JP3503708B2 - Method for producing polyamide film - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for uniformly producing a polyamide film. More specifically, a method for producing a polyamide film which suppresses a bowing phenomenon which occurs when the film is transversely stretched and heat-set by a tenter, has uniform physical, chemical and physicochemical properties in the transverse direction, and has a smooth surface. About. [0002] Polyamide films, especially biaxially oriented polyamide films, have been used for packaging and other uses, and it is desirable that the same physical property value be obtained in any portion of the film in the lateral direction. However, it has been extremely difficult to make the physical properties of the product film uniform in the lateral direction by the conventional manufacturing method. The reason is that both ends of the film are gripped by the 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 the 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. And when performing horizontal stretching and heat setting continuously with the same tenter, if a straight line is drawn along the horizontal direction on the surface of the film before entering the tenter, this straight line will be deformed in the tenter and the film will be deformed. With respect to the traveling direction of the stretching process, the film is deformed into a convex shape in a region at the beginning of the stretching process, returns straight in a region immediately before the end of the stretching process, and is deformed into a concave shape after the stretching process. Furthermore, at the beginning of the heat setting zone, the concave deformation reaches a maximum value, the curve remains unchanged and passes through the subsequent tenter, leaving the concave deformation in the film leaving the tenter. [0003] This phenomenon is called a bowing phenomenon, and this bowing phenomenon causes unevenness in the physical properties of the film in the lateral direction. Due to the bowing phenomenon, an orientation main axis inclined further in the vertical direction with respect to the bowing line occurs at the side end portion of the film, and the angle of the orientation main axis in the horizontal direction tends to be different. As a result, for example, the thermal contraction rate, the thermal expansion rate, the wet
The difference in the physical property values in the 45 ° direction differs in the lateral direction of the film. Due to this bowing phenomenon, as an example of a packaging application, it causes troubles such as printing pitch deviation, unevenness, curling, meandering, and the like in a printing lamination process, a bag making process, and the like. More specifically, as a conventional technique for providing a cooling step between transverse stretching and heat setting, Japanese Patent Publication No. 35-1 (1988)
No. 1774 discloses that 20 ° C.
There has been proposed a manufacturing method in which a relaxation step at 150 ° C. is interposed and a substantial cooling step is provided. 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 Laid-Open Publication No.
Japanese Patent Publication No. 0-73978 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 point, 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 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, and it is necessary to cool the roll and its peripheral devices. Constrained by Japanese Patent Publication No. Sho 62-43856 proposes a technique in which a film immediately after transverse stretching is cooled to a temperature lower than the glass transition point, and then heat-fixed in multiple stages to simultaneously stretch in the horizontal direction. I have. However, in this technique, the bowing phenomenon is less likely to be reduced 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 multi-stage heat setting 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. This proposal was also made in Japanese Patent Publication No. 35-
As in JP 11774, the length of the cooling step is not described. Further, Japanese Patent Application Laid-Open No. 62-183327 discloses that, after longitudinal stretching, when transverse stretching and heat setting are performed by a tenter, only the side end portion is heated to a temperature equal to or higher than the glass transition point between the transverse stretching step and the heat fixing step. A technique for installing a preheating step at the following temperature has been proposed. However, in this technique, since it is necessary to control the temperature of the preheating step while providing a temperature gradient in the lateral 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 step 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 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 technology, Japanese Patent Publication No. 62-4385
In the same manner as in the case of Japanese Patent Publication No. 6, the reason is that the effect of reducing the bowing phenomenon in the cooling step is small, or that the bowing is likely to occur in the heat fixing step. It is a complicated step with the step of 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 １ ／ of the film width.
The grounds for this are uncertain. Further, it is described that the cooling temperature is preferably higher than the glass transition point and lower than the stretching temperature. But,
When the length of the cooling step or the temperature of the cooling step is equal to or higher than the glass transition point, there is a fear that the effect of reducing the bowing phenomenon is small, and it is presumed that the complicated steps as described above have to be employed. . Furthermore, Japanese Patent Publication No. 39-292
No. 14 proposes a manufacturing method in which two nip roll groups are installed and a multi-stage heat fixing in the longitudinal direction is performed after the stretching step. In addition, Japanese Patent Publication No. 44-7159 proposes a heat treatment method in which heat is fixed and then relaxed in addition to the above Japanese Patent Publication No. 39-29214. However, both of these techniques describe a heat treatment method only in the vertical direction, and do not propose a heat treatment in the horizontal direction. In addition, Japanese Patent Publication No. 1-26944 and Japanese Patent Publication No. 25696 propose a technique in which the running direction of a film is reversed to perform horizontal stretching and heat fixing. However, in this technique, it is necessary to wind 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. [0007] In order to solve the above-mentioned problems, it is an object of the present invention to provide a production method relating to an effective transverse stretching and heat setting which can reduce a bowing phenomenon and obtain a polyamide film having uniform physical properties. It is in. 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 provided a means for reducing the bowing phenomenon. Investigations have reached the present invention. In the present invention, at least the transverse stretched polyamide film is heat-set in the first stage while performing relaxation or stretching in a range of 10% or less at a temperature not higher than the melting point by a tenter, and then a stretching temperature equal to or higher than a multi-stage roll. The temperature of the second-stage roll is lower than the melting point and the temperature of the second-stage roll is higher than that of the first-stage roll.
