JP5556080B2 - Magnetic carrier and two-component developer for electrophotographic developer - Google Patents

Description

  The present invention relates to a magnetic carrier for an electrophotographic developer having a sufficient electric resistance value and having a small voltage dependency of the electric resistance value, and has excellent gradation properties and the magnetic carrier for an electrophotographic developer, Provided is a two-component developer having a magnetic carrier for electrophotographic developer and a toner.

  As is well known, in electrophotography, a photoconductive substance such as selenium, OPC (organic semiconductor), α-Si or the like is used as a photoreceptor, and an electrostatic latent image is formed by various means. In general, a method is used in which a toner charged opposite to the polarity of the latent image is attached by electrostatic force and visualized by using a brush developing method or the like.

  In this development process, a developer composed of a toner and a carrier is used, and carrier particles called a carrier impart an appropriate amount of positive or negative electricity to the toner by frictional charging, and a magnet is used using magnetic force. The toner is conveyed to a developing area near the surface of the photoreceptor where a latent image is formed via a built-in developing sleeve.

  In recent years, the electrophotographic method has been widely used in copying machines or printers, and it is desired to be able to deal with various documents such as fine lines, lowercase letters, photographs, and color originals. There is a demand for improvement in various properties as a developer used in association with higher functions, higher image quality, and higher speed of copying machines and printers.

  Further, as is well known, the developer is required to have durability such that the electrical characteristics of the toner and the carrier do not change during use. For example, the toner adheres firmly to the surface of the carrier particles and is inherently possessed. The chargeability of the carrier is lost (so-called toner spent), and the resin coating layer on the surface of the carrier particles peels off over time, resulting in leak sites and as a result the toner can be charged properly. The phenomenon of disappearing is a problem.

The carrier is required to have a certain electric resistance value, and an electric resistance value of about 1 × 10 ⁸ to 1 × 10 ¹⁶ Ω · cm is required. That is, when the electrical resistance value is as low as 10 ⁶ Ω · cm as in the case of an iron powder carrier, the carrier adheres to the image portion of the photoreceptor due to charge injection from the sleeve, or the latent image charge escapes through the carrier, There is a problem that the latent image is disturbed or the image is lost. On the other hand, if the insulating resin is coated thickly, the electric resistance value becomes too high, the carrier charge is difficult to leak, and the charge amount of the toner is also increased, resulting in an edged image. On the other hand, there is a problem that the image density in the center is very thin on a large-area image surface.

  In addition, when the dependency of the electrical resistance value on the voltage is increased, an image having no gradation is generally obtained, and when used as a developer of a copying machine or a printer, it is difficult to improve the image quality, and the application is limited. It will be.

The iron powder carrier and the ferrite carrier are usually used by coating the particle surface with a resin, but the iron powder carrier has a true specific gravity of 7 to 8 g / cm ³ and the ferrite carrier has a true specific gravity of 4.5 to 5. Because it is as large as 5 g / cm ³ , a large driving force is required to stir in the developing machine, and mechanical wear is high, causing toner spent, charging deterioration of the carrier itself and damage to the photoreceptor. Easy to invite. Furthermore, it is difficult to say that the adhesion between the iron powder carrier and ferrite carrier surface and the coating resin is good, and the coating resin gradually peels off during use, causing a change in chargeability, resulting in image disturbance and carrier adhesion. Cause problems such as.

  However, the magnetic material-dispersed carrier comprising spherical magnetic composite particles of magnetic iron oxide particles and phenol resin described in JP-A-2-220068 has a smaller true specific gravity than the iron powder carrier and ferrite carrier. The energy at the time of collision between the toner and the carrier is reduced, and the coating resin has excellent peeling durability.

  However, the magnetic material-dispersed carrier has a low electric resistance value and a large voltage dependency of the electric resistance value. In addition, even if the electrical resistance is improved by coating with various resins, as the speed of copying machines and printers has increased, the functions and image quality have increased in recent years, the resin-coated carrier is not suitable for printing with actual copying machines and printers. When the resin coating layer is worn or the like, there is a problem that leakage tends to occur at the time of development, and the gradation property is inferior because the voltage dependency of the electric resistance value is large.

  In particular, the durability of the developer may be required until the maintenance-free machine life, and the magnetic dispersion carrier has a sufficient electric resistance, and the magnetic carrier having a low voltage dependency of the electric resistance is strong. It is requested.

  Conventionally, with respect to the magnetic material dispersed carrier, a technique for controlling the electric resistance of the carrier by coating the particle surface of the spherical magnetic composite particle with melamine resin (Patent Document 1), A technology for controlling the electric resistance of a carrier by forming a coating layer made of a copolymer resin obtained by curing two or more kinds of resins and a phenol resin (Patent Document 2), and nonmagnetic iron on the surface of spherical magnetic composite particles Techniques for controlling the electrical resistance value of a carrier by containing a compound (Patent Documents 3 and 4), carriers containing magnetic iron oxide in which a composite iron oxide of aluminum and iron is present on the particle surface (Patent Documents 5 and 6), etc. It has been known.

JP-A-3-192268 Japanese Patent Laid-Open No. 9-311505 JP-A-8-6303 JP 2003-295523 A JP 2002-72545 A JP 2008-90012 A

  In the techniques described in Patent Documents 1 and 2 described above, the electrical resistance value of the carrier can be increased, but the electrical resistance is increased when the voltage is increased because a ferromagnetic compound in which the particle surface is coated with an Al compound is not used. Greatly decreases and the voltage dependency of the electrical resistance is large.

  In the techniques described in Patent Documents 3 and 4 above, a carrier having a high electric resistance can be obtained, but magnetic iron oxide particles whose surface is coated with an Al compound are not used as the ferromagnetic compound. The voltage dependence of the electrical resistance value is large.

