JPH03106635A - Method of heat-treating crystalline thermoplastic resin film and apparatus therefor - Google Patents

Abstract

PURPOSE:To decrease bowing rate without causing the fusion of films by giving a first step heat-treatment to biaxial-oriented films at specific temperature, after that, giving a second step heat-treatment thereto at specific temperature by making air interpose between both films separated by cutting and opening both ends and then winding them up. CONSTITUTION:Biaxial orientation means 10 serve to extend a crystalline thermpolastic resin film 1. First heating means 20 by a tubular method is made at contraction commencement temperature of the film 1 or higher and a first step heat treatment is given thereto at a temperature 20 deg.C below the melting point of the film 1 or lower. Triming means 30 act to cut and open both ends of the film 1 in order to split it into two sheets of film 1A, 1B. Next, at means 40, they are superimposed while interposing air between both films 1A, 1B and then the superimposed films 1A, 1B are subjected to a heat-treatment while grasping both ends thereof by means of a tenter 50 at a temperature of the first step heat-treatment temperature or higher and at a temperature of the melting point of the film or lower. Finally, the films 1A, 1B are wound up by means of winding up means 70.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a method and apparatus for heat treating a crystalline thermoplastic resin film biaxially stretched by the tubular method, and is used for food packaging, packaging of industrial products such as computers, etc. It can be used in fields such as bag-in-boxes, drum interiors, etc. [Background Art] After a plastic film is biaxially stretched, for example, by the tubular method, it is heat-treated to fix the orientation of the film molecules and obtain dimensional stability. During this heat treatment, if a tube-shaped, for example, nylon-6 film is folded flat and subjected to ripening treatment at around 200°C using the tenter method, the upper and lower films will fuse together, resulting in
The problem was that it could not be separated into pieces and could not be used as a product. Such problems are particularly noticeable when the plastic film is a crystalline thermoplastic resin film such as polyamide. Therefore, in order to solve this problem, in the past, for example, the ears of a biaxially stretched flat tubular film were cut out and two
An improved tenter one-way system has been proposed in which the films are separated into sheets and then introduced into a tenter with an endless belt-like object maintaining a gap between the two films, and heat-treated while holding both ends of the film with clips. (Special Public Service 1977-
(See Publication No. 15439). In addition to this improved tenter method, the problem of thermal welding can also be avoided if a tubular one-way method is adopted in which compressed air is introduced into a tubular film to form bubbles and heat treatment is performed.

