JP2006308881A - Magnetic toner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide toner which is excellent in developing property and durability even at a high temperature and high humidity environment and forms an image with high picture quality. <P>SOLUTION: The magnetic toner comprises at least a binder resin and a magnetic powder. The toner particle show a dielectric loss tangent tanδ of 7.0×10<SP>-3</SP>or less at 5.0×10<SP>3</SP>Hz frequency and of 1.0×10<SP>-2</SP>to 1.4×10<SP>-2</SP>at 1.0×10<SP>5</SP>Hz frequency. Average circularity of the toner particles is 0.950 to 0.960. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a magnetic one-component toner for use in an image forming apparatus such as a copying machine, a printer, or a fax machine using an electrophotographic method or an electrostatic recording method.

  There are mainly one-component development method and two-component development method in the electrophotographic method, but one-component development because it has a simple structure, less trouble, long life and easy maintenance. A method is preferably used.

  In general, in a magnetic toner used in a one-component development system, a magnetic substance is included to make the toner magnetic. However, the magnetic substance affects the developability and durability of the magnetic toner. A number of proposals have been made regarding magnetic materials, including magnetic materials containing silicon and zinc (Patent Document 1) and magnetic materials containing silicon (Patent Document 2). Good developability is obtained.

  However, there are problems with developability and durability when used in high-temperature and high-humidity environments, when applied to high-speed machines, when the amount of copies becomes very large, or when used with positively charged magnetic toners. There is a need for improvement.

  In order to improve the developability and durability, it is important to sufficiently exhibit the performance of the magnetic material as the toner performance by uniformly dispersing the magnetic material in the toner. When the dispersion of the magnetic material is poor, the magnetic force of the toner varies, so that the formation of spikes on the developer carrying member can be uneven, the image uniformity is impaired, and the image quality is liable to be adversely affected. In addition, a toner containing a large amount of a magnetic substance is hard to be developed and accumulates on the developer carrying member for a long period of time, and inhibits frictional charging between the developer carrying member and other toners, resulting in toner charging failure. easy. In addition, the toner that does not contain much magnetic material jumps to the white background portion of the photoconductor and becomes image fogging, which easily lowers the image quality.

  Various proposals have been made on methods for controlling the dispersibility of the magnetic material in the toner. Among them, there are some proposals for controlling the dispersibility of the magnetic material by defining the dielectric loss tangent of the toner. For example, Patent Document 3 uses the dielectric loss tangent as an index of the degree of dispersion of the magnetic material, but does not show a method for improving the degree of dispersion of the magnetic material.

In Patent Document 4, the required dielectric loss tangent condition is satisfied by using a polyester resin as the binder resin. However, when the polyester resin is simply used, it is used for a positively chargeable magnetic toner. Causes problems in developability. In Patent Document 5, the dielectric loss tangent is controlled by heat-treating the surface of the toner. However, there is a problem in terms of cost, and the release agent component contained in the toner and the charge control by the surface heat-treatment are problematic. There is a problem in that the agent component oozes out on the surface and tends to adversely affect the developability and fixability.
JP-A-8-101529 JP-A-9-59025 JP-A-1-257968 Japanese Patent Laid-Open No. 4-124681 JP-A-6-51556

  An object of the present invention is to provide a toner that is excellent in developability and durability even under a high temperature and high humidity environment and that forms a high quality image.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have controlled the dielectric loss tangent and average circularity of the toner within a predetermined range, so that developability and durability are maintained even in a high temperature and high humidity environment. The present inventors have developed a new fact that a high-quality and high-quality image can be formed.

（２） 正帯電性を有することを特徴とする（１）に記載の磁性トナー。 That is, the magnetic toner of the present invention has the following characteristics.
(1) A magnetic toner containing at least a binder resin and magnetic powder, the dielectric loss tangent tan δ satisfies the following formulas (i) and (ii), and the average circularity of the toner particles is 0.950 to 0.960. Magnetic toner characterized by the above.

(2) The magnetic toner as described in (1), which has a positive charging property.

According to the invention of (1) above, by setting the dielectric loss tangent of the toner particles at a frequency of 5.0 × 10 ³ Hz to 7.0 × 10 ⁻³ or less, the degree of dispersion of the magnetic powder in the toner particles is improved, and the image density is poor. Problems such as fog and thin layer unevenness are eliminated. Further, by setting the dielectric loss tangent at a frequency of 1.0 × 10 ⁵ Hz to 1.0 × 10 ^{−2 to} 1.4 × 10 ⁻² , it is possible to maintain a preferable toner charge even in a high temperature and high humidity environment, and to have excellent developability.

  Further, by setting the average circularity of the toner particles to 0.950 to 0.960, the circularity is increased, the toner fluidity and transfer efficiency are improved, the image density is easily maintained, the charge adjustment is easy, and the thin layer unevenness is improved. Disappears. In addition, the cleaning property is improved.

