CN1130767A - Two-component type developer, developing method and image forming method - Google Patents

Abstract

A two-component type developer displaying an electrostatic image includes at least one toner and a magnetic carrier. The weight average particle diameter D ₄ of the toner is at most 10 μm, and the number average particle diameter D ₁ satisfies D ₄ /D ₁ ≦1.5. The magnetic carrier includes composite particles containing magnetic iron compound particles, nonmagnetic metal oxide particles, and a binder containing phenolic resin. The total amount of the magnetic iron compound and the non-magnetic metal oxide contained in the composite particle is 80-99wt%. The number-average particle size of the magnetic iron compound particles is γ _a , and the number-average particle size of the non-γ _a magnetic metal oxide particles is γ _b , satisfying γ _b /γ _a >1.0.

Description

Two-component developer, developing method and image forming method

The present invention relates to a two-component type developer for electrostatic images in the fields of electrophotography and electrostatic copying, a developing method and an image forming method.

Hitherto, 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 in a photoconductive layer by irradiating a light image corresponding to an original, and a toner is attached to the latent image to develop the latent image. If necessary, the resulting toner image is then fixed by heat, pressure, or both heat and pressure or solvent vapor after being transferred onto a transfer material such as paper to obtain a copy or print.

In the step of developing the latent image, the charged toner particles form a toner image by utilizing electrostatic action of the electrostatic latent image. Generally, in a method of developing an electrostatic latent image using a toner, a two-component type developer including a mixture of a toner and a carrier is suitable for obtaining a full-color copy or print of high image quality.

In recent years, with the development of computer technology, high-definition television technology, etc., devices that output high-resolution full-color images are required. For this purpose, attempts have been made to provide a toner full-color image of high quality and high resolution compared with a silver halide photographic image. In order to meet these needs, various studies have been conducted on methods and developers.

Regarding the example of the developer, a representative attempt is to use a toner and a carrier having a small particle diameter. However, the use of a toner with a small particle diameter increases difficulties in powder handling and optimization of electrophotographic properties such as transfer and fixing in addition to development. Therefore, there is a limit to improving image quality only by improving toner.

On the other hand, as an attempt for improvement in the electrophotographic process, high-quality images can be obtained by thickening the magnetic brush on the developer-belt-carrying member such as the developing sleeve. From a methodological point of view, the thickening of the magnetic brush can be achieved by developing between a part of the magnetic poles in the developing sleeve or by using less powerful magnetic poles in the developing sleeve. These measures can suppress the influence of the magnetic brush, but difficulties such as scattering and poor transfer performance also arise due to insufficient suppression of the developer. So these cannot be simply adopted. Densification of magnetic brushes can also be achieved by using smaller particle size or less magnetic magnetic carrier particles.

For example, Japanese Patent Application JP-A-59-104663 proposes the use of magnetic carriers with lower saturation magnetization. If carrier particles with lower saturation magnetization are simply applied, fine line reproducibility may be improved, however, since the confinement of the magnetic carrier particles on the developing sleeve is reduced, transfer of the magnetic carrier to the photosensitive drum tends to cause image defects. This point is referred to as "carrier attachment" phenomenon.

We also know that carrier attachment also tends to occur when magnetic carriers with smaller particle sizes are used. For example, Japanese Patent IP-B-5-8424 proposes to use a toner with a smaller particle size and a magnetic carrier to carry out non-contact development under a vibrating electric field. Also described in this Japanese Patent Specification is the effect that a magnetic carrier having a higher resistivity is effective in improving carrier attachment during development using an oscillating electric field. It has been found that in some cases the use of a higher electrical resistance magnetic carrier is not sufficient to improve carrier attachment for high quality images, especially in the case of even a small percentage of the exposed surface of the carrier core with a lower resistance. In this non-contact development method, when the magnetic carrier is provided with a large magnetization on the magnetic pole, a fairly good image density can be obtained to obtain an image without carrier attachment, but when the magnetization of the magnetic carrier decreases , the image density can drop significantly.

In general, magnetic resin supports have a higher volume resistivity than supports with iron powder cores or metal oxide cores (such as ferrite, iron tetroxide cores). In the case of using a magnetic resin carrier such as allowing to contain an increased amount of magnetic material (the increase is achieved by using a magnetic material with a different particle size ratio), if the internally added magnetic material includes a magnetic material having a low resistivity material, it can provide higher magnetic flux confinement. However, when these magnetic carriers are used in a developing process using an alternating magnetic field, it is insufficient to improve the attachment of the carrier in some cases.

As described above, various measures have been taken to obtain high image quality while preventing the adhesion of the carrier, but it is also desired to provide a two-component type developer capable of solving the above-mentioned problems.

Accordingly, an object of the present invention is to provide a two-component type developer capable of solving the above-mentioned problems.

Still another object of the present invention is to provide a two-component type developer which can eliminate carrier adhesion and prevent or suppress the occurrence of image blur, thereby providing a high-quality toner image.

Another object of the present invention is to provide a two-component type developer which is effective in preventing toner scattering.

Another object of the present invention is to provide a two-component type developer which has an extended life and causes only a small decrease in image quality in copying or printing of a large number of sheets.

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

According to the present invention, there is provided a two-component type developer for displaying a still image, which comprises at least one toner and a magnetic carrier, wherein:

The weight-average particle diameter _D4 of the toner is at most 10 μm, and the number-average particle diameter _D1 satisfies _D4 / _D1≤1.5 ; and

The magnetic carrier contains composite particles, which contain magnetic iron compound particles, non-magnetic metal oxide particles, and a binder containing phenolic resin; the total ratio of the composite particles containing magnetic iron compounds and non-magnetic metal oxides is 80-99wt %; the number average particle diameter of the magnetic iron compound particles is r _a , the number average particle diameter of the non-magnetic metal oxide is r _b , satisfying r _b /r _a >1.0.

According to another aspect of the present invention, there is provided a method of developing an electrostatic image, comprising the steps of:

carrying the above-mentioned two-component developer by means of a developer-carrying member in which a magnetic field generating means is housed;

A magnetic brush forming a two-component type developer on a developer carrying member;

bringing the magnetic brush into contact with the latent image display element;

The electrostatic image is developed on the latent image developing member to form a toner image while applying an alternating electric field to the developer carrying member.

According to another aspect of the present invention, there is provided an image forming method, wherein the above-mentioned steps are respectively repeated with at least one of a magenta developer, a cyan developer and a yellow developer satisfying the requirements of the above-mentioned two-component type developer, and at least the obtained The magenta toner image, cyan toner image, and yellow toner image form a full-color image.

These and other objects, features and advantages of the present invention will become more apparent from the following description of the preferred embodiments of the present invention when taken in conjunction with the accompanying drawings.

Fig. 1 is a schematic diagram of an apparatus for carrying out the scheme of the developing method of the present invention.

FIG. 2 is a diagram describing an apparatus used to measure the resistivity of a magnetic carrier, a carrier core, and a metal oxide.

Fig. 3 is a schematic diagram of an apparatus for carrying out a scheme of the imaging method of the present invention.

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

In the present invention, the above-mentioned objects are achieved by using a two-component type developer in which both the toner and the magnetic carrier are improved.

As a result of our detailed studies, it has been revealed that the driving force for carrier attachment during contact development under the application of an alternating magnetic field is formed by charge injection from the developing sleeve to the magnetic carrier when the developing bias is applied as the controlling factor. caused. Regarding the reproducibility of the dots in the digital latent image, it has been found that the decline of the reproducibility of the dots is caused by the leakage of the electrostatic latent image charge on the photosensitive drum due to the friction between the magnetic carrier and the surface of the photosensitive drum, so the dots of the digital latent image Broken into a non-uniform shape. Even in the case of using a carrier core with high volume resistance, such as a resin carrier dispersed with a magnetic material, if the magnetic material has low resistivity like magnetite, charges can leak through the magnetic particles.

In order to solve these problems simultaneously, the present invention has used the magnetic carrier that contains composite particle, makes composite particle contain magnetic iron compound particle, non-magnetic metal oxide particle and the binding agent that contains phenolic resin; Composite particle contains magnetic iron compound and nonmagnetic The total amount of metal oxides is 80-99wt%. The number average particle size r _a of the magnetic iron compound particles and the number average particle size r _b of the non-magnetic metal oxide satisfy r _b /r _a >1.0. As a result, the non-magnetic metal oxide particles with higher resistivity are preferentially located on the surface of the carrier particles, thereby effectively increasing the resistivity of the carrier. For this reason, the developer of the present invention is effective in preventing charge injection into the carrier and preventing carrier adhesion to faithfully reproduce electrostatic latent images.

By having the non-magnetic metal oxide particles preferentially located on the support surface or the surface of the core, rather than in the center or interior of the support particle, a higher ratio of magnetic iron oxide particles can be provided at the support surface than when the magnetic iron oxide particles are exposed to the surface of the support or core. resistance, thus effectively preventing charge injection.

As for preventing image blurring and toner scattering and improving the reproducibility of dots in the final image, by making the non-magnetic metal oxide particles with a relatively large particle size preferentially located on the surface, the surface of the magnetic carrier particles is provided with minute non-magnetic Uniformity for better loading of toner particles. With this improvement and the improvement in the toner, the charging of the toner and the image quality of the final image can be improved after the transfer and fixing steps immediately after the development in the electrophotographic process.

By using a toner having a weight-average particle diameter _D4 of up to 10 μm and a steep particle diameter distribution represented by a number-average particle diameter _D1 satisfying _D4 / _D1 of up to 1.5 and comprising magnetic iron oxide particles and A magnetic carrier of composite particles of phenolic resin-bonded non-magnetic metal oxide particles can provide a two-component type developer that does not cause image blur or toning scattering and obtains good dot reproducibility. This is possible because the toner triboelectric charge distribution is steepened by narrowing the toner particle size distribution, and since the composite particles provide minute surface non-uniformity in triboelectric charging, the toner The charging of the agent can be better completed.

The toner of the present invention is less likely to deteriorate and can continuously provide images of high quality similar to those at the initial stage for the following reasons.

Considering that the developer deteriorates during long-term use due to the damage of the toner and the magnetic carrier, this damage is mainly due to the magnetic shear between the toner and the carrier or between the carrier particles in the developing container or due to gravitational shear. The toner is basically consumed, while the magnetic carrier is reused without being consumed, so that the damage caused on the surface accumulates.

However, if a carrier including 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 steep particle size distribution, between the toner and the carrier and between the carrier particles The magnetic shear force can be reduced, thereby reducing the surface damage of the carrier particles.

In particular, the magnetic carrier particles used in the present invention provide surface heterogeneity of fine particles including magnetic particles and non-magnetic metal oxide particles so that when the magnetic carrier particles are coated with resin, the magnetic carrier particles ( core particles) and the coating resin are improved, and peeling of the coating resin layer is suppressed.