[Problems to be Solved by the Invention] According to the heat treatment using the improved tenter method described above, heat fusion does not occur, but the bowing phenomenon (as the film is stretched, the stretching of the center part compared to both ends of the film causes the film to move). This caused problems such as in-plane anisotropy of film properties and sagging that inhibited secondary processing (printing, etc.).The heat treatment temperature must be lowered. For example, the bowing rate can be lowered, but when heat treatment such as boiling or retort is applied, the shrinkage rate becomes too large, which poses a problem.Furthermore, according to the heat treatment using the tubular method described above,
If heat treatment is performed at a temperature of 180°C or higher in an attempt to obtain high dimensional stability, a problem arises in that the bubbles oscillate, making stable heat treatment difficult. If heat treatment is performed at a low temperature to avoid this problem, good dimensional stability will not be obtained. On the other hand, the present applicant has filed Japanese Patent Application No. 63-29657.
In 5, we proposed a method and apparatus for heat-treating a cohesive thermoplastic film biaxially stretched by the tubular method in two stages. In this invention, the second stage heat treatment is carried out using a tenter method, but the first stage heat treatment method is not particularly limited. However, if this first-stage heat treatment is performed using a tenter-only method like the second-stage heat treatment, the effect of reducing the bowing rate can be recognized;
Since bowing has already occurred during the first heat treatment, there is a limit to its effectiveness. In addition, since the trimming operation of cutting both ends of the film is required twice, production efficiency is poor. SUMMARY OF THE INVENTION An object of the present invention is to provide a method and apparatus for heat treating a crystalline thermoplastic resin film, which can reduce the bowing rate without causing fusion of the film. [Means and effects for solving the problem] The heat treatment method for a crystalline thermoplastic resin film according to the present invention includes a step of biaxially stretching a nodular thermoplastic resin film by a tubular method, and a step of biaxially stretching a nodular thermoplastic resin film by a tubular method. A step of subjecting the film to a first stage heat treatment at a temperature above the shrinkage start temperature of the film and below a temperature 20°C lower than the melting point of the film, and cutting both ends of the film to form two films. The film is separated into a second stage by a tenter method at a temperature higher than the heat treatment temperature of the first stage and lower than the melting point of the film, with air interposed between both films. The method is characterized by comprising a step of heat-treating the edges and a step of winding up the heat-treated film. In the above heat treatment method, the first stage heat treatment performed by the tubular method at a temperature higher than the film shrinkage start temperature and 20°C lower than the melting point of the film is preferably 20' from the film shrinkage start temperature. C. It is carried out at a temperature higher than the high temperature and lower than the temperature 30℃ lower than the melting point of the film. If the temperature is lower than the film's shrinkage start temperature, the film will curl so much that it becomes difficult to grip both ends. Further, if the temperature is higher than 20° C. lower than the melting point of the film, the films will fuse together and cannot be separated into two sheets after heat treatment. Note that the heat treatment time is preferably 1 second or more. If the time is less than 1 second, heat fixation tends to be insufficient. Although there is no upper limit, if the length is too long, a large device will be required, leading to higher costs. Therefore, about 1 to 30 seconds is preferable. In this first stage heat treatment, the relaxation rate of the film is
Set to 0 to 10% (MD direction and/or TD direction). By heat-treating the film in a slightly relaxed state, it is possible to increase the degree of crystallinity of the film and reduce the shrinkage rate, thereby obtaining a film with good dimensional stability. In the second stage heat treatment performed by the tenter method, if the temperature is lower than the first stage heat treatment temperature, the shrinkage rate will increase, which is not preferable. Furthermore, if the temperature is higher than the melting point of the film, the films will fuse together and cannot be separated into two pieces. Note that the conditions regarding the heat treatment time are the same as in the case of the first stage heat treatment. Even in this second heat treatment, the relaxation rate of the film was 0.
Set it to ~10%. Crystalline thermoplastic resins refer to resins such as polyamides, polyesters, degraded ethylene-vinyl alcohol copolymers, and polystyrene. Specific examples of polyamide resins include nylon-6 (shrinkage start temperature 45°C, melting point 215°C), nylon-6.6 (shrinkage start temperature 55°C, melting point 260'C). etc. Further, the heat treatment apparatus for carrying out the above heat treatment method includes means for biaxially stretching a crystalline thermoplastic resin film by the tubular method, and a first heating means for heat treating the film by the tubular method. , a trimming means for cutting both ends of the film and separating it into two films, a means for stacking both films with air interposed between them, and a tenter for gripping both ends of the film. The apparatus is characterized in that it has a second heating means for heat-treating the film with air interposed between both films, and a winding means for the heat-treated film. Any means for injecting air can be used to expand the film into a bubble shape using the tubular method. In the first and second heating means of the present heat treatment apparatus, it is preferable to provide a hot air stove because the heating efficiency is high and uniform heating is possible.

In addition, the rolls used in the means for stacking both films while intervening air between the two separated films are preferably rolls with grooves to ensure the interposition of air, and the surfaces are plated. It is preferable that the film be treated with a coating to prevent it from being scratched.

[Example] A heat treatment apparatus according to an example of the present invention and a method of heat treatment of a crystalline thermoplastic resin film using the same will be described with reference to FIG. This heat treatment apparatus includes a means 1o for biaxially stretching a crystalline thermoplastic resin film 1 by the tubular method, a first heating stage 20 for heat-treating the film by the tubular method, and both ends of the film. Trimming means 3 for cutting out the film and separating it into two films IA and IB
0, means 40 for stacking both films IA and IB with air interposed between them, and film I
A tenter 50 is provided for gripping both ends of the films IA and IB, and a second heating stage 60 is provided for heat-treating the films IA and IB with air interposed between the films IA and IB. and winding means 70 for the applied films IA and IB. The biaxial stretching means 10 includes a pair of first pinch rolls l1 arranged above, a heating furnace l2 for heating the crystalline thermoplastic resin film 1,
V-shaped guide temporary 13 for folding the film l flatly
and a pair of second pinch rolls 14 disposed at the lower end of the guide plate 13. The heating device of heating furnace l2 is
You can choose any infrared heater, etc. A guide roll 2 is provided between the biaxial stretching means IO and the first heating means 20.

The first heating stage 20 has a pair of first pinch rolls 2l arranged above, a guide plate 22 attached in an inverted V shape from the first pinch rolls 2l, and heats the film l. A hot air stove 23 for folding the film 1 into a flat shape, a V-shaped guide plate 24 for folding the film 1 flat, and a pair of second pinch rolls 25 arranged at the lower end of the guide plate 24 are provided.

