JP2010072174A - Electrostatic latent image developing carrier, electrostatic latent image developing developer, container, process cartridge, and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrostatic latent image developing carrier, an electrostatic latent image developing developer, a container, and a process cartridge, capable of preventing a carrier from being deposited, capable of restraining an edge effect, excellent in reproducibility of a fine line in a character part or the like, free from color contamination, and capable of obtaining a highly precise and fine image over a long period, and an image forming method. <P>SOLUTION: This electrostatic latent image developing carrier includes a core material, and a resin coating layer for coating a surface of the core material, and the resin coating layer contains a resin, and a titanium oxide fine particle coated with tin oxide. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to an electrostatic latent image developing carrier used for developing an electrostatic latent image in electrophotography, electrostatic recording, electrostatic printing, etc., an electrostatic latent image developing developer using the electrostatic latent image developing carrier, The present invention relates to a container having a developer for developing an electrostatic latent image and a process cartridge.
The present invention also relates to an image forming method such as an electrophotographic method, an electrostatic recording method, and an electrostatic printing method in which development is performed using a carrier for developing an electrostatic latent image.

  In electrophotographic image formation, an electrostatic latent image is formed by an electrostatic charge on an image carrier containing a photoconductive substance, and charged toner particles are attached to the electrostatic latent image. After the toner visible image is formed, the toner visible image is transferred to a recording medium such as paper and fixed to obtain an output image. In recent years, the technology of copying machines and printers using the electrophotographic system has been rapidly expanded from monochrome to full color, and the full color market tends to expand.

  Color image formation by full-color electrophotography generally reproduces all colors by stacking three color toners of three primary colors, yellow, magenta, and cyan, or four color toners with black added thereto. is there. At this time, in order to obtain a clear full-color image with excellent color reproducibility, it is necessary to smooth the fixed toner image surface to some extent to reduce light scattering. For these reasons, the image gloss of conventional full-color copying machines or the like is often 10 to 50% of medium to high gloss.

  In general, as a method for fixing a dry toner image on a recording medium, a contact heating fixing method in which a roller or belt having a smooth surface is heated and pressed against the toner is frequently used. This method has the advantages of high thermal efficiency and high-speed fixing, and can give gloss and transparency to the color toner. However, since the method is such that the surface of the heat fixing member and the molten toner are brought into contact with each other under pressure and then peeled off, a part of the toner image adheres to the surface of the fixing roller and is transferred onto another image. There is a problem that a so-called offset phenomenon occurs.

  In order to prevent this offset phenomenon, a method is generally adopted in which the fixing roller surface is formed of silicone rubber or fluororesin with excellent releasability, and then a release oil such as silicone oil is applied to the fixing roller surface. It had been. However, this method is extremely effective in preventing toner offset, but a device for supplying release oil is necessary, and the fixing device becomes large and unsuitable for downsizing the machine. For this reason, there is a method for increasing the viscoelasticity when the toner is melted by adjusting the molecular weight distribution of the binder resin so that the melted toner does not break internally. In addition to this method, there is a method in which a release agent such as wax is further contained in the toner so that the release oil is not applied to the fixing roller (oilless), or the amount of oil applied is very small. There is a tendency to be adopted.

  In color toners as well as monochrome, there is a trend toward oil-less for the purpose of downsizing machines and simplifying the configuration. However, as described above, in order to improve color reproducibility with color toners, it is necessary to smooth the surface of the fixed image, so the viscoelasticity at the time of melting must be lowered, and offset from a glossy monochrome toner. Easy to do. Therefore, it is more difficult to make the fixing device oil-free or to apply a small amount. In addition, when a release agent is contained in the toner, the adhesion of the toner is increased and the transfer property to the transfer paper is lowered. Further, the release agent in the toner contaminates the frictional charging member such as a carrier to reduce the charging property. This causes a problem that the durability is lowered.

On the other hand, regarding the carrier, toner component filming (hereinafter also referred to as spent) on the carrier surface is prevented, the carrier surface is uniformly formed, surface oxidation is prevented, moisture sensitivity is prevented, the life of the developer is extended, the image carrier It is necessary to prevent carrier adhesion to the surface (hereinafter also referred to as a photoreceptor), protect the photoreceptor from scratches or abrasion by the carrier, control the charge polarity, or adjust the charge amount. Therefore, a hard and high-strength coating layer is usually provided on the core material by coating with a suitable resin material. For example, a coating layer formed on the surface of a core material with a specific resin material (see Patent Document 1), a coating layer containing various additives (see Patent Documents 2 to 8), and a carrier. The thing (patent document 9) which made the surface adhere an additive is disclosed. Furthermore, the thing which contained the electroconductive particle larger than a coating film thickness in a coating film (refer patent document 10) etc. are disclosed.
Patent Document 11 describes the use of a benzoguanamine-n-butyl alcohol-formaldehyde copolymer as a main component for a carrier coating material, and Patent Document 12 describes a crosslinked product of a melamine resin and an acrylic resin as a carrier coating material. It is described to be used.

  However, the durability and the suppression of carrier adhesion to the surface of the image carrier are still insufficient. Concerning durability, there are problems such as spent on the carrier surface of the toner and the resulting unstable charging amount, reduction of the coating layer due to film removal of the coating resin, and accompanying resistance reduction. A good image can be obtained in the initial stage, but as the number of copies increases, the image quality of the copied image deteriorates, which causes a problem. Therefore, improvement in durability is required.

  Furthermore, in the copiers, printers, and the like using an electrophotographic system, there is an increasing demand for faster and more beautiful, and in response to this demand, the speed of machines in recent years has been remarkably increased. As a result, the stress received by the developer has also increased dramatically, and even a carrier that has been considered to have a long life has not been able to obtain a sufficient life, which has become a problem.

  In addition, carbon black has been used as a carrier resistance adjusting agent in the past, but color staining due to migration of the carbon black into the color image due to film scraping and / or carbon black detachment has become a problem. Yes. Various methods have been proposed as countermeasures.

  For example, Patent Document 13 proposes a carrier in which a conductive material (carbon black) is present on the surface of the core material and no conductive material is present in the resin coating layer. In Patent Document 14, the coating resin layer has a carbon black concentration gradient in the thickness direction, and the coating resin layer has a lower carbon black concentration toward the surface. Carriers that do not exist have been proposed. Furthermore, in Patent Document 15, an inner coating resin layer containing conductive carbon is provided on the surface of the core material particles, and a surface coating resin layer containing a white conductive material is further provided on the inner coating resin layer. A layer coat type carrier has been proposed. However, any of the carriers described in Patent Documents 13 to 15 cannot sufficiently cope with the recent increase in stress, and color stains have become a problem, so improvement is necessary.

  By the way, as a drastic measure against color stains, it is clear that it is most effective to eliminate carbon black that causes color stains. However, when carbon black is simply removed, as described above, carbon black has the property of low electrical resistance, resulting in an increase in carrier resistance. In general, when a carrier having high resistance is used as a developer, a so-called edge effect in which a large image area in a copy image has a very low image density in the center and only the edges are expressed sharply. It will be a good image. In addition, when the image is a character or a fine line, the image is clear due to the edge effect. However, when the image is halftone, the image has a very poor reproducibility.

