JP3875584B2 - Ferromagnetic material powder and carrier for electrophotographic developer using the magnetic material powder - Google Patents

Description

【００８８】
【表２】

【００８９】
表２の結果より、本発明の強磁性材料粉を芯材として用いた実施例１〜３及び６のキャリアは、実機評価において、画像濃度、キャリア付着量とリーク現象の画像評価項目であるハーフトーン白スジの評価及び帯電量の環境依存生は共に良好である。即ち、全鉄に対する２価の鉄の比率が１０．０〜３０．０にある強磁性材料粉を用いることによって、粒子間の磁化のバラツキを抑え、かつ抵抗が所望の範囲とすることができる。
【００９０】
この全鉄に対する２価の鉄の比率が、１．０〜３２．０の範囲外にある比較例１〜２は、キャリア付着とリーク現象が発生し、両方を満足することができない。
【００９１】
また、フェライト相中にマグネトプランバイト型フェライトが含有していない比較例３では、粒子間の磁化のバラツキが大きく、キャリア付着を満足できない。
【００９２】
比較例４は、化学量論比よりもヘマタイトが多量の配合により、焼成後マグネタイト相が存在しているキャリアであるが、マグネトプランバイト型フェライト型を含有していないため、キャリア付着が満足できておらず、かつ芯材抵抗が比較的低抵抗のため、リーク現象も見られる。さらにアルカリ金属であるリチウムを含有しているため、帯電量の環境差が大きい。
【００９３】
従来技術の例として挙げた比較例５は、マグネタイトキャリアである。芯材抵抗が低抵抗のため、リーク現象が発生し、また抵抗に起因したキャリア付着も発生している。
【００９４】
従来技術の例として挙げた比較例６は、化学量論的配合のため、マグネタイト相は発生していないフェライト単相である。キャリア付着、リーク現象は実用上使用可能なレベルに近いが、画像濃度が出ておらず、総合評価としては満足できるレベルではない。また、上記と同様にリチウムを含有しているため帯電量の環境差も大きい。
【００９５】
図１に、実施例１〜２及び比較例１〜２、５〜６の印加電圧と芯材抵抗値との関係を示す。
【００９６】
【発明の効果】
本発明の強磁性材料粉によれば、マグネタイト相とマグネトプランバイト型フェライトを含有したフェライト相の複合体において、全鉄に対する２価の鉄の比率が所望の範囲内に制御されているため、粒子間の磁化のバラツキが少なく、かつ抵抗を所望の範囲内とすることが可能となる。従って、本発明の強磁性材料粉を用いた電子写真用キャリア及び現像剤は、キャリア付着が抑えられ、かつリーク現象の見られない、高画質画像を得ることができ、また高耐久性及び周囲環境に対する安定性に優れたものとなる。
【００９７】
また、本発明の強磁性材料粉の製造方法によれば、マグネタイト相とフェライト相が均一に混在し、かつ全鉄に対する２価の鉄の比率が所定の範囲とすることができるため、目的とする強磁性材料粉を、安定的、かつ安価に製造することができる。
【図面の簡単な説明】
【図１】図１は、印加電圧と芯材抵抗値との関係を示すグラフである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a ferromagnetic material powder, a carrier for an electrophotographic developer using the magnetic material, a method for producing the carrier, and an electrophotographic developer using the carrier.
[0002]
[Prior art and problems to be solved by the invention]
The two-component developer used in the electrophotographic method is composed of a toner and a carrier. The carrier is agitated and mixed with the toner in the developing machine to give the toner a desired charge, and the charged toner is placed on the photoreceptor. Is a carrier material that carries the toner to form a toner image. Then, the carrier remains on the magnet, returns to the inside of the developing machine again, is agitated and mixed with new toner again, and is repeatedly used.
[0003]
Therefore, in order to stably maintain desired image quality during the printing durability period, it is required that the characteristics of the carrier be stable during the usage period.
[0004]
In recent years, in a two-component development system, a magnetite carrier or a ferrite carrier has been used in place of the conventional oxide-coated iron powder or resin-coated iron powder in order to obtain a high-quality image.
[0005]
Recently, digital full-color copiers, printers, etc. have become widespread, and since most of these development methods are reversal development methods, a high bias voltage is applied, so the carrier core material has a certain degree of resistance. In the development, a high-quality image having high image density and good gradation is desired.
[0006]
Therefore, in the case of a magnetite-based carrier, the core material has low resistance, so a leak phenomenon is observed, a uniform and uniform solid portion cannot be reproduced, a lot of brushes are generated on the image, and the thin line image is disturbed. There are image defects such as.
[0007]
Various attempts have been made to improve the resistance in order to compensate for the disadvantages of the above-mentioned magnetite-based carriers. However, any method basically increases the hematite phase in the magnetite phase to increase the resistance. I am letting. However, an increase in the hematite phase, which is a nonmagnetic component, causes generation of low-magnetization particles, and carrier adhesion occurs during development. For this reason, the rate of increase of the hematite phase in the magnetite phase can only be slight, and most of the magnetite phase increases the resistance at a low bias voltage, but the resistance is still low when a high bias voltage is applied. There is a leak phenomenon during development and image defects occur.
