JPH10326055A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device being excellent in fixability and capable of preventing the curling of a toner image carrier, the deformation of a pressure roller and the shortening of the life of the bearing of the pressure roller, with a simple constitution. SOLUTION: The device is provided with a heating roller 10 for heating/fixing an unfixed toner image carried on a sheet P and the pressure roller 20 for press-sticking the unfixed toner image carrying surface of the sheet P on the periphery of the heating roller 10. In such a case, the device is further provided with an auxiliary thermal roller 40 which can be brought into contact with/ separated from the pressure roller 20 by a contact/uncontact changing lever 25, a supporting lever 47, etc. In the contact state of the auxiliary thermal roller 40 with the pressure roller 20 the thermal roller 40 is rotated with the rotation of the pressure roller 20, to heat it.

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 electrophotographic image forming apparatus and the like, and a heating roller for heating and fixing an unfixed toner image carried on a sheet;
The present invention relates to a structure of a heat roller fixing device provided with a pressure roller for pressing the unfixed toner image bearing surface of the sheet on the peripheral surface of the heat roller.

[0002]

2. Description of the Related Art FIG. 10 shows a general structure of a heat roller fixing device for heating and fixing a sheet P carrying an unfixed toner image on an upper surface. The heating roller 10 is a hollow metal cylinder 12 having a heater 11 using, for example, a halogen lamp as a heat source, and its outer periphery is covered with a thin layer, for example, a surface layer 13 using a fluororesin tube. The pressure roller 20 that is pressed against the rotating heating roller 10 and is driven to rotate is provided with a sponge-like elastic layer 22 on the outer periphery of a cored bar 21 and a thin outer surface layer 23 of, for example, a fluororesin tube. Etc. The temperature of the surface of the heating roller 10 is detected by a temperature sensor (not shown), and the surface of the heating roller 10 is controlled to, for example, about 200 ° C. so as to be suitable for fixing.

The sheet P conveyed along the guide plate 31 is fixed at the pressure contact portion between the heating roller 10 and the pressure roller 20, is separated from the roller surface by separation claw portions 32a and 32b, and goes out of 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.
The fibers on the back side curl downward due to the greater shrinkage of the fibers on the back side than the front side. When the curl generated on the sheet P is strong (the radius of curvature is small), the phenomenon that the fixed sheet P is wound around the pressure roller 20 occurs, or even if the sheet P is separated, There are many problems such as a shortage of conveyance (jam) before the sheet P is ejected outside the apparatus, and the sheets P ejected one after another in a full shape even when ejected outside the apparatus are not properly stacked in a stacked state. It will be.

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. 11 shows the relationship between the surface temperature of the pressure roller 20 and the curl amount of the paper (kg paper). The curl amount is
The copy paper immediately after fixing is placed on a flat plate with the curl direction facing upward, the lifted heights of the four corners are measured in mm, and the average value is taken. The smaller the temperature difference is, the smaller the curl amount is. In the graph, the forward set and the reverse set 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,
This is due to the fact that the reverse set sheet has a history of curling downward more than the normal set sheet,
In any case, reducing the temperature difference between the heating roller 10 and the pressing roller 20 is a condition for reducing the curl amount.

Many proposals have been made to heat the pressure roller 20 to a temperature close to the surface temperature of the heating roller 10 to perform fixing. There is a proposal to provide a heat source inside the pressure roller 20, but the pressure roller 20 has a sponge-like elastic layer 22 and has poor thermal conductivity and a large thermal gradient. Requires a lot of time, and the temperature inside the pressure roller 20 becomes abnormally high. On the other hand, the pressure roller 20
It has been proposed to heat the pressure roller surface from outside. However, in this case, a heating means for heating the surface of the pressure roller is required, and it is necessary to control the temperature of the surface of the pressure roller.

