JP3384106B2 - Development method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a permanent magnet member having a cylindrical shape formed by transferring an electrostatic image formed on the surface of an image carrier carrying an electrostatic image. A developing method of visualizing an image with a two-component magnetic developer mainly composed of a toner and a magnetic carrier, which is adsorbed and held on the surface of a developer supporting and transporting means comprising: The present invention relates to a developing method capable of preventing occurrence of the occurrence and performing stable high-quality development. 2. Description of the Related Art Conventionally, in an image forming method in a printer, a facsimile, or the like to which electrophotography or electrostatic recording is applied, for example, an electrostatic charge image is formed on a surface of a photosensitive drum formed in a cylindrical shape, and then the image is formed. The magnetic developer is attracted to the surface of the sleeve by a developing roll comprising a sleeve provided opposite to the photoreceptor drum and having a permanent magnet member incorporated therein and rotatably fitted coaxially with the permanent magnet member. And transport. Thereafter, a method is employed in which a magnetic brush is formed in the developing area, and the surface of the photosensitive drum on which the electrostatic charge image is formed is rubbed with the magnetic brush so as to be visualized as a toner image. The most common means is to transfer this visualized toner image to recording paper and then fix it by heat. In recent years, there has been an increasing demand for miniaturization of apparatuses used for image formation as described above, and it has become important to reduce the size of the developing unit. As means for satisfying such demands, it has been proposed to directly adsorb the magnetic developer on the surface of the permanent magnet member without using a sleeve and to transport the magnetic developer by rotating the permanent magnet member. (See, for example, JP-A-62-201463). FIG. 2 is a cross-sectional view of an essential part showing an example of a conventional developing means. In FIG. 2, reference numeral 1 denotes a developer tank which accommodates a magnetic developer 2 containing toner and a magnetic carrier as main components, and a rotatable permanent magnet member 4 below the developer. At least the surface of the permanent magnet member 4 is made conductive, and a plurality of magnetic poles extending in the axial direction are provided on the outer peripheral surface, and are formed in a columnar shape. The above-mentioned permanent magnet member 4 is made of a resin magnet made of a mixture of a ferromagnetic powder and a resin (Japanese Patent Laid-Open No. 57-1304).
07, 59-905 and 59-226367). As a means for forming the surface to be conductive, a conductive layer may be formed on the surface by bonding, plating, or the like, or a powdered conductive substance may be added at the time of kneading the raw materials. Further, the permanent magnet member 4 may be formed of a hard ferrite magnet to be semiconductive. Reference numeral 7 denotes a photosensitive drum which is rotatable in the direction of the arrow and faces the permanent magnet member 4 via a gap g. Reference numeral 8 denotes a doctor blade, which is provided in the developer tank 1 and faces the permanent magnet member 4 via a gap t.
The thickness of the magnetic developer 2 adsorbed on the surface of the permanent magnet member 4 is regulated. Reference numeral 10 denotes a DC power source for applying a bias voltage to the surface of the permanent magnet member 4. With the above configuration, when the permanent magnet member 4 is rotated in the direction of the arrow, the magnetic developer 2 is attracted to the permanent magnet member 4 and is conveyed. The toner in the magnetic developer 2 is transferred by the electric field of the electrostatic image formed on the body drum 7,
The electrostatic charge image can be visualized. [0008] In the above image forming means, the two-component magnetic developer includes, for example, a magnetic toner having a particle size distribution of 5 to 20 μm and a magnetic toner having a particle size distribution of 70 to 140 μm. A magnetic developer 2 which is a mixed material with a ferrite carrier (for example, KBN-100 manufactured by Hitachi Metals) is used. In some cases, non-magnetic toner is used instead of magnetic toner. In this case, in order to form a high-definition image, it is necessary to use a toner having a small particle size (for example, a particle size distribution of 4 to 16 μm). When such a toner is used, fogging is likely to occur due to insufficient charging ability of the toner, and there is a problem that image quality is deteriorated. Therefore, in order to obtain a high-definition image, a toner having a small particle size is required, and a magnetic carrier having a small particle size (for example, an average particle size of 50 μm or less) is required. However, when the above-described magnetic carrier having a small particle diameter is used, an undesired phenomenon that the magnetic carrier which should originally be attracted and remains on the surface of the permanent magnet member 4 adheres to the photosensitive drum 7. Happens. This is because the magnetic carrier itself also has a particle size distribution, and a small particle size region is transferred to the photosensitive drum 7 side. Even if the magnetic carrier having such a small particle size adheres to the photosensitive drum 7, the image quality is hardly adversely affected, but the toner concentration is relatively high due to the decrease of the magnetic carrier in the magnetic developer. In addition, there is a problem that density unevenness and background fog occur. Next, in the developing roller with the sleeve, the magnetic developer adsorbed on the surface of the sleeve rotates on the surface of the sleeve, so that the height of the ears of the magnetic brush tends to be relatively uniform. In the case of the configuration lacking, the height of the ears of the magnetic brush fluctuates.
