JPH0772654A - Magnetic toner, magnetic developer and image forming method - Google Patents

Abstract

PURPOSE:To provide the magnetic toner which has excellent environmental stability, is capable of forming toner images having high image densities even in durability over a long period of time and is excellent in dot reproducibility and fixability. CONSTITUTION:This magnetic toner contains at least a binder resin, release agent and magnetic iron oxide. The weight average grain size of the magnetic toner is 2.5 to 10mum and the content of the silicon element in the magnetic iron oxide is 0.5 to 4wt.% based on the iron element. The ratio (B/A)X100 of the content B of the silicon element existing up to 20wt.% of the iron element solubility of the magnetic iron oxide and the total content A of the silicon element in the magnetic iron oxide is 44 to 84%. The ratio (C/A)X100 of the content C of the silicon element existing in the surface of the magnetic iron oxide and the content A is 10 to 55%. The magnetic toner is substantially spherical particles directly obtd. by a suspension polymn. method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic toner, a magnetic developer and an image forming method for developing an electrostatic latent image in an image forming method such as electrophotography and electrostatic recording.

[0002]

2. Description of the Related Art U.S. Pat. No. 3,909,258 proposes a developing method using a magnetic toner having electrical conductivity. This supports conductive magnetic toner on a cylindrical conductive sleeve that has magnetism inside,
This is developed by bringing it into contact with an electrostatic image. At this time, in the developing section, a conductive path is formed by the toner particles between the surface of the recording medium and the sleeve surface, and the electric charge is introduced from the sleeve to the toner particles through the conductive path, and the conductive path is formed between the image area of the electrostatic image. The toner particles adhere to the image area and are developed by the cloning force. The developing method using this conductive magnetic toner is an excellent method that avoids the problems associated with the conventional two-component developing method, but on the other hand, since the toner is conductive,
There is a problem that it is difficult to electrostatically transfer a developed image from a recording medium to a final supporting member such as plain paper.

As a developing method using a high-resistance magnetic toner that can be electrostatically transferred, there is a developing method using dielectric polarization of toner particles. However, such a method has problems that the developing speed is inherently slow and the density of the developed image is not sufficiently obtained, and is practically difficult.

As another developing method using a high-resistance insulating magnetic toner, the toner particles are triboelectrically charged by friction between the toner particles, friction between the toner particles and a sleeve, and the like, which is used as an electrostatic image holding member. A method of contacting and developing is known. However, these methods have problems that the number of contact between the toner particles and the friction member is small and triboelectric charging is apt to be insufficient, and the cloned force between the charged toner particles and the sleeve is increased and the charged toner particles are easily aggregated on the sleeve. It had, and was practically difficult.

However, in JP-A-55-18656 and the like, a new jumping developing method has been proposed which eliminates the above-mentioned problems. This involves applying a very thin coat of magnetic toner on a sleeve, tribocharging it and then developing it in close proximity to the electrostatic image. This method increases the chances of contact between the sleeve and toner by applying a very thin coating of magnetic toner on the sleeve, and enables sufficient triboelectrification. It is possible to obtain an excellent image by eliminating the agglomeration of the toner particles with each other and sufficiently rubbing the sleeve.

However, in the developing method using the improved insulating toner, there is an unstable factor related to the insulating toner used. This is because the insulating toner contains a considerable amount of fine powdery magnetic material mixed and dispersed, and a part of the magnetic material is exposed on the surface of the toner particles. The fluidity and the triboelectricity are affected, and as a result, various characteristics such as developing characteristics and durability of the magnetic toner, which are required for the magnetic toner, are changed or deteriorated.

More specifically, in the conventional jumping developing method using a magnetic toner containing a magnetic material, if a repeated developing process (for example, copying) is continued for a long period of time, the developer containing the magnetic toner is Liquidity deteriorated,
Normal frictional electrification cannot be obtained, the electrification is likely to be non-uniform, fog development is likely to occur in a low temperature and low humidity environment, and a serious problem on a toner image is likely to occur. Also,
When the adhesiveness between the binder resin constituting the magnetic toner particles and the magnetic charging property is weak, the magnetic substance is removed from the surface of the magnetic toner by repeated development steps, which adversely affects the toner image density reduction and the like. Tend.

When the dispersion of the magnetic substance in the magnetic toner particles is non-uniform, small magnetic toner particles containing a large amount of the magnetic substance accumulate on the sleeve, resulting in a decrease in image density and a sleeve ghost. Occurrence of so-called shading unevenness may be seen.

Conventionally, proposals have been made regarding magnetic iron oxide contained in magnetic toners, but there are still some points to be improved.

For example, Japanese Patent Application Laid-Open No. 62-279352 proposes a magnetic toner containing magnetic iron oxide containing silicon element. Such magnetic iron oxide is
Although silicon element is intentionally present inside the magnetic iron oxide, the fluidity of the magnetic toner containing the magnetic iron oxide still has a point to be improved.

Further, Japanese Patent Publication No. 3-9045 proposes to control the shape of magnetic iron oxide into a spherical shape by adding a silicate. The magnetic iron oxide obtained by this method has a large amount of silicon element distributed inside the magnetic iron oxide because a silicate is used for controlling the particle shape, and the amount of silicon element present on the surface of the magnetic iron oxide is small, Improved fluidity of magnetic toner and high smoothness of magnetic iron oxide,
Adhesion between the binder resin forming the magnetic toner and the magnetic iron oxide tends to be insufficient.

Further, Japanese Patent Application Laid-Open No. 61-34070 proposes a method for producing ferrosoferric oxide by adding a hydrosisosilicate solution during the oxidation reaction to ferrosoferric oxide. The iron tetroxide produced by this method has a Si element in the vicinity of the surface, but the Si element exists as a layer in the vicinity of the surface of the iron tetroxide, and the surface is vulnerable to mechanical impact such as friction. Have a point.

In recent years, the functions of image forming apparatuses using electrophotography, such as copying machines and laser beam printers, have diversified, and high definition and high image quality have been demanded. ing. At the same time, low-temperature fixability is required due to reduction in power consumption accompanying downsizing of the apparatus.

On the other hand, the toner is manufactured by manufacturing a toner having a desired particle diameter by melt-mixing a binder resin, a colorant and the like, uniformly dispersing them, pulverizing them with a fine pulverizer and classifying them with a classifier. However, the selection range of the toner material is limited. For example, the resin colorant dispersion must be sufficiently brittle to be finely pulverized in an economically available manufacturing apparatus. From this requirement, in order to make the resin colorant dispersion brittle, when the resin colorant dispersion is actually pulverized at a high speed, particles in a wide particle size range are easily formed, and particularly a relatively large proportion of fine particles ( The problem arises that it contains particles that are too crushed. Further, such highly brittle materials are often subject to further fine grinding or pulverization when used as developing toners in copying machines and the like.

Further, it is difficult for the pulverizing method to completely and uniformly disperse solid fine particles such as magnetic powder or a coloring agent in the resin. Depending on the degree of the dispersion, fogging increases and image density decreases. Cause.

In order to overcome the problems of the toner by the crushing method as described above, and further, in order to satisfy the above requirements, a method for producing a toner by the suspension polymerization method has been proposed.

That is, in the pulverization method, there is a limit to the fineness of the toner required for high definition and high image quality, and accordingly, the powder characteristics, particularly the fluidity of the toner, are significantly reduced. Further, in the toner obtained by the pulverization method, there is a limitation in adding a releasing material such as wax. That is, in order to obtain a sufficient level of dispersibility of the release material, the release material should not be melted at the kneading temperature to form a liquid, and the content of the release material should be about 5% by weight or less. And so on. Due to such restrictions, there is a limit to the fixability of the toner by the pulverization method.

On the other hand, the toner obtained by suspension polymerization (hereinafter, polymerized toner) has not only the above-mentioned restrictions, but also the wax can be encapsulated, and good fixing property and offset resistance can be obtained. Further, since the shape of the obtained toner is spherical, the fluidity is excellent, which is advantageous for high image quality.

However, when the polymerized toner contains a magnetic material, its fluidity is significantly reduced.
This is because the magnetic particles are generally hydrophilic and therefore tend to exist on the toner surface, and the surface characteristics of the magnetic material are important.

Many proposals have been made to improve the dispersibility of the magnetic material in the polymerized toner. For example, JP-A-59-2
No. 00254, JP-A-59-200256,
JP-A-59-200257, JP-A-59-224
No. 102, etc. propose various silane coupling agent treatment techniques for magnetic materials, and Japanese Patent Application Laid-Open No. 63-250660 discloses a technique for treating silicon-containing magnetic particles with a silane coupling agent. .

However, although these treatments improve the dispersibility in the toner, they do not solve the improvement in the fluidity of the toner itself.

In addition, LED and LBP printers have become the mainstream of the market in recent years, and the direction of technology is higher resolution, that is, 240, 300 dpi is now 400, 600, 800 dpi. ing. Therefore, the developing system is also required to have higher definition. Further, the functions of copiers are also becoming more sophisticated, and as a result, they are moving toward digitalization. In this direction, the method of forming an electrostatic charge image with a laser is the main method, so it is also advancing toward high resolution, and here too, as with printers, high resolution and high definition development methods are required. JP-A-1-112253 and JP-A-2-284158 propose a developer having a small particle size. Further, as the LBP becomes smaller and has higher durability, it is necessary to extend the life of the small-diameter developer carrier / small-diameter electrostatic latent image carrier.

In order to prolong the life of the electrostatic latent image bearing member, it is preferable not only to improve the surface layer of the electrostatic latent image bearing member but also to keep the charging potential low. For this purpose, development is performed with a low potential contrast. I need to do it. Further, particularly in a binary small LBP, it is preferable that the slope (γ) of the potential contrast-density curve (VD curve) is raised from the viewpoint of density stability. In order to achieve low-potential development, thin layer coating of developer by a developer carrier having a low JIS center line average roughness (Ra) / contact blade / upper peripheral speed of developer carrier / high Vpp / high frequency preferable.

However, when the weight average particle diameter of the developer becomes fine particles (generally 9 μm or less), the specific surface area of the developer increases, so that the charged developer and fine powder are subjected to a force such as a mirroring force to cause a developer carrier. The developer firmly adheres to the upper part and the force of the electric field makes it difficult to peel off the developer adhered to the developer carrier. These developers give an excessive electric potential to the developer carrying member to adversely affect the development and deteriorate the image quality.

Further, thin coating, use of a blade in contact with the developer carrying member as the developer layer regulating member, and increase of the peripheral speed of the developer carrying member are all in the direction of promoting the above fixing. Yes Some measures are required to achieve high durability. Furthermore, under high Vpp / high frequency development conditions, the collision force and probability of the developer / developer and the developer / developer carrier also increase, so that more effective measures are required at present.

Further, JP-A-3-50559, JP-A-2-79860, JP-A-1-109359, JP-A-62-14166, and JP-A-61-27.
3554, 61-94062, JP-A-61
-138259, JP-A-60-252361, JP-A-60-252360, and JP-A-60-2.
A technique for containing waxes is disclosed in Japanese Patent No. 17366.

Waxes are used for improving the offset resistance of the toner at low temperature and high temperature, and for improving the fixing property at low temperature. However, on the other hand, while improving these performances, the blocking resistance is deteriorated, the developability is deteriorated when exposed to heat due to the temperature rise of a copying machine, and the developability is deteriorated due to blooming of wax when left for a long time. It gets worse.

[0028]

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic toner having a high image density, excellent image reproducibility, fog-free properties even after long-term use, and stable charging performance. .

Another object of the present invention is to provide a magnetic toner having good fixability and excellent low temperature fixability.

Further, it is an object of the present invention to provide a magnetic toner which is excellent in offset resistance and blocking resistance and in durability against temperature rise of the machine body.

Further, an object of the present invention is to provide a highly durable and highly reproducible developer and an image forming agent in which the developer is not substantially fixed to the developer carrying member and does not scatter even under the developing conditions for achieving low potential development. To provide a method.

[0032]

The present invention relates to a magnetic toner containing at least a binder resin, a release agent and magnetic iron oxide, wherein the magnetic toner has a weight average particle diameter of 2.
5 to 10 μm, and the content of silicon element in the magnetic iron oxide is 0.5 to 4 based on the iron element.
The ratio (B / A) of the content B of the silicon element present in the magnetic iron oxide having an iron element dissolution rate of up to 20% by weight and the total content A of the silicon element of the magnetic iron oxide. × 100
Is 44 to 84%, and the ratio (C / A) of the content C of the silicon element present on the surface of the magnetic iron oxide to the content A (C / A) × 1
00 is 10 to 55%, and the magnetic toner is substantially spherical particles directly obtained by the suspension polymerization method (invention 1).

