JPS6353544B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to improvements in a two-component magnetic developer used in electrophotography, and more particularly, to a two-component magnetic developer that significantly reduces or eliminates the occurrence of brush marks in solid black image areas. Regarding. 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. 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 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, which is a fundamental problem in eliminating brush marks. It can hardly be called a countermeasure. The present inventors have selected and used a magnetic carrier in a two-component magnetic developer that is made of rounded amorphous iron powder, has a relatively fine particle size, and has a relatively large loose apparent density. It has been found that the occurrence of the brush marks described above can be effectively reduced or eliminated, and that a toner image with excellent density, sharpness, and resolution can be formed. Therefore, an object of the present invention is to provide a two-component magnetic developer in which the occurrence of brush marks is reduced or eliminated. Another object of the present invention is to provide a two-component magnetic developer in which not only brush marks but also bleeding and white spots are effectively suppressed and the life of the magnetic carrier is extended. According to the present invention, in a two-component developer for magnetic brush development consisting of a mixture of magnetic carrier particles and toner particles that can be charged by friction with the magnetic carrier, (a) the magnetic carrier has a rounded corner; Consists of shaped iron powder with a particle size of 105 microns or less.
(b) Magnetic carrier particles and toner having a particle size distribution of 90% by weight or more, with a particle size of 37 to 74 microns accounting for 50% or more of the total weight, and a loose apparent density of 2.65 to 3.15 g/cc; (b) magnetic carrier particles and toner; Particles are 100:
(c) The developer as a whole has a loose apparent density of 1.6 to 2.2 g/cc. Ru. One of the important features of the invention is the use of rounded irregular iron powder as the magnetic carrier particles. In this specification, "cutting" means cutting corners without significantly changing the particle form of irregularly shaped iron powder.
This means that only the sharp corners of the amorphous iron powder are rounded. Figure 1 of the accompanying drawings is a scanning electron micrograph (magnification: 300) of amorphous iron powder with corners used in the present invention.
Fig. 2 shows a scanning electron micrograph (300x magnification) of an irregularly shaped iron powder similar to Fig. 1 except that the corners are not cut. Referring to FIG. 2 and FIG. 1, it is clear that in the magnetic carrier used in the present invention, the sharp corners of the amorphous iron powder in FIG. 2 are rounded off. Become. According to the research conducted by the present inventors, the cause of the above-mentioned brush marks is thought to be 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 through the carrier at this contact area. It will be done. On the other hand, it has been found that when a rounded irregular shaped iron powder is used as the magnetic carrier according to the present invention, the leakage through the carrier described above is suppressed, and as a result, the occurrence of brush marks is significantly suppressed. It will be done. 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.
It is expressed as the number of white lines per mm width x 5 mm length. That is, in a developer using uncut irregular shaped iron powder as a magnetic carrier, it is generally
In contrast, the two-component developer using rounded amorphous iron powder according to the present invention generates 30 brush marks/2 mm x 5 mm even when other conditions are the same. 5 brush marks/(2mm)
x 5 mm), especially to zero. In the present invention, it is also important to use so-called amorphous iron powder as a magnetic carrier in order to improve the density of the image. Spherical iron powder for magnetic carriers is also known, but with such spherical iron powder, toner charging is insufficient, especially under high humidity conditions, resulting in poor image density. However, according to the present invention, by using irregularly shaped iron powder in a rounded state, it is possible to maintain image density at a significantly high level while effectively preventing the occurrence of brush marks. It becomes possible to suppress this. The rounded amorphous iron powder used in the present invention is
It has different characteristics from conventional amorphous iron powder. That is, the amorphous iron powder conventionally used as a magnetic carrier as shown in Fig. 2 generally has a loose apparent density of 2.1 to 2.6 g/cc, although it also differs in particle size distribution. , the rounded irregular shaped iron powder used in the present invention is 2.65 to 3.15
g/cc, particularly greater than 2.80 to 3.11 g/cc. In this specification, the loose apparent density refers to a container with an internal volume of 100 c.c., which is dropped into a container with a mesh opening of 710 microns through a vibrating sieve in 20 seconds to form a heap on the top container, and then Weight measured by /
It is defined as the ratio of apparent loose volume, and more specifically, it can be easily measured using a powder tester manufactured by Hosokawa Micron Co., Ltd. In relation to the fact that the loose apparent density of the magnetic carrier used in the present invention is adjusted within the above-mentioned relatively large range, the magnetization rate on the sleeve with a built-in magnet is not rounded during development. It can be made larger than amorphous toner, and as a result, the generation of white spots caused by the transfer of the magnetic carrier to the electrophotographic photosensitive surface can be prevented, and the magnetic toner can be This makes it possible to prevent wear and tear on the carrier. In the present invention, it is further preferred that the magnetic carrier has a particle size distribution biased towards the relatively small side, that is, 90% by weight of the magnetic carrier has a particle size of 105 microns or less.
