JPH10240010A - Developing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To uniformize the toner concentration of developer by allowing screw augers to carry the developer in respective axial directions and in opposite directions to each other while stirring the developer, and mixing the developer carried by both augers in all the area in the axial directions between the augers. SOLUTION: Toner supplied to a developer stirring part is circularly moved by the rotation of the screw augers 7 and 8. In such a case, a part of the developer is attracted to a developer carrier 3 from the auger 7 located ahead by magnetic attractive force. Since a partition wall partitioning the carrying areas of the adjacent augers 8 and 7 is not provided between the augers 7 and 8, the developer is pressed by the wing bodies of the augers 7 and 8 and carried in the axial directions of the augers 7 and 8. At such a time, the developer on the periphery is pressed to be spread to the outside of the augers 7 and 8 and the flows of the developer interfere with each other in almost all the area in the axial directions of the augers 7 and 8, whereby the developer is stirred and mixed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrophotographic copying machine,
The present invention relates to a developing device used for an image forming apparatus such as a printer, and more particularly to a developing device using a two-component developer in which a toner and a carrier are mixed.

[0002]

2. Description of the Related Art In an image forming apparatus using an electrophotographic method, an electrostatic latent image formed on an electrostatic latent image carrier is visualized by adhering toner, and this visible image is transferred onto recording paper. It is configured to copy an image or the like. As a developing device for visualizing a latent image formed on a latent image carrier in such a device, there are a developing device using a one-component developer and a developing device using a two-component developer composed of a toner and a carrier. As a developing device using a two-component developer, a developer carrier having a rotating peripheral surface is arranged close to an electrostatic latent image carrier, and a fixed magnetic field generating means having a plurality of magnetic poles is provided therein. Is commonly used. In such a developing device, a magnetic brush is formed by holding the developer supplied to the surface of the developer carrier by the magnetic force of the fixed magnetic field generating means, and the magnetic brush is statically moved by rotation of the developer carrier. It is rubbed or brought close to the latent electrostatic image carrier. Since a bias voltage is applied to the developer carrier, an electric field is generated between the developer carrier and the electrostatic latent image, and the charged toner adheres to the image portion by this action, and the electrostatic latent image is formed. The latent image on the carrier is developed.

In order to obtain an image having a constant density by using such a developing device, it is necessary to make the charge amount of the toner contained in the developer on the developer carrier constant. Generally, the amount of developed toner is determined according to the amount of charge of the toner. Generally, the toner is charged by a method based on friction at the time of mixing the toner and the carrier. By stirring the toner for a certain time or more, a substantially stable charge amount can be maintained. However, since the amount of toner that can charge the carrier is limited, as the amount of toner increases, the amount of toner charge decreases. In addition, during the actual operation of the developing device, the uncharged toner corresponding to the amount consumed in the development of the electrostatic latent image is constantly replenished, so that the toner density and the charge amount of the toner are reduced. Means for maintaining a constant state are required.

[0004] These problems in magnetic brush development are:
The problem can be solved by sufficiently mixing and agitating the carrier and the toner, and at the same time, imparting the charge amount of the toner by frictional charging. There are a method of arranging a plurality of paddles in a room and rotating the paddle to stir the developer, a method of supplying toner along the length of the developer carrier, and a method of providing a preliminary stirring chamber.

[0005] The stirring power for the developer is enhanced by increasing the rotation speed of the developer stirring and conveying member, which is effective in making the toner concentration in the developer uniform and in charging the toner.
However, when the rotational speed of the developer stirring and conveying member is increased, a strong compressive force or frictional force acts on the developer, and thus there is a problem that the deterioration of the developer is promoted. In the method using a plurality of paddles, the replenished developer can be agitated by rotating the paddle.However, since the paddle has a low ability to diffuse the developer in the longitudinal direction, the toner concentration is uniformized in a short time, It is difficult to form an image without density unevenness. Further, the method of replenishing the toner in the longitudinal direction of the developer carrying member or the method of providing a preliminary stirring chamber for the toner has a disadvantage that the apparatus becomes large.

As a technique for solving these problems, Japanese Patent Application Laid-Open No. Sho 62-153882 discloses a method in which a two-component developer is stirred and conveyed by a screw auger. In this developing device, a plurality of screw augers are provided in a developer accommodating chamber, and a partition plate is provided between the screw augers. Since the developer always flows by the screw auger and circulates through the stirring unit in the developing device while being stirred, the toner is not biased to a specific position. Also, the installation of the screw auger does not require a large space like a paddle,
The device does not increase in size.

[0007]

However, in the developing device described in Japanese Patent Application Laid-Open No. Sho 62-153882, the developer is conveyed in the axial direction with the rotation of the screw auger. Therefore, the entire toner concentration becomes non-uniform until recirculation is performed for a while after new toner is supplied.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has as its object to achieve high uniformity of the toner concentration of the developer in the developer accommodating section and high image quality stability. An object of the present invention is to provide a small developing device having excellent performance.