According to the present invention, the JIS center line average roughness (Ra) of the developer carrier is 1.0 μm or less, the alternating voltage Vpp applied to the developer carrier is 1500 V or more, and the frequency is 2100 Hz or less, the absolute value (V _cont. ) Of the difference between the DC voltage (V _dc ) and the charging potential (Vd) of the electrostatic latent image carrier is 250 V or less, and a developing process of developing with a developer In the image forming method, the developer is a magnetic developer containing at least a binder resin and magnetic iron oxide, and the magnetic iron oxide has the same constitution as in the first aspect of the invention. The image forming method is (Invention 2).

The present invention further provides a magnetic toner containing at least a binder resin, magnetic iron oxide and a hydrocarbon wax, wherein the magnetic toner has a weight average particle diameter of 13.5 μm.
In the particle size distribution of the magnetic toner, the content of the magnetic toner particles having a particle size of 12.7 μm or more is 50% by weight or less, and the magnetic iron oxide has the same constitution as in the first aspect of the invention. In the DSC curve measured by a differential scanning calorimeter, the hydrocarbon wax has an endothermic peak onset temperature of 50 to 90 ° C. with respect to the endothermic peak at the time of temperature increase and the exothermic peak at the time of temperature decrease. in the range, there is at least one endothermic peak P ₁ in the region of the temperature 90 to 120 ° C., there is a maximum exothermic peak at the time of cooling in the range of endothermic peak temperature ± 9 ° C. peak P _1, and characterized in that Magnetic toner (Invention 3).

The structures of the present inventions 1 to 3 will be described in detail below.

The main constitution common to the present inventions 1 to 3 is magnetic iron oxide. First, the magnetic iron oxide will be described in detail.

One of the characteristics of the magnetic iron oxide used in the present invention is that the content of silicon element is 0.5 to 4.0% by weight based on the iron element. The content rate of silicon element is 0.
If the amount is less than 5% by weight, the flowability of the developer is poor, which causes deterioration of the uniform chargeability of the developer, and the sticking of the developer to the developer carrier or the electrostatic latent image carrier or the occurrence of scratches. . If the content of elemental silicon is more than 4.0% by weight, the silicic acid component may remain unnecessarily on the surface of the magnetic iron oxide and may adversely affect the magnetic properties, which is not preferable.

Further, in the present invention, the ratio B of the total content A of the silicon element present in the magnetic iron oxide and the content B of the silicon element present in the magnetic iron oxide having a dissolution rate of the iron element of up to about 20%. / A × 100 (%) is 44 to 84% (preferably 6)
0 to 80%), and the ratio C / A × 10 of the content C of the silicon element present on the surface of the magnetic iron oxide particles and the content A thereof.
One of the characteristics is that 0 (%) is 10 to 55% (preferably 25 to 40%). When B / A × 100 (%) is less than 44%, a large amount of silicon element more than necessary is present in the central portion of the magnetic iron oxide, the production efficiency is likely to deteriorate, and the magnetic characteristics are unstable. Magnetic iron oxide.

When B / A × 100 (%) exceeds 84%, too much silicon element exists in the surface layer portion of the magnetic iron oxide, and a large amount of silicon element is layered on the surface of the magnetic iron oxide. Since the surface of the magnetic iron oxide is present and becomes brittle against mechanical shock, many adverse effects are likely to occur when it is used as a magnetic toner.

On the other hand, when C / A × 100 (%) is less than 10%, the silicon element on the surface of the magnetic iron oxide is small, and it is difficult to obtain good fluidity in the magnetic iron oxide and the magnetic toner. In addition, the charge amount and volume resistivity of the magnetic iron oxide are reduced, and the charge stability and environmental stability of the magnetic toner are likely to be impaired.

When C / A × 100 (%) is more than 55%, the irregularities on the surface of the magnetic iron oxide are conspicuous, and the irregularities on the surface of the magnetic iron oxide become fragments when producing the magnetic toner. And are likely to adversely affect the magnetic toner characteristics.

That is, in order to obtain good magnetic toner characteristics, the distribution of the silicon element present in the magnetic iron oxide should increase continuously or stepwise from the inside to the surface as described above. preferable.

Further, in the present invention, the charge amount of magnetic iron oxide is −25 to −70 μC / g (preferably −40 to −60 μC).
C / g) and the volume resistivity of magnetic iron oxide is 1
× 10 ⁴ to 1 × 10 ⁸ Ω · cm (preferably 5 × 10 ⁴
It is preferably about 5 × 10 ⁷ Ω · cm).

When the charge amount of the magnetic iron oxide is less than -25 μC / g, if the magnetic toner is repeatedly used for a long period of time, the charge amount required by the magnetic toner is likely to be lost, resulting in a decrease in image density and image fog. Occurs. On the other hand, when the charge amount of magnetic iron oxide exceeds -70 μC / g,
Since the charge amount of the magnetic toner becomes too high, the image density tends to decrease in a low temperature and low humidity environment.

The volume resistivity of magnetic iron oxide is 5 ×
When it is less than 10 ³ Ω · cm, it becomes difficult to maintain the charge amount required by the magnetic toner, and the image density is apt to decrease. On the other hand, when the volume resistivity of the magnetic iron oxide exceeds 1 × 10 ⁸ Ω · cm, the charge amount tends to increase more than necessary when repeatedly used in a low temperature and low humidity environment, and the image density decreases. Easy to get caught.

Further, in the present invention, the degree of aggregation of magnetic iron oxide is preferably 3 to 40% (preferably 5 to 30%).

When the coagulation degree of the magnetic iron oxide is less than 3%, blowing out of the magnetic toner called flushing is likely to occur during the production of the magnetic toner, and it is difficult to produce the magnetic toner efficiently.

On the other hand, when the cohesion exceeds 40%,
It is not easy to sufficiently disperse the magnetic iron oxide in the magnetic toner, and the image density and fog are likely to be adversely affected. In addition, uniform charging cannot be obtained, which may cause adverse effects on the image, and at the same time, the adhesiveness and adhesion to the surface of the developer carrying member or the electrostatic latent image carrying member will be high. The developer is apt to adhere to or scratch the surface of the image carrier.

Further, in the present invention, the smoothness D of the magnetic iron oxide is preferably 0.2 to 0.6 (preferably 0.3 to 0.5).

When the smoothness D is smaller than 0.2, the irregularities on the surface of the magnetic iron oxide are conspicuous, and the irregularities become fragments during the production of the magnetic toner, and the particles are dispersed in the magnetic toner, and the toner characteristics are likely to be adversely affected.

On the other hand, when the smoothness D is larger than 0.6, it is difficult to obtain sufficient adhesiveness between the binder resin used for the magnetic toner and the magnetic iron oxide, and the magnetic toner surface gradually increases after repeated use. The magnetic iron oxide is removed, and adverse effects such as reduction in image density are likely to occur.

Furthermore, in the present invention, the sphericity ψ of the magnetic iron oxide is
Is preferably 0.8 or more.

When the sphericity ψ is smaller than 0.8, the individual particles of magnetic iron oxide come into surface-to-surface contact,
With small magnetic iron oxide particles having a particle size of about 0.1 to 1.0 μm, the magnetic iron oxide particles cannot be easily separated from each other even with a mechanical shearing force. May not be sufficiently dispersed.

Further, the magnetic iron oxide used in the present invention has an average particle size of 0.1 to 0.4 μm, preferably 0.1.
It is preferable to have ~ 0.3 μm.

The method for measuring various physical property data of magnetic iron oxide will be described in detail below.

(1) Content of Silicon Element In the present invention, the content C of silicon element on the surface of the magnetic iron oxide can be determined by the following method. For example, about 3 liters of deionized water is placed in a 5 liter beaker and heated in a water bath at 50 to 60 ° C. About 25 g of magnetic iron oxide slurried with about 400 ml of deionized water is added to a 5 liter beaker together with the deionized water while being washed with about 300 ml of deionized water.

Next, while maintaining the temperature at about 60 ° C. and the stirring speed at about 200 rpm, special grade sodium hydroxide is added to prepare a sodium hydroxide solution of about 1N, and the magnetic iron oxide concentration is about 5 g / l. Initiate dissolution of silicon compounds such as silicic acid on the surface of magnetic iron oxide particles. Thirty minutes after the start of dissolution, 20 ml was sampled and 0.1 μm
Filter with a membrane filter and collect the filtrate. The filtrate is quantified for silicon element by plasma emission spectroscopy (ICP).

The content C of elemental silicon is the unit weight of magnetic iron oxide in an aqueous solution of sodium hydroxide (5 g of magnetic iron oxide /
It corresponds to the elemental silicon concentration per 1) (mg / l).

In the present invention, the content rate of silicon element (based on iron element), the dissolution rate of iron element and the content A and B of silicon element of magnetic iron oxide can be determined by the following method. it can. For example, about 3 liters of deionized water is placed in a 5 liter beaker and heated in a water bath at 45 to 50 ° C. About 25 g of magnetic iron oxide was slurried with about 400 ml of deionized water to about 3
While washing with 00 ml of deionized water, add together with the deionized water into a 5 liter beaker.

Next, while maintaining the temperature at about 50 ° C. and the stirring speed at about 200 rpm, special grade hydrochloric acid is added to start the dissolution. At this time, the magnetic iron oxide concentration is about 5 g / l and the hydrochloric acid aqueous solution is about 3 N. Approximately 20 ml was sampled several times from the start of lysis until everything became transparent, and filtered with a 0.1 μm membrane filter,
Collect the filtrate. The filtrate is quantified for iron element and silicon element by plasma emission spectroscopy (ICP).

The iron element dissolution rate for each sample is calculated by the following equation.

[0062]

[Equation 1]

The content and content of elemental silicon for each sample are calculated by the following equation.

[0064]

[Equation 2]

The total content A of silicon in the magnetic iron oxide is
Unit weight of magnetic iron oxide after all dissolved (magnetic iron oxide 5
It corresponds to the elemental silicon concentration (g / l) (mg / l).

The content B of the silicon element in the magnetic iron oxide is the silicon element concentration per unit weight of the magnetic iron oxide (magnetic iron oxide 5 g / l) detected when the dissolution rate of the magnetic iron oxide is 20%. Equivalent to (mg / l).

As a method of measuring the contents A, B and C, the magnetic iron oxide sample is divided into two and the content of silicon element and the contents A and B are measured, while the content C is Method of measuring separately, and measuring the content C of the magnetic iron oxide sample, and then using the sample after measurement, the content B '(content B minus the content C) and the content A' Examples include a method of measuring (content A minus content C) and finally calculating the contents A and B.

(2) Charge amount of magnetic iron oxide About 2 g of magnetic iron oxide and carrier iron powder (TEFV200 to 3)
00 mesh) (Nippon Iron Powder Co., Ltd.) 500 g of about 198 g
Weigh it in ml polybin, shake it by hand for 10 seconds, then shake it with a V-type blender for 20 minutes, and measure the charge amount of magnetic iron oxide using a blow-off powder charge amount measuring device (Toshiba Chemical Co., Ltd.) To do. At this time, a 400 mesh mesh made of stainless steel was set to the Faraday gauge for measurement, a measurement sample amount of about 0.4 g was weighed, and the value was calculated by performing blow-off for 30 seconds.

(3) Volume resistivity of magnetic iron oxide 10 g of magnetic iron oxide was put in a measuring cell and molded by a hydraulic cylinder (pressure 600 Kg / cm ² ). After releasing the pressure, a resistance meter (YEW MODEL 2506A manufactured by Yokogawa Electric Corporation)
DIGITAL MALTIMER) is set, and a pressure of 150 kg / cm ² is applied again by the hydraulic cylinder. Start the measurement and read the measured value after 3 minutes. Furthermore, the thickness of the sample is measured and the volume resistivity value is measured by the following formula.

[0070]

[Equation 3]

(4) Coagulation Degree of Magnetic Iron Oxide 10 g of magnetic iron oxide was pulverized with a mixer to obtain 200 mesh.
Weigh 2 g of the powder that has passed the screening. From the top to the powder tester (Hosokawa Micron Co., Ltd.),
The sieves are set in three steps in the order of 100 mesh and 200 mesh, 2 g of the sample weighed is gently placed on the sieve, vibration of 1 mm amplitude is given for 65 seconds, and the weight of the magnetic iron oxide remaining on each sieve is measured. Then, the degree of aggregation is calculated according to the following formula.

[0072]

[Equation 4]

(5) Smoothness of Magnetic Iron Oxide In the present invention, the smoothness D of magnetic iron oxide is determined as follows.

[0074]

[Equation 5]

(6) BET BET specific surface area of magnetic iron oxide was measured by Yuasa Ionics Co., Ltd., fully automatic gas adsorption amount measuring device: Autosorb 1, nitrogen was used as an adsorption gas, and the BET multipoint method was used. Ask. The sample is pretreated by degassing at 50 ° C. for 1 hour.