[0008]
On the other hand, the ferrite carrier has high resistance, and the electrostatic latent image potential on the photosensitive member does not leak to the carrier during development, and the occurrence of scratches or the like is not recognized. In addition, since it is composed of higher-order oxides, there is an advantage that no deterioration phenomenon is observed in the use process, and therefore the carrier life is long.
[0009]
However, since the core material resistance is high, a region where a desired image density is obtained is narrow, and there is a drawback that it is difficult to obtain a solid portion having a high density at an initial stage.
[0010]
Thus, a composite carrier in which magnetite is contained in the above-described ferrite has been proposed.
[0011]
For example, in JP-A-9-134036, by adding 0.1 to 10% by weight of a magnetite phase in light metal ferrite, an overcharged state is not caused in the charging step, and the toner is stabilized in a short time. It has been proposed to realize a charged state.
[0012]
However, these conventional composite magnetic powders of ferrite phase and magnetite phase cause image defects such as frequent carrier adhesion due to variation in magnetization between magnetic particles, and leakage phenomenon due to magnetite phase conductivity. . Furthermore, the alkali metal ferrite lacks environmental stability, the charging characteristics greatly fluctuate, and a stable image cannot be obtained.
[0013]
Accordingly, the object of the present invention is to provide excellent image quality and durability, particularly without the occurrence of a leakage phenomenon during development, excellent environmental stability during charging with toner, and reduced variation in magnetization between particles. An object of the present invention is to provide a carrier for an electrophotographic developer and a production method thereof, an electrophotographic developer using the carrier, and a ferromagnetic material powder used as the carrier core material.
[0014]
[Means for Solving the Problems]
  Therefore, as a result of investigations to solve these problems, the present inventors have determined that the ratio of divalent iron to total iron in a magnetic oxide in which a magnetite phase and a ferrite phase are mixed is set.10.0-30.0It was found that the above-mentioned object can be achieved by containing magnetoplumbite type ferrite in the ferrite phase, and the present invention has been completed.
[0015]
  That is, according to the present invention, in a magnetic oxide in which a magnetite phase and a ferrite phase are mixed, the ratio of divalent iron to total iron is10.0-30.0And magnetoplumbite type ferrite is contained in the ferrite phase.The content of the magnetoplumbite ferrite is 0.05 to 5.0 mol%.A ferromagnetic material powder characterized by the above is provided.
[0016]
The present invention also provides an electrophotographic developer carrier characterized in that the above-mentioned ferromagnetic material powder is used as a core and the surface thereof is resin-coated.
[0017]
Furthermore, the present invention adds a substance containing carbon atoms in an amount of 0.1 to 3% by weight in terms of carbon atoms in a raw material mixture containing hematite and other metal oxides, Each surface of the ferromagnetic material powder obtained by firing at 1400 ° C. or the surface of the ferromagnetic material powder obtained by surface oxidation treatment in the atmosphere or in an atmosphere with a controlled oxygen concentration after the firing. Further, the present invention provides a method for producing a carrier for an electrophotographic developer, which is coated with a resin.
[0018]
The present invention also provides an electrophotographic developer comprising the carrier and a toner.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the ferromagnetic material powder of the present invention will be described in detail.
[0020]
  The ferromagnetic material powder of the present invention is a magnetic oxide in which a ferrite phase and a magnetite phase are mixed as described above, and the ratio of divalent iron to total iron.Is 1It is 0.0-30.0, and contains a magnetoplumbite type ferrite in the ferrite phase. The ratio of divalent iron to total iron when the surface of the ferromagnetic material powder of the present invention is oxidized is10.0-28.0. In addition, the ferrite as used in the field of this invention means ferrite other than magnetite which is iron ferrite.
[0021]
Here, the ratio of divalent iron to the total iron (hereinafter referred to as γ) is calculated as follows.
Fe (II): Analytical value (% by weight) of divalent iron analyzed based on “Method of determining ferrous oxide in iron ore JISM8213”
T-Fe: Analytical value (% by weight) of total iron analyzed based on "Quantitative determination method of total iron in iron ore JISM8212"
When
γ = Fe (II) / T-Fe × 100
It is represented by
[0022]
In a magnetic oxide in which a magnetite phase and a ferrite phase containing magnetoplumbite type ferrite are mixed, when the value of γ increases, the electrical resistance of the ferromagnetic material powder decreases. When a ferromagnetic material powder having a value of γ exceeding 32.0 is used as a carrier, a leak phenomenon occurs in development, which is not preferable. On the other hand, when the value of γ decreases, variation in magnetization between particles is likely to occur, and when a ferromagnetic material powder having a value of γ less than 1.0 is used as a carrier, white spots appear on the image. Carrier adhesion occurs, which is also not preferable. In addition, in the ferromagnetic material powder subjected to the surface oxidation treatment, when the ferromagnetic material powder having a value of γ less than 1.0 is used as a carrier, it is easy to generate variation in magnetization between particles. In development, carrier adhesion occurs, which is not preferable.
[0023]
  the value of γ10.0-30.0By doing so, the variation in magnetization between particles can be reduced, and in development, carrier adhesion can be greatly reduced, and a ferromagnetic material powder free from leakage phenomenon can be obtained.
