JP5854541B1 - Carrier core material, electrophotographic developer carrier and electrophotographic developer using the same - Google Patents

Abstract

A carrier core material capable of suppressing the occurrence of defects such as a development memory is provided. A carrier core material composed of ferrite particles having a spinel crystal structure and containing an Sr component, the amount of water detected when heated to a temperature of 300 ° C. is 400 μmol / g or more. It is characterized by that. Here, the content of the Sr component in terms of SrO is preferably in the range of 0.2 mol% or more and less than 0.7 mol%. [Selection] Figure 1

Description

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

  For example, in an image forming apparatus such as a facsimile, printer, or copier using an electrophotographic method, a toner is attached to an electrostatic latent image formed on the surface of a photosensitive member to make a visible image, and the visible image is formed on paper. After being transferred to, etc., it is fixed by heating and pressing. A so-called two-component developer including a carrier and a toner is widely used as a developer from the viewpoint of high image quality and colorization.

  In the developing method using a two-component developer, the carrier and the toner are stirred and mixed in the developing device, and the toner is charged to a predetermined amount by friction. Then, a developer is supplied to the rotating developing roller, a magnetic brush is formed on the developing roller, and the toner is electrically moved to the photosensitive member via the magnetic brush, so that an electrostatic latent image on the photosensitive member can be formed. Visualize. The carrier after the toner movement remains on the developing roller and is mixed with the toner again in the developing device. For this reason, as a characteristic of the carrier, a magnetic characteristic for forming a magnetic brush and a charging characteristic for imparting a desired charge to the toner are required. As such a carrier, a so-called coating carrier in which the surface of a carrier core material made of magnetite, various ferrites or the like is coated with a resin has been widely used. Further, the carrier core material used so far for the coating carrier has a spherical shape.

  In recent years, in order to meet the market demand for higher image forming speed in image forming apparatuses, the rotation speed of the developing roller tends to be increased to increase the amount of developer supplied per unit time to the developing area.

  However, the coating carrier using the spherical carrier core material has a problem that the toner density to the developing area is insufficient and the image density is lowered. For example, there has been a problem called “development memory” in which the image density decreases due to the influence of the image one round before the developing roller.

  Therefore, by making the surface of the carrier core material uneven, or by making the shape of the carrier core material irregular, the frictional resistance with the surface of the photoreceptor and the frictional resistance between the carriers are increased, and the amount of toner supplied to the development area is increased. Techniques for increasing the number have been proposed (for example, Patent Documents 1 and 2).

JP 2013-25204 A JP 2007-148452 A

  However, problems such as development memory cannot be sufficiently solved by simply making the surface of the carrier core material uneven.

  Therefore, an object of the present invention is to provide a carrier core material that can suppress the occurrence of problems such as development memory.

  Another object of the present invention is to provide an electrophotographic developer carrier and an electrophotographic developer capable of stably forming a good image quality even after long-term use.

According to the present invention, a carrier core material having a spinel crystal structure and comprising ferrite particles containing an Sr component, the content of Mg component in terms of MgO being 3.6 mol% or less, Bi There is provided a carrier core material characterized in that it contains no components and the amount of water detected when heated to a temperature of 300 ° C. is 400 μmol / g or more.

  Here, the content of the Sr component is preferably in the range of 0.2 mol% or more and less than 0.7 mol% in terms of SrO.

  The volume average particle diameter of the carrier core material (hereinafter sometimes simply referred to as “average particle diameter”) is preferably 25 μm or more and less than 50 μm.

  In addition, according to the present invention, there is provided an electrophotographic developing carrier characterized in that the surface of the carrier core material described above is coated with a resin.

  Furthermore, according to the present invention, there is provided an electrophotographic developer comprising the electrophotographic developer carrier described above and a toner.

  According to the carrier core material of the present invention, it is possible to suppress the occurrence of problems such as development memory. Thereby, if the developer containing the carrier core material according to the present invention is used, a good image quality can be stably formed even for a long period of use.

2 is a cross-sectional SEM photograph of the carrier core material of Example 1. It is an outline figure showing an example of a development device which performs magnetic brush development.

  As a result of intensive investigations as to whether or not problems such as development memory can be suppressed, the present inventors have achieved good toner retention and charge of the toner when the carrier core surface is coated with a resin. It was found that development memory tends to be suppressed when the rise is good. In order to further improve the toner retention and toner charge rising property, when the resin coated carrier is used, the carrier core material exposed portion and the resin coated portion are formed on the carrier surface. I found it important to exist. The electric resistance of the coating resin is high, and the toner is charged and held in the resin-coated portion. On the other hand, the exposed portion of the carrier core material has a low electrical resistance, and the charge buildup on the carrier is released from this portion, so that the charge rising of the toner is improved.

  Then, in order to provide the exposed portion of the carrier core material and the resin-coated portion on the carrier surface, the carrier core material is formed into an uneven shape, the concave portion of the carrier core material is covered with resin, and the convex portion of the carrier core material is formed. I got the idea that it should be exposed.

  Therefore, in the present invention, first, the Sr component is added to make the carrier core material uneven. The Sr component segregates at the grain boundary of the spinel crystal in the firing step of the spheroidized carrier core material precursor (granulated product), and prevents crystal growth in the circumferential direction of the spinel crystal. As a result, the spinel crystal grows outward in the radial direction, and the carrier core material has an uneven shape.

  Next, various investigations were conducted to make the coating resin mainly exist in the concave portion of the carrier core material. When a predetermined amount of moisture was present in the carrier core material manufacturing process, the generated concave portion of the carrier core material was preferentially used. The knowledge that it was resin-coated was obtained. Although the mechanism of preferentially resin-covering the concave portion of the generated carrier core material when a predetermined amount of moisture is present in the manufacturing process of the carrier core material has not yet been fully elucidated, the present inventors I'm guessing that the mechanism is as follows.

As described above, the carrier core material has an uneven shape due to the addition of the Sr component. When a predetermined amount of moisture is present in the manufacturing process of the carrier core material, as shown in the following formula (1), the moisture and the carrier core material (ferrite, MO-Fe ₂ O ₃ ) react to form a hydroxide phase. It is formed on the surface of the carrier core material. When a hydrophilic hydroxide phase is formed on the surface of the carrier core material, moisture tends to collect near the contact points between the convex portions of the particles during resin coating, and the hydrophobic coating resin is transferred to the concave portions. Extruded and the concave portion of the carrier core material is preferentially resin-coated.

When heated, the hydroxide phase generated by the reaction between the moisture and the carrier core is decomposed into a metal oxide and water as shown in the following formula (2). Therefore, in the present invention, the moisture content per carrier core weight detected when heated to 300 ° C. is used as an indirect indicator of the abundance of the hydroxide phase in the carrier core.
MO-Fe ₂ O ₃ + H ₂ O → M (OH) ₂ + Fe ₂ O ₃ (1)
M (OH) ₂ → MO _X + H ₂ O (2)

  The amount of water detected when heated to a temperature of 300 ° C. is 400 μmol / g or more. When the water content is less than 400 μmol / g, there are few hydroxide phases present on the surface of the carrier core material, and the concave portions of the carrier core material are not sufficiently resin-coated, and problems such as development memory are not solved. A more preferable upper limit value of the water content is 642 μmol / g.

The ferrite particles constituting the carrier core material of the present invention are not particularly limited as long as they have a spinel crystal structure and contain a Sr component. For example, the composition formula M _X Fe _3-X O ₄ (M Includes at least one metal element selected from the group consisting of Mg, Mn, Ca, Ti, Cu, Zn, and Ni, represented by 0 ≦ X ≦ 1). Among these, the general formula _{(MnO) x (MgO) y} (Fe 2 O 3) is represented by z, x, y, z is 45mol% ~55mol% respectively, 0 to 20 mol%, a 30 mol% 50 mol% , MnO and / or MgO is preferably substituted by 0.15 mol% to 1.0 mol% with SrO.

  The content of the Sr component is preferably in the range of 0.2 mol% or more and less than 0.7 mol% in terms of SrO. When the content of the Sr component is within this range, the carrier core material has a concavo-convex shape, and the concave portion is likely to be preferentially coated with resin. A more preferable content of the Sr component is in the range of 0.2 mol% to 0.5 mol%.

  The volume average particle size of the carrier core material of the present invention is preferably in the range of 25 μm or more and less than 50 μm, more preferably in the range of 30 μm or more and 40 μm or less.

  Although there is no limitation in particular in the manufacturing method of the carrier core material of this invention, the manufacturing method demonstrated below is suitable.

First, the Fe component raw material, the M component raw material, and the Sr component raw material are weighed. Note that M is at least one metal element selected from metal elements capable of taking a divalent valence such as Mg, Mn, Ca, Ti, Cu, Zn, and Ni. As the Fe component material, Fe ₂ O ₃ or the like is preferably used. As the M component raw material, MnCO ₃ , Mn ₃ O _{4 and the} like can be used for Mn, and MgO, Mg (OH) ₂ and MgCO ₃ can be suitably used for Mg. As the Ca component raw material, at least one compound selected from CaO, Ca (OH) ₂ , CaCO _{3 and the} like is preferably used. As the Sr component raw material, SrCO ₃ , Sr (NO ₃ ) ₂ or the like is preferably used.

  Next, the raw material is charged into a dispersion medium to prepare a slurry. Water is preferred as the dispersion medium used in the present invention. In addition to the calcined raw material, a binder, a dispersant and the like may be blended in the dispersion medium as necessary. For example, polyvinyl alcohol can be suitably used as the binder. As a compounding quantity of a binder, it is preferable that the density | concentration in a slurry shall be about 0.5 mass%-2 mass%. Moreover, as a dispersing agent, polycarboxylate ammonium etc. can be used conveniently, for example. The blending amount of the dispersing agent is preferably about 0.5% by mass to 2% by mass in the slurry. In addition, you may mix | blend a lubricant, a sintering accelerator, etc. The solid content concentration of the slurry is desirably in the range of 50 mass% to 90 mass%. More preferably, it is 60 mass%-80 mass%. If it is 60% by mass or more, there are few intra-particle pores in the granulated product, and insufficient sintering during firing can be prevented.

  In addition, after mixing the weighed raw materials, pre-baking and pulverizing, it may be put into a dispersion medium to produce a slurry. The pre-baking temperature is preferably in the range of 750 ° C to 900 ° C. If it is 750 degreeC or more, since part ferrite-ization by calcination advances, the amount of gas generation at the time of baking is small, and reaction between solids fully advances, it is preferable. On the other hand, if it is 900 degrees C or less, since sintering by calcination is weak and a raw material can fully be grind | pulverized at a later slurry grinding | pulverization process, it is preferable. Moreover, an air atmosphere is preferable as the atmosphere at the time of temporary firing.

  Next, the slurry produced as described above is wet pulverized. For example, wet grinding is performed for a predetermined time using a ball mill or a vibration mill. The average particle diameter of the raw material after pulverization is preferably 5 μm or less, more preferably 1 μm or less. The vibration mill or ball mill preferably contains a medium having a predetermined particle diameter. Examples of the material of the media include iron-based chromium steel and oxide-based zirconia, titania, and alumina. As a form of a grinding | pulverization process, any of a continuous type and a batch type may be sufficient. The particle size of the pulverized product is adjusted depending on the pulverization time and rotation speed, the material and particle size of the media used, and the like.

  Then, the pulverized slurry is spray-dried and granulated. Specifically, the slurry is introduced into a spray dryer such as a spray dryer, and granulated into a spherical shape by spraying into the atmosphere. The atmospheric temperature during spray drying is preferably in the range of 100 ° C to 300 ° C. Thereby, a spherical granulated product having a particle size of 10 μm to 75 μm is obtained. Next, the obtained granulated product is classified using a vibration sieve to produce a granulated product having a predetermined particle size range.

  Next, the granulated material is put into a furnace heated to a predetermined temperature and fired by a general method for synthesizing ferrite particles, thereby generating ferrite particles. The firing temperature is preferably in the range of 1100 ° C to 1300 ° C. When the firing temperature is 1100 ° C. or lower, the phase transformation is less likely to occur and the sintering is less likely to proceed. On the other hand, if the firing temperature exceeds 1300 ° C., excessive grains may be generated due to excessive sintering. The rate of temperature increase up to the firing temperature is preferably in the range of 250 ° C / h to 500 ° C / h. The oxygen concentration in the firing step is preferably controlled in the range of 0.05% to 5%.

  The fired product thus obtained is pulverized. Specifically, for example, the fired product is pulverized by a hammer mill or the like. The form of the granulation step may be either a continuous type or a batch type.

  After the pulverization treatment, classification may be performed, if necessary, in order to align the particle size within a predetermined range. As a classification method, a conventionally known method such as air classification or sieve classification can be used. In addition, after primary classification with an air classifier, the particle size may be aligned within a predetermined range with a vibration sieve or an ultrasonic sieve. Furthermore, you may make it remove a nonmagnetic particle with a magnetic field separator after a classification process. The particle diameter of the ferrite particles is preferably 25 μm or more and less than 50 μm.

  Thereafter, if necessary, the ferrite particles after classification may be heated in an oxidizing atmosphere to form an oxide film on the particle surface to increase the resistance of the ferrite particles (high resistance treatment). The oxidizing atmosphere may be either an air atmosphere or a mixed atmosphere of oxygen and nitrogen. The heating temperature is preferably in the range of 200 ° C to 800 ° C, and 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.

  There is no specific method for causing carbon dioxide to be present on the surface of the ferrite particles. However, it is preferable to perform gas treatment in an atmosphere in which the gas partial pressure and the gas temperature are adjusted using a fixed bed or fluidized bed adsorption device. The gas treatment can be performed not only in the final step in the production of the carrier core material, but also in any step among the above-described firing step, pulverization step, classification step, and oxidation step.

  For example, when performing gas treatment in the firing step, any of an open firing method and a closed firing method described later can be selected. In the case of an open-type firing method that involves the flow of gas to the granulated product, in a firing furnace that uses the combustion heat of hydrocarbons as the heat source, the air-fuel ratio during firing is controlled to control the separation of carbon dioxide gas and water vapor. The gas can be treated by adjusting the pressure. Also, in a type of firing furnace that uses heat generated by flowing electricity to a heating element to a heat source, by supplying carbon dioxide gas and water vapor to the circulating gas, the gas partial pressure is adjusted to perform gas treatment can do. On the other hand, in a closed baking method in which baking is performed in a container with a lid or the like, substances that generate carbon dioxide and water vapor by thermal decomposition are mixed in advance so that an arbitrary gas partial pressure is obtained, and those in a closed container are then mixed. The gas partial pressure can be adjusted to perform gas treatment. In the oxidation step, gas treatment can be performed by the same method.

  The ferrite particles produced as described above are used as the carrier core material of the present invention. Then, in order to obtain desired chargeability and the like, the surface of the carrier core material is coated with a resin to obtain an electrophotographic developing carrier.

  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). ) Resin, polystyrene, (meth) acrylic resin, polyvinyl alcohol resin, polyvinyl chloride, polyurethane, polyester, polyamide, polybutadiene, and other thermoplastic elastomers, and fluorosilicone resins.

  In order to coat the surface of the carrier core material with the resin, a resin solution or dispersion may be applied to the carrier core material. Solvents 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, cellosolve solvents such as butyl cellosolve; ester solvents such as ethyl acetate and butyl acetate; amide solvents such as dimethylformamide and dimethylacetamide, etc. . The resin component concentration in the coating solution should generally be in the range of 0.001% to 30% by weight, particularly 0.001% to 2% by weight.

  As a method of coating the resin on the carrier core material, for example, a spray drying method, a fluidized bed method, a spray drying method using a fluidized bed, an immersion method, or the like can be used. Among these, the fluidized bed method is particularly preferable in that it can be efficiently applied with a small amount of resin. For example, in the case of the fluidized bed method, the resin coating amount can be adjusted by the amount of resin solution sprayed and the spraying time.

  The particle diameter of the carrier is generally preferably in the range of 25 μm or more and less than 50 μm, particularly in the range of 30 μm or more and 40 μm or less in terms of volume average particle diameter.

  The electrophotographic developer according to the present invention is obtained by mixing the carrier prepared as described above and a toner. The mixing ratio of the carrier and the toner is not particularly limited, and may be determined as appropriate based on the developing conditions of the developing device to be used. Generally, the toner concentration in the developer is preferably in the range of 1% by mass to 15% by mass. When the toner density is less than 1% by mass, the image density becomes too low, while when the toner density exceeds 15% by mass, toner scattering occurs in the developing device, and the toner adheres to the background portion such as internal dirt or transfer paper. This is because there is a risk of malfunction. A more preferable toner concentration is in the range of 3% by mass to 10% by mass.

  As the toner, toner produced by a conventionally known method such as a polymerization method, a pulverization classification method, a melt granulation method, or 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.

  In general, the particle diameter 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 diameter 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. These 1 type (s) or 2 or more types can be used in combination.

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

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

  The two screws 1 and 2 have spiral 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 remove the developer. Transport in opposite directions. The developer moves from one screw to the other screw at both ends of the screws 1 and 2. As a result, the developer composed of toner and carrier is constantly circulated and stirred in the apparatus.

On the other hand, the developing roller 3 has, as a magnetic pole generating means, a developing magnetic pole N ₁ , a transporting magnetic pole S ₁ , a peeling magnetic pole N ₂ , and a pumping magnetic pole N ₃ inside a metal cylindrical body having a surface with a few μm unevenness. , 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 regulated by the regulating blade 6 and then conveyed to the developing area.

  In the developing region, a bias voltage obtained by superimposing an AC voltage on a DC voltage is applied from the transfer voltage power supply 8 to the developing roller 3. The DC voltage component of the bias voltage is a potential between the background portion potential on the surface of the photosensitive drum 5 and the image portion potential. Further, the background portion potential and the image portion potential are set to a 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 to 5 kV, and the frequency is preferably in the range of 1 to 10 kHz. The waveform of the bias voltage may be any of a rectangular wave, a sine wave, a triangular wave, and the like. As a result, the toner and the carrier vibrate in the development area, and the toner adheres to the electrostatic latent image on the photosensitive drum 5 and development is performed.

Thereafter, the developer on the developing roller 3 is conveyed to the inside of the apparatus by the conveying magnetic pole S ₁ , peeled off from the developing roller 3 by the peeling electrode N ₂ , and circulated and conveyed again inside the apparatus by the screws 1 and 2 for development. Mix and stir with undeveloped developer. Then, the developer is newly supplied from the screw 1 to the developing roller 3 by the pumping pole N ₃ .

  In the embodiment shown in FIG. 2, the number of magnetic poles built in the developing roller 3 is five. However, in order to further increase the amount of movement of the developer in the developing region and to further improve the pumping performance and the like. Of course, the number of magnetic poles may be increased to 8 poles, 10 poles or 12 poles.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these examples at all.

Example 1
Pure Fe ₂ O ₃ (average particle size: 0.6 μm) 7.100 kg, Mn ₃ O ₄ (average particle size: 0.9 μm) 2.840 kg, SrCO ₃ (average particle size: 0.6 μm) 0.060 kg The mixture was dispersed in 4.256 kg of water, and 30 g of an ammonium polycarboxylate dispersant as a dispersant and 38 g of carbon black as a reducing agent were added to obtain a mixture. 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. with a spray dryer to obtain a dry granulated product having a particle size of 10 μm to 75 μm. Coarse particles having a particle size exceeding 50 μm were removed from the granulated product using a sieve.
This granulated product was put into an electric furnace and heated to 1170 ° C. over 4.5 hours. Then, it baked by hold | maintaining at 1170 degreeC for 3 hours. Thereafter, it was cooled to room temperature over 8 hours. During this time, a gas in which oxygen and nitrogen were mixed was supplied into the furnace so that the oxygen concentration in the electric furnace was 15000 ppm.
The fired product obtained was pulverized once with a hammer mill (“Hammer Crusher NH-34S” manufactured by Sansho Industry Co., Ltd., screen opening: 0.3 mm) and then further twice with a pulverizer (manufactured by DOWA Techno Engineering). By pulverization, a carrier core material having an average particle diameter of 34.0 μm was obtained.
Then, using a thermo-hygrostat (“PH-1KT”), the carrier core material is allowed to stand for 24 hours in an air atmosphere at a temperature of 25 ° C./humidity of 60% RH, and the surface of the carrier core material is treated with moisture. At the same time, carbon dioxide was present around the carrier core.
The composition of the obtained carrier core material, the amount of moisture by heating, physical properties, developer characteristics, and the like were measured by the methods described below. The measurement results are shown in Table 1. FIG. 1 shows a cross-sectional SEM photograph of the carrier core material of Example 1.

Example 2
The same procedure as in Example 1 except that 7.058 kg of Fe ₂ O ₃ , 2.774 kg of Mn ₃ O ₄ , 0.023 kg of SrCO _3, and 0.123 kg of MgCO ₃ (average particle size: 0.6 μm) were used. A carrier core material was prepared to obtain a carrier core material having an average particle diameter of 34.8 μm. The composition of the obtained carrier core material, the amount of moisture by heating, physical properties, developer characteristics, and the like were measured by the methods described below. The measurement results are shown in Table 1.

Comparative Example 1
A carrier core material was prepared in the same manner as in Example 1 except that 6.796 kg of Fe ₂ O ₃ , 3.076 kg of Mn ₃ O ₄ , 0.092 kg of SrCO ₃ and 0.035 kg of MgCO ₃ were prepared. A carrier core material having a particle size of 34.0 μm was obtained. The composition of the obtained carrier core material, the amount of moisture by heating, physical properties, developer characteristics, and the like were measured by the methods described below. The measurement results are shown in Table 1.

Comparative Example 2
A carrier core material was prepared in the same manner as in Example 1 except that 7.092 kg of Fe ₂ O ₃ , 2.371 kg of Mn ₃ O ₄ and 0.537 kg of MgCO ₃ were used, and a carrier having an average particle diameter of 34.1 μm. A core material was obtained. The composition of the obtained carrier core material, the amount of moisture by heating, physical properties, developer characteristics, and the like were measured by the methods described below. The measurement results are shown in Table 1.

Comparative Example 3
A carrier core material was prepared in the same manner as in Example 1 except that 6.706 kg of Fe ₂ O ₃ , 3.196 kg of Mn ₃ O ₄ and 0.098 kg of SrCO ₃ were prepared, and a carrier having an average particle diameter of 34.6 μm A core material was obtained. The composition of the obtained carrier core material, the amount of moisture by heating, physical properties, developer characteristics, and the like were measured by the methods described below. The measurement results are shown in Table 1.

Comparative Example 4
A carrier core material was produced in the same manner as in Example 1 except that the gas treatment step in the thermostatic humidity controller was not performed. The composition of the obtained carrier core material, the total amount of carbon dioxide by heating, physical properties, developer characteristics Etc. were measured by the method described later. The measurement results are shown in Table 1.

(Composition analysis)
As oxides (Fe ₂ O ₃ , MnO, MgO, CaO, SrO), the composition ratio (mol%) was calculated from the analysis values (% by weight) of the following elements.
(Analysis of Fe)
The carrier core material containing iron element was weighed and dissolved in a mixed acid water of hydrochloric acid and nitric acid. After evaporating this solution to dryness, sulfuric acid water 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 the solution was quantitatively analyzed by potentiometric titration with a potassium permanganate solution to obtain a titer of Fe (Fe ²⁺ ).
(Analysis of Mn)
The Mn content of the carrier core material was quantitatively analyzed according to 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 amount of Mn 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 amount of Mg obtained by this quantitative analysis by ICP.
(Ca analysis)
The Ca content of the carrier core material was determined by ICP quantitative analysis as in the case of Mg analysis.
(Sr analysis)
The Sr content of the carrier core material was determined by ICP quantitative analysis as in the case of Mg analysis.
(Analysis of Si)
The SiO2 content of the carrier core material was quantitatively analyzed according to the silicon dioxide weight method described in JIS M8214-1995.

(amount of water)
The amount of water desorption was determined by coulometric titration with the Karl Fischer method. 2.0 g of carrier core material was set in a moisture vaporization accessory device (Hiranuma Sangyo EV-6) and heated to a temperature of 300 ° C. under N ₂ flow. The flow rate of N ₂ gas was 0.3 L / min. H ₂ O contained in the outlet gas was measured using a trace moisture measuring device (Hiranuma Sangyo AQ-7). Hydranal Aqualite RS was used as the generation liquid, and Aqualite CN was used as the counter electrode liquid.

(Average particle size)
The volume average particle diameter of the carrier core material was measured using a laser diffraction particle size distribution measuring device (“Microtrack Model 9320-X100” manufactured by Nikkiso Co., Ltd.).

(Image memory)
The surface of the obtained carrier core material was coated with a resin to prepare a carrier. In particular,
A carrier was obtained by applying 75 g of an acrylic / styrene mixed resin to 2.5 kg of the carrier core material using a high speed mixer ("FS-GS-10JD type" manufactured by Fukae Pautech Co., Ltd.). The stirring speed of the high speed mixer was 400 rpm, and the stirring time was 90 minutes. Hereinafter, carriers were obtained in the same manner for all of the examples and comparative examples.

The obtained carrier and a toner having an 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 toner / (weight of toner and carrier) = 5/100. Hereinafter, developers were obtained in the same manner for all of the Examples and Comparative Examples. The developer thus obtained was developed into a developing device having a structure shown in FIG. 2 (developing sleeve peripheral speed Vs: 406 mm / sec, photosensitive drum peripheral speed Vp: 205 mm / sec, photosensitive drum-developing sleeve distance: 0. 3 mm), an image in which a solid image portion and a non-image portion are adjacent to each other in the longitudinal direction of the photosensitive drum, and a halftone of a wide area thereafter is obtained after the initial and 200,000 sheets are formed, and the developing roller 2 Measure the image density between the area where the solid image on the first development roller of the circumference is developed and the area where it is not, using a reflection densitometer (Model No. TC-6D manufactured by Tokyo Denshoku Co., Ltd.), and determine the difference. Evaluation was made according to the following criteria. The results are shown in Table 1.
“◎”: Less than 0.003 “O”: 0.003 or more and less than 0.006 “Δ”: 0.006 or more and less than 0.020 “X”: 0.020 or more

  As is clear from the comparison between Example 1 and Comparative Example 4, it can be seen that the generation of development memory is suppressed when the amount of water is large.

  Further, as is clear from the comparison between Examples 1 and 2 and Comparative Examples 1 to 3, if the content of the Sr component in the gas-treated carrier core material is in the range of 0.2 mol% or more and less than 0.7 mol%, It can be seen that the development memory is suppressed.

  According to the carrier core material of the present invention, it is possible to suppress the occurrence of problems such as development memory.

3 Developing roller 5 Photosensitive drum C Carrier

Claims (5)

A carrier core material having a spinel crystal structure and comprising ferrite particles containing a Sr component,
The content of Mg component in terms of MgO is 3.6 mol% or less,
Does not contain Bi component,
A carrier core material characterized in that the amount of water detected when heated to 300 ° C. is 400 μmol / g or more.   The carrier core material according to claim 1, wherein the content of the Sr component in terms of SrO is in the range of 0.2 mol% or more and less than 0.7 mol%.   The carrier core material according to claim 1, wherein the volume average particle diameter is 25 μm or more and less than 50 μm.   A carrier for electrophotographic development, wherein the surface of the carrier core material according to claim 1 is coated with a resin.   An electrophotographic developer comprising the carrier for electrophotographic development according to claim 4 and a toner.