JP2010014853A - Manufacturing method of magnetic carrier, and magnetic carrier manufactured by using the manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of magnetic carrier by which the surface of a magnetic carrier core is more uniformly coated with a cover resin so as to enhance the adhesiveness of a coated layer. <P>SOLUTION: The manufacturing method of magnetic carrier includes: a coating process of coating the surface of the magnetic carrier core with a resin composition by using a coating device having a means, which performs the coating by means of a mechanical impact force; and a heating process of heating the coated magnetic carrier by using a heating device having a heating means. Wherein, the heating process is satisfied by the following relations (1), (2):(1) Tg(°C)≤Th(°C)≤Tg+50(°C); and (2)1,000(°C min)≤Th×M(°C min)≤30,000(°C min). Therein, Th denotes a heating temperature in the heating process; Tg denotes a glass transition temperature of a resin component contained in the resin composition; and M denotes a heating time in the heating process. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrophotographic method in which an electrostatic latent image formed on an electrostatic latent image carrier that is an electrophotographic photosensitive member is developed with a two-component developer, and a toner is formed on the electrostatic latent image carrier. The present invention relates to a manufacturing method of a magnetic carrier used in a developing method for forming an image, and a magnetic carrier using the manufacturing method.

In recent years, two-component developers used in electrophotography have been renewed in terms of performance in order to meet market needs such as an accelerated color shift for office use, high definition for the graphics market, and high speed for light printing. High image quality and high stability are required.
At present, as the magnetic carrier constituting the two-component developer, a coated carrier in which a coating resin is coated on the surface of a ferrite particle or a magnetic material-dispersed resin core is mainly used. The coat layer plays the role of stabilizing the charge amount distribution of the toner and suppressing the injection of charges from the magnetic carrier to the photoreceptor. However, the coating of the coating resin on the surface of the magnetic carrier core is still insufficiently studied, and there are still many problems related to uniform coating.

As a conventional method for producing a magnetic carrier, there is a so-called dipping method in which a solvent is volatilized while stirring a magnetic carrier core and a coating resin solution, and a coating resin is coated on the surface of the magnetic carrier core. In many cases, a wet coating method is used, such as a method in which a coating resin solution is sprayed by a spray nozzle while forming a fluidized bed with a magnetic carrier core and the coating resin is coated on the surface of the magnetic carrier core.
However, the wet coating method has a problem that coalescence of the magnetic carrier particles easily occurs when the solvent volatilizes. Once the magnetic carrier that has been coalesced is crushed by stirring, the surface of the magnetic carrier core is exposed on the crushed surface, and so-called leakage, which is a phenomenon of charge injection from the magnetic carrier to the photoreceptor, is likely to occur. Become. When this leak occurs, the surface potential of the photosensitive member converges on the developing bias, so that the development contrast cannot be secured, and a blank image may be generated. Further, since the surface of the magnetic carrier core is exposed, it becomes impossible to retain the charge of the toner, particularly under high temperature and high humidity, and image defects due to the low charge of the toner after long-term durability are likely to occur. Furthermore, the exposed surface of the magnetic carrier core makes it easier for the coat layer to peel off from the interface between the core surface and the coat layer, which may promote a reduction in image quality after long-term durability.
In the wet coating method, when the magnetic carrier particles are coalesced, the yield tends to deteriorate. Usually, classification is performed at the final stage of the magnetic carrier manufacturing process, but the magnetic carriers that are united and not crushed are removed. Furthermore, a drying process for completely removing the solvent is also necessary, and it causes a tact-up, so that many problems still remain with respect to the wet method from the viewpoint of production.

  Therefore, a dry coating method has been proposed to overcome the above-described problems of the wet coating method. For example, using a high-speed agitation mixer, the powdered processed product is mixed and stirred with a stirring blade, and the carrier is thermally coated at or above the glass transition point (Tg) of the coating resin contained in the processed product. Is disclosed (Patent Document 1). However, in this method, the inside of the apparatus is heated with a jacket, and the temperature of the entire processed product becomes equal to or higher than the Tg of the coating resin contained in the processed product. However, it is still insufficient in terms of uniform coating.

In addition, a method of performing dry coating by mechanical impact force has also been proposed (Patent Document 2). For example, a method is disclosed in which resin particles having a particle size of 1/10 or less of magnetic particles are coated on the surface of magnetic particles using a surface treatment apparatus having a rotor and a liner. In this method, the resin particles are dispersed on the carrier surface using an apparatus different from the apparatus for coating treatment, and there is an inconvenience that a separate apparatus for dispersion is required. When a dispersion apparatus is not used, the resin particles remain in a released state, and it is difficult to satisfactorily perform the resin particle coating process on the surface of the carrier core. Even if resin particles are attached to the surface of the carrier core using an apparatus different from the apparatus for coating treatment, if an amount of resin particles that cannot be attached is added, excess resin particles are released. Therefore, it is difficult to perform uniform coating. Therefore, in this method, the coating amount is limited, and it may be difficult to control the toner charge amount and to suppress the injection of charges from the magnetic carrier to the photoconductor.

Further, as a powder processing method using mechanical impact force, a powder processing method has been proposed in which an unprecedented powerful force is applied to a processed product while taking advantage of a rotary blade type device (Patent Document 3). ). According to this method, not only mixing and drying processes but also various processes such as compounding (integration), surface modification, smoothing, shape control (spheronization, etc.) can be performed. However, in order to use this method as a method for coating the resin composition on the surface of the magnetic carrier core in a dry manner, studies on processing conditions and the like are still insufficient.
JP 09-160307 A JP 63-235959 A JP 2005-270955 A

  An object of the present invention is to provide a magnetic carrier manufacturing method in which the coating of the coating resin on the surface of the magnetic carrier core is made more uniform and the adhesion of the coating layer is improved, and a magnetic carrier using the manufacturing method. is there. Thereby, the charge imparting property to the toner is improved and the developing property is improved. In addition, the wear resistance of the coating layer on the surface of the magnetic carrier core can be improved over a long period of time, and in particular, by suppressing the decrease in charge amount of the toner under high temperature and high humidity, the decrease in image density can be suppressed. It is to obtain a magnetic carrier that can be used.

Said subject is achieved by the structure of the following this invention.
[1] Coating using a coating processing apparatus having a means for coating with a mechanical impact force, a coating processing step for coating the resin composition on the surface of the magnetic carrier core, and a heating processing apparatus having a heating means. A heat treatment step of heat-treating the treated magnetic carrier, and a method for producing a magnetic carrier obtained by coating the surface of the magnetic carrier core with a resin composition,
The coating treatment step uses a coating processing apparatus having a rotating body having at least a plurality of stirring members installed on the surface, and a casing provided with the stirring member and a gap, and rotates the rotating body, The resin composition is coated on the surface of the magnetic carrier core by mixing the magnetic carrier core and the resin composition introduced into the coating processing apparatus,
The magnetic carrier and the resin composition charged into the coating processing apparatus have a space filling rate of the magnetic carrier core and the resin composition to be charged with respect to a space between the rotating body and the inner peripheral portion of the casing. , The input amount is adjusted to be 50% or more and 98% or less,
The magnetic carrier core and the resin composition charged into the coating processing apparatus are sent in one axial direction of the rotating body by a part of the stirring members, and the plurality of stirring members The other part of the stirring member is returned to the reverse direction of the axial direction of the rotating body, and the magnetic carrier surface is coated with the resin composition while feeding and returning, and the heating The method of manufacturing a magnetic carrier, wherein the treatment step is heat-treated under conditions satisfying the following formulas (1) and (2).
Tg (° C.) ≦ Th (° C.) ≦ Tg + 50 (° C.) (1)
1000 (° C./min)≦Th×M (° C./min)≦30000 (° C./min) (2)
(Th: Heat treatment temperature in the heat treatment step, Tg: Glass transition temperature of the resin component contained in the resin composition, M: Heat treatment time in the heat treatment step)
[2] In the covering process, the temperature is controlled by introducing a fluid into a flow path provided in the rotating body and / or a flow path provided in the casing in the clothing processing apparatus, and the covering is performed. The method for producing a magnetic carrier according to claim 1, wherein the coating treatment temperature Tc (° C.) in the treatment step and the heat treatment temperature Th (° C.) in the heat treatment step satisfy the following formula (3).
Tc (° C.) ≦ Th (° C.) (3)
[3] The method for producing a magnetic carrier according to claim 1 or 2, wherein the heat treatment in the heat treatment step is performed at an oxygen concentration of 10.0% by volume or less.
[4] The resin composition according to any one of claims 1 to 3, wherein the resin composition has at least a resin component and fine particles having a number average particle diameter (D1) of 0.01 μm or more and 3.00 μm or less. Manufacturing method of magnetic carrier.
[5] A magnetic carrier manufactured by the manufacturing method according to any one of claims 1 to 4.
[6] The magnetic carrier has a volume-based 50% particle size (D50) of 15 μm or more and 100 μm or less, and a true specific gravity of 2.5 g / cm ³ or more and 5.2 g / cm ³ or less. The magnetic carrier according to claim 5.

