JP5541598B2 - Ferrite carrier core material for electrophotographic developer, ferrite carrier for electrophotographic developer, and electrophotographic developer using the ferrite carrier for electrophotographic developer - Google Patents

Description

  The present invention relates to a ferrite carrier core material for an electrophotographic developer, a ferrite carrier for an electrophotographic developer, and a ferrite carrier for the electrophotographic developer used in a two-component electrophotographic developer used in a copying machine, a printer, and the like. The present invention relates to an electrophotographic developer using

  The electrophotographic development method is a method in which toner particles in a developer are attached to an electrostatic latent image formed on a photoreceptor and developed, and the developer used in this method is composed of toner particles and carrier particles. The two-component developer and the one-component developer using only toner particles.

  Among these developers, as a developing method using a two-component developer composed of toner particles and carrier particles, the cascade method has been used in the past, but at present, the magnetic brush method using a magnet roll is the mainstream. It is.

  In the two-component developer, the carrier particles are agitated together with the toner particles in the developing box filled with the developer, thereby imparting a desired charge to the toner particles, and thus being charged. A carrier material for transporting toner particles to the surface of the photoreceptor to form a toner image on the photoreceptor. The carrier particles remaining on the developing roll holding the magnet are returned to the developing box from the developing roll, mixed and stirred with new toner particles, and used repeatedly for a certain period.

  Unlike the one-component developer, the two-component developer has the function of mixing and stirring the carrier particles with the toner particles, charging the toner particles, and further transporting the toner particles. Good controllability. Therefore, the two-component developer is suitable for a full-color developing device that requires high image quality and a device that performs high-speed printing that requires image maintenance reliability and durability.

  In the two-component developer used in this manner, image characteristics such as image density, fog, vitiligo, gradation, and resolving power show predetermined values from the initial stage, and these characteristics are in the printing life period. It needs to be kept stable without fluctuating inside. In order to maintain these characteristics stably, it is necessary that the characteristics of the carrier particles contained in the two-component developer are stable.

  Conventionally, iron powder carriers such as iron powder whose surface is covered with an oxide film or iron powder whose surface is coated with a resin have been used as carrier particles for forming a two-component developer. Since such an iron powder carrier has high magnetization and high conductivity, there is an advantage that an image with a good reproducibility of the solid portion can be easily obtained.

  However, such an iron powder carrier has a heavy true specific gravity of about 7.8 and is too high in magnetization, so that the toner constituent components on the surface of the iron powder carrier are mixed by stirring and mixing with toner particles in the developing box. Fusing, so-called toner spent, is likely to occur. The generation of such toner spent reduces the effective carrier surface area and tends to reduce the triboelectric charging ability with the toner particles.

  Moreover, in the resin-coated iron powder carrier, the resin on the surface peels off due to stress during durability, and the core material (iron powder) with high conductivity and low dielectric breakdown voltage is exposed, which may cause charge leakage. . Due to such charge leakage, the electrostatic latent image formed on the photoconductor is destroyed, and a crack or the like is generated in the solid portion, so that it is difficult to obtain a uniform image. For these reasons, iron powder carriers such as oxide-coated iron powder and resin-coated iron powder are no longer used.

  In recent years, instead of iron powder carriers, ferrite with a true specific gravity of about 5.0, which is light and has a low magnetization, or a resin-coated ferrite carrier whose surface is coated with a resin has been widely used. Lifespan has increased dramatically.

  As a method for producing such a ferrite carrier, a predetermined amount of ferrite carrier raw material is mixed, calcined, pulverized, and then fired after granulation. Depending on conditions, calcining may be omitted. is there.

  Recently, environmental regulations have become stricter, and the use of metals such as Ni, Cu, and Zn has been avoided, and the use of metals suitable for environmental regulations has been demanded, and it is used as a carrier core material. The ferrite composition has shifted from Cu-Zn ferrite, Ni-Zn ferrite to manganese ferrite using Mn, Mn-Mg-Sr ferrite, and the like.

  Patent Document 1 (Japanese Patent Laid-Open No. 8-22150) describes a ferrite carrier in which a part of manganese-magnesium ferrite is replaced with SrO. By reducing the variation in magnetization between particles by using this ferrite carrier, it is said that when used as a developer together with toner, it has excellent image quality and durability, is friendly to the environment, has a long life, and is excellent in environmental stability. However, the ferrite carrier described in Patent Document 1 cannot achieve both a uniform surface property with moderate unevenness and high charge imparting ability. If the firing temperature is increased, the surface property becomes smoother and more uneven, which not only increases the resistance and charge distribution after coating the resin, but also reduces the strength against agitation stress. . When the firing temperature is lowered, the surface is apparently wrinkled and uniform, but the BET specific surface area increases, resulting in low chargeability and large environmental differences.

  Patent Document 2 (Japanese Patent Laid-Open No. 2000-233930) discloses a carrier core composition that contains a certain amount of manganese oxide and iron (III) and contains a specific amount of titanium dioxide, and substantially forms a spinel phase material. Things are disclosed. This carrier core composition is said to be environmentally safe and harmless.

  However, since the carrier core composition described in Patent Document 2 is manganese ferrite, its resistance is low, and there is a concern about deterioration of image quality such as occurrence of fogging and deterioration of gradation.

  As an alternative to a carrier core material using Mn, a carrier core material using Mg has been proposed. For example, Patent Document 3 (Japanese Patent Application Laid-Open No. 2010-39368) describes a carrier core material containing magnesium, titanium, and iron at a certain ratio and having a BET specific surface area in a specific range. With this carrier core material, a desired resistance such as a medium resistance or a high resistance is obtained while being highly magnetized, and it has excellent charging characteristics, and has a uniform shape with a surface property having appropriate irregularities.

  Since the carrier core material described in Patent Document 3 has a low content of manganese and titanium, it basically exhibits the characteristics of magnetite and lowers the magnetization on the low magnetic field side. Is concerned about the occurrence of carrier adhesion.

  Further, Patent Document 4 (Japanese Patent Laid-Open No. 2008-96977) discloses a carrier in which the surface of the core particle is coated with a ferrite containing at least magnesium element, and the number of deformed core particles is five. %, The grain diameter of the surface is 2 to 5 μm. In Patent Document 4, by using such core particles, sufficient chargeability is imparted to the toner, and stable chargeability without causing image contamination such as fogging due to toner scattering due to insufficient charging. It is supposed to have.

  However, although the core particles have a good shape and surface property, there is no description regarding the amount of moisture adsorbed, and the environment dependency of the carrier is improved only by the resin coating. Therefore, even in the actual use, the environmental dependency immediately after the start of use of the carrier is good, but as the usage time becomes longer, the coated resin is peeled off, and the surface of the core particles is exposed to gradually lose the environmental dependency. Therefore, it is considered inadequate from the viewpoint of improving environmental dependency.

  On the other hand, Patent Document 5 (Japanese Patent Application Laid-Open No. 2001-343790) describes a carrier in which a moisture adsorption amount and a surface area under a certain condition have a specific relationship. Such a carrier is said to be able to obtain good image quality over a long period of time because the charging property of the toner is stabilized without being influenced by the environment.

  The carrier used in Patent Document 5 is a magnetic material dispersion type carrier, and the composition of the carrier core material is not specified at all. Simply specifying the moisture adsorption amount and surface area of the carrier cannot provide appropriate resistance and magnetization, and good chargeability cannot be obtained.

  Patent Document 6 (Japanese Patent Application Laid-Open No. 2004-94035) describes a two-component developer that specifies the moisture adsorption amount of toner particles and the moisture adsorption amount of carrier particles and obtains the correlation between them. In addition, it is mentioned as an effect that the environmental dependency of the charge amount is small.

  Since Patent Document 6 only defines the moisture adsorption amount of the toner particles and the moisture adsorption amount of the carrier particles, it cannot have an appropriate resistance and magnetization as described above, nor can it obtain good chargeability. .

