JP5773118B2 - Magnetic carrier for electrophotographic developer, method for producing the same, and two-component developer - Google Patents

Description

  The present invention relates to a magnetic carrier for an electrophotographic developer, and more specifically, from ferromagnetic iron oxide particles having a coating layer made of melamine resin formed on the surface of particles having fine irregularities, phenol resin and melamine resin. Due to the spherical magnetic composite particles, the electrical resistance value can be maintained appropriately during development, durability, high density and uniform solid reproduction can be obtained, and high image quality with excellent gradation etc. An electrophotographic developer that can maintain a long image, has excellent adhesion when coated with a resin, can prevent abrasion and peeling of the coating layer, and is extremely stable against mechanical stress on the carrier. The present invention provides a two-component developer comprising a magnetic carrier for use and a magnetic carrier for electrophotographic developer and a toner.

  As is well known, in electrophotography, a photoconductive material such as selenium, OPC (organic semiconductor), or a-Si is used as a photoconductor, and an electrostatic latent image is formed by various means. In general, a method is used in which a toner charged opposite to the polarity of the latent image is attached by electrostatic force and visualized by using a brush developing method or the like.

  In this development process, a two-component developer composed of a toner and a carrier is used, and carrier particles called a carrier impart an appropriate amount of positive or negative electricity to the toner by frictional charging, and magnetic force is increased. The toner is conveyed to a developing region near the surface of the photosensitive member on which a latent image is formed through a developing sleeve using a magnet.

  In recent years, the electrophotographic copying machines or printers have been digitized and combined, and demands for higher functionality, higher image quality, and higher speed have increased more than ever. In addition, along with market demands such as personalization and space saving, miniaturization of electrophotographic image forming apparatuses is promoted. In particular, with regard to full-color image quality, high-quality printing similar to high-quality printing and silver salt photography is desired. For this reason, it is important to stably maintain the developer charging in order to visualize the minute latent image faithfully over a long period of time. In order to maintain these characteristics stably, the carrier characteristics contained in the developer, that is, the charging performance of the carrier having the charging function, and various characteristics such as electrical resistance can be maintained over a long period of time. There is a need for more.

  Until now, the carrier forming the developer stays in the apparatus and repeats friction with the toner, so that there is a problem that the surface state of the carrier changes with the passage of time and the image changes. This is because the toner adheres firmly to the surface of the carrier particles and is contaminated, so that the chargeability of the original carrier is lost (so-called toner spent) and the resin formed on the surface of the carrier particles. Two major causes are the phenomenon in which the coating layer peels off due to friction, causes leak sites, and changes in electrical resistance.

  In order to prevent the toner from becoming spent on the carrier against these problems, methods for coating the surface of the carrier with various resins have been proposed. For example, the surface of the carrier core material particle is a fluororesin or a silicone resin. What coat | covered mold release resin, such as, is known. Such a coat type carrier not only has a function of controlling the charge amount and resistance, but also has a surface covered with a low surface energy substance, so that it is difficult for the toner to become spent during development, resulting in a stable charge amount. The life of the developer can be extended.

On the other hand, the carrier is required to have a certain electric resistance value, and an electric resistance value of about 1 × 10 ⁸ to 1 × 10 ¹⁶ Ω · cm is required. That is, when the electrical resistance value is as low as 10 ⁶ Ω · cm as in the case of an iron powder carrier, the carrier adheres to the image portion of the photoreceptor due to charge injection from the sleeve, or the latent image charge escapes through the carrier, There is a problem that the latent image is disturbed or the image is lost. In addition, if the insulating resin is coated thickly, the electrical resistance value becomes too high, the carrier charge is less likely to leak, and the toner charge amount is also increased, resulting in an edged image, On the other hand, there is a problem that the image density at the center is very thin on a large-area image surface.

  In addition, when the electrical resistance value is highly dependent on the voltage, the image generally has no gradation, and it is difficult to improve the image quality when used as a developer for copying machines and printers, and the application is limited. It becomes.

  Generally, as a carrier constituting a two-component developer, an iron powder carrier and a ferrite carrier, a binder type carrier in which magnetic particle powder is dispersed in a binder resin, and a coat type carrier obtained by coating a magnetic material with a coating resin Is well known.

The iron powder carrier and the ferrite carrier are usually used by coating the particle surface with a resin, but the iron powder carrier has a true specific gravity of 7 to 8 g / cm ³ and the ferrite carrier has a true specific gravity of 4.5 to 5. Because it is as large as 5 g / cm ³ , a large driving force is required to stir in the developing machine, and mechanical wear is high, causing toner spent, charging deterioration of the carrier itself and damage to the photoreceptor. Easy to invite. Furthermore, it is difficult to say that the adhesion between the iron powder carrier and ferrite carrier surface and the coating resin is good, and the coating resin gradually peels off during use, causing a change in chargeability, resulting in image disturbance and carrier adhesion. Cause problems such as.

  However, the magnetic material-dispersed carrier composed of spherical magnetic composite particles of magnetic iron oxide particles and phenol resin described in JP-A-2-220068 is more adhesive to the coating resin than the iron powder carrier and ferrite carrier. The problem that the coating resin peels off during use hardly occurs.

  However, in recent years, with the progress of colorization, there has been an increasing demand for improvement of various properties for carriers for high image quality and long life that can be stably maintained over a long period of time. In addition, there is a problem that it is insufficient for suppression of mechanical stirring in the developing device, scraping of the coating resin caused by thermal stress, or peeling. In addition, since the electrical resistance value of the spherical magnetic composite particles serving as the core material of the magnetic material dispersion type carrier is low, when the resin coating layer is peeled off, leakage occurs during development, and the voltage dependence of the electrical resistance value is There is a problem that the gradation is inferior because it becomes larger.

In particular, since there has recently been a shift to the age of maintenance-free systems, developer durability may be required until the end of the machine life, and measures to prevent peeling of the coating resin due to wear and make toner spent less likely. There is a strong demand for magnetic carriers having sufficient electrical resistance and low voltage dependence of electrical resistance.

Conventionally, as a magnetic carrier for an electrophotographic developer, there is an example in which surface unevenness is controlled by focusing on the particle surface.
For example, a technology (Patent Document 1) in which the particle surface of resin-dispersed particles or spray-dried particles is controlled by a ten-point average roughness Rz and its standard deviation, and a convex portion forming material is included to form irregularities on the particle surface. In addition, a technique (Patent Documents 2 and 3) in which the particle surface is controlled by the ten-point average roughness Rz or the height difference of the unevenness and the number of the protruding portions is included.

Further, there is an example in which melamine resin coating is attempted on composite particles composed of ferromagnetic iron oxide fine particles and a cured phenol resin.
For example, a technology for increasing the resistance by coating the surface of a composite core particle composed of ferromagnetic fine particles and a cured phenol resin with melamine resin (Patent Document 4), consisting of iron oxide particle powder and a cured phenol resin. On the particle surface of the composite core particles, a coating layer made of a cured copolymer resin of one or more resins selected from melamine resin, aniline resin, and urea resin and a phenol resin is formed, and the electric resistance value of the carrier And the like (Patent Document 5).

JP 2008-83098 A JP 2006-18129 A JP 2002-287431 A JP-A-3-192268 Japanese Patent Laid-Open No. 9-311505

  However, in each of the techniques described in Patent Documents 1 to 3 in which the surface irregularities are controlled, collision between the particles, mechanical stirring in the particles and the developing device, and the load applied to the convex portions of the particle surface irregularities due to thermal stress. Since the influence is large, there is a problem that the coating resin is not sufficient for suppressing scraping and peeling, and further, the melamine resin coating is attempted on the composite particles composed of the ferromagnetic iron oxide fine particles and the cured phenol resin. Each technique described in Patent Document 4 or 5 has problems such as insufficient electrical resistance during development, and it is difficult to say that the above-described problems are satisfied.

  The present invention solves the above-mentioned conventional problems, is excellent in durability against peeling and abrasion of the coating resin, is also stable against mechanical stress on the carrier, and does not cause toner spent, and has the above characteristics for a long time. In addition, the electrical resistance value can be maintained appropriately during development, durability, high density and uniform solid reproduction can be obtained, and gradation and other high image quality are excellent. TECHNICAL PROBLEM TO BE SOLVED: To provide a magnetic carrier for an electrophotographic developer used for an electrophotographic developer capable of maintaining an image, a method for producing the same, and a two-component developer having the magnetic carrier for an electrophotographic developer and a toner. And

  The technical problem can be achieved by the present invention as follows.

  That is, the present invention is a magnetic carrier for an electrophotographic developer in which a coating layer made of melamine resin is formed on the surface of spherical magnetic composite particles in which ferromagnetic iron oxide particles are bound with a phenol resin as a binder. The particle surface of the magnetic carrier is a magnetic carrier for an electrophotographic developer, wherein the ten-point average roughness Rz is 0.3 μm to 2.0 μm (Invention 1).

