Composite instant on fuser element

A fuser roll including a hollow cylinder having a relatively thin wall, the cylinder being a plastic composition reinforced with a conductive fiber filler, the plastic composition having a resistivity between 0.5 and 0.05 ohm.cm, the cylinder having an outside and an inside surface and enclosing ambient air, a back up roll disposed in an engaging relationship with the outside surface of the hollow cylinder defining said nip, a heating element disposed within said relatively thin wall, the heating element being said conductive fiber filler, the conductive fiber filler also providing the mechanical reinforcement of the hollow cylinder, and an additive, the additive being part of the plastic composition, the additive providing a release layer on the outside surface of the cylinder, the additive being a fluorocarbon at approximately 0.25 percent by weight.

BACKGROUND OF THE INVENTION 
This invention relates to an improved fuser apparatus and more particularly 
to a composite fusing element. 
In order to fuse toner material permanently onto a support surface by heat, 
it is usually necessary to elevate the temperature of the toner material 
to a point at which the constituents of the toner materials coalesce and 
become tacky. This heating causes the toner to flow to some extent into 
the fibers or pores of the support member. Thereafter, as the toner 
material cools, solidification of the toner material causes the toner 
material to become firmly bonded to the support member. 
PRIOR ART 
The use of thermal energy for fixing toner images onto a support member is 
well known. Several approaches to thermal fusing of electroscopic toner 
images have been described in the prior art. These methods include 
providing the application of heat and pressure substantially concurrently 
by various means, for example, a roll pair maintained in pressure contact, 
a flat or curved plate member in pressure contact with a roll, and a belt 
member in pressure contact with a roll. 
Prior art fusing systems have been effective in providing the fusing of 
many copies in relatively large fast duplicating machines, in which the 
use of standby heating elements to maintain the machine at or near its 
operating temperature can be justified. However, there is a continuing 
need for an instant-on fuser which requires no standby power for 
maintaining the fuser apparatus at a temperature above the ambient. It is 
known to use a positive characteristic thermistor having a self 
temperature controlling property as a heater for a heating roller. The 
roller is regulated to a prescribed temperature by a heating control 
temperature detection element. It is also known to employ radiation 
absorbing materials for the fuser roll construction to effect faster 
warm-up time and to use an instant-on radiant fuser apparatus made of a 
low mass reflector thermally spaced from a housing, with the housing and 
the reflector together forming a conduit for the passage of cooling air 
therein. It is also known to use a cylindrical member having a first layer 
made of elastomeric material for transporting radiant energy, a second 
layer for absorbing radiant energy, and a third layer covering the second 
layer to affect a good release characteristic on the fuser roll surface. 
The fuser roll layers are relatively thin and have an instant-start 
capability. It is also known to use an instant-on fuser having a core of 
metal or ceramic supporting a fuser roller, and including a heat 
insulating layer, an electrically insulating layer and a protective layer 
formed on the outer circumference of the core. 
In addition, U.S. Pat. No. 4,234,248 to Beck discloses a hot roll fuser for 
use in an electrostatic copying machine whose outer surface comprises 
graphite with less than 0.5 percent carbon. The hot roll fuser comprises a 
material having sufficient thermal conductivity to avoid long periods of 
fuser warm up. Due to the physical characteristics of graphite, the 
application of a supplementary release agent is therefore, eliminated. 
U.S. Pat. No. 4,360,566 to Shimizu et al. discloses a heat fixing roll, 
for fusing electrographic dry toner, which includes an outer layer of 
silicone rubber and contains reinforcing silica filler. U.S. Pat. No. 
4,544,828 to Shigenobu et al. discloses a heating device utilizing ceramic 
particles as a heat source and adapted for use as a fixing apparatus in an 
electrostatic printing machine or the like. U.S. Pat. No. 4,883,941, 
assigned to the same assignee as the present invention, discloses an 
instant on fuser roll having a heating foil secured to the outside surface 
of the fuser cylinder. 
A difficulty with the prior art fusing systems is that they are often 
relatively complex and expensive to construct and/or the mass of the 
system is relatively large to preclude an instant-start fusing capability. 
Another difficulty is that prior art fuser rolls are not always easily 
adapted to provide sufficient mechanical strength and heating 
characteristics. It is an object of the present invention, therefore, to 
provide a new and improved fuser apparatus that comprises a conductive 
fiber reinforced plastic cylinder providing the heating element. It is 
another object of the present invention to provide fuser apparatus that 
has a relatively low thermal mass and is designed for relatively ease of 
construction, in particular, a single molding process to provide a 
cylinder with both mechanical and electrical properties. 
