JP3157155B2 - Image forming method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image forming method using electrophotography.

[Prior Art] In a conventional image forming method, the surface of a photoreceptor is uniformly charged to a specific polarity by a corona discharge unit, and then the charge on the photoreceptor is selectively eliminated by image exposure to form an electrostatic image. Is formed, and a developer is supplied to the surface of the photoreceptor by a developer supplying member to which an appropriate developing bias is applied, thereby developing an electrostatic image.

By the way, an apparatus using a corona discharge means is susceptible to the use environment such as humidity and dust, and has a problem of odor and harm to a human body due to release of ozone due to corona discharge. known.

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

In this type of conventional method, a conductive substrate of a photoreceptor is grounded, and 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. To form an electrostatic image corresponding to the image. The electrostatic image is developed under a predetermined developing bias by a developing sleeve connected to a suitable developing bias power supply, 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 surface of the photoconductor without being transferred is removed from the surface of the photoconductor by a cleaning brush to which an appropriate cleaning bias is applied.

[Problem to be Solved by the Invention] In such a method using the conventional charge injection type contact charging, the above-described problems such as generation of ozone when corona discharge means is used are solved. On the other hand, however, there remains a problem that the image is liable to be ground fogged.

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

Therefore, the present invention provides a novel method in which a bias voltage is applied to an electrode of a photoreceptor, and charge is induced toward the surface of the photoreceptor by contact of an inducing member to charge the surface of the photoreceptor to a predetermined potential. This eliminates problems such as uneven charging caused by non-uniform contact or insufficient contact between the charging roller and the photoreceptor caused by the "charge injection type" contact charging method described in the original prior art, and also improves image quality. It is an object of the present invention to provide a novel image forming method that minimizes the number of power supplies used in each component for forming the image forming apparatus, thereby making the apparatus compact and inexpensive.

[Means for Solving the Problems] For this reason, the present invention relates to a photoconductor having at least a photoconductive layer provided on a conductive substrate, wherein the conductive substrate of the photoconductor has an AC voltage or a DC voltage. Is applied to the surface of the photoreceptor in accordance with the applied voltage by bringing a conductive or semiconductive grounded inducing member into contact with the surface of the photoreceptor directly or via a dielectric. After inducing the electric charge of the photoreceptor to charge the surface of the photoreceptor to a predetermined potential, and then exposing the image to form an electrostatic image,
An image forming method for developing the electrostatic image by supplying a developer with a developing sleeve connected to an induced bias power source, the method comprising: applying a bias voltage (Vdrum) applied to a conductive substrate of the photoreceptor to a sleeve; Developing bias voltage (Vsl
es) is a relation of | Vs−Vdrum |> | Vsleeve | (Vs is a spark starting voltage between the developing sleeve and the photoreceptor).

[Operation] As described above, when an AC voltage or a voltage in which a DC voltage is superimposed on a DC voltage is applied to the conductive substrate of the photoreceptor and the inducing member contacts the photoreceptor surface, the photoconductive layer, the air layer, the inducing member The applied voltage is divided according to the impedance of the photosensitive member, and the surface of the photosensitive member is charged to a predetermined potential. Next, an image is exposed, whereby an electrostatic image corresponding to the image information is formed.

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

Example Hereinafter, an image forming method according to the present invention will be described with reference to the drawings.

FIG. 1 shows an example of an apparatus for implementing an image forming method according to the present invention. The photoreceptor 1 includes a drum-shaped conductive base (collectively including a layered base) 11 and a photoconductive layer 12 provided on the base 11 by vapor deposition or coating, and is provided in a direction indicated by an arrow A. To rotate. The photoconductive layer 12 is made of OPC, Se, Zn
Any type of P-type semiconductor or N-type semiconductor such as O, CdS, and a-Si is suitable for use. In addition to the above configuration,
A configuration in which a dielectric layer is further provided on the photoconductive layer 12 may be employed. The conductive substrate 11 of the photoreceptor is electrically connected to a bias power supply 6. 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 a frequency in the range of 80 Hz to 30 kHz are particularly suitable. The superposed DC voltage is preferably a positive voltage for the N-type photoconductor and a negative voltage for the P-type photoconductor.

The inducing member 2 is arranged in contact with the surface of the photoreceptor 1 (it is not always necessary to be in strict contact with the case). In the illustrated example, the inducing member 2 has a roller shape in which a layer 22 made of a conductive elastic rubber material is electrically contacted with a conductive metal core 21 rotatably supported, and the photosensitive member is pressed by an appropriate pressure. It is pressed against the surface and rotates in the forward direction at the contact portion at a peripheral speed substantially equal to the peripheral speed of the photoconductor. The layer 22 may be, for example, a material such as NBR or silicon rubber containing a conductive material. In addition, the inducing member 2
In some cases, a dielectric layer 23 of synthetic resin or the like (an inducing member having such a configuration is shown in FIG. 4) may be provided on the outer peripheral surface of the layer 22. The layer 22 may be a semiconductive material (for example, 10 ⁵ to 10 ¹⁰ Ωcm) or a rigid metal body in addition to the elastic conductive material. The core 21 is grounded directly or via a rectifier such as a varistor, a constant voltage diode or a diode. In order to obtain a desired potential on the photoreceptor, an appropriate resistor may be interposed. In addition, the inducing member 2
May be in the form of a conductive or semiconductive blade or brush, in addition to the roller shape as described above.

