JPH03156470A - Color image forming method - Google Patents

Abstract

PURPOSE:To make exposure potentials for a toner sticking part and a naked part equal and to obtain a high-definition color image by using a photosensitive body provided with a transparent insulating layer on the surface of a photosensitive layer, using the toner of black, yellow, magenta, and cyan and repeating the cycle of corona charge, corona discharge simultaneous with signal exposure, whole surface photoirradiation, and development with the toner plural times. CONSTITUTION:The photosensitive body 25 is constituted by applying a surface insulating layer 27 such as a transparent polyester resin layer on the surface of the photosensitive layer 26 made of selenium, etc. In such a case, the toner of black, yellow, magenta, and cyan is used and the cycle of corona charge, corona discharge simultaneous with signal exposure, whole surface photoirradiation, and reversal development with the toner is repeated plural times, so that color toner images are superposed on the photosensitive body 25 to directly form the color image. Thus, the exposure potentials for the toner sticking part and the naked part are made equal and the high-definition color image is obtained.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a color image forming method that can be used in a hard copy device such as a copying machine or a printer. Various color electrophotographic methods have been proposed in which a plurality of toner images of different colors are repeatedly formed on an electrophotographic photoreceptor (hereinafter referred to as photoreceptor), and then the toner images are transferred all at once to paper to obtain a color image. An example of an apparatus applying this type of color electrophotographic method is the apparatus shown in Japanese Patent Application Laid-Open No. 1-113771. This apparatus will be explained with reference to FIG. 4. 2. 3 is a non-contact type non-magnetic one-component developer that uses a DC electric field to fly the toner. 4. A conductive fur brush that is in contact with the developing roller. 5. 6, the toner is triboelectrically charged, and an aluminum developing roller 7, 8. 9 Upper & Mi Blade 10. '11.12, the structure is such that a thin layer of toner is formed.

Yellow (Y) is placed in developer L, and magenta (M) is placed in developer 2.
), even if developer 3 contains cyan (C) insulating toner, developer 13t is a contact type developer containing a two-component developer consisting of insulating toner and magnetic carrier, which is widely used in electrophotographic devices. And the developing roller 7,
8. 9. 14 and the photoreceptor 15 (developing gap) is kept constant, and the developing devices are installed facing each other around the photoreceptor 15. However, each developing device is close to the photoreceptor during development and separated from the photoreceptor when not in development. is installed.

The specifications and development conditions of the black developer 13 and the physical properties of the toner are shown below.

[Specifications and developing conditions of developing device] Diameter of developing roller 14: 22 mm Peripheral speed of developing roller 14: 320 mm/s developing roller 14
Thickness of the developer layer on the surface: 400 μm Direction of rotation of the developing roller 14: Opposite direction to the photoreceptor 15 (same traveling direction) Development gap (gap between the surface of the developing roller and the surface of the photoreceptor): 300 μm during development, and 300 μm during non-development. 2mm [Developer physical properties] Type of developer: Two-component developer consisting of toner and carrier Average particle size of carrier: Approximately 50 μm Type of carrier: Teflon coated ferrite toner Average particle size: 8 μm Specifications of yellow, magenta and cyan developer The development conditions and physical properties of the toner are shown below.

