Carrier for electrostatic image development, electrostatic image developer, and process cartridge

Abstract

The carrier for electrostatic image development has a core material and a coating resin layer that contains inorganic particles and coats the above-mentioned core material. The content of the above-mentioned inorganic particles is 10% by mass or more and 60% by mass or less relative to the total mass of the above-mentioned coating resin layer. The volume average particle diameter D (μm) of the above-mentioned inorganic particles and the thickness T (μm) of the above-mentioned coating resin layer satisfy the following relational expression (1). Relational expression (1) ··· 0.007 ≤ D / T ≤ 0.24.

Description

Technical Field

[0001] The present invention relates to a carrier for electrostatic image development, an electrostatic image developer, and a process cartridge. Background Art

[0002] Japanese Patent Application Laid-Open No. 2007-041549 discloses a two-component developer having a carrier and a toner. The carrier includes a carrier body that is porous and has irregularities on its surface, and silica attached to the surface of the carrier body. The porosity of the carrier body is 5 to 25%, and the amount of silica attached to the surface of the carrier body is 1 to 10 parts by weight with respect to 1000 parts by weight of the carrier body. Summary of the Invention

[0003] Conventionally, when using the following electrostatic image developer, uneven image density may occur. The electrostatic image developer includes "a carrier for electrostatic image development, the carrier for electrostatic image development having a core material and a coating resin layer that includes inorganic particles and coats the core material".

[0004] Therefore, an object of the present invention is to provide an electrostatic image developer that can suppress uneven image density as compared with the following cases.

[0005] "The case of a carrier for electrostatic image development in which the content of the inorganic particles is less than 10% by mass or more than 60% by mass with respect to the total mass of the coating resin layer";

[0006] "The case of a carrier for electrostatic image development in which the volume average particle diameter D (μm) of the inorganic particles and the thickness T (μm) of the coating resin layer do not satisfy the following relational expression (1)";

[0007] Or,

[0008] "When 100 parts by mass of the carrier separated from an electrostatic image developer including an external additive containing silica particles as a toner and 10 parts by mass of a model toner are stirred at a temperature of 20°C for 2 minutes using a drum mixer, and the resulting mixture is separated again into the carrier and the model toner through a screen gauge, the case where the dissociation rate of the silica particles on the surface of the carrier before and after separation from the model toner is less than 50%".

[0009] According to a first aspect of the present invention, there is provided a carrier for electrostatic image development having:

[0010] a core material; and

[0011] a coating resin layer that includes inorganic particles and coats the core material,

[0012] The content of the above inorganic particles is 10% by mass or more and 60% by mass or less relative to the total mass of the above coating resin layer.

[0013] The volume average particle diameter D (μm) of the above inorganic particles and the thickness T (μm) of the above coating resin layer satisfy the following relational expression (1).

[0014] Relational expression (1) ··· 0.007 ≤ D / T ≤ 0.24.

[0015] According to the second aspect of the present invention, the volume average particle diameter D of the above inorganic particles exceeds 1 nm and is 80 nm or less.

[0016] According to the third aspect of the present invention, the surface roughness Ra of the carrier exceeds 0.1 μm and is less than 0.9 μm.

[0017] According to the fourth aspect of the present invention, the above inorganic particles include silica particles.

[0018] According to the fifth aspect of the present invention, the above silica particles include hydrophobized silica particles.

[0019] According to the sixth aspect of the present invention, the treating agent for the above hydrophobization treatment is at least one of hexamethyldisilazane (HMDS) and dimethylpolysiloxane (PDMS).

[0020] According to the seventh aspect of the present invention, the above coating resin layer contains an alicyclic (meth)acrylate resin.

[0021] According to the eighth aspect of the present invention, the above alicyclic (meth)acrylate resin contains cyclohexyl (meth)acrylate as a polymerization component.

[0022] According to the ninth aspect of the present invention, the above electrophotographic developer carrier satisfies the following relational expression (2).

[0023] Relational expression (2) ··· 0.003 < D / Ra < 0.50.

[0024] According to the tenth aspect of the present invention, the surface roughness Ra of the above core material is 0.5 μm or more and 1.5 μm or less.

[0025] According to the eleventh aspect of the present invention, there is provided an electrophotographic developer including an electrophotographic toner and the above electrophotographic developer carrier.

[0026] According to the twelfth aspect of the present invention, there is provided a process cartridge which is a process cartridge detachably mounted in an image forming apparatus, and the process cartridge includes: a developing unit which accommodates the above electrophotographic developer and develops an electrostatic image formed on the surface of an image holding member into a toner image.

[0027] (Effect)

[0028] According to the solutions of items 1, 4, 5, 6, 7, and 8 above, a carrier for electrostatic image development is provided, and compared with the case where the content of the above inorganic particles is less than 10% by mass or more than 60% by mass with respect to the total mass of the above coating resin layer, or the case where the volume average particle diameter D (μm) of the above inorganic particles and the thickness T (μm) of the above coating resin layer do not satisfy the above relational expression (1), unevenness in image density is suppressed.

[0029] According to the solutions of items 4, 5, 6, 7, and 8 above, a carrier for electrostatic image development is provided, and compared with the case where the release rate of the above silica particles from the surface of the carrier is less than 50%, unevenness in image density is suppressed.

[0030] According to the solution of item 2 above, a carrier for electrostatic image development is provided, and compared with the case where the volume average particle diameter D of the above inorganic particles is 1 nm or less or more than 80 nm, unevenness in image density is suppressed.

[0031] According to the solution of item 3 above, a carrier for electrostatic image development is provided, and compared with the case where the surface roughness Ra of the carrier is 0.1 μm or less or 0.9 μm or more, unevenness in image density is suppressed.

[0032] According to the solution of item 9 above, a carrier for electrostatic image development is provided, and compared with the case where the volume average particle diameter D (μm) of the above inorganic particles and the surface roughness Ra of the carrier surface do not satisfy the above relational expression (2), unevenness in image density is suppressed.

[0033] According to the solution of item 10 above, a carrier for electrostatic image development is provided, and compared with the case where the surface roughness Ra of the above core material is less than 0.5 μm or more than 1.5 μm, unevenness in image density is suppressed.

[0034] According to the solutions of items 11 and 12 above, an electrostatic image developer and a processing cartridge are provided, and compared with the case where the content of the above inorganic particles is less than 10% by mass or more than 60% by mass with respect to the total mass of the above coating resin layer, the case where the volume average particle diameter D (μm) of the above inorganic particles and the thickness T (μm) of the above coating resin layer do not satisfy the above relational expression (1), or the case where the release rate of the above silica particles from the surface of the carrier is more than 50%, unevenness in image density is suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a schematic configuration diagram showing an example of the image forming apparatus of the present embodiment.

[0036] Figure 2 It is a schematic configuration diagram showing an example of a process cartridge that can be loaded and unloaded in the image forming apparatus according to the present embodiment. Detailed Embodiment

[0037] The following describes the present embodiment. These descriptions and examples are for illustrating the embodiment and do not limit the scope of the embodiment.

