JPH07319288A - Developing method - Google Patents

Abstract

PURPOSE:To provide a developing method capable of preventing a density uneveness and a ground fogging from causing over a long period, and performing the developing of a stable and high image quality. CONSTITUTION:Regarding the developing method for developing the electrostatic charge image on the image carrier 7 moving while carrying the electrostatic charge image adopting the magnetic developer 2 of the two component system, as the means for supporting while transporting the magnetic developer 2, the permanent magnet member 4 provided with the plural number of magnetic pole on the surface and rotatably composed in a cylindrical shape is used, the magnetic developer 2 is attracted and transported on the surface of the permanent magnet member 4, the magnetic carrier is replenished together with the toner at the replenishing time of the toner, and the magnetic carrier whose particle size is equal to or smaller than that of the toner is included as the magnetic carrier for use.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic charge image formed on the surface of an image bearing member carrying an electrostatic charge image on the surface of a developer supporting and conveying means formed of a cylindrical permanent magnet member. The present invention relates to a developing method in which a toner is attracted and held and visualized by a two-component magnetic developer containing a toner and a magnetic carrier as main components. The present invention relates to a developing method capable of developing.

[0002]

2. Description of the Related Art Conventionally, in an image forming method for a printer, a facsimile, etc., to which an electrophotographic method or electrostatic recording is applied, an electrostatic charge image is formed on the surface of a photosensitive drum formed into a cylindrical shape, and then the photosensitive drum is formed. The magnetic developer is attracted to the surface of the sleeve and conveyed by a developing roll including a sleeve which is provided so as to face the sleeve and has a permanent magnet member incorporated therein and is coaxially and rotatably fitted in the permanent magnet member. To do. After that, a method is employed in which a magnetic brush is formed in the developing area and the electrostatic charge image forming surface on the photosensitive drum is rubbed by the magnetic brush to visualize as a toner image. The most general means is to transfer the visualized toner image onto recording paper and then heat fixing.

In recent years, there is an increasing demand for downsizing of the apparatus used for image formation as described above, and it is important to downsize the developing section. As a means for satisfying such a demand, it has been proposed to directly attract the magnetic developer to the surface of the permanent magnet member and convey the magnetic developer by rotating the permanent magnet member without using a sleeve. (See, for example, JP-A-62-201463).

FIG. 2 is a cross-sectional view of a main part showing an example of a conventional developing means. In FIG. 2, reference numeral 1 denotes a developer tank, which contains a magnetic developer 2 containing toner and a magnetic carrier as main components, and below which a permanent magnet member 4 is rotatably provided. At least the surface of the permanent magnet member 4 is made conductive, and a plurality of magnetic poles extending in the axial direction are provided on the outer peripheral surface of the permanent magnet member 4 to form a cylindrical shape.

The permanent magnet member 4 is made of a resin magnet made of a mixture of ferromagnetic powder and resin (Japanese Patent Laid-Open No. 57-1304).
No. 07, No. 59-905, No. 59-226367, etc.). As a means for making the surface conductive, a conductive layer may be formed on the surface by adhesion, plating, or a powdery conductive substance may be added at the time of kneading the raw materials. Further, the permanent magnet member 4 may be formed of a hard ferrite magnet so as to be semiconductive.

Reference numeral 7 denotes a photosensitive drum, which is rotatably formed in the direction of the arrow and is opposed to the permanent magnet member 4 with a gap g. Reference numeral 8 denotes a doctor blade, which is provided in the developer tank 1 and faces the permanent magnet member 4 with a gap t,
The layer thickness of the magnetic developer 2 adsorbed on the surface of the permanent magnet member 4 is regulated. A DC power source 10 applies a bias voltage to the surface of the permanent magnet member 4.

With the above structure, when the permanent magnet member 4 is rotated in the direction of the arrow, the magnetic developer 2 is adsorbed by the permanent magnet member 4 and conveyed, and when it reaches the developing area facing the photoconductor drum 7, it is exposed to light. The toner in the magnetic developer 2 is transferred by the electric field of the electrostatic charge image formed on the body drum 7,
The electrostatic charge image can be visualized.

[0008]

In the image forming means as described above, as the two-component magnetic developer, for example, a magnetic toner having a particle size distribution of 5 to 20 μm and a ferrite carrier (having a particle size distribution of 70 to 140 μm) are used. For example, the magnetic developer 2 which is a mixed material with Hitachi Metals KBN-100) is used. Note that non-magnetic toner may be used in place of magnetic toner.

