Coating processes – With post-treatment of coating or coating material – Solid treating member or material contacts coating
Reexamination Certificate
2002-07-31
2004-01-13
Cameron, Erma (Department: 1762)
Coating processes
With post-treatment of coating or coating material
Solid treating member or material contacts coating
C427S387000
Reexamination Certificate
active
06676996
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a composite material containing a preformed polydialkylsiloxane particle dispersed within a cured fluoroelastomer material. One application for this composite material is as fuser members useful for heat-fixing a heat-softenable toner material to a substrate. More particularly, the invention relates to materials usable as a toner release layer in a fuser member.
BACKGROUND OF THE INVENTION
In certain electrostatographic imaging and recording processes, for instance, in electrophotographic copying processes, an electrostatic latent image formed on a photoconductive surface is developed with a developer which is a mixture of carrier particles, e.g., magnetic particles, and a thermoplastic toner powder which is thereafter fused to a receiver such as a sheet of paper. The fusing member can be a roll, belt or any surface having a suitable shape for fixing thermoplastic toner powder images to a substrate. The fusing step commonly consists of passing the substrate, such as a sheet of paper on which toner powder is distributed in an imagewise pattern, through the nip of a pair of rolls, at least one of which is heated. Where the fusing member is a belt it is preferably a flexible endless belt having a smooth, hardened outer surface which passes around a heated roller.
A persistent problem in this operation is that when the toner is heated during contact with the heated roll or belt it may adhere not only to the paper but also to the fusing member. Any toner remaining adhered to the member can cause a false offset image to appear on the next sheet and can also degrade the fusing member. Other potential problems are thermal degradation and abrasion of the member surface which results in an uneven surface and defective patterns in thermally fixed images.
Toner fusing rolls have a cylindrical core which may contain a heat source in its interior, and a resilient covering layer formed directly or indirectly on the surface of the core. Roll coverings are commonly fluorocarbon polymers or silicone polymers, such as poly(dimethylsiloxane) polymers, of low surface energy which minimizes adherence of toner to the roll. Frequently release oils composed of, for example, poly(dimethylsiloxanes), are also applied to the roll surface to prevent adherence of toner to the roll. Such release oils may interact with the roll surface upon repeated use and in time cause swelling, softening and degradation of the roll. Silicone rubber covering layers which are insufficiently resistant to release oils and cleaning solvents are also susceptible to delamination of the roll cover after repeated heating and cooling cycles.
Toner fusing belts are composed of a continuous flexible material having a smooth surface and superior resistance to heat. The belt substrate can be metallic or polymeric. The surface of the belt is composed of a thinly coated, low surface-energy polymer such as a fluorocarbon or a silicone-polymer.
Fusing members with a surface coating of a fluoropolymer commonly a fluoroelastomer, especially vinylidene fluoride based fluoroelastomers, possess excellent heat, oil and chemical resistance as well as good fatigue and wear characteristics. However, fluoroelastomers with these excellent chemical and mechanical properties have a propensity to interact with toners, especially those formulated from polyesters, causing premature offset.
U.S. Pat. No. 4,264,181 discloses fusing members coated with a metal-filled elastomer surface obtained by nucleophilic-addition curing of a mixture of a metal filler and a vinylidene fluoride-hexafluoropropylene copolymer. Mixtures of the fluoroelastomers with silicone rubbers were mentioned (column 8, lines 26-29) but no specific examples of suitable silicones are taught. The surface coatings disclosed are used in conjunction with functionally substituted polymeric release agents capable of interacting with the metal component.
U.S. Pat. No. 4,853,737 discloses a roll useful in electrostatography having an outer layer comprising cured fluoroelastomers containing pendant polydiorgano-siloxane segments that are covalently bound to the backbone of the fluoroelastomer. This material shows poor wear properties and the silicon content described in this patent must be kept very low in practice to avoid incompatibility.
U.S. Pat. No. 5,141,788; U.S. Pat. No. 5,166,031; and U.S. Pat. No. 5,695,878 disclose a fuser member comprising a supporting substrate having an outer layer of a volume grafted elastomer which is a substantially uniform integral interpenetrating network of a hybrid composition of a fluoroelastomer and a polyorganosiloxane, where said volume graft has been formed by dehydrofluorination of said fluoroelastomer by a nucleophilic dehydrofluorinating agent, followed by addition polymerization by the addition of an alkene or alkyne functionally terminated polyorganosiloxane and a polymerization initiator. The disadvantage of this is that it usually involves at least two extra reaction step to produce higher silicone contents without phase separation. Also the resulting hybrid network structure consists substantially of silicone crosslinks which demonstrate poor wear resistance. In addition, a higher silicone concentration forms on the surface through stratification and as such has poorer wear resistance.
U.S. Patent No. 5,534,347 discloses toner fusing rolls having an oil barrier layer composed of a substrate coated with a fluorocarbon-silicone polymeric composition which is obtained by concurrently curing a fluorocarbon copolymer, a nucleophilic fluorocarbon-curing agent and a heat curable poly(C
(l-6)
alkyl)arylsiloxane polymer. This patent does not describe a release layer as the surface energy of the resulting material was too high.
Similarly, U.S. Pat. No. 5,582,917 discloses toner fusing members having a surface layer comprising a substrate coated with a fluorocarbon-silicone polymeric composition obtained by concurrently curing a fluorocarbon copolymer, a nucleophilic fluorocarbon curing agent and a heat curable polyfunctional polymethylsiloxane polymer.
U.S. pat. application Ser. Nos. 09/156,996, 09/156,831, and 09/157,391 describe materials similar in structure to U.S. Pat. No. 5,582,917 and U.S. Pat. No. 5,534,347 being formed from a different process of solution dispersion rather that mechanical incorporation as well as specific uses for those materials. One disadvantage of these is the restriction on the amount of the silicone phase which can be incorporated without large scale phase incompatibility. These materials as well as those of U.S. Pat. No. 5,582,917 and U.S. Pat. No. 5,534,347 are actually misnamed interpenetrating networks as the concentration of silicone based polymer necessary to form a co-continuous phase is outside of the range of phase compatibility.
U.S. Pat. Application Ser. No. 09/156.996. now U.S. Pat. No. 6,075,966, describes a composition whereby true interpenetrating networks are created by the incorporation of a low molecular weight material functionalized polydimethylsiloxane capable of reacting into the fluoroelastomer phase to compatibilize the secondary network of crosslinked polydimethylsiloxane at higher concentration. However at higher concentrations of polydimethylsiloxane in the fluoroelastomer, the properties of the material can be detrimentally affected.
The disadvantage of all the patents described above is in the lack of ability to either form materials with high incorporation levels of polydimethyl siloxane or incorporate silicone without substantially modifying the fluoroelastomer matrix. The formation of a continuous polydimethylsiloxane phase is detrimental to the mechanical properties, and large polydimethylsiloxane phase sizes cause poor coating properties and non-uniform wear and release properties. Modification of the fluoroelastomer invariably leads to a degradation in the mechanical properties which make fluoroelastomers attractive (for example wear, tensile strength, temperature resistance). This is due to the large phase size of the polysiloxane in conjunct
Boulatnikov Nataly
Davis Stephen V.
Pickering Jerry A.
Cameron Erma
NexPress Solutions LLC
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