JP4557168B2 - Magnetic carrier for electrophotographic developer, method for producing the same, and two-component developer - Google Patents

Description

  The present invention is a magnetic carrier for an electrophotographic developer having excellent durability, and a resin such as a fluorine-based resin having low adhesiveness can be firmly adhered to core particles, and the coating resin layer can be peeled off. Provided are a magnetic carrier for an electrophotographic developer in which wear is suppressed and toner spent on the magnetic carrier is reduced, and a two-component developer using the magnetic carrier for electrophotographic development.

  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 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, the heat and pressure generated by repeated multiple developments over a long period of time can increase the temperature.・ 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, a method for coating the surface of the carrier with various resins has been proposed. For example, a release resin such as a fluororesin or a silicone resin on the carrier core particle surface. It is known that coated. Such a coat type carrier not only has a function of controlling the charge amount and resistance, but also has a surface covered 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. However, the fluororesin has poor adhesiveness to the carrier core material, and has a drawback of poor durability, such as the coating layer being peeled off by continuous use.

  Conventionally, as a carrier constituting a two-component developer, a ferrite carrier and an iron powder 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.

  Ferrite carrier and iron powder carrier are usually used by coating the particle surface with resin, but it is difficult to say that the adhesion between the particle surface and the coating resin is good, the coating resin gradually peels off during use, This causes a change in chargeability, resulting in problems such as image disturbance and carrier adhesion.

  However, the binder-type carrier comprising spherical composite particles composed of magnetic particles and phenol resin described in JP-A-2-220068 is several times more excellent in adhesion to the coating resin than the ferrite carrier and iron powder carrier. The problem that the coating resin peels off during use hardly occurs.

  However, in recent years, with the progress of colorization, there has been an increasing demand for a long life for carriers for high image quality. Collisions between particles, mechanical stirring in the particles and the developing device, or heat generated by them. It has a problem that it is insufficient for suppressing the peeling or abrasion of the spent toner or the resin coating layer on the surface of the carrier particles, and has various characteristics such as charging performance and electric resistance of the carrier for a long time. There is a need for a longer life that can be maintained over a longer period.

  Therefore, in order to further increase the life of the magnetic carrier, a resin such as a fluorine-based resin having low adhesiveness can be firmly adhered to the core material particles, and peeling and abrasion of the coating resin are suppressed, and the toner There is a strong demand for a binder-type magnetic carrier that hardly causes spent.

  Conventionally, there has been disclosed a magnetic carrier in which core particles having fine irregularities formed on the surface thereof are coated with a resin in order to improve adhesion with the coating resin (Patent Documents 1 to 3).

JP-A-3-229271 JP-A-8-44117 Japanese Patent Laid-Open No. 2000-231224

  In each of the technologies described in Patent Documents 1 to 3, there is a problem that a coating resin with low adhesiveness such as a fluorine-based resin has insufficient adhesiveness with a core material.

  Therefore, the present invention can firmly adhere a coating resin having a low adhesive property such as a fluororesin to the surface of the core material particles by controlling the surface state of the core material particles, It is a technical object to provide a magnetic carrier for an electrophotographic developer in which wear is suppressed and toner spent on the magnetic carrier is reduced.

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

  That is, the present invention is a magnetic carrier for an electrophotographic developer having an average particle diameter of 1 to 100 μm, which is obtained by coating a particle surface of core material particles composed of ferromagnetic iron oxide fine particles and a cured phenol resin with a resin. A magnetic carrier for an electrophotographic developer, wherein the particle surface is made of a cured phenol resin having a honeycomb-like structure (Invention 1).

The present invention is also a magnetic carrier for an electrophotographic developer having an average particle diameter of 1 to 100 μm, wherein the particle surface of core material particles composed of ferromagnetic iron oxide fine particles and a cured phenol resin is coated with a resin. A magnetic carrier for an electrophotographic developer, wherein the particle surface is made of a cured phenol resin having a honeycomb-like structure, and the core material particle satisfies the following formula (3) (Invention 2): .
<Formula 3>
S = a × D ^b
S: BET specific surface area of core particles (m ² / g),
D: Average particle diameter (μm) of core material particles,
a: coefficient, 3 ≦ a ≦ 22,
b: coefficient, b = −1.05.

