JPH03158225A - Manufacture of thermoplastic resin film - Google Patents

Abstract

PURPOSE:To reduce bowing phenomenon and obtain film having uniform physical properties by a method wherein film, both ends of which are not grasped, is forcibly cooled below its glass transition temperature before and after heat setting treatment. CONSTITUTION:Thermoplastic resin extruded from a T-die 1 is formed with a chill roll 2 in the form of film, longitudinally stretched with roll stretching machines 3 and 3' and passed through a preheating zone 6 under the condition that both ends are grasped by the clips 5 of a tenter 4 so as to enter a laterally stretching zone 7 in order to be stretched laterally. Further, the resultant film is introduced in a first cooling zone 8 simultaneously under the condition that the clips 5 are released so as to be passed between first nip rolls 9 and 9'. Furthermore, under the condition that both film ends are grasped again by the clips 10 of a tenter, the film is passed through a heat setting zone 11. After being heat-set and released from the chips 10, the resultant film is passed through a second cooling zone 12 and finally taken up. Concretely, the film is forcibly cooled below its glass transition temperature under the condition that both the ends are not grasped before and after heat setting.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for uniformly producing a thermoplastic resin film. More specifically, the present invention relates to a method for producing a film that suppresses the bowing phenomenon that occurs during transverse stretching and heat setting using a tenter, and has uniform physical, chemical, and physicochemical properties in the width direction.

(Prior Art) Thermoplastic resin films, particularly biaxially oriented films of polyester, polyamide, polyolefin, polyvinyl resin, polyphenylene sulfide, etc., are used for packaging, industrial purposes, and other purposes. It is desirable that the physical property values be the same in any part of the film in the width direction.

However, with conventional manufacturing methods, it is extremely difficult to make the physical properties of the product film uniform in the width direction. The reason for this is that both ends of the film are held by clips in the tenter, and the longitudinal stretching stress generated by the stretching process and the shrinkage stress generated by the heat setting process are restrained by the clips, which are the gripping means. On the other hand, it is known that in the center of the film, the influence of the gripping means is low and the restraining force is weak, and that due to the influence of the stress mentioned above, there is a delay in the center of the film with respect to the ends held by the clips. . When transverse stretching and heat setting are performed continuously in the same tenter, if a straight line is drawn along the width direction on the surface of the film before entering the tenter, this straight line will deform inside the tenter and the film will It deforms into a convex shape in the region at the beginning of the stretching process, returns to a straight line in the region just before the end of the stretching process, and deforms into a concave shape after the end of the stretching process. Furthermore, at the beginning of the heat-setting region, the concave deformation reaches its maximum value, and the curve remains unchanged as it passes through subsequent tenters, leaving a concave deformation in the film leaving the tenter. This phenomenon is called the bowing phenomenon, and this bowing phenomenon causes the physical properties of the film to become non-uniform in the width direction.

Due to the bowing phenomenon, a main axis of orientation that is further inclined in the vertical direction with respect to the bowing line occurs in the side end portions of the film, and the angle of the main axis of orientation tends to differ in the width direction. As a result, physical property values such as longitudinal thermal contraction coefficient, thermal expansion coefficient, and wet expansion coefficient differ in the width direction of the film. This bowing phenomenon causes troubles such as printing pitch deviation, unevenness, curling, meandering, etc. in printing lamination processing, bag making processes, etc., as examples of packaging applications. Furthermore, as an example of industrial use, base films for floppy disks and the like cause problems such as deterioration of magnetic recording characteristics due to in-plane anisotropy.

To explain in more detail, as a conventional technique in which a cooling process is provided between the transverse stretching and heat setting, Japanese Patent Publication No. 11774/1987 discloses a method in which a relaxation process at 20°C to 150°C is interposed between the transverse stretching and heat setting. A manufacturing method has been proposed in which a cooling step is provided. However, the details of this cooling process are not described at all, and the effect of reducing the bowing phenomenon is also completely unknown. Furthermore, as a technique for reducing or eliminating the bowing phenomenon, Japanese Patent Laid-Open No. 50-73978 proposes a film manufacturing method in which a group of nip rolls is installed between the stretching process and the heat setting process. However, with this technique, the temperature of the intermediate zone where the nip rolls are installed is above the glass transition temperature, and the rigidity of the film at the nip point is low, so it is not very effective as an improvement measure. In addition, equity llR6
Japanese Patent No. 3-24459 proposes a process in which a film after lateral stretching is gripped at both ends, and only a narrow area near the center is forcibly moved forward using nip rolls. However, with this technology, it is necessary to install the nip roll in a high-temperature area inside the tenter, and the roll and its peripheral equipment need to be cooled.Also, since the film is at a high temperature, there is a risk of scratches caused by the roll, which is not practical. is restricted by. Furthermore, Japanese Patent Publication No. 62-43856 proposes a technique in which a film immediately after transverse stretching is cooled to below the glass transition point temperature, and then heat-set in multiple stages, and simultaneously heat-set and stretched in the transverse direction.

