Constant coefficient noiseless friction retard member

Abstract: A retard member for use in a friction retard sheet separator and feeder (Fig. 1) has a support member (16), a friction retarding surface layer (17) of an ethylene propylene diene rubber having a relatively stable coefficient of friction and an intermediate vibration absorption layer (18), between the support member and the surface layer, of a closed cell polychloroprene foam.

Description: The present invention relates generally to sheet feeding and separating apparatus and more particularly to a retard member for use in a friction retard sheet separator feeder. It has a particular but not exclusive application in the feeding of sheets in electrostatographic printing machines such as for example that illustrated in U.S. Patent No. 4,660,963 to Stemmle. The development of electrostatographic printing machines has brought about the need for simple, yet reliable, sheet separator feeder apparatus capable of handling sheets varying in length, thickness, weight, and surface conditions. One of the more common arrangements involves friction retard feeders wherein separation and feeding is dependent upon a differential friction principle. One such type of feeder utilizes a feed roller surface having a relatively high coefficient of friction with paper and a retarding surface (which may also be a roller but driven in the opposite direction or alternatively a stationary pad) having a coefficient of friction with paper less than that of the feed roller, but greater than that between two successive sheets of paper. In these feeders, the coefficient of friction of the feed roller with the paper must exceed the coefficient of friction of the retard member which must always exceed that of the coefficient of friction between two sheets of paper. In these separator feeders the region of contact between the retarding member and the feed roll forms a sheet queuing throat which is able to fan out sheets in the throat for feeding single sheets through the throat. While capable of performing satisfactorily, there are problems associated with these types of feeders. One of the more common problems is feeding reliability, that is the feeding of single sheets only from the nip between the feed roller and the retard member rather than a multifeed of from two up to perhaps five or six individual sheets. This unreliability in feeding is the result of a reduction in the coefficient of friction with the feeders surfaces and in a particular application can be traced to the loss of coefficient of friction with a polyurethane retard member. Another difficulty frequently experienced with friction retard feeders is that an unacceptable level of noise, a high pitched screech almost a squeal, may be experienced when separating and feeding heavy weight paper, 120 g.m⁻² for example, and transparencies. This unacceptable noise is caused by a stick/slip phenomenon wherein the individual sheets tend to initially stick to the retard member and then slip quickly causing vibration of the retard pad at the interface between the pad and the paper which is transmitted to the pad mounting which is mounted to a frame causing the unacceptable noise. The following prior art is noted: U.S. Patent No. 4,314,006 to Lentz et al. discloses a flexible document transport belt of ethylene propylene diene rubber (EPDM) for use in an automatic document handler. The belt has a stable coefficient of friction, high resistance to ozone, high abrasion resistance and mechanical stability. See Col. 5, lines 3-13. U.S. Patent No. 4,192,497 to Perun et al. discloses a composition for the surface of sheet separating devices such as retard rollers and abutment members having a hardness of at least 25 durometer. See Fig. 1 showing a retard roll having an outer surface 1 of a microcellular elastomer. The elastomer is mounted upon abutment member 2. See Fig. 2 which shows a retard pad having a frictional surface 6 mounted on a rigid surface 5. Examples of preferred elastomers are given on Col. 5, lines 38-46. U.S. Patents Nos. 4,579,332 and 4,555,103, both to Larson, disclose a bottom level sheet feeding apparatus having a lead surface superposed on an upper run on a belt and a retard strip superposed to the belt downstream of the lead surface. The lead surface has a relatively low coefficient of friction, the belt has a relatively high coefficient of friction and the retard strip has an intermediate coefficient of friction. See Figs. 2-4 of the '332 patent, corresponding to the preamble of claim 1, which show belt 24, retard strip 46, upper run 36, flexible sponge block 48 and lead surface plate 40. The retard strip has a coefficient of friction of about 0.5 and preferably consists of microcellular polyurethane foam. See Col. 4, lines 23-34 and Col. 5, lines 5-15 of the '332 patent for the uses of sponge block 48. In accordance with the present invention, a retard member for use in a friction retard sheet separator and feeder is provided which comprises a support member and a friction retarding surface layer, characterised in that the friction retarding surface layer is of an ethylene-propylene-diene rubber having a stable coefficient of friction, and in that an intermediate vibration absorption layer of a closed cell polychloroprene foam is provided between the support member and the surface layer. In a further aspect of the present invention, the vibration absorption layer is from about 4 to about 6 times as thick as the retarding surface layer and the retard member is in the shape of a pad. In a further aspect of the present invention, the coefficient of friction of the ethylene-propylene-diene rubber friction retarding surface is about 1.2, plus or minus 0.2. In a further aspect of the present invention, the polychloroprene foam has a hardness of from about 40 to about 60 Shore 00 Durometer. In a further aspect of the present invention, the polychloroprene foam has a density of from about 192 to about 352 Kg.m⁻³ (about 12 to about 22 pounds per cubic foot). In a further aspect of the present invention, the polychloroprene