JPS60258273A - Electrically conductive coating composition - Google Patents

Abstract

PURPOSE:To provide the titled composition having excellent electrical conductivity, and useful for the formation of layer for shielding the electromagnetic wave emission of a computer, etc., by treating electrolytic copper powder with an organic carboxylic acid, and compounding the product as the electrically conductive filler with a binder resin and an organic solvent. CONSTITUTION:The objective composition can be prepared by compounding (A) an electrically conductive filler obtained by washing (i) electrolytic copper powder having a particle size distribution characterized in that >=80wt% of the copper powder passes through the 350 mesh sieve, and having an apparent density of 0.5-1.5g/cm<3> and a specific surface area of >=2,000cm<3>/g (by sub-sieve sizing method) with (ii) an organic carboxylic acid (preferably citric acid), and drying the product, with (B) a binder resin (e.g. acrylic resin) and (C) an organic solvent (e.g. xylene, etc.).

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] The present invention relates to a conductive paint using fine copper powder having high conductivity.

[Industrial application field]

Conductive paints are used to form electromagnetic shielding layers for plastic housings of computer equipment, digital equipment, office equipment, etc. that generate or utilize electromagnetic waves such as pulses and timing signals for video games, personal computers, printers, etc.

[Prior art]

The conductive paint is made of conductive filler fine powder, such as gold, silver,
Metal particles such as copper, nickel, molybdenum, and tungsten or their derivatives, and carbon-based fine powders such as carbon black and graphite are mixed with polyphenylene ether, acrylic or cellulose thermoplastic resin, or epoxy or phenolic thermosetting resin. It is dispersed in a solution and is used for many purposes such as circuit paste, conductive adhesive, electromagnetic shielding agent, etc.
No. 8894, No. 55-39083).

Nickel powder is mainly used as the metal powder, but silver is expensive and nickel has the disadvantage that its conductivity is one step inferior to that of silver. Therefore, efforts are being made to develop conductive paints using copper, which has approximately the same conductivity as silver and about four times as much conductivity as nickel.

The copper powder used in copper-based conductive paints includes electrolytic copper powder used in powder metallurgy and electric brushes, and crushed copper powder used in ink pigments, but these were developed for use in conductive paints. However, the reality is that its conductivity is inferior to that of silver.

[Structure of the invention]

As a result of intensive research, the present inventors found that 350 meshes or less (J
IS sieve standard) has a particle size distribution of 80% or more, and a specific surface area of 2
Electrolytic copper powder having powder properties of 0.000 d/d/ or more (Pishev's Subseep Iiser method) and an apparent density of 0.5 to 1.52/d1 was treated with an organic carboxylic acid to remove the oxide layer on the surface. It was discovered that a conductive paint using electrolytic copper powder has conductivity comparable to that of a silver paint, and the present invention was achieved.

[Copper powder] The shape and powder characteristics of copper powder vary depending on the manufacturing method, as shown in Table 1, but copper powder used in paints is mainly used because the particle size must be from several microns to several tens of microns. Electrolytic copper powder and crushed copper powder are used for this purpose. Crushed copper powder is made by using fatty acids such as stearic acid as a lubricant during crushing.
Unless this is removed, conductivity will not develop, and the specific surface area is extremely large, making anti-oxidation treatment difficult, which is undesirable. On the other hand, electrolytic copper powder has a developed dendritic shape and is highly pure, so it is easy to obtain high conductivity and is most preferred as copper powder for conductive paints. Among electrolytic copper powders, those particularly suitable for use in conductive paints have a particle size distribution in which the copper powder that passes through a 350 mesh (JIS standard) sieve accounts for 80% by weight or more, and has an apparent density of o, s ~ 1.5
y/l:tA, the specific surface area measured by the subsieve sizer method is 2000, -d/f or more, and exhibits excellent conductive performance. 1 These electrolytic copper powders are soaked in an organic carboxylic acid (monocarboxylic acid, polycarboxylic acid, or hydroxycarboxylic acid) solution and stirred to remove the oxidized layer on the surface of the copper powder, and then the copper powder is filtered and separated. After that, it is used as a conductive filler after drying.