From the viewpoint of higher image quality, a smaller particle size of the magnetic carrier is preferable, but it tends to increase carrier attachment in terms of the relationship between magnetic force and particle size. Combining these viewpoints, the number average particle diameter of the magnetic carrier used in the present invention may range from 1 to 1000 μm, preferably from 1 to 300 μm, in order to provide high image quality. From the viewpoint of high image quality, prevention of carrier adhesion and prevention of developer deterioration, a number average particle diameter of 5 to 100 μm during continuous image formation is more suitable. If the number-average particle diameter of the magnetic carrier exceeds 1000 μm, the specific surface area of the magnetic brush that rubs against the photosensitive drum will decrease, so it is not easy to supply a sufficient amount of toner, and scratches of the magnetic brush are left, resulting in high density and high image quality. From a quality point of view, this is undesirable. A magnetic carrier having a number average particle diameter of less than 1 μm tends to cause carrier attachment due to the small particle diameter of each carrier particle. The method of measuring the particle diameter of the magnetic carrier particles based here will be described below.

As for the magnetic properties of the magnetic carrier used in the present invention, it may be appropriate to use a magnetic carrier having a saturation magnetization (σ _s ) of 10 to 80 emu/cm ³ . It is further preferred to use a magnetic carrier having a saturation magnetization of 15 to 60 emu/cm ³ . The magnetization of the magnetic carrier can be appropriately selected according to the particle diameter of the carrier. Although also affected by the particle size, a magnetic carrier having a magnetization of more than 80 emu/ ^cm tends to cause magnetic brush formation on a developing sleeve having a low density and a developing electrode including a rigid ear, and thus, is prone to Scratch marks are caused in the resulting toner image, and image defects such as roughening of half-tone images, and solid image irregularities are easily caused, especially due to deterioration in continuous long-term image formation on a large number of sheets. If it is less than 10 emu/cm ³ , the magnetic force generated by the magnetic carrier is insufficient, causing toner adhesion or lowering the performance of toner transfer.

The magnetic properties referred to here are values measured using an oscillating magnetic field type magnetic property automatic recording apparatus ("BHV-30", available from Riken Denshi K.K.). Specific conditions for the measurement will be described below.

The magnetic carrier used in the present invention preferably has a resistivity of at least 1×10 ¹² ohm·cm at an electric field strength of 5×10 ⁴ V/m. If the resistivity is lower than 1×10 ¹² ohm·cm, the above-mentioned carrier attachment and lowering of dot reproducibility are liable to be caused due to charge leakage of the latent image during development. The method of measuring the resistivity of the magnetic carrier referred to here will be described below.

The magnetic iron component constituting the core of the magnetic carrier preferably includes an iron-containing metal alloy, magnetite or ferrite exhibiting magnetic properties represented by the general formula MO·Fe ₂ O ₃ or MFe ₂ O ₄ , wherein M represents divalent or Monovalent metals, such as Mn, Fe, Ni, Co, Cu, Mg, Zn, Cd, or Li. M can be one or more metals. Specific examples may include alloys such as silicon steel, permalloy, sendust, Fe-Co, and alnico; and iron-based oxide materials such as magnetite, r-iron oxide, Mn-Zn-based Ferrite, Ni-Zn-based ferrite, Mn-Mg-based ferrite, Li-based ferrite, and Cu-Zn-based ferrite. Among these materials, magnetite is preferably used.

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

Examples of non-magnetic metal oxides may include one or more metals such as Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Y, Zr , Nb, Mo, Cd, Sn, Ba and Pb. Specific examples of non-magnetic 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 .

The above-mentioned magnetic iron compound and non-magnetic metal oxide may preferably be dispersed in a resin to form carrier core particles. Under such conditions, it is preferred to use a plurality of similarly shaped particles in order to provide enhanced bonding and higher carrier strength. Examples of preferred combinations may include: magnetite and hematite (α-Fe ₂ O ₃ ), magnetite and r-Fe ₂ O ₃ , magnetite and SiO ₂ , magnetite and Al ₂ O ₃ , magnetite and TiO ₂ , and magnetite and Cu-Zn-based ferrite. Among these combinations, the combination of magnetite and hematite is preferable in view of the price and the strength of the resulting carrier.

In the case of dispersing the magnetic iron compound and the nonmagnetic metal oxide into the resin to form the carrier core, the number average particle diameter of the magnetic iron compound particles is r _a , and the number average particle diameter of the nonmagnetic metal oxide particles is r _b , It is also satisfied that the ratio r _b /r _a exceeds 1.0. If the ratio is equal to 1 or less than 1, magnetic iron compound particles having lower resistivity are easily exposed to the surface, thereby failing to obtain enhanced resistivity of the carrier and prevent carrier attachment. A larger r _b /r _a ratio is preferred so that larger non-magnetic metal oxide particles appear on the surface of the carrier particles, which can prevent charge injection into the carrier, thus preventing carrier attachment and spotting due to latent image charge leakage. Reduced reproducibility. In order to provide a good combination of the effect of increasing the electrical resistivity of the magnetic carrier and enhancing the strength of the carrier, a ratio of r _b /r _a of 1.2 to 5.0 is more preferable. The above preferred particle size ratio range is based on the finding that when filler particles of different sizes are simultaneously blended and dispersed in a resin to form carrier (core) particles, larger size particles are preferentially located on the surface of the carrier (core). Therefore, it is important that the particles of the non-magnetic metal oxide having higher resistivity should have a larger particle size than the particles of the magnetic iron compound. The number average particle diameter ra of the magnetic iron compound _is preferably 0.02 to 5 µm, which may vary depending on the particle diameter of the carrier. The number average particle diameter r _b of the nonmagnetic metal oxide particles is preferably 0.05 to 10 µm. The method of measuring the particle size of the metal oxide used here will be described below.

By selectively forming the non-magnetic metal oxide particle layer on the surface of the carrier (core) particle, rather than inside the carrier particle, it is possible to provide better resistivity and to effectively suppress charge injection.

More specifically, the total volume of the magnetic iron compound particles appearing inside the cross-section of the carrier (core) particle is Pa ₁ , the total volume of the non-magnetic metal oxide particles is Pb ₁ , and the magnetic iron compound particles appearing on the surface of the carrier (core) particle The total volume of the compound particles is Pa2, and the total volume of the non-magnetic metal oxide particles is Pb ₂ , preferably Pb ₁ /Pa ₁ <1, Pb ₂ /Pa ₂ >1, so as to obtain higher resistivity.

Regarding the resistivity of the magnetic iron compound and nonmagnetic metal oxide used to be dispersed in the resin, it is preferable that the resistivity of the magnetic iron compound particles is at least 1×10 ³ ohm·cm, and that of the nonmagnetic metal oxide particles is preferably higher than Resistivity of magnetic iron compounds. More preferably, the resistivity of the non-magnetic metal oxide particles is at least 10 ⁸ ohm·cm. If the resistivity of the magnetic particles is lower than 1×10 ³ ohm·cm, even if the dispersion amount of the magnetic iron compound is reduced, it is difficult to obtain the necessary resistivity of the carrier, and therefore, charge injection tends to be caused, resulting in poor image quality and incurring Carrier attached. If the resistivity of the metal oxide having a larger particle size is lower than 1×10 ⁸ ohm·cm, it is difficult to sufficiently increase the resistivity of the carrier core, and therefore, it is difficult to obtain the above-mentioned effects. The method of measuring the resistivity of metal oxides used here will be described below.

The magnetic carrier contains magnetic iron compound and non-magnetic metal oxide in a total amount of 80-99wt%. If the total amount is less than 80% by weight, the carrier (core) particles tend to aggregate with each other during particle formation, especially during direct polymerization. This will lead to instability of particle size distribution, and good triboelectrification cannot be achieved. Above 99% by weight, the strength of the resulting carrier decreases, and problems such as carrier breakage tend to occur during continuous image formation on a large amount of paper.

In order to better achieve the effect of the present invention, in the resin carrier containing the magnetic iron compound and the nonmagnetic metal oxide in the dispersed state, the amount of the nonmagnetic metal oxide particles preferably accounts for 1% of the magnetic iron compound and the nonmagnetic metal oxide particles. 5-70wt% of the total amount. If it is less than 5 wt%, it is difficult to increase the resistivity of the carrier (core), and more than 70 wt%, the resulting magnetic carrier has only a small magnetic force, so it is easy to cause carrier attachment.

The magnetic carrier according to the invention preferably has a bulk density of 1.0-2.0 g/cm ³ . If it is less than 1.0 g/cm ³ , carrier attachment tends to occur due to the influence of magnetic force. While above 2.0 g/cm ³ , the resulting developer is also liable to deteriorate during continuous image formation on a large amount of paper due to the influence of the magnetic force of the magnetic carrier. The measurement of the bulk density of the magnetic carrier can be performed in accordance with JIS K5101.

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

The magnetic carrier used in the present invention, for example, can be prepared by mixing a monomer (ie, a binder resin precursor), a magnetic iron compound and a nonmagnetic metal oxide, and polymerizing the mixture to directly produce carrier core particles. Monomers used for polymerization may include combinations of phenols and aldehydes. More specifically, in order to produce carrier (core) particles containing cured phenolic resin, a mixture of phenol, aldehyde, magnetic iron compound and non-magnetic metal oxide can be prepared in an aqueous medium with a basic catalyst and a dispersion stabilizer. Suspension polymerization in the presence of conditions. In order to obtain a high-resistivity magnetic carrier, composite particles are preferably formed by a two-step polymerization method, wherein, for particle formation, the magnetic iron compound is first subjected to polymerization to form a slurry, and then monomers, non-magnetic metal oxides and any other necessary The additives are added to the slurry to carry out the second-step polymerization, or to carry out the polymerization process of three or more steps repeating the above-mentioned steps. Examples of the phenol as a monomer may include phenol, resorcinol; alkylphenols such as m-cresol, p-tert-butylphenol, ortho-propylphenol, and alkylphenols and their derivatives. Among them, phenol is particularly preferred because of particle forming characteristics and cost.

The phenolic resin can be crosslinked in order to strengthen the carrier core and facilitate resin coating thereon.

The magnetic carrier used in the present invention may preferably be in a form covered with an appropriate coating resin selected in accordance with the charging properties of the toner used in the present invention. This coating can be accomplished by using a resin containing non-magnetic metal oxide particles to control the resistivity of the carrier core and improve the smoothness of the magnetic carrier. This resin-coated magnetic carrier can effectively prevent charge injection into the magnetic carrier, prevent the carrier from having too high resistivity and the magnetic carrier from excessive charge, thereby stabilizing the triboelectric charge of the toner. The non-magnetic metal oxide dispersed in the coating resin may contain one or more selected from the above-mentioned metal oxides. It is further preferable to use SiO ₂ , Al ₂ O ₃ , TiO ₂ or α-Fe ₂ O ₃ having good fluidity, or to use non-magnetic metal oxides used in carrier cores to improve adhesion of coating resins. The covering amount of such coating material may be 0.5-10 wt%, especially 0.6-5 wt%, based on the weight of the carrier core.

