JP6742119B2 - Core material for carrier, carrier, developer and electrophotographic development system - Google Patents

Description

The present invention relates to a carrier core material, a carrier, a developer containing the carrier, and an electrophotographic development system using the developer.

The electrophotographic developing method is a method in which toner particles in a developer are adhered to an electrostatic latent image formed on a photoconductor to develop, and the developer used in this method is composed of toner particles and carrier particles. And a one-component developer using only toner particles.

Of these developers, the cascade method and the like have been used for a long time as a developing method using a two-component developer composed of toner particles and carrier particles, but nowadays, a magnetic brush method using a magnet roll is mainstream. Is. In the two-component developer, the carrier particles are stirred together with the toner particles in the developing box filled with the developer, thereby imparting a desired charge to the toner particles, and the carrier particles are further charged in this manner. It is a carrier material for transporting toner particles to the surface of the photoconductor to form a toner image on the photoconductor. The carrier particles remaining on the developing roll holding the magnet return from the developing roll into the developing box again, are mixed and stirred with new toner particles, and are repeatedly used for a certain period.

Unlike the one-component developer, the two-component developer has a function that the carrier particles are mixed and stirred with the toner particles to charge the toner particles and further convey the toner particles. Good controllability. Therefore, the two-component developer is suitable for a full-color developing device that requires high image quality, a device that performs high-speed printing that requires reliability and durability of image maintenance, and the like. In the two-component developer used in this manner, the image characteristics such as image density, fog, white spots, gradation, and resolution show a predetermined value from the initial stage, and these characteristics show It needs to be maintained stable and not fluctuating. In order to maintain these properties stably, it is necessary that the carrier particles contained in the two-component developer have stable properties. As carrier particles forming a two-component developer, various carriers such as iron powder carriers, ferrite carriers, resin-coated ferrite carriers, and magnetic powder-dispersed resin carriers have been conventionally used.

Recently, the network of offices has advanced, and it has evolved into an era from a single-function copying machine to a multi-function peripheral. In addition, the service system is shifting from a system in which contracted maintenance workers perform regular maintenance to replace the developer, etc., to an era of maintenance-free system, and the market is developing more developer. The demand for longer life is increasing. In such a situation, in order to reduce the weight of the carrier particles and prolong the life of the developer, a resin-filled ferrite carrier in which resin is filled in the voids of the ferrite carrier core material using porous ferrite particles is proposed. ing.

For example, in Patent Document 1 (Japanese Patent Laid-Open No. 2014-197040), a resin-filled ferrite for an electrophotographic developer, which is composed of porous ferrite particles having an average compressive strength of 100 mN or more and a variation coefficient of the compressive strength of 50% or less. A carrier core material and a resin-filled type ferrite carrier for an electrophotographic developer in which a void is filled in the ferrite carrier core material have been proposed. According to the ferrite carrier, low specific gravity and weight reduction can be achieved, and high strength can be achieved. Because of this, it is said to have effects such as excellent durability and longer life.

Further, Patent Document 2 (JP-A-2005-197490) discloses a resin-filled ferrite carrier for an electrophotographic developer, in which voids of porous ferrite particles used as a ferrite carrier core material are filled with a silicone resin. Resin-filled type for electrophotographic developer in which true specific gravity (Y) of the porous ferrite particles filled with the silicone resin and Si/Fe value (X) measured by fluorescent X-ray elemental analysis satisfy a specific relational expression A ferrite carrier has been proposed, and it is said that the ferrite carrier has a high stability of charge amount when used as a developer and has an effect that the true specific gravity can be arbitrarily controlled.

JP, 2014-197440, A JP, 2005-197490, A

Since such a resin-filled ferrite carrier can be reduced in weight, it has excellent durability and is convenient. However, since the resin-filled ferrite carrier contains a non-magnetic component such as resin, the magnetic force is weakened as a whole, and the carrier is easily scattered from the magnet roll to the photosensitive member during development, so-called carrier scattering easily occurs. Therefore, it is considered that the saturation magnetization of the carrier is increased and the magnetic force is strengthened. For example, in Example 5 of Patent Document 1, it is disclosed that the firing temperature and oxygen concentration during the production of the porous ferrite particles (ferrite carrier core material) are adjusted to produce a ferrite carrier having a saturation magnetization of 66 Am ² /kg. ing. However, since the saturation magnetization and the electric resistance of ferrite are generally in a trade-off relationship, the carrier simply increasing the saturation magnetization has a low electric resistance, and as a result, the carrier current becomes high, and the leakage phenomenon and white spots occur. Such an image defect may occur. Therefore, it is desirable not only to increase the saturation magnetization of carriers, but also to control the electric resistance so as to be appropriate.

On the other hand, it may be possible to provide a coating resin on the surface of the resin-filled ferrite carrier to control the characteristics of the carrier. For example, in Example 1 of Patent Document 1, it is disclosed that the voids of the porous ferrite particles are filled with a methyl silicone resin, and the surface thereof is further coated with an acrylic resin containing carbon black as a conductivity control agent. There is. However, in the production of the carrier, it is difficult to uniformly provide the coating resin without variation, and it is expected that it is difficult to control the electric resistance of the carrier only with the coating resin. Further, when mixed with the toner at the time of development, the coating resin may be peeled off and adhere to the toner, but if a large amount of carbon black or the like is added to the coating resin in order to control the electric resistance of the carrier, this peeling may occur. Since the coating resin becomes deeply colored, there is a risk of color transfer to the toner, so-called color stain.

