JPH087498B2 - Development device - Google Patents

Description

The present invention relates to a developing device that visualizes an electrostatic latent image formed on the surface of a carrier with a developer containing a magnetic carrier and a toner.

[Conventional technology]

In an image forming apparatus such as an electrophotographic apparatus or an electrostatic printing apparatus, at least a charging device, an exposing device and a developing device are arranged around a carrier having a photoconductor layer or a dielectric layer formed on the surface, and a transfer process is further performed. In the case of including the above, a transfer device for transferring the developed image onto the transfer sheet, a cleaning device for removing the toner remaining on the surface of the carrier after the transfer are provided, and a fixing device for obtaining the final image is provided.

As the developing device, for example, a two-component developer containing a magnetic carrier and a toner is used, and a magnetic brush is formed on a non-magnetic sleeve having a permanent magnet member inside.
The magnetic brush is used to form a toner image on the surface of the carrier by rubbing the surface of the carrier. According to this developing device, the magnetic carrier and the toner are agitated and mixed so that the toner is charged to a predetermined magnetism, and the toner electrostatically attached to the carrier is transferred to the electrostatic latent image by the coulomber to perform the development. Be done.

Iron powder carriers (Japanese Patent Publication Nos. 47-19398 and 48-8138, etc.) have been used as the magnetic carrier, and in order to improve the life and stabilize the triboelectrification characteristics,
Usually, the surface is oxidized. However, this iron powder carrier has the following problems. That is, with long-term use, a toner film is formed on the surface of carrier particles, or oxides on the surface of carrier particles are lost,
There is a problem that the resistance of the carrier particles changes significantly and the triboelectric charging characteristics change. As a result, the image density decreases,
The problem of increased fog occurs.

Therefore, instead of the iron powder carrier, a ferrite carrier composed of metal oxide particles exhibiting soft magnetism (Japanese Patent Publication No. 56-5203).
, JP-A-58-202456, etc.),
It is put to practical use. The ferrite carrier is chemically more stable than the iron powder carrier, has less resistance change during use, and has a low apparent density, so that it has advantages such as being light and requiring less torque during transportation. Further, since the saturation magnetization is smaller than that of the iron powder carrier, it has excellent fluidity and agitation property, and accordingly, a soft magnetic brush is formed, so that there is also an advantage that the halftone reproducibility is good.

[Problems to be solved by the invention]

Although the above ferrite carrier has many advantages as described above, since it has different magnetic and electrical characteristics from the iron powder carrier, the image quality is improved under the same developing conditions and developing device structure as when using the iron powder carrier. Problems such as deterioration, carrier scattering, and carrier adhesion occur.

As a countermeasure against this, the strength of the developing magnetic pole is set in the range of 300 to 700 G (JP-A-58-179853) and the developing gap is set to 0.6 to
In the range of 2 mm (Japanese Patent Laid-Open No. 60-76756), the magnetic flux density of the carrier magnetic pole is 50 to 85% of the magnetic flux density of the developing magnetic pole (Japanese Patent Laid-Open No. Sho 60-76756).
61-36774), the difference between the developing gap and the doctor gap is set within a certain range (Japanese Patent Laid-Open No. 61-128260), the moving directions of the photosensitive drum and the sleeve are the same in the developing area, and the peripheral speeds of the two are the same. The ratio is within a certain range (Japanese Patent Laid-Open No. 61
-128261) has been proposed.

However, conventionally, not all the factors related to the quality of development have been examined. That is, according to the conventional developing device, it is not possible to solve all the problems such as the deterioration of the developability, the trailing edge of the image, the scattering of the carrier, and the adhesion of the carrier due to the use of the ferrite carrier.

Therefore, it is an object of the present invention to provide a developing device which eliminates the above-mentioned drawbacks of the conventional device.