If the coating amount is less than 0.5% by weight, it is difficult to effectively cover the carrier core particles and control the ability to rub the toner with the coating resin to charge it. If it exceeds 10 wt%, the resistivity is within a desired range due to an excessively high resin coating rate, but may result in lower fluidity and image blemishes after continuous image formation on a large amount of paper.

The coating resin used in the present invention may be insulating resin, which may be thermoplastic or thermosetting resin. Examples of thermoplastic resins may include polystyrene, acrylic resins such as polymethylmethacrylate, and styrene-acrylic acid copolymers; styrene-butadiene copolymers, ethylene-vinyl acetate copolymers, dichloro Vinyl resin, vinyl acetate resin, polyvinylidene fluoride resin, fluorocarbon resin, perfluorocarbon resin, solvent-soluble perfluorocarbon resin, polyvinyl alcohol, polyvinyl acetal polyvinylpyrrolidone, petroleum resin, cellulose ; Cellulose derivatives such as cellulose acetate, nitrocellulose, methyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose; novolac resins, low molecular weight polyethylene, saturated alkanes based polyester resins; aryl polyester resins such as polyethylene terephthalate, polybutylene terephthalate, and polyarylates; polyamide resins, polyacetal resins, polycarbonate resins , polyethersulfone resin, polysulfone resin, polyphenylene sulfide resin, and polyetherketone resin.

Examples of thermosetting resins (or curable resins) may include: phenolic resins, modified phenolic resins, maleic resins, alkyd resins, epoxy resins, acrylic resins, polycondensed from maleic anhydride, terephthalic acid, and polyols Unsaturated polyester, urea resin, melamine resin urea-melamine resin, xylene resin, toluene resin, guanamine resin, melamine-guanamine resin, aetoguanamine resin, glycerin resin, furan resin, polysiloxane resins, polyimide resins, polyamideimide resins, polyetherimide resins and polyurethane esters.

The thermoplastic or thermosetting resins mentioned above may be used alone or in admixture. Mixtures of thermoplastic resins and curing or hardeners may also be used to obtain cured resins.

The coated magnetic carrier can be preferably produced by spraying a coating resin solution onto carrier (core) particles in a suspended or fluidized state, and forming a coating film on the surface of the core particles, or by spray drying.

Other coating methods may include gradual evaporation of the solvent in the coating resin solution in the presence of the metal oxide under applied shear. More specifically, solvent evaporation may be performed at a temperature above the glass transition point of the coating resin, and the resulting agglomerated metal oxide particles are then dispersed. In addition, the coating film may be cured under heating after being dispersed.

The metal oxide may have an appropriately selected particle shape for the development system used. However, the metal oxides used in the present invention may preferably have a sphericity of at most 2. If the sphericity exceeds 2, the resulting developer has poor fluidity to provide a magnetic brush with poor shape, so that it is difficult to obtain a high-quality toner image. The carrier sphericity is measured by, for example, taking 300 carrier particles at random with a field emission scanning electron microscope (such as "S-800" available from Hitachi K.K) and using an image analyzer (such as "Luzex 3" available from Nireco K.K) ″) to determine the mean value of sphericity defined by the following equation:

Sphericity (SF1)=[(MXLNG) ² /AREA]×π/4, where MXLNG represents the maximum diameter of the carrier particle, and AREA represents the projected area of the carrier particle. When the sphericity is close to 1, its shape is approximately spherical.

The weight average particle diameter (D ₄ ) of the toner used in the present invention is at most 10 μm, preferably 3 to 8 μm. It is important that the ratio (D ₄ /D ₁ ) of the weight average particle diameter (D ₄ ) to the number average particle diameter (D ₁ ) be at most 1.5.

If the weight-average particle diameter (D ₄ ) of the toner exceeds 10 μm, the particles of the toner displaying an electrostatic latent image are too large to truly display the latent image, and toner scattering tends to occur.

If the ratio (D ₄ /D ₁ ) of the weight-average particle diameter (D ₄ ) to the number-average particle diameter (D ₁ ) is greater than 1.5, the toner will have a wide charge distribution, and therefore, problems such as charging failure and coloration are likely to occur. Adjust the particle size deviation of the particles. The weight-average particle diameter and number-average particle diameter of the toner can be measured using, for example, a Coulter counter. The details thereof are described later.

The toner used in the present invention may contain a binder resin, and examples of the resin include: polystyrene; polymers of styrene derivatives, such as poly-p-chlorostyrene, and polyvinyltoluene; styrene copolymers substances, such as styrene-p-chlorostyrene copolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-acrylate copolymer, styrene-methacrylate copolymer, benzene Ethylene-α-chloromethacrylate copolymer, styrene-acrylonitrile copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer , and styrene-acrylonitrile-indene copolymers; polyvinyl chloride, phenolic resins, natural or modified phenolic resins, natural or modified maleic resins, acrylic resins, methacrylic resins, polyvinyl acetate, Silicone resins; polyester resins with structural units selected from aliphatic polyols, aromatic polyols or bisphenols and aliphatic dicarboxylic acids or aromatic dicarboxylic acids; polyurethane resins, polyamide resins, poly Petroleum resins of vinyl butyral, terpene resins, coumarone-indene resins, and crosslinked resins, such as styrene-based resins and crosslinked polyester resins, can also be used.

Comonomers used in combination with styrene monomers to obtain styrene copolymers may include vinyl monomers, which include: acrylic acid, acrylates or derivatives thereof such as methyl acrylate, ethyl dodecacrylate, butyl acrylate ester, lauryl acrylate, octyl acrylate, (2-ethylhexyl) acrylate, phenyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, octyl methacrylate, propylene Nitrile, methacrylonitrile, and acrylamide; maleic acid; maleic acid half-esters and diesters, 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; vinyl ethers, such as vinyl methyl ether and vinyl ethyl ether.

The crosslinking agent may mainly comprise compounds having at least two polymerizable double bonds. Examples are: aromatic divinyl compounds, such as divinylbenzene, and divinylnaphthalene; carboxylic acid esters with two double bonds, such as ethylene glycol diacrylate, ethylene glycol dimethacrylate , and (1,3-butanediol) dimethacrylate; divinyl compounds such as divinylaniline, divinyl ether, divinylsulfide and divinylsulfone; and Compounds with double bonds. These compounds may be used alone or in admixture. When synthesizing these binding resins, based on the binding resin, the amount of the crosslinking agent is preferably 0.01-10 wt%, more preferably 0.05-5 wt%.

In the case of a pressure-fixing system, a binder resin can be used for a pressure-fixable toner, examples of which include: polyethylene, polypropylene, polymethylene, polyurethane, elastic Body, ethylene-ethyl acrylate copolymer, ethylene-vinyl acetate copolymer, ionomer resin, styrene-butadiene copolymer, styrene-isoprene copolymer, linear saturated polyester, paraffin, and other waxes.

In the present invention, the toner may be used in combination with a charge control agent which is incorporated (inside added) or blended (outside added) with the toner particles. Due to the addition of a charge control agent, optimum charge control can be achieved according to the developing system used. Examples of positive charge control agents include: nigrosine and its products modified with fatty acid metal salts; quaternary ammonium salts such as tributylbenzylsodium-1-hydroxy-4-naphthalenesulfonate, and tetrabutyl tetrafluoroborate aryl ammonium salts; diorganotin oxides such as dialkylene oxide, dioctyltin oxide, dicyclohexyltin oxide; dibutyltin borate, dioctyltin borate and dicyclohexyltin borate. These compounds can be used alone or in combination of two or more. Among these compounds, nigrosine-based compounds and quaternary ammonium salts are particularly preferred.

Furthermore, in the present invention, negative charge control agents such as organometallic salts, organometallic complexes and chelate compounds can also be used. Among them, acetylacetone metal complexes (including monoalkyl substituted and dialkyl substituted derivatives), salicylic acid metal complexes (including monoalkyl substituted and dialkyl substituted derivatives) and their corresponding Salt is 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) acetylacetonate, complexes or salts of chromium 3,5-di-tert-butyl salicylate, and 3,5-di-tert- Complexes or salts of zinc butyl salicylate.

When added to the inside of the toner, the above-mentioned charge control agent is preferably used in an amount of 0.1-20 parts by weight, particularly preferably 0.2-10 parts by weight, per 100 parts by weight of the binder resin. When used in color imaging, colorless or light-colored charge control agents are preferably used.

As the colorant of the toner, hitherto known dyes and/or pigments can be used. Examples thereof include: carbon black, phthalocyanine blue, peacock blue, permanent red, lake red, rhodamine lake, Hansa yellow, permanent yellow, and benzidine yellow. The coloring agent is added in an amount of 0.1-20 parts by weight, preferably 0.5-20 parts by weight, per 100 parts by weight of the binder resin. In order to obtain a fixed toner image or an OHP film with good transparency, the colorant is preferably added in an amount of at most 12 parts by weight, more preferably 0.5 to 9 parts by weight, per 100 parts by weight of the binder resin.

The toner constituting the developer according to the present invention can further contain waxes such as polyethylene, low-molecular-weight polypropylene, microcrystalline wax, carnauba wax, sasoe wax, paraffin wax in order to improve the release property upon hot-press fixing.

The toner used in the present invention is suitably used as a mixture with externally added fine powders including inorganic materials such as fine particles of silica, alumina and titanium oxide; organic materials such as polytetrafluoroethylene, polyvinylidene fluoride Fine particles of vinyl, polymethylmethacrylate, polystyrene and silicone resins. If these fine powders are added to the outside of the toner, the fine powder will exist between the toner and carrier particles, or between the toner particles, so the developer will have improved fluidity and increased life. The preferred mean particle size of the fine powders mentioned above is at most 0.2 μm. If the average particle diameter exceeds 0.2 μm, the effect of improving fluidity will be insufficient, and in some cases image quality will be deteriorated due to insufficient fluidity during development or transfer. The method of measuring the particle diameters of these fine powders will be described later.

These fine powders preferably have a specific surface area of at least 30 m ² /g, in particular 50 to 400 m ² /g, as determined by nitrogen adsorption. The fine powder is suitably added at 0.1 to 20 wt parts per 100 wt parts of toner.

According to the present invention, binder resin of vinyl type or non-vinyl type thermoplastic resin, colorant, optional charge control agent and other additives can be fully blended in a mixer in the preparation of toner constituting a developer , and then, melt kneading with a hot kneading device such as a heating roll, a kneader or an extruder to suitably knead the resin and disperse or dissolve the pigment and the dye. The product thus kneaded is cooled and solidified, pulverized and classified to obtain toner particles. In order to classify the toner, it is preferable to use a multi-division classifying device utilizing an inertial force (coanda effect). With such an apparatus, a toner having a particle size distribution defined by the present invention can be efficiently produced.

The toner particles thus obtained may be used as they exist, but are preferably used in the form of a mixture with fine powder outside the above-described additives.

