LAYERED OIL TRANSFER COMPONENT

Abstract: An oil transfer component for transferring oil to a roll (2) in a fuser system of a copying machine, such as a plain paper copier or laser printer, is formed of contiguous layers (17a, 17b, 17c, etc.) of porous polytetrafluoroethylene sheet material. Typically, there are from three to twenty layers. The component may be formed by winding turns of a single length around a core (e.g. in the case of a roller (10)) or may be formed of separate sheets (32). The porous polytetrafluoroethylene may be formed from particles of granular-type polytetrafluoroethylene fused to form a porous integral network; or may be a porous expanded polytetrafluoroethylene. The oil transfer component is convenient to produce and has good oil delivery and toner wiping properties, and resists puddling of oil.

Description: LAYERED OIL TRANSFER COMPONENT FIELD OF THE INVENTION The present invention relates to an oil transfer component for transferring oil to a roll in a fuser system of a copying machine, and if necessary for wiping excess toner from the roll. The term "copying machine" as used herein relates to machines which employ heated fuser rolls, for example, plain-paper copying machines and laser printers. PRIOR ART In a plain-paper copying machine, toner images applied to the surface of paper or other recording medium are fixated by application of heat and pressure. In certain plain-paper copying machines fixation is accomplished by passing the image-bearing recording medium 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 the roll surface. On subsequent rotation of the roll, the adhered toner material may be redeposited 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 roll 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 from the paper and 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. Various devices are known in the art for applying liquid release agent to one of the rolls of the fuser system, such as described in U.S. Patent Specification 3,831,553 and European Patent Publication 479564. However, the feature these systems have in common is the provision of a reservoir for holding a quantity of liquid release agent and an oil permeation control layer which is interposed between the reservoir and the roll of the fuser system for controlling the amount of oil which is transferred on to the roll of the fuser system. Various materials are known as the oil permeation control layer, such as porous polytetrafluoroethylene film as disclosed in Japanese Patent Specification No. 62-178992. British published patent application 2242431 discloses a porous polytetrafluoroethylene structure used as a filter in industrial filtration. The porous polytetrafluoroethylene material is produced by fusing particles of polytetrafluoroethylene such as to form a porous integral network of interconnected particles. The disclosure of this patent specification is incorporated herein. Our British published patent application 2261400 (International Patent Publication WO93/08512) discloses the se of such porous polytetrafluoroethylene (PTFE) material as an oil transfer component in a copying machine and particularly as an oil permeation control layer to control the amount of release agent applied to the roll in the fuser system. Figures 1 and 2, and Examples 2 and 3 disclose the possibility of providing the porous PTFE in the form of a long continuous web which is in contact with the fuser roll in order to apply silicone oil to the fuser roll and to wipe excess toner therefrom. However, the web is attached at one end to a feed spool onto which the web is wound. At the other end the web is attached to a take-up spool. In practice, the web is supplied to a customer in this manner with one end wound on a feed spool and the other end attached to a take-up spool. In use, the web is slowly advanced from the feed spool to the take-up spool and is discarded once the feed spool is empty. However, only a single thickness of the PTFE web is in operational contact with the fuser roll as the web is advanced. There is no disclosure of using an oil transfer component comprising multiple layers of PTFE web in direct contact with the fuser roll. Only a single thickness of web is used to apply oil and wipe off excess toner. Patent publication EP0174474 (Sumitomo) shows a release oil applicator which comprises a porous body formed of PTFE held in a housing. The PTFE body is saturated with silicone oil and may be formed with various cross-sections. However, only a single layer of PTFE is used. Patent specification US 4336766 (Maher) shows the use of a compound wick assembly formed from a relatively thick layer of Nomex felt and a relatively thin layer thereof. The thick layer acts as a feeder to convey oil to the thinner layer. The function of the oil reservoir is to hold quantities of liquid release agent for application to the roll of the fuser system. The reservoir may be pre-loaded with a predetermined quantity of release oil. This is referred to as an "oil-filled device", and is generally discarded once the supply of liquid release agent is used up. Alternatively, the device may be an "oil-fed" device which is supplied with liquid release agent on a continuous basis from a supply device. In both cases, the