JP2008065060A - Electrostatic charge image developing carrier, electrostatic charge image developer, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carrier in which the toner and carrier mixability in a developing device and the conveyability on a developer holding body are assured, image deterioration is prevented, the occurrence of the image deterioration due to crazing and chipping is reduced, a developer, and an image forming apparatus using them. <P>SOLUTION: The electrostatic charge image developing carrier is characterized in that the carrier has core material particles and a coating resin layer covering the core material particles, the shape coefficient of the core material particles is ≤120, and the coating resin layer contains the magnetic particles having the saturation magnetization higher than that of the core material particles. Also, the electrostatic charge image developing developer contains the carrier and the toner and the toner contains the toner particles of ≤3 μm in particle diameter in a number distribution at ≤5% over the entire part of the toner particles. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrostatic charge image developing carrier used for electrophotography, electrostatic recording method, electrostatic printing method, etc., an electrostatic charge image developer using the electrostatic charge image developing carrier, and image formation using these Relates to the device.

  Electrophotographic methods for visualizing image information through electrostatic charge images are currently used in various fields. In conventional electrophotography, an electrostatic latent image is formed on a photosensitive member or electrostatic recording member using various means, and electrostatic charge fine particles called toner are attached to the electrostatic latent image to form an electrostatic charge image. A method for developing and visualizing the image is generally used. The developer used here is a two-component developer that imparts an appropriate amount of positive or negative charge to the toner by mutually frictionally charging both holding particles called toner and toner particles, and a toner such as a magnetic toner. It is roughly classified into a one-component developer used alone. In particular, two-component developers are widely used for reasons such as ease of design because the carrier itself has functions such as stirring, transport, and charging, and the functions required for the developer can be separated. ing.

  However, the charge amount of the two-component developer used for friction charging is easily changed due to the influence of environmental changes such as temperature and degree. In general, high charge is likely to occur under low temperature and low humidity, and low charge is likely to occur under high temperature and high humidity. For this reason, lowering the development density at the time of a high charge amount due to environmental changes and the occurrence of fogging at the time of a low charge amount are problems in the two-component developer.

  In recent years, there has been a demand for higher image quality of images formed by electrophotographic image forming apparatuses, higher process speed, and long-term stability. To cope with higher image quality, toner particles are reduced and charged. More and more studies have been made on the uniformity of the quantity and the stabilization of the charge amount. Along with the reduction in toner particles, the carrier is also considered to be reduced in particle size, and various studies such as the resin composition of the carrier coating layer have been made to equalize and stabilize the charge amount.

  In order to obtain high image quality, the characteristics required of the carrier include charging the toner as uniformly as possible to a desired charge amount. In order to obtain this characteristic, it is necessary to maintain the mixing property of the carrier and the toner and to reduce the difference in the characteristics of the carrier surface. If the mixing is insufficient or the carrier surface is non-uniform, the charge amount will be non-uniform. Further, when the core material is exposed, the charging ability is lowered and the resistance is also lowered, so that good charging cannot be obtained.

  In response to these problems, carrier deterioration during use, that is, variation in charge amount due to use environment, decrease in carrier charging ability due to adhesion of toner and external additives during the process, cracking of core material particles due to stress, Studies have been made on the peeling of the coating resin and the reduction in charging ability due to the abrasion of the coating resin. For example, in Patent Document 1, a coating resin layer is provided on a core material, and acicular conductive powder and spherical conductive powder are contained in the core material. It has been proposed to ensure stability against aging.

  Further, in Patent Document 2, the sphericity and surface roughness of the core material are defined, the surface roughness of the carrier provided with the coating resin layer containing the acicular conductive powder is provided as the core material. A carrier for developing an electrostatic charge image that can ensure stability against environmental fluctuations and changes with time has been proposed.

  However, as higher image quality is studied, uniform layer formation and chargeability of the developer are required. When a spherical core material that is generally used is used, it takes time to mix the toner in the developing device, and the transportability onto the developer holding member is deteriorated. As a result, there has been a problem that the reproducibility of fine lines at low temperatures and low humidity deteriorates. On the other hand, in order to ensure transportability and mixing properties, if a method using a carrier with a core material with an uneven surface is used, stress is easily applied in the developing device during coating resin layer production and use, and the core There was a problem in that cracks and chipping of the material occurred, and the fragments were developed together with the toner on the electrostatic latent image holding member (photosensitive member) particularly at low temperature and low humidity and stuck in the photosensitive member. As a result, there has been a problem that the image quality is deteriorated due to the omission of the solid portion. In particular, the reduction in the amount of developer in the developing device due to the downsizing of the device and the reduction in the particle size of the carrier accompanying the reduction in the toner particle size have progressed, increasing the stress on the developer in the developing device, A lot of bits were coming out.

JP-A-11-202560 JP 2006-38961 A

  Accordingly, an object of the present invention is to ensure the mixing property of the toner and the carrier in the developing device and the transportability on the developer holding body, to prevent the image deterioration, and to cause the image deterioration due to the carrier cracking and chipping. An object is to provide a small number of carriers, a developer containing the carriers, and an image forming apparatus using them.

The present invention has been solved by means described in the following <1> to <3>.
<1> A core material particle and a coating resin layer that coats the core material particle, the core material particle has a shape factor of 120 or less, and the coating resin layer is higher in saturation magnetization than the core material particle A carrier for developing an electrostatic image, comprising magnetic particles having
<2> The electrostatic charge image comprising the carrier and the toner according to <1>, wherein the toner contains toner particles having a particle size of 3 μm or less in a number distribution of 5% or less of the whole toner particles. Developer,
<3> The electrostatic latent image formed by the developer including at least a latent image forming unit that forms an electrostatic latent image on the surface of the electrostatic latent image holding member and a toner and a carrier contained in the developing device. Image forming comprising: a developing unit that visualizes an image and forms a toner image on the surface of the electrostatic latent image holding member; and a transfer unit that transfers the formed toner image to the surface of the transfer target An image forming apparatus, wherein the carrier is the electrostatic image developing carrier according to <1> or the electrostatic image developer according to <2>.

  According to the present invention, the carrier in which the toner and the carrier in the developing device are mixed and transported on the developer holding member is ensured, image deterioration is prevented, and the occurrence of image deterioration due to cracking and chipping of the carrier is small. , A developer including the carrier, and an image forming apparatus using the developer can be provided.

(Carrier for developing electrostatic image)
The carrier for developing an electrostatic charge image of the present invention (also referred to simply as “carrier” in the present invention) has core particles and a coating resin layer that covers the core particles, and the shape factor of the core particles is 120 or less, and the coating resin layer contains magnetic particles having a saturation magnetization higher than that of the core material particles.
As a result of diligent research to solve the above-mentioned problems, the present inventors have found that an electrostatic charge image having a coating resin layer on the surface of core material particles (also referred to as “core material” or “carrier core material” in the present invention). In the developing carrier, the shape factor of the core material particles is 120 or less, and the coating resin layer contains magnetic particles whose saturation magnetization is higher than the saturation magnetization of the core material particles, so that image deterioration at low temperature and low humidity can be improved. And the present invention has been completed.