[0038] In the numerical ranges described stepwise in the present invention, the upper limit value or the lower limit value described in one numerical range can be replaced with the upper limit value or the lower limit value of the other stepwise numerical ranges described. Further, in the numerical ranges described in the present invention, the upper limit value or the lower limit value of the numerical range can be replaced with the value shown in the examples.

[0039] Each component in this specification may contain two or more corresponding substances. When referring to the amount of each component in the composition, when there are two or more substances corresponding to each component in the composition, unless otherwise specified, it means the total amount of the two or more substances present in the composition.

[0040] "Carrier for Electrostatic Image Development"

[0041] The carrier for electrostatic image development according to the first embodiment has a core material and a coating resin layer that contains inorganic particles and coats the core material. The content of the inorganic particles is 10% by mass or more and 60% by mass or less with respect to the total mass of the coating resin layer. The volume average particle diameter D (μm) of the inorganic particles and the thickness T (μm) of the coating resin layer satisfy the following relational expression (1).

[0042] Relational expression (1) ··· 0.007 ≤ D / T ≤ 0.24

[0043] If an image is formed over a long period of time, the toner may scatter from the developing device. The scattered toner tends to accumulate in the bearing portion of the developing device. Therefore, in a high-temperature and high-humidity environment, the toner adheres, and the motor torque of the developing unit tends to increase. As a result, if an abnormal rotation of the motor occurs, uneven image density may occur.

[0044] In particular, after continuous printing of low-image-density images in a high-temperature and high-humidity environment and then continuous printing of high-density images in a borderless printing mode after leaving them for a whole day and night, new toner is added to the toner in which the external additive is buried. As a result, the charge distribution caused by mutual charging between toner particles easily deteriorates, and toner scattering is likely to occur. At this time, in the borderless printing mode, the toner supply amount to the non-paper passing part side increases, so there is a tendency for further increase in toner scattering to the outside of the developing device. As a result, toner adhesion is likely to occur in the bearing part. If toner adhesion occurs in this bearing part, the motor torque becomes abnormal, and density unevenness is likely to occur in the formation of halftone images.

[0045] By having the above-described configuration, the carrier for electrostatic image development according to the first embodiment can suppress adhesion in the bearing part of the developing device and suppress the occurrence of density unevenness. The reason is not necessarily clear, but it is speculated as follows.

[0046] The carrier for electrostatic image development according to the first embodiment satisfies the above-described relational expression (1). That is, the inorganic particles have high dispersibility in the coating resin layer and are contained at a high density. Therefore, when an image is formed over a long period of time, the coating resin layer is removed from the carrier body, and fragments of the coating resin layer (hereinafter also referred to as "resin flakes") generated in the developing device are developed together with the toner. At this time, the resin flakes containing inorganic particles are charged opposite to the toner. In particular, if the proportion of inorganic particles in the coating resin layer is 10% by mass or more and 60% by mass or less, an appropriate hardness is imparted to the resin flakes. Resin flakes having an opposite charge property to the toner and an appropriate hardness are easily supplied to non-image parts, non-paper passing parts, etc. when developed from the developing device, and thus are easily scattered to the outside of the developing device. Therefore, they are easily supplied to the shaft part of the developing device. Once attached to the shaft, the toner is electrostatically repelled, and there is a tendency to suppress toner accumulation. As a result, the progress of toner adhesion in the bearing part is suppressed, and it is considered that density unevenness in the image can be suppressed.

[0047] The carrier for electrostatic image development according to the second embodiment has a core material and a coating resin layer that contains inorganic particles and coats the above-described core material. When 100 parts by mass of the carrier separated from an electrostatic image developer containing silica particles as an external additive to the toner and 10 parts by mass of a model toner are stirred at a temperature of 20°C for 2 minutes using a drum mixer, and the resulting mixture is separated again into the above-described carrier and the above-described model toner by a screen gauge, the free rate of the silica particles from the surface of the carrier (=(S1 - S2) / S1 × 100), obtained from the coating rate S1 of the silica particles coating the surface of the carrier after being separated from the electrostatic image developer and before being mixed with the model toner and the coating rate S2 of the silica particles coating the surface of the carrier after being separated from the model toner, is 50% or more.

[0048] For an existing carrier for electrostatic image development having a core material and a coating resin layer containing inorganic particles and coating the above-mentioned core material, the free rate of the above-mentioned silica particles is less than 50%. That is, the coating resin layer of the carrier is relatively soft and has a tendency to be difficult to form resin flakes. Therefore, when using a developing device in a high-temperature and high-humidity environment, toner adhesion at the bearing portion is likely to occur, resulting in abnormal motor torque, and sometimes density unevenness occurs in the image.

[0049] On the other hand, in the carrier for electrostatic image development of the second embodiment, as described above, the coating resin layer contains inorganic particles, and the free rate of the above-mentioned silica particles is 50% or more. That is, the coating resin layer of the carrier is moderately hard and has a tendency to be easy to form resin flakes. In addition, the resin flakes containing inorganic particles are charged opposite to the toner. Therefore, once the resin flakes having an opposite charge to the toner and moderate hardness adhere to the shaft of the developing device, the toner is electrostatically repelled, so that the progress of toner adhesion at the bearing portion is suppressed. As a result, it is considered that it is also difficult to cause abnormal motor torque due to toner adhesion at the bearing portion, and density unevenness in the image can be suppressed.

[0050] Hereinafter, matters common to the first and second embodiments will be collectively referred to as the present embodiment for description. Hereinafter, the carrier for electrostatic image development will also be simply referred to as "carrier".

[0051] (Properties of the carrier for electrostatic image development)

[0052] For the carrier of the present embodiment, from the aspect of further suppressing density unevenness of the image, the surface roughness Ra is preferably more than 0.1 μm and less than 0.9 μm, more preferably 0.11 μm or more and less than 0.85 μm, and still more preferably 0.12 μm or more and 0.8 μm or less.

[0053] The method for controlling the surface roughness Ra of the carrier is not particularly limited, and examples thereof include: a method of adjusting the surface roughness Ra of the core material; a method of adjusting the thickness of the coating resin layer; a method of adjusting the stirring speed, stirring temperature, and stirring time for mixing and stirring the resin, core material, inorganic particles, and solvent added as needed when manufacturing the carrier; etc.

[0054] In this embodiment, the surface roughness Ra of the carrier is measured by the following method. The method for measuring Ra (arithmetic mean roughness) of the carrier surface is as follows: Using a super-depth color 3D shape measuring microscope (VK9700, manufactured by KEYENCE CORPORATION), the surface of 2000 carriers is converted at a magnification of 1000 times and calculated. This method is carried out in accordance with JIS B0601 (1994 edition). Specifically, Ra of the carrier surface is obtained as follows: The roughness curve is obtained from the three-dimensional shape of the carrier surface observed by the above microscope, and the absolute values of the measured values of the roughness curve and the deviation from the average value are summed and averaged, thereby obtaining it. The reference length when obtaining Ra of the carrier surface is 10 μm, and the cut-off value is 0.08 mm.

