JPH0772667A - Resin coated magnetic particle for electrostatically charging magnetic brush and its production as well as method for electrostatically charging magnetic brush - Google Patents

Abstract

PURPOSE:To provide the resin coated magnetic particle for electrostatically charging a magnetic brush which hardly causes dielectric breakdown in spite of changing an electrostatic charge bias condition and the process for production of this particle and further, the method for electrostatically charging the magnetic brush by utilizing this particle. CONSTITUTION:The magnetic brush 21A consisting of the resin coated magnetic particles 21 which have resin layers formed by coating the surfaces of magnetic particle core materials with a resin contg. a carbon black and have the resistance ratio of the magnetic particle core materials and the resin layers of 10<3> to 10<-3> is formed on a sleeve 22 and an AC bias voltage having a DC component is impressed to the magnetic brush 21A, to move and rub the magnetic brush 21A, by which a photosensitive drum 110 is electrostatically charged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is incorporated in an image forming apparatus such as a copying machine or a printer adopting an electrostatographic method, and has a conductive resin used in a charging method for contacting an image forming body to charge the image forming body. The present invention relates to a coated magnetic particle, a method for manufacturing the same, and a magnetic brush charging method for uniformly charging an image forming body using a magnetic brush made of resin-coated magnetic particles obtained by the manufacturing method.

[0002]

2. Description of the Related Art Since a magnetic brush formed of magnetic particles as a means for contacting an image forming body is a flexible brush, it is compared with a fur brush charging device or a contact type charging device using a conductive elastic roller. It has an advantage that the damage to the image forming body by mechanical force is small. The magnetic brush charging method referred to here is a method of charging an image forming body using a magnetic brush composed of magnetic particles formed on a cylinder (hereinafter referred to as a sleeve) formed of a conductive member. .

As a means for adopting such a magnetic brush charging method, magnetic particles are adsorbed on a sleeve containing a magnet to form a magnetic brush, and a gap between the sleeve and the image forming body (hereinafter, simply referred to as a gap D An apparatus for charging an image forming body by applying a voltage to the image forming body ( _sd ) and rubbing the surface of the image forming body with a magnetic brush is disclosed (JP-A-59-133569).
issue). Here, the following is also disclosed. The magnetic particles are particles coated with iron powder, or magnetic resin particles obtained by pulverizing magnetic particles and a resin as main components after smelting. The conductivity, magnetic properties, and particle size are taken into consideration so as to prevent them from adhering to the image forming body as much as possible. Specifically, a material having a high saturation magnetization is desired to increase the magnetic attraction force, and the particle diameter is preferably about 20 to 150 μm in order to maintain the uniformity of the magnetic brush. Simultaneous rotation of the sleeve and the magnet roll is suitable for uniform charging. However, even with the charging means, there are cases where the image forming body cannot be completely stabilized and uniformly charged.

As a method for solving such a problem, a method of applying a charging bias for uniformly charging an image forming body by a contact type charging means has been already disclosed (Japanese Patent Laid-Open Nos. 4-21873 and 4-1873).
116674). This is a charging means for charging the image forming body and its surface. A magnetic brush made of magnetic particles is used as the charging means, and an alternating current component having a peak value exceeding the discharge limit value _Vth is _added to the direct current component. The superimposed charging bias is applied and the surface of the image forming body is rubbed. When the voltage applied to the sleeve is a charging bias in which a DC component is superposed with an AC component having a peak value exceeding the discharge limit value V _th , the surface potential V _s (V) of the image forming body (hereinafter simply referred to as the surface potential V _s). Describes that the DC component voltage of the charging bias is approximately equal.

[0005]

However, in the above-described magnetic brush charging method (Japanese Patent Laid-Open Nos. 4-21873 and 4-116674), the charging condition varies depending on the resistance change of the magnetic brush. Become. For example, when the temperature is low and the humidity is low, the resistance of the magnetic particles becomes high, and the magnetic particles may adhere to the image forming body, or the charge may not be sufficiently injected, and uneven charging may occur. In addition, the surface potential V _s may fluctuate even with a charging bias in which an AC component is superimposed on the same DC component due to temperature and humidity fluctuations. Further, the image forming body may be damaged by friction.

As a method for solving such a problem, in order to perform uniform charging, for example, the resistance value of magnetic particles is set to 10 ⁵ to 10 ¹⁰ Ω · cm.
It is necessary to improve the temperature range so that it does not change depending on the temperature and humidity. As a method of adjusting the resistance value of the magnetic particles so as not to depend on the temperature and humidity, it is conceivable to coat the magnetic particle core material (hereinafter simply referred to as the core material) with a resin. The present inventor studied resin-coated magnetic particles suitable for a magnetic brush charging method by forming a resin layer made of a resin in which conductive fine particles are dispersed in order to control electric resistance in a core material.

However, there is a problem that non-uniform charging and breakdown occur only by providing the conductive resin coating layer. From this, the present inventor analyzed the relationship between the resistance ratio of the resin-coated magnetic particles, the thickness of the resin layer, the dispersed state of the conductive fine particles, and the uneven charging phenomenon of the image forming body. If the thickness of the resin layer is not uniform, the bias applied to the gap D _sd between the sleeve and the image forming body easily causes breakdown through the core material having low electric resistance or the resin layer having conductivity. In order to solve such a problem, it is important to set the resistance ratio between the core material and the resin layer having conductivity to be small.

If the conductive resin particles of the resin-coated magnetic particles have the conductive particles dispersed non-uniformly, the resin-coated magnetic particles are biased by the bias applied to the gap D _sd between the sleeve and the image forming body. In addition, the resistance value is locally reduced to cause a breakdown, and banding, which is a charge omission that occurs because a charging bias is not applied, is likely to occur. This is because the conductive resin layer is non-uniformly dispersed due to separation into a portion where a large amount of conductive fine particles are locally mixed and a pure resin portion depending on the forming method. In order to solve such a problem, it is important to uniformly disperse the conductive fine particles in the resin layer.