  In addition, in the techniques described in Patent Documents 5 and 6 described above, the electric resistance value of the carrier can be increased, but it is still difficult to say that it has a sufficient electric resistance value as shown in a comparative example described later. is there.

  Therefore, it is a technical object of the present invention to provide a spherical magnetic composite carrier having high electrical resistance and highly controlled voltage dependence of electrical resistance.

  The technical problem can be achieved by the present invention as follows.

That is, the present invention is a spherical magnetic composite particle composed of composite particles dispersed in a magnetic iron oxide particle binder resin, and has an electric resistance value R _{100 at} an applied voltage of 100 V of 1 × 10 ⁸ Ω · cm. The electric resistance value R ₃₀₀ when the applied voltage is 300 V is 0.1 ≦ R ₃₀₀ / R ₁₀₀ ≦ 1 at 1 × 10 ¹⁴ Ω · cm.
A magnetic carrier for an electrophotographic developer, characterized in that (Invention 1).

Further, the present invention provides the magnetic carrier for an electrophotographic developer according to the first aspect of the present invention, wherein the average particle diameter of the magnetic iron oxide particles is 0.05 μm to 2.0 μm, and the particle surface of the magnetic iron oxide particles is Al, Mg, Covered with a compound composed of one or more elements selected from Mn, Zn, Ni, Cu, Ti, and Si, and the abundance of the elements is 0.3 to 4.5% by weight. This is a magnetic carrier for an electrophotographic developer having an electric resistance value RM ₁₀₀ of 1 × 10 ⁸ Ω · cm or more at a voltage of 100 V (Invention 2).

The present invention also relates to a magnetic carrier for an electrophotographic developer according to the first or second aspect of the present invention, wherein the moisture adsorption amount Ma _0.9 of the magnetic iron oxide particles is 15 mg / g or less. (Invention 3).

Further, the present invention provides an electrophotographic magnetic carrier for developer according to any one of the present invention 1及至3, the electric resistance value RM ₁₀ when the applied voltage of 10V of the magnetic iron oxide particles,
0.5 ≦ RM ₁₀₀ / RM ₁₀ ≦ 1
This is a magnetic carrier for an electrophotographic developer (Invention 4).

  Further, the present invention is the magnetic carrier for electrophotographic developer according to any one of the present inventions 1 to 4, wherein the binder resin is a phenolic resin (Invention 5).

    The present invention also provides the electrophotographic developer according to any one of the inventions 1 to 5, wherein a surface coating layer mainly composed of a resin is formed on the surface of the spherical magnetic composite particles. Magnetic carrier (Invention 6).

  Further, the present invention is a two-component developer using the magnetic carrier for an electrophotographic developer according to any one of the first to sixth aspects (Invention 7).

  The magnetic carrier for an electrophotographic developer according to the present invention is suitable as a magnetic carrier for electrophotography because it has an appropriate electric resistance value and has little voltage dependency of the electric resistance value.

4 is a graph showing the relationship between the electric resistance value of the spherical magnetic composite particles obtained in Example 1 and the applied voltage.

  Hereinafter, the present invention will be described in detail.

  First, the magnetic carrier for electrophotographic developer according to the present invention will be described.

When the electric resistance value of the magnetic carrier for electrophotographic developer according to the first aspect of the present invention is measured, the electric resistance value R ₁₀₀ when the applied voltage is 100 V is 1.0 × 10 ⁸ Ω · cm to 1.0 × 10 ¹⁴ Ω. -Cm. When the electric resistance value R ₁₀₀ when the applied voltage is 100 V is less than 1 × 10 ⁸ Ω · cm, carriers are attached to the image area of the photoreceptor by charge injection from the sleeve, or latent image charges escape through the carriers. In this case, the latent image is disturbed or the image is lost. Production of a magnetic carrier exceeding 1.0 × 10 ¹⁴ Ω · cm is industrially difficult. The electric resistance value R ₁₀₀ when the applied voltage is 100 V is preferably 5.0 × 10 ⁸ Ω · cm to 5.0 × 10 ¹³ Ω · cm, more preferably 6.0 × 10 ⁸ Ω · cm to 1.0. × 10 ¹³ Ω · cm.

When the electrical resistance of the magnetic carrier for electrophotographic developer according to the present invention 1 is measured, the electrical resistance value R ₃₀₀ when the applied voltage is 300 V is 1.0 × 10 ⁸ Ω · cm to 1.0 × 10 ¹⁴ Ω · cm. Is preferred.

In the magnetic carrier for electrophotography according to the present invention, the relationship between the electrical resistance value R ₁₀₀ when the applied voltage is 100 V and the electrical resistance value R ₃₀₀ when the applied voltage is 300 V is 0.1 ≦ R ₃₀₀ / R ₁₀₀ ≦ 1.0.
It is. When R ₃₀₀ / R ₁₀₀ is less than 0.1, it indicates that the values of R ₃₀₀ and R ₁₀₀ are greatly different, and it is difficult to say that the voltage dependency of the electrical resistance value is small. Magnetic carriers with R ₃₀₀ / R ₁₀₀ greater than 1.0 are difficult to produce and are not industrial. Preferred R ₃₀₀ / R ₁₀₀ is 0.15 to 0.80, more preferably 0.20 to 0.60.

  The average particle diameter of the magnetic carrier for an electrophotographic developer according to the present invention is preferably 10 to 100 μm. When the average particle diameter is less than 10 μm, secondary aggregation tends to occur, and when it exceeds 100 μm, the mechanical strength is weak and a clear image cannot be obtained. A more preferable average particle diameter is 20 to 70 μm.

  The specific gravity of the magnetic carrier for an electrophotographic developer according to the present invention is preferably 2.5 to 4.5, more preferably 2.5 to 4.2.

The saturation magnetization value of the magnetic carrier for an electrophotographic developer according to the present invention is preferably ²⁰ to 100 Am ² / kg, more preferably 40 to 85 Am ² / kg.

