JP5170417B2 - Magnetic carrier for electrophotographic developer and two-component developer - Google Patents

Description

  The present invention is an electrophotographic developer magnetic carrier having excellent durability, having stable charging characteristics against environmental fluctuations such as temperature and humidity, and reducing the spent toner on the magnetic carrier. A magnetic carrier for developer and a two-component developer having the magnetic carrier for electrophotographic developer and a toner are provided.

  As is well known, in electrophotography, a photoconductive substance such as selenium, OPC (organic semiconductor), or a-Si is used as a photoconductor, 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 two-component 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 magnetic force is increased. The toner is conveyed to a developing region near the surface of the photosensitive member on which a latent image is formed through a developing sleeve using a magnet.

  The electrophotographic method is widely used in copying machines or printers. In recent years, the demand for higher image quality has been increasing in the market, and in this technical field, as the image quality is improved, the particle size of the developer and the speed of the device have increased, and the stress on the developer has increased. Maintaining developer properties is a major problem.

  Also, along with market demands such as personalization and space saving, miniaturization of electrophotographic image forming apparatuses such as copiers and printers has been promoted. Along with miniaturization of the apparatus, miniaturization of each unit has progressed, and there is a demand for maintenance of developer characteristics with a small developer, that is, with a small amount of developer.

  In general, in order to reduce power consumption in a small apparatus, a toner that can be sufficiently fixed with a small fixing energy, that is, a so-called low-temperature fixing toner is required. Energy savings can be achieved with toners that have low temperature fixing properties such as by using low molecular weight resins. However, due to the heat and pressure generated by repeated multiple developments over a long period of time,・ Since toner is spent on the surface of the carrier during continuous use at high humidity, or the carrier is firmly adhered to each other in a form in which the toner is caught between the spent parts, causing a phenomenon such as causing blocking of the developer. The frictional charge amount of the agent is changed, and the image density is changed or fog is generated.

  In order to prevent the toner from becoming spent on the carrier surface, conventionally, various methods for coating the carrier surface with various resins have been proposed. For example, a carrier core material particle surface coated with a release resin such as a fluororesin or a silicone resin is known. Such a coated carrier not only has a function of controlling the charge amount and resistance, but also has a surface coated with a low surface energy substance, so that it is difficult for the toner to become spent during development, resulting in a stable charge amount. The life of the developer can be extended.

  Conventionally, as a carrier constituting a two-component developer, an iron powder carrier, a ferrite carrier, a binder type carrier in which magnetic particle powder is dispersed in a binder resin, and a coat type carrier obtained by coating a magnetic material with a coating resin Is well known.

The iron powder carrier and the ferrite carrier are usually used by coating the particle surface with a resin. 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. Since it is as large as 5 g / cm ³ , a large driving force is required for stirring in the developing machine, and mechanical wear is large, resulting in spent toner, deterioration of chargeability of the carrier itself, and damage to the photoreceptor. Cheap. Furthermore, it is difficult to say that the adhesion between the particle surface and the coating resin is good, and the coating resin gradually peels off during use, causing a change in chargeability, resulting in problems such as image disturbance and carrier adhesion. End up.

However, the magnetic material-dispersed carrier comprising spherical composite particles comprising magnetic particles and a phenol resin described in JP-A-2-220068 and JP-A-8-6303 has a true specific gravity of ³ to 4 g / cm ³ . Since the true specific gravity is smaller than that of the iron powder carrier and the ferrite carrier, the energy at the time of collision between the toner and the carrier is reduced, which is advantageous for the toner spent. Furthermore, it is excellent in adhesiveness with the coating resin, and the problem that the coating resin peels off during use hardly occurs.

  A magnetic material-dispersed carrier produced by a polymerization method tends to have a high moisture adsorption amount due to a large number of fine irregularities on the surface and internal pores as compared with a ferrite carrier. In particular, in the case of a polymerization type carrier obtained by polymerization in an aqueous medium, the monomer to be polymerized has a high water affinity and is in contact with water in the production process, so a hydrophobic binder resin is used. There is a tendency for the amount of water adsorption to increase as compared with a magnetic material dispersed carrier produced by a pulverization method or a magnetic material dispersed carrier polymerized in a hydrophobic solvent. In particular, fogging and toner scattering may occur due to an extremely low charge under high temperature and high humidity.

  In addition, the magnetic substance dispersion type carrier has a large difference in the amount of moisture adsorbed at a certain relative vapor pressure in the adsorption process from low humidity to high humidity and in the desorption process from high humidity to low humidity. There is a problem that it is easy to receive and the charging ability is not stable.

  As described above, there are various characteristics required for magnetic carriers, but it is required to stably impart an appropriate charge amount and charge distribution to the toner over a long period of time, and the carrier has suitable electrical properties. In addition, it is important that resistance to environmental fluctuations such as temperature and humidity, impact resistance and friction resistance to toner, carrier, and development member are excellent, and that charging ability is not changed even in long-term use.

  Conventionally, it is known to control the moisture adsorption amount of a magnetic carrier (Patent Documents 1 and 2).

JP 2001-75315 A JP 2007-17838 A

  In Patent Document 1, it is described that humidified nitrogen is allowed to flow when the resin is coated on the core particles to adjust the amount of water. However, if the amount of water adsorbed due to environmental changes can be sufficiently reduced, Is hard to say.

  Patent Document 2 describes that the amount of adsorbed moisture of the magnetic carrier is controlled by the average particle size of the magnetic particles contained in the core particles and the content of the titanium compound. It is difficult to say that the change in adsorption amount can be made sufficiently small.

