Method and apparatus for fusing color toner images

Abstract: A method and apparatus (70) for fusing color toner images to a substrate (49) such that they exhibit uniform gloss and satisfactory color saturation properties. The substrate carrying color toner images is passed through a heated oven fuser (72), including opposing heater elements (88) and reflectors (86) for fixing the color toner images to the substrate. The substrate with the color images are then passed through a glossing section (74) where a nip (90) formed by a pair of glossing rolls (78,80) acts on the fused images. The glossing rolls (78,80)are operated at approximately the fusing temperature provided in the oven fuser (72).

Description: This invention relates generally to electrophotographic printing and more particularly relates to a method and apparatus for fusing color toner images to a substrate such that they exhibit uniform gloss and satisfactory color saturation properties. In imaging systems commonly used today, a charge retentive surface is typically charged to a uniform potential and thereafter exposed to a light source to thereby selectively discharge the charge retentive surface to form a latent electrostatic image thereon. The latent image may comprise either the discharged portions or the charged portions of the charge retentive surface. The light source may comprise any well known device such as a light lens scanning system or a laser beam. Subsequently, the electrostatic latent image on the charge retentive surface is rendered visible by developing the latent image with developer powder referred to in the art as toner. The most common development systems employ developer which comprises both charged carrier particles and charged toner particles which triboelectrically adhere to the carrier particles. During development, the toner particles are attracted from the carrier particles by the charged pattern of the image areas of the charge retentive surface to form a powder image thereon. This toner image may be subsequently transferred to a support member surface, such as plain paper, to which it may be permanently affixed by heating or by the application of pressure or a combination of both. In order to fix or fuse the toner material onto a support member permanently by heat, it is necessary to elevate the temperature of the toner material to a point at which constituents of the toner material coalesce and become tacky. This action causes the toner to flow to some extent onto the fibers or pores of the 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. One approach to thermal fusing of toner material images onto the surface of a support substrate or member has been to pass the substrate with the unfused toner images thereon between a pair of opposed roller members at least one of which is internally heated. During operation of a fusing system of this 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 heated fuser roll to thereby effect heating of the toner images within the nip. Typical of such fusing devices are two roll systems wherein the fusing roll is coated with an abhesive material, such as a silicone rubber or other low surface energy elastomer, for example, tetrafluoroethylene resin sold by E. I. DuPont De Nemours under the trademark Teflon. To further enhance release, a release agent material such as silicone oil is applied to elastomer coating. Conventional roll fusers are operated such that roll surface temperatures are in the order of 199-218°C (390-425°F). Operation at these temperatures, results in shortened roll life and less reliability due to random failures, such as rubber peeling off the rollers. "Two stage" fusing is known. For example, US-A-3,861,863 discloses a black and white image fuser comprising a first stage backside heater and a second stage soft roll fuser. US-A-3,679,302 discloses first and second stage radiant fusers, and US-A-3,566,076 discloses the combination of radiant and pressure fusing. US-A-4,791,447 discloses a heat and pressure fusing apparatus for fixing color toner images to various types of copy substrates. The apparatus includes three roll members which cooperate to form a pair of nips. All substrates pass through a first nip and a deflector plate directs certain types of substrates through the second nip. Passage of the substrates through the first nip causes the images carried thereon to contact a conformable elastomeric surface while passage through the second nip causes them to contact a relatively rigid surface. Thus, glossy and matte color copies on substrates such as plain paper and high chroma transparencies are suitably produced in a color reproduction apparatus incorporating this fuser. Matte color copies are produced by passing the substrate through only the first nip while glossy color copies and high chroma transparencies are produced by passing the substrates through both nips. In one aspect of the invention, there is provided a method of fusing color toner images