JP2007034249A - Carrier core material for electrophotographic development, carrier for electrophotographic development and method for manufacturing the same, and electrophotographic developer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carrier core material for manufacturing an electrophotographic developer which enables high-speed development with stable high image quality and ensures the long life of a magnetic carrier for replacement even when applied to an MFP (multifunction printer), etc., a method for manufacturing the carrier core material, a magnetic carrier containing the carrier core material, and an electrophotographic developer manufactured from the magnetic carrier. <P>SOLUTION: Resin particles, a binder, a dispersant, a wetting agent and water are added to raw material powder, wet-ground and dried to obtain granules, and the granules are calcined and fired to manufacture the carrier core material having an internal hollow structure. The carrier core material is coated with a resin to obtain the carrier for electrophotographic development. This carrier for electrophotographic development and a toner are mixed to manufacture the electrophotographic developer. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  Carrier core material for electrophotographic development contained in carrier for electrophotographic development used for electrophotographic development, carrier for electrophotographic development using carrier core material for electrophotographic development, production method thereof, and electrophotographic development The present invention relates to an electrophotographic developer containing a carrier for use.

  The electrophotographic dry development method is a method in which a powder toner as a developer is attached to an electrostatic latent image on a photosensitive member, and the attached toner is transferred to a predetermined paper or the like for development. Here, the electrophotographic dry development method includes a one-component development method using a one-component developer containing only toner, a toner, and a carrier for electrophotographic development having magnetism (hereinafter sometimes referred to as a magnetic carrier). And a two-component development method using a two-component developer containing the same. In recent years, two-component development methods are often used because toner charge control is easy and stable high image quality can be obtained, and high-speed development is possible.

  Electrophotographic developing machines tend to have full color, high image quality, and high speed. To achieve this, polymerized toner with a small particle size has been developed, and magnetic properties are matched to the small particle size of the polymerized toner. The carrier particle size is also being reduced. On the other hand, with the spread of personal computers, the so-called MFP (multifunction printer) market has expanded in electrophotographic developing machines, and functions have been enhanced by the attached applications, etc., and at the same time, not only the output capability for document output but also the running cost has become severe It has come to be evaluated.

  The running cost of an electrophotographic developing machine greatly depends on the cost of consumables such as toner and magnetic carrier. Many of the magnetic carriers are obtained by using spherical soft ferrite as a carrier core material for electrophotographic development (hereinafter sometimes referred to as carrier core material) and coating the surface of the spherical soft ferrite with a resin. However, as the number of times of printing proceeds, the resin on the surface deteriorates due to wear between the magnetic carriers and cannot withstand electrophotographic development. Therefore, in many electrophotographic developing machines, when the counted number of printed documents reaches a certain value, the magnetic carrier is exchanged together with the toner.

  Here, in Patent Document 1, a carbonate raw material is used as a raw material for the carrier core material, and by using a gasification component of the raw material, a hollow structure is generated in the carrier core material, and the density and specific gravity are small. A method for manufacturing a carrier core material has been proposed.

JP 61-7851 A

  The present inventors have realized that it is important to reduce the stress on the resin on the surface of the carrier core material in order to extend the exchange life of the magnetic carrier. Then, it has been conceived that by reducing the specific gravity of the carrier core material, stress applied to the carrier core material can be reduced when the electrophotographic developer is stirred and mixed in the electrophotographic developing machine. However, according to the study by the present inventors, for example, an electrophotographic developer is manufactured using a magnetic carrier manufactured by the manufacturing method described in Patent Document 1, and the electrophotographic developer is used in the MFP or the like. When applied, it has been found that the exchange life of the magnetic carrier cannot be extended.

  Here, the present inventors further examined the cause of the fact that the exchange life of the magnetic carrier was not extended in the prior art. As a result, the following was found. That is, the gasification of the carbonate raw material proceeds during the calcining of the carrier core material, and a hollow structure is formed in the calcined powder. The hollow structure is pulverized by performing a wet pulverization step with a ball mill later. Here, in the next firing step, a hollow structure is formed in the fired powder by gasification of a part of the remaining carbonate raw material, but the formation remains insufficient. It was thought to be for the purpose.

  Furthermore, Patent Document 1 also describes a configuration in which a part of the carbonate raw material is separated and added to the calcined raw material powder and then fired. However, according to the study by the present inventors, it has been found that even when an electrophotographic developer containing a magnetic carrier using this configuration is applied to the MFP or the like, the replacement life of the magnetic carrier cannot be extended. did.

  Here again, the present inventors examined the cause of the fact that the exchange life of the magnetic carrier was not extended. As a result, in the case of this configuration, the amount of gas generated from the carbonate raw material is insufficient, and again, the hollow structure formation in the firing process remains insufficient, thus extending the exchange life of the magnetic carrier. It was considered impossible.

