JP2001318488A - Magnetic toner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic toner having excellent moisture resistance, extremely easy adjustment of charging characteristics, and excellent photoreceptor polishing ability with few image defects. . SOLUTION: In a magnetic toner including at least toner particles comprising magnetic powder and a binder resin, and an external additive,
It contains the following components (A), (B) and (C) as external additives. (A) hydrophobic silica (B) low-resistance conductive abrasive particles having a specific resistance of less than 500 Ω · cm (C) high-resistance conductive abrasive particles having a specific resistance of 500 Ω · cm or more

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic toner, and more particularly, to a magnetic toner used in an electrophotographic method, an electrostatic recording method, an electrostatic printing method, etc. employed in a copying machine or a laser printer. About.

[0002]

2. Description of the Related Art Conventionally, examples of magnetic toners used in electrophotography and the like are disclosed in JP-A-52-135739 and JP-A-56-123550. It has been proposed to add, as an external additive, silica fine powder surface-treated with an aminosilane compound or the like at a ratio of 0.05 to 5% by weight to toner particles.

Japanese Patent Application Laid-Open No. 5-119616 discloses an antimony-doped tin oxide fine powder having a specific resistance of 10 Ω · cm or less on the surface of 100 parts by weight of toner base particles for the purpose of obtaining sufficient conductivity. An electrophotographic toner in which a powder or a titanium oxide fine powder having a specific resistance of 50 Ω · cm or less and a conductive film made of antimony-doped tin oxide is adhered at a rate of 0.05 to 5 parts by weight. It has been disclosed.

Japanese Patent Application Laid-Open No. 7-72650 discloses that
At least one selected from silica, titanium oxide, and alumina is used in an amount of 0.05 to 100 parts by weight of the toner particles.
There is disclosed a positively charged electrophotographic developer obtained by adding about 2 parts by weight and 0.05 to 3 parts by weight of magnetite having an ionization potential of 4.9 eV or less.

[0005]

SUMMARY OF THE INVENTION However, Japanese Patent Application Laid-Open Nos.
The magnetic toner disclosed in Japanese Patent Laid-Open Publication No. H06-27139 introduces an amino group which is a hydrophilic polar group on the surface of the silica fine powder, and thus still has poor moisture resistance, under a high-temperature and high-humidity environment, for example, at 33 ° C.
Under the condition of 85% RH, problems such as a decrease in the fluidity of the magnetic toner and a difficulty in adjusting the charging characteristics, resulting in a decrease in image density were observed. Further, a problem of deterioration of storage characteristics in the toner container and the developing device was also observed.

The magnetic toner (toner for electrophotography) disclosed in Japanese Patent Application Laid-Open No. 5-119616 has a poor charge rising property and poor moisture resistance and durability. In this case, problems such as a decrease in the fluidity of the toner and difficulty in adjusting the charging characteristics were observed. In addition, in order to adjust the charging characteristics, a specific antimony-doped tin oxide fine powder or a titanium oxide fine powder having a conductive film made of antimony-doped tin oxide formed on the surface must be used. 1
Extremely strict restrictions such as a value of 0 Ω · cm or less were observed.

Further, the magnetic toner (positively charged electrophotographic developer) disclosed in Japanese Patent Application Laid-Open No. 7-72650
Magnetite treated with an aminosilane coupling agent or the like is used to adjust the ionization potential, and its moisture resistance is poor. Therefore, in a high-temperature and high-humidity environment, the fluidity of the magnetic toner decreases and it is difficult to adjust the charging characteristics. And other problems. In addition, since magnetite cannot exert a polishing effect on the photoreceptor, there has been a problem that toner adhesion, image deletion, and the like are likely to occur. Further, when silica is added, there is also a restriction that a surface treatment for positive charging must be performed.

Accordingly, the present invention has been made to solve the above-mentioned problem. The present invention is directed to a method in which a hydrophobic silica (component (A)), which is a non-conductive abrasive particle, and a toner having a specific resistivity are used. By adding at least three or more kinds of conductive abrasive particles (components B and C), the specific resistance is 10 Ω.
・ It is excellent in moisture resistance and durability, and is easy to adjust the charging characteristics, without imposing restrictions such as the necessity of using antimony-doped tin oxide fine powder of cm or less. It is an object of the present invention to provide a magnetic toner having less image defects and capable of exhibiting excellent polishing ability against the toner.

