COATING SYSTEM FOR HEATED FIXING SURFACE

Abstract: A heated fixing surface for reprography, such as a fixing roller, is coated with a multilayer coating system wherein a first coat has fluoropolymers, polyamide-imides stainless steel flake and particulate calcined aluminum oxide and a second coat has fluoropolymers, aluminum flake and particulate calcined aluminum oxide.

Description: T I T L E COATING SYSTEM FOR HEATED FIXING SURFACE BACKGROUND OF THE INVENTION This invention relates to non-stick coating systems for a fixing surface such as a fuser roll in reprographic apparatus. More particularly, it relates to multi-layer systems for such applications having good durability and thermal conductivity. Various types of reprographic equipment include heated surfaces such as rollers or belts to fuse or fix the images applied elsewhere in the equipment, whether by laser beam, magnetic or other means. To prevent static electricity buildup, some coatings are made electrically conductive. Durability is necessary for handling large numbers of sheets of paper. Thermal conductivity is also important to permit higher throughput of pages in a given time, improved print quality and lower power consumption caused by lower stand-by temperatures and shorter start-up time. Existing coating systems do not provide the combination of advantages needed and available with the present invention. Non-stick coatings of fluoropolymers, polysiloxane resins, expoxy resins and other materials have used calcined or reactive alumina or silicon carbide. See U.S. Patent 4, 121,000 Wald (1978), 4,324,715 Emerick (1982) and Japanese Kokai 60-80883 Yamada (1985). U.S. Serial No. 07/626,491 filed December 12, 1990-Tarmenbaum discloses a superior blend of polyletrafhioroethylene (PTFE) and hexafluropropylene or fluorinated ethylene - propylene (FEP), a copolymer of tetrafluoroethylene with 8 - 18%, preferable about 12%, hexafluoropropylene. PCT 91/04750 filed July 9, 1991 discloses fuser roll non-stick coatings containing stainless steel or aluminum flake for electrical conductivity. SUMMARY OF THE INVENTION The present invention provides a coated substrated adapted for use at elevated temperatures in a reprographic apparatus, in which the substrate as coated with at least two coats with different compositions, a first coat adhered to the substrate and a second coat adhered to the first, with the first polyamide imide, and particulate fillers including 10 to 50% five particle aluminum oxide and 10 to 25% stainless steel flake, and the second coat comprising, by weight, 50 to 90% fluoropolymer and particulate fillers including 5 to 40% aluminum oxide and 5 to 40% aluminum flake. DETAILED DESCRIPTION OF THE INVENTION It has been found that a complex coating system with at least two layers provides superior results for the purposes of durability, non-stick and thermal conductivity. Preferably the coating systems of the invention are applied to a grit- blasted substrate, with which they give up to twice as good thermal conductivity and improved abrasion resistance with no loss of other properties, compared to systems of the prior art without aluminum oxide. Primer compositions, used for the first coat which adhere to the substrates can be too aggressive chemically for aluminum flake. Therefore, even though aluminum flake gives better thermal conductivity, than stainless steel flake, the latter is used in primer coats of the invention. A fiuorosurfactant also helps in wetting a grit-blasted aluminum substrate. Other additives and adjuvants such as surfactant defoamers, thickeners, pigments, colorants, and coalescing aids can be used as known in the art. For the second coat, aluminum flake has been found to give not only better heat transfer but also less intercoat adhesions difficult, due to its lower density and greater tendency to stay suspended as the coating dries. The aluminum flake should be stabilized as known in the art to minimize gassing in an aqueous system. A major key to success of the invention is the use of calcined aluminum particulate material in both the first and second coats. This aids adhesion, durability, and, due to higher thermal conductivity than the fluoropolymer, it also increases heat transfer. However, it would not do to merely add alumina to a known coating. Instead to obtain the advantages of the invention, it has been found important to use each of the features of the invention. The following examples provide the preferred ingredient of the first and second coats which were mixed and applied by spraying without drying between coats, then cured at 420° C for 10 min. Example 1 Primer Aluminum Oxide -reactive calcined type A - 155 G US Seive Series 325 mesh from Silberline 7.027 Stainless Steel Flake US Bronze type 316L-X-35 μ m average particular size 4.868 PTFE in 'T30" from Du Pont 6.837 Colloidal Silica in "Ludox AM" from Du Pont 0.983 FEP in "TE9075" from Du Pont 4.337 Amide-imide Resin in A-10 from Amoco 4.272 "Zonyl F9100" perfluoroalkyl ethoxylate Fluorinated Surfactant Mixture from Du Pont 0.464 "NOP-NDW" Non-Ionic surfactant from Henkel 0.002 'Triton X-100" octyl phenol polyether alcohol non-ionic surfactant from Rohm and Haas 0.975 Water 61.992 N, N-Diethylethanolamine 0.602 Triethylamine 1.205 Furfuryl Alcohol 3.357 N-methyl Pyrolidone 2.847 Ethylene Glycol 0.232 Example 2 Topcoat Aluminum Hake - 15 μm average particle size in Hydropaste 825 from Silberline 3.146 Aluminum Oxide 3.159 PTFE in * T30" 30.281 PFA"T335" 5.467 Colloidal Silica in "Ludox AM" 0.244 Acrylic of 39 parts by weight terpolymer of methyl methacyrlate/57 parts ethyl acrylate/4 parts methacryhc acid, dispersion as a 40% solids latex in water, 0._^tm average particle size 4.429 Cerium Octoate 0.536 Triethanolamine 1.126 "Triton X-100" 2.710 Butyl Carbitol 2.226 Water 37.910 Triethanolamine 4.225 Hydrocarbon Solvent 3.452 Ethylene Glycol 0.122 Nitropropane 0.629 Hydrocarbon Solvent 0.338

