JPH09311550A - Carrier recovering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily recover a carrier without deteriorating the printing quality by setting voltage to be impressed on a carrier recovering roller to be in a specified range. SOLUTION: This carrier recovering device 50 is arranged at a position where a photoreceptor 1 where development has been finished by the magnetic roller of a 2nd developing machine passes, and a magnet 52 is at least fixed so that its magnetic pole may be arranged at a position opposed to the photoreceptor 1. A sleeve roller 51 is rotatably constituted and arranged on the outer periphery of the magnet 52 and electrically connected to a power source 54. In the case 2nd development is revesal development, the sticking force of the carrier stuck to the area of potential V0 of the photoreceptor 1 to the photoreceptor 1 is weakened by voltage Vc impressed on the roller 51 so as to meet |V0|>=|Vc|>=|VH| (VH is bias voltage) in the case the photoreceptor 1 passes through the device 50. Then, the carrier is stuck to the roller 51 by magnetic attractive force of the magnet 52 whose magnetic pole is arranged to be opposed to the photoreceptor 1, carried by the rotation of the roller 51 and scraped by a scraper 53.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic apparatus such as a printer or a copying machine, and more particularly to a carrier collecting apparatus for an apparatus using a two-component magnetic developer using toner and magnetic carrier.

[0002]

2. Description of the Related Art As one method of electrophotography, 2 in 1 cycle
There is a one-pass color printing method for printing more than one color.

FIG. 4 shows a schematic structure of a printing apparatus using a so-called ternary exposure method described in Japanese Patent Laid-Open No. 48-37148 as one of the 1-pass color printing methods. FIG. 3 is a potential model diagram of a ternary exposure method. This method is a method of printing with black and one color other than black, for example, red, blue, green, etc. Hereinafter, one color other than black will be referred to as red, and the first development will be regular development with a red developer and the second development will be performed. A case will be described where the development is reverse development with a black developer.

The photoconductor 1 having photoconductivity is charged by the charging device 2 and then exposed by the exposure device 3 according to the image information. The black image portion is strongly exposed to the potential Vr so that the photoconductor potential becomes the minimum, the region to be printed in red is not exposed and the potential V0 is kept, and the background portion, that is, the white paper portion is weakly exposed. To a potential Vw that is about half of V0, and a ternary potential is formed. Then, the red image portion is developed by the first developing device 4a. Inside the developing device 4a, there is a magnet roller 30a having a rotatable developing sleeve roller 31a on the outer periphery of a magnet 32a fixed inside, and the developing sleeve roller 31a is electrically connected to a power source and has a bias voltage VH. Is applied so that V0> VH ≧ Vw. The red toner 21a in the first developing device 4a and the first magnetic carrier 25a that charges the red toner 21a to a polarity opposite to the charging polarity of the photoconductor 1 by friction with the red toner 21a are mixed in an appropriate ratio. The two-component developer 20a is magnetically attracted to the surface of the developing sleeve roller 31a, conveyed to the developing area 40a by the rotation of the developing sleeve roller 31a, and rubs against the surface of the photoreceptor 1. The red toner 21a adheres to the red image portion by the electric field formed by the electrostatic latent image formed on the photoconductor 1 and the bias voltage VH applied to the sleeve roller 31a, and development is performed.

A fixed magnet 52 is provided in the developing device 4a.
There is a carrier collecting device 50a equipped with a, a sleeve roller 51a and a scraper 53a, and the carrier 25a adhered to the photosensitive member at the time of development is magnetically attracted to the surface of the sleeve roller 51a and conveyed by the rotation of the sleeve roller 51a. It is scraped off by 53a and collected in the developing device 4a.

