JPH0588664B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a heat treatment method and apparatus for a thermoplastic resin film biaxially stretched by the tubular method.
It can be used in fields such as food packaging, packaging for industrial products such as computers, bag-in boxes, and drum interiors. [Background Art] In conventional plastic manufacturing methods, a plastic film is biaxially stretched, for example, by the tubular method, and then 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 heat treatment at around 200℃ using the tenter method, the upper and lower films will fuse together, so they will separate into two pieces after the treatment. The problem has arisen that it cannot be used as a product. Such problems are particularly noticeable when the plastic film is a thermoplastic resin film such as a polyamide film. Therefore, in order to solve this problem, conventionally, for example, a biaxially stretched flat tubular film is separated into two films by cutting the edges, and then an endless belt-like object is used to create a gap between the two films. An improved tenter method has been proposed in which the film is introduced into a tenter in a maintained state and heat-treated while holding both ends of the film with clips (see Japanese Patent Publication No. 15439/1983). In addition to this improved tenter method, the problem of thermal welding can also be avoided by employing a tubular method in which compressed air is introduced into a tube-shaped 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 causes problems such as in-plane anisotropy of the film's physical properties and sagging, which hinders secondary processing (printing, etc.). At this time, if the heat treatment temperature is lowered, the bowing rate will be lowered, but when heat treatment such as boiling or retorting is performed, the shrinkage rate becomes too large, which poses a problem. Further, according to the above-described heat treatment using the tubular method, when 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 proposed in Japanese Patent Application No. 63-296575 a method and apparatus for heat-treating a crystalline thermoplastic film biaxially stretched by the tubular method in two stages. In this invention, the second stage heat treatment is performed using a tenter method, but the first stage heat treatment method is not particularly limited. However, if this first stage heat treatment is carried out using a tenter method in the same way as the second stage heat treatment, the effect of reducing the bowing rate can be recognized, but bowing has already occurred in the first stage heat treatment. Therefore, its effectiveness is limited. An object of the present invention is to provide a method for producing a biaxially stretched film that can reduce the bowing rate and improve the balance of physical properties within the film plane. [Means and effects for solving the problems] The present invention provides a method for producing a biaxially stretched film in which the film is heated and biaxially stretched by a tubular method, and then folded flat. A feature of the present invention is that the heating temperature of a portion of the film that becomes an ear portion when the film is folded is set lower than the heating temperature of a portion of the film that corresponds to a product. For this purpose, in the present invention, the temperature of a heater that heats a portion of the film that becomes an edge when the film is folded, and a heater that heats a portion of the film that corresponds to a product are controlled respectively, and It is recommended that the temperature of the heater that heats the ear portion of the heater be 10 to 100 degrees Celsius lower than the average temperature of all heaters. Even if the temperature is lower than 10°C, the effect of the present invention, that is, the bowing phenomenon in the opposite direction cannot be obtained.
In addition, if the temperature is lower than 100°C, bubbles in the process of stretching tend to become unstable. In addition, in this manufacturing method, the temperature of a heater that heats a portion that becomes an edge portion when the film is folded and a heater that heats a portion of the film that corresponds to a product are controlled, respectively. The temperature of the heater that heats the portion corresponding to the product may be set to be 10 to 100° C. higher than the average temperature of all heaters. Even if the temperature is increased in a range of less than 10°C, the effect of the present invention, that is, the bowing phenomenon in the opposite direction cannot be obtained.
