JP2018128619A - Carrier core material, and carrier for electrophotographic development and developer for electrophotography using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carrier core material that can supply a larger amount of toner to a developing area, avoids the occurrence of a problem, such as developing memory even when an image forming speed is further increased, and does not damage a surface of a photoreceptor with a magnetic brush.SOLUTION: A carrier core material contains 5 number% or more and 20 number% or less of bonded particles in which 2 to 5 spherical particles are bonded, where the ratio (AD/AD) between the apparent density (AD) when the carrier core material is demagnetized by application of an attenuating alternating magnetic field and the apparent density (AD) when the carrier core material is magnetized in a magnetic field of 1000/(4π)kA/m (1000 oersted) after the demagnetization is 0.90 or more and 0.98 or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a carrier core material, an electrophotographic developer carrier and an electrophotographic developer using the same.

  For example, in an image forming apparatus such as a facsimile, printer, or copier using an electrophotographic method, a toner is attached to an electrostatic latent image formed on the surface of a photosensitive member to make a visible image, and the visible image is formed on paper. After being transferred to, etc., it is fixed by heating and pressing. A so-called two-component developer including a carrier and a toner is widely used as a developer from the viewpoint of high image quality and colorization.

  In the developing method using a two-component developer, the carrier and the toner are stirred and mixed in the developing device, and the toner is charged to a predetermined amount by friction. Then, a developer is supplied to the rotating developing roller, a magnetic brush is formed on the developing roller, and the toner is electrically moved to the photosensitive member via the magnetic brush, so that an electrostatic latent image on the photosensitive member can be formed. Visualize. The carrier after the toner movement is peeled off from the developing roller and mixed with the toner again in the developing device. For this reason, as a characteristic of the carrier, a magnetic characteristic for forming a magnetic brush and a charging characteristic for imparting a desired charge to the toner are required. As such a carrier, a so-called coating carrier in which the surface of a carrier core material made of magnetite, various ferrites or the like is coated with a resin has been widely used. Further, the carrier core material used so far for the coating carrier has a spherical shape.

  In recent years, in order to meet the market demand for higher image forming speed in image forming apparatuses, the rotation speed of the developing roller tends to be increased to increase the amount of developer supplied per unit time to the developing area.

  However, the coating carrier using the spherical carrier core material has a problem that the toner density to the developing area is insufficient and the image density is lowered. For example, there is a problem called a development memory in which the image density decreases due to the influence of the image one round before the development roller.

  Therefore, by making the surface of the carrier core material uneven, or by making the shape of the carrier core material irregular, the frictional resistance with the surface of the photoreceptor and the frictional resistance between the carriers are increased, and the amount of toner supplied to the development area is increased. Techniques for increasing the number have been proposed (for example, Patent Documents 1 and 2).

  However, if the surface of the carrier core material is made uneven only, the coating resin is thickly formed in the recesses when the surface of the carrier core material is coated with resin. It is insufficient. In addition, unequal polygonal and massive carriers have been proposed as irregularly shaped carriers. However, due to extreme irregularities that deviate from the spherical shape, the magnetic brushes become harder and harder, and the magnetic brush becomes photosensitive. The surface of the photoconductor may be damaged by rubbing the surface of the photoconductor.

  Therefore, the present applicant has proposed a carrier core material that can increase the amount of toner supplied to the development area and that does not damage the surface of the photoreceptor by the magnetic brush (Patent Document 3).

JP 2013-25204 A JP 2007-148452 A JP 2006-161741 A

  Currently, further development of image forming speed is under development, and a carrier core material corresponding to such high speed is desired.

  Accordingly, an object of the present invention is to supply more toner to the developing area, and even when the image forming speed is increased, there is no occurrence of a problem such as a developing memory. An object of the present invention is to provide a carrier core material that does not damage the surface of the photoreceptor.

  Another object of the present invention is to provide an electrophotographic developer carrier and an electrophotographic developer capable of stably forming a good image quality even after long-term use.

According to the present invention, the apparent density (AD ₁ ) when demagnetized by adding a damped alternating magnetic field, including 5% to 20% by number of bonded particles in which 2 to 5 spherical particles are combined, The ratio (AD ₂ / AD ₁ ) to the apparent density (AD ₂ ) when magnetized under a magnetic field of 1000 / (4π) kA / m (1000 oersted) after demagnetization is 0.90 or more and 0.98 or less A carrier core material is provided. In addition, the measuring method of the content rate of a binding particle and an apparent density is mentioned later.

  In the carrier core material having the above-described configuration, it is preferable that 5% by number or more of particles having a maximum mountain valley depth Rz of 1.8 μm or more are included. In addition, the measuring method of the particle | grain ratio whose maximum valley depth Rz of the particle | grain surface is 1.8 micrometers or more is mentioned later.

  The carrier core material according to the present invention preferably has a volume average particle diameter (hereinafter sometimes simply referred to as “average particle diameter”) of 25 μm or more and less than 50 μm.

  In addition, according to the present invention, there is provided an electrophotographic developing carrier (hereinafter sometimes simply referred to as “carrier”), wherein the surface of the carrier core material described above is coated with a resin. The

  Furthermore, according to the present invention, there is provided an electrophotographic developer comprising the electrophotographic developer carrier described above and a toner.

