JPH0667545A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent the short circuit between a photosensitive body and a developing roller by a process not using a corona discharger and to form an image at a high speed by covering the surface of a conductive sleeve where a bias voltage is impressed with an insulating layer, or a resistance layer, as to a developing roll provided with the conductive sleeve and a magnet installed inside the sleeve. CONSTITUTION:A photosensitive belt 1 is formed by laminating a transparent conductive layer 13 and an organic photoconductive layer 14 on a transparent supporting body 12 such as polyethylene terephthalate, etc. A developing device 4 arranged opposite to the photoconductive layer 14 and for storing toner inside is provided with the developing roll 5 constituted of a magnet roll 17, the conductive sleeve 16 and the insulating cover 15, conductive toner whose resistivity is <=10<9>OMEGAcm is attracted and held by the magnetic force of the magnet roll 17 so as to form a toner layer 6 on the insulating cover 15. A magnetic brush is formed by the toner in a toner contact area 18 where the toner layer 6 comes in contact with the photoconductive layer 14. By selecting the thickness of the insulating layer, the resistivity and inductivity in such a way, the bias voltage is distributed on the photoconductive layer, and then, charges are injected from the toner.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming a toner image on a photoconductor by using a light image as a signal.

[0002]

2. Description of the Related Art A conventional general image forming apparatus includes a photoconductor,
It consists of a corona charger, an optical writing head, a developing device, a corona copying device, a cleaner, etc., and the device is complicated, large, and expensive.

Japanese Patent Laid-Open No. 58-987 discloses a device which solves such a problem and realizes downsizing and cost reduction of the device.
No. 46 or Japanese Patent Laid-Open No. 58-153957 discloses an image forming apparatus for forming a toner image on a photosensitive member by performing development and exposure substantially at the same time. FIG. 3 shows an outline of this image forming apparatus.
An optical writing head 3 of the D array is arranged, a developing device 4 having a developing roll 5 is arranged at a position facing the optical writing head 3, and a bias voltage is applied between the photoconductor 1 and the developing roll 5. In this state, the optical writing head 3 simultaneously writes the image information on the photoconductor 1 and the developing device 4 adheres the toner to the image area to form a visible image on the photoconductor 1. This visible image is picked up from the paper feed tray 9 by the paper feed roller 10 and transferred onto the recording paper transferred to the transfer position by the transfer roller 8 to which a bias voltage is applied, and the transferred toner image is then fixed by the fixing device. It is fixed by 11.

FIG. 4 shows the principle of image formation in this process, in which a transparent conductive layer 13 made of ITO and a photoconductive layer 14 are laminated on a transparent support 12, and an LED is provided on the side of the support 12 of the photoreceptor 1. The array head 3 is arranged, and a developing roller 5 having a conductive sleeve 16 and a magnet roller 17 therein is arranged at a predetermined distance from the photoconductive layer 14. On the conductive sleeve 16, magnetic toner having conductivity is attracted and held by the magnetic force of the magnet roll 17 to form the toner layer 6. The toner layer 6 contacts the surface of the photoconductor 1 and a toner contact region 18 is formed between the photoconductor 1 and the developing roller 5. A bias voltage is applied between the transparent conductive layer 13 of the photoconductor 1 and the conductive sleeve 16 of the developing roll 5. In the toner contact area 18, the toner forms a magnetic brush, and the bias voltage is applied between the conductive sleeve 16 and the transparent conductive layer 13, so that the charge is injected from the toner into the photoconductive layer 14. When the photoconductor is charged to almost the same potential as that of the toner, the electric attraction between the toner and the photoconductor disappears, so that the toner does not adhere to the surface of the photoconductor. When light is irradiated by the optical writing head 3 in this state, the potential of the light irradiation portion is lowered, and the toner and the photoconductor 1
An electric field is formed between them and the toner adheres to the photoconductor 1 against the magnetic force of the magnet roll. In this way, a desired toner image is formed on the photoconductor 1.