（式中、Ｒ１、Ｒ２、Ｒ３、Ｒ４及びＲ５のうち、少なくとも１ヶ所が炭素数１〜４個のアルキル基又は炭素数１〜４個のアルキル基の一部または全部の水素原子が塩素原子、臭素原子で置換されたハロゲン化アルキル基であり、残部は水素原子である。） Therefore, the present invention uses phenol and a cured phenol resin composed of one or more compounds represented by the following chemical formula 2 as the binder resin of the composite particles, and is represented by phenol and chemical formula 2 below. By reducing the ratio of phenol to the sum of one or two or more compounds to 10 to 90 mol%, the water adsorption amount of the magnetic carrier for an electrophotographic developer coated on the surface of the composite particle is reduced, In addition, it is an object of the present invention to provide a magnetic carrier for an electrophotographic developer that can maintain stable charging characteristics by reducing a change in the amount of water adsorbed due to environmental changes.

(In the formula, at least one of R1, R2, R3, R4 and R5 is an alkyl group having 1 to 4 carbon atoms or a part or all of hydrogen atoms of an alkyl group having 1 to 4 carbon atoms is a chlorine atom. A halogenated alkyl group substituted with a bromine atom, and the remainder is a hydrogen atom.)

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

（式中、Ｒ１、Ｒ２、Ｒ３、Ｒ４及びＲ５のうち、少なくとも１ヶ所が炭素数１〜４個のアルキル基又は炭素数１〜４個のアルキル基の一部または全部の水素原子が塩素原子、臭素原子で置換されたハロゲン化アルキル基であり、残部は水素原子である。） That is, the present invention relates to a magnetic carrier for an electrophotographic developer in which the surface of spherical composite particles having an average particle diameter of 1 to 100 μm composed of at least ferromagnetic iron oxide fine particles and a binder resin is coated, wherein the binder resin is phenol and The ratio of phenol to the sum of phenol and one or more compounds represented by the following chemical formula 3 is a cured phenol resin composed of one or more compounds represented by the following chemical formula 3 There was 10~90mol%, a magnetic carrier for an electrophotographic developer, wherein the Henry's law constant, _{K D,} the water adsorption of the magnetic carrier is a 0.30~1.50mg / g / kPa (present Invention 1).

(In the formula, at least one of R1, R2, R3, R4 and R5 is an alkyl group having 1 to 4 carbon atoms or a part or all of hydrogen atoms of an alkyl group having 1 to 4 carbon atoms is a chlorine atom. A halogenated alkyl group substituted with a bromine atom, and the remainder is a hydrogen atom.)

  The present invention provides the magnetic carrier for an electrophotographic developer according to claim 1, wherein the coating resin is one or more selected from silicone resins, fluorine resins, acrylic resins, and styrene-acrylic resins. (Invention 2).

  Further, the present invention is a two-component developer comprising the carrier of the first or second aspect and a toner (Invention 3).

  The magnetic carrier according to the present invention can maintain stable charging characteristics by reducing the amount of water adsorbed on the magnetic carrier and reducing the amount of adsorbed water accompanying environmental changes, so that the electrophotographic developer can be maintained. Suitable as a magnetic carrier.

  The two-component developer according to the present invention is suitable as a developer corresponding to high image quality and high speed because the magnetic carrier used is excellent in durability.

  Hereinafter, the present invention will be described in detail.

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

Magnetic carrier according to the present invention, Henry's Law constant, _{K D,} in water adsorption is important to meet the 0.30~1.50mg / g / kPa.

  The Henry's law constant in the water adsorption of the magnetic carrier according to the present invention is obtained by a binary sorption model proposed by Barrer et al. And Michaels et al.

In other words, the adsorption amount C of adsorbate into the solid polymer at a pressure, the amount C _D according to Henry's Law, the amount C _H is expressed as the sum of (Equation 1 according to the adsorption theory of Langmuir, References: Polymer Society Hen, Polymer and water, Kyoritsu Shuppan Co., Ltd., 1995, p.

<Equation 1>
C = C _D + C _H = K _D p + C _H 'bp / (1 + bp)
K _D : Henry's law constant (mg / g / kPa)
C _H ': Langmuir capacity constant (mg / g)
b: Langmuir affinity constant (kPa ⁻¹ )
p: Pressure (kPa)

Among the parameters of the equation, Henry's Law constant, K _D, is a parameter indicating the solubility, i.e. penetration into solid interior of the adsorbate, Langmuir volume constant C _{H 'is} adsorbate to the solid surface in the monomolecular layer adsorption Since the Langmuir affinity constant b is defined by the ratio of the condensation rate constant and the evaporation rate constant on the solid surface of the adsorbate, it is a parameter indicating the strength of the interaction between the adsorbate and the solid.

Here, as the value of the Henry's Law constant, K _D, in water adsorption is small, the water has a hard structure adsorption, and means that the adsorption amount change of water to environmental variation is small. In other words, the fact that Henry's Law constant, _{K D,} the water absorption amount of the magnetic carrier in the present invention is 0.3~1.5mg / g / kPa holds a moderate moisture, and water due to environmental changes By reducing the change in the amount of adsorption, stable charging characteristics can be maintained. That is, charge-up and fogging can be suppressed in a low-humidity environment, and fogging and toner scattering due to a decrease in charge can be suppressed in a high-humidity environment.

