JP5715656B2 - Carrier core material for electrophotographic developer, production method thereof, carrier for electrophotographic developer, and electrophotographic developer - Google Patents

Description

  The present invention relates to a carrier core material for an electrophotographic developer (hereinafter sometimes simply referred to as “carrier core material”), a production method thereof, a carrier for an electrophotographic developer (hereinafter also simply referred to as “carrier”), And an electrophotographic developer (hereinafter sometimes simply referred to as “developer”), and in particular, an electrophotographic developer carrier provided in an electrophotographic developer used in a copying machine, an MFP (Multifunctional Printer), or the like. The present invention relates to a core material, a manufacturing method thereof, a carrier for an electrophotographic developer provided in an electrophotographic developer, and an electrophotographic developer.

  In a copying machine, MFP, etc., as a dry development method in electrophotography, a one-component developer using only toner as a component of developer and a two-component developer using toner and carrier as components of developer are provided. is there. In any of the development methods, toner charged to a predetermined charge amount is supplied to the photoreceptor. Then, the electrostatic latent image formed on the photosensitive member is visualized with toner and transferred to a sheet. Thereafter, the visible image with toner is fixed on the paper to obtain a desired image.

  Here, the development in the two-component developer will be briefly described. A predetermined amount of toner and a predetermined amount of carrier are accommodated in the developing device. The developing device includes a rotatable magnet roller in which a plurality of S poles and N poles are alternately provided in the circumferential direction, and a stirring roller that stirs and mixes the toner and the carrier in the developing device. A carrier made of magnetic powder is carried by a magnet roller. A linear magnetic brush made of carrier particles is formed by the magnetic force of the magnet roller. A plurality of toner particles adhere to the surface of the carrier particles by frictional charging by stirring. Toner is supplied to the surface of the photoconductor by rotating the magnet roller so that the magnetic brush is applied to the photoconductor. In a two-component developer, development is performed in this way.

  As for the toner, the toner in the developing device is sequentially consumed by fixing to the paper, so new toner corresponding to the consumed amount is supplied from time to time to the developing device from the toner hopper attached to the developing device. The On the other hand, the carrier is not consumed by development and is used as it is until the end of its life. The carrier which is a constituent material of the two-component developer includes a toner charging function and an insulating property for efficiently charging the toner by frictional charging by stirring, a toner transporting ability to appropriately transport and supply the toner to the photoreceptor, etc. Various functions are required.

  In recent years, the above-described carrier is composed of a core material, that is, a carrier core material constituting a core portion, and a resin provided so as to cover the surface of the carrier core material.

  Here, the carrier core material that is carried by the magnet roller and serves as the core of the carrier that is agitated and mixed in the developing device has good magnetic characteristics and electrical characteristics from the viewpoint of improving the frictional charging performance with respect to the toner. It is also desired to be good. Techniques relating to the shape of the carrier core material that requires such various characteristics are disclosed in Japanese Patent Application Laid-Open No. 2012-168284 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2011-141542 (Patent Document 2). Yes.

JP 2012-168284 A JP 2011-141542 A

  The electrostatic charge developing carrier disclosed in Patent Document 1 contains at least magnetic particles, and the average interval Sm of the irregularities on the surface of the magnetic particles and the maximum height Ry of the surface of the magnetic particles are 3.6 μm ≦ Sm ≦ 8. It is assumed that 0 μm and 0.5 μm ≦ Ry ≦ 1.0 μm. According to Patent Document 1, it is described that the occurrence of image unevenness is suppressed as compared with the case where the average interval Sm of the unevenness on the surface of the magnetic particles or the maximum height Ry is out of the above range.

  In addition, the electrostatic latent image developing carrier disclosed in Patent Document 2 is composed of magnetic particles having irregularities on the surface and conductive metal nanoparticles provided on the surface of the magnetic particles, and the surface of the magnetic particles on the surface. A conductive layer having irregularities along with the irregularities, and a resin layer provided on the conductive layer. Patent Document 2 discloses a magnetic particle having a surface roughness Ra of 0.1 μm or more and 10 μm or less and a surface roughness Sm of 0.1 μm or more and 10 μm or less.

  However, the carriers having magnetic particles disclosed in Patent Document 1 and Patent Document 2 described above may not be compatible with recent image forming apparatuses such as copying machines. That is, in a copying machine that employs a non-contact developing system, a copying machine that employs a hybrid developing system, or a so-called high-speed copying machine that can form 60 to 70 images per minute, for example, A lot of coated resin is peeled off due to the influence of long-term use, and as a result, there is a risk of causing problems such as carrier scattering. In addition, if the amount of resin coating is increased, such as complete coating in consideration of peeling of the resin over a long period of use, there is a risk of causing image density unevenness due to an increase in the amount of resin coating.

  An object of the present invention is to provide a carrier core material for an electrophotographic developer that can be used stably over a long period of time.

  Another object of the present invention is to provide a method for producing a carrier core material for an electrophotographic developer capable of producing a carrier core material for an electrophotographic developer that can be used stably over a long period of time. is there.

  Still another object of the present invention is to provide a carrier for an electrophotographic developer that can be used stably over a long period of time.

  Still another object of the present invention is to provide an electrophotographic developer capable of stably forming an image of good image quality even after long-term use.

  As a means for obtaining a carrier core material that can be used stably over a long period of time, the inventors of the present application first made a core of manganese and iron in order to ensure good magnetic characteristics as basic characteristics. The main component of the composition was considered. And from the viewpoint of ensuring ease of control of the uneven shape on the particle surface of the carrier core material, the inventors have come up with the idea of containing a small amount of strontium as a raw material.

  Furthermore, in ensuring stable use over a long period of time, attention was paid to the degree of exposure of the particle surface of the carrier core material in the carrier core material that is later coated with a resin. That is, if the coverage area of the particle surface of the carrier core material by the resin is small and the exposed area of the carrier core material is too large, the resistance of the carrier core material itself is reduced, which causes carrier scattering. On the other hand, if the exposed area of the carrier core material is too small, such as complete coating, the charge charged by frictional charging is difficult to leak, resulting in a decrease in the ability to impart charge to the toner and causing a memory image. . Of course, it is preferable that the resin coated on the particle surface of the carrier core material is not peeled off as much as possible. That is, it is preferable that the resin has good binding properties to the particle surface of the carrier core material.

