JPS61103947A - Electrically conductive foamed material - Google Patents

Abstract

PURPOSE:To obtain a foam having low electrical resistance, uniform electrical conductivity and high stability, by dispersing an electrically conductive substance in an aqueous dispersion containing fine powder of a hardly water-soluble polymer or oligomer, and impregnating and drying the obtained aqueous dispersion in a foamed article having open-cell structure. CONSTITUTION:An electrically conductive substance is dispersed in an aqueous dispersion containing hardly water-soluble polymer or oligomer, and the obtained aqueous dispersion is impregnated in a foamed article having open-cell structure, and dried. The polymer or oligomer is acrylic polymer, etc., especially a copolymer of an alkyl (meth)acrylate and a monomer having hydrophilic group and if necessary, other copolymerizable monomer. The amount of the polymer or oligomer dispersed in water is 5-50%, and that of the electrically conductive substance is 2-70%. The amount of the aqueous dispersion impregnated in the foamed article of 0.2-3pts.wt. per 1pt. of the solid component.

Description

[Detailed description of the invention] [Industrial application field] The present invention is for removing static electricity from electronic materials, OA equipment, etc.
For seals, insulation, sound absorption, and buffering for products that require electrical conductivity such as industrial equipment, as well as for electromagnetic shielding to block electromagnetic waves originating from industrial and medical equipment, home appliances, and automobiles and motorcycles. The present invention relates to a conductive foam.

[Prior art]

Conventionally, as conductive foams, polyethylene, polyurethane, neoprene rubber foams, and the like blended with conductive substances are known. From the manufacturing perspective of these foams, there are two methods: foaming a mixture of the above-mentioned foam with a conductive substance to obtain a conductive foam, and a method using existing open-cell foams such as urethane foam. There is a method of obtaining the material by impregnating and drying an impregnating liquid in which a conductive substance is dispersed in latex, emulsion, or a solvent-based solution.

However, in the case of the former, the volume resistivity is There are problems such as that the resistance decreases only to 10' to 106 Ω·am and that the conductivity varies widely.

In the latter case, there are problems with solvent-based impregnating liquids that cause the existing open-cell foam to swell and, in extreme cases, breakage or deterioration of physical properties, and emulsion-based impregnating liquids such as latex with conductivity. If you try to disperse a sexual substance, it will gel, and even if you try to disperse it forcibly, it will only stabilize at 5%, and the volume resistivity will be 1O1! It is about Ω・C■. or,
Even if a pigment emulsified with a conductive substance etc. is mixed with an emulsifier and used as an impregnation liquid, the emulsifier may remain in the foam obtained after impregnating and drying, which may absorb water or cause the conductive substance to fall off.
There is a problem in that the volume resistivity is only reduced to 10' Ω·C- due to poor dispersion.

As mentioned above, conventional conductive foams do not fully satisfy the functions of conductive foams, such as electrical resistance, foam physical properties and stability, and shedding of impregnated materials.

[Problem that the invention seeks to solve]

The present invention provides a conductive foam that solves the above-mentioned problems, that is, a conductive foam with a low electrical (volume) resistivity (10-” to 1
It is an object of the present invention to provide a conductive foam having excellent properties such as 0 sΩ·C-), no variation in conductivity, stable form, and no need for foam corrosive components such as solvents.

[Means for solving problems]

The present invention involves impregnating an open cell with an aqueous dispersion (hereinafter referred to as a conductive substance aqueous dispersion) in which a conductive substance is dispersed in an aqueous dispersion containing fine particles of a water-based polymer or oligomer, and then drying the dispersion. It is made of conductive foam.

In the aqueous dispersion containing fine particles of a poorly water-soluble polymer or oligomer used in the present invention, the particle size of the fine particles of a water w1-soluble polymer or oligomer is usually 0.05.
~0.1μ, and the aqueous dispersion exhibits both emulsion and solvent properties, ie, a hydrosil.

Since the above-mentioned hydrosil-like water dispersion has an extremely fine particle size, it exists stably without using an emulsifier. Therefore, an aqueous dispersion of a conductive substance using such a hydrosil-like aqueous dispersion is difficult to gel.
It is possible to freely change the amount of conductive material dispersed according to the purpose without causing ′′ or poor dispersion, and after impregnating and drying the foam, the conductive material does not fall off or vary. This has the advantage that there is no risk of water absorption due to residual emulsifier.

