Metallized article and process for metallizing a non-conductive article

A metallized article (10) having a non-conductive surface (11) and a plurality of depressions (12) in the surface (11). A first layer of metal (13) being mechanically bonded to the non-conductive surface (11), such that the mechanical bond is enhanced by the interaction of the first layer of metal (13) and the depressions (12). An intermediate layer of metal (14) bonded to the first layer (13). A finish layer of metal (15) being bonded to the intermediate layer (14). The finish layer (15) being a metal which readily accepts a high polish or shine. A process for metallizing such an article having a non-conductive surface including the steps of etching the surface of the article with fluoride containing salts and the depositing of a first layer of metal onto the etched surface. The process further including depositing an intermediate layer of metal in an electroless manner, and then depositing a finish layer of metal by electrolysis.

TECHNICAL FIELD 
The present invention is generally directed toward metallized, 
non-conductive articles. More particularly, the present invention is 
directed toward a non-conductive article having a finish layer of metal 
electrolytically deposited thereon. Specifically, the present invention is 
directed toward a ceramic or other non-conductive substrate having a 
mechanical bond with an intermediate metallic layer and a finish layer of 
metal electrolytically deposited upon the intermediate layer. 
The present invention also contemplates processing steps for metallizing a 
non-conductive article such as a ceramic, including depositing an 
intermediate layer of metal upon the non-conductive substrate and then 
electrolytically depositing a finish layer of metal on the intermediate 
layer. 
BACKGROUND OF THE INVENTION 
The present invention is directed toward metallizing the surface area, or 
portions thereof, of a non-conductive substrate with a suitable and 
desirable finish layer of metal. For example, it has long been considered 
desirable to provide ceramic tiles and the like, for use in bathroom or 
pool area flooring and walls where durability and water imperviousness are 
primary considerations. Such tiles have long been provided with colorants, 
or have been painted with metallic paints and "fired" in order to have 
different colors and designs thereon for aesthetic reasons. 
The type of metallic finish articles which have heretofore been known in 
the art, have had the drawback of not being capable of retaining a high 
polish or shine. Further, articles that have metallic paint applied often 
prove to be incapable of withstanding exposure to conditions normally 
encountered in their intended environment. The metallic finish frequently 
wears off or dulls in a short time period relative to the normal service 
life of the tile, leaving no choice but to replace the entirety of the 
article, usually at great expense. 
Conventional electroplating has been a known technology for many years, and 
is considered useful for providing a durable finish to a conductive 
article. Because of the requirement that the plated surface be conductive, 
conventional electroplating processes have not heretofore been useful for 
metallizing non-conductive substrates. 
The metallizing of non-conductive substrates has been limited commercially 
to only certain materials or to what are essentially experimental 
laboratory procedures. For instance, processes are known for treating 
plastics such as acrylonitrile-butadiene-styrene copolymer (ABS). These 
processes have employed acid etches such as may be accomplished in a 
chromic sulfuric bath. These processes are not useful for preparing 
non-conductive substrates such as ceramic, glass or porcelain. The 
metallizing methods heretofore known in the art for polymeric materials 
are not capable of metallizing these later types of substrates except by 
using solutions having a very high acid concentration. These high acid 
concentrations are known to be very hazardous to both the operators of the 
involved processes and to the articles themselves. 
A need exists, therefore, for a durable, metallized product having a 
non-conductive substrate of ceramic, glass, porcelain, clay or other such 
material. Further, a need exists for a process for producing such a 
metallized article without the danger to operators and the articles that 
are associated with processes employing solutions having high acid 
concentrations. 
SUMMARY OF THE INVENTION 
It is therefore, an object of the present invention to provide a metallized 
article having a non-conductive substrate of ceramic, glass, porcelain or 
clay material or the like. 
It is another object of the present invention to provide a metallized 
article wherein the metal finish of the article readily accepts a high 
polish or shine. 
It is a further object of the present invention to provide a metallized 
article wherein the metal finish is durable and capable of withstanding 
exposure to harsh conditions such as high steam and dry heat temperatures, 
abrasion, and water exposure. 
It is yet a further object of the present invention to provide a process 
for metallizing a non-conductive article without the use of solutions 
having dangerously high concentrations of acid. 