[0009]

According to the present invention, there is provided a magnetic toner comprising at least toner particles comprising magnetic powder and a binder resin and an external additive, wherein the external additive comprises the following component (A): A magnetic toner containing the components (B) and (C) is provided, and the above-mentioned problem can be solved. (A) hydrophobic silica (B) low-resistance conductive abrasive particles having a specific resistance of less than 500 Ω · cm (C) high-resistance conductive abrasive particles having a specific resistance of 500 Ω · cm or more That is, having a specific specific resistance (B) component and (C)
By containing the components, the adjustment of the charging characteristics becomes easy. Further, by containing hydrophobic silica as non-conductive abrasive particles as the component (A), the moisture resistance and durability of the magnetic toner can be improved. Further, by adding such three types of abrasive particles, it is possible to exert excellent polishing ability on the photoreceptor, and therefore, image defects can be significantly reduced.

In constituting the magnetic toner of the present invention, the addition ratio of the component (B) to the component (C) is set to a value within a range of 1: 1 to 1: 5 by weight. Is preferred. By adjusting the addition ratio of the component (B) and the component (C), it is easier to adjust the charging characteristics of the magnetic toner.

In constituting the magnetic toner of the present invention, the component (B) is, for example, tin oxide, more preferably tin oxide doped with antimony (SnO ₂ / Sb).
It is preferable that the conductive layer is made of titanium oxide particles formed on the surface, and the component (C) is a titanium oxide particle that has been treated with a titanate-based coupling agent. With the component (B) and the component (C), an excellent polishing effect can be exhibited, and the adjustment of the specific resistance becomes easier.

Further, in constituting the magnetic toner of the present invention, the hydrophobicity of the hydrophobic silica as the component (A) is set to 40.
% Is preferable. By limiting the degree of hydrophobicity of the component (A) in this manner, the moisture resistance and durability of the magnetic toner can be further improved. The degree of hydrophobicity of the hydrophobic silica can be defined by the number of methanol described later.

Further, in constituting the magnetic toner of the present invention, it is preferable that the amount of the external additive to be added is within a range of 0.5 to 10 parts by weight based on 100 parts by weight of the toner particles. By adjusting the amount of the external additive to be added, the balance between the adjustment of the charging characteristics of the magnetic toner and the improvement of the moisture resistance and the durability, and the balance between these characteristics and the expression of the polishing effect can be improved. Can be improved.

In constituting the magnetic toner of the present invention, the average particle size of the component (B) is set to a value within the range of 0.01 to 3 μm, and the average particle size of the component (C) is set to 0.05. ~ 5
It is preferable that the value be in the range of μm. By each having such an average particle diameter, the component (B) and the component (C) easily adhere to the periphery of the toner particles, and the charging characteristics of the magnetic toner and the adjustment of the polishing force on the photoreceptor are easier. Becomes

Further, in constituting the magnetic toner of the present invention, the average particle diameter of the toner particles is d1 (μm),
When the average particle diameter of the component (A) is d2 (μm), the average particle diameter of the component (B) is d3 (μm), and the average particle diameter of the component (C) is d4 (μm), It is preferable to satisfy the relation of magnitude. d1> d4 ≧ d3> d2 By satisfying such a magnitude relation, the component (B) and the component (C) are more likely to adhere around the toner particles, and the component (A) is more likely to adhere around the toner particles. Not only that, it also easily adheres to the periphery of the component (B) and the component (C), so that it is possible to further improve the balance between adjustment of charging characteristics and improvement of moisture resistance. In addition, since there are three types of abrasive particles having different average particle diameters, it is possible to exert excellent polishing ability on the photoreceptor and reduce image defects (non-uniformity of image density and occurrence of fog). Can be.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in the conceptual diagram of FIG. 1, in the embodiment of the present invention, a magnetic toner 18 containing at least toner particles 10 composed of a magnetic powder and a binder resin, and an external additive.
Wherein, as the external additive, the following component (A) 16,
The magnetic toner 18 contains the component (B) 14 and the component (C) 12. (A) component: hydrophobic silica which is non-conductive abrasive particles (B) component: low-resistance conductive abrasive particles having a volume resistance of less than 500 Ω · cm (C) component: high resistance having a volume resistance of 500 Ω · cm or more Resistive conductive abrasive particles Hereinafter, the embodiment of the present invention will be described as a one-component magnetic toner without using a carrier, but the present invention is not limited to this. It is also preferable to configure as a magnetic toner.

[1] Toner particles Constituent Materials (1) Binder Resin Preferable binder resins constituting toner particles include polystyrene resins such as polystyrene, styrene-butadiene copolymer and styrene-acryl copolymer, polyethylene, ethylene-vinyl acetate copolymer, and ethylene. -Ethylene copolymers such as vinyl alcohol copolymers, epoxy resins, phenolic resins, acrylic phthalate resins, polyamide resins, polyester resins, and maleic acid resins can be used. However, the wax component described later, the dispersibility of pigments and the like is more favorable,
In addition, it is more preferable to use a polyester resin or a styrene-acryl copolymer as a binder resin because of its excellent durability as toner particles.

