JPH08272155A - Developing method - Google Patents

Abstract

PURPOSE: To establish a developing method which permits small constructing of an image forming device and allows formation of an image of high quality. CONSTITUTION: An electrostatic charge image on an image carrier 7 to bear an electrostatic charge image and move is developed using a magnetic developer. With this method of development, a developer supporting means has a permanent magnet 4 which is capable of elastic deformation, furnished at the surface with a plurality of magnetic poles, has a specific volume resistivity of 10<7> Ω.cm or less, and is shaped in a single piece cylindrically together with a binder consisting at least of magnetic substance powder, electroconductivity agent, and organic polymeride. Therein the condition Vm=(0.8-1.2)Vp should be met, where Vp is moving speed of the carrier 7 while Vm is peripheral linear speed of the permanent magnet 4, and the magnetic developer 2 containing an insulative toner is adsorbed to the surface of the developer supporting means and transported to the region of development, and the permanent magnet 4 is contacted with the surface of the image carrier 7 through the magnetic developer 2 while the peripheral linear speed of the developer supporting means is made approx. equal to the moving speed of the carrier 7, and the electrostatic charge image thereon 7 is turned apparent.

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 composed of a permanent magnet member integrally formed in a cylindrical shape with an electrostatic charge image formed on the surface of an image carrying means carrying an electrostatic charge image. The present invention relates to a developing method of developing using a magnetic developer adsorbed and held on.

[0002]

2. Description of the Related Art Conventionally, in an image forming method using electrophotography or electrostatic recording, an electrostatic charge image formed on the surface of an image carrier made of a photoconductor or a dielectric is built in, for example, a permanent magnet member. At the same time, a developing means consisting of a sleeve which is inserted into the permanent magnet member so as to be rotatable relative to the permanent magnet member is used, and the toner image is developed by rubbing with a so-called magnetic brush made of a magnetic developer. Then, this 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. However, in the magnetic brush method, the magnetic brush made of a magnetic developer contacts not only the image portion forming the electrostatic charge image but also the non-image portion, so that the background fog is likely to occur. Therefore, a means for applying a DC bias or an electric field in which a DC bias is superimposed on an AC bias is used between the image carrier and the sleeve.

FIG. 2 is a lateral cross-sectional view of a main part showing an example of a conventional developing method. In FIG. 2, reference numeral 1 denotes a developer tank, which contains a magnetic developer 2 and is provided with a plurality of permanent magnets 3 below it to form a columnar permanent magnet member 4 and a non-magnetic metal material (for example, SUS304). A developing roller 6 is provided that is coaxially and relatively rotatable with the sleeve 5 formed in a hollow cylindrical shape.

Reference numeral 7 denotes a photosensitive drum, which is rotatably formed in the direction of the arrow and is opposed to the developing roller 6 with a gap g. Reference numeral 8 denotes a doctor blade, which is provided in the developer tank 1 and faces the developing roll 6 with a gap t therebetween to regulate the layer thickness of the magnetic developer adsorbed on the sleeve 5 constituting the developing roll 6. Is. Reference numeral 9 is an AC power source, 10 is a DC power source, and the photosensitive drum 7 and the doctor blade 8 are provided.
It is for connecting between and applying a superimposed bias of direct current and alternating current. The gap g is formed slightly larger than the gap t.

With the above construction, 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 onto the sleeve 5 and conveyed, and the developing area facing the photosensitive drum 7 is formed. Then, due to the electric field of the electrostatic charge image formed on the photosensitive drum 7, the magnetic developer 2 overcomes the attraction force of the permanent magnet member 4 to the sleeve 5 and is transferred. This allows the electrostatic charge image to be developed.

[0006]

In the developing method as described above, 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 friction force. In order to improve the transportability, it is usual that the surface roughness is made large by, for example, blasting. However, there is a problem in that the layer thickness of the magnetic developer 2 to be adsorbed changes due to the progress of wear during use, the change in the friction coefficient, or the local change, and the developability decreases.

Since the developing roll 6 for adsorbing and supporting the magnetic developer and conveying the magnetic developer is constructed by coaxially combining the permanent magnet member 4 and the sleeve 5, the processing and assembling are complicated and the manufacturing process is difficult. There is a problem that the cost increases.

Therefore, in order to downsize the printer and the like, the sleeve 5 constituting the developing roll 6 is omitted, and only the magnetic roller having at least its peripheral surface formed of conductive rubber in which magnetic powder is uniformly dispersed is rotated. There has also been proposed one which is used and develops an electrostatic charge image by a magnetic brush method (see, for example, JP-A-53-42738).

