Carrier Core Material, Carrier for Electrostatic Photographic Development Using the Same, and Developer for Electrostatic Photography

Abstract

The average volume moment D[4,3] of bluntness measured by an injection-type image analysis particle size distribution meter for the carrier core material of the present invention is 65% or more and 80% or less, and the average volume moment D[4,3] of ISO roundness is 80% or more and 86% or less. Thus, development memory and carrier adhesion can be suppressed.

Description

Technical Field

[0001] The present invention relates to a carrier core material, an electrophotographic developer carrier using the same, and an electrophotographic developer. Background Art

[0002] For example, in image forming apparatuses such as facsimile machines, printers, and copiers using the electrophotographic method, toner is attached to an electrostatic latent image formed on the surface of a photoreceptor to form a visible image, and the visible image is transferred to paper or the like and then heated / pressed to be fixed. From the viewpoints of high image quality and colorization, a so-called two-component developer containing a carrier and toner is widely used as a developer.

[0003] In a developing method using a two-component developer, the carrier and toner are stirred and mixed in a developing device, and the toner is charged to a specified amount by friction. Then, the developer is supplied to a rotating developing roller, a magnetic brush is formed on the developing roller, and the toner is electrophoretically moved toward the photoreceptor by the magnetic brush to form a visible image of the electrostatic latent image on the photoreceptor. The carrier remaining after the toner has moved stays on the developing roller and is mixed with the toner again in the developing device. Therefore, as characteristics of the carrier, magnetic characteristics for forming a magnetic brush, charging characteristics for imparting a desired charge to the toner, and durability for repeated use are required.

[0004] As such a carrier, a carrier obtained by covering the surface of magnetic particles such as magnetite and various ferrites with a resin is usually used. For the magnetic particles as the carrier core material, good magnetic characteristics are required, and good triboelectric charging characteristics with respect to the toner are also required. As carrier core materials satisfying such characteristics, core materials having various shapes have been proposed.

[0005] For example, Patent Document 1 proposes an electrophotographic ferrite carrier core material containing Sr (strontium), having a specific shape, and having non-magnetic fine particles attached to the particle surface and the inner surface of pores. In addition, Patent Document 2 proposes a carrier core material having irregularities and pores on the surface, and the ratio of the volume value of pores into which mercury is infiltrated to the volume value of pores from which mercury is leached, obtained by the mercury intrusion method, is in a specified range.

[0006] Prior Art Documents

[0007] Patent Documents

[0008] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2013-137456

[0009] Patent Document 2: Japanese Unexamined Patent Application Publication No. 2011-8199 Summary of the Invention

[0010] Problems to be Solved by the Invention

[0011] When a resin-coated carrier obtained by covering the surface of a carrier core material with a resin is mixed with toner to form a two-component developer, there is sometimes a problem called "development memory" where the image density decreases due to the influence of the image in the first lap of the developing roller. It is speculated that the cause of this development memory is that the resistance of the resin-coated carrier is high. As one of the countermeasures, it can be considered to make the surface of the carrier core material uneven so that a part of the carrier core material is exposed on the surface of the resin-coated carrier to reduce the resistance of the resin-coated carrier.

[0012] However, if the resistance of the resin-coated carrier becomes low, the following situation may occur: "carrier adhesion" where charges are injected into the resin-coated carrier in the developing area and the resin-coated carrier moves toward the photosensitive drum.

[0013] Therefore, an object of the present invention is to provide a carrier core material that can suppress development memory and also suppress carrier adhesion.

[0014] In addition, another object of the present invention is to provide an electrophotographic developing carrier and an electrophotographic developer that can stably form an image with good image quality even during long-term use.

[0015] Solutions for Solving the Problems

[0016] The carrier core material according to the present invention for achieving the above object is characterized in that the volume moment average value D[4,3] of the bluntness (O.Bluntness) measured by an injection type image analysis particle size distribution meter is 65% or more and 80% or less, and the volume moment average value D[4,3] of the ISO roundness (Roundness) is 80% or more and 86% or less.

[0017] It should be noted that the volume moment average values D[4,3] of the bluntness and ISO roundness in this specification are values measured using the following measuring device and measuring conditions.

[0018] Measuring device: "IF-3200" manufactured by JASCO Corporation, an injection type image analysis particle size distribution meter

[0019] Analysis software: PIA-Pro 14.18

[0020] Specimen preparation conditions: Disperse 0.07 g of the specimen in a screw tube bottle (capacity 9 cm 3 containing polyethylene glycol 400) and then conduct the measurement. 3 )

[0021] Measuring conditions: Telecentric zoom lens, magnification 2 times

[0022] Front lens, magnification 2 times

[0023] Calibration value 0.417μm / pixel

[0024] Spacer thickness 150μm

[0025] Sampling 20%

[0026] Analysis type Relative measurement

[0027] Measured quantity 0.95cm 3

[0028] Analysis Dark detection

[0029] Threshold 169 (Fills the hole.)

[0030] O-Roughness filter 0.5

[0031] Filter conditions during measurement:

[0032] ISO Area Diametere (Area diameter): Minimum 5, maximum 150, inner range

[0033] Analysis filter conditions:

[0034] ISO Area Diametere (Area diameter): Minimum 10, maximum 55, inner range

[0035] ISO Solidity (Hardness): Minimum 0.9, maximum 1, inner range

[0036] Bluntness: Index of the smoothness of the particle contour

[0037] Deviation of the radii of all inscribed circles in the particle image

[0038] ISO roundness: Index of the roundness of the particle

[0039] Calculation formula for ISO roundness:

[0040] (4×Pixcel Count) / (π×ISO Max distance (Maximum distance) 2 )

[0041] The aforementioned carrier core material is a carrier core material composed of ferrite particles. The composition of the ferrite particles contains MnO: 35 mol% or more and 55 mol% or less, Fe2O3: 45 mol% or more and 65 mol% or less, and a part of it is replaced with SrO: 0.1 mol% or more and 1.0 mol% or less, SnO: 0.1 mol% or more and 1.0 mol% or less.

