Powder coating compositions

Abstract: A powder-containing composition for use as a film-forming coating on substrates, comprising particulate powder and clay dispersed in water. The composition is also suitable for use in aerosol cans.

Description: The present invention relates to a powder-containing composition for use as a film-forming coating for various substrates. More particularly the present invention relates to a composition comprising particulate powders, such as, for example, boron nitride powders and clay dispersed in water. Boron nitride has been used extensively for vaporization vessels (also known as vaporization boats) used for metal evaporation. In addition to the use of solid boron nitride articles, such as, for example, vaporization vessels, boron nitride powders have found use in many applications such as, for example, coatings for high temperature molds to facilitate release of glass, metals, ceramics or the like. Boron nitride coatings can also be used as antisputter coatings for welding applications; anticorrosive coatings for various substrates; and thermally conductive/electrically insulating coatings for electronic equipment. In addition to boron nitride powders, many other powders such as, for example, borides, carbides and oxides of metals have utilization for various applications when applied to a substrate as a film-forming coating. To be a good film coating that can be sprayed on substrates, the powders have to be dispersed in a liquid vehicle along with a binder type ingredient to ensure that the dispersed powder will adhere to the substrate. Many different types of vehicle binder solutions have been used with particulate powders to provide a sprayable composition that can be used in an aerosol can with a conventional propellant gas such as isobutane. It has now been found possible to provide a powder-containing composition, such as, for example, a boron nitride-containing composition, that when applied to a surface of a substrate will produce a coating having good adherence to the substrate. It has also been found possible to provide a powder-containing composition comprising substantially particulate powder and clay dispersed in water. Particularly, it has been found possible to provide (a) a powder-containing composition that uses a minor amount of clay as a binder; (b) a boron nitride-containing composition comprising particulate boron nitride in combination with particulate clay dispersed in water; and (c) a boron nitride-containing composition comprising particulate boron nitride and particulate clay in combination with aluminium nitride, titanium diboride and/or titanium dioxide dispersed in water. It has further been found possible to provide an economical vehicle-binder for particulate powders that can be used to facilitate the depositing of the powders on a substrate as an adhered film or coating. FR-A-2041320 discloses a composition which is intended to be fired at high temperature into a hard coating whereas the aqueous composition of the present invention is intended only to be dried to make an adherent film-former. FR-A-2041320 discloses a gunite composition, gunites being thixotropic mixtures of clay and aggregate particles which necessarily are substantially larger in size than the clay particles. The composition of FR-A-2041320 also requires a metal phosphate to harden the composition when fired. SU-A-1395418 and WORLD PATENT INDEX LATEST, week 8847, discloses an anti-adhesion coating for casting moldings and cores, which is intended to be used as a release from hot metal after casting not as an adherent coating film-forming surface when dried at low temperature. A lignosulfonate is also required to bind the clay and water glass. FR-A-1580353 discloses a powder coating composition to form a vitreous film after heating above 450°C, and depends upon the formation of alkali silicates in aqueous solution to bind the clay and to form a flux on firing. JP-A-1191738 and WORLD PATENT INDEX LATEST week 8936, discloses a coating composition which includes filler particles such as mica or talc but does not disclose the use of a clay binder. According to the present invention there is provided an aqueous powder-containing composition dispersed in water for forming upon drying an adherent film-forming coating on substrates with the powder composition composed solely from fine non-aggregated particulate powders selected from borides, carbides and oxides of metals, or mixtures thereof and clay and wherein the particulate powder is sized from 0.5 µm to 30 µm and the clay is sized from 0.5 µm to 30 µm. As used herein the term "powders" or "powder" shall mean powders of a single powder component or a mixture of different powders. For example, powders could comprise boron nitride powders, or boron nitride powders mixed with titanium dioxide powders. It has been discovered that water can be used as the vehicle liquid for a blend of a particulate powders and particulate clay to produce a sprayable or spreadable composition that can be deposited on a substrate to form an adhered coating of the powder on the substrate. The clay acts as the binder for the powders so that once the composition is deposited on the substrate, the water evaporates leaving an adhered coating of the powder clay mixture on the substrate. The benefit of the present invention is that any particulate powder such as, for example, borides, carbides and oxides of metals can be used with the particulate clay along with water to provide an excellent sprayable or spreadable composition. Examples of suitable particulate powders