JP2917443B2 - Thermoplastic stretched film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a thermoplastic resin film which is uniform in the width direction. More specifically, the present invention relates to a thermoplastic resin film that suppresses a bowing phenomenon that occurs when the film is laterally stretched and thermally fixed by a tenter and has uniform physical, chemical, and physicochemical properties in the width direction.

(Prior art) Thermoplastic resin films, especially films of biaxially oriented polyester, polyamide, polyolefin, polyvinyl resin, polyphenylene sulfide, etc.
The film is used for packaging, industrial use, and other uses, and it is desirable that the film has the same physical properties at any portion in the width direction of the film.

However, it has been extremely difficult to make the physical properties of the product film in the width direction uniform by the conventional manufacturing method. The reason is that both ends of the film are gripped by clips in the tenter, and the longitudinal stretching stress generated by the stretching process and the shrinkage stress generated by the heat fixing process are restrained by the clips serving as gripping means. On the other hand, it is known that the central portion of the film is less affected by the gripping means and the binding force is weakened, and the central portion of the film is delayed with respect to the edge gripped by the clip due to the above-mentioned stress. In the case where the transverse stretching and the heat setting are continuously performed by the same tenter, if a straight line is drawn along the width direction on the surface of the film before entering the tenter, the straight line is deformed in the tenter and the film is deformed. With respect to the traveling direction of the stretching process, the film deforms into a convex shape at the beginning of the stretching process, returns straight in the region immediately before the end of the stretching process, and deforms into a concave shape after the stretching process. Further, at the beginning of the heat setting step, the concave deformation reaches a maximum value, and the curve does not change and passes through the subsequent tenter, and the concave deformation remains in the film leaving the tenter. This phenomenon is called the bowing phenomenon, and this bowing phenomenon causes unevenness in the physical properties of the film in the width direction.

Due to the bowing phenomenon, an orientation main axis which is further inclined in the vertical direction with respect to the bowing line is generated at the side end portion of the film, and the angle of the orientation main axis tends to be different in the width direction. As a result, for example, the physical property values such as the thermal contraction rate, the thermal expansion rate, and the wet expansion rate in the vertical direction differ in the film width direction. Due to this bowing phenomenon, as an example of packaging applications, printing lamination processing, printing pitch deviation in the bag making process, etc.,
It causes troubles such as spots, curling and meandering. In addition, as an example of industrial use, a base film such as a floppy disk causes in-plane anisotropy, which causes troubles such as deterioration of magnetic recording characteristics.

