JP5298481B2 - Carrier manufacturing method - Google Patents

Description

The present invention relates to a method for producing a carrier constituting a two-component developer used for electrophotographic image formation, and more particularly to a method for producing a carrier using a magnesium-containing ferrite.

  As one of the electrophotographic image forming methods, there is an image forming method in which a toner image is formed by developing an electrostatic latent image on an image carrier using a two-component developer composed of toner and carrier. The carrier constituting the two-component developer is insulated on the surface of a core particle called a conductive carrier made of iron oxide powder or non-oxidized iron powder and a carrier core made of a ferromagnetic material such as iron, nickel or ferrite. And insulative carriers uniformly coated with a conductive resin. Among these, the insulating carrier has advantages such as excellent durability and long life compared to the conductive carrier, and is particularly used as a carrier suitable for high-speed image formation.

  One of the raw materials for the carrier core is ferrite. Ferrite is a solid solution of α-iron having a body-centered cubic crystal, or a divalent transition metal such as nickel, copper, cobalt, manganese, or zinc. Of these, solid solutions of divalent transition metals such as copper and nickel exhibit good properties as a carrier core, but in recent years substances that are harmful to the human body have been excluded from office machines and home appliances. However, there is a movement to aim at product safety. For example, the RoHS directive prohibiting the use of six specific substances in products for electrical and electronic equipment handled in the European Union is a typical example.

  Copper and zinc are not regulated substances under the RoHS Directive, but there are cases where there is a concern about accumulation in the living body, so studies on solid-solution ferrites that do not contain such metals have been conducted. As a matter of fact, ferrite containing magnesium has attracted attention.

There are the following carrier technologies using ferrite containing magnesium. For example, there is a method for producing MnO · MgO · Fe ₂ O ₃ -based soft ferrite by firing an oxide raw material in a mixed gas atmosphere composed of oxygen gas and inert gas (for example, see Patent Document 1). .

In addition, there is a technique for manufacturing a carrier by coating a soft ferrite particle surface having a composition of MnO.MgO.Fe ₂ O ₃ with a resin added with polymethylalkylsiloxane (for example, see Patent Document 2).

Further, a technology for producing a carrier core by adding a metal oxide such as Bi ₂ O _{3 having} a melting point of 1000 ° C. or less and a metal oxide such as ZrO ₂ having a melting point of 1800 ° C. or more to ferrite containing magnesium. (For example, refer to Patent Document 3).

As described above, a technique relating to a carrier using a ferrite containing magnesium has been studied.
JP 2001-93720 A JP 2003-337445 A JP 2004-240321 A

  By the way, with the advance of digital technology, for example, high-definition image formation that reproduces a dot image at a level of 1200 dpi (dpi; number of dots per inch (2.54 cm)) has been demanded. As one of means for realizing the reproduction of minute dot images, the reduction of the toner diameter has been studied, and accordingly, a smaller carrier than before has been demanded. Further, studies have been made to realize a carrier having a smaller particle diameter than the conventional carrier using a ferrite containing magnesium.

  However, it has been found that when a small-diameter carrier core is made of ferrite containing magnesium, the toner cannot be sufficiently charged. In particular, when a large number of prints are made continuously, the charge imparting performance to the toner decreases as the number of sheets increases, and image contamination such as fogging occurs due to toner scattering. As described above, when a carrier having a small diameter is produced using a ferrite containing magnesium, a stable charge imparting performance to the toner cannot be obtained.

The present invention provides a method for producing a carrier having a stable charging performance that can provide sufficient charging even when combined with a small-diameter toner and does not cause image contamination such as fogging due to toner scattering due to insufficient charging. With the goal. In addition, the present invention can maintain a charging level that does not hinder image formation even under image forming conditions in which it is difficult to maintain a charging level that allows continuous printing of a large number of sheets. An object is to provide a method for producing a carrier.

1.
In the method for producing a carrier obtained by coating a resin on the surface of core particles made of ferrite containing at least magnesium element,
Said core particles are formed by sintering once, baking temperature in the calcination is at 1500 ° C. or higher, the slurry concentration used in the calcination is Ri der least 70 wt%,
The core particle is in irregular shape which is a ratio of deformed particles as defined below 5% by number or less, and method for producing a carrier, wherein the maximum grain size of the core particle surface is 2μm or more 5μm or less .
The irregularly shaped particles are measured by measuring the “maximum core particle diameter at the horizontal ferret diameter” and the “projection area of the core particle” from 100 images captured from a scanning electron microscope (SEM) image, and using the following formula: SF-1 is calculated and defined to be a core particle with SF-1 greater than 130.
SF-1 = {(maximum diameter of core particle in horizontal ferret diameter) ² / (projected area of core particle)} × (π / 4) × 100 (provided that the projected area is the projection of the particle onto the plane) The area of the image.)

