JPH04199076A - Image forming method - Google Patents

Abstract

PURPOSE:To produce a vivid image with no ground halation by using a means to impress a specific bias voltage on the base of a photo-sensitive element. CONSTITUTION:Bias voltage Vdrum impressed on an electrconductive base of a photo-sensitive element is related to the developing bias voltage Vsleeve to be impressed on a sleeve as expressed by Eq. I, and a DC bias as meeting Eq. I is impressed on developing sleeve, and electrostatic image is developed. In Eq. I, Vs represents the spark initiate voltage between the developing sleeve and photo-sensitive element. Thereby a vivid reproduced image can be obtained being free from ground halation.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an image forming method using electrophotography.

[Prior Art] In conventional image forming methods, the surface of a photoreceptor is uniformly charged to a specific polarity by a corona discharge means, and then the charges on the photoreceptor are selectively erased by image exposure to form an electrostatic image. The electrostatic image is developed by supplying developer to the surface of the photoreceptor using a developer supplying member to which an appropriate developing bias is applied.

By the way, devices using corona discharge means are easily affected by the usage environment such as humidity and dust, and also have the problem of odor and toxicity to the human body due to ozone released due to corona discharge. is known.

To solve this problem, in recent years, an image forming method using so-called contact charging has attracted attention, in which the photoreceptor is charged by pressing a charging roller to which an external voltage is applied to the surface of the photoreceptor.

Conventional methods of this type ground the conductive substrate of the photoreceptor;
A charging roller to which a bias voltage is applied is pressed against the surface of the photoreceptor to uniformly charge the surface of the photoreceptor, and then an electrostatic image corresponding to the image is formed by image exposure. The electrostatic image is developed under a predetermined development bias by a development sleeve connected to a suitable development bias power source, and the developed image is transferred onto a suitable transfer material by the action of a transfer corona discharger or a transfer roller. . The developer remaining on the photoreceptor surface without being transferred is removed from the photoreceptor surface by a cleaning brush to which an appropriate leaning bias is applied.

[Problem to be solved by the invention] The conventional method using contact charging as described above does not solve the problem of ozone generation when using corona discharge means. It can be resolved, but
On the other hand, problems remain, such as the tendency for background blur to occur in images.

Furthermore, in the above-mentioned conventional contact charging method,
A power source is required for each constituent means of image formation, that is, a large number of power sources are required, such as a p-power source for the charging roller, a power source for the developing bias, a power source for the transfer bias, and a power source for the cleaner bias. It has been difficult to provide an inexpensive and compact image forming apparatus.

Therefore, the present invention provides a novel image forming method that can form a clear reproduced image with no background blur, and that also minimizes the power required for the image forming means, thereby making it possible to make the apparatus more compact and cost-effective. The purpose is to provide

[Means for Solving the Problems] Therefore, the present invention applies an alternating current voltage or a bias voltage in which a direct current voltage is superimposed on an alternating current voltage to the conductive substrate of a photoreceptor, thereby making the surface of the photoreceptor conductive or semiconductive. The surface of the photoreceptor is charged to a predetermined potential by contacting a grounded member directly or through a dielectric material, and then the image is exposed to form an electrostatic image, followed by a developing device connected to a DC bias power source. An image forming method in which the electrostatic image is developed by supplying developer through a sleeve, the bias voltage (V drum) being applied to the conductive substrate of the photoreceptor and the developing bias voltage (V 5leeve) being applied to the sleeve. Toga, l
Vs −Vdrum l > l
Vsleevel (Vs is the spark starting voltage between the developing sleeve and the photoreceptor).

[Function] In this way, when an AC voltage or a voltage obtained by superimposing a DC voltage on an AC voltage is applied to the conductive substrate of the photoreceptor and the inducing member is brought into contact with the surface of the photoreceptor, the photoconductive layer, the air layer, and the inducing member The applied voltage is divided according to the impedance of the photoreceptor, and the surface of the photoreceptor is charged to a predetermined potential. Next, by performing image exposure, an electrostatic image is formed according to the image information.

On the other hand, the developing sleeve is applied with a DC bias that satisfies the above equation, and develops the electrostatic image.

