HK1180048A - Method for producing carrier core for electrophotographic developer, carrier core for electrophotographic developer, carrier for electrophotographic carrier, and electrophotographic developer - Google Patents

Abstract

A method for producing a carrier core for an electrophotographic developer comprises a step (A) for producing a slurry in which a slurry is produced from a starting material containing iron and a starting material containing strontium, a step (B) for granulation in which, after the step for producing a slurry, the resulting mixture is granulated, and a step (C) for baking in which the granulated powder from the granulation step is baked at a predetermined temperature to form a magnetic phase. In the step for producing a slurry, a slurry is produced from a starting material containing iron such that the volume grain diameter D50 of the starting material containing iron is 1.0 to 4.0 µm and the volume grain diameter D90 of the starting material containing iron is 2.5 to 7.0 µm, and a slurry is produced from a starting material containing strontium so that when the strontium content of the carrier core for an electrophotographic developer is y, 0 < y≤5,000 ppm is satisfied.

Description

Method for producing carrier core material for electrophotographic developer, carrier for electrophotographic developer, and electrophotographic developer

Technical Field

The present invention relates to a method for producing a carrier core material for an electrophotographic developer (hereinafter, may be referred to simply as a "carrier core material"), a carrier core material for an electrophotographic developer, a carrier for an electrophotographic developer (hereinafter, may be referred to simply as a "carrier") and an electrophotographic developer (hereinafter, may be referred to simply as a "developer"), and more particularly to a carrier core material for an electrophotographic developer provided in an electrophotographic developer used in a copying machine, an MFP (multi functional Printer), or the like, a method for producing the same, a carrier for an electrophotographic developer provided in an electrophotographic developer, and an electrophotographic developer.

Background

In copiers, MFPs, and the like, dry development methods in electrophotography include a one-component developer containing only toner as a developer component and a two-component developer containing toner and a carrier as developer components. In any of the developing methods, toner having a predetermined charge amount is supplied to the photoreceptor. The electrostatic latent image formed on the photoreceptor is visualized with toner and transferred to paper. Thereafter, the visible image obtained from the toner is fixed on paper to obtain a desired image.

The development in the two-component type developer is briefly described here. A predetermined amount of toner and a predetermined amount of carrier are accommodated in the developing unit. A developer has a plurality of rotatable magnetic rollers in which S poles and N poles are alternately arranged in a circumferential direction and an agitating roller for agitating and mixing toner and carrier in the developer. The carrier made of magnetic powder is carried by a magnetic roller. The magnetic force of the magnetic roller forms a linear magnetic brush composed of carrier particles. On the surfaces of the carrier particles, a plurality of toner particles are attached by triboelectric charging caused by stirring. The magnetic brush is brought into contact with the photoreceptor by rotation of the magnetic roller, and toner is supplied to the surface of the photoreceptor. Development was performed as above in the two-component type developer.

Since toner in the developing device is gradually consumed by fixing the toner to paper, new toner corresponding to the amount of consumption is supplied from a toner hopper attached to the developing device into the developing device as needed. On the other hand, the carrier is not consumed by development, and can be used until its life is reached. Carriers, which are constituent materials of two-component developers, are required to have various functions such as a toner charging function for effectively charging toner by frictional charging caused by agitation, insulation, and a toner transport capability for appropriately transporting and supplying toner to a photoreceptor. For example, from the viewpoint of improving the toner charging ability, it is required that the carrier resistivity (hereinafter, also simply referred to as resistivity) is appropriate and that the insulation property is appropriate.

Recently, the carrier is composed of a carrier core particle constituting a core portion, which is a core thereof, and a coating resin provided to cover a surface of the carrier core particle.

Techniques for carrier core particles or carriers are disclosed in japanese patent laid-open nos. 2006-337828 (patent document 1) and 2011-8199 (patent document 2).

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 2006-337828

Patent document 2: japanese patent laid-open publication No. 2011-

Disclosure of Invention

Technical problem to be solved by the invention

As for the carrier core material, it is desired that its electrical characteristics are good, specifically, for example, the carrier core material itself has a high electrical charge or has a high insulation breakdown voltage, and also has excellent specific resistance as described above.

In particular, recently, the charging performance of the carrier core material itself, specifically, the charging amount of the carrier core material tends to be increased. As described above, the carrier core material is often used by coating a resin on the surface thereof. Here, the partially applied resin may be peeled off by stress or the like generated by stirring in the developing device, and the surface of the carrier core particle may be exposed. In this case, the carrier core material itself is required to have a strong charging ability due to friction between the exposed surface and the toner. Of course, a carrier core material having good magnetic properties and other properties is preferable.

In recent years, the toner particles have been reduced in size from the viewpoint of improving image quality. As the toner particle size decreases, the carrier particle size decreases, and the carrier core particle size further decreases. In this case, a new problem may occur as the particle size of the carrier core particle becomes smaller.

In general, a carrier core material is prepared by mixing and granulating raw materials, and calcining the granulated powder to form ferrite and grow crystals. Here, in order to obtain a carrier core particle having a small particle diameter, the difference in the surface state of the carrier core particle tends to be large. Specifically, the crystal size of the surface of the growing particle, that is, the crystal size of the surface of the growing particle, is scattered as compared with the particle size of the carrier core particle having a smaller particle size, and coarse crystals tend to be easily formed on the surface of the particle.

Carrier core particles having such a large difference in surface state have poor surface properties and poor adhesion to a coating resin coated in a subsequent step, and as a result, the life of a carrier or a developer prepared by using such carrier core particles is shortened.

Here, patent document 1 discloses a ferrite carrier core material for electrophotography, the surface of which is divided into 2 to 50 regions in a square shape having a side of 10 μm by a groove or a skeleton, and which contains manganese ferrite as a main component. Further, patent document 1 describes that an electrophotographic developer using a ferrite carrier in which a resin is coated on a ferrite carrier core material has an increased initial charging speed and a stable charge amount over time.

