METHOD FOR SOLVENT-FREE PRINTING CONDUCTORS ON SUBSTRATE

Abstract

A solvent-free method for fabricating conductors is disclosed. A thick patterned layer up to 13 microns containing metal precursor and reducing agent precursor are initially deposited onto a substrate using laser printing technology. The deposited patterned precursor materials are then irradiated with a newly developed high energy intense pulsed light (IPL) system in order to transform the deposited materials to thick conductive metal patterns. The easy metallization of printed patterns makes this invention an especially effective method for massive production of flexible printed circuits.

Claims

1. A solvent-free method for fabricating printed electronics onto a substrate, said method comprising: I. Synthesizing reductant precursor and metal precursor containing laser printable toners. II. Depositing the precursor containing toners onto a substrate. III. Irritating said deposited precursor patterns with a high energy intense pulsed light to transform the said deposited precursor patterns to electrically conductive patterns.

2. The method of claim 1, wherein said depositing is performed by laser printing.

3. The method of claim 1, wherein said substrate is paper, PET, PI, PEI, FR-4, SEI.

4. The method of claim 1, wherein said the metal precursor material included a particulate metal.

5. The method of claim 4, wherein said metal precursor can be metal oxide, metal complex, metal salt, metal polymer compound, metal nanoparticles with capping agent.

6. The method of claim 4, wherein said particulate metal is a metal selected from the group consisting of copper, nickel, silver, cobalt gold, platinum, palladium and combinations thereof.

7. The method of claim 1, wherein said reductant precursor included a particulate polymer which decomposed to alcohol and acid under high energy pulsed light.

8. The method of claim 6, wherein said particulate polymer selected from group consisting of polyesters, styrene butadiene copolymers, styrene acrylate copolymers, polyvinylpyrrolidone, polyvinyl alcohol and combinations thereof.

9. The method of claim 1, wherein said reductant precursor has a concentration range from 0.1 wt % to 90 wt %.

10. The method of claim 1, wherein said metal precursor has a concentration range from 10 wt % to 90 wt %.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0008] The present disclosure is directed to the preparation of a novel toner, printing and post-treatment of as-printed patterns. The reductant/metal precursors are incorporated into regular toner to form novel toner that enables the further functionalization of printed patterns. Several typical thermoplastic polymer and other polymers which are rich of alcohol and acid groups are selected as the reductant precursor. Metal precursors can be, but not limited to, metal complex, metal salt, metal oxide, metal crystal, metal hydroxides. The metal elements can be silver, gold, copper, nickel, platinum, indium, tin, gallium and any other possible elements that are electrically conductive. These reductant precursors have common features, and they can be decomposed to alcohol and acid under the high power pulsed light.

[0009] In this disclosure, above-mentioned reductant precursor and metal precursor are mixed with regular toner. The regular toner is either synthesized by emulsion polymerization method, or is directly purchased from the market. Reductant and/or metal precursors are also obtained from commercial markets or are synthesized by chemical methods. After preparing toner and reductant/metal precursors, generally there are two approaches to mix them in this disclosure, liquid phase mixing and solid state blending. In liquid-phase mixing, catalysts are dissolved in the solvent firstly, such as deionized water, and the toners are dispersed in the same solvent with the assistance of surfactants. Then the reductant precursor solution or metal salt solution is slowly dropped into the toner dispersion under stirring to achieve good mixed effects. However, due to the influence of solvent, liquid phase mixing may change the initial properties of toner particles more. Naturally, solid state blending has been a good choice to prepare the novel toner. Solid state blending mainly involves ball milling, mechanical grinding, blast mixing, stirring, etc.

[0010] In this disclosure, reductant precursors or metal precursors are firstly pulverized into fine powders, less than 10 microns. Then fine as-prepared powders are mixed with toner particles. Typically, in this process, planetary ball milling is employed for the pulverization of reductant/metal precursors particles and the mixing of precursor materials and toner particles. The rotation of planetary ball milling is usually required to stay in a low speed to prevent dramatic rising of temperature. Too high temperature may fuse the toner together and affect the subsequent printing quality.

[0011] In this disclosure, the as-prepared precursor functional toners are deposited onto a substrate using laser printing. The printing quality of the reductant/metal precursors containing toners is in relation to the homogeneity of the mixture and the loading content of precursor materials. Homogeneous mixing of catalyst is beneficial for the improvement of printed quality. The printing quality is also affected by the properties of printed substrates. High surface energy can help the adhesion of other substance on the surface. Surface energy relates to surface area and surface tension. Obviously, large roughness and high surface tension are beneficial for enhanced adhesion stability. Thus, the printing substrates are required to have large roughness and surface tension. Some surface modifications to increase the surface roughness and surface tension are useful for improving the printing quality. For laser printing, the toner particles are usually melted into the substrate. The interaction between toner and substrate is non-covalence force, and thus in order to improve the adhesion force it is an effective method to increase the number of hydrogen bonds. The introduction of hydroxide group, carboxyl group, and carbonyl group into the substrate will help to improve the surface adhesion.

[0012] In this disclosure, the printed reductant/metal precursors patterns are irradiated with a high power intense pulsed light in order to transform precursor materials to pure conductive metal patterns. During the irradiation with light pulses, the reductant precursor is decomposed into alcohol and acid in gas phase creating a partial reducing environment. At the same time, the pulsed light provides the energy needed for the alcohol/acid reduction of metal precursors, yielding pure metal, water (gas) and carbon oxide. The printed patterns will become highly conductive after development. To achieve a uniform metallization of the precursor materials, a rapid high power pulse train which is synchronized to moving substrate is adopted.