In the above-mentioned proposal, when the moving speed of the magnetic toner due to the rotation of the magnetic roller is equal to the moving speed of the surface of the photosensitive member, the thickness of the toner layer is different in the developing area, so that the magnetic toner is different. A difference occurs in the amount of adhering toner and uneven density occurs in the formed image. In order to prevent this, it is preferable that the moving direction of the photosensitive member and the moving direction of the magnetic toner are the same, and further, the moving speed V _{T of the} magnetic toner.
However, it is preferable that the moving speed is higher than the moving speed V _{O of the} surface of the photoconductor, and the developing effect is best when 5 ≧ V _T / V _O ≧ 1.5.

However, if the configuration as proposed above, that is, V _T = (1.5 to 5) × V o, the number of rotations of the magnetic roller must be increased, the problems of increase of driving torque and generation of noise occur. In addition, there is a problem in that image defects such as white spots occur due to adhesion of toner to a doctor blade for controlling the layer thickness of the toner layer, change in toner fluidity, and the like.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the problems existing in the above-mentioned prior art, to provide a developing method capable of reducing the size of an image forming apparatus and forming a high quality image.

[0012]

In order to achieve the above object, in the present invention, development is carried out by developing an electrostatic charge image on an image carrying means carrying and moving an electrostatic charge image using a magnetic developer. In the method, the developer supporting means is provided with a plurality of magnetic poles on the surface and is integrally molded into a cylindrical shape with at least a magnet material powder, a conductive agent and a binder made of an organic polymer, and has a volume resistivity of 10 ⁷ Ω. It has an elastically deformable permanent magnet member of cm or less, holds the moving speed Vp of the image carrier and the peripheral speed Vm of the permanent magnet member in a relationship of Vm = (0.8 to 1.2) Vp, and contains an insulating toner. While adsorbing the magnetic developer on the surface of the developer supporting means and conveying it to the developing area,
The peripheral speed of the developer supporting means and the moving speed of the image carrying means are made substantially equal to each other, and the permanent magnet member is brought into contact with the surface of the image carrying means via the magnetic developer to visualize the electrostatic charge image on the image carrying means. We adopted the technical means of becoming

In the present invention, the gaps between the permanent magnet member and the developer layer thickness regulating means and the image bearing means are respectively t and g.
, T = 0.1 to 0.4 mm, g-t = 0.1 ± 0.1 mm
Can be

The permanent magnet member in the present invention is at least a magnetic powder 10 such as a hard ferrite magnet or a rare earth magnet.
0 to 500 parts by weight, 10 to 100 parts by weight of a conductive agent such as carbon black and carbon fiber, and a rubber material such as urethane rubber, silicone rubber, butyl rubber, ethylene-propylene terpolymer rubber, or an organic compound such as plastic. It is an elastically deformable member formed with 100 parts by weight of a binder made of a united material. In addition to 1 to 10 parts by weight of a crosslinking agent, a plasticizer, an antioxidant, a lubricant, and a small amount of an inorganic filler are added. Can be included. As a molding means, pouring, injection, extrusion or the like can be used, and after molding, it is vulcanized and the outer periphery is ground to be magnetized. However, in order to prevent uneven development, it is preferable that the permanent magnet member is integrally formed as a whole in the circumferential direction and in the axial direction. In the present invention, the developer supporting means may be one in which a conductor layer made of a nonmagnetic metal material is provided on the surface of the permanent magnet member.

On the surface of the permanent magnet member, magnetic poles having different polarities are alternately arranged in the circumferential direction with a minute interval, so that the surface magnetic flux density decreases as the number of magnetic poles increases. 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 50 G or more, and in order to make toner easily adhere to the electrostatic charge image formed on the surface of the image carrier, It is preferably 1200 G or less. The number of magnetic poles is preferably 8 to 60 corresponding to the surface magnetic flux density of 50 to 1200G. A more preferable range of the surface magnetic flux density is 100 to 800G.

Next, the permanent magnet member of the present invention has a resistance of 10 ⁷ Ω · cm or less so that a bias voltage can be applied. As the bias voltage, a DC voltage is applied 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 500 to 1 kHz which is usually used. Well, the number of magnetic poles M of the permanent magnet member, the peripheral speed Vm (mm / sec),
F = M · Vm / π · D (H determined by the diameter D (mm)
and z), the peak-to-peak voltage V _pp is 100
It is good to set it to 800V.

