JP2009237155A - Carrier core material for electrophotographic developer and its manufacturing method, carrier for electrophotographic developer, and electrophotographic developer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carrier core material for electrophotographic developer capable of preventing the occurrence of carrier scattering causing abnormality of image and achieving high effect in preventing peeling-off of the resin coated on a coat core material and to provide a carrier using this core material and a manufacturing method for the carrier core material. <P>SOLUTION: This carrier core material for electrophotographic developer contains magnetite or soft ferrite expressed in the following formula: (M<SB>x</SB>Fe<SB>3-x</SB>)O<SB>4</SB>(wherein M is divalent metal such as Fe, Mg, Mn, Ca, Ti, Cu, Zn, Sr, Ni or the like and 0≤x<1) and Al<SB>2</SB>O<SB>3</SB>having 0.1 mass% or more and 1 mass% or less by Al conversion and solid-dissolved in a ferrite phase. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a carrier core material for an electrophotographic developer and a method for producing the same, a carrier for an electrophotographic developer, and an electrophotographic developer, and more specifically, an electron used for electrophotographic development used in a printer or the like. The present invention relates to a carrier core material for a photographic developer and a method for producing the same, a carrier for an electrophotographic developer, and an electrophotographic developer.

  Conventionally, as an electrophotographic developing method used in a copying machine, a printer, etc., a cascade method, a magnetic brush developing method, and other methods are used. In recent years, a general method is a magnetic brush developing method in which an electrostatic latent image formed on a photosensitive drum is visualized with a toner image via a magnetic brush and then thermally fixed to obtain an image. . More recently, the toner is electrically formed on particles of a carrier for an electrophotographic developer (in the present invention, sometimes referred to as “carrier”) than a one-component developer that forms the magnetic brush only with toner. Two-component developers that are oriented to form a magnetic brush are often used.

  In the two-component developer, as a carrier, the surface of the core material constituting the carrier particles (in the present invention, sometimes referred to as “carrier core material”) is appropriately coated with a toner and a reversely chargeable resin. Is used. It is known that the magnetic brush formed by the carrier particles on the magnetic sleeve changes the holding force between the particles of the brush chain depending on the magnetic characteristics and the surface shape. Depending on the conditions during image development, the centrifugal force obtained by the rotation of the developing sleeve is superior to the holding force, and as a result, a phenomenon occurs in which carriers are scattered from the magnetic brush and adhere to the photosensitive member (carrier adhesion). The carrier attached on the photoconductor may reach the transfer portion as it is, but in the state where the carrier is attached on the photoconductor, the toner image around the carrier is not transferred onto the transfer paper, resulting in an image abnormality. Is.

In the market, there is a growing demand for higher image quality for electrophotography and longer life for electrophotographic developers. Accompanying this, attempts have been made to reduce the particle size of the toner particles used and to reduce the particle size of the carrier particles used by mixing with the toner to obtain high image quality.
However, the carrier particles having a reduced particle size are more likely to cause carrier adhesion and carrier scattering. The holding force between the particles of the small particle carrier that forms the magnetic brush increases in proportion to the magnetic force of each particle and the area of the part where the particles are bonded to each other. It can be inferred that it is inhibiting the power.

On the other hand, as the speed of the developing machine increases, the stirring load in the developing machine increases, and there is a problem that the resin on the surface of the magnetic carrier is peeled off due to stirring stress. As a result, the carrier core material is exposed, and charge leakage occurs. Since such charge leakage is one of the causes of image quality deterioration, the conventional magnetic carrier prevents the resin from peeling by increasing the thickness of the coating resin.
However, if the bonding force (adhesive strength) between the carrier core material and the resin is insufficient, as the usage time increases, the resin film wears and breaks due to collisions between the particles, and the film is detached. To do. At that time, the surface of the carrier core material is exposed and the chargeability becomes non-uniform, which causes image deterioration.

