JPH083673B2 - Color electrophotographic apparatus - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color electrophotographic apparatus which can be used for a color hard copy apparatus such as a color copying machine or a color printer.

2. Description of the Related Art In recent years, a plurality of toner images of different colors are formed on an electrophotographic photosensitive member (hereinafter referred to as a photosensitive member) by repeating charging, exposure, and development a plurality of times, and then the toner images are collectively transferred to a paper to perform color printing. A color electrophotographic method for obtaining an image is being studied.
Unlike the conventional color electrophotographic method, this method has an advantage that the apparatus can be downsized without a transfer drum.

A process disclosed in Japanese Patent Laid-Open No. 60-95456 is known as a typical example of a conventional single transfer color electrophotographic process. This method will be described with reference to FIGS. 2 and 3.

FIG. 2 is a schematic view of a color electrophotographic apparatus using a conventional process. 1 is a selenium-tellurium (Se-Te) photoconductor rotating in the direction of the arrow, 2 is a corona charger for charging the photoconductor, 3 is a laser beam scanner, 4 to 7 are yellow (Y), magenta (M), and Cyan (C), Black (B
k) developer containing developer separately, 8 is image receiving paper,
9 is a discharge lamp, 10 is a corona transfer device, 11 is a heat fixing device,
Reference numeral 12 is a cleaning blade, and 13 is a charge eliminating lamp for initializing the surface potential of the photoconductor after transfer.

The structure of the developing devices 4 to 7 is shown in FIG. 14 is a two-component developer (hereinafter referred to as developer) composed of a mixture of positively chargeable toner and magnetic carrier, 15 is an aluminum developing sleeve, 16 is a magnet roller, and 17 is a layer that regulates the layer thickness of the developer. Thickness control blade, 18 scraping plate, 19 developer
14 is a rotary blade that agitates, 20 is a toner for replenishment, 21 is a toner replenishing roller, and 22 is a power source for generating a voltage in which a high DC voltage is superimposed on a positive DC voltage. To make the developing device ready for development, the developing sleeve 15 is connected to the power supply 22. To make it in the undeveloped state, the developing sleeve 15
Electrically floating or grounding or developing sleeve 15
Apply a negative DC voltage to.

A method of forming a color image using this apparatus will be described. After positively charging the photoconductor 1 with the corona charger 2,
The laser beam scanner 3 scans and exposes the yellow image signal to form a negative electrostatic latent image (an electrostatic latent image in which the image area is exposed and the surface potential of the photoconductor is attenuated). Then, the electrostatic latent image is subjected to negative / positive reversal development by the developing device 4 containing Y toner to form a yellow toner image on the photoconductor 1. At this time, only the developing device 4 containing Y toner is connected to the power source 22, but the other developing devices 5 to 7 are connected.
Is adjusted to a non-developable state. After developing with Y toner, the entire surface of the photoconductor 1 is irradiated with the charge eliminating lamp 13 to erase the yellow electrostatic latent image.

Next, by the same method as the method for forming the yellow toner image, the steps of charging, exposure, development, and light removal are repeated,
Toner images of Y, M, C and Bk are formed on the photoconductor 1.
After the formation of all toner images is completed, the electrostatic latent image is photo-erased by the static elimination lamp 9, and the toner image is electrostatically transferred onto the plain paper 8 by the corona charger 2. The toner image transferred to the plain paper 8 is heated and fixed by the heat fixing unit 11. After electrostatic transfer, photoreceptor 1
The cleaning blade 12 removes the toner remaining on the photoconductor and is used for the next image formation.

Problems to be Solved by the Invention In the method described in the preceding paragraph, the toner layer formed on the photoconductor is corona-charged to charge the photoconductor, and the toner layer is superposed again on the toner layer. It includes a new process of combining, which was not available in conventional electrophotography. Because of the step of further developing the toner layer on the recharged toner layer, many new problems that cannot be considered by the conventional electrophotographic method occur.

