JPH1124370A - Charging device and image forming device - Google Patents

Abstract

(57) [Problem] To improve a charging ability of a magnetic brush charging device, to prevent overflow of conductive magnetic particles in a charging nip portion, and the like. A rotating sleeve (1), magnetic field generating means (2) contained in the sleeve, conductive magnetic particles (3) magnetically constrained as a magnetic brush on the sleeve by the magnetic field generating means, and constrained on the sleeve. In the magnetic brush charging device A, which has a regulating means 4 for regulating the amount of magnetic particles to be carried, and charges the charged object 7 by bringing the magnetic particles into contact with the charged object, the gap between the sleeve and the charged object is Lcm, When the apparent density of the magnetic particles is pg / cm ³ , when the magnetic particles on the sleeve do not contact the member to be charged, the carrying amount of the magnetic particles on the sleeve after being regulated by the regulating means is Mg / cm ² , When the volume average particle diameter is dcm, 3d <L <M / p
Is satisfied, and the amount of magnetic particles passing through the contact portion of the member to be charged and the regulating portion is always in an equilibrium state at the time of contact of the member to be charged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a charging device for charging an object to be charged (including charge elimination).

More specifically, the present invention relates to a contact charging device, and more particularly, to a magnetic brush charging device for charging a charged object by bringing conductive magnetic particles magnetically constrained as a magnetic brush into contact with the charged object.

[0003] Further, the present invention relates to an image forming apparatus such as a copying machine or a printer provided with the charging device.

[0004]

2. Description of the Related Art A transfer type electrophotographic apparatus will be described as an example. This apparatus uses an electrophotographic photosensitive member (hereinafter, referred to as a photosensitive drum or a photosensitive member) generally having a rotating drum type as an image carrier, and the surface of the rotating photosensitive drum is given a predetermined polarity and potential by a charging means. The photosensitive drum surface after charging is image-exposed by an image exposing unit to form an electrostatic latent image corresponding to the exposed image, and a developing unit attaches a toner of a developer to the electrostatic latent image. Then, the toner image is developed, and the toner image is transferred to a transfer material by a transfer unit. The transfer material onto which the toner image has been transferred is subjected to fixing processing of the toner image by a fixing unit, and is discharged as an image formed product (copy / print). After the transfer of the toner image to the transfer material, the rotating photosensitive drum is subjected to removal of the transfer residual toner by the cleaning means, and is repeatedly subjected to image formation.

Conventionally, a corona charger has been used as a charging device for electrophotography. In this method, a corona charger is disposed in non-contact with a photosensitive drum, and the surface of the photosensitive drum is charged to a predetermined polarity / potential by exposing the surface of the photosensitive drum to a corona shower generated from the corona charger to which a high voltage is applied. Things.

In recent years, a contact charging device has been put to practical use instead of this. This is intended for ozone and low power, and among them, a roller charging method using a conductive roller as a contact charging member is preferable in terms of charging stability and is widely used.

In the roller charging, a conductive elastic roller (charging roller) is brought into pressure contact with a member to be charged, and a voltage is applied to the member to charge the member.

There are two types of contact charging devices: a DC bias application method in which a DC bias is applied to a contact charging member as a charging bias, and an AC bias application method in which a DC bias is applied while being superimposed on an AC bias.

In the case of the DC bias application method, the resistance value of the contact charging member fluctuates due to environmental fluctuation or the like.
When the film thickness changes due to scraping of the photoreceptor, the charging start voltage (discharge start voltage) Vth fluctuates, so that it was difficult to set the potential of the photoreceptor to a desired value. In the case of the AC bias application method, the AC bias is not affected by disturbances such as the environment due to the leveling effect of the AC bias, but the deterioration of the photoconductor surface due to the discharge phenomenon becomes more remarkable than the DC bias. There is a problem. Also, in both types, the essential charging mechanism uses a discharge phenomenon from the contact charging member to the photoreceptor, so that a small amount of ozone is generated.

Therefore, as a new charging method, an injection charging method by directly injecting electric charge to a photosensitive member has been devised.
In this charging method, a voltage is applied to a contact conductive member (contact charging member) such as a charging roller, a charging brush, or a charging magnetic brush, and charge is injected into a charge injection layer on the surface of the photoreceptor to perform contact injection charging. It is. In this charging method, since the discharge phenomenon is not used, the voltage required for charging is only the desired photoconductor surface potential and no ozone is generated.
Further, even in the case of using the AC bias application method, since the discharge is suppressed, the generation of ozone is small, and the deterioration of the photoreceptor surface can be greatly reduced.

The charge injection layer is made of a material in which conductive fine particles such as tin oxide are dispersed in a resin, amorphous silicon, or the like.

The charging magnetic brush has a magnetic brush portion made of conductive magnetic particles magnetically constrained and supported on a supporting member also serving as a power supply electrode, and the magnetic brush portion is brought into contact with a photosensitive member as a member to be charged. By supplying power to the carrier member, the photoconductor is charged. Compared to other contact charging members, the charging magnetic brush has advantages such as excellent charging uniformity and less susceptibility to contamination by residues on the photoreceptor.

[0013]

SUMMARY OF THE INVENTION The present invention particularly relates to an improvement of a contact charging device (magnetic brush charging device) using a charged magnetic brush.

That is, the magnetic brush charging has a property of being charged only in the contact area between the member to be charged and the conductive magnetic particles of the magnetic brush portion. For this reason, in order to obtain sufficient charging ability to charge the member to be charged to a predetermined potential, it is desirable to increase the chance of contact between the surface of the member to be charged and the conductive magnetic particles of the magnetic brush portion. As means for increasing the chance of contact, it is effective to increase the rotation speed of the charging sleeve carrying the magnetic brush composed of conductive magnetic particles or to increase the contact area between the magnetic brush portion and the member to be charged. It is.

If the opportunity for contact between the surface of the member to be charged and the conductive magnetic particles of the magnetic brush portion is insufficient, not only will a predetermined charging potential not be obtained, but also the charging capability will decrease due to contamination of the magnetic brush. In the image forming apparatus, fogging and charging ghosts (when the charging ability of the charger is reduced, the history of the latent image on the member to be charged cannot be erased,
(History may appear on the next image).

