Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVE~TION
This invention relates to a fusing apparatus for
heat fusing a toner image to a sheet of final support material
including means for reducing curl of the sheet during fusing.
When a sheet of final support material having a toner
image on a side thereof is subjected to fusing by means of a
radiant heat fuser some of the moisture in the sheet is driven
out. Depending on the quantity of moisture driven out changes
in the length and width of the sheet occur as well as a severe
curl. Curl in the resulting sheet after fusing is a severe
problem for a reproducing machine, particularly those of the
xerographic type. The tendency of the sheet to curl during
fusing is one of the causes of jams in the region of the fuser.
Curl is also a significant problem in reproducing machines
adapted to provide images on both sides of the sheet, a process
referred to in the art as duplexing. A duplexing apparatus
requires that the sheet be refed through the machine. Sheets
with a severe curl are extremely difficult and sometimes
impossible to feed without persistent jamming problems along
the paper path.
The problem of sheet curl due to radiant heat fusing
has been recognized in the art as exemplified by U. S. Patent
Nos. 2,807,703 and 2,807,704. In these patents the fusing
apparatus is designed to selectively heat the toner image on
the sheet to its fusing point while leaving the sheet per se
at a temperature sufficiently below the fusing point of the
toner to avoid curl. In fact, the temperature of the sheet
is maintained below the boiling point of water so that a
substantial portion of the original moisture content of the
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sheet is not removed. The apparatuses described in these
patents are particularly applicable to record cards. In the
first of these patents, three embodiments of the fusing
apparatus for carrying out the invention are described. In
each apparatus the transfer of heat energy to the record card
by conduction and convection is kept negligible by a suitable
means, and thereby, since the record card per se is made from
paper stock and does not readily absorb radiant energy, the
temperature of the record card is kept at a lower value than
the boiling point of water. Transfer of heat energy by con-
duction and convection is reduced either by heat extraction or
so called fixing station cooling, or by the use of a heat
transfer barrier for preventing heat transfer by conduction
and convection such as a water filled glass jacket, or in
accordance with the third embodiment, by focusing and concen-
trating the radiant energy on the toner image.
; While the approaches of these patents may operate
satisfactorily for fusing toner images on record cards, this
would not necessarily follow for fusing toner images on
support sheet of other types. Toner images on record cards
are generally not very dense and, therefore, comprise very
little toner so that not as much heat energy is required to
fuse them. conventional copying machines can provide denser
toner images containing considerably greater proportions of
toner over the sheet surface, which would require a greater
quantity of heat energy to fuse them to the sheet. Therefore,
it is possible that the apparatuses of the aforenoted patents
would not operate satisfactorily in the environment of a
copying machine since by maintaining the temperature of the
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sheet below the boiling point of water insufficient heat
energy would be impressed on the toner image to consistently
fuse the toner image to the sheet.
One successful solution to this problem is set forth
in ~. S. Patent No. 3,849,905 to D. P. Bierworth et al issued
November 26, 1974. In that case a curl reducing means is
provided in a fusing apparatus which comprises at least one
seal adjacent to the fusing zone which limits the air flow at
the zone to an amount at which curl of the sheet is reduced or
eliminated. The seals preferably comprise strip-like members
- of a polymeric material.
The seals referred to in the aforemen*ioned patent
should be resilient and heat resistant. Teflon and Mylar
are disclosed as usable materials. While these materials
perform their function adequately, their useful life in the
machine environment lS not as great as desired because of the
effects of their elevated temperature environment, though
they have been used commercially. It has been found that Mylar
is not as heat resistant as desired. Teflon, while being heat
resistant, is unable to maintain its resiliency in this environ-
- ment. The elevated temperatures eventually cause the Teflon
to take a permanent set in a deflected condition thereby
reducing i*s biasing ability.
One solution which was proposed to overcome the
above-noted problems was to employ a polymeric foam, specifical-
ly polyurethane foam as the seal. This approach was not
successful since the seal which was interposed between a
transport roll and the fuser caused sufficient drag to inter-
fere with the uniform rotation of the roll.
