JP2019164292A - Electrostatic charge image developer, process cartridge, image formation device, and image formation method - Google Patents

Abstract

To provide an electrostatic charge image developer for suppressing the occurrence of density unevenness.SOLUTION: An electrostatic charge image developer includes: toner particles; a resin coated carrier that includes magnetic particles and a resin layer covering the magnetic particles and in which the exposure percentage of the magnetic particles on the surface is 5% or more and 20% or less; and strontium titanate particles in which the average circularity of primary particles is 0.82 or more and 0.94 or less and the circularity whose accumulation is 84% exceeds 0.92. An average length RSm (C) of roughness curve element of the resin coated carrier surface and an average primary particle size r of the strontium titanate particles satisfy the relation 6≤RSm(C)/r≤40.SELECTED DRAWING: None

Description

  The present invention relates to an electrostatic charge image developer, a toner cartridge, a process cartridge, an image forming apparatus, and an image forming method.

In Patent Document 1, the 10-point average roughness Rz of the surface is 2 or more and 2.5 or less, the standard deviation of the 10-point average roughness Rz is 0.3 or less, and the average circularity is 0.98 or more. An electrostatic latent image developing carrier and an electrostatic latent image developer containing the carrier are disclosed.
Patent Document 2 discloses a carrier in which a magnetic material is used as a core material and the core material is resin-coated while leaving the surface of the core material at 0.1 to 10.0%; An electrostatic charge image developer comprising a toner to which inorganic fine particles having a number average particle diameter of 30 to 500 nm are added is disclosed.

JP 2008-83098 A Japanese Patent No. 3298034

  The present disclosure provides an electrostatic charge image developer that suppresses the occurrence of density unevenness when the exposure ratio of magnetic particles is more than 20% or when RSm (C) / r is less than 6 or more than 40. The issue is to provide.

  Specific means for solving the above-described problems include the following modes.

[1]
Toner particles,
A resin-coated carrier having magnetic particles and a resin layer covering the magnetic particles, wherein the exposed ratio of the magnetic particles on the surface is 2% or more and 20% or less;
Strontium titanate particles having an average circularity of primary particles of 0.82 or more and 0.94 or less and a circularity of cumulative 84% exceeding 0.92.
An electrostatic charge in which the average length RSm (C) of the roughness curve element on the surface of the resin-coated carrier and the average primary particle diameter r of the strontium titanate particles satisfy the relationship of 6 ≦ RSm (C) / r ≦ 40 Image developer.

[2]
Toner particles,
A resin-coated carrier having magnetic particles and a resin layer covering the magnetic particles, wherein the exposed ratio of the magnetic particles on the surface is 2% or more and 20% or less;
Strontium titanate particles having a half width of a peak of (110) plane obtained by an X-ray diffraction method of 0.2 ° or more and 2.0 ° or less,
An electrostatic charge in which the average length RSm (C) of the roughness curve element on the surface of the resin-coated carrier and the average primary particle diameter r of the strontium titanate particles satisfy the relationship of 6 ≦ RSm (C) / r ≦ 40 Image developer.

[3]
The electrostatic charge image developer according to [1] or [2], wherein the strontium titanate particles are strontium titanate particles containing a dopant.

[4]
The electrostatic charge image developer according to any one of [1] to [3], wherein an average primary particle size r of the strontium titanate particles is 10 nm to 100 nm.

[5]
The electrostatic charge image developer according to [4], wherein the average primary particle size r of the strontium titanate particles is 30 nm or more and 80 nm or less.

[6]
The average length RSm (C) of the roughness curve element on the surface of the resin-coated carrier, the average length RSm (T) of the roughness curve element on the surface of the toner particles, and the average primary particle diameter r of the strontium titanate particles. The electrostatic charge image developer according to any one of [1] to [5], wherein and satisfy a relationship of 11 ≦ RSm (C) / (RSm (T) × r) ≦ 100.

[7]
The electrostatic charge image developer according to any one of [1] to [6], wherein the resin-coated carrier, the magnetic particles, and the strontium titanate particles are easily positively charged in this order.

[8]
The electrostatic image developer according to any one of [1] to [7], wherein the resin layer contains an alicyclic acrylic resin.

[9]
The electrostatic charge image developer according to [8], wherein the alicyclic acrylic resin contains cyclohexyl (meth) acrylate as a polymerization component.

[10]
The electrostatic image developer according to any one of [1] to [9], wherein the magnetic particles are ferrite particles.

[11]
Statics given in any 1 paragraph of [1]-[10] whose content of the above-mentioned strontium titanate particles is 0.005 mass% or more and 2.0 mass% or less with respect to the mass of the above-mentioned resin coat carrier. Charge image developer.

[12]
The electrostatic charge image developer according to [11], wherein the content of the strontium titanate particles is 0.01% by mass or more and 1.0% by mass or less based on the mass of the resin-coated carrier.

[13]
The electrostatic image developer according to any one of [1] to [12] is contained, and the electrostatic image formed on the surface of the image carrier is developed as a toner image by the electrostatic image developer. A process cartridge including a developing unit and detachable from an image forming apparatus.

[14]
An image carrier,
Charging means for charging the surface of the image carrier;
An electrostatic charge image forming means for forming an electrostatic charge image on the surface of the charged image carrier;
The electrostatic image developer according to any one of [1] to [12] is accommodated, and the electrostatic image formed on the surface of the image carrier is developed as a toner image by the electrostatic image developer. Developing means,
Transfer means for transferring a toner image formed on the surface of the image carrier to the surface of a recording medium;
Fixing means for fixing the toner image transferred to the surface of the recording medium;
An image forming apparatus comprising:

[15]
A charging step for charging the surface of the image carrier;
An electrostatic charge image forming step of forming an electrostatic charge image on the surface of the charged image carrier;
A developing step of developing an electrostatic image formed on the surface of the image carrier as a toner image with the electrostatic image developer according to any one of [1] to [12];
A transfer step of transferring a toner image formed on the surface of the image carrier to the surface of a recording medium;
A fixing step of fixing the toner image transferred to the surface of the recording medium;
An image forming method comprising:

  According to the invention according to [1], [2], [3], [7], [8], [9] or [10], when the exposure ratio of the magnetic particles exceeds 20%, or RSm ( C) An electrostatic charge image developer that suppresses the occurrence of density unevenness is provided as compared with the case where / r is less than 6 or more than 40.

  According to the invention according to [4] or [5], there is provided an electrostatic charge image developer that suppresses the occurrence of density unevenness as compared with the case where the average primary particle size r of the strontium titanate particles exceeds 100 nm. .

  According to the invention according to [6], there is provided an electrostatic charge image developer that suppresses the occurrence of density unevenness as compared with the case where RSm (C) / (RSm (T) × r) is less than 11 or more than 100. Is done.

  According to the invention according to [11] or [12], the content of the strontium titanate particles is less than 0.005% by mass or more than 2.0% by mass with respect to the mass of the resin-coated carrier, An electrostatic charge image developer that suppresses the occurrence of density unevenness is provided.

  According to the invention according to [13], the density of the electrostatic charge image developer is higher than that when the exposure ratio of the magnetic particles is more than 20% or when RSm (C) / r is less than 6 or more than 40. A process cartridge that suppresses the occurrence of unevenness is provided.

  According to the invention according to [14] or [15], when the exposure ratio of the magnetic particles in the electrostatic charge image developer is more than 20%, or when RSm (C) / r is less than 6 or more than 40. In comparison, an image forming apparatus or an image forming method that suppresses the occurrence of density unevenness is provided.

It is the SEM image of the resin particle which externally added SW-360 by the titanium industry company which is an example of the strontium titanate particle, and the circularity distribution graph of the strontium titanate particle calculated | required by analyzing this SEM image. It is the SEM image of the resin particle which externally added another strontium titanate particle, and the circularity distribution graph of the strontium titanate particle calculated | required by analyzing this SEM image. 1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to an exemplary embodiment. FIG. 3 is a schematic configuration diagram illustrating an example of a process cartridge that is attached to and detached from the image forming apparatus according to the present exemplary embodiment.

  Embodiments of the invention will be described below. These descriptions and examples illustrate embodiments and do not limit the scope of the invention.

  In the present disclosure, when referring to the amount of each component in the composition, when there are a plurality of substances corresponding to each component in the composition, the plurality of the substances present in the composition unless otherwise specified. It means the total amount of substance.

  In the present disclosure, numerical ranges indicated using “to” indicate ranges including numerical values described before and after “to” as the minimum value and the maximum value, respectively.

  In the present disclosure, the term “process” is not only included in an independent process, but is included in the term if the intended purpose of the process is achieved even when it cannot be clearly distinguished from other processes.

  In the present disclosure, “(meth) acryl” means either “acryl” or “methacryl”, and “(meth) acrylate” means either “acrylate” or “methacrylate”. Means.

  In the present disclosure, “electrostatic image developing toner” is also referred to as “toner”, “electrostatic image developing carrier” is also referred to as “carrier”, and “electrostatic image developer” is also referred to as “developer”.

<Electrostatic image developer>
The developer according to the first embodiment includes toner particles, a resin-coated carrier having magnetic particles and a resin layer covering the magnetic particles, and strontium titanate particles.

  In the developer according to the first embodiment, the resin-coated carrier has an exposure ratio of magnetic particles on the surface of 2% or more and 20% or less.

  In the developer according to the first embodiment, the strontium titanate particles have an average circularity of primary particles of 0.82 or more and 0.94 or less and a circularity of cumulative 84% exceeding 0.92. In the first embodiment, the fact that the primary particles of the strontium titanate particles have the above circularity means that the shape of the strontium titanate particles is rounded (details will be described later).

  In the developer according to the first embodiment, the average length RSm (C) (μm) of the roughness curve element on the surface of the resin-coated carrier and the average primary particle size r (μm) of the strontium titanate particles are The relationship 6 ≦ RSm (C) / r ≦ 40 is satisfied.

  The developer according to the second embodiment includes toner particles, a resin-coated carrier having magnetic particles and a resin layer covering the magnetic particles, and strontium titanate particles.

  In the developer according to the second embodiment, the resin-coated carrier has a magnetic particle exposure ratio on the surface of 2% or more and 20% or less.

  In the developer according to the second embodiment, the strontium titanate particles have a (110) plane peak half-value width of 0.2 ° or more and 2.0 ° or less obtained by the X-ray diffraction method. In the second embodiment, the fact that the peak of the (110) plane of the strontium titanate particles has the above half-value width means that the shape of the strontium titanate particles is rounded (details will be described later). To do.)

  The developer according to the second embodiment has an average length RSm (C) (μm) of the roughness curve element on the surface of the resin-coated carrier and an average primary particle size r (μm) of the strontium titanate particles. The relationship 6 ≦ RSm (C) / r ≦ 40 is satisfied.

  Hereinafter, matters common to the first embodiment and the second embodiment will be collectively referred to as the present embodiment.

  The developer according to this embodiment suppresses the occurrence of density unevenness. The mechanism is not necessarily clear, but is presumed as follows.