  In view of these conventional technologies, there is a demand for a ferrite carrier for an electronic developer that has appropriate resistance and magnetization, is excellent in chargeability, and can maintain high charge particularly under high temperature and high humidity, and has good environmental dependency. It was.

JP-A-8-22150 JP 2000-233930 A JP 2010-39368 A JP 2008-96977 A JP 2001-343790 A JP 2004-94035 A

  Accordingly, an object of the present invention is to provide a ferrite carrier core material for an electronic developer, which has an appropriate resistance and magnetization, is excellent in chargeability, and can maintain high charge particularly under high temperature and high humidity, and has good environmental dependency. An object is to provide a ferrite carrier for an electrophotographic developer and an electrophotographic image agent using the ferrite carrier for an electrophotographic developer.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that ferrite containing a certain amount of Mn, Mg, Ti and Fe and having a moisture adsorption amount at a relative pressure of 0.9 is not more than a certain amount. The present inventors have found that a carrier core material and a ferrite carrier coated with a resin on the carrier core material can achieve the above object, and have reached the present invention.

That is, the present invention contains 11 to 21% by weight of Mn, 0.9 to 3.5% by weight of Mg, 0.5 to 2% by weight of Ti, 48 to 60% by weight of Fe, and water vapor. In the isothermal adsorption measurement, the moisture adsorption amount at a relative pressure of 0.9 is 0.08 mg / g or less, the average value of the shape factor SF-2 is 104 to 110, and 0.5K · 1000 / 4π · A / m. The present invention provides a ferrite carrier core material for an electrophotographic developer, which has a magnetization of 35 to 50 Am ² / kg measured by VSM when a magnetic field is applied.

  The ferrite carrier core material for an electrophotographic developer according to the present invention has an absolute value of 0.01 mg / g or less of the difference in water adsorption amount between adsorption and desorption at a relative pressure of 0.7 in the measurement of water vapor isothermal adsorption. It is desirable.

  In the ferrite carrier core material for an electrophotographic developer according to the present invention, the content of ferrite particles having a shape factor SF-2 larger than 130 is 4% by number or less, and the ferrite particles having a shape factor SF-2 larger than 120 is contained. The amount is desirably 8% by number or less.

  The ferrite carrier core material for an electrophotographic developer according to the present invention preferably contains 0.1 to 1.0% of Sr.

  The ferrite carrier core material for an electrophotographic developer according to the present invention preferably has an oxide coating on the surface.

The ferrite carrier core material for an electrophotographic developer according to the present invention has a resistance of 5 × 10 ^{7 to} 5 × 10 ⁹ Ω at a voltage of 2 mm Gap applied at 50 V and a resistance at 1000 V of 5 × in a normal temperature and normal humidity (N / N) environment. 10 ⁶ ~1 × 10 ⁹ Ω, and high temperature and high humidity (H / H) environment, it is desirable resistance in 2mmGap applied voltage 50V is ^{1 × 10 7 ~1 × 10 9} Ω.

  The present invention provides a ferrite carrier for an electrophotographic developer in which the surface of the ferrite carrier core material for an electrophotographic developer is coated with a resin.

  The present invention provides an electrophotographic developer comprising the above ferrite carrier for an electrophotographic developer and a toner.

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

  The ferrite carrier core material for an electrophotographic developer according to the present invention has an appropriate resistance and magnetization, is excellent in chargeability, has a small moisture adsorption amount, and easily desorbs even when moisture is adsorbed. Since high charge under high temperature and high humidity can be maintained, environmental dependency is good. An electrophotographic developer comprising a ferrite carrier and a toner obtained by coating a resin on the ferrite carrier core material has a high charge amount and is excellent in charging stability in each environment.

Hereinafter, modes for carrying out the present invention will be described.
<Ferrite carrier core material for electrophotographic developer and ferrite carrier for electrophotographic developer according to the present invention>
The carrier core material for an electrophotographic developer according to the present invention has Mn of 11 to 21% by weight, preferably 13 to 21% by weight, more preferably 15 to 21% by weight, and Mg of 0.9 to 3.5% by weight. , Preferably 0.9 to 3 wt%, more preferably 0.9 to 2.5 wt%, Ti 0.5 to 2 wt%, preferably 0.5 to 1.8 wt%, more preferably 0 0.5 to 1.6% by weight, 48 to 60% by weight of Fe, preferably 48 to 58% by weight, more preferably 48 to 55% by weight. The balance is O and an accompanying impurity. The accompanying impurity is contained in the raw material or mixed in the manufacturing process, and the total amount is 0.5% by weight or less. The ferrite carrier core material having the above composition range is highly charged, particularly excellent in charging stability under high temperature and high humidity, and has good environmental dependency.

By containing Mn, the magnetization on the low magnetic field side can be increased, and an effect of preventing reoxidation at the time of exit from the furnace in the main firing can be expected. Is not particularly limited form of Mn is at the time of _{addition, MnO 2, Mn 2 O 3} , Mn 3 O 4, MnCO 3 are preferred since easily available in industrial applications. If the Mn content is less than 11% by weight, the magnetite component increases, the magnetization on the low magnetic field side is lowered and carrier adhesion occurs, and the resistance is also low, so fogging and deterioration of gradation are caused. , Image quality deteriorates. If it exceeds 21% by weight, the resistance becomes so high that the edge becomes too effective, image defects such as white spots may occur, and toner consumption may increase.

  By containing Mg, it is possible to obtain a developer having a good rise in charge, which is composed of a ferrite carrier and a full-color toner. Also, the resistance can be increased. When the Mg content is less than 0.9% by weight, a sufficient addition effect cannot be obtained, and when the Mn content is relatively low and the Fe content is high, the resistance becomes low and fogging occurs. And the image quality deteriorates, such as deterioration of gradation. When the content of Mn is relatively high and the content of Fe is low, the magnetization becomes too high, and the ears of the magnetic brush become hard, causing image defects such as scissors. On the other hand, when the Mg content exceeds 3.5% by weight, not only carrier scattering occurs due to a decrease in magnetization, but when the firing temperature is low, the amount of moisture adsorbed is affected by the hydroxyl group caused by Mg. It becomes large and causes the environmental dependence of electrical characteristics such as charge amount and resistance to deteriorate.

  Ti has the effect of lowering the firing temperature and not only can reduce aggregated particles, but also can obtain a uniform and wrinkled surface property despite the small value of the BET specific surface area. When the Ti content is less than 0.5% by weight, the Ti content effect cannot be obtained, the BET specific surface area becomes high, and sufficient chargeability cannot be obtained. Further, if the Ti content exceeds 2% by weight, the rise of magnetization worsens, causing not only carrier scattering but also Ti not taken into the ferrite precipitates on the surface of the core particles, A decrease in the charge amount of the core particles and an increase in the moisture adsorption amount cause deterioration of the environmental dependence of the electrical characteristics such as the charge amount and resistance.

  When the content of Fe is less than 48% by weight, when the content of Mg and / or Ti is relatively increased, it means that the nonmagnetic component and / or the low magnetization component increases, and the desired magnetic property Characteristics are not obtained. When the content of Mn is relatively increased, the magnetization becomes too high, so the ears of the magnetic brush become stiff, causing image defects such as scissors, and the edges are increased due to increased resistance. It may be too effective, causing image defects such as white spots and excessive toner consumption. If the Fe content exceeds 60% by weight, the Mg and / or Ti content effect cannot be obtained and the ferrite carrier core material is substantially equivalent to magnetite.