  The magnetic toner of the present invention will be described. The magnetic toner of the present invention is a magnetic toner containing at least a binder resin and magnetic powder, the dielectric loss tangent tan δ satisfies the above formulas (i) and (ii), and the average circularity of the toner particles is 0.950. It is a magnetic toner characterized by ˜0.960.

The dielectric loss tangent of the toner is known as an index of the degree of dispersion of the magnetic powder in the toner particles. When the dielectric loss tangent increases, the dispersion becomes poor, and when the dielectric loss tangent decreases, the dispersion improves. Satisfying the above formula (i) indicates that the degree of dispersion of the magnetic powder in the toner particles is good. When the dielectric loss tangent at a frequency condition of 5.0 × 10 ³ Hz is greater than 7.0 × 10 ⁻³ , the degree of dispersion of the magnetic powder in the toner particles is poor, resulting in a difference in the amount of magnetic powder between the toner particles, poor image density, Problems such as fogging and thin layer unevenness are likely to occur. Further, the magnetic powder is easily detached from the toner particles, and the surface of the photoreceptor is easily contaminated.
Even if the condition of the above formula (i) is satisfied, it is difficult to maintain the charge in a high temperature and high humidity environment, and the developability cannot be maintained in many cases.

Further, when the dielectric loss tangent satisfies the above formula (i) and the dielectric loss tangent under a frequency condition of 1.0 × 10 ⁵ Hz is smaller than 1.0 × 10 ⁻² , it is considered that the dispersity of the magnetic powder in the toner particles is good. Even in a normal environment at a room temperature of 23 ° C. and a humidity of 50%, the charge of the toner is difficult to escape and the charge is likely to accumulate, resulting in high charge, and thin layer unevenness occurs in the SUS development sleeve used in the high-speed development system.

On the other hand, if the dielectric loss tangent under the frequency condition of 1.0 × 10 ⁵ Hz is greater than 1.4 × 10 ⁻² even if the above formula (i) is satisfied and the dispersibility of the magnetic powder in the toner particles is good, In a wet environment, the toner easily loses its charge, it is difficult to maintain the charge, and the image density decreases.

  Further, according to the present invention, the average circularity of the toner particles is preferably 0.950 to 0.960. When the average circularity is less than 0.950, the fluidity tends to deteriorate, the transfer efficiency is low, and the image density tends to decrease.

Conversely, if the average circularity exceeds 0.960, the fluidity is good, the transfer efficiency is good, and the image density is easy to maintain, but the charge adjustment becomes difficult. In particular, in a developing device using a developing sleeve of SUS, since the charge imparting power of the sleeve is strong, the toner present in the vicinity of the sleeve surface has a very high charge, and is strongly attracted to the sleeve surface by the mirror power. Form a non-moving layer. As a result, the chance of friction with the sleeve of the toner is reduced, and charging is impeded. As a result, the toner thin layer formed on the developing sleeve is disturbed due to non-uniform charging of the toner, resulting in unevenness, and thin layer unevenness is likely to occur. Further, poor cleaning tends to occur due to the shape of the toner.
Here, the average circularity is measured using a flow type particle image analyzer, the circularity of the measured particles is obtained by the following equation, and the total circularity of all the measured particles is the total number of particles. The divided value is defined as the average circularity.

<Toner production method>
Although known methods such as a pulverization method and a polymerization method are known for the production of toner particles, the magnetic toner of the present invention is produced by a pulverization method. That is, in the pulverization method, the binder resin, magnetic powder and wax are premixed with a charge control agent and other additives as necessary with a Henschel mixer, etc., then melt-kneaded, cooled, pulverized, and classified. By doing so, a magnetic toner is obtained.
At this time, in order to obtain the toner having the above average circularity, it is preferable to carry out the pulverization process in a plurality of times. In other words, the particle shape at the time of the first pulverization is indefinite, but by applying mechanical energy by repeating pulverization / classification a plurality of times, the toner surface has corners that approximate a spherical shape. For crushing, for example, machines such as Kawasaki Heavy Industries' Cebros, Kryptron, Turbo Industry's turbo mill, Nippon Pneumatic Industry's fine mill, Hosokawa Micron's inomizer, Japan Engineering's Super Rotor, etc. It is preferable to use a type pulverizer, and a toner having a higher sphericity than that using an air type pulverizer can be obtained. In particular, by using a turbo mill manufactured by Turbo Industries, a toner having a desired average circularity can be obtained efficiently.