However, carrier core particles having a smaller particle size, specifically, carrier core particles having a volume average particle size of about 25 μm, have problems such as an increase in pores inside the particles constituting the carrier core particles and a decrease in particle strength of the carrier core particles, even if the crystal size is set within a predetermined range, in terms of surface properties of the carrier core particles.

Patent document 2 discloses a carrier core material in which the ratio of the volume value of the impregnated pores to the volume value of the impregnated pores of the carrier core material obtained by mercury intrusion is defined to be 0.2 to 0.8. Patent document 2 describes that even when the developing device is used over time, the fluidity in the developing device is not changed, the left and right development unevenness does not occur on the image, a certain amount of resin coverage causes a certain leak point, the charge amount can be prevented from increasing, the charge amount change is small, and the image density can be prevented from decreasing.

However, the volume value of the leached pores may depend on the pore shape, not on the number of pores, and it may be insufficient to define the above ratio. In particular, in carrier core particles having a small particle size, there are many cases where it cannot be said that the surface has a constant fine pore, and such a ratio is merely defined, which may cause a problem from the viewpoint of strength and the like.

The purpose of the present invention is to provide a method for producing a carrier core material for an electrophotographic developer, which can produce a carrier core material for an electrophotographic developer that can achieve a small particle diameter, has an appropriate crystal size on the particle surface, and can achieve high strength.

Another object of the present invention is to provide a carrier core material for an electrophotographic developer, which can realize a small particle diameter, an appropriate crystal size on the particle surface, and a high strength.

Further, another object of the present invention is to provide a carrier for an electrophotographic developer which can realize a small particle size and a high strength.

Further, another object of the present invention is to provide an electrophotographic developer capable of forming an image of good quality.

Means for solving the problems

The present inventors considered that, first, in order to reduce the particle size of the carrier core particles, it is necessary to reduce the particle size of the raw material of the carrier core particles. And it is considered that if the volume particle diameter D is used₅₀The small value of (b) can control the surface properties of the carrier core particles, that is, suppress the growth of crystals during firing, and make the crystal size on the particle surface suitable, while achieving a smaller particle size of the carrier core particles. However, the finding that only the volume particle diameter D of the raw material is reduced was obtained₅₀The sintering rate in the firing step is significantly increased, and it is difficult to control the sintering of the particle interior and the particle surface of the carrier core material. On the other hand, it has also been found that if the volume particle diameter D is used₅₀The large value of (a) is not only difficult to achieve a small particle diameter, but also the raw material filling ratio per particle is reduced in the state of the granulated powder, as a result, large pores, that is, void portions are generated in the particles of the carrier core material. Further, intensive studies have been made on the basis of the prior art to investigate whether or not the sintering state can be controlled using an additive which hinders sintering. However, it was found that the additive deteriorated the charging performance of the carrier core material.

Accordingly, the present inventors have conducted extensive studies and paid attention not only to the volume particle diameter D of the raw material₅₀The value of (A) is also of concern for coarse particles of the starting material, so that it is considered whether the volume particle diameter D of the starting material can be defined₉₀The value (c) is used to suppress the generation of pores and to control sintering in the firing step. Further, the inventors of the present invention have considered that a small amount of strontium (Sr) is added so as to slowly perform the reaction of ferrite and sintering without impairing the basic physical properties of the carrier core material.

That is, the method for preparing a carrier core material for an electrophotographic developer according to the present invention is a method for preparing a carrier core material for an electrophotographic developer containing iron and strontium as a core, comprising: a slurrying step of slurrying an iron-containing raw material and a strontium-containing raw material; a granulation step of granulating the obtained mixture after the slurry step; and a firing step of firing the powder granulated in the granulation step at a predetermined temperature to form a magnetic phase. In the slurry step, the raw material containing iron is made into a slurry, and the volume particle diameter D of the raw material containing iron is made₅₀1.0 to 4.0 μm, and the volume particle diameter D of the raw material containing iron₉₀2.5 to 7.0 μm; and slurrying the strontium-containing raw material so that when the strontium content in the carrier core material for an electrophotographic developer is y, it is 0<y≤5000ppm。

According to such a method for producing a carrier core material, a carrier core material having a small particle diameter, having very few pores inside the particle, and having homogeneous crystal grains on the surface of the particle can be produced. Therefore, it is possible to prepare a carrier core material for an electrophotographic developer, which can realize a small particle diameter, an appropriate crystal size on the particle surface, and a high strength. Further, regarding the volume particle diameter D₅₀、D₉₀When the cumulative curve is obtained by taking the total volume of the obtained powder as 100%, the particle diameters at the points of 50% and 90% of the cumulative curve are taken as the volume particle diameter D₅₀、D₉₀。

Here, first, in the general formula: mn_XFe_3-XO_4+v（-0.003<v) represents the carrier core material of the above structure. Preferably 0.7. ltoreq. x.ltoreq.1.2, more preferably 0.8. ltoreq. x.ltoreq.1.1. When x is 0.7 or more, high magnetization can be maintained, and therefore, it is preferable. When x is 1.2 or less, it is preferable to prevent the increase of the nonmagnetic phase in the particles by an excessive amount of Mn.

In this case, the raw material containing iron may be calcined in advance and used in the slurry step.

Preferably, in the baking step, the baking temperature is set to be within a range of 1050 to 1180 ℃, and the holding time from reaching the baking temperature is set to be within a range of 0.5 to 10 hours, and the baking is performed.

More preferably, the roasting temperature is 1085-1150 ℃ and the roasting time is 1.5-6 hours. If the firing temperature is 1085 ℃ or higher and the firing time is 1.5 hours or longer, ferrite transformation is sufficiently performed, and sintering of the inside and surface of the particles is gradually performed, so that the intended surface properties can be obtained. It is preferable that the firing temperature is 1150 ℃ or lower and the firing time is 6 hours or less because excessive sintering does not occur and coarse crystals are not generated on the particle surface.

The oxygen concentration in the baking furnace may be adjusted to a condition that ferrite reaction proceeds, and specifically, the oxygen concentration of the introduced gas is adjusted to 10^-7% to 3% by weight, and firing the mixture in a fluidized state.

