JPH0374388B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a developing method in the process of recording an image using toners of two different colors.

In recent years, with the spread of computers, facsimile machines, etc., there has been an increasing demand for the ability of printers to output data. One of these is the desire to improve usability and alert users by making the documents printed by a printer not only black but also two colors, for example, red. There is.
Conventionally, various processes for such two-color printers have been proposed, 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 device is a two-component developer, when it rubs the photoreceptor, it may scrape off the first color toner image formed by the first developer, or if the carrier deteriorates or the developer If the ratio of 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 The problem is that it becomes more likely to be damaged.

SUMMARY OF THE INVENTION An object of the present invention is to provide a new two-color development method that prevents the toners from mixing when performing first and second development using toners of two different colors. The feature is that the first development is a jumping development using a one-component non-magnetic developer made of non-magnetic toner, and the second development is a jumping development using a one-component magnetic developer made of a magnetic toner.

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. Image carrier (photoreceptor) in the following steps () and () carried out in the image recording apparatus shown in FIGS. 2 and 1.
The horizontal axis shows the surface potential of the photoreceptor, and the vertical axis shows the surface potential of the photoreceptor. 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. Se as the photoconductive layer,
Although any suitable photoconductive material can be used, such as ZnO ₂ , OPC, etc., 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 V _p due to uniform charging is approximately 1000 V in the illustrated example.

In step (), the uniformly charged surface of the photoreceptor is irradiated with light as a first light information irradiation for a portion of the recorded image other than the portion 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 lower than the intermediate potential V _S in the next step () (second step).
It is assumed that the value is sufficient to drop to approximately zero (in the figure). The above light irradiation is transmitted light or reflected light from the original, laser light scanning modulated with image information signals, CRT
This can be carried out using 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 V _S. 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 suppresses positive corona discharge, so it is maintained as it is.

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, a first latent image corresponding to an image portion having a positive potential relative to the intermediate potential V _S and to be printed in black, and a first latent image having a relatively negative potential with respect to the intermediate potential V S 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 developed, that is, visualized, by a first developing device 5 as a step, and then by a second developing device 6 as a step (). A developing bias voltage corresponding to the intermediate potential V _S 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 first latent image in the step () using the first developing device 5.
In addition, in the step () using the second developing device 6, the second developing device 6
Red toner adheres to the latent image and the intermediate potential V _S
No toner adheres to the 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 using the same method.

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 units corresponding to the first developing unit 5 and the second developing unit 6 in FIG. 1, respectively. In this embodiment, the developing device 5 performs jumping development using a one-component non-magnetic developer that is a black non-magnetic toner mainly composed of resin and does not contain carrier iron powder. 6 is a red magnetic toner mainly composed of a magnetic material such as magnetite and resin, and is subjected to jumping development using a one-component magnetic developer containing no carrier iron powder. 11 and 12
are cylindrical sleeves in contact with the toner supplied into the developing devices 5 and 6, respectively, and are approximately connected to the photoreceptor 1.
They face each other at a distance of 300μ, and rotate in the direction of movement of the photoreceptor at a circumferential speed approximately equal to the speed of movement of the photoreceptor. Sleeve 1 of magnetic jumping developer 6
A magnet 15 having a developing magnetic pole N ₁ at least at a position facing the photoreceptor is provided inside the magnet 2 . 13 and 14 are toner coating blades, and urethane blades with a hardness of about 60° are used.
60~ on the sleeves 11, 12 due to the blade
The toner is coated to a thickness of 80μ. Incidentally, in order to ensure stable toner coating, irregularities of R _Z =1 to 2 μm are formed on the sleeve surface. 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. Measure the roughness of the standard length (0.25 mm), draw a cross-sectional curve, and calculate the distance between the third peak from the highest peak and the third valley from the deepest valley. The distance between the two is 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 FIGS. 1 and 2, the non-magnetic toner in the developing device 5 is charged with a negative polarity, and the magnetic toner in the developing device 6 is charged with a positive polarity. The toner material and charge control agent of each developer are selected. Of course, the above charge may be directly applied to the toner coating on the sleeve using a corona charger or the like. Each sleeve 11,
The toner coated on 12 then approaches the photoreceptor as the sleeve rotates, and jumps from the sleeve to the photoreceptor surface depending on the photoreceptor surface potential and adheres thereto, thereby forming the first and second latent images. Each becomes visible. In this case, alternating current bias voltages 16 and 17 biased by a direct current component voltage of +500 V are applied as developing bias voltages to the respective sleeves. The alternating current bias is described in detail in Japanese Patent Application Laid-open No. 18657/1983 filed by the present applicant.

