Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
2000-03-21
2003-05-27
Le, H. Thi (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S144000, C428S149000, C428S328000, C428S331000, C428S403000
Reexamination Certificate
active
06569520
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a coating for inorganic substrates, particularly to a coating composition containing photocatalytic particles, and even more particularly to inorganic granules (e.g. roofing granules) coated with such a composition.
BACKGROUND OF THE INVENTION
Inorganic substrates have been coated with compositions that contain pigments to impart color properties to the substrate for aesthetic purposes. The coated substrates are generally applied or affixed to specific carriers to provide a desired color to the object. For example, coated inorganic granules are often utilized on granule-surfaced bituminous roll roofing and asphalt shingles. The granules, which are partially embedded in one surface of asphalt-impregnated shingles or asphalt-coated fiber sheet material, form a coating which provides an inherently weather-resistant, fire resistant, and decorative exterior surface. The layer of roofing granules functions as a protective layer to shield the bituminous material and the base material from both solar (e.g. ultraviolet radiation) and environmental degradation.
Inorganic substrates are generally coated by applying a slurry containing an inorganic binder and pigment particles onto the substrate. In granular form, the inorganic material is heated in a rotary kiln and mixed with the slurry of inorganic binder and pigment particles. The coated inorganic granules are first dried and then fired at temperatures in excess of 170° C. to insolubilize the binder. The resulting coated granule has a hardened coating that exhibits a selected coloring due to the inclusion of the pigments.
Coated granules are often produced and selected to provide a desirable color to a finished structure or building. It is desirable that the color be consistent over time in order to maintain the appearance of the building. Discoloration of roofing shingles and other building materials due to algae infestation is has become especially problematic in recent years. Algae tend to grow on building materials in areas where moisture is retained. Discoloration has been attributed to blue-green algae, Gloeocapsa magma, transported as air-borne particles. The infestation may be particularly acute on asphalt shingles.
It would be an advantage to provide a coating composition that is capable of preventing algal growth on building materials which incorporate coated inorganic substrates.
SUMMARY OF THE INVENTION
The present invention provides a coating composition for substrates. The incorporation of the present invention onto substrates prevents algal growth on building materials utilizing the coated substrates. The present invention is directed to a coating composition, a coated article resulting, from the application of the coating composition, and a process for coating an article with the inventive composition.
The coating composition of the present invention generally includes a silicate binder and a plurality of photocatalytic particles. The silicate binder functions as the bonding agent to establish the coating on the substrate. A plurality of photocatalyst particles are dispersed throughout the silicate binder. Upon insolubilization of the silicate binder, the plurality of photocatalytic particles are bound in the coating. The particles are included in an amount that provides sufficient distribution of the particles throughout the resulting coating. Sufficient distribution of the particles indicates that at least a portion of some of the individual particles are exposed on the surface of the coating to suppress or prevent algae growth. Preferably, the photocatalytic particles included in the coating composition are metal oxides. A particularly preferred metal oxide is anatase TiO
2
.
The coating composition is applied onto substrates. The substrates suitable for use with invention must be capable of withstanding the firing temperatures of the coating process required to bond the silicate composition to the substrate. Preferred substrates include inorganic granules, rock, clay, ceramics, concrete or metal.
In one aspect of the invention, a plurality of roofing granules are produced. Each of the roofing granules includes an inorganic granule with a coating applied onto an outer surface of the inorganic granule. The coating includes an amount of silicate binder to bind the coating to the inorganic granule. The coating includes a plurality of photocatalytic particles. The photocatalytic particles are sufficiently distributed throughout the coating so that at least a portion of some of the particles are exposed on the surface of the coating.
The resulting article of the present invention, when utilized in building materials, shields the building materials from solar and environmental degradation. The resulting coating reduces the transmittance of UV radiation and thereby reduces exposure of the underlying substrate to solar degradation. The present invention is capable of reducing UV transmittance to about 2% or less, and preferably about 1% or less. The photocatalytic particles also prevent the growth of algae on the substrates containing the coating.
For purposes of the present invention, the following terms used in this application are defined as follows:
“granule” is used broadly and means compounds having a diameter from about 300 micrometers to about 1600 micrometers;
“inorganic granule” means granules of rock, mineral, clay, ceramic, or concrete;
“particle” means compounds having a mean particle size in the range of about 1 nm to about 1000 nm; and
“algae resistant” means the capability to prevent or inhibit the growth of all forms of algae, including the form commonly associated with causing discoloration of roofs and other surfaces.
DETAILED DESCRIPTION
The present invention requires the application of a coating composition, containing a photocatalyst, onto a substrate. The coating composition is capable of preventing solar and environmental damage on the building materials utilizing a substrate coated with the inventive composition.
The coating composition of the present invention is generally an aqueous slurry containing an inorganic binder and a plurality of photocatalytic particles. The composition is heated at elevated temperatures to produce a ceramic-type coating on substrates. Thus, the composition must withstand temperatures of at least about 170° C., and preferably up to about 650° C., without exhibiting thermal degradation.
The function of the inorganic binder in the composition is to adhere the coating to a desired inorganic substrate. Preferably, the inorganic binder is an alkali metal silicate binding agent. Alkali silicate binding agents include those selected from the group consisting of lithium silicate, potassium silicate, sodium silicate, or combinations thereof The alkali metal silicate is generally designated as M
2
O:SiO
2
, where M is lithium, potassium, or sodium. The weight ratio of SiO
2
to M
2
O ranges from about 1.4:1 to about 3.75:1. Preferably, the weight ratio in the range of about 2.75:1 to about 3.22:1. At about 38% to about 41% solids in solution, the amount of inorganic binder included in the coating composition is in the range of about 14 to about 30 parts by weight per thousand parts by weight of granules, and preferably in the range of about 17 to about 22 parts by weight per thousand parts by weight of granules.
A plurality of photocatalytic particles are included in the coating composition of the present invention. Photocatalysts, upon activation or exposure to sunlight, establish both oxidation and reduction sites. These sites are capable of preventing or inhibiting the growth of algae on the substrate. Photocatalytic particles conventionally recognized by those skilled in the art are suitable for use with the present invention. Preferred photocatalysts include transition metal photocatalysts. Examples of suitable transition metal photocatalysts include TiO
2
, ZnO, WO
3
, SnO
2
, CaTiO
3
, Fe
2
O
3
, MoO
3
, Nb
2
O
5
, Ti
X
Zr
(1−x)
O
2
, SiC, SrTiO
3
, CdS, GaP, InP, GaAs, BaTiO
3
, KNbO
3
, Ta
2
O
5
, Bi
2
O
3
, N
3M Innovative Properties Company
Harts Dean M.
Le H. Thi
Szymanski Brian E.
LandOfFree
Photocatalytic composition and method for preventing algae... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Photocatalytic composition and method for preventing algae..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Photocatalytic composition and method for preventing algae... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3004467