JP6273870B2 - Electrostatic latent image developer - Google Patents

Description

  The present invention relates to an electrostatic latent image developer.

  In recent years, printers or copiers using an electrophotographic system have been accelerated. In particular, high-speed printers or high-speed copying machines targeted for the production print market are required to have high image quality and high image stability. Therefore, the electrostatic latent image developer is required to have a small variation in performance due to environmental changes, and is also required to have excellent durability stability.

  For example, in a high-temperature and high-humidity environment, the amount of moisture in the air increases, so that the charge charged on the toner particles easily leaks to the moisture in the air (water has a lower resistance than the toner particles). As a result, the charge amount of the toner particles is lowered, and the transfer rate is lowered. Therefore, the image density may be lowered. Such a problem becomes more conspicuous at the time of endurance than the initial stage of printing.

In addition, the above-described problem becomes remarkable when a material having excellent conductivity (for example, carbon black) is used as a colorant. When the colorant is excellent in electrical conductivity, the resistance of the toner particles is lowered, so that the charge amount of the toner particles is further lowered. Therefore, for example, Patent Document 1 describes that a pigment containing titanium iron trioxide (FeTiO ₃ ) is used instead of carbon black. However, since titanium iron trioxide is not excellent in hiding power (power to cover the paint base), a pigment containing titanium trioxide is not excellent in coloring power as compared with carbon black.

  On the other hand, in Patent Document 2, if the surface of the hematite particle powder or the surface of the hydrous iron oxide particle powder is coated with polysiloxane and carbon black adheres to at least a part of the polysiloxane, the original color of carbon black is disclosed. It is described that is exhibited.

JP 2004-54094 A Japanese Patent Laid-Open No. 2001-13730

  However, since the black toner described in Patent Document 2 contains carbon black, the amount of charge in a high-temperature and high-humidity environment is significantly reduced for the reasons described above.

  In addition, acidic carbon black is widely used as a colorant, and it is said that this carbon black is strong in red and low in quality. On the other hand, bluishness can be imparted by increasing the particle size of the primary particles of carbon black. However, such carbon black is not excellent in coloring power. Therefore, in order to obtain a jet black tone black toner using such carbon black, it is necessary to increase the content of the carbon black. Here, carbon black is excellent in electrical conductivity. Therefore, if the carbon black content is increased, the resistance of the toner particles tends to decrease, and the charge amount of the toner particles tends to decrease. Thus, when an image having a desired hue is obtained by increasing the content of carbon black, the charge amount of the toner particles is reduced.

  On the other hand, nigrosine is more excellent in insulation than carbon black. Therefore, even if the nigrosine content is increased, the resistance of the toner particles can be kept high. Therefore, an image having a desired hue can be obtained by increasing the content of nigrosine. However, nigrosine has positive charging characteristics. Therefore, when the content of nigrosine is increased, the charging characteristics of the dry developer tend to shift to the positive side.

  As a method for obtaining a jet black tone black toner, it is conceivable to use a magnetic substance or a mixture of a magnetic substance and carbon black as a colorant. However, the magnetic substance is a metal oxide and has a large specific gravity. Therefore, it is difficult to disperse the magnetic material in the resin.

  As another method for obtaining a jet black tone black toner, it is conceivable to add a cyan pigment typified by copper phthalocyanine. In order to obtain a jet black tone black toner by this method, it is necessary to increase the amount of copper phthalocyanine added. However, when the amount of copper phthalocyanine added is increased, the halftone bluish color may be increased.

  The present invention has been made in view of the above points. The object of the present invention is to reduce the variation in performance due to environmental changes, to form an image having a desired image density and hue, and to improve charging stability. It is to provide an excellent electrostatic latent image developer.

  The electrostatic latent image developer of the present invention has toner particles containing a resin and a colorant. The colorant contains nigrosine and a pigment derivative, and preferably further contains carbon black.

  When the content ratio of nigrosine in the toner particles is Wn (mass%) and the content ratio of the pigment derivative in the toner particles is Ws (mass%), Wn and Ws satisfy 0.15 ≦ Ws / Wn ≦ 0.80. It is preferable. Wn is preferably 0.3% by mass or more and 5.0% by mass or less.

  In the present invention, it is possible to provide an electrostatic latent image developer that is capable of forming an image having a desired image density and hue with little variation in performance due to environmental changes, and having excellent charging stability.

[Configuration of electrostatic latent image developer]
The electrostatic latent image developer of the present embodiment includes, for example, an electrophotographic liquid developer, paint, and the like used in an electrophotographic image forming apparatus (described later) such as a copying machine, a printer, a digital printing machine, or a simple printing machine. It is useful as a liquid developer for electrostatic recording, an oil-based ink for inkjet printers, or an ink for electronic paper. Hereinafter, a dry developer which is an example of an electrostatic latent image developer will be mainly described. However, the electrostatic latent image developer may be a liquid developer.

[Configuration of dry developer]
The dry developer includes a one-component developer and a two-component developer. The one-component developer is composed of toner particles. The two-component developer includes toner particles and a carrier.

  The dry developer preferably has a glass transition temperature of 40 ° C. or higher and 80 ° C. or lower, and more preferably 40 ° C. or higher and 70 ° C. or lower. As a result, a dry developer having excellent low-temperature fixability can be obtained.

The glass transition temperature of the dry developer can be measured using a differential scanning calorimeter (trade name “DSC-7” manufactured by Perkin Elmer Co., Ltd.). First, 4.5 mg of a measurement sample (dry developer) is placed in an aluminum pan (trade name “KIT No. 0219-0041”), and this is set in the sample holder of the differential scanning calorimeter. For the reference measurement, the above-mentioned aluminum pan without a sample is used. Next, measurement is performed under the condition of Heat-Cool-Heat, and the data obtained in the second Heat is analyzed to determine the glass transition temperature of the dry developer. Specifically, an extension line of the baseline before the rise of the first endothermic peak and a tangent line having a maximum inclination between the rising portion of the first endothermic peak and the peak of the peak are drawn, and the base The intersection of the line extension and the tangent is defined as the glass transition temperature of the dry developer.
(Heat-Cool-Heat)
Measurement temperature range: 0-200 ° C
Temperature increase rate: 10 ° C./min Temperature decrease rate: 10 ° C./min After the first heat, hold at 200 ° C. for 5 minutes, and then cool.

  The dry developer preferably has a softening point of 80 ° C. or higher and 110 ° C. or lower, and more preferably 90 ° C. or higher and 105 ° C. or lower. Such softening point can be measured as follows.

First, in an environment of 20 ° C. and 50% RH, 1.1 g of a dry developer is placed in a petri dish, leveled flat, and left for 12 hours or more. Next, the sample (dry developer) is pressurized with a force of 3820 kg / cm ² for 30 seconds using a molding machine (trade name “SSP-10A” manufactured by Shimadzu Corporation). Thereby, a cylindrical sample having a diameter of 1 cm is obtained. Subsequently, the offset temperature is measured using a flow tester (trade name “CFT-500D” manufactured by Shimadzu Corporation) in an environment of 24 ° C. and 50% RH. The measured offset temperature is the softening point of the dry developer. The offset temperature is measured according to the following method. First, the cylindrical sample is preheated at 60 ° C. for 300 seconds. Next, while applying a load of 196 N (20 kgf) to the sample, the sample is heated at a temperature increase rate of 6 ° C./min with a start temperature of 60 ° C. Then, the temperature (offset) obtained when a sample was extruded from a hole (1 mm diameter × 1 mm) of a cylindrical die using a piston having a diameter of 1 cm, and the offset value was set to 5 mm by the melting temperature measurement method by the temperature rising method. Temperature).

  The dry developer preferably has a median diameter D50 of 4 μm or more and 10 μm or less, and more preferably 6 μm or more and 9 μm or less. Thereby, since the transfer rate is increased, the image quality (for example) of the halftone is improved. That is, the image quality of fine line images and dot images is improved.

