JP2005338349A - Image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming method in which toner has high transfer efficiency and toner fogging is not caused, and which is adaptable even to a cleanerless process. <P>SOLUTION: In the image forming method including: a charging step of charging an electrostatic latent image carrier having a charge injection layer with a magnetic brush consisting of magnetic particles by a contact AC charging process using a contact charging magnetic brush; a latent image forming step; and a developing step of developing an electrostatic latent image formed on the electrostatic latent image carrier having the charge injection layer with a toner of a two-component developer comprising a magnetic carrier and the toner, the magnetic carrier comprises at least a binder resin and magnetic metal oxide particles, has an Fe (II) content of 0.001-5.0 wt.% based on the leached iron element concentration of surfaces of the magnetic carrier particles, and satisfies the expression: -6.0R+300≤M≤-3.0R+350 wherein 5≤R≤30, R is a number average particle diameter (μm) of the magnetic carrier particles, and M is a saturation magnetization (emu/cm<SP>3</SP>) of the magnetic carrier particles. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming method using a two-component developer in a developing process, which includes a contact charging device that charges a latent image carrier by contacting a charging member in an electrophotographic method or an electrostatic recording method.

  In electrophotography, an electrostatic latent image formed on a latent image carrier is developed with toner, and then transferred and fixed on transfer paper. As a developing method in this case, currently, a two-component developing method using a two-component developer consisting of a toner and a magnetic carrier as a developer, or a one-component developing using a one-component developer not using a magnetic carrier. Although a method is known, a two-component development method is suitably used when higher image quality and higher speed are required.

  In the two-component development system, a two-component developer composed of toner and a magnetic carrier forms a spike called a developing magnetic brush on the developer carrying member, and this developing magnetic brush is latent in the developing process. There are known so-called contact development, which is in contact with an image carrier, and so-called non-contact development, in which development is performed without contact. Usually, when high image quality and high density are required, the former contact development is often used.

  On the other hand, a representative example of recent technology relating to the developer is a method of reducing the particle diameter of the toner and the magnetic carrier. For example, in Japanese Patent Laid-Open No. 58-184157, in a developing process in which a two-component developer magnetic brush rubs the surface of a latent image carrier, a toner having an average particle size of 10 μm or less and an average particle size of 5-30 μm are disclosed. It is said that sufficient image quality can be achieved when using a magnetic carrier.

  However, when the particle size of the toner is small, the charge amount becomes large, and further, the adhesion force to the carrier due to van der Waals force and the like also becomes large. There arises a problem that the concentration becomes thin.

  In order to solve these problems, a developing method is used in which a two-component developer is conveyed to the developing unit by rotating a magnet disposed inside the developer carrier, and a certain amount of residual magnetization is provided as a carrier. It is known that development is improved while developing magnetic brushes rotate on the developer carrying member, so that development efficiency can be increased and image density can be increased.

  As the magnetic carrier used here, one made of a hard magnetic substance such as barium ferrite or strontium ferrite has been used. However, when these are used alone, the specific resistance of the carrier particles is low. It is used after being coated with a resin so as not to leak the bias applied from the agent carrier. This causes inconvenience when the coating material is peeled off.

  Further, due to demands for reducing the particle size, magnetic material-dispersed resin carriers have been developed as seen in, for example, Japanese Examined Patent Publication No. 59-224416. Further, as disclosed in Japanese Patent Application Laid-Open No. 10-268575, spherical composite particles have been proposed in order to freely control the magnetic characteristics and to increase the resistance.

  However, when the toner is small and the carrier particles are small, the specific resistance is still insufficient to sufficiently increase the image density and sufficiently prevent carrier adhesion, and a sufficiently satisfactory magnetic carrier has not been obtained.

  Incidentally, before forming an electrostatic latent image on the latent image carrier, a so-called primary charging process is performed in which charges are uniformly applied to the entire surface of the latent image carrier. So-called corona chargers using discharge have been used.

  However, in recent years, contact charging devices have been put to practical use instead. This is for the purpose of low ozone, low power, and downsizing of the apparatus, and a conductive roller or a magnetic brush roller is used as a charging member. As a charging method, in order to perform contact charging smoothly and uniformly and without being affected by environmental fluctuations, a voltage superimposed with an AC component is applied to the charging member as described in JP-A-63-149669. It is desirable to do.

  Even in such a contact charging device, the essential charging mechanism uses a discharge phenomenon from the charging member to the latent image carrier, and therefore generation of ozone is inevitable, and the voltage applied to the charging member Requires at least a value equal to or higher than the desired surface potential of the latent image carrier. When charging using the AC component as described above, vibration or abnormal noise is generated due to an electric field, or the surface of the latent image carrier is caused by discharge. There were problems such as deterioration.

In order to solve such a problem, charging by direct injection of charges into the latent image carrier has been desired. In order to inject charge directly onto the surface of the latent image carrier, a charging member having a low resistance value is used, and a long charge time is applied to charge the charged charge to the trap level of the charge existing on the surface of the latent image carrier. There is a way. However, such a charging method is based on the premise that the specific resistance of the charging member is as low as less than 1 × 10 ³ Ωcm, and causes a large charge leak to scratches and pinholes generated on the surface of the latent image carrier. There was a problem such as. In addition, the time required for sufficient charging is not at a practical level.

  Japanese Patent Laid-Open No. 6-3921 discloses a method in which a charge injection layer is provided on the surface of a latent image carrier and a charge is injected by a contact charging member. This makes it possible to solve various problems in the contact charging device described above.

  As the charging member used in the contact charging device as described above, a magnetic brush roller that has a large contact nip with the latent image carrier and can uniformly contact the surface of the latent image carrier is particularly preferably used.

  In the contact charging device using the magnetic brush roller, each magnetic particle constituting the magnetic brush needs to be in contact with each other to form a conductive path, and the surface of the latent image carrier is charged by the charge flowing through the conductive path. Although charged, there is a problem that the charging characteristics change when impurities are mixed in the magnetic brush. For example, when toner particles or the like are mixed in a magnetic brush in a relatively large amount for some reason, such a problem may be realized. Recently, a cleaner-less process that eliminates the waste toner recovery part has been proposed in order to reduce the overall size of the apparatus and simplify maintenance. The toner remaining on the magnetic brush is mixed with high probability in the magnetic brush without being cleaned.

In addition, the core resistance of the conventional iron powder carrier, ferrite carrier, etc. is 1 × 10 ⁹ Ωcm or less by using the contact two-component developer process and the AC developing bias as described above for high image quality. When a magnetic carrier with a resin coating on such a low-resistance core is used as a developer, carrier adhesion and toner fogging occur, and these toner and developing magnetic carrier are mixed into the contact charging member, so that the contact charging ability is improved. In some cases, it was insufficient.

  In Japanese Patent Application Laid-Open No. 6-222676, an image forming apparatus using a contact charging process of a charging magnetic brush is used to increase the resistance of a magnetic carrier used for a developer and to make an alternating current for charging and developing than magnetic particles used for a charging magnetic brush. Although a proposal has been made to share a voltage power source, particularly when a contact two-component development process is used, the resistance is controlled by changing the ferrite particle coating material described in the specification, When used for magnetic particles for electromagnetic brushes and magnetic carriers for two-component developers, it has not been possible to achieve high image quality of full-color images.

  For the above reasons, an image forming method that can achieve low ozone generation by using a contact two-component AC development process that is excellent in fine line reproducibility and obtains a full color image with high image density has been put into practical use. Absent.

  An object of the present invention is to provide an image forming method that solves the above-described problems, particularly an image forming method using a two-component developer and a contact charging process.

  An object of the present invention is to provide an image forming method in which generation of ozone is suppressed, carrier generation does not occur, and a high quality toner image excellent in halftone reproducibility can be obtained.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming method using a contact AC charging process using a contact charging magnetic brush, wherein the toner has high transfer efficiency, no toner fog, and can be used in a cleaner-less process. It is to provide.

The present invention provides a charging step of charging an electrostatic latent image carrier having a charge injection layer having a surface resistance of 1 × 10 ¹⁰ to 1 × 10 ¹⁶ Ω with a magnetic brush composed of magnetic particles;
A latent image forming step of forming an electrostatic latent image by exposure on an electrostatic latent image carrier having a charged charge injection layer; and an electrostatic latent image formed on the electrostatic latent image carrier having the charge injection layer A development step of developing a two-component developer having a magnetic carrier and toner with the toner;
In an image forming method having
The magnetic carrier contains at least a binder resin and magnetic metal oxide particles,
The specific resistance of the magnetic carrier particles is 5.0 × 10 ¹³ Ωcm or more when 25 V to 500 V is applied,
The saturation magnetization at 10 kilo-Oersted of the magnetic carrier particles is 100 to 300 emu / cm ³ , the residual magnetization is 25 to 150 emu / cm ³ ,
The true specific gravity of the magnetic carrier particles is 3.0 to 4.9 g / cm ³ ,
Fe (II) content with respect to the eluted iron element concentration on the surface of the magnetic carrier particles is 0.001 to 5.0% by weight,
The present invention relates to an image forming method that satisfies the following formula.