That is, if the shape factor of the core particles is larger than 120, the carrier surface is uneven or irregular, the core particles are likely to be stressed, and the carrier particles will be easily cracked or chipped. This is easy to develop with toner. As a result, the photosensitive member, the transfer member, the cleaning member and the like are damaged, and a problem that the image quality is deteriorated easily occurs. In the present invention, it is considered that cracking and chipping of the core material particles can be suppressed by setting the shape factor of the core material particles to 120 or less.
Furthermore, when the shape factor is 120 or less, the developer transportability may be deteriorated. However, the carrier resin surface contains magnetic particles whose saturation magnetization is higher than the saturation magnetization of the core material particles. Concavities and convexities can be formed on the surface to ensure transportability. Further, it is considered that due to the saturation magnetization of these magnetic particles, development is difficult even if cracking or chipping including the magnetic particles occurs, and as a result, deterioration of the image can be suppressed.

In the present invention, the shape factor SF1 of the core material particles of the electrostatic image developing carrier is 120 or less. It is preferable that it is 100-120, and it is more preferable that it is 100-115.
When the shape factor of the core material particles exceeds 120, cracking and chipping of the core material particles are likely to occur and image quality is deteriorated.
In the present invention, the shape factor of the core particles is determined according to the following formula.

ここでＭＬ：粒子の絶対最大長、Ａ：粒子の投影面積である。
これらは、主に顕微鏡画像又は走査電子顕微鏡画像をルーゼックス画像解析装置によって取り込み、解析することによって数値化される。具体的には、芯材粒子をスライドガラス上に散布し、顕微鏡画像又は走査電子顕微鏡画像をルーゼックス画像解析装置により取り込む。本発明において、ＳＦ１は１００個の芯材粒子について（（ＭＬ）²／Ａ）×（π／４）×１００を計算し、これを平均した値である。

Here, ML is the absolute maximum length of the particle, and A is the projected area of the particle.
These are quantified mainly by capturing and analyzing a microscope image or a scanning electron microscope image with a Luzex image analyzer. Specifically, core material particles are dispersed on a slide glass, and a microscope image or a scanning electron microscope image is captured by a Luzex image analyzer. In the present invention, SF1 is a value obtained by calculating ((ML) ² / A) × (π / 4) × 100 for 100 core particles and averaging this.

In the present invention, the coating resin layer contains magnetic particles whose saturation magnetization is higher than that of the core material particles. When the saturation magnetization of the magnetic particles contained in the coating resin layer is less than or equal to the saturation magnetization of the core particles, image degradation occurs due to cracks and chips containing the magnetic particles generated in the carrier.
Magnetic particles contained in the coating resin layer (. Hereinafter, also referred to as a covering layer magnetic particles) have a high saturation magnetization than the core particles, the difference between the saturation magnetization 5emu / g (5 × 4π × 10 - more that it is preferable 5~30emu / g (5 × 4π × 10 -7 Wb · m / kg~30 × 4π × 10 -7 Wb · m / kg) is ⁷ Wb · m / kg) or It is preferably 5 to 20 emu / g (5 × 4π × 10 ⁻⁷ Wb · m / kg to 20 × 4π × 10 ⁻⁷ Wb · m / kg). It is preferable that the difference in saturation magnetization is 5 emu / g (5 × 4π × 10 ⁻⁷ Wb · m / kg) or more because cracks and chips are hardly developed. Moreover, it is preferable that it is 30 emu / g (30 * 4 (pi) * 10 < ^-7 > Wb * m / kg) or less, since it is not necessary to make the saturation magnetization of a core material particle low.

In the present invention, the saturation magnetization of the core particles is preferably 40 emu / g (40 × 4π × 10 ⁻⁷ Wb · m / kg) or more, and 50 to 90 emu / g (50 × 4π × 10 ⁻⁷ Wb · m). m / kg to 90 × 4π × 10 ⁻⁷ Wb · m / kg), more preferably 50 to 75 emu / g (60 × 4π × 10 ⁻⁷ Wb · m / kg to 75 × 4π × 10 ^−7). Wb · m / kg) is more preferable. It is preferable for the saturation magnetization of the core particles to be in the above range because the carrier is difficult to be developed on the photoreceptor together with the toner, and development defects such as white spots are unlikely to occur in the image.
On the other hand, the saturation magnetization of the magnetic particles contained in the coating resin layer (also referred to as coating layer magnetic particles in the present invention) is 45 to 100 emu / g (45 × 4π × 10 ⁻⁷ Wb · m / kg to 100 × 4π ×). ^10-7 preferably Wb · m / kg) is, 60~90emu / g (60 × 4π × 10 -7 Wb · m / kg~90 × 4π × 10 -7 Wb · m / kg) it is Is more preferable. It is preferable that the magnetization of the magnetic particles contained in the coating resin layer be within the above range because cracks and chips containing the magnetic particles are difficult to be developed.
In the present invention, the saturation magnetization is measured by a BH tracer method using a VSM (vibration sample method) measuring device in a magnetic field of 3 kOe (2.39 kA / m).

Examples of the carrier core material include magnetic metal, magnetic oxide, or resin particles in which magnetic particles are dispersed internally. However, since these carrier core materials are all hydrophilic and have the disadvantage that the chargeability is reduced under high humidity, the environmental fluctuation of the chargeability is large. Further, since it is a high surface energy material, it is easily contaminated with toner components, and there is a problem that the chargeability is poor. The electrostatic charge image developing carrier of the present invention has a coating resin layer for coating the core particles, and the carrier surface is coated with a resin having hydrophobicity or low surface energy, so that the above-mentioned problems relating to charging can be solved. Can be improved.
On the other hand, when the surface of the core material is coated with an insulating resin at a high coverage, the electrical resistance as a carrier increases and the reproducibility of a solid image may deteriorate.
In this case, it is preferable to take measures such as dispersing conductive particles in the coating resin layer for the purpose of avoiding an increase in electrical resistance.

The carrier core material used in the present invention is not particularly limited, but in the present invention, it is necessary to use a magnetic material as the carrier core material, and magnetic powder can be used alone for the core material. Alternatively, it is also possible to use a magnetic powder that is made into fine particles and dispersed in a resin.
Examples of the magnetic powder include magnetic metals such as iron, steel, nickel, and cobalt, and magnetic oxides such as ferrite and magnetite.
As an example of ferrite, the ferrite represented by the following formula can be exemplified.
(MO) _X (Fe ₂ O ₃ ) _Y
In the formula, M contains at least one selected from Cu, Zn, Fe, Mg, Mn, Ca, Li, Ti, Ni, Sn, Sr, Al, Ba, Co, Mo and the like: X, Y Indicates a weight mol ratio and satisfies X + Y = 100.
The M is preferably a ferrite particle which is one or a combination of Li, Mg, Ca, Mn, Sr and Sn, and the content of other components is 1% by weight or less. By adding Cu, Zn, and Ni elements, the resistance tends to be low and charge leakage is likely to occur. Furthermore, it tends to be difficult to coat the resin, and the environmental dependency tends to deteriorate. In addition, it is a heavy metal, and because it is heavy, the stress applied to the carrier becomes strong and may adversely affect the life, so it is preferable not to contain these elements.
In recent years, from the viewpoint of safety, those to which Mn and Mg elements are added have become widespread.

