JP2015084118A - Magnetic carrier for electrophotographic developer, production method of the carrier, and two-component developer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carrier in which durability is further improved and peeing of a surface coating layer is highly suppressed.SOLUTION: A magnetic carrier for an electrophotographic developer is provided, which has a surface coating layer essentially comprising a resin on a particle surface of a magnetic core particle. In a measurement of charge amounts of the magnetic carrier, a ratio (charge amount at 10 seconds)/(charge amount at 120 seconds) of a measured value 10 seconds after starting the measurement to a measured value 120 seconds after starting the measurement, is 60% or more. A production method of the magnetic carrier for an electrostatic developer is provided, which includes a step of forming a surface coating layer on a particle surface of a magnetic core particle, and in the production method, the surface coating layer can be formed by sequentially using two or more types of devices.

Description

  The present invention relates to a magnetic carrier for an electrophotographic developer, and provides a magnetic carrier for an electrophotographic developer capable of forming an image free from fogging and image unevenness.

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

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

  In particular, a carrier used in a color developer needs to have higher reliability as the image quality and speed are increased. Therefore, it is necessary to extend the service life so that the charging performance of the carrier can be maintained for a long time. ing. For that purpose, it is necessary to be able to maintain the initial particle shape and state as much as possible without cracking or peeling off the surface coating layer.

  That is, a certain degree of share is always applied in the developing machine, and if the adhesion between the carrier core particles and the surface coating layer is poor, the surface coating layer is cracked or peeled off. As a result, the charging ability is lowered, and the characteristics and reliability required for the above-described color carrier cannot be maintained. In particular, as the surface coating layer becomes thicker, the adhesion between the core material particles of the carrier and the surface coating layer becomes more important.

  As a means for extending the life, it is conceivable to increase the surface coating layer on the surface of the magnetic core particles. However, if the surface coating layer is made thicker and the amount of resin is increased, the surface is coated with a device such as a kneader or Henschel, resulting in poor agglomeration and poor productivity. Thus, a carrier capable of achieving a long life cannot be stably produced, for example, a crater-like defect is formed on the surface coating layer formed on the particle surface, and the core particle surface is exposed to adversely affect carrier properties.

  Further, when a surface coating layer is formed on the surface of the magnetic core particle using an apparatus having a fluidized bed, aggregation is prevented and crater-like defects are generated in the surface coating layer formed on the surface of the magnetic core particle. However, the adhesion between the magnetic core particles and the surface coating layer is inferior, and the surface coating layer is cracked or peeled off.

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 to stir 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 magnetic core 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. Will cause.

However, a magnetic material dispersion type carrier composed of spherical composite particles composed of magnetic fine particles and a phenol resin described in JP-A-2-220068 has a true specific gravity of ³ to 4 g / cm ^3. Since the true specific gravity is smaller than that, the energy at the time of collision between the toner and the carrier is reduced, which is advantageous for toner spent. Furthermore, the adhesiveness with the coating resin is excellent several times, and the problem that the surface coating layer peels off during use is reduced compared to the iron powder carrier and ferrite carrier.

  However, with the recent enhancement in functionality, image quality, and speed of copiers and printers, there is a strong demand for magnetic carriers in which peeling of the surface coating layer is highly suppressed.

  Conventionally, with respect to a magnetic carrier in which a resin layer is formed on a magnetic core particle, a technique for controlling the electrical resistivity of a magnetic carrier in which a magnetic core particle is coated with a resin layer (Patent Document 1), two types of magnetic core particles are used. A technique for controlling the volume resistivity of a magnetic carrier coated with a resin layer (Patent Document 2), forming a coating layer by immersing magnetic core particles in a resin solution, and then spraying the resin solution in a fluidized bed A technique for forming a coating layer (Patent Document 3) is known.

JP 2006-259010 A JP 2007-206481 A JP 2004-226568 A

  The above-mentioned Patent Document 1 describes a magnetic carrier that can maintain a constant electric resistivity even when the electric field strength at the time of resistance measurement changes. However, only a centrifugal rolling granulation coating apparatus is used. Thus, a surface coating component is formed on the magnetic core particles, and it is difficult to say that a long-life carrier can be obtained.

  Patent Document 2 described above describes a magnetic carrier in which magnetic core particles are coated with a melamine resin and then coated with a resin layer containing carbon black. The magnetic carrier is coated by a polymerization reaction. After that, the resin layer is coated using a coater, and it is difficult to say that a long-life carrier can be obtained.