  Therefore, attempts have been made to adjust the resistance of the carrier using a resistance adjusting agent other than carbon black. For example, titanium oxide and zinc oxide are known as resistance adjusting agents other than carbon black, but the effect of lowering the resistance is not sufficient to replace carbon black. Not reached.

  Patent Document 16 discloses a carrier whose resistance is adjusted by an oxide doped with antimony, but antimony is problematic in terms of safety to humans and the environment. In addition to this, tin oxide powder containing antimony has the same problem as carbon black that it impairs the toner color because the color tone is bluish.

  Further, Patent Document 17 discloses a resistance adjustment technique using a conductive filler made of tin dioxide and indium oxide. However, such a technique has problems such as a narrow resistance adjustment range, poor durability, and high cost, and further has problems in practical use due to difficulty in permanent use of rare metal indium. Therefore, there is a demand for conductive particles for adjusting the resistance of carriers with a wider resistance control range, no color stain, and abundant reserves.

JP 58-108548 A JP 54-1555048 A JP 57-40267 A JP 58-108549 A JP 59-166968 A Japanese Patent Publication No. 1-19584 Japanese Examined Patent Publication No. 3-628 JP-A-6-202381 JP-A-5-273789 JP-A-9-160304 JP-A-8-6307 Japanese Patent No. 2683624 Japanese Unexamined Patent Publication No. 7-140723 JP-A-8-179570 JP-A-8-286429 JP-A-11-202560 JP 2006-39357 A

  The present invention has been made in view of the above-described problems in the prior art, and does not cause carrier adhesion, suppresses the edge effect, has good reproducibility of fine lines such as character portions, and has no color stains. It is an object to provide a carrier for developing an electrostatic latent image, a developer for developing an electrostatic latent image, a container, a process cartridge, and an image forming method capable of obtaining a fine image over a long period of time. Furthermore, a carrier for developing an electrostatic latent image and a developer for developing an electrostatic latent image, in which a change in charge amount and resistance is small, defects such as toner scattering and image density unevenness are suppressed, and a good image can be obtained over a long period of time. It is an object to provide a container, a process cartridge, and an image forming method. Another object of the present invention is to provide a carrier for developing an electrostatic latent image, a developer for developing an electrostatic latent image, a container, a process cartridge, and an image forming method that do not contain antimony and are excellent in safety to humans and the environment. And

As a result of intensive studies, the inventors of the present invention have a core material and a resin coating layer that covers the surface of the core material, and the resin coating layer includes titanium oxide fine particles that are coated with a resin and tin oxide. It has been found that the above-mentioned problem can be solved by containing.
Specifically, the electrostatic latent image developing carrier, the electrostatic latent image developing developer, the container, the process cartridge, and the image forming method according to the present invention for solving the above-described problems are specifically described in the following (1). It has the technical feature as described in (16).

(1): A core material and a resin coating layer covering the surface of the core material, wherein the resin coating layer contains a resin and titanium oxide fine particles coated with tin oxide. An electrostatic latent image developing carrier.

(2) The electrostatic latent image developing carrier according to (1), wherein the titanium oxide fine particles are further coated with carbon.

(3) The carrier for developing an electrostatic latent image according to (2) above, wherein the standard deviation σ of the tin coating area ratio is 20 or less.

(4) The electrostatic latent image developing carrier according to (1), wherein the titanium oxide fine particles do not detect antimony by thermal analysis.

(5) The electrostatic latent image developing carrier according to (1), wherein the titanium oxide fine particles have a primary particle diameter of 1 to 500 nm.

(6) The electrostatic latent image developing carrier according to (1), wherein the titanium oxide fine particles have a volume resistivity acceleration ratio of 50 times or less.

(7): The electrostatic latent image developing carrier according to (1), wherein the volume average particle size is 20 μm or more and 65 μm or less.

(8) The electrostatic latent image developing carrier according to (1), wherein the resin contains a silicone resin.

(9) The electrostatic latent image developing carrier according to (1), wherein the resin contains an acrylic resin.

(10) The electrostatic latent image developing carrier according to (1), wherein the resin is an acrylic resin and a silicone resin.

(11): Static toner comprising: a toner containing a binder resin and a colorant; and the electrostatic latent image developing carrier described in any one of (1) to (10) above. A developer for developing an electrostatic latent image.

(12) The electrostatic latent image developing developer according to (11), wherein the toner is a color toner.

(13): The toner includes a base toner containing a binder resin and a colorant, and an external additive attached to the surface of the base toner, and the external additive contains titanium oxide. The developer for developing an electrostatic latent image according to (11), which is characterized in that

(14): A container containing the developer for developing an electrostatic latent image according to any one of (11) to (13).

(15) The electrostatic latent image developing developer described in any one of (11) to (13) above and one or more selected from an image carrier, a charging unit, and a cleaning unit. And a developing unit for holding the image forming apparatus.

(16) The electrostatic latent image developing developer according to any one of (11) to (13), wherein the step of forming an electrostatic latent image on an image carrier and the electrostatic latent image are performed. And developing a visible image to transfer the obtained visible image onto a recording medium and fixing the image.

  According to the electrostatic latent image developing carrier, the electrostatic latent image developing developer, the container, the process cartridge, and the image forming method of the present invention, the carrier adhesion does not occur, the edge effect is suppressed, the character portion, etc. The reproducibility of the fine line is good, and a high-definition image without color stains can be obtained over a long period of time.

  The electrostatic latent image developing carrier, electrostatic latent image developing developer, container, process cartridge, and image forming method of the present invention will be described in detail below.

<Electrostatic latent image developing carrier>
The electrostatic latent image developing carrier of the present invention includes a core material and a resin coating layer that covers the surface of the core material, and the resin coating layer includes titanium oxide fine particles formed by coating a resin and tin oxide. And containing.

(Core material)
As the core material of the electrostatic latent image developing carrier of the present invention, known materials can be applied, for example, ferrite, Cu—Zn ferrite, Mn ferrite, Mn—Mg ferrite, Mn—Mg—Sr ferrite, magnetite. , Iron, nickel and the like. These can be appropriately selected and used in accordance with the application and purpose of use. For example, DFC-400M, 500M, MFL-3500HS, SM-350NV, etc. are mentioned, but it is not limited to these.

(Resin coating layer)
The electrostatic latent image developing carrier of the present invention comprises a resin coating layer that covers the surface of a core material, and the resin coating layer contains a resin and titanium oxide fine particles coated with tin oxide. To do.

(resin)
As the resin used for the electrostatic latent image developing carrier of the present invention, conventionally known binder resins such as silicone resins and acrylic resins are contained alone or in combination of two or more. Among these, silicone resins and acrylic resins are preferable, and two types of silicone resins and acrylic resins are more preferable.

  Silicone resin has a low surface energy, so it is difficult to spend toner components, and accumulation of spent components due to film scraping is difficult to proceed. The silicone resin referred to in the present invention refers to all generally known silicone resins, and includes straight silicone consisting only of an organosiloxane bond, and modified silicone resins such as alkyd, polyester, epoxy, acrylic, and urethane. However, it is not limited to these. Examples of commercially available straight silicone resins include KR271, KR255, and KR152 manufactured by Shin-Etsu Chemical, SR2400, SR2406, and SR2410 manufactured by Toray Dow Corning Silicon. In this case, it is possible to use the silicone resin alone, but it is also possible to simultaneously use other components that undergo a crosslinking reaction, charge amount adjusting components, and the like. Furthermore, commercially available modified silicone resins include, for example, KR206 (alkyd modified), KR5208 (acrylic modified), ES1001N (epoxy modified), KR305 (urethane modified) manufactured by Shin-Etsu Chemical, manufactured by Toray Dow Corning Silicon. SR2115 (epoxy modification), SR2110 (alkyd modification), and the like.