FIG. 2 is an equivalent circuit for explaining charging of the photosensitive member. In the dark, when a bias voltage of a predetermined value obtained by superimposing an alternating current and a direct current is applied to the conductive substrate 11 of the photoreceptor 1 and the induction member 2 which is grounded directly or via a diode or the like is brought into contact with the photoreceptor surface, An electric charge is induced on the surface, and the surface of the photoconductor is charged to a value obtained by dividing the voltage according to the impedance of the photoconductor 1, the impedance of the inducing member 2, and the impedance of the air layer therebetween.

FIG. 3 schematically shows changes in the surface potential of the photoconductor when a superposed bias voltage deviated to the positive polarity side is applied to the substrate of the photoconductor having an N-type photoconductive layer. Inducing member 2
As described above, a positive charge is induced on the surface of the photoreceptor contacted with, and the potential drops according to the partial pressure. Next, when image exposure 7 is performed by an optical means such as a laser or LED, the surface potential (V _L ) of the bright image portion (exposed area) approaches the value of the bias potential applied to the substrate 11 of the photosensitive member, A potential difference is formed between the potential (V _D ) of the dark part (the area not exposed). As described above, in the electrophotographic method according to the present invention, contrary to the conventional method using corona discharge, the potential of the image bright portion becomes the bias potential to the photoconductor, and the potential of the image dark portion becomes a low value. An image is formed.

FIG. 3 shows the light portion potential and the dark portion potential linearly for convenience of explanation, but in actuality, the surface potential of the photoconductor during bias application has a bias potential superimposed and oscillates. Fig. 4 shows a DC voltage of 400 V
A bias voltage in which an AC voltage of 2500 Vp-p is superimposed is applied to the substrate of the photoreceptor, and thereafter, a light image is irradiated to obtain an electrostatic latent image. The waveform of the bias voltage applied to the body substrate is substantially equal, and the frequency of the amplitude is also equal to the frequency of the bias voltage.

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

Description will be made again with reference to FIG. The electrostatic images formed by the image exposure are developed by developing means 3 arranged in the following order. The developing means 3 includes a conductive sleeve 31 arranged close to the surface of the photoconductor 1 and a magnet roller 32 provided inside the sleeve. The sleeve 31 and the magnet roller 32 are provided rotatably at different speeds independently of each other, and in this example, both the sleeve 31 and the magnet roller 32 are
The photosensitive member 1 rotates in a direction opposite to the rotation direction, that is, in a forward direction at the developing site. The surface of the sleeve 31 is subjected to shot blasting, 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 conveyed in the direction opposite to the rotation direction of the photoreceptor 1 (forward direction in the developing portion, direction of arrow B) at substantially the same speed as or slightly higher than the peripheral speed of the photoreceptor, and contacts the surface of the photoreceptor 1. Alternatively, the electrostatic image is developed by rubbing under the action of an alternating electric field and an alternating magnetic field. As the developer, a one-component magnetic 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. For example, when reversal development is required as in a digital printer, the bias voltage is selected such that the potential of the sleeve 31 is close to the dark portion potential of the photoconductor.

The bias voltage used here satisfies the following equation.

| Vs−Vdrum |> | Vsleeve | where Vdrum is the bias voltage (peak value of the amplitude voltage) applied to the substrate of the photoconductor, Vsleeve is the bias voltage applied to the developing sleeve, and Vs is the photoconductor. Vs = 23.85 (σl) (1 + 0.329 / σ1)) (1 ≦ 16cm, σ is p = 760mmHg, and the relative density of air at t = 20 ° C as standard condition) , Σ = 0.385 p / (273 + t ° C.)) By developing under such conditions, a clear developer image free of leakage between the photoconductor and the developing sleeve and free of background fog can be obtained.

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

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

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

FIG. 5 shows a case where the bias voltage applied to the conductive substrate of the photoreceptor 1 is only an AC voltage (no DC voltage is superimposed). In this case, the induction member 2 is grounded via the rectifying means 8. Other parts have the same configuration as the example of FIG.

EXPERIMENTAL EXAMPLE 1 In the configuration of FIG. 1, a DC voltage of 2500 Vp-p and an AC voltage of 2500 Vp-p (frequency: 80 Hz to 30 Hz) were applied to a photoconductor substrate having an N-type induced photoconductive layer on a conductive substrate. The superposed voltage was applied, and the photosensitive member was rotated at a peripheral speed of 40 mm / Sec. A grounded induction roller having an elastic layer made of NBR or silicon rubber containing conductive powder was pressed against this photoreceptor in the dark, and then irradiated with laser light to form an electrostatic image, which was subjected to reversal development. .

