GB2042478A - Stripping sheets from fuser rolls - Google Patents

Abstract

In roll fuser apparatus for fixing toner images to copy substrates such as plain paper wherein one 12 of a pair of rolls 12, 26 is heated and has a self-stripping, eg. deformable, outer layer 19 a pneumatic or vacuum device 34 is positioned adjacent the exit of the nip 20 to ensure that the lead portion of the plain paper 22 which is self-stripping remains out of contact with the heated roll 12. <IMAGE>

Description

SPECIFICATION Copy sheet lead edge control The present invention relates to heat and pressure fixing of toner images by means of a pair of rolls one of which is heated and comprises a nip forming surface, and more particularly to methods and apparatus for controlling the lead edge of a copy sheet passing out of the nip to prevent the copy sheet from becoming adhered to the heated roll after having been self-stripped therefrom.

In the process of xerography, a light image of an original to be copied is typically recorded in the form of a latent electrostatic image upon a photosensitive member with subsequent rendering of the latent image visible by the application of electroscopic marking particles, commonly referred to as toner. The visual toner image can be either fixed directly upon the photosensitive member or transferred from the member to another support, such as a sheet of plain paper, with subsequent affixing of the image thereto in one of various ways, for example, as by heat and pressure.

In order to affix or fuse electroscopic toner material onto a support member by heat and pressure, it is necessary to elevate the temperature of the toner material to a point at which the constitutents of the toner material coalesce and become tacky while simultaneously applying pressure. This action causes the toner to flow to some extent into the fibers or pores of support members or otherwise upon the surfaces thereof. Thereafter, as the toner material cools, solidification of the toner material occurs causing the toner material to be bonded firmly to the support member. In both the xerographic as well as the electrographic recording arts, the use of thermal energy and pressure for fixing toner images onto a support member is old and well known.

One approach to heat and pressure fusing of electroscopic toner images onto a support has been to pass the support with the toner images thereon between a pair of opposed roller members, at least one of which is heated. During operation of a fusing system of this type, the support member to which the toner images are electrostically adhered is moved through the nip formed between the rolls with the toner image contacting the fuser roll thereby to effect heating of the toner images within the nip. By controlling the heat transferred to the toner, virtually no offset of the toner particles from the copy sheet to the fuser roll is experienced under normal conditions.This is because the heat applied to the surface of the roller is insufficient to raise the temperature of the surface of the roller above the "hot offset" temperature of the toner whereat the toner particles in the image areas of the toner liquefy and cause a splitting action in the molten toner resulting in "hot offset". Splitting occurs when the cohesive forces holding the viscous toner mass together is less than the adhesive forces tending to offset it to a contacting surface such as a fuser roll.

Occasionally, however, toner particles will be offset to the fuser roll by an insufficient application of heat to the surface thereof (i.e.

"cold" offsetting); by imperfections in the properties of the surface of the roll; or by the toner particles insufficiently adhering to the copy sheet by the electrostatic forces which normally hold them there. In such a case, toner particles may be transferred to the surface of the fuser roll with subsequent transfer to the backup roll during periods of time when no copy paper is in the nip.

Moreover, toner particles can be picked up by the fuser and/or backup roll during fusing of duplex copies or simply from the surroundings of the reproducing apparatus.

One arrangement for minimizing the foregoing problems, particularly that which is commonly referred to as "offsetting", has been to provide a fuser roll with an outer surface or covering of polytetrafluoroethylene, known by the trade name, Teflon to which a release agent such as silicone oil is applied, the thickness of the Teflon being on the order of several mils and the thickness of the oil being less than 1 micron. Silicone based oils, (Polydimethylsiloxane), which possess a relatively low surface energy, have been found to be materials that are suitable for use in the heated fuser roll environment where Teflon consitutes the outer surface of the fuser roll.

In practice, a thin layer of silicone oil is applied to the surface of the heated roll to form an interface between the roll surface and the toner images carried on the support material. Thus, a low surface energy layer is presented to the toner as it passes through the fuser nip and thereby prevents toner from offsetting to the fuser roll surface. In such an arrangement a nip is found by the heated fuser roll deforming a backup or pressure roll.

Where the heated fuser roll is nip forming due to its relatively thick outer surface of silicone rubber being deformed by the harder pressure roll the copy sheets are self-stripping, that is to say, that the lead edge moves away from the heated fuser roll. However, it has been observed that after self-stripping occurs, the copy paper tends, particularly where light weight papers are concerned, to reassums its close association with the heated roll instead of progressing along its intended path of travel. This is believed to be caused by induced paper curl resulting from differential drying of the paper as it passes through the nip, as well as residual electrostatic forces and aerodynamic behavior of paper in the nip exit regions.

Accordingly, it is the purpose of the present invention to incorporate in a heat and pressure roll fusing apparatus, a control device for preventing the copy sheets from following (i.e.

moving in close association with the heated roll surface) the circular path of the heated fuser roll and directing them along their intended path. The preferred method contemplated comprises the employment of positive air pressure which impinges on the sheet after it strips from the heated roll. The air strikes the sheet in a direction opposite to the direction of movement caused by the induced paper curl which is in a direction tending to cause the copy sheet to wrap around the heated roll. Alternatively, a baffle may be positioned relative to the nip exit such that it engages the lead edge of the substrate that has been released from the roll to thereby effect the desired results.

Positive air pressure devices have been employed in conjunction with roll fusers, as for example, that illustrated in U.S. Patent 3,955,813. Additionally, vacuum and Bernouli effect devices have been employed.