[0009]

In order to solve the above-mentioned problems, a developing device according to the first aspect of the present invention is configured to face an image carrier on which a latent image is formed due to a difference in electrostatic potential. A developer carrier that magnetically adsorbs a two-component developer containing a toner and a magnetic carrier on the peripheral surface and transports the developer around the surface; and a position of the developer carrier opposite to the image carrier. And a housing that covers the rear and has a developer accommodating chamber for storing the two-component developer. In the developer accommodating chamber, two screw augers installed substantially horizontally and parallel to each other are provided. These screw augers, while stirring the developer,
It is assumed that the developer is conveyed in the respective axial directions and opposite directions, and that the two conveyed developers are mixed in the entire region in the axial direction between these two screw augers.

[0010] In such a developing device, a partition between two adjacent screw augers is not provided as in the prior art, and the two screw augers are provided with a developer between the respective transport areas. Are arranged to mix and stir. Then, the developer is conveyed in the opposite directions by the adjacent screw augers, and the two conveyed developers interfere with each other between the screw augers, so that stirring is performed over substantially the entire length of the screw augers. For this reason, the supplied toner is mixed and
The toner is agitated, the toner concentration is made uniform throughout the developing device, and an appropriate charge amount is provided.

According to a second aspect of the present invention, there is provided the developing device according to the first aspect.
The developing device according to claim 1, further comprising: a layer thickness regulating member that regulates a layer thickness of the two-component developer carried on the developer carrier, wherein the developer carrier is fixedly supported to generate a magnetic field. Means, and a developer transport member that moves around the outside thereof, wherein the two-component developer is magnetically adsorbed on the outer peripheral surface of the transport member, and the two-component developer is held at a position where the layer thickness regulating member is provided. The magnetic pole of the magnetic field generating means has a developer amount Mp (mg / cm) adsorbed on the developer conveying member.
² ) is the developer amount Mos (mg / cm ² ) which is regulated by the layer thickness regulating member and is conveyed to a position facing the image carrier.
It is assumed that it is set to be less than twice.

In this developing device, the amount of the developer adsorbed on the surface of the developer carrier is limited by adjusting the magnetic force of the magnetic pole of the magnetic field generating means on the upstream side of the layer thickness regulating member.
The developer adsorbed on the surface of the developer carrier is regulated to a constant layer thickness at the position of the layer thickness regulating member. However, since the amount of the developer on the developer carrier is reduced, the layer thickness is reduced. The amount of developer stagnation on the upstream side of the regulating member is reduced. Therefore, a large pressure does not act on the developer on the upstream side of the layer thickness regulating member, and the deterioration of the developer can be suppressed.

According to a third aspect of the present invention, there is provided the developing device according to the first aspect.
In the developing device described in the above, as a magnetic carrier of the two-component developing device, having a conductive core material and a surface layer containing a conductive agent, using a magnetic particles having a resistivity of 10 ⁸ Ωcm or less I do.

In general, the transfer of the toner from the developer carrier to the image carrier during the image forming process is easily affected by environmental factors such as temperature and humidity. That is, if the temperature or the humidity changes, the charge amount of the toner changes. Therefore, even if the toner concentration in the developer is kept constant, it is difficult to avoid the change in the image density. However, in the developing device having the above-described configuration, since the low-resistance magnetic particles are used as the magnetic carrier, the potential of the magnetic brush formed on the surface of the developer carrier becomes substantially equal to that of the developer carrier. Therefore, an electric field due to the developing bias voltage is generated between the vicinity of the tip of the magnetic brush and the image carrier, and only the toner adsorbed near the tip of the magnetic brush is transferred to the image carrier. By setting the developing bias voltage so that the transfer of the toner within the range of action of the electric field is saturated, a stable and good image is formed irrespective of environmental changes such as temperature and humidity. be able to. In order to perform such development, it is required that a constant toner concentration and an appropriate charge amount are always maintained. However, in this developing device, two screw augers are provided in a developer accommodating chamber. Are arranged so that these screw augers convey the developer in the directions opposite to each other in the axial direction, and mix the developer conveyed by the two in the entire axial direction between the two screw augers. Therefore, the ability to stir the toner to make the toner concentration uniform is high, and stable and good development can be performed.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. [First Embodiment] FIG. 1 is a schematic structural view showing a developing device according to an embodiment of the present invention. The developing device 1 is disposed so as to face the image carrier 2, and the image carrier 2 is 0.5 mm from the developer conveying member 4.
And rotates at a peripheral speed of 150 mm / sec in the direction indicated by the arrow in the figure. Further, the exposed portion potential -20 is formed on the image carrier 2 by a normal electrophotographic process.
A latent image of 0 V and a non-exposed portion potential of -650 V is formed. The developing device 1 has a housing for accommodating a two-component developer, and an opening is provided at a position of the housing facing the image carrier 2, and the opening is developed so as to face the image carrier. An agent carrier 3 is provided. Above the developer carrier 3, a layer thickness regulating member 6 for regulating the developer layer on the surface of the developer carrier to a constant thickness is provided.
In this housing, two screw augers 7 and 8 are arranged substantially horizontally and parallel to each other.

