Wicking Apparatus

Abstract

Apparatus for lubricating the heated fuser roll in a heated pressure xerographic fusing system. The apparatus includes an applicator roll for providing a film of oil to a wick assembly having a Teflon layer contacting the fuser roll and a Nomex layer contacting the applicator roll where the Nomex layer is flame treated to provide high oil retention and prevent binding the drive of the applicator roll.

Description

This application relates to fusing systems and in particular to an improved lubricating apparatus for removing toner particles from the fuser roll of a heated pressure fusing system.

In the practice of xerography as described in U.S. Pat. No. 2,297,691 to Chester F. Carlson, a xerographic surface comprising a layer of photoconductive insulating material affixed to a conductive backing is used to support electrostatic images. In the usual method of carrying out the process, the xerographic surface is electrostatically charged uniformily over its surface and then exposed to a light pattern of the image being reproduced to thereby discharge the charge in the areas where the light strikes the layer. The undischarged areas of the layer thus form an electrostatic charge pattern in conformity with the configuration of the orginal light pattern.

The latent electrostatic image can then be developed by contacting it with a finely divided electrostatically attractable material such as a powder. The powder is held in image areas by the electrostatic charges on the layer. Where the charge field is greatest, the greatest amount of powder is deposited; where the charge field is least, little or no material is deposited. Thus, a powder image is produced in conformity with the light image of the document or object being reproduced. The powder is subsequently transferred to a sheet of paper or other surface and suitably affixed thereto to form a permanent print.

One typical device for fixing the toner particles to the backing sheet is by a heated pressure fuser roll system in which the copy sheet is passed through the nip of a Teflon coated heated fuser roll and a backup roll as described in U.S. Pat. Nos. 3,256,002 and 3,268,351. In such fusing systems, care must be taken to remove unwanted toner particles from the heated fuser roll prior to its contact with the copy being fused. If care is not taken to keep the fuser roll free of toner particles, these toner particles can build up on the face of the fuser roll and degrade the quality of the fix by removing the fusing properties on the surface of the roll contacting the copy sheet and toner images. Furthermore, such unwanted toner particles can be released from the fusing roll upon its subsequent contact with the toner image to fuse toner particles to the copy sheet in non-imaged areas. A wick is generally used to dispense silicone oil by gravity on the external Teflon surface of the heated fuser roll by a pad overlying the heated fuser roll.

While the gravity dispensing wick which is in pad form is satisfactory where the wick is elevated over the nip, it is not altogether satisfactory in other arrangements, such as, where the heated fuser roll is disposed as the bottom roll of the fusing system.

It is therefore an object of the present invention to improve heated pressure fusing systems.

It is another object of the present invention to improve wicking assemblies of high temperature stability for use with heated pressure fusing systems.

It is another object of the invention to provide wicking assemblies capable of retaining oil over a long shutdown period against gravity.

It is still another object of the present invention to enhance the wicking properties of an oil applicator wick.

It is still another object of the present invention to provide an improved wicking assembly which is compatible with silicone oil and conforms to objects.

It is still another object of the invention to provide a wick assembly which eliminates substantially stalling of an oil applicator contacting the wick.

It is still another object of the present invention to minimize unnecessary maintenance of copier/duplicator systems.

These and other objects of the instant invention are obtained by a new and improved wicking assembly which comprises two different layers of materials, Teflon and Nomex, in which the Teflon material contacts the heated fuser roll and the Nomex material is in contact with the oil applictor roll and has been flame treated to form a smooth fuzz free surface such that sufficient oil is retained at all times by the wick assembly for dispensing to the heated fuser roll.

Further objects of this invention together with additional features and advantages thereof will become apparent from the following detailed description of the embodiment of the invention when read in conjunction with the accompanying drawings wherein:

FIG. 1 is a schematic representation of an automatic xerographic reproducing machine incorporating a heated pressure fusing system utilizing the improved wicking assembly of the present invention;

FIG. 2 is a side elevational view of the heated pressure fusing system;

FIG. 3 is an isometric view of the improved wicking assembly according to the present invention;

FIG. 4 a is an exploded view of a prior art wick surface; and

FIG. 4 b is an exploded view of the flame treated fuzz free surface of the present invention.

Referring now to the drawing as shown in FIG. 1 an embodiment of the invention in a suitable environment such as an automatic xerographic reproducing machine. The automatic xerographic reproducing machine includes a xerographic plate or surface 10 formed in the shape of a drum. The plate has a photoconductive layer or light receiving surface on a conductive backing journaled in a frame to rotate in a direction indicated by the arrow. The rotation will cause the plate surface to sequentially pass a series of xerographic processing stations.