[Developer specifications and developing conditions Diameter of the developing roller: 20 mm Peripheral speed of the developing roller: 160 mm/s Rotating direction of the developing roller: Opposite direction (same traveling direction) as the photoreceptor 15 Toner layer thickness on the developing roller = 30 μm development gap (gap between the developing roller surface and the photoconductor surface): 150 μm during development, 2 mm when not developing Toner average particle size: 10 μm 152 mm diameter as photoconductor sensitized to long wavelength in the infrared region
Using an amorphous 5e-Teli optical drum 15, the circumferential speed is 1.
Rotate at 60mm/s. This photoreceptor 15 is connected to a charger 1
6 (Scorotron charger, corona voltage: +7 kV, grid voltage: 1 kV) to charge to a charging potential of +900 V.Next step: Exposure by emitting light from the semiconductor laser 17 with a wavelength of 790 nm.4 Using this semiconductor laser 17, the photoreceptor 15 is exposed. A negative black signal is exposed to form an electrostatic latent image.
After the latent image is reversely developed by a black developing device 13 in a developing state with +600V applied to the developing roller 14 to form a black toner image, the photoreceptor 15 is neutralized by a static eliminating lamp 18 . Next, the photoreceptor 1 is charged again with the corona charger 16 (Scorotron charger, corona voltage, +7 kV, grid voltage: 600 V).
5 is charged to +600V, and the semiconductor laser 17 exposes the plate photoconductor 15 to signal light corresponding to yellow to form a yellow electrostatic latent image.Next, this photoconductor is charged to +600V to the developing roller 7. The photoreceptor 15 is then passed through a yellow developer 1 in a developed state, a magenta developer 2, a cyan developer 3, and a black developer 13 in an undeveloped state to form a yellow toner image. The photoreceptor 15 is charged to +810V again by the corona charger 16 (scorotron charge a, corona voltage: +7 kV, grid voltage: 800V) without removing the charge.Then, the semiconductor laser 17 emits signal light corresponding to magenta. The photoconductor 15 is then exposed to light to form a magenta electrostatic latent image.Next, the photoreceptor 15 is passed through a yellow developer 1 in a non-developing state and a magenta developer 2 in a developing state in which +800V is applied to the developing roller 8 to form a magenta toner. After the image is formed, the photoreceptor 15 is passed through a cyan developer 3 and a black developer 13 in a non-developing state. Next Next, the photoreceptor 15 is exposed to the AC corona charger 19 (applied voltage: 5 kVrms), and then the photoreceptor 15 is charged to + by the corona charger 16 again.
After being charged to 500V, the semiconductor laser 17 is used to expose the signal light corresponding to cyan to form a cyan electrostatic latent image.
Then, the toner is passed through a magenta developer 2 and a cyan developer 3 in a developing state in which +800V is applied to the developer roller 9 to form a cyan toner image and complete a color image on the photoreceptor.
The color toner image thus obtained on the photoreceptor 15 is transferred onto the paper 21 by the transfer charger 20. After the transfer, the surface of the photoreceptor 15 is transferred to the pre-cleaning charger 23 (4-X). Corona voltage +5.5kV
) The conductive fur brush 24 to which a voltage of -150V is applied and is positively charged is pressed against the photoreceptor 15 for cleaning.Problems to be Solved by the Invention In this conventional electrophotographic method, toners with different charging abilities adhere to each other. A scorotron charger is used to charge the bare photoreceptor equally, and the surface potential of the bare photoreceptor drops to 50V when the photoreceptor is exposed. However, since the toner adhesion area is an insulating material, the toner is electrically charged and covers the surface, so the surface potential after exposure increases to 200 to 300 V. When reversal development is performed with toner, the contrast potential between the development bias and the exposure potential differs greatly between the bare area and the toner-adhered area, so the development characteristics of the toner are different, and the amount of development that overlaps the toner-adhered area is smaller than that of the bare area, resulting in a high (9) Purpose of the present invention (In a color image forming method in which color toner is superimposed on a non-photoreceptor to form a full-color image, the exposure potential of the toner-adhered area and the bare area are made equal to each other, resulting in high-quality color reproduction.) The present invention aims to provide a color image forming method capable of obtaining color images of black, yellow, magenta, etc. Use cyan toner
＼Corona charging Corona charge removal at the same time as signal exposure Full-surface light illumination A color image forming method in which the cycle of reversal development using the toner is repeated multiple times, and a color toner image is superimposed on the photoreceptor to directly obtain a color image. The electric charge on the toner layer on the photoreceptor is erased by corona static elimination at the same time as the action signal exposure. First Section of the Embodiment An example of the configuration of the photoreceptor 25 used in the present invention is shown. The surface of the selenium photosensitive layer 26 with a thickness of 50 μm has a thickness of 25 μm.
Even in a structure in which a transparent polyester resin layer (surface insulating layer) 27 with a thickness of 25 μm is coated, the lower photosensitive layer 26 (yellow layer) is coated with a selenium-tellurium alloy layer (charge generation layer) 28 with a thickness of approximately 0.1 μm containing 25% tellurium. 50μ thick made of pure selenium
It is composed of two layers: m pure selenium layer (charge transfer layer) 29.

