JPH0251535A - Electrically conductive powder and preparation thereof - Google Patents

Abstract

PURPOSE:To obtain an electrically conductive powder having a stable and high conductivity, good dispersibility and flowability and being suitable as a raw material for manufacturing an electrically conductive composite material. CONSTITUTION:This electrically conductive powder is a spherical siloxane particle the surface of which is covered with silver by bringing the spherical siloxane particle into contact with a soln. of silver compd. and a soln. of a reducing agent. It is pref. when the spherical siloxane particles are dispersed in the coexistence of a wetting agent and said contact treatment is performed, because a homogeneous surface treatment can be attained. As the wetting agent, methyl alcohol, ethyl alcohol, ethylene glycol, etc., are pref. As the silver compd. and a reducing agent, silver nitride and a tartrate or hydrogen peroxide are respectively pref.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a novel conductive powder in which the surface of spherical siloxane particles is coated with silver, and a simple method for producing the same.

The conductive powder obtained by the present invention is suitable as a material that can be applied to conductive composite materials such as conductive paints, conductive inks, and conductive films.

[Conventional technology and its issues]

Quality requirements for conductive powders are becoming more sophisticated, especially for conductive powders used in conductive composite materials such as conductive paints, conductive inks, and conductive films.
Precision printing suitability is increasingly required. In other words, conductive powder is required to have high concentration and homogeneous dispersibility during the production of paints and inks, and fluidity of paints and inks is also required.

Silver is a conventionally known conductive powder.

There are total bending powders such as copper, nickel, and aluminum, carbon powders, and tin oxide powders. However, since these conductive powders are generally produced by a pulverization method, fine particles with high sphericity cannot be obtained, and therefore, the above-mentioned requirements for dispersibility and fluidity cannot be met. Of course, there are methods for obtaining fine and highly spherical conductive powder, but these require sophisticated and complicated processing.

Therefore, there is a desire to develop a method for easily obtaining fine and highly spherical conductive powder, and methods have been proposed in which the surfaces of glass beads or resin beads are coated with conductive metal by electroless plating or the like. However, since there is no bond between the glass beads or resin beads and the conductive metal coating layer, the conductive metal coating layer falls off when the conductive powder is dispersed in paint or ink, making it difficult to achieve the desired conductivity. There was a problem. Therefore, there has been a demand for the development of a new conductive powder and its manufacturing method.

[Means to solve the problem]

As a result of various studies in view of the above-mentioned prior art and its problems, the present inventor has completed a conductive powder and a manufacturing method thereof according to the present invention that can achieve the intended purpose.

That is, the conductive powder according to the present invention is characterized in that the surface of spherical siloxane particles is coated with silver.

The siloxane particles in the present invention are low molecular weight hydrolyzable silanes or polymers of siloxane compounds, in which 90% or more of all bonds are siloxane bonds, and include methyl groups and phenyl groups directly bonded to silicon.

β-glycidoxypropyl group, alkoxyl group.

The bond of one or more of chloro group, hydroxyl group, and hydrogen is present or 10% or less, and the main component is substantially Sing. The siloxane particles in the present invention are required to have a spherical shape, because when the conductive powder according to the present invention is used as a material for a conductive composite material, dispersibility and fluidity must not be inhibited. It is from. The siloxane particles may be homogeneous or irregular, but it goes without saying that homogeneous particles are preferred from a practical standpoint. The particle size of siloxane particles is from 0.1μ in diameter to
50μ is used. It is difficult to obtain a material with a diameter of less than 0.1 μm, and a material with a diameter of more than 50 μm is unsuitable for precision printing. Therefore, in practice, a diameter of about 1 μm to about 5 μm is preferable.

Various methods can be considered to obtain the conductive powder according to the present invention. For example, ■ a PVD method in which siloxane particles are brought into direct contact with silver vapor in a fluidized bed, ■ a method in which reduced silver is deposited on the surface of siloxane particles by electroless plating, and ■ a silver compound such as silver hydroxide is applied to the surface of siloxane particles. Any method such as a method of reducing after coating can be applied. From the point of view of simple manufacturing method, method (2) is advantageous. Claim 2 is the method (2).

That is, the method for producing a conductive powder according to the present invention involves contacting spherical siloxane particles with a solution of a silver compound and a solution of a reducing agent to produce a conductive powder in which the surface of the spherical siloxane particles is coated with silver. It is characterized by obtaining the following.

