JPH1048954A - Magnet roll - Google Patents

Abstract

PROBLEM TO BE SOLVED: To downsize a developing device and improve the developing performance by providing magnetic poles, which extends in parallel to the axis, in such a state as arranging the N, S alternatively in the circumferential direction on a permanent magnet member formed into a cylindrical shape and providing, at least, a resin layer of a specific thickness containing conductive particles around the circumferential face. SOLUTION: A permanent magnet member 4 is formed of a semiconducting or insulating, for example, isotropic ferrite magnet, and a plurality of magnet poles extending axially are provided around the outer circumferential face, formed into a cylindrical shape, and rotatably provided in the bottom of a developer tank 1. A resin layer containing conductive particles is coveringly stuck on the surface of this permanent magnet member 4. Namely, the magnetic poles extending in parallel to the axis are provided with their N, S arranged alternately on the permanent magnet member 4, which is fanned into a cylindrical shape, and, at least, the resin layer of 10-1000μm in thickness and containing the conductive particles is coveringly stuck to the circumferential face. This constitution can provide an image without any fogging, dust, fine line, and density ununiformity even in using a small-size developer support means having a structure of no sleeve.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface of a developer supporting means comprising a permanent magnet member integrally formed in a cylindrical shape with an electrostatic charge image formed on the surface of an image carrying means for carrying an electrostatic image. The present invention relates to a magnet roll that constitutes a developing device that performs development using a magnetic developer that is attracted and held on a magnetic roll, and particularly relates to a magnet roll that can prevent fog and uneven density even in continuous printing and improve developability. Things.

[0002]

2. Description of the Related Art Conventionally, in an image forming method using electrophotography or electrostatic recording, an electrostatic charge image formed on a surface of an image carrier made of a photoconductor or a dielectric is incorporated into, for example, a permanent magnet member. At the same time, a developing means comprising a sleeve which is rotatably fitted to the permanent magnet member is used, and is rubbed with a so-called magnetic brush made of a magnetic developer to develop a toner image. Next, the toner image is directly fixed, or the toner image is transferred onto a transfer sheet such as plain paper and then fixed to obtain a final image.

FIG. 3 is a cross-sectional view of an essential part showing an example of a conventional developing method. In FIG. 3, reference numeral 1 denotes a developer tank, which accommodates a magnetic developer 2 and has a plurality of permanent magnets 3 provided below the permanent magnet member 4 and a columnar permanent magnet member 4, and a nonmagnetic metal material (for example, SUS304). The developing roller 6 is configured so as to be coaxially rotatable relative to the sleeve 5 formed into a hollow cylindrical shape.

Reference numeral 7 denotes a photosensitive drum, which is rotatable in the direction of the arrow, and faces the developing roll 6 with a gap g therebetween. Reference numeral 8 denotes a doctor blade, which is provided in the developer tank 1 and faces the developing roll 6 via a gap t to regulate the layer thickness of the magnetic developer adsorbed on the sleeve 5. Reference numeral 9 denotes a DC power supply, which is connected between the photosensitive drum 7 and the sleeve 5 and applies a bias voltage. The gap g is formed slightly larger than the gap t.

With the above arrangement, when the permanent magnet member 4 is fixed and the sleeve 5 is rotated in the direction of the arrow, the magnetic developer 2 is adsorbed on the sleeve 5 and conveyed, and the developing area facing the photosensitive drum 7 Is reached, the electrostatic image formed on the photosensitive drum 7 and the electric field due to the bias cause
The magnetic developer 2 overcomes the attraction force of the permanent magnet member 4 to the sleeve 5 and transfers. Thereby, the electrostatic charge image can be developed.

[0006]

In the above-described developing method, the outer peripheral surface of the sleeve 5 attracts the magnetic developer 2 by the magnetic attraction force of the permanent magnet member 4 and conveys it by the frictional force. In order to improve the transportability, the surface roughness is usually increased by, for example, blasting. However, there is a problem that the wear proceeds, the coefficient of friction changes, or a local change occurs during use, so that the layer thickness of the magnetic developer 2 adsorbed changes and the developability decreases.

