JPS60110428A - Manufacture of biaxially oriented film made of extremely thin-filmed thermoplastic resin - Google Patents

Abstract

PURPOSE:To prevent troubles such as a tear at a holding part of a film, which is ascribable to adhesion between a clip and the film and a dynamical hang-up, and cutting resulting from concentration of stressin the vicinity of the clip, by making a thickness of a clip holding part and its vicinity most suitable. CONSTITUTION:A mean film thickness T in the inside of a clip holding part is made into t+z<=T<=t+7z [(t) is a thickness (mu) of a central part of the film directly before an introduction of a tenter part and z is a draw ratio in the tenter part and is the product of a longitudinal and lateral magnifications]. The film thickness (mu) is made to reduce gradually down to (t) almost linearly in a sphere wherein a film thickness Tc at the tip of a clip of a center side of the film running along the direction of a film width is t<=Tc<=t+3z and a length is identical with a grasping margin of the clip by facing toward the center part running along the direction of a film width. Generation of a trouble at the time of manufacture of a biaxially oriented film made of thermoplastic resin, whose thickness is less than 1mum, based on a tenter method can be controlled in a synergistic state by making use of the film like this.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing an extremely thin thermoplastic two-wheel stretched film of 1 μm or less by a tenter method. There are many interesting uses for ultra-thin films, and it is expected that they will continue to be used in a variety of ways, including current cut-off type electric capacitors, radiation sensors, acoustic vibrators, and transparent membranes.

As a method for obtaining ultra-thin films, Japanese Patent Application Laid-Open No. 58-104
There is a method of dispersing a large amount of a special compound in a polymer, forming and stretching a somewhat thick film, as shown in Publication No. 720, and then extracting this special compound from the film with a solvent to obtain a film of 1μ or less. It is known that special compounds and solvent selection are required, and extraction times are
There are many problems such as the method of drying the solvent. On the other hand, we have already developed a method for producing a thin thermoplastic two-wheel stretched film with a thickness of 5μ or less using the tenter method in Japanese Patent Publication No. 57-52895.
Although it was proposed in the above publication, it goes without saying that if the thickness of the biaxially stretched film is less than 1 μm, it will be accompanied by unprecedented manufacturing difficulties.

Stretching of a film by the tenter method involves holding both ends of an unstretched film or a longitudinally and axially stretched film with clips, and simultaneously stretching the film in the longitudinal and lateral directions or in the transverse direction.
When producing a thermoplastic biaxially stretched film of 1μ or less,
Adhesive force between the clip and the film 1 When the film is separated from the clip due to mechanical catching or other influences, the film thickness is extremely thin, so the clip gripping part of the film may tear or local damage may occur near the clip gripping part. Stress concentrations occur, often leading to breakage.

This kind of cutting becomes more severe as the film thickness becomes thinner, and to prevent this, the film thickness at the center of the film should be adjusted from the clip gripping part and the clip tip further along the film direction according to the stretching ratio in the tenter. It needs to be tightly controlled.

The thickness of the film near the clip gripping portion and the clip does not simply have to be thick.

If the film is too thick for a certain amount of time, stress concentration tends to occur near the clip gripping part, and the clip and film tend to get caught, making it easy to curl and cut.

Furthermore, loss at the edges of the film becomes large, which is economically disadvantageous.

As a result of repeated studies taking such knowledge into consideration, we have come to invent the method described below.

That is, when producing a biaxially stretched thermoplastic resin film of 1 μm or less by the tenter method, the average thickness T of the film in the clip gripping portion is set to t0z≦T≦t+7z, and (
1 is the thickness (μ) at the center of the film immediately before part of the tenter is introduced, and 2 is the stretching ratio at the part of the tenter, which is the product of the longitudinal and lateral ratios. ) The film thickness Tc at the tip of the clip on the film center side along the film center direction is t≦Tc≦t+
3z, and ``Furthermore, along the inside direction of the film toward the center, in a length area equal to the clip gripping area,
This is a method for producing an ultra-thin thermoplastic two-wheel stretched film, which is characterized by stretching a film whose thickness is gradually reduced approximately linearly to t using a tenter.