[Embodiment] The image forming method according to the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of an apparatus implementing the image forming method according to the present invention. The photoreceptor 1 includes a tram-shaped conductive substrate (generally referred to as an N-shaped substrate) 11, and a photoconductive layer 12 provided on the substrate 11 by vapor deposition or coating,
Rotate in the direction shown by arrow A. Photoconductive N12 is OPC
, Se, ZnO1CdS, and a-5i, either a P-type semiconductor or an N-type semiconductor is suitable for use. Also,
In addition to the above configuration, a dielectric layer may be further provided on the photoconductive layer N12. The conductive substrate of the photoreceptor] 1 is electrically connected to the bias voltage R6, and in this example,
The bias power supply 6 applies a voltage obtained by superimposing a DC voltage on an AC voltage to the conductive substrate 11 .

AC voltages with frequencies in the range 80 Hz to 30 kHz are particularly suitable. Further, it is preferable that the superimposed DC voltage has a positive polarity for an N-type photoreceptor and a negative polarity for a P-type photoreceptor.

The inducing portion 2 is placed in contact with the surface of the photoreceptor 1 (depending on the case, it does not necessarily have to be in exact contact). In the illustrated example, the inducing member 2 has a roller shape in which a rotatably supported conductive metal core 21 is covered with N22 made of a conductive elastic rubber material in electrical contact with the outer surface of the conductive metal core 21. It is pressed against the surface and rotates in the forward direction at the contact portion at approximately the same circumferential speed as the photoreceptor. N22 may be, for example, NBR, silicon rubber, or the like containing a conductive material.

The inducing member 2 may also include a dielectric material N23 made of synthetic resin or the like on the outer peripheral surface of N22 (FIG. 4 shows an inducing member having such a structure). ) may be provided.

In addition to elastic conductive materials, N22 can also be used for semi-conductive materials (
For example, 105 to 1011! Ωcn+) or a rigid metal body. Core 21 is directly or varistor,
It is grounded via a rectifier such as a constant voltage diode or a diode. Further, a suitable resistor may be interposed in order to obtain a desired potential on the photoreceptor. Further, the inducing member 2 may have the shape of a conductive or semiconductive plate or a brush other than the roller shape as described above.

FIG. 2 is an equivalent circuit for explaining the charging of a photoreceptor. In the dark, a bias voltage of a predetermined value, which is a combination of alternating current and direct current, is applied to the conductive base 11 of the photoreceptor 1, and when the inducing member 2, which is grounded directly or through a diode, is brought into contact with the surface of the photoreceptor, the photoreceptor Electric charges are induced on the surface, and the surface of the photoreceptor is charged to a value that is a partial voltage according to the values of the impedance of the photoreceptor 1, the impedance of the inducing member 2, and the impedance of the air layer between them.

FIG. 3 schematically shows changes in the surface potential of a photoreceptor when a superimposed bias voltage biased toward the positive polarity side is applied to the substrate of the photoreceptor having an N-type photoconductive layer. As described above, positive charges are induced on the surface of the photoreceptor in contact with the inducing member 2, and the potential drops in accordance with the partial pressure. Next, when image exposure 7 is performed using optical means such as a laser or LED, the surface potential (VL) of the bright part of the image (exposed area) approaches the value of the bias potential applied to the base 11 of the photoreceptor, and the dark part of the image Potential (V[I) of (region not exposed to N light)
A potential difference is formed between the two. As described above, in the electrophotographic method according to the present invention, contrary to the conventional method using corona discharge, the potential of the bright part of the image becomes the bias potential to the photoreceptor, and the potential of the dark part of the image becomes a static potential of a low value. Forms an electric image.

Although FIG. 3 shows the bright area potential and the dark area potential linearly for convenience of explanation, in reality, the surface potential of the photoreceptor during bias application is oscillated due to the superposition of the bias potential. Figure 4 shows a DC voltage of plus 400V and a frequency of 4k.
The potentials of the dark and bright areas are shown when a bias voltage superimposed with an AC voltage of 2500 Vp-p of Hz is applied to the base of the photoreceptor, and then a light image is irradiated to obtain an electrostatic latent image. The waveform is approximately equal to the waveform of the bias voltage applied to the substrate of the photoreceptor, and the frequency of the amplitude is similarly equal to the frequency of the bias voltage.

