JP2021088487A - Ferrite mixed powder, carrier core material for electrophotographic developer, carrier for electrophotographic developer and electrophotographic developer - Google Patents

Abstract

To provide a carrier core material for an electrophotographic developer, a carrier for an electrophotographic developer, and an electrophotographic developer, which are excellent in agitation and mixing properties between toner and carrier and can suppress the occurrence of defects at the initial stage of printing even when the environment changes.SOLUTION: There is provided a ferrite mixed powder in which a plurality of spinel-type ferrite powders (where n is an integer of 2 or more) having lattice constants different from each other are mixed and an average lattice constant (Cm) obtained based on a predetermined formula is 8.40≤Cm≤8.50 when an X-group is composed of spinel-type ferrite powders having a lattice constant value smaller than a predetermined reference value (Cs) and a Y-group is composed of spinel-type ferrite powders having a lattice constant value equal to or greater than the reference value (Cs).SELECTED DRAWING: None

Description

The present invention relates to a ferrite mixed powder, a carrier core material for an electrophotographic developer, a carrier for an electrophotographic developer, and an electrophotographic developer.

The electrophotographic developing method refers to a method of developing by adhering toner in a developing agent to an electrostatic latent image formed on a photoconductor. The developer used in this method is divided into a two-component developer composed of toner and a carrier and a one-component developer using only toner. As a developing method using a two-component developer, the cascade method or the like has been adopted in the old days, but nowadays, the magnetic brush method using a magnet roll is the mainstream.

In the magnetic brush method, the toner is charged by stirring and mixing the toner and the carrier in a developing box filled with a developer. Then, the carrier is conveyed to the surface of the photoconductor by a developing roll holding the magnet. At that time, the carrier conveys the charged toner to the surface of the photoconductor. After a toner image is formed on the photoconductor by electrostatic action, the carriers remaining on the developing roll are collected again in the developing box, stirred and mixed with new toner, and used repeatedly for a certain period of time. ..

Unlike the one-component developer, the two-component developer can be designed by separating the magnetic characteristics and electrical characteristics of the carrier itself from the toner, so that the controllability when designing the developer is good. Therefore, the two-component developer is suitable for a full-color developing device that requires high image quality, a device that performs high-speed printing that requires reliability and durability of image maintenance, and the like.

In recent years, the particle size of toner has been reduced in order to develop an electrostatic latent image with high definition. As the particle size of the toner is reduced, the particle size of the carrier is also reduced. By reducing the particle size of the carrier, the mechanical stress when the carrier and the toner are agitated and mixed can be reduced, and the generation of toner spent and the like can be suppressed. Therefore, the life of the developer is longer than that of the conventional one. However, if the particle size of the carriers is reduced, carrier scattering is likely to occur, and image defects such as vitiligo are likely to occur.

For example, Patent Document 1 contains 15 to 22% by weight of Mn, 0.5 to 3.0% by weight of Mg, 45 to 55% by weight of Fe, and 0.1 to 3.0% by weight of Sr. A carrier core material having a lattice constant of 8.430 to 8.475 and having a surface oxide film formed therein is disclosed. According to the carrier core material disclosed in Patent Document 1, by providing the surface oxide film, the particle resistance is high and the variation in resistance between the particles can be reduced in spite of the small particle size. Therefore, if the carrier core material is used as an electrophotographic developer, it is possible to suppress carrier adhesion and obtain a good printed matter having excellent fine line reproducibility.

Further, in Patent Document 2, the composition formula M _x Fe _3-X O ₄ (where M is at least one selected from the group consisting of Mn, Mg, Ca, Sr, Ti, Cu, Zn and Ni). A carrier core material represented by 0 <X ≦ 1), which is a metal, and has a half-value width of 0.15 ° or more and 0.20 ° calculated from the peak of the surface index (311) in the powder X-ray diffraction pattern. The difference in lattice constant calculated from the peak of the surface index (311) in the powder X-ray diffraction pattern before and after crushing the carrier core material is 0.005 Å or less in absolute value. The material is disclosed. It is said that the carrier core material can increase the resistance not only on the surface of the particles but also on the inside of the particles. If the carrier core material is used as an electrophotographic developer, carrier adhesion to a photoconductor or the like is suppressed and an image is formed. It is said that sufficient image density can be obtained even if the speed is increased.

Further, in Patent Document 3, it is desired that Mg and Fe are contained in a molar ratio x in the range of 0 to 0.5 so that the lattice constant f (x) satisfies a predetermined conditional expression. It is said that a magnetic core material (carrier core material) having high electrical resistance while achieving saturation magnetization can be obtained. Therefore, if the carrier core material is used as an electrophotographic developer, it is possible to cope with high speed image formation and high image quality.

Japanese Unexamined Patent Publication No. 2013-178414 Japanese Unexamined Patent Publication No. 2017-21195 Japanese Unexamined Patent Publication No. 2011-209475

By the way, in the case of a two-component developer, the manufacturing conditions are precisely set so that the magnetization and resistance of the carrier core material become predetermined initial setting values according to the characteristics of the developing device in which the electrophotographic developer is used and the characteristics of the toner. Be controlled. The carrier core material disclosed in Patent Documents 1 to 3 has little variation between particles of magnetization and resistance, and can print an image with high image quality.

However, the resistance of the carrier core is generally environmentally dependent. The conventional carrier core material is composed of particles having small variations such as resistance. Therefore, the change in the resistance of the powder behaves substantially the same as the change in the resistance of the individual particles. Therefore, under predetermined atmospheric conditions, image printing can be performed with extremely high image quality. On the other hand, if the carrier resistance fluctuates or the toner charge amount fluctuates due to changes in the environment such as a sudden change in atmospheric temperature or humidity, it may not be possible to satisfactorily stir and mix the toner and the carrier. is there. In that case, the charge rise becomes slow, and density unevenness may occur due to variations in the toner charge amount at the initial stage of printing.

Here, the toner charge amount generally tends to be high in a low temperature and low humidity environment and low in a high temperature and high humidity environment. Further, in a two-component developer containing a toner and a carrier, the toner charge amount tends to be low when the toner concentration is high, and the toner charge amount tends to be high when the toner concentration is low in the mixing ratio of the toner and the carrier. The developing device detects the image density of the printed matter and controls the toner density so that the toner charge amount becomes an appropriate value. Specifically, when printing an image or the like in a low temperature and low humidity environment, the toner charge amount tends to be high as described above, so that the image density is lowered. Therefore, in order to reduce the amount of toner charged in the developing apparatus, toner is replenished in the developer box and controlled so that the toner concentration becomes high. On the other hand, when an image or the like is printed under high temperature and high humidity, the toner charge amount tends to be low as described above, so that the image density becomes high. Therefore, the developing device performs control such as stopping the replenishment of toner until the amount of toner charged is within an appropriate range.

However, for example, in a low-temperature and low-humidity environment, the toner concentration is controlled as described above, and the toner concentration in the developer box is maintained in a high state, and the developing apparatus may not be used for a long period of time. If the atmosphere changes from a low-temperature low-humidity environment to a high-temperature high-humidity environment in such a high toner concentration, the toner charge amount fluctuates greatly the next time an image or the like is printed, and the toner and the carrier are separated from each other. It may not be possible to stir and mix well. As a result, the rise of the toner charge amount is delayed, the toner charge amount varies, and image defects such as density unevenness may occur in the printed matter.

Therefore, the present invention provides a carrier core material for an electrophotographic developer and an electrophotographic developer, which are excellent in stirring and mixing of toner and carriers and can suppress the occurrence of image defects in the initial stage of printing even when the environment changes. It is an object of the present invention to provide a carrier and an electrophotographic developer.

In order to solve the above problems, the ferrite mixed powder according to the present invention is a ferrite mixed powder obtained by mixing a plurality of spinel-type ferrite powders having different lattice constants, and has a reference value defined by the following formula (1). The group consisting of spinel-type ferrite powder having a lattice constant value smaller than (C _s ) is defined as group X, and the group consisting of spinel-type ferrite powder having a lattice constant value equal to or higher than the _{reference value (C s) is defined as group Y. , The average lattice constant (C m} ) obtained by the following formula (2) is within the range of the following formula (3).
(1) C _s = (C ₁ + C _n ) / 2
(2) C _m = (C _X x R _X + C _Y x R _Y ) / (R _X + R _Y )
(3) 8.40 ≤ C _m ≤ 8.50
However,
C ₁ is the lattice constant of the spinel-type ferrite powder having the smallest lattice constant among the plurality of spinel-type ferrite powders constituting the ferrite mixed powder.
C _n, among the plurality of spinel ferrite powder constituting the ferrite mixture powder, a lattice constant of greater spinel ferrite powder of the most lattice constants,
C _X is the average lattice constant of the spinel-type ferrite powder constituting the X group.
_CY is the average lattice constant of the spinel-type ferrite powders constituting the Y group.
R _X is a content ratio of the spinel-type ferrite powder constituting the X group in the spinel ferrite powder mixture (%)
R _y is the content ratio (%) of the spinel-type ferrite powder constituting the Y group in the spinel-type ferrite mixed powder.
_RX + _RY = 100.

In ferrite powder mixture according to the present invention, the content ratio of the spinel-type ferrite powder constituting the X group and (R _X), the content ratio of the spinel-type ferrite powder constituting the Y group (R _X) and the following formula ( It is preferable to satisfy the conditions shown in 4).
_{(4) 5 ≦ R X ≦} 90,5 ≦ R Y ≦ 90

In the ferrite mixed powder according to the present invention, each spinel type ferrite powder constituting the ferrite mixed powder has a composition formula (MO) a (Fe ₂ O ₃ ) b (where M is Fe, Mg, Mn, Cu, Zn and Ni). At least one metal element selected from the group consisting of, a + b = 100 (mol%)), or _{a part of MO and Fe 2} O _{3 in} the composition formula is replaced by an oxide of a divalent element. It is preferable to have the above composition.