Here, for example, Patent Document 1 proposes that the carrier core material contains 1 to 50% by mass of Al ₂ O ₃ to improve the durability of the resin.
Japanese Patent Laid-Open No. 9-190016

However, according to studies by the present inventors, the technique described in Patent Document 1 is concerned with a decrease in magnetic characteristics due to the presence of Al ₂ O ₃ and a deterioration in development image quality due to the decrease in the magnetic characteristics.

  The present invention has been made in view of such problems of the prior art, and the object of the present invention is to suppress the scattering of the carrier that is the cause of the image abnormality and the resin coated on the coat core material. An object of the present invention is to provide a carrier core material having a high effect of preventing peeling, a method for producing the same, a carrier, and an electrophotographic developer.

As a result of intensive studies by the present inventors to solve the above-mentioned problems, Al ₂ O ₃ is dispersed in a carrier core material at a concentration that has not been omitted in the prior art. The inventors have found that this can be solved, and have completed the present invention.

That is, the first means for solving the above problems is
Magnetite represented by Fe ₃ O ₄ or general formula (M _x Fe _3-x ) O ₄ (where M is selected from the group consisting of Mg, Mn, Ca, Ti, Cu, Zn, Sr, Ni) At least one metal having a soft ferrite represented by 0 <x <3),
Al ₂ O ₃ is dissolved in the magnetite or soft ferrite,
A carrier core material for an electrophotographic developer, wherein the magnetite or soft ferrite contains 0.1% by mass or more and 1% by mass or less of Al.

The second means is
The carrier core material for electrophotographic development according to the first means, wherein the particle diameter of Al ₂ O ₃ dissolved in the magnetite or soft ferrite is 1 μm or more and 5 μm or less.

The third means is
Dispersing Al ₂ O ₃ in a powder or colloidal state in a medium solution;
Fe powder and metal M powder (M is at least selected from the group consisting of Fe, Mg, Mn, Ca, Ti, Cu, Zn, Sr, Ni in the medium liquid in which the Al ₂ O ₃ is dispersed. 1 type of metal) is dispersed and stirred to obtain a slurry;
A step of drying and granulating the obtained slurry to obtain a granulated powder;
Firing the obtained granulated powder in an atmosphere having an oxygen concentration of 1% or less to obtain a fired product having a magnetic phase;
The obtained fired product is pulverized and powdered, and then a predetermined particle size distribution is obtained.
The method for producing a carrier core material for an electrophotographic developer according to the first means, wherein the steps are sequentially performed.

The fourth means is
The method for producing a carrier core material for an electrophotographic developer according to a third means, wherein Al ₂ O ₃ having a particle size of 1 μm or more and 5 μm or less is dispersed in a medium solution.

The fifth means is
An electrophotographic developer carrier characterized in that the carrier core material for an electrophotographic developer described in the first or second means is coated with a thermosetting resin.

The sixth means is
An electrophotographic developer comprising the carrier for an electrophotographic developer according to the fifth means and an appropriate toner.

According to the present invention, Al ₂ O ₃ is dispersed in the carrier core material at a concentration that has not been omitted in the prior art, so that carrier scattering, which is a cause of image abnormality, is suppressed, and the coated core is used. It is possible to provide a carrier core material having a high effect of preventing the resin coated on the material from being peeled off, a manufacturing method thereof, a carrier, and an electrophotographic developer.

Hereinafter, the present invention is as follows. Carrier core material, 2. Carrier, 3. 3. Carrier core material and carrier manufacturing method; The electrophotographic developer will be described in this order.
In the claims and the specification, “%” represents a mass percentage unless otherwise specified.