Since the developing roll 6 which adsorbs and supports the magnetic developer and conveys it is constituted by coaxially combining the permanent magnet member 4 and the sleeve 5, the processing and assembly are complicated and the production is complicated. There is a problem that the cost increases.

In order to reduce the size of a printer or the like, a developing method of omitting the sleeve 5 constituting the developing roll 6, using only the permanent magnet member 4 in a rotating state, and developing an electrostatic charge image by a magnetic brush method is proposed. (See, for example, JP-A-62-201463). In such a developing method, about half the height of the magnetic brush made of a magnetic developer comes into contact with the surface of the photosensitive drum 7.

However, in the magnetic brush developing method in which the sleeve 5 is omitted as described above, there is a difference in the height and developability of the magnetic brush between the magnetic poles of the permanent magnet member 4 and between the magnetic poles. There is a problem that image quality is deteriorated, especially when a halftone image is developed. On the other hand, if the number of revolutions of the permanent magnet member 4 is increased to eliminate the above-described density unevenness, the drive torque is increased and noise is generated, which is not preferable.

Therefore, the peripheral speed Vm of the permanent magnet member 4 is about 1.5 times Vp of the peripheral speed Vp of the photosensitive drum 7.
Usually, it is set to be twice or more. However, since the magnetic developer adsorbed and supported on the surface of the permanent magnet member 4 constantly rubs the surface of the photosensitive drum 7, the image becomes a state in which the magnetic developer is swept in the rotation direction of the permanent magnet member 4. However, there is a disadvantage that a high quality image cannot be obtained.

In order to solve the above-mentioned drawback, the speed ratio between the moving speed of the magnetic developer and the photosensitive drum 7 is set to 1 to 5.
It has been proposed to be less than 1.9 (JP-B-63-399).
No. 10, JP-A-6-274025). However, all of these proposals have a configuration in which a permanent magnet member and a sleeve are coaxially combined,
As described above, there is a problem that processing and assembly are complicated. Particularly, in the former, since both the magnet and the non-magnetic cylinder are configured to rotate, there is a disadvantage that the configuration of the drive system is further complicated and it is difficult to reduce the size.

As described above, the peripheral speed V of the permanent magnet member 4 is
When m is increased, especially in the case of an image having a solid black portion, there is a problem that the density at the rear end portion becomes high and density unevenness occurs.

Further, the sleeve 5 is omitted, and the permanent magnet member 4
For example, in the case of a type formed by using a ferrite magnet, there is a problem that the development current is difficult to flow in the development region and the developability is low because the electric resistance of the ferrite magnet is high. As a countermeasure, there is a method of providing a plating layer made of a conductive material on the surface of the permanent magnet member 4,
Since the thickness of the plating layer is usually small, there is a problem that it is not possible to eliminate the density unevenness of the image when the deflection of the permanent magnet member 4 is large.

Recently, there has been a tendency to reduce the particle size of toner in order to improve the quality of electrophotography. For example, fine particles having an average particle size of 4.5 to 8 μm have been used. However, since such fine particles have a large surface area per volume, the amount of charge due to triboelectric charging per mass becomes larger (charge-up) as compared with those having a large particle size, and the mirror itself has a large size. The image is strongly restrained by the surface of the developing roll. For this reason, the toner existing on the portion where the fine particle layer is formed cannot be sufficiently triboelectrically charged with the developing roll, so that it is difficult for the toner to adhere to the electrostatic image formed on the image carrier, and the developing property is deteriorated. There is a problem that. This phenomenon is noticeable when continuous printing is performed.
Fog and density unevenness occur.