  In addition, since the acrylic resin has high adhesiveness and low brittleness, it has a very excellent property of abrasion resistance, and deterioration such as scraping of the resin coating layer and peeling of the resin coating layer hardly occurs. Therefore, the acrylic resin can stably maintain the resin coating layer, and can firmly hold particles contained in the resin coating layer such as titanium oxide fine particles due to strong adhesiveness. In particular, a powerful effect can be exhibited for holding particles having a particle size larger than the resin coating layer thickness.

  The acrylic resin referred to in the present invention refers to all resins having an acrylic component, and is not particularly limited. In addition, it is possible to use the acrylic resin alone, but it is also possible to simultaneously use one or more other components that undergo a crosslinking reaction. Examples of other components that undergo a crosslinking reaction include amino resins and acidic catalysts, but are not limited thereto. Examples of amino resins include, but are not limited to, guanamine and melamine resins. In addition, as the acidic catalyst, any having a catalytic action can be used, and examples include those having reactive groups such as a fully alkylated type, a methylol group type, an imino group type, and a methylol / imino group type. However, it is not limited to these.

  However, as described above, acrylic resin has a very excellent property of abrasion resistance due to its strong adhesion and low brittleness, but on the other hand, it has a high surface energy, so in combination with a toner that is easy to spend. In some cases, the toner component spent accumulates a problem such as a decrease in charge amount. Silicone resin has a low surface energy, so it is difficult to spend toner components and accumulation of spent components due to film scraping is difficult to proceed, but on the other hand, it has poor adhesion and high brittleness, so it has high wear resistance. Inferiority may cause problems due to deterioration.

  Therefore, as a resin used for the resin coating layer, by using two types of silicone resin and acrylic resin in combination, the problem when only one of them is used is solved, and the effect when the above-described silicone resin is contained is obtained. In addition to the effects, the effects when an acrylic resin is contained are exhibited. At this time, it is important that the properties of the silicone resin and the acrylic resin are obtained in a well-balanced manner according to the desired properties. By making such a balance good, it is difficult to spend and the resin coating layer has excellent wear resistance. Can be obtained.

(Titanium oxide fine particles)
The carrier for developing an electrostatic latent image of the present invention contains fine titanium oxide particles coated with tin oxide in a resin coating layer. By containing titanium oxide coated with tin oxide in the resin coating layer, a decrease in charge when titanium oxide used as an external additive is spent from the toner can be suppressed.

In the carrier for developing an electrostatic latent image of the present invention, titanium oxide fine particles coated with tin oxide are further coated with carbon.
Although the detail about the concrete coating method is mentioned later, the outermost surface part of the titanium oxide microparticles | fine-particles coat | covered with tin oxide is coat | covered with the compound containing carbon.

  The primary particle diameter of the titanium oxide fine particles used in the electrostatic latent image developing carrier of the present invention is preferably 1 nm to 500 nm.

The method for measuring the primary particle size of the particles in the resin coating layer is performed according to the following procedure.
First, 300 ml of a toluene solution is added to 30 ml of aminosilane (SH6020: manufactured by Toray Dow Corning Silicone) in a juicer mixer. Next, 6.0 g of the sample (particles) to be measured is added to the juicy mixer, and the mixer rotation speed is set to low and dispersed for 3 minutes. Further, an appropriate amount of the dispersion is added to 500 ml of a toluene solution prepared in advance in a 1000 ml beaker and diluted to obtain a diluted solution. This diluted solution is continuously stirred with a homogenizer. Thereafter, the primary particle size is measured with an ultracentrifugal automatic particle size distribution analyzer CAPA-700 (manufactured by Horiba Seisakusho).

〔Measurement condition〕
Rotation speed: 2000rpm
Maximum particle size: 2.0 μm
Minimum particle size: 0.1 μm
Particle size interval: 0.1 μm
Dispersion medium viscosity: 0.59 mPa · s
Dispersion medium density: 0.87 g / cm ³
Particle density: The density of the sample to be measured is the true specific gravity value measured using a dry automatic bulk density meter Accupic 1330 (manufactured by Shimadzu Corporation).

  Further, in the electrostatic latent image developing carrier of the present invention, it is preferable that titanium oxide fine particles are contained in an amount of 10% by weight to 70% by weight in the resin coating layer. If the content of the titanium oxide fine particles is less than 10% by weight, resistance adjustment and impact resistance become insufficient, which is not preferable. On the other hand, when the content of the titanium oxide fine particles is more than 70% by weight, the ratio of the resin component that is a charge generation site in the resin coating layer becomes insufficient, and the charging ability is inferior. In addition, if the content of the titanium oxide fine particles is more than 70% by weight, the retention of the titanium oxide fine particles by the resin component in the resin coating layer is insufficient, resulting in mechanical stress during development over a long period of time. It is not preferable because the titanium oxide fine particles are detached from the resin coating layer.

  It is preferable that antimony is not detected by thermal analysis in the titanium oxide fine particles used in the electrostatic latent image developing carrier of the present invention.

  If the titanium oxide fine particles contain antimony to such an extent that they can be detected, the titanium oxide fine particles are bluish. That is, in the case of titanium oxide fine particles containing antimony, when used as a two-component developer, the titanium oxide fine particles are developed together with the toner due to wear of the carrier coat layer, and the color of the toner is impaired like carbon black. This is not preferable because the problem arises. Further, since antimony is feared to be toxic to humans and the environment, it is not preferable to use it as a carrier for developing an electrostatic latent image.

  The acceleration ratio of the volume resistivity of the titanium oxide fine particles used in the electrostatic latent image developing carrier of the present invention is preferably 50 times or less. The acceleration ratio of volume resistivity is calculated by the following formula 1 by measuring the change in volume resistivity before and after the acceleration test in which the test sample is heated at 100 ° C. for 2 hours.

[Formula 1]
Acceleration ratio = (Volume resistivity after acceleration test / Volume resistivity before acceleration test) (Equation 1)

  The developer for developing an electrostatic latent image locally becomes a high temperature near 100 ° C. in an environment where the actual machine is used. For this reason, when the acceleration ratio is larger than 50 times, the resistance of fine particles (hereinafter also referred to as filler) contained in the resin coating layer changes during use of the actual machine, and accordingly, the resistance of the electrostatic latent image developing carrier is changed. Will change. The closer the acceleration ratio is to 1, the less the variation due to the environment, and the less the variation due to the environment and changes with time. Therefore, the titanium oxide fine particles used in the electrostatic latent image developing carrier of the present invention preferably have an acceleration ratio of 50 times or less, more preferably 30 times or less.