The mixing of the toner and the fine powder can be performed using a blender such as a Henschel mixer. The obtained toner with external additives and magnetic carrier are mixed to obtain a two-component type developer. In the two-component type developer, the toner preferably accounts for 1-20 wt%, more preferably 1-10 wt%, which depends on the developing process in typical cases. The toner in the two-package developer may suitably be provided with a triboelectric charge of 5-100 µc/g, most preferably 5-60 µc/g. The method of measuring the triboelectric charge referred to here will be described below.

The developing method using the two-component developer of the present invention, for example, can be performed using the developing device shown in FIG. 1 . The development is preferably performed under application of an alternating electric field in a state where the magnetic brush is in contact with the latent image display member, such as the photosensitive drum 3 .

The exchange electric field preferably has a peak-to-peak voltage of 500-5000 volts and a frequency of 500-10000 Hz, preferably 500-3000 Hz, which can be appropriately selected according to the process. The waveform can be appropriately selected, such as a triangular wave, a rectangular wave, a sine wave, or a waveform obtained by changing the duty cycle. If the applied voltage is lower than 500 volts, in some cases, it is difficult to obtain a sufficient image density, and the blurred toner in the non-image area cannot be recovered satisfactorily. If it is higher than 5000 volts, in some cases, the latent image will be disturbed by the magnetic brush, thereby reducing the quality of the image.

Frequencies below 500 Hz, in some cases, can cause charge injection into the carrier, degrading image quality due to carrier attachment and latent image interference. If it is higher than 10000 Hz, it is difficult for the toner to keep up with the electric field, and therefore, image quality tends to be lowered.

In the developing method of the present invention, it is preferable to set a contact width (developing gap) C of 3-8mm for the magnetic brush on the developing sleeve 1 with the photosensitive drum 3, so as to complete the developing and provide sufficient image density and excellent point reproducibility without causing carrier attachment. If the developing gap C is narrower than 3 mm, it is difficult to satisfy the requirements of sufficient image density and good dot reproducibility. If it is wider than 8 mm, it will be difficult to sufficiently prevent the carrier from adhering. The developing gap C can be appropriately adjusted by changing the distance A between the developer regulating member 2 and the developing sleeve 1 and/or changing the gap B between the developing sleeve 1 and the photosensitive drum 3 .

By using at least three developing devices corresponding to magenta, cyan and yellow, adopting the developer and the developing method of the present invention, and preferably adopting a developing system for displaying a digital latent image, the image forming method of the present invention can effectively form an intermediate Full-color images with very correlated tone reproducibility, enabling true-to-dot latent image development while avoiding negative effects of magnetic brushes and interference from latent images. Using a toner having a steep particle size distribution is also effective in achieving a high transfer ratio in the subsequent transfer step. Therefore, it becomes possible to obtain high image quality in halftone portions and solid image portions.

In addition to high image quality in the first step of image formation, since the shear force acting on the developer in the developing container is small, the use of the two-component developer of the present invention can also effectively avoid continuous Reduces image quality after imaging.

In order to provide a clear full-color image, it is preferable to use four developing devices corresponding to magenta, cyan, yellow and black, and black development is finally completed.

An image forming apparatus suitable for carrying out the full-color image forming method of the present invention will be described with reference to FIG. 3 .

The color electrophotographic apparatus shown in FIG. 3 is roughly divided into a transfer material (copy paper)-conveying section I including a transfer drum 315 and a transfer material (copy paper) extending from the right side of the apparatus main assembly 301 (right side in FIG. 3 ) toward the center, near The transfer drum 315 configures the latent image forming section II, and the developing device III (ie, a rotary developing device).

The transfer material-conveying section 1 is constituted as follows: On the right side wall of the apparatus main assembly 301, an opening is formed, through which the transfer material supply trays 302 and 303 are detachably arranged, and a part protrudes from this opening. components. Paper (transfer material)-feed rollers 304 and 305 are arranged directly above the trays 302 and 303 . Connected to the paper supply rollers 304 and 305, the transfer drum 315 is arranged on the left so that it can rotate in the direction of arrow A, and the paper supply roller 306, paper supply guide 307 and paper supply guide 308 are arranged. Adjacent to the outer periphery of the transfer drum 315, an abutting roller 309, a glipper 310, a transfer material separation charger 311, and a separation claw 312 are arranged in the order of rotation from upstream to downstream.

In the transfer drum 315, a transfer charger 313 and a transfer material separation charger 314 are installed. The portion of the transfer drum 315 that is surrounded by the transfer material provides an attached transfer sheet (not shown) to which the transfer material is attached due to static electricity. On the upper right of the transfer drum 315 , a conveyor belt 316 is attached close to the separation claw 312 , and a fixing device 318 is arranged at the end (right side) of the conveyor belt 316 in the transfer direction. Downstream of the fixing device, a take-out tray 317 is mounted, which partially extends and detachably protrudes from the main assembly 301 .

The latent image forming portion II is constituted such that a photosensitive drum such as an OPC photosensitive drum is provided with its peripheral surface in contact with the peripheral surface of the transfer drum 315 as a latent image display member rotatable in the direction shown in the figure. A discharge charger 320 is provided above the adjacent photosensitive drum 319 , and a cleaner 321 and a main charger 323 are provided from upstream to downstream in the direction of rotation of the photosensitive drum 319 . In addition, an image exposure device including a reflection device 325 such as a laser 324 and a mirror is configured for forming an electrostatic latent image on the outer peripheral surface of the photosensitive drum 319 .

The rotary developing device III is constructed in such a way that a rotatable chamber (hereinafter referred to as a rotary member) 326 is provided at a position opposite to the photosensitive drum 319 . In the rotary member 326 , a four-color type developing device is arranged radially quartered to visualize (ie, develop) the electrostatic latent image formed on the outer peripheral surface of the photosensitive drum 319 . The four-color type developing devices include a yellow developing device 327Y, a magenta developing device 327M, a cyan developing device 327C, and a black developing device 327BK.

The entire operation steps of the image forming apparatus described above will be described in the full-color image mode. When the photosensitive drum 319 is rotated in the arrow direction, the drum 319 is charged by the main charger 323 . In the apparatus shown in FIG. 3, the peripheral moving speed (hereinafter referred to as "process speed") of the respective components, especially the photosensitive drum 319, may be at least 100 mm/sec (eg, 130-250 mm/sec). After the photosensitive drum 319 is charged by the main charger 323, the photosensitive drum 329 is imagewise exposed with laser light modulated by the yellow image signal from the original 328 to form a corresponding latent image on the photosensitive drum, and then, the latent image is captured by the rotating element A yellow developing device 327Y rotatably positioned at 326 is shown, forming a yellow toner image.

The transfer material (such as plain paper) sent in through the paper supply guide 307, the paper supply roller 306 and the paper supply roller 308 is picked up by the glipper 310 at regular intervals, and is transferred by means of the counter roller 309 and the counter roller 309 opposite to the counter roller 309. Electrodes surround the transfer drum 315 . The transfer drum 315 rotates synchronously with the photosensitive drum 319 in the direction of arrow A, and the yellow toner image formed by the yellow developing device is relatively low on the peripheral surfaces of the photosensitive drum 319 and the transfer drum 315 due to the action of the transfer charger 313 The position is transferred to the transfer material. The transfer drum 315 further rotates ready to transfer the next color (magenta in the case of FIG. 3 ).

On the other hand, the photosensitive drum 319 is decharged by the discharge charger 320, cleaned by the cleaning blade or cleaning device 321, charged by the main charger 323, and then exposed based on the next magenta image signal, thereby forming a corresponding When an electrostatic latent image is formed on the photosensitive drum 319 by exposure based on a magenta signal, the rotary member 326 rotates to position the magenta developing device 327M at a prescribed developing position, so that the magenta toner is developed. Next, the above process is repeated for cyan and black respectively, completing the transfer of four-color toner images. Thereafter, the developed images of the four colors on the transfer material are discharged by the chargers 322 and 314 (removal of charge), released from the adsorption state by the glipper 310, separated from the transfer drum by the separation claw 312, and then passed through the conveyor belt 316. It is sent to the fixing unit 318, where the toner images of the four colors are fixed under heat and pressure. Thus, a series of full-color printing or imaging steps are performed to provide a defined full-color image on one side of the transfer material.

Alternatively, toner images of corresponding colors may be transferred onto one intermediate transfer member at one time, and then transferred onto a transfer material to be fixed.

The fixing speed (eg, 90 mm/sec) of the fixing device is slower than the peripheral speed (eg, 160 mm/sec) of the photosensitive drum. This is to provide enough heat to fuse the unfixed two to four toner layer images. Therefore, by performing fixing at a slower speed than developing, increased heat can be provided to the toner image.

Now, measurement methods of various properties used here are described.

1) Magnetic carrier particle size

At least 300 particles (0.1 μm or larger in diameter) were randomly selected from the sample carrier, observed through an optical microscope with a magnification of 100-5000, and measured by an image analyzer (such as "Luzex3," purchased from Nireco K.K.) The horizontal FERE diameter of the particles is taken as the particle size, thus obtaining the number-based particle size distribution and the number-average particle size, from which the number-based particle fraction in the size range up to half the number-average particle size is calculated.

2) Magnetic properties of the magnetic carrier:

Measured by using an alternating magnetic field type magnetic automatic recording apparatus ("BHV-30", available from Riken Denshi). The magnetic carrier was placed in an external magnetic field of 10 kOe, and its saturation magnetization was measured in this state. In particular, the magnetic carrier powder sample is filled densely enough into a cylindrical plastic box with a volume of ^Ca. , divided by the actual filled sample volume to obtain the strength per unit volume (magnetization).

3) Determination of the resistivity of the magnetic carrier

Carrier resistivity is measured with the equipment (chamber) E as shown in Figure 2, and this equipment is equipped with lower electrode 21, upper electrode 22, insulator 23, ammeter/24, voltmeter 25, stabilized voltage power supply 26 and guide ring 28. For the measurement, Ca. 1 g of the carrier sample 27 was placed in the chamber E, and the electrodes 21 and 22 were brought into contact with it and a voltage was applied therebetween. The current flowing at this time was measured, and the resistivity was calculated. Since the magnetic carrier is in powder form, care should be taken to avoid changes in resistivity due to changes in filling state. The resistivity described here is measured under such conditions: the contact area between the carrier 27 and the electrode 21 or 22 = ca. 2.3 cm ² , the thickness of the carrier = ca. Applied voltage = 100 volts.

4. Particle size of magnetic iron compounds and non-magnetic metal oxides:

The sample metal oxide powder was photographed by a transmission electron microscope ("H-800", available from Hitachi Seisaknsho K.K.) at a magnification of 5,000-20,000 times. At least 300 particles (diameter 0.01 μm or larger) were randomly selected from the photographs and analyzed with an image analyzer ("Luzes 3" available from Nireco) to measure the horizontal FERE diameter of each particle. The number average particle diameter is calculated from the measured value of at least 300 sample particles. 5. There is a ratio between magnetic iron compounds and non-magnetic metal oxides:

The existence ratio between the magnetic iron compound and the nonmagnetic metal oxide inside the magnetic carrier particle and on the surface of the magnetic carrier particle or the core particle can be determined as follows.