In this case, in order to form a high-definition image, it is necessary to use a toner having a small particle size (for example, a particle size distribution of 4 to 16 μm). However, if the toner is used, there is a problem that fog is liable to occur due to the insufficient charge imparting ability to the toner and the image quality is deteriorated. Therefore, in order to obtain a high-definition image, a toner having a small particle size is required, and a magnetic carrier having a small particle size (for example, an average particle size of 50 μm or less) is also required.

However, when the above-mentioned magnetic carrier having a small particle size is used, the magnetic carrier which should originally be adsorbed and remained on the surface of the permanent magnet member 4 adheres to the photosensitive drum 7, which is an undesired phenomenon. Happens. This is because the magnetic carrier itself also has a particle size distribution, and particles having a small particle size are transferred to the photosensitive drum 7 side. Even if the magnetic carrier in the region of such a small particle size adheres to the photosensitive drum 7, the image quality is hardly adversely affected, but the toner concentration is relatively high due to the decrease of the magnetic carrier in the magnetic developer. However, there is a problem in that density unevenness and background fog occur.

Next, in the developing roll with the sleeve, the magnetic developer adsorbed on the surface of the sleeve rotates on the surface of the sleeve, so that the height of the ears of the magnetic brush tends to be relatively uniform. In the lacking configuration, the height of the magnetic brush spikes fluctuates.
That is, just above the magnetic poles of the permanent magnet member 4, the height of the ears of the magnetic brush becomes large, while between the magnetic poles it becomes small. Therefore, there is a problem in that the contact state between the magnetic brush and the photoconductor drum 7 fluctuates, resulting in uneven density.

In order to prevent the uneven density as described above,
Although it is conceivable to increase the number of rotations of the permanent magnet member 4, in order to rotate the permanent magnet member 4 at a high speed, it is necessary to increase the driving torque, noise is generated, and the magnetic force forming the magnetic developer is increased. There is a problem that it causes wear of the carrier.

The present invention provides a developing method which solves the above problems existing in the prior art, prevents the occurrence of density unevenness, background fog, etc. over a long period of time and can perform stable high-quality development. The purpose is to

[0014]

In order to achieve the above object, in the present invention, a two-component magnetic developer is used for the electrostatic charge image on the image carrier which carries and moves the electrostatic charge image. In the developing method for developing by using a permanent magnet member having a plurality of magnetic poles formed on the surface and formed rotatably in a cylindrical shape, as a means for supporting and conveying the magnetic developer, the magnetic developing is performed on the surface of the permanent magnet member. A technical means is adopted in which the agent is adsorbed and conveyed, and a magnetic carrier is replenished together with the toner at the time of replenishing the toner, and that the magnetic carrier contains particles having a particle diameter equal to or smaller than that of the toner.

In the present invention, flat iron powder having an average particle size of 1 to 30 μm can be used as the magnetic carrier. 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. Further, the permanent magnet member may be formed by integrally forming the magnet in a roll shape on the outer periphery of the shaft, or may be entirely formed of a magnetic material including the shaft. However, in order to prevent uneven development, this permanent magnet member must be seamlessly formed in the circumferential direction and the axial direction and integrally formed.

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, when the number of magnetic poles is increased, the magnetic field formed around the permanent magnet member is reduced, and the amount of the magnetic developer attached to the surface of the permanent magnet member is reduced. For this reason, the thickness of the magnetic developer layer formed on the surface of the permanent magnet member is likely to be nonuniform, and it is necessary to rotate the permanent magnet member at a high speed in order to prevent such an undesired phenomenon. However, if the rotation speed of the permanent magnet member is too fast, the driving torque becomes large and the carrier constituting the magnetic developer is worn. On the other hand, if the rotation speed is too slow, density unevenness occurs in the image. Therefore, the peripheral speed V of the permanent magnet member is
m (mm / sec) is 1 to 1 of the peripheral velocity Vp (mm / sec) of the image carrier.
It is preferably set to 0 times, more preferably 2 to 6
Double.

Next, assuming that the outer diameter of the permanent magnet member is D (mm) and the number of magnetic poles provided on the surface is M, the value of h (mm) represented by the following formula is smaller than 2. It is preferable to set D, M and Vm.

H = πD · Vp / M · Vm The above h is the pitch where the surface of the image carrier faces the magnetic poles of the permanent magnet member within a unit time. If h is 2 mm or more, uneven development occurs. Since it is conspicuous, it is preferably smaller than 2 mm, more preferably 1 mm or less. In this case, in order to reduce the value of h, the number of magnetic poles M and the peripheral speed Vm of the permanent magnet member may be increased. However, if the number of magnetic poles M is too large, the surface magnetic flux density decreases and the magnetic development Since the agent is likely to be scattered and the above-mentioned problems occur when the peripheral speed Vm is too large, the value of h is preferably set to 0.4 to 1.0 mm in practical use.