−6.0R + 300 ≦ M ≦ −3.0R + 350
5 ≦ R ≦ 30
R: Number average particle diameter of magnetic carrier particles (μm)
M: saturation magnetization of magnetic carrier particles (emu / cm ³ )
In the developing system of the present invention, a so-called contact two-component system is used in which a two-component developer is used as a developer and development is performed while an alternating electric field is applied while the developer magnetic brush contacts and rubs the latent image carrier. It is optimal that AC development is performed and the developer carrier has a cylindrical nonmagnetic sleeve and a magnet contained in the nonmagnetic sleeve, and the magnet is configured to be rotationally driven. It is. This is to obtain a high-quality toner image having excellent halftone reproducibility as described above.

Further, there is a charge injection layer having a surface resistance of 1 × 10 ¹⁰ to 1 × 10 ¹⁶ Ω of the latent image carrier, and primary charging is performed by a member that is charged in contact with the charge injection layer, thereby suppressing generation of ozone. be able to. In particular, by using a charging brush using magnetic particles, more uniform charging is possible.

  Furthermore, the magnetic force of the magnetic carrier constituting the two-component developer is controlled by mixing a soft magnetic material and a hard magnetic material, and substantially increased in resistance, thereby preventing toner fog and carrier adhesion. High-quality images with good halftone reproducibility can be obtained.

  Further, by using the toner produced by the polymerization method in the image forming apparatus having the above-described configuration, it is possible to achieve a cleaner-less image forming method with high transfer efficiency and toner without fog. .

  Further, the rotation direction of the developer carrying member and the latent image using the resin carrier having a substantially high resistance as described above and controlling the magnetic force of the magnetic carrier by mixing a soft magnetic material and a hard magnetic material. By preferably using a developing method in which the direction of rotation of the carrier is a counter direction at the opposing portion, a high-quality image with high image density and no missing dots can be obtained while preventing scavenging.

  According to the present invention, in an image forming method having a contact charging device in which a charging member is brought into contact with a latent image carrier and charged, contact two-component AC development is performed using a developing magnetic carrier having substantially high resistance. As a result, it is possible to achieve high image quality with excellent fine line reproducibility and without toner fog or carrier adhesion.

  Hereinafter, the present invention will be described in more detail with reference to preferred embodiments of the present invention.

As a result of detailed studies by the present inventors, the surface resistance of the charge injection layer of the latent image carrier in the present invention is required to be 1 × 10 ¹⁰ to 1 × 10 ¹⁶ Ω, more preferably. It has been found that it is preferably in the range of 1 × 10 ¹² to 1 × 10 ¹⁵ Ω. When the surface resistance of the charge injection layer is less than 1 × 10 ¹⁰ Ω, the charge injected from the contact charging member is not held on the surface of the charge injection layer, and as a result, in the electrophotographic process of the reversal development system, image flow and It sometimes caused the phenomenon called. This was especially seen under high humidity. When the resistance of the surface of the charge injection layer exceeds 1 × 10 ¹⁶ Ω, the charge is not sufficiently injected, and so-called charged positive ghost is generated in which the toner is unnecessarily carried on the poorly charged region of the latent image carrier. Sometimes.

As described above, even if the surface resistance of the charge injection layer of the latent image carrier is in the range of 1 × 10 ¹⁰ Ω to 1 × 10 ¹⁶ Ω, if the specific resistance of the injection charging member is not in an appropriate range, It is not properly charged. This needs to be adjusted depending on the configuration of the injection charging member. For example, when a charging brush roller made of magnetic particles is used, it is made of a magnetic material having a specific resistance of 1 × 10 ⁵ to 1 × 10 ⁸ Ωcm. The charging brush roller exhibits good chargeability.

  As the magnetic body constituting the charging magnetic brush roller, for example, a magnetic metal such as iron, cobalt, nickel, or a compound thereof can be used. It is necessary to adjust these specific resistances by coating these with an appropriate coating resin, or by performing oxidation treatment, reduction treatment, or the like. For example, hydrogen-reduced Zn—Cu ferrite, oxidized magnetite, or the like can be used. Alternatively, binder-type magnetic particles in which magnetic metal oxide and conductive fine particles are dispersed in a binder resin, or those obtained by coating the binder-type magnetic particles with an appropriate coating resin can also be used.

  As the charge injection layer of the latent image carrier, a material in which conductive fine particles are dispersed in an insulating and translucent binder resin is preferably used. The charge injection layer contacts the charged magnetic brush to which a voltage is applied, so that the conductive particles exist as innumerable independent float electrodes with respect to the conductive substrate of the latent image carrier, and these float electrodes The effect | action which charges the capacitor | condenser which forms is anticipated. Therefore, it was recognized that the voltage applied to the contact charging member and the latent image carrier surface potential converge to the same value, and the applied voltage may be minimal.

As described above, when a contact two-component development process and an AC development bias are used to achieve high image quality, the surface resistance of the charge injection layer is 1 × 10 ¹⁰ Ω to 1 × 10 ¹⁶ Ω as described above. When using a latent image carrier in the above range, it has been found that if a conventional iron powder carrier or magnetic carrier with a resin coating on ferrite is used as a developer, carrier adhesion and toner fogging will remarkably occur. .

  This is because when a latent image carrier having a relatively low surface resistivity and a development magnetic carrier having a low specific resistance such as a conventional iron powder carrier or ferrite carrier are used in combination, the latent image on the latent image carrier is used. This potential leaks through the developing magnetic carrier particles that come into contact and rubs, and the potential is changed so as to approach the developing bias potential. As a result, the fog removal potential is lowered and toner fog occurs. It was also found that the developing bias was injected into the carrier, which caused carrier adhesion to occur at the same time.

  Therefore, if a magnetic carrier having a specific magnetic property is used as the carrier, and the magnetic carrier particle having a sufficiently high specific resistance and controlling the Fe (II) content relative to the eluted iron element concentration on the surface of the magnetic carrier particle is used, The inventors have found that a sufficient image density can be obtained, there is no occurrence of carrier adhesion, and the characteristics can be maintained durability, and the present invention has been achieved.

  Furthermore, the magnetic carrier having the above-mentioned specific magnetic characteristics is a spherical resin carrier obtained by a polymerization method using a thermosetting binder resin, and two or more kinds of magnetic metal oxides having different magnetic characteristics. It was also found that it is effective to use a magnetic material-dispersed resin carrier in which these are dispersed in combination.

  Hereinafter, these will be described in more detail.

  As a result of detailed studies on the magnetic carrier by the present inventors, it is preferable to use a magnetic carrier having a number average particle size of 5 to 30 μm when the toner particle size is reduced to 1 to 10 μm. I found out that That is, in this case, when a magnetic carrier having a number average particle size smaller than 5 μm is used, development is performed while the developing magnetic brush is in contact with the latent image carrier. Even if a magnetic carrier having magnetic properties employed in the present invention is used, carrier adhesion cannot be avoided. On the other hand, when a magnetic carrier having a number average particle size larger than 30 μm is used, the surface area of the magnetic carrier becomes small, so that the carrier surface cannot be held at a preferable toner concentration. Or a sufficient image density may not be obtained.

Further, as described above, when the toner having the small particle diameter as described above is used, the magnet disposed inside the developer carrying member is rotationally driven to convey the two-component developer to the developing unit. It is known that a sufficient image density can be obtained by using a developing method having a configuration. However, as a result of further studies by the inventors, a magnetic carrier whose magnetic characteristics are appropriately controlled is used at this time. As a result, it was found that halftone reproducibility is excellent, carrier adhesion can be effectively prevented while maintaining high image density, and the performance can be maintained durability. As the magnetic characteristics of the carrier, specifically, it is important that the saturation magnetization in a magnetic field of 10 kilo-Oersted is 100 to 300 emu / cm ³ , and the residual magnetization is 15 to 150 emu / cm ³ , and further It was also found that the magnetic carrier particle size and the saturation magnetization of the carrier are closely related. When the particle size of the magnetic carrier is 5 to 30 μm, the carrier adhesion, the reproducibility of the halftone image quality, and the image density are improved with good balance by using the carrier having the saturation magnetization in the region satisfying the following relational expression. Became possible.