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* trade marks
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SUMMARY OF THE I~VENTION
In accordance with this invention a fusing apparatus
has been developed wherein curl of the sheet during fusing is
substantially reduced or eliminated. The fuser includes a
source of heat radiation. A fusing zone is defined wherein the
heat source is effective to fuse a toner image to a sheet of
final support material. A flow of air is present at the zone
due to influences which are internal and/or external of the
fuser. Curl reducing means are provided which comprise at
least one seal adjacent to the fusing zone which limits the
air flow at the zone to an amount at which curl of the sheet
is reduced or eliminated. In accordance with this invention
the seal comprises an elongated brush-like member.
Contrary to the aforenoted prior art teachings in
accordance with this invention, the air flow has to be limited
severely in order to reduce moisture gradients and to prevent
the moisture driven off from the sheet from being completely
withdrawn from the fusing zone.
In accordance with preferred embodiments, transport
means are provided at the exit and/or entrance regions of the
fuser to transport the sheet. One or more of these transports
may include suction means for holding the sheet to the transport.
The seals preferably extend between the transports and the
fuser. Preferably the seal comprises an elongated backing strip
and a plurality of elongated fibers extending out from the strip
in a brush-like configuration.
Therefore, it is an object of~this invention to
provide an improved fusing apparatus for heat fusing a toner
image to a sheet of final support material.
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It is an object of an aspect of this invention to
provide an apparatus as above including improved means for
reducing the curl of the sheet during fusing.
It is an object of an aspect of this invention to
provide an apparatus as above wherein the curl reducing means
includes a brush-like seal.
These and other objects will become more apparent
from the following description and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
-
Figure 1 shows schematically an exemplary reproducing
machine including the fusing apparatus of this invention.
Figure 2 is a perspective view of a sheet of final
support material after fusing by a prior art radiant fuser.
Figure 3 is a cross-sectional side view of the fusing
apparatus of this invention including the curl reducing means.
Figure 4 (first sheet of drawings) is a perspective
view of a brush-like seal in accordance with this invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to Figure 1 in accordance with this
invention, a fusing apparatus 1 is provided for heat fusing a
toner image to a sheet 2 of final support material. The fusing
apparatus l includes a fuser 3 having a source of heat radiation
4 for application to the sheet. The fuser 3 defines a fusing
zone 5 wherein the heat source 4 is effective to fuse the
image to the sheet 2. A f low of air is present at the zone 5
due to influences which may be internal and/or external of the
fuser 3. An essential part of this invention comprises means
which cooperate with the fuser 3 for reducing curl of the
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sheet 2 during fusing. The curl reducing means 6 preferably
comprise at least one seal comprising a brush-like member
adjacent to the fusing zone 5 which is adapted to limit air flow
through the zone to a volume at which curl of the sheet is
substantially reduced.
It is believed in accordance with this invention
that paper curl in the final support sheet after fusing by
means of a radiant fuser is the result of plastic deformation
of the paper sheet. The deformation is made up of two com-
ponents which may be summed algebraically. One component is
related to the type of paper and to the bulk paper changes
that occur during fusing. It is possible to think of these as
resulting from one or both of the following: 1. a locked in
asymmetric residual stress distribution which relaxes or
yields under a bulk temperature or moisture level excursion.
2. variations in paper properties across the thickness of the
sheet, as for example, the coefficient or expansion with
moisture. This can result in non-uniform elongation of the
sheet and curl in the absence of any assymetry or gradients.
The other component is believed to relate to the asymmetrical
conditions or gradients imposed on the paper by the fuser and
adjacent machine components or other external influences. The
curl from this component is always in the direction of the
source of radiant energy.
The curl is believed to result from stresses imposed
on the sheet associated with the gradient moisture through
the thickness of the sheet. This invention is not directed
at preventing curl induced by mechanical deformation
which may occur in the copier and which can, in
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fact, result in curl in either direction depending on the
direction of deformation. For example, curl induced by a
roll fusing apparatus.
The primary source of the stresses is the moisture
gradient which causes the top surface of the sheet to shrink
more than the bottom surface. The moisture gradient is
determined by the temperature gradient, the initial moisture
content and the moisture mass transfer effects. In many cases
the moisture mass transfer is significant. In configurations
where the fuser is near an air moving device such as a suction
box of a vacuum transport the air moving device may aggrevate
curl by increasing the rate of moisture mass transfer due to
increased air flow in the fusing zone. The rate of moisture
mass transfer is substantially increased in the top surface of
the sheet thus causing a larger moisture gradient which results
in higher stresses and greater deformation of the sheet. Other
aspects of the mechanism causing curl in the sheets are
described in U. S. Patent No. 2,807,703.
