OIL RESERVOIR

Abstract: An oil supply device, usually a pad (32) or roller (30), for applying release oil to a fuser roll in a photocopying machine comprises an open-cell melamine foam reservoir (26) capable of operating at temperatures of 200 DEG C, having an oil-permeation control layer (14, 15) over the reservoir for controlling the supply of release oil. The oil permeation control layer may be a separate cover wick (20) or may be laminated by a layer (13) of adhesive to the reservoir (26). The device may be oil-fed or prefilled with oil. The oil permeation control layer is preferably a porous PTFE network formed by fusing granular-type PTFE particles.

Description: OIL RESERVOIR TECHNICAL FIELD V The present invention relates to materials for use an oil reservoir for applying release oil to a fuser rol in a photocopying machine, particularly plain paper copying machines and laser printers, and includes oil-filled and oil-fed types of reservoir. BACKGROUND In a plain paper copying machine, toner images applied to the surface of paper or other recording mediu are fixated by application of heat and pressure. In certain plain paper copying machines, fixation is accomplished by passing the image-bearing recording medi between a hot thermal fixation roll and a pressure roll. When this type of thermal fixation device is used the toner material is directly contacted by a roll surface, and a portion of the toner usually becomes adhered to th roll surface. On subsequent rotation of the roll, the adhered toner material may be re-deposited on the recording medium resulting in undesirable offset images, stains, or smears; or in severe cases the recording medium may stick to the adhered toner material on the ro i and become wrapped around the roll. To counter these problems, materials having good release properties such as silicone rubber or polytetrafluoroethylene are often used for the roll surfaces. Although improving performance of the thermal fixation devices, use of silicone rubber or polytetrafluoroethylene roll surfaces alone does not eliminate the problem. Another approach is to include release agents with the toner materials, which prevent the toner materials from adhering to the roll surface. These oil-less toners improve the performance of the thermal fixation devices but again, particularly in the case of high-speed type copying machines, do not completely eliminate the problems associated with toner pick-up and transfer. Toner pick-up by the rolls can be controlled by coating the surface of at least one of the rolls with a liquid release agent, such as a silicone oil. It is important that the release liquid be applied uniformly and in precise quantities to the surface of the roll. Too little liquid or non-uniform surface coverage, will not prevent the toner from being picked up and re-deposited on the roll. On the other hand, excessive quantities of the release liquid may cause silicone rubber roll surfaces to swell and wrinkle, thus producing copies of unacceptable quality. Devices to uniformly meter and coat a release liquid onto copy machine roll surfaces are ' described in Japanese laid-open patent number 62-178992. These devices consist of an oil permeation control layer adhered to a thick porous material which serves as a wick or reservoir for supplying oil to the permeation control layer. The permeation control layer controls the amount of oil delivered. The thick porous material to which the permeation control layer is adhered is typically a porous thermosetting resin foam or a felt of Nomex (trademark) fibres, glass fibres, carbon fibres, polytetrafluoroethylene (PTFE) fibres, or other high temperature fibre. US patent 4,668,537 describes a sliding-type applicator for release oil formed of a felt for holding the release oil, and a porous polytetrafluoroethylene (PTFE) membrane laminated over the felt by means of an FEP (tetrafluoroethylene-hexafluoropropylene copolymer) film. The FEP film is only applied along marginal portions of the felt. US patents 3,831,553 and 3,980,424 also describe arrangements for oiling or cleaning a fuser roll. European patent application 91309005.6 (0479564) laid open on 8th April, 1992 discloses an oil-filled reservoir in the form of a roller. The device comprises a liquid permeation control layer of porous expanded PTFE membrane adhered to a porous tubular reservoir. The reservoir comprises an open-cell thermosetting polymer foam which requires to be internally reinforced to obtain the strength, resilience, . and heat resistance needed for high durability in use as part of a hot toner image fixation mechanism in a plain paper copying machine. The thermosetting polymer foam is a melamine resin, a polyimide resin, a phenolic resin, or bismaleimidetriazine resin. The internal reinforcing layer is formed of silicone oil and silicone rubber within the outer surface of the reservoir roller. The present invention is based on the discovery that open-cell melamine foam may find general applicability as reservoir materials, without the need for a silicone oil/silicone rubber internal reinforcing layer? particularly when special permeation control materials are employed. SUMMARY OF THE INVENTION Thus, the