U.S. patent number 3,578,797 [Application Number 04/861,510] was granted by the patent office on 1971-05-18 for fusing method and apparatus.
This patent grant is currently assigned to Eastman Kodak Company. Invention is credited to Claire F. Hodges, Executrix, Howard T. Hodges.
United States Patent |
3,578,797 |
Hodges , et al. |
May 18, 1971 |
FUSING METHOD AND APPARATUS
Abstract
A toner image is fused to a receiver sheet without substantial
heating of the sheet by placing the sheet, image side down, on an
endless heat-conductive web extending around at least two spaced
rotatable supports. One or more of these rotatable supports may
include a heating element to heat the endless web at or adjacent to
the point where the receiver sheet is brought into contact
therewith. A corona charger may be used to tack the receiver to the
endless web to assure positive contact therebetween.
Inventors: |
Hodges; Howard T. (Perinton,
NY), Claire F. Hodges, Executrix (Perinton, NY) |
Assignee: |
Eastman Kodak Company
(Rochester, NY)
|
Family
ID: |
25336004 |
Appl.
No.: |
04/861,510 |
Filed: |
September 26, 1969 |
Current U.S.
Class: |
432/9; 432/13;
219/388; 432/228 |
Current CPC
Class: |
G03G
15/2014 (20130101) |
Current International
Class: |
G03G
15/20 (20060101); F27b 009/28 () |
Field of
Search: |
;263/3,6,6 (E)/
;219/216,388 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Myhre; Charles J.
Claims
I claim:
1. A fusing device for heating a toner image to a fusing
temperature on a receiver sheet, said device comprising:
an endless heat-conductive web movable along a path;
drive means for moving said web along said path;
at least one heat source means for heating said web to said fusing
temperature;
means for stripping said receiver from said web at a point along
said path downstream from said heat source means; and
means for feeding said toner image on said receiver sheet into
contact with said web to fuse said image to said sheet, said
receiver acting as a sump to cool said image to a relatively high
viscosity before said receiver reaches said stripping means.
2. A fusing device, as claimed in claim 1, said device further
comprising:
means for urging said receiver sheet against said web to provide
intimate contact between said toner image and said web.
3. A fusing device, as claimed in claim 2, wherein said urging
means includes:
a corona-discharge device for causing electrostatic attraction
between said receiver and said web.
4. A fusing device, as claimed in claim 1, wherein said feeding
means feeds said receiver sheet onto said web at said heat source
means.
5. A fusing device, as claimed in claim 1, wherein said feeding
means feeds said receiver sheet onto said web downstream from said
heat source.
6. A fusing device, as claimed in claim 1, further including:
means for applying an offset-preventing material to said web to
minimize offset of said toner image onto said web.
7. A fixing device, as claimed in claim 1, wherein said heat source
means includes at least two heating elements spaced along said path
for heating said web.
8. A fusing device for fixing a toner image to a receiver sheet,
said device comprising:
an endless heat-conductive web movable along a path;
at least two spaced rotatable supports for said web;
drive means for moving said web along said path;
a heating element in at least one of said supports for heating said
web, said web having a decreasing temperature gradient in the
direction of movement of said web;
feed means for feeding said receiver sheet into intimate contact
with said web with said toner image facing said web;
a corona discharge means for electrostatically urging said receiver
sheet against said web to assure intimate contact between said
toner image and said web, to melt said toner image so that it is
fused to said receiver; and
means for stripping said receiver from said web after fusing, said
receiver serving as a sump to cool said toner image after fusing so
that it reaches a relatively high viscosity prior to stripping.
9. A method of fusing a toner image to a receiver comprising the
steps of:
positioning said receiver with said toner image in direct contact
with a source of heat having a temperature sufficient to cause said
toner image to become a viscous fluid;
decreasing said temperature while said receiver is in contact with
said source to increase the viscosity of said toner image so that
it adheres to said receiver; and
separating said receiver from said heat source.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method and apparatus for fusing a toner
image to a receiver and more particularly to a method and device
wherein a heat-conductive web is used to provide a substantial time
period over which the toner image is fused.
2. Description of the Prior Art
In a conventional electrophotographic process an electrostatic
image is formed by exposing a photoconductive material to a pattern
of radiation, and this electrostatic image is either developed on
the photoconductive material, which serves as a receiver, or is
transferred to a receiver after development. The toner image is
then securely affixed to the receiver to form a permanent image. To
accomplish this, the toner material is usually heated to its
melting point so that it flows into the fibers of the receiver
sheet and when the image is cooled, it is tightly bound to the
receiver.