  According to the carrier core material of the present invention, more toner can be supplied to the development area, and even when the image forming speed is increased, problems such as the development memory are prevented, and the magnetic brush As a result, the surface of the photoreceptor is not damaged. Thereby, if the developer containing the carrier core material according to the present invention is used, a good image quality can be stably formed even for a long period of use.

It is a schematic diagram explaining the shape change of a magnetic aggregation particle group. It is a figure which shows the filling state of the carrier core material after demagnetization and after magnetization. 4 is a SEM photograph of the carrier core material of Example 2. It is a schematic diagram showing an example of a developing device using a carrier according to the present invention.

  The present applicant has already filed an application by finding that a large number of toners can be supplied to the developing region by containing a predetermined number of binder particles in which several ferrite spherical particles are bonded in a carrier core material ( JP, 2006-161741, etc.). As a result of intensive studies to make it possible to supply more toner to the development area, it is only necessary to generate a group of particles that are aggregated by magnetic force in addition to the constitution in which the bound particles are contained in a predetermined number ratio. The present invention has been found.

  First, a particle group aggregated by magnetic force (hereinafter sometimes referred to as “magnetic aggregated particle group”) will be described. The magnetic aggregated particle group is a group of particles aggregated by magnetic force and aggregated so that the contact between the particles can move. In other words, the shape of the particle group can be deformed by the action of external force or magnetic force. For example, as shown in FIG. 1, when an external force or a magnetic force is applied to the magnetic aggregated particle group, the contact point between the particles moves while the aggregated state of the particles is maintained, and the shape of the aggregated particle group changes. Note that black dots in FIG. 1 represent toner.

  Each particle forming such a magnetic aggregated particle group has a predetermined residual magnetization. In the developing device as shown in FIG. 4, the carrier is magnetized by the magnetic force of the fixed magnet built in the developing roller 3 to form a magnetic brush on the surface of the developing roller 3. When the developing roller 3 rotates, the developer is rotated and conveyed, and the shape of the magnetic brush changes due to a change in the magnetic field. The magnetic agglomerated particle group is formed as a part of the magnetic brush, and the shape of the magnetic agglomerated particle group changes variously as the shape of the magnetic brush changes.

  Similar to the binding particles described later, the magnetic aggregated particle group has a space in which toner is taken in between the aggregated particles. The toner taken into the space between the aggregated particles is conveyed to the development area together with the magnetic aggregated particles by the rotation of the developing roller. The toner taken into the space appears on the surface of the magnetic brush and contributes to development. What is important here is that, unlike the coupled particles, the shape of the magnetic agglomerated particles changes due to the action of external force or magnetic force, so that the space between the agglomerated particles that has taken in the toner is deformed or disappears due to the shape change of the agglomerated particles. In other words, the toner that is located in the back of the space and is difficult to contribute to the development can be exposed to the outer surface and can contribute to the development. That is, more toner can contribute to development.

  In addition, the developer whose toner has been consumed by the development is peeled off from the developing roller, and is mixed with the replenishment toner and the developer that has not yet consumed the toner. At this time, since the shape of the magnetic agglomerated particles changes depending on the mixing and stirring operation, the mixing and stirring torque does not increase more than necessary and is smoothly mixed with the toner and the like. Alternatively, by deviating from the magnetic field of the fixed magnet built in the developing roller, the magnetic aggregation is eliminated to form individual particles, which are more smoothly mixed with the toner or the like. In addition, if the carrier has binding particles, a large rotational force is applied to the magnetic agglomerated particles by the binding particles, and the magnetic agglomerated particles are likely to be deformed and magnetic agglomeration is eliminated, further mixing with the toner. Will be promoted.

In the present invention, the ratio between the apparent density when demagnetized and the apparent density when magnetized is used as the presence index of such a magnetic aggregated particle group. FIG. 2 is a schematic diagram showing the state of the carrier core material after demagnetization and after magnetization. When the carrier core material is demagnetized, each particle constituting the carrier core material is closely packed, so that the apparent density (AD ₁ ) increases. On the other hand, when the carrier core material is magnetized, a plurality of particles form a magnetic aggregated particle group due to residual magnetization and behave as a large particle size particle, resulting in a space between the magnetic aggregated particle group and the magnetic aggregated particle group. Thus, the apparent density (AD ₂ ) is smaller than the apparent density (AD ₁ ) after demagnetization. Therefore, in the present invention, the apparent density ratio (AD ₂ / AD ₁ ) is used as an index of the degree of formation of the magnetic aggregate particles.

In the present invention, the apparent density ratio (AD ₂ / AD ₁ ) is set to 0.90 or more and 0.98 or less. When the apparent density ratio (AD ₂ / AD ₁ ) is less than 0.90, the magnetic aggregates of the magnetic aggregate particles are too strong, and the magnetic aggregate particles are hardly deformed by the action of external force or magnetic force. On the other hand, when the apparent density ratio (AD ₂ / AD ₁ ) exceeds 0.98, the magnetic aggregation is too weak to sufficiently form the magnetic aggregate particles.

A conventionally known method can be used to control the apparent density ratio (AD ₂ / AD ₁ ) of the carrier core material. For example, when the particles constituting the carrier core material are ferrite particles, the apparent density ratio (AD ₂ / AD ₁ ) can be controlled by the composition and firing temperature. For example, by lowering the firing temperature and leaving a defect structure in the crystal that traps domain wall motion, the residual magnetization after magnetization can be increased, and the apparent density ratio can be reduced.