1. Carrier Core Material As described above, the carrier core material according to the present invention is a magnetite represented by Fe ₃ O ₄ or a general formula (M _x Fe _3-x ) O ₄ (where M is Mg, Mn, It has at least one metal selected from the group consisting of Ca, Ti, Cu, Zn, Sr, and Ni, and has soft ferrite represented by 0 <x <3), and the magnetite or soft ferrite contains Al. ₂ O ₃ is in solid solution. That is, in the magnetite or soft ferrite, Al contained in the Al ₂ O ₃ is in a solid solution of 0.1% by mass or more and 1% by mass or less (in the present invention, “0.1% in terms of Al”. 1 mass% or more and 1 mass% or less "). Specifically, when the carrier core material is magnetite, the Fe atom in the lattice crystal having an inverse spinel structure is substituted with an Al atom to form a substitutional solid solution of Fe _x Al _3-x O ₄ . .

[Surface properties of particles constituting the carrier core]
According to the study by the present inventors, the degree of unevenness on the surface of the particles constituting the carrier core material and the grain (as seen on the surface) depending on the presence or absence and addition amount of the nonmagnetic component to the carrier core material. There is a large difference in the growth of the raised convex part surrounded by the concave streaks.
Specifically, in the carrier core material to which Al ₂ O ₃ is added, the grains grow outward from the surface, and the unevenness increases. The carrier core material has a surface property in the range of 0.1 to 0.2 m ² / g in terms of BET value and in the range of 0.4 to 0.6 μm in terms of surface roughness.
The surface property can be evaluated using BET (specific surface area), and the surface roughness can be evaluated using a laser microscope.

Thus, a carrier core material having a large BET value and surface roughness can be obtained by adding Al ₂ O ₃ to the carrier core material. And carrier scattering is suppressed by enlarging the BET value and surface roughness of a carrier core material. This is considered to be because the contact area between the particles increases in the magnetic brush formed in the electrophotographic developing machine by increasing the BET value and the surface roughness of the carrier core material, and the holding power of the magnetic brush is increased. .

[Composition of carrier core material]
As the magnetic component substance constituting the carrier core material according to the present invention, a substance having a magnetic property suitable for the characteristics of the target electrophotographic developing apparatus may be selected. For example, in consideration of image characteristics, magnetite Fe ₃ O ₄ , soft ferrite Mn _x Fe _3-x O _{4 and the} like are preferably used. This is because these magnetic substances have a sufficiently high magnetic susceptibility and low remanent magnetization.
On the other hand, in the carrier core material of the present invention, as described above, a nonmagnetic component is present in order to change the surface property. Note that the magnetic properties of the carrier are reduced according to the abundance ratio of the non-magnetic component, but it is a non-magnetic component in consideration of the balance between the surface property and the magnetic force and resistance value required for the carrier core material. By adjusting the amount of Al ₂ O ₃ added, the carrier characteristics can be adjusted with very good reproducibility.

Specifically, in the case of adding Al ₂ O ₃ , for example, it is derived from Al ₂ O ₃ with respect to the total amount of other metal oxides that synthesize ferrite with Fe ₂ O _{3 as} the main raw material of the carrier core material. What is necessary is just to add at the time of raw material mixing so that the amount of Al to be 0.1 mass% or more and 1 mass% or less. If the Al content is 0.1% or more, the unevenness of the grains constituting the carrier core material can be secured, and if it is 1% by mass or less, the carrier shape does not greatly deviate from the spherical shape, and the flow in the developing machine The magnetic force necessary for practical use can be maintained. More preferably, it is added at a ratio of 0.3% by mass or more and 1% by mass or less. The form in which Al ₂ O ₃ is added may be powder or colloidal solution.

[Particle size]
The particle size distribution of the carrier core material according to the present invention preferably has an average particle size of 10 μm or more and 80 μm or less. This is because when the particle diameter of the carrier core is within this range, the image characteristics are good and carrier scattering can be suppressed. Therefore, it is preferable to perform a classification treatment with a sieve or the like during or after the production process so as to obtain the above particle size distribution.