Similarly, when a negative potential is applied to the substrate of a photoreceptor having a P-type photoconductive layer, a negative potential charge is induced on the surface of the photoreceptor.
An electrostatic image is formed in the same manner as above.

The explanation will be given again with reference to FIG. The electrostatic image formed by image exposure is developed by developing means 3 arranged in the following order. The developing means 3 includes a conductive sleeve 31 disposed close to the surface of the photoreceptor I and a magnet roller 32 provided inside the conductive sleeve 31 . The sleeve 31 and the magnet roller 32 are provided to be rotatable independently from each other at different speeds, and in this example, the sleeve 31 and the magnet roller 3
2 rotate in the opposite direction to the rotational direction of the photoreceptor 1, that is, in the forward direction at the development site. The surface of the sleeve 310 is shot blasted, and the developer supplied from a storage case (not shown) is attracted to the surface by the magnetic force of the magnet roller 32. The developer is applied in a direction opposite to the rotational direction of the photoreceptor 1 (
At the development site, the electrostatic image is conveyed in the forward direction (direction of arrow B) and comes into contact with or rubs against the surface of the photoreceptor 1 to develop an electrostatic image under the action of an alternating electric field and an alternating magnetic field. As the developer, a one-component magnetic l-toner or a two-component developer is used.

The sleeve 31 is connected to a DC bias power supply 33, and a predetermined bias is applied thereto. For example, when reversal development is required as in a digital printer, the bias voltage is selected so that the potential of the sleeve 31 is close to the dark potential of the photoreceptor.

The bias voltage used here is one that satisfies the following equation.

l Vs −Vdrum l > l
Vsleevel Here, Vdrum is the bias voltage (peak 1a of amplitude voltage) applied to the substrate of the photoreceptor,
V 5leeve is the bias voltage applied to the developing sleeve, Vs is the spark discharge starting voltage between the photoreceptor and the developing sleeve, and V s = 23.85 ((71) (1 + 0.329/
a I)) (1≦1.6 cm, σ is p=760 mm
Hg, relative density of air with t=20℃ as standard condition, σ
=0.385p/(273+t'C)) By developing under these conditions, it is possible to obtain a clear developer image without leakage between the photoreceptor and the developing sleeve and without background fog.

The thus visualized developer image is transferred onto a transfer material such as paper by the transfer means 4. The transfer means 4 has almost the same structure as the inducing member 2, and includes a grounded metal core 41, a conductive layer 42, and optionally further includes a dielectric layer 43 (FIG. 4). The transfer means 4 transfers the developer image on the photoreceptor onto a transfer material using a transfer potential induced by a bias voltage applied to the photoreceptor.

The transfer material is then separated from the photoreceptor surface by a separating means (not shown) and sent to a fixing means (not shown) to form a permanent copy image thereon.

On the other hand, the photoreceptor after the transfer is cleaned of the developer remaining thereon by the cleaning means 5, and ready for the next image formation. Equipped with: In this example, the cleaning means 5 is a brush-type cleaner in which a conductive brush is placed on a conductive base 51. The conductive substrate 51 is grounded so that developer remaining on the photoreceptor is electrostatically and physically attracted to the conductive brush and removed from the photoreceptor. The developer attached to the brush is removed by a scraper (not shown).

FIG. 5 shows a case in which the bias voltage applied to the conductive substrate of the photoreceptor is only an alternating current voltage (no direct current voltage is superimposed); in this case, the inducing member 2 is grounded via the rectifying means 8. The other parts have the same structure as the example shown in FIG.

11. In the configuration shown in Fig. 1, a photoreceptor substrate having an N-type organic photoconductive layer on a conductive substrate is applied with a DC voltage of about 900 V plus an AC voltage of 2500 V p-p (frequency is 80 H).
A superimposed voltage (30 Hz to 30 Hz) was applied, and the photoreceptor was rotated at a circumferential speed of 40 mm/Sec. A grounded induction roller having an elastic layer made of NBR or silicone rubber containing conductive powder is brought into pressure contact with the photoreceptor in the dark, and a laser beam is irradiated with one part to form an electrostatic image. Reverse developed.