JP-A-57-122467, Shokai 61
JP-A-135358 and JP-A-3-180883 disclose techniques for preheating the surface of a pressure roller with an auxiliary heat roller having a heater such as a halogen lamp. Japanese Utility Model Application Laid-Open No. 62-103073 discloses a technique for making the surface temperature of a pressure roller uniform by using a heat pipe.

[0007]

However, these publications do not disclose any technical means for efficiently heating the surface of the pressure roller without shortening the life of the pressure roller. The present invention provides a fixing device that efficiently heats the surface of a pressure roller by an auxiliary heat roller without shortening the life of the pressure roller, has good fixing properties, and reduces the curl amount of a sheet discharged after fixing. It is intended to provide a device.

[0008]

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, an auxiliary heat roller is provided that enables the pressure roller to be brought into contact with and separated from the pressure roller and that is driven to rotate to heat the pressure roller in a contact state. Is achieved by the fixing device.

Further, in the fixing device according to the present invention, the contact position of the auxiliary heat roller with the pressure roller is within a range of 90 ° from the pressure contact position between the heating roller and the pressure roller toward the sheet entry side. Wherein the fixing device and the auxiliary heat roller have a halogen lamp inside, a hollow roller made of a metal whose inside is black-painted, both ends having a small diameter, and bearing portions at both ends. The fixing device, wherein the fixing device comprises a resin sleeve and a ball bearing, the auxiliary heat roller has a heat pipe in a hollow roller thereof, and a heater is provided at a central portion thereof, The opposite side of the pressing roller from the pressing direction with the heating roller is a sheet guide plate portion and a sheet separating claw except for a contact portion of the auxiliary heat roller and a temperature sensor mounting portion. Wherein the fixing device further comprises a heat insulating cover made of a heat reflecting material and a heat insulating material, or the auxiliary heat roller has a surface roughness of Ra = 1.0 or more. In a preferred embodiment, the fixing device has an effect of cleaning toners attached to the pressure roller.

[0010]

(Embodiment 1) The structure and operation of Embodiment 1 of the present invention will be described with reference to FIGS.

FIG. 1 is a sectional view showing an example of the configuration of the fixing device of the present invention, and FIG. 2 is a sectional view showing an example of the auxiliary heat roller of FIG. In the figure, reference numerals 10 and 20 denote a heating roller and a pressure roller, which are a pair of rotating members for fixing, 15 a cleaning roller, 16 an oil application roller, and 40 an auxiliary heat roller.

A heating heater 11 such as a halogen lamp is provided on the inner core of the heating roller 10. The ambient temperature of the heating roller 10 and the pressure roller 20 is detected by temperature sensors S1 and S2 including, for example, a thermistor or the like, and controlled by the detection signals to be maintained within a predetermined temperature range.

The heating roller 10 is a hard roller having an outer diameter of 60 mm having a surface layer 13 in which the outer periphery of a thin metal cylinder 12 is coated with a fluororesin of 30 μm.

The pressure roller 20 is provided with an elastic layer 22 made of an elastic material such as rubber having a rubber thickness of 5 mm and a rubber hardness of Asker C55 degrees around a cored bar 21.
This is a soft roller having an outer diameter of 65 mm and having a surface layer 23 coated with a 0 μm fluororesin tube or coated with a fluororesin.

The pressure roller 20 is a tension spring 2 described later.
8 is pressed against the heating roller 10 at a pressure of 90 kgf by the elastic force of the elastic layer 22 so that the nip N
Is formed. The length of the nip portion N at this time depends on the surface pressure and the hardness of the roller surface.
It has become. The heating roller 10 has a peripheral speed of 350 to 410
(Mm / sec), rotate counterclockwise,
Numeral 0 is pressed against the heating roller 10 and is driven to rotate.

The cleaning roller 15 is a heating roller 10
The cleaning roller 15 is made of a material that is non-absorbable with respect to oil, such as foamed silicone rubber, for example. If an absorbent material is used, the collected absorbed oil will be discharged, resulting in uneven oil.
Therefore, a non-absorbable material is used for the cleaning roller 15, and the variation in the amount of applied oil is suppressed. In addition, in order to improve the performance of removing foreign matter such as toner, the releasability is low.
Further, a roller having a small heat capacity is selected and used so as not to absorb the heat from the heating roller 10.
Is pressed against the heating roller 10 and is driven to rotate.