  On the surface of the developing sleeve of the developing device, irregularities or grooves are formed or blasted so that the developer can be efficiently conveyed. However, when the developing device is used for a long period of time, the surface of the developing sleeve is worn or the toner component adheres to the surface of the developing sleeve and is contaminated. When the surface of the developing sleeve is worn or contaminated, the layer thickness of the developer supplied to the photosensitive member may vary, and density unevenness may occur in the image. In particular, density unevenness is likely to occur in halftone image formation after low density images are continuously formed and then stored overnight in a high temperature and high humidity environment.

  This embodiment includes toner particles, a resin-coated carrier in which the exposure ratio of magnetic particles is 2% or more and 20% or less, and strontium titanate particles having a round shape, and the RSm (C) and the above The developer having a ratio RSm (C) / r to r of 6 or more and 40 or less suppresses the wear and contamination of the surface of the developing sleeve and suppresses the occurrence of density unevenness.

  Wear on the surface of the developing sleeve is likely to occur due to friction with the carrier, and in particular, since the magnetic particles exposed from the resin layer are highly abrasive and easy to wear the surface of the developing sleeve, the exposure rate of the magnetic particles in the resin-coated carrier Is 20% or less. However, from the viewpoint of efficiently charging the toner particles and suppressing the occurrence of image defects (for example, white spots), the exposure ratio of the magnetic particles in the resin-coated carrier is set to 2% or more.

The strontium titanate particles are likely to adhere electrostatically to the surface of the magnetic particles. By setting the ratio RSm (C) / r between the RSm (C) and the r to an appropriate range, the strontium titanate particles Are dispersed with high uniformity on the surface of the resin-coated carrier, and the strontium titanate particles function as a spacer between the resin-coated carrier and the developing sleeve surface. Since the strontium titanate particles have a rounded shape, the strontium titanate particles roll on the carrier surface at the contact point between the resin-coated carrier and the developing sleeve. Demonstrate the ability to scratch.
If RSm (C) / r is greater than 40, it is estimated that the strontium titanate particles do not easily reach the resin-coated carrier convex portion, which is the contact portion on the resin-coated carrier side with respect to the developing sleeve.
If RSm (C) / r is smaller than 6, it is presumed that strontium titanate particles are likely to be unevenly distributed in the resin-coated carrier recess.

In the present embodiment, from the viewpoint of more uniformly dispersing strontium titanate particles on the surface of the resin-coated carrier, the resin-coated carrier, the magnetic particles of the resin-coated carrier, and the strontium titanate particles are positively charged in this order. It is preferable that it is easy to do.
The above-described charging train is realized by the type of resin contained in the resin layer of the resin-coated carrier or the type of magnetic material contained in the magnetic particles of the resin-coated carrier. From the viewpoint of realizing the above charge train, the resin layer of the resin-coated carrier preferably contains an alicyclic acrylic resin, and the magnetic particles are preferably ferrite particles.

  The developer according to this embodiment is prepared by mixing toner particles, a resin-coated carrier, and strontium titanate particles at an appropriate blending ratio.

  The content of strontium titanate particles contained in the developer according to this embodiment is preferably 0.005% by mass or more and 2.0% by mass or less, and 0.01% by mass or more and 1% by mass with respect to the mass of the resin-coated carrier. 0.5 mass% or less is more preferable, and 0.015 mass% or more and 1.0 mass% or less is still more preferable.

  The content of the toner particles contained in the developer according to the exemplary embodiment is preferably 1% by mass to 30% by mass, and more preferably 3% by mass to 20% by mass with respect to the mass of the resin-coated carrier.

  Hereinafter, the resin-coated carrier, strontium titanate particles, and toner particles constituting the developer according to the present embodiment will be described in detail.

[Resin coated carrier]
The resin-coated carrier has magnetic particles and a resin layer that covers the magnetic particles.

  The exposure ratio of the magnetic particles on the surface of the resin-coated carrier is 2% or more and 20% or less, more preferably 2% or more and 10% or less, and further preferably 3% or more and 8% or less.

The exposure ratio of the magnetic particles on the surface of the resin-coated carrier is determined by the following method by X-ray photoelectron spectroscopy (XPS).
A target resin-coated carrier and magnetic particles obtained by removing the resin layer from the target resin-coated carrier are prepared. Examples of the method for removing the resin layer from the resin-coated carrier include a method of removing the resin layer by dissolving the resin component with an organic solvent, and a method of removing the resin layer by eliminating the resin component by heating at about 800 ° C. Can be mentioned. Using the resin-coated carrier and the magnetic particles excluding the resin layer as measurement samples, respectively, the amount of Fe (atomic%) is quantified by XPS, and (Fe of resin-coated carrier) ÷ (Fe of magnetic particles) × 100 is calculated. And the exposure ratio (%) of the magnetic particles.

  The exposure ratio of the magnetic particles in the resin-coated carrier can be controlled by the amount of resin used for forming the resin layer, and the exposure ratio decreases as the amount of resin with respect to the amount of magnetic particles increases.

  The resin-coated carrier preferably has an average length RSm (C) of the surface roughness curve element of 0.5 μm or more and 5.0 μm or less, more preferably 0.6 μm or more and 4.0 μm or less, More preferably, it is 0.8 μm or more and 3.5 μm or less.

  In the present embodiment, the average length RSm (C) of the roughness curve element on the surface of the resin-coated carrier is “average length RSm of the roughness curve element” in JIS B0601: 2001. RSm (C) is obtained by image analysis using a laser microscope (manufactured by Keyence Corporation, VK-9500) according to the measurement method described in JIS B0601: 2001 using a resin-coated carrier as a sample.

  In the present embodiment, the ratio RSm (C) / r between RSm (C) (μm) and the average primary particle size r (μm) of the strontium titanate particles is 6 or more and 40 or less, and 8 or more and 35 or less. More preferably, it is 10 or more and 30 or less.

  RSm (C) can be controlled by the particle size of the pre-fired product before the main firing and the firing temperature or firing time of the main firing when the magnetic particles are produced. The smaller the calcined product particle size and the lower the calcining temperature or the shorter the calcining time, the higher the RSm (C), and the smaller the calcined product particle size, the higher the calcining temperature or the longer the calcining time, the more the RSm (C). C) becomes lower.

-Magnetic particles-
The magnetic particles are not particularly limited, and known magnetic particles used as a carrier core material are applied. Specific examples of magnetic particles include particles of magnetic metals such as iron, nickel, and cobalt; particles of magnetic oxides such as ferrite and magnetite; resin-impregnated magnetic particles obtained by impregnating a resin in porous magnetic powder; Magnetic powder dispersed resin particles in which magnetic powder is dispersed and blended.

  In the present embodiment, as the magnetic particles, ferrite particles are preferable from the viewpoint of easily realizing the above-described charging train.

  The volume average particle diameter of the magnetic particles is, for example, 10 μm or more and 500 μm or less, and preferably 30 μm or more and 150 μm or less.

  As for the magnetic force of the magnetic particles, the saturation magnetization in a 3000 oersted magnetic field is, for example, 50 emu / g or more, and preferably 60 emu / g or more. The saturation magnetization is measured using a vibration sample type magnetometer VSMP10-15 (manufactured by Toei Kogyo Co., Ltd.). The measurement sample is packed in a cell having an inner diameter of 7 mm and a height of 5 mm and set in the apparatus. The measurement applies an applied magnetic field and sweeps up to 3000 oersted. Next, the applied magnetic field is reduced to create a hysteresis curve on the recording paper. Saturation magnetization, residual magnetization, and coercive force are obtained from the curve data.

The volume electrical resistance (volume resistivity) of the magnetic particles is, for example, from 10 ⁵ Ω · cm to 10 ⁹ Ω · cm, and preferably from 10 ⁷ Ω · cm to 10 ⁹ Ω · cm.
The volume electrical resistance (Ω · cm) of the magnetic particles is measured as follows. On the surface of a circular jig provided with a 20 cm ² electrode plate, the measurement object is placed flat so as to have a thickness of 1 mm or more and 3 mm or less to form a layer. The 20 cm ² electrode plate is placed on this and the layer is sandwiched. In order to eliminate gaps between objects to be measured, the thickness (cm) of the layer is measured after applying a load of 4 kg on the electrode plate arranged on the layer. Both electrodes above and below the layer are connected to an electrometer and a high voltage power generator. A high voltage is applied to both electrodes so that the electric field is 103.8 V / cm, and the current value (A) flowing at this time is read. The measurement environment is a temperature of 20 ° C. and a humidity of 50% RH. The calculation formula of the volume electrical resistance (Ω · cm) of the measurement object is as shown in the following formula.
R = E × 20 / (I−I ₀ ) / L
In the above formula, R is the volume electrical resistance (Ω · cm) of the measurement object, E is the applied voltage (V), I is the current value (A), I ₀ is the current value (A) at the applied voltage of 0 V, and L is Each layer thickness (cm) is expressed. The coefficient 20 represents the area (cm ² ) of the electrode plate.

-Resin layer covering magnetic particles-
As the resin constituting the resin layer, styrene / acrylic acid copolymer; polyolefin resin such as polyethylene and polypropylene; polystyrene, acrylic resin, polyacrylonitrile, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl carbazole, Polyvinyl resins such as polyvinyl ether and polyvinyl ketone or polyvinylidene resins; vinyl chloride / vinyl acetate copolymers; straight silicone resins composed of organosiloxane bonds or modified products thereof; polytetrafluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, Fluorine resin such as polychlorotrifluoroethylene; polyester; polyurethane; polycarbonate; amino resin such as urea / formaldehyde resin; epoxy resin; Etc., and the like.

  The resin layer preferably contains an alicyclic acrylic resin. When the resin layer contains the alicyclic acrylic resin, the strontium titanate particles are more easily dispersed with high uniformity on the surface of the resin-coated carrier. Moreover, it becomes easy to realize the above-mentioned charged column.

  As a polymerization component of the alicyclic acrylic resin, a lower alkyl ester of (meth) acrylic acid (for example, a (meth) acrylic acid alkyl ester having an alkyl group having 1 to 9 carbon atoms) is preferable, specifically, Examples include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate, cyclohexyl (meth) acrylate, and 2-ethylhexyl (meth) acrylate. These monomers may be used alone or in combination of two or more.

  The alicyclic acrylic resin shields the influence of water on the polarization component of the bond between the carbon atom and the oxygen atom due to the steric hindrance of the alicyclic functional group. It is preferable to include cyclohexyl (meth) acrylate as a polymerization component because the influence of moisture on environmental changes can be suppressed. The content of cyclohexyl (meth) acrylate contained in the alicyclic acrylic resin is preferably 75 mol% to 100 mol%, more preferably 90 mol% to 100 mol%, and more preferably 95 mol% to 100 mol%. Further preferred.

  The proportion of the alicyclic acrylic resin in the total resin contained in the resin layer is preferably 80% by mass or more, more preferably 90% by mass or more, and still more preferably substantially all the resin is an alicyclic acrylic resin. .

  The resin layer may contain inorganic particles for the purpose of controlling charging and resistance. Examples of inorganic particles include carbon black; metals such as gold, silver, copper; and barium sulfate, aluminum borate, potassium titanate, titanium oxide, zinc oxide, tin oxide, tin oxide doped with antimony, and tin. Metal compounds such as indium oxide and zinc oxide doped with aluminum; resin particles coated with metal; and the like.