When an AC bias is applied at the time of color superposition development as in the conventional example shown here, the developing roller 23 as shown in FIG.
In the developing gap between the photoconductor and the photoconductor 24, not only the toner 25 on the developing roller but also the toner 26 adhered on the photoconductor is the photoconductor.
It reciprocates between the developing roller 23 and the developing roller 23. as a result,
1) Color turbidity occurs in the image, 2) The developer is soiled with toner of another color and must be cleaned frequently, 3) The image of the image is blurred and unclear, and 4) Edge effects occur in solid areas. However, serious problems such as difficulty in overlapping colors occur. The specific problem will be described with reference to FIGS. 5 to 8.

In the process of superposing toner images of different colors on the photoconductor by repeating the cycle of charging, exposing and developing,
As shown in the figure, attach the photoreceptor 24 with toner to the toner layer.
The process of charging the photoconductor by corona charging from above 26 is newly added. In this recharged state, as shown in FIG. 6, an instable state is obtained in which the positively charged toner layer 26 is also placed on the positively charged photoreceptor 24. If an AC bias is applied to the developing roller in such a state,
It can be easily understood that not only the toner on the developing roller reciprocates with the photoconductor, but also the toner on the photoconductor moves and the image is disturbed.

Therefore, it is conceivable to apply a DC bias instead of an AC bias, but again, in this case, various problems occur, and an electrophotographic apparatus of this kind has not been put to practical use until now. For example, in the state shown in FIG. 7, the toner layer 26 attached to the photoconductor 24 is recharged from above and the photoconductor is set to +800 V, and only the portion A is exposed from above. In this state, when a DC voltage of +400 V is applied to the developing roller 23 and brought close to the photoconductor 24, a complicated electric force line as indicated by an arrow in the figure is generated in the developing state. Therefore, in the exposure section A, the toner colors can be overlapped. However, at the boundary between the exposed portion and the non-exposed portion B, lateral scattering of toner occurs due to the wraparound of the lines of electric force. In the non-exposure section B, on the contrary, from the photoconductor 24 to the developing roller.
Back flight to 23 occurs. As a result, in the color overlapping portion of the image, the image bleeding is unclear and inaccurate color overlapping results.

Besides, a serious problem as shown in FIG. 8 occurs. This is because when the layer thickness of the photoconductor 24 used is extremely thin, for example, in the case of an a-Si photoconductor, accurate color superimposition of fine line images is extremely difficult as compared with the case where a thick selenium photoconductor is used. It was found that the line width of the toner image to be superposed on the upper side is narrower than the line width A which should be originally superposed.

It is an object of the present invention to provide a color electrophotographic apparatus that obtains a beautiful color image in which toner having no color unevenness or color turbidity is accurately overlapped in a solid portion or a fine line image.

The present invention relates to a re-corona recoloring apparatus for a color electrophotographic apparatus which forms a color image on a photoconductor by superposing a plurality of toner images of different colors by repeating a cycle of charging, exposing and developing a plurality of times. The toner A of the photoconductor to which the charged toner A image is attached, and the toner B of the toner carrier carrying the toner B
And a non-contact DC electric field for developing the electrostatic latent image on the photoconductor.

Action Conditions under which this color superimposition is successful, that is, the particle size of the toner adhering to the photoconductor, the layer thickness, the thickness of the photoconductor, the range of the surface potential of the photoconductor, the gap between the photoconductor during development,
Detailed experiments were conducted on the relative speed, the toner layer thickness on the developing roller, and the like. As a result, the toner A on the photoconductor on which the re-corona-charged toner (A) image is attached and the toner B on the toner carrier carrying the toner B are brought into non-contact with each other to physically remove the toner on the photoconductor. If the toner is not disturbed electrically by preventing the disturbance and developing the DC electric field between the photoconductor and the toner carrier, the toner already attached on the photoconductor reciprocates in the developing gap. There is no mechanical peeling, and beautiful and accurate color superposition can be achieved.