Further, the reducing atmosphere required for the ferrite transformation may be controlled by adjusting a reducing agent described later.

In another aspect of the present invention, the carrier core material for electrophotographic developer is a carrier core material for electrophotographic developer comprising iron and strontium as a core, and when the content of strontium contained in the carrier core material for electrophotographic developer is y, 0 is provided<y is not more than 5000ppm, the average particle diameter is within the range of 20 μm to 30 μm, and the BET specific surface area is 0.15m²0.25m above/g²In the range of not more than 0.003ml/g and in the range of not more than 0.023ml/g, respectively, of the pore volume obtained by the mercury intrusion method.

If 0<y, that is, if strontium is contained, it is preferable because the ferrite reaction and sintering of strontium proceed slowly and the desired surface properties are easily obtained. Further, it is preferable that y is 5000ppm or less because an increase in remanence due to the generation of strontium ferrite can be prevented. Further, if the BET specific surface area value is 0.15m²A pore volume value of 0.003ml/g or more by mercury intrusion, almost no pores are present in the particles, and a high BET specific surface area value is achieved mainly by the irregular parts of the particle surface,therefore, the adhesiveness to the coating resin is improved, which is preferable. Further, if the BET specific surface area value is 0.25m²The pore volume value by mercury intrusion is preferably 0.023ml/g or less, and the particles have almost no large pores, that is, almost no pores having openings on the particle surface, and the particle strength can be improved mainly because the high BET specific surface area value is achieved by fine and minute pores.

Here, the BET specific surface area is assumed to be w (m)²(g)/g), when the pore volume obtained by the mercury intrusion method is represented by v (ml/g), it is preferable that v is 0.63w or less²-0.084w + 0.028. In the carrier core material having the relationship between the BET specific surface area value and the pore volume value obtained by the mercury intrusion method, the number of pores in the carrier core material particle is extremely small, and the crystal grains on the particle surface are homogeneous, whereby the particle strength of the carrier core material can be further improved.

As a more preferred embodiment, 500ppm<y is not more than 3400ppm, the average particle diameter is in the range of 20 to 30 μm, and the BET specific surface area is 0.15m²0.20m above/g²The pore volume obtained by mercury intrusion method is in the range of 0.003ml/g to 0.012 ml/g. Such a carrier core material for an electrophotographic developer can more reliably realize a high BET specific surface area value, and can improve the adhesion with a coating resin and the particle strength.

The carrier core material for electrophotographic developers of the present invention is a carrier core material for electrophotographic developers comprising iron and strontium as nuclei, which is obtained by slurrying an iron-containing raw material and a strontium-containing raw material, granulating the resulting mixture, and calcining the granulated powder at a predetermined temperature to form a magnetic phase. Here, the carrier core material for electrophotographic developers is prepared by slurrying an iron-containing raw material so that the volume particle diameter D of the iron-containing raw material becomes₅₀1.0 to 4.0 μm, and the volume particle diameter D of the raw material containing iron₉₀2.5 to 7.0 μm, slurrying a strontium-containing raw material,when the content of strontium contained in the carrier core material for the electrophotographic developer is y, 0<y≤5000ppm。

Such a carrier core material for an electrophotographic developer has a small particle diameter, very few pores inside the particle, and homogeneous crystal grains on the surface of the particle. Therefore, the carrier core material produced by the method for producing a carrier core material can have a small particle diameter, and can have a high strength by adjusting the crystal size on the particle surface.

Another aspect of the present invention relates to a carrier for an electrophotographic developer, which is a carrier for an electrophotographic developer used in an electrophotographic developer, and which comprises any one of the carrier core particles for an electrophotographic developer described above and a resin covering the surface of the carrier core particle for an electrophotographic developer.

Such a carrier for an electrophotographic developer can realize a small particle size and a high strength.

Another aspect of the present invention relates to an electrophotographic developer, which is an electrophotographic developer used in development of electrophotography, and which is provided with the above-described carrier for electrophotographic developer and a toner capable of being charged in electrophotography by frictional charging with the carrier for electrophotographic developer.

Such an electrophotographic developer can form an image with high image quality because it has the carrier for an electrophotographic developer having the above-described structure.

Effects of the invention

According to such a method for producing a carrier core material, a carrier core material having a small particle diameter, having very few pores inside the particle, and having homogeneous crystal grains on the surface of the particle can be produced. Therefore, it is possible to prepare a carrier core material for an electrophotographic developer which has a small particle diameter, an appropriate crystal size on the particle surface, and high strength.

In addition, the carrier core material for electrophotographic developers has a small particle size, very few pores inside the particles, and homogeneous crystal grains on the surface of the particles. Therefore, the carrier core material produced by the method for producing a carrier core material can have a small particle diameter, and also has a suitable crystal size on the particle surface and high strength.

In addition, the electrophotographic developer carrier of the present invention can realize a high strength while achieving a small particle size.

In addition, the electrophotographic developer of the present invention can form high-quality images.

Drawings

Fig. 1 is a flowchart showing representative steps in a method for producing a carrier core particle according to an embodiment of the present invention.

Fig. 2 is an electron micrograph showing the appearance of the carrier core particles of example 1.

Fig. 3 is an electron micrograph showing the appearance of the carrier core particles of comparative example 2.

Fig. 4 is an electron micrograph showing a cross section of a carrier core particle of example 1.

Fig. 5 is an electron micrograph showing a cross section of a carrier core particle of comparative example 2.

Detailed Description

Embodiments of the present invention will be described below with reference to the drawings. First, a carrier core material according to an embodiment of the present invention will be described. The carrier core material according to one embodiment of the present invention has an approximately spherical outer shape. The carrier core particles according to one embodiment of the present invention have a particle size of about 25 μm and an appropriate particle size distribution. That is, the particle diameter refers to a volume average particle diameter. The particle diameter and the particle size distribution can be arbitrarily set according to the required characteristics of the developer, the productivity in the production process, and the like. On the surface of the carrier core particles, minute irregularities mainly formed in a firing step described later are formed.