The water adsorption amount Ma _0.9 of the magnetic carrier for an electrophotographic developer according to the present invention is preferably _0.5 to 10 mg / g. A magnetic carrier having a moisture adsorption amount Ma _0.9 of less than 0.5 mg / g is difficult to produce industrially. If it exceeds 10 mg / g, the amount of moisture adsorbed is large, and in particular, the charge amount is lowered under high temperature and high humidity, and the image density is lowered. A more preferable moisture adsorption amount Ma _0.9 is 1.5 to 9.0 mg / g.

The electrical resistance value of the magnetic carrier for an electrophotographic developer in which a surface coating layer mainly composed of a resin is formed on the surface of the spherical magnetic composite particles according to the sixth aspect of the invention is the electrical resistance value R ₁₀₀ when the applied voltage is 100V. 1.0 × 10 ⁸ Ω · cm to 1.0 × 10 ¹⁶ Ω · cm is preferable. When the electric resistance value R ₁₀₀ when the applied voltage is 100 V exceeds 1 × 10 ¹⁶ Ω · cm, the carrier charge is less likely to leak, and the toner charge amount is also increased, resulting in an edged image. However, on the other hand, in the case of an image surface with a large area, there arises a problem that the image density at the center is very thin, which is not preferable. The electric resistance value R ₁₀₀ when the applied voltage is 100 V is more preferably 1.0 × 10 ⁹ Ω · cm to 5.0 × 10 ¹⁵ Ω · cm.

When the electric resistance of the magnetic carrier for an electrophotographic developer according to the sixth aspect of the invention is measured, the electric resistance value R _{300 at} an applied voltage of 300 V is preferably 1 × 10 ⁸ Ω · cm to 1 × 10 ¹⁶ Ω · cm.

In the magnetic carrier for electrophotography according to the sixth aspect of the invention, the relationship (R ₃₀₀ / R ₁₀₀ ) between the electric resistance value R ₁₀₀ when the applied voltage is 100 V and the electric resistance value R ₃₀₀ when the applied voltage is 300 V is 0.10 to 10. It is preferably 1.0, more preferably 0.30 to 0.90, and even more preferably 0.40 to 0.80.

  Next, a method for producing a magnetic carrier for an electrophotographic developer according to the present invention will be described.

  That is, the spherical magnetic composite particles constituting the magnetic carrier are obtained by reacting phenols and aldehydes in the presence of a basic catalyst in the presence of a basic catalyst in an aqueous medium. Can be obtained.

  First, the magnetic iron oxide particle powder used in the present invention will be described.

  The average particle diameter of the magnetic iron oxide particles in the present invention is preferably 0.05 μm to 2.0 μm. When it is less than 0.05 μm, the cohesive force of the magnetic iron oxide particles is large, making it difficult to produce the magnetic composite particles. When it exceeds 2.0 μm, the magnetic iron oxide tends to be detached. A more preferable average particle diameter of the magnetic iron oxide particle powder is 0.08 μm to 1.0 μm.

  In the surface layer of black magnetic iron oxide particles in the present invention, a compound composed of one or more elements selected from Al, Mg, Zn, Ni, Cu, Ti, and Si forms a uniform layer on the particle surface. doing.

  In the magnetic iron oxide particle powder of the present invention, the abundance of one or more elements selected from Al, Mg, Zn, Ni, Cu, Ti, and Si present in the surface layer of the magnetic iron oxide particles is magnetic. The content is preferably 0.3% by weight or more and 4.5% by weight or less based on the whole iron oxide particles. When the amount of the element present on the surface of the magnetic iron oxide particles is less than 0.3% by weight, the electric resistance value of the magnetic carrier produced using the magnetic iron oxide particles is low. When the abundance of the elements present on the particle surface exceeds 4.5% by weight, the hygroscopicity of the magnetic carrier produced using the magnetic iron oxide particles is undesirably high. The amount of elements present on the surface of the magnetic iron oxide particles is more preferably 0.5 to 4.0% by weight, and still more preferably 0.6 to 3.5% by weight.

The electric resistance value of the magnetic iron oxide particles in the present invention when the applied voltage is 100 V is preferably 1.0 × 10 ⁸ Ω · cm or more. When the electric resistance value at an applied voltage of 100 V is less than 1.0 × 10 ⁸ Ω · cm, the electric resistance in a high electric field is insufficient, and the electric resistance value is low when a magnetic carrier for electrophotography is used. . A more preferable electrical resistance value at an applied voltage of 100 V is 3.0 × 10 ⁸ Ω · cm or more, and even more preferable is 3.5 × 10 ⁸ Ω · cm to 1.0 × 10 ¹⁵ Ω · cm. .

The electrical resistance value of the magnetic iron oxide particles in the present invention at an applied voltage of 10 V is preferably 1.0 × 10 ⁸ Ω · cm or more, more preferably 3.0 × 10 ⁸ Ω · cm to 1.0. × 10 ¹⁵ Ω · cm.

Relationship between the electric resistance value _{RM 100} when the electric resistance value _{RM 10} and the applied voltage of 100V when the applied voltage of 10V of the magnetic iron oxide particles used in the present invention _(RM 100 / RM ₁₀₎ is,
0.5 ≦ RM ₁₀₀ / RM ₁₀ ≦ 1.0
It is preferable that When RM ₁₀₀ / RM ₁₀ is less than 0.5, the voltage dependency is large when a magnetic carrier for electrophotography is used. When RM ₁₀₀ / RM ₁₀ is larger than 1.0, it is difficult to produce industrially. More preferably _RM 100 / _{RM 10} is 0.6 to 0.95.

The moisture adsorption amount Ma _0.9 of the magnetic iron oxide particle powder in the present invention is preferably 15 mg / g or less. If it is greater than 15 mg / g, the hygroscopicity is high, and when it is used as a carrier for an electrophotographic developer, the image density is lowered and the environmental stability is poor. A more preferable moisture adsorption amount Ma _0.9 is 3.0 to 12.0 mg / g.