Example First, it was found that it is important that the toner be insulative and non-magnetic in the method of superposing colors on the photoconductor. When magnetic toner is used, it is extremely easy to convey the toner by using magnetic force, but on the other hand, it is difficult to obtain a beautiful primary color because the magnetic material is opaque, and there is a serious obstacle to color superposition on the photoconductor. . FIG. 9 shows the state of the developing state when the magnetic toner is used. For example,
In the magnetic one-component developing method disclosed in Japanese Patent Application Laid-Open No. 54-43027, the magnetic toner 28 on the developing roller 27 and the photoconductor 24 in the non-image area A are set to be in non-contact with each other. However, image part B
2 clearly shows that the toner 28 on the developing roller 27 has its ears raised by electrostatic attraction and comes into contact with the photoconductor 24. Such a developing method is effective in an ordinary electrophotographic apparatus that does not overlap colors on the photoconductor, but a toner layer already developed is present on the photoconductor as in the present invention, and a new toner layer is formed on the toner layer. This is a completely inadequate measure when developing an image. That is, the toner image on the photoconductor is disturbed by the contacting toner ears, which is a fatal defect.
However, in the present invention, since the non-magnetic toner is electrostatically adhered to the developing roller and is gently opposed to the toner on the photosensitive member without contact, there is no rise of the spikes of the toner as in the conventional example, and the non-image is not formed. The non-contact state can be maintained not only in the portion but also in the image portion.

In a general electrophotographic method, the surface potential condition has a relatively large degree of freedom, and a value of 200V to 2000V is selected.
However, in the present invention, the upper limit of the surface potential of the photoconductor is limited by the thickness of the toner layer deposited on the photoconductor, and the lower limit thereof is limited by the developing characteristics of the developing method used. In the present invention, the absolute value of the surface potential is 500 V to 1000
Must be in the V range. In recent general black-and-white copiers, it seems that a low surface potential of 200 to 500 V is preferred for the surface potential of the photoconductor in order to reduce the load on the charger. However, this color superposition method absolutely requires a surface potential of 500 V or more. The reason for this will be described with reference to FIGS. 10 and 11. 10th
The figure shows the developing characteristics of the DC electric field flight developing method used in the present invention. The horizontal axis of the figure represents the value of the developing bias that causes the toner to fly, and the vertical axis represents the density of the image obtained at that time. Since the reversal developing method is used in the present invention, the charging polarity of the toner and the charging polarity of the photoconductor are the same, and the developing bias applies a voltage having the same polarity as the surface potential of the photoconductor. When the developing method shown in the figure is used, the toner begins to fly toward the photoconductor from about 300V and reaches the maximum image density with a potential difference of about 500V. Therefore,
It can be seen that sufficient image density cannot be obtained unless the surface potential of the photoconductor is 500 V or more. On the other hand, the upper limit of the surface potential of the photoconductor is determined by the layer thickness of the toner layer attached on the photoconductor. FIG. 11 shows an equivalent circuit when the photoreceptor 24 is recharged from above the toner layer 28 by the corona charger 29. The toner layer and the photosensitive layer have a relationship in which capacitors Ct and Cp are connected in series. The charging voltage Vt due to corona charging is distributed to the toner layer 28 and the photosensitive layer 24, the electrostatic capacity of the toner layer 28 decreases as the thickness of the toner layer 28 increases, and the voltage applied to the toner layer 28 gradually increases. I understand. For example, a toner layer of 50μ on a selenium photoreceptor with a thickness of 60μ
When the toner adheres and is recharged to 1100V, a voltage of 500V or more is applied to the toner layer. However, under this condition, the toner layer on the photoconductor cannot discharge the voltage and is discharged, and the light emission at that time lowers the potential of the photoconductor to about 600V. The discharge phenomenon of the toner layer due to the excessively high surface potential of the photoconductor to which the toner layer is attached has not been known at all. The reason for this discharge is that the toner layer attached to the photoconductor contains an air layer of almost 50%, and therefore the withstand voltage of the toner layer is determined by the withstand pressure of the air layer. This phenomenon is an unavoidable problem because the air layer cannot be removed as long as powder toner is used. When the surface potential is lowered during charging, the toner is overlapped and developed even in a portion where the toner should not be overlapped, which causes undesirable color turbidity. Therefore, it was found that the upper limit of the surface potential of the photoconductor is limited to the range in which the dielectric breakdown of the toner layer does not occur, and this value must be 1100V or less.