[0055] For the carrier of this embodiment, from the aspect of further suppressing the density unevenness of the image, the volume average particle diameter D (μm) of the inorganic particles contained in the coating resin layer described later and the surface roughness Ra (μm) of the carrier surface preferably satisfy the following relational expression (2), more preferably satisfy the following relational expression (2-2), and further preferably satisfy the following relational expression (2-3).

[0056] Relational expression (2) 0.003 < D / Ra < 0.50

[0057] Relational expression (2-2) 0.005 ≤ D / Ra ≤ 0.40

[0058] Relational expression (2-3) 0.010 ≤ D / Ra ≤ 0.20

[0059] The method for controlling the volume average particle diameter D (μm) of the inorganic particles contained in the coating resin layer and the surface roughness Ra (μm) of the carrier surface to satisfy the above relational expressions (2), (2-2), and (2-3) is not particularly limited, and examples thereof include: a method of adjusting the surface roughness Ra of the core material; a method of adjusting the thickness of the coating resin layer; a method of adjusting the volume average particle diameter D of the inorganic particles; etc.

[0060] For the carrier of the second embodiment,

[0061] When 100 parts by mass of the carrier separated from the electrostatic image developer containing silica particles as an external additive of the toner and 10 parts by mass of the model toner are stirred at a temperature of 20°C for a stirring time of 2 minutes using a drum mixer, and the obtained mixture is separated again into the above carrier and the above model toner through a wire gauge,

[0062] The release rate of the silica particles from the surface of the carrier (= (S1 - S2) / S1 × 100), which is obtained from the coating rate S1 of the silica particles covering the surface of the carrier after being separated from the above-described electrostatic image developer and before being mixed with the above-described model toner, and the coating rate S2 of the silica particles covering the surface of the carrier after being separated from the above-described model toner, is 50% or more, preferably 55% or more, and more preferably 60% or more.

[0063] The above release rate is obtained as follows.

[0064] (1) Separate the toner and the carrier from the electrostatic image developer containing silica particles as an external additive of the toner by a jet sieve.

[0065] (2) By X-ray photoelectron spectroscopy (XPS), use the following method to obtain the coating rate S1 of the silica particles covering the surface of the carrier separated from the electrostatic image developer.

[0066] Observe the carrier using a scanning electron microscope (SEM) (manufactured by Hitachi High-Technologies, S-4800) equipped with an energy dispersive X-ray analyzer (EDX device) (manufactured by Horiba, Ltd., EMAX Evolution X-Max80mm 2 ) and take an image at a magnification of 40,000 times. At this time, based on the presence of Si by EDX analysis, identify the primary particles of silica within one field of view. The SEM is observed at an acceleration voltage of 15 kV, an emission current of 20 μA, and WD 15 mm, and the EDX analysis is performed under the same conditions with a detection time of 60 minutes. Import the obtained image into an image analysis device (LUZEXIII, manufactured by NIRECO Corporation), and obtain the area of each particle by image analysis.

[0067] The ratio of the total area of the silica particles to the total surface area of the carrier (total area of the silica particles / total surface area of the carrier × 100) is defined as the coating rate S1 of the silica particles covering the surface of the carrier separated from the electrostatic image developer.

[0068] (3) As the model toner, use a toner having the following composition and not having an external additive.

[0069] Binder resin: amorphous polyester resin

[0070] Volume average particle diameter: 5.7 μm

[0071] Volume average particle size distribution index (GSDv): 1.20

[0072] Average roundness: 9.55 or more and 9.74 or less

[0073] (4) Mix 100 parts by mass of the carrier separated in step (1) with 10 parts by mass of the model toner described in step (3), and stir the mixture using a drum mixer at a temperature of 20°C, a humidity of 50% RH, and a stirring time of 2 minutes.

[0074] (5) Use a wire gauge (manufactured by ASADA MESH Co., Ltd.) to separate the mixture into the model toner and the carrier.

[0075] (6) Similar to the coating rate S1 of the above silica particles, determine the coating rate S2 of the silica particles on the surface of the carrier separated from the model toner by XPS.

[0076] (7) Calculate the free rate of the silica particles on the surface of the coated carrier (= (S1 - S2) / S1 × 100) from "the coating rate S1 of the silica particles on the surface of the carrier separated from the electrophotographic developer and before mixing with the model toner" and "the coating rate S2 of the silica particles on the surface of the carrier separated from the model toner".

[0077] [Core material]

[0078] The carrier for electrophotographic development of the present embodiment contains a core material.

[0079] The core material is not particularly limited as long as it has magnetism, and known materials used as the core material of the carrier can be applied.

[0080] Examples of the core material include: granular magnetic powder (magnetic particles); resin-impregnated magnetic particles in which resin is impregnated in porous magnetic powder; magnetic powder-dispersed resin particles in which magnetic powder is dispersed and mixed in resin; etc.

[0081] Examples of the magnetic powder include: particles of magnetic metals such as iron, nickel, and cobalt; magnetic oxides such as ferrite and magnetite; etc., and magnetic oxides are preferred. The magnetic particles can be used alone or in combination of two or more.

[0082] Examples of the resin constituting the core material include polyethylene, polypropylene, polystyrene, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl ether, polyvinyl ketone, vinyl chloride-vinyl acetate copolymer, styrene-acrylic copolymer, straight silicone composed of siloxane bonds or its modified product, fluororesin, polyester, polycarbonate, phenolic resin, epoxy resin, etc. These resins can be used alone or in combination of two or more. It should be noted that additives such as conductive particles can also be included in the resin constituting the core material. Examples of the conductive particles include particles of metals such as gold, silver, and copper, carbon black, titanium oxide, zinc oxide, tin oxide, barium sulfate, aluminum borate, potassium titanate, etc.

[0083] The core material is preferably granular magnetic powder, that is, magnetic particles.

[0084] The surface roughness Ra of the core material is preferably 0.5 μm or more and 1.5 μm or less, more preferably 0.6 μm or more and 1.2 μm or less, and further preferably 0.7 μm or more and 1.0 μm or less.

[0085] The method for making the surface roughness Ra of the core material within the above range is not particularly limited. Examples include: a method of manufacturing the core material using a wet ball mill and adjusting the particle size when pulverizing the raw material of the core material or its fired product; etc.

[0086] The surface roughness Ra of the core material is measured in the same manner as the surface roughness Ra of the above carrier.

[0087] The volume average particle diameter of the magnetic particles is preferably 20 μm or more and 50 μm or less, for example.

[0088] [Coating resin layer]

[0089] The coating resin layer of the present embodiment contains inorganic particles.

[0090] The coating resin layer of the present embodiment is a resin layer that coats the above core material.

[0091] For the coating resin layer of the first embodiment, the volume average particle diameter D (μm) of the inorganic particles and the thickness T (μm) of the coating resin layer satisfy the following relational expression (1). From the aspect of further suppressing the density unevenness of the image, it preferably satisfies the following relational expression (1-2), and more preferably satisfies the following relational expression (1-3).