(7) Average Particle Size and Surface Area of Magnetic Iron Oxide Using a sample of magnetic iron oxide processed into a collodion film copper mesh with an electron microscope (Hitachi H-700H), an applied voltage of 100 KV was applied to 10,000. The image is taken at a magnification of 3 times, and the printing magnification is set to 3 times, and the final magnification is 30,000 times. With this, the shape is observed and the maximum length of each particle (μm)
Is measured, 100 particles are randomly selected, and the average is taken as the average particle diameter.

For the calculation of the surface area, it is assumed that the average particle diameter of the magnetic iron oxide is a sphere, and the density of the magnetic iron oxide is measured by the usual method to obtain the surface area value.

(8) Sphericity of Magnetic Iron Oxide The sphericity ψ of the magnetic iron oxide in the present invention is calculated as follows.

[0079]

[Equation 6]

For the sphericity ψ, 100 magnetic iron oxide particle specimens are randomly selected from the photograph, the maximum length and the minimum length are measured, and then the calculated values are averaged.

The maximum length and the minimum length of the magnetic oxide material follow the method for obtaining the average particle size.

While the cubic iron-based magnetic iron oxide has a sphericity ψ of about 0.6 to less than 0.8, the sphericity ψ preferably used in the present invention is 0.8 or more. The magnetic iron oxide (preferably 0.85 or more, more preferably 0.9 or more) has a shape close to a spherical shape without angular ends.

When the sphericity ψ is less than 0.8, the dispersibility in the binder resin is inferior to the case where the silicon element is unevenly distributed on the surface of the magnetic iron oxide particles as compared with the case where it is 0.8 or more. The developing characteristics of the obtained magnetic toner are likely to be deteriorated, and the magnetic toner tends to be inferior in dot reproducibility.

The magnetic iron oxide used in the magnetic toner of the present invention is 20 parts by weight to 2 parts by weight based on 100 parts by weight of the binder resin.
It is preferred to use 00 parts by weight. It is more preferable to use 30 to 150 parts by weight.

The magnetic iron oxide used in the magnetic toner of the present invention is preferably treated with a silane coupling agent, a titanium coupling agent, titanate, aminosilane or the like. The amount of the treating agent is preferably such that the effect of the present invention is not impaired, that is, 5% by weight or less based on the magnetic material.

Next, another feature of the present invention 1 will be described.

One of the features of the magnetic toner by the suspension polymerization method of the present invention 1 is that the weight average particle diameter is 2.5 to 10 μm.

The weight average particle diameter of the polymerized magnetic toner is 10 μm.
When it exceeds, the fluidity and charge stabilization of the magnetic toner can be maintained even if the magnetic iron oxide generally used conventionally is used.

The weight average particle diameter of the polymerized magnetic toner particles is 2.
If it is less than 5 μm, the fluidity of the magnetic toner becomes significantly low even if the special magnetic iron oxide of the present invention is used, and problems such as fog due to poor charging and thinning of the density tend to occur. The diameter is preferably 2.5 μm or more.

That is, in the polymerized magnetic toner of the present invention 1, remarkable effects such as improvement in charging stability and fluidity as compared with the conventional example are observed, in which the weight average particle diameter is 10 μm or less.2.
It is 5 μm or more, and more preferably 6.5 μm or less and 3.5 μm or more from the viewpoint of high image quality.

Next, a method for producing a toner by the suspension polymerization method in the first embodiment will be described.

In this suspension polymerization method, since the droplets of the monomer composition are generated in a dispersion medium of water, which is highly polar, the component having a polar group contained in the monomer composition is mixed with the aqueous phase. It has a so-called capsule structure in which it is likely to exist in the surface layer portion which is the interface and non-polar components do not exist in the surface layer portion. By utilizing this characteristic of the manufacturing method, it is possible to add a large amount of low-melting wax that cannot be used in the pulverizing method.

Examples of the releasing agent used in the present invention 1 include paraffin, polyolefin wax and modified products thereof, such as oxides and graft-treated products.
The melting point of these release agents is preferably 45 to 115 ° C. and is excellent in low-temperature fixability. If it is lower than 45 ° C, the blocking resistance is deteriorated.

Further, the content is 5 to 40% by weight, more preferably 10 to 30% by weight based on the toner resin component.
Is excellent in offset resistance, blocking resistance, and low-temperature fixability.

The following are mentioned as the polymerizable monomer constituting the polymerizable monomer system used in the present invention 1.

Examples of the polymerizable monomer include styrene-based monomers such as styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-methoxystyrene and p-ethylstyrene, methyl acrylate and acrylic. Ethyl acetate, n-butyl acrylate, isobutyl acrylate, n-propyl acrylate, n-octyl acrylate, dodecyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, 2-chloroethyl acrylate, phenyl acrylate, etc. Acrylic esters, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-octyl methacrylate, dodecyl methacrylate,
Examples thereof include methacrylic acid esters such as 2-ethylhexyl methacrylate, stearyl methacrylate, phenyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, and other monomers such as acrylonitrile, methacrylonitrile, and acrylamide.

These monomers may be used alone or in combination. Among the above-mentioned monomers, it is preferable to use styrene or a styrene derivative alone or in combination with other monomers, from the viewpoint of developing characteristics and durability of the toner.

In the present invention 1, a resin may be added to the monomer system for polymerization. For example, a monomer is water-soluble and cannot be used because it dissolves in an aqueous suspension to cause emulsion polymerization, and thus cannot be used as an amino group, a carboxylic acid group, a hydroxyl group, a sulfonic acid group,
When it is desired to introduce a monomer component containing a hydrophilic functional group such as a glycidyl group or a nitrile group into the toner, a random copolymer, a block copolymer, a graft copolymer or the like of these and a vinyl compound such as styrene or ethylene. ,
It can be used in the form of a copolymer or in the form of a polycondensate of polyester, polyamide or the like, or a polyaddition polymer of polyether, polyimine or the like. When such a high molecular polymer containing a polar functional group is coexisted in the toner, the wax component is phase-separated, the inclusion becomes stronger, and the performance of the toner intended by the present invention is improved. desirable. The amount used is preferably 1 to 20% by weight. The average molecular weight of the high molecular weight polymer containing these polar functional groups is preferably 5,000 or more. 5,
If it is 000 or less, especially 4,000 or less, the present polymer tends to concentrate near the surface, which is unfavorable since it tends to have a bad influence on the developability and blocking resistance. Further, when a polymer having a molecular weight different from the molecular weight range of the toner obtained by polymerizing the monomer is dissolved and polymerized, a toner having a wide molecular weight distribution and high offset resistance can be obtained. I can.

A charge control agent may be added to the toner according to the present invention 1 in order to stabilize the charge characteristics.

The polymerization initiator used in the present invention 1 has a half-life of 0.5 to 30 hours at the time of the polymerization reaction, and the polymerization reaction is carried out by adding 0.5 to 20% by weight of the polymerizable monomer. When carried out, a polymer having a maximum in the molecular weight range of 10,000 to 100,000 can be obtained, and the toner can be provided with desired strength and proper melting characteristics. Examples of the polymerization initiator include 2,2′-azobis- (2,4-dimethylvaleronitrile) and 2,2 ′.
-Azobisisobutyronitrile, 1,1'-azobis (cyclohexane-1-carbonitrile), 2,2'-
Azo-based or diazo-based polymerization initiators such as azobis-4-methoxy-2,4-dimethylvaleronitrile and azobisisobutyronitrile, benzoyl peroxide, methyl ethyl ketone peroxide, diisopropyl peroxycarbonate, cumene hydroperoxide, 2 , 4
Examples thereof include peroxide type polymerization initiators such as dichlorobenzoyl peroxide and lauroyl peroxide.

In the present invention 1, a crosslinking agent may be added,
The preferable addition amount is 0.001 to 15% by weight.

In the method for producing a toner of the present invention 1, generally, the above-mentioned toner composition, that is, a colorant in a polymerizable monomer,
Release agents, plasticizers, binders, charge control agents, cross-linking agents, magnetic substances, and other components necessary for toner, and other additives, for example, organic solvents added to reduce the viscosity of the polymer produced by the polymerization reaction. A monomer system uniformly dissolved or dispersed by a homogenizer, a ball mill, a colloid mill, a disperser such as an ultrasonic disperser, by appropriately adding a dispersant and the like,
It is suspended in an aqueous medium containing a dispersion stabilizer. At this time,
The particle size of the obtained toner particles becomes sharper when the size of the toner particles is desired at once by using a high speed disperser such as a high speed stirrer or an ultrasonic disperser. Regarding the timing of addition of the polymerization initiator, it may be added at the same time when other additives are added to the polymerizable monomer, or may be mixed immediately before being suspended in the aqueous medium. It is also possible to add a polymerization initiator dissolved in a polymerizable monomer or a solvent immediately after granulation and before starting the polymerization reaction.

After the granulation, the stirring may be carried out by using an ordinary stirrer to the extent that the particle state is maintained and the particles are prevented from floating and settling.

In the suspension polymerization method of the present invention 1, known surfactants and organic / inorganic dispersants can be used as dispersion stabilizers, and among them, the inorganic dispersants are less likely to produce harmful ultrafine powders and have steric hindrance. Since the dispersion stability is obtained, the stability is not easily deteriorated even when the reaction temperature is changed, the cleaning is easy, and the toner is not adversely affected. Examples of such inorganic dispersants include polyphosphate metal salts such as calcium phosphate, magnesium phosphate, aluminum phosphate and zinc phosphate, carbonates such as calcium carbonate and magnesium carbonate,
Examples thereof include inorganic salts such as calcium metasilicate, calcium sulfate and barium sulfate, and inorganic oxides such as calcium hydroxide, magnesium hydroxide, aluminum hydroxide, silica, bentonite and alumina.

These inorganic dispersants are composed of the polymerizable monomer 10
It is desirable to use 0.2 to 20 parts by weight per 0 parts by weight, but it is difficult to generate ultrafine particles, but it is somewhat difficult to atomize the toner, so 0.001 to 0.1 parts by weight Some surfactants may be used together.

Examples of the surfactant include sodium dodecylbenzenesulfate, sodium tetradecylsulfate, sodium pentadecylsulfate, sodium octylsulfate,
Examples thereof include sodium oleate, sodium laurate, sodium stearate, potassium stearate and the like.

When these inorganic dispersants are used, they may be used as they are, but in order to obtain finer particles, the inorganic dispersant particles can be generated in an aqueous medium. For example, in the case of calcium phosphate, a water-insoluble calcium phosphate can be produced by mixing an aqueous solution of sodium phosphate and an aqueous solution of calcium chloride under high-speed stirring, and more uniform and fine dispersion is possible. At this time, a water-soluble sodium chloride salt is by-produced at the same time, but when the water-soluble salt is present in the aqueous medium, the dissolution of the polymerizable monomer in water is suppressed, and the ultrafine toner particles due to emulsion polymerization are generated. It is more convenient because it is less likely to occur. Since it becomes an obstacle when removing the remaining polymerizable monomer at the end of the polymerization reaction, it is better to replace the aqueous medium or desalt with an ion exchange resin. The inorganic dispersant can be almost completely removed by dissolving it with an acid or an alkali after completion of the polymerization.

In the polymerization step, the polymerization temperature is 40.
Polymerization is carried out at a temperature of not lower than 0 ° C, generally 50 to 90 ° C. When the polymerization is carried out within this temperature range, the release agent and waxes to be sealed inside are precipitated by phase separation and the encapsulation becomes more complete. At the end of the polymerization reaction, the reaction temperature is set to 90 to consume the remaining polymerizable monomer.
It is possible to raise it to 150 ° C.

Next, other characteristic points of the image forming method of the present invention 2 will be described.

The invention 2 has a developer carrier having a surface having a JIS center line average roughness (Ra) of 1.0 μm or less, and the alternating voltage applied to the developer carrier. Vpp is 1500 V or more, the frequency is 2100 Hz or less, and the absolute value (V _cont. ) Of the difference between the DC voltage (V _dc ) and the charging potential (Vd) of the electrostatic latent image carrier is 250 V or less _. It is possible to greatly improve the durability of the developer carrying member, the electrostatic latent image holding member, and the developer itself, and at the same time, there is no fog or scattering,
Images with high density, high image quality, and high reproducibility can be stably obtained.

In the developing section, the electrostatic latent image carrier of the present invention 2 and the developer carrier carrying the developer layer are opposed to each other with a development interval larger than the thickness of the developer layer. It is preferable. Further, Vd is preferably negatively charged, and its absolute value is preferably 500 V or less. (More preferably 200 V or more and 400 V or less)
Further, it is preferable that the peripheral velocity of the developer bearing member with respect to the electrostatic latent image bearing member is 105% or more from the viewpoint of maintaining the image density.

Further, the above-mentioned effects obtained by using the magnetic developer according to the second aspect of the present invention are as follows: an image formed by a combination of a developer carrier having a radius of curvature of 20 mm or less and / or an electrostatic latent image carrier having a radius of curvature of 50 mm or less. When used in a device, it exhibits particularly well. This is because if the diameter is small, the number of rotations for the same number of prints (copies) increases and the adverse effect is greater.