If Henry's Law constant, K _D, the water adsorption of the magnetic carrier of the present invention is less than 0.30 mg / g / kPa, moderate charge-up because no amount of adsorbed moisture is likely to occur, causing deterioration in image quality. On the other hand, if the Henry's Law constant, K _D, the water adsorption of the magnetic carrier is more than 1.50 mg / g / kPa, the charge amount tends to occur stably difficult toner scattering due to environmental fluctuations. Specifically, in an environmental change from low humidity to high humidity, the charge amount suddenly decreases and toner scattering tends to occur, and in an environmental change from high humidity to low humidity, fog may be deteriorated. Preferably it is 0.40-1.30 mg / g / kPa, More preferably, it is 0.60-1.25 mg / g / kPa.

The amount of water adsorbed in the present invention is measured by a device that reaches solid-gas equilibrium under conditions where only the target gas (water in the present invention) exists, and measures the solid mass and vapor pressure at this time. be able to. As such an apparatus, for example, an automatic vapor adsorption amount measuring apparatus (BELSORP-aqua ³ ; manufactured by Nippon Bell Co., Ltd.) can be mentioned. In the examples described later, the amount of water adsorbed on the composite particles and the magnetic carrier at 25 ° C. is measured by the apparatus.

  The water content of the magnetic carrier according to the present invention is preferably 0.10 to 0.50% by weight. When the water content of the magnetic carrier is less than 0.10% by weight, there is no appropriate amount of adsorbed water, so that charge-up is likely to occur, causing image quality degradation. On the other hand, if it exceeds 0.50% by weight, the amount of charge is difficult to stabilize due to environmental fluctuations, and toner scattering tends to occur. More preferably, it is 0.10 to 0.45 weight%.

  The content of the ferromagnetic iron oxide fine particle powder in the magnetic carrier according to the present invention is preferably 80 to 99% by weight with respect to the magnetic carrier. When the content of the ferromagnetic iron oxide fine particle powder is less than 80% by weight, the resin content increases and large particles are 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.

  The shape factors SF1 and SF2 of the magnetic carrier according to the present invention are preferably 100 to 120 and 100 to 120, respectively. More preferably, the shape factor SF1 is 100 to 110, and the shape factor SF2 is 100 to 110.

  The shape factor SF1 indicates the degree of roundness of the particles, and the shape factor SF2 indicates the degree of unevenness of the particles. Therefore, when the shape factor SF1 moves away from a circle (spherical shape), the value of SF1 increases and the unevenness of the surface unevenness increases. The value of SF2 also increases. Each value becomes a value close to 100 as it approaches a perfect circle (sphere).

  When the magnetic carrier approaches a true sphere and the surface irregularities are small, the magnetic brush in the development region becomes more uniform, so that carrier adhesion is improved. In addition, when the shape factor SF1 of the magnetic carrier exceeds 120 or SF2 exceeds 120, the resin coating layer does not become uniform, and the carrier charge amount and resistance non-uniformity are likely to occur. High definition images cannot be obtained. In addition, since the adhesion strength between the resin coating layer and the core particles tends to decrease, sufficient durability cannot be obtained.

  The average particle diameter of the magnetic carrier according to the present invention is 1 to 100 μm. When the average particle diameter is less than 1 μm, secondary aggregation is likely to occur, and when it exceeds 100 μm, the mechanical strength is weak and a clear image is obtained. You will not be able to get. More preferably, it is 10-70 micrometers.

The bulk density of the magnetic carrier of the present invention is preferably 2.5 g / cm ³ or less, more preferably 1.0 to 2.0 g / cm ^3. The specific gravity is preferably 2.5 to 4.5, more preferably 3.0 to 4.0.

The electric resistance value of the magnetic carrier according to the present invention is preferably 1.0 × 10 ^{8 to} 1.0 × 10 ¹⁵ Ωcm, more preferably 1.0 × 10 ^{9 to} 5.0 × 10 ¹⁴ Ωcm, and even more. Preferably, it is 1.0 × 10 ^{9 to} 1.0 × 10 ¹⁴ Ωcm.

The saturation magnetization value of the magnetic carrier according to the present invention is preferably 20 to 80 Am ² / kg (20 to 80 emu / g), more preferably 40 to 80 Am ² / kg (40 to 80 emu / g).

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

（式中、Ｒ１、Ｒ２、Ｒ３、Ｒ４及びＲ５のうち、少なくとも１ヶ所が炭素数１〜４個のアルキル基又は炭素数１〜４個のアルキル基の一部または全部の水素原子が塩素原子、臭素原子で置換されたハロゲン化アルキル基であり、残部は水素原子である。） The magnetic carrier for an electrophotographic developer according to the present invention comprises phenol and an aldehyde composed of one or more compounds represented by phenol and the following formula 4 in an aqueous medium in the presence of a basic catalyst. The composite particles (core material particles) are obtained by reacting the phenols and aldehydes in the presence of ferromagnetic iron oxide fine particle powder to form composite particles (core material particles). It can be obtained by resin coating.

(In the formula, at least one of R1, R2, R3, R4 and R5 is an alkyl group having 1 to 4 carbon atoms or a part or all of hydrogen atoms of an alkyl group having 1 to 4 carbon atoms is a chlorine atom. A halogenated alkyl group substituted with a bromine atom, and the remainder is a hydrogen atom.)

  In addition, when producing | generating composite particle | grains by the said method, alcohol can be used in an aqueous medium. This is added for the purpose of controlling the sphericity of the composite particles.

