JP2003280436A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus having a fixing device which ensures stable separation performance by using one which is less in harness change caused by thermal deterioration and is less likely to change in impact elastic modulus. <P>SOLUTION: The image forming apparatus is provided with the fixing device which has a heat member having an elastic layer and a releasing layer covering the elastic layer and a pressure member disposed in pressure contact with the heat member and having an elastic layer and a releasing layer covering the elastic layer. In the image forming apparatus, if the surface hardness values of the heat member and pressure member of the fixing device before heating are A0 and B0, respectively, and the surface hardness values of the heat member and pressure member after an arbitrary lapse of time are A1 and B1, respectively, a relationship represented by (A1-A0)-(B1-B0)≤0 is always established. <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 by a heating roller method.

[0002]

2. Description of the Related Art Conventionally, in a heating roller type fixing device,
Since the toner image is conveyed while being fixed by the rotation of the heating roller, the nip portion has an upward convex shape (as shown in FIG. 5) in case the transfer material is wound around the heat roller due to toner welding. A method of increasing the separating performance by curving the roller) or a separating claw method of forcibly pressing the peeling claw to the heating roller is adopted.

FIG. 5 is a view showing a state where the transfer material is conveyed at the nip portion. In the method of separating the transfer material by making the nip portion upward convex as shown in the figure, the surface hardness of the heating roller 41 should be smaller than that of the pressure roller 42 (the heating roller 41 and the transfer material P are separated at the time of separation). The angle θ becomes larger), the heating roller 41 nips and conveys the transfer material P while being deformed by the pressure roller 42, and the repulsive elastic force (restoring force) of the heating roller 41 at the moment when the transfer material is released from the nip portion T. Acts in the direction of arrow R to separate the transfer material P.

The heating and pressure rollers are usually replaced with a predetermined usage (copy) amount (100,000 copies in this embodiment) in a periodic inspection or the like, but with an elastic layer (hereinafter also referred to as an elastic body). Certain heat resistant rubbers 412 and 422 may change in hardness due to thermal deterioration before periodic inspection due to repeated thermal stress or the like, and the impact resilience may decrease. In this case, the heating roller 41 loses stable separation performance due to lack of impact resilience,
It causes separation failure.

Further, in the separation claw method, the claw damages the roller, and vertical streaks are generated in the image, leading to deterioration in image quality.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus having a fixing device of a heating roller type having a nip portion formed in an upwardly convex shape and having stable separation performance.

[0007]

The above object can be achieved by the following constitution.

(1) A heating member having an elastic layer and a releasing layer covering the elastic layer, and a pressing member having an elastic layer and a releasing layer covering the elastic layer, which is in pressure contact with the heating member. In the image forming apparatus provided with the fixing device, the surface hardness of the heating member before heating of the fixing device is A0, the surface hardness of the pressing member is B0, and the surface hardness of the heating member after an arbitrary use time elapses. Is A1 and the surface hardness of the pressing member is B1, always (A1-A0)-(B1-B0)
An image forming apparatus characterized by a relationship of ≦ 0 (first
Invention).

(2) A fixing device having a heating roller having a cylindrical cored bar, an elastic layer provided around the cored bar, a release layer covering the elastic layer, and a pressure roller in pressure contact with the heating roller. In the image forming apparatus in which is provided, when the repulsion elastic modulus of the elastic layer is D, 40% ≦ D ≦ 60% is satisfied.

(3) A heating roller having a cylindrical cored bar, an elastic layer provided around the cylindrical core, and a release layer covering the elastic layer, and an elastic layer and the elastic layer in pressure contact with the heating roller. In an image forming apparatus provided with a fixing device having a pressure roller having a release layer for covering, the elastic modulus of the elastic layer of the heating roller is always higher than the elastic modulus of the elastic layer of the pressure roller. An image forming apparatus characterized in that a member is used (third invention).

(4) A heating roller having a cylindrical cored bar, an elastic layer provided around the cylindrical core, and a release layer covering the elastic layer, and an elastic layer and the elastic layer in pressure contact with the heating roller. In an image forming apparatus provided with a fixing device having a pressure roller having a release layer for covering, the repulsion elastic modulus of the elastic body of the heating roller after the lapse of any use time is
An image forming apparatus (fourth invention), which is characterized in that it rises from before the start of use or does not fall by 10% or more.

[0012]

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 is projected onto the photoconductor 10 by the writing device 12.

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 as the rotation direction of the photoconductor 10 at the closest position. 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 applying a direct current having a polarity opposite to that of the toner to transfer the toner image formed on the photoconductor 10 onto the intermediate transfer belt 20. 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 heating 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 / pressurizing 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 formed 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 plate 451 and the rear side plate 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 covered 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 sensors of the heating roller 41 and the pressure roller 42, which are temperature sensors 433 and 43.
The detection signal of No. 4 is transmitted to the control unit B1 (see FIG. 1), and each roller is adjusted to a specified temperature by a thermostat (not shown).