It is preferable that the superimposed voltage is applied in synchronization with the magnetic pole of the permanent magnet member. That is, when the magnetic poles of the permanent magnet member are closest to the surface of the image carrying means, the valley value Vmin of the voltage waveform is applied, while when the magnetic poles of the permanent magnet member are closest to the surface of the image carrying means. The output value of the AC power supply is controlled so that the peak value Vmax is applied. As an example of this synchronizing means, a magnetic sensor for detecting the magnetic field of the permanent magnet member may be attached to serve as a frequency trigger of the AC power source, or a synchronizing signal of the AC power source may be taken out from the rotating shaft of the permanent magnet member.

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

When a two-component type developer is used as the magnetic developer, the one whose toner concentration has been adjusted in advance is put into the developer tank or the carrier is attached to the surface of the permanent magnet member. After that, only the toner may be replenished into the developer tank. As a result, the toner density control means is not required, and the developing device can be downsized.

As the carrier constituting the magnetic developer,
Magnetic particles having an average particle size of 10 to 150 μm and a magnetization σ ₁₀₀₀ of 30 emu / g or more when measured in a magnetic field of 1000 Oe (iron powder, ferrite, magnetite, binder type particles in which magnetic powder is dispersed in resin) Etc.) can be used. If the magnetization σ ₁₀₀₀ is smaller than 30 emu / g, carrier adhesion tends to occur, which is not preferable. It is preferable that the carrier is flat rather than spherical because carrier adhesion is less likely to occur.

Further, the average particle size of the carrier is 10 to 100 μm.
m is preferable. 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 less than 10 μm, carrier adhesion is likely to occur.

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 with a large particle size of μm and an average particle size of 10 to 50 μm
Magnetic particles having a small particle size, or having an average particle size of 10 to 5
Binder type magnetic particles having a small particle size of 0 μm may be mixed. The mixing ratio may be determined in consideration of the size of the magnetic particles and the magnetic characteristics.

The toner to be mixed with the carrier may be either magnetic or non-magnetic, but has a volume resistivity of 10 ¹⁴ Ω from the viewpoint of improving transferability.
An insulating material having a cm or more is preferable, and one easily charged by friction between a carrier and a doctor blade (a triboelectric charge amount of 10 μc / g or more) is preferable.

The composition of the toner is the same as that of the toner which is usually used, such as a binder resin (styrene-acrylic copolymer, polyester resin, etc.), a coloring agent (carbon black, etc., but magnetite is used as the magnetic powder described later). In this case, it may not be added in particular) as an essential component, and as an optional component, magnetic powder (magnetite, soft ferrite, etc.), charge control agent (nigrosine, metal-containing azo dye, etc.), release agent (polyolefin, etc.), Those containing (internally and / or externally added) a fluidizing agent (hydrophobic silica) can be used.
In the case of using a magnetic toner, if the amount of magnetic powder is small, the toner is scattered, while if the amount of magnetic powder is large, the fixing property is deteriorated. A color toner can also be produced by appropriately selecting a colorant.

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

The volume resistivity is DC4KV / cm electric field, 10 dozen mg of the sample is filled in a cylinder made of Teflon (trade name) having an inner diameter of 3.05 mm, and a load of 100 gf is applied to the insulation resistance tester ( Yokogawa Hewlett Packard 432
9A type). Further, the triboelectric charge amount is a commercially available blow-off triboelectric charge amount measuring device (TB manufactured by Toshiba Chemical Co., Ltd.
-200 type), toner concentration 5% (ferrite carrier as standard carrier (Hitachi Metals KBN-100)
Is used).

[0027]

With the above construction, even if a small-sized developer supporting means having a sleeve-less construction is used, a high-quality image free from background fog can be developed.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a transverse cross-sectional view of an essential part showing an example of a developing means in an embodiment of the present invention. In FIG. 1, the permanent magnet member 4 is formed of, for example, a rubber magnet having a volume resistivity of 10 ⁷ Ω · cm or less, and a plurality of magnetic poles extending in the axial direction are provided on the outer peripheral surface to form a cylindrical shape. It is rotatably provided below.
The AC power supply 9 and the DC power supply 10 are the doctor blade 8
And the photosensitive drum 7, and an alternating electric field in which an AC bias is superposed on a DC bias is applied between the magnetic developer 2 and the photosensitive drum 7 that are attracted and conveyed to the surface of the permanent magnet member 4. It is formed so that it can be applied. The AC power supply 9 may be omitted.

The permanent magnet member 4 is composed of, for example, 80 parts by weight of magnetic powder (Ba ferrite having an average particle size of 1 μm), 15 parts of urethane rubber, and 5 parts of carbon black. The rubber has an outer diameter of 20 mm and a length of 227 mm. The magnet layer was integrally fixed to a shaft made of SUM and having a diameter of 6 mm and a length of 280 mm, and was magnetized with 16 poles. Surface magnetic flux density is 150
G and volume resistivity were 10 ³ Ω · cm.

