Heat Fixing Apparatus For Fusible Material

Abstract

A fixing system for fixing fusible material such as electroscopic particles upon support material. The system includes at least one fuser member in the form of an endless belt in pressure contact with another fuser member and between which the support material is transported. The fusing belt member is provided with a heat barrier blanket and is coated a release agent that will prevent "offset" of the particles being fused.

Parent Case Text

This is a continuation of application Ser. No. 218,570, filed Jan. 17, 1972, now abandoned which, in turn, is a continuation of Ser. No. 859,327, filed Sept. 19, 1969 now abandoned.

Description

This invention relates to heat fixing systems, and particularly, to improvements in fuser apparatus for particulate material such as resinous toner particles, that are used in electrostatic automatic copiers/reproducers capable of high speed operation.

It has been recognized that one of the preferred methods of applying heat for fusing the powder image to paper is to bring the powder image into direct contact with a hot surface, such as a heated roller. However, in order to produce fused images effectively and efficiently, it has been necessary to utilize relatively large and structurally dense fuser rollers which consume large amounts of heat in order to overcome heat losses effected by the roller supporting structures. Heater elements for these rollers fusers are generally supported interiorly of one of the rollers which has a high temperature gradient needing a relatively large power supply to overcome heat losses as well as for fusing purposes. With the requirement for high fuser element temperatures comes the need to provide elaborate temperature controls to insure against over-temperature, equipment protection. For some application in offset prevention, a tetrafluorethylene resin based material, such as, Teflon is utilized. This material has the physical characteristic of being substantially adhesive to some tackified xerographic developing materials. However, its release or adhesive characteristic to some developing material, while in a tackified condition is not completely adequate for many of the more desirable developing particles at their fusing temperatures. To aid in offset prevention, a fusing roller coated with Teflon material is usually coated with a thin film of silicone oil by means of an oil applicator wick. This arrangement requires an oil reservoir and wick supply and the cleaning thereof. There are other heat fixing devices not particularly suited for high speed copying-duplication, such as, coiled radiant element heaters with reflectors. These radiant element heaters with reflectors have the disadvantage of dissipating a large quantity of heat into the machine enclosure in which they are used, heat transfer to the powder image is inefficient, and they present a safety hazard because of the exposed heater element.

It is, therefore, the principal object of this invention to improve the construction of a direct contact fusing device for toner images which will require a minimum of heat to accomplish the rapid fusing of toner images.

This and other objects of the invention are attained by means of a direct contact fusing device in which the toner image is fused by forwarding the sheet or web of paper bearing toner images upon a fuser member in the form of a belt which is heated exteriorly and being provided with a thin blanket of an insulating material, such as silicone rubber and a coating of room temperature vulcanizing silicone rubber with better release properties as an outer coating of the roller.

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

FIG. 1 illustrates schematically a xerographic reproducing apparatus adapted for high speed automatic operation, and incorporating a heat fuser constructed in accordance with the invention;

FIG. 2 is a schematic view in section of one embodiment of a fuser apparatus;

FIG. 3 is a schematic view of another embodiment of a fuser assembly;

FIG. 4 is a schematic view of a third embodiment of a fuser assembly; and

FIG. 5 is an enlarged fragmentary sectional view of a pair of fusing belts utilized in the fuser apparatus.

For a general understanding of the illustrated copier/reproduction machine, in which the invention may be incorporated, reference is had to FIG. 1 in which the various system components for the machine are schematically illustrated. As in all electrostatic systems such as a xerographic machine of the type 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 by a fusing device whereby the powder image is caused permanently to adhere to the support surface.

In the illustrated machine, an original D to be copied is placed upon a transparent support platen P fixedly arranged in an illumination assembly generally indicated by the reference numeral 10, arranged at the left end of the machine. The image rays are projected by means of an optical system for exposing the photosensitive surface of a xerographic plate in the form of a flexible photoconductive belt arranged on a belt assembly generally indicated by the reference numeral 11.