The core particles preferably have a volume average particle diameter of 15 to 100 μm, more preferably 20 μm to 80 μm, and still more preferably 25 μm to 75 μm. A volume average particle size of 15 μm or more is preferable because the adhesion between the toner and the carrier is appropriate and a good development amount can be obtained. Moreover, it is preferable that it is 100 μm or less because a fine image can be formed and a high quality image excellent in fine line reproducibility can be obtained.
The volume average particle diameter of the core particles means the cumulative volume average particle diameter, and can be measured using a laser trapler scattered light analyzer or the like.

Core particles preferably have a true specific gravity is in the range of 2 to 6 g / cm ^3, more preferably 2.5~5.5g / cm ^3, further to be 3 to 5 g / cm ³ preferable.
A true specific gravity of 2 g / cm ³ or more is preferable because it is difficult to develop together with the toner. Further, it is preferable that the amount is 6 g / cm ³ or less because stress on the toner particles is small.

The core material particles of the carrier are preferably magnetic powder-dispersed core materials.
That is, it is also preferable that the core particles of the carrier are those obtained by making magnetic powder fine particles and dispersing them in a resin. In this case, examples of preferable magnetic powder include ferromagnetic oxides such as magnetite and ferrite, ferromagnetic metals such as iron, cobalt and nickel, and other magnetic compounds or alloys. In this case, the volume average particle diameter of the finely divided magnetic powder is preferably 0.01 to 10 μm, and more preferably 0.05 to 5 μm. It is preferable that the volume average particle diameter of the magnetic powder is within the above range because dispersibility is good.
Examples of the resin for dispersing the magnetic powder include cross-linked resins such as phenol resins and melamine resins, and thermoplastic resins such as polyethylene and polymethyl methacrylate. Among these, cross-linked resins are preferred from the viewpoint of strength.
When the core material particle is a magnetic powder-dispersed core material, the core material particle preferably contains 50 to 90 parts by weight, preferably 60 to 80 parts by weight of magnetic powder when the core material particle is 100 parts by weight. More preferably. It is preferable that the content of the magnetic powder is 50 parts by weight or more because sufficient saturation magnetization can be obtained. Moreover, it is preferable for the content of the magnetic powder to be 90 parts by weight or less because the amount of resin is appropriate and good core material strength can be obtained.

In the present invention, the core particles may be produced by any method, and can be produced by a known method. Although the manufacturing method of the core material particle which can be preferably used for this invention is illustrated below, this invention is not limited to this.
Specifically, as an example of a method for producing a ferrite core material, an appropriate amount of each oxide is first blended, pulverized and mixed for 10 hours by a wet ball mill, dried, and then held at 950 ° C. for 4 hours. This is pulverized with a wet ball mill for 24 hours to 1 μm or less. This slurry is granulated and dried, and maintained at 1,100-1300 ° C. for 6 hours while controlling the oxygen concentration for the purpose of adjusting the magnetic properties and resistance, then pulverized and further classified into a desired particle size distribution. Can be obtained.
Further, in order to set the shape factor to 120 or less, it is possible to use magnetic powder that has been processed so that the unevenness is reduced and the shape factor is 120 or less by adjusting the sintering temperature and the sintering time.
On the other hand, an example of a method for producing a magnetic powder-dispersed core material is a method in which magnetic powder and a binder resin are mixed and mechanically pulverized.

Next, the coating resin layer will be described.
In the present invention, the coating resin layer is a layer provided so as to cover the core particles on the core particles, and as described above, magnetic particles having higher saturation magnetization than the core particles (coating layer magnetic particles). Containing. The covering layer magnetic particles are preferably dispersed in the resin.
The magnetic particles dispersed in the coating resin layer (coating layer magnetic particles) are preferably added after being previously coated with the coating resin. Pre-coating with a coating resin is preferable because adhesion to the coating resin interface is improved and dispersibility in the coating resin layer is improved.
The coating resin layer preferably contains at least conductive particles other than the coating layer magnetic particles. In the present invention, the coating resin layer may contain a wax, a charge control agent and the like as other components.

The coating layer magnetic particles used in the present invention are not particularly limited as long as they are magnetic materials, and examples thereof include magnetic metals such as iron, steel, nickel, and cobalt, and magnetic oxides such as ferrite and magnetite. Can do. The coating layer magnetic particles can be used alone or in combination of two or more.
The covering layer magnetic particles used in the present invention are required to have higher saturation magnetization than the core particles. If the saturation magnetization is smaller than that of the core particle, it may fly together with the toner particle on the photosensitive member as the electrostatic charge holding member when it is separated from the carrier particle in the developing device, and may cause image deterioration. .
The addition amount of the coating layer magnetic particles can be adjusted by the particle size of the core particles and the coating film pressure, but when the core particles are 100 parts by weight, it is preferably 0.1 to 20 parts by weight, It is more preferably 1 to 10 parts by weight, and further preferably 2 to 5 parts by weight. It is preferable for the amount of coating layer magnetic particles added to be in the above range since it can be uniformly distributed on the particle surface.

The coating layer magnetic particles are preferably spherical and have an average particle diameter of 2 to 5 μm.
It is preferable that the coating layer magnetic particles have a spherical shape because the dispersibility is good and the developing member is not damaged. The shape factor of the coating layer magnetic particles is preferably 120 or less, and more preferably 110 or less. The shape factor can be measured by the same method as that for the core particles.
The average particle size of the coating layer magnetic particles is preferably 2 to 5 μm, and the average particle size of the coating layer magnetic particles is preferably adjusted by the particle size of the core material particles. The particle size is more preferably 5% to 20% of the core material particles, and further preferably 5% to 10%.
The average particle diameter of the coating layer magnetic particles is preferably within the above range because it can be uniformly dispersed on the surface of the core material and the transportability can be maintained.
Here, the average particle diameter of the coating layer magnetic particles means a cumulative volume average particle diameter, and can be measured by a laser trapler scattered light analyzer.

The coating resin / matrix resin used for the coating resin layer is polyethylene, polypropylene, polystyrene, polyacrylonitrile, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl carbazole, polyvinyl ether, polyvinyl ketone, vinyl chloride-acetic acid. Vinyl copolymer, styrene-acrylic acid copolymer, straight silicone resin composed of organosiloxane bond or modified product thereof, fluorine resin, polyester, polyurethane, polycarbonate, phenol resin, amino resin, melamine resin, benzoguanamine resin, urea resin, Examples include amide resins and epoxy resins, but are not limited thereto. Particularly preferred are polystyrene resins and acrylic resins. Use of these resins is preferable because the coating film strength is high and the coating layer magnetic particles, the conductive material described later, and the charge control agent are excellent in dispersibility.
In the present invention, as the coating resin, one kind can be used alone, or a plurality of kinds can be used in combination.

In the present invention, the coating resin layer of the carrier preferably contains a conductive material as necessary in addition to the coating layer magnetic particles described above.
By containing a conductive material, the electric resistance of the carrier can be adjusted, which is preferable.
Examples of the conductive material include metals such as gold, silver, and copper, and titanium oxide, zinc oxide, barium sulfate, aluminum borate, potassium titanate, tin oxide, and carbon black. Black is preferable in terms of dispersibility in the resin and resistance control. However, it is not limited to these. The content of the conductive material is preferably 0.01 to 10 parts by weight and more preferably 0.05 to 5 parts by weight with respect to 100 parts by weight of the resin in order to make the carrier volume specific resistance a desired characteristic.
A content of 0.01 parts by weight or more is preferable because a resistance adjusting effect can be obtained. Further, it is preferable that the content is 10 parts by weight or less because the conductive material does not come off.