That is, immediately above the magnetic poles of the permanent magnet member 4, the height of the ears of the magnetic brush becomes large, while between the magnetic poles, the height becomes small. Therefore, there is a problem that the contact state between the magnetic brush and the photosensitive drum 7 fluctuates, and density unevenness occurs. In order to prevent the above density unevenness,
Although it is conceivable to increase the number of revolutions of the permanent magnet member 4, it is necessary to increase the driving torque in order to rotate the permanent magnet member 4 at a high speed, and at the same time, it generates noise, and the magnetic material constituting the magnetic developer There is a problem that the carrier is worn. The present invention solves the above-mentioned problems in the prior art, and provides a developing method capable of preventing the occurrence of density unevenness and background fog over a long period of time and performing stable high-quality image development. The purpose is to: In order to achieve the above object, the present invention provides an electrostatic image on a moving image carrier which carries an electrostatic image and comprises a toner comprising a toner and a magnetic carrier. In the developing method of developing using a component-based magnetic developer, as a means for supporting and transporting the magnetic developer, using a permanent magnet member cylindrically and rotatably provided with a plurality of magnetic poles on its surface, The magnetic developer is attracted to and conveyed to the surface of the permanent magnet member, and is supplied together with the toner when the toner is supplied.
Together with replenishing the magnetic carrier, used having an average particle diameter of the magnetic carrier for this replenishment include average particle size <br/> and equal to or than the small particle size particles of the toner at the start, that Technical measures were adopted. The permanent magnet member in the present invention is not limited to a ferrite magnet, but may be a resin magnet containing magnetic powder and a resin material as main components. Also, this permanent magnet member
The magnet may be integrally formed in a roll shape on the outer periphery of the shaft, or may be formed entirely of a magnet material including the shaft. However, in order to prevent development unevenness, the permanent magnet member needs to be formed integrally without any joint in the circumferential and axial directions. On the surface of the permanent magnet member, magnetic poles of different polarities are alternately arranged in the circumferential direction at minute intervals, so that as the number of magnetic poles increases, the surface magnetic flux density decreases. On the other hand, from the viewpoint of preventing the magnetic developer from scattering, the surface magnetic flux density of the permanent magnet member is preferably 50 G or more, and in order to make it easier for the toner to adhere to the electrostatic image formed on the surface of the image carrier, It is preferably 1200 G or less. The number of magnetic poles is preferably 8 to 60 poles corresponding to the surface magnetic flux density of 50 to 1200 G. The more preferable range of the surface magnetic flux density is 100 to 800G. Next, when the number of magnetic poles is increased, the magnetic field formed around the permanent magnet member decreases, and the amount of the magnetic developer adhered to the surface of the permanent magnet member decreases. For this reason, the thickness of the magnetic developer layer formed on the surface of the permanent magnet member tends to be non-uniform, so that it is necessary to rotate the permanent magnet member at high speed in order to prevent such an undesirable phenomenon. However, if the rotation speed of the permanent magnet member is too high, the driving torque increases and the carrier constituting the magnetic developer is worn. On the other hand, if the rotation speed is too slow, density unevenness occurs in the image. Therefore, the peripheral speed V of the permanent magnet member
m (mm / sec) is 1 to 1 of the peripheral speed Vp (mm / sec) of the image carrier.