Carrier slicing can be prepared by dispersing carrier particles or carrier core particles into epoxy resin, curing and fixing, and cutting the carrier sample embedded in the resin with a slicing knife (such as "FC4E", available from REICHER-JUNG) sample.

Particle sections were randomly selected, observed and photographed at a magnification of 5,000-20,000 by a scanning electron microscope ("S800", available from Hitachi Seisakushok.k), and photographed using an image analyzer ("Lnzex 3", available from Nireco KK). Obtained) Analyze the photographed particle slices and determine the horizontal FERE diameter D of each dispersed particle cross-section. Assuming that the magnetic iron compound particles and the nonmagnetic metal oxide particles are spherical, the volume of each dispersed particle is calculated as πD3/6. In each particle slice, the internal area is defined as the area from the center to the radius × 0.3, and the surface area is defined as the area from the radius × 0.95 to the radius × 1.0. For each support (core) particle, the total volume per unit area (μm ² ) of the magnetic iron compound particles and nonmagnetic metal oxide particles present in the inner region of the particle slice concerned is calculated and expressed separately by pa1 and pa2 indicate that the total volume per unit area (μm ² ) of the magnetic iron compound particles and nonmagnetic metal oxide particles appearing in the surface area is also calculated, and the values pa1, pb1, pa2 and pb2 is an average value corresponding to 20 carrier (core) particles to calculate the ratios pa1/pb1 and pa2/pb2.

6), resistivity of magnetic iron compounds and nonmagnetic metal oxides

The measurement is performed similarly to the measurement of the carrier resistivity mentioned above. The sample compound or metal oxide is placed between the electrodes 21 and 22 in the chamber shown in Fig. 2 and is in uniform contact with it. In this state, a voltage is applied between the two electrodes, and the current passing therebetween is measured to calculate the resistivity. In order to ensure uniform contact between the sample and the electrode, the lower electrode 21 is reciprocally rotated when filling the sample. The values described here are based on the measured values under the following conditions, the contact area between the filled metal oxide and the electrode S = ca. 2.3 cm ² , the sample thickness d = ca. 2 mm, and the weight of the upper electrode 22 = 180 g , the applied voltage = 100 volts.

7), the particle size of the toner

To 100-150 ml of electrolyte solution (1%-NaCl aqueous solution), 0.1-5 ml of surfactant (alkylbenzene sulfonate) and 2-20 mg of sample toner were added. The sample suspended in the electrolyte liquid is dispersed and treated for 1-3 minutes, then, the sample liquid is sent to a Coultor counter ("Multisizer" available from Coulter electronics Inc, commercially available) with an aperture size of, for example, 17 μm or 100 μm, and the result is obtained in 2 - Volume-based particle size distribution in the range of 40 µm, from which the number-based particle size distribution, number average particle size (D ₁ ) and weight average particle size (D ₄ ) are calculated with a personal computer.

8. Triboelectric charge

The toner and magnetic carrier were weighed to obtain a mixture containing 5% by weight of the toner, which was mixed with a Turbula mixer for 60 seconds. The obtained powder mixture (developer) is placed in a metal container equipped with a 500-mesh conductive sieve at the bottom, and the suction fan is started to suck under a suction pressure of 250mmHg, so that the toner in the developer is selectively removed through the sieve. According to the weight difference before and after suction and the voltage obtained in the capacitor connected to the container, the triboelectric charge Q of the toner is calculated according to the following equation:

Q(μC/g)＝(C×V)/(W ₁ -W ₂ )

Where _W1 is the weight before suction, _W2 is the weight after suction, C is the capacitance of the capacitor, and V is the potential reading of the capacitor.

The present invention will be described below based on examples, and the "parts" used refer to "parts by weight" of the components.

Example 1

Phenol 10 parts

Formalin 6 parts

(Containing ca 40wt% formaldehyde, ca 10wt% methanol, the rest is water)

Magnetite 31 parts

(Magnetic iron compound, d _av (average particle size) = 0.24 μm, Rs (resistivity) = 5 ×

10 ⁵ ohm.cm) α-Fe ₂ O ₃ (hematite) 53 parts

(non-magnetic metal oxide, dav=0.6μm, Rs=8×10 ⁹ ohm.cm)

The above materials, 4 parts of 28wt% ammonia water (basic catalyst) and 15 parts of water were put into a flask, mixed under stirring, and heated to 85°C within 40 minutes, stored at this temperature for 3 hours for curing reaction . The contents were cooled to 30°C, 100 parts of water were added, the supernatant was removed, the precipitate was washed with water and dried in air. The dried precipitate is further dried at 50-60° C. and under a reduced pressure of up to 5 mmHg to obtain spherical magnetic carrier core particles containing magnetite and hematite in a phenolic resin binder, and the Rs of the carrier core particles is 8.0 ×10 ¹² ohm.cm.

The magnetic carrier core particles are surface-coated with a thermosetting silicone resin in the following manner. To obtain a resin coating rate of 1.0 wt%, a toluene solution containing 10 wt% of the carrier coating resin was prepared. To this solution are added carrier core particles, and the resulting mixture is heated under shear to evaporate the solvent to provide a coating layer on the carrier core. The resulting coated magnetic carrier particles were cured at 250°C for 1 hour. Then deagglomerated and passed through a 100-mesh sieve to obtain coated magnetic carrier particles with a number-average particle diameter (D ₁ ) of 43 μm and a sphericity (SF1) of 1.04.

The resistivity Rs of the coated magnetic carrier was 9×10 ¹³ ohm.cm, and the saturation magnetization σ _s was 28 emu/g.

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

On the other hand, the toner was prepared as follows.

yellow toner

Polyester resin 100 parts

(condensation product of bisphenol and formic acid)

C.I. Pigment Yellow (colorant) 4.5 parts

4 parts of Cr complex salt of di-tert-butyl salicylic acid

(negative charge control agent, light color)

These materials are fully blended in advance, melt-kneaded, cooled and preliminarily broken into particles with a particle size of ca.1-2mm by a hammer mill. Then the product is pulverized with an air-jet type pulverizer, and the powder is classified with an Ellow Jet classifier to recover a negatively charged yellow powder (non-magnetic yellow toner).

100 parts by weight of the above yellow toner and 0.8 parts by weight of hydrophobized titanium oxide fine powder were mixed with each other in a Henschel mixer to obtain a yellow toner with externally added titanium oxide fine powder. The yellow toner had a weight average particle diameter (D ₄ ) of 8.6 μm, a number average particle diameter (D ₁ ) of 6.5 μm, and a (D ₄ /D ₁ ) ratio of 1.32. The toner had a triboelectric charge (TC) of -27.1 µC/g (toner concentration of 5% by weight) when measured with the previously prepared coated magnetic carrier.

magenta toner

Polyester resin 100 parts

(same as yellow toner)

C.I. Dye Red 122 4 parts

C.I.Basic Red 12 1 serving

Di-tert-butyl salicylic acid Cr complex salt 4 parts

Negatively chargeable magenta powder (non-magnetic magenta toner) was prepared using the above materials in the same manner as yellow toner.

100 parts by weight of the above magenta toner and 8.0 parts by weight of hydrophobized fine titanium oxide powder were mixed with each other in a Henschel mixer to obtain a magenta toner with externally added fine titanium oxide powder. D ₄ =8.4 μm, D ₁ =6.5 μm, and D ₄ /D ₁ =1.29 of the magenta toner. The toner had a triboelectric charge (TC) of -25.3 µC/g when measured with the previously prepared coated magnetic carrier.

cyan toner

Polyester resin 100 parts

(same as yellow toner)

Copper-phthalocyanine dye 5 parts

Di-tert-butyl salicylic acid Cr-complex salt 4 parts

A negatively chargeable cyan powder (non-magnetic cyan toner) was prepared using the above materials in the same manner as the yellow toner.

100 parts of the above cyan toner and 0.8 parts of hydrophobized titanium oxide fine powder were mixed with each other in a Henschel mixer to obtain a cyan toner with externally added titanium oxide fine powder. The cyan toner D ₄ =8.6 μm, D ₁ =6.4 μm, D ₄ /D ₁ =1.34, when measured together with the previously prepared coated magnetic carrier, the triboelectric charge (TC) of the toner is -27.8 μC/g.

black toner

Polyester resin 100 parts

(same as yellow toner)

carbon black 5 parts

(Most particle size = 60nm)

Di-tert-butyl-salicylic acid Cr-complex salt 4 parts

Negatively chargeable black powder (non-magnetic black toner) was prepared in the same manner as the yellow toner.

100 wt. parts of the above black toner, and 0.8 wt. part of hydrophobized titanium oxide fine powder were mixed with each other in a Henschel mixer to obtain a black toner with externally added titanium oxide fine powder. The black toner has D ₄ =8.4 μm, D ₁ =6.5 μm, and D ₄ /D ₁ =−1.29. The toner had a triboelectric charge (TC) of -26.3 µC/g when measured with the previously prepared coated magnetic carrier.

The above-prepared coated magnetic carrier and the above-prepared toners of each color were mixed to prepare two-component type developers, each having a toner concentration of 8.0 wt.%. The two-component type developer was loaded into modified full-color laser copiers ("CLC-500", manufactured by Canon K, K) each having a developing device as shown in FIG. 1 . Referring to Fig. 1, each developing device is designed in such a way that the gap A between the developer carrying member (developing sleeve) 1 and the developer regulating member (magnetic blade) 2 is 600 μm, and the developing sleeve and the electrostatic latent image display The gap B between the elements (photosensitive drums) 3 was 500 μm. The development gap c at this time was 5 mm. The developing sleeve 1 and photosensitive drum 3 were driven at a peripheral speed ratio of 1.75:1. The s1 of the developing sleeve is designed to provide a 1 kOe magnetic field, the developing conditions include a rectangular wave oscillating electric field with a peak-to-peak voltage of 2000 volts, a frequency of 2000 Hz, a developing bias of -470 volts, and toning The agent developing back voltage (Vcont) was 325 wdy, the blur image removing voltage (Vback) was 100 volts, and the main charging voltage on the photosensitive drum was -750 volts. The digital latent image on the photosensitive drum 3 under this developing condition is displayed by the reverse developing mode.

As a result, the resulting image exhibits a high solid image density (as typified by that measured in the cyan toner image portion) without thickened dots, image distortion or in-image or non-image areas. The image is blurred.

Continuous full-color imaging on 30,000 sheets. Thereafter, image detection is performed with a method similar to the first step. Solid images of cyan toner exhibited high density, and halftones exhibited good reproducibility. In addition, image blurring and carrier attachment were not found. After the continuous imaging, the cyan developer was observed by SEM (scanning electron microscope), no peeling phenomenon of the coating resin on the carrier was observed, and a good surface state similar to the original coated magnetic carrier surface was seen.