The aforenoted description of the mechanism for
causing curl is not meant to be limitative of the invention and
is presented here by way of example. The aforenoted mechanism
is believed to be the mechanism involved in accordance with
this invention, however, other factors not yet appreciated
could be taking part in the mechanism.
Referring now to Figure 2, a sheet 2 of final support
material is shown after fusing by an apparatus not including
the curl preventing means 6 in accordance with this invention.
The sheet 2 shown therein has a substantial curl 7 of about 1.5
inches at the trailing edge portion 8 thereof. This type of
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curl 7 in a sheet 2 is formed by an apparatus 10 as will be
described in more detail with reference to Figure 1 when the
curl preventing means 6 are not employed. In other apparatuses
the curl 7 may be more or less pronounced. There may be
curl 7 at the trailing 8 and/or the leading 9 edges of the
sheet 2. Irrespectively, by following the teachings of the
present invention, it should be possible to substantially
reduce or eliminate curl 7 from the sheet 2 due to fusing
when the curl is produced by means other than mechanical
deformation.
Referring now to Figure 1, there is shown by way of
example an automatic xerographic reproducing machine 10 which
incorporates the improved fusing apparatus 1 of the present
invention. The reproducing machine 10 depicted in Figure 1
illustrates the various components utilized therein for
producing copies from an original. Although the fusing
apparatus 1 of the present invention is particularly well
adapted for use in an automatic xerographic reproducing machine
10, it should become evident from the following description
that it is equally well suited for use in a wide variety of
machines where an image is fused to a sheet of final support
material and it is not necessarily limited in its application
to the particular embodiment shown herein.
The reproducing machine 10 illustrated in Figure 1
employs an image recording drum-like member 11 the outer
periphery of which is coated with a suitable photoconductive
material 12. One type of suitable photoconductive material is
disclosed in U. S. Patent ~o. 2,970,906 issued to Bixby in
1961. The drum 11 is suitably journaled for rotation within a
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machine frame (not shown) b~ means of a shaft 13 and rotates
in the direction indicated by arrow 13, to brinq the imaqe
retaining surface 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 scene information is recorded upon a
sheet 2 of final support material.
The practice of xerography is well know in the
are and is the subject of numerous patents and texts including
Electrophotography by Schaffert, published in 1965, and
.
Xe~ography ana ~elated ~ro~esses by Dessauer and Clark,
published in 1965. The various processing stations for
- producing a copy of an original are herein represented in Figure
1 as blocks A to E. Initially, the drum 11 moves photocon-
; ductive surface 12 through carging station A. At charging
station A an electrostatic charge is placed uniformly over
the photoconductive surface 12 of the drum 11 preparatory to
imaging. The charging may be provided by a corona generating
device of a type described in U. S. Patent ~o. 2,836,725 issued
to Vyverberg in 1958.
Thereafter, the drum 11 is rotated to exposure
station B where the charged photoconductive surface 12 is
exposed to a light image of the original imput scene infor-
mation, whereby the charge is selectively dissipated in the
light exposed regions to record the original input scene in
the form of a latent electrostatic image. A suitable exposure
~ystem may be of the type described in U. S. Patent No.
3,832,057 to D. K. Shogren issued August 27, 1974.
After exposure, drum 11 rotates the electrostatic
latent image recorded on the photoconductive surface 12 to
development station C wherein a conventional developer mix is
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applied to the photoconductive surface 12 rendering the
latent image visible. A suitable development station is
disclosed in Canadian Patent No. 991,394 to R. Ashton et al
issued June 22, 1976. The Canadian patent describes a
magnetic brush development system utilizing a magnetizable
developer mix having carrier granules and a toner colorant.
The developer mix is continuously brought through a direc-
tional flux field to form a brush thereof. The electrostatic
latent image recorded on photoconductive surface 12 is deve-
loped by bringing the brush of developer mix into contact
therewith.
The developed image on the photoconductive surface
12 is then brought into contact with a sheet 2 of inal
support material within a transfer station D and the toner
image is transferred from the photoconductive surface 12 to
- the contacting side of the final support sheet 2. The final
support material may be paper, plastic, etc., as desired.
