JPH04286624A - Manufacture of thermoplastic resin film - Google Patents

Abstract

PURPOSE:To improve bowing and manufacture a biaxially-oriented thermoplastic resin film of superior heat dimension stability and improved flatness by carrying out a treatment for limpness in the longitudinal direction just after orientation in the axial direction. CONSTITUTION:An unoriented film 1 is oriented in the longitudinal direction in the longitudinal direction orientation process 2 in which a plurality of rolls and the like are disposed. The film is preheated in the preheating zone 4 of a stenter 3 and oriented in the width direction in the orientation zone 5. The limpness treatment is carried out for the biaxially-oriented thermoplastic film 6 by a longitudinal direction limpness treatment means 7 just after successive biaxially orientation. A film 6 fed from a guide roll 8 into the longitudinal direction limpness treatment process 7 is moved floatingly along the arc face of a hot air blowing means 10 provided with a plurality of hot air blow nozzles 9, during which the limpness treatment is carried out in the longitudinal direction.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a thermoplastic resin film that exhibits little dimensional change due to heat and excellent flatness. More specifically, the present invention relates to a method for producing thermoplastic resin films and sheets used in packaging materials, industrial materials, electrical insulation materials, capacitor materials, magnetic materials, etc., which require thermal dimensional stability and flatness. (The film used in the present invention also includes sheets, unless otherwise specified.)

0002

[Prior Art] A biaxially stretched thermoplastic film is, for example, first stretched in the longitudinal direction of the film, then stretched in the width direction using an oven such as a stenter, and after stretching is subjected to heat treatment such as relaxation treatment in the width direction in the stenter. It is manufactured by. In such a sequential biaxial stretching process, a so-called bowing phenomenon usually occurs to some extent when the film is stretched in the width direction within the stenter.

As shown in an exaggerated manner in FIG. 6, this bowing 101 has a structure in which the film 102 is stretched between the width direction stretching zone 104 and the heat treatment zone 105 in the stenter 103 in response to longitudinal stress in the stretching portion. This phenomenon occurs because the directional stress is small and the heat-treated area is pulled toward the stretching zone.Since both edges in the width direction of the film are held with clips, the center part is pulled toward the stretching area (upstream direction in the running direction). This is a phenomenon in which the film is stretched and curved into an arch while maintaining its flat shape. In the stenter 103, a width direction relaxation treatment zone 106 is often provided after the width direction stretching zone 104 and the heat treatment zone 105. However, since bowing is a phenomenon in which the film curves in the longitudinal direction of the film, width direction relaxation treatment is performed. Processing does not repair it. If the degree of such bowing phenomenon is severe, not only will the thermal dimensional stability (e.g. thermal shrinkage rate) and flatness of the biaxially stretched thermoplastic film to be formed be significantly impaired, but also the various mechanical properties of the film will be affected in the width direction. The dispersion becomes larger.

In connection with the present invention, as a means for imparting thermal dimensional stability, Japanese Patent Laid-Open No. 2-22038 discloses that a film having specific film characteristics after passing through an oven is heated from one side of the film. A method has been proposed in which relaxation heat treatment is performed by sending air and causing it to float in a curved manner.

However, the above-mentioned conventional method heat-treats the film after passing through the oven, and is not effective in improving bowing that occurs within the stenter. In addition, the film characteristics must be set under specific conditions before the floating relaxation treatment, and unless the film has those characteristics, sufficient thermal dimensional stability cannot be obtained. Furthermore, the same goes for satisfying thermal dimensional stability while having flatness; good flatness cannot be obtained unless a film is prepared under specific conditions.

[0006]

SUMMARY OF THE INVENTION The object of the present invention is to improve the bowing that occurs during widthwise stretching and heat treatment in a stenter in the conventional stretching method described above, and ultimately,
An object of the present invention is to provide a method for producing a thermoplastic resin film that has excellent flatness and thermal dimensional stability even if the biaxially stretched film characteristics do not meet specific conditions.

[0007]

[Means for Solving the Problems] A method for producing a thermoplastic resin film of the present invention in accordance with this object is to stretch a film made of a thermoplastic resin biaxially in the longitudinal direction and the width direction of the film, and then immediately stretch the film in the longitudinal direction of the film. Relaxation treatment is applied to
This method is then followed by a relaxing treatment in the width direction of the film.

