JPH10254281A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device being a heating roller fixing device equipped with a heater in a pressure roller where curling is not caused or curling amount is restrained to be small even when a curling is caused. SOLUTION: The heater 23A is provided inside the pressure roller 20A, a metallic core bar 21A is provided on the outside of the heater 23A, and the peripheral surface of the roller 20A is coated with an elastic body 22A having high heat conductivity being >=1.0×10<-3> cal/sec deg.C. A temperature sensor S1 is provided near an end which is not coated with the elastic body 22A at the large-diameter part 21Aa of the core bar 21A in a state where it directly comes in contact with the core bar 21A, so that the flashing control of the heater 23A is performed by the sensor S1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device for use in an image forming apparatus or the like, which includes a heating roller for heating and fixing an unfixed toner image carried on a sheet, and an unfixed sheet on the peripheral surface of the heating roller. The present invention relates to a structure of a heat roller fixing device provided with a pressure roller for pressing a toner image bearing surface.

[0002]

2. Description of the Related Art FIG. 6 is a cross-sectional view showing a general structure of a heat roller fixing device for heating and fixing a sheet carrying an unfixed toner image on an upper surface. The heating roller 10 is a hollow metal cylinder 12 having a lamp 11 as a heat source inside, and its outer periphery is covered with a thin layer, for example, a fluororesin tube 13 or the like. The pressure roller 20, which is pressed against the rotating heating roller 10 and driven to rotate, has a sponge-like elastic body 22 on the outer periphery of a cored bar 21, and the outer periphery thereof is further covered with a thin layer of, for example, a fluororesin tube 23 or the like. ing. The temperature of the surface of the heating roller 10 is detected by a temperature sensor (not shown).
The temperature is controlled at about 0 ° C. so that the fixing is appropriate.

The sheet P conveyed along the guide plate portion 31 is fixed at a pressure contact portion between the heating roller 10 and the pressure roller 20, is separated from the roller surface by a separation claw portion 32, and is outside the fixing device. Is discharged. The discharged sheet P is curled downward. This is because there is a temperature difference between the surface temperature of the heating roller 10 as the upper roller and the surface temperature of the pressure roller 20 as the lower roller, and the sheet surface of the sheet P is heated to a higher temperature during fixing than the sheet back surface. As a result, while the front surface is rapidly dried, the back surface is gradually dried, and the fibers of the back surface (of the sheet P) shrink more than the front surface. When the curl generated on the sheet P is strong (the radius of curvature is small), the sheet P after fixing is
The sheet P may be wrapped around the sheet P, or even if the sheet P is separated, a conveyance failure (jam) may occur before the sheet P is discharged to the outside of the image forming apparatus. This causes many problems such that sheets discharged one after another are not stacked in a state of being correctly overlapped.

The present inventors have determined the relationship between the temperature difference between the heating roller 10 and the pressure roller 20 and the curl amount. The temperature of the heating roller 10 is controlled at 200 ° C., and the water content is 9.4 to 9.6.
% Of A4 size commonly used copy paper (55%).
FIG. 7 shows the relationship between the surface temperature of the pressure roller 200 and the curl amount for the (kg paper). The curl amount is
Place the copy paper immediately after fixing on a flat plate with good heat insulation, with the curl direction facing upward.
The average value is measured in m units, and the smaller the temperature difference between the heating roller 10 and the pressing roller 20 is, the smaller the curl amount is. Note that the forward set and the reverse set in the graph are classified based on the mounting state (the state of the front and back) of a large number of copy sheets loaded in the sheet cassette. In this graph, the curl amount tends to be larger during reverse setting, but this is because the reverse set sheet has a history of curling downward more easily than the positive set sheet. Reducing the temperature difference between the heating roller 10 and the pressure roller 20 is a condition for reducing the curl amount.

[0005] There have been many proposals for fixing the surface by heating the pressure roller 20 to a temperature close to the surface temperature of the heating roller. Proposal of providing a heat source inside the pressure roller (for example, Japanese Patent Laid-Open No. 54-29650, 3-4
No. 5570), but the pressure roller has a sponge-like elastic layer, which has poor thermal conductivity and a large thermal gradient, so that it takes a lot of time to raise the surface temperature to the desired temperature. However, the temperature inside the pressure roller becomes abnormally high before the surface temperature rises to the desired temperature. If the inside of the pressure roller becomes abnormally high temperature of 200 ° C. or more, the deterioration of the material such as the elastic body and the adhesive for bonding the elastic body to the core metal occurs significantly.