2.
2. The method for producing a carrier according to 1 above, wherein an average particle diameter of the carrier is 20 μm or more and 40 μm or less.

3.
2. The method for producing a carrier according to 1 above, wherein the core particle contains a manganese element.

4).
2. The method for producing a carrier according to 1 above, wherein the maximum grain diameter is 2 μm or more and 4 μm or less.

5.
3. The method for producing a carrier according to 2 above, wherein the carrier has an average particle size of 25 μm or more and 37 μm or less.

6).
^{2. The} method for producing a carrier according to 1 above, wherein the magnetic force of the carrier is 40 to 70 Am ² / kg.

7).
7. The method for producing a carrier as described in 6 above, wherein the magnetic force of the carrier is 45 to 60 Am ² / kg.

8).
2. The method for producing a carrier according to 1 above, wherein the resin layer covering the surface of the core particle covers the core particle surface by 70% or more by surface area.

  In the present invention, when producing a carrier core using magnesium-containing ferrite, a carrier environment in which the shape is uniform and the grains constituting the surface are small is found by finding a production environment in which stress is minimized. Made development possible. As a result, it is possible to provide a carrier having a stable charging performance that imparts sufficient chargeability to the toner and does not cause image contamination such as fogging due to toner scattering due to insufficient charging.

  In addition, a carrier that can maintain a stable charge level that does not hinder image formation even under image forming conditions where it is difficult to maintain a charge level that allows continuous printing of a large number of sheets. Made it possible. As a result, a good toner image can be stably formed at any time.

  The effect of the present invention is that, in a carrier in which the surface of a core particle made of ferrite containing at least magnesium element is coated with a resin, the deformation rate of the core particle is 5% by number or less, and the maximum grain diameter of the core particle surface is 2 μm or more. It is expressed by using core particles of 5 μm or less. The background of finding the core particles having such characteristics is as follows.

  The inventor of the present invention made use of ferrite containing magnesium to produce a carrier core by a conventional method and observed it. The inventors observed that the shape of individual carrier cores was very uneven. The uneven shape of the carrier core has an effect on the toner charging performance. By aligning the carrier shape, all carriers can apply the same level of charging to the toner. Therefore, it was thought that stable toner charging was realized.

  Therefore, the present inventor considers that the cause of the non-uniform shape of the carrier core is due to stress applied in the carrier core manufacturing process, and minimizes firing, which is the largest factor that stresses the carrier core. A carrier core was prepared.

  The inventor also paid attention to the surface properties of the carrier core, and evaluated the surface performance of the carrier core that was able to have a uniform shape and the carrier core that was non-uniform in shape with a scanning electron microscope. When the surface of the carrier core was observed with an electron microscope, the core surface was composed of an infinite number of independent regions (grains), and the carrier core having a uniform shape tended to have a smaller area.

  That is, by the above production method, core particles made of ferrite containing magnesium element having a deforming rate of 5% by number or less and a maximum grain diameter of the core particle surface of 2 μm or more and 5 μm or less can be obtained, and the effect of the present invention can be obtained. It was expressed.

  That is, by setting the deformed ratio of the carrier particles to 5% by number or less, the shape is uniform, so that the thickness of the coating resin coated on the particles becomes more uniform, and the grain diameter on the surface of the core particles is further increased. Since the surface properties of the core particles become smoother by decreasing the size, it becomes possible to impart sufficient charge and uniform charge to the toner.

  The present invention will be described in detail below.

Carrier Characteristics The carrier according to the present invention will be described.

  The carrier according to the present invention has a structure in which the surface of core particles made of ferrite containing at least magnesium element is coated with a resin. The core particles are formed of ferrite containing a magnesium element having a deforming rate of 5% by number or less and a maximum grain diameter on the surface of the core particles of 2 μm or more and 5 μm or less.

The core particles constituting the carrier according to the present invention (hereinafter also referred to as carrier core) are a so-called ferrite substance, containing ferric oxide (Fe ₂ O ₃ ) as a main component and containing at least a magnesium element. is there. Moreover, what contains the manganese element in the said component is also used preferably.

