JPH09197829A - Developing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To miniaturize an image forming device and to form an image of high quality by applying a specific alternating electric field between a photoreceptor drum and a magnetic developer, so as to develope an electrostatic charge image on a photoreceptor drum, in a developing region. SOLUTION: A developer supporting means is composed of a permanent magnet member 4 which is provided with plural magnetic poles on the surface and integrally formed to a cylindrical shape and the electrostatic charge image on the photoreceptor drum 7 is developed with the magnetic developer 2 consisting of insulating toner and magnetic carriers. At this time, in the developing region to which the magnetic developer 2 is carried by attraction, an alternating electric field where an AC bias having a frequency (f)=Vm/(0.2-1.3)P and a peak-to-peak voltage VP- P=(1-3) VDC is superimposed on a DC bias is applied between the drum 7 and the magnetic developer 2, to develope the electrostatic charge image. At this time, the circumferential speed (mm/sec) of the permanent magnetic member 4 is defined as Vm, the pitch (mm) in a circumferential direction between the magnetic poles having polarities different from each other is defined as P and a DC bias voltage (V) is defined as VDC.

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 two-component 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 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.

Then, 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. 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 formed so as to be rotatable in the direction of the arrow and is opposed to the developing roller 6 via a developing gap g. Reference numeral 8 denotes a doctor blade, which is provided in the developer tank 1 and faces the developing roll 6 via the doctor gap t to regulate the layer thickness of the magnetic developer adsorbed on the sleeve 5 forming the developing roll 6. It is a thing.
9 is an AC power supply, 10 is a DC power supply, and the photosensitive drum 7
And a doctor blade 8 for applying a superimposed bias of direct current and alternating current. The developing gap g is formed slightly larger than the doctor gap t.

With the above structure, 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 conveyed. 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. Thereby, the electrostatic charge image can be developed.

[0007]

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 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, it is complicated to process and assemble. There is a problem that the cost increases.

Therefore, in order to downsize 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 is omitted as described above, 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, so that the image density is increased. 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 uneven density as described above, there are problems that the driving torque becomes large and noise is generated, which is not preferable.

For this reason, the peripheral speed Vm of the permanent magnet member 4 is about 1.5, where Vm is Vp with respect to 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.

On the other hand, in order to avoid an increase in drive torque,
When the peripheral speed Vm of the permanent magnet member 4 is reduced, unevenness in image density due to the magnetic pole pitch appears. Therefore, increasing the number of magnetic poles can be considered as a countermeasure. However, when the number of magnetic poles is increased, the surface magnetic flux density is reduced and the magnetic developer is scattered.
With the permanent magnet member 4 of mm, 32 poles is the limit.

By applying an AC bias voltage corresponding to the period of the maximum surface magnetic flux density that accompanies the movement of the magnetic poles formed on the surface of the permanent magnet member 4, the unevenness of image density due to the magnetic pole pitch is eliminated. However, in this case, it is necessary to completely match the cycle of the maximum magnetic flux density transfer with the cycle of the AC bias voltage. However, although the cycle of the AC bias voltage is constant and does not change, the peripheral speed of the permanent magnet member 4 changes due to uneven rotation, etc., and therefore the cycle of maximum magnetic flux density movement changes, and Differences occur in the cycle. If there is a difference between the two periods, a so-called moire phenomenon occurs,
There is a problem in that the light and shade of an image having a cycle longer than both of them appears, and the image quality is degraded.

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.

[0015]

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 the magnetic developer comprising an insulating toner and a magnetic carrier is used as the developer supporting means. And is conveyed to the developing area, and the frequency f = Vm / (0.2 is applied to the DC bias between the image carrier and the magnetic developer in the developing area.
~ 1.3) P (Vm is the peripheral speed of the permanent magnet member (mm / sec), P
Is the circumferential pitch (mm) between different magnetic poles (Hz),
Peak-to-peak voltage _Vpp = (1-3) V _DC (V
_DC adopted a technical means of applying an alternating electric field in which an alternating current bias of a direct current bias voltage (V) is superposed to visualize an electrostatic charge image on the image bearing means.

In the present invention, the developer supporting means and the image carrying means in the developing area can move in the same direction, and the developing gap and the doctor gap can be formed in 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.

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 uneven development, it is preferable that the permanent magnet member is integrally formed without any joint in the circumferential direction and the axial direction.

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 50 G or more, and in order to make it easier for the toner to adhere to the electrostatic 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 poles corresponding to the surface magnetic flux density of 50 to 1200 G. 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 The 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. If the surface of the permanent magnet member is made conductive, a bias voltage can be applied directly to the surface of the permanent magnet member, but if the permanent magnet member is grounded, sparks will occur and cause noise. Therefore, it is preferable to apply it to the shaft through the protective resistance.

