Abstract:
A method is disclosed for removing smearing material or filth deposits from a coated surface by means of spraying an aqueous dispersion to form a gel-like film on the surface. The aqueous dispersion comprises a selected amount of highly absorbent and/or water-soluble polymers dispersed in water. The gel-like film is washed down with pressured water with smearing particulate material entrained therewith.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a method of cleaning coated surfaces of various substrates such as of automobiles, rail-road vehicles, aircrafts and the like, more particularly such a cleaning method which is capable of removing objectionable inorganic particulate materials firmly deposited on substrates covered with ornamental or protective coatings. 
     2. Prior Art 
     Coated surfaces of for example an automobile are susceptible to smear by deposits of incomplete combustion material from the exhaust pipe, dirt on the road, soot floating in the air, fine coal tar or asphalt granules flying off the pavement and other foreign matters. Such deposits would be often tenaciously stuck in place over a few days to leave a smear or stain such that can hardly be removed by simple washing with water. Most typical means for removing such smear was to apply some surfactant-containing alkaline cleanser and rub the smeared surfaces by hand or tool like a car washer, followed by washing down with water. Thus, smear removal was essentially relied upon &#34;rubbing&#34;, less upon the efficacy of jet-sprayed water or cleaning liquor having a dissolving or emulsifying ability, as such abilities would not work effectively with dirt-origin inorganic particulate substances. Smear deposits were believed to be attributable to static or intermolecular force (van der Waals force). Whatever the cause might be, experience has shown that smear on coated surfaces could not be got rid of simply by blasting water or cleaner agent. Again, &#34;rubbing&#34; was considered essential for complete cleaning of smear or stain on coating layers, whether it be tediously by hand or a scratch-risking machine. 
     Japanese Laid-Open Patent Publication No. 64-90851 discloses applying over smeared surfaces an alkaline cleaning liquor having a pH of 10 or above and containing a surface-active agent, and immediately blasting the surfaces with a high jet (above 30 kg/cm 2  discharge pressure) of water dispersed with less than 2 Mohs particles or a surfactant solution. 
     Japanese Laid-Open Patent Publication No. 2-114040 teaches a blasting method in which water dispersed with 1-30 percent by weight of particulate material about 1 Mohs and about 10-30 microns in particle size is blasted at 30 kg/cm 2  over stained coated surfaces. 
     Neither of the above prior methods is satisfactory in that particulate material, should this even be soft, when blasted will fiercely impinge upon and scratch the coated surface layer. 
     SUMMARY OF THE INVENTION 
     With the foregoing drawbacks of the prior art in view, the present invention seeks to provide a method of removing smear or stain from a coated surface solely by means of coating or spraying a selected cleaning agent without resort to conventional rubbing or blasting with particulate material. 
     More specifically, the invention provides an improved method which comprises forming a gel-like film over a smeared coated surface, the film being comprised of an aqueous dispersion containing 0.01-10 parts by weight of a highly absorbent polymer and/or a water-soluble polymer per 1000 parts by weight of water, and subsequently washing down the film together with smearing material deposited on the surface with a flow of water sprayed under a pressure of above 5 kg/cm 2 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     It has now been found that an aqueous dispersion containing a highly absorbent or water-soluble polymer contemplated under the invention forms a gel-like film layer such that can absorb smearing material, typically inorganic particles, with a greater affinity than that with which such material is absorbed onto a coated surface and consequently can be washed down entraining the material. Importantly, the dispersion should have a viscosity such that will enable the same to form and maintain a gel-like film even on vertically disposed substrate surfaces to be cleaned and such that will permit the use of a spray nozzle with which to conveniently apply the dispersion to polygonal or otherwise complicated surface configurations. 
     The term highly absorbent polymer as used herein designates cross-linked products of an alkaline metal polyacrylate (typically sodium salts), starch-acrylic acid graft copolymers, hydrolyzates of starch-acrylonitrile graft copolymers, saponification products of vinylacetate-acrylic acid copolymers, acrylamide-acrylate copolymers, saponification products of vinylacetate-maleic anhydride copolymers, cross-linked products of polyethylene oxide, and polysaccharide-acrylic acid graft copolymers. 
     The term water-soluble polymer as used herein includes those which have a weight average molecular weight of above 10,000 such as an alkaline metal alginate, methylcellulose, carboxy-methylcellulose, alkaline metal polyacrylate (typically sodium salts), and polyethylene oxide. 
     The highly absorbent polymer and/or water-soluble polymer may be dispersed in water suitably by means of a high-shear mixer. 
     The inventive aqueous dispersion may be added, if desired, with nonionic, anionic, cationic as well as amphoteric cleaning surfactants. In the case of nonionic surfactants, these should have an HLB value preferably in the range of 10-15. There may also be used such additives as glycol ether solvents, metallic ion hindering agents, and the like. 
     The invention will be further described by way of the following examples. 
     PREPARATION OF TEST PANEL 
     Steel plate substrates measuring 30 cm×30 cm were coated with a black aminoalkyd resin coating and completely dried, followed by degreasing with kerosine and washing with a neutral cleanser. The thus coated substrates, after being dried, were coated uniformly with a silt aqueous dispersion and then dried at 50° C. over 24 hours thereby providing Test Panel X. 
     Another set of the above coated substrates were coated with a car-wax and polished with a towel, followed by spraying the same silt dispersion. This spraying if only once would leave just sparsely distributed silt because of the presence of wax on the substrate. Therefore, the dispersion was sprayed repeatedly with alternate wind blowing until the silt was deposited uniformly over the entire coated substrate surface. Thereafter, the substrates were dried at 50° C. over 24 hours to provide Test Panel Y. 
     PREPARATION OF CLEANING LIQUOR 
     A set of cleaning liquors were prepared from the following formulations. 
     