reservoir has to hold a finite quantity of liquid release agent and should have the ability to supply the liquid release agent at a suitable rate via the oil permeation control layer to the surface of the roll in the fuser system. However, it may be difficult to combine these properties in a single material. For example, a reservoir material having a high void volume and thus a high porosity which enables it to hold relatively large quantities of liquid release agent, may have a relatively low resistance to flow of the liquid release agent. Whilst to some extent this is obviated by the presence of the permeation control layer, problems can nonetheless arise. For example, when the reservoir is in the form of a roller, the liquid release agent may run to the lowest point of the roller whilst the roller is stationary, such as between runs or overnight. This phenomena is known as "puddling" and leads to a non-uniform distribution of liquid release agent throughout the reservoir, which may in turn cause non-uniform application of release agent to the fuser system roll. Furthermore, conventional reservoirs, such as compressed fibres or open-cell foam materials may require costly processing steps to produce. In the case of open-cell plastics foams, it is usually necessary to mill the foam to the required shape, such as a block or roller. Merely casting open-cell foams leaves a skin on the surface thereof which needs to be removed by machining or grinding in order to allow access of the liquid release agent to the foam and transference of the liquid release agent from the open-cell foam reservoir in use. It is an object of the present invention to provide an oil transfer component which mitigates the problems associated with known reservoir materials. SUMMARY OF THE INVENTION It has now ,been found that an oil transfer component which mitigates these problems can be provided by forming the oil transfer component as a plurality of contiguous layers of a porous polytetrafluoroethylene sheet material. Thus, one aspect of the present invention provides an oil transfer component for transferring oil to a roll in a fuser system of a copying machine, which comprises: first and second contiguous layers of a sheet material, the first layer defining a roll- contacting face of the component for contacting said roll and transferring oil thereto, and the second layer underlying the first layer; the contiguous layers forming a unitary structure; and the sheet material comprising porous polytetrafluoroethylene. Although the oil transfer component of the present invention is intended for holding and transferring oil to a roll in a fuser system, it also has the ability to remove excess oil if necessary. The oil transfer component may also wipe excess toner from the fuser system roll, particularly when the roll contacting face is textured. Generally speaking, the invention envisages the use of at least two contiguous layers of sheet material, more generally from three to twenty layers. The number of layers employed will depend on the thickness of the sheet material but typically five to ten contiguous layers of sheet material may be used. Each layer in itself constitutes a reservoir for holding and delivering release oil. In addition, spaces may be defined between adjacent layers of sheet material which also act to contain release oil. The component is simple to construct since a single material may be used to provide both the reservoir function and the oil permeation control functions of the prior art constructions. The volume of the spaces between adjacent layers of sheet material will depend on the extent to which the contiguous layers are held in contact with each other. This volume is increased where the sheet material has at least one face which is textured. However, it is generally preferred that the faces of the sheet material be substantially smooth so as to allow the layers to be in close contact with each other. In one preferred embodiment, at least some of the contiguous layers are formed from a single length of the sheet material. This is particularly the case when the oil transfer component is in the form of a roller which comprises a rotatable support having a single length of sheet material wound around the rotatable support. Alternatively, each layer may be made up of spirally wrapped overlapping turns. Such a construction is not limited to the production of cylindrical forms, but may also apply when the oil transfer component is in the form of a pad, when the pad may comprise a single length of sheet material wound into a pad of generally rectangular cross- section. In these cases, the single length of sheet material is generally wound in a single rotational direction under a predetermined tension. The tension holds together the contiguous layers of sheet material and is one factor which defines the volume of the spaces between the adjacent layers. If desired, the adjacent layers of sheet material may be bonded together. Bonding may be carried out by thermal fusion or by the use of a discontinuous pattern of adhesive. In a particularly preferred embodiment, a suitable adhesive is applied at the transverse edges of the length of sheet material. Once the length of sheet material has been wound to form the oil