  Next, the binding particles in the present invention will be described. One of the major characteristics of the carrier core material according to the present invention is that 5 to 20% by number of bonded particles in which 2 to 5 spherical particles are combined are included. In the carrier core material according to the present invention, the normal particles other than the binding particles are preferably spherical.

  If the carrier core material contains a predetermined number of irregularly bonded particles that are largely deviated from the spherical shape, in which 2 to 5 spherical particles are bonded, toner is taken in between the normal particles and the bonded particles. Space can arise. The toner taken into the space between the normal particles and the binding particles is transported to the developing area by the rotation of the developing roller, and the toner taken into the space appears on the surface of the magnetic brush and contributes to the development. To do. In addition, unlike conventional unequal polygonal shapes or massive carriers, the bonded particles used in the present invention are particles in which spherical particles are bonded to each other, and thus have no corners. For this reason, even if the surface of the photoreceptor is rubbed with a magnetic brush, the surface of the photoreceptor is not damaged at the corners of the particles.

  Each particle size of the spherical particles forming the binding particles is not particularly limited, but the binding particles include a mother particle having the largest particle size and 1 to 4 child particles having a smaller particle size than the mother particle. Bonded ones are preferred. Furthermore, a bonded particle in which the particle size of at least one child particle is larger than 1/4 of the particle size of the mother particle is preferable. By including such binding particles in a predetermined ratio in the carrier core material, the space between the normal particles and the binding particles where the toner can be taken in and the space between the binding particles are increased, so that a larger amount of toner can be obtained. It is conveyed to the development area, and the occurrence of development memory is effectively suppressed.

  In addition, since the binding particles exist in a form in which the base particles and the child particles share a binding portion, the particle size of the base particles and the child particles is determined by scanning electron microscope (manufactured by JEOL Ltd .: JSM-6510LA) was used to calculate each of the particles by spherical approximation from the region excluding the binding portion of the binding particles in an image taken at a magnification of 250 times.

  In the bonded particles used in the present invention, the composition of the mother particles and the child particles may be the same or different.

  Such binding particles can be obtained, for example, by increasing the firing temperature, increasing the holding time at the firing temperature, or adjusting the pulverization operation after firing in the carrier core manufacturing process described later. Can do. According to this method, the content ratio of the binding particles in the carrier core material can be easily adjusted.

  Or it can obtain by mixing and baking the granulated material from which average particle diameter differs in the manufacturing process of a carrier core material. According to this method, the content ratio of the binding particles in the carrier core material can be easily adjusted, and at the same time, the particle size of the mother particles and the child particles can be easily adjusted to a desired particle size.

  The content ratio of the binding particles in the carrier core material is 5% to 20% by number. When the content ratio of the binding particles is less than 5% by number, the amount of toner supplied to the developing region may be insufficient. On the other hand, when the content ratio of the binding particles exceeds 20% by number, the fluidity of the carrier core material However, when the image formation speed is increased, sufficient image density cannot be obtained when the carrier is not sufficiently circulated and moved within the magnetic brush. A more preferable content ratio of the binder particles is in the range of 7% by number to 20% by number.

  In the carrier core material of the present invention, it is preferable that 5% by number or more of particles having a maximum mountain valley depth Rz of 1.8 μm or more are included. When 5% by number or more of particles having a maximum peak / valley depth Rz of 1.8 μm or more are contained, a large gap is formed by these particles, and a larger amount of toner is taken into the gap and the amount of toner transported to the development area. And image defects such as development memory are further suppressed. There is no particular limitation on the upper limit value of the particles having the maximum peak / valley depth Rz of 1.8 μm or more, but it is usually preferably 70% by number or less. The content ratio of the particles having the maximum mountain valley depth Rz of 1.8 μm or more can be adjusted by the Sr and Cl contents in the raw materials and the sintering conditions in the manufacturing process. Details will be described later.

  The volume average particle size of the carrier core material of the present invention is preferably in the range of 25 μm or more and less than 50 μm, more preferably in the range of 30 μm or more and 40 μm or less.

The carrier core material of the present invention is preferably composed of ferrite particles. The composition of the ferrite particles is not particularly limited, and the composition formula M _X Fe _{3 -X} O ₄ (where M is at least one selected from the group consisting of Mg, Mn, Ca, Ti, Sr, Cu, Zn, Ni) An example is a metal element of a species represented by 0 ≦ X ≦ 1). Such soft ferrite is possible. Among these, the general formula _{(MnO) x (MgO) y} (Fe 2 O 3) is represented by z, x, y, z is 45mol% ~55mol% respectively, 0 to 20 mol%, a 30 mol% 50 mol% , MnO and / or MgO is preferably partially substituted by 0.15 mol% to 3.0 mol% with SrO.

  Although there is no limitation in particular in the manufacturing method of the carrier core material of this invention, the manufacturing method demonstrated below is suitable.