  Here, the inventors of the present application pay attention to the uneven shape on the particle surface of the carrier core material that covers a certain area by the resin, and in particular, the grains that form the uneven shape, that is, so-called peak portions of crystal grains. We focused on the difference from the valley and the steepness of the slope of the peak between the grains. Specifically, on the particle surface of the carrier core material, the maximum height Rz serving as an index of the difference between the grain peak and valley parts, and the root mean square serving as an index of the steepness of the slope of the peak between the grains. Attention was paid to the inclination angle RΔq. Then, the maximum height Rz and the root mean square inclination angle RΔq were intensively studied, and the following configuration was adopted.

  That is, in one aspect of the present invention, the carrier core material for an electrophotographic developer is a carrier core material for an electrophotographic developer containing manganese, iron, and strontium as a core composition, and the carrier for an electrophotographic developer The average of the maximum height Rz of the particle group constituting the core material is 2.00 μm or more and 3.50 μm or less, and the average of the root mean square inclination angle RΔq of the particle group constituting the carrier core material for the electrophotographic developer is 0.70 or more and 1.00 or less.

  Such a carrier core material for an electrophotographic developer can be used stably over a long period of time because an appropriate uneven shape is formed on the particle surface of the carrier core material.

  Moreover, you may comprise so that the average of the root mean square inclination | tilt angle R (DELTA) q of the particle group which comprises the carrier core material for electrophotographic developers may be 0.72 or more and 0.86 or less. By comprising in this way, it can be excellent in the viewpoint of carrier scattering and coat peeling.

Here, when manufacturing the carrier core material of the above-described configuration, the inventors of the present application have derived the following configuration as one form. First, in the slurrying step of slurrying the raw material, the carrier core in which the volume particle size of the slurry raw material, in particular, the volume particle size D ₉₀ indicating 90% of the particle size distribution is finally obtained by the firing step or the like. It paid attention to affecting the maximum height Rz of the particle group of the material and the root mean square inclination angle RΔq of the particle group. Then, as defined above a certain value the value of the volume particle diameter D ₉₀ of the slurry feed.

  Further, the inventors of the present invention added a small amount of strontium in the process of ferritization and sintering by firing, from the viewpoint of controlling the uneven shape of the particle surface of the carrier core material, and partially strontium ferrite in the firing process. The synthesis of magnetoplumbite, that is, the formation of a hexagonal crystal structure was considered. And in order to make the average of the maximum height Rz of the particle group and the average of the root mean square inclination angle RΔq of the particle group in the above-mentioned range for the uneven shape on the particle surface of the carrier core material, Two-stage firing is performed, a first firing step in which firing is performed in an atmosphere having a low temperature and a high oxygen concentration, and a second firing step in which firing is performed in an atmosphere having a relatively high temperature and a low oxygen concentration. I came up with the idea that it should be.

That is, in another aspect of the present invention, a method for producing a carrier core material for an electrophotographic developer is a method for producing a carrier core material for an electrophotographic developer containing manganese, iron, and strontium as a core composition, Obtained by slurrying a raw material containing manganese, a raw material containing iron, and a raw material containing strontium, a granulating step of granulating the resulting mixture after the slurrying step, and a granulating step A firing step for firing the granulated product, and the firing step is performed at 600 ° C. to 900 ° C. for 0.5 hours to 1.5 hours in an atmosphere having an oxygen concentration of 10.0% or more. And a first baking step in which baking is performed at a temperature of 1200 ° C. or more and 0.5 hours or more and 3.0 hours or less in an atmosphere having an oxygen concentration of more than 1.0% and less than 5.0%. And a second firing step for firing a time, slurrying step, starting materials containing manganese, raw material containing iron, and the volume particle diameter D ₉₀ of the mixed slurry of the raw material comprising strontium or more 15.0μm This is a step of making a slurry.

  According to such a method for producing a carrier core material, an appropriate irregular shape is formed on the particle surface of the carrier core material, and a carrier core material that can be used stably over a long period of time can be obtained.

  Moreover, you may comprise so that the cooling process which cools to room temperature may be included between a 1st baking process and a 2nd baking process.

  In still another aspect of the present invention, the electrophotographic developer carrier is an electrophotographic developer carrier used for an electrophotographic developer, and is any one of the above-described carrier cores for an electrophotographic developer. And a resin that covers the surface of the carrier core material for an electrophotographic developer.

  Since such a carrier core material for an electrophotographic developer includes the carrier core material for an electrophotographic developer having the above-described configuration, it can be used stably over a long period of time.

  In still another aspect of the present invention, the electrophotographic developer is an electrophotographic developer used for electrophotographic development, and the friction between the electrophotographic developer carrier and the electrophotographic developer carrier described above. And a toner capable of being charged in electrophotography by charging.

  Since such an electrophotographic developer includes the electrophotographic developer carrier having the above-described configuration, the electrophotographic developer can be used stably over a long period of time.

  The carrier core material for an electrophotographic developer according to the present invention can be used stably over a long period of time because an appropriate uneven shape is formed on the particle surface of the carrier core material.

  The method for producing a carrier core material for an electrophotographic developer according to the present invention can produce a carrier core material for an electrophotographic developer that can be used stably over a long period of time.

  The electrophotographic developer carrier according to the present invention can be used stably over a long period of time.

  In addition, the electrophotographic developer according to the present invention can be used stably over a long period of time.

It is a laser micrograph which shows the external appearance of the carrier core material which concerns on one Embodiment of this invention. It is a schematic sectional drawing which shows the external appearance of the carrier core material which concerns on one Embodiment of this invention. It is a schematic sectional drawing which shows the external appearance of the carrier which concerns on one Embodiment of this invention. It is a flowchart which shows a typical process in the manufacturing method which manufactures the carrier core material which concerns on one Embodiment of this invention. It is a graph which shows the rough relationship between the temperature and time in a baking process. 6 is a laser micrograph showing the appearance of a carrier core material according to Comparative Example 2. 6 is a laser micrograph showing the appearance of a carrier core material according to Comparative Example 4. It is the schematic which shows the particle | grain surface of a carrier core material. It is a graph which shows the relationship between the average of the maximum height Rz of the particle group which comprises a carrier core material, and the average of the root mean square inclination-angle R (DELTA) q of the particle group which comprises a carrier core material. It is a conceptual diagram which shows the state of resin coat | covered on the surface of the carrier core material with a high average value of maximum height Rz. It is a conceptual diagram which shows the state of resin coat | covered on the surface of the carrier core material with a low average value of maximum height Rz. It is a conceptual diagram which shows the state of resin coat | covered on the surface of a carrier core material with the high average value of root mean square inclination-angle R (DELTA) q. It is a conceptual diagram which shows the state of resin coat | covered on the surface of a carrier core material with the low average value of root mean square inclination-angle R (DELTA) q.

