JP2841755B2 - Polyamide film and method for producing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a polyamide film which is uniform in the width direction. More specifically, the present invention relates to a polyamide film that suppresses a bowing phenomenon that occurs when the film is transversely stretched and heat-set by a tenter and has uniform physical, chemical, and physicochemical properties in the width direction.

(Prior Art) A biaxially oriented polyamide film is used for packaging, industrial use, and other uses, and it is desirable that the film has the same physical property value in 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 for this 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 as gripping means. On the other hand, it is known that the center portion of the film is less affected by the gripping means and the binding force is weak, and the center portion of the film is delayed with respect to the end portion gripped by the clip due to the above-described 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 formed. 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. Furthermore, 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. Further, as an example of industrial use, in a base film such as a floppy disk, in-plane anisotropy causes trouble 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. 63-24459 proposes a process of forcibly advancing only a narrow area near the center by a nip roll while gripping both ends of the 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 technique, the bowing phenomenon is less likely to occur in the cooling step, or the bowing phenomenon is likely to occur again in the heat setting, or in addition to the cooling step, a complicated step of heat fixing in multiple stages and redrawing is required. 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. A technique for setting a preheating zone at a temperature equal to or lower than the temperature has 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. Japanese Patent Application Laid-Open No. 1-165423 proposes a technique in which a film after transverse stretching is cooled to a temperature not higher than the transverse stretching temperature and then stretched in the transverse direction again while increasing the temperature in multiple stages. However, in this technique, as in the case of Japanese Patent Publication No. 62-43858, 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 step as described above has to be adopted. Guessed. Also, Japanese Patent Publication No. 1-25694,
Japanese Patent Publication No. 25696/1995 proposes 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 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 focusing on the characteristics (such as molecular orientation state) of a film. 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 state of the film has almost no major axis, a sample of the entire width of the film is needed to know the degree of the bowing phenomenon, and it is necessary to determine the magnitude of the bowing phenomenon from the sample at any place on the film. Was impossible.

(Problems to be Solved by the Invention) In order to solve such problems, it is an object of the present invention to provide a film having uniform physical properties in the width direction of a polyamide-based film (particularly, physical property values such as a heat shrinkage factor) and a method for industrially producing the same. is there.

(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 the physical properties of the polyamide film in the width direction.

In the present invention, the molecular orientation angle measured by microwaves at the end of a polyamide-based film stretched in the transverse direction and heat-set (excluding contact with a heating element) at least in a tenter is determined by a moving direction or a moving direction of the film. The present inventors have found that a polyamide film characterized by being less than | 30 ° | (FIG. 1) with respect to a direction perpendicular to the direction has uniform properties with little bowing.
This film production method is a polyamide film in-line production method characterized by providing a cooling step satisfying the following formula between the horizontal stretching step and the heat setting step, and cooling the glass to a glass transition temperature or lower. is there.

L / W ≧ 1.0 In the above equation, L is the length (m) of the cooling step, W
Means the film width (m). Here, the length L of the cooling step is 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 point where the temperature is substantially longer than the temperature of the cooling step in the next step. Means film width W
Means the distance between the clips of the tenter at the tenter outlet. Here, the horizontal direction means the direction perpendicular to the running direction of the film, and the vertical direction means the running direction.

The value of the ratio L / W between the length L of the cooling process and the film W is determined by the fact that when the speed of the tenter increases, it takes time for the film temperature to reach a substantially effective cooling temperature. The value of the ratio L / W between the length L of the cooling step and the film width W, which is the main point, is substantially reduced.

Therefore, when increasing the tenter speed, the effect is improved as the value of the ratio L / W between the length L of the cooling step and the film width W is increased. For example, when the tenter speed is doubled, the ratio L / W of the length L of the cooling process to the film width W is used.
Is preferably selected to be at least 1.5 times the value before the speed increase.

 Hereinafter, the present invention will be described in detail.

In the present invention, the film is heated and melted to a temperature equal to or higher than its melting point, extruded in the form of a film from an extruding means including a slit die to the surface of a cooling drum, stretched in the longitudinal direction by a group of rolls having different roll speeds in the longitudinal direction, and horizontally stretched by a tenter. It is known that the film is stretched in a desired direction, 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.

Examples of the polyamide resin applicable to the present invention include many other simple substances such as nylon-6 and nylon-66, copolymers, mixtures, and composites.

The production method of the present invention laterally stretches a polyamide 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 larger the value of the ratio L / W between the length L of the cooling process and the film width W is, the more the effect of reducing the bowing phenomenon is improved, and the ratio L / W of the length L of the cooling process to the film width W is L / W ≧ 2.0. Cooling process length L
It is preferable to select More preferably, L / W ≧
3.0.

Further, when the tenter for performing the heat-setting step and the transverse stretching step is cut off, the film is cooled to a 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 completion of the heat setting step, it is preferable to pass the film through a group of nipple 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 of stretching longitudinally after transverse stretching, a stretching method of stretching longitudinally and transversely after stretching, a stretching method including longitudinal two-stage stretching, and a stretching method of trimming both ends of a film after transverse stretching and stretching vertically. It is not limited to the above as long as the value does not exceed.

