JP6267965B2 - COMPOSITE PARTICLES AND ELECTROPHOTOGRAPHIC DEVELOPMENT CARRIER AND ELECTROPHOTOGRAPHIC DEVELOPER USING THE SAME - Google Patents

Description

  The present invention relates to composite particles, an electrophotographic developer carrier and an electrophotographic developer using the same.

  In image forming apparatuses such as facsimiles, printers, and copiers using an electrophotographic system, powder toner as a developer is attached to an electrostatic latent image on a photosensitive member, and the attached toner image is applied to a predetermined sheet or the like. After being transferred to the sheet, it is heated and pressurized to melt and fix it on a sheet or the like. Here, the developer is roughly classified into a one-component development method using a one-component developer containing only toner and a two-component development method using a two-component developer containing toner and carrier. . In recent years, the two-component development method has been used in most cases because toner charge control is easy, stable image quality can be obtained, and high-speed development is possible.

  In the two-component development method, a developer containing toner and carrier is stirred and mixed in a developing device, and the toner is charged to a predetermined amount by friction. Then, a developer is supplied to the rotating developing sleeve, a magnetic brush is formed on the developing sleeve, and the toner is electrically moved to the photosensitive member via the magnetic brush, so that an electrostatic latent image on the photosensitive member can be formed. Visualize.

  In recent years, with the increase in the speed of image forming apparatuses, the speed of stirring and mixing of developer and rotational conveyance has also increased. On the other hand, from the viewpoint of energy saving, it is required to suppress power for stirring and mixing and rotating and transporting the developer. For this purpose, it is desirable to reduce the apparent density of the carrier used.

Therefore, for example, Patent Document 1, has at least one of 20% to 65% of the pores in the cross-sectional area basis, the magnetic core apparent density is in the range of 0.50g ^/ cm ³ ~1.50g ^/ cm 3 Particles have been proposed. Patent Document 2 proposes a magnetic powder for developing an electrostatic latent image, which is composed of composite particles having a predetermined amount of ferromagnetic fine particles and a phenol resin, and having a predetermined average particle diameter and bulk density. Yes.

JP 2008-310104 A Japanese Unexamined Patent Publication No. 3-61955

  However, particles having pores therein or particles in which magnetic powder is dispersed in a resin are usually prone to cracking or chipping.

  The present invention has been made in view of such conventional problems, and an object of the present invention is to provide composite particles having a low apparent density and maintaining a strength of a predetermined level or more.

  Another object of the present invention is to provide an electrophotographic developer carrier and an electrophotographic developer capable of achieving energy saving and high speed.

The composite particle according to the present invention that achieves the above object is a composite particle in which magnetic powder is dispersed in a binder resin, the apparent density is 1.1 g / cm ³ or less, and the area occupied by the magnetic powder in the particle cross section. The ratio is 30% to 50%, and the standard deviation σ of the area ratio obtained by dividing the particle cross section into a plurality of regions is 7.0% or less. In addition, the area ratio which the magnetic powder occupies in the particle cross section and the method of obtaining the standard deviation σ will be described in detail in the following examples.

Here, the true density of the composite particles is preferably in the range of 3.8 g / cm ^{3 to} 4.5 g / cm ³ .

  The volume average particle size of the composite particles is preferably in the range of 20 μm to 50 μm.

  The binder resin preferably contains at least one of polyurethane and polyolefin.

  The electrophotographic developer carrier according to the present invention is characterized in that the surface of the composite particle is coated with a resin.

  The electrophotographic developer according to the present invention includes the above-described electrophotographic developer carrier and toner.

  In the composite particles of the present invention, since a predetermined amount of magnetic powder is uniformly dispersed in the binder resin, the apparent density is small, and the strength exceeding a predetermined level is maintained. Thereby, stirring and mixing can be performed with small power, and cracking and chipping of particles due to stirring and mixing can be significantly reduced.

  Since the composite particle is used for the electrophotographic developer carrier and the electrophotographic developer according to the present invention, it can cope with energy saving and high speed.

2 is a SEM photograph of composite particles of Example 1. 2 is a cross-sectional SEM photograph of the composite particles of Example 1. 4 is a SEM photograph of composite particles of Example 2. 2 is a cross-sectional SEM photograph of the composite particles of Example 2. 4 is a SEM photograph of composite particles of Example 3. 6 is a cross-sectional SEM photograph of the composite particles of Example 3. 4 is a SEM photograph of composite particles of Comparative Example 1. 4 is a cross-sectional SEM photograph of composite particles of Comparative Example 1.

