KR0163996B1 - Two-component type developer developing method and image forming method - Google Patents

Abstract

The two-component developer for electrostatic image development consists of at least a toner and a magnetic carrier. The toner has a number average particle size D1 that satisfies the relationship of the weight average particle size D4 and D4 / D1? The magnetic carrier is composed of composite particles composed of magnetic iron compound particles, nonmagnetic metal oxide particles, and a binder consisting of a phenolic resin. The composite particles contain magnetic iron compound particles and nonmagnetic metal oxide particles in a ratio of 80-99% by weight in total. The magnetic iron compound particles have a number average particle size r _a , and the nonmagnetic metal oxide particles have a number average particle size r _b that satisfies the relationship of r _b / r _a 1.0.

Description

Two-component developer, developing method and image forming method

1 is a schematic diagram of an apparatus for implementing one embodiment of a developing method according to the present invention.

2 is a schematic diagram of a device for measuring the (electrical) resistivity of a magnetic carrier, a carrier core and a metal oxide.

3 is a schematic diagram of an apparatus for implementing one embodiment of an image forming method according to the present invention.

4 is a cross-sectional view of a magnetic carrier core particle according to one embodiment of the present invention, wherein the nonmagnetic metal oxide (hematite) particles are present locally on the core particle surface preferentially over the ferromagnetic metal oxide (magnetite) particles.

* Explanation of symbols for main parts of the drawings

1: developing sleeve 2: developer adjusting member

3, 319, 329: photosensitive drum 21: lower electrode

22: upper electrode 23: insulator

24 Ammeter 25 Voltmeter

26 constant voltage regulator 27 sample carrier

28: guide ring 301: the main assembly of the device

302, 303: transfer material supply tray 304, 305: transfer material supply roller

307, 308: paper feed guide 309: border roller

310: Gliper 311: transfer material separation charger

312: Disconnect Claw 313: Warrior Charger

314, 322: separate charger 315: transfer drum

316: transport belt means 317: discharge tray

318: fusing unit 320: discharge charger

321: cleaning device 323: first charger

326: rotating member 327Y: yellow developing device

327M: Magenta Developer 327C: Cyan Developer

327BK: Black Developing Device 328: Original

The present invention relates to a two-component developer, a developing method, and an image forming method for developing an electrostatic charge image in an electrophotographic method, an electrostatic recording method, and the like.

To date, various electrophotographic methods have been disclosed in US Pat. Nos. 2,297,691, 3,666,363, 4,071,361, and the like. In these methods, an electrostatic latent image is formed on the photoconductive layer by irradiating a light image corresponding to the original, and the toner adheres on the latent image to develop the latent image. The resulting toner image is then transferred to a transfer material such as paper, and then settled by heating, pressurization, heating and pressurization, or the like, or by solvent vapor, as necessary, to obtain a copy or print.

In the developing latent image, the toner image is formed by the electrostatic action of the electrostatic latent image due to the charged toner particles. In general, in the method of developing an electrostatic latent image using toner, a two-component developer composed of a mixture of toner and a carrier is suitably used in a color copier or a printer requiring high image quality.

In recent years, with advances in computer engineering, high-definition TV technology, and the like, a means for outputting high-resolution color images is desired. For this purpose, efforts have been made to provide a color image of a toner having a higher image quality and resolution than the image quality and resolution of a silver salt photographic image. In response to this demand, various studies have been made in terms of process and developer.

For example, with respect to a developer, representative attempts have been made to use smaller particles of carrier and toner. However, when smaller particles are used, the difficulty of handling the powder is further increased, and the difficulty of optimizing electrophotographic performance, for example, optimization of transfer and fixation other than development, is increased. Therefore, there is a certain limit to improving the image quality by only improving the toner.

On the other hand, as an improvement effort in terms of electrophotography, the possibility of achieving high image quality by increasing the density of the magnetic brush on a developer carrying member such as a developing sleeve can be increased. Densification of the magnetic brush can be achieved by performing development in the part between the magnetic poles in the developing sleeve in terms of processing, or by using a smaller intensity magnetic pole in the developing sleeve. These means suppress the influence of the magnetic brush, but suffer from problems such as dispersion and poor conveying performance due to insufficient restraint of the developer. Thus, they cannot be employed. In addition, densification of the magnetic brush can be achieved by the use of magnetic carrier particles having a smaller particle size or lower magnetic force.

For example, Japanese Patent Laid-Open No. 59-104663 describes using a magnetic carrier having a small degree of saturation magnetization. When a magnetic carrier having a small degree of saturation magnetization is simply used, the reproducibility for thin lines is increased, but as the restraint of the magnetic carrier particles on the developing sleeve becomes weaker, the magnetic transferred to the photosensitive drum causing image damage The so-called carrier attachment phenomenon of the carrier is likely to occur.

It is also known that carrier attachment is likely to occur when a magnetic carrier of small particle size is used. For example, Japanese Patent Publication No. 5-8424 describes the use of a smaller particle size magnetic carrier and toner to perform a non-contact phenomenon under a vibrating electric field. Japanese Laid-Open Patent Publication No. 5-8424 includes the fact that the magnetic carrier of high specific resistance is effective for improving carrier adhesion in a developing method using a vibration electric field. The use of such magnetic carriers with higher resistivity has been found to be insufficient in some cases, particularly to improve carrier adhesion to provide higher image quality, even when small amounts of carrier cores with low resistivity are exposed to the surface. . In the above method employing the non-contact developing method, a considerably good image density can be obtained to provide an image in which the carrier adhesion has been removed in the case where the magnetic carrier is provided with a large degree of magnetization in the magnetic pole, but the image density of the magnetic carrier It is easy to fall remarkably when magnetization intensity falls.

In general, magnetic resin carriers have a higher resistivity than those of carriers having iron powder cores or metal oxide cores (eg, ferrite, magnetite). For example, in the case of a magnetic resin carrier containing an increased amount of magnetic material by using magnetic materials having different particle diameter ratios, if the internally added magnetic material contains a magnetic material having a low specific resistance, a higher magnetic restraining force is provided. It is possible to do However, using the above-described magnetic carriers cannot sufficiently improve carrier adhesion in the particular case used in the developing method using an alternating magnetic field.

As described above, various methods have been devised to realize higher image quality while preventing carrier adhesion, but it is still desired to provide a two-component developer that solves the above problem.

Therefore, a general object of the present invention is to provide a two-component developer that solves the above problem.

A more specific object of the present invention is to provide a two-component developer capable of removing carrier adhesion and providing a high quality toner image by preventing or suppressing the occurrence of fog.

Another object of the present invention is to provide a two-component developer that can effectively prevent toner dispersion.

It is still another object of the present invention to provide a two-component developer which extends the life and causes less deterioration in image quality when copying and printing a plurality of papers.

Another object of the present invention is to provide a developing method and an image forming method using the two-component developer as described above.

According to the present invention, there is provided a two-component developer for developing an electrostatic charge image composed of at least one toner and one magnetic carrier, wherein the weight average particle size (D4) of the toner is 10 µm or less, and the number average particle size (D1) Satisfies D4 / D1 ≦ 1.5; The magnetic carrier is a composite particle comprising magnetic iron compound particles, nonmagnetic metal oxide particles, and a binder of a phenolic resin (the composite particles contain from 80 to 99% by weight of the total magnetic iron compound and nonmagnetic metal oxide). be) there is in, where the ratio r _b / r _a number average particle size of the magnetic iron compound particles (r _a), number average particle size of the non-magnetic metal oxide particles _(b r) is greater than 1.0.

According to another aspect of the invention, the step of conveying the two-component developer by the developer carrying member including the magnetic field generating means, forming a magnetic brush of the two-component developer on the developer carrying member, magnetic And a step of contacting the brush with the latent image-bearing member, and developing an electrostatic charge image on the latent image holding member to form a toner image while applying an alternating electric field onto the developer carrying member. to provide.

According to another embodiment of the present invention, the above steps are repeated using at least one magenta developer, a cyan developer and a yellow developer, respectively, while satisfying the requirements of the two-component developer described above, and a color image is obtained. An image forming method is formed which is formed of at least an obtained magenta toner image, a cyan toner image and a yellow toner image.

The above and other objects, features and advantages of the present invention will become more apparent upon consideration of the preferred embodiments of the present invention described below in conjunction with the accompanying drawings.

In the present invention, the above object can be achieved as a two-component developer in which toner and magnetic carrier are improved at the same time.

As a result of the detailed study by the present inventors, it became clear that the driving force of the carrier attachment in the contact developing process under the application of the alternating magnetic field is generated by charge injection from the developing sleeve to the magnetic carrier as a control factor under the application of the developing bias voltage. Considering the reproducibility of the dot in the digital latent image, it was found that the deterioration of the dot reproducibility was caused by the leakage of electric charge from the latent electrostatic image on the photosensitive drum due to the friction of the photosensitive drum by the magnetic carrier, and the dot of the digital latent image was distorted into a non-uniform shape. Even when using a carrier core having a high bulk resistivity, such as a resin carrier in which the magnetic material is dispersed, electric charge may leak from the magnetic particles when the magnetic material has a low resistivity such as magnetite.

In order to solve this problem at the same time, the present invention provides a composite particle composed of magnetic iron compound particles, nonmagnetic metal oxide particles, and a binder made of a phenolic resin. To 99% by weight), and the ratio r _b / r _a of the number average particle size (r _a ) of the magnetic iron compound and the number average particle size (r _b ) of the nonmagnetic metal oxide is 1.0. Satisfy what is exceeded. As a result, in order to effectively increase the carrier resistivity, the high resistivity nonmagnetic metal oxide particles preferentially remain on the carrier particle surface. To this end, the developer according to the present invention is effective in suppressing charge injection into the carrier and in suppressing carrier adhesion which inferiorly reproduces the electrostatic latent image.

By making non-magnetic metal oxide particles preferentially present on the carrier surface or core particles rather than the center or inside of the carrier particles, charge carriers are provided on the carrier surface by providing greater resistivity than when the magnetic iron oxide particles are exposed on the carrier or core surface. It effectively suppresses.

In order to prevent blurring or toner dispersion and to improve dot reproducibility in the final image, magnetic carriers having a relatively large particle size can be preferentially prevented from the surface thereof so that the toner particles can be transported better. Do not flatten the particle surface. With the above improvement along with the improvement of the toner, it becomes possible to improve the toner conveyance and the image quality of the final image after the developing step following the transferring step and fixing step in the electrophotographic method.

