JP2011141350A - Magnetic carrier and two-component developer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic carrier and a two-component developer which improve dot reproducibility upon printing in a high-humidity environment, improve developing properties upon printing in a low-humidity environment, suppress changes in density upon continuous printing at a high image area printing, improving uniformity of halftone upon printing at a low image printing, and suppress carrier adherence. <P>SOLUTION: The magnetic carrier includes magnetic carrier particles including porous magnetic core particles and a resin. In a reflected electron image of the cross section of the magnetic carrier particle, the proportion by number of magnetic core regions having a length of 6.0 μm or more with respect to the total number of magnetic core regions having a length of 0.1 μm or more is 5.0% by number or more and 35.0% by number or less, and the proportion by number of magnetic core regions having a length of 2.0 μm or less is 10.0% by number or more and 45.0% by number or less. The porous magnetic core particle has a parameter α, relating to a fitting function represented by expression (1): Re[Z(ω)]+ilm[Z(ω)]=Rs+R/(1+RT(iω)<SP>α</SP>), of 0.65 or more and 0.85 or less in a 100 V/cm electric field intensity. In the expression (1), Re[Z(ω)] is the real part of the impedance; lm[Z(ω)] represents the imaginary part of the impedance; i is imaginary unit; ω represents angular frequency; and Rs, R, T, α and represent parameters which are calculated by fitting, in accordance with a cole-cole plot. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a magnetic carrier and a two-component developer used in electrophotography and electrostatic recording.

  In the electrophotographic method, the step of developing the electrostatic charge image forms an image by depositing charged toner on the electrostatic charge image using Coulomb force with the electrostatic charge image. As a developer for developing an electrostatic charge image using a toner, a one-component developer using a magnetic toner in which a magnetic material is dispersed in a resin, and a two-component system using a mixture of a non-magnetic toner and a magnetic carrier. Broadly divided into developers.

  In particular, the latter is preferably used in full-color image forming apparatuses such as full-color copying machines or full-color printers that require high image quality.

  In recent years, full-color image forming apparatuses are required to have higher durability.

  Therefore, by filling the voids in the porous ferrite core material with a resin and further forming a three-dimensional laminated structure in which resin layers and ferrite layers are alternately present, high image quality is ensured over a long period of time while ensuring sufficient image density. A resin-filled ferrite carrier capable of maintaining an image is disclosed. According to the present invention, since the resin layer and the ferrite layer have a three-dimensional laminated structure, the carrier particles exhibit a role as a capacitor and achieve a stable charge imparting property. In addition, the resin-filled ferrite carrier has a low true density, and as a result, a high-quality image can be maintained over a long period of time (Patent Document 1).

  However, when printing is performed in a high humidity environment, dot reproducibility decreases. When printing is performed in a low-humidity environment, developability deteriorates. When an output having a high image area ratio such as a graphic image is continuously performed, the density fluctuates. Continuing to output in a low image area such as a character image causes problems such as deterioration of halftone image quality and adhesion of carriers.

  For this reason, conventionally used carriers and two-component developers are difficult to adapt to commercial printing, and further improvements are required.

JP 2007-057943 A

  Therefore, the object of the present invention is to improve dot reproducibility during high-humidity environment printing, improve developability during low-humidity environment printing, suppress density fluctuations during continuous printing at a high image area, and halftone uniformity during low-image area printing. An object of the present invention is to provide a magnetic carrier and a two-component developer capable of improving the adhesion and suppressing the carrier adhesion.

  As a result of intensive studies, the inventors have achieved dot reproduction by controlling the internal structure and electrical characteristics of the porous magnetic core particles in the magnetic carrier having the porous magnetic core particles and the magnetic carrier particles having a resin. It has been found that it is possible to achieve improvement in properties, density fluctuation suppression, halftone uniformity improvement, and carrier adhesion suppression.

That is, a magnetic carrier having magnetic carrier particles having at least porous magnetic core particles and a resin,
In the reflected electron image of the cross section of the magnetic carrier particle taken by a scanning electron microscope, when the midpoint of the maximum diameter Rx in the processed cross-sectional area of the magnetic carrier particle is used as a reference point, the reference point passes through the reference point and is 10 °. On a straight line with 18 intervals drawn,
The ratio of the number of magnetic core part regions having a length of 6.0 μm or more to the total number of magnetic core part regions having a length of 0.1 μm or more is 5.0% by number to 35.0% by number, And the ratio of the number of magnetic core part regions having a length of 2.0 μm or less is 10.0% by number or more and 45.0% by number or less,
The porous magnetic core particle has a parameter α obtained by fitting the frequency dependence characteristic of impedance Z obtained by alternating current impedance measurement with a fitting function represented by the following equation (1), under an electric field strength of 100 V / cm. In this case, the magnetic carrier and the two-component developer are 0.65 or more and 0.85 or less.

ただし、
Ｒｅ［Ｚ（ω）］は、インピーダンスの実部
ｌｍ［Ｚ（ω）］は、インピーダンスの虚部
ｉは、虚数単位
ωは、角周波数
Ｒｓ，Ｒ，Ｔ，αは、Ｃｏｌｅ−Ｃｏｌｅの式によるフィッティングで算出されるパラメーター

However,
Re [Z (ω)] is the real part lm [Z (ω)] of the impedance, the imaginary part i of the impedance is the imaginary unit ω, and the angular frequencies Rs, R, T, α are Cole-Cole equations. Calculated by fitting with

  According to the present invention, improved dot reproducibility during high humidity environment printing, improved developability during low humidity environment printing, reduced density fluctuation during continuous printing at a high image area, and halftone uniformity during printing at a low image area. A magnetic carrier and a two-component developer capable of improving and suppressing carrier adhesion can be provided.

It is a schematic diagram of the surface modification apparatus applicable to this invention. 2 is an example of a cross section of a magnetic core particle suitably used in the two-component developer of the present invention. It is an example of the SEM reflected electron image which designated only the process cross-sectional area | region of the magnetic carrier particle of this invention. It is the figure which showed typically the measurement example of the area | regions other than a magnetic core part area | region and a magnetic core part in the magnetic carrier particle cross section of this invention. It is an example which shows distribution of the length and number (number%) of the magnetic core part area | region which has a length of 0.1 micrometer or more in the magnetic carrier particle cross section of this invention. It is a circuit diagram which concerns on the measurement of parameter (alpha) of a magnetic core. It is explanatory drawing of an equivalent circuit.

  Hereinafter, the best mode for carrying out the present invention will be described.

  The magnetic carrier used in the present invention is a magnetic carrier having magnetic carrier particles having at least porous magnetic core particles and a resin.

The magnetic carrier has a reference point when the midpoint of the maximum diameter Rx in the processed cross-sectional area of the magnetic carrier particle is a reference point in the reflected electron image of the cross section of the magnetic carrier particle taken by a scanning electron microscope. Through 18 straight lines drawn at 10 ° intervals,
The ratio of the number of magnetic core part regions having a length of 6.0 μm or more to the total number of magnetic core part regions having a length of 0.1 μm or more is 5.0% by number to 35.0% by number, And the ratio of the number of magnetic core part regions having a length of 2.0 μm or less is 10.0% by number or more and 45.0% by number or less,
When the porous magnetic core particle is fitted to the frequency dependence characteristic of impedance Z obtained by AC impedance measurement by a fitting function represented by the following equation (1), the parameter α is 100 / cm under an electric field strength of 100 / cm. 0.65 or more and 0.85 or less.

ただし、
Ｒｅ［Ｚ（ω）］は、インピーダンスの実部
ｌｍ［Ｚ（ω）］は、インピーダンスの虚部
ｉは、虚数単位
ωは、角周波数
Ｒｓ，Ｒ，Ｔ，αは、Ｃｏｌｅ−Ｃｏｌｅの式によるフィッティングで算出されるパラメーター

However,
Re [Z (ω)] is the real part lm [Z (ω)] of the impedance, the imaginary part i of the impedance is the imaginary unit ω, and the angular frequencies Rs, R, T, α are Cole-Cole equations. Calculated by fitting with

  First, the internal structure of the magnetic carrier will be described in detail.

  As a result of intensive studies, the inventors of the present invention are magnetic carriers having magnetic carrier particles in which porous magnetic core particles are filled with resin, and in a reflected electron image of a cross section of the magnetic carrier particles taken by a scanning electron microscope. A length of 6.0 μm or more with respect to the total number of magnetic core region regions having a length of 0.1 μm or more on a straight line that passes through the reference point of the cross section of the magnetic carrier particle and is drawn at intervals of 10 °. The ratio of the number of magnetic core part regions having a length of 5.0 to 35.0% and a length of 2.0 μm or less is 10.0% by number. It has been found that by using a magnetic carrier characterized by being 45.0% by number or less, it is excellent in developability and dot reproducibility, and density fluctuation can be suppressed even during continuous printing in a high image area.

  The reason is not clear, but the present inventors consider as follows.

  When the toner is developed, counter charges having a polarity opposite to that of the toner remain in the magnetic carrier. The counter charge pulls back the toner developed on the electrostatic charge latent image carrier, so that the electrostatic charge latent image on the electrostatic charge latent image carrier is disturbed and developability is lowered. In particular, in a low-humidity environment, the movement of charges from carriers is reduced, and this phenomenon becomes remarkable.

  In order to prevent this phenomenon, it is necessary to allow the counter charge having the opposite polarity to the toner remaining on the magnetic carrier to pass smoothly through the magnetic carrier to the developer carrying member. As a result, the force for pulling back the toner is weakened and the developability is improved.

  However, when magnetic carrier particles having core particles with low resistance are simply used, the electrostatic latent image or toner image on the electrostatic latent image bearing member may be disturbed. The cause of this disturbance is that the carrier resistance is low, so that the developer carrier and the electrostatic latent image carrier leak through the spikes of the magnetic carrier formed on the developer carrier, and the electrostatic latent image This is because the toner image is disturbed. For this purpose, it is important to control the ease of leakage between the developer carrier and the electrostatic latent image carrier while letting the counter charge escape to the developer carrier.

  Therefore, in the magnetic carrier of the present invention, the number of regions other than the magnetic core portion having a length of 6.0 μm or more is 5.0% with respect to the total number of regions other than the magnetic core portion having a length of 0.1 μm or more. Number% to 35.0 number%. At the same time, the parameter α is set to 0.65 or more and 0.85 or less under an electric field strength of 100 V / cm, thereby solving the above problem.

  Although the detailed reason is not clear, it is presumed that it is important that the magnetic carrier of the present invention has a specific internal structure and at the same time has a distribution in the time constant of the electrical conductivity of the porous magnetic core. .

  First, the internal structure of the carrier will be described.

  On the developer carrier, the magnetic carrier forms a spike with a plurality of magnetic carrier particles in contact with each other at points. In particular, in the developing area where the toner is developed on the electrostatic latent image bearing member, the magnetic carrier particles are arranged in a substantially straight line along the magnetic field lines. At this time, each magnetic carrier particle comes into contact with adjacent magnetic carrier particles at two points (pole points). A straight line connecting the contact points (a straight line connecting two pole points) is the diameter of the magnetic carrier particle, and the charge moves through this shortest path.

  In the present invention, the magnetic core region in the magnetic carrier particle to which the generated counter charge moves is the region in which the charge moves. In order for the electric charge to move smoothly in this region, it is important to have a specific length and number on a straight line passing through the reference point of the cross section of the magnetic carrier particle.

  Magnetic carrier particles are a combination of grains (sintered primary particles) obtained by sintering ferrite fine particles in a high temperature state. The distribution state of the grains greatly affects the strength and electrical characteristics as a carrier.

  In the case of the porous magnetic core particles that have been proposed so far, there are cases where the contact area between grains is small, the adhesion is low, and charge transfer between grains cannot be performed smoothly. As a result, the counter charge stays in the carrier, the toner is pulled back, and the developability sometimes deteriorates.

  In order to solve this problem, it is necessary to control the magnetic core region on the shortest path between the carrier particles in the development region so as to have a certain length or more so that the charge transfer between grains is smooth. is there.

  As a result of the study by the present inventors, it has been found that when the magnetic core region has a length of 6.0 μm or more, the contact area between grains is sufficiently widened, and the adhesion is greatly improved. As a result, the counter charge can be easily transferred between grains.

