JP2000284523A - Electrophotographic developer and method for formation of image using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an electrophotographic developer and a method for the formation of images using this developer by which good images of high image quality without abnormal images can be stably obtained even when the level of the conditions for the alternating electric field is raised, and by which stable triboelectric property can be obtained even for continuous use. SOLUTION: In the electrophotographic developer containing at least a toner 28 and a carrier for the formation of images in an alternating electric field, the carrier is a resin-coated carrier prepared by coating the surface of magnetic particle core material with a resin, and it has <=1×10-3 time constant τ(=RC) obtained from the call/call plot semicircle plot in the impedance measurement obtained by the frequency dependence measured by applying sinusoidal AC voltage. In the method for the formation of images, image formation is carried out by using the developer in an alternating electric field.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic developer used for electrophotography, electrostatic printing, and the like, and an image forming method using the same.

[0002]

2. Description of the Related Art In general, an electrostatic image formed by an electrophotographic method, an electrostatic printing method, an electrostatic recording method, or the like is a colorant triboelectrically charged by a carrier formed of metal powder or the like in a dry method. After the dry toner having a binder resin as a main component is developed by an electric field, it is transferred and fixed onto copy paper. At this time, in order to obtain a high-quality image, one of the most important technical issues is how to express the latent image formed on the photoreceptor by development using toner in any situation. Various studies are currently underway.

Conventionally, in such a two-component image forming method, a developer comprising magnetic carrier particles having an average particle diameter of several tens μm to several hundreds μm and a toner having an average particle diameter of several tens μm has been used. The developer was not satisfactory in fine line reproducibility, reproducibility of a halftone portion, reproducibility such as shading difference, etc. due to coarse particles.

In recent years, there has been an increasing demand for higher image quality in copying in the market. In particular, it has become impossible to obtain a sufficiently high image quality with the conventional volume average particle diameter of toner and carrier. It is required to reduce the particle size of the toner.
However, when the particle size of the toner becomes 10 μm or less,
The effect of Van der Waals' force on the Coulomb force during development appears, so-called fog in which toner particles adhere to the background portion of the background portion of the regular developed image portion,
There is a problem that it is difficult to completely prevent fogging by applying a DC bias voltage toward the developing unit carrier. Also, when the carrier particles are made finer, the contact area with the toner increases due to the increase in the carrier surface area, the toner charge amount can be stabilized, and the image quality can be improved. There has been a problem that the toner is easily developed on a regular image portion together with the toner, and when the bias voltage is increased, a phenomenon such as adhesion to a background portion of the image occurs.

[0005] In particular, in recent years, further reduction in toner fixing energy has been demanded as part of a demand for energy saving from energy problems, and the viscosity of toner resin itself has been reduced. This direction is a direction in which a physical force other than the Coulomb force at the time of development is increased, and it is becoming difficult for the toner itself to be developed. As a method of solving such a problem and achieving high image quality, Japanese Patent Application Laid-Open No.
JP-A-181362, JP-A-59-222847, JP-A-59-222851, and JP-A-59-2
Japanese Patent Application Laid-Open No. 22852, JP-A-59-222853, and the like propose an image forming method in which an alternating electric field is applied in a developing process.

According to these methods, there can be obtained an effect that the reproducibility of fine lines, the uniformity of a solid portion, the uniformity of a halftone portion, and the like are improved and the density is increased as compared with the DC electric field application method. However, if the alternating electric field condition is forcibly strengthened to remove fog, for example, if the Vpp (difference between the highest voltage and the lowest voltage due to the AC voltage (peak-to-peak)) or the frequency of the AC is increased, the image becomes Although the resolving power and sharpness are improved, image defects such as solid white spots due to leaks between the latent image surface and the developer carrier occur. Further, if each is too high, there is a problem that image defects such as a decrease in resolution and sharpness of an image occur.

As an image improvement technique using an alternating electric field, Japanese Patent Application Laid-Open No. 9-211897 proposes a technique in which the impedance value is specified. This means that, only when a carrier having a core material of a specific material is used, a high-quality image can be obtained mainly by reducing the edge effect within a specific impedance and capacitance range. ,
In particular, the materials are limited, and there is no disclosure about the effect of improving solid white spots or the like due to leakage between the image surface and the developer carrier.

