JPH04358188A - Fixing device - Google Patents

Abstract

PURPOSE:To improve the durability of a belt member and to use it for a long period by automatically releasing the press-contacting of a press-contacting roller member with a fixing belt-like member at the time of nonfixing. CONSTITUTION:This fixing roller has a constitution that a pressure roller 5 press-contacting to a heating belt 1 is supported by a crank lever 50 turned by the pressure of an eccentric cam 52, and the pressure roller 5 is press- contacted to the heating belt 1 by the action of a tension spring 51 pressing the crank lever 50 at the time of fixing, and retreated/separated from the heating felt 1 in such a manner that the eccentric cam 52 is rotated to turn the crank lever 50 in the opposite direction, at the time of nonfixing.

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 electrophotography, and more particularly to a fixing device that eliminates lack of gloss in color images without causing offset transfer or dirt transfer.

0002

2. Description of the Related Art In the fixing process of electrophotographic toner images, hot roller fixing is the most common. In recent years, in the electrophotographic process that handles color images, it is necessary to ensure the color reproducibility and gloss of the image after fixing, and to
In order to ensure transparency when using a transfer material, it is required that the toner be sufficiently melted. When using the commonly used spherical polyester toner and setting its melting conditions to the above-mentioned level, it becomes necessary to apply a large amount of low-viscosity silicone oil as a release agent due to the problem of high-temperature offset. ing.

0003

Problems to be Solved by the Invention When a large amount of silicone oil is used as described above, problems such as spillage of the silicone oil and adhesion of the silicone oil to the transfer material occur. Particularly when using an OHP, since the transfer material is not impregnated with silicone oil, the silicone oil may stain the user's hands or significantly reduce the permeability of the OHP itself. To solve this problem, toners using general polyester, that is, wax-based toners, have been used, but at present it is difficult to obtain a sufficient melting state. In addition, as mentioned above, color images often require gloss after fixing, and in that case, within the scope of conventional technology, there are
As mentioned above, when a large amount of release agent is applied or a wax-based toner is used, an image that has been fixed once is fixed again using an optional unit.

The present invention solves these fixing problems and eliminates the use of a mold release agent such as silicone oil at all.
Even if it is used in a small amount, it ensures sufficient toner melting in the image after fixing, provides fixing with excellent color reproducibility in the toner melting, and also produces images with good gloss as required for color images. The object of the present invention is to achieve fixing with excellent transparency and color reproducibility, especially when using an OHP.

[0005]

[Means for Solving the Problems] The above object is to clamp and convey a transfer material to the belt-like member in a fixing device that fixes a toner image on a transfer material by heating and cooling with a moving belt-like member. This is achieved by a fixing device characterized in that a pressure roller member is provided and the pressure roller member is separable from the belt-like member.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention is shown in FIGS. 1 to 5.

FIG. 1 shows a fixing device according to the present invention. The fixing device is housed in an independent container and incorporated into the main body of an image forming apparatus, and is connected to a drive section and a power supply section on the main body side. It is operated by connecting to.

In FIG. 1, reference numeral 1 denotes a heating belt which is a moving belt-like member for fixing, and a tension roller 4 is provided between a heating roller 2 which is a heating roller member and a separation roller 3.
The sheet is placed in a tensioned state by the urging force, and is circulated and conveyed in a clockwise direction by the driving rotation of the heating roller 2.

Reference numeral 5 denotes a roller member, that is, a pressure roller, which is in left contact with the outer peripheral surface of the heating belt 1 around which the heating roller 2 is wound, and which is driven counterclockwise or driven and rotated at the same speed as the heating roller 2. The transfer material is clamped between the two and conveyed.

The pressure roller 5 has a higher hardness than the heating roller 2, and presses the heating belt 1 toward the heating roller 2 to form a first nip region N1, and further presses the heating belt 1 toward the heating roller 2 to form a first nip region N1, and further presses the heating belt 1 toward the heating roller 2 to form a first nip region N1. By being located on the conveying downstream side of the heating belt 1 by θ, a second nip region N2 is formed between the heating belt 1 and the heating belt 1 as shown in the figure.