  According to the present invention, it is possible to produce a magnetic carrier in which the coating of the coating resin on the surface of the magnetic carrier core is more uniform and the adhesion of the coating layer is improved. Thereby, it is possible to improve the charge imparting property to the toner and improve the developability. In addition, the wear resistance of the coating layer on the surface of the magnetic carrier core can be improved over a long period of time, and in particular, by suppressing the decrease in charge amount of the toner under high temperature and high humidity, the decrease in image density can be suppressed. Can be obtained.

  Hereinafter, the best mode for carrying out the present invention will be described in detail.

The method for producing a magnetic carrier according to the present invention includes a coating processing step of coating a resin composition on the surface of a magnetic carrier core using a coating processing apparatus having a coating processing means by mechanical impact force, and a heating means. And a heat treatment step of heat-treating the coated magnetic carrier using a heat treatment apparatus.
First, the magnetic carrier coating process of the present invention will be described in detail.

The magnetic carrier coating processing step of the present invention uses a coating processing apparatus having a rotating body having at least a plurality of stirring members installed on the surface, and a casing provided with a gap between the stirring members and the above-described rotation. The surface of the magnetic carrier core is coated with the resin composition by rotating the body and mixing the magnetic carrier core and the resin composition put into the coating processing apparatus,
The magnetic carrier and resin composition charged into the coating treatment apparatus have a space filling rate of 50% of the magnetic carrier core and resin composition charged relative to the space between the rotating body and the inner periphery of the casing. %, And the input amount is adjusted to be 98% or less,
The magnetic carrier core and the resin composition charged into the coating processing apparatus are sent in one axial direction of the rotating body by some stirring members of the plurality of stirring members, and the blades of the plurality of stirring members The other part of the stirring member is returned to the reverse direction of the axial direction of the rotating body, and the resin composition is coated on the surface of the magnetic carrier while feeding and returning. This is a so-called dry coating method. Hereinafter, the present invention will be described with reference to schematic views of the dry coat apparatus shown in FIGS. 1 and 2-1.

The coating processing step of the present invention is performed using a coating processing apparatus having means for coating processing by mechanical impact force. For example, a coating processing apparatus having the following structure can be used.
First, an object to be processed consisting of a magnetic carrier core and a resin composition is introduced from the inlet 5 in FIG. When the space filling rate of the processed product to be filled in the space 9 between the inner peripheral portion of the casing 1 and the rotating body 2 is 50% or more and 98% or less, the resin composition on the surface of the magnetic carrier core The coating process can be performed uniformly and quickly. More preferably, it is 70% or more and 98% or less. Here, the space filling rate means [amount of charged object to be processed (mass)] / [(volume of space 9 between the inner periphery of casing 1 and rotating body 2) × (slack of object to be processed). Apparent density)] × 100. When the space filling rate is 50% or more, in addition to the collision between the stirring blade 3 provided on the surface of the rotator 2 and the processing object, the objects to be processed can sufficiently collide with each other, and the inside of the casing 1 The coating process in the minute gap between the peripheral portion and the stirring blade 3 can be performed efficiently. In addition, since the space filling rate can be made higher than that of the conventional dry coating method using mechanical impact force, tact-up is also possible. When the space filling rate is less than 50%, the collision between the objects to be processed becomes insufficient, and the surplus resin composition is released, so that it is difficult to perform uniform coating. End up. Further, the adhesion of the coat layer to the surface of the magnetic carrier core is also insufficient. When the space filling rate exceeds 98% by volume, the filling rate in the space 9 is too large, the movement path of the objects to be processed becomes short, the collision between the objects to be processed becomes insufficient, and uniform coating is performed. It becomes difficult.

  In addition, as a method of charging the object to be processed, the magnetic carrier core and the coating resin composition may be charged separately, or may be mixed with a mixer or a mill before charging. In the dry coating method, which is a coating treatment method of the magnetic carrier of the present invention, the space filling rate is 50% or more and 98% or less. It is an advantage that good treatment is possible even if the materials are charged separately.

  Next, the charged object to be processed is coated and processed in a minute gap between the inner peripheral portion of the casing 1 and the stirring blade 3 while being stirred and mixed by the stirring blade 3 provided on the surface of the rotating body 2. It is discharged from the discharge port 6. In FIG. 1, the rotating body 2 rotates in a direction in which a stirring blade positioned below moves upward through the front surface of the sheet. At this time, the stirring blade 3a on the surface of the rotating body 2 shown in FIG. 2A is a feed stirring mechanism for sending the object to be processed in one axial direction of the rotating body 2 (from the inlet 5 to the outlet 6). The stirring blade 3b functions as a return stirring mechanism for sending the object to be processed in a direction opposite to one direction of the axial direction of the rotating body 2 (discharge port 6 → input port 5). By these mechanisms, the workpiece is repeatedly fed and returned, and the movement path of the workpiece in the casing 1 becomes complicated and long. By this feeding and returning, the collision between the stirring blade 3 and the object to be processed and the collision between the objects to be processed are caused more sufficiently, and the coating process in the minute gap between the inner peripheral portion of the casing 1 and the stirring blade 3 is more efficiently performed. It can be carried out. As a result, the resin composition can be uniformly and rapidly coated on the surface of the magnetic carrier core.

  The positional relationship of the stirring blades 3 provided on the surface of the rotating body 2 is preferably arranged as in the following example. For example, the stirring blade 3b has an end position on the charging port 5 side that overlaps with an end position on the discharge port 6 side of another adjacent stirring blade 3a on the charging port 5 side in an axial position. preferable. That is, in FIG. 2A, when a line is drawn in the vertical direction from the end position of the stirring blade 3a, it is preferable that the stirring blade 3a and the stirring blade 3b adjacent to the 3a overlap each other by a width d. The positional relationship is the same in other stirring blades. When the stirring blade 3a and the stirring blade 3b are in this positional relationship, the processed product easily moves from the end of the stirring blade 3a to the end of the stirring blade 3b. And return can be performed more effectively. In addition, it is preferable that the length of the width | variety d where said stirring blade 3a and the stirring blade 3b overlap is 50% or less of the axial length of the rotary body of a blade.

  Moreover, as a shape of the stirring member of the coating processing apparatus used for this invention, what was shown, for example in FIG. 2 can be used. As shown in FIG. 2-1, in addition to the agitating / returning agitating blade such as the agitating blade 3a or 3b, in the same direction as the axial direction of the rotating body as shown in FIGS. 2-2 and 2-3. There may be a stirring blade 3c arranged. Further, the shape of the stirring member may be a paddle shape as shown in FIG. The shape, installation, and angle of the stirring member can be appropriately adjusted depending on the particle diameter, true specific gravity, and fluidity of the processed material such as the magnetic carrier core and the resin composition.

The peripheral speed of the stirring member is 5 m / sec or more and 50 m / sec or less at the outermost end portion of the stirring member in that the resin composition can be uniformly and rapidly coated on the surface of the magnetic carrier core. preferable. More preferably, it is 10 m / sec or more and 20 m / sec or less.
If the peripheral speed of the stirring member is within the above range, the resin composition that is not coated on the magnetic carrier core does not remain, and the magnetic carrier core is not cracked or chipped. Good coating treatment can be performed.

  In the coating processing apparatus used in the present invention, the gap between the casing and the stirring member is 0.5 mm or more and 30.0 mm or less, so that the surface of the magnetic carrier core can be uniformly and quickly coated. It is preferable in that it can be performed. More preferably, it is 1.0 mm or more and 10.0 mm or less. As long as the gap between the casing and the stirring member is within the above range, as in the case where the peripheral speed is within the above range, stable and satisfactory treatment can be performed. Moreover, it is preferable that the processing time of the said to-be-processed object using the said coating processing apparatus is 2 minutes or more and 60 minutes or less.