The carrier according to the embodiment of the present invention has an approximately spherical shape, similar to the carrier core material. The carrier is formed by thinly coating a resin on the surface of the carrier core material, that is, by coating the resin, and the particle diameter thereof is almost unchanged from that of the carrier core material. The surface of the carrier is almost completely covered with the resin, unlike the carrier core material.

The developer according to one embodiment of the present invention is composed of the above carrier and toner. The external shape of the toner is also approximately spherical. The toner is mainly composed of a styrene acrylic resin or a polyester resin, and a predetermined amount of a pigment, wax, or the like is blended therein. Such a toner is produced, for example, by a pulverization method or a polymerization method. The particle diameter of the toner is, for example, about one-seventh of the particle diameter of the carrier, and is about 5 μm. The ratio of the toner to the carrier may be arbitrarily set according to the required properties of the developer. Such a developer can be produced by mixing prescribed amounts of the carrier and the toner with an appropriate mixer.

Next, a method for producing a carrier core material according to an embodiment of the present invention will be described. Fig. 1 is a flowchart showing representative steps in a method for producing a carrier core particle according to an embodiment of the present invention. A method for producing a carrier core material according to an embodiment of the present invention will be described below with reference to fig. 1.

First, an iron-containing raw material, a manganese-containing raw material, and a strontium-containing raw material are prepared. Then, the prepared raw materials are mixed in an appropriate ratio according to the required characteristics, and mixed and pulverized (fig. 1 (a)). Here, the appropriate compounding ratio is a compounding ratio contained in the finally obtained carrier core material.

The iron-containing raw material constituting the carrier core particles according to one embodiment of the present invention may be metallic iron or an oxide thereof. Specifically, Fe stably existing at normal temperature and pressure is suitably used₂O₃Or Fe₃O₄Fe, etc. The manganese-containing raw material may be metal manganese or an oxide thereof. Specifically, Mn and MnO which are metals stable at ordinary temperature and pressure are suitably used₂、Mn₂O₃、Mn₃O₄、MnCO₃. In addition, as the strontium-containing raw material, SrCO is suitably used₃、Sr(NO₃)₂、SrSO₄. More preferably SrCO₃. Here, the raw materials (iron raw material, manganese raw material, strontium raw material, etc.) may be used as raw materials by calcining and pulverizing the raw materials separately or mixed into a target composition. In addition, the above raw materials are calcined and pulverized only an iron raw material and a manganese raw material, and these are used as the calcination raw materials, and SrCO as a strontium-containing raw material₃More preferably, no calcination is performed. Non-calcined SrCO₃In the case of (3), in the baking step described later, SrCO is first performed₃Followed by ferrite reaction and sintering. Therefore, if SrCO is not contained as a calcination raw material₃In the baking step described later, SrCO is first performed₃Followed by ferrite reaction and sintering. Thus, the ferrite reaction and sintering can be performed slowly. As a result, a carrier core material having a small particle diameter and a homogeneous crystal grain on the particle surface can be produced.

Here, as for the iron-containing raw material, the volume particle diameter D of the iron-containing raw material is made₅₀1.0 to 4.0 μm, the volume particle diameter D of the iron-containing raw material₉₀2.5 to 7.0 μm. In addition, regarding the strontium-containing raw material, the volume particle diameter D of the strontium-containing raw material is set₅₀1.0 to 4.0 μm, the volume particle diameter D of the strontium-containing raw material₉₀2.5 to 7.0 μm. Further, the volume particle diameter D of the manganese-containing raw material is set₅₀0.1 to 3.0 μm, the volume particle diameter D of the manganese-containing raw material₉₀1.0 to 6.0 μm.

In addition, regarding the strontium-containing raw material, when the content of the strontium-containing raw material is y, 0< y is less than or equal to 5000 ppm.

Specifically, a vibrating ball mill is used for mixing an iron-containing raw material and a manganese-containing raw material according to a specified composition, forming the mixture into particles, and calcining the particles for 1 to 10 hours at 800 to 1050 ℃. The molding into a pellet is preferable because partial ferrite reaction can be carried out even at a temperature of 800 to 1050 ℃. More preferably, the temperature is set to 900 to 1000 ℃. If the temperature is above 900 ℃, partial ferrite reaction can be fully performed; when the temperature is 1000 ℃ or lower, the sintering is not excessively conducted, and the target particle size of the raw material is easily formed in the subsequent step, so that it is preferable. The calcined raw material obtained by the above method was pulverized by a vibration mill and adjusted to a certain particle size.

The mixed raw materials are finely pulverized and slurried. That is, these raw materials are weighed to the target composition of the carrier core particles, mixed and pulverized by a wet bead mill, and the slurry raw material is controlled to the target particle size. In this step, the ratio of coarse particles contained in the raw material is controlled. That is, the iron-containing raw material is slurried to have a volume particle diameter D₅₀1.0 to 4.0 μm, the volume particle diameter D of the iron-containing raw material₉₀2.5 to 7.0 μm. Further, the strontium-containing raw material is slurried so that when the strontium content in the carrier core particle is y, 0<y is less than or equal to 5000 ppm. If the volume particle diameter D of the iron-containing raw material₉₀When the particle size distribution is 2.5 μm or more, the particle size distribution of the raw material does not become sharp (シャープ), the sintering rate of the particles is slow, and the control of the particle size distribution to the target surface properties is easy, which is preferable. On the other hand, if the volume particle diameter D of the iron-containing raw material₉₀A particle size of 7.0 μm or less is preferred because the occurrence of pores in the carrier core material due to coarse particles can be reduced.

In the preparation step for preparing the carrier core material of the present invention, a reducing agent may be added to the slurry material in order to promote the reduction reaction in the partial firing step described later. As the reducing agent, carbon powder or polycarboxylic organic substance, polyacrylic organic substance, maleic acid, acetic acid, polyvinyl alcohol (pva) organic substance, and a mixture thereof are suitably used.

Water is added to the slurry material, and the mixture is stirred so that the solid content concentration is 60 wt% or more, preferably 70 wt% or more. If the solid content concentration of the slurry raw material is 70 wt% or more, the strength of the granulated particles can be maintained, the pores in the particles after the firing step can be reduced, and the strength of the carrier core material can be improved, which is preferable.