Next, the black image portion is developed by the second developing device 4b. The black developer 20 used here is used.
b is a mixture of the black toner 21b and the second magnetic carrier 25b that charges the black toner 21b to the same polarity as the photoconductor charging polarity by friction between the black toner 21b and the black toner 21b at an appropriate mixing ratio. The bias voltage VL applied to is set so that Vw ≧ VL> Vr, and the black image portion is developed. In the developing device 4b, there is a carrier collecting device 50b equipped with a fixed magnet 52b, a sleeve roller 51b and a scraper 53b, and the carrier 25b adhered to the photoconductor during the developing is magnetically attracted to the surface of the sleeve roller 51b. And sleeve roller 5
It is conveyed by the rotation of 1b, scraped by the scraper 53b, and collected in the developing device 4b.

As described above, since the image is formed by the black and red toners having different charging polarities, it is necessary to align the polarities of the toners with the polarities opposite to those of the corona irradiated by the transfer device 7 before the transfer. is there. Therefore, the pre-transfer charger 6 is installed. By this, the toner 21 having the same polarity is obtained.
Are efficiently transferred to the sheet member 8 by the transfer device 7. After the transfer, the sheet member 8 passes through the fixing device 9 and the toner 2
1 is fixed to the sheet member 8.

The toner 21 remaining on the photoconductor 1 after passing through the transfer portion or the adhered matter such as paper dust is cleaned by the cleaning device 1.
1 is separated and removed from the photoconductor 1 and collected.

The three-value exposure method for performing two-color printing by the above-described process can perform two-color printing at the same speed as single-color printing, and since there is only one exposure device, the cost is low and the position of the two-color image is low. It has a very good feature that there is no gap. However, as shown in FIG. 5, since the photoreceptor charging potential is divided into two regions to form a latent image of a two-color image, the development contrast potential of each color (V0 in the case of red Since -VH and VL-Vr in the case of black) are halved, there is a problem that it is difficult to obtain a high print density.

As a means for improving the printing density, a method of increasing the charging potential of the photoconductor to increase the contrast potential or using a developer having a low resistance can be considered. There is a limit in terms of the life of the photoconductor, and the difference between the developing bias potential and the background potential (VH-Vr for red, V0-VL for black) is inevitably large. When it is used, the amount of carrier adhered to the photoconductor increases to an extent uncomparable to that of a normal monochrome printing method. Further, the method of reducing the resistance of the developer also has a problem that carrier adhesion increases due to charge injection. If the carrier adheres to the photoconductor, the paper cannot be brought into close contact with the photoconductor at the time of transfer, and the toner image around the adhered carrier is not transferred to the paper, resulting in printing defects.

As described above, in the printing apparatus using the ternary exposure method, a stronger carrier recovery method is required as compared with the normal monochrome printing method.

As such a method, a method of applying a voltage to the sleeve roller 52 is known. FIG. 6 shows an example in which the negatively charged photoconductor is reversely developed and the positively charged carrier is attached to the region of the potential V0 of the photoconductor. In this case, the potential Vc of the sleeve roller 51 is more positive than the potential V0. On the positive side, the electric field in the direction in which the positive charge moves toward the photoconductor acts due to the potential difference from the negatively charged photoconductor, and the carrier having the positive charge adheres more strongly to the photoconductor, so that recovery is not possible. It will be difficult. Here, the sleeve roller 51
The voltage V that is on the negative side of the potential V0 of the carrier adhering region of the photoconductor so that an electric field in the direction of collecting the carriers acts on
When c is applied, the carrier can be easily recovered. As described above, the method of applying a voltage to the carrier recovery device is a very excellent method, but there is a big problem when it is used in a development method that combines regular development and reversal development such as a ternary exposure method.

[0013]

FIG. 7 is a schematic diagram showing the relationship of potentials when normal development is first performed and then reversal development is performed using a negatively charged photoreceptor. ) Shows the time when the first regular development is completed, and FIG. 7B shows the time when the next reversal development is completed. As shown in FIG. 7A, in the first regular development, the bias voltage VH is applied to the developing device in the area of the potential V0 of the photoconductor to attach the positive toner to the area of the potential V0 by the electric field. At this time, since the potential difference from the Vr region having the lowest potential is very large, a very strong electric field works in the direction in which the negative charges move to the region of the potential Vr.
The carriers will be attached to the region of the potential Vr. In this case, as in the case described above, a voltage such that an electric field in the carrier collecting direction works on the carrier collecting roller,
That is, the carrier can be easily recovered by applying the voltage Vc that is on the positive side of Vr.