[0005]

In the above process, if the photoconductor has a defect such as a pinhole, the photoconductor and the developing roll are short-circuited and an excessive current flows. Then, there is a problem that heat is generated by this current and the photoreceptor is deteriorated.

The present invention has been made in view of the above problems, and provides an image forming apparatus capable of preventing image deterioration of a photoconductor and capable of high-speed image formation by a process using no corona discharger. The purpose is to do.

[0007]

SUMMARY OF THE INVENTION According to the present invention, in a developing roller having a conductive sleeve and a magnet inside, the surface of the conductive sleeve to which a bias voltage is applied is coated with an insulating layer or a resistance layer. Characterize.

[0008]

According to the present invention, when coated with an insulating layer, it is possible to apply only an electric field to the photoconductor with almost no current flow. Further, when the resistance layer is coated, even if there is a pinhole or the like in the photoconductor and a current flows, the current value can be reduced, so that heat generation due to overcurrent hardly occurs and the photoconductor can be prevented from deterioration.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is an explanatory diagram showing a main part of an image forming apparatus as an embodiment of the present invention.

The image forming process of the present invention will be described with reference to FIG.

In FIG. 1, a photosensitive belt 1 comprises a transparent conductive layer 1 on a transparent support 12 such as polyethylene terephthalate.
3 and the organic photoconductive layer 14 are laminated.
The developing device 4, which is arranged on the side of the photosensitive belt 1 facing the photoconductive layer 14 and contains toner therein, is provided with a developing roll 5 including a magnet roll 17, a conductive sleeve 16 and an insulating coating 15. The conductive toner having a resistivity of 10 ⁹ Ωcm or less is attracted and held by the magnetic force of the magnet roll 17 on the insulating coating 15, and the toner layer 6
Are formed. In the toner contact area 18 where this toner layer 6 contacts the photoconductive layer 14, the toner forms a magnetic brush. In this state, the magnitude of the electric field applied to the photoconductive layer when a bias voltage is applied to the conductive sleeve 16 and the transparent conductive layer 13 will be considered.

FIG. 2 is an equivalent circuit diagram when the resistance of the conductive toner is ignored, and R ₁ and R ₂ are insulating layers 1 respectively.
5, the electric resistance of the photoconductive layer 14, C ₁ and C ₂ represent the electrostatic capacitances of the insulating layer 15 and the photoconductive layer 14, respectively. When the bias voltage is V, the voltage V ₂ distributed to the photoconductive layer 14 is represented by the following formula.

[0013]

[Equation 1]

Here,

[0015]

[Equation 2]

The dark resistance of the photoconductive layer 14 is very large, and in particular, since the dark resistivity of the organic photoconductor is 10 ¹⁴ Ωcm or more, if the resistivity of the insulating layer 15 is about the same,

[0017]

[Equation 3]

It is expressed as follows. Therefore, even if there is a defect such as a pinhole in the photoconductive layer, the current is about the same as the charging current of the capacitor, and deterioration of the photoconductive layer is prevented. Most of the bias voltage can be distributed to the photoconductive layer by making the dielectric constant of the insulating layer larger than that of the photoconductive layer or by making the insulating layer thinner than the photoconductive layer. .
Furthermore, if a hydrophobic plastic is used for the insulating layer, it can be made less susceptible to the influence of humidity.

When a resistance layer is used instead of the insulating layer,
After the specified relaxation time,

[0020]

[Equation 4]

By limiting the current by R ₁ , deterioration of the photoconductive layer can be prevented, and most of the bias voltage can be distributed to the photoconductive layer.

As described above, when most of the bias voltage is distributed to the photoconductive layer by selecting the layer thickness, resistivity, and dielectric constant of the insulating layer, charge is injected from the toner into the photoconductive layer to charge the photoconductive layer. To be done.