Further, good results were obtained when the weight average particle size of the developer according to the present invention 2 was 4 to 10 μm, particularly 4.5 to 9 μm. When the weight average particle diameter is less than 4 μm, the developer is significantly fixed to the developer carrier, which causes a problem in image quality. If it exceeds 10 μm, 100 μm
The following dot latent images or fine lines are not reproduced sufficiently.

The surface roughness of the developer carrier used in the present invention 2 is 1.0 μ in JIS center line average roughness (Ra).
It is preferably m or less.

When Ra exceeds 1.0 μm, the developer coat layer on the developer carrying member becomes thick and uniform charging is hindered, so that fogging is likely to occur on the image.

The surface of the developer carrier is preferably a metal or metal oxide surface not roughened by blasting or the like, or the surface of which is covered with a resin layer containing conductive fine particles. A particularly preferred range is Ra of 0.4 μm or less on the surface of metal or metal oxide which is not roughened by blasting, and R of the surface coated with a resin layer containing conductive fine particles.
a is 0.2 to 1.0 μm. As the conductive fine particles contained in the resin layer to be coated, carbon black, graphite, conductive metal oxides such as conductive zinc oxide and metal complex oxides are preferably used alone or in combination of two or more. Further, as the resin in which the conductive fine particles are dispersed, a phenol resin, an epoxy resin, a polyamide resin, a polyester resin, a polycarbonate resin,
Known resins such as polyolefin resins, silicone resins, fluorine resins, styrene resins, and acrylic resins are used. A thermosetting or photocurable resin is particularly preferable.

In the developer of the present invention 2, the member that regulates the developer on the developer carrying member is regulated by the elastic member that is in contact with the developer carrying member through the developer. It is particularly preferable from the viewpoint of uniform charging.

Vp of the alternating voltage applied to the developer carrying member
p is preferably 1500 V or more, but is preferably 1800 V or more when the waveform is a sine wave or a waveform close to a sine wave.

If Vpp of invention 2 is less than 1500 V or the peripheral speed of the developer carrier is less than 105%, the image density is not sufficient. The frequency of the applied alternating voltage is preferably 2100 or more and 6000 Hz.

Next, other features of the present invention 3 will be described.

In the magnetic toner of the present invention 3, the weight average particle diameter is 13.5 μm or less (preferably 3.5 to 13.
One of the characteristics is that the content of magnetic toner particles having a particle size of 12.7 μm or more is 50% by weight or less in the particle size distribution of the magnetic toner.

The weight average particle diameter of the magnetic toner is 13.5 μm.
Or the content of the magnetic toner particles having a particle diameter of 12.7 μm or more exceeds 50% by weight, the magnetic toner containing a large amount of relatively coarse magnetic toner particles is generally used conventionally. It is possible to stabilize the charging of the magnetic toner even by using the above-mentioned magnetic iron oxide.

The weight average particle diameter of the magnetic toner particles is 3.5 μ.
If it is smaller than m, the fluidity of the magnetic toner becomes low even if the special magnetic iron oxide of the present invention is used, and problems such as fogging due to charging failure and light density are likely to occur.
The weight average particle diameter is preferably 3.5 μm or more.

That is, in the magnetic toner of the third aspect of the present invention, remarkable effects such as improvement in charging stability and fluidity as compared with the conventional example can be seen that the weight average particle diameter is 13.5 μm or less (preferably 3. 5 to 13.5 μm, more preferably 5.0
˜13.0 μm) and the content of magnetic toner particles having a particle size of 12.7 μm or more is 50% by weight or less (more preferably 40% or less).

The hydrocarbon wax which is another feature of the present invention 3 will be described. By analyzing the data obtained by measuring the wax with a differential scanning calorimeter, the behavior between heat and the wax can be found. That is, it is possible to know the heat exchange with the wax and the change in the state of the wax from the data. And how it affects the offset and developability of the wax-containing toner, and the effect of heat during storage and actual use of the toner, for example, the blocking resistance of the toner. You can know.

At the time of temperature rise, changes can be seen when heat is applied to the wax, and endothermic peaks associated with wax transition and melting are observed. Peak onset temperature is 50-9
Within the range of 0 ° C., the developability, blocking resistance and low temperature fixability can be satisfied. If the peak onset temperature is less than 50 ° C., the change temperature of the wax is too low, resulting in a toner having poor blocking resistance or poor developability at the time of temperature rise. Change temperature is too high, and sufficient fixability cannot be obtained. Within the range of 90 to 120 ° C, preferably 95 to 1
Since the endothermic peak exists in the range of 20 ° C., particularly preferably in the range of 97 to 115 ° C., good fixability and offset resistance can be satisfied. When the peak temperature exists only below 90 ° C., the melting temperature of the wax is too low, and sufficient high temperature offset resistance cannot be obtained.
When the peak temperature exists only in the region exceeding the above range, the melting temperature of the wax is too high, and sufficient low temperature offset resistance and low temperature fixability cannot be obtained. That is, the presence of the peak temperature in this region makes it easy to balance the offset resistance and the fixability. Here, when the peak below 90 ° C. becomes the maximum peak, the same behavior as in the case where there is a peak only in this region is exhibited. Therefore, a peak in this region may exist, but in that case, 90 to 120 It must be smaller than the peak in the ° C region.

When the temperature is lowered, changes in the wax during cooling and the state at room temperature can be observed, and exothermic peaks associated with the solidification, crystallization and transition of the wax are observed. The exothermic peak at the time of cooling is the maximum exothermic peak due to the solidification and crystallization of the wax. The presence of an endothermic peak due to melting at the time of temperature rise near the exothermic peak temperature indicates that the wax is more homogeneous, such as the structure and molecular weight distribution of the wax, and the difference is within 9 ° C. The temperature is preferably within 7 ° C, particularly preferably within 5 ° C. That is, by reducing this difference,
Sharp melt wax, that is, hard at low temperature,
Since the melting at the time of melting is fast and the melt viscosity is largely reduced, the developability, blocking resistance, fixing property and offset resistance can be well balanced. The maximum exothermic peak has a temperature of 85 to 115 ° C. (preferably 90 to 11).
0 ° C.) is preferable.

In the DSC measurement of wax, each temperature is defined as follows.

Endothermic peak: peak onset temperature: temperature at the intersection of the normal line of the curve and the base line at the point where the differential value of the curve at the time of temperature rise becomes the maximum first. Peak temperature: The temperature at the top of the peak.

Exothermic peak: temperature of peak: temperature of peak top of maximum peak.

The hydrocarbon wax used in the present invention 3 is a low molecular weight alkylene polymer obtained by radical polymerization of alkylene under a high pressure or by a Ziegler catalyst under a low pressure, or an alkylene obtained by thermally decomposing a high molecular weight alkylene polymer. A hydrocarbon wax obtained by extracting and fractionating specific components from a synthetic hydrocarbon obtained by hydrogenating a distillation residue of a hydrocarbon obtained by the Arge method from a synthesis gas composed of a polymer, carbon monoxide, and hydrogen is used. Hydrocarbon wax is fractionated by a press crystallization method, a solvent method, and a fractional crystallization method utilizing vacuum distillation. That is, those obtained by removing low molecular weight components, those obtained by extracting low molecular weight components, and those obtained by further removing low molecular weight components by these methods, etc.

The hydrocarbon as a base is synthesized by the reaction of carbon monoxide and hydrogen using a metal oxide catalyst (often two or more multi-component system), for example, the gintol method or the hydrocol method ( Hydrocarbons with up to several hundred carbons (finally hydrogenated and used as the target product) obtained by the Arge method (using a fixed catalyst bed) where a large amount of waxy hydrocarbons can be obtained. Or a hydrocarbon obtained by polymerizing alkylene such as ethylene with a Ziegler catalyst is preferable because it is a saturated long-chain linear hydrocarbon with few branches and small. In particular, a hydrocarbon wax synthesized by a method that does not depend on the polymerization of alkylene is preferable because of its structure and molecular weight distribution that facilitates separation. The preferred range of the molecular weight distribution is
Number average molecular weight (Mn) is 550 to 1200, preferably 600 to 1000, and weight average molecular weight (Mw) is 800 to.
3600, preferably 900 to 3000, Mw / Mn of 3 or less, preferably 2.5 or less, particularly preferably 2.0.
It is the following. Further, the molecular weight is 700 to 2400 (preferably the molecular weight is 750 to 2000, and particularly preferably the molecular weight is 80).
That is, a peak exists in the region of 0 to 1600).
By having such a molecular weight distribution, it is possible to give the toner favorable thermal characteristics. That is, when the molecular weight is smaller than the above range, it is likely to be excessively affected by thermal effects, resulting in poor blocking resistance and developability.
When the molecular weight is larger than the above range, heat from the outside cannot be effectively used, and excellent fixability and offset resistance cannot be obtained.

As other physical properties, the density at 25 ° C. is 0.95 (g / cm ³ ) or more and the penetration is 1.5 (10 ^−1).
mm) or less, preferably 1.0 (10 ^-1 mm) or less. If it deviates from these ranges, it tends to change at low temperatures and the storage stability and developability tend to deteriorate.

The melt viscosity at 140 ° C. is 10
It is 0 cp or less, preferably 50 cp or less, and particularly preferably 20 cp or less. When the melt viscosity exceeds 100 cp, the plasticity and the releasability become poor, and the excellent fixability and offset resistance are affected. The softening point is preferably 130 ° C. or lower, and particularly preferably 120 ° C. or lower. When the softening point exceeds 130 ° C., the temperature at which the releasability works particularly effectively becomes high, and the excellent offset resistance is affected.

Further, the acid value is less than 2.0 mgKOH / g, preferably less than 1.0 mgKOH / g. If it exceeds this range, the interfacial adhesion with the binder resin, which is one of the components constituting the toner, is large and the phase separation during melting tends to be insufficient, so that good releasability is difficult to obtain. Offset resistance at high temperatures is not good, and the triboelectric charging characteristics of the toner are adversely affected, which may cause problems in developability and durability.

The content of these hydrocarbon waxes is 20 parts by weight or less with respect to 100 parts by weight of the binder resin.
It is effective to use 0.5 to 10 parts by weight.

For the DSC measurement in the present invention 3, for example, DSC-7 manufactured by Perkin Elmer Co. can be used.

The measuring method is ASTM D3418-82.
Carry out according to. As the DSC curve used in the present invention, the DSC curve measured when the temperature is raised once and the previous history is taken, and then the temperature is lowered and the temperature is raised at a temperature rate of 10 ° C./min is used.

In the present invention 3, the molecular weight distribution of the hydrocarbon wax is measured by gel permeation chromatography (GPC) under the following conditions.

(GPC measurement conditions) Device: GPC-150
C (Waters Co.) Column: GMH-HT 30 cm 2 series (manufactured by Tosoh Corp.) Temperature: 135 ° C. Solvent: o-dichlorobenzene (addition of 0.1% ionol) Flow rate: 1.0 ml / min Sample: 0.15% sample 0.4 ml injection

The molecular weight calibration curve prepared from the monodisperse polystyrene standard sample is used for the measurement of the molecular weight of the sample measured under the above conditions. In addition, Mark-Hou
It is calculated by converting to polyethylene using a conversion formula derived from the wink viscosity formula.

The penetration of waxes in the present invention 3 is as follows.
It is a value measured according to JIS K-2207. Specifically, it is a numerical value representing the penetration depth in units of 0.1 mm when a needle having a conical tip with a diameter of about 1 mm and an apex angle of 9 ° is penetrated with a constant load. The test conditions in the present invention are a sample temperature of 25 ° C., a load of 100 g, and a penetration time of 5 seconds.

The melt viscosity is a value measured with a Brookfield viscometer, and the conditions are a measurement temperature of 140 ° C., a shear rate of 1.32 rpm, and a sample of 10 ml.

The acid value is the number of mg of potassium hydroxide necessary to neutralize the acid groups contained in 1 g of the sample (JI
According to SK5902). Density is JIS K at 25 ℃
6760 and the softening point are values measured according to JIS K2207.

As the binder resin of the toner according to the present invention,
Polystyrene, homopolymers of styrene such as polyvinyltoluene and its substitution products; styrene-propylene copolymers, styrene-vinyltoluene copolymers, styrene-vinylnaphthalene copolymers, styrene-methyl acrylate copolymers, styrene- Ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-octyl acrylate copolymer, styrene-dimethylaminoethyl acrylate copolymer, styrene-methyl methacrylate acrylic acid copolymer, styrene-methacrylic acid Ethyl acid copolymer,
Styrene-butyl methacrylate copolymer, styrene-
Dimethylaminoethyl methacrylate copolymer, styrene-vinyl methyl ether copolymer, styrene-vinyl ethyl ether copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, styrene-
Isoprene copolymer, styrene-maleic acid copolymer,
Styrene-based copolymers such as styrene-maleic acid ester copolymers; polymethyl methacrylate, polybutyl methacrylate, polyvinyl acetate, polyethylene, polypropylene, polyvinyl butyral, silicone resin, polyester resin, polyamide resin, epoxy resin, polyacrylic acid Resins, rosins, modified rosins, temperel resins, phenol resins, aliphatic or alicyclic hydrocarbon resins, aromatic petroleum resins, paraffin wax, carnauba wax and the like can be used alone or in combination. In particular, styrene-based copolymers and polyester resins are preferable in terms of development characteristics, fixability and the like.

