JPS6331777B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is characterized in that two latent images of different polarities formed on a latent image carrier are formed using two-color powder toner that is charged to opposite polarities from a first and second developing unit. The present invention relates to a two-color developing device that sequentially supplies and develops.

As a method of reproducing a two-color image, two latent images with different polarities are formed on a latent image carrier such as a photoreceptor in an electrophotographic device or a dielectric material in an electrostatic recording device by image exposure, signal application, etc. However, a method is known in which this is sequentially developed using two color toners charged with opposite polarities. Two-color images in ordinary documents often have red images scattered within a black image with a white background. That is, it is a form in which red underlines, letters, etc. are scattered among letters and figures expressed in black on a white background. In the latent image formed based on such a document, first, a red image portion occupying a small portion is developed with red toner.
Subsequently, the predominantly black image area is developed with black toner. Therefore, development with black toner is performed over the already developed red toner image. As a result, especially in a method such as the magnetic flush development method, in which the surface of the latent image carrier is rubbed by a magnetic brush made of toner, the red toner image is rubbed by the magnetic brush made of black toner, and the red toner image is rubbed by the magnetic brush made of black toner. A situation occurs where part of the image is scraped off and sneaks into the black toner. Since the red toner is strongly electrostatically adsorbed to the surface of the latent image carrier, the amount that is scraped off is very small, but it gradually increases as development is repeated, changing the color tone and development characteristics of the black toner and reducing the image quality. This results in a decrease in color or the occurrence of a mixed color image.

In order to avoid such mixing of toner into the second developer, the applicant of the present application previously filed a patent application filed in 1983-
In 51916, we proposed a new developing device. This is because a charged separating roller with an insulating layer on its surface is placed downstream of the developing section of the developing roller in the second developing unit where toner is mixed in, and only the mixed toner is attached to this separating roller. The second developer is separated from the second developer. However, in this prior invention, the separation of mixed toner by a separation roller is
Since this is carried out in the vicinity of the developing roller or in the vicinity of the scraping plate for scraping toner from the developing roller, there is a drawback that the mixed toner that has penetrated into the second developer cannot be removed.

An object of the present invention is to provide a two-color developing device that overcomes the drawbacks of the prior invention.
In the second developing unit, the toner scraped off from the developing roller by a scraping plate is once dropped from the scraping plate, diffused, and then received by a separation roller or a separation belt. 2. It is characterized by being able to remove mixed toner that has gotten into the developer.

Hereinafter, the present invention will be described with reference to the attached drawings. First, an example of a two-color electrophotographic apparatus will be described with reference to FIG. A photoconductor drum 1 that rotates at a constant speed in a counterclockwise direction has a first photoconductive layer 3 that is insensitive to red light on a conductive support 2;
A second photoconductive layer 4 sensitive to red light is laminated thereon. Around the photoreceptor drum 1, from the top along the rotation direction, a first charger 5,
A second charger 6, a first development unit 7, a second development unit 8, an adjustment charger 9, a transfer charger 10,
A static eliminating charger 11 and a cleaning device 12 are respectively arranged. The first and second developing units 7 and 8 are conventional magnetic brush developing devices, and the first developing unit 7 contains a first developer 13 consisting of red toner and carrier, and the second developing unit 7 contains a first developer 13 consisting of red toner and carrier.
The developing unit 8 accommodates a second developer 14 consisting of black toner and carrier.

When the surface of the photosensitive drum 1 is first positively charged by the first charger 5 while being irradiated with red light from the red lamp 15, the given positive charge becomes conductive due to the light irradiation. second photoconductive layer 4
The photoconductive layer moves within the photoconductive layer 3 and is captured near the interface with the first photoconductive layer 3. Subsequently, when the photoreceptor 1 is negatively charged by the second charger 6, negative charges are distributed on the surface and positive charges are distributed inside. When the surface of this photoreceptor is irradiated with a light image 16 of a two-color original having a black image and a red image on a white background, almost all of the charged charges are discharged in the part of the photoreceptor that is hit by the white light. The photosensitive surface potential of that part becomes almost zero, and in the part exposed to red light, the negative charge on the second photoconductive layer sensitive to red light is discharged, so the photoreceptor surface potential of that part becomes internal. Since there is almost no light from the black part, the surface potential of that part becomes negative due to the negative charge on the surface. The latent image formed by such a charge distribution is first developed by supplying red toner negatively charged by friction with the carrier from the first developing unit 7, and then developing the red toner corresponding portion. 2. Black toner positively charged by friction with the carrier is supplied from the developing unit 8 to develop the black corresponding portion. The two-color toner image thus obtained on the photoreceptor is re-charged to negative polarity by the adjustment charger 9 to make the polarity uniform, and then a transfer paper 17 is placed on top of the two-color toner image and charged for transfer. The two-color toner image is positively charged by a container 10 and a negatively charged two-color toner image is transferred onto a transfer paper 17 . After the transfer paper 17 is separated from the surface of the photoreceptor, the toner image is fixed onto the transfer paper by the action of the fixing device 18. On the other hand, the photoreceptor drum is subjected to the action of the charger 11 for eliminating charges, so that the charges remaining on the surface and inside are erased, and then the toner remaining on the surface is removed by the cleaning device 12.