  In the present invention, the deforming rate of the core particles is 5% by number or less. Here, when the specific number of core particles is extracted, the deforming rate indicates the proportion of the core particles having irregular shapes on the basis of the number, and the uniformity of the core particle shape can be known. That is, a uniform core particle having a uniform shape is obtained as the deforming rate is lowered, and conversely, a higher deforming rate means that the shape of the core particle is uneven.

  In the present invention, the deforming rate of the core particles is 5% or less, but by making the shape of the core particles uniform so as to be in the above range, a carrier having uniform charge imparting performance can be obtained. That is, since the shape of the core particles is uniform, a resin layer is formed at the same level on the surface of the core particles, and a large amount of carriers having the same level of charge imparting performance can be obtained, so that stable toner charging can be performed. .

  A specific method for calculating the odd-formation rate is performed according to the following procedure. That is, using a scanning electron microscope (SEM), the core particles are photographed at a magnification of 300 times, and deformed by calculating the ratio of the number of deformed particles defined below in the 500 core particles on the photographic image. Calculate the rate.

  Here, the irregularly shaped particles are core particles having irregular shapes, for example, particles having a crushed shape (having a crushed cross section) or core particles having a protruding portion such as a hump.

  A specific method for defining irregularly shaped particles is shown below. From the 100 images taken from the scanning electron microscope (SEM) image, the “maximum core particle diameter at the horizontal ferret diameter” and the “projection area of the core particle” are measured, and SF-1 is calculated by the following equation: The core particles having SF-1 greater than 130 are defined as irregularly shaped particles.

SF-1 = {(maximum diameter of core particle in horizontal ferret diameter) ² / (projected area of core particle)} × (π / 4) × 100
(However, the projected area refers to the area of the projected image on the plane of the particle.)
Hereinafter, the grain of the carrier will be described.

  In the present invention, the maximum grain diameter on the surface of the carrier particles is 2 μm or more and 5 μm or less.

  When the core particles constituting the carrier according to the present invention are observed with an electron microscope at a magnification of 1500 to 3000, it is confirmed that the surface has a shape such that countless granules are crushed and stuck. In the present invention, an independent region having the crushed shape constituting the core particle surface is called “grain”, and the “maximum grain diameter” is the grain size observed on the core particle surface. The largest grain size is represented by the horizontal ferret diameter. The horizontal ferret diameter refers to the distance between two vertical lines sandwiched between two straight lines (vertical lines) perpendicular to the horizontal direction of the electron micrograph image. The grain diameter of the particle is shown.

  In the present invention, the maximum grain diameter is calculated by the following procedure.

  The measurement method is as follows: a core particle is photographed at a magnification of 3000 times using a scanning electron microscope (SEM), and the image captured by the scanner is applied to an image analyzer “Luzex AP” (manufactured by Nireco). Then, in the photographic field of view, the horizontal ferret diameter of each grain on the surface of the core particle is measured, and the largest grain diameter is extracted from the diameter.

  This measurement is performed for 100 core particles, the average value of the largest grain diameters in each core particle is calculated, and this is set as the maximum grain diameter on the core particle surface.

  In the present invention, the maximum grain diameter on the core particle surface is 2 μm or more and 5 μm or less, preferably 2 μm or more and 4 μm or less. When the maximum grain diameter is in the above range, the surface of the core particle has a uniform roughness, and it becomes easy to uniformly coat the resin. Therefore, it is estimated that an environment capable of uniformly charging the toner can be produced. The

  Moreover, it is difficult to make the maximum grain diameter less than 2 μm in the production of the core particles, and it is not practical because a process such as particle selection is required after the production of the core particles.

  The carrier according to the present invention will be further described.

  The carrier according to the present invention preferably has an average particle size of 20 μm to 40 μm, and more preferably 25 μm to 37 μm. By setting the average particle size within the above range, it is possible to perform appropriate mixing with small-diameter toner that can reproduce fine dot images, so that high-definition toner images can be formed by fully charging small-diameter toner and supporting digitization. It is possible to provide a two-component developer capable of

  The average particle diameter of the carrier can be calculated by a measurement method based on volume. The volume-based average particle diameter of the carrier can be measured by, for example, a laser diffraction particle size distribution measuring apparatus “HELOS (manufactured by Sympathec)” equipped with a wet disperser.

