JPH04142918A - Manufacture of thermoplastic resin film - Google Patents

Abstract

PURPOSE:To reduce a bowing phenomenon, and to obtain a film having uniform physical properties by orienting the film in the lateral direction by a tenter, providing a cooling process satisfying formula (I), cooling the film at a glass transition temperature or lower, conducting thermal fixing at a first stage by the tenter and performing thermal fixing at a second stage by a roll. CONSTITUTION:A thermoplastic film extruded by a T die 1 is quenched by a chill roll 2, and molded in a filmy shape. The film is oriented in the vertical direction by roll stretching machines 3 and 3', and passed through a preheating zone 6 while both ends are gripped by the clip 5 of a tenter 4, and introduced into a lateral orientation zone 7 and laterally oriented. The film is admitted into a cooling zone 8, passed through thermal fixing zones 9 and 10, thermally fixed at a first stage, removed from a clip 5 and discharged from the tenter 4, and thermally fixed at a second stage by a roll thermal fixing machine 11, and wound by a winding machine 12.

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 tender, and has uniform physical, chemical, and physicochemical properties in the transverse 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 uses. , it is desirable that the physical property values be the same in any part of the film in the lateral direction.

However, with conventional manufacturing methods, it is extremely difficult to make the physical properties of the product film uniform in the lateral direction. The reason for this is that both ends of the film are held by clips in the tender, 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, in the center of the film, the influence of the gripping means is low and the binding force is weak.
It has been found that the effects of the above-mentioned stresses cause the central portion of the film to lag relative to the edges held by the clips. When horizontal stretching and heat setting are performed continuously using the same tender, if a straight line is drawn along the horizontal direction on the surface of the film before entering the tender, this straight line will deform within the tender 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. Further, at the beginning of the heat-setting region, the concave deformation reaches its maximum value, and the curve remains unchanged as it passes through the subsequent tenders, leaving a concave deformation in the film leaving the tender. This phenomenon is called the bowing phenomenon, and this bowing phenomenon causes the film to have non-uniform physical properties in the lateral direction. Due to the bowing phenomenon, main orientation axes that are further inclined in the vertical direction with respect to the bowing line occur at the side end portions of the film, and the angles of the main orientation axes tend to differ in the lateral direction. As a result, for example, thermal contraction coefficient, thermal expansion coefficient, wet expansion coefficient, etc. ±4 from the vertical direction.
Differences in physical property values in the 5° direction vary in the lateral 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.

More specifically, as a conventional technique in which a cooling step is provided between lateral stretching and heat setting, Japanese Patent Publication No. 3511774 includes a relaxation step at 20° C. to 150° C. between lateral stretching and heat setting, A manufacturing method including a substantial cooling step has been proposed. However, the length of this cooling process is not described at all, and the effect of reducing the bowing phenomenon is also completely unknown. Further, as a technique for reducing or eliminating the bowing phenomenon, Japanese Patent Application Laid-Open No. 73978/1984 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 the improvement effect is small. Also, special public Sho E33-24
Japanese Patent No. 459 proposes a process of forcibly moving forward only in a narrow area around the center using nip rolls while holding both ends of the film after completion of lateral stretching. However, with this technology, it is necessary to install the nip roll in a high-temperature area within the tender, 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, so it is not practical. is restricted by. Furthermore, Japanese Patent Publication No. 82-43858 proposes a technique in which a film immediately after transverse stretching is cooled to a temperature below the glass transition temperature, and then heat-set in multiple stages to simultaneously stretch the film in the transverse direction. However, this technology involves a complicated process of multi-stage heat setting and re-stretching in addition to the cooling process, perhaps because the bowing phenomenon is less reduced during the cooling process, or because the bowing phenomenon tends to reoccur during heat setting. It has become. Therefore, there is concern that it may be difficult to stably control the atmospheric temperature and film temperature within the tender over a long period of time. In addition, this proposal was also
Similar to Publication No. 74, the length of the cooling process is not described. Furthermore, JP-A-62-183327 discloses that after longitudinal stretching, when transversely stretching and heat-setting with a tender, only the side end portions between the transversely stretching zone and the heat-setting zone are heated to a heat-setting temperature higher than the glass transition temperature. A technique has been proposed to install a preheating zone with a temperature of: However, with this technique, since the temperature in the preheating zone must be controlled while creating a temperature gradient in the lateral direction, there is concern that it may be difficult to control the film temperature over a long period of time.