[0024]
In the ferromagnetic material powder of the present invention, the ratio of the scattered magnetization to the main body magnetization is desirably 0.8 or more. When the ratio of the scattered magnetization to the main body magnetization is less than 0.8, carrier adhesion increases in development, which is not preferable.
[0025]
Here, the ratio of the main body magnetization to the scattered magnetization is calculated as follows.
X₀: Magnetization of main body before scattering test (emu / g)
X: Magnetization of scattered matter (emu / g)
X / X₀: Ratio of body magnetization to scattered magnetization
[0026]
[Splash test method]
When 600 g of ferromagnetic material powder is placed in a developing box for a Leo Dry 7610 copier manufactured by Toshiba Corporation and stirred for 10 minutes at a motor rotation speed of 158 rpm, the sample scattered from the developing box is collected, and the scattered matter is 5 kOe The magnetization of was determined.
[0027]
  The composition of the ferrite phase in the ferromagnetic material powder of the present invention is preferably a composite of magnetoplumbite type ferrite and spinel type ferrite. By taking such a complex, the ratio of divalent iron to total iron is reduced.10.0-30.0Thus, a ferromagnetic material powder having a characteristic that the ratio of the main body magnetization to the scattered magnetization is 0.8 or more can be obtained.
[0028]
The element constituting the ferrite phase in the ferromagnetic material powder of the present invention is preferably selected from at least one element selected from Group 2 elements of the periodic table. Since the specific gravity of the above elements is low, when used as a carrier, the stress between the carriers is low and the element can have high durability. In particular, Mg and Ca are preferable. Alkaline metal elements such as Li, K, and Rb are also light in specific gravity as elements other than those described above. However, if they are present in the ferrite phase, the environmental dependency of the charge amount is remarkably deteriorated, which is not preferable.
[0029]
  The magnetoplumbite type ferrite in the ferromagnetic material powder of the present invention preferably contains Sr and / or Ba. As a content of magnetoplumbite type ferrite, 0. It is 05-5.0 mol%, Most preferably, it is 0.35-3.0 mol%. If it is less than 0.05 mol%, the ratio of scattered magnetization to main body magnetization increases, and carrier adhesion increases during development. If it exceeds 5.0 mol%, the remanent magnetization and coercive force increase and aggregation occurs between the magnetic particles.
[0030]
The saturation magnetization of the ferromagnetic material powder of the present invention is preferably 20 to 80 emu / g, particularly preferably 30 to 70 emu / g. When used as a carrier, if the saturation magnetization exceeds 80 emu / g, the magnetic brush becomes hard, so that the eyelashes and roughness occur, and a high-quality developed image cannot be obtained. If it is less than 20 emu / g, since the magnetic force is too low, the magnetic particles are detached from the magnetic brush and carrier adhesion occurs, which is not preferable. The measurement of saturation magnetization in the present invention is performed using a BH tracer (BHU-60 type) manufactured by Riken Denshi Co., Ltd.
[0031]
The average particle size of the ferromagnetic material powder of the present invention is preferably 20 to 100 μm, particularly preferably 30 to 50 μm. When used as a carrier, if the average particle size exceeds 100 μm, the specific surface area of the carrier decreases, toner scattering and fog increase, and a high-quality image cannot be obtained. When the average particle size is less than 20 μm, the magnetization per carrier particle is lowered, and carrier adhesion to the photoreceptor is generated, which is not preferable. In addition, the measurement of the average particle diameter of this invention is performed using the Nikkiso Co., Ltd. Microtrac particle size analyzer (Model9320-X100).
[0032]
The resistance of the ferromagnetic material powder of the present invention is 1.0 × 10⁷~ 1.0 × 10¹¹Ω is preferable, and in particular, the resistance of the ferromagnetic material powder subjected to the surface oxidation treatment is 1.0 × 10⁸~ 1.0 × 10¹¹Ω is preferred. In a developing system that applies an alternating electric field in order to achieve high image quality, a high-resistance core material is required, and thus the ferromagnetic material powder subjected to surface oxidation treatment is particularly preferable. When used as a carrier, the core resistance is 1.0 × 10¹¹If it exceeds Ω, it is difficult to obtain image density, which is not preferable. Core material resistance is 1.0 × 10⁷If it is less than 1, a leak phenomenon is likely to occur, and a high-quality image cannot be obtained.
[0033]
In addition, the resistance method in this invention is as follows. That is, the N pole and the S pole are made to face each other with an interval between magnetic poles of 6.5 mm, and 200 mg of a sample is weighed and inserted into a nonmagnetic parallel plate electrode (area 10 × 40 mm). A sample was held between the electrodes by attaching magnetic poles (surface magnetic flux density: 1500 Gauss, counter electrode area: 10 × 30 mm) to the parallel plate electrodes, and the resistance at an applied voltage of 250 V was measured with an insulation resistance meter.
[0034]
Next, the manufacturing method of the ferromagnetic material powder of the present invention will be described.