  Embodiments of the present invention will be described below with reference to the drawings. First, a carrier core material according to an embodiment of the present invention will be described. FIG. 1 is a laser micrograph showing the appearance of a carrier core material according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing a carrier core material according to an embodiment of the present invention. The cross section in FIG. 2 schematically shows the carrier core material shown in FIG. 1 from the viewpoint of easy understanding.

  With reference to FIG. 1 and FIG. 2, the outer shape of the carrier core material 11 according to one embodiment of the present invention is a substantially spherical shape. The particle diameter of the carrier core material 11 according to an embodiment of the present invention is about 35.0 μm, and has an appropriate particle size distribution. The above-mentioned particle diameter means a volume average particle diameter. The particle size is arbitrarily set depending on required developer characteristics, yield in the manufacturing process, and the like.

  Here, on the surface 12 of the carrier core material 11, a minute uneven shape is formed. Specifically, on the surface 12 of the carrier core material 11, there are a recessed portion 13 having a partially recessed shape and a protruding portion 14 having a shape protruding relatively to the outer diameter side with respect to the recessed portion 13. Is formed. In FIG. 2, the minute uneven shape is exaggerated from the viewpoint of easy understanding.

  Here, the carrier core material 11 is a carrier core material 11 containing manganese, iron, and strontium as a core composition, and the average of the maximum height Rz of the particle group constituting the carrier core material 11 is 2.00 μm or more. 3. The average of the root mean square inclination angle RΔq of the particle group constituting the carrier core material 11 is 0.70 or more and 1.00 or less.

  Such a carrier core material 11 has an appropriate concavo-convex shape on the particle surface of the carrier core material 11, specifically, for example, a difference between an appropriate peak portion and a valley portion in a grain, and an inclination of a peak portion having an appropriate steep degree. Therefore, when the surface is later coated with a resin, the possibility that the coated resin may be peeled off during long-term use can be reduced. That is, the binding property of the resin to the particle surface of the carrier core material can be improved. In addition, it is possible to ensure a certain amount of exposed area of the carrier core material and appropriately leak electric charges, and it is possible to secure an area covered with a resin that can maintain the charge amount in use over a long period of time. Therefore, it can be used stably over a long period of time. This will be described later.

  FIG. 3 is a schematic sectional view showing a carrier according to an embodiment of the present invention. Referring to FIG. 3, the outer shape of the carrier 15 according to the embodiment of the present invention is substantially spherical as in the carrier core material 11. The carrier 15 is obtained by thinly coating the surface 16 of the carrier core material 11 with a resin 16, that is, the particle diameter of the carrier 15 is almost the same as that of the carrier core material 11. Unlike the carrier core material 11, the surface 17 of the carrier 15 is almost entirely covered with the resin 16, but in a part of the region 18, the surface 12 of the carrier core material 11 itself is exposed. is there.

  The developer according to an embodiment of the present invention is composed of the carrier 15 shown in FIG. 3 and toner (not shown). The outer shape of the toner is also substantially spherical. The toner is mainly composed of a styrene acrylic resin or a polyester resin, and contains a predetermined amount of pigment, wax or the like. Such a toner is manufactured by, for example, a pulverization method or a polymerization method. For example, a toner having a particle diameter of about 5.0 μm, which is about one seventh of the particle diameter of the carrier 15, is used. Further, the blending ratio of the toner and the carrier 15 is also arbitrarily set according to the required developer characteristics and the like. Such a developer is produced by mixing a predetermined amount of carrier 15 and toner with an appropriate mixer.

  Next, the manufacturing method which manufactures the carrier core material which concerns on one Embodiment of this invention is demonstrated. FIG. 4 is a flowchart showing typical steps in the manufacturing method for manufacturing the carrier core material according to the embodiment of the present invention. Hereafter, the manufacturing method of the carrier core material which concerns on one Embodiment of this invention is demonstrated along FIG.

  First, a raw material containing iron, a raw material containing manganese, and a raw material containing strontium are prepared. And the prepared raw material is mix | blended with a suitable compounding ratio according to the characteristic requested | required, and this is mixed (FIG. 4 (A)). Here, an appropriate blending ratio is a blending ratio in which the content of iron, the content of manganese, and the content of strontium are targeted in the finally obtained carrier core material.

About the iron raw material which comprises the carrier core material which concerns on one Embodiment of this invention, what is necessary is just metallic iron or its oxide. Specifically, Fe ₂ O ₃ , Fe ₃ O ₄ , Fe, and the like that exist stably at normal temperature and pressure are preferably used. The manganese raw material may be metal manganese or an oxide thereof. Specifically, metals Mn, MnO ₂ , Mn ₂ O ₃ , Mn ₃ O ₄ , and MnCO ₃ that exist stably at normal temperature and pressure are preferably used. Moreover, as a raw material containing strontium, metal strontium or an oxide thereof is preferably used. Specific examples include SrCO ₃ which is a carbonate. Note that the above raw materials (iron raw material, manganese raw material, strontium raw material, etc.) may be used as raw materials by calcining and pulverizing raw materials obtained by mixing the raw materials, respectively, or the desired composition.

  Next, the mixed raw material is slurried (FIG. 4B). That is, these raw materials are weighed according to the target composition of the carrier core material and mixed to obtain a slurry raw material.

Here, the slurrying is adjusted such that the volume particle size D ₉₀ indicating 90% of the particle size distribution in the volume particle size of the slurry raw material is 15 μm or more. For this adjustment, for example, the slurryed raw material is pulverized by a wet ball mill, a wet bead mill or the like, and the value of the volume particle size D ₉₀ is adjusted by controlling the pulverization strength, pulverization time, pulverization frequency, etc. during pulverization. I do.

  In addition, in the manufacturing process at the time of manufacturing the carrier core material according to the present invention, a reducing agent may be further added to the slurry raw material described above in order to advance the reduction reaction in a part of the baking process described later. As the reducing agent, carbon powder, polycarboxylic acid organic substance, polyacrylic acid organic substance, maleic acid, acetic acid, polyvinyl alcohol (PVA (polyvinyl alcohol)) organic substance, and a mixture thereof are preferably used.

