Electrophotography – Image formation – Fixing
Reexamination Certificate
2000-02-10
2001-10-16
Chen, Sophia S. (Department: 2852)
Electrophotography
Image formation
Fixing
C219S216000, C219S469000, C430S090000
Reexamination Certificate
active
06304740
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a fuser assembly for heat fixing a heat-softenable toner material to a substrate, and, more particularly, to externally heated fuser members.
BACKGROUND OF THE INVENTION
Heat-softenable toner materials are widely used in imaging processes, such as electrostatography, wherein electrically charged toner is deposited imagewise onto a dielectric or photoconductive element bearing an electrostatic latent image. Often in such processes, the toner is transferred to a surface of another substrate, such as a receiver sheet of paper or a transparent film, for example, where it is then fixed in place to yield the final desired toner image. When heat-softenable toners employing thermoplastic polymeric binders are used, the usual method of fixing the toner in place involves applying heat to the toner once it is on the receiver sheet surface to soften it, so that it bonds to the receiver sheet, and then allowing or causing the toner to cool.
One such well-known fusing system passes the toner-bearing receiver sheet through the nip formed by a pair of opposing rolls, at least one of which, usually referred to as a fuser roll, is heated. The fuser roll contacts the toner-bearing surface of the receiver sheet in order to heat and soften the toner. The other roll, usually referred to as a pressure roll, presses the receiver sheet into contact with the fuser roll. In other fusing systems, the configuration is varied with the fuser roll or pressure roll taking the form of a flat plate or belt. As used herein, the term fuser member is used to denote both cylindrical fuser rolls, plates and belts, and the term pressure member is used to denote both cylindrical fuser rolls, plates and belts.
A fuser member typically has a rigid core covered with a resilient material, which is referred to herein as a base cushion layer. The resilient base cushion layer and the amount of pressure exerted by the pressure member serve to establish the area of contact of the fuser member with the toner-bearing surface of the receiver sheet as it passes through the nip of the fuser member and pressure members. The size of this area of contact helps to establish the length of time that any given portion of the toner image will be in contact with and heated by the fuser member. The degree of hardness of the base cushion layer, often referred to as storage modulus, and stability of the base cushion layer are important factors in establishing and maintaining the desired area of contact.
In some previous fusing systems, it has been found advantageous to vary the pressure exerted by the pressure member against the receiver sheet and fuser member. This variation in pressure can be provided, for example in a fusing system having a pressure roll and a fuser roll, by slightly modifying the shape of the pressure roll. The variance of pressure, in the form of a gradient of pressure that changes along the direction through the nip that is parallel to the axes of the rolls, can be established, for example, by continuously varying the overall diameter of the pressure roll along the direction of its axis such that the diameter is smallest at the midpoint of the axis and largest at the ends of the axis giving the pressure roll a sort of bowtie or hourglass shape. This will cause the pair of rolls to exert more pressure on the receiver sheet in the nip in the areas near the ends of the rolls than in the area about the midpoint of the rolls. This gradient of pressure helps to prevent wrinkles and cockle in the receiver sheet as it passes through the nip. Over time, however, the fuser roll begins to permanently deform to conform to the shape of the pressure roll, and the gradient of pressure is reduced or lost, along with its attendant benefits. It has been found that permanent deformation, also known as creep, of the base cushion layer of the fuser member is the greatest contributor to this problem.
Some external heater rollers for nip forming roller fusers are internally heated. These rollers usually have either an anodized surface or a Teflon surface with very low thermal resistance because of the thinness of these coatings. The thin nature of these coatings does not allow a large contact length when a nip is formed with a fuser roller. A longer nip would allow more heating time for the fusing surface. To achieve a longer nip, an elastomer layer, thicker than the anodized or Teflon coatings, can be applied to the heater roller, but that creates a time delay for the heat energy to reach the heater roller surface because of an increase in thermal resistance due to increased thickness of the elastomer surface. A time delay increases thermal response time when altering the fuser roller temperature for any process reason. This increase in thermal response time can preclude the use of gloss control through fuser roller temperature changes, or gloss and fusion tuning for various receiver types. Various receiver types have different thermal properties that affect gloss and fusion quality. The ability to change the fuser roller surface temperature within the time between consecutive receivers allows fusion and glossing to be tuned to receivers within a document run that are of different types without reducing the productivity of the entire electrostatographic system.
SUMMARY OF THE INVENTION
The present invention is directed to overcoming one or more of the problems set forth above. According to one aspect of the invention, a fusing apparatus for fusing toner images on a receiver medium comprises a fuser member and a pressure member that is positioned adjacent the fuser member forming a nip therebetween to receive the receiver medium. The pressure member controllably exerts pressure on the fuser member and the receiver medium. A first heater member is positioned adjacent the fuser member and external thereto with a surface of the heater member contacting a surface of the fuser member to transfer heat to the fuser member. The fuser member heats the toner image on the receiver medium thereby fusing the toner image to the receiver medium. A radiant heat assembly is positioned externally of the heater member for controllably heating the contact surface of the first heater member.
According to another aspect of the invention, a method for electrostatographically producing fused toner images on a substrate comprises the steps of electrostatically forming image patterns on an image bearing member, developing the image patterns with fusible toner particles and forming a toner image, transferring the toner image to the substrate, feeding the substrate into a nip formed between a fuser member and a pressure member, and externally heating an outer surface of a heater member. The method also includes using the heater member to externally heat the fuser member, and controllably transmitting heat and pressure to the substrate through the heater member and pressure member at a predetermined fuser roller surface temperature set point that achieves a 0° F. to 200° F. increase in fuser member surface temperature between consecutive sheets thereby fusing the toner images onto the substrate at a desired toner surface roughness.
The present invention provides a fuser roller that overcomes the limitations and disadvantages associated with cored, coated rollers. It is particularly suitable for external heating, and for use in an axially unsupported configuration in a fusing apparatus. The fusing apparatus for fusing toner images to a receiver or copy sheet, through the application of heat and pressure, includes a fuser roller that is comprised entirely of a cylindrical inner portion which is made of a first elastomeric material, and of an annular outer portion which is made of a second elastomeric material overlaying the inner portion.
Direct heating of the heater roller surface allows surface temperatures to be changed to alter a fusing process within consecutive sheets. A method to do this uses an externally heated external heater roller to impart thermal energy to a fuser roller through conduction or d
Chen Jiann-Hsing
Ciaschi Andrew
Hryhorenko Socrates
Mills Borden H.
Chen Sophia S.
Kessler Lawrence P.
Nexpress Solutions LLC
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