The volume resistivity in the present invention is measured by the following procedure.
First, 5 g of a sample is put into a cylindrical vinyl chloride tube having an inner diameter of 1 inch as shown in FIG. Next, a pressure of 10 kg / cm ² is applied to these electrodes by a press. Furthermore, measurement with an LCR meter (Yokogawa-HEWLETT-PACKARD 4216A) is performed in this pressurized state to obtain a resistance value r (Ω). From the obtained resistance value, the volume resistivity is calculated using the following equation 2.

[Formula 2]
Volume resistivity (Ω · cm) = (2.54 / 2) ² × (π × r / H) (Formula 2)

  However, in said Formula 2, H represents the thickness (cm) of a sample, and r represents resistance value (ohm).

  The volume resistivity of the titanium oxide fine particles used in the electrostatic latent image developing carrier of the present invention is preferably 100 Ω · cm or less. In the present invention, the titanium oxide fine particles are contained in a carrier for developing an electrostatic latent image for the purpose of adjusting the resistance. Therefore, in order to obtain an effect of efficiently reducing the resistance, the titanium oxide fine particle should be 100 (Ω · cm) or less. Is preferred. The volume resistivity of the titanium oxide fine particles used in the electrostatic latent image developing carrier of the present invention is more preferably 0.1 Ω · cm to 100 Ω · cm, still more preferably 0.1 Ω · cm to 40 Ω · cm, Particularly preferably, it is 0.1 Ω · cm or more and 15.0 Ω · cm or less.

  In the electrostatic latent image developing carrier of the present invention, the standard deviation σ of the tin coating area ratio is preferably 20 or less, more preferably 10 or less, and still more preferably 5 or less. If the standard deviation σ of the tin coating area ratio in the electrostatic latent image developing carrier exceeds 20, carrier particles deviating from the desired resistance because the degree of tin coating of the electrostatic latent image developing carrier is biased. And the production stability is inferior.

  The standard deviation σ of the tin coating area ratio on the carrier is determined by mapping Sn under the following measurement conditions, then obtaining the area ratio of Sn with respect to the area of one particle of the carrier by image processing, and the same operation for 10 particles or more Calculate by doing.

(EDX measurement conditions)
・ Sample fixing method Carbon tape (Nisshin EM 8mm × 20m type)
・ With or without vapor deposition ・ Acceleration voltage 10 kV
・ WD 13mm
・ Aperture diameter 30μm
・ With or without drift correction ・ With or without high current use ・ No time constant 20-30
-EDX measurement magnification 1000 times, 3000 times-Integration count 100 times-Mapping Count mapping (count / quantitative / simple quantitative)
・ Characteristic X-ray used for mapping L-line (L-line / K-line)

  The electrostatic latent image developing carrier of the present invention preferably has a volume average particle size of 20 to 65 μm. When the volume average particle diameter of the electrostatic latent image developing carrier is less than 20 μm, problems such as carrier adhesion to the image bearing member occur, which is not preferable. Further, it is not preferable that the electrostatic latent image developing carrier has a volume average particle diameter of 65 μm or more because a high-definition image cannot be formed.

Furthermore, the magnetic moment at 1000 (10 ³ / 4π · A / m) (1 KOe) of the carrier for developing an electrostatic latent image of the present invention is 40 (Am ² / kg) or more and 90 (Am ² / kg) or less. It is preferable. By setting the amount within this range, the retention force between the electrostatic latent image developing carrier particles is appropriately maintained, so that the dispersion (mixing) of toner in the electrostatic latent image developing carrier or developer is quickly and favorably improved. . On the other hand, when the magnetic moment at 1 KOe is less than 40 Am ² / kg, carrier adhesion occurs due to insufficient magnetic moment, which is not preferable. On the other hand, when the magnetic moment at 1 KOe exceeds 90 Am ² / kg, the ears of the developer formed at the time of development become too hard, so that the reproducibility of image details is poor and a fine image cannot be obtained.

(Other)
The electrostatic latent image developing carrier of the present invention may contain those other than those described above as long as the effects of the present invention are not impaired. For example, the resin coating layer may contain non-conductive particles. By containing non-conductive particles in the resin coating layer, the degree of freedom of the resin coating layer configuration can be secured, and the surface shape of the electrostatic latent image developing carrier and the physical properties of the resin coating film can be arbitrarily controlled. It becomes easy. That is, by using conductive particles (titanium oxide fine particles) and non-conductive particles in a well-balanced manner, the resistance is adjusted while maintaining the film strength of the resin coating layer and the surface shape of the electrostatic latent image developing carrier. It becomes possible.
Examples of the non-conductive particles herein include inorganic oxide particles and resin fine particles. The non-conductive particles in the present invention refer to those exceeding the resistance value range of the titanium oxide fine particles described above. That is, it exceeds 100 Ω · cm, which is different from the general definition of non-conductive particles.

(Contrast with conventional technology)
In the case of titanium oxide fine particles having no tin oxide coating, the volume resistivity of the titanium oxide fine particles is increased. Therefore, when used as a filler for a carrier for developing an electrostatic latent image, if the resistance is increased, the resistance of the carrier cannot be adjusted within a suitable range. Moreover, the charge leak rate is slow in the titanium oxide fine particles having high resistance. For this reason, the leak of the counter charge generated in the carrier after toner development is slow and the charge imparting ability for new toner is inferior, so that uncharged toner is likely to be generated, and the toner scattering to the non-image portion increases. Alternatively, the counter charge generated after the toner development generates a mirror image force on the sleeve, and the developer that should originally be separated from the sleeve is brought to the sleeve. The developer whose toner density after development is reduced and the developer before toner development (consumption) are mixed, resulting in uneven toner density. As a result, the density unevenness due to the location becomes conspicuous especially during the development of a high image such as a solid image. Further, the high filler resistance contributes to the spent accumulation of toner components. When the spent component from the toner adheres to the carrier, if the filler resistance is high, the spent toner component is difficult to peel off, and spent material accumulates to lower the carrier charge.
On the other hand, fine particles of titanium oxide coated with tin oxide, which is antimony-less, have a sufficiently low volume resistivity, so that the components spent on the carrier are easily peeled off, and carrier charging is stabilized over time. As described above, the electrostatic latent image developing carrier containing titanium oxide fine particles coated with tin oxide, which is antimony-less, not only has a large carrier resistance adjustment effect, but also has a quick charge leakage, so that charging to a new toner is possible. The imparting ability is high and the margin for toner scattering is high. Further, since it is not accompanied by the post-development sleeve, it is possible to provide an image with uniform image quality without uneven image density. Furthermore, since the components spent on the carrier are easily peeled off, even when the same toner is used, the additive additive spent from the toner hardly accumulates and the carrier charge is stabilized over time.

<Developer for electrostatic latent image development>
The developer for developing an electrostatic latent image according to the present invention includes a toner containing a binder resin and a colorant and the above-described carrier for developing an electrostatic latent image.
Since the electrostatic latent image developing carrier of the present invention provides a high-definition image and has a longer life, the electrostatic latent image developing developer according to the present invention using the electrostatic latent image developing carrier is Excellent quality can be obtained. The electrostatic latent image developing carrier of the present invention is preferable because it has a long life, particularly when combined with a toner containing a release agent.

  The toner is preferably a color toner. This is because the electrostatic latent image developing carrier of the present invention does not contain carbon black in the resin coating layer, and therefore does not cause color smearing of the image due to carbon black due to film scraping or the like. Therefore, it is suitably used for a color developer in which color reproducibility is regarded as important. The color toner referred to here includes not only a color toner generally used in a single color but also yellow, magenta, cyan, red, green, blue and the like used for full color.