As described above, various methods have been tried to achieve high image quality, but no means capable of improving all the above-mentioned disadvantages has been obtained so far.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a high quality image free from abnormal images stably even in a high alternating electric field condition in electrophotography and electrostatic printing. Provided is an electrophotographic developer capable of obtaining an image having high fidelity equivalent to that of an initial image, in which the carrier coating layer does not peel off even during use, and has stable triboelectric charging, and an image forming method using the same. It is.

[0010]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that when a developer containing at least a toner and a carrier is developed on a latent image carrier under the application of an alternating electric field, the carrier is used as the carrier. In the case of using a material having a specific structure and specific physical properties, the above-mentioned disadvantages, in particular, solid white spots caused by a leak phenomenon between the latent image surface and the developer carrier can be eliminated, and high image quality can be obtained. The inventors have found that the present invention can be performed, and have completed the present invention.

That is, according to the present invention, in an electrophotographic developer for forming an image under application of an alternating electric field containing at least a toner and a carrier, the carrier is coated on the surface of a magnetic particle core material with a resin. Constant τ (= RC) obtained from Cole-Cole plot semicircle plot in impedance measurement obtained from frequency existence measured under sinusoidal AC voltage
Is 1 × 10 ⁻³ or less. In particular, the volume average particle diameter of the toner is 5 to 10 μm, the binder resin used for the toner is a polyester resin as a main component,
The electrophotographic developer is provided, wherein the carrier coating resin is a silicone resin, or the carrier coating resin layer contains a silane coupling agent having an amino group. Further, according to the present invention, in an image forming method for developing a developer containing at least a toner and a carrier on a latent image carrier under application of an alternating electric field, the carrier covers the surface of the magnetic particle core material with a resin. And the time constant τ (= RC) obtained from the Cole-Cole plot semicircle plot in the impedance measurement obtained from the frequency dependence measured under a sine AC voltage is 1 × 10 ^{− The} image forming method is characterized in that the number is ³ or less.
In particular, as a development condition, the voltage between the peaks of the alternating electric field (V
pp) is 1500 V or more, or the frequency of the alternating electric field is 5 KHz or more.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. The carrier of the electrophotographic developer containing at least a toner and a carrier according to the present invention is obtained by coating the surface of a magnetic particle core material with a resin, and the value of the time constant τ is 1 × 10 ⁻³ or less. It is characterized by being. The value of τ is
This is a measure of the ease with which the charge injected by the alternating electric field is released, and it is considered that when the charge discharge speed is faster than the charge injection speed, a leak phenomenon due to charge accumulation is less likely to occur. Therefore, the smaller the value of τ, the faster the accumulated charge disappears, and the leak phenomenon due to charge accumulation does not occur. Where the value of τ is 1 ×
If it is greater than 10 ^-3 (sec), the injected charge is likely to be accumulated by the charge injection, and when the amount of charge accumulation specific to the carrier exceeds the limit point, the photosensitive drum is rapidly discharged and partially discharged to the image area. The occurrence of white spots is observed.

As for the method of measuring τ, INPEDANCE / GAIN-PHASE manufactured by Toyo Technica Co., Ltd.
Using ANALYZER measuring device, frequency 1Hz-20
000 Hz, AC voltage: 1000 mV, DC voltage: 0 and 10 V, and the resistance value R obtained by assuming an RC parallel circuit from a Cole-Cole plot obtained from the impedance measurement, The time constant τ (= RC) was obtained from the capacitance C.

The magnetic particles of the core material of the carrier may be those conventionally known, and include, for example, ferromagnetic metals such as iron, cobalt, nickel and the like; magnetite, hematite, ferrite and the like. The average particle size of these core particles is usually 10 to 1000 μm, preferably 30 to 50 μm.
0 μm.