present invention provides an oil supply device for oiling a fuser roll in a photocopying machine, which comprises; - an oil reservoir formed of an open-cell melamine foam capable of operating in continuous service at a temperature of 200°C; and - a layer of oil permeation control material overlying the reservoir for controlling supply of oil from the reservoir to the fuser roll. PREFERRED EMBODIMENTS In one aspect of the invention, the open-cell foam material is free of any reinforcing layer internally within the foam material. In another aspect, the oil reservoir is in the form of an oil-filled or oil-fed pad, or in the form of an oil-fed roller. Preferably, the foam material will be capable of operating in continuous service at temperatures of 220°C. Conventional Nomex felt reservoirs tend to have a maximum operating temperature of about 170°C in continuous service. Generally, the foam material has a density in the region 7 to 15 kg/m 3 . Preferably, the foam material should have a pore volume in the region 50 to 95% , preferably 75 to 95%. The foam material should have a suitable speed of wicking in order to deliver sufficient quantities of oil, particularly for high speed applications, where an oil-fed reservoir will usually be employed. In an oil-fed reservoir, the reservoir is primed with oil and oil is also delivered to the pad during use, usually by a metering pump. In oil-filled reservoirs, the reservoir is pre-filled with its supply of oil, which is continuously delivered until used up, when replacement of the reservoir is necessary. The foam materials of the present invention generally contain upto 1 g/ml (for example between 0.6 and 0.9 g/ml) of oil. In comparison, conventional Nomex felt reservoirs hold a maximum of about 0.6 g/ml of oil. Thus the reservoir of the present invention has an enhanced oil holding capacity. Generally, the oil reservoir will have a thickness of 4 to 20 mm, preferably 4 to 12 mm. Usually, the foam material will have a resilient nature, so as to mould to the shape of the fuser roll. A particularly preferred open cell melamine foam is available under the trademark Basotect from BASF (available in the UK from Noise Control Centre) . The oil reservoir is employed in conjunction with an oil permeation control material, which lies between the oil reservoir and the fuser roll (or other roll onto which oil is to be applied) . The permeation control layer may be provided as a separate layer or may be laminated to the surface of the oil reservoir. Depending on the usage, the thickness is typically 75 to 500 microns, useful thicknesses being 125 and 375 microns. Thus, for use in one particular type of photocopying machine, the permeation control layer is provided as a separate cover wick, which is supported on a frame or pair of parallel rods extending along either side of the cover wick strip in order to mount it in the photocopying machine. It is a particularly preferred feature of the present invention that the permeation control layer be formed of a porous polytetrafluoroethylene structure as disclosed in a published British patent application 2242431 (9106768.6) and referred to in our pending application GB9122750.4. The porous polytetrafluoroethylene material is produced by fusing particles of granular-type polytetrafluoroethylene such as to form a porous integral network of interconnected particles. The disclosure of this patent specification is incorporated herein. The specification is particularly concerned with the filtration of aqueous slurries. A particularly useful product for use in the present invention comprises 40 to 60% of Teflon (trademark) resin grade 7A; and 40 to 60% of Teflon resin grade 9B. Teflon resin grade 7A and 9B are available from DuPont Speciality Polymers Division, Wilmington, U.S.A. The porous polytetrafluoroethylene structure is usually prepared by spraying onto a substrate, such as a ceramic tile or sheet of metal. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Embodiments of the present invention will now be described by way of example only. Figure 1 shows an oil-fed reservoir pad for use with a cover wick; Figure 1A shows an oil-filled pad having a porous PTFE oil control layer; Figure 2 shows an oil-fed roller comprising an oil reservoir and an oil control permeation outer layer; and Figures 3 to 5 show fuser roll arrangements employing oil supply pads or rollers according to the present invention. Figures 1, 1A and 2 show in detail embodiments of the present invention. Figure 1 shows a pad 26 of thickness 4mm to 20 mm and formed of Basotect (trademark) melamine open-celled foam. The pad is provided with suitable cut outs 6, 6 to enable the pad to fit into a conventional plain paper copying machine, together with a cover wick 20 (Figure 3) oil control layer. Figure 1A shows a laminated pad 32 suitable for oil-fed or oil-filled use. It comprises a pad 26 of open-celled melamine foam having laminated thereto an oil permeation control layer 15 of porous polytetrafluoroethylene (PTFE) according to GB2242431, which is adhered by means of a layer of adhesive dots 13. Figure 2 shows an oil-fed roller assembly 30. The assembly comprises a hollow central shaft 10 including oil