JPH03193329A - Reduction of bowing of thermoplastic resin stretched film - Google Patents

Abstract

PURPOSE:To reduce a physical property difference in a widthwise direction by decreasing a bowing phenomenon, by a method wherein a cooling process having a length L and satisfying a specific formula is provided between a lateral stretching process and thermal fixation process which manufacture a thermoplastic resin film stretched at least in a lateral direction and the film is cooled at the glass transition temperature or less. CONSTITUTION:At the time of lateral stretching and thermal fixation treatment of a thermoplastic resin film, simultaneously with cooling of the film prior to thermal fixation to the glass transition temperature or less once a nip roll group is installed and a bowing phenomenon to be generated with a lateral stretching process is reduced. The lower a cooling temperature becomes, the more a reduction effect of the bowing phenomenon is improved. A length L of a cooling process is selected so that the bigger a value of a ratio L/W between the length L of the cooling process and a width W of the film becomes and wider the maximum width WN of a nip within the nip roll group becomes further, the more the effect is improved and a formula (L/ W)>=0.25(2-WN/W)<2> is obtained. It is preferable that a ratio WN/W of the width of the nip to the width of the film is at least 0.2.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for producing a stretched thermoplastic resin film with low bowing and having uniform physical and chemical properties in the width direction.

(Prior Art) Thermoplastic resin stretched films are used for packaging, industrial use, and other uses, and it is desirable that all parts of the film have the same physical property values.

However, in the usual transverse stretching method, the molecular orientation is not the same in the central portion of the film and the side end portions of the film. The reason for this is that both ends of the film are held by clips in the tenter, and the stretching stress in the longitudinal direction (direction of film travel) generated by the stretching process and the shrinkage stress generated by the heat setting process are absorbed by the clips that are the gripping means. On the other hand, the center part of the film is less affected by the gripping means and the restraining force is weaker, and due to the influence of the stress mentioned above, there is a delay in the center part of the film compared to the end part held by the clip. known to occur. When transverse stretching and heat setting are performed continuously in the same tenter, the film is stretched along the width direction (perpendicular to the direction of film travel) on the surface of the film before entering the tenter.
If you draw a straight line, this straight line will be deformed in the tenter, deformed into a convex shape in the beginning area of the stretching process with respect to the film traveling direction, and return to a straight line in the area just before the end of the stretching process, and the straight line will be deformed in the tenter and become convex in the area at the beginning of the stretching process. After finishing, it transforms into a concave shape.

Furthermore, the concave deformation reaches its maximum in the middle of the heat-setting region, and the curve passes through the subsequent tenter with almost no change, leaving the concave deformation in the film that exits the tenter. This phenomenon is called the bowing phenomenon, and the bowing phenomenon causes the physical property values of the film to become non-uniform in the width direction.

Due to the bowing phenomenon, the angle of the main axis of orientation tends to vary in the width direction of the film. As a result, physical property values such as longitudinal thermal contraction coefficient, thermal expansion coefficient, wet expansion coefficient, and refractive index differ in the width direction of the film. This bowing phenomenon can cause printing pitch misalignment, unevenness, etc. in printing lamination processing, bag making processes, etc.
This causes problems such as curling and meandering.

In addition, as an example of industrial use, base films for floppy disks, etc. have low magnetic recording properties due to in-plane anisotropy.
This causes problems such as.

To explain in more detail, as a conventional technique in which a cooling process is provided between the transverse stretching process and the heat setting process, there is a
Publication No. 774 states that 20% of
A manufacturing method has been proposed in which a relaxation step of ~150°C is interposed and a substantial cooling step is provided.However, the length of this cooling step is not described at all, and the effect of reducing the bowing phenomenon has also been proposed. It is completely unknown.Furthermore, as a technology to reduce or eliminate the Boeing phenomenon,
Japanese Patent No. 73978 proposes a film manufacturing method in which a group of nip rolls is installed between the transverse 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 a measure to revise labels.