The developer carrier 3 has a developer transporting member 4 rotatably supported and a magnet roll 5 (magnetic field generating means) fixed and supported inside the developer transporting member 4. The two-component developer is attracted to the surface of the developer conveying member by magnetic force, and is conveyed to a position facing the image carrier by the rotation of the developer conveying member. The developer conveying member 4 has a gap of 0.7 mm from the layer thickness regulating member 6, and rotates at a peripheral speed of 300 mm / sec in the direction of the arrow shown in FIG. The developer conveying member 4 is made of a conductive non-magnetic material, for example, aluminum, and has a surface having fine irregularities of several microns with a ten-point average roughness Rz by blasting. Further, the developer conveying member 4 includes:
Vp-p = 1.5KV, frequency f =
A voltage in which an AC component of 6 KHz and a DC component of Vdc = -500 V are superimposed is applied.

On the magnet roll 5, a developing magnetic pole S1 forming a spike of the developer at a position facing the image carrier 2, and a developing section where the image carrier 2 and the developer carrier 3 are opposed to each other. The subsequent developer is peeled off from the surface of the developer transport member 4, and two separated magnetic poles N3 and N4 of the same polarity, which are arranged adjacently to eliminate the image history, are mixed with the developer mixed and stirred in the stirring section. An attraction magnetic pole S3 magnetically attracted to the surface of the conveying member 4, a layer-forming magnetic pole S2 for forming a spike of the developer near the layer thickness regulating member 6 to adjust the developer to a predetermined thickness, The transport magnetic poles N1 and N2 for maintaining the transported developer on the surface of the developer transport member 4 are magnetized. The magnetic flux density on the surface of the developer conveying member 4 at each magnetic pole position is 700 gauss for the magnetic pole N1, 500 gauss for the magnetic pole N3, 650 gauss for the magnetic pole N4, and 650 gauss for the magnetic pole S.
1 is 1000 gauss, magnetic pole S2, magnetic pole S3 and magnetic pole N
2 is set to 900 gauss.

The screw augers 7 and 8 have a diameter of 20 mm.
mm and a pitch of 6 mm, and is driven to rotate in the same direction to stir and transport the developer. Since these screws have spiral wings in opposite directions, the directions of the developer transported by the respective screw augers are opposite to each other.

Next, the operation of the developing device will be described. FIG. 2 is a schematic diagram showing a direction in which the developer is conveyed by the screw auger of the developing device, and the arrows in the figure show the direction of the flow of the developer. The toner supplied to the developing agitating section is supplied from point A, and is circulated and transferred by rotation of the screw augers 7 and 8. At this time, a part of the developer is attracted from the front screw auger 7 to the developer carrier 3 by magnetic attraction. Unlike the conventional apparatus, no partition wall is provided between these screw augers to partition the screw auger from the conveying area of the adjacent screw auger. Therefore, the developer is pushed by the wings of the screw augers 7 and 8,
The developer is conveyed in the axial direction of the screw auger, and the surrounding developer is pushed so as to spread outside the screw auger. Due to this force, the flow of the developer conveyed by both screw augers interferes with each other in almost the entire area in the axial direction of the screw augers, and agitation and mixing are performed. For this reason, a sufficient amount of charge is imparted to the toner, and the entire developer is agitated in a short time, so that the toner concentration becomes uniform throughout the axial direction of the screw auger.
The developer stirred and transported in this manner is attracted to the developer transport member 4 in a region where the magnetic field of the attracting magnetic pole S3 of the developer carrier 3 shown in FIG. It is transported to the layer forming magnetic pole S2 via the transport magnetic pole N2.

The developer conveyed to the layer forming magnetic pole S2 is regulated to a constant layer thickness by the layer thickness regulating member 6, but is cut off from the developer conveying member 4 by the layer thickness regulating member 6 at this time. The surplus developer falls into the stirring / conveying area, and is again subjected to stirring / conveying by the screw augers 7 and 8. On the other hand, the developer layer regulated to a certain layer thickness reaches the developing magnetic pole S1 via the transport magnetic pole N1, and the image carrier 2 facing the developing magnetic pole S1.
Transfer of the toner to the electrostatic latent image formed thereon is performed.
The toner and carrier not used for the development are transported to the areas of the separation magnetic poles N4 and N3 where the same polarity magnetic poles are arranged adjacent to each other, are separated from the developer transport member 4, and are again stirred and transported by the screw augers 7, 8. Receive.

