Release agent management system for applying release agent material which is solid at room temperature

Release agent material which is solid at room temperature is provided in a sump for application to a heated fuser roll structure. A pressure roll structure contacts the solid release agent material and a source of heat energy serves to elevate the solid release agent material to its operating temperature which is well below the operating temperature of the heated fuser roll. A metering blade contacting the pressure roll structure causes the liquefied release agent material to be metered to the desired thickness.

BACKGROUND OF THE INVENTION 
This invention relates generally to xerographic copying apparatus and, more 
particularly, to a contact fusing system for fixing electroscopic toner 
material to a support member. 
In the process of xerography, a light image of an original to be copied is 
typically recorded in the form of a latent electrostatic image upon a 
photosensitive member with subsequent rendering of the latent image 
visible by the application of electroscopic marking particles, commonly 
referred to as toner. The visual image can be either fixed directly upon 
the photosensitive member or transferred from tile member to a sheet of 
plain paper with subsequent affixing of the image thereto. 
In order to permanently affix or fuse electroscopic toner material onto a 
support member by heat, it is necessary to elevate the temperature of the 
toner material to a point at which the constituents of the toner material 
coalesce and become tacky. This action causes the toner to be absorbed to 
some extent into the fibers of the support member which, in many 
instances, constitutes plain paper. Thereafter, as the toner material 
cools, solidification of the toner material occurs causing the toner 
material to be firmly bonded to the support member. In both the 
xerographic as well as the electrographic recording arts, the use of 
thermal energy for fixing toner images onto a support member is old and 
well known. 
One approach to thermal fusing of electroscopic toner images onto a support 
has been to pass the support with the 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 fuser 
roll to thereby effect heating of the toner images within the nip. By 
controlling the heat transferred to the toner, virtually no offset of the 
toner particles from the copy sheet to the fuser roll is experienced under 
normal conditions. This is because the heat applied to the surface of the 
roller is insufficient to raise the temperature of the surface of the 
roller above the "hot offset" temperature of the toner whereat the toner 
particles in the image areas of the toner would liquefy and cause a 
splitting action in the molten toner to thereby result in hot offset. 
Splitting occurs when the cohesive forces holding the viscous toner mass 
together is less than the adhesive forces tending to offset it to a 
contacting surface such as a fuser roll. 
Occasionally, however, toner particles will be offset to the fuser roll by 
an insufficient application of heat to the surface thereof (i.e. "cold" 
offsetting); by imperfections in the properties of the surface of the 
roll; or by the toner particles insufficiently adhering to the copy sheet 
by the electrostatic forces which normally hold them there. In such a 
case, toner particles may be transferred to the surface of the fuser roll 
with subsequent transfer to the backup roll during periods of time when no 
copy paper is in the nip. 
Moreover, toner particles can be picked up by the fuser and/or backup roll 
during fusing of duplex copies or simply from the surroundings of the 
reproducing apparatus. 
One arrangement for minimizing the foregoing problems, particularly that 
which is commonly referred to as "offsetting", has been to provide a fuser 
roll with an outer surface or covering of polytetrafluoroethylene, 
commonly known as Teflon, to which a release agent such as silicone oil is 
applied, the thickness of the Teflon being on the order of several mils 
and the thickness of the oil being less than 1 micron. Silicone based 
oils, which possess a relatively low surface energy, have been found to be 
materials that are suitable for use in the heated fuser roll environment 
where Teflon constitutes the outer surface of the fuser roll. In practice, 
a thin layer of silicone oil is applied to the surface of the heated roll 
to thereby form an interface between the roll surface and the toner images 
carried on the support material. Thus a low surface energy layer is 
presented to the toner as it passes through the fuser nip and thereby 
prevents toner from offsetting to the fuser roll surface. 
The release agent material can be applied directly to the heated fuser roll 
or it can be applied indirectly via the pressure roll. Use of a donor roll 
RAM (Release Agent Management) system is one way of applying the release 
agent to the fuser roll. Donor roll RAM systems have been used as part of 
roll fuser apparatus for some time. Such a RAM system is disclosed in U.S. 
Pat. No. 4,214,549 issued on Jul. 29, 1980 to Moser This patent 
illustrates a heat and pressure roll fusing apparatus for fixing toner 
images to copy substrates, the toner comprising a thermoplastic resin. The 
apparatus includes an internally heated, fuser roll cooperating with a 
backup or pressure roll to form a nip through which the copy substrates 
pass with the images contacting the heated roll. The pressure roll is the 
softer of the two rolls, therefore, the nip is formed by the harder fuser 
roll indenting the softer pressure roll. The heated fuser roll is 
characterized by an outer layer or surface which by way of example is 
fabricated from a silicon rubber or Viton material to which a low 
viscosity polymeric release fluid is applied. Release fluid is contained 
in a sump from which it is dispensed by means of a metering roll and a 
donor roll, the former of which contacts the release fluid in the sump and 
the latter of which contacts the surface of the heated fuser roll. 
