JPS62278018A - Biaxial co-stretching of plastic film - Google Patents

Abstract

PURPOSE:To reduce the breakage of a film by a method wherein a clip, whose length in the advancing direction of a plastic film in a grip is different between an upper part and a lower part, is employed and the film is stretched while arranging the grip, whose clip is longer, on the lower surface of the plastic film. CONSTITUTION:A clip should have a length in the advancing direction of a film in a grip, which is different between an upper part and a lower part. In another word, the length of the upper part 3 and the length of the lower part 4 should be different. Further, the longer clip is arranged below the plastic film to expand it. The length of the clip is preferable to be 10-100mm and more preferable to be 20-80mm. The difference of the length is preferable to be O.5-10mm and more preferable to be 1-4mm. When the length and the difference of lengths are smaller than these values, the breakage of the film due to the concentration of stretching stress is readily generated and, on the other hand, when the same are larger than these ranges, the film is stretched between the grips of the clip and whereby not only the breakage of the film is generated readily but also the width of one set of clip becomes wide uselessly and the necking of the end portions of the film upon stretching becomes large.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for simultaneous biaxial stretching of PlusDeck film.

[Prior art] Both ends of a plastic film are held with clips,
A technique for simultaneous biaxial stretching in both longitudinal and lateral directions is known, for example, in Japanese Patent Application Laid-Open No. 145421/1983.

[Problems to be Solved by the Invention] However, when such a conventional simultaneous biaxial stretching method is used, there is a problem in that the film tends to break during stretching. An object of the present invention is to provide a simultaneous biaxial stretching method in which such film tearing is extremely less likely to occur.

Means for Solving Problem E) The present invention provides a method in which both ends of a plastic film are gripped with clips and stretched simultaneously in biaxial directions. This method relates to a method for simultaneous biaxial stretching of a plastic film, characterized in that different clips are used for the upper and lower parts, and a gripping portion having a large length of the clip is placed on the lower surface of the plastic film for stretching. be.

The plastic film in the present invention may be any biaxially stretchable plastic film. Typical examples thereof include polyethylene terephthalate film, polypropylene film, high-density or medium-density polyethylene film, nylon film, etc., and polyethylene terephthalate film is particularly preferred.

Simultaneous biaxial stretching in the present invention is a method in which the film is stretched simultaneously in the longitudinal and transverse directions in a tenter, in which the film is held between clips, and by changing the width of the tenter, the stretching in the transverse direction can be achieved, and by changing the gap between the clips, the stretching can be carried out in the longitudinal direction. A method of stretching.

Possible simultaneous biaxial stretching processes include a method of simultaneously biaxially stretching an unstretched film, a method of stretching an unstretched film longitudinally and/or laterally, and then simultaneously biaxially re-stretching. The method is particularly suitable for simultaneous biaxial stretching of a stretched film.

In order to reduce film tearing and thickness unevenness, the stretching ratio when simultaneously biaxially stretching an unstretched film is preferably 2.5 to 6.0 times in both the longitudinal and transverse directions. When simultaneously biaxially stretching a stretched film, a film having an in-plane refractive index of 1.570 to 1.630 including the longitudinal and transverse directions of the stretched film is simultaneously biaxially stretched by the method of the present invention. It is preferable to stretch the film, and the simultaneous stretching ratio at this time is preferably in the range of 1.3 to 2.0 times in both length and width.

The shape of the clip used in the present invention is not particularly limited except that the length of the upper and lower gripping portions is different. There are clips that have a square, rectangular, or round shape that can be gripped flatly, and clips that have a self-locking mechanism, among which clips that have a self-locking mechanism are preferred.

The clip used in the present invention must have different lengths in the film advancing direction at the upper and lower gripping portions.

That is, in the drawing, the lengths of 3 and 4 must be different. Furthermore, the longer end is placed under the plastic film and stretched.

The length of the gripping part of the clip (3 and 4 in the figure) is preferably 10 to 100 mm, more preferably 20 to 8 Qmm. Moreover, the difference in length is preferably 0.5 to 10 mm,
More preferably 1 to 4. It is mm.

If the value is smaller than these values, film tearing is likely to occur due to concentration of stretching stress, while if it is larger than this range, not only is the film easy to tear due to stretching between the clip gripping parts, but also the film is likely to tear due to stretching between the clip gripping parts. The width becomes unnecessarily wide, and necking (film width fluctuation) at the edges of the film increases during stretching.

The stretching method of the present invention will be explained in detail below, but it is not limited to these methods.

In order not to reduce the moisture in the raw material, dried polyethylene terephthalate is melted in an extrusion device, extruded into a sheet using a T diero gold, and wound around a 40'C metal drum.
It is cooled and cast, leaving a substantially unoriented film. This is held at both ends of the film with clips at a temperature of 80 to 120'C, and stretched 3 to 5 times in both the vertical and horizontal directions to form a biaxially stretched polyethylene terephthalate film. After this, while holding both ends of the film with clips,
The dimensions may be fixed at a temperature of 130 to 230° C., or heat setting may be performed while relaxing both vertically and horizontally.