However, in the case of the second development which is carried out subsequently, as shown in (b), the carrier adheres to the region of high potential V0 where the toner has already adhered, which facilitates the recovery of the carrier. Therefore, when a voltage Vc higher than V0 on the negative polarity side is applied to the carrier collecting device, a force in the direction of moving to the carrier collecting device acts on the toner adhering to this region as well as the carrier. There is a problem in that the toner adheres to the collecting device and the print density decreases. This is also the case when the development is performed in the order of reversal development and regular development. Again, in order to facilitate the recovery of the carrier attached in the later development, the voltage on the positive polarity side of Vr is applied. Is applied to the carrier collecting device, the toner is also collected.

[0015]

This problem is solved in a carrier recovery device having a magnet provided facing the photoconductor at a position where the photoconductor passes after the second development is completed.
When development is performed in the order of regular development and reversal development, | V
0 | ≧ | Vc | ≧ | VL |, reverse development, and normal development are performed in this order, | VH | ≧ | Vc | ≧ | Vr
It is solved by applying a voltage Vc such that |.

FIG. 8 is a diagram for explaining the principle of this system.
(A) shows the case where the second development is reversal development, and (b) shows the case of regular development. First, in the case of the reversal development of (a), in this case, the potential V0 at which the toner is attached in the first development is
Carriers adhere to the area. As described above, when a voltage larger than V0 is applied to the carrier collecting roller, the toner is also collected. However, as a result of various experiments conducted by the inventors, in the case of a carrier collecting roller having a magnet, the magnetic attraction force is strong, and therefore the electrostatic attraction force due to the bias voltage application attracts the carrier to the collection roller. It was found that the ability to collect carriers is high even if they do not work as much as they would. Therefore, the applied voltage to the carrier collecting roller is sufficiently effective even if the potential difference between the carrier adhering portion and the carrier collecting roller is reduced to reduce the pressing force acting on the carrier toward the photoreceptor.

Specifically, when a DC voltage is applied, the effect of voltage application appears as the applied voltage Vc becomes larger than the developing bias VL on the negative polarity side, and the first developing bias VH.
It was found that the larger the effect, the more remarkable the effect was, but that the recovery of the toner was not negligible at the negative side of V0. Therefore, it was found that the applied voltage Vc of the carrier recovery roller provided after the second development is preferably in the range of VL to V0, and more preferably in the range of VH to V0.

When the second development is regular development, the voltage Vc applied to the carrier recovery roller is V as shown in (b).
When it becomes H or less, the effect appears, and when it becomes the first developing bias VL or less, the effect becomes remarkable, and when it exceeds Vr, toner recovery becomes a problem. Therefore, it was found that Vc is preferably in the range of VH to Vr, and more preferably in the range of VL to Vr.

The same is true when an alternating current or a voltage obtained by superimposing an alternating current on a direct current is applied, and it has been found that the case where the peak value of the voltage is within the above range is preferable.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below with reference to examples.

[0021]

[Embodiment 1] This embodiment is an example in which a carrier recovery device is arranged inside a second developing machine.