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 chains using microwaves was used. With this evaluation method, troubles such as printing pitch deviation, uneven spots, curling, meandering, and deterioration of magnetic recording characteristics of base films such as floppy disks in industrial applications in printing and laminating processes and bag making processes in packaging applications. The relationship between the anisotropy of physical properties such as heat shrinkage and the molecular orientation by microwave is clarified, and the molecular orientation of films with little bowing and uniform properties in the width direction is clarified. The present invention has been elucidated.

In the present invention, the reason for the characteristic of the film having a small bowing phenomenon is that the molecular orientation angle at the end of the film decreases as the molecular orientation angle decreases from the end of the film toward the center of the film. If it is less than | 30 ° | with respect to the traveling direction, the molecular orientation angle will be less than | 30 ° | with respect to the film traveling direction or the direction perpendicular to the traveling direction of the film, and the molecular orientation will be almost the entire width of the film. Since the film has a small angle inclination, the yield of the film having uniform physical property values is improved. Further, when the molecular orientation angle is | 30 ° | or more with respect to the traveling direction or the direction perpendicular to the traveling direction of the film, the anisotropy of the physical property value becomes a problem due to the rotation of the distortion of the molecular orientation state. For example, when the ratio of the absolute values of the physical properties in two directions of | 45 ° | with respect to the running direction of the film is calculated, it is determined that the closer the value is to 1.0, the smaller the physical property difference in the film width direction is. The standard is set to | 3 with respect to the direction of
It was found that a film having a value of 0% | or less had little anisotropy in physical property values over the entire width of the film.

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 that can apply the element method, it is possible to estimate the propagation of stretching stress by numerical analysis. As a result, the ratio of the length L of the cooling process to the film width W, L / W = 1.0, the stress propagation is about 1/2
When L / W = 2.0, the stress propagation becomes about 1/10, and L / W = 3.0
Is calculated from the calculated value to be almost zero, and confirmed by the actual machine, and found to be applicable in any case.

 Next, examples will be described.

(Example) An example of an apparatus used in the present invention will be described. The polyamide resin extruded from the T-die is quenched 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, is heat set, and then is released from the clip, exits the tenter, and is wound by the winder.

In the present invention, the bowing distortion draws a straight line on the surface of the film before entering the tenter, and is deformed into a bow shape as shown in FIG. 2 on the finally obtained film. B = b / W × 100 (%) where B = amount of bowing distortion (%) W = film width (mm) b = maximum concave amount of bowing line (mm) ).

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.

 Hereinafter, a description will be given with some examples.

Example 1 Nylon-6 resin was melted, extracted from a T-die, formed into a film on a chill roll, stretched 3.25 times in a longitudinal direction by a roll stretching machine, and then stretched 3.5 times in a transverse direction by a tenter. Laterally by tenter
It was stretched 3.5 times to obtain a heat-fixed biaxially oriented nylon-6 film. The temperature in the tenter is 60
° C, the stretching temperature was 85 ° C, the subsequent cooling temperature was 40 ° C, and the heat setting temperature was 235 ° 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 was set to 1.0.

Example 2 A biaxially oriented nylon-6 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 nylon-6 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.

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 temperature of the cooling zone was changed to 80 ° C.

Comparative Example 3 A biaxially oriented nylon-6 film was obtained in the same manner as in Example 3, except that the temperature of the cooling zone was changed to 80 ° C.

Table 1 shows the film forming conditions and the measurement results of the bowing strain and the molecular orientation state (the end of the film) in the examples and the comparative examples.

(Effect of the Invention) In the comparative example (when cooling is not performed or the cooling temperature is equal to or higher than the glass transition point temperature even if a cooling step is provided), the molecular orientation angle at the end is large, but in the present invention, the polyamide type It can be seen that a film having a uniform physical property in the width direction of the film (the molecular orientation angle at the end is | 30 ° | or less) can be produced by suppressing the bowing phenomenon that occurs in the step of laterally stretching and thermally fixing the film.

[Brief description of the drawings]

FIG. 1 shows the range of the molecular orientation angle, and FIG. 2 shows the method of calculating the bowing distortion.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-59-169818 (JP, A) JP-A-2-103122 (JP, A) JP-A-58-114028 (JP, A) JP-A-3-3 216326 (JP, A) JP-A-57-57629 (JP, A) JP-A-3-130127 (JP, A) JP-A-3-193328 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B29C 55/02-55/16 C08J 5/18

Claims (2)

(57) [Claims] The molecular orientation angle measured by microwaves at the end of a polyamide-based film stretched in a transverse direction at least in a tenter and heat-fixed (excluding contact with a heating element) is measured in the direction of travel or in the direction of travel of the film. | 30 ° | or less with respect to the direction perpendicular to the direction, and the film is obtained by an in-line film-forming stretching heat-setting step. 2. The molecular orientation angle measured by microwaves at least at the end of a polyamide-based film stretched in the tenter in the transverse direction and heat-fixed (excluding contact with a heating element) is determined by the direction of travel or the direction of travel of the film. In producing a polyamide film characterized by being less than | 30 ° | with respect to the perpendicular direction, a cooling step satisfying the following equation is provided between the transverse stretching step and the heat setting step, and the glass transition point is obtained. A method for in-line production of a polyamide film, characterized in that the film is cooled to a temperature or lower. L / W ≧ 1.0 In the above equation, L means the length (m) of the cooling step, and W means the film width (m).