  Further, in the above-mentioned Patent Document 3, the surface of the magnetic core material particles is smoothed by immersing the magnetic core material particles having uneven magnetic core material surfaces in the resin solution, and then sprayed with the resin solution in the fluidized bed. Although it is described that a thick resin layer having a uniform film thickness is applied, obtaining a long-life magnetic carrier is not considered.

  Then, this invention makes it a technical subject to provide the carrier which durability improved more and peeling of the surface coating layer was suppressed highly.

  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 in which a surface coating layer is formed mainly from a resin on the particle surface of magnetic core particles, and the measurement of the charge amount of the magnetic carrier is 10 seconds after the measurement. A magnetic carrier for an electrophotographic developer, wherein the ratio of the measured value to the measured value after 120 seconds (charge amount after 10 seconds) / (charge amount after 120 seconds) is 60% or more. (Invention 1).

Further, the present invention provides the magnetic carrier for an electrophotographic developer according to the first aspect of the present invention,
In the measurement of the charge amount, the magnetic carrier for an electrophotographic developer is characterized in that the crack of the surface coating layer of the magnetic carrier after 10 seconds is 25% or less (Invention 2).

  In the magnetic carrier for an electrophotographic developer according to the first aspect of the present invention, the resin component constituting the surface coating layer is selected from a silicone resin, a fluorine resin, a styrene resin, an acrylic resin, and a polyester resin. A magnetic carrier for an electrophotographic developer, which is one or two or more kinds of resins (Invention 3).

  The present invention is also the magnetic carrier for electrophotographic developer according to the first aspect of the present invention, wherein the total amount of the resin component of the surface coating layer is 0.9 wt% to 10.0 wt% ( Invention 4).

  The present invention also relates to a method for producing a magnetic carrier for an electrophotographic developer, wherein a surface coating layer is formed on the surface of magnetic core particles, wherein the surface coating layer is formed using two or more types of devices in order. A method for producing a magnetic carrier for an electrophotographic developer according to any one of the present inventions 1 to 4 (Invention 5).

  Further, the present invention provides an electrophotographic method using a device having a fluidized layer as a last-formation device for forming a surface coating layer among two or more types of devices in the method for producing a magnetic carrier for an electrophotographic developer according to the present invention 5. This is a method for producing a magnetic carrier for developer (Invention 5).

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

  The magnetic carrier for an electrophotographic developer according to the present invention is suitable as a magnetic carrier for an electrophotographic developer because durability is improved and chargeability is stably maintained.

  In addition, the method for producing a magnetic carrier for an electrophotographic developer according to the present invention can sufficiently secure the characteristics required for a magnetic carrier, in which peeling of the surface coating layer is highly suppressed and the chargeability can be stably maintained. Since it is simple and excellent in productivity, it is suitable as a method for producing a magnetic carrier.

2 is a part of an electron micrograph after measuring the charge amount of the magnetic carrier of Example 1. FIG. 2 is a part of an electron micrograph after measuring the charge amount of the magnetic carrier of Comparative Example 1.

  Hereinafter, the present invention will be described in detail.

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

When the charge amount of the magnetic carrier for an electrophotographic developer according to the present invention is measured, the ratio of measured values after 10 seconds and 120 seconds after measurement (charge amount after 10 seconds) / (charge amount after 120 seconds) × 100
Is 60% or more. When the measured value is less than 60%, it is difficult to say that the surface coating layer has excellent durability because the surface coating layer is peeled off or cracked. A more preferable range is 62% or more. The upper limit is 100%.

  The magnetic carrier for an electrophotographic developer according to the present invention was observed by SEM observation of the magnetic carrier after measuring the charge amount after 10 seconds (magnification 1000 times, surface condition confirmed with about 5 to 15 carriers in one field of view) As much as possible), the crack of the surface coating layer is 25% or less. When the crack of the surface coating layer exceeds 25%, it cannot be said that it has excellent durability. A more preferable range is 20% or less.

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

The bulk density of the magnetic carrier for an electrophotographic developer according to 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 magnetic carrier for an electrophotographic developer according to the present invention preferably has an electric resistance of 1 × 10 ⁸ to 1 × 10 ¹⁷ Ωcm, more preferably 1 × 10 ⁹ to 1 × 10 ¹⁶ Ωcm.

The saturation magnetization value of the magnetic carrier for an electrophotographic developer 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). .

