JPS6021053B2 - Cooling method for biaxially oriented polyester film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for cooling polyester films that have been heat set following biaxial stretching.

In particular, the present invention involves slowly rolling a heat-set polyester film in a high-temperature state in an atmosphere above the glass transition point.
This relates to a technology that dramatically improves the surface flatness of a film. The conventional technology, as shown in Hakama Kosho No. 44-20000, is to directly transfer and cool a heated film in an atmosphere below the glass transition point of 30 to 80 pm. The surface flatness was maintained.

With this method, the maximum sagging depth, which is an index of film surface flatness, is within 25 ribs, but since the temperature difference between the heat fixing temperature and the cooling temperature is large, the surface flatness cannot be achieved unless the cooling temperature is precisely controlled. There was a problem that the system was not sufficiently improved. In order to improve the surface flatness of the film, it is necessary to apply sufficient and uniform stress relaxation to the film. The present invention was achieved by discovering what was needed to be done. An object of the present invention is to provide a novel cooling method that improves the flatness of the film and produces an excellent polyester film that is free from sagging and wrinkles.

In the present invention, when cooling a heat-set biaxially oriented polyester film following biaxial stretching, the surface heating gas of the bi-bag stretched film is sucked, and then the film is desirably placed in an atmosphere maintained at 90 to 140°C. This is a cooling method for a biaxially oriented polyester film, which is characterized in that the film is transferred so that the tension of the film is 2k9/m2 or less, and the film is slowly cooled at a cooling temperature of 100° C. or less per second.

The present invention will be explained.

The double-stretched polyester film is then heat-set, and this temperature is usually in the range of 150° C. or higher and close to the melting point.

Therefore, the cooling of this film ranges from about 200°C to 90°C.
-14,000, and further cooled to room temperature if necessary. In order to obtain a cooling effect in a short time, it is necessary to quickly remove the high temperature gas present on the film surface by heat setting.

In the present invention, high-temperature gas is removed by suction from the front surface (including the back surface) of this film.

Removal of this high temperature (heated) gas allows the film to be cooled quickly, and also has the effect of removing the heated gas leaking from the heat setting device into the cooling chamber, further enhancing the film cooling effect. The film must be cooled once to a range of 90-140 oo.

A film that momentarily passes through this temperature range has insufficient flatness, but a film that is gradually cooled has a dramatically improved flatness. The exact reason for this is not clear, but stress relaxation is likely to occur because there is a temperature range above the glass transition point, and stress distortion may not be completely removed if the cooling mirror is rapidly cooled from a high temperature to below the glass transition temperature. This is considered to be due to the occurrence of new internal strain due to rapid cooling. In the present invention, at least the shrinkage of the film corresponding to the thermal overstress coefficient due to cooling can be made uniform in the slow cooling step. Film from high temperature to 90-140
The slower the cooling rate to zero, the better the flatness.

It has been experimentally confirmed that the upper limit of the cooling temperature is approximately 100 oo/sec. At this cooling rate, the local sag of the film is less than 3 Yanagi (according to the measurement method of the present invention),
Excellent flatness. The cooling rate can be calculated from the residence time of the film in this cooling chamber and the temperature difference between the heat setting temperature and the cooling temperature. Therefore, the minimum size (length in the machine direction) of the cooling chamber is set based on the running speed of the film, the heat setting temperature, and the cooling chamber temperature. When the cooling temperature is below 50 pm/sec, the local sagging of the film is approximately 2
It will be within the side. On the other hand, significantly slowing down the cooling rate is not industrially advantageous because the cooling chamber becomes larger. Similarly, lowering the traveling speed is also undesirable from the viewpoint of productivity. For these reasons, the lower limit of the cooling rate is about 5° C./sec.
The film is limited to low tension to avoid unnecessary deformation during the cooling process.

Generally, in this temperature range of 90 to 140°C, the tension is preferably maintained at a tension limit that allows elastic recovery so as not to cause an elongation deformation of 5% or more. Therefore, it is preferable that the tension of the film running in the cooling chamber is 2 kg/pillow or less. In order to keep the tension low and constant in this way, one or more pairs of nip rolls that can cut the tension are installed between the cooling chamber and the winding machine, or multiple It is preferable to bring it into contact with a rotating roll or a printing machine. The polyester film that can be applied to the present invention is a polyester film selected from linear synthetic polymers consisting of aromatic dicarboxylic acids such as polyethylene terephthalate and polyethylene-2,6 naphthalate and glycols having 2 to 10 carbon atoms. It is a stretched film.

