JPS61222722A - Heat treatment of stretched film - Google Patents

Abstract

PURPOSE:To improve the dimensional stability due to heat treatment by also loosing longitudinally by a method wherein upstream side driving wheels and downstream side driving wheels are provided in a tenter and the peripheral speed of the downstream side driving wheel is made smaller than that of the upstream side driving wheel. CONSTITUTION:In a method to heat-treat uniaxially stretched film 1 while running in a tenter 2 under the state that both sides of the film are held with clips 3, the upstream side wheels and downstream side wheels among the running wheels of the clips are made as driving wheels. At the same time, the driving wheels are run under the condition that the peripheral speed of the downstream side driving wheel 5 is made smaller than that of the upstream side driving wheel 4. Because the stretched film is heat-treated under the state also of being loosen longitudinally due to the difference between the speeds of both said wheels, the dimensional stability is made better. Thus, the titled treatment is suitable for manufacturing magnetic tape and the like. In addition, the facilities for the treatment can simply be obtained, because the only replacement of the running wheels in the conventional device with driving wheels is enough.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a method for heat treating a stretched film in which a stretched film made of a thermoplastic resin that has been stretched in at least one axial direction is subjected to relaxation heat treatment in a tenter. .

[Prior Art] It is generally known that if a stretched film is relaxed in a certain direction under heating conditions, the heat shrinkage rate of the product film in that direction can be lowered and the dimensional stability of the film can be improved. □Ru. In particular, stretched films used in magnetic tapes, capacitors, etc. are required to have strict dimensional stability, and are also required to have dimensional stability under extremely low temperature conditions (70" 0 to 100°C). In order to meet such demands for dimensional stability, it is necessary to suppress the heat shrinkage rate of the stretched film as a product to a certain level or less in both the longitudinal direction and the width direction of the stretched film.

Therefore, appropriate relaxation heat treatment must be performed in the film manufacturing process.

As a method for relaxing a stretched film, the following method is usually used.

□To loosen the stretched film in the width direction, hold both sides of the stretched film with clips, run the stretched film together with the clips in the tenter, gradually reduce the distance between the clip running rails on both sides of the stretched film, and loosen the film. Relaxation treatment methods are known. However, in the loosening process using a tenter which has an adjustment mechanism only in the width direction of the film, it is usually not possible to loosen the film in the longitudinal direction.

Therefore, the relaxation treatment in the longitudinal direction of the film is performed by running the stretched film between rolls and using the difference in circumferential speed of each roll, that is, by setting the circumferential speed of the downstream roll smaller than that of the upstream roll. is taking.

Note that if you use a special type of tenter, for example, a known simultaneous biaxial stretching machine that can stretch the film in both the longitudinal and width directions, it is possible to loosen the stretched film in the longitudinal direction with the tenter. be.

[Problems to be Solved by the Invention] However, there are the following problems in the longitudinal direction relaxation treatment of stretched films using the conventionally known techniques as described above.

First, the method of loosening using the difference in circumferential speed of the rolls is not a method of gripping both sides of the film with clips and processing the film part that will become the product without contact, as in the loosening process in a tenter. Since this is a method in which the film is processed while running on the roll surface, there is a problem in that it is difficult to find conditions (roll circumferential speed, film temperature conditions, etc.) to process the film while keeping the speed difference between the film and the roll surface to zero. If the conditions are not set appropriately, the flatness of the film as a product may be impaired, or slippage may occur between the roll surface and the running film, resulting in fine scratches on the film surface.

In addition, if a simultaneous biaxial stretching machine is used as described above, it becomes possible to loosen the film in the longitudinal direction within a tenter, and the problems of flatness and film scratches mentioned above can be solved. All of these machines are expensive, have complicated mechanisms, and none of them can run at high speeds. Therefore, high productivity cannot be expected, and it is difficult to employ this method when the above-mentioned requirement for dimensional stability is easily satisfied using existing film manufacturing equipment.

Therefore, the present invention makes it possible to loosen the film in the longitudinal direction within the tenter by simply making improvements to the existing ordinary tenter, and allows the film to be relaxed at relatively low temperatures required for stretched films for magnetic tapes and capacitors. The purpose is to easily achieve a low heat shrinkage rate in the longitudinal direction of the film.

Means for Solving the Problem] The method for heat treating a stretched film of the present invention in accordance with this objective is as follows:
A stretched film heat treatment method in which both sides of a continuously fed stretched film are gripped with clips and the stretched film is heat-treated while the stretched film is run through a tenter by running the clips, and among the wheels for running the clip,
A wheel on the upstream side and a wheel on the downstream side in the running direction of the stretched film are both used as drive wheels, and a circumferential speed difference is provided between the two drive wheels such that the circumferential speed of the downstream drive wheel is smaller, The stretched film is relaxed between the two drive wheels in the direction of travel of the stretched film.

