JP6650300B2 - Carrier core material - Google Patents

Description

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

  2. Description of the Related Art In an image forming apparatus such as a facsimile, a printer, and a copying machine using an electrophotographic method, two-component development in which a so-called coating carrier in which the surface of a carrier core material composed of ferrite particles is coated with an insulating resin and a toner is mixed. The electrostatic latent image formed on the photoreceptor surface is visualized by the agent.

  The carrier core material used here is required to have electric characteristics and magnetic characteristics. Specifically, high resistance and high magnetic force are required. When the resistance of the carrier core material is low, the charge imparting property to the toner is reduced, and so-called fog in which the toner adheres to the non-image portion is easily generated. When the magnetic force of the carrier core material is low, the carrier is weakly attracted to the developing roller, and carrier scattering is likely to occur.

  Therefore, for example, Patent Literature 1 proposes a ferrite carrier core material in which the magnetization, the BET specific surface area, and the average particle size are in a certain range, and the number distribution of perimeter / envelope is in a specific range. Prior Document 2 proposes a porous ferrite core material containing fixed amounts of Mg, Ti, and Fe and having a specific range of a pore volume, a peak pore diameter, and magnetic properties.

JP 2012-181398 A JP 2011-112960 A

  However, the resistance and magnetic force of the carrier core material cannot be said to be sufficient in any of the proposed techniques, and further improvement is desired.

  Accordingly, an object of the present invention is to provide a carrier core material having higher resistance and higher magnetic force.

  Another object of the present invention is to provide a carrier for an electrophotographic developer and an electrophotographic developer capable of stably forming an image of good image quality without causing problems such as carrier scattering and fogging. is there.

The carrier core material according to the present invention that achieves the above object is a carrier core material composed of ferrite particles containing Ti, and has a coercive force Hc (10 ³ / 4π ·) against residual magnetization σr (Am ² / kg). (A / m) is not less than 11.0 and not more than 13.0.

  Here, the content of Ti is preferably in a range from 0.6% by mass to 1.2% by mass.

  Preferably, the ferrite particles further contain at least one element of Mn and Mg.

  Further, it is preferable that the ferrite particles further contain at least one element of Ca, Sr, and Ba.

  Further, according to the present invention, there is provided an electrophotographic developing carrier, wherein the surface of the carrier core material described in any of the above is coated with a resin.

  Further, according to the present invention, there is provided an electrophotographic developer including the carrier for electrophotographic development and a toner.

  According to the carrier core material of the present invention, desired resistance and magnetic force can be obtained, and problems such as carrier scattering and fogging are suppressed.

  Further, according to the electrophotographic developing carrier and the electrophotographic developing agent of the present invention, it is possible to stably form an image of good image quality without causing troubles such as carrier scattering and fogging even during long-term use. .

FIG. 1 is a schematic diagram illustrating an example of a developing device using an electrophotographic developer according to the present invention.

  The present inventors have intensively studied whether the carrier core material made of ferrite particles has a desired magnetic force and high chargeability, and controls the domain wall area in the ferrite particles to an appropriate range. It has been found that the resistance can be increased while suppressing a decrease in magnetic force.

  In addition, the domain wall in the ferrite particles can be effectively formed by adding a Ti component raw material having a perovskite crystal structure and firing in a high-temperature, high-oxidation atmosphere. The inventors of the present invention have found out that the present invention can be carried out depending on the amount of the Ti component material added, the sintering temperature and the oxygen concentration in the sintering step, and the present invention has been accomplished.

  That is, one of the major features of the present invention is that the ferrite particles constituting the carrier core material contain Ti. As described above, the addition of a Ti component raw material having a perovskite structure facilitates formation of a magnetic domain wall in ferrite particles, although the mechanism is not yet clear.

