JP4603943B2 - Magnetic toner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic toner stably having an optimum charged amount regardless of environments so that a high-quality image having high blackness can be formed without causing any ghost phenomenon, and so that the consumption can also be lowered. <P>SOLUTION: The magnetic toner comprises magnetic toner particles including at least a binder resin and magnetic particles, wherein an isoelectric point of the magnetic particles is pH 4.0 or less. <P>COPYRIGHT: (C)2006,JPO&amp;NCIPI

Description

  The present invention relates to a magnetic toner used in an image forming method such as an electrophotographic method, an electrostatic recording method, a magnetic recording method, and a toner jet recording method.

  A number of methods are known as electrophotographic methods. In general, a photoconductive substance is used to form an electrostatic latent image on a photoreceptor by various means, and then the electrostatic latent image is converted into a toner. The toner image is transferred to a transfer material such as paper, if necessary, and then fixed by heating, pressing, heating and pressurization, or solvent vapor to obtain a subject. The developer remaining without being transferred onto the top is cleaned by various methods, and the above steps are repeated.

Among these, a one-component developing method is preferably used as a developing method because a developing device with a simple structure has few troubles, a long life, and easy maintenance.
In such a one-component developing method, the quality of an image formed is greatly influenced by the performance of the magnetic toner used. A considerable amount of fine powdery magnetic particles are mixed and dispersed in the magnetic toner, and a part of the magnetic particles is exposed on the surface of the magnetic toner. For this reason, the type of magnetic particles affects the fluidity and tribocharging properties of the magnetic toner, and as a result, affects various properties required for the magnetic toner, such as development characteristics and durability of the magnetic toner. . Therefore, many proposals have conventionally been made regarding magnetic particles contained in magnetic toner.

Conventionally, in order to improve the characteristics of magnetic particles, a production method in which silicon is added during the formation reaction of magnetic particles has been studied. For example, after adding a silicon component to a ferrous salt solution and mixing with 1.0 to 1.1 equivalents of alkali with respect to iron, the pH is maintained at 7 to 10 and an oxidation reaction is performed. There is a method of obtaining magnetic particles by adding 0.9 to 1.2 equivalents of iron to the initial alkali and maintaining the pH at 6 to 10 to carry out an oxidation reaction (for example, Patent Document 1 and Patent Document). 2). In addition, by passing an oxygen-containing gas through a ferrous salt reaction aqueous solution containing ferrous hydroxide colloid obtained by reacting 0.82-0.99 equivalents of alkali hydroxide with Fe ²⁺ , magnetic properties are obtained. A method for obtaining a spherical magnetic particle powder by adding water-soluble silicate in an amount of 0.1 to 5.0 atomic% in terms of Si to a body and generating a spherical particle by reacting in two steps. Yes (see, for example, Patent Document 3).

  Further, the magnetic iron oxide used in the magnetic toner contains 1.7 to 4.5 atomic% of silicon with respect to iron in terms of Si, and metal elements other than iron include Mn, Zn, Ni, Cu, Magnetic particles having magnetic iron oxide containing 0 to 10 atomic% of one or more metal elements selected from the group consisting of Al and Ti with respect to iron are known (for example, Patent Document 4 and Patent Document) 5). Use of such magnetic particles improves the magnetic properties and charging properties of the magnetic toner. However, simply adding the above metal is not sufficient in terms of compatibility between developability and image quality in a high-speed development system, and there remains room for improvement.

  Further, as the magnetic particles, a silicon component is continuously contained from the center of the magnetic particles to the surface, the silicon component is exposed on the surface of the particles, and bonded to the silicon component, Zn, Mn, Cu, Ni, Co Magnetic particles are known in which particles are coated with a metal compound having at least one metal element selected from Cr, Cd, Al, Sn, Mg, and Ti (see, for example, Patent Document 6). However, the use of such magnetic particles has not yet improved the deterioration of image quality and developability associated with long-term use, particularly in a high-speed development system, and has further points to be improved.

  As magnetic particles, the content of one or more metal elements selected from the group consisting of Mn, Zn, Ni, Cu, Co, Cr, Cd, Al, Sn and Mg based on iron elements, silicon element content, Magnetic particles are known in which the content ratio of silicon elements existing up to 20% by mass of iron element and the content ratio of silicon elements present up to 10% of iron element are defined (for example, patent documents). 7 to Patent Document 9). According to such magnetic particles, although various metals are contained in magnetic iron oxide and the distribution of silicon in the magnetic particles is regulated, an improvement effect is seen in environmental stability, but in a high-speed development system Further improvements are desired for durability.

  Further, as magnetic particles, Zn, Mn, Cu, Ni, Co, Cr, Cd, Al, Sn, in which the silicon component is continuously exposed from the center of the magnetic particle to the surface and bonded to the silicon component and the aluminum component. Magnetic particles having a particle outer shell coated with a metal compound having at least one metal atom selected from the group consisting of Mg and Ti are known (for example, see Patent Document 10). However, in the case of the magnetic toner having the magnetic particles, although the electric resistance and the degree of aggregation are good, the saturation magnetic susceptibility is greatly lowered due to the increase of the silicon component and the aluminum component exposed on the surface of the magnetic particles, and the charge is still insufficient. Stability has not yet been imparted to the magnetic toner. Thus, a change in magnetic properties depending on the thickness of the coating film of magnetic particles is a problem.

  Further, magnetic particles containing magnesium (see, for example, Patent Document 11), magnetic particles containing aluminum and silicon (see, for example, Patent Documents 12 to 17), and magnetic particles containing zinc (for example, Patent Document) 18-23) and magnetic particles containing silicon and other elements (see, for example, Patent Documents 24-26) have been proposed.

  When using magnetic toners containing the above elements, each shows good developability, but when applied to a high-speed development system or when applied to a development system with a simple configuration, further developability and durability are improved. Is desired. Specifically, there is still room for improvement with respect to various problems due to the fluidity and chargeability of magnetic toner such as sleeve blotch, image scattering, and ghost, or deterioration of developability due to temperature rise in the apparatus.

  Further, as magnetic particles, a hexahedral or octahedral structure in which a layer containing a large amount of silicon element is formed on the surface of a nucleus in which iron atoms and divalent metal atoms selected from the group consisting of Zn, Mg, and Mn are uniformly mixed is formed. Magnetic particles characterized by this shape are known (for example, see Patent Document 27). The magnetic toner using the magnetic particles is free from fogging from low speed to high speed copying machines, can obtain a high density copy image, is not affected by environmental fluctuations, and has excellent durability. However, no improvement has been made in terms of maintaining blackness and reducing consumption.

As described above, the magnetic particles used in the magnetic toner have not been improved from the viewpoint of maintaining environmental stability with excellent charge amount and suppressing image defects such as blackness and ghost. In addition, there is still room for study on reduction of toner consumption by magnetic particles.
Japanese Patent Publication No. 8-25747 JP-A-5-213620 Japanese Patent Publication No. 3-9045 Japanese Patent Laid-Open No. 9-59024 JP-A-9-59025 JP 11-157843 A JP 11-316474 A Japanese Patent Laid-Open No. 11-249335 Japanese Patent Laid-Open No. 11-282201 Japanese Patent Laid-Open No. 11-189420 JP-A-6-144840 Japanese Patent Laid-Open No. 5-72801 JP-A-5-213620 JP 7-175262 A JP 7-239571 A JP-A-7-110598 Japanese Patent Laid-Open No. 11-153882 JP-A-8-50369 JP-A-8-101529 JP 7-175262 A JP-A-8-48524 JP-A-8-208236 JP-A-8-208237 JP 11-157843 A Japanese Patent Laid-Open No. 11-189420 JP 11-316474 A JP-A-8-50369

An object of the present invention is to provide a magnetic toner containing magnetic particles that solves the above problems.
That is, according to the present invention, when magnetic particles are used in the magnetic toner, an image obtained by oxidation of the magnetic particles is not reddish, and the magnetic particles having a high charge amount are used as the magnetic toner material. Accordingly, an object of the present invention is to provide a magnetic toner that stably has an optimum charge amount regardless of the environment and can obtain an image with a good ghost level.

The inventors focused on the physical properties of the magnetic particles contained in the magnetic toner, and by incorporating the magnetic particles having a specific isoelectric point in the toner, the toner has excellent uniform chargeability and suppresses the generation of ghosts. As a result, the inventors have found that an image with excellent image quality can be stably formed for a long time, and have reached the present invention.
That is, the present invention is a magnetic toner having magnetic toner particles having at least a binder resin and magnetic particles, wherein the magnetic particles have an isoelectric point of pH 3.5 or less , and the magnetic particles are The surface contains 0.8 to 20.0% by mass of SiO ₂ with respect to the total amount of magnetic particles, and the magnetic particles are composed of base magnetic particles and a coating of SiO ₂ on the base magnetic particles. The coating layer is formed by dispersing the matrix magnetic particles in water and adding sodium silicate to the water to form a coating layer of SiO ₂ on the matrix magnetic particles. In addition, the present invention relates to a magnetic toner wherein the amount of adsorbed water at a relative vapor pressure of 50% of the magnetic particles is 1 to 20% by mass relative to SiO _{2 of the} coating layer per unit mass .

  According to the present invention, a magnetic toner excellent in fluidity and dispersibility can be obtained by incorporating magnetic particles having an isoelectric point of the magnetic particles of pH 4.0 or less into the toner. As a result, it is possible to provide a high-quality image having an optimum charge amount regardless of the environment and free from a ghost phenomenon. In addition, since the stable charge amount is maintained, the magnetic toner consumption can be reduced. Furthermore, since the magnetic particles are not easily oxidized, an image with high blackness can be provided.

  As a result of examining the constituent materials of the magnetic toner, the present inventors have found that the isoelectric point of the magnetic particles, the amount of adsorbed water, and the retention before and after the heat treatment are closely related to the developability, environmental stability and image quality of the magnetic toner. I found that there is a relationship.

  That is, the present inventors have found that a magnetic toner containing at least a binder resin and magnetic particles, and the magnetic toner having an isoelectric point of pH 4.0 or less improves the rise of the charge amount. It has been found that even when used under high and low humidity, high image quality can be stably obtained, and image defects do not occur over time.