Note that the first nip area N1 and the second nip area formed by the heating roller 2 and the pressure roller 5 are in contact with each other.
The corresponding circumferential lengths and angles of the nip area N2 are shown in Figure 1 (
As shown in b), they are l1, l2 and α1, α2.

The heating roller 2 and the pressure roller 5 have the same outer diameter, and each heater H has the same calorific value.
1 and H2, the temperature of the outer peripheral surface is controlled and managed by temperature detection by the respective temperature sensors S1 and S2.

Further, F1 and F2 are cross-flow type fans (hereinafter simply referred to as fans) as cooling means disposed on the front and back sides of the conveying surface of the heating belt, and each of them is connected to a duct 7.
Air sucked in from the outside of the apparatus through A and 7B is directly applied to the lower surface of the transfer material through a plurality of slit holes 6A opened in the conveyance guide plate 6 for the fan F1, and to the rear surface of the heating belt 1 for the fan F2. It is designed to indirectly cool the top surface of the transfer material by spraying it on the surface of the transfer material.

Furthermore, cleaning rollers 1A and 5A are provided on the outer circumferential surfaces of the heating belt 1 around which the heating roller 2 is wound and the pressure roller 5, respectively, for cleaning toner adhering to the heating belt 1 and the pressure roller 5, respectively.
Further, an oil-impregnated roller 1B is pressed against the heating belt 1 to prevent toner from adhering to the heating belt 1.

The fixing action of the toner image on the transfer material by the transfer material by the fixing device will be explained.

The transfer material with the toner image transferred to its upper surface is indicated by arrow A.
When the sheet is conveyed into the apparatus from this direction, the forward portion passes through the carry-in guide plate 8A, is clamped by the heating belt 1 and the pressure roller 5, and is conveyed.

At this time, the transfer material is heated simultaneously from the upper and lower surfaces by the heating belt 1 and the pressure roller 5 to melt the toner.

That is, the toner on the transfer material is
In the nip region N1, the toner is uniformly pressed and heated by the heating belt 1 to be brought into a molten state, but since the heating is relatively short, there is no disturbance of the toner image and deterioration in image quality is suppressed.

After passing through the first nip area N1, the transfer material is heated from the back side by the pressure roller 5 in the second nip area N2 described above, but since it is heated sequentially over a relatively long period of time, it becomes molten. The toner sufficiently penetrates into the transfer material and adheres firmly to the transfer material, so that a toner image with high gloss can be obtained without fear of offset.

[0020] If the second nip area N2 is too large, the toner will melt excessively, leading to a decrease in image quality, making the transfer material more likely to curl or wrinkle, and increasing the load on the drive system. 3 of the first nip area N1 for the reason
It is desirable to reduce the amount by about twice as much.

The transfer material with the toner in a molten state is conveyed along the conveyance guide plate 6 so that its lower surface is exposed to the fan F.
1, the toner image on the upper surface is cooled by the fan F2, changes from a semi-molten state to a fixed state, and is separated from the heating belt 1 by a separation roller 3.

The transfer material separated from the heating belt 1 passes through the paper discharge guide plate 8B, passes through the paper discharge roller 9, and is then delivered to the static elimination brush BR2.
The static electricity is removed and discharged to the outside of the apparatus main body in the direction of arrow B.

On the other hand, the heating belt 1 from which the transfer material has been separated is neutralized by a static elimination brush BR1, the toner transferred from the transfer material is cleaned by the cleaning roller 1A, and oil is applied by an oil-impregnated roller 1B, and then the heating belt 1 is conveyed. Let's move on to the fixing action of the transfer material. On the other hand, the toner transferred from the heating belt 1 is also removed from the pressure roller 5 by the cleaning roller 5A at the same time. Note that when the heating belt 1 moves in the axial direction during conveyance and enters a so-called skewed state, the photosensors PS arranged on both side edges detect the heating belt 1 and tilt the tension roller 4. The heating belt 1 is automatically returned to the normal conveyance direction. The fixing temperature in the fixing device is controlled and managed as follows.