Examples of the Ti component raw material having a perovskite structure that can be used in the present invention include alkaline earth metal titanates such as CaTiO ₃ , SrTiO ₃ , BaTiO ₃ , and MgTiO ₃ . It is desirable that the amount of the Ti component material added be in a range where the Ti content in the carrier core material is 0.6% by mass or more and 1.2% by mass or less. If the Ti content of the carrier core material is less than 0.6% by mass, the domain wall area may be small and the carrier core material may not have high resistance. On the other hand, when the Ti content of the carrier core material exceeds 1.2% by mass, the domain wall area is increased, but the total amount of ferrite components in the domain wall is reduced, and the charge supply amount to the toner may be reduced.

In the present invention, the ratio Hc / σr of the coercive force Hc (10 ³ / 4πA / m) to the residual magnetization σr (Am ² / kg) is used as an index of the domain wall area in the ferrite particles. Another major feature of the present invention is that Hc / σr is 11.0 or more and 13.0 or less. If the ratio Hc / σr is less than 11.0, the domain wall area in the ferrite particles is not sufficient, the resistance of the carrier core material cannot be increased, and the charge imparting property to the toner cannot be enhanced. On the other hand, if the ratio Hc / σr exceeds 13.0, the number of magnetic domain walls becomes too large, and the amount of ferrite in the magnetic domain walls becomes small, so that the amount of charge supplied to the toner decreases, and the toner chargeability decreases.

The residual magnetization σr is preferably in the range of 0.4 to 0.6 (Am ² / kg). Further, the holding force Hc is preferably in the range of 5.0 to 7.0 (10 ³ / 4πA / m).

There is no particular limitation on the composition of the ferrite particles in the present invention, for example, the general formula _{M X Fe 3-X O 4} ( where, M is Mg, Mn, Cu, Zn, a metal such as Ni, 0 <X <1) with Particles of the composition represented are mentioned. Further, it preferably contains at least one element of Ca, Sr, and Ba. Among these compositions, Mn ferrite particles containing Ti, Mg ferrite particles containing Ti, and MnMg ferrite particles containing Ti are preferably used.

  Although the particle size of the carrier core material of the present invention is not particularly limited, the volume average particle size is preferably in the range of 20 μm to 50 μm, and the particle size distribution is preferably sharp.

  Next, a method for producing ferrite particles constituting the carrier core material of the present invention will be described. The method for producing ferrite particles is not particularly limited, but the production method described below is preferred.

First, an Fe component raw material, an M component raw material, and a Ti component raw material are weighed to prepare a raw material mixed powder. Note that M is at least one metal element selected from divalent metal elements such as Mg, Mn, Cu, Zn, and Ni. If necessary, a Ca component raw material, a Sr component raw material, and a Ba component raw material are added. As the Fe component raw material, Fe ₂ O ₃ or the like is preferably used. As the M component raw material, Mn may be MnCO ₃ , Mn ₃ O ₄ or the like, and if it is Mg, MgO, Mg (OH) ₂ or MgCO ₃ may be suitably used. For Ca, CaO, Ca (OH) ₂ , CaCO _{3 and the} like are preferably used. In the case of Sr, SrCO ₃ , Sr (NO ₃ ) _{2 and the} like are preferably used. As described above, as the Ti component raw material, one having a perovskite crystal structure is used, and alkaline earth metal titanate such as CaTiO ₃ , SrTiO ₃ , BaTiO ₃ , and MgTiO ₃ is preferably used.

  Next, the prepared raw material mixed powder is calcined. The temperature of the pre-baking is preferably in the range of 750 ° C to 900 ° C. When the temperature is 750 ° C. or higher, ferrite formation is partially promoted by calcination, the amount of gas generated during calcination is small, and the reaction between solids is sufficiently advanced. On the other hand, a temperature of 900 ° C. or less is preferable because sintering by calcination is weak and the raw material can be sufficiently pulverized in a subsequent slurry pulverization step. The atmosphere during the preliminary firing is preferably an air atmosphere.