The weight of the developer per unit area on the developer carrier 3 in the developing device is actually measured. The measuring method and the measurement result are as follows. The driving of the developing device is started and stopped after the steady state is reached. Gently remove the developer carrier from the developing device, scrape the developer away from the measurement area with a scraper, measure the total weight, and determine the measurement area based on the difference from the previously measured weight of the developer carrier. Calculate the weight of the developer carried on the. Next, the actual area from the developer attracting magnetic pole to the layer regulating member is calculated, and the weight of the developer per unit area on the developer carrier is calculated from this value and the weight of the developer in the measurement area measured earlier. When the developing device was driven and the steady state was reached, the weight of the developer in the stirring section was 550 g, and the amount of the developer adsorbed on the developer carrier was 100 g. The average weight of the developer adsorbed per unit area per unit area is about 450 mg / cm ^2.
The developer adsorbed after passing through the layer forming member is about 80
mg / cm ² .

[Experiment 1] The following experiment was conducted in order to examine the developer stirring performance of the above-mentioned developing device. Using the following toner and carrier for A-Color 635 manufactured by Fuji Xerox Co., Ltd., 6 g of uncharged toner was introduced from the toner replenishment point (indicated by A in FIG. 2) of the above-mentioned developing device, An image was formed and image densities were measured at three points at both ends and the center of the image forming width.

[Carrier] Particle size: 50 μm Core material: Ferrite (F-300, manufactured by Powder Tech) 100 parts by weight Coating material: Styrene-methacrylate copolymer (copolymerization ratio 30:70) 0.5 parts by weight Toluene 14 parts by weight Production method: The above components except ferrite are dispersed in a sand mill for 1 hour to prepare a coating layer forming solution. next,
The solution for forming a coat layer and the ferrite are placed in a vacuum deaeration type kneader and stirred at a temperature of 60 ° C. for 20 minutes while reducing the pressure to form a coat layer, thereby obtaining the carrier. [Toner] Polyester (number average molecular weight: 4,300,
Weight average molecular weight: 9,800, Tg = 58 ° C) 94w
t%, 6 wt% of coloring material are kneaded and pulverized, and the average particle size is 7 μm.
What

The image is formed 15 seconds after the toner is supplied,
Second, 45, 60, 90 and 120 seconds have elapsed, and the results are shown in FIG. 3 (a). As shown in this figure, no difference was found in the image density at any of the above three places during image formation, and a uniform image was obtained.

In the same manner as in the above experiment, after charging 6 g of uncharged toner from the toner replenishing point A, image formation was not performed, and the toner density at the portion facing the image carrier was measured at both ends and the center of the image forming width. At three locations over time. The measurement was performed immediately after the introduction of the toner, 5 seconds, 10 seconds, 15 seconds, 20 seconds, 30 seconds, 45 seconds, 60 seconds, 90 seconds and 1 second.
Performed after 20 seconds. The results are as shown in FIG. 3 (b). The toner density showed a large variation within a few seconds after the charging of the non-charged toner, but was not observed after 15 seconds. Maintained. As described above, it was found that in the above-described developing device, the toner density was stabilized early after toner replenishment, and a uniform image without image density unevenness was formed.

Further, in order to confirm the relationship between the screw auger and the developer stirring effect, the diameter of the blade of the screw auger of the developing device and the void area of the developer reservoir (FIG. 4)
(The range indicated by symbol B in (a)) was changed, and an experiment was performed on the fluctuation of the toner concentration stabilization time accompanying the ratio.
The result is as shown in FIG. 4 (b). When the ratio of the projected area of the screw auger to the area of the developer reservoir in the cross section perpendicular to the axis of the screw auger is in the range of 0.3 to 0.8, the toner injection is performed. The time required for stabilizing the post-toner concentration was short, and a good developer stirring effect was obtained. However, as the cross-sectional area ratio approaches the upper limit (area ratio = 1), the amount of developer moving between adjacent screw augers decreases extremely, and a sufficient developer stirring effect cannot be obtained. Also, when the area ratio is less than 0.2, the force acting on the developer in the outer peripheral portion of the screw auger does not reach the affected area of the adjacent screw auger, and the amount of the developer moving between the screw augers decreases, Not only was a sufficient developer stirring effect not obtained, but also circulation of the developer was not observed. When the rotation speed of the screw auger was increased in this experiment, the toner concentration stabilization time was shortened, but the range of the area ratio at which a good developer stirring effect was obtained was unchanged.

Next, in order to compare and examine the effect of the above-described developing device with a conventional developing device, an experiment using the developing device shown in FIG. 5 was conducted. This developing device is conventionally known, and a partition 10 is provided between two screw augers as shown in FIG. 5, thereby forming an independent conveyance path around each screw auger. . A communication port having a width of 3 cm is provided at an end of the partition 10 in the longitudinal direction, and the developer is circulated through the communication port while being stirred by the screw augers 17 and 18. . Other configurations of the developing device are the same as those shown in FIG. As shown in FIG. 6, the flow of the developer in this developing device is in the opposite directions along the longitudinal direction of the two screw augers 17 and 18, and the developer flows between these two conveying paths. The movement is performed only through the communication port.