FIGS. 2 and 3 show the temperature sensors S1 and S.
2 shows the temperature control circuit and process according to No. 2. During the "warm-up" stage of the device, heaters H1 and H2 remain ON, fans F1 and F2,
The pressing action of heating belt 1 and pressure roller 5 is also released (O
FF).

When the heating roller 2 and the pressure roller 5 reach predetermined circumferential temperatures after the "warm-up" and reach the fixable state, that is, the "ready" stage, the fixing temperature of the transfer material is maintained constant. Therefore, the heaters H1 and H2 change to a state where ON/OFF is repeated, and at the same time, the heating belt 1 and the pressure roller 5 start conveying and rotating, respectively.

When "printing" is performed in the image forming apparatus at the "ready" stage, the pressure roller 5 is in the pressed state (O
N), the fans F1 and F2 are in a rotating state (ON) to carry out the transport of the transferred transfer material and the fixing action in which the toner image is fixed.

During the period from the discharge of the transfer material that has finished fixing until the subsequent transfer material is brought in, that is, at the "print interval" stage, the rotation of the fans F1 and F2 is stopped (OFF).
), and unnecessary cooling of the heating belt 1 is interrupted.

The above-described operation of pressing the pressure roller 5 against the heating belt 1 and releasing the pressing operation, that is, the operation of separating the pressure roller 5 from the heating belt 1, are performed as follows.

As shown in FIGS. 4A and 4B, the pressure roller 5 has its rotating shaft 2A supported between a pair of crank levers 50 provided on both inner surfaces of the fixing device.
A through shaft 50 that fixes and integrates each crank lever 50
It is urged by a tension spring 51 to rotate clockwise about A as a fulcrum.

Further, a pair of eccentric cams 52 are provided at positions facing each of the crank levers 50, and are fixed to a rotation shaft 52A whose rotation angle is controlled by a control section of the apparatus main body.

As described above, when "printing" is started, the eccentric cam 52 is rotated to the angle shown in FIG. The pressure roller 5 is pressed against the heating belt 1 to form the contact angle N between the nip portion and the heating belt 1 described above.

On the other hand, when "printing" is not being performed, the eccentric cam 52 rotates by 1/2 and presses the crank lever 50 to rotate it counterclockwise as shown in FIG. 4(B).

Therefore, the pressure roller 5 moves relative to the heating roller 2 in a direction that substantially increases the distance between its axes, moves away from the circumferential surface of the heating belt 1, and releases the pressed state.

The ``sag'' of the heating belt 1 caused by the release of the pressure roller 5 from the pressure roller 5 can be resolved by rotating the crank lever 60, which supports the tension roller 4, counterclockwise around the shaft 60A under the force of the tension spring 61. By the action of
It is automatically absorbed and the heating belt continues to convey and rotate normally with appropriate tension.

As a result, the heating belt 1 is not subjected to unnecessary pressure or deformation except during fixing, and therefore its durability is improved, and it is possible to maintain a smooth surface over a long period of time and fix images with rich gloss. It becomes possible.

[0036] A photosensor PS2 for detecting the passage of the transfer material is installed at a position downstream of the conveyance of the fixing device, and the photosensor PS2 does not detect the transfer material even after a predetermined period of time has elapsed after the start of "printing." If this is not possible, it is assumed that a jam has occurred, and the pressing state of the pressure roller 5 is released even during fixing.

FIG. 5 is a sectional view showing an example of a color image forming apparatus equipped with the fixing device of the present invention. This image forming apparatus includes an image reading system A, a laser writing system B, and an image forming section C.
etc.