The present inventors have now found that it is important to control the design of the filler of the carrier core material in the resin-filled ferrite carrier in order to make the electric resistance appropriate. Specifically, by selecting a specific range as the saturation magnetization of the carrier core material, and by satisfying a specific relationship between the electrical resistance of the ferrite carrier core material and the electrical resistance of the carrier core material, high saturation is achieved. We obtained the finding that even a carrier with magnetization can have an appropriate electric resistance, and as a result, it is lightweight and has excellent durability, as well as less carrier scattering and good images are realized. It was

Therefore, an object of the present invention is to provide a core material for a carrier that is lightweight and excellent in durability, has less carrier scattering, and realizes a good image. Another object of the present invention is to provide a carrier provided with such a carrier core material.

According to one aspect of the present invention, a carrier core material comprising a ferrite carrier core material made of porous ferrite particles, and a filler made of a non-magnetic component filled in the voids of the ferrite carrier core material,
The carrier core material has a saturation magnetization of 63 to 90 A·m ² /kg, and the electric resistance A of the ferrite carrier core material and the electric resistance B of the carrier core material are expressed by the following formula:
−1.0≦Log ₁₀ (B/A)≦0.7
A core material for a carrier that satisfies the above is provided.

According to another aspect of the present invention, there is provided a carrier including the carrier core material and a coating layer made of a resin provided on a surface of the carrier core material, wherein a true specific gravity of the carrier is 3. Provided is a carrier having a magnetization of 5 to 4.5 and a saturation magnetization of 63 to 90 A·m ² /kg.

According to another aspect of the present invention, there is provided a developer including the carrier and toner.

According to still another aspect of the present invention, there is provided an electrophotographic development system using the developer.

Core Material for Carrier The core material for a carrier of the present invention includes a ferrite carrier core material made of porous ferrite particles and a filler made of a non-magnetic component filled in the voids of the ferrite carrier core material. This carrier core material has a structure in which the voids of the ferrite carrier core material are filled with a non-magnetic component, so that it is possible to reduce the weight, improve the durability, and prolong the service life.

Further, the carrier core material of the present invention is characterized in that its saturation magnetization is appropriately high. Specifically, this carrier core material has a saturation magnetization of 63 to 90 A·m ² /kg. According to such a core material for a carrier, it is possible to suppress carrier scattering because it has an appropriately high saturation magnetization. If the saturation magnetization is less than 63 A·m ² /kg, carrier scattering is likely to occur, and if it exceeds 90 A·m ² /kg, the ears of the magnetic brush become hard and it becomes difficult to obtain good image quality. The saturation magnetization is preferably 63 to 75 A·m ² /kg, particularly preferably 65 to 70 A·m ² /kg.

The saturation magnetization can be measured using, for example, an integral type BH tracer (BHU-60 type manufactured by Riken Denshi Co., Ltd.). In this case, an H coil for magnetic field measurement and a 4πI coil for magnetization measurement are inserted between the electromagnets, and the sample is placed in the 4πI coil. The outputs of the H coil and the 4πI coil in which the current of the electromagnet is changed and the magnetic field H is changed are integrated, and a hysteresis loop is drawn on the recording paper with the H output as the X axis and the output of the 4πI coil as the Y axis. Here, as the measurement conditions, the sample filling amount: about 1 g, the sample filling cell: inner diameter 7 mmφ±0.02 mm, height 10 mm±0.1 mm, 4πI coil: 30 turns.

Moreover, in the carrier core material of the present invention, the electric resistance A of the ferrite carrier core material and the electric resistance B of the carrier core material satisfy the formula: -1.0≤Log ₁₀ (B/A)≤0.7. I am satisfied. With such a carrier core material, it is possible to suppress image defects such as a leak phenomenon and white spots. If Log ₁₀ (B/A) is less than −1.0, the carrier current becomes too high, and image defects such as a leak phenomenon and white spots are likely to occur. On the other hand, when Log ₁₀ (B/A) exceeds 0.7, the carrier current becomes too low and it becomes difficult to obtain a sufficient image density. Preferably, the formula: -0.3 ≤ Log ₁₀ (B/A) ≤ 0.7, and particularly preferably the formula: -0.2 ≤ Log ₁₀ (B/A) ≤ 0.7 is satisfied. On the other hand, as disclosed in the above-mentioned Patent Document 1, by using a ferrite carrier core material (core material for carrier) filled with resin, a carrier provided with a coating resin with a conductivity control agent added, the carrier It is conceivable to control the electric resistance and carrier current of the carrier, thereby suppressing image defects such as a leak phenomenon and white spots, and adjusting the image density. Since it contains a control agent, the transmittance is lowered and the saturation magnetization is lowered.Therefore, it is difficult to solve the problems of color stain and carrier scattering even if the electric resistance and carrier current are controlled. Is. On the other hand, the carrier core material of the present invention is characterized by controlling the electric resistance of the carrier core material itself, and thus suppresses the problems of color stains and carrier scattering when used as a carrier, It is possible to appropriately control the electric resistance and the carrier current of, and as a result, it is possible to suppress image defects such as a leak phenomenon and white spots and obtain a desired image density.

Electrical resistance A and B can be measured as follows. That is, the N pole and the S pole are opposed to each other with a gap between the magnetic poles of 6.5 mm, and 200 mg of the sample is weighed and inserted between the non-magnetic parallel plate electrodes (10 mm×40 mm), and the magnetic poles (surface magnetic flux density: 1500 Gauss, The sample is held between the electrodes by attaching a counter electrode area: 10 mm×30 mm) to the parallel plate electrodes, and the resistance of an applied voltage of 250 V is measured with an insulation resistance meter.

The electric resistance B of the core material for a carrier of the present invention is preferably expressed by the formula: 7.0≦Log ₁₀ B≦9.0, particularly preferably by the formula: 7.0≦Log ₁₀ B≦8.5. Be satisfied. By setting Log ₁₀ B to 7.0 or more, image defects such as white spots are further suppressed, and by setting it to 9.0 or less, the image density becomes better.