First, the Fe component raw material and the M component raw material are weighed. M is at least one metal element selected from divalent metal elements such as Mg, Mn, Ca, Ti, Cu, Sr, Zn, and Ni. As the Fe component material, Fe ₂ O ₃ or the like is preferably used. As the M component raw material, MnCO ₃ , Mn ₃ O _{4 and the} like can be used for Mn, and MgO, Mg (OH) ₂ and MgCO ₃ can be suitably used for Mg. As the Ca component raw material, at least one compound selected from CaO, Ca (OH) ₂ , CaCO _{3 and the} like is preferably used. As the Sr component raw material, SrCO ₃ , Sr (NO ₃ ) ₂ or the like is preferably used.

Here, it is desirable to add a small amount of Sr and Cl (chlorine) in order to control the apparent density of the ferrite particles and the content ratio of the particles having the predetermined maximum valley depth Rz. By adding a small amount of Sr, a part of Sr ferrite is generated in the firing step, so that a magnetoplumbite type crystal structure is formed and the uneven shape on the surface of the ferrite particles is easily promoted. A suitable addition amount of Sr is in the range of 0.15 mol% to 3.0 mol% in terms of SrO with respect to 100 mol% of the main component of the ferrite particles. Further, by adding a small amount of Cl component, iron chloride gasified in the firing step reacts with oxygen on the particle surface, and magnetite (Fe ₃ O ₄ ) precipitates to promote unevenness on the particle surface. The Cl component may be contained as an inevitable impurity in raw materials such as Fe component raw materials. If necessary, HCl is added as a raw material.

  Next, the raw material is charged into a dispersion medium to prepare a slurry. Water is preferred as the dispersion medium used in the present invention. In addition to the above raw materials, a binder, a dispersant and the like may be blended in the dispersion medium as necessary. For example, polyvinyl alcohol can be suitably used as the binder. As a compounding quantity of a binder, it is preferable that the density | concentration in a slurry shall be about 0.5 mass%-2 mass%. Moreover, as a dispersing agent, polycarboxylate ammonium etc. can be used conveniently, for example. The blending amount of the dispersing agent is preferably about 0.5% by mass to 2% by mass in the slurry. In addition, you may mix | blend a lubricant, a sintering accelerator, etc. The solid content concentration of the slurry is desirably in the range of 50 mass% to 90 mass%. More preferably, it is 60 mass%-80 mass%. If it is 60% by mass or more, there are few intra-particle pores in the granulated product, and insufficient sintering during firing can be prevented.

  In addition, after mixing the weighed raw materials, pre-baking and pulverizing, it may be put into a dispersion medium to produce a slurry. The pre-baking temperature is preferably in the range of 750 ° C to 900 ° C. If it is 750 degreeC or more, since part ferrite-ization by calcination advances, the amount of gas generation at the time of baking is small, and reaction between solids fully advances, it is preferable. On the other hand, if it is 900 degrees C or less, since sintering by calcination is weak and a raw material can fully be grind | pulverized at a later slurry grinding | pulverization process, it is preferable. Moreover, an air atmosphere is preferable as the atmosphere at the time of temporary firing.

  Next, the slurry produced as described above is wet pulverized. For example, wet grinding is performed for a predetermined time using a ball mill or a vibration mill. The average particle diameter of the raw material after pulverization is preferably 5 μm or less, more preferably 1 μm or less. The vibration mill or ball mill preferably contains a medium having a predetermined particle diameter. Examples of the material of the media include iron-based chromium steel and oxide-based zirconia, titania, and alumina. As a form of a grinding | pulverization process, any of a continuous type and a batch type may be sufficient. The particle size of the pulverized product is adjusted depending on the pulverization time and rotation speed, the material and particle size of the media used, and the like.

  Then, the pulverized slurry is spray-dried and granulated. Specifically, the slurry is introduced into a spray dryer such as a spray dryer, and granulated into a spherical shape by spraying into the atmosphere. The atmospheric temperature during spray drying is preferably in the range of 100 ° C to 300 ° C. Thereby, a spherical granulated product having a particle size of 10 μm to 200 μm is obtained. Next, the obtained granulated product is classified using a vibration sieve to produce a granulated product having a predetermined particle size range.

  Next, the granulated material is put into a furnace heated to a predetermined temperature and fired by a general method for synthesizing ferrite particles, thereby generating ferrite particles. The firing temperature is preferably in the range of 800 ° C to 1300 ° C. When the firing temperature is 800 ° C. or lower, the phase transformation is less likely to occur and the sintering is less likely to proceed. On the other hand, if the firing temperature exceeds 1300 ° C., excessive grains may be generated due to excessive sintering.

  The fired product thus obtained is pulverized. Specifically, for example, the fired product is pulverized by a hammer mill or the like. The form of the granulation step may be either a continuous type or a batch type. Also by this pulverization treatment, the content ratio of the binding particles can be adjusted. That is, the stronger the impact force applied to the fired product is, the longer the binding of the binding particles is eliminated and the content ratio of the binding particles decreases.

  After the pulverization treatment, classification may be performed, if necessary, in order to align the particle size within a predetermined range. As a classification method, a conventionally known method such as air classification or sieve classification can be used. In addition, after primary classification with an air classifier, the particle size may be aligned within a predetermined range with a vibration sieve or an ultrasonic sieve. Furthermore, you may make it remove a nonmagnetic particle with a magnetic field separator after a classification process. The particle diameter of the ferrite particles is preferably 25 μm or more and less than 50 μm.