  The magnetic particles used in the present invention are magnetic particles having an isoelectric point of pH 4.0 or less, preferably pH 3.5 or less, more preferably pH 3.0 or less, that is, in the acidic region. Magnetic particles having an isoelectric point of pH 4.0 or less, that is, in the acidic region generally show a good tendency in dispersibility in the binder resin and in the binder resin. In particular, when used together with a binder resin having an isoelectric point in the acidic region, the above-mentioned tendency is shown better, and the smaller the difference between the isoelectric point of the magnetic particles and the isoelectric point of the binder resin, Dispersibility and binding properties become better. If the magnetic toner is charged non-uniformly and the distribution of the charge amount varies, the magnetic toner supplied onto the developing sleeve when developing a subsequent image when developing an image with a large print area is continuously developed. There is a case where a so-called ghost image is generated in which the image is not sufficiently charged, and as a result, the image density of the subsequent image is lowered and a difference in density is generated on the image. Due to the uniform dispersion of the magnetic particles in the binder resin, the magnetic toner having a non-uniform charge amount is reduced, and the ghost phenomenon can be effectively suppressed.

  That is, in the present invention, since the isoelectric point of the magnetic particles is pH 4.0 or less, the binding property between the magnetic particles and the binding resin, and the dispersion of the magnetic particles in the binding resin can be achieved. The ghost phenomenon can be suppressed in order to improve the property and keep the charge amount of the magnetic toner at an appropriate value. In the present invention, the isoelectric point of the magnetic particles can be adjusted to pH 4.0 or less by forming a coating layer on the surface of the magnetic particles by, for example, a method described later.

The isoelectric points of the magnetic particles and the binder resin are measured by the following method.
First, the magnetic particles are dissolved or dispersed in ion exchange water at 25 ° C., and the sample concentration is adjusted to 1.8 mass%. Using an ultrasonic zeta potential measuring device DT-1200 (manufactured by Dispersion Technology), titration with 1N-HCl is performed to measure the zeta potential. The pH when the zeta potential was 0 mV was defined as the isoelectric point in the present invention. In the case of the binder resin, the isoelectric point was measured in the same manner as the magnetic particles, except that a sieve of 60 mesh (opening diameter 250 μm) was used as a sample.

The magnetic particles used in the present invention may contain 0.8 to 20.0% by mass, more preferably 1.0 to 5.0% by mass of SiO ₂ on the surface, based on the total amount of magnetic particles. preferable. The presence of SiO _{2 on the} surface of the magnetic particles can improve the poor fluidity due to aggregation, which is a problem in the small magnetic particle. Further, the presence of SiO ₂ , which is a nonmagnetic inorganic compound, on the surface of the magnetic particles increases the electric resistance value of the magnetic toner, and the charge amount can be kept high regardless of the environment. In particular, since the charge amount can be maintained even in a severe environment of low temperature and low humidity, it is possible to keep the loading amount of the magnetic toner constant and consequently reduce the consumption amount of the magnetic toner.

When the content of SiO ₂ present on the surface of the magnetic particles is less than 0.8% by mass with respect to the total amount of the magnetic particles, the SiO ₂ does not uniformly and sufficiently cover the surface of the magnetic particles. When the magnetic particles are used for the magnetic toner, a sufficient charge amount cannot be imparted to the magnetic toner, which may cause a decrease in image density. Further, when the content of SiO ₂ is less than 0.8% by mass, the effect of improving the fluidity of the powder may be lowered. On the other hand, if the content of SiO ₂ is more than 20.0% by mass, the charge amount of the magnetic toner is too high, which may cause a decrease in density and an increase in fog due to charge-up.

That is, in the present invention, the magnetic particles are on the surface, 0.8 to the total amount of magnetic particles.
By containing 20.0 wt% of SiO _2, the magnetic particle surfaces uniformly and sufficiently SiO ₂ covers the surface texture close to SiO ₂ was applied to the magnetic particle surfaces, and improve the charge retention Can be made. As a result, the magnetic toner consumption can be reduced while having good fluidity, high image density and high image quality regardless of the environment.

The content of SiO _{2 on} the surface of the magnetic particles is determined by performing fluorescent X-ray analysis using a fluorescent X-ray analyzer SYSTEM 3080 (manufactured by Rigaku Denki Kogyo Co., Ltd.) according to JIS K0119 “General rules for fluorescent X-ray analysis”. It was measured.
Specifically, the SiO ₂ content of the magnetic particles having a coating layer, and the content of SiO ₂ before the magnetic particles forming the coating layer (base magnetic particles) the fluorescent X-ray analyzer In the present invention, a value obtained by subtracting the SiO ₂ content of the magnetic particles (matrix magnetic particles) before forming the coating layer from the SiO ₂ content of the magnetic particles having the coating layer is measured using The content of SiO _{2 on} the surface of the magnetic particles was taken.

The magnetic particles used in the present invention have a coating layer having SiO ₂ on the surface, and the amount of adsorbed water at a relative vapor pressure of 50% is 1 to 100% by mass with respect to SiO ₂ of the coating layer per unit mass. The amount is preferably 1 to 20% by mass.

Magnetic particles with a small amount of adsorbed moisture are less likely to oxidize on the surface due to contact with moisture in the air, and suppress oxidation of the surface of magnetic particles, which is particularly problematic in small-sized magnetic particles with a large surface area. In addition, the degree of blackness can be maintained. The amount of adsorbed water can be reduced by covering the magnetic particles in a dense state of the SiO ₂ coating layer. In addition, the dense SiO ₂ coating layer, which is a nonmagnetic inorganic compound, increases the electrical resistance of the magnetic particles and can maintain a high charge amount.

That is, in the present invention, magnetic particles having an adsorbed water amount of 1 to 100% by mass with respect to the amount of coated SiO ₂ per unit mass at a relative vapor pressure of 50% are used for the magnetic toner. Image can be obtained, and since the magnetic toner maintains a desired high charge amount, the consumption amount of the magnetic toner can be reduced.

  The amount of adsorbed water in the present invention is measured by an adsorption equilibrium measuring device (EAM-02; manufactured by JT Toshi Co., Ltd.). This is a device for reaching a solid-gas equilibrium under the condition where only the target gas (water vapor in the present invention) exists, and measuring the solid mass and vapor pressure at this time.

  The actual adsorption / desorption isotherm is automatically measured by a computer from the measurement of the amount of dry matter and the degassing of dissolved air in the water to the measurement of the adsorption / desorption isotherm shown below. The outline of the measurement is described in the operation manual issued by JT Toshi Co., Ltd. The specific measurement method is as follows.

  First, about 5 g of magnetic toner is filled in the sample container in the adsorption tube, and the temperature of the thermostatic chamber and the temperature of the sample part are set to 28 ° C. Thereafter, V1 (main valve) and V2 (exhaust valve) are opened, the vacuum exhaust unit is operated, and the inside of the vacuum vessel is evacuated to about 0.01 mmHg to dry the sample. The mass at the time when the weight change of the sample ceases is defined as “dry matter amount”.

  On the other hand, since air is dissolved in the solvent liquid (water in the present invention), it is necessary to perform deaeration. First, a solvent liquid (hereinafter referred to as “water”) is put into a liquid reservoir, the vacuum exhaust section is operated, V2 (exhaust valve) is closed, V3 (container valve) is opened, and dissolved air is removed. . The above operation is repeated several times, and the deaeration ends when no more bubbles are seen in the water.

  By measuring the amount of dry matter and degassing the dissolved air in the water, the V1 (main valve) and V2 (exhaust valve) are closed and the V3 (container valve) is opened while the sample container is kept under vacuum. Then, water vapor is introduced from the reservoir and V3 (the reservoir valve) is closed. Next, by opening V1 (main valve), water vapor is introduced into the sample container, and the pressure is measured by a pressure sensor. If the pressure in the sample container does not reach the set pressure, the above operation is repeated to set the pressure in the sample container to the set pressure. When equilibrium is reached, the pressure and mass in the sample container become constant, and the pressure and temperature at that time and the sample mass are measured as equilibrium data.

In this apparatus, the pressure is set by the relative vapor pressure (%), and the adsorption / desorption isotherm is displayed by the adsorption amount (%) and the relative vapor pressure (%). The calculation formulas for the adsorption amount and relative vapor pressure are shown below.
M = (Wk−Wc) / Wc × 100 (1)
Pk = Q / Q0 × 100 (2)
(In the above formulas, M is the adsorption amount [%], Pk is the relative vapor pressure [%], Wk is the sample mass [mg] at the time of adsorption, Wc is the dry substance amount [mg] of the sample, and Q0 is the adsorption / desorption equilibrium. (Saturated vapor pressure of water [mmHg] obtained by the equation of Antoine from the temperature Tk [° C.] at the time, and Q represents the pressure [mmHg] measured as equilibrium data.)

Further, the magnetic particle used in the present invention has a coating layer having SiO ₂ on the surface, contains 17% by mass or more of Fe ²⁺ before heat treatment, and is heat-treated at 160 ° C. for 1 hour in air. The Fe ²⁺ retention rate is preferably 60% or more, and more preferably 70% or more.

Use of magnetic particles containing 17% by mass or more of Fe ²⁺ before the heat treatment is more effective from the viewpoint that the magnetic particles have sufficient blackness and magnetic properties. That is, since the magnetic particles having a high Fe ²⁺ retention before and after heat treatment are less likely to oxidize the surface in the air, the degree of blackness, which is particularly problematic in small-sized magnetic particles, can be maintained. it can. In addition, by being covered with the dense coating layer having SiO ₂ which is a nonmagnetic inorganic compound, the electric resistance of the magnetic particles can be increased and a high charge amount can be maintained. In particular, in magnetic toner, magnetic particles exposed on the surface can be a leakage site of charge, but magnetic particles having such a coating layer having SiO ₂ have a high electric resistance due to the dense coating layer. The charge amount of the magnetic toner can be maintained. Further, since the magnetic particles are excellent in fluidity and dispersibility by being covered with a dense coating layer of SiO ₂ , it is possible to cope with a reduction in the particle size of the magnetic toner. As a result, a desired charge amount is maintained regardless of the environment, and the applied amount of magnetic toner is kept constant, thereby realizing high image quality with excellent stability and reduction in consumption of magnetic toner.