A magnetic developer 2 obtained by mixing magnetic toner and magnetic carrier by the developing means having the above-mentioned structure.
The result of forming an image by using is described. First, the magnetic toner is a styrene-acryl n-butyl methacrylate copolymer (Mw = 210,000, Mn = 16,000) in weight ratio.
57 parts, magnetic powder (Toda Kogyo EPT500) 40 parts,
Charge control agent (Bontron E81 manufactured by Orient Chemical Co., Ltd.)
1 part was blended, heated and kneaded, solidified by cooling, pulverized and classified to form an average particle size of 9 μm, and 0.5 part of a fluidizing agent (R972 manufactured by Nippon Aerosil) was externally added to the surface. The volume resistivity was 5 × 10 ¹⁴ Ω · cm, and the triboelectric charge amount was −22 μc / g.

Next, as the magnetic carrier, a ferrite carrier coated with silicone resin (KBN-made by Hitachi Metals)
100) to have 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 above toner (however, DC100V / cm
(In the electric field).

The above magnetic toner and magnetic carrier were mixed to prepare a magnetic developer 2 having a toner concentration of 50% by weight. On the other hand, the photosensitive drum 7 is formed by OPC to have an outer diameter of 30 mm,
Surface potential -600V, peripheral speed Vp 60, 150, 2 respectively
It was set to 50 mm / sec. A direct current bias voltage of -500 V was applied to the permanent magnet member 4, and the development gap (g) was 0 mm.
Doctor gap (t) 0.1mm, after roller transfer, 1
Heat roll fixing was performed at 80 ° C. and 1 kg / cm. Table 1 is a table showing image evaluation results when the peripheral speed Vm of the permanent magnet member 4 is changed. The environmental conditions for development and fixing are 20 ° C and 6
0% R. H. Met.

[0033]

[Table 1]

As is apparent from Table 1, when Vm / Vp is small (No. 1), the image density is lowered and fine line unevenness occurs, while when Vm / Vp is large (No. 5, 6),
As the background fog increases, dust and fine line unevenness occur. On the other hand, if Vm is almost the same as Vp (No. 2
4) It can be seen that a high image density, little background fog, and a clear image without dust and fine line unevenness can be obtained. Further, according to the present invention, a high quality image can be obtained even when the photosensitive drum rotates at a high speed (Nos. 7 and 8).

[0035]

EFFECTS OF THE INVENTION Since the present invention has the structure and operation as described above, the following effects can be obtained.

(1) Since only the permanent magnet member is used as the constituent member of the developing roll, the developing device can be downsized and the image forming apparatus as a whole can be downsized. (2) Since the peripheral speed of the developing roll and the moving speed of the image carrier are substantially equal to each other, high-speed development is possible.

(3) Since the permanent magnet member, which is the means for supporting and conveying the magnetic developer, is made of a rubber material, the developer can be surely supported and conveyed, and the contact pressure with the image carrying means can be reduced.

(4) Since the toner concentration in the magnetic developer can be set in a wide range, it is not necessary to use, for example, a toner concentration control means, and the entire apparatus can be made compact.

[Brief description of drawings]

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

FIG. 2 is a cross-sectional view of essential parts showing an example of a conventional developing method.

[Explanation of symbols]

 4 Permanent magnet member 7 Photoreceptor drum 9 AC power supply 10 DC power supply

Claims (2)

[Claims] 1. A developing method of developing an electrostatic charge image on an image carrying means for carrying an electrostatic charge image and moving the same by using a magnetic developer, wherein the developer supporting means is provided with a plurality of magnetic poles on the surface thereof. The volume specific resistance formed by integrally molding at least a magnet material powder, a conductive agent, and a binder made of an organic polymer into a cylindrical shape is 10
Having an elastically deformable permanent magnet member of ⁷ Ω · cm or less, the moving speed Vp of the image bearing means and the peripheral speed Vm of the permanent magnet member are kept in a relationship of Vm = (0.8 to 1.2) Vp, and the insulating property is maintained. A magnetic developer containing toner is adsorbed on the surface of the developer supporting means and conveyed to the developing area, and the peripheral speed of the developer supporting means and the moving speed of the image carrying means are made substantially equal to each other so as to pass through the magnetic developer. To bring the permanent magnet member into contact with the surface of the image carrier,
A developing method characterized by visualizing an electrostatic charge image on an image carrying means. 2. When the gaps between the permanent magnet member and the developer layer thickness regulating means and the image carrying means are t and g, respectively, t
= 0.1-0.4 mm, g-t = 0.1 ± 0.1 mm. 2. The developing method according to claim 1, wherein