Process for producing articles having an electrically conductive coating

Abstract

The present invention relates to a process for producing articles having on at least part of their surface an electrically conductive coating by at least partly coating a substrate with a composition comprising finely divided electrically conductive metal particles and a binder and subjecting the coated substrate to at least one treatment with water in the presence of a halide ion source at a temperature in the range from ambient temperature to 200 C. The process of the invention allows articles having an electrically conductive coating to be produced in a simple, rapid and mild way.

Claims

1. A process for producing an article having on at least part of its surface an electrically conductive coating, which article is selected from the group consisting of a printed circuit board, RFID antenna, battery and solar cell, wherein the process consists of at least partly coating a substrate with a composition comprising finely divided electrically conductive silver particles and a binder and improving the electrical conductivity of the electrically conductive coating by subjecting the coated substrate to at least one treatment with a composition that consists of water and a halide ion source at a temperature in the range from 50 to 95 C., wherein the composition optionally comprises a water soluble organic or inorganic acid, wherein the halide ion source is selected from an alkali metal halide, an alkaline earth metal halide, an aluminium halide, a zinc halide, and an ammonium halide such that the standardized specific surface resistance of the coating is less than 10 m/25 m.

2. The process according to claim 1, wherein a chloride ion source is used as halide ion source.

3. The process according to claim 1, wherein the concentration of the halide ion source is 0.01 to 10% by weight, based on the amount of water.

4. The process according to claim 1, wherein the composition comprising finely divided electrically conductive silver particles and a binder comprises as its binder an organic polymeric binder or a curable component.

5. The process according to claim 4, wherein the binder is selected from polyvinyl butyrals and (meth)acrylate-based polymers.

6. The process according to claim 1, wherein the composition comprising finely divided electrically conductive silver particles and a binder is applied by screen printing, ink-jet printing or gravure printing to the substrate.

7. A process for producing an article having on at least part of its surface an electrically conductive coating, which article is selected from the group consisting of a printed circuit board, RFID antenna, battery and solar cell, wherein the process consists of at least partly coating a substrate with a composition comprising finely divided electrically conductive silver particles and a binder, improving the electrical conductivity of the electrically conductive coating by subjecting the coated substrate to at least one treatment with a composition that consists of water and a halide ion source at a temperature in the range from 50 to 95 C., and subjecting the article to at least one after treatment by rolling at a temperature of 200 C., wherein the composition optionally comprises a water soluble organic or inorganic acid, wherein the halide ion source is selected from an alkali metal halide, an alkaline earth metal halide, an aluminium halide, a zinc halide, and an ammonium halide such that the standardized specific surface resistance of the coating is less than 10 m/25 m.

8. The process according to claim 7, wherein the rolling is carried out at ambient temperature.

9. A process for producing an article having on at least part of its surface an electrically conductive coating, which article is selected from the group consisting of a printed circuit board, RFID antenna, battery and solar cell, wherein the process comprises at least partly coating a substrate with a composition comprising finely divided electrically conductive silver particles and a binder and improving the electrical conductivity of the electrically conductive coating by subjecting the coated substrate to at least one treatment with a composition that consists of water and a halide ion source at a temperature in the range from 50 to 95 C., wherein the composition optionally comprises a water soluble organic or inorganic acid, wherein the halide ion source is selected from an alkali metal halide, an alkaline earth metal halide, an aluminium halide, a zinc halide, and an ammonium halide such that the standardized specific surface resistance of the coating is less than 10 m/25 m, wherein the article is further subjected initially to a first rolling operation at ambient temperature and subsequently to at least one further rolling operation at a temperature in the range from 70 to 200 C.

10. A process for producing an article having on at least part of its surface an electrically conductive coating, which article is selected from the group consisting of a printed circuit board, RFID antenna, battery and solar cell, wherein the process comprises at least partly coating a substrate with a composition comprising finely divided electrically conductive silver particles and a binder and improving the electrical conductivity of the electrically conductive coating by subjecting the coated substrate to at least one treatment with a composition that consists of water and a halide ion source at a temperature in the range from 50 to 95 C., wherein the composition optionally comprises a water soluble organic or inorganic acid, wherein the halide ion source is selected from an alkali metal halide, an alkaline earth metal halide, an aluminium halide, a zinc halide, and an ammonium halide such that the standardized specific surface resistance of the coating is less than 10 m/25 m, wherein the article is additionally provided with a protective coat or topcoat.

