JPH04350883A - Fixing device - Google Patents

Abstract

PURPOSE:To prevent a sheet from peeling from a fixing belt and to remove offset by providing a means for generating stress that gives pressure pressing to the fixing belt side to a transfer material on the way from a separation position to a nip part on an upstream position when the sheet passes. CONSTITUTION:The contacting degree among a heating element 1, the fixing belt 3 and the sheet is enhanced by pressing them from the back side of the sheet with a pressuring roller 4, and the effect of heating action from the back of the sheet is obtained by the heat accumulation of the roller 4 itself. The temperature of the heating element 1 is controlled based on the resistance of a thermistor. Just after the sheet passes through a heating part, it is lightly pressed to the belt 3 in a high-temperature state so as not to cause natural peeling by a peeling preventing roller. Thereafter, outside air is allowed to blow from the back of the sheet by the action of a fan, so that both the sheet and the belt 3 are cooled. Since the sheet is pressed to the belt 3 with the wind pressure, the natural peeling of the paper from the belt 3 is not caused until just after cooling is completed, and the offset is not caused.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device used in electrophotographic devices and the like.

0002

2. Description of the Related Art Hitherto, a heated roller system has been most commonly used in fixing devices for electrophotographic apparatuses. Basically, it consists of a pair of heating roller and a pressure roller that presses against the heating roller, and the unfixed image is passed between the two and fixed. It is necessary to take measures to prevent the so-called offset phenomenon, such as providing a release layer of fluororesin or coating the roller surface with oil. However, in the heat roller method, the developer tends to cause cohesive failure during the process in which the heated and molten developer separates from the solid roller surface.
It was inevitable in principle that offset would occur as a wetting phenomenon.

Recently, a new method has been proposed, for example, as described in Japanese Patent Laid-Open No. 63-313182, in which a heating element is pressed against the paper via a fixing film sheet or a fixing belt to perform fixing. A rapid heating method has been developed, but according to this rapid surface heating method,
After a sheet with a small heat capacity passes through a heating element, it is immediately cooled by heat radiation, so it is theoretically possible to prevent offset by separating the solid developer from the solid belt surface through interfacial destruction. be.

0004

[Problems to be Solved by the Invention] However, in the above-mentioned rapid surface heating method, the adhesiveness between the fixing belt and the paper deteriorates because the developer is in a molten or semi-molten state before it is completely cooled to a solid state. There was a problem in that it deteriorated and peeled easily, and when this peeling occurred, offset occurred.

[0005] The present invention is an attempt to solve the above-mentioned problems. That is, in the present invention, when passing paper,
An object of the present invention is to provide a fixing device that can prevent a transfer material from peeling off from a fixing belt and remove offset from a separation position to a nip portion upstream. It is.

[0006]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a heat-resistant fixing belt that is in contact with a transfer material on a surface having a toner image and that moves at the same speed as the conveyance speed of the transfer material. In a fixing device equipped with a pressure roller whose inner surface is in contact with a heating element and which rotates in pressure contact with the outer surface of the fixing device, when the paper is passed, the fixing device has a heating element in contact with the inner surface and a pressure roller that rotates in pressure contact with the outer surface. The fixing belt is provided with means for generating stress that exerts a pressing pressure on the fixing belt side.

[0007]

[Function] In the present invention, the speed difference between the fixing belt and the pressure roller at the nip portion during paper feeding, which has been overlooked in the above-mentioned rapid surface heating method, applies stress to the paper that causes peeling. This focuses on the following:
By eliminating the speed difference between the two at the nip, or at least suppressing it within a certain range, stress is generated on the transfer material that exerts pressure on the fixing belt side, preventing it from peeling off and preventing offset. is removed.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a first embodiment of the present invention.
In FIG. 1, the paper is conveyed from the left side, as indicated by a paper path 13, and is heated by the heating element 1 via the fixing belt 3. By applying pressure from the back side of the paper using the pressure roller 4, thermal contact between the heating element 1, the fixing belt 3, and the paper is increased, and the roller 4 itself has the effect of heating the paper from the back side due to its heat storage.

[0009] Temperature control of the heating element 1 is performed based on a change in the resistance value of the thermistor 2. Immediately after passing through the heating section, a peeling prevention roller 7 lightly presses the paper against the fixing belt 3 so that natural peeling does not occur while the paper remains at a high temperature. After that, outside air is blown from the back side of the paper by the action of the fan 8, and the paper and fixing belt 3 are
Cool both. Moreover, since the paper is pressed against the fixing belt 3 by the wind pressure, natural separation between the paper and the fixing belt 3 does not occur immediately after cooling is completed, and offset does not occur.

