JP2011164224A - Method for manufacturing carrier core material for electrophotographic developer, and carrier core material obtained by the manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a carrier core material for electrophotographic developers which contains no heavy metal, reduces a Mn content, gains prescribed resistance such as intermediate resistance or high resistance while being high in magnetization, is highly electrically charged, has a good apparent density, has surface properties having adequate concavities and convexities, and is uniform in shape. <P>SOLUTION: This is a method for manufacturing a carrier core material for electrophotographic developers which includes ferrite particles which contain at least Fe, Mg, Ti and Sr and have at least spinel structure and Ti-compound structure. In addition, the method has: (1) a first burning process in which at least a Mg compound, a Sr compound and Fe<SB>2</SB>O<SB>3</SB>are added together, mixed and then burned in a prescribed atmosphere to gain a mixture including Fe<SP>2+</SP>; (2) a granulation process in which the mixture thus gained is made to be slurry, and the slurry particles are granulated; (3) a second burning process in which the granules are burned in a prescribed atmosphere to convert them into ferrite; (4) a third burning process in which the burning is made again in the prescribed atmosphere to adjust magnetization and surface properties; and (5) an oxide film processing process in which oxide films are formed on the surfaces of the particles. In this case, the amount of the remaining Fe<SB>2</SB>O<SB>3</SB>posterior to the first burning process is 0-60 wt.%, and a Ti compound is added in the granulation process. Then, the method for manufacturing the carrier core material for electrophotographic developers is adopted. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing a carrier core material for an electrophotographic developer used for a two-component electrophotographic developer used in a copying machine, a printer, and the like, and a carrier core material obtained by the production method.

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

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

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

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

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

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

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

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

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

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

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

  Patent Document 1 (Japanese Patent Application Laid-Open No. 2006-337828) discloses a ferrite carrier core material for electrophotography in which the surface is divided into regions of 2 to 50 per 10 μm square by grooves or streaks, and the main component is manganese ferrite. Are listed. This ferrite carrier core material has a uniform composition, constant surface properties, good fluidity, high magnetization, low resistance, and an electron using a ferrite carrier in which this ferrite carrier core material is coated with a resin. Photographic developers are said to have a fast charge rise and a stable charge over time.

  In Patent Document 1, in order to produce the ferrite carrier core material as described above, a composite oxide mainly composed of Fe and Mn having a molar ratio of Fe to Mn (Fe / Mn) of 4 to 16 is crushed. It has been shown that in a production method in which granulation, firing, and further pulverization and classification are performed after mixing, firing is performed in an atmosphere having an oxygen concentration of 5% by volume or less.

  However, this ferrite carrier core material has a problem of low resistance. In addition, Mn is also subject to various laws and regulations, and there is a need for a new carrier core material that does not use Mn as well as the above-mentioned various heavy metals, or that significantly reduces the Mn content.

  As an alternative to a carrier core material using Mn as a ferrite component, a carrier core material using Mg or the like has been proposed. For example, in Patent Document 2 (Japanese Patent Laid-Open No. 2000-172017), a starting material is a composite oxide mainly composed of magnetite including a magnetite or an oxide that is not a harmful heavy metal such as MgO or CaO. A method for producing a ferrite core for an electrophotographic developer is described in which granulated and spherical granulated powder is fired at 850 to 1000 ° C. in an inert gas atmosphere.

Patent Document 3 (Japanese Patent Publication No. 2006-524627) discloses an Mg-based ferrite material (carrier core material) represented by the formula Mg _a Fe _b Ca _c O _d and has a saturation magnetization of 30 to 80 emu / g. It is said that the dielectric breakdown voltage is 1.5 to 5.0 kV, and is composed of a clean material that complies with environmental regulations, and a high-quality image that is clear, rich in gradation, and free from fog is obtained.

  Thus, although the carrier core material using Mg as a ferrite component has been proposed, since magnetization and resistance are generally in a trade-off relationship, it is difficult to achieve both high magnetization and characteristics such as medium resistance to high resistance. Therefore, by adding Mn, the trade-off relationship between magnetization and resistance is relaxed to realize high magnetization, medium resistance to high resistance, and it is currently used as a carrier core material for electrophotographic developer. However, as described above, with the strengthening of various heavy metal regulations, there is a demand for not using Mn or significantly reducing the Mn content.

  In addition, as a method of realizing high magnetization and medium resistance to high resistance even with a conventional firing method using Mg as a ferrite component, efforts are made to adjust the resistance to a desired level by surface oxidation after the main firing. I came.

Patent Document 4 (Japanese Patent Application Laid-Open No. 2004-240322) discloses a carrier core material for an electrophotographic developer composed of ferrite particles containing ZrO ₂ not dissolved in manganese-magnesium ferrite. In addition, it is described that after the main baking, an oxide film treatment is performed at 300 to 700 ° C. using an existing rotary electric furnace, batch electric furnace, or the like in an air atmosphere. Further, Patent Document 5 (Japanese Patent Laid-Open No. 2008-65106) discloses that MO · Fe ₂ O ₃ , where the M component is a magnetic part represented by one or more of divalent metal elements, particularly Mn, Mg, and Fe. Disclosed is a carrier core material for an electrophotographic developer comprising a powder having a nonmagnetic part containing SiO ₂ , and in the production thereof, after firing, it is heated to 200 to 800 ° C. in air or a mixed atmosphere of oxygen and nitrogen. It describes that the resistance is increased by heating.

  However, as described in Patent Documents 4 and 5, even when an oxide film treatment (high resistance treatment) is performed, the resistance is low or the magnetization is low. Further, when Mn is used as a ferrite component in a certain amount or more, the above-mentioned environmental regulation problem also arises.

