JPS62183328A - Manufacture of biaxially oriented film and device used for this method - Google Patents

Abstract

PURPOSE:To obtain a biaxially oriented film whose part having balanced physical properties and high uniformity has been widened, by a method wherein a preheating zone is provided between a lateral orienting zone and a heat treatment zone and a heating temperature is controlled from a high temperature to a low temperature toward the central part from an end part under a state where both end sides of the film is held by a tenter. CONSTITUTION:Although a thermoplastic film uniaxially oriented in a longitudinal direction is oriented laterally by a tenter and made into a biaxially oriented film by applying heat treatment to the same, a temperature gradient varying from high temperature to low temperature from an end part to the center part of the film is applied to the film in a preheating zone and preheat treatment is applied to the same while keeping a film temperature of the center part at less than 90 deg.C after providing the preheating zone between a lateral orienting zone and a heat treatment zone in the tenter. Then the film temperature posterior to the lateral orientation is lowered, which becomes profitable for post treatment, by providing a neutral zone between the lateral orienting zone and preheating zone in the tenter. A part corresponding to the upper bottom of a trapezoid shows uniform physical properties in a widthward direction by applying preheat treatment to the film posterior to the lateral orientation.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing a biaxially oriented film and an apparatus used therein, and more specifically, to a method for producing a biaxially oriented film, and more specifically to a process in which a thermoplastic film uniaxially stretched in the longitudinal direction is subjected to transverse stretching heat treatment using a tenter. The present invention relates to a method for widely and effectively manufacturing a highly uniform film with balanced physical properties in the direction of two wheels, and an apparatus used for manufacturing this film.

BACKGROUND ART Biaxially oriented films, especially biaxially oriented polyester films, are widely used industrially, but in particular for applications such as photography, drafting, and magnetic disks, physical properties in both the vertical and horizontal directions, especially the thermal expansion coefficient and the humidity expansion coefficient, are not well balanced. It is desirable that the It is also desirable that the properties be the same in all parts of the product film.

However, it has been extremely difficult to make the physical properties of the product film uniform in the width direction (transverse direction) using the usual sequential two-wheel stretching method, that is, a method in which longitudinal stretching is followed by lateral stretching. The reason for this is that both ends of the film are gripped in the tenter, and the shrinkage stress of the film in the longitudinal direction due to horizontal stretching is strongly restrained by the gripping means such as clips. The effect of the restraining force is weakened, and therefore the expansion of the central portion of the film is delayed due to the shrinkage stress.

If a straight line is drawn along the lateral direction on the film surface before lateral stretching, this straight line will be deformed and curved into a concave shape in the direction of film travel as the film is stretched. This phenomenon is called bowing, and this bowing phenomenon causes non-uniformity in the physical properties of the film in the lateral direction, particularly the temperature expansion coefficient and the humidity expansion coefficient. As a result of this phenomenon, a principal axis of orientation is created at both ends of the film that is further inclined vertically with respect to the bowing line, and the coefficient of temperature expansion and coefficient of humidity expansion in the direction of this principal axis becomes lower, and in the direction perpendicular to the principal axis. Both values tend to be high.

As a method for reducing or eliminating such a difference in physical properties in both wheel directions, Japanese Patent Application Laid-Open No. 50-73978 proposes a film manufacturing method in which a nip roll is placed between the transverse stretching process and the heat treatment process.

However, this technique has a habit of causing scratches on the film surface due to nip rolls, which severely limits its practical use.

Also, JP-A-51-80372, JP-A-54-13
Although the publication No. 7076 discloses measures to reduce bowing, this stretching is based on simultaneous two-wheel stretching. In this way, the bowing phenomenon is avoided in sequential two-wheel stretching (
At the very least, a stretching method that brings about uniformity of physical properties has not yet been developed.

Purpose of the Invention The purpose of the present invention is to produce a biaxially oriented film in which the bowing at the edges of the film is forcibly increased and the difference in bowing at the center of the film is significantly reduced, thereby widening the area with balanced physical properties and high uniformity. An object of the present invention is to provide a method and a device used therefor.