would be boron nitride, titanium diboride, boron carbide, aluminium oxide, magnesium oxide, zirconium oxide, aluminium nitride, silicon nitride, silicon carbide, titanium dioxide, yttrium oxide, graphite, carbon and mixtures thereof. The oxide powders may be used to produce coatings having good high temperature and oxidation resistant characteristics. The graphite or carbon powder may be used to produce coatings which have electrical conductivity and fire retardant characteristics. To change or alter the characteristics of a coating made using a single component powder, one or more other powders could be added to form a mixture which could then be used along with particulate clay in water to form the sprayable or spreadable composition. For example, titanium diboride powders could be added to boron nitride powders to increase the electrical conductivity of the boron nitride deposited coating or aluminium nitride powders could be added to boron nitride powders to increase the thermal conductivity of the boron nitride deposited coating. Also a particulate carbonaceous material could be mixed with any other powder to increase the electrical conductivity of the deposited coating. The preferred particulate powders for use in this invention would be boron nitride, titanium diboride, boron carbide, aluminum nitride, graphite and mixtures thereof. The particulate powders for use in this invention are sized from 0.5 µm to 30 µm and preferably from 5 µm to 15 µm. The powder-containing composition when intended for use in aerosol can applications preferably should have the particulate powders sized from 6 microns to 12 microns. The particulate powders may be present in the composition in an amount from 20 to 99 weight percent, preferably 30 to 96 weight percent, based on the weight of the solid components of the composition. Particulate inert filler materials, such as, for example, titanium dioxide, may also be added to the composition, if desired, so that less of an expensive particulate powder could be used. The combination of filler material and particulate powders should be within the weight percentages indicated above. For an aerosol can application, the particulate powder preferably should be from about 1.5 to 6 weight percent and the clay should be from 0.2 to 5.0 weight percent based on the weight of the overall composition in which the overall composition comprises the powder, clay, water and propellant gas. The clay for use in this invention generally comprises particles of hydrous aluminium silicates, and depending where obtained, other minerals. When the composition is intended for use in aerosol can applications, the size of the particulate clay should preferably be from 6 µm to 12 µm. The amount of clay to be employed in the composition can vary from 1 to 80 weight percent, preferably 4 to 70 weight percent, based on the weight of the solid components of the composition. A sufficient amount of the clay should be used to enable the particulate powders to adhere to a substrate to form an adhered coating on the substrate. A suitable clay for use in this invention can be obtained commercially from NL Chemicals, Inc. under its trademark Bentone EW which is an organo/clay (tetraalkyl ammonium bentonite). The water for use in this invention can be regular tap water. However if the coating is intended to be used in a particular application where any impurities could pose a problem, then it would be preferred to use deionized water. Thus the end use application of the coated deposit will dictate the purity of the powders, clay and water to be used. The amount of water in this composition may be from 20 to 80 weight percent based on the weight of the overall composition including the particulate powders and clay. Water in an amount less than 20 weight percent would not provide sufficiently low viscosity to have effective dispersion of the powders and clay. Water in excess of 80 weight percent would provide a diluted composition that would not be effective for most applications. The powder-containing composition of this invention may be brush painted or sprayed on a substrate or the substrate may be dipped in the composition to produce an adhered powder coating. The powder-containing composition of this invention may also be used in an aerosol can with a conventional propellant gas such as, for example, isobutane. In this embodiment, the novel powder-containing composition may be dispersed from the aerosol can directly onto the surface of a substrate to produce an adhered coating of the powder that will remain on the substrate. Any suitable propellant gas used in aerosol cans may be employed with the powder-containing composition of this invention. For example, suitable propellant gases are isobutane, carbon dioxide, propane and mixtures thereof and can be present in an amount of at least 30, preferably between 30 and 40, weight percent based on the weight of the overall composition. The powder-containing composition of this invention may be dispersed on any type or shape of substrate where a specific powder coating would be desirous. For example, the powder-containing composition of the invention is ideally suited to coat such substrates as, for example, graphite, paper, metal, fabrics, ceramics, and the like. Example 1 A powder-containing composition was formulated of the components listed below in Table 1. Component Weight Percent Weight kg lbs Deionized Water 65 3.10 6.83 Clay 2 0.10 0.21 Titanium Dioxide 16.5 0.78 1.73 Boron Nitride Powders 16.5 0.78 1.73 The deionized water was placed in a vessel and, while being agitated, the