  The median diameter D50 of the dry developer is a computer in which data processing software (Software V3.51) is installed in a precision particle size distribution measuring apparatus (for example, “Coulter Multisizer TA-III” manufactured by Beckman Coulter, Inc.). It can be measured using a system (measuring device connected to a system (manufactured by Beckman Coulter)). First, 0.02 g of a dry developer is mixed with 20 mL of a surfactant solution (for the purpose of dispersing the dry developer. For example, a neutral detergent containing a surfactant component is diluted 10-fold with pure water). After that, a dispersion is prepared by performing a dispersion treatment with ultrasonic waves for 1 minute. Pipette the dispersion into a beaker containing “ISOTON II” (trade name, manufactured by Beckman Coulter, Inc.) until the display concentration of the measuring apparatus is 8%. And in the said measuring apparatus, the count value of a measurement particle shall be 25000 pieces, an aperture diameter shall be 50 micrometers, a 1-30 micrometers which is a measurement range will be divided into 256, a frequency value will be calculated, and the one with a larger volume integrated fraction. The particle diameter with a frequency value of 50% is determined. The particle diameter thus determined is the median diameter D50 of the dry developer. That is, “the median diameter D50 of the dry developer” means the median diameter D50 when the particle size distribution of the dry developer is measured on a volume basis. It should be noted that reproducible measurement values can be obtained by injecting the dispersion liquid until the display density of the measuring apparatus is 8%.

  The dry developer preferably has an average circularity (average circularity) of 0.95 or more and 0.98 or less. This increases the transfer rate.

The average circularity of the dry developer can be determined using a flow type particle image analyzer (for example, trade name “FPIA-2100” manufactured by Sysmex Corporation). First, a dry developer is blended into an aqueous solution containing a surfactant, and a dispersion is prepared by carrying out an ultrasonic dispersion treatment for 1 minute. Next, using the analyzer, the dry developer is photographed at an appropriate density of 3000 or more and 10,000 or less HPF detection under the measurement condition HPF (high magnification imaging mode). Subsequently, the circularity of each dry developer is calculated using the following formula (1). The circularity of the dry developer thus determined is added and divided by the number of the dry developer, thereby obtaining the average circularity of the dry developer. In addition, a reproducible measurement value can be obtained by setting the HPF detection number within the above range.
Circularity of dry developer = (peripheral length of circle having area equal to projected area of toner particles) / (peripheral length of detected toner particles) (1)

<Toner particles>
The toner particles include a resin and a colorant dispersed in the resin. It is preferable to determine the respective contents of the resin and the colorant in the toner particles so that a desired image density can be obtained when the adhesion amount of the toner particles to a recording medium such as paper is within a predetermined range. For example, the toner particles preferably contain 0.5% by mass or more and 20% by mass or less of a colorant, and more preferably contain 2% by mass or more and 10% by mass or less of a colorant. The toner particles may contain magnetic powder, a release agent, a charge control agent, or the like in addition to the resin and the colorant. The toner particles may be obtained by adding an external additive such as a fluidizing agent or a cleaning aid to a toner base material containing a resin and a colorant.

<Colorant>
The colorant includes nigrosine and a pigment derivative. As a result, it has been found that the decrease in charge amount at high temperature and high humidity can be prevented, and it has been found that such an effect can be obtained not only at the initial stage of printing but also at the time of durability.

  The colorant includes nigrosine. Since nigrosine is superior to carbon black in insulation, it can prevent the resistance of toner particles from being lowered. Therefore, the content of nigrosine can be adjusted so that an image having a desired image density and a desired hue can be obtained.

  Further, the colorant includes nigrosine and a pigment derivative. Nigrosine has a positive charging characteristic, whereas the pigment derivative has a negative charging characteristic. Therefore, by using the pigment derivative together with nigrosine, it is possible to prevent the charging characteristics of the dry developer from being biased to the positive side. Therefore, the charging stability of the dry developer is increased. Therefore, occurrence of fog can be prevented.

  The colorant preferably further contains carbon black. Thereby, an image with a higher image density can be obtained, and an image having a desired hue (for example, black) can be obtained. In order to effectively obtain such an effect, the toner particles preferably contain 10% by mass or more and 40% by mass or less of carbon black, more preferably 10% by mass or more and 30% by mass or less of carbon black.

<Nigrosine>
“Nigrosine” is a mixture of various azine compounds that can be obtained by oxidation-reduction condensation of aniline, aniline hydrochloride and nitrobenzene in the presence of a catalyst such as iron chloride. The main component is an azine compound which is a purple black dye having a skeleton of phenazine, phenazine azine, triphenazine oxazine or the like.

  Examples of such nigrosine include C.I. I. Solvent Black 7, C.I. I. Examples thereof include Solvent Black 5 and various azine compounds. One or more of the following materials can be used as nigrosine in the present embodiment.

  C. above. I. Examples of the solvent black 5 include “Spirit Black SB”, “Spirit Black SSBB”, “Spirit Black AB”, and “Spirit Black” manufactured by Orient Chemical Industries, Ltd. Black ”ABL”, “Nubian BLACK (NH-805)”, “Nubian Black (NH-815)”, and the like.

  C. above. I. Examples of the solvent black 7 include “Nigrosine Base SA”, “Nigrosine Base SAP”, “Nigrosine Base SAPL”, and “Nigrosine Base” manufactured by Orient Chemical Industry Co., Ltd. Base "EE", "Nigrosine Base EEL", "Nigrosine Base EX", "Nigrosine Base EXBP", "Special Black EB", "Neusine Black EB" "NUBIAN BLACK) TN-870", "NUBIAN BLACK (TN-877)", What is marketed under a trade name such as “NUBIAN BLACK TH-807”, “NUBIAN BLACK TH-827” or “NUBIAN GREY IR-B”, etc. Can be mentioned.

  Examples of the azine-based compound include “Bontron N-01”, “Bontron N-04”, “Bontron N-07”, “Bontron” manufactured by Orient Chemical Co., Ltd. ) N-09 "," Bontron N-21 "," Bontron N-71 "," Bontron N-75 ", or" Bontron N-79 " Examples include those marketed by name.

<Pigment derivative>
The pigment derivative has any one of the following configurations 1 to 3. Preferably, the pigment derivative has any one of the following configurations 1 to 3 and the following configuration 4.
Structure 1: Compound that generates van der Waals force with the colorant 2: Structure having the same structure as that of the colorant, and a π-π interaction between the colorant and the colorant Compound Structure 3: Adsorbed Strongly on the Surface of the Compound: Compound Structure 4: Having a Skeleton of the Same Structure as the Pigment, and Introducing an Acidic Group (eg, Sulfate Group or Amino Group) into the Molecules of the Pigment A compound that exhibits strong interaction with dispersants. The polymer dispersant has an affinity for the solvent or resin used when dispersing the colorant. In addition, the polymer dispersant prevents re-aggregation of the colorant because the molecule is bulky.
Here, the “compound having the same structure as the colorant” includes compounds having the same chemical structure except for some functional groups or some substituents. The same applies to the “compound having the same structure as the pigment”.

  Preferably, the pigment derivative is a compound having a phthalocyanine structure whose central atom is a metal atom. Conventionally, a pigment derivative and a polymer dispersant are bonded by an acid-base interaction. However, if the pigment derivative of the present embodiment has the above phthalocyanine structure, the polymer dispersant (electron donating compound) donates electrons to the central atom of the phthalocyanine structure and is firmly bonded by coordination bond. Is done. Therefore, the pigment derivative and the polymer dispersant are firmly bonded without being affected by the polarity of the solvent or the functional group of the added resin. In addition, the polymer dispersant has an affinity for the dispersion medium and prevents re-aggregation of the colorant because the molecule is bulky. Therefore, the polymer dispersant can reduce the viscosity of the dispersion liquid of the colorant containing the resin and the colorant in the solvent in which the resin is dissolved.