  Here, water is added to the slurry raw material described above and mixed and stirred, so that the solid concentration is 40% by weight or more, preferably 50% by weight or more. If the solid content concentration of the slurry raw material is 50% by weight or more, it is preferable because the strength of the granulated pellet can be maintained.

  Next, the slurryed raw material is granulated (FIG. 4C). Granulation of the slurry obtained by mixing and stirring is performed using a spray dryer.

  The atmospheric temperature during spray drying may be about 100 to 300 ° C. Thereby, the granulated powder whose particle diameter is 10-200 micrometers can be obtained in general. The obtained granulated powder is preferably adjusted for particle size at this point in consideration of the final particle size of the product by removing coarse particles and fine powder using a vibration sieve or the like.

  Thereafter, the granulated product is fired. Here, the firing step is a first firing step in which firing is performed at 600 ° C. to 900 ° C. for 0.5 hours to 1.5 hours in an atmosphere having an oxygen concentration of 10.0% or more ( 4D), a cooling step (FIG. 4E) for cooling to room temperature between the first baking step and the second baking step, and after the cooling step, an oxygen concentration of 1. A second baking step (FIG. 4F) in which baking is performed at a temperature of 1200 ° C. or more and a holding time of 0.5 hours or more and 3.0 hours or less in an atmosphere of more than 0% and less than 5.0%. including.

Here, the firing step will be described with reference to FIG. FIG. 5 is a graph showing a schematic relationship between temperature and time in the firing step. In FIG. 5, the vertical axis represents temperature, and the horizontal axis represents time. With reference to FIG. 5, first, the first firing step will be described. At time T ₀ , the temperature rise is started from a temperature A ₀ that is room temperature, for example, about 25 ° C. Then, a predetermined firing temperature _{A 1} at time _{T 1,} specifically, for example, reaches the 700 ° C., maintaining the temperature _{A 1} from time _{T 1} to time _{T 2.} Thereafter, cooling is performed from the temperature A ₁ to the temperature A ₀ from the time T ₂ to the time T ₃ .

Then, maintaining the temperature _{A 0} from the time _{T 3} toward time _{T 4.} Thereafter, the temperature rise is restarted from the temperature A _0, and when reaching a predetermined firing temperature A ₂ higher than the firing temperature A ₁ at time T ₅ , specifically 1260 ° C., for example, from time T ₅ to time T _6. to maintain the temperature _{a 2.} Thereafter, cooling is performed from the temperature A ₂ to the temperature A ₀ from the time T ₆ to the time T ₇ . Firing is performed in this manner.

  Specifically, in the first firing step, the obtained granulated powder is put into a furnace heated to 600 ° C. or higher and 900 ° C. or lower and held for 0.5 hours or longer and 1.5 hours or shorter. At this time, the oxygen concentration in the firing furnace may be 10.0% or more, which is a condition under which the ferritization reaction proceeds favorably, and specifically, the oxygen concentration of the introduced gas is about 20.0%. The concentration is adjusted and firing is performed under flow conditions. When the oxygen concentration in the first baking step is reduced by 10.0%, the average of the maximum height Rz of the particle group of the carrier core material obtained later tends to be excessively small. Further, when the firing temperature is lower than 600 ° C., sufficient firing cannot be performed. On the other hand, when the firing temperature is higher than 900 ° C., the maximum height Rz of the particle group of the carrier core material to be obtained later Tend to be too small.

  In the second firing step, the fired powder obtained in the first firing step is put into a furnace heated to 1200 ° C. or higher and held for 1.5 hours or more and 3.0 hours or less. At this time, the oxygen concentration in the firing furnace may be an atmosphere that is greater than 1.0% and less than 5.0%, which is a condition under which the reduction reaction proceeds to some extent. The oxygen concentration of the introduced gas is adjusted so as to be about 3.0%, and firing is performed under a flow state. When the oxygen concentration in the second firing step is 1.0% or less, and when it is 5.0% or more, the average and root mean square inclination angles of the maximum height Rz of the particle group of the carrier core material obtained later The average of RΔq tends to be excessively small. Moreover, when baking temperature is made lower than 1200 degreeC, there exists a tendency for the average of the maximum height Rz of the particle group of the carrier core material obtained later to become small too much.

  Note that the cooling process is performed as necessary, and may be omitted if unnecessary. That is, following the first baking step, the second baking step may be performed by raising the temperature in the furnace so that the second baking temperature is maintained without lowering the baking temperature and lowering the oxygen concentration. Good.

  It is desirable to further adjust the particle size of the obtained fired product at this stage. For example, the fired product is coarsely pulverized with a hammer mill or the like. That is, granulation is performed on the fired granular material (FIG. 4G). After that, classification is performed using a vibrating screen. That is, classification is performed on the pulverized granular material (FIG. 4H). By carrying out like this, the particle | grains of the carrier core material with a desired particle size can be obtained.

  Next, the classified granular material is oxidized (FIG. 4I). That is, the particle surface of the carrier core material obtained at this stage is heat-treated (oxidation treatment).

  Specifically, it is held at 200 to 700 ° C. for 0.1 to 24.0 hours in an atmosphere having an oxygen concentration of 10.0 to 100.0% to obtain a target carrier core material. More preferably, it is 0.5 to 20.0 hours at 250 to 600 ° C, and more preferably 1.0 to 12.0 hours at 300 to 550 ° C. Thus, the carrier core material according to one embodiment of the present invention is manufactured. In addition, about such an oxidation treatment process, it is arbitrarily performed as needed.

Thus, the carrier core material according to one embodiment of the present invention is manufactured. That is, the method for producing a carrier core material according to one embodiment of the present invention is a method for producing a carrier core material for an electrophotographic developer containing manganese, iron, and strontium as a core composition, the raw material containing manganese, iron A slurry containing a raw material containing strontium and a raw material containing strontium, a granulating step for granulating the resulting mixture after the slurrying step, and firing the granulated product obtained by the granulating step The firing step is a first firing in which the firing is performed at 600 ° C. to 900 ° C. for 0.5 hours to 1.5 hours in an atmosphere having an oxygen concentration of 10.0% or more. And firing in an atmosphere having an oxygen concentration of more than 1.0% and less than 5.0% at a temperature of 1200 ° C. or more and a holding time of 0.5 hours or more and 3.0 hours or less. And a firing step, the slurry step is a step of slurrying to the above 15.0μm material, raw material containing iron, and the volume particle diameter D ₉₀ of the mixed slurry of the raw material comprising strontium containing manganese .