  Further, the present invention provides the magnetic carrier for an electrophotographic developer, wherein the coating resin is one or more selected from silicone resins and fluorine resins (Invention 3).

  The present invention also provides the magnetic carrier for an electrophotographic developer, wherein the coating resin is a fluororesin (Invention 4).

Further, the present invention forms composite particles having an average particle diameter of 1 to 100 μm composed of ferromagnetic iron oxide fine particles and a cured phenol resin, and then the ferromagnetic iron oxide fine particles in the vicinity of the particle surface of the composite particles. It is a magnetic carrier for an electrophotographic developer coated with a resin after being dissolved and removed with an acid and made into core material particles made of a cured phenol resin having a honeycomb-like structure in which the particle surface is formed of ferromagnetic iron oxide fine particles, The core material particles satisfy the following formula (4): a method for producing a magnetic carrier for an electrophotographic developer (Invention 5).
<Formula 4>
S = a × D ^b
S: BET specific surface area of core particles (m ² / g),
D: Average particle diameter (μm) of core material particles,
a: coefficient, 3 ≦ a ≦ 22,
b: coefficient, b = −1.05.

  Further, the present invention is a two-component developer comprising the carrier of any one of the present inventions 1 to 4 and a toner (Invention 6).

  The magnetic carrier according to the present invention has moderately sized irregularities made of a hardened phenolic resin having a honeycomb-like structure in which the surface of the core particles is formed of ferromagnetic iron oxide fine particles. Because even a coating resin with low adhesiveness can be firmly bonded, and the coating resin layer can be prevented from peeling and wearing, and has excellent durability, and the toner spent on the magnetic carrier can be reduced. Suitable as a magnetic carrier for an electrophotographic developer.

  The method for producing a magnetic carrier according to the present invention can firmly adhere a resin such as a fluorine-based resin having low adhesiveness to core particles, and has excellent durability in which peeling and wear of the coating resin layer are suppressed. In addition, a magnetic carrier for an electrophotographic developer that can reduce the spent of toner on the magnetic carrier and is suitable as a method for producing a magnetic carrier is obtained.

  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 (hereinafter referred to as “magnetic carrier”) will be described.

The magnetic carrier according to the present invention is formed by resin coating on the surface of core material particles satisfying the following formula 5.
<Formula 5>
S = a × D ^b
S: BET specific surface area of core particles (m ² / g),
D: Average particle diameter (μm) of core material particles,
a: coefficient, 3 ≦ a ≦ 22,
b: coefficient, b = −1.05.

  When the relationship between the BET specific surface area value (S) and the average particle diameter (D) in the core particle is outside the range, that is, when the a is outside the range, the surface structure of the core particle is appropriate. For example, when the formation of a honeycomb-like structure made of a cured phenol resin in the vicinity of the surface of the core particle is insufficient, the adhesion with the coating resin is deteriorated, and the coating layer of the magnetic carrier when the developer is stirred Deterioration such as peeling or wear tends to occur. On the other hand, if the formation of a honeycomb structure composed of a hardened phenolic resin in the vicinity of the core surface is excessive, the coating resin enters the recesses, making uniform coating difficult, making it impossible to obtain stable charging characteristics, The problem of inferior strength occurs. As for the range of a, 3-22 are preferable, More preferably, it is 3-18, More preferably, it is 3-14.

The BET specific surface area (S) of the core particles in the present invention preferably satisfies the above formula 5. For example, when the average particle diameter of the core particles is 20 μm, the BET specific surface area of the core particles is preferably 0.13 to 0.95 m ² / g, more preferably 0.13 to 0.60 m ² / g. . When the average particle diameter of the core material particles is 35 μm, the BET specific surface area of the core material particles is preferably 0.07 to 0.53 m ² / g, more preferably 0.07 to 0.34 m ² / g. When the average particle diameter of the core material particles is 50 [mu] m, BET specific surface area of the core particle is preferably 0.05~0.36m ² / g, more preferably 0.05~0.23m ² / g.

  As for the average particle diameter (D) of the core material particle in this invention, 1-100 micrometers is preferable.