It is yet another object of the present invention to provide a process for 
preparing a non-conductive substrate such that it will accept plating by 
conventional electroplating techniques. 
In general, the present invention relates to a metallized article having an 
exterior surface. The surface has a plurality of depressions therein, and 
a first layer of metal is mechanically bonded to the surface, such that 
the depressions in the surface enhance the mechanical bond. An 
intermediate layer of metal is bonded to the first layer, and is selected 
from the group consisting of copper, nickel, gold, silver and cobalt. A 
finish layer is provided and is bonded to the intermediate layer. The 
finish layer is a metal selected from the group consisting of gold, 
platinum, rhodium, palladium, silver, bronze, brass, copper, nickel, iron, 
chromium, tin, zinc and alloys thereof. 
A process for metallizing an article having a non-conductive surface is 
provided which comprises the steps of etching the surface of the article 
with a fluoride containing salt solution and preactivating the surface 
using a cationic wetting agent. The process also includes activating the 
surface in a solution of palladium chloride, stannous chloride and an 
acid. The next step includes reducing the palladium chloride to palladium 
metal by using a suitable reducing agent. An intermediate layer of metal 
is deposited onto the first layer of metal, and a finish layer of metal is 
deposited onto the intermediate layer. 
These and other objects of the invention, as well as the advantages thereof 
over existing and prior art forms, which will become apparent in view of 
the following specification, are accomplished by means hereinafter 
described and claimed.

PREFERRED EMBODIMENT FOR THE INVENTION 
The present invention has particular applicability to metallizing ceramic, 
glass, porcelain or other similar articles made of a non-conductive and 
relatively non-porous material. Many products are fabricated from these 
materials, and the invention is not limited with respect to any certain 
type of product. For instance, it may be desirable to produce metallized 
articles such as bathroom tiles and fixtures, lamps, beverage cups and the 
like. For the simplicity of the following specification, these products 
shall be collectively referred to by the term "article," except as 
indicated otherwise. 
Further, the present invention may have applicability to articles made of 
materials other than ceramic, glass or porcelain without departing from 
the spirit of the present invention. Metallizing processes heretofore 
known in the art, such as those known for thermoplastics, have not been 
found to be useful for metallizing ceramics, glass, porcelain and clay 
products. Therefore, although the present invention has particular 
applicability to articles fabricated from these materials, it is not 
limited to them exclusively, and the term "article" shall only be deemed 
to refer to a product made from a non-conductive material. 
An article fabricated from a non-conductive material embodying the concepts 
of the present invention, is generally indicated by the numeral 10 in the 
drawings and has a surface 11 carrying a plurality of pits or depressions 
12 formed in surface 11. The article 10 as depicted in the drawings is a 
floor or wall tile. It is to be appreciated that article 10 may be other 
types of products such as a fixture, lamp body, beverage container or the 
like, and is only represented in the drawings as a tile for exemplary 
purposes in the context of the specification. 
Surface 11 acts as a substrate in that a first layer of metal 13 is 
mechanically bonded thereto. Normally it is very difficult to bond metal 
to ceramics, glass, porcelain, clay and the like. However, the depressions 
12 provide for an improved mechanical bond between article 10 and first 
layer 13. 
The first layer of metal 13 is preferably from about 0.00000025 to about 
0.00000100 micrometers thick, and comprises any suitable metal which will 
mechanically bond with article 10, although palladium is a preferred 
element. 
An intermediate layer of metal 14 may he provided and is readily bonded to 
first layer 13 such as by electroless deposition. Intermediate layer 14 is 
made from a metal which will be efficient for use in electrolysis, such 
metals being well known in the art, but is preferably nickel or copper. 
Further, intermediate layer 14 may be from about 0.00025 to about 0.000625 
micrometers thick. 
A finish layer of metal 15 may be provided which is bonded to intermediate 
layer 14. The finish layer 15 may be of any metal, but is preferably of a 
metal which will accept a high polish or shine, such as gold, platinum, 
rhodium, palladium, silver, bronze, brass, copper, nickel, iron, chromium, 
tin, zinc and alloys thereof. Finish layer 15 may be from about 12.7 to 
about 50.8 micrometers thick. 
