaxially stretching an unstretched poly 4-' methylpentene-1 film at a temperature of 85° C. or more and less than 200° C. for a time of at least 3 times in both length and width, it is heat-set at a temperature of not less than the edge stretching temperature and not more than 230° C. This is a method for producing an axially oriented film with characteristic poly(4-methylpentene). In the method of the present invention, an unstretched film formed by melt extrusion through a die is
As described above, uniform stretching without necking can be achieved by stretching at a temperature of 100 C or higher and lower than 1850 C. as desired.

Poly-4-methylpentene-1 resin has a helical crystal structure and has good crystallinity, so at low temperatures, especially at temperatures below 85°C, necking occurs, making it impossible to stretch uniformly, and cutting is likely to occur. . On the other hand, if the film is stretched at a temperature of 185° C. or higher, crystallization will be promoted by heating, and the stretchability will deteriorate, resulting in the formation of stretched portions. The method of the present invention allows stretching without these disadvantages, but as a method to further improve the stretching properties, the unstretched film melt-extruded from a die is brought into close contact with a cooling roll of 40C or less using an electrostatic adhesion method. A method of forming a film can be adopted. In reality, a nail-type or wire-type electrode is installed near the die.
This can be carried out by applying a DC voltage of 0 kV to generate discharge, charging the film, and bringing it into close contact with a cooling roll. In this method, the film can be rapidly cooled to prevent crystallization of the film, and since no refrigerant or the like is used, handling after film formation is easy.

In addition, during stretching, the so-called bowing phenomenon, in which the central part of the film is stretched later than the edges, tends to occur in the normal tenter-set stretching method. By heating to a temperature 5c or more higher than the temperature, the occurrence of the bowing phenomenon can be reduced. In addition, as a method to further prevent the bowing phenomenon, the film immediately after stretching is cooled to a temperature at least 5°C lower than the stretching temperature.
Good results can be obtained by heat setting at temperatures below °C. All of these 7 methods modify the stress balance before and after the stretched section by temperature conditions, and in the case of poly-4-methylpentene-1 resin, the temperature between the stretched section and the preheated or heat-set section is 5°C or more. It is necessary to provide a temperature difference of

The biaxially oriented film produced by the method of the present invention has a well-balanced length and width, and can be used for food packaging or electrical purposes.
For example, it can be used for insulating tapes, capacitors, etc.

Examples will be explained below.

Comparative Example Poly 4-methylpentene-1 resin (melt index 26#/10m) chips were put into an extruder! It was melted at 7280°C, extruded through a die, and taken off while being brought into close contact with a 30C cooling roll using an electrostatic adhesion method. A nail-shaped electrode was used as the electrode, and the applied voltage was 12 kV. Further, the film thickness was 60μ.

This unstretched film was supplied to a tenter-equipped simultaneous biaxial stretching machine, and was simultaneously biaxially stretched at a magnification of 4 times in length and 5 times in width while changing temperature conditions. Table 1 shows the relationship between temperature conditions, stretchability, and hoing amount (the value obtained by dividing the length of the center of the film relative to the edge of the film by the width of the film).

6-1itl Examples The unstretched poly-4-methylpentene-1 film used in the comparative examples was stretched 4 times in length using a simultaneous biaxial stretching machine with a tenter set.
Simultaneous biaxial stretching was carried out at a transverse magnification of 5 times.

The stretching temperatures were 190°C in the preheating section, 170°C in the stretching part, 1150°C in the heat setting part, and 2220°C in the heat setting part. The stretchability is good and the bowing amount is small at 0.02.

Furthermore, the performance of the stretched film was also good as shown in Table 2.

Table 2

Claims (1)

[Claims] 1. Poly-4-methylpentene-1 resin is melt-extruded through a die to form an unstretched film, and the unstretched film is
Production of an axially oriented poly-4-methylpentene film, which is characterized by biaxially stretching for at least 3 times each length and width at a temperature of 185°C or higher, and then heat-setting at a temperature of 2,300°C or higher. Method. 2. A method for producing a biaxially oriented film according to claim 1, which comprises forming an unstretched film melt-extruded from a die while adhering it to a cooling roll at 40° C. or lower using an electrostatic adhesion method. . 3. For stretching, lower the unstretched film just before stretching to 5° below the stretching temperature.
2. The method for producing a biaxially oriented film according to claim 1, which comprises heating to a temperature higher than .degree. C. 4. Heat setting is performed by cooling the film immediately after stretching to a temperature lower than the stretching temperature by 5°C or more, and then heat-setting at a temperature higher than the stretching temperature and lower than 230°C. A method for producing an axially oriented film.