JPH05705B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a magnetic brush development method,
More specifically, the present invention relates to a magnetic brush development method for forming toner images with excellent image characteristics using a two-component developer containing a ferrite carrier and electrostatic toner particles. 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. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a magnetic brush development method using a ferrite carrier which eliminates the various drawbacks mentioned above. Another object of the present invention is to provide a magnetic brush using a ferrite carrier that can form a toner image with high density and gradation without the occurrence of brush marks or defects such as blank areas due to carrier drag or edge effects. To provide a developing method. According to the present invention, a two-component developer comprising a mixture of magnetic carrier particles and toner particles that can be charged by friction between the magnetic carrier and the magnetic carrier is supplied onto a developing sleeve provided with a magnet in a non-magnetic sleeve. A magnetic brush of developer is formed, and the magnetic brush is rubbed against the surface of the photoreceptor having an electrostatic latent image while a bias voltage is applied between the photoreceptor and the sleeve to remove the electrostatic latent image. In a magnetic brush development method comprising forming a toner image corresponding to an image,
The two-component developer is a two-component developer containing a ferrite carrier and chargeable toner particles in a weight ratio of 4:1 to 20:1. At the same time, the magnet in the sleeve is fixed and developed, and the set angle of the nearest magnetic pole in the downstream direction of the drum rotation is set to θ( development is performed under conditions that satisfy the following formula: 2.4｜v/V｜1.5｜v/V｜−0.12θ+1.8θ5, where V is the circumferential speed of the drum and v is the circumferential speed of the sleeve. A magnetic brush developing method is provided. The invention will be explained in detail below. In FIG. 1 for explaining the magnetic brush development method, a magnet roll 1 having a large number of magnetic poles NS is connected to a sleeve 2 made of a non-magnetic material such as aluminum.
The magnet roll 1 and the sleeve 2 are arranged in the relationship described in detail below.
A two-component developer 3 is supplied from a developer tank 4 to the outer peripheral surface of this sleeve 2 to form a magnetic brush 5. This magnetic brush 5 is adjusted in grain length by a grain cutting mechanism 6, and is conveyed to a position where it rubs against the electrophotographic photosensitive layer 7 on the drum base, and the electrostatic latent image on the photosensitive layer 7 is transferred to the electrostatic latent image on the electrophotographic toner 8. to form a visible image. A feature of the present invention is that the two-component developer 3 contains a ferrite carrier and electrostatic toner particles in a weight ratio of 4:1 to 20:1, particularly 5:1 to 12:1. Using a developer, the non-magnetic sleeve 2 is moved in the opposite direction to the moving direction of the drum 7 at the sliding position of the developer magnetic brush, and the magnet 1 in the sleeve is fixed to perform development. Based on the line M connecting the center and the center of the sleeve 2, the setting angle of the pole magnet N or S in the downstream direction of the drum rotation closest to this is θ (degrees), the circumferential speed of the drum 7 is V, and the sleeve 2 When the circumferential velocity of is v, under the conditions that satisfy the following formula 2.4 | v / V | 1.5 ... (1) | v / V | -0.12θ + 1.8 ... (2) θ5 ... (3) The purpose is to perform development. Generally, the electrical characteristics of a two-component developer are such that an electrode drum of the same size as the electrophotographic photoreceptor drum is installed in place of the photoreceptor drum, and the developer is supplied onto the developing sleeve to form a magnetic brush. Evaluation can be made by rubbing this magnetic brush against the electrode drum, applying a voltage between the sleeve and the drum, and measuring the current flowing between them. Figure 2 shows the iron powder carrier and electrostatic toner.