  Examples of the method for forming the resin layer on the surface of the magnetic particles include a wet manufacturing method and a dry manufacturing method. The wet manufacturing method is a manufacturing method using a solvent that dissolves or disperses the resin constituting the resin layer. On the other hand, the dry process is a process that does not use the solvent.

Examples of the wet manufacturing method include an immersion method in which magnetic particles are immersed and coated in a resin solution for forming a resin layer; a spray method in which a resin solution for forming a resin layer is sprayed on the surface of the magnetic particles; For example, a fluidized bed method in which a resin liquid for forming a resin layer is sprayed in a converted state; a kneader coater method in which magnetic particles and a resin liquid for forming a resin layer are mixed in a kneader coater to remove the solvent;
The resin liquid for forming a resin layer used in the wet manufacturing method is prepared by dissolving or dispersing a resin and other components in a solvent. The solvent is not particularly limited as long as it dissolves or disperses the resin, and examples thereof include aromatic hydrocarbons such as toluene and xylene; ketones such as acetone and methyl ethyl ketone; ethers such as tetrahydrofuran and dioxane; used.

  Examples of the dry production method include a method of forming a resin layer by heating a mixture of magnetic particles and a resin for forming a resin layer in a dry state. Specifically, for example, the magnetic particles and the resin layer forming resin are mixed in the gas phase and heated and melted to form a resin layer.

  The thickness of the resin layer is preferably from 0.1 μm to 10 μm, and more preferably from 0.3 μm to 5 μm.

[Strontium titanate particles]
In the present embodiment, the strontium titanate particles preferably have an average primary particle size of 10 nm to 100 nm. When the average primary particle size of the strontium titanate particles is 10 nm or more, burying of the resin-coated carrier in the resin layer is suppressed, and the resin-coated carrier surface is easily dispersed with high uniformity. Also, the resin-coated carrier and the developing sleeve surface Easy to function as a spacer between. When the average primary particle diameter of the strontium titanate particles is 100 nm or less, the release from the resin-coated carrier is suppressed, and the surface of the resin-coated carrier is rolled to scrape the surface of the developing sleeve.

  In view of the above, the average primary particle size r of the strontium titanate particles is preferably 10 nm to 100 nm, more preferably 20 nm to 90 nm, and still more preferably 30 nm to 80 nm.

  In this embodiment, the primary particle size of strontium titanate particles is the diameter of a circle having the same area as the primary particle image (so-called equivalent circle diameter), and the average primary particle size of strontium titanate particles is the primary particle size. In the distribution based on the number of particles, the particle diameter is 50% cumulative from the small diameter side. The primary particle size of the strontium titanate particles is obtained by analyzing an image of at least 300 strontium titanate particles.

  The average primary particle diameter of the strontium titanate particles can be controlled, for example, by various conditions when the strontium titanate particles are produced by a wet process.

  In the present embodiment, the shape of the strontium titanate particles is not a cube or a rectangular parallelepiped but a rounded shape from the viewpoint of suppressing the occurrence of density unevenness.

In the present embodiment, the strontium titanate particles preferably have an average primary particle circularity of 0.82 or more and 0.94 or less, and a circularity of 84% cumulative primary particles is more than 0.92. .
In this embodiment, the primary particle circularity of strontium titanate particles is 4π × (area of primary particle image) ÷ (peripheral length of primary particle image) ² , and the average circularity of primary particles is the circularity The circularity of 50% cumulative from the smaller side in the distribution of, and the circularity of 84% cumulative primary particles is the circularity of 84% cumulative from the smaller side in the circularity distribution. The circularity of the strontium titanate particles is determined by image analysis of at least 300 strontium titanate particles.

  Regarding the strontium titanate particles, the circularity, which is 84% of the accumulation of primary particles, is one of the indicators of a rounded shape. The circularity that is 84% of the primary particles (hereinafter also referred to as 84% cumulative circularity) will be described.

FIG. 1A is a graph of an SEM image of resin particles externally added with SW-360 manufactured by Titanium Industry, an example of strontium titanate particles, and a graph of circularity distribution of strontium titanate particles obtained by analyzing the SEM image. is there. As shown in the SEM image, SW-360 has a cubic main particle shape, and was mixed with rectangular parallelepiped particles and relatively small spherical particles. The circularity distribution of SW-360 in this example is concentrated between 0.84 and 0.92, the average circularity is 0.888, and the cumulative 84% circularity is 0.916. This means
(A) The main particle shape of SW-360 is a cube,
(B) The projected image of the cube includes a regular hexagon (circularity of about 0.907), a flat hexagon, a square (circularity of about 0.785), and a rectangle in the order close to a circle.
(C) The cubic strontium titanate particles are attached to the resin particles at an angle, and the projected image is mainly hexagonal,
It is considered to reflect this.
From the fact that the actual circularity distribution of SW-360 is as described above and the theoretical circularity of a three-dimensional projection image, cubic or cuboid strontium titanate particles have a cumulative primary particle 84% circularity. It can be estimated that it is below 0.92.
On the other hand, FIG. 1B is a graph of an SEM image of resin particles externally added with other strontium titanate particles and a circularity distribution of the strontium titanate particles obtained by analyzing the SEM image. As the SEM image shows, the strontium titanate particles of this example had a rounded shape. The strontium titanate particles of this example had an average circularity of 0.883 and a cumulative 84% circularity of 0.935.
From the above, regarding the strontium titanate particles, the cumulative 84% circularity of the primary particles becomes one of the indicators of the rounded shape, and when it exceeds 0.92, it can be said that it is a rounded shape.

  In this embodiment, the average circularity of the primary particles of the strontium titanate particles is preferably 0.82 or more and 0.94 or less, more preferably 0.84 or more and 0.94 or less, from the viewpoint of suppressing the occurrence of density unevenness, More preferably, it is 0.86 or more and 0.92 or less.

In the present embodiment, the strontium titanate particles preferably have a standard deviation of the circularity of the primary particles of 0.04 or more and 2.0 or less, more preferably 0.04 or more and 1.0 or less. More preferably, it is 04 or more and 0.50 or less.
Cubic or cuboid strontium titanate particles tend to have a narrow circularity distribution due to their shape. Therefore, the standard deviation of the circularity of the primary particles being in the above range is an index indicating that the particles are not strontium titanate particles containing a large number of cubes or cuboids.

In the present embodiment, the strontium titanate particles preferably have a (110) plane peak half-value width of 0.2 ° or more and 2.0 ° or less obtained by the X-ray diffraction method. More preferably, it is 0 ° or less.
The peak of the (110) plane obtained by the X-ray diffraction method of strontium titanate particles is a peak that appears in the vicinity of the diffraction angle 2θ = 32 °. This peak corresponds to the peak of the (110) plane of the perovskite crystal.
Strontium titanate particles having a cubic or cuboid particle shape have high crystallinity of perovskite crystals, and the (110) plane peak half-value width is usually less than 0.2 °. For example, when SW-350 (strontium titanate particles whose main particle shape is cubic) manufactured by Titanium Industry Co., Ltd. was analyzed, the half width of the peak on the (110) plane was 0.15 °.
On the other hand, rounded strontium titanate particles have relatively low crystallinity of the perovskite crystal, and the full width at half maximum of the (110) plane peak is increased.
In the present embodiment, the strontium titanate particles preferably have a rounded shape. As one of the rounded shape indexes, the half width of the peak of the (110) plane is 0.2 ° or more and 2. It is preferably 0 ° or less, more preferably 0.2 ° or more and 1.0 ° or less, and further preferably 0.2 ° or more and 0.5 ° or less.

  X-ray diffraction of strontium titanate particles is measured using an X-ray diffractometer (for example, trade name RINT Ultima-III, manufactured by Rigaku Corporation). Measurement settings are: radiation source CuKα, voltage: 40 kV, current: 40 mA, sample rotation speed: no rotation, divergence slit: 1.00 mm, divergence longitudinal restriction slit: 10 mm, scattering slit: open, light receiving slit: open, scanning mode : FT, counting time: 2.0 seconds, step width: 0.0050 °, operation axis: 10.0000 ° to 70.0000 °. In the present disclosure, the half width of the peak in the X-ray diffraction pattern is the full width at half maximum.

  In the present embodiment, the strontium titanate particles are preferably doped with a metal element other than titanium and strontium (hereinafter also referred to as a dopant). By containing a dopant, the strontium titanate particles have a rounded shape due to a decrease in crystallinity of the perovskite structure.

  The dopant of the strontium titanate particles is not particularly limited as long as it is a metal element other than titanium and strontium. A metal element having an ionic radius that can enter the crystal structure constituting the strontium titanate particles when ionized is preferable. From this point of view, the dopant of the strontium titanate particles is preferably a metal element having an ion radius of 40 pm or more and 200 pm or less, and more preferably a metal element of 60 pm or more and 150 pm or less when ionized.

  Specific examples of dopants for strontium titanate particles include lanthanoid, silica, aluminum, magnesium, calcium, barium, phosphorus, sulfur, calcium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, gallium, yttrium, Examples thereof include zinc, niobium, molybdenum, ruthenium, rhodium, palladium, silver, indium, tin, antimony, barium, tantalum, tungsten, rhenium, osmium, iridium, platinum, and bismuth. As the lanthanoid, lanthanum and cerium are preferable. Among these, lanthanum is preferable from the viewpoint of easy doping and easy control of the shape of the strontium titanate particles.

  As a dopant for the strontium titanate particles, a metal element having an electronegativity of 2.0 or less is preferable and a metal element having an electronegativity of 1.3 or less is more preferable from the viewpoint of preventing the strontium titanate particles from being excessively negatively charged. . In the present embodiment, the electronegativity is that of all-red locomotive. Examples of metal elements having an electronegativity of 2.0 or less include lanthanum (electronegativity 1.08), magnesium (1.23), aluminum (1.47), silica (1.74), calcium (1.04). ), Vanadium (1.45), chromium (1.56), manganese (1.60), iron (1.64), cobalt (1.70), nickel (1.75), copper (1.75) , Zinc (1.66), gallium (1.82), yttrium (1.11), zirconium (1.22), niobium (1.23), silver (1.42), indium (1.49), Examples include tin (1.72), barium (0.97), tantalum (1.33), rhenium (1.46), and cerium (1.06).

  The amount of dopant in the strontium titanate particles is preferably in the range where the dopant is 0.1 mol% or more and 20 mol% or less with respect to strontium from the viewpoint of a round shape while having a perovskite crystal structure. The range of 0.1 mol% to 15 mol% is more preferable, and the range of 0.1 mol% to 10 mol% is more preferable.

  In the present embodiment, the strontium titanate particles are preferably strontium titanate particles having a hydrophobized surface from the viewpoint of improving the action of the strontium titanate particles. It is assumed that the strontium titanate particles subjected to the hydrophobization treatment repel each other on the resin-coated carrier and are easily dispersed with high uniformity.