  Therefore, the problem to be solved by the present invention is to produce an electrophotographic developer capable of high-speed development with stable high image quality and long magnetic carrier replacement life even when an MFP or the like is used as an electrophotographic developing machine. A carrier core material, a magnetic carrier containing the carrier core material, a method for producing the same, and an electrophotographic developer produced from the magnetic carrier.

The present inventors produce an electrophotographic developer capable of high-speed development with stable high image quality and a long exchange life of a magnetic carrier even when an MFP or the like is used as an electrophotographic developing machine. I studied the structure and physical properties that should be used. As a result, it is not sufficient that the magnetic carrier has a hollow structure. When the apparent density / true density of the carrier core material contained in the magnetic carrier is A, 0.25 ≦ A ≦ 0.40. It was also conceived that the apparent density must satisfy the requirement of 2.0 g / cm ³ or less. The present inventors have also conceived a method for producing a carrier core material that satisfies the above requirements, and have completed the present invention.

That is, the first means for solving the problem is:
A carrier core material used in a carrier for an electrophotographic developer,
Electrophotographic development characterized in that when the apparent density / true density of the carrier core material is A, 0.25 ≦ A ≦ 0.40 and the apparent density is 2.0 g / cm ³ or less. Carrier core material.

The second means is
In the carrier core material, the value of the specific surface area measured by the BET method is BET (0), the cs value obtained from the wet dispersion type particle size distribution measuring machine is divided by the true density, and the value of the spherical equivalent specific surface area is obtained by BET. When (D)
The carrier for electrophotographic development according to the first means, wherein BET (0) ≧ 0.07 m ² / g and 3.0 ≦ BET (0) / BET (D) ≦ 10.0 It is a core material.

The third means is
The carrier core material for an electrophotographic developer according to claim 1 or 2, wherein the carrier core material contains a magnetic oxide and a nonmagnetic oxide having a true specific gravity of 3.5 or less.

The fourth means is
The carrier core material for an electrophotographic developer according to the third means, wherein the magnetic oxide is soft ferrite.

The fifth means is
The carrier core material for electrophotographic development according to the third or fourth means, wherein the carrier core material contains the nonmagnetic oxide in an amount of 1 wt% to 50 wt%.

The sixth means is
A carrier for electrophotographic development, wherein the carrier core material for an electrophotographic developer according to any one of the first to fifth means is coated with a resin.

The seventh means is
The carrier for electrophotographic development according to the sixth means, wherein the coating amount of the resin is 0.1 wt% or more and 20.0 wt% or less of the carrier core material.

The eighth means is
The carrier for an electrophotographic developer according to the sixth or seventh means, wherein the average particle size is 25 μm or more and 50 μm or less.

The ninth means is
The carrier for an electrophotographic developer according to any one of the sixth to eighth means, wherein the carrier contains 1 wt% or more and 50 wt% or less of silica.

The tenth means is
An electrophotographic developer comprising the carrier for an electrophotographic developer according to any one of the sixth to ninth means.

The eleventh means is
One or two or more metal elements M selected from carbonates, oxides and hydroxides, and Fe ₂ O ₃ are mixed and pulverized to a particle size of 1 μm. Obtaining a product;
Adding the resin particles, water, a binder, and a dispersant to the pulverized product to form a slurry, followed by wet pulverization and further drying to obtain a granulated powder;
Calcining the granulated powder to obtain a calcined product;
Firing the calcined product to obtain a fired product;
And a step of pulverizing the fired product to obtain a carrier core material.

The twelfth means is
11. The method for producing a carrier core material for electrophotographic development according to the eleventh means, wherein resin particles containing silicon are used as the resin particles to be added to the pulverized product.

The thirteenth means is
A step of mixing one or two or more metal elements M selected from carbonates, oxides and hydroxides with Fe ₂ O ₃ and pulverizing to obtain a pulverized product; ,
A step of adding silica particles, water, a binder, and a dispersant to the pulverized product to form a slurry, followed by wet pulverization and further drying to obtain granulated powder,
Firing the granulated powder to obtain a fired product;
And a step of pulverizing the fired product to obtain a carrier core material.

  An electrophotographic developing carrier manufactured using the electrophotographic developing carrier core material according to any one of the first to fifth means is resistant to stress applied during mixing and stirring of an electrophotographic developer in an electrophotographic developing machine. It becomes a carrier for electrophotographic development having a high property and a long exchange life.

  The electrophotographic developer carrier according to any one of the sixth to ninth means is a carrier for electrophotographic development that is highly resistant to stress applied during mixing and stirring of the electrophotographic developer in the electrophotographic developing machine and has a long exchange life. It becomes.

  The electrophotographic developer described in the tenth means is an electrophotographic developer capable of high-speed development with stable high image quality and long replacement life even when applied to an MFP or the like.

  According to the method for producing a carrier core material for electrophotographic development according to any one of the eleventh to thirteenth means, the durability against stress applied during mixing and stirring of the electrophotographic developer in the electrophotographic developing machine is high, and the replacement life It is possible to produce a carrier core material for electrophotographic development which is a raw material for a long electrophotographic development carrier.