  Next, a method for producing magnetic iron oxide particles in the present invention will be described.

  The magnetic iron oxide particles according to the present invention produce magnetite core particles in accordance with a conventional method, and then maintain the slurry containing the core particles in a temperature range of 70 to 95 ° C. to adjust the pH of the slurry to 8.0. After controlling to the range of ˜9.0 and adding aluminum salt at a rate of 0.015 wt% / min or less with respect to the core particles, aging for 30 minutes or more, and then adjusting the pH, followed by the usual method It can be obtained by washing with water and drying. Mg, Mn, Zn, Ni, Cu, Ti, and Si elements have the pH of the slurry containing the core particles, 9.5 to 10.5 for Mg element, and 8.0 to 9.0 for Mn element. In the case of Zn element, 8.0 to 9.0, in the case of Ni element 7.5 to 8.5, in the case of Cu element 6.5 to 7.5, in the case of Ti element 8.0 to 9 0.0, in the case of Si element, the metal salt is controlled within the range of 6.5 to 7.5, and each metal salt is added at 0.015 wt% / min or less with respect to the core particles, and then ripened for 30 minutes or more. Then, after adjusting the pH, it can be obtained by washing with water and drying according to a conventional method.

  The core particles for obtaining the magnetic iron oxide particle powder in the present invention can be selected from those having various shapes and particle diameters from the viewpoint of required magnetic properties and dispersibility, and there are various production methods. However, in order to achieve the object of the present invention more effectively, from the viewpoint of performing the surface treatment described later more uniformly, the core particle slurry contains a substance that is likely to be an inhibitor of the surface treatment, for example, unreacted. It is preferable that no iron hydroxide fine particles are mixed.

There are various methods for obtaining the slurry containing the core particles. For example, by controlling the pH during the oxidation reaction of the Fe ²⁺ aqueous solution to a predetermined value, octahedron, polyhedron, hexahedron, sphere, An uneven shape can be obtained. Moreover, the core particle of a desired particle diameter can be obtained by controlling the growth conditions of the particles during the oxidation reaction. In addition, the surface smoothness of the core particles controls the growth conditions at the end of the oxidation reaction, and as is generally known, components such as silica components, aluminum components, calcium components, and spinel ferrite crystal structures such as zinc and manganese It can also be controlled by adding a component that tends to form.

As the Fe ²⁺ aqueous solution, for example, a general iron compound such as ferrous sulfate or ferrous chloride can be used. Moreover, aqueous solutions, such as sodium hydroxide and sodium carbonate, can be used for the alkaline solution for obtaining iron hydroxide or as a pH adjuster. Each raw material may be selected in consideration of economy and reaction efficiency.

  The pH of the slurry during the Al surface treatment is preferably 8.0 to 9.0, and more preferably 8.2 to 8.8. When the pH of the slurry is less than 8.0, the Al component is not coated on the surface of the core particles and is precipitated by the Al compound alone, resulting in a low electric resistance value of the magnetic iron oxide particles themselves, and the BET specific surface area value. And the hygroscopicity of the magnetic iron oxide particles themselves increases, which is not preferable. Even when the pH of the slurry exceeds 9.0, the Al component is not coated on the surface of the core particles and is precipitated by the Al compound alone, resulting in a low electric resistance value of the magnetic iron oxide particles themselves, and the BET specific surface area value. And the hygroscopicity of the magnetic iron oxide particles themselves increases, which is not preferable. The pH of the slurry during Mg surface treatment is 9.5 to 10.5, the pH of the slurry during Mn surface treatment is 8.0 to 9.0, and the pH of the slurry during Zn surface treatment is 8.0 to 9.0. The pH during Ni surface treatment is 7.5 to 8.5, the pH during Cu surface treatment is 6.5 to 7.5, the pH during Ti surface treatment is 8.0 to 9.0, and during Si surface treatment The pH of is preferably 6.5 to 7.5. When the pH is out of the above range, the electric resistance value is low, and the hygroscopicity is high, which is not preferable.

  The temperature range of the slurry for surface-treating Al, Mg, Mn, Zn, Ni, Cu, Ti, and Si components is preferably 70 to 95 ° C. When the temperature of the slurry is less than 70 ° C., the BET specific surface area value is high, which is not preferable from the viewpoint of hygroscopicity of the magnetic iron oxide particles themselves. Although the condition value is not particularly limited, it is an aqueous slurry, and therefore the upper limit is about 95 ° C. in consideration of productivity and cost.

  The addition rate of the metal compound (metal salt) to the slurry containing the core particles is preferably added at a rate such that the metal element is 0.015 wt% / min or less with respect to the core particles. More preferably, the metal element is added at 0.01 wt% / min or less with respect to the core particles. If the addition rate of the metal element is greater than 0.015% by weight / min, the metal compound is not coated on the surface of the core particles and precipitates alone, resulting in a low electric resistance value of the magnetic iron oxide particles themselves, and a BET specific surface area. The value becomes large, and the magnetic iron oxide particles themselves have high hygroscopicity. The lower limit is not particularly limited, but considering productivity, the lower limit is 0.002% by weight / min.

  After the addition of the metal compound (metal salt), aging is preferably performed for 30 minutes or more in order to uniformly treat the metal compound on the surface of the core particles. The upper limit is not particularly limited, but considering productivity, the upper limit is about 240 minutes. The slurry is preferably well stirred.

  After aging, it is preferable to control the pH of the slurry in the range of 4.0 to 10.0. More preferably, the pH of the slurry is in the range of 6.0 to 8.0. When the pH is less than 4.0, it is difficult to uniformly form the metal compound layer on the surface of the core particles. Even when the pH exceeds 10.0, it is difficult to uniformly form the metal compound layer on the surface of the core particle. In controlling, the slurry is preferably well stirred.