（式中、Ｒ１、Ｒ２、Ｒ３、Ｒ４及びＲ５のうち、少なくとも１ヶ所が炭素数１〜４個のアルキル基又は炭素数１〜４個のアルキル基の一部または全部の水素原子が塩素原子、臭素原子で置換されたハロゲン化アルキル基であり、残部は水素原子である。） Examples of phenols used in the present invention include compounds represented by the following chemical formula 5 in addition to phenol. Specifically, alkylphenols such as m-cresol, p-cresol, p-tert-butylphenol, o-propylphenol, and halogenated phenols in which part or all of the alkyl groups are substituted with chlorine atoms or bromine atoms. Examples thereof include compounds having a phenolic hydroxyl group.

(In the formula, at least one of R1, R2, R3, R4 and R5 is an alkyl group having 1 to 4 carbon atoms or a part or all of hydrogen atoms of an alkyl group having 1 to 4 carbon atoms is a chlorine atom. A halogenated alkyl group substituted with a bromine atom, and the remainder is a hydrogen atom.)

（式中、Ｒ１、Ｒ２、Ｒ３、Ｒ４及びＲ５のうち、少なくとも１ヶ所が炭素数１〜４個のアルキル基又は炭素数１〜４個のアルキル基の一部または全部の水素原子が塩素原子、臭素原子で置換されたハロゲン化アルキル基であり、残部は水素原子である。） It is preferable that the ratio of phenol is 10 to 90 mol% with respect to the total amount of the binder resin used in the present invention, that is, phenol and one or more compounds represented by the following chemical formula 6. When the ratio of phenol is less than 10 mol%, it is difficult to produce particles or the resin is hard to proceed, so that the strength of the obtained particles is weakened. When it exceeds 90 mol%, excessive moisture is retained, and stable charging characteristics accompanying environmental changes cannot be obtained. More preferably, it is 20-80 mol%.

(In the formula, at least one of R1, R2, R3, R4 and R5 is an alkyl group having 1 to 4 carbon atoms or a part or all of hydrogen atoms of an alkyl group having 1 to 4 carbon atoms is a chlorine atom. A halogenated alkyl group substituted with a bromine atom, and the remainder is a hydrogen atom.)

  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, and when the molar ratio of aldehydes to phenols is less than 1, it is difficult to form particles or the resin is hardened. Since it does not proceed easily, the strength of the obtained 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 normal resol resin production 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.

  The ferromagnetic iron oxide fine particles in the present invention are magnetoplumbite type iron oxide fine particle powder (strontium ferrite particle powder, barium ferrite particle powder), magnetite particle powder, etc., preferably magnetite particle powder.

  The average particle size of the ferromagnetic iron oxide fine particle powder in the present invention is preferably 0.05 to 1.0 μm, more preferably 0.1 to 0.5 μm.

  The particle shape of the ferromagnetic iron oxide fine particle powder in the present invention is spherical, plate-shaped, hexahedral, octahedral, etc., preferably spherical.

  In the present invention, non-magnetic particle powder such as hematite may be used in combination with the ferromagnetic iron oxide fine particle powder.

Generally, the ferromagnetic iron oxide fine particle powder contains a slight amount of impurities derived from the starting material. Examples of such a component include SiO ₂ , Ca, Mn, Na, Mg, and sulfate ions. And anionic components such as chloride ions. Since these are factors that hinder the environmental stability of the charging characteristics, it is usually preferable that the content of impurities in the ferromagnetic iron oxide fine particle powder is as high as 2.0% or less.

  It is desirable that the ferromagnetic iron oxide fine 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.

  In the oleophilic treatment, the ferromagnetic iron oxide fine particles are dispersed in an aqueous solvent containing a surfactant or a method of treating the ferromagnetic iron oxide fine particles with a coupling agent such as a silane coupling agent or a titanate coupling agent, A method of adsorbing a surfactant on the particle surface is preferred.

  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. As the silane coupling agent having an amino group or an epoxy group, the silane coupling agent having an amino group or the silane coupling agent having an epoxy group may be used.

  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, a commercially available surfactant can be used, and it is desirable to have a ferromagnetic iron oxide fine particle or a functional group capable of bonding with a hydroxyl group on the particle surface, and the ionicity is cationic or anionic. Is 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 ferromagnetic iron oxide fine particles.

（式中、Ｒ１、Ｒ２、Ｒ３、Ｒ４及びＲ５のうち、少なくとも１ヶ所が炭素数１〜４個のアルキル基又は炭素数１〜４個のアルキル基の一部または全部の水素原子が塩素原子、臭素原子で置換されたハロゲン化アルキル基であり、残部は水素原子である。） The amount of the ferromagnetic iron oxide fine particles to be coexisted in the reaction of the phenol and one or more of the compounds represented by the following chemical formula (7) with an aldehyde in the presence of a basic catalyst is determined as follows: The amount is preferably 75 to 99% by weight based on the total amount of fine particles, phenols and aldehydes, and more preferably 78 to 99% by weight considering the strength of the magnetic carrier to be produced.

(In the formula, at least one of R1, R2, R3, R4 and R5 is an alkyl group having 1 to 4 carbon atoms or a part or all of hydrogen atoms of an alkyl group having 1 to 4 carbon atoms is a chlorine atom. A halogenated alkyl group substituted with a bromine atom, and the remainder is a hydrogen atom.)

  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 composite particles having 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 composite particles in which the ferromagnetic iron oxide fine particles are dispersed in the binder resin and the ferromagnetic iron oxide fine particles are exposed on the particle surface. can get.

  The aqueous dispersion containing the spherical composite particles is filtered, solids and liquids are separated according to a conventional method of centrifugation, and then washed and dried to obtain composite particles.

