JPH08150657A - Method for producing thermoplastic resin film - Google Patents

Abstract

(57) [Summary] [Structure] A film made of a thermoplastic resin that is continuously formed is attached to a pair of clip chains, which are arranged on both sides of the film and in which a large number of chain links are connected in an innumerable annular shape. In the method for producing a film, in which the clip is made to run in a stenter while gripping both ends thereof, preheated, stretched, heat-fixed in the stenter, and then subjected to a relaxation treatment, the relaxation treatment is (1) In the film width direction, relaxation treatment is performed in the range of 0.1 to 10%,
(2) Also in the stenter, 0.1 in the longitudinal direction of the film.
Relaxation treatment is performed in a relaxation rate range of ˜3%, (3) Relaxation treatment is performed in an arbitrary temperature range of 70 to 170 ° C., and (4) Film temperature cooling rate after heat setting is 20.
C./sec or less, and (5) a method for producing a thermoplastic resin film, characterized in that the widthwise temperature unevenness during film cooling is 10 ° C. or less. [Effect] It is achieved by eliminating the local dimensional difference of the film and obtaining a film having good flatness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a film made of a thermoplastic resin having good flatness.

[0002]

2. Description of the Related Art A thermoplastic resin such as polyethylene terephthalate or a copolymer thereof, polyethylene naphthalate or a copolymer thereof, or a blend thereof with a small proportion of another resin is melt-extracted to form a film. It is known. Then, the film obtained by heat setting after biaxial stretching, which is then subjected to a relaxation treatment in the film width direction and the longitudinal direction, maintains its dimensional stability, and the heat shrinkage rate is often kept low. Are known.

This relaxation process can obtain a proper heat shrinkage rate by giving a predetermined relaxation rate. As a method thereof, usually, in the film width direction, it can be easily realized by making the clip chain running path in the stenter run in a tapered shape. Further, regarding the longitudinal direction relaxation treatment, generally, the roll peripheral speed and the stenter oven are provided between the exit of the stenter oven and the roll on the downstream side thereof (for example, a film transport roll, a cooling roll, a tension cut roll, etc.). This is done by giving a difference to the running speed of the clip thus obtained.

However, in the case of performing the relaxation treatment in the longitudinal direction outside the room of the stenter oven, the film is exposed to the outside air, and the outside air temperature has a large variation due to seasonal variations as compared with the inside of the oven. It may not be possible to reach the desired temperature. In addition, local temperature unevenness of the film is likely to occur due to slight air flow,
The relaxation treatment effect also varies.

Generally, when the film is cooled after heat setting,
Since shrinkage stress is generated with cooling, in the above cases, the magnitude of the shrinkage stress in the longitudinal direction and the amount of relaxation of stress occur, and as a result, there is a slight dimensional difference in the obtained film. Born and hinders the flatness of the film.

Therefore, as a method of achieving a target processing temperature at a predetermined relaxation rate and keeping the variation within a predetermined range, while holding the film in a clip in an oven, the film is moved in the width direction. A method is known that enables a relaxation treatment in the longitudinal direction (Japanese Patent Publication No. 4-28).
218).

However, since it takes a certain amount of time to relax the shrinkage stress generated during film cooling,
In addition to reducing the variation in the processing temperature and performing the relaxation process at the target temperature by implementing JP-B-4-28218, the film cooling that is actually performed during the relaxation process is not performed at a predetermined cooling rate or less. Cannot obtain a film with good planarity.

[0008]

SUMMARY OF THE INVENTION In view of the above problems, the present invention performs a relaxation treatment within a predetermined film temperature range and suppresses the temperature variation in the width direction within a predetermined range. The object of the present invention is to obtain a film having excellent flatness by cooling the above at a predetermined cooling rate or less.

[0009]

According to the method for producing a film of the present invention in accordance with this object, a film made of a thermoplastic resin which is continuously formed is arranged on both sides of the film,
Clips are attached to a pair of clip chains in which a large number of chain links are connected in an annular shape, and the clips are made to run in a stenter while gripping both ends of the chain, and preheated, stretched and heat-fixed in the stenter, and then relaxed In the method for producing a film to be treated, the relaxation treatment includes (1) a relaxation treatment in the widthwise direction of the film within a relaxation rate range of 0.1 to 10% in the stenter, and (2) also a longitudinal direction of the film in the stenter. Relaxation treatment is performed in a relaxation rate range of 0.1 to 3%, (3) Relaxation treatment is performed in an arbitrary temperature range of 70 to 170 ° C., and (4) Film temperature cooling rate after heat fixation is 20. C./sec. Or less, and (5) the width-direction temperature unevenness during film cooling is 10.degree. C. or less.