As the coloring material which can be further added to the magnetic toner according to the present invention, conventionally known pigments or dyes such as carbon black and copper phthalocyanine can be used.

If desired, the magnetic toner of the present invention may contain a charge control agent.
A negative charge control agent such as a metal complex salt of a monoazo dye, a metal complex salt of salicylic acid, an alkylsalicylic acid, a dialkylsalicylic acid or a naphthoic acid is used.

In the case of a positively chargeable toner, a positive charge control agent such as a nigrosine compound or an organic quaternary ammonium salt is used.

Further, the magnetic toner of the present invention is preferably mixed with an inorganic fine powder or a hydrophobic inorganic fine powder. For example, it is preferable to add titanium oxide or silica fine powder for use.

The fine silica powder used in the present invention includes both 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. Although usable, dry silica, which has few silanol groups on the surface and inside and has no production residue, is preferable.

Further, the fine silica powder used in the present invention is preferably one which has been subjected to a hydrophobic treatment. The hydrophobic treatment is applied by chemically treating with an organic silicon compound or the like that reacts with or physically adsorbs to the fine silica powder. As a preferred method, a method of treating dry silica fine powder produced by vapor phase oxidation of a silicon halogen compound with a silane coupling agent, or simultaneously treating with a silane coupling agent and an organosilicon compound such as silicone oil Is mentioned.

Examples of the silane coupling agent used for the hydrophobic treatment include hexamethyldisilazane, trimethylsilane, trimethylchlorosilane, trimethylethoxysilane, dimethyldichlorosilane, methyltrichlorosilane, allyldimethylchlorosilane, allylphenyl. Dichlorosilane, benzyldimethylchlorosilane, bromomethyldimethylchlorosilane, α-chloroethyltrichlorosilane, β-chloroethyltrichlorosilane,
Chlormethyldimethylchlorosilane, triorganosilane mercaptan, trimethylsilylmercaptan, triorganosilylacrylate, vinyldimethylacetoxysilane, dimethylethoxysilane, dimethyldimethoxysilane, diphenyldiethoxysilane, hexamethyldisiloxane, 1,3-divinyltetramethyldimethyl Examples include siloxane and 1,3-diphenyltetramethyldisiloxane.

Examples of the organosilicon compound include silicone oil. As a preferable silicone oil, one having a viscosity of about 30 to 1,000 centistokes at 25 ° C. is used, and for example, dimethyl silicone oil, methylphenyl silicone oil, α-methylstyrene modified silicone oil, chlorophenyl silicone oil, fluorine modified. Silicone oil and the like are preferred.

As the method for treating silicone oil, for example, silica fine powder treated with a silane coupling agent and silicone oil may be directly mixed by using a mixer such as a Henschel mixer. The method of injecting Alternatively, it may be produced by dissolving or dispersing silicone oil in an appropriate solvent, mixing with silica fine powder of the base, and removing the solvent.

If necessary, external additives other than fine silica powder may be added to the magnetic toner of the present invention.

For example, a charging auxiliary agent, a conductivity-imparting agent, a fluidity-imparting agent, an anti-caking agent, a releasing agent at the time of heat roll fixing,
Resin fine particles or inorganic fine particles that act as a lubricant, an abrasive, etc.

The inorganic fine powder or hydrophobic inorganic fine powder to be mixed with the magnetic toner is used in an amount of 0.1 to 5 parts by weight (preferably 0.1 to 3 parts by weight) per 100 parts by weight of the magnetic toner. good.

To prepare the magnetic toners of the present inventions 2 and 3 by a pulverization method, magnetic powder and a vinyl-based or non-vinyl-based thermoplastic resin, and if necessary, a pigment or dye as a coloring agent,
Charge control agents, other additives, etc. are thoroughly mixed with a mixer such as a ball mill, and then melted, kneaded and kneaded with a heat kneader such as a heating roll, kneader, or extruder to mutually combine the resins. The magnetic toner according to the present invention can be obtained by dispersing or dissolving the pigment or dye in the melted solution, cooling and solidifying, crushing and strict classification.

The particle size distribution of the toner can be measured by various methods, but in the present invention, it is measured using a Coulter counter.

That is, a Coulter counter TA-II type (manufactured by Coulter) was used as a measuring device, and an interface (manufactured by Nikkaki) for outputting number distribution and volume distribution and a CX-1 personal computer (manufactured by Canon) were connected. , Electrolyte is 1st class sodium chloride
% NaCl aqueous solution is prepared. As a measuring method, a surfactant (preferably an alkylbenzene sulfonate) as a dispersant was added to 0.1 to 100 ml of the electrolytic aqueous solution.
Add ~ 5 ml, and then add 2 to 20 mg of the measurement sample.
The electrolytic solution in which the sample is suspended is subjected to a dispersion treatment with an ultrasonic disperser for about 1 to 3 minutes, and the volume and number of the toner is measured by the Coulter Counter TAII type using an aperture of 100 μm to 2 to 40 μm. Calculate the volume distribution and number distribution of the particles. Then, according to the present invention, the weight-based weight average diameter D ₄ obtained from the volume distribution (the central value of each channel is a representative value for each channel), and the weight-based 12.7 μ obtained from the volume distribution is used.
Determine the weight distribution of m or more.

A preferable image forming apparatus, apparatus unit and facsimile apparatus for using the magnetic toner of the present invention will be described.

A preferred specific example of the image forming apparatus will be described with reference to FIG.

The surface of the OPC photosensitive member 3 is negatively charged by the primary charger 11, a digital latent image is formed by image scanning by exposure 5 with a laser beam, and a urethane rubber elastic blade 9 installed in the counter direction and The latent image is reversely developed with the one-component magnetic developer 13 having magnetic toner of the developing device 1 having the developing sleeve 6 containing the magnet 15. In the developing section, the bias applying means 12 applies an alternating bias, a pulse bias and / or a DC bias between the conductive substrate of the photosensitive drum 3 and the developing sleeve 6. When the transfer sheet P is conveyed and reaches the transfer portion, the electrostatic transfer means 4 charges the developed image (toner) on the surface of the photosensitive drum by corona charging from the back surface (the surface opposite to the photosensitive drum side) of the transfer sheet P. Image) is electrostatically transferred onto the transfer paper P. The transfer paper P separated from the photosensitive drum 3 is subjected to a fixing process by the heating and pressure roller fixing device 7 in order to fix the toner image on the transfer paper P.

The one-component developer remaining on the photosensitive drum after the transfer step is removed by the cleaning device 14 having the cleaning blade 8. The photosensitive drum 3 after cleaning is erased by erase exposure 19, and the process starting from the charging process by the primary charger 11 is repeated again.

The electrostatic image carrier (photosensitive drum) has a photosensitive layer and a conductive substrate, and moves in the arrow direction. The non-magnetic cylindrical developing sleeve 6, which is a toner carrier, rotates so as to move in the same direction as the surface of the electrostatic image carrier in the developing section. Inside the non-magnetic cylindrical developing sleeve 6, a multi-pole permanent magnet 15 (magnet roll) which is a magnetic field generating means is arranged so as not to rotate. The one-component insulating developer 13 in the developing device 1 is applied on the non-magnetic cylindrical surface, and the friction between the surface of the developing sleeve 6 and the magnetic toner particles gives the magnetic toner particles a negative triboelectric charge, for example. . Further, by disposing the elastic doctor blade 9, the thickness of the developer layer is regulated to be thin (30 μm to 300 μm) and uniform, so that the developer layer thinner than the gap between the photosensitive drum 3 and the developing sleeve 6 in the developing section is formed. It is formed so as to be non-contact. By adjusting the rotational speed of the sleeve 6, the surface speed of the sleeve is made substantially equal to or close to the speed of the electrostatic image holding surface.

The sleeve 6 and the photosensitive drum 3 in the developing section.
Alternatively, an AC bias or a pulse bias may be applied between and by the bias means 12. This AC bias is f
Is 200 to 4,000 Hz, Vpp is 500 to 3,000
It is preferably 0V.

When the magnetic toner particles are transferred in the developing portion, the magnetic toner particles are transferred to the electrostatic image side by the electrostatic force on the surface of the photosensitive drum 3 holding the electrostatic image and the action of the AC bias or the pulse bias.

Further, another example of the image forming apparatus suitable for the present invention will be described with reference to FIG.

The image forming apparatus shown in FIG. 4 is different from the image forming apparatus shown in FIG. 3 in that the layer thickness of the magnetic developer on the developing sleeve 6 is regulated by the magnetic doctor blade 16. 4, the members having the same reference numerals as those in FIG. 3 indicate the same members.

As the magnetic doctor blade 16, for example, an iron doctor blade is placed close to the surface of the cylinder (interval 5
(0 μm to 500 μm), the developer layer is thinly arranged (30 μm to 300 μm) and uniformly regulated by arranging it so as to face one magnetic pole position of the multi-pole permanent magnet, and an electrostatic image is carried in the developing section. A developer layer that is thinner than the gap between the body 1 and the developing sleeve 2 is formed so as not to contact. By adjusting the rotation speed of the developing sleeve 2, the surface speed of the sleeve is made substantially equal to or close to the speed of the electrostatic image holding surface. Instead of iron as the magnetic doctor blade 6, a permanent magnet may be used to form the opposing magnetic poles.

The electrophotographic apparatus is constructed by integrally combining a plurality of constituent elements such as the electrostatic latent image carrier such as the above-mentioned photosensitive drum, the developing device, and the cleaning means as an apparatus unit. The unit may be detachably attached to the apparatus body. For example, a unit is formed by integrally supporting at least one of a charging unit, a developing unit, and a cleaning unit together with a photosensitive drum to form a unit that is detachably attached to the main body of the apparatus. It may be detachable. At this time, charging means and / or
Alternatively, it may be configured with a developing device.

FIG. 5 shows an embodiment of an apparatus unit suitable for the present invention. In this embodiment, an electrophotographic system including an image forming unit (so-called cartridge) 18 in which a developing device 1, a drum-shaped latent image carrier (photosensitive drum) 3, a cleaner 14, and a primary charger 11 are integrated. An image forming apparatus is exemplified.

In this apparatus, the image forming unit 1
When the magnetic developer 13 in the developing device 1 in 8 disappears, it is replaced with a new cartridge.

In the present embodiment, the developing device 1 uses a one-component magnetic developer as the developer 13, and at the time of development, a predetermined electric field is formed between the photosensitive drum 3 and the developing sleeve 6, and the developing process is performed. The distance between the photosensitive drum 3 and the developing sleeve 6 is very important in order to properly carry out.
In this embodiment, the center is 300 μm, and measurement and adjustment are performed so that the error is ± 30 μm.

The developing device 1 of the present invention shown in FIG. 5 includes a developer container 2 for containing a magnetic developer 13 and a developer container 2.
A developing sleeve 6 for carrying and carrying the magnetic developer 13 therein from the developer container 2 to a developing area facing the latent image carrier 3;
An elastic blade 9 is provided to regulate the magnetic developer carried by the developing sleeve 6 and conveyed to the developing area to a predetermined thickness to form a thin developer layer on the developing sleeve.

The developing sleeve 6 may have any structure. Usually, it is composed of a non-magnetic developing sleeve 6 containing a magnet 15. The developing sleeve 6 may be a cylindrical rotating body as shown. It is also possible to form a belt shape that moves circularly. The material is usually
It is preferable to use aluminum or SUS.

The elastic blade 9 is made of a rubber elastic body such as urethane rubber, silicone rubber or NBR; a metal elastic body such as phosphor bronze or a stainless steel plate; a resin elastic body such as polyethylene terephthalate or high density polyethylene. Composed of plates. The elastic blade 9 is brought into contact with the developing sleeve 6 by the elasticity of the member itself, and is fixed to the developer container 2 by the blade supporting member 10 made of a rigid body such as iron. The elastic blade 9 has a linear pressure of 5 to 80 g /
It is preferable that the contact is made in cm in the counter direction with respect to the rotation direction of the developing sleeve 6.

When the image forming apparatus of the present invention is used as a printer for a facsimile, the optical image exposure is exposure for printing received data. FIG. 6 is a block diagram showing an example of this case.

