JPH0634127B2 - Color recording device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color recording apparatus based on an electrophotographic recording method, an electrostatic recording method, or the like, and more particularly, a color recording apparatus in which color mixing does not occur even when continuous recording is performed. Regarding

(b) Background of technology With the diversification of information, there is a demand for colorization of output information. Even in the field of recording devices using electrophotographic recording methods and electrostatic recording methods, color recording and multicolor recording are being demanded without exception.

In a recording apparatus using such an electrostatic latent image, color recording is performed by visualizing the latent image with toners of different colors in each developing step when the latent image forming step and the developing step are sequentially repeated for recording. . In such a recording apparatus, it is necessary to consider so-called color mixing, in which toners of different colors are mixed with each other and recording with the original color cannot be performed.

(c) Conventional Technology and Problems This phenomenon of color mixing will be described by taking a two-color color recording apparatus adopting an electrophotographic recording system as an example.

In electrophotographic recording, the surface of the photosensitive drum is uniformly charged, a latent image corresponding to the image of the first color is formed by laser light, and the toner of the first color is supplied from the developing unit to generate the first color. To form a toner image. By carrying out such a process a plurality of times in sequence, a composite toner image composed of multicolor toners is obtained, and the composite toner image is transferred onto a recording sheet to perform color recording.

In such a color recording apparatus, paying attention to the second developing section, supplying the second color toner to the photosensitive layer on which the toner image of the first color toner has already been formed in the second developing section. Becomes At this time, a part of the toner forming the toner image of the first color is peeled off and mixed in the second developing section. As a result, if recording is performed for a long time, the toner of the first color accumulates in the developer of the second developing section, which causes a problem that color development is mixed in the second developing section. When the first color toner and the second color toner have different polarities, it is relatively easy to separate them by utilizing the difference in polarity, but in the case of the same polarity, Since it is difficult to separate, all the developers are conventionally replaced when color mixture occurs. In this situation, the occurrence of color mixing shortens the life of the developer.

(d) Object of the Invention In view of the above, the present invention separates the different color toner mixed in the developer from the developer by utilizing the difference in the adhesion threshold electric field of the toner, and thus the recording is performed for a long time. A color recording device that does not mix colors is provided.

(e) Structure of the Invention For this purpose, the present invention is directed to a latent image forming medium, a charging means for supplying electric charge to the medium, and a latent image forming electrostatic latent image corresponding to an image to be recorded on the latent image forming medium. An image forming unit, a plurality of developing units for visualizing the electrostatic latent image, and a transfer unit for transferring the visualized toner image onto a recording sheet are provided, and the charging, latent image formation and development are sequentially repeated a plurality of times. In a color recording apparatus in which a multicolor toner image is formed on a latent image forming medium and then the multicolor toner image is collectively transferred to the recording paper, the developer in each of the developing units is a toner of the same polarity. , And each of which has a different adhesion threshold electric field and has a separating roller provided in the vicinity of each developer carrying member, and between the separating roller and the developer carrying member, the different toner Separation of adhesion threshold electric field A roller for separating only the toner in the other developing means mixed in the developer from the developer carrier by having a power source means for forming an electric field having an intermediate value between the toner adhesion threshold electric field and the toner non-separation threshold electric field. And is separated from the developer.

(f) Embodiments of the Invention Hereinafter, embodiments of the color recording apparatus according to the present invention will be described in detail.

FIG. 1 is a schematic diagram of a two-color color recording apparatus that employs an electrophotographic recording system. The recording apparatus in FIG. 1 includes a photosensitive drum 11, a charger 12a, a first exposing section 13a, a first developing section.
14a, recharger 12b, second exposure section 13b, second development section
14b, a transfer unit 15, a static eliminator 16, a cleaner 17, and a static elimination lamp 18.

The photosensitive drum 11 as a latent image forming medium has a photosensitive layer on its surface.
It has 11a and rotates at a constant speed in the direction of the arrow. The charger 12a and the recharger 12b are charged by supplying charges to the photosensitive layer 11a. First exposure section 13a and second exposure section 13b
By irradiating the photosensitive layer with laser light or the like
A latent image corresponding to the color image or the second color image is formed on the photosensitive drum 11. The first developing section 14a and the second developing section 14b form toner images by supplying toners of the first color and toners of the second color which are different from each other to the corresponding latent images to visualize the latent images. To do. The transfer device 15 has a transfer corotron 15 a and transfers the toner image formed on the photosensitive drum 11 onto the recording paper 19. The static eliminator 16 neutralizes the electric charge on the photosensitive drum 11 and the electric charge of the toner, thereby facilitating the removal of the residual toner in the cleaner 17. The charge eliminating lamp 18 serves to keep the surface potential of the photosensitive layer constant, and exposes the entire surface of the photosensitive layer.

