JPH0314178B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a developing method for an electrophotographic copying machine, and more specifically, a two-component developer using magnetic particles with an average particle size of 5 to 40 μm as a carrier and non-magnetic or weaker magnetic particles than the carrier with an average particle size of 5 to 20 μm as a toner. This invention relates to a magnetic brush development method for developing an electrostatic latent image on a sensitive material into a toner image. In the two-component magnetic brush development method that uses a small-particle carrier with an average particle diameter of about 5 to 40 μm, fine image quality with no sharp edges can be obtained because there are no scratches caused by the brush, and because the total surface area of the carrier is increased. It has advantages such as increased lifespan and expanded toner mixing ratio range. However, on the other hand, a conventional magnetic brush developing machine using a two-component developer has the disadvantage that it cannot be applied because the carrier adheres to the periphery of the electrostatic latent image and development efficiency decreases. That is, in the conventional two-component magnetic brush development method, a sleeve is rotated around the outer periphery of a fixed magnet, and the rotating sleeve conveys developer to develop an electrostatic latent image. However, in the developing nip area, the gap between the sleeve and the photosensitive material is set to be smaller than the layer thickness of the developer on the sleeve, so the developer is crushed and the developer density becomes high, reducing the speed of the carrier near the photosensitive material.・Some stagnation occurs. For this reason, conventional carriers with large particle diameters (60μ to 150μ) have a sufficiently strong magnetic attraction force, and even if the carrier stagnates, it is prevented from adhering to the photosensitive material and transported outside the developing nip area. In the case of a small particle carrier as mentioned above, there is not enough magnetic force to overcome the electrostatic attraction acting on the sensitive material, so the carrier whose momentum is reduced near the sensitive material has a polarity opposite to that of the toner. It adheres to the periphery of the electrostatic latent image on the photosensitive material and deteriorates the image quality. In addition, in the case of a conventional large particle carrier, as shown in Fig. 1, when a Coulomb force acts on toner a due to the developing electric field and the toner a tries to move toward the sensitive material B, there is sufficient force for the movement. Although space exists,
In the case of a small particle diameter carrier, as shown in FIG. 2, the toner a and the carrier c are packed together, and the movement of the toner a is blocked, resulting in a decrease in development efficiency. Therefore, as shown in Fig. 3, the sleeve d is kept stationary or rotated at a low speed, and the magnet e is rotated at a high speed to convey the developer f on its axis to solve the above-mentioned problem, and the small particle diameter carrier is used for development. A method is proposed. According to this developing method, since there is no stagnation of the developer (carrier) in the development nip area, there is no decrease in the momentum of the carrier near the photosensitive material, there is almost no adhesion of the carrier to the photosensitive material side, and the developer Due to the rotation of the toner, new toner is constantly brought into contact with the surface of the photosensitive material, so high development efficiency can be obtained. However, there is a limit to the number of rotations of the magnet e, and no matter how high the magnet e rotates, it cannot follow the rotational movement of the developer, so there is a limit to the conveying speed of the developer. This limit is estimated to be 150-200 mm/sec. Therefore, if the speed of the photosensitive material is faster than the developer transport speed limit, when developing an image with a long area in the scan direction, the density may decrease from the leading edge to the trailing edge, or the density may decrease from the leading edge to the trailing edge. When a halftone image (medium density image) is adjacent to a solid black image, white spots may occur on the halftone image. In other words, the above-mentioned problem occurs because the conveyance of the developer cannot fully follow the movement of the photosensitive material, so it cannot be applied to high-speed copying machines. Further, since the magnet e is rotated, the difference in the standing state between the magnetic poles and between the magnetic poles appears as uneven shading in the halftone image. The present invention was made in view of the above circumstances, and its purpose is to obtain a high-quality toner image by using a small-particle carrier and moving a sensitive material at a high speed of 150 mm/sec or more. An object of the present invention is to provide a developing method for an electrophotographic copying machine. That is, by fixing the magnet and rotating the sleeve, the developer is conveyed and developed. This eliminates the problem of the small particle carrier adhering to the periphery of the electrostatic latent image, which is a drawback of the developing method using the small particle carrier. In addition to eliminating the decrease in developing efficiency, the photosensitive material can be
This is a developing method that allows high-quality toner images to be obtained even in high-speed copying machines that move at a high speed of 1 sec. Examples of the present invention will be described below. FIG. 4 is an explanatory diagram of a magnetic brush developing device for carrying out the method of the present invention, in which first and second developing rolls 2 ₁ and 2 ₂ are arranged facing the photosensitive material 1, and each developing roll 2 is fixed. It is equipped with a magnet 3 and a sleeve 4 that rotates around the fixed magnet 3. Each sleeve 4 is driven to rotate in the same direction as the moving direction of the photosensitive material 1, and the fixed magnet 3 of the first developing roll 21 is rotated _around the photosensitive material. The part facing the photosensitive material 1 is the N pole, and the _other part is the S pole.
The other part of the pole serves as a north pole so that a repulsive magnetic field is generated at the developing magnetic pole in the developing nip area. With this developing device, the first and second developing rolls 2
By rotating the sleeves 4 and 4 of ₁ and ₂ in the same direction as the photosensitive material 1, the electrostatic potential on the photosensitive material 1 is developed using a two-component developer having a small particle carrier with an average particle size of 5 to 40 μm. If the image is developed into a toner image, the photosensitive material 1 will be 150 to 500
Even when moving at a speed of mm/sec, a high-quality toner image can be obtained, and it is possible to prevent the carrier from adhering to the periphery of the electrostatic latent image on the sensitive material and from reducing development efficiency. Next, an experimental example will be explained. Experimental Example 1 Carrier→ST/30% by weight of acrylic resin and 70 parts by weight of magnetic powder with an average particle size of about 0.5 μm dispersed, and the average particle size is 25 μm. Toner → Polyester resin containing 10% carbon black, average particle size 12μm
It is. Developer: A mixture of the above carrier and toner at a weight ratio of 100:8. Sensitive material moving speed → 400mm/sec Gap between sensitive material and sleeve → 1mm Magnet → Maximum 1200GAUSS (2 measurements on the sleeve) Using the above developer, the shape of the fixed magnet and the shape of the sleeve are determined using the developing device shown in Figure 4. The amount of development (development efficiency) and the adhesion of the carrier to the photosensitive material (that is, the adhesion around the electrostatic latent image) were measured by changing the direction of rotation, and the following results were obtained.

