JP2822476B2 - Developing device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic brush developing device using a magnetic developer.

[Prior Art] Conventional developing devices are non-magnetic and conductive such as rotatable stainless steel, aluminum and brass as known as magnetic brush developing devices (one-component magnetic brush and two-component magnetic brush). Has a cylindrical magnet roller magnetized with a plurality of magnetic poles inside a cylindrical developer conveying member (also referred to as a developing sleeve), and the developer is transferred onto the developer conveying member according to a magnetic field generated by the magnet roller. And rotating at least one of the magnet roller and the developer transport member to transport the developer on the developer transport member. Also, using a ferrite magnet for the magnet roller,
A developer containing about 50 [wt%] of magnetic powder and having a saturation magnetization of about 44 [emu / g] was constrained on a developer carrying member to carry and develop the developer. On the other hand, as the resolution of image forming apparatuses has increased, the particle size of the developer has become smaller and smaller, and the volume magnetization of each developer has become smaller. And it was.

[Problems to be Solved by the Invention] However, in the above-described conventional technology, since the number of components of the developing device is large and each component requires high machining accuracy,
The structure is complicated and expensive. Also, when the particle size of the developer is reduced, the volume magnetization is reduced and the magnetic force of the magnet roller is small. Therefore, unless the content of the magnetic powder in the developer is increased, the developer is securely restrained on the developer conveying member. However, when the magnetic powder content of the developer was increased, the dispersibility of the magnetic powder was reduced, and the electrical characteristics of the developer were insufficient or the color tone was changed. Furthermore, the upper limit of the image density is defined by the amount of the magnetic powder, and the image density is insufficient, and there is a problem that it is difficult to prepare a color developer due to the low light transmittance of the magnetic powder. . Furthermore, if the number of magnetized poles of the magnet roller is increased, sufficient leakage magnetic flux on the developer conveying member will occur if the number of magnetized poles of the magnet roller is increased in order to reduce uneven development density due to the magnetic pole pitch of the magnet roller, which is unique to the image obtained when the magnet roller is rotated. As a result, the transfer of the developer was hindered.

Therefore, the present invention solves such a problem,
The aim is to provide a low-cost developing device with a simple structure and a small number of steps from manufacturing to assembly by using a developing device structure that directly transports the developer on the surface of the magnet roller. is there. Yet another purpose is
An object of the present invention is to provide a developing device capable of obtaining a high-concentration developing device by effectively utilizing a magnetic field generated by a magnet roller to secure a sufficient developer transport amount. Still another object is to provide a developing device capable of obtaining a clear and high-density image even when a developer having a small content of magnetic powder is used. Still another object is to provide a developing device capable of reducing unevenness in developing density by a magnet roller and obtaining high printing quality.
Still another object is to reduce the amount of magnetic powder in the developer, and stabilize the charge injection property of the triboelectric charge of the developer by using a material composition in which the electrical characteristics of the developer are not easily affected by the magnetic powder, thereby providing a stable image. It is an object of the present invention to provide a developing device capable of obtaining a density. Still another object is to provide a developing device which not only forms a high-resolution image by reducing the particle size of a developer but also has good area gradation. Still another object is to provide a developing device capable of forming a color image. Still another object is to provide a one-component magnetic developing device capable of increasing the density and color.

[Means for Solving the Problems] A developing device according to the present invention is a developing device for conveying a developer by rotating a magnet roller, wherein the magnet roller has a cylindrical shape and a rare-earth magnet whose outer periphery is magnetized to a plurality of poles. A yoke member is provided integrally with the rare earth magnet on the inner periphery of the rare earth magnet to form a magnetic circuit, and the magnet roller is rotated while the developer is directly held on the magnet roller. A developing device for conveying a developer.

[Operation] According to the above configuration of the present invention, a high magnetic flux density (magnetic gradient) can be obtained by most efficiently collecting the leakage magnetic flux of the magnet roller into the developer, and a developer having a small particle diameter having low magnetization can be obtained. The developer can be transported and developed under a sufficient magnetic binding force. Further, a high-density image can be formed by using a developer containing a sufficient amount of a coloring agent such as a pigment or a dye by reducing the content of the magnetic powder. Furthermore, since the light transmittance of the developer can be improved by reducing the amount of the magnetic powder, not only the image formation using the color developer with little color turbidity, but also the one-component magnetic of the subtractive color system of cyan, magenta and yellow can be achieved. It becomes possible to form a full-color image using a developer. Furthermore, by forming a magnet roller with a rare earth magnet, a developer transport member having high magnetic properties and excellent mass productivity can be obtained.