Above, 50% of the total particles have a particle size of 37 to 74 microns.
It is also extremely important to have a particle size distribution of at least % by weight in order to suppress the occurrence of brush marks and white spots. That is, if the particle size of the magnetic carrier is made larger than the above-mentioned range, brush marks will still occur even if rounded irregular iron powder is used, and furthermore, the saturated toner adsorption amount of the magnetic carrier will be reduced. There is also a tendency to become smaller. However, when the toner saturation adsorption amount decreases, the toner concentration in the developer decreases, resulting in a decrease in image density, and the occurrence of brush marks becomes more prominent. Even if the density is increased, toner scatters within the electrophotographic apparatus, causing contamination, and furthermore, the background of the copy becomes smudged and the so-called trailing of the copy image occurs. On the other hand, if the particle size of the magnetic carrier is made smaller than the above range, the magnetic carrier tends to migrate toward the photosensitive plate during development, resulting in the generation of white spots. In this specification, the toner saturation adsorption amount of the magnetic carrier has the following meaning. Now overmixing the magnetic carrier with toner particles and feeding this developer composition onto a rotating sleeve with an internal magnet,
As the magnetic brush continues to rotate, the relationship between the rotation time and the toner concentration in the developer composition is shown in the diagram in Figure 3, where the toner concentration decreases greatly at the beginning and gradually decreases. The drop becomes less and reaches a certain saturation value. In this specification, this saturation value of toner concentration is defined as the saturated toner adsorption amount of the magnetic carrier (hereinafter simply referred to as the saturated adsorption amount). In more detail, the magnetic flux density on the sleeve surface is 1000 Gauss, the sleeve diameter is 50 mm, and the rotation speed is
The magnetic brush was rotated at 120 rpm and the amount of spikes was 2.8 mm, and the relationship between the rotation time and the toner concentration was measured, and the saturated adsorption amount was determined as the number of parts by weight of toner per 100 parts by weight of the carrier. A magnetic carrier made of amorphous iron powder, of which more than 50% by weight of the total particle size is in the range of 100 to 150 microns, has a low saturation adsorption amount of about 3 to 5%, as shown by curve A in Figure 3. In contrast, the magnetic carrier used in the present invention has a saturation adsorption in a higher range, as shown by curve B in FIG. 3, and generally has a saturation adsorption of 7 to 10%. Thus, it will be understood that according to the present invention, remarkable advantages are achieved not only in preventing brush marks from occurring, but also in improving image density and preventing toner scattering. The magnetic carrier used in the present invention is manufactured by means known per se, except that the iron powder particles are rounded at some stage in the process of manufacturing irregularly shaped iron powder.
Magnetic carrier iron powder is produced by primary crushing of mild steel scrap, oil sintering,
After going through processes such as ore beneficiation, nitriding is performed to form brittle primary particles, which are pulverized to form final particles, which are denitrified, and finally, the surface is oxidized to remove surface electricity. Manufactured by increasing resistance. The rounded amorphous iron powder is preferably produced by rounding the particles at an arbitrary step after the nitriding process and before the surface oxidation process. This corner cutting is done by cutting the unshaped iron powder into each other.
For example, it can be obtained by mutual abrasion in a Henschel mixer and sieving. In this case, it is preferable to stir at a low speed to effectively effect friction between the particles, and generally it is preferable to perform the treatment at a rotation speed of 200 to 500 revolutions/minute for 3 to 10 hours. Processing using a hammer mill, vibratory mill, etc. is not desirable for the purposes of the present invention, since the iron powder becomes flat and plate-like and loses its amorphous particle morphology. The magnetic carrier used in the present invention desirably has a volume electrical resistance of 10 ⁶ Ω-cm to 10 ⁹ Ω-cm from the viewpoint of suppressing the occurrence of brush marks and significantly improving image density. This volume electrical resistance is measured by the method described below. That is, the magnetic carrier is held within the range of the magnetic field and placed so that no pressure other than gravity and magnetic force is applied to it. The magnetic carrier at this time appears to be solid, but its fluidity, which is a characteristic of the magnetic carrier, cannot be impaired except by very strong magnets. In this state, the carrier is brought into contact with an electrode and the electrical resistance is determined using a conventional method. If the distance between the electrodes is accurately determined using a micrometer, the volume resistivity can be obtained. The measurement conditions are as shown below. Electrode: Made by Shinchuu Thickness of counter electrode: 1mm Magnetic force: Approximately 680 gauss on the surface Distance between electrodes: 1 to 3mm Applied voltage: 50V In addition, the sample magnetic carrier is placed between the electrodes. The best way to fix the sample is to place a magnet parallel to the line of gravity, and after the sample is magnetically attracted and fixed to the bottom of the magnet,
It is sufficient to move the opposing electrode plates perpendicular to the lines of magnetic force. The two-component developer according to the invention is produced by mixing the above-mentioned magnetic carrier with an electrostatically colored toner known per se. In this case, according to the invention, magnetic carrier and toner can be used in a relatively high toner concentration range, such as a weight ratio of 100:6 to 100:17, in particular 100:8 to 100:15. is one of the notable advantages. The two-component developer according to the present invention having such a compounding ratio has a total density of 1.6 to 2.2 g/cc, particularly 1.7 to 2.2 g/cc.