Conventionally, it has been known that Mg-based ferrite can be increased in magnetization by being produced with an excess of Fe. However, the resistance is extremely low due to the excess of Fe. In addition, Fe-excess Mg-based ferrite is characterized by a sharp decrease in magnetization due to high oxygen concentration during surface firing or surface oxidation. This phenomenon is due to oxidation of Fe ²⁺ contained in magnetite. It is believed that.

  On the other hand, the firing temperature of Mg-based ferrite that does not contain a transition metal other than Fe is as high as about 1250 to 1350 ° C., and not only the surface properties required for the carrier core material can be obtained with almost no unevenness, The carrier core particles are likely to aggregate during firing and contain many particles that are not spherical. Therefore, a carrier core material for an electrophotographic developer that does not intentionally contain a heavy metal, has a high magnetization, a medium resistance to a high resistance, and has a surface shape with appropriate irregularities, and a method for producing the same are obtained. The current situation is not.

  Patent Document 6 (Japanese Patent No. 2860356) relates to an oxide magnetic material having a predetermined saturation magnetization obtained by firing hematite, hematite + magnetite, or magnetite and Mg and optionally Mn, and a method for producing the same. is there. Patent Document 7 (Japanese Patent No. 3151457) relates to an oxide magnetic material having saturation magnetization of a predetermined value by mixing and firing magnetite, magnetite + hematite, hematite with a Ti compound or Sn compound, and a method for producing the same. . In any of the documents, firing after spherical granulation is performed only once, and it is difficult and insufficient to obtain the particle shape and surface properties required as a carrier core material for electrophotography. Moreover, the said patent document 6 has illustrated hematite, wustite, and Mg (compound) as a nonmagnetic phase. On the other hand, the Mg compound present in the electrophotographic carrier core produced by the production method according to the present invention is a magnetized Mg ferrite, and the presence of a Ti compound as the nonmagnetic phase, and the carrier core In order to generate a dielectric component composed of Mg, Ti and O in addition to the ferrite component in the material, it is clearly distinguished from the above-mentioned Patent Document 6.

JP 2006-337828 A JP 2000-172017 A JP 2006-524627 A JP 2004-240322 A JP 2008-65106 A Japanese Patent No. 2860356 Japanese Patent No. 3151457

  Therefore, the object of the present invention is not only to contain each heavy metal, but also to reduce the Mn content and not only obtain a desired resistance such as medium resistance or high resistance while being highly magnetized, but also high charge and good An object of the present invention is to provide a method for producing a carrier core material for an electrophotographic developer having an apparent density and having an appropriate unevenness and a uniform shape, and a carrier core material obtained by the production method.

  As a result of intensive studies to solve the above problems, the present inventors have found that the carrier core material for an electrophotographic developer contains Fe, Mg, Ti and Sr, and has at least a spinel structure and a Ti compound structure. In the manufacturing method, while adding a specific amount of Ti compound in the granulation step, the carrier core material obtained through three firing steps including the main firing under a certain condition finds that the above-mentioned purpose is achieved, The present invention has been reached.

That is, the present invention is a method for producing a carrier core material for an electrophotographic developer comprising at least Fe, Mg, Ti and Sr, and comprising ferrite particles having at least a spinel structure and a Ti compound structure,
(1) a first firing step of adding, mixing, and firing at least a Mg compound, a Sr compound, and Fe ₂ O ₃ in a non-oxidizing atmosphere or a weak reducing atmosphere to obtain a mixture containing Fe ²⁺ ;
(2) A granulation step of granulating slurry particles after slurrying the obtained mixture;
(3) a second firing step in which the granulated material is fired in a non-oxidizing atmosphere or a weakly reducing atmosphere to be ferritized;
(4) a third firing step of firing again in a non-oxidizing atmosphere or a weak reducing atmosphere to adjust magnetization and surface properties;
(5) an oxide film treatment step for forming an oxide film on the particle surface;
A carrier core material for an electrophotographic developer, wherein the residual amount of Fe ₂ O ₃ after the first baking step is 0 to 60% by weight, and a Ti compound is added in the granulation step The manufacturing method of this is provided.

  In the method for producing a carrier core material for an electrophotographic developer according to the present invention, it is desirable to add a Ti compound and / or a Mn compound to the first firing step.

In the method for producing a carrier core material for an electrophotographic developer according to the present invention, the Ti compound generates one or more kinds of dielectric components selected from Mg ₂ TiO ₄ , MgTiO ₃ , MgTi ₂ O ₄ , and SrTiO ₃ . It is desirable.

  In the method for producing a carrier core material for an electrophotographic developer according to the present invention, it is desirable that the particle size of the Ti compound added in the granulation step is 5 to 120 nm.

  In the method for producing a carrier core material for an electrophotographic developer according to the present invention, it is desirable to add a Ti compound so that the amount of Ti contained in the ferrite particles is 10 to 100% by weight in the granulation step. .

  In the method for producing a carrier core material for an electrophotographic developer according to the present invention, in at least one step selected from the first firing step, the granulation step, and the second firing step, carbon black (CB), polyvinyl It is desirable to add at least one additive selected from alcohol (PVA), polyvinylpyrrolidone (PVP) and charcoal.

  In the method for producing a carrier core material for an electrophotographic developer according to the present invention, it is desirable that the firing in the first firing step is performed at 800 to 1200 ° C.

  In the method for producing a carrier core material for an electrophotographic developer according to the present invention, it is desirable that the second firing step is performed at 650 to 1200 ° C.

  In the method for producing a carrier core material for an electrophotographic developer according to the present invention, it is preferable that the third baking step is performed at 1100 to 1400 ° C.

  In the method for producing a carrier core material for an electrophotographic developer according to the present invention, the oxide film treatment step is preferably performed at 400 to 800 ° C.