In the present invention, silver compounds include silver nitrate and silver acetate.

In addition to water-soluble compounds such as silver sulfate and silver nitrite, even water-insoluble compounds such as silver halide, silver hydroxide, silver oxide, silver cyanide, silver thiosulfate, and silver thiocyanate can be used as ammonia. Any chelate compound reacted with a chelating agent such as sodium thionitrate, potassium cyanide, or ethylenediaminetetraacetate (EDTA), which can be dissolved or homogeneously dispersed in water or an aqueous acid or alkali solution, may be used. Silver nitrate is preferred from the viewpoint of easy availability (and easy operation).This silver compound can be used alone or in a mixture of two or more, in water or in an aqueous solution of an acid or alkali, or as a homogeneous dispersion thereof. The amount of this silver compound used varies depending on the purpose of use of the conductive powder and the particle size of the siloxane particles, and is not particularly limited.
The amount of the silver compound is at least 30 parts by weight, preferably 50 parts by weight or more, based on 100 parts by weight of the siloxane particles. When the amount is less than this, the thickness of the coating layer becomes thinner and it becomes difficult to obtain a highly conductive layer. On the other hand, if a large amount of silver compound is used, not only will the product price increase due to the use of expensive silver, but also the silver coating layer will become too thick, causing the conductive powder to become spherical and the surface The smoothness of the surface may deteriorate, resulting in a decrease in practicality. Therefore, the upper limit of the amount of silver compound used is 1000 parts by weight or less, preferably 700 parts by weight or less.

Next, the reducing agent in the present invention includes tartaric acid and its salts,
Any material can be used as long as it exhibits reducing properties for silver compounds, such as formaldehyde, hydrogen peroxide, hydrazine compounds, diphosphorous acid and its salts, and borohydride compounds such as sodium borohydride. It is advantageous to use tartrates such as sodium tartrate, potassium tartrate, or hydrogen peroxide because of their availability and ease of reaction. The amount of the reducing agent to be used is preferably the amount necessary to completely reduce the silver compound or a slight excess amount.

The excess amount is usually preferably about 10 to 300%. Even if more reducing agent is used, it will not be used and will be wasted.

In the present invention, spherical siloxane particles are brought into contact with a solution of a silver compound and a solution of a reducing agent, and various methods can be used for this purpose. For example, a method of dispersing siloxane particles in a solution of a silver compound and then adding a solution of a reducing agent, a method of dispersing siloxane particles in a solution of a reducing agent and then adding a solution of a silver compound, and a method of adding a solution of a silver compound to a solution of a dispersion of siloxane particles. There is a method of adding the solution and the reducing agent solution at the same time.

The reaction between the silver compound and the reducing agent is usually carried out under stirring, and the reaction temperature is usually 0°C to 80°C, depending on the type of reducing agent, heating or cooling.

The invention according to claim 3 is the invention according to claim 2, characterized in that spherical siloxane particles are dispersed in a coexistence system of a wetting agent.

Although the siloxane particles used in the present invention strongly bond with silver and provide excellent conductive powder, they have the following problems. In other words, the surface of the siloxane particles has high water testability, and in the method of depositing silver on the surface of the siloxane particles by electroless plating in an aqueous system, the siloxane particles float and aggregate on the surface of the aqueous reaction solution, resulting in a homogeneous surface treatment. This makes it extremely difficult to produce conductive powder. The invention described in claim 3 solves this problem by homogeneously dispersing siloxane particles in a system in which a wetting agent coexists.

In the present invention, the wetting agent can be arbitrarily selected as long as it is soluble in water and stable to reducing agents, but it contains a hydroxyl group or an ether bond in its molecular chain, and a carbonization agent that is directly connected to the hydroxyl group or ether bond. The hydrogen group preferably has an average number of carbon atoms of 5 or less, preferably 3 or less, per oxygen atom. Representative examples include monohydric alcohols having 1 to 5 carbon atoms such as methyl alcohol, ethyl alcohol, and propyl alcohol, glycols and their condensates such as ethylene glycol, propylene glycol, and butylene glycol, glycerin, neopentyl glycol, Examples include polyhydric alcohols such as pentaerythtol, cellosolves such as methyl cellosolve and ethyl cellosolve, but methyl alcohol, ethyl alcohol, and propyl alcohol are preferred from the viewpoint of ease of handling.

