JP2003280428A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus having a fixing device of a heat roller system in which durability is improved. <P>SOLUTION: The image forming apparatus has the fixing device having: a heat member which includes an elastic body and a releasing layer covering the elastic body, and a pressure member which is in pressure contact with the heat member and has an elastic body and a releasing layer covering the elastic body. In the image forming apparatus, the tensile strength of the elastic body of the heat member is set so as to become greater compared to the initial tensile force as it is used or so as not to decrease by 0.5 MPa or greater. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus having a fixing device for fixing a toner image on a transfer material using a heating roller and a pressure roller.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine, a printer or a facsimile, a fixing device for heating and fixing a recording material (hereinafter referred to as a transfer material) carrying a toner made of a heat-meltable resin or the like is used. The heat roller method is often used for the.

The heat roller type fixing device is composed of a heating roller having a heat source such as a halogen heater therein and a pressure roller in pressure contact with the heating roller. The fixing nip portion is the pressure contact portion of the pair of rollers. The toner image carried on the transfer material is heated and fixed by passing the transfer material such as paper through the sheet.

However, since the heating roller and the pressure roller are repeatedly subjected to heat and pressure, the tensile strength of the elastic body is deteriorated due to the thermal deterioration of the elastic body, so that the roller is broken and the predetermined roller life is reached. In some cases, you have to replace it.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus having a heat roller type fixing device having improved durability.

[0006]

The objects of the present invention can be achieved by the following constitutions.

(1) A heating member having an elastic body and a release layer covering the elastic body, and a pressure member having an elastic body and a release layer covering the elastic body, which is pressed against the heating member. In the image forming apparatus including the fixing device, the tensile strength of the elastic body of the heating member is increased with use or is 0.5 MPa as compared with the initial tensile strength.
An image forming apparatus (first invention) which is characterized by not decreasing as described above.

(2) A heating member having an elastic body and a release layer covering the elastic body, and a pressing member having an elastic body and a release layer covering the elastic body, which is pressed against the heating member. In an image forming apparatus equipped with the fixing device, when the surface pressure at the nip portion is A, the tensile strength of the elastic body of the heating member is B, and the tensile strength of the elastic body of the pressing member is D, always , A <B, and A <D (second invention).

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION First, an image forming apparatus of the present invention will be described.

In the description of the embodiments of the present invention, the technical scope of the present invention is not limited by the terms used in this specification.

FIG. 1 is a schematic diagram showing an example of the overall configuration of the image forming apparatus. In the figure, 10 is a photoconductor, 11 is a scorotron charger which is a charging unit, 12 is a writing device which is an image writing unit, 13 is a developing unit which is a developing unit, and 14 is cleaning for cleaning the surface of the photoconductor 10. An apparatus, 15 is a cleaning blade, 16 is a developing sleeve, and 20 is an intermediate transfer belt which is an image carrier.
The image forming means 1 includes a photoconductor 10 and a scorotron charger 1.
1, the developing device 13, the cleaning device 14, and the like, and the image forming unit 1 for each color has the same mechanical structure. Therefore, in the drawing, reference numerals are given only to the structure of the Y (yellow) series. Therefore, reference numerals are omitted for the components of M (magenta), C (cyan), and K (black).

The arrangement of the image forming means 1 for each color is in the order of Y, M, C, and K with respect to the running direction of the intermediate transfer belt 20, and each photoconductor 10 is a stretched surface of the intermediate transfer belt 20. And is rotated at the contact point in the same direction as the running direction of the intermediate transfer belt 20 and at the same linear velocity.

The intermediate transfer belt 20 includes a driving roller 21, a ground roller 22, a tension roller 23, and a charge eliminating roller 2.
7. The belt unit 3 is stretched around the driven roller 24, and these rollers, the intermediate transfer belt 20, the transfer device 25, the cleaning device 28 and the like constitute the belt unit 3.

The traveling of the intermediate transfer belt 20 is performed by the rotation of the drive roller 21 by a drive motor (not shown).