  The ferromagnetic iron oxide fine particles in the present invention may be any as long as they are soluble in acids such as oxalic acid, hydrochloric acid, acetic acid, nitric acid, sulfuric acid, and the like, for example, 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 0.5 μm, more preferably 0.1 to 0.3 μm.

  The particle shape of the ferromagnetic iron oxide fine particle powder in the present invention is a spherical shape, a hexahedral shape, an octahedral shape, or the like, and preferably a spherical shape.

  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 ; And epoxy resins.

  In the magnetic carrier according to the present invention, the surface of the core particles is 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 core material 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. In addition, these resin particles may be used individually by 1 type, and may use 2 or more types together.

  Moreover, the resin coating in the present invention may contain conductive fine particles in the resin coating layer. The inclusion of conductive fine particles in the resin is preferable in that the electric 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.

  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 is less than 80% by weight, the resin content increases and large particles are formed. It becomes easy. 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 magnetic carrier according to the present invention is spherical.

  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 5.2, more preferably 2.5 to 4.5.

The electric resistance value of the magnetic carrier according to the present invention is preferably 1 × 10 ⁸ to 1 × 10 ¹⁵ Ωcm, more preferably 1 × 10 ⁹ to 1 × 10 ¹⁵ 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.

  The magnetic carrier according to the present invention is a composite particle obtained by reacting phenols and aldehydes in an aqueous medium in the presence of a basic catalyst in the presence of a ferromagnetic iron oxide fine particle powder. Then, the iron oxide fine particles existing in the vicinity of the particle surface of the composite particles were dissolved and removed by acid to obtain core particles in a surface state exhibiting a honeycomb-like structure made of a cured phenol resin. Thereafter, the surface of the core particles can be obtained by resin coating.

  As phenols used in the present invention, in addition to phenol, alkylphenols such as m-cresol, p-tert-butylphenol, o-propylphenol, resorcinol, bisphenol A and the like, or a part or all of the benzene nucleus or alkyl group are chlorine atoms. And compounds having a phenolic hydroxyl group such as halogenated phenols substituted with a bromine atom, and phenol is most preferred in view of shape.

  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 in a molar ratio of 0.05 to 0.7 with respect to phenols. If it is less than 0.05, curing does not proceed sufficiently and granulation becomes difficult. If it exceeds 0.7, it affects the structure of the phenolic resin, resulting in poor granulation properties, making it difficult to obtain particles having a large particle size.

  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.

  The object of the present invention can be achieved by any of the above-mentioned treatment methods, but treatment with a silane coupling agent having an amino group or an epoxy group is preferable in view 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.

  When the phenols and aldehydes are reacted in the presence of a basic catalyst, the amount of the ferromagnetic iron oxide fine particles to coexist is 75 to 99% by weight based on the total amount of the ferromagnetic iron oxide fine particles, phenols and aldehydes. In view of the strength of the magnetic carrier to be generated, it is more preferably 78 to 99% by weight.

  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 lower, the ferromagnetic iron oxide fine particles are dispersed in the cured phenol resin binder, and the water of the spherical composite particles in which the ferromagnetic iron oxide fine particles are exposed on the particle surface. A dispersion is obtained.

  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 BET specific surface area of the composite particles in the present invention depends on the particle size of the composite particles. For example, when the average particle size of the composite particles is 20 μm, the BET specific surface area of the composite particles is 0.04 to 0.13 m. ² / g is preferred. When the average particle diameter of the composite particles is 35 μm, the BET specific surface area of the composite particles is preferably 0.03 to 0.07 m ² / g. When the average particle diameter of the composite particles is 50 μm, the BET specific surface area of the composite particles is preferably 0.015 to 0.05 m ² / g.

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 5.2, and the saturation magnetization value is 20 to 80 Am ^2. / Kg (20-80 emu / g) is preferred. The a value obtained by substituting the BET specific surface area and the average particle diameter of the composite particles into the formula 5 is less than 3.0.

  As the acid used in the present invention, oxalic acid, hydrochloric acid, acetic acid, nitric acid, sulfuric acid and the like are selected, and the core particles obtained by appropriately adjusting the type and concentration of the acid, the treatment temperature and the stirring time in the acid treatment step The BET specific surface area can be controlled within a range satisfying the above-mentioned formula 5.