In such an electrophotographic apparatus, contamination of red toner occurs within the second developing unit 8.
Therefore, separation of the mixed red toner takes place within the second developing unit. FIG. 2 is a schematic diagram of a second developing unit showing an embodiment of the present invention. The unit housing 21 is open on the side facing the photoreceptor drum 1, and seal members 22 are provided on both sides of the opening in the axial direction of the photoreceptor. The developing sleeve 23 is rotatably provided in the housing unit 21 in a clockwise direction so that a part of its surface can be seen through the opening of the housing unit 21. Inside the developing sleeve 23, magnets 25, 26, and 27 are attached at predetermined positions on the circumferential surface of the fixed shaft 24. magnet 25
In this case, the sleeve 23 is placed closest to the surface of the photoreceptor, that is, the developing position, the magnet 27 is placed at the lowest position, and the magnet 26 is placed approximately in the middle thereof. These constitute a developing roller. The upper tip of the scraping plate 28 is in contact with the right shoulder of the developing sleeve 23, and the entire scraping plate 28 is disposed obliquely downward. The tip of the scraping plate 28 may be placed in close proximity to the sleeve surface. Below the lower end of the scraping plate 28, there is a separation roller 29, the surface of which is a conductive roll coated with an insulating layer.
It is arranged to be rotatable in a counterclockwise direction. This insulating layer is preferably made of the same resin as the resin constituting the black toner in the developer 14 in the housing. A blade 30 is disposed on the lower surface of the separation roller 29 with its tip in contact with the blade 30 and oriented in a counter direction with respect to the rotation of the separation roller.
A receiving container 31 is arranged below the blade 30. The blade 30 is a separation roller 29
It is used to frictionally charge the surface of the separation roller by rubbing the surface, and to remove toner adhering to the separation roller.

The surface of the separation roller 29 must be charged to a polarity that attracts mixed red toner. If the red toner is negatively charged, the separation roller must be positively charged. Therefore, the material of the blade 30 is determined in consideration of the order of triboelectrification in relation to the material of the surface of the separation roller. If the separation roller surface is made of the same material as the resin that makes up the black toner, for example styrene-acrylic copolymer, and the blade is made of the same material as the carrier, for example iron oxide, then the separation roller surface will have the same polarity as the black toner. That is, since it is charged to the opposite polarity to that of the red toner and to a voltage that is approximately the same as the specific charge of the black toner, only the red toner can be effectively attracted.

The developer 14 in the housing is stirred by an impeller 32, and the black toner and magnetic carrier in the developer are triboelectrically charged. Since the particle size of the carrier is larger than that of the black toner, the black toner adheres to the periphery of the carrier. The carrier is attracted to the sleeve surface by the magnet 27 in the sleeve 23 along with the black toner. The developer adsorbed on the sleeve surface is transported upward as the sleeve rotates, but on the way, the amount of developer adhering to the developer is properly regulated by the doctor 33, and then held by the magnet 26. The magnet 25 reaches the position where it comes into contact with the surface of the photoreceptor 1 and develops the black latent image on the photoreceptor.

Since the red latent image on the photoreceptor has already been developed by the first developing unit, the black color is developed as follows.
This will be done from above the red toner image. At the developing position, the magnetic carriers of the developer are chained together along the lines of magnetic force of the magnet 25 to form brush-like spikes, and the red toner image is rubbed by these spikes, causing contact with the surface of the photoreceptor. A small amount of the red toner on the surface layer, which has weak adsorption power, is scraped off,
It gets mixed into the developer on the sleeve. After development, the developer on the sleeve is scraped off by a scraping plate 28, flows down on the scraping plate, and falls onto a separation roller 29 from its terminal end. At this time, the position of the separation roller is determined so that the developer from the scraping plate falls on the right half side of the separation roller. The separation roller surface has a blade 30 with the opposite polarity to the red toner, that is, the same polarity as the black toner.
Since the black toner is charged by the toner, the black toner is repelled and falls directly to the inner bottom of the housing, and the red toner is attracted to the surface of the separation roller. The adsorbed red toner is conveyed by the rotation of the separation roller and removed by the blade 30.
It is collected into a receiving container 31. The gap between the end of the scraping plate 28 and the surface of the separation roller is preferably equal to or smaller than the carrier diameter so that the carrier does not pass through.