The trimming means 30 is provided with a trimming device 32 having a blade 31 .

A guide roll 2, a pair of rolls 41A disposed vertically apart, and 1,000 steps 40 in which the films IA and IB are stacked with air interposed between the films IA and IB.
41B, and three grooved rolls 42A to 42C arranged in order in the moving direction of the films IA and IB. As shown in FIG. 2, these grooved rolls 42A~
42C has two grooves 43 intersecting each other with a pinch of 10 cm, for example, on its outer peripheral surface, and after the grooves are formed, the surface is plated with chrome or the like. The tenter 50 is provided with a gripping mechanism (not shown) for gripping both ends of the overlapping films IA and IB,
This tenku 50 is disposed within the second heating means 60.

The second heating means 60 includes a hot air stove 6 for heat-treating the films IA and IB held by the tenter 50 with air interposed between the films IA and IB.
l is provided. The winding means 70 is provided with a winding machine 71 for winding up each of the heat-treated films IA and IB.

Using this heat treatment apparatus, the crystalline thermoplastic resin film 1 is heat treated in the following manner.

First, in a biaxial stretching means 1O using the tubular method, a tubular crystalline thermoplastic resin film 1 heated in a heating furnace 12 is expanded into bubbles 3 by a predetermined internal pressure, thereby being stretched in the transverse direction (TD direction). At the same time, the film is stretched in the longitudinal direction (MD direction) by the difference in the take-up speed between the upper and lower pinch rolls 11 and 14, thereby performing biaxial stretching. The biaxially stretched film 1 is flattened by a guide plate l3 and a second pinch roll l4. Folded.

In this example, the method of injecting air into the film l for tubular method is arbitrary (for example,
(Refer to Japanese Patent Application Laid-Open No. 64-71727). Next, in the 1st heating stage 20 using the tubular method, the bubble 3 is heated to a temperature higher than the shrinkage start temperature of the film 1 and 20° C. lower than the melting point of the film 1 using a hot air oven 23. Perform the first stage heat treatment. This first heat treatment increases the degree of crystallinity of the film 1, which improves the slipperiness between the overlapping films and prevents fusion. In addition, since this first stage heat treatment is carried out by the tubular method, the bowing rate of the film 1 finally obtained can be reduced.

