JPH0428774A - Electrically conductive coating - Google Patents

Abstract

PURPOSE:To obtain the subject coating consisting essentially of an aqueous resin emulsion, copper (alloy) powder and phosphonic acids without deteriorating electric conductivity for a long period. CONSTITUTION:The objective coating is composed of an aqueous resin emulsion (preferably having 5-35 deg.C glass transition temperature, e.g. an acrylic resin), copper and/or copper alloy powder (having preferably 60-450 mesh particle size distribution and 0.7-2.3g/cc apparent density), phosphonic acids (preferably triphosphonic acid or alkali metal salts thereof) and preferably a silane coupling agent, a titanate coupling agent, a chelating agent and/or an ascorbic acid derivative.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a conductive paint, and more particularly to a conductive paint whose conductivity does not decrease over a long period of time.

[Conventional technology]

Recently, the development of electronic devices such as computers and word processors and VTRs has been remarkable. These electronic devices incorporate precision circuit elements. Due to the high degree of integration, these electronic circuit elements operate with a small current, making them more likely to be destroyed by external electromagnetic waves or to malfunction. When electronic circuit elements were conventionally housed in metal casings, this casing also had the function of protecting the circuit elements from electromagnetic interference, so there was no particular problem.

However, the housings of electronic devices are being replaced by plastic molded products due to demands for weight reduction and mass production, and these are now becoming film-based. Unlike metal casings, plastic casings are electrically insulating, allowing electromagnetic waves to easily pass through them.
Electronic circuit elements housed inside cannot be sufficiently protected from external electromagnetic waves.

Conventionally, various methods have been devised to impart conductivity to plastics, and many attempts have been made to prevent electromagnetic interference by using these methods.

One method is to apply conductive paint to the inner surface of plastic housings to protect electronic components from electromagnetic interference.

The mainstream of conductive paints is one in which a dried paint film exhibits conductivity by mixing conductive fine powder such as metal powder into a paint vehicle. Gold, silver, nickel, copper, etc. are commonly used as metal powders. Precious metals such as gold and silver are preferable because they have excellent conductivity, are stable against oxidation, and maintain stable conductivity over a long period of time, but they are also expensive, so they are expensive as paints for electromagnetic shielding. is difficult to put into practical use. Therefore, paints using inexpensive metal powders other than noble metals, such as nickel and copper, are often used.

Most of the conductive paints using these metal powders are solvent-based paints, with only a few nickel-type water-based conductive paints (
JP-A No. 63-6069) is only known.

However, considering the toxicity of organic solvents, the risk of fire, the problems of environmental pollution due to the volatilization of organic solvents into the atmosphere, the problems caused by solvent cracks in plastics, and the advantages of being able to clean painting equipment with water, water-based conductive paints emerged. is strongly desired. Also, when comparing nickel and copper as metal powders, their conductivity and
Copper is advantageous in many respects, including cost. In view of the above situation, the present inventors first proposed a copper type water-based conductive paint. (Patent Application No. 1-298187)
.

This newly developed copper type water-based conductive paint has excellent storage stability and stable conductivity of the paint film at room temperature, and is extremely excellent. However, when the paint film is exposed to high temperatures,
There are cases where the conductivity deteriorates over time and the electromagnetic shielding effect tends to become insufficient.

Solvent-based copper-type conductive paints use anthracene and its derivatives (Japanese Unexamined Patent Publication No. 56-163165), organic titanates (Japanese Unexamined Patent Publication No. 56-36553), and aminophenols in order to stabilize conductivity over a long period of time. Derivatives and phenylenediamine derivatives (JP-A-58-22516
No. 8) Products containing various other compounds have been proposed.

However, it is completely unthinkable to apply these compounds to the copper type water-based conductive paint proposed by the present inventor. That is, there is a fundamental difference between solvent-based and water-based systems, and in particular, the behavior of solvents and water is completely different when it comes to conductivity, so similar effects cannot be expected at all.

When the present invention was actually applied, it was found that gelation occurred and that stable conductivity was not necessarily maintained over a long period of time.

[Problem to be solved by the invention]

The problem to be solved by the present invention is to further improve the copper-type water-based conductive paint that the inventor has already developed. An object of the present invention is to provide a conductive paint having stable conductivity.

[Means for Solving the Problems] As a result of extensive research by the present inventors in order to solve the above-mentioned problems, we have found that a copper-type water-based conductive paint containing phosphonic acids can be used even in high-temperature environments. It was discovered that it has stable conductivity, leading to the present invention.

That is, the conductive paint of the present invention is characterized by containing phosphonic acids in a paint composition mainly consisting of an aqueous resin emulsion, copper and/or copper alloy powder.

[Function and structure of the invention]

The most suitable copper powder for use in the present invention is so-called ordinary electrolytic copper powder.