The average particle size of the composite particles in the present invention is preferably 1 to 100 μm, the bulk density is preferably 2.5 g / cm ³ or less, the specific gravity is preferably 2.5 to 4.5, and the saturation magnetization value is 20 to 80 Am ^2. / kg (20~80emu / g) are preferred, the electrical resistance value is preferably ^{1 × 10 8 ~1 × 10 15} Ωcm, Henry's law constant, _{K D,} in water adsorption is 0.30~1.50mg / g / kPa The water content is preferably 0.10 to 0.50% by weight.

  The contact angle of the composite particles (core particles) in the present invention is preferably 98 to 120 °, more preferably 100 to 115 °. If the contact angle of the composite particles is less than 98 °, excessive moisture may be retained, and stable charging characteristics accompanying environmental changes may not be obtained. In the configuration of the present invention, it is industrially difficult to make the contact angle larger than 120 °.

  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.

  In the magnetic carrier according to the present invention, the particle surfaces of the composite particles (core material particles) are preferably coated with a silicone resin or a fluorine resin. By coating the particle surface with the resin having a low surface energy, toner spent can be suppressed.

  As the silicone resin, a condensation reaction type silicone resin is suitable, and as the fluorine resin, polyfluorinated acrylate resin, polyfluorinated methacrylate resin, polyfluorinated vinylidene resin, polytetrafluoroethylene resin, polyhexafluoropropylene resin and A copolymer obtained by combining the above resins is preferable.

  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 composite particles (core 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 core particles, the spherical composite particles and the resin are mixed using a well-known spray dryer, a method of spraying the resin onto the spherical composite particles, a Henschel mixer, a high speed mixer, or the like. What is necessary is just to perform by the method of dry mixing, the method of impregnating spherical composite particles in a solvent containing a resin, and the like.

  Next, the two-component developer according to 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 constituents, and a release agent, 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>
The important point in the present invention is that in the magnetic carrier for an electrophotographic developer, the surface of spherical composite particles having an average particle diameter of 1 to 100 μm composed of at least ferromagnetic iron oxide fine particles and a binder resin is coated with the binder resin. A ratio of phenol to the sum of phenol and one or more compounds represented by the following chemical formula 8, which is a cured phenol resin composed of one or more compounds represented by phenol and the following chemical formula 8 There was 10~90mol%, Henry's law constant, _{K D,} the water adsorption of the magnetic carrier is that it is a 0.30~1.50mg / g / kPa.

（式中、Ｒ１、Ｒ２、Ｒ３、Ｒ４及びＲ５のうち、少なくとも１ヶ所が炭素数１〜４個のアルキル基又は炭素数１〜４個のアルキル基の一部または全部の水素原子が塩素原子、臭素原子で置換されたハロゲン化アルキル基であり、残部は水素原子である。）

(In the formula, at least one of R1, R2, R3, R4 and R5 is an alkyl group having 1 to 4 carbon atoms or a part or all of hydrogen atoms of an alkyl group having 1 to 4 carbon atoms is a chlorine atom. A halogenated alkyl group substituted with a bromine atom, and the remainder is a hydrogen atom.)

  In the present invention, a hardened phenol resin composed of phenol and one or more compounds represented by the chemical formula 8 is used as the binder resin of the composite particle, and the phenol and the chemical formula 8 are used. By setting the ratio of phenol to the sum of one or two or more compounds to 10 to 90 mol%, the amount of water adsorbed on the magnetic carrier is reduced, and the change in the amount of adsorbed water accompanying an environmental change is reduced. It became possible.

As a result, stable charging characteristics can be maintained, charge-up and fogging can be suppressed in a low-humidity environment, and fogging and toner scattering due to a decrease in charging can be suppressed in a high-humidity environment. The inventor believes that.

  Representative examples of the present invention are as follows.

Of the present invention, Henry's Law constant, _{K D,} in water adsorption, automatic vapor adsorption measuring apparatus; using (BELSORP-aqua ³ manufactured by Nippon Bell Co.), a complex of water adsorption of particles and the magnetic carrier at 25 ° C. taking measurement.

The shape factors SF1 and SF2 of the magnetic carrier were measured according to the following procedure.
SF1 and SF2 indicating shape factors are, for example, randomly sampled 100 carrier particle images magnified 300 times using a scanning electron microscope (manufactured by Hitachi, Ltd. (S-4800)), and image information thereof. Is introduced into, for example, an image analysis apparatus (Luzex AP) manufactured by Nireco Co., Ltd. via an interface and analyzed, and values obtained from the following equations are defined as shape factors SF1 and SF2.

SF1 = (absolute maximum length of particle) ² / (projected area of particle) × (π / 4) × 100
SF2 = (peripheral length of particle) ² / (projected area of particle) × (1 / 4π) × 100

  The shape factor SF1 indicates the degree of roundness of the particles, and the shape factor SF2 indicates the degree of unevenness of the particles. Therefore, when the shape factor SF1 moves away from a circle (spherical shape), the value of SF1 increases and the unevenness of the surface unevenness increases. The value of SF2 also increases. Each value becomes a value close to 100 as it approaches a perfect circle (sphere).

  The average particle diameter of the particle powder was measured with a laser diffraction particle size distribution analyzer LA750 (manufactured by Horiba, Ltd.) and indicated as a value based on volume. The particle morphology of the particles was observed with a scanning electron microscope (manufactured by Hitachi, Ltd. (S-4800)).

  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 is indicated by a value measured with a multi-volume density meter 1305 type (Micromeritics / manufactured by Shimadzu Corporation).

