Aluminum phosphate or polyphosphate particles for use as pigments in paints and method of making same

Abstract

An aluminum phosphate or polyphosphate-based pigment product is made by a process comprising contacting phosphoric acid with aluminum sulfate and an alkaline solution to produce an aluminum phosphate based product; and optionally calcining the aluminum phosphate based product at an elevated temperature, wherein the process is substantially free of an organic acid. The aluminum phosphate or polyphosphate-based pigment is amorphous. The amorphous aluminum phosphate or polyphosphate characterized by a bulk density of less than 2.30 grams per cubic centimeter and a phosphorus to aluminum mole ratio of greater than 0.8. The composition is useful in paints and as a substitute for titanium dioxide

What is claimed is: 
     
         1 . A method of making amorphous aluminum phosphate comprising the steps of:
 combining phosphoric acid with aluminum sulfate and sodium hydroxide to react and form a suspension comprising an amorphous aluminum phosphate precipitate;   filtering the suspension to isolate the precipitate; and   drying the precipitate at a temperature less than about 130° C.   
     
     
         2 . The method as recited in  claim 1  wherein the amorphous aluminum phosphate has a bulk density that is less than about 2.1 g/cc. 
     
     
         3 . The method as recited in  claim 1  where the amorphous aluminum phosphate has an average individual particle radius size from about 5 to 80 nanometers. 
     
     
         4 . The method as recited in  claim 1  wherein the amorphous aluminum phosphate consists of sodium aluminum phosphate. 
     
     
         5 . The method as recited in  claim 1  wherein the dried precipitate is substantially free of open pores. 
     
     
         6 . The method as recited in  claim 1  wherein dried precipitate comprises particles having closed voids. 
     
     
         7 . The method as recited in  claim 1  wherein the amorphous aluminum phosphate has a bulk density that is less than about 1.99 g/cc. 
     
     
         8 . The method as recited in  claim 1  wherein the dried precipitate has a macropore volume that is substantially less than 0.1 cc/gram. 
     
     
         9 . The method as recited in  claim 1  wherein during the step of combining, the phosphoric acid, aluminum sulfate, and sodium hydroxide are combined simultaneously. 
     
     
         10 . The method as recited in  claim 1  wherein after the step of combining, adding further sodium hydroxide to the mixture. 
     
     
         11 . The method as recited in  claim 1  further comprising the step of washing the precipitate after the filtering step. 
     
     
         12 . The method as recited in  claim 1  further comprising before the step of drying, adding a dispersant to the precipitate. 
     
     
         13 . The method as recited in  claim 12  wherein the dispersant is sodium tetrapyrophosphate. 
     
     
         14 . A chemical composition comprising the amorphous aluminum phosphate made according to  claim 1  combined and uniformly dispersed within a binding polymer. 
     
     
         15 . The chemical composition as recited in  claim 14  wherein when the chemical composition is dried to form a film has a structure characterized by enmeshed binding polymer and amorphous aluminum phosphate. 
     
     
         16 . A method of making amorphous aluminum phosphate comprising the steps of:
 combining phosphoric acid with aluminum sulfate and sodium hydroxide to form a mixture;   reacting the mixture to form a suspension comprising amorphous aluminum phosphate precipitate;   isolating the precipitate from the suspension;   washing the isolated precipitate; and   drying the precipitate at a temperature less than about 130° C.   
     
     
         17 . The method as recited in  claim 16  wherein the amorphous aluminum phosphate consists of sodium aluminum phosphate. 
     
     
         18 . The method as recited in  claim 16  wherein the amorphous aluminum phosphate has a bulk density that is less than about 2.1 g/cc. 
     
     
         19 . The method as recited in  claim 16  wherein the dried precipitate comprises particles having closed voids. 
     
     
         20 . The method as recited in  claim 16  wherein after the step of drying, the amorphous aluminum phosphate has a macropore volume of substantially less than 0.1 cc/gram. 
     
     
         21 . The method as recited in  claim 16  comprising combining the phosphoric acid, aluminum sulfate, and sodium hydroxide simultaneously. 
     
     
         22 . The method as recited in  claim 16  further comprising before the step of drying, adding a dispersant to the precipitate. 
     
     
         23 . The method as recited in  claim 22  wherein the dispersant is sodium tetrapyrophosphate. 
     
     
         24 . A chemical composition comprising the amorphous aluminum phosphate made according to  claim 16 , wherein the amorphous aluminum phosphate is further combined with a binding polymer to form the chemical composition. 
     
     
         25 . The chemical composition as recited in  claim 24 , wherein the amorphous aluminum phosphate has a bulk density that is less than about 2.1 g/cc, and wherein the chemical composition when dried to form a film has a structure characterized by interpenetrating phases of binding polymer enmeshed with amorphous aluminum phosphate. 
     
     
         26 . A method of making a chemical composition comprising amorphous aluminum phosphate, the method comprising the steps of:
 combining phosphoric acid with aluminum sulfate and sodium hydroxide to form a mixture;   reacting the mixture to form a suspension comprising an amorphous aluminum phosphate precipitate;   filtrating and washing the suspension to isolate the precipitate into a cake;   forming a dispersion of the washed cake;   drying the cake to form amorphous aluminum phosphate particles; and   adding the amorphous aluminum phosphate to a binding polymer to form the chemical composition.   
     
     
         27 . The method as recited in  claim 25  wherein the amorphous aluminum phosphate has a bulk density that is less than about 2.1 g/cc. 
     
     
         28 . The method as recited in  claim 25  wherein during the step of forming a dispersion, a phosphate-based dispersant is used. 
     
     
         29 . The method as recited in  claim 25  wherein when in powder form the amorphous aluminum phosphate has an average individual particle radius size of between 5 and 80 nanometers. 
     
     
         30 . The method as recited in  claim 25  wherein after the step of combining, adding further sodium hydroxide to the mixture.