The present invention relates to a magnetic brush charging device,
It is devised to increase the chance of contact between the surface of the member to be charged and the conductive magnetic particles of the magnetic brush portion.

[0017]

SUMMARY OF THE INVENTION The present invention is a charging device and an image forming apparatus having the following constitutions. (1) a rotating sleeve, magnetic field generating means contained in the sleeve, conductive magnetic particles magnetically constrained as a magnetic brush on the sleeve by the magnetic field generating means, and the conductive particles confined on the sleeve A magnetic brush charging device that has a regulating unit that regulates the amount of the conductive magnetic particles carried, and charges the charged object by bringing the conductive magnetic particles into contact with the charged object, wherein a gap between the sleeve and the charged object is provided. Is L [cm], the apparent density of the conductive magnetic particles is p [g / cm ³ ], and after the conductive magnetic particles on the sleeve are not in contact with the member to be charged, after being regulated by regulating means. When the carrying amount of the conductive magnetic particles on the sleeve is M [g / cm ² ] and the volume average particle size of the conductive magnetic particles is d [cm], 3d <L <M / p When charging and contacting the member to be charged, contacting the member to be charged A charging device, characterized in that the amount per time of the conductive magnetic particles passing through the restricting portion and the conductive magnetic particles passing through is always in equilibrium.

(2) The magnetic field generating means includes a second magnetic pole different from at least a first magnetic pole at a position facing the member to be charged and a first magnetic pole adjacent to the sleeve in a direction opposite to the rotation direction of the sleeve. A magnetic pole, a regulating position of the regulating means is located between the first magnetic pole and the second magnetic pole, and a straight line connecting the regulating position and the rotation center of the sleeve; The angle between the straight line connecting the contact position and the rotation center of the sleeve is 70
° or less, the charging device according to (1), wherein:

(3) The magnetic field generating means includes a second magnetic pole different from at least a first magnetic pole at a position facing the member to be charged and a first magnetic pole adjacent to the sleeve in a direction opposite to the rotation direction of the sleeve. A magnetic pole, and a restricting position of the restricting means is located between the first magnetic pole and the second magnetic pole, and a magnetic flux density by the magnetic field generating means at the restricting position is 400 × 10 ^-4 [T (Tesla )] The charging device according to (1), wherein:

(4) The charging device according to any one of (1) to (3), wherein the restricting means is made of a rigid body.

(5) The restricting means is made of a material exhibiting flexibility (1) to (3).
The charging device according to any one of the above.

(6) The member to be charged is an image carrier in an image forming apparatus, and has a charge injection layer on its surface or is chargeable and chargeable. A charging device according to any one of the preceding claims.

(7) The charging device according to (6), wherein the charge injection layer is made of a resin in which conductive fine particles are dispersed.

(8) The charging device according to (6), wherein the charge injection layer is made of amorphous silicon.

(9) An image forming apparatus for performing image formation by applying an image forming process including a step of charging the image carrier to the image carrier, wherein the means for charging the image carrier comprises (1)
An image forming apparatus, which is the charging device according to any one of (8) to (8).

<Operation> In the magnetic brush charging device, by satisfying the above-mentioned relational expression 3d <L <M / p, the charging nip portion (the conductivity to the charged object at the position where the sleeve and the charged object are opposed to each other) is satisfied. The closest contact state of the conductive magnetic particles can be formed by the magnetic particles (contact area of the magnetic brush), that is, the conductive magnetic particles forming the magnetic brush with the surface of the member to be charged in the charging nip portion Can be increased, and the charging ability can be greatly improved.

However, when the densest state of the conductive magnetic particles is formed at the charging nip, overflow of the conductive magnetic particles easily occurs at the charging nip. The overflow of the conductive magnetic particles is caused by the fact that the amount of the conductive magnetic particles passing through the contact portion of the member to be charged and the conductive magnetic particles passing through the regulating portion are always in an equilibrium state (self-control mechanism). Can be prevented.

More specifically, the magnetic field generating means includes at least a first magnetic pole at a position facing the member to be charged and a second magnetic pole different from the first magnetic pole adjacent in the direction opposite to the rotation direction of the sleeve. The regulating position of the regulating means is located between the first magnetic pole and the second magnetic pole, and a straight line connecting the regulating position and the rotation center of the sleeve, the closest position between the sleeve and the member to be charged, and the length of the sleeve. The angle formed by the straight line connecting the rotation centers is 70 ° or less, or the regulating position of the regulating means is located between the first magnetic pole and the second magnetic pole, and the magnetic flux density by the magnetic field generating means at the regulating position is By being equal to or less than 400 × 10 ⁻⁴ [T], the amount of the conductive magnetic particles passing through the contact portion of the member to be charged and the amount of conductive magnetic particles passing through the regulating portion are always equilibrated and charged. Prevents conductive magnetic particles from overflowing at the nip Kill.

Therefore, the close-packed state of the conductive magnetic particles can be formed in the charging nip without overflowing the magnetic particles, and the charging ability can be improved. Furthermore, in such a configuration, the supply amount of the conductive magnetic particles is self-regulated, so that the conductive magnetic particles overflow even if the fluidity of the conductive magnetic particles changes due to environmental changes or the like. And stable charging that does not occur can be performed.

[0030]

BEST MODE FOR CARRYING OUT THE INVENTION

<Embodiment 1> (FIGS. 1 to 4) FIG. 1 is a schematic cross-sectional model diagram of an example of a magnetic brush charging device according to the present invention.

(1) Overall Schematic Configuration of Charging Device A Reference numeral 1 denotes a rotating sleeve (charging sleeve) as a holding member for a magnetic brush of conductive magnetic particles. Sleeve 1 of this example
Is a non-magnetic sleeve having a diameter of 25 mm, which also serves as a power supply electrode and is made of, for example, aluminum. Equipment casing 5
Inside, both ends are rotatably supported. The sleeve 1 has its front side exposed outside from the front opening of the device casing 5.

