Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF T~IE INVENTION
The present invention relates to a fixing apparatus
with heat and pressure for electrophotographic copiers.
In accordance with a general process employed
in electrophotographic copiers, a toner image is electro-
statically formed on a photosensitive member, and said
toner image is transferred to a transfer paper, after that,
it is fixed. Fixing apparatus for fixing the toner image
heretofore employed is a fixing apparatus with heat and
pressure.
This apparatus has a structure such that a heating
roll having a surface coated with a heat-resistant releasing
material and a pressure roll having a heat resistance and
a flexibility are brought into contact with each other
by applying a given pressure to permit a paper to be fixed
to pass therebetween.
Heat resistant releasing materials for the heating
roll which have been known are tetrafluoroethylene (Teflon -
trade mark), silicone rubber, fluorocarbon resin, etc.,
and as the case may be, fixing is carried out while further
forming a film such as a suitable silicone oil.
The heating roll coated with silicone rubber
among these heat resistant materials is resilient in its
surface so that smash or deformation of the toner may be
minimized to obtain copies of good quality.
Such silicone rubber is roughly divided into
at least two kinds from its vulcanization temperature. That
is, there are room temperature vulcanized silicone rubber
(RTV) and high temperature vulcanized silicone rubber (HTV),
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the RTV being generally better than the other in terms of
the parting property relative to the toner. In the case
of rolls currently used, the good parting property remains
exhibited in the range of copies from about 5,000 to 30,000,
but when the silicone components run dry, then unfavorable
situations such as twining of paper round the offset or
roll result.
On the other hand, application of silicone oil to
the surface of the heating roll provides a significant effect
in preventing offset, but both RTV and HTV are swelled by
the presence of silicone oil to unfavorably induce
deterioration of various properties and poor adhesion.
A method for heating a heating roll is also
roughly divided into two methods, one of which is to
heat the heating roll from the interior thereof and the
other receiving heat from the external surface thereof.
In the former method, it is not complex in
construction, but heat transmission inherent in the
silicone rubber is so bad as to increase a temperature
of adhesive interface with a core of the heating roll thereby
inducing thermal deterioration of primer and deterioration
of various properties. For this reason, a method has been
proposed wherein rubber is formed into a multi-layer, into
which thermally stabilized rubber is inserted. This method,
however, results in an increase of manufacturing process
and an increse of rubber wall from a thermal standpoint,
which is not effective.
In the latter method, the external surface is
highest in temperature so that the disadvantages noted abGve
may be decreased. However, it is important how to enhance
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transmission efficiency to the external surface and it is
also important how to minimize heat loss caused by an
increase of the entire surface area. In addition, where an
infrared heating source is used as the external heating
source, there is a possible danger of fire caused
by the paper when the latter is plugged or twined.
Further, most of such heat resistant releasing
materials are small in heat conductivity, and hence, as
compared to a heating roll which uses a metal surface without
modification with respect to thermal transmission rate
to the paper to be fixed, the temperature rise is slow
internally of the transfer paper with which the heating
roll comes into contact, as a consequence of which more
heat is-required to let it increase to the same surface
temperature. However, the surface energy of the metal
surface is extremely high and lends itself to what is
called the offset phenomenon in which a part of toner
image is adhered to the heating roll surface, and even
if a film such as silicone oil is formed on the surface, the
toner passes through the film to permit the toner to
touch with the metal surface to induce offset, which is
not practical.
In order to decrease the offset, there has been
proposed a method for heating two rolls so as to provide
a temperature gradient within the toner layer, that is,
to semi-dissolve the toner surface while to dissolve the
paper to be fixed. However, since the temperature con-
ductivity of the paper to be fixed is extremely low, the
roll on the side of the paper to be fixed must be held
at a relatively high temperature, resulting in a poor
thermal efficiency.
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Further, for purposes of minimizing the aforesaid
offset, all that need be done is at least not to allow the
toner to come into contact with the surface of the heating
roll. As for example, one method has been proposed, in
which a functional group is introduced into a releasing
agent such as silicone oil to effect chemical reaction
with the surface of the metal roll thereby forming a cross
link film of which low surface energy is formed to minimize
offset. The functional group specifically used is a
polyalkylsiloxane releasing agent containing mercapto
group, carboxyl, hydroxyl group, epoxy group, amino group,
isocyanate group, and thioether, and metals well-used
are iron, copper, aluminum, zinc titanium, silver, etc.
In this case, thermal transmis-sion efficiency may be
increased to decrease electric power required, while the
surface is formed with a hard metal to smash the toner
conversely to the resilient surface such as silicone,
resulting in the lowering of image quality such as an
increase of background density of the image.