[0092] Relational expression (1) 0.007 ≤ D / T ≤ 0.24

[0093] Relational expression (1-2) 0.007 ≤ D / T ≤ 0.2

[0094] The relational expression (1-3): 0.007 ≤ D / T ≤ 0.05

[0095] For the coating resin layer of the second embodiment, the volume average particle diameter D (μm) of the inorganic particles and the thickness T (μm) of the coating resin layer preferably satisfy the above relational expression (1), more preferably satisfy the above relational expression (1-2), and further preferably satisfy the above relational expression (1-3).

[0096] The method for forming a coating resin layer that satisfies the above relational expressions (1), (1-2), and (1-3) is not particularly limited, and examples thereof include: a method of adjusting the type of resin constituting the coating resin layer; a method of adjusting the particle diameter of the inorganic particles; etc.

[0097] (Resin)

[0098] Examples of the resin constituting the coating resin layer include: styrene-acrylic copolymer; polyolefin resins such as polyethylene and polypropylene; polyvinyl-based or polyvinylidene-based resins such as polystyrene, acrylic resins, polyacrylonitrile, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl carbazole, polyvinyl ether, and polyvinyl ketone; vinyl chloride-vinyl acetate copolymer; pure silicone resins (straight silicone resin) or modified products thereof composed of organosiloxane bonds; fluororesins such as polytetrafluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, and polychlorotrifluoroethylene; polyester; polyurethane; polycarbonate; amino resins such as urea-formaldehyde resin; epoxy resin; etc.

[0099] The coating resin layer preferably contains an alicyclic (meth)acrylic resin. By making the coating resin layer contain an alicyclic (meth)acrylic resin, the dispersibility of the inorganic particles contained in the coating resin layer is likely to become higher, and there is a tendency to efficiently produce a resin sheet containing inorganic particles. As a result, there is a tendency to further suppress unevenness in image density.

[0100] As the polymerization component of the alicyclic (meth)acrylic resin, a lower alkyl ester of (meth)acrylic acid (for example, (meth)acrylic acid alkyl ester having 1 to 9 carbon atoms in the alkyl group) is preferred. Specifically, examples include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 2-(dimethylamino)ethyl (meth)acrylate, etc.

[0101] Among the above, as the polymerization component of the alicyclic acrylic resin, from the aspect of further suppressing the density unevenness of the image, it is preferably to contain at least one selected from the group consisting of methyl (meth)acrylate, cyclohexyl (meth)acrylate, and 2-(dimethylamino)ethyl (meth)acrylate, and more preferably to contain at least one of methyl (meth)acrylate and cyclohexyl (meth)acrylate. One kind of the polymerization component of the alicyclic acrylic resin can be used, or two or more kinds can be used in combination.

[0102] The alicyclic (meth)acrylic resin shields the influence of the polarization component of the bond between carbon atoms and oxygen atoms by water through the steric hindrance of the alicyclic functional group. Since it can suppress the influence of moisture on environmental changes, it is preferably to contain cyclohexyl (meth)acrylate as the polymerization component.

[0103] The content of cyclohexyl (meth)acrylate contained in the alicyclic (meth)acrylic resin is preferably 75 mol% or more and 100 mol% or less, more preferably 90 mol% or more and 100 mol% or less, and further preferably 95 mol% or more and 100 mol% or less.

[0104] Among all the resins contained in the coating resin layer, the proportion of the alicyclic (meth)acrylic resin is preferably 80% by mass or more, more preferably 90% by mass or more, and further preferably 95% by mass or more.

[0105] (Inorganic particles)

[0106] Examples of the inorganic particles include particles such as silica, alumina, titanium oxide (titanium dioxide), barium titanate, magnesium titanate, calcium titanate, strontium titanate, iron oxide, copper oxide, zinc oxide, tin oxide, silica sand, clay, mica, wollastonite, diatomaceous earth, chromium oxide, cerium oxide, iron oxide red, antimony trioxide, magnesium oxide, zirconium oxide, barium sulfate, barium carbonate, calcium carbonate, silicon carbide, and silicon nitride. Among these, as the inorganic particles, from the aspect of further suppressing the density unevenness of the image, it is preferably to contain one or more kinds of particles selected from the group consisting of silica, alumina, and titanium oxide, and more preferably to contain silica particles.

[0107] The inorganic particles preferably contain inorganic particles that have been hydrophobized with a hydrophobizing agent, and more preferably contain hydrophobized silica particles.

[0108] Examples of the hydrophobizing agent include known surface treatment agents. Specifically, examples include silane coupling agents, silicone oils, and the like.

[0109] Examples of the silane coupling agent include, for example, hexamethyldisilazane, trimethylsilane, trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane, allyldimethylchlorosilane, benzyldimethylchlorosilane, methyltrimethoxysilane, methyltriethoxysilane, isobutyltrimethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, trimethylmethoxysilane, hydroxypropyltrimethoxysilane, phenyltrimethoxysilane, n-butyltrimethoxysilane, n-hexadecyltrimethoxysilane, n-octadecyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, vinyltriacetoxysilane and the like.

[0110] Examples of the silicone oil include, for example, dimethylpolysiloxane, methylhydrogenpolysiloxane, methylphenylpolysiloxane and the like.

[0111] Among the above, as the hydrophobizing agent, it preferably contains at least one of hexamethyldisilazane (HMDS) and dimethylpolysiloxane (PDMS), and more preferably contains HMDS.

[0112] The volume average particle diameter D of the inorganic particles is preferably 1 nm or more and 80 nm or less, more preferably 5 nm or more and 50 nm or less, and still more preferably 5 nm or more and 30 nm or less.

[0113] Regarding the volume average particle diameter D of the inorganic particles, the surface of the carrier is observed with a scanning microscope, and image analysis is performed on the inorganic particles attached to the coating resin layer, thereby measuring. Specifically, for each carrier particle, 50 inorganic particles are observed with a scanning microscope, the longest diameter and the shortest diameter of each particle are measured by image analysis of the inorganic particles, and the equivalent spherical diameter is measured from the intermediate value. The equivalent spherical diameter is measured for 100 carriers. Then, the 50% diameter (D50v) in the volume-based cumulative frequency of the obtained equivalent spherical diameter is used as the volume average particle diameter D of the inorganic particles.

[0114] Regarding the content of the inorganic particles in the first embodiment, the content of the inorganic particles relative to the total mass of the coating resin layer is 10% by mass or more and 60% by mass or less, preferably 10% by mass or more and 50% by mass or less, and more preferably 10% by mass or more and 40% by mass or less.

[0115] Regarding the content of the inorganic particles in the second embodiment, the content of the inorganic particles relative to the total mass of the coating resin layer is preferably 10% by mass or more and 60% by mass or less, more preferably 10% by mass or more and 50% by mass or less, and still more preferably 10% by mass or more and 40% by mass or less.

