Note: Descriptions are shown in the official language in which they were submitted.
7b~33~
FIXING APPARATUS
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for
applying a release agent onto the surface of a fixing roll
of, for example, a plain paper copying (PPC) machine.
In a fixing mechanism of a PPC machine 9 paper bear-
ing a transferred toner image is passed between a heated
metal roll and a rubber roll or other elastic rolls under
pressure at a temperature between 150 and 200C until the
image is fixed. In this mechanism, it frequently occurs
that the paper bearing a toner image is wound around the
metal rolI or elastic roll thereby preventing complete
printing or iamming the machineO To avoid these problems,
various techniques have been proposed, among which is the
use of a fluorocarbon resin coating on the surface of the
metal roll.
Whether a fluorocarbon resin coating is applied or
not, all conventional types of fixing mechanisms apply an
additional coating of a release agent onto the surfaces of
the metal roll and elastic roll. However, it is very dif-
ficult to apply a release agent coating uniformly and in
the right amount. If the amount is too large, it forms a
blotch on the paper or discolors the paper. At the same
time, rapid consumption of the release agent requires
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frequent and uneconomical refilling, Furthe~more, excess
release agent coagulated on the surface of the roll can
cause unexpected trouble with the machine. If too small an
amount of the release agent is applied, the releasability
of the roll surface from paper is unavoidably reduced lead-
ing to the problem of the paper being wound around the
roll, Typical release agents are silicone oil and other
heat-resistant oils.
U.S. Patent Nos. 3,718,116 and 3,745,972 disclose
an applicator for the release agent which uses a two-
layered felt, a dense felt layer and a loose felt layer.
Use of this applicator prevents excessive application of
the release agent by contacting a roll and the surface of
the dense felt layer. HoweYer, the amount of release oil
applied using this applicator is still large, particularly
when its viscosity is low. A more serious defect with this
applicator is that the felt tends to become clogged by
toner or carrier particles which causes various problems in
fixing due, for example, to scratches on the surface of the
fixing roll or uneven application of the release oil. As a
consequence, the felt must be replaced frequently which is
not only uneconomical but also makes consistent operation
of the fixing apparatus difficult,
A fixing apparatus that is designed to eliminate
this defect is described in- Japanese Published Patent
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~7833(~
Application No. 110049/77. The characteristic feature of
this apparatus that the dense felt layer is eliminated and
instead at least part of the felt structure is replaced by
tetrafluoroethylene resin foam. This arrangement is in-
tended to prevent excessive application of the release oil.
But, since the pore size of the tetrafluoroethylene resin
foam is not controlled satisfactorily in this apparatus,
the amount of release oil applied is still great. Further-
more, th0 use of a large heat-resistant felt structure
makes the overall apparatus complex, large in size, and
costly. Moreover, because the felt absorbs the oil, not
only does it take a long time before the application of the
Gil onto the fixing roll can be started, but also the oil
absorbed by and held in the felt is entirely wastedO A
more serious defect is that the method of fixing the tetra-
fluoroethylene resin foam involves problems to be solved.
SUMMARY OF THE INVENTION
The disadvantages described above are eliminated
with the utilization of the present invention which pro~
vides a novel fixing apparatus that is compact in size and
simple to use for achieving the desired application of re-
lease agent. With this apparatus, a coating of the release
agent can be applied in a much smaller thickness than can
be provided with the conventional apparatus. Purthermore,
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the agent is supplied in the required amount only when the
,~ temperature of the fixing roll ~ sufficiently high and it
~ is not supplied when the copying machine is not in service.
The invention provides a fixing apparatus which
applies a coating of release agent onto the surface of a
fixing rol~ through a porous fluorocarbon resin membrane
having micropores of a uniformly controlled size, prefer-
ably in the range of from 0,01 to 10 ~m, having a porosity
of 35 to 85%, and a thickness of 50 ~m to 1 mm.
10BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 schematically represents a cross section of
a fixing apparatus using a porous fluorocarbon resin mem-
brane;
FIG. 2 shows a porous fluorocarbon resin membrane
having an area wherein the pores are closed;
FIG. 3 shows a porous fluorocarbon resin membrane
having a projection;
FIG. 4 shows the porous fluorocarbon resin membrane
of FIG. 3 as it is attached to the inner surface of the
bottom of a tank for storing a release agent with the pro
jection being filled with a shape retaining member;
FIG. 5 shows a porous fluorocarbon resin membrane
mounted between a tank for storing release agent and a
holding plate with the projection on the membrane being
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filled with a shape retaining member having a circular
cross section;
FIGo 6(a) is a cross section of the fixing appara-
tus wherein the tank for storing release agent is position-
ed below the porous fluorocarbon resin membrane and FIG~
6(b) is a plan view of the apparatus in FIG~ 6~a);
FIG~ 7 is a diagram illustrating how the porous
fluorocarbon resin membrane of FIG~ 3 is fixed to a metal-
lic tank for storing release agent;
FIGS~ 8~ 9 and lO are diagrams illustrating how the
porous fluorocarbon resin membrane is fusion-bonded to the
inner surface of the bottom of a storing tank of thermo-
plastic resin under heating;
PIGo 11 shows a porous tetrafluoroethylene resin
membrane stamped out into a form as shown in FIG~ 9;
FIG~ 12 (a) is a plan view of an injection-molded
holding plate made of a polyphenylene sulfide resin, and
FIG. 12 (b) is a cross section of FIG. 12 (a) ta~en on a line
A-A';
FIGo 13 ~a) is a plan view of an injection-molded
tank for storing release agent composed of a polyphenylene
sulfide resin, and FIG~ 13 Cb) is a cross section of FIG~
13~a) taken on a line B-B'.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
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For the purposes of the invention, porous fluoro-
carbon resin membranes of suitable characteristics are used
with the particular characteristics selected in accordance
with the viscosity and the required amount of the release
agent applied. The porous fluorocarbon resin membrane is
pTeferably a porous tetrafluoroethylene resin having pores
of a highly uniformly controlled size. An example of such
a resin is Porefl~nT~ manufactured by Sumitomo Electric
Industries, Ltd. of Japan. This product, which is describ-
ed in Japanese Published Patent Application Nos. 13560167
and 42794/78, is produced by extruding or rolling a tetra-
fluoroethylene resin blend containing a liquid lubricant,
drawing the extruded or rolled blend, and sintering the
same in a fixed state. Since the porous te~rafluoroethyl-
ene resin membTane has very fine pores of a size as small
as O.Ol to lO ~m, the release agent supplied oozes out by
passing through the pores very slowly. As the temperature
of the applicator is increased, the viscosity of the rele-
ase agent is decreased and the agent oozes out more easily.
As a result, the release agent can be supplied onto the
surface of the fixing rolI only when the copying machine is
in service.
FIG. l shows a preferred em~odiment of the appara-
tus of the in~ention wherein a porous fluorocarbon resin
membrane l is fixed to the inner surface of the bottom of a
7 ~ 7~ ~ 3 O
tank for storing release oil 2.
In another embodiment, the amount of ~he release
agent applied is reduced further and the agent is applied
onto the fixing roll only through the area where the porous
fluorocarbon resin membrane contacts the roll. This is
shown in FIG. 2 wherein the porous fluorocarbon resin mem-
brane has an area 7 the pores of which are closed and an
area 8 having open pores through which the release agent is
applied The area 7 can be formed by closing the pores in
that area by compression or by coating the area with a
heat-resistant rubber such as fluorocarbon rubber or sili-
cone rubber or by pressing a heat-resistant, high molecu-
lar, synthetic resin membrane such as a fluorocarbon resin
to the area while heating.
In the arrangement of FIG. 1, in some applications,
the porous fluorocarbon resin membrane may not contact the
fixing roll satisfactorily so that upon heating the mem-
brane ruptures thereby letting the oil tank contact and
damage the roll. An arrangement for providing good contact
between the porous fluorocarbon resin membrane and the
fixing roll is illustrated in FIG. 3(a) and ~b)o Here, the
membrane is provided with a linear zonal projection 9 that
is formed by heat and which contacts the circumferential
surface of the fixing rol~ in an axial direction. A con-
cave portion of the projection is filled with a member to
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retain the shape thereof. The shape retaining member is
required to maintain the shape of the projection of the
porous fluorocarbon resin membrane and to provide good
contact between the membrane and the fixing roll. The
member is also required to have a hardness that does not
affect thé surface of the fixing roll at all, as well as
heat-resistance and the abiliky to hold the release agent.