to the surface of a substrate including the steps of: using a first color toner image treatment device to subject the substrate surface having color toner images thereon to thermal energy sufficient to effect fusing of said color toner images to said substrate surface; and using a second color toner image treatment device, which includes a pair of rolls, at least one of which has a deformable surface to impart a uniform gloss to said colored toner images, subsequent to the step of subjecting the color toner images on the substrate surface to said thermal energy, by contacting them with said deformable surface, at a nip between said pair of rolls; characterized in that the second color toner image treatment device operates at a temperature approximately that of the first color toner image treatment device. In another aspect of the invention, there is provided apparatus for fusing color toner images to a substrate, said apparatus comprising: a first color toner image treatment device for subjecting a substrate having color toner images formed thereon to thermal energy sufficient to effect fusing of said color toner images to said substrate; and a second color toner image treatment device including a pair of glossing rolls, at least one of which having a deformable surface for imparting uniform gloss to said colored toner images, subsequent to subjecting the color toner images to said thermal energy, by contacting them with said deformable surface at a nip formed between said pair of glossing rolls; characterized in that the second color toner image treatment device operates at a temperature approximately that of the first color toner image treatment device. In the present invention, improved color image fusing and glossing is accomplished by the provision of a heated oven through which substrates carrying color toner images are conveyed for fusing the color toner images. While the color images are adequately fused in the oven they do not exhibit uniform gloss and color saturation properties resulting in color images wherein the appearance is not as robust, from a quality standpoint, as desired. The substrate with the fused color images carried thereby is then moved through a pair of nip forming glossing rolls, at least one of which is heated to a surface temperature approximately equal to the fusing temperature to which the color images were subjected as they were passed through the heated oven. Elevating the temperatures of the color toner images and substrate to less than the required fusing temperature of the toner would result in cold toner offset to the glossing roll or to both rolls in the case of duplex images. The aforementioned surface temperature is approximately 149°C (300°F). At this temperature, the fuser rollers are not subjected to the normal operating temperature of of a conventional heated roll fuser which is about 199°C (390°F). The properties, for example, soft, deformable outer surface, of the roll surface contacting the color toner are such that uniform gloss is imparted to the images and substrate self-stripping is enabled. Operating the heated rolls at the substantially lower temperature results in longer life and reliability. Thus, random failures such as rubber peeling off the roll are minimized. The requirement of the lower glossing temperature enables the use of glossing rollers which are significantly smaller in diameter than conventional fuser rolls resulting in cost savings. Variable gloss selection on demand is selectively effected by varying the operating temperature of the oven fuser thereby varying the amount of heat imparted to the substrate and color toner images carried thereby. The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic illustration of a color toner treatment apparatus according to the invention; and Figure 2 is a schematic illustration of a imaging apparatus incorporating the invention. Figure 1 schematically depicts the various components of an illustrative electrophotographic printing machine incorporating the present invention therein. It will become evident from the following discussion that the apparatus of the present invention is equally well suited for use in a wide variety of printing machines, and is not necessarily limited in its application to the particular electrophotographic printing machine shown herein. Inasmuch as the art of electrophotographic printing is well known, the various processing stations employed in the Figure 1 printing machine is shown schematically and their operation described briefly with reference thereto. In Figure 1, the electrophotographic printing machine employs a photoconductive belt 10. Preferably, the photoconductive belt 10 is fabricated from a photoconductive material coated on a grounding layer, which, in turn, is coated on an anti-curl backing layer. The photoreceptor belt 10 moves in the direction of arrow 12 to advance successive portions of the belt 10 sequentially through the various processing stations