  Furthermore, it is important that the magnetic core portion region on the shortest path between the carrier particles in the development region not only has a specific length but also exists in a specific ratio. The effect of the present invention cannot be sufficiently obtained if the above-described internal structure of the magnetic core region having a length of 6.0 μm or more exists only in a part of the magnetic carrier.

  Therefore, in the present invention, attention is paid not only to the specific direction of the magnetic carrier particles but also to “on a straight line that passes through the reference point of the cross section of the magnetic carrier particles and is drawn at intervals of 10 °”. In the measurement method to be described later, the number of each region on 18 straight lines is measured, and the ratio to the total number is defined. Thereby, not only a part of the structure of the magnetic carrier particles but also the internal structure is limited not only for the unspecified direction of the magnetic carrier particles.

  In the magnetic carrier particles of the present invention, the number of magnetic core region regions having a length of 6.0 μm or more is 5.0% by number to 35.0% by number, more preferably 10.0% by number to 30.0%. By setting the number to less than several percent, even if the toner is developed from any part of the surface of the magnetic carrier particles, the process of moving from the generation of the counter charge becomes uniform, and a stable image without density unevenness can be obtained. It is done.

  When the number of magnetic core regions having a length of 6.0 μm or more is less than 5.0% by number, the counter charge having the opposite polarity to the toner remaining on the carrier can be smoothly released from the carrier surface. In some cases, developability may be deteriorated. In addition, when the number of magnetic core regions having a length of 6.0 μm or more is more than 35.0% by number, the leakage occurs through the rising of the carrier, and the electrostatic latent image and the toner image are disturbed. Dot reproducibility may be reduced.

  Next, the distribution will be described in the time constant of electrical conductivity of the porous magnetic core.

  Specifically, when the frequency dependence characteristic of the impedance Z obtained by the AC impedance measurement of the porous magnetic core is fitted using a fitting function represented by the following equation (1), the parameter α is 100 V / cm. Under electric field strength, it is necessary to be 0.65 or more and 0.85 or less.

ただし、
Ｒｅ［Ｚ（ω）］は、インピーダンスの実部
ｌｍ［Ｚ（ω）］は、インピーダンスの虚部
ｉは、虚数単位
ωは、角周波数
Ｒｓ，Ｒ，Ｔ，αは、Ｃｏｌｅ−Ｃｏｌｅの式によるフィッティングで算出されるパラメーター

However,
Re [Z (ω)] is the real part lm [Z (ω)] of the impedance, the imaginary part i of the impedance is the imaginary unit ω, and the angular frequencies Rs, R, T, α are Cole-Cole equations. Calculated by fitting with

  The reason is not clear, but the present inventors presume as follows.

  The reason why the developability of the toner is reduced is the counter charge remaining in the carrier as described above.

  In order to smoothly release the counter charge to the developer carrying member, first, the magnetic structure having a length of 6.0 μm or more with respect to the total number of the magnetic core region having a length of 0.1 μm or more in the internal structure of the carrier. The number of the core region is set to 5.0% by number or more and 35.0% by number or less. However, this has a structure in which the counter charge is easily released, but the electrical characteristics are not specified.

  As a result of intensive studies, the present inventors have found that it is necessary to further control the electrical characteristics of the porous magnetic core in order to improve developability.

  Specifically, the parameter α when the frequency dependent characteristic Z (ω) of the impedance Z obtained by AC impedance measurement of the porous magnetic core is fitted by the fitting function written in the following (1) is set to 100 V / cm. It has been found that the above problem can be solved by setting the electric field to 0.65 or more and 0.85 or less under an electric field.

ただし、
Ｒｅ［Ｚ（ω）］は、インピーダンスの実部
ｌｍ［Ｚ（ω）］は、インピーダンスの虚部
ｉは、虚数単位
ωは交流インピーダンス測定の角周波数［Ｈｚ］
Ｒｓ，Ｒ，Ｔ，αは、Ｃｏｌｅ−Ｃｏｌｅの式によるフィッティングより算出されるパラメーター

However,
Re [Z (ω)] is the real part lm [Z (ω)] of the impedance, the imaginary part i of the impedance is the imaginary unit ω is the angular frequency [Hz] of the AC impedance measurement
Rs, R, T, and α are parameters calculated by fitting using the Cole-Cole equation.

  The parameter α can be calculated by measuring the frequency characteristics of the complex impedance by measuring the AC impedance of the porous magnetic core and fitting it by the Cole-Cole equation expressed by the equation (2). The degree of time constant distribution can be expressed.

  The parameter α takes a range of 0 ≦ α ≦ 1, and becomes smaller as the spread of the time constant distribution increases.

（ただし、Ｒｅ［Ｚ（ω）］は、インピーダンスの実部、ｌｍ［Ｚ（ω）］は、インピーダンスの虚数部、ｉは虚数単位、ωはインピーダンス測定時の角周波数）

(Where Re [Z (ω)] is the real part of the impedance, lm [Z (ω)] is the imaginary part of the impedance, i is the imaginary unit, and ω is the angular frequency during impedance measurement)

  In order to control the parameter α in the above range, the electrical resistance of the porous magnetic core is not simply controlled, but the crystal particles (grains) are connected to each other sufficiently within the carrier of one particle. "Is necessary.

  By doing so, high developability can be achieved without drastically reducing the electrical resistance of the porous magnetic core.

  When the parameter α is larger than 0.85, the distribution of the electrical conductivity time constant of the porous magnetic core is small, and the counter charge cannot be effectively released, so that the developability is lowered. When the parameter α is smaller than 0.65, the distribution of the electrical conductivity time constant of the porous magnetic core is too wide, and when a halftone image is printed, the image quality may be deteriorated due to the difference in developability.

  Further, in order to suppress density fluctuation during continuous printing with a large image area, it is necessary to improve the charging performance of the carrier. For this purpose, the ratio of the number of magnetic core regions having a length of 2.0 μm or less to the total number of magnetic core regions having a length of 0.1 μm or more is set to 10.0% to 45.0 % Or less is required.

  The reason is not clear, but the present inventors presume as follows.

  When a large area image is printed, the toner consumption is large. As a result, a large amount of toner is supplied. In such a case, the carrier needs to charge many toners simultaneously.

  In the case of a normal carrier, when the toner is charged, a charge having a reverse polarity is accumulated in the carrier itself, and as a result, the chargeability of the carrier is lowered. However, if the carrier can accumulate electric charges like a capacitor, a decrease in the charging ability of the carrier is suppressed, and as a result, a large number of toners can be charged simultaneously.

  In order to enhance the carrier function of the carrier, it is necessary to control the internal structure of the carrier. Specifically, the ratio of the number of magnetic core regions having a length of 2.0 μm or less needs to be 10.0% by number or more and 45.0% by number or less.

In the case of a general capacitor, the electric capacity C of the capacitor is proportional to εA / d.
(Ε: dielectric constant of dielectric between electrode plates, A = area of one electrode plate, d = distance between electrode plates)

  For this reason, in order to enhance the function of the carrier as a capacitor, it is necessary to have a structure in which the magnetic core portions are thinly laminated. What is important at this time is not the number of stacked layers but the stacked state.

  Specifically, it is necessary to make the laminated state of magnetic core-resin-magnetic core as thin as possible (d (distance between electrode plates) is shortened and A (area of one electrode plate) is increased).

  By doing so, for example, even if the number of stacked layers is small, each stacked state is thin and the capacitor function is large, and the capacitor function is sufficient as a carrier.

  As a result of studying how this laminated state can be expressed, the present inventors have found that it can be expressed by the ratio of the number of magnetic core portion regions having a length of 2.0 μm or less.

  The magnetic core region having a length of 2.0 μm or more is hardly involved in the role of a capacitor because one laminated state is too thick. On the other hand, the magnetic core portion region having a length of 2.0 μm or less greatly contributes to the capacitor role. The ratio of the number of magnetic core regions having a length of 2.0 μm or less that plays the role of a capacitor to the magnetic core region is set to 10.0% to 45.0% by number. Thus, the magnetic carrier exhibits a sufficient capacitor function and can exhibit high chargeability.

  When the ratio of the number of magnetic core portion regions having a length of 2.0 μm or less is less than 10.0% by number, the capacitor function of the carrier is insufficient, the charging performance is low, and the image area is continuous with a high image area. The density fluctuates during printing. When the ratio of the number of magnetic core portion regions having a length of 2.0 μm or less is more than 45.0% by number, the laminated state is too thin to have sufficient strength as a carrier, and the carrier does not have sufficient durability. It is destroyed and the carrier is deposited on the drum.

  The ratio of the magnetic core part region having a length of 6.0 μm or more to the total number of magnetic core part regions having a length of 0.1 μm or more is 5.0% to 35.0% by number, 2.0 μm or less. In order to set the ratio of the number of magnetic core regions having a length of 10.0 to 45.0% by number, the particle size and particle size distribution of the calcined ferrite finely pulverized product, the firing in the main firing step It is necessary to control temperature and baking time.

  The carrier manufacturing method will be described in detail.

  In the reflected electron image of the cross section of the magnetic carrier particle photographed with a scanning electron microscope, the magnetic carrier of the present invention has an area ratio of the magnetic core region of 50 area% or more to the total area of the cross section. The area% or less is preferable from the viewpoint of image density stability.

  By setting the area ratio of the magnetic core region of the magnetic carrier within the above range, the specific gravity of the magnetic carrier can be controlled to be small and the physical strength can be sufficiently secured. As a result, the mixing property with the toner is further improved, the stress applied to the carrier during mixing can be reduced, and stable image quality can be ensured over a long period of time.

  At the same time, the presence of the magnetic core region to some extent facilitates control of the parameter α of the porous magnetic core.

  In the magnetic carrier of the present invention, the surface of the magnetic carrier particles is preferably further coated with a resin.

  By coating the surfaces of the magnetic carrier particles with a resin, the environmental stability is further improved, and the change in image density due to a decrease in charge amount is excellent even in a high temperature and high humidity environment.

  Specifically, fine irregularities exist on the surface of the porous magnetic core particle due to crystal growth when forming the particle. By further coating the surface of the magnetic carrier with a resin, the difference due to the unevenness can be reduced, and as a result, the difference in charge imparting between the concave and convex portions can be suppressed. As a result, it is possible to suppress a decrease in chargeability of the toner particularly when left in a high humidity environment.

  The porous magnetic core particles can be produced by the following process.

  The material of the porous magnetic core particles is preferably ferrite particles.

A ferrite particle is a sintered body represented by the following formula.
(M1 ₂ O) _u (M2O) _v (M3 ₂ O ₃ ) _w (M4O ₂ ) _x (M5 ₂ O ₅ ) _y (Fe ₂ O ₃ ) _z
(In the formula, M1 is monovalent, M2 is divalent, M3 is trivalent, M4 is tetravalent, M5 is pentavalent metal, and u, v, w, x, and x when u + v + w + x + y + z = 1.0. y is 0 ≦ (u, v, w, x, y) ≦ 0.8, respectively, and z is 0.2 <z <1.0.)

  In the above formula, M1 to M5 are at least Li, Fe, Zn, Ni, Mn, Mg, Co, Cu, Ba, Sr, Ca, Si, V, Bi, In, Ta, Zr, B, 1 selected from the group consisting of Mo, Na, Sn, Ti, Cr, Al, Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu Represents more than one kind of metal element.

For example, magnetic Li-based ferrite (for example, (Li ₂ O) _a (Fe ₂ O ₃ ) _b (0.0 <a <0.4, 0.6 ≦ b <1.0, a + b = 1)), Mn based ferrite (for example, (MnO) _a (Fe ₂ O ₃ ) _b (0.0 <a <0.5, 0.5 ≦ b <1.0, a + b = 1)), Mn—Mg based ferrite ( For example, (MnO) _a (MgO) _b (Fe ₂ O ₃ ) _c (0.0 <a <0.5, 0.0 <b <0.5, 0.5 ≦ c <1.0, a + b + c = 1)), Mn—Mg—Sr ferrite (for example, (MnO) _a (MgO) _b (SrO) _c (Fe ₂ O ₃ ) _d (0.0 <a <0.5, 0.0 <b < 0.5, 0.0 <c <0.5, 0.5 ≦ d <1.0, a + b + c + d = 1), Cu—Zn based ferrite (for example, (CuO) _a (ZnO) _b (Fe ₂ O ₃ ) _c (0. <A <0.5, 0.0 <b <0.5, 0.5 ≦ c <1.0, a + b + c = 1) The above ferrite represents the main element, and other trace metals are used. It contains what it contains.

  In addition, Mn-based ferrite, Mn-Mg-based ferrite, and Mn-Mg-Sr-based ferrite containing Mn element are preferable in order to increase the area between grains and widen the grain diameter distribution.

  Below, the manufacturing process in the case of using a ferrite particle as a porous magnetic carrier particle is demonstrated in detail.

Process 1 (weighing / mixing process):
The ferrite raw materials are weighed and mixed.

  Examples of the ferrite raw material include the following. Li, Fe, Zn, Ni, Mn, Mg, Co, Cu, Ba, Sr, Y, Ca, Si, V, Bi, In, Ta, Zr, B, Mo, Na, Sn, Ti, Cr, Al, Rare earth metal particles, oxides, hydroxides, oxalates, carbonates.

  Examples of the mixing apparatus include the following. Ball mill, planetary mill, Giotto mill, vibration mill. A ball mill is particularly preferable from the viewpoint of mixing properties. Specifically, a weighed ferrite raw material and balls are placed in a ball mill, and pulverized and mixed for 0.1 to 20.0 hours.

Step 2 (temporary firing step):
The ferrite raw material thus pulverized and mixed is calcined in the atmosphere at a firing temperature of 700 ° C. or higher and 1000 ° C. or lower for 0.5 hour or more and 5.0 hours or less to form a ferrite. For firing, for example, the following furnace is used. Burner type incinerator, rotary type incinerator, electric furnace.

Step 3 (grinding step):
The calcined ferrite produced in step 2 is pulverized with a pulverizer.

  The pulverizer is not particularly limited as long as a desired particle size can be obtained. Examples include the following. Crusher, hammer mill, ball mill, bead mill, planetary mill, Giotto mill.

  One method for obtaining magnetic core particles having a desired internal structure in the present invention is to control the particle size and particle size distribution of the calcined ferrite finely pulverized product. Specifically, the volume-based 50% particle size (D50) of the calcined ferrite finely pulverized product is 0.5 to 5.0 μm, and the volume-based 90% particle size (D90) is 3.0 to 10 μm. It is preferable that the thickness be 0.0 μm or less.

  In order to make the finely pulverized ferrite product have the above particle size, for example, it is preferable to control the material, particle size, and operation time of balls and beads used in a ball mill and a bead mill. Specifically, in order to reduce the particle size of the calcined ferrite slurry, a ball having a high specific gravity may be used or the pulverization time may be increased. Further, in order to widen the particle size distribution of the calcined ferrite, it can be obtained by using balls and beads having a high specific gravity and shortening the grinding time. Also, a finely pulverized calcined ferrite product having a wide distribution can be obtained by mixing a plurality of finely pulverized calcined ferrite products having different particle sizes. Thus, the magnetic core particle which has the internal structure and parameter (alpha) of this invention can be obtained by using the calcination ferrite fine pulverization product of wide particle size distribution.

The material for the balls and beads is not particularly limited as long as a desired particle size and distribution can be obtained. For example, the following can be mentioned. Glasses such as soda glass (specific gravity 2.5 g / cm ³ ), sodaless glass (specific gravity 2.6 g / cm ³ ), high specific gravity glass (specific gravity 2.7 g / cm ³ ), quartz (specific gravity 2.2 g / cm) ³ ), titania (specific gravity 3.9 g / cm ³ ), silicon nitride (specific gravity 3.2 g / cm ³ ), alumina (specific gravity 3.6 g / cm ³ ), zirconia (specific gravity 6.0 g / cm ³ ), steel ( Specific gravity 7.9 g / cm ³ ), stainless steel (specific gravity 8.0 g / cm ³ ). Among these, alumina, zirconia, and stainless steel are preferable because of excellent wear resistance.

  The particle size of the ball or bead is not particularly limited as long as a desired particle size / distribution is obtained. For example, a ball having a diameter of φ5 mm or more and φ60 mm is preferably used. Further, beads having a diameter of φ0.03 mm or more and less than φ5 mm are preferably used.

  In addition, ball mills and bead mills have a high grinding efficiency when a wet method is used rather than a dry method, and a pulverized product does not rise in the mill. For this reason, the wet type is more preferable than the dry type.

Process 4 (granulation process):
Water, a binder, a dispersant, and, if necessary, a pore adjuster are added to the calcined ferrite pulverized product.

  Examples of the pore adjuster include a foaming agent and resin fine particles. Examples of the foaming agent include sodium hydrogen carbonate, potassium hydrogen carbonate, lithium hydrogen carbonate, ammonium hydrogen carbonate, sodium carbonate, potassium carbonate, lithium carbonate, and ammonium carbonate. Examples of resin fine particles include polyester, polystyrene, styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-acrylic acid ester copolymer, styrene-methacrylic acid ester copolymer, and styrene-α-chloromethacrylic acid. Styrene copolymers such as acid methyl copolymer, styrene-acrylonitrile copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer, styrene-acrylonitrile-indene copolymer Polyvinyl chloride, phenolic resin, modified phenolic resin, maleic resin, acrylic resin, methacrylic resin, polyvinyl acetate, silicone resin; aliphatic polyhydric alcohol, aliphatic dicarboxylic acid, aromatic dicarboxylic acid, aromatic dialcohol and Polyester resin having monomers selected from phenols as structural units; polyurethane resin, polyamide resin, polyvinyl butyral, terpene resin, coumarone indene resin, petroleum resin, hybrid resin having polyester unit and vinyl polymer unit Fine particles.

  For example, polyvinyl alcohol is used as the binder.

  In Step 3, when wet pulverization is performed, it is preferable to add a binder and, if necessary, a pore adjuster, taking into account the water contained in the ferrite slurry.

  The obtained ferrite slurry is dried and granulated using a spray dryer in a heated atmosphere of 100 ° C. or higher and 200 ° C. or lower. The spray dryer is not particularly limited as long as a desired porous magnetic core particle size can be obtained. For example, a spray dryer can be used.

Process 5 (main baking process):
Next, the granulated product is fired. Baking is performed at 800 ° C. to 1300 ° C. for 1 hour to 24 hours. 1000 degreeC or more and 1200 degrees C or less are more preferable. By controlling the firing temperature and firing time within the above range, the porous magnetic core having the desired internal structure of the present invention can be obtained.

  By increasing the firing temperature or lengthening the firing time, the growth of grains in the porous magnetic core particles proceeds, and as a result, the length of the magnetic core portion in the cross section of the magnetic carrier particles becomes longer. Further, by controlling the firing atmosphere, α of the porous magnetic core particles can be controlled within a preferable range. For example, the α of the porous magnetic core particles can be lowered by lowering the oxygen concentration or reducing atmosphere (in the presence of hydrogen).

Process 6 (screening process):
After pulverizing the baked particles as described above, if necessary, coarse particles and fine particles may be removed by removing weak magnetic materials and non-magnetic materials by magnetic separation, sieving with classification or sieving.

In addition, it is preferable that SiO ₂ is contained in the magnetic core because the developability can be improved.

The reason for this is not clear, but the present inventors present that the presence of SiO ₂ that is a non-magnetic low specific gravity component and a high resistance phase causes the carrier resistance to rapidly decrease when a development bias is applied. The developability is considered to be improved.

The following methods can be exemplified as a method for incorporating SiO ₂ in the magnetic core. Ferrite component raw materials are blended in the desired composition ratio and wet mixed. After wet mixing, ferrite is prepared by temporary firing, and then finely pulverized using a ball mill. SiO ₂ is added to the finely pulverized ferrite obtained. The weight average particle diameter of SiO ₂ is preferably 1 μm to 10 μm, and 5 parts by mass to 45 parts by mass is preferably added with respect to 100 parts by mass of the finely pulverized ferrite.

  When the volume distribution standard 50% particle size (D50) of the porous magnetic core particles is 18.0 μm or more and 68.0 μm or less becomes a magnetic carrier, it is more for the prevention of carrier adhesion to the image and roughness. desirable.

  The porous core particles obtained in this way can increase the capacitor-like function of the carrier by filling the porous magnetic core particles with a resin. Further, the charging performance as a magnetic carrier can be enhanced by coating with resin after filling with resin.

  There are two methods for incorporating the resin into the porous magnetic core particle, a method of filling the resin in the hole in the back of the porous magnetic core particle and a method of filling the resin only in the hole on the surface of the porous magnetic core particle. is there. A specific filling method is not particularly limited, but a method of filling a resin solution in which a resin and a solvent are mixed to the back of the pores of the porous magnetic core particles is preferable.

  The amount of the resin solid content in the resin solution is preferably 1% by mass or more and 50% by mass or less, and more preferably 1% by mass or more and 30% by mass or less. When a resin solution having a resin amount larger than 50% by mass is used, it is difficult to fill the resin solution to the back of the pores of the porous magnetic core particles because the viscosity is high. Further, if it is less than 1% by mass, the amount of resin is small, and there are cases where the desired amount of resin cannot be filled into the porous magnetic core particles.

  The resin filled in the pores of the porous magnetic core particle is not particularly limited, and either a thermoplastic resin or a thermosetting resin may be used, but it has a high affinity for the porous magnetic core particle. It is preferable. When a resin having high affinity is used, the surface of the porous magnetic core particles can be easily covered with the resin at the same time as the resin is filled into the pores of the porous magnetic core particles.

  As the resin to be filled, examples of the thermoplastic resin include the following. Polystyrene, polymethyl methacrylate, styrene-acrylic resin; styrene-butadiene copolymer, ethylene-vinyl acetate copolymer, polyvinyl chloride, polyvinyl acetate, polyvinylidene fluoride resin, fluorocarbon resin, perfluorocarbon resin, polyvinylpyrrolidone, petroleum Resin, novolak resin, saturated alkyl polyester resin, polyethylene terephthalate, polybutylene terephthalate, polyarylate, polyamide resin, polyacetal resin, polycarbonate resin, polyethersulfone resin, polysulfone resin, polyphenylene sulfide resin, polyetherketone resin.

  Moreover, the following are mentioned as said thermosetting resin. Phenolic resin, modified phenolic resin, maleic resin, alkyd resin, epoxy resin, unsaturated polyester obtained by polycondensation of maleic anhydride, terephthalic acid and polyhydric alcohol, urea resin, melamine resin, urea-melamine resin, xylene resin , Toluene resin, guanamine resin, melamine-guanamine resin, acetoguanamine resin, gliptal resin, furan resin, silicone resin, polyimide, polyamideimide resin, polyetherimide resin, polyurethane resin.

  Further, a resin obtained by modifying these resins may be used. Of these, fluorine-containing resins such as polyvinylidene fluoride resin, fluorocarbon resin, perfluorocarbon resin or solvent-soluble perfluorocarbon resin, modified silicone resin or silicone resin are preferred because of their high affinity for porous magnetic core particles.

  Among the above resins, a thermosetting resin is more preferable because it can increase the strength of the magnetic carrier and reduce carrier adhesion after durability at a low image ratio. Among these, a silicone resin is more preferable because it can reduce the adhesive force between the magnetic carrier and the toner, and as a result, the reduction in image density can be improved when 100 images having a high image ratio are printed in a low humidity environment.

  For example, the following are mentioned as a commercial item. Among silicone resins, KR271, KR255, and KR152 manufactured by Shin-Etsu Chemical Co., Ltd., and SR2400, SR2405, SR2410, and SR2411 manufactured by Toray Dow Corning. Among the modified silicone resins, KR206 (alkyd modified), KR5208 (acrylic modified), ES1001N (epoxy modified), KR305 (urethane modified) manufactured by Shin-Etsu Chemical, SR2115 (epoxy modified), SR2110 (alkyd) manufactured by Toray Dow Corning Co., Ltd. Denatured).

  As a method of filling the pores of the porous magnetic core particles with a resin, a method of diluting the resin in a solvent, adding this to the pores of the porous magnetic core particles, and removing the solvent can be employed. The solvent used here should just be what can melt | dissolve resin. When the resin is soluble in an organic solvent, examples of the organic solvent include toluene, xylene, cellosolve butyl acetate, methyl ethyl ketone, methyl isobutyl ketone, and methanol. In the case of a water-soluble resin or an emulsion type resin, water may be used as a solvent. As a method for filling the pores of the porous magnetic core particles with the resin, the resin solution is impregnated with the porous magnetic core particles by a filling method such as a dipping method, a spray method, a brush coating method, and a fluidized bed. The method of volatilizing is mentioned.

  In the magnetic carrier of the present invention, the degree of surface exposure of the porous magnetic core particles is further controlled, and the fog is further improved when the copying machine body is printed after being left in a high humidity environment for one week. After filling the hole with resin, the surface may be further coated with resin. In that case, the resin used for filling and the resin as the coating material used for coating may be the same or different, and may be a thermoplastic resin or a thermosetting resin.

  As the resin for forming the coating material, the resin used for filling can be used.

  Further, the coating material may contain conductive particles or a charge control substance in order to control the charge imparting property of the carrier.

  Examples of the conductive particles include carbon black, magnetite, graphite, zinc oxide, and tin oxide.

  As the charge control substance, particles having charge controllability or materials having charge controllability can be used. Examples of the particles having charge controllability include the following.

  For example, organometallic complex particles, organometallic salt particles, chelate compound particles, monoazo metal complex particles, acetylacetone metal complex particles, hydroxycarboxylic acid metal complex particles, polycarboxylic acid metal complex particles, polyol metal complex Particles, polymethyl methacrylate resin particles, polystyrene resin particles, melamine resin particles, phenol resin particles, nylon resin particles, silica particles, titanium oxide particles, alumina particles.

  Examples of materials having charge controllability include the following.

  For example, γ-aminopropyltrimethoxysilane, γ-aminopropylmethoxydiethoxysilane, γ-aminopropyltriethoxysilane, N-β- (aminoethyl) -γ-aminopropyltrimethoxysilane, N-β- (amino Ethyl) -γ-aminopropylmethyldimethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, ethylenediamine, ethylenetriamine, styrene- (meth) acrylate dimethylaminoethyl copolymer, isopropyltri (N-aminoethyl) Titanate, hexamethyldisilazane, methyltrimethoxysilane, butyltrimethoxysilane, isobutyltrimethoxysilane, hexyltrimethoxysilane, octyltrimethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane , Phenyltrimethoxysilane, o-methylphenyltrimethoxysilane, p-methylphenyltrimethoxysilane.

  The method of coating the surface of the porous magnetic core particles with the resin and then further coating the surface with the resin is not particularly limited, but the coating is performed by a coating method such as dipping, spraying, brushing, and fluidized bed. A method is mentioned.

  Next, the toner used in the present invention will be described.

  Examples of the binder resin contained in the toner include the following. Polyester, polystyrene; polymer of styrene derivatives such as poly-p-chlorostyrene and polyvinyltoluene; styrene-p-chlorostyrene copolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-acrylic Acid ester copolymer, styrene-methacrylic acid ester copolymer, styrene-α-chloromethyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, Styrene copolymers such as styrene-isoprene copolymer, styrene-acrylonitrile-indene copolymer; polyvinyl chloride, phenol resin, modified phenol resin, maleic resin, acrylic resin, methacrylic resin, polyvinyl acetate, silicone resin; Polyester resin having as a structural unit a monomer selected from aliphatic polyhydric alcohol, aliphatic dicarboxylic acid, aromatic dicarboxylic acid, aromatic dialcohol and diphenol; polyurethane resin, polyamide resin, polyvinyl butyral, terpene resin, A hybrid resin having coumarone indene resin, petroleum resin, polyester unit and vinyl polymer unit.

  The wax is preferably used in an amount of 0.5 to 20 parts by mass per 100 parts by mass of the binder resin. The peak temperature of the maximum endothermic peak of the wax is preferably 45 ° C. or higher and 140 ° C. or lower. It is preferable because both the storage stability of the toner and the hot offset resistance can be achieved.

  Examples of the wax include the following. Low molecular weight polyethylene, low molecular weight polypropylene, alkylene copolymer, hydrocarbon wax such as microcrystalline wax, paraffin wax, Fischer-Tropsch wax; oxide of hydrocarbon wax such as oxidized polyethylene wax or block copolymer thereof; Waxes composed mainly of fatty acid esters such as carnauba wax, behenic acid behenate wax, and montanic acid ester wax; fatty acid esters such as deoxidized carnauba wax that have been partially or fully deoxidized.

  The amount of the colorant used is preferably 0.1 parts by mass or more and 30 parts by mass or less, and more preferably 0.5 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the binder resin.

  It is preferable that an external additive is added to the toner in order to improve fluidity. As the external additive, inorganic fine powders such as silica, titanium oxide and aluminum oxide are preferable. The inorganic fine powder is preferably hydrophobized with a hydrophobizing agent such as a silane compound, silicone oil or a mixture thereof. The external additive is preferably used in an amount of 0.1 to 5.0 parts by mass with respect to 100 parts by mass of the toner particles. For mixing the toner particles and the external additive, a known mixer such as a Henschel mixer can be used.

  Examples of the method for producing toner particles include a pulverization method in which a binder resin and a colorant are melt-kneaded and the kneaded product is cooled and then pulverized and classified; the binder resin and the colorant are dissolved or dispersed in a solvent. Suspension granulation method in which toner particles are obtained by introducing the solution into an aqueous medium, suspending granulation, and removing the solvent; dispersing and stabilizing a monomer composition in which a colorant is uniformly dissolved or dispersed in the monomer Suspension polymerization method in which toner particles are produced by dispersing in a continuous layer (for example, an aqueous phase) containing an agent and carrying out a polymerization reaction; a monomer that is soluble in monomers but insoluble when a polymer is formed and an aqueous system Direct dispersion in the presence of a water-soluble polar polymerization initiator using a water-based organic solvent that is soluble in the monomer that directly produces toner particles using an organic solvent and is insoluble in the resulting polymer; Toner particles An emulsion polymerization method to be produced; an emulsion aggregation method obtained by aggregating at least polymer fine particles and colorant fine particles to form a fine particle aggregate, and an aging step for causing fusion between the fine particles in the fine particle aggregate; and so on.

  A procedure for producing toner by the pulverization method will be described.

  In the raw material mixing step, as a material constituting the toner particles, for example, a predetermined amount of other components such as a binder resin, a colorant and a wax, and a charge control agent as necessary are mixed and mixed. Examples of the mixing apparatus include a double-con mixer, a V-type mixer, a drum-type mixer, a super mixer, a Henschel mixer, a Nauta mixer, and a mechano hybrid (manufactured by Mitsui Mining Co., Ltd.).

  Next, the mixed material is melt-kneaded to disperse the colorant and the like in the binder resin. In the melt-kneading process, a batch kneader such as a pressure kneader or a Banbury mixer or a continuous kneader can be used, and a single-screw or twin-screw extruder has become the mainstream because of the advantage of continuous production. ing. For example, KTK type twin screw extruder (manufactured by Kobe Steel Co., Ltd.), TEM type twin screw extruder (manufactured by Toshiba Machine Co., Ltd.), PCM kneader (manufactured by Ikekai Tekko), twin screw extruder (manufactured by K.C.K. ), Ko Kneader (Bus), Needex (Mitsui Mining).

  Furthermore, the colored resin composition obtained by melt-kneading may be rolled with two rolls or the like and cooled with water or the like in the cooling step.

  Next, the cooled product of the resin composition is pulverized to a desired particle size in the pulverization step. In the pulverization step, for example, after coarse pulverization with a pulverizer such as a crusher, a hammer mill, or a feather mill, for example, a kryptron system (manufactured by Kawasaki Heavy Industries), a super rotor (manufactured by Nisshin Engineering), a turbo mill Finely pulverize with a turbomill (made by Turbo Industries) or air jet type fine pulverizer.

  Then, if necessary, classification such as inertial class elbow jet (manufactured by Nippon Steel & Mining Co., Ltd.), centrifugal classification turboplex (manufactured by Hosokawa Micron), TSP separator (manufactured by Hosokawa Micron), Faculty (manufactured by Hosokawa Micron) The toner particles are obtained by classification using a machine or a sieving machine.

  In addition, if necessary, after pulverization, a hybridization system (manufactured by Nara Machinery Co., Ltd.), mechano-fusion system (manufactured by Hosokawa Micron Co., Ltd.), Faculty (manufactured by Hosokawa Micron Co., Ltd.), Meteorbomb MR Type (manufactured by Nippon Pneumatic Co., Ltd.) is used. Thus, the surface modification treatment of the toner particles such as spheroidization treatment can also be performed.

  In addition, the toner particles used in the present invention can be obtained by obtaining the above pulverized product, performing surface treatment with hot air using, for example, the surface treatment apparatus shown in FIG. preferable. Alternatively, a pre-classified material may be subjected to surface treatment with hot air using the surface device shown in FIG. In the surface treatment with hot air, toner particles are ejected by jetting from a high-pressure air supply nozzle, and the surface of the toner particles is treated by exposing the jetted toner to hot air. The temperature of the hot air is 100 ° C. It is particularly preferable that the temperature be in the range of 450 ° C. or lower.

  Here, an outline of a surface treatment apparatus used for producing the toner of the present invention will be described with reference to FIG. FIG. 1 is a cross-sectional view showing an example of a surface treatment apparatus according to the present invention. Toner particles 114 supplied from a toner particle supply port 100 are accelerated by injection air ejected from a high-pressure air supply nozzle 115 and below that. It heads for the airflow injection member 102 in the. Diffusion air is ejected from the airflow ejecting member 102, and the toner particles are diffused outward by the diffusion air. At this time, the toner diffusion state can be controlled by adjusting the flow rate of the injection air and the flow rate of the diffusion air.

  Further, a cooling jacket 106 is provided on the outer periphery of the toner particle supply port 100, the outer periphery of the surface treatment apparatus, and the outer periphery of the transfer pipe 116 for the purpose of preventing toner particle fusion. In addition, it is preferable to pass cooling water (preferably antifreeze such as ethylene glycol) through the cooling jacket.

  The toner particles diffused by the diffusion air are treated on the surface of the toner particles by the hot air supplied from the hot air supply port 101. At this time, the temperature C (° C.) of the hot air supply port is preferably 100 ° C. or higher and 450 ° C. or lower. More preferably, it is 100 degreeC or more and 400 degrees C or less.

  When the temperature is lower than 100 ° C., the surface roughness of the toner particle surface may vary. In addition, when the temperature exceeds 450 ° C., toner particles may be coalesced due to excessive progress of the molten state, and toner particles may be coarsened or fused.

  The toner particles whose surface has been treated with hot air are cooled by cold air supplied from a cold air supply port 103 provided on the outer periphery of the upper portion of the apparatus. At this time, cold air may be introduced from the second cold air supply port 104 provided on the side surface of the main body of the apparatus for the purpose of controlling the temperature distribution in the apparatus and controlling the surface state of the toner particles. The outlet of the second cold air supply port 104 can use a slit shape, a louver shape, a perforated plate shape, a mesh shape, etc., and the introduction direction can be selected according to the purpose, horizontal to the center direction and along the device wall surface It is.

At this time, the temperature E (° C.) in the cold air supply port and the second cold air supply port is preferably −50 ° C. or more and 10 ° C. or less. More preferably, it is -40 degreeC or more and 8 degrees C or less. The cold air is preferably dehumidified cold air. Specifically, the absolute water content is preferably 5 g / m ³ or less. More preferably, it is 3 g / m ³ or less.

  When these cold air temperatures are less than −50 ° C., the temperature in the apparatus is too low, and the heat treatment that is the original purpose is not sufficiently performed, and the toner particles may not be spheroidized. When the temperature exceeds 10 ° C., the control of the hot air zone in the apparatus becomes insufficient, the coalescence of the particles proceeds, and the powder particles may be coarsened.

  Thereafter, the cooled toner particles are sucked by a blower and collected by a cyclone or the like through the transfer pipe 116.

  The magnetic carrier of the present invention can be used as a two-component developer containing toner, magnetic carrier and toner. The two-component developer can be used as a developer used for development by being carried on a developer carrier accommodated in a developing device.

  When used as a developer, the mixing ratio is preferably 2 to 20 parts by mass, more preferably 4 to 15 parts by mass with respect to 100 parts by mass of the magnetic carrier. By setting it within the above range, high image density can be achieved and toner scattering can be reduced.