First, hematite (Fe₂O_ThreeAnd an appropriate amount of each oxide containing an element capable of producing magnetoplumbite type ferrite. At this time, in order to generate magnetite at the time of firing, a blend containing a large amount of hematite is preferable to a stoichiometric blend. As a kind of raw materials other than hematite, it is preferable to include an element of Group 2 of the periodic table. In particular, an oxide containing Sr and / or Ba is preferably contained in the raw material.
[0035]
Each raw material blended in an appropriate amount is wet or dry, pulverized to an average particle size of 15 μm or less, preferably 5 μm or less, more preferably 2 μm or less by a ball mill, sand mill, vibration mill or the like, and then dispersed as necessary. Add an agent, antifoaming agent, binder, etc., adjust the viscosity, and granulate dry. Furthermore, in order to increase the uniformity of the surface grain boundaries of the sintered ferromagnetic material powder, a substance containing carbon atoms is added as a sintering aid in an amount of 0.1 to 3% by weight in terms of carbon atoms. Thereby, a sinterability improves and the growth degree of a grain boundary increases, A uniform surface grain boundary can be obtained. If the addition amount is less than 0.1% by weight, the action as a sintering aid cannot be obtained, and if it exceeds 3% by weight, the sinterability is too advanced and the spherical shape of the particles cannot be maintained. As the sintering aid, liquid substances such as polyvinyl alcohol (PVA), polyacrylamide, polyisobutylene, polycarboxylate, and alkylnaphthalene sulfonate, and powder substances such as acetylene, graphite, and carbon black can be used. Moreover, when using the sintering aid of a liquid substance, the substance which can be used also as a binder at the time of granulation is preferable. The sintering aid may be added at the time of wet pulverization, or may be added to a granulated product obtained by granulation drying if it is a powdery substance. Moreover, in order to promote a magnetite reaction, you may add a reducing agent suitably.
[0036]
Next, the obtained granulated product is held at a temperature of 1100 to 1400 ° C. for 1 to 24 hours and subjected to main firing. The firing atmosphere at this time is preferably carried out in an inert gas atmosphere having an oxygen concentration of less than 0.1% by volume, preferably 0.05% by volume or less. At the time of the main firing, excess hematite is magnetized, and the magnetite phase and the ferrite phase are uniformly mixed in one particle. If the oxygen concentration in the firing atmosphere is 0.1% by volume or more, the hematite phase increases, the magnetite phase and the ferrite phase in one particle cannot be mixed uniformly, and variation in magnetization between particles occurs. It is not preferable.
[0037]
  The fired product thus obtained is crushed and classified, and adjusted to a desired particle size. Furthermore, magnetization and resistance can be adjusted by subjecting the ferromagnetic material powder to surface oxidation treatment in the air or in an atmosphere in which the oxygen concentration is controlled. As the surface oxidation treatment method, the rotary kiln method is desirable, and the resistance is increased by raising the treatment temperature. However, if the treatment temperature is raised too much, the variation in magnetization between particles occurs, and in the development, carrier adhesion is caused. appear. However, the ferromagnetic material powder of the present invention has a ratio of divalent iron to total iron.10.0Control to ~ 28.0ByIn this range, even if the desired resistance adjustment is performed by the surface oxidation treatment, there is no variation in magnetization between the particles, so that a high-quality image free from carrier adhesion and leakage phenomenon can be obtained.
[0038]
Next, the ferromagnetic material powder of the present invention thus obtained can be used as a carrier for an electrophotographic developer by itself, but preferably the surface of the ferromagnetic material powder is used as a core material. A resin coating is applied to the film and used as a carrier for an electrophotographic developer.
[0039]
The resin used for coating the carrier core material is not particularly limited, and various resins can be used. For the positively chargeable toner, for example, a fluorine resin, a fluorine-acrylic resin, a silicone resin, a modified silicone resin, or the like can be used. Conversely, for negatively chargeable toners, for example, acrylic resins, acrylic-styrene resins, mixed resins of acrylic-styrene resins and melamine resins, cured resins thereof, silicone resins, modified silicone resins, polyesters. Resin, epoxy resin, urethane resin, polyethylene resin and the like can be used.
[0040]
If necessary, a charge control agent, an adhesion improver, a primer treatment agent, a resistance control agent, or the like may be added. Examples of charge control agents and resistance control agents include various silane coupling agents, various titanium coupling agents, borides such as conductive carbon and titanium boride, titanium oxide, iron oxide, aluminum oxide, chromium oxide, and silicon oxide. Examples of the oxide include, but are not particularly limited to.
[0041]
The coating amount of such a resin is preferably 0.05 to 10.0% by weight, particularly 0.5 to 7.0% by weight with respect to the carrier core material. If it is less than 0.05% by weight, it is difficult to form a uniform coating layer on the surface of the carrier, and if it exceeds 10.0% by weight, aggregation between carriers occurs.
[0042]
Further, as a resin coating method, the resin is generally diluted with a solvent and coated on the surface of the carrier core material. Examples of the solvent used here include toluene, xylene, cellosolve butyl acetate, methyl ethyl ketone, methyl isobutyl ketone, methanol, and the like when the resin is soluble in an organic solvent. Water may be used. Further, as a method for coating the carrier core material with the coating resin as described above, a known method, for example, brush coating method, dry method, spray drying method using a fluidized bed, rotary drying method, immersion drying using a universal stirrer It can be coated by a method or the like. In order to improve the coverage, a fluidized bed method is preferred.
