JPH053588B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to electrophotography, and more particularly to electrophotography using a magnetic brush consisting of a two-component developer of a ferrite carrier and electrostatic toner. Concerning improvements in photographic methods for developing latent images. Prior Art and Technical Problems of the Invention 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, an electrostatic toner image is formed on the 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. Generally, iron powder carriers are widely used as magnetic carriers, but these iron powder carriers still have many drawbacks. In other words, in a two-component developer using this iron powder carrier, the development sensitivity curve (curve of potential difference between the electrostatic image and the developing sleeve versus image density) rises steeply, the gradation is poor, and the middle tones are poor. It has the disadvantage of poor reproducibility. In addition, the developer containing this iron powder carrier may form a hard magnetic brush, which may damage the photosensitive layer, and when copying a solid black area, a brush mark, that is, a brush mark, may be formed on the image formed. The disadvantage is that there are many rows of thin and short white lines extending in the rubbing direction. Furthermore, the iron powder carrier is sensitive to humidity, and its development characteristics tend to change due to the influence of humidity, or it tends to rust itself, and there is also the problem that large torque is required to drive the magnetic brush. be. In recent years, as a magnetic carrier for two-component developers,
It has been proposed to use ferrites, especially soft ferrites. However, ferrite carriers have a higher electrical resistance than iron powder carriers, which causes problems such as carrier drag during development, that is, transfer of the carrier to the photosensitive layer side, and edge effects in the formed images. This problem is likely to occur. Although magnetic brush development using a ferrite carrier produces a development that is quite different from development using an iron powder carrier,
Much is still unknown about the development conditions. Purpose of the Invention The present inventors have discovered that when developing an electrostatic latent image on a photosensitive layer using a magnetic brush of a two-component developer consisting of a ferrite carrier and electrostatic toner, a magnetic brush forming sleeve is used. By selecting the magnetic flux density of the main pole for development within a certain range in relation to the charged potential of the photosensitive layer, the reproducibility of intermediate tones and fine lines can be significantly improved, and in this method, the development High image density can be obtained even when the toner concentration in the agent is low,
It has been found that problems such as toner scattering can be resolved. Structure of the Invention According to the present invention, a two-component developer consisting of a ferrite carrier and electrostatic toner is supplied onto a non-magnetic sleeve having a plurality of magnets fixed therein. A magnetic brush is formed, and the photosensitive layer having an electrostatic image is rubbed with the magnetic brush on the sleeve such that the direction of movement of the photosensitive layer and the direction of movement of the sleeve are opposite to each other at the rubbing position. The magnetic flux density B (Gauss) of the main developing pole and the charged potential E (volts) of the photosensitive layer satisfy the following equations: 2E−450≧B≧2E−750 …(1) and 1000≧B≧600 …(2) An electrophotographic method is provided, characterized in that development is carried out under satisfactory conditions. Preferred Embodiments of the Invention The present invention will be explained in detail below. Electrophotographic Method In FIG. 1 for explaining the electrophotographic method applied to the present invention, for example, an electrophotographic photosensitive layer 2 such as a selenium-based photoconductor layer is provided on the surface of a drive drum 1. Although not shown, an electrostatic latent image is formed on the surface by means such as uniform charging and image exposure. A developing device, generally designated by 3, is provided along the path of movement of the photosensitive layer 2. This device includes a magnet 4 having a plurality of magnetic poles, and around the magnet 4 is provided a sleeve 5 made of a non-magnetic material such as aluminum. This sleeve 5 is rotatably provided in the direction of arrow A, and the magnet 4 is fixedly provided within this sleeve 5. A stirring mechanism 7 is provided to stir the two-component developer 6, and the ferrite carrier and the electrostatic toner particles are mixed by this stirring mechanism 7, frictionally charged with each other, and mutually charged. A mixture is formed which is electrostatically bonded to and applied onto the sleeve 5. The two-component developer forms a magnetic brush 8 on the sleeve 5, and this magnetic brush is cut to a suitable length by a cutting mechanism 9 and supplied to a developing area 10. In the development area 10, the photosensitive layer 2 and the sleeve 5 move in opposite directions, and the magnetic brush 8 and the photosensitive layer 2 are rubbed against each other. By rubbing, the charged toner particles on the ferrite carrier are attracted to the electrostatic latent image on the photosensitive layer 2, and the electrostatic latent image is developed. After development, the magnetic brush 8 is peeled off from the sleeve 5 by a scraping plate 11, and the peeled two-component developer is stirred by the stirring mechanism 7 and then supplied onto the sleeve 5 again. In order to supply the toner 12 consumed during development, a toner storage section 13 and a toner supply roller 14 are provided, and supply the toner 12 into the developing mechanism 3 continuously or intermittently. In the developing area 10, the magnetic brush and the photosensitive layer are rubbed against each other in a positional relationship such that the main developing pole 15 and the photosensitive layer 2 are substantially opposed to each other. The density B (Gauss) is set within a certain range in relation to the charged potential E (volts) on the photosensitive layer 2, that is, within the range defined by the above formulas (1) and (2). According to the present invention, by setting the magnetic flux density B of the main pole so as to satisfy equations (1) and (2), there is no edge effect or brush mark.
