JPH08262875A - Developing method - Google Patents

Abstract

PURPOSE: To provide a developing method which achieves the miniaturization of an image forming device and ensures the formation of a high quality image. CONSTITUTION: In the developing method for developing, with magnetic developer 2, an electrostatic charge image on an image carrying means 7 moving with the electrostatic charge image held on it, a developer support means composed of a permanent magnet member 4 with a plurality of magnetic poles on its surface which are cylindrically integrated, the magnetic developer 2 comprising insulating toner is carried to a developing area by being attracted to the surface of the developer support means, and an electrostatic charge image on the image carrying means 7 is developed by making the peripheral speed of the developer support means almost equal to the moving speed of the image carrying means 7 and by bringing the magnetic developer 2 into contact with the surface of the image carrying means 7.

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 an electric field in which an AC bias is superimposed on a DC 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 miniaturize the printer and the like, a developing method is proposed in which the sleeve 5 constituting the developing roll 6 is omitted, only the permanent magnet member 4 is used in a rotating state, and the electrostatic charge image is developed by the magnetic brush method. (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 as described above is omitted, there is a difference in height and developability of the magnetic brush between the magnetic poles of the permanent magnet member 4 and between the magnetic poles. Change, and particularly when developing a halftone image, there is a problem in that the image quality deteriorates. On the other hand, if the number of rotations of the permanent magnet member 4 is increased in order to eliminate the density unevenness as described above, there are problems that the driving 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, which is Vp with respect to the peripheral speed Vp of the photosensitive drum 7.
It is usual to set it so that it is more than double. However, the magnetic developer adsorbed and supported on the surface of the permanent magnet member 4 always rubs the surface of the photoconductor drum 7, so that an image in a state where the magnetic developer is swept in the rotation direction of the permanent magnet member 4 is obtained. However, there is a drawback that high quality images cannot be obtained.

In order to solve the above-mentioned drawbacks, it has been proposed to make the relative speed between the moving speed of the magnetic developer and the photosensitive drum 7 approximately zero to less than 1.9 times (Japanese Patent Publication No. 63-3).
9910 and Japanese Patent Laid-Open No. 6-274025). However, each of these proposals has a configuration in which a permanent magnet member and a sleeve are coaxially combined, and there is a problem that the processing and assembling are complicated as described above. In particular, the former one has a drawback that the configuration of the drive system becomes more complicated and the miniaturization is difficult because the magnet and the non-magnetic cylinder are both rotated.

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

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 downsizing an image forming apparatus and forming a high quality image.

[0014]

In order to solve the above-mentioned problems, in the present invention, the development is carried out by developing the electrostatic charge image on the image carrying means carrying and moving the electrostatic charge image using a magnetic developer. In the method, the developer supporting means is constituted by a permanent magnet member having a plurality of magnetic poles formed on the surface and integrally molded in a cylindrical shape, and a magnetic developer containing an insulating toner is attracted to the surface of the developer supporting means. Then, the magnetic developer is brought into contact with the surface of the image carrying means by making the peripheral speed of the developer carrying means and the moving speed of the image carrying means substantially equal to each other and carrying the electrostatic charge image on the image carrying means. We adopted the technical means of visualizing.

In the present invention, the moving direction of the developer supporting means and the moving direction of the image carrying means in the developing area can be the same, and the developing gap and the doctor gap can be formed to have substantially the same size. That is, the doctor gap t, which is the gap between the surface of the permanent magnet member and the tip of the doctor blade.
Is formed in the same size as the developing gap g which is the gap between the permanent magnet member and the image bearing means, from the viewpoint of image quality, to t≈g. In this case, g−t ≦ 0.05 mm should be satisfied.

Further, in the present invention, the moving directions of the developer supporting means and the image carrying means in the developing area can be formed in opposite directions. The permanent magnet member in the present invention is not limited to the ferrite magnet, but may be a resin magnet containing magnetic powder and a resin material as main components. The permanent magnet member may be formed by integrally forming the magnet in a roll shape on the outer circumference of the shaft, or may be formed entirely of a magnetic material including the shaft. 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.

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. However, the number of magnetic poles is such that the magnetic pole pitch is 0.5 to 10 mm (more preferably 1 to 5 mm).
It is preferable to set so that A more preferable range of the surface magnetic flux density is 100 to 800G.

Next, since the permanent magnet member in the present invention is a semiconductive or insulating material, it is preferable to apply a bias voltage from a doctor blade when applying a bias voltage. In this case, the doctor blade is made of metal or the like. It may be formed of a conductive material.

As the bias voltage, a DC voltage alone or a combination of a DC voltage and an AC voltage is applied. The AC voltage to be superimposed on the DC voltage has a frequency lower than that of 500 to 1 kHz which is usually used. The number of magnetic poles of the permanent magnet member is M, the peripheral speed is Vm (mm / sec), and the diameter is D (mm). F = M · Vm / π · D (H
and z), the peak-to-peak voltage V _pp is 100
It is good to set it to 800V.

It is important 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 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 non-magnetic toner and a magnetic carrier are mixed. A powder (toner concentration 5 to 60%) can be used.

When a two-component developer is used as the magnetic developer, a toner whose toner concentration has been adjusted in advance is put into the developer tank or a 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 commonly used toner, 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 magnetic powder (magnetite, soft ferrite, etc.), charge control agent (nigrosine, metal-containing azo dye, etc.), release agent (polyolefin, etc.) as an optional component, 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., Ltd.). It was measured using a counter model TA-II).