The change in the content of divalent iron (Fe ²⁺ ) before and after the heat treatment of the magnetic particles is measured by the following method.
First, the magnetic particles are dissolved in sulfuric acid, and redox titration is performed using a potassium permanganate standard solution, and the content of Fe ^{2+ in} the magnetic particles before heat treatment is measured. On the other hand, 0.500 g of a magnetic particle sample heat-treated at 160 ° C. for 1 hour is precisely weighed, taken into a 500 ml Erlenmeyer flask, sealed with a rubber stopper that allows gas to pass through 10 ml of concentrated hydrochloric acid, and while passing carbon dioxide gas. Heat to completely decompose the sample. After cooling to room temperature while passing carbon dioxide, the rubber stopper is washed with pure water so that the washing liquid enters the Erlenmeyer flask, and the washing liquid is diluted to 150 ml with pure water. Next, titration is performed with a 0.1N potassium permanganate standard solution using a potentiometric titrator, and the content of Fe ^{2+ in} the magnetic particles after heat treatment is measured. The retention rate of Fe ^{2+ in} the present invention is determined as a percentage of the Fe ²⁺ content after the heat treatment relative to the Fe ²⁺ content before the heat treatment in the magnetic particles.

The content and retention of Fe ²⁺ in the magnetic particles in the present invention are, for example, the type of magnetic particles, the type and amount of non-magnetic material blended in the magnetic particles, or the material coating the magnetic particles. It can be adjusted by appropriately selecting and / or controlling the type and the coating amount or the coating state.

  The magnetic particles used in the present invention preferably have an average particle size of 0.08 to 0.25 μm from the viewpoint of dispersibility of the magnetic particles in the binder resin, blackness and magnetic properties. If the average particle size of the magnetic particles is less than 0.08 μm, it may cause a poor dispersion due to reaggregation of the magnetic particles in the magnetic toner, which is not preferable. When the average particle size of the magnetic particles is larger than 0.25 μm, it is advantageous from the viewpoint of blackness, but it may cause a deterioration in dispersion of the magnetic particles in the magnetic toner particles, which is not preferable.

  The average particle diameter of the magnetic particles is measured by the following method. Using a photograph (magnification 30,000 times) of a magnetic particle taken with a transmission electron microscope (H-7500; manufactured by Hitachi, Ltd.), randomly select 100 particles on the photograph to obtain the maximum of each magnetic particle. The length is measured, and the average value of the maximum lengths is taken as the average particle diameter. The average particle diameter of the magnetic particles can be adjusted by controlling the initial alkali concentration or the particle generation process due to the oxidation reaction in the method for producing magnetic particles described later, for example.

Magnetic particles in the present invention, as magnetic characteristics under a magnetic field 795.8 kA / m, saturation magnetization 10~200Am ² / kg, more preferably from 70~100Am ² / kg, residual magnetization 1~100Am ² / kg, more preferably ^{2 to 20} Am ² / kg, and a coercive force of 1 to 30 kA / m, more preferably 2 to 15 kA / m is preferably used. Having such magnetic properties is preferable from the viewpoint of obtaining good developability in which the magnetic toner has a good balance between image density and fog. The magnetic properties of the magnetic material can be measured under an external magnetic field of 795.8 kA / m using a “vibrating sample magnetometer VSM-3S-15” (manufactured by Toei Kogyo Co., Ltd.).

Hereinafter, specific materials used for the magnetic particles used in the present invention and a production method thereof will be described. The magnetic particles used in the present invention are magnetic particles having magnetic particles as mother particles and a coating layer having SiO ₂ formed on the surface of the magnetic particles as necessary. Hereinafter, in order to distinguish between magnetic particles having a coating layer and magnetic particles having no coating layer, the magnetic particles having no coating layer (before the formation of the coating layer) are referred to as “matrix magnetic particles”. write. That is, the magnetic particles used in the present invention may be composed only of the parent magnetic particles or may have the parent magnetic particles and the coating layer. A magnetic particle having a base magnetic particle and a coating layer is a preferred embodiment in the present invention.

  As the base magnetic particles in the present invention, any of magnetic iron oxides such as magnetite, maghemite, and ferrite containing different elements and a mixture thereof can be used. Preferably, the main component is magnetite having a high FeO content. To do. Magnetite particles are generally obtained by oxidizing a ferrous hydroxide slurry obtained by neutralizing and mixing a ferrous salt aqueous solution and an alkaline solution.

The base magnetic particles used in the present invention are preferably magnetic iron oxide particles containing a different element, and more preferably magnetic iron oxide particles containing a Si element as a different element. The Si element is preferably present both inside and on the surface of the base magnetic particle. In the process of producing the base magnetic particles, it is more preferable to add Si element stepwise because it can preferentially exist on the surface. Since the base magnetic particles contain Si element on the surface, a large number of pores are easily generated on the surface. Therefore, when forming a coating layer having SiO ₂ on the outer shell, the surface of the base magnetic particles And the adhesion force between SiO ₂ and SiO ₂ can be improved, and a dense coating layer can be formed.

  The content of the Si element is preferably 0.1 to 3.0% by mass, more preferably 0.1 to 2.0% by mass, with respect to the Fe element in the base magnetic particle. When the Si element content is less than 0.1% by mass, the adhesion with the silicate compound as the coating layer tends to be insufficient, while when it exceeds 3.0% by mass, it forms on the surface of the base magnetic particles. The denseness of the coating layer to be applied is impaired, and the smoothness of the magnetic particles after coating tends to be lost.

The magnetic particles used in the present invention are obtained by obtaining the parent magnetic particles using a general method for producing magnetic particles, and then setting the isoelectric point, the amount of adsorbed moisture, and the Fe ²⁺ retention after the heat treatment described above. In order to adjust to the range, it is obtained by forming a coating layer having SiO ₂ on the surface of the base magnetic particle.

The base magnetic particles before the formation of the coating layer containing SiO ₂ is not particularly problematic even when a known method for producing magnetic particles is used, but it has Si elements preferentially on the surface, which is preferable in the present invention. The base magnetic particles are produced, for example, by the following method.

A ferrous salt containing a ferrous hydroxide colloid by reacting a ferrous salt aqueous solution with 0.90 to 0.99 equivalent of an alkali hydroxide aqueous solution with respect to Fe ^{2+ in} the ferrous aqueous solution An aqueous reaction solution is obtained. Here, the total content (0) of water-soluble silicate in advance in terms of Si element with respect to iron element is added to either the aqueous alkali hydroxide solution or the ferrous salt reaction solution containing ferrous hydroxide colloid. .1 to 3.0 mass%) is added in an amount of 50 to 99%. And while heating the ferrous salt reaction aqueous solution containing this ferrous hydroxide colloid in the temperature range of 85-100 degreeC, an oxygen-containing gas (for example, air) is ventilated and an oxidation reaction is carried out, The said water Base magnetic nuclear particles containing Si element are produced from ferrous oxide colloid. At this time, it is preferable to carry out the oxidation reaction under the condition of pH 6.0 to 7.0. Thereafter, an aqueous alkali hydroxide solution of 1.00 equivalent or more with respect to Fe ²⁺ remaining in the suspension after completion of the oxidation reaction and the remaining water-soluble silicate [total content (0.4 to 2.0 mass) %) Is added, and the mixture is further subjected to an oxidation reaction while heating in a temperature range of 85 to 100 ° C. At this time, it is preferable to carry out an oxidation reaction under the condition of pH 8.0 to 10.5. Next, the base magnetic particles according to the present invention are obtained by filtration, washing with water, drying and crushing by a known method. Further, as a method of adjusting the average particle diameter, smoothness, and specific surface area of the base magnetic particles to preferable ranges, the base magnetic particles may be compressed, sheared and spatulated using a mix muller or a raking machine. preferable.

Examples of the silicate compound added to the base magnetic particles used in the present invention include commercially available silicates such as sodium silicate, and silicates such as sol-like silicate generated by hydrolysis.
Further, as the ferrous salt, it is possible to use iron sulfate generally produced as a by-product in the production of sulfuric acid titanium and iron sulfate produced as a by-product with the surface cleaning of the steel sheet. Furthermore, iron chloride or the like can be used.

  The base magnetic particles manufactured by the above-described manufacturing method are mainly composed of spherical particles formed with curved surfaces having no plate-like surface in the observation with a transmission electron micrograph, and most of the octahedral particles are formed. Magnetic particles that do not contain are produced. Such magnetic particles are preferably used for magnetic toner.

  On the other hand, the magnetic particles used in the present invention preferably have a small total content of Al, P, S, Cr, Mn, Co, Ni, Cu, Zn and Mg. In many cases, the above components are contained as inevitable components derived from raw materials at the time of producing magnetic particles. In the magnetic particles used in the present invention, considering the maintenance of blackness and magnetic properties, the lower the total content of the above components, the more effective the effect is, and 1 mass with respect to the mass of the magnetic particles. % Or less is preferable.

In addition, Si may be incorporated into the iron oxide crystal lattice or may be incorporated into the iron oxide as an oxide for the magnetic particles as described above. As described above, a more preferable form to achieve is to exist as an oxide on the surface of the magnetic particles. In particular, the effects of the present invention can be maximized by coating the base magnetic particles in the form of SiO ₂ by the method described below.

A suspended aqueous solution containing the parent magnetic particles at a concentration of 50 to 200 g / l is maintained at 60 to 80 ° C. Aqueous sodium hydroxide is added to bring the pH of the suspended aqueous solution to 9.0. While stirring the aqueous suspension, an aqueous sodium silicate solution corresponding to 0.1 to 10.0% by mass as SiO ₂ / Fe ₃ O ₄ is added thereto. Next, dilute sulfuric acid is added thereto to gradually lower the pH of the aqueous suspension, and finally the aqueous suspension is neutralized over about 4 hours. This can be washed, filtered, dried and pulverized to obtain magnetic particles coated with SiO ₂ .

Further, the average particle diameter of the base magnetic particles is 0.25 μm or less, more preferably 0.10 to 0.25 μm, and it is a binding when used as magnetic particles after the coating treatment with SiO _2. This is preferable from the viewpoint of dispersibility in the resin and uniformity of charging of the magnetic toner. The average particle diameter of the base magnetic particles is measured in the same manner as the average particle diameter of the magnetic particles.

  In the magnetic toner of the present invention, the magnetic particles are preferably used in an amount of 50 to 150 parts by mass, and more preferably 60 to 120 parts by mass with respect to 100 parts by mass of the binder resin. When the content of the magnetic particles is less than 50 parts by mass, not only the fogging and scattering of the image is deteriorated, but also the coloring power may be insufficient. When the amount is more than 150 parts by mass, it is difficult to sufficiently fly the magnetic toner from the charging member (developing sleeve), which may cause a decrease in image density, which is not preferable.