It is preferably set to 0 times, more preferably 2 to 6 times.
It is twice. Next, assuming that the outer diameter of the permanent magnet member is D (mm) and the number of magnetic poles provided on the surface is M, the value of h (mm) represented by the following equation is smaller than 2. It is preferable to set D, M, and Vm. H = πD · Vp / M · Vm The above h is the pitch at which the surface of the image bearing member faces the magnetic pole of the permanent magnet member within a unit time, but if h is 2 mm or more, uneven development may occur. The thickness is preferably smaller than 2 mm, more preferably 1 mm or less, for conspicuousness. In this case, to reduce the value of h, the number of magnetic poles M and the peripheral speed Vm of the permanent magnet member may be increased. However, if the number of magnetic poles M is too large, the surface magnetic flux density decreases, and The agent is liable to be scattered, and if the peripheral speed Vm is too large, the above-mentioned problem occurs. Therefore, in practice, the value of h is preferably set to 0.4 to 1.0 mm. When a doctor gap t, which is a gap between the surface of the permanent magnet member and the tip of the doctor blade, is provided, the difference between the developing gap g, which is the gap between the permanent magnet member and the image carrier, is considered from the viewpoint of image quality. With (gt) = 0.2 ±
It is preferably 0.15 mm. Note that the doctor blade is brought into contact or pressure contact with the surface of the permanent magnet member so that t
= 0. In this case, the doctor blade is formed of a magnetic material such as SK material or a non-magnetic material such as SUS304 or phosphor bronze into an elastic blade shape, one end of which is fixed to the developer tank, and the other end of which is the permanent magnet member. What is necessary is just to make it contact a surface. Next, when the permanent magnet member in the present invention is made of a semiconductive or insulating material, the place where the bias voltage is applied is preferably a doctor blade.
In this case, the doctor blade may be formed of a conductive material such as a metal. When the permanent magnet member is made of a conductive material, the bias voltage is preferably applied from a shaft or the like. Next, as a two-component magnetic developer, a toner adjusted to a predetermined toner concentration in advance is charged into a developer tank, or a predetermined amount of magnetic carrier is adhered to the surface of a permanent magnet member. After that, the toner can be charged into the developer tank and used as a two-component magnetic developer for starting. When the toner is supplied, the toner and the magnetic carrier are supplied together. In this case, it is preferable to mix the toner and the magnetic carrier in advance. In the case of a system in which the developing device is replaced, that is, in the case of a disposable developing cartridge, a configuration is adopted in which a magnetic carrier in a consumption amount or more is mixed with the toner. As the magnetic carrier constituting the magnetic developer, iron powder and ferrite particles (Ni—Zn, Mn—Zn, Cu—Z) used in a general two-component system are used.
n-type) and magnetite particles. Further, a binder type in which these magnetic powders are dispersed in a resin may be used. In this case, the use of iron powder Bian Tairajo, with the value of the magnetization is large, since the residual of the geometrically permanent magnet member is large, arbitrary preferable because carrier adhesion is small. As the magnetic carrier to be replenished together with the toner, a carrier containing particles having an average particle size equal to or smaller than the average particle size of the toner at the start is used. That is, the magnetic carrier in the magnetic developer is, for example, one having a particle size distribution of 1 to 50 μm. Since a relatively small particle size tends to be transferred to the image carrier side together with the toner and decreases during continuous use, This is because it is necessary to supply the reduced amount and to obtain a high-definition image. It is not preferable that the magnetic carrier has a large particle diameter, because the ability to impart charge to the toner is reduced and a high-definition image cannot be obtained. On the other hand, if the particle size of the magnetic carrier is too small, it is not preferable because carrier adhesion occurs. Therefore, it is preferable to use the above. The magnetic carrier may be a mixture of two or more kinds of the above magnetic particles and binder type magnetic particles, and the mixing ratio may be determined in consideration of the size of the magnetic particles, magnetic characteristics, and the like. The toner to be mixed with the carrier may be either magnetic or non-magnetic, but has a volume resistivity of 10 ¹⁴ Ω from the viewpoint of improving transferability.
