JPH0250173A - Electrostatic charging device - Google Patents

Abstract

PURPOSE:To obtain high picture quality by using a conductive elastic roller which is held rotatably so that the peripheral surface of a photosensitive body is brought into contact as a charger. CONSTITUTION:This device is provided with the elastic roller 7 which has conductivity and is held rotatably on a support shaft 6 while having its peripheral surface in contact with the peripheral surface of the photosensitive body 2 and a bias applying means 3 which applies a bias to the elastic roller 7 through the support shaft 6. When the photosensitive body 2 rotates as shown by an arrow (a), the elastic roller 7 is rotated as shown by an arrow (b) by the contact friction against the peripheral surface of the photosensitive body 2. In this state, the bias is applied to the elastic roller 7 through the bias applying means 3 while varied. Consequently, no longitudinal stripe is formed at a half-tone part and a copy image of high quality is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a g-electric device in an electrophotographic device such as a PPC, a laser printer, and a facsimile.

[Conventional technology]

- Generally, as a charging device for an electrophotographic apparatus, a Suflotron type corona charger 1 as shown in FIG. 6 is often used.

In FIG. 6, when the latent image carrier 2 (hereinafter referred to as photoreceptor) is charged with a potential of, for example, -800V, the corona charger 1 applies a high voltage of about -5 KV to the corona wire 1a, and It was necessary to apply a bias of about -800 V to the grid node 1b and the casing lc via the high-voltage power supplies 3a and 3b, respectively.

Furthermore, it is known that in this type of band@device, harmful substances such as ozone and NOx are generated by the corona charger.

On the other hand, in recent years, as the photoreceptor 2, there has been a tendency to use organic photoreceptors rather than those based on heavy metals such as selenium. Such an organic photoreceptor.

The deterioration due to the influence of ozone and NOx is more severe than that of photoconductors made of selenium, etc. Therefore, when using corona charger 1 to charge this type of organic photoconductor, ozone and NOx generated by the corona charger must be charged. The fan 4 is connected to the corona charger 1 to prevent the
It was necessary to install it near the

For these reasons, charging devices do not use corona charger 1.
However, the use of 2D has disadvantages such as increased running and manufacturing costs and reduced flexibility in layout.

On the other hand, as a charging device that achieves low cost, a device using brushes 5a and 5b as shown in FIGS. 7 and 8 has been proposed. FIG. 7 shows a charging device in which the brush 5a is arranged stationary, and FIG. 8 shows a charging device in which the brush 5b is arranged rotatably.
The brush 5b is disposed so as to bite into the circumferential surface of the photoreceptor 2, and the rotating direction of the brush 5b is set to be arbitrary.

[Issues that Mitsuaki tries to solve]

By the way, as a result of an experiment using a brush material having a resistance of about 105 ΩcI11 in a charging device using this type of brushes 5a and 5b, the high voltage power source 3c.

Apply a bias of about -1200V to each brush 5 through 3d.
It has been found that the photoreceptor 2 can be charged with a potential of about -800 V by simply applying voltage to a and 5b, and that these can be used as an inexpensive charging device.

However, in the charging device using this type of brushes 5a and 5b, vertical streaks occurred in the halftone portion of the copied image, which was thought to be caused by the rubbing of the brushes 5a and 5b. In addition, if a cleaning failure occurs in the cleaning step before the charging step, the toner remaining on the photoreceptor 2 will adhere to the tip of each brush 5815b, and the brushes 5a and 5b with the toner attached will be biased. When applied.

The charging characteristics of the brushes 5a and 5b to the photoconductor 2 changed between locations where toner adhered and locations where toner did not adhere, and uneven charging occurred on the photoconductor 2.

Furthermore, it has been found that with this charging device, as the running continues, the bristles of the brushes 5a and 5b come off and the tips of the brushes wear out, causing uneven charging on the photoreceptor 2.

In this way, the charging device using the brushes 5a and 5b is
[In order to use it as a charging device for electrophotographic equipment, which requires high image quality and high reliability while being distorted and low cost, it is necessary to solve three technical problems. .

(Means for Solving Xg) As a means for solving the above-mentioned problem M, the present invention uses a conductive elastic roller, which is rotatably held in contact with the nine circumferential surfaces of the photoreceptor, as a charger. It is characterized by

[For production]

Charging of the photoreceptor by the charging device of the present invention is as follows.

This is done by bringing the elastic roller into contact with the photoreceptor, eliminating the generation of ozone and the like. Further, the photoreceptor and the elastic roller come into surface contact.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

As shown in FIG. 1, the charging device according to the present invention includes a conductive elastic roller 7 which is rotatably held by a support shaft G with one circumferential surface in contact with the circumferential surface of the photoreceptor 2, and this elastic roller 7. It is composed of a bias applying means 3 (high voltage power supply) that applies a bias to the roller rough via the support shaft G.

The elastic roller 7 has a volume resistance of 1o7 ΩcI11
It is made of polyurethane foam sponge that has been treated to be conductive.

The bias application means 3 is configured to apply a high voltage to the elastic roller 7 similarly to a conventional high voltage power supply.

In FIG. 1, when the photoreceptor 2 rotates in the direction indicated by the arrow a, the first elastic roller 7 rotates in the direction indicated by the arrow 2 due to contact friction with the circumferential surface of the photoreceptor 2. In this state, a variable bias was applied to one elastic roller rough through the bias applying means 3, and the surface potential of photosensitive #-2 at this time was measured. The following relationship was observed. Therefore, when we formed a copy image by applying a bias of -900V to the elastic roller and setting the surface potential of the photoreceptor 2 to about -800V, we found that vertical streaks in the halftone area, as seen with the conventional brush charging method, were not observed. No occurrence of this phenomenon was observed, and a copy image of extremely high quality could be obtained.