disposed about the path of movement thereof. The belt 10 is entrained about a stripping roller 14, a tension roller 20, and a drive roller 16. Drive roller 16 is coupled to a motor 41 by suitable means such as a belt drive. The belt 10 is maintained in tension by a pair of springs (not shown) resiliently urging tension roller 20 against the belt 10 with the desired spring force. Both stripping roller 14 and tension roller 20 are rotatably mounted. These rollers are idlers which rotate freely as the belt 10 moves in the direction of arrow 12. Initially, a portion of the belt 10 passes through charging station A. At charging station A, a corona device 22 charges a portion of the photoreceptor belt 10 to a relatively high, substantially uniform potential, either positive or negative. At exposure station B, a raster output scanner (ROS) 30 is provided to imagewise discharge the photoreceptor in accordance with stored electronic information. The ROS is preferably a three level device capable of forming a tri-level image comprising two image levels and a background level intermediate the two image levels. Thereafter, the belt 10 advances the electrostatic latent image to development station C. At development station C, either developer housing 34 or 36 is brought into contact with the belt 10 for the purpose of developing the electrostatic latent image. Housings 34 and 36 may be moved into and out of developing position with corresponding cams 38 and 40, which are selectively driven by motor 41. Each developer housing 34 and 36 supports a developing system such as magnetic brush rolls 42 and 44, which provides a rotating magnetic member to advance developer mix (i.e. carrier beads and toner) into contact with the electrostatic latent image. The electrostatic latent image attracts toner particles from the carrier beads, thereby forming toner powder images on the photoreceptor belt 10. If two colors of developer material are not required, either one of the two developer housings may be inactivated by camming it away from the belt 10. The photoreceptor belt 10 then advances the developed latent image to transfer station D. At transfer station D, a sheet of support material 49, such as paper copy sheets, is advanced into contact with the developed latent images on the belt 10. A corona generating device 46 deposits electrostatic charges of a suitable polarity onto the backside of a copy sheet so that the toner powder images are attracted from the photoreceptor belt 10 to the sheet. After transfer, a corona generator 48 sprays electrostatic charges of a suitable polarity on the copy for assisting stripping of the copy sheet from the belt adjacent stripping roller 14. Sheets or substrates of image support material 49 are advanced to transfer station D from a supply tray 50. Sheets are fed from tray 50 with sheet feeder 52, and advanced into contact with the photoreceptor belt 10 in the transfer station D. After transfer, the sheet continues to move in the direction of arrow 60 to a color image treatment station E. The station E includes a color image treatment device 70, which permanently affixes the transferred color toner images to the sheets while imparting gloss to the images for producing enhanced color images. Preferably, device 70 includes a fusing section 72 and a glossing section 74. The fusing section 72 comprises a heated oven fuser 76 while the glossing section comprises a pair of glossing rolls 78 and 80. The fusing and glossing sections may form an integral structure or may be independent of each other. Copy substrates 49 move from the photoreceptor belt 10 to the heated oven fuser 76. The oven fuser comprises an outer housing 82 (see Figure 2) and an inner chamber delineated by reflector members 86. A plurality of heater elements 88 are operatively supported in the space between the members 86. The oven is operated at a temperature adequate to completely fuse the color toner images. Conventional color toners are acceptably fused in the oven at about 149°C (300°F). However, the images do not exhibit uniform gloss properties. From the oven, the substrate continues into and through a nip 90 formed between the glossing rolls 78 and 80. By way of example, the glossing rolls 78 and 80 are disclosed as simplex image glossing rolls, in that, a deformable layer 92 carried by a rigid core 94 of roll 80 is deformed by the roll 78. The unheated roll 78 has a thinner layer 96 of elastomeric material carried by a rigid core member 98. The roll 80 is provided with a heating structure 91 disposed internally for elevating the surface temperature of the roll 80. The rolls are also heated by virtue of their contact with the heated substrate 49 which is heated while passing through the oven fuser 76. Together, the heat from the substrate and a relative small amount of heat from the heating structure 91 effect elevation of the surface temperature of roll 80 to approximately the temperature at which the oven fuser is operated, that