Carrier, the magnetic force is preferably ^{40~70Am 2 / kg, 45~60Am 2 /} kg is more preferable. By setting the magnetic force of the carrier in the above range, the carrier is satisfactorily held by the magnet of the developing device, so that carrier scattering and poor conveyance do not occur.

  The magnetic force of the carrier can be measured by the following procedure, for example. That is, as a measuring device, for example, a highly sensitive vibration sample type magnetometer “VSM-P7-15 type (manufactured by Toei Kogyo Co., Ltd.)” is used, and the measurement magnetic field is 5 kOe and the amount of the sample is 20 to 30 mg. .

  Next, a method for manufacturing a carrier according to the present invention will be described.

  In the present invention, when producing a carrier core, in order to obtain a carrier core having a uniform shape and surface characteristics, it was considered that stress should not be applied as much as possible in the manufacturing process. Then, the present inventors have found a production condition that allows firing to be performed only once, which is a factor for applying the greatest stress.

  The carrier core is produced through a step of granulating and drying the raw material ferrite, followed by baking by heat treatment, and crushing the obtained fired product. In the prior art, in particular, when a carrier core is produced from ferrite containing magnesium, the dispersibility of magnesium is poor, so it is necessary to lengthen the firing time, and firing is performed twice. That is, first, heat treatment at 1200 ° C. to 1500 ° C. called pre-baking is performed, then pulverization is performed, and after granulation and drying, heat treatment at 1100 ° C. to 1400 ° C. is then called main baking. Had gone.

  In the carrier core manufacturing step, the produced fired product is crushed, and the crushed product is classified to obtain a carrier core having a desired particle size. In the crushing step, mechanical stress is applied to the fired product to form fine particles. However, the smaller the particle size of the particles, the greater the load on the fired product. Therefore, the carrier core having a smaller particle size is likely to have a non-uniform shape, and the surface grain tends to be large. As described above, it is presumed that the carrier core having a non-uniform shape and having a large surface grain could not be sufficiently charged with the toner due to the low density of ferrite.

  In the present invention, when producing the carrier core, the carrier core can be produced by one firing because the stress applied by the crushing treatment to the fired product is reduced as much as possible. Therefore, it was considered to create an environment where the magnesium component can be sufficiently sintered by one firing. Specifically, by increasing the amount of raw material added to the slurry used in the production process and increasing the slurry concentration to 70% or higher, the share for magnesium is increased, and the firing temperature is increased while increasing dispersibility. By raising the temperature to 1500 ° C. or higher, the sintering of magnesium was completed even in a short time, and a carrier core with good magnesium dispersibility was obtained.

Hereinafter, a typical manufacturing procedure of the carrier according to the present invention will be described. The carrier core is produced by the following procedure, for example.
(1) Raw material preparation step This is a step of preparing a raw material for producing a ferrite containing magnesium. When producing a ferrite containing magnesium, for example, a compound such as ferric oxide Fe ₃ O ₂ , magnesium hydroxide Mg (OH) ₂ , and manganese carbonate MnCO ₃ is mixed in a predetermined ratio. Mix. The proportion of Mg (OH) ₂ is preferably 10 to 40 mol% in the raw material.
(2) Wet mixing A step of adding slurry to the mixture obtained by the above preparation to form a slurry and adjusting the concentration of the slurry so that the next step can be processed smoothly. It is. In the present invention, by setting the slurry concentration to 70 to 80% by mass, magnesium can be sufficiently sintered by one firing.
(3) Wet pulverization A pulverized product having a predetermined size is obtained in a step of performing pulverization treatment by putting the slurry into an apparatus such as a wet ball mill or a wet vibration mill. A pulverized product having a size of 15 μm or less is obtained, and a fine pulverized product having a size of 2 μm or less can be produced.
(4) Granulation / Drying Step In this step, the pulverized processed product is supplied to a spray dryer, and the pulverized processed product is ejected by a spray dryer and dried to produce a ferrite granulated product having a predetermined particle size. (5) Firing step This is a step in which the ferrite granulated material is put into a firing furnace and subjected to heat treatment, and the granulated material is fired. In the present invention, the granulated material prepared from the aforementioned slurry is heated to 1500 ° C or higher. By heating at a temperature, magnesium can be sufficiently sintered by one firing. The firing time is 1 to 24 hours, often 2 to 10 hours.
(6) Crushing step This is a step of crushing the fired product using a crusher.
(7) Sieving step This is a step of obtaining a carrier core by sieving the crushed material and extracting ferrite having a predetermined particle size. Examples of the sieving method include a sieve filtration method, a sedimentation method, and a method using wind power.