         ______________________________________Cleaning Liquor ADrinking water           1,000  ccPartially cross-linked product                    4      gof sodium polyacrylateCleaning Liquor BDrinking water           1,000  ccSodium alginate          8      gCleaning Liquor CDrinking water           1,000  ccPartially cross-linked product                    4      gof sodium polyacrylateHepta-sodium salt of diethylene triamine                    6      gpenta(methylene phosphonic acidDipropyleneglycol monomethyl ether                    12     gPolyoxyethylene tridecyl ether                    6      g(HLB = 10.5)Cleaning Liquor DDrinking water           1,000  ccSodium hexametaphosphate 8      gSodium dioctyl sulfosuccinate                    2      gPolyoxyethylene nonylphenyl ether                    12     g(HLB = 10.5)Diethyleneglycol monomethyl ether                    10     gCleaning Liquor EDrinking water           1,000  ccPolyoxyethylene nonylphenyl ether                    12     gSodium polyoxyethylene tridecyl                    6      gether sulfateDioctylsulfo succinic acid ester                    2      gNa saltCleaning Liquor FDrinking water           1,000  ccSodium carboxylmethyl cellulose                    4      g(300,000 molecular weight)Polyoxyethylene nonylphenyl ether                    10     cc(HLB = 12.9)Polyoxyethylene nonylphenyl ether                    5      cc(HLB = 10.0)Hydroxyethylidene trisodium                    2      gdiphosphonateCleaning Liquor GDrinking water           1,000  ccPartially cross-linked product                    4      gof potassium polyacrylatePolyoxyethylene nonylphenyl ether                    10     cc(HLB = 12.9)Polyoxyethylene nonylphenyl ether                    5      cc(HLB = 10.0)Tri-sodium salt of 1-hydroxyethylidene-                    2      g1,1-diphosphonic acidCleaning Liquor HDrinking water           1,000  ccCross-linked product of  4      gstarch-acrylate graft copolymerPolyoxyethylene nonylphenyl ether                    10     cc(HLB = 12.9)Polyoxyethylene nonylphenyl ether                    5      cc(HLB = 10.0)Tri-sodium salt of 1-hydroxyethylidene-                    2      g1,1-diphosphonic acid______________________________________ 
    
     EXAMPLE 1 
     Eight pieces of Test Panel X were each sprayed with Cleaning Liquors A-H, respectively and then after a lapse of 5 minutes, washed down with water pressured at 30 kg/cm 2  . After being dried, each Panel was visually observed for the extent to which the silt had been removed from its coated surface, with the results shown in Table 1. 
     
                       TABLE 1______________________________________Cleaning Liquor     A      B      C    D    E   F    G    H______________________________________Silt Removed     O      O      O    X    X   O    O    O______________________________________ Note: O indicates complete removal of silt. X indicates the presence of silt residues. 
    
     EXAMPLE 2 
     Six pieces of Test Panel Y were each sprayed with Cleaning Liquors C-H. After a lapse of 5 minutes, each Panel was washed down with a spray of water pressured at 30 kg/cm 2  and then dried. Visual test was made for silt removal with the results shown in Table 2. 
     
                       TABLE 2______________________________________Cleaning Liquor        C     D        E   F     G   H______________________________________Silt Removed O     X        X   O     O   O______________________________________ 
    
     EXAMPLE 3 
     Another six pieces of Test Panel Y were each sprayed with Cleaning Liquors C-H, respectively, at a jet pressure of 30 kg/cm 2 , followed by washing down the liquors with a spray of water pressured at 30 kg/cm 2 . After being dried, each Panel was visually observed for silt removal with the results shown in Table 3. 
     
                       TABLE 3______________________________________Cleaning Liquor        C     D        E   F     G   H______________________________________Silt Removed O     X        X   O     O   O______________________________________