Embodiments of the present invention will be described below.
The carrier core material according to the present invention has an apparent density / true density = A at room temperature, where 0.25 ≦ A ≦ 0.40 and the apparent density is 2.0 g / cm ³ or less. . Here, the apparent density is measured in accordance with, for example, JISZ2504. On the other hand, it is convenient to measure the true density with a true density measuring device (for example, a pycnometer described later).
An electrophotographic developer manufactured using a magnetic carrier including a carrier core material having this configuration is capable of high-speed development with stable high image quality and a long replacement life of the magnetic carrier even when applied to an MFP or the like. It exhibits excellent characteristics.

  Although the detailed reason why the electrophotographic developer exhibits the above-described excellent characteristics by using the carrier core material is unclear, when the A is within a predetermined range, the electrophotographic developer can be used in an electrophotographic developing machine such as an MFP. The agitation torque when the photographic developer is agitated can be reduced, enabling high-speed development with stable image quality, and at the same time, the impact on the magnetic carrier is reduced and damage is reduced, so the replacement life of the magnetic carrier is reduced. May be longer.

And when the value of the specific surface area measured by the BET method is BET (0) and the value of the spherical equivalent specific surface area is BET (D), the carrier core material according to the present invention has BET (0) ≧ 0.07 m ^2. / G and 3.0 ≦ BET (0) / BET (D) ≦ 10.0, the hollow structure formed in the carrier core material is an aggregate of fine hollow structures, and This is because a sufficient amount of hollow structure is formed. Here, BET (0), which is the value of the specific surface area measured by the BET method, is the value of the specific surface area measured by the normal BET method. On the other hand, the value BET (D) of the spherical equivalent specific surface area is obtained by, for example, obtaining a cs value (Calculated Specific Surfaces Area) using a microtrack which is a wet dispersion type particle size distribution measuring device, and dividing the cs value by the true density. Calculated in return. The carrier core material having this configuration is mechanically strong because the hollow structure is an assembly of fine hollow structures. As a result, since the magnetic carrier having the carrier core material is also resistant to impact, the exchange life of the magnetic carrier may be extended.

  When an electrophotographic developer manufactured using a magnetic carrier having the above-described configuration is applied to an MFP or the like, high-speed development with stable high image quality is possible, and replacement life is longer than that of a conventional product. It exhibits the excellent feature of being 50% or longer.

Furthermore, the carrier core material according to the present invention preferably has a composite structure of a magnetic oxide and a nonmagnetic oxide having a true specific gravity of 3.5 g / cm ³ or less. By adopting this configuration and filling the hollow portion with a nonmagnetic oxide, the hollow capacity can be reduced while keeping the above-mentioned A value and BET (0) / BET (D) value within a predetermined range, and the carrier core material It is possible to improve the mechanical strength. Here, preferred examples of the true specific gravity of 3.5 g / cm ³ or less of non-magnetic _oxide, mention may be made of _{SiO 2, Al 2 O 3,} Al (OH) 2, B 2 O 3 and the like. When the content of the nonmagnetic oxide in the carrier core material is 1 wt% or more and 50 wt% or less, more preferably 5 wt% or more and 40 wt% or less, the magnetic characteristics and mechanical characteristics as the carrier core material are obtained. It is a preferable configuration that can achieve both. Further, as a magnetic oxide, a spinel ferrite represented by a general formula of M ²⁺ O · Fe ₂ O ₃ or M ₂ ⁺ · Fe ₂ O ₄ (M ²⁺ includes Mn, Mg, Fe, Co, Ni, Cu, Zn, etc.) ), M2 ⁺ O · 6Fe ₂ O ₃ , magnetoplumbite type ferrite represented by the general formula of M ₂ ⁺ · 6Fe ₁₂ O ₁₉ (M ²⁺ includes Ba, Sr, Pb, etc.), 3M ³⁺ ₂ O ₃ · 5Fe ₂ Garnet type ferrite represented by the general formula of O ₃ or M ³⁺ ₃ Fe ₅ O ₁₂ (M ³⁺ includes Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, etc.), perovskite type ferrite and ilmenite-type ferrite, and the like, in particular ^{M 2+} in ^M 2+ O · _Fe 2 _{O 3,} known as spinel ferrite is Mn, Mg, have at least one Fe It is preferable to use that so-called soft ferrite. This is because the use of soft ferrite has the advantage that the agitation between the toner and the carrier is improved and a high-quality image can be obtained.

  Next, a magnetic carrier can be obtained by coating the above-described carrier core material with a resin. Here, as the coating resin, for example, a silicone resin is preferably used. If the coating amount is 0.1 wt% or more of the carrier core material, it is possible to exhibit mechanical properties and durability preferable as a magnetic carrier, and if it is 20.0 wt% or less of the carrier core material, the magnetic carriers Can be avoided, and if it is 12 wt% or less, it is more preferable because a situation in which the resistance of the carrier becomes too high can be avoided.