[0043]
When the resin is coated on the carrier core and then baked, either an external heating method or an internal heating method may be used, for example, a fixed or fluid electric furnace, a rotary electric furnace, a burner furnace, or a microwave baking. But you can. Although the baking temperature varies depending on the resin to be used, a temperature equal to or higher than the melting point or the glass transition point is necessary. For a thermosetting resin or a condensation-crosslinking resin, it is necessary to raise the temperature to a point where the curing proceeds sufficiently.
[0044]
In this way, the resin is coated and baked on the surface of the carrier core material, and then cooled, and a resin-coated carrier is obtained through pulverization and particle size adjustment.
[0045]
The carrier of the present invention obtained as described above is mixed with toner and used as a two-component developer.
[0046]
Usually, the two-component developer is charged with each other by frictional charging between the carrier and the toner, but changes in the external environment (for example, low temperature and low humidity (10 ° C., 20% RH) and high temperature and high humidity (35 ° C., 80%). % RH)), the charge amount changes. Since the change in the charge amount causes a change in the image characteristics, it is preferable that the change amount of the charge amount due to the change in the external environment is small.
[0047]
The toner used in the present invention can be produced by a known method such as a suspension polymerization method, an emulsion polymerization method, or a pulverization method. As an example of the pulverization method, a binder resin, a colorant, a charge control agent and the like are sufficiently mixed with a mixer such as a Henschel mixer, and then uniformly dispersed by melt-kneading with a twin screw extruder or the like, after cooling, Finely pulverizing with a jet mill or the like, and after classification, for example, it can be classified with an air classifier or the like to obtain a toner having a desired particle size. If necessary, wax, magnetic powder, viscosity modifier, and other additives may be included. Further, an external additive or the like can be added after classification.
[0048]
The binder resin used in the toner is not particularly limited, but polystyrene, chloropolystyrene, styrene-chlorostyrene copolymer, styrene-acrylic acid ester copolymer, styrene-methacrylic acid copolymer, The rosin-modified maleic acid resin, epoxy resin, polyester resin, polyethylene resin, polypropylene resin, polyurethane resin, silicone resin and the like can be used alone or in combination as required.
[0049]
Examples of the charge control agent that can be used in the toner include nigrosine dyes, quaternary ammonium salts, organometallic complexes, chelate complexes, and metal-containing monoazo dyes.
[0050]
As the colorant used in the toner, conventionally known dyes and / or pigments can be used. For example, carbon black, phthalocyanine blue, permanent red, chrome yellow, phthalocyanine green, etc. can be used.
[0051]
As other external additives, silica, titanium oxide, barium titanate, fluorine fine particles, acrylic fine particles and the like can be used alone or in combination.
[0052]
【Example】
  Hereinafter, the present invention will be specifically described based on examples and the like.The following Examples 4 and 5 are not examples of the present invention but reference examples.
[0053]
[Example 1]
As shown in Table 1, MgO 20.0 mol%, SrO 0.5 mol%, Fe₂O_Three79.5 mol% was pulverized with a wet ball mill for 7 hours to make the average particle size 3 μm or less. An appropriate amount of a dispersant and an antifoaming agent are added to this slurry, and 1.1% by weight of PVA is added as a binder and a sintering aid in terms of carbon atoms, and then granulated and dried with a spray dryer. Under an inert atmosphere condition (oxygen concentration of 0.05% by volume or less), the temperature was maintained at 1210 ° C. for 4 hours to perform the main firing. Thereafter, the powder was crushed and further classified into powder having an average particle size of 50 μm, and then surface oxidation treatment was performed at 650 ° C. in the atmosphere in a rotary kiln to obtain ferromagnetic material powder.
[0054]
The ferromagnetic material powder was analyzed for total iron and divalent iron, and the value of the ratio of divalent iron to total iron (γ) was obtained. Further, a scattering test was performed on the ferromagnetic material powder, and the value of the scattering magnetization relative to the body magnetization (X / X₀)
[0055]
Further, resistance measurement was performed on the ferromagnetic material powder at an applied voltage of 250V.
[0056]
Using this ferromagnetic material powder as a carrier core material, a silicone resin (trade name: SR-2411, solid content 20% by weight, manufactured by Toray Dow Corning Silicone Co., Ltd.) is dissolved in a toluene solvent, and the carrier is used using a fluidized bed. The core material was coated by 0.6% by weight, and further baked at 250 ° C. for 3 hours to obtain a carrier coated with the resin.
[0057]
Thus, the average particle diameter of the carrier obtained, saturation magnetization, and resistance measurement at the time of applied voltage 250V were measured with the measuring instrument mentioned above.
[0058]
Table 2 shows each physical property or characteristic of the ferromagnetic material powder and the carrier using the ferromagnetic material powder as a core material.
[0059]
[Charge amount change due to environmental fluctuations]
Next, the change in charge amount of the carrier described above due to environmental fluctuations was determined by the following method. The results are shown in Table 2.