  The present invention also provides the magnetic carrier for an electrophotographic developer according to the first aspect of the present invention, wherein the particle surface of the magnetic carrier has a maximum height Ry of 0.7 μm to 2.5 μm (Invention 2).

  Further, according to the present invention, the particle surface of the magnetic carrier has an arithmetic average roughness Ra of 0.1 μm to 0.6 μm, and an average interval Sm of irregularities of 0.6 μm to 6.0 μm. The magnetic carrier for an electrophotographic developer described (Invention 3).

In the present invention, the spherical magnetic composite particles include a total amount of ferromagnetic iron oxide particles of 80 to 99% by weight,
The ferromagnetic iron oxide particles are composed of ferromagnetic iron oxide particles a and ferromagnetic iron oxide particles b having different average particle diameters,
The ratio of the average particle diameter ra of the ferromagnetic iron oxide particles a having a large average particle diameter to the average particle diameter rb of the ferromagnetic iron oxide particles b having a small average particle diameter is greater than 1, and the ferromagnetic iron oxide particles The weight ratio of a to the ferromagnetic iron oxide particles b is strong in the range of 1 to 50 parts by weight when the total amount of the ferromagnetic iron oxide particles a and the ferromagnetic iron oxide particles b is 100 parts by weight. A book containing magnetic iron oxide particles a, and the shape of the ferromagnetic iron oxide particles a and the ferromagnetic iron oxide particles b is any one selected from spherical, hexahedral, octahedral, polyhedral and amorphous. A magnetic carrier for an electrophotographic developer according to any one of Inventions 1 to 3 (Invention 4).

In the present invention, the electric resistance value R100 of the magnetic carrier for an electrophotographic developer when the applied voltage is 100 V is 1 × 10 ⁸ Ωcm to 1 × 10 ¹⁶ Ω · cm and the applied voltage is 300 V. Resistance value R300 is 0.1 ≦ R300 / R100 ≦ 1
This is a magnetic carrier for an electrophotographic developer according to any one of the present inventions 1 to 4 (invention 5).

  Moreover, this invention is 1 type by which the particle | grain surface of the magnetic carrier for electrophotographic developers in any one of this invention 1-5 is chosen from silicone resin, fluorine resin, acrylic resin, and styrene-acrylic resin Alternatively, a magnetic carrier for an electrophotographic developer that is coated with two or more types (Invention 6).

  In addition, the present invention is such that the ferromagnetic iron oxide particles a and the ferromagnetic iron oxide particles b having different average particle diameters are reacted and cured in an aqueous medium with phenols and aldehydes so that the surface of the particles is ferromagnetic iron oxide. A spherical magnetic composite particle composed of a ferromagnetic iron oxide particle and a phenol resin formed with irregularities due to the shape of the particle a is produced, and then an acidic catalyst is contained in an aqueous medium containing the spherical magnetic composite particle. The electrophotography according to any one of the present inventions 1 to 5, wherein a coating layer made of a melamine resin is formed by adding an acidic aqueous solution made of an acid having an acid dissociation constant pKa of 3 to 6 and an aqueous methylolmelamine solution. This is a method for producing a magnetic carrier for developer (Invention 7).

  Further, the present invention is a two-component developer using the magnetic carrier for an electrophotographic developer according to any one of the present inventions 1 to 6 (present invention 8).

  Since the magnetic carrier for an electrophotographic developer according to the present invention forms and controls minute irregularities on the particle surface, it has excellent adhesion when coated with a resin and has durability against peeling and abrasion of the coating layer. Since it is excellent, it is stable against mechanical stress on the carrier, and has an excellent life span that can be stably maintained over a long period of time without causing toner spent. Furthermore, the electric resistance value during development can be maintained appropriately, and voltage dependency is small, so that gradation is excellent, and it is suitable as a magnetic carrier for an electrophotographic developer.

  The two-component developer according to the present invention is suitable as a developer corresponding to high image quality and high speed because the magnetic carrier to be used has excellent durability and controls electric resistance.

It is an electron micrograph which shows the surface structure of the spherical magnetic composite particle obtained in Example 1 (2000 times). It is an electron micrograph which shows the surface structure of the spherical magnetic composite particle obtained in Example 1 (5000 times). It is an electron micrograph which shows the particle structure of the spherical magnetic composite particle obtained in Comparative Example 1 (2000 times). It is an electron micrograph which shows the surface structure of the spherical magnetic composite particle obtained in Comparative Example 1 (5000 times).

Hereinafter, the present invention will be described in detail.

  First, the magnetic carrier for electrophotographic developer according to the present invention (hereinafter referred to as “magnetic carrier”) will be described.

  The particle surface of the magnetic carrier according to the present invention has a ten-point average roughness Rz of 0.3 μm to 2.0 μm. If the ten-point average roughness Rz is less than 0.3 μm, the surface of the magnetic carrier becomes relatively smooth, so that the adhesiveness with the resin coating is lowered, and sufficient durability cannot be obtained. On the other hand, if the ten-point average roughness Rz exceeds 2.0 μm, the convex portions on the surface of the magnetic carrier are likely to be loaded by friction, wear, mechanical stress, etc., and sufficient durability cannot be obtained. The preferred ten-point average roughness Rz is 0.3 μm to 1.95 μm, and even more preferably 0.3 μm to 1.85 μm.

  The particle surface of the magnetic carrier according to the present invention preferably has a maximum height Ry in the range of 0.7 μm to 2.5 μm. When the maximum height Ry is less than 0.7 μm, appropriate surface unevenness cannot be obtained, and sufficient adhesiveness cannot be obtained during resin coating. Further, if the maximum height Ry exceeds 2.5 μm, the convex portion on the surface of the magnetic carrier is likely to be subjected to a load due to friction, abrasion, mechanical stress, etc., and the unevenness is detached and sufficient durability is obtained. It can no longer be obtained. A more preferable maximum height Ry is 0.7 μm to 2.45 μm.

  The particle surface of the magnetic carrier according to the present invention preferably has an arithmetic average roughness Ra in the range of 0.1 μm to 0.9 μm, more preferably 0.1 μm to 0.5 μm, and an average interval Sm of irregularities of 0. The range of 6 μm to 6.0 μm is preferable, and more preferably 0.6 μm to 5.5 μm. It is preferable that the arithmetic average roughness Ra and the average interval Sm between the concaves and convexes are within the above ranges because the adhesiveness becomes better.

  The total amount of the ferromagnetic iron oxide particles in the magnetic carrier according to the present invention is preferably 80 to 99% by weight with respect to the spherical magnetic composite particles, and if it is less than 80% by weight, the resin content increases and large particles are formed. It becomes easy. If it exceeds 99% by weight, the resin content is insufficient and sufficient strength cannot be obtained. Preferably, it is 85 to 99% by weight.

  The ferromagnetic iron oxide particles contained in the magnetic carrier according to the present invention are composed of ferromagnetic iron oxide particles a and ferromagnetic iron oxide particles b having different average particle diameters. The average particle diameter ratio ra / rb between the average particle diameter ra of the ferromagnetic iron oxide particles a having a relatively large average particle diameter and the average particle diameter rb of the ferromagnetic iron oxide particles b having a relatively small average particle diameter is 1. Greater than .0. When the ratio ra / rb of the average particle diameter is 1.0 or less, the surface layer portion is not formed by the ferromagnetic iron oxide particles a, and sufficient unevenness cannot be obtained. Cannot be obtained. A more preferable average particle diameter ratio ra / rb is 1.1 to 5.0, and still more preferably 1.2 to 4.0.

  The mixing ratio of the ferromagnetic iron oxide particles a and the ferromagnetic iron oxide particles b contained in the magnetic carrier according to the present invention is 1 when the total amount of the ferromagnetic iron oxide particles a and the ferromagnetic iron oxide particles b is 100 parts by weight. It is preferable to contain the ferromagnetic iron oxide particles a within a range of ˜50 parts by weight. When the ferromagnetic iron oxide particles a are less than 1 part by weight, the ferromagnetic iron oxide particles b forming the core portion are likely to appear on the surface of the particles, so that the surface layer portion made of the ferromagnetic iron oxide particles a is not formed. Sufficient surface irregularities cannot be obtained. Further, when the amount of the ferromagnetic iron oxide particles a exceeds 50 parts by weight, all the ferromagnetic iron oxide particles a forming the surface layer portion are difficult to be taken in and become fine powder or coarse particles, which causes a decrease in yield. , Fine irregularities are not sufficiently formed on the particle surface. Preferably it is 5-50 weight part, More preferably, it is 10-45 weight part.