  According to such a method for producing a carrier core material, an appropriate irregular shape is formed on the particle surface of the carrier core material, and a carrier core material that can be used stably over a long period of time can be obtained.

The carrier core material according to one embodiment of the present invention includes a slurrying step of slurrying a raw material containing manganese, a raw material containing iron, and a raw material containing strontium, and a mixture obtained after the slurrying step. Granulation is performed, and the obtained granulated product is fired. The firing is performed at 600 ° C. or more and 900 ° C. or less for 0.5 hours or more and 1.5 hours in an atmosphere having an oxygen concentration of 10.0% or more. A first baking step in which baking is performed with the following holding time; and an atmosphere having an oxygen concentration of more than 1.0% and less than 5.0%, at a temperature of 1200 ° C. or more and 0.5 hours or more and 3.0 hours or less And the second firing step of firing with a holding time of, and slurrying, the volume particle size D ₉₀ of the mixed slurry of the raw material containing manganese, the raw material containing iron, and the raw material containing strontium is 15.0 μm or more Do Cormorant is slurried.

  Such a carrier core material can be used stably over a long period of time because an appropriate uneven shape is formed on the particle surface of the carrier core material.

  Next, the thus obtained carrier core material is coated with a resin (FIG. 4J). Specifically, the obtained carrier core material according to the present invention is covered with a silicone resin, an acrylic resin, or the like. In this way. An electrophotographic developer carrier according to an embodiment of the present invention is obtained. A coating method such as silicone resin or acrylic resin can be performed by a known method. That is, an electrophotographic developer carrier according to an embodiment of the present invention is an electrophotographic developer carrier used for an electrophotographic developer, and includes any one of the above-described carrier core materials for an electrophotographic developer. And a resin that covers the surface of the carrier core material for an electrophotographic developer.

  Since such an electrophotographic developer carrier includes the carrier core material for an electrophotographic developer having the above-described configuration, high charging performance can be stably maintained over a long period of time.

  Next, a predetermined amount of the carrier thus obtained and the toner are mixed (FIG. 4K). Specifically, the carrier for an electrophotographic developer according to one embodiment of the present invention obtained by the above-described manufacturing method is mixed with an appropriate known toner. Thus, the electrophotographic developer according to one embodiment of the present invention can be obtained. For the mixing, for example, an arbitrary mixer such as a ball mill is used. An electrophotographic developer according to an embodiment of the present invention is an electrophotographic developer used for electrophotographic development, and is obtained by frictional charging between the above-described electrophotographic developer carrier and the electrophotographic developer carrier. And a toner capable of being charged in electrophotography.

  Since such an electrophotographic developer includes the carrier for an electrophotographic developer having the above-described configuration, an image having a good image quality can be stably formed even for a long period of use.

Example 1
In 5 kg of water, 10.75 kg of Fe ₂ O ₃ (average particle size: 0.6 μm), 5.70 kg of Mn ₃ O ₄ (average particle size: 2 μm), 190 g of strontium carbonate are added, and carbon black is used as a reducing agent. 45 g, 60 g of an ammonium polycarboxylate dispersant as a dispersant, and 33 g of polyvinyl alcohol as a binder were added to obtain a mixture. As a result of measuring the solid content concentration at this time, it was 77% by weight. This mixture was pulverized by a wet bead mill (media diameter 2 mm) to obtain a mixed slurry. At this time, the crushing strength, time, number of times, etc. were controlled, and the value of the volume particle size D ₉₀ in the slurry was adjusted to 15.8 μm. Here, the measurement of the volume particle diameter _{D 90,} a laser diffraction particle size distribution measuring apparatus, Microtrac manufactured by Nikkiso Co., was used Model 9320-X100.

  This slurry was sprayed into hot air at about 130 ° C. with a spray dryer to obtain dry granulated powder. At this time, granulated powder other than the target particle size distribution was removed by sieving.

  The granulated powder was fired. In this case, as a first firing step, the oxygen concentration was set to 20.0% in an electric furnace and fired at 700 ° C. for 0.5 hours. Then, it cooled to normal temperature. And as a 2nd baking process, it injected into the electric furnace of the atmosphere which made oxygen concentration 1.5%, and baked at 1200 degreeC for 2.0 hours. Then, it cooled to normal temperature. The obtained fired product was subjected to an oxidation treatment by heating at 330 ° C. and holding it in the atmosphere for 1.0 hour. The obtained fired product was classified using a sieve after pulverization, and the average particle size was set to 34.0 μm. Thus, the carrier core material according to Example 1 was obtained.

Note that the composition of the obtained carrier core material _is represented by _{Mn 1.07 Fe 1.92 Sr 0.01 O 4} . Hereinafter, the same applies to the compositions of all Examples and Comparative Examples.

  Next, 750 parts by weight of silicone resin and 15 parts by weight of (2-aminoethyl) aminopropyltrimethoxysilane were added to 750 parts by weight of toluene as a solvent for the carrier core material according to Example 1 thus obtained. A coating solution was prepared by dissolving in the part. This coating solution was applied to 50000 parts by weight of a carrier core material produced using a fluidized bed type coating apparatus and heated in an electric furnace at a temperature of 300 ° C. to obtain a resin-coated carrier according to Example 1. Hereinafter, resin coating carriers were obtained in the same manner for all of the examples and comparative examples.

  Next, the carrier according to Example 1 thus obtained and the toner having a particle size of about 5.0 μm are mixed for a predetermined time using a pot mill, and the two-component electrophotographic developer according to Example 1 is obtained. Obtained. In this case, the carrier and the toner were adjusted so that the toner weight / toner and carrier weight = 5/100. That is, 5% by weight of toner and 95% by weight of carrier were mixed. Hereinafter, developers were obtained in the same manner for all Examples and Comparative Examples.

  The obtained developer was evaluated on an actual machine. Table 1 and Table 2 show the parameters in the manufacturing process of the carrier core material and the actual machine evaluation.

(Example 2)
A carrier core material according to Example 2 was obtained in the same manner as in Example 1 except that the firing temperature in the second firing step was 1300 ° C.

