JPH083675B2 - Image recording device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image recording apparatus, and particularly to a first latent image and a second latent image corresponding to image portions of two different colors on the surface of an image carrier. To form the first latent image and the second latent image.
The present invention relates to an image recording apparatus for sequentially developing a latent image with a first developing device and a second developing device having toners of different colors to obtain a two-color image.

2. Description of the Related Art In recent years, with the spread of copiers, computers, computers, facsimile machines, etc., documents copied or printed out are not only printed in one color, but also in two colors including red, for example. Is required to do so.

Conventionally, various devices for such a two-color linter have been proposed, and one of the most effective devices is a first latent image corresponding to two different color image portions on the surface of an image carrier. And a second developing device which forms a second latent image and which has toner of different colors from the first latent image and the second latent image.
This is an image recording apparatus for sequentially developing with a developing device to obtain a two-color image. That is, this apparatus uses a so-called two-color superposition developing method, but has a defect that two color toners are easily mixed.

The cause is that the developing device used in such a conventional image recording apparatus is a so-called two-component developing device that uses a two-component developer in which iron powder is used as a carrier and toner is mixed in an amount of about 10% by weight. The second developing device for developing the second color has 2
When it is a component developing device, it scrapes off the toner image of the first color formed by the first developing device when rubbing the photoconductor, and when the carrier is deteriorated or toner in the developer is deteriorated. When the ratio decreases, the toner hardly adheres to the photoconductor in both the first and second developing devices, and the toner image of the first color is damaged when the photoconductor is rubbed by the second developing device. It will be easier.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image recording apparatus which can achieve color mixture prevention by superposition development using toners of two different colors and can obtain a two-color image of good image quality. .

Means for Solving the Problems The above object is completely achieved by the image recording apparatus according to the present invention. To summarize the present invention, the present invention develops a first latent image formed on an image carrier with a first developing device to form a first toner image, and then carries the first toner image. The second latent image on the body is developed by the second developing device to form a second toner image having a color different from that of the first toner image, and then the first toner image is formed.
And an image forming apparatus for collectively transferring the second toner image onto a transfer material, wherein the second developing device includes a developing roller provided at a predetermined interval with respect to the image carrier, and between the developing roller and the image carrier during development. A means for applying a bias voltage to the developing roller to form an alternating electric field on the developing roller, the bias voltage causing the toner to fly to the image carrier side, and a developing suppressing section for returning the toner to the developing roller side. An image forming apparatus, comprising: a voltage pause unit for a predetermined time between development promotion and development suppression.

The image recording apparatus of the present invention can be suitably used for an image recording apparatus such as an electrophotographic copying apparatus, a printer such as a computer, a facsimile machine, etc., but in the following, the embodiments of the present invention will be described. Will be described in relation to the case where the so-called Carlson process is applied to an image recording apparatus.

FIG. 1 is a schematic sectional view showing an example of an image recording apparatus to which the present invention can be applied. 2 (I) to (VI) are the following steps (I) to (V) performed in the image recording apparatus of FIG.
The surface potential of the image bearing member in I) is shown, the horizontal axis shows the surface area of the photoconductor, and the vertical axis shows the surface potential of the photoconductor. In this embodiment, the image bearing member is an electrophotographic photosensitive member, and the photosensitive member 1 is, for example, a so-called Carlson type photosensitive member in which a photoconductive layer is provided on a conductive base layer in a drum shape. Rotate to. S for the photoconductive layer
Any suitable photoconductive material such as e, ZnOz, OPC can be used, but Se is used in this example.

In step (I), the surface of the photoconductor 1 is uniformly charged by the corona discharger 2. Charging is performed up to the Se allowable charge level. The surface potential Vp of the photoreceptor due to uniform charging is about 1000V in the illustrated example.

In step (II), as the first light information irradiation, the uniformly charged surface of the photosensitive member is irradiated with light 3 on a portion of the recorded image other than the portion to be printed in black. The intensity of this light irradiation is such that the potential of the portion of the surface of the photoconductor that receives the light irradiation is equal to or lower than the intermediate potential Vs in the next step (III) (second
Sufficient to go down to almost zero in Figure (II). The light irradiation can be performed by using the transmitted light or the reflected light of the original, or the laser light scanning modulated by the image information signal, the CRT spot scanning, or the light of the light emitting element such as the LED array.