delivery slots 11. A cylindrical oil reservoir 12 formed of open-cell Basotect melamine foam moulded or ground to shape. On the outer surface of the roller is provided an oil permeation control layer 14 formed of a porous polytetrafluoroethylene material comprising 50% Teflon grade 7A and 50% Teflon grade 9B produced according to Example 1 of patent specification GB2242431. This is wound around the oil reservoir 12 and adhered thereto by means of adhesive dots 13. The edges of the layer 14 are slightly overlapped to form a longitudinal seam (not shown) . The same construction can be used for an oil-filled construction, where a solid shaft 10 is employed. Figure 3 shows a conventional arrangement including a PTFE covered fuser roll 2 and silicone rubber covered roll 4 to which silicone oil is supplied by oil supply mechanism 16, reservoir 26, and cover wick 20. The cover wick is supported on a pair of rods 22, 24. The reservoir . wick 26 is as shown in Figure 1; Figure 4 shows use of a roller 30 to deliver oil onto the PTFE-covered fuser roll 2. Alternatively, it may contact the silicone rubber covered roller 4. The roller may be pre-oiled, or oil may be supplied into the centre of the roller by an oil supply mechanism. The roller is as shown in Figure 2; and Figure 5 shows a laser printer arrangement having a fuser roll 2 and a silicone rubber covered roll 4. An oil-filled pad 40 of the type shown in Figure 1A in a channel 42 applies a controlled amount of oil to the PTFE-covered fuser roll 2, and also cleans excess toner from the roll. EXAMPLE 1 (laminated pad) A release oil-supply pad of the type shown in Figure 1A was produced by laminating a layer of porous PTFE (50% grade 7A and 50% grade 9B produced according to GB2242431) of thickness 380 microns (15 thousands of an inch) to an open-cell melamine foam pad (Basotect) of thickness 14mm. Lamination was carried out by gravure printing or screen printing a pattern of dots of a polyimide resin in acetone onto the porous PTFE, drying at about 130°C; and heating at about 175°C under pressure in contact with the melamine foam pad. The laminated pad of the invention was then installed in a Kodak Ektaprint 850 photocopying machine in place of the conventional pad (formed of a Nomex felt reservoir with a Nomex felt fabric cover layer) . The photocopying machine was operated in the normal way. The pad of the invention had not failed when it was replaced after a million copies, which is at least four times the normal lifetime of the conventional pad. In addition, the life of the fuser roll was found to be extended by about 25% due to the improved control of oil feed by the pad of the invention. Excess oil applied to the fuser roll causes swelling of the roll and can contribute to failure of the roll. EXAMPLE 2 A similar laminated pad to that described in Example 1 of width 38mm (reservoir thickness 7mm) was installed in a Siemens laser printer in place of the conventional oil supply pad. The pad contained 18g of oil in comparison to 6g for the conventional Nomex felt reservoir. The pad of the present invention achieved 350,000 copies (in comparison to an average of around 60,000 copies for the conventional pad) . EXAMPLE 3 An oil-supply pad of the type shown in Figure 1A was produced as described in Example 1, except that the layer of porous PTFE was laminated to the melamine foam pad using a silicone adhesive (Dow Corning 732 RTV) which was applied at room temperature without the use of heat or * pressure. The laminated pad was installed in the photocopying machine and its performance evaluated.

Claims: CLAIMS 1. An oil supply device for oiling a fuser roll in a photocopying machine, which comprises; an oil reservoir (26) formed of an open-cell melamine foam capable of operating in continuous service at a temperature of 200°C; and - a layer (14,15) of oil permeation control material overlying the reservoir , for controlling supply of oil from the reservoir to the fuser roll. 2. A device according to claim 1 wherein the layer of oil permeation material is laminated onto a surface of the oil reservoir. 3. A device according to any preceding claim in the form of a roller (30) , the reservoir being substantially cylindrical. 4. A device according to claim 3 wherein the roller is oil-fed and the cylindrical reservoir comprises a duct (10,11) for feeding oil into the centre thereof. 5. A device ace ording to any of claims 1 to 3 wherein the reservoir is prefilled with oil. 6. A device according to claim 1 or 2 in the form of a pad (32) . 7. A device according to any preceding claim wherein the oil permeation control material is formed of porous polytetrafluoroethylene (PTFE) , produced by fusing particles of granular PTFE such as to form a porous integral network of interconnected particles. 8. A device according to any of claims 1 to 6 wherein the oil permeation control layer is formed of a polytetrafluoroethylene fabric or felt, or a Nomex fabric or felt.

Inventors: DAWSON KEITH, HAYHURST ROBERT, DAWSON, KEITH, HAYHURST, ROBERT
Applicants: DAWSON KEITH, GORE W L & ASS UK, HAYHURST ROBERT, W.L. GORE & ASSOCIATES (UK) LTD.
Application year: 1993
Main classification: G03G15
IPC codes: B05C1, G03G15