In FIG. 3, reference numerals 451 and 452 denote front and rear plates of the frame body that constitutes the skeleton of the fixing device 4, and the heating roller 41 and the support lever shaft are interposed via the heat insulating sleeves 417, 437 and 436 shown in FIG. 430 and the cam rotation shaft 431 are supported. Support levers 427 and (428) are stay 4
It is reinforced with 32 and is united. 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). One end of the coil spring 435 is hooked on the support levers 427, 428, and the other end is locked by a spring hook 429 provided on the front side plate 451 and the rear side plate 452.

The pressure roller 42 is controlled so that the transfer material contacts the heating roller 41 at least while passing 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 around 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 a rotational force transmitted from a power source (not shown) to a gear 418 fixed to one side of the cored bar 413 via a gear group.

On the other hand, when pressure is applied, the pressure roller 42 contacts the heating roller 41 and rotates together. 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. Having described the mechanism, the separability of the transfer material by the fixing roller of the present invention will be described next.

The hardness is measured by Ask in the present invention.
er-C hardness meter, JISK6255 for repulsion elastic modulus measurement
Method is applied.

In the first aspect of the invention, the heating roller 41, which is a heating member, and the pressing roller 4, which is a pressing member, are heated before heating.
When the surface hardness of 2 (hereinafter, simply referred to as hardness) is A0 and B0 (A0 <B0) and the respective hardnesses are A1 and B1 after an arbitrary use (heating) time, inequalities (A1-A0) The separation performance can be improved by always maintaining the relationship of − (B1−B0) ≦ 0.

For example, A0 = 78 ° and B0 = 86 ° are A
When 1 = 80 ° and B1 = 88 °, the hardness difference between the heating roller before heating and that after optional use is 2 °, and the hardness difference between the pressure roller is 2 °, so the nip shape (upwardly convex) is formed. There is no change. Also, A0 = 78 ° and B0 = 86 ° are A1 = 75.
When B1 = 86 °, the difference in hardness between the heating roller before heating and after the lapse of optional use time is softened by 3 °, and the hardness difference of the pressure roller remains unchanged at 0 °, and the nip portion is higher. The convex direction (direction in which the angle θ in FIG. 5 increases) is advantageous for separation. In any of the above cases, the above inequality is satisfied. However, A0 = 78 °, B0 = 86 ° is A1 = 8
When 0 ° and B1 = 86 °, the hardness difference between the heating roller before heating and after the lapse of arbitrary use time is 2 °, and the hardness difference between the pressure roller is 0 °, which does not satisfy the above inequality. This is the direction in which the nip shape fluctuates in the downward convex direction, which is a disadvantageous direction for separation.

That is, since the change amount of the pressure roller 42 is larger than the change amount of the hardness of the heating roller 41,
The inequality means that the nip shape (upward convex shape) set before heating does not change in a direction in which the separation performance is disadvantageous (direction convex downward).

By making the diameter of the heating roller larger than that of the pressure roller, the transfer material is heated by the heating roller 4.
The separation effect can be improved by adopting a structure that can be easily separated from 1.

In the second invention, when the repulsion elastic modulus of the heat resistant rubber 412 before heating is D, the initial condition is 40% ≦ D.
When ≦ 60%, the hardness of the heating roller 41 is always lower than that of the pressure roller 42, and the separation performance can be improved by keeping the nip portion T in the upward convex shape.

In the third aspect of the present invention, the repulsive elastic modulus D of the heat resistant rubber 412 and the repulsive elastic modulus E of the heat resistant rubber 422 always maintain the relation of E <D, so that the transfer material P is released from the nip portion T. Separation performance can be improved by increasing the restoring force of the heating roller 41.

In the fourth aspect of the invention, the repulsion elastic modulus of the heat resistant rubber 412 after an arbitrary use time has elapsed can be improved by improving the separation performance by using a member which does not increase more than 10% or more than before heating. it can.

Next, the results of an experiment conducted on a fixing device provided in the image forming apparatus using a fixing (heating, pressing) roller of silicone rubber (high thermal conductivity LTV silicone rubber) under the following setting conditions will be described.

The linear velocity of the fixing roller was 220 mm / s, the nip shape was upward convex, and the nip pressure was 0.4 MPa. Silicone heat resistant rubber was used for both the heating and pressure rollers.

Regarding the heating roller, set temperature: 200
C, impact resilience: 43% (measurement test according to JIS K6255), heat resistant rubber hardness: 60 ° (2 mm thick Asker-
C value) and the surface hardness of the heating roller: 77 ° (Ask
er-C value), diameter: 65 mm.

