JP2000010386A - Developing device and image forming device - Google Patents

Abstract

(57) [Problem] To provide a developing device and an image forming apparatus that form a non-fogged image with a high developing ability by optimizing a charge amount of a toner by a method with less mechanical stress. SOLUTION: An electrode member 26 is provided in the vicinity of a developing sleeve downstream of a doctor blade 23 and upstream of a developing area with respect to a developer conveying direction by a developing sleeve 21 so as not to contact the developer carried on the developing sleeve. ,
By forming a magnetic field such that the magnetic flux density in the vertical direction of the developing sleeve is larger than the magnetic flux density in the horizontal direction in at least a part of the region where the electrode member and the developing sleeve face each other, A high and coarse magnetic brush is formed, and there is a space near the magnetic brush. Then, when a periodically changing electric field is formed between the electrode member and the developing sleeve, and the electric field is applied to the magnetic brush, the toner moves to separate and contact the carrier. At this time, since there is a space in the vicinity of the magnetic brush, the toner repeatedly moves efficiently, gradually increasing the charge amount, and obtaining an appropriate charge amount.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a facsimile, a printer, and the like, and a developing apparatus used for the same. More specifically, the present invention relates to a developing apparatus using a two-component developer composed of a toner and a magnetic carrier. And an image forming apparatus using the developing device.

[0002]

2. Description of the Related Art An image forming apparatus using a two-component developing apparatus is excellent in high-speed responsiveness, and can be used in a copier, a facsimile,
It has been put to practical use as many products such as printers. In a two-component developing device, a two-component developer composed of a toner and a magnetic carrier is carried on the surface of a developer carrier composed of a non-magnetic developing sleeve in which a magnet is disposed, and the developer carried by a developer regulating member is After regulating the amount, the sheet is transported to a developing area facing the image carrier on which the electrostatic latent image is formed.
In the developing area, a bias is applied to the developing sleeve to form an electric field between the image carrier and the developing sleeve, and the electric field causes the toner on the developing sleeve to selectively contact or non-contact on the image carrier. It is developed by attaching it. In recent years, a bias applied to the developing sleeve is a bias having a periodically changing waveform (hereinafter, referred to as an AC bias), so that a periodic electric field is formed between the developing sleeve and the image carrier. Many developing devices which have improved the developing ability and the image quality have been proposed and put into practical use. Further, recent studies have shown that increasing the peak-to-peak voltage of the AC bias can further improve developability and image quality.

A toner and a carrier as a two-component developer are triboelectrically charged when they come into contact with each other. Therefore, in the two-component developing device, the developer is agitated by a mechanical agitating means, so that the toner and the carrier are brought into contact with each other and charged. However, the toner charged in this way is
As shown in FIG. 9, since the developer has a distribution of the charge amount, the developer has a low charge amount of toner (hereinafter, referred to as a weakly charged toner).
Is included. The weakly charged toner easily causes a phenomenon that the toner adheres to a non-image portion of the image carrier (called fog or background stain). As a specific example, when the charge amount distribution of the toner is measured by a charge amount measuring device (for example, E-spart analyzer), as shown in FIG. Compared to
In the case of a developer such as B, which has a relatively large distribution near 0, much fog occurred. Since the weakly charged toner has a small electrostatic adhesion to the carrier, it easily floats in the developer.
Further, since the weakly charged toner is less constrained by the electrostatic latent image and the developing bias, the ratio of the weakly charged toner to the non-image portion is considered to increase. Such fogging due to the weakly charged toner is likely to occur when an AC bias is applied to the developing sleeve, and further remarkably occurs when the peak-to-peak voltage of the AC bias is increased. this is,
It is presumed that the AC bias instantaneously forms a strong electric field, so that floating toner is more likely to be generated.

In addition, since the weakly charged toner does not easily react to an electric field formed between the image carrier and the developing sleeve, the developing ability of the developer containing a large amount of the weakly charged toner is reduced. Also, the resolution of the formed image is poor.

In order to solve such a problem, the shape, number, operating conditions, and the like of the mechanical stirring means are changed to improve the stirring ability, thereby increasing the chance of contact between the toner and the carrier. It has been known. However,
Since the charging of the toner is performed only by the mechanical stirring means, the impact of the developer during the stirring increases, and the coating layer of the carrier is scraped. In addition, toner locally adheres to the carrier due to local temperature rise of the developer due to stirring. When the carrier is deteriorated due to such stress on the developer, the ability to charge the toner is reduced, which causes fog.