(Formula) −6.0R + 300 ≦ M ≦ −3.0R + 350
5 ≦ R ≦ 30
R: Number average particle diameter of magnetic carrier particles (μm)
M: saturation magnetization of magnetic carrier particles (emu / cm ³ )
When −6.0R + 300> M, as will be described later, it becomes difficult to prevent carrier adhesion no matter how much the resistance of the carrier particles is increased. When M> −3.0R + 350, the developing magnetic brush becomes rough, the halftone reproducibility is inferior, and toner deterioration is promoted.

In addition, when the residual magnetization of the magnetic carrier used is lower than 15 emu / cm ³ , the two-component developer cannot roll well on the developer carrier, and for the intended purpose of the present invention. On the other hand, if the residual magnetization of the magnetic carrier is higher than 150 emu / cm ³ , aggregation due to the magnetization of the carriers may occur even at a position away from the magnetic field of the developer carrier. Since the toner is large, the deterioration of the toner is unavoidable and the durability characteristics are deteriorated.

In the magnetic carrier of the present invention, the specific resistance of the carrier particles is important together with the magnetic properties. That is, it has been found that it is essential to have a high specific resistance of 5.0 × 10 ¹³ Ω · cm or more when a voltage of 25 to 500 V is applied. A carrier having a specific resistance lower than 5.0 × 10 ¹³ Ω · cm when any voltage is applied causes the development bias to lower the latent image potential via the carrier, causing image degradation, fogging, In addition, the carrier itself may be injected by injecting charges.

  Further, according to further studies by the present inventors, in order to efficiently obtain a magnetic carrier having the above-mentioned specific magnetic characteristics and capable of easily achieving the intended purpose of the present invention. Uses a so-called magnetic material-dispersed resin carrier in which magnetic metal oxide particles containing at least a magnetic material are dispersed in a binder resin, and has two types of magnetic materials different from those of a thermosetting binder resin. It has been found that it is effective to use at least the above magnetic metal oxide and to produce it by a polymerization method.

  As a combination of the above two or more kinds of magnetic metal oxides, so-called soft magnetic magnetic metal oxide particles having a relatively high saturation magnetization and so-called hard magnetic magnetic metal having a large residual magnetization are obtained. It has been found that it is effective to use a mixture of oxide particles.

  Furthermore, it has been found that it is effective to use a thermosetting resin such as a phenol resin or a melamine resin as a binder resin for dispersing these magnetic materials, and to use a magnetic carrier prepared by a polymerization method. That is, since such a magnetic carrier is hard, excellent in strength, and spherical, using such a magnetic carrier effectively prevents carrier destruction due to magnetic shear in the developing device, and causes carrier adhesion. For the intended purpose of the present invention, the shape is spherical and the toner is easy to roll on the developer carrying member, and the toner can be supplied to the developing unit in a good state. A certain image density improvement can be further achieved.

  Further, by providing a layer containing non-magnetic metal oxide particles in the vicinity of the surface, the above-described high resistance of the magnetic carrier can be achieved. As a measure for increasing the resistance, the present inventors have found that the Fe (II) content with respect to the eluted iron element concentration on the surface of the magnetic carrier particles is 0.001 to 5.0% by weight in the present invention.

  Furthermore, the magnetic carrier is coated with a silicone-based resin layer, so that it can be further improved in fluidity, chargeability, and strength.

  The toner that can be suitably used in the present invention preferably has a weight average particle diameter of 1 to 10 μm and a number-based variation coefficient of 0 to 35%. That is, it was found that in order to charge well with the carrier of the present invention, it is a small particle size toner and the particle size distribution at that time needs to be sharp. Further, in order to improve the fluidity and improve the chargeability, it is preferable to use a small particle size toner containing inorganic fine particles having a number average particle size of 0.2 μm or less, organic fine particles having a particle size of 0.2 μm or less, or a mixture thereof. .

  Further, it is preferable that the toner is formed entirely or partly by a polymerization method, and that the toner has a shape factor SF-1 of 100 to 130 in order to further improve fluidity and improve image quality. In order to efficiently obtain a toner having such a small particle diameter, it is preferable to produce the toner using a polymerization method such as suspension polymerization, emulsion polymerization, or dispersion polymerization.

  Hereinafter, the magnetic carrier having the above-described aspect that can be suitably used in the image forming method of the present invention will be described.

As the metal oxide that can be used in this case, for example, magnetite or soft ferrite represented by a general formula of MO · Fe ₂ O ₃ or MFe ₂ O ₄ is preferably used as the soft magnetic particles. it can. M in the formula corresponds to a divalent or monovalent metal ion such as Mn, Fe, Ni, Co, Cu, Mg, Zn, Cd, Li, and the like, and M is a single or a plurality of metals. Can be used as Examples of such materials include magnetite, γ iron oxide, Mn—Zn ferrite, Ni—Zn ferrite, Mn—Mg ferrite, Ca—Mg ferrite, Li ferrite, and Cu—Zn ferrite. And iron-based magnetic oxides.

Examples of the hard magnetic metal oxide particles used together with the soft magnetic metal oxide particles include barium ferrite and strontium ferrite represented by BaFe ₁₂ O ₁₉ and SrFe ₁₂ O ₁₉ . In addition to the above metal oxides, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, A nonmagnetic metal oxide using a single or a plurality of metals such as Sr, Y, Zr, Nb, Mo, Cd, Sn, Ba, and Pb can also be used.

  The soft ferrite mentioned above means a soft magnetic ferrite having a coercive force Hc of 100 oersted or less.

  When the above metal oxide is dispersed in a resin and used as a core, the number average particle size of the metal oxide exhibiting magnetism varies depending on the carrier particle size, but those up to 0.02 to 2 μm can be preferably used. . When two or more kinds of metal oxides are dispersed and used, the number average particle diameter of the metal oxide exhibiting magnetism can be 0.02 to 2 μm, and the other nonmagnetic metal oxide can be used. A number average particle diameter of 0.05-5 micrometers can be used. In this case, the particle size ratio rb / ra of the other nonmagnetic metal oxide (particle size rb) with respect to the magnetic particles (particle size ra) is preferably more than 1 time and more than 1 time and 5 times or less. It is more preferable. When the ratio is 1.0 times or less, magnetic metal oxide particles having a low specific resistance are likely to appear on the surface, the resistance of the carrier core cannot be sufficiently increased, and it is difficult to obtain the effect of preventing carrier adhesion of the present invention. Become. On the other hand, if it exceeds 5.0 times, the incorporation of metal oxide particles into the resin may not be successful, so that the strength of the carrier is lowered and the carrier is easily destroyed.

Further, the specific resistance of the metal oxide used dispersed in the resin can be one in which the magnetic particles are in the range of 1 × 10 ³ Ωcm or more, especially when two or more kinds of metal oxides are used in combination. It is necessary that the particles exhibiting magnetism are in the range of 1 × 10 ³ Ωcm or more, and the other nonmagnetic metal oxide particles have a higher specific resistance than the magnetic particles. The specific resistance of the other nonmagnetic metal oxide used in the present invention is preferably 1 × 10 ⁸ Ωcm or more. If the specific resistance of the magnetic particles is less than 1 × 10 ³ Ωcm, the desired carrier specific resistance cannot be obtained even if the content of the dispersed metal oxide is reduced. In addition, when two or more kinds of metal oxides are dispersed, the specific resistance of the carrier core can be sufficiently increased when the specific resistance of the nonmagnetic metal oxide having a large particle size is less than 1 × 10 ⁸ Ωcm. Therefore, it is difficult to obtain the effects of the present invention.

  The total content of metal oxides in the metal oxide-dispersed resin core of the present invention is 50% by weight to 99% by weight. When the amount of the metal oxide is less than 50% by weight, the chargeability becomes unstable, and the carrier is charged particularly in a low-temperature and low-humidity environment. Tends to adhere to the carrier surface. On the other hand, when it exceeds 99% by weight, the carrier strength is lowered, and problems such as cracking of the carrier due to durability tend to occur.

  Moreover, it is preferable that the metal oxide contained in the metal oxide-dispersed resin core used in the present invention has been subjected to a lipophilic treatment. When the oleophilic metal oxide is dispersed in the binder resin to form core particles, it can be uniformly and densely incorporated into the binder resin. In particular, when core particles are formed by a polymerization method, it is important for obtaining spherical and smooth particles and for sharpening the particle size distribution.

  In the oleophilic treatment, the metal oxide is treated with a coupling agent such as a silane coupling agent or a titanate coupling agent, or the surface is treated by dispersing the metal oxide in an aqueous solvent containing a surfactant. There are methods such as oiling.