According to the method of the present invention, since the film thickness at the clip gripping portion and the vicinity thereof is the same, when the clip and the film are separated, the adhesive force between the clip and the film is reduced.

This is caused by a mechanical catch between the two. It is possible to prevent troubles such as tearing of the film at the clip gripping portion or breakage due to stress concentration near the clip.

As described above, the optimum film thickness at the clip gripping portion and the vicinity thereof needs to be changed depending on the stretching ratio in a portion of the tenter. If the stretching ratio is low, the adhesive force between the clip and the film, the interaction force between the two, such as catching, is small, and even if the thickness inside the clip and in the vicinity of the clip is small, the film will not be cut. If the film thickness is thinner than the above conditions, cracks may run from the edge of the film when the film separates from the clip due to adhesive force between the clip and the film, catching, catching, or other forces. The film edge is torn = 5 = Sipping operation problems will occur, and conversely, if the film edge condition is thicker than the above conditions, stress concentration near the clip and thickness at the stretched film edge may occur. It becomes extremely thicker than the center, and there is more loss at the edges. By changing the thickness near the clip approximately linearly in the same area as the inside of the film inside the clip grip, the occurrence of the same troubles as described above can be suppressed synergistically.

The present invention is applicable to sequential biaxial stretching and simultaneous two-wheel stretching using the tenter method. In the case of sequential biaxial stretching, after longitudinal-axial stretching is performed using a longitudinal stretching machine consisting of a group of rolls in one stage, transverse stretching is performed using a tenter, and the present invention can be applied to the transverse stretching using this tenter method. In this case, the stretching ratio of the tenter is only horizontal stretching, so compared to simultaneous biaxial stretching,
The film thickness at the clip gripping portion and its vicinity may be thinner than that for simultaneous biaxial use. In simultaneous biaxial stretching, the total stretching ratio is the product of the longitudinal and lateral stretching ratios, so the film must be slightly thicker than the film thickness in sequential biaxial stretching.

6- Examples of film materials to which the method of the present invention can be applied include thermoplastic resins such as high-density polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, nylon 6, and nylon 66.

The present invention will be explained below with reference to Examples.

Examples and Comparative Examples Polyethylene terephthalate resin was melted at 280°C,
It was cooled from a T-die on a cooling roll at 80°C to produce an unstretched film. At this time, the film thickness at the ends and center of the unstretched film is adjusted using the T-die thickness adjustment bolt and the take-up position relationship between the T-die and the cooling roll.

Samples as shown in Table 1 were prepared by varying the discharge amount and take-up speed, and these unstretched films were simultaneously biaxially stretched by the tenter method at 85°C with various stretching ratios.
Heat-fixed at 00°C. Table 1 shows the stretching results. The film gripping margin of the clip during stretching was 25 mm. Table 1
In the clip from the result.

Claims (1)

[Claims] 1. When producing a biaxially stretched thermoplastic resin film with a thickness of 1μ or less by the tenter method, the average thickness T of the film within the clip gripping portion is set to t0z≦T≦t+7z, and the film is stretched along the inside direction of the film. The film thickness Tc at the tip of the clip on the film center side satisfies t≦Tc≦t+3z, and furthermore, as the film goes toward the center along the film center direction, the film is approximately linearly stretched in a length region equal to the clip gripping margin. A method for producing an ultra-thin thermoplastic resin two-wheel stretched film, which comprises stretching a film whose thickness is gradually reduced to t using a tenter. t: Thickness of the central part of the film immediately before introducing a part of the tenter (μ) 2: Stretching ratio (times) at a part of the tenter Product of vertical and horizontal magnification T: Average thickness of the film in the gripping part of the tenter (μ) Tc
:Crimp tip film thickness (μ)