For purposes of the present disclosure the several xerographic processing stations in the path of movement of the plate surface may be described functionally as follows:

a charging station A which the uniform electrostatic charge is deposited onto the photoconductive plate;

an exposure station B at which light or radiation pattern of copies to be reproduced is projected onto the plate surface to dissipate the charge in the exposed areas thereof to thereby form a latent electrostatic image of the copies to be reproduced;

a developing station C at which xerographic developing material including toner particles have an electrostatic charge opposite to that of the latent electrostatic image is cascaded over the latent electrostatic image to form a powdered image in configuration of the copy being reproduced;

a transfer station D which the powdered image is electrostatically transferred from the plate surface to a transfer material such as paper which is then passed through heated pressure fusing system according to the present invention as will be described hereinafter; and

a drum cleaning and discharge station E at which the plate surface is brushed to remove residual toner particles remaining thereon after image transfer and at which the plate is exposed to a relatively bright light source to effect substantially complete discharge of any residual electrostatic charge remaining thereon.

For further details of the xerographic processing stations, above reference is made to copending application Ser. No. 838,902 filed July 3, 1969.

Referring now in particular to FIG. 2 there is shown the heated pressure fusing system of the present invention which includes a heated fuser roll 16 and a backup pressure roll 18. Fuser roll 16 is a hollow circular cylinder with a metallic core 20 and a Teflon layer 22. A quartz lamp 24 serves as a source of thermal energy and is located at the center of the fuser roll. Power to the lamp is controlled by a thermal sensor generally called a thermister contacting the periphery of the fuser roll as described, for example, in U.S. Pat. No. 3,357,249. The backup roll 18 is also circular cylinder and is made up of a metal core 30 surrounded by a thick rubber layer 32 and also a Teflon layer 34 to prevent soaking silicone oil into rubber layer 32 and subsequent swelling.

When the two rollers 16 and 18 are engaged as shown in FIG. 2 the applied load deforms the rubber in the pressure roll to provide the nip with a finite width. The copy sheet 40 electrostatically bearing the toner images 42 on the underside is brought into contact with the nip of the rolls with the toner image contacting the fuser roll 16. For a given temperature of the fuser roll, the fusing rate will depend upon the contact arc length of the support material against the dwell time, i.e., the time the toner images remain between the fuser roll 16 and the backup roll 18. Dwell time can be varied either by changing the surface velocity of the rolls or by varying the contact arc length and holding the speed of the roll the same. Contact arc length depends on the softness of the rubber on backup roll 18 and on the amount of pressure between the rolls 16 and 18. The mechanism for driving the rolls and for lowering and raising the rolls into contact can be accomplished by any suitable means as that described, for example, in U.S. Pat. No. 3,291,466 or by a suitable mechanical camming device.

As a sheet of material is advanced between the rolls 16 and 18 the toner images on the support material will contact the peripheral heated surface of the roll 16 whereby the toner images become tackified and in this tackified condition the toner will tend to offset on this roll except that it is partially prevented from doing so by the Teflon coating on the roll. However, it is by the wicking apparatus of the present invention which is successful in applying a thin film of offset preventing liquid such as silicone oil to the Teflon surface 22 of the fuser roll 16 such that toner offset is prevented as will be described hereinafter.

An oil dispensing apparatus 45 includes wicking assembly 48, an oil pan 50 for maintaining a supply of silicone oil 51 and an applicator roll 52. The oil pan is loaded against the heated fuser roll 16 by a spring action mounting (not shown) as details of the mounting form no part of the present invention. Applicator roll 52 is used to convey a thin film of oil to the bottom face 55 of the wicking assembly as the applicator roll is rotated in the direction shown by the arrow. Desirably, the applicator roll 52 is driven by an oil dispensing motor 58 which is energized during the fusing operation for a period depending upon the number of copies being produced.

In accordance with the present invention, the wicking assembly 48 includes two different layers of wicking materials. One layer 62 is made of Teflon which contacts the surface of the heated fuser roll 16. Another layer 64 is made of Nomex which has its underside 55 in contact with the applicator roll 52. Both Teflon and Nomex are trademarks of DuPont Company, of Wilmington, Delaware. Layers 62 and 64 are assembled in overlapping relationship and their ends are clamped between plates 66 and 68 which are secured by any suitable means such as screws 70 as best shown in FIG. 3. Spring metal brackets 72 and 74 serve to provide support and conforming characteristics to the fuser roll for the wicking assembly. Tab portions 75 and 76 are provided for facilitating the handling of the wicking assembly for insertion and removal of the assembly into and out of the fusing system. Teflon is used as the upper layer because it has high lubricating characteristics as well as thermal stability at elevated temperatures ranging up to 400.degree. F and above. Nomex is used as the lower layer because of the thermal stability at elevated temperatures up to 400.degree. F and above and due to its high oil retention characteristics. Also both Teflon and Nomex are non-combustible materials.

