Electric heating – Heating devices – Combined with diverse-type art device
Reexamination Certificate
2002-08-07
2004-09-21
Pelham, Joseph (Department: 3742)
Electric heating
Heating devices
Combined with diverse-type art device
C399S329000
Reexamination Certificate
active
06794611
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image heating apparatus adapted for use as a fixing device of an image forming apparatus such as a copying apparatus or a printer employing electrophotographic or electrostatic recording method, a rotary member employed in such image heating apparatus and a method for producing the rotary member.
2. Related Background Art
As the heat fixing apparatus, there has conventionally been employed apparatus of heat roller type or film heating type. In particular, the Japanese Patent Application Laid-open Nos. 63-313182, 2-157878, 4-44075 and 4-204980 propose a method, more specifically a heat fixing method of film heating type in which a toner image on a recording material is fixed across a film between a heater portion and a pressure roller, of not supplying the heat fixing apparatus with an electric power at the stand-by state thereby minimizing the electric power consumption.
The configuration of the heat fixing apparatus of film heating type is known in a method of conveying a film in cooperation with a pressure roller under a tension applied by a conveying roller exclusive for film conveying and an idler roller, and a method of driving a cylindrical film by the conveying force from a pressure roller, wherein the former provides an advantage of maintaining secure conveying ability for the film while the latter provides an advantage of realizing a fixing apparatus of low cost resulting from a simpler configuration.
As a specific example,
FIG. 2
shows, in a schematic lateral cross-sectional view, a fixing apparatus of the film heating type of the aforementioned latter configuration in the pressure roller driving method, and
FIG. 3
is a magnified cross-sectional view of the principal part.
In such apparatus, there are provided a heating member (hereinafter represented as heater)
11
fixedly supported by a heater holder (support member)
12
, and an elastic pressure roller
20
maintained in pressure contact with the heater
11
thereby forming a nip portion (fixing nip) N of a predetermined nip width across a heat-resistant thin film (hereinafter represented as fixing film)
13
.
The heater
11
is heated and maintained at a predetermined pressure by electric current supply.
The fixing film
13
is a rotary member (rotation body) for heat fixing, which is composed of a cylindrical thin member conveyed in a direction, indicated by an arrow, in sliding contact with the surface of the heater
11
at the fixing nip N by the rotary driving force of the pressure roller
20
.
In a state where the heater
11
is heated and maintained at the predetermined temperature and the fixing film
13
is moved in the direction indicated by the arrow, when a recording material P bearing an unfixed toner image t is introduced, as a material to be heated, into the fixing nip N between the fixing film
13
and the pressure roller
20
, the recording material P is maintained in close contact with the surface of the fixing film
13
and is conveyed in a sandwiched state in the fixing nip N together with the fixing film
13
.
In the fixing nip N, the unfixed toner image on the recording material P is heated by the heater
11
across the fixing film
13
and is thermally fixed as a permanent image on the recording material P.
Having passed the fixing nip N, the recording material P is peeled from the surface of the fixing film
13
and is further conveyed.
The heater
11
, constituting the heating member, generally includes a ceramic heater, which will be further clarified with reference to
FIGS. 3 and 4
.
It is formed, on a surface (opposed to the fixing film
13
) of an electrically insulating ceramic substrate
11
a
of a high thermal conductivity and a low heat capacity, by forming a heat-generating resistor layer
11
b
such as of silver palladium (Ag/Pd) or Ta
2
N for example by screen printing along the longitudinal direction of the substrate (perpendicular to the plane of
FIG. 3
) and covering the surface bearing the heat-generating resistor layer with a thin glass protective layer
11
c
. In such ceramic heater
11
, by passing an electric current through the heat-generating resistor layer
11
b
, such heater generates heat to rapidly elevate the temperature of the entire heater including the ceramic substrate
11
a
and the glass protective layer
11
c
. The temperature increase of the heater
11
is detected by temperature detecting means
14
provided on the rear surface of the heater and is fed back to an current control unit (not shown), which controls the current supply to the heat-generating resistor layer
11
b
in such a manner that the heater temperature detected by the temperature detecting means
14
is maintained at a predetermined substantially constant temperature (fixing temperature). In this manner the heater
11
is heated and maintained at the predetermined fixing temperature.
The fixing film
13
, constituting the rotary member for heat fixing, is made with the thickness of 20 to 70 &mgr;m, in order to efficiently transmit the heat from the heater
11
to the recording material P to be heated, in the fixing nip N. The fixing film
13
has a three-layered structure including of a base film layer, a primer layer and a releasing layer. The base film layer is positioned at the side of the heater
11
, while the releasing layer is positioned at the side of the pressure roller
20
.
The base film layer is composed of polyimide, polyamidimide, PEEK etc. having a higher insulation than the glass protective layer
11
c
of the heater
11
, and has heat resistance and a high elasticity. Also the base film layer maintains the mechanical strength such as tear strength of the entire fixing film. The primer layer is formed with the thickness of 2 to 6 &mgr;m. The releasing layer is provided for preventing toner offsetting to the fixing film, and is formed by coating fluorinated resin such as PFA, PTFE or FEP with a thickness of about 10 &mgr;m.
The heater holder
12
is for example formed by a member of heat resistant plastics and serves as a conveying guide for the fixing film, as well as supporting the heater.
In such heating apparatus of the film heating type utilizing a thin fixing film, because of the high rigidity of the ceramic heater
11
constituting the heating member, the pressure roller
20
having an elastic layer
22
is pressed to the flat lower surface of the heater
11
to form the fixing nip portion N of a predetermined width, and quick-starting heat fixation is realized by heating the fixing nip portion N only.
In the above-described configuration, the positional relationship between the heat-generating resitor layer
11
b
of the heater
11
and the pressure roller
20
will be explained with reference to
FIG. 4
, in which the longitudinal width W of the heat-generating resistor layer
11
b
of the heater
11
is formed somewhat narrower than the width D of the elastic layer
22
of the pressure roller
20
maintained in contact across the fixing film
13
. Such relationship is adopted in order to prevent breakage of the heater
11
by a thermal stress resulting from local temperature rise therein, in case the heat-generating resistor layer
11
b
is wider than the pressure roller
20
.
Also the heat-generating resistor layer
11
b
is formed with such a width sufficiently wider than the conveying area of the recording material P bearing the toner image t. It is thus made possible to avoid the influence of temperature decrease in the end portions (caused by heat leakage to the electrical contacts, connectors etc. at the heater ends), thereby realizing satisfactory fixing performance over the entire surface of the recording material. It is also possible to form the heat-generating resistor layer narrower in the end portions of the sheet passing area to increase the heat generation in such end portions, thereby enhancing the fixing performance therein.
Thus, the heat generated by the electric current supply in the heat-generating resistor layer
11
b
of the heater
11
is efficie
Hashiguchi Shinji
Izawa Satoru
Kanamori Akihito
Kataoka Hiroshi
Uekawa Eiji
Fitzpatrick ,Cella, Harper & Scinto
Pelham Joseph
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