Electrophotography – Image formation
Reexamination Certificate
2000-07-27
2003-04-29
Cain, Edward J. (Department: 1714)
Electrophotography
Image formation
C399S066000, C399S067000, C399S068000, C399S069000
Reexamination Certificate
active
06556797
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an image-forming apparatus, such as a copying machine or a printer, which employs an electrophotographic process.
2. Related Background Art
Printers employing an electrophotographic process are conventionally constructed as shown in FIG.
1
.
A paper feed cassette
2
is set at the lower part of the main body
1
of a printer, and sheet material P is loaded into a sheet loading board
201
. With regard to the sheet materials P, a pick-up roller
202
is driven by a main motor (not shown) and rotated in the direction of an arrow A, whereby the sheet material P is sheet-by-sheet delivered to twin paper feed rollers
203
consisting of a paper feed roller
203
a
and a retard roller
203
. The uppermost sheet material P is separated then fed to first twin delivery rollers
301
consisting of a first delivery roller
301
a
and a support roller
301
b.
The sheet material P delivered to the first twin delivery rollers
301
is delivered to second twin delivery rollers
302
consisting of a second delivery roller
302
a
and a support roller
302
b,
and is further delivered to a transfer zone formed by a transfer photosensitive member
401
and a transfer roller
402
which are held in a cartridge
4
. At the transfer zone, image signals processed by a controller (not shown) are written as an electrostatic latent image on the transfer photosensitive member
401
by means of a scanner
5
. The electrostatic latent image is developed with a toner, and thereafter the developed image is transferred to the sheet material P as an unfixed image.
The sheet material P to which the unfixed image has been transferred is delivered through a transport guide
403
to a fixing assembly
6
. In the fixing assembly
6
, a heater unit
601
consists of a ceramic heater
601
a,
a fixing film
601
b,
a film guide
601
c
and a stay
601
d.
Upon applying an alternating current, the ceramic heater
601
a
heats the fixing film
601
b,
and a pressure roller
602
applies a stated pressure, thus the unfixed image on the sheet material P delivered there is fixed. The sheet material P having the image thus fixed is delivered to first twin paper-output rollers
603
consisting of a first paper-output roller
603
a
and a paper-output support roller
603
b.
In the case of double-side printing, a flap
14
moves upward to the position shown by dotted lines, and the sheet material P to which the unfixed image has been fixed is delivered to twin reversible rollers
801
of a double-side unit
8
; the rollers
801
consisting of an reversible roller
801
a
which rotates in the direction of an arrow D and an reversible support roller
801
b.
Then, the sheet material P is sent to a delivery path
807
. The rotation of the reversible roller
801
is switched to the direction of an arrow E, so that the sheet material P delivered to the delivery path
807
by a predetermined length is delivered to a delivery path
808
, and then sent on to first twin double-side-printing delivery rollers
803
consisting of a first double-side-printing delivery roller
803
a
and a support roller
803
b
and to second twin double-side-printing delivery rollers
804
consisting of a second double-side-printing delivery roller
804
a
and a support roller
804
b.
Thereafter, at given timing, the sheet material P is again delivered to the first twin delivery rollers
301
and the second twin delivery rollers
302
, and, at the transfer zone formed by the transfer photosensitive member
401
and the transfer roller
402
, an unfixed image is transferred to the second-side surface which is the back of the first-side surface, in like manner on the first-side. surface.
The sheet material P to which the unfixed image on the second-side surface has been transferred is again delivered through the transport guide
403
to the fixing assembly
6
, where the unfixed image on the second-side surface is fixed, and the sheet material P having the having the image thus fixed on the second-side surface is delivered to the first twin paper-output rollers
603
. After the fixing on the second-side surface, the flap
14
stands on the position shown by solid lines, and the sheet material P is delivered to second twin paper-output rollers
701
consisting of a second paper-output roller
701
a
and a paper-output support roller
701
b,
and discharged on a face-down tray
702
.
A detailed construction of the fixing assembly
6
is shown in FIG.
2
.
On the downstream side of the heater unit
601
and pressure roller
602
, provided are a lower guide
609
which guides the sheet material P to the first twin paper-output rollers
603
and an upper guide
612
. Materials for the lower guide
609
and upper guide
612
are formed of a polymer composition (Type P) shown in Table 1.
Numerical values of the triboelectric voltage, surface resistivity and contact angle water repellency of the polymer composition (Type P) are shown in Table 2.
TABLE 1
Type P
Components
wt. %
Base polymer: PET
53.5
Ion-conductive polymer: none
0.0
Ion feed source: none
0.0
Plasticizer: polyethylene glycol 400 bis(2-ethyl hexanoate)
1.5
Remainder ingredients: glass fiber, an antioxidant, a flame retardant, and an auxiliary flame retardant.
TABLE 2
Triboelectric voltage: 3,000 V
Surface resistivity: 7.8 × 10
16
&OHgr;
Contact angle: 75°
Triboelectric voltage is a value measured by the method prescribed in JIS L1094B.
However, the above prior art has disadvantages as stated below.
After the fixing on the fist-side surface, the toner image heat-fixed by the heater unit
601
and pressure roller
602
may adhere to the upper guide
12
before it solidifies completely onto the sheet material. Since the toner is very cohesive to each other, it may grow or accumulate gradually on the upper guide
612
every time the sheet material is delivered, so that the image on the sheet material delivered later may be scraped with the toner having accumulated on the upper guide, or the sheet material may run against the toner having accumulated on the same to cause a paper jam.
When the toner image is fixed on the second-side surface, the first-side surface is also heated because of the fixing on the second-side surface. Hence, the toner may likewise accumulate on the lower guide
609
, and in addition image scraping and paper jamming may likewise occur as a result of the accumulation of the toner.
As a means for preventing the above-mentioned problems, a method is available in which the guide is coated on its surface with an ultraviolet-curing resin so that the toner does not adhere to the guide; the resin containing fluorine resin (such as PFA or ETFE) particles dispersed therein (hereinafter “UV coating”). This UV coating provides a contact angle of 100° or above, at which water repellency is exhibited, so that the toner does not adhere to the delivery guide surface.
However, a problem in the UV coating is that the UV coating itself results in a very high cost because the guide is produced through many steps of setting a guide member to a jig, coating it with a coating material, curing coatings with ultraviolet rays, controlling the coating layer thickness and so forth when the guide member is coated.
The UV coating has another problem that the coating film formed may wear gradually as a result of its contact friction with the sheet materials. To the part from which the UV-coating film has worn away, the toner tends to adhere, as in the case of the problems in the prior art. Once it has adhered, since the toner is very cohesive to each other, it may accumulate gradually on the part where the material (PET) of the guide member is laid bare, so that the leading end of the sheet material may be caught there to cause a paper jam.
As another problem, when the UV coating is applied on the guide member, an adhesive solvent is used to make it easy that the ultraviolet-curing resin to be coated, containing fluorine resin (such as PFA or ETFE) particles dispersed therein, adheres to the guide member. Hence, dependi
Ijuin Masahiko
Kobayashi Toshikazu
Nishigaki Makoto
Sano Atsushi
Cain Edward J.
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
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