JPS6356981B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a magnetic brush development method in electrophotography using a two-component magnetic developer. Regarding improvements to resolve the issue. In electrophotography using a two-component magnetic developer, electrostatic toner and magnetic carrier are mixed,
This two-component composition is supplied onto a developing sleeve equipped with a magnet inside to form a magnetic brush made of this composition, and this magnetic brush is rubbed against an electrophotographic photosensitive plate having an electrostatic latent image. By this,
A electrostatic toner image is formed on a photosensitive plate. Due to friction with the magnetic carrier, the electrostatic toner is charged to a charge of opposite polarity to that of the electrostatic latent image on the photosensitive plate, and electrostatic toner particles on the magnetic brush are transferred onto the electrostatic latent image by Coulomb force. The electrostatic latent image is developed. On the other hand, the magnetic carrier is attracted by the magnet in the sleeve, and its electric charge is of the same polarity as the charge of the electrostatic latent image, so that the magnetic carrier remains on the sleeve. In order to form a clear and high-density image, it is necessary to provide a sufficient relative speed difference between the photosensitive plate and the magnetic brush so that the photosensitive plate is sufficiently rubbed by the magnetic brush. is important. Although the known magnetic brush development method using a two-component developer is generally satisfactory for copying ordinary characters, it is difficult to form a A disadvantage is that the resulting image contains brush marks, that is, numerous rows of thin, short white lines extending in the direction of the brush stroke. One possible way to prevent these brush marks is to increase the amount of spikes on the magnetic brush, but in this case, so-called tailing will occur in the image, and this is not a fundamental measure to eliminate brush marks. I can't say that. The present inventors set the moving direction of the magnetic brush in the magnetic brush development area in the opposite direction to the moving direction of the photosensitive layer, and created a gap between the magnetic brush and the photosensitive layer at the photosensitive layer introduction side end and both side ends of the magnetic brush development area. By providing a floating toner blocking wall made of an elastic material and setting the ratio of toner particles to magnetic carrier particles in the magnetic brush development area to be 20 to 150% higher than the saturation adsorption amount of toner particles to the magnetic carrier particles, The occurrence of the brush marks described above has been effectively reduced or eliminated, and a toner image with excellent density, sharpness, and resolution has been successfully formed. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a magnetic brush development method using a two-component magnetic developer that reduces or eliminates the occurrence of brush marks. Another object of the present invention is to provide a magnetic brush development method using a two-component magnetic developer that effectively reduces or eliminates the occurrence of brush marks without causing trailing on images. Still another object of the present invention is to effectively reduce or eliminate the occurrence of brush marks without staining the inside of an electrophotographic apparatus or copying material with toner, and to form toner images with excellent density, sharpness, and resolution. An object of the present invention is to provide a magnetic brush development method using a two-component magnetic developer that allows the development of a magnetic brush. According to the present invention, an electrophotographic photosensitive layer having an electrostatic latent image is rubbed with a magnetic brush made of a mixture of magnetic carrier particles and electrostatically colored toner particles, and the electrostatic latent image is developed with the toner particles. In the magnetic brush development method, the direction of movement of the magnetic brush in the magnetic brush development area is opposite to the direction of movement of the photosensitive layer, and the photosensitive layer is A floating toner blocking wall made of an elastic material is provided between the
A magnetic brush development method is also provided, characterized in that the ratio of toner particles to magnetic carrier particles in the magnetic brush development zone is 20 to 150% greater than the saturation adsorption amount of toner particles to the magnetic carrier particles. One of the important features of the method of the present invention is that the ratio of toner particles to magnetic carrier particles is 20 to
The aim is to increase the ratio by 150%, particularly preferably by 40 to 130%. In this specification, the saturated adsorption amount of toner particles to magnetic carrier particles has the following meaning.