When the doctor gap t, which is the gap between the surface of the permanent magnet member and the tip of the doctor blade, is provided, the difference between the developing gap g, which is the gap between the permanent magnet member and the image bearing member, from the viewpoint of image quality. (G−t) = 0.2 ±
It is preferably 0.15 mm. The doctor blade is brought into contact with or pressed against the surface of the permanent magnet member to t
It may be = 0. In this case, the doctor blade is formed of a magnetic material such as SK material or a non-magnetic material such as SUS304 or phosphor bronze into an elastic blade shape, one end of which is fixed to the developer tank and the other end of which is formed of the permanent magnet member. It may be brought into contact with the surface.

Next, when the permanent magnet member of the present invention is a semi-conductive or insulating material, a doctor blade is preferable as a portion to which a bias voltage is applied,
In this case, the doctor blade may be made of a conductive material such as metal. When the permanent magnet member is a conductive material, the bias voltage is preferably applied from the shaft or the like.

Next, as the two-component magnetic developer, one having a predetermined toner concentration adjusted in advance is put into the developer tank, or a predetermined amount of magnetic carrier is adhered to the surface of the permanent magnet member. After that, toner can be put into the developer tank and used as a two-component magnetic developer for start. When replenishing the toner, the toner and the magnetic carrier are replenished together. In this case, it is preferable to mix the toner and the magnetic carrier in advance. In the case of a system in which the developing device is replaced, that is, in the case of a disposable developing cartridge, it is configured such that the magnetic carrier of a consumption amount or more is mixed with the toner.

As the magnetic carrier constituting the magnetic developer, iron powder and ferrite particles (Ni-Zn system, Mn-Zn system, Cu-Z) which are used in usual two-component system are used.
n-based) and magnetite particles can be used. Also, a binder type in which these magnetic powders are dispersed in a resin may be used. In this case, it is not preferable to use flat iron powder because the magnetization value is large and the residual property to the permanent magnet member is large in terms of shape, so that carrier adhesion is small.

As the magnetic carrier to be replenished with the toner, one containing particles having a particle size equal to or smaller than that of the toner is used. That is, the magnetic carrier in the magnetic developer has, for example, a particle size distribution of 1 to 50 μm, but particles having a relatively small particle size are easily transferred to the image carrier side together with the toner, and are reduced during continuous use. This is because it is necessary to replenish the reduced amount and to obtain a high-definition image.

If the particle size of the magnetic carrier is large, the charge imparting ability to the toner is deteriorated and a high-definition image cannot be obtained, which is not preferable. On the other hand, if the particle size of the magnetic carrier is too small, carrier adhesion occurs, which is not preferable. Therefore, it is preferable to use the above. Further, the magnetic carrier may be a mixture of two or more kinds of the magnetic particles and the binder type magnetic particles, and the mixing ratio may be determined in consideration of the size of the magnetic particles, magnetic characteristics and the like.

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 average particle size of the toner is 5 to 10 in order to obtain a high definition image.
It is preferably formed to have a thickness of μm. The mixing ratio of the toner in the magnetic developer is preferably 10 to 90% by weight for the magnetic toner and 5 to 60% by weight for the nonmagnetic toner.

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.
When the magnetic toner is used, the fixability is deteriorated when the amount of the magnetic powder is large, and therefore the amount of the magnetic powder is preferably 70% by weight or less. A color toner can also be produced by appropriately selecting a colorant.

The volume resistivity of the toner is DC4
Teflon (product name) with an inner diameter of 3.05 mm under an electric field of KV / cm
It is a value measured by using an insulation resistance meter (Model 4329A made by Yokogawa Hewlett Packard) after filling a cylinder made by 10 mg of the sample and applying a load of 100 gf. Further, the triboelectrification amount was measured with a commercially available blow-off triboelectrification amount measuring device (TB-200 manufactured by Toshiba Chemical Co., Ltd.) with a toner concentration of 5% (ferrite carrier as a standard carrier (KB manufactured by Hitachi Metals).
N-100) is used).

