Patent Application
20080053336
The aqueous coating compositions contemplated by the instant invention include at least water, a film-forming component and at least one inorganic pigment. The film-forming component is typically a water-dispersible or water-soluble polymeric binder material, many such materials having been known and used in previous pigmented aqueous coating compositions. Any other components known or commonly-used in pigmented aqueous coating compositions, for example, rheology modifiers, biocides, wetting agents, dispersants, coalescing agents and other fillers, may also be present in the aqueous coating compositions of the present invention.
Preferably the aqueous coating compositions will utilize as an inorganic pigment titanium dioxide which has been surface treated with one or more organosilicon compounds from the alkyltrialkoxysilanes, the dialkyldialkoxysilanes and mixtures, oligomers, and copolymers of the alkyltrialkoxysilanes and dialkyldialkoxysilanes, wherein the alkyl groups of these materials contain from three to six carbon atoms and optionally contain an oxygen atom or contain fluorine and/or chlorine heteroatoms. Preferred organosilicon compounds are the alkyltrialkoxysilanes, the dialkyldialkoxysilanes and mixtures, oligomers, and copolymers of the alkyltrialkoxysilanes and dialkyldialkoxysilanes, wherein the alkyl groups contain three carbon atoms.
Surprisingly, only a very narrow range of carbon atoms in the alkyl group is useful for the instant invention. In this regard, for the usually preferred circumstance wherein the only organic surface treatments of the inorganic pigment are accomplished by means of the above-described organosilicon materials, experimental results demonstrate that when the number of carbon atoms in the alkyltrialkoxysilane or dialkyltrialkoxysilane alkyl groups is greater than six, the pigments become too difficult to disperse in water-borne coatings, and when the alkyl groups contain only one or two carbon atoms there is no beneficial effect observed in the performance of the coating. Those skilled in the art will appreciate, however, that other organic surface treatment materials known in the art may be used with the organosilicon surface treatment materials of the present invention, if desired for providing improvements in performance or imparting certain properties to the pigments.
The amount of organosilicon material added as a surface treatment according to the instant invention will be an amount sufficient to provide a treated inorganic particulate-containing coating composition with improved performance properties over that of a coating composition derived from the corresponding untreated inorganic particulate. Preferably the organosilicon material is incorporated on the inorganic particulate, again preferably being titanium dioxide, in an amount ranging from about 0.1 to about 5 weight percent in total, based on the weight of the inorganic particulate. More preferred is an organosilicon material content ranging from about 0.25 percent to about 2.5 percent, based on the weight of the inorganic particulate. Most preferably, the surface treated inorganic particulate will use from about 0.5 percent to about 1.5 percent of these materials, based on the weight of the inorganic particulate.
The pigment surface treatments can be accomplished using any of the known methods of treating pigment surfaces, such as deposition in a fluid energy mill, applying the organosilicon material to the dry pigment by mixing or spraying, or through the drying of pigment slurries containing the organosilicon material.
Inorganic pigments, which can also be referred to as fillers, extenders or reinforcing pigments, improved by the instant invention include any of the particulate inorganic pigments known in the surface coatings and plastics industries. Examples include white opacifying pigments such as titanium dioxide, basic carbonate white lead, basic sulfate white lead, basic silicate white lead, zinc sulfide, zinc oxide; composite pigments of zinc sulfide and barium sulfate, antimony oxide and the like; white extender pigments such as calcium carbonate, calcium sulfate, china and kaolin clays, mica, diatomaceous earth; and colored pigments such as iron oxide, lead oxide, cadmium sulfide, cadmium selenide, lead chromate, zinc chromate, nickel titanate and chromium oxide. Titanium dioxide, of either the anatase or rutile crystalline structure or some combination thereof, is again most preferred among the inorganic pigments. The titanium dioxide pigment can have deposited thereon any of the inorganic metal oxide and/or metal hydroxide surface coatings known to the art, prior to treatment with the organosilicon compound according to the instant invention.