(toner)
Here, the toner used in the developer for developing an electrostatic latent image of the present invention will be described in detail.
The toner referred to in the present invention is not limited as long as it contains a binder resin and a colorant, and includes all the general toners regardless of whether it is a monochrome toner, a color toner, or a full color toner. For example, conventionally kneaded and pulverized toners and various polymerized toners that have been used in recent years can be used. The toner referred to in the present invention preferably includes a base toner containing a binder resin and a colorant, and an external additive attached to the surface of the base toner. Furthermore, so-called oilless toner having a release agent can be used. Generally, since oilless toner contains a release agent, so-called spent is likely to occur on the carrier surface, but the carrier for developing an electrostatic latent image of the present invention has excellent spent resistance. Therefore, good quality can be maintained for a long time. In particular, in an oilless full-color toner, the binder resin is soft and is generally said to be easily spent. However, the electrostatic latent image developing carrier of the present invention is excellent in spent resistance and can be preferably used.
Especially for yellow toner, there is a problem that the color stain due to the carrier coat (resin coating) layer scraping becomes remarkable, but the carrier for the electrostatic latent image developing carrier of the present invention is spent on the yellow toner. However, it is preferable because the influence of color stains is very small.

(Binder resin)
As the binder resin used for the toner in the present invention, known resins can be used. For example, styrene such as polystyrene, poly-p-styrene, and polyvinyltoluene, and homopolymers thereof, styrene-p-chlorostyrene copolymer, styrene-propylene copolymer, styrene-vinyltoluene copolymer, styrene- Methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-methacrylic acid copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-methacrylic acid Butyl copolymer, styrene-α-chloromethacrylic acid methyl copolymer, styrene-acrylonitrile copolymer, styrene-vinyl methyl ether copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, Styrene-isopropyl copolymer, styrene-male Styrene copolymers such as acid ester copolymer, polythyme methacrylate, polybutyl methacrylate, polyvinyl chloride, polyvinyl acetate, polyethylene, polyester, polyurethane, epoxy resin, polyvinyl butyral, polyacrylic acid resin, rosin, modified Rosin, terpene resin, phenol resin, aliphatic or aromatic hydrocarbon resin, aromatic petroleum resin, or the like can be used alone or in combination.

  In addition to the binder resin described above, the toner in the present invention may further contain a so-called pressure fixing binder resin, which is a binder resin for improving fixability in pressure fixing. As the binder resin for pressure fixing, known resins can be mixed and used. For example, polyolefin such as low molecular weight polyethylene and low molecular weight polypropylene, ethylene-acrylic acid copolymer, ethylene-acrylic acid ester copolymer, styrene-methacrylic acid copolymer, ethylene-methacrylic acid ester copolymer, ethylene-chlorinated Vinyl copolymers, ethylene-vinyl acetate copolymers, olefin copolymers such as ionomer resins, epoxy resins, polyester resins, styrene-butadiene copolymers, polyvinyl pyrrolidone, methyl vinyl ether-maleic anhydride, maleic acid-modified phenol resins Phenol-modified terpene resins and the like can be used alone or in combination, but are not limited thereto.

(Coloring agent)
As the colorant used in the toner such as the color toner of the present invention, all known pigments and dyes capable of obtaining toners of yellow, magenta, cyan, and black can be used, and are not limited to those listed here. Examples of yellow pigments include cadmium yellow, mineral fast yellow, nickel titanium yellow, navel yellow, naphthol yellow S, Hansa Yellow G, Hansa Yellow 10G, Benzidine Yellow GR, Quinoline Yellow Lake, Permanent Yellow NCG, and Tartrazine Lake. Can be mentioned.

  Examples of the orange pigment include molybdenum orange, permanent orange GTR, pyrazolone orange, Vulcan orange, indanthrene brilliant orange RK, benzidine orange G, and indanthrene brilliant orange GK.

  Examples of red pigments include Bengala, Cadmium Red, Permanent Red 4R, Resol Red, Pyrazolone Red, Watching Red Calcium Salt, Lake Red D, Brilliant Carmine 6B, Eosin Lake, Rhodamine Lake B, Alizarin Lake, Brilliant Carmine 3B.

  Examples of purple pigments include fast violet B and methyl violet lake. Examples of blue pigments include cobalt blue, alkali blue, Victoria blue lake, phthalocyanine blue, metal-free phthalocyanine blue, phthalocyanine blue partially chlorinated, fast sky blue, and indanthrene blue BC.

  Examples of green pigments include chrome green, chromium oxide, pigment green B, and malachite green lake. Examples of black pigments include azine dyes such as carbon black, oil furnace black, channel black, lamp black, acetylene black, and aniline black, metal salt azo dyes, metal oxides, and composite metal oxides. Moreover, these colorants can use 1 type (s) or 2 or more types.

(Charge control agent)
The toner such as the color toner of the present invention may contain a charge control agent in the toner as necessary. For example, nigrosine, an azine dye containing an alkyl group having 2 to 16 carbon atoms (Japanese Patent Publication No. 42-1627), a basic dye (for example, CI Basic Yellow 2 (CI 41000), CI Basic Yellow 3, CI Basic Red 1 (CI 45160), CI Basic Red 9 (CI 42500), CI Basic Violet 1 (CI 42535), CI Basic Violet 3 (C.I. 42555), C.I.Basic Violet 10 (C.I.45170), C.I.Basic Violet 14 (C.I. 42510), C.I.Basic Violet Blue 1 (C.I. 42025), C.I.Basic Blue 3 (C.I.51005), C.I.Basic B ue 5 (C.I. 42140), C.I.Basic Blue 7 (C.I.42595), C.I.Basic Blue 9 (C.I.52015), C.I.Basic Blue 24 (C.I. I.52030), C.I.Basic Blue 25 (C.I.52025), C.I.Basic Blue 26 (C.I.44045), C.I.Basic Green 1 (C.I.42040), C.I. Lake basic pigment lake pigments such as CI Basic Green 4 (CI 42000), CI Solvent Black 8 (CI 26150), benzoylmethyl hexadecyl ammonium chloride, decyl trimethyl chloride, Quaternary ammonium salts such as dialkyl tin compounds such as dibutyl or dioctyl , Dialkyltin borate compounds, guanidine derivatives, vinyl polymers containing amino groups, polyamine resins such as amino group-containing condensation polymers, JP-B-41-20153, JP-B-43-27596, JP-B-44 No. 6397, a metal complex salt of a monoazo dye described in JP-B-45-26478, salicylic acid, dialkylsalicylic acid described in JP-B-55-42752, JP-B-59-7385, Examples thereof include metal complexes of naphthoic acid and dicarboxylic acid such as Zn, Al, Co, Cr, and Fe, sulfonated copper phthalocyanine pigments, organic boron salts, fluorine-containing quaternary ammonium salts, calixarene compounds, etc. Color toners should of course avoid the use of charge control agents that impair the intended color. , And the metal salts of white salicylic acid derivatives are preferably used.