foam has a compression force deflection of from about 0.35 to about 0.63 Kg.cm⁻² (about 5 to about 9 pounds per square inch). In a further aspect of the present invention the ethylene propylene diene rubber has a hardness from about 63 to about 73 Shore A. By way of example only, an embodiment of the invention will be with reference to the accompanying drawings, in which FIG. 1 is a schematic representation in cross-section of a friction retard sheet separator and feeder. FIG. 2 is an exploded isometric view of the retard member of the feeder. FIG. 3 is an exploded view illustrating the mounting apparatus that may be used for the retard member. Referring now to Figure 1 there is illustrated by way of an example a sheet separator feeder which includes a sheet support platform 10 urged upwardly by spring 11 to advance sheets to be separated and fed to the friction retard nip formed between the retard member 12 and feed roll 13. The feed roller surface has a relatively high coefficient friction with the paper while the retard member has a lower coefficient of friction with the paper but its coefficient of friction with the paper is greater than the coefficient of friction between two successive sheets. This relationship and geometry enables the shingling or staggering of individual sheets into the nip between the feed roll and retard pad to the path defined by the sheet guide 15. Typically the feed roll is made from a silicone rubber or other elastomer having a coefficient of friction greater than about 1.5. As seen with reference to Figures 2 and 3, the retard member comprises a support member or mount 16 having a friction retarding surface layer 17 and intermediate vibration absorbing layer 18 between the support member and the surface layer. The vibration absorption layer may be secured to the support member by any suitable mean such as with a conventional adhesive for example, an acrylic adhesive like the cyanoacrylate, Loctite (registered trade mark) 454. The friction retard surface 17 is secured to the vibration absorption layer in a similar fashion. The assembled retard member 14, is pivotally mounted about pivot pin 21 in mounting clip 22 to a frame assembly (not shown). Torsion spring 24 urges the front edge of the retard member upwardly when in position. The sheet guide 15 (Fig. 1) having a sheet guiding surface with a low coefficient of friction is provided to guide a sheet away from the separation nip formed between the retard member and feed roll. The friction retarding surface 17 is made from an ethylene propylene diene terpolymer rubber known as EPDM which provides a relatively stable coefficient of friction for the retarding surface and can be selected from those materials described in the above referenced Lentz et al Patent 4,314,006. Such materials are commercially available from various suppliers such as Exxon Chemical Co., USA under the trade designation Vistalon 2504-099, E.I. Dupont Company under the trade designation Nordell 1440. It is preferred to cure the EPDM in a free radical crosslinking system comprising a free radical initiator. Exemplary of such a system is a peroxide curing system. Examples of free radical initiators are dicumyl peroxide, benzyl peroxide, and di-t-butyl peroxide. It is also preferred that the ethylene propylene diene terpolymer rubber (EPDM) be cured in a process in which the free radical crosslinking is carried out in the presence of a co-agent which is a reactive monomer itself and which adds to the polymer radical formed by the free radical initiator. This type of coagent promotes trimolecular crosslinking. Triallyl cyanurate and triallyl isocyanurate are examples of such coagents which promote trimolecular crosslinking, that is which join three, rather than merely two, polymer chains together. When triallyl cyanurate or triallyl isocyanurate is used as the coagent, about 0.5 to 3 parts, and preferably about 2 to 2.5 parts, by weight of the coagent may be used per 100 parts of EPDM. The dicumyl peroxide free radical initiator is present in amounts of about 4 to 12 parts and preferably about 8 parts. In addition, for every 100 parts by weight of EPDM the composition may contain up to 80 parts, preferably 40 to 75 parts of various fillers and or reinforcing agents such as silica and alumina. A lubricant such as zinc stearate may be present in amounts of from about 0.25 to two parts and preferably one part by weight. A processing aid such as zinc methacryate may be present in an amount of from 0.25 to 5 parts and preferably 1.5 parts by weight. Further 2.5 to 20 parts, preferably 5 to 10 parts, by weight of zinc oxide activator stabilizer are provided in a preferred composition. A colorant such as titanium dioxide is typically present in amounts of from 2 to 20 parts, preferably 5 to 8 parts, by weight and up to 50 parts preferably about 5 to 10 parts of a plasticizer softener such as paraffinic oil such as Sunthene 4240 available from Sun Oil Company may be present. Typically, the EPDM friction retarding surface layer has a tensile strength of at least 63 Kg.cm⁻² (900 pounds per square inch), an ultimate elongation of 200 per cent ± 50 per cent, a maximum compression set of 9 per cent, a tear strength of at least 6.65 Kg.cm⁻² (95 pounds per square inch), a Shore A Durometer of between 63 and 73 and a specific gravity between 1.19 and 2.25. The above described EPDM composition provides a stable and controllable coefficient of friction for the friction retarding surface layer and in particular one wherein the coefficient of friction is relatively stable at about 1.2 with nominal variation within plus or minus 0.2. In addition, the EPDM terpolymer is resistant to abrasion and surface cracking as well as being resistant to ozone attack and exposure to ultraviolet light. The vibration absorption layer 18 is a closed cell polychloroprene foam which provides sufficient damping to the retarding surface layer 17 to reduce the noise otherwise generated from the stick slip phenomenon when feeding relatively heavy paper and transparencies. The polychloroprene foam supplies a spring