  In this embodiment, the strontium titanate particles are more preferably strontium titanate particles having a surface hydrophobized with a silicon-containing organic compound. Strontium titanate particles that have been hydrophobized with a silicon-containing organic compound are more sensitive to non-image areas on the photoreceptor than strontium titanate particles that have been hydrophobized with a processing agent with a strong positive charge, such as a fatty acid metal salt. Difficult to release and less likely to cause image defects.

The strontium titanate particles are 1% by mass or more and 50% by mass or less (preferably 5% by mass or more and 40% by mass or less, more preferably 5% by mass or more and 30% by mass or less, and still more preferably 10% by mass with respect to the mass. It is preferable to have a surface containing a silicon-containing organic compound of 25 mass% or less.
That is, the amount of hydrophobic treatment by the silicon-containing organic compound is preferably 1% by mass or more and 50% by mass or less, more preferably 5% by mass or more and 40% by mass or less, and more preferably 5% by mass or more with respect to the mass of the strontium titanate particles. 30 mass% or less is still more preferable, and 10 mass% or more and 25 mass% or less are still more preferable.
When the hydrophobic treatment amount is in the above range, it is easy to suppress the occurrence of density unevenness. When the hydrophobization amount is 30% by mass or less, the generation of aggregates due to the hydrophobized surface is suppressed.

  The surface of the strontium titanate particles hydrophobized with the silicon-containing organic compound is silicon (Si) calculated from the qualitative and quantitative analysis of fluorescent X-ray analysis from the viewpoint of improving the action of the strontium titanate particles. The mass ratio Si / Sr with strontium (Sr) is preferably 0.025 or more and 0.25 or less, and more preferably 0.05 or more and 0.20 or less.

The fluorescent X-ray analysis of the hydrophobized surface of the strontium titanate particles is performed by the following method.
Using a fluorescent X-ray analyzer (XRF1500, manufactured by Shimadzu Corporation), qualitative and quantitative analysis is performed under the conditions of X-ray output: 40 V / 70 mA, measurement area: diameter 10 mm, measurement time: 15 minutes. The elements to be analyzed are oxygen (O), silicon (Si), titanium (Ti), strontium (Sr), and other metal elements (Me), and the mass ratio ( %). The mass ratio Si / Sr is calculated from the mass ratio (%) of silicon (Si) and the mass ratio (%) of strontium (Sr) obtained by this measurement.

  In this embodiment, the volume specific resistivity R (Ω · cm) of the strontium titanate particles is preferably 11 or more, 14 or less, more preferably 11 or more and 13 or less, and still more preferably 12 or more and 13 or less in the common logarithmic value logR. .

  The volume specific resistivity R of the strontium titanate particles can be controlled by, for example, the type of dopant, the amount of the dopant, the type of the hydrophobizing agent, the hydrophobizing amount, the drying temperature and the drying time after the hydrophobizing treatment, and the like.

The volume resistivity R of the strontium titanate particles is measured as follows.
On the lower electrode plate of the measuring jig, which is a pair of 20 cm ² circular electrode plates (made of steel) connected to an electrometer (KEYTHLEY, KEITHLEY 610C) and a high-voltage power supply (FLUKE, FLUKE 415B) Strontium particles are introduced so as to form a flat layer having a thickness in the range of 1 mm to 2 mm. Next, humidity is adjusted for 24 hours in an environment of a temperature of 22 ° C. and a relative humidity of 55%. Next, in an environment of a temperature of 22 ° C./55% relative humidity, an upper electrode plate is placed on the strontium titanate particle layer, and a 4 kg weight is placed on the upper electrode plate to remove voids in the strontium titanate particle layer. In this state, the thickness of the strontium titanate particle layer is measured. Next, a voltage of 1000 V is applied to the bipolar plates, the current value is measured, and the volume resistivity R is calculated from the following formula (1).
Formula (1): Volume resistivity R (Ω · cm) = V × S ÷ (A1−A0) ÷ d
In the formula (1), V is an applied voltage 1000 (V), S is an electrode plate area 20 (cm ² ), A1 is a measured current value (A), A0 is an initial current value (A) when the applied voltage is 0 V, d is the thickness (cm) of the strontium titanate particle layer.

  In the present embodiment, the strontium titanate particles preferably have a moisture content of 1.5% by mass or more and 10% by mass or less. When the water content is 1.5% by mass or more and 10% by mass or less (more preferably 2% by mass or more and 5% by mass or less), the resistance of the strontium titanate particles is controlled within an appropriate range. Excellent in suppressing uneven distribution due to electrostatic repulsion. The water content of strontium titanate particles can be controlled, for example, by producing strontium titanate particles by a wet process and adjusting the temperature and time of the drying treatment. When hydrophobizing strontium titanate particles, the water content of the strontium titanate particles can be controlled by adjusting the temperature and time of the drying process after hydrophobizing.

The water content of the strontium titanate particles is measured as follows.
20 mg of a measurement sample was allowed to stand in a chamber at a temperature of 22 ° C./55% relative humidity for 17 hours to adjust the humidity, and then a thermobalance (TGA-50 manufactured by Shimadzu Corporation) in a room at a temperature of 22 ° C./55% relative humidity. Is heated from 30 ° C. to 250 ° C. at a temperature increase rate of 30 ° C./min in a nitrogen gas atmosphere, and the loss on heating (mass lost by heating) is measured. The moisture content is calculated by the following formula based on the measured loss on heating.
Moisture content (mass%) = (heat loss from 30 ° C. to 250 ° C.) ÷ (mass after humidity control and before heating) × 100

[Method for producing strontium titanate particles]
The strontium titanate particles may be strontium titanate particles themselves or particles obtained by hydrophobizing the surface of strontium titanate particles (sometimes referred to as mother particles). The method for producing strontium titanate particles (base particles) is not particularly limited, but is preferably a wet production method from the viewpoint of controlling the particle size and shape.

  The wet manufacturing method of the strontium titanate particles is, for example, a manufacturing method in which a reaction is performed while adding an alkaline aqueous solution to a mixed solution of a titanium oxide source and a strontium source, and then an acid treatment is performed. In this production method, the particle diameter of the strontium titanate particles is controlled by the mixing ratio of the titanium oxide source and the strontium source, the titanium oxide source concentration at the initial stage of the reaction, the temperature when adding the alkaline aqueous solution, the addition rate, and the like.

  As the titanium oxide source, a mineral acid peptized product of a hydrolyzate of a titanium compound is preferable. Examples of the strontium source include strontium nitrate and strontium chloride.

The mixing ratio of the titanium oxide source and the strontium source is preferably 0.9 or more and 1.4 or less, and more preferably 1.05 or more and 1.20 or less in terms of SrO / TiO ₂ molar ratio. The titanium oxide source concentration at the initial stage of the reaction is preferably 0.05 mol / L or more and 1.3 mol / L or less, more preferably 0.5 mol / L or more and 1.0 mol / L or less as TiO ₂ .

  From the viewpoint of making the shape of the strontium titanate particles round rather than cubic or rectangular parallelepiped, it is preferable to add a dopant source to the mixed liquid of the titanium oxide source and the strontium source. Examples of the dopant source include oxides of metals other than titanium and strontium. The metal oxide as the dopant source is added, for example, as a solution dissolved in nitric acid, hydrochloric acid or sulfuric acid. The addition amount of the dopant source is preferably such that the metal contained in the dopant source is 0.1 mol or more and 20 mol or less with respect to 100 mol of strontium contained in the strontium source, and is 0.5 mol or more and 10 mol or less. The amount is more preferred.

  As the alkaline aqueous solution, an aqueous sodium hydroxide solution is preferred. The higher the temperature of the reaction solution when adding the alkaline aqueous solution, the better the crystallinity of strontium titanate particles. The temperature of the reaction solution when adding the alkaline aqueous solution is preferably in the range of 60 ° C. or more and 100 ° C. or less from the viewpoint of making the shape round while having a perovskite crystal structure. As the addition rate of the alkaline aqueous solution, the slower the addition rate, the larger the particle size of strontium titanate particles, and the faster the addition rate, the smaller the particle size of strontium titanate particles. The addition rate of the alkaline aqueous solution is, for example, 0.001 equivalent / h or more and 1.2 equivalent / h or less, and 0.002 equivalent / h or more and 1.1 equivalent / h or less with respect to the charged raw material.

  After adding the alkaline aqueous solution, acid treatment is performed for the purpose of removing the unreacted strontium source. In the acid treatment, for example, hydrochloric acid is used to adjust the pH of the reaction solution to 2.5 to 7.0, more preferably 4.5 to 6.0. After the acid treatment, the reaction solution is subjected to solid-liquid separation, and the solid content is dried to obtain strontium titanate particles.

  The surface treatment of the strontium titanate particles is, for example, preparing a treatment liquid obtained by mixing a silicon-containing organic compound that is a hydrophobizing agent and a solvent, and mixing the strontium titanate particles and the treatment liquid with stirring. Furthermore, it is performed by continuing stirring. After the surface treatment, a drying treatment is performed for the purpose of removing the solvent of the treatment liquid.

  Examples of the silicon-containing organic compound used for the surface treatment of the strontium titanate particles include alkoxysilane compounds, silazane compounds, and silicone oils.

  Examples of the alkoxysilane compound used for the surface treatment of strontium titanate particles include tetramethoxysilane, tetraethoxysilane; methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, butyltrimethoxysilane, hexyltrimethoxysilane, n-octyltrimethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, vinyltriethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, butyltriethoxysilane, hexyltriethoxysilane, decyltriethoxysilane, dodecyltriethoxy Silane, phenyltrimethoxysilane, o-methylphenyltrimethoxysilane, p-methylphenyltrimethoxysilane, phenyltriethoxysilane, Emissions Jill triethoxysilane; dimethyldimethoxysilane, dimethyldiethoxysilane, methyl vinyl dimethoxy silane, methyl vinyl diethoxy silane, diphenyl dimethoxy silane, diphenyl diethoxy silane; trimethylmethoxysilane, trimethylethoxysilane; and the like.

  Examples of the silazane compound used for the surface treatment of strontium titanate particles include dimethyldisilazane, trimethyldisilazane, tetramethyldisilazane, pentamethyldisilazane, hexamethyldisilazane, and the like.

  Examples of the silicone oil used for the surface treatment of strontium titanate particles include silicone oils such as dimethylpolysiloxane, diphenylpolysiloxane, and phenylmethylpolysiloxane; amino-modified polysiloxane, epoxy-modified polysiloxane, carboxyl-modified polysiloxane, and carbinol. And reactive silicone oils such as modified polysiloxane, fluorine-modified polysiloxane, methacryl-modified polysiloxane, mercapto-modified polysiloxane, and phenol-modified polysiloxane.

  The solvent used for the preparation of the treatment liquid is preferably an alcohol (for example, methanol, ethanol, propanol, butanol) when the silicon-containing organic compound is an alkoxysilane compound or a silazane compound, and the silicon-containing organic compound is silicone oil. In this case, hydrocarbons (for example, benzene, toluene, normal hexane, normal heptane) are preferable.

  In the treatment liquid, the concentration of the silicon-containing organic compound is preferably 1% by mass to 50% by mass, more preferably 5% by mass to 40% by mass, and still more preferably 10% by mass to 30% by mass.