(Example 3)
A carrier core material according to Example 3 was obtained in the same manner as in Example 1 except that the firing temperature in the second firing step was 1230 ° C. 1 corresponds to the carrier core material according to the third embodiment. In addition, the laser micrograph shown in FIG. 1 expands a carrier core material 3000 times. The same applies to the laser micrographs shown in FIGS.

Example 4
Except that the volume particle diameter D ₉₀ was 18.8μm in slurrying step, in the same manner as in Example 3, to thereby obtain the carrier core material according to the fourth embodiment.

(Example 5)
Except that the volume particle diameter D ₉₀ and 16.9μm in slurrying step, in the same manner as in Example 1, to thereby obtain the carrier core material according to Example 5.

(Example 6)
A carrier core material according to Example 6 was obtained in the same manner as in Example 5 except that the oxygen concentration in the first baking step was 10.0%.

(Example 7)
A carrier core material according to Example 7 was obtained in the same manner as in Example 1 except that the firing temperature in the first firing step was 850 ° C.

(Example 8)
A carrier core material according to Example 8 was obtained in the same manner as in Example 5 except that the oxygen concentration in the second baking step was changed to 3.0%.

(Comparative Example 1)
Except that the volume particle diameter D ₉₀ and 12.0μm in slurrying step, in the same manner as in Example 3, to thereby obtain the carrier core material according to comparative example 1.

(Comparative Example 2)
Except that the volume particle diameter D ₉₀ and 8.5μm in slurrying step, in the same manner as in Example 5, to thereby obtain the carrier core material according to comparative example 2. In addition, the laser micrograph which shows the external appearance of the carrier core material obtained in this case is shown in FIG.

(Comparative Example 3)
A carrier core material according to Comparative Example 3 is obtained in the same manner as in Example 5 except that the volume particle diameter D ₉₀ is 16.5 μm in the slurrying step and the firing temperature in the first firing step is 500 ° C. It was.

(Comparative Example 4)
A carrier core material according to Comparative Example 3 is obtained in the same manner as in Example 5 except that the volume particle size D ₉₀ is 18.6 μm in the slurrying step and the firing temperature in the first firing step is 1000 ° C. It was. In addition, the laser micrograph which shows the external appearance of the carrier core material obtained in this case is shown in FIG.

(Comparative Example 5)
A carrier core material according to Comparative Example 5 was obtained in the same manner as in Example 1 except that the firing temperature in the second firing step was 1150 ° C.

(Comparative Example 6)
A carrier core material according to Comparative Example 6 was obtained in the same manner as in Example 5 except that the oxygen concentration in the first baking step was 5.0%.

(Comparative Example 7)
A carrier core material according to Comparative Example 7 in the same manner as in Example 5 except that the volume particle size D ₉₀ was 17.1 μm in the slurrying step and the oxygen concentration in the first baking step was 7.0%. Got.

(Comparative Example 8)
A carrier core material according to Comparative Example 8 was obtained in the same manner as in Example 5 except that the oxygen concentrations in the first and second firing steps were each 5.0%.

(Comparative Example 9)
A carrier core material according to Comparative Example 9 is obtained in the same manner as in Example 5 except that the volume particle size D ₉₀ is 20.2 μm in the slurrying step and the firing temperature in the first firing step is 1200 ° C. It was.

(Comparative Example 10)
10.75 kg of Fe ₂ O ₃ (average particle size: 0.6 μm), 5.70 kg of Mn ₃ O ₄ (average particle size: 2 μm), 190 g of strontium carbonate, and 45 g of carbon black were mixed thoroughly to obtain an average particle diameter _{D 50} was pulverized to be 2.1 .mu.m. The obtained mixture was calcined at 800 ° C. for 4.0 hours, the obtained calcined powder, 60 g of an ammonium polycarboxylate-based dispersant as a dispersant, and 33 g of polyvinyl alcohol as a binder were dispersed in 5 kg of water. was pulverized with a bead mill, the average particle diameter _{D 50} of the slurry 2.1 .mu.m, the volume particle diameter _{D 90} was adjusted to 15.8Myuemu. The carrier core material according to Comparative Example 10 was obtained by putting it into an electric furnace with an oxygen concentration of 1.5% and firing it at 1300 ° C. in one stage. In addition, about this manufacturing method, it is based on the method of above-mentioned patent document 1. FIG.

(Comparative Example 11)
10.75 kg of Fe ₂ O ₃ (average particle size: 0.6 μm), 5.70 kg of Mn ₃ O ₄ (average particle size: 2 μm), 190 g of strontium carbonate, and 45 g of carbon black were sufficiently mixed. The obtained mixture was calcined at 800 ° C. for 4.0 hours, and then pulverized so that the average particle diameter D ₅₀ was 1.4 μm. The obtained pulverized powder was dispersed in 5 kg of water and sprayed into hot air at about 130 ° C. with a spray dryer to obtain dry granulated powder. This granulated powder was put into an electric furnace having an oxygen concentration of 20.0% as a first firing step and fired at 1200 ° C. for 3.0 hours. Next, as a second firing step, the obtained fired product was further put into an electric furnace having an oxygen concentration of 1.5% and fired at 1200 ° C. for 2.0 hours to obtain a carrier core material according to Comparative Example 11. . In addition, about this manufacturing method, it is based on the method of above-mentioned patent document 2. FIG.

(Comparative Example 12)
A carrier core material according to Comparative Example 12 was obtained in the same manner as in Example 5 except that the oxygen concentration in the second baking step was changed to 0.5%. In addition, about this manufacturing method, it is based on the method of Unexamined-Japanese-Patent No. 2013-25204.

(Comparative Example 13)
A carrier core material according to Comparative Example 13 was obtained in the same manner as in Example 5 except that the oxygen concentration in the second firing step was 5.0%.

  For reference, Table 1 also shows the average length RSm of the elements of the particle group constituting the carrier core material and the arithmetic surface roughness Ra of the particle group constituting the carrier core material.

  Here, the maximum height Rz of the particle group constituting the carrier core material, the root mean square inclination angle RΔq of the particle group constituting the carrier core material, the average length RSm of the elements of the particle group constituting the carrier core material, the carrier About the arithmetic surface roughness Ra of the particle group which comprises a core material, it measured as follows.