  Examples of such pigment derivatives include metal phthalocyanine or metal phthalocyanine derivative whose central atom is any one of Cr, Fe, Co, Ni, Zn, Mn, Mg, and Al. The metal phthalocyanine derivative means a compound in which a hydrogen atom contained in a benzene ring of phthalocyanine is substituted with an atom (for example, a halogen atom) or an atomic group different from a hydrogen atom. Examples of the atomic group include a hydrocarbon group such as a methyl group or a vinyl group, a hydroxyl group, a carboxyl group, and an amino group. Hereinafter, the metal phthalocyanine and the metal phthalocyanine derivative are collectively referred to as “metal phthalocyanines”.

  Examples of the metal phthalocyanines include, for example, trade names “Solsperse 5000” and “Solsperse 12000” manufactured by Lubrizol Corporation, “BYK-Synergist 2100” manufactured by Big Chemie Japan Co., Ltd., or EFKA CHEMICALS B. V. The product name “EFKA745” manufactured by the company may be mentioned.

  The pigment derivative is not limited to metal phthalocyanines, and may be an azo pigment derivative or the like. For example, trade name “Solsperse 22000” manufactured by Lubrizol or EFKA CHEMICALS B.I. V. An azo pigment derivative such as a trade name “EFKA6750” manufactured by the company may also be mentioned.

One or more of the above materials can be used as the pigment derivative of this embodiment.
<Content ratio of nigrosine and pigment derivative>
When the content ratio of nigrosine in the toner particles is Wn (mass%) and the content ratio of the pigment derivative in the toner particles is Ws (mass%), Wn and Ws satisfy 0.15 ≦ Ws / Wn ≦ 0.80. It is preferable. More preferably, Wn and Ws satisfy 0.20 ≦ Ws / Wn ≦ 0.70.

  If 0.15 ≦ Ws / Wn, since the content ratio of the pigment derivative in the toner particles is high, the effect of the present embodiment (the performance fluctuation due to the environmental change is small, and the image having the desired image density and hue) And an electrostatic latent image developer excellent in charging stability can be provided. Further, since it is possible to prevent the nigrosine content ratio in the toner particles from becoming too high, it is possible to effectively prevent the reddish hue from becoming strong, and it becomes easier to obtain an image having a desired hue.

  If Ws / Wn ≦ 0.80, a high content ratio of nigrosine in the toner particles can be secured, so an image having a desired image density and a desired hue can be formed without increasing the carbon black content ratio in the colorant. It becomes easy to do. Therefore, it is possible to effectively prevent the occurrence of problems caused by increasing the content ratio of carbon black, so that the electrostatic latent image developer has a small variation in performance (for example, transfer rate or image density) due to environmental changes. It will be easier to provide.

  The nigrosine content Wn in the toner particles is preferably 0.3% by mass or more and 5% by mass or less, and more preferably 2% by mass or more and 4.5% by mass or less. If Wn is 0.3% by mass or more, a sufficient image density can be obtained. Therefore, an image having a desired image density can be obtained without increasing the carbon black content. Therefore, it is possible to prevent the occurrence of problems caused by increasing the carbon black content. If Wn is 5% by mass or less, the reddish hue can be prevented from becoming strong, and an image having a desired hue can be obtained.

  The content ratio Ws of the pigment derivative in the toner particles is preferably 0.2% by mass or more and 4.5% by mass or less, and more preferably 0.4% by mass or more and 2.0% by mass or less. If Ws is 0.2 mass% or more, the effect by adding the pigment derivative can be obtained effectively. If Ws is 4.5% by mass or less, a high content ratio of nigrosine in the toner particles can be secured, so that an image having a desired image density and a desired hue can be obtained without increasing the carbon black content ratio in the colorant. It becomes easy to form.

  Wn and Ws can be measured according to proton NMR, infrared spectroscopy, pyrolysis GC-MS analysis, or the like. When two or more materials are used as nigrosine, the total content of each nigrosine in the toner particles is Wn. When two or more kinds of materials are used as the pigment derivative, the total content of each pigment derivative in the toner particles is Ws.

<Carbon black>
“Carbon black” is a generic name for black fine particles mainly composed of carbon, and may be chemically classified as a simple substance of carbon, but may contain various functional groups as is well known. Examples of such carbon black include thermal black, acetylene black, channel black, furnace black, lamp black, and aniline black.

  Such carbon black may be subjected to a surface treatment for modifying the surface properties as necessary. As the treatment method, various conventionally known methods can be adopted. Preferably, a wet surface treatment method in which carbon black is immersed in an acidic solution such as an acetic acid solution or a sulfonic acid solution, or a liquid is used. A dry surface treatment method that is not used can be mentioned. Examples of the dry surface treatment method include a method of contacting with an oxidizing agent such as a mixed gas of nitric acid or nitrogen oxide and air, or ozone, and an air oxidation method. Some commercially available carbon blacks are already being marketed after pH adjustment.

  Preferred specific examples of carbon black include “# 2400”, “# 2400B”, “# 2650”, “OIL7B”, “MA77”, “MA100”, “MA100S”, “PCF # 10” manufactured by Mitsubishi Chemical Corporation. ”,“ Black Pearls L ”,“ Mogu L ”,“ MONARCH 1300 ”,“ MONARCH 1400 ”,“ REGAL 330R ”,“ REGAL 400R ”,“ MONARCH 1100 ”manufactured by Cabot Corporation,“ Printex V ”,“ Special Black ”manufactured by Degussa 4 ”,“ Printex 140V ”, etc. (in the above,“ ”indicates a product name). One or more of these materials can be used as carbon black. When using 2 or more types of the said material as carbon black, it is preferable that the total amount is contained in said range.

<Resin>
As the resin, a conventionally known material can be used as the binding resin contained in the dry developer without any particular limitation. For example, polyester resin, acrylic resin, styrene acrylic copolymer resin, urethane resin, vinyl chloride Examples thereof include a resin and a vinyl acetate resin. One or more of these materials can be used as the resin contained in the toner particles.

<Core / shell structure>
The toner particles preferably have a core / shell structure. The “core / shell structure” is a structure in which the first resin is a core and the second resin is a shell. The core / shell structure includes not only a structure in which the second resin covers at least a part of the surface of the first particle (the first particle includes the first resin), but also the second resin is the surface of the first particle. The structure which adheres to at least one part of is also included. When the toner particles have a core / shell structure, it becomes easy to control the median diameter D50 of the toner particles, the circularity of the toner particles, and the like.

  In the core / shell structure, the mass ratio of the shell resin (second resin) and the core resin (first resin) is preferably 1:99 to 80:20. If the shell resin is contained in the toner particle resin in an amount of 1% by mass or more, a core / shell structure is easily formed. If the shell resin is contained in the toner particle resin in an amount of 20% by mass or less, the fixability is improved.

  Examples of the shell resin include a thermoplastic resin and a thermosetting resin. Specific examples include vinyl resins, polyester resins, polyurethane resins, epoxy resins, polyamide resins, polyimide resins, silicon resins, phenol resins, melamine resins, urea resins, aniline resins, ionomer resins, or polycarbonate resins. it can. One or more of these materials can be used as the shell resin.

  Examples of the core resin include a polyester resin, a polyurethane resin, a styrene acrylic resin, and a modified polyester resin. One or more of these materials can be used as the core resin.

  In the core / shell structure, the colorant may be contained in the core resin or the shell resin, or may be contained in both the core resin and the shell resin. The same is true for additives (for example, pigment dispersants) for toner particles.

<Magnetic powder>
Examples of the magnetic powder include magnetite, γ-hematite, various ferrites, and the like. One or more of these materials can be used as magnetic powder. The magnetic powder is preferably contained in the toner particles in an amount of 10% by mass to 500% by mass, and more preferably 20% by mass to 200% by mass.

<Release agent>
As a mold release agent, conventionally well-known various wax etc. can be mentioned, for example. Examples of conventionally known waxes include polyolefins such as low molecular weight polypropylene, polyethylene or oxidized low molecular weight polypropylene, paraffin, or synthetic ester waxes. Among these, since synthetic ester wax has a low melting point and low viscosity, it is preferable to use synthetic ester wax as a release agent. Examples of the synthetic ester wax include behenyl behenate, glycerin tribehenate, pentaerythritol tetrabehenate, and the like. One or more of these materials can be used as a release agent. The release agent is preferably contained in the toner particles in an amount of 1% by mass to 30% by mass, and more preferably 3% by mass to 15% by mass.