The controller 611 controls the image reading section 610 and the printer 619. The entire controller 611 is controlled by the CPU 617. The read data from the image reading unit is transmitted to the partner station via the transmission circuit 613. The data received from the partner station is sent to the printer 619 through the receiving circuit 612. Predetermined image data is stored in the image memory. Printer controller 6
18 controls the printer 619. Reference numeral 614 is a telephone.

The image received from the line 615 (image information from the remote terminal connected through the line) is demodulated by the receiving circuit 612, and then the CPU 617 decodes the image information and sequentially stores the image memory 616. Stored in. Then, at least one page of image is stored in the memory 616.
When stored in, the image of that page is recorded. CPU
617 reads the image information of one page from the memory 616 and sends the decoded image information of one page to the printer controller 618. Printer controller 618
When receiving the image information of one page from the CPU 618, the printer 61 prints the image information of the page.
Control 9

The CPU 617 receives the next page during recording by the printer 619.

As described above, the image is received and recorded.

The magnetic iron oxide containing elemental silicon according to the present invention is produced, for example, by the following method.

An aqueous solution containing ferrous hydroxide is prepared by adding a predetermined amount of silicic acid compound to the aqueous solution of ferrous salt and then adding an equivalent amount or an equivalent amount or more of an alkali such as sodium hydroxide to the iron component. . The pH of the prepared aqueous solution is pH 7
Air is blown while maintaining the above (preferably pH 8 to 10), the ferric hydroxide is oxidized while the aqueous solution is heated to 70 ° C. or higher, and seed crystals that form the core of the magnetic iron oxide particles are first generated. To do.

Next, an aqueous solution containing about 1 equivalent of ferrous sulfate is added to the slurry-like liquid containing seed crystals, based on the amount of alkali added previously. While maintaining the pH of the solution at 6 to 10, the reaction of ferrous hydroxide is promoted while air is blown in, and magnetic iron oxide particles are grown around the seed crystal. The pH of the liquid shifts to the acidic side as the oxidation reaction progresses,
The pH of the liquid is preferably not less than 6. By adjusting the pH of the solution at the final stage of the oxidation reaction, it is preferable that a predetermined amount of the silicic acid compound is unevenly distributed on the surface layer and the surface of the magnetic iron oxide particles.

Examples of the silicic acid compound used for the addition include silicates such as commercially available sodium silicate and silicic acid such as sol-like silicic acid produced by hydrolysis. Other additives such as aluminum sulfate and alumina may be added as long as they do not adversely affect the present invention.

As the ferrous iron salt, iron sulfate generally produced as a by-product in the production of titanium by the sulfuric acid method, iron sulfate produced as a by-product when the surface of a steel sheet is cleaned can be used, and iron chloride or the like can be used. is there.

In the method for producing magnetic iron oxide by the aqueous solution method, an iron concentration of 0.5 to 2 mol / l is generally used in order to prevent the viscosity from increasing during the reaction and the solubility of iron sulfate. Generally, the thinner the concentration of iron sulfate, the finer the particle size of the product tends to be. In addition, during the reaction, the larger the amount of air and the lower the reaction temperature, the easier the particles become.

According to the above-described manufacturing method, magnetic iron oxide particles having a silicic acid component were mainly composed of spherical particles having a curved surface having no plate-like surface, as observed by transmission electron microscopy. Produces magnetic iron oxide containing almost no surface particles,
It is preferable to use the magnetic iron oxide in the toner.

[0190]

EXAMPLES The present invention will be specifically described below with reference to examples. The parts or% given in the examples refer to parts by weight or% by weight.

(Production Example 1 of Magnetic Iron Oxide) Sodium silicate was added to an aqueous ferrous sulfate solution so that the content ratio of silicon element to iron element was 1.8%, and then to iron ion. L. An aqueous solution containing ferrous hydroxide was prepared by mixing 0 to 1.1 equivalents of caustic soda solution.

The pH of the aqueous solution is adjusted to pH 7 to 10 (eg pH
While maintaining at 9), air was blown in to carry out an oxidation reaction at 80 to 90 ° C. to prepare a slurry liquid for generating seed crystals.

Next, an aqueous ferrous sulfate solution was added to this slurry liquid so that the amount of the alkali was 0.9 to 1.2 equivalents based on the initial alkali amount (sodium component of sodium silicate and sodium component of caustic soda). PH of liquid 6-10
The pH was adjusted to 8 (for example, while maintaining the pH at 8), the pH was adjusted at the end of the oxidation reaction, and the silicic acid component was unevenly distributed on the surface of the magnetic iron oxide particles. The produced magnetic iron oxide particles were washed, filtered and dried by a conventional method, and then the aggregated particles were crushed to obtain magnetic iron oxide 1 having the characteristics shown in Table 2.

Data obtained by measuring the dissolved amounts of the iron element and the silicon element every 10 minutes are shown in Table 1, and FIG. 1 shows the relationship between the dissolution rates of the iron element and the silicon element in the magnetic iron oxide.

In the magnetic iron oxide obtained in Production Example 1, the results shown in FIG.
The content C of the silicon element derived from a silicon compound such as silicic acid, which is eluted by the alkali present on the surface C of the magnetic iron oxide particles, is 17.9 mg / l, and the surface B of the magnetic iron oxide particles shown in FIG. Content B of the silicon compound derived from the silicon compound present in 3 is 38.8 mg / l, and the content A is 5
It was 9.7 mg / l.

[0196]

[Table 1]

(Production Example 2 of Magnetic Iron Oxide) The same procedure as in Production Example 1 was repeated except that sodium silicate was added so that the content ratio of silicon element to iron element was 2.9%. Magnetic iron oxide 2 having the characteristics shown in 2 was obtained.

(Manufacturing Example 3 of Magnetic Iron Oxide) The same procedure as in Manufacturing Example 1 was repeated except that sodium silicate was added so that the content ratio of silicon element to iron element was 0.9%. Magnetic iron oxide 3 having the characteristics shown in 2 was obtained.

(Production Example 4 of Magnetic Iron Oxide) The same procedure as in Production Example 1 was repeated except that sodium silicate was added so that the content ratio of silicon element to iron element was 1.7%. Magnetic iron oxide 4 having the characteristics shown in 2 was obtained.

(Comparative Production Example 1 of Magnetic Iron Oxide) A magnetic iron oxide 5 having the characteristics shown in Table 2 was obtained in the same manner as in Production Example 1 except that sodium silicate was not added in Production Example 1.

(Comparative Production Example 2 of Magnetic Iron Oxide) With respect to 100 parts of magnetic iron oxide obtained in Comparative Production Example 1, 1.5
Part of the silicic acid fine powder was mixed with a Henschel mixer to obtain a magnetic iron oxide 6 having the characteristics shown in Table 2.

[0202]

[Table 2]

Example 1 To 709 g of ion-exchanged water was added 451 g of 0.1 M Na ₃ PO ₄ aqueous solution, and the mixture was heated to 60 ° C. and then 1.0 M-Ca.
67.7 g of an aqueous Cl ₂ solution was gradually added to Ca ₃ (PO
₄ ) An aqueous medium containing ₂ was obtained.

Styrene 164 parts n-Butyl acrylate 36 parts Styrene-methacrylic acid-methyl methacrylate 8 parts (85: 5: 10) copolymer (Mw = 70,000) Negative charge control agent (dialkylsalicylic acid chromium compound) 2 parts magnetic iron oxide 1 160 parts

The above formulation was uniformly dispersed and mixed using an attritor (Mitsui Miike Kakoki Co., Ltd.).

This monomer composition was heated to 60 ° C., 40 parts of paraffin wax (mp. 70 ° C.) was mixed and dissolved therein, and the polymerization initiator 2,2′-azobis (2,4-
Dimethylvaleronitrile) [t1 / 2 = 140 minutes, 60 ° C
Bottom] 8 g and dimethyl-2,2'-azobisisobutyrate [t1 / 2 = 270 minutes, at 60 ° C; t1 / 2 = 80 minutes,
Under 80 ° C.] 2 g was dissolved.

The above polymerizable monomer system was put into the above aqueous medium, and the mixture was mixed at 60 ° C. under N ₂ atmosphere with a TK homomixer (Tokushu Kika Kogyo Co., Ltd.) at 10,000 rpm at 1 rpm.
The mixture was stirred for 5 minutes and granulated. Then, the mixture was reacted with the paddle stirring blade at 60 ° C. for 1 hour while stirring. After that, adjust the liquid temperature to 80 ° C.
The stirring was continued for another 10 hours. After the reaction was completed, the suspension was cooled, hydrochloric acid was added to dissolve Ca ₃ (PO ₄ ) _2, and the mixture was filtered, washed with water and dried to obtain a polymerized magnetic toner having a weight average particle diameter of 6.2 μm.

100 parts of this magnetic toner and 1.2 parts of hydrophobic silica fine powder treated with hexamethyldisilazane and then treated with silicone oil were mixed with a Henschel mixer (Mitsui Miike Kako Co., Ltd.) to carry out magnetic development. The agent was prepared.

Commercially available laser beam printer LBP-
An apparatus unit portion (toner cartridge) of 8II (manufactured by Canon Inc.) was modified as shown in FIG. 5, and an elastic blade made of urethane rubber was brought into contact with an aluminum developing sleeve at a contact pressure of 25 g / cm.

Using the above magnetic developer, a primary charge of -6
An electrostatic latent image for reversal development is formed on the OPC photosensitive drum 3 as 50 V, and a gap (300 μm) is set so that the developer layer on the developing sleeve 6 (including the magnet) is not in contact with the photosensitive drum 3 and AC Bias (f = 1,800 Hz, Vpp =
1500 V) and DC bias (V _DC = -550 V)
While applying and to the developing sleeve, the electrostatic charge image was developed by reversal development with _{VL set} to -150 V to form a magnetic toner image on the OPC photosensitive member. The formed magnetic toner image was transferred to a plain paper at a positive transfer potential, and the plain paper having the magnetic toner image was fixed on the plain paper through a heating and pressure roller fixing device. Also, the process speed is 60 mm / se
c. Improved to.

The image development test was conducted up to 5000 sheets under normal temperature and normal humidity environment (23.5 ° C., 60% RH) while replenishing the magnetic developer successively. Image density measured by Macbeth reflection densitometer, whiteness of transfer paper measured by reflectometer (manufactured by Tokyo Denshoku Co., Ltd.) and fog calculated by comparing solid whiteness with whiteness of transfer paper after printing, and , Fig. 7
Table 2 shows the results of the dot reproducibility of the image forming test shown in FIG.

Similarly, in a high temperature and high humidity environment (32.5
℃, 85% RH) and low temperature and low humidity environment (10 ℃, 15%
The image formation test was conducted in RH). The results are shown in Table 3.

The fixability was good.

Example 2 A polymerized magnetic toner of 3.8 μm was obtained in the same manner except that the magnetic iron oxide 1 of Example 1 was changed to 20 parts of magnetic iron oxide 2.
To 100 parts of the obtained magnetic toner, 1.5 parts of hydrophobic colloidal silica was externally added in the same manner as in Example 1 to prepare a magnetic developer.

Using this magnetic developer, a multi-sheet durability test up to 5000 sheets was conducted in the same manner as in Example 1.
The results are shown in Table 3.

The fixability was good.

Example 3 A polymerized magnetic toner of 9.2 μm was obtained in the same manner except that the magnetic iron oxide 1 of Example 1 was changed to 140 parts of magnetic iron oxide 3. To 100 parts of the obtained magnetic toner, 0.8 part of hydrophobic colloidal silica was externally added in the same manner as in Example 1 to prepare a magnetic developer.

Using this magnetic developer, a multi-sheet durability test up to 5000 sheets was conducted in the same manner as in Example 1.
The results are shown in Table 3.

The fixability was good.

Example 4 A polymerized magnetic toner of 7.8 μm was obtained in the same manner except that the magnetic iron oxide 1 of Example 1 was changed to 150 parts of magnetic iron oxide 4. To 100 parts of the obtained magnetic toner, 1.0 part of hydrophobic colloidal silica was externally added in the same manner as in Example 1 to prepare a magnetic developer.

Using this magnetic developer, a multi-sheet durability test up to 5000 sheets was conducted in the same manner as in Example 1.
The results are shown in Table 3.

The fixability was good.

Example 5 Polymerized magnetic toner of 7.7 μm was obtained in the same manner except that the magnetic iron oxide 1 of Example 1 was replaced with 150 parts of the magnetic iron oxide 4 treated with 3 wt% of titanium coupling agent. It was To 100 parts of the obtained magnetic toner, 1.0 part of hydrophobic colloidal silica was externally added in the same manner as in Example 1 to prepare a magnetic developer.

Using this magnetic developer, a multi-sheet durability test up to 5000 sheets was conducted in the same manner as in Example 1.
The results are shown in Table 3.

The fixability was good.

Comparative Example 1 A polymerized magnetic toner of 7.5 μm was obtained in the same manner except that the magnetic iron oxide 1 of Example 1 was changed to 150 parts of magnetic iron oxide 5. To 100 parts of the obtained magnetic toner, 1.0 part of hydrophobic colloidal silica was externally added in the same manner as in Example 1 to prepare a magnetic developer.