  The acid treatment conditions such as the kind of acid and its concentration, the treatment temperature and the stirring time in the treatment process may be appropriately adjusted depending on the kind of the acid. For example, when oxalic acid is used, the acid concentration is 0.1. ˜2.0 mol / L, treatment temperature is 10 to 80 ° C., preferably 15 to 40 ° C. The stirring time is 5 to 24 hours, preferably 10 to 15 hours.

  In order to dissolve the composite particles, for example, the composite particles are put into an acid solution and sufficiently stirred by a stirring device. After stirring, the mixture is allowed to stand and the supernatant is removed. Then, an acid solution is added, and after stirring, the mixture is allowed to stand and the supernatant is removed. A core material made of a hardened phenolic resin having a honeycomb-like structure in which the particle surface is formed of ferromagnetic iron oxide fine particles by removing dissolved iron ions by repeating this several times, filtering, washing with water, and drying. Particles can be obtained.

  The obtained core material particles are made of a cured phenol resin whose particle surface has a honeycomb-like structure, and the cell size, that is, the size of a single honeycomb-like structure is the particle size of the ferromagnetic iron oxide fine particles, that is, 0 It corresponds to a size of about 0.05 to 0.5 μm.

The bulk density of the core particles in the present invention is preferably 2.5 g / cm ³ or less, and the specific gravity is preferably 2.5 to 5.2. The saturation magnetization value of the core particles is slightly lower than the saturation magnetization value of the composite particles, and is preferably 20 to 80 Am ² / kg (20 to 80 emu / g).

  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 composite particles composed of the ferromagnetic iron oxide fine particles and the cured phenol resin and having an average particle diameter of 1 to 100 μm, the ferromagnetic iron oxide fine particles existing in the vicinity of the surface of the composite particles are dissolved / The core particle obtained by the removal is that the particle surface is made of a cured phenol resin having a honeycomb-like structure.

  A binder-type carrier having fine irregularities on the particle surface of the core material particles is hardly sufficient in adhesion to the coating resin. In the present invention, the ferromagnetic iron oxide fine particles present in the vicinity of the surface of the core particles are dissolved and removed, and the phenol resin having a honeycomb-like structure made of the ferromagnetic iron oxide fine particles is left. Fluorine can be formed on the particle surface of the core material particles with a moderate size, and by forming a cured phenol resin having good adhesion to the coating resin, it usually has low adhesion and is easy to peel off. Even in a coating resin such as a series resin, a uniform and sufficient coating layer can be firmly bonded. As a result, the electrophotographic development has excellent durability, prevents peeling and abrasion of the coating resin layer, and reduces the spent of toner on the magnetic carrier by coating with a resin having low surface energy. The inventor believes that a magnetic carrier for an agent can be obtained.

  Representative examples of the present invention are as follows.

  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 High-Technologies Corporation (S-4800)).

  The BET specific surface area was shown by the value measured by the nitrogen adsorption method using Monosoap MS-21 (manufactured by Yuasa Ionics).

  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 (manufactured by Micromeritics).

  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 4329A (manufactured by Yokogawa Hewlett Packard).

The forced deterioration test was performed as follows. 50 g of magnetic carrier particle powder is put into a 100 cc glass sample bottle, covered, and then shaken for 10 hours with a paint conditioner (RED DEVIL). The amount of charge was measured for each sample before and after shaking, and the peeling or abrasion of the resin coating layer was confirmed with a scanning electron microscope, and evaluated in the following three stages.
◎: No peeling or abrasion of coating layer ○: Slight peeling or abrasion of coating layer ×: Extremely severe peeling or abrasion of coating layer

  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. The change rate of the charge amount of the magnetic carrier is calculated by multiplying 100 by the value obtained by dividing the difference between the initial charge amount value and the charge amount value after shaking for 10 hours by the initial charge amount value. .

(Toner Production Example 1)
Polyester resin 100 parts by weight Copper phthalocyanine-based 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 Premixing the above materials sufficiently using 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>
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.

  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.

  After charging 1000 g of hexahedral magnetite particle powder (average particle size 0.26 μm) into a 500 ml flask and stirring sufficiently, 7.0 g of a silane coupling agent (trade name: KBM-602, Shin-Etsu Chemical Co., Ltd.) is added and mixed. The hexagonal magnetite particle powder C was obtained by operating under the same conditions as the spherical magnetite particle powder A except for the above.