<Charge control agent>
As the charge control agent, a colorless compound capable of giving a positive or negative charge by frictional charging can be used, and various conventionally known positively chargeable charge control agents or negatively chargeable charge control agents can be used. Can be mentioned. The charge control agent is preferably contained in the toner particles in an amount of 0.01% by mass to 30% by mass, and more preferably 0.1% by mass to 10% by mass.

<External additive>
The toner particles may be obtained by adding an external additive such as a fluidizing agent or a cleaning aid to a toner base material containing a resin and a colorant. Thereby, the fluidity, charging property, cleaning property, etc. of the toner particles are improved.

  Examples of the external additive include fine particles made of an inorganic oxide such as silica fine particles, alumina fine particles, or titanium oxide fine particles, fine particles made of an inorganic stearic acid compound such as aluminum stearate fine particles or zinc stearate fine particles, or strontium titanate. Or the fine particle which consists of inorganic titanic acid compounds, such as zinc titanate, can be mentioned. The fine particles comprising such an inorganic compound are preferably surface-treated with a silane coupling agent, a titanium coupling agent, a higher fatty acid, silicone oil, or the like. Such surface treatment improves the heat-resistant storage stability of the electrostatic latent image developer and also improves the environmental stability thereof. One or more of the above materials can be used as a post-treatment agent. The external additive is preferably contained in 100 parts by mass of the toner particles in an amount of 0.05 to 5 parts by mass, and more preferably 0.1 to 3 parts by mass.

<Career>
Examples of the carrier contained in the two-component developer include magnetic particles. The magnetic particles are preferably made of a conventionally known material. For example, the magnetic particles may be made of a metal such as iron, ferrite, or magnetite, or may be made of an alloy of these metals and a metal such as aluminum or lead. . One or more of these materials can be used as a carrier, but it is more preferable to use ferrite particles as a carrier.

  As the carrier, a magnetic particle whose surface is coated with a resin (coat carrier) or a magnetic fine powder dispersed in a resin (binder type carrier) may be used.

  Examples of the resin contained in the coat carrier include olefin resin, styrene resin, styrene-acrylic resin, silicone resin, ester resin, and fluorine resin.

  Examples of the resin contained in the binder type carrier include styrene-acrylic resins, polyester resins, fluororesins, and phenol resins.

  The carrier preferably has a median diameter D50 of 20 μm or more and 100 μm or less, and more preferably 20 μm or more and 60 μm or less. The median diameter D50 of the carrier can be measured using a laser diffraction type particle size distribution measuring apparatus (trade name “HELOS” manufactured by Sympathic) equipped with a wet disperser. The “carrier median diameter D50” means the median diameter D50 when the particle size distribution of the carrier is measured on a volume basis.

  Such a carrier is preferably contained in the toner particles in an amount of 2% by mass to 10% by mass. The toner particles and the carrier are preferably mixed using a mixing device such as a Nauter mixer, a W cone mixer, or a V-type mixer.

[Production of dry developer]
Examples of the method for producing a dry developer include a kneading and pulverizing method, a suspension polymerization method, an emulsion aggregation method, an emulsion polymerization aggregation method, a miniemulsion polymerization aggregation method, and other methods. It is preferable to produce a dry developer by the suspension polymerization method described in JP 2010-191043 A. Further, from the viewpoint of reducing the energy cost during the production of the dry developer, it is preferable to use the following emulsion polymerization aggregation method.

  First, emulsion polymerization or miniemulsion polymerization is performed using a specific polymerizable monomer in an aqueous medium. Thereby, fine particles (resin fine particles) made of resin are prepared. If necessary, the prepared resin fine particles are agglomerated and fused together with fine particles composed of components (for example, a colorant) of a dry developer other than the resin.

  When the resin fine particles have a structure of two or more layers composed of two or more kinds of resin materials, as a method for producing a dry developer by the emulsion polymerization aggregation method, for example, an emulsion polymerization treatment according to a conventionally known method (first step) A polymerization initiator (polymerization of the second stage) is added to the dispersion of the first resin fine particles prepared by polymerization of the first resin, and the system is polymerized (second stage polymerization). it can.

The method for producing a dry developer by the emulsion polymerization aggregation method preferably includes the following steps 1 to 7.
Step 1: In an aqueous medium, a radical polymerization initiator is allowed to act on a polymerizable monomer that forms a resin. Thereby, resin fine particles are obtained.
Step 2: If necessary, a fine particle dispersion (colorant dispersion) comprising a colorant is prepared.
Step 3: An aggregating agent is added to an aqueous medium containing resin fine particles and colorant fine particles, and salting-out proceeds and aggregation and fusion are performed. Thereby, associated particles are obtained.
Step 4: Control the shape of the associated particles. Thereby, toner particles are obtained.
Step 5: Toner particles are filtered from the aqueous medium and then washed. By this cleaning, the surfactant and the like are removed from the toner particles.
Step 6: Dry the washed toner particles.
Step 7: Add an external additive to the dried toner particles.

  “Aqueous medium” means a medium composed of 50 to 100% by mass of water and 0 to 50% by mass of a water-soluble organic solvent. Examples of the water-soluble organic solvent include methanol, ethanol, isopropanol, butanol, acetone, methyl ethyl ketone, and tetrahydrofuran. Among them, it is preferable to use an alcohol-based solvent (for example, methanol, ethanol, isopropanol, butanol, etc.) that does not dissolve the resulting resin.

  When the toner particles contain a release agent, resin fine particles containing the release agent can be formed. Further, in the step of forming the association particles, a dispersion liquid in which fine particles made of a release agent (release agent fine particles) are dispersed in an aqueous medium is added to salt the resin fine particles, the colorant fine particles, and the release agent fine particles. It may be deposited, agglomerated or fused. You may combine these methods. Toner particles containing a charge control agent can be prepared according to a similar method.

<Step 1>
In the step of obtaining resin fine particles, a polymerizable monomer that forms a resin is first added to an aqueous medium. Next, by applying mechanical energy to the aqueous medium, the polymerizable monomer is dispersed to form oil droplets, and in this state, the polymerizable monomer is subjected to radical polymerization reaction. Thereby, resin fine particles having a D50 of 50 to 300 nm are formed.

  Examples of the dispersing device for dispersing the polymerizable monomer include a commercially available stirring device (trade name “CLEARMIX” manufactured by M Technique Co., Ltd.) equipped with a roller that rotates at high speed, and an ultrasonic dispersing device. , Homogenizers, pressure homogenizers, Manton gorin and the like.

  The temperature in the radical polymerization reaction varies depending on the type of the polymerizable monomer or radical polymerization initiator, but is preferably 50 ° C. or higher and 100 ° C. or lower, and more preferably 55 ° C. or higher and 90 ° C. or lower. The time required for the radical polymerization reaction varies depending on the kind of the polymerizable monomer or the rate of the radical polymerization reaction from the radical polymerization initiator, but is preferably 2 hours or more and 12 hours or less.

  In order to stably disperse the resin fine particles in the aqueous medium, a dispersion stabilizer may be added to the aqueous medium. Examples of the dispersion stabilizer include tricalcium phosphate, magnesium phosphate, zinc phosphate, aluminum phosphate, calcium carbonate, magnesium carbonate, calcium hydroxide, magnesium hydroxide, aluminum hydroxide, calcium metasilicate, calcium sulfate, Examples thereof include barium sulfate, bentonite, silica, and alumina. Moreover, what is generally used as surfactant, for example, polyvinyl alcohol, gelatin, methylcellulose, sodium dodecylbenzenesulfonate, an ethylene oxide adduct or higher alcohol sodium sulfate, etc. can also be used. Conventionally known ionic surfactants or nonionic surfactants can also be used.