After the toner image has been transferred to the sheet of
final support material 2, the sheet with the image thereon
is advanced to a suitable fuser 3, which coalesces the
- transferred powdered image thereto. One type of suitable
- fuser is described in U. S. Patent No. 2,701,765, issued to
Codichini et al in 1955. After the fusing process, the sheet
2 is advanced by snuffing rolls 14 and then by rolls 15 to a
catch tray 16 for subsequent removal therefrom by the machine
operator.
Although a preponderance of the toner powder is
transferred to the final support material 2, invariably some
residual toner remains on the photoconductive surface 12 after
the transfer of the toner powder image to the final support
material 2. The residual toner particles remaining on the
photoconductive surface 12 after the transfer operation are
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removed therefrom as it moves throu~h cleaning station E.
Here the residual toner particles are first brought under
the influence of a cleaning corona generating device (not
shown) adapted to neutralize the electrostatic charge
remaining on the toner particles. The neutralized toner
particles are then mechanically cleaned from the photocon-
ductive surface 12 by conventional means as, for example,
the use of a resiliently biased knife blade as set forth in
U. S. Patent no. 3,660,863 issued to Gerbasi in 1972
If desired, in accordance with this invention,
the sheets 2 of final support material processed in the
automatic xerographic reproducing machine 10 can be stored
in the machine within a removable paper cassette 17. A suit-
able paper cassette is set forth in U. S. Patent No.
3,767,187 to C. Mahler et al issued October 23, 1973.
The reproducing apparatus in accordance with this
invention can also have the capability of accepting and
processing copy sheets 2 of varying lengths. The length of
thè copy sheet 2, of course, being dictated by the size of
the original input scene or information recorded on the
photoconductive surface 12. To this end the paper cassette
17 is preferably provided with an adjustable feature whereby
sheets
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of varying length and width can be conveniently accommodated.
In operation the cassette 17 is filled with a stack of final
support material 2 of pre-selected size and the cassette is
inserted into the machine by sliding along a base plate (not
shown) which guides the cassette into operable relationship
with a pair of feed rollers 18. When properly positioned in
communication with the feed rollers 18, the top sheet of the
stack is separated and forwarded from the stack into the
transfer station D by means of registration rolls 19.
It is believed that the foregoing description is
sufficient for purposes of the present application to
illustrate the general operation of the automatic xerographic
reproducing machine l which can embody the teachings of the
present invention.
Referring now to Figure 3, that portion of the
reproducing machine lO of Figure 1 embodying the fusing
apparatus l of this invention is shown in greater detail.
The view shown is a side view and it should be readily evident
that the fusing apparatus extends across the entire sheet in
a direction normal to the plane of the Figure. The-image
bearing sheet 2, after passing through the transfer station D
of Figure l upon separation from the photoconductive surface
12, is allowed to fall into contact with a vacuum belt transport
system 20 which conveys the sheet directly to the fusing
apparatus l.
The fusing apparatus l shown includes a ~rcd~ant type
fuser 3. The fuser 3 includes a heated platen 30 mounted to
engage the non-image bearing side of the copy sheet ~ which
moves in sliding contact therewith as it is transported through
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the fusing zone. The heated platen 30 is designed so that an
efficient heat flow is established between the platen and the
copy sheet 2 to raise the temperature of the sheet rapidly
to a level somewhat below the sheet's scorch temperature. By
controlling the temperature of the sheet 2 in this manner
the ability of the sheet to act as a heat sink during image
fixing is minimized. The radiant energy source for fusing is
provided by an infrared quartz lamp 31 which is mounted in a
reflector assembly 32 in opposing relationship to the heated
platen 30 and in a position to thermally communicate with the
newly imaged side of the copy sheet 2. Preferably the spectral
output of the lamp 31 is within a range at which the imaging
material which may be toner for a xerographic machine 10 is
highly absorptive and at which the support material ~F-which may
be paper is relatively non-absorptive. As a result, the toner
images are rapidly raised to the desired fusing temperature while
the support sheet 2 remains at a relatively lower temperature.
A forced air cooling chamber 33 is provided about the backside
of the reflector assembly 32 to cool the fuser 3 in operation.
A heating element 34 is provided in the platen 30
to maintain it at the desired temperature during standby
periods. When the quartz lamp 31 is operated the pre-heat
element is disconnected and the platen 30 receives its heat
input directly from the quartz lamp.
