JPS60122961A - Image forming device - Google Patents

Abstract

PURPOSE:To form an image of more colors than the number of developing devices by simple constitution, by applying a bias voltage of a different potential to plural developing devices through an applying path, respectively, and switching selectively its applying path by a switching means. CONSTITUTION:A blue toner and a red toner are supplied by the first developing device 4 and the second developing device 5, respectively, a colorless leuco dyestuff is contained in the blue toner, and a color developing agent is contained in the red toner. Also, a bias voltage of a different potential is applied to the first and the second developing devices 4, 5 through applying paths 7a, 7b by first and the second power sources 7, 8, respectively. Also, by operating a switching circuit 6, the first and the second developing devices 4, 5, the first and the second power sources 7, 8 and also an earth are switched and connected as a combination. In this way, development of red, blue and black can be executed, and development of more colors than the number of developing devices can be executed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to, for example, an electrophotographic image forming apparatus that repeatedly performs development using developers of different colors to perform multicolor recording.

[Technical background of the invention and its problems]

Conventionally, this type of image forming apparatus has been
The one disclosed in No. 5-38561 is known. This device projects light with an intensity corresponding to the recorded image onto a uniformly charged recording drum, thereby forming a latent image with a potential distribution corresponding to the color of the recorded image. A number of developing devices are provided corresponding to the number of colors, and each color is developed to produce multicolor printing.

That is, as shown in FIG.
, v2, which corresponds to the recorded color, and develop the portion η by applying a bias voltage of v2 or less to the first developing device, and then applying a slightly lower bias voltage to the second developing device. The voltage is applied to develop the portion v2.

By the way, the horse part in the second developing device mentioned above.

As a result of experiments, it has been confirmed that when developing the part, the part marked ■□ is also developed at the same time. Therefore, there was a problem that the first developer and the second developer were mixed in the part (■).

Therefore, in order to solve this problem, it has been considered to limit the color of the first developing device to black or a color close to black, so that even if other colors are mixed in, it will not cause much inconvenience. .

However, in this case, since only black and one other color can be recorded, it is extremely limited and has the disadvantage of narrowing the range of use.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide an image forming apparatus which has a simple configuration and which can form images with more colors than the number of developing units. This is what we are trying to provide.

[Summary of the invention]

In order to achieve the above object, the present invention includes switching means for selectively switching the application paths of a plurality of voltage application means that apply bias voltages to a plurality of developing devices through respective application paths.

[Embodiments of the invention]

The present invention will be described below with reference to an embodiment shown in FIGS. 2 to 5. In the figure, reference numeral 1 denotes an electrophotographic photosensitive drum as a photosensitive member, and this photosensitive drum 1 is designed to be rotated in the direction of the arrow in the figure. A charger 2 is connected to a power source (not shown) so as to uniformly charge the surface of the photosensitive drum 1 to a potential as shown in FIG. Reference numeral 3 denotes a recording light beam, and this light beam 3 is scanned by a scanning device (not shown) and exposes the surface of the photosensitive drum 1 stepwise to an intensity corresponding to the number of recording colors. Further, 4 is a first developing device, and 5 is a second developing device, the first developing device 4 supplies blue toner, and the second developing device 5 supplies red toner. It has become so.

The blue toner contains a colorless leuco dye known for thermal recording paper, and the red toner contains a color coordination developer such as a phenolic compound.

Further, bias voltages having different potentials are applied to the first and second developing units 4 and 5 through application paths 7a and 7b by the first and second power sources 7 and 8, respectively, which serve as voltage application means. It is supposed to be done. A switch circuit 6 as a switching means is provided in the application paths 7a and 7b, and when the switch circuit 6 is operated, the first and second developing units 4, 5 and the first and second power supplies are connected to each other. 7,8
Furthermore, it is possible to switch connections with earth in combination. The first power supply 7 applies a bias voltage slightly lower than the potential V, and the second power supply 8 applies a bias voltage slightly lower than the potential V. There is. Reference numeral 9 denotes a recording paper, on which a toner image developed on the photosensitive drum 1 is transferred by a transfer device 10.

Further, 11 is a cleaning device for erasing an afterimage on the photosensitive drum 1.

For example, when recording the black characters 12 and front frame 13 of a document P as shown in FIG. 30), the surface of the photosensitive drum 1 is charged by the charger 2 as shown in FIG.
Then, the part of the black letters 12 is changed to '1,' by the light beam 3.
The intensity is modulated and exposed so that the W frame 13 has a potential of v2.

Thereafter, by operating the switch circuit 6, the first developing device 4 and the first power source 2 are connected, and the second developing device 5 and the second power source 8 are connected. At this time, a bias voltage with a slightly lower potential is applied to the first developing device 4, and blue toner is supplied to the portions 12a and 12b of the photosensitive drum 1 at the potentials 1 and 1, respectively. A bias voltage with a potential slightly lower than the potential edge is applied to the second developing device 5, and red toner is supplied only to the portion 12m of the photosensitive drum 1 at the potential v1 for development.

In this state, the portion 12m of potential v8 is purple due to the mixture of red toner and blue toner, but this image is transferred to recording paper 9, sent to a fixing device (not shown), and heated and fixed, resulting in a blue color. The leuco dye in the toner and the color developer in the red toner react to turn it black.

First, a case will be described in which black characters 12 and red characters 14 are recorded as shown in FIG. 3(b).

