JPH0220117B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a developing device that develops a latent image using a non-magnetic developer. Conventionally, various devices have been proposed and put into practical use as dry one-component developing devices. However, in any of the development methods, it is extremely difficult to form a thin layer of dry one-component developer, and for this reason, a developing device has been constructed by forming a relatively thick layer. However, as improvements in the clarity and resolution of developed images are currently being sought, it is essential to develop a method for forming a thin layer of a dry one-component developer and an apparatus therefor. As a conventionally known method for forming a thin layer of a dry type one-component developer, Japanese Patent Application Laid-Open No. 43037/1983 has been proposed and has been put to practical use. However, this concerned the formation of a thin layer of magnetic developer. In order to make magnetic developers magnetic, a magnetic material must be added to the toner. Since it is internally added, there are problems such as poor color reproduction during color reproduction. For this reason, as a method for forming a thin layer of non-magnetic developer,
Proposed methods include using a cylindrical brush made of soft beaver hair to apply the developer, and applying the developer to a developing roller with a surface made of fibers such as velvet using a doctor blade. has been done. However, if an elastic blade is used as a doctor blade for the above fiber brush,
Although it is possible to regulate the amount of developer, it is not applied uniformly, and the fiber brush on the developing roller is simply rubbed, and no triboelectric charge is imparted to the developer present between the fibers of the brush. Therefore, there was a problem that ghosts and the like were likely to occur. An object of the present invention is to eliminate the problems of the conventional method described above, and to provide a new developing device that forms a non-magnetic developer as a uniform thin layer on the surface of a developer holding member and applies sufficient triboelectric charge. It is said that The present invention achieves the above object, and the particle size is 30μ~
A container for storing a mixed developer of 100μ magnetic particles and a non-magnetic developer with a concentration of 25 to 70% by weight, and a container for transporting the non-magnetic developer to a latent image carrier. a rotating developer holding member; a regulating member disposed on the non-magnetic developer supply outlet side of the container with a gap formed on the surface of the holding member; and a magnetic field generating means having a fixed magnetic pole that forms a magnetic brush made of magnetic particles on the upstream side of the regulating member on the developer outlet side of the container, and the regulating member and the magnetic pole cause the container to A thin layer of non-magnetic developer is formed on the surface of the developer holding member by restraining the magnetic brush of magnetic particles so that it does not flow out, and development is performed with this layer facing the latent image carrier. This is a developing device. As the latent image carrier of the present invention, a drum-shaped or belt-shaped member having a photoreceptor and an insulating layer is used. Furthermore, as the moving developer holding member, it is possible to use a sleeve made of non-magnetic metal such as aluminum, copper, stainless steel, brass, etc. or a synthetic resin material, or an endless belt made of resin or metal. In order to improve the electrostatic properties and charging characteristics, the surface may be roughened or provided with an uneven pattern, if necessary.
Further, as the regulating member, a blade plate or a wall made of a magnetic material such as iron or a non-magnetic material such as aluminum, copper, or resin may be used. Hereinafter, the present invention will be explained in more detail with reference to the drawings. FIG. 1 shows a sectional view of a developing device for explaining the developing principle of the present invention. In the figure, reference numeral 1 denotes an electrophotographic photosensitive drum as a latent image carrier, which holds a latent image formed by a latent image forming means (not shown), and rotates in the direction of arrow a to pass through a developing position shown in the drawing. For this photosensitive drum 1, a non-magnetic sleeve 2, which is a developer holding member that holds developer, is attached.
