JPS61233523A - Preparation of biaxially oriented polyester film - Google Patents

Abstract

PURPOSE:To improve dimensional stability and flatness, by setting the tension of a polyester film after the completion of biaxial orientation in the longitudinal direction of said film to a specific value or less and heating the central part and side edge parts of the film to specific temps. to hold said temps. CONSTITUTION:A film 4 after the completion of biaxial orientation is sent into a heat treatment apparatus and successively passed through a heating zone 1, a cooling zone 2 and a tension separation zone 3 to be taken up. As a heating means, an infrared heater is used and the temp. of the central part of the film is heated to 150 deg.C or more while each of the side edge parts of said film is heated to temp. 10 deg.C more higher than that of the central part. In order to make a heat shrinkage value sufficiently low in the longitudinal direction by heat treatment, the tension of the film in the longitudinal direction within the heating zone 1 is set to 10kg/m or less. After heating, the film is gradually cooled in the cooling zone 2 to eliminate the strain generated by heat treatment. The cooled film is released from tension and taken up on and after under proper tension.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for producing a biaxially oriented polyester film used, for example, in photographic film bases, magnetic tape bases, and the like.

(Prior Art) Since dimensional stability is poor when a polyester film is only biaxially stretched, it is usually further heat-treated. Conventional heat treatment was performed by passing hot air through a heating zone and a cooling zone. However, this method not only does not improve dimensional stability sufficiently, but also has the problem of causing sagging, sagging, bending, etc., which impairs the flatness of the film.

Bending here refers to the bending in the longitudinal direction of the base that occurs when shrinkage stress in the tenter is concentrated in the center during successive biaxial stretching, and the bending occurs when the base is cut in half by the width of the tenter. Then it becomes noticeable.

Therefore, research is being conducted in various places to solve such problems, and the following methods have been proposed.

First, Tokukai Akira! Publication R-71132 discloses that when a biaxially stretched film is heat treated between rolls, the dimensional stability and flatness are improved by controlling the temperature, tension and time within a specific range. ing.

Furthermore, Japanese Patent Application Laid-open No. 33-2407 discloses that a biaxially stretched film is heat-set while giving limited shrinkage in the width direction, and then subjected to slow heat treatment under low tension while holding the film with pressurized air. A method is disclosed for improving dimensional stability by:

Furthermore, Japanese Patent Application Laid-Open No. 17-17-27 discloses that a biaxially stretched and heat-set film is placed under low tension in its longitudinal direction, and supported by blowing hot air.
A method is disclosed for improving dimensional stability by heating at a temperature of /r°C for 3 to /j seconds.

In addition, Tokko Sho JLR-3! /JJ- Publication discloses that a polyester film is supported and conveyed by air blowing, the film is heated to a temperature higher than the secondary transition point to soften it, and then the film is bent in a curved state to a temperature lower than the secondary transition point. A method of improving flatness by cooling and curing at a temperature is disclosed.

(Problems to be Solved by the Invention) According to the studies of the present inventors, JP-A-Sho! The method disclosed in Publication No. r-7≠32 has limitations in improving the flatness, and there are still problems with the occurrence of sagging in the middle, stretch of the edges, etc., and the problem of bending still remains.

JP-A No. 1,072, JP-A No. 37-7! Each of the methods disclosed in Japanese Patent Publication No. 1F and Japanese Patent Publication No. 3113J has a problem in that the equipment becomes large-scale because they both use an air conveyance system.

Furthermore, heating with hot air requires a long heating zone. In addition, temperature unevenness often occurs during heating and cooling, which impairs flatness, and to prevent this, it is necessary to slow cooling and consider the widthwise distribution of cooling air, etc. It had become a long one.

Although a heating method using an infrared heater was known (%Open/Close! Publication No. 3-2407λ), it had not been adopted due to the difficulty of uniform heating.

(Means for Solving the Problems) The present invention has been made to solve these problems, and includes heating the film with a temperature distribution in the width direction using an infrared heater. It is characterized by

That is, in the present invention, after biaxial stretching of a polyester film, the tension in the film longitudinal direction is set to 10 Kg/m or less, and the temperature at the center of the film is set to 1zo0c or more and the temperature at the side edges is set to 100 C or higher using an infrared heater. The present invention relates to a method for producing a biaxially stretched polyester film, which is characterized by heating for 3 seconds or more so that the temperature is IO'C or more higher than the temperature at the center.