  In the carrier of the present invention, the coating resin layer preferably contains a wax. Waxes are hydrophobic, are relatively soft at room temperature, and have low film strength. This is due to the molecular structure of the wax. Because of this characteristic, it is preferable that a wax is present in the coating resin layer of the carrier because minute components called external additives added to the toner surface or toner components such as a toner bulk component hardly adhere to the carrier surface. Further, even when the toner adheres, the surface is renewed by peeling off the adhered portion at the wax molecule level, and therefore, the carrier surface is preferably hardly contaminated by adhesion, which is preferable.

Furthermore, when it is desired to provide various functions, fine resin particles corresponding to the functions can be used. For example, when it is desired to impart negative charge imparting property and charge maintaining property to the toner, the charge characteristics can be greatly improved by using nitrogen-containing resin particles as the charge control agent. In order to improve the mechanical strength of the carrier by the resin particles, it is preferable to use thermosetting resin particles that are relatively easy to increase the hardness. Since the thermosetting resin particles are already in the form of particles in the solvent, they can be easily dispersed during coating, and can be maintained in the form of primary particles without agglomeration in the carrier-coated resin layer. Thus, the resin particles to be contained in the coating resin layer may be appropriately selected from various resins according to the desired function.
Specific examples of thermoplastic resins that can be used for the resin particles include polyolefin resins such as polyethylene and polypropylene; polyvinyls and polyvinylidene resins such as polystyrene, acrylic resins, polyacrylonitrile, polyvinyl acetate, and polyvinyl acetate. Alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl carbazole, polyvinyl ether and polyvinyl ketone; vinyl chloride-vinyl acetate copolymer; styrene-acrylic acid copolymer; straight silicone resin composed of organosiloxane bond or a modified product thereof; fluorine resin Examples thereof include polytetrafluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, polychlorotrifluoroethylene; polyester; polycarbonate and the like.
Examples of thermosetting resins that can be used for the resin particles include phenol resins; amino resins such as urea-formaldehyde resins, melamine resins, benzoguanamine resins, urea resins, polyamide resins; epoxy resins, and the like.
The average particle diameter of the resin particles is preferably 0.05 to 2 μm. More preferably, it is 0.1-1 micrometer. It is preferable that the average particle diameter of the resin particles is 0.05 μm or more because the dispersibility in the coating resin layer is good. Moreover, it is preferable for the average particle diameter of the resin particles to be 2 μm or less because it is difficult for the resin particles to fall off the coating resin layer and the original function can be maintained satisfactorily.

In the present invention, it is also preferable to add a charge control agent to the coating resin layer.
Examples of the charge control agent include nigrosine dye, benzimidazole compound, quaternary ammonium salt compound, alkoxylated amine, alkylamide, molybdate chelate pigment, triphenylmethane compound, salicylic acid metal salt complex, azo chromium complex, Any known material such as copper phthalocyanine may be used. Particularly preferred are quaternary ammonium salt compounds, alkoxylated amines and alkylamides.
These charge control agents are preferable because they are easy to control the dispersion state and have good adhesion to the coating resin interface, so that desorption of the charge control agent from the carrier coating resin film can be suppressed. In addition, the charge control agent works as a dispersion aid for the conductive material, and the dispersion state of the conductive material in the coating resin layer is made uniform, and even if the coat layer is slightly peeled off, it is preferable because the change in carrier resistance can be suppressed. The reason is that the surface of the conductive material is easily oxidized or affected by moisture, so that the conductive material has high hydrophilicity and tends to aggregate due to water on the particle surface. When this is dispersed in the coating resin, since the polarity of the resin is generally low, the agglomeration described above remains as it is, so that uneven distribution tends to occur inside the coating resin. On the other hand, the charge control agent described above has good adhesion to the coating resin interface and has a certain degree of polarity, so that the adhesion with the conductive material is also improved, so it is estimated that the dispersibility can be improved. Is done.

  The addition amount of the charge control agent used in the present invention is preferably 0.001 to 5 parts by weight when the carrier core material is 100 parts by weight. More preferably, it is 0.01-0.5 weight part. It is preferable for the amount added to be 5 parts by weight or less because the strength of the carrier-coated resin layer does not decrease and deterioration due to stress during use hardly occurs. Moreover, it is preferable that the addition amount is 0.001 part by weight or more because the function of the charge control agent can be exhibited and the dispersibility of the conductive material can be improved.

Hereafter, the manufacturing method of the carrier of this invention is described.
When coating the coating resin layer on the carrier core material, typical methods are as follows: (1) The coating layer is formed by introducing the resin, coating layer magnetic particles and, if necessary, a conductive material into a resin-soluble solvent. (2) A spray method in which a coating layer forming solution is sprayed on the surface of the carrier core material, and (3) a carrier core material. A fluidized bed method in which a coating layer forming solution is sprayed in a state of being suspended by flowing air, and (4) a kneader coater method in which a carrier core material and a coating layer forming solution are mixed in a kneader coater and then the solvent is removed. Can be mentioned. The carrier of the present invention is preferably produced by a kneader coater method in which a carrier core material and a coating layer forming solution containing magnetic particles in the coating layer are mixed in a kneader coater, and then the solvent is removed.

Usually, when manufacturing by a kneader coater method, the carrier core material and the coating layer forming solution in which the conductive fine particles are dispersed are mixed, and the solvent is removed by heating and reducing pressure while stirring. During production, the adhesiveness of the coating layer resin solution varies depending on the residual amount of the solvent, due to the friction between carrier particles due to agitation stress, due to the balance between the adhesion of the core material and the coating layer resin, peeling, scraping, A burr etc. will occur. In addition, the core material with many irregularities on its surface has problems such as cracking and chipping caused by agitation stress and the like, and the uniformity of the surface of the manufactured carrier is lost.
In the present invention, it is characterized by using core particles having a shape factor of 120 or less with little cracking or chipping due to agitation stress, and magnetic particles whose magnetization is higher than the magnetization of the core particles in the coating resin layer. It is necessary to add in a dispersed manner. In the present invention, a resin layer may be provided in advance on the surface of the coating layer magnetic particles by a kneader coater method.
The resin used for the resin layer of the magnetic particles may have the same composition as the coating resin in the coating resin layer that coats the core particles, or the composition may be changed.

  The solvent used for the preparation of the coating layer forming solution is not particularly limited as long as it dissolves the coating resin, and examples thereof include aromatic hydrocarbons such as toluene and xylene, acetone, methyl ethyl ketone, and the like. Ketones, ethers such as tetrahydrofuran and dioxane, and halides such as chloroform and carbon tetrachloride can be used.

The average film thickness of the coating resin layer is preferably 0.1 to 10 μm, and more preferably 0.5 to 3 μm. It is preferable that the average film thickness of the coating resin layer be within the above range because a uniform and flat coating resin layer can be formed on the surface of the carrier core material, and the stable volume resistivity of the carrier can be expressed over time.
The average thickness of the coating resin layer is such that the carrier is dispersed in a two-component mixed epoxy solution and allowed to solidify for one day and night, and then a 100-nm thick slice is prepared with a microtome. The section is placed on a copper mesh, set in a high-resolution electron microscope JEM-2010 (manufactured by JEOL Ltd.), photographed at 3000 times with an applied voltage of 200 kV, and the negative is stretched 3 to 10 times. Print. On the print screen, particles having a cross section of 50 particles can be observed arbitrarily, and 10 arbitrary points (total 500 points) can be measured for each particle, and the measured values can be averaged and evaluated.