are opposed to each other with a predetermined gap maintained between them, and this sleeve 2 rotates in the direction of arrow b. This sleeve 2
A non-magnetic container 3 made of resin or aluminum, which stores a mixture of a non-magnetic developer 4 and magnetic particles 5, is located above the container 3, and a magnetic blade, which is a regulating member, is located downstream of the container 3 in the rotational direction of the sleeve. 6 is screwed. On the other hand, the sleeve 2 for this magnetic blade 6
On the opposite side, a magnet 7 is provided as a magnetic field generating means. The mounting position of this magnet is determined by the relationship between the position of the magnetic pole and the magnetic blade 6, and in reality, the magnetic pole is provided slightly upstream of the position of the magnetic blade 6 in the direction of movement of the sleeve. By doing this,
The action of the formed magnetic field effectively prevents the magnetic particles from flowing out and uniformly coats the developer. In the above configuration, the magnetic particles 5 in the container 3 are
A magnetic brush 8 is formed by the magnetic field generated between the S pole of the magnet 7 and the magnetic blade 6. As the sleeve 2 rotates, the magnetic brush 8
The magnetic particles and the non-magnetic developer are mixed by sliding while maintaining the magnetic particles and the non-magnetic developer. In this state, on the magnetic blade side of the container 3, due to the presence of the blade 6, the mixture of developer and magnetic particles is prevented from moving by the blade, rises, and circulates in the direction of arrow c. Non-magnetic developer is triboelectrically charged by mixing with magnetic particles. The charged developer is transferred to the magnetic blade 6
A magnetic brush 8 formed near the sleeve 2 applies a thin, uniform coating onto the surface of the sleeve 2 by reflection force, and reaches a position facing the photoreceptor drum. By the way, the magnetic particles 5 constituting the magnetic brush 8
By setting the binding force due to the magnetic field of the magnet 7 to be larger than the conveying force caused by the electrostatic adhesion force and frictional force between the sleeve and the magnetic particles, the sleeve 2
It will not leak upwards. If there is non-magnetic developer within the area of the magnetic brush 8, the ratio of the magnetic particles of the magnetic brush 8 to this developer remains approximately constant as the sleeve 2 rotates. Thereby, even if the developer on the sleeve is consumed during development, the developer is automatically supplied to the area of the magnetic brush 8. Therefore, it is possible to always supply and apply a constant amount of developer onto the sleeve 2. In addition, in the above explanation of the principle, a magnetic blade is used as the regulating member, but the non-magnetic blade or the wall of non-magnetic material such as resin or aluminum that constitutes the container can be
It can also be used as this regulating member. However, in this case, in order to prevent the magnetic particles from flowing out, it is necessary to make the gap between the sleeve and the regulating member even smaller than when using a magnetic blade. Further, when a magnetic blade is used, it is preferable because a magnetic brush can be stably formed at the developer outlet by the magnetic field between the blade and the magnetic pole, and the magnetic particles can be restrained and circulated. FIG. 2 shows an embodiment of the invention. In the figure,
The same members as those in FIG. 1 are given the same reference numerals. 1 is a photosensitive drum, 2 is a developing sleeve for holding a developer, 6 is a magnetic blade, 4 is a non-magnetic toner, and 5 is a magnetic carrier, which together form a two-component developer. 7 _-1 to 7 _-4 are magnets arranged inside the sleeve. 3 is a developing container; 9 is a bias power source for applying a bias voltage to the developing sleeve 2; the developing container 3 is provided with a sliding blade 11 that rotates around a shaft 10; In the developing container, the carrier 5 and the non-magnetic toner 4 are weakly coupled by electrostatic force and attracted to the magnets 7 _-3 and 7 _-2 . The role of the magnetic carrier is to disperse the non-magnetic toner and transport the non-magnetic toner while being attracted to the sleeve.
The developer used is the toner concentration used in normal two-component magnetic brush development (for example, 2 to 12 wt%).
A two-component developer containing 30 to 70 wt% toner is used, which is several times the amount of toner. The two-component developer attracted by the magnet is conveyed to the magnetic blade 6 by rotation of the sleeve.