[Means for solving problems]

The developing device of the present invention has a saturation magnetization of 45 to 100 emu / g, a coercive force of 1 to 30 Oe, an electric resistance of 10 ⁶ to 10 ¹⁰ Ω · cm, and an average particle size of 50 to 200 μm. A developing tank containing a developer containing a ferrite carrier and a toner, and a non-magnetic sleeve facing the electrostatic latent image carrier and forming a developing region between the non-magnetic sleeve and the developing tank. A developing device having a permanent magnet member having a plurality of magnetic poles fixed in a sleeve and a developer stirring member rotatably provided in a developing tank, wherein the sleeve is a portion facing a carrier. A gap of 0.3-1.0 mm is formed at the same time, and the surface moving speed of the carrier is 1.5-3 at this facing portion.
The developing magnetic pole, which moves in the same direction as the carrier at a double surface moving speed and faces the carrier, is on the sleeve.
It has a magnetic flux density in the range of 700 to 1000G, and the angle between the center of the developing magnetic pole and the center of the carrier magnetic pole which is adjacent to the downstream side of this magnetic pole and has different magnetism from this magnetic pole is θ (degree), and a non-magnetic sleeve. When the outer diameter of is D (mm), the following formula 800
The magnetic poles are arranged so as to satisfy <D · θ <1800, the developer stirring member rotates in the same direction as the non-magnetic sleeve, and the inner wall of the opening of the developing tank and the developer surface layer on the downstream side of the developing formula are. And / or the gap between the tip of the opening of the developing tank and the carrier is 1 mm or less.

〔Example〕

 Hereinafter, details of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view of a developing device according to an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a photosensitive drum having an electrostatic latent image (not shown) on its surface, which is rotated in the arrow z direction. The developing device 2 is installed around the photosensitive drum 1.

The developing device 2 has a developing tank 4 that contains a developer 3 containing a ferrite carrier and toner. Inside the developing tank 4, a non-magnetic sleeve 5 that rotates in the arrow x direction is provided. The non-magnetic sleeve 5 is arranged so as to face the photoconductor drum 1, and forms a developing region 12 at the closest position to the photoconductor drum 1 and in the vicinity thereof. Inside the non-magnetic sleeve 5, a permanent magnet member 6 having a plurality of magnetic poles on its surface is fixedly arranged. Of these magnetic poles, the N ₁ pole is a developing magnetic pole provided so as to face the developing area 12. Inside the developing tank 4, a stirring roller 7 that rotates in the direction of the arrow y and stirs and mixes the developer 3 is provided. This agitating roller has a structure in which a plurality of swash disks are attached around the rotating shaft, and has a function of conveying the developer in the rotating direction and a function of mixing in the axial direction. The developing tank 4 is provided with a doctor member 8 for controlling the thickness of the developer adsorbed on the non-magnetic sleeve. Further, a toner tank 9 for containing replenishment toner 11 is provided above the developing tank 3. The toner tank 9 has an opening at the bottom, and a toner supply roller is provided at this opening.
10 is rotatably provided.

With such a configuration, when the non-magnetic sleeve 5 is rotated in the direction of arrow x, the developer adsorbed on the sleeve is conveyed in the same direction, and the thickness thereof is regulated by the doctor member 8 to be formed in the developing region 12. The surface of the photosensitive drum 1 is rubbed with a magnetic brush to visualize the electrostatic latent image.
The developer that has passed through the developing area 12 is collected in the developing tank 4, stirred by the stirring roller 7 together with the toner 11 supplied by the toner replenishing roller 10, and then adsorbed on the non-magnetic sleeve 5 again. .

The ferrite carrier used in the present invention is specifically a complete mixture with a suitable metal oxide metal oxide,
Crystallographically, it is a soft magnetic material having a spinel, perovskite, hexagonal, garnet or orthoferrite structure. That is, this ferrite carrier is
n, Mn, Mg, Cu, Li, Ba, V, Cr, Ca is a sintered body of oxides and Fe ₂ O ₃ , for example, Ni-Zn ferrite, Mn-Zn ferrite, Mg-Zn Well-known are ferrites such as Cu-Zn ferrites and Li-Zn ferrites.

It is known that such a ferrite carrier has a wide range of physical properties by changing the composition and manufacturing conditions, but in the present invention, one having the following physical properties is used in consideration of image quality. If the saturation magnetization (Os) is too small, the carrier easily separates from the sleeve and adheres to the surface of the photoconductor. On the other hand, if it is too large, the transportability is too strong and the toner is easily deformed. Since it becomes hard and the reproducibility of halftone becomes poor, the range of 45 to 100 emu / g is preferable. If the coercive force ( _I Hc) is too small, the transportability will decrease, and if it is too large, it will become a permanent magnet and adhere to various members.
A range of 1-30 Oe is preferred. If the electric resistance is too low, carrier adhesion is likely to occur, and if it is too high, the developability decreases,
Further, the edge effect is too strong to obtain a uniform solid black image, so that the range of 10 ⁶ to 10 ¹⁰ Ω · cm is preferable. Particle size distribution is 50
A range of up to 200 μm is preferable. In other words, the smaller the particle size, the larger the specific surface area, the higher the maximum toner concentration, the higher the durability, and the finer the image obtained.
m or less. However, if the number of particles of 50 μm or less increases,
Although the developability is improved, carrier adhesion is likely to occur, so it is desirable that the amount of particles of 50 μm or less is 30% by weight or less. The above magnetic properties are values measured by a vibrating sample magnetometer (VSM-3 manufactured by Toei Industry Co., Ltd.), and the electrical resistance is a value measured according to the method described in JP-A-61-191522. .

In the present invention, in order to perform good development using the above ferrite carrier, the developing device shown in FIG. 1 has a structure satisfying the following conditions.

The first factor that affects development is
It is the magnetic flux density of the developing magnetic pole (N ₁ pole). When the magnetic flux density of the N ₁ pole is smaller than 700 G (value on the sleeve, the same applies below), the ferrite carrier has weaker magnetization than the iron powder carrier, and the force of adsorption on the sleeve becomes weaker, as described above. Adhesion of the carrier and accompanying transfer bleeding occur. N ₁
If the magnetic flux density of the poles is larger than 1000 G, the magnetic brush becomes hard and the streaks are generated on the image, and the carrier is fatigued and its life is shortened. Therefore, the magnetic flux density of the developing magnetic pole is preferably in the range of 700 to 1000G.

In addition, the flow of magnetic flux near the N ₁ pole is schematically shown as the second
The state shown in FIGS. The magnetic brush is formed along the magnetic flux lines. In the developing area 12, the magnetic brush is in contact with the photosensitive drum 1 with a certain width (hereinafter referred to as a contact width, indicated by W in the figure). Paying attention to the direction of the magnetic force lines at the end of this contact width (the point at which the contact between the developer and the surface of the photosensitive member ends) P, as shown in FIG. 3, the direction of the magnetic force lines is greater than the tangential direction of the photosensitive drum. When facing the drum side, the magnetic brush of the developer that has completed development again rubs the surface of the photoconductor, so that the trailing edge of the image is chipped by the cleaning action of the magnetic brush (hereinafter referred to as trailing edge chipping). Tends to occur, and this tendency is remarkable in a halftone image. On the other hand, as shown in FIG. 2, the more the magnetic force lines are directed toward the tangential line of the photosensitive drum or toward the sleeve side, the more the above-mentioned trouble, that is, the rear end chipping can be prevented. To realize the orientation of such magnetic field lines, obtained by bringing the S ₁ pole magnetic flux density of the N ₁ pole is adjacent to it be downstream of N ₁ pole within a range not out of the range N ₁ pole It was confirmed by the experiment that it was possible. Since the direction of the magnetic lines of force at which the trailing edge is not broken differs depending on the outer diameters of the photosensitive drum and the permanent magnet member, the pitch between the N ₁ pole and the S ₁ pole must be determined accordingly. According to the experimental result using the magnet roll having the sleeve outer diameter of 20 to 65 mm, the optimum magnetic pole arrangement, that is, the angle θ between N ₁ and S ₁ is 800 <D · θ <when the sleeve outer diameter is D. It was found that when the condition of 1800 was satisfied, it was particularly effective for trailing edge chipping. This indicates that the sleeve upper circumferential length (pitch) between N _{1 and} S ₁ is in the range of 7 to 16 mm.

Next, since the ferrite carrier has a shape close to a sphere and has a relatively high electric resistance, the resistance of the magnetic brush becomes high and the developing electrode effect is weak. Therefore, the development gap (g
_{Also in 1} ), unless it is narrower than the case where the iron powder carrier is used, the developability is lowered and the image density is lowered. On the other hand, if the developing gap is too narrow, the rubbing force of the magnetic brush is too strong and the surface of the photoreceptor is damaged. Therefore, the development gap is 0.3-1.0 mm
The range is good.

Further, the rotation direction of the sleeve and the peripheral speed thereof are also greatly related to the quality of the development. In the developing area 12, when the sleeve 5 rotates in the same direction as the photosensitive drum 1, the contact between the developer and the photosensitive member becomes better than in the reverse direction,
The image density is easily obtained and the halftone reproducibility is improved. The rotational speed of the sleeve may be determined so that the peripheral speed (v _s ) of the sleeve is 1.5 to 3.0 times the peripheral speed (v _p ) of the photosensitive drum. As v _s / v _p increases, the developer supply capacity to the developing area increases and the development improves. Therefore, if v _s / v _p is too large, toner scattering and carrier scattering increase, so that v _s / v _p should be 3.0 or less.

Further, regarding the toner scattering, the rotating direction of the stirring roller and the structure of the opening of the developing tank on the downstream side of the developing area are also related. As shown in FIG. 1, when the agitating roller 7 rotates in the same direction as the sleeve 5, the developer after the development is easily drawn into the developing tank 4, and the toner is hardly blown out from the opening 14 of the developing tank 4. Become. Further, in the vicinity of the opening 14, the narrower the gap g ₃ between the inner wall of the case constituting the developing tank 4 and the surface of the developer layer, the more the toner is suppressed from being blown out from the inside of the developing tank. Further, if the gap g ₄ between the tip of the case and the photosensitive drum 1 is narrow, the air resistance increases, so that the scattering of the toner downward is greatly reduced. Accordingly g ₃ and / or g ₄ may have 1.0mm or less, preferably in the range of 0.3 to 0.8 mm.

[Experimental example]

 The present invention will be specifically described by the following experimental examples.

Experimental Example 1 Using the developing device shown in FIG. 1, an experiment was conducted under the following conditions.

Photoconductor drum: Se drum with an outer diameter of 80 mm, surface potential +720 V, peripheral speed of 100 mm / sec Sleeve: SUS304 sleeve with an outer diameter of 34 mm, peripheral speed of 200 mm / sec (v _s / v _p 2.0) Permanent magnet: Ba ferrite with an outer diameter of 31 mm Angle between magnet N ₁ pole-S ₁ pole 45 ° (The vector of the magnetic field line at point P became closer to the direction shown in Fig. 2.) Gap: g ₁ 0.6mm g ₂ 1.0mm g ₃ 0.7mm g ₄ 0.8mm Carrier: Ba-Ni-Zn ferrite carrier (KBN-100 made by Hitachi Metals) Os 58emu / g _i Hc 24 Oe Electric resistance 7 × 10 ₈ Ω ・ cm Particle size distribution 74 to 149 μm Toner: Average particle size 12 μm Toner concentration: 4 Under the condition of weight% or more, the magnetic flux density of the N ₁ pole was changed to create an image and evaluated. The results are shown in Table 1.

It can be seen from Table ₁ that good development can be performed when the magnetic flux density of the N ₁ pole is 750 to 1000 G, but carrier adhesion increases at 600 G and vertical streaks occur at 1100 G.

Experimental Example 2 An experiment was conducted under the same conditions as in Experimental Example 1 except that the angle between the N ₁ pole and the S ₁ pole and the magnetic force were changed as shown in Table 2.1. The results are shown in Table 2.2.

From the above, it can be seen that the rear end chipping is less likely to occur as the direction of the magnetic force lines is closer to the sleeve. However, it can be seen that when the transport magnetic pole is too close to the developing magnetic pole, the magnetic path becomes short, so that the magnetic flux density on the sleeve surface is substantially reduced and carrier adhesion increases. Further, as a result of conducting the same experiment as above with changing the angle θ between the N ₁ pole and the S ₁ pole, θ is 24 ° or more and 53 °
It has been found that good results are obtained with less than. Further, as a result of conducting an experiment similar to the above by changing the outer diameter D (mm) of the sleeve, it was found that good development can be performed by the magnetic pole arrangement such that 800 <θ · D <1800.

Experimental Example 3 An experiment was performed under the same conditions as in Experimental Example 1 except that the magnetic flux density of the N ₁ pole was 800 G and g ₁ was changed (however, g ₂ was slightly changed according to g ₁ ). Table 4 shows the results.

It can be seen from Table 3 that a high image density can be obtained when g ₁ is 1.0 mm or less. However, when g ₁ was 0.2 mm, drum scratches occurred after 15,000 continuous copies.

Experimental Example 4 An experiment was performed under the same conditions as in Experimental Example 1 (however, the position of the doctor member was changed) except that the magnetic flux density of the N ₁ pole was 800 G and the rotating direction of the sleeve was reversed. As a result, it was found that the reproducibility of halftones was reduced.

Experimental Example 5 An experiment was conducted under the same conditions as in Experimental Example 1 except that the magnetic flux density of the N ₁ pole was 800 G and the rotation speed of the sleeve was changed. The results are shown in Table 3.

From Table 4, when v _s / v _p is 1.0, the image density is insufficient,
It can be seen that at 4.0, carrier adhesion and toner scattering increase.

Experimental Example 6 An experiment was performed under the same conditions as in Experimental Example 1 except that the magnetic flux density of the N ₁ pole was 800 G and the rotating direction of the stirring roller was reversed. As a result, it was found that the amount of toner blown out from the opening 14 of the developing tank 4 increased.

Experimental Example 7 The magnetic flux density of the N ₁ pole was 800 G, and g ₃ and g ₄ were 0.8 to 3.
An experiment was conducted under the same conditions as in Experimental Example 1 except that the range was changed to 0 mm. As a result, it was found that when g ₃ and g ₄ were larger than 1.0 mm, the toner scattering increased.

〔The invention's effect〕

As described above, in the developing device of the present invention, not only the strength of the developing magnetic pole and the developing gap, but also the moving direction and moving speed of the sleeve, the direction of magnetic force lines in the developing area, and the structure of the developing tank opening on the downstream side of the developing area are described. Since it is within a specific range, good development can be performed when a ferrite carrier is used.

[Brief description of drawings]

FIG. 1 is a sectional view of a developing device according to an embodiment of the present invention, FIG. 2 is an enlarged view of a main part of FIG. 1, and FIG. 3 is a sectional view showing a main part of a conventional developing device. 1: photoconductor drum, 2: developing device, 3: developer, 4: developing tank, 5:
Non-magnetic sleeve, 6: permanent magnet member, 7: stirring roller.

Claims (1)

[Claims] 1. A saturation magnetization of 45 to 100 emu / g and a coercive force of 1 to 30.
Oe, a developing tank for storing a developer containing a ferrite carrier and toner having an electric resistance of 10 ⁶ to 10 ¹⁰ Ω · cm and an average particle size of 50 to 200 μm, and an electrostatic latent image carrier A non-magnetic sleeve which is opposed to and which forms a developing region between the non-magnetic sleeve and the developing tank, and the permanent magnet member having a plurality of magnetic poles fixedly mounted in the non-magnetic sleeve; In a developing device having a developer stirring member rotatably provided in the developing tank, the non-magnetic sleeve forms a gap of 0.3 to 1.0 mm at a portion facing the carrier and the surface of the carrier. Movement speed of 1.5
Rotate in the same direction as the carrier at a surface moving speed of ~ 3 times,
Of the magnetic poles of the permanent magnet member, the developing magnetic pole facing the carrier has a magnetic flux density in the range of 700 to 1000 G on the sleeve, and is adjacent to the center of the developing magnetic pole and the downstream side of the magnetic pole. Is a magnetic pole that satisfies the following formula 800 <D · θ <1800, where θ (degrees) is the angle formed by the centers of the carrier magnetic poles with different polarities and D (mm) is the outer diameter of the non-magnetic sleeve. The developer stirring member rotates in the same direction as the non-magnetic sleeve, and the gap between the inner wall of the opening of the developer tank and the developer layer on the downstream side of the developing area and / or the developer tank is arranged. The developing device is characterized in that the gap between the tip of the opening and the carrier is 1 mm or less.