JP3109252B2 - Developing device for image forming apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device for an image forming apparatus, and more particularly to a developing device for an image forming apparatus provided with means for collecting a carrier detached from a developer carrier.

[0002]

2. Description of the Related Art FIG. 14 shows a structure around a developing device of an image forming apparatus proposed by the present inventors (Japanese Patent Application No. 3-297636).

After the drum-shaped photosensitive member 9 is uniformly charged by corona discharge of a charger 10, a latent image corresponding to an original image is formed by a light source 11 such as a semiconductor laser or an LED. Then, in a developing device described in detail later, only the toner of the developer 6 composed of the toner and the carrier adheres to the peripheral surface of the photoreceptor 9 to visualize (develop) the latent image. Is transferred to the transfer paper (not shown) conveyed at the timing of (1) and is fixed, and then conveyed to a paper discharge tray (not shown).

[0004] At the bottom of the developer container 1, there are provided two screw-shaped stirring members 3 and 4 having spiral wings on a rotating shaft to which a stirring auxiliary member 2 is added, and stirs and mixes the developer. The developer 6 is transported to the developer carrier 5 while the developer 6 is being transported.

A photosensitive member 9 is provided in a developer container 1 of the developing device.
The developer carrier 5 is disposed at a predetermined interval. The developer carrier 5 has a developing magnetic pole N ₁ inside.
It comprises a fixed magnet roll 18 having transfer magnetic poles S ₁ , S ₃ , N ₂ , S ₂ and a conductive sleeve 19 rotatably provided outside the magnet roll 18.

A screw-shaped first stirring member 3 is disposed diagonally below the developer carrier 5 and near the bottom of the developer container 1 in parallel with the developer carrier 5. A second stirring member 4 is disposed near the bottom of the developer container 1 and slightly obliquely above the first stirring member 3 (β = 5 to 25 degrees) in parallel with the first stirring member 3. By arranging the second stirring member 4 above the first stirring member 3 as described above, the stagnation of the developer 6 is further reduced, and good fluidity is obtained.

As shown in FIG. 15, the agitating members 3 and 4 have a shaft portion 20, blades 21 spirally wound at a predetermined pitch with respect to the shaft portion 20, and a stirrer 21 on the shaft portion 20 at every other pitch. And a stirring assisting member 2 attached thereto.
The agitation auxiliary member 2 has a direction substantially the same as that of the blade 21, that is, the blade 2.
1 so that the shaft portion 2 extends along the direction in which the developer 6 is fed.
It is attached so as to be inclined with respect to the 0 axis.
As shown in FIG. 1, the first stirring member 3 rotates counterclockwise and the second stirring member 4 rotates clockwise at the same time.

A partition plate 17 is disposed at an upper position between the first stirring member 3 and the second stirring member 4, and both ends thereof are supported by side plates (not shown) of the developer container 1.

A plate-shaped baffle member 7 is disposed between the developer carrier 5 and the first stirring member 3. The developer 6 agitated and mixed by the rotation of the first stirring member 3 collides with the baffle member 7 and is disturbed. Then, the developer 6 is supplied to the developer carrier 5 and magnetically adheres on the sleeve 19, and is regulated. Regulates the thickness of the developer layer on the developer carrier 5. The overflowing developer 6 regulated by the regulating member 8 is transferred to the inclined guide plate 12.
To the pre-stirring member 13. It is not always necessary to provide the preliminary stirring member 13 and the inclined guide plate 12
May be returned directly to the second stirring member 4 side.

The developer 6 that has passed under the regulating member 8 is opposed to the photosensitive member 9 by the rotation of the sleeve 19, and only the toner of the developer 6 adheres to the photosensitive member 9 and the developer 6 that has been developed is completed.
Is scraped off from the developer carrier 5 at the tip of the baffle member 7, and is again stirred and mixed.

The toner hopper 14 is provided on the developer container 1, and rotates the toner feed roll 15 when the toner concentration in the developer becomes lower than a certain level.
The toner 16 is put on the preliminary stirring member 13. At this time, the supplied toner 16 is preliminarily stirred with the developer 6 carried from the inclined guide plate 12, and then sufficiently stirred and mixed by the second stirring member 4 and the first stirring member 3.