When the surface potential range of this photoconductor is determined, the developing bias is determined next. Usually, in the reversal development method, the developing bias is a value lower than the surface potential of the photoconductor and can be set relatively freely, but in the present invention, the toner adheres to the photoconductor, so that the development bias is more severe. The range will be limited. For example, Vt-300 <Vb <Vs, where Vt is the surface potential of the photoconductor to which toner is attached, Vb is the applied voltage to the toner carrier that carries the toner to be overlaid with color, and Vs is the surface potential of the photoconductor. It is necessary to be within the range. For example, if the DC developing bias Vb is set to a value lower than Vt by 300 V or more, an extremely inconvenient problem occurs. The developing method used in the present invention is a DC electric field non-contact developing method, and its developing characteristics are the same as those described above.
It has the development characteristics shown in the figure. By using such a developing method, the surface potential of the photoconductor is +800 V and the developing bias is +
FIG. 7 shows the development state when set to 400V. The state shown in FIG. 7 is a state in which the toner layer 26 attached to the photoconductor 24 is recharged from above and the photoconductor is set to +800 V, and only the portion A is exposed from above. In this state, the developing roller 23
When a DC voltage of 400 V is applied and brought close to the photoconductor 24, a complicated electric force line as shown by an arrow in the figure is generated in the developing state. Therefore, in the exposed area A, the toner colors can be superimposed without any problem. On the contrary, in the non-exposed portion B, the reverse flight of the toner from the photoconductor 24 to the developing roller 23 occurs. As a result, at the time of development, the developing roller is soiled with toner of another color and cannot be used continuously. The development bias Vb cannot be set too low in order to prevent the reverse flight of toner from the photoconductor to the developing unit during this development.The surface potential of the photoconductor on which the toner adheres is Vt, and the surface potential of the photoconductor is Vs. At this time, it is necessary that Vt−300 <Vb <Vs.

Other essential conditions when the surface potential of the photoconductor and the value of the developing bias are set within the required ranges will be described below with reference to FIG. In the present invention, when the thickness of the toner layer 26 attached on the photoconductor 24 is L1, the thickness of the toner layer 25 on the developing roller 23 is L2, and the gap between the toner layer 25 and the toner layer 26 is L3, L1 < If the relationship of 50 μm L2 <80 μm L3 <200 μm is satisfied, it is possible to accurately superimpose colors with high resolution and obtain a beautiful fine line image without an edge effect. When development is performed so that the toner layer thickness L1 on the photoconductor 24 is 50 μm or more, the surface potential of the photoconductor is lowered due to the discharge phenomenon of the toner layer 26 described above, and undesired color turbidity occurs. For example, the thickness of the toner layer 25 on the developing roller 23 may be 60 μm.
When the thickness is set to m and the condition is set so that the whole is developed on the photoconductor 24, the toner layer 26 of 60 μm adheres to the photoconductor 24. This is a condition that a beautiful image is obtained with a single color, but there is a serious drawback that causes a discharge phenomenon when overlapping colors.

It was also found that the toner layer thickness L2 on the developing roller 23 needs to be 80 μm or less. This is because when the thickness of the toner layer on the developing roller 23 is 80 μm or more, the repulsion of the toner in the toner layer on the developing roller 23 causes the toner to fly from the developing roller 23 to the photoconductor 24 and the developing bias is applied to the photoconductor. This is because the background fog is generated in the non-image area even when the surface potential is less than or equal to.

Further, it was found that the gap L3 between the toner layer 26 attached on the photoconductor 24 and the toner layer 25 on the developing roller 23 should be 200 μm or less. This is because when L3 is set to 200 μm or more, a phenomenon similar to that when the photosensitive member having a thin photosensitive layer shown in FIG. 8 is used, and the toner superposed from above is developed with a width narrower than that of the electrostatic latent image. , Because it is not possible to accurately overlap colors.

As described above, in order to prevent dielectric breakdown of the toner layer on the photoconductor, the thickness of the toner layer on the photoconductor must be reduced. If you try to do so, the average particle size of the toner will be
It is advantageous to make it finer than 15 μm. Further, when the toner is piled up from above, the surface of the developing roller gradually narrows the developing gap and approaches the photoconductor, but at this time, the toner on the photoconductor temporarily receives a lateral force as the electric field strength changes. work. For this reason, the toner on the photoconductor may scatter around the image during color superposition. This is because the toner is polarized as the electric field strength changes. Since this polarization force is proportional to the cube of the particle size of the toner, the larger the particle size of the toner, the stronger the influence. In order to prevent this lateral movement, the average particle diameter of the toner needs to be 15 μm or less. By doing so, the toner layer of the photoconductor becomes more difficult to scatter.