The volume resistivity of the carrier used in the present invention is 10 ⁶ to 10 ¹⁴ Ω · cm at 1,000 V corresponding to the upper and lower limits of a normal development contrast potential in order to achieve high image quality. Preferably, it is 10 ⁸ to 10 ¹³ Ω · cm. When the volume resistivity of the carrier is 10 ⁶ Ω · cm or more, the fine line reproducibility is excellent, and the amount of carrier transferred to the photosensitive member (electrostatic image holding member) is small, so that the photosensitive member is not damaged. preferable. Further, it is preferable that the volume specific resistance value of the carrier is 10 ¹⁴ Ω · cm or less because black solid and halftone reproducibility is excellent.

(Electrostatic image developer)
The developer used in the present invention is prepared by mixing the above carrier and the toner described later at an appropriate blending ratio. The carrier content ((carrier) / (carrier + toner) × 100) is preferably 85 to 99 parts by weight, more preferably 87 to 98 parts by weight, and even more preferably 89 to 97 parts by weight. It is a range.

<Toner>
In the present invention, the method for producing the toner (toner particles) is not particularly limited, but it is desirable to produce the toner (toner particles) by a wet production method in order to obtain high image quality. As a wet manufacturing method, a polymerizable monomer of a binder resin is emulsion-polymerized, and the formed dispersion is mixed with a dispersion of a colorant, a release agent, and a charge control agent as necessary, and agglomerated. An emulsion polymerization aggregation method to obtain toner particles by heat fusion; a solution of a polymerizable monomer, a colorant, a release agent, and a charge control agent, if necessary, to obtain a binder resin in an aqueous solvent. Suspension polymerization method for turbid polymerization; dissolution suspension method in which a binder resin, a colorant, a release agent, and a charge control agent, if necessary, are suspended in an aqueous solvent and granulated; It is done. Further, a manufacturing method may be performed in which the toner particles obtained by the above method are used as a core, and further, aggregated particles are attached and heat-fused to give a core-shell structure. Further, toner particles obtained by a general kneading and pulverizing method in which a binder resin, a colorant, a release agent, and a charge control agent as necessary are kneaded, pulverized, and classified may be used.

  The toner (toner particles) used in the present invention contains at least a binder resin and, if necessary, a colorant, a release agent and other components. In addition to the so-called toner particles having the above structure, it is desirable that an external additive is added to the toner used in the present invention for various purposes.

In the present invention, it is preferable that toner particles having a particle size of 3 μm or less in the number distribution are 5% or less of the total toner particles. It is preferable that it is 0.1 to 4%, and it is more preferable that it is 0.1 to 3%.
It is preferable to adjust the toner particles having a particle diameter of 3 μm or less to 5% or less because adhesion to the carrier is reduced and development on the photoreceptor can be suppressed.
The content of the toner having a particle size of 3 μm or less can be measured by a multisizer 3 manufactured by Coulter. Specifically, the toner sample was dispersed with a surfactant, measurement was performed using a 50 μ aperture tube, and 3 μ under was measured with analysis software.

  In order to obtain toner particles having the particle distribution as described above, among the above-described toner production methods, a wet production method that facilitates the production of a small particle size toner is preferably used, and toner particles having a sharp distribution are obtained. The emulsion polymerization aggregation method is preferable in that it can be used.

  In the present invention, the shape factor (SF1) of the toner is preferably 100 to 135, more preferably 120 to 130. It is preferable that the shape factor is within the above range since good image forming properties can be obtained.

In the present invention, the cumulative volume average particle diameter D _50V of the toner is preferably 3.0 to 9.0 μm, more preferably 3.0 to 7.0 μm, still more preferably 3.0 to 5. 0 μm. It is preferable that D _50V is within the above range because adhesion is strong and developability is good. Further, it is preferable because the resolution of the image is good.
Further, the volume average particle size distribution index GSDv of the toner is preferably 1.30 or less. It is preferable that GSDv is 1.30 or less because resolution is good and image loss such as toner scattering and fogging does not occur.

Here, the cumulative volume average particle diameter D _50V and the volume average particle size distribution index GSDv can be measured by, for example, Multisizer II (manufactured by Nikka Kisha Co., Ltd.). A cumulative distribution is drawn from the smaller diameter side to the particle size range (channel) divided based on the particle size distribution, and the particle diameter that becomes 16% cumulative is the volume D _16v , the number D _16P , and the cumulative 50%. The particle diameter is _defined as a volume D _50v and a number D _50P , and the particle diameter at a cumulative 84% is defined as a volume D _84v and a number D _84P . Using these, the volume average particle size distribution index (GSDv) is calculated as (D _84v / D _16V ) ^1/2 and the number average particle size distribution index (GSDp) is calculated as (D _84P / D _16P ) ^1/2 .

(Image forming device)
The image forming apparatus according to the present invention includes at least a latent image forming unit that forms an electrostatic latent image on the surface of the electrostatic latent image holding member, and a developer including a toner and a carrier contained in the developing device. A developing unit that visualizes the formed latent image and forms a toner image on the surface of the electrostatic latent image holding member; and a transfer unit that transfers the formed toner image to the surface of the transfer target. An image forming apparatus having the electrostatic charge image developing carrier of the present invention.

FIG. 1 is a block diagram showing an example of an image forming apparatus that can be suitably used in the present invention, but the present invention is not limited to this.
As shown in FIG. 1, a so-called tandem type full-color image forming apparatus can be exemplified as an image forming apparatus that can be suitably used in the present invention. The image forming units 10 (specifically, 10Y to 10K) of four colors (Y (yellow), M (magenta), C (cyan), K (black)) in FIG. Is provided with an intermediate transfer belt B that is circulated and conveyed along the arrangement direction of the image forming units 10, and a sheet supply cassette 50 that accommodates a recording sheet S such as paper is provided below the intermediate transfer belt B. It is a thing.

In FIG. 1, each image forming unit 10 (10Y to 10K) forms, for example, yellow, magenta, cyan, and black toner images in order from the upstream side in the circulation direction of the intermediate transfer belt B. For example, a photosensitive drum 11 (11Y to 11K) that rotates in a predetermined direction is provided, and around the photosensitive drum 11, a charger 13 (13Y to 13K) that precharges the photosensitive drum 11 and a photosensitive drum. An exposure unit 15 (15Y to 15K) for writing an electrostatic latent image on the image 11 and a developing device 17 (17Y to 17K) for visualizing the electrostatic latent image written on the photosensitive drum 11 with a predetermined toner. ), A primary transfer device 20 (20Y to 20K) for primarily transferring a toner image on the photosensitive drum 11 to the intermediate transfer belt B, and a cleaner 2 for removing residual toner on the photosensitive drum 11. (25Y~25K) and is obtained by successively disposed.
The intermediate transfer belt B, which is an endless belt member, is stretched between a plurality of stretching rolls 31 to 35, and is formed so as to be able to rotate counterclockwise in the drawing along a trajectory of a horizontally long triangle. ing. The intermediate transfer belt B is driven by a drive roll 31 connected to a drive source (not shown) via a gear or the like, and travels between these rolls 31 to 35.