The photoconductive belt assembly 11 is slidably mounted upon the frame of the machine and is adapted to drive the selenium belt 12 in the direction of the arrow at a constant rate. During this movement of the belt, the light image of the original on the platen is flashed upon the xerographic surface of the belt. The flash exposure of the belt surface to the light image discharges the photoconductive layer in the areas struck by light, whereby there remains on the belt a latent electrostatic image in image configuration corresponding to the light image projected from the original on the supporting platen. As the belt surface continues its movement, the electrostatic image passes through a developing station B in which there is positioned a developer assembly generally indicated by the reference numeral 14. The developer assembly 14 deposits developing material to the upper part of the belt assembly 11 whereat the material is directed to cascade down over the upwardly moving inclined selenium belt 12 in order to provide development of the electrostatic image. As the developing material is cascaded over the xerographic plate, toner particles in the development material are deposited on the belt surface to form powder images.

The developer electrostatic image is transported by the belt to a transfer station C 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 generally indicated at 16 adapted to transport sheets of paper from a paper handling mechanism generally indicated by the reference numeral 18 to the developed image on the belt at the station C.

After the sheet is stripped from the belt 12, 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. After fusing, the finished copy is discharged from the apparatus by a belt conveyor 21 to a suitable point for collection externally of the apparatus.

Suitable drive means may be arranged to drive the selenium belt 12 in conjunction with timed flash exposure of an original to be copied, to effect conveying and cascade of toner material, to separate, and feed sheets of paper and to transport the same across the transfer station C and to convey the sheet of paper through the fuser assembly in timed sequence to produce copies of the original.

It is believed that the foregoing description is sufficient for the purposes of this application to show the general operation of an electrostatic copier using an illumination system constructed in accordance with the invention. For further details concerning the specific construction of the electrostatic copier, reference is made to copending application Ser. No. 731,934 filed May 24, 1968 in the name of Hewes et al, now U.S. Pat. No. 3,661,452, issued May 9, 1972.

As shown in FIGS. 2 to 4, the fuser apparatus 20 includes an internal heated, oven enclosure or housing through which a sheet or web of support material, indicated by the reference letter S, is adapted to be conveyed during a fusing operation. In FIG. 2, the support material S with its lower surface carrying toner particles in image configuration is projected through an entrance slot 22 formed on one side of the housing of fuser apparatus and, out of an exit slot 23 formed in an opposite wall of the housing. In passing through the apparatus housing which comprises insulated walls, the support material is conveyed by an endless belt 25 supported for movement on and by a pair of rollers 26, 27 arranged with their axis in parallel.

Positioned above the upper run of the belt 25 is a roller 28 arranged for rotation about an axis parallel to the axes of the rollers 26, 27. The roller 28 may be supported for rotation in such a manner as to contact the adjacent surface of the belt 25 so that there is a slight depression in the upper run of the belt. All of the shafts for the rollers 26, 27 and 28 may be suitably journaled and connected by driving devices such as timing belts or chains to a suitable drive system to effect continuous movement of the belt in a direction indicated by the arrow to thereby effect movement of the support material through the housing for the fuser apparatus.

Located between the upper and lower runs of the belt 25 is a heater element 30 which may be in the form of a strip or resistance heater element directed to radiate heat throughout the entire enclosure of the fuser housing and to the belt 25. By being heated in this manner, the belt 25 is, in effect, a fusing member adapted to retain heat and applying it to the under surface of the material S which carries the toner particles in image configuration. Similarly a heater 38 is positioned between the upper roller runs of the belt 34 and directed to heat the lower run thereof. With this arrangement the support material S may carry toner images to be fused on both sides thereof for simultaneous fusing by the apparatus illustrated in FIG. 3.

In the embodiment of FIG. 4, only one belt, illustrated by reference numeral 40, is shown within the housing for the fuser apparatus. The belt is directed for movement by and supported on two rollers 41, 42 arranged in the housing with their axes in parallel. The upper run of the belt 40 is maintained in slight pressure engagement with a fixed wall 43 made of insulating material with its belt contacting surface somewhat polished in order to minimize wear upon the belt 40. The material S is transported through the fuser apparatus by means of the frictional engagement of the upper run of the belt 40. With the surface 43 being polished, the friction between the surface and a sheet of paper being driven thereacross will be minimal thereby permitting the movement of the support material with relative ease. A heater 44 is positioned between the upper and lower runs of the belt 40 and heat is directed to the upper run to effect fusing of the image on the support material thereon.