transfer component, the free end of the length of sheet material which remains should preferably be bonded to the layer below so that it does not start to unwind during use. In another embodiment, a single length of sheet material may be laid down in a serpentine manner so as to provide a series of substantially parallel contiguous layers. In order to hold the layers into a unitary structure, they will be bonded together in a suitable manner. In another embodiment, the oil transfer component is in the form of a pad, and the contiguous layers are formed of separate pieces of such sheet material laid one on top of the other. Again, the separate pieces of sheet material require to be bonded together into a unitary structure. Generally speaking, the layers may be bonded together in any suitable manner known in the art, such as by the use of adhesives, by thermal fusion, by stitching etc.. Where adhesives are used, the pattern of adhesive should preferably be a discontinuous pattern, such as a pattern of dots or lines, such as not to impede the flow of liquid release oil. The oil transfer component is provided as a unitary structure for use as such. Thus, the contiguous layers of porous polytetrafluoroethylene sheet remain contiguous during use and do not become separated (or unrolled as in prior constructions) . The lower layer(s) act to retain oil and transfer it to the roll-contacting first layer during use. Although the layers may be bonded together this is not essential to the operation of the component. In some instances the presence of the oil (particularly after the component has become heated in use) and friction between the layers is sufficient to maintain a unitary structure. If the component is in the form of a roller, it may be arranged to rotate in the same direction as the sheet was wound onto the roller so as to resist unwinding. However, this is not always the best direction of rotation - which may be determined by experiment in individual cases. The layers may be formed of the same or different types of porous polytetrafluoroethylene; for example a roller might have inner layers formed from one type of polytetrafluoroethylene and outer layers formed from a different type of polytetrafluoroethylene. The first layer of sheet material defines a roll- contacting face, that is to say a face of the oil transfer component which contacts a roll (usually the fuser roll or the pressure roll) of the fuser system in use so as to apply liquid release oil thereto. The term "release oil" is used herein in a general sense to include liquid release agents in general. The second layer underlies the first layer in the sense of being in contact with the opposite face to the roll- contacting face but without implying any particular vertical orientation, and extends under substantially the entire roll-contacting face. Thus there are effectively at least two layers of sheet material beneath the roll-contacting face of the oil transfer component. The thickness of the sheet material may be in the range 10 to 1000 microns. Very thin materials are not usually preferred since a large number of layers may be required. Conversely thick materials may give rise to a step formed by the free end of the sheet material in the case of a roller construction. Whilst the particular advantage of the present invention is that the multiple layers of sheet material allow an oil transfer component to be manufactured in a particularly easy manner, the invention does not necessarily discount the possibility that the contiguous layers of sheet material may also be provided in conjunction with a conventional felt or open-cell foam reservoir as known in the prior art. In one embodiment the sheet material is a porous polytetrafluoroethylene structure formed from particles of granular-type polytetrafluoroethylene fused together . such as to form a porous integral network of interconnected particles such as disclosed in Patent Specification GB2242431. This material is able to withstand the high temperatures (around 200°C) encountered within the fuser system and has excellent mechanical properties and durability. Generally speaking, the sheet material has a thickness of 50 to 1500 microns, particularly 150 to 1000 microns. The porous polytetrafluoroethylene structure is hydrophobic but has a high affinity for liquid release agents (referred to here generically as "release oil") such as silicone oil. Generally, the layers of sheet material will be loaded with release oil before being assembled into the oil transfer component. The oil transfer component will generally be supplied pre¬ loaded with release oil. In an oil-filled type of oil transfer component, the component is discarded when this oil is substantially used up. In an oil-fed type of oil transfer component, further oil is supplied thereto by means of an oil delivery mechanism. Typically, the oil will constitute 10% to 70% by weight of the total weight of the oil-containing polytetrafluoroethylene structure of the oil transfer component, particularly 20% to 60% by weight. In order to provide such oil retention capacities, the porous polytetrafluoroethylene structure usually has a specific gravity of 0.5 to 1.8, for example 0.6 to 1.5, typically 0.7 to 1.2 measured as described herein in