  Further, a primary transfer device (primary transfer roll in this example) 20 is disposed on the back surface of the intermediate transfer belt B corresponding to each photosensitive drum 11, and a voltage having a polarity opposite to the charging polarity of the toner is applied to the primary transfer device 20. Is applied to electrostatically transfer the toner image on the photosensitive drum 11 to the intermediate transfer belt B side.

  Further, a secondary transfer device 40 is disposed at a portion corresponding to the tension roll 34 on the downstream side of the image forming unit 10K of the intermediate transfer belt B, and the primary transfer image on the intermediate transfer belt B is recorded on the recording sheet. Secondary transfer (collective transfer) to S is performed.

  In FIG. 1, the secondary transfer device 40 includes a secondary transfer roll 41 arranged in pressure contact with the toner image holding surface side of the intermediate transfer belt B, and a secondary transfer roll 41 arranged on the back side of the intermediate transfer belt B. A backup roll 43 serving as a counter electrode (in this example, the tension roll 34 is also used) is provided. For example, the secondary transfer roll 41 is grounded, and a bias having the same polarity as the toner charging polarity is applied to the backup roll 43 (driven roll 34) via the power supply roll 45. Further, the secondary transfer roll 41 is configured such that residual toner is removed by a secondary transfer roll cleaner 47.

  Further, a belt cleaner 36 is disposed on the upstream side of the image forming unit 10Y of the intermediate transfer belt B so as to remove residual toner on the intermediate transfer belt B.

  The sheet supply cassette 50 is provided with a feed roll 51 for picking up the recording sheet S. An appropriate number of conveyance rolls 53 for conveying the recording sheet S are disposed immediately after the feed roll 51, and the secondary roll A registration roll (registration roll) 55 for supplying the recording sheet S to the secondary transfer portion at a predetermined timing is disposed in the sheet conveyance path located immediately before the transfer portion.

  On the other hand, a fixing device 70 is provided via a sheet conveyance belt 60 in the sheet conveyance path located downstream of the secondary transfer site.

  According to the image forming apparatus configured as described above, each color toner image is formed on the photosensitive drum 11 by each image forming unit 10, and each color toner image is sequentially primary-transferred onto the intermediate transfer belt B, and then the sheet. The recording sheet S supplied from the supply cassette 50 at a predetermined timing is batch-transferred at the secondary transfer site, and then the recording sheet S is passed between the heating roll and the pressure roll of the fixing device 70. In the meantime, the toner is fixed on the recording sheet S, and the image is fixedly formed on the recording sheet S.

  In particular, when combined with trickle development proposed in Japanese Patent Publication No. 2-21591, the released spherical particles do not accumulate on the developer holding member, and a stable image appearance can be obtained for a long time.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited by these illustrations.

(Preparation of carrier)
<Carrier I>
Ferrite particles 100 parts (Mn—Mg ferrite, true specific gravity 4.7 g / cm ³ , volume average particle diameter 40 μm, saturation magnetization 60 emu / g (60 × 4π × 10 ⁻⁷ Wb · m / kg), shape factor 119)
・ Coating layer magnetic particles 2 parts (Mn—Mg ferrite, true specific gravity 4.7 g / cm ³ , volume average particle diameter 2 μm, saturation magnetization 66 emu / g (66 × 4π × 10 ⁻⁷ Wb · m / kg), shape factor 115)
・ Toluene 8 parts ・ Coating resin: Styrene-methyl methacrylate copolymer 4 parts (copolymerization ratio 20:80, molecular weight 85,000)
・ Carbon black (VXC-72: manufactured by Cabot Corporation) 0.1 part ・ Crosslinked melamine resin particles (Eposta S: manufactured by Nippon Shokubai Co., Ltd.) 0.1 part Coating layer magnetic particles, coating resin, carbon black, crosslinked melamine resin particles Put in toluene and stir and disperse with a sand mill to prepare a coating resin layer forming solution. Put ferrite particles in a vacuum degassing kneader and keep the temperature at 60 ° C. for 10 minutes, then monitor the current value of the stirring motor And reduced pressure to distill off toluene. Carrier I was obtained by sieving the coated resin layer-formed carrier with a mesh having an opening of 75 μm.

<Carrier II>
Ferrite particles 100 parts (Mn—Mg ferrite, true specific gravity 4.7 g / cm ³ , volume average particle diameter 40 μm, saturation magnetization 60 emu / g (60 × 4π × 10 ⁻⁷ Wb · m / kg), shape factor 119)
・ Coating layer magnetic particles 4 parts (Mn-Mg ferrite, true specific gravity 4.7 g / cm ³ , volume average particle diameter 5 μm, saturation magnetization 66 emu / g (66 × 4π × 10 ⁻⁷ Wb · m / kg), shape factor 118)
-Toluene 8 parts-Coating resin: Styrene-methyl methacrylate copolymer 4 parts-Carbon black (VXC-72: manufactured by Cabot Corporation) 0.1 part-Cross-linked melamine resin particles (Eposta S: manufactured by Nippon Shokubai Co., Ltd.) 0. Part 1 Coating layer magnetic particles, coating resin, carbon black, cross-linked melamine resin particles are put into toluene and stirred and dispersed in a sand mill to prepare a coating resin layer forming solution, and both ferrite particles are placed in a vacuum degassing kneader and temperature After stirring at 10O 0 C for 10 minutes, the current value of the stirring motor was monitored and the pressure was reduced to distill off the toluene. Carrier II was obtained by sieving the coated resin layer-formed carrier with a mesh having an opening of 75 μm.

<Carrier III>
[Preparation of resin-coated magnetic particles (coating layer magnetic particles)]
Magnetic particles 100 parts (Mn—Mg ferrite, true specific gravity 4.7 g / cm ³ , volume average particle diameter 3 μm, saturation magnetization 66 emu / g (66 × 4π × 10 ⁻⁷ Wb · m / kg), shape factor 115)
-Toluene 8 parts-Coating resin: Styrene-methyl methacrylate copolymer 4 parts-Carbon black (VXC-72: manufactured by Cabot Corporation) 0.1 part-Cross-linked melamine resin particles (Eposta S: manufactured by Nippon Shokubai Co., Ltd.) 0. 1 part Coating resin, carbon black, cross-linked melamine resin particles are put into toluene and stirred and dispersed with a sand mill to prepare a coating resin layer forming solution. The ferrite particles are put in a vacuum degassing type kneader and kept at a temperature of 60 ° C. 10 After stirring for a minute, the current value of the stirring motor was monitored and the pressure was reduced to distill off the toluene. The coated resin layer-forming magnetic particles were sieved with a mesh having an opening of 75 μm to obtain resin-coated magnetic particles.