Further, the true specific gravity of the carrier core material of the present invention is preferably 3.7 to 4.7, and particularly preferably 3.9 to 4.5. By setting the true specific gravity to 3.7 or more, the decrease of the charging speed due to too low specific gravity is further suppressed, and by setting it to 4.7 or less, the effect of lowering the specific gravity becomes sufficient and the life is long enough. Is achieved. The true specific gravity can be measured using a peak meter according to JIS R9301-2-1. At that time, it is preferable to perform measurement at a temperature of 25° C. using methanol as a solvent.

<Ferrite carrier core material>
The composition of the porous ferrite particles forming the ferrite carrier core material preferably includes at least one selected from Mn, Mg, Li, Ca, Sr, Cu, and Zn. Considering recent trends in environmental load reduction such as waste regulation, it is preferable that heavy metals such as Cu, Zn, and Ni are not contained beyond the range of inevitable impurities (accompanying impurities).

The saturation magnetization of the porous ferrite particles is preferably 65 to 93 A·m ² /kg, and particularly preferably 65 to 78 A·m ² /kg. By setting the saturation magnetization within the above range, the saturation magnetization of the carrier core material after resin filling can be controlled more appropriately.

The pore volume of the porous ferrite particles is preferably 15 to 100 mm ³ /g, and particularly preferably 40 to 80 mm ³ /g. When the pore volume is 15 mm ³ /g or more, a sufficient amount of resin can be filled and the weight can be further reduced, and when it is 100 mm ³ /g or less, the strength of the carrier is more appropriately adjusted. It becomes possible to keep.

An appropriate pore volume can be selected from the above pore volume range so as to obtain a desired true specific gravity. To obtain a carrier core material having a small true specific gravity, one having a large pore volume may be filled with a large amount of resin, and in order to obtain a carrier core material having a large true specific gravity, one having a small pore volume. It may be filled with a small amount of resin.

Further, the porous ferrite particles have a peak pore diameter of preferably 0.2 to 1.5 μm, particularly preferably 0.3 to 1.0 μm. When the peak pore diameter is 0.2 μm or more, the size of the irregularities on the surface of the core material becomes an appropriate size, the contact area with the toner increases, and the frictional charging with the toner is efficiently performed, so that Although it has no specific gravity, the charge rising characteristics are good. When the peak pore diameter is 1.5 μm or less, the generation of aggregated particles and irregularly shaped particles can be suppressed, the cracking of carrier particles themselves can be suppressed, and the charge fluctuation can be prevented.

The pore diameter and pore volume of the porous ferrite particles can be measured using, for example, a mercury porosimeter (Pascal 140 and Pascal 240 manufactured by Thermo Fisher Scientific). At that time, for example, CD3P (for powder) is used as a dilatometer, and the sample is put in a commercially available gelatin capsule having a plurality of holes and put in the dilatometer. After degassing with Pascal 140, mercury is filled and the low pressure region (0 to 400 Kpa) is measured to be 1st Run. Next, deaeration and measurement in the low pressure region (0 to 400 Kpa) are performed again to obtain 2nd Run. After 2nd Run, the combined weight of the dilatometer, mercury, capsule and sample is measured. Next, the high pressure region (0.1 Mpa to 200 Mpa) is measured with Pascal 240. The pore volume and the peak pore diameter of the porous ferrite particles are determined by the mercury intrusion amount obtained by the measurement at this high pressure part. When obtaining the pore size, the surface tension of mercury may be 480 dyn/cm and the contact angle may be 141.3°.

The electric resistance A of the ferrite carrier core material made of porous ferrite particles is preferably expressed by the formula: 6.5≦Log ₁₀ A≦9.5, particularly preferably by the formula: 7.0 Log ₁₀ A≦9.0. To be satisfied. By setting Log ₁₀ A to 6.5 or more, image defects such as white spots can be further suppressed, and by setting it to 9.5 or less, the image density becomes better. On the other hand, as described above, it is conceivable to control the electric resistance and carrier current of the carrier by using the carrier provided with the coating resin in which the conductivity control agent is added to the surface of the carrier core material. It is difficult for such a carrier to solve the problems of color stain and carrier scattering. On the other hand, the carrier core material of the present invention is characterized by controlling the electric resistance of the carrier core material itself, and thus suppresses the problems of color stains and carrier scattering when used as a carrier, It is possible to appropriately control the electric resistance and carrier current of the.

<Filling material>
The filler filled in the voids of the ferrite carrier core material is not particularly limited as long as it is a non-magnetic component. A typical non-magnetic component is a resin, preferably a silicone resin having a siloxane bond. The silicone resin may be either a straight silicone resin or a modified silicone resin. Examples of the modified silicone resin include silicone resins modified with resins such as acrylic resins, polyester resins, epoxy resins, polyamide resins, polyamideimide resins, alkyd resins, urethane resins, and fluororesins. A silane compound such as 3-glycidoxypropyltrimethoxysilane or a polymer thereof can also be used as the non-magnetic component. In this specification, a silane compound and its polymer are also referred to as a resin. In particular, it is preferable that a room temperature curable methyl silicone resin is used as the silicone resin, and that it further contains an organic titanium catalyst and an aminosilane coupling agent. Examples of the organic titanium-based catalyst include titanium diisopropoxybis(ethyl acetoacetate), and examples of the aminosilane coupling agent include 3-aminopropyltriethoxysilane.

The filling amount of the filler is preferably 0.5 to 35 parts by weight, and more preferably 4 to 20 parts by weight as a solid content with respect to 100 parts by weight of the ferrite carrier core material. When the filling amount is 0.5 parts by weight or more, the filling becomes sufficient, and the control of the charge amount by the coating resin becomes easy. Further, by setting the filling amount to 35 parts by weight or less, generation of aggregated particles at the time of filling is suppressed, and charge fluctuation is further suppressed.