Various methods of fusing the toner have been suggested. The toner
may be heated by an infrared heat source or it may be affixed to a
receiver by passing the receiver through a pair of pressure
rollers. Another way of fusing the image is to pass the receiver
over a heated drum or roller. Also, pressure and heat may be
applied simultaneously to a toner image to fuse it. Each of these
prior art methods, have certain disadvantages. Either the power
required to heat the toner to a sufficiently high temperature is
excessive or the pressures required to cause fusing are very great.
In the case of roller or pressure fusing, the nip between the rolls
is necessarily small. Therefore, at high feed-through rates, very
high roller temperatures are required because of the short contact
time. Also, separation of the receiver from the roller must
necessarily be made when the toner is at a low viscosity state
since the contact time is so short. This can result in toner
sticking to the roller and offsetting on subsequent portions of the
receiver or on another receiver subsequently fed through the
rollers. On the other hand, if the toner material is not heated
sufficiently the image will not be properly fused.
SUMMARY OF THE INVENTION
In accordance with the present invention, an endless
heat-conductive web is driven along a closed path. A receiver,
bearing the toner image, is placed face down on the web at or
adjacent to a source of heat which heats the conductive web. The
web, in turn, heats the toner image to its melting point so that it
is fused to the receiver. The image on the receiver remains in
contact with the heat conductive web for a substantial period of
time as the web moves along its path of travel. Since the receiver
need not be heated clear through to melt the toner, the image is
fused with less energy than would otherwise be required. Also,
because the receiver remains in contact with the web for a
substantial period of time, the toner, after melting, has a chance
to cool, thereby reaching a relatively high viscosity so that the
tendency of toner to stick to the belt when the receiver is
stripped therefrom is lessened. Thus, offsetting of toner onto the
web is lessened. Conveniently, an offset preventing material such
as silicone oil may be applied, as by a wick means, to the web to
further lessen offsetting onto the next receiver. Also, the
receiver may be clamped or tacked to the web by applying an
electrostatic charge to the back surface of the receiver so that
the latter is electrostatically attracted to the web.
In one embodiment, the endless web extends around two spaced
rotatable supports, one of which contains a heating element for
heating the web. The receiver is fed with the image side toward the
web so that it comes in contact with the web at the heat source.
Spaced above the heat source is a corona discharge device for
applying an electrostatic charge to the back of the receiver so
that it is electrostatically attracted to the web. In another
embodiment, the endless web extends around three rotatable supports
providing a shorter path over which the receiver is in contact with
the web, which may be desirable for some space requirements. Also,
because the fusing area is relatively short, it is necessary that
the web be raised to the fusing temperature by the time the
receiver contacts it. To assure this, the belt may be preheated by
a second heating element. In a third embodiment the web extends
around a pair of spaced rotatable supports and the receiver is fed
into contact with the web downstream from the heat source where the
web is not at its maximum temperature to prevent any possibility of
igniting the receiver should the web stop moving, due to a
malfunction, while the receiver is in contact therewith.
Additional novel features of this invention will become apparent
from the description which follows, taken in conjunction with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatical side elevation, partly in section,
showing a preferred embodiment of the invention wherein a receiver
is brought into contact with a heat-conductive web at a heat source
for the latter; and
FIG. 2 is a view, similar to FIG. 1, but showing another preferred
embodiment of the invention in which the path of contact between
the receiver and the web is relatively short; and
FIG. 3 is a third alternative embodiment wherein the receiver is
brought into contact with the heat-conductive web downstream from
the heat source.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A toner image is formed and placed on a receiver, such as by any
conventional method known in electrophotography. In accordance with
this invention, a receiver sheet 10, having a toner image 11
thereon, is fed by drive means, such as roller 12 face down so that
image 11 will be brought into direct contact with an endless
heat-conductive we 13 to fuse the image to the receiver. Web 13
extends around a pair of spaced, rotatably mounted rollers 14 and
15, as shown. Conveniently, roller 14 is made of a heat-conductive
material and is provided with a heating element 16 therein which
heats the roller 14 in turn heating heat conductive web 13. The web
is driven, as by motor 17 through a belt 18. Because of the
heat-conductive property of web 13, it serves as a heat source,
having a decreasing temperature gradient in the direction of
travel, for fusing a toner image to a receiver brought into contact
therewith.