Further, the weakly charged toner is likely to be generated when new toner is supplied to the developing device. This is probably because the existing toner and the carrier are attached to each other, and the chance of contact between the newly supplied toner and the carrier is small. For this reason, in Japanese Patent Application Laid-Open No. 8-44177,
`` Having a housing provided with a developing opening and a toner supply port, providing a developer circulation transport path between the developing opening and the toner supply port in the housing, and at least facing the developing opening of the housing. A two-component developer comprising a toner and a carrier carried on the developer carrying member, wherein a developer carrying member to which a DC developing bias is applied is provided, and a developer stirring means is provided in a developer circulating conveyance path. In the developing device, a latent image on the latent image carrier is developed in the developing device, and an auxiliary electrode is provided so as to be opposed to the developer carrier in close proximity to the developer carrier. Along with applying an AC bias, a DC bias that is the same as the DC bias applied to the developer carrying member or a DC bias that causes the toner to be electrostatically attracted toward the auxiliary electrode is applied to the auxiliary electrode. It proposes a developing device ", characterized in that the the. In this developing device, by the action of an oscillating electric field formed between the developer carrier and the auxiliary electrode, an electric vibration is given to the developer passing between the developer carrier and the auxiliary electrode, and the existing developer is removed. The toner and the carrier are forcibly once separated from each other, and the replenished new toner is agitated and mixed. Then, the replenished toner is frictionally charged with the carrier, and is controlled to a predetermined charge amount.

However, since the developer is filled between the developer carrying member and the auxiliary electrode of the developing device, a motion for separating the toner and the carrier by electric vibration,
In addition, stirring and mixing of the new toner with the developer cannot be performed sufficiently. For this reason, it is insufficient to make all the weakly charged toners have an appropriate charge amount by electric vibration.

[0008] Further, the weakly charged toner is likely to occur frequently when the toner concentration in the developer is high and the chance of the toner contacting the carrier is small. For this reason, an image forming apparatus that controls the amount of toner supplied to the developing device, keeps the toner concentration of the developer below a specified range, and reduces the generation of weakly charged toner is widely known.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and has as its object to optimize the charge amount of a toner by a method with a small mechanical stress and to increase the developing ability. Another object of the present invention is to provide a developing device and an image forming apparatus for forming an image without fog.

In Japanese Patent Application Laid-Open No. Hei 6-266234, the toner on a two-component developer layer carried on a developing sleeve having a small diameter of 5 to 15 mm is caused to fly under an oscillating electric field so that the electrostatic force on the image carrier is reduced. In a developing device for attaching to a latent image,
A leveling member that regulates the position of the magnetic pole with respect to the developing region of the magnet included in the developer carrier and the magnitude of the magnetic field and that controls the layer thickness of the developer downstream of the magnetic pole upstream of the developing region is provided. A developing device has been proposed in which a DC bias is applied to the tip of the leveling regulating member. In this developing device, the developer on the developing sleeve is laid down on the developing sleeve by the leveling regulating member, and an alternating electric field is applied between the electrode at the tip of the leveling regulating member and the developing sleeve, It is intended to facilitate the generation of toner cloud and improve the developing ability, and there is no mention of making the toner charge amount appropriate. On the contrary, the generation of the toner cloud causes the problem that the weakly charged toner is liable to be scattered, and the toner often adheres irregularly to the image as noise.

[0011]

According to a first aspect of the present invention, there is provided an image carrier having a two-component developer comprising a toner and a magnetic carrier, and having an electrostatic latent image formed thereon. An image carrier that includes a developer carrier that is conveyed to an opposite developing area, and a developer regulating member that regulates the amount of developer carried on the developer carrier; In the developing device for developing the electrostatic latent image formed on the developer carrying member, the developer is carried on the developer carrying member near the developer carrying member downstream of the developer regulating member and upstream of the developing region with respect to the developer transport direction. An electrode that does not come into contact with the developer, and a magnetic field in which the magnetic flux density in the vertical direction to the developer carrier is greater than the magnetic flux density in the horizontal direction in at least a part of the region where the electrode and the developer carrier face each other. And the electrode and It is characterized in that it has configured to form a periodically varying electric field between the image-carrying member.

In the developing device according to the first aspect, a so-called magnetic field is formed in a region where the electrode and the developer carrier are opposed to each other. A highly rough magnetic brush is formed. Further, the electrode is disposed with a gap from the magnetic brush. Therefore, a space is formed near the magnetic brush on the developer carrier. Here, the toner in the magnetic brush has a relatively wide charge amount cloth, and includes a weakly charged toner. When a periodically changing electric field (hereinafter referred to as an oscillating electric field) formed between the electrode and the developer carrier acts on such a magnetic brush, the toner having the electric charge in the magnetic brush separates from the carrier, Repeat the motion of contact again. Since there is a space around the magnetic brush where the toner can freely move, the movement of the toner can be performed efficiently. The toner repeats separation and contact with the carrier, gradually increasing the charge amount, and obtaining an appropriate charge amount. Further, since the weakly charged toner in the magnetic brush also has a small charge, the motion of separating and contacting from the carrier by the oscillating electric field can be repeatedly performed, and an appropriate charge amount can be obtained. The toner having an appropriate amount of charge reacts sensitively to an electric field formed between the image carrier and the developer carrier in the developing area, so that the developing ability is improved. Further, since the weakly charged toner disappears, an image without fog can be formed. As described above, in the developing device of the present invention, the toner is charged by the action of the oscillating electric field without relying only on the mechanical stirring, so that the stress on the developer due to the mechanical stirring can be reduced. Further, the structure of the mechanical stirring means can be simplified, and the stress on the developing device due to driving can be reduced. In addition, there is an advantage that the limit of uniform chargeability by mechanical stirring can be covered.