The leading edge of the sheet 2 bearing the image
is pushed through the entrance port 35 to the fusing zone 5 and
moves in sliding contact over the platen 30 through the fuser
exit port 36 into a pair of cooperating transport rolls 40 and
41 which comprise a flame snuffing apparatus. The lower
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snuffing roll 41 is positioned such that its outer periphery
lies below the plane of a fuser platen 30 whereby in operation
the snuffing rolls 40 and 41 are operative to hold the sheet 2
in sliding contact with the fuser platen 30. The sheet is
also held in contact with the platen 30 by means of suction
communicated via suction chamber 37 and platen suction ports
38.
The snuffing rolls 40 and 41 forward the sheet
along a guide plate 42 into the nip of a pair of advancing
rolls 43 which deposit the sheet within a collecting tray 16.
The collecting tray 16 includes a base plate 44 inclined up-
wards and an upwardly turned margin stop 45.
The advancing rolls 43 serve to drive the sheet
2 into the collecting tray 16. The advancing rolls 43 further
include a compact propelling mechanism 46 which moves the
sheet 2 rapidly and efficiently into alignment against the
stop 45. The propelling mechanism is described in greater
detail in U. S. Patent No. 3,847,388 to T. Lynch issued
November 12, 1974.
Having thus described the operation of the fusing
apparatus 1, further reference will now be given to the curl
control means 6 in accordance with this invention.
In the embodiment of Figure 3 the transport 20
; comprises a vacuum transport having a suction means 21 which
draws air in through or between the belts 22. The suction
; means is connected to any conventional cource of suction
~not shown). The suction means 21 cooperates with the belts
22 to firmly hold a sheet 2 of final support material in
contact with the transport. The suction means 21 comprises,
however, only one of many possible external influences
in the machi~e
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lO which can cause an air flow through the fusing zone 5. The
suction means 21 draws air in from an external port (not shown).
Air flows through various passageways defined by the machine
components and sub-stations. The paper path provides one of
the key flow channels for the air which flows to the suction
means 21. In the absence of the curl preventing means 6
in accordance with this invention air is drawn through the
fuser 3 in order to satisfy the requirements of the suction
means 21 as shown by the arrows 50. While this flow of air
has a beneficial effect with respect to cooling the sheet 2
prior to its being received by the snuffing rolls 40 and 41,
it has a deleterious effect in that it results in a substantial
curl being formed in the sheet during fusing.
There is also in the fuser 3 shown an internal means
which causes a flow of air through the fusing zone 5. The
internal means comprises a series of orifices 38 in the platen
30 which communicate with a suction means comprising the
chamber 37. The purpose of these orifices 38 is to provide a~
vacuum holddown for holding the sheet 2 in contact with the
platen 30 as it passes through the fuser 3. When the sheet does
not cover these orifices a substantial air flow is produced. The
direction of this air flow will vary depending on whether the
sheet is entering or leaving the fuser. Another internal cause
of air flow comprises the conductive air currents associated with
the fuser.
Therefore, as shown, an air flow through the fusing
zone is created both by external influences and by internal
influences. It is believed, however, that either of these
influences alone would be sufficient to provide an air flow
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In accordance with this invention it is desired to
reduce the flow of air through the fuser so as to reduce the
curl producing effects of the moisture gradients induced in
the sheet 2 during fusing. The mechanism by which this is
accomplished is not fully understood, but it is believed to
be the result of a localized condition in the fusing zone
which reduces the rate that the moisture is driven out of
the sheet during the period the thermal and moisture gradients
are caused in the sheet by fusing. This may, for example, be
due to a localized increased vapor pressure condition which
can orm due to the restricted air flow and which temporarily
prevents or reduces the rate at which moisture can exit from
the sheet 2 until the thermal and moisture gradients in the
sheet have been reduced or eliminated.
The temperature and moisture gradients in the portion
of the sheet 2 being heated occur for an extremely short
period of time, a matter of fractions of a second. Therefore,
if the sheet can be sufficiently restrained during this period or if
the rate of moisture evaporated from the sheet during the period
can be reduced, curl 7 can be reduced.
In the apparatus 1 shown, without the curl preventing
means 6 the sheets are subject to substantial trail edge curl
7 as shown in Figure 2. Lead edge 9 curl is not pronounced
because of the inner-action of the vacuum transport 20 with
the sheet 2. It is believed that the vacuum transport 20
prevents the sheet 2 from being deformed by the influence of
the moisture gradients by restraining deformation of the sheet.