Claims: WHAT IS CLAIMED IS: 1. A coated substrate adapted for use at elevated temperatures in a reprographic apparatus, in which the substrate is coated with at least two coats with different compositions, a first coat adhered to the substrate and a second coat adhered to the first, wherein: the first coat comprises by weight, 20 to 70% fluoropolymer and 10 to 50% polyamide imide, and particulate fillers including, 10 to 50% aluminum oxide and 10 to 25% stainless steel flake and the second coat comprises, by weight, 50 to 100% fluoropolymer and particulate fillers including 5 to 40% aluminum oxide and 5 to 40% aluminum flake. 2. The coated substrate of claim 1 wherein in each coat the fluoropolymer is selected from polytetrafluoroethylene, fluorinated ethylene- propylene, copolymer of tetrafluoroethylene with perfluoroalkyl vinyl ether, and blends of polytetrafluoro ethylene with at least one of fluorinated ethylene-propylene and copolymer of tetrafluorethylene with perfluoro alkyl vinyl ether. 3. The coated substrate of claim 2 wherein, in the first coat, the fluoropolymer is a blend by weight of 40 to 90% polytetrafluoroethylene and 10 to 60% fluorinated ethylene-propylene. 4. The coated substrate of claim 2 wherein, in the second coat, the fluoropolymer is a blend by weight of 60 to 90% polytetrafluorethylene, and 10 to 40% copolymer of tetrafluoroethylene with perfluoro alkyl vinyl ether. 5. The coated substrates of claim 1 wherein the first coat is a blend comprising by weight 25 to 60% fluoropolymers, 10 to 25% polyamide-imide, 15 to 40% aluminum oxide and 10 to 30% stainless steel flake. 6. The coated substrate of claim 5 wherein the second coat is a blend comprising by weight 65 to 95% fluoropolymer, 5 to 20% aluminum oxide and 5 to 20% aluminum flake. 7. The coated substrate of claim 3 wherein the first coat is a blend comprising by weight, 35 to 45% fluoropolymer, 12 to 17% polyamide-imide, 20 to 30% aluminum oxide and 15 to 25% stainless steel flake, and the second coat is a blend comprising 80 to 95% fluoropolymer, 5 to 10% aluminum oxide and 5 to 10% aluminum flake. 8. The coated substrate of claim 2 which also contains an amount of fluorosurfactant effective to wet the substrate. 9. The coated substrate of claim 7 wherein the first coat, the fluoropolymer blend contains 50 to 70% polytetrafluoroethylene and 30 to 50% flourinated ethylene propylene, and in the second coat, the fluoropolymer blend contains 70 to 80% polytetrafluoroethylene and 20 to 30% perfluoro alkyl vinyl ether. 10. The coated substrated of claim 1 which also has at least one other coat containing fluoropolymer adhered to the outer surface of the second coat.

Inventors: BATZAR KENNETH, DUZICK TIMOTHY, MCKEEN LAURENCE, BATZAR, KENNETH, DUZICK, TIMOTHY, MCKEEN, LAURENCE
Applicants: DU PONT, E.I. DU PONT DE NEMOURS AND COMPANY
Application year: 1992
Main classification: G03G15
IPC codes: C08L23, C08L79, C09D5, C09D127, G03G15