Examples of the resin for coating the surface of the magnetic particle core material include a styrene-unsaturated carboxylic acid copolymer, a silicone resin, a maleic resin, a fluorine resin, a polyester resin, and an epoxy resin. Of these, a styrene-unsaturated carboxylic acid-based copolymer such as a silicone resin and a styrene-acrylic copolymer is preferred. Styrene-
In the case of an acrylic copolymer, those having a styrene content of 30 to 90% by weight are preferred. In this case, the styrene content is 3
If the amount is less than 0% by weight, the developing characteristics are low. If the amount exceeds 90% by weight, the coating film becomes hard and easily peels off, shortening the life of the carrier. Specific examples of the raw material of the styrene-unsaturated carboxylic acid copolymer include the following monomers. Styrene and its derivatives, for example, methylstyrene, dimethylstyrene, trimethylstyrene, ethylstyrene, diethylstyrene, triethylstyrene, propylstyrene, butylstyrene, hexylstyrene, heptylstyrene, alkylstyrene such as octylstyrene, fluorostyrene, chlorostyrene, bromo Examples include halogenated styrenes such as styrene, dibromostyrene, and iodostyrene, and nitrostyrene, acetylstyrene, and methoxystyrene. Also, unsaturated carboxylic acids and derivatives thereof,
For example, acrylic acid, methacrylic acid, α-ethylacrylic acid, crotonic acid, isocrotonic acid, tiglic acid, addition-polymerizable unsaturated aliphatic monocarboxylic acids such as angelic acid,
Further, addition-polymerizable unsaturated aliphatic dicarboxylic acids such as maleic acid, fumaric acid, itaconic acid and mesaconic acid, and esters thereof are also included.

Among these resins for coating the magnetic particle core material, silicone resin is generated due to use over time, and the toner is fused to the carrier surface (toner spent). This is particularly preferable in that the developer can be reduced and a long-life developer can be obtained. Further, it is preferable that the resin contains a coupling agent. Examples of the coupling agent include a silane coupling agent, a titanium alkoxide, a coupling agent,
Zirconium alkoxides coupling agents, aluminum alkoxides coupling agents, and the like. Particularly, a silicone resin containing a silane coupling agent is more preferable in that the peeling of the coating layer can be effectively prevented.

The silicone resin used in the present invention may be any conventionally known silicone resin, for example, KR261, KR271, KR271, KR27 manufactured by Shin-Etsu Silicone Co., which is available as a commercial product.
2, KR275, KR280, KR282, KR28
5, KR251, KR155, KR220, KR20
1, KR204, KR205, KR206, SA-4,
ES1001, ES1001N, ES1002T, KR
3093 and SR2100, SR2 manufactured by Toray Silicone Co., Ltd.
101, SR2107, SR2110, SR2108,
SR2109, SR2115, SR2400, SR24
10, SR2411, SH805, SH806A, SH
840 or the like is used.

The silane coupling agent includes the following:
The general formula X-Si- (OR)_Three  X is a functional group that reacts with an organic substance
Wherein R is a hydrolyzable group. In particular, the positive charging
Aminosilane coupling with amino group as rear
Agents are preferred. Amino having amino group in carrier
Includes silane coupling agent to improve image quality
No deterioration of the carrier coating layer over time
Even if it is scraped, the existing inside the carrier coating layer
The appearance of the amino group keeps the chargeability,
An imaging agent can be obtained.

Specific examples of such an aminosilane coupling agent include γ- (2-aminoethyl) aminopropyltrimethoxysilane, γ- (2-aminoethyl) aminopropylmethyldimethoxysilane, γ-aminopropyl Trimethoxysilane, octadecyldimethyl [3- (trimethoxysilyl) propyl] ammonium chloride and the like.

In the present invention, the amount of the coating resin used is generally 1 to 40 parts by weight, preferably 1 to 20 parts by weight, per 1000 parts by weight of the magnetic particle core material of the carrier.
The amount of the silane coupling agent to be used is generally 0.1 to 10 parts by weight, preferably 0.2 to 5 parts by weight, based on 100 parts by weight of the coating resin.

In the present invention, the coating resin contains
It may contain an adhesion-imparting agent, a curing agent, a lubricant, a conductive material, a charge control agent, and the like. For example, the conductive fine powder as the conductive material preferably has a particle size of about 0.01 to 5.0 μm, and is preferably added in an amount of 0.01 to 30 parts by weight based on 100 parts by weight of the coating resin. Further, 0.1 to 20 parts by weight is preferable. As the conductive fine powder, conventionally known conductive powders may be used, and examples thereof include carbon black such as contact black, furnace black, and thermal black.

As for the method of forming the resin layer of the carrier of the electrophotographic developer of the present invention, the composition for forming the resin coating layer is applied to the surface of the carrier core particles by a method such as spraying or dipping, as in the prior art. What is necessary is just to apply. The composition for forming a resin coating layer is prepared by adding a conductive fine powder, a silane coupling agent, and the like to a coating resin solution and dispersing the composition with an appropriate mixer.

