JPH04292934A - Manufacture of thermoplastic resin film - Google Patents

Abstract

PURPOSE:To improve the planeness and the thermal dimensional stability of a film concerned by a method wherein thermoplastic film is floatingly run along the arcuate surface of a hot air blowing-off means having an arcuate profile just after its biaxial stretching so as to carry out heat treatment biaxially during its floating running. CONSTITUTION:Un-stretched film 1 is stretched lenghwise in longitudinal. stretching process, in which a plurality of rolls and the like are arranged, pre- heated in the pre-heating zone 4 of a stenter 3 and, after that, stretched widthwise in its stretching zone 5. Next, the resultant biaxially stretched thermoplastic film 6 is heat-treated (for example, relaxation-treated) lengthwise and widthwise simultaneously with a floating type heat-treating means 7. Concretely, the film 6, which is introduced through a guide roll 8 into the floating type heat-treating process, is floatingly run in arcuate fashion along the arcuate surface of a hot air blowing-off means 1.0 having a plurality of hot air blowing- off nozzles 9 and an arcuate profile so as to heat-treat the film lengthwise and widthwise during its floating running. After that, the film is taken up to a spool 18 on a core 17.

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 then subjected to heat treatment such as relaxation treatment in the width direction in the stenter. It is manufactured by applying In such a biaxial stretching method, 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. 5, 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 widthwise relaxation treatment zone 106 is often provided after a widthwise stretching zone 104 and a heat treatment zone 105, but since bowing is a phenomenon in which the film curves in the longitudinal direction of the film, once it occurs, It is difficult to repair things. 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 greatly impaired, but also the various mechanical properties (strength, (elongation, Young's modulus, F5 value, etc.), thermal shrinkage rate, temperature, humidity expansion coefficient, optical properties, etc., vary in the width direction, making it difficult to use depending on the application. In addition, if the width of the machine becomes large or the rigidity in the longitudinal direction after lateral stretching becomes large, bowing becomes larger, which becomes a problem.

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 conventional method described above involves reheating the heat-treated film after passing through the oven, and is not effective in improving the bowing that occurs within the stenter, or even if it is, it is extremely small. 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. moreover,
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]

[Problems to be Solved by the Invention] The present invention improves the bowing that occurs during width direction stretching and heat treatment in a stenter in the conventional stretching method as described above, and improves bowing in both the longitudinal and width directions of the film. A method for producing a film that can produce a thermoplastic resin film with excellent flatness and thermal dimensional stability even if the biaxially stretched film characteristics do not meet specific conditions by appropriately performing the intended heat treatment. The purpose is to provide

[0007]

[Means for Solving the Problems] The 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 film longitudinal direction and the film width direction, and then straighten the film in an arcuate longitudinal direction. The film is made to float in an arc along the arcuate surface of a hot air blowing means having a surface, and the film is heat-treated substantially simultaneously in both the film longitudinal direction and the film width direction during the floating motion. .

[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 biaxial stretching in the present invention may be either sequential biaxial stretching in which the film is stretched in the longitudinal direction and then in the width direction, or simultaneous biaxial stretching in which the film is stretched substantially simultaneously in the longitudinal direction and the width direction. Even in simultaneous biaxial stretching, the bowing phenomenon occurs because the edges on both sides of the film in the width direction are restrained when the film moves from stretching to heat treatment.

In the method of the present invention, immediately after the film is biaxially stretched by the above method, the film is levitated in an arc along the arcuate surface of a hot air blowing means having an arcuate longitudinal section, and the levitated film is During running, the film is heat-treated substantially simultaneously in both the film longitudinal direction and the film width direction. The heat treatment may be accompanied by a relaxation treatment, or may be performed under a substantially constant length. That is, in the method of the present invention, unlike the conventional method, heat treatment in the width direction is not performed after stretching in the width direction, but heat treatment in both the longitudinal direction and the width direction is performed immediately after this biaxial stretching. They are done at the same time.