A toner having a weight average particle size (D4) of 10 µm or less and a sharp particle size distribution as indicated by a number average particle size (D1) satisfying a ratio of D4 / D1 of 1.5 or less was obtained by combining nonmagnetic iron oxide particles and a phenolic resin. By using in combination with a magnetic carrier made of composite particles of soluble metal oxide particles, it is possible to provide a two-component developer that provides excellent dot reproducibility without blurring or toner dispersion. This is probably because the frictional charge distribution of the toner is sharp by narrowing the toner particle size distribution, and the charging of the toner is performed predominantly, which makes the frictional charge distribution sharper because the composite particles with triboelectricity have fine surface irregularities. to be.

The developer according to the present invention can continuously provide a high quality image similarly as in the early stages without being easily degraded for the following reason.

The developer deteriorates during long time use because the toner and the magnetic carrier are preferentially damaged due to the magnetic shear force or the gravity shear force acting between the toner and the carrier or between the carrier particles in the developing container. The toner is essentially consumed, but the magnetic carrier is not consumed and is used repeatedly so that damage to its surface accumulates.

However, when a magnetic carrier composed of composite particles formed of a magnetic iron compound, a nonmagnetic metal oxide, and a phenolic resin is used in combination with a toner having a sharp particle size distribution, magnetic shear force acting between the toner and the carrier and between the carrier particles. Can be reduced to reduce surface damage occurring to the carrier particles.

In particular, the magnetic carrier particles used in the present invention are provided with surface irregularities on the fine particles including the magnetic particles and the non-magnetic metal oxide particles so that the magnetic carrier particles (core particles) when the magnetic carrier particles are coated with a resin And adhesion between the coating resin is increased to suppress the coating resin layer from peeling off.

In terms of high quality, smaller particle size magnetic carriers are preferred, but this will increase carrier adhesion based on the association between magnetic force and particle size. By combining these aspects, the magnetic carrier used in the present invention may have a number average particle size in the range of 1-1000 μm, but for high image quality it would be desirable to have a number average particle size of 1-300 μm. A number average particle size of 5-100 μm is also suitable in view of high image quality, carrier adhesion prevention and developer degradation during continuous image formation. When the magnetic carrier has a number average particle size of more than 1000 mu m, the specific surface area of the magnetic brush rubbing the photosensitive drum is reduced, which does not provide a sufficient amount of toner and leaves a trace of friction in the magnetic brush, thereby resulting in high density and It is not preferable from the viewpoint of super quality. Magnetic carriers having a number average particle size smaller than 1 mu m have a smaller particle size for each carrier particle, and therefore are likely to cause carrier adhesion. The method of measuring the particle size of the magnetic carrier particles used herein will be described below.

The magnetic properties of the magnetic carrier used in the present invention may be suitable for using a magnetic carrier having a saturation magnetization degree (σ _s ) of 10-80 emu / cm 3. More preferably, a magnetic carrier having a saturation magnetization degree σ _s of 15-60 emu / cm 3 is used. The magnetization degree of the magnetic carrier can be appropriately selected according to the particle size of the carrier. Also, while being affected by particle size, magnetic carriers with a magnetization degree of at least 80 emu / cm 3 are susceptible to forming a magnetic brush formed on a developing sleeve of a developing pole of low density and composed of hard ears, resulting in Image damage such as roughness of halftone images and irregularity of beta images due to friction traces and deterioration in, for example, long-term continuous image formation on a large number of papers, are likely to occur on the toner. If less than 10 emu / cm 3, the magnetic carrier only exhibits insufficient magnetic force, resulting in low toner conveying performance.

The magnetic properties referred to herein are measured using a vibrating magnetic field magnetic characteristic automatic recording device (BHV-30, manufactured by Riken Denshi K.K.). Specific conditions for the measurement are described below.

It is important that the magnetic carrier used in the present invention has a (electrical) specific resistance of 1 × 10 ¹² ohm · cm or more at an electric field strength of 5 × 10 ⁴ V / m. When the specific resistance is less than 1 × 10 ¹² ohm · cm, the above-described carrier adhesion and low dot-reproducibility due to charge leakage from the latent image are likely to occur in the developing process. The measuring method of the specific resistance of the magnetic carrier quoted in this specification is described below.

The magnetic iron component constituting the core of the magnetic carrier is preferably a general formula MO · Fe ₂ O ₃ or MFe ₂ O ₄ (M is _{2 such} as Mn, Fe, Ni, Co, Cu, Mg, Zn, Cd or Li). Iron-containing metal alloys, magnetites or ferrites, as shown in FIG. M means a single species or a plurality of species of metals. Specific examples thereof include alloys such as silicon steel, Fermaloy, sendust, Fe-Co and alnico; Magnetite, Iron based oxide materials such as iron oxide, Mn-Zn based ferrite, Ni-Zn based ferrite, Mn-Mg based ferrite, Li based ferrite and Cu-Zn based ferrite.

The magnetic iron component used in the present invention may preferably have a saturation magnetization of at least 30 emu / g.

Examples of nonmagnetic metal oxides include Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Ba And single or plural kinds of metals such as Pb. Specific examples of nonmagnetic metal oxides include Al ₂ O ₃ , SiO ₂ , CaO, TiO ₂ , V ₂ O ₅ , CrO ₂ , MnO ₂ , Fe ₂ O ₃ , CoO, NiO, ZnO, SrO, Y ₂ O ₃ and ZrO ₂ is mentioned.

The above magnetic iron compound and nonmagnetic metal oxide may preferably be dispersed in a resin for forming carrier core particles. In this case, it is preferable to use plural kinds of particles having similar shapes in order to provide increased adhesion and high carrier strength. Examples of preferred combinations include magnetite and hematite (α-Fe ₂ O ₃ ), magnetite and -Fe ₂ O ₃ , magnetite and SiO ₂ , magnetite and Al ₂ O ₃ , magnetite and TiO ₂ , and magnetite and Cu—Zn based ferrites. Of these, a combination of magnetite and hematite is preferred in view of cost and resulting carrier strength.

When dispersed into the resin of magnetic iron compound and non-magnetic metal oxide in order to obtain the carrier core particles, a number-average particle size of the magnetic iron compound particles (r _a) and the number average particle size of the non-magnetic metal oxide particles (r _b) is r _b The value of / r _a is greater than 1.0. When the ratio is 1.0 or less, generally magnetic iron compound particles having a low specific resistance tend to be exposed to the surface, making it difficult to achieve the effect of sufficiently increasing the specific resistance of the carrier and suppressing carrier adhesion. A larger r _b / r _a ratio is desirable such that larger nonmagnetic metal oxide particles are present on the surface of the carrier particles to prevent carrier injection into the carrier, thereby preventing carrier adhesion and dot reproducibility by charge leakage from latent images Will also be lowered. The r _b / r _a ratio of 1.2 to 5.0 is desirable to provide excellent effects in both aspects of increasing the magnetic carrier resistivity and enhancing the carrier strength. The preferred range of particle size ratios is that particles of larger particle size preferentially exist on the carrier (core) surface when filler particles of different particle sizes are simultaneously blended and dispersed in the resin to form carrier (core) particles. Therefore, it is important that nonmagnetic metal oxide particles having high specific resistance have a larger particle size than that of magnetic iron compound particles. The number average particle size (r _a ) of the magnetic iron compound may vary depending on the carrier particle size, preferably 0.02 to 5 μm. It is preferable that the number average particle size (r _b ) of the nonmagnetic metal oxide particles is 0.05-10 μm. The method of measuring the particle size of the metal oxide mentioned in the present specification is described below.

By selectively forming the nonmagnetic metal oxide particle layer on the surface of the carrier (core) particles rather than inside the carrier particles, it is possible to provide higher specific resistance and effectively suppress charge injection.

More specifically, the total volume (Pa1) of the magnetic iron compound particles and the total volume (Pb1) of the nonmagnetic metal oxide particles respectively present in the interior of the carrier (core) particle portion, and the surface portion of the carrier (core) particle portion, respectively The total volume (Pa2) of the magnetic iron compound particles and the total volume (Pb2) of the nonmagnetic metal oxide particles are preferably set to satisfy Pb1 / Pa1 1 and Pb2 Pa2 1 in order to provide high resistivity.

In the resistivity of the magnetic iron compound and the nonmagnetic metal oxide dispersed in the resin, the magnetic iron compound particles have a resistivity of at least 1 × 10 ³ ohm · cm and the nonmagnetic metal oxide particles have a higher resistivity than that of the magnetic iron compound particles. It may be desirable to have. More preferably, the nonmagnetic metal oxide particles may have a resistivity of at least 10 ⁸ ohm · cm. In the case where the specific resistance of the magnetic particles is less than 1 × 10 ³ ohm · cm, even if the amount of the dispersed magnetic iron compound decreases, it is difficult to obtain a carrier having a desired specific resistance, causing deterioration of the image quality and causing charge injection resulting in adhesion of the carrier. Easy to let When the specific resistance of the metal oxide having a larger particle size is less than 1 × 10 ⁸ ohm · cm, it is difficult to sufficiently increase the carrier core specific resistance, which makes it difficult to achieve the above effects. Hereinafter, a method of measuring the specific resistance of the metal oxide mentioned in the present specification will be described.

The magnetic carrier contains 80 to 99% by weight of the magnetic iron compound and the nonmagnetic metal oxide. When the total content is 80% by weight or less, the carrier (core) particles are likely to agglomerate with each other during the production of their particles, especially by direct polymerization. This causes the particle size distribution to fluctuate and destroy the superiority of the triboelectricity. If it exceeds 99% by weight, the resulting carrier strength is lowered, causing problems such as carrier cracking to occur during successive image formation on a plurality of papers.

In order to achieve the effect of the present invention satisfactorily, in the resinous carrier containing the magnetic iron compound and the nonmagnetic metal oxide in the dispersed state, the nonmagnetic metal oxide particles are formed of the total amount of the magnetic iron compound particles and the nonmagnetic metal oxide particles. It is preferred to occupy 5-70% by weight. If less than 5% by weight, it is difficult to increase the specific resistance of the carrier (core). At 70% by weight or more, the resulting magnetic carriers have a low magnetic force causing carrier attachment.

The magnetic carrier according to the invention may preferably have a bulk density of 1.0 to 2.0 g / cm 3. Below 1.0 g / cm 3, carrier adhesion tends to occur depending on the magnetic force. Above 2.0 g / cm 3, the resulting developer is also susceptible to deterioration during continuous image formation on a plurality of papers, depending on the magnetic force of the magnetic carrier. The bulk density of the magnetic carrier can be measured according to JIS K5101.

In the present invention, the magnetic carrier can be constructed using a phenolic resin as the binder resin.