2. Carrier The carrier according to the present invention is obtained by coating the above-described carrier core material with a thermosetting resin according to a required chargeability or a resin according to any combination thereof.
By adopting such a configuration, carrier scattering is suppressed and the crushing characteristics are greatly improved as compared with a carrier to which a nonmagnetic oxide is not added. The reason why the crushing test strength of the carrier after the resin coating is good is that the bonding force increases according to the contact area between the surface irregularities of the carrier particles and the resin coating surface, and peeling can be suppressed.

3. Carrier Core Material and Carrier Manufacturing Method In the manufacture of the carrier core material according to the present invention, a nonmagnetic component such as Al ₂ O ₃ is used in addition to the raw material to be magnetic powder. At this time, if the particle size of the nonmagnetic component is large, uniform dispersibility in the particles may be deteriorated, and grain growth may be uneven. For this reason, it is preferable that a nonmagnetic component is 5 micrometers or less.

[material]
Magnetite represented by Fe ₃ O ₄ , or general formula (M _x Fe _3-x ) O ₄ (where M is Mg, Mn, Ca, Ti, Cu, Zn, Sr or Ni, or any of these) As an Fe supply source of soft ferrite represented by 0 <x <3), Fe ₂ O ₃ can be preferably used. As a raw material of M, Fe, Mg, Mn, Ca, Ti, Cu, Zn, Sr or Ni, and any combination of these divalent metals can be suitably used. For example, Mn can be MnCO ₃ , Mn ₃ O ₄ or the like, and Mg can be suitably used MgO, Mg (OH) ₂ , or MgCO ₃ . Then, the mixing ratio of these raw materials is matched with the target composition of the magnetite or soft ferrite and weighed and mixed to obtain a metal raw material mixture.

As the form of Al blended with the metal raw material, Al ₂ O ₃ which is an oxide is preferably used.
Al ₂ O ₃ may be in a powder form or a colloidal liquid in which particles are uniformly dispersed in moisture. If the particle size of the Al ₂ O ₃ particles is 1 μm or more and 5 μm or less, the unevenness of the grains constituting the carrier core material can be secured.

[Slurry]
After weighing the above raw materials, they are slurried by mixing and stirring them in a medium solution (slurry process). Prior to the slurrying, if necessary, the raw material mixture may be subjected to a dry pulverization treatment. The mixing ratio of the raw material powder and the medium liquid is preferably such that the slurry has a solid content concentration of 50 to 90% by mass. The medium liquid is prepared by adding a binder, a dispersant and the like to water. As the binder, for example, polyvinyl alcohol can be suitably used, and the concentration in the medium liquid may be about 0.5 to 2% by mass. As the dispersant, for example, an ammonium polycarboxylate-based one can be preferably used, and the concentration in the medium liquid may be about 0.5 to 2% by mass. In addition, phosphorus, boric acid, or the like can be added as a lubricant or a sintering accelerator. It is preferable to further wet-grind the slurry obtained by mixing and stirring.

Moreover, it is preferable to disperse Al ₂ O ₃ first in the medium liquid before adding the Fe raw material and the M raw material. As described above, the amount of Al ₂ O ₃ added is 0.1% by mass or more and 1% by mass or less in terms of Al.
Since the addition amount of the Al ₂ O ₃ is very small with respect to the amounts of the Fe raw material and the M raw material, a uniform dispersion state can be obtained by first dispersing in the medium liquid. However, the order of dispersion of the Fe raw material, the M raw material and the Al ₂ O _{3 in} the medium liquid can be reversed as described above or simultaneously. However, in that case, it is required to increase the dispersibility of Al ₂ O ₃ by sufficiently stirring the slurry or performing a treatment such as increasing the number of wet pulverizations.

