JPH0895386A - Developing device - Google Patents

Abstract

PURPOSE: To provide an inexpensive developing device by which excellent image quality is secured, which is miniaturized as to a mgnetic roll type developing device developing an electrostatic latent image formed on an image carrier. CONSTITUTION: As for a fixed magnet where a magnetic roll is constituted of a cylindrical rotary sleeve 311 and the fixed magnet 312 arranged on the inside of the sleeve 311 and a magnetic sheet 314 is wound on a fixing shaft 313; both ends of the magnetic sheet in a peripheral direction are arranged to be on a downstream side from a developing area and on an upstream side from a developer peeling area.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device for developing an electrostatic latent image formed on an image bearing member with toner in an image forming apparatus such as a copying machine and a printer using an electrophotographic system.

[0002]

2. Description of the Related Art Conventionally, various proposals and improvements have been made as electrophotographic image forming apparatuses, and in recent years, many improvements have been made in the field of color image forming apparatuses. As a typical one of them, there is a system in which toner images of a plurality of colors are superposed and developed on a cylindrical rotating electrostatic latent image carrier. This method is widely adopted because it has the advantage of easily obtaining a small device, but in the case of this method, since toner images of multiple colors are superposed and developed on the image carrier, the other colors of previously formed It is necessary to use a non-contact type developing device so as not to destroy the toner image.

There are many types of non-contact type developing devices, such as a magnetic roll type in which a fixed magnet is provided inside the developing roll so as to face the image carrier, and a rotating sleeve is provided outside the fixed magnet. Furthermore, this fixed magnet is provided with a plurality of magnetic poles of the same polarity, a repulsive magnetic field is created between the magnetic poles, and a "brush" of the developer is erected perpendicularly to the roll surface from the magnetic poles, and the toner at the tip of the brush is electrostatically charged to the image carrier. There is a soft brush method (see JP-A-56-144452).

Also in the non-contact type developing system, a system in which a one-component developer containing only toner is magnetically or electrostatically carried on a developing roll, and a two-component developer containing toner and a magnetic carrier is used in the developing roll. There is a method of magnetically supporting. By the way, in the case of the non-contact type developing device, a certain gap is required to prevent the developer on the developing roll and the toner on the image carrier from coming into contact with each other, and a required amount of toner is skipped from the developing roll. In order to fly to the image carrier, a considerably stronger electric field than that of the contact type is required. In order to obtain a strong electric field, a large-capacity power supply device may be used, or the gap between the image carrier and the rotating sleeve may be made as small as possible. However, making the power supply device larger leads to an increase in size and cost of the device. In addition, narrowing the gap reduces the amount of developer on the developing roll, and thus the amount of toner, so that the required amount of development cannot be obtained. Therefore, how to narrow the above-mentioned gap after securing a sufficient toner supply amount is an important issue. In the case of the soft brush method, it is difficult to narrow the gap because the supply of toner depends on the spikes of the developer rising from the developing roll. Further, since the developer is not held between the magnetic poles, only a part of the developing roll surface is used and the efficiency is low.

Therefore, in order to obtain a compact and highly efficient developing device, the gap between the magnetic poles of the developing roll is made as narrow as possible, the saturation magnetization of the magnetic carrier is made small, or the magnetic pole of the developing roll is provided inside the image carrier. Many attempts have been made, such as arranging magnetic poles of opposite polarities facing each other to lower the height of the developer (see JP-A-1-291268).

On the other hand, recently, the demand for higher image quality of an image forming apparatus using an electrophotographic system is increasing, and the particle size of toner is being reduced. However, as the particle size is reduced, the toner tends to scatter. In addition to the problem of securing the amount of development described above, how to prevent the toner from scattering in the developing device has become a major problem. This is "The 68th Annual Meeting of the Electrophotographic Society"
Japan Hardcopy, 92 Proceedings 93-96
As theoretically considered on the page.