[0008] The thermoplastic resin in the present invention is a resin that exhibits plasticity when heated, and typical resins include polyethylene terephthalate, polyethylene naphthalate, etc., and copolymers thereof. Polyesters with ester bonds, polypropylene,
Polyolefins represented by polystyrene, nylon 6, nylon 66, nylon 610, nylon 12
These include polyamides, such as polyphenylene sulfide, and copolymers and modified products thereof. In the case of the present invention, polyethylene terephthalate, polyethylene naphthalate, polypropylene, polyphenylene sulfide, and copolymers thereof are particularly preferred because the effects of the present invention are remarkable. Of course, the above polymer may contain known additives such as stabilizers, viscosity modifiers, antioxidants, fillers, slip agents, antistatic agents, antiblocking agents, release agents, mold release agents, and the like.

[0009] The biaxially stretched film in the present invention particularly refers to a film produced by biaxially stretching in the longitudinal direction and the width direction.

In the method of the present invention, immediately after the film is stretched in the width direction by the above-mentioned biaxial stretching, a relaxation treatment is performed in the longitudinal direction of the film, and then a relaxation treatment is performed in the width direction of the film. That is, unlike the conventional method, the width direction relaxation treatment is not performed after the width direction stretching, but the longitudinal direction relaxation treatment is performed first, and then the width direction relaxation treatment is performed. In this way, when the longitudinal relaxation treatment is performed immediately after the widthwise stretching, the force that acts on the film to cause bowing, which is a bending strain in the longitudinal direction, is substantially cut off in the longitudinal relaxation treatment section. , Boeing will be improved extremely efficiently. and,
By improving the bowing at this stage, the thermal dimensional stability and flatness of the final biaxially stretched film are greatly improved, and variations in mechanical properties depending on the film position are also minimized.

[0011] The longitudinal relaxation for improving the bowing is preferably carried out by floating heat treatment, which does not substantially restrict the film's widthwise end edge portions in the film running direction (film longitudinal direction). However, if the edge portions at both ends are relatively thin, it is also possible to perform roll heat treatment, that is, to perform a relaxation treatment by passing the film between a plurality of rolls and utilizing the difference in circumferential speed between the rolls. Alternatively, the edge part may be loosened in the longitudinal direction between the ovens without gripping the edge part (the gripping clips in the stretching part and the heat treatment part are driven in a separate manner and are relaxed in the longitudinal direction between them), and the edge part is cut immediately after stretching. You can go.

[0012] In the floating heat treatment for the longitudinal relaxation treatment, for example, a method in which the film is floated with hot air while drawing an arc shape is preferable. By floating the film in an arc shape, it is possible to give the film a degree of freedom and to inflate the film, thereby making it difficult for wrinkles to form in the film. In addition, surface defects such as scratches are also prevented by floating. Furthermore, by adjusting the length of the arc, it is also possible to provide sufficient heat treatment (relaxation treatment) time. By adopting this method, it is also possible to regulate the relaxation rate in the width direction, which is preferable.

However, simply floating the film in an arc may cause wrinkles in the longitudinal direction of the film, so it is preferable to do the following. The film introduced into the longitudinal direction relaxation treatment process is floated in an arc shape along the arcuate surface of the hot air blowing means having an arcuate longitudinal cross section, and during the floatation run, the film is relaxed in the longitudinal direction. In particular, at the final hot air blowing position of the hot air blowing means in the film running direction, the film is guided inward from the tangential direction of the arcuate surface of the hot air blowing means. By regulating the direction in which the film is drawn out in this way, the pressure of the hot air blown out from the hot air blowing means is appropriately and uniformly contained, especially in the vicinity of the outlet, and the stretching force in the width direction acts uniformly on the film being processed. This effectively prevents wrinkles from forming on the film. Since wrinkles do not form at the outlet of the hot air blowing means, wrinkles do not occur even on the upstream arc surface. Since the longitudinal relaxation treatment is carried out and completed without any wrinkles, the flatness of the film after treatment is maintained extremely well.

[0014] Regarding the occurrence of wrinkles, there is a very noticeable difference depending on whether or not the direction in which the film is led out at the final hot air blowing position of the hot air blowing means is restricted to be inside the tangential direction of the arcuate surface of the hot air blowing means. occurs. In other words, by restricting it inward from the tangential direction, wrinkles can be completely prevented from forming.