_{In the ferrite mixed powder according to the present invention, the content ratio (RX} ) of the spinel-type ferrite powder constituting the X group constituting the ferrite mixed powder by performing a Rietbelt analysis of the powder X-ray diffraction pattern, and the Y The content ratio ( _RX ) of the spinel-type ferrite powder constituting the group shall be quantified, and the average lattice constant (C _x ) of the spinel-type ferrite powder constituting the X group and the spinel constituting the Y group shall be quantified. average lattice constant of type ferrite powder _{(C Y)} are different it is preferred that at least 0.005Å.

The carrier core material for an electrophotographic developer according to the present invention is a carrier core material for an electrophotographic developer, which comprises the above-mentioned ferrite mixed powder.

The carrier for an electrophotographic developer according to the present invention is characterized by comprising the above-mentioned ferrite mixed powder and a resin coating layer for coating the surface of the ferrite mixed powder.

The electrophotographic developer according to the present invention is characterized by containing the above-mentioned carrier for an electrophotographic developer and toner.

The electrophotographic developer according to the present invention is also preferably used as a supplementary developer.

According to the present invention, a carrier core material for an electrophotographic developer and an electrophotographic developer capable of excellent mixing and stirring properties of toner and carriers and suppressing the occurrence of image defects in the initial stage of printing even when the environment changes. Carriers and electrophotographic developers can be provided.

Hereinafter, embodiments of the ferrite mixed powder, the carrier core material for an electrophotographic developer, the carrier for an electrophotographic developer, and the electrophotographic developer according to the present invention will be described. In the present specification, the ferrite mixed powder, the carrier core material for an electrophotographic developer, the carrier for an electrophotographic developer, and the electrophotographic developer mean an aggregate of individual particles, that is, a powder, unless otherwise specified. It shall be. First, an embodiment of a ferrite mixed powder and a carrier core material for an electrophotographic developer will be described. Further, in the following, the ferrite mixed powder of the present embodiment will be described as being used as a carrier core material for an electrophotographic developer, but the ferrite mixed powder according to the present invention is a magnetic ink, a magnetic fluid, a magnetic filler, and a bond magnet. It can be used for various functional fillers such as fillers for electromagnetic wave shielding materials and various applications such as materials for electronic parts, and the applications of the ferrite mixed powder are not limited to carrier core materials for electrophotographic developers. ..

1. 1. Ferrite mixed powder First, the ferrite mixed powder will be described. The ferrite mixed powder is a mixture of a plurality of spinel-type ferrite powders having different lattice constants.

1-1. Equations (1) to (3)
A plurality of spinel ferrite powder mixture constituting the ferrite powder mixture, compares the reference value determined by the following formula (1) and (C _s) and the lattice constants of the spinel ferrite powder mixture, the reference value (C _{When the} group consisting of spinel-type ferrite powder having a lattice constant value smaller than s) is defined as group X, and the group consisting of spinel-type ferrite powder having a lattice constant value equal to or higher than the _{reference value (C s) is defined as group Y.} , the ferrite powder mixture has an average lattice constant determined by the following formula (2) (C _m) is assumed to be within the scope of formula (3).

(1) C _s = (C ₁ + C _n ) / 2
(2) C _m = (C _X x R _X + C _Y x R _Y ) / (R _X + R _Y )
(3) 8.40 ≤ C _m ≤ 8.50
However,
C ₁ is the lattice constant of the spinel-type ferrite powder having the smallest lattice constant among the plurality of spinel-type ferrite powders constituting the ferrite mixed powder.
C _n, among the plurality of spinel ferrite powder constituting the ferrite mixture powder, a lattice constant of greater spinel ferrite powder of the most lattice constants,
C _X is the average lattice constant of the spinel-type ferrite powder constituting the X group.
_CY is the average lattice constant of the spinel-type ferrite powders constituting the Y group.
R _X is a content ratio of the spinel-type ferrite powder constituting the X group in the spinel ferrite powder mixture (wt%),
R _y is a content ratio of the spinel-type ferrite powder constituting the Y groups in the spinel ferrite powder mixture _(wt%), a R _X + R Y = 100.

1-1-1. 1st spinel type ferrite powder to nth spinel type ferrite powder The ferrite mixed powder is derived from n or more spinel type ferrite powders (first spinel type ferrite powder to nth spinel type ferrite powder) having different lattice constants. It is assumed that it is substantially configured, and "n" may be an integer of 2 or more. For example, the value of "n" is preferably 2 ≦ n ≦ 10. In particular, 2 ≦ n ≦ 6 is preferable, 2 ≦ n ≦ 4 is more preferable, and n = 2 or 3 is more preferable, but the value of “n” is particularly limited in the present invention. It's not something. Further, the value of "n" may be a numerical value within a range in which these upper limit values and lower limit values are appropriately combined. Further, the phrase "substantially composed of spinel-type ferrite powders having n or more lattice constants different from each other" means that the ferrite mixed powder contains impurities and the like that are inevitably associated with raw materials and the like. Although it is permissible, it means that the substantial components governing the characteristics and the like of the ferrite mixed powder are a plurality of spinel-type ferrite powders having different lattice constants. Further, it is assumed that each spinel type ferrite powder constituting the ferrite mixed powder is a single ferrite powder composed of particles having the same composition, manufacturing method and the like. By changing the composition, manufacturing conditions (firing conditions such as firing temperature (firing temperature, holding time, atmospheric oxygen concentration, etc.), presence / absence of surface oxidation treatment, surface oxidation treatment conditions (oxidation treatment temperature, oxidation treatment time), etc.) Spinel-type ferrite powders having different lattice constants can be produced. The ferrite mixed powder may be, for example, a mixed powder of ferrite particles having the same composition but different firing temperatures, a mixed powder of ferrite particles having different compositions, a mixed powder of ferrite particles with oxidation treatment and a mixture of ferrite particles without oxidation treatment, and the like. Includes mixed powders of various aspects, such as mixed powders further mixed with.

Hereinafter, for convenience, the spinel-type ferrite powder constituting the ferrite mixed powder is in ascending order from the first spinel-type ferrite powder to the n-th spinel-type ferrite powder in order from the one having the smallest lattice constant value to the one having the largest lattice constant value. Number with. That is, the spinel-type ferrite powder having the smallest lattice constant is referred to as the first spinel-type ferrite powder, and the spinel-type ferrite powder having the largest lattice constant is referred to as the nth spinel-type ferrite powder. Therefore, C ₁ is the lattice constant of the first spinel-type ferrite powder, and C _n is the lattice constant of the n-th spinel-type ferrite powder.

1-1-2. Equation (1)
The formula (1), the reference value used to grouping a first spinel ferrite powder-spinel ferrite powder of the n constituting the ferrite powder mixture in the X group and Y group of the (C _s) This is an equation for obtaining, and the reference value (C _s ) is equal to the average value of the lattice constant (C ₁ ) of the first spinel-type ferrite powder and the lattice constant (C _{n) of the n-th spinel-type ferrite powder.} ..

Comparing a first spinel ferrite powder - the lattice constant of the spinel ferrite powder of the n constituting the ferrite powder mixture, the above formula (1) reference value as determined by the (C _s), the reference value A spinel-type ferrite powder having a lattice constant value smaller than (C _s ) is defined as a constituent powder of group X, and a spinel-type ferrite powder having a lattice constant value equal to or higher than a _{reference value (C s) is designated as a constituent powder of group Y.} ..

1-1-3. Equation (2)
The formula (2) is an equation for calculating the average lattice constant of the ferrite powder mixture (C _m). The average lattice constant _{(C m),} the average lattice constant of the X group and _{(C X)} and the content of the X groups in the ferrite mixture powder _{(R X),} the average lattice constant of the Y group _{(C Y)} with the ferrite It is calculated using _{the content ratio (RY} ) of group X in the mixed powder. These (C _X , _CY , _RX , _RY ) are obtained by identifying and quantifying the crystal phase structure of the X-ray diffraction pattern obtained by the method described later by performing Rietveld analysis by the method described later. Let it be the obtained value.

1-1-4. Equation (3)
The formula (3) defines the range of _{the average lattice constant (C m} ) of the ferrite mixed powder obtained according to the formula (2). As a result of diligent studies by the present inventors _{, a plurality of spinel-type ferrite powders are mixed so that the average lattice constant (Cm} ) is within the range of the above formula (3), so that the temperature and humidity can be adjusted. It has been found that under predetermined conditions, the magnetization, resistance, and charging characteristics equivalent to those of the spinel-type ferrite single powder having the same lattice constant as the average lattice constant of the ferrite mixed powder are exhibited, and the desired characteristics can be obtained. Furthermore, by mixing a plurality of spinel-type ferrite powders so as to be within the range of the above formula (3), even when the environment such as atmospheric temperature and humidity changes significantly, the charge rising property which is substantially the same as the initial setting value is maintained. I found that I could do it.

I think this is due to the following reasons. The lattice constant of the spinel-type ferrite powder is a parameter representing various characteristics such as magnetization, resistance, and charging characteristics of the spinel-type ferrite powder. Conventionally, the manufacturing conditions of the carrier core material have been precisely controlled so that the variation in the lattice constant between the particles is small. Therefore, the variation in various characteristics of the particles constituting the spinel-type ferrite single powder is small. On the other hand, the ferrite mixed powder contains particles having different lattice constant values. Therefore, it can be said that the ferrite mixed powder is a mixed powder of ferromagnetic particles and weak magnetic particles in relative terms, and is a mixed powder of particles having different charging characteristics. When performing electrophotographic printing, the toner is charged by stirring and mixing the carrier and the toner in the developing box. When the toner concentration is high, such as when replenishing toner, it is necessary to sufficiently mix the toner and carriers and triboelectrically charge them while loosening the carrier particles that are magnetically bonded to each other during stirring and mixing.

Here, the spinel-type ferrite single powder is a powder composed of particles having the same degree of magnetization. The smaller the value of the lattice constant, the higher the magnetization tends to be. Therefore, it can be said that the spinel-type ferrite single powder having a relatively small lattice constant is a powder composed of ferromagnetic particles. On the other hand, the ferrite mixed powder can be said to be a mixed powder of ferromagnetic particles and weak magnetic particles as described above. The presence of weak magnetic particles in the ferrite mixed powder can reduce the probability that the ferromagnetic particles are magnetically bonded to each other. Further, compared with the case where the ferromagnetic particles are magnetically bonded to each other, it is easier to loosen the ferromagnetic particles and the weak magnetic particles when they are magnetically bonded, and the flow of the powder The sex becomes good. Therefore, by using the ferrite mixed powder as the carrier core material, it is possible to satisfactorily contact and separate the individual particles constituting the powder, and it is possible to uniformly perform triboelectric charging between the carrier and the toner. ..

Further, the spinel type ferrite single powder is a powder composed of particles having the same charging characteristics. On the other hand, the ferrite mixed powder is a mixed powder of particles having different charging characteristics. In the spinel type ferrite single powder, since the charge amount of each particle is the same, the difference in surface potential is unlikely to occur. On the other hand, in the ferrite mixed powder, a surface potential difference occurs due to the difference in the charge amount of each particle. Therefore, in the ferrite mixed powder, when the particles come into contact with each other during stirring, charge transfer between the particles is rapidly performed.

From these facts, when the ferrite mixed powder is used as the carrier core material, the friction of the toner when the carrier and the toner are agitated and mixed in the developing box is compared with the case where the spinel type ferrite single powder is used as the carrier core material. The amount of charge increases significantly per unit time. When a spinel-type ferrite single powder is used as a carrier core material, when the environment such as ambient temperature and humidity changes, the charge rising property at the time of initial printing is poor and image defects such as density unevenness may occur. In particular, when the usage atmosphere changes from a low temperature / low humidity state to a high temperature / high humidity state and the toner is stored for a long period of time in a high toner concentration, such a problem is likely to occur in the conventional carrier core material. On the other hand, by using the ferrite mixed powder as the carrier core material, it is possible to maintain good charge riseability at the time of initial printing even when the environment such as atmospheric temperature and humidity changes. Even when the operating atmosphere changes from a low-temperature low-humidity state to a high-temperature high-humidity state, it is possible to maintain the same charge rising property as the initial setting value. Therefore, according to the present invention, the occurrence of image defects such as density unevenness is satisfactorily generated. It can be suppressed.

In order to obtain these effects, in the formula (3), the lower limit of the average lattice constant (C _m) is more preferably 8.41, further preferably 8.42. Further, the upper limit of the average lattice constant (C _m ) is more preferably 8.45, and even more preferably 8.44. In the above formula (3), these lower limit values and upper limit values can be appropriately replaced, and in the above formula (3), the equal sign inequality sign (≦) and the inequality sign (<) can be replaced. The same applies to the other equations (4) and (5), and the inequality sign (<) and the equality sign inequality sign (≦) can be replaced.

When the average lattice constant ( _Cm ) of the ferrite mixed powder is less than the lower limit of the above formula (3), the ferrite mixed powder is composed of spinel-type ferrite powder having a relatively high magnetization. It becomes difficult to loosen the magnetic bond, and the fluidity of the ferrite mixed powder decreases. Therefore, it is difficult to obtain the above-mentioned effect, which is not preferable. On the other hand, when the average lattice constant ( _Cm ) of the ferrite mixed powder exceeds the upper limit of the above formula (3), the ferrite mixed powder is composed of spinel-type ferrite powder having a relatively high resistance value. Therefore, the surface potential difference between the particles becomes small, and the effect of accelerating the charge transfer between the particles is reduced, which is not preferable.

1-2. Group X and Group Y 1-2-1. Content ratio of group X and group Y (formula (4))
_{In the ferrite mixed powder, the content ratio (RX} ) of the spinel-type ferrite powder constituting the X group and _{the content ratio (RY} ) of the spinel-type ferrite powder constituting the Y group are as described above. _{It is preferable that the condition of X} + _RY = 100 (wt%) is satisfied and the condition represented by the following formula (4) is satisfied.
_{(4) 5 ≦ R X ≦} 90,5 ≦ R Y ≦ 90

By satisfying the formula (4), it becomes easy to keep the magnetization, resistance, charge amount, etc. of the ferrite mixed powder within an appropriate range for performing desired image printing. In addition, even when the environment changes significantly, it is possible to maintain the same charge rising property as the initial setting value, and it is possible to suppress image defects such as image unevenness. If the content of the spinel-type ferrite powder constituting the X group (R _X) is less than 5 (wt%), in the ferrite powder mixture, the proportion of small spinel ferrite powder of the value of the lattice constant decreases .. That is, the ferrite mixed powder is composed of spinel-type ferrite powder having a relatively high resistance value. Therefore, the surface potential difference between the particles becomes small, and the effect of accelerating the charge transfer between the particles is reduced, which is not preferable. On the other hand, if the content of the spinel-type ferrite powder constituting the X group (R _X) is greater than 90 (wt%), in the ferrite powder mixture, the proportion of small spinel ferrite powder of the value of the lattice constant is high Become. That is, the ferrite mixed powder is composed of spinel-type ferrite powder having a relatively high magnetization. Therefore, it becomes difficult to loosen the magnetic bond between the particles at the time of stirring, and it becomes difficult to obtain the effect described by the equation (3).

In order to obtain the above effect, it is preferable that the ferrite mixed powder satisfies the above formula (4). In this case, the lower limit of Equation (4) _is, R X, is preferably a _{R Y} respectively 10 (wt%), more preferably 15 (wt%), to be 20 (wt%) It is even more preferably 25 (wt%). The upper limit _is, R X, is preferably _{R Y} are each 85 (wt%), 80 more preferably (wt%), still more preferably 75 (wt%).

1-2-2. Average lattice constant difference between group X and group Y (Equation (5))
In the ferrite mixture powder, and the average lattice constant of the spinel ferrite powder constituting the X group (C _x), the difference between the average lattice constant of the spinel ferrite powder (C _Y) constituting the Y group to the following formula ( It is preferable to satisfy the conditions shown in 5).
_{(5) 0.03Å <C Y -C} x <0.10Å

By satisfying formula (5), and the average lattice constant of the spinel ferrite powder constituting the X group (C _x), the difference between the average lattice constant of the spinel ferrite powder constituting the Y group (C _Y) The present invention can be ensured by mixing a plurality of spinel-type ferrite powders having significant differences in magnetization, resistance, and charging characteristics while keeping _{the average lattice constant (C m) within the range of the above formula (3).} The above-mentioned effect of the ferrite mixed powder according to the above can be obtained more reliably.

The lower limit of the above formula (5) is preferably 0.04 Å, more preferably 0.05 Å, further preferably 0.06 Å, and even more preferably 0.07 Å. It is even more preferably 0.08 Å. Further, the upper limit of the above formula (5) is more preferably 0.09 Å.

1-3. Composition Each spinel-type ferrite powder constituting the ferrite mixed powder shall have a spinel-type crystal structure. Ferrite is a magnetic oxide containing ferric oxide (Fe ₂ O ₃ ) as a main component, and spinel-type ferrite powder is _{represented by (MO) a (Fe 2} O ₃ ) b. Here, M is a transition metal element and is not particularly limited as long as it is an element capable of forming a spinel-type crystal structure. For example, M is a group consisting of Fe, Mg, Mn, Cu, Zn and Ni. It is preferably at least one metal element selected from. Further, in the above composition formula, it is preferable that a + b = 100 (mol%).

Further, in the above composition formula, _{a part of MO and / or Fe 2} O ₃ may be replaced with an oxide of a divalent element. The oxides of divalent elements include, for example, SrO, CaO, TiO, ZrO, CuO, ZnO, and NiO.

In particular, each spinel-type ferrite powder constituting the ferrite mixed powder is preferably represented by a composition formula of _{(MnO) x (MgO) y (Fe 2} O _{3) z.} At this time, it is preferable that x + y + z = 100 (mol%), x is 15 mol% to 60 mol%, y is 15 mol% to 60 mol%, and z is 0.1 mol% to 35 mol%. Further, in the spinel type ferrite powder represented by the composition formula, _{at least a part of MnO, MgO and Fe 2} O ₃ is 0 due to any one of SrO, CaO, TiO, ZrO, CuO, ZnO and NiO. It is preferably substituted in an amount of .4 mol% to 2.0 mol%, and more preferably substituted within the range by SrO and / or ZrO.

Each spinel-type ferrite powder constituting the ferrite mixed powder may have the above composition, and the lattice constants of the respective spinel-type ferrite powders may be different from each other. The composition of each spinel-type ferrite powder may be the same, or may be different within the range represented by the above composition formula. It is sufficient that the composition is substantially the same.

1-4. Lattice constant The lattice constants of the first spinel-type ferrite powder to the n-th spinel-type ferrite powder constituting the ferrite mixed powder may satisfy the above formula (3) when viewed as a whole ferrite mixed powder, and each of them may satisfy the above formula (3). The lattice constant of the spinel-type ferrite powder is not particularly limited. However, it is preferably about 8.400 Å or more and 8.500 Å or less.

The lattice constant here refers to a value specified by identifying the crystal phase by Rietveld analysis of the powder X-ray diffraction pattern obtained by the following method by the method described later. It may be difficult to identify and quantify each crystal phase by waveform separation of the powder X-ray diffraction pattern, but according to the Rietbelt analysis based on the crystal structure model, each phase is also identified and quantified in such a case. Becomes possible.

(Powder X-ray diffraction)
As the X-ray diffractometer, "X'PertPRO MPD" manufactured by PANalytical Co., Ltd. can be used. A Co tube (CoKα ray) can be used as an X-ray source. As the optical system, a centralized optical system and a high-speed detector "X'Celarator" can be used. The measurement conditions are as follows.

Scan speed: 0.08 ° / sec Divergence slit: 1.0 °
Scattering slit: 1.0 °
Light receiving slit: 0.15 mm
Encapsulated tube voltage and current value: 40kV / 40mA
Measurement range: 2θ = 15 ° to 90 °
Accumulation number: 5 times

(Identification of crystal phase)
Based on the above-mentioned measurement results (powder X-ray diffraction pattern), "National Institute for Materials Science," AtomWork ", Internet <URL: http: // crystaldb.anime.go.jp/>" The crystal structure was identified as follows from the structures disclosed in the above, and the lattice constant was specified from each crystal structure.

In the case of ferrite mixed powder, the following model was adopted.
Group X: Crystal phase composed of manganese ferrite (spinel type crystal) Crystal structure: Space group F d -3 m (No. 227)
Group Y: Crystal phase composed of manganese ferrite (spinel type crystal) Crystal structure: Space group F d -3 m (No. 227)

In the case of single ferrite powder, the following model was adopted.
Crystal phase composed of manganese ferrite (spinel type crystal) Crystal structure: Space group F d -3 m (No. 227)

1-5. Content ratio After identifying the crystal phase as described above, by refining the identified crystal structure using the analysis software "RIETAN-FP v2.83", groups X and Y in the ferrite mixed powder the existence ratio of the mass conversion was calculated phase composition ratio of each crystal phase (content), and it said R _X, and R _Y.

As the profile function, the pseudo-Voigt functions of Thompson, Cox, and Hasting are used to perform asymmetry by the Howard method. The Rwp value and S value indicating the accuracy of fitting are Rwp: 2% or less and S value: 1.5 or less, respectively, and the main peaks of the B and C phases are fitted at 2θ = 35 to 37 °. After confirming that, each parameter was optimized. Here, the profile function uses a pseudo Voigt function of Thomason, Cox, and Hasting, and asymmetry is performed by the Howard method.
Further, the following parameters are optimized so that the Rwp value and the S value indicating the fitting accuracy are Rwp: 2% or less and S value: 1.5 or less, respectively.

(Parameters to be optimized)
・ Shift factor ・ Scale factor ・ Background parameter ・ Gaussian function U, V, W
・ Lorentz function X, Y
・ Asymmetric parameter As
・ Lattice constant ・ Oxygen atom coordinates ・ Atomic displacement parameter B is fixed at 0.75 for iron and manganese atoms and 1.0 for oxygen atoms.

1-6. Average volume particle size (D ₅₀ )
When the ferrite mixed powder is used as the carrier core material, the average volume particle size (D ₅₀ ) of the ferrite mixed powder is preferably 20 μm or more and 50 μm or less. When the volume average particle size (D ₅₀ ) of the ferrite mixed powder is less than 20 μm, the particle size is small, so that the ferrite mixed powder is likely to aggregate. When the ferrite mixed particles are used as a core material and the surface thereof is coated with a resin to form a carrier, if the ferrite mixed powders are aggregated, the surface of each ferrite mixed powder can be satisfactorily coated with the resin. It disappears. After that, when the agglomeration of the particles is loosened during the production or use of the developer, the developer has a high content of carriers in a region not covered with the resin. Therefore, if a developer is produced using a ferrite mixed powder having an average volume particle size (D ₅₀ ) of less than 20 μm as the core material, sufficient charge-imparting property to the toner may not be obtained, which is not preferable. Further, when the average volume particle size (D ₅₀ ) is less than 20 μm, the particle size is small and it becomes difficult to suppress carrier scattering. From these viewpoints, the average volume particle size (D ₅₀ ) is more preferably 25 μm or more, and more preferably 30 μm or more.

On the other hand, when the volume average particle size (D ₅₀ ) of the ferrite mixed powder exceeds 50 μm, the particle size of each particle constituting the ferrite mixed powder becomes large. Therefore, the surface area of the carrier that contributes to triboelectric charging with the toner is smaller than that of the ferrite mixed powder having a small volume average particle size (D _50). Therefore, sufficient chargeability cannot be obtained for the toner, and it becomes difficult to print an image with high definition. From these viewpoints, the volume average particle size (D ₅₀ ) of the ferrite mixed powder is more preferably 45 μm or less, and even more preferably 40 μm or less. The more preferable range of the volume average particle diameter (D ₅₀ ) of the ferrite mixed powder can be any combination of the numerical values listed as the upper limit value and the lower limit value, and may be a range that does not include these numerical values. The same applies to other numerical ranges.

Further, in the ferrite mixed powder, the content ratio of particles having a volume particle size of less than 16 μm is preferably 4.5% by volume or less. When the content ratio of the particles having a volume particle size of less than 16 μm is 4.5% by volume or less, the aggregation of the ferrite mixed powder can be better suppressed and the carrier scattering can be suppressed when used as a developer. ..

The average volume particle size (D ₅₀ ) referred to here is a value measured according to JIS Z 8825: 2013 by a laser diffraction / scattering method. Specifically, it can be measured as follows using a Microtrack particle size analyzer (Model9320-X100) manufactured by Nikkiso Co., Ltd. First, using the ferrite mixed powder (or ferrite single powder) to be measured as a sample, 10 g of the sample and 80 ml of water are placed in a 100 ml beaker, 2 to 3 drops of a dispersant (sodium hexametaphosphate) are added, and an ultrasonic homogenizer is used. Using (SMT.Co. LTD. UH-150 type), set the output level to 4, disperse for 20 seconds, prepare a sample by removing bubbles formed on the beaker surface, and use the sample. The volume average particle size of the sample measured by the microtrack particle size analyzer is defined as the sample volume average particle size (D ₅₀ ).

1-7. Apparent density (AD)
The apparent density (AD) of the ferrite mixed powder ^{is preferably 2.0 g / cm 3} or more and 2.8 g / cm ³ or less. The apparent density here is a value measured in accordance with JIS Z 2504: 2012. When carriers are obtained using the ferrite mixed powder, if the apparent density of the ferrite mixed powder is within the range, the fluidity of the carriers is good and the charging characteristics due to stirring stress in the developing machine are exhibited. Deterioration can be suppressed.

The apparent density of the ferrite mixed powder ^{is more preferably 2.1 g / cm 3} or more, and further preferably 2.2 g / cm ³ or more. Further, the apparent density of the ferrite mixed powder ^{is more preferably 2.7 g / cm 3} or less, and further preferably 2.6 g / cm ³ or less.

More specifically, the apparent density can be measured as follows using a powder apparent density meter. As the powder apparent density meter, one composed of a funnel, a cup, a funnel support, a support rod, and a support base is used. A balance having a weighing capacity of 200 g and a sensitivity of 50 mg is used. Then, the value obtained by measuring by the following procedure and calculating as follows is used as the apparent density here.

(1) Measurement method (a) The sample should be at least 150 g or more.
(B) The sample is poured into a funnel having an orifice with a pore size of 2.5 + 0.2 / -0 mm, and the sample that flows out is poured until the glass is full and overflows.
(C) Immediately stop the inflow of the sample as soon as it starts to overflow, and scrape the raised sample on the cup flat with a spatula along the upper end of the cup so as not to give vibration.
(D) The side surface of the cup is tapped to sink the sample, the sample adhering to the outside of the cup is removed, and the weight of the sample in the cup is weighed with an accuracy of 0.05 g.

(2) Calculation The value obtained by multiplying the measured value obtained in (d) above by 0.04 is rounded to the second decimal place by JIS-Z8401 (rounding method of the value), and the unit is ^{"g / cm 3".} The apparent density.

1-8. Volumetric fluidity The volumetric fluidity (FR) (s / 50g) of the ferrite mixed powder is a value measured in accordance with JIS-Z2502: 2012. The volumetric fluidity of the ferrite mixed powder is preferably 15 (s / 50 g) or more and 50 (s / 50 g) or less. Here, the volumetric fluidity of the ferrite mixed powder is more preferably 18 (s / 50 g) or more, and further preferably 20 (s / 50 g) or more. Further, the volumetric fluidity of the ferrite mixed powder is more preferably 45 (s / 50 g) or less, and further preferably 40 (s / 50 g) or less. When the volumetric fluidity of the ferrite mixed powder is within such a numerical range, the fluidity of the ferrite mixed powder is good. Therefore, the ferrite mixed powder can be satisfactorily agitated with the toner even in the developing box.

1-9. Magnetic characteristics Next, the magnetic characteristics of the ferrite mixed powder will be described. When the ferrite mixed powder is used as the core material of a carrier for an electrophotographic developer, VSM measurement (room temperature) when a magnetic field of ^{1K · 1000 / 4π · A / m (= 79.58 × 10 4 A / m) is applied.} It is preferable that the saturation magnetization by the dedicated vibration sample magnetometer) is 55 Am ² / kg or more and 95 Am ^{2 / kg or less.} When the saturation magnetization of the ferrite mixed powder is within the above range, an electrophotographic developer capable of satisfactorily performing high-quality electrophotographic printing can be obtained by using the ferrite mixed powder as a core material. If the saturation magnetization of the ferrite mixed powder is ^{less than 55 Am 2} / kg, the magnetic force of the core material is weak and carrier scattering due to low magnetization is likely to occur, which is not preferable. On the other hand, there is a trade-off relationship between saturation magnetization and electrical resistance, and the higher the saturation magnetization of the ferrite powder, the lower the electrical resistance. Therefore, if the saturation magnetization of the ferrite mixed powder ^{exceeds 95 Am 2} / kg, the resistance of the ferrite mixed powder becomes low, and carrier scattering due to the low resistance is likely to occur, which is not preferable.