When the electrical resistance value of the magnetic carrier according to the present invention is measured, the electrical resistance value R ₁₀₀ when the applied voltage is 100 V is preferably 1 × 10 ⁸ Ω · cm to 1 × 10 ¹⁴ Ω · cm. By setting the electric resistance value R ₁₀₀ in the above range, the carrier is more prevented from adhering to the image portion of the photoconductor by the charge injection from the sleeve, the latent image charge escapes through the carrier, the latent image is disturbed, Defects and the like can be further suppressed.

When the electrical resistance of the magnetic carrier according to the present invention is measured, the electrical resistance value R ₃₀₀ when the applied voltage is 300 V is preferably 1 × 10 ⁸ Ω · cm to 1 × 10 ¹⁴ Ω · cm.

In the magnetic carrier according to the present invention, the relationship between the electric resistance value R ₁₀₀ when the applied voltage is 100 V and the electric resistance value R ₃₀₀ when the applied voltage is 300 V is 0.1 ≦ R ₃₀₀ / R ₁₀₀ ≦ 1.0.
It is. By setting R ₃₀₀ / R ₁₀₀ within the above range, the voltage dependency of the electrical resistance value can be further reduced.

  The average particle diameter of the magnetic carrier according to the present invention is preferably 10 to 100 μm. When the average particle diameter is less than 10 μm, secondary aggregation tends to occur, and when it exceeds 100 μm, the mechanical strength is weak and a clear image cannot be obtained. A more preferable average particle diameter is 20 to 70 μm.

  The specific gravity of the magnetic carrier according to the present invention is preferably 2.5 to 4.5, more preferably 2.5 to 4.2.

The saturation magnetization value of the magnetic carrier according to the present invention is preferably ²⁰ to 100 Am ² / kg, more preferably 40 to 85 Am ² / kg.

  The magnetic carrier according to the present invention preferably has a sphericity represented by the following formula of 1.0 to 1.4.

Sphericity = l / w
l: Average major axis diameter of spherical magnetic composite particles w: Average minor axis diameter of spherical magnetic composite particles

  The amount of melamine resin relative to the spherical magnetic composite particles is preferably 0.05 to 1.0% by weight, more preferably 0.07 to 0.8% by weight, still more preferably 0.1 to 0.7% by weight. It is. If the amount is less than 0.05% by weight, it is difficult to sufficiently coat, and the voltage dependency of the electrical resistance value of the spherical magnetic composite particles may increase. On the other hand, if it exceeds 1.0% by weight, the electric resistance value becomes too high, which is not preferable.

The particle surface of the magnetic carrier according to the present invention can be coated with one or more resins selected from silicone resins, fluorine resins, acrylic resins, and styrene-acrylic resins. electric resistance of the magnetic carrier, the electric resistance value _{R 100} when the applied voltage of 100V is preferably ^{1 × 10 8 Ω · cm~1 ×} 10 16 Ω · cm. When the electric resistance value R _{100 at} an applied voltage of 100 V exceeds 1 × 10 ¹⁶ Ω · cm, the carrier charge is less likely to leak, and the toner charge amount is also increased, resulting in an edged image. However, on the other hand, in the case of an image surface with a large area, there arises a problem that the image density in the central portion becomes very thin, which is not preferable. The electric resistance value R _{100 at} an applied voltage of 100 V is more preferably 1 × 10 ⁹ Ω · cm to 5.0 × 10 ¹⁵ Ω · cm.

When the electric resistance of the magnetic carrier formed by coating the surface of the spherical magnetic composite particles according to the present invention with a resin is measured, the electric resistance R ₃₀₀ when the applied voltage is 300 V is 1 × 10 ⁸ Ω · cm to 1 ×. 10 ¹⁶ Ω · cm is preferable.

Magnetic carrier obtained by the resin coated on the particle surfaces of the spherical magnetic composite particles according to the present invention, the relationship between the electric resistance value R ₃₀₀ when the electric resistance value R ₁₀₀ and the applied voltage 300V when the applied voltage 100 V (R preferably ₃₀₀ / _{R 100)} is 0.1 to 1.0, more preferably 0.2 to 1.0.

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

  That is, the magnetic carrier according to the present invention reacts phenols and aldehydes in an aqueous medium in the presence of a basic catalyst in the presence of a ferromagnetic iron oxide particle powder to react with phenols and aldehydes. Spherical magnetic composite particles composed of iron oxide particles and a cured phenol resin are produced, and then an acid having an acid dissociation constant pKa of 3 to 6 as an acidic catalyst in an aqueous medium containing the spherical magnetic composite particles. By adding an acidic aqueous solution and a methylolmelamine aqueous solution, a coating layer made of a melamine resin can be formed on the surface of the spherical magnetic composite particles.

  First, the ferromagnetic iron oxide particles used in the present invention will be described.

The average particle diameter ra of the ferromagnetic iron oxide particles a in the present invention is preferably 0.25 μm to 2.0 μm. When the average particle diameter ra is less than 0.25 μm, sufficient unevenness cannot be obtained on the magnetic carrier surface. In addition, when the average particle diameter ra exceeds 2.0 μm, the load applied to the convex portions of the surface irregularities becomes large, and the ferromagnetic iron oxide particles a are desorbed to remove the irregularities, or sufficient for the coating resin. Durability cannot be obtained.
The average particle diameter rb of the ferromagnetic iron oxide particles b in the present invention is preferably 0.05 μm to 0.25 μm. When the average particle diameter rb is less than 0.05 μm, the cohesive force of the magnetic iron oxide particles b becomes large, and it becomes difficult to produce a magnetic carrier. On the other hand, when the average particle size rb exceeds 0.25 μm, there is no difference in particle size from the ferromagnetic iron oxide particles a, and it becomes difficult to form a surface layer portion with the ferromagnetic iron oxide particles a.

  The ferromagnetic iron oxide particles a and the ferromagnetic iron oxide particles b according to the present invention are ferromagnetic iron oxide particles such as magnetite particles and maghematite particles. The particle shape of the ferromagnetic iron oxide particles a and the ferromagnetic iron oxide particles b is any one selected from spherical, hexahedral, octahedral, polyhedral, and indeterminate, and the combination may be the same shape or shape. You may combine things with different.

  In the present invention, the ferromagnetic iron oxide particles a and the ferromagnetic iron oxide particles b are coated with one or more compounds selected from Al, Mg, Mn, Zn, Ni, Cu, Ti, and Si on the particle surface. Ferromagnetic iron oxide particles may be used. When using the above-mentioned compound coated, the amount of the coating element present on the surface of the ferromagnetic iron oxide particles is preferably 0.35 to 4.0% by weight based on the total amount of the ferromagnetic iron oxide particles, More preferably, it is 0.4 to 3.5% by weight. By using ferromagnetic iron oxide particles whose particle surface is coated with one or more compounds selected from Al, Mg, Mn, Zn, Ni, Cu, Ti, and Si, a magnetic carrier having a high electrical resistance value is obtained. Can be easily obtained.

  Ferromagnetic iron oxide particles whose surface is coated with one or more compounds selected from Al, Mg, Mn, Zn, Ni, Cu, Ti, and Si can be obtained by the following production method.

  Ferromagnetic iron oxide particles whose particle surfaces are coated are produced in accordance with a conventional method to produce magnetite core particles, and then the slurry containing the core particles is maintained in a temperature range of 70 to 95 ° C. to adjust the pH of the slurry. By adding the coating element salt at a rate of 0.015 wt% / min or less to the core particles under control, aging for 30 minutes or more, then adjusting the pH, and then washing and drying according to a conventional method Can get.

  The core particles for obtaining the ferromagnetic iron oxide particles coated with the particle surface in the present invention can be selected from those having various shapes and particle sizes from the viewpoint of required magnetic properties and dispersibility. Although there are various production methods, in order to achieve the object of the present invention more effectively, from the viewpoint of performing the surface treatment more uniformly, in the core particle slurry, a substance that tends to be an inhibitor of the surface treatment, For example, it is preferable that no unreacted iron hydroxide fine particles are mixed.

There are various methods for obtaining the slurry containing the core particles. For example, by controlling the pH during the oxidation reaction of the Fe ²⁺ aqueous solution to a predetermined value, octahedron, polyhedron, hexahedron, sphere, An uneven shape can be obtained. Moreover, the core particle of a desired particle diameter can be obtained by controlling the growth conditions of the particles during the oxidation reaction. In addition, the surface smoothness of the core particles controls the growth conditions at the end of the oxidation reaction, and as is generally known, components such as silica components, aluminum components, calcium components, and spinel ferrite crystal structures such as zinc and manganese It can also be controlled by adding a component that tends to form.

As the Fe ²⁺ aqueous solution, for example, a general iron compound such as ferrous sulfate or ferrous chloride can be used. Moreover, aqueous solutions, such as sodium hydroxide and sodium carbonate, can be used for the alkaline solution for obtaining iron hydroxide or as a pH adjuster. Each raw material may be selected in consideration of economy and reaction efficiency.

