JPH01204722A - Manufacture polyester film - Google Patents

Abstract

PURPOSE:To obtain a film which is superior in isotropy of thermal expansivity and has a low thermal coefficient of shrinkage, by a method wherein the title method is designed so that stretching is performed while raising a temperature at a specific speed and passes through a relaxation process also. CONSTITUTION:An unstretched sheet is produced by melting and extruding polyester resin to undergo a stretching process. Stretching is performed in a longitudinal direction, to begin with. Then the same is heated at a temperature of 90 deg.C or higher and then stretched larerally while performing a temperature rise at a speed not exceeding 10 deg.C/second. Then a tightly-drawn heat treatment process is performed at a temperature rising speed of not exceeding the 10 deg.C/ second and a fixed tenter width until the temperature attains to the necessary maximum temperature. Then a relaxation process is performed at need. The relaxation of 0.5-6% in a lateral direction is performed, to begin with, in the relaxation processes. Then the title method is designed so that after cooling, the relaxation of 0.1-1.0% is performed in the longitudinal direction at 80-120 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing a polyester film, which makes it possible to obtain a polyester film with improved isotropy in thermal expansion coefficient.

[Conventional technology]

Polyester films are generally made as follows. The polyester resin is fed into an extruder, melted and extruded, and formed into a sheet using a die. This is wound around a cooling drum and cooled and solidified to produce an unstretched sheet. This unstretched sheet is stretched in the longitudinal direction at a constant temperature of 90°C. Next, as shown in FIG. 2, the film is stretched in the transverse direction at a constant temperature of 100°C. Thereafter, tension heat treatment is performed at 170 to 230° C. with a constant tenter width, and cooling is performed to obtain a polyester film. This polyester film is slit to a predetermined width and wound up, if necessary. Note that after the tension heat treatment, lateral relaxation may be performed for the purpose of improving lateral thermal shrinkage.

[Problem to be solved by the invention]

The polyester film obtained in this way had a problem in that the thermal expansion coefficient at the end portions had poor isotropy.

That is, although the temperature expansion coefficient of the polyester film differs depending on the direction, a problem arises in that the difference Δα between the maximum value and the minimum value is large at the end portions. This was more pronounced as the width of the polyester film increased.According to the inventors' investigation, it is effective to reduce the tension heat treatment temperature to reduce Δα at the edges of the polyester film. In addition, the effect is not sufficient, and when the tension heat treatment temperature is lowered, the longitudinal heat shrinkage rate of the polyester film increases, making it unsuitable for practical use.

In order to reduce the thermal shrinkage rate, it is better to increase the tension heat treatment temperature, but if this is done, Δα at the film edges becomes large.

This invention was made in view of the above circumstances, and it is possible to improve the isotropy of the coefficient of thermal expansion at the edge of a polyester film, and also to reduce the coefficient of thermal contraction, if necessary. The objective of the present invention is to provide a method for producing polyester film that can also be used.

[Means to solve the problem]

In order to solve the above-mentioned problems, the present invention starts the lateral stretching in the stretching process at a temperature of 90°C or higher and then continues the stretching at 10°C.
The temperature should be increased at a rate of 10°C/second or less, and the tension heat treatment process should be performed at a rate of 10°C/second or less starting from the temperature at the end of transverse stretching until the required maximum temperature is reached. do. Also, after this heat treatment process,
Either go through a relaxation process of relaxing 0.1 to 1.0% in the longitudinal direction at 80°C to 120°C, or first,
0.5 in the transverse direction at a temperature below the maximum temperature of the tension heat treatment process
It is made to relax by ~6%, and then undergo a relaxing process in which it is relaxed by 0.1 to 1.0% in the longitudinal direction at 80°C to 120°C.