Further, the volume resistivity is 10 Kg of the sample filled in a Teflon (trade name) cylinder having an inner diameter of 3.05 mm in an electric field of DC 4 KV / cm, 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).

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, dust, fine line unevenness and density unevenness can be developed. You can do it.

[0031]

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 a semiconductive or insulating, for example, isotropic ferrite magnet having a volume resistivity of more than 10 ⁶ Ω · cm, and a plurality of magnetic poles extending in the axial direction are provided on the outer peripheral surface, Formed into a cylindrical shape,
It is rotatably provided below the developer tank 1. The AC power source 9 and the DC power source 10 are connected between the doctor blade 8 and the photosensitive drum 7, and between the magnetic developer 2 and the photosensitive drum 7 that are attracted and conveyed to the surface of the permanent magnet member 4,
An alternating electric field in which an AC bias is superimposed on a DC bias is formed so that an alternating electric field can be applied. The AC power supply 9 may be omitted.

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,
2 parts of polypropylene (TP32 manufactured by Sanyo Kasei) and 1 part of a charge control agent (Bontron E81 manufactured by Orient Chemical Co., Ltd.) are blended, heated and kneaded, cooled and solidified, crushed and classified to form an average particle size of 10 μm, and a fluidizing agent on the surface. (Nihon Aerosil R972) 0.5 part was externally added. Volume resistivity is 5
It was × 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-
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).

On the other hand, the photosensitive drum 7 is formed by OPC and has a surface potential of -600 V and peripheral speeds of 25, 50 and 10, respectively.
It was set to 0 mm / sec. The permanent magnet member 4 is formed by a ferrite magnet (YBM-3 manufactured by Hitachi Metals) with an outer diameter of 20 mm, A4 size, 32 poles, and a surface magnetic flux density of 350 G. The developing gap (g) is 0.4 mm and the doctor gap (t) is 0.3 mm. Then, a DC bias voltage of -500 V was applied from a doctor blade 8 made of brass. In this case, it is preferable that g−t = 0.2 ± 0.15 mm from the viewpoint of image quality. Table 1 is a table showing image evaluation results when the developed image was corona-transferred and heat roll-fixed at 180 ° C. and 1 kg / cm. The developing and fixing environment is 20 ° C. and 60% R.S. H.
Met.

[0035]

[Table 1]

As is clear from Table 1, in No. 1, the image density was low and the occurrence of background fog was recognized. Further, in No. 5, although there is no background fog or other defects, the image density value is low. On the other hand, in Nos. 2 to 4, high quality images are obtained. From this, it is understood that Vm / Vp is preferably 0.8 to 1.2.

Next, even in Nos. 6 and 7 in which the peripheral speed of the photosensitive drum 7 was set to Vm / Vp = 1.0 and the high-speed development was performed, a high-quality image without defects was obtained. That is, by making the moving speeds of the permanent magnet member 4 and the photosensitive drum 7 substantially equal to each other, the contact time of the magnetic developer with the electrostatic charge image can be lengthened, the image density can be improved, and the magnetic developer The state in which the permanent magnet member 4 is swept in the rotation direction is prevented, and the occurrence of background fog and other defects is prevented.

Next, in the developing means, the peripheral speed Vm of the permanent magnet member 4 and the peripheral speed Vp of the photosensitive drum 7 are set to Vm.
= Vp = 25 mm / sec, the developing gap (g) is 0.4 mm and 0.3 mm, the doctor gap (t) is 0.3 mm, and the permanent magnet member 4 for the photosensitive drum 7 in the developing area is set.
Table 2 shows the image evaluation results when the moving direction of the was changed. The magnetic developer used and the development conditions other than the above are the same as those described above.

[0039]

[Table 2]

As is apparent from Table 2, in No. 11, density unevenness is recognized. In this case, it is remarkable in the case of an image having a solid black portion. On the other hand, in Nos. 12 and 13, the image density was good, and an image without background fog, fine line unevenness, and density unevenness was obtained. This is for No. 12, g = t
It is recognized that the formation of No. 2 causes formation of a pool of the magnetic developer in the developing area, resulting in elimination of uneven density. In the case of No. 13, since the moving directions of the permanent magnet member 4 and the photosensitive drum 7 in the developing area are opposite to each other, the pool of the magnetic developer is irrespective of the dimensional relationship of g and t. Can be formed.

[0041]

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 the magnetic developer, is hard, it is possible to improve the durability with little wear of the surface and little change with time. (4) A stable and high-quality image can be obtained even if the development gap is large.

(5) Since the toner concentration in the magnetic developer can be set in a wide range, it is not necessary to use, for example, 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

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[Procedure amendment]

[Submission date] September 28, 1995

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 1

[Correction method] Change

[Correction content]

FIG.

Claims (3)

[Claims] 1. A developing method for developing an electrostatic charge image on an image carrying means carrying and moving an electrostatic charge image using a magnetic developer, wherein a developer supporting means is provided with a plurality of magnetic poles on the surface thereof. It is composed of a permanent magnet member integrally formed in a cylindrical shape, and a magnetic developer containing an insulating 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 is increased. A developing method characterized in that a magnetic developer is brought into contact with the surface of the image carrying means at substantially the same moving speed of the image carrying means to visualize an electrostatic charge image on the image carrying means. 2. The developing method according to claim 1, wherein in the developing area, the developer supporting means is moved in the same direction as the image carrier, and the developing gap and the doctor gap are formed to have substantially the same size. 3. The developing method according to claim 1, wherein the moving directions of the developer supporting means and the image carrying means in the developing area are opposite to each other.