  After the reaction, it may be washed with water and dried according to a conventional method.

  It is desirable that the magnetic iron oxide particles used in the present invention have a lipophilic treatment on the particle surface in advance. By carrying out the oleophilic treatment, it is possible to obtain a magnetic carrier having a spherical shape more easily.

  The oleophilic treatment is a method of treating magnetic iron oxide particles with a coupling agent such as a silane coupling agent or a titanate coupling agent or by dispersing magnetic iron oxide particles in an aqueous solvent containing a surfactant, A method of adsorbing the surfactant on the surface is suitable.

  Examples of the silane coupling agent include those having a hydrophobic group, an amino group, and an epoxy group. Examples of the silane coupling agent having a hydrophobic group include vinyl trichlorosilane, vinyl triethoxysilane, vinyl tris (β- Methoxy) silane and the like. Examples of the silane coupling agent having an amino group include γ-aminopropyltrietoquinopran, N-β (aminoethyl) -γ-aminopropyltrimethoxysilane, N-β (aminoethyl) -γ-aminopropylmethyldimethoxysilane. N-phenyl-γ-aminopropyltrimethoxosilane and the like. Examples of the silane coupling agent having an epoxy group include γ-glycidoxypropyl methyldiethoxysilane, γ-glycidoxypropyltrimethoxylane, β- (3,4-epoxycyclohexyl) trimethoxysilane and the like.

  As the titanate coupling agent, isopropyl triisostearoyl titanate, isopropyl tridodecylbenzenesulfonyl titanate, isopropyl tris (dioctyl pyrophosphate) titanate or the like may be used.

  As the surfactant, commercially available surfactants can be used, and those having a functional group capable of binding to a magnetic iron oxide particle or a hydroxyl group on the particle surface are desirable, and ionicity is cationic or anionic. Are preferred.

  Although the object of the present invention can be achieved by any of the above-mentioned treatment methods, the treatment with a silane coupling agent having an amino group or an epoxy group is preferable in consideration of adhesiveness with a phenol resin.

  The treatment amount of the coupling agent or surfactant is preferably 0.1 to 10% by weight with respect to the magnetic iron oxide particles.

  In the present invention, a method for producing spherical magnetic composite particles comprising magnetic iron oxide particles and a binder resin is as follows.

  As phenols used in the present invention, in addition to phenol, alkylphenols such as m-cresol, p-cresol, p-tert-butylphenol, o-propylphenol, and a part or all of alkyl groups are chlorine atoms and bromine atoms. And compounds having a phenolic hydroxyl group, such as halogenated phenols substituted with.

  The total content of the magnetic iron oxide particles in the spherical magnetic composite particles as phenols is preferably 80 to 99% by weight with respect to the spherical magnetic composite particles, and if it is less than 80% by weight, the resin content increases. Large particles can be easily formed. If it exceeds 99% by weight, the resin content is insufficient and sufficient strength cannot be obtained. More preferably, it is 85 to 99% by weight.

  Examples of aldehydes used in the present invention include formaldehyde, acetaldehyde, furfural, glyoxal, acrolein, crotonaldehyde, salicylaldehyde, glutaraldehyde and the like in the form of either formalin or paraaldehyde, with formaldehyde being most preferred.

  The molar ratio of aldehydes to phenols is preferably 1.0 to 4.0. When the molar ratio of aldehydes to phenols is less than 1.0, it is difficult to produce particles, Since curing is difficult to proceed, the strength of the resulting particles tends to be weak. When it exceeds 4.0, there is a tendency that unreacted aldehydes remaining in the aqueous medium after the reaction increase. More preferably, it is 1.2-3.0.

  As the basic catalyst used in the present invention, a basic catalyst used in the production of ordinary resole resins can be used. For example, ammonia water, hexamethylenetetramine, alkylamines such as dimethylamine, diethyltriamine, and polyethyleneimine can be mentioned, and ammonia water is particularly preferable. The basic catalyst is preferably 0.05 to 1.50 in molar ratio to phenols. If it is less than 0.05, curing does not proceed sufficiently and granulation becomes difficult. If it exceeds 1.50, the structure of the phenol resin is affected, so that the granulation property is deteriorated and it is difficult to obtain particles having a large particle size.

  Although the reaction in the present invention is carried out in an aqueous medium, the solid content concentration in the aqueous medium is preferably 30 to 95% by weight, particularly preferably 60 to 90% by weight. .

  The reaction solution to which the basic catalyst has been added is heated to a temperature range of 60 to 95 ° C., and reacted at this temperature for 30 to 300 minutes, preferably 60 to 240 minutes, followed by a polycondensation reaction of a phenol resin and curing.

  At this time, in order to obtain spherical magnetic composite particles with high sphericity, it is desirable to raise the temperature gently. The heating rate is preferably 0.5 to 1.5 ° C./min, more preferably 0.8 to 1.2 ° C./min.

  At this time, it is desirable to control the stirring speed in order to control the particle size. The stirring speed is preferably 100 to 1000 rpm.

  After curing, when the reaction product is cooled to 40 ° C. or less, an aqueous dispersion of spherical magnetic composite particles in which the magnetic iron oxide particles are dispersed in the binder resin and the magnetic iron oxide particles are exposed on the particle surface is obtained. It is done.

  The aqueous dispersion containing the spherical magnetic composite particles is filtered and centrifuged to separate solids and liquids, and then washed and dried to obtain spherical magnetic composite particles.