An article 10 according to the present invention exhibits high resistance 
to abrasion, high steam and dry heat temperatures and water. Further, such 
an article will readily accept a high polish or shine. 
The process according to the present invention makes use of fluoride salts 
to etch surface 11 of the article to be metallized. Fluoride salts have 
been found to have the advantageous result of sufficiently etching the 
surface of the article without the hazards accompanying the use of highly 
concentrated acid solutions. Fluoride salts will etch ceramics, glass, 
porcelain and clay articles. Heretofore, etching has been accomplished 
with chromic sulfuric acid solutions, nitric acid solutions and the like. 
Known processes employing these acids have been for use etching ABS or 
other plastics where relatively low concentrations of acid prove 
sufficient. These acid solutions are not useful for etching certain 
materials such as ceramics and the like, except with the aforementioned, 
dangerous, high concentrations of acid. 
The following is an example of the pre-plating process steps carried out 
according to the present invention. The term "substrate" refers to the 
surface of the non-conductive article to be metallized. 
The substrate was cleaned by immersing the article in a solution of from 
about 30 to about 150 grams of an alkaline cleaner, such as sodium 
hydroxide, in one liter of water at from about 49 to about 60 degrees 
centigrade. The substrate was then allowed to soak for about one minute in 
order to remove oils, dust, and the like, and was then rinsed in cold 
water. While an alkaline cleaner is preferred, it is to be appreciated 
that other types of cleaners would have equal applicability to cleaning 
the substrate. For example, alcohols and other organic solvents may have 
an extent of usefulness in cleaning the substrate. 
It is further to be appreciated by one skilled in the art, that the amount 
of cleaner employed will be varied in order to optimize the cleaning 
procedures. It is preferred to use from about 45 to about 75 grams of an 
alkaline cleaner. However, if more time is allowed for the substrate to 
soak in the cleaner, a lower amount of cleaner may be employed. 
The substrate was then etched by immersing the article in a solution of 
from about 60 to about 120 grams of fluoride containing salts, such as 
ammonium bifluoride, in one liter of water at from room temperature to 
about 49 degrees centigrade. The substrate was allowed to soak in the 
solution at room temperature for from about one to about three minutes. 
The etching creates a plurality of depressions or pits in the surface of 
the substrate. These depressions serve to increase the effectiveness of 
the mechanical bond between the substrate and the metal layers deposited 
thereon in subsequent process steps. 
As with the cleaning step, one skilled in the art will recognize that the 
amounts of the etching salt employed, the time allowed for the etching 
process and the temperature of the etch solution will be varied to 
optimize the amount of etching obtained. The etching process is allowed to 
proceed until the surface of the substrate is "wettable" or until water 
run over the surface of the substrate is trapped in the pits or 
depressions uniformly over the surface of the substrate. A lower amount of 
the etch salt may be employed if the substrate is exposed to the etch 
solution for a longer period of time. The range of the amount of etch 
salts, the solution temperature and the length of time the substrate is 
exposed to the etch solution set forth above are preferred. 
It is also within the scope of the present invention to provide for 
depressions or pits in the surface of the article by other than chemical 
etching techniques. For example, a mechanical roughening of the article 
surface which would provide for the above described "wettability" of the 
substrate surface, would accomplish the goals and be within the spirit of 
the present invention. 
Next, after a cold water rinse, the surface of the substrate was 
neutralized by immersing the article in a liquid neutralizer solution 
comprising from about three to ten percent by volume of water at from 
about 21 to about 32 degrees centigrade with an acidity of from about 0.4 
to about 0.45 normal for about one to about two minutes. After a further 
cold water rinse, the substrate was preactivated by immersing the article 
in a liquid conditioning solution comprising from five to about ten 
percent by volume of water or a cationic wetting agent at from about 21 to 
about 32 degrees centigrade for about one to five minutes in order to 
promote more uniform absorption of the activator to follow. Again, 
conditions are varied for optimiztion. Examples of cationic wetting agents 
may be found in McCutcheon, Deterqents and Emulsifiers. 1979 North 
American Edition, Glen Rock, N.J. which is hereby fully incorporated by 
reference with respect to cationic wetting agents. 