The oil application roller 16 is an oil application roller that applies the release oil to the peripheral surface of the heating roller 10 cleaned by the cleaning roller 15. The oil application roller 16 always contacts the heating roller 10, It rotates following the rotation of 10. Oil application roller 1
In addition to the oil that oozes and replenishes from the inside, oil replenishment may be performed from the outer periphery by an oil replenishment pad. With this configuration, the sheet P, which is the toner image carrier to be fixed, is prevented from being stained, and the sheet P is easily separated from the heating roller 10. The cleaning roller 15 is disposed upstream of the oil application roller 16 with respect to the rotation direction of the heating roller 10 as shown in FIG. 1, and the cleaning roller 15 is disposed before the toner adhered to the heating roller 10 adheres to the oil application roller 16. It is configured to remove by. 31 is a guide plate provided above and below the entrance of the fixing device for the sheet P, and 32a and 32b are separation claws respectively provided on the heating roller 10 and the pressure roller 20 to prevent the sheet P from winding. The separation claw 32a is in non-contact or light contact with the peripheral surface of the heating roller 10 by the urging force of a tension spring (not shown), and the separation claw 32b is lightly pressed against the peripheral surface of the pressure roller 20.

Reference numeral 40 denotes an auxiliary heat roller for heating the surface of the pressure roller 20, for example, a heater 42 such as a halogen lamp, which will be described in detail later.

In the fixing device of the present invention, when the power is turned off, the pressure roller 20 is separated from the heating roller 10, and when the power is turned on, the pressure roller 20 is pressed against the heating roller 10. It is in. Reference numeral 25 denotes a contact / separation change lever which enables the pressure roller 20 to be brought into contact with or separated from the heating roller 10, and a contact / separation change lever 25b is provided rotatably about a support shaft 26 implanted on a side wall of the apparatus. The bearing portion of the pressure roller 20 is supported at the central portion 25a. 27
Is an eccentric cam that is provided between the fork-shaped tip portions 25b of the contact / separation changing lever 25, is rotated by 180 ° by a rotating member such as a motor or a rotary solenoid, and is rotated to a position shown by a solid line or a two-dot chain line in the figure. There is a pin 71 with one end implanted on the tip 25b and the other end implanted on the side wall of the device.
This is a tension spring that is stretched over the cable. A support 47 has one end supporting a bearing portion of the auxiliary heat roller 40, and the other end fitted to a support shaft 48 implanted on a side wall of the apparatus and rotatably provided around the support shaft 48. Lever, 49 is support lever 4
A compression spring 73 is provided between the supporting member 7 and the support fitting 72 implanted on the side wall of the apparatus, and a stopper pin 73 is implanted on the side wall of the apparatus.

With such a configuration, when the eccentric cam 27 is in the position shown by the two-dot chain line, the pressure roller 20 is separated from the heating roller 10, and when the eccentric cam 27 is in the position shown by the solid line, the tension spring 28 is used. The pressure roller 20 is pressed against the heating roller 10 with a predetermined pressing load,
The pressure roller 20 is driven to rotate with the rotation of. When the pressure roller 20 is pressed against the heating roller 10, the auxiliary heat roller 4
Reference numeral 0 indicates that the compression spring 49 presses the pressure roller 20 against the pressure roller 20 with a predetermined pressure load, and heats the roller while rotating following the rotation of the pressure roller 20. When the power supply is stopped, the eccentric cam 27 rotates by 180 ° under the control of a control unit (not shown), and the pressing roller 20 is separated from the heating roller 10. At this time, the auxiliary heat roller 40 slightly follows the movement of the pressure roller 20 by the compression spring 49, but the support lever 47 is stopped by the stopper pin 73 implanted on the side wall of the apparatus, and the auxiliary heat roller 4
0 is separated from the pressure roller 20. By separating from the heating roller 10, the auxiliary heat roller 40 presses the same position of the pressure roller 20, whose rotation has been stopped, for a long time to deform the pressure roller 20. No load is applied. According to experiments conducted by the present inventors, it has been recognized that the service life is extended by 30% by using the configuration in which the auxiliary heat roller 40 is brought into contact with and separated from the pressure roller 20. Note that the contact / separation changing lever 25 and the support lever 47 are provided symmetrically at both ends of the pressure roller 20 and both ends of the auxiliary heat roller 40. However, when the two members at both ends are integrally formed by a rigid material, they are eccentric. The cam 27 and the compression spring 49 can be provided at only one end to simplify the configuration.