Moreover, if the temperature is raised above 100°C, bubbles in the process of stretching tend to become unstable. As mentioned above, in order to control the temperature of the heater that heats the portion that becomes the edge when the film is folded, and the heater that heats the portion of the film that corresponds to the product, for example, the edge of the film must be controlled. At least four heaters in total are provided: two heaters for heating the portion of the film that corresponds to the product, and two heaters for heating the portion of the film that corresponds to the product. In addition, in order to improve the controllability of the heating state of the film and to make the temperature gradient gentle over the entire circumference of the film, it is preferable to configure the heating device to include, for example, four or more heaters. For this purpose, it is preferable to heat the film so that the heating temperature is the lowest at the extreme end of the portion that will become the selvage portion, and the heating temperature is set at the highest approximately at the center of the portion of the film that corresponds to the product. . Further, in the present invention, the film folded by the above manufacturing method is heat-treated at a temperature equal to or lower than the melting point of the film. In this case, the heat treatment is preferably a two-stage heat treatment in which the first stage is performed by a tenter method or a tubular method, and the second stage is performed by a tenter method. At this time, the first stage heat treatment by the tenter method is performed at a temperature 30° C. or more lower than the melting point, and the heat treatment by the tubular method is performed at a temperature 20° C. or more lower than the melting point. Further, the heat treatment by the second stage tenter method is performed at a temperature that is 30° C. lower than the melting point or higher and lower than the melting point. In addition, each heat treatment time is preferably about 1 to 30 seconds. Examples of the resin used as the resin for the biaxially stretched film according to the present invention include thermoplastic resins such as polyamide, polyester, saponified ethylene-vinyl alcohol copolymer, polyethylene, polypropylene, and polystyrene. Specific examples of polyamide resins include nylon-6 (melting point 215°C), nylon-6,6 (melting point
260℃) etc. [Example] A manufacturing apparatus used in Examples and a method for manufacturing a biaxially stretched film using the same will be described with reference to the drawings. As shown in FIG. 1, this manufacturing apparatus includes a means 10 for biaxially stretching a thermoplastic resin film 1 by a tubular method, a first heating means 20 for heat-treating the film 1 by a tenter method, and a first heating means 20 for heat-treating the film 1 by a tenter method. Cut both ears of the film into two pieces of film 1A,
A trimming means 30 for separating the films 1A and 1B, a means 40 for stacking both films 1A and 1B with air interposed between them, and a means 40 for stacking both films 1A and 1B with air interposed between them by a tenter method. A second heating means 50 for heat-treating the films 1A and 1B, and a heat-treated film 1
A and 1B winding means 60 are provided. The biaxial stretching means 10 includes a pair of first pinch rolls 11 disposed above, a heating device 13 provided with a heater 12 for heating the thermoplastic resin film 1, and a heating device 13 for flattening the film 1. A V-shaped guide plate 14 for folding and a pair of second pinch rolls 15 arranged at the lower end of the guide plate 14 are provided. As shown in FIG. 2, the heater 12 of this heating device 13 consists of four heaters 12A to 12D that are disposed close to each other along the outer peripheral surface of the bubble 2.
Of these heaters 12A to 12D, one pair of opposing heaters 12A and 12B is connected to the edge portions 3A and 3B of the film 1 when the bubble 2 is folded flat.
A heater is used to heat the portions 2A and 2B (see FIG. 3). Further, the other pair of opposing heaters 12C and 12D are used to heat the portions 2C and 2D of the bubble 2 corresponding to the products. These heaters 12A to 12D can be arbitrarily selected such as infrared heaters. The first heating means 20 is provided with a tenter 21 for gripping both edges 3A and 3B of the film 1 folded flat, and a hot air stove 22 for heating the film 1. The trimming means 30 is provided with a trimming device 32 having a blade 31 for separating the tube-shaped film 1 into two films 1A and 1B. The means 40 for overlapping both the films 1A, 1B with air interposed between the films 1A, 1B includes a guide roll 5, a pair of rolls 41A, 41B arranged vertically apart, and the films 1A, 1B.
Three grooved rolls 42A to 42C are provided which are arranged in order in the moving direction of 1B. As shown in FIG. 4, these grooved rolls 42A to 42C
is, for example, 2 lines that intersect with the outer circumferential surface at a pitch of 10 cm.
A strip groove 43 is formed, and after grooving, the surface is plated with chrome or the like. The tenter 50 has the films 1A, 1
A tenter 51 for gripping both ears 3A, 3B of film B, and a hot air oven 52 for heating films 1A, 1B are provided. The winding means 60 is provided with a winding machine 61 for winding up each of the heat-treated films 1A and 1B. Using this manufacturing apparatus, the thermoplastic resin film 1 is heat-treated in the following manner. First, biaxial stretching means 10 using the tubular method
In this step, a tube-shaped thermoplastic resin film 1 heated by a heating device 13 is expanded into bubbles 2 by a predetermined internal pressure, so that the tube-shaped thermoplastic resin film 1 is heated in a transverse direction (TD
direction) and the longitudinal direction (MD
direction) to perform biaxial stretching. The biaxially stretched bubble 2 is folded flat by the guide plate 14 and the second pinch roll 15. Note that the method of injecting air into the film 1 for making the tubular method is arbitrary (for example, JP-A-64
(Refer to Publication No. 71727). During heating by this heating device 13, the temperature of the heaters 12A and 12B placed on the sides 2A and 2B of the bubble 2, which will become the ear portions 3A and 3B, is adjusted to the temperature of all the heaters 1.