  An electrophotographic developer can be produced by mixing a magnetic carrier having the above-described structure with a toner having a particle size of about 10 μm produced by a pulverization method or a polymerization method. The electrophotographic developer exhibits an excellent feature that, even when applied to an MFP or the like, high-speed development with stable high image quality is possible, and the replacement life is 50% or more longer than that of a conventional product. It is.

  Next, regarding a carrier core material according to the present invention and a method for producing a magnetic carrier including the carrier core material, 1. resin addition method; Two methods, the silica particle addition method, will be described.

1. Resin addition method [weighing and mixing]
The magnetic oxide (preferably soft ferrite) used for the carrier core material included in the magnetic carrier according to the present invention is represented by the general formula: MO · Fe ₂ O ₃ . Here, examples of M include metals such as Fe, Mn, and Mg. Fe, Mn, and Mg can be used alone, but a mixed composition is preferable because the controllable range of magnetic properties in the carrier core material is widened.

And, as a raw material of M, if the Fe is _Fe 2 _{O 3} can be suitably used. If Mn is MnCO ₃ can be suitably used, it may be used without any _Mn 3 _{O 4,} etc. It is not limited to this, but if Mg MgCO ₃ can be suitably used, Mg not limited thereto (OH) ₂ etc. can also be used conveniently. Then, the blending ratio of these raw materials is matched with the target composition of the magnetic oxide and weighed and mixed to obtain a metal raw material mixture.

Next, resin particles are added to the metal raw material mixture. Here, there are a configuration in which carbon-based resin particles such as polyethylene and acrylic are added and a configuration in which silicon-containing resin particles such as silicone resin are added. The carbon-based resin particles and the silicon-containing resin particles are the same in that they burn in the calcining step described later and a hollow structure is generated in the calcined powder by the gas generated during the combustion. However, after the combustion, the carbon-based resin particles only generate a hollow structure in the calcined powder, but the resin particles containing silicon remain as SiO ₂ after combustion and remain in the generated hollow structure. The particle size and addition amount of the resin particles are preferably 2 to 8 μm in average particle size for both carbon and silicon, and the addition amount is preferably 0.1 wt% or more and 20 wt% or less in the total raw material powder, most preferably 12 wt%.

[Crushing and granulation]
The metal raw material mixture such as M and Fe and the resin particles weighed and mixed are introduced into a pulverizer such as a vibration mill, and pulverized to a particle size of 2 μm to 0.5 μm, preferably 1 μm. Next, water, 0.5-2 wt% of binder, and 0.5-2 wt% of a dispersant are added to the pulverized product to form a slurry having a solid content concentration of 50-90 wt%, and the slurry is wet-pulverized with a ball mill or the like. . Here, polyvinyl alcohol or the like is preferable as the binder, and ammonium polycarboxylate or the like is preferable as the dispersant.

  In the granulation step, the wet-pulverized slurry is introduced into a spray dryer and sprayed into hot air having a temperature of 100 ° C. to 300 ° C. to be dried to obtain granulated powder having a particle size of 10 μm to 200 μm. In the obtained granulated powder, the final particle size of the product is taken into consideration, and coarse particles and fine powders that deviate from the granulated powder are excluded with a vibration sieve to adjust the particle size. Although the detailed reason will be described later, since the final particle size of the product is preferably 25 μm or more and 50 μm or less, the particle size of the granulated powder is preferably adjusted to 15 μm to 100 μm.

[Calcination]
The mixed granulated product of the metal raw material mixture and the resin particles is put into a furnace heated to 800 ° C. to 1000 ° C. and calcined in the atmosphere to obtain a calcined product. At this time, a hollow structure is formed in the granulated powder by the gas generated by burning the resin particles. When a resin containing silicon is used as the resin particles, SiO ₂ that is a nonmagnetic oxide is generated in the hollow structure.

[Baking]
Next, the calcined product in which the hollow structure is formed is put into a furnace heated to 1100 ° C. to 1250 ° C. and fired to be ferritized into a fired product. The atmosphere at the time of firing is appropriately selected depending on the type of metal raw material. For example, when the metal raw materials are Fe and Mn (molar ratio 100: 0 to 50:50), a nitrogen atmosphere is required, and when Fe, Mn, and Mg, a nitrogen atmosphere or an oxygen partial pressure adjustment atmosphere is preferable, and Fe, Mn In the case of Mg, when the molar ratio of Mg exceeds 30%, an air atmosphere may be used.

[Disintegration, classification]
The obtained fired product was coarsely pulverized by hammer mill pulverization or the like, and then primary classified by an air classifier. Furthermore, after aligning the particle size with a vibration sieve or an ultrasonic sieve, it was subjected to a magnetic beneficiator to remove non-magnetic components to obtain a carrier core material.