[0029]

With the above construction, when continuously developing with a two-component magnetic developer, not only the toner in the magnetic developer but also the magnetic carrier adheres to the image carrier side and decreases. By supplying the magnetic carrier together with the toner, it is possible to prevent the occurrence of density unevenness, background fog, etc., and perform stable high-quality development even in a wide toner density range.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a transverse cross-sectional view of a main part showing an example of a developing means in an embodiment of the present invention, and the same parts are designated by the same reference numerals as those 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 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. A direct current power source 10 is connected between the doctor blade 8 and the photosensitive drum 7.

Next, as the magnetic toner, the average particle size is 10 μm.
m, particle size distribution 4 to 16 μm, volume resistivity 10 ¹⁵ Ω · c
m and triboelectrification amount-23 μc / g were prepared. The blending ratio is a weight ratio of styrene-n-butyl methacrylate 45, magnetite (Toda Kogyo EPT500) 50,
Polypropylene (TP32 manufactured by Sanyo Kasei) 3, charge control agent (Bontron E-81 manufactured by Orient Chemical Co., Ltd.) 2,
An external additive (R972 manufactured by Nippon Aerosil) 0.5 was added to the particles formed by these.

The magnetic carrier has an average particle size of 30 μm.
m, particle size distribution 1 to 50 μm, volume resistivity 10 ⁶ Ω · c
The magnetization σ _{1000 at} m and 1000 Oe is 120 emu /
g of flat iron powder was used. For the volume resistivity of the carrier, a DC10
It was calculated based on the resistance value measured by applying an electric field of 0 V / cm. For the magnetization value, a vibrating sample magnetometer (VSM-3 type manufactured by Toei Industry Co., Ltd.) was used, and the average particle size (volume) of the toner was measured using a particle size analyzer (Coulter counter model TA-II manufactured by Coulter Electronics Co., Ltd.). Was measured using.

On the other hand, the photosensitive drum 7 was formed by OPC, and had a surface potential of -700 V and a peripheral speed of 30 mm / sec. The permanent magnet member 4 is a ferrite magnet (YBM-made by Hitachi Metals).
3), outer diameter 20 mm, 16 poles, surface magnetic flux density 500
After being formed in G, a developing gap g = 0.4 mm, a doctor gap t = 0.3 mm, and a DC bias voltage of −550 V were applied via a doctor blade 8.

Under the above-mentioned development conditions, the toner concentration T / C (% by weight) in the magnetic developer for start, that is, the magnetic developer 2 charged into the developer tank 1 at the time of start is changed to perform continuous development, Table 1 shows the measurement results of the amount D (% by weight) of the recovered carrier after continuous printing of 10,000 sheets (A4 size). The recovered carrier amount D is a value obtained by the following formula.

D = A / (A + B + C) (% by weight) where A: carrier amount recovered by the cleaner B: toner amount recovered by the cleaner C: toner amount consumed

[0036]

[Table 1]

As is apparent from Table 1, the toner in the magnetic developer is naturally consumed and reduced by continuous development, but at the same time, the magnetic carrier in the magnetic developer 2 is also transferred to the photosensitive drum 7. Is recognized. It is understood that the transfer amount of the magnetic carrier is larger as the toner concentration T / C in the magnetic developer 2 for start is lower.
By consuming the magnetic carrier in the magnetic developer 2 in this way, the toner concentration in the magnetic developer 2 increases,
As a result, uneven density and background fog occur as described above.

Table 2 shows the image evaluation results after continuous printing of 10,000 sheets while replenishing the magnetic developer consisting of toner and magnetic carrier under the above-mentioned developing conditions. The magnetic developer for replenishment had the same composition as that for the starter, but the magnetic carrier with different average particle diameters is also shown.

[0039]

[Table 2]

As can be seen from Table 2, in Comparative Examples Nos. 5 to 8 in which only the toner is replenished in the continuous development, as shown in Table 1 above, the toner and the magnetic carrier are also shown in FIG. As a result of transferring to the 7 side and being consumed, the toner concentration in the magnetic developer 2 becomes high, and generation of background fog and dust is recognized.

On the other hand, with the toner, the average particle size is 10 μm.
It can be seen that in Nos. 1 to 4 in which the magnetic carrier of m is replenished, the toner concentration in the magnetic developer 2 can be stabilized, and as a result, a good image without background fog and dust is obtained. The carrier weight% in the replenishing magnetic developer is preferably a value that is approximately inversely proportional to the toner concentration in the starting magnetic developer. This is because, as shown in Table 1, the lower the toner concentration of the magnetic developer, the greater the amount of transfer of the magnetic carrier to the photosensitive drum 7 side.

Next, even when the toner concentration of the magnetic developer for start is made constant and the average particle size of the magnetic carrier for replenishment is changed, there is no background fog or dust as shown in Nos. 9 to 12. It can be seen that a good image can be obtained. The average particle size of the magnetic carrier for replenishment is preferably equal to or smaller than that of the toner in the magnetic developer for starting.

