Saturated soluble salt slurries for coloring ceramics

Details Saturated soluble salt slurries for coloring ceramics Saturated soluble salt slurries for coloring ceramics

2000-09-29

2002-10-15

Klemanski, Helene (Department: 1755)

Compositions: coating or plastic

Coating or plastic compositions

Marking

C106S031600, C106S031860

Reexamination Certificate

active

06464765

ABSTRACT:

FIELD OF INVENTION
The present invention provides a slurry for use in decorating a ceramic substrate and a method of decorating a ceramic substrate using the slurry.
BACKGROUND OF THE INVENTION
It is known that solutions of metal salts can be used to decorate ceramic substrates. These solutions of metal salts can be applied using a variety of known application techniques including flat or rotative printing, flexogravure, rotogravure, tampography, spraying, and various disk techniques. The ceramic substrates are then fired to drive off any volatile components and permanently fix the decoration to the ceramic substrate.
One of the problems with using solutions of metal salts to decorate ceramic substrates is that the resulting coloration tends not to be particularly intense. The lack of intense color is particularly noticeable when the metal salt solutions are applied by rotogravure processes, such as, for example, ROTOCOLOR by System S.p.A. The intensity of the coloration obtained after firing depends, in large part, upon the particular metal used and the concentration of the metal dissolved in the solvent. The maximum concentration of metal in solution is generally limited by the solubility of the metal salt in the solvent being used. Other considerations include the compatibility of the various different types of metal salts that are sometimes blended to obtain various colors. Yet another consideration is the viscosity of the solution, which must be kept within particular ranges in order to be applied by known decoration techniques.
SUMMARY OF INVENTION
The present invention provides a slurry for use in decorating a ceramic substrate. The slurry according to the invention comprises solid particles of at least one color-contributing metal salt dispersed in a saturated solution of at least one color-contributing metal salt. Preferably, the solid particles have a diameter of less than about 40 microns, and the slurry itself has a viscosity of from about 10 to about 20,000 centipoise. This makes the slurry particularly suitable for application to a ceramic substrate using known application processes such as, for example, rotogravure and tampography.
The present invention also provides a method of decorating a ceramic substrate. The method according to the invention comprises applying a slurry that comprises solid particles of at least one color-contributing metal salt dispersed in a saturated solution of at least one color-contributing metal salt having a viscosity of from about 10 to about 20,000 centipoise to the surface of a ceramic substrate, applying a solvent to the surface of the ceramic article in amount sufficient to at least partially dissolve the solid particles, and firing the ceramic article.
The slurry and method according to the present invention allow for the application of higher concentrations of color-contributing metals to the ceramic substrate than can be applied using metal salt solutions. The resulting coloration that can be obtained on a ceramic substrate using the slurry and method according to the present invention is therefore substantially more intense than the coloration that can be obtained using a solution of a metal salt. Moreover, a higher definition can be achieved in decorative designs, and the decorations tend to be more consistent.
The foregoing and other features of the invention are hereinafter more fully described and particularly pointed out in the claims, the following description setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principles of the present invention may be employed.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The present invention provides a slurry for use in decorating a ceramic substrate. The slurry comprises solid particles of at least one color-contributing metal salt dispersed in a saturated solution of at least one color-contributing metal salt. Throughout the instant specification and in the appended claims, the term “color-contributing metal” means a metal that contributes to the development of color when applied to a ceramic substrate and fired. It will be appreciated that a metal that does not produce or generate a color when applied to a ceramic substrate by itself may nevertheless be considered a “color-contributing metal” if the metal influences the color produced or generated by another metal. Metals that are considered to be “color-contributing metals” include, but are not limited to, transition metals (e.g., Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, La, Hf, Ta, W, Re, Os, Ir, Pt, and Au), alkaline earth metals (e.g., Ca, Mg, Ba, and Sr), alkali metals (e.g., Li, Na, K, Rb, and Cs), metals from the lanthanide series (e.g., Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu), and “post transition” (filled d shell) metals (e.g., Zn, Cd, Al, Si, In, Sn, Pb, Sb, and Bi).
The particle size of the solid color-contributing metal salts used in the slurry must be sufficiently small to accommodate the conditions encountered during application. For example, if the slurry is to be applied by screen printing, the solid particles must be small enough to easily pass through a screen. Likewise, if the slurry is to be applied by rotogravure, the solid particles must be small enough to easily fill the holes of the rotogravure equipment being used. Preferably, the solid particles have a diameter of less than about 40 microns. Various known techniques such as milling and/or grinding can be used to obtain solid particles having the desired diameter.
The solid particles of color-contributing metal salts used in the slurry must be at least partially soluble in a solvent, preferably water. Suitable color-contributing metal salts include, but are not limited to, carboxylates, such as acetates, formates, ascorbates, citrates, propionates, lactates, tartrates, glycolates, and maleates, other organic salts such as substituted carboxylates (e.g., aminic or hydroxyl), salts of glycine and urea, thiocyanates, and various metal complexes. In addition, inorganic salts such as halides, nitrates, nitrites, sulfates, sulfites, and phosphates can be used.
As noted, the preferred solvent for use in forming the saturated solution is water. However, other solvents such as alcohols can be used. Furthermore, co-solvents such as water and alcohols can also be used. Solvent selection will depend in large part upon the solubility of the color-contributing metal salts to be used, the application method being used, cost, and environmental and/or processing concerns.
The saturated solution of at least one color-contributing metal salt into which the solid particles are dispersed preferably comprises a saturated solution of the same color-contributing metal salt as the solid particles. For example, if the solid particles used in the slurry comprise cobalt acetate, then preferably the saturated solution comprises a saturated solution of cobalt acetate. However, it will be appreciated that compatible blends of solid particles of different color-contributing metal salts and compatible blends of different saturated solutions of color-contributing metal salts may be used in some circumstances in order to obtain the desired coloration.
The amount of solids used in the slurry will depend, in large part, upon the desired intensity of the coloration in the final ceramic article. Typically, the slurry will comprise from about 50 to about 90 parts by weight of solid particles and from about 20 to about 50 parts by weight of the saturated solution.
Preferably, the viscosity of the slurry is from about 10 to about 20,000 centipoise, which makes the slurry suitable for application using known processes and equipment. It will be appreciated that the viscosity of the slurry can be affected by a number of factors. For example, it is known that viscosity can be affected by the degree of intermolecular bonding, such as hydrogen bonding, that occurs in solution. Viscosity can also be affected by the choice of solvent or co-solvents used to for

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