 Hereinafter, the present invention will be described in detail with reference to examples.

FIG. 1 is a schematic cross-sectional view of an image forming apparatus including a developing device according to an embodiment of the present invention. The latent image carrier 1 is formed by coating an organic or inorganic photoconductive photosensitive layer 3 on a conductive support 2. After the photosensitive layer 3 is charged using a charger 4 such as a corona charger, light emitted from a light source 5 is selectively irradiated on the photosensitive layer 3 through an imaging optical system 6 in accordance with an image, and the photosensitive layer 3 is charged. An electrostatic latent image is formed by obtaining a potential contrast thereon. On the other hand, the developing device 7 charges the developer 8 which is an image forming body, and conveys the developer 8 with a cylindrical magnet roller 9 so that the latent image carrier 1 and the magnet roller 9 are close to each other at a developing gap. And developing the developer 8 in accordance with the potential of the electrostatic latent image and the bias voltage by the developing bias voltage applying means 10.
Is visualized by the developer 8. The developer 8 that visualizes the electrostatic latent image is transferred to a recording paper 15 by a transfer unit 14 using corona discharge, electric field, pressure, or adhesive force.
The developer 8 is fixed on the recording paper 15 by a means such as pressurization or heating, and a desired image by the developer 8 is obtained on the recording paper 15. In the developing device shown in FIG. 1, the magnet roller 9 holds the supplied developer 8 by magnetic force, regulates the supplied developer 8 to an appropriate amount by the transport amount regulating member 11, and transports the developer 8. A magnetic circuit is composed of a magnet 12 having a cylindrical outer periphery magnetized to a plurality of poles and a soft magnetic cylindrical yoke 13, and a magnetic developer 8 is applied onto a magnet roller 9 by leakage magnetic flux on the outer periphery of the magnet 12. With the magnet roller 9 held directly
Is rotated to transport the developer 8, the magnetic flux can be used most effectively, and even with a thin-walled magnet, a magnetic restraining force higher than before can be obtained. In FIG. 1, the arrows indicate the rotation directions of the respective members. However, the present invention is not limited thereto, and the developing method may be used regardless of regular development, reversal development, contact development, and non-contact development. can do.

FIG. 2 is a schematic cross-sectional view of a magnet roller of a developing device according to another embodiment of the present invention, in which a developer is applied to the outer peripheral surface of a cylindrical rare-earth magnet 22 radially magnetized to a plurality of poles. The magnet roller 21 holds and transports according to the distribution.
Are arranged on the inner peripheral side by means of bonding or the like to constitute a magnetic circuit. In addition, the magnet 22 is made thin by using a rare earth magnet to reduce the weight of the magnet to less than half of the conventional one, and the number of magnetized poles of the magnet 22 is increased to 10 or more, preferably about 100, and the yoke 23 is magnetized. Weight can also be reduced.
In addition, after the soft magnetic yoke 23 is previously set in the molding die at the time of molding the magnet, the magnet roller 21 is integrally formed with the magnet 22 and the yoke 23 by injection molding a magnetic material containing magnetic powder, resin, and the like on the outer periphery thereof. If it is formed, it can be easily formed integrally by injection molding of plastic as is well known, and it is possible to form a magnet roller having sufficient mechanical strength even with a thin magnet and a small run-out of an outer diameter portion. Variations in the transport amount and variations in the development gap can be reduced, and stable development characteristics can be obtained.