(2) Wax Component Examples of the wax component to be blended into the toner particles include polyethylene wax, polypropylene wax, modified polypropylene, and polyester wax. The molecular weight of the wax component is determined in consideration of the releasability of the toner particles from the fixing roll and the ease of handling. For example, the weight average molecular weight in terms of polystyrene measured by GPC is 1,000 to 40, Preferably, the value is in the range of 000. The reason for this is that when the weight average molecular weight of the wax component is less than 1,000,
This is because handling may be difficult, bleeding may be easy, or affinity between the toner particles and the coating layer of the carrier may be improved, and spent may easily occur. On the other hand, when the weight average molecular weight of the wax component is 4
If it exceeds 000, the releasability of the toner particles from the fixing roll may be reduced, or it may be difficult to uniformly mix the toner particles. Therefore, the weight average molecular weight of the wax component is more preferably set to a value within the range of 5,000 to 30,000, because the balance between the releasability and the handleability of the toner particles with respect to the fixing roll becomes better. , Weight average molecular weight of 80,000 to 20,0,0
More preferably, the value is in the range of 00.

The amount of the wax component is preferably in the range of 0.1 to 5% by weight based on the total amount of the toner particles. This is because if the amount of the wax component is less than 0.1% by weight, the adhesion of the toner particles to the fixing roller may not be sufficiently prevented. If the content exceeds 5% by weight, it may be difficult to uniformly disperse it in the binder resin. Therefore, the balance between the anti-adhesion property of the toner particles to the fixing roller and the dispersibility becomes better, so that the addition amount of the wax component is 0.5 to
More preferably, the value is within the range of 3% by weight.
More preferably, the value is in the range of 8 to 2% by weight.

(3) Magnetic Powder Ferrite, magnetite, ferromagnetic ferrite and the like can be mentioned as the magnetic powder to be added to the toner particles. Also,
The shape of the magnetic powder is not particularly limited, either, and may be spherical or irregular. The average particle size of the magnetic powder is not particularly limited, but is preferably, for example, a value in the range of 0.05 to 0.5 μm. The reason is that the average particle size of the magnetic powder is 0.
When the average particle diameter is less than 0.5 μm, fog may easily occur.
This is because if the value exceeds, the transportability may be reduced, and the image quality characteristics may be deteriorated (image density may be reduced). Also, if the particles are too large, the charging characteristics of the toner tend to be charged up, and if the particles are too small, charging tends to be poor. Therefore, the average particle size of the magnetic powder is 0.10 to 0.10.
More preferably, the value is in the range of 0.40 μm,
More preferably, the value is in the range of 0.15 to 0.25 μm.

The amount of the magnetic powder to be added to the toner particles is 30 to 70% by weight based on the total amount of the toner particles.
It is preferable to set the value within the range. The reason for this is that if the amount of the magnetic powder is less than 30% by weight, the transportability of the magnetic toner may be reduced. On the other hand, if the amount of the magnetic powder exceeds 70% by weight. This is because it may be difficult to uniformly disperse the binder resin in the binder resin. Therefore, the amount of the magnetic powder to be added is more preferably in the range of 35 to 60% by weight, and more preferably in the range of 40 to 50% by weight, based on the total amount of the toner particles. preferable.

(4) Colorant It is preferable to add a colorant, for example, a pigment in order to impart color development and durability to the toner particles.
Such pigments include, for example, carbon black,
Phthalocyanine blue, induslen blue, peacock blue, permanent red, bengala, alizanin lake, chrome green, malachite green lake,
Methyl violet lake, Hansa Yellow, Permanent Yellow, titanium oxide and the like may be used alone or in combination of two or more.

The amount of the colorant to be added to the toner particles is 0.1 to 5% by weight based on the total amount of the toner particles.
It is preferable to set the value within the range. The reason for this is that if the amount of the colorant is less than 0.1% by weight, the color developability and durability may not be exhibited, while the amount of the colorant may be 5% by weight. If the amount exceeds the above range, it may be difficult to uniformly disperse the binder resin in the binder resin or the heat resistance may decrease. Therefore, the amount of the colorant to be added is 0.5 to 0.5% of the total amount of the toner particles.
More preferably, the value is in the range of 3.5% by weight.
More preferably, the value is in the range of 1.0 to 3.0% by weight.

