Electric heating – Heating devices – With heating unit structure
Reexamination Certificate
2002-06-25
2004-09-14
Evans, Robin O. (Department: 3742)
Electric heating
Heating devices
With heating unit structure
Reexamination Certificate
active
06791069
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a heating device incorporated in e.g. a photocopier for fusing a transferred toner image onto recording paper. It also relates to a method of making such a heating device.
2. Description of the Related Art
Referring to
FIGS. 11 and 12
of the accompanying drawings, a conventional heating device (called “heater” below) may have the following structure. The heater
9
, as best shown in
FIG. 11
, includes an elongated supporting base
90
upon which two heating elements
91
,
92
are formed to extend longitudinally of the base
90
. The heating elements
91
,
92
are made by printing and baking an Ag—Pd resistive material for example. Except for the ends
91
a
and
92
a
, the heating elements
91
and
92
are covered by a crystalline glass layer
93
and a noncrystalline glass layer
94
, as shown in FIG.
12
. The exposed ends
91
a
,
92
a
of the heating elements are connected to an alternator
95
. Upon application of the driving voltage, the heating elements generate heat, as required.
In operation, as shown in
FIG. 12
, recoding paper
96
is held in sliding contact with the outer glass layer
94
by a platen roller
97
, so that the transferred toner image is fused onto the recording paper due to the heat generated by the heater
9
.
In order to achieve high-speed printing, the recording paper
96
should be quickly heated up to a temperature beyond the melting point of the toner (up to about 230~250° C.) by the heater
9
.
If the supporting base
90
has high thermal conductivity, the heat generated by the heating elements will readily be dissipated through the base
90
. Accordingly, the paper-contacting portion of the outer glass layer
94
may be cooled rather quickly down to e.g. the room temperature after the fixing unit is switched into the ready mode, where the power supply to the heating elements is temporarily stopped. Due to this, it may take a long time for the paper-contacting portion of the glass layer
94
to be heated up again to the temperature required for fusing the toner image. Apparently, this is disadvantageous to achieving high-speed printing.
If the supporting base
90
has low thermal conductivity, on the other hand, an uneven temperature distribution will result in the base
90
upon application of the driving voltage to the heating elements
91
,
92
. As a result, the base
90
, subjected to an unacceptably great thermal stress, will be cracked or more severely damaged.
SUMMARY OF THE INVENTION
The present invention has been proposed under the circumstances described above. It is, therefore, an object of the present invention to provide a heater that is thermally durable and capable of exhibiting an immediate thermal response.
According to a first aspect of the present invention, there is provided a heater that includes: a supporting base that has a first surface and a second surface opposite to the first surface and has a predetermined thermal conductivity; a heating element formed on the first surface; and a heat conductor having a thermal conductivity greater than the thermal conductivity of the base.
With the use of a heat conductor, the heat diffusion characteristics of the heater is improved to the extent that the supporting base is not thermally damaged, or that the warm-up time of the heater can be shortened than is conventionally possible.
Preferably, the heat conductor may be provided on the side of the second surface or the first surface. Further, the heat conductor may be provided between the first surface and the heating element.
Preferably, the heater of the present invention may further comprise a glass layer interposed between the first surface and the heat conductor.
Preferably, the heater of the present invention may further comprise a heat conduction restrictor having a thermal conductivity lower than the thermal conductivity of the base, wherein the heat conductor is provided on the side of the first surface of the base.
Preferably, the base may be made of an insulating material including Al
2
O
3
, and the heat conductor may be made of an insulating material including one of SiC, AlN, Ag, Al, BN and WC. As another possible example, the base may be made of an insulating material including AlN, while the heat conductor may be made of an insulating material including SiC.
According to a second aspect of the present invention, there is provided a heater that comprises: a supporting base including a first surface and a second surface opposite to the first surface, wherein the base has a predetermined thermal conductivity; a heating element formed on the first surface; and a heat conduction restrictor provided on the side of the second surface and having a thermal conductivity lower than the thermal conductivity of the base.
According to a third aspect of the present invention, there is provided a heater that comprises: a supporting base including a first surface and a second surface opposite to the first surface; and a heating element formed on the first surface of the base. The base includes a first and a second heat conduction restrictors and a heat conductor interposed between the first and the second heat conduction restrictors. The heat conductor is greater in thermal conductivity than the heat conduction restrictors.
According to a fourth aspect of the present invention, there is provided a method of making a heater. The method comprises the steps of: preparing a supporting base including a first surface and a second surface opposite to the first surface, wherein the base has a predetermined thermal conductivity; forming a heating element on the first surface; and providing a heat conductor on the base, wherein the heat conductor has a predetermined thermal conductivity. The thermal conductivity of the heat conductor is made greater than the thermal conductivity of the base.
Preferably, the heat conductor may be formed by sputtering, spraying, plating or screen printing.
Other features and advantages of the present invention will become apparent from the detailed description given below with reference to the accompanying drawings.
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Hayashi Hiroaki
Nagahata Takaya
Sako Teruhisa
Evans Robin O.
Merchant & Gould P.C.
Pate Vinod
Rohm & Co., Ltd.
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