  The pH of the slurry during the Al surface treatment is preferably 8.0 to 9.0, and more preferably 8.2 to 8.8. When the pH of the slurry is less than 8.0, the Al component is not coated on the surface of the core particles and is precipitated by the Al compound alone, resulting in a low electrical resistance value, a high BET specific surface area value, and hygroscopicity. It becomes high and is not preferable. Even when the pH of the slurry exceeds 9.0, the Al component is not coated on the surface of the core particles and is precipitated by the Al compound alone, resulting in a low electrical resistance value, and a high BET specific surface area value. Is undesirably high. The pH of the slurry during Mg surface treatment is 9.5 to 10.5, the pH of the slurry during Mn surface treatment is 8.0 to 9.0, and the pH of the slurry during Zn surface treatment is 8.0 to 9.0. The pH during Ni surface treatment is 7.5 to 8.5, the pH during Cu surface treatment is 6.5 to 7.5, the pH during Ti surface treatment is 8.0 to 9.0, and during Si surface treatment The pH of is preferably 6.5 to 7.5. When the pH is out of the above range, the electric resistance value is low, and the hygroscopicity is high, which is not preferable.

  The temperature range of the slurry for surface-treating the coating component is preferably 70 to 95 ° C. When the temperature of the slurry is less than 70 ° C., the BET specific surface area value is high, which is not preferable from the viewpoint of hygroscopicity of the ferromagnetic iron oxide particles themselves. Although the condition value is not particularly limited, it is an aqueous slurry, and therefore the upper limit is about 95 ° C. in consideration of productivity and cost.

  The coating compound is preferably added to the slurry containing the core particles at a coating element content of 0.015% by weight / min or less with respect to the core particles. More preferably, the coating element is added at 0.01% by weight / min or less with respect to the core particles. When the coating element is added at a rate greater than 0.015% by weight / min, the coating compound is not coated on the surface of the core particles and precipitates alone, resulting in a low electrical resistance value of the ferromagnetic iron oxide particles themselves, and the BET ratio. The surface area value becomes large and the ferromagnetic iron oxide particles themselves have high hygroscopicity. The lower limit is not particularly limited, but considering productivity, the lower limit is 0.002% by weight / min.

  After adding the coating compound, aging is preferably performed for 30 minutes or more in order to uniformly treat the coating compound on the surface of the core particles. The upper limit is not particularly limited, but considering productivity, the upper limit is about 240 minutes. The slurry is preferably well stirred.

  After aging, it is preferable to control the pH of the slurry in the range of 4.0 to 10.0. More preferably, the pH of the slurry is in the range of 6.0 to 8.0. When the pH is less than 4.0, it is difficult to uniformly form the coating compound layer on the core particle surface. Even when the pH exceeds 10.0, it is difficult to uniformly form the coating compound layer on the core particle surface. In controlling, the slurry is preferably well stirred.

  After the reaction, it may be washed with water and dried according to a conventional method.

  The ferromagnetic iron oxide particles a and the ferromagnetic iron oxide particles b used in the present invention are preferably subjected to lipophilic treatment on the particle surfaces in advance. By carrying out the oleophilic treatment, it is possible to obtain a magnetic carrier having a spherical shape more easily.

  In the oleophilic treatment, the ferromagnetic iron oxide particles a and the ferromagnetic iron oxide particles b are treated with a coupling agent such as a silane coupling agent or a titanate coupling agent, or ferromagnetic in an aqueous solvent containing a surfactant. A method in which iron oxide particles are dispersed and a surfactant is adsorbed on the particle surface is suitable.

  Examples of the silane coupling agent include those having a hydrophobic group, an amino group, and an epoxy group. Examples of the silane coupling agent having a hydrophobic group include vinyl trichlorosilane, vinyl triethoxysilane, vinyl tris (β- Methoxy) silane and the like. As the silane coupling agent having an amino group or an epoxy group, the silane coupling agent having an amino group or the silane coupling agent having an epoxy group may be used.

  As the titanate coupling agent, isopropyl triisostearoyl titanate, isopropyl tridodecylbenzenesulfonyl titanate, isopropyl tris (dioctyl pyrophosphate) titanate or the like may be used.

  As the surfactant, commercially available surfactants can be used, and those having a functional group capable of binding to a ferromagnetic iron oxide particle or a hydroxyl group on the particle surface are desirable, and the ionicity is cationic or anionic. Is preferred.

  Although the object of the present invention can be achieved by any of the above-mentioned treatment methods, the treatment with a silane coupling agent having an amino group or an epoxy group is preferable in consideration of adhesiveness with a phenol resin.

  The treatment amount of the coupling agent or surfactant is preferably 0.1 to 10% by weight with respect to the ferromagnetic iron oxide particles a and the ferromagnetic iron oxide particles b.

  The ferromagnetic iron oxide particles a and the ferromagnetic iron oxide particles b may be preliminarily mixed and then subjected to the oleophilic treatment or separate treatment. It is essential to use the iron particles a and the ferromagnetic iron oxide particles b in a sufficiently mixed state (hereinafter, the state in which the ferromagnetic iron oxide particles a and the ferromagnetic iron oxide particles b are sufficiently mixed is referred to as “ Blend powder).

  The manufacturing method of the spherical magnetic composite particle which consists of the blend powder concerning this invention, a phenol resin, and a melamine resin is as follows.

  As phenols used in the present invention, in addition to phenol, alkylphenols such as m-cresol, p-cresol, p-tert-butylphenol, o-propylphenol, and a part or all of alkyl groups are chlorine atoms and bromine atoms. And compounds having a phenolic hydroxyl group, such as halogenated phenols substituted with.

  Examples of aldehydes used in the present invention include formaldehyde, acetaldehyde, furfural, glyoxal, acrolein, crotonaldehyde, salicylaldehyde, glutaraldehyde and the like in the form of either formalin or paraaldehyde, with formaldehyde being most preferred.

  The molar ratio of aldehydes to phenols is preferably 1.0 to 4.0. When the molar ratio of aldehydes to phenols is less than 1.0, it is difficult to produce particles, Since curing is difficult to proceed, the strength of the resulting particles tends to be weak. When it exceeds 4.0, there is a tendency that unreacted aldehydes remaining in the aqueous medium after the reaction increase. More preferably, it is 1.2-3.0.

  As the basic catalyst used in the present invention, a basic catalyst used in the production of ordinary resole resins can be used. For example, ammonia water, hexamethylenetetramine, alkylamines such as dimethylamine, diethyltriamine, and polyethyleneimine can be mentioned, and ammonia water is particularly preferable. The basic catalyst is preferably 0.05 to 1.50 in molar ratio to phenols. If it is less than 0.05, curing does not proceed sufficiently and granulation becomes difficult. If it exceeds 1.50, the structure of the phenol resin is affected, so that the granulation property is deteriorated and it is difficult to obtain particles having a large particle size.

  Although the reaction in the present invention is carried out in an aqueous medium, the solid content concentration in the aqueous medium is preferably 30 to 95% by weight, particularly preferably 60 to 90% by weight. .

  The reaction solution to which the basic catalyst has been added is heated to a temperature range of 60 to 95 ° C., and reacted at this temperature for 30 to 300 minutes, preferably 60 to 240 minutes, followed by a polycondensation reaction of a phenol resin and curing.

  At this time, in order to obtain spherical magnetic composite particles with high sphericity, it is desirable to raise the temperature gently. The rate of temperature rise is preferably 0.3 to 1.5 ° C / min, more preferably 0.5 to 1.2 ° C / min.

  At this time, it is desirable to control the stirring speed in order to control the particle size. The stirring speed is preferably 100 to 1000 rpm.

  The reaction for forming a coating layer made of melamine resin on the surface of the spherical magnetic composite particles in the present invention is continuously performed in the aqueous medium in which the spherical magnetic composite particles are generated. That is, while maintaining the reaction solution in the temperature range of 60 to 95 ° C., methylol prepared by reacting an acidic aqueous solution composed of an acid having an acid dissociation constant pKa of 3 to 6 as an acidic catalyst with water and melamine and aldehydes. An aqueous melamine solution is added and reacted while stirring for 30 to 300 minutes, preferably 60 to 240 minutes, and the melamine resin is cured on the surface of the spherical composite core particles.

  At this time, in order to form a thin and uniform coating layer made of melamine resin on the surface of the spherical magnetic composite particles, it is desirable to control the reaction temperature and the treatment time according to the amount of melamine added and the concentration of the acidic aqueous solution.

  At this time, it is desirable to control the stirring speed in order to form a thin, uniform melamine resin coating layer on the surface of the spherical magnetic composite particles. The stirring speed is preferably 100 to 1000 rpm.