(5) Charge Control Agent Further, it is preferable to add a charge control agent such as a positive charge control agent or a negative charge control agent to the toner particles because the charge polarity can be easily controlled. Such positive charge control agents include, for example, quaternary ammonium compounds, nigrosine compounds,
Nigrosine base compound, triphenylmethane compound,
One kind of polyvinylpolyzine and the like or a combination of two or more kinds may be mentioned. In addition, as a negative charge control agent,
Metal complexes of alkyl-substituted salicylic acids, for example di-te
chromium complex salts of rt-butylsalicylic acid, di-tert
And zinc complex salts of -butylsalicylic acid.

(6) Fluidizer A fluidizer is preferably added to the toner particles in order to improve the fluidity of the magnetic toner. Examples of such a fluidizing agent include one kind alone or a combination of two or more kinds such as tetrafluoroethylene (Teflon (registered trademark)), zinc stearate, and polyvinylidene fluoride.

2. Average Particle Size of Toner Particles The average particle size of the toner particles is not particularly limited, either.
The following values are preferred. The reason for this is that if the average particle size of the toner particles exceeds 20 μm, the transportability may decrease or so-called fog may occur. Therefore, the average particle size of the toner particles is 3 to 18
More preferably, the value is in the range of 5 μm.
More preferably, the value is in the range of μm.

3. Method for Producing Toner Particles The toner particles of the present invention can be produced by a known method, for example, by using a suspension polymerization method, a pulverization method, a microcapsule method, a spray drying method, or a mechanochemical method. Is preferred. That is, as an example, it is preferable that the constituent materials of the toner particles are sufficiently mixed by a high-speed mixer or the like, then kneaded by an extruder or the like, pulverized and classified to obtain toner particles having an average particle diameter in a predetermined range.

[2] External additive (A) Component type In the present invention, as an external additive of toner particles,
It is necessary to add hydrophobic silica particles as the component (A). This is because the addition of the component (A) improves the moisture resistance and durability of the magnetic toner, increases the fluidity, and facilitates the control of the charging property. That is,
The mere addition of the conductive abrasive particles of the component (B) and the component (C) described below results in poor moisture resistance and durability of the magnetic toner, and also makes it difficult to control the chargeability, resulting in an increase in image density. It is because it becomes low.

As the component (A) as the hydrophobic silica, a commercially available product can be used.
R81 manufactured by Nippon Aerosil Co., Ltd.
And RY20 (trade name, both having a degree of hydrophobicity of about 70), commercially available products such as 2000 and 2000/4 (trade name, both having a degree of hydrophobicity of about 70) manufactured by Wacker Chemicals. Further, when increasing the charge amount of the positively charged toner, it is preferable to use silica particles having negative charge characteristics, and when increasing the charge amount of the negatively charged toner, it is preferable to add silica particles having positive charge characteristics. . When the charge amount of the magnetic toner is reduced, it is preferable to use silica particles having the same polarity as the magnetic toner.

The degree of hydrophobicity of the component (A) is preferably at least 40%. The reason is that if the degree of hydrophobicity is less than 40%, the improvement of the moisture resistance of the toner particles becomes insufficient. Therefore, it is more preferable that the degree of hydrophobicity of the component (A) is 50% or more, and it is further preferable that the degree of hydrophobicity of the component (A) is 60% or more. On the other hand, when the degree of hydrophobicity of the component (A) is 95% or more, the surface treatment time may be remarkable, or the surface treatment agent may peel off in a short time. Therefore, it is more preferable to set the degree of hydrophobicity of the component (A) to a value within the range of 40 to 95%.

The degree of hydrophobicity of the component (A) is as follows.
It can be defined as the number of methanol represented by the following formula measured by the so-called methanol method. Methanol number (%) = [(a) / (50 + a)] × 10
0a: Amount of methanol (ml) required to completely bring silica particles into a wet state More specifically, 0.2 g of silica particles was added to 50 ml of distilled water to form a mixture, and this mixture was stirred with a stirrer. The methanol was titrated with stirring (10 ppm). The amount of methanol required until the silica particles were completely wetted and precipitated was the amount a (ml).

The method for hydrophobizing the component (A) is not particularly limited. For example, an alkoxysilane coupling agent or an aluminum silane coupling agent is used to apply a surface treatment to silica particles. Is preferably applied. By adopting such a surface treatment method, the degree of hydrophobicity can be easily adjusted, and the silica particles and the alkoxysilane coupling agent are firmly bonded. The value of the degree of conversion can be maintained. In addition, since it exhibits particularly excellent hydrophobicity even in a small amount and can maintain a predetermined value of the degree of hydrophobicity for a long time, γ-glycidoxypropylmethyldimethoxysilane or γ-glycidoxypropylmethyldimethoxysilane can be used as an alkoxysilane coupling agent. -It is preferable to use glycidoxypropyltrimethoxysilane and the like.