Further, Japanese Patent Publication No. 63-24459 proposes a process in which a film after lateral stretching is held at both ends and forcibly moved forward only in a narrow area near the center using nip rolls. However, with this technology, it is necessary to install the nip roll in a high-temperature area within the tenter, and the roll and its peripheral equipment must be cooled. Also, since the film is at a high temperature, there is a risk of scratches caused by the roll on the film surface. , there are practical constraints. In addition, special public official Sho 6
2-43856 discloses that after cooling the film immediately after transverse stretching to below the glass transition point temperature, heat setting is performed in multiple stages.
Techniques have been proposed that involve heat fixation and simultaneous lateral stretching.

However, this technology involves a complicated process of multi-stage heat setting and re-stretching in addition to the cooling process, perhaps because the reduction in bowing during the cooling process is small, or because bowing is likely to reoccur during the heat setting process. It has become. Therefore, there is a concern that it may be difficult to stably control the ambient temperature and film temperature within the tenter over a long period of time. Further, like Japanese Patent Publication No. 35-11774, this proposal also does not describe the length of the cooling process. Furthermore, JP-A-62-18
Publication No. 3327 describes a film manufacturing method in which after longitudinal stretching, transverse stretching and heat treatment are performed using a tenter, only the side end portions are heated to a temperature higher than the glass transition point between the transverse stretching zone and the heat treatment zone.
Techniques have been proposed in which a preheating zone is provided at a temperature below the heat treatment temperature. However, with this technology, the temperature in the preheating zone must be controlled while creating a temperature gradient in the width direction.
There is concern that it may be difficult to stably control the film temperature over a long period of time. In addition, in the proposed example, since the length of this preheating zone is as short as half the film width, it is presumed that the effect of reducing bowing by the preheating zone is small.

Furthermore, Japanese Patent Application Laid-Open No. 1-165423 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, as in the case of Japanese Patent Publication No. 62-43856, the reduction in bowing during the cooling process is small.
Or maybe it is because bowing tends to occur again during the heat setting process.
In addition to the cooling process, it is a complex process that includes multiple heat-setting processes and re-stretching. Therefore, there is a concern that it may be difficult to stably control the ambient temperature and film temperature within the tenter over a long period of time.

Furthermore, although this proposal states that the length of the cooling process should preferably be at least one-half of the film width, the basis for this is not clear, and the bowing reduction effect may not be effective at this level of cooling process length and temperature. It is presumed that they had no choice but to adopt the above-mentioned complicated process because they were worried that the number would be low. Also, Japanese Patent Publication No. 1-25694, Japanese Patent Publication No. 1-25698
The publication proposes a technique for transverse stretching and heat setting by reversing the running direction of the film. However, this technique has problems such as the need to wind up the film once in order 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) To solve this problem, the present invention aims to provide an industrially advantageous method for producing a stretched thermoplastic resin film that reduces the bowing phenomenon and has little difference in physical properties in the width direction.

(Means for Solving the Problems) The present inventors observed changes in the bowing line inside the tenter, clarified the process of occurrence of the bowing phenomenon through various studies, and studied means to reduce the bowing phenomenon. We have arrived at the present invention.

In the present invention, when producing a thermoplastic resin film stretched at least in the transverse direction, a cooling process of a length satisfying the following formula is provided between the transverse stretching process and the heat setting process, so that the glass transition point temperature This is a method for producing a thermoplastic resin film, which is characterized by cooling as follows.

(L/W)≧0.25 (2-WN4/W) 2.
- In the formula, L means the length of the cooling process, W means the film width, and WN means the width of the largest nip roll in the nip roll group.

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-6,6, polypropylene,
Polyolefin resins such as polyethylene, polyphenylene sulfide, polyether sulfone, polysulfone, polyether ether ketone, polyether ketone ketone, polyethylene trimellited imide, and many other ψ forms, copolymers, mixtures, composites, etc. Can be mentioned.

The thermoplastic resin stretched film oriented at least in the transverse direction of the present invention refers to a film that has been stretched at least in the transverse direction at a stretching ratio of 2.5 times or more to impart molecular orientation. Specifically, it may be a biaxially oriented film in which a longitudinally stretched film is oriented in advance in the longitudinal direction and then stretched in the lateral direction, or a transversely oriented film in which a substantially non-oriented film is oriented in the lateral direction. It may be a film, or it may be a biaxially oriented film obtained by stretching this horizontally uniaxially stretched film in the longitudinal direction. Further, after stretching the oriented film in at least the transverse direction, the temperature of the oriented film is from -1- to 2-2 below the melting point of the thermoplastic resin after stretching at least in the transverse direction.
Heat treatment may be performed at a temperature lower than 0°C.