A typical polyester film is polyethylene terephthalate film.

Inorganic pigments, organic pigments, antioxidants, ultraviolet absorbers, etc. can be added to the polyester as appropriate.

The biaxial stretching may be carried out separately in the longitudinal direction and in the longitudinal direction, or may be carried out simultaneously in both directions. However, the bending phenomenon is unique to sequential biaxial stretching.

After biaxial stretching, the polyester film is
Heat treatment is performed using the equipment shown in the figure.

This device consists of a heating zone 11, a cooling zone 1, and a tension separation zone 3. In the heating zone L, there is a long infrared heater that heats the entire width of the film!
The cooling zone is equipped with a cold air duct that blows out cold air. The film that has been biaxially stretched is fed into this heat treatment equipment from the bottom right of Fig. 7, and heated into the heating zone 11? lI zone co and tension separation zone 3
It is wound up after passing through it one after another.

The method of the present invention is characterized in that an infrared heater is used as the heating means, and the film is heated with a temperature distribution in the width direction.

The type of infrared heater does not matter, and ceramic heaters, Pycor heaters, sheathed heaters, etc. can be used. These heaters are arranged parallel to the longitudinal direction of the film in order to provide temperature distribution in the width direction of the film. An example is shown in FIG. As shown in the figure, a long infrared unit heater ja,!
a, . . . , ra are arranged on the film board parallel to its longitudinal direction. The number of unit heaters is suitably about 3 to 10 per m of film, particularly about 3 to 10 per m. The total width of the infrared heater is determined so that the entire width of the film can be heated to a predetermined temperature distribution, and is usually the same as or slightly wider than the total width of the film. On the other hand, the total length of the infrared heater only needs to be able to heat the film to a predetermined temperature for a predetermined time, and this varies depending on the heat generation capacity of the heater, the transport speed of the film, etc.

The temperature distribution is such that the temperature at the center of the film is /J-°C or more and the temperature at the side edges is 100C or more higher than the temperature at the center. The temperature at the center is /J-0'c--zoo
A temperature of about 0c, especially /60°C-, /1r°C is generally appropriate, and the temperature at the side edge is 140'CN220'
The temperature difference between the center and the side edges is 10'C-6O'c.
Normally, about io'c-to'c is appropriate. The temperature distribution in the width direction of the film at the exit of the heating zone is generally boat-shaped. Each unit heater is appropriately controlled to prevent sagging or bending of the film. In particular, bending is a problem when dividing and slitting food products, but it is also possible to perform partial heating and correct the bending of each slit product.

In order to achieve a sufficiently small thermal shrinkage value in the longitudinal direction by heat treatment, the tension in the longitudinal direction of the film in the heating zone is set to be less than /OKg/m. This tension is usually 7~/OK, taking into account ensuring the flatness of the film.
Approximately g/m is appropriate. The tension can be adjusted, for example, by using part or all of the rolls on which the film is hung as drive rolls and adjusting the driving force of the rolls.

The heating time is set to be 3 seconds or longer so as to ensure the necessary dimensional stability, and this varies depending on the heating temperature, film conveyance speed, etc.

After heating, it is slowly cooled in a cooling zone to eliminate distortion caused by heat treatment. This cooling is preferably carried out for 3 seconds or more to sufficiently shrink the polyester until it reaches the glass transition temperature. In the case of the apparatus shown in FIG. 7, the film μ is gradually cooled by cold air blown out from blowing holes 7 at approximately equal intervals in a cold air duct 7 provided on the film μ to be conveyed.

The cooled film is then subjected to tension separation, after which an appropriate tension is applied and the film is wound up.
As shown in the figure, this is carried out by providing a driving roller such as a suction drum rubber roll between tenter windings.

(Function) The shrinkage stress in the longitudinal direction of the polyester film is concentrated in the center of the film in the transverse stretching zone, and the center comes out of the stretching zone later than the edges on both sides.