The biaxially stretched thermoplastic film described above is manufactured, for example, as shown in FIGS. 1 to 3. Figure 1, Figure 2
In this process, the unstretched film 1 is stretched in the longitudinal direction in a longitudinal stretching step 2 using a plurality of rolls, preheated in the preheating zone 4 of the stenter 3, and stretched in the width direction in the stretching zone 5. This biaxially stretched thermoplastic film 6 is subjected to the longitudinal relaxation treatment means 7 immediately after the sequential biaxial stretching described above.
Relaxed in the longitudinal direction. As shown in FIG. 3, the film 6 introduced into the longitudinal relaxation process from the guide roll 8 is arc-shaped along the arc-shaped surface of the hot-air blowing means 10 having a plurality of hot-air blowing nozzles 9 and having an arc-shaped longitudinal section. It is floated as shown in the picture, and during the floatation it is loosened in the longitudinal direction. Then, at the final hot air blowing position in the film running direction (the position of the final hot air blowing nozzle 9a), the film is guided in a direction 12 inside the tangential direction 11 of the arcuate surface of the hot air blowing means 10. In the figure, it is directed inward by an angle θ. After passing through the guide rolls 14, the derived film 13 is introduced into the oven 15 again, where it is subjected to relaxation treatment in the width direction of the film in a zone 16 within the oven, and is heat-set in a zone 17 as necessary to obtain a predetermined shape. A biaxially stretched film 18 is obtained and sent to a winding process or the like. The longitudinal relaxation treatment step is also preferably covered with an oven 19, and heating is controlled to a predetermined temperature while circulating hot air. In this way, by setting the film leading direction 12 at the exit to the inside of the tangential direction 11,
Wrinkling is completely prevented and thermal dimensional stability is ensured while the bowing is improved due to longitudinal relaxation treatment (
A film with a low thermal shrinkage rate) and extremely good flatness can be obtained.

[0016] In the above-mentioned arc-shaped floating run, it is preferable that the radius of the arc is 250 to 1000 mm from the viewpoint of preventing wrinkles. If the radius is less than 250 mm, wrinkles are likely to occur and meandering is likely to occur. Also, the radius is 1000
If it exceeds mm, wrinkles tend to occur and the device becomes larger, which is not preferable.

[0017] The arcuate winding angle is desirably 120° or more, preferably 150° or more, and more preferably 180° or more. Depending on the radius of the arc, 120
If the winding angle is less than 0.0 degrees, wrinkles will easily occur, and the film will also tend to meander.

[0018] Also, this arc-shaped longitudinal direction relaxation treatment step is as follows:
Two or more hot air blowing means 1 in succession as shown in FIG.
0a and 10b. In that case, it is preferable to run in an arc shape in the opposite direction from the viewpoint of preventing wrinkles and maintaining good flatness.

As shown in the figure, this arc-shaped heat treatment has a structure in which hot air is blown from inside the arc, and has a hot-air blowing nozzle consisting of a slit or the like extending in the width direction of the film. It must have a nozzle. The speed of the hot air blown out in this arc-shaped heat treatment step is preferably 5 to 200 m/sec, and if it is less than 5 m/sec, the processing effect will decrease and cause meandering of the film. Moreover, if the speed exceeds 200 m/sec, the film will flap, causing scratches.

In addition, in this arc-shaped heat treatment process, the flying height of the film is 1 to 20 mm outward from the edge of the film.
It is preferable to provide a baffle plate with a flying height of about -10 mm. Without this baffle plate, the film tends to meander, the edges of the film become tense, and the center of the film tends to sag.

[0021] Regarding the temperature conditions for the heat treatment for longitudinal relaxation, for example, in the case of a polyester resin film, it is preferable to perform the treatment in a temperature range of 90 to 230°C. It is sufficient to process at a temperature (approximately ±20° C.) that requires thermal dimensional stability. In addition, for example, in the case of polyester resin, the appropriate temperature for the relaxation treatment in the width direction is 150 to 250°C.

[0022] The treatment time for the longitudinal relaxation treatment is 0.1 to 30 seconds, depending on the type of thermoplastic resin used.
Preferably, the time is 1 to 20 seconds. If it is less than 0.1 seconds, the treatment effect will be insufficient and the target thermal dimensional stability will not be achieved. On the other hand, if the heating time exceeds 30 seconds, the physical properties may be satisfied, but the apparatus will become larger, which is not preferable.

In addition, in this heat treatment, it is necessary to relax in the longitudinal direction, and although it varies depending on the characteristics of the film before heat treatment, the relaxation rate is 15% or less, preferably 8%.
% or less. This will greatly improve Boeing.