In FIG. 1, the carrier recovery device 50 is
A sleeve roller 51 made of a non-magnetic material such as aluminum or stainless steel is disposed at a position where the photoconductor 1 that has been developed by the magnet roller 30b of the second developing machine passes, a magnet 52, a scraper 53, and a power supply 54. The magnet 52 is fixed so that the magnetic poles are arranged at least at a position facing the photoconductor 1, and the sleeve roller 51 is arranged on the outer periphery of the magnet 52 so as to be rotatable and electrically connected to the power supply 54. There is. When the second development is reversal development, the photoconductor 1
The carrier 25b attached to the area of the potential V0 of V is caused by the voltage Vc applied to the sleeve roller 51 such that | V0 | ≧ | Vc | ≧ | VH | The adhesion to the photoconductor is weakened,
It is attached to the sleeve roller by the magnetic attraction force of the magnet 52 having a magnetic pole arranged opposite to the photoconductor 1, is conveyed by the rotation of the sleeve roller 51, is scraped by the scraper 53, and is collected in the developing machine.

[0023]

Second Embodiment In FIG. 2, the carrier recovery device 50 is arranged downstream of the second developing device 4b. Magnet 52 is N
The poles and the S poles are magnetized so as to alternate with each other, and are configured to be rotatable, and rotate in the arrow direction in the figure at a peripheral speed higher than the peripheral speed of the photoconductor. There is a sleeve around the magnet 52.
A blower 51 is provided, and the three blower 51 is electrically connected to a power source 54. When the second development is reversal development, a voltage that is | V0 | ≧ | Vc | ≧ | VH | Vc is applied.

The carrier 25b adhered to the region of potential V0 in the second development has its adhesion to the photoconductor 1 weakened by the voltage Vc, and the N pole and the S pole are alternately placed at positions facing the photoconductor. It is vibrated by the alternating magnetic field formed by passing at a high speed and is recovered from the photoconductor 1. The three-roller 51 may be fixed or rotatable.

The sleeve blower 51 is removed and the magnet 5
2 has a conductive layer on the surface thereof, the conductive layer is electrically connected to the power source 54, and the above voltage is applied to obtain the same result. Further, the second developing device 4b and the carrier recovery device 50
If a lighting device 13 such as an LED is installed between the two and light irradiation is performed, carrier recovery becomes easier.

[0026]

[Embodiment 3] Embodiment 3 shows a two-color printing apparatus using a carrier collecting apparatus which is another embodiment.

In FIG. 3, as the photoconductor 1, photoconductors such as selenium, selenium tellurium, arsenic triselenide, and OPC can be used. Hereinafter, negatively charged OPC is used and a red developer is used. Description will be made regarding the case where the normal development and the reversal development using the black developer are performed in this order. Photoconductor 1
Is charged to the potential V0 by the charging device 2. Potential V0
An appropriate value of -500V to -1000V is used as the value of, but it is desirable that it is within the range of -800V to -900V and the uneven charging is within 50V. As the charging device 2, a corona discharge device such as a corotron or a scorotron, or a contact type charging device such as a brush or a roller charging device can be used. Next, the exposure device 3
Thus, the exposure is performed according to the image information. Strong exposure is performed on the black image portion so that the potential Vr is −150 V or more, preferably −50 V or more, and a value of the potential Vw in the range of −350 V to −550 V is used for the background portion, that is, the white paper portion. Weak exposure is preferably carried out so as to be -400V to -500V. Next, development is performed, but the developing device 4 is the first developing device 4a containing the red developer 20a.
And a second developing device 4b containing the black developer 20b, each of which applies an appropriate bias voltage to the sleeve roller 31 by an electrically connected power source. The bias voltage value is about -450V to -700V for the first developing device 4a that develops a high potential portion of the photoconductor 1, and the second developing device 4b that develops a low potential portion of the photoconductor 1 is It is preferably about -450V to -200V. The red developer 20a used in the first developing device 4a includes a carrier 25a obtained by coating a ferrite powder, magnetite powder or the like having a volume average particle diameter of 80 to 120 microns with a silicon-based, acrylic-based or fluorine-based coating agent. , Styrene acrylic resin, polyester resin, etc., with a red pigment added, the volume average particle size is 7 to 12
Micron red toner 21a is mixed to have a toner concentration of 2 to 6%, and the charge amount is 5 to 25%.
μC / g can be used. Black developer 2b
Is a carrier 25b obtained by coating a ferrite powder or magnetite powder having a volume average particle diameter of 80 to 120 microns with an acrylic resin, a silicon resin or the like, and a styrene acrylic resin, a polyester resin or the like with a pigment such as carbon black. Use is made by mixing the added black toner 21b having a volume average particle size of 7 to 12 microns so that the toner concentration is 2 to 6%, and having a charge amount of -5 to -25 μC / g. Can be done.

