Electrophotography – Image formation – Fixing
Reexamination Certificate
2003-04-02
2004-08-03
Ngo, Hoang (Department: 2852)
Electrophotography
Image formation
Fixing
C219S216000, C399S328000, C399S324000, C399S341000
Reexamination Certificate
active
06771926
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a fixing belt and a fuser using the fixing belt for fixing a toner image formed in an image formation apparatus such as a printer or a copier using electrophotography on a record sheet and in particular to a fuser for heating and pressurizing the record sheet to fix a toner image and then cooling the record sheet by cooling means with the record sheet abutted against an endless belt before peeling off the record sheet.
2. Description of the Related Art
In recent years, a fuser comprising an endless belt placed on at least a heating roll and a peeling roll spaced from the heating roll and rotating, a pressurizing roll for pressing the endless belt against the heating roll, and a cooling structure for coming in contact with the inner peripheral surface of the endless belt from the heating roll to the peeling roll and cooling wherein the endless belt is rotated in a passage direction in the order of the heating roll, the cooling structure, and the peeling roll, a record sheet supporting a toner image is introduced into a press area (nip part) between the endless belt placed on the heating roil and the pressurizing roll, the portion of the record sheet with which the cooling structure comes in contact in a state in which the record sheet is abutted against the endless belt is passed through, and the record sheet is transported to the portion of the endless belt placed on the peeling roll and is peeled off, whereby the toner image is fixed onto the record sheet has been proposed as a fuser used with an image formation apparatus using electrophotography (for example, JP-A-4-216580, JP-A-5-72926, etc.,).
The fuser described in JP-A-4-216580 adopts as the cooling structure, a cooling roll of air cooling type disposed so that the cooling roll can come in and out of contact with the inner peripheral surface of the endless belt (refer to FIG. 5, etc., in JP-A-4-216580) and the fuser described in JP-A-5-72926 adopts as the cooling structure, an air cooling box comprising a large number of air ventilation holes made in a contact face with the inner peripheral surface of the endless belt (refer to FIG. 2, etc., in JP-A-5-72926) In both fusers, the record sheet supporting the toner image is heated and pressurized and then is cooled by the cooling roll or the air cooling box with the record sheet abutted against the endless belt before the record sheet is peeled off the endless belt for fixing the toner image.
By the way, in such a fuser for heating and pressurizing the record sheet to fix the toner image and then cooling the record sheet with the record sheet abutted against the endless belt and peeling the record sheet, how the cooling is executed uniformly and stably is one problem.
That is, in the fuser adopting the cooling roll, the cooling roll is simply brought into contact with the endless belt and thus the endless belt comes in insufficient contact with the cooling roll and an uncooled portion occurs because of deformation like wrinkles or waves occurring on the endless belt and consequently the toner image on the record sheet after being heated and pressurized is not uniformly cooled and it is feared that unevenness may also occur in the image quality accordingly.
In the fuser adopting the air cooling box, the air cooling box is pressed against the endless belt and thus can be brought into almost sufficient contact with the endless belt for uniformly cooling the endless belt except that the contact is impaired as much as the presence of a large number of air ventilation holes. However, if the amount of pressing the air cooling box against the endless belt is too large and the belt is bent largely, the record sheet after being heated and pressurized easily peels off the endless belt portion against which the record sheet is pressed by the air cooling box, or also easily peels off the endless belt when it leaves the endless belt portion against which the record sheet is pressed and consequently the toner image on the record sheet after being heated and pressurized is not uniformly cooled and it is feared that an image quality failure may occur because of such cooling unevenness. Moreover, although such cooling unevenness is prevented to some extent if on the opposite side of the air cooling box with the endless belt between, an endless belt with an air cooling box coming in contact with the outer peripheral surface of the endless belt is also disposed, as disclosed in JP-A-5-72926, a condition in which the record sheet easily peels off the belt always exists depending on the pressing amount of the air cooling box cooling the inner peripheral surface of the belt and thus it is feared that cooling unevenness may be induced.
Incidentally, as fixing belts, there has been known an image fixing film described in, for example, JP-A-10-111613, a fixing belt described in JP-A-11-143279, and the like have been known as fixing belts.
The former fixing belt comprises a rubber elastic layer (JIS-A hardness 1-70°, layer thickness 0.1-3 mm) made of silicone rubber, etc., and a release property surface layer (layer thickness 5-50 &mgr;m) made of fluorine resin placed in order on a base material of a polyimide film. The latter fixing belt comprises a heat-resistant elastic layer (layer thickness 0.07 mm or more) made of fluorine rubber, silicone rubber, etc., on a base material of metal, etc., and comprises an outermost layer made of fluorine resin having a surface coarseness of Ra 1 &mgr;m or less (layer thickness 2-100 &mgr;m). Moreover, splanchnic release oil (fluorosilicone oil) is applied to the belt surface for use.
By the way, if such a fixing belt in the related art is applied to a fuser of the type wherein a record sheet P formed on the surface of a base material
1140
with a transparent resin layer
1150
made of a thermoplastic resin, etc., for supporting toner T and a fixing belt
1200
are heated and pressurized in a state in which they are overlaid on each other so that the toner T and belt surface
1200
a
face each other, whereby the toner T is fixed into the transparent resin layer
1150
of the record sheet P as shown in
FIG. 29A
, the following problem is involved:
In the fuser, as illustrated in
FIG. 29B
, the toner T needs to be sufficiently buried into the thermoplastic transparent resin layer
1150
and thus the record sheet P supporting the toner T and the fixing belt
1200
are heated and pressurized in a state in which they are overlaid on each other as described above, whereby the toner T and the transparent resin layer
1150
are fused and the toner T is buried into the fused transparent resin layer
1150
through the fixing belt
1200
.
If the fixing is executed, an air bubble pool (so-called edge void)
1300
occurs in an edge part of an image made of the toner T (particularly a cross part of line drawings crossing each other) as illustrated in
FIG. 30A
; this is a problem. Such an image edge part void easily occurs if a hard fixing belt
1200
(formed with a hard resin coat layer). The possible reason is as follows: As shown in
FIG. 31A
, the hard fixing belt
1200
cannot sufficiently follow level difference h between an image portion of the toner T and a non-image portion (exposure face of the transparent resin layer
1150
) on the record sheet P and cannot become deformed and thus a gap k is formed between the fixing belt
1200
and the transparent resin layer
1150
and pressurizing through the fixing belt
1200
at the fixing time (hollow arrows in the figure) becomes non-uniform in the presence of the gap k (namely, high pressurization state for the high-level image portion and low pressurization state for the low-level non-image portion). Consequently, the toner T is strongly and rapidly buried into the transparent resin layer
1150
by the fixing belt
1200
and thus air bubbles are involved in the boundary portion between the toner T and the resin layer, are not sufficiently lost, are cooled and hardened, and remain in the boundary portion.
If the fixing is executed, smoothing
Daishi Fumio
Ishikawa Kiyotaka
Kanesawa Yoshio
Masuko Kazuhisa
Noya Motoi
Fuji 'Xerox Co., Ltd.
Morgan & Lewis & Bockius, LLP
Ngo Hoang
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