Electric heating – Heating devices – Combined with diverse-type art device
Reexamination Certificate
2001-12-04
2002-11-26
Pelham, Joseph (Department: 3742)
Electric heating
Heating devices
Combined with diverse-type art device
C219S469000, C399S333000
Reexamination Certificate
active
06486441
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to members useful in fusing apparatus for heat-fixing a heat-softenable toner material to a substrate. More particularly, the invention relates to a heater member useful for transferring heat to a fuser member in said fusing apparatus, wherein the heater member is externally heated and has an overcoat layer thereon comprised of a cured fluorocarbon thermoplastic copolymer composition described hereinafter.
BACKGROUND OF THE INVENTION
Heat-softenable toners are widely used in imaging methods such as electrostatography, wherein electrically charged toner particles are deposited imagewise on a dielectric or photoconductive element bearing an electrostatic latent image. Most often in such methods, the toner is then transferred to a surface of another substrate, such as a receiver sheet comprising paper or a transparent film, where it is then fixed in place to yield a final desired toner image.
When heat-softenable toners, comprising for example thermoplastic polymeric binders, are employed, 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, and then allowing or causing the toner to cool.
One such fusing method comprises passing the toner-bearing receiver sheet through a nip formed by a pair of opposing members, typically in the form of cylindrical rollers, wherein at least one of the members (usually referred to as a fuser member) is heated and contacts the toner-bearing surface of the receiver sheet in order to heat and soften the toner. The other member (usually referred to as a pressure member) serves to press the receiver sheet into contact with the fuser member. In some other fusing methods, the configuration is varied and the “fuser member” or “pressure member” can take the form of a flat plate or belt. The description herein, while directed to a generally cylindrical fuser roller in combination with a generally cylindrical pressure roller, should not be construed as limited to such a roller configuration.
The fuser member typically comprises a rigid core covered with a resilient material, which can be referred to as a base cushion. The resilient base cushion and the amount of pressure exerted by the pressure member serve to establish an area of contact for the fuser member with the toner-bearing surface of the receiver sheet as it passes through the nip formed by contact of the fuser member with the pressure member. The size of this area of contact helps 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 (often referred to as “storage modulus”) and stability thereof, of the base cushion are important factors in establishing and maintaining the desired area of contact for fusing.
In some prior fusing systems, it has been 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, in order to give the pressure roll a subtle “bow tie” or “hourglass” shape. This causes 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 (alternatively referred to as “creep”) of the base cushion of the fuser member is a contributor to this problem.
While some fuser members are internally heated by placing a quartz lamp or other type of heat source internally within the fuser core, fuser members can also be externally heated by use of one or more external heater members, i.e., rollers, belts, plates or the like, placed in an opposed, contacting relationship with the fuser member. External heater members for fuser members can themselves be internally heated by use of a quartz lamp or other heat source. Apparatus for externally heating a heater member by a radiant heat source are disclosed in copending U.S. patent application Ser. Nos. 09/500,826 and 09/501,459 filed on Feb. 10, 2000, the teachings of which are incorporated herein by reference.
Heater members which are internally heated and used commercially have either an anodized surface or a very thin fluoropolymer resin, i.e., Teflon® fluorocarbon available from E.I. DuPont deNemours and Co. of Wilmington, Del., coating thereon, both of which have very low thermal resistance due to the relative thinness of such coatings. However, such heater members, when used in an opposed and contacting relationship adjacent to a fuser member, are not resilient or conformable, and therefore, do not allow for a relatively large area of contact (referred to as a “nip width” hereinafter) with the fuser member when a nip is formed by contact of the heater member with the fuser member. Further, such coatings also have little or no ability to store heat. This arrangement results in inefficient heat transfer and undesirable heat loss.
A greater area of contact between the heater member and fuser member would allow for greater and more efficient heat transfer to the surface of the fuser member. To achieve a longer nip width, a conformable elastomer layer could be applied to the heater member. For internally heated heater members, however, a disadvantage with the use of such an elastomer layer is that it could create a time delay for heat energy to transfer to the surface of the heater member due to an increase in thermal resistance. A time delay would increase thermal response time when altering the fuser member surface temperature for any process reason. This increase in thermal response time could preclude the use of image gloss control by making changes in the fuser member temperature, or gloss and fusion tuning for various receiver types. Various receiver types, such as papers or films, have different thermal properties that can affect gloss and fusion quality. Having the ability to change the fuser member surface temperature rapidly within the time between consecutive receiver sheets allows fusion and gloss to be tuned to receivers within a document run that are of different types without reducing the productivity of the entire electrophotographic system. The foregoing ability to control gloss is particularly important for color electrophotographic systems.
U.S. patent application Ser. No. 09/501,459 previously mentioned herein, discloses a heater member which is externally heated and comprised of a core; a fluoroelastomer foam layer, such as Viton® fluoroelastomer available from DuPont, overlying the core; and an outer cured poly(perfluoromethylvinylether) layer thereover, such as a Kalreze® polymer also available from DuPont. While this externally heated heater roller is an improvement over prior commercially used internally heated heater rollers, the fluoroelastomer foam layer disclosed therein may not have sufficient mechanical strength in some apparatus designs to withstand stress imposed by what is known in the art as “velocity overdrive”. As a result, the polymeric layers placed over the core could delaminate therefrom, thereby causing premature failure. Further, the poly(perfluoromethylvinylether) material is difficult to dissolve in commonly used solvents, thereby
Boulatnikov Nataly
Chen Jiann Hsing
Ciaschi Andrew
Pavlisko Joseph A.
Kessler Laurence P.
NexPress Solutions LLC
Pelham Joseph
LandOfFree
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