JP2012141635A - Carrier powder for electrophotographic developer, and electrophotographic developer containing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress deterioration of image characteristics and more particularly carrier scattering increasingly actualized by progress of an electrophotographic developing machine.SOLUTION: An internal pore rate of carrier particles used for electrophotographic developer is lowered and thereby magnetic force per particle is kept high. A start of the magnetic force on a low magnetic field side is raised and thereby holding force of a magnetic brush formed by carrier powder is improved and carrier scattering is suppressed.

Description

  The present invention relates to a carrier powder for an electrophotographic developer used in an electrophotographic developer and an electrophotographic developer containing the carrier powder.

In the field of electrophotographic development, in recent years, higher image quality and full color have been developed. With the increase in image quality and full color, the load on carrier powder used in electrophotographic developers (hereinafter sometimes simply referred to as carrier powder) tends to increase. For this reason, the problem of “carrier scattering”, which is considered to be a result of the increased load on the carrier powder, has become apparent. This carrier scattering is a phenomenon in which image defects such as white streaks occur on electrophotography. The image defect is caused by a decrease in the holding power of carrier particles constituting the carrier powder forming the magnetic brush formed by the carrier powder on the magnetic sleeve in the electrophotographic developing machine, and the carrier powder is applied to the photoreceptor. It is thought to be caused by scattering.
Accordingly, there has been a demand for a carrier powder that can suppress carrier scattering even in electrophotographic development with high image quality and full color.

  For example, in Patent Document 1, 90% or more of pores observed in the cross section of carrier particles constituting carrier powder for electrophotographic developer are formed as pores having an outer diameter of 5 μm or less, and By including at least 80% or more of core material particles having an area ratio (hereinafter sometimes referred to as internal pore ratio) in the range of 3 to 30% with respect to the entire cross section of the particles, the electric resistance depends on the applied voltage. It is described that a carrier powder having a small degree can be obtained.

Japanese Patent No. 2950480

  Patent Document 1 describes that by adjusting the pore ratio of carrier particles, the applied voltage dependence of electric resistance can be adjusted in the carrier powder, and a clear image with high density and no fog can be formed. However, according to the study by the present inventors, under conditions assuming high image quality and full color of electrophotography, for example, an electrophotographic developer using carrier powder described in Patent Document 1 is used. However, there was a problem that carrier scattering occurred.

  In view of the above-described situation, the object of the present invention is to provide carrier powder for an electrophotographic developer that exhibits anti-carrier scattering characteristics even when used in an electrophotographic developing machine that achieves high image quality and full color, a method for producing the same, and the carrier. It is to provide an electrophotographic developer containing powder.

The present inventors have examined the cause of the problem that carrier scattering occurs when the carrier powder according to the prior art is placed under conditions assuming high image quality and full color. As a result of the investigation, in the carrier powder, the rising of magnetic force in a high magnetic field (hereinafter sometimes referred to as σs and σ1k, respectively) such as saturation magnetization and 1 kA / m × 10 ³ / 4π, and further 200 A / m. The inventors have conceived that the rising characteristics of magnetic force in a low magnetic field (hereinafter sometimes referred to as σ200 and σ100, respectively) such as × 10 ³ / 4π and 100 A / m × 10 ³ / 4π are important.

  Here, the present inventors continue further investigation, and in the carrier particles constituting the carrier powder, by reducing the internal pore ratio to a predetermined value or less, σs, σ1k, and further in a low magnetic field such as σ100, σ200 The present inventors have found that the carrier powder has improved magnetic rising characteristics. Furthermore, the present invention was completed by conceiving a manufacturing method capable of manufacturing carrier powder containing carrier particles whose internal pore ratio is reduced to the predetermined value or less with high productivity.

That is, the first means for solving the problem is:
A carrier powder for an electrophotographic developer composed of carrier particles,
The carrier particles are represented by the general formula: MO · Fe ₂ O ₃ (where M is a metal element),
The carrier powder for an electrophotographic developer is characterized in that the number ratio of carrier particles having an internal pore ratio of less than 3% is 70% or more.