Subsequently, the slurried raw material is granulated (fig. 1B). The slurry obtained by the above mixing and stirring was granulated by using a spray dryer. Further, it is preferable that the slurry is further subjected to wet grinding before granulation.

The temperature of the atmosphere during spray drying is about 100-300 ℃. This can give a granulated powder having a particle diameter of substantially 10 to 200 μm. In view of the final particle size of the product, it is preferable to remove coarse particles or fine particles from the obtained granulated powder by using a vibrating screen or the like, and at this time, the particle size is adjusted.

Thereafter, the granulated material is fired (fig. 1 (C)). Specifically, the obtained granulated powder is put into a furnace heated to about 1050 to 1180 ℃ as a roasting temperature, and is kept for 0.5 to 10 hours to be roasted to generate a target roasted product. At this time, the oxygen concentration in the baking furnace may be set to a condition that ferrite reaction can proceed, and specifically, the oxygen concentration of the introduced gas is adjusted to 10^-7% to 3% by weight, and firing the mixture in a fluidized state.

Specifically, in the baking step, the temperature is raised at a rate of 0.5 to 100 ℃/min, the baking temperature is in the range of 1050 to 1180 ℃, the holding time from reaching the baking temperature is in the range of 0.5 to 10 hours, and the cooling rate from the baking temperature is 0.5 to 10 ℃/min, and the baking is performed.

More preferably, the roasting temperature is set within the range of 1085-1150 ℃ and the roasting time is set within the range of 1.5-6 hours. When the firing temperature is 1085 ℃ or higher and the firing time is 1.5 hours or longer, ferrite is sufficiently formed, and the inside and surface of the particles can be gradually sintered, so that the desired surface properties can be obtained. It is preferable that the firing temperature be 1150 ℃ or lower and the firing time be 6 hours or less because excessive sintering does not occur and coarse crystals do not form on the particle surface.

Further, the reducing atmosphere required for ferrite in the furnace may be controlled by adjusting the amount of the reducing agent or the like.

Further, in the calcination step, as to exhaust gas generated at the time of calcination, especially CO₂Gas, which is required to flow without being retained in the furnace, and CO control₂The concentration of the gas is low. Thus, SrCO₃The decomposition reaction and ferrite reaction of (2) are remarkably retarded, and insufficient strength of the carrier core material due to non-sintering inside the particles can be prevented, which is preferable.

The particle size of the calcined product obtained is preferably adjusted at this stage. For example, the calcined material is coarsely pulverized by a hammer mill or the like. That is, the calcined particulate matter is pulverized (fig. 1 (D)). Thereafter, classification is performed with a vibrating screen or the like. Namely, the crushed particles are classified (fig. 1E). In this way, particles having a carrier core particle with a desired particle diameter can be obtained.

Next, the classified particulate matter is oxidized (fig. 1F). That is, at this stage, the particle surface of the obtained carrier core particle is subjected to heat treatment (oxidation treatment). The dielectric breakdown voltage of the particles is increased to 250V or more so that the resistivity is 1 x10 which is appropriate⁶～1×10¹³Omega cm. By increasing the resistivity of the carrier core material by the oxidation treatment, carrier scattering due to charge leakage can be reduced.

Specifically, the target carrier core material is obtained by keeping the temperature of the target carrier core material at 200-700 ℃ for 0.1-24 hours in an atmosphere with the oxygen concentration of 10-100%. More preferably, the temperature is maintained at 250 to 600 ℃ for 0.5 to 20 hours, and still more preferably at 300 to 550 ℃ for 1 to 12 hours. Such an oxidation treatment step may be optionally performed as needed.

Thus, a carrier core material according to an embodiment of the present invention is produced. Namely, the electricity of one embodiment of the present inventionA method for preparing a carrier core material for a developing agent for electrophotography, which comprises iron and strontium as a core, comprising: a slurrying step of slurrying an iron-containing raw material and a strontium-containing raw material; a granulation step of granulating the obtained mixture after the slurry step; and a baking step of baking the powder granulated in the granulating step at a predetermined temperature to form a magnetic phase. In the slurry step, the raw material containing iron is slurried to have a volume particle diameter D₅₀1.0 to 4.0 μm, and the volume particle diameter D of the raw material containing iron₉₀2.5 to 7.0 μm; and slurrying the strontium-containing raw material so that when the strontium content in the carrier core material for an electrophotographic developer is y, 0<y≤5000ppm。

According to such a method for producing a carrier core material, a carrier core material having a small particle diameter, having very few pores inside the particle, and having homogeneous crystal grains on the surface of the particle can be produced. Therefore, it is possible to prepare a carrier core material for an electrophotographic developer, which can realize a small particle diameter, an appropriate crystal size on the particle surface, and a high strength.

In addition, a carrier core material for an electrophotographic developer according to an embodiment of the present invention is a carrier core material for an electrophotographic developer containing iron and strontium as nuclei, which is produced by slurrying an iron-containing raw material and a strontium-containing raw material, granulating the resultant mixture, and firing the granulated powder at a predetermined temperature to form a magnetic phase. Here, the carrier core material for electrophotographic developers is produced by slurrying an iron-containing raw material so that the volume particle diameter D of the iron-containing raw material becomes₅₀1.0 to 4.0 μm, the volume particle diameter D of the iron-containing raw material₉₀2.5 to 7.0 μm; slurrying a strontium-containing raw material so that when the content of strontium contained in a carrier core material for an electrophotographic developer is y, 0<y≤5000ppm。

Such a carrier core material for an electrophotographic developer has a small particle diameter, very few pores inside the particle, and homogeneous crystal grains on the surface of the particle. Therefore, the carrier core material produced by such a method for producing a carrier core material can achieve a small particle diameter, an appropriate crystal size on the particle surface, and high strength.