Next, in the trimming means 30, both ends of the flat film 1 are cut with the blade 3l of the trimming device 32 to separate it into two films IA and IB. Incidentally, the cutting of the flat film 1 may be performed by positioning the blade 31 slightly inward from both ends so as to partially form an ear, or by positioning the blade 5 at the fold of the flat film 1. This may be done so that the ears do not grow. Trimming at this stage can reduce trimming loss in subsequent processes. Next, in the means 40 for overlaying both films IA and IB with air interposed, the films IA and IB are separately fed to the upper and lower sides of the rolls 41A and 41B, respectively, so that air is introduced into the inner surface of each film IA and IB. Bring it into contact.
Next, as shown in FIG. 2, three grooved rolls 42
By sequentially feeding A to 42C, both films IA
, IB with air interposed between them. I
Overlap B. In this way, the grooved rolls 42A to 42
By using C, a good contact state between the films IA and IB and air can be obtained through this groove 43, and it is possible to effectively prevent the films IA and IB from being fused together. Next, in the second heating means 60, while gripping both ends of the overlapping films IA and IB with the tenter 50, the temperature is higher than the heat treatment temperature of the first stage and lower than the melting point of the film l. These two films IA,I at temperature
Heat treat B. This second heat treatment imparts dimensional stability to the films IA and IB. Finally, in the winding means 70, the film IA, which has been heat-treated by the winder 71 via the guide roll 2,
Wind up the IB. Experimental examples and comparative examples in which the crystalline thermoplastic resin film 1 was heat-treated under specific conditions in the above examples will be explained. 1 Tomb and Eni 1 Boria ξ-do type nylon-6 as a crystalline thermoplastic resin
Ube nylon (trade name, relative viscosity 3.7) is used, and 15k
After extruding at a rate of g/hr, it was rapidly cooled in cooling water at 15°C.
A tubular nylon film (shrinkage start temperature: 45°C, melting point: 215°C) with a diameter of 90 m and a thickness of 135 μm was prepared. Next, in the biaxial stretching means 10 using the tubular method, this raw nylon film 1 is
After simultaneous biaxial stretching at a stretching ratio of 3.0/3.2, a flat tubular nylon film 1 with a thickness of 15 μm was produced by folding. Next, the nylon film 1 was heat-treated by setting the processing temperature and relaxation rate of each experimental example in the first heating means 20 and the second heating means 60 as shown in Table 1 below. The shrinkage rate (95°C (!: 115°C)) and bowing rate were measured for the nylon film l obtained after heat treatment,
The presence or absence of fusion was examined and the final pass/fail judgment was made. The results are shown in Table 1. As shown in FIG. 3, the bowing rate is determined by drawing a marked line S of a predetermined width on the raw nylon film 1 in a direction perpendicular to its moving direction (see FIG. 3 (A)), and stretching and heat treatment. This value is calculated from Δb/ffix100% by measuring the delay amount Δb and width l of the line S afterward (see FIG. 3(B)). In addition, in the fusion column, O indicates that fusion does not occur, × indicates that fusion occurs, and in the pass/fail judgment column, ◎ indicates that there is no fusion, and the bowing rate is 5% or less and the shrinkage rate is (115℃) is less than 5%, O will not fuse and the bowing rate will be 5%.
and/or when the shrinkage rate (at 115°C) exceeds 5%, × indicates that fusion occurs and the shrinkage rate exceeds 5%. Hair stopper - 1 In the same manner as in the above example, a tubular nylon film was prepared using nylon-6, and then this original film was biaxially stretched. Next, this nylon film was subjected to heat treatment only by the tenter method, and otherwise a heat-treated nylon film was obtained in the same manner as in the above example. Regarding the nylon films related to each of these comparative examples,
As in the above example, the shrinkage rate (95°C and 115°C) and bowing rate were measured, the presence or absence of fusion was examined, and the final pass/fail judgment was made. The results are shown in Table 1. From Table 1, the nylon film l according to each experimental example was heat-treated at 60 to 180°C by the tubular method in the first stage, and at 210°C by the tenter method in the second stage.
It can be seen that because the heat treatment is applied, fusion between the films does not occur and a low bowing rate is obtained, resulting in a pass/fail judgment of O or ◎.On the other hand, in each comparative example According to the nylon film, since it is only heat-treated by the tenter method, not only fusion occurs but also the bowing rate becomes high.
It can be seen that the pass/fail judgment is ×. In the above embodiment, the first and second heating means 20.60 are provided with hot air stoves 23.61, but for example, infrared heaters or the like may be provided. [Effect of the invention] According to the method and apparatus for heat treatment of a crystalline thermoplastic resin film according to the present invention, heat treatment for heat setting can be performed without causing fusion, and therefore the bowing rate is low and high. It is possible to stably supply films with dimensional stability.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of the heat treatment apparatus of the example, Fig. 2 is a perspective view of a grooved roll, and Figs. 3 (A) and (B) are diagrams showing a method for measuring the bowing rate. 1... Crystalline thermoplastic resin film, 3... Bubble, lO... Biaxial stretching means,
12... Heating furnace, 20... First heating means, 23.
61...Hot stove, 30...Trimming means, 40...
...Means for stacking films, 50...tenter 60
. . . second heating means, 70 . . . winding means.

Claims (4)

[Claims] (1) A step of biaxially stretching a crystalline thermoplastic resin film by the tubular method, and a step of biaxially stretching the crystalline thermoplastic resin film by the tubular method at a temperature above the shrinkage start temperature of the film and below a temperature 20°C lower than the melting point of the film. A step of subjecting this film to a first stage of heat treatment, a step of cutting both ends of this film to separate it into two films, and a step of separating the film into two films with air interposed between both films by a tenter method. The method includes the steps of subjecting the film to a second heat treatment at a temperature higher than the first heat treatment temperature and lower than the melting point of the film, and winding up the heat treated film. A method for heat treating a crystalline thermoplastic resin film, characterized by: (2) means for biaxially stretching a crystalline thermoplastic resin film by the tubular method; a first heating means for heat-treating the film by the tubular method; A trimming means for separating the films into two sheets, a means for stacking both films with air interposed between them, and a tenter for gripping both ends of the films, and a tenter is provided for gripping both ends of the films, and air is interposed between the two films. A heat treatment apparatus for a crystalline thermoplastic resin film, comprising: a second heating means for heat-treating the film in a heated state; and a winding means for the heat-treated film. (3) The heat treatment apparatus for crystalline thermoplastic resin films according to claim 2, wherein the first and second heating means are provided with hot air ovens. (4) In the heat treatment apparatus for crystalline thermoplastic resin films according to the second or third claim, a grooved roll is used as a means for stacking the two separated films while interposing air between the two films. A heat treatment apparatus for crystalline thermoplastic resin film.