[0042] In addition, in the aforementioned carrier core material, the saturation magnetization σS Preferably 75 Am 2 / kg or more and 88 Am 2 / kg or less.

[0043] In addition, in the foregoing carrier core material, the pore volume is preferably 0.01 cm 3 / g or less.

[0044] In addition, according to the present invention, there is provided a carrier for electrophotographic development, characterized in that the surface of the carrier core material described in any one of the foregoing is covered with a resin.

[0045] Furthermore, according to the present invention, there is provided a developer for electrophotography, which comprises the carrier for electrophotographic development and a toner described above.

[0046] Effects of the Invention

[0047] Even when used in a high-speed image forming apparatus, the carrier core material according to the present invention can suppress development memory and suppress carrier adhesion.

[0048] In addition, if a developer containing the carrier core material of the present invention is used, a good-quality image can be stably formed even during long-term use. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 is an overview diagram showing an example of a developing device obtained using the carrier of the present invention. DETAILED DESCRIPTION

[0050] The inventors of the present invention repeatedly conducted in-depth research to obtain a carrier core material capable of suppressing development memory and carrier adhesion, and as a result, found that: the roundness of the particles constituting the carrier core material and the smoothness of the particle surface (particle contour) have a significant impact on development memory and carrier adhesion, thereby completing the present invention. That is, the remarkable feature of the carrier core material of the present invention is that the volume moment average value D[4,3] of bluntness is 65% or more and 80% or less, and the volume moment average value D[4,3] of ISO roundness is 80% or more and 86% or less.

[0051] It should be noted that bluntness serves as an index of the smoothness of the particle contour, and the smoothest case is denoted as "100%", and the smaller it is than "100%", the rougher the particle contour. In addition, ISO roundness serves as an index of the roundness of the particles, and the spherical case is denoted as "100%", and the smaller it is than "100%", the more irregular the particle shape. And the volume moment average value D[4,3] reflects the diameter of most of the particles constituting the carrier core material, excluding the influence of combined particles formed by combining multiple particles, etc.

[0052] In the present invention, if the volume moment average value D[4,3] of bluntness is less than 65%, when the carrier core material is covered with resin to form a carrier, the exposure of the carrier core material on the carrier surface becomes excessive, and thus charge injection is likely to occur in the carrier, and carrier adhesion is likely to occur. On the other hand, if the volume moment average value D[4,3] of bluntness exceeds 80%, when the carrier core material is covered with resin to form a carrier, the exposure of the carrier core material on the carrier surface becomes less, and the back charge remaining in the carrier core material is difficult to be released, and image retention is likely to occur. The preferred range of the volume moment average value D[4,3] of bluntness is in the range of 70% or more and 75% or less.

[0053] In the present invention, if the volume moment average value D[4,3] of ISO roundness is less than 80%, the carrier is overly shaped and the fluidity cannot be ensured. On the other hand, if the volume moment average value D[4,3] of ISO roundness exceeds 86%, the degree of shape irregularity of the carrier decreases, it is not easy to triboelectrically charge with the toner, the chargeability of the toner in the developing machine deteriorates, and image retention is likely to occur.

[0054] The composition of the carrier core material of the present invention is not limited, and it is preferably formed of ferrite particles. When the carrier core material is composed of ferrite particles, the composition of the ferrite particles is represented by the composition formula M X Fe 3-X O4 (wherein, M is at least one metal element selected from the group consisting of Mg, Mn, Ca, Ti, Sr, Cu, Zn, Sn, Ni; 0 < X < 1). Among these, preferably: represented by the general formula (MnO) a (Fe2O3) b , a and b are respectively 35 mol% or more and 55 mol% or less, 45 mol% or more and 65 mol% or less, and a substance obtained by replacing a part of MnO with SrO by 0.1 mol% or more and 1.0 mol% or less and replacing it with SnO by 0.1 mol% or more and 1.0 mol% or less.

[0055] In addition, the saturation magnetization σ of the carrier core material described in the present invention S is preferably in the range of 75 Am 2 / kg or more and 88 Am 2 / kg or less. By making the saturation magnetization σ of the carrier core material S within this range, the occurrence of carrier adhesion in which the carrier moves to the photosensitive drum is effectively suppressed. The saturation magnetization σ of the carrier core material S is more preferably in the range of 80 Am 2 / kg or more and 85 Am 2 / kg or less. And, the magnetization σ of the carrier core material of the present invention when a magnetic field of 79.58 × 10 3 A / m (1000 Oe) is applied 1kPreferably 65Am 2 / kg or more and 72Am 2 / kg or less.

[0056] The pore volume in the carrier core material of the present invention is preferably 0.01 cm 3 / g or less. If the pore volume exceeds 0.01 cm 3 / g, the voids inside the particles become larger, and the magnetization of each particle of the carrier core material becomes smaller. Therefore, carrier adhesion is likely to occur.

[0057] The volume average particle diameter (hereinafter sometimes referred to as "average particle diameter") of the carrier core material of the present invention is preferably in the range of 25 μm or more and less than 50 μm, and more preferably in the range of 30 μm or more and 40 μm or less.

[0058] The manufacturing method of the carrier core material of the present invention is not particularly limited, and is preferably the manufacturing method described below. It should be noted that in this specification, "~" means including the numerical values before and after it as the lower limit value and the upper limit value.