  In order to adjust the dielectric loss tangent tan δ within the range of the above formula (i), the dispersibility of the magnetic powder in the binder resin may be improved. For this purpose, it is preferable to perform sufficient kneading. For kneading, it is preferable to use, for example, a twin screw extruder. On the other hand, in order to adjust the dielectric loss tangent tan δ within the range of the formula (ii), as will be described later, the shape and addition amount of the magnetic powder and the premixing time are important.

  The binder resin is not particularly limited. For example, styrene-acrylic resin, polyester resin, polyacrylic resin, polyethylene resin, polypropylene resin, vinyl chloride resin, polyamide resin, polyurethane resin, polyvinyl alcohol resin. Examples thereof include thermoplastic resins such as resins, vinyl ether resins, N-vinyl resins, and styrene-butadiene resins. Of course, if necessary, other resins may be used in combination with these resins, or two or more of these resins may be used.

  Examples of the monomer serving as the base of the styrene-acrylic resin include styrene derivatives such as styrene, α-methylstyrene, p-methylstyrene, pt-butylstyrene, p-chlorostyrene, and hydroxystyrene; methacrylic acid, Methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, glycidyl (meth) acrylate, methoxyethyl (meth) acrylate, propoxyethyl (meth) acrylate, methoxydiethylene glycol (meth) acrylate , Ethoxydiethylene glycol (meth) acrylate, benzyl (meth) acrylate, cyclohexyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, (meth) acrylonitrile, (meth ) Acrylamide, N-methylol (meth) acrylamide, ethylene glycol di (meth) acrylate, 1,3-butylene glycol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, trimethylol ethanetri (meth) Examples include (meth) acrylic acid esters such as acrylate.

  The mixture of the above various monomers can be polymerized by any method such as solution polymerization, bulk polymerization, emulsion polymerization, suspension polymerization, etc., to obtain a binder resin used in the present invention. In the polymerization, usable polymerization initiators include acetyl peroxide, decanoyl peroxide, lauroyl peroxide, benzoyl peroxide, azobisisobutyronitrile, 2,2′-azobis-2,4-dimethylvaleronitrile, 2 , 2′-azobis-4-methoxy-2,4-dimethylvaleronitrile and other known polymerization initiators can be used. These polymerization initiators are preferably used in the range of 0.1 to 15% by weight based on the total weight of the monomers.

  The polyester resin is mainly obtained by polycondensation of polyvalent carboxylic acids and polyhydric alcohols. Examples of the polyvalent carboxylic acids include phthalic acid, isophthalic acid, terephthalic acid, succinic acid, 1, 2 , 4-benzenetricarboxylic acid, 2,5,7-naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, pyromellitic acid and other aromatic polycarboxylic acids; maleic acid, fumaric acid, succinic acid, adipic acid Aliphatic dicarboxylic acids such as sebacic acid, malonic acid, azelaic acid, mesaconic acid, citraconic acid and glutaconic acid; cycloaliphatic dicarboxylic acids such as cyclohexanedicarboxylic acid and methylmedicic acid; anhydrides and lower alkyl esters of these carboxylic acids 1 type or 2 types or more of these are used.

  Here, the content of the trivalent or higher component depends on the degree of cross-linking, and the addition amount may be adjusted in order to obtain a desired degree of cross-linking. In general, the content of trivalent or higher components is preferably 15 mol% or less.

  Examples of the polyhydric alcohol used in the polyester resin include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,4-butenediol, neopentyl glycol, 1 Alkylene glycols such as 1,5-pentane glycol and 1,6-hexane glycol; alkylene ether glycols such as diethylene glycol, triethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol and polytetramethylene glycol; 1,4-cyclohexane Aliphatic polyhydric alcohols such as dimethanol and hydrogenated bisphenol A; bisphenols such as bisphenol A, bisphenol F, and bisphenol S, and bisphenols Can be mentioned alkylene oxide adducts can be used in combination of two or more thereof.

  For the purpose of adjusting the molecular weight and controlling the reaction, monocarboxylic acid and monoalcohol may be used as necessary. Examples of the monocarboxylic acid include benzoic acid, paraoxybenzoic acid, toluene carboxylic acid, salicylic acid, acetic acid, propionic acid, and stearic acid. Examples of the monoalcohol include monoalcohols such as benzyl alcohol, toluene-4-methanol, and cyclohexanemethanol.

  The glass transition temperature of the binder resin is preferably in the range of 54 to 62 ° C. This is because if the glass transition temperature is less than 54 ° C., the toner may be hardened in the developing device or the toner cartridge, and if it exceeds 62 ° C., the toner may not be sufficiently fixed on the transfer object such as paper.

  In the magnetic toner, the toner color is blackened by the magnetic powder, so that it is generally not necessary to use a colorant when used as a black toner, but carbon black such as acetylene black, lanblack, aniline black, etc. is used as a color reinforcement. It may be dispersed and mixed in the particles. In this case, the content of the colorant is preferably 0.1 to 10 parts by weight with respect to 100 parts by weight of the binder resin.