Section (B) . In comparison, pure non-porous PTFE typically has a specific gravity of 2.16. Preferably, the porous polytetrafluoroethylene structure does not include any filler materials, since these are generally of mineral origin and tend to be of an abrasive nature which would damage the rolls in the fuser system. As mentioned above, the porous polytetrafluoroethylene structure may be produced as described in Patent Specification GB 2242431. It is particularly preferred to form the structure from a mixture of particles of different grades of granular- type polytetrafluoroethylene. As is well known, polytetrafluoroethylene (PTFE) is produced in two distinct types so-called "granular" PTFE and so-called "fine powder" PTFE. These materials have quite different properties. A particularly useful product for use in the present invention is formed from a mixture of unsintered and sintered granular type PTFE particles, for example 40% to 60% of Teflon (trademark) resin grade 7A; and 40% to 60% of Teflon resin grade 9B, respectively. However, generally speaking from 0-100% unsintered PTFE (e.g. grade 7A) and conversely 100-0% sintered PTFE (e.g. grade 9B) may be used to produce the sheet material. Teflon granular-type resin grades 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, and then peeling the formed structure from the substrate. In an alternative embodiment, the sheet material is formed of porous polytetrafluoroethylene which has been expanded. Such porous expanded polytetrafluoroethylene may be produced as disclosed in US 3,953,566. Generally a structure formed of so- called fine powder polytetrafluoroethylene is expanded along a single direction (i.e. monoaxially) or along two directions (i.e. biaxially expanded) usually at right angles to each other. The expanded porous polytetrafluoroethylene sheet material generally has a pore size in the range 0.02 to 15 microns as measured by the bubble point method described herein. The choice of pore size may have an effect on the amount of release oil retained by the sheet material and its rate of delivery. The problem of puddling discussed above is also mitigated by such expanded porous polytetrafluoroethylene. The expanded porous polytetrafluoroethylene generally has a porosity determined from specific gravity measured as described herein in the range 10 to 98% (preferably 50 to 98%) and the porosity is also a parameter effecting the amount of release oil retained by the sheet material. The thickness may be in the range 12 to 1000 microns, though very thin materials are less preferred since a large number of layers of sheet material may be required to build up a required thickness. The oil will typically constitute 10 to 98% by weight of the oil-containing expanded polytetrafluoroethylene structure, particularly 20 to 70% by weight. However, sheet material formed of other types of porous polytetrafluoroethylene may be used such as those formed of fibrous polytetrafluoroethylene wherein the polytetrafluoroethylene fibres are bonded into a porous matrix. One such material is available under the Zitex trademark (Norton Chemplast, New Jersey, USA) . DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Embodiments of the present invention will now be described by way of example only in conjunction with the attached drawings wherein:- Figure 1 is a schematic cross-sectional view of an oil transfer component in the form of a roller; Figure 2 is a further embodiment in the form of a roller having a conventional reservoir material, and several lavers of sheet material wound thereon; Figure 3 is another embodiment in the form of a pad made up of a plurality of layers of sheet material bonded together; Figure 4 is a cross-section of a still further embodiment in the form of a pad made by winding a single length of sheet material in a rectangular manner; Figure 5 is a schematic elevation of the fuser section of a plain-paper copying machine employing a oil transfer component in the form of a roller; and Figure 6 is a schematic elevation of the fuser section of a different plain-paper copying machine which employs an oil transfer component in the form of a pad. Figure 1 shows in cross-section an oil transfer component according to the invention in the form of a roller 10. The roller comprises a hollow cylindrical core 12 equipped with suitable bearings (not shown) for mounting in a copying machine. The core 12 has a hollow interior 13 for containing release oil which is delivered therefrom via apertures 14 provided in the core. Alternatively, the core could be formed of a sintered ceramic material. A single length 16 of sheet material is wound around the outside of the core so as to form six contiguous layers (17a, 17b, 17c etc. ) . Before winding, an adhesive is applied along a marginal portion of the length of sheet material so that the contiguous layers become adhered together at the ends of the cylindrical roller. In the same way, the free end 18 of the length of sheet material is adhered to the underlying layer to prevent it coming loose in use. The length of sheet material had a width sufficient to cover the desired area on the roller. That is to say the width of the sheet material provides the full width of the oil transfer component. However, the length of