A method of performing heat setting in a step, wherein after a transverse stretching performed before the heat setting in the first step, a cooling step that satisfies Formula 1 is provided to cool the polyamide film below the glass transition point. It is a manufacturing method. The length L of the cooling step in Equation 1
Is the length from the point where the temperature is substantially equal to or lower than the temperature of the previous step of the cooling step to the longest point from the temperature of the cooling step to the temperature of the next step that is substantially higher than the temperature of the cooling step.
It shall mean the distance between the clips of the tenter at the tenter outlet. The lateral direction means the direction perpendicular to the running direction of the film, and the vertical direction means the running direction. Hereinafter, the present invention will be described in detail. In the present invention, the polyamide resin is heated and melted to a temperature equal to or higher than its melting point, extruded in a film shape from the extrusion means including a slit die to the surface of the cooling drum, and stretched 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 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 stretching conditions, such resin melting and extrusion conditions,
Casting conditions, longitudinal stretching conditions, transverse stretching conditions, heat setting conditions, winding conditions, and the like can be appropriately selected. Also, in the present invention, the case where the horizontal stretching, cooling, and heat fixing steps are connected, or the case where the above-mentioned steps include re-stretching in the vertical direction or the horizontal direction or both in the vertical and horizontal directions, and relaxation and constant length steps 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 longitudinal stretching, and a stretching method including longitudinal multi-stage stretching,
The present invention is not limited to the above as long as it does not exceed the gist, such as a stretching method in which both ends of the film after the transverse stretching are trimmed at both ends and stretched longitudinally. The polyamide resin applicable to the present invention includes nylon-4, nylon-6, nylon-9, nylon-11, nylon-66.6, nylon-6.10.
Many other simple substances, such as aliphatic polyamide resins such as nylon-10 and 10, aromatic polyamide resins such as polyhexamethylylene adipamide, semi-aromatic amorphous nylon composed of isophthalic acid and hexamethylenediamine,
Copolymers, mixtures, composites and the like can be mentioned. According to the present invention, when a polyamide film is subjected to transverse stretching and heat setting, the film before the heat setting step is cooled below the glass transition point to reduce the bowing phenomenon generated by the transverse stretching step. The lower the cooling temperature, the better the effect of reducing the bowing phenomenon. The larger 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 length L / W of the cooling step is reduced.
It is preferable to select the length L of the cooling step so that the ratio of L / W ≧ 2.0 is satisfied. More preferably, L
/W≧3.0. Further, the value of the ratio L / W of the length L of the cooling step 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 substantially decreases. It takes time to reach a certain cooling temperature, and the value of the ratio L / W of the length L of the cooling step to the film width W, which is the gist of the present invention, is substantially reduced. Therefore, when the tenter speed is increased, the effect is improved as the ratio L / W of the length L of the cooling step to the film width W is increased. For example, if you double the tenter speed,
The value of the ratio L / W of the length L of the cooling step to the film width W is preferably selected to be at least 1.5 times the value before the speed increase. When the tenter for performing the transverse stretching step and the heat setting step is cut off, the film is cooled to a temperature equal to or lower than the glass transition point to allow the film to run in the atmosphere. As long as the ratio L / W ≧ 1.0 is satisfied, 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 nip rolls whose speed can be controlled, and the effect is remarkably improved. The material of this 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. Further, it is preferable that the nip rolls can be controlled independently or both. In the heat setting, the present invention includes a case where no relaxation or stretching is performed. In the first stage heat setting, it is preferable that the heat setting is performed at a temperature equal to or higher than the stretching temperature and lower than (Tm−20) ° C., more preferably (Tg + 8
0) The temperature is not lower than (Cm-20) C. Further, in the second stage of heat setting, it is preferable to perform at a temperature of (Tm-40) ° C or more and less than (Tm-20) ° C. Etc. occur, making film formation difficult. In the above, Tg means the glass transition point of the polyamide film, and Tm means the melting point of the film. In the present invention, by performing the second-stage heat setting by a roll method, it is possible to compensate for insufficient heat-setting in the first-stage heat setting and to perform relaxation or stretching in both the vertical and horizontal directions. A film having uniform physical properties and capable of performing sufficient crystallization, suppressing the heat shrinkage stress in the first-stage heat setting, thereby reducing the bowing phenomenon and having uniform physical properties in the width direction. Can be obtained. Also, in the second stage heat setting, by setting the temperature of each stage roll higher than that of the preceding stage roll, sufficient crystallization can be performed while maintaining a smooth film surface without generating a stick or the like on each roll. By performing relaxation or stretching at a maximum temperature of 10% or less, a film having excellent dimensional stability and a low heat shrinkage at a high temperature can be obtained. The reason why good effects can be obtained in the present invention is as follows. In determining the length of the cooling step required to reduce the bowing phenomenon, a mathematical model which can be applied to the finite element method which no one could do is used. Is set, and the propagation of the stretching stress can be estimated by numerical analysis. As a result, the stress propagation becomes about 1/2 at the ratio L / W = 1.0 of the length L of the cooling process and the film width W, From L / W = 2.0, the stress propagation becomes about 1/10, and it becomes almost zero when L / W = 3.0. From the calculated value, it is confirmed by the actual machine that it can be applied in any case. Because he was found. Next, an embodiment will be described. (Embodiment) FIG. 1 shows an example of an apparatus used in the present invention. The polyamide resin extruded from the T die 1 is rapidly cooled by the chill roll 2 and formed into a film. The film is stretched in the machine direction by the roll stretching machines 3 and 3 ′.