As the developer, a toner having a resistance of about 10 ⁷ to 10 ⁹ Ω · cm and a spherical average particle diameter of 50 parts with respect to 5 parts of a toner mainly containing an acrylic resin is used.
A mixture obtained by mixing 100 parts of a μ ferrite carrier was used. The developing sleeve used was a SUS304 sleeve having an outer diameter of 18 mm and shot blasted with a surface of about 400 mesh and connected to a DC bias power supply. 6 in the developing sleeve
The magnet roller of the pole is rotated so that an alternating magnetic field of about 600 Gauss acts on the toner on the surface of the sleeve, and the interval between the photosensitive member and the developing sleeve is set to 0.3 mm so that the developer on the developing sleeve contacts the photosensitive member surface. Development was performed.

In such a configuration, when an experiment was performed by sequentially changing the bias voltage to the sleeve, the bias voltage was selected so as to satisfy the range of | Vs−Vdrum |> | Vsleeve |. A clear image with no leakage to the surface and no soil was obtained.

Experimental Example 2 Under the same conditions as in Experimental Example 1, the average particle diameter was used as the developer.
A similar experiment was performed using a one-component magnetic toner of 10 ¹⁴ to 10 ¹⁵ Ωcm at ¹² μm. Similarly, by satisfying the above range, there was no leakage from the photoconductor to the developing sleeve, and there was no background contamination A clear image could be obtained.

Experimental Example 3 Under the same conditions as in Experimental Example 1, a spherical ferrite powder of 35 to 60 μm was previously formed on the surface of the developing sleeve as a developer carrier.
6 g evenly adhered and 10 ¹⁴
A similar experiment was performed using a toner of about 10 ¹⁵ Ω · cm. As a result, a result similar to that of Experimental Example 1 was obtained.

[Effects of the Invention] As described above, according to the present invention, a bias voltage is applied to an electrode of a photoreceptor, and a charge is induced toward the photoreceptor surface by contact of an inducing member to bring the surface of the photoreceptor to a predetermined potential. In other words, by letting the charging method of the "charge induction type" be performed, uneven contact or insufficient contact between the charging roller and the photoreceptor caused in the "charge injection type" contact charging method described in the earlier related art was initially performed. In addition to eliminating problems such as uneven charging caused by contact, the use of a means for applying a bias voltage to the photoreceptor substrate eliminates the need for a large number of high-voltage power supplies for charging means and developing bias. The configuration of the device to be implemented can be made extremely simple and inexpensive.

By maintaining the above-mentioned relationship between the bias voltage applied to the photoconductor substrate and the bias voltage applied to the developing sleeve, it is possible to obtain a clear image with no leakage between the photoconductor and the developing sleeve and no fogging. Can be.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a main part of an example of an image forming method in which the method according to the present invention is carried out, FIG. 2 is an equivalent circuit relating to a photoconductor and an inducing member, and FIGS.
FIG. 4 is a diagram for explaining a change in surface potential of a photoconductor when a positive potential is applied to a substrate of the photoconductor having a photoconductive layer of a type.
FIG. 5 is a schematic view showing another example different from FIG. DESCRIPTION OF SYMBOLS 1 ... Photoreceptor, 2 ... Inducing member, 3 ... Developing means, 4 ... Transfer means, 5 ... Cleaning means, 6 ... Bias power supply, 11 ... Conductive substrate, 12 ... Photoconductive layer, 31 ... developer supply member.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-149668 (JP, A) JP-A-52-35639 (JP, A) JP-A-55-147651 (JP, A) 54447 (JP, A) JP-A-56-110967 (JP, A) JP-A-58-88770 (JP, A) JP-A-60-138566 (JP, A) JP-A-1-156775 (JP, A) JP-B-63-30622 (JP, B2) (58) Field surveyed (Int. Cl. ⁷ , DB name) G03G 15/06-15/08 G03G 13/02 G03G 15/02

Claims (1)

(57) [Claims] An AC voltage or a bias voltage obtained by superimposing a DC voltage on an AC voltage is applied to a photoconductor having at least a photoconductive layer provided on a conductive substrate. A conductive or semiconductive grounded inducing member is brought into contact with the body surface directly or via a dielectric to induce a charge of a predetermined polarity on the surface of the photoconductor in accordance with the applied voltage, thereby causing the surface of the photoconductor to be a predetermined surface. Charged to potential,
Then, an image is formed by exposing the image to form an electrostatic image, and then supplying a developer with a developing sleeve connected to an induced bias power supply to develop the electrostatic image. Bias voltage applied to the substrate (Vdrum)
And a developing bias voltage (Vsleeve) applied to the sleeve has a relationship of | Vs−Vdrum |> | Vsleeve | (Vs is a spark starting voltage between the developing sleeve and the photosensitive member). .