The carrier core material of the present invention desirably has a non-magnetic component constituting the filler having a siloxane bond, and the Si/Fe value of the carrier core material measured by fluorescent X-ray elemental analysis is: It is preferably 0.002 to 0.015, and particularly preferably 0.004 to 0.01. Examples of the non-magnetic component having a siloxane bond include silicone resin. Here, the Si/Fe value is an index of the filling property of the filler having a siloxane bond, and by setting the Si/Fe value within the above range, the filling property can be controlled more appropriately. Therefore, the electric resistance of the carrier core material can be controlled more strictly. The fluorescent X-ray elemental analysis is a method of measuring the amount of an element existing in the vicinity of a few μm from the surface of the carrier core material, whereby the amount of resin existing in the vicinity of the carrier core material surface can be evaluated. This measurement can be carried out as follows. That is, using a fluorescent X-ray elemental analyzer (manufactured by Rigaku Corporation, ZSX100s), about 5 g of a sample was placed in a powder sample container for vacuum (manufactured by Rigaku Corporation, RS640), set in a sample folder, and with the above apparatus, Si and Fe are measured. Here, as the measurement conditions, for Si, a Si-Kα line can be used as a measurement line, a tube voltage of 50 kV, a tube current of 50 mA, PET as a dispersive crystal, and a PC (proportional counter) as a detector. With respect to Fe, it is possible to use a Fe-Kα line as a measurement line, a tube voltage of 50 kV, a tube current of 50 mA, a dispersive crystal of LiF, and a detector of SC (scintillation counter). The intensity ratio (Si intensity/Fe intensity) is calculated using each of the obtained fluorescent X-ray intensities to obtain the Si/Fe value.

In the core material for a carrier of the present invention, it is desirable that the filler contains a conductivity control agent for the purpose of controlling the electric resistance, the charge amount, and the charging speed. When the filler contains the conductivity control agent, the coating resin of the carrier does not need to contain a large amount of the conductivity control agent that may reduce the permeability, and as a result, the permeability is sufficiently high and the conductivity is high. It is possible to obtain a carrier whose resistance is appropriately controlled. The addition amount of the conductivity control agent is preferably 5 to 35 parts by weight, particularly preferably 7 to 20 parts by weight, based on 100 parts by weight of the non-magnetic component of the filler. By adjusting the addition amount to 5 parts by weight or more, it becomes possible to more appropriately control the electric resistance of the carrier core material, and as a result, there is a possibility that the coating resin of the carrier may have reduced permeability. There is no need to include a large amount of. By setting the addition amount to 35 parts by weight or less, abrupt current leakage is further suppressed. Examples of the conductivity control agent include conductive carbon, oxides such as titanium oxide and tin oxide, and various organic conductivity control agents.

Further, the filler may 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 a large amount of the filler is filled, the charge imparting ability may decrease, but it can be controlled by adding various charge control agents and silane coupling agents. The type of charge control agent or coupling agent that can be used is not particularly limited, but is a charge control agent such as a nigrosine dye, a quaternary ammonium salt, an organometallic complex, a metal-containing monoazo dye, an aminosilane coupling agent, or a fluorine silane coupling agent. Agents and the like are preferred.

As described above, the carrier core material of the present invention has high saturation magnetization by appropriately controlling the design of the filler, particularly the filling amount of the filler and the amount of the conductivity control agent in the filler. However, it becomes possible to make the electric resistance appropriate. As a result, it is possible to obtain a carrier which is light in weight, excellent in durability, less likely to cause carrier scattering, and capable of realizing good images.

Further, while the conventional resin-filled ferrite carrier has a problem that the pore volume of the porous ferrite particles fluctuates to some extent during the production of the carrier, and the electric resistance of the carrier fluctuates. The core material for a carrier is a filler design, in particular, by appropriately controlling the filling amount of the filler and the amount of the conductivity control agent in the filler, even if the pore volume of the porous ferrite particles varies to some extent, It has the feature that the electric resistance does not fluctuate easily.

Carrier The carrier of the present invention comprises the above core material for a carrier and a coating layer made of a resin provided on the surface of the core material for a carrier. Carrier characteristics, especially electrical characteristics such as charging characteristics, are often affected by the materials and properties present on the carrier surface. Therefore, desired carrier characteristics can be accurately adjusted by coating the surface with an appropriate resin.

The carrier of the present invention has a true specific gravity of 3.5 to 4.5. If the true specific gravity is less than 3.5, the specific gravity may be too low, so that the charging speed may be too low, and if the true specific gravity is more than 4.5, the effect of lowering the specific gravity may not be obtained and the life may be extended. There are things you can't do. The true specific gravity is preferably 3.7 to 4.3, particularly preferably 3.8 to 4.2.

Further, the carrier of the present invention has a saturation magnetization of 63 to 90 A·m ² /kg. If the saturation magnetization is less than 63 A·m ² /kg, carrier scattering is likely to occur, and if it exceeds 90 A·m ² /kg, the ears of the magnetic brush become hard and it becomes difficult to obtain good image quality. The saturation magnetization is preferably 63 to 75 A·m ² /kg, particularly preferably 65 to 70 A·m ² /kg.

The coating resin is not particularly limited. Examples of the coating resin include fluororesin, acrylic resin, epoxy resin, polyamide resin, polyamideimide resin, polyester resin, unsaturated polyester resin, urea resin, melamine resin, alkyd resin, phenol resin, fluoroacrylic resin, acrylic-styrene. Examples thereof include resins, silicone resins, modified silicone resins and the like. Examples of the modified silicone resin include silicone resins modified with each resin such as acrylic resin, polyester resin, epoxy resin, polyamide resin, polyamideimide resin, alkyd resin, urethane resin, and fluororesin. Considering the detachment of the resin due to mechanical stress during use, a thermosetting resin is preferably used. A preferred resin is acrylic resin. By coating the surface with an acrylic resin, desired carrier characteristics can be adjusted with high precision. The coating amount of the resin is preferably 0.5 to 5.0 parts by weight, and particularly preferably 1.0 to 3.0 parts by weight with respect to 100 parts by weight of the carrier before resin coating.

