JP2675886B2 - Fixing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is used in copying machines, electrophotographic printers, and the like to fix an unfixed toner image by sandwiching and conveying the unfixed toner image between a pair of moving bodies. Regarding the device.

BACKGROUND ART FIG. 5 shows a conventional fixing device.

The fixing roller 21 on the upper side is a hollow cored bar 30 made of aluminum, iron, or the like, and the outer peripheral surface of the hollow cored bar 30 is covered with a material 41 having good releasability such as PTIFE / PFA / silicone rubber. 23 is provided, and the fixing roller 21 is heated by this heater. The lower pressure roller 22 is
The outer periphery of a cored bar made of iron, stainless steel or the like is covered with an elastic body having releasability such as silicone rubber. The fixing roller 21 and the pressure roller 22 are brought into contact with each other with a predetermined pressure by an urging means such as a spring (not shown), and are rotationally driven in the arrow direction.

Reference numeral 24 denotes a temperature-sensitive element such as a thermistor brought into contact with the surface of the fixing roller 21, and detects the surface temperature of the fixing roller 21. The heater is controlled by a temperature control circuit according to the temperature detected by the temperature sensing element 24.
The energization of the fixing roller 23 is controlled, and the surface temperature of the fixing roller 21 is automatically controlled to a predetermined heat fixing temperature.

Reference numeral 25 denotes a separation claw for separating the transfer material from the surface of the fixing roller 21. The separation claw is arranged such that the leading edge portion is brought into contact with the surface of the fixing roller 21 with an appropriate pressing force. Reference numeral 26 denotes a cleaner, such as felt, which is brought into pressure contact with the surface of the fixing roller 21, and wipes and removes toner, paper powder, and the like attached to the surface of the fixing roller 21. 27
Is a metal bottom plate of the fixing device, and 28 and 29 are transfer material inlet guides and outlet guides, which are attached to and supported by the upwardly bent front wall and rear wall of the bottom plate 27, respectively.

The recording material P carrying the unfixed toner image is supplied to the entrance guide 28.
Through the nip part of the fixing roller 21 and the pressure roller 22 which are rotationally driven in pressure contact with each other and pass through the nip parts of both the rollers 21 and 22.
In the course of passing through the nip portion, the unfixed toner image ta on the recording material P surface is permanently fixed on the recording material P surface by the heat of the fixing roller 21 and the pressing force between the fixing roller 21 and the pressure roller 22. It is fixed by heat and pressure.

The recording material P, which has passed through the nip portion of the rollers 21 and 22 and has undergone image fixing, has its leading end separated from the surface of the fixing roller 21 by the separating claw 25 and enters the sheet bus 13 through the exit guide 29.
The paper is ejected to the paper ejection tray 14.

As described above, the offset of toner becomes a serious problem in the fixing device in which the recording material is sandwiched and conveyed between the pair of moving bodies to fix the toner image.

Factors of this offset include a temperature factor and an electrostatic factor.

The temperature factor can be solved by properly maintaining the roller surface temperature at an appropriate temperature, but the electrostatic factor is difficult to solve.

Therefore, in JP-A-55-96970, an electrostatic offset is attempted to be solved by applying a bias voltage to the roller core metal by power sources 42a and 42b as shown in FIG.

However, depending on the potential difference between the roller surface and the core metal, the electric charge may move to the surface and the core metal side. In particular, in the case of OHP paper, if the electric charge held on the back surface side of the paper flows out from the roller surface to the core metal, the binding force of the paper to the toner is reduced and the offset easily occurs.

As measures against this, one is to accumulate electric charges of the same polarity as toner on the fixing roller and to accumulate electric charges of opposite polarity on the pressure roller, as shown in FIG. The applicant has previously proposed connecting 40a and 40b.

[Problems to be Solved by the Invention] However, since this method relies on triboelectrification of the surface of the recording material and each roller, there is a drawback in that the effect varies depending on the environmental change and the type of the recording material. .

[Means for Solving Problems] The present invention for solving the above problems provides a fixing device for fixing a toner image by sandwiching and conveying a recording material carrying an unfixed toner image between a pair of moving bodies. Bias voltage is applied to the moving body from the power source, and one moving body is grounded via a rectifying element.

[Examples of the Invention] Examples of the present invention will be described below.

FIG. 4 is a sectional view of an image forming apparatus to which the fixing device of the embodiment of the invention is applied.