The results are shown in Table 2 below.

Example 2

Phenol 10 parts

Formalin (same as Example 1) 6 parts

Magnetite (same as embodiment 1) 44 parts

α-Fe ₂ O ₃ (same as embodiment 1) 44 parts

The above materials were polymerized in a manner similar to Example 1 except that the amounts of basic catalyst and water were varied. The aggregated particles are classified to obtain dispersed magnetic powder carrier cores. The resistivity (Rs) of the obtained carrier core was 5.2×10 ¹² ohm.cm.

The core particles were coated in the same manner as in Example 1 with a coating resin mixture of styrene-acrylic resin/fluorine-containing resin of 7/3 at a coating ratio of 1.0 wt%.

The coated magnetic carrier particles had D ₁ =55 μm and a sphericity (SF1) of 1.06.

Rs = 8.0 x 10 ¹³ ohm.cm, σ _s = 39 emu/g for the coated carrier particles.

The coated magnetic carrier thus obtained and the four toners prepared in Example 1 were blended to prepare four two-component type developers each having a toner concentration of 7 wt.%. When measured at a toner concentration of 5 wt.%, the triboelectric charges of each toner were yellow: -30.2 μC/g, magenta: -28.7 μC/g, cyan: -32.9 μC/g, and Black: -29.8 μC/g.

The developer was loaded into the same image forming apparatus as in Example 1, and used for development under the same developing conditions. As a result, similar to Example 1, the image formed for the first time showed excellent reproducibility of dots and fine lines and high resolution, and no carrier was attached. The results of continuous full-color imaging on 30,000 sheets showed images very similar to the quality of the first image. No carrier attachment was observed in the sequential imaging, and the surface of the carrier after the serial imaging was as good as the first time.

Example 3

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

first step

Phenol 8 parts

Formalin (same as implementation 1) 4.8 parts

Magnetite (same as embodiment 1) 75 parts

second step

Phenol 2 parts

Formalin (same as implementation 1) 1.2 parts

α-Fe ₂ O ₃ (same as Example 1) 9 parts

Except changing the consumption of basic catalyst and water, carry out the first step polymerization similarly to embodiment 1, inject the above-mentioned material that is used in the second step into the obtained slurry and carry out similar suspension polymerization reaction, obtain polymer particle. The polymer particles are classified to obtain magnetic powder-dispersed resin carrier core particles. These core particles showed Rs = 7.4 x 10 ¹² ohm.cm. Observed by scanning electron microscope, the cross-section of the core particles is shown in Figure 4, magnetite particles exist in the interior, and larger α-Fe ₂ O ₃ particles exist on the surface. The existence ratio of magnetic iron compound/nonmagnetic metal oxide in the core particle pb1/pa1=0, pb2/pa2=19.3.

The core particles were coated with the same coating resin as in Example 1, but with a different coating rate of 1.3 wt.%.

D ₁ of the coated magnetic carrier particles was 40 µm, and the sphericity (SF1) was 1.11.

Rs = 3.5 x 10 ¹³ ohm.cm, σ _s = 68 emu/g for the coated carrier particles.

The coated magnetic carrier thus obtained was blended with the four color toners prepared in Example 1 to prepare four two-component type developers each having a toner concentration of 8 wt.%. The triboelectric charge of each toner was yellow: -25.1 µC/g, magenta: -24.3 µC/g, cyan: -27.7 µC/g, black: -23.0 µC/g.

The developer was loaded into the same image forming apparatus, and developed under the same developing conditions as in Example 1 except that the gap A between the developing sleeve 1 and the magnetic blade was changed to 800 μm. As a result, similar to Example 1, the resulting image exhibited excellent reproducibility of dots and thin lines and high resolution, and was free from carrier attachment. The results of continuous full-color imaging on 30,000 sheets showed images very similar to the quality of the first image. No carrier attachment was observed in the sequential imaging, and the surface of the carrier after the serial imaging was as good as the first time.

Example 4

Phenol 6.5 parts

Formalin (same as Example 1) 3.5 parts

Magnetite (same as embodiment 1) 81 parts

Al ₂ O ₃ (same as embodiment 1) 9 parts

(dav=0.63μm, Rs=5×10 ¹³ ohm.cm)

The above material was polymerized in a manner similar to Example 1. The polymerized particles are classified to obtain a magnetic powder-dispersed resin carrier core. The Rs of the obtained carrier core was 4.2×10 ¹¹ ohm.cm.

The core particles were coated with the same coating resin as in Example 1, but with a different coating rate of 2.0 wt.%.

D ₁ of the coated magnetic carrier particles was 24 µm, and the sphericity (SF1) was 1.09.

Rs=7.2×10 ¹³ ohm.cm, σ _s =73 emu/g of the coated carrier particles.

On the other hand, a toner was prepared with the following components.

cyan toner

Polyester resin (same as embodiment 1) 100 parts

Copper-phthalocyanine pigment 6 parts

Di-tert-butyl salicylic acid Cr-complex salt 5 parts

Except changing the crushing and classifying conditions, prepare negatively charged cyan powder (cyan toner) in the manner of Example 1, and 100 parts of cyan toner and 1.5 wt. Titanium oxide fine powders are blended with each other to obtain a cyan toner with externally added titanium oxide fine powders, D ₄ =5.1 μm, D ₁ =4.0 μm of the cyan toner, D ₄ /D ₁ =1.27, when When measured together with the coated magnetic carrier prepared above, its triboelectric charge (TC) was -46.2 µC/g.

The cyan toner was blended with the coated magnetic carrier at a toner concentration of 8 wt.%, and under the same developing conditions as in Example 1, single-color mode imaging was performed in the same developing device. As a result, good images were obtained both at the first time and after continuous imaging on 30,000 sheets according to Example 1. The state of the carrier surface after continuous imaging is similar to that of the first time.

Example 5

The magnetic carrier prepared in Example 1 was used as an uncoated magnetic carrier, and was blended with the four toners prepared in Example 1 to prepare four developers, each with a toner concentration of 8 wt%. The triboelectric charges of the four toners were yellow: -38.4 μC/g, magenta: -35.7 μC/g, cyan: -39.4 μC/g, and black: -36.6 μC/g.

Four kinds of developers were put into the same imaging device, developed under the same developing conditions as in Example 1, the result was similar to Example 1, the first imaging had high resolution, no carrier was attached, on 30,000 sheets of paper After continuous imaging, the images have the quality similar to the first imaging, and there is no carrier attached in the continuous imaging.

Example 6

Phenol 6.5 parts

Formalin (same as Example 1) 3.5 parts

Magnetite (same as embodiment 1) 54 parts

TiO ₂ 36 parts

(d _av =0.24μm, Rs=3×10 ⁴ ohm.cm)

The above materials are polymerized similarly to Example 1, and the polymerized particles are classified to form dispersed magnetic powder resin carrier cores. Rs of the obtained carrier core was 2.8×10 ¹³ ohm.cm.

Similar to Example 1, the core particles were coated with a copolymer of styrene/(2-ethylhexyl)methacrylate (50/50), resulting in a coating rate of 1.2 wt%.

The coated magnetic carrier particles D ₁ = 45 µm, sphericity (SF1) 1.05.

Coated carrier particles Rs=9.8×10 ¹³ ohm.cm, σs=48 emu/cm ³ .

The coated magnetic carrier thus obtained was blended with the cyan toner of Example 1 to obtain a developer, and the triboelectric charge of the toner was -27.2 µC/g.

The developer was loaded into the same image forming apparatus, and under the developing conditions as in Example 1, a single-color mode development was performed. Good image quality was obtained similarly to the examples after the first imaging and after continuous imaging on 30,000 sheets. Good performance in preventing carrier attachment before and after continuous imaging. The carrier surface was as good as after the first imaging after serial imaging.

Comparative Example 1

Weigh Fe ₂ O ₃ , CuO and ZnO to obtain a composition whose contents are 50mol%, 27mol%, and 23mol% respectively, and then mix together with a ball mill. The mixture is sintered at 1000°C and pulverized with a ball mill. 100 parts of the obtained powder, 0.5 Parts of sodium polymethacrylate and water are mixed together in a wet ball mill to form a slurry. The slurry was granulated by spray drying. Then, the particles were sintered at 1200°C to obtain carrier core particles, Rs=4.0×10 ⁸ ohm.cm.

The surface of the support was coated with resin in the same manner as in Example 1. The obtained carrier particle D ₁ =47 μm, Rs =1.1×10 ¹⁰ ohm.cm, sphericity (SF1) =1.24, σ _s =62 emu/g.

The obtained carrier was blended with the cyan 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 into the same image forming apparatus, and the monochrome mode development was carried out under the conditions similar to those of Example 1. As a result, the resulting image has a high solid image density, but has rough dots and poor halftone reproducibility. No image distortion was found in the image portion and non-image portion, but a blurring phenomenon of the toner image was observed due to the carrier attachment. Also, fusion bonding of the toner was observed on the carrier after continuous image formation similar to Example 1. The image formed after the continuous imaging is also accompanied by further thickening of the mid-tone portion and further image blurring.

Comparative Example 2

Phenol 10 parts

Formalin (same as Example 1) 6 parts

Magnetite 31 parts

(d _av =0.61μm, Rs=5×10 ⁵ ohm.cm)

α-Fe ₂ O ₃ 53 parts

(d _av = 0.6 μm, Rs = 8×10 ⁹ ohm.cm)

Polymerization was carried out in a manner similar to Example 1 using the above materials except changing the amount of basic catalyst and water. The obtained polymer particles were classified to obtain a resin carrier core in which magnetic material was dispersed, and Rs of the obtained carrier core was 5.9×10 ⁸ ohm.cm.

The core particles were coated as in Example 1.

D ₁ of the obtained magnetic carrier particles was 45 μm, and the sphericity (SF1) was 1.07.

Rs=1.0×10 ¹¹ ohm.cm, σ _s =29 emu/g of the obtained carrier particles.

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

The developer was placed in the same image forming apparatus, and developed under the developing conditions similar to those of the examples. On the first half-tone image there is thickening and carrier adhesion can be seen.

Comparative Example 3

Phenol 6.5 parts

Formalin (same as Example 1) 3.5 parts

Magnetite (same as embodiment 1) 45 parts

α-Fe ₂ O ₃ 45 parts

(d _av =0.61μm, Rs=5×10 ⁵ ohm.cm)

Aggregated particles were obtained from the above materials as in Example 1, and classified to obtain resin carrier cores dispersed with magnetic materials. Rs of the obtained support was 7.5×10 ⁷ ohm.cm.

The core particles were coated as in Example 1.

The coated magnetic carrier particles D ₁ =45 μm, sphericity (SF1 )=1.06.