Now mix the toner particles in excess on the magnetic carrier,
When this developer composition is supplied onto a rotating sleeve equipped with an internal magnet and continues to rotate in the form of a magnetic brush, the relationship between the rotation time and the toner concentration in the developer composition is as shown in the diagram in Figure 1. As shown, the decrease in toner concentration is large in the initial stage, and the decrease in toner concentration gradually decreases until a certain saturation value is reached. In the present invention, this saturation value of toner concentration is defined as the saturation adsorption amount of toner particles to the magnetic carrier particles (hereinafter simply referred to as the saturation adsorption amount). More specifically, the magnetic flux density on the sleeve surface is 1000 Gauss, the sleeve diameter is 50 mm, the rotation speed is 120 rpm, and the amount of spikes is 2.8 mm.
The magnetic brush is rotated under the following conditions, and the relationship between the rotation time and the toner concentration is measured, and the saturated adsorption amount is determined as the number of parts by weight of toner per 100 parts by weight of the carrier. This saturation adsorption amount varies depending on the combination of the particular magnetic carrier and the particular toner. for example,
The larger the specific surface area of the magnetic carrier, the more
The saturated adsorption amount becomes large, and the specific surface area of the magnetic carrier is influenced by the particle size and shape of the magnetic carrier. Further, as the particle size of toner particles becomes finer, the saturated adsorption amount generally increases. However, it is easy for those skilled in the art to determine the saturation adsorption amount for a specific combination of magnetic carrier and toner using the above-described means. In the present invention, the ratio of toner particles to magnetic carrier particles is 20 to 150% higher than the saturation adsorption amount.
This is based on the new finding that by increasing the ratio, the occurrence of brush marks can be effectively suppressed. Toner particles contained in a ratio greater than the saturated adsorption amount are ultimately scattered around by the rotation of the magnetic brush.Thus, in the conventional magnetic brush development method, toner particles in the two-component developer It has been avoided to set the ratio to be larger than the saturated adsorption amount because it causes stains inside the device due to toner scattering. According to the research conducted by the present inventors, the reason for the occurrence of the above-mentioned brush marks is that the magnetic carrier comes into direct contact with the surface of the photosensitive plate, and the electrostatic latent image on the surface of the photosensitive plate leaks or current leaks through the carrier at this contact area. I think that the. On the other hand, in accordance with the present invention, when toner particles are used in an amount that is a certain percentage higher than the saturated adsorption amount, such excess toner particles are prevented from leaking through the carrier, resulting in noticeable brush marks. It is recognized that this will be suppressed. For example, as shown in the example below, the degree of occurrence of brush marks is determined by the interval 2 for a solid black image.
Expressed as the number of white lines per mm width x 5 mm length. A two-component developer containing a saturated adsorption amount of toner particles generally shows brush marks of 10 to 30 lines/5 mm, whereas the method of the present invention reduces the brush marks to smaller than 5 lines/5 mm, especially It becomes possible to suppress it to zero. In the present invention, the ratio of toner particles to magnetic carrier particles is 20 to 150 times higher than the saturation adsorption amount.
% is also important; when the ratio of toner particles is less than this range, it is difficult to suppress the occurrence of brush marks to less than the above range, while on the other hand, when the ratio is higher than this range, Free toner powder smoke is generated during development, which causes background stains, trailing, and stains within the apparatus, which is undesirable. In the present invention, it is also extremely important that the direction of movement of the magnetic brush in the magnetic brush development area is opposite to the direction of movement of the photosensitive layer. That is,
It is known that toner image density increases depending on the relative sliding speed difference between the photosensitive layer and the magnetic brush. On the other hand, in the two-component magnetic developer used in the present invention, since toner particles are contained in a ratio higher than the saturated adsorption amount, increasing the circumferential speed of the magnetic brush too much may cause free The toner causes powder smoke, which causes background stains (fogging). According to the present invention, by making the moving direction of the magnetic brush opposite to the moving direction of the photosensitive layer, the photosensitive layer can be exposed to light without increasing the circumferential speed of the magnetic brush, that is, without increasing the centrifugal force too much. It is possible to increase the relative speed with the layer, and it is possible to increase image density without fear of generating free toner dust. Not only that, the occurrence of brush marks,