Ethylene glycol and glycerin are preferred. Furthermore, the following nonionic surfactants can also be used as the lubricant of the present invention. For example, polyoxyethylene alkyl ethers such as polyoxyethylene oleyl ether and polyoxyethylene lauryl ether, polyoxyethylene alkyl phenol ethers such as polyoxyethylene nonyl phenol ether and polyoxyethylene octyl phenol ether, and polyoxyethylene monolaurate. Polyoxyethylene monoalkylates such as polyoxyethylene monooleate, polyoxyethylene sorbitan alkylates such as polyoxyethylene sorbitan monolaurate, and polyoxyethylene sorbitan monooleate, and these nonionic surfactants It is preferable that the HLB is 4 or more, preferably 8 or more, that is, it has many hydrophilic groups. These wetting agents may be used alone or in mixtures of two or more.

The amount of this wetting agent used cannot be specified as it varies depending on the reaction conditions, the type of wetting agent, etc., but the amount of siloxane particles 100
1 to 10,000 parts by weight is used. This is because if it is too small, no wetting effect can be expected, and if it is too large, the reduction reaction may be inhibited.

The wetting agent is preferably added before the reaction between the silver compound and the reducing agent starts. For example, before the siloxane particles are brought into contact with the silver compound solution or the reducing agent solution, the siloxane particles and the wetting agent are dispersed in advance. Alternatively, a wetting agent may be present in the solution of the silver compound or the solution of the reducing agent, and then the siloxane particles may be mixed. In addition, in the case of the former,
The siloxane particles and the wetting agent may be mixed and then added to water for dispersion, or a lubricant may be added to the dispersion system of the siloxane particles for redispersion.

In addition, in the present invention, in addition to the wetting agent, a dispersing agent for stabilizing siloxane particles, a chelating agent for stabilizing the silver compound,
There are no restrictions on the combined use of commonly used additives for electroless heating, such as pH adjusters.

〔Effect of the invention〕

(2) Since the conductive powder according to the present invention uses spherical siloxane as a base material, the adhesion of the silver forming the conductive layer is good and high conductivity can be obtained. Furthermore, since the conductive powder according to the present invention uses spherical siloxane as a base material, it has good dispersibility and fluidity, enables high filling, and provides stable high conductivity.

(2) Since the method for producing conductive powder according to the present invention simply involves bringing a solution of spherical siloxane and a silver compound into contact with a solution of a reducing agent, conductive powder can be easily obtained.

Therefore, the conductive powder obtained by the present invention is suitable as a material that can be applied to conductive composite materials such as conductive paints, conductive inks, and conductive films, and has high industrial utility value. .

Note that the conductive powder according to the present invention can also be used as a silver catalyst.

〔Example〕

Next, the configuration of the present invention will be explained based on examples.

Example 1 Spherical siloxane particles (trade name: "Tospearl 120")
, manufactured by Toshiba Silicone Co., Ltd., average particle size 2 μ) was added to a solution of 4 g of silver nitrate and 6 mil of 28% ammonia water dissolved in 150 g of water to prepare a dispersion in which some spherical siloxane particles were suspended. While stirring, 200 g of a 10% solution of potassium sodium tartrate was added dropwise over about 30 minutes, and while maintaining stirring, the reaction solution was heated to 50°C.
After reacting for 1 hour, the mixture was filtered, washed with water, and dried to obtain 4.4 g of silver-gray conductive powder.

In addition, in the above reaction, the suspended matter of spherical siloxane particles did not completely disappear (although a small amount of white particles were observed in the recovered conductive material, the conductivity was 1.0% under a pressure of 100 kg/-). It showed poor conductivity of 2×10 −2 Ωcm.

Example 2 Spherical siloxane particles (trade name: "Tospearl 120")
To a homogeneous mixture of 2g (manufactured by Toshiba Silicone Co., Ltd., average particle size 2μ) and 0.5g of ethylene glycol dispersed in 50g of water, 4g of silver nitrate and 6d of 28% aqueous ammonia dissolved in 150g of water were added. While stirring, 200 g of a 10% solution of potassium sodium tartrate was added dropwise over a period of about 30 minutes. While stirring was continued, the reaction solution was heated to 50°C, reacted for 30 minutes, and then filtered. , washed with water, and dried to obtain 4.5 g of silver-gray conductive powder.