Numeral 2 denotes a magnet roller as magnetic field generating means which is substantially concentrically inserted into and contained in the sleeve 1. This embodiment is a four-pole magnet roller, which is a non-rotatably fixed roller. N1, S1, N2, and S2 are magnetic pole portions.

The sleeve 1 is driven to rotate around the fixed magnet roller 2 at a peripheral speed of 200 mm / sec by a driving system (not shown) in a counterclockwise direction indicated by an arrow R1.

Reference numeral 3 denotes conductive magnetic particles (magnetic carriers, hereinafter referred to as magnetic particles) or magnetic brushes of the magnetic particles, and is magnetically constrained on the outer surface of the sleeve 1 by the magnetic force of the magnet roller 2 inside the sleeve. .

Reference numeral 4 denotes a regulating plate (regulating member) as regulating means for regulating the amount of magnetic particles carried on the sleeve 1.
It is. In this embodiment, the regulating plate 4 is a non-magnetic rigid blade. The regulating plate 4 is fixedly arranged on the front wall on the upper side of the front opening of the device casing 5 with a predetermined gap α [cm] set between the lower side of the regulating plate and the outer surface of the sleeve 1. . This gap α portion is a magnetic particle regulating position by the regulating plate 4.

Reference numeral 7 denotes an object to be charged. In this example, an electrophotographic photosensitive drum is used as an image carrier in an electrophotographic apparatus.
More specifically, the photosensitive drum 7 has an outermost layer as a charge injection layer, and has a charge generation layer in which a disazo pigment is dispersed in a resin, and a charge transport layer in which hydrazone is dispersed in a polycarbonate resin. Further, the outermost layer has an organic photosensitive layer composed of a charge injection layer in which ultrafine SnO ₂ (conductive filler) is dispersed in a photocurable acrylic resin,
It is rotationally driven at a peripheral speed of 100 mm / sec in the counterclockwise direction of arrow R2.

A predetermined gap L (cm) (a gap dimension at the closest position of 1.7) is set between the sleeve portion exposed to the outside from the front opening of the apparatus casing 5 and the photosensitive drum 7 so as to face each other. It is.

The magnetic particles 3 which are magnetically bound to and adhere to the outer surface of the sleeve 1 are conveyed in the same direction as the sleeve 1 rotates in the counterclockwise direction R1.
A large pool (residence) is formed and held in a space defined by the upper surface of the sleeve 1, the back surface of the regulating plate 4, and the back surface of the front wall of the device casing 5.

A part of the magnetic particles in the pool is
As the magnetic brush rotates, it passes through the gap between the lower side of the regulating plate 4 and the outer surface of the sleeve 1, that is, passes through the magnetic particle regulating position α to the outside of the device casing 5 and is held on the sleeve 1 as a magnetic brush whose layer thickness is regulated. Then, the sheet is conveyed to a position where the sleeve 1 and the photosensitive drum 7 face each other.

The magnetic brush of the magnetic particles conveyed to the position where the sleeve 1 and the photosensitive drum 7 are opposed to each other is a first magnetic pole N1 (hereinafter referred to as a main pole) on the magnet roller 2 located substantially corresponding to the opposed position. ), And comes into contact with the surface of the rotating photosensitive drum 7, and the surface of the rotating photosensitive drum 7 is rubbed with a magnetic brush of magnetic particles. At a position where the sleeve 1 and the photosensitive drum 7 face each other, a contact area of the magnetic particles (magnetic brush) with respect to the surface of the photosensitive drum 7 is a charging nip portion a.

The magnetic particles that have passed through the gap L between the position where the sleeve 1 and the photosensitive drum 7 face each other are magnetically constrained and held on the sleeve 1, are returned to the inside of the apparatus casing 5 by the subsequent rotation of the sleeve 1, and are cyclically used. Is done.

A predetermined charging bias is applied to the sleeve 1 from a power supply 6, and the surface of the rotating photosensitive drum 7 is charged at a charging nip a
In the above, the contact charging process is performed to a predetermined polarity and potential by the rubbing of the magnetic particles by the magnetic brush and the applied charging bias. In this embodiment, a superimposed bias having a DC bias of -700 V, an AC bias of 1000 V, and a frequency of 1 kHz was applied from the power source 6 to the sleeve 1 as a charging bias.

In the present embodiment, the photosensitive drum 7 as the member to be charged has the outermost layer as the charge injection layer as described above, and therefore, the photosensitive drum 7
Contact charging is performed at approximately -700 V in accordance with the C bias by an injection charging method.

(2) Magnetic Particles 3 As the magnetic particles constituting the magnetic brush, the following are preferably used.

A. A resin and a magnetic powder such as magnetite are kneaded to form particles, or mixed with conductive carbon or the like to adjust resistance, b. Sintered magnetite, ferrite, or those obtained by reducing or oxidizing these to adjust the resistance value; c. The above magnetic particles are coated with a coating material (for example, a phenol resin in which carbon is dispersed) in which the resistance is adjusted, or plated with a metal such as Ni so as to have an appropriate resistance value.

If the resistance value of these magnetic particles is too high, charges cannot be uniformly injected onto the surface of the photosensitive drum, and a fog image due to minute charging failure will result. If the temperature is too low, when there is a pinhole on the surface of the photosensitive drum, current concentrates on the pinhole and the charging voltage drops, so that the surface of the photosensitive drum cannot be charged.
Therefore, the resistance value of the magnetic particles is 1 × 10 ⁴ to 1 × 1
0 ⁷ Ω is desirable.

The resistance value of the magnetic particles was measured by placing 2 g of the magnetic particles in a metal cell (bottom area: 228 mm ² ) to which a voltage could be applied, applying a weight, and applying a voltage of 1 to 1000 V.

Regarding the magnetic properties of the magnetic particles, it is better to increase the magnetic binding force in order to prevent the magnetic particles from adhering to the surface of the photosensitive drum, and the saturation magnetization is desirably 50 (A · m ² / kg) or more.