Other components of the aqueous coating systems of the present invention can (as mentioned previously) be any previously known to the art, with substituting the organosilicon compound surface-treated inorganic oxide pigments contemplated by the present invention for the inorganic oxide pigments previously known and used in any such aqueous coating systems. Various conventional components are evident from the examples below, but those skilled in the art will recognize that very many different combinations of materials and very many different aqueous coating compositions are known in which the organosilicon compound surface-treated inorganic oxide pigments of the present invention can be used with success. Recent United States Patents pertaining to aqueous coating systems include, for example, U.S. Pat. Nos. 6,969,734, 6,869,996, 6,762,230 and 6,646,058. While undoubtedly such other components will in any commercial sense be required for the aqueous coating compositions of the present invention, in addition to the water, film-forming component and organosilicon compound surface-treated inorganic pigment components, these other components are in any event well-known and need not be described further herein.
The following examples serve to illustrate specific embodiments of the instant invention without intending to impose any limitations or restrictions thereto. Concentrations and percentages are by weight unless otherwise indicated.
Particulate titanium dioxide pigment intermediate obtained from the vapor phase oxidation of titanium tetrachloride containing 1.0% alumina was dispersed in water in the presence of 0.15% by weight (based on pigment) of sodium hexametaphosphate dispersant, along with a sufficient amount of sodium hydroxide to adjust the pH of the dispersion to 9.5 and greater, to achieve an aqueous dispersion with a solids content of 35% by weight. The resulting titanium dioxide slurry was sand milled, using a zircon sand-to-pigment weight ratio of 4 to 1, until a volume average particle size was achieved wherein more than 90% of the particles were smaller than 0.63 microns, as determined utilizing a Microtrac X100 Particle Size Analyzer (Microtrac Inc. Montgomeryville, Pa.).
The resulting slurry, diluted to 30% solids by weight, was heated to 90° C. then treated with 3.0%, calculated as silica by weight of final pigment, of sodium silicate, added over 20 minutes as a 250 gram/liter aqueous sodium silicate solution (SiO2:Na2O=3.5). While maintaining the temperature at 90° C., the pH of the slurry was slowly decreased to pH=5.0 using 25% by weight aqueous sulfuric acid solution, over a 55 minute period. Following a digestion period of 15 minutes, 2.0% alumina, by weight of final pigment, was added over 15 minutes as a 357 gram/liter aqueous sodium aluminate solution while maintaining the pH of the slurry between a value of 8.0 and 8.5 via the concomitant addition of 25% aqueous sulfuric acid.
The dispersion was allowed to equilibrate at 90° C. for 15 minutes, at which point the pH of the slurry was re-adjusted to 5.8, prior to filtration while hot. The resulting filtrate was washed with an amount of water, which had been preheated to 60° C. and pre-adjusted to a pH of 7.0, equal to the weight of recovered pigment.
The washed semi-solid filtrate was subsequently re-dispersed in water with agitation in the presence of 0.50%, by weight based on pigment, of hexyltrimethoxysilane. The resulting pigment dispersion was spray dried using an APV Nordic PSD52 Spray Dryer (Invensys APV Silkeborg, Denmark), maintaining a dryer inlet temperature of approximately 280° C., to yield a dry pigment powder. The dry pigment powder was then steam micronized in the presence of 0.35% by weight based on pigment of trimethylol propane, utilizing a steam to pigment weight ratio of 2.5, with a steam injector pressure set at 146 psi and micronizer ring pressure set at 118 psi, completing the finished pigment preparation.
As a comparative example, the same procedure described above was repeated, but in the absence of the addition of the hexyltrimethoxysilane. The resulting pigment produced according to the inventive process and the comparative pigment were both evaluated for paint film gloss and tint strength performance in a water-borne coating, according to the recipe and test procedures presented below. Results are provided in Table 1.
The above components were added in the sequence indicated and mixed at high shear for twenty minutes, after which the components listed below were added in sequence with continued, but lower shear, mixing until homogeneous, to yield a 22% PVC (percent pigment volume concentration), 36% NVV (percent non-volatiles by volume), water-borne coating with final pH=8.8 and final viscosity=five poise.