Set 10 to 100°C lower than the average temperature of 2A to 12D. In addition, part 2 corresponding to the product of bubble 2
The temperature of the heaters 12C and 12D placed on the C and 2D sides is determined from the average temperature of all heaters 12A to 12D.
Set the temperature 10 to 100℃ higher. By heating and stretching under these conditions, as shown in Figures 5 and ₆ , the straight line A bowing phenomenon occurs in the opposite direction, which is shifted in the MD direction with 2C and 2D as the centers, resulting in a curve _X2 . Next, in the first stage heat treatment by the first heating means 20, the tenter 21 grips both edges 3A and 3B of the film 1, and the hot air oven 22 heats the film 1 at a temperature 30°C or more lower than the melting point. give
In this heat treatment, a bowing phenomenon occurs in a direction that cancels out the bowing phenomenon in the opposite direction during the biaxial stretching. Note that this first stage heat treatment may be performed by the tubular method, and in this case, the heat treatment is performed at a temperature 20° C. or more lower than the melting point. During this heat treatment, the relaxation rate of film 1 is 0 to
Set to 10% (MD direction and/or TD direction).
By heat-treating the film 1 in a slightly relaxed state, the degree of crystallinity of the film 1 can be increased and the shrinkage rate can be reduced, thereby providing a film 1 with good dimensional stability. Next, in the trimming means 30, both ears 3A and 3B of the flat film 1 are cut with the blade 31 of the trimming device 32, and the two films 1 are separated.
Separate into A and 1B. In addition, this flat film 1
Make the incision with the blade 3 slightly inward from the crease.
By positioning the blade 1, a portion of the edge piece may be formed, or by positioning the blade 5 at the fold of the flat film 1,
This may be done in such a way that no ear pieces occur. By trimming at this stage, trimming loss in subsequent steps can be reduced. Next, with air interposed, both films 1A,
In the means 40 for stacking 1B, rolls 41A,
By separately feeding the films 1A and 1B to the upper and lower sides of 41B, each film 1A and 1
B Bring air into contact with the inner surface. Next, as shown in FIG. 4, both films 1A and 1B are sequentially passed through three grooved rolls 42A to 42C.
Both films 1A, 1 with air interposed between them
Overlap B. In this way, the grooved roll 42A
By using the grooves 42C to 42C, good contact between the films 1A and 1B and air can be obtained through the grooves 43, and it is possible to effectively prevent the films 1A and 1B from being fused together. Next, in the second stage heat treatment by the second heating means 50, the overlapping films 1A, 1
These two films 1A and 1B are heat-treated at a temperature that is 30° C. lower than the melting point and lower than the melting point while holding the film B by the tenter 51 at both edges 3A and 3B. In this heat treatment as well, a bowing phenomenon occurs in a direction that further cancels out the bowing phenomenon in the opposite direction during the biaxial stretching, and as a result, the bowings in both directions cancel each other out, resulting in film 1A,
1B's bowing rate becomes smaller. Also in this second stage heat treatment, the relaxation rate of the films 1A and 1B is set to 0 to 10%. Finally, in the winding means 60, the heat-treated films 1A and 1B are wound up by the winding machine 61 via the guide roll 2. Experimental examples and comparative examples will be described in which the thermoplastic resin film 1 is heat-treated under specific conditions in the above embodiments. Experimental Examples 1 to 6 Polyamide-based nylon as thermoplastic resin
6 Ube nylon (trade name, relative viscosity 3.7)
The film was extruded at 15 kg/hr from an extruder with a screw diameter of 40 mm, and then rapidly cooled in cooling water at 15°C to produce a tubular nylon film (melting point: 215°C) with a diameter of 90 mm and a thickness of 135 μm. Next, biaxial stretching means 10 using the tubular method
The raw nylon film 1 was simultaneously biaxially stretched at a stretching ratio of MD direction/TD direction = 3.0/3.2, and then folded to produce a flat tube-shaped nylon film 1 with a thickness of 15 μm. During this stretching, the temperature of the heaters 12A and 12B placed on the sides 2A and 2B of the heating device 13 that are the ear parts 3A and 3B of the bubble 2 and the parts 2C and 2D of the bubble 2 that correspond to the product are adjusted. The temperatures of the heaters 12C and 12D were set as shown in Table 1 below. Next, the treatment temperature and relaxation rate of each experimental example in the first stage heat treatment and the second stage heat treatment were set as shown in Table 1 below, and the nylon film 1 was