However, these devices are employed for actually stripping the copy sheet from the heated fuser roll. As illustrated in the aforementioned patent, the copy sheet which is air stripped is precluded from following the heated roll 50 by means of a stripping bar 80. Where space is a limiting factor, a control device of the type contemplated may be the only vehicle by which proper control of the paper may be accomplished.

In order that the invention may be more readily understood, reference will now be made to the figure which is a side elevational schematic view of a roll fuser apparatus according to the invention.

Referring to the figure it can be seen that the invention is directed to a roll fuser apparatus generally indicated by the reference character 10.

The roll fuser apparatus 10 comprises a heated roll structure 1 2 having supported internally thereof a conventional radiant heat source 14 of the type employed in such devices. The heat source 14 is disposed within a hollow area 1 6 provided by a rigid thermally conductive cylinder 1 8. Adhered to the outer surface of the cylinder 1 8 is a relatively thick (i.e. for a roll with approximately a three inch outside diameter a minimum thickness on the order of 10-15 mils) layer 1 9 of silicone rubber or other suitable elastomeric material, for example, Viton a trademark of E.l. duPont.The layer 19 is deformed to form a nip 20 through which copy substrates 22, usually comprising plain paper but not necessarily limited thereto, pass with the toner images 24 thereon contacting the heated roll structure 1 2. The aforementioned deforming of the layer 1 9 is effected by forces exerted between the heated roll structure 1 2 and a much harder surfaced backup or pressure roll 26. As will be appreciated, external heating of the heated roll structure 1 2 could alternately be employed.

The backup roll 26 preferably comprises a rigid, thermally conductive core 28 coated with a thin (i.e. several mils) layer 30 of Teflon, a trademark of E.l. dupont. While the layer 30 is disclosed as being directly adhered to the core 28, it will be appreciated by those skilled in the art that the same relative hardness between the rolls can be obtained where the layer 30 is provided as an overlayer or coating which is applied to an intermediate layer of elastomeric material such as silicone rubber.

In order to enhance release of the copy substrates and therefore assist the effect that the deformation of the outer layer of the heated roll has on stripping, a thin coating of release agent material such as silicon oil may be applied to the surface of the layer in any one of a number of conventional manners.

As mentioned hereinabove, after the substrates 22 self strip from the heated roll 1 2 there is a tendency for them, particularly with 1 3 to 1 6 pound papers, to re-adhere to the heated roll due to induced paper curl and/or aerodynamic forces. Accordingly, in order to insure that the copy substrates 22 move along a predetermined path comprising a guide 32 which may be a passive member or an active one in the form of a belt transport, a lead edge control device 34 including an air manifold 35 is provided. The control device 34 comprises a conduit for directing a flow of air in the direction of the lead of the copy substrates when the lead edge is beyond the nip 20 and therefore, has already self-stripped from the heated roll.The air functions to keep the substrates from re-adhering to the heated roll and to support them until they engage the guide 32. It should be appreciated that the beam strength of the substrates will serve the aforementioned function until the lead edge comes under the control of the device 34. The control device comprises a manifold having a plurality of air outlets which are suitable distributed along the longitudinal extent of the rolls 12 and 26.

An electronically controlled solenoid valve 36 functions to provide a 2 PSI inlet pressure to the manifold for a duration of 0.2 sec. in synchronism with the process speed through the fuser to thereby provide puffs of air for controlling the lead edge of the sheets.

While the control device is depicted as comprising a positive pressure device, vacuum mechanisms may also be employed. Also, different orientations of the rolls can satisfactorily utilize the concepts by repositioning the guide 32 and the control 34.

Claims (10)

1. Roll fuser apparatus for fixing toner images by the application of heat and pres sure wherein a pair of rolls form a nip through which copy substrates having toner images thereon pass with the toner images contacting a heated roll of the pair of rolls, the surface of the roll contacted by the toner images being such that it releases at least the lead edges of the substrates, said apparatus including means for controlling the lead edges of the copy substrates whereby they are precluded from reassuming a close association with the heated roll from which they are released and are controlled until they contact a guide positioned in a desired path of movement.

2. Apparatus according to Claim 1 wherein said controlling means comprises a source of positive air flow directed at the lead edge of said copy substrates after self-stripping has occurred.

3. Apparatus according to Claim 2 wherein said source of positive air is pulsed in synchronism with the exodus of said lead edges leaving the surface of said heated roll.

4. Apparatus according to Claim 3 wherein said heated roll has an outer layer comprising silicone rubber having a thickness of at least 10-15 mils.

5. Roll fuser apparatus constructed, arranged and adapted to operate substantially as hereinbefore described with reference to the accompanying drawing.

6. A method of controlling copy sheets containing toner images after their passage out of the nip formed between a pair of rolls one of which is heated and deformed by the other wherein the toner images contact the heated roll said method including directing a flow of air in the direction of the lead edge of the copy sheets at the side contacting the heated roll only after said edges detach from said heated roll.

7. A method according to Claim 6 wherein said air flow is intermittent.

8. A method according to Claim 7 wherein the duration of said air flow is for a period of approximately 0.2 seconds.

9. A method according to Claim 6 substantially as hereinbefore described.

10. For use in conjunction with a roll fuser apparatus for fixing toner images by the application of heat and pressure wherein a pair of rolls form a nip through which copy substrates having toner images thereon pass with the toner images contacting a heated roll of the pair of rolls and further wherein the surface of the roll contacted by the toner images is such that it releases at least the lead edges of the substrates; means for controlling the lead edges of the copy substrates whereby they are precluded from reassuming a close association with the heated roll from which they are released and are controlled until they contact a guide positioned in a desired path of movement.