  The carrier core material for an electrophotographic developer according to the present invention preferably contains 0.1 to 1.0% by weight of Sr. Sr contributes to the adjustment of resistance and surface properties, and not only has the effect of maintaining high magnetization during surface oxidation, but also contains the effect of increasing the charging ability of the core material when contained. When Sr is less than 0.1% by weight, the effect of containing Sr cannot be obtained, and the decrease in magnetization tends to increase. Furthermore, since the effect of moving Sr to the surface of the core material particles cannot be obtained at the time of debuying and main firing, the effect of increasing the resistance and the charge amount of the core material cannot be expected. In particular, when printing is continuously performed at a high printing rate such as a photograph, there is a possibility that a decrease in charge occurs, causing problems such as toner scattering and an increase in toner consumption. When the Sr content exceeds 1.0% by weight, the residual magnetization and coercive force increase, and when used as a developer, image defects such as scissors occur and image quality deteriorates.

(Contents of Fe, Mn, Mg, Ti and Sr)
The contents of these Fe, Mn, Mg, Ti and Sr are measured by the following.
0.2 g of ferrite carrier core material is weighed, 60 ml of pure water added with 20 ml of 1N hydrochloric acid and 20 ml of 1N nitric acid is heated to prepare an aqueous solution in which the ferrite carrier core material is completely dissolved, and an ICP analyzer ( The content of Fe, Mn, Mg, Ti and Sr was measured using Shimadzu ICPS-1000IV).

  The carrier core material for an electrophotographic developer according to the present invention has a water adsorption amount of 0.08 mg / g or less at a relative pressure of 0.9 in water vapor isothermal adsorption measurement.

  If the water adsorption amount at a relative pressure of 0.9 is 0.08 mg / g or less in the water vapor isotherm adsorption measurement, the influence of moisture adsorbed on the core material on the charging can be minimized. On the other hand, when the amount of moisture adsorbed at a relative pressure of 0.9 is larger than 0.08 mg / g, the charge easily escapes through the adsorbed moisture even when Ti is contained. There is a possibility that sufficient charging characteristics cannot be obtained.

This water vapor isothermal adsorption measurement is measured as follows.
The moisture adsorption amount is measured by using an “automatic vapor adsorption amount measuring apparatus Belsorb 18” (manufactured by Nippon Bell Co., Ltd.), changing the relative pressure until the relative pressure exceeds 0.1 to 0.9, and thereafter The relative pressure was continuously changed until the pressure was less than 0.5, and the adsorbed gas H ₂ O was adsorbed and desorbed, and the moisture adsorption amount was measured. Before the measurement, the measurement sample tube was baked for 2 hours in a reduced pressure state at 50 ° C., and then the measurement sample tube was filled with a sample of 10 g of core material particles. The pretreatment for 2 hours was performed in the reduced pressure state. The value of the moisture adsorption amount at each relative pressure was read by plotting the relative pressure and the moisture adsorption amount and taking the value when crossing each relative pressure.

  Further, in the water vapor isothermal adsorption measurement, it is preferable that the difference between the moisture adsorption amount at the time of adsorption and desorption at a relative pressure of 0.7 is 0.01 mg / g or less in absolute value.

  In the isothermal adsorption measurement of water vapor, if the difference in water adsorption amount between adsorption and desorption at a relative pressure of 0.7 is 0.01 mg / g or less in absolute value, it means that the adsorbed water is easily desorbed. When used as a carrier, it becomes easy to obtain a developer with small environmental fluctuations. On the other hand, when the difference between the amount of water adsorption at the time of adsorption and desorption at a relative pressure of 0.7 exceeds 0.01 mg / g in absolute value, it means that the moisture once adsorbed is difficult to desorb, Once exposed to an environment with high humidity, not only does the charge characteristics deteriorate due to adsorption of moisture, but it also maintains that the charging characteristics remain deteriorated even when the environment returns to a low humidity environment. Show.

  In the water vapor isothermal adsorption measurement, the amount of moisture adsorption at the time of adsorption and desorption at a relative pressure of 0.7 is measured by the same method as the amount of moisture adsorption at the above relative pressure of 0.9.

  The carrier core material for an electrophotographic developer according to the present invention has an average value of the shape factor SF-2 of 104 to 110. Further, it is preferable that the content of ferrite particles having SF-2 larger than 130 is 4% by number or less and the content of ferrite particles having SF-2 larger than 120 is 8% by number or less.

  If the average value of the shape factor SF-2 is 104 to 110, it means that moderate irregularities are formed on the surface of the core material, and the resin anchor effect is obtained when the surface is coated with resin. Cheap. When the average value of SF-2 is smaller than 104, the unevenness of the surface is extremely reduced. Therefore, when the resin is coated and used as a carrier, the resin is easily peeled off, and the developer characteristics change greatly with time. Probability is high. In addition, when the average value of SF-2 is larger than 110, the surface unevenness is too large, and the resin is excessively impregnated when resin coating is performed. Resistance characteristics may not be obtained with a good balance.

  When the ferrite particles having SF-2 larger than 130 are contained in an amount of more than 4% by number, it means that particles having a relatively small particle size contain many aggregated particles. When such a core material is coated with a resin and used as a carrier, the agglomerated particles are divided into small-sized particles with many core material parts exposed by agitation stress in the developing device, which causes drum scratches. In addition, since the electrical resistance decreases with an increase in the portion not coated with resin, it causes white spots and carrier scattering.

  In addition, when the ferrite particles having SF-2 larger than 120 are contained in an amount of more than 8% by number, in addition to the above, the core material contains many particles with large surface roughness, The growth of the constituent grains is not uniform in the main firing, which means that the grains that have grown abnormally and those that have not grown so much are mixed. When such a core material is coated with a resin, the exposed portion of the core material is large, and the electric resistance is lowered even with the same resin coating amount. Therefore, when used as a carrier, white spots and carrier scattering are caused.

(Shape factor SF-2 (roundness))
The shape factor SF-2 is a value obtained by dividing the value obtained by squaring the carrier projection perimeter length by the value obtained by dividing the value by the carrier projection area by 4π, and multiplying it by 100. The shape of the carrier is close to a sphere. The value becomes closer to 100. This shape factor SF-2 (roundness) is measured by the following.

3000 core particles were observed using a particle size / shape distribution measuring instrument PITA-1 manufactured by Seishin Enterprise Co., Ltd., and S (projected area) and L (projected perimeter) were obtained using software Image Analysis included with the apparatus. This is a value calculated from the equation. The closer the carrier shape is to a spherical shape, the closer to 100.
The sample liquid was prepared by preparing a xanthan gum aqueous solution having a viscosity of 0.5 Pa · s as a dispersion medium, in which 0.1 g of core material particles were dispersed in 30 cc of the xanthan gum aqueous solution. Thus, by appropriately giving the viscosity of the dispersion medium, the core particles can be kept dispersed in the dispersion medium, and the measurement can be performed smoothly. Furthermore, the measurement conditions are (objective) lens magnification of 10 times, filter is ND4 × 2, carrier liquid 1 and carrier liquid 2 are xanthan gum aqueous solutions having a viscosity of 0.5 Pa · s, and the flow rate is 10 μl / sec. The sample liquid flow rate was 0.08 μl / sec.

The ferrite carrier core material for an electrophotographic developer according to the present invention has a magnetization of 35 to 50 Am ² / kg measured by VSM when a magnetic field of 0.5 K · 1000 / 4π · A / m is applied. When the magnetization at 0.5 K · 1000 / 4π · A / m is less than 35 Am ² / g, the scattered matter magnetization is deteriorated, which causes image defects due to carrier adhesion. On the other hand, the composition range of the present invention does not exceed 50 Am ² / g. This magnetic property (magnetization) is measured as follows.

(Magnetic properties)
A vibrating sample type magnetometer (model: VSM-C7-10A (manufactured by Toei Kogyo Co., Ltd.)) was used. The measurement sample was packed in a cell having an inner diameter of 5 mm and a height of 2 mm and set in the apparatus. The measurement was performed by applying an applied magnetic field and sweeping to 5 KOe. Next, the applied magnetic field was decreased to prepare a hysteresis curve on the recording paper. The magnetization at an applied magnetic field of 0.5 KOe was read from the data of this curve.