The magnetic toner of the present invention has at least a binder resin in addition to the magnetic particles.
The isoelectric point of the binder resin is preferably pH 2.0 to 4.0. The difference between the isoelectric point of the magnetic particles and the isoelectric point of the binder resin is preferably small. The isoelectric point of the magnetic particles is X, and the isoelectric point of the binder resin is Y. The difference (XY) between the isoelectric point of the magnetic particles and the isoelectric point Y of the binder resin is the following formula (i)
−2.0 ≦ (XY) ≦ 2.0 (i)
It is preferable to satisfy. When the isoelectric point of the magnetic particles and the isoelectric point of the binder resin satisfy the above formula (i), the dispersibility of the magnetic particles in the binder resin and the binding between the binder resin and the magnetic particles are determined. Since the adherence becomes better, the magnetic toner having a non-uniform charge amount is reduced, and the ghost phenomenon can be effectively suppressed.
As the binder resin used in the present invention, various resins conventionally known as binder resins can be used. For example, vinyl resin, phenol resin, natural resin modified phenolic resin, natural resin modified maleic acid resin, acrylic resin, methacrylic resin, polyvinyl acetate, silicone resin, polyester resin, polyurethane, polyamide resin, furan resin, epoxy resin, xylene Examples thereof include resins such as resins, polyvinyl butyral, terpene resins, coumaroindene resins, and petroleum resins. In particular, the binder resin is preferably a resin having at least a polyester unit. In the present invention, “polyester unit” refers to a portion derived from polyester. That is, the “resin having a polyester unit” in the present invention refers to a resin having at least a repeating unit having an ester bond.

Resin having a polyester unit obtained from an acid component and an alcohol component has an isoelectric point equivalent to the isoelectric point of the magnetic particles in the present invention, and is excellent in miscibility with the magnetic particles and difficult to desorb. And particularly preferred in terms of binding properties.
In the present invention, the resin having a polyester unit preferably used is preferably 45 to 55 mol% of an alcohol component and 55 to 45 mol% of an acid component in all components.

  Examples of alcohol components include ethylene glycol, propylene glycol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, diethylene glycol, triethylene glycol, 1,5-pentanediol, and 1,6- Xanthdiol, neopentyl glycol, 2-ethyl-1,3-hexanediol, hydrogenated bisphenol A, bisphenol derivatives represented by the following formula (B), diols represented by the following formula (C), glycerin, sorbit And polyhydric alcohols such as sorbitan.

(In the formula, R represents an ethylene group or a propylene group, x and y are each an integer of 1 or more, and the average value of x + y is 2 to 10.)

  Moreover, a carboxylic acid can be illustrated preferably as an acid component. Divalent carboxylic acids include benzene dicarboxylic acids such as phthalic acid, terephthalic acid, isophthalic acid, and phthalic anhydride, or anhydrides thereof; alkyldicarboxylic acids such as succinic acid, adipic acid, sebacic acid, and azelaic acid, or anhydrides thereof. ; Unsaturated dicarboxylic acids such as fumaric acid, maleic acid, citraconic acid, itaconic acid or their anhydrides, etc., and trivalent or higher carboxylic acids include trimellitic acid, pyromellitic acid, benzophenone tetra Examples thereof include carboxylic acid and its anhydride.

  A particularly preferable alcohol component of the polyester resin is a bisphenol derivative represented by the above formula (B), and examples of the acid component include phthalic acid, terephthalic acid, isophthalic acid or anhydride thereof, succinic acid, n-dodecenyl succinic acid, or the like. Examples thereof include dicarboxylic acids such as anhydride, fumaric acid, maleic acid, and maleic anhydride; trimellitic acid or tricarboxylic acid of anhydride thereof. A magnetic toner using a polyester resin obtained from these acid components and alcohol components as a binder resin has an isoelectric point similar to the isoelectric point of the magnetic particles in the present invention, and has good fixability. This is because of excellent offset resistance.

In the present invention, in addition to the resin having a polyester unit, the following vinyl resins may be used as the binder resin.
Examples of vinyl resins include styrene; o-methylstyrene, m-methylstyrene, p-methylenestyrene, p-methoxystyrene, p-phenylstyrene, p-chlorostyrene, 3,4-dichlorostyrene, p-ethyl. Styrene, 2,4-dimethylstyrene, pn-butylstyrene, p-tert-butylstyrene, pn-hexylstyrene, pn-octylstyrene, pn-nonylstyrene, pn-decylstyrene , Styrene derivatives such as pn-dodecylstyrene; ethylene unsaturated monoolefins such as ethylene, propylene, butylene and isobutylene; unsaturated polyenes such as butadiene; vinyl chloride, vinylidene chloride, vinyl bromide, vinyl fluoride, etc. Of vinyl halides; vinyl acetate, vinyl propionate, benzo Vinyl esters such as vinyl acid; methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-octyl methacrylate, dodecyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, Α-methylene aliphatic monocarboxylic acid esters such as phenyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate; methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, propyl acrylate, acrylic Acrylic acid esters such as n-octyl acid, dodecyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, 2-chloroethyl acrylate, phenyl acrylate; vinylmethyl Vinyl ethers such as ether, vinyl ethyl ether and vinyl isobutyl ether; Vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone and methyl isopropenyl ketone; N-vinyl pyrrole, N-vinyl carbazole, N-vinyl indole, N-vinyl pyrrolidone N-vinyl compounds such as; vinyl naphthalenes; acrylic acid or methacrylic acid derivatives such as acrylonitrile, methacrylonitrile, acrylamide; esters of α, β-unsaturated acids, diesters of dibasic acids; acrylic acid, methacrylic acid, Acrylic acid such as α-ethylacrylic acid, crotonic acid, cinnamic acid, vinyl acetic acid, isocrotonic acid, angelic acid and α- or β-alkyl derivatives thereof; fumaric acid, maleic acid, citraconic acid, alkenyl succinic acid, itaconic acid And polymers using vinyl monomers such as unsaturated dicarboxylic acids such as mesaconic acid, dimethylmaleic acid and dimethylfumaric acid, and monoester derivatives or anhydrides thereof. In the vinyl resin, the vinyl monomers as described above are used alone or in combination of two or more. Among these, a combination of monomers that becomes a styrene copolymer or a styrene-acrylic copolymer is preferable.

  The method for synthesizing a binder resin composed of a vinyl-based homopolymer or copolymer is not particularly limited, and various conventionally known production methods can be used. For example, a bulk polymerization method, a solution polymerization method, Polymerization methods such as suspension polymerization and emulsion polymerization can be used. When a carboxylic acid monomer or an acid anhydride monomer is used, it is preferable to use a bulk polymerization method or a solution polymerization method because of the properties of the monomer.

  In addition, the binder resin used in the present invention may be a polymer or copolymer cross-linked with a cross-linkable monomer as exemplified below if necessary. As the crosslinkable monomer, a monomer having at least two crosslinkable unsaturated bonds can be used. As such a crosslinkable monomer, various monomers as shown below are conventionally known and can be suitably used for the developer of the present invention.

  Examples of the crosslinkable monomer include divinylbenzene and divinylnaphthalene as aromatic divinyl compounds; diacrylate compounds linked with an alkyl chain such as ethylene glycol diacrylate, 1,3-butylene glycol diacrylate, 1,4-butanediol diacrylate, 1,5-pentanediol diacrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, and those obtained by replacing acrylate of the above compounds with methacrylate; ether bond Examples of diacrylate compounds linked by an alkyl chain containing, for example, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol Coal # 400 diacrylate, polyethylene glycol # 600 diacrylate, dipropylene glycol diacrylate and the above compounds in which the acrylate is replaced with methacrylate; diacrylate compounds linked by a chain containing an aromatic group and an ether bond For example, polyoxyethylene (2) -2,2-bis (4-hydroxyphenyl) propane diacrylate, polyoxyethylene (4) -2,2-bis (4-hydroxyphenyl) propane diacrylate and the above The thing which replaced the acrylate of the compound with the methacrylate is mentioned; As a polyester type diacrylate, a brand name MANDA (Nippon Kayaku) etc. are mentioned, for example.

  Polyfunctional cross-linking agents include pentaerythritol triacrylate, trimethylol ethane triacrylate, trimethylol propane triacrylate, tetramethylol methane tetraacrylate, oligoester acrylate, and acrylates of the above compounds replaced with methacrylate; triallylcia Examples thereof include nurate and triallyl trimellitate.

  Among the above-mentioned crosslinkable monomers, aromatic divinyl compounds (particularly divinylbenzene), aromatic groups and ether bonds are preferred for use in binder resins from the viewpoint of fixability and offset resistance of the obtained magnetic toner. And diacrylate compounds linked by a chain containing.

  The amount of the crosslinking agent is preferably adjusted according to the type of monomer to be crosslinked, the physical properties required of the binder resin, etc., but generally 100 parts by mass of other monomer components constituting the binder resin. In contrast, 0.01 to 10.00 parts by mass (more preferably 0.03 to 5.00 parts by mass) can be used.

In the present invention, a vinyl polymer homopolymer or copolymer other than the above, polyester, polyurethane, epoxy resin, polyvinyl butyral, rosin, modified rosin, terpene resin, phenol resin, aliphatic or alicyclic hydrocarbon resin, Aromatic petroleum resin or the like can be used by mixing with the above-described binder resin as necessary. When two or more kinds of resins are mixed and used as the binder resin, it is more preferable to mix those having different molecular weights at an appropriate ratio.
In the present invention, it is preferable that the binder resin contains at least a hybrid resin component in which both the polyester resin and the vinyl resin are partially reacted in order to obtain the intended effect of the present invention. This hybrid resin has two types of resin that are difficult to be compatible with each other in a uniform dispersion, making it possible to take advantage of the characteristics of both resins, such as chargeability, fixability, and storage stability, as well as other internal additives. Excellent compatibility with.

  The binder resin used in the magnetic toner of the present invention preferably has an acid value. The acid value of the binder resin is preferably 1 to 50 mgKOH / g, and more preferably 4 to 40 mgKOH / g.

  As a result of investigations, the inventors have studied that the charge amount and charge stability of the magnetic toner are affected by the charge amount distribution on the magnetic toner surface, and if the charge amount distribution is uneven, the charge leakage locally occurs. It has been found that the charging stability of the magnetic toner tends to be impaired by becoming a site or charging up. Further, by using a binder resin having an acid value in the above range, the difference in the amount of adsorbed moisture between the magnetic particle portion exposed on the surface of the magnetic toner and the other binder resin portion can be reduced. Therefore, it has been found that the charge amount distribution on the surface of the magnetic toner can be made uniform.