Magnetic carriers used in the present invention can be prepared, for example, by mixing monomers (ie, binder resin precursors), magnetic iron compounds and nonmagnetic metal oxides, and by polymerizing this mixture to directly prepare carrier core particles. Can be. Monomers for polymerization may include combinations of phenols and aldehydes. More specifically, to prepare carrier (core) particles of a cured phenolic resin, a mixture of phenol, aldehyde, magnetic iron compound and nonmagnetic metal oxide is suspended in the presence of a base catalyst and a dispersion stabilizer in an aqueous medium. May be polymerized. In order to provide a magnetic carrier having a high resistivity, the magnetic iron compound is first polymerized for particle formation to form a slurry, and if necessary, monomer, nonmagnetic metal oxide and other additives are added to the slurry to perform second stage polymerization, or It is preferable to form a composite particle by three or more stages of polymerization reaction. Examples of phenol as the monomer include phenol, resorcinol; Alkylphenols such as m-cresol, p-t-butylphenol, o-propylphenol, and alkylphenols and derivatives thereof. Among them, phenol is particularly preferred because of the particle formation properties and the price.

In order to reinforce the carrier core and facilitate its resin coating, phenolic resins can be crosslinked.

It is preferable that the magnetic carrier used in the present invention is in a form coated with a suitable coating resin selected according to the charge of the toner used in the present invention. Coating can also be carried out by using a resin containing nonmagnetic metal oxide particles to control the resistivity of the carrier core and to improve the lubricity of the magnetic carrier. Such a resin-coated magnetic carrier can be effective in suppressing charge injection into the magnetic carrier, suppressing high specific resistance of the carrier for excess charge of the magnetic carrier, and stabilizing the amount of frictional charge of the toner. The nonmagnetic metal oxide dispersed in the coating resin may be included in one or more kinds in a mixture selected from the above metal oxides. It is more preferable to use SiO ₂ , Al ₂ O ₃ , TiO ₂ or α-Fe ₂ O ₃ or nonmagnetic metal oxides used in the carrier core for improving the adhesion of the coating resin. The coating amount of the coating material described above may suitably be 0.5 to 10% by weight, in particular 0.6 to 5% by weight, based on the weight of the carrier core.

If the coating amount is less than 0.5% by weight, it is difficult to control the ability to sufficiently coat the carrier core particles and triboelectrically charge the toner with the coating resin. When more than 10% by weight, the resistivity may be within a desired range, but due to the excess resin coating rate, low dispersibility and image degradation occur after continuous image formation on a large number of papers.

As the coating resin used in the present invention, an insulating resin is suitable, which may be a thermoplastic resin or a thermosetting resin. Examples of the thermoplastic resin include polystyrene; Acrylic resins such as polymethyl methacrylate and styrene-acrylic acid copolymers; Styrene-butadiene copolymer, ethylene-vinyl acetate copolymer, vinyl chloride resin, vinyl acetate resin, polyvinylidene fluoride resin, fluorocarbon resin, perfluorocarbon resin, solvent-soluble perfluorocarbon resin, polyvinyl Alcohols, polyvinyl acetal polyvinyl pyrrolidone, petroleum resins, celluloses; Cellulose derivatives (eg cellulose acetate, nitrocellulose, methyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose); Novolak resins, low molecular weight polyethylene, saturated alkyl polyester resins; Aromatic polyester resins (eg, polyethylene terephthalate, polybutylene terephthalate and polyarylate); Polyamide resin, polyacetal resin, polycarbonate resin, polyether sulfone resin, polysulfone resin, polyphenylene sulfide resin, and polyether ketone resin.

Examples of thermosetting (or curable resins) include unsaturated polyesters and urea resins obtained by multicondensation of phenolic resins, modified phenolic resins, maleic acid resins, alkyd resins, epoxy resins, acrylic resins, anhydrides, terephthalic acid and polyhydric alcohols. , Melamine resin urea-melamine resin, xylene resin, toluene resin, guanamine resin, melamine-guanamine resin, acetoguanamine resin, glutal resin, furan resin, silicone resin, polyimide resin, polyamideimide resin, polyether Mid resin and a polyurethane resin are mentioned.

The above thermoplastic resins or thermosetting resins may be used alone or in combination. Mixtures of thermoplastic resins and curing or immersion agents may also be used to provide the cured resin.

The coated magnetic carrier may be prepared by spraying or drying the coating resin solution on the carrier core particles in a floating or flowing state to form a coating film on the core particle surface.

Other coating methods include a method of gradually evaporating the solvent in the coating resin liquid in the metal oxide while applying a shear force. More specifically, the solvent evaporation method may be performed at a temperature equal to or higher than the glass transition temperature of the coating resin, and then the resulting agglomerated metal oxide particles may be pulverized. Alternatively, the coating can be cured under heating and then comminuted.

The metal oxide can take the shape of particles selected to be suitable for the developing system used. However, it may be desirable for the metal oxides used in the present invention to have a sphericity of up to two. When the sphericity exceeds 2, the resultant developer has poor fluidity and provides a deteriorated magnetic brush, making it difficult to obtain a high quality toner image. The sphericity of the carriers is randomly sampled for 300 carrier particles, for example via a field-emission scanning electron microscope (e.g., S-800, Hitachi KK), and an image analyzer (e.g. Using Luxex 3, manufactured by Nireco KK, the sphericity can be measured by measuring the mean with the following equation.

Spherical Diagram (SF1) = [(MX LNG) ² / AREA] × π / 4

(Wherein, MX LNG represents the maximum diameter of the carrier particles, AREA represents the projection area of the carrier particles). The closer the sphericity is to 1, the closer the shape is to the sphere.

The toner used in the present invention may have a weight average particle size (D4) of 10 μm or less, preferably 3-8 μm. It is also important to provide a ratio of D4 / D1 of the weight average particle size D4 and the number average particle size D1 to 1.5 or less.

When the number average particle size (D4) of the toner exceeds 10 mu m, the toner particles for developing the electrostatic latent image become large, and the faithful development of the latent image cannot be performed, and toner scattering is likely to occur.

When the ratio of the weight average particle size (D4) to the number average particle size (D1) of D4 / D1 exceeds 1.5, the toner exhibits a wide range of charge distribution, causing disadvantages such as poor charging and deviation of the particle size of the developing toner particles. Let's do it. The weight average particle size and the number average particle size of the toner may be measured using, for example, a Coulter counter. Detailed description thereof will be described later.

The toner used in the present invention contains a binder resin, examples of which are polymers of styrene derivatives such as polystyrene, poly-p-chlorostyrene and polyvinyl toluene, styrene-p-chlorostyrene copolymer, styrene-vinyl toluene copolymer , Styrene-vinylnaphthalene copolymer, styrene-acrylate copolymer, styrene-methacrylate copolymer, styrene-methyl α-chloromethacrylate copolymer, styrene-acrylonitrile copolymer, styrene-vinyl methyl ketone copolymer Styrene copolymers such as styrene-butadiene copolymer, styrene-isoprene copolymer and styrene-acrylonitrile-indene copolymer, polyvinyl chloride, phenolic resin, natural or modified phenolic resin, natural or modified maleic acid resin, Acrylic resin, methacryl resin, polyvinyl acetate, silicone resin, aliphatic polyhydric alcohol, aromatic polyhydric egg Polyester resins, polyurethane resins, polyamide resins, polyvinyl butyral, terpene resins, coumarone-indene resins, styrene bases having structural units selected from cole or diphenols and aliphatic dicarboxylic acids or aromatic dakir acids Petroleum resin crosslinked styrene based resins such as resins and crosslinked polyester resins.

Examples of comonomers used with styrene monomers to provide styrene copolymers include vinyl monomers, which include acrylic acid, acrylic esters or derivatives thereof such as methyl acrylate, ethyl acrylate, butyl acrylate and dodecyl. Acrylate, octyl acrylate, 2-ethylhexyl acrylate, phenyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, octyl methacrylate, acrylonitrile, methacrylonitrile and acrylamide; Maleic acid; Half esters and diesters of maleic acid such as butyl maleate, methyl maleate and dimethyl maleate; Vinyl esters such as vinyl acetate and vinyl chloride; Vinyl ketones such as vinyl methyl ketone and vinyl hexyl ketone; And vinyl ethers such as vinyl methyl ether and vinyl ether ether.

Crosslinkers include in principle compounds which have at least two polymerizable double bonds. Examples thereof include aromatic divinyl compounds such as divinylbenzene and divinyl naphthalene; Carboxylic acid esters having two double bonds such as ethylene glycol diacrylate, ethylene glycol dimethacrylate and 1,3-butane diol dimethacrylate; Divinyl compounds such as divinylaniline, divinyl ether, divinyl sulfide and divinyl sulfone; And compounds having three or more ethylene double bonds. These compounds may be used alone or in combination. In the synthesis of the binder resin, the crosslinking agent may be used in a ratio of preferably 0.01-10 wt%, more preferably 0.05-5 wt%, based on the binder resin.

When using a pressure-fixing system, it is possible to use binder resins for pressure-lockable toners, for example polyethylene, polypropylene, polymethylene, polyurethane elastomers, ethylene-ethyl acrylate copolymers, ethylene- Vinyl acetate copolymers, ionomer resins, styrene-butadiene copolymers, styrene-isoprene copolymers, linear saturated polyesters, paraffins and other waxes.

The toner used in the present invention can be used in combination with a charge control agent incorporated (internally added) or blended (externally added) to toner particles. By adding a charge control agent, it becomes possible to perform optimum charge control depending on the developing system used. Examples of positive charge control agents include nigrosine and its modification products with aliphatic acid metal salts; Quaternary ammonium salts such as tributylbenzylammonium-1-hydroxy-4-naphthosulfonate and tetrabutylammonium tetrafluoroborate; And diorganotin oxides such as dibutyltin oxide, dioctyltin oxide, dicyclohexyltin oxide, dibutyltin borate, dioctyltin borate and dicyclohexyltin borate. These compounds may be used alone or in a mixture of two or more thereof. Of these, nigrosine-based compounds and quaternary ammonium salts are particularly preferred.

Alternatively, in the present invention, it is also possible to use negative charge control agents such as organometallic salts, organometallic complexes and chelate compounds. Of these, acetylacetone metal complexes (including monoalkyl substituted and dialkyl substituted derivatives), salicylic acid metal complexes (including monoalkyl substituted and dialkyl substituted derivatives) and their corresponding salts are preferred. Salicylic acid based metal complexes or salicylic acid based metal salts are particularly preferred. Specific examples of preferred negative charge control agents include aluminum acetylacetonate, iron (II) acetylacetoate, 3,5-di-t-butylsalicylic acid chromium complex or salt, and 3,5-di-t-butylsalicylic acid zinc complex or salt Can be mentioned.

