JPH0566411B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a method for forming pores in a plastic film. The present invention relates to a method for forming pores in a plastic film.

Technical background of the invention and its problems Adding breathability to plastic film,
Alternatively, it may be required to impart directionality to the gas passing through the plastic film. For example, plastic films used to form agricultural gloves, kitchen gloves, supports, finger pads, breathable adhesive tapes, etc. are desired to have breathability.

It is known that in order to impart air permeability to a plastic film, it is sufficient to form a large number of pores in the plastic film, and many methods for forming pores in the plastic film have been proposed. For example, a method of blending a filler into a plastic film and stretching it, a method of mechanically perforating the plastic film using a roll with needles, a method of irradiating the plastic film with a laser, a method of directly corona discharge treatment of the plastic film, etc. There are known methods to do this. However, in the method of blending a filler into a plastic film and stretching it, the size of the pores formed varies depending on the type of filler or filler conditions, and the process of blending the filler may vary. There was a problem in that the manufacturing process was time-consuming because it required Furthermore, with the method of mechanically perforating plastic film or the method of irradiating it with laser, it is not possible to accurately control the size or shape of the holes formed, and the equipment itself is expensive and has poor productivity. There was a problem. Furthermore, the method of directly subjecting a plastic film to a corona discharge treatment has the problem that the size or shape of the pores formed cannot be accurately controlled. Further, with the above method, it is particularly difficult to form pores having small and uniform pore diameters.

The inventors of the present invention have conducted extensive research to solve the above-mentioned problems, and have found that if a plastic film is subjected to a specific treatment, then subjected to an electric discharge treatment, and then the plastic film is heated and shrunk,
The present invention was completed by discovering that it is possible to precisely control the shape or arrangement of the holes to be formed, and also to form holes with extremely small diameters and uniform sizes.

Purpose of the Invention The present invention aims to solve all of the problems associated with the prior art as described above, and aims to accurately control the size, shape, and arrangement of holes formed in a plastic film. The purpose of the present invention is to provide a method for forming pores in plastic film that can be controlled and form pores with extremely small diameters, has excellent productivity, and does not require expensive equipment. It is said that

Summary of the Invention The method of forming pores in a plastic film according to the present invention involves stretching a plastic film beyond its elastic limit and then applying embossing to the plastic film to reduce the thickness of the embossed portion of the film. The thickness of the plastic film is set to 1/2 to 1/5 of the film thickness of the part, and then the plastic film is subjected to electrical discharge treatment to form pores in the non-embossed parts of the plastic film, and then the plastic film is heated and shrunk. It is characterized by

According to the method of forming pores in a plastic film according to the present invention, after the plastic film is stretched beyond its elastic limit, the plastic film is embossed, and the thickness of the embossed part is reduced to the thickness of the non-embossed part. After reducing the film thickness to 1/2 to 1/5 of the film thickness, the plastic film is subjected to electrical discharge treatment to form pores, and then the plastic film is heated to shrink, so that the pores formed are It is possible to precisely control the shape and arrangement of the pores, form pores with very small diameters, have excellent productivity, and do not require expensive equipment.

DETAILED DESCRIPTION OF THE INVENTION The method for forming pores in a plastic film according to the present invention will be specifically described below.

Plastic Film Specifically, the plastic film in which pores are formed by the process according to the present invention includes:
Polyethylene film, polypropylene film, polyvinyl chloride film, polystyrene film, polyethylene terephthalate film, polycarbonate film, polyimide film,
Conventionally known plastic films such as nylon film, polyvinylidene chloride film, and polyvinyl alcohol film are widely used.

It is desirable that such a plastic film has a thickness of about 10 to 100 .mu.m, preferably about 20 to 60 .mu.m.

Stretching Treatment The plastic film described above is first subjected to a stretching treatment beyond its elastic limit. The plastic film is stretched biaxially or uniaxially under conventionally known equipment and conditions, and the stretching ratio is at least 2 times, preferably 3 times.
It is preferable that it is ~8 times.

The temperature during stretching is preferably below the melting point of plastic film, and in the case of polyethylene film, it is preferably 115 to 127 degrees Celsius, preferably 120 to 125 degrees Celsius.
It is desirable that the temperature be as low as ℃.

Embossing The plastic film that has been stretched as described above is then subjected to embossing.
When embossing is applied to a plastic film, an embossed portion (hereinafter sometimes referred to as an embossed portion) and a non-embossed portion (hereinafter sometimes referred to as a non-embossed portion) are formed on the plastic film.

The embossed portions of the plastic film are thinner than the non-embossed portions. Assuming that the thickness of the non-embossed part of the plastic film is t, the thickness of the embossed part is preferably 1/2 to 1/5t, preferably 1/3 to 1/5t.