Examples of the magnetic powder include triiron tetroxide (Fe ₃ O ₄ ), iron sesquioxide (γ-Fe ₂ O ₃ ), zinc iron oxide (ZnFe ₃ O ₄ ), and iron yttrium oxide (Y ₃ Fe ₅ O _12). ), Iron cadmium oxide (CdFe2O4), iron gadolinium oxide (Gd3Fe5O12), iron oxide copper (CuFe ₂ O ₄ ), iron oxide lead (PbFe ₁₂ O ₁₉ ), iron oxide nickel (NiFe ₂ O ₄ ), iron neodymium oxide ( NdFeO ₃ ), iron barium oxide (BaFe ₁₂ O ₁₉ ), magnesium iron oxide (MgFe ₂ O ₄ ), iron manganese oxide (MnFe ₂ O ₄ ), iron lanthanum oxide (LaFeO ₃ ), iron powder (Fe), cobalt powder (Co), nickel powder (Ni), etc. are mentioned. A particularly suitable magnetic powder is particulate iron trioxide (magnetite). A suitable magnetite is a regular octahedron-shaped magnetite having a particle diameter of 0.05 to 1.0 μm. The magnetite particles may be surface-treated with a silane coupling agent, a titanium coupling agent, or the like.

The magnetic powder in the present invention has an octahedral shape, which is preferable for adjusting the dielectric loss tangent tan δ of the obtained toner within the range of the above formula (ii). That is, the octahedral magnetic powder has a lower bulk density than the spherical magnetic powder, has a large oil absorption, and has a relatively sharp particle size distribution, and is therefore easily dispersed in the toner particles. Therefore, the release of the magnetic powder from the toner can be suppressed, and the chargeability of the toner can be stabilized and uniformly charged even in a high temperature and high humidity environment. That is, when the magnetic powder is a polyhedron, the magnetic powder is prevented from being released from the toner, and the charging characteristics of the toner can be stabilized and uniformly charged even in a high temperature and high humidity environment.
On the other hand, the closer the magnetic powder shape is to a polyhedron that exceeds the octahedron and the spherical body, the more the magnetic powder is exposed to the toner surface and the more easily it is released from the toner. In order to make the shape of the magnetic powder octahedral, for example, the magnetic powder may be manufactured as follows. That is, when the magnetic powder is produced, for example, at the time of neutralization mixing with the ferrous salt aqueous solution and the alkaline solution, the amount of the alkaline solution added to the ferrous salt is set within a predetermined range (1 to 2 equivalents). A face-shaped magnetic powder can be obtained.

The content of the magnetic powder is 35 to 60 parts by weight, preferably 55 to 140 parts by weight with respect to 100 parts by weight of the binder resin. When the content of the magnetic powder is out of this range, it becomes difficult to adjust the dielectric loss tangent tan δ of the obtained toner within the range of the above formula (ii).

  Conventionally known charge control agents can be used as the charge control agent. Examples of the positively chargeable charge control agent include nigrosine dyes, fatty acid-modified nigrosine dyes, carboxyl group-containing fatty acid-modified nigrosine dyes, quaternary ammonium salts, amine compounds, and organometallic compounds. Examples of the negatively chargeable charge control agent include metal complexes of oxycarboxylic acids, metal complexes of azo compounds, metal complex dyes and salicylic acid derivatives.

  As the mold release agent, for example, various waxes, low molecular weight olefin resins, and the like can be used. Examples of waxes include polyhydric alcohol esters of fatty acids, higher alcohol esters of fatty acids, alkylene bis fatty acid amide compounds, and natural waxes. Examples of the low molecular weight olefin resin include polypropylene, polyethylene, and propylene-ethylene copolymer having a number average molecular weight in the range of 1,000 to 10,000, particularly 2,000 to 6,000.

  Surface treatment agents include inorganic fine powders such as silica, alumina, titanium oxide, zinc oxide, magnesium oxide, and calcium carbonate; organic fine powders such as polymethyl methacrylate to adjust the charge controllability and fluidity of the toner. A fatty acid metal salt such as zinc stearate can be used, and one or more of these can be used in combination. The addition amount of the surface treatment agent is preferably in the range of 0.1 to 2.0% by weight per toner particle. The surface treatment agent and toner particles can be mixed using, for example, a Henschel mixer, a V-type mixer, a turbula mixer, a hybridizer, or the like.

  In order to obtain a high quality image, the volume average particle diameter of the toner is preferably in the range of 5.0 to 12.0 μm.

  The binder resin, magnetic material, charge adjusting agent, waxes, etc. in the magnetic toner of the present invention are not particularly limited, and known materials can be appropriately selected and used.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated in detail, this invention is not limited only to a following example.