The heat treatment step of the magnetic carrier in the present invention is characterized in that the heat treatment is performed under the conditions satisfying the following formulas (1) and (2) following the above-described coating treatment step.
Tg (° C.) ≦ Th (° C.) ≦ Tg + 50 (° C.) (1)
1000 (° C./min)≦Th×M (° C./min)≦30000 (° C./min) (2)
(Th: Heat treatment temperature in the heat treatment step, Tg: Glass transition temperature of the resin component contained in the resin composition, M: Heat treatment time in the heat treatment step)

  Although the reason is not clear by performing the heat treatment satisfying the above formulas (1) and (2) following the coating treatment step, the adhesion between the coat layer and the magnetic carrier core in the magnetic carrier is improved, and long-term It has been found that a magnetic carrier capable of obtaining a good image can be obtained.

When the heat treatment temperature Th (° C.) in the heat treatment step is in the range of the formula (1), the resin component in the coating layer after the coating treatment is in a semi-molten state, and the coating layer and the surface of the magnetic carrier core are slightly It is considered that the formation of a gap can be prevented, and the distortion of the adhesive surface between the coated magnetic carrier core and the resin composition can be reduced. This makes it possible to form a coat layer with high adhesion to the magnetic carrier core. More preferably, Th (° C.) is Tg (° C.) or more and Tg + 30 (° C.) or less. Moreover, even if the heat treatment temperature is higher than the glass transition temperature of the resin component in the heat treatment step because the coating treatment step in the present invention is the above method, the surplus resin composition at the time of the coating treatment is obtained. It does not promote the union of magnetic carriers. When the heat treatment temperature Th (° C.) is lower than the glass transition temperature Tg (° C.) of the resin component contained in the resin composition, the resin component in the coat layer in the magnetic carrier after the coating treatment step is in a semi-molten state. It is considered that the wear resistance of the surface of the magnetic carrier in the long term cannot be improved. When the heat treatment temperature Th (° C.) is higher than the glass transition temperature Tg + 50 (° C.) of the resin component contained in the resin composition, the resin component in the coat layer in the magnetic carrier after the coating treatment step is in a molten state. It is thought that will become,
The union of magnetic carriers is promoted in the heat treatment process.

  Furthermore, when the relationship between the heat treatment temperature Th (° C.) in the heat treatment step and the heat treatment time M (min) in the heat treatment step is in the range of the formula (2), appropriate heat energy is given to the magnetic carrier. Therefore, it is possible to form a coat layer having higher adhesion to the magnetic carrier core. More preferably, Th × M (° C./min) is 3000 (° C./min) or more and 15000 (° C./min) or less. When Th × M (° C./min) is smaller than 1000, further improvement in adhesion cannot be expected. If Th × M (° C. · min) is greater than 30000, the thermal energy applied may be too large, or the magnetic carriers may be merged.

  As a heat treatment apparatus that can be used in the heat treatment step in the present invention, a bat-type treatment apparatus in which a coating treatment product is put in a metal or heat-resistant glass container and processed by a vacuum dryer, and the coating treatment article is a rotating container. Any of a rotary type heat treatment apparatus, a batch mixer equipped with a stirring blade and heat treatment means, and a continuous mill can be used. In the present invention, a rotary heat treatment apparatus is preferably used from the viewpoint that the coalescence of the magnetic carriers is suppressed and the heat treatment can be performed uniformly.

Further, in the coating process in the present invention, the temperature is controlled by introducing a fluid into the channel provided in the rotating body and / or the channel provided in the casing in the clothing processing apparatus, and the coating process It is preferable that the coating treatment temperature Tc (° C.) in and the heat treatment temperature Th (° C.) in the heat treatment step satisfy the following formula (3).
Tc (° C.) ≦ Th (° C.) (3)
Therefore, it is preferable that the coating processing apparatus used in the coating processing step of the present invention is provided with a flow path for temperature control in the rotating body and the casing in the coating processing apparatus. For example, as shown by 4 in FIG. 1, a jacket 4 exists in the casing 1 and the jacket is used as a flow path. Moreover, the inside of a rotary body and a rotary body axis | shaft can be made into a cavity, and the cavity can be made into a flow path.
In the coating treatment step of the present invention, uniform coating treatment is possible even when the coating treatment temperature Tc is lower than the glass transition temperature Tg of the resin component. The reason for this is that the casing and the stirring member collide with the input processing object by adjusting the space filling rate of the processing object to be input to the coating processing apparatus and the feed / return mechanism in the coating processing apparatus in the present invention. In addition, it is conceivable that Tc is locally greater than or equal to Tg due to the heat of collision caused by the effective collision between objects to be processed. Therefore, a coating layer having higher adhesion with the magnetic carrier core can be formed by performing a coating process with Tc set at a lower temperature and performing a heat treatment with Th set to Tc or higher. When Th is lower than Tc, it is considered that the resin component in the coat layer of the magnetic carrier after the coating treatment is not in a semi-molten state, and it is possible to improve the wear resistance of the surface of the magnetic carrier over a long period of time. Absent.

  Moreover, it is preferable that the heat processing of the heat processing process in this invention are performed by oxygen concentration 10.0 volume% or less. This is because the magnetic material used for the magnetic carrier core may be oxidized when the oxygen concentration is high at high temperatures. As the oxidation of the magnetic carrier core proceeds, the specific resistance of the prepared magnetic carrier increases, and there is a tendency that good developability cannot be obtained. Further, as means for reducing the oxygen concentration to 10.0% by volume or less, it is performed by a decompression process using a vacuum pump and a flow of an inert gas such as nitrogen gas. In the present invention, by performing a heat treatment under a condition in which the oxygen concentration is suppressed to 10.0% by volume or less by the flow of nitrogen gas, the charge imparting property to the toner as a magnetic carrier is improved, and the magnetic carrier core and the coating are coated. Since the adhesiveness of a layer improves, it is used preferably.

In the method for producing a magnetic carrier of the present invention, the resin composition covering the magnetic carrier core has at least a resin component and fine particles having a number average particle diameter (D1) of 0.01 μm or more and 3.00 μm or less. It is preferable. This is because when the resin component of the resin composition is coated on the surface of the magnetic carrier core, the fine particles are interposed between the magnetic carrier cores to exert a spacer effect. Thereby, generation | occurrence | production of the unification | combination of a magnetic carrier can further be suppressed, and coat uniformity can further be improved. Also in the heat treatment step, since the fine particles are interposed between the magnetic carrier cores and exhibit a spacer effect, a magnetic carrier with high coat uniformity and high wear resistance can be obtained. As the fine particles, crosslinkable resin particles, metal oxides, carbon black and the like are preferably used, and spherical shapes are preferably used. On the other hand, when the number average particle diameter of the fine particles is smaller than 0.01 μm, the spacer effect cannot be obtained, and further improvement in coat uniformity cannot be expected. On the other hand, when the number average particle diameter of the fine particles exceeds 3.00 μm, the spacer effect can be obtained, but the dispersion of the fine particles becomes non-uniform, and thus there may be variations in the charge imparted to the toner. .

The magnetic carrier obtained by the production method of the present invention has a volume-based 50% particle size (D50) of 15 μm or more and 100 μm or less, and a true specific gravity of 2.5 g / cm ³ or more and 5.2 g / cm ³ or less. Preferably there is.
When the magnetic carrier obtained by the present invention has a D50 of 15 μm or more and 100 μm or less, the mixing property of the magnetic carrier core and the resin composition during the production of the magnetic carrier is improved, and the coat uniformity is improved. In addition, when the obtained magnetic carrier is used as a two-component developer, the density of the magnetic brush at the development pole is optimized and the toner charge amount distribution can be sharpened. Can be planned.
When D50 exceeds 100 μm, the mixing property between the magnetic carrier core and the resin composition becomes insufficient in the coating treatment process at the time of manufacture, and the coalescence between the magnetic carriers tends to be promoted due to the unevenly distributed resin composition. It is in. Further, when the obtained magnetic carrier is used as a two-component developer, the density of the magnetic brush at the developing pole is sparse and the image quality tends to be lowered.
When D50 is less than 15 μm, the collision force between the magnetic carrier core and the resin composition becomes insufficient in the coating process during manufacturing, and the unification between the magnetic carriers is promoted due to the unevenly distributed resin composition. Tend to be. Further, when the obtained magnetic carrier is used as a two-component developer, the magnetic binding force of the magnetic brush at the developing pole is reduced, and the magnetic carrier tends to adhere to the photoreceptor. More preferably, D50 is 20 μm or more and 80 μm or less.
In the magnetic carrier obtained by the production method of the present invention, the volume-based 50% particle size (D50) can be adjusted to the above range by adjusting the particle size and the coating amount of the magnetic carrier core.