The aqueous coating composition produced according to the instant invention, comprising a titanium dioxide pigment having deposited thereon an inorganic oxide surface treatment of 3.0% silica and 2.0% alumina, both by weight of the pigment, and an organic surface treatment comprising 0.50% by weight of pigment of hexyltrimethoxysilane according to the present invention, thus demonstrates improved properties as indicated by the increased gloss and tint strength values for the inventive coating composition versus the comparative example.
Particulate titanium dioxide pigment intermediate obtained from the vapor phase oxidation of titanium tetrachloride containing 1.0% alumina was dispersed in water in the presence of 0.15% by weight (based on pigment) of sodium hexametaphosphate dispersant, along with a sufficient amount of sodium hydroxide to adjust the pH of the dispersion to a value of 9.5 and greater, to achieve an aqueous dispersion with a solids content of 35% by weight. The resulting titanium dioxide slurry was sand milled, using a zircon sand-to-pigment weight ratio of 4 to 1, until a volume average particle size was achieved wherein more than 90% of the particles were smaller than 0.63 microns, as determined utilizing a Microtrac X100 Particle Size Analyzer.
The resulting slurry, diluted to 30% solids by weight, was heated to 90° C. then treated with 3.0%, calculated as silica by weight of final pigment, of sodium silicate, added over 20 minutes as a 250 gram/liter aqueous sodium silicate solution (SiO2:Na2O=3.5). While maintaining the temperature at 90° C., the pH of the slurry was slowly decreased to pH=5.0 using 25% by weight aqueous sulfuric acid solution, over a 55 minute period. Following a digestion period of 15 minutes, 2.0% alumina, by weight of final pigment, was added over 15 minutes as a 357 gram/liter aqueous sodium aluminate solution while maintaining the pH of the slurry between a value of 8.0 and 8.5 via the concomitant addition of 25% aqueous sulfuric acid.
The dispersion was allowed to equilibrate at 90° C. for 15 minutes, at which point the pH of the slurry was re-adjusted to 5.8, prior to filtration while hot. The resulting filtrate was washed with an amount of water, which had been preheated to 60° C. and pre-adjusted to a pH of 7.0, equal to the weight of recovered pigment. The washed semi-solid filtrate was subsequently re-dispersed in water with agitation in the presence of 1.0%, by weight based on pigment, of propyltrimethoxysilane according to the present invention. The resulting pigment dispersion was spray dried using an APV Nordic PSD52 Spray Dryer, maintaining a dryer inlet temperature of approximately 280° C., to yield a dry pigment powder. The dry pigment powder was then steam micronized in the presence of 0.35% by weight based on pigment of trimethylol propane, utilizing a steam to pigment weight ratio of 2.5, with a steam injector pressure set at 146 psi and micronizer ring pressure set at 118 psi, completing the finished pigment preparation.
As a comparative example, the same procedure described above was repeated, but in the absence of the addition of the propyltrimethoxysilane. The resulting pigment produced according to the inventive process and the comparative pigment were both evaluated for paint film gloss and tint strength performance in a water-borne coating, according to the recipe and test procedures described in Example 1. Results are provided in Table 2.
The coating composition produced according to the instant invention, comprising a titanium dioxide pigment having deposited thereon an inorganic oxide surface treatment of 3.0% silica and 2.0% alumina, both by weight of the pigment, and an organic surface treatment comprising 1.0% by weight of pigment of propyltrimethoxysilane, further demonstrates improved properties as indicated by the increased gloss and tint strength values for the inventive coating composition versus the comparative example.