After being cooled in this manner, the paper and the fixing belt 3 are separated by curvature by the separating claw 12 and the separating roller 11, and the fixing process is completed.

An anti-wrapping sheet 15 is brought into contact with the pressure roller 4 to prevent paper from wrapping around the sheet.

In FIG. 1, 6 is a cleaning pad, 9 is a driven roller, and 10 is a driving roller.

By the way, in the conventional structure, the fixing belt is conveyed by a drive roller, and the pressure roller is driven by the frictional force of the nip portion.

However, when paper is passed through, the paper is interposed between the fixing belt and the pressure roller, so the surface speed of the two differs depending on the degree of slippage and paper stiffness. The speed was about a few percent slower.

Furthermore, even if the drive is simply applied to the conventional pressure roller side, in addition to problems related to the accuracy of the drive gear pitch or slippage between the intervening paper and the roller, there are problems with the slippage between the belt and the roller. Because of this, it was difficult to suppress the surface speed properly. Therefore, even if the speeds of both the belt and the rollers are attempted to be approximately equal, in reality stress is often generated on the paper due to the above-described uneven speeds of the rollers and the belt, which often causes peeling.

In the experiment, keeping this in mind, we made efforts such as increasing the frictional resistance on the inner surface of the belt to minimize slippage with the drive roller, and making the gear pitch finer than before. .

For example, even when there is no slippage,
For paper with low stiffness, the belt circumferential speed V1 and the pressure roller circumferential speed V2 do not match, as V1>V2, and as shown in FIG.
), since the feeding speeds of the front and back sides of the paper 5 are different, the paper 5 peels off toward the pressure roller 4 side. When the paper 5 completely follows the surface of the pressure roller 4,

0
018]

[Math 1]

Therefore, the circumferential speed of the pressure roller must be at least faster than this.

[0020] In experiments, usually V1 = 50 to 60 mm/
The fixing time was 10 seconds using a roller with a diameter of 20φ.
When feeding paper with a thickness of 0μ, there is a possibility that the roller speed can be increased to about 1% due to slippage.

In this embodiment, the pressure roller 4 side is also driven, and the speed of the pressure roller 4 side is made slightly higher than that of the fixing belt 3 side, thereby applying stress to the paper 5 that causes peeling. First, as shown in FIG. 2(A), the fixing belt 3
It is possible to eliminate peeling between the paper 5 and the paper 5 and prevent offset.

On the other hand, if only the pressure roller 4 side is driven and all the transport rollers on the fixing belt 3 side are driven, there is no risk that V2<V1 even if V2≧V1. However, if the speed difference is too large, the fixing belt 3 between the heating element 1 and the separation roller 11 is likely to become slack, which is not preferable for preventing peeling. From the above, the most preferable state for peeling is slightly V2>V1. When the fixing belt 3 and the pressure roller 4 have the same circumferential speed, stress that causes peeling of the paper 5 is not generated in the nip portion, and pressing pressure is applied to the fixing belt 3 side. Otherwise, it is preferable that the difference in circumferential speed between the two is within 1% with respect to the fixing belt 3 side.

FIG. 3 shows the relationship between the circumferential speed difference and the degree of offset occurrence due to peeling.

The horizontal axis of the figure represents the circumferential speed difference of (V2-V1)/V1 as a percentage, and the vertical axis represents the area ratio at which offset occurs using a character image with an image area ratio of 5% as a sample. According to experiments, the smaller the amount of toner present between the fixing belt 3 and the paper 5, the weaker the adhesion force between the two, and peeling was more likely to occur. Therefore, in order to check the degree of peeling, thin line patterns, character patterns, or halftone patterns are more conspicuous and suitable than solid images or photographic patterns.

Regarding toner, even toner having a low melt viscosity, such as non-Magsharp melt toner, will not peel off with this configuration. In the experiment, Canon Sales Co., Ltd.'s C was used as a non-magsharp melt toner.
The toner for LC200 was mainly used.

The heating element 1 is made of a low heat capacity linear element fixedly supported by the device, and has a thickness of 1.0 m, for example.
This is an alumina substrate with a width of 10 mm and a length of 240 mm coated with a resistive material to a width of 1.0 mm, and electricity is applied from both ends in the longitudinal direction. Current is DC 100V, cycle 20m
sec pulse waveform, a pulse corresponding to the desired temperature and energy release amount controlled by the thermistor 2 is given by changing the pulse width. The pulse width is approximately 0.5 to 5 msec.