11. A process for producing an article having on at least part of its surface an electrically conductive coating, which article is selected from the group consisting of a printed circuit board, RFID antenna, battery and solar cell, wherein the process comprises at least partly coating a substrate with a composition comprising finely divided electrically conductive silver particles and a binder and improving the electrical conductivity of the electrically conductive coating by subjecting the coated substrate to at least one treatment with a composition that consists of water and a halide ion source at a temperature in the range from 50 to 95 C., wherein the composition optionally comprises a water soluble organic or inorganic acid, wherein the halide ion source is selected from an alkali metal halide, an alkaline earth metal halide, an aluminium halide, a zinc halide, and an ammonium halide such that the standardized specific surface resistance of the coating is less than 10 m/25 m, wherein the article is submitted to at least one after treatment by rolling at a temperature of 200 C., wherein the article is additionally provided with a protective coat or topcoat.

Description

Example 1

(1) A conductive screen-printing ink is prepared by stirring together 4 parts by weight of a polyvinyl butyral resin (Pioloform BL18; Wacker), 28 parts by weight of butyl glycol acetate and 68 parts by weight of silver flakes (SF9AL from Ferro) and subsequently homogenizing the mixture on a triple-roll mill. The desired screen-printing viscosity is set by addition of ethoxypropyl acetate.

(2) A semi-automatic screen-printing apparatus is used with a screen (120-31) to print RFID antennas for UHF applications in a film thickness of 4 m on a polyimide film 50 m thick. After they have been dried at room temperature, these antennas have a specific surface resistance of 400 to 600 m, corresponding to a standardized specific surface resistance of 64 to 96 m/25 m. Subsequently the antennas are treated for 10 seconds by immersion in an aqueous aluminium chloride solution (10 g of aluminium chloride in 200 ml of water) which has been heated to 90 C.

(3) One batch of the samples is then subjected to aftertreatment by cold-rolling between two steel rolls with a pressure of 30 bar and also three-fold hot-rolling (calendering) in a laminator (Pouchman 12 from IBICO Trading GmbH). The figures for the standardized specific surface resistance are compiled in the table below.

(4) TABLE-US-00001 Standardized specific surface Treatment resistance [m/25 m] none 64-96 water + AlCl.sub.3 5-7 water + AlCl.sub.3 + rolling 2.6-3.0

Example 2

(5) A conductive gravure ink is prepared by stirring together 4 parts by weight of a polyvinyl butyral resin (Pioloform BL18, Wacker), 26 parts by weight of ethanol, 2 parts by weight of ethoxypropyl acetate and 68 parts by weight of silver flakes (SF9AL, Ferro). The desired gravure-printing viscosity is set by addition of ethanol.

(6) Printing is carried out using a test cylinder with 40-line engraving, hexagonal cell shape, 70 m depth and 60 angle. Lines 2 mm wide are printed on a polyimide film (of thickness 50 m). The printed thickness is approximately 3 m and the lines are inhomogeneous in structure. The specific surface resistance is 180 m and the standardized specific surface resistance is 21.6 m/25 m. Subsequently the printed specimens are immersed for 10 seconds in a solution of 10 g of aluminium chloride in 200 ml of water that has been heated to 90 C. The standardized specific surface resistance falls to a figure of 5.4 m/25 m.

(7) After treatment by rolling as specified in Example 1 causes the standardized specific surface resistance to fall to a figure of 4.1 m/25 m.

Example 3

(8) Example 1 is repeated but the aluminium chloride in the immersion bath is replaced by 15 g of sodium chloride and 10 ml of 25% strength acetic acid. This is followed by aftertreatment by rolling as specified in Example 1. The standardized specific surface resistance of the articles obtained is 2.8 m/25 m.

Example 4

(9) A conductive gravure ink is prepared by stirring to give 16.8 parts by weight of a varnish (film extender 111350 PN for half-tone printing, A.M. Ramp & Co GmbH), 0.2 parts by weight of a dispersing additive (Byk 301, Byk-Chemie GmbH), 9.1 parts by weight of ethoxypropanol and 73.9 parts by weight of silver powder (7000-35, Ferro) and the ink is homogenized in a bead mill. The desired gravure-printing viscosity is set by addition of ethoxypropanol.

(10) A gravure printing press (Moser) is used to print UHF test antennas with a thickness of 3.5 m onto a PET film (HSPL 100, Coveme) which is 75 m thick, with a speed of 50 m/min.

(11) After these antennas have been dried their specific surface resistance is greater than 200 k. Subsequently the printed specimens are immersed for 1 second in a solution of 10 g of sodium chloride in 200 ml of water that has been heated to 90 C. The specific surface resistance falls to 67 m. Subsequent two-fold cold-rolling with a pressure of 30 bar (roll diameter 100 mm, web width 30 mm) reduces the specific surface resistance to 41 m. Renewed immersion for one second in the NaCl solution identified above reduces the specific surface resistance further to 26 m, corresponding to a standardized specific surface resistance of 3.6 m/25 m.