JP2003215925A - Developing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device for forming a stable image for a long term by preventing the accumulation of toner at the end part of the devel oping device (the end of a developer carrier), the disarrangement of a toner layer, etc., in the case of the occurrence of reverse polarity toner and endurance and also stress by toner with respect to a surface processing at the end of the developer carrier. <P>SOLUTION: When the axial directional length of the developer carrier is L and the magnetic flux densities of respective magnetic poles in a fixed magnet assembly are T<SB>1</SB>, T<SB>2</SB>, T<SB>3</SB>and T<SB>4</SB>(mT), a magnetic force T<SB>4</SB>(mT) in an area which is 4/L from both axial directional ends of N2-pole (pole 4) is indicated as follows. T<SB>4</SB><1/2(T<SB>1</SB>, T<SB>3</SB>, T<SB>2</SB>), (T<SB>1</SB>, T<SB>3</SB>, T<SB>2</SB>are nearly equal to T<SB>4</SB>in a center part). <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device in an image forming apparatus such as a copying machine, a printer, a facsimile, and a composite machine thereof using an electrophotographic system, and more particularly to a toner which is apt to occur inside a magnetic one-component jumping developing device. The present invention relates to a developing device that prevents accumulation of toner and prevents image defects.

[0002]

2. Description of the Related Art Magnetic one-component jumping developing device 20
As shown in FIG. 2, an example is a fixed magnet assembly 22 that has a plurality of magnetic poles inside, and is opposed to the electrostatic latent image carrier (photosensitive drum) 21 in a non-contact manner, and a rotating developing sleeve 23. A developer (toner) carrying member 24, a stirring rod 26 for stirring the developer in the developer container 25, and a magnetic field provided at a position facing the fixed magnet assembly 22 in the developer carrying member 24. To form a thin layer of toner on the developing sleeve 23 by controlling the toner layer thickness on the developing sleeve 23, a toner container 28 for replenishing the toner, and a toner in the developer container 25. A toner sensor 2 for detecting that the toner amount is low and performing control for replenishing toner from the toner container 28.
9 and so on. Then, the toner in the developer container 25 is agitated by a stirring rod 26 and charged, and the magnetic blade 27
A thin layer of toner is formed on the developing sleeve 23 while the layer thickness is regulated by.

In forming an image, first, the photoconductor drum 21 is charged by the charger 30 and the electrostatic latent image is formed by the exposure unit 31. Then, an alternating electric field is applied between the photosensitive drum 21 and the developer carrying member 24, and the developing sleeve 2
By applying an electric field of the photoconductor drum 21 to the toner on 3, the gap between the two is caused to fly, and the latent image on the photoconductor drum 21 is developed. Then, the developed image is transferred by the transfer roller 32 to a recording medium sent between the transfer roller 32 and the photosensitive drum 21, and then fixed and discharged by a fixing device (not shown). The remaining toner is scraped off by the cleaner 33 to prepare for the next image formation.

The magnitude of the force that causes the toner in the magnetic one-component jumping developing device 20 to fly from the developer carrier 24 to the photosensitive drum 21 depends on the magnitude of the electric field in which the toner exists and the charge amount of the toner itself. And the charge amount of the toner itself is determined by the electric charge existing on the surface of the toner. The toner itself has a considerably high resistance, and the smaller the particle size, the larger the electrostatic capacity, which is the ability to retain the electric charge of the toner itself, and the greater the ability to retain the electric charge on its surface. In addition, the smaller the particle size of the toner, the smaller its mass, and therefore the more easily it flies when an alternating electric field is applied.

Therefore, generally, in a developing device using a magnetic one-component toner, the toner having a small particle size is consumed by repeating image formation, and the toner having a large particle size tends to remain in the developing device 20. This is referred to as selective development. The residual toner having a large particle size as described above has a small specific charge amount and is difficult to develop, which causes a decrease in image density and fog. In particular, the toner container 2 is provided as a means for replenishing toner for extending the life of the process unit.
In the developing method in which the toner replenishment control is performed by using the No. 8 and the toner sensor 29 in the developing device, it is often observed when the number of printed sheets increases.