Further, the magnetic carrier obtained by the present invention has a mixing property of the magnetic carrier core and the resin composition in the coating treatment process at the time of manufacture when the true specific gravity is 2.5 g / cm ³ or more and 5.2 g / cm ³ or less. The impact force is improved and the coat uniformity is further improved. In addition, when the obtained magnetic carrier is used as a two-component developer, the difference in true specific gravity between the toner and the magnetic carrier becomes good, and charging to the toner can be made better. More preferably, it is 2.5 g / cm ³ or more and 4.2 g / cm ³ or less. That is, when the true specific gravity is adjusted within the above range, the toner and the magnetic carrier in the developing device are optimized to be charged, so that the toner is quickly charged. Further, toner deterioration can be suppressed, and when used as a carrier for a replenishing developer, a good image can be obtained over a long period of time even if the reinforcing developer is replenished. In the magnetic carrier obtained by the production method of the present invention, the value of the true specific gravity can be adjusted within the above range by adjusting the true specific gravity and the coating amount of the magnetic carrier core.

In addition, the magnetic carrier obtained by the production method of the present invention has a specific resistance value of 1.0 × 10 ⁶ Ω · cm or more and 1.0 × 10 ¹⁵ Ω · cm or less at an electric field strength of 5000 V / cm. preferable. If the specific resistance value is lower than 1.0 × 10 ⁶ Ω · cm, the possibility of leakage of charges from the magnetic carrier increases, and charges are injected from the magnetic carrier into the electrostatic latent image on the surface of the electrostatic latent image carrier. Therefore, there is a tendency that a so-called leak image is generated in which a toner layer is not formed and an image is lost. When the specific resistance value exceeds 1.0 × 10 ¹⁵ Ω · cm, the developability is lowered, and a so-called white-out image tends to be generated, which results in an edge-enhanced image. When the production method of the present invention is used, since the uniform coating property of the resin composition on the magnetic carrier core and the union of the magnetic carrier are less likely to occur, the resistance value of the magnetic carrier core is in the above range, Sufficient developability is obtained, and a high image density is obtained. In addition, the specific resistance value of the magnetic carrier obtained by the production method of the present invention can be adjusted to the above range by adjusting the coating amount and the resistance of the fine particles.

  As the magnetic carrier core used in the present invention, known magnetic carrier cores such as ferrite particles, magnetite particles, and magnetic material-dispersed resin carrier cores can be used. For example, the magnetic carrier core is manufactured as described below.

The magnetic carrier core is manufactured using a magnetic material. Magnetic materials include magnetic ferrite particles containing one or more elements selected from iron, lithium, beryllium, magnesium, calcium, rubidium, strontium, nickel, copper, zinc, cobalt, manganese, chromium and titanium, or magnetite Particles. Preferably, it is a magnetite particle or a magnetic ferrite particle having at least one element selected from copper, zinc, manganese, calcium, lithium and magnesium.
Specific examples of the magnetic material for ferrite include the following. Such as Ca—Mg—Fe ferrite, Li—Fe ferrite, Ca—Li—Fe ferrite, Mn—Mg—Fe ferrite, Mn—Mg—Sr—Fe ferrite, and Li—Mg—Fe ferrite. Ferrite magnetic body of iron oxide.

  Ferrites of iron-based oxides can be obtained by mixing metal oxides, carbonates and nitrates in a wet or dry manner and pre-firing to obtain a desired ferrite composition. Next, the obtained iron-based oxide ferrite is pulverized to submicron. To the pulverized ferrite, 20 to 50% by mass of water for adjusting the particle size is added, and 0.1 to 10% by mass of polyvinyl alcohol (molecular weight of 500 to 10,000) is added as a binder resin. Prepare. The slurry is granulated using a spray dryer and fired to obtain a ferrite core.

  In addition, in order to adjust the true specific gravity of the magnetic carrier, when obtaining a porous ferrite core, the pores such as sodium carbonate and calcium carbonate and various organic substances are used for controlling the pore density during granulation. It can be obtained by adding a modifier to form a slurry, granulating using a spray dryer, and baking. Further, by adding a material that inhibits the particle growth during the ferritization reaction, a complicated void can be formed inside the ferrite. Examples of such materials include tantalum oxide and zirconium oxide.

In order to produce a magnetic material-dispersed resin carrier core, for example, a vinyl-based or non-vinyl-based thermoplastic resin, a magnetic material, and other additives are sufficiently mixed by a mixer. The obtained mixture is melted and kneaded using a kneader such as a heating roll, a kneader, or an extruder. A magnetic material-dispersed resin carrier core can be obtained by pulverizing and classifying the cooled melt-kneaded product. The obtained magnetic material-dispersed resin carrier core may be further spheroidized thermally or mechanically. As another method, a monomer for forming the binder resin of the magnetic material-dispersed resin carrier core can be obtained by polymerizing in the presence of the magnetic material. Examples of the monomer for forming the binder resin include the following.
Bisphenols and epichlorohydrin to form vinyl monomers, epoxy resins; phenols and aldehydes to form phenolic resins; urea and aldehydes to form urea resins, melamine and aldehydes.

  A method of synthesizing a phenol resin from phenols and aldehydes is particularly preferable. In this case, a magnetic substance, phenols and aldehydes are added to an aqueous medium, and the phenols and aldehydes in the aqueous medium are present in the presence of a basic catalyst. By polymerizing under the above, a magnetic material-dispersed resin carrier core can be produced.

  The phenols for producing the phenol resin may be compounds having a phenolic hydroxyl group in addition to phenol (hydroxybenzene). Examples of the compound having a phenolic hydroxyl group include alkylphenols such as m-cresol, p-tert-butylphenol, o-propylphenol, resorcinol, and bisphenol A; hydrogen of an aromatic ring (for example, benzene ring) or part of hydrogen of an alkyl group Or, halogenated phenols, all of which are substituted with chlorine atoms or bromine atoms.

  Examples of aldehydes for producing a phenol resin include the following. For example, formalin, formaldehyde in any form of paraformaldehyde, and furfural, more preferably formaldehyde.

  The molar ratio of aldehydes to phenols is preferably 1 to 4, and more preferably 1.2 to 3. If the molar ratio of aldehydes to phenols is less than 1, particles are difficult to produce, and even if they are produced, the resin does not easily cure, and the strength of the particles produced tends to be weak. On the other hand, when the molar ratio of aldehydes to phenols is larger than 4, unreacted aldehydes remaining in the aqueous medium after the reaction may increase, and the granulation property may decrease. The condensation of phenols with aldehydes can be performed using a basic catalyst. The basic catalyst may be any catalyst used in the production of ordinary resol type resins. Examples of the basic catalyst include aqueous ammonia, hexamethylenetetramine, dimethylamine, diethyltriamine, and alkylamines such as polyethyleneimine. Is included. The molar ratio of these basic catalysts to phenols is preferably 0.02 to 0.3.

Next, the resin composition for coating the magnetic carrier core surface used in the present invention will be described.
The resin composition used in the present invention contains at least a resin component. As the resin component, a thermoplastic resin is preferably used. Moreover, as a resin component, one type of resin may be sufficient and the combination of 2 or more types of resin may be sufficient. Examples of the thermoplastic resin as the resin component include polystyrene; acrylic resins such as polymethyl methacrylate and styrene-acrylic acid copolymer; styrene-butadiene copolymer; ethylene-vinyl acetate copolymer; polyvinyl chloride; Polyvinyl acetate; polyvinylidene fluoride resin; fluorocarbon resin; perfluorocarbon resin; solvent-soluble perfluorocarbon resin; polyvinyl alcohol; polyvinyl acetal; polyvinyl pyrrolidone; petroleum resin; cellulose; Cellulose derivatives such as propyl cellulose; novolak resin; low molecular weight polyethylene; saturated alkyl polyester resin, polyethylene terephthalate, Polybutylene terephthalate, such as polyarylate polyester resin; include polyether ketone resin; polyamide resin; polyacetal resin; polycarbonate resins; polyether sulfone resins; polysulfone resin; polyphenylene sulfide resin.

When the weight average molecular weight Mw of the tetrahydrofuran (THF) soluble part of the resin component contained in the resin composition is 15,000 to 1,000,000, the adhesion to the magnetic carrier core and the coating are performed. This is particularly preferable in that the surface of the magnetic carrier core can be uniformly coated.

  Moreover, about the glass transition temperature (Tg) measured with the differential scanning calorimetry apparatus of the resin component contained in a resin composition, 50 to 150 degreeC is preferable for performing the heat processing in this invention.