It has a loose apparent specific gravity of 2.0 g/cc, and the developer as a whole has a larger loose apparent density than conventional ones, and under actual development conditions, it is denser and more dense than the conventional developer. It will be appreciated that a magnetic brush with less transfer to the photosensitive layer of the carrier can be formed. 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, 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 (CI26150) and Spiron Black, naphthenic acid metal salts, fatty acid metal soaps, resin acid soaps, etc. are used as necessary. The two-component developer according to the present invention is suitably used in magnetic brush development described below. That is, an electrophotographic photosensitive layer having an electrostatic latent image is brought into sliding contact 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 area, the moving direction of the magnetic brush is opposite to the moving direction of the photosensitive layer, and the ratio of toner particles to magnetic carrier particles in the magnetic brush development area is set to be lower than the saturation adsorption amount of toner particles to the magnetic carrier particles. 20～
Development is carried out at a ratio of 150%, especially 40 to 130%. That is, the magnetic carrier used in the present invention not only increases the saturation adsorption amount of toner due to the above-mentioned unique particle characteristics, but also increases the toner's magnetic absorption even when the toner ratio is higher than the saturation adsorption amount. By being included in the brush at this concentration, further advantages are achieved in terms of suppressing the occurrence of brush marks and improving the density. Furthermore, in this development method, it is extremely important that the direction of movement of the magnetic brush is opposite to the direction of movement of the photosensitive layer in the magnetic brush development area. That is, it is known that the toner image density increases depending on the relative sliding speed difference between the photosensitive layer and the magnetic brush. On the other hand, 2 used in the present invention
In component-based magnetic developers, 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 the generation of powder smoke due to free toner. This may cause background stains (fogging). According to the above-described development method, by setting the moving direction of the magnetic brush in the opposite direction to the moving direction of the photosensitive layer,
Without increasing the circumferential speed of the magnetic brush too much, that is, without increasing the centrifugal force too much,
It becomes possible to increase the relative speed with the photosensitive layer, and it becomes possible to increase image density without fear of generating free toner powder smoke. In addition, the occurrence of brush marks is also influenced by the circumferential speed of the magnetic brush and, therefore, the centrifugal force, and under conditions where the centrifugal force becomes large, the occurrence of brush marks tends to increase. According to the above-described development method, 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. can. 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. The invention is illustrated by the following example. Example 1 Styrene resin (Picolastic D150 Pennsylvania Chemical) 100 parts by weight Carbon (Special Degussa) 5 parts by weight Spiron Black B-HH (Hodogaya Chemical)
3 parts by weight The above composition was pre-mixed in a ball mill for 24 hours, kneaded with a heated roll at 150°C, cooled and solidified, and then coarsely pulverized and finely pulverized with a jet mill. Product particle size ranges from ~25 microns. Next, 11 parts by weight of the above-mentioned toner was added to 100 parts by weight of a carrier made of rounded amorphous iron powder, and sufficient mixed triboelectrification was carried out. Using a Se photoreceptor, corona charging at +6.5KV, exposure, development, transfer, and fixing were performed, and a copy of very high density and good image quality with no fog could be obtained. Example 2 Acrylic resin (X-106 IONATSUKU Co., Ltd.)
100 parts by weight Carbon (MA-8 Mitsubishi Kasei) 6 parts by weight Bontron (S-31 Orient Chemical)
5 parts by weight polypropylene (Viscol 550P Sanyo Chemical Co., Ltd.)
8 parts by weight The above composition was treated in the same manner as in Example 1 to give 5 to 25 parts by weight.
Carrier adjusted micron toner
When 10 parts by weight of toner per 100 parts by weight was added and thoroughly mixed with the carrier, copies were made using a commercially available DC-161 (manufactured by Sanda Kogyo Co., Ltd. copying machine). Excellent printability was also obtained. Example 3 Acrylic resin (BR-105.Mitsubishi Rayon Co., Ltd.)