In addition to blowing hot air at the above-mentioned speed from the inside of the arc in the longitudinal direction relaxation treatment step, it is preferable to blow hot air from the opposite side (outside) of the film in order to prevent curling and the like. In this case, the wind speed must be inside > outside. When the wind speed on the outside is the same or higher, problems such as wrinkles and scratches occur on the film.

In the method of the present invention, when the film has relatively thin edge portions at both ends immediately after being stretched in the film width direction,
It is also possible to carry out the longitudinal relaxation treatment by means of rolls. For example, as shown in FIG.
Multiple rolls (preferably heated rolls) instead of 0 2
0, and the longitudinal direction relaxation process is performed with a circumferential speed difference between the rolls. The temperature conditions and processing time are the same as in the above-mentioned levitation process. Such longitudinal relaxation treatment using a group of rolls also improves bowing and greatly improves the thermal dimensional stability and flatness of the resulting biaxially stretched film.

Next, one of the preferable conditions for the manufacturing method of the present invention will be explained, but the conditions are not limited thereto. Polyethylene terephthalate is supplied to an extruder, melted by a conventional method, discharged from a T-die nozzle, and solidified by electrostatic charge onto a cooling drum. This film is heated to 50 to 130℃.
Stretch 2 to 9.0 times in the longitudinal direction at 80 to 120°C (a two-step longitudinal stretching method may also be used, in which case the effect of bowing etc. will be more pronounced), and 3 to 9.0 times in the width direction at 80 to 120°C. Immediately after stretching 5 times, using the device shown in Fig. 3, the winding angle is 120° to 270° in an arc shape, and the temperature of the hot air blown from the inside of the arc is 90 to 230°.
℃, and heat treatment is performed with relaxation of 10% or less in the longitudinal direction. After this longitudinal direction relaxation treatment, widthwise relaxation treatment is performed in an oven at a temperature of 150 to 250° C., heat fixation is performed as necessary, and after cooling, winding is performed.

[0027]

Effects of the Invention According to the method for producing a thermoplastic resin film of the present invention, since the longitudinal direction relaxation treatment is performed immediately after the width direction stretching, the bowing is significantly improved in this processing step, and the width direction relaxation treatment performed after the longitudinal direction relaxation treatment is performed. By adding this, a biaxially stretched thermoplastic resin film having excellent thermal dimensional stability and extremely excellent flatness can be obtained. Furthermore, if a film floating process using a hot air blowing means is applied to the above-mentioned longitudinal direction relaxation process,
A film with the above-mentioned excellent properties can be stably obtained without wrinkles or scratches.

[0028]

[Evaluation method] (1) Sample the entire width of a flat film of 3 m, attach one end to a flat shaft, and run it along a flat, free-rotating roll at an interval of 2.5 m. The film was set so that a load of 50 g/mm2 was applied uniformly across the entire width of the film. A thread is stretched horizontally across the entire width of the film at the center in the longitudinal direction, that is, at a position of 1.25 m. This thread is set so that it contacts at least one location on the film. At this time, the film with poor flatness was located at a distance from this thread, and this distance was read and indicated using the following evaluation criteria. If there is no problem with flatness, the entire width will be in contact with this thread. Evaluation criteria (evaluation at the farthest part) ○: Film-to-thread distance is less than 2 mm △: Film-to-thread distance is 2 mm or more and less than 10 mm ×: Film-to-thread distance is 10 mm or more and film-to-thread distance is less than 2 mm, use There is no problem at all, so I marked it with an ○. If it is 10 mm or more, it is completely unusable as a film and is indicated by an x mark. 2mm or more, 10m
It is recognized that the flatness is poor when the thickness is less than m, but it can be used depending on the usage, and is indicated by a △ mark.

(2) Thermal dimensional stability Evaluated by thermal shrinkage rate. Since the required temperature differs depending on the material and application, the evaluation is shown each time. Other evaluation methods are as follows. Film width 10mm, length 300m
m, and marks are placed in the center in the longitudinal direction at intervals of 200 mm. A load of 3 g is applied to this sample, the sample is processed at the temperature and processing time to be measured, and then the interval (L) between the mark positions described above is read and determined by the following equation. Heat shrinkage rate (%) = (200-L)/200x100

0
(3) Between the bowing longitudinal direction stretching process and the width direction stretching process, a thread was stretched in the direction perpendicularly across the film just above the running film, and the thread was impregnated with ink and the stretched thread was lifted. It is then separated and momentarily brought into contact with substantially the entire width of the film surface, and a line is drawn with ink on the film surface. By measuring how curved this line is on the final biaxially stretched film, that is, by measuring the maximum deviation from the straight line that crosses the film at right angles in the width direction, the Boeing The degree was evaluated using the following criteria. ○: Maximum deviation from the straight line is less than 5 mm/per m width △: Maximum deviation from the straight line is 5 mm or more and less than 30 mm/per m width ×: Maximum deviation from the straight line is 30 mm or more/per m width