  The amount of the silicon-containing organic compound used for the surface treatment is preferably 1 part by mass or more and 50 parts by mass or less, more preferably 5 parts by mass or more and 40 parts by mass or less, with respect to 100 parts by mass of the strontium titanate particles. 30 parts by mass or less is more preferable.

[Toner particles]
The toner particles may be toner particles having a single layer structure, or toner particles having a so-called core / shell structure composed of a core (core particle) and a coating layer (shell layer) covering the core. May be. The toner particles having a core / shell structure are preferably composed of, for example, a core containing a binder resin, a colorant, and other additives such as a release agent, and a coating layer containing the binder resin.
The toner particles may be toner particles to which an external additive is externally added.

  In this embodiment, the average length RSm (C) (μm) of the roughness curve element on the surface of the resin-coated carrier, the average length RSm (T) (μm) of the roughness curve element on the surface of the toner particle, and titanic acid. The average primary particle size r (μm) of the strontium particles preferably satisfies the relationship of 11 ≦ RSm (C) / (RSm (T) × r) ≦ 100 from the viewpoint of further suppressing the occurrence of density unevenness. RSm (C) / (RSm (T) × r) is more preferably 11.5 or more and 80 or less, further preferably 12 or more and 75 or less, and further preferably 12.4 or more and 70 or less.

  In the present embodiment, the toner particles preferably have an average length RSm (T) of a roughness curve element on the toner particle surface of 0.05 μm or more and 2.0 μm or less, and 0.1 μm or more and 1.5 μm or less. More preferably, it is 0.15 μm or more and 1.0 μm or less.

  In this embodiment, the average length RSm (T) of the roughness curve element on the toner particle surface is “average length RSm of roughness curve element” in JIS B0601: 2001. RSm (T) is obtained by analyzing the image using a laser microscope (manufactured by Keyence Corporation, VK-9500) according to the measurement method described in JIS B0601: 2001 using toner particles as a sample.

  Hereinafter, components constituting the toner particles will be described.

-Binder resin-
Examples of the binder resin include styrenes (eg, styrene, parachlorostyrene, α-methylstyrene, etc.), (meth) acrylic acid esters (eg, methyl acrylate, ethyl acrylate, n-propyl acrylate, acrylic acid). n-butyl, lauryl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, lauryl methacrylate, 2-ethylhexyl methacrylate, etc.), ethylenically unsaturated nitriles (for example, acrylonitrile, Methacrylonitrile, etc.), vinyl ethers (eg, vinyl methyl ether, vinyl isobutyl ether, etc.), vinyl ketones (eg, vinyl methyl ketone, vinyl ethyl ketone, vinyl isopropenyl ketone, etc.), olefins (eg, ethylene, Propylene, a homopolymer of a monomer such as butadiene) and the like, or a vinyl-based resin composed of these monomers with two or more combinations copolymer.
As the binder resin, for example, epoxy resin, polyester resin, polyurethane resin, polyamide resin, cellulose resin, polyether resin, non-vinyl resin such as modified rosin, a mixture of these with the vinyl resin, or these Examples also include a graft polymer obtained by polymerizing a vinyl monomer in the coexistence.
These binder resins may be used alone or in combination of two or more.

  A polyester resin is suitable as the binder resin. Examples of the polyester resin include known polyester resins.

The glass transition temperature (Tg) of the polyester resin is preferably 50 ° C. or higher and 80 ° C. or lower, and more preferably 50 ° C. or higher and 65 ° C. or lower.
The glass transition temperature is obtained from a DSC curve obtained by differential scanning calorimetry (DSC), and more specifically, it is described in “Supplement” described in the method for obtaining the glass transition temperature in JIS K7121-1987 “Method for measuring glass transition temperature”. It is determined by “outer glass transition start temperature”.

The weight average molecular weight (Mw) of the polyester resin is preferably from 5,000 to 1,000,000, and more preferably from 7,000 to 500,000. The number average molecular weight (Mn) of the polyester resin is preferably from 2,000 to 100,000. The molecular weight distribution Mw / Mn of the polyester resin is preferably 1.5 or more and 100 or less, and more preferably 2 or more and 60 or less.
The weight average molecular weight and the number average molecular weight are measured by gel permeation chromatography (GPC). The molecular weight measurement by GPC is performed with a THF solvent using a Tosoh GPC / HLC-8120GPC as a measuring device and a Tosoh column / TSKgel SuperHM-M (15 cm). The weight average molecular weight and the number average molecular weight are calculated using a molecular weight calibration curve prepared from a monodisperse polystyrene standard sample from this measurement result.

  The content of the binder resin is preferably 40% by mass to 95% by mass, more preferably 50% by mass to 90% by mass, and still more preferably 60% by mass to 85% by mass with respect to the entire toner particles.

-Colorant-
Examples of the colorant include carbon black, chrome yellow, hansa yellow, benzidine yellow, sren yellow, quinoline yellow, pigment yellow, permanent orange GTR, pyrazolone orange, vulcan orange, watch young red, permanent red, brilliant carmine 3B, and brilliant. Carmine 6B, Dupont Oil Red, Pyrazolone Red, Resol Red, Rhodamine B Lake, Lake Red C, Pigment Red, Rose Bengal, Aniline Blue, Ultramarine Blue, Calco Oil Blue, Methylene Blue Chloride, Phthalocyanine Blue, Pigment Blue, Phthalocyanine Green, Pigments such as malachite green oxalate; acridine, xanthene, azo, benzox , Azine, anthraquinone, thioindico, dioxazine, thiazine, azomethine, indico, phthalocyanine, aniline black, polymethine, triphenylmethane, diphenylmethane, thiazole, etc. It is done.
A coloring agent may be used individually by 1 type, and may use 2 or more types together.

  As the colorant, a surface-treated colorant may be used as necessary, or it may be used in combination with a dispersant. A plurality of colorants may be used in combination.

  The content of the colorant is preferably 1% by mass or more and 30% by mass or less, and more preferably 3% by mass or more and 15% by mass or less with respect to the entire toner particles.

-Release agent-
Examples of mold release agents include hydrocarbon waxes; natural waxes such as carnauba wax, rice wax, and candelilla wax; synthetic or mineral / petroleum waxes such as montan wax; and ester waxes such as fatty acid esters and montanic acid esters. And so on. The release agent is not limited to this.

The melting temperature of the release agent is preferably 50 ° C. or higher and 110 ° C. or lower, and more preferably 60 ° C. or higher and 100 ° C. or lower.
The melting temperature is determined from the DSC curve obtained by differential scanning calorimetry (DSC) according to the “melting peak temperature” described in JIS K7121-1987 “Method for measuring the melting temperature of plastics”.

  The content of the release agent is preferably 1% by mass or more and 20% by mass or less, and more preferably 5% by mass or more and 15% by mass or less with respect to the entire toner particles.

-Other additives-
Examples of other additives include known additives such as a magnetic material, a charge control agent, and inorganic powder. These additives are contained in the toner particles as internal additives.

-Toner particle characteristics-
The toner particles may be toner particles having a single layer structure, or toner particles having a so-called core / shell structure composed of a core (core particle) and a coating layer (shell layer) covering the core. May be. The toner particles having a core / shell structure include, for example, a core that includes a binder resin and, if necessary, other additives such as a colorant and a release agent, and a binder resin. And a coating layer.

The volume average particle diameter (D50v) of the toner particles is preferably 2 μm or more and 10 μm or less, and more preferably 4 μm or more and 8 μm or less.
The volume average particle diameter (D50v) of the toner particles is measured using Coulter Multisizer II (manufactured by Beckman Coulter), and the electrolyte is measured using ISOTON-II (manufactured by Beckman Coulter). In the measurement, 0.5 mg to 50 mg of a measurement sample is added to 2 ml of a 5% by mass aqueous solution of a surfactant (preferably sodium alkylbenzenesulfonate) as a dispersant. This is added to 100 ml or more and 150 ml or less of the electrolytic solution. The electrolyte in which the sample is suspended is dispersed for 1 minute with an ultrasonic disperser, and the particle size distribution of particles in the range of 2 μm to 60 μm is measured using a Coulter Multisizer II with an aperture having an aperture diameter of 100 μm. To do. The number of particles to be sampled is 50,000.

-External additive-
Examples of the external additive include inorganic particles. As the inorganic particles, SiO ₂ , TiO ₂ , Al ₂ O ₃ , CuO, ZnO, SnO ₂ , CeO ₂ , Fe ₂ O ₃ , MgO, BaO, CaO, K ₂ O, Na ₂ O, ZrO ₂ , CaO. _{SiO 2, K 2 O · (} TiO 2) n, Al 2 O 3 · 2SiO 2, CaCO 3, MgCO 3, BaSO 4, MgSO 4 , and the like.

The surface of the inorganic particles as an external additive is preferably subjected to a hydrophobic treatment. The hydrophobic treatment is performed, for example, by immersing inorganic particles in a hydrophobic treatment agent. The hydrophobizing agent is not particularly limited, and examples thereof include silane coupling agents, silicone oils, titanate coupling agents, aluminum coupling agents and the like. These may be used individually by 1 type and may use 2 or more types together.
The amount of the hydrophobizing agent is usually, for example, 1 part by mass or more and 10 parts by mass with respect to 100 parts by mass of the inorganic particles.

  As external additives, resin particles (resin particles such as polystyrene, polymethyl methacrylate, melamine resin, etc.), cleaning activators (for example, metal salts of higher fatty acids represented by zinc stearate, particles of fluorine-based high molecular weight) And so on.

  The external addition amount of the external additive is preferably 0.01% by mass or more and 5% by mass or less, and more preferably 0.01% by mass or more and 2.0% by mass or less with respect to the toner particles.

-Toner Particle Manufacturing Method-
The toner particles may be produced by any of a dry production method (for example, a kneading pulverization method) and a wet production method (for example, an aggregation coalescence method, a suspension polymerization method, a dissolution suspension method, etc.). There is no restriction | limiting in particular in these manufacturing methods, A well-known manufacturing method is employ | adopted. Among these, it is preferable to obtain toner particles by an aggregation and coalescence method. After the toner particles are produced, an external additive may be externally added to the toner particles.

<Image forming apparatus and image forming method>
An image forming apparatus and an image forming method according to the present embodiment will be described.
The image forming apparatus according to the present embodiment includes an image carrier, a charging unit that charges the surface of the image carrier, an electrostatic image forming unit that forms an electrostatic image on the surface of the charged image carrier, and an electrostatic charge. Development means for containing an image developer and developing the electrostatic image formed on the surface of the image carrier as a toner image with the electrostatic image developer, and the toner image formed on the surface of the image carrier as a recording medium Transfer means for transferring to the surface of the recording medium, and fixing means for fixing the toner image transferred to the surface of the recording medium. The electrostatic charge image developer according to this embodiment is applied as the electrostatic charge image developer.

  In the image forming apparatus according to this embodiment, a charging process for charging the surface of the image carrier, an electrostatic charge image forming process for forming an electrostatic image on the surface of the charged image carrier, and an electrostatic charge according to this embodiment. A developing step of developing an electrostatic charge image formed on the surface of the image carrier as a toner image with an image developer; a transfer step of transferring the toner image formed on the surface of the image carrier to the surface of the recording medium; An image forming method (an image forming method according to the present embodiment) including a fixing step of fixing the toner image transferred onto the surface of the recording medium is performed.