(External additive)
In the developer for developing an electrostatic latent image of the present invention, a toner containing titanium oxide as an external additive attached to the surface of the base toner containing a binder resin and a colorant, and the developer for developing an electrostatic latent image of the present invention When combined with a carrier, it is preferable because it has excellent charging stability and a long life.

It is known that titanium oxide, which is generally used as an external additive for toners, greatly reduces charging during carrier spent. For this reason, as a countermeasure against the toner for suppressing the charge reduction, for example, the method of firmly attaching titanium oxide used as an external additive to the toner or the method of embedding in the toner can suppress the spent on the carrier. Are known. Furthermore, it is possible to suppress a change in charge when spent on carrier by a method of hydrophobizing titanium oxide used as an external additive. However, with the above-described methods, it is difficult to sufficiently suppress the decrease in charge while maintaining the various characteristics of the toner.
On the other hand, in the present invention, there is a titanium oxide spent used as an external additive from the toner by using titanium oxide for the charge and resistance control filler substrate in the resin coating layer of the electrostatic latent image developing carrier. However, it is possible to suppress a decrease in charging. On the other hand, indium oxide-doped alumina and antimony-doped alumina are also known as white conductive agents. However, in an alumina substrate, the charge is greatly lowered when titanium oxide is spent from the toner.

  As the external additive used in the toner, inorganic fine particles such as the above-mentioned titanium oxide, silica, alumina, silicon carbide, silicon nitride, and boron nitride, resin fine particles, and the like are known and transferred by external addition to the base toner. The durability and durability are further improved. This effect can be obtained by covering the wax that lowers transferability and durability with these external additives and reducing the contact area due to the toner surface being covered with fine particles. The surface of these inorganic fine particles is preferably subjected to a hydrophobic treatment, and metal oxide fine particles such as silica and titanium oxide subjected to the hydrophobic treatment are preferably used.

  As the resin fine particles, polymethyl methacrylate or polystyrene fine particles having an average particle size of about 0.05 to 1 μm obtained by a soap-free emulsion polymerization method are suitably used. In addition, the combination of hydrophobized silica and hydrophobized titanium oxide increases the amount of hydrophobized titanium oxide externally added compared to the amount of hydrophobized silica externally charged. The toner can also be excellent in stability.

In combination with the above-described titanium oxide, silica having a specific surface area of 20 to 50 m ² / g or resin fine particles having an average particle diameter of 1/100 to 1/8 of the average particle diameter of the toner can be used. The durability can be improved by externally adding an external additive having a particle size larger than that of the additive to the toner. This is because the external additive such as metal oxide fine particles added externally to the toner tends to be embedded in the base toner particles in the process where the toner is mixed and stirred with the carrier in the developing device and charged and used for development. However, it is possible to prevent the metal oxide fine particles from being embedded by externally adding an external additive having a particle size larger than those of the metal oxide fine particles to the toner. The above-mentioned inorganic fine particles and resin fine particles are contained (internally added) in the toner, but the effect is reduced as compared with the case of external addition, but the effect of improving transferability and durability can be obtained and the pulverization property of the toner can be improved. Can do. In addition, since external addition and internal addition can be used together to suppress embedding of externally added fine particles, excellent transferability can be stably obtained and durability can be improved.

  In addition, the following are mentioned as a typical example of the hydrophobization processing agent used here. Dimethyldichlorosilane, trimethylchlorosilane, methyltrichlorosilane, allyldimethyldichlorosilane, allylphenyldichlorosilane, benzyldimethylchlorosilane, bromomethyldimethylchlorosilane, α-chloroethyltrichlorosilane, p-chloroethyltrichlorosilane, Chloromethyldimethylchlorosilane, chloromethyltrichlorosilane, p-chlorophenyltrichlorosilane, 3-chloropropyltrichlorosilane, 3-chloropropyltrimethoxysilane, vinyltriethoxysilane, vinylmethoxysilane, vinyl-tris (β-methoxyethoxy) ) Silane, γ-methacryloxypropyltrimethoxysilane, vinyltriacetoxysilane, divinyldichlorosilane, dimethylvinylchlorosilane, octyl Trichlorosilane, decyl-trichlorosilane, nonyl-trichlorosilane, (4-t-propylphenyl) -trichlorosilane, (4-t-butylphenyl) -trichlorosilane, diventyl-dichlorosilane, dihexyl-dichlorosilane, dioctyl-dichlorosilane, dinonyl -Dichlorosilane, didecyl-dichlorosilane, didodecyl-dichlorosilane, dihexadecyl-dichlorosilane, (4-t-butylphenyl) -octyl-dichlorosilane, dioctyl-dichlorosilane, didecenyl-dichlorosilane, dinonenyl-dichlorosilane, di-2-ethylhexyl-dichlorosilane, di- 3,3-dimethylbenthyl-dichlorosilane, trihexyl-chlorosilane, trioctyl-chlorosilane, tridecyl-chlorosilane Dioctyl-methyl-chlorosilane, octyl-dimethyl-chlorosilane, (4-t-propylphenyl) -diethyl-chlorosilane, octyltrimethoxysilane, hexamethyldisilazane, hexaethyldisilazane, diethyltetramethyldisilazane, hexaphenyldisilazane , Hexatolyl disilazane and the like. In addition, titanate coupling agents and aluminum coupling agents can also be used. In addition, as an external additive for the purpose of improving cleaning properties, a lubricant such as a fatty acid metal salt or a fine particle of polyvinylidene fluoride can be used in combination.

(Other)
Further, the toner used in the present invention may contain a fixing aid in addition to the binder resin and the colorant. Accordingly, it can be used in a fixing system in which toner fixing prevention oil is not applied to the fixing roll, so-called oilless system. Known fixing aids can be used. For example, polyolefins such as polyethylene and polypropylene, fatty acid metal salts, fatty acid esters, paraffin waxes, amide waxes, polyhydric alcohol waxes, silicone varnishes, carnauba waxes and ester waxes can be used, but are not limited thereto.

(Toner production method)
Any conventionally known method such as a pulverization method or a polymerization method can be applied to the toner production method of the present invention. For example, in the case of the pulverization method, as a kneading apparatus for kneading the toner, a batch type two roll, a Banbury mixer or a continuous type twin screw extruder, for example, KTK type twin screw extruder manufactured by Kobe Steel, Toshiba Machine Co., Ltd. TEM type twin screw extruder, KCK twin screw extruder, Ikegai Iron Works PCM type twin screw extruder, Kurimoto Iron Works KEX type twin screw extruder, continuous single screw kneader, for example Buss Co-kneader etc. are preferably used. The melt-kneaded product obtained by kneading with a kneading device is cooled and then pulverized. For example, the pulverization is roughly pulverized using a hammer mill, a funnel plex or the like, and further a fine pulverizer using a jet stream or A mechanical pulverizer or the like can be used.

  The pulverization is desirably performed so that the average particle size of the obtained pulverized product is 3 to 15 μm. Furthermore, it is preferable that the particle size of the pulverized product is adjusted to 5 to 20 μm by a wind classifier or the like. Subsequently, the external additive is externally added to the base toner. The base toner and the external additive are mixed and stirred using a mixer, and the external additive is crushed and coated on the toner surface. At this time, it is important from the viewpoint of durability that external additives such as inorganic fine particles and resin fine particles are uniformly and firmly attached to the base toner. The above is only an example, and the present invention is not limited to this.