[For production]

Start the lateral stretching process at a temperature of 90°C or higher and then increase the temperature to 10°C.
The temperature should be increased to the required maximum temperature at a rate of 10°C/second or less, and the tension heat treatment step should be performed at a rate of 10°C/second or less starting from the temperature at the end of transverse stretching until the required maximum temperature is reached. When this is done, the resulting polyester film will have a small Δα at the edges and will have excellent isotropy in its thermal expansion coefficient. After the tension heat treatment step, the longitudinal direction is 0.1-13 at 80°C-120°C.
When 0% relaxation is performed, the obtained polyester film has excellent isotropy in the coefficient of thermal expansion and has a low thermal shrinkage rate in the longitudinal direction. Prior to the longitudinal relaxing step, by performing 0.5 to 6% relaxation in the transverse direction at a temperature below the maximum temperature of the tension heat treatment step, the obtained polyester film has a thermal shrinkage rate in the transverse direction as well as in the longitudinal direction. The resulting film also has a low heat shrinkage rate in the direction.

〔Example〕

The method for producing a polyester film according to the present invention is carried out, for example, as follows. First, as in the past, polyester resin is supplied to an extruder, melted and extruded, and formed into a sheet using a die. This is wound around a cooling drum and cooled and solidified to produce an unstretched sheet. The following stretching process is performed on this unstretched sheet. First, it is stretched in the longitudinal direction. The temperature at this time is 90-120
℃, and the stretching ratio is preferably 3.2 times or more. Next, cooling is performed.

This cooling is preferably to about 25°C.

Thereafter, it is heated to a temperature of 90° C. or higher, and as shown in FIG. 1, starting from this temperature, the film is stretched in the transverse direction while increasing the temperature at a rate of 10° C./second or lower. The temperature increase rate at this time is preferably 5° C./second or less. After that, the temperature was increased from the temperature at the end of the horizontal stretching to the required maximum temperature for 10 days.
The tension heat treatment step is carried out at a heating rate of ℃/second or less and with a constant tenter width. The required maximum temperature is usually 1
It is considered to be 70℃ or higher. The temperature increase rate at this time is preferably 5° C./second or less. The above two temperature increase rates do not necessarily have to be constant, and may be a stepwise temperature increase as long as the average temperature increase does not exceed the above-mentioned value. The average temperature increase rate can be determined, for example, by setting up one or more temperature measurement points per 5 m in the longitudinal direction in a tenter during the polyester film manufacturing process, and measuring the temperature of the film itself or the atmosphere near the film during the manufacturing process. It is measured by a method in which the value obtained by dividing the temperature difference between points by the film passing time in that section is the average temperature increase rate in that section. After this, a relaxing step is performed as necessary. In this relaxing step, first, relaxation is performed by 0.5 to 6% in the lateral direction at a temperature below the required maximum temperature. Next, after cooling, relaxation is performed by 0.1 to 1.0% in the longitudinal direction at 80° C. to 120° C. Cool immediately without performing the lateral relaxation 80
It is also possible to perform longitudinal relaxation at a temperature of 120°C to 120°C. In this way, a polyester film is obtained. This polyester film is wound to a predetermined width and wound up as necessary, as in the past.

Next, more specific examples will be described together with comparative examples.

(Example 1) Polyester resin was supplied to an extruder and melted and extruded,
It was formed into a sheet using a die. This was wound around a cooling drum and cooled and solidified to produce an unstretched sheet. This unstretched sheet was stretched in the longitudinal direction at 90°C. The stretching ratio at this time was 3.3 times. Next, -dan, 25
Cooled to ℃.

Thereafter, the film was heated to 100°C, and as shown in FIG. 1, starting from this temperature, the film was stretched in the transverse direction while increasing the temperature at an average rate of 1.6°C/sec. The stretching ratio at this time was 3.7 times. The temperature at the end of the lateral stretching was 120°C. Thereafter, tension heat treatment was performed until the temperature reached 200°C at an average heating rate of 4.1°C/sec and with a constant tenter width. After this, 6% Lila Nox in the lateral direction was performed at a temperature below the maximum heat treatment temperature. After cooling to 100°C, relaxation was performed by 0.2% in the longitudinal direction. In this way, width 4
A polyester film of m was obtained.