The second means is
The carrier powder for an electrophotographic developer according to the first means, wherein the number ratio of carrier particles having an internal pore ratio of 10% or more is 20% or less.

The third means is
The carrier powder for an electrophotographic developer according to the first or second means, wherein the saturation magnetization is 87 Am ² / kg or more.

The fourth means is
The carrier powder for an electrophotographic developer according to any one of the first to third means, wherein the magnetic force at a magnetic field of 200 A / m × 10 ³ / 4π is 18 Am ² / kg or more.

The fifth means is
A method for producing a carrier for an electrophotographic developer according to any one of the first to fourth means,
A slurry of a mixture of a raw material containing M element and Fe ₂ O ₃ is wet pulverized three times or more, then granulated, and the resulting granulated powder is temporarily heated to 800 ° C. to 1000 ° C. in a nitrogen atmosphere. It is a method for producing a carrier powder for an electrophotographic developer, characterized in that it is fired and then heated to 1100 ° C. to 1300 ° C. and fired, and the fired product obtained is pulverized.

The sixth means is
A method for producing a carrier for an electrophotographic developer according to any one of the first to fourth means,
A step of pulverizing a mixture of a raw material containing a predetermined amount of M element and Fe ₂ O ₃ to produce a pulverized product,
Adding water, a binder, and a dispersant to the pulverized product to form a slurry, wet-pulverizing the slurry three times or more, and producing a wet-pulverized slurry;
Producing granulated powder from the wet-pulverized slurry;
The granulated powder is heated to 800 ° C. to 1000 ° C. in a nitrogen atmosphere and calcined to produce a calcined product,
The calcined product is heated to 1100 ° C. to 1300 ° C. and fired to produce a fired product,
And a step of pulverizing the fired product and further removing the non-magnetic component.

The seventh means is
An electrophotographic developer comprising the carrier powder for an electrophotographic developer according to any one of the first to fourth means and a toner.

  Since the carrier powder for an electrophotographic developer according to the present invention has a high magnetic force rise in both high and low magnetic fields, the holding power of the magnetic brush formed with the carrier powder is improved. Even when the developing machine has high image quality and full color, the carrier particles contained in the electrophotographic developer having carrier scattering resistance can be prevented from causing carrier scattering.

It is a SIM image (magnification: 1000 times) of the cut surface of the carrier particles according to the present invention.

FIG. 1 is a cross-sectional SIM (scanning ion) of carrier particles contained in a carrier powder represented by a general formula: MO.Fe ₂ O ₃ (where M is a metal element) according to Example 1 described later. (Microscope) photograph (magnification: 1000 times).
Specifically, the carrier particles according to Example 1 are cut using a focused ion beam sample processing apparatus (FIB: JEM-9310FIB manufactured by JEOL Ltd.), and the carrier particles are considered to have the largest cross-sectional area. Several surfaces were cut, and the surface where the largest cross-sectional area was obtained was taken as the cut surface. FIG. 1 shows a photograph of the cut surface observed with a SIM (hereinafter, the SIM photograph may be referred to as a SIM image). As a result of observation by the SIM, it was confirmed that pores having an outer diameter of 5 μm or less were scattered inside the carrier particles according to the present embodiment.

  Then, commercially available image analysis software (analysisFIVE made by Olympus) was applied to the photograph, and the ratio of the area occupied by pores in the cross-sectional area of the carrier particles was calculated as “internal pore ratio”. 0.69 to 2.1 %Met.

  Here, as a result of manufacturing various carrier powder samples by the present inventors and measuring the internal pore ratio of each sample, the abundance ratio of carrier particles having a predetermined internal pore ratio in each sample and the respective samples And found the relationship with magnetic properties. Furthermore, the present inventors have found a relationship between the abundance ratio and magnetic characteristics of carrier particles having a predetermined internal pore ratio and image characteristics exhibited by an electrophotographic developer sample produced from the carrier powder sample.