[0011] Immediately after biaxial stretching, the film is released from the restraints on both sides in the width direction and becomes substantially free in the longitudinal direction due to floating running, so that bowing, which is a bending strain in the longitudinal direction, occurs. The force that acts on the film to cause this is substantially cut in this floating heat treatment section, and the bowing is improved extremely efficiently. By improving the bowing at this stage and performing the necessary heat treatment in both the longitudinal and width directions, the thermal dimensional stability and flatness of the final biaxially stretched film are greatly improved. Also, variations in properties such as mechanical properties (strength, elongation, Young's modulus, F5 value, etc.), thermal shrinkage rate, temperature, humidity expansion coefficient, optical properties, etc. depending on the position in the film width direction can be suppressed to an extremely small level.

[0012] Conventionally, this part could only be heat-treated in the width direction of the film within the stenter, and if the film was to be heat-treated in the longitudinal direction after biaxial stretching, the only way was to process it by a roll method or the like after the stenter. but,
Since the heat treatments are performed at different times, it is difficult to uniformly perform the desired heat treatment (for example, relaxation treatment) in all two-dimensional directions. However, in the method of the present invention, during the film floating run, the film is kept in a free state in virtually all two-dimensional directions, and it is possible to apply the desired heat load, so it is extremely uniform in both the longitudinal and width directions. heat treatment becomes possible.

Furthermore, in the above-mentioned floating heat treatment, the film is floated in an arc shape to give the film a degree of freedom and to swell the film, thereby making it difficult for wrinkles to form in the film. Furthermore, surface defects such as scratches are also prevented because the vehicle travels in a floating manner. Furthermore, by adjusting the length of the arc, it is also possible to provide sufficient heat treatment (relaxation treatment) time.

[0014] In addition, in the above-mentioned floating heat treatment, depending on the pressure (wind speed) and temperature of the hot air blown out, there is a risk that wrinkles may occur in the longitudinal direction of the film if the film is simply floated in an arc shape. , it is preferable to do as follows. The film introduced into this heat treatment step is floated in an arc along the arcuate surface of the hot air blowing means having an arcuate longitudinal cross section, and heat-treated in both the longitudinal and width directions during the floatation. In particular, at the final hot air blowing position of the hot air blowing means in the film traveling 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 heat treatment is carried out and completed without any wrinkles, the flatness of the film after treatment is maintained extremely well.

Regarding the occurrence of wrinkles, there is a significant 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. arise. In other words, by restricting it inward from the tangential direction, wrinkles can be completely prevented from forming.

Furthermore, in the floating heat treatment in the method of the present invention, even if the hot air blowing means is covered with an oven or the like,
Even if the hot air is circulated, the overall size of the oven and the hot air circulation path can be made smaller compared to conventional stenter systems. Therefore, even if there are oligomers, volatile additives, etc. that precipitate from the film, they are less likely to adhere to the hot air circulation system, and even if they float in the hot air, they can be easily removed with a filter or the like. As a result, the occurrence of film surface defects caused by these oligomers and additives is prevented, and a film with excellent surface quality can be obtained.

Furthermore, in the floating heat treatment in the method of the present invention, the relaxation rate and the like can be controlled by controlling the speed of the blown hot air. That is, the blown hot air escapes between the hot air blowing means and the floating film in the film longitudinal direction and width direction, but the hot air escaping in the film width direction exerts a force on the film to spread the film in the width direction. . On the other hand, since the film is also in a free state in the width direction, it tends to shrink in the width direction by heating. By balancing the force in the width expansion direction and the force in the width reduction direction, the relaxation rate can be adjusted and heat treatment can be performed under a constant length. The force in the width expanding direction is mainly controlled by the speed of the hot air blown from the hot air blowing means.

Regarding the relaxation treatment in the longitudinal direction of the film,
By adjusting the film running speed at the inlet and outlet of this floating heat treatment process, it can be set virtually freely.If the outlet side is 5% slower than the inlet side, a 5% relaxation process can be performed, and the inlet side can be relaxed by 5%. If the velocity on the exit side is the same as that on the exit side, heat treatment can be performed under a fixed length.