The present inventor is investigating resin-coated magnetic particles having conductivity, which are produced by various methods.

The so-called wet resin-coated magnetic particles in which conductive particles are dispersed in a solution such as fluidized bed resin-coated magnetic particles and permeation-type magnetic particles have a high granulation rate, so that the resin-coated magnetic particles are large. It is difficult to obtain a desired particle size distribution due to sizing, and the coating layer is likely to be non-uniform.In addition, since the conductive fine particles are dispersed in the solution to contain the conductive particles in the coating layer, the dispersion state becomes non-uniform. As a result, fluctuations in characteristics occur, or conductive fine particles that are not fixed and are released in the coating layer are generated, tend to adhere to the surface of the core material, and uneven charging and breakdown are likely to occur.

On the other hand, the core material and the polymer particles are mechanically mixed, the polymer particles are attached to the surface of the core material to form a coating layer, and then the polymer particles are melted by heat to be fixed, or Alternatively, there is so-called dry resin-coated magnetic particles in which a resin layer is coated on the surface of a core material by dissolving and fixing it in a solvent (Japanese Patent Laid-Open No. 63-37358). Since the resin-coated magnetic particles can solve the non-uniform dispersion of the conductive fine particles and the release of the conductive fine particles, it is possible to find the possibility of preventing the characteristic fluctuation.

Japanese Patent Publication No. 63-26385 discloses that a core material is coated with a resin by dry coating and then heated,
A technique for fusing a resin on a core material is disclosed.

Further, JP-A-63-37858 discloses that a titanium coupling agent is dry-coated on a core material, and further 0.5 μm of resin particles are coated on the core material by dry coating, followed by heating. Techniques for fusing resin layers are disclosed.

As described above, in order to obtain resin-coated magnetic particles for magnetic brush charging suitable for the severe use conditions of a high-speed image forming apparatus, there are still problems to be solved in terms of production and quality. There is.

In view of the above problems, the first object of the present invention is to
Another object of the present invention is to provide resin-coated magnetic particles for magnetic brush charging which are less likely to cause dielectric breakdown even when the charging bias conditions are changed.

The second object of the present invention is to solve the above problems.
It is an object of the present invention to provide a method for producing resin-coated magnetic particles for magnetic brush charging, in which dielectric breakdown is unlikely to occur even if the charging bias condition is changed, and the charging performance does not deteriorate even when used for a long period of time.

The third object of the present invention is to solve the above problems.
Provided is a magnetic brush charging method capable of obtaining a desired charging potential V _s according to an image forming body without being affected by the fluctuations of various conditions related to the contact type charging device. To do.

[0018]

In order to achieve the first object of the present invention, there is provided a resin-coated magnetic particle for a magnetic brush, which is formed by coating the surface of a magnetic particle core material with a resin having conductivity. And a resistance ratio between the magnetic particle core material and the resin-coated magnetic particles is 10 ⁻³ to 10 ³ .

In order to achieve the second object of the present invention, the conductive resin layer is prepared by mixing and stirring conductive fine particles and resin particles having thermoplasticity with the magnetic particle core material and stirring the magnetic particle core material. The surface is coated with the resin particles.

In order to achieve the third object of the present invention, a magnetic brush made of magnetic particles is formed on a carrier, and an AC bias voltage having a DC component is applied to the magnetic brush to form an image forming body. Is a magnetic brush charging method for charging the image forming body by moving and rubbing against the movement of the magnetic particles, wherein the magnetic particles are formed by coating the surface of a magnetic particle core material with a conductive resin. And a resistance ratio between the magnetic particle core material and the resin-coated magnetic particles is 10 ⁻³ to 10 ³ . Further, the resistance of the resin-coated magnetic particles is 1 × 10 ⁵ Ω · cm or more, which is 1 × 10 ¹⁰
It is preferably Ω · cm or less.

[0021]

The present invention will be described in detail below.

[Magnetic Brush Charging Resin Coated Magnetic Particles] FIG. 1 is a schematic view showing the magnetic brush charging resin coated magnetic particles of the first invention.

The resin-coated magnetic particles 21 used for charging the magnetic brush in the present embodiment use a magnetic particle core material (hereinafter simply redefined as core material) 211, which will be described later. Average particle size of tin oxide, chromium oxide (CrO ₂ ) etc. less than 1 μm, resistivity 10 ⁴ Ω · cm
A thermoplastic resin containing the following conductive fine particles 213 dispersed in a weight ratio of 3/100 to 20/100 and having a thickness of 0.05 to 5 μm.
Preferably, the resin-coated magnetic particles obtained by coating to a thickness of 0.5 to 2 .mu.m are subjected to particle size selection by a conventionally known average particle size selection means to obtain the resin-coated magnetic particles 21 having conductivity shown in FIG. To be 212 is a conductive resin layer that covers the surface of the core material 211, and 213 is conductive particles. The resin-coated magnetic particles 21 have an average particle diameter (weight average) of 30 to 150 μm, a saturation magnetization of 20 to 100 emu / g, and a saturation magnetization of 40 to 80 emu / g.
g, and the resistance ratio between the resin layer 212 and the core material 211 is preferably 10 ⁻³ to 10 ³ .

Here, the resistance ratio is a value obtained by dividing the resistance (Ω · cm) of the core material 211 obtained by the method for measuring the resistance (Ω · cm) described later and the resistance after coating the resin layer 212 on the core material 211. It is obtained from.

The resistance (Ω · cm) was measured by placing the core material 211 in a container having a cross-sectional area of 0.50 cm ² and tapping it, and then applying a load of 1 kg / cm ² on the packed core material 211. It is a value obtained by reading the current value when a voltage that generates an electric field of 1,000 V / cm is applied between the bottom electrode.
Similarly, the resistance of the resin-coated magnetic particles 21 is obtained.