Average Particle Size The average particle size of component (A) (sometimes referred to as d2) is preferably set to a value of 40 nm or less as a primary particle size. The reason is that the primary particle size of the component (A) is 40%.
If the thickness exceeds nm, the gap between the hydrophobic silica particles becomes large, and the effect of improving the fluidity of the magnetic toner may not be exhibited. Therefore, the average particle size of the component (A) is preferably set to a value in the range of 5 to 35 nm, and more preferably to a value in the range of 10 to 30 nm.

Addition Amount of the component (A) to be externally added to the toner particles is preferably in a range of 0.05 to 3.0% by weight based on the total amount of the toner particles. . This is because (A)
If the amount of the component is less than 0.05% by weight, the moisture resistance and the fluidity of the magnetic toner may not be improved, while the amount of the component (A) is 3.0% by weight. %, It becomes difficult not only to adjust the charge of the toner particles but also to increase the cost. Therefore, it is more preferable that the amount of the component (A) is in the range of 0.2 to 2.0% by weight based on the total amount of the toner particles, and 0.5 to 1.5% by weight. It is more preferable to set the value within the range.

2. (B) Component Type The low-resistance conductive abrasive particles of the component (B) are 500Ω.
Any type of conductive abrasive particles having a specific resistance of less than cm can be used, for example,
Titanium oxide particles having a conductive layer made of tin oxide formed on the surface are preferable. This is because such titanium oxide particles can exhibit excellent polishing effects and chargeability controllability, and also have excellent durability.
Also, the method for forming the conductive layer is not particularly limited, but a solution in which conductive fine particles are dispersed in a binder resin is applied to the surface of the core material by spray coating, dipping, or the like. Can be formed. Further, it is also possible to form the conductive layer by bringing the core material, the conductive fine particles and the binder resin into a solution state and kneading and pulverizing them.

Resistance value The specific resistance of the component (B) is set to a value of less than 500 Ω · cm, together with the component (C).
When the specific resistance is not less than cm, it may be difficult to adjust the charge amount of the toner particles. on the other hand,
When the specific resistance of the component (B) is less than 1 Ω · cm, (B)
It has been found that it may be difficult to obtain the components or the resistance may be too low to make it difficult to adjust the charge amount of the toner particles. Therefore, more preferably, the specific resistance of the component (B) is set to a value within a range of 1 to less than 500 Ω · cm, and further preferably,
The specific resistance of the component (B) is set to a value within a range of 20 to 300 Ω · cm.

Addition Amount of the component (B) is preferably in the range of 0.05 to 2.0% by weight based on the total amount of the toner particles. The reason for this is that if the amount of the component (B) falls outside these ranges, it may be difficult to adjust the charge amount of the toner particles due to the relationship with the amount of the component (C) added. Because there is. Therefore, the addition amount of the component (B) is 0.1 to 1.0 with respect to the total amount of the toner particles.
%, More preferably within a range of 0.2% by weight.
More preferably, the value is in the range of 0.8% by weight.

It is preferable that the amount of the component (B) is determined in consideration of the amount of the component (C). That is,
The addition ratio of the component (B) and the component (C) is expressed in terms of weight ratio,
It is preferable to set the value in the range of 1: 1 to 1: 5. The reason is that the addition ratio of the component (B) and the component (C) is
If the values are outside these ranges, it may be difficult to adjust the charge amount of the toner particles even when the component (B) and the component (C) are combined. Therefore, the addition ratio of the component (B) and the component (C) is
It is more preferable that the weight ratio be in the range of 1: 2 to 1: 4.

Average Particle Size The average particle size of the component (B) (sometimes referred to as d3) is preferably set to a value within a range of 0.01 to 3 μm as a primary particle size. The reason for this is that if the average particle diameter of the component (B) is less than 0.01 μm, it becomes difficult to adjust the chargeability of the magnetic toner or to handle the magnetic toner even when it is combined with the component (C). This is because there are cases. Therefore, the average particle size of the component (B) is set to 0.1.
It is preferable that the value be in the range of 0.5 to 2 μm.
More preferably, the value is in the range of 1 to 1 μm.