The coated carrier particles Rs = 2.2 x 10 ¹⁰ ohm, σ _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 is put into the same image forming equipment and developed under the developing conditions of Example 3. Carrier adhesion prevention performance was good, but halftone images were distorted in dot shape and thickened.

Comparative Example 4

The carrier was the same coated carrier as in Example 1, and a cyan toner was prepared in the same manner and composition as in Example 1, except that the pulverization and classification conditions were different.

Similar to Example 1, the toner incorporates 0.5% by weight of externally added titanium oxide. The resulting cyan toner had D ₄ =12.6 µm, D ₁ =8.3 µm, and D ₄ /D ₁ =1.52. The triboelectric charge was -20.1 µC/g when measured together with the above-prepared magnetic carrier at a toner concentration of 5 wt%. A cyan toner was blended with the above-mentioned coated magnetic carrier to prepare a developer.

The developer was put into the same image forming equipment and developed under the same developing conditions as in Example 1. The result is high image density, but the halftone image exhibits poor dot reproducibility with thickening.

Example 7

100 parts of the carrier core prepared in Example 1 were mixed with 2 parts of thermosetting phenolic resin and 6 parts of α-Fe ₂ O ₃ (same as Example 1) with a concentration of 10% in toluene. The solvent is evaporated under shear for coating. Also at 160°C, the resin was cured under application of shear force to form coated magnetic carrier particles. The coated carrier particles are deagglomerated and classified. The resulting coated magnetic carrier D ₁ = 45 μm, SF1 = 1.06, Rs = 1.0×10 ¹³ ohm.cm, the ratio of magnetic iron compound/nonmagnetic metal oxide pb1/pa1 = 0, 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 type developers each having a toner concentration of 8.0% by weight. The triboelectric charges of the toners were yellow: -25.5 μC/g, magenta: -25.1 μC/g, cyan: -25.9 μC/g, and black -24.3 μC/g.

The developer is put into the same imaging device and developed under the same developing conditions. Images with excellent halftone reproducibility and high image density are obtained. In particular, the triboelectric charge of the toner is stable in continuous image formation.

Example 8

In a similar manner to Example 1, the coated magnetic carrier prepared in Example 7 was further coated with the same silicone resin as in Example 1. The resulting coated magnetic carrier D ₁ = 45 μm, SF1 = 1.05, Rs = 9.8×10 ¹³ ohm.cm, and the ratio of magnetic iron compound/nonmagnetic metal oxide pb1/pa1=0.pb2/pa2=29.3.

The coated magnetic carrier thus obtained was blended with the four-color toner prepared in Example 1 to prepare four kinds of two-component type developers. The toner concentration thereof was 8.0 wt%, and the triboelectric charges thereof were yellow: -23.0 µC/g, magenta: -22.5 µC/g, cyan: -24.4 µC/g, and black: -23.2 µC/g.

The developer is placed in the same imaging device and developed under the same developing conditions. Images with excellent halftone reproducibility and high image density are obtained. The developer exhibits a particularly wide range of Vback against blurring and carrier attachment, and excellent stability.

Example 9

Magnetic carrier cores were obtained by two-step polymerization with the following materials:

first step

Phenol 7.5 parts

Formalin (same as Example 1) 4.5 parts

Magnetite (with embodiment 1) 70 parts

second step

Phenol 2.5 parts

Formalin (same as Example 1) 1.5 parts

Magnetite (same as embodiment 1) 5 parts

α-Fe ₂ O ₃ (same as Example 1) 9 parts

Similar to Example 3, core particles were obtained, Rs=3.3×10 ¹² ohm.cm, the ratio of magnetic iron compound/nonmagnetic metal oxide pb1/pa1=0, pb2/pa2=4.58.

The core particles were coated as in Example 1.

The coated magnetic carrier particle D ₁ =40 μm, the sphericity (SF1) was 1.10.

Coated carrier particles Rs = 3.2 x 10 ¹³ ohm.cm, σ _s = 67 emu/g.

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

The developer was put into the same image forming device and developed under the same developing conditions as in Example 1. As a result, similar to Example 1, an image with excellent halftone reproducibility and high image density was obtained. Also, there is no distortion due to carrier attachment in the image portion and non-image portion, and there is no image blur of the toner. As a result of 30,000 consecutive full-color image formations, the resulting image was free from toner scatter, had high image density of solid portions, and good reproducibility of halftones and line images. Carrier attachment was not observed in serial imaging. When the cyan developer was observed by SEM after continuous imaging, peeling of the coating layer was not observed, and the surface state was as good as that of the carrier at the first time.

Example 10

The polymeric particles prepared in Example 9 were further coated with polymerization of the following components.

Phenol 2 parts

Formalin (same as Example 1) 1.2 parts

α-Fe ₂ O ₃ (same as Example 1) 10 parts

Suspension polymerization was performed in the same manner as in Example 3 to obtain spherical carrier cores. The core magnetism of the obtained carrier was 9.3×10 ¹² ohm.cm, and the ratio of magnetic iron compound/nonmagnetic metal oxide was pb1/pa1=0, pb2/pa2=32.3.

The core particles were coated with the coating resin of Example 2, but with a different coating rate of 1.0 wt%.

The coated magnetic carrier particle D ₁ =42 μm, and the sphericity (SF1) was 1.11.

Coated carrier particles Rs = 1.1 x 10 ¹⁴ ohm.cm, σ _s = 60 emu/g.

The coated magnetic carrier thus obtained was blended with the four color toners prepared in Example 1 to prepare four two-component type developers with a toner concentration of 8% by weight. The triboelectric charges of the toners were yellow: -32 μC/g, magenta: -29.9 μC/g, cyan: -32.4 μC/g, and black: -30.3 μC/g.

The developer was put into the same image forming equipment and developed under the same developing conditions as in Example 1. Similar to Example 1, the image obtained at one time showed particularly good reproducibility and high resolution of dots and thin lines. At the same time, no toner scattering, image blurring or carrier adhesion was found. As a result of sequential full-color imaging on 30,000 sheets, subsequent image quality was very similar to that of the first image. No toner scattering, image blurring or carrier adhesion was found in continuous image formation. The carrier surface after successive imaging was as good as the first imaging.

The above-mentioned characteristic properties of the carrier are summarized in Table 1, the evaluation results are summarized in Table 2, and the evaluation criteria are listed after Table 2.

Table 1 core carrier magnetic iron compound non-magnetic metal oxide r _a /r _b Adhesive* dosage (wt.%) Rs(ohm.cm) Rs(ohm.cm) σ _s (emu/g) D1(μm) d _B ^** (g/cm ³ ) r _a (D ₁ )(μm) Amount (wt.%) r _b (D ₁ )(μm) Amount (wt.%) Example 123456 Comparative Implementation 1 Example 23 Example 78910 Magnetite 0.24″ 0.24″ 0.24″ 0.24″ 0.24″ 0.24CuZn Ferrite Magnetite 0.61″ 0.24″ 0.24″ 0.24″ 0.24″ 0.24 314475813154100314531317566.2 a-Fe ₂ O ₃ 0.6″ 0.4″ 0.6 Aluminum oxide 0.63α-Fe ₂ O ₃ 0.6TiO ₂ 0.7-α-Fe ₂ O ₃ 0.4 Magnetite 0.61α-Fe ₂ O ₃ 0.6″ 0.6″ 0.6″ 0.6 5344995336-53455353916.8 2.51.72.52.62.52.9-0.662.52.52.52.52.5 161616101610-161016161617 8.0×10 ¹² 5.2×10 ¹² 7.4×10 ¹² 4.2×10 ¹¹ 8.0×10 ¹² 2.8×10 ¹³ 4.0×10 ⁸ 5.9×10 ⁸ 7.5×10 ⁸ 8.0×10 ¹² 8.0×10 ¹² 3.3×10 ¹² 9.3× 10 ¹² 9.0× ^{10 13 8.0} ×10 13 3.5×10 ¹³ 7.2×10 ^{13 8.0} ×10 ¹² 9.8×10 ^{13 1.1} ×10 ¹⁰ 1.0×10 ¹¹ 2.2×10 10 1.0× ^{10 13} 9.8×10 ¹³ 3.2×10 ¹³ 1.1× 10 ¹⁴ 28396871284862297326256760 43554024434547454545454042 1.851.881.861.91.851.912.351.851.841.891.871.871.92 *. Unless otherwise stated, the binder is phenolic resin. *.d _B means bulk density.

Table 2 Example or Comparative Example Clearance C(mm) Solid Cyan ID Midtones thicken carrier attachment image blur Example 123456 Comparative Example 1234 Example 78910 556.5655.56.555.55556.56.5 1.631.611.691.681.591.621.581.551.61.711.611.651.651.66 ◎◎◎◎○◎xΔxΔxΔx◎◎◎6 ○○◎○○○○x○○○○◎◎ ◎◎○◎○◎x○Δ○○◎○◎ ◎: Excellent, ○: Good, Δ: Medium, Δx: Slightly poor, x: Poor

[Notes to Table 2] Solid cyan I.D The image density of the solid cyan image portion as measured with a Macbeth densitometer ("RD-918 type" using an SPI filter, manufactured by Macbeth Co., Ltd.), printed on a sheet of plain paper The relative density of the image on. Midtones thicken

Estimate by eye the degree of thickening of half-tone image portions with reference to the original image and a standard sample.

carrier attachment

After forming a solid white image, put the transparent adhesive tape in a 5cm×5cm area between the developing area and the cleaning area of the photosensitive drum, recover the magnetic carrier particles attached to the photosensitive drum, and count the particles attached to the 5cm×5cm area. The number of carrier particles, based on the calculated number of particles attached to the carrier per ^cm2 , is then evaluated according to the following criteria:

◎(excellent): less than 10 grains/cm ²

○ (good): 10—less than 20 grains/cm ²

Δ(medium): 20—less than 50 grains/cm ²

ΔX: (slightly worse) 50—less than 100 grains/cm ²

X (poor): 100 grains/ ^cm2 or more

Image blur rate

Before printing, the average reflectance Dr (%) of the plain paper was measured with a reflectometer ("REFLECTOMETER MODEL TC-6DS" manufactured by Tokyo Denshoku k.k.). On the other hand, the solid white image is printed on plain paper, and the reflectance Ds (%) of the solid white image is measured with a reflectometer, and the image blur rate (%) is calculated by the following equation: image blur rate (%)=Dr( %)－Ds(%) is evaluated according to the following criteria ◎ (excellent): less than 1.0% ○ (good): 1.0—below 1.5% Δ(medium): 1.5—below 2.0% ΔX: (slightly worse) 2.0— Less than 3.0% X (poor): 3.0% or more.