sheet material may in an alternative embodiment be spirally wound in a series of overlapping turns on to the roller core so as to build up the desired width and thickness. In a specific example, a single length of porous polytetrafluoroethylene sheet produced as described in Example 1 was wound onto a hollow aluminium core having four rows of 3mm diameter oil delivery apertures arranged at 90° apart around the circumference thereof. The thickness of the sheet was about 375 microns. The porous polytetrafluoroethylene had a length of 545 mm and a width of 365 mm. In order to minimise steps at each end, both ends of the sheet were cut with a knife inclined at about 30"C to the horizontal in order to chamfer the ends. Alternatively, the ends could be feathered by abrading with sandpaper. One end was adhered to the aluminium core using two lines of silicone sealant RTV732 (Dow Corning) . Then 60,000 cS silicone release oil (Dow Corning 200) was spread evenly over the flat porous polytetrafluoroethylene sheet and left for one hour to allow the oil to soak into the sheet. The aluminium core was then rolled up so as to wrap the porous polytetrafluoroethylene sheet around the core in about eight turns, the textured surface of the polytetrafluoroethylene being outermost. The ends of the cylindrical roller were then sealed with RTV732 silicone sealant so as to seal together the margins of the polytetrafluoroethylene sheet, and the sealant allowed to cure at room temperature. The free end of the polytetrafluoroethylene length was not adhered to the layer beneath. The weight of the core and dry polytetrafluoroethylene sheet was 141 g, and the weight of oil applied was 29 g. The core diameter was about 22mm and 27mm after wrapping the polytetrafluoroethylene sheet around. This roller was then fitted into a Kodak Ektoprint 300 copier and run for 250,000 copies giving satisfactory copy quality. This exceeds the number of copies which can be handled using a conventional roller formed of Nomex (trademark) aramid felt. Figure 2 is a cross-section of a roller 20 having a core 12 as before. This differs from the embodiment shown in Figure 1 in that a hollow sleeve 22 of known reservoir material, such as a felt formed of Nomex fibres or an open-cell foam plastics material is employed. The fibres sold under the Nomex trademark are aramid fibres, a type of polyamide. The open-cell foam might be an open-cell melamine foam. Around the outside of the reservoir 22 is wound a number of turns of a single length of sheet material 16. The edges and free end of the sheet material are bonded as before. Although it is convenient to employ a single length of sheet material, since this may be easily wound around the core or around the reservoir, it should be understood that this may be replaced by separate layers individually bonded in place if required. Moreover, in an alternative embodiment the hollow sleeve 22 could itself be formed of a length of one type of porous polytetrafluoroethylene (e.g. from 100% Teflon grade 9B) and the outer length 16 from a different type of porous polytetrafluoroethylene (e.g. from 50% grade 7A and 50% grade 9B) . Figure 3 is a cross-section of a pad 30 formed of a plurality of contiguous layers 32 of sheet material. The layers are bonded together by means of a pattern of adhesive dots. The adhesive may be silicone adhesive as mentioned above. It will be noted that the roll- contacting face 34 of the oil transfer pad 30 is slightly curved so as to follow the curvature of the roll in the fuser system on to which the pad transfers release oil in use. Figure 4 also shows an oil transfer component in the form of a pad having a roll-contacting face 34. In this case, the pad has a substantially rectangular cross-section and has been formed by winding a single length of sheet material (16) in a substantially rectangular manner. Although not shown, it may be convenient to wind the length of sheet material about a flat central former, which former may be left in place or may be withdrawn after production of the oil transfer pad. Figures 5 and 6 show fuser systems employing oil transfer components according to the present invention either in the form of a roller 10 (or roller 20) or a pad 30 (or pad 40) . The fuser system comprises a PTFE-covered (or silicone rubber covered) fuser roll 2 and a silicone rubber covered pressure roll 4, which are oiled and wiped by means of an oil transfer component of the present invention. In the case of the Figure 5 embodiment, oil is applied directly on to the fuser roll 2 by means of the oil transfer roller 10. In the case of Figure 6, release oil is applied to the fuser roller 2 by means of a pad 30 held within a channel 42. In both cases, the release oil may be applied to the pressure roll 4 instead of the fuser roll 2, if desired. Also, the oil transfer components may either be provided as oil-filled components, that is to say they contain a predetermined quantity of silicone release oil and are discarded after the release oil is used up; or may be provided as an oil- fed type, in which case a supply of release oil is constantly fed to the oil transfer component (which is usually supplied pre-loaded with release oil) by a conventional oil delivery means (not shown) . The sheet material was a porous polytetrafluoroethylene sheet made as follows: EXAMPLE 1. (production of PTFE sheet) (a) Preparation of unsintered granular PTFE suspension. 