JPH04366874A - Fixing device - Google Patents

Abstract

PURPOSE:To lower the temp. of a heating belt member in contact with a toner image surface after a toner image is melt-stuck and to prevent an offset at the time of separating a transfer material by providing a cooling means on both surface of a belt-like member, and setting the temp. of the rear surface side lower than that of a transfer material side. CONSTITUTION:Fans F1 and F2 are the cooling means disposed on the front/rear sides of the carrying surface of a heating belt 1, and the fan F2 is disposed at a position nearer to a heating roller 2 on the upstream side of the carrying of the transfer material, compared with the fan F1, and simultaneously, a thing having an air capacity larger than that of the fan F1, is used if necessary. In this state, the toner image on the transfer material is melted by the holding/ fixing of the heating belt 1 and a pressure roller 5, then, an interface temp. of the heating belt 1 and the toner image is lowered ahead, than the temp. of the transfer material itself, and a temp. difference is set. In other words, the surface layer member of the toner image is solidified, simultaneously, the affinity of the toner image to the transfer material is maintained, and the offset at the time of separating can be prevented.

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 and fixes them 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 glossiness of the image after fixing, and to
In order to ensure transparency when using a P transfer material, it is required to melt the toner sufficiently. When polyester toner, which is widely used in general, is used and the melting conditions are set to the above-mentioned level, it becomes necessary to apply a large amount of low-viscosity silicone oil as a mold release agent due to the problem of high-temperature offset. There is.

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. Because of 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.
To provide a fixing device that ensures sufficient toner melting in the image after fixing even if only a small amount is used, and has excellent color reproducibility in toner melting, and furthermore, provides an image with good gloss as required for color images. The purpose 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 provide a fixing device that fixes a toner image on a transfer material by heating and cooling a moving belt-like member, in which belt cooling means are provided on both sides of the belt-like member. The cooling means changes the temperature (T1) on the back side of the belt-like member to the temperature (T2) on the transfer material side.
) is achieved by a fixing device characterized by being set at a lower temperature.

[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 is stretched between a heating roller 2 and a separation roller 3 by the urging of a tension roller 4. It is circulated and conveyed clockwise by the driving rotation.

Reference numeral 5 denotes a roller member, that is, a pressure roller, which presses against the outer peripheral surface of the heating belt 1 around which the heating roller 2 is wound. 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.

Furthermore, 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.
The 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 of the conveyance guide plate 6 for the fan F1;
Regarding No. 2, the liquid is sprayed onto the back surface of the heating belt 1 to indirectly cool the top 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, which is heated sequentially over a relatively long period of time, so that it becomes molten. The toner is sufficiently penetrated into the transfer material and firmly adheres to the transfer material, resulting in a toner image with high gloss without the risk 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, gradually changes from a semi-molten state to a fixed state, and is separated from the heating belt 1 by the 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.

Control and management of the fixing temperature in the fixing device is performed 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. When the device is in the "warm-up" stage, heaters H1 and H2 remain ON, fans F1 and F2,
Both the heating belt 1 and the pressure roller 5 are in a stopped state (O
FF), and therefore the pressing action of the 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 fixing ready 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), and conveyance of the transferred transfer material and fixing of the toner image are performed.

[0028] During the period from the discharge of the transfer material that has been fixed to the time when 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).
As a result, unnecessary cooling of the heating belt 1 is interrupted.

In the fixing device of the present invention, after the toner image on the transfer material is brought into a molten state by being sandwiched between the heating belt 1 and the pressure roller 5, the interface temperature between the heating belt 1 and the toner image is adjusted to the temperature of the transfer material itself. By lowering the temperature in advance of the temperature to provide a temperature difference, the surface layer member of the toner image is solidified, and at the same time, the affinity of the toner image to the transfer material is maintained to prevent offset during separation.

That is, the fan F2 is disposed at a position closer to the heating roller 2 on the upstream side of the conveyance of the transfer material than the fan F1, and if necessary, a fan having a larger air volume than the fan F1 is used.

FIG. 4 shows an example of the relationship between the temperature curve C2 on the transfer material side, indicated by the temperature T2, which changes due to the cooling action of the fans F1 and F2, and the temperature curve C1 on the back surface of the heating belt 1, indicated by the temperature T1. This is what is shown.