In FIG. 1, θ is the angle from the center of the nip N to the center of the auxiliary heat roller 40 at the contact position measured on the side of the sheet P in which the rotation axis of the pressure roller 20 is centered. It is. The smaller this angle, the smaller the auxiliary heat roller 4
The elapsed time from the pressure roller 20 heated by 0 to the entrance of the sheet P is short, and therefore the surface temperature at the entrance of the sheet P becomes high. It has been found that the pressure roller 20 at the nip N can be heated. Θ is 9
If the auxiliary heat roller 40 is provided at a position equal to or less than 0 °, an effect of warming the rear surface of the sheet entering the nip portion N also occurs. Therefore, the value of θ is preferably 90 ° or less.

As shown in FIG. 2, the auxiliary heat roller 40 has a rod-shaped halogen lamp 42 as a heater inside, and a heat-resistant black painted hollow roller 41 on the inside 43. And a flange 44 made of SUS material or the like is press-fitted. A heat-resistant and heat-insulating resin sleeve 7 made of synthetic resin is provided on the small-diameter portion of the flange portion 44.
4 are fitted, and a ball bearing 75 is provided around it to form a bearing. Bearing portions at both ends of the auxiliary heat roller 40 are supported by one end of the support lever 47. With this configuration, the auxiliary heat roller 40 whose inside is painted black and heat absorption is improved is efficiently heated by the halogen lamp 42. The material of the hollow roller 41 is a metal material having good thermal conductivity, such as copper or aluminum, or a thin SU.
S material is preferred. In the present embodiment, the surface of the hollow roller 41 is coated with PFA to prevent the surface of the auxiliary heat roller 40 from being stained due to long-term use.

FIG. 7 shows a state in which the surface temperature of the heating roller 10 is maintained at 200 ° C. and the output of the halogen lamp 42 of the auxiliary heating roller 40 (watt of power consumption) during copying of the image forming apparatus having the fixing device of the present invention. 3 is a graph showing the relationship between the surface temperature of the auxiliary heat roller 40 and the surface temperature of the pressure roller 20 (represented by numbers). The heating roller 2 of the auxiliary heating roller 40 is used.
The contact angle θ to 0 is set to 90 °. To measure the surface temperature, a temperature sensor such as a thermistor is installed at two places of the sheet P entrance portion of the pressure roller 20 (temperature sensor S2 in FIG. 1) and the auxiliary heat roller 40, and the temperature is measured during copying under the same conditions. went. FIG. 8 shows the conventional hollow roller 4 shown in FIG.
3 shows a similar graph when the auxiliary heat roller 40b having one end released is used. In the case of the auxiliary heat roller 40 shown in FIG. 2 of the present invention, the halogen lamp 4 is used to set the temperature (surface temperature) at the sheet P entry portion of the pressure roller 20 to 200 ° C.
2, the output of 375 W is sufficient, whereas the conventional auxiliary heat roller 40b shown in FIG.
Required an output of 650 W, the temperature varied widely, and a large difference was observed. The reason for this difference is that in the present invention, the reduction in the amount of heat escaping from both sides of the roller by reducing the diameter of the bearing portion of the auxiliary heat roller 40 is recognized, and the thermal efficiency is greatly improved. did. The contact load of the auxiliary heat rollers 40 and 40b when contacting the pressure roller 20 was 1 kgf.