  In the method for producing a carrier core material for an electrophotographic developer according to the present invention, it is desirable that a rotary kiln is used in the oxide film treatment step.

  In the method for producing a carrier core material for an electrophotographic developer according to the present invention, it is desirable that the particle size of the slurry particles used in the granulation step is 1.0 to 3.0 μm.

  The present invention provides a carrier core material for an electrophotographic developer obtained by the above production method.

  In the carrier core material for an electrophotographic developer according to the present invention, at least 48.0 to 70.0% by weight of Fe, 1 to 5% by weight of Mg, 0.1 to 3.5% by weight of Ti, and Sr It is desirable to contain 0.1 to 5.0 weight%.

  The carrier core material for an electrophotographic developer according to the present invention preferably contains 0.1 to 20% by weight of Mn.

  In the carrier core material for an electrophotographic developer according to the present invention, the thickness of the oxide film is preferably 0.0001 to 10.0 μm.

  By the production method according to the present invention, not only each heavy metal is not contained, but also the Mn content can be reduced, and not only a desired resistance such as medium resistance or high resistance can be obtained while being highly magnetized, but also high charge and good A carrier core material for an electrophotographic developer having an apparent density, an appropriate surface irregularity, and a uniform shape can be stably produced on an industrial scale.

Hereinafter, modes for carrying out the present invention will be described.
<Method for producing carrier core material for electrophotographic developer according to the present invention>
Next, a method for producing a carrier core material for an electrophotographic developer according to the present invention will be described.
The manufacturing method of the carrier core material for an electrophotographic developer according to the present invention is as follows.

(First firing step)
As the carrier core material, Mg compound, Sr compound and Fe ₂ O ₃ and, if necessary, Ti compound and / or Mn compound are used. A non-oxidizing atmosphere or a weak reducing atmosphere is added by adding one kind of additive material selected from carbon black (CB), polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), and charcoal as required. Below, addition, mixing, and baking are performed to obtain a mixture containing Fe ²⁺ . In this firing, a state of a ferrite precursor in which a spinel phase containing at least divalent Fe and a composite oxide phase containing Fe, Mg, Ti and the like are present is generated, and the Fe ₂ O ₃ residual amount is 0 to 60 Adjust so that it becomes weight%.

  By firing as described above, a crystal structure having a lattice constant with little variation, that is, a structure with good crystallinity, and particles with a small decrease in magnetization after the surface oxidation treatment can be obtained. The firing temperature is desirably performed at 800 to 1200 ° C. in the above atmosphere. When the firing temperature is less than 800 ° C., the lattice constant varies greatly and is easily oxidized, so that the magnetization is significantly reduced during the oxide film treatment. On the other hand, if the firing temperature exceeds 1200 ° C., too much heat is applied, making it difficult to control the shape and surface properties.

In the conventional manufacturing method, since a spinel phase is generated from Fe ₂ O ₃ during the main firing, a considerable amount of energy is required to change the crystal structure, but Mg compound, Sr compound and Fe ₂ O ₃ , and Ti compound as necessary And / or an Mn compound, and if necessary, one additional material selected from carbon black (CB), polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP) and charcoal, and mixing and firing. In the main firing (second firing), which will be described later, the combustion heat of the additive is generated and the effective temperature is equal to or higher than the firing temperature, so that low temperature firing is possible and the carrier core has good crystallinity. A material can be obtained. Furthermore, there is little decrease in magnetization due to the oxide film treatment, and high magnetization and high resistance can be achieved.

  The non-oxidizing atmosphere or weakly reducing atmosphere used here means that the oxygen concentration is 2% by volume or less, preferably 1% by volume or less, more preferably 0.2% by volume or less. Nitrogen gas, argon gas, helium gas, carbon dioxide gas or the like can be used as the atmosphere, but nitrogen gas is preferably used for industrial purposes. Furthermore, when performing 0.2% volume% or less easily and baking, it is desirable to vaporize and use liquid nitrogen.

(Granulation process)
Next, after slurrying the obtained mixture, the slurry particles are granulated with a spray dryer or the like. The particle size of the slurry particles is desirably 1.0 to 3.0 μm. If the particle size of the slurry particles is less than 1.0 μm, the viscosity becomes high, nozzle clogging is likely to occur, and it takes time to grind, which is economically disadvantageous. When the particle size of the slurry particles exceeds 3.0 μm, the raw materials are not uniformly mixed, the distribution of magnetic force and resistance becomes wide, and carrier adhesion occurs when the developer is used. In addition, the shape deteriorates.

  In the granulation step, a Ti compound is added. Due to the presence of Ti, there is little decrease in magnetization due to the oxide film treatment, and the resistance and surface properties can be adjusted. In this granulation step, it is desirable to add a Ti compound so that it becomes 10 to 100% by weight of the total amount of Ti contained in the finally obtained ferrite particles. When the addition amount of the Ti compound is less than 10% by weight of the total Ti amount, the effect of adding the Ti compound is not sufficient, so that it is difficult to control the surface property and particles having a desired shape may not be obtained. is there.

  The particle size of the Ti compound added here is desirably 5 to 120 nm. In this particle size range, addition and dispersion are easy in the production process, and the surface properties of the core material can be easily controlled. When the particle size of the Ti compound is less than 5 nm, the apparent bulk density becomes too large even if the addition amount is small, and the addition and dispersion may take a long time, resulting in poor productivity. Productivity can be improved by preparing a dispersion of Ti compound in advance, but a large amount of dispersion medium and dispersant are required, and solid content adjustment and viscosity adjustment during granulation may be difficult. . If the particle size exceeds 120 nm, the added Ti compound is likely to be localized in the particles, so that it may not be possible to uniformly form surface properties with appropriate irregularities.