Next, the carrier and toner described above (full color copying machine manufactured by TOSHIBA TEC: magenta toner for Fantasia 22: T-FC22M) are respectively supplied to L / L (10 ° C., 20% RH) and H / H (35 ° C., 80% RH) after exposure for 24 hours, put 93.0g of carrier and 7.0g of toner in 100cc polybin and stir for 30 minutes with Turbula mixer to create a developer. The charge amount was measured with a suction type blow-off device (model number TB-203 type) manufactured by the company.
here
Q_LL: Measured charge amount of developer prepared by exposing carrier and toner to L / L environment, respectively
Q_HH: Measured charge amount of developer prepared by exposing carrier and toner to H / H environment
Then, the difference ΔQ was obtained by the following equation, and the environmental dependency of the charge amount was evaluated.
ΔQ = Q_LL-Q_HH
Charge amount measurement conditions: Blow pressure 3.0 kPa, suction pressure 4.0 kPa
Blow time = 10 seconds value, network = 500M
[0060]
Further, T-FC22M was used as a toner for the above-mentioned carrier as a toner, and a full-color copier manufactured by Toshiba Tec Corporation: Magenta toner for Fantasia 22 to prepare a developer having a toner concentration of 7.0% by weight. Full-color copier manufactured by the company: Fantasia 22 was used only for the magenta station, and the actual machine evaluation of image density, white spots (carrier adhesion amount), and halftone white streaks in the initial live action was performed. These developer characteristics are shown in Table 2. In addition, this actual machine evaluation was performed in N / N environment (23 degreeC, 55% RH). These results are shown in Table 2.
[0061]
1. Image density evaluation method
The solid image density (ID) was measured with a Macbeth densitometer RD-918, and the following ranking was performed.
A: I. D. Is more than 1.80, the document density is reproduced very well, and there is no density unevenness, and it is a uniform solid.
○: I. D. Is more than 1.65 and not more than 1.80, the document density is reproduced, and there is no density unevenness.
Δ: I. D. Is more than 1.50 and not more than 1.65, and the document density is high and is practically possible.
X: I.I. D. Is more than 1.40 and not more than 1.50, the density is low, and the image is negatively uniform.
XX: I. D. Is 1.40 or less, the overall density is low and the edge effect is large, and the density is greatly reduced compared to the original density.
[0062]
2. Evaluation method of vitiligo (carrier adhesion)
The carrier adhesion on the image, ie, the level of vitiligo, was evaluated and ranked.
A: None in 10 sheets of A3 paper.
A: 1 to 5 pieces in 10 A3 sheets.
Δ: More than 5 in 10 A3 sheets, 3 or less in 3 A3 sheets.
X: Over 5 and 10 or less in 3 sheets of A3 paper.
XX: More than 10 in 3 sheets of A3 paper.
[0063]
3. Halftone white stripe evaluation method
When a leak phenomenon occurs in development, a halftone white streak occurs on the image. The level of this halftone white streak was evaluated and ranked.
A: None in A3 paper.
◯: About 1 to 3 fine white lines are confirmed in A3 paper.
(Triangle | delta): About a fine white stripe is confirmed in A3 paper more than three and ten or less.
X: About 10 white streaks are confirmed in A3 paper.
XX: Many white streaks occur in A3 paper, and there are places where white lines are missing.
[0064]
4). Comprehensive evaluation
The overall evaluation of the above evaluation items was evaluated based on the following.
A: Very good level in actual machine evaluation.
○: No problem in actual machine evaluation.
Δ: Practically possible level in actual machine evaluation.
×: Level that cannot be used due to problems in the actual machine evaluation.
XX: Level that cannot be used due to problems in all items in actual machine evaluation.
[0065]
[Example 2]
As shown in Table 1, MgO 20.0 mol%, SrO 0.5 mol%, Fe₂O_Three79.5 mol% was pulverized with a wet ball mill for 7 hours to make the average particle size 3 μm or less. Appropriate amounts of dispersant and antifoaming agent are added to this slurry, and 1.1% by weight of PVA is added as a binder and sintering aid in terms of carbon atomic weight, and then granulated and dried with a spray dryer. The main calcination was performed under an inert atmosphere condition (oxygen concentration of 0.05 vol% or less) at a temperature of 1210 ° C. for 4 hours. Then, it was crushed and further classified to obtain a ferromagnetic material powder having an average particle size of about 50 μm.
[0066]
Using this ferromagnetic material powder, a carrier for an electrophotographic developer and a developer were prepared in the same manner as in Example 1. The physical properties and image characteristics of the ferromagnetic material powder, the carrier for electrophotographic developer, and the developer were evaluated, and the results are shown in Table 2.
[0067]
Example 3
As shown in Table 1, MgO 15.0 mol%, CaO 1.0 mol%, SrO 0.5 mol%, Fe₂O_ThreeWas obtained in the same manner as in Example 1 except that 83.5 mol% was used.
[0068]
Using this ferromagnetic material powder, a carrier for an electrophotographic developer and a developer were prepared in the same manner as in Example 1. The physical properties and image characteristics of the ferromagnetic material powder, the carrier for electrophotographic developer, and the developer were evaluated, and the results are shown in Table 2.
[0069]
Example 4
As shown in Table 1, MgO is 5.0 mol%, SrO is 0.5 mol%, Fe₂O_ThreeWas used in the same manner as in Example 2 except that 94.5 mol% was used.