Setting the resistance ratio to the above value means that the difference in electric resistance between the resin layer 212 and the core material 211 is small, and even if the resin-coated magnetic particles 21 are incompletely coated or are worn. Even if it changes, it does not affect the characteristics. Therefore, fluctuations in electrical conductivity and the like are prevented, and the resin-coated magnetic particles 21
Will always have a constant performance. In order to effectively bring the resistance ratio of the core material 211 having the resin layer 212 to the above-mentioned value, the resin is usually 0.1 wt% or more, preferably 0.5 to 10.0 wt% with respect to the weight of the core material 211. It is preferable that the resin layer 212 is formed by adjusting so as to fall within the range. The thickness of the resin layer 212 formed by using a resin such as a styrene resin in the above weight ratio with respect to the weight of the core material 211 is preferably 0.5 to 2 μm.
It is within the range of m.

The surface of the core material 211 is preferably surface-treated with a coupling agent.

The above coupling agent preferably comprises at least one of titanium coupling agent, aluminum coupling agent and silane coupling agent.

Specifically, as the silane coupling agent, vinyltrichlorosilane, vinyltriethoxysilane, γ-chlorochloropyrtrimethoxysilane, γ-
Chloropropylmethyldichlorosilane, γ-chloropropylmethyldiethoxysilane, γ-chloropropyldimethoxysilane, γ-aminopropyltriethoxysilane, N
-(β-aminoethyl) -γ-aminopropylmethyldimethoxysilane, N- (β-aminoethyl) -γ-aminopropylmethyldimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropylmethyldimethoxysilane and the like.

Examples of the titanium coupling agent include a monoalkoxy type having an isopropoxy group, a chelate type having an oxyacetic acid residue or an ethylene glycol residue, and a coordinate type in which a phosphite ester is added to tetraalkyl titanate. .

The monoalkoxy type compounds include isopropyl dimethacryl isostearoyl titanate, isopropyl tri (dioctyl phosphate) titanate, isopropyl tricumyl phenyl titanate and isopropyl tri
(N-aminoethylaminoethyl) titanate, isopropyl trioctanoyl titanate, isopropyl triisostearoyl titanate, isopropyl tridecylbenzene sulfonyl titanate, isopropyl tridodecyl benzene sulfonyl titanate, isopropyl tris
(Dioctyl pyrophosphate) titanate and the like.

Examples of the chelate type include bis (dioctyl pyrophosphate) oxyacetate titanate, dicumylphenyloxyacetate titanate, dicumylphenyloxyacetate titanate and diisostearoyl ethylene titanate.

Coordinated types include tetraisopropyl bis (ditridecyl phosphite) titanate and tetraoctyl bis (ditridecyl phosphite) titanate.

Examples of the aluminum coupling agent include acetoalkoxy aluminum diisopropylate.

As the coating resin for the core material 211, a styrene resin (styrene homopolymer, styrene and alkyl (meth)) is used.
Copolymer with acrylate), epoxy resin (copolymer of bisphenol A and epichlorohydrin, etc.), acrylic resin (polymethylmethacrylate, etc.), polyolefin resin (polyethylene, LLDPE, polybutadiene resin, etc.), Polyurethane resin (polyurethane resin, polyester-polyurethane resin, etc.), nitrogen-containing vinyl copolymer (polyvinyl pyridine, etc.), polyester resin (diol such as ethylene glycol and maleic acid, diol such as phthalic acid and maleic acid or Polymers produced from divalent organic carboxylic acids such as phthalic acid), polyimide resins (6 nylon, 6-6 nylon, etc.), polycarbonate (polyethylene phthalate, etc.), cellulose derivatives (nitrocellulose, alkyl cellulose, etc.) ) And Shi It can be mentioned con resin.

Of these, styrene and acrylic resins are particularly preferable.

Styrene and acrylic resin are core materials 211
The resulting resin-coated magnetic particles 21 have good adhesion with
The mechanical strength is improved and the electric resistance is more stable than when other resins are used. Further, even if the resin-coated magnetic particles 21 are stored or used for a long time under high temperature and high humidity conditions (for example, temperature: 30 ° C., humidity: 80%), the potential resistance of the resin-coated magnetic particles 21 hardly changes.

Examples of the styrene resin include styrene, methylstyrene, dimethylstyrene, trimethylstyrene, ethylstyrene, diethylstyrene, triethylstyrene, propylstyrene, butylstyrene,
Alkyl styrenes such as hexyl styrene, heptyl styrene and octyl styrene, halogenated styrenes such as fluorostyrene, chlorostyrene, bromostyrene, dibromostyrene and iodostyrene, nitrostyrene, acetylstyrene and methoxystyrene,
Homopolymers of strene-based monomers such as acetylstyrene and methoxystyrene and methyl (meth) acrylate, ethyl (meth) acrylate, and homopolymers of alkyl (meth) acrylate-based monomers consisting of butyl (meth) acrylate and These copolymers are mentioned.

Among these styrene resins, a copolymer of styrene and an alkyl (meth) acrylate is preferable, and in this case, the alkyl (meth) acrylate is
Usually, methyl methacrylate (MMA) is used. In this case, the molar ratio of the styrene repeating unit to the methyl methacrylate repeating unit in the copolymer is preferably within the range of 5:95 to 95: 5 (more preferably 10:90 to 90:10). By using the copolymer within the above range, the powder maintaining property of the core material 211 under high temperature and high humidity conditions can be maintained for a longer period of time.

The number average molecular weight of the styrene homopolymer or the above copolymer used in this example is usually 50,000.
Is in the range of up to 200,000 and the value of Mw / Mn is usually
It is in the range of 1.0 to 5.0, preferably in the range of 1.5 to 2.5.