Here, the apparent density (AD ₂ ) of the carrier core material after magnetization can be adjusted by the residual magnetization of the ferrite particles constituting the carrier core material, and the apparent density can be reduced by increasing the residual magnetization. In order to increase the residual magnetization of the ferrite particles, it is preferable to leave the defect structure that traps the domain wall motion by lowering the firing temperature.

  On the other hand, the content ratio of the binding particles can be adjusted by the firing temperature and the holding time at the firing temperature. Usually, the content ratio of the binding particles increases when the firing temperature is increased and the holding time is increased. Similarly, the maximum crest depth Rz of the particle surface caused by the formation of Sr ferrite in the ferrite particles can also be adjusted by the firing temperature and the retention time at the firing temperature. Usually, the firing temperature is increased and the retention time is increased. When the length is increased, the maximum valley depth Rz increases. The holding time is preferably 3 hours or more, and more preferably 6 hours or more. The rate of temperature increase up to the firing temperature is preferably in the range of 250 ° C / h to 500 ° C / h. The oxygen concentration in the firing step is preferably controlled in the range of 0.05% to 5%.

Thus, there are portions where the firing conditions for obtaining the desired apparent density ratio (AD ₂ / AD ₁ ) and the firing conditions for obtaining the desired content of the binding particles are in conflict, and the possible firing conditions are wide. Absent.

Therefore, as shown in the examples described later, after preparing two types of ferrite particles under different firing conditions, they are mixed at a desired ratio to obtain a desired apparent density ratio (AD ₂ / AD ₁ ) and the binding particles. Ferrite particles having a desired content are preferable.

  Thereafter, if necessary, the ferrite particles may be heated in an oxidizing atmosphere to form an oxide film on the particle surface to increase the resistance of the ferrite particles (high resistance treatment). The oxidizing atmosphere may be either an air atmosphere or a mixed atmosphere of oxygen and nitrogen. The heating temperature is preferably in the range of 200 ° C to 800 ° C, and more preferably in the range of 250 ° C to 600 ° C. The heating time is preferably in the range of 0.5 hours to 5 hours.

  The ferrite particles produced as described above are used as the carrier core material of the present invention. Then, in order to obtain desired chargeability and the like, the outer periphery of the carrier core material is coated with a resin to obtain an electrophotographic developing carrier.

  As the resin for coating the surface of the carrier core material, conventionally known resins can be used, for example, polyethylene, polypropylene, polyvinyl chloride, poly-4-methylpentene-1, polyvinylidene chloride, ABS (acrylonitrile-butadiene-styrene). ) Resin, polystyrene, (meth) acrylic resin, polyvinyl alcohol resin, polyvinyl chloride, polyurethane, polyester, polyamide, polybutadiene, and other thermoplastic elastomers, and fluorosilicone resins.

  In order to coat the surface of the carrier core material with the resin, a resin solution or dispersion may be applied to the carrier core material. Solvents for the coating solution include aromatic hydrocarbon solvents such as toluene and xylene; ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; cyclic ether solvents such as tetrahydrofuran and dioxane; ethanol, propanol, and butanol Alcohol solvents such as ethyl cellosolve, cellosolve solvents such as butyl cellosolve; ester solvents such as ethyl acetate and butyl acetate; amide solvents such as dimethylformamide and dimethylacetamide, etc. . The resin component concentration in the coating solution should generally be in the range of 0.001% to 30% by weight, particularly 0.001% to 2% by weight.

  As a method of coating the resin on the carrier core material, for example, a spray drying method, a fluidized bed method, a spray drying method using a fluidized bed, an immersion method, or the like can be used. Among these, the fluidized bed method is particularly preferable in that it can be efficiently applied with a small amount of resin. For example, in the case of the fluidized bed method, the resin coating amount can be adjusted by the amount of resin solution sprayed and the spraying time.

  The particle diameter of the carrier is generally preferably in the range of 25 μm or more and less than 50 μm, particularly in the range of 30 μm or more and 40 μm or less in terms of volume average particle diameter.

  The electrophotographic developer according to the present invention is obtained by mixing the carrier prepared as described above and a toner. The mixing ratio of the carrier and the toner is not particularly limited, and may be determined as appropriate based on the developing conditions of the developing device to be used. Generally, the toner concentration in the developer is preferably in the range of 1% by mass to 15% by mass. When the toner density is less than 1% by mass, the image density becomes too low, while when the toner density exceeds 15% by mass, toner scattering occurs in the developing device, and the toner adheres to the background portion such as internal dirt or transfer paper. This is because there is a risk of malfunction. A more preferable toner concentration is in the range of 3% by mass to 10% by mass.

  As the toner, toner produced by a conventionally known method such as a polymerization method, a pulverization classification method, a melt granulation method, or a spray granulation method can be used. Specifically, a binder resin containing a thermoplastic resin as a main component and containing a colorant, a release agent, a charge control agent and the like can be suitably used.

  In general, the particle diameter of the toner is preferably in the range of 5 μm to 15 μm, more preferably in the range of 7 μm to 12 μm, as a volume average particle diameter measured by a Coulter counter.

  If necessary, a modifier may be added to the toner surface. Examples of the modifier include silica, alumina, zinc oxide, titanium oxide, magnesium oxide, polymethyl methacrylate and the like. These 1 type (s) or 2 or more types can be used in combination.

  A known mixing device can be used for mixing the carrier and the toner. For example, a Henschel mixer, a V-type mixer, a tumbler mixer, a hybridizer, or the like can be used.