  Examples of the ionic surfactant include sodium dodecylbenzenesulfonate, sodium arylalkylpolyethersulfonate, 3,3-disulfonediphenylurea-4,4-diazo-bis-amino-8-naphthol-6-sulfonic acid. Sulfonates such as sodium, o-carboxybenzene-azo-dimethylaniline or 2,2,5,5-tetramethyl-triphenylmethane-4,4-diazo-bis-β-naphthol-6-sulfonate Can be mentioned. Moreover, sulfate ester salts, such as sodium dodecyl sulfate, sodium tetradecyl sulfate, sodium pentadecyl sulfate, or sodium octyl sulfate, can also be mentioned. Moreover, aliphatic acid salts, such as sodium oleate, sodium laurate, sodium caprate, sodium caprylate, sodium caproate, potassium stearate or calcium oleate, etc. can also be mentioned.

  Nonionic surfactants include, for example, polyethylene oxide, polypropylene oxide, mixtures of polypropylene oxide and polyethylene oxide, esters of polyethylene glycol and higher fatty acids, alkylphenol polyethylene oxide, esters of polypropylene oxide and higher fatty acids, or sorbitan esters. Can be mentioned.

  The polymerization initiator used in the radical polymerization reaction may be a water-soluble polymerization initiator such as potassium persulfate, ammonium persulfate or azobiscyanovaleric acid, or a water-soluble redox such as hydrogen peroxide-ascorbic acid. The polymerization initiator may be an oil-soluble polymerization initiator such as azobisisobutyronitrile or azobisvaleronitrile.

  In this step, a conventionally known chain transfer agent may be used for the purpose of adjusting the molecular weight of the polymer or copolymer. Examples of the chain transfer agent include n-octyl mercaptan, n-dodecyl mercaptan, tert-dodecyl mercaptan, and tetrachloromethane.

<Process 2>
The step of preparing the dispersion of the colorant fine particles is performed as necessary, and the colorant fine particle dispersion is obtained by dispersing the colorant in the aqueous medium in the form of fine particles.

  The colorant is preferably dispersed using mechanical energy. D50 of the colorant fine particles is preferably 10 nm or more and 300 nm or less, more preferably 100 nm or more and 200 nm or less, and further preferably 100 nm or more and 150 nm or less, in a state dispersed in an aqueous medium. The D50 of the colorant fine particles is measured using an electrophoretic light scattering photometer (“ELS-800” manufactured by Otsuka Electronics Co., Ltd.).

<Steps 3 to 7>
Steps 3 to 7 can be performed according to various conventionally known methods. In addition, as a coagulant | flocculant used in the association process of the process 3, a metal salt can be mentioned, for example. Examples of the metal salt include a monovalent metal salt such as an alkali metal salt such as lithium, sodium or potassium, a divalent metal salt such as magnesium, calcium, manganese or copper, or a trivalent metal such as iron or aluminum. A metal salt etc. can be mentioned. Specific examples of the metal salt include lithium chloride, sodium chloride, potassium chloride, magnesium chloride, calcium chloride, manganese chloride, zinc chloride, or copper chloride. From the viewpoint that aggregation can be advanced in a relatively small amount, it is preferable to use a divalent metal salt. One or more of the above materials can be used as the flocculant.

[Image formation using dry developer]
In image formation using a dry developer, first, an electrostatic latent image is formed on a photoconductor using a dry developer. Next, the electrostatic latent image formed on the photoreceptor is developed to obtain a toner image, and the toner image is transferred to a recording medium. Subsequently, the toner image transferred to the recording medium is fixed to the recording medium by a fixing process using a thermal pressure fixing method.

  The thermal pressure fixing method means that fixing is performed while applying pressure and heating. The dry developer according to the exemplary embodiment can be suitably used in an image forming method including a fixing step using a heat and pressure fixing method. In particular, the surface temperature of the heating member in the fixing nip portion is 80 ° C. or higher and 110 ° C. or lower (preferably The fixing temperature is set to 80 ° C. or more and 95 ° C. or less, and the method can be suitably used for a method of forming an image. Further, the dry developer of this embodiment can also be suitably used in an image forming method in which the recording medium conveyance speed (fixing linear speed) in the fixing unit is 200 mm / sec or more and 600 mm / sec or less.

  Examples of the recording medium include plain paper from thin paper to thick paper, high-quality paper, coated printing paper such as art paper or coated paper, or various commercially available printing paper such as Japanese paper or postcard paper. it can.

[Configuration of liquid developer]
The electrostatic latent image developer may be a liquid developer in which the toner particles are dispersed in an insulating liquid. The toner particles of the liquid developer may contain a pigment dispersant, wax or charge control agent in addition to the resin and the colorant.

<Insulating liquid>
The insulating liquid is not particularly limited as long as it is used as the insulating liquid of the liquid developer, but is preferably a solvent shown below.

The insulating liquid is preferably a solvent having a resistance value that does not disturb the electrostatic latent image (about 10 ¹¹ to 10 ¹⁶ Ω · cm) and low in odor and toxicity. Examples of the insulating liquid generally include aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons, or polysiloxanes. From the viewpoint of odor, toxicity, cost, and the like, It is preferable to use a normal paraffin solvent or an isoparaffin solvent. For example, as the insulating liquid, Moresco White (trade name, manufactured by Matsumura Oil Co., Ltd.), Isopar (trade name, manufactured by ExxonMobil), Shellsol (trade name, manufactured by Shell Petrochemical Co., Ltd.), IP Solvent 1620, IP solvent 2028, IP solvent 2835 (both trade names, manufactured by Idemitsu Kosan Co., Ltd.) and the like can be used. One or more of these materials can be used as the insulating liquid.

[Manufacture of liquid developer]
Toner particles are produced based on a known method such as a pulverization method or a granulation method, and the obtained toner particles are dispersed in an insulating liquid. Thereby, the liquid developer of this embodiment can be manufactured.

  In the pulverization method, a resin and a colorant such as a pigment are kneaded and then pulverized. Such pulverization is preferably performed in a dry state or a wet state in oil.

  Examples of the granulation method include suspension polymerization method, emulsion polymerization method, fine particle aggregation method, method of adding a poor solvent to a resin solution to deposit, spray drying method, or core / shell with two different types of resins. Examples thereof include a method for forming toner particles having a structure.

  In order to obtain toner particles having a small diameter and a sharp particle size distribution, it is preferable to produce toner particles using a granulation method. Resins with high meltability and high crystallinity are soft even at room temperature. Therefore, it is difficult to pulverize a mixture of such a resin and a colorant such as a pigment. On the other hand, if the granulation method is used, the particle size of the toner particles containing such a resin can be set to a desired size.

  Among the granulation methods, it is preferable to produce toner particles using the following method. First, a resin is dissolved in a good solvent to obtain a core resin forming solution. Next, the core resin forming solution is mixed with a poor solvent having an SP value different from that of the good solvent together with an interfacial tension adjusting agent (shell resin material), and a droplet is formed by applying shear. Thereafter, the good solvent is volatilized. In this way, particles made of the core resin are obtained. In this method, the particle size of the toner particles or the shape of the toner particles can be easily controlled by changing the way of applying shear, the difference in interfacial tension or the interfacial tension adjusting agent.

[Image formation using liquid developer]
The configuration of an apparatus (image forming apparatus) for forming an image made of the liquid developer of the present embodiment is not particularly limited. The image forming apparatus is, for example, a single color image forming apparatus in which a single color liquid developer is secondarily transferred to a recording medium after primary transfer from the photosensitive member to the intermediate transfer member, and a single color liquid developer is directly transferred from the photosensitive member to the recording medium. It is preferable that the image forming apparatus is a multicolor image forming apparatus that forms a color image by superimposing a plurality of liquid developers.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these.

[Example 1]
In Example 1, a dry developer (two-component developer) containing toner particles having a core / shell structure and a coat carrier was produced.

<Manufacture of a dispersion of core resin particles (core particles)>
(Preparation of polymerization initiator solution)
9 parts by mass of potassium persulfate (polymerization initiator) was dissolved in 200 parts by mass of ion-exchanged water. As a result, a solution of the polymerization initiator was obtained.

