Method of manufacturing a sag-resistant bonded particulate matter

Abstract

A method for the production of improved bonded particulate articles, and the articles so produced, are disclosed. Specifically, the manufacture of particulate articles having a reduced tendency to undergo humidity-induced sag is disclosed. These articles have utility in such application as ceiling tiles.

We claim: 
     
       1. A method of preventing or minimizing humidity-induced sag in bonded particulate substrates comprising applying to at least one side of said particulate substrate a coating composition comprising an aqueous dispersion of a mixture of an effective amount of a glyoxal resin or derivative thereof and an effective amount of a starch compound .Iadd.which contains less than about 50% by weight of insolubles.Iaddend., and an effective amount of a filler material, and curing said coating composition. 
     
     
       2. The method of claim 1 wherein said glyoxal resin of said coating composition is selected from the group consisting of dimethylol dihydroxy ethylene urea, partially akylated dimethylol dihydroxy ethylene urea alkylated dimethylol dihydroxy ethylene urea and tetramethylol glycoluril. 
     
     
       3. The method of claim 2 wherein the glyoxal resin is dimethylol dihydroxy ethylene urea. 
     
     
       4. The method of claim 1 wherein said substrate comprises processed fiberous material. 
     
     
       5. The method of claim 1 wherein said starch component is selected from the group consisting of starches derived from corn, potatoes, waxy maize, sorgum and wheat. 
     
     
       6. The method of claim 1 wherein said starch component comprises a high amylopectin starch. .[.7. The method of claim 1 wherein said starch components contains less than about 50% weight percent of insolubles..]. 
     
     
           The method of claim 1 wherein the filler comprises an alumina silicate. 
     
     
        . The method of claim 1 wherein the filler is selected from the group consisting of alkali metal carbonates, kaolin, bentonite, clays, silica, 
     
     
        mineral wool and mixtures thereof. 10. The method of claim 1 wherein the 
     
     
        filler is silica. 11. The method of claim 1 wherein the glyoxal resin and said starch component are present in amounts ranging from about 1:3 to 
     
     
        about 2:1 by weight. 12. The method of claim 11 wherein the glyoxal resin and said starch component are present in amounts ranging from about 2:3 to 
     
     
        about 3:2 by weight. 13. The method of claim 1 wherein the coating composition further comprises an acid catalyst which is present in amounts ranging from about 1 to about 50 weight percent based upon the weight of 
     
     
        the glyoxal resin and said starch compound. 14. The method of claim 13 wherein the catalyst is selected from the group consisting of zinc nitrate, zirconium ammonium carbonate, ammonium sulfate and mixtures 
     
     
        thereof. 15. The method of claim 1 wherein the coating composition is applied to said substrate in quantities such that subsequent to its curing it will form a layer upon said substrate having a weight of about 1 to 
     
     
        about 100 grams/ft 2 . 16. The method of claim 15 wherein the coating composition is applied to said substrate in quantities such that subsequent to its curing it will form a layer upon said substrate having a 
     
     
        weight of about 5 to about 40 grams/ft 2 . 17. The method of claim 1 wherein curing of said coating composition is conducted at temperature ranging from about 300° F. to about 700° F. for a period of 
     
     
        between about 0.5 to about 4 minutes. 18. A method of preventing or minimizing humidity-induced sag in bonded particulate substrates a coating composition comprising an aqueous dispersion of an effective amount of mixture of a resin selected from the group of dimethylol dihydroxy ethylene urea, tetramethylol glycoluril and mixtures thereof, an effective amount of a starch .Iadd.which contains less than about 50% by weight of insolubles, .Iaddend.and an effective amount a filler selected from the group consisting of kaolin, bentenite, clays, alkali metal carbonates and mixtures thereof, said dimethylol dihydroxy ethylene urea and starch being present in about a 1:1 weight % ratio and said composition being applied in quantities sufficient to result, upon curing, in a layer upon said substrate having a weight of about 5 to about 40 grams/ft 2  of substrate, and curing said composition at a temperature of between about 250° F. to about 375° F. for a time sufficient to result in 
     
     
        curing of said composition. 19. A bonded particulate article resistant to humidity-induced sag produced in accordance with the method of claim 1. 
     
     
            A bonded particulate article resistant to humidity-induced sag produced in accordance with the method of claim 18.