  The developing method using the developer of the present invention is not particularly limited, but a magnetic brush developing method is preferable. FIG. 4 is a schematic diagram showing an example of a developing device that performs magnetic brush development. The developing device shown in FIG. 4 is arranged in parallel to a horizontal direction, and a rotatable developing roller 3 incorporating a plurality of magnetic poles, a regulating blade 6 for regulating the amount of developer on the developing roller 3 conveyed to the developing unit. Formed between the two screws 1 and 2 that stir and convey the developer in opposite directions and the two screws 1 and 2, and develops from one screw to the other at both ends of both screws. And a partition plate 4 that allows the developer to move and prevents the developer from moving except at both ends.

  The two screws 1 and 2 have spiral blades 13 and 23 formed on the shaft portions 11 and 21 at the same inclination angle, and are rotated in the same direction by a drive mechanism (not shown) to remove the developer. Transport in opposite directions. The developer moves from one screw to the other screw at both ends of the screws 1 and 2. As a result, the developer composed of toner and carrier is constantly circulated and stirred in the apparatus.

On the other hand, the developing roller 3 has, as a magnetic pole generating means, a developing magnetic pole N ₁ , a transporting magnetic pole S ₁ , a peeling magnetic pole N ₂ , and a pumping magnetic pole N ₃ inside a metal cylindrical body having a surface with a few μm unevenness. , comprising a fixed magnet disposed five pole blade pole S ₂ in order. When the development roller 3 is rotated in the arrow direction, by the magnetic force of the magnetic pole N _3, the developer is pumped from the screw 1 to the developing roller 3. The developer carried on the surface of the developing roller 3 is regulated by the regulating blade 6 and then conveyed to the developing area.

  In the developing region, a bias voltage obtained by superimposing an AC voltage on a DC voltage is applied from the transfer voltage power supply 8 to the developing roller 3. The DC voltage component of the bias voltage is a potential between the background portion potential on the surface of the photosensitive drum 5 and the image portion potential. Further, the background portion potential and the image portion potential are set to a potential between the maximum value and the minimum value of the bias voltage. The peak-to-peak voltage of the bias voltage is preferably in the range of 0.5 to 5 kV, and the frequency is preferably in the range of 1 to 10 kHz. The waveform of the bias voltage may be any of a rectangular wave, a sine wave, a triangular wave, and the like. As a result, the toner and the carrier vibrate in the development area, and the toner adheres to the electrostatic latent image on the photosensitive drum 5 and development is performed.

Thereafter, the developer on the developing roller 3 is conveyed to the inside of the apparatus by the conveying magnetic pole S ₁ , peeled off from the developing roller 3 by the peeling electrode N ₂ , and circulated and conveyed again inside the apparatus by the screws 1 and 2 for development. Mix and stir with undeveloped developer. Then, the developer is newly supplied from the screw 1 to the developing roller 3 by the pumping pole N ₃ .

  In the embodiment shown in FIG. 4, the number of magnetic poles built in the developing roller 3 is five. However, in order to further increase the amount of movement of the developer in the developing region, and to further improve the pumping performance and the like. Of course, the number of magnetic poles may be increased to 8 poles, 10 poles or 12 poles.

(Measurement method of apparent density (AD ₁ ) of carrier core when demagnetized)
The apparent density (AD ₁ ) is measured within 30 minutes after demagnetizing the carrier core material by applying a damped alternating magnetic field to the carrier core using a demagnetizer (KMD-20C, manufactured by Kanetec Corporation). The apparent density of the carrier core material is measured according to JIS Z 2504.

(Measurement method of apparent density (AD ₂ ) of carrier core when magnetized)
After demagnetization, the carrier core material is magnetized under a magnetic field of 1000 / (4π) kA / m (1000 oersted), and then the apparent density (AD ₂ ) is measured within 30 minutes. The apparent density of the carrier core material is measured according to JIS Z 2504.

(Measurement method of the content rate and particle size of the binding particles)
The content rate of the binding particles can be measured by an observation image. From the total number of observed particles in the observed image, the number% may be obtained by the ratio with the number of coupled particles.
The shape of the carrier core material was photographed at a magnification of 200 times using a scanning electron microscope (manufactured by JEOL Ltd .: JSM-6510LA). From the photographed image, the number of particles in which the outer edge of the particle could be confirmed in the field of view was counted to determine the total number of particles, and the number of bound particles contained in all the particles was counted to calculate the bound particle content. The total number of particles counted in the calculation of the bound particle content is at least 100 or more, and when the total number of particles in the field of view is less than 100, the same number of particles is counted by using another field image of the same sample. did.
However, in the image, fine particles having a particle size (maximum length) of 3 μm or less are not counted as particles. This is because the fine particles are in the form of raw material powder or are broken powder for some reason, and are an impurity that cannot be expected to function as a carrier core material. It is usually very small and must be negligible. Furthermore, the particles whose outer edges are confirmed can be counted. It is desirable to confirm the image by enlarging the same particle or changing the viewing angle when the image uses monodispersed particles and it is not possible to determine whether the particles overlap and are bound particles. In the case of a bound particle, the center of gravity of the bound particle is different from the center of gravity of the mother particle, so that it is easy to roll over (rotate), and in the image, the field of view from the side is easy to observe.
The bonded particles were particles in which 2 to 5 spherical particles were bonded. In the binding particles, since the spherical particles and the spherical particles exist in a form in which the binding portion is shared, the particle diameter of each spherical particle is determined by scanning electron microscope (manufactured by JEOL Ltd .: JSM). -6510LA), the image was calculated by approximating the particles in a spherical shape from the area excluding the binding portion of the binding particles.

