JP2002139956A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device which can realize stabilization of glossiness, hot offset, prevention of jam, and prevent lowering of copy speed, the rupture of a fixation belt after a heating roll reaches a prescribed temperature, and a temperature overrun when rotation suspension occurs. SOLUTION: The fixing device 1 is provided with a heat radiating means 7 consisting of a metal member having radiation fins to increase heat radiation according to the temperature rise of a fixation belt 2 on the nip upstream of a fixing roller 4 and the pressure roller 5 on the surface of the fixing roller 4. A detection/control means controls a heating member 3 so as to hold the temperature of a thermistor 8 at 140 to 150 deg.C. A pressing means 13 controls the contact area of the heat radiating member 7 for the fixing roller 4 so as to hold the temperature of a thermistor 12 at 125 to 130 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device of a type using a fixing belt used in an image forming apparatus such as a copying machine, a printer, a facsimile, and the like.

[0002]

2. Description of the Related Art In general,
2. Description of the Related Art In an image forming apparatus such as an electrophotographic copying machine, a printer, and a facsimile, a fixing device in which a pressure roller is pressed against a heat fixing roller is used. In this fixing device, while rotating the heated fixing roller, the printing paper on which the toner is transferred is inserted into a fixing nip formed between the rotating fixing roller and the pressure roller, and the toner is heated and melted to perform printing. It fuses on paper. In addition to the heat roller type, there is a belt type fixing device. This type of fixing device heats the fixing belt by contact with a heating member such as a heating member that can easily reduce the heat capacity, and then the fixing belt and the pressure roller are transferred to the transfer paper on which the fixing belt has transferred the toner. And the toner is melted at a predetermined temperature. The use of a belt with a small heat capacity reduces the temperature of the transfer paper rapidly when passing through the nip, and when separating from the fixing belt at the nip exit, enables oil-less due to the cohesive force of toner or release by applying a small amount of oil. ing.

FIG. 1 is a sectional view showing an example of a conventional belt-type fixing device as described above. The illustrated fixing device 1
An endless fixing belt 2 that conveys the transfer sheet, a heating member 3 and a fixing roller 4 that stretch the fixing belt 2, a pressure roller 5 that is disposed to face the fixing roller 4 via the fixing belt 2, It has a heater 6 provided on the surface of the heating member 3. In order to apply a predetermined tension to the fixing belt 2, the heating member 3 is urged by an elastic body (not shown) such as a spring in a direction to separate the heating member 3 from the fixing roller 4 as shown by an arrow a.

The fixing belt 2 in contact with the fixing roller 4
A thermistor 12 for detecting the temperature at the nip exit of the fixing roller 4 and the pressure roller 5 is disposed on the outer periphery of the fixing roller 4 and the pressing roller 5. A thermistor 8 for detecting the temperature of the fixing belt 2 is disposed on the fixing belt 2 on the heating member 3 side.

[0005] The fixing roller 4 comprises a metal core 9 and a heat-resistant porous elastic layer 10 covering the metal core 9.
Is rotatably supported by a stationary member (not shown) by an end shaft 11. The pressure roller 5 is urged by an elastic body (not shown) such as a spring in a direction in which the pressure roller 5 comes into pressure contact with the fixing roller 4 as shown by an arrow b. The pressure roller 5 is in pressure contact with at least the fixing roller so as to form a nip. Reference numeral 11 in the figure denotes a guide for guiding the transfer paper to be fixed toward the first fixing unit A.
The pressure roller 5 has a core metal surface coated with PFA.

The fixing belt 2 is a thin belt made of nickel, heat-resistant resin (polyimide or the like), carbon steel or stainless steel, and has a heat-resistant release layer (fluorine resin, high release silicon rubber, etc.) on its surface. ) Is coated. In this example, a high release silicone rubber layer of 100 μm is provided on the surface of the endless belt made of a polyimide resin having a thickness of 50 μm.
The coated one is used.