[Example: Production of binder resin]
Binder resins A and B were prepared according to the following formulation.
[Binder Resin A]
The materials shown in Table 1 were reacted at 220 ° C. for 8 hours under a nitrogen atmosphere, and then reacted until reaching a softening point of 155 ° C. under reduced pressure, to produce a binder resin A.

[Binder resin B]
The materials shown in Table 2 were reacted at 220 ° C. for 8 hours under a nitrogen atmosphere, and then reacted until reaching a softening point of 90 ° C. under reduced pressure, to produce a binder resin B.

[Example: Production of magnetic powder]
Magnetic powders 1 to 5 were prepared according to the following formulation.

[Magnetic powder 1]
60 liters of a 1.8 mol / L ferrous sulfate aqueous solution and 45 liters of a 5 mol / L sodium hydroxide aqueous solution are sufficiently stirred and mixed to prepare a ferrous hydroxide slurry. While maintaining this ferrous hydroxide slurry at 80 to 90 ° C., air was blown at 20 liters / minute to initiate the oxidation reaction. When the oxidation reaction has progressed to 50% of the total Fe ²⁺ , add 10 liters of 0.1 mol / L sodium hexametaphosphate aqueous solution over 60 minutes to the ferrous hydroxide slurry containing magnetite during the oxidation reaction. , PH was maintained at 6-9 to complete the oxidation reaction. The magnetic particle slurry after the reaction was washed, filtered, and dried by a conventional method, and then the slightly agglomerated particles were crushed to prepare a magnetic powder 1.

[Magnetic powder 2]
Magnetic powder 2 was produced in the same manner as magnetic powder 1 except that the amount of sodium hexametaphosphate aqueous solution added was changed to 1.8 liters.

[Magnetic powder 3]
Magnetic powder 3 was produced in the same manner as magnetic powder 1 except that the sodium hexametaphosphate aqueous solution was changed to a sodium aluminate aqueous solution.

[Magnetic powder 4]
Magnetic powder 4 was prepared in the same manner as magnetic powder 1 except that the sodium hexametaphosphate aqueous solution was changed to a sodium aluminate aqueous solution and the addition amount was changed to 12.5 liters.

[Magnetic powder 5]
60 liters of a 1.8 mol / L ferrous sulfate aqueous solution and 45 liters of a 5 mol / L sodium hydroxide aqueous solution are sufficiently stirred and mixed to prepare a ferrous hydroxide slurry. While maintaining the ferrous hydroxide slurry at 80 to 90 ° C., 100 liters / minute of air was blown in for 220 minutes, and the pH was maintained at 6 to 9, and an oxidation reaction was performed to generate magnetic particles. The magnetic particle slurry after the reaction was washed, filtered, and dried by a conventional method, and then the slightly agglomerated particles were crushed to prepare magnetic powder 5.

[Example: Preparation of toner]
Toners A to N were prepared according to the following formulation.

[Toner A]
Each material shown in Table 3 was premixed with a Henschel mixer, and then melt-kneaded using a twin screw extruder. Next, the melt-kneaded product was cooled and then pulverized to a volume average particle size of 11.0 μm with a mechanical pulverizer (Turbo Mill, turbo industry). Further, this pulverized product was pulverized with the above pulverizer to a volume average particle size of 6.8 μm. Next, fine powder and coarse powder were classified at the same time by an airflow classifier to obtain toner particles having a volume average particle diameter of 7.2 μm and an average circularity of 0.954. Next, 0.8 part by weight of hydrophobic silica (trade name “TG820F” manufactured by Cabot Corporation) was externally added to 100 parts by weight of the toner particles, and the mixture was mixed with a Henschel mixer to prepare toner A. As the charge control agent, a positively chargeable charge control agent, styrene acrylic quaternary ammonium salt (trade name “FCA222P” manufactured by Fujikura Kasei Co., Ltd.) is used, and as the wax, Hiroyuki Kato is used. The brand name “Carnauba Wax No. 1” manufactured by the company was used.

[Toner B]
A kneaded material was obtained by the same method using the same material as that of the toner A except that the amount of the magnetic powder was changed to 90 parts by mass. After the melt-kneaded product was cooled, it was pulverized with the above pulverizer to a volume average particle size of 11.0 μm. Furthermore, this pulverized product was pulverized with the above pulverizer to a volume average particle size of 7.0 μm. Next, fine powder and coarse powder were classified at the same time by an airflow classifier to obtain toner particles having a volume average particle diameter of 7.5 μm and an average circularity of 0.953. Next, toner B was prepared in the same manner as toner A described above.