  Then, the calcined raw material is disintegrated and charged into a dispersion medium to produce a slurry. In addition, the raw material mixed powder may be charged into the dispersion medium without calcination to prepare a slurry. Water is suitable as the dispersion medium used in the present invention. A binder, a dispersant, and the like may be added to the dispersion medium, if necessary, in addition to the calcined raw material. As the binder, for example, polyvinyl alcohol can be suitably used. It is preferable that the amount of the binder is about 0.5% by mass to 2% by mass in the slurry. As the dispersant, for example, ammonium polycarboxylate and the like can be suitably used. It is preferable that the amount of the dispersing agent is adjusted so that the concentration in the slurry is about 0.5% by mass to 2% by mass. In addition, a lubricant, a sintering accelerator and the like may be blended. The solid concentration of the slurry is desirably in the range of 50% by mass to 90% by mass. More preferably, it is 60% by mass to 80% by mass. When the content is 60% by mass or more, pores in the particles are small in the granulated product, and insufficient sintering during firing can be prevented. On the other hand, when the content is 80% by mass or less, the amount of the binder particles is small, and the deterioration of the fluidity due to the particle shape can be prevented.

  Next, the slurry prepared as described above is wet-pulverized. For example, wet pulverization is performed for a predetermined time using a ball mill or a vibration mill. The volume average particle size of the pulverized raw material is preferably 10 μm or less, more preferably 5 μm or less. It is preferable that a medium having a predetermined particle diameter is included in a vibration mill or a ball mill. Examples of the material of the media include iron-based chromium steel, oxide-based zirconia, titania, and alumina. The form of the pulverizing step may be any of a continuous type and a batch type. The particle size of the pulverized material is adjusted according to the pulverizing time, the rotation speed, the material and the particle size of the medium used, and the like.

  Then, the pulverized slurry is granulated by spray drying. Specifically, the slurry is introduced into a spray drier such as a spray drier, and is sprayed into the atmosphere to granulate into a sphere. The ambient temperature during spray drying is preferably in the range of 100C to 300C. Thereby, a spherical granulated product having a particle size of 10 μm to 200 μm is obtained. In addition, it is desirable that the obtained granules have a sharp particle size distribution by removing coarse particles and fine powder using a vibration sieve or the like.

  Next, the granulated material is put into a furnace heated to a predetermined temperature and fired to generate ferrite particles. The firing temperature is preferably in the range of 1100 ° C. to 1300 ° C., which is higher than usual. If the firing temperature is lower than 1100 ° C., phase transformation hardly occurs and sintering hardly proceeds. Further, the appearance of domain walls may not be promoted. On the other hand, if the firing temperature exceeds 1300 ° C., excessive grains may be generated due to excessive sintering. The heating rate up to the firing temperature is preferably in the range of 200 ° C./h to 500 ° C./h.

  In addition, the oxygen concentration in the firing step is set higher than usual. By increasing the oxygen concentration in the firing step, the appearance of domain walls is promoted, and the resistance of the particles is increased. Specifically, the oxygen concentration is preferably in the range of 6% to 15%. Thereby, the appearance of the magnetic domain wall in the particles is promoted in combination with the mixing of the Ti component raw material having the perovskite structure.

  The ferrite particles thus obtained are pulverized if necessary. Specifically, for example, the fired product is pulverized by a hammer mill or the like. The form of the pulverizing step may be any of a continuous type and a batch type. Then, if necessary, classification may be performed to adjust the particle diameter to a predetermined range. As the classification method, a conventionally known method such as air classification or sieve classification can be used. After the primary classification by an air classifier, the particle size may be adjusted to a predetermined range by a vibration sieve or an ultrasonic sieve. Further, after the classification step, the nonmagnetic particles may be removed by a magnetic field separator. The volume average particle diameter of the ferrite particles is preferably in the range of 20 μm to 50 μm.

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

  The ferrite particles produced as described above are used as the carrier core material of the present invention. Then, in order to obtain a desired charging property or the like, the outer periphery of the carrier core material is coated with a resin to obtain a carrier for electrophotographic development.

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

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

  As a method for coating the carrier core material with a resin, for example, a spray drying method, a fluidized bed method, a spray drying method using a fluidized bed, an immersion method, and the like can be used. Among them, the fluidized bed method is particularly preferred in that the coating can be performed efficiently with a small amount of resin. The resin coating amount can be adjusted by, for example, the amount of the resin solution to be sprayed or the spraying time in the case of the fluidized bed method.