When added to the toner internally, it may be desirable to use the charge control agent in a proportion of 0.1-20 parts by weight, in particular 0.2-10 parts by weight, per 100 parts by weight of the binder resin. When used for color image formation, it is preferable to use a colorless or weakly colored charge control agent.

As the colorant of the toner, conventional dyes and / or pigments can be used. Examples include carbon black, phthalocyanine blue, peacock blue, permanent red, lake red, rhodamine rate, Hansa yellow, permanent yellow and benzidine yellow. The colorant may be added in an amount of 0.1 to 20 parts by weight, preferably 0.5 to 20 parts by weight, per 100 parts by weight of the binder resin. In order to provide a fixed toner image having good transparency or OHP film, the colorant may preferably be added in a proportion of up to 12 parts by weight, more preferably from 0.5 to 9 parts by weight, per 100 parts by weight of the binder resin.

In addition, the toner constituting the developer according to the present invention may be a wax, for example, polyethylene, low molecular weight polypropylene, microcrystalline wax, carnauba wax, sasol wax or paraffin wax, in order to improve the releasability at the time of heat press fixing. It may further include.

Toners used in the present invention include fine particles of inorganic materials such as silica, alumina and titanium oxide; And fine particles of organic matter such as polytetrafluoroethylene, polyvinylidene fluoride, polymethylmethacrylate, polystyrene, and silicone resins, and can be suitably used as a mixture with externally added fine powders. When such fine powder is added to the toner externally, the fine powder may be present between the toner and the carrier particles or between the toner particles to improve the fluidity and life of the developer. It may be preferable that the average particle size of the fine powder is 0.2 μm or less. If the average particle size exceeds 0.2 m, the fluidity-improving effect is insufficient, and in some cases, the image quality is degraded due to insufficient fluidity during development or transfer. A method for measuring the particle size of such a powder referred to herein is then disclosed.

The specific surface area of the fine powder as described above is measured by the BET method using a nitrogen adsorption method, and is preferably 30 m 2 / g or more, particularly 50 to 400 m 2 / g. The fine powder may be appropriately added in a ratio of 0.1 to 20 parts by weight per 100 parts by weight of toner.

In preparing the toner constituting the developer according to the present invention, binder resin, colorant, optional charge control agent and other additives of vinyl type or non-vinyl type thermoplastic resin are sufficiently blended in a mixer, and then heated roller, Melt kneading with a hot kneading apparatus such as a kneader or an extruder completely kneaded the resin and disperses or dissolves the pigment or dye therein. Thereafter, the kneaded product is cooled to solidify, pulverized and classified to obtain toner particles. For toner sorting, it is desirable to use a multi-separation sorting apparatus that utilizes the Coanda effect. By using the above apparatus, it is possible to efficiently produce a toner having a particle size distribution defined in the present invention.

The toner particles thus obtained can be used as they are, but can be preferably used as a mixture with the externally added fine powder as described above.

Mixing of the toner and the fine powder can be performed using a blender such as a Henschel mixer. The resulting toner comprising such an external additive is mixed with a magnetic carrier to provide a two-component developer. In a two-component developer, the toner accounts for 1 to 20% by weight, more preferably 1 to 10% by weight in a typical case, but this may depend on the developing process. A triboelectric charge of 5 to 100 μC / g, most preferably 5 to 60 μC / g, may be provided suitably for the toner in the two-component developer. The method of measuring the frictional charge referred to herein is described below.

The developing method using the two-component developer according to the present invention can be carried out using, for example, developing means as shown in FIG. It is preferable to develop under application of an alternating electric field in a state in which the magnetic brush is brought into contact with the latent image holding member, for example, the photosensitive drum 3.

It may be desirable for the peak-to-peak voltage of the alternating electric field to be between 500 and 5000 volts and with a frequency between 500 and 10000 Hz, preferably between 500 and 3000 Hz, which can be suitably selected according to the process. The waveform for this can be suitably selected, such as a waveform obtained by changing a triangular wave, a rectangular wave, a sine wave or an impact coefficient. When the applied voltage is less than 500 volts, it may be difficult to obtain sufficient image density and the blurring of the toner on the non-image area may not be satisfactorily recovered in some cases. If it is 5000 volts or more, the latent image may be disturbed by the magnetic brush, which in some cases may cause deterioration of image quality.

If the frequency is less than 500 Hz, charge can be released into the carrier, which in some cases can cause deterioration in image quality due to carrier attachment and latent image disturbances. When it is 10000 Pa or more, the toner is difficult to follow the electric field, and therefore, the image quality is easy to deteriorate.

In the developing method according to the present invention, the contact width (developing nip) C of the magnetic brush on the developing sleeve 1 and the photosensitive drum 3 is fixed to 3 to 8 mm so that sufficient image density is achieved and no carrier adhesion occurs. It is desirable to perform a phenomenon that provides dot reproducibility. If the developing nip C is narrower than 3 mm, it may be difficult to satisfy sufficient image density and good dot reproducibility. When wider than 8 mm, it may become difficult to sufficiently prevent development carrier attachment. The developing nip C can be appropriately adjusted by changing the distance A between the developer adjusting member 2 and the developing sleeve 1 and / or by changing the gap B between the developing sleeve 1 and the photosensitive drum 3. have.

The image forming method according to the present invention can be used particularly effectively for forming a color image, in which halftone reproducibility is an important factor, using at least three developing devices for magenta, cyan and yellow, and the developer according to the present invention. And a developing method, preferably applying a developing system together with a developing digital latent image to enable faithful development of the dot latent image while avoiding adverse effects of the magnetic brush and disturbance of the latent image. The use of a toner having a sharp particle size distribution is also effective in raising the transfer ratio in the subsequent transfer step. As a result, the image quality can be high in both the halftone portion and the beta image portion.

In addition to the high image quality in the initial stage of image formation, the use of the two-component developer according to the present invention in order to avoid deterioration in image quality in the formation of a large number of continuous images, because of the low shear force acting on the developer in the developing container. effective.

In order to provide a color image that provides a clearer appearance, it is preferable to use four developing devices for magenta, cyan, yellow and black, respectively, and finally develop black.

An image forming apparatus suitable for implementing the color image forming method according to the present invention will be described with reference to FIG.

The color electrophotographic apparatus shown in FIG. 3 includes a transfer drum 315 and a transfer material (recording paper) -transporter I, a transfer drum, which extends from the right side (right side in FIG. 3) to the center of the apparatus main assembly 301. It is briefly divided into a latent image forming portion II disposed close to 315, and a developing means (i.e., a rotary developing device) III.

The transfer material-carrying part I consists of: In the right wall of the apparatus main assembly 301, an opening is formed, through which the transfer material supply trays 302 and 303 are detachably arranged so that some of them protrude out of the assembly. The paper (transcription material) -feeding rollers 304 and 305 are disposed almost right upper of the trays 302 and 303. Paper-feeding guides 307 and 308 are disposed with respect to the paper-feeding rollers 304 and 305 and the transfer drum 315 disposed to the left thereof so as to rotate in the direction of arrow A. FIG. Proximity to the outer surface of the transfer drum 315, the border roller 309, the gripper 310, the transfer material separation charger 311 and the separation claw 312 in the order of rotation in the lower stream in the upper stream in the order of rotation It is arranged.

Inside the transfer drum 315, a transfer charger 313 and a transfer material separating charger 314 are disposed. A portion of the transfer drum 315 wound around the transfer drum 315 is supplied with a transfer paper (not shown) adhered thereto, and the transfer material is electrostatically closely applied thereto. On the right side of the upper portion of the transfer drum 315, the conveying belt means 316 is disposed after the separating claw 312, and the fixing device 318 is provided at the end (right side) in the conveying direction of the conveying belt means 316. It is arranged. In another lower stream of the fixing device is arranged an outlet tray 317, which is partially extended outwardly and detachably arranged from the main assembly 301.

The latent image forming part III is comprised as follows. As the latent image retention member rotatable in the direction of the arrow shown in the figure, a photosensitive drum (eg, an OPC photosensitive drum) is arranged to have a circumferential surface in contact with the circumferential surface of the transfer drum 315. Generally, the discharge charger 320, the sweeping device 321, and the first charger 323 are continuously disposed from the upper stream to the lower stream in the rotational direction of the photosensitive drum 319 in the upper and proximal portions of the photosensitive drum 319. It is. Imaging exposure means, including a laser 324 and a reflecting device 325 such as a mirror, are also arranged to form an electrostatic latent image on the outer circumferential surface of the photosensitive drum 319.

Rotary developing apparatus III is comprised as follows. In a position opposite to the photosensitive drum 319, a rotatable housing (hereinafter referred to as a rotating member) 326 is disposed. In the rotating member 326, four types of developing devices are arranged in four rotation directions at equal distances so as to visualize (ie, develop) an electrostatic latent image formed on the outer circumferential surface on the photosensitive drum 319. Four types of developing apparatuses include a yellow developing apparatus 327Y, a magenta developing apparatus 327M, a cyan developing apparatus 327C, and a black developing apparatus 327BK.

The whole process sequence of the above-mentioned image forming apparatus is described on the basis of the natural color scheme. As the photosensitive drum 319 rotates in the direction of the arrow, the drum 319 is charged by the first charger 323. In the apparatus shown in FIG. 3, the moving circumferential speed (hereinafter referred to as process speed) of each member, especially the photosensitive drum 319, may be 100 mm / sec or more, for example, 130 to 250 mm / sec. After the photosensitive drum 319 is charged by the first charger 323, the photosensitive drum 329 is image-exposed to the laser light modulated from the original 328 to the yellow image signal to correspond to the photosensitive drum 319. A latent image is formed, which is then developed by the yellow developing device 327Y fixed in position by the rotation of the rotating member 326 to form a yellow toner image.

The transfer material (e.g., white paper) transported through the paper feed guide 307, the paper feed roller 306, and the paper feed guide 308 is selected by the glyph 310 at a predetermined time so that the border roller 309 and It is wound around the transfer drum 315 by an electrode disposed opposite the border roller 309. The transfer drum 315 rotates in the direction of the arrow A in accordance with the photosensitive drum 319, whereby the yellow toner image formed by the yellow developing device is subjected to the photosensitive drum 319 and the transfer drum 315 under the action of the transfer charger 313. Circumferential surfaces) are transferred onto the transfer material at a position bordering each other. The transfer drum 315 is further rotated to prepare for the transfer of the next color (magenta in FIG. 3).