FIG. 2 shows the detailed structure of the developing unit 14a, and FIG. 3 shows the developing unit 14b.
The detailed configuration of is shown.

In FIG. 2, the developing section 14a includes a housing 21, a developing roller 22 as a developing carrier, and a doctor blade 23. The developing roller 22 includes a magnet roller 22a and a sleeve 22b made of a non-magnetic material (for example, aluminum). The developer 24 is a two-component developer including a carrier 24a and a toner 24b. The carrier 24a has a resistivity of 10 ¹² to 10 ¹⁶ Ωcm and a particle size of 5 to 50.
The toner 24b is a so-called microcarrier made of a magnetic substance of μm, and the toner 24b is made of an insulating nonmagnetic substance. The sleeve 22b is fixed, and the developer 24 is conveyed in the arrow direction by rotating the magnet roller 22a in the arrow direction. The layer thickness of the developer 24 is defined by the doctor blade 23. The developing roller 22 and the photosensitive drum 11 face each other so that the photosensitive layer 11a and the developer layer maintain a contact depth δ. Although not shown, a developing bias voltage is applied between the developing roller 22 and the photosensitive drum 11.

On the other hand, the developing unit 14b has substantially the same configuration as the developing unit 14a, but they are different in the following points. That is, as shown in FIG. 3, the developing unit 14b has a roller 31 for separating a conductor which faces the developing roller 22 with a gap and rotates in the arrow direction. The position where the separating roller 31 is provided is the developer 34.
Immediately after contact with the photosensitive layer. A power source 32 is provided between the separating roller 31 and the developing roller 22. The power supply 32 forms an electric field between the separating roller 31 and the developing roller 22, and in this example, a DC voltage is applied between the two as shown in the figure.

The developer 34 in the second developing section 14b is a two-component developer and has the same carrier resistivity and particle size as those of the developer 24 in the developing section 14a, but the toner adhesion threshold electric field is different. That is, FIG. 4 is a toner adhesion characteristic diagram, in which the horizontal axis represents the latent image intensity ΔV and the vertical axis represents the print density. When the D value is taken, the developer 24 shows a rapid OD at a latent image intensity of 100 V as shown in (A). D value increased, toner 24
However, as shown in FIG. 7B, the developer 34 has a latent image strength of 200 V or more. The D value does not increase and the amount of toner 34b attached does not increase sharply. Therefore,
Even if the toner 24b of the developer 24 is mixed in the developer 34, the voltage of the power source 32 for forming the electric field between the separating roller 31 and the developing roller 22 is set to an intermediate value between 100V and 200V. It is possible to adhere only the toner 24b from the developer 34 to the surface of the separating roller 31 without adhering the toner 34b to the surface of the separating roller 31. The toner 24b attached to the separating roller 31 is removed from the surface of the roller 31 by the scraping plate 33.

Next, the recording process will be briefly described with reference to FIG. Note that FIG. 5 shows the potential on the photosensitive drum in each step.

First, the surface of the photosensitive layer 11a is charged to the potential Vs by the charger 12a (FIG. 5 (a)). A latent image corresponding to the image of the first color is formed by the first exposure unit 13a (Fig. 5).
(b)). This electrostatic latent image is visualized by forming a toner image by supplying the toner 24b of the first color by the first developing section 14a set to the developing bias voltage VB1 (Fig. 5).
(c)). At this time, the developing bias voltage VB1 is equal to the threshold voltage 100
It is set so that 100V <VB1 with respect to V.

Further, the potential of the image portion of the first color is raised by the recharging device 12b (FIG. 5 (d)), and a latent image is formed by the second exposure portion 13b (FIG. 2 (e)), and development is performed. The second developing unit 14b having the bias voltage set to VB2 forms an image with the toner 34b of the second color (FIG. 5 (f)).
At this time also, similarly to the above, the developing bias voltage VB2 is set so that 200V ≦ VB2 with respect to the threshold voltage of 200V.

Therefore, when the photosensitive drum 11 has passed the second developing portion 14b, a composite toner image of the two color toners 24b and 34b is formed on the surface of the photosensitive drum. This synthetic toner image is transferred onto the recording paper 19 by the transfer device 15, and is fixed on the recording paper by passing through a fixing unit (not shown). The residual toner on the surface of the photosensitive drum 11 on which the transfer is completed is removed by the static eliminator 16, the cleaner 17, and the static elimination lamp 18, and the potential is made constant.

Here again, focusing on the second developing unit 14b, the developing unit 14b
Since the toner image of the toner 24b has already been formed on the surface of the photosensitive layer 11a, the toner formed on the surface of the developing roller 22 is partly separated from the toner image during the development. May be mixed in layers. However, 100V is applied between the developing roller 22 and the separating roller 31.
Toner mixed in because voltage between 200V and 200V is applied
Only 24b is attached to the surface of the separation roller 31 by the electric field and separated from the developer, so that the different color toner 24b is prevented from being mixed into the developer 34.