Examples of organic carboxylic acids used for surface treatment include:
Hydroxycarboxylic acids such as lactic acid, tartaric acid, glyceric acid, malic acid, citric acid, gluconic acid, trobic acid, benzylic acid, mandelic acid, tartronic acid, atrolactic acid and glycolic acid; monocarboxylic acids such as acetic acid and glopionic acid , succinic acid, itaconic acid, tricarballylic acid,
Examples include polycarboxylic acids such as ethylenediaminetetraacetic acid.

Particularly preferred among these organic carboxylic acids are hydroxycarboxylic acids. The surface oxidation layer of the copper powder can be easily removed by adding copper powder to a solution in which these organic carboxylic acids are dissolved in a suitable solvent, immersing the solution for a certain period of time, and leaving it to stand, or stirring it.

The reduction loss of this copper powder is 0.2% by weight or less.

As the solvent for dissolving the organic carboxylic acid, there are water and various organic solvents, but water and alcohols such as methanol, ethanol, propatool, etc. are preferable in view of their high ability to solvate copper ions.

[Paint components]

Copper powder treated with an organic carboxylic acid to remove the abrasive layer (hereinafter sometimes referred to as "copper powder treated with an organic carboxylic acid") has a conductive property of the conductive paint composition of the present invention. Copper powder is blended as a filler into the coating composition together with a resin binder and an organic solvent, and the blending ratio of the copper powder is 10 to 90% by weight, preferably 30 to 70% by weight of the coating composition. The resin components of the paint include thermoplastic resins such as acrylic fats, polyvinyl chloride, and ethyl cellulose polymers, and thermosetting PE resins such as epoxy resins, phenolic resins, urethane resins, and urea resins. Mixtures are available. In addition, solvents used to reduce the viscosity of coating compositions may vary depending on the method of use (spraying: painting, dipping, screen printing, etc.) and the material to be coated (plastic, wood, etc.). Hydrocarbons such as toluene and xylene; Alcohols such as ethyl alcohol and probyl alcohol; Ketones such as methyl ethyl ketone and methyl imbutyl ketone; Esters such as ethyl acetate and butyl acetate; Ethers such as ethyl selonup and butyl cellosolve etc. can be mentioned.

These solvents are appropriately selected and used depending on the type of binder resin. One type of solvent may be used alone, or two or more types may be used in combination.

The composition of conductive paints containing these components varies depending on the coating method and application used, but examples include spray coating for electromagnetic shielding, organic carboxylic acid treated copper powder 40-60% by weight solvent 20- 55% by weight In addition to the above-mentioned components, various additives can be added to the conductive coating composition of the present invention as required.

In particular, various surfactants, anti-settling agents, thickeners, thixotropic agents, 111 dispersants, which are used to prevent settling of copper powder, and various leveling agents, which are used to make the coating smooth, and maintain conductivity over a long period of time. Rust preventive agents, antioxidants, and flame retardants may be added as necessary to the extent that conductivity and physical properties of the coating film are not impaired.

The conductive coating composition of the present invention is prepared by mixing the above-mentioned binder resin, organic carboxylic acid-treated copper powder, solvent, various additives to be added as necessary, etc. It may be made into a paint using a dispersing means (for example, a disper, a ball mill, a sand mill, an attritor, a three-roll mill, a Huber muller, etc.). The nine-band coating composition of the present invention thus obtained can be sprayed,...
It is used by coating or printing on the object to be coated by means such as coating, dipping, or screen printing.

The present invention will be explained with reference to examples below. In the examples, "parts" means "parts by weight" and "%" means "% by weight."

picture,. It's hbo, □. ４□□Eeee. . (c) "Measurement was carried out by the method. In other words, as shown in Figure 1, a copper-clad paper phenolic laminate with a length of 10 mm and a width of 53 mm was prepared by etching away the copper foil portions leaving a width of 1.5 mm from both ends. (The distance between both copper foil parts 2 and 2 on the board is 7LMl.) On top, conductive paint is applied to a width of 1 m, and
After leaving it for 4 hours, measure the thickness of the coating film 3 using a digital micrometer (Digimatic Indicator 5 manufactured by Mitoyo Seisakusho Co., Ltd.).
43), and the electrical resistance of the coating film was measured using a Wheatstone bridge (type 2755 manufactured by Yokogawa Electric Co., Ltd.).
The volume resistivity was calculated using the following formula.