On the other hand, the photosensitive drum 319 is charged-removed by the discharge charger 320, cleaned by the sweep blade or the sweep means 321, recharged by the first charger 323, and then followed by a magenta image signal. The image is exposed on the basis of this to form a corresponding electrostatic latent image. The electrostatic latent image is formed on the photosensitive drum 319 by image exposure on the basis of the magenta signal, the rotating member 326 is rotated, and the magenta developing device 327M is installed at a predetermined developing position using magenta toner. Perform the phenomenon. Subsequently, the above-mentioned steps are repeated for cyan and black colors respectively to complete the transfer of the four color toner images. Thereafter, an image developed in four colors on the transfer material is released (charge-removed) by the chargers 322 and 314, and is released from the holding by the gripper 310, by the separating claw 312. Separated from the transfer drum 315 and conveyed to the fixing device 318 via the transport belt 316, where the four-color toner image is fixed under heat and pressure. Thus, a series of color printing or image forming sequences is completed to provide a predetermined color image on one surface of the transfer material.

In a separate manner, each color toner image can be once transferred onto an intermediary transfer member and then transferred to and immobilized thereon with a transfer material.

The fixing speed of the fixing device is slower than the circumferential speed of the photosensitive drum (eg 160 mm / sec) (eg 90 mm / sec). This is to provide a sufficient amount of heat to melt-mix the yet unfixed images of two to four toner layers. Therefore, by performing the fixing at a gentler speed than the developing speed, the amount of heat supplied to the toner image is increased.

We now describe a method of measuring the various properties mentioned herein.

1) particle size of magnetic carrier

By observing through an optical microscope at a magnification of 100 to 5000, at least 300 particles (diameter: 0.1 μm or more) were randomly selected from the sample carrier, and an image analyzer (e.g., Luzex 3, manufactured by Nireco KK) was used to The horizontal FERE diameter is measured as particle size to obtain a number based particle size distribution and a number average particle size from which the number based ratio of particles having a size in the range of at least 1/2 of the number average particle size is calculated.

2) the magneticity of the magnetic carrier

Measurement is performed using a vibrating magnetic field magnetic recording device (BHV-30, manufactured by Riken Denshi K.K.). The magnetic carrier is placed in an external magnetic field of 1 kilo Oersted and the saturation magnetization is measured under this condition. More specifically, the magnetic carrier powder sample is packed sufficiently tightly in a cylindrical plastic cell with a volume of about 0.07 cm 3 so that the carrier particles do not move during movement. In this state, the magnetic moment is measured and divided by the actually packed sample volume to obtain the degree of magnetization (magnetization strength) per unit volume.

3) Measurement of the (electric) resistivity of the carrier

The specific resistance of the carrier is made of the lower electrode 21, the upper electrode 22, the insulator 23, the ammeter 24, the voltmeter 25, the constant-voltage regulator 26 and the guide ring 28, Measure using the device (cell) E as shown in FIG. 2. For the measurement, the cell E is charged with about 1 g of sample carrier 27 and placed in contact with the electrodes 21 and 22, and a voltage is applied therebetween, whereby the current flowing at this time is measured to calculate the specific resistance. do. Since the magnetic carrier is in powder form, care must be taken not to change the resistivity due to the change in packing state. The resistivity described herein is about 2.3 cm 2 in contact area between the carrier 27 and the electrode 21 or 22, the carrier thickness is about 2 mm, the weight of the upper electrode 22 is 180 g, Based on measurements under conditions of 100 volts applied voltage.

4) Grain size of magnetic iron compound and nonmagnetic metal oxide

Photos at 5,000 to 20,000 magnification of the metal oxide powder samples are taken through a transmission electron microscope (H-800, manufactured by Hitachi Seisakusho K.K.). In the photograph, 300 or more particles (diameter of 0.01 μm or more) are randomly taken and analyzed by an image analyzer (Luzex 3 :, manufactured by Nireco K.K.) to measure the horizontal FERE diameter of each particle as its particle size. The number average particle size is calculated from the measurements for at least 300 sample particles.

5) abundance between magnetic iron compounds and nonmagnetic metal oxides

The abundance ratio between the magnetic iron compound and the nonmagnetic metal oxide in the magnetic carrier particles and on the surface of the magnetic carrier particles or the core particles can be measured in the following manner.

The carrier particles or carrier core particles were dispersed in an epoxy resin, then fixed by solidification, and the carrier impregnated resin sample was sliced by a microtome (eg, FC4E, manufactured by REICHER-JUNG) to prepare a carrier portion sample.

Randomly selected particles were observed through a scanning electron microscope (S-800, manufactured by Hitachi Seisakusho KK) and photographed at 5,000 to 10,000 magnification, and the captured particles were photographed using an image analyzer (Luzex 3, manufactured by Nireco KK). The horizontal FERE diameter D for the dispersed particle parts was measured. Assuming the spherical shape of the magnetic iron compound particles and the nonmagnetic metal oxide, the volume of the discretely dispersed particles is calculated as πD ³ / σ. On the individual particles, the inner zone is defined as a zone of radius x 0.3 from the center and the surface zone is defined as a zone of radius x 0.95 to radius x 1.0. For the individual carrier (core) particles, calculate the total volume per unit area (μm ² ) of each of the magnetic iron compound particles and the nonmagnetic metal oxide particles appearing in the inner zone of the particle part under consideration and denoted Pa1 and Pb1, respectively, and the surface zone. The total volume per unit area (μm ² ) of each of the magnetic iron compound particles and the nonmagnetic metal oxide particles shown in is calculated and denoted Pa2 and Pb2, respectively. The Pa1 / Pb1 and Pa2 / Pb2 ratios are calculated by averaging Pa1, Pb1, Pa2 and Pb2 values for 20 carrier (core) particles.

6) Specific resistance of magnetic iron compounds and nonmagnetic metal oxides

Measure similarly to the specific resistance measurement mentioned above for the carrier. A sample compound or metal oxide is placed between the electrodes 21 and 22 in the cell shown in FIG. 2, in this state, a voltage is applied between the electrodes, and as a result, the current passing therebetween is measured, and Calculate the resistivity. In order to make the electrode contact the sample uniformly, the sample is packed while reciprocating the lower electrode 21. The numerical values described herein have a contact area between the packed metal oxide and the electrode S of about 2.3 cm 2, a sample thickness d of about 2 mm, a weight of the upper electrode 22 of 180 g, and an applied voltage of 100 volts. Based on the measurements under conditions.

7) particle size of toner

To 100 to 150 ml of the electrolyte solution (1% -NaCl aqueous solution), 0.1 to 5 ml of the surfactant (alkylbenzenesulfonic acid salt) is added, and 2 to 20 mg of the sample toner is added. Samples suspended in electrolyte solution are dispersed for 1 to 3 minutes. The sample liquid is then supplied to a Coulter counter (Multisizer, manufactured by Coulter Electronics Inc.) having an opening size of, for example, 17 μm or 100 μm, suitably selected according to the toner size level, to a volume in the range of 2 to 40 μm. A reference particle size distribution is obtained from which a number reference particle size distribution, a number average particle size (D1) and a weight average particle size (D4) are calculated by a personal computer.

8) frictional charge

The toner and the magnetic carrier are weighed to provide a mixture containing 5% by weight of the toner, and the mixture is mixed for 60 seconds with a Turbula mixer. The resulting powder mixture (developer) is placed in a metal container with a 500-mesh conductive screen at the base, and the toner in the developer is sucked through the screen at a suction pressure of 250 mmHg and selectively operated by an aspirator. Remove The frictional charge Q of the toner is calculated based on the following equation from the weight difference before and after suction and the voltage generated in the capacitor connected to the container:

In the above formula, W ₁ is the weight before suction, W ₂ is the weight after suction, C is the capacitance of the capacitor, and V is the potential read from the capacitor.

The present invention will now be described with reference to Examples, wherein parts used to indicate the amount of components represent parts by weight.

Example 1

(Nonmagnetic metal oxide, d _av = 0.60 mu m, R _s = 8x10 ⁹ ohmcm)

The material, 4 parts of 28 wt% aqueous ammonia (basic catalyst) and 15 parts of water were placed in a flask, heated to 85 ° C. for 40 minutes with stirring for mixing, and then left at a temperature for a curing reaction of 3 hours. The contents were then cooled to 30 ° C. and 100 parts of water was added thereto, then the supernatant was removed, washed with water and the precipitate was dried in air. The dried precipitate was further dried at 50 to 60 ° C. under reduced pressure of 5 mmHg or less to obtain spherical magnetic carrier core particles containing magnetite and hematite in the phenol binder. The carrier core particles showed R _s = 8 × 10 ¹² ohm · cm.

The magnetic carrier core particles were surface coated with a thermosetting silicone resin in the following manner. In order to provide a coating resin proportion of 1.0% by weight, 10% by weight of a carrier coating resin solution in toluene was prepared. To this solution, carrier core particles were added and the resulting mixture was heated under the action of shear force to evaporate the solvent to provide a coating on the carrier core. The resulting coated magnetic carrier particles were cured at 250 ° C. for 1 hour, then collapsed through a 100 mesh sieve and filtered to obtain coated magnetic carriers having a number average particle size (D1) of 43 μm and a sphericity (SF1) of 1.04. .

The coated magnetic carrier exhibited a resistivity (R _s ) of 9 × 10 ¹³ ohm · cm and a saturation magnetization (σ _s ) of 28 emu / g.

The properties of the coated magnetic carriers are shown in Table 1 below.

On the other hand, the toner was prepared in the following manner.

[Yellow Toner]

The materials were sufficiently preblended, melt kneaded, cooled and coarsely ground to a particle size of about 1 to 2 mm using a hammer mill. The product was then further ground using an air jet-type mill. The ground was sorted with an Elbow Jet classifier to recover negatively charged yellow powder (nonmagnetic yellow toner).

100 parts by weight of the yellow toner and 0.8 parts by weight of hydrophobic titanium oxide fine powder were respectively blended in a Henschel mixer to obtain a yellow toner having externally added titanium dioxide fine powder. The yellow toner showed a weight average particle size (D4) of 8.6 μm, a number average particle size (D1) of 6.5 μm, and a ratio (D4 / D1) of 1.32. The toner showed a triboelectric charge (TC) of -27.1 μC / g when measured with the coated magnetic carrier prepared above (toner concentration = 5 wt%).

[Magenta Toner]

From the above materials, negatively charged magenta powder (nonmagnetic magenta toner) was prepared in the same manner as the yellow toner.