(Example 2) A polyester film with a width of 4 m was obtained in the same manner as in Example 1, except that relaxation in the longitudinal direction was not performed.

(Example 3) A polyester film with a width of 4 m was obtained in the same manner as in Example 1, except that during the tension heat treatment, the heating rate was 3.1°C/sec on average and the maximum temperature was 180°C (comparison Example 1) An unstretched sheet was produced in the same manner as in Example 1. This unstretched sheet was stretched in the longitudinal direction at 90°C. The stretching ratio at this time was 3.3 times. Next, it was cooled to 25°C.

Thereafter, it was heated to 100° C. and stretched in the transverse direction at this temperature, as shown in FIG. The stretching ratio at this time is 3
．． It was made 7 times. Next, the temperature was raised to 220° C., and tension heat treatment was performed at this temperature with a constant tenter width. The temperature increase rate during this temperature increase was 24° C./sec. Furthermore, we perform 6% relaxation in the lateral direction below the maximum temperature of tension heat treatment,
A polyester film with a width of 4 m was obtained.

(Comparative Example 2) Heat treatment was performed at 200°C. The temperature increase rate during this temperature increase was 20° C./sec. Other than this, a polyester film having a width of 4 m was obtained in the same manner as in Comparative Example 1.

(Comparative Example 3) A polyester film with a width of 4 m was obtained in the same manner as in Comparative Example 1, except that after relaxing in the horizontal direction, the film was cooled to 100° C. and relaxed by 0.2% in the vertical direction.

(Comparative Example 4) After lateral glue lux, cooled to 100'C,
In addition to applying 0.2% glue lax in the vertical direction,
A polyester film with a width of 4 m was obtained in the same manner as in Comparative Example 2.

For the polyester films obtained in Examples 1 to 3 and Comparative Examples 1 to 4, the Δα and heat shrinkage rate of the edges were measured. The results are shown in Table 1.

The difference Δα in thermal expansion coefficient and the thermal contraction rate were measured as follows.

one'! &Agency・'1 Δα, 1 method One test piece with a length of 150+u and a width of 10 mm was prepared along the optical orientation direction (major axis) and the orthogonal direction (minor axis) determined in advance using a polarizing microscope. After sampling and aging by setting in a TMA device in a constant temperature and humidity chamber, dimensional changes at 20° C. to 30° C. are measured, and the coefficient of thermal expansion in each direction is determined using the following formula.

(Unit: 10-6/''C) Although the coefficient of thermal expansion varies depending on the direction, it is known that it is approximately minimum in the long sleeve direction and approximately maximum in the short axis direction.

Δα is determined by the following formula.

A test piece with a medium IQam and a length of 300111 is taken from each direction in the vertical and horizontal directions. Insert the measurement interval marks into the test piece and measure the original length using a cathedometer or a similar method.

After measuring the original length, the test piece is placed in a hot air circulation oven maintained at 80±1°C, taken out after 30 minutes, and left to cool for about 10 minutes. Measure this test piece again using a cathedometer or a similar method. Find the average value of each test piece and calculate the heat shrinkage rate using the following formula.

Original length (1 meeting) - Length after heat treatment (dragon) Heat shrinkage rate = X
From Table 1, it can be seen that the polyester films obtained in Examples 1 and 2.3 have excellent isotropy in the coefficient of thermal expansion at the edges and a small coefficient of thermal contraction. On the other hand, the ones obtained in Comparative Examples 1 and 2 have poor isotropy of the thermal expansion coefficient at the end and have a large thermal contraction coefficient (the ones obtained in Comparative Example 3.4 have a high thermal contraction coefficient). Although the coefficient is small, it can be seen that the isotropy of the thermal expansion coefficient at the end is poor.