It is also affected by the circumferential speed of the magnetic brush and therefore by the centrifugal force, and under conditions where the centrifugal force becomes large, brush marks tend to occur more frequently. According to the invention,
By setting the moving direction of the magnetic brush and the moving direction of the photosensitive layer in opposite directions, it is possible to avoid increasing the centrifugal force of the magnetic brush too much and to further reduce the occurrence of brush marks. In the present invention, the ratio of toner particles to magnetic carrier particles is higher than the saturation adsorption amount, and the direction of movement of the magnetic brush in the development zone is opposite to the direction of movement of the photosensitive layer. Therefore, a floating toner blocking wall made of an elastic material is provided between the photosensitive layer introduction side end and both side ends of the magnetic brush development area to prevent toner contamination inside the device, especially the charging mechanism and the exposure mechanism. This is important in preventing toner contamination such as. That is, under the conditions of the method of the present invention, although the generation of powder smoke due to free toner is effectively prevented, it is impossible to avoid a trace amount of free toner from floating in the development area. In the present invention, by providing the above-mentioned elastic blocking wall at a specific position, it is possible to effectively prevent such a small amount of floating toner from scattering and accumulating in the charging mechanism, exposure mechanism, etc. outside the development area. It can be prevented. In the method of the present invention, since the direction of movement of the magnetic brush is opposite to the direction opposite to the photosensitive layer, there is no need to provide a floating toner blocking wall on the discharge end side of the photosensitive layer. It is possible to prevent external disturbances from being added. Further, since the floating toner blocking wall provided on the side where the photosensitive layer is introduced is made of an elastic material, it is possible to avoid adverse effects on the electrostatic latent image on the photosensitive layer. Next, the configuration of a preferred developing device 1 used in the present invention will be described with reference to FIGS. 2 to 3-1 and 3-2. The illustrated developer device 1 includes a developer housing generally designated by the number 2. As most clearly illustrated in FIG.
A developer container 4 is configured to contain a developer 3, which is a two-component developer containing magnetic carrier particles and toner particles in the above-mentioned ratio. Inside the developer housing 2, a developer magnetic brush forming mechanism 5, a toner particle supply mechanism 6, and a rotating stirring member 7 are arranged. The developer magnetic brush forming mechanism 5 includes a cylindrical rotating sleeve member 8 that is rotationally driven in the direction shown by an arrow 17 (FIG. 2), and a rolled stationary permanent magnet 9 disposed within the rotating sleeve member 8. It is composed of. Such developer magnetic brush forming mechanism 5
magnetically retains a portion of the developer 3 present in the developer container 4 in the developer draw-up zone 10 on the surface of the rotating sleeve member 8 by the action of the magnetic field generated by the stationary permanent magnet 9; As the rotating sleeve member 8 rotates, the developer 3 held on the surface of the rotating sleeve member 8 is conveyed to the developing area 11 as a magnetic brush. In the development zone 11, the rotary sleeve member 8 is inserted through an opening 13 formed in the front surface of the developer housing 2, that is, the surface facing the surface of the rotary drum 12.
A magnetic brush of developer 3 held on the surface of is brought into contact with a photosensitive layer on a rotating drum 12 which is rotated in the direction shown by arrow 14. Thus,
The toner particles in the developer 3 are applied to the photosensitive layer, and the electrostatic latent image formed on the photosensitive layer is developed into a visible image (toner image). If the toner concentration in the developer 3 falls below the above range due to consumption of the toner particles 3, etc.
The concentration is detected by a well-known toner concentration detection sensor (not shown) provided in the developer storage container 4, and toner is replenished by the toner particle supply mechanism 6. Between the developer pumping area 10 and the developing area 11, there is a magnetic brush amount of the developer 3 held on the surface of the rotating sleeve member 8 and carried to the developing area 11, in other words, the thickness of the layer of the developer 3. A panicle length setting member 15 is provided to set the length to an appropriate value. As clearly shown in FIG.
a main portion 15b extending from a to a position close to the surface of the rotating sleeve member 8;
It is preferable to have an extension part 15c extending from the tip of b to a position close to the surface of the rotating drum 12. In such a panicle length setting member 15, the tip of the main portion 15b located close to the surface of the rotating sleeve member 8 performs the panicle length setting function;
A developing area 11 is held on the surface of the rotating sleeve member 8.