  Moreover, the resin composition may contain fine particles. The content of the fine particles in the resin composition covering the magnetic carrier core is preferably contained in a ratio of 2 to 100 parts by mass of the fine particles with respect to 100 parts by mass of the resin component. When the content of the fine particles is within the above range, the spacer effect that is the effect of adding the fine particles is sufficiently exhibited, and it is possible to perform good resin coating on the magnetic carrier core. On the other hand, the durability of the coating layer is not impaired.

  The fine particles contained in the resin composition used in the present invention may be any fine particles of an organic material and an inorganic material, but are crosslinked having a strength capable of maintaining the shape of the fine particles when coated. Resin fine particles and inorganic fine particles are preferred. Examples of the crosslinked resin forming the crosslinked resin fine particles include a crosslinked polymethyl methacrylate resin, a crosslinked polystyrene resin, a melamine resin, a guanamine resin, a urea resin, a phenol resin, and a nylon resin. Examples of the inorganic fine particles include magnetite, hematite, silica, alumina, and titania. In particular, the above-mentioned inorganic fine particles are preferable from the viewpoint of promoting charging imparted to the toner, reducing charge-up, and improving releasability from the toner. As the shape of the fine particles, a spherical shape is preferably used in order to obtain a spacer effect during the coating treatment.

Moreover, the resin composition used in the present invention may contain conductive fine particles. The conductive fine particles preferably have a volume resistance of 1 × 10 ⁸ Ω · cm or less, and more preferably 1 × 10 ⁶ Ω · cm or less. Moreover, it is preferable that an average primary particle diameter is 10 nm or more and 100 nm or less. Examples of the conductive fine particles include carbon black fine particles, graphite fine particles, zinc oxide fine particles, and tin oxide fine particles. In particular, carbon black fine particles are preferable as the conductive fine particles. These conductive fine particles can appropriately control the specific resistance of the magnetic carrier due to the good conductivity with a small addition amount.

  As an example of the method for producing the resin component contained in the resin composition used in the present invention, any polymerization method such as a solution polymerization method, an emulsion polymerization method, and a suspension polymerization method can be applied. The resin composition has a Db / Dc of 0.10 or more, where 50% particle size (D50) of the resin composition is Db (μm) and D50 of the electrophotographic carrier core is Dc (μm). It is preferably introduced into the apparatus in the form of fine particles satisfying 50 or less. A resin composition in this particle size range can be obtained by changing the conditions during the polymerization reaction or by crushing the binder resin after drying after the polymerization reaction. Moreover, when adding microparticles | fine-particles to a resin composition, it may add at the time of a polymerization reaction, and may mix with a mixer after a grinding | pulverization.

  Moreover, it is also possible to dry up the resin solution which melt | dissolved the resin component in the solvent by the spray-drying method, and to use it as a resin composition. When adding fine particles when obtaining a resin composition by the spray drying method, after the fine particles are dispersed in the resin solution with a bead mill using a medium, the particles may be dried up by the spray drying method. The resin composition and fine particles may be mixed. Furthermore, when the resin component used in the resin composition is a solid having a large particle size, the resin component and the fine particles are mixed, and the resin component and the fine particles are kneaded with a twin screw extruder, and then pulverized. A method of obtaining a resin composition by pulverizing with a machine is also preferably used.

  The toner used with the magnetic carrier of the present invention is not particularly limited, and known toners such as a binder resin, a colorant, and wax can be used. For example, it may be produced by any method such as a pulverization method, a polymerization method, an emulsion aggregation method, and a dissolution suspension method. Further, it is preferable to use a polyester resin, a vinyl resin, or a hybrid resin as the main component of the binder resin.

Below, the measuring method concerning this invention is described in detail.
<Method for Measuring Space Filling Ratio of Magnetic Carrier Core and Resin Composition Charged into Coating Treatment Apparatus>
First, water is filled in the space between the inner peripheral portion of the casing constituting the coating processing apparatus and the rotating body, and the volume of the water (space volume in the coating processing apparatus) is measured. Next, the loose apparent density (g / cm ³ ) of the mixture of the magnetic carrier and the resin composition is measured using a powder tester PT-R (manufactured by Hosokawa Micron). The measurement environment was 23 ° C. and 50% RH. For the measurement, the mixture was collected in a metal cup having a capacity of 100 cc using a sieve having an aperture of 150 μm and vibrating at an amplitude of 1 mm until it became exactly 100 cc. Then, the loose apparent density (g / cm ³ ) is measured from the amount of the mixture collected in the metal cup.
Subsequently, the space filling rate (%) was obtained by the calculation formula shown below.
Space filling rate (%) = preparation amount (mass) of the mixture / (sloose apparent density of the mixture × volume of the space) × 100

<Measurement of glass transition point (Tg) of resin component contained in coating resin composition>
The glass transition point (Tg) of the resin component contained in the resin composition is measured according to ASTM D3418-82 using a differential scanning calorimeter “Q1000” (manufactured by TA Instruments). The temperature correction of the device detection unit uses the melting points of indium and zinc, and the correction of heat uses the heat of fusion of indium. Specifically, about 10 mg of the resin composition is precisely weighed and placed in an aluminum pan, and an empty aluminum pan is used as a reference. Measurement is performed at ° C / min. In this temperature rising process, a specific heat change is obtained in the temperature range of 40 ° C to 100 ° C. At this time, the intersection of the intermediate point line of the baseline before and after the specific heat change and the differential heat curve is defined as the glass transition temperature Tg of the resin component contained in the resin composition.

<Measurement of number average particle diameter (D1) of fine particles contained in coating resin composition>
The particle size distribution of the fine particles was measured in a state where the resin component contained in the resin composition was dissolved in a soluble organic solvent and the fine particles were dispersed in the solution. As a measuring device, a laser diffraction particle size distribution analyzer LS-230 type (manufactured by Beckman Coulter) was used for measurement with a small amount of module attached. The optical model used in the measurement was a real part 1.5 and an imaginary part 0.3, and the refractive index of the organic solvent used was input as the refractive index of the solvent.

<Measurement of volume-based 50% particle size (D50) of coating resin composition, magnetic carrier core, and magnetic carrier>
The particle size distribution was measured with Microtrac MT3300EX (Nikkiso Co., Ltd.). For the measurement, a Turbotrac sample feeder for dry measurement was attached. As the particle size, a volume-based 50% particle size (D50) was obtained.

<Measurement of true specific gravity of magnetic carrier core, coating resin composition, and magnetic carrier>
As sample preparation, the magnetic carrier, magnetic carrier core, and resin composition can be measured as they are. When it was necessary to separate the magnetic carrier core and the resin composition from the magnetic carrier, the separation was performed by the following method. First, 100 parts by mass of a magnetic carrier was weighed into a glass bottle with a lid, 200 parts by mass of toluene was added, and the mixture was shaken with a shaker (YS-8D type: manufactured by Yayoi Co., Ltd.). The amplitude condition of the shaker was 200 rpm for 2 minutes. After shaking, the toluene solution was separated while collecting the magnetic carrier core from the outside of the bottle with a magnet. After repeating this 5 times, it was dried in a vacuum dryer at 50 ° C. for 8 hours, cooled to room temperature to obtain a magnetic carrier core, while obtaining a resin composition by removing toluene from the toluene solution. These were used as measurement samples.
As a method for measuring the true specific gravity, a gas replacement method using helium was used. Accupic 1330 (manufactured by Shimadzu Corporation) was used as the measuring apparatus. Measurement conditions are as follows: 4 g of a measurement sample is put in a stainless steel cell having an inner diameter of 18.5 mm, a length of 39.5 mm, and a capacity of 10 cm ³ . Next, the volume of the sample in the sample cell is measured by changing the pressure of helium, and the true specific gravity is obtained from the obtained volume and the mass of the sample.

<Molecular weight measurement of resin component contained in resin composition for coating>
The molecular weight distribution of the tetrahydrofuran (THF) soluble part of the resin component contained in the resin composition is measured by gel permeation chromatography (GPC) as follows.
First, the resin composition is dissolved in tetrahydrofuran (THF) at room temperature over 24 hours. The obtained solution is filtered through a solvent-resistant membrane filter “Maescho Disc” (manufactured by Tosoh Corporation) having a pore diameter of 0.2 μm to obtain a sample solution. The sample solution is adjusted so that the concentration of the component soluble in THF is 0.8% by mass. Using this sample solution, measurement is performed under the following conditions.
Apparatus: HLC8120 GPC (detector: RI) (manufactured by Tosoh Corporation)
Column: Seven series of Shodex KF-801, 802, 803, 804, 805, 806, 807 (manufactured by Showa Denko KK)
Eluent: Tetrahydrofuran (THF)
Flow rate: 1.0 ml / min
Oven temperature: 40.0 ° C
Sample injection volume: 0.10 ml
In calculating the molecular weight of the sample, standard polystyrene resin (for example, trade name “TSK Standard Polystyrene F-850, F-450, F-288, F-128, F-80, F-40, F-20, F— 10, F-4, F-2, F-1, A-5000, A-2500, A-1000, A-500 ", manufactured by Tosoh Corporation) are used.