The composite particles according to the present invention are composite particles in which magnetic powder is dispersed in a binder resin, the apparent density is 1.1 g / cm ³ or less, and the area ratio of the magnetic powder in the particle cross section is 30% to The standard deviation σ of the area ratio obtained by dividing the particle cross section into a plurality of regions is 7.0% or less. By setting the area ratio of the magnetic powder in the particle cross section to the above range and uniformly dispersing the magnetic powder in the particles, the apparent density can be reduced and the high particle strength can be maintained.

  When the area ratio of the magnetic powder in the particle cross section is less than 30%, the apparent density is decreased but the particle strength is decreased. On the other hand, if the area ratio exceeds 50%, the particle strength increases but the apparent density increases. A more preferable range of the area ratio is 35% to 45%.

  Further, when the standard deviation σ of the area ratio exceeds 7.0%, in other words, when the dispersion of the magnetic powder in the particles is not uniform, a weak portion appears in the particles, and the particles are cracked or chipped. There is a fear. A more preferable upper limit value of the standard deviation σ of the area ratio is 6.0%.

The true density of the composite particles is preferably in the range of 3.8 g / cm ^{3 to} 4.5 g / cm ³ . By setting the true density of the composite particles within this range, for example, when the composite particles are used as the carrier core material, the stirring power of the developer containing the carrier can be reduced. Moreover, the stirring stress which a composite particle receives can be reduced significantly. More preferably a true density range of the composite particles is ^{3.9g / cm 3 ~4.2g / cm 3} . The true density of the composite particles can be controlled by the blending ratio of the binder resin and the magnetic powder.

  The volume average particle size of the composite particles is preferably in the range of 20 μm to 50 μm. By setting the volume average particle size of the composite particles in this range, for example, when the composite particles are used as a carrier core material, carrier adhesion to the surface of the photoreceptor can be suppressed, and the image quality can be clarified. it can. Furthermore, the stirring stress that the composite particles receive can be reduced. In order to make the volume average particle diameter of the composite particles within the above range, classification may be performed using a sieve or the like in the manufacturing process of the composite particles. The particle size distribution is preferably sharp.

  In addition, the composite particles of the present invention are preferably spherical. This is because, when the composite particles are used as, for example, a carrier core material, the stirring power of the developer containing the carrier can be reduced.

Examples of the magnetic powder used in the present invention include ferrite, γ-Fe ₂ O ₃ , and magnetite containing one or more metals other than iron such as Mg, Ca, Ti, Cu, Zn, Sr, and Ni. Moreover, you may use 2 or more types of magnetic powder from which a kind differs. The particle size of the magnetic powder is preferably in the range of 0.05 μm to 5 μm, more preferably in the range of 0.1 μm to 3 μm. If the particle size of the magnetic powder used is too large relative to the desired particle size of the composite particle, the particle strength may decrease when the composite particle is bound by a resin, and the particle shape of the composite particle is not good. Since it becomes easy to spheroidize, it is not preferable.

  Examples of the binder resin used in the present invention include thermoplastic resins and thermosetting resins in the form of uncured or precondensed materials, such as vinyl aromatic resins such as polystyrene, polyvinyl acetal resins, polyester resins, Examples thereof include an epoxy resin, a phenol resin, a polyurethane resin, and a polyolefin resin. Further, these resins may be modified resins. Among these, polyurethane resins and polyolefin resins are preferably used.

  When the composite particles of the present invention are used as a carrier core material, auxiliary agents known per se, such as carbon black for adjusting electric resistance, dispersing agents, dispersing aids, low-molecular or high-molecular charge control agents, etc. May be blended.

  The composite particles of the present invention can be used for various applications, for example, electrophotographic developing carriers, electromagnetic wave absorbing materials, electromagnetic shielding material powders, rubber, fillers / reinforcing materials for plastics, paints, paints / adhesives It can be used as a matting material, filler, reinforcing material and the like. Among these, it is particularly preferably used as a carrier for electrophotographic development.

  Although there is no limitation in particular in the manufacturing method of the composite particle of this invention, the manufacturing method demonstrated below is suitable.