Under these circumstances, a plurality of magnetic poles having different polarities are arranged on the circumference of the developing roll, and the developer is conveyed in a lying state by being placed on the magnetic force line running between the adjacent magnetic poles. Therefore, a method of narrowing the gap between the image bearing member and the developing roll and increasing the developer transport amount of the developing roll has been attracting attention. By the way, in order to increase the developer transport amount, it is effective to form as many magnetic poles as possible on the circumference of the magnet, but in the case of an ordinary magnet, there is a limit to magnetizing at a narrow interval.

Therefore, a method of winding a sheet-shaped rubber magnet or the like around a fixed shaft to form a fixed magnet has been considered. According to this method, it is possible to obtain a fixed magnet in which a large number of magnetic poles are arranged on a constant circumference at extremely narrow intervals.

[0009]

As described above, the developing device in which a sheet-shaped rubber magnet or the like is wound around a fixed shaft to form a fixed magnet, and a rotary sleeve is arranged around the fixed magnet to form a developing roller is described above. Although it is a promising means for solving the above problem, according to the experiments by the present inventors,
It has been found that the magnetic field is disturbed due to the position of the seam formed when the magnetic sheet is wound, and this causes unevenness in the conveyance of the developer by the rotating sleeve, which in turn causes unevenness in development and causes image deterioration.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a small-sized and low-cost developing device which prevents such a magnetic field disturbance and has good image quality.

[0011]

SUMMARY OF THE INVENTION A developing device of the present invention which achieves the above-mentioned object holds a magnetic developer, and the developer is subjected to a predetermined development in the vicinity of an image carrier on which an electrostatic latent image is formed. The image bearing member includes a cylindrical rotating sleeve that conveys the toner to the area, and a columnar fixed magnet that is provided in the rotating sleeve and that has a plurality of magnetic poles formed in the circumferential direction to magnetically attract the developer. In the developing device for developing the formed electrostatic latent image by using the developer conveyed by the rotary sleeve, the fixed magnet includes (1) a columnar shaft portion and (2) a developing direction in the rotating direction of the rotary sleeve. Each magnetic pole is wound around the shaft so that both ends in the circumferential direction are located on the downstream side of the area and on the upstream side of the peeling area where the developer after development is peeled from the rotating sleeve. Direction of the shaft and Characterized by comprising a magnetic sheet having a plurality of magnetic poles in the direction is formed.

Here, in the developing device of the present invention,
Of the plurality of magnetic poles formed on the magnetic sheet, it is preferable that the magnetic poles present at both circumferential edges of the magnetic sheet have the same polarity. Further, in the case where the developing device of the present invention is a developing device for developing an electrostatic latent image using a two-component developer having toner and magnetic carrier, in the vertical direction of each magnetic pole formed on the magnetic sheet. Maximum magnetic flux density is 200
It is also preferable that the magnetic carrier has a saturation magnetization of 20 to 70 emu / g, and the magnetic carrier has an average particle size of 20 to 70 μm.

Further, in the case where the developing device of the present invention is a developing device for developing an electrostatic latent image using a two-component type developer having toner and a magnetic carrier, the rotary sleeve is made of a magnetic carrier. It is also a preferred embodiment that the surface roughness is 10 to 70% of the average particle diameter. Here, "surface roughness" means JIS-B-0601.
"Ten-point average roughness" of the three types of surface roughness measurement methods specified by -76. Further, the "average particle diameter" in the present invention means "weight average particle diameter", the particle diameter is divided into several sections, the weight of the particles belonging to each section is measured, and the central particle of the section is measured. It is a value calculated by weighted average by diameter. Incidentally, another method of calculating the average particle diameter is a “number average particle diameter” in which the number of particles belonging to each particle diameter section is counted and the weighted average is taken by the central particle diameter of the section.

[0014]

In the developing device of the present invention, as described above, since both end edges of the magnetic sheet forming the fixed magnet are located on the downstream side of the developing area and on the upstream side of the developer peeling area, It is possible to prevent the occurrence of uneven development due to the disturbance of the magnetic field in the.