[0059] When the carrier core material is formed of the ferrite particles having the above-described composition, it preferably contains a specified amount of Sn (tin) and Sr (strontium). By containing Sr, Sr ferrite is partially generated in the firing process, forming a lead ferrite garnet-type crystal structure, which easily promotes the uneven shape on the surface of the carrier core material and also easily promotes the formation of irregular shapes. And by containing Sr and Sn, even when the firing temperature is set to 1200 °C or higher, which is higher than in the past, spheroidization caused by decomposition / melting of the material components is suppressed, and the uneven shape on the particle surface and the degree of irregular shape of the particles are maintained.

[0060] First, weigh the Fe component raw material, M component raw material (including Sr component raw material, Sn component raw material, etc. as required). As the Fe component raw material, Fe2O3, etc. are preferably used. As the M component raw material, if it is Mg, MgO, Mg(OH)2, MgCO3 can be preferably used, if it is Mn, MnCO3, Mn3O4, etc. can be used, as the Ca component raw material, CaO, Ca(OH)2, CaCO3, etc. can be used, if it is Ti, TiO2 can be used, if it is Zr, ZrO2 can be used. In addition, as the Sn component raw material, SnO2, SnO can be used, and as the Sr component raw material, SrCO3, Sr(NO3)2, etc. are preferably used.

[0061] Next, the raw materials are put into a dispersion medium to prepare a slurry. As the dispersion medium used in the present invention, water is suitable. In the dispersion medium, in addition to the aforementioned pre-fired raw materials, a binder, a dispersant, etc. may be blended as needed. As the binder, for example, polyvinyl alcohol can be suitably used. As the blending amount of the binder, the concentration in the slurry is preferably set to about 0.1% by mass to 2% by mass. In addition, as the dispersant, for example, ammonium polycarboxylate can be suitably used. As the blending amount of the dispersant, the concentration in the slurry is preferably set to about 0.1% by mass to 2% by mass. Further, a reducing agent such as carbon black, a pH regulator such as ammonia, a lubricant, a sintering accelerator, etc. may also be blended. It is ideal that the solid content concentration of the slurry is in the range of 50% by mass to 90% by mass. More preferably, it is 60% by mass to 80% by mass. If it is 60% by mass or more, there are few fine pores inside the particles in the granulated product, and insufficient sintering during firing can be prevented.

[0062] It should be noted that the weighed raw materials can be mixed, pre-fired and deflaked, and then put into a dispersion medium to prepare a slurry. As the temperature of the pre-firing, the range of 750°C to 1000°C is preferred. If it is 750°C or more, partial ferrite formation based on pre-firing is promoted, the gas generation amount during firing is small, and the solid-state reaction proceeds sufficiently, so it is preferred. On the other hand, if it is 1000°C or less, the sintering based on pre-firing is weak, and the raw materials can be sufficiently pulverized in the subsequent slurry pulverization process, so it is preferred. In addition, as the atmosphere during pre-firing, an air atmosphere is preferred.

[0063] Next, the slurry prepared as described above is wet-pulverized. For example, a ball mill or a vibration mill is used for wet-pulverization for a specified time. The average particle size of the pulverized raw material is preferably 5 μm or less, more preferably 1 μm or less. The vibration mill and the ball mill can contain media with a specified particle size. As the material of the media, iron-based chromium steel, oxide-based zirconia, titanium dioxide, alumina, etc. can be listed. As the form of the pulverization process, it can be either a continuous type or an intermittent type. The particle size of the pulverized product is adjusted according to the pulverization time, the rotation speed, the material / particle size of the media used, etc.

[0064] And, the pulverized slurry is spray-dried to granulate. Specifically, the slurry is introduced into a spray dryer such as a spray drying machine and sprayed into the atmosphere to granulate into spherical shapes. The atmosphere temperature during spray drying is preferably in the range of 100°C to 300°C. Thereby, spherical granulated products with a particle size of 10 μm to 200 μm can be obtained. Next, if necessary, the obtained granulated products are classified using a vibrating screen to produce granulated products within a specified particle size range.

[0065] Next, the aforementioned granulated product is put into a furnace heated to a specified temperature and fired by a general method for synthesizing ferrite particles, thereby generating ferrite particles. As the firing temperature, a range of 1100°C to 1350°C is preferred. If the firing temperature is 1100°C or lower, phase transformation is less likely to occur and sintering is easy. In addition, if the firing temperature exceeds 1350°C, there may be over-sintering resulting in over-sized particles. As the heating rate up to the aforementioned firing temperature, a range of 250°C / h to 500°C / h is preferred. The holding time at the firing temperature is preferably 2 hours or more. The unevenness on the surface of the ferrite particles can also be adjusted using the oxygen concentration during the firing process. Specifically, the oxygen concentration is set to 0.05% to 10%. In addition, by making the oxygen concentration during cooling less than that during firing, adjustment of the oxidation state of the ferrite phase can be achieved. Specifically, the oxygen concentration is set to a range of 0.05% to 1.5%. The oxygen concentration during heating / sintering / cooling is preferably controlled within a range of 0.05% to 10%.

[0066] If necessary, the fired product obtained in this way is de-agglomerated. Specifically, the fired product is de-agglomerated using, for example, a hammer mill. The form of the de-agglomeration process can be either continuous or batch. In addition, after the de-agglomeration treatment, if necessary, in order to unify the particle size to a specified range, classification can be performed. As the classification method, known methods such as air classification and sieve classification can be used. In addition, after one-time classification using an air classifier, the particle size can be unified to a specified range using a vibrating sieve or an ultrasonic sieve. Furthermore, after the classification process, non-magnetic particles can be removed using a magnetic separator. As the particle size of the ferrite particles, a range of 25 μm or more and less than 50 μm is preferred.

