Resilient stripper members forming a part of a fuser roll

Abstract

A roll fusing apparatus for electrostatic reproducing apparatus wherein the heated roll has a resilient surface including a plurality of discrete protrusions or ridges which extend from the surface thereof. The protrusions are so constructed that they compress when they pass through the nip area formed between the heated roller and the back-up roller. Once they move out of the nip the protrusions assume the normally uncompressed state and thereby serve to lift the copy paper from the heated fuser roll.

Description

BACKGROUND OF THE INVENTION

This invention relates to roll fuser apparatus for use in a xerographic reproducing apparatus and particularly, to means for stripping copy paper from the heated roll thereof in order to prevent the paper from curling and wrapping around the fuser roll.

In the process of zerography, 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 image can be either fixed directly upon the photosensitive member or transferred from the member to a sheet of plain paper with subsequent affixing of the image thereto.

In order to permanently affix or fuse an electroscopic toner material onto a support member by heat, it is necessary to elevate the temperature of the toner material to a point at which the constituents of the toner material coalesce and become tacky. This action causes the toner to be absorbed to some extent into the fibers of the support member which in many instances constitutes plain papers. Thereafter, as the toner material is cooled, solidification of the toner material occurs causing the toner material to be firmly bonded to the support member.

In both the electrographic as well as the xerographic recording arts, the use of thermal energy for fixing toner images onto a support member is old and well-known.

One approach to thermal 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 either externally or internally heated.

During operation of a fusing system of the above-described type, the support member to which the toner images are electrostatically adhered is moved through the nip formed between the rolls with the toner image contacting the fuser roll to thereby provide heating of the toner image within the nip. By controlling the heat transferred to the toner and by the provision of proper roll surface materials virtually no offsetting 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 would liquify and cause a shearing action in the molten toner to thereby result in offset. Shearing occurs when the interparticle forces holding the viscous toner mass together is less than the surface energy forces tending to offset it to a contacting surface such as the fuser roll.

Occasionally, however, extraneous toner particles will be offset to the fuser roll by an insufficient application of heat to the surface thereof; by imperfections in the properties of the entire 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, extraneous toner particles may be transferred to the surface of the fuser roll beyond the nip, with subsequent transfer to the back-up roll during periods of time when no copy paper is in the nip and before the back-up roll can be moved out of contact with the fuser roll.

It will be appreciated that in order to prevent such toner particles being transferred to the copy paper it is necessary to remove the toner particles from the fuser roll and/or the back-up roll. It will be further appreciated that if enough toner accumulates on the back-up roll the paper feed will be affected.

One arrangement for minimizing the foregoing phenomena, commonly referred to as "offsetting," has been to provide a fuser roll with an outer covering or sleeve of polytetraflourethylene, commonly known as Teflon, to which a release agent such as silicone oil is applied. Silicone based oils, which possess a relatively low surface energy, have been found to be a material that is suitable for use in the heated roll fuser environment. In practice, a thin layer of silicone oil is applied to the surface of the heated roll to thereby 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 adhering to the fuser roll surface. Although the low surface energy oils generally act as non-wetting fluids in regard to most support materials, it has been found that a mechanical flowing of the release agent from the roll onto the support material will occur if an excess of oil is allowed to accumulate in a region where it can come into contact with the copy paper. Accordingly, the amount of oil applied to the roll surface is generally metered under controlled conditions to maintain a relatively thin coating of the release agent on the roll surface.

As the copy sheet passes out of the nip formed between the heated fuser roll and the back-up roll it is necessary to provide means for insuring that the copy paper proceeds along a predetermined path from the aforementioned nip to a conveyor belt or the like for moving the copy paper toward the exit of the machine.

It has been the practice in prior art devices to employ stripper fingers for the purpose of stripping the copy paper from the heated fuser roll and for also guiding the copy paper from the nip area to the conveyor belt or the like. In order to strip the copy paper by means of stripper fingers, it is necessary that the leading edges of the stripper fingers contact the surface of the fuser roll such that they can become interposed between the roll surface and the copy paper. It will be appreciated that such contacting of the fuser roll surface has attendant disadvantages, for example, they cause the fuser roll surface to wear due to frictional contact and sometimes due to gouging of the roll surface, particularly, when the roll is used in a dry (i.e. without release agent) fuser system and where the fuser roll outer surface comprises a high coefficient of friction material such as silicone rubber.