<Process cartridge, image forming method>
The developer for developing an electrostatic latent image of the present invention can be used in, for example, an image forming apparatus provided with a process cartridge as shown in FIG.
The process cartridge according to the present invention integrally supports one or more selected from the image carrier, the charging unit, and the cleaning unit, and the developing unit that holds the developer for developing the electrostatic latent image. The image forming apparatus main body is detachable.

  The process cartridge shown in FIG. 2 includes an image carrier, a charging unit, a developing unit, and a cleaning unit. In operation, the image carrier 1 is rotationally driven at a predetermined peripheral speed. In the rotating process, the image carrier 1 is uniformly charged at a predetermined positive or negative potential on its peripheral surface by the charging unit 301, and then receives image exposure light from the image exposure unit 6 such as slit exposure or laser beam scanning exposure. In this way, electrostatic latent images are sequentially formed on the peripheral surface of the image carrier 1. The formed electrostatic latent image is developed with toner by the developing unit 10, and the developed toner image is primarily transferred onto the intermediate transfer member 8 by the primary transfer unit 4. Next, the secondary transfer unit 54 sequentially transfers the transfer material 7 fed between the intermediate transfer body 8 and the secondary transfer unit 54 from the sheet feeding unit in synchronization with the rotation of the intermediate transfer unit 8. . The transfer material 7 that has received the image transfer is separated from the surface of the intermediate transfer member 8, introduced into the image fixing means 9, fixed on the image, and printed out as a copy (copy). After the image transfer, the surface of the image carrier 1 is cleaned by removing the transfer residual toner by the cleaning means 5, and after being further neutralized, it is repeatedly used for image formation.

  EXAMPLES Next, although an Example and a comparative example are given and this invention is demonstrated further more concretely, this invention is not limited to these. Parts are based on weight.

(Titanium oxide fine particles 1)
Commercially available antimony-containing tin oxide-coated titanium oxide powder (specific surface area 20 m ² / g; manufactured by Mitsubishi Materials Corporation, trade name W-1) was used as titanium oxide fine particles 1.

(Titanium oxide fine particles 2)
Commercially available antimonyless tin oxide coated titanium oxide powder (specific surface area 10 m ² / g; manufactured by Mitsubishi Materials Corporation, trade name EPW-4) was used as the titanium oxide fine particles 2.

(Titanium oxide fine particles 3)
Commercially available antimonyless tin oxide powder (trade name S-1 manufactured by Mitsubishi Materials Corporation) was used as the titanium oxide fine particles 3.

(Titanium oxide fine particles 4)
Commercially available titanium oxide powder was used as the titanium oxide fine particles 4.

(Titanium oxide fine particles 5)
Alumina obtained by surface-treating antimonyless tin oxide with a titanium coupling agent was used as the titanium oxide fine particles 5.

(Titanium oxide fine particles 6)
Titanium oxide fine particles 6 were obtained by carrying out the same treatment as titanium oxide fine particles 2 except that acetone gas was used instead of ethanol when producing titanium oxide fine particles 2.

(Titanium oxide fine particles 7)
Titanium oxide fine particles 7 were obtained by performing the same treatment as titanium oxide fine particles 2 except that hexamethyldisilazane was used in place of ethanol when producing titanium oxide fine particles 2.

[Example 1]
(Carrier production)
<Resin coating layer prescription>
・ Acrylic resin solution (solid content 50 wt%) 39.7 parts ・ Guanamine solution (solid content 70 wt%) 12.4 parts ・ Acid catalyst (solid content 40 wt%) 0.22 parts ・ Silicone resin solution 185.8 Parts [solid content 20% by weight (SR2410: manufactured by Toray Dow Corning Silicone)]
Aminosilane 0.42 part [solid content 100% by weight (SH6020: Toray Dow Corning Silicone)]
・ Titanium oxide fine particle 2 66.2 parts ・ Toluene 800 parts

The resin coating layer formulation was dispersed with a homomixer for 10 minutes to obtain a resin coating film forming solution. A sintered ferrite powder having a volume average particle size of 35 μm is used as the core material, and the coating film forming solution is coated on the surface of the core material at a coating inner temperature of 40 ° C. by a Spira coater (Okada Seiko Co., Ltd.). It was applied and dried. The obtained carrier was baked by standing in an electric furnace at 300 degrees for 1 hour. After cooling, the ferrite powder bulk was crushed using a sieve having an aperture of 63 μm to obtain [Carrier 1] having a volume resistivity of 12.8 Log (Ω · cm) and a magnetization of 68 Am ² / kg.

(Manufacture of toner)
<Toner prescription>
Binder resin: Polyester resin 100 parts number average molecular weight (Mn); 3800
Weight average molecular weight (Mw): 20000
Glass transition point (Tg); 60 ° C
Softening point: 122 ° C
Colorant: azo yellow pigment 5 parts C.I. I. P. Y. 180
Charge control agent: 2 parts of zinc salicylateRelease agent: 3 parts of carnauba wax Melting point: 82 degrees

The above toner formulation is mixed with a Henschel mixer, melt-kneaded at 120 ° C. for 40 minutes with two rolls, cooled, coarsely pulverized with a hammer mill, finely pulverized with an air jet pulverizer, and the resulting fine powder is classified. Thus, toner base particles having a weight average particle diameter of 5 μm were prepared. Further, 100 parts of the toner base material is added with 1 part of silica whose surface has been hydrophobized and 1 part of titanium oxide 1 made by a wet method to be described later, and mixed with a Henschel mixer to obtain a yellow toner [ Toner 1] was obtained.
Further, [toner 2] was obtained by changing titanium oxide 1 used in toner 1 to titanium oxide 2 described later.

(Titanium oxide 1)
Titanium oxide (MT-150A manufactured by Teika Co., Ltd.) containing 0.35% of a water-soluble component made by a wet method is washed with water to obtain (titanium oxide 1) having a water-soluble component of 0.15%. It was.
(Titanium oxide 2)
300 g of titanium oxide 1 was added to and dispersed in an aqueous toluene solution in which 35 g of isobutyltrimethoxysilane was dissolved. Thereafter, the solvent was dried up, finely pulverized by a jet mill, and further highly dispersed by a pin mill to obtain a coupling agent-treated titanium oxide (titanium oxide 2).

(Developer 1)
7 parts of [Toner 1] thus obtained and 93 parts of [Carrier 1] were mixed and stirred to obtain Developer 1 having a toner concentration of 7% by weight. Using the obtained developer 1 and carrier 1, and developers 2 to 8 and carriers 2 to 7 obtained in Examples 2 to 3 and Comparative Examples 1 to 5 described later, volume resistivity, color, Acceleration ratio, edge effect, image definition, toner scattering, color mixture, durability (charge reduction amount, resistance change amount) were evaluated. The measurement method is shown below, and the obtained measurement results are shown in Table 1.

〔Measuring method〕
<Standard deviation σ of tin coating area ratio>
It measures based on the measuring method of the standard deviation (sigma) of the tin covering area rate mentioned above. (See paragraphs 0062-0063.)