The present invention solves the above-mentioned problems in the prior art, can reduce the size of the developing device, and can prevent the occurrence of fog and uneven density even in continuous printing, thereby improving the developability. It is an object to provide a magnet roll.

[0016]

In order to solve the above-mentioned problems, in the present invention, magnetic poles extending parallel to the axis are provided alternately in the circumferential direction on a permanent magnet member formed in a cylindrical shape, and the magnetic poles are alternately arranged in a circular direction. Thickness containing at least conductive particles on the peripheral surface 10
The technical means of applying a resin layer of ~ 1000 µm was employed.

The permanent magnet member in the present invention is not limited to a ferrite magnet, but may be a resin magnet containing magnetic powder and a resin material as main components. Also, this permanent magnet member
The magnet may be integrally formed in a roll shape on the outer periphery of the shaft, or may be formed entirely of a magnet material including the shaft. However, in order to prevent development unevenness, the permanent magnet member preferably has no joint in the circumferential direction and the axial direction, and is preferably integrally formed as a whole.
The permanent magnet member is preferably formed to have a diameter of 6 to 30 mm in order to reduce the size of the developing device.

On the surface of the permanent magnet member, magnetic poles of different polarities are alternately arranged in the circumferential direction at minute intervals, so that as the number of magnetic poles increases, the surface magnetic flux density decreases. On the other hand, from the viewpoint of preventing the magnetic developer from scattering, the surface magnetic flux density of the permanent magnet member is preferably 200 G or more, and 800 G in order to make it easier for the toner to adhere to the electrostatic image formed on the surface of the image carrier. The following is preferred. The pitch between the magnetic poles on the surface of the permanent magnet member is the above-mentioned surface magnetic flux density 2
Range corresponding to 00 to 800 G, ie, pitch between magnetic poles
Preferably it is 1.0 to 3.0 mm.

Next, in the present invention, when a bias voltage is applied, it may be applied directly from the resin layer,
The voltage may be applied from the resin layer via a shaft having at least a surface made conductive. Alternatively, the voltage may be applied from a doctor blade. In this case, the doctor blade may be formed of a conductive material such as a metal.

As the bias voltage, a DC voltage alone or a DC voltage and an AC voltage are superimposed and applied. The AC voltage to be superimposed on the DC voltage has a lower frequency than that of a commonly used 500 to 1000 Hz. Are good, the number of magnetic poles of the permanent magnet member is M, and the peripheral speed is Vm (mm /
Second), f = M · Vm / π · determined by the diameter D (mm)
D (Hz), and the peak-to-peak voltage _Vpp is 1
It is good to be 00-800V.

Next, in the present invention, as a resin material constituting the resin layer to be adhered to the surface of the permanent magnet member, thermoplastic resin such as polyamide, polycarbonate, polyphenylene sulfide, acrylic, etc., melamine, phenol, silicone, etc. Thermosetting resin can be used.

The resin layer has a thickness of 10 to 1000 μm, preferably 50 to 20 μm, in consideration of adherence and durability.
It is formed to 0 μm. That is, if the thickness is less than 10 μm, it is easy to peel off, and the stability is poor. Therefore, it is not preferable.

Next, the surface roughness of the resin layer (10-point average roughness defined by JIS B 0601 and represented by symbol Rz) is 1 to 30 μm.
However, if it is out of this range, the transport amount of the magnetic developer to be absorbed and transported to the surface is not an appropriate value, and it is not preferable because it tends to cause fog and ghost.

The resin layer contains conductive particles,
It is preferable that the electric resistance is formed to 10 ³ to 10 ⁶ Ω. That is, when the electric resistance is less than 10 ³ Ω, the amount of conductive particles increases, and the adhesive strength to the surface of the permanent magnet member decreases, which is not preferable. On the other hand, the electric resistance is 10 ⁶ Ω
When the value exceeds, the charge hardly leaks, and the toner is excessively charged, so that it is difficult to separate from the developing roll, which causes a decrease in image density and a ghost, which is inconvenient.