250 grams of DuPont (trademark) granular PTFE grade 9B which had been milled to a weight average particle size of about 40 microns (particle size distribution 99.5% less than 124 microns, and zero% less than 2.8 microns) , 250 grams of DuPont granular PTFE grade 7A, 13 ml of Zonyl (trademark) FSN 100 surfactant (a non-ionic perfluoroalkyl ethoxylate mixture) , 10ml of isopropyl alcohol, 41 ml of Pluronic ( t r a d ema rk ) L 121 s u r f a c t a nt ( a polyoxyethylene/polyoxypropylene block copolymer) , and 1.14g of a sodium carboxy-methyl-cellulose dissolved in water (thickening agent) as a 1% wt/wt solution; were added to 460 grams of water and blended in a Waring blender for 5 minutes. (b) Formation of porous granular PTFE structure. The above suspension was sprayed on to a smooth stainless steel plate to a nominal net film thickness of 1000 microns using a Binks BBR spray gun and L88 pressure cup, then dried in an oven. The air temperature was brought up to 115°C and when the temperature of the stainless steel plate had reached 100°C drying was continued for 30 ins. The air temperature was then progressively increased over a few hours up to 365°C. Once the plate temperature had reached 350°C drying was continued for a further 2.5 hrs. The resultant structure was then cooled. The specific gravity was 0.80 g/cc. After the structure had cooled, the PTFE sheet was carefully peeled from the stainless steel plate. The thickness was about 750 microns. The lower face which had been in contact with the stainless steel plate was smooth and the upper face was slightly textured as a result of the spray application. The oil retention capacity could be modified by varying the proportion of Teflon grade 7A from 50% by weight upto 100% by weight. In fact, the proportion of grade 7A could vary from 0% to 100% by weight depending on the desired properties of the PTFE sheet. However, in the case of 100% grade 9B, the suspension was sprayed onto a fine stainless steel mesh to anchor the material and resist shrinkage during baking; and was then peeled off. EXAMPLE 2 oil retention- For comparison, two types of Nomex (trademark) felt were compared with two types of porous PTFE sheet material produced in the manner of Example 1: Nomex 1 Thickness 4.40mm (Comparison) Weight/Area 677 g/m 2 Density 0.15 g/cc Nomex 2 Thickness 2.16mm (Comparison) Weight/Area 509 g/m 2 Density 0.23 g/cc Product XI - 100% PTFE grade 9B Thickness = 0.8mm Weight/Area = 572 g/m 2 Density = 0.72 g/cc Product X2 - 100% PTFE grade 7A Thickness = 0.18mm Weight/Area = 205 g/m 2 Density = 1.14 g/cc In each case above, the weight/area was measured according to ASTM 0461-87 (Section 11) and the thickness was measured according to ASTM D461-87 (Section 10) . The density was calculated as the weight/area divided by lOOOx thickness. This method of measuring the density was adopted for this comparison example (rather than the method given in Section (B) herein) in order to allow valid density measurements for the comparison Nomex felt to be made. All the samples were tested for oil retention as per the modified procedure of ASTM D461-87 as described herein under "(E) Oil Retention" and the results obtained are shown below in Table I. TABLE 1 Sample Oil Retention (cm 3 /cm 3 ) Nomex 1 0.73 Nomex 2 0.83 Product XI 0.52 Product X2 0.36 These results give the volume of oil that can be retained by a unit volume of felt. EXAMPLE 3 oil pudding) However, the oil retention figures of Example 2 do not give an indication as to the distribution of oil within the materials' structures. To determine this, the samples were left hanging for a further 20 hours approximately orientated as per the modified ASTM D-461 procedure. Each sample was then cut in half in a horizontal direction at the vertical mid point to form an upper half and a lower half. The upper and lower halves of the samples were then weighed and the results were as shown in Table II. TABLE II SAMPLE PORTION WEIGHT (g) Nomex 1 Upper 3.2584 (Comparison) Lower 8.2022 Nomex 2 Upper 3.3973 (Comparison) Lower 4.3247 Product X-l Upper 1.7894 Lower 1.7801 Product X-2 Upper 0.4954 Lower 0.5109 The oil was then extracted from each of the sample halves using methylene chloride (as described herein) to give the weights set out in Table III; from which net oil in each portion was calculated and compressed as an oil retention figure for the particular portion. TABLE III SAMPLE PORTION DRY WEIGHT(g) SAMPLE DIMENSIONS NET OIL(g) Oil Retention cc/cc Nomex 1 Upper 1.6392 25mmx75mm 1.6192 0.20 " Lower 2.2222 5.98 0.76 Nomex 2 Upper 1.2133 2.184 0.56 " Lower 1.0773 3.2474 0.84 Product XI Upper 1.1661 0.6233 0.43 " Lower 1.0759 0.7042 0.49 Product X2 Upper 0.3842 0.1112 0.34 " Lower 0.3861 0.1248 0.38 This demonstrates the ability of the porous PTFE to act as a reservoir to hold oil more evenly than the conventional Nomex aramid felt material. The benefit of this is that within an oiling device oil does not puddle as severly during idle periods. An oil transfer component according to the present invention which is formed of multiple layers of the porous PTFE sheet material