At this time, after uniformly charging the photosensitive drum 1 to a potential, the light beam 3 charges the black text area 12 to the potential ■ 1 red text area 1
4 is exposed to a potential v2. Next, by operating the switch circuit 6, the first developing device 4 is switched to the second developing device 4.
At the same time, the second developing device 5 is connected to the first power source 7.

Accordingly, a bias voltage slightly lower than the potential V is applied to the first developing device 4, and a bias voltage slightly lower than the potential V0 is applied to the second developing device 5. Due to this application, the potential on the photosensitive drum 1 from the first developing device 4 is
Blue toner is supplied to only the □ portion 12m and developed, and then the second developing device 5 is used to develop the stain position v1 and the potential v2.
Red toner is supplied to both portions 12h and 13IL and developed.

In this state, the portion 12a at the potential v1 is purple due to the developer and the mixture of blue toner and red toner, as described above, but it becomes black during fixing.

Next, as shown in FIG. 3(a), a case will be described in which black characters 12, room frames 13, and red characters 14 are recorded. At this time, during the first rotation of the photosensitive drum 1, as shown in FIG. 5, exposure is performed so that the black letters 12 are at the potential V□ and the back frame 13 is at the potential end.

Thereafter, by operating the switch circuit 6, the first developing device 4 is connected to the first power source 7, and the second developing device 5 is connected to the second power source 8. As a result, the portion 12h of the potential v1 on the photosensitive drum 1 is developed with both red and blue toners, and the portion 13a of the potential v2 is developed with blue toner. Then, during the second rotation of the photosensitive drum 1, as shown in FIG.
The red text portion 14 is exposed to the potential of (■). Afterwards,
By operating the switch circuit 6, the first power source 7 applied to the first developing device 4 is connected to the ground line, and the second power source 8 is connected only to the second developing device. Potential V and a lower bias voltage are applied to the developing device 5, and the portion 12h of potential N is developed again with red toner, but the potential V2
A portion 13m with potential V corresponding to the red character portion 14 is developed with red toner.

Note that during this development, it is necessary to separate the cleaner 11 from the photosensitive drum 1 and not allow it to act until the photosensitive drum 1 begins to rotate twice.

Further, the recording paper 9 is conveyed in synchronization with the timing of the 102nd rotation of the photosensitive drum, and the black characters (purple at the time of the sword J and F images), back frame, and red characters are transferred and fixed.

As described above, the connection of Ml and the second power supplies 7 and 8 to the first and second developing units 4.5 is made by the switch circuit 6.
By switching, it is possible to develop red, blue, and black colors, and it is possible to perform multicolor development regardless of the number of developing devices.

In the above embodiment, a light beam is used for exposure, but the invention is not limited to this. Light from a light source can be turned on using a light switching array such as a laser diode and its playback, a cathode ray tube, or a liquid crystal. - A multi-stylus or ion injector may be used instead of light by using a photosensitive drum as a dielectric. / element may be used.

Further, as the developing method, for example, a developing method such as that disclosed in Japanese Patent Application Laid-Open No. 56-27158 may be used. According to this, mixing between toners can be prevented and good results can be obtained.

Of course, the toner color is not limited to red or evening, and any color may be used, and furthermore, the order of development is not similarly restricted.

Furthermore, when the toner image is transferred to the recording paper and fixed,
In order to make the black area sufficiently black, it is preferable that the toner containing the colorless dye be on top, and therefore it is better to develop the toner containing the colorless dye first.

〔Effect of the invention〕

As described above, the present invention selectively switches the application paths of the plurality of voltage application means for applying bias voltages of different potentials to the plurality of developing devices through the application paths, so that the application paths of the plurality of developing devices are selectively switched. It is possible to carry out development in more colors than the number of colors, and has the effect of widening the range of use.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing potential distribution on the surface of a photoreceptor in a conventional example, FIGS. 2 to 5 show an embodiment of the present invention, and FIG. 2 is a schematic configuration showing an image forming apparatus. 3(a) to 3(c) are plan views showing various types of originals, and FIGS. 4 and 5 are explanatory diagrams showing potential distribution on the surface of the photoreceptor. 1... Photoreceptor, 4... First developing device (developing device), 5
... second developing device (developing device), 7... first power supply (
voltage application means), 8... second power supply (voltage application means)
, 7h, 8k... application path, 6... switch circuit (switching means). Fig. 1 Drum circumference ii 1 Fig. 2 Fig. 3 (A) (B) (l\) 1'2 Fig. 4 Y-ram circumferential direction Fig. 5 69 Ram circular direction

Claims (3)

[Claims] (1) In a device that forms a latent image with different potentials on a photoreceptor and develops the latent image in multiple colors by supplying different color developers to the latent image using a plurality of developing devices, each of the plurality of developing devices is provided with an application path. 1. An image forming apparatus comprising: a plurality of voltage applying means for applying different bias voltages to supply the developer; and a switching means for selectively switching application paths of these voltage applying means. (2) One of the developers of the plurality of developing devices contains a colorless dye that turns the colorless dye black by a color developer, and the other developer contains a color developer that turns the colorless dye black. An image forming apparatus according to claim 1. (3) Claim 1 or 2 that allows switching between two modes in which images are formed by rotating the photoreceptor once or twice.
The image forming apparatus described in .