  The water content of the magnetic carrier for an electrophotographic developer according to the present invention is preferably 0.2 to 1.0 wt%. More preferably, it is 0.3-0.8 wt%.

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

  The magnetic carrier for an electrophotographic developer according to the present invention is obtained by forming a surface coating layer on a magnetic core particle using two or more kinds of devices in order.

  As the magnetic core particles in the present invention, any of ferrite particles, iron powder, binder-type magnetic particles in which magnetic particle powder is dispersed in a binder resin, and the like can be used, but considering the adhesion to the surface coating layer. Binder type magnetic particles are more preferable.

  A method for producing a binder-type magnetic particle comprising magnetic particles and a binder resin used as magnetic core particles in the present invention is as follows.

  That is, the binder-type magnetic particles include phenols and aldehydes in the presence of a basic catalyst in an aqueous medium, magnetite particle powder, maghemite particle powder, magnetoplumbite-type iron oxide particle powder (strontium ferrite particle powder, barium ferrite particle). Magnetic particles such as powder) can be obtained by reacting the phenols with aldehydes. The total content of the magnetic particle powder in the magnetic core particles of the binder type carrier is preferably 80 to 99% by weight with respect to the magnetic core particles, and if it is less than 80% by weight, the resin content increases and large particles Is easier to do. 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.

  A method for forming a surface coating layer on the particle surface of the magnetic core particles in the present invention mainly from a resin is as follows.

  First, in the first processing apparatus, the magnetic core particles and the components that form the surface coating layer are placed in the apparatus and heated as necessary while stirring and mixing. If necessary, the resin coating layer is formed while maintaining the conditions.

  In the first processing apparatus, in particular, the apparatus is selected with an emphasis on the adhesion between the magnetic core particles and the surface coating layer, and an apparatus that can sufficiently apply a shearing force and a kneading force is used. is necessary. Not only the magnetic core particles and the constituent components of the surface coating layer are mixed as a whole, but also the constituents in which the aggregation of the magnetic core particles are dispersed and the magnetic core particles and the surface coating layer are formed. Those that can be combined with each other are preferred. According to the mechanical classification of the mixer, the container rotation type (horizontal cylinder, inclined cylinder, V type or double cone, etc.) with a built-in stirring blade, the mechanical stirring type with a horizontal rotation axis (double axis paddle, etc.), the vertical rotation axis It is preferable to use an apparatus corresponding to a mechanical stirring type (high-speed flow, muller, etc.) having

  Specifically, the first processing apparatus is a double cone type mixer manufactured by Fuji Powder Co., Ltd., a universal mixing stirrer, a drum mixer manufactured by Sugiyama Heavy Industries, Ltd., an axial mixer, and a vertical granulator manufactured by POWREC Co., Ltd. , Henschel mixer manufactured by Mitsui Mining Co., Ltd., PV mixer manufactured by Shinko Environmental Solution Co., Ltd., SV mixer, Pow mixer manufactured by Tsukasa Industry Co., Ltd., and the like.

  As for the processing conditions in the first processing apparatus, the temperature in the apparatus is preferably 10 ° C to 100 ° C, more preferably 40 ° C to 80 ° C. If the temperature exceeds 100 ° C., the drying speed increases, and the solvent evaporates before the surface coating layer is sufficiently formed. Therefore, the adhesion between the magnetic core particles and the coating layer is poor, and the surface coating layer is peeled off as described above. However, the characteristics as a highly suppressed magnetic carrier cannot be achieved. Further, when the temperature is too low, not only the productivity is lowered, but also the processing in the apparatus for a long time tends to make it difficult to control the carrier characteristics. As operation conditions at this time, operation at the temperature in the apparatus is more preferable.

  The atmosphere in the apparatus is not particularly limited, such as an inert gas atmosphere such as nitrogen, or an atmospheric atmosphere, but an inert atmosphere is preferable.

  In order to improve the adhesion between the magnetic core particles and the surface coating layer, it is more preferable to perform the first treatment under reduced pressure.

In addition, as a measure of the electric resistance of the magnetic core particles on which the surface coating layer is formed after the surface coating layer is formed using the first treatment apparatus, for example, if the coating is made of only resin, the amount of resin is In the case of 0.1 wt% or more and less than 0.8 wt%, the ratio of the magnetic core particles before coating to the electric resistance is preferably less than 1 × 10 ² , and the resin amount is 0.8 to 1.0 wt%. In this case, the ratio of the magnetic core particles before coating to the electric resistance is preferably 1 × 10 ² or more and 1 × 10 ³ or less.