Accordingly, when the number ratio of carrier particles having an internal pore ratio of less than 3% is 70% or more and the number ratio of carrier particles having an internal pore ratio of 10% or more is 20% or less, the carrier particles As a result, the saturation magnetization σs is 87.2 to 92.2 Am ² / kg, σ1k is 73.6 to 74.8 Am ² / kg, and σ100 is 0.76 to 1.03 Am ^2. / Kg and σ200 were 18.5 to 20.2 Am ² / kg.

From the above, it has been found that the carrier particles according to the present embodiment have a low internal pore ratio and high values of σs, σ1K, σ100, and σ200. It was also found that when the carrier powder containing the carrier particles is used as an electrophotographic developer, the carrier scattering characteristics are particularly excellent. Specifically, if the carrier powder contains 65% or more of particles having an internal pore ratio of 1% or less, the magnetic properties are σ100 is 0.7 Am ² / kg or more, and σ200 is 17 Am ^2. / Kg or more. Furthermore, even when the particle size of the carrier particles is reduced to 30 μm or less, carrier scattering is suppressed, and even when the electrophotographic developing machine is improved in image quality and full color, it exhibits good image characteristics. Carrier powder could be obtained.

Next, the method for producing carrier powder according to the present invention will be described.
[Weighing and mixing]
The magnetic oxide (preferably soft ferrite) used for the carrier particles contained in the carrier powder according to the present invention is represented by the general formula: MO · Fe ₂ O ₃ . Here, M is a metal such as Fe, Mn, or Mg. The metals such as Fe, Mn, and Mg can be used alone, but a mixed composition is preferable because the controllable range of magnetic properties in the carrier particles is widened.

Here, Fe ₂ O ₃ can be suitably used for Fe. As the raw material of M, it is desirable to use a compound having a higher content (purity) of M element, and it is preferable to use a compound of 70% by mass or more. If Mn, Mn ₃ O ₄ can be preferably used, but not limited to this, MnCO ₃ or the like can be used, and Mg can be preferably used Mg (OH) ₂ , and MgCO ₃ is also preferable. Can be used for
The mixing ratio of these raw materials is matched with the target composition of the magnetic oxide and weighed and mixed to obtain a metal raw material mixture.

[Crushing and granulation]
The mixed metal raw material mixture of M and Fe, which is weighed and mixed, is introduced into a pulverizer such as a vibration mill, and pulverized to a particle size of 2 μm to 0.2 μm, preferably 0.5 μm. Next, water, binder 0.5 to 2 wt%, and dispersant 0.5 to 2 wt% are added to the pulverized product to obtain a slurry having a solid content concentration of 50 to 90 wt%, and the slurry is wet pulverized with a ball mill or the like. To do. Here, polyvinyl alcohol or the like is preferable as the binder, and ammonium polycarboxylate or the like is preferable as the dispersant.
Here, by increasing the number of wet pulverizations, the particle density at the time of granulation is improved, which contributes to the suppression of internal pores at the time of firing. Therefore, the number of times is repeated 3 times or more, preferably about 5 times.

  In the granulation step, the wet-pulverized slurry is introduced into a spray dryer and sprayed into hot air having a temperature of 100 ° C. to 300 ° C. to dry, thereby obtaining granulated powder having a particle size of 10 μm to 200 μm. In the obtained granulated powder, the final particle size of the product is taken into consideration, and coarse particles and fine powders that deviate from the granulated powder are excluded with a vibration sieve to adjust the particle size. Although the detailed reason will be described later, since the final particle size of the product is preferably 20 μm or more and 50 μm or less, the particle size of the granulated powder is preferably adjusted to 10 μm to 100 μm.

[Calcination]
The granulated powder whose particle size has been adjusted is put into a furnace heated to 800 ° C. to 1000 ° C., and calcined in a nitrogen atmosphere for 1 hour to 5 hours, preferably 3 hours to obtain a calcined product. At this time, the amount of pores generated inside the carrier particles can be reduced by calcination in a nitrogen atmosphere.

