Fixing apparatus

Details Fixing apparatus Fixing apparatus

2000-04-25

2001-04-03

Lee, Susan S. Y. (Department: 2852)

Electrophotography

Image formation

Fixing

C399S320000

Reexamination Certificate

active

06212356

ABSTRACT:

FIELD OF TECHNOLOGY
The present invention relates to a fixing apparatus which is used for fusing and pressing an unfixed toner carried on a recording medium to fix the toner to the recording medium.
TECHNICAL BACKGROUND
Recently, a fixing apparatus for use in an electric image forming apparatus has been developed which is disclosed in Japanese Patent Laid-Open Publication HEI 9-73243, for example, not employing a conventional heating roller type fixing system. The conventional fixing process is provided with a heat accumulation step of accumulatively heating a thin heating medium on upstream side of a fixing stage with respect to a feeding direction of the heating medium which is fed along the fixing stage, a heat/press step of clamping the heating medium and a recording medium to contact with each other, being sandwiching an unfixed toner image on the recording medium therebetween in the fixing stage after the heat accumulating step to heat and fuse the unfixed toner image on the recording medium using the heat accumulated in the heating medium as well as to press it to fix the toner image onto the recording medium, a peeling step of peeling off the fixed recording medium from the heating medium after the heat/press step. The aim to constitute such a conventional fixing process is to enable to quickly start, to correspond to a high-speed type machine, to eliminate an offset phenomenon in a case of full-color image, to obtain the color image with good quality, to reduce the electric power consumption, and to respond to a toner image having a different glossiness. Especially, in the conventional fixing process, it is disclosed that a preheat step of preheating the recording medium on the upstream side of the fixing stage with respect to the feeding direction of the recording medium is further provided.
In the conventional fixing apparatus as described above, the heating medium is constructed so as not to discharge the heat energy being accumulating the heat energy therein prior to the fixing stage, and to heat the toner image on the recording medium using the heat energy accumulated in the heating medium at the heat/press step (fixing step). Accordingly, with respect to a speed of heat transfer which is defined from the heater housed in the heating roller through the fixing belt (heat transfer belt) to the recording medium at the heat/press step (fixing step), it was difficult to accelerate a transfer speed of the recording medium which passes through the fixing stage. Even though the recording medium has been preheated prior to the fixing stage, it was also difficult to accelerate the transfer speed of the recording medium. Thus, it was difficult to accelerate the transfer speed of the recording medium to increase the copying number per a unit time (i.e., per one minute) even though the conventional technical skill disclosed in the aforesaid Laid-Open Publication was applied. As a result, it causes to set a nip width at the fixing stage to be large, whereby it was in danger of occurring the other bad influence in the fixing apparatus.
On the other hand, a fixing apparatus for an electro-photographic machine disclosed in Patent Laid-Open Publication HEI 8-2865335 is known as a preceding patent application with the same applicant as the present patent application. In the preceding patent application, a fixing belt is trained around the fixing roller and the heating roller and is constructed to preheat the unfixed toner formed on the recording sheet prior to pass a nip portion defined between the fixing roller and the pressing roller, using the heat radiation from the fixing belt which is heated by the heat conduction from the heating roller. Since the temperature of the heating roller is so controlled as to maintain the temperature thereof to a constant value, it is possible to accomplish the preheat effect certainly.
However, the atmosphere temperature in a preheat space which is defined from a space between the fixing belt and a guide plate for guiding the sheet with the unfixed toner image thereon to the nip portion and being provided under the fixing belt varies widely due to the influence of the temperature of the guide plate. Furthermore, the sheet with the unfixed toner image thereon guided on the guide plate would be preheated by a contact with the guide plate. However, the effect of the preheat from the guide plate will depend on the temperature of the guide plate. Please note that the temperature of the guide plate is different between a case just after a warming up operation is finished and a case in a continuous feeding period, depending on feed modes, as shown in a Table 1. Also, the temperature of the guide plate is different between at least a case in which the image is of mono-color and a case in which the image is of full-color, depending on the thickness (t) of the guide plate, as shown in FIG.
16
. Thus, the preheat effect by the guide plate is not maintained certainly, but conversely a problem due to the bad influence of the preheat by the guide plate has been pointed out. It should be noted that the numerals indicated in the table 1 are temperature (°C.) at each measuring point.
TABLE 1
mono-
full-color
color
mode
mode
idle rotating time after warming up
feeding
feeding
object to be
initial
just after
1 minute
3 minutes
5 minutes
7 minutes
10 minutes
speed
speed
measured
time
warming up
later
later
later
later
later
(5 cpm)
(20 cpm)
Guide plate
at first
heating roller
28
155
158
161
161
162
162
(Thickness
in
fixing roller
28
155
160
163
165
166
167
1.6 mm)
morning
pressing rollerg
28
130
140
149
153
155
157
guide plate
28
 44
 58
 72
 77
 80
 83
stand-by
heating roller
173 
159
160
161
162
162
162
163
156
fixing roller
70
155
160
163
166
167
168
159
154
pressing roller
53
126
141
150
154
156
158
151
102~116
guide plate
51
 56
 66
 78
 82
 84
 85
 64
 49
Guide plate
at first
heating roller
26
156
159
159
159
159
161
156
155
(Thickness
in
fixing roller
26
148
155
158
159
161
161
154
147
0.5 mm)
morning
pressing roller
26
128
137
146
150
152
153
144
102
guide plate
26
 74
100
109
110
112
113
 79
 45
stand-by
heating roller
168 
160
160
159
160
160
160
155
155
fixing roller
62
149
157
161
163
163
163
153
149
pressing roller
47
139
141
150
154
156
157
144
118
guide plate
58
 80
112
114
115
115
116
 78
 48
Guide plate
at first
heating roller
32
157
159
161
162
162
163
157
(Thickness
in
fixing roller
32
156
161
164
166
167
167
154
0.2 mm)
morning
pressing roller
32
129
140
149
154
156
157
 96~109
guide plate
32
 98
131
138
140
141
142
48~52
stand-by
heating roller
171 
160
161
162
162
163
163
163
160
fixing roller
73
156
162
165
167
168
168
166
156
pressing roller
59
127
143
151
154
156
157
152
120
guide plate
85
102
131
140
141
142
142
104
48~54
On the other hand, where fixing apparatuses each of which has temperature characteristics of the heating roller, the fixing roller and the pressing roller as shown in
FIGS. 4 through 6
, in a case that the sheet feeding speed is changed among 40 mm/sec, 80 mm/sec and 120 mm/sec, are utilized, a glossiness of the fixed image on the sheet after the nip portion is totally different among a case just after a warm up operation in the morning (that is, from a cold condition), a case just after a warm up operation from a stand-by mode (that is, from a condition in which the temperature of the fixing roller
22
is set below 60 (°C.)), and a case of a stable feeding mode (that is, just after the fixing apparatus has been actuated for 6 minutes), as shown in
FIGS. 17 through 19
, respectively. In other words, there is problems in which the glossiness of the fixed toner image is not stable, the quality of the fixed toner image could not be maintained to be good, when the feeding speed of the sheet is changed.
When the temperature of the heating roller is maintained in a constant value so that a predetermined glossiness would be given just after the warm up operation (that is, in a case where the temperatur

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