(1. First stage polymerization)
2 parts by mass of sodium lauryl sulfate (anionic surfactant) and 2900 parts by mass of ion-exchanged water were placed in a reaction vessel equipped with a stirrer, a temperature sensor, a temperature controller, a cooling pipe, and a nitrogen introducing device. The solution temperature was raised to 80 ° C. while stirring the surfactant solution thus obtained at 230 rpm and flowing nitrogen.

  The polymerization initiator solution was added to the surfactant solution. The liquid temperature was set to 78 ° C., and a mixed solution of monomers containing 540 parts by mass of styrene, 270 parts by mass of n-butyl acrylate, and 65 parts by mass of methacrylic acid was dropped into the solution over 3 hours. After dropping, the liquid temperature was maintained at 78 ° C. and stirred for 1 hour. As a result, a polymerization reaction occurred and a dispersion of the first resin fine particles was obtained.

(2. Second stage polymerization)
94 parts by mass of styrene, 60 parts by mass of n-butyl acrylate, and 11 parts by mass of methacrylic acid were mixed to obtain a monomer mixture. To this mixed solution, 5 parts by mass of n-octyl mercaptan (chain transfer agent) was added to dissolve the monomer in n-octyl mercaptan. To this solution, pentaerythritol tetrabehenate (release agent, wax having an ester bond) was added and heated to 85 ° C. to dissolve the monomer in pentaerythritol tetrabehenate.

  The solution thus obtained was mixed and dispersed for 1 hour using a stirring device having a circulation path (trade name “CLEARMIX” manufactured by M Technique Co., Ltd.). As a result, a dispersion containing emulsified particles (a dispersion of emulsified particles) was obtained.

  1100 parts by mass of ion-exchanged water and 2 parts by mass of sodium lauryl sulfate were placed in a reaction vessel equipped with a stirrer, a temperature sensor, a temperature controller, a cooling pipe, and a nitrogen introducing device. The surfactant solution thus obtained was heated to 90 ° C., and a dispersion of the first resin fine particles (28 parts by mass in terms of solid content) was added to the solution. Thereafter, the liquid temperature was raised to 80 ° C., and then a dispersion of emulsified particles was added. Thereafter, a solution of a polymerization initiator was further added, and the mixture was heated to 90 ° C. and stirred for 2 hours. Thereby, a polymerization reaction occurred, and a dispersion liquid of second resin fine particles was obtained.

(3. Third stage polymerization)
A solution of the polymerization initiator was added to the dispersion of the second resin fine particles. The liquid temperature was set to 80 ° C., and a monomer mixture containing 230 parts by mass of styrene, 100 parts by mass of n-butyl acrylate, and 13 parts by mass of n-octyl mercaptan was added dropwise over 1 hour. After dropping, the solution was stirred for 3 hours while maintaining the liquid temperature at 80 ° C. This caused a polymerization reaction. Then, it cooled to 28 degreeC. In this way, a dispersion of core particles was obtained.

  The core particle thus obtained was a styrene acrylic polymer containing 31% by mass of n-butyl acrylate (polymerizable monomer having an ester bond), and its glass transition temperature was 43 ° C.

<Manufacture of dispersion liquid of shell resin particles (shell particles)>
In a reaction vessel equipped with a nitrogen introducing device, a dehydrating tube, a stirring device, and a thermocouple, 500 parts by mass of bisphenol A propylene oxide 2 mol adduct, 154 parts by mass of terephthalic acid, 45 parts by mass of fumaric acid, and 2 parts by mass of tin octylate The polycondensation reaction was carried out at 230 ° C. for 8 hours. Thereafter, a polycondensation reaction was carried out at 8 kPa for 1 hour and then cooled to 160 ° C. A polyester resin was thus obtained.

  Next, 10 mass parts of acrylic acid was added and mixed for 15 minutes with the liquid temperature kept at 160 ° C. Thereafter, a mixture containing 142 parts by mass of styrene, 35 parts by mass of n-butyl acrylate, and 10 parts by mass of di-t-butyl peroxide (polymerization initiator) was added dropwise over 1 hour with a dropping funnel. Thereafter, an addition polymerization reaction was performed for 1 hour while maintaining the liquid temperature at 160 ° C., and then the liquid temperature was increased to 200 ° C. and maintained at 10 kPa for 1 hour. This obtained the styrene acrylic modified polyester resin containing a 20 mass% styrene acrylic copolymer molecular chain.

  100 parts by mass of the obtained styrene acrylic modified polyester resin was pulverized using a commercially available pulverizer (trade name “Landel Mill RM-1S” manufactured by Deoksugaku Kogyo Co., Ltd.). Thereafter, this styrene acrylic modified polyester resin was mixed with 638 parts by mass (concentration: 0.26% by mass) of sodium lauryl sulfate solution and stirred, and an ultrasonic homogenizer (trade name “US” manufactured by Nippon Seiki Seisakusho Co., Ltd.) was used. -150T ") and sonication (V-LEVEL, 300 μA, 30 minutes). As a result, a dispersion of shell particles having a D50 of 250 nm was obtained.

<Preparation of colorant dispersion>
While stirring a solution prepared by dissolving 90 parts by mass of sodium dodecyl sulfate in 1600 parts by mass of ion-exchanged water, 60 parts by mass of nigrosine (trade name “Nubian Black TH-827” manufactured by Orient Chemical Co., Ltd.) and a pigment derivative 25 parts by mass (trade name “Solsperse 12000”, manufactured by Lubrizol Co., Ltd.) and 200 parts by mass of carbon black (manufactured by Cabot Co., Ltd., product name “Moul L”) were gradually added. The solution was subjected to dispersion treatment using a stirrer (trade name “CLEARMIX” manufactured by M Technique Co., Ltd.). In this way, a colorant dispersion was obtained. It was 117 nm when the particle size of the particle | grains contained in the said dispersion liquid was measured using the particle size distribution measuring apparatus ("Microtrack UPA-150" by Nikkiso Co., Ltd.).

<Preparation of toner base material>
In a reaction vessel equipped with a stirrer, a temperature sensor, a cooling pipe, and a nitrogen introducing device, a dispersion of core particles (288 parts by mass in terms of solid content), 1500 parts by mass of ion-exchanged water, and a dispersion of colorant (solids) 40 parts by mass in terms of conversion). Further, a dispersion stabilizer solution in which 3 parts by mass of sodium polyoxyethylene-2-dodecyl ether sulfate was dissolved in 120 parts by mass of ion-exchanged water was added to bring the liquid temperature to 30 ° C. Thereafter, a 5 mol / L sodium hydroxide aqueous solution was added to adjust the pH to 10.

  While stirring this solution, a solution of an aggregating agent in which 35 parts by mass of magnesium chloride hexahydrate is dissolved in 35 parts by mass of ion-exchanged water is added at 30 ° C. over 10 minutes. The temperature was kept at 30 ° C. Thereafter, the liquid temperature was raised to 90 ° C. over 60 minutes, and the core particles and the colorant were agglomerated and fused while maintaining the liquid temperature at 90 ° C.

  Using a particle size distribution measuring device (trade name “Multisizer 3” manufactured by Beckman Coulter, Inc.), the particle size of the growing particles (aggregated particles) was measured. When the D50 of the aggregated particles reached 5.2 μm, a dispersion of shell particles (72 parts by mass in terms of solid content) was added, and heating and stirring were performed until the shell particles adhered to the surface of the aggregated particles. A small amount of the solution was taken out and centrifuged, and when the supernatant became transparent, a solution in which 150 parts by mass of sodium chloride was dissolved in 600 parts by mass of ion-exchanged water was added to stop the growth of aggregated particles. The liquid temperature was set to 90 ° C., and a heat stirring process was performed to promote the fusion of the aggregated particles (aging process). In this state, the fusion of the aggregated particles proceeds until the average circularity of the dry developer becomes 0.965 by measurement using a flow type particle image analyzer (trade name “FPIA-2100” manufactured by Sysmex Corporation). I let you. Thereafter, the liquid temperature was cooled to 30 ° C., the pH of the solution was adjusted to 2 using hydrochloric acid, and stirring was stopped. Thereby, a dispersion liquid of the toner base material was prepared.