[Toner C]
A kneaded material was obtained in the same manner using the same material as toner A except that the amount of magnetic powder was changed to 80 parts by mass. After the melt-kneaded product was cooled, it was pulverized with the above pulverizer to a volume average particle size of 11.0 μm. Further, this pulverized product was pulverized with the above pulverizer to a volume average particle size of 6.8 μm. Next, fine powder and coarse powder were classified at the same time by an airflow classifier to obtain toner particles having a volume average particle diameter of 7.3 μm and an average circularity of 0.957. Next, toner C was prepared in the same manner as toner A described above.

[Toner D]
A kneaded material was obtained in the same manner as in the toner A, except that the magnetic powder 1 was changed to the magnetic powder 2 and the amount of the magnetic powder was changed to 95 parts by mass. After the melt-kneaded product was cooled, it was pulverized with the above pulverizer to a volume average particle size of 11.0 μm. Further, this pulverized product was pulverized with the above pulverizer to a volume average particle size of 6.8 μm. Next, fine powder and coarse powder were classified at the same time by an airflow classifier to obtain toner particles having a volume average particle diameter of 7.2 μm and an average circularity of 0.953. Next, a toner D was prepared in the same manner as the toner A.

[Toner E]
A kneaded material was obtained by the same method as in the toner A except that the magnetic powder 1 was changed to the magnetic powder 2 and the amount of the magnetic powder was changed to 80 parts by mass. After the melt-kneaded product was cooled, it was pulverized with the above pulverizer to a volume average particle size of 11.0 μm. Further, this pulverized product was pulverized with the above pulverizer to a volume average particle size of 6.6 μm. Next, fine powder and coarse powder were classified at the same time by an airflow classifier to obtain toner particles having a volume average particle diameter of 7.1 μm and an average circularity of 0.958. Next, a toner E was produced in the same manner as the toner A.

[Toner F]
A kneaded material was obtained by the same method using the same material as that of the toner A except that the magnetic powder 1 was changed to the magnetic powder 3. After the melt-kneaded product was cooled, it was pulverized with the above pulverizer to a volume average particle size of 11.0 μm. Further, this pulverized product was pulverized with the above pulverizer to a volume average particle size of 6.8 μm. Next, fine powder and coarse powder were classified at the same time by an airflow classifier to obtain toner particles having a volume average particle diameter of 7.3 μm and an average circularity of 0.956. Next, toner F was produced in the same manner as toner A described above.

[Toner G]
A kneaded material was obtained in the same manner using the same material as toner A except that magnetic powder 1 was changed to magnetic powder 3 and the amount of magnetic powder was changed to 80 parts by mass. After the melt-kneaded product was cooled, it was pulverized with the above pulverizer to a volume average particle size of 11.0 μm. Further, this pulverized product was pulverized with the above pulverizer to a volume average particle size of 6.8 μm. Next, fine powder and coarse powder were classified at the same time by an airflow classifier to obtain toner particles having a volume average particle diameter of 7.2 μm and an average circularity of 0.952. Next, a toner G was prepared in the same manner as the toner A.

[Toner H]
A kneaded material was obtained in the same manner using the same material as toner A. After the melt-kneaded product was cooled, it was pulverized with the above pulverizer to a volume average particle size of 11.0 μm. Further, this pulverized product was pulverized with the above pulverizer to a volume average particle size of 6.6 μm. Next, fine powder and coarse powder were classified at the same time by an airflow classifier to obtain toner particles having a volume average particle diameter of 7.1 μm and an average circularity of 0.948. Next, a toner H was prepared in the same manner as the toner A.

[Toner I]
A kneaded material was obtained in the same manner using the same material as toner A. After this melt-kneaded product was cooled, it was pulverized with the above pulverizer to a volume average particle size of 12.5 μm. Further, this pulverized product was pulverized with the above pulverizer to a volume average particle size of 8.7 μm. Again, this pulverized product was pulverized with the above pulverizer to a volume average particle size of 6.7 μm. Next, fine powder and coarse powder were classified at the same time by an airflow classifier to obtain toner particles having a volume average particle diameter of 7.2 μm and an average circularity of 0.963. Next, toner I was prepared in the same manner as toner A described above.

[Toner J]
A kneaded material was obtained in the same manner using the same material as in the toner A except that the magnetic powder 1 was changed to the magnetic powder 2 and the amount of the magnetic powder was changed to 100 parts by mass. After the melt-kneaded product was cooled, it was pulverized with the above pulverizer to a volume average particle size of 11.0 μm. Further, this pulverized product was pulverized with the above pulverizer to a volume average particle size of 6.5 μm. Next, fine powder and coarse powder were classified at the same time by an airflow classifier to obtain toner particles having a volume average particle diameter of 7.0 μm and an average circularity of 0.954. Next, toner J was produced in the same manner as toner A described above.

