HU192359B - Process for producing activated-surface laminar-structure silver pigment suitable for electronics purpose - Google Patents

Abstract

The invention relates to a process for the preparation of platelet-shaped silver pigments having an active surface for electronic application. The essential characteristic of the method is that the silver powder is ground in a suspension of organic solvent in the presence of surface-active additives and fatty acids or their derivatives in a ball mill or bead mill.

Description

FIELD OF THE INVENTION This invention relates to a process for the production of small pigments, high specific surface area, special surface properties, sheet-like silver pigments for use in the manufacture of conductive varnishes, pastes, adhesives and screen-printable compositions for use in the electronics industry.

This special feature of the silver pigment can only be achieved by the subsequent surface treatment of a very fine particle size (1 3 μ) of powder produced by chemical reduction.

No. 2,002,891. According to the process described in US patent, 150 μl Al powder is ground in a petroleum fraction with 3% by weight of stearic acid and 1% by weight of aluminum stearate. The pigment produced by this process has a shiny, sheet-like structure but is not suitable for screen printing because of its large particle size.

No. 1,191,204. According to the British patent, easily machinable metals can be ground in water in the presence of 2 to 10 weight percent high fatty acids. According to the process, the parent metal is a powder having a particle size of less than 4 mm and a film having a surface area of less than 5 mm ² . Because of the particle size of the product thus produced, it cannot be used for screen printing

No. 0 021 439. According to European Patent Specification, silver powders with a particle size of less than 8 µm are ground in an aqueous medium containing 0.2 to 0.5% by weight of fatty acid (oleic, stearic, linoleic or linolenic acid). The fatty acid is chemisorbed in a monolayer layer on the silver surface. Grinding is carried out with glass beads 3 to 6 mm in diameter for 48 to 64 hours. The resulting silver pigment according to the description given data capacity and the degree of anizometria far behind the thick film electronics technology needs, such as the volume sprayed from 2.5 to 4.7 g / cm optimum from 0.7 to 0.8 g / ^cm-3 - against her. In addition, due to the long processing time, process productivity is low.

The present invention is based on the discovery that when powdered metal is readily machined, a powder of near isometric particles in a slurry in an organic medium in the presence of additives, such as anion and / or cationic surfactants and fatty acids, After 32 to 36 hours of treatment, there is a significant change in shape and properties. Due to the flattening effect of the balls, the particles will have a lamellar structure (typical ratios (length, width, thickness) of 15: 10: 1 to 100: 10: 1 based on electron microscopy) and the additives adsorbed onto the surface of the plates they improve the properties of the product, increase its dispersibility, that is, make it organophilic.

The plate pigment is prepared from chemically reduced silver powders with a particle size of less than 10 μη and containing at least 98.0% silver.

The organic treatment medium consists of a solvent, a surfactant and a fatty acid and is intended to deliver additives to the silver surface and to prevent metal powder particles from sticking together. The choice of an organic solvent is determined by the solubility of the additives, i.e. the surfactant tube, in the fatty acid.

When preparing the treatment medium, it should be taken into account that, in the case of an excessively viscous medium, the free floating of the metal powder particles is eliminated and the medium becomes a thick slurry. This will inhibit the flattening process.

The viscosity of the treatment medium at 25 ° C is preferably not more than 0.003 Pa.

The solvents we find suitable, aromatic compounds, benzene and homologues thereof, preferably toluene or xylene, esters, preferably methyl, ethyl, and butyl acetate and mixtures thereof in various ratios, as well as kerosene fractions such as white spirit.

Surfactants prevent dust from sticking during treatment and in the dry state, making it easy to apply in lacquers, pastes and adhesives. The chemisorbable, high-molecular-weight organic matter makes the silver-pigmented organophyll an organophile, so that any further air bubbles are removed during further processing.