In order to deal with such a problem, for example, in Japanese Patent Laid-Open No. 10-333437, a magnet having the same polarity as the magnetic pole of the fixed magnet assembly facing the magnetic blade is attached to the magnetic blade so as to face the magnetic blade. A repulsive magnetic field is formed between the magnet assembly and the fixed magnet assembly to properly share the toner and promote triboelectrification to accelerate the electrification of the toner and stabilize the specific charge amount of the toner for a long time. A developing device adapted to obtain various images is shown. By doing so, for example, the transition of the image density and the transition of the specific charge amount of the toner between the developing device A in which the magnet is attached to the magnetic blade and the developing device B in which the magnet is not attached are shown in FIG. Graph 1 Developer A,
B durability comparison, and (b) Graph 2 developing device A of FIG.
As can be seen from the comparison of the toner charge amount transition of B, the image stability can be increased by mounting the magnet.

[0007]

However, although the image stability can be increased by mounting the magnet on the magnetic blade 27 in this manner, the toner inside the developing device 20 is the toner generated by the stirring bar 26 or the like. Stirring does not reach the end of the developer container 25, and retention easily occurs at both end sides of the developer carrying member 24, so that contact between toners increases and toner of opposite polarity is generated. The surface treatment of the toner at both ends of the carrier 24 is also subjected to a load (stress), and the degree of deterioration is faster than that at the center.

Further, as the fixed magnet assembly 22 inside the developer carrying member 24, N1 located near the photosensitive drum is used.
In the case of using four poles, S2 pole facing the magnetic blade and S1 pole and N2 pole for carrying toner to the developing sleeve,
Due to the presence of the two poles, the accumulation of toner is more likely to occur, and in addition to the occurrence of the opposite polarity toner, the decrease in the specific charge amount due to the peeling of the external additive of the toner, the decrease in the density, the fog, etc. In some cases, a toner adhesion phenomenon (hereinafter referred to as a toner layer disorder) or the like occurred in No. 23, resulting in an image defect.

Therefore, in the present invention, accumulation of toner at the end of the developing device (end of the developer carrying member) is prevented,
To provide a developing device capable of forming a stable image for a long period of time by preventing generation of reverse polarity toner, disturbance of a toner layer at the time of endurance, etc., and prevention of stress due to toner on surface treatment at an end portion of a developer carrier. That is the challenge.

[0010]

Therefore, in the present invention, as described in claim 1, a magnet assembly having a plurality of magnetic poles is provided so as to face a photoconductor drum for forming an image by an electrophotographic method. And a developer carrier configured such that the magnet assembly, or the developing sleeve, or both the magnet assembly and the developing sleeve rotate, and the magnet assembly, which is provided on the upstream side of the developing position of the developing sleeve. In a developing device having a magnetic blade attached with a magnet to regulate the layer thickness of a magnetic developer layer formed on the developing sleeve, when the total length in the axial direction of the developer carrying member is L, development is performed. The magnetic flux density in the region of L / 4 or less from both axial ends of the agent carrier is smaller than the magnetic flux density in the central part.

With respect to the magnetic flux densities of the end portion and the central portion of the developer carrying member, as described in claim 2, the magnetic poles close to the photosensitive drum in the fixed magnet assembly are poles 1,
When the magnetic poles facing the magnetic blade are poles 2, the magnetic poles for carrying the toner to the developer carrier are poles 3 and 4, respectively, and the magnetic flux densities are T ₁ , T ₂ , T ₃ and T ₄ , respectively, The magnetic flux density at the central portion of the magnetic pole in the axial direction is made substantially the same,
Magnetic force T _{4 in} a region of L / 4 or less from both axial end portions in
Is preferably configured so that T ₄ <1/2 (T ₁ , T ₂ , T ₃ ).