At the top of the image forming apparatus, there is a document table made of a transparent glass plate, and a document D placed on the document table.
There is a document placement section 11 consisting of a document cover, etc. that covers the document table, and is located below the document table. A reading system A is provided. The first mirror unit 12 includes an exposure lamp 14 and a first mirror 15, and is mounted so as to be movable linearly parallel to the document table and in the left-right direction of the drawing, and optically scans the entire surface of the document D. The second mirror unit 13 is the second mirror 1
6 and a third mirror 17 are integrally provided, and move linearly in the same left and right direction at 1/2 the speed of the first mirror unit 12 so as to always maintain a predetermined optical path length. Of course, the movement of the second mirror unit 13 is parallel to the document table similarly to the first mirror unit 12. The image of the document D on the document table illuminated by the exposure lamp 14 is captured by the main lens 20.
Accordingly, the first mirror 15, the second mirror 16, and the third mirror 1
7 and is then imaged onto a color CCD 23. When the scanning is finished, the first mirror unit 12 and the second
The mirror unit 13 returns to its original position and waits until the next copy.

The image data of each color obtained by the color CCD 23 is subjected to image processing and output from the laser writing system B as an image signal.

The image forming section C includes a charger 35 disposed around the periphery of the photosensitive drum 30, which is an image forming body, and an image exposing section 55.
, developing device 36Y, 36M, 36C, 36BK, transfer device 3
7, a separator 38, a cleaning device 39, a paper feed cassette 40 disposed near the photosensitive drum 30, a conveyor belt 44, and a fixing device 45 according to the present invention.

[0041] The above developing units 36Y, 36M, 36C, 36
BK has a developing device 36Y at the most upstream part of the periphery of the photoreceptor drum 30.
However, the developing device 36 containing black toner BK is located at the most downstream part.
BK is installed. The color toner and black toner BK contained in the developing units 36Y, 36M, 36C, and 36BK are well-known ones, so their explanation will be omitted.

When the copy button is pressed, each process of the image reading system A, laser writing system B, and image forming section C described above is operated to form a color copy image. That is, when an image signal from the image reading system A is inputted to the writing system B, which includes a drive motor 31, a polygon mirror 32, and a semiconductor laser (not shown), an fθ lens, a correction lens, etc., under the control of the control unit CPU, a copy operation is performed. Start. That is, the photosensitive drum 30 rotates clockwise as shown by the arrow.
Uniformly charged by the charger 35, the image exposure section 55
A yellow (Y) image corresponding to the image on the document D is written by a laser beam from a laser writing system B, and an electrostatic latent image of the Y image is formed. This photosensitive drum 3
The above-mentioned electrostatic latent image on Y is reversely developed with Y toner by the developing device 36Y, and becomes a visible Y toner image. That is, an AC bias voltage is further applied to the DC region of the developing sleeve containing the magnet roll of the developing device 36Y, and a Y toner image is formed by non-contact development using the two-component developer serving as the developing means. . The photosensitive drum 30 on which this Y toner image has been formed passes under the cleaning device 39 that has been retracted, and is then charged by a charger 35 and written with a magenta (M) image by a laser beam by a laser writing system B. , an electrostatic latent image of a magenta (M) image is formed on the Y toner image. This latent image is reversely developed by a developing device 36M containing magenta toner and becomes an M toner image. Next, in the same way, cyan (C) toner image, black (B)
K) Toner images are formed by superimposing them.

[0043] If the original D is a monochrome image, the developing device 3
Only 6BK operates, and a toner image of only black toner BK is formed.