Further objects and advantages of the present invention will become 
apparent as the following description proceeds and the features of novelty 
characterizing the invention will be pointed out with particularity in the 
claims annexed to and forming a part of this specification. 
SUMMARY OF THE INVENTION 
The present invention is concerned with fuser roll including a hollow 
cylinder having a relatively thin wall, the cylinder being a plastic 
composition reinforced with a conductive fiber filler, the plastic 
composition having a resistivity between 0.5 and 0.05 ohm.cm, the cylinder 
having an outside and an inside surface, a source of thermal energy 
affixed to the surface of the cylinder, a back up roll disposed in an 
engaging relationship with the outside surface of the hollow cylinder 
defining said nip, a heating element disposed within said relatively thin 
wall, the heating element being said conductive fiber filler, the 
conductive fiber filler also providing the mechanical reinforcement of the 
hollow cylinder, and an additive, the additive being part of the plastic 
composition, the additive providing a release layer on the outside surface 
of the cylinder, the additive being a fluorocarbon at approximately 0.25 
percent by weight.

DESCRIPTION OF THE INVENTION 
Referring now to FIG. 1, there is shown by way of example an automatic 
xerographic reproducing machine 10 including an image recording drum like 
member 12, its outer periphery coated with suitable photoconductive 
material. The drum 12 is suitably journalled for rotation within a machine 
frame (not shown) by means of shaft 14 and rotates in the direction 
indicated by arrow 15 to bring the image-bearing surface 13 thereon past a 
plurality of xerographic processing stations. Suitable drive means (not 
shown) are provided to power and coordinate the motion of the various 
cooperating machine components whereby a faithful reproduction of the 
original input information is recorded upon a sheet of final support 
material or copy sheet 16. 
Initially, the drum 12 moves the photoconductive surface 13 through a 
charging station 17 providing an electrostatic charge uniformly over the 
photoconductive surface 13 in known manner preparatory to imaging. 
Thereafter, the drum 12 is rotated to exposure station 18 and charged 
photoconductive surface 13 is exposed to a light image of the original 
document to be reproduced. The charge is selectively dissipated in the 
light exposed regions to record the original document in the form of an 
electrostatic latent image. After exposure drum 12 rotates the 
electrostatic latent image recorded on photoconductive surface 13 to 
development station 19 wherein a conventional developer mix is applied to 
the photoconductive surface 13 of the drum 12 rendering the latent image 
visible. Typically, a suitable development station could include a 
magnetic brush development system utilizing a magnetizable developer mix 
having coarse ferromagnetic carrier granules and toner colorant particles. 
The copy sheets 16 of the final support material are supported in a stack 
arrangement on an elevating stack support tray 20. With the stack at its 
elevated position a sheet separator 21 feeds individual sheets therefrom 
to the registration system 22. The sheet is then forwarded to the transfer 
station 23 in proper registration with the image on the drum. The 
developed image on the photoconductive surface 13 is brought into contact 
with the sheet 16 of final support material within the transfer station 23 
and the toner image is transferred from the photoconductive surface 13 to 
the contacting side of the final support sheet 16. 
After the toner image has been transferred to the sheet of final support 
material or copy sheet 16, the sheet with the image is advanced to fusing 
station 24 for coalescing the transferred powder image to the support 
material. After the fusing process, the copy sheet 16 is advanced to a 
suitable output device such as tray 25. 
Although a preponderance of toner powder is transferred to the copy sheet 
16, invariably some residual toner remains on the photoconductive surface 
13. The residual toner particles remaining on the photoconductive surface 
13 after the transfer operation are removed from the drum 12 as it moves 
through a cleaning station 26. The toner particles may be mechanically 
cleaned from the photoconductive surface 13 by any convenient means, as 
for example, by the use of a cleaning blade. 
Normally, when the copier is operated in a conventional mode, the original 
document to be reproduced is placed image side down upon a horizontal 
transparent platen 27 and the stationary original then scanned by means of 
a moving optical system. The scanning system includes a stationary lens 30 
and a pair of cooperating movable scanning mirrors, half rate mirror 31 
and full rate mirror 32 supported upon suitable carriages. 
A document handler 33 can also be provided including registration assist 
roll 35 and switch 37. When a document is inserted, switch 37 activates 
registration assist roll 35 and the document is fed forward and aligned 
against a rear edge guide for the document handler 33. The pinch rolls 38 
are activated to feed a document around 180.degree. curved guides onto the 
platen 27 for copying. The document is driven by a platen belt transport 
including platen belt 39. After copying, the platen belt 39 is activated 
and the document is driven off the platen by the output pinch roll 41 into 
the document catch tray 43. 
