JPS6345108B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrophotographic developing method and apparatus,
In particular, electrostatic latent images with different polarities formed corresponding to two-color images formed on the white background of the document are developed with two types of toners that are charged to different polarities and colored in different colors. The present invention relates to an electrophotographic developing method and apparatus.

Generally, in this type of image reproduction method, two types of electrostatic latent images having mutually different polarities or mutually different potentials are formed on an electrostatic latent image carrier such as a photoconductor, corresponding to a two-color image. These two types of electrostatic latent images are developed using two types of developers colored in different colors using two developing devices.

In such an image reproduction method, when the second development is performed, a visible image has already been formed on the electrostatic latent image carrier by the first development, and therefore,
The second development is performed in a manner that overlaps the first development.

Further, in such an image reproduction method, a magnetic brush developing device is generally used, and in this magnetic brush developing device, the magnetic force of the developing roller causes
A magnetic brush is formed on the surface of the electrostatic latent image carrier, and the magnetic brush moves while contacting the surface of the electrostatic latent image carrier.
As a result, the electrostatic latent image on the electrostatic latent image carrier is developed.

In such a magnetic brush developing device, it is very easy to transport the developer to the developing section, but when the stiff magnetic brush comes into contact with the developed image,
An image that has already been developed may be destroyed or a portion of it may be scraped off, and the scraped developer may mix into the second developer and contaminate it.

The present invention provides an electrophotographic development method and method in which a two-color image can be developed with two magnetic brushes without disturbing or destroying the first, already developed image during the second development process. The purpose is to provide equipment.

According to the present invention, the second developing device is constructed such that the second magnetic brush of the second developing device contacts the electrostatic latent image more lightly than the first magnetic brush of the first developing device; The first developed image is not destroyed by the second magnetic brush. Further, the amount of charge per unit weight of the first developer for developing the first electrostatic latent image is the amount of charge per unit weight of the second developer for developing the second electrostatic latent image. By increasing the adhesion force of the first developed image to the electrostatic latent image carrier compared to that of the second image, the first developed image is I'm trying to keep it from being destroyed.

Hereinafter, the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows an example of an electrophotographic apparatus capable of two-color copying, red and black, which is applied to an embodiment of the present invention. It consists of a first photoconductive layer 1b having a high spectral sensitivity and a second photoconductive layer 1c formed on the first photoconductive layer 1b and having sensitivity only to red light. Around the photosensitive drum 1, in the order of the image forming process for two-color copying, a primary charger 3, a secondary charger 4, an image exposure section 5, a magnetic brush type first developing device 6, and a magnetic brush type first developing device 6 are installed. A second developing device 7, a polarity adjustment charger 8, a transfer charger 9, a fixing device 11, a quenching charger 12, and a cleaning device 13 are provided. In addition, code 2 in the figure
indicates a light source provided in the primary charger 3, and 14 indicates a red filter.

The photosensitive drum 1 rotates counterclockwise,
First, the surface is positively charged by the first charger 3 while being irradiated with light from the red light source 2 . Then, a positive charge is held on the surface of the photoreceptor and a negative charge is held inside. Next, when the surface of the photoreceptor is negatively charged by the second charger 4, the positive charges on the surface of the photoreceptor are neutralized except for some of the charges that are bound to the internal negative charges. The photoreceptor surface potential is reversed to negative. When an optical image of an original having red and black images on a white background is projected onto the surface of such a photoreceptor,
Light from the area corresponding to the red image passes through the second photoconductive layer 1c on the surface of the photoreceptor, dissipates the negative charge held in the first photoconductive layer 1b inside, and increases the surface potential of that area. Turn it right again. On the other hand, since light from a portion corresponding to a black image hardly acts on the surface of the photoreceptor, the surface potential of the photoreceptor in that portion also remains negative. In this way, an electrostatic latent image is formed in which the portion corresponding to the red image is positive and the portion corresponding to the black image is negative. This process is described in US Pat. No. 912,273. First, an electrostatic latent image corresponding to a red image is developed using the negatively charged red toner 6a in the first magnetic brush developing device 6. To facilitate understanding, the toner on the surface of the photoreceptor is illustrated in a large scale. Next, the positively charged black toner 7a in the second magnetic brush developing device 7 develops an electrostatic latent image corresponding to a black image. The red toner and black toner on the photoreceptor are charged with opposite polarities, so before transfer, they are aligned negative or positive with the adjustment charger 8, and then transferred with the transfer charger 9. The image is transferred onto the transfer paper 10 by the following steps. After the transfer, the transfer paper 10 is separated from the photoreceptor surface,
The two-color toner image is permanently fixed on the transfer paper through the fixing device 11. After the surface of the photoreceptor is neutralized by the static eliminating charger 12, the cleaning device 1
3 removes residual toner on the surface.