[coating]
A resin carrier is applied to the obtained carrier core material to manufacture a magnetic carrier. As the coating resin, a silicone resin such as KR251 (manufactured by Shin-Etsu Chemical Co., Ltd.) is preferable. The coating resin is dissolved in an appropriate solvent (toluene or the like) at 20 to 40 wt% to prepare a resin solution. Here, the coating resin material to the carrier core material can be controlled by the concentration of the resin solution. And after mixing the prepared resin solution and carrier core material in the ratio of carrier core material: resin solution = 10: 1 to 5: 1, it is heated and stirred at 150 ° C. to 250 ° C., A resin-coated carrier core material is obtained. The amount of resin coated here is
It is preferable that it is 0.1 wt% or more and 20.0 wt% or less of the carrier core material.

The resin-coated carrier core material is further heated to cure the coating resin layer, whereby a magnetic carrier that is a carrier core material coated with the coating resin can be produced.
Here, the final particle size of the magnetic carrier is preferably 25 μm or more and 50 μm or less. If the particle size is 25 μm or more, it is preferable from the viewpoint that the carrier adhesion is small and high image quality can be obtained. If the particle size is 50 μm or less, the toner retaining ability of the carrier particles is high, the uniformity of the solid image, the toner This is because it is preferable from the viewpoint of reducing the amount of scattering and reducing fog.
Furthermore, an electrophotographic developer can be produced by mixing the magnetic carrier and a toner having an appropriate particle size.

2. Silica particle addition method [weighing and mixing]
The magnetic oxide (preferably soft ferrite) used for the carrier core material included in the magnetic carrier according to the present invention is also 1. It is the same as that described in the resin addition method, and a metal raw material mixture is obtained using the same raw materials and blending.

Next, silica particles are added to the metal raw material mixture. Here, the silica particles are: Unlike the resin particles described in the resin addition method, it does not burn and generate gas, but is taken into the fired product that is ferritized in the firing step described below. Then, the fired product in which the silica particles are incorporated is as follows: It will have a structure similar to the “baked product in which SiO ₂ remains in the hollow structure” described in the resin addition method. Here, according to the study by the present inventors, when the average particle diameter of the silica particles is 1 μm to 10 μm and the addition amount is 1 wt% to 50 wt% in the total raw material powder, the carrier obtained in the subsequent step In the core material, when the apparent density / true density of the carrier core material is A, 0.25 ≦ A ≦ 0.40, and the apparent density is 2.0 g / cm ³ or less, The inventors have conceived that the electrophotographic developer produced by using the carrier core material does not adversely affect the electrophotographic development.

[Crushing and granulation]
1. Weighed and mixed the metal raw material mixture such as M and Fe and silica particles into a pulverizer such as a vibration mill. It grind | pulverizes similarly to what was demonstrated by the resin addition method, makes a slurry, wet-grinds, Then, it granulates and obtains the granulated powder with a particle size of 10 micrometers-200 micrometers. 1. As described above, also in the manufacturing method, since the final particle size of the product is preferably 25 μm or more and 50 μm or less, the particle size of the granulated powder is preferably adjusted to 15 μm to 100 μm. .

[Calcination]
The mixed granulated product of the metal raw material mixture and the silica particles is fired in the next step without being calcined.

[Baking]
The mixed granulated product of the metal raw material mixture and the silica particles is put into a furnace heated to 1100 ° C. to 1250 ° C. and fired to be ferritized into a fired product. The firing atmosphere is as follows: This is the same as that described in the resin addition method. By the firing, a fired product in which silica particles are incorporated is generated.

[Disintegration, classification]
The obtained fired product is obtained as follows. The carrier core material was crushed and classified in the same manner as described for the resin addition method.

[coating]
For the obtained carrier core material: A resin coating is applied in the same manner as described in the resin addition method, and the coating resin layer is cured to produce a magnetic carrier.
Furthermore, an electrophotographic developer can be produced by mixing the magnetic carrier and a toner having an appropriate particle size.

1. 1. resin addition method, and The production of the magnetic carrier by the silica particle addition method 2 has been described. In any production, when a silicone resin or silica particles are added, the magnetic carrier contains a silica content of 1 wt% or more and 50 wt% or less. It will be. As a result, when the apparent density / true density of the carrier core material contained in the magnetic carrier is set to A, 0.25 ≦ A ≦ 0.40 and the apparent density is 2.0 g / cm ³ or less. A porous low-density carrier satisfying the above can be obtained.

Hereinafter, the present invention will be described more specifically with reference to examples.
Example 1
As a raw material of the carrier core material is prepared _Fe 2 _{O 3} and MgCO ₃ were finely pulverized. The _Fe 2 _O 3 molar ratio: MgO = 80: weighed such that 20. On the other hand, polyethylene resin particles (LE-1080 manufactured by Sumitomo Seika Co., Ltd.) having an average particle diameter of 5 μm corresponding to 10 wt% with respect to all raw materials in water, and 1.5 wt% of a polycarboxylate ammonium-based dispersant as a dispersant are wet. Prepared by adding 0.05 wt% of San Nopco SN wet 980 as the agent and 0.02 wt% of polyvinyl alcohol as the binder, and then weighed in the Fe ₂ O ₃ and MgCO ₃ weighed earlier. A slurry with a concentration of 75 wt% was obtained. The slurry was wet pulverized with a wet ball mill, stirred for a while, and then sprayed with a spray dryer to produce a dry granulated product having a particle size of 10 μm to 200 μm. From this granulated product, coarse particles were separated using a sieve mesh having a mesh size of 61 μm, and then heated to 900 ° C. in the atmosphere and calcined to decompose the resin particle components. Thereafter, it was baked at 1160 ° C. in a nitrogen atmosphere for 5 hours to make it ferritic. The ferritized fired product was crushed 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 to obtain a carrier core material.