A material that satisfies all of these requirements is
heat-resistant felt 10 that is fitted in the pTojection as
shown in FIG. 4. Howeverg it is very difficul~ and expen-
sive to fit a sufficiently large volume of heat-resistant
felt in the projection as shown in FIG. 4 that it provides
a suitable degree of hardness and forms a flat top of the
projection that is necessary for achieving good contact
between the porous membrane and the fixing roll. There-
fore, a more suitable material for the shape retaining
membrane is a hollow or solid porous material having a
circular cross section, Preferred examples are a porous
tetrafluoroethylene resin tube having pores larger than
those of the porous fluorocarbon resin membrane and a
porosity of 50 to 85~, a porous tetrafluorocarbon resin
cylinder having a porosity of 35 to 85%, and a heat-
resistant felt cylinder. These materials can be simply
installed by holding them under a slotted plate 11 as shown
in FIGo 5. By using one of these materials, all the disad-
9 ~ 3 3
vantages men~ioned above can be eliminated.
If the function and relative position of the tankfor storing the release agent make it difficult to position
it above the fixing roll, the following arrangement shown
in FIG. 6~a) can be used. One end of member 12 by which
supplies the release agent 3 is immersed in the agent in
the storing tank and the other end is in placed contact
with at least part of a shape retaining member having a
circular cross section 10 fitted in the concave portion of
a projection in the porous fluorocarbon resin membrane (1)
with the point of contact being indicated at 13. The rele-
ase agent is supplied to the shape retaining member by
capillary action and is then applied onto the surface of
the fixing roll through the porous fluorocarbon resin mem-
brane. The member used to supply the release agent neednot be heat-resistant, and it may be made of felt, sponge,
nonwoven fabric, woven fabric or a microfine glass tube
having an inside diameter of not more than 0.5 mm. FIG.
6(b) is a plan view of FIG. 6(a). As shown therein, the
size of the member 12 used to supply the release agent can
be properly selected depending upon the absorption rate of
the release agent and the amount to be applied. In FIG.
6~a) and (b), a spring member for controlling the pressure
of contact between the porous fluorocarbon resin membrane
and the fixing roll is indicated at 14.
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A method for fixing the porous fluorocarbon resin
membrane in the shapes described above is illustrated in
FIG. 7, wherein a porous fluorocarbon resin membrane 1 is
held between the inner surface of the bottom of a metal
tank 2 which stores release agent and a layer of packing 15
such as fluorocarbon rubber or silicone rubber. A plate 15
is fixed to the packing by screws 17.
This procedure is complicated enough to involve
much labor and time. Moreover, the fitting of the shape
retaining member increases the number of parts to be assem-
bled and hence the cost. As a further disadvantage, the
release oil may tend to leak from around the screws and
other gaps through the packing after it has been used for
an extended period of time. Thus, the release oil may leak
out through an area other than the area of the porous fluo-
rocarbon resin membrane where the pores are provided.
Another aspect of the invention is the solution of
this problem and the provision of a fixing apparatus that
can be assembled in a short time. Accordirg to this as-
pect, the porous fluorocarbon resin membrane 1 is held, asshown in FIG. 5, between the tank for storing release agent
and a holding plate 11, each formed of thermoplastics. A
slot is formed in both the bottom of the tank and the hold-
ing plate extending in a longitudinal direction. The poro-
us membrane, which should be not larger than the holding
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plate, is placed on the bottom of the tank in such a manner
that the linear zonal projection 9 that contacts the cir-
cumferential surface of the fixing roll fits into the slot
in the bottom of the tank. Subsequently, the holding plate
is fusion-bonded to the inner surface of the bottom of the
tank with heat. In this embodiment, the pores in the area
of the porous fluorocarbon resin membrane other than the
linear ~onal projection that contact the circumferential
surface of the fixing roll in an axial direction are also
closed, as shown in FIGo 3 ~ so that the release agent oo~es
out of the membrane only through the pores in that zonal
projection. The concave portion of the projection is fill-
ed with a shape retaining member 10 before or after the
porous fluorocarbon resin membrane is fixed to the bottom
of ~ storage tank.