has a markedly reduced tendency for the oil to puddle when the copying machine is not operating. TESTING AND PREPARATIVE METHODOLOGIES (A) Preparation of PTFE grade 7A and 9B TEFLON (trademark) granular-type PTFE fluorocarbon resin grades 7A and 9B are available from DuPont Speciality Polymers Division, Wilmington U.S.A. Grade 9B is a premelted sintered resin. The manufacturers product specification indicates an average specific gravity of 2.16, and an average particle size of 35 microns (grade 7A) and 500 microns (grade 9B prior to milling) . PTFE grade 7A was unsintered and was used as supplied. Prior to use, the PTFE grade 9B was milled to a weight average particle size of about 40 microns by grinding an aqueous slurry thereof between grinding stones at room temperature as follows. The PTFE grade 9B was mixed with water to form a slurry, and the slurry fed between closely spaced grinding surfaces of a grinding mill as disclosed in US- A-4841623, to crush and shear the pieces of PTFE into particles. The ground slurry was then filtered or centrifuged to separate the porous expanded PTFE particles from water, and the separated finely ground particles were oven dried at from 125°C - 150°C. (B) Specific Gravity Unless otherwise stated, the specific gravity of the PTFE sheet is determined by weighing a sample thereof in two different media, viz; air and water. The weights were determined using an Avery VA124 analytical balance. The specific gravity is calculated as being equal to (weight in air)/(weight in air - weight in water). (C) Particle Size Particle size of ground PTFE grade 9B was determined as follows: using a magnetic stirrer and ultrasonic agitation, 2.5 grams of milled PTFE powder were dispersed in 60 ml isopropyl alcohol. (Ultrasonic Probe Model W- 385, manufactured by Heat Systems-Ultrasonics, Inc.) . Aliquots of 4-6ml of the dispersed particles were added to approximately 250ml of circulating isopropyl alcohol in a Leeds & Northup Microtrac FRA Particle Size Analyzer of analysis. Each analysis consisted of three 30-second runs at a sample circulation rate of 2 litres/minute during which light scattering by the dispersed particles is automatically measured and the particle size distribution automatically calculated from the measurements. ( D) Pore Size Pore size of expanded polytetrafluoroethylene was determined from the bubble point, defined in this patent as the pressure required to blow the first bubble of air detectable by its rise through a layer of liquid covering the sample. A test device, similar to the one employed in ASTM F316-80, was used consisting of a filter holder, manifold and pressure gauge (maximum gauge pressure of 275.8 kPa) . The filter holder consisted of a base, a locking ring, an o-ring seal, support disk and air inlet. The support disk consisted of a 150 micron mesh screen and a perforated metal plate for rigidity. The effective area of the test sample was 8.0 plus or minus 0.5 cm 2 . The test sample was mounted on the filter holder and wet with anhydrous methanol until clarified. The support screen was then placed on top of the sample and the top half of the filter holder was tightened in place. Approximately 2 cm of anhydrous methanol at 21°C was poured over the test sample. The pressure on the test sample was then gradually and uniformly increased by the operator until the first steady stream of bubbles through the anhydrous methanol were visible. Random bubbles or bubble stream of the outside edges were ignored. The bubble point was read directly from the pressure gauge. The pore size of the test sample is related to the amount of gas pressure required to overcome surface tension and is given by bubble point (psi) = K.4.Y.cos T /d where K = shape factor Y = surface tension of methanol T = contact angle between pore and surface d = maximum pore diameter. (E) Oil Retention (i) The oil retention capcity of the porous PTFE sheet material and comparison felts was determined by a modification of ASTM D461-87. The oil used was Dow Corning 200 silicone oil of viscosity 100 centistokes and a density of 0.96 g/cc. Test samples of size 25mm x 150mm were cut at random from the sheet material. Each sample was weighed to the nearest O.Olg. The samples were placed on the surface of a vessel which had been fitted with oil to a depth of 50mm and allowed to sink under gravity to avoid air entrapment. The samples remained immersed for 3 hours. Thereafter each sample was removed from the oil and hung from a wire hook with the long dimension vertical to drain for 60 ins. A stirring rod was used to remove any visible drops of oil adhering to the sample before weighing the sample. The oil retention was calculated according to ASTM D461-37 Section 21.6.1. (ii) Oil extraction was carried out as follows. The oil-containing sample was weighed to an accuracy of O.Olg to give an initial weight. The sample was then immersed in methylene chloride at a temperature of 20±2°C and agitated for 1 minute. The sample was then removed and hung in an oven at 110°C for 15 minutes. This procedure was repeated until a constant weight (measured to O.Olg accuracy) was achieved; giving the final weight. The net oil content was calculated from the difference between the initial and final weights of the sample.

