JPH07261556A - Image forming method - Google Patents

Abstract

PURPOSE:To provide an image forming method requiring little torque for carrying and conveying a magnetic developer and capable of forming a high-quality image in a wide toner density range. CONSTITUTION:An electrostatic charge image on an image carrier 7 moved while carrying the electrostatic charge image is developed with a two-constituent magnetic developer in this image forming method. The means carrying and conveying the magnetic developer is constituted of a permanent magnet member 4 provided multiple magnetic poles on the surface and formed cylindrically and rotatably. The magnetic carrier constituting the magnetic developer attracted and conveyed on the surface of the permanent magnet member 4 has the average grain size of 5-20mum, the opposite electrification polarity to that of the toner, and the magnetization delta1000 of 50emu/g or below in the magnetic field of 1000Oe.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface of a developer supporting means comprising a permanent magnet member integrally formed in a cylindrical shape with an electrostatic charge image formed on the surface of an image carrying means carrying an electrostatic charge image. The present invention relates to an image forming method in which a two-component magnetic developer mainly composed of a toner and a magnetic carrier adsorbed and held on a magnetic recording medium is visualized, and in particular, a hollow cylindrical sleeve is omitted as a supporting and conveying means of the magnetic developer. The magnetic carrier that has a small particle size and a low magnetic force is used as the magnetic carrier that constitutes the magnetic developer, and the torque required to support and convey the developer can be reduced, and a high-quality image can be obtained in a wide toner concentration range. And an image forming method capable of obtaining

[0002]

2. Description of the Related Art In a conventional image forming method for a printer, a facsimile, etc., to which an electrophotographic method or electrostatic recording is applied, for example, an electrostatic charge image is formed on the surface of a cylindrical photosensitive drum 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 To do. After that, a method is adopted 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 requirement, 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 above-mentioned permanent magnet member 4 is 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 the like, or a powdery conductive substance may be added at the time of kneading the raw materials. Alternatively, 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 formed to be rotatable in the direction of the arrow and is opposed to the permanent magnet member 4 with a gap g. 8 is 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 supply 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) ( 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. However, when a magnetic carrier having a large particle size is used as described above, a charge is imparted to the toner. There is a problem that fog is apt to occur due to lack of ability, and 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 is also required.

However, in the conventional developing roller with a sleeve, when the above-mentioned magnetic carrier having a small particle diameter is used, carrier adhesion occurs and the image quality deteriorates. On the other hand, in the image forming means of the type in which the sleeve as shown in FIG. 2 is omitted and the magnetic developer 2 is directly attracted and conveyed by the permanent magnet member 4, carrier adhesion does not occur unlike in the developing roll with the sleeve. When a magnetic carrier having a high magnetic force is used, the rotation torque for driving the permanent magnet member 4 becomes large, so that a so-called spent phenomenon in which the resin component constituting the toner sticks to the surface of the magnetic carrier easily occurs, There are problems such as shortening the life of the magnetic carrier and fogging.

Further, the toner concentration in the two-component magnetic developer in the conventional image forming means is in the range of 3 to 5% by weight when the non-magnetic toner is contained, and 20 ± 5% by weight when the magnetic toner is contained. Since it is a relatively narrow range,
A toner density control means such as a toner density sensor is required, which has the problems of low operability and a complicated apparatus.

The present invention solves the above-mentioned problems existing in the prior art, and requires a small torque for supporting and conveying the magnetic developer, and is capable of forming a high-quality image in a wide toner concentration range. The purpose is to provide.

[0013]

To achieve the above object, in the present invention, a two-component magnetic developer is used for an electrostatic charge image on an image carrier which carries and moves the electrostatic charge image. In the image forming method of developing by developing, the means for supporting and conveying the magnetic developer is constituted by a permanent magnet member formed in a cylindrical shape and rotatably with a plurality of magnetic poles on the surface, and the surface of the permanent magnet member is formed. The magnetic carrier constituting the magnetic developer that is adsorbed and conveyed has an average particle size of 5 to 20 μm,
The technical means of forming the magnetization σ ₁₀₀₀ in the magnetic field of 1000 Oe to 50 emu / g or less with the polarity opposite to that of the toner was adopted.