In addition, the unoriented film was stretched 3 to 5 times in the longitudinal direction at a temperature of 80 to 120°C with a group of rolls having different peripheral speeds, and then stretched 3 to 5 times in the transverse direction at a temperature of 90 to 120°C with a tenter. The film is stretched twice to form a sequentially biaxially stretched film. Both ends of this film are held with clips, and simultaneously stretched by 1.3 to 2.0 times in both the vertical and horizontal directions at a temperature of 120 to 170'C.
It can also be highly oriented biaxially oriented polyethylene terephthalate. In this case, it is preferable to further heat-set it in the same manner as the above method.

In the stretching method of the present invention, the thickness of the film held by the clip is preferably 30 to 1000 μm.

Moreover, the thickness of the central part of the film after stretching is 1 to 75 μm.
m is preferred.

[Effect of the Invention 1 = 6- According to the method of the present invention, the concentration of stretching stress in the film during simultaneous biaxial stretching is alleviated, and film tearing can be extremely reduced.

The plastic film produced by the method of the present invention is suitable for uses such as magnetic tape bases, floppy disk bases, and capacitors.

[Measurement method] (1) Film tear The film was simultaneously biaxially stretched, and the film was judged based on the number of times it was torn during film formation of 10,000 m.

◎ No tears 01-2 times △　3~5 times × 6 or more times (2) In-plane refractive index Based on Atsube's refractometer.

[Example] The embodiments of the present invention are shown below, but it goes without saying that the present invention is not limited to these Examples.

Examples 1-3, Comparative Examples 1-2 Polyethylene terephthalate pellets (intrinsic viscosity 0.
61> is sufficiently vacuum-dried, and then supplied to an extruder.
It was melt-extruded at 280'C, taken out from a T-type nozzle in the form of a sheet, wound around a cooling drum with a surface temperature of 50°C, and cooled and solidified to produce an unstretched film with a thickness of 200 μm. This was stretched by a conventional sequential biaxial stretching method, first by 3.0 times in the longitudinal direction at 90°C using a roll, then fed into a tenter, gripped at both ends with clips, and stretched at 95°C by 3.0 times in the transverse direction.
．． The film was stretched 0 times to obtain a biaxially stretched film.

Next, both ends of this beaded biaxially stretched film were held with clips and biaxially stretched at 150'c in both length and width directions at 1.6 times the circumference, and then heat set at 200°C for 3 seconds to fix the dimensions. A biaxially stretched film with a thickness of 8 μm was obtained. At this time, the thickness of the film held by the clip was approximately 60 μm.

The clips used in this example have a self-locking mechanism that grips the edges of the film, and the pitch between the clips is 45 mm before stretching, and due to longitudinal stretching, the pitch between the clips is 72 mm after stretching. I made it so that

The upper gripping body of the clip is semicircular with a radius of 5Qmm, and the length of the clip is constant at 30mm.The upper gripping body of the clip is flat, and the clip length is set as shown in Table 1. The film was changed and stretched. The results are shown in Table 1.

Table 1 Clip length (mm) Film tear Upper part Lower part Example 1 30 40 ◎Comparative example 1
30 30 Δ23026
X From the above results, it can be seen that making the clip length at the bottom of the film longer than the clip length at the top of the film is effective in preventing film tearing.

[Brief explanation of the drawing]

The drawing is an example of a cross-sectional view of the clip used in the present invention in the longitudinal direction of the film. In the figure: 1: Upper clip gripper 2: Lower clip gripper 3: Upper clip length 4: Lower clip length 1 Figure 1, Display of the case Patent Application No. 121274 filed in 1985 2, Name of the invention Method for simultaneous biaxial stretching of plastic film 3, Person making the amendment Relationship to the case Patent applicant address 2-chome, Nihonbashi Muromachi, Chuo-ku, Tokyo Address 2 July 29, 1985 (shipping date) 5. Column "Brief explanation of 1 drawing of the specification subject to amendment" and Drawing 6, Contents of amendment 1> Specification width, page 10, line 2 Correct the title ``Drawing'' to ``Figure 1''. (2) Amend the drawing as shown in the attached sheet.

Claims (2)

[Claims] (1) In a method in which both ends of a plastic film are held with clips and stretched simultaneously in biaxial directions, a clip is used in which the length of the gripping part in the MD direction (the direction of travel of the plastic film) is different at the top and bottom, and A method for simultaneous biaxial stretching of a plastic film, which comprises arranging a long gripping portion of the clip on the lower surface of the plastic film and stretching the plastic film. (2) The difference in length between the upper grip part and the lower grip part is 0.5~
The method for simultaneous biaxial stretching of a plastic film according to claim 1, characterized in that the stretching is carried out using a clip of 10 mm.