  If the acid value of the binder resin is less than 1 mg KOH / g or more than 50 mg KOH / g, not only will it be difficult to control the amount of water absorbed by the magnetic toner, but the environmental fluctuation of the charging property of the magnetic toner will be large. Tend to be.

  The OH value (hydroxyl value) of the binder resin is preferably 60 mgKOH / g or less, and more preferably 45 mgKOH / g or less. This is because as the number of terminal groups in the molecular chain increases, the magnetic toner's charging characteristics become more environmentally dependent, and the magnetic toner's fluidity, electrostatic adhesion, and developer surface resistance (effect of adsorbed water) fluctuate. This is because there is a case where a decrease in the number of times occurs.

In addition, an acid value is calculated | required by operation of following 1) -5). Basic operations belong to JIS K 0070.
1) The sample is used by removing additives other than the binder resin (polymer component) in advance, or the acid value of the component other than the binder resin of the sample is obtained in advance. A magnetic toner or binder resin pulverized product 0.5 to 2.0 (g) is precisely weighed. The binder resin component at this time is defined as W (g).

2) A sample is put into a 300 (ml) beaker, and a mixed solution 150 (ml) of toluene / ethanol (toluene mass / ethanol mass = 4/1) is added and dissolved.

3) Using an ethanol solution of 0.1 (mol / l) KOH, measurement is performed using a potentiometric titration measuring device. For this titration, for example, automatic titration using a potentiometric titration measuring device AT-400 (winworkstation) of Kyoto Electronics Co., Ltd. and an ABP-410 electric burette can be used.

4) The amount of KOH ethanol solution used is S (ml). At the same time, a blank is measured, and the amount of KOH ethanol solution used at this time is defined as B (ml).

5) Calculate the acid value according to the following formula. In the following formula, f is a factor of KOH.
Acid value (mgKOH / g) = {(SB) × f × 5.61} / W

Moreover, OH value is calculated | required by operation of following 1) -8). Basic operation conforms to JIS K 0070.
1) The sample is used by removing additives other than the binder resin (polymer component) in advance, or the content of components other than the binder resin in the sample is obtained. 0.5 to 2.0 (g) of a pulverized product of magnetic toner or binder resin is precisely weighed into a 200 (ml) flat bottom flask.

2) Add 5 ml of an acetylating reagent (take 25 g of acetic anhydride into a 100 ml volumetric flask, add pyridine to bring the total volume to 100 ml and stir well). If the sample is difficult to dissolve, add a small amount of pyridine, or dissolve by adding xylene or toluene.

3) Place a small funnel in the mouth of the flask and immerse the bottom of about 1 cm in a glycerin bath at a temperature of 95-100 ° C. and heat. In order to prevent the temperature of the neck of the flask from rising due to the heat of the glycerin bath, a cardboard disc with a round hole in it is put on the base of the neck of the flask.

4) After 1 hour, remove from the glycerin bath to the flask, allow to cool, add 1 ml of water from the funnel and shake to decompose acetic anhydride.

5) To further complete the decomposition, the flask is again heated in a glycerin bath for 10 minutes, allowed to cool, and then the funnel and flask wall are washed with 5 ml of ethanol.

6) Add a few drops of phenolphthalein solution as an indicator, titrate with 0.5 kmol / m ³ potassium hydroxide ethanol solution, and end when the indicator is light red for about 30 seconds.

7) Perform 2) to 6) as blank tests without adding resin.

8) The OH value (hydroxyl value) is calculated by the following formula.
Hydroxyl value (mgKOH / g) = [{(DE) × 28.05 × f ′} / S] + F
(In the above formula, D is the titration (ml) of the 0.5 kmol / m ³ potassium hydroxide ethanol solution used for the blank test, and E is the 0.5 kmol / m ³ potassium hydroxide ethanol solution used for the titration. Titration amount (ml), f ′ is a factor of 0.5 kmol / m ³ potassium hydroxide ethanol solution, S is the amount (g) of binder resin contained in the sample, and F is the acid of the sample In the formula, “28.05” is the formula amount of potassium hydroxide (56.11 × 1/2)).

  Moreover, it is preferable that the glass transition temperature of the binder resin used for this invention is 45-80 degreeC, More preferably, it is 55-70 degreeC. The number average molecular weight (Mn) of the binder resin is preferably 2,500 to 50,000, and the weight average molecular weight (Mw) of the binder resin is 10,000 to 1,000,000. It is preferable.

The glass transition temperature of the binder resin is generally determined from the published polymer handbook 2nd edition III-
P. 139 to 192 (John Wiley & Sons), the theoretical glass transition temperature is 45 to 8
The temperature can be adjusted by selecting a constituent material (polymerizable monomer) of the binder resin so as to indicate 0 ° C. The glass transition temperature of the binder resin can be measured according to ASTM D3418-82 using a differential scanning calorimeter, for example, DSC-7 manufactured by PerkinElmer or DSC2920 manufactured by TA Instruments Japan. If the glass transition temperature of the binder resin is lower than the above range, the storage stability of the magnetic toner may be insufficient, and if the glass transition temperature of the binder resin is higher than the above range, the fixability of the developer is poor. May be sufficient.

The magnetic toner of the present invention may further contain a wax.
The waxes used in the present invention include the following. For example, aliphatic hydrocarbon waxes such as low molecular weight polyethylene, low molecular weight polypropylene, polyolefin copolymers, polyolefin wax, microcrystalline wax, paraffin wax and Fischer-Tropsch wax; oxides of aliphatic hydrocarbon waxes such as oxidized polyethylene wax Or block copolymers thereof; plant waxes such as candelilla wax, carnauba wax, wax wax and jojoba wax; animal waxes such as beeswax, lanolin and spermaceti; mineral systems such as ozokerite, ceresin and petrolactam; Waxes; waxes based on aliphatic esters such as montanic acid ester wax and castor wax; those obtained by partially or fully deoxidizing aliphatic esters such as deoxidized carnauba wax And the like. Further, saturated linear fatty acids such as palmitic acid, stearic acid, montanic acid, and long-chain alkyl carboxylic acids having a long-chain alkyl group; unsaturated fatty acids such as brassic acid, eleostearic acid and valinalic acid; stearyl alcohol Saturated alcohols such as eicosyl alcohol, behenyl alcohol, cannavir alcohol, seryl alcohol, melyl alcohol and alkyl alcohols having a long chain alkyl group; polyhydric alcohols such as sorbitol; linoleic acid amide, oleic acid amide and lauric acid Aliphatic amides such as amides; saturated aliphatic bisamides such as methylene bisstearic acid amide, ethylene biscapric acid amides, ethylene bislauric acid amides and hexamethylene bisstearic acid amides; Unsaturated fatty acid amides such as inamide, hexamethylenebisoleic acid amide, N, N′-dioleyl adipic acid amide and N, N′-dioleyl sebacic acid amide; m-xylene bisstearic acid amide and N, Aromatic bisamides such as N'-distearylisophthalamide; aliphatic metal salts such as calcium stearate, calcium laurate, zinc stearate and magnesium stearate (commonly referred to as metal soaps); aliphatic hydrocarbons Wax grafted with vinyl monomers such as styrene and acrylic acid on wax; Partial esterification product of fatty acid such as behenic acid monoglyceride and polyhydric alcohol; Hydroxyl group obtained by hydrogenating vegetable oil Methyl ester compounds It is below.

  In addition, these waxes have a sharp molecular weight distribution using a press perspiration method, a solvent method, a recrystallization method, a vacuum distillation method, a supercritical gas extraction method or a melt liquid crystal deposition method, a low molecular weight solid fatty acid, a low A molecular weight solid alcohol, a low molecular weight solid compound, or other impurities are preferably used.

The wax used in the present invention preferably has a melting point of 60 to 120 ° C, more preferably 70 to 110 ° C.
During the kneading step of the magnetic particle binder resin and the wax, the kneading temperature rises and the magnetic particles are oxidized, which may cause redness of the magnetic toner. The magnetic material used in the present invention preferably has a high divalent iron retention before and after heat treatment at 160 ° C., but by using a wax having a lower melting point, the kneading temperature is lowered and the magnetic material is used. Oxidation of particles and redness of the magnetic toner due to the oxidation can be suppressed. In addition, by using a wax having a melting point in a more preferable range, an optimum viscosity is exhibited in the kneading step of the magnetic particles and the binder resin, and as a result, the dispersibility of the magnetic particles and the binder resin is excellent. A magnetic toner is obtained.

  The magnetic toner of the present invention preferably contains a charge control agent. Specific examples of the negative charge control agent include monoazo dyes described in JP-B No. 41-20153, JP-B No. 42-27596, JP-B No. 44-6397, JP-B No. 45-26478, and the like. Nitrohumic acid and its salts described in JP-A-50-133838 or C.I. I. Dyes and pigments such as 14645; salicylic acid, naphthoic acid and dicarboxylic acid described in JP-B-55-42752, JP-B-58-41508, JP-B-58-7384, JP-B-59-7385, etc. Examples thereof include metal compounds of acids Zn, Al, Co, Cr, Fe and Zr; sulfonated copper phthalocyanine pigments; styrene oligomers introduced with nitro groups and halogens; chlorinated paraffins and the like. Particularly, an azo metal compound represented by the following formula (I) or a basic organic acid represented by the following formula (II), which is excellent in dispersibility in a magnetic toner and is effective in reducing image density stability and fogging. Metal compounds are preferred.

[Wherein M represents a coordination center metal and represents Cr, Co, Ni, Mn, Fe, Ti, or Al. Ar is an arylene group such as a phenylene group and a naphthylene group, and may have a substituent. In this case, examples of the substituent include a nitro group, a halogen group, a carboxyl group, an anilide group, an alkyl group having 1 to 18 carbon atoms, and an alkoxy group having 1 to 18 carbon atoms. X, X ′, Y, and Y ′ each independently represent —O—, —CO—, —NH—, or —NR— (R represents an alkyl group having 1 to 4 carbon atoms). A ⁺ represents hydrogen, sodium ion, potassium ion, ammonium ion or aliphatic ammonium ion. ]

  Among these, the azo metal compound represented by the above formula (I) is more preferable, and the azo iron compound represented by the following formula (III) or (IV) in which the central metal is Fe is most preferable.