By doing so, the toner is not accumulated at the end portion of the developer carrying member, the generation of reverse polarity toner and the disturbance of the toner layer at the time of endurance are prevented, and the end portion of the developer carrying member is prevented. It is possible to provide a developing device capable of forming a stable image over a long period of time by preventing the stress caused by the toner due to the surface treatment in the above.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be exemplarily described in detail below with reference to the drawings. However, the dimensions, materials, shapes, relative positions, and the like of the constituent parts described in this embodiment are not intended to limit the scope of the present invention thereto, unless otherwise specified, and are merely It is only an example.

FIG. 1 is a schematic sectional view of an apparatus showing an embodiment of the present invention. In the figure, 1 is a developing device according to the present invention, 2 is a developing sleeve 3 having a surface that has been blasted with regular or irregular particles, and rotating.
, The magnetic pole close to the photosensitive drum 12 is the N1 pole (pole 1), the magnetic pole facing the magnetic blade 5 is the S2 pole (pole 2), and the magnetic pole for conveying the toner to the developing sleeve 3 is the S1 pole (pole 3). , N2 poles (poles 4) and the magnetic flux densities of T ₁ , T ₂ , T ₃ , and T ₄ [mT], respectively, the developer carrier 5 containing the fixed magnet assembly 4 having a plurality of magnetic poles is A magnetic blade mounted on the upstream side of the developing position of the developing sleeve 3 with a magnet 6 to regulate the thickness of the magnetic one-component toner layer formed on the developing sleeve 3, 7 is a developer container, and 8 is a developing container. A stirring rod for stirring the toner in the developer container 7, 9 is a toner container for replenishing the toner, and 10 is a control for detecting that the toner in the developer container 7 is low and replenishing the toner from the toner container 9. To Toner sensor for cause I, 12
Is a photosensitive drum (electrostatic latent image carrier), 13 is a charger, 1
Reference numeral 4 is an exposure unit, 15 is a transfer roller, and 16 is a cleaner for cleaning the residual toner on the photosensitive drum 12. Although the developer carrying member 2 is described as being composed of the developing sleeve 3 and the fixed magnet assembly 4, in addition to this, the sleeve 3 is fixed and the magnet assembly 4 is rotated. 3 and the magnet assembly 4 are both rotated, and the present invention can be used in any configuration.

In the present invention, such a developing device 1
Let L be the total axial length of the developer carrier 2 in FIG.
In the range of L / 4 or less from both axial ends of the developer carrying member 2,
Make the magnetic flux density in the area smaller than that in the central area.
Magnet assembly included in developer carrier 2
The magnetic flux density of the body 4 is laid out. Ie
More specifically, two toners that convey the toner to the developing sleeve 3
N2 pole of S1 pole (pole 3) and N2 pole (pole 4) of
For (pole 4), L / 4 or less from both ends of the developer carrying member
Density T in the region of_Four[MT] T_Four<1/2 (T₁, T_Two, T_Three) In addition, the magnetic flux density of other magnetic poles is
Identical, ie T_Four  ≈ T₁, T_Two, T_Three It is what

By doing so, the toner, which has conventionally been trapped and stayed at both ends of the N2 pole (pole 4) of the fixed magnet assembly 4, in the present invention, at both ends of the N2 pole (pole 4). Since the magnetic flux density is small, the restraining force is weakened to prevent stagnation, and the magnetic blade 5 made of a magnetic material is provided on the upstream side in the rotation direction of the developer carrying member 2,
Since the magnet 6 having the same polarity as the magnetic pole facing the magnetic blade 5 is attached, a repulsive magnetic field is formed between the magnetic blade 5 and the fixed magnet assembly S2 pole (pole 2) to face the toner. Appropriately share and promote triboelectrification to promote charging to toner, prevent selective development and stabilize specific charge of toner for a long period of time to increase image stability and obtain good image be able to.

As described above, as a method of making the magnetic flux density T ₄ [mT] in the region of L / 4 or less from both axial end portions of the N2 pole (pole 4) in the fixed magnet assembly 4 different from the central portion, A method in which the magnetic force is made different between the central portion in the axial direction of one magnet and the region of L / 4 or less from both ends, N2
There is a method in which the axial central portion of the pole (pole 4) and the region of L / 4 or less from both ends are made of different magnets so that the respective magnetic forces are different. For example, the magnetic force is in the height direction of the magnet. The height may be adjusted because it is proportional to the width.