Moreover, since the polymer or oligomer particles themselves are extremely fine, they have very good dispersibility between polymers (oligomers), and when a conductive substance aqueous dispersion is produced using such a hydrosil-like water dispersion, the conductivity of the conductive substance can be improved. Furthermore, the conductive foam of the present invention obtained by impregnating and drying such an aqueous dispersion of a conductive substance has good conductivity (102Ω・cm
).

Furthermore, since the conductive material aqueous dispersion does not contain a organic solvent, it can be impregnated with foams that are degraded by organic solvents such as polyurethane and polyvinyl chloride without causing a decrease in mechanical strength.

Therefore, the aqueous dispersion of a conductive substance used in the present invention has the advantage that it is extremely stable for various open-cell foams and that conductive foams with good conductivity can be easily obtained.

Examples of poorly water-soluble polymers and oligomers used in the present invention include monomers having wood-philic groups such as carboxyl groups, hydroxyl groups, and acid amide groups, and polymers of mixed monomers with monomers copolymerizable with these monomers. .

The hydrosilic aqueous dispersion of the present invention can be easily produced, for example, by subjecting the monomers to bulk polymerization or solution polymerization, followed by neutralization with an aqueous solution of a basic substance such as aqueous ammonia or potassium hydroxide. The basic substance acts as an activator for stabilizing the dispersion of the polymer particles.

Any hydrosilic aqueous dispersion can be obtained by appropriately selecting monomers in the bulk polymerization or solution polymerization, and particularly preferred are those in which the monomers are acrylic.

That is, when the polymer itself mixes and disperses adhesive properties, this adhesive property becomes a good binder, and after being impregnated into a slider and heated and dried, it brings about good results such as preventing the conductive substance from separating or falling off. By covering the surface of the foam air wall with an acrylic polymer that has excellent weather resistance, weather resistance can also be greatly improved.

In order to obtain such an acrylic hydrosilic aqueous dispersion, generally an acrylic acid alkyl ester (e.g., 2-ethylcyhexyl acrylate) or a methacrylic acid alkyl ester (e.g., butyl methacrylate) is used as the main monomer. In addition, acrylic acid, methacrylic acid, maleic acid, itaconic acid, 2-hydroxyethyl acrylate, acrylamide, etc. are used as a monomer having a hydrophilic group, and if necessary, styrene which can be copolymerized with these,
Other monomers such as acrylonitrile and maleic acid ester may be used in combination, polymerized by the method described above, and neutralized.

The electrically conductive substance used in the present invention is, for example, electrically conductive and in powder form (preferably, the fine particle size is 1 μ to 10 μm).
There is no particular restriction as long as it is μ and water-insoluble, and examples thereof include carbon black, metal powder (eg, aluminum, nickel, metal powder, and copper).

A method of mixing and dispersing a conductive substance in a hydrosil-like aqueous dispersion is, for example, by mixing the conductive substance directly into the hydrosil,
This is done by dispersing with a high-speed stirrer, ball mill, paint roll, etc., and then diluting it to an appropriate amount.

In the conductive substance aqueous dispersion, the amount of the polymer and oligomer dispersed in water is, for example, about 5 to 50%, preferably about 10 to 20%, and the amount of the conductive substance blended is:
For example, it is about 2 to 70%, preferably about 10 to 30%.

Furthermore, the open-cell foam used in this invention is not particularly limited as long as it has the property of being able to absorb a dispersion liquid by compressing it in the dispersion liquid, such as polyurethane, polyethylene, polyvinyl chloride, etc. , acrylic, ethylene-vinyl acetate copolymer (EVA), ethylene propylene terpolymer (EPT) rubber, and chloroprene rubber, as well as open cell foams, semi-closed cell foams, and other conventionally known foams. can be widely applied
The hydrosil-based impregnating liquid according to the present invention can also be used for polyurethane and polyvinyl chloride foams, which tend to swell and reduce their mechanical strength with conventional organic solvent-based impregnating liquids. Therefore, it can be applied more advantageously.

The conductive foam of the present invention is usually produced by impregnating the above-mentioned open cell foam with an impregnating liquid in which a conductive material is mixed and dispersed in a hydrosilic aqueous dispersion, and then drying. Drying is usually done by heating. The impregnation step and the drying step may be continuous steps or discontinuous steps. In the case of continuous steps, for example, the foam wound into a roll is introduced into an impregnation tank via a roll, and is impregnated with an appropriate amount by an impregnation control roll. Afterwards, the water may be volatilized by connecting it to a heating drying chamber.

