JPH04270641A - Preparation of thermoplastic resin film - Google Patents

Abstract

PURPOSE:To obtain a film excellent in thermal dimensional stability and flatness by applying reheating treatment even to a film wherein the characteristics of a biaxially stretched film subjected to reheating treatment are not specific without generating wrinkles. CONSTITUTION:In a process subjecting a heat-treated biaxially stretched film composed of a thermoplastic resin to reheating treatment, the film introduced into a reheating treatment process is allowed to glide along the arc surface of a hot air blowoff means having an arc longitudial cross section so as to draw an arc and subjected to slackening treatment during the gliding and led out at the final hot air blowoff position in the film gilding direction of the hot air blowoff means in the direction inside the tangential direction of the arc surface of the hot air blowoff means.

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] As a means of imparting thermal dimensional stability, Japanese Patent Laid-Open No. 2-22038 discloses a method in which a film having specific film characteristics is formed into a curved surface by blowing heated air from one side of the film. A method has been proposed in which the material is floated and subjected to relaxation heat treatment.

0003

However, the above-mentioned conventional method for obtaining thermal dimensional stability has the following problems, and there are problems in putting it into practical use. First, the characteristics of the film before the floating relaxation treatment must be set under specific conditions, and unless the film has those characteristics, sufficient thermal dimensional stability cannot be obtained. The same goes for satisfying thermal dimensional stability while also having flatness, and good flatness cannot be obtained unless a film under specific conditions is prepared. In particular, when the film is floated along a curved surface, wrinkles are generated that extend in the running direction, and these wrinkles deteriorate the flatness of the film.

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 before heat treatment do not meet specific conditions. shall be.

[0005]

[Means for Solving the Problems] The method for producing a thermoplastic resin film of the present invention in accordance with this object includes a step of heat-treating a biaxially stretched film made of a thermoplastic resin and then reheating the film. The introduced film,
The hot air blowing means having an arcuate longitudinal cross section is floated in an arc shape along the arcuate surface, the film is loosened in the longitudinal direction during the floating run, and the hot air blowing means is at the final hot air blowing position in the film running direction. , a method in which the film is guided inward from the tangential direction of the arcuate surface of the hot air blowing means.

[0006] 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.

[0007] The biaxially stretched film in the present invention refers to a film subjected to sequential biaxial stretching in which the film is stretched in the longitudinal direction and then stretched in the width direction, or a film subjected to simultaneous biaxial stretching in which the longitudinal direction and the width direction are stretched almost simultaneously. However, the stretching method is not particularly limited.

Further, the heat treatment in the present invention is not particularly limited, and any known heat treatment method may be used. For example, after the biaxial stretching is completed, the film is subjected to tensioning and relaxing heat treatment in the longitudinal and/or width directions at a temperature of about (melting point -5)°C to (melting point -70)°C for about 1 to 30 seconds. (Hereinafter, when we refer to a biaxially stretched film, we refer to a film that has undergone these heat treatments unless otherwise specified).

[0009] The reheat treatment in the present invention refers to a step of heat-treating the above-mentioned biaxially stretched film again, and in particular, in the present invention, a relaxation treatment in the longitudinal direction of the film is performed. This reheat treatment further improves the thermal dimensional stability of the resulting film, more specifically the thermal shrinkage rate.

[0010] In the method of the present invention, it is necessary to carry out the above-mentioned reheating treatment by floating the object in an arcuate manner using hot air. 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. Further, by adjusting the length of the arc, it is possible to provide sufficient reheating time.

However, it is difficult to reliably prevent the formation of wrinkles extending in the longitudinal direction of the film as described above simply by floating the film in an arc shape, and when such wrinkles occur, the flatness of the film is greatly impaired.

In the method of the present invention, the film introduced into the reheating step 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 float run, the film is moved in the longitudinal direction. During the relaxation process, the film is guided inward from the tangential direction of the arcuate surface of the hot air blowing means at the final hot air blowing position of the hot air blowing means in the film running direction. 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 reheat treatment is performed and completed in a state where no wrinkles are generated, the flatness of the film after treatment is extremely good.

[0013] 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.