The oil applicator apparatus utilizes an auxiliary wick 75 which may be made out of any suitable wicking material. Suitable materials are Nomex and Dacron. Preferably the auxiliary wick material is able to withstand high temperatures, as high as 400.degree. F. The auxiliary wick is arranged so that it is touching the applicator roll in close proximity to the wicking assembly and is secured in place by a support member 77 and a holding member 80 located adjacent to the bottom of the oil pan. The auxiliary wick 75 serves to bring the oil up to the applicator roll to a level such that upon rotation of the roll during one-half of one copy time the oil contacts the wick assembly. It has been found that auxiliary wick is useful especially during a short run operation when rotation of the applicator roll is small and the oil must be supplied to the wick assembly to equalize the differential supplied during a much longer run. Thus, in the case of a long run, the oil will be primarily supplied by the applicator roll due to a lag in the capillary action of the auxiliary wick.

In order to enhance the oil retention characteristics of wicking assembly 48 and also enable trouble free application of oil to the surface of the Nomex layer 64, the lower surface 55 is flame treated to burn all the loose fibers or fuzz to render a substantially smooth membrane-like surface free of loose fibers as best shown in FIG. 4 b. Burning should be sufficient to form the surface fibers into a porous membrane finished pattern. It has been found that removal of these fibers from the Nomex layer has enabled a high oil retention of the layer while insuring that the applicator roll does not stall which is normally the case where the layer is dry which is caused by oil leaking through loose fiber material or fuzz. Since the applicator roll motor is desirably of a low power unit, it is essential that there be no binding between the Nomex layer and the applicator roll causing the motor to stall. It has been observed that with the fuzz and/or loose fibers removed that motor stalling is prevented and high oil retention qualities retained.

The effect of the membrane-like substantially smooth fuzz-free surface acts in the same manner as a one-way valve. More specifically, the oil film from the applicator roll surface is transmitted through the flame treated surface on the bottom of the wicking assembly by capillary action forces against gravity. Once the oil is in the body of the wick it cannot return to the applicator roll because the membrane-like fuzz free surface prevents oil droplets from forming on its surface. In the case of conventional wicks (FIG. 4 a) loose fiber materials or fuzz serve as a basis for oil droplet formation. Since the weight of the oil droplet is greater than the wetting forces of an oil droplet on the fiber material the oil droplet would ordinarily drain off. In the case of the present invention the draining properties of the wick surface are minimized by the unique wick structure described above. In this manner, the oil retention gradient normally established by the thickness of the wick layer is minimized because the amount of oil retained throughout the layer is uniform irrespective of its thickness.

In the past it has been observed that in heated pressure roll fusing systems that uniform application of oil to the heated fuser roll was difficult to achieve because of an excessive lag in the capillary action from the bottom to the top of the wicking assembly. By the present invention, the lag is minimized due to the improved oil retaining properties of the substantially smooth membrane-like fuzz free surface contacting the oil applicator roll.

While the instant invention as to its object and advantages has been described as being carried in a specific embodiment thereof it is not intended to be limited thereby but it is intended to be covered broadly within the scope of the appended claims.

Claims

What is claimed is:

1. In a heated pressure roll fusing system for fusing toner images of electrostatic copying machine and in which a heated fuser roll disposed below the copy path is coated with an oil to prevent toner offset, an improved wicking apparatus comprising

an applicator roll for dispensing oil onto the lower surface of a wick assembly when copies are being processed,

a wick assembly positioned between the applicator roll and a heated fuser roll including a top layer and a lower layer,

said lower layer having the lower surface thereof flame treated to establish a substantially smooth membrane-like fuzz free area to retain oil over a sufficiently long period when the dispensing roll is inoperative.

2. Apparatus according to claim 1 wherein said layers are clamped together by retaining members to form a unitary assembly.

3. Apparatus according to claim 2 wherein the unitary assembly has tab members extending therefrom to facilitate handling thereof.

4. Apparatus according to claim 2 wherein said top layer is made of Teflon and said lower layer is made of Nomex.