In addition to this selenium, the photosensitive layer used in the present invention may be a general electrophotographic photoreceptor such as a cadmium sulfide organic photoreceptor. First of all, this photoreceptor 25 is charged with -1800V using a corona charger.
(Figure 2a). At this time, it is desirable to irradiate light at the same time to facilitate the movement of charges from the base of the photosensitive layer 26 to the interface between the photosensitive layer 26 and the surface insulating layer 27. When the signal light is exposed while removing the static charge, in this state both the signal exposed area and the signal unexposed area have a surface potential of Ov. At this time, instead of the AC corona, the corona of the opposite polarity of the corona charger used in Fig. 2a is used. A charger may also be used (~ After that, when this photoreceptor is exposed on the entire surface, the signal exposed area remains OV. A potential of -830V appears in the signal unexposed area (dark area) (Figure 2C). The photoreceptor is reversely developed using a yellow developer to which a developing bias of -800V is applied, and yellow toner, for example, is attached to the signal exposure area. When the photoreceptor to which the toner has adhered is recharged again using a corona charger, the bare area becomes 11800 m as shown in Figure 2d.
VGQ) The toner-adhered area is charged to -2385 V. When this photoreceptor is exposed to a signal while eliminating AC corona charge, the surface potential of the toner layer becomes OV in both the signal-exposed area and the signal-unexposed area (Fig. 2e). Next, when the entire surface of this photoreceptor is exposed,
The bare signal exposed area is Ov and the signal unexposed area is 1830Vi.
,.

Further, the signal exposed portion of the toner adhesion portion is Ov, and the signal unexposed portion is 1935V (FIG. 2f).

Here, in the second color signal exposure area, the surface potential of both the bare photoreceptor and the photoreceptor in the toner-adhered area is the same Ov.The second color toner is overlaid on the first color toner and developed. Uniform development characteristics were obtained for both areas, and good color images were obtained.The principle explanation for this is as follows: The dielectric constant of the transparent insulating layer 27 on the surface of the photoreceptor 25 is 3. Since the capacitance Cii & the dielectric constant of the selenium photosensitive layer 26 of the photoconductor 25 is 6.3, the capacitance Cpζ is therefore the capacitance Cal & Ca of the photoconductor 25 = 57
pF/cm" Electrostatic capacitance Ct of the toner layer developed on the photoreceptor 25 (from the above experimental results, it is estimated that Ct = 320 pF/cm2.9 When the photoreceptor 25 is first charged to -1800V with corona charging, , the amount of charge on the surface of the photoreceptor 25 is −〇a.

Further, an amount of charge Qa is accumulated between the photosensitive layer 26 and the surface insulating layer 27. This amount of charge Qc = CaxV = 1.908 9070 m'' is calculated, but if this is exposed to a signal while removing the corona charge, the surface potential of both the signal exposed area and the signal unexposed area becomes Ov. Then, there is a charge amount Ql on the surface of the photoreceptor) and a charge amount Qb remains between the surface insulating layer 27 and the photosensitive layer 26.
b is the following value aQb-0,889070m" When this is exposed on the entire surface, there is no charge remaining in the signal exposed area, so it remains Ov. In the signal unexposed area, the surface insulating layer 27 and Now that the space between the photosensitive layers 26 is grounded, this Qb appears as a potential on the surface of the photosensitive body and becomes VO = -830V. Next, let's consider a photoreceptor with toner attached.

As mentioned above, the bare surface insulating layer 2 where toner does not adhere
On the other hand, the capacitance C1t (,t
Cit = 80 pF/cm2 Therefore, when the photoreceptor 25 to which toner is attached is charged with a constant current type corona charger and the bare part is charged to -18017,
Because the capacitance of the toner attachment area is small, the charging potential V
Although Ot is as high as VOt -2385V, when this photoreceptor is exposed to signal light while eliminating corona static electricity, the surface potential of both the signal exposed area and the signal unexposed area becomes Ov. Charge amount - Ql
l- Also, a charge Qc remains between the surface insulating layer 27 and the selenium photosensitive layer 26. This Qc has the following value Qc -0.75 μc/cm'' Finally, when the entire surface of the photoreceptor is exposed, There should be no residual charge in the signal exposed area.The force that remains Ov in both the bare area and the toner-attached area (this Q in the signal-unexposed area of the toner-attached area)
c now appears as a potential on the surface of the toner layer, and its value &
By using this method, the exposure potential of the toner-attached area and the bare area can be equalized. Here, although the charging potential of the toner-attached area and the bare area (other signal) is different in the unexposed area, this does not affect the development result at all in this method using reversal development. A specific example of this will be explained in more detail with reference to FIG. 3. Developing units 30, 31, and 32 are non-contact type non-magnetic l-component developing units that fly toner using a DC electric field, and are in contact with the developing roller. The toner is charged by friction with a conductive fur brush 33°34.35, and an aluminum developing roller 36.
37. 38 up Blades 39, 40. Even if the configuration is such that a thin layer of toner is formed by the developer 3
0 is yellow (Y), developing device 31 is magenta (M),
Even if the developer 32 contains cyan (C) insulating toner, the black developer 42? A contact type developer containing a two-component developer consisting of an insulating toner and a magnetic carrier, which is widely used in electrophotographic devices, and a developing roller 36.
37. 38. 43 and the photoreceptor 44 (developing gap) is kept constant, and each developer is installed opposite to the photoreceptor 44 around the photoreceptor 44 t4. Structure 45. 46. 4
7. 48 is attached.