  Next, a silicone resin (trade name: KR251, manufactured by Shin-Etsu Chemical Co., Ltd.) was dissolved in toluene to prepare a coating resin solution. Then, the carrier core material and the resin solution are introduced into the stirrer at a ratio by weight of carrier core material: resin solution = 9: 1, and the carrier core material is immersed in the resin solution for 3 hours at 150 ° C. to The mixture was heated and stirred at 250 ° C. Thereby, the resin was coated at a ratio of 1.0 wt% with respect to the weight of the carrier core material. The resin-coated carrier core material was placed in a hot-air circulating heating device, heated at 250 ° C. for 5 hours, and the coated resin layer was cured to obtain a magnetic carrier according to Example 1.

(Example 2)
A magnetic carrier according to Example 2 was obtained in the same manner as in Example 1 except that 0.1 wt% of polyethylene resin particles were added to all raw materials.

(Example 3)
A magnetic carrier according to Example 3 was obtained in the same manner as in Example 1 except that 20 wt% of polyethylene resin particles were added to all raw materials.

Example 4
Implementation was performed except that MnCO ₃ was added in addition to finely pulverized Fe ₂ O ₃ and MgCO ₃ as raw materials for the carrier core material, and the molar ratio was Fe ₂ O ₃ : MnO: MgO = 52: 34: 14. In the same manner as in Example 1, a magnetic carrier according to Example 4 was obtained.

(Example 5)
Except that the polyethylene resin particles were changed to silicone resin particles having an average particle size of 2.4 μm (Tospearl 120 manufactured by GE Toshiba Silicone Co., Ltd.), which is a resin containing silicon, and the firing temperature was 1200 ° C. In the same manner as in Example 2, a magnetic carrier according to Example 5 was obtained.

(Example 6)
MgCO ₃ is omitted as a raw material for the carrier core, finely pulverized Fe ₂ O ₃ and MnCO ₃ are added, weighed so that the molar ratio is Fe ₂ O ₃ : MnO = 65: 35, and the firing temperature is 1160 ° C. A magnetic carrier according to Example 6 was obtained in the same manner as Example 5 except for the above.

(Example 7)
Except that the polyethylene resin particles were changed to silicone resin particles having an average particle diameter of 2.4 μm, which is a resin containing silicon (Tospearl 120 manufactured by GE Toshiba Silicone Co., Ltd.), and the firing temperature was 1180 ° C. In the same manner as in Example 4, a magnetic carrier according to Example 7 was obtained.

(Example 8)
MgCO ₃ is omitted as a raw material for the carrier core, finely pulverized Fe ₂ O ₃ and Mn ₃ O ₄ are added, weighed so that the molar ratio is Fe ₂ O ₃ : MnO = 65: 35, and the firing temperature is 1130. A magnetic carrier according to Example 8 was obtained in the same manner as Example 3 except that the process was performed at ° C.

Example 9
Except that the polyethylene resin particles were changed to silicone resin particles having an average particle size of 2.4 μm (Tospearl 120 manufactured by GE Toshiba Silicone Co., Ltd.), which is a resin containing silicon, and the firing temperature was 1160 ° C. In the same manner as in Example 8, a magnetic carrier according to Example 9 was obtained.

(Example 10)
In addition to finely pulverized Fe ₂ O ₃ and Mn ₃ O ₄ as raw materials for the carrier core material, Mg (OH) ₂ is added and weighed so that the molar ratio is Fe ₂ O ₃ : MnO: MgO = 52: 34: 14. Then, a magnetic carrier according to Example 10 was obtained in the same manner as in Example 9, except that the firing temperature condition was 1180 ° C.

(Example 11)
Finely pulverized Fe ₂ O ₃ and Mg (OH) ₂ are prepared as raw materials for the carrier core material. The _Fe 2 _O 3 molar ratio: MgO = 80: weighed such that 20. On the other hand, silica particles with an average particle size of 4 μm (SIKRON M500 manufactured by SIBELCO) corresponding to 20 wt% of all raw materials in water, 1.5 wt% of an ammonium polycarboxylate dispersant as a dispersant, and San Nopco as a wetting agent. Co. SN wet 980 0.05 wt%, polyvinyl alcohol 0.02 wt% as a binder was prepared, and the weighed Fe ₂ O ₃ and Mg (OH) ₂ were added and stirred here. A slurry with a concentration of 75 wt% was obtained. The slurry was wet pulverized with a wet ball mill, stirred for a while, and then sprayed with a spray dryer to produce a dry granulated product having a particle size of 10 μm to 200 μm. From this granulated product, coarse particles were separated using a sieve mesh having a mesh size of 25 μm, and then baked at 1150 ° C. in a nitrogen atmosphere for 5 hours to be ferritized. The ferritized fired product was crushed 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 to obtain a carrier core material.