Next, the toner of the present invention will be described in detail. The toner of the electrophotographic developer of the present invention comprises at least a colorant and a binder resin. The volume average particle diameter of the toner is preferably 5 to 10 μm. By using a toner having a volume average particle diameter in such a range, it is possible to obtain a high-quality image excellent in fine line reproducibility and the like in which the above-mentioned disadvantages are eliminated. it can. Here, the toner volume average diameter can be measured by various methods. In the present invention, a Coulter Counter TAn manufactured by Coulter Electronics Co., Ltd. was used. Further, the toner of the present invention may be a toner produced by a pulverization method, a toner produced by a production method other than the pulverization method, for example, a polymerization method, or a mixture thereof.

As the binder resin constituting the toner of the present invention, any of those conventionally used can be used. In particular, when the binder resin used for the toner mainly contains a low-temperature fixing type polyester resin, a high-quality image can be obtained using a toner having low-temperature fixing properties and eliminating the above-mentioned disadvantages.

The polyester resin used as a binder in the present invention is mainly obtained by polycondensation of a dihydric alcohol and a dicarboxylic acid. Examples of the dihydric alcohol include polyethylene glycol, diethylene glycol, triethylene glycol, Diols such as propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1,4-butenediol, 1,4-bis (hydroxymethyl) cyclohexane, bisphenol A, hydrogenated Examples include etherified bisphenols such as bisphenol A, polyethylenated bisphenol A, and polyoxypropyleneated bisphenol A, and dihydric alcohols obtained by substituting these with a saturated or unsaturated hydrocarbon group having 3 to 22 carbon atoms. Kill.

Examples of the dicarboxylic acid include maleic acid, fumaric acid, mesaconic acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, succinic acid, and the like.
Adipic acid, sebacic acid, malonic acid, which have 3 carbon atoms
2 to 22 substituted with saturated or unsaturated hydrocarbon groups
Divalent carboxylic acids, their anhydrides, lower alkyl esters, and dimers of linoleic acid.

In order to obtain a polyester resin used as a binder resin, not only a polymer obtained from only the above-mentioned bifunctional monomer but also a monomer containing a component composed of a trifunctional or higher polyfunctional monomer is used. It is also preferred to use polymers obtained from the body. Examples of the trihydric or higher polyhydric alcohol monomer which is a polyfunctional monomer include, for example, sorbitol, 1,2,3,6-hexanetetrol, 1,4-
Sorbitan, pentaethritol, dipentaethritol, tripentaethritol, fujisugar, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, 2-methylpropanetriol, 2- Methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, 1,3,5-trihydroxymethylbenzene and the like can be mentioned. Examples of the trivalent or higher polyvalent carboxylic acid monomer include, for example, 1,2,
4-benzenetricarboxylic acid, 1,2,5-benzenetricarboxylic acid, 1,2,4-cyclohexanetricarboxylic acid, 2,5,7-naphthalenetricarboxylic acid,
2,4-naphthalenetricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane, tetra (methylenecarboxyl) Examples thereof include methane, 1,2,7,8-octanetetracarboxylic acid, trimer acid of embol, and acid anhydrides thereof.

In the present invention, a resin other than the polyester resin can be used as the binder resin, and the polyester resin and another binder resin can be used in combination. As such a binder resin, all known resins can be used alone or in combination. For example, styrene such as polystyrene, poly-P-chlorostyrene, polyvinyltoluene and a homopolymer of a substituted product thereof; styrene-
p-chlorostyrene copolymer, styrene-propylene copolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer,
Styrene-butyl acrylate copolymer, styrene-octyl acrylate copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer,
Styrene-butyl methacrylate copolymer, styrene-α
-Methyl chloromethacrylate copolymer, styrene-acrylonitrile copolymer, styrene-vinyl methyl ether copolymer, styrene-vinyl ethyl ether copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, Styrene-isoprene copolymer, styrene-acrylonitrile indene copolymer,
Styrene-based copolymers such as styrene-maleic acid copolymer and styrene-maleic acid ester copolymer are exemplified. Further, the following resins can be used in combination. Polymethyl methacrylate, polybutyl methacrylate,
Polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, polyurethane, polyamide, epoxy resin, polyvinyl butyral, polyacrylic acid resin, rosin, modified rosin, terpene resin, phenol resin, aliphatic or alicyclic hydrocarbon resin, aromatic Group petroleum resin, chlorinated paraffin, paraffin wax and the like.