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. F = V determined by the peripheral speed Vm (mm / sec) of the permanent magnet member and the circumferential pitch P (mm) between magnetic poles of different polarities.
It is preferable that m / (0.2 to 1.3) P and the peak-to-peak voltage _Vpp = (1 to 3) V _DC (V _DC is a DC bias voltage (V)).

In the present invention, the magnetic developer is a mixed powder of a magnetic toner and a magnetic carrier (toner concentration of 10 to 10).
90% by weight) and mixed powder of non-magnetic toner and magnetic carrier (toner concentration 5 to 60%) can be used.

In the case of using the two-component magnetic developer as described above, the one whose toner concentration is adjusted in advance is put into the developer tank, or the magnetic carrier is provided on the surface of the permanent magnet member. The toner may be attached, and then only the toner may be replenished in the developer tank. This eliminates the need for the toner density control means, and can reduce the size of the developing device.

The magnetic carrier constituting the magnetic developer has an average particle size of 10 to 150 μm and is 1000 Oe.
Magnetic particles having a magnetization σ ₁₀₀₀ of 30 emu / g or more (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. Note that the magnetic carrier is preferably flat rather than spherical because carrier adhesion is less likely to occur.

Further, the average particle size of the magnetic carrier is 10 to 10
Those having a thickness of 0 μm are preferred. This has an average particle size of 100 μm
This is because when the amount is below, a sufficient charge amount of the toner is obtained, but when the average particle size is less than 10 μm, carrier adhesion is likely to occur.

The magnetic carrier may be a mixture of two or more of the above magnetic particles. For example, the average particle size is 60-1
Magnetic particles having a large particle size of 20 μm and an average particle size of 10 to 50
Magnetic particles with a small particle size of μm, or an average particle size of 10
You may mix with binder type magnetic particles with a small particle diameter of up to 50 μm. The mixing ratio may be determined in consideration of the size and magnetic characteristics of the magnetic particles.

The volume resistivity of the magnetic carrier is 10 ⁸
It is preferably from 10 ¹³ Ω · cm. If the volume resistivity of the magnetic carrier is too low, carrier adhesion is likely to occur, which is inconvenient. On the other hand, if the volume specific resistance of the magnetic carrier is too high, the developing electrode effect becomes small and the image density decreases, which is not preferable.

The toner to be mixed with the magnetic carrier may be either magnetic or non-magnetic, but has a volume resistivity of 10 ¹⁴ from the viewpoint of improving transferability.
An insulating material having an Ω · cm or more is preferable, and an electrically insulating material that is easily charged by friction between the magnetic carrier and the doctor blade (friction 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 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 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.

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 value of the volume resistivity is the inner diameter obtained by improving the dial gauge by weighing an appropriate amount of sample (tens of mg).
Fill into a 3.05mm Teflon (trade name) cylinder,
Under a load of 0.1 kg, D.D. C. 100
V / cm electric field, and D.C. C. 400
The resistance was calculated by applying an electric field of 0 V / cm and measuring.
4329 made by Yokogawa Hewlett-Packard for measurement of resistance
A type insulation resistance meter was used. Also, the triboelectric charge amount of toner is
First, ferrite carrier (KBN-10 manufactured by Hitachi Metals)
0) and toner were mixed well with a developer adjusted to a toner concentration of 5% by weight, and the toner was blown at a blow pressure of 1.0 kgf / cm ² , and this was blown off with a powder charge measuring device (TB-200 manufactured by Toshiba Chemical Co., Ltd.). Type).

With the above structure, a high-quality image free from background fog, dust, fine line unevenness, and density unevenness can be developed even if a small-sized developer supporting means having a sleeve is used. You can do it.

[0032]

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.

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 toner is 90 parts by weight of bisphenol A type polyester (glass transition temperature Tg = 65 ° C.) and a colorant (cyan:
C. I. Pigment Blue 15-3) 5 parts, polypropylene (Sanyo Kasei TP-32) 3 parts, charge control agent (Orient Chemical Co. Bontron E88) 2 parts are blended,
Average particle diameter of 7μ after kneading by heating, solidification by cooling, crushing and classification
m, and a fluidizing agent (R9 manufactured by Nippon Aerosil Co., Ltd. on the surface
72) 0.5 part was externally added. Volume resistivity is 7 × 10 ¹⁴ Ω
-Cm, triboelectric charge was -25 μc / g.