More specifically, as a conventional technique for providing a cooling step between the horizontal stretching and the heat setting, Japanese Patent Publication No. 35-11774 discloses a method in which a relaxation step of 20 ° C. to 150 ° C. is interposed between the horizontal stretching and the heat fixing step. A manufacturing method having a substantial cooling step has been proposed. However, the length of the cooling step is not described at all, and the effect of reducing the bowing phenomenon is not completely known. Further, as a technique for reducing or eliminating the bowing phenomenon, Japanese Patent Application Laid-Open No. 50-73978 proposes a method for producing a film in which a nip roll group is provided between a stretching step and a heat setting step. However, in this technique, the temperature of the intermediate zone where the nip roll is installed is equal to or higher than the glass transition temperature, and the rigidity of the film at the nip point is low. Japanese Patent Publication No. Sho 63-24459 proposes a process in which a nip roll is used to forcibly advance only a narrow area near the center while gripping both ends of a film after completion of the transverse stretching. However, in this technique, it is necessary to install the nip roll in a high-temperature area in the tenter, it is necessary to cool the roll and its peripheral devices, and since the film is high in temperature, there is a possibility that the roll may be damaged, so that practical use is not possible. Constrained by Also,
Japanese Patent No. 43856 proposes a technique in which a film immediately after transverse stretching is cooled to a temperature equal to or lower than the glass transition temperature, and then heat-fixed in multiple stages to simultaneously stretch in the transverse direction. However, in this technology, in addition to the cooling process, because the bowing phenomenon is less likely to be reduced in the cooling process, or because the bowing phenomenon is likely to occur again in the heat setting process, there are multiple steps of heat setting and a complicated process of redrawing. Has become. Therefore, there is a concern that it may be difficult to stably control the ambient temperature and the film temperature in the tenter for a long time. Also, this proposal does not describe the relationship between the length of the cooling step and the film width. Further, JP-A-62-183327 discloses that, after longitudinal stretching, when transversely stretching with a tenter and heat setting, only the side end portion between the horizontal stretching zone and the heat fixing zone is heat-set at a glass transition point temperature or higher. Techniques for setting a preheating zone below the temperature have been proposed. However, in this technique, since it is necessary to control the temperature of the preheating zone while giving a temperature gradient in the width direction, there is a concern that it may be difficult to control the film temperature for a long time. In the embodiment of the present invention, since the length of the preheating zone is as short as half of the film width, it is presumed that the effect of reducing the bowing phenomenon is small. Further, Japanese Patent Application Laid-Open No. 1-165423 proposes a technique in which a film after transverse stretching is cooled to a temperature equal to or lower than a transverse stretching temperature and then stretched again in the transverse direction while increasing the temperature in multiple stages. However, in this technique, as in the case of Japanese Patent Publication No. 62-43856, the effect of reducing the bowing phenomenon in the cooling step is small, or because the bowing is likely to occur in the heat fixing step, In addition, it is a complicated step of a step of heat setting in multiple stages and a step of re-stretching. Therefore, there is a concern that it may be difficult to stably control the ambient temperature and the film temperature in the tenter for a long time. In this proposal, there is a description that the length of the cooling step is preferably equal to or more than の of the film width, but the basis is not clear. Further, it is described that the cooling temperature is preferably equal to or higher than the glass transition temperature and equal to or lower than the stretching temperature. However, when the length of the cooling step or the temperature of the cooling step is equal to or higher than the glass transition point temperature, there is a fear that the effect of reducing the bowing phenomenon is small, and the complicated steps as described above have to be adopted. Guessed. Further, Japanese Patent Publication No. 1-25694 and Japanese Patent Publication No. 1-25696 propose a technique in which the running direction of a film is reversed to perform transverse stretching and heat fixing. However, in this technique, it is necessary to take up the film once in order to reverse the running direction of the film, and there is a problem in that the production method is off-line, so that the productivity is restricted.

As described above, attempts to reduce the bowing phenomenon have been made so far, but these proposals relate to a manufacturing method and an apparatus, and no invention has been made in which attention is paid to characteristics of a film (such as a molecular orientation state). For example, JP-A-58-21
As seen in 5318 and JP-A-61-8326,
Regardless of the degree of the Boeing phenomenon, in the center of the film,
Since the molecular orientation of the film has almost no misalignment of the main axes of the film, a sample of the entire width of the film is needed to know the extent of the bowing phenomenon, and it is necessary to determine the magnitude of the bowing phenomenon from the sample anywhere in the film. Was impossible.

(Problems to be Solved by the Invention) In order to solve such problems, an object of the present invention is to provide a film having uniform physical properties in the film width direction (in particular, physical properties such as heat shrinkage) and an industrially advantageous production method thereof.

(Means for Solving the Problems) The present inventors have observed the change of the bowing line in the tenter, clarified the generation process of the bowing phenomenon from various studies, and examined means for reducing the bowing phenomenon. The present invention was achieved by analyzing physical properties in the width direction of the film.

The present invention relates to a change in molecular orientation angle (anisotropy index) of a thermoplastic resin film stretched at least in the transverse direction and thermally fixed (excluding contact with a heating element), which is measured by a microwave in an arbitrary film width direction. However, it has been found that a thermoplastic resin film characterized by satisfying the formula (1) has uniform properties with little bowing, and the present invention has been accomplished. This film manufacturing method is characterized in that a cooling step that satisfies the formula (2) is provided between the transverse stretching step and the heat fixing (excluding contact with a heating element) step, and the film is cooled to a glass transition temperature or lower. This is a method for producing a thermoplastic resin film.