After the article was again rinsed in cold water, the substrate was 
activated by immersing the article in a solution containing about five to 
about fifteen grams of palladium chloride and from about four to about 
twelve grams of stannous chloride and from about 100 to about 300 grams of 
hydrochloric acid per liter of water. The temperature of the solution 
ranged from about 25 to about 45 degrees centigrade and immersion took 
place for about three to about five minutes, again varying the conditions 
for optimization. The activation catalyzed the deposition of the palladium 
metal onto the substrate. Activation of the substrate may be accomplished 
by activation constituents other than hydrochloric acid. For example, 
sodium chloride is useful as an activation constituent. Any useful 
activator is within the scope of the present invention. 
Following a rinse in cold water, the deposition of palladium metal onto the 
substrate was accelerated by immersing the article in a suitable reducing 
agent from about five to about ten percent by volume. This step was 
carried out at a temperature of from about 46 to about 55 degrees 
centigrade and for about one to about three minutes, varying for 
optimization. As a result, a first layer of metal was formed on the 
substrate, and a mechanical bond was created between the substrate and the 
first layer which was enhanced by the "gripping" effect of the first layer 
of metal to the depressions formed in the etching step. 
After another cold water rinse, an intermediate layer of metal was then 
deposited onto the first layer of metal by immersing the article in a 
solution containing a metal anion at about room temperature for about 7 to 
about 15 minutes depending upon the thickness of the intermediate layer 
desired. 
Any metal which will electrolessly deposit onto the first layer of metal is 
useful for the intermediate layer deposition. Further, the intermediate 
layer must be itself conductive to electricity. For example, copper, 
nickel, gold, silver and cobalt are useful for this step. Two exemplary 
solutions which may be used for copper and nickel, respectively, are 
listed in Tables I and II hereinbelow. 
TABLE I 
______________________________________ 
Ingredient Amount.sup.a 
______________________________________ 
copper sulfate 
7.2- 8.8 grams/liter 
formaldehyde 2.1-3.0 grams/liter 
EDTA.sup.b 0.040-0.050 grams/liter 
sodium hydroxide 
6.2-6.89 grams/liter 
______________________________________ 
TABLE II 
______________________________________ 
Ingredient Amount.sup.a 
______________________________________ 
nickel sulfate 8.0- 12.0 grams/liter 
sodium hypophosphite 
8.0-12.0 grams/liter 
ammonium hydroxide 
0.5% by volume 
______________________________________ 
.sup.a parts by weight 
.sup.b ethylenediaminetetraacetic acid 
The metal anion solution employed in the electroless deposit of the 
intermediate layer to the first layer of metal may include complexing 
agents such as sodium hypophosphite in order to complex the metal 
ingredients. Further, stabilizing agents such as lead, cyanide, thiourea 
or bismuth, may be employed which help to maintain the metal ingredients 
in solution. The invention may be practiced with or without complexing 
agents and stabilizers. 
The article produced by these steps comprises a non-conductive substrate 
having a first layer of metal, preferably palladium, deposited thereon and 
bonded thereto by a mechanical bond enhanced by the interaction of the 
metal with the depressions formed in the surface of the substrate. An 
intermediate layer of metal, preferably copper or nickel, is deposited in 
an electroless manner to the first layer. 
The article thus prepared may have a finish layer of a metal 
electrolytically bonded to the intermediate layer. Any metal that may be 
deposited by electrolysis may be used. A metal which will attain a high 
polished shine or lustre is preferred, such as gold, platinum, rhodium, 
palladium, silver, bronze, brass, copper, nickel, iron, chromium, tin, 
zinc and alloys thereof. 
Although any known, conventional technique may be employed to deposit the 
finish layer of metal to the intermediate layer electrolytically, the 
present invention includes an electrolysis process which has been found to 
provide a highly durable finish which readily accepts a high polish or 
shine. 
The article described hereinabove was placed upon a plating fixture 
carrying an electric current, and was subjected to a cold water rinse. 
This step was followed by an acid dip and a further cold water rinse. The 
acid dip is used in order to activate the intermediate layer of metal. 
While any acid which will accomplish the activation is useful for this 
step, such as the various mineral acids, a solution of 100-200 grams of 
concentrated sulfuric acid per liter of water is preferred. 