Regarding the use of such magnets having different magnetic flux densities, for example, Japanese Patent Laid-Open No. 11-1
JP-A-02117 discloses that when a member for controlling the layer thickness of the toner on the developer carrying member is held at both ends, a difference in pressure contact pressure distribution for controlling the layer thickness between the central portion and both ends is corrected. The thickness regulating member has a magnetic force having the same polarity as the magnetic substance inside the developer carrier and a distribution that has a maximum at the center and decreases toward the ends, so that the maximum pressure contact force distribution is obtained at the center of the layer thickness regulating member. A device is shown which is made possible.

However, this Japanese Patent Laid-Open No. 11-10211
As described above, the device disclosed in Japanese Patent Publication No. 7 only uses magnetic force to make the difference in pressure contact force between the central portion and the end portion of the layer thickness regulating member uniform. In order to prevent the toner from staying in the developing device, the magnetic flux density in a region of L / 4 or less from both axial ends of the developer carrying member is set to be smaller than the magnetic flux density in the central part. Is not mentioned at all.

In the image forming apparatus provided with the developing device 1 of the present invention having the above-described structure, the normal image forming operation is
First, the toner in the developer container 7 is sufficiently stirred and charged, and a thin layer of toner is formed on the developing sleeve 3 while the layer thickness is regulated by the magnetic blade 5. In forming an image, first, the photosensitive drum 12 made of, for example, a-Si, which rotates in the direction of the arrow by the charger 13, is uniformly charged to about 240 (V) as an example. An electrostatic latent image is formed on the drum 12. At this time, the surface potential of the photosensitive drum 12 after exposure is about 10 (V). Between the photosensitive drum 12 and the developing sleeve 3, for example, a direct current Vdc of about 160 (V) is applied.
And rectangular electric field, triangular wave, sine wave, etc. alternating electric field (Vpp =
A bias in which 1.8 (kV) and f = 2.4 (kHz)) are superposed is applied to cause the thin layer toner on the developing sleeve 3 to fly between the developing drum 3 and the photosensitive drum 12 so as to fly.
The exposed part on 2 is developed.

In the case of reversal development, the developed toner image on the photosensitive drum 12 is transferred to a recording medium sent between the transfer roller 15 to which a negative transfer bias is applied and the photosensitive drum 12. Transferred with transfer bias,
It is fixed by a fixing device (not shown) and is discharged. The residual toner remaining on the photoconductor drum 12 is scraped off by the cleaner 16 to prepare for the next image formation. It should be noted that the values of the charging voltage, the surface potential, the DC bias, and the alternating electric field are examples, and it is obvious that the values are not limited to these values.

As described above, the magnetic flux density at both axial ends of the N2 pole (pole 4) in the fixed magnet assembly 4 inside the developer carrying member 2 is smaller than that in the central portion. The magnetic blade 5 is weaker than the central portion in the direction and is prevented from staying. Further, the presence of the magnetic blade 5 provided on the upstream side in the rotation direction of the developer carrying member 2 and the magnet 6 having the same polarity as the opposing magnetic pole makes it A repulsive magnetic field is formed between the opposing fixed magnet assembly S2 pole (pole 2), and a proper share is applied to the toner,
The triboelectrification is promoted to accelerate the electrification of the toner. Therefore, selective development is also prevented, the specific charge amount of the toner is stabilized over a long period of time, the image stability is increased, and a good image can be obtained. It is obvious that the pole arrangement of the magnets is not limited to the arrangement described above, and similar effects can be obtained even if S and N are reversed.