  As a silane coupling agent here, what has a hydrophobic group, an amino group, or an epoxy group can be used. Examples of the silane coupling agent having a hydrophobic group include vinyltrichlorosilane, vinyltriethoxysilane, and vinyltris (β-methoxy) silane. Examples of silane coupling agents having an amino group include γ-aminopropylethoxysilane, N-β (aminoethyl) -γ-aminopropyltrimethoxysilane, and N-β (aminoethyl) -γ-aminopropylmethyldimethoxysilane. N-phenyl-γ-aminopropyltrimethoxysilane and the like. Examples of the silane coupling agent having an epoxy group include γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropyltriethoxysilane, β- (3,4-epoxycyclohexyl) trimethoxysilane, and the like. .

  Examples of titanate coupling agents include isopropyl triisostearoyl titanate, isopropyl tridodecylbenzenesulfonyl titanate, isopropyl tris (dioctyl pyrophosphate) titanate, and the like.

  As the surfactant, a commercially available surfactant can be used as it is.

  As a method for producing the above-described magnetic carrier of the present invention, a composition containing at least a polymerizable monomer and two or more kinds of magnetic metal oxides is mixed and granulated, the monomer is polymerized, and the carrier is directly produced. There is a way to get it. As the polymerizable monomer used for polymerization, vinyl monomers that are raw materials for thermosetting resins such as the phenol resins and melamine resins listed above, for example, phenol resins and aldehydes, urea resins in the case of phenol resins In the case of urea and aldehydes, in the case of melamine resin, melamine and aldehydes, and other bisphenols and epichlorohydrin used as starting materials for epoxy resins are used. For example, as a specific method for producing a magnetic carrier using a curable phenolic resin, in the aqueous medium, phenols and aldehydes which are polymerizable monomers are present in the presence of a basic catalyst in the presence of a magnetic material as described above. A magnetic material-dispersed spherical resin carrier is obtained directly by putting a metal oxide, preferably a lipophilic magnetic metal oxide, and polymerizing the monomer monomer.

  The magnetic carrier of the present invention is preferably one whose surface is further coated with an appropriate coating resin in accordance with the charge amount of the toner used together with the carrier.

  The coating resin used at this time is preferably an insulating resin. The insulating resin that can be used in this case may be a thermoplastic resin or a thermosetting resin. Specifically, for example, thermoplastic resins include acrylic resins such as polystyrene, polymethyl methacrylate and styrene-acrylic acid copolymer, styrene-butadiene copolymer, ethylene-vinyl acetate copolymer, polyvinyl chloride. , Polyvinyl acetate, polyvinylidene fluoride resin, fluorocarbon resin, perfluorocarbon resin, solvent-soluble perfluorocarbon resin, polyvinyl alcohol, polyvinyl acetal, polyvinylpyrrolidone, petroleum resin, cellulose, cellulose acetate, cellulose nitrate, methylcellulose, hydroxymethylcellulose, hydroxyethylcellulose , Cellulose derivatives such as hydroxypropylcellulose, novolac resin, low molecular weight polyethylene, saturated alkyl polyester resin, polyethylene terephthalate Polybutylene terephthalate, polyarylate such aromatic polyester resins, polyamide resins, polyacetal resins, polycarbonate resins, polyethersulfone resins, polysulfone resins, polyphenylene sulfide resins, polyether ketone resins.

  Specific examples of thermosetting resins include phenol resins, modified phenol resins, maleic resins, alkyd resins, epoxy resins, acrylic resins, or polycondensation of maleic anhydride, terephthalic acid, and polyhydric alcohols. Unsaturated polyester, urea resin, melamine resin, urea-melamine resin, xylene resin, toluene resin, guanamine resin, melamine-guanamine resin, acetoguanamine resin, gliptal resin, furan resin, silicone resin, polyimide, polyamide-imide resin , Polyetherimide resin, polyurethane resin and the like.

  The above-described resins can be used alone or in combination. In addition, a curing agent or the like can be mixed with a thermoplastic resin and cured for use.

  A particularly preferred form is a silicone-based cured resin. In order to control the amount of charge, it is more preferable to use a mixture of an amino group-containing silane compound or the like.

Furthermore, the magnetic carrier of the present invention can be suitably used when the true specific gravity is 3.0 to 4.9 g / cm ³ . That is, a magnetic carrier having a true specific gravity of less than 3.0 g / cm ³ substantially means a carrier having a high fat content such that the proportion of the resin in the weight of the carrier is 50% or more, There may be a problem in strength. On the other hand, when the true specific gravity is larger than 4.9 g / cm ³ , the share given to the toner in the developing device tends to be large depending on the magnetic characteristics of the carrier, and there is a risk of causing toner deterioration during durability. In some cases, the binder component is insufficient and the strength is reduced.

  In the development step in the image forming method of the present invention, the two-component developer is carried on a developer carrying member and conveyed to the developing unit, and the two-component developer is formed on the developer carrying member in the developing unit. In the step of forming a magnetic brush and developing the electrostatic latent image formed on the latent image carrier by bringing the magnetic brush into contact with the latent image carrier, the developer carrier is a cylindrical nonmagnetic material. It is necessary to have a sleeve and a magnet contained in the non-magnetic sleeve, and to be configured so that the magnet is driven to rotate.

  That is, the magnetic carrier in the present invention is used after being magnetized. At that time, a magnet is disposed in a non-magnetic sleeve which is a developer carrying member, and the developer is conveyed to the developing unit by rotating at high speed.

  As a method of magnetizing the magnetic carrier of the present invention, a known method can be used. Preferably, it is used by being magnetized in a magnetic field that is at least three times the coercive force.

  In the contact two-component AC developing system in the image forming method of the present invention, the alternating electric field applied to the developer magnetic brush is preferably 500 Hz to 5000 Hz. When the alternating electric field to be applied is less than 500 Hz, no matter how substantially the development magnetic carrier has a high resistance as in the present invention, the charge is injected into the latent image carrier through the development magnetic carrier, and the carrier adheres. There was a case. In addition, when the alternating electric field to be applied exceeds 5000 Hz, the toner cannot follow the electric field and the image quality is liable to deteriorate.

  As the alternating electric field to be applied, a conventional sine wave, triangular wave or rectangular wave can be used, but an alternating electric field whose waveform is appropriately controlled can also be used. For example, a first voltage for directing toner from the latent image carrier to the developer carrier, a second voltage for directing toner from the developer carrier to the latent image carrier, and a voltage between the first voltage and the second voltage An alternating electric field that forms a waveform pattern with the third voltage can be used. In such a case as well, the frequency is within the frequency range of the alternating electric field in the present invention, that is, 500 Hz with respect to one period of the repeating pattern of the waveform. It is preferable to be ˜5000 Hz.

  The toner used in the image forming method of the present invention preferably has a weight average particle diameter in the range of 1 to 10 μm. When the toner particle diameter exceeds 10 μm, one particle for developing the latent image becomes large, so that a high-definition toner image that is the object of the present invention cannot be obtained.

  By the way, it is possible to combine a cleanerless process with the image forming method of the present invention. However, when a magnetic brush roller is used as a contact charging member and a cleanerless process is combined with this as described above, When the toner is mixed, there is a problem that the charging characteristic is changed.

  In order to avoid such a problem, when the cleaner-less process is combined with the image forming method of the present invention, toner having a transfer efficiency of 95% or more is essential, and more preferably, toner having 98% or more is used. Is good.

The transfer efficiency is measured by developing a solid black image and then transferring it onto paper, and measuring the toner weight (T1) transferred per unit area and the toner weight (T2) remaining on the latent image carrier without being transferred. The following formula: Transfer efficiency (%) = 100 × T1 / (T1 + T2)
It was calculated by calculating by

  For this reason, when a cleaner-less process is combined with the image forming method of the present invention, it is preferable that part or all of the toner is manufactured by a polymerization method. Further, it is preferable that an appropriate external additive is present around the toner. The toner produced by the polymerization method generally has a high sphericity, so that the toner is placed on the latent image carrier with a small contact area, so that the transfer efficiency is high. Further, the external additive serves as a spacer between the latent image carrier and the toner particles, and can improve toner transferability. Further, since the sphericity is high, the frictional charging of the toner becomes good and the toner fog due to the charging failure is eliminated. Therefore, it is possible to avoid the fog toner from being transferred to the contact charging magnetic brush without being transferred.

As the external additive of the toner, conventionally used external additives can be used, and inorganic fine particles, organic fine particles, or a mixture thereof can be used. These external additives preferably have a specific surface area of 100 m ² / g or more by the BFT method. When the specific surface area is less than 100 m ² / g, the fluidity of the toner is lost and the transferability of the toner cannot be sufficiently improved.