For the measurement of the magnetic properties of the magnetic particles, a DC magnetization BH characteristic automatic recording apparatus BHH-50 manufactured by Riken Denshi Co., Ltd. can be used. At this time, the diameter (inner diameter) is 6.5 m
m, magnetic particles in a cylindrical container with a height of 10 mm
The filling is performed at about g weight, and the saturation magnetization is measured from the BH curve of the container while keeping the magnetic particles from moving in the container.

Actually, the magnetic particles used in this example had a volume average particle size of 30 μm and an apparent density of 2.0 g / cm 2.
² ], resistance value 1 × 10 ⁶ Ω, saturation magnetization 58 (A · m ² /
kg).

The apparent density of the magnetic particles is JIS Z25041.
Performed according to the method described.

Further, the particle size of the magnetic particles affects charging ability and uniformity of charging. That is, if the particle size is too large, the contact ratio with the surface of the photosensitive drum decreases, which causes charging unevenness.
If the particle size is small, both charging ability and uniformity are improved,
Adhesion to the photosensitive drum surface is likely to occur. Therefore, a magnetic particle having a diameter of 5 to 100 μm is preferably used.

The volume average particle diameter of the magnetic particles is represented by the maximum chord length in the horizontal direction, and the measurement was carried out by randomly selecting 300 or more magnetic particles by a microscope, measuring the diameter, and taking the arithmetic average. .

(3) Gap L, magnetic poles N1, S1, N2, S
2. Magnetic particle regulating position α, etc. a) The gap L between the facing position of the sleeve 1 and the photosensitive drum 7
[Cm] is 0.05 cm (500 μm) in this embodiment.

If L is too small, leakage to the photoreceptor is likely to occur, and if L is too large, the charging ability will decrease. L shows generally good chargeability in the range of 0.01 [cm] to 0.2 [cm].

B) The non-rotating / fixed magnet roller 2 as a magnetic field generating means which is substantially concentrically inserted into and contained in the sleeve 1 is a four-pole magnet roller in this embodiment. Magnetic poles N1, S1, N2, S of this magnet roller
2, the magnetic flux density on the sleeve 1 of the main pole N1 (first magnetic pole) positioned substantially corresponding to the facing position between the sleeve 1 and the photosensitive drum 7 is 800 × 10 3 in this embodiment.
^-4 [T].

If the magnetic flux density of the main pole N1 is too small, magnetic particles will adhere to the photosensitive drum 7, and if it is too strong, the magnetic particles will stagnate in the charging nip portion a.
For this reason, the magnetic flux density of the main pole N1 is 600 to 120
0 × 10 ⁻⁴ [T] is preferable.

The angle θ _{3 of the} main pole N1 facing the photosensitive drum 7 (hereinafter referred to as the main pole position angle), that is, the rotation center axis O ₁ of the sleeve 1 and the closest position between the sleeve 1 and the photosensitive drum 7 are connected. angle between the straight line c connecting the straight line b (= a line connecting the rotation center axis O ₇ of the rotation center axis O ₁ and the photosensitive drum 7 of the sleeve 1), the rotation center axis O ₁ and the main pole N1 of the sleeve 1 they θ ₃ is preferably −10 ° ≦ θ ₃ ≦ 5 °, with the straight line b as a boundary (0 °), plus the upstream side in the sleeve rotation direction and the downstream side as minus.

Outside this range, the holding power of the magnetic particles in the charging nip portion a becomes insufficient, so that the adhesion of the magnetic particles to the photosensitive drum 7 increases and the conveying force of the magnetic particles becomes insufficient.

In this embodiment, θ ₃ = −5 °, that is, 5 ° is inclined (position shift) downstream of the straight line b in the sleeve rotation direction.

C) The magnetic pole S1 is a second magnetic pole on the magnet roller 2 (hereinafter referred to as a regulating pole), and is located upstream of the main pole N1 in the sleeve rotation direction (the direction opposite to the rotation direction of the sleeve 1). The magnetic pole is adjacent to the pole N1.

The restricting pole S1 is formed in a space formed in the apparatus casing 5 by a space defined by the upper surface of the sleeve 1, the rear surface of the restricting plate 4, and the rear surface of the front wall of the device casing 5. It is located substantially corresponding to the location of the large reservoir of particles.

In this embodiment, the regulating pole S1 is set with respect to the main pole N1.
, Relative to the straight line c connecting the rotation center axis O ₁ and the main pole N1 of the sleeve 1, the angle theta ₁ of the straight line d connecting the rotation center axis O ₁ and the regulating pole S1 of the sleeve 1 (hereinafter, regulating pole position angle ) Are provided in a 90 ° relationship.

The magnetic flux density of the regulating pole S1 on the sleeve 1 was set to 350 × 10 ^-4 [T] in this embodiment. If the magnetic flux density of the regulating pole S1 is too small, the force for transporting the magnetic particles may be insufficient, or the magnetic particles may not be able to be held behind the regulating plate 4; The regulation of the layer thickness of the magnetic particle magnetic brush is not stable, or the magnetic particles are excessively stressed, which causes toner spent on the magnetic particles.

Therefore, the magnetic flux density of the regulating pole S1 is preferably 200 to 1000 × 10 ^-4 [T].

D) The magnetic pole N2 is magnetized on the magnet roller at a position substantially 180 ° opposite to the main pole N1, and the magnetic pole S2 is magnetized on the magnet roller at a position almost 180 ° opposite to the regulating pole S1. , Function as a transport pole of magnetic particles.

E) In this example, the regulating plate 4 is located between the main pole N1 and the regulating pole S1 and the rotation center axis O of the sleeve 1.
₁ , a straight line b connecting the closest position between the sleeve 1 and the photosensitive drum 7, a rotation center axis O _{1 of the} sleeve ₁ and a regulating plate 4
Line e connecting the magnetic particle regulating position α by the lower side edge
Angle θ ₂ (hereinafter referred to as a magnetic particle regulating position angle) is 8
It was arranged at a position of 0 °.