An insulating material having a size of not less than cm is preferable, and a material which is easily charged by friction between the carrier and the doctor blade (having a frictional charge of 10 μc / g or more) is preferable. In order to obtain a high-definition image, the average particle size of the toner is 5 to 10%.
It is preferably formed to a thickness of μm. The mixing ratio of the toner in the magnetic developer is preferably 10 to 90% by weight for the magnetic toner, and 5 to 60% by weight for the non-magnetic toner. The composition of the toner is the same as that of a commonly used toner, such as a binder resin (styrene-acrylic copolymer, polyester resin, etc.), a colorant (carbon black, etc., but magnetite is used as a magnetic powder described later). In some cases, it may not be added) as essential components, and as optional components, magnetic powder (magnetite, soft ferrite, etc.), charge control agent (nigrosin, metal-containing azo dye, etc.), release agent (polyolefin, etc.), Those containing (internally and / or externally) a fluidizing agent (hydrophobic silica) can be used.
In the case of using a magnetic toner, the amount of the magnetic powder is preferably 70% by weight or less, since the fixability is deteriorated when the amount of the magnetic powder is large. By appropriately selecting a coloring agent, a color toner can be produced. The volume resistivity of the toner is DC4
Teflon (trade name) with an inner diameter of 3.05 mm in an electric field of KV / cm
A value measured by an insulation resistance meter (type 4329A manufactured by Yokogawa Hewlett-Packard) with a sample cylinder filled with several tens of mg of a sample and a load of 100 gf applied. Further, the triboelectric charge was measured using a commercially available blow-off triboelectric charge meter (TB-200, manufactured by Toshiba Chemical Co., Ltd.).
N-100)). According to the above arrangement, when continuous development is performed with a two-component magnetic developer, not only the toner in the magnetic developer but also the magnetic carrier adheres to the image carrier and decreases. However, by replenishing the magnetic carrier together with the toner, the occurrence of density unevenness and background fog can be prevented, and stable high-quality image development can be performed even in a wide toner density range. FIG. 1 is a cross-sectional view of an essential part showing an example of a developing means in an embodiment of the present invention, and the same parts are denoted by the same reference numerals as in FIG. In FIG. 1, the permanent magnet member 4 is formed of a semiconductive or insulating, for example, isotropic ferrite magnet having a volume resistivity exceeding 10 ⁶ Ω · cm, and a plurality of magnetic poles extending in the axial direction are provided on the outer peripheral surface. Formed into a columnar shape,
It is rotatably provided below the developer tank 1. Reference numeral 10 denotes a DC power supply, which is connected between the doctor blade 8 and the photosensitive drum 7. Next, an average particle diameter of 10 μm was used as the magnetic toner.
m, particle size distribution 4-16 μm, volume resistivity 10 ¹⁵ Ω · c
m and a triboelectric charge of -23 μc / g. The blending ratio is a weight ratio, styrene-n-butyl methacrylate 45, magnetite (Toda Kogyo EPT500) 50,
Polypropylene (TP32, Sanyo Kasei) 3, charge control agent (Bontron E-81, Orient Chemical) 2,
An external additive (R972 manufactured by Nippon Aerosil) 0.5 was added to the particles formed by these methods. The magnetic carrier has an average particle diameter of 30 μm.