As the magnetic brush developing devices 6 and 7, all conventionally known magnetic brush developing devices can be applied. Both of the illustrated magnetic brush developing devices attract developer onto a non-magnetic developing sleeve that statically houses a magnet to form a magnetic brush, which is transported by the rotation of the sleeve. Developing is carried out by bringing a magnetic brush into contact with the surface of the photoreceptor.

As described above, the present invention prevents the first toner image developed by the first developing device 6 from being destroyed by the second developing device 7, thereby preventing the first toner image and the second developing device from being destroyed. The purpose is that the second toner image developed by the device 7 is equally developed, and the following factors are important for this purpose, for example: The rotational direction and rotational speed of the first developing sleeve 6b and the second developing sleeve 7b with respect to the rotational direction and rotational speed of the photosensitive drum 1, the magnetic flux density in the first developing device 6 with respect to the magnetic flux density in the second developing device 7, and the The first developer and the second developer, including the charge amount of the toner of each of the first developer and the second developer.
Properties of development, first developing device 6 and second developing device 7
developer concentration and toner concentration.

The above factors are important because by appropriately setting at least one of the above factors, the above objectives are achieved.

In the first method according to the present invention for achieving the above object, the respective rotational directions of the first developing sleeve 6b and the second developing sleeve 7b with respect to the rotational direction of the photoreceptor drum 1 are set as follows. This causes the magnetic brush formed on the second developing sleeve 7b to come into contact with the surface of the photosensitive drum 1 weaker than the magnetic brush formed on the first developing sleeve 6b. The one toner image is not disturbed or destroyed during the second development.

That is, in this first method, the developing sleeve 6b of the first developing device 6 is placed on the photosensitive drum 1.
The developing sleeve 7b of the second developing device 7 is rotated in the same direction as the photosensitive drum 1, that is, in the opposite direction at the point where both are closest, and the developing sleeve 7b of the second developing device 7 is rotated in the opposite direction to the photosensitive drum 1, that is, in the same direction at the point where both are closest. , and rotate at the same speed as the linear velocity of the photoreceptor drum. Hereinafter, in this specification, the direction of movement of the developing sleeve and the photoreceptor is assumed to be at a point where the developing sleeve and the photoreceptor are close to each other. By doing this, in the first developing device, the magnetic brush comes into contact with the rotating photoreceptor surface from the opposite direction, so the sliding force is strong, and in the second developing device, the magnetic brush comes into contact with the rotating photoreceptor surface from the opposite direction. , contact the surface of the photoreceptor from the same direction and at the same speed, so the sliding force is also weak.

In the second method according to the present invention, the magnetic flux density on the second developing sleeve 7b is set lower than the magnetic flux density on the first developing sleeve 6b. This makes the second magnetic brush softer than the first magnetic brush. In this second method, the second magnetic brush, which is softer than the first magnetic brush, prevents the first toner image from being destroyed. The magnetic flux density of each of the developing sleeves 6b and 7b can be set by adjusting the magnetic force of each of the magnets 6c and 7c, or by adjusting the magnetic flux density of each of the developing sleeves 6b and 7b.
and 7b by adjusting the positions of magnets 6c and 7c.

In the third method of the present invention, the distance between the second developing sleeve 7b and the surface of the photoreceptor drum 1 is
The distance is set larger than the distance between the developing sleeve 6b and the surface of the photoreceptor drum 1. Second developing sleeve 7
As the distance between b and the surface of the photoreceptor drum 1 increases, the magnetic brush formed on the second developing sleeve 7b becomes larger than the magnetic brush formed on the first developing sleeve 6b. The second magnetic brush contacts the first toner image more softly, thereby preventing destruction of the first toner image by the second magnetic brush.