With the above-described fixing device, the paper was passed while controlling the temperature of the fixing belt 2 at 140 to 150 ° C. Although there was no problem at the initial stage of paper passing, the temperature of the fixing roller 4 increased during continuous paper passing, and when the nip exit temperature (detected by the thermistor 12) exceeded 130 ° C., offset and jam occurred in the thin paper. Next, the nip exit temperature (thermistor 1
2) exceeds 125 ° C. (hereinafter, referred to as “at the time of control switching”).
When the circuit was switched and controlled so as to be 25 to 130 ° C., no offset and no jam of thin paper occurred during continuous paper feeding. However, when the gloss was evaluated, the gloss varied depending on the number of sheets passed. This is because the nip entrance temperature is not controlled to be constant from the time of control switching. As a safety evaluation of the fixing device, when the fixing belt 2 was broken after the control was switched, a temperature runaway occurred, and smoke was generated from the heating member 3. Also,
Similarly, when the rotation of the fixing belt 2 was stopped after the control was switched, the temperature runaway occurred again, and smoke was generated from the heating member 3.

That is, in such a belt fixing system, the nip exit temperature is important, and a method of detecting the nip downstream temperature of the fixing roller and controlling the nip exit temperature is known. For example, in a control method of a fixing device for an electrophotographic apparatus disclosed in JP-A-10-115996, in a belt fixing device, in addition to temperature detection and control of a heating roller,
When the temperature of the heating roller reaches a temperature at which fixing can be performed, the temperature is switched to temperature detection and control such that the temperature of the fixing roller does not exceed a predetermined temperature, so that an offset or a jam does not occur.

However, if the belt breaks or stops rotating after the heating roller reaches a predetermined temperature, the heat of the heating roller is not transmitted to the fixing roller.
There is a danger that the heating roller will be heated to keep the fixing roller in a predetermined temperature range, causing a temperature runaway. Further, since the nip entrance temperature is not always constant, the glossiness of the image is not constant. In addition, since the detection and control of the temperature of the fixing roller are essential, a simple structure cannot be achieved.

Accordingly, the present invention solves the above-mentioned conventional problems, realizes stabilization of glossiness, prevention of hot offset and jamming, and at the same time, prevention of a reduction in copy speed, and a heating roller at a predetermined temperature. It is an object of the present invention to provide a fixing device that prevents a temperature runaway when the fixing belt breaks or stops rotating after the fixing belt has been broken.

It is another object of the present invention to provide a fixing device which prevents image disturbance due to torque fluctuation of a fixing roller and simplifies a unit.

[0012]

According to a first aspect of the present invention, there is provided a fixing device for fixing toner on transfer paper by applying pressure and heat to achieve the above object. A fixing roller, a pressing unit provided to be pressed against the fixing roller, a heating unit disposed upstream of a nip between the fixing roller and the pressing unit, and a stretcher between the fixing roller and the heating unit. A fixing belt formed between the fixing roller and the pressing unit via the fixing belt, and a unit for detecting and controlling the temperature of the fixing belt upstream of the nip. In the apparatus, on the surface of the fixing roller upstream of the nip, a heat radiating means for increasing a heat radiating amount in accordance with a rise in the temperature of the fixing belt is provided. And controlling the following raw temperature.

According to a second aspect of the present invention, in order to achieve the above object, in the fixing device of the first aspect, the heat radiating member is a rotatable metal roller.

According to a third aspect of the present invention, in order to achieve the above object, in the fixing device according to the first or second aspect, the heat radiating member is disposed so that the heat radiating member comes into contact due to thermal expansion of the fixing roller. It is characterized by becoming.

[0015]

Embodiments and examples of the present invention will be described below with reference to the drawings. In the following, portions common to the related art are denoted by the same reference numerals, and redundant description is omitted.

FIG. 2 is a cross-sectional view showing a first embodiment of the fixing device according to the present invention. The fixing device 1 of the present embodiment includes:
On the surface of the fixing roller 4 upstream of the nip between the fixing roller 4 and the pressure roller 5, there is provided a heat radiating means 7 whose heat radiation increases in accordance with the temperature rise of the fixing belt 2. In the illustrated example, the heat radiation member 7 is used.
Is a metal member having a radiation fin as shown in the figure, but other various shapes and materials can be used.

In the embodiment, the heating member 3 is controlled by a detection / control means (not shown) so that the temperature of the thermistor 8 becomes 140 to 150 ° C.
The contact area of the heat radiating member 7 with respect to the fixing roller 4 is controlled by the pressing means 13 so that the temperature of the fixing roller 4 becomes 125 to 130 ° C.
In addition, it is also possible to radiate heat to the outside through the heat radiating member 7 by an air current or the like, and to control the amount of heat radiated by the strength of the air current.