It becomes possible to form high-density images with excellent reproducibility of halftones and fine lines. FIG. 2 of the accompanying drawings shows the results of plotting the quality of the image formed, with the vertical axis representing the magnetic flux density B of the main developing pole and the horizontal axis representing the surface potential E on the photosensitive layer. In the plot in Figure 2, ◎ marks indicate that the γ-value is 1.4 to 1.6 and the image quality is excellent, while × marks indicate that the γ-value is smaller than 1.4 or that edge effects or brush marks occur. In this case, the circle mark indicates the case where the γ-value is larger than 1.6. Moreover, each straight line in FIG. 2 has the following meaning. L ₁ ... B = 2E - 450 L ₂ ... B = 2E - ₇₅₀ L ₃ ... B = _{1000 L 4 ...} B = 600 This sets the upper limit of the development conditions in terms of image quality such as brush marks, while the straight line _L3 and
_L4 defines the lower limit of development conditions in terms of reproducibility of halftones and fine lines. On the other hand, the straight line L ₅ and
L ₆ has the following meaning L ₅ ... E = 600 L ₆ ... E = 850, and the straight line L ₅ determines the lower limit of the charging potential in terms of image density and contrast for the selenium photosensitive plate. The straight line _L6 defines the upper limit of the charging potential in terms of the durability of the photosensitive plate. Of course, the values of these straight lines L ₅ and L ₆ will change depending on the type of photosensitive layer. Thus, regarding the selenium-based photosensitive layer, if it satisfies the above formulas (1) and (2), and especially when B is 700 to 900 Gauss, most preferably 800 to 900 Gauss, it can have a relatively wide surface potential. In contrast, it is clear that toner images with high density, excellent gradation, resolution, and image quality can be formed. Developer In the present invention, a two-component developer comprising a ferrite carrier and electrostatic toner is used for magnetic brush development under the above conditions. Sintered ferrite particles are used as ferrite carriers. Sintered ferrite particles are known per se, and include known sintered ferrite particles,
Particular preference is given to using spherical sintered ferrite particles. The composition of ferrite is also known, and includes what is generally called soft ferrite, such as, but not limited to, Zn-based ferrite,
Examples include Ni-based ferrite, Cu-based ferrite, Mn-based ferrite, Mn-Zn-based ferrite, Mn-Mg-based ferrite, Cu-Zn-based ferrite, Ni-Zn-based ferrite, Mn-Cu-Zn-based ferrite, and the like.
Suitable ferrites are % by atomic weight, Fe35 to
65%, Cu5-15%, Zn5-15% and Mn0-15%
It is Cu-Zn type or Cu-Zn-Mn type ferrite consisting of 0.5%. The sintered ferrite particles used generally have an average particle size of 30 to 100 microns, preferably 35 to 45 microns. 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 an uncured or initial condensate thermosetting resin is used. Suitable examples thereof, in order of importance, are vinyl aromatic resins such as polystyrene, acryl resins, polyvinyl acetal resins, polyester resins, epoxy resins, phenolic resins, petroleum resins, olefin resins, etc. As the pigment, for example, one or more of carbon black, cadmium yellow, molybdenum orange, pyrazolone red, fast violet B, phthalocyanine blue, etc. are used, and as the charge control agent, for example, nigrosine base (CI50415), oil, etc. are used. Oil-soluble dyes such as Black (CI26150) and Spiron Black, naphthenic acid metal salts, fatty acid metal soaps, resin acid soaps, etc. are used as necessary. Other developing conditions In the present invention, a two-component developer containing a ferrite carrier and electrostatic toner particles in a weight ratio of 4:1 to 20:1, particularly 5:1 to 12:1, is used. And the following formula 5×10 ⁹ R1×10 ⁸ …(3) d1.485×10 ⁵ / (logR) ^5.3 …(4) d1.485×10 ⁵ /(logR) ^5.5 …(5) is satisfied. It is preferable to carry out the development under the following conditions. In the above formula, the symbol d indicates the clearance (mm) between the photoreceptor drum and the sleeve, while the symbol R indicates the resistance (Ω) of the two-component developer under the developing conditions of the magnetic brush. More specifically, an electrode drum of the same size as the electrophotographic photoreceptor drum is installed in place of the photoreceptor drum, a developer is supplied onto the developing sleeve to form a magnetic brush, and this magnetic brush is connected to the electrode. Let it rub against the drum,
This refers to the resistance value calculated by applying a voltage between the sleeve and the drum and measuring the current flowing between them. In the present invention, the development clearance (d) can be easily adjusted by mechanically adjusting the relative position between the photosensitive drum and the development sleeve. On the other hand, the electrical resistance of the magnetic brush of the two-component developer is also adjusted by various means. That is, it goes without saying that the ferrite carrier and toner particles should be selected to have electrical resistance within a certain range.