In the present invention, the thermoplastic resin means polyethylene terephthalate or a copolymer thereof, polyethylene naphthalate or a copolymer thereof, or a blend thereof with a small proportion of another resin.

In the film used in the present invention, the effect of obtaining such good flatness is more remarkably exhibited in a wide apparatus having a film width of 2 to 8 m at the exit of the stenter. In terms of the film thickness of the final product, the thickness is preferably up to 500 μm.

The film after heat setting is cooled while shrinking stress is generated at the time of cooling.
When the relaxation treatment is carried out in the temperature range of 0 ° C., a slight difference in temperature causes a difference in stress. Therefore, when performing the relaxation treatment in the above range, the film temperature unevenness in the width direction is 1
It is important to keep the temperature below 0 ° C, preferably below 5 ° C. Even if the stresses generated are the same, the film temperature cooling rate is 20 ° C /
It is necessary to set the rate to not more than seconds, preferably 10 ° C./second or less.

The relaxation rate in the stenter is determined by the final target heat shrinkage rate of the film.

[0014]

[Characteristic evaluation method]

(1) Flatness The target film is spread on a cork plate with a flat surface, the air sandwiched between the cork plate and the film is removed, and the air is removed and reflected on the film surface several minutes later. There is a method of observing the planarity from the side opposite to the irradiation direction while irradiating with light. As an air elimination method between the film and the cork plate, for example, there is a method in which a roll having a weight of several kg and a diameter of about 100 mm is rolled on the film and air is pushed out by the weight.

[0015]

EXAMPLES Preferred examples of the method for producing a film of the present invention will be described below.

Example Polyethylene terephthalate is melt extruded by a known method, biaxially stretched, and then heat set at an appropriate temperature of 180 ° C to 250 ° C. The heat setting temperature is determined by the properties such as the heat shrinkage rate of the final film product to be obtained.

Then, in the stenter oven, relaxation treatment is performed in the longitudinal direction and the width direction. This relaxation treatment is performed within the film temperature range of 100 to 160 ° C. The relaxation rate during the relaxation treatment is 6% in the width direction and 0.5% in the longitudinal direction. These relaxation rates are determined by properties such as the heat shrinkage rate of the final film product desired to be obtained.

The film advances in the stenter oven toward the same outlet while being relaxed, and the temperature distribution in the width direction of the oven is controlled so that the temperature unevenness in the width direction of the film at that time is 5 ° C. or less. .

Further, by setting the temperature of each chamber in the oven after heat setting, the film cooling rate after heat setting is
Control so that the temperature is 10 ° C / sec or less.

As described above, a film having good flatness can be obtained by the effect of the present invention.

Comparative Example A film heat-set under the same conditions as those of the examples is subjected to relaxation treatment in the lengthwise direction and width direction in a stenter oven under the same conditions as those of the above examples.

At that time, the temperature unevenness in the width direction of the film is set to the same condition as in the above embodiment.

The film cooling rate after heat setting is 25
The temperature of each chamber in the oven after heat setting is set so that it becomes ℃ / sec.

The film obtained as described above has a defective flatness portion due to the local dimensional difference of the film.

[0025]

INDUSTRIAL APPLICABILITY According to the present invention, the relaxation treatment after heat setting in the stenter oven is performed within a predetermined film temperature range, and the temperature variation in the width direction is suppressed within the predetermined range. By cooling at less than a predetermined cooling rate, eliminate the local dimensional difference of the film,
This is achieved by obtaining a film with good flatness.

Claims (1)

[Claims] 1. A clip attached to a pair of clip chains, in which a large number of chain links are connected in an infinite number of rings, which are arranged on both sides of the film, and which are made of a thermoplastic resin which is continuously formed. In the method for producing a film, which is run in a stenter while gripping both ends thereof, preheated, stretched, heat-fixed in the stenter, and then subjected to a relaxation treatment, the relaxation treatment includes (1) a film width direction in the stenter. To a relaxation rate range of 0.1 to 10%, and (2) in the same stenter, a relaxation rate range of 0.1 to 3% in the longitudinal direction of the film.
(3) The film temperature is relaxed in an arbitrary temperature range of 70 to 170 ° C., (4) the film temperature cooling rate after heat setting is 20 ° C./sec or less, and (5) the width direction during film cooling. A method for producing a thermoplastic resin film, wherein the temperature unevenness is 10 ° C. or less.