[Operation] In this heat treatment method, drive wheels are provided on the upstream and downstream sides of the tenter, and by creating a difference in circumferential speed between the two drive wheels, the running speed of the clips holding both sides of the stretched film can be adjusted. becomes slower from the upstream drive wheel to the downstream drive wheel. That is, during this period, the mechanical clearance between adjacent clips is gradually accumulated, and the further downstream there is, the more the number of accumulated openings increases, and the clip speed is slowed down. In this manner, the clipping speed is made slower toward the downstream side, so that the film traveling speed also becomes slower during this time, and the stretched film is relaxed in the longitudinal direction.

This circumferential speed difference between the drive wheels is obtained as the cumulative amount of mechanical clearance of the coupling mechanism of the clips arranged between them, so it is not possible to set an extremely large value, but the low heat shrinkage of the stretched film Since the required relaxation rate to obtain a given relaxation rate is usually not very high, a given relaxation rate can be easily obtained as long as the dimensions between the drive wheels are sufficient to allow for a sufficient amount of cumulative mechanical clearance. It will be done. Then, by heat treatment with this predetermined relaxation rate, a longitudinal heat shrinkage rate that is a desired standard for the stretched film can be obtained by treatment in a tenter.

Preferred embodiments of the present invention will be described below with reference to the drawings.

(Example 1) Linear polyethylene terephthalate made of IV-0,60 was melt-extruded at 280°C, then discharged into a sheet from a die, cooled and molded in close contact with a casting roll to form a 160μ sheet. did. Then, the sheet was stretched 3.2 times from a number of heated rolls in a longitudinal stretching device at a stretching temperature of 92'C using a difference in roll circumferential speed to form a uniaxially stretched film. Thereafter, the -axially stretched film was stretched in the width direction by 3.4 times in a first tenter at a temperature of 90°C to obtain a biaxially stretched film. As shown in FIG. 1, this biaxially stretched film 1 is placed in a second tenter 2 with a relaxation rate of 5% in the width direction A and a relaxation rate of 3% in the longitudinal direction B.
%, and the stretched film was wound with a winder.

FIG. 1 shows a schematic planar configuration of the second tenter 2, in which the stretched film 1 is held by a large number of clips 3 arranged in an endless ring on both sides of the film, and as the clips 3 run, the stretched film 1 moves inside the tenter. It runs in the direction of the arrow. The clips 3 are connected in large numbers by suitable means, for example chain links (not shown), with a small mechanical clearance between the connecting mechanisms of adjacent clips.

In addition, the clip 3 is run on rails provided on both sides of the stretched film running direction via a chain link, etc., runs from the tenter population side, passes through the tenter, to the tenter exit, and runs on the return side. Then return to the tenter population side again.

Wheels 4.5 for clip running are provided on the entrance side and the exit side of the tenter 2, respectively, and in this actual flow example, both wheels 4.5 are used as drive wheels. In this embodiment, the circumferential speed of the downstream drive wheel 5 (outlet side wheel) is adjusted to the above-mentioned relaxation rate of 3%, and the circumferential speed of the upstream drive wheel 4 (inlet side wheel) is
The speed is set to -3%. Note that it is desirable that the circumferential speed difference of the drive wheels 4.5 can be set steplessly.

Further, the tenter 2 is divided into 6 zones with each zone having a length of 3-3, and the temperatures of zones #1 to #6 are as shown below.

#1 zone: 210"C #2 zone: 210"C #3 zone: 210"C #44 zone: 180C #5 zone: 150'C #6'/-n: 140"C Note that the relaxation in the film width direction As shown, #4, #
This was done by narrowing the left and right rail widths in 5 zones.

In such a tenter 2, a circumferential speed difference is forcibly created between the upstream drive wheel 4 and the downstream drive wheel 5, so that the clip 3 running between them has a mechanical clearance between the clips 3. gradually accumulates,
The traveling speed becomes slower toward the downstream side. Accordingly, the speed of the stretched film 1 in the tenter also gradually decreases, and the film is subjected to a relaxation heat treatment corresponding to the decrease in speed. The final relaxation rate is determined by the peripheral speed difference between the drive wheels 4.5.

(Comparative Example) In the same stretched film manufacturing process as in Example 1, the second tenter was a tenter with the same structure as the conventional one.

That is, only one of the entrance-side wheel 4 and the exit-side wheel 5 is used as a driving wheel, the clip speeds on the tenter intake side and the exit side are the same, and the film is not relaxed in the longitudinal direction in the second tenter 2. Ta.

8 of the stretched films obtained in Example 1 and Comparative Example above.
Thermal shrinkage rates under a temperature condition of 0'C for 30 minutes were measured and compared. The results are shown in Table-1.

[Table 1] As is clear from the table, in Example 1, the heat shrinkage rate in the longitudinal direction of the film was able to be significantly reduced. Incidentally, the target value of the longitudinal heat shrinkage rate of the film for magnetic tapes and capacitor films was 0.2% or less, and a fully satisfactory result was obtained.