Measured resistance value x thickness Example 1 400 parts of a 10% citric acid aqueous solution was added to 100 parts of industrial electrolytic copper powder having the powder characteristics shown in Table 2, and the mixture was mixed with a stirrer for 15 minutes.
After stirring for an hour, the copper powder was separated by filtration, thoroughly washed with water, and dried.

Next, 92 parts of the above-mentioned citric acid-treated copper powder
A conductive coating composition was prepared by dispersing a mixture of 40% toluene solution (63 parts, methyl ethyl ketone, 23 parts, xylene, 23 parts) by high-speed dispersion. This coating composition was applied to a width of 1 crn on the substrate 1 shown in FIG. 1, and after being left for 24 hours under conditions of 23° C. and 50% RH, the volume resistivity value of the obtained coating film 3 was measured. However, it was on the 7.4×1σ-Ω· side.

Example 2 Surface oxides of industrial electrolytic copper powder having the powder properties shown in Table 2 were removed in the same manner as in Example 1, except that tartaric acid was used instead of citric acid. The reduction loss of this copper powder is 0.
It was 12 heavy horsemen%.

The above tartaric acid treatment electrolysis@8 100 parts Epoxy resin (Epikoat +815) 50 parts (Oil F Hishiel Epoxy Co., Ltd.) Hardening agent (Epicure +3025) 25 parts (Oil shell epoxidation) The above mixture was roll-kneaded to form a conductive paste. Obtained. This product was screen printed with a 1-width width on the substrate 1 shown in FIG. 1 using a 200-mesh Tetron screen to form a coating film. The volume resistivity of the coating film was measured after being left at 23° C. and 50% RH for 24 hours, and found to be 3.5×10 Ω·m. , Comparative Examples 1 to 5 Commercially available electrolytic copper powders shown in Table 2 with particle sizes suitable for use in paints were treated with citric acid in the same manner as in Example 1, and paints with the same composition were prepared. A composition was prepared, a coating film was formed under the same conditions as in Example 1, and the volume resistivity of this was measured, and the results shown in Table 2 were obtained.

Note that the reduction loss of the citric acid-treated copper powder used in Comparative Example 5 was 0.14% by weight.

Comparative Example - A coating composition was prepared in the same manner as in Example 1 except that flaky silver powder was used instead of citric acid-treated copper powder, and a coating film was created using the same, and the volume of the coating film was When the specific resistance value was measured, it was 1.7×10 −4 ΩaCrn.

Comparative Example A coating composition was prepared in the same manner as in Example 1 except for step 1, using carbonyl nickel powder as a substitute for citric acid-treated copper powder. When the volume resistivity value of the film was measured, it was found to be 3.2×10-3Ω1ICrn
It was made.

(Margin below) ).

[Brief explanation of the drawing]

The attached drawing is a perspective view of a partially copper-clad laminate used for measuring the volume resistivity of a paint film. In the drawing, 1 represents a paper phenol substrate, 2d a copper foil portion, and 3 a paint film, respectively. Patent Applicant Mitsubishi Yuka Co., Ltd. Agent Patent Attorney Hidetoshi Furukawa Agent Patent Attorney Masahisa Hase Figure 1

Claims (1)

[Claims] 1) (a) Copper powder passing through a 3s o mesh sieve has a particle size distribution of 80% by weight or more, and has an apparent density of o, s to t, s y /cwl, Specific surface area is 2000
A conductive paint made by washing the electrolytic copper powder of cd/ (sub-seep sizer method) with an organic carboxylic acid, drying it, using it as a conductive filler, and blending it with (b) a binder resin and (c) an organic solvent. Composition. 2) The conductive coating composition according to claim 1, wherein the organic carboxylic acid is citric acid.