The photoconductor 10 is formed by forming a conductive layer, an a-Si layer, or a photosensitive layer such as an organic photoconductor (OPC) on the outer periphery of a cylindrical metal substrate formed of, for example, an aluminum material. Rotate in the counterclockwise direction indicated by the arrow in the figure with the grounded.

An electric signal corresponding to the image data from the reading device 80 is converted into an optical signal by the image forming laser, and the writing device 12 projects the light signal onto the photoconductor 10.

The developing device 13 is made of a cylindrical non-magnetic stainless steel or aluminum material which keeps a predetermined distance from the peripheral surface of the photoconductor 10 and rotates in the same direction at the position closest to the rotation direction of the photoconductor 10. The developing sleeve 16 is provided.

The intermediate transfer belt 20 has a volume resistivity of 10 ⁶
It is an endless belt of -10 ¹² Ω · cm, and has a conductive material dispersed in engineering plastics such as modified polyimide, thermosetting polyimide, ethylene tetrafluoroethylene copolymer, polyvinylidene fluoride, and nylon alloy, and has a thickness of 0.1. A seamless belt having a two-layer structure in which a semi-conductive film substrate having a thickness of ˜1.0 mm is coated with fluorine to a thickness of 5 to 50 μm, preferably as a toner filming prevention layer, is provided. In addition to this, a semi-conductive rubber belt having a thickness of 0.5 to 2.0 mm in which a conductive material is dispersed in silicon rubber or urethane rubber can be used as the base of the belt.

A transfer device 25 has a function of transferring a toner image formed on the photoconductor 10 onto the intermediate transfer belt 20 by applying a direct current having a polarity opposite to that of the toner. Transfer device 2
As 5, a transfer roller can be used in addition to the corona discharger.

Reference numeral 26 denotes a transfer roller which can be released from contact with the earth roller 22 and retransfers the toner image formed on the intermediate transfer belt 20 onto the transfer material P.

A cleaning device 28 is provided so as to face the driven roller 24 with the intermediate transfer belt 20 interposed therebetween. After transferring the toner image to the transfer material P, the intermediate transfer belt 20
The charge of the residual toner is weakened by the static elimination roller 27 to which an AC voltage having a DC voltage of the same polarity or the opposite polarity of the toner is applied, and the cleaning blade 29 cleans the toner remaining on the peripheral surface.

A fixing device 4 has a heating roller 41 as a heating member and a pressure roller 42 as a pressure member.

Reference numeral 70 is a paper feeding roller, 71 is a timing roller, 72 is a paper cassette, and 73 is a conveying roller.

The fixing device according to the present invention will be described below. FIG. 2 is a schematic view showing a cross section of a heat roller type fixing device.

FIG. 3 is a schematic view of a pressure bonding mechanism of the pressure roller 42. FIG. 3A shows a pressurized state, and FIG. 3B shows a released state.

2 and 3, the front side of the paper is the front side and the back side is the rear side.

FIG. 4 is a cross-sectional view of the heating and pressure roller portion (see FIG. 2, AA arrow). In FIG. 2, the heating roller 41
Is heat-resistant rubber 412 of silicone type, which is an elastic body, is baked on a cylindrical core metal (hereinafter, simply referred to as core metal) 413 molded from an aluminum tube, and a release layer 411 is formed on the outer periphery of the heat resistant rubber 412. Made of coated construction. The heating roller 41 is supported by the front side plates 451 and 452 via the heat insulating sleeves 417 shown in FIG. Reference numeral 415 denotes a heater, which is disposed in the hollow portion of the heating roller 41 and has both ends supported by the support plates 416 shown in FIGS. 3 and 4 attached to the front side plate 451 and the rear side plate 452. A connector (not shown) is attached to the.

The pressure roller 42 includes a core metal 423 formed of an aluminum tube and a silicone-based heat-resistant rubber 4 which is an elastic body.
22 is baked, and the outer periphery of the heat resistant rubber 422 is coated with a release layer 421. The pressure roller is supported via a heat insulating sleeve 429 fitted in support levers 427 and 428 shown in FIGS. Reference numeral 425 denotes a heater, which is disposed in the hollow portion of the pressure roller 42 and has both end portions having support levers 427 (428).
It is supported by a support plate 426 shown in FIGS. 3 and 4 attached to the connector, and connectors (not shown) are inserted into both terminals.