100 parts by weight of the magenta toner and 8.0 parts by weight of hydrophobic titanium dioxide fine powder were blended in a Henschel mixer to obtain a magenta toner having externally added titanium dioxide fine powder. Magenta toner showed D4 of 8.4 μm, D1 of 6.5 μm and D4 / D1 of 1.29. The toner exhibited a triboelectric charge (TC) of -25.3 μC / g when measured with the coated magnetic carrier prepared above.

[Cyan Toner]

From the above materials, negatively charged cyan powder (nonmagnetic cyan toner) was produced in the same manner as a yellow toner.

100 parts by weight of the cyan toner and 0.8 parts by weight of hydrophobic titanium dioxide fine powder were blended in a Henschel mixer to obtain a cyan toner having externally added titanium dioxide fine powder. The cyan toner showed a D4 of 8.6 mu m, a D1 of 6.4 mu m and a D4 / D1 of 1.34. The toner showed a triboelectric charge (TC) of -27.8 μC / g when measured with the coated magnetic carrier prepared above.

[Black Toner]

From the above materials, negatively charged black powder (nonmagnetic black toner) was prepared in the same manner as yellow toner.

100 parts by weight of the black toner and 0.8 parts by weight of hydrophobic titanium dioxide fine powder were blended in a Henschel mixer to obtain a black toner having externally added titanium dioxide fine powder. The black toner showed D4 of 8.4 μm, D1 of 6.5 μm and D4 / D1 of 1.29. The toner showed a triboelectric charge (TC) of -26.3 μC / g when measured with the coated magnetic carrier prepared above.

The coated magnetic carrier prepared above was mixed with the prepared individual color toner to prepare four two-component developers having a toner concentration of 8.0% by weight. The two-component developer was filled in a color laser copying machine (CLC-500, manufactured by Canon K.K.) of a model remodeled to have a developing device as shown in FIG. In FIG. 1, each developing apparatus has a distance A between the developer holding member (developing sleeve) 1 and the developer adjusting member (magnetic blade) of 600 m, and the developing sleeve 1 and the electrostatic latent image holding member (photosensitive). The gap B between the drums (3) was designed to be 500 mu m. The developing nip C at this time was 5 mm. The developing sleeve 1 and the photosensitive drum 3 were operated at a circumferential speed ratio of 1.75: 1. The developing sleeve S1 of the developing sleeve is designed to provide a magnetic field of 1 kilo ulsted, a right-angle waveform alternating electric field with a peak-to-peak voltage of 2000 volts and a frequency of 2000 Hz, developing bias of -470 volts, Toner development contrast (Vcont) of 325 volts, blur suppression voltage (Vback) of 100 volts, and main charge voltage on the photosensitive drum of -570 volts. Under the developing conditions, the digital latent image on the photosensitive drum 3 was developed in the reverse developing mode.

The resulting image, which exhibited a high beta image density (typically measured on the cyan toner), was free of dot irregularities and did not exhibit non-images due to image obstruction or blurring or carrier adhesion on the image.

Continuous color image formation was performed on many 30,000 sheets of paper. Thereafter, an image test was performed similar to the initial stage. The solid image of the cyan toner showed high density, and the halftones showed good reproducibility. In addition, no blurring or carrier adhesion was observed. When the cyan developer was observed with a scanning electron microscope (SEM) after continuous image formation, no peeling phenomenon of the coating resin on the carrier was observed, and a good surface state was observed similar to the initial coated magnetic carrier surface.

The results are shown in Table 2 below.

Example 2

The above materials were polymerized similarly to Example 1 except that the amounts of basic catalyst and water were varied. The polymerized factor was classified to obtain a magnetic powder dispersed in the carrier core. The resulting carrier core exhibited a resistivity (Rs) of 5.2 × 10 ¹² ohm · cm.

The core particles were coated similarly to the method of Example 1 at 1.0 wt% coverage using a coating resin in which a styrene-acrylate resin and a fluorine-containing resin were mixed at a ratio of 7 to 3.

The coated magnetic carrier particles showed a D1 = 55 μm and a sphericity of 1.06 (SF1).

The coated carrier particles exhibited Rs = 8.0 × 10 ¹³ ohm · cm and σ _s = 39 emu / g.

The coated magnetic carrier thus obtained was blended with the four-color toner prepared in Example 1 to prepare four two-component developers having a toner concentration of 7% by weight. Each of the toners showed a triboelectric charge of yellow: -30.2 μC / g, magenta: -28.7 μC / g, cyan: -32.9 μC / g and black: -29.8 μC / g as measured at the toner concentration of 5% by weight.

The developer was filled in the same image forming apparatus as in Example 1, and developed using the same developing conditions. As a result, similar to Example 1, the image at the initial stage showed particularly excellent dot reproducibility and high resolution, and there was no carrier adhesion. The images after the continuous color image formation on 30,000 sheets of images showed almost the same image quality as the initial stage. There was no carrier bonding even in continuous image formation. The carrier surface condition after continuous image formation was good to a similar extent as in the initial stage.

Example 3

Magnetic carrier cores were prepared by two-step polymerization using the following materials.

[Step 1]

[Step 2]

The first step of the polymerization was carried out similarly to the method of Example 1 except that the amount of base catalyst and water were changed. Polymerized particles were obtained by filling the resulting slurry liquid with the second step material described above and performing a similar suspension polymerization. Polymerized particles were classified to obtain resin carrier core particles in which magnetic powder was dispersed. The core particle showed Rs = 7.4 × 10 ¹² ohm · cm. As observed by scanning electron microscopy, the core particles are as schematically shown in FIG. 4, where the magnetite particles are larger in size and α-Fe ₂ O ₃ particles are present on the magnetic surface. The core particles had a ratio of magnetic iron compound to nonmagnetic metal oxide of Pb1 / Pa1 = 0 and Pb2 / Pa2 = 19.3.

The core particles were coated using the same coating resin as in Example 1 at different coverage rates of 1.3% by weight.

The coated magnetic carrier particles exhibited a sphericity of D1 = 40 μm and 1.11.

The coated magnetic carrier particles showed Rs = 3.5 × 10 ¹³ ohm · cm and σ _s = 68 emu / g.

The coated magnetic carrier obtained by the above method was combined with the four-color toner prepared in Example 1 to obtain four two-component developers each having a toner concentration of 8% by weight. Each toner showed a triboelectric charge of yellow: -25.1 μC / g, magenta: -24.3 μC / g, cyan: -27.7 μC / g and black: -23.0 μC / g.

The developer was filled in the same image forming apparatus as in Example 1, and developed under the same developing conditions as in Example 1 except that the distance A between the developing sleeve 1 and the magnetic blade 2 was changed to 800 µm. As a result, similar to Example 1, the image at the initial stage showed particularly excellent reproducibility of dot and high resolution, and there was no carrier adhesion. As a result of the continuous color image formation on 30,000 sheets of paper, subsequent images showed almost the same image quality as the initial stage. There was no carrier adhesion even at the time of continuous image formation. The carrier surface condition after continuous image formation was good to a similar extent as in the initial stage.

Example 4

The materials were polymerized similarly to Example 1. Polymerized particles were classified to obtain core particles of a resin carrier in which magnetic powder was dispersed. Rs of the resulting carrier cores was 4.2 × 10 ¹¹ ohm · cm.

The core particles were coated using the same coating resin as in Example 1 at different coverage rates of 2% by weight.

The coated magnetic carrier particles exhibited a sphericity of D1 = 24 μm and 1.09.

The coated carrier particles exhibited Rs = 7.2 × 10 ¹³ ohm · cm and σ _s = 73 emu / g.

On the other hand, toner was prepared using the following components.

[Cyan Toner]

From the above components, a negatively charged cyan powder (cyan toner) was prepared in the same manner as in Example 1 except that the grinding and sorting conditions were changed. 100 parts of cyan toner and 1.5% by weight of hydrophobized titanium oxide fine powder were blended in a Henschel mixer to obtain a cyan toner carrying externally added titanium fine powder. The cyan toner showed D4 = 5.1 μm, D1 = 4.0 μm, D4 / D1 = 1.27, and the triboelectric charge (TC) was -46.2 μC / g as measured with the prepared coated magnetic carrier.

The cyan toner was blended with a magnetic carrier coated at a toner concentration of 8% by weight and used for monochrome mode image formation under the same developing apparatus and developing conditions as in Example 1. As a result, a good image was obtained after forming continuous images in 30,000 sheets similarly to the initial stage and Example 1. After continuous image formation, the surface state of the carrier was similar to that of the initial state.

Example 5

The carrier core prepared in Example 1 was used as a magnetic carrier without coating, and four developers having respective concentrations of 8% by weight were prepared by blending with four toners as in Example 1. The triboelectric charges of the toners were yellow: -38.4 µC / g, magenta: -35.7 µC / g, cyan: -39.4 µC / g, and black: -36.6 µC / g.

The developer was filled in the same image forming apparatus as in Example 1, and developed using the same developing conditions. As a result, similarly to Example 1, the image at the initial stage showed high resolution and there was no carrier adhesion. As a result of the continuous color image formation on 30,000 sheets of paper, subsequent images showed almost the same image quality as the initial stage. Carrier adhesion was not observed even after continuous image formation.

Example 6

The materials were polymerized similarly to Example 1. Polymerized particles were classified to obtain core particles of a resin carrier in which magnetic powder was dispersed. Rs of the resulting carrier cores was 2.8 × 10 ¹³ ohm · cm.

The core particles were coated similarly to Example 1 using a copolymer having a styrene to 2-ethylhexyl methacrylate ratio of 50 to 50 to give a 1.2 wt% coverage.

The coated magnetic carrier particles had a D1 of 45 μm and a sphericity of 1.05.

The coated carrier particles exhibited Rs = 9.8 × 10 ¹³ ohm · cm and σ _s = 48 emu / cm 3.

The developer was prepared by blending the coated magnetic carrier thus obtained with the cyan toner prepared in Example 1. The triboelectric charge of the toner was -27.2 µC / g.

The developer was charged into the same image forming apparatus and developed for use in the same monochrome mode development as in Example 1. As a result, good images were obtained as in Example 1 both in the initial stage and after 30,000 continuous image formations. Carrier adhesion prevention performance was good both before and after continuous image formation. After continuous image formation, the surface state of the carrier was similar to that of the initial state.