The image forming apparatus according to the present embodiment is a direct transfer type apparatus that directly transfers a toner image formed on the surface of an image carrier to a recording medium; the toner image formed on the surface of the image carrier is transferred to an intermediate transfer member An intermediate transfer type apparatus that primarily transfers the toner image transferred to the surface of the intermediate transfer body and then secondary transfer the toner image to the surface of the recording medium; after the toner image is transferred, the surface of the image carrier before charging is cleaned. A known image forming apparatus such as an apparatus provided with cleaning means; an apparatus provided with charge eliminating means for irradiating the surface of the image carrier with charge removing light after the toner image is transferred and before charging is applied.
In the case where the image forming apparatus according to this embodiment is an intermediate transfer type apparatus, for example, the transfer unit intermediately transfers an intermediate transfer body on which a toner image is transferred onto the surface and a toner image formed on the surface of the image holding body. A configuration having primary transfer means for primary transfer onto the surface of the body and secondary transfer means for secondary transfer of the toner image transferred onto the surface of the intermediate transfer body onto the surface of the recording medium is applied.

  In the image forming apparatus according to the present embodiment, for example, the part including the developing unit may be a cartridge structure (process cartridge) that is detachable from the image forming apparatus. As the process cartridge, for example, a process cartridge that accommodates the electrostatic charge image developer according to this embodiment and includes a developing unit is preferably used.

  Hereinafter, an example of the image forming apparatus according to the present embodiment will be described, but the present invention is not limited thereto. In the following description, the main part shown in the figure will be described, and the description of other parts will be omitted.

FIG. 2 is a schematic configuration diagram illustrating the image forming apparatus according to the present embodiment.
The image forming apparatus shown in FIG. 2 is a first electrophotographic system that outputs an image of each color of yellow (Y), magenta (M), cyan (C), and black (K) based on color-separated image data. To fourth image forming units 10Y, 10M, 10C, and 10K (image forming means). These image forming units (hereinafter sometimes simply referred to as “units”) 10Y, 10M, 10C, and 10K are arranged in parallel at a predetermined distance from each other in the horizontal direction. These units 10Y, 10M, 10C, and 10K may be process cartridges that can be attached to and detached from the image forming apparatus.

Above each unit 10Y, 10M, 10C, 10K, an intermediate transfer belt (an example of an intermediate transfer member) 20 is extended through each unit. The intermediate transfer belt 20 is wound around the drive roll 22 and the support roll 24 and travels in a direction from the first unit 10Y toward the fourth unit 10K. A force is applied to the support roll 24 in a direction away from the drive roll 22 by a spring or the like (not shown), and tension is applied to the intermediate transfer belt 20 wound around the support roll 24. An intermediate transfer member cleaning device 30 is provided on the side of the image carrier of the intermediate transfer belt 20 so as to face the drive roll 22.
Each unit 10Y, 10M, 10C, 10K developing device (an example of developing means) 4Y, 4M, 4C, 4K has yellow, magenta, cyan, black in toner cartridges 8Y, 8M, 8C, 8K, respectively. Each toner is supplied.

  Since the first to fourth units 10Y, 10M, 10C, and 10K have the same configuration and operation, the first image forming the yellow image disposed upstream in the traveling direction of the intermediate transfer belt is formed here. The unit 10Y will be described as a representative.

The first unit 10Y includes a photoreceptor 1Y that functions as an image holding member. Around the photoreceptor 1Y, a charging roll (an example of a charging unit) 2Y that charges the surface of the photoreceptor 1Y to a predetermined potential, and the charged surface is exposed by a laser beam 3Y based on the color-separated image signal. Then, an exposure device (an example of an electrostatic image forming unit) 3 that forms an electrostatic image, and a developing device (an example of a developing unit) 4Y that develops the electrostatic image by supplying toner charged to the electrostatic image, developed A primary transfer roll 5Y (an example of a primary transfer unit) that transfers a toner image onto the intermediate transfer belt 20, and a photoconductor cleaning device (an example of a cleaning unit) 6Y that removes toner remaining on the surface of the photoconductor 1Y after the primary transfer. Are arranged in order.
The primary transfer roll 5Y is disposed inside the intermediate transfer belt 20, and is provided at a position facing the photoreceptor 1Y. A bias power source (not shown) for applying a primary transfer bias is connected to the primary transfer rolls 5Y, 5M, 5C, and 5K of each unit. Each bias power source changes the value of the transfer bias applied to each primary transfer roll under the control of a control unit (not shown).

Hereinafter, an operation of forming a yellow image in the first unit 10Y will be described.
First, prior to operation, the surface of the photoreceptor 1Y is charged to a potential of −600V to −800V by the charging roll 2Y.
The photoreceptor 1Y is formed by laminating a photosensitive layer on a conductive base (for example, a volume resistivity of 1 × 10 ⁻⁶ Ωcm or less at 20 ° C.). This photosensitive layer usually has a high resistance (general resin resistance), but has a property of changing the specific resistance of the portion irradiated with the laser beam when irradiated with the laser beam. Therefore, the laser beam 3Y is irradiated from the exposure device 3 on the surface of the charged photoreceptor 1Y in accordance with yellow image data sent from a control unit (not shown). Thereby, an electrostatic charge image of a yellow image pattern is formed on the surface of the photoreceptor 1Y.

The electrostatic charge image is an image formed on the surface of the photoreceptor 1Y by charging, and the specific resistance of the irradiated portion of the photosensitive layer is lowered by the laser beam 3Y, and the charged charge on the surface of the photoreceptor 1Y flows. On the other hand, this is a so-called negative latent image formed by the charge remaining in the portion not irradiated with the laser beam 3Y.
The electrostatic charge image formed on the photoreceptor 1Y rotates to a predetermined development position as the photoreceptor 1Y travels. At this development position, the electrostatic charge image on the photoreceptor 1Y is developed and visualized as a toner image by the developing device 4Y.

  In the developing device 4Y, for example, an electrostatic charge image developer containing at least yellow toner and a carrier is accommodated. The yellow toner is triboelectrically charged by being agitated inside the developing device 4Y, and has a charge of the same polarity (negative polarity) as the charged electric charge on the photoreceptor 1Y, and has a developer roll (a developer holding member). Example) is held on. Then, as the surface of the photoreceptor 1Y passes through the developing device 4Y, the yellow toner is electrostatically attached to the latent image portion on the surface of the photoreceptor 1Y, and the latent image is developed with the yellow toner. The The photoreceptor 1Y on which the yellow toner image is formed continues to run at a predetermined speed, and the toner image developed on the photoreceptor 1Y is conveyed to a predetermined primary transfer position.

When the yellow toner image on the photoreceptor 1Y is transported to the primary transfer position, a primary transfer bias is applied to the primary transfer roll 5Y, and an electrostatic force from the photoreceptor 1Y toward the primary transfer roll 5Y acts on the toner image, thereby causing the The toner image on the body 1Y is transferred onto the intermediate transfer belt 20. The transfer bias applied at this time has a (+) polarity opposite to the polarity (−) of the toner, and is controlled to, for example, +10 μA by the control unit (not shown) in the first unit 10Y.
On the other hand, the toner remaining on the photoreceptor 1Y is removed and collected by the photoreceptor cleaning device 6Y.

The primary transfer bias applied to the primary transfer rolls 5M, 5C, and 5K after the second unit 10M is also controlled according to the first unit.
In this way, the intermediate transfer belt 20 onto which the yellow toner image has been transferred by the first unit 10Y is sequentially conveyed through the second to fourth units 10M, 10C, and 10K, and the toner images of the respective colors are superimposed to perform multiple transfer. Is done.

  The intermediate transfer belt 20 onto which the four color toner images have been transferred in multiple ways through the first to fourth units includes the intermediate transfer belt 20, a support roll 24 in contact with the inner surface of the intermediate transfer belt, and an image holding surface of the intermediate transfer belt 20. To a secondary transfer portion composed of a secondary transfer roll (an example of secondary transfer means) 26 arranged on the side. On the other hand, recording paper (an example of a recording medium) P is fed at a predetermined timing into a gap where the secondary transfer roll 26 and the intermediate transfer belt 20 are in contact with each other via a supply mechanism, and the secondary transfer bias is supplied to the support roll. 24. The transfer bias applied at this time is a (−) polarity that is the same polarity as the polarity (−) of the toner, and an electrostatic force from the intermediate transfer belt 20 toward the recording paper P acts on the toner image, and the transfer bias is applied to the intermediate transfer belt 20. The toner image is transferred onto the recording paper P. The secondary transfer bias at this time is determined according to the resistance detected by a resistance detecting means (not shown) for detecting the resistance of the secondary transfer portion, and is voltage-controlled.

  Thereafter, the recording paper P is sent to a pressure contact portion (nip portion) of a pair of fixing rolls in a fixing device (an example of a fixing unit) 28, and the toner image is fixed on the recording paper P to form a fixed image. .

Examples of the recording paper P to which the toner image is transferred include plain paper used in electrophotographic copying machines, printers, and the like. As the recording medium, in addition to the recording paper P, an OHP sheet and the like are also included.
In order to further improve the smoothness of the image surface after fixing, it is preferable that the surface of the recording paper P is also smooth. For example, coated paper in which the surface of plain paper is coated with resin, art paper for printing, etc. Preferably used.

  The recording paper P on which the color image has been fixed is carried out toward the discharge unit, and a series of color image forming operations is completed.

<Process cartridge>
The process cartridge according to this embodiment will be described.
The process cartridge according to the present embodiment accommodates the electrostatic image developer according to the present embodiment, and develops the electrostatic image formed on the surface of the image carrier as a toner image by the electrostatic image developer. And a process cartridge that can be attached to and detached from the image forming apparatus.

  The process cartridge according to the present embodiment is not limited to the above-described configuration, and is selected from a developing unit and other units such as an image holding member, a charging unit, an electrostatic charge image forming unit, and a transfer unit, if necessary. And at least one of the above may be provided.

  Hereinafter, an example of the process cartridge according to the present embodiment will be shown, but the present invention is not limited to this. In the following description, the main part shown in the figure will be described, and the description of other parts will be omitted.

FIG. 3 is a schematic configuration diagram showing a process cartridge according to the present embodiment.
The process cartridge 200 shown in FIG. 3 is provided around the photosensitive member 107 and the photosensitive member 107 by, for example, a housing 117 provided with an attachment rail 116 and an opening 118 for exposure. A charging roller 108 (an example of a charging unit), a developing device 111 (an example of a developing unit), and a photoconductor cleaning device 113 (an example of a cleaning unit) are integrally combined and held to form a cartridge. Yes.
In FIG. 3, 109 is an exposure device (an example of an electrostatic charge image forming unit), 112 is a transfer device (an example of a transfer unit), 115 is a fixing device (an example of a fixing unit), and 300 is a recording paper (an example of a recording medium). Is shown.