Further, it was found that the thickness of the photoconductor has an influence on the condition of superimposing the fine line image of the photoconductor having the toner layer on the resolution during color superposition. It has been found that good color superposition can be achieved by setting L4> L3 / 10, where L4 is the thickness of the photoreceptor. This is because when the thickness of the photoconductor becomes thin, the lines of electric force generated from the electrostatic latent image wrap around in the lateral direction when developed with the same development gap as the thickness of the photoconductor having a large thickness, resulting in a thin image line. It is thought to be because. It was found that when a photoconductor having a thickness smaller than the above value is used, an image in which colors are superposed on the photoconductor has a remarkably thin image line of the toner to be superposed thereon as shown in FIG. It was

As described above, if the toner layer thickness on the developing roller, the toner layer thickness on the photoconductor, the thickness of the photoconductor, the developing gap, the developing bias, etc. are strictly specified, as shown in FIG. The shaded area can be accurately projected onto the electrostatic latent image on the photoreceptor, and can be specified so that beautiful color superposition can be achieved.

Since the toner layer on the photoconductor is in an unstable state attached to the photoconductor charged with the same polarity as described above, not only be careful not to give electrostatic vibration to the toner,
The movement of the toner should be as quiet as possible and slow so as not to give mechanical vibration. Therefore, it is preferable that the toner carrier has a roller shape in which the developing gap changes gently. If this roller shape is used and further quiet development is attempted, the surface of the toner layer on the photoconductor,
It is necessary that the moving direction of the surface of the toner layer on the developing roller is the same as the moving direction and the moving speed is substantially the same. Under these conditions, there is no unwanted air flow between the narrow gap between the developing roller and the photoreceptor and the toner layer on the photoreceptor is never disturbed. At this time,
For example, as shown in FIG. 13, the rotation speed of the developing roller is set to 2
When the speed is doubled, the toner 30 at the edge of the image line is scattered as shown in the figure, and the image is blurred, which is not preferable. On the contrary, as shown in FIG. 14, even if the developing roller 23 surface and the photosensitive member 24 surface are traveling in opposite directions, the toner in the opposite direction
31 scatters easily occur.

Experiments have shown that a nip width of development of at least about 2 mm is required when attempting color superposition using the DC electric field flight development method having the characteristics shown in FIG. In order to secure this nip width, it was found that the diameter of the developing roller needs to be at least 6 mm or more when the size of the photoconductor is 80 mm or more. At this time, if the curvature of the developing roller is too large (developing roller diameter is too small),
When the photoconductor approaches the developing unit, the rate of change of the electric field strength increases, and the above-mentioned polarization force for the large toner particles acts, and bleeding easily occurs around the image line. Further, since it is necessary to increase the number of rotations in order to obtain the same moving speed, an excessive centrifugal force acts on the large-sized toner on the developing roller, and the toner easily scatters around the apparatus.
Therefore, it is desirable that the roller diameter is not too small.
However, on the contrary, if the roller diameter is too large, the developing nip width increases and the developing time becomes long, so that the toner adhesion amount on the photoconductor excessively increases, and the toner adhesion amount on the photoconductor may exceed 50 μm. . At this time, as described above, the toner layer on the photoconductor causes air discharge during recharging, the surface potential of the photoconductor decreases, and undesired color turbidity occurs. Therefore, the diameter of the photoconductor is D1,
When the diameter of the developing roller is D2, D2 <D1 / 4 is desirable.

Before entering a specific embodiment, the color overlapping condition will be described in more detail with reference to FIG.

When the thickness of the toner layer 26 adhered on the photoconductor 24 is L1, the thickness of the toner layer 25 on the developing roller is L2, and the gap between the toner layers 25 and 26 is L3, L1 is 50 μm or less, preferably 10 μm.
It is desirable that L2 is 80 μm or less, L2 is 80 μm or less, preferably 10 μm or more and 50 μm or less, and L3 is 200 μm or less, preferably 50 μm or more and 150 μm or less.