  The volume average particle size of the carrier is preferably in the range of 10 μm to 200 μm, particularly preferably in the range of 20 μm to 50 μm.

  The electrophotographic developer according to the present invention is obtained by mixing the carrier and the toner prepared as described above. The mixing ratio of the carrier and the toner is not particularly limited, and may be appropriately determined based on the developing conditions of the developing device used. Generally, the toner concentration in the developer is preferably in the range of 1% by mass to 15% by mass. If the toner concentration is less than 1% by mass, the image density becomes too low, while if the toner concentration exceeds 15% by mass, the toner scatters in the developing device, and the toner adheres to the inside of the apparatus and the background portion such as transfer paper. This is because there is a possibility that a malfunction may occur. A more preferred toner concentration is in the range of 3% by mass to 10% by mass.

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

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

  If necessary, a modifier may be added to the toner surface. Examples of the modifier include silica, alumina, zinc oxide, titanium oxide, magnesium oxide, polymethyl methacrylate, and the like. One or more of these can be used in combination.

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

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

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

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

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

Developer then on the developing roller 3 is conveyed into the apparatus by the conveyor pole S _1, and peeled from the developing roller 3 by the peeling electrode N _2, in the apparatus is recirculated conveyed by the screw 1 and 2, subjected to developing Mixed with undeveloped developer. In the developer using the carrier core material of the present invention, peeling from the developing roller 3 by peeling the electrode N ₂ it can be smoothly performed. Then the scooping pole N _3, new developer is supplied from the screw 1 to the developing roller 3. This prevents image density unevenness. Further, the developer by the conveyance pole S ₁ and the developing magnetic pole N ₁ is firmly adsorbed to carrier scattering to the developing roller 3 can be suppressed.

  In the embodiment shown in FIG. 1, the developing roller 3 has five magnetic poles. However, in order to further increase the amount of movement of the developer in the developing area and to further improve the pumping property and the like. Of course, the number of magnetic poles may be increased to eight, ten, or twelve.

Reference Example 1
A carrier core material was produced as follows. 17.04 kg of Fe ₂ O ₃ (average particle size: 0.3 μm) as a raw material, 6.51 kg of Mn ₃ O ₄ (average particle size: 0.5 μm), 0.86 kg of MgO (average particle size: 0.6 μm) 0.39 kg of MgTiO ₃ (perovskite structure, average particle size: 1.5 μm) was dispersed in 6.2 kg of pure water, and 0.6 wt% of an ammonium polycarboxylate-based dispersant was added as a dispersant to form a mixture. . The solid content concentration of this mixture was 80% by weight. This mixture was pulverized by a wet ball mill (media diameter: 2 mm) to obtain a mixed slurry.

  This mixed slurry was sprayed into hot air of about 130 ° C. by a spray dryer to obtain a dried granulated product having a particle size of 10 to 75 μm. Coarse particles were separated from the granulated material using a sieve mesh having a mesh of 54 μm, and fine particles were separated using a sieve mesh having a mesh of 33 μm.

  The granulated product was put into an electric furnace and heated to 1200 ° C. over 5 hours. After that, baking was performed by holding at 1200 ° C. for 4.5 hours. Then, it was cooled to 500 ° C. at a cooling rate of 2 ° C./min. A gas mixture of oxygen and nitrogen was supplied into the furnace so that the oxygen concentration in the electric furnace was 10%.

  The obtained fired product was pulverized with a hammer mill and classified using a vibration sieve to obtain a fired product having a volume average particle diameter (average particle diameter) of 35.5 μm.

  Next, the obtained fired product was kept at 450 ° C. for 1.5 hours in an air atmosphere to perform an oxidation treatment (resistance increasing treatment) to obtain a carrier core material.

  The composition, magnetic properties, charging properties and the like of the obtained carrier core material were measured by the methods described below. Table 2 shows the measurement results.