[0116] As a method for forming a coating resin layer on the surface of a core material, for example, a wet method and a dry method can be cited. The wet method is a method using a solvent that dissolves or disperses the resin constituting the coating resin layer. On the other hand, the dry method is a method that does not use the above solvent.

[0117] As the wet method, for example, the dipping method, in which the core material is dipped in a resin liquid for forming a coating resin layer for coating; the spraying method, in which the resin liquid for forming a coating resin layer is sprayed onto the surface of the core material; the fluidized bed method, in which the resin liquid for forming a coating resin layer is sprayed in a state where the core material is fluidized in a fluidized bed; the kneading coater method, in which the core material and the resin liquid for forming a coating resin layer are mixed in a kneading coater and the solvent is removed; etc.

[0118] The resin liquid for forming a coating resin layer used in the wet method is prepared by dissolving or dispersing a resin and other components in a solvent. As the solvent, there is no particular limitation as long as it dissolves or disperses the resin, and for example, aromatic hydrocarbons such as toluene and xylene; ketones such as acetone and methyl ethyl ketone; ethers such as tetrahydrofuran and dioxane; etc. are used.

[0119] As the dry method, for example, a method of heating a mixture of a core material and a resin for forming a coating resin layer in a dry state to form a coating resin layer can be cited. Specifically, for example, the core material and the resin for forming a coating resin layer are mixed in a gas phase and heated and melted to form a coating resin layer.

[0120] The thickness T (μm) of the coating resin layer is preferably 0.1 μm or more and 10 μm or less, more preferably 0.2 μm or more and 5 μm or less, and further preferably 0.3 μm or more and 3 μm or less.

[0121] The thickness T of the resin-coated layer is measured by the following method. The carrier is embedded in epoxy resin or the like, and thin sections are prepared by cutting using a diamond knife or the like. The thin sections are observed with a transmission electron microscope (TEM) or the like, and cross-sectional images of two or more carrier particles are taken. The thickness of the coating resin layer at 20 places is measured from the cross-sectional images of the carrier particles, and the average value is adopted.

[0122] Electrostatic Image Developer

[0123] The developer of the present embodiment contains a toner and the carrier of the present embodiment.

[0124] The developer of the present embodiment is prepared by mixing a toner and the carrier of the present embodiment at an appropriate mixing ratio. The mixing ratio (mass ratio) of the toner to the carrier is preferably toner:carrier = 1:100 to 30:100, and more preferably 3:100 to 20:100.

[0125] [Toner for Electrostatic Image Development]

[0126] There is no particular limitation on the toner, and known toners are used. For example, a colored toner containing toner particles containing a binder resin and a colorant can be cited, and an infrared absorbing toner using an infrared absorber instead of a colorant can also be cited. The toner may also contain a release agent, various internal additives, external additives, etc.

[0127] -Binder resin-

[0128] As the binder resin, for example, styrene-based (such as styrene, p-chlorostyrene, α-methylstyrene, etc.), (meth)acrylate-based (such as methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, lauryl methacrylate, 2-ethylhexyl methacrylate, etc.), ethylenically unsaturated nitrile-based (such as acrylonitrile, methacrylonitrile, etc.), vinyl ether-based (such as vinyl methyl ether, vinyl isobutyl ether, etc.), vinyl ketone-based (such as vinyl methyl ketone, vinyl ethyl ketone, vinyl isopropenyl ketone, etc.), olefin-based (such as ethylene, propylene, butadiene, etc.) homopolymers of monomers, or copolymers formed by combining two or more of these monomers can be cited as vinyl-based resins.

[0129] As the binder resin, for example, non-vinyl-based resins such as epoxy resins, polyester resins, polyurethane resins, polyamide resins, cellulose resins, polyether resins, modified rosin, mixtures of these resins with the above vinyl-based resins, or graft polymers obtained by polymerizing vinyl-based monomers in the coexistence of these resins can also be cited.

[0130] These binder resins can be used alone or in combination of two or more.

[0131] As the binder resin, a polyester resin is preferred. As the polyester resin, for example, known polyester resins can be cited.

[0132] The glass transition temperature (Tg) of the polyester resin is preferably 50°C or higher and 80°C or lower, more preferably 50°C or higher and 65°C or lower.

[0133] The glass transition temperature is obtained from the DSC curve obtained by differential scanning calorimetry (DSC). More specifically, it is obtained by the "extrapolated glass transition start temperature" described in the method for determining the glass transition temperature of JIS K7121-1987 "Method for Measuring the Transition Temperature of Plastics".

[0134] The weight-average molecular weight (Mw) of the polyester resin is preferably 5,000 or more and 1,000,000 or less, more preferably 7,000 or more and 500,000 or less. The number-average molecular weight (Mn) of the polyester resin is preferably 2,000 or more and 100,000 or less. The molecular weight distribution Mw / Mn of the polyester resin is preferably 1.5 or more and 100 or less, more preferably 2 or more and 60 or less.

[0135] The weight-average molecular weight and the number-average molecular weight are measured by gel permeation chromatography (GPC). In the molecular weight measurement using GPC, as the measurement device, Tosoh GPC·HLC-8120GPC is used, Tosoh column·TSKgel SuperHM-M (15 cm) is used, and the measurement is carried out using THF solvent. The weight-average molecular weight and the number-average molecular weight are calculated from the measurement results according to the molecular weight calibration curve prepared using a monodisperse polystyrene standard sample.

[0136] The content of the adhesive resin is preferably 40% by mass or more and 95% by mass or less, more preferably 50% by mass or more and 90% by mass or less, further preferably 60% by mass or more and 85% by mass or less with respect to the whole toner particles.

[0137] - Colorant -

[0138] Examples of the colorant include pigments such as carbon black, chrome yellow, Hansa yellow, benzidine yellow, vat yellow, quinoline yellow, pigment yellow, permanent orange GTR, pyrazolone orange, sulfur-fast orange, Vulcan Fast Red, permanent red, brilliant carmine 3B, brilliant carmine 6B, DuPont oil red, pyrazolone red, lithol red, rhodamine B lake, lake red C, pigment red, rose red, aniline blue, ultramarine blue, oil-soluble blue, methylene blue chloride, phthalocyanine blue, pigment blue, phthalocyanine green, malachite green oxalate, etc.; dyes such as acridine-based, xanthene-based, azo-based, benzoquinone-based, azine-based, anthraquinone-based, thioindigo-based, dioxazine-based, thiazine-based, azomethine-based, indigo-based, phthalocyanine-based, aniline black-based, polymethine-based, triphenylmethane-based, diphenylmethane-based, thiazole-based dyes.

[0139] The colorant can be used alone or in combination of two or more.

[0140] As the colorant, a colorant that has been surface-treated as needed can be used, or it can be used in combination with a dispersant. In addition, two or more colorants can be used in combination.

[0141] The content of the colorant is preferably 1% by mass or more and 30% by mass or less, more preferably 3% by mass or more and 15% by mass or less with respect to the whole toner particles.