Advantageously, receiver 10 is brought into contact with web 13
directly above heating element 16 and may be tacked or clamped
thereto by a corona discharge device 19 so that image 11 is held in
intimate contact with web 13. Because rollers 14 and 15 are spaced
apart a substantial distance, the receiver remains in contact with
web 13 for a substantial period of time to assure that the toner
image melts and fuses as completely as possible to the receiver.
With the toner side toward the heated belt, only the toner and the
surface of the receiver where the fusing action is needed is heated
without requiring that the receiver be heated all the way through.
This saves heat energy and allows faster feed-through than devices
wherein the receiver is heated from the back side, since actual
physical contact and low thermal conductivity of conventional
receiver material normally would prevent or retard sufficient
heating. However, in the present instance the low conductivity of
the receiver becomes an asset because it tends to minimize heat
transfer through the paper and retains heat at the image where it
can be utilized. Also, the toner has sufficient time to flow into
the fibers of the receiver and to cool so that as it is at a
relatively high viscosity by the time it is stripped from belt 13
at roller 15, as by a stripper finger 21. Roller 15 may be
grounded, as shown, to dissipate the electrostatic charge on the
belt so that the receiver may more easily be stripped from the
receiver. Although the only force serving to hold the receiver
against the web is due to the electrostatic forces created by
corona charger 19, the added contact time more than compensates for
this lack of pressure to absorb toner into the receiver
material.
Since the belt is cooled by the sump effect of the receiver, a
downward temperature gradient in the direction of belt travel
exists on the belt between the rollers. Thus, after application of
maximum heat at the input to the fusing device, toner flow time at
reducing temperature is provided as the receiver progresses toward
roller 15. This reducing temperature along the direction of travel
provides higher toner viscosity at the strip point which results in
an optimum toner-to-paper bond which provides cleaner stripping of
toner from the belt. By adjustment of the distance between the
rollers, the belt tightness and the heating arrangement, the
temperature gradient can be controlled for optimum transfer taking
into account the temperature versus viscosity characteristic of a
preferred toner. Also, toner may be prevented from sticking to belt
13 by application of an offset-preventing material such as silicon
oil applied as by means of a wick 22 from a supply 23.
An alternative embodiment is illustrated in FIG. 2 which finds
utility where space requirements limit the amount of contact time.
In this case, an endless heat-conductive web 25 extends around
three spaced rollers 26, 27, and 28. Conveniently, rollers 26 and
28 are made of heat-conductive material and are provided with
heating elements 29 and 30 respectively. Thus, the web may be
preheated by roller 28 and brought to its optimum temperature by
roller 26 just as receiver 10 is fed against web 25. Receiver 10
will be held against web 25 due to electrostatic forces created by
corona-discharge element 31 with toner image 11 being fused to the
receiver over the relatively short path between rollers 26 and 27
whereupon the receiver will be stripped from web 25 by stripper
finger 32 at roller 27, which roller may be grounded. The endless
web may be driven by a motor 33 through belt 34 extending to roller
28.
In the embodiment of FIG. 3, the elements are all arranged exactly
as in FIG. 1 except that corona-discharge element 19 is moved
downstream from roller 14 and receiver 10 is fed into contact with
web 13 at a point downstream from roller 14. In this way, the
ceiling temperature of the receiver is limited by the finite heat
energy stored in web 13 as it passes roller 14. Thus, the
temperature may be adjusted so that it is below the ignition
temperature of the receiver at the point where the receiver comes
in contact with the belt so that the receiver will not burn even if
the web should stop with the paper in contact therewith due to a
malfunction.
From the foregoing, the advantages of the present invention are
readily apparent. A fusing device has been provided wherein a
minimum amount of heat and pressure is required for fusing. This is
accomplished by feeding a receiver with the image side against a
heat-conductive web which heats only the toner and the portion of
the receiver adjacent thereto thereby reducing the amount of energy
necessary to fuse the image. In addition, because of the sump
effect of the receiver, a downward temperature gradient exists, in
the direction of web travel so that the toner reaches a relatively
high viscosity level by the time the receiver is stripped from the
web. This assures better fusing and reduces the possibility of
offset of toner material onto the web. In an alternative embodiment
a plurality of heat sources may be provided to assure that the web
is at optimum temperature whereby a shorter fusing path may be
provided. In a further alternative embodiment, the receiver is fed
into contact with the web downstream from the heat source so that
the receiver will not burn even if the web is stopped with the
receiver in contact therewith.
Although the heating elements have been illustrated as being
located in the rollers, it will be understood that heating of the
web may be accomplished by any other methods as would occur to one
skilled in the art. Also pressure rollers could be used in
combination with a heated belt to insure fusing.
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.
* * * * *