Moreover, it is preferable to disperse Al ₂ O ₃ first in the medium liquid before adding the Fe raw material and the M raw material. As described above, the amount of Al ₂ O ₃ added is 0.1% by mass or more and 1% by mass or less in terms of Al.
Since the addition amount of the Al ₂ O ₃ is very small with respect to the amounts of the Fe raw material and the M raw material, a uniform dispersion state can be obtained by first dispersing in the medium liquid. However, the order of dispersion of the Fe raw material, the M raw material and the Al ₂ O _{3 in} the medium liquid can be reversed as described above or simultaneously. However, in that case, it is required to increase the dispersibility of Al ₂ O ₃ by sufficiently stirring the slurry or performing a treatment such as increasing the number of wet pulverizations.

[Granulation]
Granulation can be suitably carried out by introducing the slurry into a spray dryer. The atmospheric temperature during spray drying may be about 100 to 300 ° C. Thereby, the granulated powder whose particle diameter is 10-200 micrometers can be obtained in general (granulation process). It is desirable to adjust the particle size of the resulting granulated powder by removing coarse particles and fine powder using a vibration sieve or the like in consideration of the final particle size of the product.

[Baking]
Next, the granulated powder is put into a furnace heated to about 700 to 1500 ° C. and fired by a general technique for synthesizing magnetite or soft ferrite, thereby generating ferrite (firing step). If the firing temperature is 700 ° C. or higher, sintering proceeds to some extent, the shape can be maintained, and the magnetic properties of the generated ferrite are maintained, so that carrier scattering is suppressed. When the temperature is higher than 1500 ° C., excessive sintering between particles does not occur, and irregular particles do not occur. From this point of view, it is preferable to fire at about 700 to 1500 ° C. By controlling the firing temperature, a desired BET specific surface area can be imparted to the carrier core material. Specifically, the value of the BET specific surface area is decreased by raising the firing temperature, and the value of the BET specific surface area can be increased by lowering the firing temperature.
In addition, the firing atmosphere is related to carrier powder characteristics such as magnetic force and electrical resistance of the fired product.
In particular, since the magnetic force is greatly affected by the type of ferrite, it is desirable that the oxygen concentration in the firing furnace be a highly reducing atmosphere with a concentration of 1% or less.

  It is desirable to adjust the particle size of the obtained fired product at this stage. For example, the baked product is coarsely pulverized with a hammer mill or the like, then subjected to primary classification with an airflow classifier, and further subjected to a process of aligning the particle size with a vibration sieve or an ultrasonic sieve to obtain a baked product with adjusted particle size. Obtainable. After adjusting the particle size, it is desirable to remove the non-magnetic particles by applying a magnetic field separator.

[High resistance treatment]
By heating the fired product in an oxidizing atmosphere, a high resistance layer may be formed and the resistance may be increased (high resistance treatment step). The heating atmosphere may be air or a mixed atmosphere of oxygen and nitrogen. The heating temperature is 200 to 800 ° C., preferably 250 to 600 ° C., and the treatment time is about 30 min to 5 h.
Thus, the carrier core material according to the present invention can be obtained.

[Manufacture of carriers]
The obtained carrier core material is coated with a resin. As a coating method, it can be coated by a dry method, a fluidized bed, a dipping method or the like. More preferably, from the viewpoint of filling the resin inside the carrier, an immersion method or a dry method is more preferable.
Here, the dipping method will be described as an example. As the coating resin, a silicone resin or an acrylic resin is preferable. About 20 to 40% by mass of the coating resin is dissolved in a solvent (toluene or the like) to prepare a resin solution. The coating operation can be carried out by heating and stirring at 150 to 250 ° C. after mixing in a container so that the solid content is 0.7 to 10% of the carrier core material. The coating amount of the resin can be controlled by the concentration of the resin solution and the mixing ratio of the resin solution and the carrier core material. After the resin coating, the carrier according to the present invention is obtained by further heat-treating the resin coating layer to cure it.

4). Electrophotographic Developer An electrophotographic developer can be obtained by mixing the obtained carrier according to the present invention with a toner having an appropriate particle size.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example, this invention is not limited to these Examples.