<Volume specific resistance>
As shown in FIG. 1, the carrier has a volume resistivity of a cell 33 made of a fluororesin container containing an electrode 32a and an electrode 32b having a distance between electrodes of 0.2 cm and a surface area of 2.5 cm × 4 cm. Carrier) is loaded, and tapping is performed with a drop height of 1 cm, a tapping speed of 30 times / min, and a tapping frequency of 10 times. Next, a DC voltage of 1000 V was applied between both electrodes, and the resistance value after 30 seconds was measured with a high resistance meter 4329A (High Resistance Meter manufactured by Yokogawa Hewlett-Packard Co., Ltd.). The volume resistivity R is calculated by the following formula.

  R = Log [r × (2.5 cm × 4 cm) ÷ 0.2 cm] [Log (Ω · cm)]

<Edge effect>
A developer is set on a commercially available digital full color printer (IPSiO CX8200 manufactured by Ricoh), and a test pattern having a large area image is output. The difference between the thinness of the image density at the central portion of the image pattern thus obtained and the darkness of the edge portion was ranked as follows.
The evaluation criteria for ranking are as follows: ◎ if there is no difference, ◯ if there is a slight difference, △ if there is a difference but acceptable, × if there is a difference to an unacceptable level, ◎, ○, Δ was acceptable and x was unacceptable.

<Image definition>
The image definition was evaluated by the reproducibility of the character image portion. The evaluation method is to set a developer on a commercially available digital full-color printer (IPSiO CX8200 manufactured by Ricoh), and output a character chart (size of one character: about 2 mm × 2 mm) with an image area of 5%. The reproducibility was evaluated by images and ranked as follows.
The evaluation criteria for ranking were as follows: ◎: very good, ○: good, △: acceptable, ×: unusable level for practical use, ◎, ○, △ passed, and x rejected.

<Durability>
A developer was set on a commercially available digital full color printer (IPSiO CX8200 manufactured by Ricoh Co., Ltd.) and a running evaluation of 100,000 sheets in a single color was performed. The determination was made based on the charge reduction amount and resistance reduction amount of the carrier after the running.
The amount of charge reduction referred to here is a general blow-off method [blow-off device: manufactured by Toshiba Chemical Co., Ltd.] obtained by friction charging the sample by mixing 7% by weight of toner with respect to 93% by weight of the initial carrier. The carrier obtained by removing the toner in the developer after running with the blow-off device from the charge amount (Q1) measured in TB-200] is mixed with the toner as in the case of the initial carrier and friction This is the amount obtained by subtracting the amount of charge (Q2) measured after charging. The target value of the amount of charge reduction is within 10.0 (μc / g). Further, since the cause of the decrease in the charge amount is the toner spent on the carrier surface, the decrease in the charge amount can be suppressed by reducing the toner spent.
In addition, the amount of resistance change referred to here is a value obtained by applying an initial carrier between electrodes of a resistance measuring parallel electrode (gap 2 mm), applying a DC 1000V, and measuring a resistance value after 30 sec with a high resist meter. The value obtained by removing the toner in the developer after running by the blow-off device from the value (R1) converted into the rate is subtracted from the value (R2) measured by the same method as in the case of the initial carrier. Say that amount. The target value of the resistance change amount is within 3.0 [Log (Ω · cm)] in absolute value. In addition, the cause of the resistance change is scraping of the binder resin film of the carrier, spent toner component on the carrier surface, large particle detachment from the carrier coating film, etc. Can be suppressed.

[Example 2]
A developer 2 was obtained in the same manner as in Example 1 except that the toner 2 was used instead of the toner 1 in Example 1.

Example 3
A carrier 2 and a developer 3 were obtained in the same manner as in Example 2 except that the titanium oxide fine particles 6 were used in place of the titanium oxide fine particles 2 in Example 2.

[Comparative Example 1]
A carrier 3 and a developer 4 were obtained in the same manner as in Example 2 except that the titanium oxide fine particles 7 were used instead of the titanium oxide fine particles 2 in Example 2.

[Comparative Example 2]
A carrier 4 and a developer 5 were obtained in the same manner as in Example 2 except that the titanium oxide fine particles 5 were used instead of the titanium oxide fine particles 2 in Example 2.

[Comparative Example 3]
A carrier 5 and a developer 6 were obtained in the same manner as in Example 2 except that the titanium oxide fine particles 4 were used in place of the titanium oxide fine particles 2 in Example 2.

[Comparative Example 4]
A carrier 6 and a developer 7 were obtained in the same manner as in Example 2 except that the titanium oxide fine particles 3 were used instead of the titanium oxide fine particles 2 in Example 2.

[Comparative Example 5]
A carrier 6 and a developer 7 were obtained in the same manner as in Example 2 except that the titanium oxide fine particles 1 were used instead of the titanium oxide fine particles 2 in Example 2.

It is the schematic which shows the structure of the apparatus used for the measurement of the volume solid resistance of a carrier. It is the schematic which shows the structure of the process cartridge of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image carrier 4 Primary transfer means 5 Cleaning means 6 Image exposure means 7 Transfer material 8 Intermediate transfer body 9 Image fixing means 10 Developing means 54 Secondary transfer means 301 Charging means 31 Cell 32a, 32b Electrode 33 Carrier

Claims (16)

A core material,
A resin coating layer covering the surface of the core material,
The carrier for electrostatic latent image development, wherein the resin coating layer contains a resin and titanium oxide fine particles coated with tin oxide.   2. The electrostatic latent image developing carrier according to claim 1, wherein the titanium oxide fine particles are further coated with carbon.   The carrier for developing an electrostatic latent image according to claim 2, wherein the standard deviation σ of the tin coating area ratio is 20 or less.   2. The electrostatic latent image developing carrier according to claim 1, wherein antimony is not detected in the titanium oxide fine particles by thermal analysis.   The carrier for developing an electrostatic latent image according to claim 1, wherein the titanium oxide fine particles have a primary particle diameter of 1 to 500 nm.   2. The electrostatic latent image developing carrier according to claim 1, wherein the titanium oxide fine particles have a volume resistivity acceleration ratio of 50 times or less.   The electrostatic latent image developing carrier according to claim 1, wherein the volume average particle diameter is 20 μm or more and 65 μm or less.   The carrier for developing an electrostatic latent image according to claim 1, wherein the resin contains a silicone resin.   The electrostatic latent image developing carrier according to claim 1, wherein the resin contains an acrylic resin.   The electrostatic latent image developing carrier according to claim 1, wherein the resin is an acrylic resin or a silicone resin.   An electrostatic latent image developing developer comprising: a toner containing a binder resin and a colorant; and the electrostatic latent image developing carrier according to any one of claims 1 to 10. .   The developer for developing an electrostatic latent image according to claim 11, wherein the toner is a color toner. The toner includes a base toner containing a binder resin and a colorant, and an external additive attached to the surface of the base toner,
The developer for electrostatic latent image development according to claim 11, wherein the external additive contains titanium oxide.   A container containing the developer for developing an electrostatic latent image according to claim 11. One or more selected from an image carrier, a charging unit, and a cleaning unit;
A developing means for holding the developer for developing an electrostatic latent image according to any one of claims 11 to 13, and
A process cartridge which is detachable from an image forming apparatus main body. Forming an electrostatic latent image on the image carrier;
A step of developing the electrostatic latent image with the developer for developing an electrostatic latent image according to any one of claims 11 to 13 to form a visible image;
And a step of transferring and fixing the obtained visible image to a recording medium.

Images