Electrophotography – Image formation – Fixing
Reexamination Certificate
2001-03-28
2003-01-28
Chen, Sophia S. (Department: 2852)
Electrophotography
Image formation
Fixing
C219S216000, C399S333000
Reexamination Certificate
active
06512913
ABSTRACT:
FIELD OF THE INVENTION
The present disclosure relates to a fusing system including a heat storage mechanism. More particularly, the disclosure relates to a fusing system including a fuser roller that includes a heat transport layer having high thermal capacity.
BACKGROUND OF THE INVENTION
Electrophotographic printing and copying devices typically are provided with fusing systems that serve to thermally fuse a toner image onto a recording medium, such as a sheet of paper. Such fusing systems normally comprise a heated fuser roller and a heated pressure roller that presses against the fuser roller to form a nip in which the fusing occurs.
FIG. 1
illustrates a simplified end view of a typical prior art fusing system
100
. As indicated in
FIG. 1
, the fusing system
100
generally comprises a fuser roller
102
, a pressure roller
104
, internal heating elements
106
, and a temperature sensor
108
. The fuser and pressure rollers
102
and
104
comprise hollow tubes
110
and
112
that are coated with outer layers
114
and
116
of elastomeric material.
The internal heating elements
106
typically comprise halogen lamps that uniformly irradiate the inner surfaces of the rollers
102
and
104
. Through this irradiation, the inner surfaces are heated and this heat diffuses to the outer surfaces of the fuser and pressure rollers
102
and
104
until they reach a temperature sufficient to melt the toner (e.g., approximately between 160° C. to 190° C.). The fuser roller and the pressure rollers
102
and
104
rotate in opposite directions and are urged together so as to form a nip
118
that compresses the outer layers
114
and
116
of the rollers together. The compression of these layers increases the width of the nip
118
, which increases the time that the recording medium resides in the nip. The longer the dwell time in the nip
118
, the larger the total energy that the toner and recording medium can absorb to melt the toner. Within the nip
118
, the toner is melted and fused to the medium by the pressure exerted on it by the two rollers
102
and
104
. After the toner has been fused, the recording medium is typically forwarded to a discharge roller (not shown) that conveys the medium to a discharge tray.
The outer layers
114
and
116
are normally constructed of rubber materials (e.g., silicon rubber) that have high thermal resistance and low thermal capacity. These characteristics can be explained with the thermal model
200
shown in FIG.
2
. The thermal model
200
represents the thermal characteristics of the fuser roller
102
shown in
FIG. 1
as a recording medium (e.g., sheet of paper) passes through the nip
118
. As indicated in
FIG. 2
, the model
200
comprises a circuit that includes a thermal energy source
202
representative of the internal heating element
106
. The energy source
202
delivers a constant amount of energy to a thermal capacitor C
1
that is representative of the hollow tube
110
of the fuser roller
102
. The energy provided by the energy source
202
must overcome the thermal resistance provided by the resistor R
1
, which represents the outer layer
114
. Due to the large thermal resistance of the materials used to construct the outer layer
114
, the resistance provided by R
1
is very large. In addition, the energy from the source
202
must overcome the thermal resistance of the resistor R
2
, which represents heat loss due to convection. This energy also reaches a second thermal capacitor C
2
representative of the thermal capacitance of the outer layer
110
. Due to the low thermal capacity of materials used to construct the outer layer
114
, the thermal capacitance of C
2
is very small. Finally, the energy encounters the thermal resistance of resistor RL, which represents the thermal load of the recording medium that passes through the nip
118
. Heat generated by the passage of the energy through the resistor RL is represented by “+” and “−” in FIG.
2
.
As will be appreciated by persons having ordinary skill in the art, the large resistance of the resistor R
1
poses an impediment to the transfer of energy from the interior of the fuser roller
102
to the fuser roller outer surface of the outer layer
114
. This impediment creates the heat transport delay which is the primary cause of delay in the warming of the fusing system
100
. In addition, the small thermal capacity of capacitor C
2
means that the outer layer
114
can store little energy. Because of this fact, the energy stored within the outer layer
114
is quickly dissipated as recording media are passed through the nip
118
.
In addition to increasing the warm-up time of the fusing system
100
, use of conventional fusing systems such as that shown in
FIG. 1
can also result in gloss variation along the length of the recording media. As is known in the art, gloss variation relates to the phenomenon in which the gloss of the fused toner changes over the length of the recording medium. This variation is due to the fact that the fuser roller
102
typically has a circumference which is smaller than the length of the recording medium. Therefore, the fuser roller
102
will normally pass through several revolutions as the recording medium passes through the nip
118
. Due to the transfer of heat to the medium through each revolution and to the fact that the outer layer
114
cannot store large amounts of thermal energy, the temperature of the outer surface of the fuser roller
102
can drop significantly from the leading edge of the medium to its trailing edge. This can result in the printed recording medium having a first section adjacent its leading edge in which the printed media is highly glossy, a second section at its middle where the printed media has a less glossy finish, and a third section adjacent its trailing edge in which the printed media has a non-glossy (i.e., matte) finish.
Gloss variation is undesirable for several reasons. First, printed materials having gloss variation are unaesthetic in that the printed media have an inconsistent appearance. This is particularly true in the case of color printing or photocopying in that the glossy portions of the printed media will appear more vibrant than less glossy portions. Second, a glossy finish normally indicates better fusing to the recording medium. With good fusing, there will be better adhesion between the toner and the recording medium and therefore less chance of the toner flaking off of the recording medium.
From the foregoing, it can be appreciated that it would be desirable to have a fusing system that avoids one or more of the disadvantages described above associated with conventional fusing systems such as gloss variation.
SUMMARY OF THE INVENTION
The present disclosure relates to a fusing system for fusing toner to a recording medium. The fusing system comprises a fuser roller including an elastomeric layer and a heat transport layer disposed around the elastomeric layer, the heat transport layer having high thermal capacity, and a pressure roller in contact with the fuser roller.
The present disclosure also relates to a fusing method that helps reduce gloss variation of printed media fused to a recording medium with a fusing system. The method comprises the steps of forming a heat transport layer having high thermal capacity at an outer surface of a fuser roller of the fusing system, heating the heat transport layer, and transferring heat from the heat transport layer to the recording medium as it passes through a nip of the fusing system.
The features and advantages of the invention will become apparent upon reading the following specification, when taken in conjunction with the accompanying drawings.
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patent: 6154629 (2000-11-01), K
Heath Kenneth E.
Hirst B. Mark
Wibbels Mark
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