  After curing, when the reaction product is cooled to 40 ° C. or less, the blended powder is dispersed in the binder resin, and the structure is such that a surface layer portion is formed by the ferromagnetic iron oxide particles a, and the surface of the particles is thin and uniform. An aqueous dispersion of spherical magnetic composite particles having a coating layer made of melamine resin is obtained.

  The aqueous dispersion containing the spherical magnetic composite particles is filtered and solid / liquid is separated according to a conventional method of centrifugation, followed by washing and drying to obtain spherical magnetic composite particles.

  Further, in the method of adding melamine to the aqueous medium containing the spherical magnetic composite particles, since melamine is insoluble in water, if melamine is added directly to the aqueous medium in a solid state, the particle surface of the spherical magnetic composite particles Further, since spherical magnetic composite particles having a melamine resin coating layer formed non-uniformly are obtained, the voltage dependency of the spherical magnetic composite particles becomes large, which is not preferable.

  In the method of adding melamine to the aqueous medium containing the spherical magnetic composite particles, it is preferably added in the state of an aqueous methylolmelamine solution prepared by reacting melamine and aldehydes with separately prepared water. When the methylolation reaction proceeds rapidly in the aqueous solution, the solution becomes cloudy due to the polycondensation reaction of methylol melamine, and a coating layer made of a thin and uniform melamine resin is formed on the particle surface of the spherical magnetic composite particles. Since it becomes difficult, it is preferable to add to the aqueous medium containing the spherical magnetic composite particles in the state of a transparent methylolmelamine aqueous solution in which the polymerization has progressed to some extent.

  In addition, since the melamine resin is positively charged, the positive chargeability of the magnetic carrier can be improved.

  Moreover, since a melamine resin forms a hard film | membrane, durability of a magnetic carrier can be improved.

  The amount of melamine added to the spherical magnetic composite particles is preferably 0.1 to 5.0% by weight. If the amount is less than 0.1% by weight, it is difficult to sufficiently coat, and the voltage dependency of the electrical resistance value of the spherical magnetic composite particles may increase. On the other hand, if it exceeds 5.0% by weight, the electric resistance value becomes too high, which is not preferable.

  Aldehydes used in the formation of the melamine coating layer can be selected from those that can be used in the formation reaction of the spherical magnetic composite particles.

  The molar ratio of aldehydes to melamine in the aqueous methylolmelamine solution is preferably 1 to 10, and the melamine concentration is preferably 5 to 50% by weight.

  The aqueous methylolmelamine solution is prepared by adding melamine and aldehydes to water and stirring the reaction solution up to a temperature range of 40 to 80 ° C., and at this temperature for 30 to 240 minutes, preferably 60 to 180 minutes. It is formed by carrying out a methylolation reaction.

  At this time, the heating rate is preferably 0.5 to 1.5 ° C./min, and the stirring rate is preferably 100 to 1000 rpm.

As the acidic catalyst used in the present invention, a weak acid having an acid dissociation constant pKa of 3 to 6 is preferably used. For example, formic acid, oxalic acid, acetic acid and the like can be mentioned, and acetic acid is most preferable. The acid content in the aqueous medium for producing the spherical magnetic composite particles is preferably 0.5 to 3% by weight.

The present invention is characterized in that an acidic aqueous solution composed of an acid having an acid dissociation constant pKa of 3 to 6 and an aqueous methylolmelamine aqueous solution are added as an acidic catalyst to the aqueous medium containing the spherical magnetic composite particles. That is, by adding both aqueous solutions to an aqueous medium, the reaction and curing rate of methylolmelamine are optimized, and the surface of the spherical magnetic composite particle composed of ferromagnetic iron oxide particles and cured phenol resin is thin and uniform. Since a coating layer made of melamine resin can be formed, a spherical shape that can keep the electrical resistance value at the time of development appropriate by making the voltage dependency of the electrical resistance value small and having an appropriate electrical resistance value. Magnetic composite particles can be obtained.

An acidic catalyst having an acid dissociation constant pKa of less than 3, for example, a strong acid hydrochloric acid such as ammonium chloride, makes it difficult to form a coating layer made of melamine resin uniformly, and the electrical resistance value of the spherical magnetic composite particles The voltage dependency is increased, which is not preferable. On the other hand, when the acid dissociation constant pKa exceeds 6, it is difficult to sufficiently form a coating layer made of melamine resin, which is not preferable.

In the magnetic carrier according to the present invention, the surface of the spherical magnetic composite particles may be coated with a resin.

  The coating resin used in the present invention is not particularly limited, but polyolefin resins such as polyethylene and polypropylene; polystyrene; acrylic resin; polyacrylonitrile; polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl carbazole, polyvinyl ether, polyvinyl ketone. Polyvinyl-based or polyvinylidene-based resins such as: vinyl chloride / vinyl acetate copolymer, styrene / acrylic acid copolymer; straight silicone resin composed of organosiloxane bonds or modified products thereof; polytetrafluoroethylene, polyvinyl fluoride, Fluorine resins such as polyvinylidene fluoride and polychlorotrifluoroethylene; polyesters; polyurethanes; polycarbonates; amino-based trees such as urea and formaldehyde resins ; Epoxy resin; polyamide resin, polyimide resin, polyamide imide resin, fluorine - polyamide resins, fluorine - polyimide resins, fluorine - polyamide-imide resins, and the like.

  In the magnetic carrier according to the present invention, the surface of the spherical magnetic composite particles may be coated with one or more resins selected from silicone resins, fluorine resins, acrylic resins, and styrene-acrylic resins. preferable. By coating the particle surface with a silicone-based resin or a fluorine-based resin having a low surface energy, toner spent can be suppressed. In addition, both the acrylic resin and the styrene-acrylic resin have the effect of improving the adhesion with the core particles and the charging property.

  As the silicone resin, a condensation reaction type silicone resin is preferable. As the fluorine resin, polyfluorinated acrylate resin, polyfluorinated methacrylate resin, polyfluorinated vinylidene resin, polytetrafluoroethylene resin, polyhexafluoropropylene resin, and the above resin are used. A copolymer based on a combination of these is preferred.

  Acrylic resins include methyl acrylate, methyl ethacrylate, ethyl methacrylate, butyl methacrylate, lauryl methacrylate, stearyl methacrylate, alkyl acrylates such as behenyl methacrylate, cycloalkyl acrylates such as cyclopentyl methacrylate, cyclohexyl methacrylate, and aromatics such as phenyl methacrylate. Examples of the carrier include acrylates, copolymers of these with acrylic acid, copolymers of epoxy compounds such as glycidyl methacrylate, and copolymers of alcohol compounds such as glycerin monomethacrylate and 2-hydroxyethyl methacrylate. In view of environmental dependency, short chain alkyl acrylates such as methyl methacrylate and ethyl ethacrylate are preferable.

  Examples of the styrene-acrylic resin include a copolymer of the acrylic monomer and the styrene monomer, and the styrene-acrylic resin has a short charge difference between a high temperature and high humidity environment and a low temperature and low humidity environment. A copolymer with a chain alkyl methacrylate is preferred.

  The coating amount of the magnetic carrier according to the present invention with the resin is preferably 0.1 to 5.0% by weight with respect to the spherical magnetic composite particles. If the coating amount is less than 0.1% by weight, it may be difficult to sufficiently coat and uneven coating may occur. When the amount exceeds 5.0% by weight, the resin coating can be brought into close contact with the surface of the spherical magnetic composite particles. However, aggregation of the produced spherical magnetic composite particles occurs, It becomes difficult to control the particle size. Preferably, it is 0.5 to 3.0% by weight.

  The resin coating in the present invention may contain fine particles in the resin coating layer. As the fine particles, fine particles made of a quaternary ammonium salt compound, a triphenylmethane compound, an imidazole compound, a nigrosine dye, a polyamine resin, or the like are preferable, for example, to impart negative chargeability to the toner. On the other hand, fine particles made of a dye containing a metal such as Cr or Co, a salicylic acid metal compound, an alkylsalicylic acid metal compound, or the like are preferable as those that impart positive chargeability to the toner. These particles may be used alone or in combination of two or more.

  Moreover, the resin coating in the present invention may contain conductive fine particles in the resin coating layer. It is preferable that conductive fine particles are contained in the resin because the resistance of the magnetic carrier can be easily controlled. Known conductive fine particles can be used, for example, carbon black such as acetylene black, channel black, furnace black and ketjen black, metal carbide such as Si and Ti, metal nitride such as B and Ti, Examples thereof include metal borides such as Mo and Cr. These may be used alone or in combination of two or more. Among these, carbon black is preferable.

  When the resin is coated on the surface of the spherical magnetic composite particles, any known method may be used. For example, a dry method, a fluidized bed method, a spray dry method, a rotary dry method, a universal stirrer, a Henschel mixer, a high speed mixer or the like may be used.

  Next, the two-component developer in the present invention will be described.