Next, the transfer paper P, which is fed out one by one by the paper feed roller 41 from the paper feed cassette 40 containing the transfer paper P serving as the transfer material, is synchronized with the toner image on the photoreceptor drum 30. The photosensitive drum 30 is delivered onto the photosensitive drum 30 by a timing roller 42 which is operated by the timing roller 42 . The toner image on the photoreceptor drum 30 is transferred to the transfer paper P by the action of the transfer device 37, and the toner image on the photoreceptor drum 30 is transferred to the transfer paper P by the separator 38.
After being separated from the top, the toner image is sent to a fixing device 45 via a conveyor belt 44 with the toner image facing upward.

The transfer paper P that has undergone the fixing action in the fixing device 45 is discharged to the outside of the device via the paper discharge roller 46, while the photosensitive drum 30 continues to rotate, and the toner remaining on its surface without being transferred is removed. is a cleaning device 3 having a cleaning blade 39A etc. that has been released from retraction.
9, it is collected and cleaned and is ready for the next copying.

For reference, the fixing device of the present invention is constituted by the following members as an example.

The heating belt consists of two layers, the inner layer of which is made of polyimide resin with a thickness of 50 to 75 μm as a heat-resistant base, and the outer layer is made of polyimide resin with a thickness of 50 to 100 μm.
Silicone rubber is used because it has high elasticity and good mold release properties.

Both the heating roller and the pressure roller each have a 40 mm diameter core at the center of a pipe-shaped core metal having a heat-resistant synthetic rubber layer, for example, a 2 mm thick silicone rubber layer formed on the outer periphery.
A roller with a built-in 0W heater is used, and in particular, for the pressure roller, a rubber layer is further covered with a 50 μm thick fluorine tube.

Further, as each cleaning roller provided on the heating belt and the pressure roller, foamed sponge rollers made of silicone rubber or urethane rubber are used.

Furthermore, the conveyance distance of the transfer material in the fixing device, that is, the distance from the pressure roller to the separation roller, is set in the range of 12 to 15 cm.

[0051]

[Effects of the Invention] According to the present invention, a low-temperature melting toner can be produced without the use of a release agent such as silicone oil, or even if it is used in a very small amount, without causing the transfer (offset) problem of the oil. By using the toner, it has become possible to sufficiently melt the toner and obtain a fixed image with excellent transparency and color reproducibility.

The transfer material at this time is not contaminated by silicone oil or the like. Furthermore, it has become possible to obtain glossy images of a sufficient level required for color images.

[Brief explanation of the drawing]

FIG. 1(a) is a cross-sectional configuration diagram of a fixing device of the present invention;
b) is an enlarged explanatory diagram of the main part.

FIG. 2 is a control circuit diagram of heating temperature in the device.

FIG. 3 is an explanatory diagram showing the operating status of each member in the device.

FIG. 4 is a sectional view showing (A) operation and (B) non-operation of the device.

FIG. 5 is a cross-sectional configuration diagram of a color image forming apparatus including a fixing device of the present invention.

[Explanation of symbols]

1...Heating belt 1A
…Cleaning roller 1B…Oil-impregnated roller 2…Heating roller 3…Separation roller 4
…Tension roller 5…Pressure roller
6... Conveyance guide plate 6A... Slit hole
7A, 7B...Duct 8A...Carry-in guide plate 8B...Paper discharge guide plate 9...Paper discharge roller H
1, H2...Heater S1, S2...Temperature sensor
F1, F2...Fan BR1, BR2...Static elimination brush
PS…Photo sensor 45…Fixing device

Claims (3)

[Claims] 1. A fixing device that fixes a toner image on a transfer material by heating and cooling with a moving belt-like member, wherein a pressure roller member is provided for pinching and conveying the transfer material to the belt-like member, A fixing device characterized in that a pressure roller member can be separated from the belt-like member. 2. The fixing device according to claim 1, wherein the separation operation of the pressing roller member from the belt-like member is performed when the transfer material is not fixed and when a jam occurs. 3. The direction in which the pressing roller member moves away from the belt-like member is a direction that increases the distance between the axes of the heating roller member that drives the belt-like member and the pressing roller member. The fixing device according to claim 1 or claim 2, characterized in that: