JPH03267172A - Production of foam - Google Patents

Abstract

PURPOSE:To easily obtain an electric wire and cable insulated with a thin and small-diameter foam having good appearance at a high speed by applying a liquid UV curing type compsn. or thermosetting type compsn. internally contg. fine pores as a coating material to a base body. CONSTITUTION:The liquid UV curing type compsn. or thermosetting type compsn. internally contg. the fine pores is applied as the coating material to the base body and is cured to simultaneously obtain the foam. The fine pores are included therein by injecting arbitrary gas, such as air, into the liquid compsn. and stirring the compsn. at a high speed. The UV curing type resin coating to be used is exemplified by a base oligomer of a radical polymn. type, etc., contg. a monofunctional acrylate, etc., as a monomer (for example, polyester acrylate). The thermosetting type resin coating may be resin coatings of an epoxy base, etc., of a condensation type, addition polymn. type, etc., which can contain the fine pores and are cold or thermally cured in the presence of a crosslinking agent or catalyst. The highly expanded foam is easily obtd. by the simple method in this way and the remarkable improvement in productivity is attained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a method for simply and efficiently producing insulation coatings for thin-walled, small-diameter, highly foamed electric wires and cables, and other foamed materials such as foamed sheets and films. It is related to.

[Conventional technology] In recent years, communication equipment and precision electronic equipment have shown a remarkable trend toward miniaturization and high-density packaging, and to meet this demand, cable cores are also becoming smaller and smaller in diameter. Insulated wires with small diameters, such as those with an outer diameter of 1.0 mm or less, have also come to be used.

On the other hand, in computers and other devices, there is a remarkable tendency to require even faster transmission signals, and the insulator layer of the above-mentioned thin insulated wires used for this purpose is highly foamed and has a dielectric constant as low as possible. Therefore, there is an increasing demand for so-called high-speed cables that increase the speed of transmission signals.

A method of covering wires and cables for signal transmission in computers, etc. with foam insulation is to wrap a pre-foamed film around the conductor, but an extrusion method is used to form the foam insulation coating. This is often the case.

As means for foaming such an insulator, there are known a physical gas foaming method in which foaming is performed using gas, and a chemical foaming method that utilizes a chemical reaction.

The former gas foaming method involves forcibly injecting a volatile foaming liquid such as liquid chlorofluorocarbon into the molten resin and causing foaming by its vaporization pressure, or directly injecting the foaming gas into the molten resin in an extruder. There is a method of generating uniformly distributed cellular fine closed cells in a resin by press-fitting the resin.

The latter chemical foaming method involves molding a resin with a foaming agent dispersed therein, and then applying heat to chemically decompose the foaming agent to generate gas and foam.

[Problems to be Solved by the Invention] The former method of gas foaming described above involves once melting the resin and forcibly injecting a volatile foaming liquid into it, which often requires strong pressure. Furthermore, such liquefied gas has a strong vaporization pressure, making it difficult to obtain a fine foamed structure and also difficult to obtain a good product appearance. Furthermore, since the injection speed of the liquefied gas is slow, it is difficult to increase the speed, resulting in poor productivity.

Further, the method of directly pressurizing gas into an extruder requires special equipment and special techniques.

On the other hand, in the case of chemical foaming, as mentioned above, it is necessary to knead and disperse the foaming agent into the resin in advance, and after the molding process, this foaming agent is reacted and decomposed by heat, and the gas generated is used to cause foaming. It is something you can do. Therefore, there is a problem in that the molding temperature of the resin in this case must be kept lower than the decomposition temperature of the blowing agent in order to prevent the blowing agent from decomposing during the molding process, and the blowing agent used itself has a large There is a problem in that it is limited in width.

Furthermore, in the case of the extrusion coating method, there is another problem in that as the diameter of the wire becomes smaller, it is more likely to break due to pressure, making it difficult to increase the speed. There are also problems that are difficult to deal with.

An object of the present invention is to solve the problems of the prior art as described above, and to easily and quickly obtain thin-walled, small-diameter foamed insulated wires/cables or foamed sheets or films with a good appearance. The purpose is to provide a manufacturing method.

[Means for Solving the Problems] The present invention involves applying a liquid ultraviolet curable composition or thermosetting composition containing microbubbles to a substrate as a paint,
By curing this, a foam can be obtained at the same time as curing, making it possible to significantly improve productivity.