In step (III), the photoconductor that has received the first light information irradiation is controlled by the control corona discharger 11 to obtain the corona discharger 2
Then, a positive corona discharge having the same polarity as that of the above is applied, and as a result, the portion of the surface of the photoconductor that has been irradiated with light in step (II) has a positive intermediate potential Vs of about 500V. This control corona discharger has a control grid, and a voltage corresponding to the intermediate potential Vs is applied to the control grid, and the fluctuation of the sensitivity of the photoconductor 1 and the fluctuation of the light information irradiation intensity are caused. It is possible to compensate for an undesired fluctuation factor and enable stable and favorable image formation. At this time, the first light information irradiation step, that is, the step (I
In I), the electric potential of the portion of the photoreceptor surface that has not received light irradiation is about 1000 V, which is an electric field that suppresses positive corona discharge between the portion of the photoreceptor surface and the control grid of the control corona discharger 11. Is formed and is maintained as it is.

Next, in step (IV), the surface of the photoconductor is irradiated with light 4 as the second light information irradiation on the portion of the recorded image to be printed in red. The intensity of this light irradiation is sufficient so that the potential of the surface of the photoconductor that has received the light irradiation falls to a sufficiently low value (about +100 V in this embodiment).

As described above, the first latent image corresponding to the image portion to be printed in black and having a positive potential relative to the intermediate potential Vs, and the negative potential relative to the intermediate potential are negative. A second latent image having an electric potential and corresponding to the image portion to be printed in red is formed on the surface of the photoreceptor 1.

The first and second latent images formed on the photoconductor are then subjected to the step (V) by the first developing device 5 for the first latent image, and then in the step (VI) for the second developing device by the second developing device. 6 develops, that is, visualizes. That is, each developing device is applied with a developing bias voltage corresponding to the intermediate potential Vs, and the first developing device 5 is charged with negatively charged black toner, and the second developing device 6 is charged with positively. Use red toner. Therefore, on the surface of the photoreceptor 1, the first developing device 5
In the step (V) according to step (V), the black toner is applied to the first latent image, and in the step (VI) by the second developing device 6, the second toner is added to the second toner.
Red toner adheres to the latent image, and none of the toner adheres to the intermediate potential Vs portion.

The photoconductor thus developed is then subjected to a corona discharger 7
After the polarities of the toners are aligned by, the toner image is transferred onto the transfer paper 9 by the transfer corona discharger 8. As a result, the transfer paper 9 gives a recorded image printed in two colors, black and red, on a white background color paper.

On the other hand, the photoreceptor after transfer is repeatedly used after the residual toner on the surface is removed by the cleaning blade 10.

In the image recording apparatus, the first latent image is formed so as to correspond to the red image portion, and the second latent image is formed so as to correspond to the black image portion, and the first developing device receives the red toner and the second developing device produces the black toner. Even if each of these latent images is developed with toner, a two-color print image can be recorded in the same manner.

Further, the present invention is not limited to the above-mentioned two colors of black and red,
Of course, it can be carried out in the case of another two-color latent image forming process.

Next, in the above-mentioned image recording apparatus, according to the present invention, as will be understood with reference to FIG. 3, the jumping developing method is used in the second developing apparatus.

The developing apparatus has a developing sleeve 22, as disclosed in detail in Japanese Patent Publication No. 58-32375. The developing sleeve 22 and the photosensitive drum 21 are separated by about 300
Opposing them with a small gap of μ, forming a thin layer of magnetic toner or non-magnetic toner on the sleeve, moving in the same direction as the photosensitive drum at almost the same speed, and applying an alternating bias voltage to the developing sleeve. By doing so, the toner is flown from the developing sleeve 22 to the surface of the photosensitive drum 21 through the narrow gap to visualize the latent image on the photosensitive drum.

At this time, a bias voltage is applied to the developing device in order to cancel the mirroring force acting on the toner layer and the sleeve surface, and to give the toner a chance to fly in the drum direction and a sufficient flying speed. An alternating voltage having a frequency f = 400 to 2000 Hz and a peak-to-peak voltage Vpp = 1000 to 2000 V is applied as a bias voltage AC component by 23.