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. Also, this permanent magnet member is
The magnet may be integrally formed 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, the 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 therefore the permanent magnet member must be rotated 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 equation 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 high, 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 made 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 made of a semiconductive or insulating material, a doctor blade is preferable as a portion for applying a bias voltage,
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 prepared in advance to have a predetermined toner concentration is put into the developer tank, or a carrier is attached to the surface of the permanent magnet member, and then, Only the toner may be replenished in 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 5 to 20 μm and a magnetization σ ₁₀₀₀ of 50 emu / g or less 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 greater than 50 emu / g,
The torque required for attracting and transporting the magnetic developer becomes large, the spent phenomenon of the carrier is likely to occur, the life of the carrier is shortened, and fogging is unfavorable.

Further, if the average particle size of the carrier is 20 μm or less, a sufficient charge amount of the toner can be obtained, but if the average particle size is less than 5 μm, carrier adhesion tends to occur, which is not preferable. The carrier may be a mixture of two or more of the above 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 composition of the toner is the same as that of a commonly used toner, such as a binder resin (styrene-acrylic copolymer, polyester resin, etc.), a coloring agent (carbon black, etc., but magnetite is used as the magnetic powder described later). In this case, it does not need to be added in particular, and 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, the toner is scattered, and if the amount of the magnetic powder is large, the fixing property is deteriorated. Further, a color toner can be produced by appropriately selecting a colorant.

A vibrating sample magnetometer (VSM-3 manufactured by Toei Industry Co., Ltd.) was used for the measurement of 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).

The volume resistivity is DC4KV / cm electric field, and 10 mg of the sample is filled in a Teflon (trade name) cylinder having an inner diameter of 3.05 mm, and a load of 100 gf is applied to the insulation resistance meter ( 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 (KBN-100 made by Hitachi Metals))
Is used).

[0028]

With the above construction, a small-sized magnetic developer supporting and conveying means having a sleeve-less construction can be used to develop a high-quality image without background fog in a wide toner density range. is there.

[0029]

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, 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 semi-conductive 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 DC power source 10 is connected between the doctor blade 8 and the photosensitive drum 7.

Next, as a magnetic toner, an average particle size of 7 μm,
Volume resistivity 2 × 10 ¹⁴ Ω · cm, triboelectric charge −21.5 μc
/ G was produced. In addition, the compounding ratio is a weight ratio, and is a polyester resin (NCP33B manufactured by Nippon Carbide Industry) 7
0, magnetite (Toda Kogyo EPT500) 25,
Polypropylene (TP32 manufactured by Sanyo Kasei) 4 and charge control agent (Bontron E81 manufactured by Orient Chemical Co., Ltd.) 1 were used, and an external additive (R972 manufactured by Nippon Aerosil) 0.5 was added to the particles formed by these.

The magnetic carrier has a particle size distribution of 10 to 3
7 μm, average particle size 18.5 μm, magnetization σ _{1000 at 1000} Oe is shown in Table 1, volume resistivity 7.2 × 10 ⁸ Ω
・ Cm Ba-Ni-Zn ferrite (KB, Hitachi Metals
N-100) was used.

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 25 mm / sec. The permanent magnet member 4 has an outer diameter of 20 mm, 16 poles, and a surface magnetic flux density of 50.
It was formed at 0 G, and the developing gap g was 0.4 mm, the doctor gap was t 0.3 mm, and the DC bias voltage was -550V.
Table 1 shows the image evaluation results when the toner density and σ ₁₀₀₀ are changed.

[0033]

[Table 1]

As is clear from Table 1, when the toner density is changed while keeping σ ₁₀₀₀ constant, the toner density is low in No. 1 and the image density is low.
In No. 6, since the toner concentration is high, the occurrence of fogging is recognized. On the other hand, in Nos. 2 to 5, good image with high image density and no fog was obtained.

Even in Nos. 7 to 9 in which the toner concentration was kept constant and σ ₁₀₀₀ was changed to a low value, carrier adhesion,
A good image without defects such as fogging is obtained. Next, under the condition of No. 4 in Table 1, a continuous print test of 10,000 sheets was carried out, and the toner density remained at 45 to 60% by weight, and a good image with an image density of 1.35 or more and fog of 0.5 or less was obtained. Was obtained. The torque of the permanent magnet member 4 (see FIG. 1) stayed at 0.7 kg-cm.