(4) 3d <L <M / p and Prevention of Overflow of Magnetic Particles Under the above-described conditions, the carried amount and charging of the magnetic particles on the sleeve 1 after the non-contact with the photosensitive drum are regulated. Examination of the relationship between the capacities revealed that the charging capacity sharply improved when the supported amount exceeded 0.1 [g / cm ² ].

This is shown in FIG. The vertical axis represents the initial potential convergence rate, which is expressed as a ratio of the initial potential to the convergence potential. The higher the initial potential convergence rate, the higher the charging ability.

Observation of the state of the charging nip portion a at a load of about 0.1 [g / cm ² ] revealed that the load was 0.1 [g / cm ² ].
cm ² ] or more, the magnetic particles were in a packing state (closest packed state) in the charging nip portion a.

As a result, in addition to the magnetic particles being packed most closely in the charging nip portion a, the charging capability sharply increases due to a synergistic effect due to an increase in the charging nip area due to a slight retention of the magnetic particles. I knew it was done.

Further, as a result of investigation under various conditions using several kinds of magnetic particles, when packing of magnetic particles occurs in the charging nip portion a, 3d <L <M / p... 1 L: Gap [cm] between sleeve 1 and photosensitive drum p: Apparent density of magnetic particles [g / cm ³ ] M: Carrying amount of magnetic particles on sleeve 1 after non-contact with photosensitive drum [g / cm ³ ] cm ² ] d: Volume average particle diameter of magnetic particles [cm].

In the region of L <3d, the magnetic particles could not stably pass through the charging nip, and conversely, the magnetic particles became sparse.

Under the conditions of the above equation 1, the magnetic nip is in the state of being most closely packed with the magnetic particles in the charging nip, and the charging ability can be greatly increased.

However, under the condition of Expression 1, the magnetic particles overflowed in the charging nip portion a.

As a result of closely observing the process of the magnetic particle overflow, the magnetic particle overflow was as follows. This will be described with reference to the model diagrams of FIGS.

When the magnetic particles overflow, the sleeve 1
Magnetic particles larger than the amount of magnetic particles per unit time that can pass through the gap L between the photosensitive drums 7, that is, the opposing positions of the sleeve 1 and the photosensitive drum 7, are fixed to the regulating unit, that is, the lower side of the regulating plate 4 and the outer surface of the sleeve 1. Is supplied onto the sleeve 1 from the magnetic particle regulating position α, which is a gap between them.

Therefore, the magnetic particle pool f gradually accumulates in the magnetic brush contact portion, that is, the charging nip portion a with respect to the photosensitive drum 7.
Is formed ((a) → (b)).

This magnetic particle pool f is magnetically restrained and stays, and the operation of the magnetic particles is extremely slow. The magnetic particle pool f grows as the sleeve 1 rotates, and when it grows so as not to be held by the magnetic restraining force, it becomes a magnetic particle overflow g ((b) → (c)).

As a result of studying a method for preventing the magnetic particle overflow g, it was found that the magnetic particle overflow g was suppressed by bringing the regulating plate 4 closer to the charging nip portion a.

[0081] Further, the magnetic particles restriction position angle theta ₂ and main pole position angle theta ₃ using a magnet roller 2 with several restriction pole position angle theta ₁ of the magnetic pole patterns, restriction pole position angle theta _1, their magnetic particles As a result of examining the relationship of the overflow g, it was found that magnetic particles did not overflow under the following conditions.

That is, the regulating plate 4 is arranged between the main pole N1 and the regulating pole S2 on the sleeve 1 and the magnetic particle regulating position angle θ ₂ is 70 ° or less, so that the magnetic particles are It turned out that overflow did not occur.

Table 1 shows the experimental results. In the directionality, the lower limit of the magnetic particle regulating position angle θ ₂ was 20 °, but no overflow of the magnetic particles occurred at the lower limit.

The diameter of the sleeve 1 is 25 in this embodiment.
In addition to 15 mm and 35 mm, the dependence on the diameter of the sleeve 1 was not observed.

[0085]

[Table 1] Here, the reason why the magnetic particles do not overflow due to the above configuration will be described with reference to model diagrams of FIGS.

Under this condition, a magnetic particle pool f is formed in the charging nip a as in the case where the magnetic particles overflow (FIG. 3) ((a) → (b)).

In the vicinity of the magnetic particle pool f, a region where the flow of the magnetic particles is slow is generated by the magnetic particle pool acting as an obstacle to the flow of the magnetic particles.
The flow becomes slower as it approaches the magnetic particle pool f. This can be rephrased that the formation of the magnetic particle pool f acts as a resistance to the flow of the magnetic particles.

The resistance increases as the distance from the magnetic particle pool f increases, and decreases as the distance increases. Also, the resistance increases as the magnetic particle pool f increases, and decreases as the magnetic particle pool f decreases.

The approach of the regulating plate 4 to the magnetic brush contact portion with respect to the photosensitive drum 7, that is, the side of the charging nip a is nothing but placing the regulating plate 4 within a range where the resistance reaches. That is, as the magnetic particle pool f is formed, resistance acts on the magnetic particles near the regulating plate 4, and the amount of magnetic particles per time passing through the magnetic particle regulating position α decreases.

When the amount becomes equal to the amount of magnetic particles per unit time that can pass through the gap L between the sleeve 1 and the photosensitive drum 4, the magnetic particle pool f does not grow. As a result, no overflow of the magnetic particles occurs ((b) → (c)).

[0091] When the magnetic particle overflow g (Fig. 3) is repeated, when the regulating plate 4 is far from the magnetic brush contact portion, that is, the charging nip portion a, a large resistance is applied to the magnetic particle regulating position α. This is because the magnetic particles are released from the magnetic constraint and collapse before the magnetic particle pool f grows.

In this embodiment, a non-magnetic regulating plate 4 is used. However, the regulating plate 4 has the same tendency whether it is a magnetic material or a non-magnetic material with a magnetic plate adhered thereto.

As described above, by bringing the magnetic particle regulating position α closer to the charging nip portion a, it is possible to supply more magnetic particles than the amount of magnetic particles per time that can pass through the gap L between the sleeve 1 and the photosensitive drum 7. become able to. As a result, the magnetic particles enter a packing state in the charging nip portion a, and the charging ability is greatly improved.