It is therefore the principal object of this invention to provide an improved roll fusing device for fixing toner images to a substrate in an electrostatic reproducing apparatus.

Another object of this invention is to provide improved means for removing copy paper from the surface of the heated fuser roll.

Yet another object of this invention is to provide means for stripping copy paper from a heated fuser roll wherein such means forms an integral part of the heated fuser roll.

BRIEF SUMMARY OF THE INVENTION

Briefly, the above-cited objects are accomplished by the provision of a fuser apparatus comprising a heated fuser roll and a back-up roll. The fuser roll is constructed of a rigid substrate or support overcoated with a resilient layer of, by way of example, silicone rubber which has been applied to the rigid substrate such that a plurality of protrusions extend radially outward therefrom.

The aforementioned protrusions are such that as they pass through the nip formed by the fuser and back-up rolls they are compressed to thereby present a flat surface to the powder images to be fixed. Once the protrusions move out of the nip they assume their normal protruding orientation and thereby serve to lift the copy paper off the fuser roll.

For a better understanding of the present invention as well as other objects and further features thereof, reference may be hade to the following detailed description of the invention to be read in conjunction with the accompanying drawings wherein:

FIG. 1 is a side elevational view of a xerographic reproducing apparatus incorporating the present invention;

FIG. 2 is a front elevational view, partly in section, of a fuser representing the invention; and

FIG. 3 is an end view in elevation of the fuser illustrated in FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

For a general understanding of the apparatus incorporating the improved fusing device, reference may be had to FIG. 1 in which the various system components for the xerographic copying apparatus are schematically illustrated. In the apparatus illustrated, a light image of a document to be reproduced is projected onto the sensitized surface of a xerographic plate to form an electrostatic latent image thereon. Thereafter, the latent image is developed with an oppositely charged developing material to form a xerographic powder image corresponding to the latent image on the plate surface. The powder image is then electrostatically transferred to a support surface to which it is fused whereby the powder is caused to permanently adhere to the support surface, which surface usually comprises plain paper.

In the illustrated apparatus, an original to be copied is placed upon a transparent support platen P fixedly arranged in an illumination assembly and image rays are projected by means of an optical system for exposing the photosensitive surface of a xerographic plate in the form of a drum generally indicated by the reference numeral 10.

The drum 10 is mounted upon the frame of the machine and is adapted to rotate in the direction of the arrow at a constant rate. During this movement of the drum, it passes a charging station A where a uniform electrostatic charge is applied to the surface thereof. Next to an exposure station B, exposure of the drum surface to the light image discharges the xerographic plate in the areas struck by light, whereby there remains on the surface a latent electrostatic image in image configuration corresponding to the light image projected from the original on the supporting platen. As the drum surface continues its movement, the electrostatic images passes through a developing station C in which there is positioned a developer assembly. The developer assembly delivers developing material to the upper part of the drum whereat the material is directed to cascade over the drum surface in order to provide development of the electrostatic image. As the developing material is cascaded over the drum surface toner particles in the development material are deposited on the surface to form powder images.

The developed electrostatic image is transported by the drum to a transfer station D whereat a sheet of copy paper is moved at a speed in synchronism with the moving belt in order to accomplish transfer of the developed image. There is provided at this station a sheet transport mechanism adapted to transport sheets of paper from a paper handling mechanism to the developed image on the drum at the station D.

After the sheet is stripped from the drum, it is conveyed to a fuser apparatus generally indicated by the reference numeral 20 whereat the developed and transferred xerographic powder image on the sheet material is permanently affixed thereto as will be described more fully hereinafter. After fusing, the finished copy is discharged from the apparatus by a belt conveyor to a suitable point for collection externally of the apparatus. Suitable drive means are arranged to drive the drum in conjunction with timed exposure of an original to be copied, to effect conveying and cascading of toner material to separate and feed sheets of paper and to transport the same across the transfer station D and to convey the sheet of paper through the fuser apparatus in timed sequence to produce copies of the original.