Further, in the developing device of the present invention, when the magnetic poles at both edges of the magnetic sheet have the same polarity, a magnetic pole having a different polarity from the magnetic poles at the both edges is formed between the edges due to the influence of the surrounding magnetic field. It is possible to effectively prevent the magnetic field from being disturbed. Further, in the developing device of the present invention, by limiting the maximum value of the magnetic flux density in the vertical direction of each magnetic pole formed on the magnetic sheet, the saturation magnetization and the average particle diameter of the magnetic carrier to an appropriate range, carrier scattering and It is possible to prevent the carrier from adhering to the image carrier.

Here, if the maximum value of the magnetic flux density in the vertical direction of each magnetic pole is less than 200 gauss, carrier scattering occurs, while if it exceeds 1000 gauss, the spikes of the developer are too high, and the developing roll and the image carrier. It becomes impractical because the space between and cannot be narrowed. That is, the practical range of the maximum value of the magnetic flux density of each magnetic pole is 200 gauss or more and 1000 gauss or less.

Regarding the saturation magnetization of the magnetic carrier,
If it is less than 20 emu / g, carrier adhesion to the image bearing member is likely to occur, and if it exceeds 70 emu / g, carrier aggregation occurs on the developing roll, making it difficult to form a developer layer having a large surface area. Therefore, the saturation magnetization of the magnetic carrier is preferably 20 emu / g or more and 70 emu / g or less.

Further, regarding the average particle size (weight average particle size) of the magnetic carrier, if the carrier is less than 20 μm, it is easy to cause carrier adhesion to the image carrier due to the relationship between the magnetic force acting on one carrier and the electrostatic force. If it exceeds, the surface area of the carrier decreases and the surface area of the developer layer also decreases, so that the image density becomes insufficient. Therefore, the average particle diameter (weight average particle diameter) is preferably 20 μm or more and 70 μm or less.

In the developing device of the present invention, when the surface roughness of the rotary sleeve is limited to an appropriate range, slippage of the magnetic carrier when passing through the layer thickness regulating member can be prevented. When a magnetic carrier of 20 μm having the smallest average particle diameter within the above-mentioned average particle diameter range is used, if the surface roughness is Rz = 2 μm (10% of the average particle diameter of the magnetic carrier) or more, the layer regulating member is used. The slip when passing can be suppressed practically. Further, in the case of using the one having the largest average particle diameter of 70 μm in the above-mentioned average particle diameter range,
If the surface roughness exceeds Rz = 50 μm (70% of the average particle diameter of the magnetic carrier), uneven image density occurs, which is not practical. Therefore, the surface roughness of the magnetic carrier is Ra = 2.
It is desirable that it is at least μm (10% or more of the average particle size of the magnetic carrier) and Rz = 50 μm or less (about 70% or less of the average particle size 70 μm).

[0020]

EXAMPLES Examples of the present invention will be described below. FIG. 1 is a sectional view showing the main part of an embodiment in which the developing device of the present invention is applied to a color image forming apparatus. The cylindrical image carrier 110 rotates in the direction of the arrow, and after static electricity is charged by the primary charger 120, laser light 220 from a laser light generator 200 incorporating a semiconductor laser and a polygon rotation mirror 210 is first used. An electrostatic latent image corresponding to black is formed at a predetermined position on the surface of the image carrier. Next, of the plurality of developing devices arranged around the image carrier, the black developing device 301 performs the black developing process. In the development, the toner having the same polarity potential as the surface potential polarity of the image carrier 110 charged by the primary charger 120 is transferred to the image carrier 1.
It is performed by jumping from the developing device 301 to the laser light irradiation portion on the image carrier by an alternating electric field in which a direct current applied in the developing region near 10 is superimposed.

In FIG. 1, four developing devices 301, 302,
303 and 304 are arranged adjacent to each other and operate as developing devices for black, yellow, magenta, and cyan, respectively. Each of these developing devices has a structure which is not in contact with the image carrier so as not to disturb other toner images formed on the image carrier. A magnetic one-component toner is used as the black developer, while a two-component developer including a magnetic carrier and a non-magnetic toner is used as the other color developers.