[0067] Thereafter, if necessary, the classified ferrite particles can be heated in an oxidizing atmosphere to form an oxidation coating on the particle surface to achieve high resistance of the ferrite particles (high-resistance treatment). As the oxidizing atmosphere, either an air atmosphere or a mixed atmosphere of oxygen and nitrogen can be used. In addition, the heating temperature is preferably in the range of 200°C or more and 800°C or less, and more preferably in the range of 360°C or more and 550°C or less. The heating time is preferably in the range of 0.5 hours or more and 5 hours or less. It should be noted that from the perspective of homogenizing the surface and interior of the ferrite particles, a low heating temperature is ideal.

[0068] The ferrite particles produced by the above operations are used as the carrier core material of the present invention. And, in order to obtain desired charging properties, etc., the outer periphery of the carrier core material can be covered with resin to form a carrier for electrophotographic development.

[0069] As the resin for covering the surface of the carrier core material, known resins can be used, and examples include polyethylene, polypropylene, polyvinyl chloride, poly-4-methylpentene-1, polyvinylidene chloride, ABS (acrylonitrile-butadiene-styrene) resin, polystyrene, (meth)acrylic resin, polyvinyl alcohol resin, and thermoplastic elastomers such as polyvinyl chloride series, polyurethane series, polyester series, polyamide series, polybutadiene series, and fluoroorganosilicon resin.

[0070] In order to cover the surface of the carrier core material with resin, it is only necessary to apply a solution or dispersion of the resin to the carrier core material. As the solvent for the coating solution, 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; alcohol solvents such as ethanol, propanol, and butanol; cellosolve solvents such as ethyl cellosolve and butyl cellosolve; ester solvents such as ethyl acetate and butyl acetate; amide solvents such as dimethylformamide and dimethylacetamide, etc. can be used, and one or more of them can be used. The concentration of the resin component in the coating solution can usually be 0.001% by mass or more and 30% by mass or less, and particularly preferably in the range of 0.001% by mass or more and 2% by mass or less.

[0071] As a method for covering the carrier core material with resin, for example, a spray drying method, a fluidized bed method, a spray drying method using a fluidized bed, an impregnation method, etc. can be used. Among these, from the viewpoint of being able to effectively coat with a smaller amount of resin, the fluidized bed method is particularly preferred. Regarding the resin coating amount, for example, in the case of the fluidized bed method, it can be adjusted according to the amount of the blown resin solution and the blowing time.

[0072] The particle size of the carrier is usually preferably in the range of 25 μm or more and less than 50 μm in terms of volume average particle size, and particularly preferably in the range of 30 μm or more and 40 μm or less.

[0073] The electrophotographic developer of the present invention is formed by mixing the carrier produced as described above with a toner. The mixing ratio of the carrier and the toner is not particularly limited and can be appropriately determined according to the developing conditions of the developing device used. Generally, the toner concentration in the developer is preferably in the range of 1% by mass or more and 15% by mass or less. This is because when the toner concentration is less than 1% by mass, the image density becomes too thin. On the other hand, when the toner concentration exceeds 15% by mass, the following adverse conditions may occur: toner scattering in the developing device, and toner adhering to the background parts such as the internal dirt of the machine and the transfer paper. The toner concentration is more preferably in the range of 3% by mass or more and 10% by mass or less.

[0074] As the toner, a toner manufactured by a conventionally well-known method such as a polymerization method, a pulverization classification method, a melt granulation method, a spray granulation method, etc. can be used. Specifically, a toner in which a binder resin having a thermoplastic resin as a main component contains a colorant, a release agent, a charge control agent, etc. can be preferably used.

[0075] The particle diameter of the toner is usually preferably in the range of 5 μm or more and 15 μm or less, more preferably in the range of 7 μm or more and 12 μm or less, in terms of the volume average particle diameter based on a Coulter counter.

[0076] If necessary, a modifier can be added to the toner surface. Examples of the modifier include silica, alumina, zinc oxide, titanium oxide, magnesium oxide, polymethyl methacrylate, etc. One of them can be used, or two or more of them can be used in combination.

[0077] The mixing of the carrier and the toner can be performed using a conventionally well-known mixing device. For example, a Henschel mixer, a V-type mixer, a drum agitator, a Hybridizer, etc. can be used.

[0078] The developing method using the developer of the present invention is not particularly limited, and a magnetic brush developing method is suitable. Figure 1 Fig. shows a schematic diagram showing an example of a developing device for performing magnetic brush development. Figure 1 The shown developing device includes: a freely rotatable developing roller 3 having a plurality of magnetic poles built therein; a restricting blade 6 for restricting the amount of the developer on the developing roller 3 to be transported to the developing portion; two screws 1 and 2 arranged in parallel with the horizontal direction and transporting the developer in opposite directions to each other; and a partition 4 formed between the two screws 1 and 2, at both ends of the two screws, the developer can move from one screw to the other screw, and the movement of the developer outside both ends is prevented.

[0079] In the two screws 1 and 2, spiral blades 13 and 23 are formed on the shaft portions 11 and 21 at the same inclination angle, and are rotated in the same direction by a driving mechanism (not shown), and the developer is transported in opposite directions to each other. And at both ends of the screws 1 and 2, the developer moves from one screw to the other screw. Thus, the developer containing the toner and the carrier is continuously circulated and agitated in the device.

