Patent GB-898901-A (GB)
Title: Powdered coating compositions and the method for their application
IPC: C09D5/46
Filed: 1958-07-24
Abstract: A coating composition in the form of a powder sufficiently free-flowing to be applied by a fusion coating process is made by intensively mixing particles of a fusible polymeric film-forming component with a plasticizer, the film-forming component comprising a cellulose derivative and the mixing being effected at an elevated temperature until a fused plastic mass is obtained, and then pulverizing the mass to a particle size within the range 25-600 microns.  Heat may be applied while the intensive mixing is taking place.  Intensive mixing is defined as mixing on a Banbury mill or two-roll mill or device effecting a similar mixing effect, viz. particle shearing and shear-heating, whereby the particulate material is reduced to a fused plastic mass.  The fusion coating index of the mixture may be within the range 300 DEG -700 DEG F., the fusion coating index being the temperature in  DEG F. to which an aluminium rod of length 2 1/2 inches and diameter 1/2 inch must be preheated at the time of initial contact with the powdered coating composition to obtain complete fusion of the composition into a continuous film coating the surface of the rod when applied by immersion for 5 secs. in a uniformly fluidized bed of the powdered composition, the composition and the fluidizing gas being at ambient temperature and the fluidization being such as to increase the depth of the previously unfluidized bed by no more than 30%, there being no heating after immersion. The cellulose derivative may constitute at least 90% by weight of the film-forming component and the plasticizer may be present in an amount at least 10% by weight of the cellulose derivative.  A fusion coating process is defined as a process in which the coating composition is applied to the surface to be coated in the form of finely-divided, solid particles which are either melted as they approach the surface to be coated or are melted only after they come into contact with a pre-heated surface and are deposited thereon.  The composition may be a mixture of individual particles of colloidal size, and the film-forming component may constitute at least 30% of the total weight of the composition.  The cellulose derivative may be selected from the group consisting of cellulose esters of carboxylic acids and cellulose ethers, and may be an aliphatic cellulose ether, e.g. methyl or ethyl cellulose, or cellulose acetate, propionate, butyrate, aceto-propionate, or acetobutyrate, or a cellulose ester of a longer-chain carboxylic acid, e.g. lauric or stearic acid.  Mixtures of these esters may be used.  Specified plasticizers include:- (a) for cellulose acetate:- acetyl triethyl citrate, camphor, diethyl-and diallyl phthalates, p-toluene sulphonamide, triethyl citrate, triphenyl phosphate, and tripropionin, (b) for ethyl cellulose:- triphenyl-, tricresyl-, cresyl diphenyl- and tri(2-ethyl-hexyl) phosphates, diethyl, dibutyl and dioctyl phthalates, butyl oleate, the methyl ester of hydrogenated resin, triethylene glycol di(2-ethyl-hexoate), triethylene glycol dipelargonate, dibutyl lauramide, p-toluene sulphonamide, refined mineral oil, linseed and tung oils, cetyl alcohol, hydroabietyl alcohol, benzene hexachloride, camphor, polymethylstyrene and chlorinated naphthalene.  Other plasticizers are specified for use with other cellulose derivatives.  The composition may also include a minor proportion of a resin and a finely-divided solid infusible at 700 DEG F., e.g. a pigment. Pigments specified include zinc oxide, zinc sulphide, titanium dioxide, lithopone, chromic oxide, iron oxide, powdered or flaked aluminium, zinc and copper.  Specified fillers include calcium carbonate, magnesium oxide, asbestos, barium sulphate, aluminium oxide, slate and silicon carbide.  Anti-oxidants include diamylphenol, 2-6 ditert.-butyl-p-cresol, octylphenol, p-tert.-amylphenol (especially for use with ethyl cellulose and cellulose acetate), and magnesium carbonate (for use with cellulose aceto-butyrate).  Light-stabilizers include 2-4 dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone and phenyl salicylate.  The constituents may be mixed on the two-roll mill or Banbury mixer at 250 DEG 425 DEG F. and the plastic mass so formed may be reduced to a free-flowing powder of average particle size 25-600 microns by cooling with liquid nitrogen, followed by pulverization in a hammer mill.  Articles may be coated by pre-heating them to a temperature above the fusion temperature of the coating composition and at least 300 DEG F. and, while at that temperature, depositing a uniform layer of the free-flowing powdered coating composition on the surface of the article, and permitting the composition to fuse to a continuous coating thereon.  