[0142] - Release agent -

[0143] As a release agent, for example, hydrocarbon waxes; natural waxes such as carnauba wax, rice bran wax, and candelilla wax; synthetic or mineral / petroleum-based waxes such as montan wax; ester-based waxes such as fatty acid esters and montanic acid esters; and the like can be cited. The release agent is not limited thereto.

[0144] The melting temperature of the release agent is preferably 50°C or higher and 110°C or lower, more preferably 60°C or higher and 100°C or lower.

[0145] The melting temperature is determined by the "melting peak temperature" described in the method for determining the melting temperature of JIS K7121-1987 "Method for Measuring the Transition Temperature of Plastics" based on the DSC curve obtained by differential scanning calorimetry (DSC).

[0146] Relative to the entire toner particles, the content of the release agent is preferably 1% by mass or more and 20% by mass or less, more preferably 5% by mass or more and 15% by mass or less.

[0147] - Other Additives -

[0148] As other additives, for example, known additives such as magnetic materials, charge control agents, and inorganic powders can be cited. These additives can be included as internal additives in the toner particles.

[0149] - Characteristics of Toner Particles, etc. -

[0150] The toner particles can be single-layered toner particles or so-called core-shell structured toner particles composed of a core part (core particles) and a coating layer (shell layer) covering the core part.

[0151] The core-shell structured toner particles can be composed of a core part and a coating layer, for example. The core part is composed by including a binder resin and other additives such as a colorant and a release agent when necessary, and the coating layer is composed by including a binder resin.

[0152] The volume average particle diameter (D50v) of the toner particles is preferably 2 μm or more and 10 μm or less, more preferably 4 μm or more and 8 μm or less.

[0153] Regarding the volume average particle diameter (D50v) of the toner particles, measurement is carried out using a Coulter Multisizer II (manufactured by Beckman Coulter), and ISOTON-II (manufactured by Beckman Coulter) is used as the electrolyte. At the time of measurement, 0.5 mg or more and 50 mg or less of the measurement sample is added to 2 ml of a 5 mass% aqueous solution of a surfactant (preferably sodium alkylbenzene sulfonate) as a dispersant. This is added to 100 ml or more and 150 ml or less of the electrolyte. The electrolyte in which the sample is suspended is subjected to a dispersion treatment for 1 minute using an ultrasonic disperser, and the particle size distribution of particles having a particle diameter in the range of 2 μm or more and 60 μm or less is measured using a Coulter Multisizer II with a pore diameter of 100 μm. The number of sampled particles is 50,000.

[0154] -External additive-

[0155] Examples of the external additive include inorganic particles. Examples of the inorganic particles include SiO2, TiO2, Al2O3, CuO, ZnO, SnO2, CeO2, Fe2O3, MgO, BaO, CaO, K2O, Na2O, ZrO2, CaO·SiO2, K2O·(TiO2)n, Al2O3·2SiO2, CaCO3, MgCO3, BaSO4, MgSO4, etc.

[0156] The surface of the inorganic particles as the external additive is preferably subjected to a hydrophobization treatment. The hydrophobization treatment is carried out, for example, by immersing the inorganic particles in a hydrophobization treatment agent. The hydrophobization treatment agent is not particularly limited, and examples thereof include silane-based coupling agents, silicone oils, titanate-based coupling agents, and aluminum-based coupling agents. These treatment agents can be used alone or in combination of two or more.

[0157] Generally, for example, with respect to 100 parts by mass of the inorganic particles, the amount of the hydrophobization treatment agent is 1 part by mass or more and 10 parts by mass or less.

[0158] Examples of the external additive also include resin particles (resin particles such as polystyrene, polymethyl methacrylate, and melamine resin), cleaning agents (for example, metal salts of higher fatty acids represented by zinc stearate, particles of fluorine-based high molecular weight substances), etc.

[0159] With respect to the toner particles, the addition amount of the external additive is preferably 0.01 mass% or more and 5 mass% or less, more preferably 0.01 mass% or more and 2.0 mass% or less.

[0160] -Method for manufacturing toner-

[0161] The toner is obtained by externally adding an external additive to toner particles after the toner particles are manufactured. The toner particles can be manufactured by any one of a dry method (such as a kneading and pulverizing method, etc.), a wet method (such as an aggregation and coalescence method, a suspension polymerization method, a dissolution and suspension method, etc.). There is no particular limitation on the method for manufacturing the toner particles, and a known method is adopted. Among these, the toner particles can be obtained by the aggregation and coalescence method.

[0162] "Image Forming Apparatus and Image Forming Method"

[0163] The image forming apparatus and the image forming method of the present embodiment will be described.

[0164] The image forming apparatus of the present embodiment includes: an image holding member; a charging unit that charges the surface of the image holding member; an electrostatic image forming unit that forms an electrostatic image on the charged surface of the image holding member; a developing unit that houses an electrostatic image developer and develops the electrostatic image formed on the surface of the image holding member into a toner image; a transfer unit that transfers the toner image formed on the surface of the image holding member to the surface of a recording medium; and a fixing unit that fixes the toner image transferred to the surface of the recording medium. In addition, as the electrostatic image developer, the electrostatic image developer of the present embodiment is applied.

[0165] The image forming apparatus of the present embodiment implements an image forming method (the image forming method of the present embodiment), which has the following steps: a charging step of charging the surface of the image holding member; an electrostatic image forming step of forming an electrostatic image on the charged surface of the image holding member; a developing step of developing the electrostatic image formed on the surface of the image holding member into a toner image using the electrostatic image developer of the present embodiment; a transfer step of transferring the toner image formed on the surface of the image holding member to the surface of a recording medium; and a fixing step of fixing the toner image transferred to the surface of the recording medium.

[0166] The image forming apparatus of the present embodiment is applicable to the following known image forming apparatuses: an apparatus of a direct transfer type that directly transfers the toner image formed on the surface of the image holding member to a recording medium; an apparatus of an intermediate transfer type that transfers the toner image formed on the surface of the image holding member to the surface of an intermediate transfer member once and then transfers the toner image transferred to the surface of the intermediate transfer member to the surface of a recording medium twice; an apparatus having a cleaning unit that cleans the surface of the image holding member after the transfer of the toner image and before charging; an apparatus having a discharging unit that discharges the surface of the image holding member by irradiating a discharging light after the transfer of the toner image and before charging; and so on.

[0167] When the image forming apparatus of the present embodiment is an apparatus using an intermediate transfer method, the transfer unit to be applied has, for example, the following components: an intermediate transfer member onto which a toner image is transferred; a primary transfer unit that transfers the toner image formed on the surface of the image holding member to the surface of the intermediate transfer member at once; and a secondary transfer unit that transfers the toner image transferred to the surface of the intermediate transfer member to the surface of the recording medium at second time.

[0168] In the image forming apparatus of the present embodiment, for example, a portion including the developing unit may be a cartridge structure (processing cartridge) that can be attached to and detached from the image forming apparatus. As the processing cartridge, for example, a processing cartridge that accommodates the electrostatic image developer of the present embodiment and includes a developing unit is suitable for use.