<Measurement of resistivity of magnetic carrier>
The specific resistance of the magnetic carrier is measured using a measuring device outlined in FIG. The resistance measuring cell A includes a cylindrical holder 15 having a hole with a cross-sectional area of 2.4 cm ² , a lower electrode (stainless steel) 11, a lower electrode base (made of PTFE resin) 14, and an upper electrode (made of stainless steel) 12. Is done. A cylindrical holder 15 is placed on the lower electrode base 14, 0.7 g of a sample (for example, carrier) 13 is filled, the upper electrode 12 is placed on the filled sample 13, and the thickness of the sample is measured. Assuming that the thickness when there is no sample in advance is d ′ (blank), the thickness d of the actual sample when 0.7 g is filled, and the thickness d ′ (sample) when the sample is filled, the thickness of the sample is I can express.
d = d ′ (sample) −d ′ (blank)
The specific resistance of the carrier and the carrier core can be obtained by applying a voltage between the electrodes and measuring the current flowing at that time. For the measurement, an electrometer 16 (manufactured by Kesley 6517 manufactured by Kesley) and a processing computer 17 are used for control.
The measurement conditions are a contact area S = 2.4 cm ² between the magnetic component and the electrode, and a load of 240 g on the upper electrode. The voltage application condition uses an internal program of the electrometer. First, the electrometer itself determines whether a maximum of 1000 V can be applied (a range not exceeding the current limiter), and automatically determines the maximum value of the applied voltage. The voltage value obtained by dividing the maximum voltage value into five steps is used as a step, and the current value after being held for 30 seconds is measured. For example, when the maximum applied voltage is 1000 V, 1000 V, 800 V, 600 V, 400 V, and 200 V are applied, and the current value after holding for 30 seconds is measured in each step. By processing it by a computer, the electric field strength and the specific resistance are calculated and plotted on a graph. The specific resistance and the electric field strength are obtained by the following formula.
Specific resistance (Ω · cm) = (applied voltage (V) / measured current (A)) × S (cm ² ) / d (cm) electric field strength (V / cm) = applied voltage (V) / d (cm)
The specific resistance at 5000 V / cm of the magnetic carrier is read from the specific resistance at 5000 V / cm on the graph. The intersection of the vertical line of 5000 V / cm on the graph and the measured specific resistance line is taken as the specific resistance value at 5000 V / cm. If there is no intersection point, extrapolation of the measurement point is performed, and the intersection point of the vertical line of 5000 V / cm is set to a specific resistance value at 5000 V / cm.

  Hereinafter, the present invention will be described in more detail with reference to specific production examples and examples, but the present invention is not limited thereto.

<Magnetic carrier core production examples 1 to 3>
A magnetic carrier core (a-1) was produced using the materials shown below.
-Phenol 10 parts by mass-Formaldehyde solution (37% by mass aqueous solution) 6 parts by mass-Magnetite particles (number average particle size 0.3 μm) 84 parts by mass The above materials, 5 parts by mass of 28% by mass ammonia water, and 25 parts by mass water The mixture was placed in a flask, heated and maintained at 85 ° C. for 30 minutes with mixing, and polymerized for 3 hours to be cured. Then, it cooled to 30 degreeC, after adding water, the supernatant liquid was removed, the precipitate was washed with water, and then air-dried. Subsequently, this was dried under reduced pressure (5 hPa or less) at a temperature of 60 ° C. to obtain a magnetic carrier core (a-1) of a magnetic fine particle dispersed type in which magnetite particles were dispersed in a phenol resin. Table 1 shows the physical properties of the magnetic carrier core (a-1) obtained. Moreover, magnetic carrier cores (a-2) and (a-3) having different particle diameters were obtained by changing the amounts of water to 10 parts by mass and 90 parts by mass, respectively. Table 1 shows the physical properties of the magnetic carrier cores (a-2) and (a-3) thus obtained.

<Magnetic carrier core production example 4>
A ferrite carrier core was produced using the following materials.
Fe ₂ O ₃ 66.5 parts by mass MnCO ₃ 28.1 parts by mass Mg (OH) ₂ 4.8 parts by mass SrCO ₃ 0.6 parts by mass After wet mixing the ferrite composition at 900 ° C. 2 The time-calcined and calcined ferrite composition was pulverized with a ball mill. The number average particle size of the obtained pulverized product was 0.4 μm.
Water (300 parts by mass with respect to the pulverized product) and polyvinyl alcohol having a weight average molecular weight of 5,000 (3 parts by mass with respect to the pulverized product) were added to the obtained pulverized product, and granulated with a spray dryer. In an electric furnace, the granulated product is sintered at 1300 ° C. for 6 hours in a nitrogen atmosphere with an oxygen concentration of 1.0%, and then pulverized and further classified to form a magnetic carrier core having a Mn—Mg—Sr—Fe ferrite composition (A-4) was obtained. Table 1 shows the physical properties of the magnetic carrier core (a-4) obtained.

<Magnetic carrier core production example 5>
A ferrite carrier core was produced using the following materials.
Fe ₂ O ₃ 66.5 parts by mass MnCO ₃ 28.1 parts by mass Mg (OH) ₂ 4.8 parts by mass SrCO ₃ 0.6 parts by mass After wet mixing the ferrite composition at 900 ° C. 2 The time-calcined and calcined ferrite composition was pulverized with a ball mill. The average particle size of the obtained pulverized product was 0.4 μm.
To the obtained pulverized product, water (300 parts by mass with respect to the pulverized product), polyvinyl alcohol having a weight average molecular weight of 5,000 (2 parts by mass with respect to the pulverized product), and sodium carbonate (number average particles as a pore-forming agent). 5 parts by mass (diameter 2 μm) was added and granulated with a spray dryer. Firing in an electric furnace in a nitrogen atmosphere with an oxygen concentration of 1.0% at 1150 ° C. for 4 hours, further sintering in a nitrogen atmosphere not containing oxygen at 750 ° C. for 30 minutes, and then pulverizing and further classification. Thus, a magnetic carrier core (a-5) having a porous Mn—Mg—Sr—Fe ferrite composition was obtained. Table 1 shows the physical properties of the magnetic carrier core (a-5) obtained.

<Magnetic carrier core production example 6>
A magnetic carrier core (a-6) was produced using the materials shown below.
・ Polymethylmethacrylate resin (weight average molecular weight 80000) 30 parts by mass ・ Magnetite particles (number average particle size 0.3 μm) 70 parts by mass After the above materials were mixed with a Henschel mixer or the like, they were melt-kneaded with a twin screw extruder. . The obtained kneaded material was cooled, coarsely pulverized to 1 mm or less with a hammer mill, and further finely pulverized using a mechanical pulverizer. Next, after classifying the finely pulverized product with a wind classifier, a magnetic carrier core (a-6) was obtained by performing surface modification using a hybridization system (manufactured by Nara Machinery Co., Ltd.). Table 1 shows the physical properties of the magnetic carrier core (a-6) obtained.

<Magnetic carrier core production example 7>
Add magnetite particles (number average particle size 0.3 μm), water (300 parts by mass with respect to 100 parts by mass of magnetite particles) and polyvinyl alcohol having a weight average molecular weight of 5,000 (3 parts by mass with respect to the pulverized product), and spray. Granulated with a dryer. In an electric furnace, the granulated product is sintered at 1300 ° C. for 6 hours in a nitrogen atmosphere with an oxygen concentration of 1.0%, pulverized, and further classified to obtain a magnetic carrier core (a-7) having a magnetite composition. It was. Table 1 shows the physical properties of the magnetic carrier core (a-7) obtained.