The polymer or styrene homopolymer may contain other repeating units. However,
When it is formed of a styrene-based copolymer, in order to effectively use the characteristics of the styrene-based copolymer,
The content of styrenic copolymer in this layer is usually 50
Make it more than weight%.

When the weight average particle diameter of the resin particles is excessively large, the resin particles are less likely to be delayed on the surface of the core material 211, which makes the dry coating process difficult.

The resin particles described above include conductive fine particles 213.
Carbon black, tin oxide, chromium oxide, etc. are dispersed in advance. The mixing weight ratio of the two differs depending on the specific gravity and the like and cannot be specified unconditionally, but for example, about 3 to 20 parts of conductive fine particles are preferable to 100 parts of resin particles. When the content rate of the conductive fine particles 211 is too small, the resistance ratio of the resin-coated magnetic particles 21 does not decrease, and proper conductivity cannot be obtained, while when the content rate is too large, triboelectrification Deteriorates and the durability of the resin-coated magnetic particles 21 deteriorates. Further, the resin particles are less likely to be delayed on the surface of the core material 211, which makes the dry coating process difficult.

The weight average particle diameter is "Microtrac".
(Leads & NORTHRUP)
TYPE7981-OX manufactured by the company) was used for dry measurement. As the carbon black of the conductive fine particles 213, for example, furnace black, acetylene black,
All conductive particles such as channel black can be used. The particle size may be any size as long as it can be dispersed in the resin particles, for example, about 1 to 500 nm.

The dispersion of the conductive fine particles 213 in the resin particles is
Any suitable method may be used. For example, resin particles and conductive fine particles 21
3 is mixed, and the product obtained by heating and kneading this is pulverized, and further, the pulverized product is classified to obtain resin particles having a desired particle diameter, or when forming resin particles. ,
There is a method in which conductive particles 213 are dispersed in a polymerization solvent, a polymerization initiator and a raw material monomer for resin particles are added, and polymerization is performed while incorporating the conductive particles to obtain resin particles.
The particle size of these is preferably 0.1 to 5 μm.

As the core material 211, metals such as iron and nickel, metal oxide particles such as iron oxide, ferrite and magnetite can be used. Especially, if ferrite is used as the core material 211, a material having preferable electric resistance can be obtained. In this embodiment, the resistance of the core material 211 itself is preferably 1 × 10 ¹³ Ω · cm or less, more preferably 1 × 10 ² Ω · cm or more. Also, resin-coated magnetic particles are 1 x 10 ¹⁰
It is preferably Ω · cm or less, more preferably 1 × 10 ⁵ Ω · cm or more. This resistance is obtained by the method described above.

Here, ferrite is a general term for acidic oxides containing iron, and is not limited to spinel type ferrite represented by the chemical formula of MO.FeO ₃ . The ferrite preferably used as the core material 211 may have an indefinite shape, but preferably has a spherical shape. The size of the ferrite is preferably in the range of 20 to 200 μm in weight average particle diameter, and more preferably in the range of 30 to 150 μm. Particles smaller than 20 μm are difficult to form a resin layer. Since the resin-coated magnetic particles 21 obtained have a small diameter, they easily adhere to the image forming body. On the other hand, 20
Particles larger than 0 μm have a large diameter of the resin-coated magnetic particles 21 to be obtained, so that the specific surface area is small, so that it is difficult to uniformly carry the resin-coated magnetic particles 21 on the sleeve 22 at a high density. As a result, the carry amount becomes unstable, and the charge amount becomes unstable.

The ferrite preferably has a circularity of 0.70 or more. When the core material 211 having such a high circularity is used, the resin-coated magnetic particles 21 obtained have a high circularity, so that the fluidity of the resin-coated magnetic particles 21 is high, and as a result, an appropriate amount of resin is used. Since the coated magnetic particles 21 can be stably transported to D _sd , more excellent uniform charging can be expected.

The circularity referred to here is defined by the following equation.

Circularity = (circumferential length of a circle having the same area as the projected area of the particle / contour length of the projected image of the particle) ² The circularity is measured using, for example, an image analyzer (manufactured by Japan Avionics Co., Ltd.) can do.

[Manufacturing Method of Resin-Coated Magnetic Particles for Magnetic Brush Charging] The resin-coated magnetic particles 21 used for magnetic brush charging in this example are the core material 211 surface-treated with magnetic particles and a coupling agent, and carbon black. , Tin oxide,
Chromium oxide (CrO ₂ ) etc. average particle size 1μm or less, resistivity
Weight ratio of conductive particles 213 of 10 ⁴ Ω · cm or less 3/100 to 20
The resin particles dispersed and contained at a ratio of 100/100 are placed in, for example, a device improved from a normal rotary blade type mixing and stirring device and mixed and stirred, whereby the above-mentioned resin particles are electrostatically charged on the surface of the core material 211. After mechanically adhering, mechanical impact force is repeatedly applied at a predetermined temperature for a predetermined time to obtain resin-coated magnetic particles 21. The impact force applied to the mixing of the core material 211 and the resin particles may be, for example, a size such that the ferrite as the core material 211 is not worn or crushed and the resin particles are not crushed, and the details will be described later.

As a device for applying mechanical impact force, a high speed stirring device can be preferably used. Specifically, a high-speed stirring device or the like equipped with a product temperature control device described below can be used. 2 to 6 are explanatory diagrams of the high-speed stirring device, and FIG. 2 is an explanatory diagram schematically showing the structure of the high-speed stirring device. 3 is a plan view of the horizontal rotating body, FIG. 4 is a front view of the horizontal rotating body, and FIG.
Is an enlarged view of a main part of the horizontal rotating body, and FIG.

First, for example, resin particles and fine particles 213 of carbon black as an example of conductive fine particles are mixed,
The product obtained by kneading this is crushed, and further, the crushed product is classified to obtain a resin particle having a desired particle diameter in a resin dispersion step, or when the resin particle is formed, a conductive solvent is used in a polymerization solvent. The resin dispersion step is performed in which the conductive fine particles 213 are dispersed, the polymerization initiator and the raw material monomer of the resin particles are added, and the polymerization is performed while incorporating the conductive fine particles. Thus, the resin-coated magnetic particle 21 raw material is obtained.

