Electrophotography – Control of electrophotography process – Control of fixing
Reexamination Certificate
2002-10-04
2004-07-13
Ngo, Hoang (Department: 2852)
Electrophotography
Control of electrophotography process
Control of fixing
C399S328000, C399S330000, C399S331000, C219S216000
Reexamination Certificate
active
06763205
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to an image heating apparatus for heating the image on recording medium. In particular, it relates to an image heating apparatus effective as a fixing apparatus mounted in a copying machine, printer, etc.
Heretofore, as a fixing apparatus employed by an image forming apparatus employing an electrophotographic method, an electrostatic recording method, or the like, a so-called thermal fixing apparatus has been widely used, which comprises a fixing roller and a pressure roller, and which passes the recording medium bearing an unfixed toner image, through the nipping portion formed by the fixing roller and pressing roller, in order to fix the unfixed toner image on the recording medium to the recording medium to effect a permanent toner image.
FIG. 10
is a schematic view of a typical thermal fixing apparatus which employs a heat roller. The fixing roller
40
comprises: a hollow metallic core
42
formed of aluminum, stainless steel, or the like; a heating member
41
, such as a halogen lamp, disposed within the hollow of the metallic core
42
; and a release layer
43
formed of fluorinated resin, or the like, on the peripheral surface of the metallic core
42
to prevent toner offset. The surface temperature of the fixing roller is detected using a temperature detecting means such as a thermistor, and the power supply to the heating member
41
is controlled by an unshown power supply control circuit, so that the surface temperature of the fixing roller detected by the temperature detecting means
44
remain constant.
A pressure roller
50
comprises a metallic core
51
, an elastic layer
52
formed on the peripheral surface of the metallic core
51
, and a release layer
53
formed on the peripheral surface of the elastic layer
52
. The elastic layer
52
is formed of silicon rubber, sponge formed by foaming silicon rubber, or the like. The release layer
53
is formed of fluorinated resin, or the like, as is the release layer of the fixing roller
40
.
The fixing roller
40
and pressure roller
50
are kept pressed upon each other, with the application of a predetermined amount of pressure, so that a nipping portion is formed as a fixing nip N. The two rollers
40
and
50
are rotationally driven so that their peripheral surfaces are moved in the direction indicated by the arrow marks in the drawing. In operation, a recording medium P bearing an unfixed toner image is introduced into the fixing nip N, and is passed through the fixing nip N, remaining nipped by the two rollers
40
and
50
. While the recording is passed through the fixing nip N, the unfixed toner image on the recording medium P is permanently fixed to the recording medium P by heat and pressure.
In some of high speed image forming apparatuses, and some of image forming apparatuses which use color toners, an approximately 2 mm thick elastic layer formed of silicon rubber or the like is provided between the hollow metallic core
42
and release layer
43
of the fixing roller
40
of the fixing roller
40
, in order to satisfactorily fix the toner, more specifically, in order to prevent the unfixed toner image from being nonuniformly fixed. The provision of this elastic layer softens the peripheral surface of the fixing roller
40
. Therefore, as the recording medium P is nipped by the two rollers
40
and
50
, the softened peripheral surface of the fixing roller
40
presses the recording medium and the toner particles in the toner image, in a manner to embrace the toner particles on the recording medium P, improving the efficiency with which heat is transmitted from the fixing roller
40
to the recording medium and toner particles thereon.
In recent years, there has been a strong desire for reducing electrical power consumption because of the environmental concern. On the other hand, the market has been demanding higher image quality and higher image output. Thus, in order to meet both the desire for the reduction in electrical power consumption and the market demand for higher speed and higher image quality, various proposals have been made to improve the above described thermal fixing apparatus employing a heat roller.
Referring to
FIG. 11
, one of the such proposals is disclosed, being realized in the form of a thermal heating apparatus low in power consumption and superior in thermal efficiency, in Japanese Laid-open Patent Applications, 10-301417, 11-073050, etc., according to which in order to reduce the electrical power consumption by reducing the time it takes for the fixing roller
40
to reach the operational temperature, heating rollers
47
and
55
containing the heating members
46
and
54
are placed in contact with the peripheral surfaces of the fixing roller
40
and pressure roller
50
, respectively, to heat the peripheral surfaces thereof.
The heating members for heating the peripheral surface of the fixing roller
40
or pressure roller
50
can be divided into two types: a type which is kept in contact with the peripheral surface of the fixing roller
40
or pressure roller
50
; and a type which is not placed in contact therewith. The contact type is higher in heat transmission efficiency. Further, in terms of another heating roller property different from the preceding ones, the heating rollers can also be divided into two types: a type which contains the heating members
46
and
54
, as shown in
FIG. 11
, and a type, in which the internal surface of its hollow metallic core is coated with a heat generating resistive layer, that is, an electrically resistive layer which generates heat as electrical current is flowed through it, with the interposition of an electrically insulative layer formed of organic resin (polyimide, for example), glass, or the like material.
As an example of the latter type, a thermal fixing method of a film heating type is proposed in Japanese Laid-Open Patent Applications 63-313182, 2-157878, 4-44075, 4-204980, etc. According to this thermal fixing method, a toner image on recording medium is fixed through a piece of film which is thin and low in thermal capacity, and which is placed between the heating portion and pressure roller, and power consumption is minimized by not supplying power to the thermal fixing apparatus while an image forming apparatus is on standby.
FIG. 12
shows the general structure of an example of a film heating type fixing apparatus. In the drawing, a referential code
60
stands for a film assembly, which comprises: a heater
61
comprising a plate of ceramic, such as alumina, aluminum nitrate, etc., and a heat generating resistive layer formed on the ceramic plate; a stay/holder
62
which is formed of heat resistant resin, and to which the heater
62
is solidly fixed; a heat resistant thin film
63
(which hereinafter will be referred to as fixing film) which is formed of polyimide, or the like, and which is loosely fitted around the stay/holder
62
. The heater
61
of this film assembly
60
, and the pressure roller
50
, are kept pressed against each other, with the interposition of the fixing film
63
, forming the fixing nip N.
As the pressure roller
50
is rotationally driven in the direction indicated by an arrow mark, the fixing film
63
is conveyed by the rotation of the pressure roller
50
in the direction indicated by another arrow mark, through the fixing nip N, while being kept in contact with the heating roller
61
(sliding on the heating roller
61
). The temperature of the heater
61
is detected by a temperature detecting means
64
, such as a thermistor, disposed on the back surface of the heater, and is fed back to an unshown power supply control portion so that the temperature of the heater
61
is kept at a predetermined level (fixing temperature).
Compared to image forming apparatuses, such as printers, copying machines, etc., employing a thermal heating apparatus in accordance with the prior art, which employs a thermal roller, the image forming apparatuses employing a thermal fixing apparatus of a film heating type such as the
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Ngo Hoang
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