A partition plate 17 provided between the left and right agitating members 3 and 4 is provided with an insufficiently charged toner which is not sufficiently mixed and agitated immediately after the toner 16 is replenished, or a floating toner. 5 is prevented, the developer 6 is prevented from stagnation, and the developer 6 on the first stirring member 3 side is prevented.
It is effective to keep the layer thickness (level) of the film constant.

As described above, according to the developing device proposed by the inventors of the present invention, it has become clear that the stirring and transport of the developer 6 in the developer container 1 can be performed very efficiently and stably. However, at the portion of the developer carrier 5 facing the photoconductor 9, a new problem arises in that the carrier that must adhere to the developer carrier 5 comes off during development.

Hereinafter, this carrier detachment phenomenon will be described.
The case of reversal development using a component developer will be described as an example.

[0015] Upon exposure based on the photosensitive member on the image information which is charged to a surface potential V ₀ which as shown in FIG. 2, the residual potential of the exposed portion becomes V _R. As described above, the magnet roll 18 is provided inside the developer carrier 5, and the magnet roll 18 causes the surface of the developer carrier 5 to
Since the magnetic brush of the component developer is formed, the bias voltages V _B and V _R applied to the developer carrier 5 when the exposed portion reaches the vicinity of the magnetic brush with the rotation of the photosensitive member 9.
With the potential difference, the toner triboelectrically charged to the same polarity as the charged potential is separated from the carrier and adheres to the exposed portion. At this time, the carrier constituting the magnetic brush is held on the surface of the developer carrier 5 by the magnet roll 18 in the developer carrier 5.
When the force attracted to the upper latent image and the background portion (non-latent image portion) becomes stronger, a phenomenon occurs in which the carrier separates from the developer carrier 5 and adheres to the photoconductor 9 (this phenomenon is generally caused). Called a carrier stick). It is considered that carrier sticking occurs mainly in the following cases.

(1) Adhesion of Carrier on Background Part This is a phenomenon in which the carrier adheres to the background part where the toner does not originally adhere. Assuming that the toner 100 is negatively charged and the carrier 101 is triboelectrically charged to a positive polarity as shown in FIG. 3A and that the two are balanced, the sum of the charges as the developer is 0, so that the photosensitive member is charged. The sucked force does not work. However, during development, as shown in FIG. 3B, when the toner 102 used for development is separated from the carrier 101, and the toner having originally zero polarity is biased toward the positive polarity, it is likely to be attracted to the background portion. Since the carrier is charged with a polarity opposite to the charging potential of the photoreceptor, the force attracted to the photoreceptor increases as | V ₀ −V _B | increases. It is considered that when this force becomes stronger than the magnetic attraction force of the developer carrier, carrier adhesion occurs.

The carrier adhered to the background on the photoreceptor does not affect the image quality unless it is transferred. However, when the carrier is moved to the cleaning system while being adhered to the photoreceptor, the cleaning brush or cleaning blade may be damaged, Even when the image is transferred onto a sheet, the replacement of consumable parts may be accelerated, for example, the fixing roller is damaged during fixing.

(2) Carrier Attachment on Latent Image Area Normally, only toner adheres and the carrier has a different polarity from the toner, so that suction force does not work. However, since a bias voltage opposite to the charge polarity of the carrier is applied to the developer carrier, when the electric resistance of the carrier decreases, electric charges of the same polarity as the bias voltage are accumulated on the carrier through the developer carrier. There is.

In such a case, the carrier adheres to the latent image portion in the same manner as the toner is developed. If the toner image is transferred onto the paper with the carrier adhered to the latent image portion, the portion where the carrier is adhered will not be transferred. When the image is developed, the character may be lost and cannot be identified. In recent years, image forming apparatuses such as laser beam printers have been increasingly used for financial-related bills, statements, bar codes, and the like. Omission due to carrier sticking is an important problem.