After the development of black is completed, in the second cycle, the image carrier 110 is recharged by the primary charger 120, and the portion where the potential is lowered by the irradiation of the laser beam 220 in the previous (black) step. Recovers to the original potential again. Then, an electrostatic latent image is formed by irradiating a predetermined position on the surface of the image carrier with the image corresponding to yellow by the laser beam 220, and then the developing device 302 for yellow has the same surface potential polarity as that of the image carrier. The yellow electrostatic latent image on the image carrier is developed with the yellow toner having a polar charge. The yellow developing device 302 prevents the toner image formed on the image carrier in the previous step from being disturbed, and prevents the toner on the image carrier from back-transferring to the developing device side. The gap between the image carrier and the rotating sleeve is optimized.

Thereafter, the magenta and cyan developments are carried out in the same manner, and when the four color development steps are completed, the toner images of black, yellow, magenta and cyan are superposed on each other on the image carrier. Is formed. Next, the image carrier 110 is charged or discharged by the pre-transfer charger 480 to an optimum state for transfer. Next, the transfer charger 410 collectively transfers the toners of a plurality of colors on the image carrier onto the transfer paper supplied from the paper guide 720. After the transfer is completed, the transfer paper is de-charged by the peeling charger 440, separated from the image carrier 110, and sent to the fixing device (not shown) by the conveyor belt 750 to be fixed.

On the other hand, the image carrier 110 after the transfer process is completed.
The toner remaining on the surface is removed by the brush and blade of the cleaning device 500, and then the residual charge of the image carrier is removed by the exposure from the static eliminator exposure device 130, and a series of processes starting from the primary charger can be started again. It becomes a state. The above-mentioned cleaning device has a retractable structure so that it is extended to the contact position only during the cleaning step after the transfer is completed, and during development, all or part of the device is retracted to the standby position. This retracting operation may be performed before the next image to be formed reaches the cleaning device, or the time for one rotation of the image carrier for cleaning may be separately provided. In the former case, it is possible to increase the image forming speed as a whole because the time for one rotation for cleaning is not required, but the time during which the cleaning device is performing the retract operation overlaps with the image forming cycle. However, the rotation speed of the image carrier may be changed, which may cause deterioration of image quality. In the latter case, the influence of the retract on the image is small, but since the time required for one rotation is additionally required, the image forming speed as a whole decreases, so it is necessary to select in consideration of the advantages and disadvantages of both. .

Next, the details of the developing device in the above embodiment will be described with reference to FIGS. FIG. 2A is a sectional view showing the outline of the developing device of the present invention. In this developing device, a hollow cylindrical rotating sleeve 311 made of a non-magnetic and conductive material that conveys the developer to a predetermined developing area near the image carrier 110, and a columnar fixed magnet 312 provided inside thereof. And a developing roll 310 composed of The developing roll 310 includes the developer stirring member 33.
The developer stirred at 0 is attracted by the fixed magnet 312 provided inside the rotating sleeve 311, and the layer thickness regulating member 320 forms a thin layer of the developer on the rotating sleeve 311 with the arrow mark. Image carrier 11
The developer is conveyed to the development area D facing 0. In addition,
The developer used in this example was prepared by mixing and stirring a magnetic carrier having an average particle size of 40 μm and a saturation magnetization of 60 emu / g with a polyester-based color toner having an average particle size of 7 μm. The mixing ratio is approximately 10% by weight, and the toner charge amount at a relative humidity of 30% to 85% is 1
The one adjusted to 2 to 25 μc / g was used.

FIG. 3 is a detailed sectional view of the developing roll 310. Since the magnetic sheet 314 forming the fixed magnet magnetically attracts the developer, a plurality of magnetic poles 315a, 315b, 315c, ...
have n. As shown in FIG. 2B, the plurality of magnetic poles form a so-called magnetic bridge in which the developer is connected like an arch bridge along a magnetic line of force extending between adjacent magnetic poles. The developer is conveyed by the movement of the magnetic bridge as the rotary sleeve rotates.

Of these magnetic poles, the magnetic poles 315a and 315n have the same polarity, and a repulsive magnetic field generated by these magnetic poles forms an area R for separating the developer from the rotating sleeve. As described above, the usual integrated fixed magnet has a limit even if it is attempted to reduce the magnetic pole interval, and specifically, the limit is 5 mm. Therefore, in this embodiment, a magnetic sheet is wound around the columnar shaft portion to form a fixed magnet, so that a fixed magnet having a magnetic pole interval of 2.5 mm is obtained.