The method for producing the thermoplastic resin film of the present invention as described above is carried out, for example, as shown in FIGS. 1 to 3. In FIGS. 1 and 2, an unstretched film 1 is stretched in the longitudinal direction in a longitudinal stretching step 2 using a plurality of rolls, etc., preheated in a preheating zone 4 of a stenter 3, and stretched in the width direction in a stretching zone 5. be done. Immediately after the biaxial stretching, this biaxially stretched thermoplastic film 6 is subjected to heat treatment (for example, relaxation treatment) substantially simultaneously in both the longitudinal direction and the width direction by the floating heat treatment means 7. Guide roll 8
The film 6 introduced into the floating heat treatment process is shown in FIG.
As shown in FIG. 2, the hot air blowing means 10 having a plurality of hot air blowing nozzles 9 and having an arcuate vertical cross section is floated in an arc shape along the arc-shaped surface, and heat treatment is performed in both the longitudinal direction and the width direction during the floating run. be done. Then, at the final hot air blowing position in the film running direction (the position of the final hot air blowing nozzle 9a), the tangential direction 1 of the arcuate surface of the hot air blowing means 10 is
The film is drawn out in a direction 12 inward from direction 1. In the figure, it is directed inward by an angle θ. The extracted film 13 passes through a guide roll 14 and then a transport roll 15.
, 16 (for example, cooling rolls), and is wound onto a core 17 as a spool 18 of biaxially stretched film. The floating heat treatment step is also preferably covered with an oven 19, and heating is controlled to a predetermined temperature while hot air is circulated. In the above, by setting the film outlet direction 12 at the outlet of the hot air blowing means to be inside the tangential direction 11, the occurrence of wrinkles is completely prevented, and while the bowing is improved by floating heat treatment, thermal dimensional stability is ensured. (maintained at a low heat shrinkage rate) and a film with extremely good flatness can be obtained.

[0020] 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.

[0021] 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.

This arc-shaped floating heat treatment process is shown in FIG.
Two or more hot air blowing means 10a in succession as shown in FIG.
, 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. In addition, when a plurality of stages of hot air blowing means are provided in this way, it is also possible to change the temperature settings for each stage, such as a temperature suitable for longitudinal heat treatment and a temperature suitable for width direction heat treatment. For example, in the case of a polyester resin film, the temperature conditions for the heat treatment for longitudinal relaxation are 90-230°C.
Preferably, the treatment is carried out in the temperature range of °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. Further, it is also preferable to perform processing by changing the temperature of each nozzle within the same arc-shaped processing device from the viewpoint of improving flatness and preventing bowing.

Furthermore, as shown in the figure, this arc-shaped heat treatment has a structure in which hot air is blown from the inside of 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 multiple nozzles. 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. As described above, the wind speed may be set within this range according to the target relaxation rate, etc.

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.

The treatment time for the floating heat treatment is preferably 1 to 30 seconds, preferably 5 to 20 seconds, although it depends on the type of thermoplastic resin used. If it is less than 1 second, 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.

The relaxation in the longitudinal direction during this heat treatment varies depending on the characteristics of the film before heat treatment, but the relaxation rate is preferably 15% or less, preferably 8% or less. This will greatly improve Boeing. Although thick edges may be included during this relaxation treatment, it is preferable to slit the edges before this treatment, which is more preferable from the viewpoint of flatness and prevention of bowing.

Furthermore, in the floating heat treatment process, hot air is preferably blown from the opposite side (outside) of the film, in addition to being blown from the inside of the arc at the above-mentioned wind speed, from the viewpoint of preventing 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.

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 each of the longitudinal and width directions. After performing this floating heat treatment, it is heat-set if necessary, and after cooling, it is wound up.