rate or constant that allows the retard member to deflect at a steady rate without vibration. Further the polychoroprene foam tends to isolate any vibration in the retard member so that it is not transmitted to the frame. The polychoroprene is an elastomer made by the vulcanization of 2-chlorol-1,3-butadiene with metal oxides rather than sulfur. The 2 clorol-1,3-butadiene is prepared by the action of hydrogen chloride on monoviny-acetylene. The expanded polychloroprene has a uniform closed cell structure and is free from cracks or tears or other surface defects which will be detrimental to its function. The closed cell nature of the foam enables bonding at the surface of the foam to the mount and the surface layer without adhesive penetrating the surface to affect the properties of the foam. The foam may have a skin on all surfaces or each surface may be free from skin. When the skin is used it is of the same compound and vulcanized intricately with the cellular structure. The foam typically has an apparent density between 192 and 352 Kg.m⁻³ (12 and 22 pounds per cubic foot), a compression force deflection of between 5 and 9 pounds per square inch, a tensile strength of at least 70 pounds per square inch, an ultimate elongation of at least 130 percent, a maximum compression set after 24 hours at 23° C of 25 percent after 24 hours at 50° C of 40 percent and Shore 00 Durometer between 40 and 60. Such a polychloroprene foam enables control of the spring force at a steady rate in response to deflection by the force of the feed roll in the separating feeding nip. Typical commercially available materials includes the polychloroprene foam R-425-N available from Rubatex Corp; Bedford, Va. and 4219-N available from American National Rubber Co., Huntington, W. Va. The retard member may be assembled in any suitable fashion. Typically the vibration absorption layer 18 of polychloroprene foam is glued to the support member 16 with a suitable adhesive such as the Loctite 454 previously mentioned when the support member is a plastic. Similarly the EPDM friction retarding surface layer 17 may be glued to the polychloroprene foam layer 18 with the same adhesive. Particularly satisfactory results in reducing the noise created by the stick slip phenomenon have been achieved with a retard member wherein the vibration absorption layer 18 is from about 4 to about 6 times as thick as the friction retarding surface layer 17.This provides a retard member having a sufficiently thick foam layer to absorb the vibration and thin enough to control deformation under lead. Typically the friction retarding surface layer 17 is of the order of 0.75 to 1.0 millimeters thick and the vibration absorption layer 18 is of the order of 3 to 6 millimeters thick. In a preferred embodiment the friction retarding surface layer 17 is 0.85 millimeters thick and the vibration absorption layer 18 is from 4 to 4.8 millimeters thick. Thus, according to the above description, a retard member for use in a friction retard sheet separator feeder can be provided wherein highly reliable sheet separation and feeding without multifeeds can be experienced and wherein sufficient dampening of the retarding surface layer 17 is provided by the polychloroprene foam layer 18 in separating and feeding heavy weight papers and transparencies that the noise generated is reduced to an acceptable level. The selection of a specific material for the friction and retarding layer 17 and the provision of a specific material for the vibration absorption layer 18 enables those advantages to be achieved. It will be apparent that modifications within the scope of the claims may be made to the embodiment of the invention described above. For example, while the friction feed member has been illustrated as a roll 13 it could equally well be a belt.

Claims: A retard member for use in a friction retard sheet separator and feeder, comprising a support member (16) and a friction retarding surface layer (17), characterised in that the friction retarding surface layer is of an ethylene propylene diene rubber having a stable coefficient of friction, and in that an intermediate vibration absorption layer (18) of a closed cell polychloroprene foam is provided between said support member and said surface layer. A retard member as claimed in claim 1, wherein the vibration absorption layer is from about 4 to about 6 times as thick as said retarding surface layer and said friction retard member is in the shape of a pad. A retard member as claimed in claim 1 or claim 2, wherein the coefficient of friction of said ethylene propylene diene rubber friction retarding surface is stable at about 1.2. A retard member as claimed in any one of the preceding claims, wherein said polychloroprene foam has a hardness of from about 40 to about 60 Shore 00 Durometer. A retard member as claimed in any one of the preceding claims, wherein said polychloroprene foam has a density of from about 192 to about 352 kg.m⁻³ (about 12 to about 22 pounds per cubic foot). A retard member as claimed in any one of the preceding claims, wherein said polychloroprene foam has a compression force deflection of from about 0.35 to about 0.63 kg.cm⁻² (about 5 to about 9 pounds per square inch). A retard member as claimed in any one of the preceding claims, wherein said ethylene propylene diene rubber has a hardness of from about 63 to about 73 Shore A Durometer. A friction retard sheet separator and feeder comprising a sheet support platform (10) for supporting a stack of sheets, sheet feed means (13) mounted for sheet feeding engagement with the top sheet of a stack of sheets when a stack of sheets is on said sheet support platform and a retard member (12) mounted for engagement with said sheet feed means to form a separating nip therebetween for separating any overlapped sheets reaching the nip, said retard member being as claimed in any one of the preceding claims.

Inventors: LAFICA RONALD G, MUCK DENNIS N, LAFICA, RONALD G, MUCK, DENNIS N.
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1991
Main classification: B65H3
IPC codes: B65H3, G03G15