In constructing the fixed magnet, a magnetized magnetic sheet may be wound around the shaft portion, or a non-magnetized sheet may be wound and then magnetized. by the way,
When the magnetic sheet 314 is wound around the shaft portion 313, the shaft portion 3
A magnetic sheet seam is formed on both circumferential edges of 13.
At this joint, it is difficult to control the magnetic force in detail, and the magnetic field tends to be disturbed. When the magnetic field is disturbed, the developer is unevenly conveyed, which results in uneven development and deteriorates the image.

It is considered that this is because it is difficult to bond both end edges of the magnetic sheet over the entire length of the shaft portion without a gap, so that the magnetic field is disturbed in the vicinity of the both end edges to cause uneven transportation. It is difficult to prevent the disturbance of the magnetic field only by devising the processing method and the assembling method, which leads to an increase in cost. Therefore, the inventors of the present invention should position these both edges in appropriate regions on the developing roll. We thought that the influence of the above-mentioned magnetic field disturbance could be avoided by conducting various experiments. First, I tried to locate both edges between the magnetic pole 315a and the magnetic pole 315n that form the developer peeling area R, but a ghost magnetic pole, which is considered to be due to the influence of the peripheral magnetic field lines, is induced between both magnetic poles. The developer did not peel well. Positioning both edges near the developing area D adversely affects the most important developing function for the developing roll, and if positioned on the upstream side of the developing area D in the rotational direction of the rotary sleeve, the conveyance of the developer is disturbed. , Neither of them gave good results.

Therefore, when both edges are located downstream of the developing region D in the rotational direction and upstream of the developer peeling region R, uneven development can be prevented. It is considered that this is because the region between the developing region D and the peeling region R is less likely to affect the image quality due to the magnetic field disturbance than other regions. However, this area also plays an important role in transporting the developed developer to the peeling area, and if there is a magnetically blank portion in this area, the developer may spill from the rotating sleeve. It was considered, but even if some gap a was actually provided between both edges, a ghost magnetic pole was induced in the gap, and the magnetic force did not hinder the transport of the developer. The gap a between the both edges T ₁ and T ₂ of the magnetic sheet may or may not be provided, but it is preferable to provide the gap a when the accuracy of bonding the both edges without a gap is not sufficiently high.

The second magnetic pole of the opposite end edges T1, T ₂ moieties are not necessarily the same polarity, even S-N, but may be N-S, in order to further enhance the effect of the present invention, the magnetic poles It is preferable that they have the same polarity. If the two magnetic poles do not have the same polarity, it is better not to have the gap a. Figure 4
3 shows the result of measuring the distribution of magnetic flux density on the sleeve surface of the developing roll of FIG. As shown in FIG. 4, the ghost N pole shown by the diagonal lines is induced in the portion corresponding to the gap a sandwiched between the two S poles of the both edges T1 and T2 shown in FIG. However, the developer is conveyed without any trouble.

Next, considering the magnetic characteristics of the developing roll, if the maximum value of the magnetic flux density in the vertical direction from each magnetic pole on the rotating sleeve is less than 200 Gauss, the coercive force on the surface of the rotating sleeve is weakened, and the electric field and rotation are reduced. Since the carrier is scattered under the influence of the centrifugal force due to the above, the maximum value of the magnetic flux density is preferably 200 gauss or more. Regarding the upper limit of the magnetic flux density, the present invention is not particularly limited,
If the magnetic flux density is too high, for example, if it exceeds 1000 gausses, the spikes of the developer will be too high, and the distance between the developing roll and the image carrier cannot be narrowed, which is not practical.

With respect to the magnetic carrier constituting the developer, when the saturation magnetization is less than 20 emu / g, the carrier is apt to adhere to the image carrier, and when it exceeds 70 emu / g, the carriers are agglomerated on the developing roll and the surface area is increased. It becomes difficult to form a large developer layer. Therefore, the saturation magnetization is preferably 20 to 70 emu / g.
When the average particle size of the magnetic carrier is less than 20 μm,
Due to the relationship between the magnetic force acting on one carrier and the electrostatic force, the carrier is likely to adhere to the image bearing member. If it exceeds 70 μm, the surface area of the carrier decreases, the amount of toner to be held decreases, and the image density decreases. Average particle size is 20 ~
It is preferably 70 μm.