0
031]

EXAMPLES The present invention will be explained below based on examples. Examples 1-2 In the examples, polyethylene terephthalate ([η
] = 0.6) was fed to the extruder and melted at 290°C,
After being discharged from a T-die nozzle, it was adhered and solidified by electrostatic charge onto a cooling drum whose surface temperature was 30°C. 90% of this film
The film was stretched 4.5 times in the longitudinal direction at 90°C using a difference in peripheral speed of the rolls, and then 4.0 times in the width direction at 90°C and a stretching speed of 2000%/min in a tenter. Immediately after stretching in the width direction, Using the device shown in Figure 1, the biaxially stretched film was then floated in an arc shape with a wrapping angle of 270°, and the temperature of the hot air blown out from the inside of the arc was set to 150°.
The heat treatment was carried out at a temperature of 5% in the longitudinal direction. Subsequently, the film was introduced into an oven, heat-treated at 200° C. with 5% relaxation in the width direction, and after cooling, it was wound up. In Example 2, compared to Example 1, the longitudinal relaxation rate was changed within the range of the present invention. As shown in Table 1, by the reheat treatment method of the present invention, a biaxially stretched polyester film with extremely low bowing and excellent heat shrinkage and flatness was obtained.

Comparative Examples 1 to 3 In Comparative Example 1, the relaxation rate was set to 0 in the longitudinal direction relaxation treatment step in the above example, and only heat treatment was performed under a constant length without any relaxation treatment. In this case, a biaxially stretched polyester film was obtained under the same conditions as in Example 1 in a manufacturing process that does not include a longitudinal relaxation treatment step, that is, a step in which only a width direction relaxation treatment is performed after stretching in the width direction. Ta. As a result, as shown in Table 1, the degree of bowing was greater than in each of the above examples, and the heat shrinkage rate and
Only a product with poor flatness was obtained.

[0033]

[Table 1]

[Brief explanation of the drawing]

FIG. 1 is a schematic side view of a film manufacturing process according to the method of the present invention.

FIG. 2 is a plan view of the manufacturing process of FIG. 1;

FIG. 3 is an enlarged longitudinal sectional view of a longitudinal relaxation treatment step in the manufacturing process of FIG. 1;

FIG. 4 is a schematic side view showing a modification of the process shown in FIG. 3;

FIG. 5 is a schematic side view of a film manufacturing process according to a method of the present invention according to an embodiment different from that shown in FIG. 1;

FIG. 6 is a schematic perspective plan view of a stenter for explaining Boeing.

[Explanation of symbols]

1 Unstretched film 2 Longitudinal stretching process 3 Stenter 5 Width stretching zone 6 Biaxially stretched film 7, 20 immediately after width stretching
Longitudinal relaxation treatment means 8, 14 Guide roll 9 Hot air blowing nozzles 10, 10a, 10b Hot air blowing means 11 Tangential direction 12 Direction inside the tangent 13 Biaxially stretched film 15 after longitudinal relaxation treatment
Oven 16 Width direction relaxation treatment zone 18 Biaxially stretched film 19 after width direction relaxation treatment
oven

Claims (4)

[Claims] 1. Immediately after a film made of a thermoplastic resin is biaxially stretched in the longitudinal direction and the width direction of the film, a relaxation treatment is performed in the longitudinal direction of the film, and then a relaxation treatment is performed in the width direction of the film. A method for producing a thermoplastic resin film. 2. The relaxation treatment in the longitudinal direction of the film is performed by:
2. The thermoplastic resin film according to claim 1, wherein the film is floated in an arc shape along the arcuate surface of a hot air blowing means having an arcuate longitudinal section, and the film is subjected to a relaxation treatment in the longitudinal direction during the floatation. Production method. 3. The method for producing a thermoplastic resin film according to claim 2, wherein at the final hot air blowing position of the hot air blowing means in the film running direction, the film is guided inward from the tangential direction of the arcuate surface of the hot air blowing means. 4. The relaxation treatment in the longitudinal direction of the film is performed by:
2. The method of manufacturing a thermoplastic resin film according to claim 1, wherein the film is passed between a plurality of rolls and the difference in circumferential speed between the rolls is utilized.