In the method of the present invention, when transversely stretching and heat-setting a thermoplastic resin film, a group of nip rolls is installed at the same time as the film before heat-setting is cooled to below the -H glass transition temperature, and the bowing phenomenon that occurs during the transverse stretching process is carried out. The lower the cooling temperature of 4 degrees, the better the effect of reducing the bowing phenomenon. Furthermore, the larger the value of the ratio L/W between the length of the cooling process and the film width W, and the wider the nip width WN, the better the effect of reducing the bowing phenomenon, and (L/W)≧0. It is preferable to select the length L of the cooling process so as to obtain 5 (2-WN/W). Further, the ratio WN/W of the nip width to the film width is preferably 0.2 or more. If it is 0.2 unfinished, not only will the effect of reducing the bowing phenomenon be small, but also shear force will be generated by the nip rolls, causing wrinkles and significantly reducing productivity. Also,
If (L/W) does not satisfy the formula (1), the effect of reducing the bowing phenomenon will be extremely small, making it impossible to achieve the object of the present invention. The nip roll group of the present invention may be just one pair of normally used nip rolls, or may be a plurality of pairs of nip rolls, or may be a roll group combined with other rolls other than the nip rolls. It is also possible to use a roll group consisting of a special roll described in the above publication, or a combination of a plurality of rolls or a nip roll or other rolls. Here, the length L of the cooling process is from the point where the temperature is substantially below the temperature of the previous process of the cooling process to the longest point immediately before reaching the temperature of the next process that is substantially higher than the temperature of the cooling process. The film width W means the distance between the clips of the tenter at the exit of the tenter, and the nip width WN
shall mean the length of the surface where the roll substantially contacts the film. Note that the length L1 of the cooling process, the film width W, and the nip width WN are expressed in the same unit, and meters (m) are usually used. The present invention includes lateral stretching,
If the cooling and heat-setting steps are continuous, or if there are at least two other steps between the above steps, such as re-transverse stretching, longitudinal stretching, horizontal relaxation, longitudinal relaxation, constant length width, etc. Even if it exists, it will of course be destroyed.

In addition, when separating the tenter that performs horizontal stretching and the tenter that performs heat setting, the film is cooled because it is run in the atmosphere, so the ratio of the length of the cooling process to the film width W is correct. The present invention also includes performing the transverse stretching and heat setting using separate tenters as long as the scope of the claims is substantially supplemented.

(Examples) Next, the present invention will be described in more detail based on Examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof.

Example 1 Polyethylene terephthalate resin was melted and extruded through a T-die, formed into a film with a chill roll-L, and then stretched 3.6 times in the longitudinal direction with a roll stretching machine, and then 3.7 times in the transverse direction with a tenter. A biaxially oriented polyethylene terephthalate film was stretched and heat set. In the tenter, the film was preheated at 90°C, then stretched at 00°C, and then the film was stretched to L/W=1.
Once cooled in the cooling process of 0 length at 55°C, WN
The film is heat-treated at 220° C. while being nipped in the cooling step with one nip roll having a width of /W=0.8,
After further heat treatment at 200°C, the film was cooled to 100°C. I then removed it from the clip and wound the film as usual.

Example 2 A biaxially oriented polyethylene terephthalate film was obtained in the same manner as in Example 1, except that the ratio (L/W) between the length L of the cooling process and the film width W was 0.5. Ta.

Example 3 A biaxially oriented polyethylene terephthalate film was obtained in the same manner as in Example 2 except that the number of nip rolls was changed to two.

Example 4 In Example 1, the nip roll width WN and the film width W
A biaxially oriented polyethylene terephthalate film was obtained in the same manner as in Example 1 except that the ratio (WN/W) was 0.4.

Example 5 In Example 1, the nip roll width WN and the film width W
A two-wheel oriented polyethylene terephthalate film was obtained in the same manner as in Example 1 except that the ratio (w, /W) was 0.2.