In such a state, the supply amount of the magnetic particles is controlled as if it were self-controlled. Therefore, even if the supply amount of magnetic particles changes due to fluctuations in the fluidity of the magnetic particles due to environmental fluctuations, etc., only the amount of accumulated magnetic particles changes, no overflow occurs, and extremely stable charging Becomes possible.

Embodiment 2 (FIG. 5) A flexible member may be used as a regulating member for regulating the amount of magnetic particles carried on the sleeve.

This embodiment is an example, and FIG. 5 is a schematic cross-sectional model diagram of the apparatus.

The magnetic brush charging device A of this embodiment has the same configuration as that of the device A of the first embodiment except that a flexible member is used as the regulating plate. And the description thereof will not be repeated.

Reference numeral 4A denotes a flexible regulating plate. In this embodiment, urethane rubber is formed in a plate shape. The flexible regulating plate 4A is bonded and fixed on a metal support 8, and the metal support 8 is attached to the device casing 5 to be disposed.

In the state without magnetic particles, the flexible regulating plate 4A
Is in contact with or very close to the sleeve 1, but with the rotation of the sleeve 1, the flexible regulating plate 4 </ b> A is bent by the force of the magnetic particles 3 being conveyed, and the magnetic particles Is regulated on the sleeve 1.

The carrying amount of the magnetic particles depends on the contact pressure and distance of the flexible regulating plate 4A against the sleeve 1 or the metal support 8
Can be controlled by changing the length from the end to the tip of the flexible regulating plate 4A.

In this embodiment, the closest position between the flexible regulating plate 4A and the sleeve 1 is defined as the magnetic particle regulating position α on the sleeve.

Similarly to the apparatus A of the first embodiment, in the apparatus of the present embodiment, by satisfying the expression 3d <L <M / p in the above equation 1, the densest state of the magnetic particles is formed at the charging nip portion a. can do. Further, the magnetic particle regulating position θ by the flexible regulating plate 4A for regulating the layer thickness of the magnetic particles.
By adopting a configuration in which ₂ is 70 ° or less, it is possible to prevent the magnetic particles from overflowing at the charging nip portion a.

As described above, even if a flexible material is used for the regulating plate 4A, the magnetic particles are formed in the close-packed state without causing magnetic particles to overflow at the charging nip portion A. Ability can be greatly improved.

In addition, even when the supply amount of the magnetic particles becomes self-regulated and the fluidity of the magnetic particles changes due to environmental fluctuations, etc., stable charging without occurrence of magnetic particle overflow can be performed. .

As the material of the flexibility regulating plate 4A, urethane rubber is used in the present embodiment, but other flexible materials such as a silicon rubber or SUS metal plate can also be used.

<Embodiment 3> (FIGS. 6 to 13) The magnetic particle overflow g (FIG. 3) described in the embodiment 1 is obtained by disposing the regulating plate 4 between the main pole N1 and the regulating pole S2 on the sleeve 1. In addition, it was found that the magnetic flux density at the magnetic particle restricting position α by the restricting plate 4 did not become 400 × 10 ⁻⁴ [T] or less.

Representative results of some of the experiments are shown in Tables 2 to 9. In each of the tables, in the overflow occurrence status column, ○ means no overflow, Δ means small overflow, and × means large overflow.

The graphs in FIGS. 6 to 13 show the magnetic flux density [× 10 ⁻⁴ T] on the sleeve 1 of the magnet roller used as the magnetic field generating means in each experiment.
Tables 2 to 9 respectively correspond to Tables 2 to 9.

[0109] Each table 2, Table 3, restriction pole position angle theta ₁ is is 90 °, the magnetic flux density is 500 × the regulating pole S1
^10-4 and the magnet roller 2 is [T], restriction pole position angle theta ₁ is is 90 °, the magnetic flux density of the regulating pole S1 is 800
The relationship between the magnetic particle regulating position α in the magnet roller 2 of × 10 ⁻⁴ [T] and the occurrence of magnetic particle overflow is shown.

When these results are compared with the magnetic flux densities on the sleeve 1 shown in FIGS. 6 and 7 corresponding to Tables 2 and 3, respectively, the magnetic particle overflow is independent of the magnitude of the magnetic flux density of the regulating pole S1. And the magnetic flux density at the magnetic particle regulating position α is 40
It can be seen that almost no occurrence occurs when the value is 0 × 10 ⁻⁴ [T] or less.

[0111] Table 4 respectively, Table 5 is the restriction pole position angle theta ₁ is 120 °, the magnetic flux density of the regulating pole S1 is 800
× 10 ^-4 magnet roller 2 is [T], restriction pole position angle theta ₁ is 120 °, the magnetic flux density of the regulating pole S1 is 5
The relationship between the magnetic particle regulating position α of the magnet roller 2 which is 00 × 10 ⁻⁴ [T] and the occurrence of magnetic particle overflow is shown.

By comparing these results with the magnetic flux densities on the sleeve 1 shown in FIGS. 8 and 9 corresponding to Tables 4 and 5, respectively, the angle between the main pole N1 and the regulating pole S1, that is, the regulating pole position angle θ _{1 is shown.} Alternatively, it can be seen that the magnetic particles do not overflow when the magnetic flux density at the magnetic particle regulating position α is 400 × 10 ⁻⁴ [T] or less regardless of the magnetic flux density of the regulating pole S1.

[0113] Table 6 - Table 7, Table 8, Table 9 in regulating pole position angle theta ₁ is 90 °, the magnetic flux density of each regulating pole S1 5
This is a result of examining the relationship between the main pole position angle θ ₃ and occurrence of magnetic particle overflow using two magnet rollers 2 of 00 × 10 ⁻⁴ [T] and 800 × 10 ⁻⁴ [T]. Main pole position angle θ
₃ is −10 ° and 15 °.