The carrier core material for electrophotographic developer is a carrier core material for electrophotographic developer comprising iron and strontium as a core, and when the content of strontium contained in the carrier core material for electrophotographic developer is y, 0<y is less than or equal to 5000 ppm. The average particle size is in the range of 20 to 30 μm. Further, the BET specific surface area value was 0.15m²0.25m above/g²Within a range of,/g or less. The pore volume obtained by the mercury intrusion method is in the range of 0.003ml/g to 0.023 ml/g.

Next, the carrier core particles thus obtained are covered with a resin (fig. 1G). Specifically, the obtained carrier core material of the present invention is covered with a silicone resin, an acrylic resin, or the like. Thus, a carrier for an electrophotographic developer according to an embodiment of the present invention was obtained. The coating method of the silicone resin, the acrylic resin, or the like can be performed by a known method. That is, the carrier for an electrophotographic developer according to one embodiment of the present invention is a carrier for an electrophotographic developer used in an electrophotographic developer, and includes the carrier core material for an electrophotographic developer and a resin covering a surface of the carrier core material for an electrophotographic developer. Such a carrier for an electrophotographic developer can realize a small particle size and a high strength.

Subsequently, the carrier and the toner thus obtained are mixed in predetermined amounts (fig. 1H). Specifically, the carrier for electrophotographic developers according to one embodiment of the present invention obtained by the above-described production method and a suitable known toner are mixed. Thus, an electrophotographic developer according to an embodiment of the present invention can be obtained. The mixing is carried out using any mixer such as a ball mill. That is, the electrophotographic developer according to one embodiment of the present invention is an electrophotographic developer used for developing electrophotography, and includes the above-mentioned carrier for electrophotographic developer and a toner which is triboelectrically charged with the carrier for electrophotographic developer and can be charged in electrophotography. Such an electrophotographic developer can form an image with high image quality by the carrier for an electrophotographic developer having the above-described structure.

Examples

(example 1)

10kg of Fe₂O₃(volume particle diameter D)₅₀: 0.6 μm, volume particle diameter D₉₀：3.0μm）、4kg Mn₃O₄(volume particle diameter D)₅₀: 0.3 μm, volume particle diameter D₉₀: 2.0 μm) was calcined at 900 ℃ for 2 hours. Then, the mixture was pulverized for 1 hour by a vibratory ball mill. 14kg of the calcined raw material was dispersed in 5kg of water, 84g of a polycarboxylic ammonium dispersant was added as a dispersant, 42g of carbon black was added as a reducing agent, and 103g of SrCO was added as a strontium-containing raw material₃(volume particle diameter D)₅₀: 1.0 μm, volume particle diameter D₉₀: 4.0 μm) to give a mixture. The solid content concentration at this time was measured, and found to be 74% by weight. The mixture was pulverized by a wet ball mill (medium diameter 2 mm) to obtain a mixed slurry having a volume particle diameter D of the calcined material₅₀Has a volume particle diameter D of 1.6 μm₉₀And 3.1 μm. That is, the iron-containing raw material in this case is a calcined raw material. Sr was added so that the amount of Sr added was 4350 ppm.

The slurry was sprayed by a spray dryer in hot air at about 130 ℃ to obtain dry granulated powder. At this time, the granulated powder other than the target particle size distribution is removed by a sieve. The granulated powder was charged into an electric furnace and calcined at 1130 ℃ for 3 hours. At this time, the electric furnace was circulated through a circuit in which the atmosphere was adjusted so that the oxygen concentration was 0.8%, i.e., 8000 ppm. The cooling temperature during firing was set to 2 ℃ per minute. Here, the cooling rate at the time of firing, that is, the cooling rate to room temperature after the end of firing is preferably 10 ℃/min or less, and more preferably 3 ℃/min. The obtained calcined product was pulverized and then classified by a sieve so that the average particle diameter was 25 μm, thereby obtaining a carrier core material of example 1. The average particle diameter referred to herein is a volume averageMean particle diameter, and volume particle diameter D₅₀The meaning of (A) is the same. The particle size of the raw material, i.e., the particle size of the calcined raw material, the composition of the carrier core material, and the electrical and magnetic properties of the obtained carrier core material are shown in table 1. The composition of the carrier core particles shown in table 1 is a result of measurement of the obtained carrier core particles by the analysis method described later. In this case, the amount of addition, i.e., the strontium content y contained in the carrier core material for electrophotographic developer, was 3400 ppm. For the measurement of the particle diameter, a microtrack (Model 9320-X100) manufactured by Nikkiso K.K. was used. Further, as for the oxygen concentration, the oxygen concentration in the furnace atmosphere was measured using a zirconia type oxygen meter (ECOAZ TB-II F-S manufactured by first Heat research corporation).

(analysis of Sr)

The strontium content of the carrier core material was analyzed by the following method. The carrier core material of the present invention was dissolved in an acid solution, and quantitative analysis was performed by ICP. The strontium content of the carrier core material described in the present invention is the amount of strontium obtained by quantitative analysis based on this ICP.

(analysis of Mn)

The Mn content of the carrier core particles was quantitatively analyzed by the ferromanganese analysis method (potentiometric titration) described in JIS G1311-1987. The Mn content of the carrier core particles described in the present invention is an Mn content quantitatively analyzed by the ferromanganese analysis method (potentiometric titration).

In the table, the magnetic susceptibility was measured using VSM (VSM-P7, manufactured by tokyo co., ltd.) for the measurement of magnetization representing magnetic properties. Here, "σ" in the table_1k（1000）"refers to the magnetization at an external magnetic field of 1k (1000) Oe.

The BET specific surface area was measured by using a BET single-point method specific surface area measuring apparatus (model: Macsorb HM-1208, manufactured by Union, Mountech). Specifically, 8.500g of a sample was weighed and filled into a 5ml (cc) sample tube, degassed at 200 ℃ for 30 minutes, and measured.

