JPS6332612B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a foaming method for containing countless minute closed cells at desired locations in a heat-softening foamed article, and more specifically, the present invention relates to a foaming method for forming a heat-softening foamed article into a predetermined shape. The purpose of the present invention is to provide a foaming method in which a permeable foaming material is permeated into an article to be foamed to form a foamed layer consisting of numerous fine closed cells by vaporization and foaming.

Generally, molded bodies or layers made of foamed rubber or synthetic resin contain a pyrolytic foaming agent,
It is obtained by molding a foamable composition made by mixing a foaming material such as a gas or solvent into a predetermined shape, or by coating the surface of the applied object and foaming it at room temperature or under heating. The foamed body or foamed layer obtained by this method is formed entirely of uniform cells.

The foaming method of the present invention essentially differs from such conventional foaming methods in the following points.

One method is to supply the foamed material from the surface after molding the composition without pre-blending the foaming material that forms cells into the molding composition, thereby forming a foam consisting of countless minute closed cells inside the molded article. It is to form layers.

Second, it is possible to form a foam layer in a desired shape not all over the molded article but at desired locations.

The present invention is characterized in that a permeable foam material supply body is brought into contact with the surface of an article to be foamed made of an adhesive film-like material, and the article and the supply body are heated to form countless minute closed cells within the article. The present invention provides a foaming method that achieves this.

According to the method of the present invention, a foam layer consisting of minute closed cells can be formed at desired locations or on the entire surface of the surface layer or inner layer of a foamed article made of an adhesive film-like material.

The foamed article made of adhesive film used in the practice of the present invention is made of thermoplastic resins such as polyethylene, polypropylene, polyvinyl chloride, styrene-butadiene polymers, styrene-isoprene (or butadiene)- Molded articles such as sheets, films, and strips made of thermoplastic materials such as thermoplastic rubbers such as styrene block copolymers alone or in mixtures, especially those based on said materials and having a glass transition temperature of - A film adhesive whose temperature is adjusted to 70 to -15°C is preferred.

The permeable foam material supplier is a material that uniformly or partially distributes the permeable foam material that foams and permeates into the thermally softened foamed article by bringing it into contact with the foamed article and heating the articles together. It consists of a porous base material containing ~30% by weight, for example, a permeable foam material made of a vaporizable substance such as water or an organic solvent such as ethyl acetate, toluene, or alcohol, and a porous base that can impregnate and retain the material. Materials such as paper,
Composed of nonwoven fabrics, woven fabrics, felt, porous plastic films, etc.

One surface of the supply body (the surface that does not come into contact with the foamed article) is subjected to an impermeable barrier treatment in advance or during the process in order to prevent the permeable foam material contained therein from striking through. The treatment is selected depending on the heat softening temperature of the foamed article and the temperature at which the foam material can permeate, and at least it does not heat soften at these temperatures, or even if it heat softens, it does not have a barrier effect. It is made of materials that do not lose their functionality. Treatment is accomplished by laminating or overlapping non-transparent materials such as plastic films or metal foils.

The method of the present invention will be specifically explained. First, a permeable foaming material supplier is brought into contact with the surface of an article to be foamed made of an adhesive film-like material with microscopically fine voids formed therein over the entire surface or in a portion thereof. At this time, the permeable foam material in the supply body may be impregnated and held in advance, or may be held after contact.
When the surface of the supply body that is in contact with the non-foamed article is not subjected to barrier treatment, a non-permeable material having a barrier function may be further superimposed thereon.

The article to be foamed and the supply body are then heated in contact. The heating temperature varies depending on the thermal softening temperature of the article and the temperature at which the permeable foam material can vaporize and permeate.
A temperature of about 100 to 500°C for 0.1 seconds to 10 minutes is appropriate.