From these viewpoints, more preferably saturation magnetization of the ferrite powder mixture is 60 Am ² / kg or more, further preferably 65 Am ² / kg or more. Further, more preferably the saturation magnetization of the ferrite powder mixture is less than 90 Am ² / kg, more preferably not more than 85Am ² / kg.

2. Carrier for Electrophotodeveloping Agent Next, the carrier for electrophotographic developing agent according to the present invention will be described. The carrier for an electrophotographic developer according to the present invention includes the above ferrite mixed powder and a resin coating layer provided on the surface of the ferrite mixed powder. That is, the ferrite mixed powder is used as a core material for a carrier for an electrophotographic developer. Since the ferrite mixed powder is as described above, the resin coating layer will be mainly described here.

(1) Type of coating resin The type of resin (coating resin) constituting the resin coating layer is not particularly limited. For example, fluororesin, acrylic resin, epoxy resin, polyamide resin, polyamideimide resin, polyester resin, unsaturated polyester resin, urea resin, melamine resin, alkyd resin, phenol resin, fluoroacrylic resin, acrylic-styrene resin, silicone resin, etc. Can be used. Further, a modified silicone resin or the like obtained by modifying a silicone resin or the like with each resin such as an acrylic resin, a polyester resin, an epoxy resin, a polyamide resin, a polyamideimide resin, an alkyd resin, a urethane resin or a fluororesin may be used. For example, the coating resin is preferably a thermosetting resin from the viewpoint of suppressing resin peeling due to mechanical stress received during stirring and mixing with toner. Examples of the thermosetting resin suitable for the coating resin include epoxy resin, phenol resin, silicone resin, unsaturated polyester resin, urea resin, melamine resin, alkyd resin, and resins containing them. However, as described above, the type of coating resin is not particularly limited, and an appropriate one can be appropriately selected according to the type of toner to be combined, the usage environment, and the like.

Further, the resin coating layer may be formed by using one kind of resin, or the resin coating layer may be formed by using two or more kinds of resins. When two or more kinds of resins are used, two or more kinds of resins may be mixed to form one resin coating layer, or a plurality of resin coating layers may be formed. For example, in order to provide the surface of the ferrite mixed powder with a first resin coating layer having good adhesion to the ferrite mixed powder, and to impart the desired charge-imparting performance to the carrier on the surface of the first resin coating layer. It is also preferable to provide a second resin coating layer of the above.

(2) Resin coating amount The resin coating amount (resin coating amount) that covers the surface of the ferrite mixed powder is preferably 0.1% by mass or more and 10% by mass or less with respect to the ferrite mixed powder used as the core material. If the resin coating amount is less than 0.1% by mass, it becomes difficult to sufficiently coat the surface of the ferrite mixed powder with the resin, and it becomes difficult to obtain a desired charging ability. Further, if the resin coating amount exceeds 10% by mass, carrier particles agglomerate during manufacturing, resulting in a decrease in productivity such as a decrease in yield and a decrease in the fluidity of the developer in the actual machine or with respect to the toner. It is not preferable because the developer characteristics such as chargeability vary.

(3) Additive The resin coating layer may contain an additive for controlling the electric resistance, the amount of charge, and the charge rate of carriers such as a conductive agent and a charge control agent. Examples of the conductive agent include conductive carbon, oxides such as titanium oxide and tin oxide, and various organic conductive agents. However, since the electrical resistance of the conductive agent is low, if the amount of the conductive agent added is too large, a charge leak is likely to occur. Therefore, the content of the conductive agent is preferably 0.25% by mass or more and 20.0% by mass, and preferably 0.5% by mass or more and 15.0% by mass or less with respect to the solid content of the coating resin. More preferably, it is 1.0% by mass or more and 10.0% by mass or less.

Examples of the charge control agent include various charge control agents generally used for toner and a silane coupling agent. The types of these charge control agents and coupling agents are not particularly limited, but charge control agents such as niglosin dyes, quaternary ammonium salts, organometallic complexes, and metal-containing monoazo dyes, aminosilane coupling agents, and fluorine-based silane cups. A ring agent or the like can be preferably used. The content of the charge control agent is preferably 0.25% by mass or more and 20.0% by mass or less, and 0.5% by mass or more and 15.0% by mass or less, based on the solid content of the coating resin. More preferably, it is more preferably 1.0% by mass or more and 10.0% by mass or less.

3. 3. Electrophotodeveloping agent Next, an embodiment of the electrophotographic developing agent according to the present invention will be described. The electrophotographic developer includes the carrier for the electrophotographic developer and toner.

As the toner constituting the electrophotographic developer, for example, either a polymerized toner produced by a polymerization method or a pulverized toner produced by a pulverization method can be preferably used. These toners may contain various additives and may be any toner as long as it can be used as an electrophotographic developer in combination with the above carriers.

The volume average particle size (D ₅₀ ) of the toner is preferably 2 μm or more and 15 μm or less, and more preferably 3 μm or more and 10 μm or less. When the volume average particle size (D ₅₀ ) of the toner is within the range, an electrophotographic developer capable of performing high-quality electrophotographic printing can be obtained.

The mixing ratio of the carrier and the toner, that is, the toner concentration is preferably 3% by mass or more and 15% by mass or less. An electrophotographic developer containing toner at the concentration can easily obtain a desired image density, and fog and toner scattering can be suppressed more satisfactorily.

On the other hand, when the electrophotographic developer is used as a supplementary developer, it is preferably 2 parts by mass or more and 50 parts by mass or less of the toner with respect to 1 part by mass of the carrier.

In the electrophotographic developer, a carrier is attracted and adhered to a magnetic drum or the like by magnetic force to form a brush, and the toner is conveyed. While applying a bias electric field, the toner is applied to an electrostatic latent image formed on a photoconductor or the like. It can be suitably used for various electrophotographic developing devices to which a magnetic brush developing method for forming a visible image by adhering is applied. The electrophotographic developer is used not only in an electrophotographic developing device that uses a DC bias electric field when applying a bias electric field, but also in an electrophotographic developing device that uses an alternating bias electric field in which an AC bias electric field is superimposed on a DC bias electric field. be able to.

4. Manufacturing Method The following describes the manufacturing method of the ferrite mixed powder, the carrier core material for an electrophotographic developer, the carrier for an electrophotographic developer, and the electrophotographic developer according to the present invention.

4-1. Carrier core material for ferrite mixed powder and electrophotographic developer The ferrite mixed powder and carrier core material for electrophotographic developer according to the present invention can be produced as follows.

The ferrite mixed powder according to the present invention includes a plurality of spinel-type ferrite powders having different lattice constants. As a method for producing the ferrite mixed powder, for example, a plurality of ferrite single powders (spinel type ferrite powder) produced by changing the composition or production conditions (firing conditions or presence / absence of surface oxidation treatment, surface oxidation treatment conditions, etc.). Can be obtained by mixing at a predetermined mixing ratio. Here, first, a method for producing a single ferrite powder will be described.

When producing a single ferrite powder, the raw materials are weighed appropriately so that the composition ratio after firing becomes the desired ferrite composition, and then pulverized with a ball mill or a vibration mill for 0.5 hours or more, preferably 1 hour or more and 20 hours or less. Mix and tentatively bake.

For example, in the composition formula of (MnO) x (MgO) y (Fe ₂ O ₃ ) z (however, 15 ≦ x ≦ 50, 2 ≦ y ≦ 35, 45 ≦ z ≦ 60, x + y + z = 100 (mol%)). In order to produce a ferrite single powder having the represented spinel-type crystal structure, each raw material is weighed and pulverized and mixed so that x, y, and z have desired values. As the raw material, for example, a _{Fe 2 O 3, Mg (OH} ) ₂ and / or _{MgCO 3, MnO 2, Mn 2} O 3, Mn 3 O 4 and one or more manganese selected from the group consisting of MnCO ₃ It is preferable to use a compound. At this time, for example, in _{order to produce a ferrite powder in which a part of MO and / or Fe 2} O ₃ is replaced with an oxide of an element capable of divalent in the above composition formula, the oxide of these elements is produced. Alternatively, a carbonate or the like is used as a raw material, weighed so as to have a desired addition amount, and pulverized and mixed with other raw materials. For example, SrCO ₃ can be used as a raw material for SrO, and ZrO ₂ can be used as a raw material for ZrO.

The pulverized product thus obtained is pulverized and mixed, and calcined. Then, the obtained calcined product is further pulverized with a ball mill, a vibration mill or the like, water is added, and the calcination is finely pulverized with a bead mill or the like to obtain a slurry. The degree of crushing can be controlled by adjusting the diameter, composition, and crushing time of the beads used as the medium. In order to uniformly disperse the raw materials, it is preferable to use fine beads having a particle size of 1 mm or less as a medium. Further, in order to uniformly disperse the raw materials, _{it is preferable to pulverize the pulverized product so that the volume average particle diameter (D 50} ) is 2.5 μm or less, and it is more preferable to pulverize the pulverized product so that the volume average particle diameter (D 50) is 2.0 μm or less. preferable. Further, in order to suppress abnormal grain growth, it is preferable to grind so that _{the particle size (D 90) on the coarse side of the particle size distribution is 3.5 μm or less.} It is preferable to add a dispersant, a binder, or the like to the slurry thus obtained to adjust the viscosity to 2 or more and 4 or less, if necessary. At this time, polyvinyl alcohol or polyvinylpyrrolidone can be used as the binder.

The slurry prepared as described above is sprayed with a spray dryer and dried to obtain a granulated product.

Next, it is preferable to classify the granulated product before firing and remove the fine particles contained in the granulated product in order to obtain a ferrite powder having a uniform particle size. The classification of the granulated product can be performed using a known air flow classification, a sieve, or the like.

Next, the classified granules are calcined. It is preferable that the granulated product is subjected to the main firing after the primary firing (temporary firing) as necessary. When the primary firing is performed, the firing temperature is preferably 600 ° C. or higher and 1050 ° C. or lower.

Further, this firing is preferably carried out by holding the firing at a temperature of 850 ° C. or higher for 4 hours or longer and 24 hours or shorter in an inert atmosphere or a weakly oxidizing atmosphere. It is preferable to keep the temperature (850 ° C. or higher and 1250 ° C. or lower) suitable for producing a ferrite powder having a spinel-type crystal structure for 3 hours or longer. However, the main firing temperature and the holding time are not particularly limited as long as a ferrite powder having a spinel-type crystal structure can be obtained. Further, the term "inert atmosphere" or "weakly oxidizing atmosphere" means that the oxygen concentration is 0% by volume (0 ppm) or more and 10% by volume (100,000 ppm) or less in a mixed gas atmosphere of nitrogen and oxygen. The oxygen concentration is more preferably 7% by volume (70,000 ppm) or less, further preferably 6% by volume (60,000 ppm) or less, and even more preferably 5% by volume (50,000 ppm) or less.

When performing the main firing, granulation is performed like a tunnel kiln or an elevator kiln, rather than a firing furnace of a type such as a rotary kiln in which a granulated object (object to be fired) is passed through a hot portion while flowing. It is preferable to carry out the operation in a firing furnace of a type that allows hot air to pass through while the object is placed in a kiln or the like and left to stand. In a firing furnace such as a rotary kiln that allows the granulated material to pass through the hot part while flowing, if the oxygen concentration in the firing atmosphere is low, the granulated material adheres to the inner surface of the furnace when it passes through the hot part. However, it may not be possible to sufficiently apply heat to the granulated material that passes through the inside while flowing. In that case, since the granulated product passes through the hot portion without being able to sufficiently sinter the granulated product, the obtained fired product has an internal surface even if the surface is sufficiently sintered. Sintering is often inadequate. Such a fired product does not satisfy the strength required as a carrier core material for an electrophotographic developer, and the ferrite reaction inside is insufficient, so that the magnetic properties required as a carrier core material for an electrophotographic developer and the magnetic properties It may not meet the electrical characteristics.

On the other hand, if the granulated product is fired in a firing furnace of a type in which the granulated product is placed in a kou pot or the like and allowed to pass through a hot portion, the inside of the product to be fired can be sufficiently sintered. Therefore, it becomes easy to obtain a single ferrite powder having high magnetization and high resistance and in which a spinel-type crystal phase is sufficiently formed. For these reasons, it is preferable to use a tunnel kiln, an elevator kiln, or the like when performing the main firing step.

After firing, the fired product is crushed and classified to obtain a single ferrite powder. As the classification method, the particle size is adjusted to a desired particle size by using an existing wind power classification, mesh filtration method, sedimentation method, or the like. When performing dry recovery, it is also possible to recover with a cyclone or the like. When adjusting the particle size, two or more of the above-mentioned classification methods may be selected and carried out, or the conditions may be changed by one type of classification method to remove the coarse powder side particles and the fine powder side particles.

Further, after firing or classification, if necessary, the surface of the ferrite single powder is heated at a low temperature to perform surface oxidation treatment, and the surface resistance of the ferrite single powder can be adjusted. For the surface oxidation treatment, a rotary electric furnace, a batch electric furnace, or the like is used, and the ferrite single powder is heat-treated at 400 ° C. or higher and 730 ° C. or lower, preferably 450 ° C. or higher and 680 ° C. or lower in an oxygen-containing atmosphere such as the atmosphere. It can be done by. If the heating temperature during the surface oxidation treatment is lower than 400 ° C., the surface of the ferrite mixed powder cannot be sufficiently oxidized, and the desired surface resistance characteristics may not be obtained. On the other hand, when the heating temperature is higher than 730 ° C., the oxidation of the single ferrite powder proceeds too much, and the magnetization of the single ferrite powder decreases, which is not preferable. In order to uniformly form an oxide film on the surface of the ferrite mixed powder, it is preferable to use a rotary electric furnace. However, the surface oxidation treatment is an arbitrary step.

The ferrite mixed powder according to the present invention can be obtained by appropriately mixing a plurality of types of ferrite single powders produced as described above at a predetermined ratio so as to satisfy the above-mentioned formula (3). Various mixers can be used when mixing the single ferrite powder. Either a container rotary type mixer or a container fixed type mixer may be used, and as the container rotary type mixer, for example, a V-type mixer, a locking mixer (dry powder mixer), or the like is used. As the container-fixed mixer, for example, a Redige mixer (manufactured by Redigge Co., Ltd.), a Nautamixer (registered trademark) (manufactured by Hosokawa Micron Co., Ltd.) and the like can be used.

4-2. Carrier for Electrophotodeveloping Agent The carrier for electrophotographic developing agent according to the present invention is formed by using the above ferrite mixed powder as a core material and providing a resin coating layer on the surface of the ferrite mixed powder. The resin constituting the resin coating layer is as described above. When forming the resin coating layer on the surface of the ferrite mixed powder, a known method such as a brush coating method, a spray drying method using a fluidized bed, a rotary drying method, an immersion drying method using a universal stirrer, or the like can be adopted. .. In order to improve the ratio of the resin coating area to the surface of the ferrite mixed powder (resin coating ratio), it is preferable to adopt a spray-drying method using a fluidized bed. Regardless of which method is adopted, the ferrite mixed powder can be subjected to the resin coating treatment once or a plurality of times. The resin coating liquid used when forming the resin coating layer may contain the above additives. Further, since the amount of resin coated on the surface of the ferrite mixed powder is as described above, the description thereof is omitted here.

After applying the resin coating liquid to the surface of the ferrite mixed powder, baking may be performed by an external heating method or an internal heating method, if necessary. In the external heating method, a fixed or fluid electric furnace, a rotary electric furnace, a burner furnace, or the like can be used. In the internal heating method, a microwave furnace can be used. When a UV curable resin is used as the coating resin, a UV heater is used. Baking is required to be performed at a temperature equal to or higher than the melting point of the coating resin or the glass transition point. When a thermosetting resin, a condensation-crosslinked resin, or the like is used as the coating resin, it is necessary to bake at a temperature at which the curing of these resins proceeds sufficiently.

4-3. Electrophotodeveloping agent Next, a method for producing the electrophotographic developing agent according to the present invention will be described.
The electrophotographic developer according to the present invention includes the carrier for the electrophotographic developer and toner. As described above, either a polymerized toner or a pulverized toner can be preferably used as the toner.

The polymerized toner can be produced by a known method such as a suspension polymerization method, an emulsification polymerization method, an emulsification agglutination method, an ester extension polymerization method, or a phase transfer emulsification method. For example, a colored dispersion in which a colorant is dispersed in water using a surfactant, a polymerizable monomer, a surfactant and a polymerization initiator are mixed and stirred in an aqueous medium, and the polymerizable monomer is aqueous. After emulsifying and dispersing in a medium and polymerizing while stirring and mixing, a salting-out agent is added to salt out the polymer particles. Polymerized toner can be obtained by filtering, washing, and drying the particles obtained by salting out. Then, if necessary, an external additive may be added to the dried toner particles.

Further, in producing the polymerized toner particles, a toner composition containing a polymerizable monomer, a surfactant, a polymerization initiator, a colorant and the like is used. A fixability improver and a charge control agent can be added to the toner composition.

For the pulverized toner, for example, a binder resin, a colorant, a charge control agent, etc. are sufficiently mixed with a mixer such as a Henschel mixer, then melt-kneaded with a twin-screw extruder or the like to uniformly disperse, and after cooling, a jet mill is used. After classification, toner having a desired particle size can be obtained by, for example, classifying with a wind classifier or the like. If necessary, wax, magnetic powder, viscosity modifier, and other additives may be included. Further, an external additive can be added after the classification.

Next, the present invention will be specifically described with reference to Examples and Comparative Examples. However, the present invention is not limited to the following examples.

In this embodiment, seven types of spinel-type ferrite powders having different lattice constants (hereinafter referred to as ferrite particles 1 to ferrite particles 7) are produced, and by appropriately mixing these, a ferrite mixed powder as an example of the present invention (implementation). Examples 1 to 5) were obtained. Further, in the comparative example, a single powder (ferrite single powder) composed of each of these ferrite particles 1 to 7 was used. A carrier for an electrophotographic developer was manufactured using each ferrite powder as a core material.

1. 1. Production of Ferrite Particles 1 to 7 (1) Ferrite Particles 1
As the ferrite particle 1, it is represented by the composition formula (x = 38.0 mol%, y = 11.0 mol%, z = 50.3 mol%) of (MnO) x (MgO) y (Fe ₂ O _{3) z, and is MO.} And / or a spinel-type ferrite powder in which a part of _{Fe 2} O _{3 was substituted with SrO by 0.7 mol% was produced.}

First, the MnO raw material, the MgO raw material, and the Fe ₂ O ₃ raw material were weighed so that the composition ratios of MnO, MgO, and Fe ₂ O _{3 after firing were the above-mentioned values of x, y, and z.} Further, the SrO raw material was weighed so that the molar ratio was SrO: 0.7 with respect to the main component raw material: 100. Here, 29.0 kg of trimanganese tetraoxide was used as the MnO raw material, 6.4 kg of magnesium hydroxide was used as the MgO raw material _{, 80.5 kg of ferric oxide was used as the Fe 2} O ₃ raw material, and strontium carbonate was used as the SrO raw material. 1.0 kg was used.

Next, the weighed raw material was pulverized with a dry media mill (vibration mill, stainless beads having a diameter of 1/8 inch) for 5 hours, and the obtained pulverized product was made into pellets of about 1 mm square by a roller compactor. The obtained pellets are subjected to coarse powder removal by a vibrating sieve having a mesh opening of 3 mm, then fine powder is removed by a vibrating sieve having a mesh opening of 0.5 mm, and then heated in a rotary electric furnace at 1000 ° C. for 3 hours and calcined. Was done.

Then, after crushing using a dry media mill (vibration mill, 1/8 inch diameter stainless beads), water is added, and a wet media mill (horizontal bead mill, 1/16 inch diameter stainless beads) is used. Grinded for 5 hours. A binder and a dispersant were added to the slurry prepared in this manner. PVA (polyvinyl alcohol, 20% by mass solution) was used as a binder so that PVA was 0.2% by mass with respect to the solid content (amount of tentatively calcined product in the slurry). Further, as a dispersant, a polycarboxylic acid-based dispersant was added so that the viscosity of the slurry became 2 poisons.

Then, it was granulated and dried by a spray dryer. The obtained granulated product was heated in an air atmosphere at 700 ° C. for 2 hours in a rotary electric furnace to remove organic components such as a dispersant and a binder.

Then, the granulated product was mainly fired by holding it in a tunnel type electric furnace at a firing temperature (holding temperature) of 1210 ° C. and an atmosphere of an oxygen concentration of 4.5% by volume for 5 hours. At this time, the temperature rising rate was set to 150 ° C./hour and the temperature falling rate was set to 110 ° C./hour. Further, the atmospheric gas was introduced from the outlet side of the tunnel type electric furnace, and the internal pressure of the tunnel type electric furnace was set to 0 to 10 Pa (positive pressure). The obtained fired product is crushed by a hammer crusher, further classified by a gyro shifter (vibration sieve) and a turbo classifier (air flow classifier) to adjust the particle size, and low magnetic force products are separated by magnetic force beneficiation to separate ferrite particles. 1 was manufactured.

(2) Ferrite particles 2
Ferrite particles 2 were produced in the same manner as the ferrite particles 1 except that the oxygen concentration at the time of the main firing was 0.5% by volume.

(3) Ferrite particles 3
Ferrite particles 3 were produced in the same manner as the ferrite particles 1 except that the firing temperature (holding temperature) during the main firing was 1050 ° C. and the oxygen concentration during the main firing was 1.5% by volume.

(4) Ferrite particles 4
The point where the oxygen concentration at the time of the main firing was 0.0% by volume, and the ferrite particles after the main firing were heated to 600 ° C. by a rotary electric furnace provided with a hot portion and a cooling portion following the hot portion. Ferrite particles 4 were produced in the same manner as the ferrite particles 1 except that the surface oxidation treatment was performed in the above.

(5) Ferrite particles 5
It is represented by the composition formula (x = 30.0 mol%, y = 2.0 mol%, z = 67.5 mol%) of (MnO) x (MgO) y (Fe ₂ O _{3 ) z, and MO and / or Fe 2} In _{order to produce a spinel-type ferrite powder in which a part of O 3} is substituted with ZrO by 0.5 mol%, the MnO raw material and the MgO raw material are prepared so that the composition ratio after firing becomes these values of x, y and z. Similar to ferrite particles 1, except that the Fe ₂ O ₃ raw material and the ZrO raw material were weighed, the oxygen concentration during the main firing was 0.0% by volume, and the surface oxidation treatment was performed. Ferrite particles 5 were produced. The surface oxidation treatment was carried out in the same manner as the ferrite particles 4 except that the surface oxidation treatment temperature was set to 650 ° C.

(6) Ferrite particles 6
In order to produce a spinel-type ferrite powder represented by the composition formula (x = 30.0 mol%, z = 70.0 mol% (y = 0.0 mol%)) of (MnO) x (Fe ₂ O _{3) z, Except for the points where the MnO raw material and the Fe 2} O ₃ raw material were weighed so that the composition ratio after firing was these x and z values, and the point where the oxygen concentration at the time of the main firing was 5.5% by volume. The ferrite particles 6 were produced in the same manner as the ferrite particles 1.

(7) Ferrite particles 7
In order to produce a spinel-type ferrite powder represented by the composition formula (x = 20.0 mol%, z = 80.0 mol% (y = 0.0 mol%)) of (MnO) x (Fe ₂ O _{3) z, Except for the points where the MnO raw material and the Fe 2} O ₃ raw material were weighed so that the composition ratio after firing would be these x and z values, and the point where the oxygen concentration at the time of main firing was 6.5% by volume. The ferrite particles 5 were produced in the same manner as the ferrite particles 1.

2. Example (1) Example 1
a) Ferrite mixed powder In the ferrite mixed powder of Example 1, the ferrite particles 1, the ferrite particles 2, and the ferrite particles 3 are mixed using a mixer so that the mass ratio is “3: 3: 4”. Obtained by that.

b) Carrier for electrophotographic developer Using the above ferrite mixed powder as a core material, a resin coating layer was formed on the surface of the ferrite mixed powder as shown below to obtain a carrier of Example 1.

First, a condensation-crosslinked silicone resin (weight average molecular weight: about 8000) containing T units and D units as main components was prepared. 2.5 parts by mass of this silicone resin solution (since a resin solution concentration of 20% by mass was used, the silicone resin solid content was 0.5 parts by mass, the diluting solvent: toluene), and 100 parts by mass of the ferrite mixed powder. The surface of the ferrite mixed powder was coated with a silicone resin while volatilizing the solvent by mixing and stirring with a universal mixing stirrer. After confirming that toluene had sufficiently volatilized, the mixture was taken out of the apparatus, placed in a container, and heat-treated at 250 ° C. for 2 hours in a hot air-heated oven. Then, the mixture was cooled to room temperature, the ferrite mixed powder having the surface resin cured was taken out, the particles were disaggregated with a vibrating sieve having a mesh of 200 mesh, and the non-magnetic substance was removed using a magnetic beneficiation machine. Then, the coarse particles were removed again with a 200-mesh open vibrating sieve to obtain a carrier for an electrophotographic developer of Example 1 having a ferrite mixed powder as a core material and a resin coating layer on the surface thereof.

(2) Example 2
In Example 2, the ferrite particles 1 and the ferrite particles 3 and the ferrite particles 4 are mixed in the same manner as in Example 1 except that the ferrite particles 4 are mixed so as to have a mass ratio of “3: 3: 4”. A mixed powder was obtained. Then, a carrier for an electrophotographic developer was produced in the same manner as in Example 1 except that the ferrite mixed powder of Example 2 was used.

(3) Example 3
In Example 3, a ferrite mixed powder was obtained in the same manner as in Example 1 except that the ferrite particles 3 and the ferrite particles 7 were mixed so as to have a mass ratio of “5: 5”. Then, a carrier for an electrophotographic developer was produced in the same manner as in Example 1 except that the ferrite mixed powder of Example 3 was used.

(4) Example 4
In Example 4, a ferrite mixed powder was obtained in the same manner as in Example 1 except that the ferrite particles 4 and the ferrite particles 5 were mixed so as to have a mass ratio of “5: 5”. Then, a carrier for an electrophotographic developer was produced in the same manner as in Example 1 except that the ferrite mixed powder of Example 4 was used.

(5) Example 5
In Example 5, the above-mentioned ferrite particles 2, the above-mentioned ferrite particles 4, the above-mentioned ferrite particles 6, and the above-mentioned ferrite particles 7 were mixed so as to have a mass ratio of “3: 3: 2: 2”. A ferrite mixed powder was obtained in the same manner as in Example 1. Then, a carrier for an electrophotographic developer was produced in the same manner as in Example 1 except that the ferrite mixed powder of Example 5 was used.

5. Comparative Example (1) Comparative Example 1
In Comparative Example 1, a carrier for an electrophotographic developer was produced in the same manner as in Example 1 except that a single powder (spinel type ferrite powder) composed of only the ferrite particles 1 was used as a core material.

(2) Comparative Example 2 to Comparative Example 7
In Comparative Examples 2 to 7, a carrier for an electrophotographic developer was produced in the same manner as in Example 1 except that a single powder composed of each of the above-mentioned ferrite particles 2 to 7 was used as a core material. did.

Table 1 shows the composition and production conditions of each of the ferrite particles 1 to 7 produced as described above. Further, Table 2 shows the mixing ratio (mass ratio) of each ferrite particle constituting the ferrite mixed powder produced in Examples 1 to 5.

6. Evaluation 6-1. Evaluation items (1) Various basic characteristics Regarding the ferrite powders (ferrite mixed powders or ferrite single powders) of the above Examples and Comparative Examples, (a) volume average particle size (D50), (b) apparent density (AD), (C) Fluidity (FR), (d) Saturation magnetization, and (e) Lattice constant were measured. These measuring methods are as described above.
The lattice constant of the ferrite mixed powders of Examples 1 to 5 is the above-mentioned average lattice constant ( _Cm ). The ferrite mixed powder of Examples 1 to 5 is a mixture of two or more ferrite particles. Therefore, in these ferrite mixed powder after having grouped the reference value based on the value of the lattice constant of each ferrite particles seeking (C _s) to the X group and Y group of each ferrite particles, based on the method described above , C _X , _RX , _CY , and _RY were obtained, and the average lattice constant (C _m ) of the ferrite mixed powder was calculated.