In the image forming method of the present invention, the developer carrier has a surface shape of 0.2 μm ≦ centerline average roughness (Ra) ≦ 5.0 μm.
10 μm ≦ Unevenness average interval (Sm) ≦ 80 μm
0.05 ≦ Ra / Sm ≦ 0.5
It is preferable to satisfy the above conditions.

  Ra and Sm are values that define the centerline average roughness and the average interval between the irregularities described in JIS-B0601 and ISO468, and are obtained by the following equation.

Ｒａが０．２μｍより小さいと、現像剤の搬送性が不十分なため耐久による画像むらや画像の濃度むらが発生しやすくなる。Ｒａが５μｍを超えると、現像剤の搬送性には優れるもののブレード等の現像剤搬送量規制部における規制力が大きくなりすぎるために外部添加剤が摺擦による劣化を受けて耐久時の画質が低下する。

If Ra is less than 0.2 μm, the developer transportability is insufficient, and image unevenness due to durability and image unevenness are likely to occur. When Ra exceeds 5 μm, although the developer transportability is excellent, the regulating force in the developer transport amount regulating portion such as a blade becomes too large, so that the external additive is deteriorated by rubbing and the image quality at the time of durability is deteriorated. descend.

  When Sm is larger than 80 μm, the developer on the developer carrying member becomes difficult to be held, so that the image density is lowered. Although the details of the cause of Sm are unknown, slipping with the developer carrying member occurs in the developer carrying member conveyance amount regulating portion or the like. It is considered that the force acts as a lump packed in the container and its force exceeds the holding force between the developer carrier and the developer. If the Sm is less than 10 μm, many of the irregularities on the surface of the support are smaller than the average particle size of the developer, so that the particle size selectivity of the developer entering the concave portion is generated, and fusion due to the developer fine powder component is likely to occur. . It is also difficult to manufacture.

Further, from the above viewpoint, the convex / concave slope (≈f (Ra / Sm)) obtained from the height of the convex portion on the developer carrying member and the interval between the concave and convex portions is an important cause in the present invention. In the present invention, 0.05 ≦ Ra / Sm ≦ 0.5
It is preferable that it is 0.07 or more and 0.3 or less.

  If Ra / Sm is less than 0.05, the developer holding force on the developer carrying member is weak, so that the developer is difficult to be held on the developer carrying member. As a result, image unevenness occurs. When Ra / Sm exceeds 0.5, the developer entering the recess on the surface of the developer carrying member becomes difficult to circulate with other developers, and thus developer fusion occurs.

  By further processing several grooves (so-called knurls) in the length direction of the developer carrying member, it becomes easy to uniformly coat the developer carrying member with a developer having further excellent fluidity.

  In the present invention, Ra and Sm were measured according to JIS-B0601 using a contact surface roughness measuring instrument SE-3300 (manufactured by Kosaka Laboratory).

  As a method for producing a developer carrier having a predetermined surface roughness according to the present invention, for example, a sand blasting method using amorphous and regular particles as abrasive grains, sandpaper for forming irregularities in the sleeve circumferential direction is used. A sandpaper method in which the sleeve surface is rubbed in the axial direction, a method by chemical treatment, a method of forming a resin convex portion after coating with an elastic resin, or the like can be used.

  In the present invention, any of negative and positive can be used as the amorphous silicon photoreceptor. However, in the case of a full-color image forming method, the negative toner can be used more stably with the negative toner, and accordingly, the negative chargeability can be used. It is preferable to reversely develop the electrostatic latent image using a negative toner on the amorphous silicon photoconductor.

  In addition, when a positively chargeable amorphous silicon photoconductor is used, an image forming method in which the electrostatic latent image is normally developed with a positive toner is also preferable.

  Below, the measuring method used by this invention is described.

  The particle size of the toner particles used in the present invention is measured within a range of 0.4 μm to 60 μm using a laser scan type particle size distribution measuring device (CIS-100 GALAI). The sample was added to 0.5 to 2 mg of toner in a solution obtained by adding 0.2 ml of a surfactant (alkylbenzene sulfonate) to 100 ml of water, dispersed for 2 minutes with an ultrasonic disperser, and then placed in a cubic cell containing a magnetic stirrer. Add about 80% of the water, and add 1 or 2 drops of the sample sprinkled ultrasonically into the pipette. The weight average particle diameter, the number average particle diameter Dn, and the S.D. D. Based on (standard deviation), the weight average particle diameter and coefficient of variation are obtained.

Coefficient of variation (%) = S. D. / Dn × 100
As for the particle size of the magnetic carrier, 300 or more magnetic carrier particles having a particle size of 0.1 μm or more are randomly extracted by a scanning electron microscope (100 to 5,000 times), and an image processing analyzer manufactured by Nireco Corporation. The number average particle diameter of the carrier was defined as the number average horizontal ferret diameter analyzed by Luzex3.

The magnetic properties of the magnetic carrier were measured using a vibrating magnetic field type magnetic property automatic recording device BHV-30 manufactured by Riken Denshi Co., Ltd. The magnetic characteristic value of the carrier powder was determined as the saturation magnetization and the residual magnetization when the carrier powder was returned to 0 Oersted from an external magnetic field of 10 kiloOersted. The sample for measuring the magnetic carrier is prepared in a packed state so as to be sufficiently dense in a cylindrical plastic container. In this state, the magnetization moment is measured, and the actual weight of the sample filled above is measured to determine the magnetization strength (emu / g). Next, the true specific gravity of the carrier particles is obtained by a dry automatic densimeter Accupick 1330 (manufactured by Shimadzu Corporation), and the unit defined by the present invention is multiplied by the true specific gravity of the magnetization strength (emu / g). The intensity of magnetization per volume (emu / cm ³ ) is determined.

In the measurement of the specific resistance of the magnetic carrier in the present invention, the cell is filled with carrier powder, two electrodes are arranged so as to be in contact with the upper and lower sides of the carrier-filled layer, and a load is applied to the upper electrode between these electrodes. This was done by applying a voltage to and measuring the current flowing at that time. The measurement conditions were such that the contact area between the carrier and the electrode was about 2.3 cm ² , the thickness of the carrier packed layer was about 2 mm, the load applied to the upper electrode was 180 g, and the applied voltage was 1000V. In this case, since the carrier is powder, a difference occurs in the filling rate into the cell, and the measured value of the specific resistance may change accordingly.

  In the present invention, the Fe (II) content relative to the eluted iron element concentration on the surface of the magnetic carrier particles can be determined by the following method.

  Place 3 l of deionized water in a 5 l beaker and warm to 45-50 ° C. 400 ml of deionized water and 25 g of magnetic carrier particles are mixed to form a slurry and added to a 5 liter beaker while being washed with 805 ml of deionized water. Next, 695 ml of special grade sulfuric acid is added to the 5 l beaker while maintaining the solution temperature in the 5 l beaker at 50 ° C. and the stirring speed at 200 rpm, and dissolution is started. One hour after the start of dissolution, 20 ml of the solution is sampled and filtered through a 0.1 μm membrane filter to collect the filtrate.

  10 ml of the filtrate is weighed and the dissolved concentration of iron element is quantified by plasma emission spectroscopy (ICP).

On the other hand, 100 ml of ion-exchanged water is added to 10 ml of the filtrate of the lysate, and titration is performed using a 0.1 N aqueous KMnO ₄ solution, and the titration is determined with the slight red color as the end point. A blank test is performed in parallel, and the Fe (II) content with respect to the eluted iron element concentration on the surface of the magnetic carrier particles can be obtained by the following formula.

以下に本発明で使用した摩擦帯電量の測定方法を記載する。トナーとキャリアをトナー重量が５重量％となるように混合し、ターブラミキサーで１２０秒混合する。この現像剤を底部に６３５メッシュの導電性スクリーンを装着した金属製の容器にいれ、吸引機で吸引し、吸引前後の重量差と容器に接続されたコンデンサーに蓄積された電位から摩擦帯電量を求める。この際、吸引圧を２５０ｍｍＨｇとする。この方法によって摩擦帯電量を下記式を用いて算出する。

The method for measuring the triboelectric charge amount used in the present invention will be described below. The toner and the carrier are mixed so that the toner weight becomes 5% by weight, and mixed for 120 seconds with a turbula mixer. This developer is put in a metal container with a 635 mesh conductive screen attached to the bottom, and sucked with a suction machine, and the triboelectric charge amount is calculated from the weight difference before and after suction and the potential accumulated in the capacitor connected to the container. Ask. At this time, the suction pressure is 250 mmHg. By this method, the triboelectric charge amount is calculated using the following formula.