The foamed article is moderately thermally softened by heating, and the foamed material contained in the porous base material, which is the material carrier, is vaporized by heating and fills the voids at the interface between the foamed article and the carrier. As the vapor pressure increases as it moves, it penetrates into the thermally softened foamed article in the form of bubbles, reaches a certain point on the surface or inner layer of the article along the flowability of the article, and forms countless bubbles within the article. It forms a foam layer consisting of minute closed cells.

In the method of the present invention, the foamed article has a thickness of 100 μm.
It is useful when foaming articles that are as thin as below and in which bubbles are difficult to escape and a uniform foamed layer is difficult to form even when a normal foaming agent is mixed and heated.

It is extremely useful to foam a thin pressure-sensitive adhesive layer of 100 μm or less formed on a tape support using the foaming method of the present invention. The tape support made of a porous base material has the function of a foam material supporter, and the foam material supplied from the tape support is used to form a foamed pressure-sensitive adhesive in which countless minute closed cells are formed approximately in the inner layer. The layer exhibits good retention characteristics by following the deformation of the adherend, and has removability that allows it to be peeled off from the surface of the adherend such as corrugated paper without damaging the surface of the adherend. Furthermore, the air bubbles formed in this manner do not collapse or coalesce over time even when wound into a roll, which is the general shape of adhesive tape.

The following examples show adhesive tapes in which the effects of the foaming method of the present invention are most prominently exhibited.
From the above description, it will be understood that the present invention is also useful when forming a foam layer on a foamed article made of other adhesive film-like materials.

Example 1 A film adhesive consisting of 100 parts by weight (hereinafter referred to as "parts") of a styrene-isoprene-styrene block copolymer, 100 parts of a petroleum resin, and 1 part of an anti-aging agent is used as a non-foamed article.

The adhesive is prepared by mixing a mixture of the above-mentioned components in a heated kneader (130° C.) and melt-coating the mixture onto one side of dried kraft paper to a thickness of 30 μm.

Next, water droplets are dripped onto the back of the kraft paper carrying the film-like adhesive to absorb water, and a polyester film as a barrier treatment material is layered on top of this, dried at 120℃ for 4 minutes, and then separated. A tape with an adhesive layer containing air bubbles was obtained.

The film adhesive treated in this way expanded to a thickness of approximately 70 to 80 μm only in the areas where water was absorbed by dropping water droplets on the kraft paper, and there was almost no change in the adhesive thickness in the areas where water was not absorbed. I couldn't help it.

The glue surface of the expanded part has turned white, and when this is observed from the glue surface with a microscope, circular closed cells with a diameter of about 50 to 60 μm are uniformly distributed, and further, when looking at the cross section of this part, there are bubbles. The particles had a substantially flat shape and were distributed in an aligned manner approximately in the middle of the adhesive layer.

The tape thus obtained had a smooth adhesive surface and good retention properties and removability.

Example 2 A silicone release treatment layer was formed on the back of the kraft paper prepared in Example 1, one side of which was coated with a film adhesive, and the paper was wound into a roll for 50 minutes.
Cut the tape roll into mm width at 40℃×90%R.
The paper was stored in an atmosphere of H for 24 hours to allow the kraft paper to retain approximately 8% water by weight.

This was heated at 120° C. for 3 minutes to obtain a tape with an adhesive layer containing closed cells.

When this tape was rewound and the foaming state was observed, the thickness of the glue was about 80 μm, and the thickness was about 40 to 50 μm from the glue surface.
In the cross section, it was seen that flattened bubbles were distributed in an array in the middle of the perfectly circular bubbles.

Claims (1)

[Claims] 1. Bringing a permeable foaming material supplier into contact with the surface of an article to be foamed made of an adhesive film-like material, and heating the article and the supplier to form countless minute closed cells within the article. A foaming method characterized by: 2. The foaming method according to claim 1, wherein the permeable foam material supplying body is a porous base material containing a vaporizable substance, and one side of the base material is treated with a barrier. 3. The foaming method according to claim 2, wherein the vaporizable substance is at least one selected from the group of water and organic solvents.