Regarding the surface roughness of the rotary sleeve of the developing roll, if the surface roughness is too small, the developer is apt to slip on the rotary sleeve when passing through the layer thickness regulating member, and the toner concentration in the developer fluctuates. As a result, the developer transport amount is likely to change, and as a result, the image density becomes unstable. Further, if the surface roughness is too large, it will overlap with the shake of the developing roll, and image density unevenness in synchronization with the rotation cycle of the developing roll will easily occur. In this embodiment, when the magnetic carrier having the smallest average particle size of 20 μm is used, the surface roughness is Rz = 2 μm, that is, the average particle size of the magnetic carrier is 1 μm.
When the surface roughness was 0% or more, slippage when passing through the layer thickness regulating member could be suppressed. Further, when an experiment was carried out using a magnetic carrier having a large average particle diameter of 70 μm in the developing roll shown in this embodiment, the surface roughness was Rz = 50 μm, that is, the average particle diameter of the magnetic carrier was 7 μm.
If it exceeds 0%, uneven image density occurs. Therefore, the surface roughness of the rotating sleeve is preferably at least 10% of the average particle diameter of the magnetic carrier and 70% or less of the average particle diameter.

The outer diameter of the sleeve 311 in this embodiment is 20 mm. Further, in the developing area of the fixed magnet facing the image carrier 110, N poles and S poles are alternately arranged on the sleeve surface so as to have a magnetic flux density of about 2.5 mm and 450 gausses. The height of the spikes is 350 μm. Further, the distance between the image carrier 110 and the rotary sleeve 311 is set to 500 μm, and in this state, effective development when an alternating electric field in which a DC component is superimposed is applied between the image carrier 110 and the sleeve 311. The area has a width of about 10 mm.

Here, the effective developing area refers to an effective area on the image carrier on which the toner is actually developed. The toner is actually developed by applying a predetermined electric field with the developing roll and the image carrier stationary. The width of the area flying from the developing roll to the image carrier is measured and displayed in mm. As described above, the width of the effective developing region is an important factor that influences the efficiency of the developing device as the toner particle size becomes smaller. To increase the efficiency of the developing device, widen this width. Is effective. Therefore, it is preferable that the magnetic pole spacing of the fixed magnet is as narrow as possible.

In general, when the magnetic flux density is the same, the height of the spikes of the developer decreases as the magnetic pole spacing decreases, and the distance between the developing roll and the image carrier can be reduced, so that a strong electric field can be applied. However, if the magnetic pole spacing is too narrow in the developer currently in practical use,
A sufficient amount of paper cannot be secured, resulting in insufficient image density. At the same time, the strength of the magnetic field of the magnet becomes insufficient, and the magnet tends to be scattered, which may cause carrier scattering.

FIG. 5 is a graph showing the results of measuring the amount of toner developed on the image bearing member by changing the magnetic pole interval on the surface of the rotary sleeve from 0 to 12 mm using the developing device of this embodiment. . It can be seen from FIG. 5 that the amount of developing toner increases as the magnetic pole spacing becomes narrower, but it is actually difficult to create a magnetic pole spacing of 0.5 mm or less, and it is 1 mm.
The above magnetic pole spacing is appropriate. Further, if the magnetic pole interval is widened, there is an advantage that the amount of developer conveyed can be increased, but the height of the spikes of the developer is increased and the interval between the developing roll and the image carrier must be widened. , It is disadvantageous in applying a strong electric field. Therefore, the magnetic pole spacing is preferably 5 mm or less.

As described above, the developing roll 310 has 10
Since the effective developing area width is 3 mm, and 3 to 4 bristles are formed between them, the effective surface area of the developer in the effective developing area is increased, and the number of toner particles seen from the image carrier is increased. In other words, the amount of toner that can fly to the image carrier increases. Further, since the front and back surfaces of the developer layers are exchanged 3 to 4 times in the effective developing area, almost all the developer transported into the effective developing area participates in the development, so that the developing efficiency is significantly improved.