FIG. 3 shows the principle of the mechanism described above. In FIG. 3, developer particles 2 on the developing roller 21
2 are connected in a chain along the lines of magnetic force of a magnet 23 provided inside the developing roller 21 to form a magnetic brush. The density of the magnetic brush, that is, the developer density is high near the developing roller 21, while the density of the magnetic brush, that is, the developer density is low near the electrostatic latent image carrier 24. Therefore, the larger the distance between the developing roller 21 and the electrostatic latent image carrier 24, the lower the density of the magnetic brushes near the electrostatic latent image carrier 24. Conversely, the smaller the distance between the developing roller 21 and the electrostatic latent image carrier 24, the higher the magnetic brush density near the electrostatic latent image carrier 24, and the greater the magnetic brush scraping force.

In the fourth method of the present invention, the first developing sleeve 6
By finishing the surface of the first developing sleeve 6b, the second developing sleeve 7b, or both surfaces so that the surface area of b is larger than that of the second developing sleeve 7b, the first developing sleeve 6
The developer density on the second developing sleeve 7b is made higher than that on the second developing sleeve 7b.

In the fifth method of the present invention, the amount of charge per unit weight of one toner is made larger than the amount of charge per unit weight of the other toner. By charging the two toners in this manner, the two toner images can be formed independently without being adversely affected by each other.

The above five methods hold other conditions constant,
Each can be used separately or in combination.

In the following examples, in order to understand the effectiveness of each of the above-mentioned methods, each method was evaluated while keeping other conditions constant.

Example 1 This is an example of the first method described above, and the conditions are as follows.

First, a photoreceptor drum 1 was prepared by the following method.

Se is applied onto the Al drum substrate 1a at a substrate temperature of 50℃.
The first photoconductive layer 1b was formed by vapor deposition to a thickness of 40 μm. A solution having the composition shown below was applied onto this layer to a thickness of 22 μm by a dipping method, and dried at 50° C. for 5 minutes to form a second photoconductive layer 1c.

4-P-dimethylaminophenyl-2.6-diphenylthiopyrylium perchlorate 0.1g 4.4'-bis(diethylaluminum)-2.2'-dimethyltriphenylmethane 2.1g Teijin Panlite K-1300 2.8g Methylene chloride 60g The first developer was prepared by the following method.

First, 100 parts by weight of polystyrene and 5 parts by weight of C.I. A first developer was prepared by mixing treated iron powder (Fe ₃ O ₄ ) (hereinafter referred to as "carrier").

Next, FT-200O for Ricoh's FT-2500 copier
Black toner 3% by weight and carrier 97 above
A second developer was prepared by mixing the weight percentages.

The red toner is negatively charged to have a charge amount of 15 μc/g, and the black toner is charged to a negative polarity of 15 μc/g.
It was positively charged to have a charge amount of .

The distance between the photosensitive drum 1 and each of the developing sleeves 6b and 7b was set to 3.5 mm.

First developing sleeve 6b and second developing sleeve 7
The magnetic flux density of each on b was set to 450 Gauss.

A bias voltage of +100 volts is applied to the first developing sleeve 6b, while the second developing sleeve 7b
A bias voltage of -150 volts was applied to. A red filter 14 is placed on the surface of this photoreceptor drum 1.
Using an R-64 filter manufactured by Hoya Glass Co., Ltd.,
While irradiating the light from a 100W tungsten lamp through this, primary charging is performed at +6.5KV to obtain a surface potential of +1500V on the photoreceptor drum 1, and then secondary charging is performed at -5.7KV in a dark place. Set the surface potential of drum 1 to -600V. The surface of this photoreceptor drum 1 is irradiated with a light image of an original image consisting of red, white, and black, and the surface potential of the photoreceptor drum 1 in the portion corresponding to red is +390V, and the surface potential in the portion corresponding to white is −50V. The surface potential of the black portion was set to -580V. Under the conditions shown in FIG. 2, this change in the surface potential of the photosensitive drum 1 causes the photosensitive drum 1, the first developing sleeve 6b, and the second developing sleeve 7b to move in the direction of the arrow shown in FIG. Rotated. The best development was obtained when the linear velocity of the photosensitive drum 1 was 180 mm/sec and the first developing sleeve 6b and the second developing sleeve 7b were each rotated at a linear velocity of 540 mm/sec.

Example 2 This is an example of the second method described above.