FIG. 3 is a diagram showing the relationship between the surface magnetic flux density of the magnet roller and the formation of the magnetic brush of the developer, and the surface magnetic flux density of the magnet roller required for forming the magnetic brush in the region indicated by the arrow in the figure. It shows the saturation magnetization of the developer.
It can be seen that when the saturation magnetization of the developer becomes small, it is difficult to form a magnetic brush unless the magnet roller has a large surface magnetic flux density. In the example of FIG. 3, the number average particle diameter of the developer is about 8 [μm], the volume magnetization of each developer is approximately proportional to the cube of the particle diameter, and the charge amount of each developer is Since a developer having a smaller number average particle diameter is used, a magnet roller having a large surface magnetic flux density or a developer having a large saturation magnetization is required because a developer having a smaller number average particle diameter is used.

FIG. 4 shows the values by which the magnetic brush is formed and a sufficient image density (OD value of about 1.4) can be secured using the number average particle diameter of the developer and the saturation magnetization as parameters. And the upper limit (about 10 μm) of the number average particle diameter at which high resolution and sufficient area gradation can be ensured.
Indicates the type of magnet of the magnet roller, B is a region where a magnet roller made of a ferrite magnet having a maximum energy product of 1 [MGOe] can secure a sufficient image density, and C is a magnet roller made of a 6 [MGOe] rare earth bonded magnet. D indicates an area where a sufficient image density can be ensured by a magnet roller of a rare earth magnet of 18 [MGOe]. Therefore, by using a magnet having a large surface magnetic flux density such as a rare earth magnet for the magnet roller, a sufficient image density can be ensured even when a developer having a small particle diameter and a low saturation magnetization is used. A developing device having a simplified structure can be formed, and a color developing device using a magnetic developer by reducing the amount of magnetic powder of the developer can be provided.

When a developer is prepared using a developer containing a known subtractive colorant (yellow, magenta, cyan), the magnetic confinement force of the magnet roller can be sufficiently increased, so that the color turbidity is the largest. By reducing the content of magnetic powder, which is the cause, it is possible to use a developer having a small magnetization and a small particle diameter per developer, and an image having small color turbidity, high resolution and excellent gradation. Can be formed.

As the developer used in the present invention, not only a one-component magnetic developer but also a developer obtained by mixing a developing property improving agent such as a carrier into a one-component magnetic developer can be used, and a developer having magnetism is used. It is widely applicable to developing devices. Examples of the magnet material used in the present invention include a ferrite magnet, an alnico magnet, a manganese aluminum magnet, and a rare earth magnet. Among them, rare earth magnets have atomic number 58
At least 14 rare earth elements ranging from Ce to Lu of 71, and at least one of rare earth elements represented by Nd, Pr, and Sm, and at least one of 3d transition metals represented by Fe, Ni, and Co. In addition, the use of an additive that improves the formability can be used to form a magnet roller that has excellent mass productivity and high magnetic properties. Inexpensive and accurate magnet rollers can be formed by using injection molding, extrusion molding, or compression molding.

 Hereinafter, more detailed examples will be described.

Example 1 In a developing apparatus as shown in FIG. 1, a ferrite magnet having a maximum energy product of 1 [MGOe] and a soft magnetic yoke forming a magnetic circuit inside the ferrite magnet were used to form a magnet roller, and the magnet was 16 poles. When magnetized separately, 10
A magnetic flux density of 00 [Gauss] or more is obtained, and the number average particle diameter is 1
When the magnetic brush was observed using a developer having a saturation magnetization of 20 to 40 [emu / g] at 0 [μm], a sufficient amount of developer ears and a sufficient transport amount were obtained. Further, when an image was formed using this developing device, an image having a high density and a high contrast could be formed stably.

Example 2 In a developing apparatus as shown in FIG. 1, a magnet roller is integrated with a samarium-cobalt-based thin injection-molded magnet having a maximum energy product of 6 [MGOe] and a soft magnetic yoke constituting a magnetic circuit therein. When the magnet is divided and magnetized into 40 poles, a magnetic flux density of 1000 [Gauss] or more is obtained on the magnet surface, and a number average particle diameter of 10 [μm] is 20 to 40 [emu / g].
Observation of the magnetic brush using a developer having the saturation magnetization indicated that a sufficient amount of the developer and the transport amount were obtained. Also, the weight of the magnet roller was reduced to less than half that of the conventional one using a ferrite magnet and a metal sleeve. Further, when an image was formed using this developing apparatus, a high-density and high-contrast image could be stably formed.