U.S. Pat. No. 3,716,221 issued on Feb. 13, 1973 to Gorka et al discloses a 
heat and pressure fuser roll wherein the heated fuser roller includes a 
fusing roller having a resilient fusing blanket supported on the periphery 
thereof and heating means to heat the fusing blanket to a temperature 
sufficient to fuse the particulate material on a copy sheet. A backup 
roller is urged toward engagement with the deformable fusing blanket to 
press the receptor sheet carrying the particulate material into contact 
with the fusing roller. The fuser roller is coated with an offset 
preventing liquid which is applied thereto from the backup roller at 
predetermined intervals during operation of the device. The offset 
preventing liquid is applied to the backup roller via a wick, one end of 
which is immersed in a quantity of the liquid which is contained in a 
receptacle. The application of the liquid to the backup roller is 
controlled such that it is applied once every eleventh revolution of the 
fuser roller. In other words ten copy sheets are passed through the fuser 
and then the fuser and backup rollers are rotated an eleventh time without 
a copy sheet passing therebetween at which time the liquid is applied to 
the fuser roller via the wick and backup roller. 
U.S. Pat. No. 3,929,094 granted to Raghulinga R. Thettu on Dec. 30, 1975 
discloses a contact fuser assembly wherein a heater is provided in a sump 
of a RAM system for melting a release agent material which is solid at 
room temperature. The melted release agent is applied to a heated fuser 
roll supported for pressure contact with a Viton (Trademark of E. I. 
dupont de Nemours and Company) coated pressure roll. 
U.S. Pat. No. 3,934,547 granted to Jelfo, et al. on Jan. 27, 1976 discloses 
a contact fuser assembly for use in an electrostatic reproducing apparatus 
including an internally heated fuser roll structure comprising a rigid, 
thermally conductive core which is coated during operation of the assembly 
with a thin layer of a normally solid thermally stable material with 
subsequent application of a liquid release agent to the coated core. In 
the preferred embodiment of the invention the coating material comprises a 
fluorocarbon telomer such as Vydax 1000 and the liquid release agent 
comprises a liquid silicone oil. 
U.S. Pat. No. 3,941,085 granted to Hattier, et al on Mar. 2, 1976 discloses 
an apparatus in which release material is applied to a heated fuser 
member. A backup member is in communication with the fuser member and a 
sheet of support material having particles thereon passes therebetween. 
The particles on the sheet of support material contact the fuser member. 
The apparatus reciprocates a bar of release material into and out of 
contact with the fuser member. 
U.S. Pat. No. 4,770,116 granted to Rabin Moser on Sept. 13, 1988 discloses 
a heat and pressure roll fusing apparatus for fixing toner images to copy 
substrates, the toner comprising a thermoplastic resin. The apparatus 
includes an internally heated fuser roll cooperating with a bare metal 
backup or pressure roll to form a nip through which the copy substrates 
pass with the images contacting the heated roll. The heated fuser roll is 
characterized by an outer layer or surface which by way of example is 
fabricated from a silicon rubber or Viton material to which a low 
viscosity polymeric release fluid is applied. Release fluid is contained 
in a sump and the pressure roll is partially immersed in the fluid. Thus, 
the release fluid is applied to the surface of the internally heated fuser 
roll via the bare metal pressure. 
RAM systems such as the ones discussed above are either spill proof and 
expensive or vice versa. Moreover, the use of liquid release agents such 
as silicone oil with silicone rubber coated fuser or pressure rolls 
results in roll swell. As will be appreciated, it is highly desirable that 
a RAM system be spill proof, highly reliable and be capable of dispensing 
a low rate of oil. Also, is desirable that the release agent not cause 
either the pressure or fuser roll to swell. 
BRIEF SUMMARY OF THE INVENTION 
In accordance with the present invention as will be described hereinafter 
in greater detail, a release agent material which is solid at room 
temperature is applied to the pressure roll of a heat and pressure roll 
fuser apparatus. The pressure roll comprises a hard bare metal roll 
similar to the metering roll in the aforementioned Moser patent. The 
pressure roll contacts a quantity of release agent contained in a sump and 
a metering blade is provided for effecting the application of a thin layer 
of oil of a predetermined thickness onto the pressure roll. The fuser roll 
has a relatively thick outer layer of silicone rubber thereby providing a 
conformable roll which cooperates with the hard pressure roll to form a 
nip forming heat and pressure fuser. 
Application of release agent material to a fuser roll via the pressure roll 
enables high reliability and a low oil rate Release Agent Management (RAM) 
system. 
A heater structure disposed internally of the pressure roll serves to 
liquefy the solid release agent for application to the pressure roll and 
to the fuser roll via the pressure roll. The power supplied to the 
pressure roll is substantially less than that applied to the fuser roll. 