According to a second aspect of the present invention, there is provided an image forming apparatus using the developing device of the first aspect and having a toner replenishing section for replenishing toner to the developing device. N is the mass ratio of the toner occupied in the developer, r is the mass average radius of the toner, ρ is the true specific gravity of the toner,
When the mass average radius of the carrier is R and the true specific gravity of the carrier is Ρ, (r / R) · (ρ / Ρ) · (1 / n−1) is a value of 0.25 or more and 1.0 or less. Thus, the amount of toner supplied from the toner supply unit to the developing device is controlled.

In the image forming apparatus according to the second aspect, since the developing device according to the first aspect is used, as described above, the toner moves efficiently by the oscillating electric field, and an appropriate charge amount can be obtained. Accordingly, it is possible to provide an image forming apparatus having a high developing ability and forming an image without fogging. In this image forming apparatus, the charge amount can be optimized even when the toner concentration is relatively high and the toner contains a weakly charged toner.
Because the toner is charged by contact with the carrier,
It is considered that the relationship between the total surface area of the toner particles and the total surface area of the carrier particles controls the charge amount of the toner. Their ratio is represented by the equation h = (r / R) · (ρ / Ρ) · (1 / n−1). In the experiment of the inventor, the value h of the equation is 0.2
It became clear that the charge amount of the toner can be controlled within a predetermined range within the range of 5 to 1.0. Therefore, the toner supply amount to the developing device is set in the above range, and a developer having a relatively high toner concentration is used. When a developer having a high toner concentration is used, the amount of toner supplied to the latent image carrier increases, and the developing ability can be improved. By applying this, the rotation speed of the developing sleeve can be made slower than before, or the dynamic range of the electrostatic latent image can be narrowed, and an image forming apparatus with less stress can be configured.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to an electrophotographic laser printer (hereinafter referred to as a printer) as an image forming apparatus will be described below. FIG. 1 is a system block diagram of the printer according to the present embodiment. The flow of image formation will be described with reference to FIG. Image information from the computer is input to the printer via the interface. After the image information is converted into a bitmap image, the image information is transferred to the LD driving unit, and the laser light L is turned on and off in pixel units. The laser beam L is applied to the image carrier of the toner image forming unit, and an electrostatic latent image is formed. Then, a toner image is formed in a toner image forming unit described later.

FIG. 2 is a schematic configuration diagram of a toner image forming unit of the printer. The toner image forming section supplies a toner around a drum-shaped organic photoconductor (OPC) 1 as a latent image carrier, a charging roller 2 as a charging device, an exposure device 3 for irradiating a laser beam L, and toner. A developing device 4 for converting the electrostatic latent image on the photoconductor 1 into a toner image, a transfer roller 5 as a transfer device for transferring the toner image on the surface of the photoconductor 1 onto the transfer paper P, and a surface of the photoconductor 1 And a cleaning device 6 for removing the residual toner from the cleaning device. Also, the transfer paper P
And a fixing device 8 for fixing the toner image transferred onto the transfer paper P.

FIG. 3 is a schematic structural view of the developing device 4. The developing device includes a developing sleeve 21 as a developer carrying member for carrying a two-component developer including a toner and a magnetic carrier, and a fixed magnet 22 included in the developing sleeve 21.
And a doctor blade 23 as a developer amount regulating member for regulating the amount of the developer on the developing sleeve 21, a developer storing section 24 for storing the developer, and a developer in the developer storing section 24, And two stirring members 25 that move while stirring in the directions. The developing sleeve 21 is a cylindrical member made of a non-magnetic conductive member, and a developing bias is applied from a power source 27.
Further, a magnetic field is formed in the developing sleeve 21 facing the photoreceptor 1 such that the magnetic flux density in the vertical direction to the developing sleeve 21 is larger than the magnetic flux density in the horizontal direction in at least a part of the facing area. Magnetic poles are provided.