In Example 1, the magnetic flux density above the first developing sleeve 6b and the magnetic flux density above the second developing sleeve 7b were respectively varied. Specifically, the former
in the range of 500 to 700 Gauss, the latter in the range of 200 to 350 Gauss. First developing sleeve 6b
The best development was obtained when the upper magnetic flux density was set at 500 Gauss and the magnetic flux density on the second developing sleeve 7b was set at 360 Gauss. When the magnetic flux density on the surface of the second developing sleeve 7b is smaller than 360 Gauss, the magnetic brush formed on the second developing sleeve 7b is too weak for development, and carrier adhesion is observed on the surface of the photoreceptor drum 1. It was done. Further, when the magnetic flux density on the surface of the second developing sleeve 7b exceeds 360 Gauss, the magnetic brush on the second developing sleeve 7b is so strong that some of the toner is scraped off from the first toner image.

Example 3 This is an example in which the effect of the third method described above was confirmed.

In Example 1, the surface of the photoreceptor drum 1;
The distance between each of the developing sleeves 6b and 7b was changed.

Prior to this third embodiment, for the purpose of investigating the relationship between two distances: the distance between the surface of the photoreceptor drum 1 and the first developing sleeve 6b, and the distance between the surface of the photoreceptor drum 1 and the second developing sleeve 7b. , conducted preliminary experiments. In this preliminary experiment, the first developer was placed in the first developing device 6, and only the carrier was placed in the second developing device 7. The results are shown in FIGS. 4 and 5. FIG. 4 shows the relationship between the adhesion of toner to the photoreceptor drum 1 and the distance between the first developing sleeve 6b and the surface of the photoreceptor drum 1. As can be seen from FIG. 4, when this distance d is set larger than 2 mm, toner adhesion decreases, and therefore,
The density of the developed image decreased. Figure 5 shows the second
The relationship between the adhesion of toner to the photoreceptor drum 1 and the distance between the second developing sleeve 7b and the surface of the photoreceptor drum 1 when only the carrier is put into the developing device 7 is shown. As can be seen from the graph in FIG. 5, when this interval became smaller than 5 mm, the toner that had already adhered to the surface of the photoreceptor drum 1 was scraped off from the surface of the photoreceptor drum 1.

The amount of toner scraped off from the surface of the photoreceptor drum 1 decreased as the distance between the surface of the photoreceptor drum 1 and the second developing sleeve 7b increased, but if the distance was too large, the image of the second toner image Example 3 confirmed that the concentration was too low. According to the results of Example 3, the distance between the surface of the photoreceptor drum 1 and the first developing sleeve 6b was set to 3.5 mm, and the distance between the surface of the photoreceptor drum 1 and the second developing sleeve 7 was set to 3.5 mm.
The best development was obtained when the distance from the surface of b was set to 4.0 mm.

Example 4 This is an example of the fourth method described above.

In the first embodiment, as shown in FIG. 6, the surface of the first developing sleeve 6b is knurled or mesh-like, and the surface of the second developing sleeve 7b is uneven.
As shown in FIG. 7, the surface of b is flat or coarsely textured. As a result, the surface area of the first developing sleeve 6b is made relatively larger than that of the second developing sleeve. As a result of making 5,000 copies using these developing sleeves 6b and 7b, the red toner was not mixed into the developer of the second developing device 7, and good quality copies were obtained.

For comparison, 3000 copies were made by replacing both the first developing sleeve 6b and the second developing sleeve 7b with developing sleeves having twilled surfaces. As a result, it was observed that red toner was mixed into the developer of the second developing device 7. Furthermore, when only the first developing sleeve 6b was replaced with a developing sleeve having a planar surface, a decrease in the image density of the red toner image was observed.

Example 5 This is an example of the fifth method described above.

In Example 1, the second developer FT-
2000 black toner, commercially available U-
I used Bix toner.

Similarly to Example 1, the red toner was negatively charged to have a charge amount of 15 μc/g, while the black u-Bix toner was positively charged.
It was made to have a charge amount of 8 μc/g.

