JPH024903B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrophotographic recording apparatus, and particularly to a developing section thereof.

Electrophotography involves uniformly charging a photoconductive recording material in a dark place, then irradiating the recording material with light to form a latent charge image, and then electrostatically applying a developer to the recording material. There is an imaging method in which the charge latent image is visualized by adhesion, and this is called a reversal development method. This developing method is widely used in non-impact printers that mainly record characters, symbols, graphic images, etc.

A schematic configuration of a conventional recording apparatus that performs recording in two or more colors using this developing method will be explained with reference to FIG. A drum-shaped recording medium 1 having photoconductivity is charged, for example, positively with a charger 2, and the surface of the recording medium 1 is irradiated with first exposure light L1 to form a first charge latent image. A developing device D1 applies a first color developer to the surface of the recording medium 1 to visualize the first charge latent image. Next, the first exposure light L1 is applied to the surface of the recording medium 1.
A second developing device D2 applies a second color developer different from the first color to the recording material. 1
to visualize the second charge latent image. Subsequently, in the same manner as described above, the third exposure light L3 is irradiated to form a third charge latent image, and the latent image is visualized using a third color developer in the third developing device D3. The visible images of three colors that do not overlap each other thus created are transferred at once to a recording medium 3 such as recording paper by a transfer charger 4. After the transfer, the residual developer adhering to the surface of the recording medium 1 is removed by a cleaner 5, and the recording medium 1 is prepared for the next recording.

However, in this conventional recording device, since each developer comes into sliding contact with the surface of the rotating recording medium, the second
When developing after the developing device, the developer adhering to the surface of the recording medium in the previous stage is mechanically rubbed off by sliding contact with the developer in the developing device. As a result, the desired image density may not be obtained, or a developer of a different color may be mixed into the developing device, resulting in changes in color and development characteristics. In addition, if the previous stage of development is not done sufficiently and the latent image is not neutralized by the developer charge, it will be developed with a developer of a different color in the next development, resulting in color mixture.
It has drawbacks such as not being the original color.

SUMMARY OF THE INVENTION An object of the present invention is to provide an electrophotographic recording apparatus that eliminates the drawbacks of the prior art described above and can obtain clear images without color mixture with a simple structure.

To achieve this object, the present invention provides a first latent image forming means for forming a first charged latent image on a photoconductive drum-shaped recording medium, and a A first development step for visualizing the first charge latent image using a magnetic developer having a charged toner of a first color on the drum-shaped recording body on which the first charge latent image is formed. a second latent image forming means for forming a second charge latent image on the drum-shaped recording medium after development by the first developing means;
The second latent charge image is developed on the drum-shaped recording body on which the second latent charge image is formed by the second latent image forming means using a magnetic developer having a charged toner of a second color. In the electrophotographic recording apparatus, the second developing means includes a fixed magnet roll whose portion facing the drum-shaped recording body is formed to have the same polarity, and a fixed magnet roll that faces the drum-shaped recording member. The polarity of the charge latent image formed on the drum-shaped recording body between a sleeve-shaped developer conveying rotating body loosely fitted around the outer periphery of the magnet roll and the opposing portion of the conveying rotating body and the drum-shaped recording body. a DC bias electric field applying means for applying a DC bias electric field having the same polarity as the magnetic developer; and a means for applying an AC bias electric field, the gap being 0.05 between the surface of the magnetic developer adhered to the outer circumferential surface of the conveyance rotor and the surface of the drum-shaped recording body opposing thereto. It is characterized by being held at ~0.5mm.

Next, examples of the present invention will be described. In the present invention, both a two-component developer consisting of a carrier and toner and a one-component developer consisting only of toner can be used. A respective toner is used, and the toner is in a charged form.

In the first development according to the present invention, the developer of the developing device may be in contact with the recording medium or may be in a non-contact state through a minute interval, but it is possible to simplify the device and facilitate development. For chromatic color development, 2
It is preferable to use a component developer to form a contact type.

FIGS. 2 to 4 are schematic diagrams of a developing device used after the second development in each embodiment of the present invention.

In FIG. 2, the developing roll is composed of a magnet roll 6 and a non-magnetic and electrically conductive sleeve 7 loosely fitted around the outer periphery of the magnet roll 6. The developer 8 is attached to the outer peripheral surface of the sleeve 7 due to the magnetic attraction force of the magnet roll 6, and there is a minute gap of 0.05 to 0.5 mm between the surface of the developer 8 and the surface of the recording medium 1. is maintained, and therefore the developer 8 is in a non-contact state with respect to the recording medium 1.

The photoconductive recording medium 1 is uniformly charged with a charger in a dark place, and a first charged latent image is formed by the exposure operation of the first latent image forming means. The first charge latent image is visualized with a first color developer. Subsequently, the recording body 1 rotates, and a second latent charge image is formed in the second latent image forming means, and this second charge latent image is moved to the position of the developing device shown in FIG. 2 by the rotation of the recording body 1. Moving.

A DC bias voltage Vb is applied to the sleeve 7 by a DC bias power supply 9, and an AC bias voltage Vc is applied by an AC bias power supply 10. The polarity of the DC bias voltage Vb is the same as that of the charge latent image on the recording medium 1, and there are a plurality of developing means including the second developing means such as a third developing means and a fourth developing means after the second developing means. In this case, it is better to gradually increase the voltage applied by the DC bias power supply 9. In this way, the DC bias electric field caused by the applied DC bias voltage Vb exerts a force that causes the developer already attached to the recording medium 1 to stick more strongly to the recording medium 1.
The developer in the previous stage is difficult to separate from the recording medium 1.