The following binder resins are particularly suitable for pressure fixing. These can be used alone or in combination. Polyolefin (low molecular weight polyethylene, low molecular weight polypropylene, polyethylene oxide, polytetrafluoroethylene, etc.), epoxy resin, polyester resin, styrene-butadiene copolymer (monomer ratio 5-30: 95-70), olefin copolymer ( Ethylene-acrylic acid copolymer, ethylene-acrylic acid ester copolymer, ethylene-methacrylic acid copolymer, ethylene-methacrylic acid ester copolymer, ethylene-vinyl chloride copolymer, ethylene-vinyl acetate copolymer, Ionomer resin), polyvinylpyrrolidone, methyl vinyl ether-maleic anhydride copolymer, maleic acid-modified phenol resin, phenol-modified terpene resin.

As the colorant constituting the toner of the present invention, any known colorants for toner can be used. As the black colorant, for example, carbon black, aniline black, furnace black, lamp black and the like can be used. As the cyan coloring agent, for example, phthalocyanine blue, methylene blue, Victoria blue, methyl violet, aniline blue, ultramarine blue and the like can be used. Further, as the magenta colorant, for example, rhodamine 6G lake, dimethylquinacridone, watching red, rose bengal, rhodamine B, alizarin lake, and the like can be used. As a yellow colorant, for example, chrome yellow, benzidine yellow, Hanza yellow, naphthol yellow
Molybdenum orange, quinoline yellow, tartrazine and the like can be used.

Further, the toner of the present invention preferably contains a charge control agent. As such a charge control agent, all conventionally known charge control agents can be used. Examples of positive charge control agents include nigrosine, basic dyes, lake dyes of basic dyes, quaternary ammonium salt compounds, and the like.As negative charge control agents, metal salts of monoazo dyes, salicylic acid, naphthoic acid, and dicarboxylic acid Examples include an acid metal complex. The amount of the charge control agent used is determined by the type of the binder resin, the presence or absence of additives used as necessary, the toner production method including the dispersion method, and is not limited to a specific one. It is used in an amount of 0.01 to 8 parts by weight, preferably 0.1 to 2 parts by weight, based on 100 parts by weight of the binder resin. If the amount is less than 0.01 part by weight, the effect on the variation of the charge amount Q / M during the environmental change is small, and if it exceeds 7 parts by weight, the low-temperature fixability is inferior.

Further, in the present invention, a releasing agent can be contained in the toner, and all known releasing agents can be used. In particular, carnauba wax, montan wax and defatty acid fatty acid type can be used. Oxidized rice wax can be used alone or in combination.
The carnauba wax is preferably a microcrystalline wax, and preferably has an acid value of 5 or less and a particle diameter of 1 μm or less when dispersed in a toner binder. The montan wax generally refers to a montan-based wax refined from a mineral, and is preferably a microcrystal and has an acid value of 5 to 14 like carnauba wax. The oxidized rice wax is obtained by oxidizing rice bran wax with air, and preferably has an acid value of 10 to 30. When the acid value of each wax is less than the respective range, the low-temperature fixing temperature rises and the low-temperature fixing becomes insufficient. Conversely, when the acid value exceeds each range, the cold offset temperature rises, and the low-temperature fixing becomes insufficient. The wax is used in an amount of 1 to 15 parts by weight, preferably 3 to 10 parts by weight, based on 100 parts by weight of the binder resin. If the added amount is less than 1 part by weight, the releasing effect is so thin that a desired effect is hardly obtained, and if it exceeds 15 parts by weight, problems such as remarkable spent on a carrier are caused.

Further, the toner of the present invention can be used as a magnetic toner by further containing a magnetic material. Examples of the magnetic material contained in the magnetic toner of the present invention include magnetite, hematite, iron oxides such as ferrite, metals such as iron, cobalt, and nickel, and aluminum, cobalt, copper, lead, magnesium, tin, and zinc of these metals. , Antimony, beryllium, bismuth, cadmium,
Examples include alloys of metals such as calcium, manganese, selenium, titanium, tungsten, and vanadium, and mixtures thereof. These ferromagnetic materials have an average particle size of 0.1.
About 2 to about 2 μm, and the amount contained in the toner is about 20 to 200 parts by weight per 100 parts by weight of the resin component.
4 parts by weight, particularly preferably 100 parts by weight of the resin component.
0 to 150 parts by weight.