  First, a magnetic powder and a binder resin are weighed, put into a dispersion medium, and mixed to prepare a slurry. Water is preferred as the dispersion medium used in the present invention. In addition to the magnetic powder and the binder resin, a dispersant or the like may be added to the dispersion medium as necessary. As the blending amount of the dispersant, the concentration in the slurry is preferably about 0.5 to 2 wt%.

  And the produced slurry is sprayed and granulated. Specifically, the slurry is introduced into a spray granulator such as a spray dryer and sprayed into the atmosphere to granulate into a spherical shape. The atmospheric temperature during spray granulation is preferably in the range of 120 ° C to 250 ° C. Thereby, the spherical granulated material with an average particle diameter of 20-50 micrometers is obtained. In addition, it is desirable that the obtained granulated product has a sharp particle size distribution by removing coarse particles and fine powder using a vibration sieve or the like.

  Next, the granulated product is put into a blower dryer and dried at a drying temperature (curing temperature) of 120 ° C. to 200 ° C. for 0.5 hour to 5 hours to cure the binder resin to obtain composite particles.

  When the composite particles are fixed to each other, they are pulverized as necessary. Specifically, for example, the composite particles are pulverized by a hammer mill or the like. The form of the granulation step may be either a continuous type or a batch type. And if necessary, classification may be performed in order to make the particle size in a predetermined range. As a classification method, a conventionally known method such as air classification or sieve classification can be used. In addition, after primary classification with an air classifier, the particle size may be aligned within a predetermined range with a vibration sieve or an ultrasonic sieve.

  When the composite particles of the present invention produced as described above are used as an electrophotographic development carrier, the composite particles can be used as they are as an electrophotographic development carrier. However, from the viewpoint of chargeability and the like, It is preferable to coat the surface with a resin.

  As the resin for coating the surface of the composite particles, conventionally known resins can be used, for example, polyethylene, polypropylene, polyvinyl chloride, poly-4-methylpentene-1, polyvinylidene chloride, ABS (acrylonitrile-butadiene-styrene). Examples thereof include resins, polystyrene, (meth) acrylic resins, polyvinyl alcohol resins, polyvinyl chloride-based, polyurethane-based, polyester-based, polyamide-based, polybutadiene-based thermoplastic elastomers, fluorine silicone-based resins, and the like.

  In order to coat the surface of the composite particles with a resin, a resin solution or dispersion may be applied to the composite particles. Solvents for the coating solution include aromatic hydrocarbon solvents such as toluene and xylene; ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; cyclic ether solvents such as tetrahydrofuran and dioxane; ethanol, propanol, and butanol Alcohol solvents such as ethyl cellosolve, cellosolve solvents such as butyl cellosolve; ester solvents such as ethyl acetate and butyl acetate; amide solvents such as dimethylformamide and dimethylacetamide, etc. . The resin component concentration in the coating solution should generally be in the range of 0.0010 wt% to 30 wt%, particularly 0.0010 wt% to 2 wt%.

  As a method for coating the composite particles with the resin, for example, a spray drying method, a fluidized bed method, a spray drying method using a fluidized bed, an immersion method, or the like can be used. Among these, the fluidized bed method is particularly preferable in that it can be efficiently applied with a small amount of resin. For example, in the case of the fluidized bed method, the resin coating amount can be adjusted by the amount of resin solution sprayed and the spraying time.

  The electrophotographic developer according to the present invention is obtained by mixing the electrophotographic developer carrier prepared as described above and a toner. The mixing ratio of the electrophotographic developing carrier and the toner is not particularly limited, and may be appropriately determined from the developing conditions of the developing device to be used. Generally, the toner concentration in the developer is preferably in the range of 1 wt% to 20 wt%. When the toner density is less than 1 wt%, the image density becomes too low, and when the toner density exceeds 20 wt%, the toner scatters in the developing device, and the toner adheres to the background portion such as internal dirt or transfer paper. This is because there is a risk of occurrence. A more preferable toner concentration is in the range of 3 wt% to 15 wt%.

  For mixing the electrophotographic carrier and the toner, a conventionally known mixing device can be used. For example, a Henschel mixer, a V-type mixer, a tumbler mixer, a hybridizer, or the like can be used.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these examples at all.