[Baking]
Next, the calcined product is put into a furnace heated to 1100 ° C. to 1300 ° C. and fired for 3 hours to 30 hours to be ferritized into a fired product. The atmosphere at the time of firing is appropriately selected depending on the type of the metal raw material M. For example, when the metal raw material M is Fe or Fe and Mn (molar ratio 100: 0 to 50:50), a nitrogen atmosphere is required. When the metal raw material M is Fe, Mn, or Mg, a nitrogen atmosphere or an oxygen partial pressure adjustment atmosphere in which the O ₂ partial pressure is adjusted to 1 to 5%, preferably 3% is preferable. On the other hand, when the metal raw material M is a mixture of Fe, Mn, and Mg and the molar ratio of Mg exceeds 30%, the atmosphere may be an air atmosphere.

[Disintegration, classification]
The obtained fired product was coarsely pulverized by hammer mill pulverization or the like, and then the coarsely pulverized product was primarily classified by an air classifier. The primary classified product was further adjusted in particle size using a vibration sieve or an ultrasonic sieve, and then applied to a magnetic field separator to remove non-magnetic components to produce a carrier powder for an electrophotographic developer according to the present invention.
Here, the final particle size of the carrier particles is preferably 10 μm or more and 50 μm or less, more preferably 10 μm or more and 30 μm or less. This is because when the final particle size is 10 μm or more, an electrophotographic developer capable of obtaining high image quality can be manufactured in combination with a toner designed and manufactured for a small particle size. On the other hand, if the final particle size is 50 μm or less, more preferably 30 μm or less, the toner retention ability of the carrier particles is kept high. In addition, since the toner holding ability is kept high, toner scattering is suppressed in an electrophotographic image to be developed, and an excellent image with less fog can be obtained.
As described above, an electrophotographic developer can be produced by mixing the carrier powder and a toner having an appropriate particle size.

Hereinafter, based on an Example, this invention is demonstrated more concretely.
Example 1
Finely pulverized Fe ₂ O ₃ and Mn ₃ O ₄ were prepared as carrier powder materials, and weighed so that the molar ratio was Fe ₂ O ₃ : Mn ₃ O ₄ = 55: 45. At this time, the Mn ₃ O ₄ raw material is prepared with a Mn element content (purity) of 70% by mass or more, and previously adjusted to a number average particle size of 0.6 μm by crushing treatment such as a vibration mill. I used what I had.
On the other hand, 1.5 wt% dispersant (ammonium polycarboxylate dispersant) in water, 0.05 wt% wetting agent (manufactured by San Nopco Co., Ltd., SN wet 980), 0.02 wt% binder (polyvinyl alcohol) What was added was prepared, and Fe ₂ O ₃ and Mn ₃ O ₄ weighed previously were added and stirred therein to obtain a slurry having a concentration of 70 wt%.
The slurry was wet pulverized with a wet ball mill, and the wet pulverization operation was repeated three times. The wet pulverized product was further stirred and then sprayed with a spray dryer to produce a dry granulated product having a particle size of 10 μm to 100 μm.
After separating coarse particles from the dried granulated product using a sieve mesh having a mesh size of 75 μm, the granulated product is calcined for 3 hours by heating to 900 ° C. in a nitrogen atmosphere, and then 1180 ° C., nitrogen atmosphere The product was fired for 5 hours under the condition of being ferritized to obtain a fired product.
This ferritized fired product is crushed with a hammer mill, then fine particles are removed using an air classifier, and the particle size is adjusted with a vibrating screen having a mesh size of 37 μm. A laser diffraction particle size distribution measuring device (Nikkiso Co., Ltd.) A carrier core material according to Example 1 having a number average particle diameter (D50) measured by Microtrak, Model 9320-X100) of 25.4 μm was obtained. (The number average particle diameter (D50) was also measured in the same manner in each of the examples and comparative examples described below.)

  Next, a coating resin solution prepared by dissolving 50% by weight of a silicone resin (trade name: KR251, manufactured by Shin-Etsu Chemical Co., Ltd.) in toluene was prepared. And the carrier core material which concerns on Example 1 and the said resin solution are introduce | transduced into a stirrer in the ratio of core material: resin solution = 9.1: 0.9 by weight ratio, and carrier core material is put into a resin solution. The mixture was heated and stirred at 150 ° C. to 250 ° C. while being immersed for 3 hours. As a result, the carrier core material according to Example 1 was coated with the resin at a ratio of 1.0% by weight with respect to the core material weight. The carrier core material coated with the resin was placed in a hot air circulation type heating device, heated at 250 ° C. for 5 hours, and the resin coat was cured to obtain a carrier powder sample 1.

