JPH0374392B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a developing method in the process of electrophotographically recording images using two different toner colors.

In recent years, with the spread of computer fax machines, there has been an increasing demand for printer functions that output data. As one of them,
There is a desire to improve usability and alert users by making documents printed by a printer not only black but also two colors, such as red. Conventionally, various electrophotographic processes have been proposed as such two-color printers, but they have the disadvantage that two-color toners tend to mix. The reason for this is that the developing devices used in these processes are so-called two-component developing devices that use iron powder as a carrier and a two-component developer mixed with about 10 percent by weight of toner.
When the developing device is a two-component developing device, when it rubs the photoreceptor, it may scrape off the first color toner image formed by the first developing device, or if the carrier deteriorates or the toner image in the developer If the ratio of the toner in the toner changes, it becomes difficult for the toner to adhere to the photoconductor in both the first and second developing devices, and when the second developing device rubs the photoconductor, the toner image of the first color becomes , which means that it becomes more susceptible to damage.

An object of the present invention is to provide a new two-color development method that prevents the above-mentioned drawbacks and prevents the toners from mixing when first and second development are sequentially performed using two different color toners. The feature is that the first and second development steps are performed by jumping development using a one-component developer without developer deterioration, and the particle size of the toner used in the second development step is smaller than that of the toner used in the first development step. This is due to the fact that the particle size is larger.

Examples of the present invention will be described below.

FIG. 1 is a schematic cross-sectional view showing an example of an image recording apparatus to which the present invention can be applied. 2() to 2() respectively show the surface potential of the image carrier (photoreceptor) in the following steps () to () performed in the image recording apparatus of FIG. 1, and the horizontal axis represents the surface potential of the photoreceptor. The surface portion and the vertical axis indicate the photoreceptor surface potential. The photoreceptor 1 is a so-called Carlson type photoreceptor in the form of a drum, in which a photoconductive layer is provided on a conductive base layer, and rotates in the direction of the arrow. Any suitable photoconductive material such as Se, ZnO ₂ , OPC, etc. can be used as the photoconductive layer, but Se is used in this example.

In step (), the photoreceptor 1 is discharged by the corona discharger 2.
uniformly charges the surface of Charging is carried out to an acceptable charging level for Se. The photoreceptor surface potential Vp due to uniform charging is approximately 1000V in the illustrated example.

In step (), the uniformly charged surface of the photoreceptor is irradiated with light as a first light information irradiation for parts of the recorded image other than the part to be printed in black (3 in FIG. 1). The intensity of this light irradiation is such that the potential of the portion of the photoreceptor surface that has been irradiated with light is below the intermediate potential Vs in the next step () (second step).
In the figure (), it is assumed to be sufficient to drop to approximately zero). The above light irradiation is transmitted light or reflected light from the original,
or laser light scanning modulated with image information signals;
This can be carried out using CRT spot scanning or light from a light emitting element such as an LEP array.

The photoreceptor that has been irradiated with the first light information is processed in the process ().
In this step, a positive corona discharge of the same polarity as that of the corona discharger 2 is applied by the control corona discharger 11, and as a result, the portion of the surface of the photoreceptor that has been irradiated with light in step () has a positive intermediate voltage of about 500V. The potential becomes _Vs. This control corona discharger has a control grid to which a voltage corresponding to the intermediate potential V _s is applied, and the photoreceptor 1
It is possible to compensate for undesirable fluctuation factors such as fluctuations in sensitivity and fluctuations in the intensity of light irradiated with optical information, thereby enabling stable and good image formation. At this time, the potential of the portion of the surface of the photoreceptor that was not irradiated with light in the first optical information irradiation step, that is, step (), is about 1000 V, which is the same as that of the portion of the surface of the photoreceptor and the control corona discharger 11. An electric field is created between the grids that controls the positive corona discharge and remains intact.

Next, in step (), a second
As light information irradiation, light is irradiated onto the portion of the recorded image that is to be printed in red (4 in FIG. 1). The intensity of this light irradiation is sufficient to reduce the potential of the portion of the photoreceptor surface that has been irradiated to a sufficiently low value (approximately +100V in this example).

