Compositions – Radiation sensitive
Reexamination Certificate
1999-10-06
2001-09-18
Tucker, Philip (Department: 1712)
Compositions
Radiation sensitive
C252S514000, C252S501100
Reexamination Certificate
active
06290881
ABSTRACT:
TECHNICAL FIELD
The present invention relates to silver-containing compositions and more particularly to photocurable silver-containing compositions, to methods for making and applying a photocurable silver-containing compositions as a coating on a substrate.
BACKGROUND ART
There are many instances in which it is necessary or desirable to apply a coating, plating or layer of silver or a silver-containing compound to a substrate. Examples of such applications would include electrode plating for switches such as those used on pressure-sensitive switches or control panels, for example, as are used on appliances such as microwave ovens, conventional ovens, and the like. Such silver plating also is commonly used in the semiconductor fabrication arts to apply silver metalizations on silicon or germanium semiconductor wafers. Other examples of such substrates include, without limitation, such things as polyesters, polycarbonates, vinyls, ceramics, glass, and the like.
The predominant approach heretofore used in applying silver to substrates has involved using a solvent-based silver solution to the substrate, and chemically or thermally curing the solution to evaporate the solvent. This leaves the solid silver plating on the substrate.
This conventional approach is disadvantageous in a number of respects. Of perhaps the greatest concern is the fact that the solvents currently used for this purpose are toxic. They require special handling and disposal facilities and techniques, and correspondingly increase inefficiencies and costs. Even while observing these special handling techniques, they present hazards to workers using these toxic materials. The solvent-based compositions and methods also are disadvantageous in that it can be difficult to predict the uniformity and thickness of the resultant silver plating after the solvent has evaporated. This leads to quality and performance variations.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a silver composition and method in which silver can be disposed on a substrate without requiring a toxic solvent.
Another object of the invention is to provide a silver composition and method in which disposition of the silver layer can be done more quickly and efficiently than prior art solvent-based techniques.
Another object of the invention is to provide a silver composition and method in which a silver coating may be created which has more predictable and uniform layer thickness relative to prior art solvent-based systems.
To achieve the foregoing objects, and in accordance with the purposes of the invention as embodied and broadly described in this document, a silver composition is provided for deposition as a coating, plating, film or layer on a substrate. The terms coating, plating, film and layer in the context of this document are used to refer generally to a covering on the surface of a substrate, which covering may be of a variety of thicknesses depending on the application and the design goals.
DISCLOSURE OF INVENTION
In accordance with one aspect of the invention, a photocurable silver composition is provided. The silver composition comprises a photocurable organic mixture, a photoinitiator, a silver powder, and a silver flake composition. The silver flake composition is present in an amount of at least 20% of the weight of the silver powder present in the composition.
The photocurable silver composition preferably comprises an aliphatic acrylated oligomer, wherein the aliphatic acrylated oligomer is present in an amount of about 3% to 8% based on the weight of the silver composition. All percentages of the silver composition as expressed in this document, unless otherwise stated, refer to the mass percentage of the stated component to the total mass of the silver composition in its fluid uncured state at standard temperature and pressure.
The silver composition also preferably comprises an acrylated epoxy oligomer, wherein the acrylated epoxy oligomer is present in an amount of about 2% to 4% of the silver composition.
The silver composition also preferably comprises an isobornyl acrylate monomer in an amount of about 4% to 8% of the silver composition, a photoinitiator in an amount of about 3% to 6% of the silver composition, a flow promoting agent in an amount of about 0.1% to 2% of the silver composition, a silver powder in an amount of about 50% to 60% of the silver composition, and a silver flake composition in an amount of about 25% to 35% of the silver composition.
In accordance with this aspect of the invention, the aliphatic acrylated oligomer preferably comprises a urethane oligomer. In presently preferred versions of the silver composition, the aliphatic acrylated oligomer is present in an amount of about 8% of the silver composition.
The acrylated epoxy oligomer is preferably present in an amount of about 3% of the silver composition. The isobornyl acrylate monomer is preferably present in an amount of about 5% of the silver composition. The photoinitiator is preferably present in an amount of about 5% of the silver composition. The flow promoting agent is preferably present in an amount of about 1% of the silver composition.
In presently preferred embodiments according to this aspect of the invention, the silver powder preferably but optionally is present in an amount of about 52% of the silver composition. In these preferred embodiments, the silver powder has a particle size range of about 5 microns to about 15 microns. In a more preferred embodiment, the silver powder has a particle distribution such that about 5% to 20% of the particles have a particle size of less than about 4.7 microns, about 30% to 60% of the particles have a particle size of less than about 7.6 microns, and about 70% to 95% of the particles have a particle size of less than about 14.9 microns. In the most preferred embodiment, the silver powder has a particle distribution such that about 10% of the particles have a particle size of less than about 4.7 microns, about 50% of the particles have a particle size of less than about 7.6 microns, and about 90% of the particles have a particle size of less than about 14.9 microns.
According to the presently preferred embodiments, the silver flake is present in an amount of about 30% of the silver composition. Preferably the silver flake has a particle size range of about 5 microns to about 32 microns. The silver flake preferably has a flake distribution such that about 10% of the particles have a particle size of less than about 5.5 microns, about 50% of the particles have a particle size of less than about 12.5 microns, and about 90% of the particles have a particle size of less than about 32.0 microns.
In a further refinement of the presently preferred embodiment, an adhesion promoter is present in about 1 to 4% of the silver composition. This further refinement improves adhesion to substrates coated with transparent conductors such as indium tin oxide (ITO).
In accordance with another aspect of the invention, a photocurable silver composition suitable for producing a coating that is capable of shielding electromagnetic radiation is provided. This embodiment is preferably applied to a substrate by spraying. The silver composition comprises an acrylated epoxy oligomer, wherein the acrylated epoxy oligomer is present in an amount of about 2% to 8% of the silver composition. The silver composition preferably comprises an isobornyl acrylate monomer in an amount of about 15% to 30% of the silver composition, an photoinitiator in an amount of about 3% to 7% of the silver composition, a flow promoting agent in an amount of about 0.1% to 2% of the silver composition, a silver powder in an amount of about 20% to 40% of the silver composition, and a silver flake composition in an amount of about 20% to 40% of the silver composition.
In accordance with another aspect of the invention, a photocurable silver composition suitable for producing a coating that is capable of forming resistive links on circuit boards is provided. This embodiment of the invention preferably does not c
Allied Photochemical, Inc.
Brooks & Kushman P.C.
Tucker Philip
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