JPH04292937A - Manufacture of thermoplastic resin film - Google Patents

Abstract

PURPOSE:To improve the planeness and the thermal dimensional stability of the film concerned by a method wherein biaxially stretched thermoplastic resin film is heat-treated and then the re-heat-treatment of the film is carried out by blowing-off steam from a steam blowing-out means under the condition that the film is floatingly run on the steam blowing-off means, in the re-heat- treating process of the film. CONSTITUTION:Unstretched film 1 is stretched lengthwise in longitudinal stretching process 2 and then, after being preheated in the preheating zone 4 of a tenter 3, stretched widthwise in its stretching zone 5. Further, the film is heat-set or relaxation-treated widthwise in the heat treating zone 6 of the tenter so as to be turned in biaxially stretched thermoplastic film 7. Next, the film is re-heat-treated with a re-heat-treating means 8 so as to be relaxation- treating lengthwise. Concretely, the film 7, which is introduced through a guide roll 9 into the re-heat-treating process, is floatingly run in arcuate fashion along the arcuate surface of a steam blowing-off means 11 having a plurality of steam blowing-off nozzles 10 and an arcuate profile so as to re-heat-treat, including relaxation treatment, in the longitudinal direction during its floating running.

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. Furthermore, since it is a reheat treatment after (biaxial) stretching, it needs to be carried out at a fairly high temperature, but since the film is heated with heated air, the heat transfer coefficient is not so high, and the film is heated to a specified temperature for a specified period of time. For heat treatment, the equipment must be quite large.

The present invention focuses on the above-mentioned problems of the conventional floating reheating treatment using heated air, and even if the biaxially stretched film characteristics before the reheating treatment do not meet specific conditions, the film can be easily reheated. It is an object of the present invention to provide a method for producing a film that can be reheated efficiently under relatively low temperature conditions using a small device, and that can produce a thermoplastic resin film that has excellent flatness and thermal dimensional stability.

[0005]

[Means for Solving the Problems] The method for producing a thermoplastic resin film of the present invention in accordance with this object includes heat-treating a biaxially stretched film made of a thermoplastic resin, and then reheating the film by steaming the film. It consists of a method in which reheating treatment is carried out using steam blown out from the steam blowing means while floating on the 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 particularly preferably includes a relaxation treatment in the longitudinal direction of the film in the present invention. 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 reheating treatment while floating and traveling with steam blown out from a steam blowing means. By reheating with steam, the heat transfer rate to the film is significantly increased compared to the conventional method using heated air, and the film is quickly heated to a predetermined temperature in a short period of time. Therefore, this steam blowing means can be significantly downsized compared to conventional heated air blowing means. In addition, this relaxation treatment using steam can greatly reduce the thermal shrinkage rate of the film.

Furthermore, since the heat transfer coefficient is good, the film can be efficiently heated to a predetermined temperature in a short time even if the temperature of the blown steam is relatively low, that is, lower than conventional heated air. Therefore, even under relatively low-temperature conditions, it is possible to obtain the same heat treatment effect as in the case of high-temperature treatment using heated air, and moreover, it is possible to significantly reduce the thermal shrinkage rate.

[0012] The blown steam may be pressurized steam having an atmospheric pressure (1 atm) or higher, and can be arbitrarily set from a range of about 1 atm or more to 5 atm or less depending on the reheat treatment conditions.

The steam blowing means may be of a type in which steam blowing nozzles are simply arranged in the film running direction and the steam blowing nozzles are floated over the nozzles, but from the viewpoint of performing reheating treatment while preventing the occurrence of wrinkles etc. of the film, Preferably, it has an arcuate longitudinal section. That is, in this method, the film is floated in an arc along the arcuate surface of a steam blowing means having an arcuate longitudinal section, and during the floatation, the film is subjected to a reheat treatment, for example, a relaxation treatment in the longitudinal direction of the film.

[0014] As described above, by floating and traveling in an arc shape, the film can be made to swell while giving the film a degree of freedom, 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, simply floating the film in an arc shape cannot completely eliminate the possibility of wrinkles extending in the longitudinal direction of the film. Preferably, the film is drawn out in a direction inward from the tangential direction of the arcuate surface of the blowing means. By regulating the direction in which the film is led out in this way, the pressure of the steam blown out from the steam 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 occur at the outlet of the steam blowing means, wrinkles do not occur on the upstream arc surface either. 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.

[0016] 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 steam blowing position of the steam blowing means is restricted to be inside the tangential direction of the arcuate surface of the steam blowing means. arise. In other words, by restricting it to the inside of the tangential direction,
The appearance of wrinkles is completely prevented.

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 shaped like an arc along the arcuate surface of a steam blowing means 11 having a plurality of steam blowing nozzles 10 and having an arcuate longitudinal section. During the floating run, reheating treatment including relaxation treatment is performed in the longitudinal direction. Then, at the final steam blowing position in the film running direction (the position of the final steam blowing nozzle 10a), the tangential direction 12 of the arcuate surface of the steam blowing means 11 is
The film is drawn out in a direction 13 inwardly. In the figure, it is directed inward by an angle θ. The extracted film passes through a cooling means, for example, a cooling roll 14, and then is sent to a winding process or the like as a reheat-treated film 15. In the reheating process, the oven 16 is covered, and steam is supplied at a predetermined temperature and pressure, and the blown steam is collected by suction or recycled for use so as not to leak outside the oven 16. In this way, by setting the film leading-out direction 13 at the exit to be inside the tangential direction 12, the generation of wrinkles is completely prevented, and thermal dimensional stability is ensured through reheating (while maintaining a low thermal shrinkage rate). However, a film with extremely good flatness can be obtained.

In the above-mentioned arc-shaped floating run, it is preferable that the arc-shaped radius 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.

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.