The pore volume was measured as follows. The evaluation apparatus was POREMASTER-60GT manufactured by Quantachrome (Quantachrome). Specifically, the following measurement conditions were used to measure the tube trunk Volume (Cell Stem Volume): 0.5ml, head pressure (head pressure): 20PSIA, surface tension of mercury: 485.00erg/cm²Contact angle of mercury: 130.00 degrees (degrees), high pressure assay mode: fixed ratio (Fixed Rate), motor Speed (motor Speed): 1. high pressure measurement range: 20.00 to 10000.00PSI, 1.200g of sample is weighed and filled into a sample tube of 0.5ml (cc), and the measurement is carried out. The pore volume was determined by subtracting the volume A (ml/g) at 100PSI from the volume B (ml/g) at 10000.00 PSI.

The strength of the carrier core particles was measured as follows. 30g of the carrier core material of the present invention was put into a sample mill (SK-M10, Co., Ltd.) and subjected to a crushing test at 14000rpm for 60 seconds. Then, the change rate of the volume cumulative value in the crushed pieces of 22 μm or less before and after the crushing was measured as an intensity by using a laser diffraction particle size distribution measuring apparatus (Model 9320-X100, a microtrack manufactured by Nikkiso K.K.). A small value of the strength of the carrier core particle indicates a high strength.

(example 2)

Except for the volume particle diameter D of the calcination raw material used₅₀Has a volume particle diameter D of 1.0 μm₉₀The carrier core particles of example 2 were obtained in the same manner as in example 1 except that the particle diameter was 6.0. mu.m.

(example 3)

Except for the volume particle diameter D of the calcination raw material used₅₀Has a volume particle diameter D of 2.3 μm₉₀Added SrCO of 6.0 μm₃The carrier core particles of example 3 were obtained in the same manner as in example 1 except that the amount of (d) was 7.0 g.

(example 4)

Except for the volume particle diameter D of the calcination raw material used₅₀Has a volume particle diameter D of 3.0 μm₉₀Added SrCO of 6.3 mu m₃The same procedure as in example 1 was repeated except that the amount of (2) was changed to 34.6g, to obtain a carrier core particle of example 4.

(example 5)

Except for the volume particle diameter D of the calcination raw material used₅₀Has a volume particle diameter D of 2.2 μm₉₀The carrier core particles of example 5 were obtained in the same manner as in example 1 except that the particle diameter was 5.7 μm.

(example 6)

Except for the volume particle diameter D of the calcination raw material used₅₀Has a volume particle diameter D of 3.5 μm₉₀Added SrCO of 7.0 μm₃The carrier core particles of example 6 were obtained in the same manner as in example 1 except that the amount of (d) was 95.1 g.

(example 7)

Except for the volume particle diameter D of the calcination raw material used₅₀Has a volume particle diameter D of 2.0 μm₉₀The carrier core particles of example 7 were obtained at 6.9 μm in the same manner as in example 1.

(example 8)

Except for the volume particle diameter D of the calcination raw material used₅₀Has a volume particle diameter D of 3.3 μm₉₀A carrier core particle of example 8 was obtained in the same manner as in example 4 except that the particle diameter was 7.0. mu.m.

Comparative example 1

Except for the volume particle diameter D of the calcination raw material used₅₀Has a volume particle diameter D of 0.5 μm₉₀A carrier core particle of comparative example 1 was obtained in the same manner as in example 1 except that the particle size was 2.0 μm and the strontium-containing raw material was not added.

Comparative example 2

Except thatBy volume particle diameter D of the calcined raw material₅₀Has a volume particle diameter D of 3.4 μm₉₀A carrier core particle of comparative example 2 was obtained in the same manner as in example 1 except that the particle diameter was 9.5. mu.m.

Comparative example 3

Except for the volume particle diameter D of the calcination raw material used₅₀Has a volume particle diameter D of 2.2 μm₉₀Added SrCO of 6.1 μm₃The carrier core particles of comparative example 3 were obtained in the same manner as in example 1 except that the amount of (d) was 114.7 g.

[ Table 1]

Referring to table 1, regarding the magnetic properties, σ is shown in examples 1 to 8₁₀₀₀The values of (A) are 58.8emu/g, 58.5emu/g, 59.2emu/g, 58.9emu/g, 57.2emu/g, 56.5emu/g, 57.2emu/g and 58.1emu/g, respectively, and are all 56.0emu/g or more, which is a high value. In contrast, the values of 55.0emu/g or less in comparative example 2 and 54.3emu/g in comparative example 3 were low, respectively. In addition, regarding the remanence σ_rThe value of comparative example 3 was 2.5emu/g, which is very high. This is presumably because a relatively large amount of Sr is added, and relatively large amount of strontium ferrite is formed during firing. Such a high value of remanence is not preferable because it tends to prevent effective formation of the magnetic brush.

In examples 1 to 8, the BET specific surface area was 0.15m²0.25m above/g²In the range of not more than 0.003ml/g and in the range of not more than 0.023ml/g, respectively, of the pore volume obtained by the mercury intrusion method. As a result, in examples 1 to 8, although the BET specific surface area was 0.15m²The pore size is higher than that of the usual carrier core material in comparative example 1, but the pore size solvent value is as low as 0.023ml/g or less, so that there is substantially no large open pores and it is possible to grasp fine and minute pores existing and crystals on the particle surfaceThe boundary or the unevenness maintains a high value of the BET specific surface area. On the other hand, in comparative examples 2 and 3, although a high BET specific surface area value was maintained, it is presumed that large pores were present as shown in fig. 5 described later. As a result, the values of examples 1 to 8 were 2.2, 2.9, 2.5, 3.1, 4.2, 5.6, and 5.2, respectively, and all of the strengths of the carrier core particles were low values of 6.0 or less, and high strengths. In contrast, the values in comparative examples 1 to 3 were 6.5, 7.1 and 10.2, respectively, and the values were high values of 6.0 or more, and low strengths.

Here, in order to further improve the strength, the following configuration is preferable. That is, the BET specific surface area is set to a value of w (m)²V (ml/g) so that it has a value of pore volume obtained by mercury intrusion porosimetry of v.ltoreq.0.63 w²-0.084w + 0.028. Further, the value for w is the above range, i.e., 0.15. ltoreq. w.ltoreq.0.25, and the value for v is the above range, i.e., 0.003. ltoreq. v.ltoreq.0.023. The carrier core material having the relationship between the BET specific surface area value and the pore volume value obtained by the mercury intrusion method can further improve the particle strength of the carrier core material. Specifically, in examples 1 to 6 having such a relationship, the strength value was less than 4.5, and further improvement in strength was achieved.