Further, as the Ti compound added at the time of raw material charging or in the granulation step, TiO ₂ that generates one or more kinds of dielectric components selected from Mg ₂ TiO ₄ , MgTiO ₃ , MgTi ₂ O ₄ , SrTiO ₃ , etc. desirable.

(Second firing step)
Next, the granulated material is fired in a non-oxidizing atmosphere or a weakly reducing atmosphere to be ferritized. By this baking, a crystal structure having a lattice constant with little variation is obtained, and particles with a small decrease in magnetization after the surface oxidation treatment can be obtained.

In the granulation step or the second baking step, one or more additive substances selected from carbon black (CB), polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), and charcoal may be added. The desired magnetic properties can be obtained simply by adding polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP) during the granulation step, but in this step (second baking step), carbon black, polyvinyl alcohol (PVA), polyvinyl By adding at least one additive selected from pyrrolidone (PVP) and charcoal, wustite (FeO) is generated excessively, and wustite is preferentially oxidized during the surface oxidation treatment, thereby increasing the iron-excess Mg ferrite component. It is more preferable because a decrease in magnetization due to oxidation can be suppressed. Fe ²⁺ and Fe ₂ O ₃ are present in a crystal structure analysis by powder X-ray diffraction, or when Fe ²⁺ has a low Mn content and redox titration is possible, potassium permanganate or potassium dichromate. It can be grasped by oxidation-reduction titration.

  The firing temperature is preferably 650 to 1200 ° C. When the firing temperature is less than 650 ° C., the crystal structure is not strong, and thus the magnetization is significantly reduced in the oxide film treatment step. On the other hand, if the firing temperature exceeds 1200 ° C., too much heat is applied, the shape deteriorates, and the surface property becomes difficult to control.

(Third firing step)
Next, the ferrite particles are fired again in a non-oxidizing atmosphere or a weak reducing atmosphere to adjust the magnetization and surface properties. By this firing, a crystal structure having a lattice constant with little variation is obtained, and the decrease in magnetization after the surface oxidation treatment is further reduced. Moreover, the formation of pores on the surface can be suppressed.

  The temperature is desirably 1100 to 1400 ° C. When the firing temperature is less than 1100 ° C., the crystal structure is not strong, and thus the magnetization is significantly reduced in the oxide film treatment step. Further, if the firing temperature exceeds 1400 ° C., too much heat is applied, and not only the shape and surface properties cannot be easily controlled, but also it is hard and easily cracked, which is disadvantageous economically.

  Then, collect, dry and classify. As a classification method, the particle size is adjusted to a desired particle size using an existing air classification, mesh filtration method, sedimentation method, or the like. When dry collection is performed, it can also be collected with a cyclone or the like.

(Oxide film treatment process)
An oxide film is formed on the surface of the particles thus obtained. The electrical resistance can be adjusted by forming this oxide film. For the oxide film treatment, a general rotary electric furnace, batch electric furnace or the like is used. In order to uniformly form the oxide film on the core particles, it is preferable to use a rotary electric furnace, that is, a rotary kiln. By using the rotary kiln, the heat application becomes uniform, the distribution range of the magnetic force and the resistance is narrow, and it is possible to prevent the carrier adhesion when the developer is used.

  The temperature of the oxide film treatment is preferably 400 to 800 ° C. When the temperature of the oxide film treatment is less than 400 ° C., the resistance cannot be increased sufficiently, and when it exceeds 800 ° C., the magnetization is greatly reduced.

<Carrier core material for electronic developer obtained by the production method of the present invention>
A carrier core material for an electronic developer can be obtained by the manufacturing method described above.

  The carrier core material for an electronic developer has a composition of at least 48.0 to 70.0% by weight of Fe, 1 to 5% by weight of Mg, 0.1 to 3.5% by weight of Ti, and Sr of 0.0. 1 to 5.0% by weight is contained. Further, it is desirable to contain 0.1 to 20% by weight of Mn, more desirably 0.1 to 10% by weight, still more desirably 0.1 to 5% by weight, and 0.1 to 2.0% by weight. Most desirable. By having such a composition, a desired resistance such as medium resistance or high resistance can be obtained while being highly magnetized. In addition, although Mn has a favorable effect in the said range, it is desirable to reduce as much as possible from a viewpoint of environmental regulation.

  The thickness of the oxide film of the carrier core material for electrophotographic developer is preferably 0.0001 to 10 μm. By having such an oxide film, a desired resistance such as medium resistance or high resistance can be obtained while being highly magnetized. The thickness of the oxide film can be measured from a high-magnification SEM photograph that can confirm that the oxide film is formed. The oxide film may be formed uniformly on the surface of the core material, or may be partially formed with an oxide film.

The ferrite carrier core material for an electrophotographic developer desirably contains at least one temperature-compensated dielectric component selected from Mg ₂ TiO ₄ , MgTiO ₃ , and MgTi ₂ O ₄ . The total content of these substances is preferably 0.2 to 10% by weight. By containing such a substance, a high charge amount can be obtained, and when it is used as an electrophotographic developer, it is excellent in charging stability in each environment.

Mg ₂ TiO ₄ , MgTiO ₃ , and MgTi ₂ O ₄ are all representative of temperature compensation type dielectric components, and Mg ₂ TiO ₄ is cubic and contains well with the same cubic spinel structure. Easy to be. MgTi ₂ O ₄ is likely to be produced when the reducibility is strong in any of the firing steps of the core material. MgTiO ₃ has a rhombohedral structure and is likely to be produced when oxidation is strong in any of the firing steps of the core material.