<Production of spherical composite particles>
Phenolic resin 11 parts by weight 37% formalin 17 parts by weight Lipophilic spherical magnetite particle powder A 100 parts by weight 25% aqueous ammonia 3 parts by weight Water 10 parts by weight The above materials are placed in a flask and stirred at a stirring speed of 250 rpm. Then, the temperature was raised to 85 ° C. in 60 minutes, 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 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. 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 diameter of 36 .mu.m, a bulk density of 1.85 g / cm ^3, a specific gravity of 3.64 g / cm ^3, a saturation magnetization value 73.5Am ² / kg, the electric resistance value It was 3.8 × 10 ⁸ Ω · cm, and a BET specific surface area was 0.05 m ² / g. The a value obtained by substituting the BET specific surface area and the average particle diameter of the composite particles into the formula 5 was 2.2.

  The micrograph of the surface of the spherical composite particle A obtained here is shown in FIGS. FIG. 1 shows the particle structure, and FIG. 2 shows the surface structure of the particle. The spherical composite particles a had a spherical shape close to a true sphere, and spherical ferromagnetic iron oxide fine particles were exposed on the particle surface.

Composite particles B to E:
Except for various changes in the type, amount, amount of phenol, amount of formalin, amount of ammonia water as a basic catalyst, amount of water and stirring speed of the lipophilic ferromagnetic iron oxide fine particles, composite particles The composite particles B to E were obtained by operating under the same conditions as A.

  Various properties of the obtained composite particles are shown in Table 1.

<Manufacture of core particle>
15 L of 0.50 mol / L oxalic acid aqueous solution was added to 10 kg of the composite particle A obtained here, and the mixture was stirred at a treatment temperature of 15 ° C. for about 10 hours. After standing, the supernatant was removed, the acid solution was added, and after further stirring, the mixture was allowed to stand to remove the supernatant. After repeating this several times, by filtering, washing and drying, the core material particles are made of a phenol resin whose particle surface is hardened and have a honeycomb-like structure based on the shape of ferromagnetic iron oxide fine particles existing in the vicinity of the surface A was obtained.

Core particles A obtained here, the average particle diameter of 36 .mu.m, a bulk density of 1.84 g / cm ^3, a specific gravity of 3.64 g / cm ^3, a saturation magnetization value 73.0Am ² / kg, the electric resistance 5 It was 0.7 × 10 ⁹ Ω · cm and a BET specific surface area was 0.20 m ² / g.

  Photomicrographs of the obtained core material particles A are shown in FIGS. 3 shows the particle structure, FIG. 4 shows the surface structure of the particle, and FIG. 5 shows the cross-sectional structure of the particle. The core material particle A had a spherical shape close to a true sphere, and had a honeycomb-like structure based on the shape of ferromagnetic iron oxide fine particles from which the particle surface was dissolved and removed.

Core particles BF
Core material particles B to F were obtained by performing the same operation as the core material particle A, except that the type, amount, acid type, concentration, treatment temperature, and stirring time of the composite particles were variously changed.

  Table 2 shows the production conditions and the characteristics of the obtained core particles.

Example 1
<Manufacture of magnetic carrier>
In a Henschel mixer, 1 kg of the core material particle A and 10 g of fluorine resin (trade name: FM300, manufactured by Daikin) were added as solids in a Henschel mixer, and the temperature was raised to 100 ° C. while stirring. The resin coating layer which consists of a fluorine resin was formed by stirring for 1 hour.

The magnetic carrier A thus obtained has an average particle diameter of 37 μm, a bulk density of 1.76 g / cm ³ , a specific gravity of 3.54 g / cm ³ , a saturation magnetization value of 72.8 Am ² / kg, and an electric resistance value of 1. It was 8 × 10 ¹⁵ Ω · cm.

  6 and 7 show micrographs of the magnetic carrier A thus obtained. 6 shows the particle structure of the magnetic carrier A, and FIG. 7 shows the cross-sectional structure of the magnetic carrier A. The coating with the fluororesin was sufficient and uniform.