During this conveyance process, the two-component developer consisting of the non-magnetic toner 4 and the carrier 5 is attracted to the surface of the sleeve 2 by magnetic force and rubs against the sleeve, so the non-magnetic toner 4 also flows onto the surface of the developing sleeve 2. It is attracted by electrostatic force. In the magnetic blade 6, carrier particles are retained in the magnetic blade 6 due to the magnetic field in the gap e formed by the magnet _7-1 and the magnetic blade 6, forming a brush-like shape, and are scraped off from the surface of the sleeve 2. On the other hand, the non-magnetic toner 4 adhering to the surface of the sleeve 2 passes through the blade 6 without being affected by this magnetic field, and a thin layer of non-magnetic toner 4 is formed on the surface of the sleeve 2. The sleeve 2 is supplied to the adjacent developing section. In order to prevent the particles of the carrier 5 from leaking out from the blade 6 part, the cut magnetic pole 7 _-1 is set at an angle of 5 to 15 degrees (θ in the figure).
Tilt it toward the developer container 3 side. In this way, all magnetic poles 3
By limiting _-1 to 3 _-4 within the developing container, leakage of magnetic flux from the magnetic blade 6 to the developing section side is prevented.
Since the magnetic flux is limited only within the developer container 3, it is almost impossible for the carrier 5 to be taken out of the developer container from the blade 6 section. To explain this state in more detail, the non-magnetic toner 4
The developer containing the developer is attracted to the sleeve 2 and conveyed to the magnetic blade 6 section. Since the magnetic poles 7 _{- 7} inside the sleeve are attached at a slightly inclined position with respect to the magnetic blade 6, the magnetic flux there is weakened. Therefore, the force with which the developer is restrained by the sleeve is small, and the developer is pushed by other developers adsorbed on the upstream side of the sleeve in the direction of movement and moves away from the sleeve along the magnetic blade. Further, as shown in the figure, the developer moves greatly within the developer container in the direction shown by arrow c, and is circulated and agitated. In addition, near the tip of the magnetic blade, as the sleeve rotates, small loop rotation and vibration movements appear to occur, increasing the chance of contact between the non-magnetic toner and the sleeve, creating a sufficient triboelectric charge on the non-magnetic toner. . At the same time, the large amount of toner contained in the carrier is separated from the developer by the rotational and vibrating motion and adheres to the sleeve surface, resulting in uniform toner coating. At this time, the carrier particles each act as a small guiding magnet, exert a restraining force on each other, and are restrained within the developer container 3.
Since the magnetic field in this state is as shown in FIG. 3, almost no magnetic flux is generated on the downstream side of the magnetic blade 6. Therefore, the carrier 5 will not be pulled by the conveying force of the sleeve and go out between the magnetic blade and the sleeve. The gap d between the photosensitive drum 1 and the developing sleeve 2 is sufficiently wide (about 300 μ) so that the thin toner layer (about 100 μ) on the sleeve does not come into contact with the surface of the photosensitive drum 1 in the absence of an external electric field. It is said. During development, by setting the developing sleeve to a predetermined potential using the bias power supply 9, desired image quality can be obtained. In this embodiment, the non-magnetic toner is charged by friction with the carrier and sleeve surfaces. Preferably, the surface of the carrier is coated with an oxide film or an insulating treatment such as a resin that is at almost the same electrostatic level as the toner, so that the amount of triboelectricity imparted from the carrier to the toner is reduced, and the triboelectricity necessary for development is applied only from the sleeve surface. By doing so, deterioration of the carrier can be prevented and toner can be easily applied to the sleeve surface. Since the carrier is not directly involved in development and only plays the role of transporting and stirring the non-magnetic toner to the sleeve surface, it is only necessary to replenish the non-magnetic toner. Fixed magnet inside the sleeve 7 _-1
~7 _-4 is an arrangement where the magnetic field exists only on the developer container 3 side, and the magnetic flux density on the sleeve surface is 400~
600G is required. The surface of the sleeve 2 has a surface roughness of Rz=1 by sandblasting etc. in order to promote the transport of the two-component developer and to increase the chance that the non-magnetic toner 4 comes into contact with the surface.