[Production of Carrier III]
Ferrite particles 100 parts (Mn—Mg ferrite, true specific gravity 4.7 g / cm ³ , volume average particle diameter 40 μm, saturation magnetization 50 emu / g (50 × 4π × 10 ⁻⁷ Wb · m / kg), shape factor 119)
・ Coating layer magnetic particles (resin coated magnetic particles) 2 parts (Mn—Mg ferrite, true specific gravity 4.7 g / cm ³ , volume average particle diameter 3 μm, saturation magnetization 66 emu / g (66 × 4π × 10 ⁻⁷ Wb · m / Kg), shape factor 115)
-Toluene 8 parts-Coating resin: Styrene-methyl methacrylate copolymer 4 parts-Carbon black (VXC-72: manufactured by Cabot Corporation) 0.1 part-Cross-linked melamine resin particles (Eposta S: manufactured by Nippon Shokubai Co., Ltd.) 0. Part 1 Coating resin, carbon black, cross-linked melamine resin particles are put into toluene and stirred and dispersed in a sand mill to prepare a coating resin layer forming solution. Both ferrite particles and resin-coated magnetic particles are put in a vacuum degassing kneader and temperature After stirring at 10O 0 C for 10 minutes, the current value of the stirring motor was monitored and the pressure was reduced to distill off the toluene. The coated resin layer-formed carrier was sieved with a mesh having an opening of 75 μm to obtain Carrier III.

<Carrier IV>
Ferrite particles 100 parts (Mn—Mg ferrite, true specific gravity 4.7 g / cm ³ , volume average particle diameter 40 μm, saturation magnetization 50 emu / g (50 × 4π × 10 ⁻⁷ Wb · m / kg), shape factor 119)
Magnetic particles 2 parts (Mn—Mg ferrite, true specific gravity 4.7 g / cm ³ , volume average particle diameter 1 μm, saturation magnetization 66 emu / g (66 × 4π × 10 ⁻⁷ Wb · m / kg), shape factor 115)
-Toluene 8 parts-Coating resin: Styrene-methyl methacrylate copolymer 4 parts-Carbon black (VXC-72: manufactured by Cabot Corporation) 0.1 part-Cross-linked melamine resin particles (Eposta S: manufactured by Nippon Shokubai Co., Ltd.) 0. 1 part Magnetic particles, coating resin, carbon black, cross-linked melamine resin particles are put into toluene and stirred and dispersed with a sand mill to prepare a solution for forming a coating resin layer, and ferrite particles are put in a vacuum degassing type kneader at a temperature of 60 ° C. After stirring for 10 minutes, the current value of the stirring motor was monitored and the pressure was reduced to distill off the toluene. The coated resin layer-formed carrier was sieved with a mesh having an opening of 75 μm to obtain Carrier IV.

<Carrier V>
Magnetic powder dispersed core material particles 100 parts (manufactured by Toda Kogyo Co., Ltd., matrix resin: phenol resin, true specific gravity 3.7 g / cm ³ , volume average particle size 40 μm, saturation magnetization 60 emu / g, shape factor 105)
・ Coating layer magnetic particles 2 parts (Mn—Mg ferrite, true specific gravity 4.7 g / cm ³ , volume average particle diameter 2 μm, saturation magnetization 66 emu / g (66 × 4π × 10 ⁻⁷ Wb · m / kg), shape factor 115)
・ Toluene 8 parts ・ Coating resin: Styrene-methyl methacrylate copolymer 4 parts (copolymerization ratio 20:80, molecular weight 85,000)
・ Carbon black (VXC-72: manufactured by Cabot Corporation) 0.1 part ・ Crosslinked melamine resin particles (Eposta S: manufactured by Nippon Shokubai Co., Ltd.) 0.1 part Coating layer magnetic particles, coating resin, carbon black, crosslinked melamine resin particles Put in toluene and stir and disperse with a sand mill to prepare a coating resin layer forming solution. Put the magnetic particle-dispersed carrier core particles in a vacuum degassing kneader and keep the temperature at 60 ° C. and stir for 10 minutes. The current value of the motor was monitored and the pressure was reduced to distill off toluene. The carrier V was obtained by sieving the coated resin layer-formed carrier with a mesh having an opening of 75 μm.

<Carrier VI>
Ferrite particles 100 parts (Mn—Mg ferrite, true specific gravity 4.7 g / cm ³ , volume average particle diameter 40 μm, saturation magnetization 60 emu / g (60 × 4π × 10 ⁻⁷ Wb · m / kg), shape factor 125)
Magnetic particles 2 parts (Mn—Mg ferrite, true specific gravity 4.7 g / cm ³ , volume average particle diameter 3 μm, saturation magnetization 60 emu / g (60 × 4π × 10 ⁻⁷ Wb · m / kg), shape factor 115)
・ Toluene 8 parts ・ Coating resin: Styrene-methyl methacrylate copolymer 4 parts ・ Carbon black (VXC-72: manufactured by Cabot Corporation) 0.1 part ・ Crosslinked melamine resin particles (Eposta S: manufactured by Nippon Shokubai Co., Ltd.) 0. 1 part Magnetic particles, coating resin, carbon black, cross-linked melamine resin particles are put into toluene and stirred and dispersed in a sand mill to prepare a solution for forming a coating resin layer, and ferrite particles are put in a vacuum degassing kneader and the temperature is 60 ° C. After stirring for 10 minutes, the current value of the stirring motor was monitored and the pressure was reduced to distill off the toluene. The coated resin layer-formed carrier was sieved with a mesh having an opening of 75 μm to obtain Carrier VI.

(toner)
<Preparation of resin particle dispersion>
・ Styrene 296 parts ・ N-butyl acrylate 104 parts ・ Acrylic acid 6 parts ・ Dodecanethiol 10 parts ・ Divinyl adipate 1.6 parts (above, manufactured by Wako Pure Chemical Industries, Ltd.)
A mixture obtained by mixing and dissolving the above components was mixed with 12 parts of a nonionic surfactant (Sanyo Kasei Co., Ltd .: Nonipol 400) and an anionic surfactant (Daiichi Kogyo Seiyaku Co., Ltd .: Neogen SC) 8 Ion exchange with 8 parts of ammonium persulfate (manufactured by Wako Pure Chemical Industries, Ltd.) dissolved in 610 parts of ion-exchanged water, dispersed in a flask, emulsified, and slowly mixed for 10 minutes. 50 parts of water was added and nitrogen substitution was performed at 0.1 liter / min for 20 minutes. Thereafter, the contents in the flask are heated with an oil bath until the content reaches 70 ° C., and emulsion polymerization is continued as it is for 5 hours. A resin particle dispersion having an average particle size of 200 nm and a solid content concentration of 40% ( 1) was prepared. When a part of the dispersion was left on an oven at 100 ° C. to remove moisture, DSC (differential scanning calorimeter) measurement was performed. The glass transition point was 53 ° C. and the weight average molecular weight was 32,000. Met.

<Preparation of Colorant Dispersion (C)>
・ C. I. Pigment Blue 15: 3 100 parts (Phthalocyanine pigment: Dainichi Seika Co., Ltd .: Cyanine Blue 4937)
・ Anionic surfactant (Neogen RK: manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 10 parts ・ Ion-exchanged water 490 parts The above ingredients were mixed and dissolved, and dispersed for 10 minutes using a homogenizer (manufactured by IKA: Ultra Tarrax). A colorant dispersant (C) was prepared.

<Preparation of release agent particle dispersion>
-Paraffin wax (Nippon Seiwa Co., Ltd .: HNP-9) 100 parts-Anionic surfactant (Lion Co., Ltd .: Lipar 860K) 10 parts-Ion-exchanged water 390 parts After mixing and dissolving the above components, Release agent particles which are dispersed using a homogenizer (IKA: Ultra Tarrax) and dispersed with a pressure discharge type homogenizer to disperse release agent particles (paraffin wax) having an average particle size of 220 nm. A dispersion was prepared.