  The coating resin used in the present invention is not particularly limited, but polyolefin resins such as polyethylene and polypropylene; polystyrene; acrylic resin; polyacrylonitrile; polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl carbazole, polyvinyl ether, polyvinyl ketone. Polyvinyl-based or polyvinylidene-based resins such as: vinyl chloride / vinyl acetate copolymer, styrene / acrylic acid copolymer; straight silicone resin composed of organosiloxane bonds or modified products thereof; polytetrafluoroethylene, polyvinyl fluoride, Fluorine resins such as polyvinylidene fluoride and polychlorotrifluoroethylene; polyesters; polyurethanes; polycarbonates; amino-based trees such as urea and formaldehyde resins ; Epoxy resin; polyamide resin, polyimide resin, polyamide imide resin, fluorine - polyamide resins, fluorine - polyimide resins, fluorine - polyamide-imide resins, and the like.

  The coating amount of the magnetic carrier according to the present invention with the resin is preferably 0.1 to 5.0% by weight with respect to the spherical magnetic composite particles. If the coating amount is less than 0.1% by weight, it may be difficult to sufficiently coat and uneven coating may occur. When the amount exceeds 5.0% by weight, the resin coating can be brought into close contact with the surface of the composite particles, but the generated composite particles are aggregated and it is difficult to control the particle size of the composite particles. become. Preferably, it is 0.5 to 3.0% by weight.

  The resin coating in the present invention may contain fine particles in the resin coating layer. As the fine particles, fine particles made of a quaternary ammonium salt compound, a triphenylmethane compound, an imidazole compound, a nigrosine dye, a polyamine resin, or the like are preferable, for example, to impart negative chargeability to the toner. On the other hand, fine particles made of a dye containing a metal such as Cr or Co, a salicylic acid metal compound, an alkylsalicylic acid metal compound, or the like are preferable as those that impart positive chargeability to the toner. These particles may be used alone or in combination of two or more.

  Moreover, the resin coating in the present invention may contain conductive fine particles in the resin coating layer. It is preferable that conductive fine particles are contained in the resin because the resistance of the magnetic carrier can be easily controlled. Known conductive fine particles can be used, for example, carbon black such as acetylene black, channel black, furnace black and ketjen black, metal carbide such as Si and Ti, metal nitride such as B and Ti, Examples thereof include metal borides such as Mo and Cr. These may be used alone or in combination of two or more. Among these, carbon black is preferable.

  When the resin is coated on the surface of the spherical magnetic composite particles, a method of spraying the resin on the spherical magnetic composite particles using a known spray dryer, a spherical magnetic composite particle using a Henschel mixer, a high speed mixer, etc. And a method of dry mixing the resin and the resin, a method of impregnating spherical magnetic composite particles in a solvent containing the resin, and the like.

  Next, the two-component developer in the present invention will be described.

  As the toner used in combination with the carrier of the present invention, a known toner can be used. Specifically, a binder resin and a colorant as main components, and a release agent, a magnetic material, a fluidizing agent, and the like added as necessary can be used. In addition, a known method can be used as a method for producing the toner.

<Action>
An important point in the present invention is that the phenolic resin is bound as a binder using magnetic iron oxide particles having an appropriate electric resistance value and less voltage dependency of the electric resistance, and has sufficient electric resistance and electric resistance. It is to produce a magnetic carrier for electrophotography having a small voltage dependency of the value.

  As a result, the inventor believes that when the electrophotographic magnetic carrier according to the present invention is used, an image having excellent gradation can be obtained.

A typical embodiment of the present invention is as follows.

<Measurement method>
The average particle diameter of the magnetic iron oxide particles is a value obtained from a photograph taken with a transmission electron micrograph and a ferret diameter for 300 particles.

  The particle shape of the magnetic iron oxide particle powder was judged from a photograph observed with a transmission electron microscope and “scanning electron microscope S-4800” (manufactured by Hitachi High-Technologies Corporation).

The water adsorption amount Ma _0.9 of the magnetic iron oxide particle powder is the adsorption at the time of adsorption at 25 ° C. and a relative pressure of 0.9 using “Highly accurate vapor adsorption amount measuring apparatus BELSORP-aqua3” (Nippon Bell Co., Ltd.). It was indicated by the value of moisture content.

  The BET specific surface area value was determined by the BET method using “Mono Sorb MS-II” (manufactured by Yuasa Ionics Co., Ltd.).

  The amount of Al and the amount of metal elements contained in the magnetic iron oxide particle powder are measured with a “fluorescence X-ray analyzer RIX-2100” (manufactured by Rigaku Denki Kogyo Co., Ltd.), and converted into elements with respect to the magnetic iron oxide particle powder. This is the calculated value.

  The electrical resistance value of the magnetic iron oxide particle powder was determined by weighing 2.0 g of the sample powder to be measured, putting it in a measurement container and applying a pressure of 14 MPa, and applying a constant voltage of 100 V or 10 V, “HIGH REISTANCE METER 4339B” (The volume specific resistance value was calculated | required from the resistance value at that time, the electrode area of a sample, and thickness.) (Made by Hewlett-Packard Co., Ltd.).

  The average particle diameter of the spherical magnetic composite particle powder was measured by a laser diffraction particle size distribution analyzer LA500 (manufactured by Horiba, Ltd.) and indicated as a value based on volume.

  The particle shape of the spherical magnetic composite particles was judged from a photograph observed with “Scanning Electron Microscope S-4800” (manufactured by Hitachi High-Technologies Corporation).

  The saturation magnetization was indicated by a value measured under an external magnetic field of 795.8 kA / m (10 kOe) using a vibrating sample magnetometer VSM-3S-15 (manufactured by Toei Kogyo Co., Ltd.).

  The true specific gravity was measured with a multi-volume density meter (1305 type, manufactured by Shimadzu Corporation).

  The electric resistance value (volume specific resistance value) of the spherical magnetic composite particles was shown as a value measured with a high resistance meter 4339B (manufactured by Yokogawa Hewlett Packard) with a sample of 1.0 g.

  For the image evaluation, Epson LP8000C was remodeled and used to change the carrier to the carrier of the present invention, and the printing test was performed by changing the bias voltage.