is, about 149°C (300°F). An operating temperature of the glossing rolls above the temperature of the oven fuser is not required because the color toner images are fused before they reach the glossing rolls. The sole purpose of the glossing rolls is to produce a uniform gloss in the color images. Thus, the glossing rolls will exhibit longer life and reliability compared to rolls normally employed in the image fixing process which must be operated at a substantially higher temperature than the 149°C (300 °F) at which the glossing rolls are operated. Disclosed in Figure 2 is a modified embodiment 99 of the image treatment station 70 of Figure 1. The embodiment 99 differs from the station 70, in that, a pair of glossing rolls 100 and 101 both have rigid cores 106 and 107 with outer deformable layers 102 and 103, respectively, fabricated, for example, from silicone rubber. The rolls 100 and 101 form a symmetrical nip 104 therebetween for fusing duplex color toner images. In this embodiment, the rolls are provided with internal heat lamps 91. A Release Agent Management (RAM) system, not shown, may be employed for applying a release agent material to one or both of the glossing rolls. Referring to Figure 1, residual particles, remaining on the photoreceptor belt 10 after each copy is made, may be removed at cleaning station F. The cleaning apparatus comprises a brush 106. Removed residual particles may be stored for disposal in a conventional manner. A machine controller 105, preferably a known programmable controller or combination of controllers, is provided for controlling the machine steps and functions described above. The controller 105 is responsive to a variety of conventional sensing devices, not shown, to enhance control of the machine, and also provides connection of diagnostic operations to a user interface (not shown) where required. The motor 41 for driving the belt drive roller 16 is also controlled by the controller 105.

Claims: A method of fusing color toner images to the surface of a substrate (49) including the steps of: using a first color toner image treatment device (72) to subject the substrate surface having color toner images thereon to thermal energy sufficient to effect fusing of said color toner images to said substrate surface; and using a second color toner image treatment device (74), which includes a pair of rolls (78, 80; 100, 101), at least one of which has a deformable surface (92; 102, 103) to impart a uniform gloss to said colored toner images, subsequent to the step of subjecting the color toner images on the substrate surface to said thermal energy, by contacting them with said deformable surface, at a nip (90; 104) between said pair of rolls (78, 80; 100, 101); characterized in that the second color toner image treatment device (74) operates at a temperature approximately that of the first color toner image treatment device (72). Apparatus (70; 99) for fusing color toner images to a substrate (49), said apparatus comprising: a first color toner image treatment device (72) for subjecting a substrate (49) having color toner images formed thereon to thermal energy sufficient to effect fusing of said color toner images to said substrate (49); and a second color toner image treatment device (74) including a pair of glossing rolls (78; 80; 100, 101), at least one of which having a deformable surface (92; 102, 103) for imparting uniform gloss to said colored toner images, subsequent to subjecting the color toner images to said thermal energy, by contacting them with said deformable surface at a nip (90; 104) formed between said pair of glossing rolls (78, 80; 100, 101); characterized in that the second color toner image treatment device (74) operates at a temperature approximately that of the first color toner image treatment device (72). Apparatus according to claim 2, wherein said first color toner image treatment device (72) comprises a heated oven (76) operating at approximately 149°C (300°F); and wherein said deformable surface (92) comprises a heating structure (91) for heating thereof. Apparatus according to claims 2 or 3, wherein the deformable outer layer (92) of one of said pair of rolls (78, 80) is deformed by the other roll of said pair of rolls. Apparatus according to claim 3 or 4, wherein at least one of said pair of rolls (78, 80; 100, 101) has a rigid core (94; 106, 107) and a deformable outer layer (92; 102, 103) comprising silicone rubber. Apparatus according to claim 5, wherein each of said pair of rolls (100, 101) comprises a rigid core (106, 107) and an outer layer (102, 103) of deformable material. Apparatus according to claim 6, wherein said pair of rolls (100, 101) form a symmetrical nip (104). Apparatus according to claim 6 or 7, wherein the thickness of said outer layers (102, 103) on said pair of rolls (100, 101) is equal.

Inventors: MOSER RABIN, MOSER, RABIN
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1996
Main classification: G03G15
IPC codes: G03G15