BRIEF SUMMARY OF THE INVENTION
~h The present invention has been realized in view
of circumstances noted above, and it is an object oflthe
invention to provide a fixing apparatus with heat and
pressure for electrophotographic copiers, wherein a first
roll, which comes into contact with a toner image on a
paper to be fixed, has a surface coated with a heat
resistant resilient releasing material while a second roll
arranged on the side not placed in contact with the toner
image comprises a metal roll, a heating source is provided
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at least in the second roll, and a releasing agent having
a functional group is supplied to the second roll, thereby
enabling to increase thermal transmission efficiency with-
out lowering image quality, to enhance durability of
apparatus, and to simplify apparatus.
In accordance with another aspect of this invention
there is provided apparatus for fixing toner images to copy
substrates, said apparatus comprising:
a first roll including an elastomeric outer
layer;
a second roll contacting said first roll
and cooperating therewith to form a nip through which
said copy substrates pass with said toner images contacting
said elastomeric outer layer;
means supported internally of said first roll
for elevating the surface temperature thereof;
means disposed internally of said second roll
for elevating the surface temperature thereof directly and
indirectly serving to assist said means disposed internally
of said first roll to thereby elevate the surface tempera-
ture of said first roll;
said elastomeric layer comprising silicone
rubber and said second roll being fabricated from metal
and
m~ans for applying a functional release agent
to the surface of said second roll and subsequently to said
first roll through contact of said second roll with said
first roll.
DETAILED DESCRIPTION OF THE DRAWINGS
The drawing is a schematic section of a
heating, contacting and fixing device according to the
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present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention will now be described by way of
a preferred embodiment.
The attached figure is a schematic sectional view
showing one embodiment according to the present invention. A
first roll indicated as at 1 rotates in the direction of
arrow A while a second roll indicated as at 2 rotates in the
direction of arrow B. The first roll 1 is internally pro-
vided with a heating source 3a and has a metal core 4 onwhich silicone rubber 5 is coated. The second roll 2 is the
metal roll which is also internally provided with a heating
source 3b. At least one of rolls 1 and 2 is provided with a
temperature detection end 6 for the purpose of temperature
control.
In the periphery of the second roll 2, there are
arranged a releasing agent supply member 8 composed of
Teflon ttrade mark), felt or the like of which one end is
immersed into a releaslng agent 7 and for supplying the
releasing agent on the surface of roll, and a blade 9 for
uniformly controlling a supply of the releasing agent.
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The heating contacting and fixing apparatus
construction as mentioned above has features, which will
be explained in order as follows.
First, in order to raise temperatures of the
first and second rolls 1, 2 to desired temperature, at
least the heating source 3b within the second roll or
the heating sources 3a and 3b within the first and second
rolls 1, 2, respectively, are heated. In this case, the
quantity of heat is suitably distributed so that more
heat is applied to the second roll 2 having a metal surface
and both the rolls 1 and 2 are brought into contact with
each other for rotation in a well-known manner, whereby
the silicone rubber 5 round the first roll 1 may be heated
internally and externally. Hence, the temperature gradient
within the silicone layer 5 is small and the rising speed
of the surface temperature of the silicone rubber 5
is increased, and in addition, heat required to heat the
metal core 4 of the first roll l is prevented from being
consumed more than needed. At this time, the releasing
agent 7 containing a functional group is supplied to
the second roll 2 and to the silicone layer 5 of the first
roll l.
After both the rolls l and 2 have reached the
desired temperature, the temperature is controlled by the
temperature control device 6. Since the consumption of
electric power in a normal operation is less than that
consumed at the time of temperature rise or at the time of
passage of the paper to be fixed, it is no~ necessary to
place both the rolls l and 2 in a condition of contact
and rotation so that a difference of temperatures within
the silicone rubber 5 may be maintained small.
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Next, both rolls 1 and 2 are brought into contact
with each other before the paper to be fixed bearing a
toner image 11 subjected to fixation in a fixing process
is reached a fixing device to thereby permit the paper 10
to pass through, for fusion, a contact or nip portion 12
formed between the rolls 1 and 2. Incidentally, since both
front and back surfaces of the paper 10 to be fixed receive
heat, the temperature gradient and also the viscosity
gradient within the toner image 11 are gentle to provide a
good condition in order to avoid at least offset. In this
case, since the surface of the first roll 1 is formed
with silicone 5 having a good releasing property and coated
with a releasing material 7, it is not necessary to par-
ticularly raise the temperature in the vicinity of a contact
sur ace between the toner image-and the paper lO to be
fixed to a level higher than the temperature of a contact
surface between the toner and the first roll l.