Current value (μA) measured by the method described above for developer A mixed at a weight ratio of 10:1 and developer B mixed with a ferrite carrier and the same electrostatic toner at a weight ratio of 10:1. and the operating time (hr) of the drum and sleeve. According to the measurement results, the developer using a ferrite carrier shows significantly higher electrical resistance than the developer using an iron powder carrier, and the developer using a ferrite carrier has an electrical resistance even during long-term operation. It is clear that while the resistance is approximately constant, the electrical resistance changes rapidly in the developer using the iron powder carrier, resulting in a significant increase in electrical resistance. In this way, when an iron powder carrier is used, the reason why the electrical resistance of the developer increases over time is that the toner particles are pulverized by the carrier and their particle size becomes finer, and that the carrier contains resin that makes up the toner particles. It is recognized that the cause is the formation of a film-like coating. The results shown in Figure 2 show that the combination of ferrite carrier and electrostatic toner has stable electrical characteristics even during long-term operation, and that the combination of toner particles does not This proves that defects such as pulverization and resin coating on the carrier surface do not occur. In the present invention, sintered ferrite particles, in particular spherical sintered ferrite particles, are advantageously used as ferrite carriers. The particle size of the sintered ferrite particles is generally in the range of 20 to 100 microns. If the particle size of the sintered ferrite particles is smaller than 20 microns, it tends to be difficult to make the magnetic brush stand up well, while if the particle size is larger than 100 microns, The toner images that are formed tend to have the aforementioned brush marks or scratches. The sintered ferrite particles used in the present invention are known per se, such as zinc iron oxide (ZnFe ₂ O ₄ ), yttrium iron oxide (Y ₃ Fe ₅ O ₁₂ ),
Iron cadmium oxide (CdFe ₂ O ₄ ), iron gadolinium oxide (Gd ₃ Fe ₅ O ₁₂ ), iron copper oxide (CuFe ₂ O ₄ ), iron lead oxide (PbFe ₁₂ O ₁₉ ), iron nickel oxide (NiFe ₂ O ₄ ), neodymium iron oxide (NdFeO ₃ ), barium iron oxide (BaFe ₁₂ O ₁₉ ), magnesium iron oxide (MgFe ₂ O ₄ ), manganese iron oxide (MnFe ₂ O ₄ ),
Sintered ferrite particles having a composition consisting of one or more types of lanthanum iron oxide (LaFeO ₃ ) and the like are used. Particularly suitable for the purposes of the present invention are sintered ferrite particles consisting of iron manganese zinc oxide. 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, acrylic 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 (CI 26250) and Spiron Black, naphthenic acid metal salts, fatty acid metal soaps, resin acid soaps, etc. are used as necessary. In the present invention, it is also important to use the ferrite carrier and the electrostatic toner in the above-mentioned weight ratio; if the amount of the ferrite carrier is greater than the above-mentioned range, the image density tends to decrease; If it is less than the range, fogging (coloring of the background) in non-image areas will increase. In the present invention, in connection with the use of a two-component developer consisting of a ferrite carrier and electrostatic toner, the moving directions of the drum and sleeve at the magnetic brush rubbing position are opposite to each other, and the standard It is also important that the magnetic pole closest to line M is offset by an angle θ in the downstream direction of drum rotation.
The hardness of the ferrite carrier is lower than that of the iron powder carrier, and the particle shape of the ferrite carrier is almost spherical. It has the characteristic of being softer than a brush. In the present invention, the moving directions of the drum and the sleeve are opposite to each other at the sliding position, which means that the magnetic brush can rub the photosensitive layer evenly and many times, while the reference line By knitting the magnetic poles with respect to M in the downstream direction of the drum rotation, the peaks of the spikes correspond to the magnetic poles, which means that the development area or development time of the sleeve is expanded. When using a developer that uses an iron powder carrier, if the rubbing frequency of the magnetic brush is increased and the rubbing area is expanded, there is a tendency for noticeable brush marks to occur in the image. By using the rear brush, it is possible to prevent the occurrence of brush marks, and by increasing the rubbing frequency and expanding the rubbing area, it is possible to form a high-density, uneven image. The development conditions used in the present invention are shown in FIG.
It is represented as an area surrounded by four lines 1-a, 1-b, 2 and 3. Here, line 1-a is |v/V|=1.5, line 1-b is |v/V|=2.4, line 2 is |v/V |-0.12θ+1.8, and line 3 is θ=5. We will respond accordingly. That is, in the region below the straight line 1-a, the frequency of rubbing decreases, resulting in a significant decrease in density, and the formed image is likely to have an edge effect. Straight line 1-
In the area above b, the rubbing frequency is too high,