(Example 2) Next, under the same conditions as in the above example, linear polyethylene terephthalate was melt extruded, discharged into a sheet form from a die, sheet cooling molded, -axially stretched, and widthwise stretched in a first tenter. After this, the stretched film was passed through a second longitudinal stretching device consisting of a large number of heated rolls, where the film was stretched in the longitudinal direction by a factor of 1.3 at 130°C due to the difference in the circumferential speed of the rolls. Thereafter, the film was wound up with a winder using the same second tenter 2 as in Example 1, with a relaxation rate of 4% in the width direction of the film and 3% in the longitudinal direction of the film. The temperature conditions in the second tenter 2 are the same as in Example 1.

As a result, the heat shrinkage rate of the obtained stretched film was 0.12% in the longitudinal direction of the film and 0.05% in the width direction of the film.
As expected, a good value that was well within the target range was obtained. In this way, the F-5 value (5%
Although the tensile strength (strength in elongation) was as high as 16 kQ/II', a low heat shrinkage rate of the product film was obtained by the relaxation heat treatment in the second tenter.

(Example 3) In this example, the film production conditions are almost the same as those in the above-mentioned Example 1, as described later. However, the structure of the second tenter was changed as shown in FIG.

As shown in FIG. 2, a drive wheel 11 is newly installed in the second tenter 10, and the drive wheels are an upstream drive wheel 11 in the tenter, an outlet drive wheel 12 as a downstream drive wheel, and an inlet drive wheel. 13 is a non-driving wheel (freewheel) as in the conventional device. In this way, the relaxation rate S1 in the longitudinal direction of the film is determined by the circumferential speed V1 of the drive wheel 11 and the circumferential speed 2 of the drive wheel 12, and is expressed by the following equation.

S+ = (Vl-Vz ・)/V+ Xl 00 (
%) Also, the relaxation rate S2 in the film width direction is calculated for each clip 1 at the position of each wheel 13.11.12.
Assuming that the distance between the left and right rails of the four running rails is Ll, Ll, and 13, and that Ll and L3 are of the same size, it is expressed by the following equation.

82 = (L+ -12)/L+ X100 (%)
In this way, by making Ll and 13 the same size and providing a difference in circumferential speed between the drive wheels 11 and 12, the stretched film 1 can be relaxed in the film width direction and in the film longitudinal direction within the same tenter. It becomes possible to completely separate the parts to be relaxed, and each part can be relaxed reliably and at an accurate relaxation rate.

Next, the conditions in this Example 3 and the characteristics of the obtained stretched film will be explained.

Linear polyethylene terephthalate made of IV-0.60 is melt-extruded at 280°C, then tightly passed through a casting roll through a die to form a 160μ thick sheet. After stretching 3.2 times in a stretching device at a stretching temperature of 92°C due to the difference in roll circumferential speed, the stretched film was stretched 3.8 times in a first tenter at a stretching temperature of 90''C. In the second tenter 10, the film was subjected to a relaxation heat treatment with a relaxation rate of 4% in the width direction and a relaxation rate of 2% in the longitudinal direction, and was wound up with a winder.The temperature conditions in the second tenter 10 were as follows: @ is 220°
The temperature between C1 wheel 11 and wheel 12 was 120°C.

As a result, the heat shrinkage rate of the obtained stretched film was 80°
Under hot air conditions of C130 minutes, small and fully satisfactory values of 0.06% in the longitudinal direction of the film and 0.02% in the width direction of the film were obtained.

[Effects of the Invention] As detailed above, according to the present invention, the tenter is provided with an upstream drive wheel and a downstream drive wheel, and a predetermined circumferential speed difference is provided between them, and the stretched film is stretched in the tenter. Since we have made it possible to perform relaxation heat treatment in the longitudinal direction as well, by simply improving the conventional tenter equipment, we can reliably and easily relax the film in the longitudinal direction at a predetermined relaxation rate in a non-contact state. The effect is that the heat shrinkage rate of the stretched film can be kept within a predetermined range without impairing the flatness of the stretched film or damaging the film surface with a roll or the like. Therefore, it is possible to satisfy the strict dimensional stability of magnetic tapes and capacitor films under low-temperature conditions while ensuring high-speed film formation and high productivity.

[Brief explanation of the drawing]

FIG. 1 is a schematic plan view of a tenter used to carry out a method for heat treatment of stretched film according to an embodiment of the present invention, and FIG. 2 is a schematic plan view of a tenter showing an example of a structure different from that in FIG. 1. . 1...Stretched film 2.10...Tenter 3.14...Clip 4.11...Upstream drive wheel 5.12...
...Downstream drive wheel 13...Inlet wheel

Claims (1)

[Claims] (1) A stretched film heat treatment method in which both sides of a continuously fed stretched film are gripped with clips, and the stretched film is heat-treated while being run in a tenter by the running of the clips. Of these, the wheel on the upstream side and the wheel on the downstream side in the running direction of the stretched film are both drive wheels, and there is a difference in circumferential speed between the two drive wheels such that the circumferential speed of the downstream drive wheel is smaller. . A method for heat treating a stretched film, comprising relaxing the stretched film in the running direction of the stretched film between the two drive wheels.