The ferrite carrier core material for an electrophotographic developer according to the present invention has a resistance of 5 × 10 ^{7 to} 5 × 10 ⁹ Ω at a voltage of 2 mmGap applied at 50 V and a resistance at 1000 V of 5 × in a normal temperature and normal humidity (N / N) environment. 10 ⁶ ~1 × 10 ⁹ Ω, and high temperature and high humidity (H / H) environment, it is desirable that the resistance in 2mmGap applied voltage 50V is ^{1 × 10 7 ~1 × 10 9} Ω.

Here, the conditions under each environment are as follows.
Normal temperature and humidity (N / N) environment = temperature 20-25 ° C, relative humidity 50-60%
High temperature and high humidity (H / H) environment = temperature 30-35 ° C, relative humidity 80-85%
The low temperature and low humidity (L / L) environment is a temperature of 10 to 15 ° C. and a relative humidity of 10 to 15%.

In a N / N environment, when the resistance at 2 mm Gap applied voltage 50V is smaller than 5 × 10 ^{7, the} resistance is too low, and when used as a carrier, white spots may occur or carriers may be scattered. When it is higher than 5 × 10 ⁹ Ω, an image with an excessively effective edge may be obtained when used as a carrier.

When the resistance at 2 mm Gap applied voltage 1000V is smaller than 5 × 10 ⁶ under N / N environment, the resistance is too low and white spots may occur or carriers may be scattered when used as a carrier. If it is higher than 1 × 10 ⁹ Ω, the charge cannot be released appropriately when used as a carrier, which causes charge-up.

Further, when the resistance at a 2 mm Gap applied voltage of 50 V is smaller than 1 × 10 ⁷ in an H / H environment, it may cause carrier scattering due to low resistance. In addition, when it is larger than 1 × 10 ⁹ Ω, the toner consumption is reduced due to a synergistic effect that the edge of the obtained image easily stands and the charge amount of the carrier is likely to decrease relatively in the H / H environment. There is a possibility of increasing. This electrical resistance is measured by:

(Electrical resistance)
A non-magnetic parallel plate electrode (10 mm × 40 mm) is made to oppose with a distance between electrodes of 2.0 mm, and 200 mg of a sample is weighed and filled between them. A sample is held between electrodes by attaching a magnet (surface magnetic flux density: 1500 Gauss, area of magnet in contact with electrode: 10 mm × 30 mm) to parallel plate electrodes, a voltage of 50 V or 1000 V is applied, and an applied voltage of 50 V or 1000 V is applied. The resistance was measured with an insulation resistance meter (SM-8210, manufactured by Toa Decay Co., Ltd.).

  The carrier core material for an electrophotographic developer according to the present invention preferably has an average particle size measured by a laser diffraction particle size distribution measuring device of 15 to 120 μm, more preferably 15 to 80 μm, and most preferably 15 to 60 μm. . If the volume average particle size is less than 15 μm, carrier adhesion tends to occur, which is not preferable. If the volume average particle diameter exceeds 120 μm, the image quality tends to deteriorate, which is not preferable. This volume average particle size is measured by:

(Volume average particle size)
As a device, a Nikkiso Co., Ltd. Microtrac particle size analyzer (Model 9320-X100) was used. Water was used as the dispersion medium.

  The surface of the carrier core material for an electrophotographic developer according to the present invention is desirably oxidized. The thickness of the oxidized film formed by this surface oxidation treatment is preferably 0.1 nm to 5 μm. If the thickness of the coating is less than 0.1 nm, the effect of the oxide coating layer is small, and if the thickness of the coating exceeds 5 μm, the magnetization is obviously lowered or the resistance becomes too high, so the developing ability is lowered. Inconveniences such as being likely to occur. Moreover, you may reduce | restore before an oxidation process as needed. The thickness of the oxide film may be measured directly from a high-magnification SEM photograph that can confirm that an oxide film is formed, or by X-ray photoelectron spectroscopy (XPS). And / or from the change in peak and / or integral intensity associated with a change in valence to tetravalence. The presence / absence of the oxidation treatment film can also be indirectly known from the change in resistance before and after the surface oxidation treatment. The oxide film may be formed uniformly on the surface of the core material, or the oxide film may be partially formed. The surface oxidation treatment temperature is preferably 450 ° C to 600 ° C. When the temperature is lower than 450 ° C., the oxidation of the core particle surface does not proceed sufficiently, so that desired resistance characteristics may not be obtained. A temperature higher than 600 ° C. is not preferable because oxidation of Mn proceeds excessively and the crystallinity of the spinel structure is deteriorated, so that the resistance of the core material is lowered.

  In the carrier for an electrophotographic developer according to the present invention, the surface of the carrier core material is coated with a resin. The number of times of resin coating may be only once, or two or more times of resin coating may be performed, and the number of times of coating can be determined according to desired characteristics. Further, the composition of the coating resin, the coating amount, and the apparatus used for resin coating may be changed or may not be changed when the number of times of coating is two times or more.

  The resin-coated carrier for an electrophotographic developer according to the present invention desirably has a total resin coating amount of 0.1 to 10% by weight with respect to the carrier core material. When the total coating amount is less than 0.1% by weight, it is difficult to form a uniform coating layer on the carrier surface. When the total coating amount exceeds 10% by weight, the carriers are aggregated, resulting in a decrease in productivity such as a decrease in yield. At the same time, it may cause fluctuations in developer characteristics such as fluidity or charge amount in the actual machine.

  The film-forming resin used here can be appropriately selected depending on the toner to be combined, the environment in which it is used, and the like. The type is not particularly limited, for example, fluorine resin, acrylic resin, epoxy resin, polyamide resin, polyamideimide resin, polyester resin, unsaturated polyester resin, urea resin, melamine resin, alkyd resin, phenol resin, fluorine acrylic resin, Examples thereof include acrylic-styrene resins, silicone resins, or modified silicone resins modified with resins such as acrylic resins, polyester resins, epoxy resins, polyamide resins, polyamideimide resins, alkyd resins, urethane resins, and fluororesins. In the present invention, acrylic resin, silicone resin or modified silicone resin is most preferably used.

  In addition, a conductive agent can be contained in the film forming resin for the purpose of controlling the electric resistance, charge amount, and charging speed of the carrier. Since the conductive agent has a low electric resistance, if the content is too large, it is likely to cause a rapid charge leak. Accordingly, the content is 0.25 to 20.0% by weight, preferably 0.5 to 15.0% by weight, particularly preferably 1.0 to 10.0% by weight, based on the solid content of the film-forming resin. %. Examples of the conductive agent include conductive carbon, oxides such as titanium oxide and tin oxide, and various organic conductive agents.

  In addition, the film forming resin can contain a charge control agent. Examples of the charge control agent include various charge control agents generally used for toners and various silane coupling agents. This is because, when the core material exposed area is controlled to be relatively small by film formation, the charge imparting ability may decrease, but it can be controlled by adding various charge control agents and silane coupling agents. It is. The types of charge control agents and coupling agents that can be used are not particularly limited, but charge control agents such as nigrosine dyes, quaternary ammonium salts, organometallic complexes, and metal-containing monoazo dyes, aminosilane coupling agents, and fluorine-based silane couplings. An agent or the like is preferable.

<Carrier Core Material for Electrophotographic Developer According to the Present Invention and Carrier Manufacturing Method>
Next, the carrier core material for an electrophotographic developer and the method for producing the carrier according to the present invention will be described.

  The method for producing a carrier core material for an electrophotographic developer according to the present invention comprises Fe, Mn, Mg, and Ti, and if necessary, pulverizing, mixing, and pre-baking each compound of Sr, and then again pulverizing, mixing, The granulated product obtained by granulation is subjected to primary firing and main firing, and further pulverized, classified, and subjected to surface oxidation treatment as necessary.