Generally speaking, pulverized copper powder or atomized copper powder, which is produced using a pulverizer such as a ball mill or crusher, is well known as copper powder, but pulverized copper powder has a small apparent density and a slightly rough particle size distribution, and is Since oil and fat often adhere to the surface, it is difficult to say that it is a preferable copper powder in the present invention. Furthermore, atomized copper powder is spherical in shape and has a rougher particle size distribution than electrolytic copper powder, so it is not preferable. On the other hand, the electrolytic copper powder preferably used in the present invention has a dendritic shape, a particle size distribution of usually 60 to 450 mesh, and an apparent density of about 0.7 to 2.3 g/cc. Therefore, it has less adhesion of oils and fats. In the present invention, copper powder other than electrolytic copper powder can be preferably used as long as it satisfies all the above-mentioned physical properties. The amount of copper powder used is 40 to 95% by weight, preferably 60 to 90% by weight in the dry coating film.

The copper alloy is an alloy of copper and other metals, and the proportion of other metals is 40% by weight or less, preferably 20% by weight or less. Preferred examples of other metals include zinc, tin, lead, nickel, and aluminum.

Examples of the aqueous resin emulsion (hereinafter referred to as emulsion) in the present invention include resin emulsions such as acrylic resin, vinyl acetate resin, ethylene-vinyl acetate copolymer resin, vinyl chloride resin, and vinyl chloride-vinylidene chloride copolymer resin. However, the glass transition temperature of these resins is -5
It is preferable to use a temperature of 5°C to 35°C or higher. These emulsions may be prepared by emulsion polymerization of the hexamer from the beginning to form an emulsion, or by forming a polymer once and then forming it into an emulsion again. Furthermore, it is preferable that the emulsion contains an emulsifier, particularly a nonionic emulsifier. The concentration of resin in the emulsion is as high as 30-60% by weight.

Examples of the phosphonic acids in the present invention include diphosphonic acids, triphosphonic acids, tetraphosphonic acids, pentaphosphonic acids, and alkali metal salts thereof such as sodium, preferably aminotrimethylenephosphonic acid and aminotriethylidenephosphonic acid. , triphosphonic acids such as aminotriethylenephosphonic acid, and alkali metal salts thereof. More preferred are aminotrimethylenephosphonic acid and its alkali metal salts. Representative examples of the alkali metal of the alkali metal salt include sodium and potassium, with potassium being particularly preferred.

These phosphonic acids are thought to contribute to maintaining conductivity by preventing oxidation of the copper powder. Furthermore, since these are compounds that dissolve in water, they can be preferably incorporated into water-based paints.

The blending amount of these phosphonic acids is 0.1 to 10 parts by weight, preferably 0.5 to 5 parts by weight, per 100 parts by weight of copper and/or copper alloy powder. If the amount is less than 0.1 part by weight, a sufficient effect will not be obtained, and if it exceeds 10 parts by weight, the effect will not increase, and on the contrary, the coating film will become brittle and properties other than conductivity will deteriorate. Undesirable.

The conductive paint of the present invention further includes a silane coupling agent,
It is preferable to incorporate at least one compound selected from the group consisting of titanate coupling agents, chelate forming agents, and ascorbic acid derivatives. These compounds work together with the above-mentioned phosphonic acids to further improve the conductivity during coating film formation and to increase the stability over time in a high temperature environment.

As the silane coupling agent, T-glycosidoxypropyltrimethoxysilane, vinylmethoxysilane, γ-
Examples include (2-aminoethyl)aminopropylmethyldimethoxysilane.

Examples of the titanate coupling agent include isopropyltriisostearoyltitanate, bis(dioctylpyrophosphate)oxyacetate titanate, isopropyltri(N-aminoethyl-aminoethyl)titanate, and the like.

As the chelate forming agent, a compound capable of forming a chelate is used, and examples thereof include ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, and alkali metal salts or alkaline earth metal salts thereof.

Examples of ascorbic acid derivatives include ascorbic acid phosphate, L-ascorbic acid-2 sulfuric acid disodium trihydrate, and the like.

The blending amount of these compounds is copper and/or copper alloy powder 1
0.1 to 5 parts by weight, preferably 0.5 parts by weight
~3 parts by weight. If the amount is less than 0.1 part by weight, a sufficient effect will not be obtained, and if it exceeds 5 parts by weight, the effect will not increase and the coating film will become brittle or properties other than conductivity will deteriorate. Undesirable.

When producing the conductive paint of the present invention, the method of adding these compounds is not particularly limited; they are added and mixed in advance to the emulsion to be used, and then copper and/or copper alloy powder is added. How to add and mix,
There are two methods: a method of mixing copper and/or copper alloy powder and an emulsion and adding and mixing these compounds after forming a paint, and a method of simultaneously mixing copper and/or copper alloy powder, an emulsion, and these compounds. Can be adopted.

The conductive paint of the present invention can contain various additives that are usually added to general water-based paints, such as pigment dispersants, thickeners, plasticizers, and antifoaming agents. Additionally, generally known antioxidants can be added as appropriate. Furthermore, when a resin emulsion with a high glass transition temperature is used, a wide range of film-forming aids used in ordinary water-based paints can be used so that film formation can be achieved even at room temperature. Examples of film-forming aids include aromatic hydrocarbons such as toluene and xylene, esters such as butyl acetate, and mono- and dialkyl ether derivatives of ethylene glycol or diethylene glycol such as cellosolve acetate and butylcarpitol acetate.