Claims (40)

1. A two-component type developer for developing electrostatic images, comprising at least one toner and a magnetic carrier; wherein

Weight average particle diameter D of toner₄A maximum of 10 μm, number-average particle diameter D₁Satisfies D₄/D₁≤1.5；

The magnetic carrier comprises composite particles containing magnetic iron compound particles, non-magnetic metal oxide particles and a binder containing a phenol resin, the composite particles containing the magnetic iron compound particles and the non-magnetic metal oxide particles in a total proportion of 80 to 99 wt%; magnetic fieldThe number average particle diameter of the iron compound is gamma alpha, the number average particle diameter of the nonmagnetic metal oxide particles is gamma b, and the gamma is satisfied_b/γ_a＞1.0。

2. The developer according to claim 1, wherein the number average particle diameter γ of the magnetic iron compound particles_a0.02 to 5 μm, number average particle diameter gamma of non-magnetic metal oxide particles_b0.05-10 μm.

3. The developer according to claim 1 or 2, wherein the nonmagnetic metal oxide particles are contained in an amount of 5 to 70 wt% based on the total amount of the magnetic iron compound particles and the nonmagnetic metal oxide particles, and the bulk density of the magnetic carrier is 1.0 to 2.0g/cm³。

4. The developer according to claim 1, wherein the surface of the magnetic carrier is coated with a resin containing nonmagnetic metal oxide particles.

5. The developer according to claim 1 or 4, wherein the surface of the magnetic carrier is coated with 0.1 to 10% by weight of the resin.

6. The developer according to claim 1, wherein the magnetic carrier has a saturation magnetization σ_sIs 10-80 emu/g.

7. A developer according to claim 1, wherein the magnetic iron compound comprises magnetite and the non-magnetic metal oxide comprises hematite.

8. The developer according to claim 1, wherein the toner is a non-magnetic toner.

9. The developer according to claim 1, wherein the magnetic carrier contains magnetic iron compound particles and nonmagnetic metal oxide particles distributed such that: the total volume of the magnetic iron compound particles present inside the cross section of the carrier (core) particle is pa1, the total volume of the non-magnetic metal oxide particles is pb1, the total volume of the magnetic iron compound particles present at the surface portion of the cross section of the carrier (core) particle is pa2, and the total volume of the non-magnetic metal oxide particles is pb2, which satisfy pb1/pa1 < 1, and pb2/pa2 > 1, to provide higher resistivity.

10. The developer according to claim 1, wherein the magnetic carrier comprises a carrier core coated with 0.5 to 10% by weight of the coating material.

11. A developer according to claim 10, wherein the magnetic carrier comprises a carrier core coated with 0.6 to 5% by weight of the coating material.

12. The developer according to claim 1, wherein the sphericity of the magnetic carrier is at most 2.

13. A developing method of developing an electrostatic image, comprising:

carrying a two-component type developer with a developer carrying member having magnetic field generating means, said two-component type developer comprising a toner and a magnetic carrier; wherein,

weight average particle diameter D of toner₄A maximum of 10 μm, number-average particle diameter D₁Satisfies D₄/D₁≤1.5；

The magnetic carrier includes composite particles containing magnetic iron compound particles, nonmagnetic metal oxide particles, and a binder containing a phenol resin; the composite particles contain magnetic iron compound particles and non-magnetic metal oxide particles in a total proportion of 80 to 99 wt%; the number average particle diameter of the magnetic iron compound particles is gamma_aThe number average particle diameter of the nonmagnetic metal oxide particles is gamma_bSatisfy gamma_b/γ_a＞1.0。

Forming a magnetic brush of a two-component type developer on the developer carrying member;

contacting the magnetic brush and the latent image bearing member; and

an electrostatic image is developed on the latent image bearing member to form a toner image, while an alternating electric field is applied to the developer carrying member.

14. A process according to claim 13 wherein the electrostatic image comprises a digital image.

15. The developing method according to claim 13 or 14, wherein the electrostatic image is developed by a reversal development mode.

16. The developing method according to claim 13, wherein the number average particle diameter γ of the magnetic iron compound particles_a0.02 to 5 μm, number average particle diameter gamma of non-magnetic metal oxide particles_b0.05-10 μm.

17. The developing method according to claim 13 or 16, wherein the amount of the nonmagnetic metal oxide particles is 5 to 70% by weight based on the total amount of the magnetic iron compound particles and the nonmagnetic metal oxide particles, and the bulk density of the magnetic carrier is 1.0 to 2.0g/cm³。

18. A developing method according to claim 13, wherein the surface of the magnetic carrier is coated with a resin containing nonmagnetic metal oxide particles.

19. A developing method according to claim 13, wherein the surface of the magnetic carrier is coated with 0.1 to 10% by weight of the resin.

20. Developing method according to claim 13, wherein the magnetic carrier has a saturation magnetization σ₃Is 10-80 emu/g.

21. A developing method according to claim 13, wherein the magnetic iron compound comprises magnetite and the non-magnetic metal oxide comprises hematite.

22. The developing method according to claim 13, wherein the toner is a non-magnetic toner.

23. The developing method according to claim 13, wherein the magnetic carrier contains magnetic iron compound particles and non-magnetic metal oxide particles distributed such that the total volume of the magnetic iron compound particles appearing inside the cross section of the carrier (core) particles is pa1, the total volume of the non-magnetic metal oxide particles is pb1, the total volume of the magnetic iron compound particles appearing at the surface portion of the cross section of the carrier (core) particles is pa2, and the total volume of the non-magnetic metal oxide particles is pb2 which satisfy pb1/pa1 < 1 and pb2/pa2 > 1, to provide a higher resistivity.

24. A developing method according to claim 13, wherein the magnetic carrier comprises a carrier core coated with 0.5 to 1.0% by weight of the coating material.

25. A developing method according to claim 24, wherein the magnetic carrier comprises a carrier core coated with 0.6 to 5% by weight of the coating material.

26. A developing method according to claim 13, wherein the sphericity of the magnetic carrier is at most 2.

27. An imaging method, comprising: (I) a developer carrying member enclosed therein with a magnetic field generating device carries a two-component type developer including a magenta toner and a magnetic carrier; wherein

Weight average particle diameter D of magenta toner₄A maximum of 10 μm, number-average particle diameter D₁Satisfies D₄/D₁≤1.5；

The magnetic carrier includes composite particles containing magnetic iron compound particles, nonmagnetic metal oxide particles, and a binder containing a phenol resin; the composite particles contain the magnetic iron compound and the nonmagnetic metal oxide in a total proportion of 80 to 99 wt%;the number average particle diameter of the magnetic iron compound is gamma_aThe number average particle diameter of the nonmagnetic metal oxide particles is gamma_bSatisfy gamma_b/γ_a＞1.0，

A magnetic brush of a two-component type developer is formed on the developer carrying member,

contacting the magnetic brush and the latent image bearing member;

developing the electrostatic image on the latent image bearing member to form a magenta toner image while applying an alternating electric field to the developer carrying member; (II) a two-component type developer carried by a developer carrying member enclosed therein with a magnetic field generating device, said two-component type developer containing a cyan toner and a magnetic carrier; wherein

Weight average particle diameter D of cyan-red toner₄A maximum of 10 μm, number-average particle diameter D₁Satisfies D₄/D₁≤1.5；

The magnetic carrier comprises composite particles comprising particles of a magnetic iron compound, particles of a non-magnetic metal oxide and a binder comprising a phenol resin, the composite particles comprising the magnetic iron compound particles and the non-magnetic metal oxide particles in a total proportion of 80 to 99 wt%; the number average particle diameter of the magnetic iron compound particles is gamma alpha, and the number average particle diameter of the nonmagnetic metal oxide particles is gamma_bSatisfy gamma_b/γa＞1.0，

A magnetic brush of a two-component type developer is formed on the developer carrying member,

contacting the magnetic brush and the latent image bearing member;

developing an electrostatic image on the latent image bearing member to form a cyan toner image while applying an alternating electric field to the developer carrying member; (III) a two-component type developer carried by a developer carrying member enclosed therein with a magnetic field generating device, said two-component type developer containing a yellow toner and a magnetic carrier; wherein

Weight average particle diameter D of yellow toner₄A maximum of 10 μm, number-average particle diameter D₁Satisfies D₄/D₁≤1.5；

The magnetic carrier comprises particles containing magnetic iron compound, non-magnetic metal oxide particles and particles containing phenol formaldehydeComposite particles of a binder of a resin; the composite particles contain the magnetic iron compound and the non-magnetic metal oxide in a total proportion of 80 to 99 wt%; the number average particle diameter of the magnetic iron compound particles is gamma_aThe number average particle diameter of the nonmagnetic metal oxide particles is gamma_bSatisfy gamma_b/γ_a＞1.0，

A magnetic brush of a two-component type developer is formed on the developer carrying member,

the magnetic brush is brought into contact with the latent image bearing member,

developing an electrostatic image on the latent image bearing member to form a yellow tone image while applying an alternating electric field to the developer carrying member; (IV) forming a full-color image with at least the magenta toner image, the cyan toner image, and the yellow toner image formed above.

28. The imaging method of claim 27, wherein the electrostatic image comprises a digital image.

29. The image forming method according to claim 27 or 28, wherein the electrostatic image is developed by a reversal development mode.

30. The imaging method according to claim 27, wherein the number average particle diameter γ of the magnetic iron compound particles_a0.02 to 5 μm, number average particle diameter gamma of non-magnetic metal oxide particles_b0.05-10 μm.

31. An image forming method according to claim 27, wherein the amount of the nonmagnetic metal oxide particles is 5 to 70% by weight based on the total amount of the magnetic iron compound particles and the nonmagnetic metal oxide particles, and the bulk density of the magnetic carrier is 1.0 to 2.0g/cm³。

32. An image forming method according to claim 27, wherein the surface of the magnetic carrier is coated with a resin containing nonmagnetic metal oxide particles.

33. An imaging method according to claim 27, wherein the surface of the magnetic carrier is coated with 0.1 to 10 wt% of the resin.

34. The imaging method according to claim 27, wherein the saturation magnetization σ s of the magnetic carrier is 10-80 emu/g.

35. An imaging method according to claim 27, wherein the magnetic iron compound comprises magnetite and the non-magnetic metal oxide comprises hematite.

36. An image forming method according to claim 27, wherein the toner is a non-magnetic toner.

37. An image forming method according to claim 27, wherein the magnetic magnet contains magnetic iron compound particles and non-magnetic metal oxide particles distributed such that the total volume of the magnetic iron compound particles appearing inside the cross section of the carrier (core) particles is pa1, the total volume of the non-magnetic metal oxide particles is pb1, the total volume of the magnetic iron compound particles appearing at the surface portion of the cross section of the carrier (core) particles is pa2, and the total volume of the non-magnetic metal oxide particles is pb2 which satisfy pb1/pa1 < 1 and pb2/pa2 > 1, to provide higher resistivity.

38. An imaging method according to claim 27, wherein the magnetic carrier comprises a carrier core coated with 0.5 to 10 wt% of the coating material.

39. An imaging method according to claim 38, wherein the magnetic carrier comprises a carrier core coated with 0.6 to 5 wt% of the coating material.

40. An imaging method according to claim 27, wherein the sphericity of the magnetic carrier is at most 2.

Images