  The magnetic carrier of the present invention is used as a replenishing developer used in a two-component developing method for mixing with a replenishing toner to replenish the developing unit, and discharging at least the excess magnetic carrier inside the developing unit from the developing unit. It can also be used.

  When used as a replenishing developer, the mixing ratio is preferably 2 parts by mass or more and 50 parts by mass or less of toner with respect to 1 part by mass of the magnetic carrier from the viewpoint of enhancing the durability of the developer.

  A method for measuring various physical properties of the magnetic carrier and toner will be described below.

<Measurement method of length of magnetic core region in cross section of magnetic carrier particle, and area ratio of magnetic core region, measurement method of number of repetitions of laminated structure>
A focused ion beam processing observation apparatus (FIB) (manufactured by Hitachi High-Technologies Corporation, FB-2100) was used for cross-section processing of the magnetic carrier particles. A carbon paste is applied on an FIB sample stage (metal mesh), a small amount of magnetic carrier particles are fixed on the FIB sample stand so as to exist independently, and a sample is prepared by depositing platinum as a conductive film. The sample is set in an FIB apparatus, and rough processing is performed (beam current: 39 nA) using an acceleration voltage of 40 kV and a Ga ion source, followed by finishing processing (beam current: 7 nA), and the sample cross section is cut out.

  Note that the magnetic carrier particles used as samples are magnetic carriers satisfying D50 × 0.9 ≦ Dmax ≦ D50 × 1.1, where Dmax is the maximum diameter of each sample. Further, the position of the plane including the maximum length in the direction parallel to the fixing surface of each sample is set as a distance h from the fixing surface (for example, h = r in the case of a perfect sphere having a radius r). . A cross section is cut out in a direction perpendicular to the fixing surface within a range of 0.9 × h to 1.1 × h from the fixing surface.

The sample whose cross section has been processed can be directly applied to observation with a scanning electron microscope (SEM). In observation with a scanning electron microscope, it is known that the amount of reflected electrons emitted from a sample is larger as a heavy element. For example, in the case of a sample in which a metal such as an organic compound and an iron element is distributed in a planar shape, the amount of reflected electrons emitted from the iron element is detected more, so the iron element portion is bright on the image ( (Luminance, white). On the other hand, since the amount of reflected electrons from the organic compound composed of the light element compound is small, it appears dark on the image (low brightness and black). In the cross-sectional observation of the magnetic carrier particle of the present invention, the metal oxide portion derived from the magnetic core region is bright (high brightness, white), and the region other than the magnetic core portion appears dark (low brightness, black). Therefore, an image having a large contrast difference can be obtained. Specifically, it observed on the following conditions using the scanning electron microscope (SEM) and S-4800 (made by Hitachi High-Technologies Corporation). In addition, it observed after performing flushing operation.
SignalName = SE (U, LA100)
AcceleratingVoltage = 5000Volt
EmissionCurrent = 10000nA
Working distance = 4000um
LensMode = High
Condencer1 = 3
ScanSpeed = Slow4 (40 sec)
Magnification = 1500
DataSize = 1280x960
ColorMode = Grayscale
SpecimenBias = 0V

  In addition to the above conditions, the reflected electron image is captured by adjusting the brightness to “Contrast 5 and Brightness-5” on the control software of the scanning electron microscope S-4800, setting the magnetic pair observation mode to OFF, and the 256th floor. Toned grayscale image was obtained.

  The length of the magnetic core region in the cross section of the magnetic carrier particle, the calculation of the length of the region other than the magnetic core portion (resin portion and / or void) is calculated for the gray scale SEM reflected electron image of the magnetic carrier particle cross section. Calculation is performed by the following procedure using image analysis software Image-ProPlus 5.1J (Media Cybernetics).

  Here, FIG. 2 shows an example of an SEM reflected electron image of a processed cross section of the magnetic carrier particle of the present invention. In FIG. 2, a processed cross-sectional area 10 of magnetic carrier particles, a magnetic core portion 11, and a magnetic carrier surface 13 are shown.

  Only the processed cross-sectional area 10 of the magnetic carrier particles is designated in advance on the image. The boundary between the processed cross-sectional area of the magnetic carrier particles and the background can be easily distinguished from the reflected electron observation image. A cross-sectional area designated by particles is a 256-scale gray scale image. On the image, 0 to 129 gradations are divided into two areas other than the magnetic core part, and 130 to 254 gradations are divided into two areas of the magnetic core part region from the lower part of the gradation value. The 255th gradation is a background portion outside the processed cross-sectional area. The processed cross-sectional area 10 of the magnetic carrier particles is the magnetic core portion 11 and 12 other than the magnetic core portion, and is shown in FIG.

  FIG. 4 schematically shows a measurement example of the magnetic core region and the region other than the magnetic core portion in the cross section of the magnetic carrier particle of the present invention.

  1. Let Rx be the maximum diameter in the processed cross-sectional area of the magnetic carrier particles.

  2. The midpoint of Rx is taken as the reference point of the cross section of the magnetic carrier particle. Furthermore, let Ry be the diameter in the direction perpendicular to Rx at the midpoint.

  3. The measurement is performed on magnetic carrier particles having a substantially spherical shape and Rx / Ry ≦ 1.2.

  4). A magnetic core region having a length of 0.1 μm or more on a straight line passing through a reference point of the cross section of the magnetic carrier particle and drawn at intervals of 10 °, and regions other than the magnetic core portion, Measure the number.

  From the above measured values, the number (number%) of “magnetic core part regions having a length of 6.0 μm or more with respect to the total number of magnetic core parts regions having a length of 0.1 μm or more”, “0.1 μm or more The number (number%) of “magnetic core part regions having a length of 2.0 μm or less with respect to the total number of magnetic core part regions having a length of

  5. The above measurement is repeated for 25 magnetic carrier particles with Rx / Ry ≦ 1.2 selected at random, and the average value is calculated.

  FIG. 5 shows an example of the distribution of length and number (number%) obtained by measuring the magnetic core region having a length of 0.1 μm or more in the cross section of the magnetic carrier particle of the present invention by the above method.

  The three-dimensional laminated structure is repeated except for the magnetic core region having a length of 0.1 μm or more on the straight line passing through the reference point of the cross section of the magnetic carrier particle and drawn at intervals of 10 °, and the magnetic core portion. The repeated structure of the region was counted. Then, it divided by 18 and calculated | required the average number per straight line, and made it the repeating number of laminated structure.

  In the method for measuring the area ratio of the magnetic core portion in the cross section of the magnetic carrier particles, the processing cross-sectional area of the magnetic carrier particles is designated in advance on the image, and the cross sectional area of the magnetic carrier particles is set. A value obtained by dividing the area occupied by the magnetic core portion 1 by the cross-sectional area of the magnetic carrier particles is defined as “area ratio (area%) of the magnetic core portion”. In the present invention, the same measurement is performed on the 25 magnetic carrier particles described above, and the average value is used.

<Method of measuring parameter α of magnetic core>
A method for measuring parameter α will be described in detail with reference to the drawings.

  The value of the parameter α of the magnetic core can be measured by the following procedure.

(Weighing sample)
The magnetic core to be measured is sealed in a sample holder having a cylindrical electrode (diameter: 2.5 cm) having an electrode area of 4.9 cm ² , and the thickness of the sealed sample is measured when a pressure of 100 N is applied between the electrodes. The magnetic core was weighed so as to be in the range of 0.95 mm to 1.05 mm.

(Explanation of measurement circuit)
Wiring was performed between the electrodes of the sample holder as shown in FIG. 6, and AC impedance measurement of the magnetic core enclosed in the sample holder was performed in a state where a pressing pressure of 100 N was applied between the electrodes of the sample holder.

  In this measurement, as described in claim 1, in order to obtain α under an electric field, AC impedance measurement is performed in a state where a DC voltage is applied. For this reason, as shown in FIG. 6, an alternating bias obtained by superimposing the DC voltage Vo on the sine wave voltage Vac is applied between the electrodes of the sample holder.

  Here, the amplitude of the sine wave voltage Vac is 3V in effective value, and the DC voltage Vo is set such that the electric field applied to the magnetic core is 100 V / cm. Details will be described later.

  Furthermore, the impedance under a direct current electric field was measured by taking out and analyzing only the alternating current component of the response current flowing between the abs.

  As the impedance measuring apparatus, a 1260 type frequency response analyzer (FRA) manufactured by Solartron and a 1296 type dielectric constant measuring interface manufactured by the same company were used.

  The DC voltage Vo used for the alternating bias was obtained by amplifying a DC voltage signal output from a waveform oscillator with a PZD2000 type high voltage power source manufactured by Trek. The sine wave voltage Vac is output from the SAMPLE-HI terminal of the 1296 type dielectric constant measurement interface. Furthermore, as shown in FIG. 7, the alternating bias was obtained by arranging the capacitor C1 (66 μF) and the Zener diode ZD1 (5 V) in the measurement system and superimposing the DC voltage Vo on the sine wave voltage Vac.

  The response current can be separated into a direct current component and an alternating current component by using a shunt circuit using the resistor R2 (10 kΩ), the capacitor C2 (33 μF), and the Zener diode ZD2 (5 V) in FIG. it can. At this time, only the AC component flowing to the capacitor C2 side is input to the INPUT-V1-LO terminal of the 1260 type impedance analyzer and the SAMPLE-LO terminal of the 1296 type dielectric constant measurement interface, the response current waveform is analyzed, and the impedance is calculated. It was measured.

  Note that the resistor R1 (10 kΩ) in FIG. 6 is a protective resistor, and limits the maximum amount of current flowing through the measurement system.

(Measurement of complex impedance)
In this example, automatic impedance measurement was performed using the impedance measurement software SMaRT manufactured by Solartron. In SMaRT, the complex impedance Z (ω) = Re [Z (ω)] + ilm [Z (ω)] with respect to the frequency f is calculated from the sine wave voltage of the predetermined frequency f and the response current to the sine wave voltage.
Can be measured. However, Re [Z (ω)] is the real part of the impedance, and lm [Z (ω)] is the imaginary part of the impedance. Further, ω is an angular frequency, and there is a relationship of ω = 2πf with the frequency f.

  In order to measure the frequency characteristic of the impedance, the frequency f (Hz) of the sine wave voltage was measured at a plurality of frequencies in a range from 1 Hz to 1 MHz.

Specifically, 1.0, 1.6, 2.5, 4.0, 6.3, 1.0 × 10 ¹ , 1.6 × 10 ¹ , 2.5 × 10 ¹ , 4.0 × 10 ¹ , 6.3 × 10 ¹ , 1.0 × 10 ² , 1.6 × 10 ² , 2.5 × 10 ² , 4.0 × 10 ² , 6.3 × 10 ² , 1.0 × 10 ³ , 1.6 × 10 ³ , 2.5 × 10 ³ , 4.0 × 10 ³ , 6.3 × 10 ³ , 1.0 × 10 ⁴ , 1.6 × 10 ⁴ , 2.5 × 10 ⁴ 4.0 × 10 ⁴ , 6.3 × 10 ⁴ , 1.0 × 10 ⁵ , 1.6 × 10 ⁵ , 2.5 × 10 ⁵ , 4.0 × 10 ⁵ , 6.3 × 10 ⁵ , Measurement was performed at 1.0 × 10 ⁶ Hz.

  The amplitude of the sine wave voltage Vac is 3V as an effective value.

  As described above, a so-called Cole-Cole plot (Nyquist diagram) was created by plotting the complex impedance Z measured at a plurality of frequencies in a frequency range of 1 Hz to 1 MHz in a complex plane.

(Fitting by equivalent circuit)
Next, a method for obtaining α from complex impedance measurement data obtained by AC impedance measurement will be specifically described.

  The created Cole-Cole plot is fitted in accordance with the complex impedance of the equivalent circuit shown in FIG. 7 using the Instant Fit function of the analysis software ZView2 manufactured by Solartron, and α is used as the fitting parameter of the impedance measurement data. Asked.

Here, in FIG. 7, Rs and R are resistors, CPE is a circuit element called a Constant Phase Element (constant phase element), and the frequency characteristic of the complex impedance Z _CPE of the _CPE is expressed by the following equation (3). .

  Here, ω is an angular frequency of impedance measurement, and i is an imaginary unit. Α is a real parameter from 0 to 1.

The impedance of the entire fitting circuit in FIG. 7 is expressed as follows, and finally expressed by the following equation (1).
Z (ω) = Rs + (1 / R + 1 / Z _CFE ) ⁻¹
= Rs + (1 / R + 1 / ((iω) ^α T) ⁻¹ ) ⁻¹

  Note that Rs is a virtual resistance introduced into the fitting circuit in order to improve the fitting accuracy, and therefore may take a negative value.

(Α under electric field)
The value of α of the magnetic core under an electric field of 100 V / cm was determined as follows.

  When measuring the impedance, the average electric field strength Essample applied to the sample is expressed by Vsample / L using the DC component Vsample of the voltage shared by the sample between the electrodes and the interelectrode distance L during the impedance measurement. . The value of Vsample can be measured by the difference between the potential at point a and the potential at point b shown in the circuit diagram of FIG. In this measurement, the potential at points a and b was measured using a high voltage probe P6015A manufactured by Tktronix, and the shared voltage Vsample between the electrodes of the sample holder was measured based on the difference between these potentials. Further, the value of Vsample was adjusted by changing the voltage of the DC voltage Vo output from the high voltage power supply.

  Thus, impedance measurement was performed at a plurality of electric field strengths E, α under each electric field strength was obtained, and plotted on a graph to calculate α of the magnetic core under an electric field of 100 V / cm.

<Measuring method of 50% particle size (D50) based on volume distribution and 90% particle size (D90) based on volume distribution of calcined ferrite finely pulverized product>
The volume distribution standard 50% particle size (D50) and the volume distribution standard 90% particle size (D90) of the calcined ferrite finely pulverized product are measured by the laser diffraction / scattering type particle size distribution measuring device “ It was performed by attaching a sample circulator “Sample Delivery Control (SDC)” (manufactured by Nikkiso Co., Ltd.) for wet use with “Microtrack MT3300EX” (manufactured by Nikkiso Co., Ltd.). The calcined ferrite (ferrite slurry) was dropped into the sample circulator so as to have a measured concentration. The flow rate was 70%, the ultrasonic output was 40 W, and the ultrasonic time was 60 seconds. Control is automatically performed on software. For the particle size, a 50% particle size (D50), which is a cumulative value based on volume, is obtained. Control and analysis are performed using attached software (version 10.3.3-202D).

The measurement conditions are as follows.
SetZero time: 10 seconds Measurement time: 30 seconds Number of measurements: 10 times Solvation index: 1.33
Particle refractive index: 2.42
Particle shape: Non-spherical measurement upper limit: 1408 μm
Measurement lower limit: 0.243 μm
Measurement environment: 23 ° C / 50% RH

<Volume distribution standard 50% particle size (D50) of magnetic carrier and porous magnetic core>
The volume distribution standard 50% particle size (D50) of the magnetic carrier and the porous magnetic core is measured with a laser diffraction / scattering type particle size distribution measuring device “Microtrack MT3300EX” (manufactured by Nikkiso Co., Ltd.). The measurement was performed by mounting a sample feeder “One-shot dry type sample conditioner Turbotrac” (manufactured by Nikkiso Co., Ltd.). As the supply conditions of Turbotrac, a dust collector was used as a vacuum source, the air volume was 33 liters / sec, and the pressure was 17 kPa. Control is automatically performed on software. For the particle size, a 50% particle size (D50), which is a cumulative value based on volume, is obtained. Control and analysis are performed using attached software (version 10.3.3-202D).

The measurement conditions are as follows.
SetZero time: 10 seconds Measurement time: 10 seconds Number of measurements: 1 time Particle refractive index: 1.81
Particle shape: Non-spherical measurement upper limit: 1408 μm
Measurement lower limit: 0.243 μm
Measurement environment: 23 ° C / 50% RH

<Weight average particle diameter of toner (D4)>
The weight average particle diameter (D4) of the toner is determined based on the precise particle size distribution measuring apparatus “Coulter Counter Multisizer 3” (registered trademark, manufactured by Beckman Coulter, Inc.) having a 100 μm aperture tube. Using the attached dedicated software “Beckman Coulter Multisizer 3 Version 3.51” (manufactured by Beckman Coulter, Inc.) for setting and analyzing the measurement data, the measurement data is measured with 25,000 effective channels. Analysis was performed and calculated.

  As the electrolytic aqueous solution used for the measurement, a solution obtained by dissolving special grade sodium chloride in ion-exchanged water so as to have a concentration of 1% by mass, for example, “ISOTON II” (manufactured by Beckman Coulter, Inc.) can be used.

  Prior to measurement and analysis, the dedicated software was set as follows.

  In the “Standard measurement method (SOM) change screen” of the dedicated software, set the total count in the control mode to 50000 particles, the number of measurements is 1 and the Kd value is “standard particles 10.0 μm” (Beckman Coulter Set the value obtained using The threshold and noise level are automatically set by pressing the threshold / noise level measurement button. Also, the current is set to 1600 μA, the gain is set to 2, the electrolyte is set to ISOTON II, and the aperture tube flash after measurement is checked.

  In the “pulse to particle size conversion setting screen” of the dedicated software, the bin interval is set to logarithmic particle size, the particle size bin is set to 256 particle size bin, and the particle size range is set to 2 μm to 60 μm.

The specific measurement method is as follows.
(1) In a glass 250 ml round bottom beaker for exclusive use of Multisizer 3, 200 ml of the electrolytic aqueous solution is placed and set on a sample stand, and the stirrer rod is stirred counterclockwise at 24 rpm. Then, dirt and bubbles in the aperture tube are removed by the “aperture flush” function of the analysis software.
(2) 30 ml of the electrolytic aqueous solution is placed in a glass-made 100 ml flat bottom beaker, and “Contaminone N” (nonionic surfactant, anionic surfactant, organic builder pH 7 precision measuring instrument as a dispersant is added therein. 0.3 ml of a diluted solution obtained by diluting a 10% by weight aqueous solution of a neutral detergent for washing (made by Wako Pure Chemical Industries, Ltd.) with ion-exchanged water 3 times by mass is added.
(3) Two oscillators with an oscillation frequency of 50 kHz are incorporated in a state where the phase is shifted by 180 degrees, and placed in a water tank of an ultrasonic dispersion device “Ultrasonic Dissipation System Tetora 150” (manufactured by Nikki Bios Co., Ltd.) having an electrical output of 120 W. A fixed amount of ion-exchanged water is added, and 2 ml of the above-mentioned Contaminone N is added to this water tank.
(4) The beaker of (2) is set in the beaker fixing hole of the ultrasonic disperser, and the ultrasonic disperser is operated. And the height position of a beaker is adjusted so that the resonance state of the liquid level of the electrolyte solution in a beaker may become the maximum.
(5) In a state where the electrolytic aqueous solution in the beaker of (4) is irradiated with ultrasonic waves, 10 mg of toner is added to the electrolytic aqueous solution little by little and dispersed. Then, the ultrasonic dispersion process is continued for another 60 seconds. In the ultrasonic dispersion, the temperature of the water tank is appropriately adjusted so as to be 10 ° C. or higher and 40 ° C. or lower.
(6) To the round bottom beaker (1) installed in the sample stand, the electrolyte aqueous solution (5) in which the toner is dispersed is dropped using a pipette, and the measurement concentration is adjusted to 5%. Measurement is performed until the number of measured particles reaches 50,000.
(7) The measurement data is analyzed with the dedicated software attached to the apparatus, and the weight average particle diameter (D4) is calculated. The “average diameter” on the analysis / volume statistics (arithmetic average) screen when the graph / volume% is set by the dedicated software is the weight average particle diameter (D4).

<Average circularity of toner>
The average circularity of the toner was measured with a flow type particle image analyzer “FPIA-3000 type” (manufactured by Sysmex Corporation) under the measurement and analysis conditions during calibration.

  The measurement principle of the flow-type particle image analyzer “FPIA-3000 type” (manufactured by Sysmex Corporation) is to take a flowing particle as a still image and perform image analysis. The sample added to the sample chamber is fed into the flat sheath flow cell by a sample suction syringe. The sample fed into the flat sheath flow is sandwiched between sheath liquids to form a flat flow. The sample passing through the flat sheath flow cell is irradiated with strobe light at 1/60 second intervals, and the flowing particles can be photographed as a still image. Further, since the flow is flat, the image is taken in a focused state. The particle images are picked up by a CCD camera, and the picked-up image is 512 pixels × 512 pixels in one field of view, and image processing is performed at an image processing resolution of 0.37 × 0.37 μm per pixel, and the contour of each particle image Extraction is performed, and the projected area and perimeter of the particle image are measured.

Next, the projected area S and the perimeter L of each particle image are obtained. Using the area S and the perimeter L, the equivalent circle diameter and the circularity are obtained. The circular equivalent diameter is the diameter of a circle having the same area as the projected area of the particle image, and the circularity is a value obtained by dividing the circumference of the circle obtained from the circular diameter by the circumference of the projected particle image. Defined and calculated by the following formula.
Circularity C = 2 × (π × S) ^1/2 / L

  When the particle image is a perfect circle, the circularity becomes 1.000, and the circularity becomes smaller as the degree of irregularities on the outer periphery of the particle image increases.

  After calculating the circularity of each particle, the range of the circularity of 0.2 or more and 1.0 or less is distributed to 800 divided channels, and the average value is calculated by using the center value of each channel as a representative value to calculate the average circularity. .

  As a specific measurement method, 0.02 g of a surfactant as a dispersant, preferably sodium dodecylbenzenesulfonate, is added to 20 ml of ion-exchanged water, 0.02 g of a measurement sample is added, an oscillation frequency of 50 kHz, electrical Dispersion treatment was performed for 2 minutes using a desktop ultrasonic cleaner / disperser with an output of 150 W (for example, “VS-150” (manufactured by Velvo Crea Co., Ltd.)) to obtain a dispersion for measurement. Is suitably cooled so that the temperature becomes 10 ° C. or higher and 40 ° C. or lower.

  The flow type particle image analyzer equipped with a standard objective lens (10 ×) was used for the measurement, and a particle sheath “PSE-900A” (manufactured by Sysmex Corporation) was used as the sheath liquid. The dispersion prepared in accordance with the above procedure is introduced into the flow type particle image analyzer, 3000 toner particles are measured in the total count mode in the HPF measurement mode, and the binarization threshold at the time of particle analysis is 85%. The analysis particle diameter was limited to a circle equivalent diameter of 2.00 μm to 200.00 μm, and the average circularity of the toner was determined.

  In the measurement, automatic focus adjustment is performed using standard latex particles (for example, Duke Scientific 5200A diluted with ion-exchanged water) before the measurement is started. Thereafter, it is preferable to perform focus adjustment every two hours from the start of measurement.

  In the examples of the present application, a flow type particle image analyzer that has been issued a calibration certificate issued by Sysmex Corporation is used, and the analysis particle diameter is limited to a circle equivalent diameter of 2.00 μm to 200.00 μm. The measurement was performed under the measurement and analysis conditions when the calibration certificate was received.

  Specific examples of the present invention will be described below, but the present invention is not limited to these examples.

<Production Example 1 of Porous Magnetic Core>
Process 1 (weighing / mixing process):
Fe ₂ O ₃ (D50 = 1 μm) was pulverized and mixed for 2 hours in a dry ball mill using zirconia (φ10 mm) balls.

Step 2 (temporary firing step):
After pulverization and mixing, firing was performed in the atmosphere at 950 ° C. for 2 hours using a burner-type firing furnace to prepare calcined ferrite.

Step 3 (grinding step):
A calcined ferrite was obtained by crushing to about 0.5 mm with a crusher. Thereafter, the calcined ferrite was divided in half.

  Half of the calcined ferrite was zirconia (φ10 mm) balls, 30 parts by mass of water was added to 100 parts by mass of calcined ferrite, and pulverized with a wet ball mill for 2 hours to obtain a ferrite slurry 1-1.

  Half of the ferrite slurry 1-1 was further pulverized for 3 hours by a wet bead mill using zirconia beads (φ1.0 mm) to obtain a ferrite slurry 1-2.

  Ferrite slurries 1-1 and 1-2 were mixed with a wet bead mill using zirconia beads (φ1.0 mm) for 10 minutes to obtain ferrite slurry 1 (calcined ferrite finely pulverized product 1).

  The obtained calcined ferrite pulverized product 1 had a volume-based 50% particle size (D50) of 1.7 μm and a volume-based 90% particle size (D90) of 5.0 μm.

Process 4 (granulation process):
To the ferrite slurry 1, with respect to 100 parts by mass of calcined ferrite as a binder, 2.0 parts by mass of polyvinyl alcohol, 5 parts by mass of SiO ₂ and 1.5 parts by mass of ammonium polycarboxylate as a dispersant are added, and a spray dryer (Manufacturer: Okawara Chemical Industries) granulated into spherical particles.

Process 5 (main baking process):
In order to control the firing atmosphere, firing was performed at 1050 ° C. for 4 hours in a nitrogen atmosphere (oxygen concentration of 0.01% by volume or less) in an electric furnace.

Process 6 (screening process):
After the aggregated particles were crushed, coarse particles were removed by sieving with a sieve having an opening of 250 μm to obtain a porous magnetic core 1.

<Production Example 2 of Porous Magnetic Core>
Process 1 (weighing / mixing process):
Fe ₂ O ₃ 92.0 mass%
Mg (OH) ₂ 8.0 mass%
The ferrite raw material was weighed so that Thereafter, the mixture was pulverized and mixed for 2 hours in a dry ball mill using zirconia (φ10 mm) balls.

  Except for the above, a porous magnetic core 2 was obtained in the same manner as in Production Example 1 of the porous magnetic core.

<Production Example 3 of Porous Magnetic Core>
Process 1 (weighing / mixing process):
Fe ₂ O ₃ 62.8% by mass
MnCO ₃ 31.2% by mass
Mg (OH) ₂ 6.0% by mass
The ferrite raw material was weighed so that Thereafter, the mixture was pulverized and mixed for 2 hours in a dry ball mill using zirconia (φ10 mm) balls.

  Except for the above, a porous magnetic core 3 was obtained in the same manner as in Production Example 1 of the porous magnetic core.

<Production Example 4 of Porous Magnetic Core>
In the same manner as in Production Example 3 of the porous magnetic core, except that 5 parts by weight of SiO ₂ and 1.5 parts by weight of ammonium polycarboxylate as a dispersant are not added in Step 4 (granulation step) A magnetic core 4 was obtained.

<Production Examples 5 to 12, 17 of Porous Magnetic Core>
Of the porous magnetic core production example 4, the ball mill and bead mill grinding conditions in step 3 (grinding step), the amount of polyvinyl alcohol in step 4 (granulation step), the firing atmosphere and firing temperature in step 5 (main firing step) In place of the conditions shown in Table 1, porous magnetic cores 5 to 12 and 17 were obtained.

<Production Examples 13 to 16 of porous magnetic core>
Of the porous magnetic core production example 4, the ball mill and bead mill grinding conditions in step 3 (grinding step), the amount of polyvinyl alcohol in step 4 (granulation step), the firing atmosphere and firing temperature in step 5 (main firing step) Changed as shown in Table 1. In addition, the porous magnetic core production example 4 except that after crushing to about 0.5 mm with a crusher in step 3 (pulverization step), the calcined ferrite was not halved and all was pulverized with a wet ball mill and a wet bead mill. In the same manner, Production Examples 13 to 16 of the porous magnetic core were obtained.

<Production Example 18 of Porous Magnetic Core>
Process 1 (weighing / mixing process):
Fe ₂ O ₃ 62.4% by mass
MnCO ₃ 30.5% by mass
Mg (OH) ₂ 6.4% by mass
SrCO ₃ 0.7% by mass
Was pulverized and mixed for 2 hours in a dry ball mill using zirconia (φ10 mm) balls.

Step 2 (temporary firing step):
After pulverization and mixing, firing was performed in the atmosphere at 950 ° C. for 2 hours using a burner-type firing furnace to prepare calcined ferrite.

Step 3 (grinding step):
A calcined ferrite was obtained by crushing to about 0.5 mm with a crusher.

  Using calcined ferrite balls made of stainless steel (φ10 mm), 30 parts by mass of water was added to 100 parts by mass of calcined ferrite, and pulverized with a wet ball mill for 1 hour to obtain ferrite slurry 18-1.

  The ferrite slurry 18-1 was further pulverized for 4 hours by a wet bead mill using stainless beads (φ1.0 mm) to obtain a ferrite slurry 18 (calcined ferrite finely pulverized product 18).

Process 4 (granulation process):
To the ferrite slurry 18, 2.0 parts by mass of polyvinyl alcohol was added as a binder with respect to 100 parts by mass of calcined ferrite, and granulated into 36 μm spherical particles with a spray dryer (manufacturer: Okawahara Chemical).

Process 5 (main baking process):
In order to control the firing atmosphere, firing was performed at 1100 ° C. for 4 hours in an electric furnace under a nitrogen atmosphere (oxygen concentration of 0.01% by volume or less).

Process 6 (screening process):
After the aggregated particles were crushed, coarse particles were removed by sieving with a sieve having an opening of 250 μm to obtain a porous magnetic core 18.

<Manufacture example 1 of a magnetic core>
Step 1:
Fe ₂ O ₃ 71.0 mass%
CuO 12.5 mass%
ZuO 16.5% by mass
The ferrite raw material was weighed so that Thereafter, the mixture was pulverized and mixed for 2 hours in a dry ball mill using zirconia (φ10 mm) balls.

Step 2:
After pulverization and mixing, firing was performed at 950 ° C. for 2 hours in the air to prepare calcined ferrite.

Step 3:
After crushing to about 0.5 mm with a crusher, 30 parts by mass of water was added to 100 parts by mass of calcined ferrite using a stainless ball (φ10 mm), and the mixture was pulverized with a wet ball mill for 6 hours. The obtained calcined ferrite finely pulverized product had D50 = 0.5 μm and D90 = 2.8 μm.

Step 4:
To the ferrite slurry, 2.0 parts by mass of polyvinyl alcohol was added as a binder with respect to 100 parts by mass of calcined ferrite, and granulated into spherical particles with a spray dryer (manufacturer: Okawahara Chemical).

Step 5:
Firing was performed at 1300 ° C. for 4 hours in the air.

Step 6:
After the aggregated particles were crushed, coarse particles were removed by sieving with a sieve having an opening of 250 μm to obtain a magnetic core 1.

  The physical properties of the obtained porous magnetic cores 1 to 18 and magnetic core 1 are shown in Table 2.

Preparation of resin solution:
・ Resin liquid 1
Straight silicone (SR2411 Toray Dow Corning) 20.0 parts by mass γ-aminopropyltriethoxysilane 0.5 parts by mass Toluene 79.5 parts by mass The above is mixed for 1 hour using a ball mill (soda glass ball φ10 mm), and resin Liquid 1 was obtained.
・ Resin liquid 2
Polymethylmethacrylate polymer (Mw = 66,000) 5.0 parts by mass Bontron P51 (Orient Chemical Co., Ltd.) 2.0 parts by mass Toluene 93.0 parts by mass Using a bead mill (zirconia beads φ1.0 mm) The mixture was dispersed and mixed for 3 hours to obtain a resin liquid 2.

<Example of production of magnetic carrier 1>
Process example 1 (resin filling process example):
100.0 parts by mass of the porous magnetic core 1 is put into a universal stirring mixer (manufactured by Dalton) and stirred while heating to 80 ° C. under reduced pressure. Subsequently, the resin liquid 1 was added to 100 parts by mass of the porous magnetic core 1 so as to be 8 parts by mass as a resin component, and heating was continued for 2 hours to remove the solvent. The obtained sample was transferred to a Julia mixer (manufactured by Tokuju Kogakusha Co., Ltd.), heat-treated at 200 ° C. for 2 hours in a nitrogen atmosphere, and classified with a mesh having an opening of 70 μm to obtain a filled core 1.

Process example 2 (resin coating process example):
100.0 parts by mass of the filling core 1 was put into a Nauta mixer (manufactured by Hosokawa Micron), and further, the resin liquid 2 was put into the Nauta mixer so as to be 0.5 parts by mass as a resin component. The mixture was heated to 70 ° C. under reduced pressure, mixed at 1.7 s ⁻¹ (100 rpm), and subjected to solvent removal and coating operation over 4 hours. Thereafter, the obtained sample was transferred to a Julia mixer (manufactured by Tokuju Kogakusha Co., Ltd.), heat-treated at a temperature of 200 ° C. for 2 hours in a nitrogen atmosphere, and then classified with a mesh having an opening of 70 μm to obtain a magnetic carrier 1.

<Examples of manufacturing magnetic carriers 2 to 20>
Magnetic carriers 2 to 20 were obtained by changing the amount of core, filling resin, and coating resin as shown in Table 3.

  Table 4 shows the physical properties of the obtained carriers 1 to 20.

[Production Example 1 of Resin]
The following materials were weighed in a reaction vessel equipped with a cooling tube, a stirrer, and a nitrogen introducing tube.
Terephthalic acid 22.6 parts by weight trimellitic anhydride 1.7 parts by weight polyoxypropylene (2.2) -2,2-bis (4-hydroxyphenyl) propane
75.6 parts by mass Titanium dihydroxybis (triethanolamate) 0.1 parts by mass

  Then, it heated at 200 degreeC, it was made to react for 10 hours, removing the water produced | generated, introduce | transducing nitrogen, Then, it pressure-reduced to 10 mmHg and made it react for 1 hour, and the resin 1 was synthesize | combined. The molecular weight of the resin 1 determined by GPC was a weight average molecular weight (Mw) of 6200, a number average molecular weight (Mn) of 2500, a peak molecular weight (Mp) of 2900, a glass transition point of 55 ° C., and a softening point of 93 ° C. .

[Resin Production Example 2]
The following materials were weighed in a reaction vessel equipped with a cooling tube, a stirrer, and a nitrogen introducing tube.
Terephthalic acid 17.2 parts by weight polyoxyethylene (2.2) -2,2-bis (4-hydroxyphenyl) propane
76.6 parts by mass Titanium dihydroxybis (triethanolamate) 0.1 parts by mass

  Then, it heated at 220 degreeC and made it react for 10 hours, removing the water produced | generated, introducing nitrogen.

  Further, 6.1 parts by mass of trimellitic anhydride was added, heated to 180 ° C., and reacted for 2 hours to synthesize resin 2. The molecular weight of the resin 2 determined by GPC was a weight average molecular weight (Mw) of 86000, a number average molecular weight (Mn) of 6000, a peak molecular weight (Mp) of 12800, a glass transition point of 62 ° C., and a softening point of 132 ° C.

[Toner Production Example 1]
Resin 1 50.0 parts by mass Resin 2 50.0 parts by mass Paraffin wax (DSC maximum endothermic peak 75 ° C.) 7.5 parts by mass C.I. I. Pigment Blue 15: 3 5.0 parts by mass After the above materials were thoroughly mixed with a Henschel mixer (FM-75 type, manufactured by Mitsui Miike Chemical Co., Ltd.), a twin-screw kneader (PCM-30) set at a temperature of 130 ° C. Kneaded with a mold, manufactured by Ikekai Tekko Co., Ltd. The obtained kneaded material was cooled and coarsely pulverized to 1 mm or less with a hammer mill to obtain a coarsely pulverized material. The obtained coarsely crushed material was finely pulverized using a collision-type airflow pulverizer using high-pressure gas.

Next, the obtained finely pulverized product was subjected to surface modification using a surface modification apparatus shown in FIG. Surface reforming conditions were as follows: the raw material supply rate was 2.0 kg / hr, the hot air flow rate was 4.5 m ³ / min, the hot air discharge temperature was 220 ° C., the cold air temperature was 3 ° C., and the cold air flow rate was 3.0 m ³ / min. Modification was performed. Next, classification was performed with an air classifier (Elbow Jet Lab EJ-L3, manufactured by Nippon Steel Mining Co., Ltd.) using the Coanda effect, and fine powder and coarse powder were simultaneously removed to obtain toner particles 1.

  To 100.0 parts by mass of the obtained toner particles 1, 1.0 part by mass of hydrophobic silica fine particles surface-treated with 20% by mass of hexamethyldisilazane having a primary average particle diameter of 16 nm is added as inorganic fine particles. Toner 1 was obtained by externally mixing 1.0 part by mass of a sol-gel silica fine powder having a diameter of 200 nm and treated with hexamethyldisilazane.