  Using an ultra-deep color 3D shape measurement microscope (VK-X100, manufactured by Keyence Corporation), the surface was observed with a 150 × objective lens. Specifically, the carrier core particles are first fixed on an adhesive tape with a flat surface, the measurement field of view is determined with a 150 × objective lens, and then the focus is adjusted to the adhesive tape surface using the autofocus function. The three-dimensional shape of the particle surface of the carrier core material was captured using the imaging function.

  Each parameter was measured using software VK-H1XA attached to the apparatus. First, as a pretreatment, a portion used for analysis was taken out from the three-dimensional shape of the particle surface of the obtained carrier core material. FIG. 8 is a schematic view showing the particle surface of the carrier core material. Specifically, when a line segment 23 having a length of 15.0 μm in the horizontal direction is drawn at the center of the particle surface 22 of the carrier core material 21 and 10 parallel lines are added at intervals of 4 above and below the line segment 23. A total of 21 roughness curves corresponding to the line segments were taken out. In FIG. 8, the upper ten line segments 24a and the lower ten line segments 24b are simply shown.

  Next, since the carrier core material has a substantially spherical shape and has a certain curvature as the background, the optimum roughness curve is fitted as a background correction, and the roughness curve is taken out. Correction was made to subtract from. In this case, the cutoff value λs was 0.25 μm, and the cutoff value λc was 0.08 mm.

  The maximum height Rz was obtained as the sum of the highest mountain height and the deepest valley depth in the roughness curve.

  The root mean square slope angle RΔq was calculated by applying a roughness curve to the equation shown in Equation 1 below.

  Here, in the formula (1), dRn / dXn indicates the local slope of the n-th peak or valley at the reference length of 15.0 μm, and is basically obtained by the seven-point formula shown in the following formula (2).

  Here, the obtained root mean square inclination angle RΔq indicates that the larger the value, the larger the inclination.

  The arithmetic average roughness Ra indicates the average of the absolute values of the roughness curve, and is obtained by the following equation (3).

  Here, 1r indicates the length of the roughness curve.

  The average length RSm of the elements is obtained by defining a combination of valleys and peaks in the roughness curve as one element and calculating the average length of each element.

  The measurement of the maximum height Rz, the root mean square inclination angle RΔq, the arithmetic average roughness Ra, and the average element length RSm is performed according to JIS B0601 (2001 edition).

  Moreover, about the average particle diameter of the carrier core material used for an analysis, it limited to 32.0-34.0 micrometers. In this way, by limiting the average particle diameter of the carrier core material to be measured to a narrow range, it is possible to reduce an error due to a residue generated during curvature correction.

  In addition, the average value of 30 particles was used as the average value of each parameter.

  The actual machine evaluation was performed as follows. The developers according to the examples and comparative examples obtained by the above-described methods were used, and the amount of the developer to be set was 500 g. In addition, as an evaluation machine, an evaluation machine equivalent to a 70 sheet machine (70 cpm) adopting a digital reversal development method improved so as to apply an AC bias in the development region was used.

  The evaluation of carrier scattering was performed as follows. 1000 blank sheets were printed, and the number of black spots on the 1000th sheet was visually judged. “◎” (excellent) when no black spots are seen, “◯” (good) when the number of discovered black spots is 1 to 5, and “6” when the number of discovered black spots is 6 to 10. “Δ” (slightly inferior), and a case where the number of discovered black spots was 11 or more was judged as “x” (inferior).

  Further, the evaluation of coat peeling was performed as follows. About the carrier before and after the measurement of carrier scattering, the amount of carbon was quantified based on JIS G1211 “Method for quantifying carbon in iron and steel” (2001 version), and the reduction rate was calculated from the following formula.

Carbon content reduction rate (%) = before test / after test × 100
Regarding the calculated carbon amount reduction rate, “◎” (excellent) when less than 1%, “◯” (good) when 1 to 3%, “△” (somewhat inferior) when 4 to 10%. The case of 11% or more was judged as “x” (poor).

  The image density unevenness was performed as follows. 1000 solid images are printed, and 10 predetermined positions on the 1000th sheet are measured with an image densitometer, and image density unevenness is determined from the difference between the maximum value and the minimum value (maximum value-minimum value). Evaluated. When the difference is less than 0.3, “「 ”(excellent), when the difference is 0.3 to 0.5,“ ◯ ”(good), and when the difference is 0.6 to 1,“ △ ”(somewhat Inferior), the case where the difference was 1.1 or more was judged as “x” (inferior).

  For Examples 1 to 8 and Comparative Examples 1 to 13, the horizontal axis represents the average of the maximum height Rz of the particle group constituting the carrier core material, and the vertical axis represents the carrier core material. The average of the root mean square inclination angle RΔq of the group and the plotted graph is shown in FIG. 9 for reference. In FIG. 9, an example is indicated by a black rhombus mark, and a comparative example is indicated by a black square mark.

  Referring to Tables 1 and 2, in the case of Examples 1 to 8, all of the parameters of carrier scattering, coat peeling, and image density unevenness were evaluated as “◎” (excellent) or “◯” (good) ).

  On the other hand, Comparative Examples 1 to 13 are evaluations in which at least one of the above-described parameters includes “Δ” (somewhat poor) or “×” (bad).

  Here, the maximum height Rz of the particle group constituting the carrier core material and the root mean square inclination angle RΔq of the particle group constituting the carrier core material are as follows when the numerical values are high and low. It is thought that such a phenomenon occurs.

  FIG. 10 is a conceptual diagram showing the state of the resin coated on the surface of the carrier core material having a high average value of the maximum height Rz. Referring to FIG. 10, in carrier core material 31a having a high average value of maximum height Rz, the carrier core material 31a is positioned between a plurality of convex portions 34a constituting a peak portion formed on particle surface 32a of carrier core material 31a. The tendency that the cavity 35a is generated between the concave portion 33a constituting the valley portion and the resin 36a to be coated becomes remarkable. Then, the binding property between the resin 36a and the particle surface 32a of the carrier core material 31a is lowered, and it is considered that the resin 36a is easily peeled off after long-term use. On the other hand, FIG. 11 is a conceptual diagram showing the state of the resin coated on the surface of the carrier core material having a low average value of the maximum height Rz. Referring to FIG. 11, in the carrier core material 31b having a low average value of the maximum height Rz, the heights of the convex portions 34b forming the peak portions and the concave portions 33b forming the valley portions formed on the particle surface 32b. There is no difference, it is considered that the so-called hooked portion is reduced when the resin 36b is coated, the binding property is lowered, and the resin 36b is easily peeled off after long-term use. Further, in this case, the tendency to completely cover the particle surface 32b of the carrier core material 31b with the resin 36b becomes strong, and it is difficult for charge leakage to occur, which tends to cause image problems.