Next, the image forming operation of the copying machine will be described. In FIG. 2, the photosensitive member 1 is uniformly charged by the charge from the charging roller 2 while rotating in the direction of the arrow a, and then is irradiated with the laser beam L from the exposure device 3 to form an electrostatic latent image. This electrostatic latent image is developed by the developing device 4 to form a toner image as a visible image. The toner image developed by the developing device 4 is supplied to the photosensitive member 1 by a paper feeding device 7.
The image is transferred by the transfer roller 5 onto the transfer sheet P conveyed to the front surface. The transfer paper P on which the toner image has been transferred is the photosensitive member 1
The sheet is separated from the sheet, and is discharged outside the apparatus after the fixing process is performed by the fixing device 8. On the other hand, the untransferred toner is collected and removed from the photoconductor 1 after the transfer by the cleaning device 6. Here, the surface potential of the photoreceptor 1 after exposure is -100
v, the non-exposed portion is about -800 v, and development (reversal development) is performed so that toner adheres to the light irradiation portion.

Next, the developing operation of the developing device 4 will be described. In FIG. 3, the developer is carried in a brush shape (hereinafter, referred to as a magnetic brush) on the surface of the developing sleeve 21 by a magnetic field formed by an internal fixed magnet 22. The magnetic brush on the developing sleeve 21 is
After the amount is regulated by 3, the developing sleeve 21 is conveyed to the developing area facing the photoreceptor 1 by rotating the developing sleeve 21 in the direction of the arrow b.

In the developing device 4, an electrode member 26 is provided on the downstream side of the doctor blade 23 in the rotation direction of the developing sleeve 21 and on the upstream side of the developing area. The electrode member 26 is made of a conductive material such as a metal, is a part of a cylinder having the same axis as the developing sleeve 21, and faces the developing sleeve 21 with a certain area. The electrode member 26 has a certain distance from the developing sleeve 21 and is arranged with a gap so as not to contact the magnetic brush on the developing sleeve 21. Inside the developing sleeve 21 facing the electrode member 26, the developing sleeve 21
Are provided with magnetic poles for generating a magnetic field such that the magnetic flux density in the vertical direction is larger than the magnetic flux density in the horizontal direction. Further, a power supply 28 for applying a constant or periodically changing voltage to the electrode member 26 is connected to generate an oscillating electric field between the electrode member 26 and the developing sleeve 21.

By the magnetic field in the region facing the electrode member 26, a so-called high and coarse magnetic brush is formed, which is substantially perpendicular to the surface of the developing sleeve and has an interval between the brushes. Further, the electrode member 26 is arranged with a gap from the magnetic brush. Therefore, a space is formed around the magnetic brush. Here, the toner in the magnetic brush is charged, but the distribution of the charge amount is relatively wide,
It also contains weakly charged toner. When an oscillating electric field formed between the electrode member 26 and the developing sleeve 21 acts on such a magnetic brush, the magnetic brush receives a force substantially perpendicular to the surface of the developing sleeve, and the charged toner in the magnetic brush is discharged from the carrier. The movement of separating and contacting the carrier again is repeatedly performed. Here, since there is a space around the magnetic brush where the toner can freely move, the movement of the toner by the oscillating electric field can be efficiently performed. The toner repeats separation and contact with the carrier, gradually increasing the charge amount, and obtaining an appropriate charge amount. Further, since the weakly charged toner in the magnetic brush also has a small charge, the motion of separating and contacting from the carrier by the oscillating electric field can be repeated, and an appropriate charge amount can be obtained.

In this process, when the developer containing properly charged toner is transported to the developing area, the developing sleeve 2
The magnetic brush is formed so that the magnetic brush contacts the surface of the photoconductor 1 facing the surface of the photoreceptor 1 by a magnetic pole that forms a magnetic field such that the magnetic flux density in the vertical direction inside the photoconductor 1 is larger than the magnetic flux density in the horizontal direction. Then, the toner moves onto the photoconductor 1 by an electric field formed between the development sleeve 21 and the electrostatic latent image on the photoconductor 1 by the developing bias applied to the developing sleeve 21 from the power supply 27. Here, the properly charged toner is
Since it reacts sensitively to the electric field, the developing ability is enhanced. Furthermore, since there is no weakly charged toner, adhesion to non-image areas is reduced, and the resolution is improved. In addition, the magnetic field formed in the developing area prevents the carrier from adhering to the photoreceptor 1 and scattering of the carrier. When the toner is consumed by the development, a corresponding amount of the toner is supplied to the developer storage unit 24 from a toner supply unit (not shown). The supplied toner is mixed with the developer in the developer storage section 24 by the stirring member 25. When the developer agitated and transported by the two agitating members reaches the vicinity of the developing sleeve 21, it is pumped up to the developing sleeve 21 by the action of the internal magnet 22.

Here, various types of fixed magnets 22 installed in the developing sleeve 21 are manufactured, the magnetic flux density on the surface of the developing sleeve 21 opposed to the electrode member 26 is measured, and the developing bias applied to the developing sleeve 21 is adjusted. An experiment was performed under the condition that the bias applied to the electrode member 26 was changed, and the charge amount of the toner conveyed to the developing area and the image quality were examined.