Example 3 In a developing device as shown in FIG. 1, a magnet roller is formed by a praseodymium-based thin extruded magnet having a maximum energy product of 6 [MGOe] and a soft magnetic yoke constituting a magnetic circuit therein. When the magnet was divided and magnetized into 40 poles, a magnetic flux density of 1000 [Gauss] or more was obtained on the magnet surface, and the number average particle diameter was 10 [μm] and the saturation magnetization was 20 to 40 [emu / g]. When the magnetic brush was observed using the developer, a sufficient amount of the developer and the transport amount were obtained.
Also, the weight of the magnet roller was reduced to less than half that of the conventional one using a ferrite magnet and a metal sleeve. Further, when an image was formed using this developing apparatus, a high-density and high-contrast image could be stably formed.

Example 4 In a developing device as shown in FIG. 1, a magnet roller is formed by a samarium-cobalt-based thin compression molded magnet having a maximum energy product of 12 [MGOe] and a soft magnetic yoke constituting a magnetic circuit inside the magnet. Then, when the magnet is divided and magnetized into 100 poles, a magnetic flux density of 2000 [Gauss] or more is obtained on the magnet surface, and has a number average particle diameter of 10 [μm] and a saturation magnetization of 10 to 20 [emu / g]. Observation of the magnetic brush using the developer showed that a sufficient amount of developer and the amount of transport were obtained.
Also, the weight of the magnet roller was reduced to less than half that of the conventional one using a ferrite magnet and a metal sleeve. Furthermore, when an image was formed using this developing device, it was found that when a developer having a saturation magnetization of 10 to 20 [emu / g] was used, a high-density, high-contrast image could be stably formed. done.

Embodiment 5 In a developing apparatus as shown in FIG. 1, a magnet roller is constituted by a ferrite magnet having a maximum energy product of 1 [MGOe] and a soft magnetic yoke constituting a magnetic circuit therein, and the magnet has 16 poles. When magnetized separately, 10
When a magnetic brush was observed using a developer having a magnetic flux density of 00 [Gauss] or more and a saturation magnetization of 40 [emu / g] with a number average particle diameter of 5 [μm], sufficient developer was found. And the amount of transport were obtained. Further, when an image was formed using this developing device, an image having high density, high contrast and high gradation was able to be formed stably.

Example 6 In a developing apparatus as shown in FIG. 1, a magnet roller is integrated with a samarium-cobalt-based thin injection-molded magnet having a maximum energy product of 6 [MGOe] and a soft magnetic yoke constituting a magnetic circuit therein. When the magnet is divided and magnetized into 40 poles, a magnetic flux density of 1000 [Gauss] or more is obtained on the magnet surface, and a number average particle diameter of 5 [μm] is 30 to 40 [emu / g].
Observation of the magnetic brush using a developer having a saturation magnetization indicated that a sufficient amount of the developer and the amount of transport were obtained. Also, the weight of the magnet roller was reduced to less than half that of the conventional one using a ferrite magnet and a metal sleeve. Further, when an image was formed using this developing device, an image having a high density, a high contrast and a high gradation could be stably formed.

Example 7 In a developing apparatus as shown in FIG. 1, a magnet roller is formed by a praseodymium-based thin extruded magnet having a maximum energy product of 6 [MGOe] and a soft magnetic yoke constituting a magnetic circuit inside thereof. When the magnet is divided and magnetized into 40 poles, a magnetic flux density of 1000 [Gauss] or more can be obtained on the magnet surface, and a number average particle diameter of 5 [μm] and a saturation magnetization of 30 to 40 [emu / g]. When the magnetic brush was observed using the developer, a sufficient amount of the developer and the transport amount were obtained.
Also, the weight of the magnet roller was reduced to less than half that of the conventional one using a ferrite magnet and a metal sleeve. Further, when an image was formed using this developing device, an image having a high density, a high contrast and a high gradation could be stably formed.