The upper lid 2 of the mixing and stirring tank 1 is provided with a raw material charging port 3 in which a charging valve 4 is installed, a filter 5 and an inspection port 6. A resin layer 212 in which fine particles 213 of carbon black that have been charged from the raw material charging port 3 through the charging valve 4 are dispersed
The raw material of the resin-coated magnetic particles 21 formed with is agitated by the rotor blades 9A, 9B, 9C of the horizontal rotating body 9 driven by the motor 13, and thereby a mechanical impact force is applied. As shown in FIG. 3, the horizontal rotating body 9 includes a central portion 9D that is rotated in the arrow direction and three rotary blades 9A, 9B, and 9C that are provided at symmetrical positions with respect to the central portion 9D. Be prepared. As shown in FIGS. 4 and 5, these rotary blades are inclined at an angle θ from the bottom 1A of the mixing and stirring tank 1 (see FIG. 2).
It has a slope that stands up at. The angle θ is preferably 20 to 60 °.

Therefore, the charged resin-coated magnetic particle 21 raw material is scraped upward by these rotary blades. The raw material of the resin-coated magnetic particles 21 that has been scraped up collides with the inclined upper inner wall or lower inner wall of the mixing and stirring tank 1, and falls into the rotation range of the rotary blades 9A, 9B, 9C of the horizontal rotating body 9. On the other hand, a vertical rotator 10 is provided above the horizontal rotator 9, and the vertical rotator 10 is composed of two rotor blades and is rotated in the vertical direction so that the inner wall of the mixing and stirring tank 1 is rotated. It collides with the bounced core material 211. This vertical rotating body 10
Serves to promote the stirring of the raw material for the resin-coated magnetic particles 21 and prevent the aggregation thereof.

Thus, the raw material of the resin-coated magnetic particles 21 repeatedly collides with the horizontal rotating body 9, the vertical rotating body 10, the inner wall of the mixing and stirring tank 1, or the raw materials of the resin-coated magnetic particles 21 collide with each other, As a result, mechanical impact force is applied, and the surface of the resin coating layer 212 is improved. The resin-coated magnetic particles 21 thus obtained are taken out from the product discharge port by opening the discharge valve 12.

The jacket 8 is made of, for example, resin-coated magnetic particles.
When the 21 raw materials are stirred, they function as heating means, and after the raw materials of the resin-coated magnetic particles 21 are stirred, they function as cooling means. With this jacket 8, the outer wall of the mixing and stirring tank 1 has a height of approximately 3/4, It is covered to the height at which the vertical rotating body 10 is attached. Resin coated magnetic particles
21 The material temperature of the raw material is measured by a thermometer 7 and is preferably a temperature at which the resin particles do not melt due to the jacket 8. In particular, the upper limit is a temperature 50 ° C. higher than the glass transition point of the resin particles. Controlled by.

When the temperature exceeds 50 ° C. higher than the glass transition point of the resin particles, the tackiness of the resin particles gradually increases, and as a result, the resin particles tend to aggregate and agglomerate. Further, as the product temperature becomes higher, the core material 211 is bonded by the resin particles and granulated, so that the resin particles cannot be uniformly attached.

The thermometer 7 is a chromel-alumel thermocouple with a length of 10 cm and a diameter of 6.4 mm and a cover made of stainless steel (T40-K-2-6.4-100-U-304-K manufactured by Hayashi Denko Co., Ltd.).
X-G-3000) is used. This thermometer 7 is inserted from the height of approximately 1/3 of the mixing and stirring tank 1 toward the center of the horizontal rotating body 9 in parallel with the bottom 1A of the mixing and stirring tank 1, thereby It is attached to 1. The insertion depth is set so that the tip of the thermometer is located at a length of about 1/5 from the tip side of the blade, and only the horizontal rotating body 9 is provided. Good. Therefore,
The product temperature referred to here is to insert the product temperature probe into a particle group in which the resin-coated magnetic particles 21 raw material in which the resin particles are attached to the core material 211 and to which the impact force is applied and flows, and the particles are attached to the probe. Resin-coated magnetic particles obtained by contact with a randum
It is the average of 21 approximate surface temperatures.

The glass transition point is the differential scanning calorimetry (DS
According to C), for example, "DSC-20" (manufactured by Seiko Denshi Kogyo KK) can be used for measurement. Specifically, about 10 mg of the sample is heated at a constant temperature rising rate (10 ° C./min) and obtained by the intersection of the baseline and the slope of the endothermic peak.

The high-speed stirring device described above has a so-called scraping mechanism, and D has a so-called blow-up mechanism. This allows
Resin-coated magnetic particles impacted by a horizontal rotating body
Since 21 can return to the rotating direction of the blade of the horizontal rotating body again, the stirring efficiency is good, which is preferable.

The time for applying the mechanical impact force is usually 5
~ 40 minutes. The magnitude of mechanical impact force is usually 3
-20 m / s, preferably 4-15 m / s. When the peripheral speed is lower than 3 m / s, blocking is likely to occur. If it is higher than 15 m / s, the resin layer 212 may be broken. Alternatively, resin coated magnetic particles 21
The core material 211 itself may be destroyed.

Resin-coated magnetic particles thus obtained
Reference numeral 21 is for providing the resin layer 212 having good film-forming property and high coating efficiency.

Although the dry coating process is not always clear, it is considered as follows.

Core material 21 in the state of ordered mixture
The resin particles adhering to 1 are rearranged while being moved or deformed on the core material 211 under the impact force. Further, the resin particles are fixed while being in contact with the core material and the adjacent resin particles, and the deformation is pushed into the voids, and the resin layer 212 becomes coarse and dense.