The specifications and development conditions of the black developing device 42 and the physical properties of the toner are shown below.

[Developer specifications and developing conditions Diameter of developing roller 43: 22 mm Circumferential speed of developing roller 43: 340 mm/s Developing roller 43
Thickness of the developer layer on the surface: 400 μm Direction of rotation of the developing roller 43: Opposite direction to the photoreceptor 45 (same traveling direction) Development gap (gap between the surface of the developing roller and the surface of the photoreceptor): 400 μm during development to 400 μm during non-development 2mm [Developer physical properties Type of developer: Two-component developer consisting of toner and carrier Average particle size of carrier: Approximately 50 μm Type of carrier: Teflon coated ferrite Toner Charge amount: -10 μC/g Average particle size of toner: 8 μm Toner Specification of yellow/magenta/cyan developer and developer 1
The physical properties of the toner and toner are shown below.

[Developer specifications and development conditions Diameter of the developing roller: 20 mm Peripheral speed of the developing roller: 160 mm/s Rotating direction of the developing roller: Opposite direction to the photoconductor 44 (same traveling direction) Toner layer thickness on the developing roller: Rotation direction of the 32 μm developing roller: Opposite direction from the photoreceptor 44 Development gap (gap between the surface of the developing roller and the surface of the photoreceptor): 15 during development
0 μ nail 2 mm when not developed [Physical properties of toner] Toner charge amount: -3 μC/g Average particle size: 10 μm Relative dielectric constant: Approximately 2 The photoreceptor 44 is charged with a charging potential by a charger 49 (corotron charged image corona voltage: -7 kV) At this time, at the same time as charging, a lamp 50 is used to irradiate light from above the charger, and a corona static eliminator 51 (corona applied voltage: AC 4.5 kVrma, 1 kHz, grid voltage: Ov) is used. While removing static electricity from the surface of the photoreceptor, the semiconductor laser 52 is emitted to expose a negative black signal onto the photoreceptor 44, and then the entire surface of the photoreceptor 44 is irradiated with light from the lamp 53. is Ov, and a potential of -830V appears in the signal non-exposed area.This latent image is reversely developed by the black developer 42 in the developing state with -600V applied to the developing roller 43, and a black toner image is formed. Corona static eliminator 54 (Corona applied voltage: AC 4.5k
Vrma, 1kHz) to eliminate static electricity and go to the ninth stage.Lamp 50 again.
While irradiating light with
At this time, the charged potential of the photoreceptor 44 on the part where the black toner was attached becomes -2400V.
Vrma, 1 kHz, grid voltage: Ov) while eliminating static electricity on the surface, the semiconductor laser 52 was made to emit light, and a negative yellow signal was exposed on the photoreceptor 44. Thereafter, the entire surface of the photoreceptor 44 was irradiated with light from the lamp 53, and the result was A potential of Ov appears in the laser signal exposed part of the bare part and the toner-adhered part, -1830v in the bare part unexposed to the laser signal, and -930v in the laser signal-unexposed part of the toner-adhered part.
Next, this photoconductor is applied to the developing roller 36 in a yellow developing device 30 in a developing state and a magenta developing device 31 in a non-developing state. The toner is passed through a cyan developer 32 and a black developer 42 to form a yellow toner image.Then, a corona static eliminator 54 (corona applied voltage: AC 4
．． 5 kVrms, 1 kHz), and place the photoreceptor 44 at 9. While irradiating light with the lamp 50 again, the photoreceptor 44 is charged with a corona charger 49 (corotron charged image, corona voltage near kV).
At this time, the charged potential of the photoreceptor 44 on the part to which the black and yellow toners are attached becomes -2400V, which is 800V.Corona static eliminator 51 (corona applied voltage:
Semiconductor laser 5 while eliminating static electricity on the surface with AC 4, 5 kVrms, 1 kHz, grid voltage: OV)