The belts 25, 31, 34 and 40 are constructed of the same material and, for all practical purposes, are identical. In FIG. 5 a portion of co-acting rollers 33, 36 from the embodiment of FIG. 3 together with the corresponding fuser belts 31, 34 are shown on an enlarged scale. Since all of the belts are identical, only the belts 31, 34 will be described and discussed in detail with reference to FIG. 5.

Each of the belts 31, 34 comprises a heat insulating sheet or blanket 50 made of material such as silicone rubber which possesses some resiliency while exhibiting tensil strength of the sufficient magnitude to permit its use as a conveying member. For insuring that heat will be conducted to the toner particles to-be-fused, the sheet 50 should be relatively thin, for example, approximately 0.030 inches. Each of the rollers 33, 36 and all of the other rollers illustrated in FIGS. 2, 3 and 4 are preferably made of heat resistant, heat insulating material and are secured to their respective supporting shafts by way of insulating caps or supports. Any other high temperature electrical and thermal insulation material may be utilized for the sheet 50, such as glass fibers or other ceramic forms which can be made with sufficient tensil strength and flexibility, as well as high temperature resisting foams or sealed elastomeric belts which can be made highly pliable.

The sheet 50, in turn, is coated with a thin coating 51 of a room temperature vulcanizing compound, such as the Dow Corning Release Agent 236, produced by the Dow Corning Company. Since this material, as such, is highly reflective it is preferred that it be mixed by approximately 5 percent by weight with the Dow Corning RTV 735 Sealant Adhesive which diminishes the reflective quality of the basic material without effecting the release quality thereof and thereby greatly enhancing the heat retainability of the coating 51 with the sheet 50. Diminishing the reflective quality can be accomplished also by mixing carbon black or dyes with the release agent. The coating 51 serves as a release agent for the resinous toner particles that are brought into contact with the coating during fusing operation and, the sheet 50 serves as a heat barrier relative to the supporting structure for the rollers 33, 36.

In the embodiment of FIG. 2, the periphery of roller 28, which contacts the side of the support material S that does not carry the toner particles to-be-fused, may be coated with an insulating material such as Teflon in order to minimize heat losses through the supporting shaft and structure for this roller.

For each of the three embodiments, the distance between the supporting rollers for each of the belts 25, 31, 34 and 40 and the lengths of the respective belts may be chosen in accordance with necessary or desirable fusing results. For instance, the distance between the rollers 26 and 27 may be shortened in the event that the rate of movement of the support material S through the electrostatic copying or duplicating machine utilizing the fuser apparatus 20 is relatively slow. On the other hand, for electrostatic duplicating machine arrangements capable of high speed reproduction wherein the speed of movement for the support material is relatively fast, it may be desirable to extend the distance between the rollers 26, 27 in order to compensate for the speed of movement of support material through the fuser apparatus.

In operation a sheet or web of support material such as paper is directed into the nip between the belt 25 and the roller 28 for the embodiment of FIG. 2; the belts 31 and 34 in the embodiment of FIG. 3 and; the belt 40 and the adjacent surface 43 in a manner wherein the toner image to be fused is on the lower surface of the horizontally moving support material. Heat circulating within the fuser apparatus and that which is radiated directly from the respective heaters is applied to the adjacent surface of the sheet 50 for each of the belts illustrated.

The sheets 50, being made of silicone rubber, or an equivalent thereof, serves to some degree as a heat barrier to heat applied thereto thereby minimizing the heat that would otherwise be conducted through the supporting rollers for the corresponding belts. The thickness of any of the belts 25, 21, 34 and 40 in the order of 0.030 of an inch is small enough that heat can be conducted through the belts with heater elements located on one side of a belt run and a toner image located on the other side. However once out of the direct influence of the heater elements, the heater insulating characteristics of the belts minimize the transfer of heat to the belt supporting structure. With this arrangement, the response time for the heating elements in the illustrated fusers is relatively fast and, for high speed electrostatic copying or duplicating, the heat that can be applied to a belt will be adequate for any speed of that belt. In addition, the warm up period to bring the belt surfaces to a fusing temperature is relatively short and no stand-by periods are required for maintaining the heating elements energized before or during production runs of an electrostatic machine. Since there is a minimum loss of heat by way of conduction and radiation, the amount of energy necessary to energize the heating elements may be substantially reduced.