  Hereinafter, embodiments of the present invention will be described in detail by way of examples, but the embodiments of the present invention are not limited to these examples. In the following description, “part” and “%” are all based on mass unless otherwise specified.

<Production of toner>
[Preparation of resin particle dispersion (1)]
・ Ethylene glycol (Wako Pure Chemical Industries) 37 parts ・ Neopentyl glycol (Wako Pure Chemical Industries) 65 parts ・ 1,9-nonanediol (Wako Pure Chemical Industries) 32 parts ・ Terephthalic acid (Wako Pure Chemical Industries) 96 parts Into a flask, the temperature was raised to 200 ° C. over 1 hour, and after confirming that the inside of the reaction system was uniformly stirred, 1.2 parts of dibutyltin oxide was added. The temperature was raised to 240 ° C. over 6 hours while distilling off the generated water, and stirring was continued at 240 ° C. for 4 hours. A polyester resin (acid value 9.4 mgKOH / g, weight average molecular weight 13,000, glass transition temperature) 62 ° C.). The polyester resin was transferred in a molten state to an emulsifying disperser (Cavitron CD1010, Eurotech) at a rate of 100 g / min. Separately, 0.37% dilute aqueous ammonia diluted with ion-exchanged water with reagent-exchanged water is placed in a tank and emulsified simultaneously with the polyester resin at a rate of 0.1 liter per minute while heating to 120 ° C with a heat exchanger. Transferred to a disperser. The emulsifier / disperser was operated under conditions of a rotor rotation speed of 60 Hz and a pressure of 5 kg / cm ² to obtain a resin particle dispersion (1) having a volume average particle size of 160 nm and a solid content of 30%.

[Preparation of resin particle dispersion (2)]
・ Decandioic acid (Tokyo Kasei Kogyo) 81 parts ・ Hexanediol (Wako Pure Chemical Industries) 47 parts The above materials were charged into a flask and the temperature was raised to 160 ° C. over 1 hour, and the reaction system was uniformly stirred. After confirming this, 0.03 part of dibutyltin oxide was added. The temperature was raised to 200 ° C. over 6 hours while distilling off generated water, and stirring was continued at 200 ° C. for 4 hours. Next, the reaction solution was cooled, solid-liquid separation was performed, and the solid was dried at a temperature of 40 ° C./reduced pressure to obtain a polyester resin (C1) (melting point: 64 ° C., weight average molecular weight: 15,000).

・ Polyester resin (C1) 50 parts ・ Anionic surfactant (Neogen SC, Daiichi Kogyo Seiyaku) 2 parts ・ Ion-exchanged water 200 parts The above materials are heated to 120 ° C. and homogenizer (Ultra Turrax T50, IKA). And then dispersed with a pressure discharge type homogenizer. When the volume average particle diameter reached 180 nm, the polymer was recovered to obtain a resin particle dispersion (2) having a solid content of 20%.

[Preparation of Colorant Particle Dispersion (1)]
・ Cyan pigment (Pigment Blue 15: 3, Dainichi Seika Kogyo) 10 parts ・ Anionic surfactant (Neogen SC, Daiichi Kogyo Seiyaku) 2 parts ・ Ion-exchanged water 80 parts Mixing the above materials, high-pressure impact disperser (Altimizer HJP30006, Sugino Machine Co., Ltd.) was dispersed for 1 hour to obtain a colorant particle dispersion (1) having a volume average particle size of 180 nm and a solid content of 20%.

[Preparation of Release Agent Particle Dispersion (1)]
-Paraffin wax (HNP-9, Nippon Seiwa) 50 parts-Anionic surfactant (Neogen SC, Daiichi Kogyo Seiyaku) 2 parts-Ion-exchanged water 200 parts The above materials are heated to 120 ° C and homogenizer ( (Ultra Turrax T50, IKA) was sufficiently dispersed, and then dispersed with a pressure discharge type homogenizer. When the volume average particle diameter reached 200 nm, the particles were collected to obtain a release agent particle dispersion (1) having a solid content of 20%.

[Production of Toner Particles (1)]
-Resin particle dispersion (1) 150 parts-Resin particle dispersion (2) 50 parts-Colorant particle dispersion (1) 25 parts-Release agent particle dispersion (1) 35 parts-Polyaluminum chloride 0.4 Part / Ion-exchanged water 100 parts The above materials are put into a round stainless steel flask and thoroughly mixed and dispersed using a homogenizer (Ultra Turrax T50, IKA). Then, an oil bath for heating is used while stirring the flask. To 48 ° C. After maintaining the reaction system at 48 ° C. for 60 minutes, 70 parts of the resin particle dispersion (1) was gradually added. Subsequently, the pH is adjusted to 8.0 using a 0.5 mol / L sodium hydroxide aqueous solution, the flask is sealed, the seal of the stirring shaft is magnetically sealed, and the mixture is heated to 90 ° C. while stirring is continued for 30 minutes. Retained. Next, the mixture was cooled at a temperature lowering rate of 5 ° C./min, separated into solid and liquid, and sufficiently washed with ion exchange water. Next, it was separated into solid and liquid, redispersed in ion exchange water at 30 ° C., and stirred for 15 minutes at a rotational speed of 300 rpm for washing. This washing operation is further repeated 6 times. When the filtrate has a pH of 7.54 and an electric conductivity of 6.5 μS / cm, solid-liquid separation is performed, and vacuum drying is continued for 24 hours. 7 μm toner particles (1) were obtained.

  The average length RSm (T) of the roughness curve element on the surface of the toner particles (1) was measured and found to be 0.5 μm.

  Toner (1) was obtained by mixing 100 parts of the toner particles (1) and 0.7 part of hydrophobic silica (RY50 manufactured by Nippon Aerosil Co., Ltd.) using a Henschel mixer.

<Preparation of strontium titanate particles>
[Strontium titanate particles (1)]
0.7 mol of metatitanic acid, which is a desulfurized and peptized titanium source, was collected as TiO ₂ and placed in a reaction vessel. Next, 0.77 mol of an aqueous strontium chloride solution was added to the reaction vessel so that the SrO / TiO ₂ molar ratio was 1.1. Next, a solution in which lanthanum oxide was dissolved in nitric acid was added to the reaction vessel in such an amount that the lanthanum was 2.5 mol per 100 mol of strontium. The initial TiO ₂ concentration in the mixed solution of the three materials was adjusted to 0.75 mol / L. Next, the mixed solution is stirred, and the mixed solution is heated to 90 ° C. While maintaining the liquid temperature at 90 ° C. while stirring, 153 mL of a 10N aqueous sodium hydroxide solution is added over 4 hours. Stirring was continued for 1 hour while maintaining the temperature. Next, the reaction solution was cooled to 40 ° C., hydrochloric acid was added until pH 5.5, and the mixture was stirred for 1 hour. The precipitate was then washed by repeating decantation and redispersion in water. Hydrochloric acid was added to the slurry containing the washed precipitate to adjust the pH to 6.5, and the solid content was filtered off and dried. An ethanol solution of i-butyltrimethoxysilane (i-BTMS) was added to the dried solid content so that 20 parts of i-BTMS was added to 100 parts of the solid content, followed by stirring for 1 hour. The solid content was separated by filtration and the solid content was dried in air at 130 ° C. for 7 hours to obtain strontium titanate particles (1).

[Strontium titanate particles (2)]
Strontium titanate particles (2) were produced in the same manner as the production of strontium titanate particles (1) except that the surface treatment using i-BTMS was not performed.

[Strontium titanate particles (3)]
Strontium titanate particles (3) were produced in the same manner as the production of strontium titanate particles (1) except that the time taken for dropping the 10N aqueous sodium hydroxide solution was changed to 1 hour.

[Strontium titanate particles (4)]
Strontium titanate particles (4) were produced in the same manner as the production of strontium titanate particles (1) except that the time taken for dropping the 10N aqueous sodium hydroxide solution was changed to 2.8 hours.

[Strontium titanate particles (5)]
Strontium titanate particles (5) were produced in the same manner as the production of strontium titanate particles (1) except that the time taken for dropping the 10N aqueous sodium hydroxide solution was changed to 11 hours.

[Strontium titanate particles (6)]
Strontium titanate particles (6) were produced in the same manner as the production of strontium titanate particles (1) except that the time taken for dropping the 10N aqueous sodium hydroxide solution was changed to 14.5 hours.

[Strontium titanate particles (7)]
Strontium titanate particles (7) were prepared in the same manner as the preparation of strontium titanate particles (1) except that the time taken for dropping the 10N aqueous sodium hydroxide solution was changed to 17 hours.

[Strontium titanate particles (8)]
Commercially available strontium titanate particles (SW-360 manufactured by Titanium Industry Co., Ltd.) were prepared, and this was subjected to the same surface treatment as i-BTMS treatment in the production of strontium titanate particles (1), and strontium titanate particles (8 ) Was produced. SW-360 manufactured by Titanium Industry Co., Ltd. is a strontium titanate particle that is not doped with a metal element and has an untreated surface.

[Measurement of the shape of strontium titanate particles]
Separately prepared resin particles and any one of the strontium titanate particles (1) to (8) were mixed for 15 minutes at a stirring peripheral speed of 30 m / sec using a Henschel mixer. Subsequently, strontium titanate particles were adhered to the resin particles by sieving using a vibrating sieve having an opening of 45 μm.
About the resin particle to which the strontium titanate particle was made to adhere, the image was image | photographed by 40,000 times magnification using the scanning electron microscope (SEM) (Hitachi High-Technologies make, S-4700). The image information of 300 randomly selected strontium titanate particles was analyzed by image processing analysis software WinRof (Mitani Corporation) via the interface, and the equivalent circle diameter, area and perimeter of each primary particle image Further, circularity = 4π × (area) ÷ (peripheral length) ² was obtained. Then, the equivalent circle diameter that is 50% cumulative from the smaller diameter side in the distribution of equivalent circle diameters is the average primary particle diameter, the circularity that is cumulative 50% from the smaller side in the circularity distribution is the average circularity, and the circularity The circularity that is 84% cumulative from the smaller side in the distribution was defined as the cumulative 84% circularity.

[X-ray diffraction of strontium titanate particles]
Using each of the strontium titanate particles (1) to (8) as a sample, a crystal structure analysis was performed using an X-ray diffractometer (trade name: RINT Ultimate-III, manufactured by Rigaku Corporation) under the above-described condition settings. The strontium titanate particles (1) to (8) had a peak corresponding to the peak of the (110) plane of the perovskite crystal at a diffraction angle of 2θ = 32 °.

[Volume resistivity R of strontium titanate particles]
Using each of the strontium titanate particles (1) to (8) as a sample, the volume resistivity R was measured by the measurement method described above.

[Water content of strontium titanate particles]
Using each of the strontium titanate particles (1) to (8) as samples, the water content was measured by the measurement method described above.

  Table 1 shows the characteristics of the strontium titanate particles (1) to (8).