m, particle size distribution 1-50 μm, volume resistivity 10 ⁶ Ω · c
m, the magnetization σ _{1000 at 1000} Oe is 120 emu /
Using the g-bian flat iron powder. The volume resistivity of the carrier is determined by taking a sample in the
It was calculated based on the resistance value measured by applying an electric field of 0 V / cm. The value of magnetization was measured using a vibrating sample magnetometer (VSM-3 manufactured by Toei Kogyo Co., Ltd.), and the average particle size (volume) of the toner was measured using a particle size analyzer (Coulter Counter Model TA-II manufactured by Coulter Electronics Co., Ltd.). Measured using On the other hand, the photosensitive drum 7 was formed by OPC and had a surface potential of -700 V and a peripheral speed of 30 mm / sec. The permanent magnet member 4 is made of a ferrite magnet (YBM-
According to 3), outer diameter 20 mm, 16 poles, surface magnetic flux density 500
G, a developing gap g = 0.4 mm, a doctor gap t = 0.3 mm, and a DC bias voltage of −550 V were applied via a doctor blade 8. According to the above-mentioned developing conditions, continuous development is performed by changing the toner concentration T / C (% by weight) in the magnetic developer for start, that is, the magnetic developer 2 to be charged into the developer tank 1 at the start. Table 1 shows the results of measuring the amount D (% by weight) of the collected carrier after continuous printing (A4 size) of 10,000 sheets. Note that the collected carrier amount D is a value obtained by the following equation. D = A / (A + B + C) (% by weight) where A: the amount of carrier collected by the cleaner B: the amount of toner collected by the cleaner C: the amount of toner consumed As is clear from Table 1, the toner in the magnetic developer is naturally consumed and reduced by the continuous development. At the same time, the magnetic carrier in the magnetic developer 2 is also transferred to the photosensitive drum 7. Is recognized. It can be seen that the transfer amount of the magnetic carrier is larger as the toner concentration T / C in the starting magnetic developer 2 is lower.
As the magnetic carrier in the magnetic developer 2 is consumed as described above, the toner concentration in the magnetic developer 2 increases,
As a result, density unevenness and background fog occur as described above. Table 2 shows the results of image evaluation after continuous printing of 10,000 sheets while replenishing a magnetic developer consisting of a toner and a magnetic carrier under the above-mentioned developing conditions. The replenishing magnetic developer used had the same composition as that of the starting magnetic developer. However, the replenishing magnetic developer in which the average particle size of the magnetic carrier was changed was also described. [Table 2] As apparent from Table 2, in Comparative Examples Nos. 5 to 8 in which only the toner is supplied in the continuous development, as shown in Table 1, both the toner and the magnetic carrier are used as shown in FIG. As a result, the toner concentration in the magnetic developer 2 increases, and background fog and dust are observed. On the other hand, together with the toner, the average particle diameter is 10 μm.
It can be seen that in Nos. 1 to 4 in the mode of replenishing the magnetic carrier of m, the toner concentration in the magnetic developer 2 can be stabilized, and as a result, a good image without background fog and dust can be obtained. The carrier weight% in the replenishing magnetic developer is preferably a value substantially in inverse proportion to the toner concentration in the starting magnetic developer. This is because, as shown in Table 1, as the toner concentration of the magnetic developer is lower, the transfer amount of the magnetic carrier to the photosensitive drum 7 is larger. Next, even when the toner concentration of the magnetic developer for start is kept constant and the average particle size of the magnetic carrier for replenishment is changed, as shown in Nos. 9 to 12, there is no ground fog or dust. It can be seen that a good image can be obtained. The average particle size of the replenishing magnetic carrier is preferably equal to or smaller than that of the toner in the starting magnetic developer. Next, as a non-magnetic toner, the average particle size is 8.5 μm.
m, particle size distribution 10 to 70 μm, volume resistivity 5 × 10 ¹⁴
Ω · cm and a triboelectric charge of −29 μc / g were prepared.
The compounding ratio is a weight ratio, polyester (KTR KTR)
2150) 87, carbon black (Mitsubishi Chemical Industries)
# 44) 10, polypropylene (TP3 manufactured by Sanyo Chemical Industries, Ltd.)
2) 2, a charge control agent (T2N) 1 and an external additive (R97 manufactured by Nippon Aerosil Co., Ltd.)