(3) In addition to the above (1) and (2), the carrier 1 between the developer carrier 103 and the photosensitive member 104 as shown in FIG.
05, the working centrifugal force F ₁ and the magnetic attraction force F _2. F
₁ and F ₂ are the following equations

[0021]

(Equation 1)

Can be expressed by As shown in FIG. 5, some carriers have different particle diameters and different magnetic permeability during the manufacturing process.
Lower carrier is less carrier or permeability of the particle size, since the F ₁ from equation (1) is stronger than F _2, easily scattered from the developer carrying member. If such a scattered carrier or a carrier attached to the photoreceptor due to gravity falls into the image forming apparatus and enters a part of the paper transport system, the part is damaged, and if it is damaged, it may cause a paper jam. Become. In addition, when the inside of the apparatus is contaminated with the scattered carrier, an operation for removing the inside during maintenance is required.

[0023]

As described above, it is essential for the image forming apparatus to prevent trouble due to carrier stick and carrier scattering in order to obtain high image quality and high reliability.

An object of the present invention is to provide a member for recovering a carrier detached from a developer carrying member without largely changing the structure of the developing device proposed by the inventors of the present invention. The agent carrier and the carrier recovery member can be arranged close to each other, and as a result, the size of the developing device can be reduced.

[0025]

SUMMARY OF THE INVENTION The object of the present invention is to provide a member for recovering a carrier detached from a developer carrier, which is provided close to a transport magnetic pole adjacent to a developing magnetic pole, and provided in the carrier recovery member. Is opposed to the photoreceptor surface and
This is achieved by providing a single magnetic pole having the same polarity as the developing magnetic pole. Further, this is achieved by applying a voltage equal to or higher than a bias voltage applied to the developer carrier to the carrier recovery member.

[0026]

According to the present invention, the carrier is recovered by providing a carrier recovery member provided with one magnet having a magnetic pole facing the surface of the photoreceptor near the developer carrying member having a polarity opposite to that of the magnetic pole. As a result, the carrier recovery member can be configured without changing the magnetic pole arrangement of the magnet roll provided in the developer carrier of the developing device proposed by the present inventors. In addition, since there is almost no magnetic interference between the magnet roll and the carrier collecting member, the carrier collecting member can be arranged close to the developer carrier, and as a result, the size of the developing device can be reduced.

Further, by applying a voltage equal to or higher than the bias voltage applied to the developer carrying member to the carrier collecting member, the force for sucking the carrier is further increased, and the carrier can be surely sucked.

[0028]

Embodiments of the present invention will be described below with reference to the drawings. Note that members having the same configuration as the configuration in FIG. 14 are denoted by the same reference numerals, and description thereof will be omitted.

FIG. 1 is a sectional view showing the vicinity of the developing device according to the present invention. The developer carrier 5 is obliquely below the developer carrier 5.
A carrier collection member 30 is provided for collecting the carrier that has separated from the carrier. A permanent magnet 31 is provided in a fixed state in the carrier collection member 30, and a sleeve 32 rotates in the direction of arrow a on the outside thereof to convey the collected carrier to the developer container 1 side. The transported carrier is
It is attracted to the developer carrier 5 by a magnetic force acting between a carrier collection member 30 described later and a magnetic pole S ₁ of the developer carrier 5.

The photosensitive member 9 and the carrier collecting member 30 are held at a constant interval, and the center line 33 of the magnetic force distribution of the permanent magnet 31 is a line 34 connecting the center of the carrier collecting member 30 and the center of the photosensitive member 9. Is located above.
Assuming that the angle between the center line 33 and the line 34 is θ, θ is 3 to 1
The angle is 0 degrees, preferably 3 to 5 degrees, but is not limited to this, and an effect can be obtained even in a positional relationship shifted by 0 degrees or several degrees downward.

FIG. 9 is a sectional view showing the structure and function of the carrier collecting member. Carrier 35 adhered on photoreceptor 9
Is attracted by the magnetic force of the carrier recovery member 30.
In addition, since the carrier 36 detached from the developer carrier 5 also has a force of dropping due to gravity, it is attracted by the magnetic force near the carrier recovery member 30. Carrier recovery member 30
Has a block-shaped magnet 31 bonded to a holding member 37 made of a magnetic material such as iron or a non-magnetic material such as aluminum or stainless steel. The sleeve 32 is intermittently rotated in the direction of arrow a via a drive gear of a developing device (not shown).
Conveyed in the direction. The driving method of the sleeve 32 is not necessarily limited to the intermittent operation, and may be constantly rotated.