3. (C) Component Type The high resistance conductive abrasive particles as the component (C) include 50
Any kind of conductive abrasive particles having a specific resistance of 0 Ω · cm or more can be used, but for example, titanium oxide particles that have been surface-treated using a titanate-based coupling agent are preferable. . This is because titanium oxide particles subjected to such a hydrophobic treatment can exhibit excellent polishing effect and charge controllability, and also have excellent durability. The method of the hydrophobization treatment is not particularly limited, but a solution in which a titanate coupling agent is dissolved in an organic solvent or water is prepared, and spray coating is performed on the surface of the titanium oxide particles. It can be formed by applying using dipping or the like. Further, in the hydrophobizing treatment, the titanium oxide particles and the titanate-based coupling agent are reacted at 50 to 170 ° C. for 1 minute to ensure a reaction.
The heat treatment is preferably performed for 24 hours.

Resistance value The specific resistance of the component (C) is set to a value of 500 Ω · cm or more because both the component (B) and the component (B) have a specific resistance of 500 Ω · c.
When the specific resistance is less than m, it is difficult to adjust the charge amount of the toner particles. On the other hand, if the specific resistance of the component (C) exceeds 100 MΩ · cm, it is difficult to obtain the component (C) or the specific resistance is too high, and it is difficult to adjust the charge amount for the toner particles. This is because it may be. Therefore, more preferably, the specific resistance of the component (C) is set to a value within the range of 1 to 100 MΩ · cm, and still more preferably, the specific resistance of the component (C) is set to 3 to 50 MΩ · cm. Value within the range.

Addition Amount of the component (C) is preferably in the range of 0.05 to 5.0% by weight based on the total amount of the toner particles. The reason for this is that if the amount of the component (C) is out of these ranges, it may be difficult to adjust the charge amount of the toner particles due to the relationship with the amount of the component (B). Because there is. Therefore, the addition amount of the component (C) is 1.5 to 4.5 with respect to the total amount of the toner particles.
%, More preferably within a range of 2.5% by weight.
More preferably, it is set to a value within the range of 4.0% by weight.

Average Particle Size The average particle size (sometimes referred to as d4) of the component (C) is preferably set to a value within a range of 0.05 to 5 μm as a primary particle size. The reason for this is that if the average particle diameter of the component (C) is less than 0.05 μm, it becomes difficult to adjust the chargeability of the magnetic toner and to handle the magnetic toner, even when combined with the component (B). On the other hand, if the average particle size of the component (C) exceeds 5 μm, it may adhere to the toner particles, making it difficult to control the chargeability. Therefore,
The average particle size of the component (C) is preferably in the range of 0.1 to 3 μm, more preferably 0.2 to 2 μm.

4. Addition amount The addition amount of the external additive, that is, the total amount of the components (A), (B), and (C) is 0.5 to 10 parts by weight based on 100 parts by weight of the toner particles. It is preferable to set the value within the range. By adjusting the amount of the external additive to be added, the balance between the adjustment of the charging characteristics of the magnetic toner and the improvement of the moisture resistance and the durability, and the balance between these characteristics and the expression of the polishing effect can be improved. Can be improved. Therefore, it is more preferable that the amount of the external additive be in the range of 1 to 5 parts by weight, and more preferably in the range of 1.2 to 3 parts by weight, based on 100 parts by weight of the toner particles. Is more preferred.

[0045]

EXAMPLES Example 1 (1) Production of Toner Particles In the production of toner particles, the following materials were thoroughly mixed by a high-speed mixer, kneaded, pulverized, classified, and a toner having an average particle diameter of 10 μm was obtained. Obtained. Styrene-n-butyl acrylate copolymer 93% by weight (copolymerization ratio 80/20) Carbon black 4% by weight (manufactured by Mitsubishi Kasei Kogyo Co., Ltd., MA-100 (trade name)) Quaternary ammonium salt 2% by weight 1% by weight of polypropylene wax (NP-055 (trade name), manufactured by Mitsui Chemicals, average weight molecular weight about 10,000)

(2) Production of Magnetic Toner The toner particles obtained in (1) and the following external additives were uniformly mixed with a mixer to obtain a magnetic toner. Toner particles 100 parts by weight Hydrophobic silica 1 part by weight (R812 (trade name, manufactured by Nippon Aerosil Co., Ltd., degree of hydrophobicity: 70)) Low-resistance conductive abrasive particles 1.0 part by weight (a conductive layer made of tin oxide is formed on the surface) Titanium oxide particles, specific resistance 22.5 Ω · cm, average particle size (primary) 0.13 μm) high-resistance conductive abrasive particles 0.4 parts by weight (titanium oxide particles treated with a titanate coupling agent, specific resistance 10) 0.9 MΩ · cm, average particle size (primary) 0.25 μm)

(3) Measurement of Image Density Image density was measured with a Macbeth densitometer. That is,
In measuring the image density, 400 g of the developer of Example 1 was placed in a printer modified from Ecosys FS-3700 (trade name) manufactured by Kyocera Corporation, and the surface potential was set to 25.
The actual marking was performed on A4 paper under the conditions of 0 V and the bias voltage fixed at 180 V, respectively. And early,
After printing 300,000 sheets, and under high temperature and high humidity conditions (33 ° C, 80%
RH), the image density of the solid screen obtained at the time of printing was measured using a Macbeth densitometer. Table 2 shows the obtained results.
And FIG.