100 parts by weight Carbon (Special. Degussa) 5 parts by weight Nigrosine EX (Orient Chemical) 5 parts by weight Polypropylene (Viscol 550P. Sanyo Chemical)
10 parts by weight The above composition was adjusted to a toner size of 5 to 25 microns in the same manner as in Example 1. 10 parts by weight per 100 parts by weight of carrier was added, and the developer mixed thoroughly with the carrier was mixed with a commercially available Mita developer. copister
251R (manufactured by Sanda Kogyo Co., Ltd.), the resulting copy was of good quality with high contrast and no brush marks or fog. Example 4 Using the toner of Example 2, a developer of 100 parts by weight of the carrier and 15 parts by weight of the toner was prepared and copies were made using a commercially available Sanda Copister DC-131 copying machine. Very good copies were obtained. Obtained. In addition, even though the number of copies was 50,000 copies, the copies were free from brush marks and had excellent copy image quality. It has also been found that the carrier of the present invention has an excellent lifespan. That is, the image quality was extremely stable even after 50,000 copies were made.
Furthermore, when the spent toner rate was measured after 50,000 sheets, it was found to be extremely low at 0.5%, which is evidenced by the effect of corner cutting. Example 5 Priorite VTAC (Gutsutoiya)
100 parts by weight carbon (MA-8. Mitsubishi Kasei) 5 parts by weight polypropylene (Viscol 550P. Sanyo Chemical)
6 parts by weight Bontron (S-31. Orient Chemical Co., Ltd.)
3 parts by weight were kneaded in the same manner as in Example 1 using a kneader at 150°C for 1 hour to obtain a toner of 5 to 25 microns. This toner per 100 parts by weight of carrier
13 parts by weight were added and mixed to prepare a developer. When 50,000 copies were made using a commercially available Copistar DC-161 copying machine, stable copies with no fogging, brush marks, smudges, line reproducibility, or edge effects could be obtained continuously. Comparative Example 1 Commonly used "cornering" using 5-25 micron toner produced and granulated according to Example 2
For 100 parts by weight of untreated carrier,
A developer was prepared by mixing 10 parts by weight of toner. When this developer was used to make copies using a commercially available Mita DC-161 copying machine, the resulting copies had many brush marks and edges. Also, when we conducted a continuous copying test,
After printing 10,000 sheets, the image density decreased and at the same time fog occurred, so I measured the toner concentration of the developer and found that (toner/carrier = 10/100)
Even though the toner was contained in a high proportion, the toner spent rate showed a high value (i.e. 1.2%), indicating deterioration of the carrier. Comparative Example 2 A developer prepared by adding 11 parts by weight to 100 parts by weight of the carrier using a plate-treated carrier using the toner having a particle size of 5 to 25 microns produced in Example 1 was prepared using a commercially available ( Mita DC-161) When I tested the copy using a copy machine, many brush marks appeared. This proves that when the plate-like particles form ears on the magnetic sleeve, the magnetic flux density is strong in the tip shape, and therefore the tip is in strong contact with the surface of the photoreceptor. Comparative Example 3 By adding toner to the developer of Comparative Example 2,
Although the toner/carrier ratio was increased to 15/100 to increase the toner density, fogging occurred and brush marks were not improved. A comprehensive comparison table (Table-1) of the present invention and comparative examples is summarized below. Table 1 also shows the particle size distribution, copy test results, etc. of the carrier used in each Example and Comparative Example.

【table】

[Table] *1 For brush marks, place a 2 mm x 5 mm blank mask on the black solid image area, and use a Nikon measure scope.
The number of pieces was counted using a metallurgical microscope (Nippon Kogakusha).

[Brief explanation of the drawing]

FIG. 1 is a scanning electron micrograph of the magnetic carrier with the chamfered edges used in the present invention, FIG. 2 is a scanning electron micrograph of the magnetic carrier without the chamfered edges, and FIG. FIG. 3 is a diagram showing the relationship between rotation time and toner concentration in developer.

Claims (1)

[Scope of Claims] 1. A two-component developer for magnetic brush development comprising a mixture of magnetic carrier particles and toner particles that can be charged by friction with the magnetic carrier, in which (a) the magnetic carrier is rounded; Consists of irregularly shaped iron powder, with a particle size of 105 microns or less.
(b) Magnetic carrier particles and toner having a particle size distribution of 90% by weight or more, with a particle size of 37 to 74 microns accounting for 50% or more of the total weight, and a loose apparent density of 2.65 to 3.15 g/cc; (b) magnetic carrier particles and toner; Particles are 100:
A two-component developer for magnetic brush development, characterized in that: (c) the developer as a whole has a loose apparent density of 1.6 to 2.2 g/cc;