Example 1
As raw materials, Al ₂ O ₃ powder and Fe ₂ O ₃ powder finely pulverized to an average particle diameter D50 of about 2.2 μm were prepared. The Al ₂ O ₃ powder was weighed so as to be 1.0 mass% in terms of Al (as mass% of Al contained in the Al ₂ O ₃₎ with respect to the amount of Fe ₂ O ₃ powder. The Al ₂ O ₃ component may be added in a liquid form such as a colloidal form instead of a powdery form.
On the other hand, 1.0% by mass of an ammonium polycarboxylate dispersant as a dispersant, 0.05% by mass of “SN Wet 980” manufactured by San Nopco Co., Ltd., and 0.02% of polyvinyl alcohol as a binder in water. A liquid (medium liquid) added at a mass% was prepared. After the Al ₂ O ₃ powder is charged into this medium solution and sufficiently dispersed, the weighed Fe raw material powder is charged and stirred to obtain a slurry having a concentration of 76% by mass of these charged substances. It was.
This slurry was wet pulverized with a wet ball mill, stirred for a while, and then sprayed into hot air at about 180 ° C. with a spray dryer to obtain a dry granulated product having a particle size of 10 to 200 μm.

  From this granulated material, coarse particles were separated using a sieve mesh having a mesh size of 61 μm, fine particles were separated using a sieve mesh having a mesh size of 25 μm, and then calcined at 1000 ° C. for 5 hours in a nitrogen atmosphere to be magnetized. The magnetized fired product was pulverized with a hammer mill, fine powder was removed using an air classifier, and the particle size was adjusted with a vibrating screen having a mesh size of 54 μm.

The fired product whose particle size was adjusted was held at 350 ° C. in the atmosphere for 3 hours to give a resistance increasing treatment, and the carrier core material according to Example 1 was obtained. Table 1 shows the amount of the carrier core additive added, powder characteristics, magnetic characteristics, and evaluation test results described later.
Furthermore, the SEM photograph image (2500 times) of the carrier core material which concerns on the said Example is shown in FIG.

(Example 2)
A carrier core material of this example was obtained by repeating the same operation as in Example 1 except that the granulated product was fired at 1100 ° C.
Table 1 shows the amount of the carrier core additive added, powder characteristics, magnetic characteristics, and evaluation test results described later.
Furthermore, the SEM photograph image (2500 times) of the carrier core material which concerns on the said Example is shown in FIG.

(Example 3)
Al ₂ O ₃ powder finely pulverized to an average particle diameter D50 of about 4.6 μm was prepared. The carrier core of the present example was repeated by repeating the same operation as in Example 1, except that the Al ₂ O ₃ powder was weighed to 1.0 mass% in terms of Al with respect to the amount of Fe ₂ O ₃ powder. The material was obtained.
Table 1 shows the amount of the carrier core additive added, powder characteristics, magnetic characteristics, and evaluation test results described later.
Furthermore, the SEM photograph image (2500 times) of the carrier core material which concerns on the said Example is shown in FIG.

Example 4
Al ₂ O ₃ powder finely pulverized to an average particle diameter D50 of about 4.6 μm was prepared. The Al ₂ O ₃ powder was weighed to 1.0 mass% in terms of Al with respect to the amount of Fe ₂ O ₃ powder, and the calcining temperature of the obtained dried granulated product was 1100 ° C. The same operations as in Example 1 were repeated to obtain a carrier core material of this example.
Table 1 shows the amount of the carrier core additive added, powder characteristics, magnetic characteristics, and evaluation test results described later.
Furthermore, the SEM photograph image (2500 times) of the carrier core material which concerns on the said Example is shown in FIG.

(Example 5)
Al ₂ O ₃ powder finely pulverized to an average particle diameter D50 of about 1.0 μm was prepared. The carrier of this example was repeated by repeating the same operation as in Example 1 except that the Al ₂ O ₃ powder to be added was weighed so as to be 0.5% by mass in terms of Al with respect to the amount of Fe ₂ O ₃ powder. A core material was obtained.
Table 1 shows the amount of the carrier core additive added, powder characteristics, magnetic characteristics, and evaluation test results described later.