Example 1
Composite particles were produced by the following method. As starting materials, 1000 g of ferrite powder (composition: Mn _0.86 Fe _2.14 O ₄ , average particle size: 2.9 μm) and 231 g of polyurethane resin (resin concentration 30 wt%) were mixed with 587 g of pure water. To obtain a mixed slurry having a concentration of 58.0 wt% and a viscosity of 690 cp. This mixed slurry was sprayed into hot air at about 150 ° C. with a spray dryer to obtain a granulated product. The obtained granulated material was put into a blower dryer and dried at a temperature of 150 ° C. for 60 minutes to cure the polyurethane resin to obtain composite particles. The obtained composite particles were classified using a vibration sieve to obtain composite particles having a volume average particle size of 32.0 μm.

  In the composite particle cross section, the area ratio of the magnetic powder and its standard deviation, the apparent density of the composite particles, the particle strength, the true density, the volume average particle size, the magnetic properties, and the electrical resistance were measured by the following methods. The results are summarized in Table 2. 1 and 2 show an SEM photograph and a cross-sectional SEM photograph of the composite particles of Example 1, respectively.

(Measurement of area ratio of magnetic powder in composite particles)
After the obtained composite particles were dispersed in a thermosetting resin, the resin was cured by heating. The surface of the cured product was polished using a cross section polisher (manufactured by JEOL Ltd.). The polished particle surface was observed using a scanning electron microscope (manufactured by JEOL Ltd.), and a cross-sectional photograph of the particle was taken. Then, the cross-section of 100 particles is equally divided into 9 parts, and the particle part and resin part in each section are measured using image analysis software “Image-Pro”, and the magnetic powder part relative to the total area is measured. The area ratio (magnetic powder area ratio) was calculated, and the average value and standard deviation were calculated.

(Apparent density measurement)
The apparent density of the composite particles was measured according to JIS Z 2504.

(Particle strength)
30 g of composite particles were put into a sample mill. The sample mill used a SK-M10 model manufactured by Kyoritsu Riko Co., Ltd., and a crushing test was performed at a rotational speed of 14,000 rpm for 60 seconds. Next, using a laser diffraction particle size distribution measuring apparatus (“Microtrack Model 9320-X100” manufactured by Nikkiso Co., Ltd.), the cumulative particle frequency with a particle size of 20 μm or less is measured. And the increase rate (%) of the cumulative particle frequency with a particle size of 20 μm or less before and after the treatment with the sample mill was calculated and used as an index of particle strength.
○: Increase rate in crushed pieces of 20 μm or less after crushing is less than 40% ×: Increase rate in crushed pieces of 20 μm or less after crushing is 40% or more

(True density)
The true density of the composite particles was measured using “ULTRA PYCNOMETER 1000” manufactured by Quantachrome.

(Measurement of volume average particle diameter)
The volume average particle diameter was measured using a Microtrack, Model 9320-X100 manufactured by Nikkiso Co., Ltd.

(Measurement of magnetic properties)
Saturation magnetization σs, magnetization σ _1k , residual magnetization σr, and coercive force Hc were measured using VSM (manufactured by Toei Kogyo Co., Ltd., VSM-P7).

(Electrical resistance)
Two brass plates as electrodes having a thickness of 2 mm whose surfaces were electropolished were arranged to face each other with a distance of 2 mm. After inserting 200 mg of composite particles between the electrodes, a magnet having a cross-sectional area of 240 cm 2 (ferrite magnet having a surface magnetic flux density of 1500 gauss) was placed behind each electrode to form a bridge of composite particles between the electrodes. . Then, a DC voltage of 1000 V was applied between the electrodes, the value of the current flowing through the composite particles was measured, and the electrical resistance of the composite particles at a voltage of 1000 V was calculated.

Example 2
As starting materials, 1000 g of ferrite powder (composition: Mn _0.86 Fe _2.14 O ₄ , average particle size: 2.9 μm) and 188 g of polyurethane resin (resin concentration 35 wt%) were added to 578 g of pure water. A mixed slurry having a concentration of 57.7 wt% and a viscosity of 654 cp was obtained. This mixed slurry was sprayed into hot air at about 150 ° C. with a spray dryer to obtain a granulated product. The obtained granulated material was put into a blower dryer and dried at a temperature of 150 ° C. for 60 minutes to cure the polyurethane resin to obtain composite particles. The obtained composite particles were classified using a vibration sieve to obtain composite particles having a volume average particle diameter of 39.9 μm.
The properties of the obtained composite particles were measured in the same manner as in Example 1. The results are summarized in Table 2. 3 and 4 show a SEM photograph and a cross-sectional SEM photograph of the composite particles of Example 2, respectively.