  In the forced deterioration test of the carrier particles A and the positively chargeable cyan toner a obtained here, the rate of change in charge amount was 9%, and no deterioration such as peeling or abrasion of the coating layer was observed.

Example 2
In a Henschel mixer, 1 kg of the core particle B and 11 g of a silicone resin (trade name: KR251, manufactured by Shin-Etsu Chemical Co., Ltd.) are added as solids in a Henschel mixer, and the temperature is raised to 200 ° C. while stirring. The mixture was stirred for 1 hour to form a resin coating layer made of a silicone resin.

  Table 3 shows the characteristics of the magnetic carrier particles B having the obtained resin coating layer and the results of the forced deterioration test with the negatively chargeable cyan toner b. The coating with the silicone resin on the surface of the core material particles was sufficient and uniform.

Example 3
Under a nitrogen stream, 1 kg of the core material particle C, 10 g of fluorine resin (trade name: FM300 manufactured by Daikin) and carbon black (trade name: MA600 manufactured by Mitsubishi Chemical Corporation) are placed in a Henschel mixer. 0 g was added, the temperature was raised to 100 ° C. while stirring, and the mixture was stirred at the same temperature for 1 hour to form a resin coating layer made of a fluororesin containing carbon black.

  Table 3 shows the characteristics of the obtained magnetic carrier particles C having a resin coating layer and the results of a forced deterioration test with the positively chargeable cyan toner a. In addition, the coating with the fluororesin on the surface of the core material particles was sufficient and uniform.

Example 4
1. Under a nitrogen stream, 1 kg of the core material particle D, 13 g of fluorine resin (trade name: FM300, manufactured by Daikin) and carbon black (trade name: MA600, manufactured by Mitsubishi Chemical Corporation) are placed in a Henschel mixer. 6 g was added, the temperature was raised to 100 ° C. while stirring, and the mixture was stirred for 1 hour at the same temperature to form a resin coating layer made of a fluorocarbon resin containing carbon black.

  Table 3 shows the characteristics of the magnetic carrier particles D having the resin coating layer obtained and the results of the forced deterioration test with the positively chargeable cyan toner a. In addition, the coating with the fluororesin on the surface of the core material particles was sufficient and uniform.

Example 5
In a Henschel mixer, 1 kg of the core material particle E and 22 g of fluorine resin (trade name: FM300, manufactured by Daikin) were added as solids in a Henschel mixer, and the temperature was raised to 100 ° C. while stirring. The mixture was stirred for 1 hour to form a resin coating layer made of a fluororesin.

  Table 3 shows the characteristics of the magnetic carrier particles E having the resin coating layer obtained and the results of the forced deterioration test with the positively chargeable cyan toner a. In addition, the coating with the fluororesin on the surface of the core material particles was sufficient and uniform.

Comparative Example 1
Under a nitrogen stream, 1 kg of the composite particle A and 10 g of fluorine resin (trade name: FM300, manufactured by Daikin) were added as solids in a Henschel mixer, and the temperature was raised to 100 ° C. while stirring. A resin coating layer made of a fluororesin was formed by stirring for 1 hour.

  Table 3 shows the characteristics of the magnetic carrier particles F having the obtained resin coating layer and the results of a forced deterioration test with the positively chargeable cyan toner a. 8 and 9 show micrographs of the carrier particles F obtained here. FIG. 8 shows a particle structure, and FIG. 9 is a photograph of the particle surface structure. The coating with the fluororesin was in the shape of a sea island. Since the composite particles A were not subjected to acid treatment and did not exhibit a honeycomb-like structure made of a cured phenol resin on the particle surface, the coating with the fluorine-based resin was not sufficiently performed.

Comparative Example 2
Under a nitrogen stream, 1 kg of the core particle F and 10 g of fluorine resin (trade name: FM300, manufactured by Daikin) were added as solids in a Henschel mixer, and the temperature was raised to 100 ° C. while stirring. The resin coating layer which consists of a fluorine resin was formed by stirring for 1 hour.

  Table 3 shows the characteristics of the magnetic carrier particles G having the resin coating layer obtained and the results of the forced deterioration test with the positively chargeable cyan toner a. In addition, the coating with the fluororesin on the surface of the core material particles was uneven. The core material particle F has an excessive honeycomb-like structure made of a hardened phenol resin on the particle surface, and the coating resin is insufficient due to increased penetration of the coating resin into the core material particle. Particle exposure occurred.