  The carrier core thus obtained can be coated with resin as it is, but it is also possible to adjust the electrical resistivity by heating the carrier core in an air atmosphere and performing an oxide film treatment. . In the oxide film treatment, for example, the electrical resistivity of the carrier core may be increased by performing a heat treatment at a temperature of 300 ° C. to 700 ° C. for 1 to 180 minutes using a rotary electric furnace or a batch electric furnace. it can.

  Examples of the resin that can be coated on the surface of the carrier core include olefin resins, styrene resins, styrene acrylic resins, acrylic resins, silicone resins, ester resins, and fluorine-containing polymer resins. Moreover, as a resin coating method, there are a wet coating method and a dry coating method.

  The coating layer preferably covers 70% or more of the surface of the core particles (carrier core) in terms of surface area.

  The spray coating method, which is a wet coating method, is a method in which a coating solution in which a coating resin is dissolved in a solvent is spray-coated on the surface of a carrier core and then dried to produce a coating. The immersion coating method, which is also a wet coating method, is a method in which a carrier core is immersed in a coating solution in which a coating resin is dissolved in a solvent, followed by coating treatment, and then dried.

  Examples of the dry coating method include a method in which resin particles are deposited on the surface of a carrier core to be coated, and a mechanical impact force is applied to weld or soften the resin particles.

  There is also a coating method called a polymerization method. This is a method of coating by immersing a carrier core in a coating solution in which a polymerizable monomer is dissolved in a solvent and then applying a polymerization reaction by applying heat or the like.

In the present invention, the carrier can be used as a two-component developer obtained by mixing the toner with a toner having a median diameter (D ₅₀ ) of 3 μm or more and 8 μm or less on a volume basis.

  With the advancement of digital technology, small-diameter toner capable of faithfully reproducing fine dot images has been studied, and a small-diameter carrier capable of appropriately charging such a small-diameter toner has been demanded. It was done. The carrier made of ferrite containing magnesium can reduce the diameter of the carrier, and can provide a two-component developer suitable for forming a fine dot image.

The median diameter (D ₅₀ ) based on the volume of toner can be measured and calculated using a device in which a computer system for data processing is connected to Multisizer 3 (manufactured by Beckman Coulter).

  As a measurement procedure, 0.02 g of toner is blended with 20 ml of a surfactant solution (for example, a surfactant solution obtained by diluting a neutral detergent containing a surfactant component 10 times with pure water for the purpose of dispersing the toner). After that, ultrasonic dispersion is performed for 1 minute to prepare a toner dispersion. This toner dispersion is poured into a beaker containing ISOTON II (manufactured by Beckman Coulter) in a sample stand with a pipette until a measurement concentration of 5 to 10% is reached, and the measuring machine count is set to 25,000. To do. The aperture size of the multisizer 3 is 50 μm.

  The toner image developed with the carrier or the two-component developer according to the present invention is suitably used in an image forming apparatus having a contact-type fixing device that passes through a heating member and fixes the toner image.

  The image forming apparatus will be described below.

  FIG. 1 is a schematic view showing an example of an image forming apparatus used in the present invention.

  In FIG. 1, 1Y, 1M, 1C and 1K are photosensitive members, 4Y, 4M, 4C and 4K are developing means, 5Y, 5M, 5C and 5K are primary transfer rolls as primary transfer means, and 5A is a secondary transfer. Secondary transfer rolls as means, 6Y, 6M, 6C and 6K are cleaning means, 7 is an intermediate transfer member unit, 24 is a heat roll type fixing device, and 70 is an intermediate transfer member.

  This image forming apparatus is called a tandem color image forming apparatus, and includes a plurality of sets of image forming units 10Y, 10M, 10C, and 10K, an endless belt-shaped intermediate transfer body unit 7 as a transfer unit, and a recording member P. An endless belt-shaped sheet feeding / conveying means 21 and a heat roll type fixing device 24 as a fixing means. A document image reading device SC is disposed on the upper part of the main body A of the image forming apparatus.

