Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
1999-02-10
2001-05-29
Le, H. Thi (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C427S218000, C427S219000, C427S444000, C428S404000
Reexamination Certificate
active
06238794
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a coating for inorganic substrates, particularly to a coating composition containing carbon black pigment particles, and even more particularly to inorganic granules (e.g. roofing granules) coated with such a composition.
BACKGROUND
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 roofing shingles.
Composite roofing shingles usually employ a web of fibrous base material. The base material typically is a nonwoven fabric such as felt, fiberglass, or similar materials, which are impregnated with a bituminous composition such as asphalt. A layer of bituminous material typically is also applied onto one side of the base material. Roofing granules are then pressed into the layer of bituminous material while it is in a warm, softened condition. Upon cooling, the roofing granules remain attached as a surface layer. 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. Additionally, the roofing granules are generally colored to provide an aesthetically pleasing appearance to the building or structure upon which the shingles are applied.
The coloring of the shingles is an important feature which renders a desired appearance to a structure. It is preferred that the color of the shingles resist fading and maintain the original color over time. Certain colors have had a greater tendency to fade thus yielding an undesirable effect in the color of the granular coated shingle. Black colors, specifically medium blacks, have a greater tendency to fade when exposed to weathering conditions, such as temperature cycles and acidic precipitation. Medium blacks, as defined with CIELAB color scale coordinates, generally have an L* value within the range of about 24 to 37. Black colored roofing granules are often blended with one or more colored granules of a different hue to provide a specific color blend. This blend, when viewed from a distance, appears as a uniform color. Any resulting color change due to fading can adversely affect the desired color of the shingle.
Inorganic granules having a black color are produced by coating an inorganic granular material with a slurry containing an inorganic binder and black pigment particles. The pigments are generally carbon black particles with a mean particle size of less than 110 nm. The inorganic granular 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. While each of the resulting coated granules exhibit a desirable black color, the color has a tendency to fade over time when exposed to weathering conditions.
Thus, it would be an advantage to provide a coating composition that is capable of imparting a fade resistant black color to an inorganic granular substrate.
SUMMARY OF THE INVENTION
The present invention provides a novel coating composition which exhibits a greater resistance to fade from environmental conditions. The composition includes an inorganic binder and carbon black pigment particles having specific size parameters. Additionally, the present invention discloses coated inorganic substrates, a roofing shingle utilizing the coated substrates, and a method for producing the coated substrates.
The present invention is a composition suitable for coating an inorganic substrate. The composition comprises an amount of an inorganic binder that is sufficient to bind the composition to a substrate. A plurality of carbon black pigment particles are included in the composition. The particles have a mean particle size in the range of about 150 nm to about 500 nm. Additionally, the particles have a surface area per weight of particles in the range of about 20 m
2
/g or less. The carbon black particles impart a black appearance to the substrate granule after the composition has been applied and heated to form a coating on the granule. The black color of the coated granule exhibits a greater resistance to fade.
The present invention also includes coated granules having a black fade resistant coating. The granules are generally inorganic granules upon which the inventive coating composition is applied. The coated granules are ideally suited for such applications as roofing granules. When utilized as roofing granules, the coated granules of the present invention are generally pressed onto a carrier substrate. The carrier substrate is preferably a bituminous layer applied onto a base substrate of felt or fiberglass.
The coated granules of the present invention exhibit a greater resistance to environmentally induced fade than granules coated with smaller carbon black pigment particles. The resistance to fade is measured by subjecting the granular material to an accelerated weathering test. The test is utilized to indicate the extent of color change from the initial color of the coated granule. The color value is measured in accordance with CIELAB color scale coordinates. The change is color is reported as the difference in L* values. The coatings of the present invention exhibit a resistance to fade indicated by an L* value change of 5 or less.
Additionally, the present invention includes a method of coating the inorganic substrates. The method includes the application of the inventive coating composition onto an inorganic substrate. The composition covering the substrate is then heated to form a coating on the substrate. The coating exhibits a greater resistance to fade.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
In accordance with the present invention, it has been discovered that a composition containing carbon black pigment particles of a specific size is suitable for use as a coating on inorganic substrates which provides a greater resistance to fade than conventional coating compositions. The present invention is particularly applicable to the use of this composition for coating inorganic granules, the method of making the coated granule, and the specific use of the coated granule in a roofing shingle.
The coating composition of the present invention is generally an aqueous slurry containing an inorganic binder and a plurality of carbon black pigment particles. The composition is heated at elevated temperatures to produce a ceramic-type coating on inorganic 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.
Carbon black pigment particles are utilized in coatings to reduce the reflectance of visible light and thereby impart a darker color to the coating. Carbon black pigments are often preferred because of their economy and color strength. The particles may also be used to provide
Beesley Arthur H.
George Bill L.
Sobon Christine A.
Waletzko Nancy A.
3M Innovative Properties Company
Le H. Thi
Szymanski Brian E.
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