Preferably the article is pre-heated to 300 DEG -1000 DEG F. and the composition sifted on to the surface of the article, excess being later removed. Alternatively, the article, pre-heated to 300 DEG -1000 DEG F., especially 400 DEG -800 DEG F., may be immersed in a body of the coating composition, e.g. in a fluidized bed, removed therefrom and the excess composition removed.  The composition may also be applied by blowing it on to the surface of the pre-heated article by the use of a stream of compressed gas.  Metal, wood, glass and ceramic articles may be coated.  Specification 759,214 is referred to.ALSO:A coating composition in the form of a powder sufficiently free-flowing to be applied by a fusion coating process is made by intensively mixing particles of a fusible polymeric film-forming component with a plasticizer, the film-forming component comprising a cellulose derivative and the mixing being effected at an elevated temperature until a fused plastic mass is obtained, and then pulverizing the mass to a particle size within the range 25-600 microns.  Heat may be applied while the intensive mixing is taking place.  Intensive mixing is defined as mixing on a Banbury mill or two-roll mill or device effecting a similar mixing effect, viz. particle shearing and shearheating, whereby the particulate material is reduced to a fused plastic mass.  The fusion coating index of the mixture may be within the range 300 DEG -700 DEG F., the fusion coating index being the temperature in  DEG F. to which an aluminium rod of length 2 1/2 inches and diameter 1/2 inch must be preheated at the time of initial contact with the powdered coating composition to obtain complete fusion of the composition into a continuous film coating the surface of the rod when applied by immersion for 5 secs. in a uniformly fluidized bed of the powdered composition, the composition and the fluidizing gas being at ambient temperature and the fluidization being such as to increase the depth of the previously unfluidized bed by no more than 30%, there being no heating after immersion. The cellulose derivative may constitute at least 90% by weight of the film-forming component and the plasticizer may be present in an amount at least 10% by weight of the cellulose derivative.  A fusion coating process is defined as a process in which the coating composition is applied to the surface to be coated in the form of finely-divided, solid particles which are either melted as they approach the surface to be coated or are melted only after they come into contact with a pre-heated surface and are deposited thereon. The composition may be a mixture of individual particles of colloidal size, and the film-forming component may constitute at least 30% of the total weight of the composition.  The cellulose derivative may be selected from the group consisting of cellulose esters of carboxylic acids and cellulose ethers, and may be an aliphatic cellulose ether, e.g. methyl or ethyl cellulose, or cellulose acetate, propionate, butyrate, aceto-propionate, or aceto-butyrate, or a cellulose ester of a longer-chain carboxylic acid, e.g. lauric or stearic acid. Mixtures of these esters may be used.  Specified plasticizers include:- (a) for cellulose acetate:- acetyl triethyl citrate, camphor, diethyl- and diallyl phthalates, p-toluene sulphonamide, triethyl citrate, triphenyl phosphate, and tripropionin, (b) for ethyl cellulose:- triphenyl-, tricresyl-, cresyl diphenyl- and tri(2-ethyl-hexyl) phosphates, diethyl, dibutyl and dioctyl phthalates, butyl oleate, the methyl ester of hydrogenated resin, triethylene glycol di(2-ethyl-hexoate), triethylene glycol dipelargonate, dibutyl lauramide, p-toluene sulphonamide, refined mineral oil, linseed and tung oils, cetyl alcohol, hydroabietyl alcohol, benzene hexachloride, camphor, polymethylstyrene and chlorinated naphthalene.  Other plasticizers are specified for use with other cellulose derivatives.  The composition may also include a minor proportion of a resin and a finely-divided solid infusible at 700 DEG F., e.g. a pigment.  Pigments specified include zinc oxide, zinc sulphide, titanium dioxide, lithopone, chromic oxide, iron oxide, powdered or flaked aluminium, zinc and copper.  Specified fillers include calcium carbonate, magnesium oxide, asbestos, barium sulphate, aluminium oxide, slate and silicon carbide.  Anti-oxidants include diamylphenol, 2-6 ditert.-butyl-p-cresol, octylphenol, p-tert.-amylphenol, (especially for use with ethyl cellulose and cellulose acetate) and magnesium carbonate (for use with cellulose aceto-butyrate).  Light-stabilizers include 2-4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone and phenyl salicylate.  The constituents may be mixed on the two-roll mill or Banbury mixer at 250 DEG -425 DEG F. and the plastic mass so formed may be reduced to a free-flowing powder of average particle size 25-600 microns by cooling with liquid nitrogen, followed by pulverization in a hammer mill.  For details of the method of applying the coating composition, see Group III.  Specification 759,214 is referred to.