Q (μC / g) = (C × V) × (W ₁ −W ₂ ) ⁻¹
(W ₁ is the weight before suction, W ₂ is the weight after suction, C is the capacity of the condenser, and V is the potential accumulated in the condenser.)
A method for measuring the surface resistance of the electrostatic latent image carrier used in the present invention will be described. A comb-shaped electrode having an effective electrode length of 2 cm and an interelectrode distance of 120 μm is gold-deposited on the surface of the latent image carrier, and measurement is performed by applying a voltage of 100 V with a resistance measuring device (4140BpAMATER manufactured by Hewlett-Packard Company).

(Example)
Examples of the present invention will be specifically described below, but the present invention is not limited thereto.

(Manufacture of toner)
[Toner 1]
Propoxylated bisphenol and fumaric acid
100 parts by weight of polyester resin obtained by condensation C.I. I. Pigment Blue 15: 3 5 parts by weight Chromium complex salt of di-tert-butylsalicylic acid 4 parts by weight These were mixed by a fixed tank type dry mixer, and the vent port was connected to a suction pump and sucked with a twin screw extruder. Melt kneading was performed.

  This melt-kneaded product was roughly crushed with a hammer mill to obtain a 1 mm mesh pass toner composition crushed product. Further, this coarsely crushed material was pulverized with a mechanical pulverizer to a weight average diameter of 20 to 30 μm, then pulverized with a jet mill using collision between particles in a swirling flow, and then with a multistage split classifier. Classification was performed to obtain cyan colored particles.

Toner 100 was obtained by adding 1.8 parts by weight of hydrophobic titanium oxide having a specific surface area of 200 m ² / g by BET method to 100 parts by weight of the toner composition. The obtained particles had a weight average particle diameter of 4.8 μm. The coefficient of variation of the number distribution was 28%.

[Toner 2]
450 parts by weight of 0.1M Na ₃ PO ₄ aqueous solution was added to 710 parts by weight of ion-exchanged water, heated to 60 ° C., and then 12,000 rpm using a TK homomixer (manufactured by Tokushu Kika Kogyo). Was stirred at. To this, 75 parts by weight of 1.0 M CaCl ₂ aqueous solution was gradually added to prepare an aqueous medium containing Ca ₃ (PO ₄ ) ₂ in a uniformly and finely dispersed state.

160 parts by weight of styrene 35 parts by weight of n-butyl acrylate C.I. I. Pigment Blue 15: 3 15 parts by weight Aluminum complex salt of di-tert-butylsalicylic acid 15 parts by weight Saturated polyester (acid value 14, peak molecular weight: 8000) 10 parts by weight Ester wax (melting point 70 ° C.) 50 parts by weight The mixture was mixed, heated to 60 ° C., and uniformly dissolved and dispersed at 12,000 rpm using a TK homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.). Into this, 10 parts by weight of a polymerization initiator 2,2′-azobis (2,4-dimethylvaleronitrile) was dissolved to prepare a composition containing a polymerizable monomer.

Next, the composition containing the obtained polymerizable monomer is put into the aqueous medium prepared in advance as described above, and 10% at 10,000 rpm with a TK homomixer in an N ₂ atmosphere at 60 ° C. Stir for minutes to granulate the composition. Then, while stirring with a paddle stirring blade, the temperature was raised to 80 ° C. and reacted for 10 hours. After completion of the polymerization reaction, the residual monomer was distilled off under reduced pressure. After cooling, hydrochloric acid was added to dissolve calcium phosphate, followed by filtration, washing with water, and drying to obtain cyan colored suspended particles.

Thereafter, classification was performed twice with a multistage split classifier. To 100 parts by weight of the colored particles, 3.5 parts by weight of hydrophobic titanium oxide having a specific surface area of 200 m ² / g by the BET method was externally added to obtain toner 2 produced by a polymerization method. The obtained particles had a weight average particle size of 3.1 μm. The coefficient of variation of the number distribution was 18%.

[Toner 3]
Cyan colored particles were produced in the same manner as toner 1 except that the classification conditions of the toner 1 with a multi-division classifier were changed. To 100 parts by weight of the cyan colored particles, 1.8 parts by weight of hydrophobic titanium oxide having a specific surface area by the BET method of 200 m ² / g was externally added to obtain a toner 3 produced by a pulverization method. The weight average particle diameter of the obtained particles was 5.2 μm. The variation coefficient of the number distribution was 37%.

(Carrier production)
[Carrier 1]
First, 4.8% by weight of a silane coupling agent (3- (2-aminoethylamino) with respect to a magnetite powder having a number average particle diameter of 0.25 μm and a barium ferrite powder having a number average particle diameter of 0.25 μm, respectively. Propyl) dimethoxysilane) was added, and the mixture was stirred and mixed at a high speed at 100 ° C. or higher to make the metal oxide fine particles lipophilic.

-Phenol 10 parts by weight-Formaldehyde solution (formaldehyde 40%, methanol 10%, water 50%) 6 parts by weight-Lipophilic treated magnetite 80 parts by weight-Lipophilic treated barium ferrite 20 parts by weight The above materials and 28% 5 parts by weight of ammonia water and 10 parts by weight of water were placed in a flask, heated and maintained at 85 ° C. over 30 minutes with stirring and mixing, and then cured by polymerization reaction for 3 hours.

  Further, 1.5 parts by weight of hematite powder having a number average particle size of 0.20 μm and lipophilic treatment with (3- (2-aminoethylaminopropyl) dimethoxysilane) as described above, 1 part by weight of phenol, formaldehyde solution 0.4 part by weight was added, and the polymerization reaction was further continued for 3 hours.

  Then, it cooled to 30 degreeC, and also added water, Then, the supernatant liquid was removed, the precipitate was washed with water, and then air-dried. Next, this was dried at a temperature of 50 to 60 ° C. under reduced pressure (5 mmHg or less) to obtain spherical particles.

  Furthermore, the surface of the particles obtained above was coated with a thermosetting silicone resin by the following method. At that time, a 10 wt% carrier coat solution was prepared using toluene as a solvent so that the amount of the coat resin on the surface of the carrier core particles was 1.5 wt%. While the coating solution was continuously applied with shear stress, the solvent was volatilized at 70 ° C. to coat the surface of the carrier core. The coated magnetic carrier particles were heat-treated with stirring at 200 ° C. for 3 hours, cooled, crushed, and classified with a 200-mesh sieve to obtain carrier 1.

The number average particle diameter of the obtained carrier 1 was 22.0 μm. Further, the obtained carrier was subjected to a magnetic field of 10 kilo-Oersted and the magnetic properties were measured. The saturation magnetization at 10 kilo Oersted was 248 emu / cm ³ and the residual magnetization was 48 emu / cm ³ . Further, the true specific gravity of the carrier 1 was 3.55 g / cm ³ . The Fe (II) content with respect to the concentration of eluted iron element on the surface of the carrier particles was 2.1% by weight.

[Carrier 2]
First, 4.8% by weight of a silane coupling agent (3- (2-aminoethylamino) with respect to a magnetite powder having a number average particle diameter of 0.25 μm and a strontium ferrite powder having a number average particle diameter of 0.27 μm, respectively. Propyl) dimethoxysilane) was added, and the mixture was stirred and mixed at a high speed at 100 ° C. or higher in the container, and the metal oxide fine particles were oleophilicized in the same manner as Carrier 1.

・ Phenol 12 parts by weight ・ Formaldehyde solution (formaldehyde 40%, methanol 10%, water 5
0%) 7 parts by weight • Lipophilicized magnetite 60 parts by weight • Lipophilicized strontium ferrite 40 parts by weight The above material, 6% by weight of 28% ammonia water, and 12 parts by weight of water are placed in a flask, and stirred and mixed. Then, the temperature was raised to 85 ° C. and maintained for 30 minutes, followed by polymerization reaction for 3 hours to cure.

  Furthermore, 1.5 parts by weight of a hematite powder having a number average particle size of 0.20 μm, lipophilically treated in the same manner as Carrier 1, 1.5 parts by weight of phenol and 0.4 parts by weight of a formaldehyde solution are added, and a polymerization reaction is further performed for 3 hours. I let you. Thereafter, spherical particles were obtained in the same manner as carrier 1.

  Further, a carrier 2 was obtained by coating the surface of the particles obtained above with a thermosetting silicone resin in the same manner as the carrier 1.

The number average particle diameter of the obtained carrier 2 was 29.3 μm. The saturation magnetization at 10 kilo-Oersted was 233 emu / cm ³ and the remanent magnetization was 78.5 emu / cm ³ . The true specific gravity of the carrier 1 was 3.60 g / cm ³ . Further, the Fe (II) content with respect to the concentration of the eluted iron element on the surface of the carrier particles was 1.2% by weight.

[Carrier 3]
Polymerization was carried out with the following formulation using lipophilic magnetite and barium ferrite used in Carrier 1.