[0169] An example of the image forming apparatus of the present embodiment is shown below, but is not limited thereto. In the following description, main parts shown in the drawings are described, and other descriptions are omitted.

[0170] Figure 1 It is a schematic configuration diagram showing the image forming apparatus of the present embodiment.

[0171] Figure 1 The shown image forming apparatus includes: electrophotographic first to fourth image forming units 10Y, 10M, 10C, 10K (image forming units) that output yellow (Y), magenta (M), cyan (C), and black (K) color images based on color separation image data. These image forming units (hereinafter sometimes simply referred to as "units") 10Y, 10M, 10C, 10K are arranged side by side at a preset distance from each other in the horizontal direction. These units 10Y, 10M, 10C, 10K may be processing cartridges that can be attached to and detached from the image forming apparatus.

[0172] Above each of the units 10Y, 10M, 10C, 10K, an intermediate transfer belt (an example of an intermediate transfer member) 20 is provided so as to extend through each unit. The intermediate transfer belt 20 is wound around a driving roller 22 and a support roller 24 so as to travel in a direction from the first unit 10Y toward the fourth unit 10K. The support roller 24 applies a force in a direction away from the driving roller 22 by a spring or the like (not shown), and applies a tension to the intermediate transfer belt 20 wound around the two rollers. An intermediate transfer member cleaning device 30 opposed to the driving roller 22 is provided on the image holding member side of the intermediate transfer belt 20.

[0173] Developing devices (an example of developing units) 4Y, 4M, 4C, 4K of the respective units 10Y, 10M, 10C, 10K are respectively supplied with yellow, magenta, cyan, and black toners accommodated in toner cartridges 8Y, 8M, 8C, 8K.

[0174] Since the first to fourth units 10Y, 10M, 10C, and 10K have the same configuration and operation, the first unit 10Y that forms a yellow image and is disposed on the upstream side in the traveling direction of the intermediate transfer belt will be described as a representative here.

[0175] The first unit 10Y has a photoreceptor 1Y that functions as an image holding member. Around the photoreceptor 1Y, a charging roller (an example of a charging unit) 2Y that charges the surface of the photoreceptor 1Y to a preset potential, an exposure device (an example of an electrostatic image forming unit) 3 that exposes the charged surface with a laser beam 3Y based on a color separation image signal to form an electrostatic image, a developing device (an example of a developing unit) 4Y that supplies charged toner to the electrostatic image to develop the electrostatic image, a primary transfer roller 5Y (an example of a primary transfer unit) that transfers the developed toner image to the intermediate transfer belt 20, and a photoreceptor cleaning device (an example of a cleaning unit) 6Y that removes the toner remaining on the surface of the photoreceptor 1Y after primary transfer are sequentially arranged.

[0176] The primary transfer roller 5Y is disposed inside the intermediate transfer belt 20 and is arranged at a position facing the photoreceptor 1Y. The primary transfer rollers 5Y, 5M, 5C, and 5K of each unit are respectively connected to a bias power source (not shown) that applies a primary transfer bias. Each bias power source changes the value of the transfer bias applied to each primary transfer roller by the control of a control unit (not shown).

[0177] Next, the operation of forming a yellow image in the first unit 10Y will be described.

[0178] First, before the operation, the surface of the photoreceptor 1Y is charged to a potential of -600V to -800V by the charging roller 2Y.

[0179] The photoreceptor 1Y is formed by laminating a photosensitive layer on a substrate having conductivity (for example, a volume resistivity of 1 × 10 -6 Ωcm or less at 20°C). This photosensitive layer usually has a high resistance (the resistance of a common resin), but has the property that the resistivity of the portion irradiated with the laser beam changes when irradiated with the laser beam. Therefore, according to the yellow image data sent from a control unit (not shown), the laser beam 3Y is irradiated from the exposure device 3 to the surface of the charged photoreceptor 1Y. Thus, an electrostatic image of a yellow image pattern is formed on the surface of the photoreceptor 1Y.

[0180] The electrostatic image is an image formed on the surface of the photoreceptor 1Y by charging, which is a so-called negative latent image. The negative latent image is formed as follows: the resistivity of the irradiated portion of the photosensitive layer is reduced by the laser beam 3Y, causing the charged charges on the surface of the photoreceptor 1Y to flow; on the other hand, the charges in the portion not irradiated with the laser beam remain, thereby forming the negative latent image.

[0181] The electrostatic image formed on the photoreceptor 1Y rotates to a preset development position as the photoreceptor 1Y advances. And at this development position, the electrostatic image on the photoreceptor 1Y is developed into a toner image by the developing device 4Y and is visualized.

[0182] The electrostatic image developer containing, for example, at least yellow toner and a carrier is accommodated in the developing device 4Y. The yellow toner is triboelectrically charged by being agitated inside the developing device 4Y, has a charge with the same polarity (negative polarity) as the charging charge charged on the photoreceptor 1Y, and is held on the developer roller (an example of a developer holding body). After that, as the surface of the photoreceptor 1Y passes through the developing device 4Y, the yellow toner electrostatically adheres to the discharged latent image portion on the surface of the photoreceptor 1Y, and the latent image is developed using the yellow toner. The photoreceptor 1Y on which the yellow toner image is formed continues to rotate at a preset speed, and the toner image developed on the photoreceptor 1Y is transferred to a preset primary transfer position.

[0183] When the yellow toner image on the photoreceptor 1Y is transferred to the primary transfer position, a primary transfer bias is applied to the primary transfer roller 5Y, and the electrostatic force from the photoreceptor 1Y toward the primary transfer roller 5Y acts on the toner image, transferring the toner image on the photoreceptor 1Y to the intermediate transfer belt 20. The transfer bias applied at this time has a (+) polarity opposite to the polarity (-) of the toner, and is controlled, for example, to +10 μA by a control unit (not shown) in the first unit 10Y.

[0184] On the other hand, the photoreceptor cleaning device 6Y removes and recovers the toner remaining on the photoreceptor 1Y.

[0185] The primary transfer bias applied to the primary transfer rollers 5M, 5C, 5K after the second unit 10M is also controlled according to the first unit.

[0186] In this way, the intermediate transfer belt 20 on which the yellow toner image has been transferred by the first unit 10Y is sequentially transferred through the second to fourth units 10M, 10C, 10K, and the toner images of each color are multi-transferred in a superimposed manner.

[0187] The intermediate transfer belt 20 on which the toner images of four colors have been multiply transferred through the first to fourth units reaches the secondary transfer section, which is composed of the intermediate transfer belt 20, a support roller 24 in contact with the inner surface of the intermediate transfer belt, and a secondary transfer roller (an example of a secondary transfer unit) 26 disposed on the image holding surface side of the intermediate transfer belt 20. On the other hand, a recording paper (an example of a recording medium) P is sent to the gap where the secondary transfer roller 26 and the intermediate transfer belt 20 are in contact at a preset timing by a supply unit, and a secondary transfer bias is applied to the support roller 24. The transfer bias applied at this time has the same (-) polarity as the polarity (-) of the toner, and an electrostatic force acting from the intermediate transfer belt 20 toward the recording paper P acts on the toner image, transferring the toner image on the intermediate transfer belt 20 onto the recording paper P. The secondary transfer bias at this time is determined based on the resistance detected by a resistance detection unit (not shown) that detects the resistance of the secondary transfer section, and the voltage is controlled.