  Even after coating, if the electrical resistance of the magnetic core particles before coating is about the same, the coating layer is not uniform and the magnetic core particles cannot be coated uniformly. From the point of view, it is not sufficient, and it cannot play the role required for carriers such as the above-mentioned long life. In addition, when the upper limit electric resistance in each resin amount is exceeded, it is not considered that the shearing force and the kneading force are sufficiently applied, and there is a gap between the magnetic core particle and the surface forming layer. Therefore, it cannot be said that sufficient adhesion is secured.

  In the second and subsequent rounds, a component that forms a surface treatment layer in a state where the magnetic core particles obtained in the first treatment are retained in the fluidized bed is added, and the surface of the particles of the magnetic core particles is added to the surface. A coating layer is formed. For the second and subsequent layers, select a device that prevents agglomeration due to an increase in the amount of resin and crater-like cracks that are generated when the agglomeration is crushed, and that ensures sufficient productivity and characteristics required for the carrier. .

The second processing apparatus is, for example, Granurex manufactured by Freund Sangyo Co., Ltd., flow coater, spiraflow, multiplex manufactured by Paulek, Inc., SFP, Spiracoater manufactured by Okada Seiko Co., Ltd., agromaster manufactured by Hosokawa Micron Co., Ltd., etc. Can be used.
If the device has a fluidized bed, aggregation can be suppressed and the characteristics required of the carrier can be secured, but preferably a rolling fluidized bed, more preferably a rolling fluidized bed with a crushing mechanism, Aggregation can be effectively suppressed.

  The conditions for using the second treatment apparatus are preferably 30 to 100 ° C., preferably 50 to 90 ° C., for the air supply temperature of the fluidized bed. When the supply air temperature exceeds 100 ° C., the drying rate of the components forming the surface coating layer is increased, and the solvent evaporates before the coating layer is sufficiently formed. Adhesion with the first surface-forming layer as the coating layer also deteriorates, and a magnetic carrier in which peeling of the surface coating layer is highly suppressed cannot be obtained. On the other hand, if the supply air temperature is too low, the drying efficiency becomes poor and the formation of the coating layer is not sufficient, the characteristics required for the magnetic carrier such as electric resistance cannot be controlled, and the above-mentioned requirements are also applied. Thus, it is impossible to obtain a magnetic carrier in which peeling of the surface coating layer is highly suppressed.

  In an apparatus having a fluidized bed, the residence time of the sample, the amount of air supplied, etc. may be appropriately set so that a uniform surface coating layer can be formed.

  The atmosphere in the apparatus is not particularly limited, such as an inert atmosphere such as nitrogen or an atmospheric atmosphere, but an inert atmosphere is preferable.

  Although it does not specifically limit as a resin component which comprises a surface coating layer, For example, polyolefin resin, such as polyethylene and a polypropylene; Polystyrene, acrylic resin, polyacrylonitrile, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl carbazole , Polyvinyl ether or polyvinylidene resin such as polyvinyl ether, polyvinyl ketone, etc .; vinyl chloride / vinyl acetate copolymer, styrene / acrylic acid copolymer; straight silicon resin comprising organosiloxane bond or modified product thereof; polytetrafluoro Fluorine resins such as ethylene, polyvinyl fluoride, polyvinylidene fluoride, and polychlorotrifluoroethylene; polyester; polyurethane; polycarbonate; urea formaldehyde , And the like epoxy resins; amino resins such as de resin.

  As the resin component constituting the surface coating layer, one or two or more resins selected from silicone resins, fluorine resins, styrene resins, acrylic resins, and polyester resins are more preferable.

  The surface coating layer in the present invention may contain fine particles in the 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.

  The surface coating layer in the present invention may contain conductive fine particles in the coating layer. 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 surface coating layer formed by the first processing apparatus and the surface coating layer formed by the second processing apparatus may have the same composition or different compositions from each other. I do not care.

  In particular, in the first processing, the component forming the surface coating layer may contain carbon black or the like, but forming the surface coating layer only with the resin further improves the adhesion. This is preferable.