The thus obtained conductive paint of the present invention has high conductivity when applied or printed by an appropriate method such as spray painting, brush painting, roll coater or screen printing, and has stable conductivity for a long period of time. A coating film can be easily obtained. Also, since it is water-based, it can be diluted with water and painting equipment can be washed with water. Furthermore, it has the characteristics that there is no risk of environmental pollution, poisoning, or fire caused by organic solvents.

Furthermore, the paint of the present invention can be used not only as a paint but also as a molded product for electromagnetic shielding.

[Examples] The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these Examples. Note that "parts" in these examples mean parts by weight.

Example 1 Dissolve 0.3 parts of polyoxyethylene nonyl phenyl ether and 2 parts of aminotrimethylene phosphonic acid in 15 parts of water, add to 32 parts of an acrylic emulsion mainly composed of acrylic esters and methacrylic esters, and mix until homogeneous. Stir and mix until combined. Furthermore, 5 parts of butyl cellosolve was added and stirred until uniform. Electrolytic copper powder (Fukuda Metal Foil Powder Industry ■ rCE-) 15J, particle size 250-350
Add 46 parts of anti-foaming agent under stirring, and finally add 0.2 parts of antifoaming agent.
A conductive paint was obtained. To evaluate this paint, it was applied to art paper to a dry film thickness of 60 μm.
After standing overnight at 20°C and 65% RH, the initial surface resistance was measured. Then in a hot air circulation dryer at 70°C for 10
Surface resistance was measured after 00 hours and 2000 hours of exposure. The results are shown in Table 1.

Example 2 In Example 1, 2 parts of aminotrimethylenephosphonic acid was replaced with 1 part, and 0.5 part of T-glycosidoxypropyltrimethoxysilane was added, and the other conditions were the same as in Example 1 to prepare a conductive material. Obtained sex paint.

This paint was evaluated in the same manner as in Example 1.

The results are shown in Table 1.

Example 3 Without adding 0.5 parts of γ-glycosidoxyprobyltrimethoxysilane and 5 parts of butyrocellosolve in Example 2,
A conductive coating material was obtained in the same manner as in Example 1 except that 5 parts of butylcarpitol acetate in which 0.5 parts of isopropyl triisostearoyl titanate was dissolved was added instead. This paint was evaluated in the same manner as in Example 1.

The results are shown in Table 1.

Example 4 A conductive paint was obtained in the same manner as in Example 1 except that 1 part of sodium ethylenediaminetetraacetic acid was further used. This paint was evaluated in the same manner as in Example 1. The results are shown in Table 1.

Example 5 In Example 1, 2 parts of aminotrimethylenephosphonic acid was changed to 0.5 parts, and L-ascorbic acid-2-
A conductive paint was obtained in the same manner as in Example 1 except that 0.5 part of sulfuric acid/disodium dihydrate was added.

This paint was evaluated in the same manner as in Example 1.

The results are shown in Table 1.

Comparative Example 1 A conductive paint was obtained in the same manner as in Example 1 except that aminotrimethylenephosphonic acid was not used.

This paint was evaluated in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 2 A conductive coating material was obtained in the same manner as in Example 1 except that 2 parts of T-glycosidoxypropyltrimethoxysilane was added without using the aminotrimethylenephosphonic acid in Example 2. This paint was evaluated in the same manner as in Example 1.

The results are shown in Table 1.

Comparative Example 3 A conductive coating material was obtained in the same manner as in Example 1 except that 2 parts of isopropyl triisostearoyl titanate was added instead of using the aminotrimethylenephosphonic acid in Example 3. This paint was evaluated in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 4 Instead of using aminotrimethylenephosphonic acid and butyrocellosolve in Example I, 5 parts of butylcarpitol acetate in which 1 part of T-glycosidoxypropyltrimethoxysilane and 2 parts of isopropyl triisostearoyl titanate were dissolved was used. In addition, a conductive paint was obtained in the same manner as in Example 1 except for the above.

This paint was evaluated in the same manner as in Example 1.

The results are shown in Table 1.

Comparative Example 5 A conductive paint was obtained in the same manner as in Example 1 except that the aminotrimethylenephosphonic acid in Example 4 was not used.

This paint was evaluated in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 6 A conductive paint was obtained in the same manner as in Example 1 except that the aminotrimethylenephosphonic acid in Example 5 was not used.

This paint was evaluated in the same manner as in Example 1. The results are shown in Table 1.

Claims (3)

[Claims] (1) A conductive paint characterized by being mainly composed of an aqueous resin emulsion, copper and/or copper alloy powder, and phosphonic acids. (2) The conductive paint according to claim (1), wherein the phosphonic acid is at least one of triphosphonic acid and an alkali metal salt thereof. (3) The conductive paint according to claim (1), further comprising at least one selected from the group consisting of a silane coupling agent, a titanate coupling agent, a chelate forming agent, and an ascorbic acid derivative.