[0006]

SUMMARY OF THE INVENTION According to the present invention, a heat source is provided inside a pressure roller, and the heat source is preheated.
An object of the present invention is to provide a fixing device that reduces the curl amount of a sheet discharged after fixing.

[0007]

An object of the present invention is to provide a heating roller for heating and fixing an unfixed toner image carried on a sheet, and to press the unfixed toner image carrying surface of the sheet on a peripheral surface of the heating roller. In a fixing device provided with a pressure roller, the pressure roller includes a metal core having a heating unit provided therein and an elastic layer provided on the outer periphery of the core. Thermal conductivity of 1.0 × 10 ^-3 cal
/ Sec ° C. or higher, wherein the heating means is controlled in temperature by a temperature sensor directly in contact with the peripheral surface of the cored bar which is not covered by the elastic layer. Is done.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The fixing device of the present invention has an elastic body (thermal conductivity of 0.4 to 0.6 × 10 ^-3 cal) conventionally used as an elastic body provided on the peripheral surface of a pressure roller. / S
ec ° C.) and thermal conductivity of 1.0 × 10 ⁻³ cal / s
an elastic body having a high thermal conductivity of ec ° C. or more, and a temperature detecting means such as a thermistor directly contacting the cored bar on the peripheral surface of the pressure roller outside the transfer paper passing area without the elastic body is provided; Based on the detection temperature detected by the detection means, it controls the blinking of the heater provided inside the pressure roller, and according to the present invention, it is possible to control the temperature of the pressure roller as compared with the conventional one which is much better than that of the related art as described later. It became.

FIG. 1 shows a cross-sectional shape of a pressure roller 20A according to an embodiment of the present invention. Inside the heater 23A, there is a 500 to 1000 W rod-shaped halogen lamp having a diameter of about 8 mm. A metal core 21A using a hollow metal material such as stainless steel is provided on the outside. The core metal 21A has a small-diameter portion 21A that serves as a rotation axis at both ends.
b (φ30 mm in this embodiment) and the outer diameter is φ60 mm
There is a large diameter portion 21Aa. The large-diameter portion 21Aa has a width of 15 to
It has a length of about 40 mm (approximately 470 mm in the present embodiment) and is covered with a rubber-like elastic body 22A to a thickness t of 6.5 mm except for one end thereof. The elastic body 22A has a thermal conductivity of 1.0 × 10 ⁻³ cal / sec ° C. or more by selecting a material having a good thermal conductivity or mixing a material having a good thermal conductivity (in the present embodiment, It has a high thermal conductivity of 1.2 × 10 ⁻³ cal / sec ° C.). The elastic body 22A has a margin slightly larger than the maximum paper passing width, and is in a pressure contact relationship with the heating roller. In this embodiment, the elastic body 22A is pressed at a linear velocity of 410 mm / sec from the back surface of the transfer paper to perform fixing. .

In this embodiment, when paper is fed on the basis of one side of the large diameter portion 21Aa, the elastic body 2 is attached to the end on the reference side.
2A, a temperature sensor S1 such as a thermistor that directly contacts the large-diameter portion 21Aa where the base metal portion is exposed is provided.
3A temperature control is performed. By providing the temperature sensor S1 near the reference position for paper feeding, it is possible to more accurately detect a temperature change of the pressure roller 20A accompanying the passage of the transfer paper.

FIG. 4 shows a state in which a heater is provided in a conventional pressure roller to control the temperature of the pressure roller.

FIG. 4 shows a pressure roller having a thermal conductivity of 0.4 to 0.6.times.10.sup.- ³ cal / sec.degree. This graph shows the temperature course between the temperature of the cored bar and the surface temperature of the elastic body from the warm-up to the standby state when the temperature of the pressure roller is controlled by a temperature sensor disposed with a gap of . When the pressure roller has a core metal temperature of 200 ° C. or more, the performance of the elastic body or the adhesive for bonding the elastic body to the peripheral surface of the core metal is significantly reduced. Temperature control by the above temperature sensor is 1
The temperature is controlled at 20 ° C. and the surface temperature of the elastic body is set to 120 to
Bring to 135 ° C. This is shown in FIG. When such conditions are controlled, the pressure roller surface temperature is maintained at about 130 ° C.