When the surface of the core material 211 is further treated with a coupling agent, the resin particles are strongly adhered to the core material 211. Therefore, even if the resin amount is increased to thicken the resin layer 212, unfixed resin is not generated. Therefore, the coating efficiency does not decrease. The resin-coated particles thus obtained have a resin layer 21 even if they are repeatedly used.
Since the 2 is not easily scratched and the characteristics of the core material 211 are not exposed on the surface, uniform charging can be performed.

[Magnetic Brush Charging Device and Biasing Method Thereof] A schematic structure of an image forming apparatus suitable for adopting the contact charging method of the present invention will be described.

FIG. 9 is a sectional view showing the outline of the construction of an image forming apparatus which employs the contact charging method of the present invention.

In the figure, an image forming member 110 is a drum-shaped photosensitive member composed of a (-) charged coating type OPC which rotates in the direction of an arrow (hereinafter, this is abbreviated as a photosensitive drum). , A conductive substrate 110b and a photosensitive layer covering the surface thereof
110a, the film thickness is 15 to 30 μm, the dielectric constant is 2.0 to 5.0, and the conductive base material 110b is grounded.

A uniform exposure lamp 15, a charging device 20, an exposure part on which the image light L from the writing device is incident, a developing device 30, a transfer roller 43, and a cleaning device 50 are provided on the peripheral portion of the photosensitive drum 110. A sheet feeding system including a sheet feeding tray 40, a second sheet feeding roller 42, a transfer roller 43, and the like.

FIG. 7 is a sectional view showing the magnetic brush charging device in this embodiment. FIG. 8 is a graph showing the charging bias applied to the magnetic brush charging device of this embodiment.

The configuration of the magnetic brush charging device in this embodiment will be described.

A uniform exposure lamp 15 is set on the upstream side of the charging device 20 to eliminate the potential of the photoconductor before charging. As a result, the surface potential V _s of the photosensitive drum 110 becomes approximately 0 V, so that the current of the DC component that flows during charging becomes constant.

The charging device 20 includes a magnetic particle 21 on the sleeve 22.
By forming a magnetic brush 21A made up of the above and applying a charging bias in which an AC component is superimposed on a DC component to the sleeve 22, a gap D _sd between the sleeve 22 and the photosensitive drum 110 (hereinafter simply referred to as a gap D _sd) A magnetic brush charging device which forms an oscillating electric field at least twice as high as the charging start voltage, and causes the magnetic brush 21A to slide on the moving photosensitive drum 110 under the oscillating electric field to charge the same. Is charged with a charging bias from a DC constant current source 28 and an AC constant current source 27 via a protection resistor 29, and is particularly desired in accordance with the information relating to the resistance change of the photosensitive layer 110a of the photosensitive drum 110 and the magnetic particles 21. It has a function of adjusting the DC and AC constant current sources 27 and 28 so as to obtain the charging potential V _s .

The casing 25 has a storage portion for the resin-coated magnetic particles 21, and a sleeve 22 containing a magnet roller 23 is arranged therein. A regulation plate 26 made of a non-magnetic member is provided at the opening of the casing 25 to regulate the thickness of the resin-coated magnetic particle 21 layer attached to the sleeve 22 and carried out. The gap between the regulation plate 26 and the sleeve 22 is the conveyance amount of the resin-coated magnetic particles 21, that is, the sleeve 22 in the charging area.
The existing amount of the resin-coated magnetic particles 21 is adjusted to 10 to 300 mg / cm ² , and particularly preferably 30 to 150 mg / cm ² . The gap D _sd between the photosensitive drum 110 and the sleeve 22 is connected by a magnetic brush 21A made of resin-coated magnetic particles 21 regulated to a predetermined layer thickness, and adjusted to a desired charging voltage.

The resin-coated magnetic particles 21 are spherical ferrite particles coated so as to have the above-mentioned conductivity. In order to perform good charging, the outer shape is spherical and the particle size is adjusted to 50 μm and the specific resistance is set to 10 ⁸ Ω · cm. The frictional charge amount with the toner is −5 μC / g under the condition that the toner concentration is 1%. .

The average particle size of the resin-coated magnetic particles 21 is
It is preferably 150 μm or less and 30 μm or more. In the contact type charging device shown in the present embodiment, a magnetized strength of 20 to 100 emu / g, more preferably 40 to 80 emu / g is preferably used.

The sleeve 22 is a sleeve formed of a non-magnetic and conductive metal such as stainless steel. The surface of the sleeve 22 has an average surface roughness of 2 to 2 for stable and uniform transfer of the resin-coated magnetic particles 21. It is preferably 15 μm. If it is smooth, it cannot be sufficiently conveyed, and if it is too rough, an overcurrent flows from the convex portions on the surface, and uneven charging tends to occur in either case. Sandblasting is preferably used to achieve the above surface roughness. Further, the surface of the sleeve 22 may be covered with a high resistance member. Such a sleeve 22
In the above, the relative rotation with the magnet roller 23 causes the particle layer formed on the surface of the sleeve 22 to undulate and move in a wavy shape, so that new resin-coated magnetic particles 21 are successively supplied to the sleeve. 22 Even if the particle layer on the surface has some unevenness in layer thickness, the effect is sufficiently covered by the above-mentioned wavy undulation so as not to cause a practical problem. The carrying amount of the resin-coated magnetic particles 21 is preferably 30 to 150 mg / cm ² . The conveyance speed of the resin-coated magnetic particles 21 due to the rotation of the sleeve 22 may be slower than the moving speed of the photosensitive drum 110, but it is preferable that it is almost the same or higher. Further, it is preferable that the conveying direction by the rotation of the sleeve 22 is the same in the charging section. Uniformity of charging is better in the same direction than in the opposite direction. However, it is not limited thereto.