・ Phenol 10 parts by weight ・ Formaldehyde solution (formaldehyde 40%, methanol 10%, water 5
6 parts by weight-90 parts by weight of oleophilic magnetite-10 parts by weight of barium ferrite oleophilically treated 4 parts by weight of 28% ammonia water and 8 parts by weight of water are placed in a flask and stirred and mixed. Then, the temperature was raised to 85 ° C. and maintained for 30 minutes, followed by polymerization reaction for 3 hours to cure.

  Furthermore, 1.5 parts by weight of a hematite powder having a number average particle size of 0.28 μm, lipophilic treatment similar to Carrier 1, 1.5 parts by weight of phenol and 0.4 parts by weight of formaldehyde solution were added, and the polymerization reaction was continued for 3 hours. I let you. Thereafter, spherical particles were obtained in the same manner as carrier 1.

  Further, the surface of the particles obtained above was coated with a thermosetting silicone resin in the same manner as in the carrier 1 to obtain a carrier 3.

The number average particle diameter of the obtained carrier 3 was 15.7 μm. The saturation magnetization at 10 kilo-Oersted was 260 emu / cm ³ and the remanent magnetization was 35.8 emu / cm ³ . The true specific gravity of the carrier 1 was 3.58 g / cm ³ . Further, the Fe (II) content with respect to the eluted iron element concentration on the surface of the carrier particles was 4.4% by weight.

[Carrier 4]
3.8% by weight of a silane coupling agent (3- (2-aminoethylamino) with respect to the copper zinc ferrite powder having a number average particle diameter of 0.25 μm and the barium ferrite powder having a number average particle diameter of 0.25 μm. Propyl) dimethoxysilane) was added, and the mixture was stirred and mixed at a high speed at 100 ° C. or higher to make the metal oxide fine particles lipophilic.

・ Phenol 12 parts by weight ・ Formaldehyde solution (formaldehyde 40%, methanol 10%, water 5
0%) 7 parts by weight-Lipophilicized copper zinc ferrite 30 parts by weight-Lipophilicized barium ferrite 70 parts by weight The above materials, 6 parts by weight of 28% ammonia water, and 12 parts by weight of water are placed in a flask and stirred. The mixture was heated and maintained at 85 ° C. for 30 minutes while mixing and reacted and cured in 3 hours.

  Further, 1.0 part by weight of hematite powder used in carrier 1, 1 part by weight of phenol and 0.4 part by weight of formaldehyde solution were added, and the polymerization reaction was further performed for 3 hours. Thereafter, spherical particles were obtained in the same manner as carrier 1.

  Further, the surface of the particles obtained above was coated with a thermosetting silicone resin in the same manner as the carrier 1 to obtain a carrier 4.

The number average particle diameter of the obtained carrier 4 was 28.1 μm. The saturation magnetization at 10 kilo Oersted was 177 emu / cm ³ and the remanent magnetization was 106.7 emu / cm ³ . The true specific gravity of the carrier 1 was 3.53 g / cm ³ . Further, the Fe (II) content with respect to the eluted iron element concentration on the surface of the carrier particles was 0.2% by weight.

[Carrier 5]
First, a 3.0% by weight silane coupling agent (3- (2-aminoethylamino) was used for each of magnetite powder having a number average particle diameter of 0.40 μm and barium ferrite powder having a number average particle diameter of 0.61 μm. Propyl) dimethoxysilane) was added, and the mixture was stirred and mixed at 100 ° C. or higher at high speed in the same manner as in the carrier 1 to make the metal oxide fine particles lipophilic.

・ Phenol 10 parts by weight ・ Formaldehyde solution (formaldehyde 40%, methanol 10%, water 5
6 parts by weight-60 parts by weight of lipophilic magnetite-40 parts by weight of barium ferrite subjected to lipophilic treatment The above materials, 5 parts by weight of 28% ammonia water, and 10 parts by weight of water are placed in a flask and stirred and mixed. Then, the temperature was raised to 85 ° C. and maintained for 30 minutes, followed by polymerization reaction for 3 hours to cure. Then, it cooled to 30 degreeC, and also added water, Then, the supernatant liquid was removed, the deposit was washed with water, and then air-dried. Next, this was dried at a temperature of 50 to 60 ° C. under reduced pressure (5 mmHg or less) to obtain spherical particles.

  Further, a carrier 5 was obtained by coating the surface of the particles obtained above with a thermosetting silicone resin in the same manner as in the carrier 1.

The number average particle diameter of the obtained carrier 4 was 20.3 μm. The saturation magnetization at 10 kilo-Oersted was 229 emu / cm ³ and the remanent magnetization was 75.4 emu / cm ³ . The true specific gravity of the carrier 1 was 3.58 g / cm ³ . Further, the Fe (II) content with respect to the eluted iron element concentration on the surface of the carrier particles was 8.8% by weight.

[Carrier 6]
The mixture was weighed so that Fe ₂ O ₃ = 50 mol%, CuO = 27 mol%, and ZnO = 23 mol% in terms of molar ratio, and mixed using a ball mill. After calcining this, it was pulverized with a ball mill and further granulated with a spray dryer. This was sintered and further classified to obtain carrier core particles.

  Further, a carrier 5 was obtained by coating the surface of the particles obtained above with a thermosetting silicone resin in the same manner as in the carrier 1.

The number average particle diameter of the obtained carrier 4 was 38.1 μm. The saturation magnetization at 10 kilo-Oersted was 325 emu / cm ³ and the remanent magnetization was 0.4 emu / cm ³ . The true specific gravity of the carrier 1 was 5.02 g / cm ³ . Further, the Fe (II) content with respect to the concentration of the eluted iron element on the surface of the carrier particles was 0.1% by weight.

<Magnetic particles for contact charging magnetic brush>
(Core particles)
200 parts by weight of hydrogen-reduced Zn—Cu ferrite (number average particle diameter 40.0 μm, specific resistance 5 × 10 ⁶ Ωcm)
(Coating resin solution)
Polycarbonate 1.0 part by weight Epoxy-modified silicone resin 1.0 part by weight Conductive titanium oxide 4.0 part by weight Tetrafluoroethylene resin particles (0.25 μm) 0.2 part by weight Xylene solution 14.0 part by weight Each formulation of the resin solution was dispersed with a paint shaker containing glass beads for 2 hours to prepare a coated resin solution. This was coated on the above core particles using the aforementioned Spira coater and dried at 150 ° C. for 1 hour. The resulting magnetic particles for contact-charged magnetic brush had a specific resistance of 8.9 × 10 ⁶ Ωcm and a number average particle size of 40.1 μm. The magnetization intensity at 1 kilooersted (σ1000) = 250.3 emu / cm ³ (the true specific gravity of the magnetic particles is 5.02 g / cm ³ ).

  The specific resistance and the number average particle size of the magnetic particles for the contact-charged magnetic brush and the core particles used here were determined by the method for measuring the characteristics of the magnetic carrier for development described above.

  The carrier A and the toner 1 were mixed so as to have a toner concentration of 8% by weight to obtain a two-component developer. The triboelectric charge amount of the toner was −25.0 μC / g.

  The developer was imaged using a Canon full color laser copier CLC-500 remodeling machine. A schematic diagram around the developing portion is shown in FIG. The distance A between the developer carrying member (developing sleeve) 1 and the developer regulating member (magnetic blade) 8 of the full color laser copying machine developer made by Canon is 600 μm, the developing sleeve 1 and the electrostatic latent image carrying member (photosensitive drum) 2 The distance B was set to 400 μm. The developing nip C at this time was 5 mm.

  The developing sleeve is sand-plasted using a pneumatic plaster (manufactured by Fuji Seisakusho) on the surface of the developing sleeve (material: SUS, manufactured by Hitachi Metals, 25φ) used in the developing device of CLC-500, A plasto sleeve (Ra / Sm = 0.07) with Ra = 2.1 μm and Sm = 29.6 μm was used.

  Further, the peripheral speed ratio between the developing sleeve 1 and the photosensitive drum 2 is 2.2: 1, the traveling directions are counter directions as shown in FIG. 1, the magnetic field of the developing pole S1 of the developing sleeve 1 is 1 kilo Oersted, Further, the developing conditions were such that the alternating electric field was 1800 V having a waveform as shown in FIG. 2 and the frequency was 3000 Hz, and the developing bias was −480 V. Further, the toner development contrast (Vcont) is 350V, and the fog removal voltage (Vback) is 80V.

  As a voltage applied to the contact charging member 3, a DC bias of −560V was used.

  As the photosensitive drum, an OPC photosensitive member having five layers of the following functional layers on an aluminum φ80 drum was used.