Further, the toner of the present invention may optionally contain additives. Examples of the additive include a lubricant such as Teflon and zinc stearate or a polishing agent such as cerium oxide and silicon carbide; a fluidity imparting agent such as colloidal silica and aluminum oxide; a caking inhibitor; or carbon black and tin oxide. And a fixing aid such as a low-molecular-weight polyolefin.

Next, an image forming method using the developer of the present invention will be described. FIG. 1 is an example of a developing device used in the present invention. In FIG. 1, 3 is a latent image holding member, 21 is a toner supply container, 22 is a non-magnetic sleeve, 2
3 is a fixed magnet, 24 is a magnetic or non-magnetic blade, 26
Is a magnetic particle circulation region limiting member, 27 is a magnetic particle, 28 is a toner, 29 is a developer collection container portion, 30 is a scattering prevention member,
31 is a magnetic member, 32 is a development area, and 34 is a bias power supply. The sleeve 22 rotates in the direction b, and accordingly, the magnetic particles 27 circulate in the direction c. Thereby, contact and rubbing between the sleeve surface and the magnetic particle layer occur, and a toner layer is formed on the sleeve surface. The magnetic particles are c
While circulating in the direction, a part thereof is regulated to a predetermined amount by a gap between the magnetic or non-magnetic blade 24 and the sleeve 22, and is applied on the toner layer. That is, the toner is
The coating is applied to both the sleeve surface and the magnetic particle surface, and an effect equivalent to substantially increasing the surface area of the sleeve is exhibited. From this, it is clear that the magnetic particles are different from the conventional carrier which imparts triboelectric charging to the toner. Therefore, the deterioration of the developer such as spent is basically impossible. Further, the development area 3
In No. 2, a clear developing pole is formed by opposing one of the magnetic poles of the fixed magnet 23 to the latent image surface, and the toner is fly-reversed and developed on the sleeve and from the magnetic particles by the alternating electric field. After the development, the magnetic particles and the undeveloped toner are collected in the developing container with the rotation of the sleeve. The sleeve 22 may be a paper cylinder or a cylinder made of a synthetic resin. However, if the surface of these cylinders is subjected to a conductive treatment or is made of a conductor such as aluminum, brass or stainless steel, it can be used as a developing electrode roller. As the developing bias voltage 34, an alternating voltage having the same peak voltage on the plus side and the minus side or a voltage obtained by superimposing a DC voltage on this alternating voltage can be used.

In particular, by setting the voltage (Vpp) between the peaks of the alternating electric field to 1500 V or more as a developing condition, the movement of the toner is activated to solve the above-mentioned drawback of the conventional method, and to reproduce fine lines at high density. It is possible to obtain a high-quality image with good properties. In particular, as a development condition, the frequency of the alternating electric field is set to 2 kHz or more, preferably 5 kHz or more, so that the movement of the toner is further activated, thereby eliminating the drawback of the conventional method, and achieving high image density and fine line reproducibility. Good and high quality images can be obtained.

[0037]

The present invention will be described more specifically with reference to the following examples. The present invention is not limited to this. All parts are parts by weight.

First, a production example of a carrier having a silicone resin in a coating layer will be described. These can be performed by known means. Production Example 1 of Carrier Particles Styrene-methyl methacrylate copolymer 10 parts Toluene 100 parts The above formulation was dispersed with a homomixer to prepare a coating layer forming liquid. This coating layer forming solution is used to form a coating layer on the surface of 1000 parts by weight of ferrite particles using a fluidized bed type coating apparatus,
The carrier A was obtained by heating the obtained carrier at a temperature of 200 ° C. for 1 hour in a firing device.

Preparation Example 2 of Carrier Particles Carrier B was obtained in the same manner as in Preparation Example 1, except that styrene-methyl methacrylate was changed to silicone resin (SR2100, manufactured by Dow Corning Toray Silicone Co., Ltd.).

Preparation Example 3 of Carrier Particles Carrier C was obtained in the same manner as in Preparation Example 1, except that 1 part of an aminosilane coupling agent (SH6020, manufactured by Dow Corning Toray Silicone Co., Ltd.) was added.

Production Example 4 of Carrier Particles Carrier D was obtained in the same manner as in Production Example 1, except that styrene-methyl acrylate was changed to 80 parts.