The diameter of the sleeve 22 is preferably 5 to 20 mmφ. With the above diameter, a contact area necessary for charging is secured. If the contact area is unnecessarily large, the charging current will be excessive, and if it is small, uneven charging is likely to occur. When the diameter is small as described above, the resin-coated magnetic particles 21 are
Is likely to scatter or adhere to the photosensitive drum 110, it is preferable that the linear velocity of the sleeve 22 be slower in the circumferential direction than the photosensitive drum 110.

The magnet roller 23 is a columnar magnet body fixedly arranged inside the sleeve 22, and the magnet roller 23 has an S pole and an N pole at the periphery so that the surface of the sleeve 22 has 500 to 1,000 Gauss. It is arranged and magnetized. Of these magnetic poles, the magnetic pole in the charging area closest to the photosensitive drum 110 is referred to as the main magnetic pole.

The position of the main magnetic pole of the magnet roller 23 closest to the photosensitive drum 110 is the sleeve 22 and the photosensitive drum 11.
At the position closest to 0, that is, near the center line connecting the center of the photosensitive drum 110 and the center of the sleeve 22,
Angle θ formed by the straight line connecting the center of the
Is preferably in the range of −15 ° ≦ θ ≦ 15 °, particularly preferably on the upstream side (θ> 0). Here, the sleeve 22
Will be described using a magnet including a magnet in a conductive cylinder, but the present invention is not limited to this, and a magnet roller alone and a method of rotating the magnet roller may be used.

The charging power source comprises an AC constant current source 27 and a DC constant current source 28. The DC constant current source 28 supplies a DC component preset so that the charging potential V _S becomes constant, and an AC constant current is supplied. The source 27 is a power source that supplies a charging bias on which an AC component for transferring charges to the photosensitive drum 110 or removing dust such as toner from the photosensitive drum 110 is superimposed.
_{Although it} depends on the size of _sd , the charging voltage for charging the photosensitive drum 110, etc., the gap is maintained between 0.1 and 5 mm,
600-corresponding to a DC component of -150 μA, which is more than twice the discharge start voltage V _th -300--1500 V as a peak-to-peak voltage V _PP.
3,000V, current value of 0.3-10KHz is 500μA-5000μA
By supplying the charging bias superposed with the AC component of (1) through the protective resistor 29, the preferable charging condition could be obtained. Although the AC component is within the white range shown in FIG. 8, the charging is performed stably. In FIG. 8, the range shaded by vertical lines is the range where dielectric breakdown is likely to occur, the range shaded is the range where charging unevenness is likely to occur, and the low-frequency region shaded with dots is uneven charging. Is the range that produces. The waveform of the AC component is not limited to a sine wave, and may be a rectangular wave, a triangular wave, or the like. The photosensitive drum 110 is hardly charged when the AC component is not superposed on the DC component.

The process CPU 70 generally controls each process member for executing the electrostatographic process. The direct current I _DC and the DC current I _DC set by the operation panel 72 corresponding to each photosensitive drum 110 are set. A conversion table of I _DC and I _AC to be reset when the temperature and humidity change corresponding to the above set values is written in the ROM 71.

The basic operation of the copy process of this embodiment is as follows.
When a copy start command is sent from the operation panel 72 to the process CPU 70, the photosensitive drum 110 starts rotating in the arrow direction under the control of the process CPU 70. While rotating the photosensitive drum 110 in the direction of the arrow, the sleeve 22 is rotated in the same direction as the arrow at a peripheral speed of 0.2 to 0.9 times the peripheral speed of the photosensitive drum 110. The layer of the coated magnetic particles 21 is magnetically connected in a chain shape at a position facing the photosensitive drum 110 on the sleeve 22 by a magnetic force line of the magnet roller 23 to form a kind of brush, a so-called magnetic brush.
Form 21A. The magnetic brush 21A is conveyed in the rotating direction of the sleeve 22 and contacts the photosensitive layer 110a of the photosensitive drum 110 to rub it. According to the rotation of the photosensitive drum 110 between the sleeve 22 and the photosensitive drum 110, an oscillating electric field is first formed by the charging device 20 at the same time as or after the rotation of the photosensitive drum 110 is started, and then with respect to the range including the image forming area. As a result, a DC electric field is formed so as to be superimposed on the oscillating electric field, and this image forming area is uniformly charged and passes. On the photosensitive drum 110, for example, image light L from a writing device is irradiated to form an electrostatic latent image in an image forming area.

A two-component developer (hereinafter, simply referred to as a developer) is loaded in the developing device 30, and the developer is agitated by agitating screws 33A and 33B and then placed outside the magnet roller 32. Is attached to the outer circumference of the rotating developing sleeve 31 to form a magnetic brush 21A of the developer, and a predetermined bias voltage is applied to the developing sleeve 31 so that the photosensitive drum
Reverse development is performed in the development area facing 110.

From the paper feed cassette 40, the recording papers P are fed one by one by the first paper feed roller. The fed recording paper P is transferred to the photosensitive drum 11 by the second paper feed roller 42 which operates in synchronization with the toner image on the photosensitive drum 110.
Dispatched on 0. Then, by the action of the transfer roller 43,
The toner image on the photosensitive drum 110 is transferred onto the recording paper P,
Separated from above the photosensitive drum 110. The recording paper P on which the toner image has been transferred is sent to a fixing device (not shown) via a conveying means, is sandwiched by a heat fixing roller and a pressure roller, is fused and fixed, and is then discharged to the outside of the apparatus. The photosensitive drum 110 that rotates with the toner remaining without being transferred to the recording paper P.
The surface of 1 is scraped off and cleaned by a cleaning device 50 equipped with a blade 51 and the like, and stands by for the next copying.