In addition, in the proposed embodiment, since the length of this preheating zone is as short as half the film width, it is presumed that the effect of reducing the bowing phenomenon is small. Also, JP-A-1-16542
No. 3 proposes a technique in which a film after being laterally stretched is cooled to a temperature below the laterally stretching temperature, and then stretched again in the laterally direction while increasing the temperature in multiple stages. However, with this technology,
Perhaps because the effect of reducing the bowing phenomenon in the cooling process is small as in the case of Publication No. 32-43856, or perhaps because bowing is likely to occur in the heat setting process, the process of heat setting in multiple stages in addition to the cooling process It is a complicated process that includes the step of stretching and re-stretching. Therefore, there is concern that it may be difficult to stably control the atmospheric temperature and film temperature within the tender over a long period of time. Although this proposal states that the length of the cooling step is preferably 1/2 or more of the film width, the basis for this is not clear. Further, there is a description that the cooling temperature is preferably equal to or lower than the glass transition temperature and drawing temperature. However, it is feared that the length of the cooling process and the temperature of the cooling process in the glass transition temperature device will be less effective in reducing the bowing phenomenon, so the complicated process described above has to be adopted. It is assumed that Furthermore, Japanese Patent Publication No. 39-29214 proposes a manufacturing method in which two groups of nip rolls are installed after the stretching process to perform multi-stage heat setting in the longitudinal direction. In addition, special public service
In addition to the method described in Japanese Patent Publication No. 39-29214 (1), Japanese Patent Publication No. 59 proposes a heat treatment method of relaxing after heat setting. However, both of these techniques describe heat treatment methods only in the vertical direction, and do not propose heat treatment in the lateral direction. In addition, Japanese Patent Publication No. 1-25694 and Japanese Patent Publication No. 1-25696 propose a technique for transverse stretching and heat setting by reversing the running direction of the film. However, this technique requires the film to be wound up once in order to reverse the running direction of the film, and since it is an off-line manufacturing method, there is a problem in that it is not limited in terms of productivity.

(Problems to be Solved by the Invention) It is an object of the present invention to solve this problem and 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) The present inventors observed changes in the bowing line inside the tender, clarified the process by which the bowing phenomenon occurs through various studies, and studied means to reduce the bowing phenomenon. We have arrived at the present invention. When producing a thermoplastic resin film stretched at least in the transverse direction, the present invention stretches the film in the transverse direction with a tender, and then provides a cooling step that satisfies formula (1) to cool the film to below the glass transition temperature. This method of producing a thermoplastic resin film is characterized in that a first stage of heat setting is then performed using a tender, and then a second stage of heat setting is performed using a roll.

L/W≧1.0 (1) In the formula (1), L means the length of the cooling process (m), and W means the film width (m). Here, the length L of the cooling process is the length from the point where the temperature is substantially lower than the temperature of the previous step of the cooling step to the longest point where the temperature of the next step is substantially higher than the temperature of the cooling step. The film width W means the distance between the clips of the tender at the exit of the tender. Further, the lateral direction means a direction perpendicular to the running direction of the film, and the longitudinal direction means the running direction.

The present invention will be explained in detail below.

In the present invention, a thermoplastic resin is heated and melted to a temperature above its melting point, extruded into a film from an extrusion means including a slit die onto the surface of a cooling drum, and then rolled in the longitudinal direction by a group of rolls having different roll speeds in the longitudinal direction. It is known that the film is stretched, transversely stretched with a tender, heat-set if necessary, and wound up with a film winder or the like. In the present invention, as the film forming φ stretching conditions, such resin melting/extrusion conditions, casting conditions, longitudinal stretching conditions, lateral stretching conditions, heat setting conditions, winding conditions, etc. can be appropriately selected.