Particulate titanium dioxide pigment intermediate obtained from the vapor phase oxidation of titanium tetrachloride containing 1.0% alumina was dispersed in water in the presence of 0.15% by weight (based on pigment) of sodium hexametaphosphate dispersant, along with a sufficient amount of sodium hydroxide to adjust the pH of the dispersion to a value of 9.5 and greater, to achieve an aqueous dispersion with a solids content of 35% by weight. The resulting titanium dioxide slurry was sand milled, using a zircon sand-to-pigment weight ratio of 4 to 1, until a volume average particle size was achieved wherein more than 90% of the particles were smaller than 0.63 microns, as determined utilizing a Microtrac X100 Particle Size Analyzer.
The resulting slurry, diluted to 30% solids by weight, was heated to 90° C. then treated with 3.0%, calculated as silica by weight of final pigment, of sodium silicate, added over 20 minutes as a 250 gram/liter aqueous sodium silicate solution (SiO2:Na2O=3.5). While maintaining the temperature at 90° C., the pH of the slurry was slowly decreased to pH=5.0 using 25% by weight aqueous sulfuric acid solution, over a 55 minute period. Following a digestion period of 15 minutes, 2.0% alumina, by weight of final pigment, was added over 15 minutes as a 357 gram/liter aqueous sodium aluminate solution while maintaining the pH of the slurry between a value of 8.0 and 8.5 via the concomitant addition of 25% aqueous sulfuric acid.
The dispersion was allowed to equilibrate at 90° C. for 15 minutes, at which point the pH of the slurry was re-adjusted to 5.8, prior to filtration while hot. The resulting filtrate was washed with an amount of water, which had been preheated to 60° C. and pre-adjusted to a pH of 7.0, equal to the weight of recovered pigment. The washed semi-solid filtrate was subsequently re-dispersed in water with agitation in the presence of 1.0%, by weight based on pigment, of 3-chloropropyltrimethoxysilane according to the present invention. The resulting pigment dispersion was spray dried using an APV Nordic PSD52 Spray Dryer, maintaining a dryer inlet temperature of approximately 280° C., to yield a dry pigment powder. The dry pigment powder was then steam micronized in the presence of 0.35% by weight based on pigment of trimethylol propane, utilizing a steam to pigment weight ratio of 2.5, with a steam injector pressure set at 146 psi and micronizer ring pressure set at 118 psi, completing the finished pigment preparation.
As a comparative example, the same procedure described above was repeated, but in the absence of the addition of the chloropropyltrimethoxysilane. The resulting pigment produced according to the inventive process and the comparative pigment were both evaluated for paint film gloss and tint strength performance in a water-borne coating, according to the recipe and test procedures described in Example 1. Results are provided in Table 3.
The coating composition produced according to the instant invention, comprising a titanium dioxide pigment having deposited thereon an inorganic oxide surface treatment of 3.0% silica and 2.0% alumina, both by weight of the pigment, and an organic surface treatment comprising 1.0% by weight of pigment of chloropropyltrimethoxysilane, further demonstrates improved properties as indicated by the increased gloss and tint strength values for the inventive coating composition versus the comparative example.
Particulate titanium dioxide pigment intermediate obtained from the vapor phase oxidation of titanium tetrachloride and containing 0.6% alumina in its crystalline lattice was dispersed in water in the presence of 0.18% by weight (based on pigment) of sodium hexametaphosphate dispersant, along with a sufficient amount of sodium hydroxide to adjust the pH of the dispersion to a value of 9.5 or greater, to achieve an aqueous dispersion with a solids content of 35% by weight. The resulting titanium dioxide slurry was sand milled, using a zircon sand-to-pigment weight ratio of 4 to 1, until a volume average particle size was achieved wherein more than 90% of the particles were smaller than 0.63 microns, as determined utilizing a Microtrac X100 Particle Size Analyzer. The slurry was heated to 50° C., acidified to a pH of about 5.0 using concentrated sulfuric acid, then treated with 0.25% zirconia, added rapidly as a 200 gram/liter aqueous zirconium orthosulfate solution, over a five minute period. After the addition of the zirconium orthosulfate, the slurry was maintained at 50° C., adjusted to a pH of 8.0 using 20% by weight aqueous sodium hydroxide solution, then treated with 2.8% alumina, added as a 357 gram/liter aqueous sodium aluminate solution over a fifteen minute period. During the addition of the sodium aluminate solution, the pH of the slurry was maintained between a value of 8.0 and 8.5 via the addition of sulfuric acid, prior to an additional 15 minute digestion at 50° C., after the completion of the addition of the sodium aluminate solution. The dispersion was then filtered while hot. The resulting filtrate was washed with an amount of water, which had been preheated to 60° C. and pre-adjusted to a pH of 7.0, equal to the weight of recovered pigment. The washed filtrate was subsequently re-dispersed in water with agitation. A 1.0% aliquot, by weight based on pigment, of chloropropyltrimethoxysilane was added to the resulting titanium dioxide dispersion with mixing, and the resulting pigment dispersion was spray dried using an APV Nordic PSD52 Spray Dryer, maintaining a dryer inlet temperature of approximately 280° C., to yield a dry pigment powder. The dry pigment powder was then steam micronized in the presence of 0.35% by weight based on pigment of trimethylol propane utilizing a steam to pigment weight ratio of five, with a steam injector pressure set at 146 psi and micronizer ring pressure set at 118 psi, completing the finished pigment preparation.