Because the release agent material is solid at room temperature, it does 
not spill when the fuser is being transported, either with the machine in 
which it is used or by itself. The use of a solid release agent as 
described facilitates the use of such fusers as an integral part of a 
Customer Replaceable Unit (CRU). Recycling of the fuser unit or CRU is 
also facilitated by the use of a release agent that is solid at room 
temperature.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION 
Referring now to the FIGURE, it can be seen that the invention is directed 
to a roll fuser apparatus generally indicated 10. The fuser apparatus 
comprises a heated roll structure 12 cooperating with a heated backup or 
pressure roll structure 14 to form a nip 16 through which a copy substrate 
18 passes with toner images 20 formed thereon in a well known manner. The 
toner images 20 contact the heated roll structure while a force is applied 
between the roll structure in a well known manner to create pressure 
therebetween resulting in the deformation of the fuser roll structure by 
the pressure roll structure to thereby form the nip 16. 
As the substrate passes out of the nip, it is stripped from the heated roll 
structure by a plurality (only one shown) of stripping devices 22 after 
which it is free to move along a predetermined path toward the exit of the 
machine(not shown) in which the fuser apparatus 10 is to be utilized. 
A contact temperature sensor 24 is provided for sensing the surface 
temperature of the roll structure 12 and in conjunction with conventional 
circuitry (not shown) maintains the surface temperature to a predetermined 
value, for example, in the order of 300.degree.-400.degree. F. The heated 
roll structure 12 comprises a hollow cylinder 26 having a radiant quartz 
heater 28 disposed in the hollow thereof. When suitably energized via the 
aforementioned circuitry, the heating element 28 radiates heat to the 
cylinder which is then conducted to the outer surface of an outer layer 30 
of the structure 12 which layer is preferably fabricated from silicone 
rubber or "Viton" and is conformable. 
The backup or pressure roll structure 14 which comprises a bare metal roll, 
contacts a release agent material 32 contained in a sump 35. The release 
agent material 32 comprises a low molecular weight material which is solid 
at room temperature and has a relatively low viscosity at its operating 
temperature. An example of such a material is a polyethylene homopolymer 
manufactured by Allied Chemical Co. and which is designated AC-8 
homopolymer. A heating element 37 is supported internally of the pressure 
roll 14 and serves; to elevate the temperature of the release agent 
material to an operating temperature approximately in the range of 
200.degree. to 300.degree. F. A contact temperature sensor 39 is used to 
monitor the surface temperature of the pressure roll for maintaining it at 
a suitable temperature for raising the temperature of the release agent 
material to its operating temperature. Other solid release agents are 
contemplated such as silicone greases that are solid at room temperature. 
As will be appreciated,toners having different fusing temperatures may be 
utilized in the practice of the invention. In practice, when toners 
requiring an operating temperature of around 300.degree. F. are used a 
release agent that has an operating temperature near the lower temperature 
in the aforementioned range is used. When using toners that require a 
higher operating temperature, for example 400.degree. F., the operating 
temperature of the release agent material is at or near the top of the 
aforementioned temperature range, for example, around 300.degree. F. 
A metering blade 36 which may be mounted in a conventional manner adjacent 
to and in contact with the pressure roll serves to meter the release agent 
material on the surface of the pressure roll to a desired thickness. A 
wick 38 supported by the sump 35 contacts the surface of the pressure roll 
14 and is immersed in the release agent 32 when it is in its liquid state. 
The purpose of the wick is to provide an air seal which disturbs the air 
layer formed at the surface of the roll 14 during rotation thereof. If it 
were not for the function of the wick, the air layer would be coextensive 
with the surface of the roll immersed in the release agent thereby 
precluding contact between the pressure roll and the release agent. 
The blade 36 is preferably fabricated from "Viton" is 3/4.times.1/8 in 
cross section and has a length coextensive with the pressure roll. The 
edge of the blade contacting the metering roll has a radius of 0.001-0.010 
inch. The blade functions to meter the release agent picked up by the roll 
14 to a predetermined thickness, such thickness being of such a magnitude 
as to resulting a fraction of a microliter to several microliters of 
release agent consumption per copy. 
While the pressure roll has been disclosed as a rigid bare metal roll and 
the heated fuser roll structure as being conformable, it will be 
appreciated that any construction that yields the desired results is 
within the spirit and scope of this invention. In other words, any 
combination of roll structures that provides minimum contact between the 
pressure roll and the backside of the copy substrate and a maximum of 
contact between it and the heated roll structure. An important aspect of 
the invention resides in the application of the release agent material as 
a thin layer on the pressure roll. The thickness of the release agent on 
the pressure roll is such that the release agent is transferred only to 
the areas of contact between the pressure roll and the copy substrate or 
the heated roll structure. Thus, where the area of contact is small, as in 
the case of the pressure roll and the copy substrate due to the surface 
structure of paper, only very little release agent is transferred. In the 
case of the heated roll structure where the area of contact is great due 
to conformability of the fuser roll surface, the transfer of release agent 
is maximized. 
If the release agent were applied as a relatively thick layer or as drops 
or droplets, a greater transfer of release agent would occur between the 
pressure roll and the copy substrate even though the area is not large. 
This is because the transfer is not solely a function of contact area but 
also release agent thickness.