<Manufacture of cyan toner 1>
-Resin particle dispersion 320 parts-Colorant dispersion (C) 80 parts-Release agent particle dispersion 96 parts-Aluminum sulfate (manufactured by Wako Pure Chemical Industries, Ltd.) 1.5 parts-Ion-exchanged water 1,270 parts The above components were housed in a round stainless steel flask with a temperature control jacket, dispersed for 5 minutes at 5,000 rpm using a homogenizer (manufactured by IKA, Ultra Turrax T50), transferred to the flask, and 25 The mixture was allowed to stand with stirring with 4 paddles at 20 ° C. for 20 minutes. Thereafter, the mixture was heated with a mantle heater while stirring and heated at a heating rate of 1 ° C./min until the inside reached 48 ° C., and held at 48 ° C. for 20 minutes. Next, 80 parts of the resin particle dispersion was gradually added and kept at 48 ° C. for 30 minutes, and then a 1N aqueous sodium hydroxide solution was added to adjust the pH to 6.5.
Thereafter, the temperature was raised to 95 ° C. at a rate of 1 ° C./min and held for 30 minutes. A 0.1N nitric acid aqueous solution was added to adjust the pH to 4.8, and the mixture was allowed to stand at 95 ° C. for 2 hours. Thereafter, the 1N aqueous sodium hydroxide solution was further added to adjust the pH to 6.5, and the mixture was allowed to stand at 95 ° C. for 5 hours. Thereafter, it was cooled to 30 ° C. at 5 ° C./min.

The resulting toner particle dispersion was filtered, (A) 2,000 parts of ion-exchanged water at 35 ° C. was added to the obtained toner particles, (B) allowed to stand for 20 minutes, and (C) then filtered. After the operations from (A) to (C) were repeated 5 times, the toner particles on the filter paper were transferred to a vacuum dryer and dried at 45 ° C. and 1,000 Pa or less for 10 hours. The above-mentioned toner particles are not more than 1,000 Pa. The above-mentioned toner particles are in a water-containing state, and in the initial stage of drying, the water freezes even at 45 ° C. and then the water sublimates. This is because the pressure does not become constant. However, it was stable at 100 Pa at the end of drying. After returning the inside of the dryer to normal pressure, this was taken out to obtain toner mother particles, and 1.5 parts of silica external additive (manufactured by Nippon Aerosil Co., Ltd., RY-50) was added to 100 parts of the toner mother particles. The mixture was added and mixed with a Henschel mixer at 3,000 rpm for 3 minutes to obtain cyan toner 1.
The obtained cyan toner 1 had a D50v of 5.8 μm, and the number of toner particles of 3 μm or less was 3.7% of the total toner particles.

<Manufacture of cyan toner 2>
101 parts of isophthalic acid, 180 parts of a 2 mol adduct of bisphenol A propylene oxide and 5.4 parts of dibutyltin oxide were put into a flask, and a dehydration condensation reaction was carried out at a temperature of 230 ° C. in a nitrogen atmosphere and continued for 18 hours. The acid value of the obtained polyester resin was 42 mgKOH / g. The weight average molecular weight was 6,800.
174 parts of this polyester resin, C.I. I. Pigment Blue 15: 3 (phthalocyanine pigment: Dainichi Seika Co., Ltd .: Cyanine Blue 4937) 16 parts and paraffin wax (Nippon Seiwa Co., Ltd .: HNP-9) 10 parts were placed in a Banbury mixer (Kobe Steel). Pressure was applied so that the internal temperature was 110 ± 5 ° C., and kneading was performed at 80 rpm for 10 minutes. The obtained kneaded product is cooled, coarsely pulverized with a hammer mill, finely pulverized to about 6.2 μm with a jet mill, and then classified with an elbow jet classifier (manufactured by Matsuzaka Trading Co., Ltd.). In the same manner as in Example 1, an external additive was added to obtain 2 cyan toner particles.
The obtained cyan toner 2 had a D50v of 6.5 μm, and toner particles of 3 μm or less accounted for 4.7% of the total toner particles in number distribution.

(Preparation of developers of Examples 1 to 7 and Comparative Example 1)
Cyan toner 1 and carriers I to VI, cyan toner 2 and carriers I and III were mixed at a ratio of 5 parts by weight of toner and 95 parts by weight of carrier using a V blender for 20 minutes at 40 rpm, and sieved using a 125 μm mesh sieve. To obtain a developer.

(Evaluation of Examples and Comparative Examples)
-Evaluation method-
<Thin wire reproducibility>
Using the developers described in the above Examples and Comparative Examples, actual machine evaluation was performed at 10 ° C. and 20% HR using a Fuji Xerox Copier Docu Center Color 500 modified machine. Ten sheets of fine line images were printed after 100,000 sheets were printed, and the reproducibility of the fine line part was visually evaluated.
The case where it was difficult to read the characters clearly visually was evaluated as x, the case where there was a slight problem was evaluated as Δ, and the case where there was no problem was evaluated as ○. The fine lines were evaluated on A4 paper having 2 cm × 2 cm and 125 lines / inch.

<Image defect>
[Line]
The streaks on the image generated during the output of the thin line image were evaluated. Evaluation was performed based on the number of lines remaining.

<Wallet, bite>
The produced carrier and the developer after printing 10,000 sheets were confirmed by FE-SEM, and the crack of the carrier and the number of chips were visually confirmed with a 350 times photograph.
The case where cracks and chips could be clearly confirmed visually was evaluated as x, the case where cracks and chips were slightly observed was evaluated as Δ, and the case where cracks and chips were not observed was evaluated as ○.

(Evaluation results)
As the results of Examples 1 to 7 show, the core material particles have a shape factor of 120 or less, and magnetic particles having a saturation magnetization higher than the saturation magnetization of the core particles are dispersed and added to the coating resin layer. The print quality was maintained in a low humidity environment.

1 is a configuration diagram illustrating an example of an image forming apparatus that can be used in the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming unit 11 Photoconductor 13 Charger 15 Exposure unit 17 Developing device 20 Primary transfer device 25 Cleaner 31 Drive roll 32, 34 Drive roll 33, 35 Stretch roll 36 Belt cleaner 40 Secondary transfer device 41 Secondary transfer roll 43 Backup roll 45 Power feeding roll 47 Secondary transfer roll cleaner 50 Sheet supply cassette 51 Feed roll 53 Conveying roll 55 Registration roll 60 Sheet conveying belt 70 Transfer device B Intermediate belt S Recording sheet

Claims (3)

Having a core resin particle and a coating resin layer covering the core particle;
The core particles have a shape factor of 120 or less, and
The electrostatic charge image developing carrier, wherein the coating resin layer contains magnetic particles having saturation magnetization higher than that of core particles. Containing the carrier and toner of claim 1;
The electrostatic image developing developer, wherein the toner contains toner particles having a particle size of 3 μm or less in a number distribution of 5% or less of the total toner particles. At least latent image forming means for forming an electrostatic latent image on the surface of the electrostatic latent image holding member;
Developing means for visualizing the formed electrostatic latent image with a developer containing toner and a carrier contained in a developing device to form a toner image on the surface of the electrostatic latent image holding body; and ,
Transfer means for transferring the formed toner image to the surface of the transfer target;
An image forming apparatus having
An image forming apparatus, wherein the carrier is the electrostatic image developing carrier according to claim 1 or the electrostatic image developer according to claim 2.

Images