clay was fed into the water until a smooth blend was obtained. While still being agitated, the boron nitride and titanium dioxide powders were added until a smooth consistency blend was obtained. The titanium dioxide powder was added as an inert filler so as to reduce the amount of boron nitride in the composition. The boron nitride-containing composition was deposited on a graphite substrate by brush and then the water in the dispersed composition evaporated leaving a coating containing boron nitride, titanium dioxide and clay secured to the substrate. The overall coating had a relatively hard surface and adhered to the graphite substrate. Example 2 A powder-containing composition was formulated of the components listed below in Table 2. Component Weight Percent Weight kg lbs Deionized Water 65 3.10 6.83 Clay 2 0.10 0.21 Titanium Diboride 33 1.57 3.46 The deionized water was placed in a vessel and, while being agitated, the clay was fed into the water until a smooth blend was obtained. While still being agitated, the titanium diboride powder was added until a smooth consistency blend was obtained. The titanium diboride-containing composition was deposited on a graphite substrate by brush and then the water in the dispersed composition evaporated leaving a coating containing titanium diboride and clay secured to the substrate. The overall coating had a relatively hard surface and was well adhered to the substrate. Example 3 A powder-containing composition was formulated of the components listed below in Table 3. Component Weight Percent Weight kg lbs Deionized Water 65 3.10 6.83 Clay 2 0.10 0.21 Boron Carbide 33 1.57 3.46 The deionized water was placed in a vessel and, while being agitated, the clay was fed into the water until a smooth blend was obtained. While still being agitated, the boron carbide powder was added until a smooth consistency blend was obtained. The boron carbide-containing composition was deposited on a graphite substrate by brush and then the water in the dispersed composition evaporated leaving a coating containing boron carbide and clay secured to the substrate. The overall coating had a relatively hard surface and was well adhered to the substrate. Example 4 Using conventional techniques a composition may be formulated of the components listed in Table 4 and then fed into a conventional aerosol can. Deionized Water 59 weight percent Clay 0.2 weight percent Titanium Dioxide** 2.9 weight percent Boron Nitride Powder 2.9 weight percent Propellant Gas Isbutane 35 weight percent The composition may be sprayed from the aerosol can onto any substrate until a desired thickness layer of coating is produced.

Claims: An aqueous powder-containing composition dispersed in water for forming upon drying an adherent film-forming coating on substrates with the powder composition composed solely from fine non-aggregated particulate powders selected from borides, carbides and oxides of metals, or mixtures thereof and clay and wherein the particulate powder is sized from 0.5 µm to 30 µm and the clay is sized from 0.5 µm to 30 µm. A composition according to claim 1, wherein the particulate powder is selected from boron nitride titanium diboride, boron carbide, aluminium oxide, magnesium oxide, zirconium oxide, aluminium nitride, silicon nitride, silicon carbide, titanium dioxide, yttrium oxide, graphite, carbon and mixtures thereof. A composition according to claim 1 or claim 2, wherein the particulate powder is selected from boron nitride, titanium diboride, aluminium nitride, titanium dioxide, boron carbide and mixtures thereof. A composition according to any of claims 1 to 3, wherein the particulate powder is present in the composition in an amount from 20 to 99 weight percent based on the weight of the solid components of the composition and the clay is present in the composition in an amount from 1 to 80 weight percent based on the weight of the solid components of the composition. A composition according to claim 4, wherein the particulate powder is present in an amount from 30 to 96 weight percent based on the weight of the solid components of the composition and the clay is present in an amount from 4 to 70 weight percent based on the weight of the solid components of the composition. A composition according to any of claims 1 to 3, wherein at least 20 weight percent water is present in the composition based on the weight of the composition. A composition according to any of claims 1 to 6, wherein the water is deionized. A composition according to any of claims 1 to 6, for use in aerosol spray cans and further comprising a propellant gas. A composition according to claim 8, wherein the propellant gas is selected from isobutane, carbon dioxide, propane and mixtures thereof. A composition according to claim 8 or 9, wherein the propellant gas is present in an amount of at least 30 weight percent based on the weight of the composition. A composition according to any of claims 8 to 10, wherein the particulate powder is from 1.5 to 6.0 weight percent, the clay is from 0.2 to 5.0 weight percent, the water is at least 20 weight percent and the propellant is from 30 to 40 weight percent based on the weight of the composition. A composition according to any of claims 8 to 11, wherein the particulate powder is boron nitride and titanium dioxide, and the propellant gas is carbon dioxide.

Inventors: OSBORNE TIMOTHY WILFRED, OSBORNE, TIMOTHY WILFRED
Applicants: ADVANCED CERAMICS CORP, ADVANCED CERAMICS CORPORATION
Application year: 1990
Main classification: C04B41
IPC codes: C03C17, C04B41, C09D1, C23C26, C09D5, C23C30