[Table] From the above results, it is advantageous to use a fixed magnet that forms a repulsive magnetic field to reduce the amount of development, and it is advantageous to rotate the sleeve in the same direction for adhesion of the carrier to the sensitive material, as well as increase the amount of development. It has also been found that the best way to prevent carrier adhesion is to combine a fixed magnet that forms a repulsive magnetic field and rotation of the sleeve in the same direction. Here, the reason why the fixed magnet that forms the repulsion magnetic field contributes to improving the amount of development (that is, development efficiency) is that when a repulsion magnetic field is generated at the development magnetic pole in the development nip area, there is a gap between the developer particles in the repulsion part A. This is thought to be due to the fact that the toner at the bottom can move toward the photosensitive material as long as an electric force is applied, and the difficulty in moving the toner in the layer due to the small particle diameter carrier described in Fig. 2 can be overcome. . Furthermore, when the sleeve is rotated in the same direction as the moving direction of the photosensitive material, carrier adhesion to the photosensitive material is reduced, and when a fixed magnet that forms a repulsive magnetic field is combined, the amount of carrier adhesion to the photosensitive material is minimized. There is no stagnation of developer in the nip area.
It is also believed that because the carrier movement speed in the repulsion section is fast, the carrier near the photosensitive material can constantly have momentum to overcome the electric force. Experimental Example 2 Using the same developer as in Experimental Example 1, one developing roll and two developing rolls were rotated in the same direction relative to the photosensitive material around a fixed magnet that formed a repulsive magnetic field.
We compared the case of books. The result was the table shown in Figure 5. From the above results, in the conventional development method, the effect of using two developing rolls was simply to increase the amount of development, but in the development method using a small particle diameter carrier, it was found that the effect of using two developing rolls was to prevent the carrier from adhering to the photosensitive material. It turned out to have a big effect. The reason for this is that due to the action of electric force, the fringe electric field of the carrier attached to the photosensitive material by the first developing roll is weakened by the development of the toner image, so the magnetic force of the second developing roll is stronger and moves toward the sleeve. This is considered to be development due to separation. According to Experimental Examples 1 and 2 above, a high-speed copying machine using a small-diameter carrier is realized by using two developing rolls that rotate the sleeve in the same direction as the moving direction of the sensitive material with respect to a fixed magnet that forms a repulsive magnetic field. It turned out to be the most suitable developing method. Note that the fixed magnet 3 is located at the first
The part of the fixed magnet 3 of the second developing roll 2 ₁ facing the photosensitive material 1 is the N pole, and the other part is the S pole, and the part of the fixed magnet 3 of the second developing roll 2 ₂ facing the photosensitive material 1 is the S pole.
The pole and other parts may be set as N poles.

[Brief explanation of the drawing]

1 and 2 are explanatory diagrams of the developing nip area when using a large particle carrier and a small particle carrier, FIG. 3 is an explanatory diagram of a conventional example, and FIG. 4 is a magnetic field for carrying out the method of the present invention. FIG. 5 is an explanatory diagram of the brush developing device, FIG. 5 is a table showing the results of the second experimental example, and FIG. 6 is an explanatory diagram of another example of the fixed magnet. 1 is a photosensitive material, 2 is a developing roll, 3 is a fixed magnet, 4
is a sleeve.

Claims (1)

[Claims] 1. Using a two-component developer consisting of toner and a small particle carrier with an average particle size of 5 to 40 μm, the developer is transported to the development nip area with the photosensitive material by a development roll that rotates a sleeve around the outer circumference of a fixed magnet. In a developing method for developing an electrostatic latent image on a photosensitive material into a toner image, the sleeve is rotated in a developing area so that the developer moves in the same direction as the photoreceptor, and a repulsive magnetic field is formed in the developing nip area. A developing method for an electrophotographic copying machine, characterized in that the developing method is performed using at least two developing rolls.