  The bulk density was measured according to the method described in JIS K5101.

  The electric resistance value (volume specific resistance value) is a value measured with a high resistance meter 4339B (manufactured by Yokogawa Hewlett Packard).

  The water content is measured by the Karl Fischer coulometric titration method. As a measuring instrument, a trace moisture measuring device AQ-2100 manufactured by Hiranuma Sangyo Co., Ltd. was used. 1 g of a sample that has been conditioned for 24 hours or more in a 24 ° C., 60% RH environment is precisely weighed into a glass sample tube and covered with aluminum foil. (At this time, in order to correct the amount of moisture contained in the air, an empty sample tube with a similar lid is prepared.)

  Sent from a moisture vaporizer (EV-2010, manufactured by Hiranuma Sangyo Co., Ltd.) connected to a trace moisture analyzer AQ-2100 under conditions of a heating temperature of 150 ° C. and a carrier gas (nitrogen gas) flow rate of 100 ml / min. The water was titrated under conditions of INTERVAL = 30 seconds and TIMER = 1 minute. The generation liquid used was Hydranal Aqualite RS manufactured by Riedel de Haen, and the counter electrode liquid used was Aqualite CN manufactured by Kanto Chemical Co., Inc.

  The contact angle was measured using a WTMY-232A wet tester manufactured by Sankyo Piotech Co., Ltd.

The composite particles are put into a powder measuring cell, and tapping is performed for 1 minute at a tapping speed of 120 times / min using TAP-120 manufactured by Kuramochi Scientific Instruments. This is attached to a measuring device and measured. The weight of the composite particles is set so that the porosity of the powder layer falls within the range of 0.30 to 0.70. The porosity is given by the following equation.
ε = 1−m / (ρ · L · A)
ρ: true density of composite particles (g / cm ³ ),
L: powder layer height (cm)
A: Cell cross-sectional area (cm ² ),
m: Weight of composite particles (g)

  First, the capillary radius of the powder layer is obtained by the air permeation method, and then the pressure inflection point is obtained by the constant flow method. The contact angle of the composite particle is calculated from both of them.

The environmental difference test of the charge amount was performed as follows.
After being left for 1 day at room temperature and normal humidity (24 ° C., 60%), the triboelectric charge is measured. Thereafter, the developer is allowed to stand at high temperature and high humidity (30 ° C., 80%) for 1 day, and the triboelectric charge is measured. As shown in the following formula, the environmental difference in the charge amount was expressed in terms of the change width of the charge amount under normal temperature and normal humidity and the charge amount under high temperature and high humidity, and was performed according to the following evaluation criteria.
Environmental difference of charge amount (%) = (Q _N −Q _H ) / Q _N × 100
Q _N : Charge amount under normal temperature and humidity Q _H : Charge amount under high temperature and humidity

A: Change range between normal temperature and normal humidity and high temperature and high humidity is 0% or more and less than 11% B: Change range between normal temperature and normal humidity and high temperature and high humidity is 11% or more and less than 20% C: Normal temperature and normal humidity and high temperature The change width under high humidity is 20% or more and less than 30% D: The change width between room temperature and normal humidity and high temperature and high humidity is 30% or more and less than 40% E: The change width between normal temperature and normal humidity and high temperature and high humidity is 40 %that's all

  The toner charge amount was measured using a blow-off charge measuring device TB-200 (manufactured by Toshiba Chemical Co., Ltd.) after thoroughly mixing 95 parts by weight of the magnetic carrier and 5 parts by weight of the toner produced by the following method.

(Toner Production Example 1)
Polyester resin 100 parts by weight Copper phthalocyanine colorant 5 parts by weight Charge control agent (quaternary ammonium salt) 4 parts by weight Low molecular weight polyolefin 3 parts by weight Preliminarily mixed with a Henschel mixer, using a twin screw extruder The mixture was melt-kneaded, cooled and then pulverized and classified using a hammer mill to obtain a positively charged blue powder having a weight average particle diameter of 7.1 μm.

  100 parts by mass of the positively charged blue powder and 1 part by weight of hydrophobic silica were mixed with a Henschel mixer to obtain a positively charged cyan toner a.

(Toner Production Example 2)
Polyester resin 100 parts by weight Copper phthalocyanine-based colorant 5 parts by weight Charge control agent (di-tert-butylsalicylic acid zinc compound) 3 parts by weight Wax 9 parts by weight Preliminarily mixed with a Henschel mixer and biaxial extrusion kneading The mixture was melt-kneaded by a machine, cooled and then pulverized and classified using a hammer mill to obtain a negatively chargeable blue powder having a weight average particle size of 7.4 μm.

  100 parts by weight of the negatively charged blue powder and 1 part by weight of hydrophobic silica were mixed with a Henschel mixer to obtain a negatively charged cyan toner b.

<Lipophilic treatment of ferromagnetic iron oxide fine particles: Ferromagnetic iron oxide fine particles A>
After charging 1000 g of spherical magnetite particle powder (average particle size 0.24 μm) into a 500 ml flask and stirring sufficiently well, 7.0 g of a silane coupling agent having an epoxy group (trade name: KBM-403 manufactured by Shin-Etsu Chemical Co., Ltd.) The resulting mixture was heated to about 100 ° C. and mixed and stirred for 30 minutes to obtain spherical magnetite particle powder A coated with a coupling agent.