Using this magnetic developer, a multi-sheet durability test up to 5000 sheets was conducted in the same manner as in Example 1.
The results are shown in Table 3.

The fixability was good.

Comparative Example 2 A polymerized magnetic toner of 6.4 μm was obtained in the same manner except that the magnetic iron oxide 1 of Example 1 was changed to 160 parts of magnetic iron oxide 6. To 100 parts of the obtained magnetic toner, 1.2 parts of hydrophobic colloidal silica was externally added in the same manner as in Example 1 to prepare a magnetic developer.

Using this magnetic developer, a multi-sheet durability test up to 5000 sheets was conducted in the same manner as in Example 1.
The results are shown in Table 3.

The fixability was good.

Comparative Example 3 Resin which was suspension polymerized only with the resin component of Example 1 208 parts Negative charge control agent (dialkyl salicylic acid type chromium complex) 2 parts Magnetic iron oxide 1 160 parts

Paraffin wax (mp.
(70 ° C.) was mixed in an amount of 40 parts, and an attempt was made to produce a toner by an ordinary pulverizing method, but fusion with the apparatus occurred in the pulverizing step, and the toner could not be formed.

Then, 10 parts of paraffin wax was mixed with the above composition to obtain a pulverized toner. The evaluation was performed in the same manner as in Example, but the fluidity of the toner was significantly deteriorated, and the developing property,
It was inferior in fixability.

[0235]

[Table 3]

A) Fog was calculated by the following formula.

[0237]

[Equation 7]

Fog is a good image if it is 1.5% or less.

B) The dot reproducibility is 80 × 5 as shown in FIG.
An image output test was carried out using a checker pattern of 0 μm, and the sharpness of the toner image, the scattering of the toner to the non-image area, and the presence or absence of a black portion defect were evaluated by a microscope.

(Developer Production Examples 1 to 5) Styrene-n-butyl acrylate copolymer 100 parts (copolymerization weight ratio 8: 2 Mw = 260,000) Magnetic iron oxide 1 100 parts Negative charge control agent (monoazo dye type) Iron complex) 0.8 part Ethylene-propylene copolymer (Mw = 6000) 3 parts

The above mixture was melt-kneaded in a twin-screw extruder heated to 140 ° C., the kneaded product was cooled, coarsely pulverized with a hammer mill, and the coarsely pulverized product was finely pulverized with a jet mill to obtain fine pulverization. Wind-classify objects to weight average particle size (D
₄ ) A negatively chargeable magnetic developer having a thickness of 7.0 μm was obtained. To 100 parts of this developer, 1.0 part of hydrophobic silica fine powder (hexamethyldisilazane treated BET value 200 m ^{2 /} g) was added and mixed with a Henschel mixer to prepare developer (1).
And

In the same manner, magnetic iron oxides 2 to 5 are used in place of magnetic iron oxide 1 to develop developers (2) to (5).
Was manufactured.

FIG. 8 is a schematic view of the image forming apparatus used in Examples 6 to 8 below. In FIG. 8, the electrostatic latent image carrier 2
1 is composed of a developer carrying member 25 and a developer regulating member 23 whose tip portion is arranged so as to be in pressure contact with the developer carrying member 25, and these are a developing device 22 containing a magnetic developer. It is arranged inside. An AC high voltage power supply 26 for applying a developing bias voltage is applied to the developer carrying member 25.
And a DC high voltage power supply 27 are connected. The developer carrying member 25 has a plurality of magnetic poles (N1, S
1, N2, S2) are magnetized and fixed and supported, and a cylindrical developer carrier that rotates around the magnet roll 24, and the developer carrier rotates as the developer carrier rotates. The magnetic developer 28 is adsorbed and conveyed, the developer layer is formed, and the fog developer is pulled back. The charging roller 31, the DC high-voltage power supply 32, and the AC high-voltage power supply 3 that are in contact with the outer periphery of the electrostatic latent image carrier 21.
3, a charging bias is applied to the electrostatic latent image carrier 21.
Is charged. Next, an electrostatic latent image 29 is formed by exposure with the laser beam 34, and the magnetic developer 28 is subjected to reversal development.

The developed visible image on the electrostatic latent image carrier is transferred onto the transfer material 36 by the transfer roller 35 and fixed by a fixing device (not shown) to form a fixed image. Also,
The developer partially left on the electrostatic latent image carrier is cleaned by a cleaning unit (not shown).

FIG. 9 illustrates the alternating voltage used in the present invention 2.

Vdc represents a DC power supply voltage, Vd represents a dark portion potential on the electrostatic latent image carrier, and V1 represents a light portion potential. f is the frequency of the alternating voltage, and Vpp is the peak-to-peak voltage of the alternating voltage.

Example 6 An OPC electrostatic latent image bearing member having a diameter of 30 mm was used as the electrostatic latent image bearing member, and the dark portion potential Vd = -400 V and the light portion potential VL =.
It was set to -30V. The distance between the electrostatic latent image carrier and the developer carrier is 350 μm, the developer carrier has a layer thickness of about 7 μm, and the JIS center line average roughness (Ra) is 0.8 μm.
A resin carrier of m is formed on an aluminum cylinder having a mirror surface and a diameter of 16 mm, and a developing magnetic pole of 850 gauss and a thickness of 1.0 m as a developer regulating member are used.
m, 15 g of urethane rubber blade with free length of 10 mm
The contact was made with a linear pressure of / cm.

Phenolic resin 100 parts Graphite (particle size of about 7 μm) 90 parts Carbon black 10 parts

Next, as the developing bias, a DC bias component Vdc = -230V and an AC bias component Vpp = 2.
A sine wave of 100 V and a frequency of 2400 Hz was used, and the developer (1) of Production Example 1 was used as the developer under the condition that the peripheral speed of the developer carrier was 110% with respect to the electrostatic latent image carrier, and the temperature was 23 ° C. 6
Images were printed on 10,000 sheets in a 5% RH environment. As a result, good images without scattering were obtained even after continuous printing of 10,000 sheets. Further, after the developer on the sleeve was removed by air, visual observation was carried out, but no developer adhered to the sleeve at all. The amount of fog at this time is measured by a reflection densitometer (reflectometer ODEL manufactured by Tokyo Denshoku Co., Ltd.).
TC-6DS) (when the worst value of the reflection density of the white background after printing is Ds and the average reflection density of the paper before printing is Dr, the fog amount is Ds-Dr), 1. It was as good as 2%. (A fogging amount of 2% or less is a good image with substantially no fog, and a fogging amount of more than 5% is an unclear image with a noticeable fogging.)
The resolution of the 1-dot latent image of m was also sufficient.

When the same test was performed using the developers (2) to (4) under the above conditions, no sticking of the developer on the sleeve was observed at all as in the case of the developer (1). A high-resolution image free from scatter and fogging was obtained.

Example 7 The same procedure as in Example 1 was carried out except that an aluminum mirror surface cylindrical sleeve having a JIS center line average roughness (Ra) of 0.1 μm was used as the developer carrying member in Example 6. A good image without fog or scatter was obtained.
Further, after the developer on the sleeve was removed by air, visual observation was carried out, but no developer adhered to the sleeve at all.

Example 8 As a developer carrier, a layer thickness of about 5 μm JIS center composed of phenol resin 100 parts graphite (particle size about 3 μm) 40 parts carbon black 10 parts on an aluminum cylinder having a mirror surface and a diameter of 16 mm Line average roughness (Ra)
The same test as in Example 6 was carried out except that a developer carrier having a resin layer of 0.4 μm was used. As a result, a good image free from fogging and scattering was obtained and no developer was fixed on the sleeve. It was

Comparative Example 3 As a developer carrying member, JIS center line average roughness (Ra)
The same procedure as in Example 6 was carried out except that a 1.5 μm aluminum cylindrical sleeve was used and the developer (5) was used as the developer. However, the particles gradually scattered and fog increased, and a good image was not obtained. Further, the developer was also fixed on the sleeve.

(Production Example of Wax) Next, the hydrocarbon wax used in Examples 9 to 13 below will be described.

Hydrocarbon wax E (comparative example) synthesized by the Arge process and wax A (example),
Wax B (Example) and Wax C (Example) were obtained by fractional crystallization.

Ethylene was low-pressure polymerized using a Ziegler catalyst to obtain a wax F having a relatively high molecular weight (Comparative Example),
Wax D by extracting low molecular weight components by fractional crystallization
(Example) was obtained.

These physical properties are shown in Tables 4, 5 and 6, and the results of DSC of wax A and wax E are shown in FIG.
Through FIG.

[0258]

[Table 4]

[0259]

[Table 5]

[0260]

[Table 6]

Example 9 Styrene-2-ethylhexyl acrylate 100 parts-Maleic acid n-butyl half ester copolymer (copolymerization weight ratio 7.5: 1.5: 1, Mw 250,000) Magnetic iron oxide 1100 Part-Negatively charged property control agent (dialkyl salicylic acid-based chromium complex) 1 part-Wax A 3 parts

The above mixture was melt-kneaded in a twin-screw extruder heated to 140 ° C., the cooled mixture was coarsely pulverized with a hammer mill, and the coarsely pulverized product was finely pulverized with a jet mill. Was classified with a fixed type air classifier to produce classified powder. Furthermore, the weight-average particle diameter (D ₄ ) is obtained by strictly classifying the obtained classified powder at the same time by strictly classifying and removing ultrafine powder and coarse powder with a multi-division classifier utilizing the Coanda effect (Elbow Jet classifier manufactured by Nippon Steel Mining Co., Ltd.). 6.8 μm (particle size 12.7 μ
A negatively chargeable magnetic toner having a magnetic toner particle content of m of 0.2%) was obtained.

A magnetic developer was prepared by mixing 100 parts of this magnetic toner with 1.2 parts of hydrophobic silica fine powder treated with hexamethyldisilazane and then treated with silicone oil using a Henschel mixer.

Commercially available Laser Bee Printer LBP-8
An apparatus unit portion (toner cartridge) of II (manufactured by Canon Inc.) was modified as shown in FIG. 5, and an elastic blade made of urethane rubber was brought into contact with an aluminum developing sleeve at a contact pressure of 30 g / cm.

Using the above magnetic developer, the primary charge is set to -7.
An electrostatic latent image for reversal development is formed on the OPC photosensitive drum 3 as 00V, and a gap (300 μm) is set in the developer layer on the developing sleeve 6 (including the magnet) so as not to contact the photosensitive drum, and an AC bias is applied. (F = 1,800 Hz, Vpp = 1
600 V) and a DC bias (V _DC = -500 V) are applied to the developing sleeve, while setting _VL to -170 V, the electrostatic charge image is developed by reversal development to obtain a magnetic toner image.
It was formed on a PC photoreceptor. The formed magnetic toner image is transferred to the plain paper with a positive transfer potential, and the plain paper having the magnetic toner image is heated and pressed by a roller fixing device (fixing device set temperature is 17
The magnetic toner image was fixed through (set at 0 ° C.).

At the environmental temperature of 7.5 ° C., the first copy immediately after the power was turned on showed no offset and good fixing property. Furthermore, under normal temperature and humidity environment (23.5 ° C,
In 85% RH), the image development test was conducted up to 6000 sheets while successively supplying the magnetic developer. The developability and fixability were good, and no stain was found on the heating roller and the pressure roller.

Image density measured by Macbeth reflection densitometer, whiteness of transfer paper measured by reflectometer (manufactured by Tokyo Denshoku Co., Ltd.) and solid white were calculated from comparison of whiteness of transfer paper after printing. Table 7 shows the results of dot reproducibility and fixability obtained by performing an image generation test of the fog and the pattern shown in FIG. 7.

In addition, as a storage stability blocking test, about 2
Table 7 shows the results of visual evaluation after placing 0 g of a developer in a 100 cc poly cup and leaving it at 50 ° C. for 3 days.

Excellent: No agglomerates are seen, Good: Agglomerates are seen but easily collapsed, Good: Agglomerates are seen but collapsed when shaken, No: Aggregates can be grabbed and cannot be easily collapsed

Similarly, under a high temperature and high humidity environment (32.5
℃, 85% RH) and low temperature and low humidity environment (10 ℃, 15%
The image formation test was conducted in RH). The results are shown in Table 7.

Example 10 -Styrene-butyl acrylate copolymer 100 parts (copolymerization weight ratio 8: 2, Mn 10000) -Magnetic iron oxide 260 parts-Negative charge control agent (monoazo dye-based chromium complex) 0.8 Part ・ Wax B 3 parts

The above mixture was melt-kneaded with a twin-screw extruder heated to 140 ° C., the cooled mixture was coarsely pulverized with a hammer mill, and the coarsely pulverized product was finely pulverized with a jet mill. The finely pulverized powder obtained is subjected to air classification to obtain a weight average particle diameter (D
₄ ) A negatively chargeable magnetic toner having 11 μm (content of magnetic toner particles having a particle size of 12.7 μm or more, 33%) was obtained.