[0029]

[Effects of the Invention] According to the method for producing a thermoplastic resin film of the present invention, floating heat treatment is performed substantially simultaneously in both the longitudinal direction and the width direction immediately after biaxial stretching, so that bowing can be significantly reduced in this processing step. A biaxially stretched thermoplastic resin film with improved thermal dimensional stability and extremely flatness can be obtained. Furthermore, the floating heat treatment can be carried out more efficiently using a smaller device than a conventional stenter or the like, so that stains caused by oligomers, additives, etc. can be easily prevented.

[0030]

[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 (evaluated 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, cannot be used 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 a direction perpendicular to 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
(4) Amount of surface oligomer The film was immersed in ethanol and washed with ultrasonic treatment for 90 seconds. After concentrating this liquid, acetonitrile was added and analyzed by high performance liquid chromatography (HPLC).

[0034]

EXAMPLES The present invention will be explained below based on examples. Examples 1 and 2 In Example 1, polyethylene terephthalate ([
η]=0.6) was supplied to an extruder, melted at 290°C, discharged from a T-die nozzle, and solidified by electrostatic charge on a cooling drum with a surface temperature of 30°C. This film is 9
Stretched 4.5 times in the longitudinal direction at 0°C due to the difference in peripheral speed of the rolls,
Subsequently, the biaxially stretched film was stretched 4.0 times in the width direction at 90° C. and a stretching speed of 2000%/min in a tenter, and immediately after stretching in the width direction, the biaxially stretched film was further stretched using the apparatus shown in FIG. The winding angle is 2 for both hot air blowing means so as to draw an arc shape.
The temperature of the hot air blown out from the arc-shaped interior was set to 230℃, and the temperature was 5.0% in the longitudinal direction.
The heat treatment was performed while relaxing 5.0% in the width direction. The heat-treated film was cooled and then wound up. In Example 2, the relaxation rate was 1.5% in the longitudinal direction and 1.5% in the width direction.
The other conditions were the same as in Example 1. As shown in Table 1, by the heat 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 and 2 The same conditions as in Example 1 were used in a manufacturing process that did not include a floating heat treatment process, that is, a process in which only a widthwise relaxation treatment was performed in the same stenter after widthwise stretching. A biaxially stretched polyester film was obtained. Comparative Example 2 was clipped off in the longitudinal direction and then treated using an infrared heater at the relaxation rate shown in Table 1. 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.

[0036]

[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 vertical cross-sectional view of a floating heat treatment step in the manufacturing process of FIG. 1;

FIG. 4 is a schematic side view of a film manufacturing process according to a method of the present invention according to a different embodiment from FIG. 1;

FIG. 5 is a schematic perspective plan view of a stenter for explaining Boeing.

[Explanation of symbols]

1 Unstretched film 2 Longitudinal stretching step 3 Stenter 5 Width stretching zone 6 Biaxially stretched film 7 immediately after biaxial stretching Floating heat treatment means 8, 14 Guide roll 9 Hot air blowing nozzles 10, 10a, 10b Hot air blowing means 11 Tangent line Direction 12 Direction inside the tangent 13 Biaxially stretched films 15, 16 after floating heat treatment
Conveyance roll 18 Spool 19 Oven

Claims (3)

[Claims] 1. Immediately after a film made of a thermoplastic resin is biaxially stretched in the film longitudinal direction and the film width direction, the film is levitated in an arc shape along the arc surface of a hot air blowing means having an arc longitudinal section. . A method for producing a thermoplastic resin film, characterized in that the film is heat-treated substantially simultaneously in both the film longitudinal direction and the film width direction during the floating run. 2. The method for producing a thermoplastic resin film according to claim 1, 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. 3. A plurality of hot air blowing means are arranged in the film running direction, and downstream of the upstream hot air blowing means, another hot air blowing means having an inverted arcuate longitudinal section is provided, and the upstream hot air blowing means 3. The method for producing a thermoplastic resin film according to claim 1, wherein the film is continuously floated and run from the hot air blowing means to the hot air blowing means on the downstream side.