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Title: Prolonging the stability of coating baths
Claims: I claim: 1. In the method wherein an organic resinous coating is applied to a metallic surface by immersing said surface in an acidic aqueous coating composition containing an oxidizing agent and dispersed solid particles of an organic coating-forming resin dispersed in said composition by a dispersing agent associated therewith, said dispersing agent and resin being present in a predetermined proportion, and wherein metal ions are formed by the dissolution of said metallic surface through the chemical action of said coating composition, and wherein said metal ions are oxidized to a form which renders said dispersed resin unstable in the region of said surface and wherein said unstabilized resin deposits and forms on said surface a resinous coating, the thickness or amount of which increases during at least a portion of the time said surface is immersed in said composition, and wherein said resinous coated surface is withdrawn from said composition and is heated to fuse the resin, and wherein additional metallic surfaces are immersed in said composition and are coated as set forth, and wherein ingredients of said composition are consumed as said surfaces are coated, and wherein additional amounts of said ingredients are added to said composition to replenish the concentrations thereof, and wherein as said metallic surfaces are coated as set forth, there is formed in said composition additional excess oxidized metal ions which tend to cause said dispersed resin to become unstable, not only in the region of said metallic surface, but also throughout the other portions of said coating compositions, as characterized by flocculation, coagulation or gelation of the dispersed resin particles, thereby rendering said composition inoperative for coating, the improvement comprising adding dispersing agent and resin to said composition in amounts to replenish these ingredients and in a proportion such that the proportion of said added dispersing agent to said added resin is greater than said predetermined proportion and sufficient to maintain the stability of said dispersed resin in said other portions of said composition thereby prolonging the operability of said coating composition. 2. The method according to claim 1 wherein said excess oxidized metal ions are removed from said composition. 3. In the method wherein an organic resinous coating is applied to a metallic surface by immersing said surface in an aqueous coating composition comprising: i. hydrogen ion in an amount sufficient to make the composition acidic; ii. fluoride ion; iii. an oxidizing agent selected from the class consisting of hydrogen peroxide and dichromate; and iiii. solid particles of resin dispersed in said composition by a dispersing agent associated therewith, said dispersing agent and resin being present in a predetermined proportion; and wherein said ingredients are present in amounts such that said dispersed resin is rendered unstable in the region of said surface and wherein said unstabilized resin deposits on said metallic surface a resinous coating, the thickness of which increases during at least a portion of the time said surface is immersed in said composition, said coating being initially adherent to said surface, and wherein metal ions are dissolved from said surface by the chemical action of said coating composition, and wherein additional metallic surfaces are immersed in said composition and are coated as set forth, and wherein ingredients of said composition are consumed as said surfaces are coated, and wherein additional amounts of said ingredients are added to said composition to replenish the concentrations thereof, and wherein as additional metallic surfaces are immersed in said composition and are coated as set forth, said dispersed resin tends to become unstable, not only in the region of said metallic surfaces, but also in other portions of said coating composition, as characterized by flocculation, coagulation or gelation of the dispersed resin particles, thereby rendering said composition inoperative for coating, the improvement comprising maintaining the surface tension of said aqueous composition at a value at which said resin is maintained in its dispersed state, except in the region of said metallic surface, by adding to said composition dispersing agent and resin in amounts to replenish these ingredients and in a proportion such that the proportion of said added dispersing agent to said added resin is greater than said predetermined proportion and sufficient to maintain the stability of said dispersed resin in said other portions of said composition thereby prolonging the operability of said coating composition. 4. The method according to claim 3 including removing metal ions which are dissolved from said surfaces from said composition. 5. The method according to claim 1 wherein said composition has a surface tension within the range of about 30 to about 40 dynes/cm and wherein said surface tension is maintained within said range by adding to said composition said dispersing agent. 6. The method according to claim 5 wherein said surfaces are ferriferous surfaces and wherein said metal ions are iron ions. 7. The method according to claim 6 wherein said composition tends to become unstable as the surface tension of said composition rises to about 40 to about 50 dynes/cm and as said iron ions in said composition build up to a concentration of about 1 to about 3 g/l or higher, and wherein said surface tension is maintained below about 40 dynes/cm by the addition of said dispersing agent. 