The results of the internal pore observation of the obtained carrier sample 1 are shown in FIG. Table 1 shows the types of raw materials used, the composition ratio of the raw materials used, the purity and particle size of the M element (Mn) raw material, the number of times the slurry was wet pulverized by a wet ball mill, and the atmosphere during calcination. In the produced carrier powder sample 1, a predetermined internal pore ratio (0 to 0.5%, 0.5 to 1%, 1 to 1.5%, 1.5 to 2%, 2 to 2.5%, Table 2 shows the abundance ratio of carrier particles having 2.5 to 3%, 3 to 5%, 5 to 10%, ˜20%, ˜30%, and ˜50%, and Table 3 shows the magnetic property measurement results. did.
Here, FIG. 1 shows that the ferrite particles according to the carrier powder sample 1 are cut by using a focused ion beam sample processing apparatus, and by cutting some cut surfaces that are considered to be able to obtain the largest cross-sectional area in the carrier particles. FIG. 5 is a photograph (SIM image) (magnification: 1000 times) of the surface where the largest cross-sectional area was obtained as a cut surface, and the cut surface that appeared was observed with a SIM. The commercially available image analysis software described above was applied to the photographic data, and the ratio of the area occupied by pores in the cross-sectional area of the carrier particles was calculated as the “internal pore ratio”, which was 0.69%.
In calculating the internal pore ratio, in order to obtain the average value of the entire carrier powder, the average value per 60 particles of the carrier particles was used as the internal pore ratio of the carrier particles.

Furthermore, the developer powder 1 was manufactured by mixing the carrier powder sample 1 with a commercially available toner having a particle diameter of about 1 μm. A 40-sheet machine employing a predetermined digital reversal development method was used as an evaluator, the initial image of the developer sample 1 was evaluated, and the results are shown in Table 4. Carrier scattering was not observed and good, the spent resistance was good, the image density was appropriate, there was no fog density, fine line reproducibility was good, and the image quality was good.
In the evaluation of Examples 1 to 3 and Comparative Examples 1 to 3 in Table 4, “◎” indicates a very good level, “○” indicates a good level, and “×” indicates a practically unusable level.

(Example 2)
In the carrier powder manufacturing process of Example 1, Fe ₂ O ₃ and Mn ₃ O ₄ molar ratio were weighed and used so as to be Fe ₂ O ₃ : Mn ₃ O ₄ = 60: 40 as a raw material for carrier powder. The carrier core material according to Example 2 having a number average particle diameter D50 of 26.2 μm was obtained under the same conditions as in Example 1, and a carrier powder sample 2 was further obtained.

  As in Example 1, the type of raw material used, the composition ratio of the raw material used, the purity and particle size of the M element (Mn) raw material, the number of times the slurry was wet crushed with a wet ball mill, Table 1 shows the atmosphere during firing, Table 2 shows the abundance ratio of carrier particles having a predetermined internal pore ratio in the produced carrier powder sample 2, and Table 3 shows the magnetic property measurement results.

  Further, a developer sample 2 was produced in the same manner as in Example 1. A 40-sheet machine employing a predetermined digital reversal development system was used as an evaluation machine, and an initial image was evaluated using developer sample 2. The results are shown in Table 4. Carrier scattering, spent resistance, image density, fog density, fine line reproducibility were good, and image quality was good.

(Example 3)
In the carrier powder production process of Example 1, Fe ₂ O ₃ and Mn ₃ O ₄ molar ratio were weighed and used so as to be Fe ₂ O ₃ : Mn ₃ O ₄ = 65: 35 as a carrier powder raw material. The carrier core material according to Example 3 having a number average particle diameter D50 of 26.6 μm was obtained under the same conditions as in Example 1, and a carrier powder sample 3 was further obtained.