The developing bias applied to the developing roller is Vt, where Vt is the surface potential of the photoconductor on which the toner is attached, Vb is the DC bias of the developing roller carrying the toner to be color-superposed from above, and Vs is the surface potential of the photoconductor. -300 <Vb <Vs is desirable. For example, when a selenium photoconductor is used and one toner layer is attached to the photoconductor, Vs is 850V and Vt is 950V. At this time, the developing bias Vb needs to be 650V <Vb <850.

The toner used is a non-magnetic insulating toner which has been used conventionally, and for example, a styrene resin or an acrylic resin is used as a binder, and a pigment or a charge control agent is dispersed therein. It is desirable that the toner has an average particle size of 15 μm or less, preferably between 8 and 12 μm.

Materials that can be used as the photoconductor include selenium, CdS, a-Si, and various organic photoconductors. Although the thickness of the photosensitive member is related to the developing gap as described above, the thickness of 15 to 90 μm is preferable.

The size of the photoconductor drum is generally 30 mm to 26 mm.
A diameter of about 0 mm is used, but when the photosensitive member diameter is D1 mm and the developing roller diameter is D2 mm, it is preferable that D2 <D1 / 4.

It is more desirable that the developing roller diameter is in the range of 6 <D1 <30 mm at the process speed of 100 to 300 mm / s so that the optimum nip width for development can be obtained.

Concrete Example 1 Hereinafter, a concrete example of the present invention will be described in more detail with reference to FIG.

The developing units 32, 33, 34 and 35 are non-contact type non-magnetic one-component developing units that fly toner by a DC electric field. The conductive fur brushes 36, 37, 38 and 39 contact the developing roller to remove toner. The toner is triboelectrically charged, and a thin layer of toner is formed on the developing rollers 40, 41, 42, 43 made of aluminum by the blades 44, 45, 46, 47. The developing device 32 is yellow (Y), the developing device 33 is magenta (M), the developing device 34 is cyan (C),
The developing device 35 contains black (Bk) insulating toner. Then, each developing device was installed opposite to the periphery of the photoconductor 48 with a constant gap (development gap) between the developing rollers 40, 41, 42, 43 and the photoconductor 48. Each developing device is provided with a separation / contact mechanism that is close to the photoconductor during development and is separated during non-development. The specifications and developing conditions of the developing device and the physical properties of the toner are shown below.

Development device specifications and development conditions Development roller diameter: 16 mm Development roller peripheral speed: 150 mm / s Development roller rotation direction: Opposite to photoconductor Toner layer thickness on development roller: 30 μm Development roller rotation direction: Photosensitive Opposite direction to body 48 Development gap (gap between surface of developing roller and surface of photoconductor): 150 μm at development, 700 μm at non-development Physical properties of toner Toner charge: +3 μC / g Average particle size: 10 μm Dielectric constant: Approx. 2 As a photosensitive member, an amorphous Se-Te photosensitive drum 48 (diameter: 60 μm, relative permittivity: 6.3) with a diameter of 100 mm, which was sensitized to a long wavelength in the infrared region, was used and rotated at a peripheral speed of 150 mm / s. Charge this photoreceptor 48 to a charger 49 (scorotron charger, corona voltage:
It was charged to a surface potential of + 700V by + 7kV, grid voltage: 820V. Next, a light emitting diode array 50 with a wavelength of 670 nm
Was exposed to light through a self-focusing rod lens array 51 (Selfoc lens array SLA-20, manufactured by Nippon Sheet Glass Co., Ltd.). At this time, the light intensity on the photoconductor surface is 2.
It was ² μJ / cm ² . Using this light emitting diode array 50, a negative yellow signal was exposed on the photoconductor 48 to form an electrostatic latent image. After the latent image is reversely developed by the yellow developing device 32 in the developing state in which + 600V is applied to the developing roller 40, the photoreceptor 48 is undeveloped in the magenta developing device 33 and the cyan developing device 34.
And passed through the black developing device 35 to form a yellow toner image. At this time, the thickness of the yellow toner layer on the photoconductor 48 was 1 to 2 layers, and the thickness of the toner layer was 10 to 20 μm.