[0080] On the other hand, the developing roller 3 has a fixed magnet having five magnetic poles, namely, a developing magnetic pole N1, a transporting magnetic pole S1, a peeling magnetic pole N2, a pumping magnetic pole N3, and a blade magnetic pole S2, arranged in sequence inside a metal cylindrical body having irregularities of several μm on the surface as a magnetic pole generating means. When the cylindrical body of the developing roller 3 rotates in the arrow direction, the developer is pumped up from the screw 1 to the developing roller 3 by the magnetic force of the pumping magnetic pole N3. The developer carried on the surface of the developing roller 3 is layer-restricted by the restricting blade 6 and then transported to the developing area.

[0081] In the developing area, a bias voltage obtained by superimposing an AC voltage on a DC voltage is applied from a transfer voltage power source 8 to a developing roller 3. The DC voltage component of the bias voltage is regarded as the potential between the background part potential and the image part potential on the surface of the photosensitive drum 5. In addition, the background part potential and the image part potential are regarded as the potential 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 kV to 5 kV, and the frequency is preferably in the range of 1 kHz to 10 kHz. In addition, the waveform of the bias voltage can be any one of a rectangular wave, a sine wave, a triangular wave, etc. Thereby, in the developing area, the toner and the carrier vibrate, and the toner adheres to the electrostatic latent image on the photosensitive drum 5 for development.

[0082] Thereafter, the developer on the developing roller 3 is conveyed into the apparatus by the conveying magnetic pole S1, peeled off from the developing roller 3 by the peeling electrode N2, circulated and conveyed again in the apparatus by the screws 1 and 2, and mixed and stirred with the developer not supplied for development. And, a new supply of developer is made from the screw 1 to the developing roller 3 by the pumping magnetic pole N3.

[0083] It should be noted that Figure 1 in the embodiment shown, there are 5 magnetic poles built in the developing roller 3, but in order to further increase the moving amount of the developer in the developing area or further improve the pumping property, etc., the number of magnetic poles can also be increased to 8 poles, 10 poles, or 12 poles.

[0084] Examples

[0085] (Example 1)

[0086] A carrier core material is produced by the following method. Fe2O3, SnO2, SrCO3, and Mn3O4 are dispersed in water at a ratio of 11.1 mol of Fe, 0.05 mol of Sn, 0.04 mol of Sr, and 4.4 mol of Mn, and 0.600 wt% of a polycarboxylic acid ammonium-based dispersant as a dispersant and 0.300 wt% of carbon black as a reducing agent are added. The solid content concentration of this mixture is 75 wt%.

[0087] This mixture is pulverized using a wet ball mill (medium diameter: 2 mm) to obtain a mixed slurry. This mixed slurry is sprayed in hot air at about 210 °C using a spray dryer to obtain a dried granulated product with a particle size of 10 to 75 μm. Coarse particles are separated from this granulated product using a sieve with a mesh of 50 × 54 μm, and fine particles are separated using a sieve with a mesh of 25 × 32 μm.

[0088] The granulated product is put into an electric furnace and heated to 1230 °C over 5 hours. Thereafter, it is maintained at 1230 °C for 3 hours to effect firing. Thereafter, it is cooled to 500 °C at a cooling rate of 2 °C per minute. A gas mixture of oxygen and nitrogen is supplied into the furnace such that the oxygen concentration in the electric furnace during the heating stage and the holding stage of the firing temperature is 15000 ppm and the oxygen concentration reaches 4000 ppm during the cooling stage.

[0089] After the obtained fired product is granule-disintegrated using a hammer mill, it is classified using a vibrating sieve to obtain a fired product with an average particle size of 34.6 μm.

[0090] Next, the obtained fired product is maintained at 410 °C for 1.5 hours in an atmospheric atmosphere to effect oxidation treatment (high-resistance treatment), thereby obtaining a carrier core material.

[0091] The composition, shape characteristics, powder characteristics, magnetic characteristics, electrical characteristics, etc. of the obtained carrier core material are measured using the method described later. The measurement results are shown in Tables 1 and 2.

[0092] Next, the surface of the carrier core material obtained by such operations is covered with a resin to fabricate a carrier. Specifically, 450 parts by mass of a silicone resin and 9 parts by mass of (2-aminoethyl)aminopropyltrimethoxysilane are dissolved in 450 parts by mass of toluene as a solvent to prepare a coating solution. Using a fluidized bed type coating apparatus, the coating solution is coated on 50000 parts by mass of the carrier core material and heated in an electric furnace at 300 °C to obtain a carrier. The same operations are performed for the following Examples and Comparative Examples to obtain carriers.

[0093] The obtained carrier and a toner with an average particle size of about 5.0 μm are mixed using a pot mill for a specified time to obtain a two-component type electrophotographic developer. In this case, the carrier and the toner are adjusted such that the mass of the toner / (the mass of the toner and the carrier) = 5 / 100. The same operations are performed for the following Examples and Comparative Examples to obtain developers. For the obtained developers, the actual machine evaluation described later is performed. The evaluation results are shown in Table 2.

[0094] (Example 2)

[0095] The temperature of the electric furnace in the firing process is changed to 1275 °C, and the oxygen concentration in the electric furnace during the heating stage and the holding stage of the firing temperature is changed to 4000 ppm. Otherwise, the same operations as in Example 1 are performed to fabricate a carrier core material with an average particle size of 34.8 μm.

[0096] (Example 3)

[0097] The temperature of the electric furnace in the firing process is changed to 1300 °C. Otherwise, the same operations as in Example 1 are performed to fabricate a carrier core material with an average particle size of 34.5 μm.

[0098] (Example 4)

[0099] Use a sieve with a mesh size of 48 μm during granulation to separate coarse particles, and use a sieve with a mesh size of 37 μm to separate fine particles. Otherwise, operate in the same manner as in Example 3 to produce a carrier core material with an average particle size of 35.0 μm.