While being gripped at both ends by (not shown), it enters the horizontal stretching step 7 through the preheating step 6 and is horizontally stretched. Further, the film enters a cooling step 8, passes through heat setting steps 9 and 10, is heat-set in the first stage, is then removed from the clip 5, exits the tenter, and is heat-set in the second stage by the roll heat setting machine 11. After being wound, it is wound up by the winder 12. 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. ## EQU2 ## Here, B = Boeing distortion (%) W = Film width (mm) b = Maximum concave amount of bowing line (mm) Hereinafter, description will be given with some examples. Example 1 A nylon-6 resin was melted, extruded from a T-die, formed into a film on a chill roll, stretched 3.4 times in a longitudinal direction by a roll stretching machine, and then stretched in a transverse direction by a tenter. The film was stretched 9 times to obtain a biaxially oriented nylon-6 film heat-set in two steps. The temperature in the tenter is 60 ° C. for preheating, 105 ° C. for stretching temperature, 40 ° C. for the subsequent cooling temperature, 190 ° C. for the first heat setting temperature, and the second heat setting temperature by three multi-stage rolls is the pre-heating temperature. Roll temperature (= T1) is 180 ° C., middle heating roll temperature (= T2)
At 185 ° C, and the temperature of the subsequent heating roll (= T3) at 190 ° C
And Thereafter, the film was wound up as usual. Note that the ratio L / L of the length L of the cooling step to the film width W is
W = 1.0. Example 2 A biaxially oriented nylon-6 film was prepared in the same manner as in Example 1 except that the heat-set of the second stage was carried out by 3.8% in the longitudinal direction after the subsequent roll. Got. Example 3 A biaxially oriented nylon-6 film was prepared in the same manner as in Example 1 except that the ratio L / W of the length L of the cooling step to the width W of the film was set to L / W = 2.0. Obtained. Example 4 A biaxially oriented nylon-6 film was prepared in the same manner as in Example 1 except that the ratio L / W of the length L of the cooling step to the width W of the film was set to 3.0. Obtained. 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 prepared in the same manner as in Example 1 except that the temperature of the three heating rolls was set to 190 ° C. during the second stage of heat setting. Obtained. Comparative Example 3 A biaxially oriented nylon-6 film was obtained in the same manner as in Example 1, except that the second stage heat setting was not performed. Comparative Example 4 A biaxially oriented nylon-6 film was obtained in the same manner as in Example 1 except that the cooling step and the second-stage heat setting were not performed. Table 1 shows film forming conditions and bowing distortions in Examples and Comparative Examples. Comparative Example (No cooling is performed, or the second-stage roll using a multi-stage roll in which the temperature of the second-stage roll is higher than that of the first-stage roll)
In the case where the step is not heat-fixed), a remarkable bowing distortion is generated. However, in the embodiment of the present invention, the bowing phenomenon which occurs in the step of transversely stretching and heat-setting the polyamide film is suppressed, and a uniform film is formed in the transverse direction of the film. It can be seen that a polyamide film having physical properties and a smooth surface can be produced. [Table 1]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic sectional view showing an example of an apparatus used to carry out the present invention. FIG. 2 illustrates a method of calculating a bowing distortion. [Description of Signs] 1: T die 2: Chill rolls 3 and 3 ′: Roll stretching machine 4: Tenter 5: Clip of tenter 6: Preheating step 7: Lateral stretching step 8: Cooling steps 9 and 10: Heat fixing step 11: Roll heat setting machine 12: Winding machine W: Film width (mm) b: Maximum concave amount of boeing line (mm)

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-142918 (JP, A) JP-A-3-216326 (JP, A) JP-A-4-74635 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) B29C 55/12-55/14

Claims (1)

(57) [Claim 1] The first-stage heat-setting is performed while a polyamide film stretched at least in the transverse direction is relaxed or stretched in a range of 10% or less at a temperature not higher than a melting point by a tenter. Then, the stretching temperature is higher than the melting point and lower than the melting point by the multi-stage roll, and the temperature of the rear-stage roll is higher than that of the previous stage,
This is a method of performing the second-stage heat setting while performing relaxation or stretching in the range of 10% or less at the maximum temperature, and after the horizontal stretching performed before the first-stage heat setting, a cooling process satisfying Formula 1 is provided. And cooling the mixture to a temperature below the glass transition temperature. (Equation 1) In addition, in Formula 1, L means the length (m) of the cooling step, and W means the film width (m).