A magnetic developer was prepared by mixing 100 parts of the obtained magnetic toner and 0.6 part of hydrophobic colloidal silica treated with dimethyl silicone oil with a Henschel mixer.

Using this magnetic developer, the fixing unit portion of the device unit of laser bee printer LBP-8II,
As shown in FIG. 14, the unfixed image 44 is set at a set temperature of 150 ° C.
To a heating member 41 opposed to the heating member 41, and the transfer material is closely adhered to the heating member 41 via a film 42. The fixing device 43 is modified to have a nap of 4.0 mm and a linear pressure of 0.4.
An image drawing test was performed with Kg / cm. As the material of the fixing film 42, an endless film in which a release layer of fluororesin having a conductive material added to a polyimide film was coated to a thickness of 10 μm was used.

[0275] At the environmental temperature of 7.5 ° C, the first copy immediately after the power was turned on showed no offset and good fixability. Furthermore, under normal temperature and humidity environment (23.5 ° C, 8
An image output test of 6000 sheets was performed at 5% RH). The developability and fixability were good, and the heating film and the pressure roller were not stained. The results are shown in Table 7.

Example 11 -Styrene-butyl acrylate 100 parts (copolymerization weight ratio 8: 2, Mn 10000) -Magnetic iron oxide 3 120 parts-Negatively charged control agent (monoazo dye-based chromium complex) 2 parts-Wax C 3 Department

Using the above materials, a magnetic toner having a weight average particle size (D ₄ ) of 4 μm (content of magnetic toner particles having a particle size of 12.7 μm or more, 0%) was obtained in the same manner as in Example 9.

A magnetic developer was prepared by mixing 100 parts of the obtained magnetic toner and 1.6 parts of hydrophobic colloidal silica treated with silicone oil with a Henschel mixer.

Using this magnetic developer, a multi-image printing test up to 6000 sheets was conducted in the same manner as in Example 10. The results are shown in Table 7.

Example 12 Styrene-n-ethylhexyl acrylate 100 parts-Maleic acid n-butyl half ester copolymer (copolymerization weight ratio 7.5: 1.5: 1, Mw 250,000) Magnetic iron oxide 490 Part-Negatively charged property control agent (dialkyl salicylic acid type chromium complex) 1 part-Wax D 3 parts

Using the above materials, a magnetic toner having a weight average particle diameter (D ₄ ) of 8.5 μm (content of magnetic toner particles having a particle diameter of 12.7 μm or more 4%) was obtained in the same manner as in Example 9.

A magnetic developer was prepared by mixing 100 parts of the magnetic toner obtained and 1 part of a hydrophobic colloidal silica fine powder which had been treated with hexamethyldisilazane and then treated with silicone oil with a Henschel mixer.

This magnetic developer was applied to a laser B printer LBP-8II in a vertical image on an A4 copy paper to produce 16 images.
The image was supplied to the apparatus unit (toner cartridge) of the modified machine modified to the number of sheets / minute, and the image output test was performed in the same manner as in Example 9. The results are shown in Table 7.

Example 13 Styrene-n-butyl acrylate copolymer 100 parts (copolymerization weight ratio 8: 2, Mw = 280,000) -Magnetic iron oxide 150 parts-Negative charge control agent (monoazo dye-based chromium Complex) 0.8 part Wax B 3 parts

Using the above materials, a magnetic toner having a weight average particle diameter of 13 μm (content of magnetic toner particles having a particle diameter of 12.7 μm or more: 45%) was obtained in the same manner as in Example 9.

100 parts of the magnetic toner obtained and a hydrophobic colloidal silica fine powder treated with silicone oil were added.
4 parts were mixed with a Henschel mixer to prepare a magnetic developer.

This magnetic developer was supplied to an apparatus unit (toner cartridge) of a commercially available laser bee printer LBPA404, and a multi-sheet durability test of 4000 sheets was conducted in the same manner as in Example 9. The results are shown in Table 7.

Comparative Example 4 The weight average particle size was 7 μm in the same manner as in Example 9 except that the magnetic iron oxide 5 and wax E of Comparative Production Example 1 were used.
m (the content of the magnetic toner particles having a particle diameter of 12.7 μm or more is 0.3%) was obtained. Using the obtained magnetic toner, a magnetic developer was prepared in the same manner as in Example 9, and an image forming test was conducted in the same manner as in Example 9 using the prepared magnetic developer. The results are shown in Table 7.

Comparative Example 5 A magnetic toner having a weight average particle diameter of 8.7 μm (a magnetic toner having a particle diameter of 12.7 μm or more) was obtained in the same manner as in Example 10 except that the magnetic iron oxide 6 and the wax F of Comparative Production Example 1 were used. A magnetic toner having a particle content of 5%) was obtained. A magnetic developer was prepared in the same manner as in Example 10 using the obtained magnetic toner, and an image development test was conducted in the same manner as in Example 10 using the prepared magnetic developer. The results are shown in Table 7.

Comparative Example 6 A weight average particle diameter of 14 μm (particle diameter 12.7) was used in the same manner as in Example 9 except that the magnetic iron oxide 1 of Production Example 1 and Wax A were used.
A magnetic toner having a magnetic toner particle content of 60 μm or more) was obtained, a magnetic developer was prepared in the same manner as in Example 9, and an image development test was conducted in the same manner as in Example 9. The results are shown in Table 7.

As compared with the magnetic developer of Example 9, the dot reproducibility was inferior, and the toner was found to be hitch.

[0292]

[Table 7]

[0293]

According to the present invention, the magnetic iron oxide characterized by the intra-particle distribution of the elemental silicon is added to have a weight average particle diameter of 2.5-1.
When used in a substantially spherical toner directly obtained by a suspension polymerization method having a fine particle diameter of 0 μm, the developing characteristics of the magnetic toner can be improved. Further, it is possible to obtain a toner having excellent fixability.

Further, the present invention stably supplies a highly durable and highly reproducible image free from fogging and scattering without the developer sticking to the developer carrier even under the developing conditions for achieving low potential development. it can.

Further, in the present invention, when a specific magnetic iron oxide and a specific hydrocarbon wax are used in a magnetic toner at the same time, the magnetic toner is provided with preferable thermal characteristics, and environmental stability and developability are improved. Therefore, it is possible to provide a magnetic toner excellent in durability against a temperature rise of a machine body such as a copying machine or a printer.

[Brief description of drawings]

FIG. 1 is a diagram showing a dissolution curve of magnetic iron oxide.

FIG. 2 is a schematic view of magnetic iron oxide particles for explaining the distribution of a silicon compound.

FIG. 3 is a schematic view showing a specific example of an image forming apparatus (comprising an elastic blade) used in the present invention.

FIG. 4 is a schematic explanatory view showing a specific example of an image forming apparatus (comprising an elastic blade) used in the present invention.

FIG. 5 is a schematic explanatory view showing a specific example of an apparatus unit used in the present invention.

FIG. 6 is a block diagram showing a specific example of a facsimile apparatus of the present invention.

FIG. 7 is an explanatory diagram of a checker pattern for testing the developing characteristics of magnetic toner.

FIG. 8 is a schematic diagram showing a developing / transferring process of the image forming method of the present invention.

FIG. 9 is a diagram showing a pattern of developing bias in the image forming method of the present invention.

FIG. 10 is a diagram showing a DSC curve when the temperature of wax A is raised.

11 is a diagram showing a DSC curve when the temperature of Wax A is decreased. FIG.

FIG. 12 is a diagram showing a DSC curve when the temperature of wax E is raised.

FIG. 13 is a diagram showing a DSC curve when the temperature of wax E is lowered.

FIG. 14 is a schematic explanatory diagram illustrating a specific example of a fixing device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Developing device 2 Developer container 3 Latent image carrier 4 Transfer means 5 Laser light or analog light 6 Developing sleeve 7 Heating / pressurizing fixing means 8 Cleaning blade 9 Elastic blade 11 Charger 12 Bias applying means 13 Magnetic developer 14 Cleaning means 15 magnetic field generating means 19 erase exposure 21 electrostatic latent image carrier 23 developer regulating member 24 magnet roll 25 developer carrier 41 heating body 42 film 43 pressure member 44 unfixed image

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication location G03G 9/08 384 (72) Inventor Takao Ishiyama 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon (72) Inventor Takehiko Chiba 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Koichi Tomiyama 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. ( 72) Inventor Hiroshi Yusa 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Naofuni Kobori 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Invention Person Motoki Hisaki 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Hirohide Tanikawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Non non corporation

Claims (12)

[Claims] 1. A magnetic toner containing at least a binder resin, a release agent and magnetic iron oxide, wherein the magnetic toner has a weight average particle diameter of 2.5 to 10 μm, and the magnetic iron oxide is The content of the silicon element in the iron oxide is 0.5 to 4% by weight based on the iron element, and the content B of the silicon element in which the iron element dissolution rate of the magnetic iron oxide is up to 20% by weight, The ratio (B / A) of the magnetic iron oxide to the total content of silicon element A (B / A) × 100 is 44 to 84%, and the content C of silicon element present on the surface of the magnetic iron oxide and the content A Ratio (C / A) x 100 is 10-55
%, And the magnetic toner is substantially spherical particles directly obtained by a suspension polymerization method. 2. Magnetic iron oxide has a charging property of -25 to -70.
μC / g, volume resistivity 5 × 10 ³ to 1 × 10 ⁸ Ω ・
The magnetic toner of claim 1 having a cm. 3. The magnetic toner according to claim 1, wherein the magnetic iron oxide has an aggregation degree of 3 to 40%. 4. The magnetic iron oxide has a smoothness (D) of 0.2 to.
The magnetic toner according to claim 1, which has 0.6. 5. The magnetic toner according to claim 1, wherein the magnetic iron oxide has a sphericity (Ψ) of 0.8 or more. 6. The JIS center line average roughness (Ra) of the developer carrying member is 1.0 μm or less, the alternating voltage Vpp applied to the developer carrying member is 1500 V or more, and the frequency is 2100 Hz or less. , The absolute value (V _cont. ) Of the difference between the DC voltage (V _dc ) and the charging potential (Vd) of the electrostatic latent image carrier _.
In the image forming method including a developing device having a voltage of 250 V or less and a developing step of developing with a developer, the developer is a magnetic developer containing at least a binder resin and magnetic iron oxide, and the magnetic iron oxide is The content of silicon element in the magnetic iron oxide is 0.5 to 4% by weight based on the iron element, and the content B of silicon element in which the dissolution rate of the iron element in the magnetic iron oxide is up to 20% by weight. And the ratio (B / A) × 100 of the total content A of silicon element of the magnetic iron oxide is 44 to 84%, and the content C of silicon element present on the surface of the magnetic iron oxide and the content Ratio with amount A (C / A) x 100 is 10-55
% Is an image forming method. 7. A magnetic toner containing at least a binder resin, a magnetic iron oxide and a hydrocarbon wax, wherein the magnetic toner has a weight average particle diameter of 13.5 μm or less. The content of the magnetic toner particles having a particle diameter of 12.7 μm or more is 50% by weight or less, and the magnetic iron oxide has a silicon element content of 0.5 to 4 based on the iron element. The ratio (B / A) of the content B of the silicon element present in the magnetic iron oxide having an iron element dissolution rate of up to 20% by weight and the total content A of the silicon element of the magnetic iron oxide. X100 is 44 to 84%, and the ratio (C / A) of the content C of the silicon element present on the surface of the magnetic iron oxide to the content A (C / A) x100 is 10 to 55.
% In the DSC curve measured by a differential scanning calorimeter with respect to the endothermic peak at the time of temperature increase and the exothermic peak at the time of temperature decrease, the onset temperature of the endothermic peak being in the range of 50 to 90 ° C. There, there is at least one endothermic peak P ₁ in the region of the temperature 90 to 120 ° C., there is a maximum exothermic peak at the time of cooling in the range of endothermic peak temperature ± 9 ° C. peak P _1, characterized in that Magnetic toner. 8. Magnetic iron oxide has charging characteristics of -25 to -70.
Having μC / g, volume resistivity value 5 × 10 ³ to 1 × 10
The magnetic toner according to claim 7, having ⁸ Ω · cm. 9. The magnetic toner according to claim 7, wherein the magnetic iron oxide has an aggregation degree of 3 to 40%. 10. The magnetic iron oxide has a smoothness (D) of 0.2 to.
The magnetic toner according to claim 7, having 0.6. 11. The magnetic toner according to claim 7, wherein the magnetic iron oxide has a sphericity (Ψ) of 0.8 or more. 12. The magnetic toner has a weight average particle diameter of 3.5 to 3.5.
The magnetic toner according to claim 7, which has a thickness of 13.5 μm.