It is very difficult to achieve uniform fusion
bonding between the bottom of the storage tank and the
holding plate throughout an area as large as at least 100
cm2. Therefore, according to the invention, a rib 18 is
formed around the holding plate 11 as shown in FIG. 8, and
the holding plate is bonded to the bottom of the storage
tank on the periphery of the plate by quick ultrasonic or
high-frequency welding. The rib 18 may be thicker than the
porous fluorocarbon resin membrane by 0.05 to 0.5 mm. With
such a thickness, the membrane is securely held between the
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11~7~33~
1 holding plate and the bottom of the tank by the welding process,
the membrane will not easily slip off and a good seal is provided
between the holding plate and the bottom of the tank,
Nonetheless, it is still difficult to weld a small
portion of the porous fluorocarbon resin membrane and achieve a
high resistance to slippage from between the holding plate and
the bottom of the tank, To weld a small portion of the porous
fluorocarbon resin membrane that will not easily slip from between
the holding plate and the bottom of the tank, a flank of porous
fluorocarbon resin shee-t can be stamped into a form having lugs
as shown in FIG, ~(a2, positioned between the holding plate and
bottom of the tank, and welded in the manner shown in FIG. 9~b)
and (c). The portions where the lug, holding plate and the
bottom of the tank are welded together alternate with those where
only the plate and bottom of the tank are welded, By this arrange~
ment, a good seal is obtained between the holding plate and the
bottom of the tank and the resistance of the mem~rane against
slippage is three to five times as great as the value obtained
otherwise. To provide an even better seal, a groove 2Q is formed
in the inner surface of the bottom of the tank 2 and a projection
21 is formed in the holding plate 11 as shown in FIG, 10.
The thermoplastic resin of which the storage tank
A
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and the holding plate are made is selected with advantage
from glass fiber reinforced engineering plastics because
such materials have a good resistance to heat and oil and
are heat-sealable by ultrasonic or high-frequency welding.
Particularly preferred examples are a polyphenylene sulfide
~PPS) resin containillg 10 ~o 35% of glass fibers, 6,6-nylon
containing not more than 40% of glass fibers, and a poly-
ethylene terephthalate (FR-PET) resin containing 5 to 40%
of glass fibers~
The fixing apparatus of the invention will now be
described in greater detail by reference to the following
examples which are given here for illustrative purposes
only and are by no means intended to limit the scope of the
invention,
Example 1
A porous tetrafluoroethylene resin membrane ("Pore-
flonTM" manufactured by Sumitomo Electric Industries, Ltd.
having a pore size = 0.05 ~m~ porosity = 35~, thickness =
100 ~m) and a tetrafluoroethylenejhexafluoroethylene resin
sheet (50 ~m thick) having a slot 10 mm wide and 35 cm long
were pressed together by a hot press (2 kg/cm2) at 280C to
provide a laminated sheet as shown in FIG, 2 wherein the
pores in the area of PoreflonTM - corresponding to the slot
(lO mm wide and 35 cm long) remained open. The sheet was
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14 ~ 78~3~
reinforced with felt (5 mm thick) that was placed on the
side opposite the tetrafluoroethylene/hexafluoroethylene
resin sheet. The thus prepared sheet was set in a commeT-
cial PPC copying machine (available from Ricoh Co., Ltd.)
in such a manner that slotted side of the sheet was in
contact with the surface of the smaller TeflonTM-coated
fixing roll.
The copying machine was of a type using silicone
oil #KF 96 tlOO cS) as a release agent. About 5 minutes
after the machine was switched on, when the temperatuTe of
the surface of the fixing roll reached about 160C, sili-
cone oil oozed only through the slotted area of the porous
tetrafluoroethylene resin membrane. During a hundred thou-
sand passes of copying paper, no paper was wound around the
roll, the membrane wore little, and there was no blocking
problem due to toner or carrier particles.
Subsequently, the supply unit was removed from the
copying machine and sheets of copying paper were fed
through the machine. The paper than tended to be wound
around the fixing roll without being released easily. This
demonstrates that the supply unit of the invention supplied
only a very small amount of silicone oil onto the surface
of the fixing roll as in fact is desired.
Example 2
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A porous tetrafluoroethylene resin membrane ("Pore-
flon" having a pore size = 2.0 ~m, porosity = 80~, thick-
ness=0.4 mm) having a projection was formed using heating.