[Wherein, X ₂ and X ₃ represent a hydrogen atom, a lower alkyl group, a lower alkoxy group, a nitro group or a halogen atom, k and k ′ represent an integer of _{1 to 3} , and Y ₁ and Y ₃ represent a hydrogen atom. , An alkyl group having 1 to 18 carbon atoms, an alkenyl group having 2 to 18 carbon atoms, a sulfonamide group, a mesyl group, a sulfonic acid group, a carboxyester group, a hydroxy group, an alkoxy group having 1 to 18 carbon atoms, acetyl An amino group, a benzoyl group, an amino group or a halogen atom, l and l ′ represent an integer of 1 to 3, Y ₂ and Y ₄ represent a hydrogen atom or a nitro group (the above X ₂ and X ₃ , k And k ′, Y ₁ and Y ₃ , l and l ′, Y ₂ and Y ₄ may be the same or different). A ″ ⁺ represents an ammonium ion, a sodium ion, a potassium ion, a hydrogen ion or a mixed ion thereof, and preferably has an ammonium ion of 75 to 98 mol%.]
In the present invention, “lower” means 1 to 6 carbon atoms.

[Wherein R _{1 to} R ₂₀ represent a hydrogen atom, a halogen atom, or an alkyl group, and A ⁺ represents an ammonium ion, a sodium ion, a potassium ion, a hydrogen ion, or a mixed ion thereof. ]

Next, specific examples of the azo-based iron compound represented by the above formula (III) are shown.

  Specific examples of the charge control agent having a structure represented by the above formulas (I), (II), and (IV) are shown below.

  In the above formula, tBu means a tertiary butyl group.

  These metal compounds can be used alone or in combination of two or more. The amount of these charge control agents used is preferably 0.1 to 5.0 parts by mass per 100 parts by mass of the binder resin from the viewpoint of the charge amount of the magnetic toner.

Among the negative charge control agents as described above, preferable ones as commercial products are, for example, Spiron Black TRH, T-77, T-95 (Hodogaya Chemical Co., Ltd.), BONTRON (registered trademark) S-34, S-44, S-54, E-84, E-88, E-89 (Orient Chemical Co., Ltd.) and the like.
When the magnetic toner of the present invention is used as a negatively chargeable toner, the effects of the present invention are more easily exhibited.

  On the other hand, there are the following substances that control the toner to be positively charged. Modified products with nigrosine and fatty acid metal salts; oniums such as quaternary ammonium salts such as tributylbenzylammonium-1-hydroxy-4-naphthosulfonate, tetrabutylammonium tetrafluoroborate, and phosphonium salts which are analogs thereof Salts and their lake pigments; triphenylmethane dyes and their lake pigments (the rake agents include phosphotungstic acid, phosphomolybdic acid, phosphotungsten molybdic acid, tannic acid, lauric acid, gallic acid, ferricyanide, Russian salts, etc.); metal salts of higher fatty acids; diorganotin oxides such as dibutyltin oxide, dioctyltin oxide, dicyclohexyltin oxide; dibutyltin borate, dioctyltin borate, dicyclohexyl Diorgano tin borate such as Suzuboreto; they can be used alone or in combinations of two or more.

  Among the positive charge control agents as described above, preferred as commercially available products are, for example, TP-302, TP-415 (Hodogaya Chemical Co., Ltd.), BONTRON (registered trademark) N-01, N-04, N- 07, P-51 (Orient Chemical Co., Ltd.), Copy Blue PR (Clariant) and the like.

The magnetic toner of the present invention is preferably mixed with inorganic fine powder or hydrophobic inorganic fine powder. For example, it is preferable to add and use silica fine powder.
As the silica fine powder used in the present invention, both a so-called dry method produced by vapor phase oxidation of a silicon halogen compound or dry silica called fumed silica, and so-called wet silica produced from water glass or the like are used. Although possible, dry silica with less silanol groups on the surface and inside and no production residue is preferred.

  The silica fine powder used in the present invention is preferably hydrophobized. Hydrophobing treatment includes a chemical treatment with an organosilicon compound that reacts with silica fine powder or is physically adsorbed on silica fine powder. Preferable methods include a method in which a dry silica fine powder produced by vapor phase oxidation of a silicon halogen compound is treated with a silane compound or with a silane compound and simultaneously with an organosilicon compound such as silicone oil.

Examples of the silane compound used for the hydrophobization treatment include hexamethyldisilazane, trimethylsilane, trimethylchlorosilane, trimethylethoxysilane, dimethyldichlorosilane, methyltrichlorosilane, allyldimethylchlorosilane, allylphenyldichlorosilane, and benzyl. Dimethylchlorosilane, bromomethyldimethylchlorosilane, α-chloroethyltrichlorosilane, β-chloroethyltrichlorosilane, chloromethyldimethylchlorosilane, triorganosilane mercaptan, trimethylsilyl mercaptan, triorganosilyl acrylate, vinyldimethylacetoxysilane, dimethylethoxy Silane, dimethyldimethoxysilane, diphenyldiethoxysilane, hexamethyldisiloxane, 1,3-divinyltetramethyl Examples include tildisiloxane and 1,3-diphenyltetramethyldisiloxane.

Examples of the organosilicon compound include silicone oil. Preferred silicone oils are those having a viscosity at 25 ° C. of about 3 × 10 ⁻⁵ to 1 × 10 ⁻³ m ² / s, such as dimethyl silicone oil, methyl hydrogen silicone oil, methyl phenyl silicone oil, α -Methylstyrene modified silicone oil, chlorophenyl silicone oil, fluorine modified silicone oil and the like are preferable.

  The silicone oil treatment method may be, for example, a method in which silica fine powder treated with a silane compound and silicone oil are directly mixed using a mixer such as a Henschel mixer, or a method in which silicone oil is sprayed onto the base silica. Good. Alternatively, the treatment may be performed by dissolving or dispersing the silicone oil in an appropriate solvent and then mixing with the base silica fine powder to remove the solvent.

  The inorganic fine powder or hydrophobic inorganic fine powder added to and mixed with the magnetic toner is preferably 0.1 to 5.0 parts by mass, more preferably 0.1 to 3. part by mass with respect to 100 parts by mass of the magnetic toner. 0 parts by mass.

  If necessary, an external additive other than silica fine powder may be added to the magnetic toner of the present invention. For example, resin fine particles and inorganic fine particles that function as a charge auxiliary agent, conductivity imparting agent, fluidity imparting agent, anti-caking agent, lubricant, abrasive, and the like. Specific examples include lubricants such as polyvinyl fluoride, zinc stearate, and polyvinylidene fluoride. Among these, polyvinylidene fluoride is preferable. Or abrasive | polishing agents, such as a cerium oxide, silicon carbide, and strontium titanate, are mentioned, Among these, strontium titanate is preferable. Alternatively, fluidity imparting agents such as titanium oxide and aluminum oxide can be used, and among them, hydrophobic ones are particularly preferable. In addition, an anti-caking agent; for example, a conductivity imparting agent such as carbon black, zinc oxide, antimony oxide, tin oxide; and a small amount of white and black fine particles having opposite polarity can be used as a developing improver.

  In order to produce the magnetic toner of the present invention, a mixture containing at least a binder resin and magnetic particles is used as a material, and other waxes, charge control agents, and other additives may be used as necessary. . These materials are mixed thoroughly by a mixer such as a Henschel mixer or a ball mill, and then melted, kneaded and kneaded using a heat kneader such as a roll, a kneader and an extruder so that the resins are mutually compatible. Further, a pigment or dye as a colorant is dispersed or dissolved, cooled and solidified, and then pulverized and classified to obtain a magnetic toner. Further, silica fine powder and / or other external additives are externally mixed as needed with the obtained magnetic toner.

  Examples of the mixer used in the production of the magnetic toner include Henschel mixer (manufactured by Mitsui Mining); Super mixer (manufactured by Kawata); Ribocorn (manufactured by Okawara Seisakusho); Nauter mixer, turbulizer, cyclomix (Hosokawa Micron) Spiral pin mixer (manufactured by Taiheiyo Kiko Co., Ltd.); Ladige mixer (manufactured by Matsubo Co., Ltd.), and KRC kneader (manufactured by Kurimoto Iron Works Co.); TEM type extruder (manufactured by Toshiba Machine Co., Ltd.); TEX twin-screw kneader (manufactured by Nippon Steel Co., Ltd.); PCM kneader (manufactured by Ikegai Iron Works Co., Ltd.); ); Kneedex (Mitsui Mining Co., Ltd.); MS pressure kneader, Nider Ruder (Moriyama Seisakusho); Banbury Kiser (manufactured by Kobe Steel Co., Ltd.) can be mentioned, and as the pulverizer, counter jet mill, micron jet, inomizer (manufactured by Hosokawa Micron Co.); IDS type mill, PJM jet pulverizer (manufactured by Nippon Pneumatic Industrial Co., Ltd.); cross jet Mill (manufactured by Kurimoto Iron Works); Urmax (manufactured by Nisso Engineering); SK Jet O Mill (manufactured by Seishin Enterprise); Kryptron (manufactured by Kawasaki Heavy Industries); Turbo mill (manufactured by Turbo Industry); Super Rotor (Nisshin Engineering) is listed, and classifiers include: Classy, Micron Classifier, Spedic Classifier (manufactured by Seishin Enterprise); Turbo Classifier (manufactured by Nisshin Engineering); Micron Separator, Turboplex ( ATP), TSP separator Hosokawa Micron Co., Ltd.); Elbow Jet (Nittetsu Mining Co., Ltd.), Dispersion Separator (Nihon Pneumatic Kogyo Co., Ltd.); YM Micro Cut (Yaskawa Shoji Co., Ltd.), and the like are used to screen coarse particles. As a sieving device, Ultrasonic (manufactured by Sakae Sangyo Co., Ltd.); Resonator Sheave, Gyroshifter (manufactured by Deoksugakusho Co., Ltd.); Vibrasonic System (manufactured by Dalton Co., Ltd.); A turbo shifter); a micro shifter (manufactured by Hadano Sangyo Co., Ltd.); and a circular vibrating sieve.

Although the configuration of the magnetic toner of the present invention has been described above, the present invention will be described below based on examples. However, the present invention is not limited to these examples. In addition, the number of parts in an Example means a mass part.
The magnetic particles used in Examples and Reference Examples are shown in Table 1, and the wax is shown in Table 2. In addition, the manufacturing method of a base magnetic body particle | grain, a magnetic body particle | grain, and binder resin is as follows.