In addition, the AC bias electric field caused by the applied AC bias voltage Vc weakens the attraction force of the developer on the developing roll to each other or to the developing roll, thereby compensating for the decrease in developing ability due to non-contact. . The AC bias voltage value is appropriately selected from the range of 100 to 1000 V depending on the structural conditions of the developing roll, operating conditions such as the gap between the recording medium and the developer, and the like.

A two-component magnetic developer is used as the developer, and the magnet roll 6 is fixed and the developer 8 is conveyed by rotating the sleeve 7. By widening the magnetic pole width of the part of the magnet roll 6 that faces the recording body 1, or by arranging the magnetic poles of the magnet roll 6 so as to face the recording body 1 at different angles, adjacent magnetic poles can be made to have the same polarity. If this is done, the brush becomes soft and the toner is easily separated from the carrier, resulting in good developing performance. It is desirable that the toner concentration of the developer is slightly higher than that used in the contact method; for example, if the toner concentration in the contact method is 3%, it is 4 to 6.
It is better to set it as %. When the toner concentration is increased in this manner, free toner is easily formed, and the development efficiency is good even in a non-contact method.

When the potential of the charge latent image is 700V, the DC bias voltage Vb is 100 to 800V, and the AC bias voltage Vc is
When the voltage is set to 100 to 1000 V, there is little so-called fog, the image density is high, and a clear image can be obtained.

If there are multiple developing means after the second developing means,
It is preferable to sequentially increase the DC bias voltage within a range where fogging and color mixing do not occur, so that the previous color toner does not fall off. Also, if the toner charge amount of the developer is larger in the later stages, the toner will be less likely to separate from the carrier, so the development level will be high and areas where the latent image potential is low, that is, areas where the development in the earlier stages is insufficient, will be developed. As a result, an image with good color tone can be obtained without color mixture.

FIG. 3 shows a second embodiment, in which an insulating layer 11 is formed on the conductive sleeve 7 in order to prevent electrical discharge with the recording medium 1 when a high bias voltage is applied to the conductive sleeve 7. For this insulating layer 11, an insulating layer having a resistance of 10 ⁶ Ωcm or more is used.

FIG. 4 shows a third embodiment, in which a high-resistance sleeve 15 is used, a DC bias voltage Vb is applied to it, and an electrode 13 is arranged inside the high-resistance sleeve 15 on the side facing the recording medium 1. , to which an AC bias voltage Vc is applied. Said high resistance sleeve 1
5 is a type that allows a rapidly changing alternating current electric field to pass through, but has a counter electrode effect during development, and has a resistance of 10 ⁸ to 10 ¹¹ Ω.
A material having a volume resistivity of cm or a conductive film having a surface resistance of 10 ⁸ to ^{10 11} Ωsq formed on an insulating sleeve is used.

The configurations shown in FIGS. 2 to 4 can be combined as appropriate. The present invention can also be applied to regular or reverse development in which charging, exposure, development, and full-surface exposure are repeated.

As described in the embodiment, when there are a plurality of developing means after the second developing means, the developer can be prevented from falling off from the recording medium by increasing the bias voltage in sequence. In addition, by gradually increasing the toner charge amount so that it becomes higher as the development level progresses to the later stages, and by combining conditions such as two-component developer and one-component developer, there is no color mixture in the image, and good image formation is achieved. Can be done.

The present invention has the above-mentioned configuration, and the second
During development after the developing means, the recording medium and the developer do not come into contact with each other, so the developer attached to the recording medium may fall off in the next development process, and as a result, developer of a different color may be mixed in. It can be resolved. Further, by applying disturbance based on electromagnetic action, there is no reduction in development efficiency due to non-contact, and therefore, a clear image can be obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a conventional electrophotographic recording device, and FIGS. 2 to 4 are schematic diagrams of developing means after the second developing device of the electrophotographic recording device according to each embodiment of the present invention. . 1...recording body, 6...magnet roll, 7...
... Sleeve, 8 ... Developer, 10 ... AC bias power supply, L1 ... First exposure light, L2 ... Second exposure light, L3 ... Third exposure light, D1 ... First developer,
D2...Second developing device, D3...Third developing device.

Claims (1)

[Claims] 1. A first latent image forming means for forming a first charge latent image on a photoconductive drum-shaped recording medium;
The first charged latent image is developed on the drum-shaped recording body on which the first charged latent image is formed by the first latent image forming means using a magnetic developer having a charged toner of a first color. a first developing means for forming an image; a second latent image forming means for forming a second charge latent image on the drum-shaped recording body after development by the first developing means; A second charge latent image is formed on the drum-shaped recording body on which the second charge latent image is formed by the forming means.
and a second developing means for visualizing the second charged latent image using a magnetic developer having charged toner of a different color, the second developing means is configured to a fixed magnet roll whose portion facing the shaped recording body is formed with the same polarity;
A sleeve-shaped developer conveying rotating body loosely fitted around the outer periphery of the fixed magnet roll, and a charge latent image formed on the drum-shaped recording body between the conveying rotating body and the opposing portion of the drum-shaped recording body. a DC bias electric field applying means for applying a DC bias electric field having the same polarity as the polarity of the magnetic developer; an alternating current bias electric field applying means for applying an electric field, and a gap between the surface of the magnetic developer adhered to the outer circumferential surface of the conveyance rotating body and conveyed and the surface of the drum-shaped recording body opposing thereto; An electrophotographic recording device characterized in that the distance is maintained at 0.05 to 0.5 mm.