However, after the sheet 2 leaves the vacuum transport 20 the
trail edge ~ of the sheet is not sufficiently restrained and,
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therefore, is subject to substantial curl as, for example,
that shown in Figure 2.
When the lead edge 9 of the sheet 2 enters the
fusing zone 5 the remainder of the sheet closes off some of
the suction ports (not shown) in the top of the vacuum transport
20 thus reducing the flow of air flow through the fusing zone
5. As the sheet 2 progresses through the zone 5 more of the
suction ports, particularly those adjacent to the fuser 3,
are uncovered by the sheet 2 thereby increasing the air flow
through the zone. This is also believed to be a major factor
in causing the pronounced trail edge 8 curl and insignificant
lead edge 9 curl using the specific apparatus 1 shown.
Therefore, in accordance with this invention curl
preventing means 6 are provided which comprise in the embodiment
shown one or more seals 61, 62, 63 and 64 adjacent to the fusing
zone 5 which are adapted to limit the air flow at the zone
to an amount at which curl of the sheet is substantially
reduced or eliminated. In the apparatus 1 shown which
includes the external influence of the vacuum transport 20,
the provision of the seal 61 between the top portion 65 of
the fuser 3 and the upper transport roll 40 at the exit side
of the fuser provides a substantial reduction in curl as
compared to the same apparatus without the seal 61.
Experimentally, the reduction in curl due to this seal 61 has
been shown to be as much as about 60% or more. Further
reductions in curl can be achieved by providing additional
seals 62, 63 and 64 as, for example, the lower seal 62 between
the bottom portion 66 of the fuser 3 and the lower transport
roll 41 has been determined to provide a further 5% to 10%
or more improvement in curl reduction. At the upstream
.
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side of the fuser 3, because of the external influence of the
vacuum transport 20, it has been found desirable to provide
slots or holes 67 in the seal 63 between the fuser and the
cleaning station E. This allows air flow from the channel
68 as shown by arrow 69 to flow to the transport and thereby
reduces the amount of flow drawn through the fuser. The
provision of holes 67 in this particular seal 63 which also
serves to guide the sheet provides a further 15% or more
improvement in curl 7 reduction. Finally, a seal 64 between
the vacuum transport 20 and the lower portion 66 of the fuser
3 provides some improvement, but not that significant, namely,
less than 5%.
It is quite apparent that the fusing apparatus
illustrated in Figure 3 requires seals between the downstream
sheet transport 40 and 41 and the fusing apparatus 3 in order
to substantially reduce or eliminate curl 7. It should also
be apparent that had the vacuum transport 20 or other external
source of substantial air flow through the fuser 3 been
downstream of the fuser rather than upstream thereof then the
effective seals for reducing air flow through the fuser would
have been the upstream seals 63 and 64, rather than the
downstream seals 61 and 62. In this case the seal 63 between
the upper portion 65 of the fuser 3 and the adjacent housing
E would have had to be impervious, whereas the seals 61 and 62
on the downstream side of the fuser could have been pervious
as desired.
In the embodiment shown the internal suction means
37 and 38 does not exert a controlling influence on the amount
of curl which is formed. Regulation of the suction force here,
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in cooperation with the seals 61 - 64 could help reduce air
flow through the fusing zone 5. Conversely increasing the
suction force would restrain deformation caused by the moisture
gradient, however, it would also increase the retardation
forces on the sheet 2 which could cause the sheet to stall in
the fuser 3 which is undesirable.
The location of the seals 61 - 64 has to be determined
based on the air flow conditions in the apparatus in which the
fuser 3 is employed and seals 61 - 64 may be employed at one
or all of the locations shown in order to provide the reduced
air flow through the fuser. The most significant seals will
be those adjacent the image containing side of the sheet 2, for
an apparatus 10 where the sheet is passed over a platen 30, since
it is on this side of the sheet that the greatest air flow occurs.
It is an essential aspect of this invention that
at least one of the seals 61 - 64 comprises an alongated member
having a brush-like configuration. The seals 61-64 are at least
coextensive with the fusing zone in the transverse direction,
(e.g., the direction normal to the plane of Figure 3).
Referring to Figure 4, a seal 100 in accordance with this
invention is shown. The seal 100 comprises a backing strip
101 having a plurality of elongated fibers 102 extending out
therefrom in a brush-like configuration. The fibers 102 may
comprise individual fibers or tufts of fibers formed, for
example, from a pile of yarn. The density of the fibers should
be such as to provide a substantial baffle or seal to the
flow of air through the seal. Preferably it should prevent
air flow through the channel being sealed.