When these results are compared with the results shown in FIGS. 10 to 13 corresponding to Tables 6 to 9, respectively, the overflow of the magnetic particles at this time also shows that the overflow of the magnetic particles does not depend on the main pole position angle θ ₃ but the magnetic flux at the regulating pole. It can be seen that almost no occurrence occurs when the density is 400 × 10 ⁻⁴ [T].

The above experimental results show that if the magnetic flux density at the magnetic particle regulating position α is 400 × 10 ⁻⁴ [T] or less,
This indicates that the supply force of the magnetic particles can be sufficiently balanced with the resistance force of the magnetic particle pool.

As described above, by setting the magnetic flux density at the magnetic particle regulating position α to 400 × 10 ⁻⁴ [T] or less, it becomes possible to form a magnetic particle pool while preventing magnetic particles from overflowing. In the charging nip portion a, the magnetic particles are in a packing state, and the charging ability is greatly improved.

In such a state, the supply amount of the magnetic particles is in a self-controlled state. Therefore, even if the supply amount of magnetic particles changes due to fluctuations in the fluidity of the magnetic particles due to environmental fluctuations, etc., only the amount of accumulated magnetic particles changes, no overflow occurs, and extremely stable charging Becomes possible.

In this configuration, the lower limit of the magnetic particle regulating position angle θ ₂ is 20 °. However, judging from the experimental results, even if the magnetic particle regulating position angle θ ₂ is less than 20 °, no magnetic particles overflow. This can be inferred.

The diameter of the sleeve 1 was 15 mm and 35 mm in addition to the diameter of 25 mm in this embodiment, but no dependence on the diameter of the sleeve 1 was observed.

In this embodiment, a non-magnetic regulating plate 4 is used. However, the same tendency is exhibited regardless of whether the regulating plate 4 is a magnetic material or a non-magnetic material with a magnetic plate adhered thereto.

Also in the apparatus of the present embodiment, a flexible member 4A is used as a restricting member as a restricting means for restricting the amount of magnetic particles carried on the sleeve, as in the apparatus of the second embodiment. Of course, you can do that.

[0122]

[Table 2]

[0123]

[Table 3]

[0124]

[Table 4]

[0125]

[Table 5]

[0126]

[Table 6]

[0127]

[Table 7] <Embodiment 4> (FIG. 14) FIG. 14 is a schematic configuration diagram of an example of an image forming apparatus using a magnetic brush charging device A according to the present invention as a charging unit for an image carrier.

The image forming apparatus of this embodiment is a copying machine or a laser printer using a transfer type electrophotographic process and a cleanerless system (simultaneous development and cleaning).

Reference numeral 7 denotes an image bearing member. In this embodiment, a photosensitive drum having the same charge injection charge as that of the first embodiment is rotated at a predetermined peripheral speed (process speed) in a counterclockwise direction indicated by an arrow R2. . The photosensitive drum 7 is uniformly contact-charged to a predetermined polarity and potential by a charge injection charging method by a magnetic brush charging device A during the rotation process. The charging device A is, for example, the charging device of the first embodiment.

Next, an image exposure apparatus 11 (not shown) such as an original image slit exposure apparatus or a laser beam scanning exposure apparatus exposes the charged surface of the rotating photosensitive drum 7 to an image exposure 11 of target image information. By doing so, an electrostatic latent image corresponding to the image exposure is formed on the rotating photosensitive drum surface.

Next, the electrostatic latent image is subjected to regular development or reverse development as a toner image by the developing device 12.
12a is a developing roller or a developing sleeve. 12
S is a power supply for applying a developing bias to the developing roller or the developing sleeve.

The toner image is transferred to a transfer section 14 which is a contact nip between the photosensitive drum 7 and the transfer roller 13.
The image is sequentially transferred onto the transfer material P fed to the transfer unit 14 from a sheet feeding mechanism (not shown) at a predetermined timing. 13S is a transfer bias application power supply for the transfer roller.

The transfer material P that has exited the transfer section 14 is separated from the surface of the rotating photosensitive drum 7 and introduced into the fixing device 15, where it is subjected to a fixing process of the transferred toner image and discharged as an image formed product (copy, print). Is done.

The photosensitive drum after the transfer of the toner image onto the transfer material P is repeatedly subjected to image formation. In this case, in the image forming apparatus of the present embodiment, the transfer residual toner remaining on the surface of the photosensitive drum after the transfer of the toner image to the transfer material P reaches the developing device 12 and is collected by the developing device 12 (simultaneous cleaning with development) and developed. Reused as an agent.

The transfer residual toner mixed into the magnetic brush of the magnetic particles of the magnetic brush charging device A is discharged to the photosensitive drum surface naturally or by application of a discharge bias, and is collected by the developing device 12.

In the simultaneous cleaning for development, the transfer residual toner on the photosensitive drum is recovered by a fogging bias (fogging potential difference Vback, which is a potential difference between the DC voltage applied to the developing device and the surface potential of the photosensitive drum) at the time of the subsequent development. How to According to this method, waste toner can be eliminated, and troublesome maintenance can be reduced. In addition, the cleaner-less has a great advantage in terms of space, and the size of the image forming apparatus can be significantly reduced.

However, between the transfer section 14 and the magnetic brush charging device A, a dedicated cleaning device for removing the transfer residual toner from the photosensitive drum surface may be provided.

<Others> 1) The magnetic brush charging device according to the present invention is not limited to the charging means for the image carrier in the image forming apparatus, but can be widely used as the charging means for the charged object.

2) AC is used for charging bias and developing bias, etc.
As a waveform of the AC voltage when a voltage (alternating voltage) is included, a sine wave, a rectangular wave, a triangular wave, or the like can be used as appropriate. Alternatively, a rectangular wave formed by periodically turning on / off a DC power supply may be used. As described above, a bias whose voltage value periodically changes can be used as the waveform of the alternating voltage.

3) The image carrier of the image forming apparatus may be an electrostatic recording dielectric or the like. In this case, after the dielectric surface is primarily charged to a predetermined polarity and potential, the charge is selectively removed by a charge removing means such as a charge removing needle head or an electron gun to write and form a target electrostatic latent image.