The fusing station 24 includes a heated fuser roll 45 and a back up or 
pressure roll 47 forming a nip through which the copy sheets to be fused 
are advanced. The copy sheet is stripped from the fuser rolls by suitable 
(not shown) stripper fingers. The pressure roll 47 comprises a rotating 
member suitably journaled for rotation about a shaft and covered with an 
elastomeric layer of silicone rubber, PFA or any other suitable material. 
The fuser roll 45 comprises a rotating cylindrical member 48 mounted on a 
pair of end caps 49 as seen in FIGS. 2 and 3. 
To be instant-on, a fuser should achieve operating temperatures in a time 
shorter than the arrival time of the paper at the fuser, at machine 
start-up, approximately a 5-10 second warm-up time. This is, assume a copy 
sheet 16 takes from 5-10 seconds to be transported from the support tray 
20 to the transfer station 23 to fuser 24 after a start print or start 
copy button is pushed. It is usually then necessary for the fuser to be 
elevated at least 120.degree. C. Raising the temperature of a rigid 
structure at a change of temperature of approximately 120.degree. C. in 
five seconds using reasonable power levels, for example, 700 watts 
requires a small mass to be heated. In accordance with the present 
invention, the cylindrical, member 48 is a hollow cylinder of fiber glass 
carbon graphite, or boron carbide fibers or any other suitable fiber 
material of suitable mechanical strength. Preferably, the thickness of the 
cylindrical member 48 wall is approximately 20-40 mils. It should be noted 
that, although very advantageous in an instant on fuser, the present 
invention is applicable to any type of fuser apparatus requiring combined 
mechanical and heating characteristics. 
With reference to prior art, FIGS. 2 and 3, supported on the filament wound 
cylindrical member 48 is a poly adhesive securing fiber glass backing 50. 
Supported on the fiber glass backing 50 is suitable heating wire, printed 
circuit or photo etched circuit pattern 52. A suitable release agent 54 
such as PFA or rubber covers the heating element. 
It is important for the fuser roll to have sufficient mechanical strength 
including hoop strength and beam strength. The hoop strength is the 
property of the fuser roll core material to resist inward radial pressure 
and beam strength is the property of the fuser roll core material to 
resist bending. It is also known in the prior art to use a filament wound 
tube or cylinder with the fibers wound at approximately 50 degrees or any 
other suitable orientation with respect to the longitudinal axis to 
provide sufficient mechanical strength. However, such filament wound 
cylinders still require a separate backing and heating element. 
In accordance with the present invention, the need for a separate backing 
and heating element is eliminated by the use of conductive fillers in the 
cylinder. As illustrated in FIG. 4, there is a much simpler construction 
including only a cylinder wall 58 and suitable release agent 60. Using 
conductive fillers in plastics to make heaters is not new--e.g., cable 
heaters, sold to prevent water pipes from freezing, are made of 
carbon-black filled PE or rubber. However, these are typically used at 
relatively low temperatures. As shown below, such a system can be used in 
a roll fuser at significantly higher temperatures (up to 
400.degree.-450.degree. F.). The data used in these calculations is taken 
from the Modern Plastics Encyclopedia, Vol. 62, 1985-1986 (hereinafter 
referred to as MPE). 
For thermal stability the following materials (and others) would be 
suitable: 
a) Epoxy: 
unfilled, HDT=up to 550.degree. F. 
glass filled, HDT=500.degree. F. 
b) Polyamide-imide: 
Unfilled, HDT=500.degree.-525.degree. F. 
glass or graphite filled, HDT=525.degree. F. 
c) Carbon fiber: &gt;600.degree. F. (protected from oxidizing atmosphere) 
(HDT=heat distortion temperature under load) 
For electrical resistivity consider a thin-walled tube with dimensions: 
length=10", outside diameter=1". Let the thickness be t mils, and let the 
material have a volume resistivity of .rho. ohm.cm. 
Assume an input power of 650 W. It can be shown that this power is quite 
adequate. 
A heater having the proper electrical resistance along its length to draw 
650 W at 110 V, with the above dimensions, will need to have a thickness t 
(mils) given by 
EQU t=67.rho. 
Thus, using a 20 mil thick tube it will be necessary to use a material 
having a volume resistivity p=0.3 ohm.cm,. This can be achieved using 
conventional., readily-aviailable, commercial materials for example, 
Polyamide-imide (PAI) with 25% Ni-coated carbon fiber, p=0.2 ohm.cm. 