Although the above-mentioned embodiment describes the electrophotographic recording method, the same applies to a recording apparatus of a method of forming an electrostatic latent image on a drum having an electrostatic recording layer by a pin electrode or an ion flow control method. it can. Further, the present invention is not limited to two colors, and the same applies to multicolor recording of three or more colors. However, at that time, since the toner adhesion threshold electric field in each developing portion is different, the value of the voltage applied between the developing roller and the separation roller in each developing portion needs to be different. Further, the developer is not limited to the two-component developer, and the one-component developer containing magnetic powder in the toner can be considered in the same manner. Further, the separating roller 31 may have an endless belt shape instead of the roller shape.

Here, the developing method will be considered. The developing method is roughly classified into a contact developing method and a non-contact developing method. The former is for developing with the developer and the photosensitive layer in contact with each other. In the above-described embodiments, as the contact developing method, the soft developing method in which the contact depth δ is reduced by using the microcarrier having a small particle size and the already formed toner image is not destroyed is described.
On the other hand, in the non-contact developing method, the photosensitive layer and the developer are opposed to each other through a gap, and an alternating voltage or a biased alternating voltage is applied between the two to fly the toner to develop the toner image. More effective against destruction. The present invention can be applied to a recording apparatus that employs any developing method, but in the case of a recording apparatus that employs the non-contact developing method, the voltage applied between the developing roller and the separation roller is It must be an AC voltage that is AC or DC biased in synchronism with the voltage applied to. Although the voltage changes when an alternating voltage is applied to the developing roller and the separation roller, the potential difference between the rollers can be made constant by applying a synchronized alternating voltage. That is,
Since the voltage is applied so that this potential difference becomes a voltage between 100 V and 200 V, only the mixed toner 24b is attached to the surface of the separation roller 31 by the electric field and separated from the developer, so that the developer Mixing of the different color toner 24b into the 34 is prevented.

Further, this separation step can be always performed only by applying a voltage to the separation roller during the normal development step.

(g) Effect of the Invention As described above, according to the present invention, the toner adhesion threshold electric field of the developer in each developing means is made different, and the developer carrying member is used in the second and subsequent developing means among the developing means. A separating roller provided in the vicinity of the developing roller is arranged, and an electric field is formed between the separating roller and the developer carrying member so that only the toner in the other developing means mixed in the developer is carried by the developer carrying member. From the developer and is attached to a separating roller. Therefore, it is possible to prevent the toner of a different color from being mixed into the developer, and it is possible to perform stable recording without color mixture without replacing the developer for a long time.

[Brief description of drawings]

The drawings relate to the present invention. FIG. 1 is a schematic diagram showing a two-color recording apparatus using an electrophotographic recording system, and FIG.
3 is a block diagram showing the details of the first developing unit 14a in the drawing, FIG.
1 is a block diagram showing the details of the second developing section 14b in FIG. 1, FIG. 4 is a characteristic diagram of adhesion threshold with respect to the electric field of toner, and FIGS. 5 (a) to 5 (f) are photosensitive drum surfaces in each recording step. FIG. 6 is an electric potential diagram showing a potential change of FIG. In the figure, 11 is a photosensitive drum, 12a is a charger, 12b is a recharger, 13a and 13b are exposure parts, 14a and 14b are development parts, 22 is a development roller, 24 and 34 are developers, and 24a and 34a are carriers. ,twenty four
b and 34b are toners, 31 is a separation roller, and 32 is a power source.

Claims (1)

[Claims] 1. A latent image forming medium (11), charging means (12a, 12b) for supplying electric charges to the medium, and an electrostatic latent image corresponding to an image to be recorded on the latent image forming medium (11). And a plurality of developing means (14a) for visualizing the electrostatic latent image having latent image forming means (13a, 13b) for forming an electrostatic latent image and a developer carrier (22) for conveying the developer to the electrostatic latent image. , 14b) and the visualized toner image on the recording paper (1
And a transfer means (15) for transferring to the latent image forming medium (11) by sequentially repeating the charging, latent image formation and development a plurality of times.
In a color recording apparatus in which a multicolor toner image is formed on the recording paper (19) after the multicolor toner image is formed thereon, the developer in each of the developing means (14a, 14b) is triboelectrically charged. The toners having the same charging polarity according to, and different adhesion threshold electric fields, each have a separation roller (31) provided in the vicinity of each developer carrying member (22). 31) and the developer carrier (22), an electric field of an intermediate value between the adhesion threshold electric field of the toner to be separated and the adhesion threshold electric field of the toner not to be separated among the different toner adhesion threshold electric fields. Forming power means (3
The roller for separating only the toner in the other developing means mixed in the developer by having 2) from the developer carrier (22).
A color recording device characterized in that it is attached to (31) and separated from the developer.