The fuser apparatus 20, as illustrated in FIG. 2, comprises a fuser roll 22 and a back-up roll or pressure roll 24 having a nip 26 defined therebetween, through which copy paper 28 is moved in order to permanently affix images of toner particles 30 thereto.

The copy paper 28 having the toner images electrostatically adhered therto is moved to the nip 26 by means of a conveyor belt 32 which receives the copy paper from the photosensitive member 10, herein disclosed by way of example as a drum structure.

The fuser roll 22 may be fabricated from any conventional material by well-known techniques in the art whereby a roll structure is provided which comprises a rigid, heat conductive substrate or support 34 such as aluminum, overcoated with an adhesive layer 36 of silicone rubber.

The fuser roll 22 is provided with a plurality of ridges or circumferential protrusions 46 formed integrally with the layer 36. The ridges 46 are preferably on the order of 0.005-0.010 inches and are spaced preferably between 0.5-2.0 inches along the longitudinal axis of the fuser roll 22. The thickness of the silicone layer, to the base of the ridge is approximately 0.250 inches. The layer 36 together with the ridges 46 may be molded on the core 34 or otherwise suitably applied thereto.

The ridges are deformable to such an extent that as they pass through the nip 26 they completely flatten out thereby presenting a flat surface to the copy paper and the images carried thereby. As the ridges move out of the nip they return to their pre-stressed conditions thereby lifting the paper from the fuser roll.

To heat the fuser roll 22 a radiant heat element 50 and reflector 52 are provided.

Power is supplied to the element 50 such that during operation the outermost surface temperature is on the order of 200.degree.-400.degree.F.

While the heating source has been disclosed as being external, it will be appreciated that an internal source would give satisfactory results. Additionally, it will be appreciated that the ridges can take on other forms, for example, individual projections.

The back-up or pressure roll 24 comprises a rigid support 40 having a layer of polytetraflourethylene 42 thereon. A structure is thus provided whose surface is relatively hard compared to the ridges 46, for effecting compression of the ridges.

While the invention has been disclosed with reference to the preferred embodiments it will be appreciated by those skilled in the art that further modifications and advantages of the present invention may be had without departing from the spirit and scope thereof. Accordingly, it is intended that such modifications and advantages be covered by the claims appended hereto.

Claims

What is claimed is:

1. Xerographic reproducing apparatus having means for forming toner images on a substrate including means for moving said substrate through said apparatus for such purposes, said moving means comprising at least one pair of nip forming members through which said substrate moves, and wherein said substrate tends to adhere to one of said members, the improvement comprising:

means formed integrally with said one of said nip forming members for insuring separation of said substrate from said one of said members after movement through said nip, said integrally formed means comprising a plurality of protrusions on the surface of said one of said members, said protrusions constituting means being capable of being compressed as they move through said nip to form substantially a flat surface at the nip and returning to their protruding positions thereafter.

2. Apparatus according to claim 1 including means for elevating the surface temperature of one of said nip forming members for fixing said toner images to said substrate.

3. Apparatus according to claim 2, wherein said nip forming members comprise a heated roll fuser and a backup roll.

4. Apparatus according to claim 3, wherein said substrate comprises plain paper.

5. Apparatus according to claim 3, wherein said protrusions comprise circumferential ridges on said fuser roll.

6. Apparatus according to claim 4, wherein the outer surface of said fuser roll comprises a layer of silicone rubber including a unitary structure comprising a base portion and said circumferential ridges.

7. The method of affixing toner images to a substrate including the steps of:

providing a pair of nip forming members, at least one of which has substrate stripping means comprising a plurality of protrusions on the surface thereof, said protrusions constituting means being capable of being compressed as they move through said nip to form substantially a flat surface at the nip and returning to their protruding positions thereafter;

moving said members in synchronism to thereby move said substrate through said nip and moving said protrusions to a compressed position as they move through said nip; and

allowing said protrusions to move to protruding positions after leaving said nip.

8. The method according to claim 7, wherein said nip forming members are continous and said protrusions comprise a plurality of continuous ridges.

9. The method according to claim 8, including the step of heating said at least one nip forming member.