Δθ _or × W / W _f ≦ 64.0 (1) L / W ≧ 1.0 (2) In the expressions (1) and (2), Δθ _OR is an arbitrary 2
The difference in molecular orientation angle measured by microwave at a point (
^. ), W _f is the film width (m) between any two points, W is the distance between the clips of the tenter at the tenter outlet (m),
L means the length (m) of the cooling step.

Here, for example, the molecular orientation angle of a film whose orientation is stronger in the vertical direction than in the horizontal direction is plus (+) in the clockwise direction with respect to the vertical direction as shown in FIG. The clockwise direction is minus (-). Similarly to the above, the molecular orientation angle of a film whose orientation is stronger in the horizontal direction than in the vertical direction is positive in the clockwise direction with respect to the horizontal direction and negative in the counterclockwise direction with respect to the horizontal direction.

Further, the length L of the cooling step means a length from a point where the temperature is substantially equal to or lower than the temperature of the previous step of the cooling step to a longest point from a temperature of the next step which is substantially higher than the temperature of the cooling step. It shall be. Further, the lateral direction means a direction perpendicular to the running direction of the film, and the vertical direction means the running direction.

Further, the value of the ratio L / W of the length L of the cooling process to the film width W does not essentially depend on the speed of the tenter, but as the speed of the tenter increases, the temperature of the film becomes substantially more effective. It takes time to reach the temperature, and the ratio L / W of the length L of the cooling step and the film width W, which is the gist of the present invention,
Becomes substantially smaller. Therefore, when increasing the tenter speed, the ratio between the length L of the cooling process and the film width W is determined.
The effect improves as the value of L / W increases. For example, when the tenter speed is doubled, it is preferable that the value of the ratio L / W between the length L of the cooling step and the film width W be 1.5 times or more the value before the speed increase.

 Hereinafter, the present invention will be described in detail.

In the present invention, the thermoplastic resin is heated and melted to a temperature equal to or higher than its melting point, extruded in a film form from an extruding means including a slit die to a cooling drum surface, and stretched in the longitudinal direction by a group of rolls having different longitudinal roll speeds. It is known that the film is stretched in a transverse direction by a tenter, heat-fixed if necessary, and wound up by a film winder or the like. In the present invention, as the film forming / stretching conditions, such resin melting / extrusion conditions, casting conditions, longitudinal stretching conditions, transverse stretching conditions, heat fixing conditions, winding conditions, and the like can be appropriately selected.

As the thermoplastic resin applied to the present invention, polyethylene terephthalate, polyethylene 2,6-naphthalate, polyethylene isophthalate, polyester resins such as polybutylene terephthalate, nylon-6, polyamide resins such as nylon-66, polypropylene,
Polyolefin resins such as polyethylene, polyphenylene sulfide, polyether sulfone, polysulfone, polyether ether ketone, polyether ketone ketone, polyethylene trimellited imide, and many other simple substances, copolymers, mixtures, composites, and the like. Can be

The production method of the present invention laterally stretches a thermoplastic resin film,
During the heat setting process, the film before the heat setting process is cooled to a temperature lower than the glass transition temperature to reduce the bowing phenomenon generated by the transverse stretching process. The lower the cooling temperature is, the more the effect of the bowing phenomenon is reduced. Is improved. The greater the value of the ratio L / W between the length L of the cooling step and the film width W, the more the effect of reducing the bowing phenomenon is improved, and the ratio of the length L of the cooling step to the film width W is made L / W ≧ 2.0. It is preferable to select the length L of the cooling step. More preferably, L / W
≧ 3.0.

Further, when the tenter for performing the transverse stretching step and the heat setting step is cut off, the film is cooled to the glass transition temperature or lower to allow the film to run in the atmosphere, and the length L of the cooling step and the film width W are determined. As long as the ratio L / W ≧ 1.0 is satisfied, it is included in the present invention that the transverse stretching step and the heat setting step are performed by different tenters.

Further, in the cooling step and the cooling step after the heat fixing step, it is preferable to pass the film through a group of nip rolls whose speed can be controlled, and the effect is remarkably improved. 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 relative speed to the clip of the tenter, so that the speed control is easy. It is preferable that the nip rolls can be controlled independently or both.