<Production Example 1 of Magnetic Particle>
After mixing 0.96 equivalent sodium hydroxide aqueous solution with respect to Fe ^<2+ > in the ferrous sulfate solution, the ferrous salt aqueous solution containing Fe (OH) ₂ was produced | generated. Then, sodium silicate was added so that it might become 1.0 mass% in conversion of Si element with respect to Fe element. Next, the aqueous ferrous salt solution containing Fe (OH) ₂ was subjected to an oxidation reaction at a temperature of 90 ° C. by passing air at a temperature of 90 ° C.

Furthermore, an aqueous solution of sodium hydroxide in which 0.2% by mass of sodium silicate was dissolved (in terms of Si element relative to Fe element) was added to this suspension at 1.05 equivalents relative to the remaining Fe ²⁺ , Oxidation reaction was carried out under the condition of pH 9.0 while heating at a temperature of 90 ° C., and washed, filtered and dried by a conventional method to obtain base magnetic particles A. The content of Si element in the base magnetic particle A was 1.2% by mass with respect to the Fe element in the base magnetic particle A. The Si element content corresponds to 0.6% by mass based on the mass of the base magnetic particle A in terms of the SiO ₂ content of the base magnetic particle A.

The base magnetic particle A was dispersed in water to obtain a suspended aqueous solution having a concentration of 100 g / l. The aqueous suspension was kept at 80 ° C. or higher, and an aqueous sodium hydroxide solution was added to adjust the pH of the aqueous suspension to 9.0. While stirring the aqueous suspension, an aqueous sodium silicate solution corresponding to 4.7% by mass as SiO ₂ / Fe ₃ O ₄ was added thereto. Then, dilute sulfuric acid was added to gradually lower the pH of the aqueous suspension, and finally the aqueous suspension was neutralized over about 4 hours. This was washed, filtered, dried, and crushed by a conventional method to obtain high-density silica-coated magnetic particles 1. The magnetic particles 1 were spherical and the average particle size was 0.15 μm. The silica coating amount was 4.3% by mass based on the mass of the magnetic particles. In addition, when washing | cleaning and taking out the base magnetic body particle | grains after a process from suspension aqueous solution, the part equivalent to 0.4 mass% of the addition amount of sodium silicate will flow out. Table 1 shows the physical properties of the magnetic particles 1.

<Production Example 2 of Magnetic Particle>
In the production of the base magnetic particles A in Production Example 1 of the magnetic particles, the concentration of sodium hydroxide added to the ferrous sulfate solution is adjusted so that the average size of the obtained base magnetic particles is 0.16 μm. The concentration of sodium silicate added at the first time is 1.5% by mass, the concentration of sodium silicate added at the second time is 0.3% by mass, and the content of Si element in the obtained base magnetic particles is the base. It was 1.8 mass% with respect to Fe element in a magnetic particle. Further, the amount of sodium silicate aqueous solution added when the base magnetic particles were coated with SiO ₂ was equivalent to 1.7% by mass as SiO ₂ / Fe ₃ O ₄ . Except for these, the magnetic particles ₂ coated with SiO 2 were obtained in the same manner as in Production Example 1 of the magnetic particles. Table 1 shows the physical properties of the magnetic particles 2.

<Production Example 3 of Magnetic Particle>
In the production of the base magnetic particles A in Production Example 1 of the magnetic particles, the concentration of sodium hydroxide added to the ferrous sulfate solution is adjusted so that the average size of the obtained base magnetic particles is 0.16 μm. The concentration of sodium silicate added at the first time is 2.3% by mass, the concentration of sodium silicate added at the second time is 0.6% by mass, and the content of Si element in the obtained base magnetic material particles is the base material. It was set to 2.9% by mass with respect to Fe element in the magnetic particles. Further, the amount of sodium silicate aqueous solution added when the base magnetic particles were coated with SiO ₂ was added in an amount corresponding to 1.4% by mass as SiO ₂ / Fe ₃ O ₄ . Except for these, the magnetic particles 3 coated with SiO ₂ were obtained in the same manner as in Production Example 1 of the magnetic particles. Table 1 shows the physical properties of the magnetic particles 3.

<Production Example 4 of Magnetic Particle>
In the production of the parent magnetic particles A in Production Example 1 of the magnetic particles, the concentration of sodium hydroxide added to the ferrous sulfate solution is adjusted so that the average particle diameter of the obtained parent magnetic particles is 0.10 μm. Concentration of sodium silicate added at the first time is 3.0% by mass, concentration of sodium silicate added at the second time is 1.0% by mass, and the content of Si element in the obtained base magnetic particles is the base. It was 4.0 mass% with respect to Fe element in a magnetic particle. Further, the amount of sodium silicate aqueous solution added when the base magnetic particles were coated with SiO ₂ was added in an amount corresponding to 1.4% by mass as SiO ₂ / Fe ₃ O ₄ . Except for these, the magnetic particles 4 coated with SiO ₂ were obtained in the same manner as in Production Example 1 of the magnetic particles. Table 1 shows the physical properties of the magnetic particles 4.

<Production Example 5 of Magnetic Particle>
In the production of the base magnetic particles A in Production Example 1 of the magnetic particles, the concentration of sodium hydroxide added to the ferrous sulfate solution is adjusted so that the average particle size of the obtained base magnetic particles is 0.22 μm. The concentration of sodium silicate added at the first time is 1.3% by mass, and the concentration of sodium silicate added at the second time is 0.5% by mass. It was 1.8 mass% with respect to Fe element in a magnetic particle. Further, the amount of the sodium silicate aqueous solution added when the base magnetic particles were coated with SiO ₂ was added in an amount corresponding to 14.0% by mass as SiO ₂ / Fe ₃ O ₄ . Except for these, magnetic particles 5 coated with SiO ₂ were obtained in the same manner as in magnetic particle production example 1. Table 1 shows the physical properties of the magnetic particles 5.

<Production Example 6 of Magnetic Particle>
In the production of the parent magnetic particles A in Production Example 1 of the magnetic particles, the concentration of sodium hydroxide added to the ferrous sulfate solution is adjusted so that the average particle diameter of the obtained parent magnetic particles is 0.23 μm. The concentration of sodium silicate added at the first time is 2.0% by mass, the concentration of sodium silicate added at the second time is 0.6% by mass, and the content of Si element in the obtained base magnetic particles is the base. It was 2.6 mass% with respect to Fe element in a magnetic substance particle. Further, the amount of the sodium silicate aqueous solution added when the base magnetic particles are coated with SiO ₂ is added in an amount corresponding to 21.1% by mass as SiO ₂ / Fe ₃ O ₄ , and the pH of the solution is adjusted to form an octahedral shape. Magnetic particles exhibiting Except for these, the magnetic particles 6 coated with SiO ₂ were obtained in the same manner as in Production Example 1 of the magnetic particles. Table 1 shows the physical properties of the magnetic particles 6.

<Production Example 7 of Magnetic Particle>
In the production of the parent magnetic particles A in Production Example 1 of the magnetic particles, the sodium hydroxide concentration added to the ferrous sulfate solution is adjusted so that the average particle diameter of the obtained parent magnetic particles is 0.07 μm. The concentration of the sodium silicate added at the first time is 1.4% by mass, the concentration of the sodium silicate added at the second time is 0.6% by mass, and the content of the Si element in the obtained base magnetic particles is the base. It was 2.0 mass% with respect to the Fe element in a magnetic particle. Further, the amount of the sodium silicate aqueous solution added when the base magnetic particles were coated with SiO ₂ was added in an amount corresponding to 23.0 mass% as SiO ₂ / Fe ₃ O ₄ . Except for these, the magnetic particles 7 coated with SiO ₂ were obtained in the same manner as in Production Example 1 of the magnetic particles. Table 1 shows the physical properties of the magnetic particles 7.

<Production Example 8 of Magnetic Particle>
In the production of the base magnetic particles A in Production Example 1 of the magnetic particles, the concentration of sodium hydroxide added to the ferrous sulfate solution is adjusted so that the average size of the obtained base magnetic particles is 0.12 μm. Further, no sodium silicate was added. In addition, the amount of sodium silicate aqueous solution added when the base magnetic particles were coated with SiO ₂ was equivalent to 19.5% by mass as SiO ₂ / Fe ₃ O ₄ . Except for these, magnetic particles 8 coated with SiO ₂ were obtained in the same manner as in magnetic particle production example 1. Table 1 shows the physical properties of the magnetic particles 8.

<Production Example 9 of Magnetic Particle>
In the production of the base magnetic particles A in Production Example 1 of the magnetic particles, the concentration of sodium hydroxide added to the ferrous sulfate solution is adjusted so that the average particle size of the obtained base magnetic particles is 0.22 μm. The concentration of sodium silicate added at the first time is 1.5% by mass, the concentration of sodium silicate added at the second time is 0.3% by mass, and the content of Si element in the base magnetic particles is set as the base magnetic material. It was 1.8 mass% with respect to Fe element in particle | grains. In addition, a manganese sulfate aqueous solution as MnO / Fe ₃ O ₄ was added in an amount corresponding to 3.5% by mass in place of the sodium silicate aqueous solution during the coating treatment of the base magnetic particles. Except for these, magnetic particles 9 coated with MnO were obtained in the same manner as in magnetic particle production example 1. Table 1 shows the physical properties of the magnetic particles 9.

<Example 10 of magnetic particle production>
In the production of the parent magnetic particles A in Production Example 1 of the magnetic particles, the concentration of sodium hydroxide added to the ferrous sulfate solution is adjusted so that the average particle diameter of the obtained parent magnetic particles is 0.10 μm. Concentration of sodium silicate added at the first time is 3.0% by mass, concentration of sodium silicate added at the second time is 1.0% by mass, and the content of Si element in the obtained base magnetic particles is the base. It was 4.0 mass% with respect to Fe element in a magnetic particle. Further, without performing the SiO ₂ coating treatment of the mother magnetic particles, to obtain magnetic particles 10. Table 1 shows the physical properties of the magnetic particles 10.