[Toner K]
A kneaded material was obtained by the same method as in the toner A except that the magnetic powder 1 was changed to the magnetic powder 2 and the amount of the magnetic powder was changed to 90 parts by mass. After the melt-kneaded product was cooled, it was pulverized with a jet pulverizer to a volume average particle size of 11.0 μm. Further, this pulverized product was pulverized with a jet pulverizer to a volume average particle size of 7.0 μm. Next, fine powder and coarse powder were classified at the same time by an airflow classifier to obtain toner particles having a volume average particle diameter of 7.4 μm and an average circularity of 0.931. Next, toner K was prepared in the same manner as toner A described above.

[Toner L]
A kneaded material was obtained in the same manner as in the toner A, except that the magnetic powder 1 was changed to the magnetic powder 3 and the amount of the magnetic powder was changed to 90 parts by mass. After this melt-kneaded product was cooled, it was pulverized with the above pulverizer to a volume average particle size of 11.0 μm. Further, this pulverized product was pulverized with the above pulverizer to a volume average particle size of 6.8 μm. Next, fine powder and coarse powder were classified at the same time by an airflow classifier to obtain toner particles having a volume average particle diameter of 7.3 μm and an average circularity of 0.952. Next, a toner L was produced in the same manner as the toner A.

[Toner M]
A kneaded material was obtained in the same manner using the same material as toner A except that magnetic powder 1 was changed to magnetic powder 4. After the melt-kneaded product was cooled, it was pulverized with the above pulverizer to a volume average particle size of 11.0 μm. Further, this pulverized product was pulverized with the above pulverizer to a volume average particle size of 6.6 μm. Next, fine powder and coarse powder were classified at the same time by an airflow classifier to obtain toner particles having a volume average particle diameter of 7.1 μm and an average circularity of 0.956. Next, a toner M was produced in the same manner as the toner A.

[Toner N]
A kneaded material was obtained in the same manner using the same material as toner A except that magnetic powder 1 was changed to magnetic powder 5. After the melt-kneaded product was cooled, it was pulverized with the above pulverizer to a volume average particle size of 11.0 μm. Further, this pulverized product was pulverized with the above pulverizer to a volume average particle size of 6.9 μm. Next, fine powder and coarse powder were classified at the same time by an airflow classifier to obtain toner particles having a volume average particle diameter of 7.4 μm and an average circularity of 0.956. Next, toner N was produced in the same manner as toner A described above.

<Measurement of magnetic powder shape and average particle size and magnetic properties>
About the magnetic powder obtained above, the shape of magnetic powder, the average particle diameter, and the value of the magnetic characteristic were measured. Regarding the shape and average particle diameter of the magnetic powder, the particle shape was observed at a magnification of 20,000 times using a scanning electron microscope, and the ferret diameter was measured for 200 particles to determine the average particle diameter. The measurement of the ferret diameter and the number average value of the ferret diameter is performed by taking a particle image of the magnetic powder with a scanning electron microscope and measuring and calculating the ferret horizontal diameter with an image analyzer. In addition, the ferret horizontal diameter of the magnetic powder used in the present invention represents the maximum length in one arbitrary direction of each magnetic powder in the plurality of magnetic powders photographed by the electron microscope. The maximum length refers to the distance between parallel lines when two parallel lines that are perpendicular to the one arbitrary direction and are in contact with the outer diameter of the particle are drawn.
The magnetic properties were measured using a vibration type magnetometer (manufactured by Toei Industry Co., Ltd .: VSM-P7 type) under an external magnetic field of 79.6 kA / m.

  Table 4 shows the shape, average particle diameter, and magnetic properties of the magnetic powder obtained by the above method.

<Volume average particle diameter, dielectric loss tangent and average circularity measurement>
The toners A to N obtained above were measured for volume average particle diameter, dielectric loss tangent, and average circularity. The volume average particle size was measured using Multisizer II (manufactured by Coulter, Inc.) with an aperture diameter of 100 μm for an electrolytic solution in which a magnetic toner was suspended with a surfactant. The dielectric loss tangent is measured by placing 0.5 g of magnetic toner into an electrode for powder (manufactured by Ando Electric: SE-43 type), molding it into a 17 mmΦ pellet under a pressure of 20 kgf / cm ² , and using an LCR meter (YHP 4192A Type). In the measurement, the frequency was 5.0 × 10 ³ Hz and 1.0 × 10 ⁵ Hz. For measuring the average circularity of the magnetic toner, a flow type particle image analyzer FPIA-2100 (manufactured by Sysmex Corporation) was used to determine the average circularity of a particle group having a circle equivalent diameter of 2 μm or more.

Table 5 shows the values of the volume average particle diameter, dielectric loss tangent and average circularity obtained by the above method.