Although the width of the effective developing region is naturally influenced by the electric field condition, it generally becomes wider as the electric fields of the DC component and the AC component become larger. Regarding the influence of frequency, in the range of up to 10 and several kHz, the width of the effective developing region is widest at around 1 to 3 kHz, so it is desirable to select the optimum condition. In this embodiment, the dark potential of the image carrier 110 is −60 so as not to disturb the toner image previously developed on the latent image carrier 110.
0 to -900V, bright potential is -50 to -200V, difference between dark potential and DC component of bias applied to sleeve 311 is 50 to 150V, peak value of AC component of bias is 1.5 to 2kV, It is desirable to perform development in the frequency range of 4 to 10 kHz, and as a result of such optimization, the width of the effective development region was about 10 mm as described above.

Next, the characteristic value of the toner of the developer will be described. When the average particle diameter of the toner is less than 3 μm, the toner is scattered from the developing device within the range of the charge amount for ensuring a sufficient development amount. It was terribly not practical. In the developing device of this embodiment, the moving speed of the image carrier is 1
00 mm / sec or more, and in this case, the average particle size is 5 μ
A toner of m or more is desirable. On the other hand, when the average particle diameter of the toner exceeds 15 μm, the sharpness of fine lines of the image and the graininess in the low density region become poor. Further, in the developing device of the present embodiment, laser exposure is performed by pulse modulation of 256 gradations of 63.5 μm per pixel to form an electrostatic latent image with a sharp fine line image, and the toner for developing the electrostatic latent image is also conventional. Since the aim is to make it finer to improve the sharpness of fine lines and the graininess in the low density region, the average particle diameter of the toner is preferably 10 μm or less.

Further, referring to the triboelectric charging between the toner and the carrier, when the charge amount is less than 5 μc / g, the electrostatic bond between the toner and the carrier is weakened, and not only the toner scattering but also the developing electric field is caused. Response becomes slower and sharpness of fine lines and reproducibility of low density are reduced. Further, when the toner charge amount is high, the latent image on the image carrier is electrostatically saturated with a small amount of toner, and a latent image with a very high voltage is required to secure image density. . Therefore, if it exceeds 50 μc / g, it becomes difficult to use a general-purpose image carrier used at a primary charging potential of 1000 V or less. Therefore, the toner charge amount is 5 to 50 μc.
It is desirable to set it in the range of / g.

In the above embodiment, the first developing device is a magnetic one-component black developing device, but it is also possible to apply a developing system other than the magnetic one-component developing device to the first developing device. Yes, for example, when non-magnetic black toner is used in a non-contact two-component developing device similar to the second to fourth developing devices, the black toner on the image carrier is the second to fourth developing devices. Since there is no fear of image disturbance due to the magnet when passing through the sheet, it is possible to further narrow the distance between the image carrier and the developing roll and to strengthen the alternating electric field containing the DC component. Therefore, it is possible to build a high-quality image forming apparatus with a sufficient margin for the above-mentioned image disturbance, securing of image density, and the like.

Further, in the first developing device, the
It is also possible to develop non-magnetic black toner by the component contact method, and there are similar advantages, but in this case, it is necessary to provide the first developing device with a retracting mechanism for preventing image distortion after black toner development. . Further, in the above-described embodiment, the black developing device uses the magnetic one-component developer, so naturally, in consideration of magnetic interference between the black developing device and the yellow developing device which are adjacent thereto, the black developing device is used. It is necessary to design the magnetic pattern of the fixed magnet of the developing device.

In the above-mentioned embodiments, an example in which a two-component developer is used as the developer other than black is given, but the present invention is not limited to the two-component developer, and any developer may be used. Can also be applied to. Further, although the above description relates to an embodiment in which the developing device of the present invention is applied to a full-color image forming device having all four developing devices, the present invention is not limited to the full-color image forming device. It is not something that can be done.