When the surface of the photoconductive layer is charged to substantially the same potential as that of the toner layer, the electric attraction between the toner and the photoconductor does not occur, so that the toner does not adhere to the surface of the photoconductor. When light is irradiated by the optical writing head 3 in this state, the electric potential is lowered in the light irradiation portion, an electrostatic attractive force is exerted between the toner and the photoconductor, and the toner resists the magnetic force of the magnet roll on the photoconductor. To form a toner image. Incidentally, in order to improve the transfer efficiency, even when the developer containing the conductive toner and the insulating toner is used, the deterioration of the photoconductor can be prevented as in the case of using only the conductive toner.

(Experimental Example 1) An image was formed under the following conditions using a photosensitive belt coated with an organic photoconductive material having a layer thickness of 20 μm as a photoreceptor and polyvinylidene fluoride having a layer thickness of 10 μm as an insulating layer. Developing roll bias voltage;
DC voltage of -650V and AC voltage of 1KHz superposed on each other. Bias voltage of transfer roll; DC + 600V. As a result, DC-500V as developing roll bias when there is no insulating layer.
Was obtained, the toner potential was high, a high-quality image was obtained, and the photoreceptor was not deteriorated.

(Experimental Example 2) Instead of the polyvinylidene fluoride of Experimental Example 1, carbon has a resistivity of 10 ⁹ Ωc dispersed therein.
image was formed in the same manner as in Experimental Example 1 except that 100 μm of a conductive rubber of 100 m was used as the bias voltage of the developing roll and DC of −500 V and AC of 300 kHz at 1 KHz were obtained. . Also, the photoconductor did not deteriorate.

(Experimental Example 3) Instead of the polyvinylidene fluoride of Experimental Example 1, carbon has a resistivity of 10 ⁹ Ωcm.
Image was formed in the same manner as in Experimental Example 1 except that the conductive rubber of 100 .mu.m and Teflon of 5 .mu.m coated thereon were used, and the DC bias voltage of the developing roll was -750 V. Image of good quality was obtained, and deterioration of the photoconductor was not observed.

(Experimental Example 4) In order to improve transfer efficiency, 50% by weight of a conductive toner having a resistivity of 10 ³ Ωcm and a resistivity of 10 ¹⁴ Ω.
When a toner prepared by mixing 50% by weight of an insulating toner having a size of cm was used, the transfer efficiency was improved and no deterioration of the photosensitive member was observed.

[0028]

As described above, according to the present invention, by using the insulating layer, the short circuit between the developing roll and the photoconductor can be surely prevented, and the bias voltage to be applied is the same as when there is no insulating layer. There is an excellent effect that a large difference can be prevented and a high quality image can be formed without using a corona discharger.

[0029]

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a main part of an image forming apparatus of the present invention.

FIG. 2 is an equivalent circuit diagram of FIG.

FIG. 3 is a schematic configuration diagram showing a conventional image forming apparatus.

FIG. 4 is an explanatory diagram showing the principle of a conventional image forming method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor 3 Optical writing head 5 Development roll 4 Developing device 6 Toner layer 12 Transparent support 13 Transparent conductive layer 14 Photoconductive layer 15 Insulating layer 16 Conductive sleeve 17 Magnet roll 18 Toner contact area

Claims (3)

[Claims] 1. A developing roll having a photoconductor in which a photoconductive layer is provided on a transparent and conductive support, a conductive sleeve disposed in the vicinity of the photoconductive layer, and a magnet disposed therein. A conductive and magnetic toner held on the developing roll, an exposing means for exposing from the support side of the photoconductor, and a means for applying a bias voltage between the support and the developing roll. An image forming apparatus for forming a toner image by substantially simultaneously contacting and exposing the surface of the photoconductor with a toner, wherein the surface of the developing roll is covered with an insulating layer or a resistance layer. Forming equipment. 2. The image forming apparatus according to claim 1, wherein an insulating plastic is used as the insulating layer. 3. The image forming apparatus according to claim 1, wherein conductive rubber is used as the resistance layer.