  Next, a carrier was prepared by coating the surface of the carrier core material thus obtained with a resin. Specifically, a coating solution was prepared by dissolving 450 parts by weight of a silicone resin and 9 parts by weight of (2-aminoethyl) aminopropyltrimethoxysilane in 450 parts by weight of toluene as a solvent. The coating solution was applied to 50,000 parts by weight of a carrier core material using a fluidized bed type coating apparatus, and heated in an electric furnace at a temperature of 300 ° C. to obtain a carrier. Hereinafter, a carrier was obtained in the same manner as in the comparative example.

  The obtained carrier and a toner having a volume average particle diameter of about 5.0 μm were mixed for a predetermined time using a pot mill to obtain a two-component electrophotographic developer. In this case, the carrier and the toner were adjusted so that the weight of the toner / (the weight of the toner and the carrier) = 5/100. Hereinafter, a developer was obtained in the same manner for all the comparative examples. The obtained developer was evaluated in an actual machine described later. Table 2 shows the evaluation results.

( Example 1 )
16.92 kg of Fe ₂ O ₃ (average particle size: 0.3 μm), 6.47 kg of Mn ₃ O ₄ (average particle size: 0.4 μm), 0.85 kg of MgO (average particle size: 0.6 μm) as raw materials, A carrier core material having an average particle size of 35.2 μm was prepared in the same manner as in Reference Example 1 except that 0.55 kg of CaTiO ₃ (perovskite structure, average particle size: 1.5 μm) was used.

( Reference Example 2 )
16.76 kg of Fe ₂ O ₃ (average particle size: 0.3 μm), 6.40 kg of Mn ₃ O ₄ (average particle size: 0.4 μm), 0.85 kg of MgO (average particle size: 0.6 μm) as raw materials, A carrier core material having an average particle size of 35.1 μm was prepared in the same manner as in Reference Example 1, except that 0.79 kg of SrTiO ₃ (perovskite structure, average particle size: 1.5 μm) was used.

( Example 2 )
16.34 kg of Fe ₂ O ₃ (average particle size: 0.3 μm), 6.24 kg of Mn ₃ O ₄ (average particle size: 0.4 μm), 0.82 kg of MgO (average particle size: 0.6 μm) as raw materials, A carrier core material having an average particle size of 33.4 μm was prepared in the same manner as in Reference Example 1 except that 1.39 kg of BaTiO ₃ (perovskite structure, average particle size: 1.8 μm) was used.

(Comparative Example 1)
A carrier core material having an average particle size of 34.4 μm was prepared in the same manner as in Reference Example 1 except that MgTiO ₃ was not added.

(Comparative Example 2)
15.32 kg of Fe ₂ O ₃ (average particle size: 0.3 μm), 5.85 kg of Mn ₃ O ₄ (average particle size: 0.4 μm), 0.77 kg of MgO (average particle size: 0.6 μm) as raw materials, Using 2.85 kg of SrTiO ₃ (perovskite structure, average particle size: 1.5 μm), a carrier core material having an average particle size of 35.7 μm was prepared in the same manner as in Reference Example 1 except that the firing temperature was 900 ° C.

(Comparative Example 3)
17.14 kg of Fe ₂ O ₃ (average particle size: 0.3 μm), 6.55 kg of Mn ₃ O ₄ (average particle size: 0.4 μm), 0.87 kg of MgO (average particle size: 0.6 μm) as raw materials, A carrier core material having an average particle size of 33.7 μm was prepared in the same manner as in Reference Example 1, except that 0.25 kg of TiO ₂ (rutile structure, average particle size: 0.4 μm) was used.

(Comparative Example 4)
17.08 kg of Fe ₂ O ₃ (average particle size: 0.3 μm), 6.53 kg of Mn ₃ O ₄ (average particle size: 0.4 μm), 0.86 kg of MgO (average particle size: 0.6 μm) as raw materials, A carrier core material having an average particle size of 34.3 μm was prepared in the same manner as in Reference Example 1 except that 0.33 kg of TiO ₂ (rutile structure, average particle size: 0.4 μm) was used.