As a comparative example, the same procedure described above was repeated, but in the absence of the addition of the chloropropyltrimethoxysilane. The resulting pigment produced according to the inventive process and the comparative pigment sample were both evaluated in a water-borne coating, according to the recipe and test procedures described in Example 1. Results are provided in Table 4.
The coating composition produced according to the instant invention, comprising a titanium dioxide pigment having deposited thereon an inorganic oxide surface treatment of 0.25% zirconia and 2.8% alumina, both by weight of the pigment, and an organic surface treatment comprising 1.0% by weight of pigment of chloropropyltrimethoxysilane according to the present invention, further demonstrates improved properties as indicated by the increased gloss and tint strength values for the inventive coating composition versus the comparative example.
Particulate titanium dioxide pigment intermediate obtained from the vapor phase oxidation of titanium tetrachloride and containing 0.6% alumina in its crystalline lattice was dispersed in water in the presence of 0.18% by weight (based on pigment) of sodium hexametaphosphate dispersant, along with a sufficient amount of sodium hydroxide to adjust the pH of the dispersion to a value of 9.5 and greater, to achieve an aqueous dispersion with a solids content of 35% by weight. The resulting titanium dioxide slurry was sand milled, using a zircon sand-to-pigment weight ratio of 4 to 1, until a volume average particle size was achieved wherein more than 90% of the particles were smaller than 0.63 microns, as determined utilizing a Microtrac X100 Particle Size Analyzer. The slurry was heated to 50° C., acidified to a pH of about 5.0 using concentrated sulfuric acid, then treated with 0.25% zirconia, added rapidly as a 200 gram/liter aqueous zirconium orthosulfate solution, over a five minute period. After the addition of the zirconium orthosulfate, the slurry was maintained at 50° C., adjusted to a pH of 8.0 using 20% by weight aqueous sodium hydroxide solution, then treated with 2.8% alumina, added as a 357 gram/liter aqueous sodium aluminate solution over a fifteen minute period. During the addition of the sodium aluminate solution, the pH of the slurry was maintained between a value of 8.0 and 8.5 via the addition of sulfuric acid, prior to an additional 15 minute digestion at 50° C., after the completion of the addition of the sodium aluminate solution. The dispersion was then filtered while hot. The resulting filtrate was washed with an amount of water, which had been preheated to 60° C. and pre-adjusted to a pH of 7.0, equal to the weight of recovered pigment. The washed filtrate was subsequently re-dispersed in water with agitation, in the presence of 0.25% by weight based on pigment, of methanesulfonic acid as a fluidizing agent. A 0.65% aliquot, by weight based on pigment, of hexyltrimethoxysilane was added to the resulting titanium dioxide dispersion with mixing, and the resulting pigment dispersion was spray dried using an APV Nordic PSD52 Spray Dryer, maintaining a dryer inlet temperature of approximately 280° C., to yield a dry pigment powder. The dry pigment powder was then steam micronized in the presence of 0.35% by weight based on pigment of trimethylol propane utilizing a steam to pigment weight ratio of five, with a steam injector pressure set at 146 psi and micronizer ring pressure set at 118 psi, completing the finished pigment preparation.