As described above, the first latent image, which has a positive potential relative to the intermediate potential V _s and corresponds to the image portion to be printed in black, and the first latent image, which has a relatively negative potential with respect to the intermediate potential A second latent image is formed on the surface of the photoreceptor 1 which has a potential and corresponds to the part of the image to be printed in red.

This photoreceptor is then processed by a first developing device 5 in a step (), and then by a second developing device 6 in a step ().
The image is developed, that is, visualized. A developing bias voltage corresponding to the intermediate potential _Vs is applied to the developing sleeves of these developing devices, and the first developing device 5 receives negatively charged black toner, and the second developing device 6 receives positively charged black toner. Uses charged red toner.
Therefore, on the surface of the photoreceptor 1, black toner is applied to the second latent image in the step () using the first developing device 5, and black toner is applied to the second latent image in the step () using the second developer 6. red toner adheres to the intermediate potential.
No toner adheres to the _Vs area.

The thus developed photoreceptor is then subjected to uniform polarity of toner in a corona discharger 7, and then the toner image is transferred onto a transfer paper 9 by a transfer corona discharger 8. As a result, the transfer paper 9 provides a recorded image printed in two colors, black and red, on paper with a white background color. On the other hand, the photoreceptor after the transfer is used repeatedly after the residual toner on the surface is removed by the cleaning blade 11.

In the above image recording process, a first latent image is formed in a red image area and a second latent image is formed in a manner corresponding to a black image area, and red toner is applied to the first developer and black toner is applied to the second developer. A two-color print image can be similarly recorded even if these latent images are developed respectively using the following methods.

Next, an embodiment of the developing method according to the present invention when applied to the above-described image recording process will be described with reference to FIG. In FIG. 3, numerals 5 and 6 are developing devices corresponding to the first developing device 5 and the second developing device in FIG. 1, respectively. In this embodiment, both developing devices 5 and 6 perform jumping development using a one-component non-magnetic developer whose main component is non-magnetic toner and which does not contain carrier iron powder. . However, the particle size of the toner in the developing device 5 is smaller than that in the developing device 6, and the former is black and the latter is red. Reference numerals 11 and 12 indicate cylindrical sleeves in contact with the toner in the developing units 5 and 6, respectively, which face the photoreceptor 1 at a distance of approximately 300 μm, and whose moving speed is approximately equal to that of the photoreceptor along the direction of movement of the photoreceptor. Rotates at equal circumferential speed. Reference numerals 13 and 14 denote toner coating blades, which are urethane blades having a hardness of about 60°, and coat the sleeves 11 and 12 with toner to a thickness of 60 to 80 μm.
Further, the sleeve surface is formed with irregularities of R _z =1 to 2 μ so that the toner can be coated stably. As the toner coating means, for example, a rotating roller, a brush roller, etc. can be used. Note that R _z is a value that represents the surface roughness, and the roughness of the standard length (0.25 mm) is measured and a cross-sectional curve is drawn between the third peak from the highest peak and the third valley from the deepest valley. is the distance expressed in μm. During this coating process, the toner is given a triboelectric charge from the sleeve surface. When applied to the latent image forming process described in FIG. 1 and FIG. Appropriate toner materials and charge control agents are selected so as to provide a charge of . Of course, a corona discharger or the like may be used to directly apply the above charge to the toner coating on the sleeve. The toner coated on each of the sleeves 11 and 12 then reaches the developing section near the photoreceptor as the sleeve rotates, and jumps from the sleeve to the photoreceptor surface depending on the photoreceptor surface potential and adheres thereto, as described above. The first and second latent images are visualized. In this case, an alternating current bias voltage biased by a direct current component voltage of +500V is applied as a developing bias voltage to each sleeve. (Regarding AC bias, please refer to Japanese Patent Application Laid-Open No. 1983-1999, filed by the present applicant.
18657. ) Next, the developing characteristics of the first and second developing devices are
This will be explained with reference to FIG. Figure 4 shows the average particle size of approx.
The developing characteristics of the first developing device using a non-magnetic toner having a particle size of 8μ are shown. The horizontal axis shows the difference between the photoreceptor surface potential and the DC bias voltage, and the vertical axis shows the image density obtained by development. In order to obtain sufficient image density when using non-magnetic toner, apply an AC voltage with a peak-to-peak voltage _Vpp of 2000V or more as the AC component of the developing bias voltage to the 300μ gap between the sleeve and the photoreceptor. It is necessary to violently reciprocate the toner between the sleeve and the photoconductor to make it easier to adhere to the photoconductor surface (this effect is tentatively called toner activation).
In addition, in order to prevent fogging, it is necessary that the alternating current component be a high frequency voltage of 2 kHz or more. In FIG. 4, 4-a is a characteristic curve when an AC component voltage of _Vpp =2000V and frequency=2kHz is used. 4-b in the same figure shows the characteristics when an AC voltage of V _pp =1.2 kV and =1000 Hz is used, and in this case, the activation of the toner is weak and the image density is insufficient.