Considering data for polyamide (PA) instead of PAI: 
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15% 20% 30% 40% 
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PA + Ni-coated carbon, 
p = 0.5 0.1 0.05 0.02(ohm.cm) 
PA + carbon p = -- 1.4 0.7 --(ohm.cm) 
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This demonstrates that any p in the desired (p.perspectiveto.0.3 ohm.cm) 
can be easily obtained by a judicious blend of Ni-coated carbon with 
carbon or glass fiber. 
For mechanical rigidity, recently it has been demonstrated that a 
glass-reinforced epoxy tube (OD.perspectiveto.1", 
length.perspectiveto.10") has more than adequate rigidity at a thickness 
of 35 mils, and apparently adequate rigidity even at 20 mils. The limiting 
factor is rigidity; strength is much in excess of requirements. If carbon 
(graphite) fiber were used instead of glass, the strength would be 
slightly increased and the rigidity would be increased by almost 2.times. 
as demonstrated by the following data from MPE. 
______________________________________ 
PAI PAI + PAI + 
(unfilled) 
30% glass graphite 
______________________________________ 
Modulus (.times. 10.sup.6 psi) 
0.6-0.7 1.7 2.9 
Ultimate Strength (.times. 10.sup.3 psi) 
17-27 28 30 
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Consequently, a 20 mil tube made of carbon-reinforced plastic would be 
adequately rigid. 
The warm up time for such a fuser has been calculated, although it was 
necessary to estimate values for the thermal conductivity k and thermal 
diffusivity .alpha.. By analogy with polyamide date (MPE), 
k.perspectiveto.24.times.10.sup.-4 cal/(cm.s .degree.C.) and 
.alpha..perspectiveto.0.004 cm.sup.3 /s for carbon-reinforced PAI was 
used. The following warm-up response, predicted for an input power of 650 
W and dimensions as specified earlier was obtained. 
______________________________________ 
Time (sec) to Reach Surface Temp. of 
350.degree. F. 
390.degree. F. 
400.degree. F. 
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a) 20 mil tube 
6.0 7.0 7.2 
b) 35 mil tube 
10.3 11.9 12.3 
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Thus, 650 W is quite adequate power for a 20 mil tube. 
Hot roll fusers need an outer release layer of low-energy material (e.g., 
Teflon) to prevent molten toner from sticking to it. Such a layer is 
normally applied by spray or molding techniques, adding significantly to 
the cost of fabrication. This step, in accordance with another aspect of 
the present invention, can be eliminated by adding appropriate materials 
to the bulk of the fuser core before fabrication as shown in FIG. 5. This 
method is of course not applicable to the typical metallic fuser cores, 
but should be suitable for the polymeric cores. As illustrated in FIG. 5, 
a single cylinder wall 62 comprises the heating element, the mechanical 
rigidity for the wall, and the release agent. 
Low energy additives can migrate to a solid surface and drastically lower 
its surface tension. For instance, 0.25 percent by weight of some 
fluorocarbon additives drastically reduces the surface tensions of 
polystyrene, poly(methyl methacrylate), and poly (vinylidene chloride) to 
about 15-20 dyne/cm, resembling those for pure fluoro-carbon surfaces. 
The surfaces of mixtures of two poly(fluoroalkyl methacrylates), differing 
in fluoroalkyl side chain length, have been investigated by contact angle 
measurement. The lower-energy component (having a longer fluoroalkyl side 
chain) is found to concentrate on the surface. In other examples, 
fluorocarbon polymers are shown to exhibit pronounced surface activity 
when blended with hydrocarbon polymers. Surface activity of the 
lower-energy component in a copolymer has also been reported. For further 
examples see S. Wu, "Polymer Interface and Adhesion", Dekker (1982), p 
209-210. 
Very small amounts (0.25%) of additives produce drastic reductions in yc in 
many cases well below that for the classic non-stick polymer Teflon, which 
has yc.apprxeq.19 dyn/cm. The resulting surface layer can be made more 
durable by using polymeric addoitives, or by using additives (monomeric, 
oligomeric or polymeric) which are bi-segmented, one segment being the 
low-energy component, the other being compatible with the matrix resin to 
form an "anchor". 
Even if the release layer is applied separately (e.g., a silicone rubber 
spray) the above concept would provide a means of bonding the rubber by 
making one of the segments silicone-like, the other resin-like. 
While there has been illustrated and described what is at present 
considered to be a preferred embodiment of the present invention, it will 
be appreciated that numerous changes and modifications are likely to occur 
to those skilled in the art, and it is intended in the appended claims to 
cover all those changes and modifications falling within the true spirit 
and scope of the present invention.