FIG. 3 shows another embodiment of the present invention, with one elastic roller 7,
An extremely fine conductive foamed polyurethane foam with a cell diameter of approximately 10 to 20 μm (for example, the product name Rubicel manufactured by Kusho Denzai Co., Ltd.) is used, and the circumferential surface of the photoreceptor 2 is placed on the circumferential surface of the elastic roller 7. 0.2+am An elastic roller is rotatably held by a spindle 6 so as to bite, and a cleaning blade 8 made of polyester film with a knob size t=0.1ml1 is placed in contact with the circumferential surface of the elastic roller 7. [1g
! has been completed.

In FIG. 3, the elastic roller 7 is not shown in II! 2
11 in the direction indicated by the arrow.

The linear velocity of the elastic roller 7 at this time was set to be v'R=1, 5v'pc with respect to the linear velocity pc of the photoreceptor 2. Furthermore, an organic photoreceptor was used as the photoreceptor 2, the surface of which was negatively charged, and the following experiment was conducted using toner having positive charging characteristics.

First, a cleaning failure tL occurs in a cleaning section (not shown), and when the photoconductor 2 and the elastic roller 7 are rotated in contact with the toner remaining on the photoconductor 2, the remaining toner is removed. After adhering to the circumferential surface of the elastic roller 7, it was peeled off from the circumferential surface of the elastic roller 7 by the cleaning blade 8.

In other words, there is no residual [-ner] adhering to the part A of the elastic roller rough, and the photoreceptor 2 is always uniformly charged.
It has been found that the problem can be solved by providing the cleaning blade 8.

Further, in the embodiment shown in FIG. 3, when the relationship between the volume resistance of the elastic roller rough and the chargeability of the photoreceptor 2 was investigated, it was found that the volume resistivity of the elastic roller rough was 10r'ΩcI11~10
In the region of 10 ΩcII, Tf voltage could be applied to the photoreceptor 2 satisfactorily. In particular, the volume resistance of the elastic roller rough is 1
01 ΩCIO to 10' CIm, the electrical current to the photoreceptor 2 was the most stable. In addition.

If the volume resistance of the elastic roller rough is 101'ΩC11 or more, uneven charging tends to occur, and the charging efficiency decreases significantly.・If the volume resistivity of the elastic rollerf is less than IO'' 00m, the charging current will be excessive if there is a coating defect (pinhole) in the coating film of the 1C body 2. This caused dielectric breakdown.

The charging device of the present invention configured as described above does not cause uneven charging due to hair removal or falling off, unlike conventional brush charging devices, and does not cause internal contamination, and is inexpensive and reliable. The high-voltage electrical equipment roars.

In the above example of actual #L, the elastic roller 7 is rotated in the direction of rotation of the photoconductor 2, but as shown in FIG. It may also be configured to be forcibly driven in the same direction (the contact portions of the partners move in opposite directions). As a result, squeezing rotation is applied to the elastic roller luff, and cleaning rotation is applied to the elastic roller luff, allowing the elastic roller 7 to function as a cleaning roller.

Furthermore, when forcibly driving in the co-rotation direction, by providing a relatively large linear velocity ratio between the elastic roller 7 and the photoreceptor 2, the lj! can be made to have the ability.

Further, as the cleaning blade 8, a blade made of metal or urethane foam may be used instead of a polyester film.

On the other hand, when the photoreceptor 2 is formed of a hard drum, the hardness of the elastic roller in contact with the drum needs only to be 40 degrees or less according to JISA. In particular, when the elastic roller 7 with a hardness of 20 degrees or less is used, the photoreceptor There was little occurrence of uneven contact with the circumferential surface of the body 2. As shown in FIG. 5, if a soft photoconductor or a belt photoconductor is used as the photoconductor 2, even if the roller 7' as the g-electric means is made of a rigid body, the photoconductor 2 will not be the same as the photoconductor 2. 6. You can obtain stable contact with
[Effects of the Invention] According to the present invention, as in the brush TFN method, since the photoconductor is charged by contact with the photoconductor, ozone etc. are not generated and the running cost is low. Additionally, in the brush IEfl method described above, the contact between the photoreceptor and the brush is point contact.

In the charging according to the present invention, since the photoreceptor and the elastic roller come into surface contact, it is possible to prevent the occurrence of vertical streaks in the copy image and the occurrence of charging unevenness due to wear, thereby obtaining a highly reliable and high-quality copy image. Can be done.

[Brief explanation of the drawing]

FIG. 1 is a side view of an embodiment of the present invention, FIG. 2 is a graph showing the relationship between applied bias and surface potential in the above embodiment, and FIG. 3 is a side view of another embodiment of the present invention. FIG. 4 is a side view of still another embodiment of the present invention, FIG. 5 is a side view of another embodiment of the present invention, and FIGS. 6 to 8 are side views of a conventional charging device. 2...Photoreceptor, 3...Bias application means, 6...
...Spindle, 7...Elastic roller, 8...Cleaning blade. Helmet 7 %6

Claims (1)

[Claims] A charging device comprising: a conductive elastic roller rotatably held with its circumferential surface in contact with the circumferential surface of a submersible carrier; and bias applying means for applying a bias to the elastic roller.