Electrophotography – Control of electrophotography process – Control of fixing
Reexamination Certificate
2000-01-27
2001-10-23
Grainger, Quana M. (Department: 2852)
Electrophotography
Control of electrophotography process
Control of fixing
C399S068000, C399S069000
Reexamination Certificate
active
06308021
ABSTRACT:
This application is based on applications Nos. 11-19746 11-19761 and 11-19779 filed in Japan, the contents in which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a fixing device which is used in an image forming apparatus according to the electrophotographic system such as a copying machine, a printer, or a facsimile apparatus to heat and fuse a developer image that has been transferred from an image bearing body to a transfer sheet such as normal paper or a transparency resin sheet for an overhead projector (OHP sheet), thereby fixing the image to the sheet.
Conventionally, as shown in
FIG. 46
, a known fixing device of this kind comprises fixing members
3
and
4
configured by a pair of rollers in each of which an elastic member
2
is disposed on the outer periphery of a metal cylinder
1
, heating means
5
for heating the fixing members
3
and
4
, driving means
6
for rotatingly driving at least one fixing member
3
, and a spring
7
which causes the fixing members
3
and
4
to contact with each other at a constant abutting force. A transfer sheet
9
is transported to a contact portion (nip portion
8
) between the elastic members
2
of the pair of fixing members
3
and
4
. A developer on the transfer sheet
9
is fused by heat supplied from the fixing members
3
and
4
and then fixed to the transfer sheet
9
.
In order to improve the productivity in a copying machine, a printer or the like, the rotational speeds of the fixing members
3
and
4
should be increased so as to increase a speed at which the transfer sheet
9
is passed through the nip portion
8
(fixing speed).
In the conventional fixing device, silicone rubber constituting the elastic members
2
has a heat conductivity of about 0.6 to 0.8×10
−3
cal/cm·sec·° C. Therefore, the efficiency of absorbing heat from the surfaces of the elastic members
2
into the transfer sheet
9
passed through the nip portion
8
is higher than that of supplying heat from the heating means
5
to the surfaces of the elastic members
2
. As a result, a phenomenon takes place in which, when the fixing speed is set to be higher, the surface temperatures of the elastic members
2
are temporarily decreased during a period when an operation of continuously supplying sheets is started. The decrease of surface temperature causes a failure in image gloss or a fixing failure.
In order to increase the efficiency of the heat supply from the heating means
5
to the surfaces of the elastic members
2
, a countermeasure may be taken in which a reinforcing inorganic filler such as silica or iron oxide added to the silicone rubber is replaced with a high thermal conductive filler such as alumina or magnesium oxide, and the addition amount of the filler is increased. However, a high thermal conductive filler has no effect of improving the heat resistance. Furthermore, as the addition amount of the filler is increased, the polymer component having excellent heat resistance is inevitably reduced. Therefore, the elastic members are decreased in strength in high temperature and hence susceptible to be thermally degraded. In the case where the contact abutting force between the fixing members
3
and
4
is constant as in the fixing device shown in
FIG. 46
, when the hardness is reduced as a result of thermal degradation, the width of the nip portion
8
(nip width) is increased. When the nip width is increased, the quantity of heat supplied from the nip portion
8
to the transfer sheet
9
is varied and hence the image quality is changed.
Further, when the addition amount of the filler is increased, the hardness of the silicone rubber is increased and the elastic members
2
are decreased in elasticity. When the elasticity of the elastic members
2
is decreased, it is necessary to perform the abutting of the fixing members
3
and
4
at a very high pressure or to thicken the elastic members
2
in order to ensure the width of the nip portion
8
, thereby causing an image to be obscured or a sheet to become crinkled, or reducing the heat supply quantity to cause a fixing failure or the like.
Furthermore, when the density of cross-link of the silicone rubber is increased higher by changing the polymer component, it is possible to suppress the reduction of the hardness due to the thermal degradation. However, the increased density of cross-link causes the elasticity of the elastic members
2
to be decreased.
SUMMARY OF THE INVENTION
As described above, it is difficult to enhance all the heat conductivity, the heat resistance, and the elasticity of silicone rubber constituting the elastic members
2
. When the heat conductivity is set to be high in order to improve the productivity, it is impossible to eliminate an effect of reduction of the hardness due to the thermal degradation. In other words, in order to maintain the image quality, fixing conditions such as the surface temperatures of the elastic members
2
(fixing temperature), and the transporting speed of a transfer sheet (fixing speed) must be changed in accordance with the degree of advancement of thermal degradation.
It is an object of the invention to provide a fixing device in which an effect of reduction of the hardness of an elastic member due to thermal degradation is corrected, thereby attaining a high productivity.
A first aspect of the invention provides a fixing device comprising: first and second fixing members each of which has an elastic member and which are abutted against each other so that said elastic members contact with each other; a heater which heats at least one of said first and second fixing members; and a controller which corrects fixing conditions in accordance with an integrated energizing time that is an integrated value of an energizing time of said heater, wherein a sheet carrying an image of a developer is passed between said first and second fixing members, whereby the developer is heated and fused under a pressure exerted by said first and second fixing members, to be fixed onto the sheet.
In a fixing device of the first aspect of the invention, fixing conditions are corrected in accordance with the integrated energizing time that is the integrated value of the energizing time of the heater. Therefore, even when the efficiency of the heat supply to a transfer sheet is decreased because of reduction of the hardness of an elastic member of a heating member due to thermal degradation, a sufficient quantity of heat is supplied to the transfer sheet. As a result, reduction of the fixing property and that of the reproducibility of a transparent color which are respectively caused by reduction of the hardness of the elastic member in the cases where the transfer sheet is normal paper and where the transfer sheet is an OHP sheet can be prevented from occurring.
A second aspect of the invention provides a fixing device comprising: first and second fixing members each of which has an elastic member and which are abutted against each other so that said elastic members contact with each other; a heater which heats at least one of said first and second fixing members; and a controller which corrects fixing conditions in accordance with an integrated energizing time that is an integrated value of an energizing time of said heater, and information of an image to be fixed, wherein a sheet carrying an image of a developer is passed between said first and second fixing members, whereby the developer is heated and fused under a pressure exerted by said first and second fixing members, to be fixed onto the sheet.
In a fixing device of a second aspect of the invention, fixing conditions are corrected in consideration of not only the integrated energizing time but also of the image information. Therefore, reduction of the fixing property in the case where the transfer sheet is normal paper, and that of the reproducibility of a transparent color in the case where the transfer sheet is an OHP sheet can be compensated more surely. Further, as a result of the correction of the fixing conditions,
Isogai Mitsuru
Ito Tetsuro
Oonishi Taizou
Yamada Tetsuya
Grainger Quana M.
McDermott & Will & Emery
Minolta Co. , Ltd.
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