FIG. 5 shows the temperature of the pressure roller when the temperature is controlled so as to be exactly the same as the core metal temperature shown in FIG. 4 and a high thermal conductivity rubber is used as the elastic body instead of the conventional elastic body. Shows the temperature. The high thermal conductivity rubber used in FIG. 5 has a thermal conductivity of 1.2 × 10 ⁻³ cal / sec ° C. and a thickness of 6.5 mm as in FIG. By comparing the temperature progress from the warming up of the pressure roller to the standby state with reference to FIGS. 4 and 5, when the high thermal conductivity rubber is used, the surface temperature of the pressure roller is maintained at about 140 ° C. This shows that under the same temperature conditions, the surface temperature is controlled to be about 10 to 15 ° C. higher than that of a general thermal conductivity rubber.

Further, in the fixing device of the present invention, the temperature sensor S1 is connected to the elastic body 22 of the high thermal conductivity of the pressure roller 20A.
FIG. 2 shows a situation in which the temperature sensor S1 performs temperature control from warm-up to a standby state, since the core metal 21A is directly contacted with the core metal 21A that is not covered by A. Temperature sensor S
1 detects 180 ° C or higher, turns off heater 23A
It is controlled to be ON when it is below F,
It shows the surface temperature of the core metal 21A and the elastic body 22A when such temperature control is performed. For comparison, the temperature change on the surface of the elastic body having the conventional thermal conductivity is also shown. According to the present invention, it is shown that the pressure roller surface can be controlled and maintained at a high temperature without overheating. That is, when the surface temperature of the heating roller is controlled at 200 ° C., the surface temperature of the pressing roller is conventionally 65 to 80 with respect to the heating roller as is apparent from FIG.
Although the apparatus was in a standby state with a temperature difference of ° C., in the present invention, the temperature was controlled at a temperature difference of 20 to 30 ° C.

FIG. 3 shows a change in the surface temperature when the pressure roller in the standby state shifts to the continuous copy state. When the transfer paper passes, the heat is removed from the heat roller and the heat roller is heated. The surface temperature is gradually reduced to 150
The pre-heating effect on the pressure roller is almost lost before and after the zero copy. However, in the meantime, in the present invention, since the pressure roller is at a considerably higher surface temperature than in the prior art, the sheet after fixing hardly shows any curl, or even if it shows a very little curl. In the state of the curl amount, the sheet is discharged out of the apparatus without causing separation failure or the like.

According to the study of the present inventors, the effect of the present invention is remarkable when the elastic body 22A is a high thermal conductive elastic body having a thermal conductivity of 1.0 × 10 ⁻³ cal / sec ° C. or higher. Admitted.

[0017]

According to the present invention, the pressure roller containing the heater is not overheated and the temperature is controlled to a high temperature, and the transfer paper is fixed by being sandwiched between the heating roller and the pressure roller. The paper was discharged out of the apparatus without curling, and even if it was provisionally curled, there was no problem in practical use.

[Brief description of the drawings]

FIG. 1 is a sectional view of a pressure roller of the present invention.

FIG. 2 is a surface temperature curve of the pressure roller from warm-up to standby according to the present invention.

FIG. 3 is a surface temperature curve of a pressure roller after a copy is started.

FIG. 4 is a surface temperature curve of a conventional pressure roller from warm-up to standby.

FIG. 5 is a surface temperature curve of a pressure roller when an elastic body is replaced.

FIG. 6 is a sectional view of a conventional fixing device.

FIG. 7 is a graph showing a relationship between a roller surface temperature and a curl amount.

[Explanation of symbols]

 Reference Signs List 10 heating roller 20, 20A pressure roller 21A core 21Aa large diameter part (core) 21Ab small diameter part (core) 22A elastic body 23A heater S1 temperature sensor

Claims (1)

[Claims] 1. A fixing device comprising: a heating roller for heating and fixing an unfixed toner image carried on a sheet; and a pressure roller for pressing the unfixed toner image carrying surface of the sheet on a peripheral surface of the heating roller. In the apparatus, the pressure roller includes a metal core having a heating unit provided therein and an elastic layer provided on the outer periphery of the metal core, and the elastic layer has a thermal conductivity of 1.0 ×. An elastic body having a temperature of 10 ⁻³ cal / sec ° C. or higher, wherein the heating unit is controlled in temperature by a temperature sensor directly in contact with the peripheral surface of the cored bar that is not covered by the elastic body layer. Fixing device.