(Measuring method of average particle size)
The average particle size of the carrier core material was measured using a laser diffraction type particle size distribution measuring device (“Microtrack Model 9320-X100” manufactured by Nikkiso Co., Ltd.).

(Measuring method of the number ratio of particles having a predetermined maximum valley depth Rz)
Using an ultra-deep color 3D shape measurement microscope (“VK-X100” manufactured by Keyence Corporation), the surface was observed with a 100 × objective lens. Specifically, first, ferrite particles were fixed to an adhesive tape having a flat surface, a measurement field of view was determined with a 100 × objective lens, and then the focus was adjusted to the adhesive tape surface using an autofocus function. The flat adhesive tape surface on which the ferrite particles were fixed was irradiated with a laser beam from the vertical direction (Z direction) and scanned in the X direction and Y direction of the surface. Also, data in the Z direction was acquired by connecting the height positions of the lenses when the intensity of the reflected light from the surface was maximized. These X, Y, and Z direction position data were connected to obtain a three-dimensional shape of the ferrite particle surface. Note that an auto photographing function was used to capture the three-dimensional shape of the ferrite particle surface.
Measurement of each parameter was performed using particle roughness inspection software (manufactured by Mitani Corporation). First, as pretreatment, three-dimensional shape particle recognition and shape selection on the surface of the obtained ferrite particles were performed. Particle recognition was performed by the following method. Of the three-dimensional shape obtained by photographing, the maximum value in the Z direction is set to 100% and the minimum value is set to 0%. The region corresponding to 100 to 35% was extracted, and the contour of the independent region was recognized as the particle contour. Next, coarse, fine, and association particles were excluded by shape selection. By performing this shape selection, it is possible to reduce an error at the time of correcting the polarities thereafter. Specifically, particles corresponding to an area equivalent diameter of 28 μm or less, 38 μm or more, and an acicular ratio of 1.15 or more were excluded. Here, the acicular ratio is a parameter calculated from the ratio of the maximum length / diagonal width of the particle, and the diagonal width is the shortest distance between two straight lines when the particle is sandwiched between two straight lines parallel to the maximum length. Represents.
Next, the part used for analysis was extracted from the three-dimensional shape of the surface. First, a 15.0 μm square is drawn around the center of gravity obtained from the particle contour recognized by the above method. 21 parallel lines were drawn in the drawn square, and 21 roughness curves corresponding to the line segment were taken out.

  Since the ferrite particles are substantially spherical, the extracted roughness curve has a certain curvature as the background. For this reason, as a background correction, an optimal quadratic curve was fitted and correction subtracted from the roughness curve was performed. In this case, a low-pass filter was applied with an intensity of 1.5 μm, and the cut-off value λ was 80 μm.

  The maximum mountain valley depth Rz was obtained as the sum of the highest mountain height and the deepest valley depth in the roughness curve. The measurement of the maximum height Rz described above is performed according to JIS B0601 (2001 edition). The maximum mountain valley depth Rz was measured for 50 particles, and among 50 particles, particles having an Rz of 1.8 μm or more were counted to calculate the number ratio (%).

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these examples at all.

Example 1
As a raw material, 10,000 g of Fe ₂ O ₃ was dispersed in 3340 g of pure water, and 25 g of carbon black as a reducing agent and 35 g of an ammonium polycarboxylate dispersant as a dispersing agent were added to obtain a mixture. This mixture was pulverized by a wet ball mill (media diameter 2 mm) to obtain a mixed slurry.
This mixed slurry was sprayed into hot air of about 140 ° C. with a spray dryer (disk rotation speed: 17000 rpm) to obtain a dry granulated product having a particle size of 10 μm to 200 μm.
(Preparation of carrier core material A)
The dried granulated product obtained above was put into an electric furnace and calcined at a temperature of 1050 ° C. for 3 hours in an oxygen atmosphere of 3000 ppm. The obtained fired product was crushed with a hammer mill and then classified using a vibrating sieve to obtain a carrier core material A having a volume average particle size of 35 μm.
(Preparation of carrier core B)
The dried granulated material obtained above was put into an electric furnace and fired at a temperature of 1250 ° C. for 3 hours in an oxygen atmosphere of 5000 ppm. The obtained fired product was crushed with a hammer mill and then classified using a vibration sieve to obtain a carrier core material B having a volume average particle size of 35 μm.
(Preparation of carrier core material)
The carrier core material A and the carrier core material B were mixed at a weight ratio of 90:10 to obtain the carrier core material of Example 1.
Apparent density and ratio after demagnetization and magnetization of the carrier core material, fluidity, average particle diameter, number% of particles having maximum peak / valley depth Rz of 1.8 μm or more, magnetic properties, ratio of bonded particles, development memory Was measured by the method described above and below. The measurement results are shown in Table 2. Moreover, the SEM photograph of the carrier core material of Example 1 is shown in FIG.