Reference numerals 433 and 434 denote temperature detecting sensors for the heating roller 41 and the pressure roller 42, respectively.
The detection signals of 3 and 434 are transmitted to the control unit B1 (see FIG. 1), and a thermostat (not shown) adjusts each roller to a prescribed temperature.

In FIG. 3, reference numerals 451 and 452 denote front and rear plates of a frame body that constitutes the skeleton of the fixing device 40. The heating roller 41 and the support lever shaft are provided via the heat insulating sleeves 417, 437 and 436 shown in FIG. 430 and the cam rotation shaft 431 are supported. The support levers 427 and (428) are reinforced by a stay 432 and integrated. Reference numeral 435 is a coil spring that abuts the pressure roller 42 against the heating roller 41 at a predetermined pressure via the support levers 427 and (428).
The coil spring 435 is connected to the support levers 427 and 428.
To the front side plate 451 and the rear side plate 452.
It is locked by a spring hook 429 provided on the.

The pressure roller 42 is controlled so as to contact the heating roller 41 at least while the transfer material passes through the nip portion T.

Reference numeral 424 denotes a cam for releasing the contact of the pressure roller 42 from the heating roller 41 against the coil spring 435. One cam is provided at the position where the cam surface comes into contact with the support levers 427 and (428) in the same phase. Each of them is attached to the cam rotation shaft 431, and a rotational force is obtained from a power transmission unit (not shown) for rotation.

The support levers 427 and (428) are rotatable about a support shaft 430 as a fulcrum, and are counterclockwise rotated by the coil spring 435, so that the cam 4 is rotated.
The pressure roller 42 is swung up and down by a phase of 180 degrees by 24, and the pressure roller 42 is brought into contact with the heating roller 41 at a predetermined pressure.

In FIG. 4, the heating roller 41 has its rotational force transmitted from a power source (not shown) to a gear 418 fixed to one side of the core metal 413 via a gear group.

On the other hand, the pressure roller 42 comes into contact with the heating roller 41 and rotates along with it when pressure is applied. When the pressure is released, the cam 424 pushes down the support levers 427 and (428) against the coil spring 435 to release the contact between the heating roller 41 and the pressure roller 42.

The structure and mechanism of the heating and pressure roller have been described above. Next, the durability of the heating and pressure roller will be described.

The heating and pressing rollers are usually replaced with a predetermined usage (copy) amount (100,000 copies in the present embodiment) in a regular inspection or the like. There is a case where the predetermined life cannot be maintained due to breakage on the surface or peeling between the heat insulating rubber and the core metal.

The present invention pays attention to the tensile strength of heat resistant rubber which is an elastic body of the heating roller and the pressure roller, and selects the material which satisfies the condition of improving the durability in the specified temperature range to prolong the life of the roller. The feature is that the above failures can be avoided.

That is, in the first invention, the tensile strength of the heat resistant rubber 412 of the heating roller 41 is 0.6 MPa or more at the start of heating (initial stage), and at the start of heating after any heating (use) time. Compared with the above, a material that is constantly increasing or does not decrease by 0.5 MPa or more is used, and the set temperature of the pressure roller 42 is set in a temperature range in which the tensile strength of the heat resistant rubber 422 does not decrease. As a result, the durability of the roller can be improved.

In the second invention, the surface pressure at the nip portion T is A
[MPa] and the tensile strength of the heating roller 41 is B
[MPa], the tensile strength of the pressure roller 42 is D [M
Pa], the relationship between the heating roller and the pressure roller is always maintained so that A <B and A <D. That is, the durability of the roller is enhanced by using a heat-resistant rubber having a material having a tensile strength larger than the surface pressure at the nip portion T.

The tensile strength referred to here is the breaking strength, and in the present invention, it is assumed to be measured in accordance with JIS K6251. If a load corresponding to the tensile strength is applied, the elastic body will break.