(2) Charge amount change rate An electrophotographic developer is prepared as follows using the carriers for the electrophotographic developer manufactured in each Example and Comparative Example, and the electrophotographic developer is applied for a predetermined time in a high temperature and high humidity environment. The amount of charge after exposure and the amount of charge after exposing the electrophotographic developer to a predetermined time in a low temperature and low humidity environment are measured, and the ratio (charge amount in a high temperature and high humidity environment / charge in a low temperature and low humidity environment) is measured. Amount) was determined as the rate of change in the amount of charge. It should be noted that the change in the charge amount when the atmosphere changes can be evaluated by the charge amount change rate.

(A) Electrophotodeveloping agent The electrophotographic developing agent as a sample was prepared as follows. A predetermined amount of the carrier for the electrophotographic developer and the toner produced in each example were stirred and mixed for 30 minutes using a turbo mixer to produce an electrophotographic developer having a toner concentration of 12.0% by mass. As the toner, a commercially available negative electrode toner (cyan toner, for DocuPrint C3530 manufactured by Fuji Xerox Co., Ltd .; average volume particle size (D50) of about 5.8 μm) used in a full-color printer was used.

(B) Temperature and Humidity Conditions The low temperature and low humidity environment means an atmospheric temperature of 10 ° C. and an atmospheric relative humidity of 20%.
The high temperature and high humidity environment means an atmospheric temperature of 40 ° C. and an atmospheric relative humidity of 80%.

(C) Sample preparation When measuring the charge amount in each environment, 20 g of the electrophotographic developer prepared as described above is used as a charge amount measurement sample, and each sample is used in a high temperature and high humidity environment (40 ° C. relative humidity). An electrophotographic developer exposed in a high temperature and high humidity environment by storing it in a constant temperature and humidity room in which the ambient temperature and humidity are adjusted in a low temperature and low humidity environment (10 ° C. and 20% relative humidity) for 24 hours. An electrophotographic developer exposed in a low temperature and low humidity environment was obtained.

(D) Measurement Using the sample prepared as described above, the charge amount was measured by the following charge amount measuring device. In order to accurately measure the rising charge, the developer placed in a 50 cc glass container was stirred for 2 minutes with a ball mill at a rotation speed of 150 rpm immediately before the charge measurement.

As a charge measuring device, a total of 8 magnets (magnetic flux density 0.1T) are arranged inside a cylindrical aluminum tube (hereinafter, sleeve) with a diameter of 31 mm and a length of 76 mm, alternating between N and S poles. The magnet roll, the sleeve, and a cylindrical electrode having a Gap of 5.0 mm were placed on the outer circumference of the sleeve. After 0.5 g of the developer is uniformly adhered onto this sleeve, the DC voltage 2500 V is connected between the outer electrode and the sleeve while rotating the inner magnet roll at 100 rpm while keeping the outer aluminum tube fixed. Was applied for 60 seconds to transfer the toner to the outer electrode. At this time, an electrometer (insulation resistance tester model 6517A manufactured by KEITHLEY) was connected to the cylindrical electrode, and the amount of electric charge of the toner transferred to the outer electrode was measured. The charge amount was calculated from the measured charge amount and the transferred toner mass.

By the above method, the charge amount of the electrophotographic developer exposed for 24 hours in a high temperature and high humidity environment and the charge amount of the electrophotographic developer exposed for 24 hours in a low temperature and low humidity environment are measured, and the charge amount change rate is measured. Calculated.
Based on the calculated rate of change in the amount of charge, they were ranked A to D as follows. The smaller the value of the charge amount change rate, the smaller the change in charge riser due to the change in atmosphere, and even when the atmosphere in which the electrophotographic developer is used changes significantly from a low-temperature low-humidity environment to a high-temperature high-humidity environment at the initial stage of printing. This means that the occurrence of image defects can be suppressed.
A: 1.0 or more and less than 1.1 B: 1.1 or more and less than 1.2 C: 1.2 or more and less than 1.3 D: 1.3 or more

2. Evaluation Results Table 3 shows the measurement results for each evaluation item. As shown in Table 3, for example, the average lattice constants of the ferrite powder mixture of Example 1 _{(C m)} is 8.425Å, the lattice constant of the ferrite single powder of Comparative Example 3 (Ferrite particles 3) (8.425Å ) Has the same value. The ferrite mixed powder of Example 1 has the same saturation magnetization and volume average particle size (D ₅₀ ) as the ferrite single powder of Comparative Example 3, but has good fluidity (FR) and apparent density (AD). ) Is also getting bigger. By mixing a plurality of spinel-type ferrite powders, as described above, the ferrite mixed powder becomes a mixed powder composed of ferromagnetic particles and weak magnetic particles when viewed relatively. Therefore, as shown in Table 3, the ferrite mixed powder makes it easier to loosen the magnetic bonds between the particles during stirring and improves the fluidity, as compared with the ferrite single powder having the same lattice constant. it is conceivable that.

Further, as shown in Table 3, the rate of change in the amount of charge was evaluated as "C" in the electrophotographic developer using the ferrite single powder of Comparative Example 3 as the core material, whereas the ferrite mixture of Example 1 was mixed. In the electrophotographic developer using the powder as the core material, the charge amount change rate is evaluated as "A", and when the ferrite mixed powder of Example 1 is used as the core material, the environment such as atmospheric temperature and humidity changes significantly. However, it was confirmed that the change in the amount of charge was small. Similarly, in the other examples and the comparative examples, by using a ferrite mixed powder in which a plurality of ferrite particles are mixed as the core material, ferrite particles (ferrite single powder) having the same lattice constant and saturation magnetization can be used as the core material. The fluidity is improved while maintaining the same degree of magnetization characteristics, and the contact and separation between individual particles can be performed well at the time of stirring. As a result, it is considered that triboelectric charging between the carrier and the toner can be uniformly performed even when the environment changes, and the rate of change in the amount of charge can be reduced.
As described above, according to the ferrite mixed powder of the present invention, the rate of change in the amount of charge due to the change in the environment can be reduced, and the occurrence of image defects at the initial stage of printing can be suppressed even when the environment changes.

According to the present invention, a carrier for an electrophotographic developer, a carrier for an electrophotographic developer, and a carrier for an electrophotographic developer, which are excellent in stirring and mixing of toner and carriers and can suppress the occurrence of defects in the initial stage of printing even when the environment changes. And an electrophotographic developer can be provided.

Claims (8)

A ferrite mixed powder obtained by mixing a plurality of spinel-type ferrite powders having different lattice constants.
A group consisting of spinel-type ferrite powder having a lattice constant value smaller than _{the reference value (C s} ) defined by the following formula (1) is defined as group X, and a spinel having a lattice constant value equal to or higher than the _{reference value (C s).} groups of type ferrite powder and Y groups, the following formula (2) in the average lattice constant determined (C _m) is represented by the following formula (3) ferrite powder mixture, characterized in that in the range of.
(1) C _s = (C ₁ + C _n ) / 2
(2) C _m = (C _X x R _X + C _Y x R _Y ) / (R _X + R _Y )
(3) 8.40 ≤ C _m ≤ 8.50
However,
C ₁ is the lattice constant of the spinel-type ferrite powder having the smallest lattice constant among the plurality of spinel-type ferrite powders constituting the ferrite mixed powder.
C _n, among the plurality of spinel ferrite powder constituting the ferrite mixture powder, a lattice constant of greater spinel ferrite powder of the most lattice constants,
C _X is the average lattice constant of the spinel-type ferrite powder constituting the X group.
_CY is the average lattice constant of the spinel-type ferrite powders constituting the Y group.
R _X is a content ratio of the spinel-type ferrite powder constituting the X group in the spinel ferrite powder mixture (wt%),
R _y is a content ratio of the spinel-type ferrite powder constituting the Y groups in the spinel ferrite powder mixture _(wt%), a R _X + R Y = 100. The content of the spinel-type ferrite powder constituting the X group and (R _X), and the content ratio of the spinel-type ferrite powder constituting the Y group (R _X) satisfies the condition represented by the following formula (4) The ferrite mixed powder according to claim 1.
_{(4) 5 ≦ R X ≦} 90,5 ≦ R Y ≦ 90 Each spinel-type ferrite powder constituting the ferrite mixed powder has a composition formula (MO) a (Fe ₂ O ₃ ) b (where M is at least one selected from the group consisting of Fe, Mg, Mn, Cu, Zn and Ni. A claim having a composition represented by one metal element, a + b = 100 (mol%)), or in which _{a part of MO and / or Fe 2} O ₃ is substituted with an oxide of a divalent element in the composition formula. The ferrite mixed powder according to claim 1 or 2. _{By performing a Rietbelt analysis of the X-ray diffraction pattern, the content ratio (RX} ) of the spinel-type ferrite powder constituting the X group constituting the ferrite mixed powder and the content of the spinel-type ferrite powder constituting the Y group are contained. ratio (R _X) and shall quantify, the average lattice constant of the spinel ferrite powder constituting the X group (C _x), the average lattice constant (C _Y spinel ferrite powder constituting the Y group The ferrite mixed powder according to any one of claims 1 to 3, which differs from) by at least 0.005 Å. A carrier core material for an electrophotographic developer, which comprises the ferrite mixed powder according to any one of claims 1 to 4. A carrier for an electrophotographic developer, which comprises the ferrite mixed powder according to any one of claims 1 to 4 and a resin coating layer for coating the surface of the ferrite mixed powder. An electrophotographic developer according to claim 6, wherein the carrier for an electrophotographic developer and a toner are included. The electrophotographic developer according to claim 7, which is used as a replenishing developer.