As shown in the figure, after the toner image is melted, it is heated to a heating belt 1 whose temperature is lower than that of the transfer material itself.
Since the surface layer portion is quickly cooled and solidified, it is conveyed in close contact with the heating belt 1 and then easily separated at the separating section.

On the other hand, since the transfer material itself is maintained at a temperature higher than the interface temperature of the heating belt 1 until it is separated from the belt surface, it maintains its affinity for the toner image, and as a result, it maintains its gloss without causing offset upon separation. It will be established as a rich image of

According to experiments, it is sufficient that the difference between the temperature T1 on the back side of the heating belt 1 and the temperature T2 on the transfer material side is within 5°C, so that even the transfer material to which a particularly high density image has been transferred is It has been confirmed that separation can be achieved without causing offset.

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 parallel to the document table so as to be movable linearly in the horizontal direction of the drawing, and optically scans the entire surface of the document D. The second mirror unit 13 integrally includes a second mirror 16 and a third mirror 17, and moves linearly in the same left and right directions 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 2.
0, the image is formed onto the color CCD 23 via the first mirror 15, second mirror 16, and third mirror 17. When scanning is completed, the first mirror unit 12 and the second mirror unit 13 return to their original positions and wait 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 exposure 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.

[0039] 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. Developing device 36Y, 36M, 36C
, 36BK and black toner B.
As for K, a well-known one is used, so a description thereof 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 activated to form a color copy image. That is, when the image signal from the image reading system A is input 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 CPU of the control unit, copying is performed. Start operation. That is, the photosensitive drum 30 rotates clockwise as shown by the arrow, is uniformly charged by the charger 35, and is exposed to the image exposure section 5.
In step 5, writing of a yellow (Y) image corresponding to the image of the original D is performed by a laser beam from the laser writing system B, and an electrostatic latent image of the Y image is formed. The electrostatic latent image on the photosensitive drum 30 is developed by a developing device 36Y.
Reversal development with toner is performed to form a visible Y toner image. That is, a direct current or even alternating current bias voltage is applied to the developing sleeve containing the magnet roll of the developing device 36Y, and non-contact development is performed using a two-component developer serving as a developing means to form a Y toner image. . 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 the charger 35 and written with a magenta (M) image by a laser beam by the laser writing system B. , magenta (M) on top of the Y toner image.
An electrostatic latent image of the image is formed. This latent image is reversely developed by a developing device 36M containing magenta toner and becomes an M toner image. Subsequently, a cyan (C) toner image and a black (BK) toner image are similarly formed in a superimposed manner. When the document D is a monochrome image, only the developing device 36BK operates to form a toner image of only black toner BK.

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

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 any remaining particles remain on its surface without being transferred. The toner is collected and cleaned by the cleaning device 39 having the cleaning blade 39A and the like whose evacuation is canceled, and is placed on standby for the next copy.

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

[0044] 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 have a diameter of 40 mm at the center of a pipe-shaped core metal on which a heat-resistant synthetic rubber layer, for example, a 2 mm thick silicone rubber layer is 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.

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.

[0048]

Effects of the Invention According to the present invention, a mold release agent such as silicone oil is not used at all, or even if it is used in a very small amount, the problem of transfer (offset) of the oil does not occur, and a low-temperature melting mold can be manufactured. By using the toner, it has become possible to sufficiently melt the toner and obtain a fixed image with excellent transparency and color reproducibility.

[0049] At this time, the transfer material 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 drawings]

FIG. 1(a) is a cross-sectional configuration diagram of a fixing device of the present invention;
b) is an enlarged explanatory view 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 graph showing temperature changes of the belt and transfer material.

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 Carrying guide plate 8B Paper discharge guide plate 9 Paper ejection roller H1, H2 heater S1, S2 Temperature sensor F1, F2 fan BR1, BR2...Static elimination brush PS Photo sensor 45 Fixing device

Claims (2)

[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 belt cooling means are provided on both sides of the belt-like member,
The cooling means lowers the temperature (T
A fixing device characterized in that 1) is set at a temperature lower than the temperature (T2) on the transfer material side. [Claim 2] The temperature (T1) and the temperature (T2)
Claim 1 characterized in that the temperature difference between the
fixing device.