Example 3
As starting materials, 1000 g of ferrite powder (composition: Mn _0.86 Fe _2.14 O ₄ , average particle size: 2.9 μm) and 316 g of polyolefin resin (resin concentration 22 wt%) were added to 225 g of pure water. To obtain a mixed slurry having a concentration of 68.9 wt% and a viscosity of 1234 cp. This mixed slurry was sprayed into hot air at about 150 ° C. with a spray dryer to obtain a granulated product. The obtained granulated material was put into a blower dryer and dried at a temperature of 120 ° C. for 60 minutes to cure the polyolefin resin to obtain composite particles. The obtained composite particles were classified using a vibration sieve to obtain composite particles having a volume average particle diameter of 32.5 μm.
The properties of the obtained composite particles were measured in the same manner as in Example 1. The results are summarized in Table 2. 5 and 6 show an SEM photograph and a cross-sectional SEM photograph of the composite particles of Example 3, respectively.

Comparative Example 1
As starting materials, 700 g of ferrite powder (composition: Mn _0.86 Fe _2.14 O ₄ , average particle size: 2.9 μm) and 96 g of acrylic resin (resin concentration 50 wt%) were added to 476 g of pure water. A mixed slurry having a concentration of 63.9 wt% and a viscosity of 1122 cp was obtained. This mixed slurry was sprayed into hot air at about 150 ° C. with a spray dryer to obtain a granulated product. The obtained granulated material was put into a blower dryer and dried at a temperature of 180 ° C. for 60 minutes to cure the acrylic resin to obtain composite particles. The obtained composite particles were classified using a vibration sieve to obtain composite particles having a volume average particle diameter of 30.6 μm.
The properties of the obtained composite particles were measured in the same manner as in Example 1. The results are summarized in Table 2. 7 and 8 show an SEM photograph and a cross-sectional SEM photograph of the composite particles of Comparative Example 1, respectively.

As is clear from Table 2, the composite particles of Examples 1 to 3 had a small apparent density of 1.04 g / cm ³ or less and a high particle strength. On the other hand, the composite particles of Comparative Example 1 had insufficient dispersion of the magnetic powder in the particles, the particle strength was low, and cracks and chips were generated. The higher the apparent density, the higher the strength. However, in Comparative Example 1, the strength was insufficient. This is because the standard deviation (%) of the area ratio of the magnetic powder exceeded 10.

  In order to confirm the influence of the standard deviation, a confirmation test was similarly conducted by the production method of Example 1 except that the magnetic powder in Example 1 had an average particle diameter of 5.0 μm and an area ratio of 30%. As a result, the standard deviation (%) of the area ratio of the magnetic powder exceeded 10, and the strength was insufficient. It was confirmed that the homogeneity within the composite particles affects the strength.

Claims (5)

Composite particles in which magnetic powder is dispersed in a binder resin,
The apparent density is 1.1 g / cm ³ or less,
The true density is in the range of 3.8 g / cm ^{3 to} 4.5 g / cm ³ ;
The area ratio of the magnetic powder in the particle cross section is 30% to 50%, and the standard deviation σ of the area ratio obtained by dividing the particle cross section into a plurality of regions is 7.0% or less. Composite particles. Composite particles in which magnetic powder is dispersed in a binder resin,
The apparent density is 1.1 g / cm ³ or less,
Area ratio of the magnetic powder in the particle cross section is 30% to 50% state, and are the standard deviation σ is 7.0% or less of the area ratio obtained by dividing the particle cross sections into a plurality of regions,
The composite particle, wherein the binder resin contains at least one of polyurethane and polyolefin .   The composite particles according to claim 1 or 2, wherein the volume average particle diameter is in the range of 20 µm to 50 µm. Electrophotographic development carrier, characterized in that the surface of the composite particles according to any one of claims 1 to 3 is coated with a resin. An electrophotographic developer comprising the electrophotographic developer carrier according to claim 4 and a toner.