Control to about ~5 μm. The present invention clarifies the characteristics of the developer in the above-mentioned development method. In the above-mentioned development method, it is necessary that the non-magnetic toner be dispersed in the magnetic carrier, be integrated into the magnetic carrier, be attracted to the sleeve surface, and be conveyed in front of the blade. When the developer moves in the blade portion, it is necessary that the concentration is such that the toner is separated from the carrier. It is also necessary that the carriers are bound to each other as magnetic particles and do not leak out from the blade portion. Therefore, in the present invention, as a developer that satisfies the above conditions, the carrier particle size is 30μ to 100μ and the toner concentration is
25wt% to 70wt% is used. When carriers with a diameter smaller than 30μ are used, their magnetic properties as powder particles are low, and the binding force between the carriers is small, and some of the carriers pass through the magnetic blade along with the toner as the sleeve rotates, causing damage to the developing section. When the photoreceptor is transported to the sleeve, an electric discharge occurs between the photoreceptor and the sleeve. In addition, if a carrier larger than 100 μm is used, the magnetic properties of the powder particles are large, and the binding force between the carriers is too large, and the carrier does not make sufficient rotational or vibrational movement on the front surface of the blade. The toner is difficult to separate, and a so-called white streak occurs in which a thin layer of toner runs in the same direction in a white streak-like manner. Toner that has been tribocharged by frictional electrification with the carrier or sleeve must escape from the restraint of the carrier and adhere to the sleeve surface, so the toner concentration is lower than that of the toner used in normal two-component magnetic brush development. concentration (e.g. 2~
12wt%). FIG. 4 is a graph showing the relationship between the copy density and the toner layer thickness formed on the sleeve when the toner amount (wt%) is changed. As is clear from the figure, as the amount of toner increases, the toner layer thickness tends to gradually increase. On the other hand, the copy density once increases rapidly due to an increase in the amount of toner, but thereafter the copy density does not show a significant increase even if the amount of toner increases. If the amount of toner is increased too much, the copy density will decrease. This is thought to be because when the amount of toner increases too much, the chance of friction between the toner and the carrier decreases, and the tribocharge necessary for development is not imparted to the toner. Therefore, in the present invention, the toner density is selected within the range of 25 wt% to 70 wt% of the toner amount at which the copy density is 1.0 or more. In fact, when the toner concentration is less than 25 wt%, the amount of toner separated from the two-component developer is small and the toner coating on the sleeve is thin, making it impossible to obtain a sufficient image density. Further, when the toner concentration was 70 wt% or more, the adsorption force of the toner to the sleeve was small, causing uneven conveyance. In addition, toner adhered around non-image areas, resulting in noticeable fogging. An experiment was conducted using a two-component developer having the configuration shown below and setting the configuration of the developing device shown in FIG. 2 as follows. Developing sleeve 2: Outer diameter 32φ Sleeve rotation: Same peripheral speed as the drum (300 mm/S) Magnet 7: 400 Gauss on the surface of the developing sleeve Gap between developing sleeve 2 and magnetic blade 6 = 0.5 mm Magnetic pole 7 _-1 and magnetism Inclination angle θ with the blade 6 = 10° Gap between the developing sleeve 2 and the photosensitive drum 1 d = 0.3 mm, and the frequency applied to the developing sleeve 2 by the bias power supply 9.