The developer has a maximum magnetization of 60 emu / g and a particle size of 5
A carrier whose core material is 0 μm ferrite particles and whose surface is coated with a silicone resin;
A mixture of a toner mainly composed of a thermoplastic resin colored with carbon black at 5 μm at a toner concentration of 5% by weight (carrier: toner at a mass ratio of 95: 5) was used.

The experimental conditions are shown in Tables 1, 2, 3 and 4.
Shown in

[Table 1]

[Table 2]

[Table 3]

[Table 4]

First, in Experiment No. 1 of Table 1, 1, No. 2, N
o. 3 will be described. Experiment No. 1, No. 2, N
o. In FIG. 3, the fixed magnet 22 in the developing sleeve 21 in a region opposed to the electrode member 26 is provided perpendicular to the surface of the developing sleeve 21, and in a portion where the magnetic flux density of the vertical component shows the maximum value, The magnetic flux density becomes zero. Under this condition, 0.8 m perpendicular to the surface of the developing sleeve 21 opposed to the electrode member 26 with a 1.0 mm gap.
Magnetic brushes having a height of about m to 0.9 mm are formed at intervals. As described above, in the region facing the electrode member 26, the magnetic brush is not in contact with the electrode member 26, and
It is high and rough, and has a space around the magnetic brush where toner can move.

By applying an AC bias to the developing sleeve 21 and a DC bias to the electrode member 26, an oscillating electric field is formed between the two. The magnetic brush receives the action of the oscillating electric field, and the toner separates from the carrier and vibrates. The toner repeats separation and contact with the carrier, gradually increasing the charge amount, and obtaining an appropriate charge amount.
Even a weakly charged toner, which is almost uncharged, has a small charge, so that it starts to move under the action of an oscillating electric field and gradually obtains an appropriate charge amount. The movement of the toner is performed efficiently since a sufficient space for the movement of the toner is formed around the magnetic brush.

Further, such a movement of the toner is most effective when the carrier does not move due to the oscillating electric field. Under the condition that the carrier moves by the oscillating electric field, the toner and the carrier move together without separating, and the charge amount of the toner hardly increases. In order for the toner and the carrier to separate and only the toner to vibrate, it is necessary that the frequency and the time-varying speed as well as the magnitude of the oscillating electric field are equal to or more than predetermined values.

FIG. 4 shows the waveform of the developing bias applied to the developing sleeve 21. The horizontal axis represents time, and the vertical axis represents a voltage value with the direction in which the toner receives a force toward the photoconductor 1 taken upward. In FIG. 4, the voltage value when the toner receives the maximum force toward the photoconductor 1 is V1, the voltage value when the toner receives the maximum force toward the developing sleeve 21 is V0, and the time when V1 lasts is t1. , And the period is t2. The integrated average Va of the voltage value is set to about -500 to -700 V, similarly to a normal DC bias. Where V
a = V0 + (V1-V0) t1 / t2. Where t1 /
t2 is called a duty. AC bias frequency 5kHz
When z was set, no vibration of the carrier was observed. Also,
It is desirable that the time t1 shown in FIG. 4 be 100 μsec or less. Experiment No. 1, No. 2, No. Under any of the three bias conditions, the movement of the toner was efficiently performed, and the toner had an appropriate charge amount.

Further, when such a movement of the toner is performed, the toner may collide not only with the carrier but also with the electrode member 26. For this reason, it is also effective to perform contact charging by coating the surface of the electrode member 26 with a material substantially equivalent to the coating material on the carrier surface.

The developer containing the toner having the proper charge amount by the above movement reaches the developing area by rotating the developing sleeve 21 in the direction of arrow b. A properly charged toner sensitively reacts to an electric field formed by an electrostatic latent image and a developing bias, so that developing ability is enhanced. In addition, since there is no weakly charged toner, adhesion to non-image areas is reduced, and the resolving power is improved.

Further, under these conditions, the waveform of the AC bias is an asymmetric rectangular wave as shown in FIG. 4, and the developing ability and the resolving power are further improved. This is because a strong electric field acts on the toner repeatedly for a short time, so that the movement of the toner becomes active, and further, a force for moving the carrier charged to the opposite polarity to the toner to the photoconductor 1 hardly acts. it is conceivable that.

Next, the experiment Nos. 4, no. 5, N
o. 6 will be described. Experiment No. 4, no. 5, N
o. In 6, the magnet installed in the developing sleeve 21 is:
The experiment No. Same as 1. Experiment No. Similarly to 1, a space is formed around the magnetic brush on the developing sleeve 21 facing the electrode member 26 so that the toner can move.