<Binder Resin Production Example 1>
40 parts by mass of PO (propylene oxide) 2 mol adduct of bisphenol A, 30 parts by mass of EO (ethylene oxide) 2 mol adduct of bisphenol A, 25 parts by mass of terephthalic acid, 4 parts by mass of fumaric acid, anhydrous 5 parts by mass of trimellitic acid and 0.5 parts by mass of dibutyltin oxide were added, and these were subjected to condensation polymerization at 220 ° C. to obtain a binder resin 1 which was a polyester resin. The binder resin 1 had an acid value of 22 mgKOH / g, a hydroxyl value of 32 mgKOH / g, a glass transition temperature (Tg) of 59 ° C., an Mw of 220,000, and a THF (tetrahydrofuran) insoluble content of 14% by mass. . Further, the isoelectric point of the binder resin 1 was pH 2.4.

<Binder Resin Production Example 2>
In Binder Resin Production Example 1, the monomer composition is 40 parts by mass of PO2 mol adduct of bisphenol A, 70 parts by mass of EO2 mol adduct of bisphenol A, 50 parts by mass of terephthalic acid, 1 part by mass of trimellitic anhydride and dibutyl. Except for using 0.5 parts by mass of tin oxide, condensation polymerization was performed in the same manner as in Production Example 1 to obtain a binder resin 2 that was a polyester resin. The binder resin 2 had an acid value of 3.6 mgKOH / g, a hydroxyl value of 22 mgKOH / g, Tg of 65 ° C., Mw of 50,000, and a THF-insoluble content of 4% by mass. The isoelectric point of the binder resin 2 was pH 3.1.

<Binder Resin Production Example 3>
In Production Example 1 of the binder resin, the monomer composition was 100 parts by mass of a PO2 molar adduct of bisphenol A, 32 parts by mass of isophthalic acid, 12 parts by mass of terephthalic acid, 1 part by mass of trimellitic anhydride, and 0.5 parts of dibutyltin oxide. Except for the mass part, condensation polymerization was carried out in the same manner as in Production Example 1 to obtain a binder resin 3 which was a polyester resin. This binder resin 3 had an acid value of 2.0 mgKOH / g, Mw of 60,000, a hydroxyl value of 54 mgKOH / g, Tg of 52 ° C., and a THF-insoluble content of 0% by mass. Further, the isoelectric point of the binder resin 3 was pH 2.1.

<Binder Resin Production Example 4>
In Binder Resin Production Example 1, the monomer composition was 40 parts by mass of an EO2 molar adduct of bisphenol A, 12 parts by mass of terephthalic acid, 7 parts by mass of trimellitic anhydride, 5 parts by mass of dodecenyl succinic acid, and 0. 2 parts of dibutyltin oxide. Except for 5 parts by mass, condensation polymerization was carried out in the same manner as in Production Example 1 to obtain a binder resin 4 which was a polyester resin. The binder resin 4 had an acid value of 42 mgKOH / g, a hydroxyl value of 4.8 mgKOH / g, an Mw of 280,000, a Tg of 55 ° C., and a THF-insoluble content of 5% by mass. The isoelectric point of the binder resin 4 was pH 2.2.

<Binder Resin Production Example 5>
Into a four-necked flask, 300 parts by mass of xylene is charged, heated to reflux, and mixed with 80 parts by mass of styrene, 20 parts by mass of acrylate-n-butyl and 2 parts by mass of di-tert-butyl peroxide. Was dropped over 5 hours to obtain a low molecular weight polymer (L-1) solution.

  In addition, 180 parts by mass of degassed water and 20 parts by mass of a 2% by weight aqueous solution of polyvinyl alcohol were charged into a four-necked flask, and then 75 parts by mass of styrene, 25 parts by mass of acrylic acid-n-butyl, 0.005 of divinylbenzene. A mixed liquid of 0.1 part by mass and 2,2-bis (4,4-di-tert-butylperoxycyclohexyl) propane (half-life 10 hours temperature: 92 ° C.) is added and stirred to suspend. Liquid. After sufficiently substituting the inside of the flask with nitrogen, the temperature was raised to 85 ° C. and polymerized, and after maintaining for 24 hours, 0.1 part by mass of benzoyl peroxide (half-life 10 hours temperature: 72 ° C.) was additionally added, The polymer was further maintained for 12 hours to complete the polymerization of the high molecular weight polymer (H-1).

  25 parts by mass of the high molecular weight polymer (H-1) was added to 300 parts by mass of the homogeneous solution of the low molecular weight polymer (L-1), and after mixing well under reflux, the organic solvent was distilled off. A styrene-based binder resin 5 was obtained. The binder resin 5 had an acid value of 0 mgKOH / g, a hydroxyl value of 0 mgKOH / g, a Tg of 57 ° C., an Mw of 300,000, and a THF-insoluble content of 0% by mass. The isoelectric point of the binder resin 5 was pH 4.8.

<Example 1>
-Binder resin 1 100 parts by mass-Magnetic particles 1 90 parts by mass-Wax 4 (see Table 2) 4 parts by mass-Charge control agent T-77 (Hodogaya Chemical Co., Ltd.) 2 parts by mass The mixture is melt-kneaded with a twin-screw extruder heated to a high temperature, the cooled kneaded product is coarsely pulverized with a hammer mill, the coarsely pulverized product is finely pulverized with a jet mill, and the resulting finely pulverized powder is classified with a fixed wall type air classifier Thus, classified powder was produced. Furthermore, the fine powder and coarse powder are strictly classified and removed at the same time by processing the obtained classified powder with a multi-division classifier (Elbow Jet Classifier manufactured by Nittetsu Mining Co., Ltd.) using the Coanda effect, and the weight average Negatively chargeable magnetic toner particles having a particle diameter (D4) of 6.7 μm were obtained. Magnetic toner 1 was prepared by adding 1.2 parts by mass of hydrophobic silica fine powder having a BET specific surface area of 120 m ² / g hydrophobized to 100 parts by mass of the obtained magnetic toner particles.

  As an image output test machine for evaluation of this magnetic toner 1, a commercially available LBP printer (LBP-950, manufactured by Canon Inc.) modified to 1.5 times the printing speed was used. Using this testing machine, 20,000 print tests were performed in an environment of 30 ° C. and 80% RH (high temperature and high humidity) and 15 ° C. and 10% RH (low temperature and low humidity), and the following evaluation was performed. .

(1) Image Density Under high temperature and high humidity (30 ° C, 80% RH) environment, print out 20,000 sheets on ordinary copier plain paper (75g / m ² ). Evaluation was performed. The image density is a relative density with respect to a printout image of a white background portion (that is, plain paper for a copier before image formation) having a document density of 0.00 using an SPI filter with a Macbeth densitometer (manufactured by Macbeth). Was measured. The evaluation results are shown in Table 4.

(2) Sleeve negative ghost In a low-temperature, low-humidity (15 ° C, 10% RH) environment, print out 20,000 sheets of ordinary copier paper (75 g / m ² ), and sleeve negative ghost every 5,000 sheets. Was evaluated. When evaluating the image regarding the ghost, a solid black belt-shaped image was output for the entire length of the sleeve, and then a halftone image was output. Of one printed image, measured by a Macbeth densitometer on the second round of the sleeve where the black image was formed in the first round (solid black print area) and where it was not (non-image area). The difference in reflection density was calculated using the following formula.
Difference in reflection density = reflection density (place where no image is formed)-reflection density (place where an image is formed)

  In a negative ghost, in an image that appears in the second round of the sleeve, the image density of the black printed portion in the first round of the sleeve is lower than the image density of the non-image portion in the first round of the sleeve. It is a ghost phenomenon in which the shape of the pattern produced on the circumference appears as it is. This density difference was measured as a reflection density difference. The smaller the reflection density difference, the better the occurrence of ghosts. The obtained reflection density difference is evaluated in the following four stages of A, B, C, and D, and the worst evaluation result in the evaluation for every 5,000 sheets is shown in Table 4 as an overall evaluation of the ghost. .

A: Reflection density difference is 0.00 or more and less than 0.02 B: Reflection density difference is 0.02 or more and less than 0.04 C: Reflection density difference is 0.04 or more and less than 0.06 D: Reflection density difference is 0.00. 06 or more

(3) Magnetic toner consumption After printing 1,000 sheets in a low-temperature and low-humidity environment (15 ° C., 10% RH) using the above-described imaging tester, the latent image line width is 10 dpi horizontal line pattern of 600 dpi. The image was set to 360 μm, 5,000 images with a printing rate of 4% were output on A4 size paper, and the change in the amount of magnetic toner in the developing device before and after output was determined as the amount of magnetic toner consumed. The results are shown in Table 4.

(4) Color measurement The blackness of the magnetic toner was measured by the following method. A solid black image is output on ordinary copying machine plain paper (75 g / m ² ), measured with a spectrocolorimeter “Spectrolino” (manufactured by Gretag Macbeth), and L *, a specified by the International Lighting Commission *, B * The lightness L * of the color system, a * representing the degree of red or green, and a numerical value indicated by b * representing the degree of yellow or blue. In the evaluation, a solid black image was output by adjusting the amount of exposure light so that L * was in the range of 18-22. The blackness indicates that the smaller the value of both a * and b *, the stronger the blackness. The evaluation results are shown in Table 4.

<Examples 2 and 3 and Reference Examples 1 to 5 >
Magnetic toners 2 to 8 were produced in the same manner as in Example 1 except that the formulation of the magnetic toner was changed as shown in Table 3, and the same evaluation was performed. The results are shown in Table 4.

<Comparative Examples 1 and 2>
Magnetic toners 9 and 10 were prepared in the same manner as in Example 1 except that the formulation of the magnetic toner was changed as shown in Table 3, and the same evaluation was performed. The results are shown in Table 4.

Claims (4)

A magnetic toner having magnetic toner particles having at least a binder resin and magnetic particles, wherein the isoelectric point of the magnetic particles is pH 3.5 or less ,
The magnetic particles include at least base magnetic particles and a coating layer of SiO ₂ on the base magnetic particles ,
The coating layer is obtained by dispersing the matrix magnetic particles in water and forming a coating layer of SiO ₂ on the matrix magnetic particles by adding sodium silicate in water .
The magnetic toner according to claim 1 , wherein the adsorbed water content at a relative vapor pressure of 50% of the magnetic particles is 1 to 20% by mass with respect to SiO _{2 of the} coating layer per unit mass . The magnetic particles, the magnetic toner according to claim 1, wherein the retention of Fe ²⁺ of the magnetic particles when the heat-treated for 1 hour at 160 ° C. in a air is 60% or more. 3. The magnetic toner according to claim 1, wherein the magnetic particles have an average particle size of 0.08 to 0.25 μm. The magnetic toner according to claim 1 , wherein an acid value of the binder resin is 1 to 50 mg KOH / g.