8. The method according to claim 3 wherein said composition has a surface tension within the range of about 30 to about 40 dynes/cm and wherein said surface tension is maintained within said range by adding to said composition said dispersing agent. 9. The method according to claim 8 wherein said surfaces are ferriferous surfaces and wherein said metal ions are iron ions. 10. The method according to claim 9 wherein said composition tends to become unstable as the surface tension of said composition rises to about 40 to about 50 dynes/cm and as said iron ions in said composition build up to a concentration of about 1 to about 3 g/l or higher, and wherein said surface tension is maintained below about 40 dynes/cm by the addition of said dispersing agent. 11. The method according to claim 1 wherein said composition contains: i. about 5 to about 550 g/l of a polymeric coating-forming resin dispersed in the composition, the source of the resin being a latex thereof; ii. about 0.4 to about 5 g/l of fluoride ion; iii. hydrogen peroxide in an amount sufficient to provide from about 0.01 to about 0.2 of oxidizing equivalent per liter of composition; and iiii. hydrogen ion in an amount sufficient to impart a pH of about 1.6 to about 3.8 to the composition. 12. The method according to claim 11 wherein said surfaces are ferriferous surfaces and wherein said metal ions are iron ions. 13. The method according to claim 12 wherein said composition tends to become unstable as the surface tension of said composition rises to about 40 to about 50 dynes/cm and as said iron ions in said composition build up to a concentration of about 1 to about 3 g/l or higher, and wherein said surface tension is maintained below about 40 dynes/cm by the addition of said dispersing agent. 14. The method according to claim 13 wherein said excess oxidized iron ions are removed from said composition. 15. The method according to claim 14 wherein said resin is styrene-butadiene copolymer and wherein the amount of said oxidized iron ions removed from said composition is such that the amount thereof is maintained below about 3 g/l. 16. The method according to claim 15 wherein the amount of said oxidized iron ions is maintained below about 1.5 g/l. 17. The method according to claim 14 wherein said excess oxidized iron ions are removed from said composition by adding thereto an alkaline earth metal hydroxide or an alkaline earth metal oxide or an alkali metal hydroxide to precipitate them and wherein the resulting precipitate is separated from said composition. 18. The method according to claim 17 wherein said excess oxidized iron ions are precipitated by adding to said composition calcium hydroxide. 19. In the method wherein an organic resinous coating is applied to a metallic surface by immersing said surface in an acidic aqueous coating composition containing an oxidizing agent and dispersed solid particles of an organic coating-forming resin dispersed in said composition by a dispersing agent associated therewith, said dispersing agent and resin being present in a predetermined proportion, and wherein said ingredients are present in amounts such that said dispersed resin is rendered unstable in the region of said surface and wherein said unstabilized resin deposits on said metallic surface a resinous coating, the thickness of which increases during at least a portion of the time said surface is immersed in said composition, and wherein metal ions are dissolved from said surface by the chemical action of said coating composition, and wherein additional metallic surfaces are immersed in said composition and are coated as set forth, and wherein ingredients of said composition are consumed as said surfaces are coated, and wherein additional amounts of said ingredients are added to said composition to replenish the concentrations thereof, and wherein as additional metallic surfaces are immersed in said composition and are coated as set forth, said dispersed resin tends to become unstable, not only in the region of said metallic surface, but also in other portions of said coating composition, as characterized by flocculation, coagulation or gelation of the dispersed resin particles, thereby rendering said composition inoperative for coating, the improvement comprising adding dispersing agent and resin to said composition in amounts to replenish these ingredients and in a proportion such that the proportion of said added dispersing agent to said added resin is greater than said predetermined proportion and sufficient to maintain the stability of said dispersed resin in said other portions of said composition thereby prolonging the operability of said coating composition. 20. The method according to claim 19 including removing from said composition metal ions dissolved from surface. 21. The method according to claim 19 wherein said surfaces are ferriferous surfaces. 22. The method according to claim 20 wherein said surfaces are ferriferous surfaces and wherein iron ions are removed from said composition. 23. The method according to claim 1 wherein said surfaces are ferriferous surfaces. 24. The method according to claim 23 wherein said excess oxidized metal ions are ferric ions and including removing ferric ions from said composition. 25. The method according to claim 3 wherein said surfaces are ferriferous surfaces. 26. The method according to claim 25 wherein said metal ions are iron ions and including removing said iron ions from said composition. Other info: Inventors: Hall, Wilbur S. (Plymouth Meeting, PA, US) Application Number: 365699 Filing Date: 1973-05-31 Publication_date: 1976-02-03 Assignee: Amchem Products, Inc. (Ambler, PA) Primary Class(es): 427/375 427/309, 427/345, 427/435 Other Classes: US Patent Ref:
Other Refs:
Primary Examiner: Gwinnell, Harry J. Assistant Examiner: Attorney: Synnestvedt & Lechner |
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