FIG. 5 shows the developing characteristics of the second developing device. Horizontal axis,
The meaning of the vertical axis is the same as in FIG. It is important that the non-magnetic toner used in the developing device shown in FIG. 2 has a larger particle size than the non-magnetic toner used in the first developing device. In this embodiment, the average diameter of the nonmagnetic toner used in the second developing device is 15 μm. It is also important that the AC bias used in the second developing device has a V _pp value smaller than that of the AC bias used in the first developing device. In this example, in the second developing device = 2k
Hz V _pp = 1200V. As is clear from Figure 5, sufficient image density is obtained in the second developer even at _Vpp = 1200V, but this is because as the toner particle size increases, the reflection force on the sleeve surface becomes significantly weaker. The main reason is that the toner is sufficiently activated at the value of _Vpp . In the second developer
When V _pp =2 kV, the toner becomes too dark, resulting in an image with background fog even in bright areas, which is undesirable.

All of the toners described herein are toners having a relatively irregular shape that have been appropriately classified using a powder pulverization method such as a hammer mill or a jet mill.
If you change the manufacturing method of the toner, for example, use a spray dryer method and use a toner that has a relatively spherical tendency and sufficiently cuts out fine particles of 5μ or less, the
A toner having an average diameter of 13μ is suitable as the toner for the second developer.

As explained above, according to the present invention, the first developing step and the second developing step for respectively visualizing the first latent image and the second latent image corresponding to the image portions of two different colors are performed using non-magnetic toner. Because it is a jumping development method that uses a one-component developer consisting of Therefore, since the activation voltage of the toner can be lowered, there is less damage to the first toner image on the photoreceptor during the second development process, and it is possible to obtain a clear two-color image with less color mixture. This is the result.

Note that although the description of the embodiment was for the case of jumping development using non-magnetic toner, in the case of jumping development using magnetic toner, the particle size of the second developing toner is made larger than the particle size of the first developing toner. A similar effect can be achieved by doing so.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of an example of an image recording apparatus to which the developing method of the present invention can be applied, FIG. 4 is a schematic sectional view of an example of a developing device implementing the developing method of the present invention.
The figure shows the development characteristics of a jumping developer using the non-magnetic toner with a relatively small particle size shown in Fig. 3, and the figure 5 shows the development characteristics of a jumping developer using the magnetic toner with a relatively large particle size shown in Fig. 3. FIG. 3 is a diagram showing the development characteristics of a jumping developer. 1: Photoreceptor, 2: Corona discharger, 3: Light irradiation corresponding to the first color image portion, 4: Light irradiation corresponding to the second color image portion, 5: First developer, 6: Second developer , 7, 8: Corona discharger, 9: Transfer material, 10:
Cleaning blade, 11: Control corona discharger, 11, 12: Developing sleeve, 13, 14: Toner coating blade, 15: Magnet.

Claims (1)

[Claims] 1 The first electrostatic latent image formed on the image bearing member is developed with a first developing device, and the second electrostatic latent image formed on the image bearing member is developed with a second developing device using toner of a different color from that of the first developing device. In a two-color developing method in which a two-color image is obtained on an image carrier by sequential development in a device, both the first and second developing devices use a one-component developer; In either case, the developer supporting member supports a developer layer thinner than the gap between the image carrier and the developer supporting member and faces the image carrier, and the average particle diameter of the toner used in the second developing device is The average particle size of the toner used in the first developing device is larger than that of the toner used in the first developing device, and the first AC bias voltage is applied to the developer supporting member of the first developing device, and the first AC bias voltage is applied to the developer supporting member of the second developing device. A two-color development method characterized by applying a second AC bias voltage with a small peak-to-peak voltage.