(4) Uniformity of Image Density The uniformity of image density was visually evaluated. That is, when measuring the uniformity of the image density, 400 g of the developer of Example 1 was stored in a printer modified from Ecosys FS-3700 (trade name) manufactured by Kyocera Corporation, and the surface potential was set to 250 V. The actual printing was performed on A4 paper under the condition that the bias voltage was fixed at 180 V. Then, after initial printing of 300,000 sheets, and under high temperature and high humidity conditions (33
℃, 80% RH)
The uniformity of the image density was evaluated according to the following criteria. Table 2 shows the obtained results. ：: Image density is recognized to be uniform. Δ: The image density is recognized to be slightly uneven. X: It is recognized that there is significant unevenness in image density.

(5) Fogging Measurement The fogging property in the image was visually evaluated. That is, in evaluating the fogging property, a solid screen similar to that used for evaluating the uniformity of the image density was prepared, and evaluated according to the following criteria. Table 2 shows the obtained results. ：: No fog is visually observed. Δ: Fog is slightly observed visually. ×: Remarkable fog is visually observed.

[0050]

[Table 1]

[0051]

[Table 2]

Example 2 In Example 2, the effect of the addition ratio of the low-resistance conductive abrasive particles (B) and the high-resistance conductive abrasive particles (C) was examined. That is, in Example 1, the addition ratio of the low-resistance conductive abrasive particles to the high-resistance conductive abrasive particles was 0.4 part by weight: 1.
Magnetic toner particles were prepared in the same manner as in Example 1 except that the parts by weight were changed to 0.7 parts by weight: 0.7 parts by weight, and the image density, the uniformity of the image density, and the fogging property were evaluated. . The results obtained are shown in Table 1 and FIG. As understood from these results, the low-resistance conductive abrasive particles (B
Component) and high-resistance conductive abrasive particles (Component C), the initial image density tended to be slightly higher at 1: 1 than at 1: 0.4.

Example 3 In Example 3, the influence of the average particle size on the high-resistance conductive abrasive particles was examined. That is, in Example 1, the average particle diameter of the high-resistance conductive abrasive particles as the component (C) was from 0.25 μm to 0.1 μm.
Except that m was changed, magnetic toner particles were prepared in the same manner as in Example 1, and the image density, the uniformity of the image density, and the fogging property were evaluated. Table 1 shows the obtained results. As understood from these results, the average particle size of the high-resistance conductive abrasive particles (C component) is more than 0.25 μm.
At 0.1 μm, the initial image density tended to be slightly higher.

[Examples 4 and 5] In Examples 4 and 5, low-resistance conductive abrasive particles as component (B) and (C)
The effect of the addition ratio with the high-resistance conductive abrasive particles as a component was studied. That is, in Example 4, the addition ratio of the low-resistance conductive abrasive particles to the high-resistance conductive abrasive particles was changed to 0.1 part by weight: 1 part by weight.
Except that the addition ratio of the low-resistance conductive abrasive particles and the high-resistance conductive abrasive particles was changed to 1.0 part by weight: 0.2 part by weight,
Magnetic toner particles were prepared in the same manner as in Example 1, respectively.
The image density, the uniformity of the image density, and the fogging property were evaluated. Table 1 shows the obtained results. As understood from these results, low-resistance conductive abrasive particles (component B)
And the addition ratio of the high-resistance conductive abrasive particles (component C) to 0.1: 1 or 1.0: 0.
In the case of No. 2, there was a tendency that the value of the image density was lower and the moisture resistance and the durability were lowered.

Comparative Example 1 In Comparative Example 1, the effect of adding high-resistance conductive abrasive particles as the component (C) was examined. That is, magnetic toner particles were prepared in the same manner as in Example 1 except that in Comparative Example 1, 1.4 parts by weight of low-resistance conductive abrasive particles were added and no high-resistance conductive abrasive particles were added. The density, the uniformity of the image density, and the fogging property were evaluated. Table 1 shows the obtained results. As understood from these results, the durability and the moisture resistance tended to be poor unless the high-resistance conductive abrasive particles as the component (C) were added.