By applying a DC bias to the developing sleeve 21 and an AC bias to the electrode member 26, an oscillating electric field is formed between the two. When an oscillating electric field acts on the magnetic brush, the toner repeats separation and contact with the carrier, gradually increasing the charge amount, and obtaining an appropriate charge amount. If the waveform of the AC bias applied to the electrode member 26 is an asymmetric rectangular wave as shown in FIG.
o. 4, no. 5, no. 6 Under any of the conditions,
The movement of the toner was performed efficiently, and the toner came to have an appropriate charge amount. Then, the developer containing the toner having an appropriate charge amount reaches the developing area by the rotation of the developing sleeve 21 and supplies the toner onto the photoconductor 1 according to the electrostatic latent image. Here, the toner having an appropriate amount of charge reacts sensitively to the electrostatic latent image and the electric field formed by the DC bias applied to the developing sleeve 21, so that the developing ability is enhanced. Furthermore, since there is no weakly charged toner, adhesion to non-image areas is reduced, and the resolution is improved.

Next, in Experiment 3 of Table 3, 7, no. 8 will be described. Experiment No. 7, no. In No. 8, the magnet 22 provided in the developing sleeve 21 was replaced to change the vertical component of the magnetic flux density. Even under this condition, a space where the toner can move is formed around the magnetic brush on the developing sleeve 21 facing the electrode member 26.

By applying a DC bias to the developing sleeve 21 and an AC bias to the electrode member 26, an oscillating electric field is formed between the two. When an oscillating electric field acts on the magnetic brush, the toner repeats separation and contact with the carrier, gradually increasing the charge amount, and obtaining an appropriate charge amount. Experiment No. 7, no. Under any of the eight conditions, the movement of the toner was efficiently performed, and the toner had an appropriate charge amount. For this reason, the developing capacity was increased in the developing area, the adhesion to the background portion was reduced, and the resolution was improved.

Next, in Experiment 3 of Table 3, 9 will be described. Experiment No. In No. 9, the magnet is installed so as to be inclined so that the direction of the vector when the magnetic flux density becomes maximum is not perpendicular to the sleeve surface. Even under this condition, a space where the toner can move around the magnetic brush on the developing sleeve 21 facing the electrode member 26 is formed.
o. 7, no. The same results as in Example 8 were obtained.

Next, the experiment Nos. 10, No. 1
1, No. 12 will be described. Experiment No. 10, N
o. 11, No. The magnet installed in the developing sleeve 21 of the experiment No. 1, No. Same as 2. The distance between the electrode and the developing sleeve and the distance between the photoconductor and the developing sleeve (developing gap) are changed. Experiment N
o. 10, No. In Experiment No. 11, The distance between the electrode and the developing sleeve is narrower than that of No. 1. Further, the gap between the doctor blade 23 and the developing sleeve 21 is adjusted to form a magnetic brush having a height of 0.8 mm or less perpendicular to the surface of the developing sleeve 21 facing the electrode member 26 with a gap of 0.8 mm. . In a region facing the electrode member 26, the magnetic brush is not in contact with the electrode member 26 and is in a high and rough state, and a space around the magnetic brush where toner can move is formed.

When an AC bias was applied to the developing sleeve 21 and a DC bias was applied to the electrode member 26 to apply an oscillating electric field to the magnetic brush. 1
The same result was obtained. As a comparative example, the gap between the doctor blade 23 and the developing sleeve 21 was adjusted, and a magnetic brush was formed on the surface of the developing sleeve 21 so as to be in contact with the electrode member 26. When the same bias was applied and an oscillating electric field was applied to the magnetic brush, toner adhered to the electrode member 26. Further, the toner adheres to the electrode member 26 by the long-term operation, and the developing sleeve 21
, The developer conveyed was uneven, and an uneven image was formed.

Experiment No. In Experiment 12, 2
The distance between the electrode and the developing sleeve is wider than that of the first embodiment. In a region opposed to the electrode member 26, the magnetic brush is not in contact with the electrode member 26, and is in a high and rough state.
A space around which the toner can move is formed around the magnetic brush. Then, when an oscillating electric field was applied to the magnetic brush, the above experiment No. The same result as in Example 2 was obtained.

As described above, in the above experimental example, only an example in which an asymmetric rectangular wave shown in FIG. 4 is used as the AC bias waveform is shown. The amount was adjusted, developing ability was improved, adhesion to the background was reduced, and resolution was improved.

Further, in the above-described embodiment, the example of the contact development in which the magnetic brush on the developing sleeve 21 supplies the toner while contacting the photosensitive member 1 in the development area has been described. Is seen.