Next, the developing characteristics of the first and second developing devices will be explained with reference to FIGS. 4 and 5. FIG. 4 shows the characteristics of jumping development using non-magnetic toner. 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 developing with non-magnetic toner, the relationship between the sleeve and the photoreceptor must be
An AC voltage with a peak-to-peak voltage V _pp of 2000 V or more is applied as the AC portion of the developing bias voltage to the 300μ gap, and the toner is moved back and forth between the sleeve and the photoconductor to make it easier to adhere to the photoconductor surface. (This effect is tentatively called toner activation.) Also, in order to prevent fogging, the amount of alternating current should be
It is necessary to use a high frequency voltage of 2kHz or higher.
In Figure 4, 4-a is V _pp = 2000V, frequency = 2k
This is a characteristic curve when using an AC component voltage of Hz. 4-b in the same figure shows the characteristics when an AC voltage of V _pp =1.2 kV, =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 characteristics of jumping development using magnetic toner. The meanings of the horizontal and vertical axes are the same as in FIG. 4. In addition, in the figure, conditions 5-a and 5-b are the fourth
This is the same as 4-a and 4-b in the figure. In this case, sufficient image density can be obtained even with a lower frequency and lower voltage alternating current than in the case of non-magnetic toner, for example, =1000 Hz, V _pp =1.2 kV. When using magnetic toner, the reason why the toner is sufficiently activated and the image density is high even at V _pp = 1.2 kV despite the magnetic binding force acting in the developing section (the area where the photoreceptor and sleeve are close) The main reason for this is that the magnetic toner fluffs up to a height of about 200μ along the lines of magnetic force in the developing section, and the binding force due to the mirroring force acting between it and the sleeve surface is significantly weakened. In the case of development using magnetic toner, the same AC bias conditions as in the case of development using non-magnetic toner, i.e. =
If it is 2000Hz and V _pp =2kV, the toner will be too dark and the image will be foggy, which is not desirable.

Based on the above, the first developing device 5 has = 2k
A developing bias voltage is applied which is a superimposition of an AC component of Hz, V _pp = 2000 V and a DC component of V _DC = +500 V, and a developing bias voltage of = 1 kHz, V _pp =
It is desirable to apply a developing bias voltage in which an alternating current component of 1.2 kV and a direct current component of V _DC = +500 V are superimposed.

With this configuration, the non-magnetic toner deposited on the photoreceptor by the first developer 5 does not become acicularly fluffy in the developing magnetic field of the second developer 6, and is not disturbed in the magnetic field. It never happens. Further, under the above-mentioned developing bias voltage condition applied to the second developing device, the non-magnetic toner adhering to the photoreceptor is hardly activated between the photoreceptor and the sleeve of the second developing device. Therefore, it is possible to obtain beautiful two-color copies without color mixture.

As described above, according to the present invention, the first color images corresponding to the image portions to be printed in two different colors, respectively, are printed in two different colors.
A first step to visualize the latent image and the second latent image, respectively.
Both the development step and the second development step are jumping development using a one-component developer, and
By using a non-magnetic toner in the developing step and a magnetic toner in the second developing step, it is possible to obtain clear two-color copies without developer deterioration and color mixture.

Although the above embodiments have been described only in the case of the latent image forming process described in FIGS. 1 and 2, the present invention can also be implemented in the case of other two-color latent image forming processes. Of course.

[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 the jumping developer using the non-magnetic toner shown in Figure 3.
FIG. 3 is a diagram showing the development characteristics of a jumping developer using the magnetic toner shown in the figure. DESCRIPTION OF SYMBOLS 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 developing device, 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 development method in which a two-color image is obtained on an image carrier by sequential development in a device, the developer supporting member of the first developing device is a non-magnetic one-component developer thinner than the gap between this and the image carrier. The developer support member of the second developing device supports the magnetic one-component developer layer, which is thinner than the gap between the developer layer and the image carrier, and supports the developer layer to face the image carrier.
A first AC bias voltage is applied to the developer support member of the first developing unit, and a second A two-color development method characterized in that a second AC bias voltage having a peak-to-peak voltage and a frequency smaller than the first AC bias voltage is applied to a developer supporting member of a developing device.