  As one of the different color toner images formed on each photoconductor, an image forming unit 10Y that forms a yellow image includes a drum-shaped photoconductor 1Y as a first photoconductor, and a periphery of the photoconductor 1Y. A charging unit 2Y, an exposure unit 3Y, a developing unit 4Y, a primary transfer roll 5Y as a primary transfer unit, and a cleaning unit 6Y. An image forming unit 10M that forms a magenta image as another different color toner image is disposed around a drum-shaped photoconductor 1M as a first photoconductor, and the photoconductor 1M. A charging unit 2M, an exposure unit 3M, a developing unit 4M, a primary transfer roll 5M as a primary transfer unit, and a cleaning unit 6M. In addition, an image forming unit 10C that forms a cyan image as one of different toner images of different colors is arranged around a drum-shaped photoconductor 1C as a first photoconductor, and around the photoconductor 1C. The charging unit 2C, the exposure unit 3C, the developing unit 4C, the primary transfer roll 5C as the primary transfer unit, and the cleaning unit 6C are provided. Further, an image forming unit 10K that forms a black image as one of other different color toner images is disposed around a drum-shaped photoconductor 1K as a first photoconductor, and around the photoconductor 1K. It has a charging means 2K, an exposure means 3K, a developing means 4K, a primary transfer roll 5K as a primary transfer means, and a cleaning means 6K.

  The endless belt-like intermediate transfer body unit 7 has an endless belt-like intermediate transfer body 70 as an intermediate transfer endless belt-like second image carrier that is wound around a plurality of rolls and is rotatably supported.

  Each color image formed by the image forming units 10Y, 10M, 10C, and 10K is sequentially transferred onto the rotating endless belt-shaped intermediate transfer body 70 by the primary transfer rolls 5Y, 5M, 5C, and 5K, and is combined. A colored image is formed. A recording member P such as a sheet as a transfer material accommodated in the sheet feeding cassette 20 is fed by the sheet feeding / conveying means 21, passes through a plurality of intermediate rolls 22 A, 22 B, 22 C, 22 D, and a registration roll 23, and is secondary. A color image is transferred onto the recording member P at a time by being conveyed to a secondary transfer roll 5A as a transfer means. The recording member P to which the color image has been transferred is fixed by the heat roll type fixing device 24, is sandwiched by the paper discharge roll 25, and is placed on the paper discharge tray 26 outside the apparatus.

  On the other hand, after the color image is transferred to the recording member P by the secondary transfer roll 5A, the residual toner is removed from the endless belt-shaped intermediate transfer body 70 from which the recording member P is separated by the curvature by the cleaning means 6A.

  During the image forming process, the primary transfer roll 5K is always in pressure contact with the photoreceptor 1K. The other primary transfer rolls 5Y, 5M, and 5C are in pressure contact with the corresponding photoreceptors 1Y, 1M, and 1C, respectively, only during color image formation.

  The secondary transfer roll 5A comes into pressure contact with the endless belt-shaped intermediate transfer body 70 only when the recording member P passes through the secondary transfer roll 5A and secondary transfer is performed.

  Further, the housing 8 can be pulled out from the apparatus main body A through the support rails 82L and 82R.

  The housing 8 includes image forming units 10Y, 10M, 10C, and 10K, and an endless belt-shaped intermediate transfer body unit 7.

  The image forming units 10Y, 10M, 10C, and 10K are arranged in tandem in the vertical direction. An endless belt-shaped intermediate transfer body unit 7 is disposed on the left side of the photoreceptors 1Y, 1M, 1C, and 1K in the figure. The endless belt-shaped intermediate transfer body unit 7 includes an endless belt-shaped intermediate transfer body 70 that can be rotated by winding rolls 71, 72, 73, 74, and 76, primary transfer rolls 5Y, 5M, 5C, and 5K, and a cleaning unit. 6A.

  The image forming units 10Y, 10M, 10C, and 10K and the endless belt-shaped intermediate transfer body unit 7 are integrally pulled out from the main body A by the drawer operation of the housing 8.

  In this way, toner images are formed on the photoreceptors 1Y, 1M, 1C, and 1K by charging, exposure, and development, and the toner images of the respective colors are superimposed on the endless belt-shaped intermediate transfer body 70, and are collectively applied to the recording member P. The image is transferred, and fixed by pressing and heating with a heat roll type fixing device 24 and fixed. The photoreceptors 1Y, 1M, 1C, and 1K after transferring the toner image to the recording member P are cleaned with the cleaning device 6A to remove the toner remaining on the photoreceptor, and then the above-described charging, exposure, and development cycle. The next image formation is performed.