[0046]

As described above, according to the present invention,
With the above-described configuration, it is possible to prevent the developer conveyance failure due to the unevenness of the magnetic field generated at the both edges of the magnetic sheet forming the fixed magnet, and to obtain the developing device with good image quality. Further, in the developing device of the present invention, by making the magnetic poles at both edges of the magnetic sheet have the same polarity, it is possible to effectively suppress the occurrence of the magnetic field unevenness and further enhance the effects of the present invention.

Further, in the developing device of the present invention, carrier scattering or scattering can be prevented by defining the magnetic flux density in the vertical direction of each magnetic pole formed on the magnetic sheet and the saturation magnetization and average particle diameter of the magnetic carrier within appropriate ranges. It is possible to prevent the carrier from adhering to the image carrier. Further, in the developing device of the present invention, the surface roughness of the rotary sleeve is regulated within an appropriate range, so that the magnetic carrier can be prevented from slipping when passing through the layer thickness regulating member.

[Brief description of drawings]

FIG. 1 is a sectional view showing a main part of an image forming apparatus including a developing device according to an embodiment of the present invention.

FIG. 2 is a sectional view showing a main part of a developing device according to an embodiment of the present invention, and a partially enlarged view thereof.

FIG. 3 is a detailed cross-sectional view of a developing roll of the developing device according to the exemplary embodiment of the present invention.

FIG. 4 is a diagram showing a result of measuring a distribution of magnetic flux density on a rotating sleeve of a developing device according to an embodiment of the present invention.

FIG. 5 is a graph plotting the relationship between the distance between magnetic poles on the surface of the rotating sleeve of the developing device according to the exemplary embodiment of the present invention and the amount of developing toner.

[Explanation of symbols]

 110 Image Carrier 120 Primary Charger 130 Discharge Exposure Device 200 Laser Light Generator 210 Semiconductor Laser and Polygon Rotating Mirror 220 Laser Light 301 Developing Device (for Black) 302 Developing Device (for Yellow) 303 Developing Device (for Magenta) 304 Developing Device (for cyan) 310 Developing roll 311 Rotating sleeve 312 Fixed magnet 313 Shaft part 314 Magnetic sheet 315a to 315n Magnetic pole 320 Layer thickness regulating member 330 Developer stirring member 410 Transfer charger 440 Peeling charger 480 Pre-transfer charger 500 Cleaning Device 720 Paper guide 750 Conveyor belt

Claims (4)

[Claims] 1. A cylindrical rotary sleeve which holds a magnetic developer and conveys the developer to a predetermined developing area in the vicinity of an image bearing member on which an electrostatic latent image is formed, and in the rotary sleeve. And a columnar fixed magnet having a plurality of magnetic poles formed in the circumferential direction and magnetically attracting the developer,
In a developing device for developing an electrostatic latent image formed on the image bearing member by using the developer conveyed by the rotating sleeve, the fixed magnet includes a columnar shaft portion and a rotating direction of the rotating sleeve. With respect to each magnetic pole, each magnetic pole is wound around the shaft portion so that both ends in the circumferential direction are located on the downstream side of the developing area and on the upstream side of the peeling area where the developer after development is peeled from the rotating sleeve. And a magnetic sheet having a plurality of magnetic poles formed in the circumferential direction of the shaft and extending in the longitudinal direction of the shaft. 2. The magnetic poles of the plurality of magnetic poles formed on the magnetic sheet, the two magnetic poles existing at both circumferential edges of the magnetic sheet being magnetic poles having the same polarity. Developing device. 3. The developing device is a developing device for developing an electrostatic latent image by using a two-component developer having a toner and a magnetic carrier, wherein each magnetic pole formed on the magnetic sheet is in a vertical direction. The maximum value of the magnetic flux density is 200 to 1000 Gauss, the saturation magnetization of the magnetic carrier is 20 to 70 emu / g, and the average particle size of the magnetic carrier is 20 to 70 μm. Developing device. 4. The developing device is a developing device for developing an electrostatic latent image using a two-component developer having a toner and a magnetic carrier, wherein the rotating sleeve constitutes the developer. The developing device according to claim 1, wherein the developing device has a surface roughness of 10 to 70% of the average particle diameter of.