Offset prevention during fixing

A contact fixing device for fixing electrostatic marking particles carried on a support material is disclosed. The device includes a rotatably mounted fixing roller, a container for a supply of offset preventing material and applicator means for spraying the offset preventing material directly onto the peripheral surface of the fixing roller. Control means are provided for activating the applicator means after a predetermined period of operation of the fixing roller.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to devices for distributing offset 
preventing material to the peripheral surface of a fixing roller, and more 
particularly to apparatus for applying such material without direct 
contact to the roller by intermediate feed devices. 
2. Description of the Prior Art 
In the process of xerography, a xerographic plate comprising a layer of 
photoconductive insulating material on a conductive backing is given a 
uniform electric charge over its surface and is then exposed to the 
subject matter to be reproduced, usually by conventional projection 
techniques. This exposure discharges the plate areas in accordance with 
the radiation intensity that reaches them, and thereby creates an 
electrostatic latent image on or in the photoconductive layer. Development 
of the latent image is effected with an electrostatically charged, finely 
divided developing material or electrostatic marking particles (toner) 
which is brought into surface contact with the photoconductive layer and 
is held thereon electrostatically in a pattern corresponding to the 
electrostatic latent image. Thereafter, the developed toner image is 
usually transferred to the surface of a support material such as paper, to 
which it may be fused by heat or vapor fixing techniques. During such 
fusing, the individual toner particles soften and become tacky so that 
they readily adhere to the surface of the support material. 
It is common practice in the art to apply heat for fusing the toner image 
to paper by bringing the toner image into direct contact with a hot 
surface, such as the peripheral surface of a heated roller such as for 
example the roller disclosed in U.S. Pat. No. 3,437,032, which issued Apr. 
8, 1969 to A. T. Manghirmalani et al. However, since the toner image is 
tackified by heat, part of the image carried by the support material will 
stick to the surface of the heated roller so that, as a second sheet is 
brought into contact with that surface, the tackified image partially 
removed from the first sheet will partly transfer to the second sheet and, 
at the same time, part of the tackified image from the second sheet will 
itself adhere to the heated roller. Also, during revolution of rollers 12 
and 14 (FIG. 1) without paper therebetween, toner on the fusing roller may 
transfer to the pressure roller. These conditions are commonly referred to 
in the printing art as "set off" or "offset," the latter term being 
preferred and used throughout the remainder of the present specification. 
The offset of toner onto the heated roller has led to the use of other 
types of fixing devices, such as coiled radiant element heaters with 
reflectors. However, such devices have the disadvantages of dissipating a 
large quantity of heat into the machine enclosure, insufficiently heating 
the toner image and presenting a safety hazard because of the exposed 
radiant element. Therefore, improved methods for direct contact fusing 
devices which will rapidly fuse toner images without causing the toner 
particles to adhere to the fusing roller while in a tackified state have 
been developed. 
One such method involves direct fusing devices in which the fusing roller 
is coated with an abhesive material such as tetrafluoroethylene resin sold 
under the trademark Teflon by the DuPont Corporation or silicone rubber or 
elastomer. Such rollers may be provided with an offset preventing film 
such as a silicone oil film to prevent toner offset. Teflon, silicone 
rubber and silicone oil have physical characteristics such that they form 
a "release" surface which is highly repellent to tacky substances. 
The silicone oil film may be applied to the fusing roller by various 
techniques. For instance, U.S. Pat. No. 3,132,047, which issued May 5, 
1964 to W. G. Van Dorn, discloses the use of an applicator roller to 
transfer oil from a pan directly to the surface of a fusing roller. In 
U.S. Pat. No. 3,256,002, which issued June 14, 1966 to F. W. Hudson, a 
wick is provided between the applicator roller and the fusing roller 
surface, and in British Pat. No. 1,399,740 published July 2, 1975, an oil 
pump was substituted for the applicator roller of the Hudson patent. In 
these and every other prior art method known to us for applying offset 
preventing material to fusing rollers, wicks and/or applicator rollers 
contact the fusing roller. Such contact tends to abrade the adhesive 
surface of the fusing roller resulting in premature failure of the roller. 