After 6 g of the non-charged toner is charged into the developing device, an image is formed after 15 seconds, 30 seconds, 45 seconds, 60 seconds, 90 seconds and 120 seconds have elapsed, and both ends and the center of the image forming width are formed. Image density was measured at several locations. The results are as shown in FIG. 7 (a), and the image density fluctuated 15 seconds and 30 seconds after the toner was injected. Also, 6 g of uncharged toner is charged into the developing device, and the toner density at the portion facing the image carrier is measured at three positions at both ends and the center of the image forming width, 5 seconds after the toner is charged, and 15 seconds after the toner is charged.
Seconds, 20 seconds, 30 seconds, 45 seconds, 60 seconds, 90 seconds
As a result of the measurement after seconds and 120 seconds, as shown in FIG. 7 (b), the toner concentration varied from 5 seconds to 30 seconds after the toner was injected. This requires a longer time to stabilize the toner concentration than the developing device of the embodiment of the present invention.

Further, as a result of comparing the toner charge amount applied by stirring when the toner density is set high and when the toner density is set low, as shown in FIG. 8, the toner density is low regardless of the stirring time. In the case, the toner charge amount was larger than that in the case where the toner concentration was high.

From these results, it was found that the cause of the variation in image density caused by the developing device was that the replenished uncharged toner was conveyed onto the developer carrier without being sufficiently stirred and diffused. Therefore, Experiment 1
It was confirmed that the developing device of the present invention used in Example 1 had a higher stirring effect of the developer than the conventional developing device described above, and was able to impart a sufficient amount of toner charge.

[Second Embodiment] FIG. 9 is a schematic diagram showing a developing device according to an embodiment of the present invention. In this developing device, of the magnetic poles provided on the magnet roll 25, the developer adsorbing magnetic pole S3 to the layer forming magnetic pole S3
Up to two magnetic poles are weakly magnetized as compared with the corresponding magnetic poles of the developing device shown in FIG. 1, and the magnetic flux density on the surface of the developer conveying member 24 is 450 gauss.
Other configurations of this developing device are the same as those of the developing device shown in FIG.

As shown in FIG. 9, the flow of the developer in this developing device is attracted from the developer reservoir by the attracting magnetic pole S3 of the developer carrier 23 and is conveyed to the layer forming magnetic pole S2. The adsorption force of the developer by S3 is shown in FIG.
Since the size of the developing device is smaller than that of the developing device shown in FIG. Then, the developer having a small magnetic binding force falls into the developer reservoir in a flow indicated by an arrow C in FIG. 9 and is stirred again. On the other hand, the developer adsorbed on the surface of the developer carrier by the attracting magnetic pole S3 is regulated by the layer forming member 26. However, since the amount of the adsorbed developer is small, the developer follows the flow indicated by the arrow D in FIG. The amount of surplus developer falling into the developer reservoir is also small. Therefore,
Excessive pressure is less applied to the developer upstream of the layer regulating member, and deterioration of the developer is prevented. In the developer agitating section of this developing device, a flow of the developer as shown in FIG. 2 is generated similarly to the developing device shown in FIG. 1, and both of the screw augers 27 and 28 extend in the longitudinal direction. The developer conveyed by the screw augers 27 and 28 is stirred and mixed, and even when new toner is replenished, the toner concentration is made uniform in a short time.

In this developing device, when the flow of the developer was in a steady state, the weight of the developer adsorbed on the developer carrier and the developer contained in the developer stirring section were measured. , Respectively, about 30 g and 620 g. The average developer weight adsorbed per unit area from the attraction magnetic pole S to the layer forming member 26 is about 1
Was 50 mg / cm ^2, after passing through the layer forming member 26 was 80 mg / cm ^2.

[Experiment 2] In order to compare the stirring performance of this developing device with the developing device of Experiment 1, the amount of developer contained in the stirring section was set to 450 g, which is the same as in Experiment 1, and 6 g of uncharged toner was charged. After 15 seconds, 30 seconds, 45 seconds, 60 seconds, 9
An image was formed at the passage of 0 seconds and 120 seconds, and an experiment was performed to measure the image density at both ends and the center of the image formation width. The result is as shown in FIG.
No variation in image density was observed at any measurement time.

Further, 6 g of uncharged toner is charged into this developing device, and immediately after the charging, 5 seconds, 10 seconds, 15 seconds,
After 30 seconds, 30 seconds, 45 seconds, 60 seconds, 90 seconds, and 120 seconds, the toner concentration was measured at both ends and the center of the image forming width. As a result, as shown in FIG. 10B, a large variation in the toner density was observed at the lapse of 5 seconds and 10 seconds after the introduction of the toner, but became substantially uniform after 15 seconds. I didn't see it. As described above, this developing device has a function of reducing the deterioration of the developer, and uniformizing the toner concentration and imparting a sufficient charge amount to the toner by good stirring and transporting properties of the developer. Was confirmed.