(Comparative Example 1)
Al ₂ O ₃ powder finely pulverized to an average particle diameter D50 of about 0.24 μm was prepared. The carrier of this example was repeated by repeating the same operation as in Example 1 except that the Al ₂ O ₃ powder was weighed so as to be 1.5% by mass in terms of Al with respect to the amount of Fe ₂ O ₃ powder. A core material was obtained.
Table 1 shows the amount of the carrier core additive added, powder characteristics, magnetic characteristics, and evaluation test results described later.
Furthermore, the SEM photograph image (2500 times) of the carrier core material which concerns on the said comparative example is shown in FIG.

(Creation of carrier)
The carrier core material obtained in each of the above Examples and Comparative Examples was coated with a resin by the method described below.
First, a silicone resin (manufactured by Shin-Etsu Chemical Co., Ltd., KR251) was dissolved in toluene to prepare a coating resin solution. The coating resin solution and the carrier core material were introduced into a stirrer. At this time, the solid content in the coating resin solution was 3% of the carrier core material.
And it heat-stirred in the range of 150-250 degreeC, immersing the carrier core material in the resin solution for 3 hours. Thereby, resin was coat | covered in the ratio of 3.0 mass parts with respect to 100 mass parts of carrier core materials.
The resin-coated carrier core material was heated at 250 ° C. for 5 hours with a hot-air circulating heating device to cure the resin coating layer, thereby obtaining carriers according to the above-described examples and comparative examples.

(Evaluation test of carrier scattering)
An evaluation test of carrier scattering of the carriers according to the above examples and comparative examples will be described.
First, a magnetic drum having a diameter of 50 mm and a surface magnetic force of 1000 Gauss was filled with the carrier according to each of the above examples and comparative examples. And after rotating the said magnetic drum at 270 rpm for 30 minutes, the particle | grains which scattered from the said magnetic drum were collect | recovered, and it measured by measuring the weight. The carrier scattering amount is evaluated by standardizing the carrier scattering amount according to Comparative Example 1 as “1.00”, and the larger this value, the larger the carrier scattering amount.
The evaluation test results are shown in Table 1.

(Fracture evaluation test)
Next, 100 g of the carrier according to the example and the comparative example was put into a sample mill (Kyoritsu Riko Co., Ltd. SK-M10 type), and a crushing test was performed at a rotational speed of 16000 rpm for 120 seconds. And the change rate (%) of the volume average particle diameter D50 before the said crushing and after the crushing was measured by a laser diffraction type particle size distribution measuring device (Microtrack, Model 9320-X100 manufactured by Nikkiso Co., Ltd.). And the crushing evaluation of the carrier which concerns on an Example and a comparative example was performed with the value of the change rate (%) of the said D50.
The evaluation test results are shown in Table 1.

(Summary)
The carrier core material according to Example 1 to Example 5 in which the Al ₂ O ₃ powder addition amount is in the range of 0.1% by mass or more and 1% by mass or less in terms of Al with respect to the Fe ₂ O ₃ powder amount. , Both had good magnetic properties.
Further, Al ₂ O ₃ is solid-dissolved in a particle diameter of 1 to 5 μm in the carrier core material according to Examples 1 to 5. As a result, when the carrier scattering test result of the carrier manufactured from the carrier core material according to Example 1 to Example 5 is standardized to 1.00, the carrier scattering test result of the carrier according to Comparative Example 1 described later, It was good in the range of 0.39 to 0.44.