In the present invention, the case where the horizontal stretching, the cooling, and the heat setting steps are connected to each other, and the case where the above steps include the steps of re-stretching, relaxation, and fixed length are naturally included. Further, a stretching method other than the manufacturing method of performing the transverse stretching after the longitudinal stretching is also included in the present invention. For example, a stretching method in which longitudinal stretching is performed after transverse stretching, a stretching method in which longitudinal stretching is performed after longitudinal and transverse stretching, a stretching method including longitudinal two-stage stretching, a stretching method in which both ends of a film after transverse stretching are longitudinally stretched, and the like. It is not limited to the above unless it exceeds.

In general, the physical properties of a film are determined not only by the crystal part of the film but also by the state of the amorphous part. In particular, it is said that the heat shrinkage behavior of the film depends on the state of the amorphous part. Therefore, for the measurement of the molecular orientation state, an apparatus for evaluating the orientation of the amorphous chain using a microphone mouth wave was used. According to this evaluation method, printing lamination processing in packaging applications, deviation of printing pitch in the bag making process, occurrence of spots, curling, meandering, and deterioration of magnetic recording characteristics in base films such as floppy disks in industrial applications. Clarify the relationship between the anisotropy of physical properties such as heat shrinkage, etc., which is the cause of trouble, and the molecular orientation state by microwaves, and the molecular orientation state of films with little bowing and uniform properties in the width direction And elucidated the present invention.

In the present invention, the reason for the characteristic of the film having little bowing phenomenon is that the molecular orientation angle changes almost linearly in the width direction from the center of the film to the end of the film, so that the film can be oriented in any width direction of the film. When the anisotropy index is 64.0 or less in the film, the change in the molecular orientation angle is small over the entire width of the film, and the yield of the film having uniform physical property values is improved. If the anisotropy index exceeds 64.0, the anisotropy of the physical property value becomes a problem due to rotation of the strain in the molecular orientation state. For example, ± 45 ° relative to the running direction of the film ^. The ratio of the absolute values of the physical properties in two directions was calculated, and the criterion was determined that the closer the value was to 1.0, the smaller the difference in physical properties in the film width direction was. As an example, when the curl at the time of bag making related to the anisotropy such as the heat shrinkage and the boiling water shrinkage is evaluated, it is found that the film satisfying the expression (1) is a film with little bag making curl over the entire width of the film. understood.

Further, the reason why an industrially advantageous effect can be obtained in the production of a film having a small bowing phenomenon can be explained by the finite limit that no one could make in determining the length of the cooling process required to reduce the bowing phenomenon. By setting a mathematical model to which the element method can be applied, it is possible to estimate the propagation of the stretching stress by numerical analysis. As a result, when the length L / W of the cooling process length L and the film width W is 1.0, the stress propagation is about 1 / 2, L / W = 2.0, the stress propagation is about 1/10, and L / W = 3.0, it is almost zero, calculated from the calculated value, backed up with the actual machine, applicable in any case This is because I found them.

 Next, examples will be described.

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

The film is stretched in the machine direction by a roll stretching machine, and then is stretched into a transverse stretching zone through a preheating zone while being gripped at both ends by clips of a tenter. Further, the film enters the cooling zone, passes through the heat setting zone, and is heat set, then is released from the clip, exits the tenter, and is wound by the winder.

Further, in the present invention, the measurement of the molecular orientation state of the film after the film forming step by microwave is performed by measuring the molecular orientation angle (ANGLE) using a molecular orientation meter (MOA-2001A) manufactured by Kanzaki Paper Co., Ltd. It was measured. This molecular orientation state was measured at an arbitrary position in the width direction of the film.

The evaluation of the bag-making curl was represented by ○, Δ, and × indicating the degree of curling caused by heat treatment at the time of bag-making, storage, or after filling. (See Table 1) Hereinafter, description will be given with some examples.