However, this technology requires a complex process that involves multiple heat-setting steps and re-stretching in addition to the cooling process, perhaps because the bowing phenomenon is less likely to occur during the cooling process, or because bowing tends to reoccur during heat-setting. .

Therefore, there is concern that it may be difficult to stably control the ambient temperature and film temperature within the tenter over a long period of time. In addition, Equity Hei 1-25694 Publication, Equity Hei 1
Japanese Patent No. 2589E3 proposes a technique in which the film is laterally stretched and heat-set by reversing the running direction of the film. However, this technique has problems such as the need to wind up the film once to reverse the running direction of the film, and because it is an off-line manufacturing method, it is limited in terms of productivity.

(Problems to be Solved by the Invention) In order to solve these problems, it is an object of the present invention to provide a manufacturing method involving effective transverse stretching and heat setting that can reduce the bowing phenomenon and obtain a film with uniform physical properties. .

(Means for Solving the Problems) When producing a thermoplastic resin film stretched in at least one axis, the present invention forcibly increases the glass transition temperature without gripping both ends of the film before and after heat-setting treatment. This is a method for producing a thermoplastic resin film, which is characterized by cooling as follows.

The present invention will be explained in detail below.

Thermoplastic resins applicable to the present invention include polyester resins such as polyethylene terephthalate, polyethylene 2,6-naphthalate, polyethylene isophthalate, and polyethylene terephthalate, polyamide resins such as nylon-6 and nylon-66, polypropylene,
Examples include polyolefin resins such as polyethylene, polyphenylene sulfide, polyethersulfone, polysulfone, polyetheretherketone, polyetherketoneketone, polyethylene trimellited imide, and many other simple substances, copolymers, mixtures, and composites. It will be done.

When heat-setting a thermoplastic film, the present invention forcibly cools the film before and after heat-setting to below the glass transition temperature without gripping both ends, thereby reducing the bowing phenomenon that occurs during the heat-setting process. It is something. In addition, the cooling method may include providing a cooling zone within the tenter, or if the temperature does not drop sufficiently in the cooling zone,
The transverse stretching and heat setting may be performed in separate tenters, and the film may be forced to pass through the atmosphere and cooled to below the glass transition temperature by air cooling. The lower this cooling temperature is, the more effective it is in reducing the bowing phenomenon.

Further, the longer the length of this cooling step, the greater the effect of reducing the bowing phenomenon, but the length is preferably at least at least the film width, and more preferably the length is at least three times the film width.

Furthermore, in this cooling step, it is preferable to pass the film through a group of speed-controllable nip rolls, which significantly improves its effectiveness. The material of the nip roll installed before and after this heat-setting process is a combination of gold B mirror surface and rubber elastic body, and the nip roll tensions the film at a speed relative to the tenter's clip, making it easy to control the speed. The condition is that there is. Further, it is preferable that the nip rolls before and after the heat-setting step can be controlled individually or both.

(Effect) When transverse stretching and heat setting are performed continuously in the same tenter, it has been confirmed that the bowing phenomenon occurs to some extent even after the end of the stretching process, and reaches its maximum value immediately after the subsequent heat setting process. ing. There are stretching stress due to stretching and shrinkage stress due to heat setting between the stretching process and heat setting process, but because the temperature of the film in the heat setting process is high, the rigidity of the film decreases and the center part of the film is on the stretching process side. It is thought that the bowing phenomenon will occur.

In the present invention, the bowing phenomenon is reduced by forcibly cooling the film to below the glass transition temperature in the region between the stretching process and the heat setting process to eliminate the propagation of stress generated by stretching. However, since the film is then heat-set, the bowing phenomenon also occurs during the heat-setting process. This is because both ends of the film are restrained by clips, which are gripping means, even during the heat setting process.
It is thought that the central part of the film is less affected by the gripping means and the binding force is weaker, causing the bowing phenomenon.

Furthermore, since the temperature in the heat setting step is higher than that in the stretching step, the temperature of the film is also higher and the rigidity of the film is also lowered. In other words, it is thought that the bowing phenomenon during the heat setting process is greater than the bowing phenomenon due to the stretching process. Therefore, in order to reduce the bowing phenomenon that occurs during the heat setting process, it is necessary to cool the film to below the glass transition temperature even after the heat setting process is completed. As described above, the present invention reduces the bowing phenomenon that occurs due to heat setting by forcibly cooling the film before and after heat setting to below the glass transition temperature without gripping both ends.

Next, examples will be shown.

(Example) FIG. 1 shows an example of an apparatus used in the present invention. The thermoplastic resin extruded from the T-die 1 is rapidly cooled by a chill roll 2 and formed into a film.