  In this carrier core material for an electrophotographic developer, when the total content of the temperature-compensated dielectric component is less than 0.2% by weight, not only a high charge level can be exhibited but also the charge amount of the carrier core material depends on the environment. It becomes a big thing. The target charge level and charge stability can be obtained even when the total content of the temperature-compensated dielectric component is larger than 10% by weight, but the charge level reaches a peak, so that it exceeds 10% by weight. Is also meaningless. Considering the environmental dependence of the ferrite carrier core material charge amount, the content of the temperature compensated dielectric component is more preferably 0.2 to 7% by weight, and most preferably 0.2 to 5% by weight.

  In the ferrite carrier core material for an electrophotographic developer according to the present invention, the content of the temperature-compensated dielectric component preferably satisfies the following relational expressions (1) and (2).

When the content of the temperature-compensated dielectric component does not satisfy the relational expression (1), the oxidation is strong in any one of the firing steps of the core material, and not only MgTiO ₃ but also Fe ₂ O _{3 is} also generated in a large amount, and the magnetization is too low to cause carrier scattering, so that there is a possibility that it cannot be used as a carrier.

When the content of the temperature-compensated dielectric component does not satisfy the relational expression (2), the reducing property is strong in any one of the firing steps of the core material, and not only MgTi ₂ O ₄ but also FeO May be generated in a large amount and the magnetization is too low to cause carrier scattering, so that it may not be used as a carrier.

Mg ₂ TiO ₄ , MgTiO ₃ , and MgTi ₂ O ₄ are temperature-compensated dielectrics whose relative permittivity varies depending on the measurement conditions, but those with a dielectric constant of about 16 to 18 are known and control the composition and manufacturing method. Thus, it is common practice to reduce the temperature coefficient of the dielectric constant so that it is not affected by the temperature of the dielectric. On the other hand, the dielectric constant of the ferrite component changes due to the temperature, and the charge level of the ferrite carrier core material changes. Therefore, if the temperature coefficient of the relative permittivity of the temperature-compensated dielectric component is controlled so as to offset the change in the relative permittivity due to the temperature of the ferrite component, environmental fluctuations in the charge amount of the ferrite carrier core material can be minimized. It becomes possible. Alternatively, the temperature of the ferrite carrier core material can be increased by containing one or more substances selected from Mg ₂ TiO ₄ , MgTiO ₃ , and MgTi ₂ O ₄ at a certain ratio according to the temperature change of the relative permittivity of the ferrite component. Regardless of this, a constant dielectric constant can always be maintained. Furthermore, although the relative dielectric constant of the ferrite component varies depending on the measurement conditions, it is often around 8 to 12, and one or more substances selected from Mg ₂ TiO ₄ , MgTiO ₃ and MgTi ₂ O ₄ are present in the core material. This contributes to increasing the charge level of the ferrite carrier core material itself.

In addition, although the temperature coefficient of SrTiO ₃ is large, the relative dielectric constant varies depending on the measurement conditions, but it has a high dielectric constant of 200 or more, and the charging level of the ferrite carrier core material can be further increased by adding it to an extent that does not deteriorate the environment dependency. Can be raised. The content is desirably 3% by weight or less, and when the content exceeds 3% by weight, the temperature change of the dielectric constant of the ferrite carrier core material becomes too large, and the environmental dependency of the charge amount becomes too large. .

The presence or absence of crystal structures such as Mg ₂ TiO ₄ , MgTiO ₃ , MgTi ₂ O ₄ and SrTiO ₃ is measured by the following.

(Measurement of crystal structure: X-ray diffraction measurement)
“X′PertPRO MPD” manufactured by Panalical Co., Ltd. was used as a measuring apparatus. Measurement was performed by continuous scanning at 0.2 ° / sec using a Co tube (CoKα ray) as an X-ray source and a concentrated optical system and a high-speed detector “X'Celarator” as an optical system. The measurement results were processed using data for analysis “X'Pert HighScore” in the same manner as in the crystal structure analysis of ordinary powders, and the crystal structure was identified. In identifying the crystal structure, Fe and O are essential elements, and Mn, Mg, Ti, and Sr are elements that may be contained. In addition, the X-ray source can be measured without problems even with a Cu tube, but in the case of a sample containing a large amount of Fe, the background becomes larger than the peak to be measured, so it is better to use a Co tube. preferable. In addition, the optical system may obtain the same result even when the parallel method is used, but measurement with a concentrated optical system is preferable because the X-ray intensity is low and measurement takes time. Furthermore, the speed of continuous scanning is not particularly limited, but in order to obtain a sufficient S / N ratio when analyzing the crystal structure, the peak intensity of the (113) plane of the spinel structure is set to about 50000 cps, The measurement was performed by setting the carrier core material in the sample cell so that there was no orientation in a specific preferred direction.

Typical spinel structures according to the present invention are MgFe ₂ O ₄ , Fe ₂ TiO _4, and Fe ₃ O _4, but these crystal structures and parts thereof are substituted with Mn and / or Sr. All of them are included, and include those in which lattice defects are periodically included in the spinel structure by firing in a non-oxidizing atmosphere.

There are Mg ₂ TiO ₄ , MgTiO ₃ , MgTi ₂ O ₄ , SrTiO _3, etc. as the crystal structure of the Ti compound other than the spinel structure according to the present invention, and the above crystal structure is periodically formed by firing in a non-oxidizing atmosphere. Including those including lattice defects.

The carrier core material for an electrophotographic developer has a shape factor SF-1 (circularity) of 105 to 140, a BET specific surface area of 0.09 to 0.25 m ² / g, and an apparent density of 2.0 to 2.45 g. Each is preferably / cm ³ . These measuring methods will be described later.