Next, a production example of the toner will be described. These can be performed by known means. Toner Production Example 1 Styrene-methyl methacrylate copolymer 60 parts Polyester resin (weight average molecular weight 230,000) obtained from bisphenol A propylene oxide adduct / cyclohexanedimethanol / terephthalic acid 40 parts Carbon black (Mitsubishi Carbon # 44 manufactured by Mitsubishi Carbon Corporation) 8 parts Acid value rice wax 5 parts Salicylic acid metal salt compound 5 parts After sufficiently stirring and mixing the mixture having the above composition in a Henschel mixer, the mixture is rolled at 130 to 140 ° C at a temperature of about 3 to about 3 with a roll mill.
After heating and melting for 0 minutes and cooling to room temperature, the obtained kneaded material was pulverized and classified by a jet mill to obtain toner particles having a particle size of 12 μm. Next, 0.7 part of an additive (titanium oxide fine powder after hydrophobic treatment) was added to 100 parts of the toner particles,
After stirring and mixing with a Henschel mixer, large particles were removed through a mesh to obtain toner a.

Toner Production Example 2 Toner b was obtained in the same manner as in Toner Production Example 1, except that only the particle size was changed to 7 μm.

Toner Production Example 3 Polyester resin (weight average molecular weight 250,000) 90 parts Styrene-methyl methacrylate copolymer 10 parts Carbon black (Mitsubishi Carbon Co. # 44) 8 parts Acid value rice wax 5 parts Salicylate metal salt compound 5 parts Toner c was obtained in the same manner as in Toner Production Example 1, except that the composition for toner production was changed to a mixture having the above composition.

Next, Examples and Comparative Examples of a method for producing a developer and an image forming method will be described. These developers were mixed with 2.5 parts of the toner and 97.5 parts of a carrier by a ball mill to obtain a developer.

Example 1 Using the carrier A obtained in the carrier production example 1 and the toner a obtained in the toner production example 1, a developer was prepared after mixing additives. Using a modified digital copying machine MF200 manufactured by Ricoh Co., Ltd. as described above, an alternating electric field peak voltage (Vpp) of 1000 V and a frequency of 3 kHz were set, and an image was displayed. As a result, a good image was obtained in which the density of the solid image portion was high, the dot reproducibility was good, and the blank portion of the solid portion did not occur.

Example 2 The same procedure as in Example 1 was carried out except that the developing conditions of Example 1 were changed and the voltage (Vpp) between the peaks of the alternating electric field was set to 2000 V.
An image was displayed.

Example 3 An image was formed in the same manner as in Example 1, except that the frequency between the peaks of the alternating electric field was changed to 5 kHz.

Example 4 An image was formed in the same manner as in Example 1 except that a developer was prepared using the carrier A obtained in Carrier Production Example 1 and the toner b obtained in Toner Production Example 2. .

Example 5 An image was formed in the same manner as in Example 1 except that a developer was prepared using the carrier A obtained in Carrier Production Example 1 and the toner c obtained in Toner Production Example 3. .

Example 6 An image was formed in the same manner as in Example 1 except that a developer was prepared using the carrier B obtained in Carrier Production Example 2 and the toner a obtained in Toner Production Example 1. .

Example 7 An image was formed in the same manner as in Example 1 except that a developer was prepared using Carrier C obtained in Carrier Production Example 3 and toner a obtained in Toner Production Example 1. .

Comparative Example 1 An image was formed in the same manner as in Example 1 except that a developer was prepared using Carrier D obtained in Carrier Production Example 4 and Toner a obtained in Toner Production Example 1. .

Table 1 shows the content of each developer and each alternating electric field condition, and Table 2 shows the evaluation of an image obtained by performing image formation. Regarding the image evaluation of each developer, a digital copying machine MF200 manufactured by Ricoh Co., Ltd. was modified so that an alternating electric field could be applied to the developing section, the distance between the developer carrier and the developer regulating member: 0.5 mm, The distance between the developer carrier and the electrostatic latent increasing carrier: 0.4 mm, under the alternating electric field condition shown in Table 1,
Fogging voltage (Vback): 150 V, developing bias: -600 V, photoconductor charging potential: -800 V.