The image forming apparatus may be a direct type apparatus that forms an image directly on photosensitive paper (electrofax paper) or electrostatic recording paper without transferring.

[0142]

As described above, according to the present invention, in the magnetic brush charging apparatus, the closest state of the magnetic particles can be formed at the charging nip, that is, the surface of the charged body at the charging nip can be formed. And the chance of contact with the magnetic particles constituting the magnetic brush can be increased, and the charging ability can be greatly improved.

Further, it is possible to prevent the magnetic particles from overflowing at the charging nip.

Therefore, the closest packed state of the magnetic particles can be formed in the charging nip portion without overflowing the magnetic particles, and the charging ability can be improved. Furthermore, in such a configuration, the supply of the magnetic particles is in a state of being self-regulated, so that even if the fluidity of the magnetic particles changes due to environmental fluctuations, etc., stable charging without magnetic particle overflow occurs. Can be executed.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional schematic view of a magnetic brush charging device according to a first embodiment.

FIG. 2 is a graph showing the relationship between the amount of magnetic particles carried on a sleeve and the potential convergence rate.

FIG. 3 is an explanatory model diagram when magnetic particles overflow.

FIG. 4 is a schematic diagram for explaining a case where no overflow of magnetic particles occurs.

FIG. 5 is a schematic cross-sectional model diagram of a magnetic brush charging device according to a second embodiment.

FIG. 6 is a graph showing the relationship between the magnetic flux density at the magnetic particle regulation position and the state of occurrence of magnetic particle overflow (part 1).

FIG. 7 is a graph showing the relationship between the magnetic flux density at the magnetic particle regulating position and the state of occurrence of magnetic particle overflow (part 2).

FIG. 8 is a graph showing the relationship between the magnetic flux density at the magnetic particle regulating position and the state of occurrence of magnetic particle overflow (part 3).

FIG. 9 is a graph showing the relationship between the magnetic flux density at the magnetic particle regulating position and the state of occurrence of magnetic particle overflow (part 4).

FIG. 10 is a graph showing the relationship between the magnetic flux density at the magnetic particle regulating position and the state of occurrence of magnetic particle overflow (part 5).

FIG. 11 is a graph showing the relationship between the magnetic flux density at the magnetic particle regulating position and the state of occurrence of magnetic particle overflow (part 6).

FIG. 12 is a graph showing the relationship between the magnetic flux density at the magnetic particle regulating position and the state of occurrence of magnetic particle overflow (part 7).

FIG. 13 is a graph showing the relationship between the magnetic flux density at the magnetic particle regulating position and the state of occurrence of magnetic particle overflow (part 8).

FIG. 14 is a schematic configuration diagram of an image forming apparatus according to a fourth embodiment.

[Explanation of symbols]

A magnetic brush charging device 1 rotating sleeve 2 fixed magnet roller (magnetic field generating means) N1 first magnetic pole (main pole) S1 second magnetic pole (regulating pole) 3 magnetic brush of magnetic particles or magnetic particles 4.4A regulating plate 5 apparatus casing 6 charge bias application power source 7 the photoconductive drum (member to be charged, the image bearing member) a charging nip L sleeve and the opposite position of the photosensitive drum gap α regulating plate and the sleeve gap (magnetic particle regulating position) theta ₁ regulation Polar position angle θ ₂ Magnetic particle regulating position angle θ ₃ Main pole position angle

Claims (9)

[Claims] 1. A rotating sleeve, magnetic field generating means included in the sleeve, conductive magnetic particles magnetically constrained as a magnetic brush on the sleeve by the magnetic field generating means, and constrained on the sleeve A magnetic brush charging device that has a regulating unit that regulates the amount of the conductive magnetic particles carried, and charges the charged object by bringing the conductive magnetic particles into contact with the charged object; Is defined as L [cm], the apparent density of the conductive magnetic particles is p [g / cm ³ ], and the control means is used when the conductive magnetic particles on the sleeve are not in contact with the member to be charged. When the carrying amount of the conductive magnetic particles on the sleeve after performing the above is M [g / cm ² ] and the volume average particle size of the conductive magnetic particles is d [cm], 3d <L <M / p, and when the member to be charged is in contact with the member to be charged, Wherein the amount of the conductive magnetic particles passing through the contact portion and the amount of the conductive magnetic particles passing through the regulating portion are always in an equilibrium state. 2. The magnetic field generating means, wherein at least a first magnetic pole at a position facing the member to be charged and a second magnetic pole different from a first magnetic pole adjacent in a direction opposite to a rotation direction of the sleeve. A regulating position of the regulating means is located between the first magnetic pole and the second magnetic pole, and a straight line connecting the regulating position and the rotation center of the sleeve; 2. The charging device according to claim 1, wherein an angle between a straight line connecting the position and the rotation center of the sleeve is set to 70 ° or less. 3. The magnetic field generating means, wherein at least a first magnetic pole at a position facing the member to be charged and a second magnetic pole different from a first magnetic pole adjacent in a direction opposite to a rotation direction of the sleeve. The restricting position of the restricting means is located between the first magnetic pole and the second magnetic pole, and the magnetic flux density by the magnetic field generating means at the restricting position is 400 × 10 ^-4 [T] or less. The charging device according to claim 1, wherein: 4. The charging device according to claim 1, wherein said restricting means is made of a rigid body. 5. The charging device according to claim 1, wherein said regulating means is made of a material exhibiting flexibility. 6. The image forming apparatus according to claim 1, wherein the member to be charged is an image carrier in the image forming apparatus, and has a charge injection layer on its surface or is chargeable and chargeable. 3. The charging device according to claim 1. 7. The charging device according to claim 6, wherein the charge injection layer is made of a resin in which conductive fine particles are dispersed. 8. The charging device according to claim 6, wherein the charge injection layer is made of amorphous silicon. 9. An image forming apparatus for performing image formation by applying an image forming process including a step of charging the image carrier to the image carrier, wherein the means for charging the image carrier is provided. An image forming apparatus, comprising: the charging device according to any one of 8.