  This carrier core material for an electrophotographic developer is coated with a resin on the surface thereof, and used as an electrophotographic developer together with a toner as a resin-coated carrier. The mixing ratio of the carrier and the toner (toner weight / (carrier weight + toner weight)), that is, the toner concentration is preferably set to 3 to 15% by weight. If it is less than 3% by weight, it is difficult to obtain a desired image density. If it exceeds 15% by weight, toner scattering and fogging are likely to occur.

  The electrophotographic developer according to the present invention can also be used as a replenishment developer. In this case, the mixing ratio of the carrier and the toner (toner weight / (carrier weight + toner weight)), that is, the toner concentration is preferably set to 50% by weight and less than 100% by weight.

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

(First firing step)
Fe ₂ O ₃ , Mg (OH) ₂ , TiO ₂ , SrCO ₃ so that Fe is 7 mol, Mg is 0.435 mol, Ti is 0.075 mol, Sr is 0.075 mol, and Mn is 0.075 mol. And MnO were weighed, water was added so that the solid content was 50% by weight, and the mixture was mixed with a bead mill, and the mixed slurry was granulated with a spray dryer. At this time, PVA is added as a binder component so that the solid content is 0.75% by weight, and a polycarboxylic acid-based dispersant is added so that the slurry has a viscosity of 1 to 2 poises, and the resulting granulated product is obtained. Was baked in a rotary kiln at 1050 ° C. in a non-oxidizing atmosphere, and ferrite was advanced while removing organic substances, and at the same time a part of iron oxide was reduced.

(Granulation process)
The obtained baked product D ₅₀ of the slurry particle size with a bead mill and ground to a 1.59. At this time, PVA was added as a binder component so that the solid content of the slurry was 0.5% by weight, and a polycarboxylic acid dispersant was added so that the viscosity of the slurry was 2 to 3 poises. The pulverized slurry was granulated again with a spray dryer. At this time, TiO ₂ was added as an additional material so that Ti might be 0.05 mol. The particle size of this TiO ₂ is 25 nm, and the amount added corresponds to 40% by weight of the total amount of Ti.

(Second firing step)
Firing was performed in a rotary kiln at 850 ° C. in a non-oxidizing atmosphere, and ferrite was advanced while removing organic substances, and at the same time a part of iron oxide was reduced.

(Third firing step)
After the coarse particles were removed from the fired product using an 80-mesh sieve, it was fired at 1150 ° C. for 16 hours in a non-oxidizing atmosphere to obtain a fired product. The obtained fired product was crushed, classified, and magnetically separated to obtain carrier core particles having a volume average particle size of 28.41 μm.

(Oxide film treatment process)
Further, the obtained carrier core particles were subjected to a surface oxidation treatment with a rotary kiln under the conditions of a surface oxidation treatment temperature of 540 ° C. and an atmospheric atmosphere to obtain surface oxidized carrier core particles.

  Carrier core particles were obtained in the same manner as in Example 1 except that the firing temperature was 1100 ° C. in the first firing step and the amount of PVA added was 0.25 wt% in the granulation step.

  Carrier core particles were obtained in the same manner as in Example 1 except that the firing temperature was 900 ° C. in the first firing step and the amount of PVA added was 0.75 wt% in the granulation step.

  In the second firing step, carrier core particles were obtained in the same manner as in Example 1 except that the firing temperature was 1050 ° C.

  In the third firing step, carrier core particles were obtained in the same manner as in Example 1 except that the firing temperature was 1135 ° C.

  In the third baking step, carrier core particles were obtained in the same manner as in Example 1 except that the baking temperature was 1215 ° C.

  Carrier core particles were obtained in the same manner as in Example 1 except that the addition amount of PVA was 1 wt% in the first firing step and the addition amount of PVA was 0.25 wt% in the granulation step.

  Carrier core particles are obtained in the same manner as in Example 1 except that the amount of PVA added is 0.3 wt% in the first firing step and the amount of PVA added is 0.75 wt% in the granulation step. It was.

  In the first firing step, carrier core particles were obtained in the same manner as in Example 1 except that PVP was used instead of PVA.

  In the first firing step, PVP was used instead of PVA, the addition amount was 1.1 wt%, and the addition amount of PVA was 0.25 wt% in the granulation step, as in Example 1. Thus, carrier core particles were obtained.

  Carrier core material particles are obtained in the same manner as in Example 1 except that the addition amount of PVA is 0.75 wt% in the first firing step and the addition amount of PVA is 0.75 wt% in the granulation step. It was.

  In the first firing step, charcoal is used instead of PVA, the addition amount is 1.5% by weight, the raw materials are mixed with a Henschel mixer, and granulation in the first firing step is performed with a roller compactor, Carrier core material particles were obtained in the same manner as in Example 1.

  In the first firing step, CB was used instead of PVA, the amount added was 1% by weight, the raw materials were mixed with a Henschel mixer, and granulation in the first firing step was performed with a roller compactor. In the same manner as in Example 1, carrier core particles were obtained.

  Carrier core material particles were obtained in the same manner as in Example 1 except that the surface oxidation treatment was 690 ° C.

  Carrier core material particles were obtained in the same manner as in Example 1 except that the surface oxidation treatment was 410 ° C.

Carrier core in the same manner as in Example 1 except that the Ti compound (TiO ₂ ) was added so that the feed amount of raw material Ti was 0.1 mol and the addition amount of Ti in the granulation step was 0.025 mol. Material particles were obtained.

Carrier core in the same manner as in Example 1 except that the Ti compound (TiO ₂ ) was added so that the amount of raw material Ti charged was 0.025 mol and the amount of Ti added in the granulation step was 0.1 mol. Material particles were obtained.

Carrier core material particles are obtained in the same manner as in Example 1 except that the raw material Ti is not added and the Ti compound (TiO ₂ ) is added so that the amount of Ti added in the granulation step is 0.125 mol. It was.