Next, in order to compare the effects of the developing device used in Experiment 2 with those of the conventional developing device, a similar experiment was performed using the developing device shown in FIG. The developing device includes a partition 30 between two screw augers 37 and 38.
Is the same as the developing device shown in FIG. In this developing device, as in the developing device shown in FIG. 9, since the amount of the developer adsorbed on the developer carrier 33 is limited, the developer conveyed to the layer forming magnetic pole S2 and regulated by the layer regulating member 36 is used. The amount is small. In the developer stirring section, the developer is stirred and conveyed by screw augers 37 and 38. Here, the flow of the developer by the screw auger is
As shown in FIG. 7, the developer is transported in opposite directions along the longitudinal direction of the two screw augers, and the movement of the developer between the two transport paths partitioned by the partition wall is in the longitudinal direction of the screw auger. This is performed only through the communication ports provided at both ends of the.

After charging 6 g of the uncharged toner into this developing device, an image is formed after 15 seconds, 30 seconds, 60 seconds, 90 seconds and 120 seconds have elapsed, and the image is formed at three positions at both ends and the center of the image forming width. Was used to measure the image density. The result is shown in FIG.
(A) As shown in FIG.
Until the lapse of seconds, the image density fluctuated. Moreover,
This variation is caused by the developing device (FIG. 5) used for comparison in Experiment 1.
(Developer shown in FIG. 3), the degree of variation was large and the duration was long.

Further, 6 g of uncharged toner is charged into this developing device, and immediately after the charging, 5 seconds, 10 seconds, 15 seconds,
After 30 seconds, 30 seconds, 45 seconds, 60 seconds, 90 seconds, and 120 seconds, the toner density was measured at both ends and the center of the image forming width, as shown in FIG. 12B. 9, a large variation is observed from 5 seconds to 30 seconds after the toner is injected, and the duration of the variation is longer than the variation in the developing device (the embodiment of the invention described in claim 2) shown in FIG. The degree of the variation was larger than the developing device shown in FIG. 9 and the developing device shown in FIG. 5 (comparative example used in Experiment 1).

As described above, the variations in image density and toner density in the developing device of this comparative example (the developing device shown in FIG. 11) are the same as those of the developing device used in the experiment 1 (the developing device shown in FIG. 5). The reason for this was that it had a function to stir the developer from the adsorption part on the developer carrier to the layer formation part, and this stirring force was reduced if the amount of developer existing in this section was small. However, it is considered that stirring and mixing of the developer tend to be insufficient. In other words, if the amount of the developer upstream of the layer forming portion is small, the compressive and frictional forces acting on the developer are reduced, and the deterioration of the developer can be prevented, but on the other hand, the developer stirring function is reduced. In addition, variations in toner density and image density are likely to occur. However, in the developing device according to the present invention, even if the amount of the developer upstream of the layer forming portion is reduced to prevent the deterioration of the developer, the stirring by the screw auger is efficiently performed.
It can compensate for the reduced stirring function on the developer carrier,
It is possible to prevent the deterioration of the developer while providing a uniform image.

[Third Embodiment] The developing device described here is an embodiment of the third aspect of the present invention, and the configuration of each part of the developing device is the same as that shown in FIG. As the carrier in the developer, a carrier subjected to a low-resistance magnetizing treatment is used. This carrier is obtained by coating a low-resistance magnetic core to a thickness of 0.8 μm with a coating material in which conductive powder is dispersed at 10% by volume in a coating resin. Magnetite (MX) having an average particle size of 50 μm is used as the low-resistance magnetic core.
030A, manufactured by Fuji Electric Chemical Co., Ltd., and a styrene-methacrylate copolymer (copolymerization ratio: 20: 8)
0), and carbon black (VXC
72, manufactured by Cabot Corporation).

The resistance of the carrier and magnetite alone was measured by the following method. The above-described developing device is disposed to face the aluminum plate so as to have a space of 0.5 mm,
During this time, a DC voltage is applied between the developing device and the aluminum plate while the carrier or the magnetite particles are filled, and the current value is measured. From this current value, a generally known relationship between electrolysis E and current density J, log J = E ^1/2
To determine the resistance value. As a result, the resistance of the carrier in an electric field of 10 ⁴ V / cm was 10 ⁸ Ω · cm, and the resistance of magnetite alone was 10 ^-5 Ω · cm. Further, the conductive substrate is coated with the coating material to a thickness of 0.8 μm,
A metal electrode was deposited thereon, and the resistance of the coating layer alone determined from current-voltage characteristics was 10 ⁵ under an electric field of 100 V / cm.
Ω · cm.

