Compositions: coating or plastic – Coating or plastic compositions – Alkali metal silicate containing
Reexamination Certificate
1999-05-11
2001-01-23
Wood, Elizabeth D. (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Alkali metal silicate containing
C106S612000, C106S635000, C106S636000, C106S038300, C106S038900, C106S425000, C106S431000, C428S357000, C428S426000, C428S428000, C428S432000
Reexamination Certificate
active
06176919
ABSTRACT:
FIELD OF THE INVENTION
This invention is directed to a water-based paint composition especially useful on automotive windshields. More particularly, it is a sodium silicate based paint including fused silica.
BACKGROUND OF THE INVENTION
Various paint compositions are known for use on automotive and architectural glass. Such paints are used, for example, to form opaque borders around the peripheral marginal surfaces of glazings used as windshields, sidelites, and backlites of motor vehicles. These borders are used to obstruct from view attachment means for the glazings and protect adhesives which might be used from exposure to light which could degrade them.
Generally these compositions are ceramic compositions formed from a mixture of metal oxides in an organic (oil based) vehicle like mineral oil. The opaque peripheral marginal paint bands fired onto automotive glazings are generally black provided by colorant oxides like chrome oxide, cobalt oxide and nickel oxide. In view of environmental and commercial considerations, more desirable water-based paints have been developed for use in place of such organic vehicle paints. One such paint is disclosed in U.S. Pat. No. 5,698,026, commonly assigned herewith, which is a soda-lime silicate based paint which uses metal oxide pigment to color the glass. That water based paint advantageously is curable at relatively low temperatures compared to the relatively high temperatures generally required for ceramic/organic vehicle paint curing. Subjecting the glass to high temperatures to cure the paint can impart undesirable optical distortions into the glass sheets.
It is known in the automotive industry that the outer edge of a windshield is most sensitive to stone chips because of stresses contained in this region. Adding paint to this region, and later subjecting the glass to heating and shaping, I believe can intensify this stress, particularly weakening the glass in the painted area and making it more susceptible to stone chipping or breakage. Automotive windshields are made of two panes of glass laminated together with a layer of polyvinyl in-between. Even applying the paint to the inside glass surface near the occupant, which is not directly contacted by stones, can have a negative impact on stone chip resistance of the glass surface facing outside the vehicle.
It is an object of the present composition to provide a water-based paint composition which has improved stone chip resistance for the glass on which it is applied. It is an object of the invention to provide a water-based paint with excellent adhesion to glass on which it is applied. I have found that these objects can be accomplished by including fused silica in a water based silicate paint. These and other objects are accomplished by the present invention paint which is curable at relatively low temperatures and which exhibits excellent durability.
DISCLOSURE OF THE INVENTION
The invention disclosed herein is a water-based paint composition particularly useful as a coating on soda-lime-silica glass. The composition comprises:
(i) water-soluble sodium silicate forming 30 to 50 weight percent of the composition,
(ii) water forming 20 to 30 weight percent of the composition;
(iii) water-soluble base in an amount sufficient to provide the composition with a pH of at least 10.5;
(iv) finely divided metal oxide powder selected from the group consisting of oxides of copper, iron, nickel, cobalt and mixtures thereof forming 25 to 40 weight percent of the composition and having a particle size, on average, less than 7 microns;
(v) fused silica frit powder having, on average, a particle size of up to about 20 microns and forming 1 to 20 weight percent of the composition;
(vi) low-melting glass frit powder melting below 1300° F. forming 0 to 10 weight percent of the composition and having a particle size, on average, less than 10 microns;
(vii) particles of soda-lime-silica glass forming 0 to 10 weight percent of the composition and having a diameter, on average, less than 20 microns and having a melting point of at least about 1700° F.; and
(viii) zinc oxide forming 0 to 10 weight percent of the composition.
In addition, preferably the composition comprises small amounts of aluminum hydroxide. According to another aspect of the invention, it is a cured coating of the paint on a glass sheet.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The invention composition is a water-based paint useful as a coating on glass, such as for the “black out” area around the periphery of a windshield. The glass paint components comprise, as disclosed in detail above, silicate, water, water-soluble base, metal oxide powder like copper oxide, low-melting glass frit powder, fused silica, and optionally, one or both of high-melting glass particles comprising soda-lime-silica glass and zinc oxide. Each of these components, including optional components, will be discussed in detail below.
The present invention paint with fused silica has been unexpectedly found by the inventor to significantly improve the ability of a windshield to resist stone chipping when it carried the present invention paint as compared to prior art water based paints such as the one disclosed in the above referenced patent.
Water-soluble sodium silicates form between about 20 and 50 weight percent of the composition of this invention, more preferably, between about 20 and 40 weight percent of the composition, most preferably being about 25 weight percent, i.e., as used herein “weight percent of the composition” meaning a fraction of the total weight of the composition. They may comprise a single sodium silicate or a mixture of different sodium silicates. Water-soluble sodium silicates useful in this invention composition can be represented by the formula SiO
2
:Na
2
O, wherein the mole ratio therein of the two oxides is from about 2:1 to about 4:1. In addition to the water-soluble sodium silicate, water-soluble potassium silicates of similar formula may also be included in the composition. When they are included, they are generally present in minor amounts, preferably less than 5 percent by weight, generally between about 5 and 10 weight percent of the composition.
Yet another required component of the composition is water which is included in an amount between about 20 and 30 weight percent of the total composition weight, preferably in an amount between about 22 and 28 weight percent. The composition also includes a water-soluble base which is employed to provide the paint composition with a pH of at least about 10.5, preferably being above 12.5, more preferably about 13.5. The pH is required to be on the basic side as is indicated by the required pH. Providing the composition with this pH is necessary to impart desirable shelf life to the paint. Examples of water-soluble bases which may be employed include but are not limited to sodium hydroxide and potassium hydroxide, with sodium hydroxide being preferred. The amount of base employed is dependent, e.g., on the particular base and concentration employed. For example, using a 2N sodium hydroxide base, is generally included in about 2 to 10 weight percent of the composition, more preferably in about 3 to 8 weight percent, and most optimally, in about 3 to 6 weight percent. Optimal amounts and types of bases which may be employed would be apparent to those skilled in the art in view of the present disclosure.
The composition further comprises as a pigment finely divided metal oxide selected from copper oxide, iron oxide, nickel oxide, cobalt oxide and mixtures thereof, with the inclusion of copper oxide being preferred. This pigment gives the paint a black color and forms 25 to 40 weight percent of the composition, preferably between about 30 to 40 weight percent of the composition. The finely divided powder pigment has a particle size (diameter) on average less than about 7 microns, preferably being between about 3 and 7 microns, most preferably being about 5 microns. These compositions would vary in color from black to dark gray, depending on the mixture and percentages of the meta
McCoy-Pfau Rhonda L.
Visteon Global Technologies Inc.
Wood Elizabeth D.
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