  FIG. 12 is a conceptual diagram showing the state of the resin coated on the surface of the carrier core material having a high average value of the root mean square inclination angle RΔq. Referring to FIG. 12, in the carrier core material 31c having a high average value of the root mean square slope angle RΔq, between the plurality of convex portions 34c constituting the peak portions formed on the particle surface 32c of the carrier core material 31c. The tendency that the cavity 35c is generated between the concave portion 33c constituting the valley portion positioned and the resin 36c to be coated becomes remarkable. Then, the binding property between the resin 36c and the particle surface 32c of the carrier core material 31c is reduced, and it is considered that the resin 36c is easily peeled off after a long period of use. On the other hand, FIG. 13 is a conceptual diagram showing the state of the resin coated on the surface of the carrier core material having a low average value of the root mean square inclination angle RΔq. Referring to FIG. 13, in the carrier core material 31d having a low mean value of the root mean square slope angle RΔq, the so-called hooked portion when the resin 36d is coated is reduced, and the binding property is lowered. It is considered that the resin 36d is easily peeled off by use. In this case as well, the tendency to completely cover the particle surface 32d of the carrier core material 31d with the resin 36d is strong, and it is difficult for charge leakage to occur, which tends to cause image defects. Note that the two upper and lower dotted lines shown in FIGS. 12 and 13 indicate the same height.

  Note that the roundness of the slurry raw material is preferably 2.0 μm or more in order to suppress the value of the root mean square inclination angle RΔq from becoming unnecessarily low. By doing so, at least one of the above three evaluation items can be made excellent from the viewpoint of actual machine evaluation. Regarding the roundness of the slurry raw material, Example 1 is 1.3 μm, Example 2 is 1.3 μm, Example 3 is 1.3 μm, Example 4 is 1.8 μm, and Example 5 is 2.2 μm, Example 6 was 2.2 μm, Example 7 was 1.8 μm, and Example 8 was 2.2 μm.

  Here, the method for measuring the roundness of the slurry raw material is as follows. The wet pulverized slurry is diluted 10 times, and the diluted slurry is dropped on the preparation. The preparation to which the diluted slurry was dropped was heated to 120 ° C. or lower using a hot plate or the like to sufficiently evaporate water. The residue on the slide was collected with an adhesive tape, and an image was taken with SEM (manufactured by Hitachi, Ltd., model S-4700). The magnification was 30000 times. The roundness of the obtained image was calculated from the following equation using image analysis software (image-plus 7.0, manufactured by Media Cybernetics). The average value of 100 particles was used as a representative value.

Roundness = (perimeter) ² / area / 4 / π
Although the embodiments of the present invention have been described with reference to the drawings, the present invention is not limited to the illustrated embodiments. Various modifications and variations can be made to the illustrated embodiment within the same range or equivalent range as the present invention.

  A method for producing a carrier core material for an electrophotographic developer according to the present invention, a carrier core material for an electrophotographic developer, a carrier for an electrophotographic developer, and an electrophotographic developer used for a long period of time, etc. It is used effectively when applied to.

  11, 21, 31a, 31b, 31c, 31d Carrier core, 12, 17, 22, 32a, 32b, 32c, 32d Surface, 13, 33a, 33b, 33c Concavity, 14, 34a, 34b, 34c Convex, 15 Carrier, 16, 36a, 36b, 36c, 36d Resin, 18 regions, 23, 24a, 24b Line segment, 35a, 35c Cavity.

Claims (8)

A carrier core material for an electrophotographic developer containing only manganese, iron, and strontium as a core composition,
The average of the maximum height Rz of the particle group constituting the carrier core material for an electrophotographic developer is 2.00 μm or more and 3.50 μm or less,
The carrier core material for an electrophotographic developer, wherein an average of the root mean square inclination angle RΔq of the particle group constituting the carrier core material for an electrophotographic developer is 0.70 or more and 1.00 or less. 2. The carrier core material for an electrophotographic developer according to claim 1, wherein an average of a root mean square inclination angle RΔq of a particle group constituting the carrier core material for the electrophotographic developer is 0.72 or more and 0.86 or less. . 3. The carrier core for an electrophotographic developer according to claim 1, wherein an average of arithmetic surface roughness Ra of the particle group constituting the carrier core material for the electrophotographic developer is 0.333 μm or more and 0.479 μm or less. Wood. The electron according to any one of claims 1 to 3, wherein an average length RSm of elements of a particle group constituting the carrier core material for an electrophotographic developer is 4.648 µm or more and 8.341 µm or less. Carrier core material for photographic developer. It is a manufacturing method of the carrier core material for electrophotographic developers given in any 1 paragraph of Claims 1-4 ,
A slurrying step of slurrying a raw material containing manganese, a raw material containing iron, and a raw material containing strontium;
After the slurrying step, a granulation step for granulating the resulting mixture;
A firing step of firing the granulated product obtained by the granulation step,
The firing step includes a first firing step in which firing is performed at a temperature of 600 ° C. or more and 900 ° C. or less for 0.5 hours or more and 1.5 hours or less in an atmosphere having an oxygen concentration of 10.0% or more; A second baking step of baking at a temperature of 1200 ° C. or higher and a holding time of 0.5 hours or more and 3.0 hours or less in an atmosphere having a concentration of more than 1.0% and less than 5.0%,
The slurrying step is a step of slurrying to the above 15.0μm material, the raw material containing iron, and the volume particle diameter D ₉₀ of the mixed slurry of the raw material containing the strontium containing the manganese, electrophotographic A method for producing a carrier core material for a developer. The method for producing a carrier core material for an electrophotographic developer according to claim 5 , comprising a cooling step of cooling to room temperature between the first baking step and the second baking step. A carrier for an electrophotographic developer used in an electrophotographic developer,
The carrier core material for an electrophotographic developer according to any one of claims 1 to 4 ,
An electrophotographic developer carrier comprising: a resin that covers a surface of the carrier core material for the electrophotographic developer. An electrophotographic developer used for electrophotographic development,
The carrier for an electrophotographic developer according to claim 7 ,
An electrophotographic developer comprising: a toner capable of being charged in electrophotography by frictional charging with the carrier for electrophotographic developer.