In the development using a carrier as described above,
Due to the saturation characteristic of the developing toner amount with respect to the increase in the developing bias voltage, an image having an appropriate density can be stably obtained even if the environment changes. This is explained as follows. As shown in FIG. 13, when the developing contrast voltage Vs increases, the developing toner amount increases, but reaches a saturation region where the developing toner amount hardly increases at a certain developing contrast voltage Vsa or higher. By setting the DC component V bias of the developing bias potential and the potential of the exposed portion of the electrostatic latent image so that the developing contrast voltage Vs enters the region where the saturation occurs, the environment such as temperature and humidity changes. Even if the potential of the image carrier fluctuates, the amount of developed toner is in the saturation region,
There is no change in the development amount. Further, even if the charge amount of the toner fluctuates, if the toner concentration in the developer is constant, only the slope of the development amount curve shown in FIG.
No change occurs in the amount of developed toner. For this reason, it is possible to obtain a stable image with no change in the development density even when the environment changes or the potential of the image carrier changes.

In order to utilize such a saturation development characteristic, the magnetic carrier needs to have a low resistivity. As shown in FIG. 14, a so-called magnetic brush is formed on the developer carrier, in which magnetic carriers having toner attached thereto are connected in a spike shape. , The electric field becomes zero, and the position of the so-called virtual developing electrode approaches the image carrier.
Therefore, an electric field for transferring the toner is formed between the vicinity of the tip of the magnetic brush and the surface of the image carrier. As a result, the amount of toner in the region to which the electric field extends is limited to the amount near the tip of the magnetic brush, that is, near the image carrier,
Since the amount of toner contributing to development is limited, the amount of developed toner becomes saturated above a certain potential. If the amount of toner adhering to the carrier, that is, the concentration of the toner with respect to the carrier, is always kept constant, even if the charge amount of the toner changes due to environmental fluctuation or the like, the developing toner amount is kept almost constant, Development at an appropriate density is always performed.

In order to perform stable development even when the environment fluctuates as described above, it is necessary to maintain the toner concentration constant and uniform in the developing device. Thus, the stirring efficiency by the screw auger is high, and the toner concentration becomes uniform in a short time even after replenishing new toner. In order to use such a saturation characteristic of the amount of developed toner, the resistance value of the carrier is set to about 10 ⁸ Ω.
-It is desirable to set it to cm or less.

[Experiment 3] Using the above-described developing device and developer, 15 g, 30 sec, and 4 g of 6 g of uncharged toner were introduced.
After 5 seconds, 60 seconds, 90 seconds, and 120 seconds, images were formed, and image densities were measured at both ends and the center of the image forming width. The result is as shown in FIG. 15 (a). No variation in image density occurred,
A uniform image was formed as early as 5 seconds later.

Using the developing device and the developer, immediately after 6 g of uncharged toner was charged, 5 seconds later, 10 seconds later, and 1 second
5 seconds, 20 seconds, 30 seconds, 45 seconds, 60 seconds, 9 seconds
After 0 second and 120 seconds, the toner density was measured at three places at both ends and the center of the image forming width. The result is shown in FIG.
As shown in FIG. 5 (b), variations were observed 5 seconds and 10 seconds after the introduction of the toner, but no significant variations were observed after 15 seconds. As described above, it was confirmed that even when the developing device and the developer were used, the toner density was stabilized early after toner replenishment, and an image with a uniform density was obtained.

Further, in order to confirm the effect of the combination of the developing device and the developer, the developer containing the carrier was accommodated in the conventional developing device (developing device shown in FIG. 11) used in Experiment 2. A similar experiment was performed. The density of the image formed after replenishing 6 g of the uncharged toner to this developing device is as shown in FIG. 16A, and the density of the image varies from 15 seconds to 60 seconds after toner replenishment. It can be seen that the degree of the variation is significantly larger than that using the low-resistance carrier in the developing device shown in FIG. 9 and that a general untreated developer is used in the conventional developing device shown in FIG. It is even larger than the result of the introduction.

Further, 6 g of uncharged toner is added to this developing device.
Immediately after replenishment, 5 seconds, 10 seconds, 15 seconds, 20 seconds, 30 seconds, 45 seconds, 60 seconds, 90 seconds and 1
Twenty seconds later, toner densities were measured at both ends and the center of the image forming width. As a result, as shown in FIG.
From 5 seconds to 45 seconds after toner replenishment, a clear variation in toner density was observed. The degree of the variation in the toner density is clearly larger than that in the developing device shown in FIG. 9 using the low-resistance carrier. Further, the duration of the variation is longer, which is longer than that of the conventional developing device shown in FIG. 11 in which a carrier that has not been subjected to the resistance reduction process is used. Has become.

As can be seen from the result of comparison with the experiment using the developer not subjected to the low-resistance treatment, when the developer subjected to the low-resistance magnetizing treatment is used, the toner It was confirmed that the image density was easily varied due to the above, but when the image was formed by the developing device according to the present invention, the developer was sufficiently stirred, and the influence on the image density variation was observed. Did not.