Of course, the present invention can also be applied to the case where a heated film that has been heat-set is cooled to room temperature.

In this case, the heated film may first be subjected to the cooling method of the present invention, and then naturally or forcedly cooled to room temperature. According to the method of the present invention, there is an advantage that a film with extremely excellent flatness can be obtained, and a biaxially stretched polyester film without any stretch or sag can be obtained.

It is characterized by extremely superior flatness compared to conventional methods. The method for measuring flatness (sag) of the present invention will be explained with reference to FIG.

As shown in Figure 1, the length of the tapered 3 is approximately 6 cm, which is sufficiently flat and 5 skins apart with base line 1 on the A end and base line 2 on the B end.
Spread the film m uniformly, align the A end with the base line 1, and fix it with adhesive tape 4.

Next, after drawing a straight line 5 perpendicularly to the film along the base line 2 of the B end, a tanzak-shaped cut is made along the length direction to a total width of 5 m/m. Next, add 0.0 to B Oribe of each tanzak.
A minute load 6 of 2k9/mun is applied to the film, and the length difference 7 between the base line 2 on the table and the length 5 moved as a result of cutting into a tanzak shape is sequentially measured in the width direction of the film.

From this measurement result, the difference between the maximum length and minimum length is taken as the sagging depth and is used as an index of flatness.

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

Examples 1-4, Comparative Examples 1-2 Polyethylene terephthalate (hereinafter abbreviated as TPET)
was melt-extruded from an extruder and cooled and solidified in a casting drum to form a non-oriented sheet with a thickness of about 160 microns.

This sheet was heated to about 85 qo and stretched 3.5 times in the machine direction, then fed into a stenter and stretched 3.5 times in the transverse direction in an atmosphere of about 100 qo. Stretch the needle and continue to heat set for 20 minutes.
Heat setting was carried out at a temperature of 0oC to obtain a 12 micron film. When leading the film from the heat fixing chamber to the cooling chamber, the surface heating temperature is sucked and the temperature of the cooling chamber is set to 90 oo.
Table 1 shows the flatness of the films that were cooled at various cooling rates while maintaining the same temperature, then cooled naturally to near room temperature, and then rolled up. The cooling rate is determined by the temperature of the film when it leaves the heat fixing chamber, T, and the temperature of the film when it leaves the cooling chamber in an atmosphere of 140 to 9,000 ℃, T2, and the time required to pass through the cooling chamber, t seconds. is expressed as T, -T2/t.

Table 1 Examples 5 to 8, Comparative Examples 3 to 6 A 21 micron thick film heat-set at 20,000 degrees Celsius after being stretched twice in the same manner as Examples 1-4 was led outside the heat-setting room, and at this time the surface of the film Table 2 shows the flatness of the films that were cooled at various cooling rates while drawing in heated air and changing the temperature in the cooling chamber from 50 to 150°C.

Table 2 Examples 9 to 13 Comparative Examples 7 to 10 A 12 micron thick film that had been biaxially stretched and heat set at 200 oo in the same manner as Examples 1 to 4 was led outside the heat setting room. Table 3 shows the flatness of the films cooled at various cooling rates while drawing heated air and changing the temperature in the cooling chamber from 30 to 15,000.

At this time, applying the method described in Special Publication No. 44-2000,
Cooling was carried out while suppressing temperature variations in the direction of the film in the cooling chamber to within 1,000 ℃, and preventing shrinkage in the direction of the film. 3 As shown from Comparative Examples 7 to 10 above, the
Although the method described in No. 00 tends to be better as the cooling rate is slower or as the cooling chamber temperature is higher, a significant difference in flatness is observed when compared with the examples of the present invention.

The cooling rate is determined by the manufacturing speed and the length of the cooling chamber.
It can be seen that there is a limit to slowing down the cooling rate, and the method of the present invention has excellent cooling performance.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a method for measuring the flatness of a film. Mackerel'4

Claims (1)

[Claims] 1. When cooling the heat-set biaxially oriented polyester film following biaxial stretching, the heated air on the surface of the biaxially stretched oriented film is sucked, and then transferred to an atmosphere maintained at 90 to 140 ° C. A method for cooling a biaxially oriented polyester film, characterized by slow cooling at a cooling rate of 100°C or less per second.