<Preparation of magnetic particles>
[Ferrite particles (1)]
74 parts of Fe ₂ O ₃ , 4 parts of Mg (OH) ₂ and 21 parts of MnO ₂ were mixed and calcined using a rotary kiln at a temperature of 950 ° C./7 hours (first time). The obtained calcined product was pulverized for 7 hours using a wet ball mill to have an average particle size of 2.0 μm, and then granulated using a spray dryer. The obtained granulated product was temporarily fired using a rotary kiln at a temperature of 950 ° C./6 hours (second time). The obtained calcined product was pulverized for 3 hours using a wet ball mill to have an average particle size of 5.6 μm, and then granulated using a spray dryer. The obtained granulated material was calcined under conditions of a temperature of 1300 ° C./5 hours using an electric furnace. The obtained fired product was crushed and classified to obtain ferrite particles (1) having a volume average particle size of 32 μm.

[Ferrite particles (2)]
Except that the calcined product after the second calcining was pulverized for 2 hours using a wet ball mill to have an average particle size of 6.5 μm, and that the conditions for the main calcining were changed to 1200 ° C./4 hours. Ferrite particles (2) were produced in the same manner as the production of ferrite particles (1).

[Ferrite particles (3)]
The calcined product after the second calcining was pulverized for 5 hours using a wet ball mill to an average particle size of 4.7 μm, and the conditions for the main calcining were changed to a temperature of 1350 ° C./5.5 hours. Except for the above, ferrite particles (3) were prepared in the same manner as the preparation of ferrite particles (1).

  Table 2 shows the particle diameters and surface properties of the ferrite particles (1) to (3). The arithmetic average height Ra (μm) of the roughness curve and the average length RSm (μm) of the roughness curve element were determined by image analysis using a laser microscope (VK-9500, manufactured by Keyence Corporation).

<Production of resin-coated carrier>
[Resin coated carrier (1)]
Ferrite particles (1) 100 parts Cyclohexyl methacrylate / methyl methacrylate copolymer (copolymerization ratio 95 mol: 5 mol) 3 parts Toluene 14 parts Of the above materials, cyclohexyl methacrylate / methyl methacrylate copolymer and toluene Glass beads (diameter 1 mm, the same amount as toluene) were put into a sand mill (Kansai Paint Co., Ltd.) and stirred at a rotational speed of 1200 rpm for 30 minutes to obtain a resin layer forming solution (1). Put ferrite particles (1) into a vacuum degassing kneader, and then add resin layer forming solution (1). The temperature is increased and reduced with stirring to distill off toluene, and the ferrite particles (1) are coated with resin. did. Subsequently, fine powder and coarse powder were removed with an elbow jet to obtain a resin-coated carrier (1).

[Resin-coated carriers (2) to (7)]
Resin coated carriers (2) to (2) are prepared in the same manner as in the preparation of the resin coated carrier (1) except that the amount of cyclohexyl methacrylate / methyl methacrylate copolymer (CHMA / MMA copolymer) used is changed as shown in Table 3. (7) was produced.

  Table 3 shows the compositions and surface properties of the resin-coated carriers (1) to (7). The exposure ratio of the magnetic particles was determined by the measurement method described above. RSm (C) was obtained by image analysis using a laser microscope (manufactured by Keyence Corporation, VK-9500).

<Production of developer>
[Example 1]
100 parts of resin-coated carrier (1), 20 parts of toner (1), and 0.1 part of strontium titanate (1) were charged in a V blender and stirred for 20 minutes. Thereafter, the mixture was sieved with a sieve having an opening of 212 μm to obtain a cyan developer.

[Examples 2-31, Comparative Examples 1-13]
As in Example 1, except that the type of the resin-coated carrier and the type or external addition amount of the strontium titanate particles (mass% with respect to the mass of the resin-coated carrier) were changed as shown in Table 4, A developer was prepared.

<Performance evaluation>
[Density unevenness]
Using a modified machine of the image forming apparatus DocuCenterColor400 (Fuji Xerox), an image was formed on A4 size plain paper (Fuji Xerox, C2 paper) as follows.
Day 1 to Day 10: 10,000 images each day with rectangular patches of cyan solid images arranged at an image density of 1% under an environment of temperature 22.5 ° C./relative humidity 50%, Each was continuously output. Therefore, a total of 100,000 images were output on the first day to the tenth day.
After the image formation on the 10th day was completed, the image forming apparatus was placed in a high temperature and high humidity environment (temperature 30 ° C./relative humidity 90%) for 24 hours or more.
Day 11: 10 cyan halftone images of 10 cm × 27 cm were output in the same high temperature and high humidity environment as above.

A spectrophotometer (X-Rite Ci62, manufactured by X-Rite) is used in the vicinity of each of the two corners that are diagonal to the first halftone image, and the L ^* value, a ^* value, and b ^* value. Was measured, color difference ΔE was calculated based on the following formula, and classified into A to D as follows. A to C are practically acceptable.

In the formula, L ₁ , a ₁ , and b ₁ are L ^* values, a ^* values, and b ^* values near one corner, and L ₂ , a ₂ , and b ₂ are L ^* values near the other corner. , A ^* value, b ^* value.

A (◎): ΔE <0.3, and no density unevenness is observed visually.
B (◯): 0.3 ≦ ΔE <0.5, and slight density unevenness is visually observed.
C (Δ): 0.5 ≦ ΔE <1.0, and density unevenness is visually observed.
D (x): 1.0 ≦ ΔE, and clear density unevenness is observed visually.

[Outline]
Ten halftone images were visually observed, and white spots were classified into A to D as follows. A to C are practically acceptable.

A (◎): No white spots are observed on all 10 sheets.
B (◯): White spots are observed on one to two sheets.
C (Δ): White spots are observed on 3 to 5 sheets.
D (x): White spots are observed on 6 sheets or more.

  When A is scored as 4 points, B is scored as 3 points, C is scored as 2 points, and D is scored as 1 point, a total of 5 points or more of the density unevenness score and the white spot score is an acceptable level.

  Table 4 shows the composition and performance evaluation results of Examples 1 to 31 and Comparative Examples 1 to 13.

1Y, 1M, 1C, 1K photoconductor (an example of an image carrier)
2Y, 2M, 2C, 2K charging roll (an example of charging means)
3. Exposure device (an example of electrostatic charge image forming means)
3Y, 3M, 3C, 3K Laser beams 4Y, 4M, 4C, 4K Developing device (an example of developing means)
5Y, 5M, 5C, 5K primary transfer roll (an example of primary transfer means)
6Y, 6M, 6C, 6K Photoconductor cleaning device (an example of cleaning means)
8Y, 8M, 8C, 8K Toner cartridge 10Y, 10M, 10C, 10K Image forming unit 20 Intermediate transfer belt (an example of an intermediate transfer member)
22 Drive roll 24 Support roll 26 Secondary transfer roll (an example of secondary transfer means)
28 Fixing device (an example of fixing means)
30 Intermediate transfer member cleaning device P Recording paper (an example of a recording medium)

107 photoconductor (an example of an image carrier)
108 Charging roll (an example of charging means)
109 Exposure apparatus (an example of electrostatic charge image forming means)
111 Developing device (an example of developing means)
112 Transfer device (an example of transfer means)
113 photoconductor cleaning device (an example of cleaning means)
115 Fixing device (an example of fixing means)
116 Mounting rail 117 Housing 118 Opening 200 for exposure Process cartridge 300 Recording paper (an example of a recording medium)

Claims (15)

Toner particles,
A resin-coated carrier having magnetic particles and a resin layer covering the magnetic particles, wherein the exposed ratio of the magnetic particles on the surface is 2% or more and 20% or less;
Strontium titanate particles having an average circularity of primary particles of 0.82 or more and 0.94 or less and a circularity of cumulative 84% exceeding 0.92.
An electrostatic charge in which the average length RSm (C) of the roughness curve element on the surface of the resin-coated carrier and the average primary particle diameter r of the strontium titanate particles satisfy the relationship of 6 ≦ RSm (C) / r ≦ 40 Image developer. Toner particles,
A resin-coated carrier having magnetic particles and a resin layer covering the magnetic particles, wherein the exposed ratio of the magnetic particles on the surface is 2% or more and 20% or less;
Strontium titanate particles having a half width of a peak of (110) plane obtained by an X-ray diffraction method of 0.2 ° or more and 2.0 ° or less,
An electrostatic charge in which the average length RSm (C) of the roughness curve element on the surface of the resin-coated carrier and the average primary particle diameter r of the strontium titanate particles satisfy the relationship of 6 ≦ RSm (C) / r ≦ 40 Image developer.   The electrostatic charge image developer according to claim 1, wherein the strontium titanate particles are strontium titanate particles containing a dopant.   The electrostatic charge image developer of any one of Claims 1-3 whose average primary particle diameter r of the said strontium titanate particle is 10 nm or more and 100 nm or less.   The electrostatic charge image developer according to claim 4, wherein an average primary particle size r of the strontium titanate particles is 30 nm or more and 80 nm or less.   The average length RSm (C) of the roughness curve element on the surface of the resin-coated carrier, the average length RSm (T) of the roughness curve element on the surface of the toner particles, and the average primary particle diameter r of the strontium titanate particles. The electrostatic charge image developer according to claim 1, wherein and satisfy a relationship of 11 ≦ RSm (C) / (RSm (T) × r) ≦ 100.   The electrostatic charge image developer according to any one of claims 1 to 6, wherein the resin-coated carrier, the magnetic particles, and the strontium titanate particles are easily positively charged in this order.   The electrostatic charge image developer of any one of Claims 1-7 in which the said resin layer contains an alicyclic acrylic resin.   The electrostatic image developer according to claim 8, wherein the alicyclic acrylic resin contains cyclohexyl (meth) acrylate as a polymerization component.   The electrostatic image developer according to claim 1, wherein the magnetic particles are ferrite particles.   The static content according to any one of claims 1 to 10, wherein a content of the strontium titanate particles is 0.005 mass% or more and 2.0 mass% or less with respect to a mass of the resin-coated carrier. Charge image developer.   The electrostatic charge image developer according to claim 11, wherein the content of the strontium titanate particles is 0.01% by mass or more and 1.0% by mass or less with respect to the mass of the resin-coated carrier.   An electrostatic image developer according to any one of claims 1 to 12 is accommodated, and the electrostatic image formed on the surface of the image carrier is developed as a toner image by the electrostatic image developer. A process cartridge including a developing unit and detachable from an image forming apparatus. An image carrier,
Charging means for charging the surface of the image carrier;
An electrostatic charge image forming means for forming an electrostatic charge image on the surface of the charged image carrier;
An electrostatic charge image developer according to any one of claims 1 to 12 is accommodated, and the electrostatic charge image formed on the surface of the image carrier is developed as a toner image by the electrostatic charge image developer. Developing means,
Transfer means for transferring a toner image formed on the surface of the image carrier to the surface of a recording medium;
Fixing means for fixing the toner image transferred to the surface of the recording medium;
An image forming apparatus comprising: A charging step for charging the surface of the image carrier;
An electrostatic charge image forming step of forming an electrostatic charge image on the surface of the charged image carrier;
A developing step of developing an electrostatic charge image formed on the surface of the image carrier as a toner image with the electrostatic charge image developer according to any one of claims 1 to 12,
A transfer step of transferring a toner image formed on the surface of the image carrier to the surface of a recording medium;
A fixing step of fixing the toner image transferred to the surface of the recording medium;
An image forming method comprising: