JP4948342B2 - Carrier core material for electrophotographic development and method for producing the same, magnetic carrier, and electrophotographic developer - Google Patents

Description

  The present invention relates to a carrier core material for dry development, a production method thereof, a magnetic carrier using the carrier core material, and an electrophotographic developer.

  The electrophotographic dry development method is a method in which powder toner, which is an electrophotographic developer, is attached to an electrostatic latent image on a photoreceptor, and the attached toner is transferred to a predetermined medium such as paper and developed. is there. This method is roughly classified into a method using a one-component developer containing only toner and a method using a two-component developer containing toner and a magnetic carrier as an electrophotographic developer. In recent years, a two-component development method in which toner charge control is easy and stable high image quality can be obtained and high-speed development is possible has become the mainstream of electrophotographic developers.

  In the developing method using a two-component developer, the magnetic carrier is stirred and mixed with the toner in the developing machine, thereby giving the toner a desired charge, forming a magnetic brush on the magnet roll, and charging the charged toner. Transport to the photoreceptor. The magnetic carrier remaining on the magnet roll returns to the developing machine again, and is agitated and mixed with new toner, and is repeatedly used for a certain period. Therefore, it is necessary for the magnetic carrier to maintain a stable initial characteristic without changing during the printing durability period.

  Conventionally, in a two-component electrophotographic developer, the magnetic carrier is subjected to agitation stress in the developing device for long-term use, and the resin film is peeled off or the core material is exposed, so that charge leakage occurs. Such charge leakage is one of the causes of image quality degradation.

Therefore, in Patent Document 1, electric resistance is increased by adding ZrO ₂ or Bi ₂ O ₃ to the magnetic carrier and further performing an oxide coating process to form a layer having a high proportion of Fe ₂ O _3. Enhanced magnetic carriers have been proposed.

The inventors of the present invention are studying to lower the particle density of the magnetic carrier by adding SiO ₂ which is a low density substance. The present inventors have intensively studied paying attention to the resistance of the carrier core material added with SiO ₂ . As a result, when SiO ₂ was dispersed in a magnetic carrier, it was conceived that the resistance value increased depending on the amount of SiO ₂ added, and disclosed as Patent Document 2.

In addition, the inventors have made the average particle size of SiO ₂ 2 μm or less so that the apparent density is small, the residual magnetization is small, and the resistance is increased in the high resistance treatment process, thereby increasing the electric power during voltage application. Patent Document 3 discloses that a carrier core material having high resistance is obtained.

Japanese Patent Laid-Open No. 2004-240322 Japanese Patent Application No. 2005-285652 Japanese Patent Application No. 2006-243672

The inventors of the present invention conducted intensive research on the magnetic carrier having a high electrical resistance according to the prior art and the durability of the magnetic carrier.
As a result, it was confirmed that the magnetic carrier according to Patent Document 1 causes peeling of the resin film, breakage of the magnetic carrier, and application of the magnetic carrier, resulting in deterioration of image characteristics.
Next, when the magnetic carrier according to Patent Document 2 is added with an amount of SiO ₂ sufficient to reduce the voltage dependency, there arises a problem that the magnetization necessary for the magnetic carrier powder may not be obtained.
In addition, the magnetic carrier according to Patent Document 3 generates a phase other than the magnetic phase, SiO ₂ phase (such as Fe ₂ O ₃ ) when the resistivity is increased by the resistivity increasing process step. There was a problem that the strength decreased.

  The present invention has been made under the above-described situation, and the carrier core material that can increase the exchange life of the magnetic carrier by having a low voltage dependency of the core material resistance and having a high resistivity, And a manufacturing method thereof, a magnetic carrier using the carrier core material, and an electrophotographic developer.

The inventors have the necessary magnetization as magnetic carrier powder, have low voltage dependency and high resistance, and have the composition formula: Mn _x Fe _3-x O ₄ (where 0 ≦ x ≦ 1.0). We eagerly investigated whether the soft ferrite carrier indicated can be provided. Then, paying attention to SiO ₂ in the carrier core material of the soft ferrite carrier, in the process of synthesizing the magnetic carrier, the crystal structure of SiO ₂ is structurally transferred to form a strong three-dimensional network structure of SiO ₂ inside the particles. I came up with it. When the SiO ₂ in the carrier core material in so as to form the three dimensional network structure, the XRD pattern of the SiO ₂ of the carrier core material, the peak intensity of the quartz crystal of SiO _{2 I} 1, SiO ₂ cristobalite Assuming that the peak intensity of the crystal is I ₂ , the inventors found that the three-dimensional network structure can be strengthened by setting the peak intensity ratio (I ₁ / I ₂ ) to 0.35 or more, thereby completing the present invention. .

That is, the first means for solving the above-described problem is:
And soft ferrite, and SiO _2, a carrier core material for an electrophotographic developer composed of particles comprising,
In the carrier core material for the electrophotographic developer, SiO ₂ forms a three-dimensional network structure,
In the powder XRD pattern of the carrier core material for an electrophotographic developer, when the peak intensity of the SiO ₂ quartz crystal is I ₁ and the peak intensity of the cristobalite crystal of SiO ₂ is I ₂ , the peak intensity ratio (I ₁ / I ₂ ) is a carrier core material for an electrophotographic developer, wherein the carrier core material is 0.35 or more.

The second means is
The carrier core material for electrophotographic developer according to the first means, wherein the content of SiO ₂ in the carrier core material for electrophotographic developer is 15 wt% or less in terms of Si.

The third means is
The soft ferrite is represented by a general formula M _x Fe _3-x O ₄ (where M is one or more metals having a valence of 2 or 0 ≦ x ≦ 1.0). The carrier core material for an electrophotographic developer according to the first or second means.

The fourth means is
The carrier core material for an electrophotographic developer according to the third means, wherein M is one or more metals selected from Fe, Mg, and Mn.

The fifth means is
When the resistivity at an applied voltage of 10 V of the carrier core material for an electrophotographic developer is R ₁ and the resistivity at an applied voltage of 100 V is R ₂ , the resistivity ratio (R ₁ / R ₂ ) is 10 or less. The carrier core material for electrophotographic development according to any one of the first to fourth means.

The sixth means is
The carrier core material for an electrophotographic developer according to any one of the first to fifth means, wherein an average particle diameter is 15 μm or more and 70 μm or less.

The seventh means is
An Fe raw material and an Mn raw material whose components are adjusted so that a soft ferrite having a composition represented by a general formula: Mn _x Fe _3-x O ₄ (where 0 ≦ x ≦ 1.0) is generated, and crystalline silica Mixing to obtain a slurry;
A step of spray-drying the slurry to obtain a granulated product;
Firing the granulated product at 1200 ° C. or more and 1400 ° C. or less to obtain a fired product having a magnetic phase;
The electrophotographic developer according to any one of the first to third means, wherein the obtained fired product is pulverized by pulverization and then given a predetermined particle size distribution. It is a manufacturing method of the carrier core material.

The eighth means is
A magnetic carrier powder for electrophotographic development, wherein the carrier core material for an electrophotographic developer according to any one of the first to sixth means is filled with a resin, or filled and coated with a resin. It is.

The ninth means is
An electrophotographic developer comprising the magnetic carrier powder for an electrophotographic developer according to the eighth means and a toner.

According to the present invention, in the process of synthesizing the carrier core material, the crystal structure of SiO ₂ is structurally changed, and the three-dimensional network structure of SiO ₂ is formed in the soft ferrite constituting the carrier core material. A carrier core material having low voltage dependency and high resistivity could be obtained.

  Hereinafter, matters for specifying the present invention will be described.

[Carrier Core Material According to the Present Invention]
The carrier core material according to the present invention is formed by forming a three-dimensional network structure of SiO _{2 in} soft ferrite.
First, the soft ferrite constituting the carrier core material is preferably one represented by the general formula M _x Fe _3-x O ₄ (where 0 ≦ x ≦ 1.0). At this time, M is preferably one or more selected from divalent metals such as Fe, Mg, Mn, Ca, Ti, Cu, Zn, Sr, and Ni. Here, considering recent environmental problems, M preferably does not contain heavy metals. Therefore, from this point of view, magnetite represented by Fe ₃ O _{4 in} which M is Fe, manganese ferrite represented by Mn _x Fe _3-x O _{4 in} which M is Mn, and Mg _x in which M is Mg. Magnesium ferrite represented by Fe _3-x O ₄ is most preferable.

Next, the three-dimensional network structure of SiO _{2 in} soft ferrite will be described.
The SiO ₂ in the carrier core material according to the present invention forms a three-dimensional network structure. This uses crystalline silica as the SiO ₂ raw material in the carrier core material, and has a firing temperature of 1200 ° C. to 140 ° C.
It is considered that by firing within the range of 0 ° C., the crystal structure of SiO ₂ changes in the soft ferrite constituting the carrier core material, and further, a three-dimensional network structure of SiO ₂ is formed.

Further, the three-dimensional network structure of SiO ₂ contained in the soft ferrite in the carrier core material according to the present invention is a cristobalite crystal or a quartz crystal. Here, the peak intensity of SiO ₂ at 2θ = about 25.6 ° is a peak of a quartz crystal (in this specification, sometimes referred to as peak intensity I ₁ ), and at 2θ = about 31.1 °. The peak intensity of SiO _{2 is} a peak of cristobalite crystal (in this specification, it may be described as peak intensity I ₂ ). At this time, when the peak intensity ratio (I ₁ / I ₂ ) is 0.35 or more in the powder XRD pattern, it was also found that the three-dimensional network structure of the SiO ₂ exhibits strong mechanical strength. . That the peak intensity ratio (I ₁ / I ₂ ) is 0.35 or more is considered to indicate that the structure of SiO ₂ inside the particle is changed by firing.
And since the three-dimensional network structure of the SiO ₂ also has mechanical strength, it has necessary magnetization when the carrier core material becomes magnetic carrier powder, and has high resistance and low voltage dependency. It is considered that a carrier core material having mechanical strength can be obtained.

[Method for Measuring Powder XRD Pattern of Carrier Core Material According to the Present Invention]
A method for measuring a powder XRD pattern of SiO ₂ contained in the carrier core material for an electrophotographic developer will be described.
First, the carrier core material according to the present invention is boiled in hydrochloric acid to dissolve the ferrite phase, the residue is filtered and washed, and then dried, and the SiO ₂ contained in the carrier core material for electrophotographic developer and did. The obtained powder XRD pattern of SiO ₂ was measured using an X-ray diffractometer (Rigaku, RINT2000). Cobalt was used as the X-ray source, and X-rays were generated at an acceleration voltage of 40 kV and a current of 30 mA. Measurement conditions of powder X-ray are scanning mode; FT, divergence slit; 1/2 °, scattering speed; 1/2 °, light receiving slit; 0.15 mm, rotation speed: 5.000 rpm, scanning range; Measurement was performed at .000 °, sampling width: 0.01 °, counting time of 5 seconds, and number of integrations of 3 times. The peak intensity was calculated from the obtained XRD pattern with the peak top as the peak position.

[Particle diameter of carrier core material]
Carrier core material of the present invention is the average value of the particle diameter _{D 50} by laser diffraction particle size distribution analyzer (manufactured by Nikkiso Co., Ltd. Microtrac, Model 9320-X100),
Generally about 15-70 micrometers is preferable and the thing of 25-50 micrometers is more suitable. If it is 15 μm or more, it is preferable that carrier adhesion hardly occurs. Moreover, if it is 70 micrometers or less, a desired image can be obtained and it is preferable.

[Electric resistance]
The carrier core material of the present invention preferably has a ratio (R ₁ / R ₂ ) of resistivity R _{1 at} an applied voltage of 10 V and resistivity R _{2 at} an applied voltage of 100 V of 10 or less. This means that (R ₁ / R ₂ ) is 10 or less, in other words, the voltage dependency of resistivity is low, and charge leakage is less likely to occur. As a result, a stable image can be obtained in electrophotographic development, which is preferable.

The electrical resistance at an applied voltage of 10 V and an applied voltage of 100 V can be obtained as follows. Two brass plates having a thickness of 2 mm and having an electropolished surface as electrodes are placed on an insulating plate (for example, an acrylic plate coated with Teflon (registered trademark)) placed horizontally so that the distance between the electrodes is 2 mm. To place. At this time, the normal direction of the two electrode plates is horizontal. After inserting 200 ± 1 mg of the powder to be measured into the gap between the two electrode plates, a magnet having a cross-sectional area of 240 mm ² is arranged behind each electrode plate to form a bridge of the powder to be measured between the electrodes. . In this state, a DC voltage of 10 V or 100 V is applied between the electrodes, the current value flowing through the powder to be measured is measured by the four-terminal method, and the electric resistance value is calculated. The resistivity of the powder to be measured is calculated from the electrical resistance value, the distance between electrodes of 2 mm, and the cross-sectional area of 240 mm ² (where resistivity = electric resistance value × cross-sectional area / distance between electrodes). Various magnets can be used as long as the powder can form a bridge. In the examples described later, a permanent magnet (ferrite magnet) having a surface magnetic flux density of 1000 gauss or more is used.

  Such a carrier core material of the present invention can be obtained, for example, by the following manufacturing method.

〔material〕
As the Fe supply source, metal Fe, Fe ₃ O ₄ , and Fe ₂ O ₃ can be preferably used. As a raw material of Mn, metal Mn, MnO ₂ , Mn ₂ O ₃ , Mn ₃ O ₄ and MnCO ₃ can be suitably used as a Mn supply source. Then, the mixing ratio of these raw materials is weighed and mixed so as to match the target composition of the soft ferrite. Further, as the SiO ₂ crystalline silica can be suitably used. A predetermined amount of SiO ₂ is weighed and mixed in the blending ratio to obtain a metal raw material mixture.

The raw material of SiO _{2 to be} added is preferably crystalline silica having a maximum peak intensity at 2θ = 30 to 32 ° in the XRD pattern. This is because the crystalline silica is stably present even at high temperatures and does not significantly reduce the magnetization of the carrier core material when dissolved. Amorphous silica, on the other hand, generates a liquid phase of amorphous silica during the firing process, which solidly dissolves and significantly lowers the magnetization of the carrier core material and promotes sintering of the particles to maintain the spherical particle shape. It will be difficult.
In addition, the said crystalline silica can use a commercial item, if the above-mentioned XRD pattern is satisfy | filled. In that case, the crystalline silica preferably has an average particle diameter of about 1 μm (0.5 μm to 4 μm).

[Slurry]
After weighing the above raw materials, they are slurried by mixing and stirring them in a medium solution (slurry process). Prior to slurrying, the raw material mixture may be subjected to a dry pulverization treatment as necessary. The mixing ratio of the raw material powder and the medium liquid is preferably such that the slurry has a solid content concentration of 50 to 90% by mass. The medium liquid is prepared by adding a binder, a dispersant and the like to water. In addition, phosphorus, boric acid, or the like can be added as a lubricant or a sintering accelerator. It is preferable to further wet-grind the slurry obtained by mixing and stirring.

[Granulation]
Granulation can be suitably carried out by introducing the slurry into a spray dryer. Thereby, the granulated powder whose particle diameter is 10-200 micrometers can be obtained in general (granulation process). It is desirable to adjust the particle size of the obtained granulated powder in consideration of the final particle size of the product by removing excessively large particles and fine powder using a vibration sieve or the like.

[Baking]
Next, the granulated powder is put into a furnace heated to 1200 to 1400 ° C. and fired by a general method for synthesizing soft ferrite, thereby generating ferrite (firing step). In firing, firing is performed by controlling the oxygen partial pressure in the furnace. Control of the oxygen partial pressure in the furnace can be achieved by flowing an inert gas such as nitrogen gas or argon gas, or a mixed gas of these inert gas and oxygen into the furnace.

The inventors have repeatedly studied a method for producing a magnetic powder that forms a three-dimensional network structure of SiO ₂ inside the particles in the firing step. As a result, it was found that firing at a temperature within a predetermined range in the firing step is extremely effective.

Here, the optimum firing temperature in the firing step will be described.
The present inventors have conducted studied SiO ₂ states within the crystal structure and particle of SiO _2. As a result, it was found that SiO ₂ inside the particles undergoes a structural transition in the temperature range of 1200 ° C. to 1400 ° C., and SiO ₂ begins to grow. When the temperature is 1200 ° C. or higher, the structural transition of SiO ₂ occurs, and the three-dimensional network structure of SiO ₂ is strengthened inside the particle, so that a desired resistance value can be obtained, which is preferable. A temperature of 1400 ° C. or lower is preferable because sintering of particles due to generation of a liquid phase of SiO ₂ does not occur.

  The obtained fired product is pulverized by a hammer mill, ball mill, etc., and then subjected to sieving to give the intended particle size distribution, thereby providing the magnetic properties for the electrophotographic developer according to the present invention. Obtain a carrier core.

[Manufacture of magnetic carrier powder]
A magnetic carrier for an electrophotographic developer can be obtained by coating the carrier core material for an electrophotographic developer according to the present invention with a silicone-based resin, an acrylic resin, or the like to impart chargeability and improve durability. The method for coating the silicone resin or the like may be performed by a known method.

[Manufacture of electrophotographic developer]
The electrophotographic developer according to the present invention can be obtained by mixing the magnetic carrier for the electrophotographic developer according to the present invention and an appropriate toner.

Example 1
10 kg of Fe ₂ O ₃ , 3.6 kg of Mn ₃ O ₄ , 2.7 kg of SiO ₂ and 5 kg of pure water were dispersed, and 60 g of an ammonium polycarboxylate dispersant was added as a dispersant to obtain a mixture.
As SiO ₂ , crystalline silica having a maximum peak intensity at 2θ = 30 to 32 ° in the XRD pattern was used.
The mixture was pulverized by a wet ball mill to obtain a mixed slurry of Fe ₂ O ₃ , Mn ₃ O ₄ and SiO ₂ . The mixing ratio of the raw materials was calculated so that x = 0.82 in the above-described ferrite composition formula Mn _x Fe _3-x O ₄ .

  The slurry was wet pulverized with a wet ball mill and stirred for a while, and then the slurry was sprayed into hot air with a spray dryer to obtain a dry granulated product having a particle size of 10 μm to 200 μm.

  The granulated product after separating coarse and fine particles from the granulated product using a sieve screen having a mesh size of 61 μm and 25 μm was calcinated at 1200 ° C. in a nitrogen atmosphere for 5 hours to be ferritized. The ferritized fired product is pulverized with a hammer mill, fine powder is removed using an air classifier, the particle size is adjusted with a vibrating screen having a mesh size of 54 μm, and the average particle size is 35 μm for the electrophotographic developer according to Example 1. A magnetic carrier core material was obtained.

In the obtained magnetic carrier core material for an electrophotographic developer according to Example 1, a powder XRD pattern of SiO ₂ phase forming a three-dimensional network structure and its peak intensity ratio (I ₁ / I ₂ ) were measured. did.
As described in the detailed description of the invention, the ferrite phase is boiled and dissolved in hydrochloric acid, the residue is filtered and washed, and then dried to contain SiO ₂ contained in the carrier core material for electrophotographic developer. Obtained. The XRD pattern of the SiO ₂ was measured. The measured values and measured data are shown in Table 1, FIG. 1 (B) (XRD pattern), and FIG. 2 (B) using ▲ and thick solid lines, and a 1000 times SEM photograph of the SiO ₂ phase structure in the carrier core material. Is shown in FIG. 2B and FIGS. 2A and 2C described later are graphs in which the vertical axis represents resistivity and the horizontal axis represents applied voltage.

Example 2
A magnetic carrier core material for an electrophotographic developer according to Example 2 having an average particle size of 35 μm was obtained in the same manner as in Example 1 except that the firing temperature was 1250 ° C. in the firing.
The obtained magnetic carrier core material for an electrophotographic developer according to Example 2 was measured in the same manner as in Example 1, and the measured values and measured data are shown in Table 1, FIG. 1B (XRD pattern), and FIG. 2 (B) is shown using ● and a thick one-dot chain line, and FIG. 3 (H) shows a 1000 times SEM photograph of the SiO ₂ phase structure in the carrier core material.

Example 3
The electrons according to Example 3 having an average particle diameter of 35 μm were obtained in the same manner as in Example 1 except that Fe ₂ O ₃ was changed to 10 kg, Mn ₃ O ₄ was changed to 3.6 kg, and SiO ₂ (crystalline silica) was changed to 5.4 kg. A carrier core material for a photographic developer was obtained.
The obtained magnetic carrier core material for an electrophotographic developer according to Example 3 was measured in the same manner as in Example 1, and the measured values and measured data are shown in Table 1, FIG. 1C (XRD pattern), and FIG. 2 (C) is shown by using a solid line and a solid line, and a 1000 times SEM photograph of the SiO ₂ phase structure in the carrier core material is shown in FIG. 3 (K).

Example 4
A carrier core material for an electrophotographic developer according to Example 4 having an average particle size of 35 μm was obtained in the same manner as in Example 3 except that the firing temperature was 1250 ° C. in the firing.
The obtained magnetic carrier core material for an electrophotographic developer according to Example 4 was measured in the same manner as in Example 1, and the measured values and measured data are shown in Table 1, FIG. 1C (XRD pattern), and In FIG. 2 (C), a black and thick one-dot chain line is used, and a 1000 times SEM photograph of the SiO ₂ phase structure in the carrier core material is shown in FIG. 3 (L).

Example 5
The average particle size was the same as in Example 1 except that 10 kg of Fe ₂ O ₃ , 3.6 kg of Mn ₃ O ₄ and 1.4 kg of SiO ₂ (crystalline silica) were used, and the firing temperature was 1200 ° C. in firing. A carrier core material for an electrophotographic developer according to Example 5 having a diameter of 35 μm was obtained.
The obtained magnetic carrier core material for an electrophotographic developer according to Example 5 was measured in the same manner as in Example 1, and the measured values and measured data are shown in Table 1, FIG. 1 (A) (XRD pattern), and FIG. 2 (A) is shown using ▲ and a thick solid line, and a 1000 times SEM photograph of the SiO ₂ phase structure in the carrier core material is shown in FIG. 3 (C).

Example 6
A carrier core material for an electrophotographic developer according to Example 8 having an average particle size of 35 μm was obtained in the same manner as in Example 5 except that the baking temperature was 1250 ° C. in the baking.
For the obtained magnetic carrier core material for electrophotographic developer according to Example 8, the same measurement as in Example 1 was performed, and the measured values and measurement data were shown in Table 1, FIG. 1A (XRD pattern), FIG. 2 (A) is shown using ● and a thick one-dot chain line, and a 1000 times SEM photograph of the SiO ₂ phase structure in the carrier core material is shown in FIG. 3 (D).

<< Comparative Example 1 >>
The average particle size was 3 in the same manner as in Example 1 except that the firing temperature was 1120 ° C. in the firing.
A carrier core material for an electrophotographic developer according to Comparative Example 1 having a thickness of 5 μm was obtained.
About the obtained magnetic carrier core material for electrophotographic developer according to Comparative Example 1, the same measurement as in Example 1 was performed, and the measurement values and measurement data were shown in Table 1, FIG. 1B (XRD pattern), and FIG. 2B shows the SEM photograph of 1000 times the SiO ₂ phase structure in the carrier core material shown in FIG.

<< Comparative Example 2 >>
A carrier core material for an electrophotographic developer according to Comparative Example 2 having an average particle size of 35 μm was obtained in the same manner as in Example 1 except that the firing temperature was 1150 ° C. in the firing.
For the magnetic carrier core material for electrophotographic developer according to Comparative Example 2 obtained, the same measurement as in Example 1 was performed, and the measured values and measurement data are shown in Table 1, FIG. 1B (XRD pattern), and In FIG. 2 (B), it is shown by using ■ and an elongated broken line, and a 1000 times SEM photograph of the SiO ₂ phase structure in the carrier core material is shown in FIG. 3 (F).

<< Comparative Example 3 >>
A carrier core material for an electrophotographic developer according to Comparative Example 3 having an average particle size of 35 μm was obtained in the same manner as Example 3 except that the firing temperature was 1120 ° C. in the firing.
The obtained magnetic carrier core material for electrophotographic developer according to Comparative Example 3 was measured in the same manner as in Example 1, and the measured values and measured data are shown in Table 1, FIG. 1C (XRD pattern), and FIG. 2 (C) is shown using ◆ and a thin broken line, and an SEM photograph of 1000 times the SiO ₂ phase structure in the carrier core material is shown in FIG. 3 (I).

<< Comparative Example 4 >>
A carrier core material for an electrophotographic developer according to Comparative Example 4 having an average particle size of 35 μm was obtained in the same manner as in Example 3 except that the firing temperature was 1150 ° C. in the firing.
For the magnetic carrier core material for electrophotographic developer according to Comparative Example 4 obtained, the same measurement as in Example 1 was performed, and the measured values and measurement data are shown in Table 1, FIG. 1C (XRD pattern), and In FIG. 2 (C), it is shown by using ■ and an elongated broken line, and a 1000 times SEM photograph of the SiO ₂ phase structure in the carrier core material is shown in FIG. 3 (J).

<< Comparative Example 5 >>
A carrier core material for an electrophotographic developer according to Comparative Example 5 having an average particle size of 35 μm was obtained in the same manner as in Example 5 except that the firing temperature was 1120 ° C. in the firing.
For the magnetic carrier core material for electrophotographic developer according to Comparative Example 5 obtained, the same measurement as in Example 1 was performed, and the measured values and measurement data are shown in Table 1, FIG. 1A (XRD pattern), and FIG. 2 (A) is shown by using ◆ and a thin broken line, and a 1000 times SEM photograph of the SiO ₂ phase structure in the carrier core material is shown in FIG. 3 (A).

<< Comparative Example 6 >>
A carrier core material for an electrophotographic developer according to Comparative Example 6 having an average particle size of 35 μm was obtained in the same manner as in Example 5 except that the firing temperature was 1150 ° C. in the firing.
The obtained magnetic carrier core material for electrophotographic developer according to Comparative Example 6 was measured in the same manner as in Example 1, and the measured values and measured data are shown in Table 1, FIG. 1 (A) (XRD pattern), and FIG. 2 (A) is shown by using ■ and an elongated broken line, and FIG. 3 (B) shows a 1000 times SEM photograph of the SiO ₂ phase structure in the carrier core material.

<< Comparative Example 7 >>
A carrier core material for an electrophotographic developer according to Comparative Example 7 having an average particle size of 35 μm is obtained in the same manner as in Example 1 except that the firing temperature is 1130 ° C. and amorphous silica is used as SiO ₂ in firing. It was.
For the obtained magnetic carrier core material for electrophotographic developer according to Comparative Example 7, the same measurements as in Example 1 were performed, and the measured values and measured data are shown in Table 1, FIG. 1B (XRD pattern), and FIG. 2 (B) shows a SEM photograph 1000 times as large as the SiO ₂ phase structure in the carrier core material.

<< Comparative Example 8 >>
A carrier core material for an electrophotographic developer according to Comparative Example 8 having an average particle size of 35 μm is obtained in the same manner as in Example 1 except that the firing temperature is 1250 ° C. and amorphous silica is used as SiO _2. It was.
About the obtained magnetic carrier core material for electrophotographic developer according to Comparative Example 8, the same measurement as in Example 1 was performed, and the measurement values and measurement data were shown in Table 1, FIG. 1B (XRD pattern), and In FIG. 2 (B), a circle and a thin one-dot chain line are used, and a 1000 times SEM photograph of the SiO ₂ phase structure in the carrier core material is shown in FIG. 4 (N).

(Summary of Examples 1-6 and Comparative Examples 1-8)

As is clear from FIGS. 1A to 1C, the I ₂ peak intensity of the SiO ₂ peak decreases with an increase in the firing temperature, but the I ₁ peak increases. That is, in the ferrite firing process, SiO ₂ is polymorphic (having different crystal structures with the same composition but different crystal forms) in the inside and on the surface of the carrier core material. It turns out that it is changing. Furthermore, (G) Example 1, (H) Example 2, (K) Example 3, (L) Example 4, (C) Example 5, (D) Example 6 which concerns on the Example of FIG. As can be seen from the graph, it can be seen that SiO ₂ grows inside the particles along with the change in the crystal structure, forming a strong three-dimensional network structure. On the other hand, as is clear from FIGS. 2A to 2C, the carrier core materials according to Examples 1 to 6 have low voltage dependency and high resistivity.

In contrast, as is clear from FIGS. 1A to 1C, the carrier core materials according to Comparative Examples 1 to 6 have a peak intensity of I ₂ higher than that of I ₁ . Further, (E) Comparative Example 1, (F) Comparative Example 2, (I) Comparative Example 3, (J) Comparative Example 4, (A) Comparative Example 5, and (B) Comparative Example 6 according to the comparative example of FIG. As can be observed from the above, it is considered that the three-dimensional network structure inside the particle does not exist, or the structure is weak even if it exists. On the other hand, as is clear from FIGS. 2A to 2C, the carrier cores according to Comparative Examples 1 to 6 have high voltage dependency and low resistivity. In Comparative Examples 5 and 6, high voltage is applied. On the side, there was a breakdown (BD).

Furthermore, as is clear from FIG. 1B, the peaks of I ₁ and I ₂ did not exist in Comparative Examples 7 and 8 using amorphous silica as the SiO ₂ raw material. And as can be observed from (M) Comparative Example 7 and (N) Comparative Example 8 according to the comparative example of FIG. 4, there is no SiO ₂ three-dimensional network structure inside the particles, and instead SiO ₂ is partially It can be seen that another phase other than the ferrite phase is formed. On the other hand, as is clear from FIG. 2B, it can be seen that the carrier cores according to Comparative Examples 7 and 8 have a low resistivity although they have low voltage dependency.

From the above, a carrier core material composed of particles containing soft ferrite and SiO ₂ according to an example, and in the carrier core material for an electrophotographic developer, SiO ₂ has a three-dimensional network structure. In the powder XRD pattern of the carrier core material for an electrophotographic developer, the peak intensity when the peak intensity of the SiO ₂ quartz crystal is I ₁ and the peak intensity of the cristobalite crystal of SiO ₂ is I ₂ The carrier core material having a ratio (I ₁ / I ₂ ) of 0.35 or more has low voltage dependency and high resistivity. As a result, the carrier powder produced by filling the carrier core material with resin or filling and coating the resin had a long exchange life while maintaining high quality image characteristics.

(A) Samples according to Examples 5 and 6 and Comparative Examples 5 and 6, (B) Samples according to Examples 1 and 2 and Comparative Examples 1, 2, 7, and 8, (C) Examples 3 and 4 10 is a graph showing an XRD pattern of samples according to Comparative Examples 3 and 4; (A) Samples according to Examples 5 and 6 and Comparative Examples 5 and 6, (B) Samples according to Examples 1 and 2 and Comparative Examples 1, 2, 7, and 8, (C) Examples 3 and 4 5 is a graph showing the resistivity of samples according to Comparative Examples 3 and 4; 1000 × SEM photograph of the SiO ₂ structure of the samples according to examples and comparative examples. 1000 × SEM photograph of the SiO ₂ structure of the sample of the comparative example.

Claims (9)

And soft ferrite, and SiO _2, a carrier core material for an electrophotographic developer composed of particles comprising,
In the carrier core material for the electrophotographic developer, SiO ₂ forms a three-dimensional network structure,
In the powder XRD pattern of the carrier core material for an electrophotographic developer, when the peak intensity of the SiO ₂ quartz crystal is I ₁ and the peak intensity of the cristobalite crystal of SiO ₂ is I ₂ , the peak intensity ratio (I ₁ / I ₂ ) The carrier core material for an electrophotographic developer, wherein the carrier core material is 0.35 or more. 2. The carrier core material for electrophotographic developer according to claim 1, wherein the content of SiO ₂ in the carrier core material for electrophotographic developer is 15 wt% or less in terms of Si. The soft ferrite is represented by a general formula M _x Fe _3-x O ₄ (where M is one or more metals having a valence of 2 or 0 ≦ x ≦ 1.0). The carrier core material for an electrophotographic developer according to claim 1 or 2.   The carrier core material for an electrophotographic developer according to claim 3, wherein the M is one or more metals selected from Fe, Mg, and Mn. When the resistivity at an applied voltage of 10 V of the carrier core material for an electrophotographic developer is R ₁ and the resistivity at an applied voltage of 100 V is R ₂ , the resistivity ratio (R ₁ / R ₂ ) is 10 or less. The carrier core material for electrophotographic development according to any one of claims 1 to 4, wherein the carrier core material is for electrophotographic development.   6. The carrier core material for electrophotographic development according to any one of claims 1 to 5, wherein an average particle diameter is 15 μm or more and 70 μm or less. An Fe raw material and an Mn raw material whose components are adjusted so that a soft ferrite having a composition represented by a general formula: Mn _x Fe _3-x O ₄ (where 0 ≦ x ≦ 1.0) is generated, and crystalline silica Mixing to obtain a slurry;
A step of spray-drying the slurry to obtain a granulated product;
Firing the granulated product at 1200 ° C. or more and 1400 ° C. or less to obtain a fired product having a magnetic phase;
The obtained fired product is pulverized to be powdered, and thereafter has a predetermined particle size distribution. 4. The electrophotographic developer according to claim 1, Manufacturing method of carrier core material.   A magnetic carrier powder for electrophotographic development, wherein the carrier core material for an electrophotographic developer according to any one of claims 1 to 6 is filled with a resin, or filled and coated with a resin.   An electrophotographic developer comprising the magnetic carrier powder for an electrophotographic developer according to claim 8 and a toner.