Examples 2-4, Comparative Examples 1-3
The carrier core material A is prepared with the raw material blending amount and the firing temperature shown in Table 1 below, and mixed with the carrier core material A and the carrier core material B at the mixing ratio shown in Table 1, and Examples 2 to 4 and Comparative Examples 1 to 4 are mixed. 3 carrier core material was produced. Apparent density and ratio after demagnetization and magnetization of the produced carrier core material, fluidity, average particle diameter, number of particles having maximum peak / valley depth Rz of 1.8 μm or more, magnetic properties, ratio of coupled particles, The development memory was measured by the method described above and below. The measurement results are shown in Table 2. Moreover, the SEM photograph of the carrier core material of Example 2 is shown in FIG.

(Fluidity)
The fluidity of the carrier core material was measured according to JIS Z 2502.

(Magnetic properties)
Using a vibration sample type magnetometer (VSM) dedicated to room temperature (“VSM-P7” manufactured by Toei Kogyo Co., Ltd.), the external magnetic field ranges from 0 to 79.58 × 10 ⁴ A / m (10000 Oersted) for one cycle. The magnetization σ _1k , saturation magnetization σ _s , residual magnetization σ _r , and coercive force Hc when a magnetic field of 79.58 × 10 ³ A / m (1000 oersted) was applied were measured.

(Image memory)
The surface of the obtained carrier core material was coated with a resin to prepare a carrier. Specifically, 450 parts by weight of a silicone resin and 9 parts by weight of (2-aminoethyl) aminopropyltrimethoxysilane were dissolved in 450 parts by weight of toluene as a solvent to prepare a coating solution. This coating solution was applied to 50000 parts by weight of a carrier core material using a fluid bed type coating apparatus and heated in an electric furnace at a temperature of 300 ° C. to obtain a carrier. Hereinafter, carriers were obtained in the same manner for all of the examples and comparative examples.

The obtained carrier and a toner having an average particle diameter of about 5.0 μm were mixed for a predetermined time using a pot mill to obtain a two-component electrophotographic developer. In this case, the carrier and the toner were adjusted so that the weight of toner / (weight of toner and carrier) = 5/100. Hereinafter, developers were obtained in the same manner for all of the Examples and Comparative Examples.
The developer thus obtained was developed into a developing device having the structure shown in FIG. 4 (developing sleeve peripheral speed Vs: 406 mm / sec, photosensitive drum peripheral speed Vp: 205 mm / sec, photosensitive drum-developing sleeve distance: 0. 3 mm), an image in which a solid image portion and a non-image portion are adjacent to each other in the longitudinal direction of the photosensitive drum, and a halftone of a wide area thereafter is obtained after the initial and 200,000 sheets are formed, and the developing roller 2 Measure the image density between the area where the solid image on the first development roller of the circumference is developed and the area where it is not, using a reflection densitometer (Model No. TC-6D manufactured by Tokyo Denshoku Co., Ltd.), and determine the difference. Evaluation was made according to the following criteria. The results are shown in Table 2.
“◎”: Less than 0.003 “O”: 0.003 or more and less than 0.006 “Δ”: 0.006 or more and less than 0.020 “X”: 0.020 or more

In the carrier core materials of Examples 1 to 4 in which the apparent density ratio (AD ₂ / AD ₁ ) is in the range of 0.91 to 0.97 and the content of the binder particles is in the range of 8.6 to 17.0 number%. As a result of a large amount of toner being taken into the space of the magnetic agglomerated particles and the binding particles and transported to the development area, the carrier core materials of Examples 1 to 3 do not cause a shortage of toner supply amount and no development memory is generated. It was. Further, the carrier core material of Example 4 had some development memory, but had no problem in practical use.

On the other hand, in the carrier core material of Comparative Example 1 in which the content rate of the binding particles is as high as 21.0% by number, the fluidity is deteriorated, and the carrier is not sufficiently circulated and moved in the magnetic brush, which is a problem in practical use. A certain level of development memory has occurred. Further, in the carrier core material of Comparative Example 2 in which the apparent density ratio (AD ₂ / AD ₁ ) is as high as 0.99, the magnetic aggregate particles are not sufficiently generated, and the amount of toner conveyed to the development area is insufficient. Development memory was generated. Even in the carrier core material of Comparative Example 3 in which the binding particle content was as low as 4.5% by number, the amount of toner transported to the development area by the binding particles was insufficient, resulting in development memory.

3 Developing roller 5 Photosensitive drum

Claims (5)

5 to 20% by number of bonded particles in which 2 to 5 spherical particles are combined are included,
The apparent density (AD ₁ ) when demagnetized by applying a damped alternating magnetic field, and the apparent density (AD ₂ ) when magnetized under a magnetic field of 1000 / (4π) kA / m (1000 oersted) after demagnetization The carrier core material characterized in that the ratio (AD ₂ / AD ₁ ) is 0.90 or more and 0.98 or less.   The carrier core material according to claim 1, wherein 5% by number or more of particles having a maximum mountain valley depth Rz of 1.8 μm or more are contained.   The carrier core material according to claim 1, wherein the volume average particle diameter is 25 μm or more and less than 50 μm.   A carrier for electrophotographic development, wherein the surface of the carrier core material according to claim 1 is coated with a resin.   An electrophotographic developer comprising the carrier for electrophotographic development according to claim 4 and a toner.