  As in Example 1, the type of raw material used, the composition ratio of the raw material used, the purity and particle size of the M element (Mn) raw material, the number of times the slurry was wet crushed with a wet ball mill, Table 1 shows the abundance of carrier particles having a predetermined internal pore ratio in the produced carrier powder sample 3, and Table 3 shows the magnetic property measurement results.

  Further, a developer sample 3 was produced in the same manner as in Example 1. A 40-sheet machine employing a predetermined digital reversal development system was used as an evaluation machine, and the developer sample 3 was used to evaluate an initial image. The results are shown in Table 4. Carrier scattering, spent resistance, image density, fog density, fine line reproducibility were good, and image quality was good.

(Comparative Example 1)
Finely pulverized Fe ₂ O ₃ and Mn ₃ O ₄ were prepared as carrier powder materials, and weighed so that the molar ratio was Fe ₂ O ₃ : Mn ₃ O ₄ = 55: 45. At this time, the Mn ₃ O ₄ raw material was prepared with a Mn element content (purity) of 68% by mass, and was previously adjusted to a number average particle size of 2.5 μm by crushing treatment such as a vibration mill. We used what was.
On the other hand, 1.5 wt% dispersant (ammonium polycarboxylate dispersant) in water, 0.05 wt% wetting agent (manufactured by San Nopco Co., Ltd., SN wet 980), 0.02 wt% binder (polyvinyl alcohol) What was added was prepared, and the weighed Fe ₂ O ₃ and Mn ₃ O ₄ were added and stirred here to obtain a slurry with a concentration of 70 wt%.
The slurry was wet pulverized once with a wet ball mill and further stirred, and then the slurry was sprayed with a spray dryer to produce a dry granulated product having a particle size of 10 μm to 100 μm.
After separating coarse particles from the dried granulated product using a sieve mesh having a mesh size of 75 μm, the granulated product is calcined by heating to 900 ° C. in an air atmosphere, and then at 1180 ° C. in a nitrogen atmosphere. Firing was carried out for 5 hours and ferrite was obtained to obtain a fired product.
The ferritized fired product is crushed 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 37 μm, and the number average particle size D50 is 26.3 μm. The carrier core material which concerns was obtained, and also the carrier powder sample 4 was obtained.

  As in Example 1, the type of raw material used, the composition ratio of the raw material used, the purity and particle size of the M element (Mn) raw material, the number of times the slurry was wet crushed with a wet ball mill, Table 1 shows the abundance ratio of carrier particles having a predetermined internal pore ratio in the produced carrier powder sample 4 and Table 3 shows the magnetic property measurement results.

  Further, a developer sample 4 was produced in the same manner as in Example 1. A 40-sheet machine employing a predetermined digital reversal development system was used as an evaluation machine, and a developer sample 4 was used to evaluate an initial image. The results are shown in Table 4. Spent resistance, image density, fog density, and fine line reproducibility were good, but carrier scattering was practically unusable and image quality was practically unusable.

(Comparative Example 2)
In the carrier powder production process of Example 4, the molar ratio of Fe ₂ O ₃ and Mn ₃ O ₄ as a raw material for the carrier powder was measured so that Fe ₂ O ₃ : Mn ₃ O ₄ = 50: 50. And the sample was manufactured on the same conditions as Example 1 except omitting the temporary baking process of granulated powder, and performing main baking immediately, and the number average particle diameter D50 is a comparative example which is 35.2 micrometers. 2 and a carrier powder sample 5 were obtained.

  As in Example 1, Table 1 shows the types of raw materials used, the composition ratio of the raw materials used, the purity and particle size of the M element (Mn) raw material, and the number of times the slurry was wet crushed by a wet ball mill. Table 2 shows the abundance ratio of carrier particles having a predetermined internal pore ratio in Sample 5, and Table 3 shows the magnetic property measurement results.