(Comparative Example 5)
16.96 kg of Fe ₂ O ₃ (average particle size: 0.3 μm), 6.48 kg of Mn ₃ O ₄ (average particle size: 0.4 μm), 0.86 kg of MgO (average particle size: 0.6 μm) as raw materials, A carrier core material having an average particle size of 35.2 μm was prepared in the same manner as in Reference Example 1 except that 0.50 kg of TiO ₂ (rutile structure, average particle size: 0.4 μm) was used.

(Comparative Example 6)
A carrier core material having an average particle diameter of 35.1 μm was prepared in the same manner as in Comparative Example 2 except that the firing temperature in the firing step was 1200 ° C. and the oxygen concentration in the electric furnace was 0.1%.

(Composition analysis)
The compositions (% by mass) of the carrier core materials of Examples and Comparative Examples were calculated by the following methods.
(Analysis of Fe)
A carrier core material containing an iron element was weighed and dissolved in a mixed acid aqueous solution of hydrochloric acid and nitric acid. After evaporating the solution to dryness, sulfuric acid aqueous solution is added and redissolved to volatilize excess hydrochloric acid and nitric acid. Solid Al is added to this solution to reduce all Fe ³⁺ in the solution to Fe ²⁺ . Subsequently, the amount of Fe ²⁺ ions in this solution was quantitatively analyzed by potentiometric titration with a potassium permanganate solution to determine the titer of Fe (Fe ²⁺ ).
(Analysis of Mn)
The Mn content of the carrier core material was quantitatively analyzed in accordance with the ferromanganese analysis method (potentiometric titration method) described in JIS G1311-1987. The Mn content of the carrier core material described in the present invention is the Mn content obtained by quantitative analysis by this ferromanganese analysis method (potentiometric titration method).
(Analysis of Mg)
The Mg content of the carrier core material was analyzed by the following method. The carrier core material according to the present invention was dissolved in an acid solution, and quantitative analysis was performed by ICP. The Mg content of the carrier core material described in the present invention is the Mg content obtained by the quantitative analysis by this ICP.
(Analysis of Ca)
The Ca content of the carrier core material was determined by quantitative analysis by ICP as in the analysis of Mg.
(Sr analysis)
The Sr content of the carrier core material was determined by ICP quantitative analysis in the same manner as Mg analysis.
(Analysis of Ba)
The Ba content of the carrier core material was determined by quantitative analysis using ICP as in the analysis of Mg.
(Analysis of Ti)
The Ti content of the carrier core was determined by quantitative analysis by ICP as in the analysis of Mg.

(Measurement of magnetic force)
Using a vibrating sample magnetometer (VSM) ("VSM-P7" manufactured by Toei Industry Co., Ltd.) exclusively for room temperature, an external magnetic field is continuously applied for one cycle in a range of 0 to 79.58 × 10 ⁴ A / m (10000 Oersted). And the magnetization σ _1k (Am ² / kg) in a magnetic field of 79.58 × 10 ³ A / m (1000 Oe) was measured, respectively.

(Charge amount)
9.5 g of carrier core material and 0.5 g of commercially available full-color toner are placed in a 100 ml glass bottle with a stopper, and left to stand at 25 ° C. and 50% relative humidity for 12 hours to adjust humidity. The conditioned carrier core material and toner are shaken with a shaker for 15 minutes to mix. The shaking was performed at 126 times / min at an angle of 60 ° using a NEW-YS model manufactured by Yayoi Co., Ltd. 300 mg of the electrophotographic developer after 15 minutes of stirring was collected, EA02 manufactured by U-Tech and an automatic suction device were used, the suction pressure was High, the separation mesh was 795 mesh made of SUS, and the toner collecting device was a filter capsule (U-Tech) EA010C), the charge amount after suction for 90 seconds was measured. The same sample was measured twice, and the average value was defined as the charge amount of the carrier core material. The charge amount of the carrier core material was calculated from the following equation. The measurement environment was a temperature of 25 ° C. and a relative humidity of 50%.
Charge amount (μC / g) = Measured charge (μC) / toner weight (where toner weight = weight after suction of filter capsule (g) −weight before suction of filter capsule (g))

