Electrophotography – Control of electrophotography process – Control of fixing
Reexamination Certificate
2001-11-21
2003-06-17
Lee, Susan S. Y. (Department: 2852)
Electrophotography
Control of electrophotography process
Control of fixing
C219S216000, C399S033000, C399S043000
Reexamination Certificate
active
06580883
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an image heating apparatus such as a fixing apparatus or an apparatus for improving the surface property of an image carried on an image forming apparatus such as a copier or a printer.
2. Related Art
Apparatuses of the heat roller type and the film heating type have heretofore been widely used as fixing apparatuses used in image forming apparatuses of the electrophotographic type, the electrostatic recording type, etc. Particularly, a method of minimizing electric power consumption to the utmost without supplying electric power to a fixing apparatus during standby, and more particularly a heating and fixing method by a film heating system of heating and pressurizing a recording material while passing the recording material to a nip area formed by a pressure member being in pressure contact with a heating member with a film member interposed therebetween to thereby fix a toner image on the recording material as an unfixed image on the recording material are proposed in Japanese Patent Application Laid-Open No. 63-313182, Japanese Patent Application Laid-Open No. 2-157878, Japanese Patent Application Laid-Open No. 4-44075, Japanese Patent Application Laid-Open No. 4-204980, etc.
FIG. 10
of the accompanying drawings schematically shows the construction of the essential portions of an example of the fixing apparatus adopting the film heating process.
Such a fixing apparatus, as shown in
FIG. 10
, has a heater
111
which is a heating member fixedly supported by a stay holder (supporting body)
112
, fixing film
113
which is a thin and heat-resistant film member, and an elastic pressure roller
120
which is a pressure member brought into pressure contact with the heater
111
with the film member
113
interposed therebetween to thereby form a nip area (hereinafter referred to as the fixing nip portion) N of a predetermined nip width.
The fixing film
113
is a cylindrically shaped or endless-belt-shaped or rolled web-shaped member conveyed in the direction of arrow a by driving means (not shown) or the rotational force of the pressure roller
120
while being in close contact with the surface of the heater
111
in the fixing nip portion N.
The heater
111
receives the supply of electric power from a power source (not shown) and generates heat and is controlled to a predetermined temperature.
When in a state in which the heater
111
has been heated and controlled to the predetermined temperature and the fixing film
113
has been conveyed in the direction of arrow, a recording material P bearing an unfixed toner image t thereon as a material to be heated is introduced between the fixing film
113
in the fixing nip portion N and the pressure roller
120
, the recording material P comes into close contact with the surface of the fixing film
113
and is nipped and conveyed by the fixing nip portion N with the fixing film
113
. In this fixing nip portion N, the recording material P and the toner image t are heated by the heater
111
through the fixing film
113
and the toner image t on the recording material P is fixed. That portion of the recording material P which has passed through the fixing nip portion N is peeled off from the surface of the fixing film
113
and is conveyed.
A ceramic heater is generally used as the heater
111
as a heating member. For example, the heater
111
comprises a substrate
111
a
made of ceramics having electrically insulativeness, good heat conductivity and low heat capacity such as alumina, and a heat-generating resistance layer
111
b
of silver palladium (Ag/Pb), Ta
2
N or the like formed on the surface (the surface facing the fixing film
13
) of the substrate
111
a
along the lengthwise direction (a direction perpendicular to the conveying direction of the recording material P) of the substrate
111
a
as by screen printing, that surface of the substrate
111
a
on which the heat-generating resistance layer
111
b
is formed being covered with a thin glass protective layer
111
c.
This heater
111
which is a ceramic heater is such that by electric power being supplied to the heat-generating resistance layer
111
b
, the heat-generating resistance layer
111
b
generates heat and heat the substrate
111
a
made of ceramics and the glass protective layer
111
c
and the entire heater
111
rapidly rises in temperature. This temperature rise of the heater
111
is detected by temperature detecting means
114
disposed on the back of the heater
111
and is fed back to a power supply control portion (not shown) which is control means. The power supply control portion controls the electric power supplied to the heat-generating resistance layer
111
b
so that the temperature of the heater
111
detected by the temperature detecting means
114
may be maintained at a predetermined substantially constant temperature (fixing temperature). In this manner, the heater
111
is heated and controlled to the predetermined fixing temperature.
The fixing film
113
has its thickness formed considerably small, e.g. to 20 to 70 &mgr;m, in order to efficiently give the heat of the heater
111
to the recording material P as the material to be heated in the fixing nip portion N. This fixing film
113
is formed by three layers, i.e., a film base layer, a primer layer and a releasing property layer, and the film base layer side is the heater
111
side and the releasing property layer side is the pressure roller
120
side. The film base layer is formed of polyimide, polyamideimide, PEEK or the like higher in insulativeness than the glass protective layer
111
c
of the heater
111
, and has heat resistance and high elasticity. Also, the mechanical strength such as the tearing strength of the entire fixing film
113
is kept by the film base layer. The above-mentioned primer layer is formed by a thin layer having a thickness of the order of 2 to 6 &mgr;m. The above-mentioned releasing property layer is a toner offset preventing layer for the fixing film
113
, and is formed by coating the primer layer with fluorine resin such as PFA, PTFE or FEP to a thickness of the order of 10 &mgr;m.
Also, the stay holder
112
is formed, for example, by a member made of heat-resistant plastic, and holds the heater
111
and serves also as the conveyance guide of the fixing film
113
.
In a heating apparatus of the film heating type using such thin fixing film
113
, due to the high rigidity of the heater
111
made of ceramics, the pressure roller
120
having an elastic layer
122
becomes flat in the pressure contact portion thereof, following the flat underside of the heater
111
with which it is brought into pressure contact, and formes the fixing nip portion N of a predetermined width, and only the fixing nip portion N is heated to thereby realize heating and fixing of quick start.
In the fixing apparatus of the above-described construction, the disposition relation between the heat-generating resistance layer
111
b
of the heater
111
and the pressure roller
120
will now be described with reference to
FIG. 11
of the accompanying drawings.
As shown in
FIG. 11
, the width W of the heat-generating resistance layer
111
b
of the heater
111
in the longitudinal direction thereof is somewhat narrow as compared with the width D of the elastic layer
122
of the pressure roller
120
brought into contact therewith with the fixing film
113
interposed therebetween in the same direction. This is for preventing the heat-generating resistance layer
111
b
from protruding from the pressure roller
120
in the same direction to thereby locally rise in temperature and be damaged by the thermal stress thereof. Also, the heat-generating resistance layer
111
b
is formed with a width sufficiently wider than the sheet passing area of the recording material P bearing the toner image t thereon. Thereby, the temperature fall of the end portions (due to the leakage of the heat to electrical contacts for power supply and connectors in the lengthwisely end portions of the heater
111
) ca
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