Reference numeral 1 denotes a drum type electrophotographic photosensitive member (hereinafter abbreviated as a drum) which is rotationally driven around an axis 1a in a direction indicated by an arrow at a predetermined peripheral speed. The photoconductor layer is mainly provided with a photoconductor.

The drum 1 is an eraser (full-face exposure device) 2 during its rotation process.
Is uniformly exposed by the entire surface to uniformly remove static electricity, then is uniformly charged by the primary charger 3 to a predetermined positive or negative potential, and then the target image information is subjected to laser beam scanning exposure L by the laser scanner 5 at the exposure unit 4. Receive scan writing. As a result, electrostatic latent images corresponding to the target image information are sequentially formed on the surface of the drum 1. 5a is a laser scanner 5
It is a laser beam folding mirror that deflects the laser beam L output from the exposure unit 4 to the exposure unit 4 for the drum 1.

The surface of the drum 1 on which the latent image is formed is then applied with a developer (toner) t by the developing device 6 to be visualized as a toner image.

Next, the toner image passes through the position of the transfer charger 7, and is sequentially transferred to the surface of the transfer material P, which is a recording material fed from the paper feed mechanism 8 between the transfer charger 7 and the drum 1. Will be transferred to. The transfer of the toner image from the surface of the drum 1 to the surface of the transfer material P is performed by charging the back surface of the transfer material P with a polarity opposite to the charge polarity of the toner image by the transfer charger 7. In the paper feeding mechanism 8, reference numeral 8a is a paper feeding cassette in which a large number of transfer materials P are stacked and housed, and the cassette is inserted and set in a cassette insertion portion 8b of the apparatus, and a paper feeding roller 8c.
Each time the intermittent rotation drive is performed, the transfer material P is fed out from the topmost one in the cassette, and the drum 1 is transferred by the registration roller 8d.
The toner is taken out in synchronism with the rotation of and is fed between the transfer charger 7 and the drum 1.

The transfer material P that has passed the position of the transfer charger 7 is then arranged next to the transfer charger 7, and is discharged by the separation charge-eliminating needle 9 to which a voltage having a polarity opposite to that of the charger is applied to remove the charge. The unfixed toner image, which is separated from the surface, is introduced into the fixing device 12 via the conveying device 11, and is transferred to the transfer material P surface, is fixed on the transfer material P surface as a permanently fixed image. Then, the image-fixed transfer material is used as an image-formed product in the sheet path 13
Printed on the discharge tray 14 outside the machine through the.

After the transfer material is separated, the surface of the drum 1 is cleaned by removing dirt such as transfer residual toner and paper dust adhered to the surface of the drum by the cleaning device 10, and then subjected to uniform exposure by the eraser 2 and electrically. The history is removed (uniform charge removal), and the image is repeatedly formed.

Various types of fixing means are known for fixing an unfixed toner image (unfixed developer image) formed and carried on the transfer material (image carrier) P surface, but the transfer material is introduced into the nip portion of the pair of rotary fixing rollers. The unfixed toner image formed and carried on the surface is heat-pressure fixed on the transfer material surface as a permanently fixed image.

FIG. 1 is an enlarged sectional view of a fixing device according to an embodiment of the present invention.

The fixing roller 21 is formed by coating a cored bar 30 made of iron, aluminum or the like with a heat-resistant material having good releasability such as PFA, PTFE, silicone rubber or fluororubber. A heater is provided in the core bar to heat the roller surface to a predetermined temperature.

Further, in this embodiment, the power source 32 is connected to the core metal 30 of the fixing roller 21.
A negative voltage having the same polarity as that of the toner is applied so that even if positive charges are accumulated in the surface salt, the electric field becomes negative. As a result, a repulsive force is generated between the negatively charged toner and the fixing roller 21, so that offset due to the electric field can be prevented.

Further, the pressure roller 22 is obtained by attaching a heat resistant elastic body 39 such as silicon rubber or fluororubber on the core metal 31, and the core metal 31 is
Grounded by diode 27. Heat resistant elastic 39
Is frictionally charged with the transfer material, and when a negative charge having the same polarity as the toner is generated, the charge flows to the ground through the diode 33.

Further, the elastic body 39 is made of carbon to facilitate the flow of electric charge,
It is preferable to mix a conductive material such as a metal powder or a conductive whisker to make resistance. Especially, the volume resistivity is 10
It is preferably ¹¹ Ω or less.

The electric charge flows to the ground. In order to facilitate the flow of electric charges, it is preferable that the heat resistant elastic body 39 is made conductive by mixing carbon or metal powder or whiskers.