  Next, the carrier core material was coated with a silicone resin and cured in the same manner as in Example 1 to obtain a magnetic carrier according to Example 11.

(Example 12)
Example 11 except that Mg (OH) ₂ was omitted as a raw material for the carrier core, finely pulverized Mn ₃ O ₄ was added, and the mixture was weighed so that the molar ratio was Fe ₂ O ₃ : MnO = 80: 20. Similarly, a magnetic carrier according to Example 12 was obtained.

(Example 13)
A magnetic carrier according to Example 13 was obtained in the same manner as in Example 12 except that 40 wt% of silica particles was added to all raw materials.

(Example 14)
A magnetic carrier according to Example 14 was obtained in the same manner as Example 11 except that the firing temperature was 1110 ° C.

(Example 15)
A magnetic carrier according to Example 15 was obtained in the same manner as Example 11 except that the firing temperature was 1140 ° C.

(Example 16)
A magnetic carrier according to Example 16 was obtained in the same manner as in Example 11 except that Mg (OH) ₂ was replaced with MgCO ₃ and the firing temperature was 1170 ° C.

(Example 17)
Mg (OH) ₂ was omitted as a raw material for the carrier core material, finely pulverized Mn ₃ O ₄ was added, and the mixture was weighed so that the molar ratio was Fe ₂ O ₃ : MnO = 57: 43. On the other hand, a magnetic carrier according to Example 17 was obtained in the same manner as Example 11 except that 5 wt% was added and the firing temperature was 1100 ° C.

(Example 18)
A magnetic carrier according to Example 18 was obtained in the same manner as in Example 17 except that 10 wt% of silica particles was added to all raw materials and the firing temperature was set to 1070 ° C.

Example 19
A magnetic carrier according to Example 19 was obtained in the same manner as in Example 17 except that 20 wt% of silica particles were added to the total raw material and the firing temperature was 1170 ° C.

(Example 20)
A magnetic carrier according to Example 20 was obtained in the same manner as in Example 17 except that 40 wt% of silica particles were added to all raw materials and the firing temperature was 1140 ° C.

(Example 21)
A magnetic carrier according to Example 20 was obtained in the same manner as in Example 17 except that 60 wt% of silica particles were added to the total raw material and the firing temperature was 1130 ° C.

(Comparative Example 1)
A magnetic carrier according to Comparative Example 1 was obtained in the same manner as in Example 1 except that the polyethylene resin particles were not added and calcined.

(Comparative Example 2)
Comparison was made in the same manner as in Comparative Example 1 except that Fe ₂ O ₃ and MgCO ₃ pulverized as raw materials for the carrier core were weighed so that the molar ratio was Fe ₂ O ₃ : MgO = 75: 25. A magnetic carrier according to Example 2 was obtained.

(Comparative Example 3)
A magnetic carrier according to Comparative Example 3 was obtained in the same manner as in Example 4 except that the polyethylene resin particles were not added and calcined.

(Comparative Example 4)
A magnetic carrier according to Comparative Example 4 was obtained in the same manner as Example 4 except that no polyethylene resin particles were added.

(Comparative Example 5)
A magnetic carrier according to Comparative Example 5 was obtained in the same manner as Example 10 except that the silicone resin particles were not added.

(Comparative Example 6)
A magnetic carrier according to Comparative Example 6 was obtained in the same manner as in Example 9, except that the silicone resin particles were not added, calcined, and the firing temperature was 1160 ° C.

(Summary of Examples 1-21 and Comparative Examples 1-6)
Table 1 shows a list of manufacturing conditions of the above Examples and Comparative Examples, and Table 2 shows a list of physical property values of each manufactured carrier core material.
However, the apparent density was measured according to JIS-Z2504: 2000. The true density was measured using a pycnometer 1000 manufactured by QUANTA CHROME. The specific surface area BET (0) was measured using Sorb U2 manufactured by Yuasa Ionics. The spherical specific surface area BET (D) was calculated by first measuring the cs value (Calculated Specific Surfaces Area) using a Microtrac HRA manufactured by Nikkiso Co., Ltd. and dividing the cs value by the true density. In Table 2, the value of BET (0) / BET (D) is shown as an index B. The average particle diameter was measured by Microtrack HRA manufactured by Nikkiso Co., Ltd. Saturation magnetization and coercive force were measured by a room temperature dedicated vibration sample magnetometer (VSM) (manufactured by Toei Industry Co., Ltd.). The nonmagnetic content (silica) content was measured by a method according to JIS standards (JIS G 1212).