There is no particular limitation on the method of preparing a granulated product by pulverizing, mixing, and calcining each compound of Fe, Mn, Mg, and Ti, as necessary, and then pulverizing, mixing, and granulating again. A conventionally known method can be employed, and either a dry method or a wet method may be used. For example, Fe ₂ O ₃ , TiO ₂ , Mg (OH) ₂ and / or MgCO ₃ , SrCO ₃ and Mn ₃ O ₄ are mixed as raw materials and pre-baked in the atmosphere. After calcination, the obtained calcined product is further pulverized with a ball mill or a vibration mill, etc., then added with water and, if necessary, a dispersant, a binder, etc., adjusted for viscosity, granulated with a spray dryer, and granulated. I do. When pulverizing after calcination, water may be added and pulverized by a wet ball mill, a wet vibration mill or the like. In addition, it is preferable to use polyvinyl alcohol or polyvinylpyrrolidone as a binder. If desired characteristics can be obtained, this temporary firing is not necessarily performed.

  In the production method of the present invention, the obtained granulated product is subjected to primary firing after primary firing. Here, the primary baking is performed at 600 to 1000 ° C., and the main baking is performed in an inert atmosphere or a weakly oxidizing atmosphere, for example, a nitrogen atmosphere or a mixed gas atmosphere of nitrogen and oxygen having an oxygen concentration of 3% by volume or less, It is carried out at 1100-1220 ° C.

  Thereafter, the fired product is crushed and classified to obtain a carrier core material (ferrite particles). As a classification method, the particle size is adjusted to a desired particle size using an existing air classification, mesh filtration method, sedimentation method, or the like. When dry collection is performed, it can also be collected with a cyclone or the like.

  Thereafter, if necessary, the surface can be heated at a low temperature to perform an oxide film treatment to adjust electric resistance. For the oxide film treatment, a general rotary electric furnace, batch electric furnace or the like is used, and for example, heat treatment is performed at 600 ° C. or lower. In order to uniformly form the oxide film on the core particles, it is preferable to use a rotary electric furnace.

  Although the method for controlling the moisture adsorption amount of the ferrite carrier core material is arbitrary, for example, the firing temperature is adjusted within a range in which the surface property of the desired core material can be obtained, or the amount of Ti added can be controlled by controlling the amount of addition of Ti. Examples thereof include a method of controlling the degree of generation of surface irregularities or a combination of these methods.

  The ferrite carrier for an electrophotographic developer of the present invention coats the above resin on the surface of the ferrite carrier core material to form a resin film. As a coating method, it can be coated by a known method such as a brush coating method, a spray drying method using a fluidized bed, a rotary drying method, an immersion drying method using a universal stirrer, or the like. In order to improve the coverage, a fluidized bed method is preferred.

  When the resin is coated on the ferrite carrier core and then baked, either an external heating method or an internal heating method may be used, for example, a fixed or fluid electric furnace, a rotary electric furnace, a burner furnace, or a microwave oven Baking by may be used. When a UV curable resin is used, a UV heater is used. Although the baking temperature varies depending on the resin to be used, a temperature equal to or higher than the melting point or the glass transition point is necessary. For a thermosetting resin or a condensation-crosslinking resin, it is necessary to raise the temperature to a point where the curing proceeds sufficiently.

<Electrophotographic developer according to the present invention>
Next, the electrophotographic developer according to the present invention will be described.
The electrophotographic developer according to the present invention comprises the above-described ferrite carrier for electrophotographic developer and toner.

  The toner particles constituting the electrophotographic developer of the present invention include pulverized toner particles produced by a pulverization method and polymerized toner particles produced by a polymerization method. In the present invention, toner particles obtained by any method can be used.

  The pulverized toner particles are, for example, a binder resin, a charge control agent, and a colorant are sufficiently mixed with a mixer such as a Henschel mixer, then melt-kneaded with a twin screw extruder or the like, cooled, pulverized, classified, After adding the external additive, it can be obtained by mixing with a mixer or the like.

  The binder resin constituting the pulverized toner particles is not particularly limited, but polystyrene, chloropolystyrene, styrene-chlorostyrene copolymer, styrene-acrylic acid ester copolymer, styrene-methacrylic acid copolymer, Furthermore, rosin modified maleic acid resin, epoxy resin, polyester resin, polyurethane resin and the like can be mentioned. These may be used alone or in combination.

  Any charge control agent can be used. For example, nigrosine dyes and quaternary ammonium salts can be used for positively charged toners, and metal-containing monoazo dyes can be used for negatively charged toners.

  As the colorant (coloring material), conventionally known dyes and pigments can be used. For example, carbon black, phthalocyanine blue, permanent red, chrome yellow, phthalocyanine green, etc. can be used. In addition, external additives such as silica powder and titania for improving the fluidity and aggregation resistance of the toner can be added according to the toner particles.

  The polymerized toner particles are toner particles produced by a known method such as a suspension polymerization method, an emulsion polymerization method, an emulsion aggregation method, an ester elongation polymerization method, or a phase inversion emulsification method. Such polymerized toner particles are prepared by, for example, mixing and stirring a colored dispersion in which a colorant is dispersed in water using a surfactant, a polymerizable monomer, a surfactant, and a polymerization initiator in an aqueous medium. Then, the polymerizable monomer is emulsified and dispersed in an aqueous medium, polymerized while stirring and mixing, and then a salting-out agent is added to salt out the polymer particles. Polymerized toner particles can be obtained by filtering, washing and drying the particles obtained by salting out. Thereafter, if necessary, an external additive may be added to the dried toner particles to provide a function.

  Further, in the production of the polymerized toner particles, in addition to the polymerizable monomer, the surfactant, the polymerization initiator, and the colorant, a fixability improving agent and a charge control agent can be blended and obtained. Various characteristics of the polymerized toner particles can be controlled and improved. A chain transfer agent can be used to improve the dispersibility of the polymerizable monomer in the aqueous medium and adjust the molecular weight of the resulting polymer.

  The polymerizable monomer used for the production of the polymerized toner particles is not particularly limited. For example, styrene and its derivatives, ethylene unsaturated monoolefins such as ethylene and propylene, vinyl halides such as vinyl chloride, Α-methylene aliphatic monocarboxylic acids such as vinyl esters such as vinyl acetate, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, 2-ethylhexyl methacrylate, dimethylamino acrylate and diethylaminoester methacrylate Examples include esters.

  Conventionally known dyes and pigments can be used as the colorant (coloring material) used in the preparation of the polymerized toner particles. For example, carbon black, phthalocyanine blue, permanent red, chrome yellow, phthalocyanine green, and the like can be used. Moreover, the surface of these colorants may be modified using a silane coupling agent, a titanium coupling agent, or the like.

  As the surfactant used in the production of the polymerized toner particles, an anionic surfactant, a cationic surfactant, an amphoteric surfactant and a nonionic surfactant can be used.

  Here, examples of the anionic surfactant include fatty acid salts such as sodium oleate and castor oil, alkyl sulfates such as sodium lauryl sulfate and ammonium lauryl sulfate, alkyl benzene sulfonates such as sodium dodecyl benzene sulfonate, and alkyl naphthalene sulfonic acids. Salt, alkyl phosphate ester salt, naphthalene sulfonic acid formalin condensate, polyoxyethylene alkyl sulfate ester salt and the like. Examples of the nonionic surfactant include polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene alkylamine, glycerin, fatty acid ester, and oxyethylene-oxypropylene block polymer. . Furthermore, examples of the cationic surfactant include alkylamine salts such as laurylamine acetate, and quaternary ammonium salts such as lauryltrimethylammonium chloride and stearyltrimethylammonium chloride. Examples of amphoteric surfactants include aminocarboxylates and alkylamino acids.