The gradation of the printed image was visually evaluated using a gray scale (0-19 gradation test chart) manufactured by KODAK.
◎: 15 gradations or more ○: 12-14 gradations △: 8-11 gradations X: 7 gradations or less

Iron oxide 1
<Method for producing magnetic iron oxide particles>
After 100 L of a slurry containing 90 g / l of Fe ₃ O ₄ iron oxide core particles A having a spherical shape and an average particle diameter of 0.24 μm was adjusted to pH 8.5 by adding a sodium hydroxide solution at a temperature of 90 ° C., 1.9 mol / l 1 L of an aqueous aluminum sulfate solution and an aqueous sodium hydroxide solution were added over 190 minutes while simultaneously adjusting the pH to 8.5 ± 0.2. Next, after aging for 60 minutes, diluted sulfuric acid was added to adjust the pH to 7.0, followed by filtration, washing with water, and drying to obtain magnetic iron oxide particles surface-treated with Al.

The obtained magnetic iron oxide particles had a BET specific surface area of 7.4 m ² / g, an Al amount of 1.68%, and an electric resistance value RM _{100 at} an applied voltage of 100 V of 7.1 × 10 ⁹ Ω · cm, When the applied voltage is 10 V, the electric resistance value RM ₁₀ is 8.2 × 10 ⁹ Ω · cm, RM ₁₀₀ / RM ₁₀ is 0.87, the saturation magnetization is 83.8 Am ² / kg, and the adsorbed water amount Ma _0.9 is It was 7.2 mg / g.

Iron oxide 5
A magnetic iron oxide particle powder was obtained in the same manner as the iron oxide 1 except that an aluminum sulfate aqueous solution and a magnesium sulfate aqueous solution were mixed and added.

Iron oxide 6
A magnetic iron oxide particle powder was obtained under the conditions shown in Table 2 by adding a titanyl sulfate aqueous solution in place of the aluminum sulfate aqueous solution.

Iron oxide 7
A magnetic iron oxide particle powder was obtained under the conditions shown in Table 2 by adding a sodium silicate aqueous solution in place of the aluminum sulfate aqueous solution.

Iron oxide 8
<Method for producing magnetic iron oxide particles>
100 l of a slurry containing 90 g / l of Fe ₃ O ₄ iron oxide core particles A having a spherical shape and an average particle diameter of 0.24 μm was adjusted to pH 11 by adding a sodium hydroxide solution at a temperature of 90 ° C., and then 1.9 mol / l. After adding 3.5 l of an aluminum sulfate aqueous solution and stirring, 0.3 l of a 1.1 mol / l magnesium sulfate solution was added and mixed for 20 minutes, then the pH was adjusted to 9.0 and mixed for 5 minutes. Then, dilute sulfuric acid was added to adjust the pH to 7.0, followed by filtration, washing with water and drying to obtain magnetic iron oxide particles surface-treated with Al and Mg.

Iron oxide 14
80 L of a slurry containing 70 g / l of Fe ₃ O ₄ iron oxide core particles A having a spherical shape and an average particle diameter of 0.24 μm is 6.9 L of an aluminum sulfate aqueous solution of 0.5 mol / l at a temperature of 80 ° C. and 1.5 mol / l. After adding 4.6 liters of ferrous sulfate aqueous solution and sodium hydroxide solution to adjust to pH 9.0, 80 liters of air was passed through every minute to terminate the oxidation reaction, followed by filtration, washing with water and drying. Magnetic iron oxide particles having an iron oxide layer were obtained.

Iron oxide 15
20 l of an aqueous ferrous sulfate solution containing 1.6 mol / l Fe2 +, 20.8 l of a 1.5 mol / l sodium hydroxide solution and 4 l of a 0.4 mol / l sodium carbonate solution were mixed with 80 l of air at a temperature of 90 ° C. And the oxidation reaction was terminated by carrying out an oxidation reaction. The slurry was adjusted to pH 9.0 by adding 1.2 l of 0.5 mol / l aluminum sulfate aqueous solution, 0.75 l of 1.6 mol / l first sulfuric acid aqueous solution and sodium hydroxide aqueous solution. 80 l of air per minute was vented again to terminate the oxidation reaction, followed by filtration, washing with water and drying to obtain tetrahedral magnetic iron oxide particles.

Iron oxide 2-4, 9-13
A magnetic iron oxide particle powder was obtained in the same manner as in Example 1 except that the production conditions of the magnetic particle powder were variously changed.

  Various properties of the magnetic iron oxide core particles are shown in Table 1, and the production conditions of the magnetic iron oxide particles are shown in Table 2. Table 3 shows various characteristics of the obtained magnetic iron oxide particle powder.

<Manufacture of spherical magnetic composite particles: lipophilic treatment of magnetic iron oxide particles>
After 1000 g of magnetic iron oxide particles of iron oxide 1 were charged into the flask and sufficiently stirred, 7.0 g of a silane coupling agent having an epoxy group (trade name: KBM-403 manufactured by Shin-Etsu Chemical Co., Ltd.) was added, and about 100 The temperature was raised to 0 ° C. and mixed and stirred well for 30 minutes to obtain spherical magnetite particle powder coated with the coupling agent.

Example 1
<Production example of spherical magnetic composite particles>
Phenolic resin 10 parts by weight 37% formalin 15 parts by weight Iron oxide 1 magnetic iron oxide particles powder subjected to lipophilic treatment 100 parts by weight 25% ammonia water 3 parts by weight Water 13 parts by weight The above materials are placed in a flask and stirred at 250 rpm. The mixture was heated to 85 ° C. over 60 minutes while stirring at a speed, and then reacted and cured at the same temperature for 120 minutes to produce composite particles composed of magnetic iron oxide particles and a cured phenol resin.