The film is stretched in the machine direction by roll stretching machines 3 and 3', and then, while being held at both ends by clips 5 (not shown) of a tenter 4, it passes through a preheating zone 6 and enters a transverse stretching zone 7 for transverse stretching. be done. Furthermore, as soon as the film enters the first cooling zone 8, it is removed from the clip 5 and passes between the first two tube rolls 9 and 9'. Further, the film is gripped at both ends by the clips 10 (not shown) of the tenter, passes through the heat setting zone 11, is heat set, passes through the second cooling zone 12, is removed from the clips 10, and exits the tenter. It passes through second nip rolls 13 and 13' and is wound up by winder 14. The speed control device 16 is a device that controls the speed of the first two rolls 9 and 9' and the second nip rolls 13 and 13'.
Preferably, an electrical speed stabilizing device such as a DC servo motor is provided.

In addition, the first two tube rolls 9 and 9' and the second nip roll 1
3 and 13' are intended to tension the center of the film in the film's traveling direction, so it is better to use rolls with a drum-shaped bulge in the center than in both ends of the roll, as shown in Figure 2. is preferred. This will be explained below with some examples.

Example 1 Polyethylene terephthalate resin was melted and extruded through a T-die, formed into a film on a chill roll, and then stretched 3.6 times in the longitudinal direction with a roll stretching machine, and then stretched 3.7 times in the transverse direction with a tenter. A biaxially oriented polyethylene terephthalate film was prepared. The temperature in the tenter was such that the stretching temperature was 100°C, the subsequent first cooling temperature was 40°C, the heat setting temperature was 220°C, and the subsequent second cooling temperature was 40°C. The film was then wound as usual.

Example 2 Polyethylene terephthalate resin was melted and extruded through a T-die, formed into a film on a chill roll, and then stretched in a tenter at a stretching temperature of 100"C in the transverse direction for 3.
Stretched 7 times, then 3.
A biaxially oriented polyethylene terephthalate film was obtained by stretching 6 times and heat-setting it again using a tenter. The temperature of the first cooling zone is 30℃ due to air cooling because the tenter is used separately for transverse stretching and heat setting, and the temperature of the tenter in the heat setting process is 220℃.
The temperature was set to 0''C.The film was then wound up in the usual manner.

Example 3 A biaxially oriented polyethylene terephthalate film was obtained in the same manner as in Example 1 except that the second cooling step was performed in the first and second cooling steps. In the region where the film was passed through the nip rolls, the metal roll side was controlled at a speed 2% faster than the clips of the tenter without gripping both ends R of the film, and the film was nipped by the rubber rolls.

Example 4 A biaxially oriented polyethylene terephthalate film was obtained in the same manner as in Example 2 except that nipping was performed in the first and second cooling steps. Note that the conditions of the nip roll were the same as in Example 3.

Comparative Example 1 A biaxially oriented polyethylene terephthalate film was obtained in the same manner as in Example 1 except that the first and second cooling steps in Example 1 were not performed.

Comparative Example 2 A biaxially oriented polyethylene terephthalate film was obtained in the same manner as in Example 1 except that the first and second cooling steps in Example 2 were not performed.

Table 1 shows the film forming conditions and bowing distortions of Examples and Comparative Examples. Bowing distortion involves drawing a straight line on the surface of the film before it enters the tenter, and creating a third straight line on the final film.
It has been deformed into a bow shape as shown in the figure, and the condition of this bow shape is as follows: B=b/WxlOO(%) Where, B=Amount of bowing distortion (%) W=Width of film (m11) b=Boeing Calculated by the maximum bulge of the line (,,).

(Effect of the invention) In the comparative example, a significant bowing phenomenon occurs, but in the present invention, the bowing phenomenon that occurs in the process of transversely stretching and heat-setting a thermoplastic film is suppressed, and the film has uniform physical properties in the width direction of the film. It can be seen that it is possible to manufacture

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of an example of an apparatus used to carry out the present invention, and FIG. 2 is a schematic plan view of an example of a roll suitable for use as a roll for a group of nip rolls. This is shown in . Figure 3 shows the calculation method for Boeing distortion. In the figure, 1 is a T die, 2 is a chill roll, 3 and 3' are roll stretching machines, 4 is a tenter, S and 10 are clips, 6 is a preheating zone, 7 is a transverse stretching zone, 8 is a first cooling zone,
9 and 9' are the first two tube rolls, 11 is the heat fixing zone,
12 is a second cooling zone, 13 and 13' are second nip rolls, 14 is a winder, and 15 is a speed control device.

Claims (1)

[Claims] When producing a thermoplastic resin film stretched in at least one axial direction, the thermoplastic resin film is forcibly cooled to below the glass transition temperature without gripping both ends of the film before and after heat-setting treatment. manufacturing method.