Example 8 In a developing apparatus as shown in FIG. 1, a magnet roller is formed by a samarium-cobalt-based thin compression molded magnet having a maximum energy product of 12 [MGOe] and a soft magnetic yoke constituting a magnetic circuit inside the magnet. Then, when the magnet is divided and magnetized into 100 poles, a magnetic flux density of 2,000 [Gauss] or more is obtained on the magnet surface, and has a saturation magnetization of 10 to 20 [emu / g] with a number average particle diameter of 5 [μm]. Observation of the magnetic brush using the developer showed that a sufficient amount of developer and the amount of transport were obtained.
Also, the weight of the magnet roller was reduced to less than half that of the conventional one using a ferrite magnet and a metal sleeve. Furthermore, when an image was formed using this developing device, when a developer having a saturation magnetization of 10 to 20 [emu / g] was used, an image having high density, high contrast, and high gradation was stably obtained. Was formed.

Comparative Example 1 In a conventional one-component magnetic developing device, a ferrite magnet having a maximum energy product of 1 [MGOe] was disposed inside a developer transport member (non-magnetic metal sleeve), and a magnet roller was configured. When the magnet was divided and magnetized into 16 poles, only a magnetic flux density of 400 [Gauss] or less was obtained on the surface of the developer conveying member, and the number average particle diameter was 10 [μm] and the saturation magnetization was 40 [emu / g]. When the magnetic brush was observed using the developer, no spikes of the developer were observed, and the developer could not be transported by the magnetic force. Further, when an image was formed using this developing device, only an image having a low contrast and a lot of ground covering could be formed.

Comparative Example 2 In a conventional one-component magnetic developing device, a ferrite magnet having a maximum energy product of 1 [MGOe] was disposed inside using a developer transport member (non-magnetic metal sleeve) to form a magnet roller. When the magnet was divided and magnetized into 16 poles, only a magnetic flux density of 400 [Gauss] or less was obtained on the surface of the developer transfer member, but a saturation magnetization of 60 [emu / g] with a number average particle diameter of 10 [μm] was obtained. Observation of the magnetic brush using the developer having the above indicated that a sufficient amount of developer and the amount of conveyance were obtained. However, when an image was formed using this developing device, only an image having a low density and poor fixability and a lot of roughness was obtained.

Embodiment 9 In a developing apparatus as shown in FIG. 1, a magnet roller is formed by a samarium-cobalt-based thin compression molded magnet having a maximum energy product of 12 [MGOe] and a soft magnetic yoke constituting a magnetic circuit inside thereof. Then, the magnet was divided and magnetized into 100 poles, and the developing agent was 10 wt% of ferrite particles (saturation magnetization 84 [emu / g]) with good transparency to polyester resin, and the cyan coloring agent 4 wt% %] And about 1 [wt%] of other additives, and a saturation magnetization of 8 [μm] with a number average particle diameter of 6 [μm].
Observation of the magnetic brush using a one-component magnetic developer having a saturation magnetization of [emu / g] revealed that a sufficient amount of the developer and the transport amount were obtained. Further, when an image was formed using this developing device, a color image having high density, little color turbidity and excellent area gradation was able to be formed stably.

Example 10 In a developing apparatus as shown in FIG. 1, a magnet roller is formed by a samarium-cobalt-based thin compression molded magnet having a maximum energy product of 12 [MGOe] and a soft magnetic yoke constituting a magnetic circuit therein. Then, the magnet is divided and magnetized into 100 poles, and the developer is 10 wt% of ferrite particles (saturation magnetization 84 [emu / g]) with good light transmission to polyester resin, and the magenta colorant 4 [wt] %], And about 1 [wt%] of other additives, using a one-component magnetic developer having a number average particle diameter of 6 [μm] and a saturation magnetization of 8 [emu / g]. When the brush was observed, a sufficient amount of the developer and the transport amount were obtained. Further, when an image was formed using this developing device, a color image having high density, little color turbidity and excellent area gradation was able to be formed stably.

Example 11 In a developing apparatus as shown in FIG. 1, a magnet roller is formed by a samarium-cobalt-based thin compression molded magnet having a maximum energy product of 12 [MGOe] and a soft magnetic yoke constituting a magnetic circuit inside the magnet. Then, the magnet is divided and magnetized into 100 poles, and the developer is made of polyester resin and 10 [wt%] of ferrite particles (saturation magnetization 84 [emu / g]) having good light transmittance, and the yellow colorant 4 [wt] %], And about 1 [wt%] of other additives, using a one-component magnetic developer having a number average particle diameter of 6 [μm] and a saturation magnetization of 8 [emu / g]. When the brush was observed, a sufficient amount of the developer and the transport amount were obtained. Further, when an image was formed using this developing device, a color image having high density, little color turbidity and excellent area gradation was able to be formed stably.