Next, as a magnetic carrier, Ba--Ni--
Zn type ferrite carrier (KBN-10 manufactured by Hitachi Metals)
0, average particle size 50 μm), Cu—Zn ferrite carrier (KBN-220H manufactured by Hitachi Metals, average particle size 50 μm)
m) and an iron powder carrier coated with a silicone resin (A
SC-300, average particle size 30 μm) was used and mixed with the above-mentioned toners to obtain magnetic developers each having a toner concentration of 40% by weight.

On the other hand, the photosensitive drum 7 was formed by OPC and had a surface potential of -600 V and a peripheral speed of 50 mm / sec. The permanent magnet member 4 is a ferrite magnet (YBM-made by Hitachi Metals).
3), outer diameter 20 mm, A4 size, 32 poles (circumferential pitch between magnetic poles 1.96 mm), surface magnetic flux density 350 G, development gap (g) 0.3 to 0.4 mm, doctor gap (t) 0.2 to The thickness was set to 0.3 mm, and a DC bias voltage of −550 V and an AC bias voltage were applied from a doctor blade 8 made of brass. Table 1 is a table showing image evaluation results when the developed image was corona-transferred and heat roll-fixed at 160 ° C. and 1 kg / cm. The environment for development and fixing was 20 ° C. and 60% R.F. H. Met.

In Table 1, R is the volume resistivity, and the peripheral speed ratio is the ratio of the peripheral speed Vm of the permanent magnet member to the peripheral speed Vp of the photosensitive drum. The symbol in the image quality column is ◎: excellent,
◯: good, Δ: bad, x: bad.

[0037]

[Table 1]

In Table 1, Nos. 1 to 5 were developed only by applying a DC bias voltage without applying an AC bias voltage, but in Nos. 1 and 2, fog and image shading were remarkable, Image density is low. Also No. 3
In Nos. 5 to 5, the image density is improved and the fog disappears, but the image density is still remarkable and the density pitch is large.

Next, Nos. 6 and 7 are applied by superimposing the AC bias voltage in addition to the DC bias voltage. Since the frequency of the AC bias voltage is high,
Adhesion of the carrier was recognized and the image density was not resolved.

On the other hand, Nos. 8 to 14 are 15 to 20
It is shown that by applying an alternating voltage of low frequency of 0 Hz, a high-quality image with high image density, no fog and carrier adhesion, and less image density can be obtained. However, in Nos. 8 and 14, the resolution of image shading was not recognized, and in Nos. 9 to 13, good results were shown.

Nos. 15 and 16 are those in which the peripheral speed ratio between the permanent magnet member and the photosensitive drum is changed, and in each case, high quality images without image shading are obtained. From the above results, the frequency f of the AC bias voltage is determined by the peripheral speed Vm (mm / sec) of the permanent magnet member 4 shown in FIG. 1 and the circumferential pitch P between the magnetic poles of different polarities f = Vm / (0.2
~ 1.3) It is recognized that P is preferable. This relationship is No. 1 which changed the volume resistivity of the magnetic carrier.
7 and 18 are also established, and high quality images are obtained in both cases.

[0042]

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

(1) The frequency of the AC bias voltage to be superimposed and applied to the DC bias voltage is limited to a specific range in relation to the peripheral speed of the permanent magnet member and the circumferential pitch between the magnetic poles of different polarities. As a result, a high-quality image with little image density can be obtained.

(2) The peripheral speed ratio of the permanent magnet member to the image carrier can be reduced to, for example, 2 or less, and the driving torque can be reduced. (3) 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.

(4) High-speed development is possible because development is performed with the peripheral speed of the developing roll and the moving speed of the image carrier being substantially equal. (5) Since the permanent magnet member, which is a means for supporting the magnetic developer, is hard, the surface is less worn, the change over time is less, and the durability can be improved.

(6) A stable and high-quality image can be obtained even if the development gap is large. (7) 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 (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 composed of an insulating toner and a magnetic carrier is adsorbed on the surface of the developer supporting means and conveyed to a developing area, and an image is carried in the developing area. Frequency f = Vm / (0.2 to 1.3) P (Vm is the peripheral speed of the permanent magnet member (mm / sec), and P is the circumferential direction between the magnetic poles of opposite polarity between the means and the magnetic developer. Pitch (mm)) (Hz), peak-to-peak voltage _Vpp = (1 to 3) _VDC ( _VDC is DC bias voltage (V)). Development method characterized by visualizing an electrostatic charge image on an image carrier Law. 2. The volume resistivity of the magnetic carrier is 10 ⁸ to
The developing method according to claim 1, wherein the developing process is 10 ¹³ Ω · cm. 3. The developing method according to claim 2, wherein a non-magnetic toner is used.