<Lipophilic treatment of ferromagnetic iron oxide fine particles: Ferromagnetic iron oxide fine particles B>
After charging 1000 g of spherical magnetite particle powder (average particle size 0.31 μm) into a 500 ml flask and stirring well enough, 5.0 g of a silane coupling agent having an amino group (trade name: KBM-602, manufactured by Shin-Etsu Chemical Co., Ltd.) The spherical magnetite particle powder B was obtained by operating under the same conditions as the spherical magnetite particle powder A except for addition and mixing.

<Production of spherical composite particles>
Phenolic resin 5 parts by weight p-cresol 6 parts by weight 37% formalin 17 parts by weight Lipophilic spherical magnetite particle powder A 100 parts by weight 25% ammonia water 3 parts by weight Water 9 parts by weight The above materials are placed in a flask and 250 rpm The mixture was heated to 85 ° C. over 60 minutes while stirring at a stirring speed of, and then reacted and cured at the same temperature for 120 minutes to produce composite particles composed of ferromagnetic iron oxide fine particles and a binder resin.

The chemical formula of p-cresol is as follows.

  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. Subsequently, this was dried at 150-180 degreeC under pressure reduction (5 mmHg or less), and the spherical composite particle A was obtained.

Spherical composite particles A obtained here is the average particle size of 37 [mu] m, a bulk density of 1.86 g / cm ^3, a specific gravity of 3.68 g / cm ^3, a saturation magnetization value 75.7Am ² / kg, the electric resistance value It was 3.4 × 10 ⁹ Ω · cm.

Composite particles B to H:
Same as composite particle A, except that the type and amount of the lipophilic iron oxide fine particles, the type and amount of binder resin, the amount of aldehydes, the amount of basic catalyst and the amount of water were variously changed. The composite particles B to H were obtained by operating under the following conditions. Table 1 shows the specifications of the obtained composite particles.

  Table 2 shows various properties of the obtained composite particles.

Example 1
<Manufacture of magnetic carrier>
In a Henschel mixer, 1 kg of the core material particle A and 10 g of a fluororesin (trade name: FM300, manufactured by Daikin) were added as solids in a Henschel mixer, and the mixture was stirred for 1 hour at a temperature of 50 to 150 ° C. A resin coating layer made of a resin was formed.

Magnetic carrier A thus obtained here is the average particle size of 38 [mu] m, a bulk density of 1.77 g / cm ^3, a specific gravity of 3.58 g / cm ^3, a saturation magnetization value 74.6Am ² / kg, the electrical resistance 7. It was 2 × 10 ¹³ Ω · cm.

  The change rate of the charge amount in the environmental difference test of the characteristics of the magnetic carrier particles A having the resin coating layer obtained here and the charge amount with the positively chargeable cyan toner a was 13%. In addition, when the coating | cover with the fluororesin on the core particle surface was observed with the scanning electron microscope (made by Hitachi, Ltd. (S-4800)), it was sufficient and uniform.

Example 2
In a Henschel mixer under nitrogen flow, 1 kg of the core material particle B and 10 g of silicone resin (trade name: KR251, manufactured by Shin-Etsu Chemical Co., Ltd.) are added as solids and stirred at a temperature of 50 to 150 ° C. for 1 hour. A resin coating layer made of a silicone resin was formed.

  The change rate of the charge amount in the environmental difference test of the various characteristics of the magnetic carrier particle B having the resin coating layer obtained and the charge amount with the negatively chargeable cyan toner b was 7%. In addition, when the coating with the silicone resin on the surface of the core material particles was observed with a scanning electron microscope (manufactured by Hitachi, Ltd. (S-4800)), it was sufficient and uniform.

Example 3
In a Henschel mixer under nitrogen flow, 1 kg of the core material particles C, 15 g of fluorine resin (trade name: FM300, manufactured by Daikin) and 3 g of carbon black (trade name: MA600, manufactured by Mitsubishi Chemical Corporation) are added. And it stirred at the temperature of 50-150 degreeC for 1 hour, and the resin coating layer which consists of a fluororesin containing carbon black was formed.

  The change rate of the charge amount in the environmental difference test of various characteristics of the obtained magnetic carrier particles C having the resin coating layer and the charge amount with the positively chargeable cyan toner a was 10%. In addition, when the coating | cover with the fluororesin on the core particle surface was observed with the scanning electron microscope (made by Hitachi, Ltd. (S-4800)), it was sufficient and uniform.

Example 4
In a Henschel mixer under a nitrogen stream, 1 kg of the core particle D, 15 g of silicone resin (trade name: KR251 manufactured by Shin-Etsu Chemical Co., Ltd.) as a solid content, and 3 g of carbon black (trade name: MA600 manufactured by Mitsubishi Chemical Corporation) The resultant was stirred for 1 hour at a temperature of 50 to 150 ° C. to form a resin coating layer made of a silicone resin containing carbon black.

  The change rate of the charge amount in the environmental difference test of the characteristics of the magnetic carrier particles D having the resin coating layer obtained and the charge amount with the negatively chargeable cyan toner b was 17%. In addition, when the coating with the silicone resin on the surface of the core material particles was observed with a scanning electron microscope (manufactured by Hitachi, Ltd. (S-4800)), it was sufficient and uniform.

Example 5
Under a nitrogen stream, 1 kg of the core material particle E and 10 g of styrene-acrylic resin (trade name: UNI3000 manufactured by Sanyo Chemical Co., Ltd.) as a solid content are added into a Henschel mixer and stirred at a temperature of 50 to 150 ° C. for 1 hour. Then, the resin coating layer made of styrene-acrylic resin was formed.