An AC bias voltage of 150V was applied at 600Hz, the peak value was 1.5KV, and the center value was the same polarity as the latent image. Images were formed in this manner, and sufficient image density was obtained in all cases. (Example 1) 200 to 300 meshes (particle size 80μ to
100μ) was used. The average toner particle size was 10 μm, and the toner weight concentration was 40 wt%. (Example 2) 400~ treated with surface oxide film as a carrier
500 mesh (particle size 30μ to 40μ) was used. The average particle size of the toner was 10 μm, and the weight concentration of the toner was 60 wt%. In order to compare the two-component developer shown in these Examples with a two-component developer used in a general two-component magnetic brush development method, the composition of the two-component developer is generally shown below. (Comparative Example 1) Two-component developer manufactured by Company A Average particle size of carrier: 100μ Average particle size of toner: 8μ Toner weight concentration: 2wt% A selenium photoreceptor is developed. (Comparative Example 2) Two-component developer manufactured by Company B Average particle size of carrier: 30μ Average particle size of toner: 8μ Toner weight concentration: 8wt% A CDS photoreceptor is developed. (Comparative Example 3) NP5000 developer manufactured by Canon Inc. Average particle size of carrier: 60μ Average particle size of toner: 7μ Toner weight concentration: 12wt% A photoreceptor having a surface insulating layer is developed. As described above, in normal two-component magnetic brush development, a toner with a relatively low concentration of 2 to 12 wt% is used. The reason for this is that in general, in the two-component magnetic brush development method, toner adheres sufficiently when developing the dark areas of the photoreceptor, but once the toner adheres to the bright areas of the photoreceptor, it is scraped off again in the final rubbing step. This is because, in order to form so-called fog-free images, the toner concentration must be maintained in an appropriately low range depending on the carrier particle size and the type of photoreceptor. On the other hand, in the developing method of the present invention, only the non-magnetic toner is coated on the non-magnetic sleeve, and the non-magnetic sleeve and the photoreceptor are separated by at least the thickness of the toner for development. It becomes possible to use a developer, and it becomes possible to maintain stable image density over a long period of time. As the non-magnetic developer that can be applied to the present invention, developers conventionally used in electrophotography, such as those prepared by kneading pigments or dyes with resin and forming a frame or encapsulating the mixture, can be used. . As the magnetic particles, iron powder, ferrite, or those bound with resin can be used. As detailed above, the present invention is an apparatus for agitating and circulating a non-magnetic developer and magnetic particles in a developer container, forming only the non-magnetic developer as a thin layer on a developer holding member, and developing a latent image. By specifying the particle size of the magnetic particles and the concentration of the non-magnetic developer used, stable image formation has become possible at all times. Furthermore, since a non-magnetic developer can be used, color development can also be performed.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of a developing device for explaining the principle of the present invention, Fig. 2 is a cross-sectional view of an embodiment of the developing device according to the present invention, and Fig. 3 is an explanation showing the state of magnetic flux on the sleeve surface due to the magnet. FIG. 4 is a graph showing the relationship between copy density and toner layer thickness when the amount of toner is changed. In the figure, 2...Developing sleeve, 3...Developing container, 4...Nonmagnetic toner, 5...Carrier, 6
. . . magnetic blade, 7 . . . magnet, 9 . . . bias power supply.

Claims (1)

[Scope of Claims] 1. A mixture of magnetic particles with a particle size of 30 μm to 100 μm and a non-magnetic developer, wherein the concentration of the non-magnetic developer is 25-70 μm.
a container for storing a mixed developer of % by weight; a rotating developer holding member for conveying the non-magnetic developer to the latent image carrier; and a developer holding member located on the non-magnetic developer supply outlet side of the container;
A regulating member is arranged with a gap formed on the surface of the holding member, and a magnetic material is arranged on the opposite side of the regulating member through the holding member, and is located upstream of the regulating member on the developer outlet side of the container. a magnetic field generating means having a fixed magnetic pole that forms a magnetic brush of particles, and the regulating member and the magnetic pole restrain the magnetic brush of the magnetic particles so that they do not flow out of the container, and a non-magnetic material is applied to the surface of the developer holding member. A developing device is characterized in that it forms a thin layer of developer and performs development by making the thin layer face a latent image carrier. 2. The developing device according to claim 1, wherein a voltage having an alternating current component is applied to the developer holding member.