FIG. 5 shows three types of heat-resistant rubber (high heat conduction LTV).
3 is a graph showing the relationship between the tensile strength of silicone rubber) and the copy amount.

This graph shows values obtained by leaving the heat-resistant rubber in a temperature environment of 260 ° C. for a period of time corresponding to 80 kp (80,000 copies) continuously, and measuring the tensile strength at every predetermined time (copy amount).

Now, the proper nip surface pressure for fixing is 0.45.
Considering the case of setting to MPa, even if the initial tensile strength is high like the rubber types A and C, there are some that decrease below 0.45 MPa as the copy amount increases, and like the rubber type B, 0. Some of them maintain 60 MPa or more. Therefore, the breakage of the roller can be avoided by using a material such as the rubber type B whose tensile strength does not decrease due to thermal deterioration, or by using a heating / pressurizing member with a small decrease amount.

Here, the durability test will be described by applying the heat resistant rubber (high thermal conductivity LTV silicone rubber) under the above conditions and setting the temperature.

The durability test was carried out under the following setting conditions for a single unit of the fixing device. Regarding the heating roller, set temperature: 200 ° C., initial tensile strength of heat resistant rubber: 0.7 MPa (JIS K6251
Tensile strength test according to JIS) Regarding the pressure roller, set temperature: 180 ° C., initial tensile strength of heat resistant rubber: 0.7 MPa (JIS K6251)
Tensile strength test by N.) As a result of the condition of nip surface pressure: 0.38 MPa, no abnormality was observed even with a copy amount of 120,000, and the tensile strength of the heat resistant rubber gradually increased to 1.1 MPa without decreasing.

On the other hand, the same set temperature (heating roller: 200
℃, pressure roller: 180 ℃), nip surface pressure (0.38
In the case of heat-resistant rubber (initial tensile strength: 0.3 MPa) lower than the nip surface pressure, roller breakage occurred at 100 copies. That is, it is considered that the initial tensile strength was lower than the surface pressure of the nip portion, which resulted in early fracture.

The same set temperature (heating roller: 200
℃, pressure roller: 180 ℃), nip surface pressure is 0.45
In the case of a heat-resistant rubber having an initial tensile strength of 0.6 MPa as the MPa (however, the heat-resistant rubber decreases to 0.45 MPa or less), roller breakage occurred at 6000 to 7,000 copies. At 6000 copies or less, the tensile strength did not decrease to 0.45 MPa, and
It is considered that the roller broke when the pressure became equal to or lower than MPa.

Next, the image forming process will be described with reference to FIG. Simultaneously with the start of image recording, the photoconductor 10 of the color signal Y is rotated in the counterclockwise direction by the start of a photoconductor drive motor (not shown), and at the same time, a potential is applied to the photoconductor 10 by the charging action of the scorotron charger 11. Is started.

After a potential is applied to the photoconductor 10, the writing device 12 starts writing an image corresponding to the Y image data, and the surface of the photoconductor 10 is printed with Y of the original image.
An electrostatic latent image corresponding to the image is formed.

The electrostatic latent image is reversely developed by the Y developing device 13 in a non-contact state, and Y is developed according to the rotation of the photoconductor 10.
Toner image is formed on the photoconductor 10.

The Y toner image formed on the photoconductor 10 is transferred to the intermediate transfer belt 2 by the action of the Y transfer device 25.
0 is transcribed.

After that, the photoconductor 10 is cleaned by the cleaning device 14 and the next image forming cycle is started (the same applies to the M, C, and K cleaning processes, so the description thereof is omitted).

Next, the writing device 12 writes an image corresponding to the M (magenta) color signal, that is, the image data of M, and the M of the original image is printed on the surface of the photoconductor 10.
An electrostatic latent image corresponding to the image is formed. The electrostatic latent image becomes an M toner image on the photoconductor 10 by the M developing device 13, and the intermediate transfer belt 20 is transferred to the M transfer device 25.
It is synchronized with the Y toner image above and is superimposed on the Y toner image.