Heat treatment was performed. Note that the first stage heat treatment in Experimental Examples 1 to 5 was performed by the tenter method as shown in the above manufacturing apparatus, but only the first stage heat treatment in Experimental Example 6 was performed by the tubular method. As shown in Table 1, the forming stability of bubble 2 during biaxial stretching was evaluated, and the bowing rate of nylon film 1 after stretching and nylon films 1A and 1B after second stage heat treatment was measured. , made the final pass/fail judgment. The bowing rate is determined by drawing a marked line _S1 of a predetermined width on the raw nylon film 1 in a direction perpendicular to its moving direction (see FIG. 7A), as shown in FIG. After the heat treatment, the delay amount Δb and the width l of the marked line S ₂ were measured (see Figure 7B), and Δb/l
This is a value calculated from ×100%. In addition, in the present invention, a bowing of -Δb ₁ minute occurs first due to a bowing phenomenon in the opposite direction in the biaxial stretching process, and then a bowing of +Δb ₂ minutes occurs in the first and second heat treatment steps. In order to
Δb after the heat treatment of the second stage ultimately corresponds to |Δb ₂ −Δb ₁ |. In addition, in the bubble forming stability column, ○ indicates that the bubble diameter fluctuation is ±1% or less, and bubble breakage and unstable phenomena (vertical movement, lateral vibration, etc.) do not occur, and △ indicates that bubble folding is less than ±1%. If the diameter variation is ±3% or less, no bubble breakage or unstable phenomenon (vertical movement, lateral movement, etc.) will occur.
Continuous stable molding is difficult due to the occurrence of horizontal vibration, etc.)
shows. In addition, in the pass/fail judgment column, ◎ means that the bubble molding stability is ○ and the bowing rate after the second stage heat treatment is less than 5%; If the bowing rate after heat treatment is 5% or more, or if the bubble molding stability is △ and the bowing rate after the second stage heat treatment is less than 5%, ×
indicates the case where the bubble molding stability is × or the case where the bowing rate after the second stage heat treatment is 5% or more, respectively. Comparative Examples 1 to 5 In the same manner as in the above experimental examples, a tubular nylon film 1 was prepared using nylon-6, and then this original film was biaxially stretched. During this stretching, the ears 3A and 3B of the bubble 2 of the heating device 13
Heater 12 placed on the portions 2A and 2B side
Heaters 12C and 1 are placed on the sides 2C and 2D corresponding to the temperature of A and 12B and the product of bubble 2.
The 2D temperature was set as shown in Table 1 below. Next, these nylon films 1 were subjected to first and second heat treatments at the temperatures and relaxation rates shown in Table 1, and the other nylon films were subjected to the heat treatment in the same manner as in the above experimental example. 1A, 1B
I got it. In addition, in the case of Comparative Example 5, the first stage heat treatment was not performed. Regarding the nylon films according to each of these comparative examples, the forming stability of bubble 2 during biaxial stretching was evaluated in the same manner as in the above experimental examples, and the nylon film 1 after stretching and after the second stage heat treatment were evaluated. The bowing rates of nylon films 1A and 1B were measured, and a final judgment of pass/fail was made.

[Table] From Table 1, according to each experimental example, one pair of heaters 12A and 12B were placed on the side of the portions 2A and 2B that would become the ears 3A and 3B of the bubble 2 during heating in biaxial stretching. Set the temperature of 20 to 100 degrees Celsius lower than the average temperature (300 degrees Celsius) of all heaters, and also set the temperature of the other pair of heaters 12C and 12D placed on the portions 2C and 2D corresponding to the products of bubble 2. By setting the temperature 20 to 100℃ higher than the average temperature of all heaters, the bubble 2 during biaxial stretching is stable, and the final bowing rate after the second stage heat treatment is low, resulting in a pass/fail judgment. It can be seen that is ○ or ◎. Therefore, according to this embodiment,
Since the boeing rate can be kept small,
Films 1A and 1B with very good in-plane physical property balance can be obtained. On the other hand, according to Comparative Example 1, during heating in biaxial stretching, the heaters 12A,
12B temperature and heaters 12C and 12D placed on the parts 2C and 2D sides corresponding to the products of bubble 2.