Carrier core material particles in the same manner as in Example 1 except that the raw material Mn was not added and the Mn compound (Mn ₃ O ₄ ) was added so that the amount of Mn added in the granulation step was 0.075 mol. Got.

  Carrier core particles were obtained in the same manner as in Example 1 except that the particle size of the Ti compound added to the granulation step was 100 nm.

Comparative example

[Comparative Example 1]
Carrier core in the same manner as in Example 1 except that the amount of raw material Ti was 0.125 mol, the amount of PVA added in the first firing step was 0.3% by weight, and no Ti compound was added in the granulation step. Material particles were obtained.

[Comparative Example 2]
(First firing step)
Fe ₂ O ₃ , Mg (OH) ₂ , SrCO _3, and Mn ₃ O ₄ are weighed so as to be 10 mol Fe, 1 mol Mg, 0.02 mol Sr, and 4 mol Mn, and then mixed with a Henschel mixer. The mixture was granulated with a roller compactor. At this time, additives (reducing agent and binder component) were not added. The obtained granulated material was baked in a rotary kiln in the air at 980 ° C., and ferritization was advanced while removing organic substances.

(Granulation process)
The obtained baked product D ₅₀ of the slurry particle size with a bead mill and ground to a 1.33. At this time, PVA was added as a binder component so that the solid content of the slurry was 0.5% by weight, and a polycarboxylic acid dispersant was added so that the viscosity of the slurry was 2 to 3 poises. The pulverized slurry was granulated again with a spray dryer.

(Second firing step)
Firing was performed in a rotary kiln at 650 ° C. in an air atmosphere to remove organic substances.

  Thereafter, the third baking and the oxide film treatment were carried out in the same manner as in Example 1, and in the same manner as in Example 1, carrier core material particles were obtained.

  About Examples 1-20 and Comparative Examples 1-2, the manufacturing conditions (preparation amount, atmosphere, temperature) of each step of the carrier core material, the type of Ti compound, the particle size, the added amount, and the ratio of total Ti, of the Mn compound Type and addition amount, type and addition amount of additive element, particle size of slurry particles used in granulation process, X-ray diffraction of each process, chemical analysis (ICP) after third firing process and various characteristics (magnetization, apparent Tables 1 to 7 show the density, average particle diameter, residual magnetization, coercive force, resistance, SF-1, BET specific surface area, true density and charge amount (under N / N environment). Various characteristics were evaluated according to the following.

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

(BET specific surface area)
Using an automatic specific surface area measuring apparatus GEMINI 2360 (manufactured by Shimadzu Corp.), it can be determined from the N ₂ adsorption amount of carrier particles measured by adsorbing N ₂ as an adsorption gas. Here, the measurement tube used for measuring the N ₂ adsorption amount was baked for 2 hours at 50 ° C. in a reduced pressure state before the measurement. Further, 5 g of carrier particles were filled in this measuring tube, and after pretreatment at a temperature of 30 ° C. for 2 hours under reduced pressure, N ₂ gas was adsorbed at 25 ° C., and the amount of adsorption was measured. These adsorption amounts are values calculated from the BET equation by drawing an adsorption isotherm.

(Apparent density)
It measured based on JISZ2504. Details are as follows.
1. Apparatus The powder apparent density meter is composed of a funnel, a cup, a funnel support, a support bar and a support base. A balance with a weighing of 200 mg and a weighing of 50 mg is used.
2. Measuring method (1) The sample shall be at least 150 g or more.
(2) The sample is poured into a funnel having an orifice with a pore diameter of 2.5 ^{+ 0.2 / −0} mm, and poured until the sample that has flowed out fills the glass and overflows.
(3) Stop the inflow of the sample as soon as it begins to overflow, and scrape the sample raised on the cup flatly with a spatula along the top edge of the cup so as not to give vibration.
(4) Tap the side surface of the cup to sink the sample and remove the sample attached to the outside of the cup, and weigh the sample in the cup with an accuracy of 0.05 g.
3. Calculation The numerical value obtained by multiplying the measured value obtained in 2- (4) above by 0.04 is rounded to the second decimal place by JIS-Z8401 (how to round the numerical value), and the unit of “g / cm ³ ” appears. Density.

(Magnetic properties)
It measured using the integral type BH tracer BHU-60 type (made by Riken Denshi Co., Ltd.). A magnetic field measuring H coil and a magnetization measuring 4πI coil are placed between the electromagnets. In this case, the sample is placed in a 4πI coil. The outputs of the H coil and the 4πI coil whose magnetic field H is changed by changing the current of the electromagnet are respectively integrated, and the H output is drawn on the X axis, the output of the 4πI coil is drawn on the Y axis, and a hysteresis loop is drawn on the recording paper. As measurement conditions, sample filling amount: about 1 g, sample filling cell: inner diameter 7 mmφ ± 0.02 mm, height 10 mm ± 0.1 mm, 4πI coil: measured with 30 turns.

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

(True density)
The true density of the carrier core material and the filled carrier particles was measured using a pycnometer in accordance with JIS R9301-2-1. Here, methanol was used as a solvent, and measurement was performed at a temperature of 25 ° C.

(Volume resistance)
A sample was filled in a fluororesin cylinder having a cross-sectional area of 4 cm ² so that the height was 4 mm, electrodes were attached to both ends, and a weight of 1 kg was further placed thereon to measure resistance. The resistance was measured by applying a voltage of 50 V and / or 1000 V with a Keithley 6517A type insulation resistance measuring instrument and calculating the resistance from the current value after 10 sec (current value of 10 sec) to obtain volume resistance.