The coating layer of the carrier may include a conductivity control agent. The content of the conductivity control agent is preferably 0.3 to 8.0% by weight, and particularly preferably 1.0 to 6.0% by weight, based on the resin of the coating layer. When the content is 0.3% by weight or more, the electric resistance of the carrier is more appropriately controlled, and when the content is 8.0 parts by weight or less, the decrease in the carrier permeability is further suppressed.

In addition, the resin of the coating layer may contain a charge control agent. The types of the conductivity control agent and the charge control agent are the same as in the case of the filler.

The carrier of the present invention has a transmittance of preferably 90% or more, particularly preferably 95% or more. By setting the transmittance to 90% or more, the problem of color stain is further suppressed. The upper limit of the transmittance is not particularly limited and may be 100%. Permeability can be measured as follows. That is, 15 g of a carrier, which is a sample, and 25 g of water are put into a 50 cc glass bottle, the glass bottle is stirred with a ball mill at 150 rpm for 20 minutes, and then allowed to stand, and then a supernatant is collected. After that, the absorption spectrum of the recovered supernatant is measured with a spectrophotometer (UV-1800, manufactured by Shimadzu Corporation), the transmittance at 500 nm is measured, and the measured value is taken as the transmittance.

Further, the carrier current of the carrier of the present invention is preferably 5 to 50 μA or more, more preferably 10 to 50 μA, and particularly preferably 10 to 40 μA. By setting the carrier current to 50 μA or less, image defects such as leak phenomenon and white spots are further suppressed, and by setting it to 5 μA or more, a desired image density can be obtained. Carrier current may be measured as follows. That is, 800 g of a sample was weighed and exposed to an environment of a temperature of 20 to 26° C. and a humidity of 50 to 60% RH for 15 minutes or more, and then a magnet roller and an Al tube were used as electrodes, and the current was arranged at a distance of 4.5 mm. It is measured at an applied voltage of 500 V using a measuring device.

Developer The developer of the present invention contains the above carrier and toner. The toner particles include pulverized toner particles produced by a pulverization method and polymerized toner particles produced by a polymerization method, but the toner particles obtained by any method can be used in the invention.

Electrophotographic Development System The electrophotographic development system of the present invention uses the above developer. An electrophotographic development system reverse-develos an electrostatic latent image formed on a latent image carrier having an organic photoconductor layer by a magnetic brush of a two-component developer having a toner and a carrier while applying a bias electric field. Examples thereof include a digital copying machine, a printer, a fax machine, and a printing machine using the developing method. In addition, a full-color machine that uses 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, may be used.

Method for producing a core material and carrier for carrier Next, a method for manufacturing the core material and carrier for carrier of the present invention.

<Manufacture of core material for carrier>
In order to produce the porous ferrite particles used as the ferrite carrier core material of the carrier core material of the present invention, first, an appropriate amount of raw materials is weighed, and then 0.5 hours or more, preferably 1 to 1 with a ball mill or a vibration mill. Grind and mix for 20 hours. The raw material is not particularly limited.

The pulverized product thus obtained is pelletized using a pressure molding machine or the like, and then calcined at a temperature of 700 to 1200°C.

After temporary calcination, it is further pulverized by a ball mill or a vibration mill, and then water is added and finely pulverized by a bead mill or the like. Next, if necessary, a dispersant, a binder and the like are added, the viscosity is adjusted, and then the mixture is granulated with a spray dryer to granulate. When pulverizing after calcination, water may be added and the mixture may be pulverized by a wet ball mill, a wet vibration mill, or the like. The above-mentioned ball mill, vibration mill, bead mill, or other pulverizer is not particularly limited, but in order to effectively and uniformly disperse the raw materials, it is necessary to use fine beads having a particle diameter of 5 mm or less as the medium to be used. preferable. The crushing degree can be controlled by adjusting the diameter, composition and crushing time of the beads used.

Next, the obtained granulated product is heated at 400 to 800° C. to remove the added organic components such as the dispersant and the binder. If main baking is performed with the dispersant and binder remaining, the oxygen concentration in the main baking device tends to fluctuate due to the decomposition and oxidation of organic components, which greatly affects the magnetic properties, making stable manufacture difficult. Is. In addition, these organic components cause the control of the porosity, that is, the fluctuation of the ferrite crystal growth.

After that, the obtained granulated product is held at a temperature of 800 to 1500° C. for 1 to 24 hours in an atmosphere in which the oxygen concentration is controlled to perform main firing. At that time, a rotary electric furnace, a batch electric furnace, a continuous electric furnace, or the like is used, and an atmosphere during firing is also introduced by introducing an inert gas such as nitrogen or a reducing gas such as hydrogen or carbon monoxide. The oxygen concentration may be controlled.

The fired product thus obtained is pulverized and classified. As the classification method, the existing air classification, mesh filtration method, sedimentation method or the like is used to adjust the particle size to a desired particle size. In this way, porous ferrite particles (ferrite carrier core material) having a predetermined pore volume and peak pore diameter are prepared.

In order to control the pore volume and peak pore diameter of the porous ferrite particles, it is desirable to adjust the manufacturing process as follows. That is, the pore volume of the porous ferrite particles can be controlled mainly by the main calcination temperature. When the temperature is high, the pore volume is small, and when the temperature is low, the pore volume is large. The peak pore size of the porous ferrite particles can be controlled mainly by the crushing strength after calcination. When the crushing is weak, the peak pore size is large, and when the crushing is strong, the peak pore size is small.