2 to emit light and expose a negative magenta signal onto the photoreceptor 44. After that, the entire surface of the photoreceptor 44 is irradiated with light from the lamp 53. 183 in the non-exposed part of the laser signal
0v, 193 for the laser signal non-exposed area of the toner adhesion area.
A potential of 0 V appears and the photoreceptor 44 is then passed through the yellow developing device 30 in a non-developing state and the magenta developing device 31 in a developing state where 1800 V is applied to the developing roller 37 to form a magenta toner image. , the photoreceptor 44 is passed through the cyan developer 32 and the black developer 42 in a non-developing state.
kVrma, 1kHz) to the end. While irradiating light with the lamp 50 again, the photoreceptor 44 is charged with a corona charger 49 (corotron charged image, corona voltage 27kV).
At this time, the charged potential of the photoreceptor 44 on the part to which black, yellow, and magenta toner is attached is -240V.
When the voltage reaches 0V, the surface is static-eliminated with a corona static eliminator 51 (corona applied voltage: AC 4.5 kVrms, 1 kHz, grid voltage: Ov).The semiconductor laser 52 is made to emit light, and a negative cyan film is placed on the photoreceptor 44. After the signal is exposed, the entire surface of the photoreceptor 44 is not irradiated with light by the lamp 53, and the laser signal exposed portions of the bare and toner-attached portions are exposed to OV, and the bare portions that are not exposed to the laser signal are exposed to 18%.
30V, 19V for the laser signal non-exposed area of the toner adhesion area.
A potential of 30 V appears and the photoreceptor 44 is passed through the yellow developing device 30 and magenta developing device 31 in a non-developing state, and the cyan developing device 32 in a developing state where 1800 V is applied to the developing roller 38. Forming an image on the photoreceptor 4
The color toner image thus obtained on the photoreceptor 44 is transferred to a paper 58 (... Vessel 5
The coffin was transferred by 9. The coffin was thermally fixed by the fixing device 60.
- Person transfer machine The surface of the photoreceptor 44 is removed by the corona static eliminator 54
(Corona applied voltage 2 AC 4.5 kV rms,
After being negatively charged with a DC voltage of -800 V (superimposed at 1 kHz), a conductive fur brush 61 to which a voltage of 150 V was applied was brought into pressure contact with the photoreceptor 44 for cleaning. A beautiful color image with uniform toner development amount and overlapping colors can be obtained.9 Effects of the Invention According to the present invention, in a color image forming method in which a full color image is obtained by overlapping color toners on a photoreceptor, the toner-adhered area and the bare area are Accordingly, it is possible to obtain a color image forming method in which a high quality color image can be obtained by equalizing the exposure potentials of the parts.

[Brief explanation of the drawing]

Fig. 1 shows an embodiment of the structure of the photoreceptor used in the present invention. Fig. 2 shows the operation of an embodiment of the color image forming method using the photoreceptor shown in Fig. 1. 4 is a sectional view of a color image forming apparatus used in the method of the present invention. FIG. 4 is a sectional view of the apparatus used in the conventional color image forming method. 30...Yellow developed image 31...Magenta developed image 3
2...Cyan developer 42...Black developer 44...
・Photoreceptor 49... Corona charged image 50... Lamp, 51... Corona static eliminator 52... Semiconductor laser,
53... Lance

Claims (2)

[Claims] (1) Using a photoreceptor having a transparent insulating layer on the surface of the photosensitive layer, using black, yellow, magenta, and cyan toners, performing corona charging, corona static elimination simultaneously with signal exposure, full-surface light irradiation, and development with the toners. A color image forming method in which a cycle is repeated multiple times to directly superimpose a color toner image on the photoreceptor to obtain a color image. (2) The color image forming method according to claim 1, wherein the transparent insulating layer has approximately the same capacitance as the photosensitive layer.