As a comparative example, the same procedure described above was repeated, but in the absence of the addition of the hexyltrimethoxysilane. The resulting pigment produced according to the inventive process and the comparative pigment sample were both evaluated in a water-borne coating, according to the recipe and test procedures described in Example 1. Results are provided in Table 5.
The coating composition produced according to the instant invention, comprising a titanium dioxide pigment having deposited thereon an inorganic oxide surface treatment of 0.25% zirconia and 2.8% alumina, both by weight of the pigment, and an organic surface treatment comprising 0.65% by weight of pigment of hexyltrimethoxysilane, further demonstrates improved properties as indicated by the increased tint strength value for the inventive coating composition versus the comparative example.
Particulate titanium dioxide pigment intermediate obtained from the vapor phase oxidation of titanium tetrachloride and containing 0.6% alumina in its crystalline lattice was dispersed in water in the presence of 0.18% by weight (based on pigment) of sodium hexametaphosphate dispersant, along with a sufficient amount of sodium hydroxide to adjust the pH of the dispersion to a value of 9.5 and greater, to achieve an aqueous dispersion with a solids content of 35% by weight. The resulting titanium dioxide slurry was sand milled, using a zircon sand-to-pigment weight ratio of 4 to 1, until a volume average particle size was achieved wherein more than 90% of the particles were smaller than 0.63 microns, as determined utilizing a Microtrac X100 Particle Size Analyzer. The slurry was heated to 50° C., acidified to a pH of about 5.0 using concentrated sulfuric acid, then treated with 0.25% zirconia, added rapidly as a 200 gram/liter aqueous zirconium orthosulfate solution, over a five minute period. After the addition of the zirconium orthosulfate, the slurry was maintained at 50° C., adjusted to a pH of 8.0 using 20% by weight aqueous sodium hydroxide solution, then treated with 2.8% alumina, added as a 357 gram/liter aqueous sodium aluminate solution over a fifteen minute period. During the addition of the sodium aluminate solution, the pH of the slurry was maintained between a value of 8.0 and 8.5 via the addition of sulfuric acid, prior to an additional 15 minute digestion at 50° C., after the completion of the addition of the sodium aluminate solution. The dispersion was then filtered while hot. The resulting filtrate was washed with an amount of water, which had been preheated to 60° C. and pre-adjusted to a pH of 7.0, equal to the weight of recovered pigment. The washed filtrate was subsequently re-dispersed in water with agitation. A 0.65% aliquot, by weight based on pigment, of hexyltrimethoxysilane was added to the resulting titanium dioxide dispersion with mixing, and the resulting pigment dispersion was spray dried using an APV Nordic PSD52 Spray Dryer, maintaining a dryer inlet temperature of approximately 280° C., to yield a dry pigment powder. The dry pigment powder was then steam micronized in the presence of 0.35% by weight based on pigment of trimethylol propane utilizing a steam to pigment weight ratio of five, with a steam injector pressure set at 146 psi and micronizer ring pressure set at 118 psi, completing the finished pigment preparation.
As a comparative example, the same procedure described above was repeated, but in the absence of the addition of the hexyltrimethoxysilane. The resulting pigment produced according to the inventive process and the comparative pigment sample were both evaluated in a water-borne coating, according to the recipe and test procedures described in Example 1. Results are provided in Table 6.
The coating composition produced according to the instant invention, comprising a titanium dioxide pigment having deposited thereon an inorganic oxide surface treatment of 0.25% zirconia and 2.8% alumina, both by weight of the pigment, and an organic surface treatment comprising 1.0% by weight of pigment of hexyltrimethoxysilane, still further demonstrates improved properties as indicated by the increased gloss value for the inventive coating composition versus the comparative example.