[0070]
Using this ferromagnetic material powder, a carrier for an electrophotographic developer and a developer were prepared in the same manner as in Example 1. The physical properties and image characteristics of the ferromagnetic material powder, the carrier for electrophotographic developer, and the developer were evaluated, and the results are shown in Table 2.
[0071]
Example 5
As shown in Table 1, 49.5 mol% MgO, 0.5 mol% SrO, Fe₂O_ThreeA ferromagnetic material powder was obtained in the same manner as in Example 1 except that 50.0 mol% was used and the surface oxidation treatment temperature was set to 750 ° C.
[0072]
Using this ferromagnetic material powder, a carrier for an electrophotographic developer and a developer were prepared in the same manner as in Example 1. The physical properties and image characteristics of the ferromagnetic material powder, the carrier for electrophotographic developer, and the developer were evaluated, and the results are shown in Table 2.
[0073]
Example 6
As shown in Table 1, MgO 20.0 mol%, SrO 0.1 mol%, Fe₂O_ThreeWas obtained in the same manner as in Example 2 except that 79.9 mol% was used.
[0074]
Using this ferromagnetic material powder, a carrier for an electrophotographic developer and a developer were prepared in the same manner as in Example 1. The physical properties and image characteristics of the ferromagnetic material powder, the carrier for electrophotographic developer, and the developer were evaluated, and the results are shown in Table 2.
[0075]
[Comparative Example 1]
As shown in Table 1, MgO is 2.5 mol%, SrO is 0.5 mol%, Fe₂O_ThreeWas obtained in the same manner as in Example 2 except that 97.0 mol% was used.
[0076]
Using this ferromagnetic material powder, a carrier for an electrophotographic developer and a developer were prepared in the same manner as in Example 1. The physical properties and image characteristics of the ferromagnetic material powder, the carrier for electrophotographic developer, and the developer were evaluated, and the results are shown in Table 2.
[0077]
[Comparative Example 2]
As shown in Table 1, ferromagnetic material powder was obtained in the same manner as in Example 5 except that the surface oxidation treatment temperature was changed to 1000 ° C.
[0078]
Using this ferromagnetic material powder, a carrier for an electrophotographic developer and a developer were prepared in the same manner as in Example 1. The physical properties and image characteristics of the ferromagnetic material powder, the carrier for electrophotographic developer, and the developer were evaluated, and the results are shown in Table 2.
[0079]
[Comparative Example 3]
As shown in Table 1, 20.0 mol% MgO, Fe₂O_ThreeA ferromagnetic material powder was obtained in the same manner as in Example 2 except that 80.0 mol% was used.
[0080]
Using this ferromagnetic material powder, a carrier for an electrophotographic developer and a developer were prepared in the same manner as in Example 1. The physical properties and image characteristics of the ferromagnetic material powder, the carrier for electrophotographic developer, and the developer were evaluated, and the results are shown in Table 2.
[0081]
[Comparative Example 4]
As shown in Table 1, Li₂10.0 mol% O, Fe₂O_ThreeWas obtained in the same manner as in Example 2 except that 90.0 mol% was used and the firing temperature was 1250 ° C.
[0082]
Using this ferromagnetic material powder, a carrier for an electrophotographic developer and a developer were prepared in the same manner as in Example 1. The physical properties and image characteristics of the ferromagnetic material powder, the carrier for electrophotographic developer, and the developer were evaluated, and the results are shown in Table 2.
[0083]
[Comparative Example 5]
As shown in Table 1, Fe₂O_ThreeFerromagnetic material powder (magnetite powder) was obtained in the same manner as in Example 2 except that only the raw material was used and the firing temperature was 1300 ° C.
[0084]
Using this magnetite powder, a carrier for an electrophotographic developer and a developer were prepared in the same manner as in Example 1. The physical properties and image characteristics of the ferromagnetic material powder, the carrier for electrophotographic developer, and the developer were evaluated, and the results are shown in Table 2.
[0085]
[Comparative Example 6]
As shown in Table 1, Li₂16.7 mol% O, Fe₂O_ThreeA ferromagnetic material powder was obtained in the same manner as in Example 2 except that 83.3 mol% of the stoichiometric composition was used and baking was performed at 1250 ° C. in the air.
[0086]
A carrier for an electrophotographic developer and a developer were prepared in the same manner as in Example 1 using this ferromagnetic material powder. The physical properties and image characteristics of the ferromagnetic material powder, the carrier for electrophotographic developer, and the developer were evaluated, and the results are shown in Table 2.
[0087]
[Table 1]

[0088]
[Table 2]

[0089]
  From the results in Table 2, Examples 1 to 1 using the ferromagnetic material powder of the present invention as a core material were used.3 andFor the carrier No. 6, evaluation of halftone white streaks, which are image evaluation items of image density, carrier adhesion amount and leak phenomenon, and environmental dependency of the charge amount are good in the actual machine evaluation. That is, the ratio of divalent iron to total iron is10.0-30.0By using the ferromagnetic material powder in the above, it is possible to suppress the variation in magnetization between the particles and to make the resistance within a desired range.