  The total coating amount of the magnetic carrier according to the present invention by the resin is 0.9 to 10.0% by weight with respect to 100% by weight of the magnetic core particles. When the coating amount is less than 0.9% by weight, the carrier used for the color developer as described above requires higher reliability as the image quality and speed are increased. There is a need for a long life that allows the charging performance to be maintained over a long period of time, which is not appropriate in terms of such a long life. On the other hand, if it exceeds 10.0% by weight, the coating amount becomes too large to control the necessary characteristics as a carrier. Preferably it is 0.9 to 8.0 weight%, More preferably, it is 0.9 to 5.0 weight%.

  Further, in the first processing apparatus and the second processing apparatus, the ratio of the amount of resin used in each apparatus is not particularly limited, but in addition to the characteristics as a magnetic carrier, the shearing force and the kneading force are sufficient. In addition, from the viewpoint of improving the adhesion between the magnetic core particles and the surface coating layer by performing treatment, it is preferable that at least the first layer is 0.1 wt% to 1.0 wt%.

  Further, in the first treatment apparatus, when the resin amount exceeds 1.5% by weight, the aggregation becomes severe, and as a result of the agglomerated particles being crushed, the surface coating layer formed on the particle surface has crater-like defects. This makes it impossible to stably produce a carrier that can achieve a long service life, such as exposing the core particle surface and adversely affecting carrier properties.

  When the surface coating layer is formed on the magnetic core particles using three or more kinds of apparatuses, the apparatus used for the first time is the same as the apparatus used for the first time, and the apparatus used last is the flow A device having a layer. Any device may be used as the device used on the way. It is also possible to use the same device again.

  If necessary, heat treatment may be performed after the treatment in the first apparatus and / or after the treatment in the second apparatus. In addition, you may heat-process in pressure reduction, in order to improve the adhesiveness of a magnetic core material particle and a surface coating layer.

  When performing the said heat processing, it is preferable to set the process temperature conditions according to the kind of resin.

  For example, in the case of a thermoplastic resin such as a polyolefin resin, a styrene resin, or an acrylic resin, 80 ° C. to 200 ° C. after treatment in the first apparatus and / or after treatment in the second apparatus. It is preferable to heat-process in the temperature range of this, More preferably, it is 90 to 150 degreeC. If the temperature is lower than 80 ° C, it is difficult to sufficiently remove the solvent component. If the temperature exceeds 200 ° C, the resin forming the coating layer deteriorates, and the strength of the coating layer itself decreases. In addition, the carrier characteristics cannot be maintained, and agglomeration occurs, resulting in poor productivity.

  In the case of a thermosetting resin such as an epoxy resin or a silicone resin, the temperature range is 100 ° C. to 250 ° C. after the treatment with the first apparatus and / or the treatment with the second apparatus. It is preferable to perform the heat treatment at 120 ° C., more preferably from 120 ° C. to 200 ° C. If the temperature is less than 100 ° C, the surface forming layer does not sufficiently harden to form a surface layer that can cope with the long life as described above. If the temperature exceeds 250 ° C, a coating layer is formed in the same manner as the thermoplastic resin. In addition to not being able to physically and chemically maintain the carrier characteristics such as the deterioration of the resin, and the strength of the coating layer itself being lowered, agglomeration is also caused and the productivity is deteriorated.

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

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

<Action>
The important point in the present invention is to form a surface coating layer using two or more processing devices in order, the first device places importance on adhesion, and the second and subsequent devices agglomerate. In addition, it is possible to control the characteristics required for the carrier by suppressing the occurrence of crater-like defects that are generated when pulverized after aggregation.

  The first treatment apparatus is preferably an apparatus that gives more importance to the adhesion between the magnetic core particles and the surface coating layer and can give sufficient kneading force and shearing force.

  In the second and subsequent treatment apparatuses, in order to suppress aggregation caused by an increase in the amount of resin forming the surface coating layer and crater-like defects caused by pulverization of the aggregate, 1 of the magnetic core particles is used. It is preferred to use a fluidized bed, which is an apparatus that can be individually flowed and coated.

  As a result, the adhesion between the magnetic core particles and the surface coating layer is improved, the change in charge amount is reduced, and a carrier having excellent durability can be produced. Moreover, the carrier excellent also in environmental stability can be produced by improving the adhesiveness of a magnetic core material particle and the coating layer formed with the 1st processing apparatus.

A typical embodiment of the present invention is as follows.