Next, the photoreceptor 48 was charged to + 850V again by the corona charger 49. At this time, the surface potential of the photoconductor to which the yellow toner adhered became 950V. After that, the light-emitting diode array 50 exposed the signal light corresponding to magenta on the photoconductor 48 to form a magenta electrostatic latent image. Next, the photoconductor 48 is passed through the yellow developing device 32 in the non-developing state, the magenta developing device 33 in the developing state in which + 700V is applied to the developing roller 41, the cyan developing device 34 in the non-developing state, and the black developing device 35. A magenta toner image was formed. At this time, the toner layer in the portion where yellow and magenta overlapped on the photoreceptor was 2 to 4 layers, and the thickness thereof was 20 to 40 μm.

Next, again use the corona charger 49 to move the photoconductor 48 to + 880V.
Charged. At this time, the surface potential of the photoconductor to which only the yellow and magenta toner adhered became 950V. In addition, the surface potential of the photoconductor in the portion where the yellow and magenta toners overlap was 970V. Then, the light-emitting diode array 50 exposed the signal light corresponding to cyan to form a cyan electrostatic latent image. Next, the photoconductor 48 is applied to the yellow developing device 32 in the non-developing state, the magenta developing device 33, and the developing roller 42 by + 800V.
Then, a cyan toner image is formed by passing the toner through a cyan developing device 34 in a developing state to which is applied. After that, the photoconductor 48 was passed through the black developing device 35 in the non-developing state. At this time, the toner layers at the portions where the yellow and cyan toners and the magenta and cyan toners are overlapped on the photoconductor are 2 to 4 layers,
Its thickness was 20-40 μm.

Next, again use the corona charger 49 to move the photoconductor 48 to + 880V.
Charged. At this time, the surface potential of the photoconductor to which only the yellow, magenta, and cyan toners were attached became 950V. Further, the surface potential of the photoconductor in the portion where the yellow and magenta toners, the yellow and cyan toners, and the magenta and cyan toners overlap was 970V. After that, the LED array 50
To expose a signal light corresponding to black to form a black electrostatic latent image. Next, the photoreceptor 48 is undeveloped in the yellow developing device 32,
A magenta developing device 33, a cyan developing device 34, and a black developing device 35 in the developing state in which +800 V is applied to the developing roller 43 are passed to form a black toner image.

The color toner image thus obtained on the photoconductor 48 was transferred onto the paper 53 by the transfer charger 52, and then thermally fixed by the fixing device 54. On the other hand, after the transfer, the surface of the photoconductor 48 is positively charged by the pre-cleaning charger 55 (corona voltage +5.5 kV), and then the conductive fur brush 56 is applied with a voltage of -150 V.
Was pressed against the photoconductor 48 and cleaned.

As a result, the color density of the solid color of red, green, and blue is 1.
A clear color image was obtained with a line image of 5 or more and the line images were accurately overlapped.

Example 2 Using the apparatus of Example 1, an organic photoreceptor having a τ-type phthalocyanine dispersed in a resin (thickness 30 μm, relative dielectric constant 3)
Was used for negative charging, and other conditions (charging device, transfer device, developing bias, toner polarity, voltage applied for cleaning, etc.) were all reversed, and printing was performed.

As a result, the color density of the solid color of red, green, and blue is 1.
A clear color image was obtained with a line image of 5 or more and the line images were accurately overlapped.

Comparative Example 1 Using the apparatus of Example 2, a τ-type phthalocyanine photoconductor was used with a thickness of 10 μm. All other conditions were the same as in Example 2.
Same as.

As a result, the resolution is poor and red, green, and
An unclear color image in which the blue colors did not overlap was obtained.

Comparative Example 2 Using the apparatus of Example 1, the rotation speed of the developing roller was the same and the rotation direction was opposite to that of Example 1.

As a result, the resolution is poor and red, green, and
An unclear color image in which the blue colors did not overlap was obtained.

Comparative Example 3 Using the apparatus of Example 1, only the developing gap was 250 μm.
And printed under the same conditions as in Example 1 except for the above.

As a result, the resolution is poor and red, green, and
An unclear color image in which the blue colors did not overlap was obtained.