Further, this arc-shaped reheating process is performed by continuously using two or more steam blowing means 11a as shown in FIG.
, 11b. 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 reheating process has a structure in which steam is blown out from inside the arc, and has a steam blowing nozzle consisting of a slit extending in the width direction of the film. Preferably one with a nozzle. The pressure of the blown steam in this arc-shaped reheating process is such that the speed of the blown steam is 5 to 2.
It is preferable to set the speed to 00 m/sec. If the steam blowing speed is less than 5 m/sec, the processing effect will be reduced and the film will become meandering. Moreover, if the speed exceeds 200 m/sec, the film will flap, causing scratches.

Further, in this arcuate reheating process, 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. 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.

[0023] Regarding 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 temperature of the steam itself has a good heat transfer rate to the film, so it can be much lower than the conventional case of using heated air.

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. Although this processing time depends on the processing temperature, film thickness, etc., it can be significantly shortened compared to the conventional case using heated air.

[0025] Further, in this reheat treatment, it is desirable to perform relaxation in the longitudinal direction. Although it varies depending on the characteristics of the film before reheating, the relaxation rate is 15% or less,
It is preferably 8% or less.

In the reheating process, steam may be blown from the opposite side (outside) of the film, in addition to being blown from the inside of the arc at the speed described above. This can also help prevent film curling. However, the steam blowing speed in this case must be inside>outside. If the speed on the outside is the same or higher, problems such as wrinkles and scratches may occur in 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, even better flatness and dimensional stability can be achieved. It is preferable because it has excellent properties.

In the method of the present invention, cooling following the floating reheat treatment is also important. from the reheat treatment temperature so that the cooling step is located on or inside the tangent of the arc, and/or while tracing an arc in the opposite direction (for example, using the steam blowing means 11b in FIG. 4 as a cold air blowing means). It is desirable to lower the temperature to below 40°C. 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℃.
The film is stretched 2 to 9.0 times in the longitudinal direction (a two-step longitudinal stretching method may be used), and then stretched 3 to 5 times in the width direction at 80 to 120°C, and then heat treated 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 above-mentioned biaxially stretched film is continuously floated in an arc shape at a winding angle of 120° to 270°, and the temperature of the steam blown out from inside the arc is adjusted to 60° to 270°.
Reheat treatment is performed at 200° C. with relaxation of 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.

[0031]

[Effects of the Invention] According to the method for producing a thermoplastic resin film of the present invention, the desired reheating treatment can be performed at a relatively low temperature and in a short time with a high heat transfer coefficient by performing the reheating treatment while floating the film with steam. Therefore, using a small device, it is possible to significantly reduce the thermal shrinkage rate of the film, and to obtain a biaxially stretched thermoplastic resin film with excellent thermal dimensional stability and extremely flatness. can. 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. Furthermore, even without relaxation, the same level of thermal dimensional stability can be obtained as with 2 to 5% relaxation treatment, and further dimensional stability can be obtained with several percent relaxation treatment.

[0032]

[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).

[0035]

EXAMPLES The present invention will be explained below based on examples. Examples 1 to 3 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 film was stretched 4.0 times in the width direction at 90° C. and a stretching rate of 2000%/min using a tenter, and then heat-treated at 200° C. for 5 seconds at a constant length. This biaxially stretched film was then wrapped in an arc shape using the apparatus shown in Figure 1, with a winding angle of 2
The specimen was floated at an angle of 70°, and the temperature of the steam blown out from the arc-shaped interior was set to 150° C., and reheat treatment was performed without relaxing 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 4 In Comparative Example 1, the apparatus shown in FIG. 1 did not have the reheat treatment means 8, and only the heat treatment within the stenter 3 was performed. In Comparative Examples 2 to 4, in the apparatus shown in FIG.
Heated air was sent to the film, and the film was reheated while being floated by the heated air. The temperature conditions etc. were the same as in Example 1. As a result, Comparative Example 1 was inferior in both heat shrinkage rate and flatness, and had a large amount of surface oligomers, as compared to the above-mentioned Examples. In Comparative Examples 2 to 4, although each characteristic was improved compared to Comparative Example 1, it was far inferior to the above-mentioned example using steam.

[0037]

[Table 1]

[Brief explanation of drawings]

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;

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 stretching zone 7 Biaxially stretched film 8 Reheat treatment process 10 Steam blowing nozzles 11, 11a, 11b Steam blowing means 12
Tangential direction 13 Direction inside the tangent 14 Cooling roll 15 Reheat treatment film

Claims (6)

[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 is reheated by blowing steam from the steam blowing means while floating on the steam blowing means. A method for producing a thermoplastic resin film, characterized by: 2. The method for producing a thermoplastic resin film according to claim 1, wherein the reheat treatment using the blown steam includes a relaxation treatment in the longitudinal direction of the film. 3. The relaxation treatment in the longitudinal direction of the film is performed by:
3. The method of producing a thermoplastic resin film according to claim 2, wherein the film is floated in an arc along an arcuate surface of a steam blowing means having an arcuate longitudinal cross section, and the film is subjected to a relaxation treatment in the longitudinal direction during the floatation. Production method. 4. The method for producing a thermoplastic resin film according to claim 3, wherein at the final steam blowing position in the film running direction of the steam blowing means, the film is guided inward from the tangential direction of the arcuate surface of the steam blowing means. 5. Another steam blowing means having an inverted arcuate longitudinal section is further provided downstream of the steam blowing means in the film running direction, and the film is continuously passed from the steam blowing means to the another steam blowing means. The method for producing a thermoplastic resin film according to claim 3 or 4, wherein the thermoplastic resin film is run in a floating state. 6. The method for producing a thermoplastic resin film according to claim 1, wherein the step following the reheating treatment by floating is a film cooling step.