The developing device 1 of the present invention configured as described above
Table 1 shows the results of experimentation of the image state during use.
Shown in. Experiment 1 in Table 1 is a collection of fixed magnets.
Adult 4 N1 pole (pole 1), N2 pole (pole 4), S1 pole (pole)
3), magnetic flux density in the axial center of S2 pole (pole 2)
Are approximately the same, and about 15 [mm] from both ends in the axial direction (L /
The magnetic flux density at the position 4) is T at the N1 pole (pole 1).₁
= 80 [mT], T at S1 pole (pole 3)_Three= 85 [m
T], S2 pole (pole 2) is T_Two= 75 [mT], N2 pole
(Pole 4) T_Four= 30 [mT], N2 pole (pole 4)
Magnetic flux density T_FourTo T _Four<1/2 (T₁, T_Three, T_Two)When
did. On the other hand, in Experiment 2, the N of the fixed magnet assembly 4 was
Magnetic flux density T at both ends of two poles (pole 4)_FourAlso with other poles
80 [mT] which is almost the same.

[0024]

[Table 1]

As can be seen from the results in Table 1, the magnetic flux density T ₄ at both ends of the N2 pole (pole 4) of the fixed magnet assembly ₄ was T ₄ <1/2 (T ₁ , T ₃ , T ₂ ). In Experiment 1, compared with Experiment 2 in which the magnetic flux density was substantially the same in this portion, toner accumulation did not occur, and the toner adhesion phenomenon (toner layer disorder) did not occur on the developing sleeve 3 during durability, It can be seen that a stable image can be provided.

[0026]

As described above, according to the present invention, the toner is not accumulated even at the end portion of the developer carrying member, the generation of the opposite polarity toner and the disturbance of the toner layer at the time of durability are prevented, and the development is performed. It is possible to provide a developing device capable of preventing the stress on the surface treatment at the end portion of the agent carrier due to the toner and forming a stable image for a long period of time.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the configuration of a developing device according to the present invention.

FIG. 2 is a diagram for explaining the structure of a conventional magnetic one-component jumping developing device.

FIG. 3 is a graph showing changes in image density and changes in toner charge amount when a magnet is attached to a magnetic blade in a magnetic one-component jumping developing device (a) and when not attached (b).

[Explanation of symbols]

1 Development device 2 Developer support 3 Development sleeve 4 Fixed magnet assembly 5 Magnetic blade 6 magnets 7 developer container 8 stir bar 9 Toner container 10 Toner sensor 12 Photoconductor drum (electrostatic latent image carrier) 13 Charger 14 Exposure unit 15 Transfer roller 16 cleaner

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Toshinori Nishimura             704 No. Matabei, Noshino, Tamaki Town, Tokai District, Mie Prefecture             19 Kyocera Corporation Mie Factory Tamaki Block             Within (72) Inventor Eiji Ochiai             704 No. Matabei, Noshino, Tamaki Town, Tokai District, Mie Prefecture             19 Kyocera Corporation Mie Factory Tamaki Block             Within F term (reference) 2H031 AC08 AC20 AC31 AD03 AD16                       BA03 CA11

Claims (2)

[Claims] 1. A developing sleeve which is provided so as to face a photoconductor drum for forming an image by an electrophotographic method and which contains a magnet assembly having a plurality of magnetic poles. The magnet assembly or the developing sleeve, or A developer carrier configured such that both the magnet assembly and the developing sleeve rotate; and a magnetic developer layer provided on the upstream side of the developing position of the developing sleeve, to which a magnet is attached and which is formed on the developing sleeve. In a developing device having a magnetic blade that regulates the layer thickness, when the axial total length of the developer carrying member is L, the magnetic flux density in a region of L / 4 or less from both axial ends of the developer carrying member. A developing device having a magnetic flux density lower than that of the central portion. 2. A magnetic pole in the fixed magnet assembly which is close to the photosensitive drum is a pole 1, a magnetic pole which faces the magnetic blade is a pole 2, and magnetic poles which convey the toner to the developer carrying member are a pole 3 and a pole 4, respectively. , The magnetic flux density of each is T ₁ ,
When T ₂ , T ₃ and T ₄ are set, the magnetic flux densities of the magnetic poles in the axial center portion are substantially the same, and the magnetic force T _{4 in} a region L / 4 or less from both axial end portions of the pole 4 is T ₄ <1/2 (T ₁ , T ₂ , T ₃ ), The developing device according to claim 1.