[0050]

As described above, the developing device according to the present invention has good developer stirring performance, so that the toner concentration can be made uniform and a sufficient toner charge amount can be provided. This developing device compensates for the reduced developer stirring function in a configuration in which the amount of the developer adsorbed and conveyed upstream of the layer forming portion on the developer carrying member is reduced to prevent the deterioration of the developer. Can be. Further, when an image is formed using a developer subjected to a low-resistance magnetizing process, a high stirring performance of the developer in the developing device is required, and if the toner concentration is not uniform, the image density is significantly uneven. Thus, it is difficult to use such a developer in the conventional developing device, but in the developing device according to the present invention, the developer is sufficiently stirred, and the toner concentration is made uniform in a short time. In addition, an image having a uniform density can be obtained stably with respect to environmental fluctuations using the carrier subjected to the low-resistance magnetizing treatment.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating a developing device according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a flow of a developer in the developing device shown in FIG.

FIG. 3 is a diagram showing changes in image density and toner density after toner is supplied to the developing device shown in FIG. 1;

FIG. 4 is an explanatory diagram showing a relationship between a screw auger area ratio and a toner concentration stabilization time in the developing device shown in FIG. 1;

FIG. 5 is a schematic configuration diagram showing a conventional developing device used for comparing effects with the developing device of FIG. 1;

6 is a schematic diagram showing a flow of a developer in the developing device shown in FIG.

7 is a diagram showing changes in image density and toner density after toner is supplied to the developing device shown in FIG. 5;

FIG. 8 is a schematic diagram illustrating a relationship between a stirring time of a developer in a developing device and a charge amount of a toner.

FIG. 9 is a schematic configuration diagram showing a developing device according to an embodiment of the present invention.

10 is a diagram illustrating changes in image density and toner density after toner is supplied to the developing device illustrated in FIG. 9;

FIG. 11 is a schematic configuration diagram showing a developing device used for comparing effects with the developing device of FIG. 9;

12 is a diagram showing changes in image density and toner density after toner is supplied to the developing device shown in FIG. 11;

FIG. 13 is a diagram illustrating a saturation region of a developing toner amount with respect to a contrast voltage.

FIG. 14 is a schematic diagram illustrating a state of a magnetic brush at a position where an image carrier and a developer carrier are opposed to each other.

15 is a diagram showing the results of measuring the image density and the toner density after replenishing the toner by using the carrier subjected to the low-resistance magnetizing process in the developing device shown in FIG. 9;

16 is a diagram illustrating a result of measuring an image density and a toner density after replenishing toner by using a carrier subjected to a low-resistance magnetizing process in the developing device illustrated in FIG. 11;

[Explanation of symbols]

1, 11, 21, 31 Developing device 2, 12, 22, 32 Electrostatic latent image carrier 3, 13, 23, 33 Developer carrier 4, 14, 24, 34 Developer transport member 5, 15, 25, 35 Magnet roll (magnetic field generating means) 6, 16, 26, 36 Layer thickness regulating member 7, 8, 17, 18, 27, 28 Screw auger 9, 19, 29, 39 Layer forming portion 10, 30 Partition member

Claims (3)

[Claims] 1. A two-component developer including a toner and a magnetic carrier, which is disposed so as to face an image carrier on which a latent image is formed due to a difference in electrostatic potential, and magnetically adsorbs on a peripheral surface of the developer. A developing device comprising: a developer carrier to be conveyed; and a housing having a developer accommodating chamber that covers the rear of the developer carrier at a position facing the image carrier and stores the two-component developer. In the developer accommodating chamber, there are two screw augers installed substantially horizontally and parallel to each other, these screw augers, while stirring the developer, in the respective axial directions and opposite to each other A developing device which transports the developer in the direction and mixes the developer transported by the two screw augers in the entire axial direction between the two screw augers. 2. The developing device according to claim 1, further comprising a layer thickness regulating member that regulates a layer thickness of the two-component developer carried on the developer carrier. Is a fixedly supported magnetic field generating means,
A developer transport member that moves around the outside thereof, wherein the magnetic field generating means magnetically adsorbs the two-component developer on the outer peripheral surface of the transport member and holds the two-component developer at a position where the layer thickness regulating member is provided. The amount of developer Mp (mg / cm ² ) adsorbed on the developer conveying member is regulated by the layer thickness regulating member, and the amount of developer Mos conveyed to the position facing the image carrier is determined. (Mg / cm ² ), which is set to be three times or less. 3. The developing device according to claim 1, wherein the magnetic carrier of the two-component developing device has a conductive core material and a surface layer containing a conductive agent, and has a resistivity of 10 ⁸ Ω · c.
m, wherein a magnetic particle having a particle size of m or less is used.