  The embodiments of the present invention will be specifically described below with reference to examples, but the present invention is not limited thereto.

1. Production of core particles (Production of core particles A)
The raw materials were prepared so that Fe ₂ O ₃ was 50 mol%, Mg (OH) ₂ was 25 mol%, and MnCO ₃ was 25 mol%. A 1% by mass binder (trade name: San Nopco SN Desperthant 5468) and water were added to this mixture to prepare a slurry having a concentration of 80% by mass. The prepared slurry was wet pulverized with a wet ball mill, and the pulverized product was put into a spray dryer to prepare a granulated product, which was then dried.

  Next, the granulated material was put into a firing furnace, and fired at 1600 ° C. (first firing) in an air atmosphere for 3 hours. The obtained fired product was pulverized and sieved to obtain “core particles A”. Table 1 shows the average particle diameter, deformation rate, and maximum grain diameter of the obtained core particles A.

(Preparation of core particles B to E)
“Core particles B to E” were obtained in the same manner except that the production conditions (slurry concentration, firing conditions) of the core particles A were changed as shown in Table 1.

(Preparation of core F)
The raw materials were prepared at the same compounding ratio as the core particles A were produced. 1% binder (trade name: San Nopco SN Desperthant 5468) and water were added to this mixture to prepare a slurry having a concentration of 70% by mass. The prepared slurry was wet pulverized with a wet ball mill, and the pulverized product was put into a spray dryer to prepare a granulated product, which was then dried.

  Next, the granulated product was put into a firing furnace, and preliminary firing (first firing) was performed for 3 hours at 1100 ° C. in an air atmosphere. The obtained calcined product was cooled and pulverized to a size of about 1 μm with a vibration mill. A slurry obtained from the powder obtained by pulverization was prepared by the same method as described above, wet pulverized by a wet ball mill, and then charged into a spray dryer to prepare a granulated product, followed by drying treatment.

  Next, the granulated product was put into a firing furnace, and firing (second firing) was performed at 1450 ° C. in an air atmosphere for 3 hours. The obtained fired product was pulverized and sieved to obtain “core particles F”.

(Preparation of core particles G and H)
“Core particles G and H” were obtained in the same manner except that the production conditions (slurry concentration and firing conditions) of the core particles F were changed as shown in Table 1.

  Table 1 shows the production conditions of the core particles, the average particle diameter of the obtained particles, the deformation rate, and the maximum grainin diameter.

(Creation of carrier)
100 parts by mass of the above-prepared “core particles A to H” and 5 parts by mass of copolymer resin fine particles of cyclohexyl methacrylate / methyl methacrylate (copolymerization ratio 5/5) are put into a high-speed mixer equipped with stirring blades. Then, the mixture was stirred and mixed at 120 ° C. for 30 minutes to form a resin coating layer on the surface of the core particles by the action of mechanical impact force, and “carriers A to H” coated with the resin were produced.

(Toner preparation)
Three types: black toner (referred to as toner 1) having a median diameter (D ₅₀ ) of 3.0 μm on the volume basis of toner, black toner (referred to as toner 2) of 6.0 μm, and black toner (referred to as toner 3) of 9.0 μm “Toners 1 to 3” were prepared.

(Preparation of developer)
100 parts by mass of “Carriers A to H” prepared above and “Toners 1 to 3” prepared above were mixed with a Henschel mixer (Mitsui Miike Chemical Co., Ltd.) at the toner concentration (mass%) shown in Table 2. ) ”To prepare“ Developers 1 to 8 ”.

Evaluation of Actual Photographs “Developers 1 to 8” prepared above were put into an image forming apparatus “bizhub C450 (manufactured by Konica Minolta Business Technologies)”, and the pixels were used in an environment of normal temperature and normal humidity (25 ° C., 50% RH). A black image with a rate of 10% (a character image with a pixel rate of 6%, a human face photo, a solid white image, and an original image with a solid black image of 1% each) is printed on A4 high-quality paper in a single-sheet intermittent mode. Ten thousand sheets were printed.