In addition, the present invention naturally includes cases in which horizontal stretching, cooling, and heat setting steps are continuous, and cases in which re-stretching in the longitudinal direction, in the transverse direction, or in both longitudinal and lateral directions, and relaxation and constant length steps are included between the above steps. . Furthermore, the present invention also includes stretching methods other than the manufacturing method of longitudinal stretching followed by transverse stretching. For example, a stretching method in which the film is longitudinally stretched again after being stretched in the longitudinal and lateral directions, a stretching method that includes longitudinal multi-stage stretching, a stretching method in which both ends of the film are trimmed after the transverse stretching and then longitudinally stretched, etc. are not limited to the above unless exceeding the gist. do not have.

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. Among them, it is particularly preferable to select polyamide resin.

In the present invention, when a thermoplastic resin film is laterally stretched and heat-set, the film before the heat-setting step is cooled to below the glass transition temperature, thereby reducing the bowing phenomenon that occurs during the lateral stretching step. The lower the temperature, the better the effect of reducing the bowing phenomenon. The larger the value of the ratio L/W between the length of the cooling process and the film width W, the better the effect of reducing the bowing phenomenon. It is preferable to select the length L of the cooling step at .0. More preferably, L/W≧3
．． It is 0.

Furthermore, although the value of the ratio L/W between the length L of the cooling process and the film width W does not essentially depend on the tendering speed, as the tendering speed increases, the temperature of the film becomes substantially lower than the effective cooling. It takes time to reach the temperature, and the ratio of the length L of the cooling process to the film width W, which is the gist of the present invention, is L/
The value of W becomes substantially smaller. Therefore, when increasing the tendering speed, the effect improves as the ratio L/W between the length of the cooling process and the film width W increases.

For example, when the tender speed is doubled, the value of the ratio L/W of the length L of the cooling process to the film width W is preferably selected to be 1.5 times or more the value before speed increase.

In addition, when cutting out the tender that performs the transverse stretching process and the heat setting process, the film is cooled to below the glass transition temperature in order to run in the atmosphere, and the ratio between the length L of the cooling process and the film width W is As long as L/W≧1.0 is satisfied, the present invention also includes performing the transverse stretching step and the heat setting step in separate tenders.

Furthermore, in the cooling step after this cooling step and the heat setting step, it is preferable to pass the film through a group of nip rolls whose speed can be controlled, and the effect is significantly improved. child'
The material of the nip roll is a combination of a metal mirror surface and a rubber elastic body, and the nip roll tensions the film at a speed relative to the tender clip, so the speed must be easily controlled. Further, it is preferable that the nip rolls can be controlled singly or both together.

In addition, in the first stage heat setting, the stretching temperature (Tm
The temperature is preferably -20)'C or less, more preferably (Tg+80)°C or more and (Tm-20)'C or less. Furthermore, in the second stage of heat fixation, (
It is preferable to conduct the film at a temperature of (Tm-40) or higher and (Tm-20) °C or lower. For example, if it is carried out at a temperature of (Tm-20) °C or higher, sticks or the like will occur on the roll, making it difficult to form a film. In addition, in the above, Tg means the glass transition point of the thermoplastic resin film, and Tm means the melting point of the film.

In the present invention, by performing the second stage heat setting using a roll method, it is possible to compensate for the lack of heat fixation in the first stage heat setting, and to relax or stretch in both the vertical and horizontal directions, resulting in uniform physical properties. To obtain a film having uniform physical properties in the width direction by reducing the bowing phenomenon by suppressing the heat shrinkage stress in the first stage of heat setting, and which can be sufficiently crystallized. I can do it.