  The magnetic carrier according to the present invention can firmly adhere a resin such as a fluorine-based resin with low adhesion to the core particles, and has excellent durability in which peeling and wear of the coating resin layer are suppressed, Since the spent of toner on the magnetic carrier can be reduced, it is suitable as a magnetic carrier for an electrophotographic developer.

  The method for producing a magnetic carrier according to the present invention can firmly adhere a resin such as a fluorine-based resin having low adhesiveness to core particles, and has excellent durability in which peeling and wear of the coating resin layer are suppressed. In addition, a magnetic carrier for an electrophotographic developer that can reduce the spent toner on the magnetic carrier can be obtained.

In the two-component developer according to the present invention, the magnetic carrier can firmly adhere a resin such as a fluorine-based resin having low adhesion to the core material particles, and the peeling and abrasion of the coating resin layer are suppressed. Therefore, it is possible to reduce the spent of the toner on the magnetic carrier, and therefore, it is suitable as an electrophotographic developer comprising a magnetic carrier for electrophotographic developer and a toner.

2 is an electron micrograph showing the particle structure of composite particle A (2000 times). It is an electron micrograph which shows the surface structure of the composite particle A (15000 times). It is an electron micrograph which shows the particle structure of the core material particle A (2000 times). It is an electron micrograph which shows the surface structure of the core material particle A (15000 times). It is an electron micrograph which shows the cross-section of the core particle A (40000 times). 2 is an electron micrograph showing the particle structure of magnetic carrier A obtained in Example 1 (2000 times). It is an electron micrograph which shows the cross-sectional structure of the magnetic carrier A obtained in Example 1 (20000 times). 2 is an electron micrograph showing the particle structure of magnetic carrier F obtained in Comparative Example 1 (2000 times). 4 is an electron micrograph showing the surface structure of the magnetic carrier F obtained in Comparative Example 1 (10,000 times).

Claims (6)

A magnetic carrier for an electrophotographic developer having an average particle diameter of 1 to 100 μm, wherein the particle surface of core material particles composed of ferromagnetic iron oxide fine particles and a cured phenol resin is coated with a resin, and the particle surface of the core material particles is a honeycomb A magnetic carrier for an electrophotographic developer, comprising a cured phenol resin exhibiting a shape structure. A magnetic carrier for an electrophotographic developer having an average particle diameter of 1 to 100 μm, wherein the particle surface of core material particles composed of ferromagnetic iron oxide fine particles and a cured phenol resin is coated with a resin, and the particle surface of the core material particles is a honeycomb A magnetic carrier for an electrophotographic developer, comprising a hardened phenolic resin having a shape-like structure, wherein the core material particles satisfy the following formula (1).
<Formula 1>
S = a × D ^b
S: BET specific surface area of core particles (m ² / g),
D: Average particle diameter (μm) of core material particles,
a: coefficient, 3 ≦ a ≦ 22,
b: coefficient, b = −1.05. The magnetic carrier for an electrophotographic developer according to claim 1 or 2, wherein the coating resin is one or more selected from silicone resins and fluorine resins. The magnetic carrier for an electrophotographic developer according to claim 1 or 2, wherein the coating resin is a fluororesin. Forming composite particles having an average particle diameter of 1 to 100 μm composed of ferromagnetic iron oxide fine particles and a cured phenol resin, and then dissolving and removing the ferromagnetic iron oxide fine particles near the particle surface of the composite particles with an acid, A core carrier particle made of a cured phenol resin having a honeycomb-like structure in which the particle surface is a form of ferromagnetic iron oxide fine particles, and then a resin-coated magnetic carrier for an electrophotographic developer, wherein the core particle is A method for producing a magnetic carrier for an electrophotographic developer, wherein Formula 2 is satisfied.
<Formula 2>
S = a × D ^b
S: BET specific surface area of core particles (m ² / g),
D: Average particle diameter (μm) of core material particles,
a: coefficient, 3 ≦ a ≦ 22,
b: coefficient, b = −1.05. A two-component developer comprising the carrier according to any one of claims 1 to 4 and a toner.