(Actual machine evaluation)
The developing device having the structure shown in FIG. 1 (the peripheral speed of the developing roller Vs: 406 mm / sec, the peripheral speed of the photosensitive drum Vp: 205 mm / sec, the distance between the photosensitive drum and the developing roller: 0.3 mm) was manufactured. After the two-component developer was charged and image formation (printing rate 5%) was performed on 1000 sheets, carrier scattering and fog were evaluated according to the following procedures and criteria.

Carrier scattering 1000 white sheets were printed, and the number of black spots on the 1000th sheet was visually determined. The evaluation criteria are as follows.
“○”: When the number of discovered black spots is 1 to 5 “×”: When the number of discovered black spots is 11 or more

Fog The image density of the non-image forming portion of the 1,000th sheet was measured at 10 points, the density measured for unused white paper was subtracted from the average value, and this value was used to evaluate the following criteria. The image density was measured using a reflection densitometer “TC-6D” (manufactured by Tokyo Denshoku Co., Ltd.).
"O": Density difference is less than 0.006 "X": Density difference is 0.006 or more

In the carrier core materials of Examples 1 and 2 and Reference Examples 1 and 2 in which a Ti component raw material having a perovskite structure was used, the firing temperature was increased to 1200 ° C., and the oxygen concentration in the electric furnace was increased to 10%, It is considered that Hc / [sigma] r as an index of the area has a desired domain wall area of 11.2 to 12.1, the charge amount was as high as 38 to 42 [mu] C / g, and no image fogging occurred. Also, the magnetization σ _1k was 56 Am ² / kg or more, and carrier scattering did not occur.

  On the other hand, in the carrier core material of Comparative Example 1 in which the Ti component raw material was not blended, Hc / σr was as low as 10.8 and did not have a desired domain wall area, and the charge amount was 35 μC / g. And image fog was low.

In Comparative Example 2, a large amount of a Ti component raw material (SrTiO ₃ ) having a perovskite structure was added, and the firing temperature was lowered to 900 ° C., so that the obtained carrier core material had an excessively high Hc / σr of 13.7. The magnetization σ _1k was as low as 37 Am ² / kg, and carrier scattering occurred. Further, the charge amount was as low as 25 μC / g, and image fogging occurred.

In Comparative Examples 3, 4, and 5, the compounding amount of the rutile structure Ti component raw material (TiO ₂ ) was changed, and the carrier core materials obtained all had a low Hc / σr of 10.8 or less. The charge amount was as low as 35 μC / g or less, and image fogging occurred. In the carrier core material of Comparative Example 5, the magnetization σ _1k was as low as 54 Am ² / kg, and carrier scattering occurred.

In Comparative Example 6, a large amount of Ti component raw material (SrTiO ₃ ) having a perovskite structure was added, and the oxygen concentration in the electric furnace in the firing step was reduced to 0.1%, so that Hc / σr of the obtained carrier core material was reduced. The charge amount was as low as 9.1, and the image was fogged.

  According to the carrier core material of the present invention, desired resistance and magnetic force can be obtained, and problems such as carrier scattering and fogging are suppressed, which is useful.

3 developing roller 5 photosensitive drum

Claims (4)

A carrier core material composed of ferrite particles containing Ti,
The content of Ti is in the range of 0.6% by mass or more and 1.2% by mass or less;
The ferrite particles contain at least one element of Ca and Ba,
A carrier core material, wherein a ratio Hc / σr of a coercive force Hc (10 ³ / 4πA / m) to a residual magnetization σr (Am ² / kg) is 11.0 or more and 13.0 or less.   The carrier core material according to claim 1, wherein the ferrite particles further contain at least one element of Mn and Mg. An electrophotographic developing carrier, wherein the surface of the carrier core material according to claim 1 or 2 is coated with a resin. An electrophotographic developer comprising the electrophotographic carrier according to claim 3 and a toner.