The average temperature of all heaters (300
℃), the bowing phenomenon in the opposite direction did not occur, and the bowing rate after the second stage heat treatment increased. Furthermore, according to Comparative Examples 2 and 3, the temperature of one pair of heaters 12A, 12B is set higher than the average temperature (300°C) of all heaters, and the temperature of the other pair of heaters 12C, 12D is set to Since the temperature was set lower than the average temperature of all heaters (300℃), the normal bowing phenomenon occurred, resulting in a high final bowing rate. According to Comparative Example 4, one pair of heaters 12
The temperature of A and 12B is the average temperature of all heaters (300
Because the temperature of the other pair of heaters 12C and 12D was set at least 100°C higher than the average temperature of all heaters (300°C), a bowing phenomenon in the opposite direction occurred. Although the final bowing rate was lower, the molding stability of Bubble 2 was poor. According to Comparative Example 5, one pair of heaters 12
A, 12B temperature and the other pair of heaters 12
Although the temperature of C and 12D was within the temperature range of the present invention and bowing in the opposite direction was obtained, the final bowing rate was high because the first stage heat treatment was not performed. In the above embodiment, the heater 12 is divided into four parts, and the temperature of one pair of heaters 12A, 12B and the other pair of heaters 12C, 12D is controlled separately. Portions 2A and 2B that become ears 3A and 3B of bubble 2
If the heating device 13 is configured by arranging a total of 10 heaters, two on each side and three on each of the parts 2C and 2D corresponding to the product of the bubble 2, the temperature controllability of the heating state of the bubble 2 can be improved. The temperature gradient can be further improved and the temperature gradient can be made gentle over the entire circumference of the film. In the above embodiment, the heater 12 is divided into parts, but by adjusting the winding density of the coil of the infrared heater, for example, the portions 2A and 2B that become the ears 3A and 3B of the bubble 2 can be separated. The heating temperature of parts 2C and 2D of bubble 2 corresponding to products can be controlled respectively. Furthermore, in the above embodiment, the first and second heating means 20, 50 are provided with hot air stoves 22, 52, but for example, infrared heaters or the like may be provided. [Effects of the Invention] According to the method for producing a biaxially stretched film according to the present invention, the bowing phenomenon caused by heat treatment can be suppressed to a small level, so that a film with a very good balance of physical properties in the film plane can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the manufacturing equipment used in the examples;
Fig. 2 is a plan sectional view showing the bubble heated by the heater, Fig. 3 is a sectional view showing the bubble in a folded state, Fig. 4 is a perspective view of the grooved roll,
FIG. 6 is a front view showing the bowing phenomenon in the opposite direction during biaxial stretching, and FIGS. 7A and 7B are diagrams showing the method for measuring the bowing rate. 1...Thermoplastic resin film, 2A, 2B...
Portion that becomes the ear of the bubble, 2C, 2D... Portion corresponding to the bubble product, 3A, 3B... Ear, 1
0... Biaxial stretching means, 12, 12A to 12D...
Heater, 20... First heating means, 22, 52...
... hot air oven, 30 ... trimming means, 40 ... means for stacking films, 50 ... second heating means,
60... Winding means.

Claims (1)

[Scope of Claims] 1. A method for producing a biaxially stretched film in which the film is heated and biaxially stretched by a tubular method, and then folded flat, wherein when the film is heated, when the film is folded, an edge is formed. A method for producing a biaxially stretched film, characterized in that the heating temperature of the portion of the film that corresponds to the product is set lower than the heating temperature of the portion of the film that corresponds to the product. 2. A method for producing a biaxially stretched film in which the film is heated and biaxially stretched by the tubular method, and then folded flat, comprising: a heater that heats a portion that becomes an edge when the film is folded; The temperature of the heater that heats the part corresponding to the product is controlled individually, and the temperature of the heater that heats the part that becomes the edge of the film is set to 10 to 10% higher than the average temperature of all heaters.
A method for producing a biaxially stretched film characterized by lowering the temperature by 100°C. 3. A method for producing a biaxially stretched film in which the film is heated and biaxially stretched by the tubular method, and then folded flat, comprising: a heater that heats a portion that becomes an edge when the film is folded; The temperature of each heater that heats the part corresponding to the product is controlled, and the temperature of the heater that heats the part of the film corresponding to the product is determined from the average temperature of all heaters.
A method for producing a biaxially stretched film characterized by increasing the temperature by 10 to 100°C. 4. In the method for producing a biaxially stretched film according to claim 2 or 3, the heating temperature of the extreme end of the portion of the film that becomes the ear portion is set to the lowest, and the heating temperature of the portion of the film that corresponds to the product is set to the lowest temperature. A method for producing a biaxially stretched film, characterized by maximizing the heating temperature in the central part. 5. A biaxially stretched film, characterized in that the film folded by the method for producing a biaxially stretched film according to any one of claims 2 to 4 is heat treated at a temperature below the melting point of the film. manufacturing method.