[Toner Production Example 2]
Styrene 78.4 parts by mass Acrylic acid-n-butyl 20.8 parts by mass Methacrylic acid 2.0 parts by mass was added to the reaction vessel, and the mixture was heated to 110 ° C. A solution obtained by dissolving 1 part by mass of tert-butyl hydroperoxide as a radical polymerization initiator in 10 parts by mass of xylene under a nitrogen atmosphere was added dropwise to the mixture over 30 minutes. Further, the mixture was kept at that temperature for 10 hours to complete the radical polymerization reaction. Further, the pressure of the mixed solution was reduced while heating, and the solvent was removed to obtain Resin 3. The molecular weight of the resin 3 determined by GPC was a weight average molecular weight (Mw) of 35000, a number average molecular weight (Mn) of 8000, a peak molecular weight (Mp) of 12000, and a glass transition point (Tg) of 58 ° C.

Resin 3 100.0 parts by mass Purified normal paraffin (DSC maximum endothermic peak 70 ° C.) 5.0 parts by mass C.I. I. Pigment Blue 15: 3 5.0 parts by mass After the above materials were thoroughly mixed with a Henschel mixer (FM-75 type, manufactured by Mitsui Miike Chemical Co., Ltd.), a twin-screw kneader (PCM-30) set at a temperature of 130 ° C. Kneaded with a mold, manufactured by Ikekai Tekko Co., Ltd. The obtained kneaded material was cooled and coarsely pulverized to 1 mm or less with a hammer mill to obtain a coarsely pulverized material. The obtained coarsely crushed material was finely pulverized using a collision-type airflow pulverizer using high-pressure gas.

  Next, the obtained finely pulverized product was subjected to surface modification treatment while removing fine particles using a faculty (manufactured by Hosokawa Micron Corporation) to obtain toner particles 2.

  To 100.0 parts by mass of the obtained toner particles 2, 2.0 parts by mass of hydrophobic silica fine particles surface-treated with 20% by mass of hexamethyldisilazane having a primary average particle diameter of 16 nm are added as inorganic fine particles. Obtained.

[Toner Production Example 3]
An aqueous solution obtained by adding 450 parts by mass of 0.12 mol / l-Na ₃ PO ₄ aqueous solution to 710 parts by mass of ion-exchanged water and heating to 60 ° C. is used as a TK homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.). And stirred at 250 s ⁻¹ . To this, 68 parts by mass of a 1.2 mol / l-CaCl ₂ aqueous solution was gradually added to obtain an aqueous medium containing Ca ₃ (PO ₄ ) ₂ .

Next, the following materials, C.I. I. Pigment Blue 15: 3 10 parts by mass, styrene 160 parts by mass, n-butyl acrylate 30 parts by mass, paraffin wax (peak temperature of maximum endothermic peak 78 ° C.) 20 parts by mass, aluminum compound of 3,5-di-t-butylsalicylate 0.4 parts by mass / polyester resin (terephthalic acid-polyoxypropylene (2.2) -2,2-bis (4-hydroxyphenyl) propane polycondensation; acid value 15 mg KOH / g, peak molecular weight 6000) 10 parts by mass Was heated to 60 ° C., and uniformly dissolved and dispersed at 166.7 s ⁻¹ using a TK homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.). To this, 10 parts by mass of a polymerization initiator 2,2′-azobis (2,4-dimethylvaleronitrile) was dissolved to prepare a monomer mixture.

The obtained monomer mixture was put into the aqueous medium. The resulting mixture was stirred at 200 s ⁻¹ (12000 rpm) for 10 minutes at 60 ° C. under a nitrogen atmosphere using a TK homomixer to granulate the polymerizable monomer composition. Then, it heated up at 80 degreeC, stirring with a paddle stirring blade, and was made to react for 10 hours. After completion of the polymerization reaction, the remaining monomer was distilled off under reduced pressure. After cooling, hydrochloric acid was added to dissolve Ca ₃ (PO ₄ ) ₂ . The resulting solution was filtered, and the filtered product was washed with water and dried to obtain toner particles 3.

  To 100 parts by mass of the obtained toner particles 3, 0.8 parts by mass of titanium oxide fine particles having a primary average particle diameter of 50 nm surface-treated with 15% by mass of isobutyltrimethoxysilane and a primary treated with 20% by mass of hexamethyldisilazane. Toner 3 was obtained by adding 0.7 part by mass of hydrophobic silica fine particles having an average particle size of 16 nm and mixing with a Henschel mixer (FM-75 type, manufactured by Mitsui Miike Chemical Co., Ltd.).

  Table 5 shows the physical properties of Toners 1 to 3.

[Examples 1 to 13 and Comparative Examples 1 to 7]
Next, the magnetic carrier and the toner thus prepared were mixed with 100 parts by mass of the magnetic carrier and 8 parts by mass of the toner to prepare a two-component developer. The two-component developer was mixed with a V-type mixer for 5 minutes.

  Table 6 shows the combinations of magnetic carrier and toner.

As an image forming apparatus, a Canon color copier imageRUNNER iR C3580 modified machine was used. The developer was placed in a cyan position developer and evaluated. The development conditions were modified so that the peripheral speed of the developing sleeve with respect to the developing drum was 1.5 times and the process speed was 245 mm / sec. An AC voltage and a DC voltage VDC having a frequency of 2.0 kHz and Vpp of 1.3 kV were applied to the developing sleeve. The DC voltage _VDC was adjusted so that the amount of toner on the paper of the FFH image (solid portion) was 0.5 mg / cm ² .

  The initial dot reproducibility, image density stability, developability, halftone uniformity, and carrier adhesion were evaluated by the evaluation methods and evaluation criteria described later.

  Next, after continuously printing 100,000 sheets at an image area ratio of 1%, dot reproducibility, density fluctuation, developability, halftone uniformity, and carrier adhesion were evaluated.

  The above evaluation was performed in two environments of a temperature of 23 ° C./humidity of 50% RH and a temperature of 30 ° C./humidity of 80% RH. The evaluation results are shown in Tables 7 to 9.

The FFH image is a value in which 256 gradations are displayed in hexadecimal, and 00H is the first gradation (white background part) and FFH is the 256th gradation (solid part).
Printing environment Temperature 23 ° C / Humidity 50% RH (hereinafter “N / N”)
Temperature 23 ° C / Humidity 5% RH (hereinafter “N / L”)
Temperature 30 ° C / Humidity 80% RH (hereinafter "H / H")
Paper Plain paper for color copiers and printers CS-814 (A4, 81.4 g / m ² )
(Sold from Canon Marketing Japan Inc.)

<Dot reproducibility>
A dot image (FFh image) in which one pixel is formed by one dot was created. The spot diameter of the laser beam was adjusted so that the area per dot on the paper was 20000 μm ² or more and 25000 μm ² or less. The area of 1000 dots was measured using a digital microscope VHX-500 (lens wide range zoom lens VH-Z100, manufactured by Keyence Corporation). The number average (S) of dot areas and the standard deviation (σ) of dot areas were calculated, and the dot reproducibility index was calculated by the following formula.
Dot reproducibility index (I) = σ / S × 100
A: I is less than 4.0 (very good)
B: I is 4.0 or more and less than 6.0 (good)
C: I is 6.0 or more and less than 8.0 (Acceptable level in the present invention)
D: I is 8.0 or more (not acceptable in the present invention)

<Image density stability>
Before performing the durability evaluation, one 20 mm × 20 mm FFH image was printed. The image density of the FFH image portion was measured using an X-Rite color reflection densitometer (500 series: manufactured by X-Rite). Then, after printing 10 sheets at an image area ratio of 30%, one 20 mm × 20 mm FFH image was printed, and the image density of the FFH image portion was measured. The difference in image density before and after printing 10 sheets was calculated at an image area ratio of 30%.

(Evaluation criteria)
A: 0.00 or more and less than 0.05 (very good)
B: 0.05 or more and less than 0.10 (good)
C: 0.10 or more and less than 0.20 (Acceptable level in the present invention)
D: 0.20 or more (not acceptable in the present invention)

<Developability>
The DC voltage V _DC was fixed at 300 V, and an AC voltage and a DC voltage V _DC were applied in which Vpp was changed from 0.7 kV to 2.0 kV in increments of 0.1 kV. Vpp when the applied toner amount was 0.50 mg / cm was obtained.
(A) Vpp less than 1.4 kV (very good)
(B) Vpp 1.4 kV or more and less than 1.6 kV (good)
(C) Vpp 1.6 kV or more and less than 1.9 kV (acceptable level in the present invention)
(D) Vpp 1.9 kV or more (not acceptable in the present invention)

<Halftone uniformity>
Three 90h images were output on the entire surface of A3 paper, and the third image was used for evaluation. The image uniformity was evaluated by measuring the image density at five locations and determining the difference between the maximum value and the minimum value. The image density was measured with an X-Rite color reflection densitometer (Color reflection densitometer X-Rite 404A).
A: Less than 0.04 (very good)
B: 0.04 or more and less than 0.08 (good)
C: 0.08 or more and less than 0.12 (Acceptable level in the present invention)
D: 0.12 or more (not acceptable in the present invention)

<Concentration fluctuation before and after durability>
Before performing the durability evaluation, one 20 mm × 20 mm FFH image was printed. The image density of the FFH image portion was measured using an X-Rite color reflection densitometer (500 series: manufactured by X-Rite).

  After endurance, the same image was printed and the image density was measured.

  The difference in image density between the initial stage and the endurance was evaluated based on the following criteria.

(Evaluation criteria)
A: 0.00 or more and less than 0.05 (very good)
B: 0.05 or more and less than 0.10 (good)
C: 0.10 or more and less than 0.20 (Acceptable level in the present invention)
D: 0.20 or more (not acceptable in the present invention)

<Carrier adhesion>
A 00H image is printed, and the part on the photosensitive drum is sampled by attaching a transparent adhesive tape, and the number of magnetic carrier particles adhering to the photosensitive drum in 1 cm × 1 cm is counted, and the adhering per 1 cm ^2. The number of carrier particles was calculated.
A: 3 or less (very good)
B: 4 or more and 10 or less (good)
C: 11 or more and 20 or less (Acceptable level in the present invention)
D: 21 or more (not acceptable in the present invention)

  100: Toner particle supply port, 101: Hot air supply port, 102: Airflow injection member, 103: Cold air supply port, 104: Second cold air supply port, 106: Cooling jacket, 114: Toner particles, 115: High pressure air supply nozzle 116: transfer pipe, 10: cross-sectional area of the magnetic carrier particle, 11: magnetic core part, 12: area other than the magnetic core part, 13: surface of the magnetic carrier particle

Claims (4)

A magnetic carrier having magnetic carrier particles having at least porous magnetic core particles and a resin,
In the reflected electron image of the cross section of the magnetic carrier particle taken by a scanning electron microscope, when the midpoint of the maximum diameter Rx in the processed cross-sectional area of the magnetic carrier particle is used as a reference point, the reference point passes through the reference point and is 10 °. On a straight line with 18 intervals drawn,
The ratio of the number of magnetic core part regions having a length of 6.0 μm or more to the total number of magnetic core part regions having a length of 0.1 μm or more is 5.0% by number to 35.0% by number, In addition, the ratio of the number of magnetic core portion regions having a length of 2.0 μm or less is 10.0% by number to 45.0% by number,
The porous magnetic core particle has a parameter α obtained by fitting the frequency dependence characteristic of impedance Z obtained by alternating current impedance measurement with a fitting function represented by the following equation (1), under an electric field strength of 100 V / cm. Wherein the magnetic carrier is 0.65 or more and 0.85 or less.

However,
Re [Z (ω)] is the real part lm [Z (ω)] of the impedance, the imaginary part i of the impedance is the imaginary unit ω, and the angular frequencies Rs, R, T, α are Cole-Cole equations. Calculated by fitting with   In the reflected electron image of the cross section of the magnetic carrier particle photographed by a scanning electron microscope, the area ratio of the magnetic core region is from 50 area% to 80 area% with respect to the total area of the cross section. The magnetic carrier according to claim 1, wherein the magnetic carrier is a magnetic carrier.   3. The magnetic carrier according to claim 1, wherein the magnetic carrier particles are further coated with a resin on the surface of the particles in which the pores of the porous magnetic core particles are filled with the resin.   The two-component developer containing at least a toner and a magnetic carrier, wherein the magnetic carrier is the magnetic carrier according to any one of claims 1 to 3.

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