With such a structure, first the developing device 4
The area of high potential is normally developed with a, and the carrier 25a attached at this time is recovered by the first carrier recovery device 50a, but the voltage applied to this carrier recovery device is higher than V0 regardless of the present invention. It may be a low value. Next, the area of potential Vr is developed by the second developing device 4b, and the carrier 2 attached to the photoconductor by this development is developed.
5b is the first | V0 | ≧ | V installed in the developing device.
Carriers are recovered by the carrier recovery device 50b of the present invention to which a voltage Vc satisfying c | ≧ | VH | is applied. The carriers not recovered at this point are further recovered by the carrier recovery device 50c according to the present invention after being further irradiated with light and passed through pre-transfer charging to reduce the adhesion to the photoconductor. . As described above, by using the carrier recovery device of the present invention in a device that performs two-color printing by combining regular development and reversal development, it is possible to easily recover carriers without degrading print quality. .

In the three-value exposure type one-pass two-color machine, the first development was described as regular development using a red developer and the second development was described as reversal development using a black developer. Any color other than red, such as blue, green, or brown,
The order of development may be reversed, regular development may be performed, and a black developer may be used for the first development and a color developer may be used for the second development.

[0030]

According to the present invention, it is possible to provide a small-sized and low-cost carrier collecting apparatus which can easily collect carriers without deteriorating print quality.

[Brief description of drawings]

FIG. 1 is a schematic view of a carrier recovery device that is an embodiment of the present invention.

FIG. 2 is a schematic view of a carrier recovery device according to another embodiment of the present invention.

FIG. 3 is a schematic configuration diagram of a ternary-exposure printing apparatus using a carrier recovery apparatus according to another embodiment of the present invention.

FIG. 4 is a schematic configuration diagram of a printing apparatus using a three-value exposure method.

FIG. 5: Potential model diagram of three-value exposure method

FIG. 6 is a potential model diagram when voltage is applied.

FIG. 7 is an explanatory diagram of problems in the three-value exposure method.

FIG. 8 is a potential model diagram in the present invention.

[Explanation of symbols]

1 is a photoconductor, 4 is a developing device, 50 is a carrier collecting device,
51 is a sleeve low, 52 is a magnet, 53 is a scraper

Claims (3)

[Claims] 1. A photosensitive member is charged to a potential V0 by a charging unit and then exposed to a region of a potential Vr and V0 and Vr by an exposing unit.
And an area of an intermediate potential Vw are formed, and the area of the potential V0 is normally developed by a developing device to which the developing bias voltage VH is applied by using a two-component magnetic developer, and the area of the potential Vr of the developing bias voltage VL is formed. In a two-color printing electrophotographic apparatus in which reversal development is performed using a two-component magnetic developer by an applied developing device, after the development of the region of potential V0 and the development of the region of potential Vr are completed, a position where the photoconductor passes is set. | V0 when normal development and reversal development are carried out in the order of normal development and reverse development on a carrier recovery device having a magnet provided opposite to the photoconductor
| VH | ≧ | Vc | ≧ | Vr | when development is performed in the order of | ≧ | Vc | ≧ | VL |, reversal development, and regular development.
A carrier recovery device characterized by applying a voltage Vc such that 2. The carrier recovery device according to claim 1, wherein at least one magnetic pole of the magnet is fixedly arranged at a position facing the photoconductor. 3. The carrier recovery apparatus according to claim 1, wherein the magnet is rotatably supported and rotates in a direction opposite to the photoconductor at a surface velocity higher than the photoconductor surface velocity.