  Next, after cooling the content in the flask to 30 ° C., the supernatant was removed, and the precipitate in the lower layer was washed with water and then air-dried. Next, this was dried at 150 to 200 ° C. under reduced pressure (5 mmHg or less) to obtain spherical magnetic composite particles for magnetic core particles.

The obtained spherical magnetic composite particles have an average particle diameter of 32 μm, a specific gravity of 3.72 g / cm ³ , a saturation magnetization value of 74.1 Am ² / kg, and an electric resistance value R ₁₀₀ of 1.100 when applied voltage is 100V. The electric resistance value R _{300 at} 3 × 10 ¹¹ Ω · cm and an applied voltage of 300 V is 4.9 × 10 ¹⁰ Ω · cm, R ₃₀₀ / R ₁₀₀ is 0.38, and the adsorbed water amount Ma _0.9 is 5. It was 3 mg / g.

  Next, after cooling the content in the flask to 30 ° C., the supernatant was removed, and the precipitate in the lower layer was washed with water and then air-dried. Next, this was dried at 150 to 200 ° C. under reduced pressure (5 mmHg or less) to obtain a magnetic carrier composed of spherical magnetic composite particles.

Examples 2-7, Comparative Examples 1-8
A magnetic carrier was obtained in the same manner as in Example 1 except that the production conditions of the magnetic carrier were variously changed.

  Table 4 shows the production conditions for the magnetic carrier comprising the obtained spherical magnetic composite particles, and Table 5 shows the characteristics of the magnetic carrier.

  As shown in the examples of Table 5, the spherical magnetic composite particles according to the present invention have a sufficient electric resistance, and since the voltage dependency of the electric resistance is small, it is suitable as a magnetic carrier for an electrophotographic developer. is there.

Example 8 <Production of resin-coated magnetic carrier>
In a Henschel mixer, 1 kg of the spherical magnetic composite particle powder of Example 1 and 9 g of a silicone resin (trade name: KR251, manufactured by Shin-Etsu Chemical Co., Ltd.) were added as solids in a Henschel mixer, and the temperature was raised to 200 ° C. with stirring. The mixture was heated and stirred at the same temperature for 1 hour to form a resin coating layer made of a silicone resin.

The obtained magnetic carrier comprising spherical magnetic composite particles having a resin coating layer has an average particle diameter of 32 μm, a specific gravity of 3.50 g / cm ³ , a saturation magnetization value of 73.4 Am ² / kg, and an applied voltage of 100 V. The electric resistance value R ₁₀₀ of the electrode was 4.7 × 10 ¹² Ω · cm, and the electric resistance value R ₃₀₀ when the applied voltage was 300 V was 3.6 × 10 ¹² Ω · cm.

  Table 6 shows the production conditions and various properties of the resin-coated spherical magnetic composite particles, and Table 7 shows the evaluation results of the magnetic carrier printing durability.

Examples 9-14, Comparative Examples 9-16
A magnetic carrier for an electrophotographic developer in which a surface coating layer is formed on a spherical magnetic composite particle in the same manner as in Example 11 except that various types of spherical magnetic composite particles, types of resin, and resin coating amount are changed. Obtained.

  Table 6 shows the production conditions and various properties of the resin-coated spherical magnetic composite particles, and Table 7 shows the evaluation results of the magnetic carrier printing durability.

  As shown in Table 7, since the magnetic carrier according to the present invention is excellent in gradation even after printing 50,000 sheets, the voltage dependence of the magnetic carrier is small and the voltage dependence is maintained for a long time. It was confirmed that the magnetic carrier had excellent image characteristics.

Since the magnetic carrier for an electrophotographic developer according to the present invention is composed of magnetic iron oxide particles having a high electric resistance and spherical magnetic composite particles dispersed in a binder resin, it has an appropriate electric resistance and an electric resistance is applied. Since it is stable against voltage, it is suitable as a magnetic carrier for electrophotographic development.

Claims (7)

An electrophotographic development magnetic carrier comprising magnetic iron oxide particles from the spherical magnetic composite particles obtained by dispersing in a binder resin, the electrical resistance value R ₁₀₀ when the applied voltage 100V of the magnetic carrier for electrophotographic developer of 1 × 10 ⁸ Ω · cm to 1 × 10 ¹⁴ Ω · cm, and the electric resistance value R ₃₀₀ when the applied voltage is 300 V is 0.1 ≦ R ₃₀₀ / R ₁₀₀ ≦ 1
A magnetic carrier for electrophotographic development characterized by the above. 2. The magnetic carrier for electrophotographic development according to claim 1, wherein the magnetic iron oxide particles have an average particle diameter of 0.05 [mu] m to 2.0 [mu] m and the surface of the magnetic iron oxide particles is Al, Mg, Mn, Zn, Ni, Cu , Ti, and Si are coated with a compound composed of one or more elements, the abundance of the elements is 0.3 to 4.5% by weight, and the applied voltage of the magnetic iron oxide particles A magnetic carrier for an electrophotographic developer having an electric resistance value RM100 of 1 × 10 ⁸ Ω · cm or more at ₁₀₀ V. The magnetic carrier for an electrophotographic developer according to claim 1 or 2, wherein the water adsorption amount Ma _0.9 of the magnetic iron oxide particles is 15 mg / g or less. When the applied voltage of the magnetic iron oxide particles is 10 V, the electrical resistance value RM ₁₀ is
0.5 ≦ RM ₁₀₀ / RM ₁₀ ≦ 1
The magnetic carrier for an electrophotographic developer according to any one of claims 1 to 3. The magnetic carrier for an electrophotographic developer according to any one of claims 1 to 4, wherein the binder resin is a phenol resin. The magnetic carrier for an electrophotographic developer according to any one of claims 1 to 5, wherein a surface coating layer mainly composed of a resin is formed on the surface of the spherical magnetic composite particles. A two-component developer using the magnetic carrier for an electrophotographic developer according to any one of claims 1 to 6.

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