FIG. 10 is a diagram showing a magnetic force distribution between the carrier recovery member and the developer carrier. In the present invention, the inside of the carrier recovery member 30 is constituted by one permanent magnet 31 alone. In this case, a different pole 40 having a substantially same area around the carrier recovery member 30 as the magnetic force 39 generated by the permanent magnet 31 and having a different polarity from the magnetic pole is generated. Due to the magnetic force 40 having the different polarity, a force in the direction of arrow a acts on the recovery carrier, and the carrier can move. Reference numeral 41 denotes a magnetic force distribution of the developer carrier 5. Thus, the carrier collection member 30
Since the distribution due to the different polarity occurs at the position close to the developer carrier 5, the collection carrier can be transported without causing magnetic interference between the magnetic poles of the developer carrier 5. At this time, if the surface of the sleeve 32 is subjected to a metal fusion treatment, a sand blasting process, a groove process, or the like, the friction between the collection carrier and the surface of the sleeve 32 increases, so that the conveyance can be further improved.

The surface of the developer carrier 5 facing the carrier recovery member 30 is provided with the permanent magnet 3 of the carrier recovery member 30.
Since the magnetic pole S1 opposite to ₁ is provided, a magnetic force b that attracts the transported carrier 42 is formed as shown in FIG. Therefore, the transported carrier 42 is attracted to the developer carrier 5 by a magnetic field generated between the permanent magnet 31 of the carrier recovery member 30 and the magnetic pole S ₁ of the developer carrier 5, and is recovered in the developing device. Used again.

When the attached carrier and the detached carrier on the photoreceptor 9 have the opposite polarity to the bias voltage, applying the bias voltage to the carrier collecting member 30 increases the force for electrostatically attracting the carrier. The effect can be improved. The voltage applied at this time is
When a voltage equal to or higher than the voltage applied to the developer carrying member or a voltage higher than the voltage applied thereto or an AC voltage is superimposed on the DC voltage, the force for attracting the carrier increases.

The carrier collecting member 30 also has a function of sucking scattered toner. The charge amount of the toner during development has a distribution as shown in FIG. Among them, a toner having a low charge amount or a low charge amount toner having the opposite polarity is scattered due to a stronger centrifugal force than an electrostatic adhesion to a carrier.
Among the scattered toners, those charged to the opposite polarity (+) are attracted by the bias voltage (−) applied to the carrier collection member 30. The sucked toner and carrier are scraped off by the scraper 43.

FIG. 13 is a view showing another embodiment of the carrier collecting member. The internal permanent magnet is a rod-shaped holding member 44.
Then, a columnar magnet material 45 is adhered and magnetized to form only the magnetic pole 46.

FIGS. 6 to 8 show an example of a carrier collecting member which was tested by the present inventors before obtaining the carrier collecting member of the present invention.

Assuming that it is not considered that the magnetic pole arrangement of the magnet roll provided in the developer carrier 5 is changed, first, as shown in FIG. Placed at a distance. However, in this case, a sufficient magnetic force did not act between the magnet 47 and the magnet 48, and the carrier could not be transported. Conversely, when the magnet 48 is brought close to the magnet 47 as shown in FIG. 7 in order to exert a sufficient magnetic force, the magnetic pole S ₁ , the magnetic pole N ₁ and the magnets 47 and 48 cause magnetic interference, and the magnet 48 and the magnetic pole N
Or pillars 49 of the developer I caused by the magnetic force acting between _1, repulsive force works between the magnet 48 and the magnetic pole S ₁ as shown in FIG. 8, the developer ends up flowing out of the developing device, excellent Carrier recovery could not be realized.

[0039]

According to the developing device of the image forming apparatus of the present invention, the carrier recovery member provided with one magnet having the magnetic pole facing the surface of the photoreceptor is provided near the developer carrying member having a polarity opposite to that of the magnetic pole. The carrier can be collected smoothly without changing the magnetic pole arrangement of the magnet roll provided in the developer carrier of the developing device proposed by the present inventors. The members could be configured.