As a developer, toner 5 whose main component is acrylic resin is used.
A ferrite carrier l having a resistivity of 10 7 to 10 9 Ω·cm and a spherical average particle diameter of 50 μm.

A mixture of 0 parts was used. The developing sleeve was a 5US304 sleeve with an outer diameter of IElni, the surface of which had been shot-blasted to a thickness of about 400 mesh, and was connected to a DC bias power source. A 6-pole magnetic roller is rotated within the developing sleeve so that an alternating magnetic field of about 600 Gauss acts on the toner on the sleeve surface, and the distance between the photoreceptor and the developing sleeve is 0°3 mm, and the developer on the developing sleeve is exposed to light. Development was performed by contacting the body surface.

In this configuration, when we conducted an experiment by sequentially changing the bias voltage to the sleeve, we found that l Vs - Vdr
By selecting the bias voltage so as to satisfy the range of um l > l Vsleevel, it was possible to obtain a clear image without leakage from the photoreceptor to the developing sleeve and without background smudge.

Loss of 10 minus 2 Under the same conditions as Experimental Example 1, the average particle size of the developer was 1
A similar experiment was conducted using a single-component magnetic toner with 2 μ and 1014 to 1 Q I5 Ω' cm, and it was found that by meeting the above range, there was no leakage from the photoconductor to the developing sleeve, and there was no background smudge. I was able to get a nice image.

Under the same conditions as in Test Example 1, 6 g of spherical 35-60μ ferrite powder was uniformly adhered to the surface of the developing sleeve as a developer carrier, and the average particle size of the toner was 2.
A similar experiment was conducted using a toner having a μ of 1014 to 1015 Ω·cm, and the same results as in Experimental Example 1 were obtained.

[Effects of the Invention] As described above, according to the present invention, by using a means of applying a bias voltage to the base of the photoreceptor, the present invention can be carried out without requiring a large number of high voltage power supplies for charging means, developing bias, etc. The configuration of the device can be made extremely simple and inexpensive.

In addition, by maintaining the values of the bias voltage applied to the base of the photoreceptor and the bias voltage applied to the developing sleeve in the above relationship, a clear image with no leakage between the photoreceptor and the developing sleeve and no background blur can be obtained. be able to.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the main parts of an example of an image forming apparatus implementing the method according to the present invention, FIG. 2 is an equivalent circuit between a photoreceptor and an inducing member, and FIGS. Based on N
A diagram illustrating a change in the surface potential of a photoreceptor when a positive potential is applied to the substrate of the photoreceptor having a type photoconductive layer,
FIG. 5 is a schematic diagram showing a different example from FIG. 1. l...Photoreceptor, 2...Inducing member, 3...
- Developing means, 4... Transfer means, 5... Cleaning means, 6... Bias power source, 11... Conductive substrate, 12... Photoconductive layer, 31... Developer supply body. Figure 2 Figure 3-〉at darkness Figure 5

Claims (1)

[Scope of Claims] An AC voltage or a bias voltage in which a DC voltage is superimposed on an AC voltage is applied to the conductive substrate of the photoreceptor, and a conductive or semiconductive grounded member is applied directly or dielectrically to the surface of the photoreceptor. The surface of the photoreceptor is charged to a predetermined potential by contacting the photoreceptor through the body, and then the image is exposed to form an electrostatic image, and then a developer is supplied by a developing sleeve connected to a DC bias power source to charge the photoreceptor surface to a predetermined potential. An image forming method for developing an electrostatic image, wherein a bias voltage (Vdrum) applied to the conductive substrate of the photoreceptor and a developing bias voltage (Vsleeve) applied to the sleeve are: |Vs-Vdrum|>|Vsleeve ｜(Vs is
An image forming method characterized by a relationship between a developing sleeve and a photoreceptor (spark starting voltage).