Example 12 A developing apparatus using the cyan developer of Example 9, Example 10
When a full-color image formation was performed as a developing device using a magenta developer and a plurality of developing device configurations of a developing device using a yellow developer in Example 11, although there was some color turbidity, the maximum OD value was 1.5. As a result, a full-color image having a high gradation of 64 or more gradations of each color was obtained with no background covering.

COMPARATIVE EXAMPLE 3 A plurality of conventional one-component magnetic developing devices each using a developer conveying member (non-magnetic metal sleeve) and having a ferrite magnet roller having a maximum energy product of 1 [MGOe] disposed therein are used. Each developing device formed a full-color image using cyan, magenta, and yellow developers each containing 50 [wt%] of magnetic powder.
A magnetic brush is formed on the developer transport member, and a high density image with a maximum OD value of 1.5 in the solid image area can be obtained. I couldn't.

Although the embodiments have been described above, the present invention can be widely applied not only to the above-described embodiments but also to a developing device such as an electrophotograph, and is particularly effective when applied to a printer, a copying machine, a facsimile, and a display.

[Effects of the Invention] As described above, according to the present invention, the number average particle diameter of the developer is 10 [μm] or less, the magnetic powder content of the developer is 40 [wt%] or less, By using a developing device configuration in which the maximum energy product of the magnets constituting the roller is 4 [MGOe] or more, it is possible to obtain a clear and high-density image even when using a developer with a small amount of magnetic powder and low magnetic properties. Therefore, by reducing the amount of the magnetic powder, the production of the developer is facilitated, and the frictional charging property and the charge injection property of the developer are reduced as a material composition whose electric characteristics are not easily affected by the magnetic powder. It is possible to provide a developing device which is stabilized, can obtain a stable and high image density. Further, it is possible to provide a developing device which not only forms a high-resolution image by reducing the particle diameter of the developer but also has good area gradation.

In addition, by using a subtractive color developer as a developer, a developing device using a low-magnetic developer capable of performing subtractive color mixing with improved light transmittance and a magnet roller having high magnetic characteristics can be used. It is possible to provide a magnetic developing device capable of supporting a full-color image forming apparatus by combining a plurality of such developing devices.

Furthermore, by forming the magnet roller with a rare-earth magnet, a compact and lightweight developing device can be constructed, a high image density can be obtained even with a low-magnetic developer or a developer with a small particle size, and full-color can be achieved even with a magnetic developer. It has an excellent effect that a possible one-component magnetic developing device can be provided.

[Brief description of the drawings]

1 is a schematic cross-sectional view of an image forming apparatus including a developing device of the present invention, FIG. 2 is a schematic cross-sectional view of a magnet roller of the developing device of the present invention, and FIG. 3 is a surface of a magnet roller in an embodiment of the present invention. FIG. 4 shows the relationship between the magnetic flux density and the formation of the magnetic brush of the developer. FIG. 4 shows that the magnetic brush is formed using the number average particle diameter of the developer and the saturation magnetization as parameters in the embodiment of the present invention and a sufficient image density is secured. The figure which shows the possible value. 8: Developer 9, 21: Magnet roller

Claims (3)

(57) [Claims] 1. A developing device for conveying a developer by rotating a magnet roller, wherein the magnet roller has a cylindrical shape and a rare earth magnet whose outer periphery is magnetized to a plurality of poles, and the rare earth magnet is provided on an inner periphery of the rare earth magnet. A magnetic circuit is formed integrally with a yoke member, and the developer is transported by rotating the magnet roller while the developer is directly held on the magnet roller. apparatus. 2. The developing device according to claim 1, wherein said rare earth magnet has ten or more magnetized poles. 3. The developing device according to claim 1, wherein the number average particle diameter of said developer is 10 μm or less.