Where the first and second rolls l and 2 are
designed to have silicone and a metal surface, respectively,
as seen in the apparatus according to the present invention,
if the surface temperatures are set to be the same, the
quantity of heat transmitted from the first roll 1 to the
paper lO and toner image ll is about one half (1/2) of the
second roll 2 in terms of thermal conductivity, while the
first roll l is greater in the surface temperature drop
in terms of temperature conductivity. This temperature
and quantity of heat may be recovered by the heating sources
3a and 3b. However, the surface temperature of the first
roll l is supplied between the paper 10 to be fixed and
a subsequent paper 10' to be fixed from the metal surface
` of the second roll 2 so that the quantity of heat supplied
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from the heating source 3a within the first roll 1 is less
than the quantity transmitted at a contact portion 12 to
the paper 10 to be fixed and the toner image 11. Therefore,
an absolute temperature rise within the silicone rubber 5
round the first roll 1 is extremely effective against
at least thermal deterioration of silicone and primer.
It will of course be noted that the desired temperatures
of the first and second rolls 1, 2.are not necessarily
the same temperature but the second roll 2 may be set
somewhat higher to avoid thermal deterioration of silicone.
As disclosed in Japanese Patent Laid-Open
No. 39,554~1975, the quantity of heat generated from the
heating sources 3a and 3b may also be controlled in
accordance with a given relationship so that the temperature
within the toner layer may substantially be maintained
constant.
It will be understood that the releasing agent 7
may be supplied from the second roll 2 to the first roll 1
even between the paper 10 to be fixed as previously
mentioned,
As described above, the second roll 2 is formed
into a roll having a metal surface, whereby the first roll
1 may obtain an effect of external heat to minimize thermal
deterioration of the silicone rubber layer 5 and to increase
a heat transmission efficiency on the side of the paper 10
to be fixed on the toner image 11, thereby decreasing a
possibility of occurring offset at the time of fixing
process to obtain copied images of good quality. These.
advantages can be achieved only by the use of the re~easing.
3~ agent 7 containing a functional group according to the
present invention to obtain a stabilized performance for
a long period of time.
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That is, adhesion of the toner image 11 already
fused on the back of the paper 10 to be fixed, paper
powder on the paper to be fixed, the toner particles
floating in the vicinity of the fixing device, and the
toner offset to the first roll, to the second roll having
a metal surface can be avoided by the presence of a cross
link thin layer formed by the reaction between the functional
group contained in the releasing agent 7 and the metal to
always maintain a fresh metal surface, whereby a stabilized
fixing process may be maintained for a long period of time.
In addition, also in the first roll 1, the releasing agent 7
has no reactivity with respect to the silicone rubber 5,
but the offset phenomenon may be minimized by the low
surface energy characteristic inherent in the silicone and
the function inherent in the releasing agent.
Further, since the toner has a wide distribution
- in molecular weight, there is possibility that offset may
occur however hard you may control the surface temperature
of rolls. However, if the quantity thereof is small, it
may be re-transferred to the paper 10' to be fixed subse-
quently fed. The surface may accurately be maintained in
its initial condition by the provision of a cleaning roll
13 at least on either of the first and second rolls 1, 2,
as shown in the figuré. The surface of the cleaning roll
13 may comprise metal having no reactivity with a functional
group within the releasing agent 7, for example, such as
stainless steel and the like, or thermoplastic resins and
the like having the same quality as that of toner.
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EXAMPLE
The first roll 1 has an aluminum core 4 of
- which surface is coated with 1.5 mm thick of HTV (KE-530
of Shin-etsu Chemical make) to form a coated layer 5
having a diameter of 30 mm while the second roll 2 com-
prises a copper pipe, wall thick 3 mm x diameter 30 mm.
It was assumed that the surface speed is 100 mm/sec.,
feed speed of paper 10 to be fixed is 1000 copies/hour,
and the surface temperature of the rolls 1 and 2 is 140C.
It was assumed that the maximum 400W may be applied to
the heating source 3a of the first roll 1 and the maximum
600W to the heating source 3b of the second roll 2.
In the case of the releasing agent 7, which comprises poly-
alkylsiloxane containing a mercapto group, the rise time
to the desired temperature was about two and half minutes
and heat loss in normal condition was 180 W for both rolls.
The paper 10 to be fixed was fed under these conditions,
and a as a result, good fixing performance was obtained,
consumption electric power being 170 W for the first roll
while 300 W for the second roll. The average temperature
- at the adhesive surface between the silicone coated layer 5
and the core 4 was 155C. Unserviceable copies due to
separation of the silicone coated layer 5 from the core 4
have appeared after more than 100,000 to 150,000 copies
have been produced, and during that time, no lowering in
performance due to offset or the like has been found. In
the case where the temperature has been controlled in a
given relation (in this case, surface temperature of the
first roll + surface temperature of the second roll =
3~ constant) as previously described, fixing condition has
been stabilized.
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It will be understood from the foregoing that
employment of arrangement wherein the first roll l is coated
with silicone rubber and the second roll 2 comprises a metal
roll and the parting agent 7 comprises a material having a
functional group m~y provide a heating, contacting and
fixing device which is higher in thermal efficiency, service
life and reliability than is obtained by prior art devices.
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