Electrolysis was then begun by immersing the article in a solution 
comprising from about 165 to about 225 grams per liter of copper sulfate, 
from about 60 to about 90 grams/liter of sulfuric acid, and from about 40 
to about 80 parts per million of chloride in acid copper solution. A low 
level D.C. current of from about 2 to about 5 amps per square foot was 
applied to the fixture for from about three to about five minutes and then 
the D.C. current was raised from about 30 to about 40 amps per square 
foot. 
After a cold water rinse, the article was removed from the fixture and the 
surface thereof was buffed on a standard open-faced buffing wheel using a 
buffing compound of silicone and aluminum oxide. This buffing step 
provided the article with a mirrored surface. 
The substrate was then cleaned by immersing the article in from about 45 to 
about 75 grams per liter of alkaline cleaner. The temperature of the 
cleaning solution was from about 49 to about 93 degrees centigrade and the 
substrate was soaked for about one to about three minutes, varying as 
needed for optimization. 
The substrate was again cleaned by being subjected to a conventional 
electrocleaning procedure. The electrocleaning is useful in removing 
oxidized materials and left over polish from the substrate. Further, the 
electrocleaning step again activates the metal surface. 
Following a cold water rinse, the article was immersed in an acid dip of 
about five percent by volume of sulfuric acid at room temperature for 
about one minute, in order to activate the copper surface. After again 
rinsing in cold water, a second electroplating operation was then 
conducted. While second, third or subsequent electroplating steps are not 
required to practice the present invention, such further electroplating 
may be accomplished in order to plate the article with desired finishes. 
If it is desireable to provide the article with a copper finish, then a 
second plating procedure would not be required. Further, it is not 
necessary to buff the copper finish, and such buffing is provided only 
when a mirrored, highly polished surface is desired. Also, it is known 
that when various metals are plated one on top of the other, different 
color patterns emerge. The following descriptions of further 
electroplating are exemplary of these further electroplating techniques. 
Whether the article is buffed or not, and whether or not layers of metal 
are electroplated subsequent to the first copper layer, all such articles 
are within the scope of the present invention. 
Further still, copper is preferred for the first layer of electroplated 
metal because it is relatively inexpensive and because it will accept a 
mirrored polish. However, any metal which will be deposited by 
electrolysis is within the scope of the present invention. 
The second electroplating solution comprised a metal sulfate, a metal 
chloride and an acid. For instance, one solution contained 300 grams per 
liter of nickel sulfate, 60 grams per liter of nickel chloride and 45 
grams per liter of boric acid. This solution was found to have a pH of 
from about 3.8 to about 4.2. Further, the temperature of the solution was 
from about 54 to 66 degrees centigrade, and the electroplating process was 
carried out for from about 7 about 15 minutes, varying for optimization. 
The second electroplated layer is plated thin enough that the color of the 
plated metal is apparent to an observer, and yet the mirrored surface of 
the first copper electroplated layer is allowed to show through. The 
thickness of the second electroplated layer is such that the article 
appears to have a mirrored surface. 
It is possible to apply a third electroplated layer to the article in a 
manner similar to that described hereinabove. The second and third layers 
can comprise any metal capable of being deposited by electrolysis, such as 
gold, platinum, rhodium, palladium, silver, bronze, brass, copper, nickel, 
iron, chromium, tin, zinc and alloys thereof. 
Following a cold water rinse, the substrate was dried in a hot air oven at 
100 degrees centigrade. 
The resulting article was found to exhibit high resistance to abrasion and 
high steam and dry heat temperatures. 
As should now be apparent, the present invention teaches a metallized 
article and a method of metallizing a non-conductive article, 
accomplishing the objects as set forth above, and otherwise constituting 
an advantageous improvement in the known art. The examples provided herein 
are illustrative of certain properties and are not to be construed as 
limiting practice of the invention. It is to be understood that any 
variations evident fall within the scope of the claimed invention and that 
the specific selection of composition constituents can be determined 
without departing from the spirit of the invention herein described and 
claimed. Moreover, the scope of the invention shall include all 
modifications and variations that may fall within the scope of the 
attached claims.