  The surfactant as described above can be used usually in an amount in the range of 0.01 to 10% by weight with respect to the polymerizable monomer. Such a surfactant affects the dispersion stability of the monomer and also affects the environmental dependency of the obtained polymerized toner particles. Use in an amount within the above range is preferable from the viewpoint of ensuring the dispersion stability of the monomer and reducing the environmental dependency of the polymerized toner particles.

  For the production of polymerized toner particles, a polymerization initiator is usually used. The polymerization initiator includes a water-soluble polymerization initiator and an oil-soluble polymerization initiator, and any of them can be used in the present invention. Examples of the water-soluble polymerization initiator that can be used in the present invention include persulfates such as potassium persulfate and ammonium persulfate, water-soluble peroxide compounds, and oil-soluble polymerization initiators. Examples thereof include azo compounds such as azobisisobutyronitrile and oil-soluble peroxide compounds.

  When a chain transfer agent is used in the present invention, examples of the chain transfer agent include mercaptans such as octyl mercaptan, dodecyl mercaptan, tert-dodecyl mercaptan, carbon tetrabromide, and the like.

  Further, when the polymerized toner particles used in the present invention contain a fixability improver, a natural wax such as carnauba wax, an olefin wax such as polypropylene or polyethylene can be used as the fixability improver. .

  Further, when the polymerized toner particles used in the present invention contain a charge control agent, the charge control agent to be used is not particularly limited, and nigrosine dyes, quaternary ammonium salts, organometallic complexes, metal-containing monoazo dyes, etc. Can be used.

  Examples of the external additive used for improving the fluidity of polymerized toner particles include silica, titanium oxide, barium titanate, fluororesin fine particles, and acrylic resin fine particles. Can be used in combination.

  Furthermore, examples of the salting-out agent used for separating the polymer particles from the aqueous medium include metal salts such as magnesium sulfate, aluminum sulfate, barium chloride, magnesium chloride, calcium chloride, and sodium chloride.

  The volume average particle size of the toner particles produced as described above is in the range of 2 to 15 μm, preferably 3 to 10 μm, and the polymerized toner particles have higher particle uniformity than the pulverized toner particles. . If the toner particles are smaller than 2 μm, the charging ability is lowered, and it is easy to cause fogging and toner scattering, and if it exceeds 15 μm, the image quality is deteriorated.

  An electrophotographic developer can be obtained by mixing the carrier and toner manufactured as described above. The mixing ratio of the carrier and the toner, that is, the toner concentration is preferably set to 3 to 15% by weight. If it is less than 3% by weight, it is difficult to obtain a desired image density. If it exceeds 15% by weight, toner scattering and fogging are likely to occur.

  The electrophotographic developer according to the present invention can also be used as a replenishment developer. At this time, the mixing ratio of the carrier and the toner, that is, the toner concentration is preferably set to 100 to 3000% by weight.

  The electrophotographic developer according to the present invention prepared as described above uses an electrostatic latent image formed on a latent image holding member having an organic photoconductor layer, while applying a bias electric field to the toner and the carrier. The present invention can be used in digital copiers, printers, fax machines, printers, and the like that use a developing method in which reversal development is performed using a two-component developer magnetic brush. Further, the present invention can also be applied to a full color machine using an alternating electric field, which is a method of superimposing an AC bias on a DC bias when a developing bias is applied from the magnetic brush to the electrostatic latent image side.

  Hereinafter, the present invention will be specifically described based on examples and the like.

Fe ₂ O ₃ , Mg (OH) ₂ , TiO ₂ , Mn ₃ O ₄ and SrCO ₃ were adjusted so that Fe was 104 mol, Mn was 39 mol, Mg was 9 mol, Sr was 1 mol and Ti was 3 mol. Weighed and pelletized with a roller compactor. The obtained pellet was calcined at 1000 ° C. in a rotary calciner.

This is coarsely pulverized with a dry bead mill, then pulverized with a wet bead mill for 6 hours, and PVA is added as a binder component so as to be 3.2% by weight based on the solid content of the slurry, and the polycarboxylic acid dispersant is slurried. Was added so that the viscosity of the mixture became 2 to 3 poise. At this time, D ₅₀ of the slurry particle diameter was 1.92 μm.

  The pulverized slurry thus obtained is granulated and dried with a spray dryer, and primary-fired at 1000 ° C. using a rotary under atmospheric conditions, and an oxygen concentration of 0.5% by volume using an electric furnace. The main baking was performed by maintaining the temperature at 1170 ° C. for 4 hours under the above conditions. Thereafter, it was crushed and further classified to obtain a carrier core material composed of ferrite particles.

  Further, the obtained carrier core material composed of ferrite particles is subjected to a surface oxidation treatment in a rotary electric furnace under a surface oxidation treatment temperature of 500 ° C. in an air atmosphere to obtain a surface oxidation-treated carrier core material (ferrite particles). It was.

  A carrier core material (ferrite particles) was obtained in the same manner as in Example 1 except that the primary firing temperature was 850 ° C.

  A carrier core material (ferrite particles) was obtained in the same manner as in Example 1 except that the oxygen concentration during the main firing was 0.05% by volume.

  A carrier core material (ferrite particles) was obtained in the same manner as in Example 1 except that the oxygen concentration during the main firing was 1% by volume.

  A carrier core material (ferrite particles) was obtained in the same manner as in Example 1 except that the main firing temperature was 1205 ° C.

  A carrier core material (ferrite particles) was obtained in the same manner as in Example 1 except that the main firing temperature was 1130 ° C.

  A carrier core material (ferrite particles) was obtained in the same manner as in Example 1 except that the surface oxidation treatment temperature was 470 ° C.

  A carrier core material (ferrite particles) was obtained in the same manner as in Example 1 except that the surface oxidation treatment temperature was 570 ° C.

Fe ₂ O ₃ , Mg (OH) ₂ , TiO ₂ , Mn so that the addition amount of Fe is 139 mol, the addition amount of Mn is 27 mol, the addition amount of Mg is 5 mol, and the addition amount of Ti is 3 mol. _A carrier core material (ferrite particles) was obtained in the same manner as in Example 1 except that ₃ O ₄ was added and SrCO ₃ was not added.

Fe ₂ O ₃ , Mg (so that the addition amount of Fe is 121 mol, the addition amount of Mn is 46 mol, the addition amount of Mg is 14 mol, the addition amount of Sr is 1 mol, and the addition amount of Ti is 5 mol. A carrier core material (ferrite particles) was obtained in the same manner as in Example 1 except that OH) ₂ , TiO ₂ , Mn ₃ O ₄ , and SrCO ₃ were added.

Fe ₂ O so that the addition amount of Fe is 104 mol, the addition amount of Mn is 46 mol, the addition amount of Mg is 5 mol, the addition amount of Sr is 0.5 mol, and the addition amount of Ti is 2.5 mol. ₃ , Mg (OH) ₂ , TiO ₂ , Mn ₃ O ₄ and SrCO ₃ were added to obtain a carrier core material (ferrite particles) in the same manner as in Example 1.

Fe ₂ O so that the addition amount of Fe is 104 mol, the addition amount of Mn is 34 mol, the addition amount of Mg is 14 mol, the addition amount of Sr is 0.5 mol, and the addition amount of Ti is 2.5 mol. ₃ , Mg (OH) ₂ , TiO ₂ , Mn ₃ O ₄ and SrCO ₃ were added to obtain a carrier core material (ferrite particles) in the same manner as in Example 1.

A carrier core material (ferrite particles) was obtained in the same manner as in Example 1 except that TiO ₂ was added so that the amount of Ti added was 1.25 mol.

A carrier core material (ferrite particles) was obtained in the same manner as in Example 1 except that TiO ₂ was added so that the amount of Ti added was 3.75 mol.