By a similar process, the Y and M superimposed toner images are synchronized with each other, and the C (cyan) toner image is transferred onto the Y and M superimposed toner images at the C transfer device 25. The toner images of K (black) are superposed and synchronized with the superposed toner images of Y, M, and C.
In the K transfer device 25, the superimposed toner images of Y, M, and C are superimposed, and the superimposed toner images of Y, M, C, and K are formed on the intermediate transfer belt 20.

The intermediate transfer belt 20 carrying the superposed toner image is sent in the clockwise direction as shown by the arrow, and the transfer material P is sent out from the paper cassette 72 by the paper sending roller 70, and passes through the carrying roller 73, The transfer roller 26 is conveyed to the timing roller 71 and driven by the timing roller 71 so as to be synchronized with the superimposed toner image on the intermediate transfer belt 20 and to which a DC voltage having a polarity opposite to that of the toner is applied (intermediate transfer roller 26). The superposed toner image on the intermediate transfer belt 20 is transferred to the transfer material P by being fed to the transfer area S (which is in contact with the belt 20).

After that, the intermediate transfer belt 20 runs, the charge of the residual toner is weakened by the charge eliminating roller 27, and the cleaning blade 29 contacting the intermediate transfer belt 20 cleans the intermediate transfer belt 20 to start the next image forming cycle.

Transfer material P on which the superimposed toner images have been transferred
Is further conveyed to the fixing device 4, and is nipped and conveyed while heat and pressure are applied in the nip portion T between the heating roller 41 and the pressure roller 42, and the transfer material P on which the superimposed toner images are fused and fixed The sheet is conveyed to the sheet discharge tray 82 by the sheet discharge roller 81.

[0059]

EFFECTS OF THE INVENTION By using heat-resistant rubber for the heating roller and the pressure roller, the tensile strength of which does not decrease or the amount of decrease is small due to heat deterioration, breakage of the roller and separation from the core bar are eliminated, and durability is improved. To do.

[Brief description of drawings]

FIG. 1 is a schematic diagram illustrating an example of the overall configuration of an image forming apparatus.

FIG. 2 is a schematic view showing a cross section of a heat roller type fixing device.

FIG. 3 is a schematic view of a pressure bonding mechanism of a pressure roller 42.

FIG. 4 is a cross-sectional view of the heating / pressurizing roller portion (see FIG. 2, AA arrow).

FIG. 5 is a graph showing the relationship between tensile strength and copy amount of three types of heat resistant rubber.

[Explanation of symbols]

4 fixing device 41 heating roller 42 Pressure roller 412,422 heat resistant rubber 413,423 core metal 415,425 heater 433,434 Temperature detection sensor

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) F16C 13/00 F16C 13/00 EF term (reference) 2H033 AA23 BB06 BB14 BB15 BB29 BB33 BB34 CA07 CA12 CA27 CA39 3J103 AA02 AA13 AA21 AA51 BA03 BA41 BA43 CA05 CA66 FA01 FA12 GA02 GA57 GA58 GA60 HA03 HA12 HA13

Claims (4)

[Claims] 1. A heating member having an elastic body and a release layer covering the elastic body, and a pressing member having an elastic body and a release layer covering the elastic body, which is pressed against the heating member. An image forming apparatus including a fixing device is characterized in that the tensile strength of the elastic body of the heating member increases with use or does not decrease by 0.5 MPa or more as compared with the initial tensile strength. Image forming apparatus. 2. The initial tensile strength of the heating member is 0.
The image forming apparatus according to claim 1, further comprising a fixing device having a pressure of 6 MPa or more. 3. The image forming apparatus according to claim 1, further comprising a fixing device, wherein the set temperature of the pressure member is a temperature range in which the tensile strength of the elastic body of the pressure member does not decrease. . 4. A heating member having an elastic body and a release layer covering the elastic body, and a pressure member having pressure contact with the heating member and having the elastic body and the release layer covering the elastic body. In an image forming apparatus equipped with a fixing device, when the surface pressure at the nip portion is A, the tensile strength of the elastic body of the heating member is B, and the tensile strength of the elastic body of the pressure member is D, An image forming apparatus wherein A <B and A <D.