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

The amount of charge was measured by thoroughly mixing 95 parts by weight of a magnetic carrier and 5 parts by weight of toner prepared by the following method, preparing a sample that was left and conditioned for 24 hours or more in an environment of 24 ° C. and 60% RH, and performing blow-off charging. It measured using quantity measuring apparatus TB-200 (made by Toshiba Chemical Corporation). The measurement time was set to 10 seconds and 120 seconds, and the ratio of the values measured at that time was an index indicating the strength of the surface coating layer with the value calculated by the following formula 1.
<Equation 1>
(Charge amount after 10 seconds) / (charge amount after 120 seconds)) × 100
Example of toner production Polyester resin 100 parts by weight Copper phthalocyanine colorant 5 parts by weight Charge control agent (di-tert-butylsalicylic acid zinc compound) 3 parts by weight Wax 9 parts by weight The mixture was melt-kneaded with a shaft extrusion kneader, cooled and then pulverized and classified using a hammer mill to obtain a negatively charged 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.

  Using the obtained toner, the charge amount was measured according to the measurement method.

  The particle morphology of the particles was observed with a scanning electron microscope (manufactured by Hitachi, Ltd. (S-800)). In addition, the state of the surface coating layer is confirmed by checking the observation sample 10 seconds after the charge amount measurement, and the number of cracks in the surface coating layer with about 5 to 15 carriers in one field of view at 1000 times the field of view. Is confirmed.

  The moisture content was measured by Karl Fischer (manufactured by Hiranuma Sangyo Co., Ltd., automatic heating vaporization moisture measurement system AQ-2100). A sample for measurement was prepared by accurately weighing 1 g of a sample that had been conditioned at 24 ° C. and 60% RH for 24 hours or more in a glass sample tube and covered with an aluminum foil (at this time in air) In order to correct the moisture content, prepare two empty sample tubes with the same lid).

  Titration of water sent from a moisture vaporizer (EV-2010 AUTO SOLID EVAPCRATOR) at a heating temperature of 150 ° C. and a carrier gas (nitrogen gas) flow rate of 100 ml / min under the conditions of INTERVAL = 30 seconds and TIMER = 1 minute. Went. 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 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 fluidity was measured with reference to JIS Z2502.

  The bulk density was measured with reference to JIS K5101.

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

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

  The image evaluation was performed by modifying Epson LP8000C. The carrier was changed to the carrier of the present invention, and the image was printed by changing the bias voltage, and 50,000 plate life tests were conducted.

The fog of the printed image was evaluated in the following four stages.
A: Very good.
○: Good.
Δ: Acceptable level.
X: Bad.

The image density of the printed image was evaluated in the following four stages.
A: Very good.
○: Good.
Δ: Acceptable level.
X: Bad.

<Manufacture of spherical composite particles: 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.

<Production of spherical composite particle A for magnetic core>
Phenolic resin 11 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 10 parts by weight

  The above materials are put into a flask, heated to 85 ° C. over 60 minutes while stirring at a stirring speed of 250 rpm, and then reacted and cured at the same temperature for 120 minutes to thereby remove the ferromagnetic iron oxide fine particles and the cured phenol resin. A composite particle was produced.

  Next, after cooling the content in the flask to 30 ° C., the supernatant was removed, and the precipitate in the lower layer was washed with water and then air-dried. Next, this was dried at 150 to 180 ° C. under reduced pressure (5 mmHg or less) to obtain spherical composite particles A for magnetic core particles.

The obtained spherical composite particles A have an average particle diameter of 35.8Myuemu, bulk density 1.91 g / cm ^3, a specific gravity of 3.61 g / cm ^3, a saturation magnetization value 74.1Am ² / kg, flow rate 35 0.1 sec / 50 g, water content 0.55%, electric resistance value 3.4 × 10 ⁸ Ω · cm.

<Production of spherical composite particle B for magnetic core>
Except for various changes in the amount of the ferrophilic iron oxide fine particles, the amount of phenol, the amount of formalin, the amount of ammonia water as the basic catalyst, the amount of water and the stirring speed, the composite particles A and The operation was performed under the same conditions to obtain spherical composite particles B for magnetic core particles.

The obtained spherical composite particles B have an average a particle size of 52.1Myuemu, bulk density 1.92 g / cm ^3, a specific gravity of 3.57 g / cm ^3, a saturation magnetization value 73.1Am ² / kg, flow rate 33 0.1 sec / 50 g, water content 0.56%, and electrical resistance value 2.6 × 10 ⁸ Ω · cm.