[0014] The above-mentioned reheat treatment step and film derivation are performed, for example, as shown in FIGS. 1 to 3. Figure 1,
In FIG. 2, the unstretched film 1 is stretched in the longitudinal direction in a longitudinal stretching step 2, and the film 1 is stretched in the preheating zone 4 of the tenter 3.
Preheating in Stretching Zone 5, stretching in the width direction in Stretching Zone 5, Heat Treatment Zone 6
The film is heat-set or, if necessary, relaxed in the width direction, and then formed into a biaxially stretched thermoplastic film 7. This biaxially stretched thermoplastic film 7 is reheated by a reheating means 8 provided at the outlet of the tenter, and subjected to a relaxation treatment in the longitudinal direction. As shown in FIG. 3, the film 7 introduced into the reheating process from the guide roll 9 is transferred to a hot air blowing means 1 having a plurality of hot air blowing nozzles 10 and having an arcuate longitudinal section.
It is floated in an arc shape along the arc-shaped surface of No. 1, and is subjected to a relaxation treatment in the longitudinal direction during the floatation run. Then, at the final hot air blowing position in the film running direction (the position of the final hot air blowing nozzle 10a), the film is drawn out in a direction 13 inside the tangential direction 12 of the arcuate surface of the hot air blowing means 11. In the figure, it is directed inward by an angle θ. The drawn-out film is cooled by a cooling means, for example, a cooling roll 14.
After passing through, the film is sent to a winding process etc. as a reheat-treated film 15. In the reheating process, the oven 16 is used to control heating to a predetermined temperature while circulating hot air. In this way, the film leading direction 13 at the exit is
By placing the film on the inside of the tangential direction 12, the generation of wrinkles is completely prevented, and the thermal dimensional stability is ensured by reheating (maintaining a low heat shrinkage rate), while a film with extremely good flatness can be obtained. It will be done.

[0015] 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.

[0016] 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.

In addition, this arc-shaped reheating process is performed by consecutively using two or more hot air blowing means 11a, 1 as shown in FIG.
1b, and 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.

This arc-shaped reheating process has a structure in which hot air is blown from the inside of the arc, as shown in the figure, and has a hot-air blowing nozzle consisting of a slit or the like extending in the film width direction. It must have a nozzle. The speed of the hot air blown out in this arcuate reheating process is preferably 5 to 200 m/sec, and if it is less than 5 m/sec, the processing effect will be reduced and the film will meander. Moreover, if the speed exceeds 200 m/sec, the film will flap, causing scratches.

Further, in this arcuate reheating step, it is preferable to provide a baffle plate 1 to 20 mm outward from the edge of the film with a distance of about 10 mm from the flying height of the film to the flying height of the film. 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.

As for the temperature conditions for the reheat treatment, it is preferable to carry out the treatment in a temperature range from below the above-mentioned heat treatment temperature to above the secondary transfer temperature. Temperatures requiring thermal dimensional stability (±20
℃)

The treatment time depends on the type of thermoplastic resin used, but is 0.1 to 30 seconds, preferably 1 to 20 seconds.
Seconds are good. 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.

[0022] Further, this reheat treatment requires relaxation in the longitudinal direction, and although this varies depending on the characteristics of the film before the reheat treatment, the relaxation rate is preferably 15% or less, preferably 8% or less. .

In addition to blowing hot air from the inside of the arc at the above-mentioned speed, it is preferable to blow hot air from the opposite side (outside) of the film in the reheating step to prevent curling. 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.

Furthermore, the temperature in the steps from width direction stretching and heat treatment to reheat treatment may be below Tg (glass transition point), but by keeping it at 100 to 180°C, flatness and dimensional stability can be improved. It is preferable because it has excellent properties.

[0025] In the method of the present invention, cooling subsequent to the reheat treatment is also important. The cooling process is located on or inside the tangent of the arc, and/or while tracing an arc in the opposite direction (e.g. hot air blowing means 1 in FIG. 4).
1b as a cold air blowing means), it is desirable to lower the reheat treatment temperature to 40° C. or lower. If this condition is not met, there is a risk that the film will be prone to wrinkles, which may cause problems such as deterioration of flatness.

The cooling time at this time is preferably 1 minute or less, more preferably 30 seconds or less, and even more preferably 0.001 to 20 seconds. Cooling time that is too early or too slow will lead to deterioration of flatness and generation of wrinkles. For this reason, it is preferable to control the temperature of the cooling roll 14 or the arc-shaped cooling device so as to satisfy the above-mentioned cooling time depending on the mounting position thereof.