(Charge amount measurement)
The charge amount is measured as follows. That is, 3.5 g of a styrene-acrylic negatively chargeable commercially available toner (volume average particle size 5.8 μm) and 46.5 g of a carrier core material are weighed and placed in a 50 ml glass bottle so that the glass bottle is rotated 100 times with a ball mill. Mixing and stirring were performed at the same rotational speed. The stirring time was 30 min, and the developer was exposed to an N / N environment (room temperature 25 ° C., humidity 55%) for 1 hour, and then the charge amount was measured with an Epping charge amount measuring device q / m-meter. At this time, the charge amount was a value 90 seconds after the start of measurement.

In Examples 1 to 20, as is apparent from the results of Tables 1 and 2, a fired product containing a spinel phase substance, a nonmagnetic Ti compound, and Fe ₂ O ₃ was obtained in the first firing step. As is apparent from the results of Tables 3 and 4, the fired product obtained in the first firing step is used as a raw material, and a T compound that has not been fired in the same composition is further added, and firing is further performed in the second firing step. A fired product with high magnetization was obtained by adding an additive material so as to facilitate the progress. As is clear from the results in Table 5, the nonmagnetic wustite (FeO) produced in the second firing step was maintained in the third firing step, and despite containing the Ti compound, 2 Firing process A fired product having a higher magnetization was obtained as compared with the firing process. From the results in Table 6, it was also clear that after the third firing step, it had a constant ferrite composition. For this reason, as is apparent from the results in Table 7, a core material for an electrophotographic carrier having an excellent balance between magnetization and resistance while minimizing the decrease in magnetization in the surface oxidation treatment was obtained.

  On the other hand, as is clear from Table 7, Comparative Example 1 has a high resistance, a small SF-1, a small BET specific surface area, and a large apparent density and true density because there are few surface irregularities. Yes, the intended carrier core material was not obtained. Further, as is clear from Table 7, the charge amount of Comparative Example 2 was extremely low.

  The production method of the present invention not only does not contain each heavy metal, but also reduces the Mn content and provides not only a desired resistance such as medium resistance or high resistance while having high magnetization, but also high charge and good appearance. A carrier core material for an electrophotographic developer having a density, a surface property having moderate unevenness and a uniform shape can be stably obtained on an industrial scale.

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

Claims (16)

A method for producing a carrier core material for an electrophotographic developer comprising at least Fe, Mg, Ti and Sr, and comprising ferrite particles having at least a spinel structure and a Ti compound structure,
(1) a first firing step of adding, mixing, and firing at least a Mg compound, a Sr compound, and Fe ₂ O ₃ in a non-oxidizing atmosphere or a weak reducing atmosphere to obtain a mixture containing Fe ²⁺ ;
(2) A granulation step of granulating slurry particles after slurrying the obtained mixture;
(3) a second firing step in which the granulated material is fired in a non-oxidizing atmosphere or a weakly reducing atmosphere to be ferritized;
(4) a third firing step of firing again in a non-oxidizing atmosphere or a weak reducing atmosphere to adjust magnetization and surface properties;
(5) an oxide film treatment step for forming an oxide film on the particle surface;
A carrier core material for an electrophotographic developer, wherein the residual amount of Fe ₂ O ₃ after the first baking step is 0 to 60% by weight, and a Ti compound is added in the granulation step Manufacturing method.   The method for producing a carrier core material for an electrophotographic developer according to claim 1, wherein a Ti compound and / or a Mn compound is added to the first firing step. The carrier core material for an electrophotographic developer according to claim 1 or 2, wherein the Ti compound generates one or more kinds of dielectric components selected from Mg ₂ TiO ₄ , MgTiO ₃ , MgTi ₂ O ₄ , and SrTiO _3. Method.   The method for producing a carrier core material for an electrophotographic developer according to any one of claims 1 to 3, wherein a particle diameter of the Ti compound added in the granulation step is 5 to 120 nm or less.   The carrier core material for an electrophotographic developer according to any one of claims 1 to 4, wherein in the granulation step, a Ti compound is added so as to be 10 to 100% by weight of the total Ti amount contained in the ferrite particles. Manufacturing method.   In at least one step selected from the first firing step, the granulation step and the second firing step, at least one selected from carbon black (CB), polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP) and charcoal. The method for producing a carrier core material for an electrophotographic developer according to any one of claims 1 to 5, wherein the additive substance is added.   The method for producing a carrier core material for an electrophotographic developer according to any one of claims 1 to 6, wherein the firing in the first firing step is performed at 800 to 1200 ° C.   The method for producing a carrier core material for an electrophotographic developer according to any one of claims 1 to 7, wherein the firing in the second firing step is performed at 650 to 1200 ° C.   The method for producing a carrier core material for an electrophotographic developer according to any one of claims 1 to 8, wherein the firing in the third firing step is performed at 1100 to 1400 ° C.   The method for producing a carrier core material for an electrophotographic developer according to any one of claims 1 to 9, wherein the oxide film treatment step is performed at 400 to 800 ° C.   The method for producing a carrier core material for an electrophotographic developer according to any one of claims 1 to 10, wherein a rotary kiln is used in the oxide film treatment step.   The method for producing a carrier core material for an electrophotographic developer according to any one of claims 1 to 11, wherein the particle size of the slurry particles used in the granulation step is 1.0 to 3.0 µm.   A carrier core material for an electrophotographic developer obtained by the production method according to claim 1.   14. At least 48.0 to 70.0% by weight of Fe, 1 to 5% by weight of Mg, 0.1 to 3.5% by weight of Ti and 0.1 to 5.0% by weight of Sr. The carrier core material for an electrophotographic developer described in 1.   The carrier core material for an electrophotographic developer according to claim 13 or 14, comprising 0.1 to 20% by weight of Mn.   The carrier core material for an electrophotographic developer according to any one of claims 13 to 15, wherein the oxide film has a thickness of 0.0001 to 10.0 µm.