  As the toner used in combination with the magnetic carrier of the present invention, a known toner can be used. Specifically, a binder resin and a colorant as main components, and a release agent, a magnetic material, a fluidizing agent, and the like added as necessary can be used. In addition, a known method can be used as a method for producing the toner.

<Action>
The important point in the present invention is a spherical magnetic composite particle composed of a blended powder of ferromagnetic iron oxide particles having different particle sizes, a phenol resin, and a melamine resin, and the surface layer of the ferromagnetic iron oxide particles a having a large particle size. The surface forms minute irregularities on the particle surface, improves adhesion to the coating resin and durability against wear, is stable against mechanical stress on the carrier, and is coated with a thin and uniform melamine resin on the particle surface. By forming the layer, the magnetic carrier has an appropriate electrical resistance value, and it is possible to reduce the voltage dependency of the electrical resistance value. In addition, a uniform solid portion can be reproduced, and a high-quality image with excellent gradation and the like can be maintained over a long period of time.

The method for manufacturing a magnetic carrier for an electrophotographic developer according to the present invention uses a mixed powder of ferromagnetic iron oxide particles a and ferromagnetic iron oxide particles b having different average particle diameters, and the average particles of the ferromagnetic iron oxide particles a. The ratio ra / rb between the diameter ra and the average particle diameter rb of the ferromagnetic iron oxide particles b is greater than 1, and the weight ratio of the ferromagnetic iron oxide particles a and the ferromagnetic iron oxide particles b is determined by the ferromagnetic iron oxide particles a When the total amount of the iron oxide and the ferromagnetic iron oxide particles b is 100 parts by weight, the composition contains the ferromagnetic iron oxide particles a in the range of 1 to 50 parts by weight. Therefore, the phenol resin is combined as a binder. At this time, spherical magnetic composite particles having a surface layer portion made of ferromagnetic iron oxide particles a are stably obtained, and the surface layer portion has minute irregularities along the particle diameter and shape of the used ferromagnetic iron oxide particles a. An aqueous medium containing the spherical magnetic composite particles During an acidic aqueous solution having an acid dissociation constant pKa as an acidic catalyst comprises 3-6 acids, and, by adding a methylolmelamine solution, further, to form a coating layer comprising a thin, uniform melamine resins.
As shown in the SEM photographs of FIGS. 1 and 2, the magnetic carrier according to the present invention is characterized in that the surface layer portion has minute irregularities resulting from the particle diameter and shape of the ferromagnetic iron oxide particles having a large average particle diameter. And That is, as shown in the SEM photographs of FIGS. 3 and 4, the magnetic carrier with a smooth particle surface as in the conventional example is clearly different.

In the magnetic carrier formed by coating the particle surface of the spherical magnetic composite particles according to the present invention with a resin, the adhesion at the time of resin coating is greatly improved, the durability against peeling and abrasion of the coating layer is excellent, and the machine for the carrier Since it is stable against mechanical stress and a coating layer made of a thin and uniform melamine resin is formed on the surface, the electrical resistance value of the spherical magnetic composite particles is appropriately controlled and the voltage dependency is reduced. Therefore, it has become possible to easily design the electrical resistance characteristics and charging characteristics of a magnetic carrier in which a coating resin is formed on the surface of the spherical magnetic composite particles.

  The two-component developer according to the present invention can maintain a high-quality image excellent in image density, gradation and the like, and in particular, charge leakage at a high voltage that is easily affected by the electrical resistance of the core material. It has become possible to suppress image defects such as the occurrence of scratches on the solid portion due to the phenomenon and inferior gradation, and to suppress deterioration over time due to scraping or peeling of the coating resin associated with long-term use of the carrier.

Hereinafter, typical embodiments of the present invention will be described as follows, but the present invention is not limited to these examples. In the following description, “parts” and “%” mean “parts by weight” and “% by weight” unless otherwise specified.

<Measurement method>
The average particle diameter of the ferromagnetic iron oxide particles is shown by a photograph taken with a transmission electron micrograph and a value obtained from the ferret diameter for 300 particles.

  The particle shape of the ferromagnetic iron oxide particle powder or the spherical magnetic composite particle was judged from a photograph observed with a transmission electron microscope and “scanning electron microscope S-4800” (manufactured by Hitachi High-Technologies Corporation).

  The BET specific surface area value was shown by the value calculated | required by BET method using "Mono Sorb MS-II" (made by Yuasa Ionics Co., Ltd.).

  The saturation magnetization was indicated by a value measured under an external magnetic field of 795.8 kA / m (10 kOe) using a vibrating sample magnetometer VSM-3S-15 (manufactured by Toei Kogyo Co., Ltd.).

  The amount of metal element contained in the ferromagnetic iron oxide particle powder is measured with a “fluorescence X-ray analyzer RIX-2100” (manufactured by Rigaku Denki Kogyo Co., Ltd.), and is calculated in terms of element with respect to the ferromagnetic iron oxide particle powder. The value is shown.

  The average particle diameter of the spherical magnetic composite particles was measured with a laser diffraction particle size distribution analyzer LA750 (manufactured by Horiba, Ltd.) and indicated as a value based on volume.

The 10-point average roughness Rz, the maximum height Ry, the arithmetic average roughness Ra, and the average interval Sm of the irregularities on the surface of the magnetic carrier are in accordance with JIS B0601, an ultra-depth color 3D shape measurement laser microscope (VK-9700, manufactured by Keyence). ) Was observed in a field of view 1000 times that of one magnetic carrier particle. In the shape measurement, the measurement distance is set to 10 μm with the central portion of the magnetic carrier as the center point, and 8 points measured at 45 ° intervals are shown as average values, and the surface of 100 arbitrarily selected carrier surfaces is further measured. The measured average value was averaged and indicated as a value. When measuring the shape, the measurement is performed after performing a correction process for reducing the measurement error.

  The true specific gravity is indicated by a value measured with a multi-volume density meter 1305 type (Micromeritics / manufactured by Shimadzu Corporation).

  The electric resistance value (volume specific resistance value) of the spherical magnetic composite particles was shown as a value measured with a high resistance meter 4339B (manufactured by Yokogawa Hewlett Packard) with a sample of 1.0 g.

  The sphericity is determined from an SEM photograph showing 200 or more spherical magnetic composite particles observed with “Scanning Electron Microscope S-4800” (manufactured by Hitachi High-Technologies Corporation). l) and the minor axis diameter (w) were measured and expressed in l / w ratio.

  The content of melamine with respect to the spherical magnetic composite particles was calculated by converting from the amount of nitrogen obtained with a trace total nitrogen analyzer TN-110 (manufactured by Dia Instruments Co., Ltd.).

  The charge amount of the toner was measured using a blow-off charge amount measuring device TB-200 (manufactured by Toshiba Chemical Co., Ltd.) after thoroughly mixing 95 parts of the magnetic carrier and 5 parts of toner manufactured by the following method.

(Example of toner production)
Polyester resin 100 parts Copper phthalocyanine-based colorant 5 parts Charge control agent (di-tert-butylsalicylic acid zinc compound) 3 parts Wax 9 parts The above materials are sufficiently premixed with a Henschel mixer and melt kneaded with a twin screw extrusion kneader. After cooling, the mixture was pulverized and classified using a hammer mill to obtain a negatively charged blue powder having a weight average particle size of 7.4 μm.

  100 parts of the negatively charged blue powder and 1 part of hydrophobic silica were mixed with a Henschel mixer to obtain a negatively charged cyan toner a.

<Forced deterioration test of spherical magnetic composite particles and coated resin carrier>
The spherical magnetic composite particles or 50 parts of the resin-coated magnetic carrier are placed in a 100 cc glass sample bottle, covered, and then shaken for 24 hours with a paint conditioner (manufactured by RED DEVIL). The charge amount and the electric resistance value of each sample before and after shaking were measured, and peeling or abrasion of the particle surface was confirmed with a scanning electron microscope S-4800 (manufactured by Hitachi, Ltd.).

  The charge amount before and after the forced deterioration test is expressed in% as the change amount of the charge amount at normal temperature and humidity (24 ° C., 60% RH) for each sample before and after shaking as shown by the following formula. The evaluation criteria were used. C or higher is a practically possible level. The developer was prepared by thoroughly mixing 95 parts of the composite particles of the present invention or a resin-coated magnetic carrier and 5 parts of the negatively chargeable cyan toner a.

Change rate of charge amount (%) = (1−Q / Q _INI ) × 100
Q _INI : _Charge amount before forced deterioration test Q: Charge amount after forced deterioration test

A: The change rate before and after the forced deterioration test is 0% or more and less than 5% B: The change rate before and after the forced deterioration test is 5% or more and less than 10% C: The change rate before and after the forced deterioration test is 10% or more and less than 20% D: Change rate before and after forced deterioration test is 20% or more and less than 30% E: Change rate before and after forced deterioration test is 30% or more

  As shown by the following formula, the electrical resistance value represents the rate of change in electrical resistance value at room temperature and normal humidity (24 ° C., 60% RH) for each of the samples before and after shaking, expressed in%. evaluated. C or higher is a practically possible level.