FIG. 3 shows a second embodiment of the invention.
FIG. 2 is a schematic configuration diagram showing a developing unit. A major difference from the embodiment shown in FIG. 2 is that a wide separation belt 35 is used instead of a separation roller. The separation belt 35 is a conductive rubber belt coated with an insulating layer, and the support roller 3
6 and 37, and the whole is arranged tilting upward to the right. A tip of a blade 30 for frictional charging and toner removal is in contact with the lower belt portion, and a toner collection container 38 is constituted by the blade 30 and a housing cover outside the blade 30. An auger 39 for conveying toner is arranged inside the bottom of the container 38 to transport the collected toner.
It is carried out to the outside of the apparatus and, if necessary, transported into the first developing unit. Reference numeral 40 is a black toner replenishing device for maintaining developer concentration.

The black second developer containing the red toner scraped off from the top of the developing sleeve 23 by the scraping plate 28 falls onto the separation belt 35 that moves upward from the end of the scraping plate 28 . Since the surface of the separation belt 35 is charged by the blade 30 to the same polarity as the black toner or the opposite polarity to the red toner, among the fallen developer, the black toner and its carrier fall on the belt due to their own weight. The red toner is collected in the second black developer 14 in the device, and is adsorbed by the belt and conveyed as the belt rotates, and is transferred to the toner collection container 3 by the blade 30.
It is removed in 8. In this embodiment, since the separation belt is flat, the contact area with the developer from the scraping plate is large, and the toner recovery efficiency is further improved.

In these two embodiments, instead of charging the separation roller or separation belt with the blade 30, a bias voltage of opposite polarity to the red toner is applied to the conductive support of the separation roller or separation belt to charge the red toner. The surface can be charged. In this case, these surface insulating layers are not necessarily required.

FIG. 4 shows the structure of the second developing unit in yet another embodiment of the invention. A developer pumping sleeve 41 is disposed below the developing sleeve 23 so as to be rotatable in the clockwise direction, and magnets 43 and 44 are provided on a fixed shaft 42 therein. The black developer 14 is adsorbed onto the surface of the pumping sleeve 41 and then transferred onto the surface of the developing sleeve 23. The separation belt 45 consists of one flat wide conductive spring coil belt or a large number of ordinary conductive spring coil belts having a circular cross section, which are passed around a lower impeller 46, an upper drive roller 47, and an intermediate roller 48. A bias power supply 49 having a polarity opposite to that of the red toner is connected to the drive roller 47.
The separation roller 45 may be a conductive mesh belt or may have its surface coated with an insulating layer. An impeller 50 is disposed within the loop formed by the separation belt 45 and drives the drive roller 4 .
A rotating eccentric polygonal roller 51 is in contact with the belt portion between the roller 7 and the intermediate roller 48 .

The black developer containing the red toner scraped off by the scraping plate 28 falls from the end of the scraping plate 28 onto the coil spring belt 45 which is charged to the opposite polarity to the red toner. Since the coil spring belt 45 has many gaps, the black toner and its carrier fall downward through the gaps, and the red toner is attracted to the belt 45 and conveyed, and the eccentric roller 51 moves the belt. By hitting it, it falls into the container 38 and is carried out under the apparatus by the auger 39. Impeller 5
0 is for stirring and convecting the developer when the developer passing through the belt still contains red toner so that the contained red toner is adsorbed onto the belt. In this example,
Since the belt 45 is constantly vibrated by the eccentric roller 51, the black developer and red toner can be separated more effectively.

In the above explanation, it is the red toner that is separated from the black developer, but in the black developer, the black toner, which should originally be charged to the opposite polarity to the red toner, may also be separated to some extent due to various conditions. Since the toner may be charged to the same polarity as the red toner, such unnecessary black toner is also separated along with the red toner. However, in the present invention, the toner color is not limited to these colors.

Further, in the above description, the case is explained in which a two-component developer consisting of toner and carrier is used as the developer, but the present invention applies equally to the case where a one-component developer consisting only of toner is used. Can be implemented. When the one-component developer is a non-magnetic toner, a magnet is not required, and the structure of the developing roller is, of course, different. Further, the developer supplying member typified by the developing roller can also be configured in the form of a belt.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing an example of a two-color electrophotographic copying apparatus, FIG. 2 is a schematic configuration diagram of a second developing unit in an embodiment of the present invention, and FIG.
FIG. 4 is a schematic diagram of the second developing unit in another embodiment of the invention. FIG. 4 is a schematic diagram of the second developing unit in yet another embodiment of the invention. 23...Developing sleeve, 28...Scraping plate, 29
... Separation roller, 30 ... Blade, 31 ... Toner collection container.

Claims (1)

[Claims] 1. A two-color developing device in which two latent images of different polarities formed on a latent image carrier are sequentially developed by first and second developing units with toners charged to opposite polarities and of different colors, The second developing unit includes a rotatable developer supplying member for supporting a second developing toner on its surface and supplying the second developing toner to the surface of the latent image carrier, and a toner on the surface of the developer supplying member after development. a scraping plate whose tip is in contact with or in close proximity to the surface of the development donor member and is inclined diagonally downward; A two-color developing device comprising a toner separation member disposed opposite to the lower end of the removal plate and to which a bias having a polarity opposite to the charge polarity of the toner for first development is applied.