Example 1 A polyethylene terephthalate resin was melted, extruded from a T-die, formed into a film on a chill roll, stretched 3.5 times in a longitudinal direction by a roll stretching machine, then stretched 3.6 times in a transverse direction by a tenter, and heat-fixed. A biaxially oriented polyethylene terephthalate film was obtained. The temperature in the tenter is 90 ° C for the preheating temperature and 100% for the stretching temperature.
° C, the subsequent cooling temperature was 40 ° C, and the heat setting temperature was 210 ° C. Thereafter, the film was wound up as usual.
The ratio L / W of the length L of the cooling zone to the film width W = L / W =
1.0.

Example 2 A biaxially oriented polyethylene terephthalate film was obtained in the same manner as in Example 1 except that the ratio L / W of the length L of the cooling zone to the film width W was L / W = 2.0.

Example 3 A biaxially oriented polyethylene terephthalate film was obtained in the same manner as in Example 1, except that the ratio L / W of the length L of the cooling zone to the film width W was set to L / W = 3.0.

Example 4 A biaxially oriented polyethylene terephthalate film was obtained in the same manner as in Example 1 except that the temperature of the cooling zone was changed to 65 ° C.

Comparative Example 1 A biaxially oriented polyethylene terephthalate 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 polyethylene terephthalate film was obtained in the same manner as in Example 1, except that the temperature of the cooling zone was changed to 100 ° C.

Comparative Example 3 A biaxially oriented polyethylene terephthalate film was obtained in the same manner as in Example 2 except that the temperature of the cooling zone was changed to 100 ° C.

Comparative Example 4 A biaxially oriented polyethylene terephthalate film was obtained in the same manner as in Example 3, except that the temperature of the cooling zone was changed to 100 ° C.

Example 5 Nylon-6 resin was melted, extruded from a T-die, formed into a film on a chill roll, then stretched 3.3 times in a longitudinal direction by a roll stretching machine, then stretched 3.4 times in a transverse direction by a tenter, and heat set. Biaxially oriented nylon-6
Film. The temperature in the tenter was 60 ° C. for preheating, 90 ° C. for stretching, 40 ° C. for cooling, and 225 ° C. for heat setting. Thereafter, the film was wound up as usual. The ratio L / W of the length L of the cooling zone to the film width W was set to 1.0.

Example 6 A biaxially oriented nylon-6 film was obtained in the same manner as in Example 5, except that the ratio L / W of the length L of the cooling zone to the film width W was L / W = 2.0.

Example 7 A biaxially oriented nylon-6 film was obtained in the same manner as in Example 5 except that the ratio L / W of the length L of the cooling zone to the film width W was set to L / W = 3.0.

Comparative Example 5 A biaxially oriented nylon-6 film was obtained in the same manner as in Example 5 except that the cooling step was not performed.

Comparative Example 6 A biaxially oriented nylon-6 film was obtained in the same manner as in Example 5 except that the temperature of the cooling zone was changed to 80 ° C.

Comparative Example 7 A biaxially oriented nylon-6 film was obtained in the same manner as in Example 7, except that the temperature of the cooling zone was changed to 80 ° C.

Table 1 shows the film forming conditions, the anisotropy index, and the measurement results of the degree of curl in bag making in Examples and Comparative Examples.

(Effect of the Invention) The comparative example (in which cooling is not performed or the cooling temperature is equal to or higher than the glass transition point temperature even when a cooling step is performed) has a large anisotropy index. It can be seen that a film having uniform physical properties (small anisotropy index) in the width direction of the film can be produced by suppressing the bowing phenomenon that occurs in the step of transversely stretching and heat-setting the resin film.

[Brief description of the drawings]

 FIG. 1 shows the definition of the molecular orientation angle.

Claims (1)

(57) [Claims] 1. A thermoplastic resin film stretched at least in the lateral direction and heat-set (excluding contact with a heating element),
A thermoplastic resin film characterized in that a change in molecular orientation angle (anisotropy index) measured by microwaves in an arbitrary film width direction satisfies the expression (1). Δθ _or × W / W _f ≦ 64.0 (1) (In the equation (1), Δθ _or is the difference (゜) between molecular orientation angles measured by microwaves at any two points of the film, and W _f is (The film width (m) between any two points, and W means the distance (m) between clips at the exit of the tenter.)