Set temperature for the pressure roller: 180
C, impact resilience: 20% (measurement test according to JIS K6255), heat resistant rubber hardness: 52 ° (2 mm thick Asker-
C value), surface hardness of pressure roller: 86 ° (Asker-
C value), diameter: 55 mm As a result of conducting an experiment under the above conditions,
No abnormality was found in the separation performance even after 100 kp (100,000 copies) had elapsed.

FIG. 6 is a view showing the results of the separation performance evaluation experiment when the impact resilience is lowered. In this figure, the separation performance evaluation was performed by changing the set temperature with a heating roller having a repulsion elastic modulus of 43% before heating, and the separation performance evaluation after the repulsion elastic modulus decreased to 20% after using the same roller for 100 kp. The results and are shown in FIGS. 6 (a) and 6 (b), respectively.

In FIG. 6A, the initial impact resilience is 4
In the case of 3% heating roller (unused, no thermal deterioration), the temperature of heating (up) / pressing (down) roller is 150 ° C / 130
Abnormality is observed in the separation performance only after the temperature is lowered to ℃, whereas in Fig. 6 (b), when the repulsion elastic modulus is reduced to 20% after thermal deterioration of the same roller, 180 ° C / 160
Abnormality in separation performance is observed at ℃. That is, 100k
It is considered that when the impact resilience decreases due to heat deterioration due to the use of p, the region where the separation performance is good (denoted by ◯) becomes narrow due to the influence.

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 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 cleaning process of M, C, and K, so the description 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 the same 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, passes through the carrying roller 73, and 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 travels, the electric charge of the residual toner is weakened by the charge eliminating roller 27, and the intermediate transfer belt 20 is cleaned by the cleaning blade 29 which is in contact with the intermediate transfer belt 20, and the next image forming cycle is started.

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.

[0063]

The separation performance can be improved by using an elastic member whose repulsion elastic modulus is less likely to change due to heat deterioration to the fixing roller without changing the structure of the fixing device.

[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 diagram showing a cross section of a heating roller type fixing device.

FIG. 3 is a schematic view of a pressure roller pressing mechanism. Figure 3
FIG. 3A shows a pressurized state, and FIG. 3B shows a released state.

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

FIG. 5 is a diagram showing a state in which a transfer material is conveyed at a nip portion.

FIG. 6 is a diagram showing a result of a separation performance evaluation experiment when the impact resilience is lowered.

[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 sensor

Continued front page    F-term (reference) 2H033 AA16 BB04 BB05 BB06 BB15                       BB29 BB30 BB33 BB34                 3J103 AA02 AA13 AA24 AA51 AA85                       BA05 BA41 BA43 CA03 CA66                       FA09 GA02 GA57 HA03 HA12

Claims (7)

[Claims] 1. A heating member having an elastic layer and a release layer covering the elastic layer, and a pressing member having an elastic layer and a release layer covering the elastic layer, which is in pressure contact with the heating member. In an image forming apparatus provided with a fixing device, the surface hardness of the heating member before heating the fixing device is A0, the surface hardness of the pressure member is B0, and the surface hardness of the heating member after an arbitrary use time has elapsed An image forming apparatus characterized by having a relationship of (A1−A0) − (B1−B0) ≦ 0 at all times, where A1 and the surface hardness of the pressing member are B1. 2. The image forming apparatus according to claim 1, wherein the relationship between the surface hardness A0 of the heating member and the surface hardness B0 of the pressing member is A0 <B0. 3. The image forming apparatus according to claim 1, wherein the heating member and the pressure member have a roller shape, and the diameter of the heating roller is larger than the diameter of the pressure roller. 4. A fixing device having a heating roller having a cylindrical cored bar, an elastic layer provided around the cored bar, a release layer covering the elastic layer, and a pressure roller in pressure contact with the heating roller. In the image forming apparatus provided, when the impact resilience of the elastic layer is D, 40% ≦ D ≦ 60%. 5. The image forming apparatus according to claim 4, wherein the surface hardness of the heating roller is lower than the surface hardness of the pressure roller. 6. A heating roller having a cylindrical cored bar, an elastic layer provided around the cylindrical core, and a release layer covering the elastic layer, and an elastic layer press-contacting the heating roller and covering the elastic layer. In an image forming apparatus provided with a fixing device having a pressure roller having a release layer, the elastic modulus of the elastic layer of the heating roller is always higher than the elastic modulus of the elastic layer of the pressure roller. An image forming apparatus characterized by being used. 7. A heating roller having a cylindrical cored bar, an elastic layer provided around the cored bar, and a release layer covering the elastic layer, an elastic layer press-contacting the heating roller, and the elastic layer covering the elastic layer. In an image forming apparatus provided with a fixing device having a pressure roller having a release layer, the repulsion elastic modulus of the elastic layer of the heating roller after the lapse of any use time is higher than that before the start of use, An image forming apparatus characterized in that it does not fall by 10% or more.