All of the membrane area except the projection, which mea-
sured 6 mm wide and 35 cm long, was covered with a fluoro-
carbon rubber adhesive to form an area as shown in FIGo 3
wherein the pores were collapsed. The concave portion of
the projection was filled with a shape retaining member
that was a porous tetrafluoroethylene resin tube having a
pore size of 3.0 ~m, porosity of 70% and a wall thickness
of 2 mm. The thus prepared sheet was attached to the
bottom of a metal oil tank and set in a commercial PPC
machine of the same type as in Example 1 so that the porous
side was in close contact with the surface of the fixing
roll. After filling the tank with 20 cc of silicone oil
~30,000 cS), a test was conducted as in Example 1. Because
the oil had a high viscosity, none of it would pass through
the porous side at room temperature. However, the tempera-
ture of the surface of the fixing roll reached 150C, the
slotted area of the membrane became transparent indicating
that the oil was oozing out through the membrane. Sheets
of copying paper were fed through the machine when it was
operational, and no paper was wound around the fixing roll
and hence a large number of copies could be made without
difficultyO Almost all of the initial charge of silicone
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oil remained in the tank even after a hundred thousand
passes demonstrating tha~ the consumption of the silicone
oil in the supply unit of the invention was very small. In
addition, it was surprising indeed that not a single sheet
of paper was wound around the roll during 100,000 opera-
tions.
Example 3
A porous tetrafluoroethylene resin membrane (pore
size - 0.5 ~m, porosity = 75%, thickness = 200 ~m) having a
projection and a tetrafluoroethylene/hexafluoroethylene
resin film (50 ~m thick) having a slot 3 mm wide and 28 cm
long were pressed together by a hot press (2 kg/cm2) at
305C to provide a laminated sheet in such a manner that
the slot was along the center of the projection as shown in
FIGo 3~ The laminate thus prepared was stamped into a form
as illustrated in FIG~
By injection molding, a holding plate and a tank
for storing release agent of the shapes shown in FIGS~ 12
and 13 were made of a polyphenylene sulfide (PPS) resin
with a glass fiber content of 30%O As described herein-
above, a rib 18 was formed around the holding plate 11 and
to provide a good seal, a projection was formed in the
holding plate and a groove 20 in the tank. The sheet of
FIGo 11 was placed in the tank so that the projection 9
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fitted in a slot 23 formed in the bottom of the tank. The
conca~e portion of the projection was filled with a porous
tetrafluoroethylene resin tube (pore size=l.0 ~m~ porosity
= 75%, wall thickness = l mm) 3 and thereafter the holding
plate was bonded to the bottom of the tank with an ultra-
sonic plastic welder. The overall setup time including the
welding period was only about one minute, and the resulting
assembly was light i~ weight. The tank was filled with 50
cc of silicone oil ~lO,000 cS). Even at room temperature,
it took only a few hours before the oil passing through the
porous tetrafluoroethylene resin tube came out through the
area of the porous fluorocarbon resin membrane that corre-
sponded to the slot in the tetrafluoroethylene/hexafluoro-
ethylene resin film. The ~hus prepared supply unit of the
invention was set in a commercial PPC machine of the same
type as in Example 1. The area of the porous fluorocarbon
resin membrane that corresponded to the slot in the tetra-
fluoroethylene/hexafluoroethylene resin film made very
intimate contact with the surface of the fixing roll, and
throughout 100,000 passes, no paper was wound around the
roll, and the consumption of the silicone oil was no more
than about 40 cc indicating that the supply system of the
invention continuously applied a coating of the silicone
oil uniformly and in a very small quantity. The oil leaked
through no part of the porous fluorocarbon resin membrane
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- 18 -
other than that corresponding to the slot in the tetrafluo-
roethylene/hexafluoroethylene resin film.
The fixing apparatus of the invention achieves the
following advantages:
(1) A highly uniform coating of Telease agent in a
minimum required amount is supplied resulting in economical
use of the release agent.
(2) The porous fluorocarbon resin membrane used will
not become clogged by toner or carrier particles and it is
little worn by contact with the fixing roll. As a conse-
quence, the apparatus can be used for a very extended
perlod .
(3) The apparatus is very simple to set up, and oil
will not leak out through any area of the porous fluoro-
carbon resin membrane other than that which corresponds tothe slot in the overlying sheet.
It is to be understood that the apparatus of the
present invention can be applied not only to a copying
machine but also to facsimile devices and other machines
that have a fixing mechanism.
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