Comparative Example 1

Fe ₂ O ₃ , CuO and ZnO were weighed to provide 50 mol%, 27 mol%, and 23 mol%, respectively, and mixed in a ball mill, respectively. The mixture was calcined at 1000 ° C. and triturated with a ball mill. 100 parts of the resulting powder, 0.5 parts of polysodium methacrylate and water were each mixed under a wet ball to form a slurry. The slurry was formed into particles using a spray dryer. The particles were then sintered at 1200 ° C. to provide carrier core particles with Rs of 4.0 × 10 ⁸ ohm · cm.

The carrier was surface-coated with resin in the same manner as in Example 1. The resulting carrier particles exhibited D1 = 47 μm, Rs = 1.1 × 10 ¹⁰ ohm · cm, sphericity of 1.24 and sigma _s = 62 emu / g.

The carrier thus obtained was blended with the cyan color toner prepared in Example 1 to obtain a developer. The triboelectric charge of the cyan toner was -26.9 μC / g.

The developer was charged in the same chemical conversion apparatus and used for monochrome mode development under the same developing conditions as in Example 1. As a result, the obtained image showed high beta image density, but the dot roughness and the halftone reproducibility were poor. Image irregularity due to carrier adhesion was not observed in both the image portion and the non-image portion, but the toner blur phenomenon was confirmed. In addition, as a result of observing the carrier after continuous image formation in a similar manner as in Example 1, a melt-sticking phenomenon of the toner was found in the carrier. The image formed after continuous image formation became more severe in the halftone portion, and showed a more severe blur phenomenon.

Comparative Example 2

The polymerization of the above materials was carried out similarly to the method of Example 1 except that the amount of base catalyst and water were changed. Subsequently, the produced polymerized particles were classified to obtain a resinous carrier core in which magnetic materials were dispersed. Rs of the resulting carrier cores was 5.9 × 10 ⁸ ohm · cm.

The core particles were coated similarly to Example 1.

The coated magnetic carrier particles exhibited a roundness of D1 = 45 μm and 1.07.

The coated carrier particles exhibited Rs = 1.0 × 10 ¹¹ ohm · cm and σ _s = 29 emu / g.

The coated magnetic carrier thus obtained was blended with the cyan toner prepared in Example 1 to prepare a developer. The triboelectric charge of the toner was -28.8 μC / g.

The developer was charged in the same image developing apparatus and used for monochrome mode development under the same developing conditions as in Example 1. As a result, the halftone image of the initial stage was accompanied by roughness, and carrier adhesion was also confirmed.

Comparative Example 3

After obtaining the polymerized particles from the material, it was classified similarly to Example 1 to obtain a resinous carrier core in which the magnetic material was dispersed. The resulting carrier particles exhibited Rs = 7.5 × 10 ⁷ ohm · cm.

The core particles were coated similarly to Example 1.

The coated magnetic carrier particles exhibited a roundness of D1 = 45 μm and 1.06.

The coated carrier particles exhibited Rs = 2.2 x 10 ¹⁰ ohmcm and _{s s} = 73 emu / g.

The coated magnetic carrier thus obtained was blended with the cyan toner prepared in Example 1 to prepare a developer. The triboelectric charge of the cyan toner was -30.8 μC / g.

The developer was filled in the same image developing apparatus and used for developing under the same developing conditions as in Example 3. As a result, the carrier bonding prevention was good, but the halftone image was accompanied by dot irregularities and roughness was confirmed.

Comparative Example 4

The carrier is the same as the coated carrier of Example 1. Cyan toner was prepared in the same composition and method as in Example 1 except for the grinding and sorting conditions.

The toner was blended with 0.5% by weight of externally added titanium oxide as in Example 1. The resulting cyan toner showed D4 = 12.6 μm, D1 = 8.3 μm, D4 / D1 = 1.52. The frictional charge of the cyan toner was -20.1 μC / g as measured with the prepared magnetic carrier at 5% by weight of the toner. The developer was prepared by blending the cyan toner with the coated magnetic carrier described above.

The developer was filled in the same image forming apparatus and used for monochrome mode development under the same developing conditions as in Example 1. As a result, a high image density was obtained, but the dot reproducibility was poor and accompanied by roughness.

Example 7

100 parts by weight of the carrier core prepared in Example 1 was blended in toluene at a concentration of 10% with a coating solution containing 2 parts by weight of a thermosetting phenolic resin and α-Fe ₂ O ₃ (the same as Example 1), and the application of shear force. Under evaporation to coat the solvent. The resin was also cured under application of shear force at 160 ° C. to coat the magnetic carrier particles. Subsequently, the coated carrier particles were decomposed and classified. The resulting carrier particles were D1 = 45 μm, SF1 = 1.06, Rs = 1.0 × 10 ¹³ ohm · cm, and the abundance ratios of magnetic iron compound to nonmagnetic metal oxidation were Pb1 / Pa1 = 0 and Pb2 / Pa2 = 27.6.

The coated magnetic carrier thus obtained was blended with the four-color toner prepared in Example 1 to prepare four two-component developers each having a toner concentration of 8.0% by weight. The frictional charge of each toner was yellow: -25.5 µC / g, magenta: -25.1 µC / g, cyan: -25.9 µC / g, and black: -24.3 µC / g.

The developer was filled in the same image developing apparatus and used for developing under the same developing conditions. As a result, an image showing excellent halftone reproducibility and high beta image density was obtained. In particular, the frictional charge of the toner was stable during continuous image formation.

Example 8

The coated magnetic carrier prepared in Example 7 was further coated by the same method with the same silicone resin as used in Example 1 in a similar manner to Example 1. The resulting coated magnetic carriers had D1 = 45 μm, SF1 = 1.05, Rs = 9.8 × 10 ¹³ ohm · cm and abundance ratios of magnetic iron compound to nonmagnetic metal oxidation of Pb1 / Pa1 = 0 and Pb2 / Pa2 = 29.3 .

The coated magnetic carrier thus obtained was blended with the four-color toner prepared in Example 1 to prepare four two-component developers each having a toner concentration of 8.0% by weight. The frictional charge of each toner was yellow: -23.0 µC / g, magenta: -22.5 µC / g, cyan: -24.4 µC / g, and black: -23.2 µC / g.

The developer was filled in the same image developing apparatus and used for developing under the same developing conditions. As a result, an image showing excellent halftone reproducibility and high beta image density was obtained. In particular, the developer exhibited a wide range of Vback and good stability to prevent blur and carrier adhesion.

Example 9

Magnetic carrier cores were prepared by two-step polymerization using the following materials.

[Step 1]

[Step 2]

The core particles obtained similarly to Example 3 were Rs = 3.3 × 10 ¹² ohm · cm and the abundance ratios of the magnetic iron compound to the nonmagnetic metal oxidation were Pb1 / Pa1 = 0 and Pb2 / Pa2 = 4.58.

The core particles were coated similarly to Example 1.

The coated magnetic carrier particles had a D1 of 40 µm and a sphericity (SF1) of 1.10.

The coated carrier particles exhibited Rs = 3.2 x 10 ¹³ ohmcm and σ _s = 67 emu / g.

The coated magnetic carrier thus obtained was blended with the four-color toner prepared in Example 1 to prepare four two-component developers each having a toner concentration of 8% by weight. The frictional charge of each toner was yellow: -25.6 µC / g, magenta: -25.0 µC / g, cyan: -26.2 µC / g, and black: -24.9 µC / g.

The developer was charged into the same image developing apparatus as in Example 1, and developed using the same developing conditions. As a result, similarly to Example 1, the obtained image showed high halftone reproducibility and image density. In addition, image irregularities due to carrier adhesion did not appear in both the image portion and the non-image portion, and there was no toner blurring phenomenon. As a result of 30,000 continuous color image formation, the image was free of toner dispersion, exhibited high beta image density, and exhibited good halftone and line image reproducibility. Carrier adhesion was not observed in continuous image formation. As a result of observing the cyan developer through SEM after continuous image formation, no peeling phenomenon of the coating was observed, and the surface condition was similar to that of the initial stage carrier.

Example 10

The polymerized particles prepared in Example 9 were further polymerized with the following components.

Suspension polymerization was carried out in the same manner as in Example 3 to obtain a spherical carrier core. The Rs of the generation carrier core particles was 9.3 × 10 ¹² ohm · cm, and the abundance ratios of the magnetic iron compound to the nonmagnetic metal oxide were Pb1 / Pa1 = 0 and Pb2 / Pa2 = 32.3.

The core particles were coated with the same coating resin as in Example 2, but the coverage was different at 1.0% by weight.

D1 of the coated magnetic carrier particles was 42 μm and the sphericity (SF1) was 1.11.

The coated carrier particles exhibited Rs = 1.1 x 10 ¹⁴ ohmcm and σ _s = 60 emu / g.

The coated magnetic carrier thus obtained was blended with the four-color toner prepared in Example 1 to obtain four two-component developers each having a toner concentration of 8.0% by weight. The frictional charge of each toner was yellow: -32.3 µC / g, magenta: -29.9 µC / g, cyan: -32.4 µC / g, and black: -30.3 µC / g.

The developer was charged into the same developing apparatus as in Example 1, and developed using the same developing conditions. As a result, similarly to Example 1, the obtained image showed particularly good dot and thin line reproducibility and high resolution. In addition, no toner dispersion, blurring or carrier adhesion appeared. As a result of 30,000 continuous color image formation, the image showed almost the same picture quality as in the initial stage. Toner dispersion, blurring, or carrier adhesion were not observed even after continuous image formation. After continuous image formation, the surface condition of the carrier was good, similar to the initial stage.

The characteristics of the carriers described above are summarized in Table 1 below, and the results of the evaluation are summarized in Table 2 which follows. The criteria for evaluation are shown separately after Table 2.

Footnote to Table 2

[Beta Cyan Image Density]

The image density of the beta cyan image portion was measured by the relative density of an image printed on white paper with a Macbeth density meter (model RD-918, manufactured by Macbeth Co., using an SPI filter).

[Halftone Roughness]

The degree of roughness of the halftone image portion was visually evaluated with reference to the original image and the reference sample.

[Carrier attached]

After formation of the solid white image, a transparent adhesive tape was applied to the 5 cm x 5 cm zone between the developing zone and the sweep zone of the photosensitive drum for recovery of the magnetic carrier particles attached to the photosensitive drum. The number of carrier adhered particles attached to the 5 cm × 5 cm zone was counted and evaluation was performed by the following criteria based on the number of carrier particles attached per cm 2.

(Excellent): less than 10 particles / cm 2

○ (good): 10 or more to less than 20 particles / cm 2

△ (usually): 20 or more to less than 50 particles / cm 2

Δ × (somewhat poor): 50 or more to less than 100 particles / cm 2

× (defect): 100 or more particles / cm 2

[Blur]

The average reflectance Dr (%) of the white paper before printing was measured with a reflectometer (REFLECTOMETER MODEL TC-6DS, manufactured by Tokyo Denshoku K.K.). On the other hand, a solid white image was printed on white paper, and the reflectance Dr (%) of the solid white image was measured with a reflectometer. The percentage blurring was calculated by the following formula.