The thickness of the magnetic brush layer of the developer 3 transported to is
It is defined by the distance l ₁ between the tip of the main portion 15b and the surface of the rotating sleeve member 8. On the other hand, the extension portion 15c prevents the toner particles in the developer 3 from scattering from the development area 11 through between the development housing 2 and the rotating drum 12 into the electrostatic copying machine. Also, as shown in Figures 3-1 and 3-2,
On both side walls around the opening 13 and at the end on the side where the photosensitive layer is introduced, there are blocking walls 16a, 16b made of elastic material, respectively.
16c is attached by adhesive or the like to isolate the developing area from other areas, and the synergistic effect with the above-mentioned spike length setting member 15 further prevents floating toner from scattering into the electrostatic copying machine. are doing. As the elastic body, fibrous materials such as felt, flocked hair, brushes, foamed resin, foamed rubber, etc. are used as appropriate. They may be opposed to each other with a small gap between them to prevent the above. The photosensitive layer includes selenium, CdS, zinc oxide,
Although layers of organic photoconductors are used, the present invention is particularly useful for photosensitive layers such as selenium, CdS, etc., which are prone to brush marks. It is generally advantageous for the ratio of the circumferential speeds of the photosensitive layer and the magnetic brush to be between 2:1 and 1:2, in particular between 1:1 and 1:2. Magnetic carriers generally have a particle size of 50 to
Iron powder in the range of 150 microns is used, spherical,
Iron powder of irregular shape is preferably used. As the toner, any colored toner having electrostatic property and fixing property can be used, and the toner has a particle size of 5 to 30 mm and has a coloring pigment, a charge control agent, etc. dispersed in a binder resin.
A micron granular composition is used. As the resin, a thermoplastic resin or a thermosetting resin in the form of an uncured or initial condensate is used. Suitable examples are, in order of importance, vinyl aromatic resins, acrylic resins, polyvinyl acetal resins, polyester resins, epoxy resins, phenolic resins,
Petroleum resins, olefin resins, etc. Examples of pigments include carbon black, cadmium yellow,
1 such as molybdenum orange, pyrazolone red, fast violet B, phthalocyanine blue, etc.
As the charge control agent, for example, oil-soluble dyes such as Nigrosynpase (CI50415), Oil Black (CI26150), and Spiron Black, naphthenic acid metal salts, fatty acid metal soaps, and resin acids are used. Soap etc. may be used as necessary. The invention is illustrated by the following example. Example 1 Styrene acrylic resin (HIMER SBM73 Sanyo Chemical Co., Ltd.) 93 parts by weight Carbon Black (Special Black 4 Degussa Co., Ltd.) 5 parts by weight Dye (Nibrosyn EX Orient Chemical Co., Ltd.)
2 parts by weight were pre-mixed in a ball mill for 24 hours at 150°C.
The mixture was kneaded at a roll temperature of 1,000 yen, taken out, cooled and solidified, and then coarsely pulverized in a jet mill, which was then used in a classifier to obtain toner having a particle size in the range of 5 to 25 microns. This toner was prepared in an amount greater than the saturated adsorption amount of 3.5, that is, a positively charged developer was prepared using 100 parts by weight of an oxidized iron powder carrier having an average diameter of 150 microns per 8 parts by weight of the above toner. This developer was applied to the device shown in Figure 2 (photosensitive layer: selenium drum, magnetic brush/photosensitive layer circumferential speed ratio: 1.23/
1) was filled and a copy was taken, but the image density was very high, there was no fogging at all, and the brush marks were not noticeable. In addition, even after printing 10,000 copies, there was no toner scattering around the copier. Example 2 Styrene acrylic resin (Himer SBM-73 Sanyo Chemical Co., Ltd.) 93 parts by weight Carbon Black (Special Black 4 Degusa Co., Ltd.) 5.5 parts by weight Dye (Bontron S-32 Orient Chemical Co., Ltd.)