[0100] (Example 5)

[0101] Disperse Fe2O3, SnO2, SrCO3, and Mn3O4 in water at a ratio of 10.0 mol of Fe, 0.05 mol of Sn, 0.04 mol of Sr, and 5.0 mol of Mn. Use a sieve with a mesh size of 48 μm during granulation to separate coarse particles, and use a sieve with a mesh size of 37 μm to separate fine particles. Set the temperature of the electric furnace in the firing process to 1315 °C. Otherwise, operate in the same manner as in Example 1 to produce a carrier core material with an average particle size of 36.6 μm.

[0102] (Comparative Example 1)

[0103] Do not add Sn and Sr. Set the temperature of the electric furnace in the firing process to 1200 °C. Set the oxygen concentration in the electric furnace during the heating stage and the holding stage of the firing temperature to 5000 ppm, and set the oxygen concentration in the cooling stage to 10000 ppm. Otherwise, operate in the same manner as in Example 1 to produce a carrier core material with an average particle size of 34.4 μm.

[0104] (Comparative Example 2)

[0105] Disperse Fe2O3, SrCO3, and Mn3O4 in water at a ratio of 10.0 mol% of Fe, 0.08 mol% of Sr, and 5.0% mol of Mn. Add 0.600 wt% of a polycarboxylic acid ammonium-based dispersant as a dispersant, 0.300 wt% of carbon black as a reducing agent, and 0.177 wt% of 36.5% concentrated hydrochloric acid. The solid content concentration of this mixture is 75 wt%.

[0106] Crush this mixture using a wet ball mill (media diameter: 2 mm) to obtain a mixed slurry. Spray this mixed slurry in hot air at about 210 °C using a spray dryer to obtain a dried granulated product with a particle size of 10 - 75 μm. Use a sieve with a mesh size of 50×54 μm to separate coarse particles from this granulated product, and use a sieve with a mesh size of 33 μm to separate fine particles.

[0107] The granulated product was put into an electric furnace and heated to 900 °C over 3 hours. Thereafter, it was maintained at 900 °C for 5.5 hours to effect firing. The oxygen concentration in the electric furnace at this time was 210,000 ppm. Thereafter, the obtained fired product was then put into the electric furnace and heated to 1165 °C over 5 hours. Thereafter, it was maintained at 1165 °C for 3 hours to effect firing. Thereafter, it was cooled to 500 °C at a cooling rate of 2 °C per minute. The oxygen concentration in the electric furnace during the heating stage, the holding stage of the firing temperature, and the cooling stage was kept constant at 7000 ppm, and a gas mixture of oxygen and nitrogen was supplied into the furnace.

[0108] The obtained fired product was granulated using a hammer mill and then classified using a vibrating screen to obtain a carrier core material with an average particle size of 36.2 μm.

[0109] (Comparative Example 3)

[0110] Weighed Fe2O3, Mg(OH)2, SrCO3, and Mn3O4 such that Fe was 10.0 mol%, Mg was 1.1 mol%, Sr was 0.08 mol%, and Mn was 3.80 mol%, and pulverized them for 10 hours using a dry media mill (vibratory mill, 1 / 8-inch diameter stainless steel beads). The obtained pulverized product was heated in an electric furnace at 1200 °C for 3 hours for pre-firing. Then, using a dry media mill (vibratory mill, 1 / 8-inch diameter stainless steel beads), it was pulverized for 10 hours until the average particle size was about 5 μm, after which water was added, and it was further pulverized for 10 hours using a wet ball mill (media diameter 2 mm). The average particle size of this slurry was about 2.3 μm. A dispersant was added in an appropriate amount to this slurry, and PVA (10% solution) as a binder was added at 0.4 mass% relative to the solid content to obtain a mixed slurry. The mixed slurry was spray-dried in hot air at about 210 °C using a spray dryer to obtain a dried granulated product with a particle size of 10 - 75 μm. Coarse particles were separated from this granulated product using a sieve with a mesh size of 50 × 54 μm, and fine particles were separated using a sieve with a mesh size of 33 μm. Thereafter, using a rotary electric furnace, it was heated at 750 °C in an air atmosphere for 2 hours to remove organic components such as the dispersant and binder.

[0111] The granulated product was put into an electric furnace and heated to 1300 °C over 5 hours. Thereafter, it was maintained at 1300 °C for 3 hours to effect firing. Thereafter, it was cooled to 500 °C at a cooling rate of 2 °C per minute. The oxygen concentration in the electric furnace during the heating stage, the holding stage of the firing temperature, and the cooling stage was kept constant at 7000 ppm, and a gas mixture of oxygen and nitrogen was supplied into the furnace.

[0112] The obtained fired product was granulated using a hammer mill and then classified using a vibrating screen to obtain a carrier core material with an average particle size of 36.9 μm.

[0113] (Comparative Example 4)

[0114] The temperature of the electric furnace in the firing process was set to 1275 °C, and otherwise, the same operation as in Example 5 was performed to produce a carrier core material with an average particle size of 36.6 μm.

[0115] (Composition analysis)

[0116] (Analysis of Fe)

[0117] Weigh the carrier core material containing iron element and dissolve it in the mixed acid aqueous solution of hydrochloric acid and nitric acid. After evaporating and drying the solution, add sulfuric acid aqueous solution for re-dissolution to volatilize the excessive hydrochloric acid and nitric acid. Add solid Al to this solution to reduce all the Fe 3+ in the liquid to Fe 2+ . Then, perform potentiometric titration on the amount of Fe 2+ ions in this solution to conduct quantitative analysis, and determine the titration amount of Fe (Fe 2+ ).

[0118] (Analysis of Mn)

[0119] The Mn content of the carrier core material was quantitatively analyzed according to the iron and manganese analysis method (potentiometric titration method) described in JIS G1311 - 1987. The Mn content of the carrier core material described in this application is the Mn amount obtained by quantitatively analyzing using this iron and manganese analysis method (potentiometric titration method).

[0120] (Analysis of Mg)

[0121] The Mg content of the carrier core material was analyzed using the following method. Dissolve the carrier core material described in this application in an acid solution and conduct quantitative analysis using ICP. The Mg content of the carrier core material described in this application is the Mg amount obtained by quantitative analysis based on this ICP.

[0122] (Analysis of Sn)

[0123] The Sn content of the carrier core material was carried out by quantitative analysis based on ICP in the same way as the analysis of Mg.

[0124] (Analysis of Sr)

[0125] The Sr content of the carrier core material was carried out by quantitative analysis based on ICP in the same way as the analysis of Mg.

[0126] (Measurement of the volume moment average value D[4,3] of bluntness and ISO roundness)

[0127] Measurement was carried out using the following measuring device and measuring conditions.

[0128] Measuring device: "IF-3200" manufactured by JASCO Corporation, an injection-type image analysis particle size distribution analyzer

[0129] Analysis software: PIA-Pro 14.18

[0130] Sample preparation conditions: 0.07 g of the sample was dispersed in a screw-cap bottle containing 9 cm 3 of polyethylene glycol 400 (capacity 9 cm 3 ), and then the measurement was carried out.

[0131] Measurement conditions: Telecentric zoom lens, magnification 2 times

[0132] Front lens, magnification 2 times

[0133] Calibration value: 0.417 μm / pixel

[0134] Spacer thickness: 150 μm

[0135] Sampling: 20%

[0136] Analysis type: Relative measurement

[0137] Measurement amount: 0.95 cm 3

[0138] Analysis: Dark detection

[0139] Threshold: 169 (filling the holes)

[0140] O-Roughness filter: 0.5

[0141] Filter conditions during measurement:

[0142] ISO Area Diametere (area diameter): minimum 5, maximum 150, inner range

[0143] Analysis filter conditions:

[0144] ISO Area Diametere (area diameter): minimum 10, maximum 55, inner range

[0145] ISO Solidity (hardness): minimum 0.9, maximum 1, inner range

[0146] Bluntness: An index of the smoothness of the particle contour

[0147] Deviation of the radius of all inscribed circles in the particle image

[0148] ISO roundness: An index of the circularity of the particle

[0149] Calculation formula for ISO roundness:

[0150] (4 × Pixel Count) / (π × ISOMax distance 2 )

[0151] (Apparent density AD)

[0152] The apparent density of the carrier core material is measured in accordance with JIS Z 2504.

[0153] (Flowability FR)

[0154] The flowability of the carrier core material is measured in accordance with JIS Z 2502.

[0155] (Volume average particle diameter D 50 and the ratio of particles with a particle diameter of 26 μm or less)

[0156] The volume average particle diameter D of the carrier core material 50 and the number ratio of particles with a particle diameter of 26 μm or less are measured using a laser diffraction particle size distribution measuring device (“MICROTRAC Model9320-X100” manufactured by Nikkiso Co., Ltd.).

[0157] (Pore volume)

[0158] For the measurement of the pore volume, it is carried out as follows. The evaluation device used is POREMASTER-60GT manufactured by Quantachrome Corporation. Specifically, as the measurement conditions, set Cell Stem Volume: 0.5 cm 3 , Headpressure (discharge pressure): 20 PSIA, surface tension of mercury: 485.00 erg / cm 2 , contact angle of mercury: 130.00 degrees, high-pressure measurement mode: Fixed Rate, Moter Speed: 1, high-pressure measurement range: 20.00 - 10000.00 PSI, weigh 1.200 g of the sample and fill it into a 0.5 cm 3 cell, and carry out the measurement. In addition, the value obtained by subtracting the volume A (cm 3 / g) at 100 PSI from the volume B (cm 3 / g) at 10000.00 PSI is taken as the pore volume.

[0159] (Internal porosity)

[0160] Disperse the carrier core material in the resin. After filling the resin into the carrier core material through vacuum degassing treatment, coat it on the auxiliary plate and perform heat treatment at a temperature of 200 °C for 20 minutes to cure the resin. Thereafter, cut the carrier core material using a cross-section polishing machine (SM-09010, manufactured by JEOL Ltd.). And take a photograph of the cross-section of the carrier core material using a scanning electron microscope (JSM-6510LA type, manufactured by JEOL Ltd.).

[0161] Based on the taken images, use image analysis software (Image-Pro Plus, manufactured by Media Cybernetics Inc.) to measure the number and area of internal voids with a void area of 20 μm 2 or more for 100 particles, calculate the total void area of internal voids with a void area of 20 μm 2 or more, divide it by the total particle area A of 100 particles (the cross-sectional area of the particle including the internal voids), and calculate the "internal void ratio of internal voids with a void area of 20 μm 2 or more".

[0162] (Magnetic properties)

[0163] Use a room temperature dedicated vibrating sample magnetometer (VSM) ("VSM-P7" manufactured by Toei Industry Co., Ltd.) to continuously apply one cycle within the range of an external magnetic field of 0 to 79.58×10 4 A / m (10000 Oe) to measure the saturation magnetization σ S , magnetization σ 1k , and residual magnetization σ r .