A core material for a carrier can be obtained by filling the voids of the ferrite carrier core material made of the porous particles thus obtained with a filler made of a non-magnetic component. As the filling method, various methods can be used, and examples thereof include a dry method, a spray dry method using a fluidized bed, a rotary dry method, and an immersion drying method using a universal stirrer.

In the step of filling the filler, it is preferable to fill the voids of the porous ferrite particles with the filler while mixing and stirring the porous ferrite particles and the filler under reduced pressure. By filling the filler under reduced pressure in this way, it is possible to efficiently fill the voids with the filler. The degree of pressure reduction is preferably 10 to 700 mmHg. If it exceeds 700 mmHg, there is no effect of reducing the pressure, and if it is less than 10 mmHg, the filling material solution is likely to boil during the filling step, which makes efficient filling difficult.

After the filling material is filled, it is heated by various methods as necessary to bring the filled resin into close contact with the core material. The heating method may be either an external heating method or an internal heating method, for example, a fixed or fluid type electric furnace, a rotary electric furnace, a burner furnace, or a microwave baking. The temperature varies depending on the filling material to be filled, but a temperature equal to or higher than the melting point or the glass transition point is necessary, and by raising the temperature to a temperature at which curing sufficiently proceeds, it is possible to obtain a core material for a carrier that is resistant to impact.

By the way, as described above, when the filler having a siloxane bond such as a silicone resin is used as the non-magnetic component, the Si/Fe value of the carrier core material measured by fluorescent X-ray elemental analysis is controlled. Is desirable. In order to control the Si/Fe value, it is desirable to adjust the manufacturing process as follows.

At this time, the most important thing is to increase/decrease the filling amount of the filler according to the pore volume of the porous ferrite particles, and the Si/Fe value of the carrier core material can be controlled by this. Furthermore, when the filler is filled in the porous ferrite particles, the filler is filled under a reduced pressure, and after returning to the atmosphere to remove toluene, an appropriate stirring stress for a certain period of time is further added to the particle surface. Is to be cured by heating after a step of homogenizing. As a result, the filling property of the surface of the ferrite particles filled with the filler becomes uniform, the variation in Si/Fe value is reduced, and the carrier characteristics can be controlled.

<Manufacturing of carriers>
A carrier can be obtained by providing a coating layer made of resin on the surface of the carrier core material obtained as described above. Carrier characteristics, especially electrical characteristics such as charging characteristics, are often affected by the materials and properties present on the carrier surface. Therefore, by coating the surface with an appropriate resin, desired carrier characteristics can be accurately adjusted. As a coating method, a known method such as a brush coating method, a dry method, a spray drying method using a fluidized bed, a rotary drying method, or an immersion drying method using a universal stirrer can be used. In order to improve the coverage, a fluidized bed method is preferable. When baking after resin coating, either an external heating method or an internal heating method may be used. For example, a fixed or fluidized electric furnace, a rotary electric furnace, a burner furnace, or microwave baking may be used. Although the baking temperature varies depending on the resin used, it is preferably set to a temperature equal to or higher than the melting point or the glass transition point, and more preferably raised to a temperature at which curing is sufficiently advanced.

The present invention will be described more specifically by the following examples.

Example 1
(1) Preparation of ferrite carrier core material The raw materials were weighed so that MnO: 38 mol%, MgO: 11 mol%, Fe ₂ O ₃ : 50.3 mol% and SrO: 0.7 mol%, and a dry media mill (vibration) was used. It was crushed for 4.5 hours with a mill and 1/8 inch diameter stainless beads), and the crushed product was made into pellets of about 1 mm square by a roller compactor. Trimanganese tetroxide was used as the MnO raw material, magnesium hydroxide was used as the MgO raw material, and strontium carbonate was used as the SrO raw material. Coarse powder was removed from the pellets using a vibrating screen with an opening of 3 mm, and fine powder was removed using a vibrating screen with an opening of 0.5 mm. I went.

Then, after pulverizing with a dry media mill (vibration mill, 1/8 inch diameter stainless steel beads) to an average particle size of about 4 μm, water is added, and a wet media mill (vertical bead mill, 1/16 It was ground for 10 hours using inch-sized stainless beads. As a result of measuring the particle size (primary particle size after pulverization) of this slurry by Microtrac, D ₅₀ was 1.4 μm. An appropriate amount of a dispersant was added to this slurry, PVA (20% solution) was added as a binder in an amount of 0.2% by weight based on the solid content, and then the mixture was granulated and dried by a spray dryer to obtain the obtained particles (granulated product ) Was adjusted, and then the mixture was heated in a rotary electric furnace at 700° C. for 2 hours to remove organic components such as a dispersant and a binder.

Then, it was held in a tunnel type electric furnace at a firing temperature of 1085° C. and an oxygen gas concentration of 0% by volume for 5 hours. At this time, the rate of temperature increase was 150° C./hour and the rate of temperature decrease was 110° C./hour. Then, it was crushed, further classified to adjust the particle size, and the low magnetic force product was separated by magnetic separation to obtain a ferrite carrier core material composed of porous ferrite particles.

(2) Preparation of core material for carrier 30 parts by weight of a methyl silicone resin solution (6 parts by weight as a solid content because the resin solution concentration is 20%) and titanium diisopropoxybis(ethylacetoacetate) as a catalyst are added. After adding 25 wt% (3 wt% in terms of Ti atom) to the resin solid content, 5 wt% of 3-aminopropyltriethoxysilane was added as an aminosilane coupling agent to the resin solid content, and Carbon black (Mogul L, manufactured by Cabot, Inc.) was added as a conductivity control agent in an amount of 10.0% by weight based on the resin solid content to obtain a filled resin solution.