As shown in Table 1, the resistance of the resin-coated magnetic particles 21 is selected to be 10 ³ to 10 ¹² Ω · cm, and the resistance ratio of the resin-coated magnetic particles 21 obtained by the above-described manufacturing method is set to the core material 211. On the other hand, the charging device 20 shown in the present embodiment is adjusted by 10 ⁻³ to 10 ^3.
3 shows the result of observing the surface condition of the photosensitive drum 110 adopted in FIG.

[0088]

[Table 1]

When the resistance of the resin-coated magnetic particles 21 is 10 ⁴ Ω · cm or less, the charging becomes non-uniform and the breakdown is large.
On the other hand, at 10 ¹¹ Ω · cm or more, charging was not sufficiently performed due to the high resistance. These areas are unfavorable areas, and are unfavorable areas, and are therefore marked with an X.

Further, when the resistance ratio of the resin-coated particles to the resistance of the core material 211 is smaller than 10 ^-4 or larger than 10 ^-4 , a cross mark is also given to cause uneven charging.

Δ indicates that the resin-coated magnetic particles 21 did not cause dielectric breakdown under the charging bias conditions described above, but slightly generated uneven charging.

◯ indicates that even if a charging bias was applied, dielectric breakdown was not caused, and the charging could be performed substantially uniformly over about 10,000 copies.

⊚ indicates that even if a charging bias is applied according to the photosensitive drum and temperature and humidity, charging unevenness does not occur, dielectric breakdown does not occur, and this state continues for about 10,000 copies.

Thus, the resistance ratio between the core material 211 and the resin-coated magnetic particles 21 obtained by resin-coating the core material 211 is small, that is, between 10 ^{−3 and} 10 ³ resin-coated magnetic particles. With No. 21, stable charging was possible.

A particularly preferred range is from 10 ^-1 to 10 ¹ . The resistance of the resin-coated magnetic particles 21 is 10 ⁵ to 10 ¹⁰
Ω · cm is preferable, and a particularly preferable range is 10 ⁷ to 10 ⁹ Ω · cm.
Is.

[0096]

According to the first invention of the present application, in a resin-coated magnetic particle for a magnetic brush, which is formed by coating the surface of a magnetic particle core material with a conductive resin, the magnetic particle core material and the resin-coated magnetic particle are provided. By setting the resistance ratio with respect to 10 ⁻³ to 10 ³ it was possible to provide resin-coated magnetic particles for magnetic brush charging, which are less likely to cause dielectric breakdown even when the charging bias conditions are changed.

In the second invention of the present application, in the resin layer having conductivity, conductive fine particles, resin particles having thermoplasticity, and magnetic particle core material are mixed and stirred to coat the surface of the magnetic particle core material with the resin particles. By doing so, it was possible to provide a method for producing resin-coated magnetic particles for magnetic brush charging, in which dielectric breakdown is unlikely to occur even when the charging bias condition is changed, and the charging performance does not deteriorate even after long-term use.

In the third invention of the present application, a magnetic brush made of magnetic particles is formed on a carrier, and an AC bias voltage having a DC component is applied to the magnetic brush so that the magnetic brush moves with respect to the movement of the image forming body. In the magnetic brush charging method for charging the image forming body by rubbing, the magnetic particles have a resin layer formed by coating a surface of a magnetic particle core material with a conductive resin, By setting the resistance ratio between the particle core material and the resin-coated magnetic particles to be 10 ^-3 to 10 ³ , even if various conditions related to the contact type charging device are changed, they are affected by those changes. In other words, it was possible to provide a magnetic brush charging method capable of obtaining a desired charging potential V _s according to the image forming body.

[Brief description of drawings]

FIG. 1 is a schematic view showing resin-coated magnetic particles for charging a magnetic brush of the first invention.

FIG. 2 is an explanatory diagram schematically showing the structure of a high-speed stirring device.

FIG. 3 is a plan view of a horizontal rotating body.

FIG. 4 is a front view of a horizontal rotating body.

FIG. 5 is an enlarged view of a main part of a horizontal rotating body.

FIG. 6 is a plan view of a high speed stirring device.

FIG. 7 is a cross-sectional view showing a magnetic brush charging device in this embodiment.

FIG. 8 is a graph showing a charging bias applied to the magnetic brush charging device of the present embodiment.

FIG. 9 is a cross-sectional view showing an outline of the configuration of an image forming apparatus adopting the contact charging method of the present invention.

[Explanation of symbols]

 20 Charging device 21 Resin-coated magnetic particles 21A Magnetic brush 22 Sleeve 23 Magnet roller 26 Regulation plate 110 Image forming body (photosensitive drum) 211 Magnetic particle core material 212 Resin layer 213 Conductive fine particles

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yukie Hososhizawa, Konica stock company, 2970 Ishikawa-cho, Hachioji, Tokyo (72) Inventor Masayasu Onodera, 2970 Ishikawa-machi, Hachioji, Tokyo Konica stock, company

Claims (3)

[Claims] 1. A resin-coated magnetic particle for a magnetic brush, which is formed by coating the surface of a magnetic particle core material with a conductive resin, wherein a resistance ratio between the magnetic particle core material and the resin-coated magnetic particle is 10 ^{−. A} resin-coated magnetic particle for charging a magnetic brush, characterized by having a particle size of ³ to 10 ³ . 2. The conductive resin layer is characterized in that conductive particles and thermoplastic resin particles and magnetic particle core material are mixed and stirred to coat the surface of the magnetic particle core material with the resin particles. Method for producing resin-coated magnetic particles for magnetic brush charging. 3. A magnetic brush made of magnetic particles is formed on a carrier, and an AC bias voltage having a DC component is applied to the magnetic brush so that the magnetic brush moves and rubs against the movement of the image forming body. In the magnetic brush charging method for charging the image forming body, the magnetic particles have a resin layer formed by coating the surface of the magnetic particle core material with a resin having conductivity, and the magnetic particle core material and the magnetic particle core material A method for charging a magnetic brush, wherein the resistance ratio to the resin-coated magnetic particles is 10 ^-3 to 10 ³ .