Next, as the non-magnetic toner, the average particle size is 8.5 μm.
m, particle size distribution 10 to 70 μm, volume resistivity 5 × 10 ¹⁴
Ω · cm and triboelectric charge amount of −29 μc / g were prepared.
The blending ratio is by weight, and is based on polyester (KTR KTR
2150) 87, carbon black (manufactured by Mitsubishi Kasei Co., Ltd.
# 44) 10, polypropylene (TP3 manufactured by Sanyo Kasei)
2) 2, charge control agent (T2N) 1, and external additives (R97 manufactured by Nippon Aerosil Co., Ltd.) added to the particles formed by these.
2) 0.5 was added.

The magnetic carrier has an average particle size of 50 μm.
m, particle size distribution 10 to 70 μm, volume specific resistance 10 ⁸ Ω ・
The magnetization σ _{1000 at} cm and 1000 Oe is 120 emu /
g of flat iron powder was used.

On the other hand, the photosensitive drum 7 was formed by OPC and had a surface potential of -650 V and a peripheral speed of 30 mm / sec. The permanent magnet member 4 is a ferrite magnet (YBM-made by Hitachi Metals).
3), outer diameter 20 mm, 32 poles, surface magnetic flux density 350
After being formed in G, a developing gap g = 0.4 mm, a doctor gap t = 0.25 mm, and a DC bias voltage of −500 V were applied via a doctor blade 8.

Under the above-mentioned developing conditions, the toner concentration in the magnetic developer for start was changed in the same manner as in the above-mentioned embodiment to carry out continuous printing, and the amount D (% by weight) of the recovered carrier after printing 10,000 sheets was measured. The results obtained are shown in Table 3. The value of the recovery carrier amount D corresponds to the value in the above embodiment.

[0047]

[Table 3]

As is clear from Table 3, as in the case of Table 1, it is recognized that the magnetic carrier in the magnetic developer is transferred to the photosensitive drum 7 together with the toner by continuous printing. The tendency of the amount of recovered carrier depending on the toner concentration is similar to that in Table 1 above, but the range of the amount of recovered carrier is slightly smaller than that in Table 1. After all, even in a developing method using a magnetic developer composed of a non-magnetic toner and a magnetic carrier, it is recognized that continuous development increases the toner concentration in the magnetic developer, resulting in uneven density and background fog. .

Next, Table 4 shows the image evaluation results after continuous printing of 10,000 sheets was carried out while replenishing the magnetic carrier together with the toner under the above developing conditions. The image evaluation is
This was done for a character pattern of 5%.

[0050]

[Table 4]

As is clear from Table 4, the replenishment of the toner alone, which is a comparative example, results in a low image density, uneven density, dust and background fog, and a large change in toner density. On the other hand, it can be seen that in the case where the toner and the magnetic carrier of the present invention are replenished, the image quality is significantly improved and the change in toner concentration is small.

[0052]

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

(1) Since the magnetic carrier is replenished together with the toner, the toner concentration of the magnetic developer is prevented from increasing due to the transfer of the magnetic carrier to the image carrier, and the occurrence of background fog and dust is prevented, which is excellent. Development can take place.

(2) 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. (3) 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.

(4) High-definition and high-quality images can be obtained by using a magnetic carrier having a small particle size. (5) Since the toner concentration in the magnetic developer can be set in a wide range, it is not necessary to use a toner concentration control means, for example, and the entire apparatus can be made compact.

(6) It is not necessary to process the permanent magnet member constituting the developing roll with higher precision than necessary, and the manufacturing cost can be reduced.

[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 a main part showing an example of a conventional developing unit.

[Explanation of symbols]

 4 Permanent magnet member 7 Photoconductor drum

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Claims (2)

[Claims] 1. In a developing method for developing an electrostatic charge image on an image carrier, which carries and moves an electrostatic charge image, by using a two-component magnetic developer, as a means for supporting and transporting the magnetic developer, A cylindrical permanent magnet member is used which has a plurality of magnetic poles and is rotatably formed. The magnetic developer is attracted and conveyed to the surface of the permanent magnet member, and the magnetic carrier is replenished with the toner when replenishing the toner. In addition, the developing method is characterized in that the magnetic carrier contains particles having a particle diameter equal to or smaller than that of the toner. 2. The developing method according to claim 1, wherein the magnetic carrier is a flat iron powder having an average particle diameter of 1 to 30 μm.