This resin solution was mixed with 100 parts by weight of the above-mentioned porous ferrite particles at 60° C. under a reduced pressure of 6.7 kPa (about 50 mmHg) and stirred, and the resin was permeated into the voids of the porous ferrite particles while evaporating toluene. Filled. After returning the inside of the container to normal pressure and removing the toluene almost completely while continuing stirring under normal pressure, take out from the filling device, put it in a container, put it in a hot air heating type oven, and keep it at 220°C for 1.5 hours. , Heat treatment was performed.

Then, it was cooled to room temperature, the ferrite particles in which the resin had been hardened were taken out, the particles were agglomerated with a vibrating sieve having an opening of 200 M, and the non-magnetic material was removed using a magnetic separator. After that, coarse particles were removed again with a vibrating screen to obtain resin-filled ferrite particles.

(3) Preparation of Carrier A solid acrylic resin (BR-73 manufactured by Mitsubishi Rayon Co., Ltd.) is prepared, 20 parts by weight of the acrylic resin is mixed with 80 parts by weight of toluene, and the acrylic resin is dissolved in toluene to prepare a resin solution. Was prepared. Carbon black (Mogul L, manufactured by Cabot) as a conductivity control agent was further added to this resin solution in an amount of 5% by weight based on the acrylic resin to obtain a coating resin solution.

The ferrite particles filled with the obtained resin were put into a universal mixing stirrer, the above acrylic resin solution was added, and resin coating was performed by an immersion drying method. At this time, the acrylic resin was 2% by weight with respect to the weight of the ferrite particles after resin filling. After coating, the mixture was heated at 145° C. for 2 hours, then the particles were agglomerated with a vibrating sieve having 200 M openings, and the non-magnetic substance was removed using a magnetic separator. After that, coarse particles were removed by a vibrating screen again to obtain a resin-filled ferrite carrier having a surface coated with a resin.

(4) Evaluation Various characteristics of the obtained ferrite carrier core material, carrier core material and carrier were evaluated as follows.

<Pore volume and pore diameter>
The pore volume and pore diameter were measured as follows. That is, the measurement was performed using a mercury porosimeter (Pascal 140 and Pascal 240 manufactured by Thermo Fisher Scientific). CD3P (for powder) was used as the dilatometer, and the sample was placed in a commercially available gelatin capsule having a plurality of holes and placed in the dilatometer. After degassing with Pascal 140, mercury was filled and measurement was carried out in a low pressure region (0 to 400 Kpa) to obtain 1st Run. Next, deaeration and measurement in the low pressure region (0 to 400 Kpa) were performed again, and the result was 2nd Run. After 2nd Run, the combined weight of the dilatometer, mercury, capsule and sample was measured. Next, it measured with Pascal240 in the high voltage|pressure area|region (0.1Mpa-200Mpa). The pore volume and the peak pore diameter of the porous ferrite particles were determined by the mercury intrusion amount obtained by the measurement of this high pressure part. Further, when the pore diameter was calculated, the surface tension of mercury was 480 dyn/cm and the contact angle was 141.3°.

<Saturation magnetization>
The saturation magnetization was measured by using an integral type BH tracer (BHU-60 type manufactured by Riken Denshi Co., Ltd.). An H coil for magnetic field measurement and a 4πI coil for magnetization measurement were placed between the electromagnets, and the sample was placed in the 4πI coil. The outputs of the H coil and the 4πI coil in which the electric field of the electromagnet is changed to change the magnetic field H are integrated, and the H output is drawn on the X-axis, the output of the 4πI coil is drawn on the Y-axis, and a hysteresis loop is drawn on the recording paper. I asked. Here, the measurement conditions were as follows: sample filling amount: about 1 g, sample filling cell: inner diameter 7 mm±0.02 mm, height 10 mm±0.1 mm, 4πI coil: 30 turns.

<Electrical resistance>
The electric resistance was measured as follows. That is, the N pole and the S pole were opposed to each other with a gap between magnetic poles of 6.5 mm, and 200 mg of the sample was weighed and inserted into a non-magnetic parallel plate electrode (area 10×40 mm). By attaching a magnetic pole (surface magnetic flux density: 1500 Gauss, counter electrode area: 10×30 mm) to parallel plate electrodes, a sample is held between the electrodes, and the resistance at an applied voltage of 250 V is measured with an insulation resistance meter to obtain the electrical resistance. did.

<Si/Fe value>
The Si/Fe value was measured as follows. That is, using a fluorescent X-ray elemental analyzer (ZSX100s manufactured by Rigaku Co., Ltd.), about 5 g of a sample was placed in a powder sample container for vacuum (RS640 manufactured by Rigaku Co., Ltd.) and set in a sample folder. , Si and Fe were measured. Here, as measurement conditions, for Si, a Si-Kα line was used as a measurement line, a tube voltage of 50 kV, a tube current of 50 mA, PET as a dispersive crystal, and a PC (proportional counter) as a detector. For Fe, a Fe-Kα ray was used as a measurement line, a tube voltage of 50 kV, a tube current of 50 mA, LiF as a dispersive crystal, and SC (scintillation counter) as a detector. The intensity ratio (Si intensity/Fe intensity) was calculated using each of the obtained fluorescent X-ray intensities, and the result was taken as the Si/Fe value.

<True specific gravity>
The true specific gravity was measured using a peak meter according to JIS R9301-2-1. Here, measurement was performed at a temperature of 25° C. using methanol as a solvent.

<Transparency>
The transmittance was measured as follows. That is, 15 g of carrier and 25 g of water were placed in a 50 cc glass bottle, the glass bottle was stirred with a ball mill at 150 rpm for 20 minutes, and allowed to stand, and then a supernatant was collected. The absorption spectrum of the collected supernatant was measured with a spectrophotometer (UV-1800, manufactured by Shimadzu Corporation), the transmittance at 500 nm was measured, and the measured value was taken as the transmittance.

<Carrier current>
The carrier current was measured as follows. That is, 800 g of a sample was weighed and exposed to an environment of a temperature of 20 to 26° C. and a humidity of 50 to 60% RH for 15 minutes or more, and then a magnet roller and an Al tube were used as electrodes, and the current was arranged at a distance of 4.5 mm. The carrier voltage was obtained by measuring at an applied voltage of 500 V using a measuring device.

<Amount of scattering>
The scattering amount was measured as follows. That is, 500 g of a carrier was filled in a magnetic drum having a diameter of 50 mm and a surface magnetic force of 1000 Gauss, rotated at 270 rpm for 30 minutes, and the scattered particles were collected, and the weight thereof was measured to obtain the scattered amount.

Examples 2 and 4-15
(1) Preparation of Ferrite Carrier Core Material A ferrite carrier core material (porous material) was prepared in the same manner as in Example 1 except that the firing temperature and the oxygen gas concentration in the main firing step in the tunnel type electric furnace were as shown in Table 1. Fine ferrite particles) were produced.

(2) Production of core material for carrier Example 1 except that the amount of methyl silicone resin (solid content) and the amount of conductivity control agent (carbon black) added in the step of producing a filled resin solution were as shown in Table 1. A core material for a carrier was manufactured in the same manner as in.

(3) Preparation of Carrier The procedure of Example 1 was repeated except that the amount of the conductivity control agent (carbon black) added in the coating resin solution preparation step and the amount of acrylic resin in the resin coating step were as shown in Table 1. The carrier was produced by

Example 3
(1) Preparation of Ferrite Carrier Core Material A ferrite carrier core material (porous material) was prepared in the same manner as in Example 1 except that the firing temperature and the oxygen gas concentration in the main firing step in the tunnel type electric furnace were as shown in Table 1. Fine ferrite particles) were produced.

(2) Preparation of core material for carrier 100 parts by weight of porous ferrite particles, 12 parts by weight of a silane coupling agent (3-glycidoxypropyltrimethoxysilane), and 10 parts by weight of carbon black with respect to the silane coupling agent. %, and the resin was filled in the universal mixer by the immersion drying method until it was sufficiently dried. Then, it was taken out from the apparatus, put in a hot air heating type oven, and heat-treated at 250° C. for 1.5 hours.

(3) Preparation of Carrier The procedure of Example 1 was repeated except that the amount of the conductivity control agent (carbon black) added in the coating resin solution preparation step and the amount of acrylic resin in the resin coating step were as shown in Table 1. The carrier was produced by

Results The evaluation results obtained in Examples 1 to 15 are as shown in Table 2. In Examples 1 to 6 which are Examples, the amount of scattering was small, the carrier current value was within an appropriate range, and the transmittance was sufficiently high. On the other hand, in Comparative Examples 7-12 and 14-15, there was a problem in any of the transmittance, the amount of scattering, and the carrier current value. In addition, in Example 13, sufficient resin filling could not be performed and a core material for a carrier could not be obtained. From these results, according to the present invention, it is possible to provide a carrier core material and a carrier including the carrier core material, which is lightweight and excellent in durability, has less carrier scattering, and realizes a good image. I understand.

Claims (13)

A core material for a carrier comprising a ferrite carrier core material made of porous ferrite particles, and a filler made of a non-magnetic component filled in the voids of the ferrite carrier core material,
The carrier core material has a saturation magnetization of 63 to 90 A·m ² /kg , the carrier core material has a true specific gravity of 3.9 to 4.7 , and the ferrite carrier core material has an electric resistance A and a carrier. The electric resistance B of the core material is expressed by the following formula:
−1.0≦Log ₁₀ (B/A)≦0.7
Satisfied,
A core material for a carrier, wherein the filler contains a conductivity control agent, and the content of the conductivity control agent is 5 to 35 parts by weight based on 100 parts by weight of the non-magnetic component of the filler. The electric resistance A and the electric resistance B are represented by the following formulas:
−0.3≦Log ₁₀ (B/A)≦0.7
The core material for a carrier according to claim 1, which satisfies the above condition. The core material for a carrier according to claim 1 or 2, wherein the saturation magnetization of the core material for a carrier is 63 to 75 A·m ² /kg. The electric resistance B is represented by the following formula:
7.0≦Log ₁₀ B≦9.0
The core material for a carrier according to any one of claims 1 to 3, which satisfies the above condition. The core material for a carrier according to claim 1, wherein the pore volume of the porous ferrite particles is 15 to 100 mm ³ /g. The core material for a carrier according to any one of claims 1 to 5, wherein the saturation magnetization of the porous ferrite particles is 65 to 93 A·m ² /kg. The non-magnetic component of the filler has a siloxane bond, and the Si/Fe value of the carrier core material measured by fluorescent X-ray elemental analysis is 0.002 to 0.015. The core material for a carrier according to any one of 1 to 6. A carrier comprising the carrier core material according to any one of claims 1 to 7 and a coating layer made of a resin provided on a surface of the carrier core material, wherein a true specific gravity of the carrier is 3 Carrier of 0.5 to 4.5 and saturation magnetization of 63 to 90 A·m ² /kg. The carrier according to claim 8, wherein the coating layer contains a conductivity control agent, and the content of the conductivity control agent is 0.3 to 8.0% by weight based on the resin of the coating layer. The carrier according to claim 8 or 9, wherein the carrier has a transmittance of 90% or more. The carrier according to claim 8, wherein a current value of the carrier is 5 to 50 μA. A developer comprising the carrier according to any one of claims 8 to 11 and a toner. An electrophotographic development system using the developer according to claim 12.