In order from the aluminum base layer side, the first layer is an undercoat layer, the second layer is a positive charge injection prevention layer, the third layer is a charge generation layer, the fourth layer is a charge transport layer, and the fifth layer is a charge injection layer . This charge injection layer is a photo-curing acrylic resin in which SnO ₂ ultrafine particles are further dispersed and tetrafluoroethylene resin particles are dispersed in order to achieve uniform charging by increasing the contact time between the contact charging member and the photoreceptor. It is. Specifically, SnO ₂ particles having a particle size of about 0.03 μm doped with antimony and reduced in resistance are 70% by weight with respect to the resin, and further 20% by weight of tetrafluoroethylene resin particles having a particle size of 0.25 μm. , And 1.2% by weight of a dispersing agent. The surface resistance of this photosensitive drum was 1 × 10 ¹² Ω.

  Images were produced under the above development conditions. As a result, an excellent image with excellent fine line reproducibility and a solid image with high density was obtained. Furthermore, image disturbance and toner fogging in the image area and non-image area due to carrier adhesion were not recognized.

  The toner transfer efficiency when transferring the solid black image from the photosensitive drum onto the paper was 99.5%, which was a level that could sufficiently cope with the cleaner-less process.

  In fact, when the cleaner was removed and the endurance of printing 10,000 images was performed, there was no change in the charging property of the charging magnetic brush, and no charging ghost was observed.

  The results of this example are shown in Table 2. The results of the following examples and comparative examples are also shown in Table 2.

  As the developer, the same developer as in Example 1 was used, and the developing condition was changed to a rectangular wave with an alternating electric field of 2000 V (peak-to-peak voltage) and a frequency of 1000 Hz. went.

  As a result, a satisfactory image having a satisfactory level was obtained.

  Carrier B and toner 1 were mixed at a toner concentration of 5% by weight to obtain a two-component developer. The triboelectric charge amount of the toner was −22.1 μC / g.

  In exactly the same manner as in Example 1, an image was printed and a 10,000-image printing durability test was performed. Fine line reproducibility, carrier adhesion, toner fogging, and the like obtained the same good results as in Example 1.

  Carrier C and toner 1 were mixed to a toner concentration of 8% by weight to obtain a two-component developer. The triboelectric charge amount of the toner was −24.9 μC / g.

  Images were produced in exactly the same manner as in Example 1, and good results were obtained as in Example 1.

  Carrier A and toner 2 were mixed to a toner concentration of 8% by weight to obtain a two-component developer. The triboelectric charge amount of the toner was −24.0 μC / g.

  Images were produced in exactly the same manner as in Example 1. Good results similar to Example 1 were obtained with respect to carrier adhesion, toner fog, and the like. However, when the transfer efficiency was measured as in Example 1, it was 90%.

The same photosensitive drum is used except that the tetrafluoroethylene resin particles and the dispersant are not dispersed in the fifth charge injection layer among the surface functional layers of the photosensitive drum of Example 1, and other developers and developments are performed. Images were produced under the same conditions as in Example 1. The surface resistance of the photosensitive drum was 3 × 10 ¹⁰ Ω.

  As a result, good results were obtained as in Example 1.

(Comparative Example 1)
Carrier D and toner 1 were mixed to a toner concentration of 8% by weight to obtain a two-component developer. The triboelectric charge amount of the toner was −23.5 μC / g.

  As a result of performing image formation in exactly the same manner as in Example 1, the solid image density was sufficient, but fine line reproducibility, carrier adhesion, and toner fogging were all poor.

(Comparative Example 2)
Except that the low resistance SnO ₂ particles to be added to the fifth charge injection layer in the surface functional layer of the photosensitive drum of Example 1 are dispersed in an amount of 125% by weight with respect to the photocurable acrylic resin. The image was printed out in the same manner as in Example 1 except for the other developer, development conditions, and the like. The surface resistance of the photosensitive drum was 5 × 10 ⁹ Ω.

  As a result, it was found that fine line reproducibility was poor, and image flow occurred when viewed microscopically.

(Comparative Example 3)
Except for the configuration in which the fifth layer is excluded from the surface functional layer of the photosensitive drum of the first embodiment, the same photosensitive drum is used, and other developers, development conditions, and the like are exactly the same as in the first embodiment and image output is performed. went. The surface resistance of the photosensitive drum was 3 × 10 ¹⁶ Ω.

  As a result, generation of a charging ghost, deterioration of fine line reproducibility resulting from it, and generation of toner fog were observed.

  Evaluation methods and standards are as follows.

  (1) Image density: The image density was measured as a relative density of an image formed on plain paper using a Macbeth Color Checker RD-1255 equipped with an SPI filter.

  (2) Line reproducibility: Visual evaluation was made with reference to an original image and a standard sample.

  (3) Carrier adhesion: A solid white image is drawn, and the part on the photosensitive drum between the developing unit and the cleaner unit is sampled by sticking a transparent adhesive tape on the photosensitive drum in a size of 5 cm × 5 cm. Adhered magnetism.

When the above metal oxide is dispersed in a resin and used as a core, the number average particle diameter of the metal oxide exhibiting magnetism varies depending on the carrier particle diameter, but those having a particle diameter of 0.02 to 2 μm can be preferably used. In addition, when two or more kinds of metal oxides are dispersed and used, a metal oxide exhibiting magnetism is mixed and used. The average reflectance Dr (%) of the printed plain paper was measured with a Densitometer TC-6MC manufactured by Tokyo Denshoku Co., Ltd. On the other hand, a solid white image was drawn on plain paper, and then the reflectance Ds (%) of the solid white image was measured. The fog (%) is expressed by the following formula: fog (%) = Dr (%) − Ds (%)
Calculate from

Excellent: Less than 1.0 (%) Good: Less than 1.0-1.5 (%) Possible: Less than 1.5-2.0 (%) Slightly bad: Less than 2.0-3.0 (%) Poor : 3.0 (%) or more

Claims (6)

A charging step of charging an electrostatic latent image carrier having a charge injection layer having a surface resistance of 1 × 10 ¹⁰ to 1 × 10 ¹⁶ Ω with a magnetic brush composed of magnetic particles;
A latent image forming step of forming an electrostatic latent image on an electrostatic latent image carrier having a charged charge injection layer by exposure; and an electrostatic latent image formed on the electrostatic latent image carrier having the charge injection layer A developing step of developing a two-component developer having a magnetic carrier and toner with the toner;
The magnetic carrier contains at least a binder resin and metal oxide particles,
The number average particle diameter Dn is 5 to 25 μm,
The specific resistance is 5.0 × 10 ¹³ Ωcm or more when 25 V to 500 V is applied,
The true specific gravity is 3.0 to 4.9 g / cm ³ ;
The magnetization intensity at 1 kilo Oersted is 100 to 300 emu / cm ³ ;
Fe (II) content with respect to the eluted iron element concentration on the surface of the magnetic carrier particles is 0.001 to 5.0% by weight,
An image forming method characterized by satisfying the following formula:
−6.25R + 307 ≦ M ≦ −4.47R + 319
5 ≦ R ≦ 25
R: Number average particle diameter of magnetic carrier (μm)
M: Magnetization strength (emu / cm ³ ) at 1 kilo-Oersted of the magnetic carrier   In the developing step, a magnetic brush of a two-component developer having a magnetic carrier and a toner carried on a developer carrying member disposed opposite to the electrostatic latent image carrying member having the charge injection layer is used as a charge injection layer. An electrostatic latent image carrier having the charge injection layer by contacting the developer carrier with a developing bias voltage in which a continuous or non-continuous AC bias is superimposed on a DC bias. The image forming method according to claim 1, wherein the electrostatic latent image formed on the surface is developed with toner.   The magnetic carrier particles have a binder resin, a magnetic metal oxide and a nonmagnetic metal oxide whose surface has been made lipophilic, and the total amount of the metal oxide in the carrier core particles is 50 to 99% by weight. The image forming method according to claim 1, wherein the image forming method comprises:   The magnetic carrier contains hematite in the vicinity of the surface, and the Fe (II) content with respect to the eluted iron element concentration on the surface of the magnetic carrier particles is 0.001 to 5.0% by weight. The image forming method described in 1.   The image forming method according to claim 1, wherein the magnetic carrier is surface-coated with a silicone resin.   In the developing step, the two-component developer is carried on a developer carrying member and conveyed to a developing unit, and a magnetic brush of the two-component developer is formed on the developer carrying member in the developing unit. In the step of developing the electrostatic latent image formed on the latent image carrier by bringing the magnetic brush into contact with the latent image carrier, the developer carrier is attached to the cylindrical nonmagnetic sleeve and the nonmagnetic sleeve. The image forming method according to claim 1, further comprising: a magnet contained therein, wherein the magnet is rotationally driven.