The use of organophilic bentonite as the surfactant, preferably montmorillonite by ion exchange with cationic surfactants, reduces the electrical resistance of the lacquered silver pigment varnish, paste or adhesive, and low-density silver settling rate. The fatty acids used as an additive promote the slip of silver platelets onto the surface of the organic medium of the varnish or paste, so that the top coat when coated with conductive pastes and varnishes is rich in pigment and therefore a good electrical conductor and low in binder. It can be used as surfactants even at high carbon numbers (C $ - C ₂₅₎ unsaturated carboxylic acids alkotottt lower alcohols, esters (preferably butyl ester) is.

For surface treatment we use a ball mill. In order to ensure that the treatment process does not involve a grinding process, but rather a flattening and flattening process, it is essential to select the appropriate treatment conditions, such as material quality, size, ball to Ag powder weight, drum volume and rotation, and treatment time. .

In a ball mill with steel balls having a diameter of 6 to 10 mm, rotated at 90 to 140 rpm, balls having a diameter of 5 dm ^{3 are} balls having a mass ratio of Ag: 15: 1 to 5: 1 and 3: 1 to 1: 1 by weight. The organic media to Ag powder is treated with a weight ratio of the starting Ag powder for 28 to 40 hours, preferably 32 to 36 hours.

After treatment, the flaked pigment is washed first with the solvent used in the treatment medium and then with acetone and then dried at a temperature of up to 50 ° C. The resulting product always contains a small amount of pigment having a larger particle size and can only be used for screen printing.

For electronic purposes, the silver-pigmented active surface pigment of the sheet structure can be used in admixture with thixotropic lacquers, pastes or adhesives required by the electronics industry.

Example 1

A 5 dm ³ drum was charged with 2500 g of a 6 mm diameter steel ball at 400 g of 3 μπι small granular, chemically reduced silver powder, 150 g of a 1: 1 mixture of toluene / ethyl acetate, 10 g of an organophilic benton, and 25 g. Palmitic acid (g) The mixture was treated at 100 rpm for 36 hours with a rotating million and then washed with a mixture of toluene / ethyl acetate and rinsed twice with tons of ace. Drying at room temperature.

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Example 2

In a 5 dm 'drum, 4000 g steel balls of 10 mm diameter, 400 g, silver powders, auctioned by chemical <<, 25 µl of a 1: 3 mixture of ethylene / ethyl acetate, 15 g of riclinoleic acid ethyl ester, 10 g of stearic acid were charged. The mill heats up at 120 rpm. Treatment time 32 oca. Wash with toluene-ethyl acetate. rinse with acetylene cloth 2. Drying at room temperature. 10

EXAMPLE 3 3500 g of a steel ball of 8 ttttn diameter, 300 g of a sefile droplet of less than 3 μπι, 15 milliliters of silver reduction, 50 μl of white spirit, 10 grams of oleic acid, and 10 grams of oesfahite are added to a dm' drum. The speed is 140 rpm. Treatment time is 32 hours. Wash with white spirit.

rinse 2 times with acetone. Drying at 40 ° C.

Claims (4)

CLAIMS 1. A process for the production of a silver pigment having an activated surface-active plate structure for electronic use, characterized in that the silver powder produced by chemical reduction is less than 10 μg per milliliter of Iz anionic and / or cationic surfactant and 23 to 7.5% by weight of 15 to 20 carbon fatty acids in a balloon solvent for 28 to 40 hours, preferably 32 to 36 hours, in a powder to medium ratio of 3: 1 to 1: 1, and the steel ball - silver powder of 6 mm to 5 mm diameter is adhered to in a 15: j to 5: j cake tin, in a 5 din ³ volume drum, at 9 to 40 rpm / ptc. 2. A process according to claim 1 wherein the acidifying solvent is an aromatic hydrocarbon, preferably toluene, acetic acid esters of alcohols of from 1 to 4, preferably ethyl acetate, or a mixture thereof, and a petroleum fraction, preferably white spirit. A process according to any one of claims 1 to 2, wherein the esters of carbon monohydrates of carbon number 1525, preferably ethyl ester or organophilic beryllium, are used as the halide. 4. The.-3. A process according to any one of the preceding claims wherein the fatty acid is stearic acid, palmitic acid or oleic acid.