Rate of change in electrical resistance value (%) = R / R _INI × 100
R: electrical resistance value after forced degradation test at applied voltage 100V R _INI : electrical resistance value before forced degradation test at applied voltage 100V

A: The change width before and after the forced deterioration test is 0% or more and less than 5% B: The change width before and after the forced deterioration test is 5% or more and less than 10% C: The change width before and after the forced deterioration test is 10% or more and less than 20% D: The range of change before and after the forced deterioration test is 20% or more and less than 30% E: The range of change before and after the forced deterioration test is 30% or more

The surface condition such as peeling and abrasion of the resin coating layer after the forced deterioration test was evaluated by the following three stages using a scanning electron microscope. B or higher is a practically possible level.
A: No peeling or wear of the coating layer B: Slight peeling or wear of the coating layer C: Extremely severe peeling or wear of the coating layer

<Durability test of coated resin carrier>
In the durability test of the coated resin carrier, 10 g of the coated resin carrier sample was added by a sample mill SK-M10 (manufactured by Kyoritsu Riko Co., Ltd.) and stirred for 30 seconds at a rotational speed of 16000 rpm.

  The durability evaluation was performed by measuring the change in particle size distribution before and after stirring as shown by the following formula, calculating the fine particle generation rate from the increase in the volume ratio of particles having a particle diameter of 22 μm or less, and performing the evaluation in the following five stages. C or higher is a practically possible level.

Fine particle generation rate (%) = (Volume ratio of particle diameter of 22 μm or less after stirring) − (Volume ratio of particle diameter of 22 μm or less before stirring)

A: Fine powder generation rate before and after durability test is 0% or more and less than 0.1% B: Fine powder generation rate before and after durability test is 0.1% or more and less than 0.5% C: Fine powder generation rate before and after durability test 0.5% or more and less than 1.0% D: The generation rate of fine powder before and after the durability test is 1.0% or more and less than 3.0% E: The generation rate of fine powder before and after the durability test is 3.0% or more

Surface conditions such as peeling and abrasion of the resin coating layer were evaluated by the scanning electron microscope in the following three stages. B or higher is a practically possible level.
A: No peeling or abrasion of the coating layer B: Slight peeling or abrasion of the coating layer, etc. C: Extremely severe peeling or abrasion of the coating layer

<Evaluation of coated resin carrier in image evaluation>
The developer was prepared by thoroughly mixing 95 parts of the magnetic carrier of the present invention and 5 parts of the negatively chargeable cyan toner a. For image evaluation, Epson LP8000C was remodeled and used to evaluate the printing durability of 1,000,000 sheets by changing the bias voltage under the environmental conditions of 24 ° C and 60% RH and 30 ° C and 80% RH. Evaluation based on the evaluation method.

  Note that the image evaluation results were ranked. The specific evaluation method is as follows.

(1) Image density (including uniformity of solid black areas)
Based on the printing durability evaluation, the solid image density was measured with a Macbeth densitometer for the 1000th (initial) image, the 100,000th image, and the 1 millionth image. For the uniformity of the solid black portion, a limit sample was provided, visually judged, and evaluated according to the following five levels. C or higher is a practically possible level.

A: The original density is reproduced very well, and there is no density unevenness and a uniform solid black portion.
B: The document density is reproduced and there is no density unevenness.
C: The image density is well on board.
D: Although the image density is on the surface, the image is non-uniform and has many white stripes.
E: The density is low overall and the edge effect is large, and the density is greatly reduced compared to the original density.

(2) Fog For the 1000th image (initial), the 100,000th image, and the 1 millionth image based on the printing durability evaluation, the fog on the image is the same as the toner fog on the white background image. Measurement was performed in the L * a * b * mode of a total CR-300, ΔE was obtained, and evaluated in the following four stages. B or higher is a practically possible level.

A: ΔE is less than 1.0 B: ΔE is 1.0 or more and less than 2.0 C: ΔE is 2.0 or more and less than 3.0 D: ΔE is 3.0 or more

(3) Gradation property KODAK's gray scale (0 to 19 gradation test chart) is applied to the 1000th (initial), 100,000th and 1 millionth images based on the printing durability evaluation. It was evaluated according to the following five levels depending on the number of gradation patterns that can be visually used. C or higher is a practically possible level.

A: 15 (B) gradation or more B: 13-14 gradation C: 11-12 gradation D: 7 (M) -10 gradation E: 6 gradations or less

<Ferromagnetic iron oxide particles>
Table 1 shows various characteristics of the ferromagnetic iron oxide particles used as the ferromagnetic iron oxide particles a and the ferromagnetic iron oxide particles b.

<Lipophilic treatment of ferromagnetic iron oxide particles>
[Example 1]
(Lipophilic treatment 1)
After 1000 parts of iron oxide particles 4 were charged into the flask and sufficiently stirred, 5.0 parts of a silane coupling agent having an epoxy group (trade name: KBM-403, manufactured by Shin-Etsu Chemical Co., Ltd.) was added and the temperature was raised to about 100 ° C. By heating and mixing well for 30 minutes, a ferromagnetic iron oxide particle powder a coated with a coupling agent was obtained.

(Lipophilic treatment 2)
After 1000 parts of iron oxide particles 1 were charged into the flask and sufficiently stirred, 10.0 parts of an epoxy group-containing silane coupling agent (trade name: KBM-403, manufactured by Shin-Etsu Chemical Co., Ltd.) was added and the temperature was raised to about 100 ° C. By heating and mixing well for 30 minutes, a ferromagnetic iron oxide particle powder b coated with a coupling agent was obtained.

<Mixing of ferromagnetic iron oxide particles after oleophilic treatment>
The flask was charged with 30 parts of ferromagnetic iron oxide particle powder a subjected to lipophilic treatment 1 and 70 parts of ferromagnetic iron oxide particle powder b subjected to lipophilic treatment 2 (ra / rb = 1.5), and 250 rpm. The mixture was well mixed and stirred at a stirring speed for 30 minutes.

[Example 1]
<Production of spherical magnetic composite particles>
Phenol 10 parts 37% formalin 15 parts Mixed powder of ferromagnetic iron oxide particles a powder and b powder 100 parts 25% ammonia water 3.5 parts water 15 parts The above material is put into a 1 L four-necked flask and stirred at 250 rpm The mixture was heated to 85 ° C. over 60 minutes with stirring, and then reacted and cured at the same temperature for 120 minutes to produce spherical magnetic composite particles composed of ferromagnetic iron oxide particles and a cured phenol resin. .

  Separately, an acidic catalyst composed of 0.3 part of water and 0.5 part of 99% glacial acetic acid aqueous solution was prepared.

  Separately, an aqueous solution composed of 1.5 parts of water, 0.5 parts of melamine powder and 1.3 parts of 37% formalin was raised to about 60 ° C. over 60 minutes while stirring at a stirring speed of 250 rpm, and then stirred for about 40 minutes. As a result, a transparent methylolmelamine solution was prepared.

Next, after adding the acidic catalyst and the transparent methylolmelamine solution into a flask maintained at a reaction temperature of 85 ° C. while stirring the reaction solution that produced the spherical magnetic composite particles at a stirring speed of 250 rpm. For 120 minutes to obtain a magnetic carrier in which a coating layer made of a melamine resin was formed on the surface of the spherical composite core particles.

Next, after cooling the content in the flask to 30 ° C., the supernatant was removed, and the precipitate in the lower layer was washed with water and then air-dried. Subsequently, this was dried at 150-200 degreeC under pressure reduction (5 mmHg or less), and the magnetic carrier 1 was obtained.

The obtained magnetic carrier has an average particle diameter of 37.0 μm, a ten-point average roughness Rz of 0.90 μm, a maximum height Ry of 1.90 μm, and an arithmetic average roughness Ra of 0.30 μm. The average interval Sm between the irregularities is 4.00 μm, the specific gravity is 3.80 g / cm ³ , the saturation magnetization value is 75.4 Am ² / kg, and the sphericity (l / w) is 1.1. The electrical resistance value R ₁₀₀ when the applied voltage is 100 V is 9.8 × 10 ¹⁰ Ω · cm, and the electrical resistance value R ₃₀₀ when the applied voltage is 300 V is 4.2 × 10 ¹⁰ Ω · cm. And R ₃₀₀ / R ₁₀₀ was 0.43.

The SEM photographs of the magnetic carrier image and the particle surface image obtained here are shown in FIGS. FIG. 1 shows the particle structure, and FIG. 2 shows the surface structure of the particle. It was confirmed that the magnetic carrier had a spherical shape close to a true sphere, and the particle surface was formed with convex portions due to the ferromagnetic iron oxide particles a, and fine surface irregularities were formed on the particle surface. .