[0090]
In Comparative Examples 1 and 2 in which the ratio of the divalent iron to the total iron is outside the range of 1.0 to 32.0, carrier adhesion and a leak phenomenon occur, and both cannot be satisfied.
[0091]
Further, in Comparative Example 3 in which the magnetoplumbite type ferrite is not contained in the ferrite phase, the variation in magnetization between particles is large, and carrier adhesion cannot be satisfied.
[0092]
Comparative Example 4 is a carrier in which a magnetite phase is present after firing by blending a larger amount of hematite than the stoichiometric ratio, but since it does not contain a magnetoplumbite type ferrite type, carrier adhesion is satisfactory. In addition, since the core material resistance is relatively low, a leak phenomenon is also observed. Further, since lithium, which is an alkali metal, is contained, the environmental difference in charge amount is large.
[0093]
The comparative example 5 mentioned as an example of a prior art is a magnetite carrier. Since the core material resistance is low, a leak phenomenon occurs, and carrier adhesion due to the resistance also occurs.
[0094]
Comparative Example 6 cited as an example of the prior art is a ferrite single phase in which no magnetite phase is generated due to the stoichiometric composition. The carrier adhesion and leakage phenomenon are close to practically usable levels, but the image density is not obtained and is not satisfactory for comprehensive evaluation. Further, since lithium is contained in the same manner as described above, the environmental difference in charge amount is also large.
[0095]
In FIG. 1, the relationship between the applied voltage of Examples 1-2 and Comparative Examples 1-2 and 5-6 and a core material resistance value is shown.
[0096]
【The invention's effect】
According to the ferromagnetic material powder of the present invention, in the composite of the ferrite phase containing the magnetite phase and the magnetoplumbite type ferrite, the ratio of divalent iron to total iron is controlled within a desired range, There is little variation in magnetization between particles, and the resistance can be within a desired range. Therefore, the electrophotographic carrier and developer using the ferromagnetic material powder of the present invention can obtain a high-quality image with suppressed carrier adhesion and no leakage phenomenon, and has high durability and surroundings. Excellent environmental stability.
[0097]
Further, according to the method for producing a ferromagnetic material powder of the present invention, the magnetite phase and the ferrite phase are uniformly mixed, and the ratio of divalent iron to the total iron can be within a predetermined range. The ferromagnetic material powder can be manufactured stably and inexpensively.
[Brief description of the drawings]
FIG. 1 is a graph showing a relationship between an applied voltage and a core material resistance value.

Claims (14)

In the magnetic oxide magnetite phase and a ferrite phase are mixed, and the ratio of divalent iron to total iron is 10.0 to 30.0, and contains a magnetoplumbite ferrite in the ferrite phase, the magneto ferromagnetic materials powder content of ferrite is characterized in that it is a 0.05~5.0mol%.   The ferromagnetic material powder according to claim 1, wherein a ratio of scattered magnetization to main body magnetization is 0.8 or more.   The ferromagnetic material powder according to claim 1 or 2, wherein the ferrite phase is a composite of magnetoplumbite type ferrite and spinel type ferrite.   The ferromagnetic material powder according to claim 1, 2 or 3, wherein the ferrite phase contains a Group 2 element in the periodic table.   The ferromagnetic material powder according to any one of claims 1 to 4, wherein the magnetoplumbite type ferrite contains Sr and / or Ba.   The ferromagnetic material powder according to claim 1, which has a saturation magnetization of 20 to 80 emu / g.   The ferromagnetic material powder according to any one of claims 1 to 6, having an average particle diameter of 20 to 100 µm. The ferromagnetic material powder according to claim 1, wherein the resistance is 1.0 × 10 ^{7 to} 1.0 × 10 ¹¹ Ω. Surface oxidation treatment is performed, the ratio of the divalent iron to the total iron is 10.0 to 28.0, and the resistance is 1.0 × 10 ^{8 to} 1.0 × 10 ¹¹ Ω. The ferromagnetic material powder according to any one of 1 to 8.   A carrier for an electrophotographic developer, wherein the ferromagnetic material powder according to any one of claims 1 to 9 is used as a core, and the surface thereof is coated with a resin.   The carrier for an electrophotographic developer according to claim 10, wherein the resin coating amount is 0.05 to 10% by weight.   A material containing carbon atoms is added to the raw material mixture containing hematite and other metal oxides in an amount of 0.1 to 3% by weight in terms of carbon atoms, and the mixture is fired at 1100 to 1400 ° C. in an inert atmosphere. A method for producing a carrier for an electrophotographic developer, wherein the surface of the ferromagnetic material powder according to any one of claims 1 to 9 is coated with a resin.   After adding 0.1 to 3% by weight of a carbon atom-containing substance in a raw material mixture containing hematite and other metal oxides in terms of carbon atoms and firing at 1100 to 1400 ° C. in an inert atmosphere The surface of the ferromagnetic material powder according to any one of claims 1 to 9, which is obtained by subjecting the surface to an oxidation treatment in the atmosphere or in an atmosphere in which the oxygen concentration is controlled, is characterized in that a resin is coated. A method for producing a carrier for an electrophotographic developer.   An electrophotographic developer comprising the carrier according to claim 10 or 11 and a toner.

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