<Evaluation test>
[Examples 1-7, Comparative Examples 1-7]
One of the toners A to N is mounted on a printer LS-9500DN manufactured by Kyocera Mita (development sleeve peripheral speed: 370 mm / second, development sleeve: stainless steel (SUS)) adopting a magnetic one-component development system, Image density, fog and image quality were evaluated.

  For image density, fogging and image evaluation, 100,000 sheets were printed in an environment of normal temperature and humidity (room temperature 23 ° C./relative humidity 50%), and high temperature and humidity (room temperature 35 ° C./relative humidity 85%). In an environment, 10,000 sheets were printed, and image density, fog and image were measured. Image density and fog were measured with a reflection densitometer (manufactured by Tokyo Denshoku Co., Ltd .: TC-6D). The image quality was measured visually. The results are shown in Tables 6 and 7. The criteria for determining image density, fog, and image quality are shown below.

(Image density criteria)
Image density: Density at the solid black portion of the printer image 1.3 or higher ………… ○: Good
1.2 to 1.3 ……: No problem in practical use Less than 1.2 ………… ×: Unusable in practical use

(Fog criteria)
Fog: (Non-image area density)-(Base paper density)
Less than 0.008 ………… ○: No problem in practical use
0.008 or more ………… ×: Unusable for practical use

(Quality criteria for image quality)
◎: Vivid image without scattering even when viewed with a loupe ○: Vivid image as long as it is visually observed △: Slightly scattered but no problem for practical use ×: Other than scattering, the blurring of characters is conspicuous

(Examples 1-7)
As shown in Tables 6 and 7, the toner particles of Examples 1 to 7 satisfy the conditional expressions (i) and (ii) of the dielectric loss tangent, and the average circularity of the toner particles is in the range of 0.950 to 0.960. Therefore, even in an environment of normal temperature and normal humidity (23 ° C./50%), and also in an environment of high temperature and high humidity (35 ° C./85%), the image density is sufficiently maintained, there is little fogging, and the image quality is also high. This indicates that there is no problem in practical use.

(Comparative Example 1)
Although satisfying conditional expressions (i) and (ii) of dielectric loss tangent, since the average circularity of toner particles is less than 0.950, the fluidity is poor and the environment is high temperature and high humidity (35 ° C./85%). The image density is decreasing below.

(Comparative Example 2)
While satisfying the above conditions (i) and (ii) of dielectric loss tangent, since the average circularity of the toner particles exceeds 0.960, the charge amount becomes too high and normal temperature and normal humidity (23 ° C./50 %) Thin layer unevenness occurs in the environment. On the other hand, there is no practical problem in a high temperature and high humidity (35 ° C./85%) environment where it is difficult to maintain charging.

(Comparative Example 3)
Since the value of the dielectric loss tangent exceeds 7.0 × 10 ⁻³ in the formula (i), the dispersion of the magnetic powder in the toner is poor, and the ambient temperature and humidity (23 ° C./50%) environment and high temperature and high humidity (35 (° C / 85%) The image density is low in an environment, and it is difficult to faithfully reproduce a latent image such as a fine line, and the image quality is poor.

(Comparative Example 4)
Although satisfying conditional expressions (i) and (ii) of the dielectric loss tangent, the average circularity of the toner particles is less than 0.950, and this value is smaller than that of Comparative Example 1, so that the fluidity is poor. It becomes difficult to uniformly apply charges, and the image density is lowered.

(Comparative Example 5)
Since the value of the dielectric loss tangent exceeds 1.4 × 10 ^-2 in formula (ii), the toner charge is easy to escape and it is difficult to maintain the charge in a high temperature and high humidity (35 ° C / 85%) environment. The image density decreases.

(Comparative Example 6)
Since the value of the dielectric loss tangent exceeds 7.0 × 10 ⁻³ in the formula (i) and 1.4 × 10 ⁻² in the formula (ii), the dispersion of the magnetic powder in the toner is poor, and the toner Is also non-uniform, and thin layer unevenness occurs even in a normal temperature and normal humidity (23 ° C./50%) environment.

(Comparative Example 7)
Since the value of dielectric loss tangent is less than 1.0 × 10 ^-2 in equation (ii), it is practical in high temperature and high humidity (35 ° C / 85%) environment where electric charge tends to accumulate in toner particles and it is difficult to maintain the charge. Although there is no problem above, conversely, in an environment of normal temperature and normal humidity (23 ° C./50%), high charge occurs and thin layer unevenness occurs.

Claims (2)

A magnetic toner containing at least a binder resin and magnetic powder, wherein the dielectric loss tangent tan δ satisfies the following formulas (i) and (ii), and the average circularity of the toner particles is 0.950 to 0.960. Magnetic toner.

The magnetic toner according to claim 1, which has a positive charging property.