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℃.
After stretching 2 to 6.5 times in the longitudinal direction at 80 to 160°C and 3 to 5 times in the width direction, heat treatment is performed at 180 to 240°C. At this time, relaxation may be performed in the width direction and the longitudinal direction if necessary. This stretching is just one example, and it may be two-stage longitudinal stretching and then transverse stretching, or biaxial stretching and then longitudinal stretching again. If multi-stage stretching, particularly in the longitudinal direction, is performed during the above steps and combined with this method, a product with even better thermal dimensional stability can be obtained. Next, the biaxially stretched film is continuously wrapped in an arc shape at an angle of 120° to
It is floated at 270 degrees, the temperature of the hot air blown out from the arc-shaped interior is set to 60 to 200 degrees Celsius, and the reheating treatment is performed while relaxing 10% or less in the longitudinal direction. A cooling roll is arranged so that the cooling time from the reheating temperature to 40° C. is 0.1 to 20 seconds and the film runs inward from the tangent to the arc, and after cooling, it is wound up.

[0028]

Effects of the Invention According to the method for producing a thermoplastic resin film of the present invention, the film can be relaxed in the longitudinal direction without causing any wrinkles in the reheating process, so it has excellent thermal dimensional stability. Moreover, a biaxially stretched thermoplastic resin film with extremely excellent flatness can be obtained. Furthermore, target reheat treatment conditions can be easily and stably set, and desired reheat treatment can result in a material with a significantly reduced amount of surface oligomers.

[0029]

[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) 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).

[0032]

EXAMPLES The present invention will be explained below based on examples. Examples 1 to 3 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 by the difference in circumferential speed of the rolls, then 4.0 times in the width direction at 90°C in a tenter at a stretching rate of 2000%/min, and then stretched at 200°C at a constant length. The sample was heat-treated for 5 seconds. Using the apparatus shown in FIG.
The specimen was floated at 0°, the temperature of the hot air blown out from the arc-shaped interior was set to 150°C, and reheat treatment was performed while relaxing the specimen by 5% in the longitudinal direction. Taking natural cooling into consideration, the film was cooled so that the cooling time from the temperature of the reheat treatment to 40° C. was 3 seconds, and then the film was wound up. In Examples 2 and 3, compared to Example 1, various conditions were changed within the scope of the present invention. As shown in Table 1, by the reheat treatment method of the present invention, a biaxially stretched polyester film excellent in heat shrinkage rate, flatness, and surface oligomer content was obtained.

Comparative Examples 1 to 3 In the above examples, when the angle at which the film was taken out in the reheating process was set to be on the outside with respect to the tangential direction of the arc of the hot air blowing means, many wavy wrinkles were generated on the film. However, the flatness was poor. Furthermore, because the reheat treatment was not stable, it was difficult to obtain the target heat shrinkage rate, and the variation was large. In addition, in Comparative Example 3,
When reheat treatment was not performed, the heat shrinkage rate did not decrease and the amount of surface oligomers increased.

[0034]

[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 shown in FIG. 1;

3 is an enlarged vertical cross-sectional view of a reheat treatment step in the manufacturing process of FIG. 1. FIG.

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

[Explanation of symbols]

2 Longitudinal stretching process 3 Tenter 5 Width direction stretching zone 7 Biaxially stretched film 8 Reheating process 10 Hot air blowing nozzles 11, 11a, 11b Hot air blowing means 12 Tangential direction 13 Direction inside the tangent 14 Cooling roll 15 Reheating film

Claims (3)

[Claims] [Claim 1] In the step of heat treating a biaxially stretched film made of a thermoplastic resin and then reheating the film, the film introduced into the reheating step is passed along an arcuate surface of a hot air blowing means having an arcuate longitudinal section. The film is levitated in an arc shape, and during the levitated run, the film is loosened in the longitudinal direction, and at the final hot air blowing position of the hot air blowing means in the film running direction, the hot air blowing means is placed inside the tangential direction of the arcuate surface of the hot air blowing means. 1. A method for producing a thermoplastic resin film, characterized in that the film is produced in a direction. 2. The method for producing a thermoplastic resin film according to claim 1, wherein the step following the relaxation treatment by floating is a film cooling step. 3. Another hot air blowing means having an inverted arcuate longitudinal section is further provided downstream of the hot air blowing means in the film traveling direction, and the film is continuously passed from the hot air blowing means to the other hot air blowing means. 2. The method for producing a thermoplastic resin film according to claim 1, wherein the thermoplastic resin film is carried out while floating.