FIG. 3 is a sectional view showing a second embodiment of the fixing device according to the present invention. In this embodiment, a metal roller is used as the heat radiating member 7a instead of the heat radiating member 7 having the heat radiating fin of the previous embodiment.

FIG. 4 is a sectional view showing a third embodiment of the fixing device according to the present invention. In the present embodiment, a metal roller is used as the heat radiating member 7a as in the second embodiment, but a small gap is set between the fixing roller 4 and the pressing means 13 without providing the pressing means 13, and the temperature of the fixing roller 4 is reduced. Rises and its outer diameter expands, so that the fixing roller 4 and the heat radiating member 7a come into contact with each other.

In any of the first to third embodiments, no jam offset occurred in continuous paper passing, and the gloss fluctuation was smaller than in the conventional case. Further, even if the belt was broken or the belt was stopped, no danger due to temperature runaway occurred. In the case of the first embodiment, in a fine image, image disturbance was observed due to linear velocity fluctuation at the time of contact of the heat radiating member 7, but improvement by a drive system was also possible.

For temperature detection, the solid line A in FIG. 5 having a high correlation with the position of the thermistor 8 in the illustrated embodiment can be used, and for the thermistor 12, the dotted line B in FIG.
The use of parts is possible. The heating member 3 may be fixed as in the illustrated embodiment, or may be a conventionally known rotatable roller.

[0022]

Since the fixing device of the present invention is as described above, stabilization of glossiness, prevention of hot offset, prevention of jamming, prevention of reduction of copying speed, and reduction of copy speed can be achieved. This has the effect of preventing breakage of the belt after the occurrence of the temperature and runaway of the temperature when the belt is stopped.

Since the fixing device according to the second aspect is as described above, in addition to the above-mentioned common effects, there is an effect that image disturbance due to torque fluctuation of the fixing roller can be prevented.

Since the fixing device according to the third aspect is as described above, there is an effect that the unit can be simplified in addition to the above common effects.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an example of a conventional belt-type fixing device.

FIG. 2 is a sectional view showing a first embodiment of a fixing device according to the present invention.

FIG. 3 is a sectional view showing a second embodiment of the fixing device according to the present invention.

FIG. 4 is a cross-sectional view illustrating a fixing device according to a third embodiment of the invention.

FIG. 5 is a cross-sectional view showing a modification of the temperature detection position.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fixing device 2 Fixing belt 3 Heating member 4 Fixing roller 5 Pressure roller 6 Heater surface 7, 7a Heat radiating member 8 Thermistor 9 Core metal of fixing roller 10 Elastic body layer of fixing roller 11 Transfer paper guide 12 Thermistor 13 Pressing means

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Jun Nakato 1-3-6 Nakamagome, Ota-ku, Tokyo F-term in Ricoh Co., Ltd. (Reference) 2H033 AA09 AA14 AA20 AA42 BA11 BA12 BA29 BA32 CA07 CA30 3K058 AA12 AA41 BA18 CA12 CA23 CA61 CE13 DA01

Claims (3)

[Claims] 1. A fixing device for fixing toner on transfer paper by applying pressure and heat, comprising: a fixing roller; a pressing unit provided to press against the fixing roller; A heating unit disposed upstream of the nip, and a fixing belt stretched between the fixing roller and the heating unit. The nip is provided between the fixing roller and the pressing unit via the fixing belt. A fixing device having means for detecting and controlling the temperature of the fixing belt upstream of the nip, wherein the amount of heat radiation increases on the surface of the fixing roller upstream of the nip in accordance with an increase in the temperature of the fixing belt. A fixing device comprising a heat radiating means, wherein the detecting / controlling means controls the nip exit temperature to be equal to or lower than a hot offset occurrence temperature. 2. The fixing device according to claim 1, wherein the heat radiating member is a rotatable metal roller. 3. The fixing device according to claim 1, wherein
A fixing device, wherein the heat radiating member is disposed so that the heat radiating member comes into contact with the fixing roller due to thermal expansion of the fixing roller.