On the other hand, as a comparative example, the magnetic developer is applied to an image forming means of a type in which a sleeve is provided outside the permanent magnet member 4 and only the sleeve is rotated to form an image. Surface magnetic flux density of member 4 850G
(The surface magnetic flux density on the sleeve was 790 G), but the toner concentration range in which fogging did not occur was 20 to 30% by weight, and when the toner concentration exceeded 30% by weight, fogging was 0.5.
%, While carrier concentration occurred when the toner concentration was less than 20% by weight.

Next, as the non-magnetic toner, the average particle size is 8.5 μm.
m, volume resistivity 5 × 10 ¹⁴ Ω · cm, triboelectric charge-25.8
A microc / g one was prepared. The mixing ratio is a weight ratio of styrene-acrylic resin 87, carbon black (Mitsubishi Chemical Co., Ltd. MA-100) 8, charge control agent (Orient Chemical Co., Ltd. Bontron S-34) 1, polypropylene (Sanyo Chemical Co., Ltd. TP32) 4, An external additive (H2000 manufactured by Hoechst Wacker) 0.5 was added to the particles formed by these.

The magnetic carrier has an average particle size of 10 μm.
m, volume resistivity 5 × 10 ⁸ Ω · cm, σ ₁₀₀₀ = 35 em
A u / g resin composite carrier was used. The compounding ratio is a weight ratio and is composed of styrene-acrylic resin 49, magnetite (KBC-100 manufactured by Hitachi Metals) 50, and a charge control agent (oil black BY manufactured by Orient Chemical Co., Ltd.) 1, and carbon black (MA600 manufactured by Mitsubishi Kasei Kogyo) on the particle surface. )
0.5 wt% was adhered. The triboelectric charge is +5.1 μc /
It was g.

On the other hand, the photosensitive drum 7 (see FIG. 1) is the same as in the above embodiment, and the permanent magnet member 4 has an outer diameter of 20 mm, 32 mm.
Pole, surface magnetic flux density 400G, development gap g =
0.4 mm, doctor gap t = 0.25 mm, and DC bias voltage −600 V. Table 2 shows the image evaluation results when the toner density is changed.

[0040]

[Table 2]

As is clear from Table 2, the toner density is 3%.
In No. 11 of No. 11, the image density is low, while in No. 15 of 85% of toner density, fogging occurs. On the other hand, in Nos. 12 to 14, there is no fogging,
A good image with high image density was obtained.

Next, when a continuous print test of 10,000 sheets was carried out under the condition of No. 13 in Table 2, the toner density was 40 to 65% by weight without the toner density sensor, and the image density was 1.35. As described above, good images with fog of 0.5% or less were obtained. The torque of the permanent magnet member 4 (see FIG. 1) remained at 0.3 kg-cm 3.

On the other hand, as a comparative example, a magnetic developer comprising the above magnetic developer and a spherical reduced iron powder carrier (σ ₁₀₀₀ = 125 emu / g) having an average particle size of 100 μm (particle size distribution 74 to 149 μm) was used. When an image was formed under the developing conditions (10% by weight of initial toner concentration), the toner concentration was changed to 10 to 20% by weight. When the toner concentration is 15% by weight or more, fogging is recognized, and the permanent magnet member 4
The torque required was 2.0 kg-cm.

Further, when a continuous print test was carried out with the toner concentration sensor attached at an initial toner concentration of 10% by weight, fog exceeded 0.5% after 5,000 sheets and fog exceeded 1% after 10,000 sheets. Spent phenomenon was observed on the surface of the magnetic carrier.

[0045]

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 permanent magnet member, which is the means for supporting the magnetic developer, is hard, the surface wear is small, the change over time is small, and the durability can be improved.

(3) High-definition and high-quality images can be obtained by using a magnetic carrier having a small particle size. (4) 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.

(5) 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

Claims (1)

[Claims] 1. An image forming method for developing an electrostatic charge image on an image carrier, which carries and moves an electrostatic charge image, using a two-component magnetic developer, comprising means for supporting and conveying the magnetic developer. , A magnetic carrier that is composed of a permanent magnet member that is cylindrically and rotatably formed by providing a plurality of magnetic poles on the surface, and that constitutes a magnetic developer that is attracted and conveyed to the surface of the permanent magnet member. An image forming method characterized in that the magnetization σ ₁₀₀₀ in a magnetic field of 1000 Oe is set to 50 emu / g or less.