In order to incorporate fine bubbles, any gas such as air, oxygen, or nitrogen may be injected into the liquid composition, and the mixture may be stirred at high speed to easily disperse the fine bubbles. As a dispersion stirring device for this purpose, it is sufficient as long as it can uniformly disperse fine air bubbles, and for example, a general purpose stirring device such as a juicer mixer may be used as is.

The ultraviolet curable resin coating used in the present invention may be any coating that is cured by ultraviolet rays, such as radical polymerization type, cationic polymerization type, ene/thiol polymerization type, etc. Examples of the pace oligomer include polyester acrylate, urethane acrylate, Epoxy acrylate, polyether acrylate, polybutadiene acrylate,
Examples include epoxy urethane acrylate, silicon acrylate, polyester urethane acrylate, polyether urethane acrylate, vinyl/acrylic oligomer, polyene/thiol, polystyrylethyl methacrylate, etc. Chlorinated or fluorinated versions of these may also be used, and two or more types of these may be used. may be used in combination.

In addition, as monomers, in addition to photopolymerizable monomers (reactive diluents) such as vinyl monomers, monofunctional acrylates, polyfunctional acrylates, allyl alcohol derivatives, non-reactive diluents can be used as necessary. .

As the photoinitiator, acetophenone type, benzoin type, benzophenone type, thioxanthone type, and other arbitrary photoinitiators can be combined. A photoinitiation aid may also be used in combination.

In addition, the thermosetting resin coating used in the present invention may contain fine bubbles and may be a condensation type, addition polymerization type, or other type that cures at room temperature or by heating in the presence of a crosslinking agent or catalyst. , epoxy type, polyurethane type,
It may be a one-component type, a two-component type, such as an acrylic type, or a combination of more.

In addition, thermal polymerization inhibitors, fillers, adhesion promoters, thixotropic agents, plasticizers, non-reactive polymers, colorants,
Flame retardants, flame retardant aids, antioxidants, mold release agents, etc. may also be used.

Coating methods such as spray, roll coater, and dipping may be selected and combined depending on the purpose, application, and product shape.

Any curing method may be used as long as it emits the necessary ultraviolet rays, such as a high-pressure mercury lamp or a metal halide lamp.

This foamed crosslinked composition can be made into a film or sheet, and can also be applied to plastic or metal objects. In addition, foamed electric wires and cables can be easily made by coating and curing metal wires.

[Example] The present invention will be described below with reference to Examples.

Note that the degree of foaming in each of the following examples is a value calculated using the following formula.

Here, A: Composition cured with internal bubbles B: Composition cured without internal bubbles Example 1 An ultraviolet curable urethane acrylate paint containing internal microbubbles was applied onto a glass plate. Pour into a thickness of 3ml (55
μm) doctor blade (Toyo Seiki type reference standard JI
A coating (film) was formed on S- using -5101, JISK-5400, etc.), and this was irradiated with ultraviolet rays in a nitrogen atmosphere (lamp intensity 80 W/am, irradiation distance 1).
00mm, cumulative irradiation dose 100mJ/aIr) was cured to obtain a foamed crosslinked product, and the foaming degree was measured to be 65 to 73%.
A highly foamed film was obtained.

Example 2 A metal wire (Suzmetsuki wire) with a conductor diameter of 127 μm was coated with ultraviolet curable urethane acrylate paint containing microbubbles.
was coated at a line speed of 200 m/min, and then uniformly irradiated with ultraviolet rays to cure the wire to obtain a foamed wire with a coating thickness of 50 μm.The degree of foaming was measured, and a highly foamed crosslinked wire of 60 to 71% was obtained.

Example 3 A thermosetting epoxy paint containing microbubbles was applied to a metal wire (silver-plated wire) with a conductor diameter of 127 μm at a line speed of 100 m/
After coating at min., it was cured in a heating oven (800°C) to obtain a foamed wire with a coating thickness of 50 μm.The degree of foaming was measured, and a highly foamed crosslinked wire of 65 to 80% was obtained.

It has great significance in meeting the contemporary demands of this field.

Claims (1)

[Claims] (1) A method for producing a foam, in which a liquid ultraviolet curable composition or thermosetting composition containing microbubbles is applied as a paint to a substrate, and then cured.