Structure and Effects of the Invention According to the present invention, the present invention provides a method for producing a biaxially oriented film in which a thermoplastic film that has been uniaxially stretched in the longitudinal direction is stretched in the transverse direction using a tenter, and then subjected to heat treatment. A preheating zone is provided between the stretching zone and the heat treatment zone, and in the preheating zone, a temperature gradient is created from a high temperature to a low temperature from the edge of the film toward the center, and the film temperature in the center is maintained at 90°C or less. A method for producing a biaxially oriented film, which is characterized in that a thermoplastic film that has been uniaxially stretched in the longitudinal direction is gripped at both ends, stretched in the transverse direction, and then subjected to a heat treatment. A preheating zone is provided between the stretching zone and the heat treatment zone, and is equipped with a heating means that can adjust the heating temperature from a high temperature to a low temperature from the ends toward the center while holding both ends of the film. This is achieved by a tenter for producing biaxially oriented films.

In the present invention, the thermoplastic polymer is not limited in any way as long as it can be made into a biaxially oriented film.For example,
Polyethylene terephthalate, polyethylene-2,6-
Polyesters such as naphthalene dicarboxylate, poly-1,4-cyclohexylene dimethylene terephthalate, polytetramethylene terephthalate, etc.; polyamides such as nylon 6, nylon 6.6, etc.; polyolefins such as polypropylene; synthetic polymers such as polyphenylene sulfide. Can be mentioned. These may be used alone, as a mixture, or as a copolymer. Suitable polymers include polyesters, especially polyethylene terephthalate. They may also contain small amounts of inorganic or organic additives.

A method for producing a biaxially oriented film using such a thermoplastic polymer can be a method of obtaining an unstretched film by a conventionally known method and sequentially biaxially stretching it in the longitudinal and lateral directions. It is preferable to use a method in which the material is melt-extruded from a gooey (for example, a T-die), rapidly cooled on a cooling rotating drum, then stretched in the longitudinal direction at a stretching orientation temperature, then stretched in the transverse direction in a tenter, and heat treated.

The stretching in the longitudinal direction is preferably carried out by a roll stretching method that utilizes the speed difference between two rolls (the speed difference between the supply roll and the stretching roll). At this time, the stretching in the longitudinal direction may be performed in one stage or in multiple stages.

In the present invention, a thermoplastic film that has been uniaxially stretched in the longitudinal direction is stretched in the transverse direction using a tenter, and then heat-treated to obtain a biaxially oriented film. established,
Preheating treatment is performed in the preheating zone by creating a temperature gradient from high temperature to low temperature from the edges of the film toward the center, and maintaining the film temperature at the center below 90°C. The length of the preheating zone varies depending on the running speed and thickness of the film, but it is preferably long enough to allow the film to stay for 3 seconds or more. In addition, methods for creating a temperature gradient in the width direction include blowing hot air at a predetermined temperature through each slit that is finely divided in the width direction of the film, and arranging multiple infrared heaters in parallel to the direction of film travel, each heater having one temperature. Examples include a method of adjusting the spacing of the heaters, a method of increasing the installation interval of the heaters from close to coarse from the ends toward the center, or a combination thereof, but the method is not limited to these methods. The temperature of the film in this preheating step has a temperature gradient from high temperature to low temperature from the ends to the center, and the temperature gradient may be continuous or stepwise. However, the temperature at the center of the film is 90° C. or lower. This is because the higher the temperature at the center, the worse the thickness unevenness of the film becomes, and when this temperature rises above 90°C, the thickness unevenness of the film becomes extremely poor. It is most preferable to keep the film temperature at the center below the glass transition temperature, since thickness unevenness will be improved. The temperature gradient from the edge of the film means from the vicinity of the film gripping tool, and it is not permissible to keep the temperature in the immediate vicinity of the gripping part low in order to prevent cutting at the gripping part such as a clip. be. The heating temperature depends on the processing time and the degree of orientation of the film and cannot be determined unconditionally, but it is preferable that the high temperature portions at the ends are at least 10° C. higher than the temperature in the center. Further, the temperature is preferably lower than the temperature of the subsequent heat treatment.

If it is lower than the heat treatment temperature, the crystallinity degree in the width direction can be made uniform by the subsequent heat treatment, but if it is higher, the crystallinity degree will be high only in the treated area, resulting in differences in physical properties in the width direction, and the width yield of the film will be reduced. descend.

By subjecting the film after horizontal stretching to the above-mentioned preheating treatment, a large shrinkage force is generated at the edges of the film, and the edges are significantly delayed with respect to the film's traveling direction, and at the same time, the shrinkage force gradually decreases toward the center of the film. As the delay in the direction of movement gradually decreases, the shape of the bowing is modified from an arc as shown in FIG. 1 to a nearly trapezoid as shown in FIG. The part corresponding to the upper base of the trapezoid has uniform physical properties in the width direction.