As a more preferable embodiment, the constitution of 500ppm can be made as follows<y is not more than 3400ppm, the average particle diameter is in the range of 20 to 30 μm, and the BET specific surface area is 0.15m²0.20m above/g²The pore volume obtained by mercury intrusion method is in the range of 0.003ml/g to 0.012 ml/g. Such a carrier core material for an electrophotographic developer can more reliably realize a high BET specific surface area value, and can improve the adhesion to a coating resin and the particle strength. Specifically, as shown in examples 1 to 4, the intensity value can be set to 3.0 or less.

Fig. 2 is an electron micrograph showing the appearance of the carrier core particles of example 1. Fig. 3 is an electron micrograph showing the appearance of the carrier core particles of comparative example 1. Fig. 4 is an electron micrograph showing a cross section of a carrier core particle of example 1. Fig. 5 is an electron micrograph showing a cross section of a carrier core particle of comparative example 2.

Referring to fig. 2 to 5, the surface properties of example 1 were good. That is, it was found that the crystal grains had many grain boundaries, had appropriate irregularities, and were homogeneous on the particle surface. In addition, according to example 1, it is understood that voids and pores in the carrier core material are very small. On the other hand, in comparative example 2, the crystal grain boundaries were smaller than in example 1, and the degree of unevenness was not sufficient. In addition, it is clear from comparative example 2 that the number of voids and pores inside the carrier core material is very large.

As described above, the carrier core material for electrophotographic developers, the carrier for electrophotographic developers, and the electrophotographic developer according to the present invention are excellent in their characteristics.

In the above embodiment, manganese is used as a raw material for the carrier core particles, but a structure containing no manganese may be used.

In the above embodiment, the raw material containing iron is calcined Fe₂O₃And Mn₃O₄Then, the resulting mixture is pulverized by a ball mill, and the pulverized calcined raw material is used, but the present invention is not limited thereto, and only Fe may be used₂O₃Itself, and the like. In this case, as the iron-containing raw material, Fe may be used₂O₃Volume particle diameter D of₅₀1.0 to 4.0 μm, volume particle diameter D of the iron-containing raw material₉₀Is an iron-containing raw material with the particle size of 2.5-7.0 mu m.

The embodiments of the present invention have been described above with reference to the drawings, but the present invention is not limited to the illustrated embodiments. Various modifications and variations can be made to the illustrated embodiments within the same scope as or equivalent to the present invention.

Industrial applicability

The carrier core material for electrophotographic developers, the method for producing the same, the carrier for electrophotographic developers, and the electrophotographic developer according to the present invention can be effectively applied to a copying machine or the like, which is required to have high image quality.

Claims (9)

1. A method for preparing a carrier core material for an electrophotographic developer, which is a method for preparing a carrier core material for an electrophotographic developer containing iron and strontium as a core, comprising:

a slurrying step of slurrying an iron-containing raw material and a strontium-containing raw material;

a granulation step of granulating the obtained mixture after the slurry step; and

a roasting step of roasting the powder granulated in the granulation step at a predetermined temperature to form a magnetic phase;

the pulping process is used for pulping the raw material containing iron to ensure that the volume particle diameter D of the raw material containing iron₅₀1.0 to 4.0 μm, and the volume particle diameter D of the raw material containing iron₉₀2.5 to 7.0 μm; and slurrying a strontium-containing raw material so that when the strontium content contained in the carrier core material for an electrophotographic developer is y, 0<y≤5000ppm。

2. The method of producing a carrier core material for an electrophotographic developer according to claim 1, wherein the slurry-making step is performed by calcining a raw material containing iron in advance.

3. The method of producing a carrier core material for an electrophotographic developer according to claim 1, wherein the baking step is performed at a baking temperature in a range of 1050 to 1180 ℃ and a holding time after reaching the baking temperature in a range of 0.5 to 10 hours.

4. The method of producing a carrier core material for an electrophotographic developer according to claim 1, wherein the firing step adjusts the oxygen concentration to 10^-7% to 3% by weight, and baking.

5. A carrier core material for an electrophotographic developer, which is a carrier core material for an electrophotographic developer comprising iron and strontium as a core,

when the content of the strontium contained in the carrier core material for the electrophotographic developer is y, 0< y is less than or equal to 5000 ppm;

the average particle diameter is in the range of 20 to 30 μm;

the BET specific surface area value was 0.15m²0.25m above/g²In the range of/g or less;

the pore volume obtained by mercury intrusion method is in the range of 0.003ml/g to 0.023 ml/g.

6. The carrier core material for electrophotographic developers according to claim 5, wherein when the value of BET specific surface area is given as w (m)²V (ml/g) when the pore volume obtained by the mercury intrusion method is v (ml/g), v is not more than 0.63w²-0.084w + 0.028.

7. A carrier core material for an electrophotographic developer, which is a carrier core material for an electrophotographic developer comprising iron and strontium as a core,

the method comprises slurrying a raw material containing iron and a raw material containing strontium, granulating the obtained mixture, and roasting the granulated powder at a predetermined temperature to form a magnetic phase;

and is obtained by slurrying an iron-containing raw material so that the volume particle diameter D of the iron-containing raw material becomes₅₀1.0 to 4.0 μm, and the volume particle diameter D of the raw material containing iron₉₀2.5 to 7.0 μm, and slurrying a strontium-containing raw material so that when the strontium content in the carrier core material for an electrophotographic developer is y, 0<y≤5000ppm。

8. A carrier for an electrophotographic developer, which is used in an electrophotographic developer, characterized in that,

the electrophotographic developer carrier core material of claim 6 and a resin covering the surface of the electrophotographic developer carrier core material.

9. An electrophotographic developer used in development of electrophotography, characterized in that,

the electrophotographic developer carrier according to claim 8, and a toner that can be charged in electrophotography by frictional charging with the electrophotographic developer carrier.