Blur Percentage (%) = Dr (%)-Ds (%)

Evaluation was performed by the following criteria.

◎ (excellent): Less than 1.0%

○ (good): 1.0 or more to less than 1.5%

(Moderate): 1.5 or more and less than 2.0%

Δ × (somewhat bad): 2.0 or more and less than 3.0%

× (bad): 3.0% or more

Claims (40)

At least a toner having a number average particle size D1 that satisfies a relationship of weight average particle size D4 and D4 / D1 ≦ 1.5 of 10 μm or less; And magnetic iron compound particles having _a number average particle size r _a and nonmagnetic metal oxide particles having a number average particle size r _b satisfying a relationship of r _b / r _a 1.0 in a ratio of 80-99% by weight in total. A two-component developer for electrostatic image development, comprising a magnetic carrier composed of composite particles containing a binder made of a phenolic resin. The developer according to claim 1, wherein the magnetic iron compound particles have a number average particle size r _a of 0.02-5 μm, and the nonmagnetic metal oxide particles have a number average particle size r _b of 0.05-10 μm. The nonmagnetic metal oxide particles according to claim 1 or 2, wherein the nonmagnetic metal oxide particles are contained in an amount of 5-70% by weight of the magnetic iron compound particles and the nonmagnetic metal oxide particles as a whole, and the magnetic carrier has a bulk density of 1.0-2.0 g / cm 3. Developer having a. The developer according to claim 1, wherein the magnetic carrier is surface-coated with a resin containing nonmagnetic metal oxide particles. The developer according to claim 1 or 4, wherein the magnetic carrier is surface coated with a resin of 0.1-10% by weight. The developer according to claim 1, wherein the magnetic carrier has a saturation magnetization sigma _s of 10-80 emu / g. The developer according to claim 1, wherein the magnetic iron compound consists of magnetite and the nonmagnetic metal oxide consists of hematite. The developer according to claim 1, wherein the toner is a nonmagnetic toner. 2. The total volume of magnetic iron compound particles Pa1 and total volume of nonmagnetic metal oxide particles, respectively, according to claim 1, wherein the magnetic carriers are provided inside the carrier (core) particle cross section in order to provide a higher specific resistance, and The magnetism is such that the total volume Pa2 of the magnetic iron compound particles and the total volume Pb2 of the nonmagnetic metal oxide particles present in the surface portion of the cross-section of the carrier (core) particle are a distribution satisfying the relationship between Pb1 / Pa1 1 and Pb2 / Pa2 1. A developer containing iron compound particles and nonmagnetic metal oxide particles. The developer of claim 1, wherein the magnetic carrier consists of a carrier core coated with 0.5-10% by weight of the coating material. The developer according to claim 10, wherein the magnetic carrier consists of a carrier core coated with 0.6-5% by weight of the coating material. The developer according to claim 1, wherein the magnetic carrier has a sphericity of 2 or less. A toner having a number average particle size D1 that satisfies the relationship of the weight average particle size D4 and D4 / D1 ≦ 1.5 of 10 μm or less, by the developer carrying member including the magnetic field generating means; And magnetic iron compound particles having _a number average particle size r _a and nonmagnetic metal oxide particles having a number average particle size r _b satisfying a relationship of r _b / r _a 1.0 in a ratio of 80-99% by weight in total. And carrying a two-component developer composed of a magnetic carrier composed of composite particles containing a binder composed of a phenolic resin; Forming a magnetic brush of a two-component developer on a developer carrying member; Contacting the magnetic brush with the latent image retention member; And developing an electrostatic charge image on the latent image retaining member while applying an alternating electric field onto the developer carrying member to form a toner image. The developing method according to claim 13, wherein the electrostatic charge image is a digital image. The developing method according to claim 13 or 14, wherein the electrostatic charge image is developed in an inverse developing manner. The developing method according to claim 13, wherein the magnetic iron compound particles have a number average particle size r _a of 0.02-5 μm, and the nonmagnetic metal oxide particles have a number average particle size r _b of 0.05-10 μm. The nonmagnetic metal oxide particles according to claim 13 or 16, wherein the nonmagnetic metal oxide particles are contained in an amount of 5-70% by weight of the total magnetic iron compound particles and the nonmagnetic metal oxide particles, and the magnetic carrier has a bulk density of 1.0-2.0 g / cm 3. Development method having a. The developing method according to claim 13, wherein the magnetic carrier is surface-coated with a resin containing nonmagnetic metal oxide particles. The developing method according to claim 13, wherein the magnetic carrier is surface coated with 0.1-10% by weight of resin. The method according to claim 13, wherein the magnetic carrier has a saturation magnetization σ _s of 10-80 emu / g. The developing method according to claim 13, wherein the magnetic iron compound consists of magnetite and the nonmagnetic metal oxide consists of hematite. The developing method according to claim 13, wherein the toner is a nonmagnetic toner. 14. The total volume of magnetic iron compound particles Pa1 and total volume Pb1 of nonmagnetic metal oxide particles, respectively, according to claim 13, wherein the magnetic carrier is provided inside the carrier (core) particle cross section, in order to provide a higher specific resistance, and The magnetism is such that the total volume Pa2 of the magnetic iron compound particles and the total volume Pb2 of the nonmagnetic metal oxide particles present in the surface portion of the cross-section of the carrier (core) particle are a distribution satisfying the relationship between Pb1 / Pa1 1 and Pb2 / Pa2 1. A developing method containing iron compound particles and nonmagnetic metal oxide particles. The developing method according to claim 13, wherein the magnetic carrier consists of a carrier core coated with 0.5-10% by weight of the coating material. A developing method according to claim 24, wherein the magnetic carrier consists of a carrier core coated with 0.6-5% by weight of the coating material. The developing method according to claim 13, wherein the magnetic carrier has a sphericity of 2 or less. (I) magenta toner having a number average particle size D1 satisfying the relationship of weight average particle size D4 and D4 / D1? 1.5 of 10 µm or less by the developer carrying member including the magnetic field generating means; And magnetic iron compound particles having _a number average particle size r _a and nonmagnetic metal oxide particles having a number average particle size r _b satisfying a relationship of r _b / r _a 1.0 in a ratio of 80-99% by weight in total. And carrying a two-component developer composed of a magnetic carrier composed of composite particles containing a binder composed of a phenolic resin; Forming a magnetic brush of a two-component developer on a developer carrying member; Contacting the magnetic brush with the latent image retention member; And developing an electrostatic charge image on the latent image retaining member while applying an alternating electric field onto the developer carrying member to form a magenta toner image; (II) a cyan toner having a number average particle size D1 that satisfies the relationship of the weight average particle size D4 and D4 / D1 ≦ 1.5 of 10 μm or less by the developer carrying member including the magnetic field generating means; And magnetic iron compound particles having _a number average particle size r _a and nonmagnetic metal oxide particles having a number average particle size r _b satisfying a relationship of r _b / r _a 1.0 in a ratio of 80-99% by weight in total. And carrying a two-component developer composed of a magnetic carrier composed of composite particles containing a binder composed of a phenolic resin; Forming a magnetic brush of a two-component developer on a developer carrying member; Contacting the magnetic brush with the latent image retaining member, and developing an electrostatic charge image on the latent image retaining member while applying an alternating electric field onto the developer carrying member to form a cyan toner image; (III) a yellow toner having a number average particle size D1 that satisfies the relationship of weight average particle size D4 and D4 / D1 ≦ 1.5 of 10 μm or less, by the developer carrying member including the magnetic field generating means; And magnetic iron compound particles having _a number average particle size r _a and nonmagnetic metal oxide particles having a number average particle size r _b satisfying a relationship of r _b / r _a 1.0 in a ratio of 80-99% by weight in total. Conveying a two-component developer composed of a magnetic carrier composed of composite particles containing a binder composed of a phenolic resin; Forming a magnetic brush of a two-component developer on a developer carrying member; Contacting the magnetic brush with the latent image retention member; And developing an electrostatic charge image on the latent image holding member while applying an alternating electric field onto the developer carrying member to form a yellow toner image; And (IV) forming a color image having at least the formed magenta toner image, cyan toner image and yellow toner image. An image forming method according to claim 27, wherein the electrostatic charge image is a digital image. 29. The image forming method according to claim 27 or 28, wherein the electrostatic charge image is developed in an inverse developing manner. 28. The image forming method according to claim 27, wherein the magnetic iron compound particles have a number average particle size r _a of 0.02-5 탆, and the nonmagnetic metal oxide particles have a number average particle size r _b of 0.05-10 탆. 29. An image according to claim 27, wherein the nonmagnetic metal oxide particles are contained in an amount of 5-70% by weight of the total magnetic iron compound particles and the nonmagnetic metal oxide particles, and the magnetic carrier has a bulk density of 1.0-2.0 g / cm 3. Forming method. The image forming method according to claim 27, wherein the magnetic carrier is surface-coated with a resin containing nonmagnetic metal oxide particles. 28. The image forming method according to claim 27, wherein the magnetic carrier is surface coated with a resin of 0.1-10% by weight. 28. The image forming method of claim 27, wherein the magnetic carrier has a saturation magnetization σ _s of 10-80 emu / g. 28. The image forming method according to claim 27, wherein the magnetic iron compound is made of magnetite and the nonmagnetic metal oxide is made of hematite. An image forming method according to claim 27, wherein the toner is a nonmagnetic toner. 29. The total volume of magnetic iron compound particles Pa1 and total volume of nonmagnetic metal oxide particles, respectively, according to claim 27, wherein the magnetic carriers are provided inside the carrier (core) particle cross section to provide a higher resistivity, and The magnetism is such that the total volume Pa2 of the magnetic iron compound particles and the total volume Pb2 of the nonmagnetic metal oxide particles present in the surface portion of the cross-section of the carrier (core) particle are a distribution satisfying the relationship between Pb1 / Pa1 1 and Pb2 / Pa2 1. An image forming method containing iron compound particles and nonmagnetic metal oxide particles. 28. The method of claim 27, wherein the magnetic carrier consists of a carrier core coated with 0.5-10% by weight of the coating material. The image forming method according to claim 38, wherein the magnetic carrier consists of a carrier core coated with 0.6-5% by weight of the coating material. The image forming method according to claim 27, wherein the magnetic carrier has a sphericity of 2 or less.