However, when using toner with a diameter of about 10μ,
When an alternating electric field of 0 Hz is applied, a proper image is obtained at Vpp = 1000 to 1200 V. If it is higher than 1200 V, toner fog occurs on a white background, and if it is lower than 1000 V, fine lines are not sufficiently reproduced. When an alternating electric field of about 2000 Hz is used, Vpp = 1300-2000V is the voltage range for obtaining an appropriate image, and fog occurs at a voltage higher than this, and if it is lower than this, the image of fine line reproduction is insufficient. Becomes

In other words, the toner flying condition has an appropriate range determined by f and Vpp, and if the ratio of toner staying near the drum in a low frequency and high electric field is high, a fogging image is formed, and in a high frequency and low electric field. It was found that the image reproduction, especially the fine line portion, becomes insufficient as the ratio of the toner staying near the sleeve increases.

Further, when the image quality with respect to the peripheral speed of the photosensitive drum was examined under the above bias conditions, it was found that the image reproducibility was approximately the same under the same bias conditions between about 50 mm / sec and 300 mm / sec. This means that the developing property reaches saturation when the toner reciprocates through the narrow gap between the photosensitive drum and the sleeve a dozen times.

According to the present invention, the Jean developing method is adopted for the second developing device, and the number of reciprocation of the toner between the developing sleeve and the surface of the photosensitive drum is minimized to minimize the color mixture. is there.

FIG. 4 shows an AC alternating voltage waveform according to the present invention. Basically, one round trip of the conventional alternating waveform is taken out,
It is applied intermittently at a specific interval to a narrow gap by a waveform converter. The position t _{1 of the} voltage waveform is the development promoting portion, and the toner is caused to fly to the drum to develop the toner. Further, t ₂ is a development suppressing portion, which has an effect of pulling back the toner in the vicinity of the drum to the sleeve side, and in particular has a function of pulling back the toner adhering to the white background portion of the drum to prevent the occurrence of fog. At the subsequent voltage rest part t ₃ , the toner is conveyed while being adsorbed on the sleeve.

As will be understood from the above description, according to the present invention, the bias is applied as described above until the photosensitive drum latent image bearing surface has completely passed through the developing area facing the developing sleeve. By selecting the minimum number of times necessary to obtain good image quality,
Since the influence of the second development on the first development can be suppressed to a minimum, it is possible to obtain a two-color image with less color mixture in the development using different toners.

Examples will be shown below to illustrate the present invention, but these do not limit the present invention in any way.

Example 1 When developing a second latent image formed on a photosensitive drum having a peripheral speed of 200 mm / sec, a sleeve is rotated at a substantially constant speed in the same direction as the drum, and a frequency of 80 is generated in a narrow gap between the drum and the sleeve.
An alternating voltage of 0 Hz and Vpp1300V was applied for each frequency. The color mixture on the obtained two-color copy was very small.

Example 2 In developing the second latent image on the photosensitive drum similar to that in Example 1, a frequency of 1800 Hz, Vp was applied between the drum and the sleeve.
An alternating voltage of p1800V was applied for one cycle, and waveform-controlled so as to pause the following two cycles. The obtained two-color copy was an image with very little color mixture as in Example 1.

Example 3 Frequency 1800 Hz, Vpp180 was set in the narrow gap between the drum and the sleeve.
An alternating voltage of 0 V was applied for 3 cycles, and a bias was applied in such a manner that the following 6 cycles were paused, and an image with less color mixture was obtained as in Example 2.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an example of an image recording apparatus according to the present invention. 2 (I) to (VI) are diagrams showing the surface potential of the photoconductor in the steps performed in the image recording apparatus of FIG. FIG. 3 is a schematic sectional view of an example of a developing device used in the image recording apparatus of the present invention. FIG. 4 is a diagram showing a waveform of an AC alternating voltage in the present invention. 1: Photoconductor 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 developing device 7, 8: Corona Discharger 9: Transfer material 10: Cleaning blade 11: Control corona discharger 21: Photosensitive drum 22: Development sleeve 23: AC bias source

Claims (1)

[Claims] 1. A first latent image formed on an image bearing member is developed by a first developing device to form a first toner image, and then a second toner image on the image bearing member bearing the first toner image. In an image forming apparatus that develops a latent image with a second developing device to form a second toner image having a color different from that of the first toner image, and then transfers the first and second toner images collectively onto a transfer material, The second developing device includes a developing roller provided at a predetermined distance from the image carrier, and means for applying a bias voltage to the developing roller to form an alternating electric field between the developing roller and the image carrier during development. This bias voltage includes a development promoting section that causes the toner to fly to the image carrier side, a development suppressing section that returns the toner to the developing roller side, and a voltage pause section for a predetermined time between the development promotion and the development suppression. An image forming apparatus having.