Further, prior art wicking apparatus require low viscosity offset 
preventing liquids. For instance, Dow-Corning's FS 1265 fluorosilicone 
oil, having a viscosity of 1,000 centistokes, has been wicked onto a 
thermally conductive silicone elastomer. Although such an oil functions 
well for prevention of offset, it is expensive, it adversely affects the 
physical properties of silicone elastomers, it deteriorates the bond 
between the silicone elastomers and aluminum roller cores and its 
degradation products are toxic. 
Dimethyl silicone oil such as Dow-Corning's DC 200 is a logical replacement 
for fluorosilicone oil, but at viscosities similar to FS 1265, it 
excessively swells silicone rubbers. We have found that higher viscosity 
silicone oils have considerably less effect on silicone elastomers, but 
wicking such high viscosity oils (i.e., oils having viscosities of at 
least 10,000 centistokes) presents additional problems. That is, wicks may 
occasionally be dismembered upon start-up or may clog after long use of 
high viscosity oils. Besides having less effect on the physical properties 
of silicone elastomers. silicone oils with viscosities up to about 100,000 
centistokes provide better release characteristics for a given quantity of 
oil and greater persistence on the fusing and pressure rollers. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide improved 
apparatus for applying offset preventing materials to fixing rollers 
wherein less wear is caused to the fixing roller because there is no 
contact with the roller by an applicator. 
It is another object of the present invention to provide an improved 
apparatus for applying such materials to fixing rollers wherein very high 
viscosity oils may readily be applied. 
These and other objects and advantages of our invention are achieved by 
applying offset preventing material to fixing rollers in a controlled 
manner without physically contacting the fixing roller. In a preferred 
embodiment, this is accomplished by use of a spraying device to apply the 
offset preventing material, thereby avoiding direct contact of the 
applicator with the fixing roller and also avoiding the aforementioned 
problems encountered with the clogging of wicks. 
The invention, and its objects and advantages, will become more apparent in 
the detailed description of the preferred embodiments presented below.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Although the present invention relates to an improved roll fixing device 
which may have general application, it is particularly useful in the field 
of xerography and has an important application in the fixing of resinous 
powder images produced by electrophotography onto sheets of paper and the 
like to which the powder images have been transferred after they have been 
formed by deposition of powder on an electrostatic latent image. 
Therefore, for convenience of illustration, the invention is described 
with reference to its use as a heat fuser for xerographic powder images. 
However, it is to be understood that it may be employed with equal 
facility in pressure (no heat) fixing devices, in electrography and/or in 
other fields. As used herein, the term "fixing" is meant to refer to heat 
fusing as well as to pressure fixing. Because xerographic devices are well 
known, the present description will be directed in particular to elements 
forming part of, or cooperating more directly with, apparatus in 
accordance with the present invention. It is to be understood that 
elements not specifically shown or described may take various forms well 
known to those skilled in the art. 
Fiear Embodiment 
Referring to FIG. 1, we have shown an exemplary embodiment of an offset 
preventing material applicator in accordance with the present invention. 
Direct contact fixing of a powder image on a support material is achieved 
for forwarding a sheet 10 of such support material, bearing the powder 
image, between a heated fixing roller 12 and a heated or unheated pressure 
roller 14 as is conventional in the art. The various constructions of 
rollers 12 and 14, means for rotatably supporting them and means for 
driving them in the directions of arrows 16 and 18, respectively, are 
known in the art and reference is made to the various patent literature 
set forth hereinbefore for suitable constructions which may be used for 
these purposes. 
As a sheet of support material 10 is advanced between rollers 12 and 14, 
the powder image on the support material will contact the peripheral 
heated surface surface of roller 12, whereby the powder image becomes 
tackified and, in this tackified condition, the power will tend to offset 
onto this roller. Such offset may be partially prevented by coating roller 
12 with a tetrafluorethylene resin (Teflon) or with silicon rubber 20. 
However, to prevent even this limited tendency of toner offset onto the 
heated contact surface of roller 12, a thin film of offset preventing 
material such as silicone oil, is commonly applied to the peripheral 
surfce of roller 12; and we have found that such such offset preventing 
materials may be applied to fixing rollers in a controlled manner without 
physically contacting the roller, such as by spray application. 
Positioned adjacent fixing roller 12 is a spray applictor 22 consisting of 
a bracket 24 which carries a rubber receptacle 26 into which a standard, 
commercially available aersol can 28 is receivable. A duct 30 in the upper 
portion of receptacle 26 receives the activator button 32 of aerosol can 
28 and provides communication between button 32 (which is the output of 
can 28) and a nozzle 34. The annular side wall 36 of receptacle 26 is 
highly flexible so that depression of a portion 38 of the receptacle will 
in turn depress button 32, causing the contents of can 28 to be released 
through duct 30 and nozzle 34. 