As a result, as shown in Figure 3, the film ≠ has a sag i
produces o. Also, for example, film ≠ is shown in μ (1/!
When the film is slit as shown in Fig. 5 (1/4 slit) and Fig. 5 (1/4 slit), in addition to the middle sag, the side edges are stretched out and the film is bent in the longitudinal direction (bending). come. These are removed by heating with a boat-bottom temperature distribution under the aforementioned low tension.

The dimensional stability of the film in the width direction is improved in the high-temperature zone in the latter half of the tenter, but the dimensional stability in the longitudinal direction is not sufficiently stable because both edges of the film are held with clips when the tenter is in use. do not have. This is also improved during the heat treatment of the present invention.

(Example) The polyethylene terephthalate film that came out of the tenter was once wound up and then heat-treated using the apparatus shown in FIGS. 1 and 2. The tension in the heating zone 1 was set to 1 Kq/m, and the infrared heater j was adjusted so that the temperature distribution in the width direction of the film at the exit of the heating zone 1 was as shown in the figure. The time taken for the film to pass through the heating zone was set to 3 seconds. The passage time through the cooling zone was 3 seconds, and the film temperature at the constant speed rotor was zo''c.

Meanwhile, each unit heater for comparison! The heat treatment was performed in the same manner as above except that the calorific value of a was made uniform. The temperature distribution in the width direction of the film at the exit of the heating zone 1 was as shown in FIG.

As a result, when heated with a boat-shaped temperature distribution, the Q1 flatness of the full-width film was significantly improved as shown in Figure 11, and the A-slit product was shown in Figure 11. On the other hand, in the comparative example where the heating was uniform, all the parts
As shown in Figure 1, the slit product is as shown in Figure 1.
The flatness was significantly worse than that of the untreated product. In the untreated product, all parts were set as shown in Fig. io, and the A-slit product was flat as shown in Fig. 13, and there was sag in the center and extension at the edges.

Heat shrinkability and bending were as shown in the table below.

Example product Untreated product heat yield MD=o, o3, MD=0, /, 4
Width bending Left 0.2 dew Left /, 0 dew (V2 slot) Right O■ Right λ, om* Maximum venting value for 3m film (effect of the invention) By dividing the heater parallel to the longitudinal direction, We were able to correct certain sagging, sagging, and bending, and obtain a film with good flatness. By eliminating bending, it was possible to eliminate the difference between slits when cutting multiple shafts from the original fabric.

A film with excellent dimensional stability could be obtained by heat treatment. Thermal shrinkage in the MD direction was particularly improved because the heat treatment was performed while released from the clips.

By using an infrared heater, we were able to shorten the heating time and shorten the heating zone. By adopting the roll conveyance method, the equipment was simpler than the air conveyance method.

In the past, in many cases, flatness was hindered because temperature unevenness occurred during heating and cooling, and a long cooling zone was required to eliminate this temperature unevenness. However, in the method of the present invention in which a temperature distribution is provided in the width direction of the film, the inhibition of flatness due to temperature unevenness is reduced, and the cooling zone can be shortened.

Since the method of the present invention can be carried out in a space-saving manner, it does not require large-scale modification even if the film forming machine already exists and space is limited.

[Brief explanation of the drawing]

FIG. 1 is a side view showing an outline of an example of an apparatus used for carrying out the method of the present invention, and FIG. 2 is a partial perspective view of the heating portion thereof. Figure 3 ~ No. 3! The figure is a plan view of the film taken out from the tenter, FIG. 3 shows all parts, FIG. 3 shows a member slit product, and FIG. 3 shows a V4 slit product. Figure 7 shows the temperature distribution in the width direction of the film at the exit of the heating zone in the example and Figure 7 in the comparative example. Figures 1 to 1O are all plan views of all the parts. Figure R shows an example product, Figure 1 shows a comparative example product, and Figure 1Q shows an untreated product. Figures 1/73 are all plan views of the A-slit product, Figure 11 shows the example product, Figure 1 shows the comparative example product, and Figure 13 shows the untreated product. .

Claims (1)

[Claims] After the polyester film is biaxially stretched, the tension in the longitudinal direction of the film is set to 10 kg/m or less, and an infrared heater is used to raise the temperature of the center of the film to 150°C or higher and the temperature of the side edges to be lower than the temperature of the center. A method for producing a biaxially stretched polyester film, which comprises heating the film to a temperature of 10°C or more.