On the other hand, in the case of a resin film such as OHP paper, the diode 33 has a function to prevent the positive charge from flowing out to the earth against the transfer material P having a strong positive charge for transfer on the back surface and entering the fixing device. Since the positive charge on the back surface of the OHP paper is not reduced and the binding force for the toner is not reduced, the offset caused by the reduction in the toner holding force can be prevented.

Next, FIG. 2 shows an example in which a positively chargeable toner is used.

In this embodiment, a positive bias is applied by the power source 34 so that a repulsive force is generated on the fixing roller side with the toner, and a negative charge is accumulated by frictional charging on the pressure roller side so that an attractive force is generated with the toner, Moreover, the diode 35 is connected in such a direction that the electric charge on the back surface of the transfer material does not flow to the ground.

As in the above two examples, a bias from a power source is applied to the roller that is in direct contact with the toner to generate a constant repulsive electric field regardless of the environment and the roller that is not in direct contact with the toner. Can obtain an offset prevention effect by accumulating charges so as to generate an electric field that attracts toner. Especially, the diode 35 connected to the pressure roller has a capacity C _{1 of} several pF and the capacity C _{2 of the} pressure roller is much larger than the capacity of the diode. Therefore, the combined capacity after connection = C = C ₁ C ₂ / (C
₁ + C ₂ ) is close to C ₂ . As a result, even if a small amount of electric charge having a polarity different from that of the toner is accumulated in the pressure roller, a high surface potential is obtained, and electrostatic force acts in the direction of attracting the toner to the transfer material, so that offset can be prevented.

In order to maximize this result, the capacitance of the diode to be connected is preferably larger than 0.1 pF and smaller than 50 pF.

FIG. 3 shows another embodiment. The fixing roller 21 is composed of a cored bar 30 made of iron, aluminum or the like and a heat-resistant surface layer such as PFA, PTFE, silicone rubber, or fluororubber having good releasing property, and the pressure roller 22 is the same. Similarly, a heat resistant elastic body such as fluororubber or silicone rubber is attached to the surface of the core metal 31, and this example shows the case where a negatively charged toner is used. A negative voltage is applied to the fixing roller by the power source 36 in the same manner as in the above-described example, so that the toner is repelled. Further, even if an excessive positive charge is applied to the surface of the pressure roller from OHP paper or the like and the roller surface has a higher voltage than the core metal, the diode 37 prevents the outflow, so that no offset occurs. For a transfer material such as ordinary paper, a positive charge flows from the power source 38 so as to erase the negative charge generated on the surface of the pressure roller, so that the toner is repelled by the charging of the pressure roller. Offset can also be prevented.

For positively charged positive toner, if the power source and the diode are connected in opposite directions, the offset prevention effect can be obtained for the same reason.

[Effects of the Invention] As described above, according to the present invention, regardless of changes in the environment.
Even if a resin film such as OHP paper is used, the occurrence of offset can be prevented.

[Brief description of the drawings]

1, 2, and 3 are cross-sectional views of the fixing device according to the embodiment of the present invention, and FIG. 4 is a cross-sectional view of the image forming apparatus to which the fixing device according to the embodiment of the present invention is applicable. FIG. 7 is a cross-sectional view of a conventional fixing device, and FIG. 6 is a cross-sectional view of a fixing device which is the background of the present invention. 21 is a fixing roller 22 is a pressure roller 30, 31 is a core metal 32,34,38,42a, 42b is a power supply 33,35,37,40a, 40b is a diode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hideo Nanaki 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Takayasu Yukino 3-30-2 Shimomaruko, Ota-ku, Tokyo Ki In Canon Inc. (72) Inventor Hiroto Hasegawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) Reference JP-A-63-85775 (JP, A) JP-A-49-91459 (JP, A) JP-A-59-180571 (JP, A)

Claims (3)

(57) [Claims] 1. A fixing device for fixing a toner image by sandwiching and transporting a recording material carrying an unfixed toner image between a pair of moving bodies, and applying a bias voltage from a power source to one of the moving bodies. A fixing device in which one moving body is grounded via a rectifying element. 2. A moving body to which a bias voltage is applied is a moving body which is in contact with an unfixed toner image, the bias voltage has the same polarity as the toner, and the rectifying element applies a charge having a polarity opposite to the toner to the moving body. The fixing device according to claim 1, wherein the fixing device is connected in a storage direction. 3. A bias power supply is provided between the rectifying element and ground.
And the fixing device according to item 2.