A lever 40, pivotally mounted at 42 to bracket 24 is urged by a spring 44 
in a clockwise direction as viewed in FIG. 1, tending to depress portion 
38 of receptacle 26. The lever is normally held against such movement by a 
disc 46 eccentrically mounted on a shaft 48 for rotation therewith upon 
actuation of a motor 49 by a control 50. p A cup 51 is held adjacent can 
28 such as for example by a rubber strap 52 molded as an integral unit 
with receptacle 26. Cup 51 is supplied with an offset preventing material 
53 to be supplied to fixing roller 12. An aspirator tube 54 extends into 
the contents of cup 51 and has its upper end just beneath the path of 
propellant emitted from nozzle 34 so that offset preventing material 53 
will be drawn from cup 51 at a predetermined rate when activator button 32 
is depressed, and will mix with the propellant from can 28 for application 
to the peripheral surface of fixing roller 12. 
We have hereinbefore set forth the advantages of high viscosity silicone 
oils as offset preventing materials, as well as many problems associated 
with the use of high viscosity oils which would arise in prior art 
application techniques. The present invention provides a very efficient 
way to dispense high viscosity oils by spraying techniques by using 
emulsions having a water-like viscosity even though the silicone oil 
viscosity itself may actually be greater than 100,000 centistokes. The 
water which is evaporated from such emulsions when sprayed onto heated 
fusing roller 12 might be expected to present a cause for concern since 
steam can adversely affect silicone rubber. However, the amount of water 
released, assuming a rather high application rate of 1 gram of fluid every 
100 copies produced, would in fact be less than 5 percent of that 
ordinarily released by 100 sheets of paper during fusing. The actual 
emulsion viscosity is not critical as long as the emulsion can be sprayed 
with the apparatus used. Enough oil should be in the emulsion to prevent 
offset without undue water evaporation. 
EXAMPLE 1 
We have stated that one of the advantages of the present invention is the 
ability to apply high viscosity oils to a fusing roller, resulting in 
greater persistence on the roller. We have conducted experiments, the 
results of which appear to confirm this belief. During such experiments, 
we also looked for traces of oil on the copy paper since it is important 
that such not be noticeable. 
Initial experiments were conducted with a hard cylindrical 
poly(tetrafluoroethylene)-coated steel pressure roller and a resilient 
fixing roller which had previously been used to fuse 30,000 copies. The 
fixing roller and an aluminum core with an external silicone rubber 
surface comprised of 50 mils of Emerson-Cuming Eccosil 4952 silicone 
rubber. The fixing roller was internally heated with an infrared lamp to 
400.degree. F. Surface speed of the roller fuser was approximately 10 
inches per second, and the pressure was approximately 15 pounds per linear 
inch. 
The following three silicon oil emulsions were tested as release agents by 
applying them to the fixing roller with an aerosol can at an application 
rate of approximately 1 gram per spray: 
______________________________________ 
Approximate 0.1 
Emulsion Source Viscosity (CS) 
______________________________________ 
SM-62 General Electric 
300 
SM-2040 General Electric 
10,000 
HV-490 Dow Corning 100,000 
______________________________________ 
Several sheets of International Xerographic 20 pound bond paper with a 
toner stripe were passed through the experimental apparatus with no 
release emulsion applied to the fusing roller. Offset was immediate and 
severe. 
After cleaning the apparatus, the three emulsions were each tested at least 
three times by spraying the fixing roller for approximately one second and 
then running copy with a toner stripe through the fuser until offset 
occurred. The first copy through the fuser after spraying was carefully 
checked to be certain it did not contain an objectionable, i.e., 
noticeable, amount of oil. With SM-62 fluid, offsetting occurred after 
approximately 300 11-inch copies, while both SM-2040 and HV-490 emulsions 
were consistently able to run at least 500 copies before offset occurred. 
EXAMPLE 2 
Another series of tests were run using a similar fusing roller which had 
previously fused 80,000 copies. During the tests, pressure was 
approximately 15 pounds per linear inch, the roller speed was increased to 
11.5 inches per second and two fusing temperatures, 380.degree. and 
400.degree. F, were tested. HV-490 emulsion was chosen to be sprayed onto 
the roller because of its favorable persistence characteristic 
demonstrated in the previously described test. 