The gradation of the formed image deteriorates, and further defects such as trailing occur. Furthermore, in the area to the left of the straight line 2, the contact time with the magnetic brush is short, so toner is not sufficiently applied, resulting in a decrease in image density and a tendency for brush marks and edge effects to occur in the image. Furthermore, on the right side of the straight line 3, since the contact time with the magnetic brush is long, too much toner is applied, which also tends to reduce the gradation. In this way, the development area surrounded by the four lines in Figure 3 is extremely critical in terms of the quality of the image formed, as conditions far away from this area will cause significant image deterioration. It seems clear from the facts in the examples described below that this is acceptable. The development conditions in the present invention are such that when the value of |v/V| is small, the allowable range of the magnetic pole setting angle θ is small, while as the value of |v/V| becomes large, the allowable range of θ is widened. This is clear from Figure 3. |v/V| and θ are the following formulas: 2.35|v/V|1.6 ...(1') |v/V|-0.6θ+2.0...(2') |v/V|-0.6θ+2.0 ...(3') It is most preferable to be in the range that satisfies the following, that is, in the shaded area in FIG. 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 so that the magnetic brush can sufficiently rub the surface of the photoreceptor at a clearance d between the photoreceptor drum and the developing sleeve. Generally, 1.1 to 3.0 times the development clearance d, especially 1.2
It is desirable to cut the ears so that the length of the ears is 2.0 times longer. In the present invention, since a ferrite carrier with low residual magnetization is used, one of the advantages is that ears can be cut at small intervals. 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 following ferrite carrier and toner were well mixed and stirred at a weight ratio of 9:1 to prepare a developer with an electrical resistance of 2.0×10 ⁸ Ω in the measurement of electrical characteristics between the electrode drum and the developing sleeve. . (a) Ferrite carrier Electrical resistance: 2.6×10 ⁹ Ω to 2.5×10 ¹⁰ Ω, maximum magnetization: 49.8 emu/g, residual magnetization:
0.25emu/g, retention force: 3.380e, center particle size:
40μ (b) Toner Hymer SBM73 (styrene resin: manufactured by Sanyo Chemical Industries) ... 87 parts by weight Viscoel 550p (low molecular weight polypropylene: manufactured by Sanyo Chemical Industries) ... 5 parts by weight Special Black 4 (carbon black: manufactured by Degussa) )...5.5 parts by weight Pontron S-32 (dye: manufactured by Orient Chemical Co., Ltd.)
...1.5 parts by weight The mixture consisting of the above composition was sufficiently melted and kneaded and dispersed in a heated three-roll mill, taken out and coarsely ground to about 2 mm in a cooling reciprocal coarse grinder (Rotoplex Cutting Mill: manufactured by Albine), After that, supersonic jet mill (NIPPON PNEUMATIC MFC)
(manufactured by Co. Ltd.) to a particle size of approximately 10 to 20μ. Next, using this developer, the radius of the photoreceptor drum: R = 45.0 mm, the surface potential of the photoreceptor: 750 volts,
Table 1 shows that the photoreceptor drum and the developing sleeve were rotated in opposite directions under the following conditions: radius of the developing sleeve: γ = 19.0 mm, bias voltage: 250 volts, developer spike gap: δ = 1.0 mm. Copying tests were conducted with various combinations of drum and sleeve rotational speeds as shown, and by changing the setting angle of the magnetic pole closest to the photoconductor drum in the downstream direction of the drum rotation. As a result, the developing clearance d was 1.5 mm to Copy image evaluations as shown in Tables 2 to 9 were obtained in the range of 1.9 mm. In each table, the x marks represent defects such as poor gradation, fogging, white spots due to edge effects, low density images, brush marks, trailing, etc. Tables 2 to 9 show image evaluations based on changes in the set angle of the magnetic poles in Experimental Examples A to H in Table 1, respectively. The overall evaluation of the image is shown in FIG. 3 by ○ mark: excellent, △ mark: good, and × mark: poor.

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【table】 [Brief explanation of the drawing]

Fig. 1 is a principle diagram explaining the magnetic brush development method according to the present invention, Fig. 2 is a diagram showing changes in electrical characteristics of the developer over time, and Fig. 3 is a diagram showing the circumferential speed ratio of the developing sleeve and photoreceptor drum and the developing roll. FIG. 3 is a diagram showing the relationship between the set angles of the magnetic poles. 1... Magnet roll, 2... Developing sleeve, 3... Developer, 5... Magnetic brush, 7... Photosensitive layer.

Claims (1)

[Claims] 1. A two-component developer consisting of a mixture of magnetic carrier particles and toner particles that can be charged by friction between the magnetic carrier and the magnetic carrier is supplied onto a developing sleeve having a magnet in a non-magnetic sleeve. forming a magnetic brush of the developer, and rubbing the magnetic brush against the surface of a drum-shaped photoreceptor having an electrostatic latent image while a bias voltage is applied between the photoreceptor and the sleeve. , a magnetic brush development method comprising forming a toner image corresponding to an electrostatic latent image, the two-component developer comprising a ferrite carrier and chargeable toner particles in a weight ratio of 4:1 to 20:1. This is a two-component developer that contains a non-magnetic sleeve that moves in the opposite direction to the drum movement direction at the developer rubbing position, and develops by fixing the magnet inside the sleeve. When the set angle of the nearest magnetic pole in the downstream direction of drum rotation is θ (degrees) based on the line connecting /V|≧1.5 |v/V|≧−0.12θ+1.8 θ≦5 A magnetic brush developing method characterized by performing development under conditions that satisfy the following.