  A carrier core material (ferrite particles) was obtained in the same manner as in Example 1 except that the oxygen concentration during the main firing was 0.001% by volume.

Comparative example

[Comparative Example 1]
Fe ₂ O ₃ , Mg (OH) ₂ , TiO ₂ and SrCO so that the added amount of Fe is 104 mol, the added amount of Mg is 48 mol, the added amount of Sr is 1 mol, and the added amount of Ti is 3 mol. _A carrier core material (ferrite particles) was obtained in the same manner as in Example 1 except that ₃ was added and Mn ₃ O ₄ was not added.

[Comparative Example 2]
Fe ₂ O so that the addition amount of Fe is 104 mol, the addition amount of Mn is 48 mol, the addition amount of Mg is 5 mol, the addition amount of Sr is 0.5 mol, and the addition amount of Ti is 2.5 mol. ₃ , Mg (OH) ₂ , TiO ₂ , Mn ₃ O ₄ and SrCO ₃ were added to obtain a carrier core material (ferrite particles) in the same manner as in Example 1.

[Comparative Example 3]
Fe ₂ O ₃ , Mg (OH) ₂ , TiO ₂ , and so that the added amount of Fe is 145 mol, the added amount of Mn is 20 mol, the added amount of Mg is 4 mol, and the added amount of Ti is 3 mol. A carrier core material (ferrite particles) was obtained in the same manner as in Example 1 except that Mn ₃ O ₄ was added and SrCO ₃ was not added.

[Comparative Example 4]
Fe ₂ O ₃ , Mn ₃ O ₄ , SrCO ₃ , TiO ₂ so that the addition amount of Fe is 104 mol, the addition amount of Mn is 48 mol, the addition amount of Sr is 1 mol, and the addition amount of Ti is 3 mol. A carrier core material (ferrite particles) was obtained in the same manner as in Example 1 except that Mg (OH) ₂ was not added.

[Comparative Example 5]
Fe ₂ O so that the addition amount of Fe is 104 mol, the addition amount of Mn is 30 mol, the addition amount of Mg is 18 mol, the addition amount of Sr is 0.5 mol, and the addition amount of Ti is 2.5 mol. ₃ , Mg (OH) ₂ , TiO ₂ , Mn ₃ O ₄ and SrCO ₃ were added to obtain a carrier core material (ferrite particles) in the same manner as in Example 1.

[Comparative Example 6]
A carrier core material (ferrite particles) was obtained in the same manner as in Example 1 except that TiO ₂ was added so that the amount of Ti added was 5 mol.

[Comparative Example 7]
A carrier core material (ferrite particles) was obtained in the same manner as in Example 1 except that TiO ₂ was not added.

[Comparative Example 8]
A carrier core material (ferrite particles) was obtained in the same manner as in Example 1 except that the main firing temperature was 1270 ° C.

[Comparative Example 9]
A carrier core material (ferrite particles) was obtained in the same manner as in Example 1 except that the main firing temperature was 1050 ° C.

  Mixing ratio (number of moles of raw materials charged) of Examples 1 to 15 and Comparative Examples 1 to 9, provisional firing conditions (temperature and atmosphere), slurry particle size at the time of main granulation, primary firing conditions (temperature and atmosphere), main firing The conditions (temperature and atmosphere) are shown in Table 1. Table 2 shows the chemical compositions of the carrier core materials obtained in Examples 1 to 15 and Comparative Examples 1 to 9.

  Furthermore, the moisture adsorption amount (relative pressures 0.9 and 0.7), magnetization and powder characteristics (average particle size, SF-2 and SF−) before the surface oxidation treatment of Examples 1 to 15 and Comparative Examples 1 to 9 The number distribution of 2) is shown in Table 3. Further, surface oxidation treatment conditions (temperature and atmosphere) of Examples 1 to 15 and Comparative Examples 1 to 9, moisture adsorption amount after surface oxidation treatment (relative pressures 0.9 and 0.7), magnetization and resistance (N / N environment and H / H environment) are shown in Table 4. Further, Table 5 shows the charge amount (under L / L environment, N / N environment, and H / H environment). Here, the measurement method of the charge amount shown in Table 5 is as follows. In Tables 2 to 5, other measurement methods are as described above.

(Charge amount)
A sample (carrier or carrier core material) and a commercially available negative-polarity toner used in full-color printers having an average particle diameter of about 6 μm and a toner concentration of 6.5% by weight (toner weight = 3.25 g, carrier) Weight = 46.75 g). The weighed carrier and toner were exposed to each environment described later for 12 hours or more. Thereafter, the carrier and the toner were put into a 50 cc glass bottle and stirred for 30 minutes at a rotation speed of 100 rpm.
As a charge quantity measuring device, magnets with a total of 8 poles (flux density 0.1T) are arranged alternately in the N and S poles inside a cylindrical aluminum tube (hereinafter referred to as a sleeve) having a diameter of 31 mm and a length of 76 mm. The magnet roll, the sleeve, and a cylindrical electrode having a gap of 5.0 mm were disposed on the outer periphery of the sleeve.
After 0.5 g of developer is uniformly deposited on the sleeve, a DC voltage of 2000 V is applied between the outer electrode and the sleeve while rotating the inner magnet roll at 100 rpm while fixing the outer aluminum tube. Was applied for 60 seconds to transfer the toner to the outer electrode. At this time, an electrometer (insulation resistance meter model 6517A manufactured by KEITHLEY) was connected to the cylindrical electrode, and the charge amount of the transferred toner was measured.
After 60 seconds, the applied voltage was turned off and the rotation of the magnet roll was stopped. Then, the outer electrode was removed, and the weight of the toner transferred to the electrode was measured.
The charge amount was calculated from the measured charge amount and the transferred toner weight.

  Each environment includes a low temperature and low humidity (L / L) environment, a normal temperature and normal humidity (N / N) environment, and a high temperature and high humidity (H / H) environment, and the temperature and humidity conditions are as described above.

  As is clear from the results of Tables 3 to 4, the ferrite carrier core materials of Examples 1 to 15 have the desired resistance and magnetization, have a small amount of moisture adsorption, and easily desorb moisture, so that the chargeability is high. And a developer excellent in durability and the like can be obtained.

  On the other hand, the ferrite carrier core material of Comparative Example 1 does not have the desired magnetization because Mn is not added, but also has a large amount of moisture adsorption due to excessive Mg content, and resistance depends on the environment. The result was inferior. In the ferrite carrier core material of Comparative Example 2, the magnetization was high because the amount of Mn added was too large. Therefore, when used as a carrier, not only was there concern about the occurrence of image defects such as streak, but the surface irregularities of the core particles were too large to be used as a carrier core. . Furthermore, the core material resistance after the surface oxidation treatment is high, and it is difficult to adjust the resistance as a carrier.

  In Comparative Example 3, the contents of Mn and Mg are small, and as a result, the content of Fe is relatively large. Therefore, sufficient magnetization cannot be obtained by calcination and primary firing, and it cannot be used as a core material for a carrier. there were. Furthermore, the charge amount under each environment was also low. Since Comparative Example 4 did not add Mg, the magnetization was high as in Comparative Example 2, and not only the occurrence of image defects such as streak was a concern when used as a carrier. Since the surface irregularities of the particles were too large, they could not be used as a carrier core material. Furthermore, the charge amount under each environment was also low.

  In Comparative Example 5, since the amount of Mg added is too large, the magnetization becomes low, and the charge amount in each environment is also low. In Comparative Example 6, since the amount of Ti added was too large, the magnetization was low. Since Comparative Example 7 did not add Ti, the amount of moisture adsorption was large, the difference between the amount of adsorption and the amount of desorption was a core material that was easily affected by moisture, the resistance was highly dependent on the environment, and each The charge amount under the environment was also low. In Comparative Example 8, since the main firing temperature was too high, not only the surface irregularities of the core material particles were large, but also the number of core material particles having SF-2 of 120 or more and core material particles of 130 or more were large. It was. For this reason, when this core material particle is coated with a resin and used as a carrier, the resin coating is performed while containing aggregated particles, so that a small particle size in which a large amount of the core material portion is exposed due to agitation stress in the developing device. As a result, the carrier core material was likely to be divided into particles, and good image characteristics could not be obtained.