  Furthermore, an electrophotographic developer was produced by mixing the magnetic carrier according to each of Examples and Comparative Examples and a commercially available toner having a particle size of about 1 μm, and an image evaluation test was performed using the electrophotographic developer. The results are listed in Table 3. In the evaluation, ◎ is a very good level, ◯ is a good level, Δ is a usable level, and x is a non-usable level.

  In Table 2, it can be said that the lower the index A, the lower the density of the carrier core material. If the index B is 3.0 or more, the actual specific surface area is larger than the specific surface area calculated from the apparent particle size. Since it is large, a fine hollow structure is formed inside the carrier, and if it is 10 or less, it can be said that a sufficient amount of hollow structure is formed. Therefore, since Examples 1-10 have a lower index A value than Comparative Examples 1-6, it can be seen that the density of the carrier core material can be reduced beyond the difference in the raw material composition. Moreover, Examples 1-21 are also contained in the preferable range also about the value of the parameter | index B compared with Comparative Examples 1-6, and a fine hollow structure is enough inside a carrier core material exceeding the difference in a raw material composition. Was found to be formed.

Further, in Examples 5 to 7, 9, and 10, since the silicone resin particles are added, the Si component in the silicone resin becomes SiO ₂ particles during calcination, and the SiO ₂ particles are combined with the ferrite composition. As a result, a carrier core material having a lower true specific gravity could be produced. In Examples 11 to 21 as well, silica particles were incorporated into the ferrite composition and combined, and as a result, the carrier core material having a low true specific gravity could be produced.

From the image evaluation test results shown in Table 3, the following was found.
First, with respect to the initial image characteristics, except for the image quality of Comparative Example 1, both the Examples and Comparative Examples were very good or good levels. And in 50K sheets, the example maintained a very good or good level, but in Comparative Examples 1 to 6, the level began to decrease. In 100K sheets, some examples also showed a decrease in level, but in Comparative Examples 1-6, all items were unusable in any item and exceeded the replacement time. There was found. Furthermore, in 150K sheets, there were no unusable levels in Examples 1-21, but it was found that Comparative Examples 1-6 were at unusable levels.

Claims (13)

A carrier core material used in a carrier for an electrophotographic developer,
Electrophotographic development characterized in that when the apparent density / true density of the carrier core material is A, 0.25 ≦ A ≦ 0.40 and the apparent density is 2.0 g / cm ³ or less. Carrier core material. In the carrier core material, the value of the specific surface area measured by the BET method is BET (0), the cs value obtained from the wet dispersion type particle size distribution measuring machine is divided by the true density, and the value of the spherical equivalent specific surface area is obtained by BET. When (D)
^{2. The} carrier core for electrophotographic development according to claim 1, wherein BET (0) ≧ 0.07 m ² / g and 3.0 ≦ BET (0) / BET (D) ≦ 10.0. Wood.   The carrier core material for an electrophotographic developer according to claim 1 or 2, wherein the carrier core material contains a magnetic oxide and a nonmagnetic oxide having a true specific gravity of 3.5 or less.   The carrier core material for an electrophotographic developer according to claim 3, wherein the magnetic oxide is soft ferrite.   The carrier core material for electrophotographic development according to claim 3 or 4, wherein the carrier core material contains the nonmagnetic oxide in an amount of 1 wt% to 50 wt%.   6. A carrier for electrophotographic development, wherein the carrier core material for an electrophotographic developer according to claim 1 is coated with a resin.   The electrophotographic developer carrier according to claim 6, wherein a coating amount of the resin is 0.1 wt% or more and 20.0 wt% or less of the carrier core material.   The carrier for an electrophotographic developer according to claim 6 or 7, wherein the average particle size is 25 µm or more and 50 µm or less.   The carrier for an electrophotographic developer according to claim 6, comprising 1 wt% or more and 50 wt% or less of silica.   An electrophotographic developer comprising the carrier for an electrophotographic developer according to claim 6. A step of mixing one or two or more metal elements M selected from carbonates, oxides, and hydroxides with Fe ₂ O ₃ and crushing to obtain a pulverized product. When,
Adding the resin particles, water, binder, and dispersant to the pulverized product to form a slurry, followed by wet pulverization and further drying to obtain a granulated powder;
Calcining the granulated powder to obtain a calcined product;
Firing the calcined product to obtain a fired product;
And a step of pulverizing the fired product to obtain a carrier core material.   12. The method for producing a carrier core material for electrophotographic development according to claim 11, wherein resin particles containing silicon are used as the resin particles added to the pulverized product. A step of mixing one or two or more metal elements M selected from carbonates, oxides and hydroxides with Fe ₂ O ₃ and pulverizing to obtain a pulverized product; ,
A step of adding silica particles, water, a binder, and a dispersant to the pulverized product to form a slurry, followed by wet pulverization and further drying to obtain granulated powder,
Firing the granulated powder to obtain a fired product;
And a step of pulverizing the fired product to obtain a carrier core material.