In the present invention, the transverse stretching zone and the heat treatment zone of the tenter may be conventionally known ones, and the conditions can also be those that have been accumulated in the past. Moreover, a neutral zone can be provided in the tenter between the transverse stretching zone and the preheating zone. By providing this neutral zone, the temperature of the film after lateral stretching is lowered, which is advantageous for subsequent processing.

In the above heat treatment, a predetermined temperature...for example, 200 to 23
It is preferable to heat the entire film at a constant temperature of 0°C.

According to the present invention, a biaxially oriented thermoplastic film having uniform physical properties along the film width direction can be obtained at a high yield. When the film is used to manufacture, for example, a flexible magnetic disk, a highly prized disk with a well-balanced thermal expansion coefficient and humidity expansion coefficient can be manufactured at a high yield.

Example The present invention will be further explained below with reference to Examples.

Example 1 Polyethylene terephthalate was melted and extruded through a T-die, formed into a film on the surface of a cooling rotating drum, cooled, and then stretched 3.6 times in the longitudinal direction at 80°C, followed by a transverse stretching zone and a neutral zone. The stretching heat treatment was performed in a tenter equipped with a preheating zone and a heat fixing zone. In the transverse stretching zone, the film was heated to 90° C. by hot air heating and stretched 3.9 times at a running speed of 10 m/a+in.

The above preheating zone has a length of 1m and a diameter of 10mφ and a length of 90cm.
11 infrared heaters each 401F from both ends
Twelve heaters are installed in a pitch, and by adjusting the temperature of each heater, the temperature at both ends of the film is 110℃, and the temperature is gradually lowered from this point toward the center, and the temperature at a position 50C11 from each edge is adjusted. was heated to 70°C, and the film temperature at the center was maintained at 60°C.

The above heat fixation zone has a length of 1.5m kept at 180℃.
A hot air heating zone with a length of 3 m maintained at 190° C. was provided. The biaxially oriented film that came out of the tenter was cooled to room temperature by a conventional method and wound up onto a roll. The shape of the Boeing in this film was similar to that shown in Figure 2, and was almost trapezoidal.

Example 2 The temperature at both ends of the film in the preheating zone was set to 120°C.
A biaxially oriented film was obtained in the same manner as in Example 1, except that the temperature at the position 50 m from the end was 85°C, and the temperature at the center of the film was 85°C.

The bowing shape of this film was similar to that shown in FIG. 2 as in Example 1.

Comparative Example 1 A biaxially oriented film was obtained in the same manner as in Example 1, except that the infrared heater was not energized in the preheating zone and no heating was performed by the heater. The bowing in this film was arcuate, similar to Figure 1.

Bowing amount of these films (maximum distance between string and arc M)
is within 3011 and the difference between the maximum value and the minimum value of the temperature expansion coefficient of the film in the circumferential direction is within 0.20 x 10-'/°C. In Example 1, the effective width is 170 aa.
In Example 2, the width was as wide as 150 cm, while in Comparative Example 1, it was only 60 cm. In addition, the thickness unevenness in the width direction of the film was 4% in Example 1, 7% in Example 2, and Comparative Example 1.
It was 4%.

[Brief explanation of drawings]

FIGS. 1 and 2 are diagrams showing the bowing shape of the stretched film. Power 11yo 21a

Claims (1)

[Claims] 1. In a method for producing a biaxially oriented film in which a thermoplastic film that has been uniaxially stretched in the longitudinal direction is stretched in the transverse direction using a tenter and then heat treated, preheating is performed between the transverse stretching zone and the heat treatment zone. The film is characterized by providing a zone, creating a temperature gradient from high temperature to low temperature from the edge of the film toward the center in the preheating zone, and performing preheating treatment while maintaining the film temperature in the center at 90°C or less. A method for producing a biaxially oriented film. 2. The method for producing a biaxially oriented film according to claim 1, wherein the preheating treatment is carried out in the preheating zone by maintaining the film temperature at the center below the glass transition temperature of the polymer. 3. In a tenter that grips both ends of a thermoplastic film that has been uniaxially stretched in the vertical direction, stretches it in the horizontal direction, and then heat-treats it, the film is held between the horizontal stretching zone and the heat treatment zone while gripping both ends of the film. A tenter for producing a biaxially oriented film, characterized in that a preheating zone is provided with a heating means that can adjust the heating temperature from a high temperature to a low temperature from the end toward the center.