The fixing belt 3 moves in the direction of the arrow in the figure while coming into contact with the heating element 1 whose energy and temperature are controlled in this way. As an example of this fixing belt 3, a thickness of 2
It is an endless film in which a 0μ heat-resistant film, such as polyimide, polyetherimide, PES, or PFA, is coated with a release layer of 10μ, which is made of a fluororesin such as PTFF or PAF and a conductive material added thereto, on at least the image contact side. Generally the total pressure is less than 100μ, more preferably less than 40μ. The fixing belt 3 is driven by the driving force and tension of a driving roller 10 and a driven roller (tension roller) 9, and moves in the direction of the arrow without wrinkles.

The pressure roller 4 is made of silicone rubber or the like having a rubber elastic layer with good mold releasability, and has a total pressure of 4 to 7.
kg, the heating element 1 is pressurized via the fixing belt 3 and rotates in pressure contact with the fixing belt 3. The shape is crown, inverted crown,
Others may be used.

FIG. 4 shows a second embodiment of the invention.

In this second embodiment, as a means for preventing peeling, a pressure belt 14 presses the paper against the fixing belt 3 after heating until it is cooled and separated, thereby preventing offset.

Even in the configuration of the second embodiment, the fixing belt 3 and the pressure belt 14 do not come into direct contact with each other during paper passing, and a speed difference is likely to occur due to slippage. It is best to send it quickly.

FIG. 5 shows a third embodiment of the invention.

In this third embodiment, the paper that is conveyed from the transfer section directly or via a fan belt with the transfer surface facing down is fixed, and the device configuration is just different from that shown in FIG. is upside down.

That is, there is no difference in circumferential speed between the fixing belt 3 and the pressure roller 4, and the paper is pressed against the fixing belt 3 by the action of gravity without any peeling force, so there is no fear of peeling. In addition, since gravity acts in the direction of eliminating the wrapping around the pressure roller 4, the wrapping prevention sheet 1 shown in FIG.
5 is no longer needed.

In the conventional configuration, peeling occurred due to the difference in circumferential speed even when the top and bottom were turned upside down, but according to the third embodiment, peeling no longer occurs.

[0036]

[Effects of the Invention] As explained above, according to the present invention,
A surface rapid heating type fixing device is provided with means for generating stress on the transfer material from the separation position to the nip portion upstream of the fixing belt side when paper is passed through so as to apply pressure to the fixing belt side. This eliminates peeling of the fixing belt and transfer material before they are cooled and separated, eliminating offset, and as a result, high-quality and stable images can be obtained across all types of photographs, text images, fine line patterns, and halftone patterns. It has the effect of being

[Brief explanation of the drawing]

FIG. 1 is an elevational view showing a first embodiment of the present invention.

FIGS. 2A and 2B are explanatory diagrams of paper peeling.

FIG. 3 is an explanatory diagram showing the relationship between circumferential speed difference and offset.

FIG. 4 is an elevational view showing a second embodiment.

FIG. 5 is an elevational view showing a third embodiment.

[Explanation of symbols]

Claims (4)

[Claims] 1. A heat-resistant fixing belt that is in contact with a transfer material on the surface having a toner image and moves at the same speed as the conveyance speed of the transfer material; In a fixing device equipped with a pressure roller,
A fixing device characterized in that the fixing device is equipped with means for generating stress that applies pressure to the fixing belt side on the transfer material from the separation position to the nip portion upstream of the separation position when the paper passes through the transfer material. . 2. The fixing device according to claim 1, wherein drive control is performed on both of the pressure rollers so that the circumferential speed of the pressure roller in the nip portion becomes equal to the circumferential speed of the fixing belt during paper passing. . 3. Drive control is performed for both of the fixing belts so that the circumferential speed of the pressure roller at the nip portion is slightly higher than the circumferential speed of the fixing belt when paper is passed through the fixing belt. Fusing device. 4. When passing a sheet, when the circumferential speed of the fixing belt at the nip portion is V1 and the circumferential speed of the pressure roller is V2, the relationship between the two speeds is 0<(V2-V1)/V1≦
4. The fixing device according to claim 3, wherein drive control is performed on both of them so that the ratio is 0.01.