  Using a basket-type centrifuge (trade name “MARKIII”, model number “60 × 40” manufactured by Matsumoto Machinery Co., Ltd.), the dispersion of the toner base material is solid-liquid separated to obtain a wet cake made of the toner base material. Produced. The wet cake was washed using the basket type centrifuge and ion exchange water at 45 ° C. until the electric conductivity of the filtrate reached 5 μS / cm. The wet cake was transferred to an air-flow dryer (trade name “Flash Jet Dryer” from Seishin Co., Ltd.), and the wet cake was dried until the water content reached 0.5% by mass. As a result, particles (toner base material particles) made of a toner base material were obtained. When the D50 of the toner base material particles was measured using the above particle size distribution measuring apparatus (trade name “Multisizer 3” manufactured by Beckman Coulter, Inc.), it was 5.5 μm.

  The obtained toner base material particles have a core particle dispersion of 288 parts by mass (solid content conversion), a colorant dispersion of 40 parts by mass (solid content conversion), and a shell particle dispersion of 72 parts by mass. (In terms of solid content). Therefore, the total pigment content in the toner base particles was 10% by mass.

<External addition treatment for toner base material particles>
10 parts by mass of particles comprising the first external additive (first external additive particles) and 1.5 parts by mass of particles comprising the second external additive (second external additive particles) with respect to 100 parts by mass of the toner base material particles And external addition processing was performed using a Henschel mixer (trade name “FM10B” manufactured by Mitsui Miike Chemical Industries, Ltd.). In this external addition treatment, the peripheral speed of the stirring blade was 40 m / second, the treatment temperature was 30 ° C., and the treatment time was set to 20 minutes. Thereafter, coarse particles were removed using a sieve having an opening of 90 μm. Thus, toner base material particles subjected to external addition treatment were obtained. In addition, the 1st external additive particle | grains were manufactured in accordance with the method shown below, and the 2nd external additive particle | grains shown below were prepared.

<Production of first external additive particles>
Silica (SiO ₂ ) particles were produced by a sol-gel method. First, 625 parts by mass of methanol, 40 parts by mass of water, and 50 parts by mass of 28% by mass of ammonia water were placed in a reaction vessel equipped with a stirrer, a dropping funnel and a thermometer. The temperature of the mixed solvent thus obtained was 35 ° C., and 800 parts by mass of tetramethoxysilane and 420 parts by mass of 5.4% by mass of ammonia water were added dropwise to the mixed solvent while stirring the mixed solvent. Although these compounds were simultaneously dripped at the mixed solvent, tetramethoxysilane was dripped over 3.5 hours, and 5.4 mass% ammonia water was dripped over 5 hours.

  Stirring was continued for 0.5 hours after the completion of the tetramethoxysilane addition, and the hydrolysis reaction was allowed to proceed at 30 ° C. Centrifugation was performed on the obtained solution to obtain a dispersion liquid in which silica fine particles were dispersed in a mixed solvent.

  Hexamethyldisilazane was added to the obtained dispersion so that 3 mol of hexamethyldisilazane was 1 mol with respect to 1 mol of silica. This solution was heated to 60 ° C. and reacted for 3 hours, whereby the silica fine particles were subjected to a hydrophobic treatment. The mixed solvent was distilled off from the resulting solution under reduced pressure. This obtained the hydrophobic silica particle (1st external additive particle) whose number average particle diameter of a primary particle is 50 nm.

<Preparation of second external additive particles>
Commercially available silica particles were prepared as the second external additive particles. Such silica particles had a primary particle number average particle size of 7 nm, a BET specific surface area of 300 m ² / g, and were hydrophobized with hexamethyldisilazane.

<Preparation of coat carrier>
(1. Preparation of ferrite core particles)
Ferrite particles (commercially available) having a D50 of 35 μm were prepared as magnetic particles. The ferrite particles contain 21.0 mol% manganese in terms of MnO, 3.3 mol% magnesium in terms of MgO, 0.7 mol% in terms of SrO and strontium, and 75 in terms of Fe ₂ O _3. Contained 0.0 mol%. The D50 of the ferrite particles was measured using a commercially available laser diffraction particle size distribution measuring apparatus (trade name “HELOS” manufactured by Sympatec Corporation) equipped with a wet disperser.

(2. Preparation of particles made of coating resin (coating resin particles))
A surfactant solution in which 1.7 parts by mass of sodium dodecyl sulfate was dissolved in 3000 parts by mass of ion-exchanged water was placed in a reaction vessel equipped with a stirrer, a temperature sensor, a cooling pipe, and a nitrogen introduction apparatus. The temperature inside the reaction vessel was raised to 80 ° C. while stirring this solution at a stirring speed of 230 rpm and flowing nitrogen. After adding an initiator solution in which 10 parts by mass of potassium persulfate was dissolved in 400 parts by mass of ion-exchanged water to this solution, the liquid temperature was raised to 80 ° C. Thereafter, a monomer mixture composed of 400 parts by mass of cyclohexyl methacrylate and 400 parts by mass of methyl methacrylate was added dropwise over 2 hours, and then the mixture was stirred for 2 hours while maintaining the liquid temperature at 80 ° C. As a result, a polymerization reaction occurred and a dispersion of coating resin particles was obtained. By drying this dispersion using a spray dryer, resin particles for coating were obtained.

(3. Preparation of coat carrier)
3000 parts by mass of ferrite particles and 120 parts by mass of coating resin particles were put into a carrier manufacturing apparatus, the peripheral speed of the horizontal rotary blade was set to 4 m / sec, and the mixture was stirred at 22 ° C. for 15 minutes. After heating to 120 ° C., stirring was performed for 40 minutes to obtain a coated carrier having a D50 of 35 μm.

<Preparation of dry developer>
To 100 parts by mass of the coat carrier, 7 parts by mass of externally-treated toner base material particles were blended. Stirring was performed using a V blender at room temperature and normal humidity (20 ° C., 50% RH) (rotation speed: 20 rpm, stirring time: 20 minutes), and coarse particles were removed using a sieve having an opening of 125 μm. In this way, a dry developer of Example 1 was obtained.

[Examples 2 to 16, Comparative Examples 1 to 6]
In accordance with the method shown in Example 1 except that the respective contents of nigrosine, pigment derivative, carbon black, and organic pigment were changed to the values shown in Table 1, Examples 2 to 16 and Comparative Examples 1 to 6 dry developer was produced.

  In Table 1, “NS1” represents a trade name “Nubian Black TH-827” manufactured by Orient Chemical Industries, Ltd., and “NS2” represents a trade name “Bontron N-09” manufactured by Orient Chemical Industries, Ltd. “S1” represents a trade name “Solsperse 12000” manufactured by Lubrizol Corporation, and “S2” represents a trade name “Solsperse 22000” manufactured by Lubrizol Corporation. “CB1” represents a product name “Mul L” manufactured by Cabot Corporation, and “CB2” represents a product name “MA77” manufactured by Mitsubishi Chemical Corporation.

<Image formation>
Using an image forming apparatus (trade name “bizhub PRO C6500” manufactured by Konica Minolta Business Technologies, Inc.), images composed of the dry developers of Examples 1 to 16 and Comparative Examples 1 to 6 were formed.

<Evaluation of charging stability>
A belt-like solid image (test image) was formed on a high-quality A4 size paper (65 g / m ² ) at a printing rate of 5% at room temperature and normal humidity (20 ° C., 50% RH). Thereafter, the charge amount of the dry developer (charge amount of the dry developer at the initial stage of printing) was measured. The charge amount of the dry developer is measured by sampling the dry developer in the image forming apparatus, and using a blow-off charge amount measuring device (trade name “TB-200” manufactured by Toshiba Chemical Corporation). It was.