〔Effect of the invention〕

A method for producing a polyester film comprising a stretching step of stretching an unstretched polyester sheet in the longitudinal direction and then stretching it in the transverse direction, and a heat treatment step of performing tension heat treatment with a constant tenter width after this stretching step, according to claims 1 to 3. In the invention, the stretching in the lateral direction in the stretching step is started at a temperature of 90° C. or higher and thereafter carried out while increasing the temperature at a rate of 10° C./sec or less, and the tension heat treatment step is also carried out at a temperature at the end of the lateral stretching. Starting from 10 until the required maximum temperature is reached.
Since the heating is carried out while increasing the temperature at a rate of .degree. C./second or less, it is possible to improve the isotropy of the thermal expansion coefficient at the edges of the polyester film.

The invention according to claim 2 provides that after the same tension heat treatment step, the
Since the polyester film is also subjected to a relaxing step of relaxing by 0.1 to 1.0% in the longitudinal direction at a temperature of 120°C to 120°C, the heat shrinkage rate of the polyester film in the longitudinal direction can also be reduced. In the invention according to claim 3, after the tension heat treatment step, the tension heat treatment step is first relaxed by 0.5 to 6% in the lateral direction at a temperature lower than the maximum temperature of the tension heat treatment step, and then 80°C.
Since the film also undergoes a relaxation process in which it is relaxed by 0.1 to 1.0% in the longitudinal direction at ~120°C, both the longitudinal and transverse heat shrinkage rates of the polyester film can be reduced. .

[Brief explanation of the drawing]

FIG. 1 is a graph showing film width and temperature changes in one embodiment of the polyester film manufacturing method according to the present invention, and FIG. 2 is a graph showing film width and temperature changes in a conventional polyester film manufacturing method. Agent Patent Attorney Takehiko Matsumoto

Claims (1)

[Claims] 1. A method for producing a polyester film comprising a stretching step of stretching an unstretched polyester sheet in the longitudinal direction and then stretching it in the transverse direction, and a heat treatment step of performing tension heat treatment with a constant tenter width after this stretching step. Therefore, the stretching in the lateral direction in the stretching step was started at a temperature of 90° C. or higher, and then 10
The temperature should be increased at a rate of 10°C/second or less, and the tension heat treatment step should also be performed while increasing the temperature at a rate of 10°C/second or less, starting from the temperature at the end of transverse stretching until the required maximum temperature is reached. A method for producing a polyester film characterized by: 2. A method for producing a polyester film comprising a stretching step of stretching an unstretched polyester sheet in the longitudinal direction and then stretching it in the transverse direction, and a heat treatment step of performing tension heat treatment with a constant tenter width after this stretching step, the stretching step 10 after starting the transverse stretching at a temperature of 90°C or higher.
The temperature should be increased at a rate of 10°C/second or less, and the tension heat treatment step should also be performed while increasing the temperature at a rate of 10°C/second or less, starting from the temperature at the end of transverse stretching until the required maximum temperature is reached. A method for producing a polyester film, which is characterized in that, after the same tension heat treatment step, a relaxation step is performed in which the film is relaxed by 0.1 to 1.0% in the longitudinal direction at 80° C. to 120° C. 3. A method for producing a polyester film comprising a stretching step of stretching an unstretched polyester sheet in the longitudinal direction and then stretching it in the transverse direction, and a heat treatment step of performing tension heat treatment with a constant tenter width after this stretching step, the stretching step 10 after starting the transverse stretching at a temperature of 90°C or higher.
The temperature should be increased at a rate of 10°C/second or less, and the tension heat treatment step should also be performed while increasing the temperature at a rate of 10°C/second or less, starting from the temperature at the end of transverse stretching until the required maximum temperature is reached. and after the same tension heat treatment step, it is first relaxed by 0.5 to 6% in the lateral direction at a temperature below the maximum temperature of the tension heat treatment step, and then 80 to 12
A method for producing a polyester film, characterized in that it also undergoes a relaxing step of relaxing 0.1 to 1.0% in the longitudinal direction at 0°C.