<Production Example 1 of Resin Composition>
100 parts by weight of methyl methacrylate monomer was added to a four-necked flask having a reflux condenser, a thermometer, a nitrogen suction tube, and a friction stirrer. Further, 90 parts by mass of toluene, 110 parts by mass of methyl ethyl ketone, and 2.0 parts by mass of azobisisovaleronitrile were added. The obtained mixture was kept at 70 ° C. for 10 hours under a nitrogen stream to obtain an MMA polymer solution. The solvent was removed from the solution, and the resulting solid was roughly pulverized with a hammer mill, and further pulverized with a mechanical pulverizer to obtain a resin component. 10 parts by mass of carbon black (c-1) having an average primary particle size of 20 nm and a volume resistance of 9.8 × 10 ⁻² Ω · cm is added to 100 parts by mass of the obtained resin component, and a Henschel mixer is added. The mixture was stirred and mixed for 2 minutes to obtain a resin composition (b-1) which is a mixture of a resin component and a conductive agent. Table 2 shows the physical properties of the obtained resin composition (b-1).

<Production Example 2 of Resin Composition>
In Production Example 1 of the resin composition, the amount of carbon black (c-1) added was changed to 20 parts by mass, and the crosslinked polymethyl methacrylate fine particles (d-1) having a number average particle size of 0.3 μm were further 30 parts by mass. Except for the addition, a resin composition (b-2) was obtained in the same manner as in Production Example 1 of the resin composition. Table 2 shows the physical properties of the obtained resin composition (b-2).

<Example of toner production>
30 parts by mass of polyoxypropylene (2.2) -2,2-bis (4-hydroxyphenyl) propane, 20 parts by mass of polyoxyethylene (2.2) -2,2-bis (4-hydroxyphenyl) propane, Put 20 parts by mass of terephthalic acid, 3 parts by mass of trimellitic anhydride, 27 parts by mass of fumaric acid and dibutyltin oxide into a 4 liter glass four-necked flask, and add four thermometers, stirring rods, condensers and nitrogen inlet tubes. The flask was attached to a neck flask, and this four-neck flask was placed in a mantle heater. The reaction was allowed to proceed for 3 hours at 210 ° C. in a nitrogen atmosphere to obtain a polyester resin. The obtained polyester resin had a peak molecular weight Mp of 6500 and a glass transition temperature Tg of 65 ° C.
Next, a toner for evaluation was produced using the following materials and production method.
-100 mass parts of said polyester resin-C.I. I. Pigment Blue 15: 3 5 parts by mass, paraffin wax (melting point 75 ° C.) 5 parts by mass, 3,5-di-t-butylsalicylic acid aluminum compound 0.5 part by mass Henshell mixer (FM-75 type, Mitsui) After mixing with Miike Chemical Industries, Ltd., the mixture was melt-kneaded with a twin-screw extruder (PCM-30, manufactured by Ikegai Seisakusho). The obtained kneaded product was cooled and coarsely pulverized to 1 mm or less with a hammer mill to obtain a coarsely pulverized toner. The resulting coarsely pulverized toner was finely pulverized using a mechanical pulverizer and then classified by an air classifier to obtain a toner classified product. To 100 parts by mass of the obtained toner classified product, 1.0 part by mass of anatase-type titanium oxide having a BET specific surface area of 100 m ² / g and 1.0 part by mass of hydrophobic silica having a BET specific surface area of 130 m ² / g were added. The toner was added and mixed with a Henschel mixer (FM-75 type, manufactured by Mitsui Miike Chemical Co., Ltd.) to obtain a toner for evaluation. The obtained toner had a weight average particle diameter (D4) of 6.4 μm.

<Example 1>
Magnetic carriers were prepared using the materials and manufacturing methods shown below.
Magnetic carrier core (a-1) 100 parts by mass Resin composition (b-1) 4 parts by mass The resin composition is coated on the surface of the magnetic carrier core using the coating apparatus shown in FIG. went. As coating treatment conditions, the filling rate was 95% by volume, the outer peripheral edge peripheral speed of the stirring blade was 12 m / sec, the gap between the stirring blade and the casing was 3.0 mm, and the processing time was 20 minutes. In addition, 15 degreeC cooling water was introduce | transduced into the flow path (jacket) in the casing for temperature control. The temperature during the coating process was 80 ° C.
Next, the obtained coating treatment was heat-treated. As the heat treatment conditions, the coated product is put in a stainless steel container and treated at a treatment temperature of 100 with a vacuum dryer (apparatus i: DP63, Yamato Science).
The treatment temperature was 120 ° C., the oxygen concentration was 0.1 volume%. Table 3 shows coating conditions and heat treatment conditions, Table 4 shows physical properties of the obtained magnetic carrier, and Table 5 shows evaluation results of developability. In addition, the reference | standard of physical property evaluation of the obtained magnetic carrier and developability evaluation is shown below.

<Evaluation items>
[Evaluation of unity degree of magnetic carriers]
The obtained magnetic carrier was observed with an electron microscope (SEM). The magnification was observed at about 250 times so that about 100 magnetic carriers could be included in one field of view. This observation was performed 10 times and judged according to the following criteria.
A: Less than 3 united magnetic carriers.
B: 3 or more and less than 6 united magnetic carriers.
C: The number of united magnetic carriers is 6 or more and less than 10.
D: 10 or more and less than 15 united magnetic carriers E: 15 or more united magnetic carriers

[Effective coat amount]
10 g of the obtained magnetic carrier was weighed into a glass bottle with a lid, 20 g of toluene was added, and the mixture was shaken with a shaker (YS-8D type: Yayoi Co., Ltd.). The amplitude condition of the shaker was 200 rpm for 2 minutes. After shaking, toluene was removed while collecting the magnetic carrier from the outside of the bottle with a magnet. After repeating this 5 times, it was dried at 50 ° C. for 8 hours in a vacuum dryer, cooled to room temperature, then the remaining mass M2 was measured, and (10−M2) / (of the resin composition relative to the magnetic carrier core) Ratio [%] / 100) × 100 = effective coating amount (%). In addition, it was judged that the coating process was performed favorably, so that the effective coating amount was close to 100%. Further, the reason why it does not become 100% is considered to be due to uneven distribution of the resin composition that cannot be covered or due to uneven distribution of coalesced particles, or due to fusion or adhesion to the apparatus. The evaluation of the effective coat amount was judged according to the following criteria. Note that the evaluation B or higher was regarded as a practical level.
A: The effective coat amount with respect to the charged amount is 90% or more.
B: The effective coat amount with respect to the charged amount is 80% or more and less than 90%.
C: The effective coat amount with respect to the charged amount is 70% or more and less than 80%.
D: The effective coat amount with respect to the charged amount is 60% or more and less than 70%.
E: The effective coat amount with respect to the charged amount is less than 60%.

[Image density maintenance]
First, 90 parts by mass of the obtained magnetic carrier and 10 parts by mass of the toner for evaluation were mixed with a V-type mixer to obtain a two-component developer. The obtained two-component developer was evaluated using a Canon full-color copier IRC3220N to determine whether a normal image density could be obtained. The evaluation was performed by adjusting the developing bias so that the applied amount of toner on the photoconductor was 0.6 g / cm ² at high temperature and high humidity (H / H (30 ° C., 80 RH)) and outputting an image. For the image density, a solid image was output, density measurement was performed with a densitometer X-Rite500 type, and an average value of 6 points was taken as the image density.
The initial image density is set to 100%, and then the printing ratio is 10 in an environment of 35 ° C. and 90 RH.
Durability of 50,000 sheets (50k) with% image was calculated, and the maintenance ratio of H / H image density after 50k durability was calculated and judged according to the following criteria. In addition, the evaluation C or higher was regarded as a practical level.
A: Image density maintenance rate after 50k durability is 90% or more.
B: Image density maintenance rate after 50k durability is 80% or more and less than 90%.
C: Image density maintenance rate after 50k durability is 70% or more and less than 80%.
D: Image density maintenance rate after 50k durability is 60% or more and less than 70%.
E: Image density maintenance rate after 50k durability is less than 60%.

[Maintenance of Q / M (mC / kg) on the photoreceptor]
When the toner density on the photoconductor reached 0.6 g / cm ² during the evaluation of image density maintenance, the toner on the photoconductor was collected by suction with a metal cylindrical tube and a cylindrical filter. At that time, the charge quantity Q stored in the condenser through the metal cylindrical tube and the collected toner mass M are measured, and the charge quantity Q / M (mC / kg) per unit mass is calculated from the measured quantity. Q / M (mC / kg).
The initial Q / M on the photoconductor is assumed to be 100%. Subsequently, the image is subjected to 50,000 sheets (50k) in an image with a printing ratio of 10% in an environment of 35 ° C. and 90RH, and the Q / M on the photoconductor after 50k is used. The maintenance rate of M was calculated and judged according to the following criteria. In addition, the evaluation C or higher was regarded as a practical level.
A: The maintenance ratio of Q / M on the photoreceptor after 50k durability is 90% or more.
B: The maintenance ratio of Q / M on the photoconductor after 50k durability is 80% or more and less than 90%.
C: The maintenance ratio of Q / M on the photoconductor after 50k durability is 70% or more and less than 80%.
D: The maintenance ratio of Q / M on the photoreceptor after 50k durability is 60% or more and less than 70%.
E: The maintenance ratio of Q / M on the photoconductor after 50k durability is less than 60%.