Comparative Example 4 Using the apparatus of Example 1, the surface potential of the selenium photoconductor was raised to 1200 V during cyan and black cycles for printing.

As a result, an unclear color image was formed in which the cyan and black toners were in the red part and the black part was in the blue part and the green part.

Comparative Example 5 Using the apparatus of Example 1, a developing roller having a diameter of 50 mm was used. The moving speed of the surface was the same as in Example 1. The other conditions were the same as in Example 1.

As a result, an unclear color image was formed in which the cyan and black toners were in the red part and the black part was in the blue part and the green part.

Comparative Example 6 Using the apparatus of Example 1, a developing roller having a magnet roller inside a cyan and black developing roller was used, and a magnetic toner was used for the cyan and black toners. All other conditions such as developing conditions were the same as in Example 1.

As a result, an unclear color image in which cyan and black toner adhered to all color portions was formed.

Comparative Example 7 Using the apparatus of Example 1, the developing bias for magenta, cyan and black was set to 400V. All other conditions were the same as in Example 1.

As a result, the yellow toner was mixed in the magenta developing unit, the yellow and magenta toners were mixed in the cyan developing unit, and the yellow, magenta, and cyan toners were mixed in the black developing unit.

EFFECTS OF THE INVENTION According to the present invention, it is possible to obtain a color electrophotographic apparatus that obtains a beautiful color image in which toner having no color unevenness or color turbidity is accurately overlapped in a solid portion or a fine line image.

[Brief description of drawings]

FIG. 1 is a principle diagram for explaining color superimposition development of a color electrophotographic apparatus in one embodiment of the present invention, FIGS. 2 and 3 are principle diagrams of a conventional color electrophotographic apparatus, and FIG. FIG. 5 is a principle diagram for explaining problems in color overlapping in the example, FIG. 5 is a diagram for recharging the photoconductor to which the toner of the present invention is attached, and FIG. 6 is charging of the toner layer and the photoconductor after recharging. FIG. 7 is a diagram for explaining the state, FIG. 7 is a principle diagram showing the case where the developing state is inappropriate, and FIG. 8 is a principle diagram showing that the developing condition is also inappropriate and the accuracy of color superimposition is poor, and FIG. Is a diagram for explaining the developing state of the conventional developing method using magnetic toner, FIG. 10 is a characteristic diagram showing typical developing characteristics of the developing conditions used in the present invention, and FIG. 11 is corona charging from above the toner. FIG. 12 is an explanatory view showing an ideal developing state, and FIG. 13 is a developing roller. FIG. 14 is a diagram illustrating a problem that occurs when the surface speed and the surface velocity of the photoconductor are different, and FIG. 14 is a diagram that illustrates a problem that occurs when the moving direction of the developing roller and the moving direction of the photoconductor are different. FIG. 15 is a principle view of a color electrophotographic apparatus for explaining one embodiment of the present invention. 23: developing roller, 24: photoconductor, 25: toner layer on developing roller, 26: toner layer on photoconductor, 32, 33, 34,
35 …… Developer, 40, 41, 42, 43 …… Developing roller, 49 ……
Corona charger, 50 ... Light emitting diode array

Claims (1)

[Claims] 1. A color electrophotographic apparatus, which uses yellow, magenta, and cyan toners, and repeats a cycle of charging, exposing, and developing to superimpose toner images on a photoconductor to form a color image, and is re-corona charged. A color electrophotographic apparatus, characterized in that a toner layer A of a photoconductor and a toner layer B on a toner carrier are opposed to each other in a non-contact manner, and an electrostatic latent image of the photoconductor is developed by a DC electric field. , L4> L3 / 10 and L4> 10 [μm] when the photoconductor thickness is L4, and 500 <| Vs | <1000 [V when the surface potential of the photoconductor is Vs. ], Where L1 is the thickness of the toner layer A deposited on the photoreceptor, and 10 <L1 <40 [μm], and the thickness of the toner layer B on the toner carrier is L2, When 10 <L2 <50 [μm] and the gap between the toner layers A and B is L3, 50 <L3 < A color electrophotographic apparatus having a size of 150 μm, in which the surface of the toner layer A and the surface of the toner layer B are in the same traveling direction and at substantially the same traveling speed.