Again, the fixing roller severely offset when no release agent was applied. 
Several runs at 380.degree. and 400.degree. F were carried out and the 
number of acceptable copies counted until the slightest detectable amount 
of offsetting occurred. As with the previous test, the first copy after 
spraying was examined to be certain it did not have noticeable oil. The 
results were as follows, the number of copies indicating legal size (14 
inch) paper run in the long direction: 
______________________________________ 
Roller No. of Copies 
Run No. Temperature (F.degree. ) 
to offset 
______________________________________ 
1 380 300 
2 380 270 
3 380 350 
4 380 200 
5 400 100 
6 400 83 
7 400 84 
8 400 84 
9 400 110 
______________________________________ 
The last run (number 9) was continued beyond the point of initial offset 
until the offsetting was equivalent to that experienced before the 
emulsion was sprayed onto the roller; 370 copies passed through the fuser 
before this condition was reached, indicating that some release properties 
are maintained long after the first slight offsetting is noticed. It is 
believed that the poorer results obtained in the second example, compared 
to the first, even taking into account the difference in paper length, 
resulted from the use of a worn fusing roller. 
Second Embodiment 
Referring to FIG. 2, we have schematically shown apparatus in accordance 
with a second illustrative embodiment of our invention. Fixing roller 60 
and pressure roller 62 may be the same as those previously described with 
respect to the embodiment illustrated in FIG. 1. 
A cup 64 positioned adjacent fixing roller 60 is supplied with an offset 
preventing material 66 to be applied to the fixing roller surface. An 
aspirator tube 68 extends into the liquid contents of cup 64 and has its 
upper end just beneath the path of propellant emitted from a nozzle 70 so 
that offset preventing material 66 will be drawn from cup 64 through tube 
68. 
Propellant for nozzle 70 may be derived from a pneumatic pump 72 and stored 
in an air pressure accumulator 74 until a valve 76 is opened by a control 
78. While we estimated that the amount of spray needed for each 
application in the examples given was roughly one gram, this, as well as 
the number of copies which can be satisfactorily produced per spray, 
should be empirically determined for each apparatus and method of use. 
Once determined, controls 50 (FIG. 1) and 78 (FIG. 2) can be preprogrammed 
to regulate the amount and frequency of release material applied to the 
fixing rollers. For instance, the controllers may be set to operate after 
a predetermined period of fixing roller use in response to, say, a copy 
counter, a roller revolution counter, timing signals emitted anywhere in 
the apparatus, etc. 
The nozzles of spray applicators would preferably spray in a line pattern 
along the length of the fixing rollers. As shown in FIG. 3, for long 
rollers 82, a plurality of nozzles 84 and 86 could be positioned along the 
roller. The multiple nozzles could share propellant and/or release 
material sources, or would have independent sources. 
Alternatively, full coverage of a long fixing roller may be accomplished by 
a traversing device such as, for example, as shown in FIG. 4, wherein a 
bracket 24' is similar to bracket 24 of the FIG. 1 embodiment except that 
it is mounted for movement along a reversing helical gear 90 driven by a 
motor 92 upon command of control 94. 
As in FIG. 1, rotation of lever 40' by spring 44' releases propellant. The 
reader is referred to FIG. 1 and the portion of this specification 
relating thereto for details of the apparatus not shown in FIG. 4. 
Normally, bracket 24' rests at the left-most end of helical gear 90 with 
the end of lever 40' held depressed against the force of spring 44 by a 
cam block 96. Upon activation of motor 92 by control 94, helical gear 90 
begins turning to move block 24' to the right. As soon as lever 40' clears 
cam block 96, release material begins to be sprayed on the fixing roller. 
When block 24' reaches the right-hand end of gear 90, its direction is 
reversed and it travels to the left until cam block 96 again depresses 
lever 40', turning off the spray. 
Throughout this specification, we have used silicone oil as an example of 
offset preventing material which may be sprayed onto fixing rollers in 
accordance with out invention. However, it will be recognized that other 
materials, say, powders such as Teflon powder prepared in latex form, 
could be used as offset preventing materials. 
The invention has been described in detail with particular reference to 
preferred embodiments thereof, but it will be understood that variations 
and modifications can be effected within the spirit and scope of the 
invention.