Example 6 Polyethylene terephthalate resin was melted and extruded through a T-die, formed into a film using a chill roll, and then stretched 3.7 times in the transverse direction using a tenter at 100°C, and then stretched 3.7 times in the longitudinal direction using a roll stretching machine. After stretching .6 times, the film was again heat-treated at 220°C using a tenter, and then further heat-treated at 200°C, and then cooled to 100°C to obtain a biaxially oriented polyethylene terephthalate film. I then removed it from the clip and wound the film as usual. In addition, between the transverse stretching process and the heat setting process, a length in which the ratio (L/W) between the length of the cooling process at 65°C or less and the film width W is substantially 5.0 or more is required. There was a cooling step and a nip roll with a width of WN/W = 0.8.

Comparative Example 1 A biaxially oriented polyethylene terephthalate film was obtained in the same manner as in Example 1 except that the cooling step and the nip roll were not provided (L/W=O).

Comparative Example 2 In Example 2, no nip rolls were provided (WN/W
A biaxially oriented polyethylene terephthalate film was obtained in the same manner as in Example 2 except for =O).

Comparative Example 3 In Example 1, nip rolls are not provided (WN/W
A biaxially oriented polyethylene terephthalate film was obtained in the same manner as in Example 1 except for =O).

Comparative Example 4 A biaxially oriented polyethylene terephthalate film was obtained in the same manner as in Example 1, except that the ratio (L/W) between the length L of the cooling process and the film width W was 0.3. the law of nature.

Comparative Example 5 A biaxially oriented polyethylene terephthalate film was obtained in the same manner as in Example 4, except that the ratio (L/W) between the length of the cooling process and the film width W was 0.5. Ta.

Comparative Example 6 In Example 1, the nip roll width WN and the film width W
A two-wheel oriented polyethylene terephthalate film was obtained in the same manner as in Example 1 except that the ratio (WN/W) was 0.1.

Example 7 Nylon-6 resin was melted and extruded through a T-die, formed into a film using chill rolls, stretched 3.25 times in the longitudinal direction using a roll stretching machine, and then stretched 3.25 times in the transverse direction using a tenter. A biaxially oriented nylon-6 film was stretched 5 times and heat-set.

In the tenter, the film was preheated at 60°C, then stretched at 85°C, and then the film was stretched to L/W=1.0.
Once cooled in the 40℃ cooling process of the length of WN
The film was heat-treated at 235° C. while being nipped in the cooling step with one double roll having a width of /W=0.8, further heat-treated at 210° C., and then cooled to 100° C.

I then removed it from the clip and wound the film as usual.

Example 8 A two-wheel oriented polyethylene terephthalate film was obtained in the same manner as in Example 7, except that the ratio (L/W) between the length of the cooling process and the film width W was 0.5. .

Comparative Example 7 A two-wheel oriented nylon-6 film was obtained in the same manner as in Example 7 except that the cooling step and the nip roll were not provided (L/W=O; Ws/W=O).

Comparative Example 8 A biaxially oriented nylon-6 film was prepared in the same manner as in Example 7, except that the ratio (L/W) between the length L of the cooling process and the film width W was 0.3. Obtained.

Table 1 shows the bowing distortions (B) of the examples and comparative examples. In addition, bowing distortion is calculated by drawing a straight line on the surface of the film before entering the tenter, and calculating the ratio of the bow-shaped deformation amount (b) to the film width as shown in Figure 1 in the final film L as a percentage (100b). /W).

As can be seen by comparing the margin examples and comparative examples below, the bowing phenomenon can be reduced by providing the nip rolls of the present invention, but the effect is significantly lower when the conditions of the present invention are not met (comparative examples). It turns out that there are few.

(Effects of the Invention) According to the present invention, a thermoplastic resin film having uniform physical and chemical properties in the width direction can be obtained, and the film is extremely useful for packaging, industrial use, and other uses. I understand.

[Brief explanation of drawings]

FIG. 1 shows a method for calculating Boeing distortion.

Claims (1)

[Claims] (1) When producing a stretched thermoplastic resin film oriented at least in the transverse direction, a cooling process with a length L that satisfies formula (1) is provided between the transverse stretching process and the heat setting process. A method for reducing bowing of a stretched thermoplastic resin film, characterized by cooling the film to a temperature below its glass transition point. (L/W)≧0.25(2-W_N/W)^2...(
1) In equation (1), L is the length of the cooling process,
W means the film width, and W_N means the maximum nip width in the nip roll group.