Next, a modification of the shape of the electrode member 26 of the developing device 4 will be described with reference to FIG. This developing device 4
In the embodiment, the electrode member 26 is arranged so that the gap between the electrode member 26 and the developing sleeve 21 is increased on the downstream side in the developer conveyance direction due to the rotation of the developing sleeve 21. The electrode member 26 may be flat or curved. In the developing device 4, the amount of the developer pumped up from the developer storing section 24 by the internal magnet 22 of the developing sleeve 21 is regulated by the doctor blade 23, and then reaches the portion facing the electrode member 26. Inside the developing sleeve 21 facing the electrode member 26, a magnetic pole for forming a magnetic field such that the magnetic flux density in the vertical direction of the developing sleeve 21 is larger than the magnetic flux density in the horizontal direction is provided. This magnetic field forms a high and coarse magnetic brush on the sleeve surface. (Hereinafter, margin)

The toner in the magnetic brush receives the action of an oscillating electric field formed between the developing sleeve 21 and the electrode member 26, and starts to separate and contact the carrier. At this time, the electric field is strong on the upstream side in the developer conveyance direction in the region where the electrode member 26 faces, and the electric field becomes weaker on the downstream side. The electric field formed between the developing sleeve 21 and the electrode member 26 is curved. FIG. 6 shows an electric field when the toner (negatively charged) receives a force toward the electrode member 26. The movement of the toner subjected to such an electric field will be described with reference to FIGS. FIG. 7A shows the electric field E when the positively charged toner t receives a force toward the developing sleeve 21.
E is decomposed into a component E ₁ parallel to the vertical component E ₂ to the developing sleeve surface. Since the locus of E is convex on the downstream side, E ₁ is always directed to the downstream side. For this reason, the toner t starting near the point A of the electrode member 26 tends to move downstream from the vicinity of the point B of the developing sleeve 21. Further, as show in FIG. 7 (b), when the positively charged toner t is subjected to a side force toward the electrode member 26, the electric field E'the component parallel to the developing sleeve surface _E'1 perpendicular component E' is decomposed into _two and, _E'1 always faces the downstream side. For this reason, the toner t starting from the vicinity of the developing sleeve 21 tends to move to the downstream side near the electrode member 26. Although the positively charged toner has been described here for convenience, the same result can be obtained with a negatively charged toner if E is considered in the opposite direction. As described above, a force for moving the toner placed downstream in the curved electric field acts. When the charge amount of the toner is small, the moving speed is low, but when the charge amount is large, the moving speed becomes large. That is, in a region sandwiched between the developing sleeve 21 and the electrode member 26, the toner having a small charge amount takes a long time to pass, the number of times of contact with the carrier increases, and the charge amount tends to increase. Further, since the toner having a predetermined charge amount passes in a short time,
The increase in charge amount is small. As a result, the amount of weakly charged toner decreases, and the charge amounts of the individual toners become substantially the same. Therefore, the variability of the response to the electrostatic latent image is reduced, and the sharpness and the resolving power are increased.

Next, toner replenishment for replenishing consumed toner in the developing device 4 of the printer of the present embodiment will be described. In a conventional developing device, when a large amount of toner is supplied into the developing device 4, the amount of weakly charged toner increases, which causes a deterioration in image quality such as fogging. For this reason, the toner supply amount has been controlled so that the developer toner concentration of the developing device falls within a certain range. However, in the developing device of the present invention, even when the toner concentration is in a relatively wide range, the toner can have an appropriate charge amount as described above. Since the toner is charged by contact with the carrier, it is considered that the relationship between the total surface area of the toner particles and the total surface area of the carrier particles controls the charge amount of the toner. Their ratio is h
= (R / R) · (ρ / Ρ) · (1 / n-1). Here, n is the toner concentration of the developer in the developing device (mass ratio occupied by the toner in the developer), r is the mass average radius of the toner, ρ is the true specific gravity of the toner, R is the mass average radius of the carrier, and Ρ is the carrier Is the true specific gravity of According to an experiment conducted by the inventor, it has become clear that the charge amount of the toner can be controlled to a predetermined range when the value h of the above expression is in the range of 0.25 to 1.0. When the value of h is less than 0.25, the amount of toner becomes excessive, and the amount of toner that cannot be charged in contact with the carrier rapidly increases. For this reason, fogging and toner scattering increase, image quality remarkably deteriorates, and operation of the image forming apparatus becomes difficult. On the other hand, when the value of h exceeds 1.0, the amount of toner is insufficient, and the charge amount of the toner obtained by contact with the carrier is too large. The small amount of toner supply to the development area is also overlapped, and a necessary development amount cannot be obtained. For this reason, an image in which the solid density is insufficient and the line portion and the halftone portion cannot be reproduced.