The above-mentioned conductive powder showed a homogeneous spherical shape when observed with an electron microscope, and the conductive powder under a pressure of 100 kg/c+ll was
It exhibited excellent conductivity of lXl0-3 Ωcm.

Examples 3 to 8 The same procedure as in Example 2 was carried out except that the lubricant ethylene glycol in Example 2 was changed to one listed in Table 1. The results are shown in Table-1.

Table 1 Example 9 In Example 2, the spherical siloxane particles were replaced with phenyl group-containing siloxane particles (Product 22 "Trefil: E-603").
J, manufactured by Toray Silicon Co., Ltd., average particle size 5 μ) was carried out in the same manner as in Example 2, and 4.5 g of silver-gray conductive powder was used.
I got it.

The above conductive powder showed a homogeneous spherical shape when observed with an electron microscope, and the conductivity under pressure of 100 kg/cr was 9X10.
It showed poor conductivity of -'Ωcm.

Example 10 In Example 2, spherical siloxane particles were replaced with epoxy group-containing siloxane particles (trade name: [Trefill: E-601
J, manufactured by Toray Silicon Co., Ltd., average particle size 5μ) was carried out in the same manner as in Example 2, and 4.4 g of silver-gray conductive powder was used.
I got it.

The above conductive powder showed a homogeneous spherical shape when observed with an electron microscope, and the conductivity was 1.2X under a pressure of 100 kg/cTA.
It showed poor conductivity of 10-3 Ωcm.

Example 11 1.5 g of the same spherical siloxane particles as in Example 2 were moistened with 15 g of ethanol and dispersed in 150 ml of water, and 7.5 g of disodium ethylenediaminetetraacetate was added.
g dissolved in 100 ml of water, and while stirring, 5 g of silver nitrate dissolved in 25 g of water was added dropwise over about 15 minutes. Then, the reaction solution was cooled to 5°C and 30% peroxide was added. After adding 50 ml of hydrogen water, 50 ml of 20% sodium hydroxide
g for about 20 minutes, then add 75% of 30% hydrogen peroxide solution.
g was added dropwise over about 30 minutes, followed by stirring, heating to room temperature, aging for 30 minutes, filtering, washing with water, and drying to obtain 4.6 g of silver-gray conductive powder.

The conductive powder had a homogeneous spherical shape when observed using an electron microscope, and exhibited excellent conductivity of 1.9×10 −′Ωcm.

Example 12 By carrying out the same procedure as in Example 3 except for changing polyoxyethylene zirubikune monooleate to sorbitan monostearate (HLB4), 4.3 g of silver-gray conductive powder was obtained, Conductivity is 8. lXl
It was a 0-'Ω mark.

Comparative Example 1 4.3 g of gray-white conductive powder was obtained by carrying out the same procedure as in Example 2 except that the spherical siloxane particles were changed to titanium oxide particles (particle size 2 μ). The conductivity was 3400 Ωcm.

Comparative Example 2 In Comparative Example 1, the amount of titanium oxide particles used was 0.5 g.
The procedure was carried out in the same manner as in Comparative Example 1, except that 2.7 g of silver-gray conductive powder was obtained, and the conductivity was 2.4X10-
However, in order to obtain the same conductivity as when using granular siloxane particles, more roots were required.

Comparative Example 3 In Example 2, spherical siloxane particles were replaced with amorphous siloxane particles (trade name: [Trefill: R-902J
, manufactured by Toray Silicon Co., Ltd., average particle size 5μ) was carried out in the same manner as in Example 2, and a gray-white conductive powder 4.1
g, but the electrical conductivity was 7200Ωcrn.

Comparative Example 4 Commercially available silver powder was pulverized to have a particle size of 5 μm and conductivity of 168×10
The conductivity was measured for a mixture of a conductive powder of −'Ωcm and the siloxane particles used in Example 2. The results are shown in Table 2 together with the conductivity of the conductive powder obtained in Example 2 and the siloxane particles used in Example 2.

Table-2

Claims (3)

[Claims] (1) A conductive powder in which the surface of spherical siloxane particles is coated with silver. (2) A conductive powder characterized in that the surface of the spherical siloxane particles is coated with silver by contacting the spherical siloxane particles with a solution of a silver compound and a solution of a reducing agent. Manufacturing method. (3) The method for producing a conductive powder according to claim 2, wherein spherical siloxane particles are dispersed in a coexistence system of a wetting agent.