A wide variety of conventionally known methods can be used to emboss a plastic film. For example, a plastic film may be passed between a pair of embossing rolls and a rubber roll while being heated, and embossed portions corresponding to the shape of the convex portions of the embossing rolls may be formed on the plastic film.

As will be described later, pores are formed in the embossed portions of the plastic film by corona discharge treatment. Therefore, the density of the pores formed in the plastic film can be controlled by determining the shape and density of the embossed portions formed in the plastic film. Furthermore, when plastic is embossed, if the embossed portion is given directionality, the pores that will be formed later will also be given directionality, and the gas passing through these pores will also be given directionality.

Discharge treatment After adding embossing to the plastic film as described above to form embossed areas and non-embossed areas, the plastic film is subjected to electric discharge treatment to selectively form pores in the embossed areas. do. At this time, no pores are formed in the non-embossed portions.

The discharge treatment is carried out using a conventionally known device, and the discharge conditions are such that pores are formed in the embossed portions of the plastic film and no pores are formed in the non-embossed portions. . For example, after stretching polyethylene with a film thickness of 30 μm, embossing is added to increase the film thickness at the embossed part.
If the thickness of the film is 10 μm and the thickness of the non-embossed part is 20 μm, the distance between the electrodes is 1 mm, and approximately
All you have to do is apply a voltage of 7KV and perform discharge treatment.

For example, as an electrode during discharge treatment,
Using a bundle of multiple copper wires as the positive electrode,
Further, by using a flat negative electrode, discharge can be generated from each copper wire of the positive electrode. Specifically, when a plastic film with a diameter of 0.21 mm is subjected to electrical discharge treatment using a copper wire as the positive pole and a flat copper plate as the negative pole, pores of approximately 0.12 to 0.17 mm are formed in the embossed part of the plastic film. Ru.

Heat shrinkage treatment The plastic film that has been subjected to the discharge treatment as described above and has pores formed in the embossed portions is then brought into contact with a heating roll or passed through a heating chamber to be heated and shrink. be done. This heating is carried out at a temperature below the melting point of the plastic film, and in the case of polyolefin films such as polyethylene, it is preferably about 115 to 120°C.

Plastic film has already undergone a stretching process, so it shrinks considerably when heated, and the pores formed by the discharge become smaller, forming fine pores with uniform diameters. be done. For example, if the pore diameter before heating is 0.12 to 0.17 mm, it will be reduced to 0.08 to 0.1 mm by heat shrinkage treatment.
It will be about.

In the method for forming pores in a plastic film according to the present invention, each step may be performed separately, but
A series of processes may be performed continuously.

Effects of the Invention According to the method for forming pores in a plastic film according to the present invention, after the plastic film is stretched beyond its elastic limit, the plastic film is embossed to reduce the thickness of the embossed portion. After reducing the thickness of the film to 1/2 to 1/5 of the unfilled part, the plastic film is subjected to electrical discharge treatment to form pores, and then the plastic film is heat-treated to shrink. The shape of the pores or their arrangement can be precisely controlled, pores with a very small diameter can be formed, and the productivity is excellent and expensive equipment is not required.

EXAMPLES The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples.

Example 1 After uniaxially stretching a polyethylene film with a film thickness of 50 μm to a stretching ratio of 3, embossing was added to the polyethylene film to increase the film thickness at the embossed part.
The thickness of the film was 10 μm, and the film thickness of the non-embossed portion was 20 μm.

Next, the embossed plastic film was subjected to electrical discharge treatment. The discharge treatment was carried out by using a plurality of copper wires with a diameter of 0.21 mm as the positive electrode and a flat copper plate as the negative electrode, and applying a voltage of about 7 KV with the distance between the two electrodes being 1 mm.

No pores were formed in the non-embossed part of the plastic film, but there were pores in the embossed part with a diameter of approx.
Multiple pores of 0.12 to 0.17 mm were formed.

When the plastic film that had been subjected to the electrical discharge treatment was then heated to 115°C to shrink, the pores had a diameter of approximately 0.08 mm.

Claims (1)

[Scope of Claims] 1. After stretching the plastic film beyond its elastic limit, the plastic film is embossed, and the thickness of the embossed part is 1/2 to 1/2 of the thickness of the non-embossed part. Five
A method for forming pores in a plastic film, which comprises: applying electrical discharge treatment to the plastic film to form pores in the embossed portions of the plastic film, and then heating the plastic film to shrink it. . 2. The method according to claim 1, wherein the plastic film is a polyethylene film or a polypropylene film.