In the toner concentration control, the toner concentration of the developer in the developing device is detected, and the toner is supplied from a toner supply unit (not shown) based on the value of h calculated from the toner concentration. The flow of this toner density control is shown in the flowchart of FIG. The toner density detecting method is a conventionally known method, for example, a method of forming an image on the photoreceptor 1 and reading the reflection density of the image, or a method of estimating the toner density by measuring the magnetic permeability in the developer. Is used. The value of h in the above formula is calculated from the detected toner density value, and it is determined whether the value is within a predetermined range (0.25 or more and 1.0 or less). The mode is a mode in which the toner is replenished and the toner replenishment is stopped when the amount is too small, and the toner is discharged as necessary. In this mode, a solid image is formed and toner is consumed. The solid image may be directly cleaned without being transferred to the transfer material, or may be transferred and the transfer material may be discharged as it is.

As described above, in the printer using the developing device 4 of the present invention, the allowable value of the toner supply amount is greatly expanded,
The developing ability can be improved by using a developer having a high toner concentration. By applying this, the rotation speed of the developing sleeve can be made lower than before. Further, since the charging of the developer does not depend only on the mechanical stirring means, the stirring and conveying path can be shortened. Therefore, a low-stress developing device can be configured. Further, by improving the developing ability, the dynamic range of the electrostatic latent image can be narrowed, and a low-stress printer can be configured.

[0048]

According to the first aspect of the present invention, it is possible to provide a developing device which optimizes the charge amount of toner by a method with less mechanical stress, has a high developing ability, and forms an image without fog. There is an excellent effect.

Further, according to the second aspect of the present invention, it is possible to provide an image forming apparatus which optimizes the charge amount of toner by a method with less mechanical stress, has a high developing ability, and forms an image without fog. There is an excellent effect that it can be done. Further, since a developer having a high toner concentration can be used, there is an excellent effect that the developing ability can be improved and an image forming apparatus with less stress can be provided.

[Brief description of the drawings]

FIG. 1 is a system block diagram of a printer according to an embodiment.

FIG. 2 is a schematic configuration diagram of a toner image forming unit of the printer according to the embodiment.

FIG. 3 is a schematic configuration diagram of a developing device used in the printer according to the embodiment.

FIG. 4 is an explanatory diagram of a waveform of an AC bias applied to a developing sleeve of the developing device.

FIG. 5 is a schematic configuration diagram of another developing device used in the printer according to the embodiment.

FIG. 6 is an explanatory diagram of an electric field formed between a developing sleeve and an electrode member.

FIG. 7A is an explanatory diagram when a toner between a developing sleeve and an electrode member receives a force toward a developing sleeve. (B) Explanatory drawing when the toner between the developing sleeve and the electrode member receives a force toward the electrode member.

FIG. 8 is a flowchart relating to toner density control of the printer according to the embodiment.

FIG. 9 is an explanatory diagram of a charge amount distribution of a toner of a developer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Charging roller 3 Exposure device 4 Developing device 5 Transfer roller 6 Cleaning device 7 Fixing device 21 Developing sleeve 22 Fixed magnet 23 Doctor blade 24 Developer storing part 25 Stirring member 26 Electrode member 27 Power supply 28 Power supply 50 Computer 51 Interface 52 LD driver

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoshiko Ishii 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (72) Inventor Hirokatsu Suzuki 1-3-6 Nakamagome, Ota-ku, Tokyo F term in Ricoh Co., Ltd. (reference) 2H031 AC08 AC20 AC30 AD01 BA05 BA09 BB01 BC07 CA07 CA10 CA13 CA15 DA05 2H073 AA03 BA02 BA03 BA06 BA13 BA15 BA45 CA03 2H077 AD06 AD13 AD18 AD36 AE06 DA10 DA42 DB02 EA03

Claims (2)

[Claims] A developer carrying member for carrying a two-component developer comprising a toner and a magnetic carrier, and transporting the developer to a developing area opposed to an image carrier on which an electrostatic latent image is formed; A developer regulating member that regulates the amount of developer carried, wherein the developer is transported in a developing device that applies a bias to the developer carrier to develop an electrostatic latent image formed on the image carrier. Provided in the vicinity of the developer carrier downstream of the developer regulating member with respect to the direction and upstream of the development region, an electrode that does not contact the developer carried on the developer carrier,
At least a part of the region where the electrode and the developer carrier face each other forms a magnetic field such that the magnetic flux density in the vertical direction is larger than the magnetic flux density in the horizontal direction in the developer carrier, and the electrode and the developer carrier are formed. A developing device characterized by forming a periodically changing electric field between itself and a body. 2. An image forming apparatus using the developing device according to claim 1 and having a toner replenishing section for replenishing toner to the developing device, wherein the toner concentration of the developer in the developing device (toner occupies the developer) (R / R) · (ρ / Ρ) where n is the mass average radius of the toner, r is the mass average radius of the toner, ρ is the true specific gravity of the toner, R is the mass average radius of the carrier, and Ρ is the true specific gravity of the carrier.・
An image forming apparatus, wherein an amount of toner replenishment from a toner replenishment unit to a developing device is controlled such that (1 / n-1) is a value of 0.25 or more and 1.0 or less.