The amount of impregnation depends on the characteristics of the desired conductive foam, such as the type and specific gravity of the open-cell foam, the type and viscosity of the hydrosilic aqueous dispersion of the impregnating liquid, and the type and amount of conductive material mixed and dispersed. Although they vary considerably, generally the solids weight ratio relative to the open cell foam is 0.2 to 3 times, and the weight percentage of the conductive material is 1 to 50%, particularly preferably 0.2 to 3 times each.
It is preferable to set it as 5 to 1 times and 10 to 20%.

[Action/Effect]

Since the conductive foam of the present invention uses hydrosil as an impregnating liquid to impregnate the foam, there are no restrictions on the material of the foam (and there are no restrictions on the type and amount of conductive material to be mixed and dispersed). The polymer particles are extremely small and have very good dispersibility, and especially in the case of acrylics, which have tackiness, this tackiness makes them the best binder. The body has the advantage that low electrical resistance can be obtained with a small amount of conductive material, there is little variation throughout, and there is no shedding or separation of the conductive material.

Hereinafter, the present invention will be explained in more detail with reference to Examples, Comparative Examples, and Test Examples, but the present invention is not equally limited by these.

Example 1 A monomer mixture consisting of 76 parts of 2-ethylhexyl acrylate, 4 parts of acrylic acid, and 20 parts of acrylonitrile was subjected to bulk polymerization using 0.5 parts of benzoyl peroxide as a polymerization initiator, and then mixed with 4 parts of aqueous ammonia and water. 500 parts were added thereto, and the mixture was thoroughly stirred and mixed to obtain an acrylic hydrosil. Add 60 parts of acetylene black to this acrylic hydrosil, mix and disperse in a ball mill to prepare an impregnating liquid,
, 03 was impregnated with a solid content of 1 to 2 times the weight ratio, and then heated at 120°C in a heating drying chamber.
The conductive foam of the present invention was obtained by blowing hot air at 2@3/min (foam travel speed 0.2+g/min) and drying.

Example 2 Under the same conditions as Example 1, instead of the acetylene blank,
A conductive foam was obtained using silver powder (average particle size of about 50 μm).

Example 3 Solution polymerization using a monomer mixture consisting of 20 parts of acrylic acid amide, 30 parts of ethyl acrylate, and 50 parts of 2-ethylhexyl methacrylate as a solvent using 250 parts of dioxane and 0.5 parts of benzoyl peroxide as a polymerization initiator. After that, dioxane was collected and removed by vacuum 7A distillation,
10 parts of aqueous ammonia and 500 parts of water were added and mixed with thorough stirring to obtain an acrylic hydrosil. 80 parts of carbon black was added to this hydrosil and mixed and dispersed in a ball mill to form an impregnating liquid, which was then impregnated into a polyvinyl chloride foam with a specific gravity of 0.15 to a weight ratio of 0.5 to 1. A conductive foam was obtained by heating and drying under the same operating conditions as in Example 1.

Comparative Example 1 Chloroprene latex (Kaikagaku LM-60) 60%
Add water-soluble pigment (Carpump 57230% by weight) to the weight solution.
, emulsifier 10% by weight) was added, mixed and stirred to prepare an impregnating solution, which was impregnated into a polyurethane foam having a specific gravity of 0.03 and dried in the same manner as in Example 1 to obtain a conductive foam.

Although an attempt was made to directly mix and disperse 70 parts of carbon black, it gelled and a dispersion liquid could not be obtained.
l.

As a result, the limit was 5 parts of carbon black.

Comparative Example 2 Chloroprene rubber 100 parts oil
95 stearic acid
zinc pentoxide
5 Carbon blank 120 Sodium bicarbonate 15 Sulfur
1.5 tetramethylthiuram monosulfate 3.0 fit (vulcanization accelerator) The mixture having the above composition was extruded and vulcanized and foamed at 150°C to obtain a conductive foam.

When various properties of each of the conductive foams of the above examples and comparative examples were evaluated, the results were as shown in the following table.

Soshita Nahaku -35°

Claims (3)

[Claims] (1) A conductive foam obtained by impregnating open cells with an aqueous dispersion in which a conductive substance is dispersed in an aqueous dispersion containing fine particles of a poorly water-soluble polymer or oligomer, and then drying the dispersion. (2) Claim No. 1 in which the poorly water-soluble polymer or oligomer is an acrylic polymer or oligomer.
) Monoconductive foam according to item 1. (3) Claim (2) in which the acrylic polymer is a copolymer of an alkyl (meth)acrylic ester, a monomer having a hydrophilic group, and other monomers that can be further copolymerized as necessary. conductive foam.