The reason why good effects can be obtained in the present invention is as follows.
In determining the length of the cooling process necessary to reduce the bowing phenomenon, we set up a mathematical model that could apply the finite element method, which no one had been able to do, and made it possible to estimate the propagation of stretching stress through numerical analysis. As a result, when the ratio of the length of the cooling process to the film width W is L/W=1.0, the stress propagation is approximately 1.
/2, stress propagation is approximately 1/10 at L/W = 2.0, and becomes almost zero at L/W = 3.0. This is because we were able to find something that was applicable.

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 tender 4, it passes through a preheating zone 6 and enters a transverse stretching zone 7 for transverse stretching. be done. Further, the film enters a cooling zone 8, passes through heat setting zones 9 and 10, is subjected to first stage heat setting, is removed from the clip 5, exits the tender, and is heat set in a second stage by a roll heat setting machine 11. It is wound up by a post-winding machine 12.

In the present invention, bowing distortion is caused by drawing a straight line on the surface of the film before entering the tender, and deforming it into an arched shape on the final film as shown in Figure 2. B=b/WX100 (%) Here, B=Boeing distortion (%) W=Film width (mm) b=Maximum rotation of Boeing line (mm) It was calculated as follows.

This will be explained below with some examples.

Example 1 Nylon-6 resin was melted and extruded through a T-die, formed into a film on a chill roll, stretched 3.3 times in the machine direction with a roll stretching machine, and then stretched 3.4 times in the cross direction with a tender. A biaxially oriented nylon-6 film was then heat-set in two stages.

The temperature in the tender was as follows: preheating temperature was 60°C, stretching temperature was 90°C, subsequent cooling temperature was 40°C, first heat setting temperature was 220°C, and second heat setting temperature by the rolls was 190°C. The film was then wound in the usual manner. Note that the ratio L/W of the length of the cooling zone to the film width W was set to 1°0.

Example 2 In Example 1, the length of the cooling zone and the film width W
A biaxially oriented nylon-6 film was obtained in the same manner as in Example 1 except that the ratio L/W was 2.0.

Example 3 In Example 1, the length L of the cooling zone and the film width W
A biaxially oriented nylon-6 film was obtained in the same manner as in Example 1 except that the ratio L/W was 3.0.

Comparative Example 1 A biaxially oriented nylon-6 film was obtained in the same manner as in Example 1 except that the cooling step was not performed.

Comparative Example 2 A biaxially oriented nylon 6 film was obtained in the same manner as in Example 1 except that the second heat setting was not performed.

Comparative Example 3 Biaxially oriented nylon-6 was prepared in the same manner as in Example 1 except that the cooling step and the second heat setting were not performed.
I got the film.

Table 1 shows the film forming conditions and bowing distortion in the examples and comparative examples.
Shown below.

(Effect of the invention) In the comparative example (without cooling or without performing the second stage heat setting using rolls), significant bowing distortion occurs, but in the example of the present invention, the thermoplastic film is horizontally stretched and heated. It can be seen that it is possible to suppress the bowing phenomenon that occurs during the fixing process and to produce a film that has uniform physical properties in the lateral direction of the film.

[Brief explanation of drawings]

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 diagram showing a method for calculating bowing distortion. In the figure, 1 is a T die, 2 is a chill roll, 3 and 3' are roll stretching machines, 4 is a tender, 5 is a clip of the tender, 6
is a preheating zone, 7 is a transverse stretching zone, 8 is a cooling zone, 9
and 10 indicate a heat fixing zone, 1 indicates a roll heat fixing machine, and 12 indicates a winding machine.

Claims (2)

[Claims] (1) When producing a thermoplastic resin film stretched at least in the transverse direction, the film is stretched in the transverse direction using a tender, and then a cooling step that satisfies formula (1) is provided to cool the film to below the glass transition temperature; A method for producing a thermoplastic resin film, which comprises performing a first stage of heat setting using a tender, and then performing a second stage of heat setting using a roll. L/W≧1.0…(1) In equation (1), L is the length of the cooling process (m),
W means film width (m). (2) The method for producing a thermoplastic resin film according to claim (1), wherein the thermoplastic resin film is a polyamide film.