2) 0.5 was added. The magnetic carrier has an average particle diameter of 50 μm.
m, particle size distribution 10-70 μm, volume resistivity 10 ⁸ Ω
cm, the magnetization σ _{1000 at 1000} Oe is 120 emu /
Using the g-bian flat iron powder. On the other hand, the photosensitive drum 7 was formed by OPC, and had a surface potential of -650 V and a peripheral speed of 30 mm / sec. The permanent magnet member 4 is made of a ferrite magnet (YBM-
According to 3), outer diameter 20 mm, 32 poles, surface magnetic flux density 350
G, a developing gap g = 0.4 mm, a doctor gap t = 0.25 mm, and a DC bias voltage of −500 V were applied via a doctor blade 8. Under the above-described developing conditions, continuous printing is performed by changing the toner concentration in the magnetic developer for start in the same manner as in the above embodiment, and the recovered carrier amount D (% by weight) after printing 10,000 sheets is measured. Table 3 shows the results. The value of the collected carrier amount D corresponds to the value in the above embodiment. [Table 3] As is clear from Table 3, similarly to Table 1, it is recognized that the magnetic carrier in the magnetic developer has been transferred to the photosensitive drum 7 together with the toner by continuous printing. The tendency of the amount of the collected carrier depending on the toner concentration is the same as in Table 1 above, but the range of the collected carrier amount is slightly smaller than that in Table 1. In the end, even in a developing method using a magnetic developer composed of a non-magnetic toner and a magnetic carrier, it is recognized that the toner density in the magnetic developer increases due to continuous development, and uneven density and background fog occur. . Next, Table 4 shows the image evaluation results after continuous printing of 10,000 sheets was performed under the above development conditions while replenishing the magnetic carrier together with the toner. The image evaluation is
This is performed for a 5% character pattern. [Table 4] As is apparent from Table 4, in the case of replenishment with toner alone, which is a comparative example, the image density is low, the density unevenness, dust and background fog occur, and the change in toner density is large. On the other hand, in the case of replenishing the toner and the magnetic carrier in the present invention, it can be seen that the image quality is greatly improved and the change in the toner density is small. Since the present invention has the above-described configuration and operation, the following effects can be obtained. (1) Since the magnetic carrier is replenished together with the toner, an increase in the toner concentration of the magnetic developer due to the transfer of the magnetic carrier to the image carrier is prevented, and the occurrence of background fog and dust is prevented. Development can take place. (2) Since only the permanent magnet member is used as a component of the developing roll, the size of the developing device can be reduced, and the size of the entire image forming apparatus can be reduced. (3) Since the permanent magnet member, which is a means for supporting the magnetic developer, is hard, the surface wear is small, the change with time is small, and the durability can be improved. (4) By using a magnetic carrier having a small particle size, a high definition and high quality image can be obtained. (5) Since the toner concentration in the magnetic developer can be set in a wide range, it is not necessary to use, for example, a toner concentration control means, and the entire apparatus can be made compact. (6) The permanent magnet member constituting the developing roll does not need to be processed with higher precision than necessary, and the manufacturing cost can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a main part cross-sectional view showing an example of a developing unit in an embodiment of the present invention. FIG. 2 is a cross-sectional view of a main part showing an example of a conventional developing unit. [Description of Signs] 4 Permanent magnet member 7 Photoconductor drum

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Claims (1)

(57) [Claim 1] Developing an electrostatic image on an image carrier that carries an electrostatic image and moves using a two-component magnetic developer composed of a toner and a magnetic carrier. In the developing method, as a means for supporting and transporting the magnetic developer, a permanent magnet member having a plurality of magnetic poles on its surface and formed cylindrically and rotatably is used, and the magnetic developer is coated on the surface of the permanent magnet member. The magnetic carrier for replenishment is supplied together with the toner at the time of suction conveyance and toner replenishment, and the average particle size of the magnetic carrier for replenishment is equal to or smaller than the average particle size of the toner at the start. A developing method comprising using particles containing particles having a particle size.