Table 2 shows the production conditions of the obtained magnetic carrier , and Table 3 shows the results of various characteristics and forced deterioration tests.

In the forced deterioration test of the magnetic carrier, the rate of change of the charge amount and the electric resistance value was small, and there was almost no peeling or wear of the particle surface.

[Examples 2, 3, 5, 6], [Comparative Example 3]
The type and mixing ratio of the ferromagnetic iron oxide particles a and b, the type of lipophilic treatment agent, except that the production conditions of the magnetic carrier was changed variously, the magnetic carrier by performing the operation under the same conditions as in Example 1 Obtained.

Table 2 shows the production conditions of the obtained magnetic carrier , and Table 3 shows the results of various characteristics and forced deterioration tests.

[Example 4]
(Lipophilic treatment 3)
A flask was charged with 300 parts of iron oxide particles 2 and 700 parts of iron oxide particles 1, and after sufficient stirring, 10.0 parts of a silane coupling agent having an epoxy group (trade name: KBM-403, manufactured by Shin-Etsu Chemical Co., Ltd.) The resulting mixture was heated to about 100 ° C. and mixed and stirred for 30 minutes to obtain a mixed powder of ferromagnetic iron oxide particles a and b coated with a coupling agent.

For the preparation of the magnetic carrier, except that the production conditions were changed variously to obtain a magnetic carrier by performing the operation under the same conditions as in Example 1.

Table 2 shows the production conditions of the obtained magnetic carrier , and Table 3 shows the results of various characteristics and forced deterioration tests.

[Comparative Example 1]
The magnetic carrier was operated under the same conditions as in Example 1 except that only the ferromagnetic iron oxide particle powder 3 subjected to the lipophilic treatment 2 was used and the production conditions of the spherical magnetic composite particles were variously changed. Got.

Table 2 shows the production conditions of the obtained magnetic carrier , and Table 3 shows the results of various characteristics and forced deterioration tests.

[Comparative Example 2]
The operation was carried out under the same conditions as in Example 1 except that the lipophilic ferromagnetic iron oxide particle powder a and the ferromagnetic iron oxide particle powder b were used for the production of spherical magnetic composite particles without being mixed at all. A magnetic carrier was obtained.

Table 2 shows the production conditions of the obtained magnetic carrier , and Table 3 shows the results of various characteristics and forced deterioration tests.

<Manufacture of resin-coated carrier>
[Example 7]
In a Henschel mixer under a nitrogen stream, 1000 parts of the magnetic carrier of Example 1 and 10 parts of silicone resin (trade name: KR251, manufactured by Shin-Etsu Chemical Co., Ltd.) as solids and carbon black (trade name: Talker Black # 4400) 1.5 parts of Tokai Carbon Co.) was added and stirred at a temperature of 50 to 150 ° C. for 1 hour to form a resin coating layer composed of a silicone resin containing carbon black.

The resin-coated magnetic carrier obtained here has an average particle diameter of 39 μm, a specific gravity of 3.75 g / cm ³ , a saturation magnetization value of 74.7 Am ² / kg, and an electric current at an applied voltage of 100 V. The resistance value R ₁₀₀ was 5.6 × 10 ¹³ Ω · cm, and the electric resistance value R ₃₀₀ when the applied voltage was 300 V was 3.3 × 10 ¹³ Ω · cm.

  The coating of the obtained resin-coated carrier particles 1 with a silicone resin was uniform and sufficient when observed with a scanning electron microscope (manufactured by Hitachi, Ltd. (S-4800)).

[Examples 8 to 12], [Comparative Examples 4 to 6]
A resin-coated magnetic carrier was obtained by operating under the same conditions as in Example 7 except that the type of magnetic carrier, the type of coating resin, and the amount of resin coating were variously changed.

  Table 4 shows the manufacturing conditions and various characteristics of the obtained resin-coated magnetic carrier, and Table 5 shows the results of durability evaluation, forced deterioration test evaluation, and printing durability evaluation.

  As shown in Table 5, the magnetic carrier and developer according to the present invention are excellent in adhesion to the coating resin without causing resin peeling or wear in the durability test, and further, the voltage dependency of the electrical resistance value is small, and Since it has an appropriate electrical resistance value, it was excellent in image quality, and high density and uniform solid black reproduction was obtained. In addition, by using a ferromagnetic iron oxide particle powder that has undergone coating treatment to form a resin coating layer made of melamine resin, the electrical resistance of the magnetic carrier is controlled and the voltage dependence is maintained for a long time. It was confirmed that the magnetic carrier was excellent in image characteristics with excellent gradation even after printing 1 million sheets.

The magnetic carrier for an electrophotographic developer according to the present invention has a small voltage dependency of the electric resistance value and has an appropriate electric resistance value, and further forms minute irregularities on the particle surface, thereby providing irregularities on the particle surface. By controlling, the adhesion at the time of resin coating is very excellent, the durability against peeling and abrasion of the coating layer is excellent, it is stable against mechanical stress on the carrier, and it may cause toner spent Excellent longevity that can be maintained stably over a long period of time, satisfying the demands in recent years, and further making it possible to maintain an appropriate electrical resistance value during development and voltage dependence A magnetic carrier for an electrophotographic developer used in an electrophotographic developer and a two-component developer having the magnetic carrier for an electrophotographic developer and a toner. It is preferred.

Claims (8)

A magnetic carrier for an electrophotographic developer in which a coating layer made of a melamine resin is formed on the surface of spherical magnetic composite particles in which ferromagnetic iron oxide particles are bound with a phenol resin as a binder, the ferromagnetic iron oxide The particles are composed of ferromagnetic iron oxide particles a and ferromagnetic iron oxide particles b having different average particle diameters,
The ratio of the average particle diameter ra of the ferromagnetic iron oxide particles a having a large average particle diameter to the average particle diameter rb of the ferromagnetic iron oxide particles b having a small average particle diameter is greater than 1, and the ferromagnetic iron oxide particles The weight ratio of a to the ferromagnetic iron oxide particles b is strong in the range of 1 to 50 parts by weight when the total amount of the ferromagnetic iron oxide particles a and the ferromagnetic iron oxide particles b is 100 parts by weight. Containing magnetic iron oxide particles a,
Particle surfaces of those magnetic carriers for an electrophotographic developer magnetic carrier, wherein the ten-point average roughness Rz is 0.3Myuemu～2.0Myuemu. The magnetic carrier for an electrophotographic developer according to claim 1, wherein the particle carrier has a maximum height Ry of 0.7 μm to 2.5 μm. 3. The electrophotographic developer according to claim 1, wherein the particle surface of the magnetic carrier has an arithmetic average roughness Ra of 0.1 μm to 0.9 μm, and an average interval Sm of irregularities of 0.6 μm to 6.0 μm. Magnetic carrier. The spherical magnetic composite particles are ferromagnetic iron oxide particles Ri Contact contains 80 to 99 weight percent based on the total amount, the shape of the ferromagnetic iron oxide particles a and the ferromagnetic iron oxide particles b are spherical, hexahedral The magnetic carrier for an electrophotographic developer according to any one of claims 1 to 3, wherein the magnetic carrier exhibits any shape selected from octahedron, polyhedron, and amorphous. When the applied voltage of the magnetic carrier for electrophotographic developer is 100V, the electrical resistance value R100 is 1 × 10 ⁸ Ωcm to 1 × 10 ¹⁶ Ω · cm, and when the applied voltage is 300V, the electrical resistance value R300 is 0.00. 1 ≦ R300 / R100 ≦ 1
The magnetic carrier for an electrophotographic developer according to any one of claims 1 to 4. The particle surface of the magnetic carrier for an electrophotographic developer according to any one of claims 1 to 5 is further selected from one or two selected from silicone resins, fluorine resins, acrylic resins, and styrene-acrylic resins. A magnetic carrier for an electrophotographic developer which is coated as described above. The ferromagnetic iron oxide particles a and the ferromagnetic iron oxide particles b having different average particle diameters are reacted and cured with phenols and aldehydes in an aqueous medium, and the particle surface is caused by the shape of the ferromagnetic iron oxide particles a. The spherical magnetic composite particles composed of the ferromagnetic iron oxide particles and the phenol resin having the irregularities formed thereon are produced, and then the acid dissociation constant pKa as an acidic catalyst is formed in the aqueous medium containing the spherical magnetic composite particles. The magnetic carrier for an electrophotographic developer according to any one of claims 1 to 5, wherein a coating layer made of a melamine resin is formed by adding an acidic aqueous solution made of 3-6 acids and a methylolmelamine aqueous solution. Production method. A two-component developer using the magnetic carrier for an electrophotographic developer according to claim 1.