  Further, a developer sample 5 was produced in the same manner as in Example 1. A 40-sheet machine employing a predetermined digital reversal development system was used as an evaluation machine, and the developer sample 5 was used to evaluate an initial image. The results are shown in Table 4. Spent resistance and image density were good, but carrier scattering, fog density, and fine line reproducibility were practically unusable levels, and image quality was practically unusable.

(Comparative Example 3)
In the carrier powder production process of Comparative Example 2, the production was carried out under the same conditions as in Comparative Example 2 except that the step of wet pulverizing the raw slurry was omitted, and the number average particle diameter D50 was 36.4 μm. A carrier core material according to Example 3 was obtained, and further a carrier powder sample 6 was obtained.

  As in Example 1, Table 1 shows the types of raw materials used, the composition ratios of the raw materials used, and the purity and particle size of the M element (Mn) raw material. The abundance ratio of the particles is shown in Table 2, and the magnetic property measurement results are shown in Table 3.

  Further, a developer sample 6 was produced in the same manner as in Example 1. A 40-sheet machine employing a predetermined digital reversal development system was used as an evaluation machine, and an initial image was evaluated using a developer sample 6. The results are shown in Table 4. Although the spent resistance was good, carrier scattering, image density, fog density, and fine line reproducibility were practically unusable levels, and image quality was practically unusable.

From the results of Examples 1 to 3 and Comparative Examples 1 to 3, the following was found.
In Samples 1 to 3 manufactured by the manufacturing method according to the present invention, the number ratio of carrier particles having an internal pore ratio of less than 3% is 90% or more, and the number ratio of carrier particles having an internal pore ratio of 10% or more. Was about 2%.
And the saturation magnetization of the samples 1 to 3 was 87.2 Am ² / kg or more. Furthermore, σ200 was 18.5 Am ² / kg or more.
As a result, when developer samples 1 to 3 manufactured by mixing the samples 1 to 3 and toner are used, carrier scattering, spent resistance, image density, fog density, fine line reproduction are obtained in the initial image evaluation results. The image quality was also good.

On the other hand, in the sample 4 of Comparative Example 1 according to the conventional technique, the number ratio of carrier particles having an internal pore ratio of less than 3% was less than 70%.
Therefore, the saturation magnetization of Sample 4 was 83.2 Am ² / kg, and σ200 was 15.4 Am ² / kg, which was lower than those of Examples 1 to 3.
As a result, in the evaluation results of the initial image using the developer sample 4 produced by mixing the sample 4 and the toner, carrier scattering is practically unusable and the image quality is not practically usable. It was the level of.

Further, in Samples 5 and 6 of Comparative Examples 2 and 3 according to the prior art, the number ratio of carrier particles having an internal pore ratio of less than 3% is less than 20%, and the number ratio of carrier particles having an internal pore ratio of 10% or more. Was 20% or more.
As a result, carrier scattering, image density, fog density, and fine line reproducibility are practically used in the initial image evaluation results using the developer samples 5 and 6 produced by mixing the samples 5 and 6 and the toner. It was impossible and the image quality was practically unusable.

Claims (6)

A carrier powder for an electrophotographic developer composed of carrier particles,
The carrier particles are represented by the general formula: MO.Fe ₂ O ₃ (where M is a metal element), the number ratio of carrier particles having an internal pore ratio of less than 3% is 70% or more, and saturation magnetization Is a carrier powder for an electrophotographic developer, wherein the carrier powder is 87 Am ² / kg or more.   The carrier powder for an electrophotographic developer according to claim 1, wherein the number average particle diameter of the carrier particles is 10 µm or more and 50 µm or less.   2. The carrier powder for an electrophotographic developer according to claim 1, wherein the number average particle diameter of the carrier particles is 10 μm or more and 30 μm or less.   4. The carrier powder for an electrophotographic developer according to claim 1, wherein the number ratio of carrier particles having an internal pore ratio of 10% or more is 20% or less. 5. The carrier powder for an electrophotographic developer according to claim 1, wherein the magnetic force at a magnetic field of 200 A / m × 10 ³ / 4π is 18 Am ² / kg or more.   An electrophotographic developer comprising the carrier powder for an electrophotographic developer according to claim 1 and a toner.