  The change rate of the charge amount in the environmental difference test of various characteristics of the obtained magnetic carrier particles E having the resin coating layer and the charge amount with the positively chargeable cyan toner a was 27%. The coating of the core particle surface with the styrene-acrylic resin was sufficient and uniform when observed with a scanning electron microscope (manufactured by Hitachi, Ltd. (S-4800)).

Example 6
In a Henschel mixer, 1 kg of the core material particle F and 10 g of acrylic resin (trade name: BR83 manufactured by Mitsubishi Rayon Co., Ltd.) are added as solids in a Henschel mixer, and stirred at a temperature of 50 to 150 ° C. for 1 hour. Then, a resin coating layer made of an acrylic resin was formed.

  The change rate of the charge amount in the environmental difference test of the characteristics of the magnetic carrier particles F having the resin coating layer obtained and the charge amount with the negatively chargeable cyan toner b was 17%. In addition, when the coating with the acrylic resin on the surface of the core particles was observed with a scanning electron microscope (manufactured by Hitachi, Ltd. (S-4800)), it was sufficient and uniform.

Comparative Example 1
In a Henschel mixer, 1 kg of the composite particles G and 10 g of a silicone resin (trade name: KR251, manufactured by Shin-Etsu Chemical Co., Ltd.) are added as solids in a Henschel mixer, and stirred at a temperature of 50 to 150 ° C. for 1 hour. A resin coating layer made of a silicone resin was formed.

  The change rate of the charge amount in the environmental difference test of the various characteristics of the magnetic carrier particles G having the resin coating layer and the charge amount of the negatively chargeable cyan toner b was 37%. In addition, when the coating with the silicone resin on the surface of the core material particles was observed with a scanning electron microscope (manufactured by Hitachi, Ltd. (S-4800)), it was sufficient and uniform.

Comparative Example 2
In a Henschel mixer under nitrogen flow, 1 kg of the core particle H and 10 g of silicone resin (trade name: manufactured by KR251, Shin-Etsu Chemical Co., Ltd.) are added as solids and stirred at a temperature of 50 to 150 ° C. for 1 hour. A resin coating layer made of a silicone resin was formed.

  The change rate of the charge amount in the environmental difference test of the various characteristics of the magnetic carrier particles H having the resin coating layer obtained and the charge amount with the negatively chargeable cyan toner b was 50%. In addition, when the coating with the silicone resin on the surface of the core material particles was observed with a scanning electron microscope (manufactured by Hitachi, Ltd. (S-4800)), it was sufficient and uniform.

  Table 3 shows various properties of the obtained magnetic carrier particles.

  Since the magnetic carrier according to the present invention has a change amount of the charge amount of less than 30%, the charging performance can be stably maintained regardless of the environmental change.

The magnetic carrier according to the present invention uses a phenol resin and a cured phenol resin composed of one or more of the compounds represented by the following chemical formula 10 as the binder resin of the composite particles. The water adsorption amount of the magnetic carrier is reduced by changing the ratio of phenol to the sum of one or two or more compounds represented by 10 to 90 mol%, and the amount of water adsorption change due to environmental changes By reducing the thickness, stable charging characteristics can be maintained, which is suitable as a magnetic carrier for an electrophotographic developer.

（式中、Ｒ１、Ｒ２、Ｒ３、Ｒ４及びＲ５のうち、少なくとも１ヶ所が炭素数１〜４個のアルキル基又は炭素数１〜４個のアルキル基の一部または全部の水素原子が塩素原子、臭素原子で置換されたハロゲン化アルキル基であり、残部は水素原子である。）

(In the formula, at least one of R1, R2, R3, R4 and R5 is an alkyl group having 1 to 4 carbon atoms or a part or all of hydrogen atoms of an alkyl group having 1 to 4 carbon atoms is a chlorine atom. A halogenated alkyl group substituted with a bromine atom, and the remainder is a hydrogen atom.)

In the two-component developer according to the present invention, a magnetic carrier is a cured phenol resin composed of one or more of a phenol resin and a compound represented by Chemical Formula 10 as a binder resin for the composite particles. The ratio of phenol to the sum of phenol and one or more compounds represented by the chemical formula 10 is 10 to 90 mol%, thereby reducing the water adsorption amount of the magnetic carrier and changing the environment. Since the stable charge characteristic can be maintained by reducing the change in the amount of water adsorbed due to this, it is suitable as an electrophotographic developer comprising a magnetic carrier for electrophotographic developer and a toner.

Claims (3)

In a magnetic carrier for an electrophotographic developer in which the surface of spherical composite particles having an average particle diameter of 1 to 100 μm composed of at least ferromagnetic iron oxide fine particles and a binder resin is coated with resin, the binder resin is represented by phenol and the following chemical formula 1 Is a cured phenol resin composed of one or more compounds, and the ratio of phenol to the sum of phenol and one or more compounds represented by the following chemical formula 1 is 10 to 90 mol% There, for an electrophotographic developer magnetic carrier, wherein the Henry's law constant, _{K D,} the water adsorption of the magnetic carrier is a 0.30~1.50mg / g / kPa.

(In the formula, at least one of R1, R2, R3, R4 and R5 is an alkyl group having 1 to 4 carbon atoms or a part or all of hydrogen atoms of an alkyl group having 1 to 4 carbon atoms is a chlorine atom. A halogenated alkyl group substituted with a bromine atom, and the remainder is a hydrogen atom.) 2. The magnetic carrier for an electrophotographic developer according to claim 1, wherein the coating resin is one or more selected from silicone resins, fluorine resins, acrylic resins, and styrene-acrylic resins. A two-component developer comprising the magnetic carrier according to claim 1 and a toner.