[0164] (Resistance)

[0165] Arrange two brass plates with a thickness of 2 mm and an electrolytically polished surface as electrodes so that the distance between the electrodes reaches 2 mm. After loading 200 mg of the carrier core material into the gap between the two electrode plates, arrange magnets with a cross-sectional area of 240 mm 2 behind each electrode plate. With the state where an electric bridge of the powder to be measured is formed between the electrodes, apply DC voltages of 100 V, 500 V, and 1000 V between the electrodes, use the four-terminal method to measure the current value flowing through the carrier core material, and calculate the resistance of the carrier core material. It should be noted that in Table 2, "B.D." means that dielectric breakdown has occurred in the carrier core material.

[0166] (Evaluation of developing memory)

[0167] The surface of the obtained carrier core material is covered with a resin to produce a carrier. Specifically, 450 parts by mass of a silicone resin and 9 parts by mass of (2-aminoethyl)aminopropyltrimethoxysilane are dissolved in 450 parts by mass of toluene as a solvent to prepare a coating solution. Using a fluidized bed type coating apparatus, this coating solution is coated on 50000 parts by mass of the carrier core material and heated using an electric furnace at a temperature of 300°C to obtain a carrier. Hereinafter, the same operation is performed for all the examples and comparative examples to obtain a carrier.

[0168] Using a pot mill, the obtained carrier and a toner having an average particle diameter of about 5.0 μm are mixed for a specified time to obtain a two-component type electrophotographic developer. In this case, the carrier and the toner are adjusted such that the mass of the toner / (the mass of the toner and the carrier) = 5 / 100. Hereinafter, the same operation is performed for all the examples and comparative examples to obtain a developer. The obtained developer is put into Figure 1 a developing device having the structure shown (circumferential speed Vs of the developing sleeve: 406 mm / sec, circumferential speed Vp of the photosensitive drum: 205 mm / sec, distance between the photosensitive drum and the developing sleeve: 0.3 mm). Solid image portions and non-image portions adjacent to each other along the circumferential direction of the photosensitive drum are obtained at the initial stage and after forming 200,000 images, and then a large-area halftone continuous image is obtained. Using a reflection densitometer (model: TC-6D manufactured by Tokyo Denshoku Co., Ltd.), the image density of the solid image developing area and the non-developed area of the first circle of the developing roller at the second circle of the developing roller is measured, the difference therebetween is obtained, and evaluation is performed according to the following criteria. The results are shown in Table 2.

[0169] “◎”: Less than 0.003

[0170] “○”: 0.003 or more and less than 0.006

[0171] “△”: 0.006 or more and less than 0.020

[0172] “×”: 0.020 or more

[0173] (Carrier adhesion (solid image portion))

[0174] Into Figure 1 the developing device having the structure shown (circumferential speed Vs of the developing roller: 406 mm / sec, circumferential speed Vp of the photosensitive drum: 205 mm / sec, distance between the photosensitive drum and the developing roller: 0.3 mm), the prepared two-component developer is put in, a solid image is formed on the surface of the photosensitive drum, the solid image on the surface of the photosensitive drum is peeled off with transparent tape, and the number of white spots due to carrier adhesion per unit area is evaluated according to the following criteria. The evaluation results are shown in Table 2.

[0175] “◎”: No carrier adhesion is seen at all.

[0176] “○”: Slight carrier adhesion was observed, but it is within the range where there is no problem in actual use.

[0177] “△”: Carrier adhesion was observed and it cannot be used.

[0178] “×”: Strong carrier adhesion was observed and it cannot be used at all.

[0179] [Table 1]

[0180]

[0181] [Table 2]

[0182]

[0183] In the carrier cores of Examples 1 to 5 where the volume moment average value D[4,3] of bluntness and ISO roundness is within the specified range of the present invention, the development memory is suppressed, and no carrier adhesion to the solid image portion is confirmed, or there is no problem in actual use.

[0184] In contrast, in the carrier cores of Comparative Example 1 and Comparative Example 3 where the volume moment average value D[4,3] of bluntness and ISO roundness is larger than the specified range of the present invention, no carrier adhesion to the solid image portion is confirmed, or there is no problem in actual use, but development memory occurs significantly.

[0185] In addition, in the carrier cores of Comparative Example 2 and Comparative Example 4 where the volume moment average value D[4,3] of ISO roundness is larger than the specified range of the present invention, no carrier adhesion to the solid image portion is confirmed, or there is no problem in actual use, but development memory occurs and there are problems in use.

[0186] Industrial Applicability

[0187] The carrier core according to the present invention is useful because it can suppress development memory and carrier adhesion even when used in a high-speed image forming apparatus.

Claims

1. A carrier core material, characterized in that, It is a carrier core material composed of ferrite particles. The composition of the ferrite particles contains MnO: 35 mol% or more and 55 mol% or less, Fe2O3: 45 mol% or more and 65 mol% or less, and a part of which is replaced by SrO: 0.1 mol% or more and 1.0 mol% or less, SnO: 0.1 mol% or more and 1.0 mol% or less. The average volume moment D[4,3] of bluntness measured by an injection-type image analysis particle size distribution meter is 65% or more and 80% or less. The average volume moment D[4,3] of ISO roundness is 80% or more and 86% or less.

2. The carrier core material according to claim 1, with its saturation magnetization σ S being 75 A·m 2 / kg or more and 88 A·m 2 / kg or less.

3. The carrier core material according to claim 1 or 2 has a pore volume of 0.01 cm 3 / g or less.

4. A carrier for electronic photo development, characterized in that, The surface of the carrier core material according to any one of claims 1 to 3 is covered with a resin.

5. A developer for electrophotography, which comprises the carrier for electrophotographic development and a toner according to claim 4.

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