Claims: CLAIMS 1. An oil transfer component for transferring release oil to a roll in a fuser system of a copying machine, which comprises: first and second contiguous layers (17a,17b) of a sheet material, the first layer defining a roll-contacting face of the component for contacting said roll and transferring oil thereto, and the second layer underlying the first layer; the contiguous layers forming a unitary structure; and the sheet material comprising porous polytetrafluoroethylene. 2. A component according to claim 1 which comprises a plurality of contiguous layers of said sheet material in the range from three to twenty layers. 3. A component according to claim 2 which comprises from five to ten contiguous layers of sheet material. 4. A component according to any preceding claim, wherein at least some of said contiguous layers are formed from a single length (16) of said sheet material. 5. A component according to claim 4 which is in the form of a roller (10) , and which comprises a rotatable support (12) having said single length of sheet material wound around the rotatable support. 6. A component according to claim 4 which is in the form of a pad, and which comprises said single length (16) of sheet material wound into a pad (40) of generally rectangular cross-section. 7. A component according to any of claims 1 to 3 which is in the form of a pad (30) , the contiguous layers (32) being formed of separate pieces of said sheet material. 8. A component according to any preceding claim wherein said contiguous layers are bonded to each other. 9. A component according to any preceding claim wherein the sheet material has a thickness of 50 to 1500 microns. 10. A component according to any preceding claim wherein the porous polytetrafluoroethylene is formed from particles of granular-type polytetrafluoroethylene fused together such as to form a porous integral network of interconnected particles. 11. A component according to claim 10 wherein the particles of granular-type polytetrafluoroethylene from which the network is formed are sintered particles. 12. A component according to claim 10 wherein the particles of granular-type polytetrafluoroethylene from which the network is formed are unsintered particles. 13. A component according to claim 10 wherein the particles of granular-type polytetrafluoroethylene from which the network is formed comprise a mixture of sintered and unsintered particles. 14. A component according to any of claims 1 to 9 wherein the porous polytetrafluoroethylene is porous expanded polytetrafluoroethylene. 15. A component according to any preceding claim which comprises a quantity of release oil. 16. A component according to claim 15 wherein the release oil constitutes 20% to 60% by weight of the component. 17. A component according to any preceding claim wherein said layers of porous polytetrafluoroethylene each have a thickness of 150 to 1000 microns. 18. A component according to any preceding claim wherein the porous polytetrafluoroethylene has a specific gravity of 0.7 to 1.2 g/cc. 19. A component according to any preceding claim wherein the roll-contacting face thereof is textured.

Inventors: MCCOLLAM FRANCIS MICHAEL JOHN, PITCAIRN ALISTAIR, MCCOLLAM, FRANCIS, MICHAEL, JOHN, PITCAIRN, ALISTAIR
Applicants: GORE W L & ASS UK, MCCOLLAM FRANCIS MICHAEL JOHN, PITCAIRN ALISTAIR, MCCOLLAM, FRANCIS, MICHAEL, JOHN, PITCAIRN, ALISTAIR, W.L. GORE & ASSOCIATES (UK) LTD.
Application year: 1995
Main classification: G03G15
IPC codes: G03G15