Image evaluation: (solid white spots)
The number of white spots in the 20 A3 solid images after outputting the 100,000 sheets of images was evaluated on the following five levels. ：: excellent, ：: good, □: normal, Δ: bad, ×: worst (image density) As a scale of image density, the initial and 100,000-sheet images were evaluated on the following five levels. ◎: Excellent, ○: Good, □: Normal, Δ: Poor, ×: Worst (Image quality) The standard of image quality is as follows: fine line reproducibility and dot reproducibility are as follows: Were evaluated on the following five levels. ：: excellent, ：: good, □: normal, Δ: poor, ×: worst (fog (background stain)) As a measure of background stain, the image after initial image output was evaluated on the following five levels. ◎: Excellent, ○: Good, □: Normal, △: Poor, ×: Worst (Evaluation of fixability) Using a device with a modified Ricoh MF200 fixing unit using a Teflon roller as a fixing roller. Type 6200 paper was set and a copy test was performed to determine the cold offset occurrence temperature and the high temperature offset occurrence temperature by changing the fixing temperature. In addition, the linear speed of paper feed was evaluated to be 500 mm / s by the evaluation of cold offset.
ec and the high-temperature offset were set to 50 mm / sec. The cold offset occurrence temperature was evaluated in the following five stages. ：: excellent, ：: good, □: normal, Δ: bad, ×: worst (developer life)
The change of the background stain on the copy image after the output of the million images was evaluated on the following five levels. ◎: Excellent, ○: Good, □: Normal, △: Bad, ×: Worst

[0056]

[Table 1]

[0057]

[Table 2]

[0058]

As described above, according to the present invention, a high quality and good image without abnormal images can be stably obtained even under a high alternating electric field condition, and the carrier coating layer does not peel off even during continuous use. Therefore, an image having stable triboelectricity and high fidelity equivalent to the initial image can be obtained.

[Brief description of the drawings]

FIG. 1 is a vertical sectional front view of a developing device using a developing method according to the present invention.

[Explanation of symbols]

 3 Latent Image Holding Member 21 Developer Supply Container 22 Non-Magnetic Sleeve 23 Fixed Magnet 24 Magnetic or Non-Magnetic Blade 26 Magnetic Particle Circulation Area Limiting Member 27 Magnetic Particle 28 Toner 29 Developer Collection Container Part 30 Splash Prevention Member 31 Magnetic Member 32 Developing area 34 Bias power supply 50 Electrostatic latent image 51 Magnetic brush

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03G 15/08 507L 507X (72) Inventor Hiroaki Matsuda 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Company Ricoh (72) Inventor Hiroto Higuchi 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company (72) Inventor Masao Yoshikawa 1-3-6 Nakamagome, Ota-ku, Tokyo Ricoh Company F Term (reference) 2H005 AA01 BA02 BA06 BA07 CA08 CA12 CA26 CA28 EA01 EA05 EA10 FA01 2H073 AA03 BA03 BA13 BA43 BA45 CA03 2H077 AD02 AD06 AD13 AD36 EA01

Claims (8)

[Claims] 1. An electrophotographic developer for forming an image under application of an alternating electric field containing at least a toner and a carrier, wherein the carrier is a resin-coated carrier having a surface of a magnetic particle core material coated with a resin. And a value of a time constant τ (= RC) obtained from a Cole-Cole plot semicircle plot in impedance measurement obtained from frequency existence measured under a sine AC voltage is 1 × 10 ⁻³ or less. Developer for electrophotography. 2. The volume average particle diameter of the toner is 5 to 10 μm.
2. The electrophotographic developer according to claim 1, wherein: 3. The binder resin used for the toner,
2. The electrophotographic developer according to claim 1, comprising a polyester resin as a main component. 4. The electrophotographic developer according to claim 1, wherein the carrier coating resin is a silicone resin. 5. The electrophotographic developer according to claim 1, wherein the carrier coating resin layer contains a silane coupling agent having an amino group. 6. A toner containing at least a toner and a carrier.
Image of developer developed on latent image carrier under alternating electric field
In the forming method, the carrier may be a surface of a magnetic particle core material.
Is a resin-coated carrier coated with a resin, and
Obtained from frequency dependence measured under sinusoidal AC voltage
Cole-Cole plot half in impedance measurement
The value of the time constant τ (= RC) obtained from the circle plot is 1
× 10 ^-3An image forming method characterized by the following. 7. The image forming method according to claim 6, wherein a voltage (Vpp) between peaks of the alternating electric field is 1500 V or more as a developing condition. 8. The developing condition is such that the frequency of the alternating electric field is
7. The image forming method according to claim 6, wherein the frequency is 5 KHz or more.