(Embodiment 2) FIG. 3 shows a fourth embodiment of the present invention.
And FIG. 4 is a cross-sectional view showing the configuration of the auxiliary heat roller 40a of FIG. In order to simplify the drawing, the contact / separation changing lever 25 and the support lever 47 are omitted. In the figure, the same parts as those in FIG. 1 are denoted by the same reference numerals, and their operations are also the same, so that detailed description is omitted.

In the present embodiment, reference numeral 40a denotes another example of the auxiliary heat roller, and reference numeral 41a denotes a thick hollow roller having holes formed at a plurality of positions (three positions in FIG. 3). A heat pipe 45 provided in a liquid or the like circulating therein to uniform the temperature in the axial direction is inserted. With this configuration, the surface temperature of the auxiliary heat roller 40a is maintained more uniformly, and
Is also heated uniformly.

At the time of fixing, heat is taken away by the passing sheet. Therefore, when a large number of copies are continuously made on a small-sized sheet having a narrow paper width in the sheet conveying direction, the sheet passing portion and the sheet passing portion are removed. A temperature difference occurs between the portion where the sheet does not pass and a portion where the temperature exceeds a predetermined temperature, which degrades the performance of the fixing device. This cannot be eliminated even if the temperature is controlled by the temperature sensor. By providing the heat pipe 45 with the auxiliary heat roller 40a of the present embodiment, the pressure roller 20
Further, it was recognized that there was an effect in the direction of reducing the temperature difference in the axial direction of the heating roller 10 which was in pressure contact with this.

(Embodiment 3) FIG. 5 shows a fifth embodiment of the present invention.
1 is a cross-sectional view illustrating a fixing device according to the first embodiment of the present invention. In the figure, the same parts as those in FIG. 1 are denoted by the same reference numerals, and their operations are also the same, so that detailed description is omitted.

In this embodiment, reference numeral 51 denotes a two-layer heat retaining cover made of a heat-resistant material having a high heat insulating property and a material having a high heat reflectivity provided inside. The heat insulating cover is provided so as to wrap the pressure roller 20 between the guide plate 31 of the sheet P and the separation claw 32b of the sheet P, except for the contact portion of the sheet P and the attachment portion of the temperature sensor S2.

By installing the heat insulating cover 51, the thermal efficiency increases. As a result of the test, when the heat retaining cover 51 is provided as compared with the case where the heat retaining cover 51 is not provided, the halogen lamp 4 of the auxiliary heat roller 40 is used to maintain the pressure roller 20 at the same temperature.
2 was able to save about 30% of power consumption.

In the third embodiment, with such a configuration, the auxiliary heat roller 40 is installed within the range of the best thermal efficiency of θ = 90 °, and the thermal insulation cover 51 is further provided to improve the thermal efficiency. The thermal efficiency can be further improved by covering the auxiliary heat roller 40 with the heat retaining cover 52 as well.

(Embodiment 4) FIG. 6 shows a sixth embodiment of the present invention.
FIG. 10 is a cross-sectional view illustrating still another example of the fixing device according to the present invention. In order to simplify the drawing, the contact / separation changing lever 25 and the support lever 47 are omitted. In the figure, the same parts as those in FIG.

In this embodiment, the auxiliary heat roller 40
Is a metal roller made of aluminum, SUS, or the like, and has a surface with a roughness of Ra = 1.0 or more.
As a result, toner and other dust adhering to the surface of the pressure roller 20 were moved to the auxiliary heat roller 40 that is driven and rotated, and cleaning was successfully performed. Reference numeral 46 in the drawing denotes a heat-resistant scraping member made of, for example, hard urethane rubber, which scrapes off the toner and dust moved to the auxiliary heat roller 40 and drops it into a toner reservoir (not shown).