  Here, when the crush evaluation test results of the carrier according to Example 1 to Example 5 and the carrier according to Comparative Example 1 are examined, the carrier according to Example 1 to Example 5 is related to Comparative Example 1. It can be seen that the D50 change rate is less than half that of the carrier. That is, it is considered that the carriers according to Example 1 to Example 5 have a high bonding force between the carrier core material and the resin-coated surface, and the resin coating is prevented from being peeled in the crushing test. As a result, in the carriers according to Example 1 to Example 5, it is considered that the generation of fine powder was suppressed even in the carrier scattering test.

On the other hand, the magnetic properties (σs) of the carrier core material according to Comparative Example 1 in which the Al ₂ O ₃ powder addition amount is as high as 0.15% by mass in terms of Al with respect to the Fe ₂ O ₃ powder amount, It was low compared with the Example. Furthermore, the carrier according to Comparative Example 1 generated much fine powder in the carrier scattering test, and the D50 change rate was large in the crushing test.

From the above results, the present inventors show that the carrier crushing test strength after resin coating in the carriers according to Example 1 to Example 5 is good when the Al ₂ O dissolved in the carrier core material is used. _When the particle size of No. ₃ is in the range of 1 to 5 μm, the surface irregularities of the carrier core particles become prominent and the contact area of the resin-coated surface increases. I believe that.
The difference in surface state between the carrier core material according to Example 1 to Example 4 and the carrier core material according to Comparative Example 1 is that the carrier core material according to Example 1 to Example 4 is a comparative example from the results of FIG. The carrier core material according to No. 1 is considered to be supported by the fact that the surface irregularities are remarkable.

Industrial application fields

  Apply to developing machines such as copiers, printers, etc. as a carrier for electrophotographic developer with reduced development and removal of the resin coating in the developing machine of the equipment while significantly reducing carrier scattering while maintaining the developed image quality. it can.

2 is an SEM photographic image of a carrier core material according to Example 1. 3 is a SEM photographic image of a carrier core material according to Example 2. 4 is an SEM photographic image of a carrier core material according to Example 3. 6 is an SEM photographic image of a carrier core material according to Example 4. 2 is an SEM photographic image of a carrier core material according to Comparative Example 1.

Claims (6)

Magnetite represented by Fe ₃ O ₄ or general formula (M _x Fe _3-x ) O ₄ (where M is selected from the group consisting of Mg, Mn, Ca, Ti, Cu, Zn, Sr, Ni) At least one metal having a soft ferrite represented by 0 <x <3),
Al ₂ O ₃ is dissolved in the magnetite or soft ferrite,
A carrier core material for an electrophotographic developer, wherein 0.1 mass% or more and 1 mass% or less of Al is contained in the magnetite or soft ferrite. _{2. The} carrier core material for electrophotographic development according to claim 1, wherein the particle diameter of Al ₂ O ₃ solid-dissolved in the magnetite or soft ferrite is 1 μm or more and 5 μm or less. Dispersing Al ₂ O ₃ in a powder or colloidal state in a medium solution;
Fe powder and metal M powder (M is at least selected from the group consisting of Fe, Mg, Mn, Ca, Ti, Cu, Zn, Sr, Ni in the medium liquid in which the Al ₂ O ₃ is dispersed. 1 type of metal) is dispersed and stirred to obtain a slurry;
A step of drying and granulating the obtained slurry to obtain a granulated powder;
Firing the obtained granulated powder in an atmosphere having an oxygen concentration of 1% or less to obtain a fired product having a magnetic phase;
The obtained fired product is pulverized and powdered, and then a predetermined particle size distribution is obtained.
The method for producing a carrier core material for an electrophotographic developer according to claim 1, wherein: The method for producing a carrier core material for an electrophotographic developer according to claim 3, wherein Al ₂ O ₃ having a particle size of 1 µm or more and 5 µm or less is dispersed in a medium liquid.   An electrophotographic developer carrier, wherein the carrier core material for an electrophotographic developer according to claim 1 or 2 is coated with a thermosetting resin.   An electrophotographic developer comprising the carrier for an electrophotographic developer according to claim 5 and an appropriate toner.