FIG. 2 is an explanatory view showing a means for measuring the electric resistance of the resin layer adhered to the surface of the permanent magnet member 4. In FIG. 2, reference numeral 12 denotes a measuring terminal, which is 1
The permanent magnet member 4 is formed on the surface of the resin layer of
Attach at mm intervals. Note that the measurement terminal 12 may be formed of another conductive material, and may be detached by a jig or the like.

A DC power source 1 is connected between the measuring terminals 12 and 12.
Voltage V (volt) when a current of 3 to 100 μA flows
Is measured, and the electric resistance R is calculated from this voltage. That is, R = (V / 100) × 10 ⁶ = 10 ⁴ V (Ω).

As the conductive particles to be contained in the resin layer, carbon black, carbon fiber, metal powder and the like can be used.
The amount is preferably 0 to 150 parts by weight. These conductive particles have a particle size of 0.1 from the viewpoint of dispersion in the resin layer and characteristics.
The thickness is preferably from 10 to 10 μm. As means for forming a resin layer of a resin material containing these conductive particles,
Known means such as a spray method and a powder coating method can be applied.
Note that a charge control agent and the like can be added to the resin layer as needed.

In the case where the fluctuation of the circumferential surface when rotating the permanent magnet member, the variation in the layer thickness when coating the resin layer, etc. appear in the image, or the case where high image quality is required, the resin is used. After the formation of the layer, a part of the resin layer is polished on the outer periphery with reference to the axis, so that run-out and the like can be suppressed to an extremely small value. The surface roughness of the resin layer can be adjusted by the polishing conditions such as the roughness of the grindstone, the depth of cut, the feed rate, etc. during the outer peripheral polishing. Further, a charge control agent and the like can be added to the resin layer as needed.

In the present invention, the magnetic developer includes not only a magnetic toner but also a mixed powder of a magnetic toner and a magnetic carrier (toner concentration of 10 to 90% by weight) and a mixed powder of a non-magnetic toner and a magnetic carrier. A powder (toner concentration of 5 to 60%) can be used.

When a two-component developer is used as the magnetic developer, a developer adjusted to a predetermined toner concentration is charged into the developer tank, or a carrier is adhered to the surface of the permanent magnet member. Then, only the toner may be supplied into the developer tank. This eliminates the need for the toner density control means, and can reduce the size of the developing device.

As a carrier constituting the magnetic developer,
Magnetic particles having an average particle size of 10 to 150 μm (eg, iron powder, ferrite, magnetite, and binder-type particles in which the magnetic powder is dispersed in a resin) can be used. Note that the carrier is preferably a flat carrier rather than a spherical carrier because carrier adhesion hardly occurs.

Further, the average particle size of the carrier is 10 to 100 μm.
m is preferred. This is because when the average particle diameter is 100 μm or less, a sufficient charge amount of the toner can be obtained, but when the average particle diameter is smaller than 10 μm, carrier adhesion easily occurs.

The carrier may be a mixture of two or more of the above magnetic particles. For example, the average particle size is 60 to 120.
magnetic particles having a large particle diameter of μm and an average particle diameter of 10 to 50 μm
And magnetic particles having an average particle diameter of 10 to 5
It may be mixed with binder type magnetic particles having a small particle size of 0 μm. The mixing ratio may be determined in consideration of the size and magnetic characteristics of the magnetic particles.

Next, the toner to be mixed with the carrier has a volume resistivity of 10 ¹⁴ Ω from the viewpoint of improving transferability.
Insulating material having a size of not less than cm is preferable, and a material which is easily charged by friction between the carrier and the doctor blade (the frictional charge amount is 10 μc / g or more in absolute value) is preferable.