(Fog evaluation)
The fog evaluation was evaluated by the density difference between the white paper that was not printed and the white background after printing. First, with respect to blank paper that is not printed, the absolute image density at 20 locations is measured using a reflection densitometer “RD-918” (manufactured by Macbeth) and averaged to obtain the blank paper density. Next, the absolute image density at 20 locations was similarly measured and averaged for the white background portion of the 50,000th printed image, and the value obtained by subtracting the white paper density from this average density was evaluated as the fog density. If the fog density is 0.01 or less, it can be said that fog is practically no problem.

(Electric charge evaluation)
The charge amount at the initial stage and after the completion of printing 50,000 sheets was measured. The charge amount evaluation was performed based on the difference between the initial stage and the end of printing 50,000 sheets. The charge amount is a value obtained by the following blow-off method.

  The measurement of the charge amount by the blow-off method was performed using a blow-off charge amount measuring device “TB-200 (manufactured by Toshiba Chemical Co.)”.

  The two-component developer to be measured was set in the charge amount measuring device equipped with a 400 mesh stainless steel screen, and blown with nitrogen gas for 10 seconds under the condition of a blow pressure of 50 kPa, and the charge was measured. The charge amount (μC / g) was calculated by dividing the measured charge by the flying toner mass.

  If the charge amount difference is 5 μC / g or less after the initial printing and after the completion of printing 50,000 sheets, there is no problem.

(Toner scattering)
The evaluation of toner scattering was based on the result of visually observing the toner spillage around the developing device and the contamination inside the apparatus due to toner scattering after the completion of printing 50,000 sheets and the stain defect of the printed image due to toner scattering.

Evaluation criteria A: No spillage or toner contamination in the machine due to toner spilling, and no smudge defects in the printed image due to toner scatter ○: Slight toner spillage or toner spillage in the machine due to toner scattering, but smudge defects in the printed image due to toner scattering No, practically no problem level ×: Level in which in-machine contamination due to toner spillage and toner scattering is severe, and contamination of the printed image due to toner scattering is recognized, causing a practical problem.

  Table 2 shows the evaluation results.

  From Table 2, it can be seen that "Examples 1 to 5" according to the present invention have a small variation in charge amount, a small fog value, and no problem with toner scattering. On the other hand, “Comparative Examples 1 to 3” for comparison shows that there is a problem with any of the evaluation items.

1 is a schematic diagram illustrating an example of an image forming apparatus used in the present invention.

Explanation of symbols

1Y, 1M, 1C, 1K Photoconductors 4Y, 4M, 4C, 4K Developing means 5Y, 5M, 5C, 5K Primary transfer roller as primary transfer means 5A Secondary transfer roller as secondary transfer means 6Y, 6M, 6C, 6K Cleaning means 7 Endless belt-shaped intermediate transfer body unit

Claims (8)

In the method for producing a carrier obtained by coating a resin on the surface of core particles made of ferrite containing at least magnesium element,
The core particles are formed by one firing, the firing temperature in the firing is 1500 ° C. or more, and the slurry concentration used in the firing is 70% by mass or more,
The core particles have a deformed ratio, which is a proportion of deformed particles defined below, of 5% by number or less, and a maximum grain diameter on the surface of the core particles is 2 μm or more and 5 μm or less. .
The irregularly shaped particles are measured by measuring the “maximum core particle diameter at the horizontal ferret diameter” and the “projection area of the core particle” from 100 images captured from a scanning electron microscope (SEM) image, and using the following formula: SF-1 is calculated and defined to be a core particle with SF-1 greater than 130.
SF-1 = {(maximum diameter of core particle in horizontal ferret diameter) ² / (projected area of core particle)} × (π / 4) × 100 (provided that the projected area is the projection of the particle onto the plane) The area of the image.) The method for producing a carrier according to claim 1, wherein an average particle diameter of the carrier is 20 μm or more and 40 μm or less. The method for producing a carrier according to claim 1, wherein the core particles contain a manganese element. The carrier manufacturing method according to claim 1, wherein the maximum grain diameter is 2 µm or more and 4 µm or less . The carrier manufacturing method according to claim 2 , wherein an average particle diameter of the carrier is 25 μm or more and 37 μm or less . The method of manufacturing a carrier according to claim 1 , wherein the carrier has a magnetic force of 40 to 70 Am ² / kg . The method of manufacturing a carrier according to claim 6 , wherein the magnetic force of the carrier is 45 to 60 Am ² / kg . The method for producing a carrier according to claim 1, wherein the resin layer covering the surface of the core particle covers the surface of the core particle by 70% or more by surface area .

Images