As a result, a red toner image with an image density of 0.7 and a black toner image with an image density of 1.0 were obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of a two-color electrophotographic copying apparatus equipped with a developing method and apparatus according to an embodiment of the present invention, and FIG. FIG. 3 is a schematic diagram of the magnetic brush formed on the photosensitive drum of the copying machine of FIG. 1, and FIG. Figure 5 shows the relationship between toner adhesion on the first developing roller and the distance between the photosensitive drum and the developing roller. A diagram showing the relationship between the adhesion of toner on the roller and the distance between the second developing roller and the photosensitive drum. FIG. 6 is a perspective view of a non-magnetic sleeve having a twill-like uneven surface. FIG. , a perspective view of a non-magnetic sleeve having a planar uneven surface. DESCRIPTION OF SYMBOLS 1... Electrostatic latent image bearing member, 6... First magnetic brush developing device, 6b... First non-magnetic developing sleeve, 6c... First magnet, 7... Second magnetic brush developing device, 7b... ...Second non-magnetic developing sleeve, 7
c...Second magnet.

Claims (1)

[Claims] 1. Electrostatic latent images formed with different polarities on an electrostatic latent image bearing member are developed with two types of toners each charged with a different polarity and colored with a different color. The electrophotographic developing device includes a first non-magnetic developing sleeve and a first magnet provided therein, and the first non-magnetic sleeve is provided close to the surface of the electrostatic latent image carrier. a first magnetic brush developing device capable of forming a magnetic brush on its surface; a second non-magnetic material developing sleeve; and a second magnet provided inside the second non-magnetic material developing sleeve; The developing sleeve is provided close to the surface of the electrostatic latent image carrier and includes a second magnetic brush developing device capable of forming a magnetic brush on the surface thereof, and the developing sleeve includes a second magnetic brush developing device capable of forming a magnetic brush on the surface of the developing sleeve. The second magnetic brush developing devices are provided adjacent to each other, and the force of the second magnetic brush developing device for scraping off toner from the surface of the electrostatic latent image carrier is equal to that of the first magnetic brush. An electrophotographic developing device characterized by being set smaller than. 2. The electrostatic latent image carrier and the first non-magnetic developing sleeve are rotated in the same direction, and the second non-magnetic developing sleeve is rotated in a direction opposite to the rotating direction of the electrostatic latent image carrier. As a result, the force of the second magnetic brush developing device for scraping off toner from the surface of the electrostatic latent image carrier is set to be smaller than that of the first magnetic brush developing device. Claim 1 characterized in that
The electrophotographic developing device described in Section 1. 3. The magnetic flux density on the second non-magnetic developing sleeve is set lower than the magnetic flux density on the first non-magnetic developing sleeve, so that the electrostatic latent image carrier of the second magnetic brush developing device 2. The electrophotographic developing device according to claim 1, wherein a force for scraping toner from the surface is set smaller than that of the first magnetic brush developing device. 4 The distance between the second non-magnetic developing sleeve and the surface of the electrostatic latent image carrier is set to be larger than the distance between the first non-magnetic developing sleeve and the surface of the electrostatic latent image carrier, and According to the patent, the force of the second magnetic brush developing device for scraping toner from the surface of the electrostatic latent image carrier is set smaller than that of the first magnetic brush developing device. An electrophotographic developing device according to claim 1. 5. The surface area of the first non-magnetic sleeve is set larger than the surface area of the second non-magnetic developing sleeve, so that toner from the surface of the electrostatic latent image carrier of the second magnetic brush developing device is 2. The electrophotographic developing device according to claim 1, wherein a scraping force of said first magnetic brush developing device is set smaller than that of said first magnetic brush developing device. 6. An electrophotographic developing device that develops electrostatic latent images formed with mutually different polarities on an electrostatic latent image bearing member using two types of toners charged with mutually different polarities and colored with different colors. It consists of a first non-magnetic developing sleeve and a first magnet provided inside the first non-magnetic developing sleeve, the first non-magnetic developing sleeve being provided close to the surface of the electrostatic latent image carrier, It consists of a first magnetic brush developing device capable of forming a magnetic brush on its surface, a second non-magnetic developing sleeve, and a second magnet provided inside the second non-magnetic developing sleeve, and the second non-magnetic developing sleeve comprises: a second magnetic brush developing device that is provided close to the surface of the electrostatic latent image carrier and capable of forming a magnetic brush on the surface thereof, the first magnetic brush developing device and the second magnetic brush developing device; The brush developing device is an electrophotographic developing device that is installed adjacent to each other and is characterized in that the amount of charge per unit weight of one toner is set to be larger than the amount of charge per unit weight of the other toner. Photographic development method.