The composition of the toner is the same as that of a commonly used toner, such as a binder resin (styrene-acrylic copolymer, polyester resin, etc.), a colorant (carbon black, etc., but using magnetite as a magnetic powder described later). In some cases, it may not be added) as essential components, and as optional components, magnetic powder (magnetite, soft ferrite, etc.), charge control agent (nigrosin, metal-containing azo dye, etc.), release agent (polyolefin, etc.), Those containing (internally and / or externally) a fluidizing agent (hydrophobic silica) can be used.
In the case of using a magnetic toner, if the amount of the magnetic powder is small, toner scattering increases, while if the amount of the magnetic powder is large, the fixing property is deteriorated. By appropriately selecting a coloring agent, a color toner can be produced.

The above magnetization was measured using a vibrating sample magnetometer (VSM-3 manufactured by Toei Kogyo Co., Ltd.), and the average particle size (volume) of the toner was measured using a particle size analyzer (Coulter Electronics Co., Ltd.). It was measured using a counter model TA-II).

The volume specific resistance was determined by filling an insulated resistance meter (10 g or more) with a Teflon (trade name) cylinder having an inner diameter of 3.05 mm and applying a load of 100 gf under an electric field of DC 4 KV / cm. Yokogawa Hewlett Packard 432
9A). Furthermore, the amount of triboelectric charge can be measured using a commercially available blow-off triboelectric charge meter (TB, manufactured by Toshiba Chemical).
-200 type), toner concentration 5% (ferrite carrier as standard carrier (Hitachi Metal KBN-100))
Is used).

According to the above configuration, even if a small developer supporting means having no sleeve is used, a high quality image free from background fog, dust, fine line unevenness and density unevenness can be developed. You can.

[0039]

FIG. 1 is a cross-sectional view of an essential part showing an example of a developing means in an embodiment of the present invention, and the same parts are denoted by the same reference numerals as in FIG. In FIG. 1, the permanent magnet member 4 is formed of a semiconductive or insulating, for example, isotropic ferrite magnet having a volume resistivity exceeding 10 ⁶ Ω · cm, and a plurality of magnetic poles extending in the axial direction are provided on the outer peripheral surface.
It is formed in a cylindrical shape, and is provided rotatably below the developer tank 1. Then, a resin layer (not shown) containing conductive particles is applied to the surface of the permanent magnet member 4.

The DC power supply 9 is connected between the doctor blade 8 and the photosensitive drum 7 and is connected between the magnetic developer 2 attracted and conveyed to the surface of the permanent magnet member 4 and the photosensitive drum 7. An alternating electric field in which an AC bias is superimposed on a bias is formed so as to be applied.

[0041]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The results of image formation using a magnetic developer 2 obtained by mixing a magnetic toner and a magnetic carrier with the developing means constructed as described above will be described.

First, the magnetic toner is a styrene-acryl n-butyl methacrylate copolymer (Mw = 21) in weight ratio.
10,000 parts, Mn = 16,000) 57 parts, magnetic powder (Toda Kogyo E
PT500) 40 parts, polypropylene (T Sanyo Chemical T
P32) 2 parts and a charge controlling agent (Bontron E81 manufactured by Orient Chemical Co.) are mixed, heated and kneaded, cooled and solidified, pulverized and classified to form an average particle diameter of 10 μm. Agent (made by Nippon Aerosil)
R972) 0.5 part was externally added. Volume resistivity is 5 × 10
¹⁴ Ω · cm and the triboelectric charge amount was −22 μc / g.

