Sol-gel catalyst for electroless plating

Details Sol-gel catalyst for electroless plating Sol-gel catalyst for electroless plating

1999-09-10

2002-02-05

Dawson, Robert (Department: 1712)

Coating processes

With pretreatment of the base

Preapplied reactant or reaction promoter or hardener

C427S098300, C427S304000, C427S314000, C427S319000, C427S320000, C427S397700, C427S402000, C427S405000, C427S421100, C427S429000, C427S437000, C427S443100, C106S001110, C106S287160, C106S287170, C106S287180, C428S620000, C244S11700R, C516S099000

Reexamination Certificate

active

06344242

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to electroless plating compositions, more particularly, to electroless plating compositions for applying metal films to substrates having smooth surfaces i.e. glass or ceramic surfaces, without using hazardous chemicals or extreme conditions. The present invention is also directed to a process for forming electroless plating compositions and a method of applying these compositions to a substrate.
2. Description of the Prior Art
Multi-layer laminates of metal and dielectric materials are useful in various applications. For example, such coatings may be used as thermal barriers applied to substrates subjected to high temperatures, and as conductive coatings applied to electrical resistance elements.
Traditionally, metallic coatings are applied to substrates in one of three different ways. In the first process, the so called wet method, a slurry of metallic filler and a cementitious or sinterable metal binder is sprayed, in a suitable aqueous or organic solvent, to a desired thickness on the substrate. The substrate is then fired to remove the solvent and any organic binders, and to form or sinter the ceramic binder. In the second process, the so-called dry spray method, the metallic ingredients are sprayed without solvent at a high velocity onto the substrate through a flame or plasma which causes the component materials to melt prior to impact with the substrate. In the third process, the surface of the substrate to be coated (e.g. glass, ceramic or polished metal) is pretreated and a sol-gel is applied to the pretreated substrate to produce solid films in the form of monoliths, thin films, particles or fibers.
These conventional methods suffer from several shortcomings. For example, the traditional wet spray method is quite labor intensive and in situations where direct measurement is impossible, thickness control is difficult. In order to provide metallic coatings of substantial thickness, several layers of coating, each approximately two to three mils thick, must be applied to the part to be coated. Prior to applying each subsequent coat, the part must be dried, i.e., the solvent must be evaporated, to prevent dripping and sagging of the coating and to prevent the solvent from becoming entrapped as subsequent layers are applied. Blistering may occur if any solvent remains entrapped when the next layer is applied. After the coating is built up to a sufficient thickness by applying several layers, it is fired to a temperature sufficient to react the cementitious binder or to sinter the metallic binder.
In the case of cementitious binders and especially in the case of sinterable binders, supplemental organic thickeners are needed to prevent settling, to control rheology, and to impart real strength to the coating so as to minimize shrinkage or cracking during drying. The use of these additives may require slow curing of the coated part to remove organic decomposition products without disrupting the coating structure.
Metallic coatings applied using the traditional wet spray method are often applied from aqueous solutions which require increased drying times and impart an increased porosity to the resulting metallic coatings after drying. Moreover, because the metallic coatings are applied as aqueous solutions, it is extremely difficult to make repairs of damaged components. This is especially true when the part requiring repair is large and must be repaired in the field, e.g., an aircraft wing, or when the damaged portion of the coated part is difficult to access.
Using the conventional dry spray method, specialized equipment is required to apply the coatings. Although this equipment is usually available where the initial coating is applied, it may not be available at locations where coating repairs must be made. Also, the extreme heat and velocity used in this method can damage certain fillers incorporated in the metallic formulations by oxidizing or distorting the fillers on the substrate surface as the composition is applied. Such damage can, in certain instances, impair the performance of the coatings.
When using conventional sol-gel technology extreme conditions are required, usually involving very high temperatures and/or pressures. In addition, some material forms and combinations are just not possible using the existing sol-gel techniques because of the limitations imposed by these older techniques.
Moreover, if a metallic coating is to be applied to a smooth surface, additional steps arc required to prepare the surface so that the coating adheres correctly and equally. These steps are required no matter which of the above techniques are utilized. For example, a substrate having a smooth surface must be chemically treated with hazardous chemicals, exposed to extreme conditions or mechanically etched prior to coating. This makes the process even more laborious and therefore more costly.
As stated above, various problems and disadvantages exist with conventional methods for applying metallic coatings to substrates, especially on smooth glass or ceramic surfaces. These problems and disadvantages are overcome by the present invention.
SUMMARY OF THE INVENTION
The present invention provides a sol-gel catalyst composition for electroless plating, a process for producing the sol-gel catalyst composition and a method for applying the sol-gel catalyst composition to a substrate to be coated.
The sol-gel catalyst composition for electroless plating of the present invention comprises:
a metal alkoxide in a polar organic solvent;
an acid in an amount of from about 1 percent by weight to about 30 percent by weight of the composition;
a chloride salt or an acid chloride; and
a catalytic metallic salt wherein the metal is selected from the group consisting of Co, Pd, Pt, Ni, Au, and Ag.
The invention also provides a process for producing a sol-gel catalyst composition which comprises:
(a) preparing a metal alkoxide mixture comprising from about 30 percent to about 50 percent by weight of the composition of a metal alkoxide such as tetraethylortlhosilicate (TEOS) and a polar-organic solvent;
(b) combining a portion of the metal alkoxide mixture prepared in step (a) with an acidic solution containing an acid dissolved in a polar-organic solvent and allowing the resulting mixture to hydrolyze and cool to room temperature to produce a stock solution for the sol-gel catalyst composition;
(c) preparing a metalic plating solution comprising about 10 percent to about 20 percent by weight of the plating solution of a chloride salt or an acid chloride, about 30 percent to about 40 percent by weight of the plating solution of a catalytic metallic salt, the salt containing a metal selected from the group consisting of Pd, Co, Ni, Au, and Ag and a concentrated acid; and
(d) combining a portion of the stock solution prepared in step (b) with a portion of the metallic plating solution prepared in step (c) to produce a sol-gel catalyst composition for electroless plating.
The sol-gel catalyst composition produced is relatively stable, having a shelf-life of greater than six months when stored at room temperature in closed containers.
The invention also provides a method for applying a metal coating composition to a substrate comprising:
(a) applying a portion of the sol-gel catalyst composition of the invention to a substrate and heating the substrate to about 100° C. to about 500° C. for about 10 to about 60 minutes; and
(b) contacting the coated substrate from step (a) with a plating solution for a predetermined amount of time.
The amount of time in which the coated substrate is placed in contact with the plating solution is proportional to the thickness of the plating material deposited on the substrate.
DETAILED DESCRIPTION OF THE INVENTION
The metal alkoxide used in the sol-gel catalyst composition of the present invention can be any metal alkoxide. Preferably, it is a member selected from the group consisting of tetraethoxyorthosilicate (TEOS), tetramethoxyorthosilicate (TMOS), aluminum isopropoxide, titanium i

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