  After forming a test image on 100,000 sheets of the above-mentioned high quality paper, the charge amount of the dry developer (charge amount of the dry developer after printing 100,000 sheets) was measured according to the above method. Then, the difference (charge amount change amount) between the charge amount of the dry developer at the initial stage of printing and the charge amount of the dry developer after printing 100,000 sheets was obtained. The results are shown in “Charging stability” in Table 2. In Table 2, “A1” is described when the change amount of the charge amount is less than 4 μC / g, and “B1” is described when the change amount of the charge amount is 8 μC / g or more. It can be said that the smaller the change amount of the charge amount, the better the dry developer is in charge stability.

<Evaluation of fog>
A character image was printed on 200,000 sheets of recording medium at a normal temperature and humidity (20 ° C., 50% RH) at a printing rate of 5%. Thereafter, printing was performed on A4 size white paper, and the white paper density was measured. The blank paper density was obtained by averaging the absolute image density at 20 locations on the blank paper, and the absolute image density was measured using a reflection densitometer (trade name “RD-918” manufactured by Macbeth). The results are shown in “Fog” in Table 2. If the numerical value shown in “Fog” in Table 2 is 0.01 or less, it can be said that the occurrence of fog is prevented.

<Evaluation of transfer rate>
A 10 cm square solid image was printed at high temperature and high humidity (30 ° C., 80% RH). Thereafter, the mass of the dry developer remaining on the photoreceptor and the mass of the dry developer transferred to the recording medium were measured, and the transfer rate was determined using the following formula (2). The results are shown in “Transfer rate” in Table 2. If the numerical value shown in “Transfer rate” in Table 2 is 80 (%) or more, it can be said that the dry developer is excellent in the transfer rate.
(Transfer rate) = (Mass of dry developer transferred to recording medium) / (Mass of dry developer remaining on photoconductor) × 100 (2).

<Image density>
The adhesion amount of the dry developer to the recording medium was adjusted so that the image density of the solid image was 1.30 at room temperature and normal humidity (20 ° C., 50% RH). A solid image was formed on 20,000 recording media at a high temperature and high humidity (30 ° C., 80% RH) at a printing rate of 5%. Thereafter, the image density of the solid image formed on the 20,000th recording medium was measured. The image density was measured using a reflection densitometer (trade name “RD-918” manufactured by Macbeth). The results are shown in “Image Density” in Table 2. The closer the numerical value shown in “Image Density” in Table 2 is to 1.30, the smaller the variation in the performance of the dry developer due to environmental changes. If the numerical value shown in “Image Density” in Table 2 is 1.20 or more, it can be said that the variation in the performance of the dry developer due to environmental changes is sufficiently small.

<Evaluation of hue>
A solid image was formed at room temperature and normal humidity (20 ° C., 50% RH). Next, the hue of the solid image was evaluated using a color difference meter (trade name “CM-3600d” manufactured by Konica Minolta Co., Ltd.) and a target mask having a diameter of 4 mm. Specifically, the color difference ΔE between this solid image and the offset sheet-fed printing color standard Japan Color color reproduction printing 2001 chart (paper type: coated paper, aspect: black dot area ratio 100% site) was determined. Color difference ΔE was in the L ^* a ^* b ^* uniform color space color system defined in JIS Z 8729, L ^* axis, a ^* axis, and the square root of the sum of those squares each difference b ^* axis (See formula (3) below). The results are shown in “Hue” of Table 2. In Table 2, when the color difference ΔE is less than 3, it is described as “A2”, when the color difference ΔE is 3 or more and less than 6, it is described as “B2”, and when the color difference ΔE is 6 or more, “C2 " The smaller the color difference ΔE, the better the hue.

<Discussion>
In Comparative Example 1, fogging occurred, and the transfer rate and image density decreased when used in a high temperature and high humidity environment. The reason why such a result is obtained is considered as follows. The colorant of Comparative Example 1 does not contain nigrosine and a pigment derivative, but only contains carbon black. Therefore, when the content of carbon black is adjusted so that an image having a desired hue can be obtained, the charge amount of the toner particles is reduced, and thus fogging occurs.

  In addition, in a high temperature and high humidity environment, the charge charged on the toner particles of the electrostatic latent image developer is likely to leak into moisture in the air, so the charge amount of the toner particles is considered to decrease. In addition, carbon black is excellent in conductivity, and it is considered that the charge amount of the toner particles is lowered by this. For these reasons, the transfer rate and the image density decreased when used in a high temperature and high humidity environment.

  In Comparative Examples 2 to 5, fogging occurred, and when used in a high-temperature and high-humidity environment, the transfer rate and image density decreased, and the color difference ΔE was 6 or more. Since the colorant of Comparative Examples 2 to 5 did not contain a pigment derivative, fogging occurred without preventing the tendency of the charging characteristics of the dry developer to shift to the positive side, and in a high temperature and high humidity environment. When used, the transfer rate and image density decreased. Further, since the colorants of Comparative Examples 2 to 5 did not contain a pigment derivative, the influence of the hue of nigrosine became significant, and thus the color difference ΔE was 6 or more.

  In Comparative Example 6, fogging occurred, the transfer rate and image density decreased when used in a high temperature and high humidity environment, and the color difference ΔE was 3 or more and less than 6. For the same reason as in Comparative Example 1, it is considered that fogging occurred and the transfer rate and the image density were lowered when used in a high temperature and high humidity environment.

  In Comparative Example 6, the carbon black content in the toner particles was lower than that in Comparative Example 1. Therefore, in Comparative Example 6, the color difference ΔE was 3 or more and less than 6.

  In the examples except Examples 8, 13, 14 and 16, the fog was 0.005 or less and the transfer rate was larger than 90%. On the other hand, in Examples 8, 13, 14 and 16, the fog was larger than 0.005 and the transfer rate was 80% or more and 90% or less. The reason why such a result is obtained is considered as follows. In the examples except Examples 8, 13, 14, and 16, Ws / Wn was 0.80 or less, but in Examples 8, 13, 14, and 16, Ws / Wn was larger than 0.80. . That is, in the examples except Examples 8, 13, 14 and 16, the nigrosine content in the toner particles was lower than in Examples 8, 13, 14 and 16. Therefore, in the examples other than Examples 8, 13, 14 and 16, generation of fog is prevented more than in Examples 8, 13, 14 and 16, and the transfer rate is lowered when used in a high temperature and high humidity environment. Prevented.

  In Examples 1 to 14, the color difference ΔE was less than 3. On the other hand, in Examples 15 and 16, the color difference ΔE was 3 or more and less than 6. The reason why such a result is obtained is considered as follows. In Examples 1 to 14, carbon black was included, whereas in Examples 15 and 16, carbon black was not included. Therefore, in Examples 1 to 14, images having a hue superior to those of Examples 15 and 16 were obtained.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 1 Image forming apparatus, 2 Liquid developer, 3 Developing roller, 4 Control blade, 5 Photoconductor, 6 Intermediate transfer body, 7 Cleaning blade, 8 Charging apparatus, 9 Backup roller, 10 Coated paper, 11 Heat roller

Claims (4)

An electrostatic latent image developer having toner particles containing a resin and a colorant,
The colorant, only contains a nigrosine and the pigment derivatives,
The pigment derivative includes a metal phthalocyanine having a sulfuric acid group whose central atom is any one of Cr, Fe, Co, Ni, Zn, Mn, Mg and Al, or a derivative thereof, or an azo pigment derivative,
The derivative is a compound in which a hydrogen atom contained in a benzene ring of phthalocyanine is substituted with an atom or atomic group different from a hydrogen atom,
The atomic group includes a hydrocarbon group, a hydroxyl group, a carboxyl group, or an amino group,
The azo pigment derivative Solsperse 22000 or EFKA6750 the including electrostatic latent image developer.   The electrostatic latent image developer according to claim 1, wherein the colorant further comprises carbon black.   When the content ratio of the nigrosine in the toner particles is Wn (mass%) and the content ratio of the pigment derivative in the toner particles is Ws (mass%), the Wn and the Ws are 0.15 ≦ Ws / Wn. The electrostatic latent image developer according to claim 1, which satisfies ≦ 0.80.   The electrostatic latent image developer according to claim 1, wherein Wn is 0.3% by mass or more and 5.0% by mass or less.