  In Comparative Example 9, since the firing temperature was low and the surface irregularities were too large, the amount of moisture adsorption was large, and the environmental dependency of the charge amount of the core material was large.

  Carrier core material particles having an average particle size of 44.39 μm were prepared in the same manner as in Example 6, and a universal mixing stirrer using Shin-Etsu Silicone's acrylic-modified silicone resin KR-9706 and Lion Ketjen Black EC600JD as coating resins It applied by. At this time, the resin solution is weighed so that the resin solid content is 1% by weight with respect to the carrier core material, and 7.5% by weight of Ketjen Black EC600JD is added to the resin solid content. A solvent in which toluene and MEK were mixed at a weight ratio of 3: 1 so as to be 20% by weight was added, and pre-dispersed for 3 minutes with an IKA homogenizer T65D ULTRA-TURRAX, and then dispersed for 5 minutes in a vertical bead mill. What was processed was used as a resin solution. After the resin was applied, it was dried with stirring for 3 hours with a heat exchange type stirring and heating apparatus set at 200 ° C. in order to completely eliminate volatile matter. Then, after crushing the aggregated particles, acrylic modified silicone resin KR-9706 manufactured by Shin-Etsu Silicone Co., Ltd. was applied again using a fluidized bed coating apparatus. At this time, the resin solution is weighed so that the solid content of the resin with respect to the carrier core material is 0.5% by weight, and toluene and MEK are used in a weight ratio of 3 so that the solid content of the resin is 10% by weight as a solvent. A solvent mixed with 1 was added. After applying the resin, in order to completely eliminate the volatile matter, the resin-coated carrier was obtained by drying with stirring in a heat exchange type stirring and heating apparatus set at 200 ° C. for 3 hours.

  Carrier core particles having an average particle size of 36.91 μm were prepared in the same manner as in Example 6. Silicone resin KR-350 manufactured by Shin-Etsu Silicone Co., Ltd., aluminum catalyst CAT-AC manufactured by Toray Dow Corning Co., Ltd. Chain Black EC600JD was applied as a coating resin by a universal mixing stirrer. At this time, the resin solution is weighed so that the resin solid content with respect to the carrier core is 2% by weight, the aluminum catalyst CAT-AC is 2% by weight, and the ketjen black EC600JD is 10% with respect to the resin solid content. Each wt% was added. Further, toluene was added so that the solid content of the resin would be 20% by weight, and after pre-dispersing for 3 minutes with a homogenizer T65D ULTRA-TURRAX made by IKA, the resin solution was subjected to dispersion treatment for 5 minutes in a vertical bead mill. Used as. After applying the resin, it was dried for 3 hours with a hot air dryer set at 250 ° C. in order to completely eliminate the volatile matter. Thereafter, after the aggregated particles are crushed, again the silicone resin KR-350 manufactured by Shin-Etsu Silicone, the aluminum catalyst CAT-AC manufactured by Toray Dow Corning, and the aminosilane coupling agent KBM-603 manufactured by Shin-Etsu Silicone are used by a fluidized bed coating apparatus. Applied. At this time, the resin solution was weighed so that the resin solid content with respect to the carrier core was 1% by weight, the aluminum catalyst CAT-AC was 2% by weight, and the aminosilane coupling agent KBM- A solution obtained by adding 603 to 10% by weight and toluene as a solvent so as to be 10% by weight based on the solid content of the resin was used. After applying the resin, in order to completely eliminate the volatile matter, the resin-coated carrier was obtained by drying with a hot air dryer set at 250 ° C. for 3 hours.

  Carrier core material particles having an average particle size of 26.43 μm were prepared in the same manner as in Example 6, and coated with acrylic resin Dianal BR-80 manufactured by Mitsubishi Rayon Co., Ltd. as a coating resin using a universal mixing stirrer. At this time, a resin solution was used in which the resin was weighed so that the solid content of the resin with respect to the carrier core was 1.5 wt%, and toluene was added so that the solid content of the resin would be 10 wt%. Since the resin is a powder, the resin solution was bathed in water so that the temperature was 50 ° C., and the resin powder was completely dissolved. After applying the resin, in order to completely eliminate the volatile matter, the resin-coated carrier was obtained by drying with stirring in a heat exchange type stirring and heating apparatus set at 145 ° C. for 3 hours.

  For Examples 16 to 18, Table 6 shows the charge amount measurement results after resin coating. The method for measuring the charge amount is as described above.

  As is apparent from the results in Table 6, in Examples 16 to 18 in which the ferrite carrier core material according to the present invention was coated with various resins, a ferrite carrier for electrophotographic developer having sufficient charging characteristics was obtained.

  The ferrite carrier core material for an electrophotographic developer according to the present invention has an appropriate resistance and magnetization, is excellent in chargeability, has a small moisture adsorption amount, and easily desorbs even when moisture is adsorbed. Since high charge under high temperature and high humidity can be maintained, environmental dependency is good. An electrophotographic developer comprising a ferrite carrier and a toner obtained by coating a resin on the ferrite carrier core material has a high charge amount and is excellent in charging stability in each environment.

  Therefore, the present invention can be widely used in the field of full-color machines that particularly require high image quality and high-speed machines that require image maintenance reliability and durability.

Claims (9)

Containing 11 to 21% by weight of Mn, 0.9 to 3.5% by weight of Mg, 0.5 to 2% by weight of Ti and 48 to 60% by weight of Fe, and relative pressure in water vapor isothermal adsorption measurement When the moisture adsorption amount at 0.9 is 0.08 mg / g or less, the average value of the shape factor SF-2 is 104 to 110, and a magnetic field of 0.5 K · 1000 / 4π · A / m is applied. A ferrite carrier core material for an electrophotographic developer, which has a magnetization of 35 to 50 Am ² / kg as measured by VSM measurement.   2. The ferrite carrier core material for an electrophotographic developer according to claim 1, wherein a difference in water adsorption amount between adsorption and desorption at a relative pressure of 0.7 is 0.01 mg / g or less in absolute value in water vapor isothermal adsorption measurement. .   The content of ferrite particles having a shape factor SF-2 greater than 130 is 4% by number or less, and the content of ferrite particles having a shape factor SF-2 greater than 120 is 8% by number or less. A ferrite carrier core material for an electrophotographic developer described in 1.   The ferrite carrier core material for an electrophotographic developer according to any one of claims 1 to 3, comprising 0.1 to 1.0% by weight of Sr.   The ferrite carrier core material for an electrophotographic developer according to any one of claims 1 to 4, wherein an oxide coating is formed on the surface. In a normal temperature and normal humidity (N / N) environment, the resistance at 2V Gap applied voltage 50V is 5 × 10 ^{7 to} 5 × 10 ⁹ Ω, the resistance at 1000V is 5 × 10 ⁶ to 1 × 10 ⁹ Ω, and high temperature and high humidity (H 6. The ferrite carrier core material for an electrophotographic developer according to claim 5, wherein the resistance at an applied voltage of 2 mm Gap at 50 V is 1 × 10 ⁷ to 1 × 10 ⁹ Ω under an / H) environment.   A ferrite carrier for an electrophotographic developer, wherein the surface of the ferrite carrier core material according to any one of claims 1 to 6 is coated with a resin.   An electrophotographic developer comprising the ferrite carrier for an electrophotographic developer according to claim 7 and a toner.   The electrophotographic developer according to claim 8, which is used as a replenishment developer.