Example 1 <Production of resin-coated magnetic carrier>
Next, using a universal mixing stirrer (Dalton) as the first apparatus, 1500 g of the spherical composite particles A and an acrylic resin (manufactured by Mitsubishi Rayon Co., Ltd .: BR-105) are placed in the apparatus under the atmosphere. 11.25g was added as solid content, it heated up to 70 degreeC, stirring, and it hold | maintained at the same temperature for 2 hours, and formed the resin coating layer which consists of acrylic resins.

Using a fluidized bed as the second apparatus, 1500 g of the spherical composite particles A subjected to the first treatment were charged into a rolling fluidized bed (SFP, manufactured by POWREC) and retained in the fluidized bed. The component which forms a surface coating layer in the state was added, and the surface coating layer was formed on the particle surface. The supply air was taken from the atmosphere, the supply air temperature was 80 ° C., and the supply air flow rate was 0.8 m ³ / min. The nozzle for spraying the surface forming layer has an atomizing air amount of 30 L / min, a spraying speed of 7 g / min, and an acrylic resin (manufactured by Mitsubishi Rayon Co., Ltd .: BR-105) that forms the second layer as a solid content. 18.75 g was sprayed. The rotor speed is 600 r. p. m. It was.

  The obtained electrophotographic magnetic carrier having a resin coating layer was kept at 100 ° C. for 4 hours and subjected to heat treatment. At this time, the rate of temperature increase was controlled to 5 ° C./min, and the rate of temperature decrease was controlled to 5 ° C./min.

The magnetic carrier for electrophotography having the obtained resin coating layer has an average particle diameter of 36.0 μm, a bulk density of 1.79 g / cm ³ , a specific gravity of 3.48 g / cm ³ , a saturation magnetization value of 73.2 Am ² / kg, flow rate 37.3 sec / 50 g, water content 0.58%, electric resistance 6.8 × 10 ¹⁴ Ω · cm.

  The ratio of the measured values after 10 seconds and 120 seconds after the charge amount measurement was 65.0.

  As a result of observing the sample 10 seconds after the measurement of the charge amount with a scanning electron microscope, 3 field observations were performed with a 1000 × field of view, and cracks in the surface coating layer were confirmed for 3 out of 18 total magnetic carriers. Was 16.7%. Further, the coating state of the surface coating layer of the magnetic carrier before the charge amount measurement was uniform.

  Tables 1 and 2 show production methods of the magnetic carrier having the obtained resin coating layer, and Tables 3 and 4 show the characteristics and printing durability evaluation results of the obtained magnetic carrier.

Examples 2-17, Comparative Examples 1-10
Surface coating on magnetic core particles in the same manner as in Example 1 except that the type of magnetic core particles, the first time, and the second time treatment, the apparatus used, the type of resin, and the resin coating amount were variously changed. A magnetic carrier for an electrophotographic developer having a layer formed thereon was obtained.

  The production conditions at this time are shown in Tables 1 and 2, and the characteristics of the magnetic carrier for electrophotographic developer in which the surface coating layer is formed on the obtained magnetic core particles and the printing durability evaluation results are shown in Tables 3 and 4.

  The silicone resin used was KR-251 manufactured by Shin-Etsu Chemical Co., and the carbon black used was MA600 manufactured by Mitsubishi Chemical Corporation.

  The magnetic carrier for an electrophotographic developer according to the present invention provides adhesion between the magnetic core particles and the surface coating layer in the first treatment by using two or more kinds of processing apparatuses. A second treatment is performed on the surface. Therefore, an apparatus having a shearing force and a kneading force is preferable for the first time. In the second and subsequent times, a fluidized bed that is difficult to agglomerate and can be individually caused to flow individually to prevent the occurrence of crater-like cracks seen when the agglomerated material is crushed. Is preferred.

  As a result, the adhesion between the magnetic core particles and the surface coating layer is improved, and the strength of the formed surface coating layer is improved, whereby a carrier excellent in durability and environmental stability can be produced.

  Since the durability is improved and the charging property is stably maintained, it is suitable as a magnetic carrier for an electrophotographic developer.

Claims (1)

A magnetic carrier for an electrophotographic developer in which a surface coating layer is formed mainly from a resin on the surface of magnetic core particles, and the measured value after 10 seconds and 120 seconds after measurement of the charge amount of the magnetic carrier. A magnetic carrier for an electrophotographic developer, wherein a ratio (charge amount after 10 seconds) / (charge amount after 120 seconds) to a later measured value is 60% or more.