[Abrasion resistance of coat layer]
The initial effective coat amount of the magnetic carrier is assumed to be 100%, followed by 50,000 sheets (50k) with an image of 10% printing ratio in an environment of 35 ° C and 90RH, and the effective coat amount of the magnetic carrier after 50k endurance. The maintenance ratio was calculated based on the following criteria. In addition, the evaluation C or higher was regarded as a practical level.
A: The maintenance ratio of the effective coat amount after 50k durability is 90% or more.
B: The maintenance ratio of the effective coat amount after 50k durability is 80% or more and less than 90%.
C: The maintenance ratio of the effective coat amount after 50k durability is 70% or more and less than 80%.
D: The maintenance ratio of the effective coat amount after 50k durability is 60% or more and less than 70%.
E: Maintenance rate of effective coat amount after 50k durability is less than 60%.

<Example 2>
In Example 1, the heat treatment apparatus is changed from the apparatus (i) to the drum mixer (UD-LH-00).
Type 1: Made of Sugiyama Heavy Industries, apparatus ii), a magnetic carrier was prepared in the same manner as in Example 1 except that nitrogen was flowed during the heat treatment to make the oxygen concentration 8.0% by volume. went. Table 4 shows the physical properties of the obtained magnetic carrier, and Table 5 shows the evaluation results of developability.

<Examples 3 to 9>
In Example 2, a magnetic carrier was prepared and evaluated in the same manner as in Example 2 except that the manufacturing conditions were changed as shown in Table 3. Table 4 shows the physical properties of the obtained magnetic carrier, and Table 5 shows the evaluation results of developability.

<Example 10>
In Example 1, except that the heat treatment apparatus was changed from the apparatus () to Hiflex glal (LFS-GS-2J type: Fukae Powtech, apparatus iii), and the heat treatment conditions were changed as shown in Table 3. A magnetic carrier was prepared in the same manner as in Example 1, and each evaluation was performed. Table 4 shows the physical properties of the obtained magnetic carrier, and Table 5 shows the evaluation results of developability.

<Example 11>
In Example 1, the magnetic treatment was performed in the same manner as in Example 1 except that the heat treatment apparatus was changed from the apparatus (i) to solid air (manufactured by Hosokawa Micron, apparatus iv), and the heat treatment conditions were changed as shown in Table 3. Carriers were prepared and evaluated. Table 4 shows the physical properties of the obtained magnetic carrier, and Table 5 shows the evaluation results of developability.

<Examples 12 to 20>
In Example 2, a magnetic carrier was prepared and evaluated in the same manner as in Example 2 except that the manufacturing conditions were changed as shown in Table 3. Table 4 shows the physical properties of the obtained magnetic carrier, and Table 5 shows the evaluation results of developability.

<Comparative Example 1>
In Example 2, a magnetic carrier was produced in the same manner as in Example 2 except that no heat treatment was performed, and each evaluation was performed. Table 4 shows the physical properties of the obtained magnetic carrier, and Table 5 shows the evaluation results of developability.

<Comparative Examples 2 to 6>
In Example 2, a magnetic carrier was prepared and evaluated in the same manner as in Example 2 except that the manufacturing conditions were changed as shown in Table 3. Table 4 shows the physical properties of the obtained magnetic carrier, and Table 5 shows the evaluation results of developability.

<Comparative Example 7>
In Example 2, a magnetic carrier was prepared and evaluated in the same manner as in Example 2 except that the coating treatment apparatus was changed to Hiflex glal (manufactured by Fukae Powtech), which is a thermal dry coat apparatus. Table 4 shows the physical properties of the obtained magnetic carrier, and Table 5 shows the evaluation results of developability.

<Comparative Example 8>
In Example 2, a magnetic carrier was prepared in the same manner as in Example 2 except that the coating treatment apparatus was changed to a hybridizer (manufactured by Nara Machinery), which is a dry coating apparatus using mechanical impact force. went. Table 4 shows the physical properties of the obtained magnetic carrier, and Table 5 shows the evaluation results of developability.

It is a schematic diagram which shows an example of the coating processing apparatus which can be used for the manufacturing method of the magnetic carrier of this invention. It is a schematic diagram which shows the structure of the stirring member used for the coating processing apparatus which can be used for the manufacturing method of the magnetic carrier of this invention. It is a schematic diagram which shows the structure of the stirring member used for the coating processing apparatus which can be used for the manufacturing method of the magnetic carrier of this invention. It is a schematic diagram which shows the structure of the stirring member used for the coating processing apparatus which can be used for the manufacturing method of the magnetic carrier of this invention. It is a schematic diagram which shows the structure of the stirring member used for the coating processing apparatus which can be used for the manufacturing method of the magnetic carrier of this invention. It is a schematic diagram which shows an example of the measuring apparatus which measures the specific resistance of the magnetic carrier of this invention.

Explanation of symbols

1: Casing 2: Rotating body 3, 3a, 3b, 3c: Stirring blade 4: Jacket 5: Input port 6: Discharge port 7: Support body 8: Drive unit d: Interval indicating the positional relationship of the stirring blades 11: Lower electrode 12: Upper electrode 13: Sample 14: Lower electrode base 15: Holder 16: Electron meter 17: Processing computer A: Resistance measurement cell d: Sample height

Claims (6)

Using a coating processing apparatus having a means for coating by mechanical impact force, a coating processing step for coating the resin composition on the surface of the magnetic carrier core, and a magnetic film coated by using a heating processing apparatus having a heating means A heat treatment step of heat-treating the carrier, and a method for producing a magnetic carrier obtained by coating the surface of the magnetic carrier core with a resin composition,
The coating treatment step uses a coating processing apparatus having a rotating body having at least a plurality of stirring members installed on the surface, and a casing provided with the stirring member and a gap, and rotates the rotating body, The resin composition is coated on the surface of the magnetic carrier core by mixing the magnetic carrier core and the resin composition introduced into the coating processing apparatus,
The magnetic carrier and the resin composition charged into the coating processing apparatus have a space filling rate of the magnetic carrier core and the resin composition to be charged with respect to a space between the rotating body and the inner peripheral portion of the casing. , The input amount is adjusted to be 50% or more and 98% or less,
The magnetic carrier core and the resin composition charged into the coating processing apparatus are sent in one axial direction of the rotating body by a part of the stirring members, and the plurality of stirring members The other stirring member of the blade is returned in the reverse direction of the axial direction of the rotating body, and the coating treatment of the resin composition is performed on the surface of the magnetic carrier while performing feeding and returning,
The said heat processing process heat-processes on the conditions which satisfy | fill following formula (1) and (2), The manufacturing method of the magnetic carrier characterized by the above-mentioned.
Tg (° C.) ≦ Th (° C.) ≦ Tg + 50 (° C.) (1)
1000 (° C./min)≦Th×M (° C./min)≦30000 (° C./min) (2)
(Th: Heat treatment temperature in the heat treatment step, Tg: Glass transition temperature of the resin component contained in the resin composition, M: Heat treatment time in the heat treatment step) In the covering process, the temperature is controlled by introducing a fluid into the flow path provided in the rotating body and / or the flow path provided in the casing in the clothing processing apparatus. The method for producing a magnetic carrier according to claim 1, wherein the coating temperature Tc (° C.) and the heat treatment temperature Th (° C.) in the heat treatment step satisfy the following formula (3).
Tc (° C.) ≦ Th (° C.) (3)   The method for manufacturing a magnetic carrier according to claim 1 or 2, wherein the heat treatment in the heat treatment step is performed at an oxygen concentration of 10.0% by volume or less.   4. The magnetic carrier according to claim 1, wherein the resin composition has at least a resin component and fine particles having a number average particle diameter (D1) of 0.01 μm or more and 3.00 μm or less. Production method.   A magnetic carrier manufactured by the manufacturing method according to claim 1. The magnetic carrier has a volume-based 50% particle size (D50) of 15 μm or more and 100 μm or less, and a true specific gravity of 2.5 g / cm ³ or more and 5.2 g / cm ³ or less. Item 6. The magnetic carrier according to Item 5.

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