1.5 parts by weight After thoroughly pre-mixing the above composition, heat kneading it in a Banbury type pressure kneader at a kettle temperature of 150°C, take it out, cool it and solidify it.
A toner with a micron particle size distribution was obtained. A negative developer in which toner is mixed with an oxidized iron powder carrier having an average particle size of 100 microns at a ratio of (100:9) in excess of the saturated adsorption amount (5) is placed in the developing device shown in Figure 2. When the copying process was carried out, a high-quality copy with very high image density and contrast, no fog, and no conspicuous brush marks was obtained. Example 3 Using the toner of Example 2, the saturated adsorption amount was determined on an oxidized iron powder carrier with an average particle size of 74 microns.
(7) When a larger amount of toner, that is, a negative developer mixed at a ratio of (100:11), is copied using the developing device shown in Figure 2, the image density is very high and the contrast is high with no brush marks. Got a copy. In addition, as shown in the comparative example, although the print life was 50,000 copies, there was no scattering around the inside of the copying machine. Example 4 Vinyltoluene resin (Bryolite VTACL)
Goodyear〓) 94 parts by weight Cargin Black (MA-8 Mitsubishi Kasei〓)
5 parts by weight Dye (Spiron Black BHH Hodogaya Chemical Co., Ltd.) 1 part by weight The above composition was heated and kneaded at 130°C in a heating roll mill, cooled and solidified, and after pulverization, a toner having a particle size distribution of 5 to 25 microns was obtained. . After thoroughly mixing the toner with an oxidized iron powder carrier having an average diameter of 50 microns at a ratio of (100:17) toner in excess of the saturated adsorption amount (8), the negative developer is developed as shown in Figure 2. When the copy was made using the machine, a copy with very high image density and high contrast without any brush marks was obtained. Even after copying 50,000 sheets, there was no scattering around the device. Comparative Example Copying was carried out in the same manner using the same combination of carrier and toner used in each Example, but using the same developer except that the toner ratio was adjusted to the saturation adsorption amount. continuous
Table 1 shows the copying characteristics after a 50,000-sheet test and the results of examining the number of brush marks using a Nikon Measurescope (metallurgical microscope, manufactured by Nippon Kogaku Co., Ltd.) in correspondence with each Example. Note 1: When measuring brush marks, measure the black solid image area.
Displays the number of lines in a 2.0 x 5.0 mm blank mask. Note 2 Edge ratio is expressed as a value measured using a commercially available reflection densitometer (manufactured by Konishirokusha) at the center of the copy image density obtained by making 5 mm square and 25 mm square black originals. Edge ratio = 5mm square / 25mm square x 100 Note 3 Edge fading refers to a case where the edge of an image with large letters or black image area is poorly defined (notched). Note 4 Re-line reproducibility refers to cases where thin lines are not obtained and become dotted lines, or are missing. 【table】

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the amount of toner in a two-component developer and a magnetic brush, and FIG. 2 is a side sectional view of a developing device preferably used in the present invention.
3-1 is a perspective view of the developing device shown in FIG. 2, seen from the opening side, and FIG. 3-2 is a perspective view of the device shown in FIG. 3-1 with the floating toner blocking wall removed. It is. 1 is a developing device, 13 is an opening, 16a, 16b,
16c is a floating toner blocking wall.

Claims (1)

[Claims] 1. An electrophotographic photosensitive layer having an electrostatic latent image is rubbed with a magnetic brush made of a mixture of magnetic carrier particles and electrostatically colored toner particles, so that the electrostatic latent image is covered with the toner particles. In the magnetic brush development method, which consists of developing, in the magnetic brush development area, the direction of movement of the magnetic brush is opposite to the direction of movement of the photosensitive layer, and the end of the photosensitive layer introduction side and both ends of the magnetic brush development area are A floating toner blocking wall made of an elastic material is provided between the photosensitive layer and the magnetic brush development area, and the ratio of toner particles to magnetic carrier particles is set to 20 to 150% of the saturated amount of toner particles adsorbed to the magnetic carrier particles. A magnetic brush development method characterized by a high ratio.