The coatings 51 serve to prevent offset of toner particles and, when in a tacky condition during a fusing operation, from adhering to the fusing belt members and being brought into contact with other portions of the support material. The amount of heat that each of the heating elements 30, 37, 38 and 44 for the illustrated embodiments must supply is that which is given up to the toner particles and the support material therefor plus the very small amount of heat that will be lost in being transferred from its point of application to the support material.

While the invention has been described with reference to the structure disclosed herein it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the purpose of improvements or the scope of the following claims.

Claims

What is claimed is:

1. In a heat fusing apparatus for fixing thermoplastic particles carried on a support material in image configuration and having first and second fusing members mounted for movement in endless paths positionable in contact with each other to move the support material therebetween with the image to-be-fixed in contact with the second member, the improvement including

the formation of the second fusing member as an endless flexible belt made of heat insulating material with a run thereof in contact with the image to be fixed,

and means for applying heat to the side of said second member opposite that side which the image to be fixed is placed upon during movement of said member, the heat being of sufficient temperature for tackifying and fixing the image upon the support material.

2. The apparatus of claim 1 wherein the second fusing member includes a flexible sheet of a release agent upon said insulating material for preventing offset of particles during a fixing operation.

3. The apparatus of claim 1 wherein the first fusing member is in the form of an endless flexible belt being arranged so that a run thereof engages a run of the first fusing member, the nip between the runs being adapted to receive the support material.

4. The apparatus of claim 2 wherein the first fusing member is made of heat insulating material adapted to engage the side of the support material that does not bear the image.

5. The apparatus of claim 3 wherein each of the fusing members includes a flexible sheet of release agent and wherein the apparatus includes means to heat the side of the first member opposite that in contact with the second member whereby images on both surfaces of the support material may be fixed when carried by and between said fusing members.

6. A heat fusing apparatus for fixing thermoplastic particles carried on a support material in image configuration, said apparatus including,

a housing,

means for moving the support material in a predetermined, substantially straight path of travel through the housing, heat fixing means mounted for movement along a substantial portion of said predetermined path of travel,

said fixing means being in heat exchange relationship with the image to be fixed during its movement along said path of travel.

7. In a heat fusing apparatus for fixing thermoplastic particles carried on a support material in image configuration and having first and second fusing members mounted for movement in endless paths positionable in contact with each other to move the support material therebetween with the image-to-be-fused in contact with the second member, the improvement wherein:

said second member comprises a belt structurally formed with a thin layer of silicone rubber material, with an unsupported segment of said belt arranged to physically contact the image-to-be-fused, said layer being the sole offset preventing material for said belt,

means for applying heat only to the side of said layer directionally opposite that side upon which the image-to-be-fused is placed during movement of said belt and adjacent said unsupported segment of said belt the heat being of sufficient quantity as to cause tackifying and fixing of the image upon the support material in contact with said layer on the belt.

8. In a heat fusing apparatus for fixing thermoplastic particles carried on a support material in image configuration and having first and second fusing members mounted for movement in endless paths positionable in contact with each other to move the support material therebetween with the image-to-be-fused in contact with the second member, the improvement wherein:

said second member comprises a belt structurally formed with a thin layer of thermally insulating material with an unsupported segment of said belt arranged to physically contact the image-to-be-fused, said material being adapted to conduct heat therethrough during a fusing operation,

means for applying heat only to the side of said layer directionally opposite that side upon which the image-to-be-fused is placed during movement of said belt and adjacent said unsupported segment of said belt the heat being conducted through the material and applied to the image and of sufficient quantity as to cause tackifying and fixing of the image upon the support material in contact with said layer on the belt.

9. In a heat fusing apparatus for fixing thermoplastic particles carried on a support material in image configuration and having first and second fusing members mounted for movement in endless paths positionable in contact with each other to move the support material therebetween with the image-to-be-fused in contact with the second member, the improvement wherein:

said second member comprises a belt structurally formed with a thin layer of offset preventing material, with an unsupported segment of said belt arranged to physically contact the image-to-be-fused, said layer being the sole offset preventing material for said second member,

means for applying heat only to the side of said layer directionally opposite that side upon which the image-to-be-fused is placed during movement of said belt and adjacent said unsupported segment of said belt, the heat being of sufficient quantity as to cause tackifying and fixing of the image upon the support material in contact with said layer on the belt.