Furthermore, if the amount of toner particles is increased or the diameter of the toner particles is decreased, the resistance of the magnetic brush increases. Furthermore, if the diameter of the ferrite carrier is increased, the resistance of the magnetic brush will be increased. Of course, if these were reversed, the result would be the opposite. In the present invention, a bias voltage is applied between the photoreceptor drum and the developer sleeve, and although this bias voltage sufficiently injects charge into the toner during development, it causes discharge damage to the photoreceptor and magnetic brush. Establishments shall be established to prevent such troubles from occurring. This voltage is generally between 100 and 300 volts, especially
A range of 150 to 250 volts is suitable. The polarity of the bias voltage is of course selected so that it becomes positive when the charge on the photoreceptor is positive, that is, the polarity is the same. According to the present invention, by employing the development conditions described above, development can be performed with the application of a relatively low bias voltage, and as a result, the printing durability of the photoreceptor can be improved. In the magnetic brush development of the present invention, the tip of the magnetic brush is determined at the above-mentioned clearance d so that the magnetic brush can sufficiently rub the surface of the photoreceptor. Generally, it is desirable to cut the ears so that the length of the ears is 1.1 to 3.0 times, particularly 1.2 to 2.0 times, the development clearance d. One of the advantages of the present invention is that it is possible to cut ears at small intervals because a ferrite carrier with low residual magnetization is used. When developing, fix the magnet inside the sleeve,
A method is adopted in which only the sleeve is rotated and the magnetic brush is moved in the same direction as the rotation direction of the sleeve, but this method has the advantage that the torque is small when driving the developing mechanism and it is easy to drive. . As the photoreceptor, any known electrophotographic photoreceptor such as a selenium vapor-deposited photoreceptor, an amorphous silicon photoreceptor, a CdS photoreceptor, an organic photoconductor photoreceptor, etc. is used, and the electrostatic latent image is Formation is easily carried out in a manner known per se, for example by a combination of charging and imagewise exposure. The invention is illustrated by the following example. Example: The magnetic force of the main pole 15 of the magnet 4 of the developing device shown in FIG.
We changed the surface potential E to four types: 1000, 900, 800, and 700, and examined the effect on the image. The developing conditions of the developing device and the physical properties of the two-component developer used at this time are as follows. (Development conditions) Γ drum-sleeve distance 1.7 mm Γ tip interval 1.0 mm Γ sleeve rotation speed 141 rpm (Two-component developer) Γ ferrite carrier Saturation magnetization 60 emu/g Residual magnetization 0.3 emu/g Retention force 3 Oe Average particle size 45μ Γ toner average particle size 12μ Γ toner concentration 11% Note that the surface potential was varied from 700 to 1000V. The results are shown in Table 1. 【table】

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining the electrophotographic method applied to the present invention, and FIG. 2 is a diagram for explaining the magnetic flux density B of the main developing pole.
FIG. 3 is a diagram showing the relationship between the surface potential E and the quality of the formed image. In the figure, 2 is a photosensitive layer, 3 is a developing device, 4 is a magnet, 5 is a non-magnetic sleeve, and 6 is a two-component developer.

Claims (1)

[Claims] 1. A two-component developer consisting of a ferrite carrier and electrostatic toner is supplied onto a non-magnetic sleeve having a plurality of magnets fixed therein, and the magnetism of the developer is A brush is formed, and the photosensitive layer having an electrostatic image and the magnetic brush on the sleeve are rubbed so that the direction of movement of the photosensitive layer and the direction of movement of the sleeve at the rubbing position are opposite to each other. Pole magnetic flux density B (Gauss) and photosensitive layer charging potential E
An electrophotographic method characterized in that development is carried out under conditions where (volt) satisfies the formulas 2E-450≧B≧2E-750 and 1000≧B≧600.