Further, since magnetic interference hardly occurs between the magnet roll and the carrier collecting member, the carrier collecting member can be arranged close to the developer carrier, and as a result, the size of the developing device can be reduced. did it.

Further, since a voltage higher than the bias voltage applied to the developer carrying member is applied to the carrier collecting member, the force for sucking the carrier is more sufficient, and the carrier can be surely sucked.

[Brief description of the drawings]

FIG. 1 is a sectional view of a developing device according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a relationship between a latent image portion, a non-latent image portion, and a bias voltage on a photoconductor.

FIG. 3 is a diagram showing a frictionally charged state of toner and carrier before and during development.

FIG. 4 is a diagram showing a force acting on a carrier on a developer carrying member.

FIG. 5 is a diagram showing a particle size distribution of a carrier.

FIG. 6 is a cross-sectional view showing an example of a carrier recovery member that was tested before obtaining the carrier recovery member of the present invention.

FIG. 7 is a cross-sectional view illustrating an example of a carrier recovery member that was tested before obtaining the carrier recovery member of the present invention.

FIG. 8 is a cross-sectional view showing an example of a carrier recovery member that was tested before obtaining the carrier recovery member of the present invention.

FIG. 9 is a diagram illustrating a configuration and a function of a carrier collection member.

FIG. 10 is a diagram illustrating a magnetic force distribution of a carrier collection member and a developer carrier.

FIG. 11 is a diagram illustrating a magnetic force generated between a carrier collection member and a developer carrier.

FIG. 12 is a diagram showing a charge amount distribution of toner.

FIG. 13 is a view showing another embodiment of the carrier collection member.

FIG. 14 is a sectional view of a developing device according to the related art.

FIG. 15 is an enlarged view of a main part of a stirring member.

[Explanation of symbols]

1 is a developer container, 2 is a stirring auxiliary member, 3 and 4 are stirring members, 5 is a developer carrier, 6 is a developer, 7 is a hindrance member, 8
Is a regulating member, 9 is a photoreceptor, 10 is a charger, 11 is a light source,
12 is an inclined guide plate, 14 is a toner hopper, 15 is a toner feed roll, 16 is toner, 17 is a partition plate, 18
Is a magnet roll, 19 and 32 are sleeves, 30 is a carrier collection member, 31 is a permanent magnet, 37 is a holding member,
3 is a scraper.

Continuing from the front page (72) Inventor Katsuhiro Akinaga 1060 Takeda, Katsuta-shi, Ibaraki Pref.Hitachi Koki Co., Ltd. (72) Inventor Masaaki Akutsu 1060 Takeda, Katsuta-shi, Ibaraki Pref. (56) References JP-A-3-144467 (JP, A) JP-A-63-163475 (JP, A) JP-A-58-105555 (JP, U) (58) Fields investigated (Int. Cl. ⁷⁾ G03G 15/08-15/095 G03G 15/00 550

Claims (2)

(57) [Claims] A magnetic pole for development, and at least one transport magnetic pole arranged at a stage subsequent to the magnetic pole for development, and
Using a developer carrier in which the polarity of the transport magnetic pole adjacent to the developing magnetic pole is different from the polarity of the developing magnetic pole, the toner and carrier are mainly used on the developer carrier. In a device for forming a two-component developer magnetic brush and developing an electrostatic latent image formed on a photoreceptor, a member for recovering a carrier detached from the developer carrier is provided adjacent to the developing magnetic pole. Along with the transport magnetic pole, a single magnetic pole having the same polarity as the developing magnetic pole is provided in the carrier collecting member, facing the photoconductor surface, and the developer carrying member is provided with a single magnetic pole. An image forming apparatus, wherein a magnetic pole opposite to the single magnetic pole is provided on a surface facing a carrier collecting member, and the carrier collecting member is rotated in the same direction as the photoconductor and the carrier is collected in a developing device. Developing equipment Place. 2. A bias voltage is applied to the developer carrier and the carrier collection member, and the carrier collection member has the same bias voltage as that applied to the developer carrier.
2. The developing device for an image forming apparatus according to claim 1, wherein a voltage of the same polarity having a larger value is applied.