With this configuration, in addition to the effect of maintaining the surface temperature of the pressure roller 20 at a high temperature, toner and dust adhering to the surface of the pressure roller 20 are cleaned, and the back surface of the sheet at the time of fixing is soiled. This has the effect of preventing this.

[0034]

As described above, according to the present invention, in the fixing device of the present invention, an auxiliary heat roller for heating the surface of the pressure roller is provided, and the auxiliary heat roller can be brought into contact with and separated from the pressure roller. Therefore, with a simple configuration, the surface temperature of the pressure roller is increased, the temperature difference between the front and back of the sheet, which is the toner image carrier, is reduced, and the fixing of the sheet is prevented, and the occurrence of curling of the sheet is prevented.
In addition, since the auxiliary heat roller is separated from the pressure roller when the rotation of the pressure roller is stopped, it is possible to provide a fixing device that prevents deformation of the pressure roller and shortens the life of the bearing.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an example of a configuration of a fixing device of the present invention.

FIG. 2 is a sectional view showing a configuration of an auxiliary heat roller of FIG. 1;

FIG. 3 is a cross-sectional view illustrating another example of the configuration of the fixing device of the present invention.

FIG. 4 is a sectional view showing another example of the configuration of the auxiliary heat roller of FIG. 3;

FIG. 5 is a sectional view showing still another example of the configuration of the fixing device of the present invention.

FIG. 6 is a cross-sectional view illustrating still another example of the configuration of the fixing device of the present invention.

FIG. 7 is a graph showing a relationship between the halogen lamp output of the auxiliary heat roller and the surface temperatures of the auxiliary heat roller and the pressure roller of the present invention.

FIG. 8 is a graph showing the relationship between the halogen lamp output of the conventional auxiliary heat roller and the surface temperatures of the auxiliary heat roller and the pressure roller.

FIG. 9 is a sectional view showing a general configuration of a conventional auxiliary heat roller.

FIG. 10 is a cross-sectional view illustrating a general configuration of a conventional fixing device.

FIG. 11 is a graph showing a relationship between a pressure roller temperature and a curl amount of a sheet.

[Explanation of symbols]

 Reference Signs List 10 heating roller 11 heating heater 20 pressure roller 22 elastic layer 23 surface layer 25 contact / separation changing lever 27 eccentric cam 40, 40a auxiliary heat roller 41, 41a hollow roller 42 halogen lamp (heater) 43 inner (hollow roller) 44 flange Part 45 heat pipe 47 support lever 51, 52 heat retaining cover N nip part P sheet (toner image carrier)

Claims (6)

[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. The fixing device according to claim 1, further comprising an auxiliary heat roller configured to be able to contact and separate from the pressure roller and to be driven and rotated to heat the pressure roller in a contact state. 2. A contact position of the auxiliary heat roller with the pressure roller is within a range of 90 ° from a pressure contact position between the heating roller and the pressure roller toward a sheet entry side. The fixing device according to claim 1. 3. The auxiliary heat roller has a halogen lamp inside, a hollow roller made of black-painted metal on the inside, and has a small diameter at both ends, and a bearing at both ends is a resin sleeve and a ball bearing. The fixing device according to claim 1, wherein the fixing device is configured. 4. The fixing device according to claim 1, wherein the auxiliary heat roller has a heat pipe provided in a hollow roller thereof and a heater provided at a central portion thereof. 5. A sheet guide plate portion and a sheet separating claw on a side of the pressure roller opposite to a pressing direction with the heating roller except for a contact portion of the auxiliary heat roller and a temperature sensor mounting portion. The fixing device according to claim 1, wherein a heat insulating cover made of a heat reflecting material and a heat insulating material is provided between the fixing unit and the fixing unit. 6. The auxiliary heat roller has a surface roughness Ra.
2. The fixing device according to claim 1, wherein the fixing device is a metal roller having a value of 1.0 or more and has an effect of cleaning toners attached to the pressure roller. 3.