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The backing strip 101 preferably comprises a com-
posite comprising a metal backing component 103 and a poly-
meric support component 104, preferably nylon, adjacent to
the brush fibers 102. The brush fibers 102 are woven into
the nylon support 104 and the metal component 103 is crimped
over the support to provide added mechanical strength. While
nylon appears to be the preferred material for use as the
fibers 102 in the brush-type seals of this invention, other
heat resistant materials could also be employed if desired,
particularly other polymeric materials. The brush-type seals
may be secured to the fuser by any conventional means as,
for example, the use of screws (not shown).
In the apparatus of Fig. 3, the upper roll 40 is an
idler roll and when the seal 100 is interposed between an idler
roll 40 and the fuser 3, it is necessary to avoid too dense a
brush or else a drag is placed on the idler roll which prevents
its uniform rotation.
By using a brush configuration instead of a strip-
type member the life of the seals 61 - 64 can be substantially
extended. The brush-type seal 100 does not require the same
degree of resiliency for the flbers 102 as is required for the
material of the strip-type seals. Further, the resiliency of
the individual fibers 102 is maintained by the added support
they receive from adjacent fibers.
In the apparatus shown a plurality of spaced apart
circumferential ridges 47 are provided on the upper roll 40
to provide an efficient flame snuffing action while reducing
off-set problems associated with the upper roll. A strip-
type seal leaves a gap of less than about .030" between the
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seal 61 and the hub of the roll 40 which allows a slight air
flow through the sealed air channel. The amount of air flow
has been found to be very slight and not enough to cause a
substantial curl. However, it is desirable to completely seal
the channel between the roll 40 and the fuser 3. A brush-type
seal 100 as in accordance with the present invention performs
the function of completely sealing off the passageway since
the brush fibers 102 follow the contour of the roll surface
and, therefore, fill in the valleys between the ridges 47 to
substantially close off the air channel.
In the apparatus 1 shown, brush-type seals 100 are
employed between the upper and lower transport rolls 40
and 41 on the downstream side of the fuser 3 whereas a strip
type seal 64 is employed on the upstream side of the fuser
between the fuser base 66 and the transport 20. It is apparent
therefore that it is possible in accordance with this invention
to employ seals of both the brush type 100 of this invention
and the strip type 63 where desired.
The strip type seals 63 comprise an elongated strip
type member formed of a resilient material which is biased
against the transports 40, 41 or 20 and extends over the
respective gap between the transport and the fuser. As with
the brush type seal 100 they may be secured to the fuser by
any desired means. Preferably they are formed of a polymeric
material such as polytetrafluoroethylene sold under the
trademark Teflon and polyethyleneterethalate sold under the
trademark Mylar.
An exemplary brush 100 usable in accordance with
the present invention which has been employed was formed
1~45672
of flame proof Nomex nylon with a pile yarn size of 2/10;
with a plain weave for the backing; with a thread count
for the pile ticks of 6.25+ .25/inch and for the pile ends
of 24~ l/inch; with the number of tufts per square inch at
150 + 8% and with a tiger texture for the brush. A brush of
this type has been found to be effective as seen from the
following example.
By way of example for a fuser 3 having a gap
between the platen 30 and the reflector 32 o about 1/8 inch
and a length normal to the plane of Figure 3 of about 15"
an air flow of less than about .2 cfm will substantially reduce
or elimiPate curl. If the seals 61 - 63 are removed the
air flow through the fuser 3 shown would be about 5 cfm.
It is believed that for most radiant fusers the
air flow should be maintained below about 1 cfm and pre-
ferably below about .2 cfm in order to reduce or eliminate
curl.
The toner images of this invention may be formed
from toner of the type described in U. S Patent Nos.
2,807,703 and 2,807,704.
It is apparent that there has been provided in
accordance with this invention a fusing apparatus which fully
satisfies the objects , means and advantages set forth
hereinbefore. While the invention has been described in
conjuction with specific embodiments thereof, it is evident
that many alternatives, modifications and variations will be
apparent to those skilled in the art in light of the foregoing
description. Accordingly, it is intended to embrace all
such alternatives,
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1045~7Z
modifications and variations as fall within the spirit and
broad scope of the appended claims.
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