Comparative Example 2 In Comparative Example 2, the effect of adding low-resistance conductive abrasive particles as the component (B) was examined. That is, in Comparative Example 2, magnetic toner particles were prepared in the same manner as in Example 1, except that 1.4 parts by weight of high-resistance conductive abrasive particles were added without adding low-resistance conductive abrasive particles. The density, the uniformity of the image density, and the fogging property were evaluated. Table 1 shows the obtained results. As understood from these results, a tendency that the fog property was particularly poor was observed when the low-resistance conductive abrasive particles (component B) were not added.

Comparative Example 3 In Comparative Example 3, the effect of adding low-resistance conductive abrasive particles as the component (B) and high-resistance conductive abrasive particles as the component (C) was examined. That is, a magnetic toner was prepared in the same manner as in Example 1 except that low-resistance conductive abrasive particles and high-resistance conductive abrasive particles were not added in Comparative Example 2, and image density, image density uniformity and The fog properties were evaluated respectively. Table 2 shows the obtained results. As understood from these results, the durability of the magnetic toner tends to be particularly poor unless the low-resistance conductive abrasive particles (component B) and the high-resistance conductive abrasive particles (component C) are added. .

Comparative Example 4 In Comparative Example 4, the effect of adding high-resistance conductive abrasive particles as the component (C) was examined. That is, in Comparative Example 4, insulating titanium oxide (a volume resistivity of 2.2 × 10 ¹¹⁾ was used instead of the high-resistance conductive abrasive particles.
Magnetic toner particles were prepared in the same manner as in Example 1 except that Ω · cm and the primary particle diameter was 0.10 μm), and the image density, the uniformity of the image density, and the fogging property were evaluated. Table 1 shows the obtained results. As understood from these results, even when insulating particles having a specific resistance of 100 MΩ · cm or more are added without adding the high-resistance conductive abrasive particles as the component (C), the durability of the magnetic toner can be improved. Tend not to improve.

[0059]

As described above in detail, according to the magnetic toner of the present invention, as the external additive, the component (A)
By using the components (B) and (C) in combination, the durability and the moisture resistance of the magnetic toner are improved, the printing durability is remarkably improved, and the adjustment of the charging characteristics is extremely easy. Therefore, conventionally, in order to obtain good charging characteristics, fine powder of antimony-doped tin oxide or the like having a specific resistance of 10 Ω · cm or less had to be added, but such a restriction was not required. Moreover, according to the magnetic toner of the present invention, the component (A) and the component (B)
A magnetic toner that can exhibit excellent polishing performance on a photoreceptor and contains few image defects (non-uniformity of image density and occurrence of fog) because it contains abrasive particles of the component and the component (C). Can now be offered.

[Brief description of the drawings]

FIG. 1 is a view schematically showing a magnetic toner of the present invention.

FIG. 2 is a diagram provided for comparing image densities in Examples 1 to 5 and Comparative Examples 1 to 4.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 toner particles 12 high-resistance conductive abrasive particles 14 low-resistance conductive abrasive particles 16 hydrophobic silica particles

Claims (7)

[Claims] 1. A magnetic toner comprising at least toner particles comprising magnetic powder and a binder resin and an external additive, wherein the external additive comprises the following components (A), (B) and (C): A magnetic toner characterized by containing. (A) hydrophobic silica (B) low-resistance conductive abrasive particles having a specific resistance of less than 500 Ω · cm (C) high-resistance conductive abrasive particles having a specific resistance of 500 Ω · cm or more 2. The method according to claim 1, wherein the addition ratio of the component (B) to the component (C) is a value within a range of 1: 1 to 1: 5 by weight. The magnetic toner as described in the above. 3. The component (B) is a titanium oxide particle having a conductive layer made of tin oxide formed on the surface thereof, and the component (C) is a titanium oxide particle treated with a titanate-based coupling agent. 3. A method according to claim 1, wherein
3. The magnetic toner according to item 1. 4. The magnetic toner according to claim 1, wherein the degree of hydrophobicity of the component (A) is set to 40% or more. 5. The toner according to claim 1, wherein the amount of the external additive is in a range of 0.5 to 10 parts by weight based on 100 parts by weight of the toner particles. The magnetic toner according to claim 1. 6. The component (B) having an average particle size of 0.01
The value according to any one of claims 1 to 5, wherein the average particle diameter of the component (C) is a value within a range of 0.05 to 5 µm. Magnetic toner. 7. An average particle diameter of the toner particles is d1 (μ
m), the average particle diameter of the component (A) is d2 (μm), the average particle diameter of the component (B) is d3 (μm), and the average particle diameter of the component (C) is d4 (μm). 7. The magnetic toner according to claim 1, wherein the following relationship is satisfied. d1> d4 ≧ d3> d2