Next, as a magnetic carrier, a ferrite carrier coated with a silicone resin (KBN-
100) to form an average particle size of 50 μm. The volume resistivity was 10 ⁸ Ω · cm. The volume resistivity is the same as that of the toner described above (however, DC 100 V / cm
In an electric field of

The magnetic toner and the magnetic carrier were mixed to prepare a magnetic developer having a toner concentration of 50% by weight. On the other hand, the photosensitive drum 7 is formed by OPC and has a surface potential of -600.
V, the peripheral speed was 60 mm / sec. Permanent magnet member 4 is made of ferrite magnet (YBM-3 manufactured by Hitachi Metals) and has an outer diameter of 30 m.
m, formed for A4 size. Next, epoxy resin 100
After melting and kneading 23 to 50 parts by weight of carbon black, the mixture is cooled, solidified and pulverized to obtain a powder having a diameter of 10 to 40 μm.
To a thickness of 50 to 1000 by heat treatment.
A μm resin layer was formed. Thereafter, the run-out was reduced to 0.03 mm or less by polishing the outer periphery. The permanent magnet member 4 is magnetized with 30 magnetic poles at equal intervals in the circumferential direction, and has a surface magnetic flux density of 5 poles.
00G. As comparative examples, those having no resin layer and those having a thickness of 1200 μm were prepared.

Next, the developing gap (g) was set to 0.4 mm and the doctor gap (t) was set to 0.3 mm, and a DC bias voltage of -500 V was applied from the doctor blade 8 made of brass. In this case, it is preferable that gt = 0.2 ± 0.15 mm from the viewpoint of image quality. Table 1 shows the corona-transferred image after development.
9 is a table showing the results of image evaluation when heat roll fixing is performed at a temperature of 180 ° C. and a linear pressure of 1 kg / cm. The environment for development and fixing was 20 ° C. and 60% R.F. H. Met.

[0046]

[Table 1]

In Table 1, W,
C indicates that the rotation direction of the permanent magnet member 4 is counterclockwise and clockwise in FIG. The peripheral speed ratio is
The ratio of the peripheral speed of the permanent magnet member 4 to the peripheral speed of the photosensitive drum 7 is shown.

As is clear from Table 1, in No. 1, since the surface of the permanent magnet member 4 lacks a conductive resin layer, not only the image density is low but also the fog
Density unevenness and carrier adhesion have occurred.

Next, in No. 13, the surface magnetic flux density was lowered because the resin layer was too thick, and fog and carrier adhesion occurred. In No. 12, although the image density was good, the surface magnetic flux density was rather low, and fogging and carrier adhesion were slightly observed, indicating that the thickness of the resin layer was at its limit.

On the other hand, in Nos. 5 and 6, since the electric resistance of the resin layer was large, not only the image density was low, but also the occurrence of fog and density unevenness was observed. In contrast, in Nos. 2 to 4 and Nos. 7 to 11, high quality images free from fog, density unevenness and carrier adhesion were obtained.

[0051]

Since the present invention has the configuration and operation as described above, the following effects can be obtained.

(1) Since only the permanent magnet member is used as a component of the developing roll, the size of the developing device can be reduced, and the size of the entire image forming apparatus can be reduced. (2) Since the conductive resin layer is applied to the surface of the permanent magnet member, charge-up of the toner is prevented, and a high-quality image free from fog and density unevenness is obtained even in continuous printing.

(3) A stable high-quality image can be obtained even when the developing gap is increased. (4) Since the toner concentration in the magnetic developer can be set in a wide range, there is no need to use, for example, a toner concentration control means, and the entire apparatus can be made compact.

[Brief description of the drawings]

FIG. 1 is a main part cross-sectional view showing an example of a developing unit in an embodiment of the present invention.

FIG. 2 is an explanatory view showing a means for measuring electric resistance of a resin layer adhered to the surface of a permanent magnet member 4;

FIG. 3 is a cross-sectional view of a main part showing an example of a conventional developing method.

[Explanation of symbols]

 4 Permanent magnet member 7 Photoconductor drum

Claims (2)

[Claims] 1. A cylindrical permanent magnet member having magnetic poles extending parallel to an axis alternately arranged N and S in a circumferential direction, and having a thickness of at least 10 to 100 containing at least conductive particles on a circumferential surface.
A magnet roll having a resin layer of 0 μm applied thereon. 2. The magnet roll according to claim 1, wherein the outer periphery of the applied resin layer is polished on an axis basis.