[0188] After that, the recording paper P is sent into the crimping section (biting section) of a pair of fixing rollers in a fixing device (an example of a fixing unit) 28, and the toner image is fixed on the recording paper P to form a fixed image.

[0189] As the recording paper P for transferring the toner image, for example, ordinary paper used in electrophotographic copiers, printers, etc. can be cited. As the recording medium, in addition to the recording paper P, OHP transparent films, etc. can also be cited.

[0190] In order to further improve the smoothness of the surface of the image after fixing, it is preferable that the surface of the recording paper P is also smooth. For example, coated paper obtained by coating the surface of ordinary paper with resin or the like, art paper for printing, etc. are suitable for use.

[0191] The recording paper P on which the fixing of the color image has been completed is sent to the discharge section, ending a series of color imaging operations.

[0192] 《Processing Cartridge》

[0193] The processing cartridge of the present embodiment will be described.

[0194] The processing cartridge of the present embodiment is a processing cartridge that can be loaded and unloaded in an image forming apparatus, and includes: a developing unit that accommodates the electrostatic image developer of the present embodiment and develops the electrostatic image formed on the surface of the image holding body into a toner image.

[0195] The processing cartridge of the present embodiment is not limited to the above configuration, and may also be a configuration including a developing unit and at least one of other units such as an image holding body, a charging unit, an electrostatic image forming unit, and a transfer unit, etc. when necessary.

[0196] An example of the processing cartridge according to the present embodiment is shown below, but it is not limited thereto. In the following description, the main parts shown in the drawings will be described, and other descriptions will be omitted.

[0197] Figure 2 It is a schematic configuration diagram showing the processing cartridge according to the present embodiment.

[0198] Figure 2 The processing cartridge 200 shown is formed, for example, by integrally combining and holding a photosensitive member 107 (an example of an image holding member), a charging roller 108 (an example of a charging unit) located around the photosensitive member 107, a developing device 111 (an example of a developing unit), and a photosensitive member cleaning device 113 (an example of a cleaning unit) with a housing 117 having a mounting rail 116 and an opening 118 for exposure, and is made into a cartridge.

[0199] Figure 2 In it, 109 represents an exposure device (an example of an electrostatic image forming unit), 112 represents a transfer device (an example of a transfer unit), 115 represents a fixing device (an example of a fixing unit), and 300 represents a recording paper (an example of a recording medium).

[0200] Examples

[0201] Hereinafter, embodiments of the invention will be described in detail by way of examples, but the embodiments of the invention are not limited by any of these examples. In the following description, unless otherwise specified, "parts" and "%" are based on mass.

[0202] <Preparation of toner>

[0203] [Preparation of resin particle dispersion liquid (1)]

[0204]

[0205] The above materials are put into a flask, the temperature is raised to 200 °C in 1 hour, and after confirming that the reaction system is stirred evenly, 1.2 parts of dibutyltin oxide are added. While distilling off the generated water, the temperature is raised to 240 °C in 6 hours, and stirring is continued at 240 °C for 4 hours to obtain a polyester resin (acid value 9.4 mgKOH / g, weight average molecular weight 13,000, glass transition temperature 62 °C). The polyester resin is kept in a molten state and fed to an emulsifying and dispersing machine (Cavitron CD1010, Eurotec) at a rate of 100 g per minute. In addition, dilute ammonia water with a concentration of 0.37% obtained by diluting reagent ammonia water with ion-exchanged water is put into a tank, and while heating it to 120 °C with a heat exchanger, it is fed to the emulsifying and dispersing machine at a rate of 0.1 liter per minute simultaneously with the polyester resin. When the rotational speed of the rotor is 60 Hz and the pressure is 5 kg / cm 2The emulsifying and dispersing machine was operated under the following conditions to obtain a resin particle dispersion (1) having a volume average particle diameter of 160 nm and a solid content of 30%.

[0206] [Preparation of Resin Particle Dispersion (2)]

[0207] · 81 parts of sebacic acid (Tokyo Chemical Industry Co., Ltd.)

[0208] · 47 parts of hexanediol (FUJIFILM Wako Pure Chemical Corporation)

[0209] The above materials were put into a flask, the temperature was raised to 160 °C over 1 hour, and after confirming that the reaction system was stirred evenly, 0.03 part of dibutyltin oxide was added. While distilling off the generated water, the temperature was raised to 200 °C over 6 hours and stirring was continued at 200 °C for 4 hours. Next, the reaction solution was cooled, solid-liquid separation was performed, and the solid substance was dried at 40 °C under reduced pressure to obtain a polyester resin (C1) (melting point 64 °C, weight average molecular weight 15,000).

[0210] · 50 parts of polyester resin (C1)

[0211] · 2 parts of anionic surfactant (NEOGEN SC, Daiichi Kogyo Seiyaku Co., Ltd.)

[0212] · 200 parts of ion-exchanged water

[0213] The above materials were heated to 120 °C, sufficiently dispersed using a homogenizer (ULTRA-TURRAXT50, IKA), and then subjected to a dispersion treatment using a pressure ejection type homogenizer. After the volume average particle diameter reached 180 nm, it was recovered to obtain a resin particle dispersion (2) having a solid content of 20%.

[0214] [Preparation of Colorant Particle Dispersion (1)]

[0215] · 10 parts of blue pigment (Pigment Blue 15:3, Dainichi Seika Chemicals Co., Ltd.)

[0216] · 2 parts of anionic surfactant (NEOGEN SC, Daiichi Kogyo Seiyaku Co., Ltd.)

[0217] · 80 parts of ion-exchanged water

[0218] The above materials were mixed and dispersed for 1 hour using a high-pressure impact type disperser (Ultimaizer HJP30006, Sugino Machine Co., Ltd.) to obtain a colorant particle dispersion (1) having a volume average particle diameter of 180 nm and a solid content of 20%.

[0219] [Preparation of Release Agent Particle Dispersion (1)]

[0220] · 50 parts of solid paraffin (HNP-9, Nippon Seiro Co., Ltd.)

[0221] · 2 parts of anionic surfactant (NEOGEN SC, Daiichi Kogyo Seiyaku Co., Ltd.)

[0222] · 200 parts of ion-exchanged water

[0223] Heat the above materials to 120 °C, fully disperse them using a homogenizer (ULTRA-TURRAXT50, IKA), and then perform dispersion treatment using a pressure ejection type homogenizer. After the volume average particle size reaches 200 nm, recover to obtain the release agent particle dispersion (1) with a solid content of 20%.

[0224] [Preparation of Toner (1)]

[0225]

[0226] Put the above materials into a round stainless steel flask, fully mix and disperse them using a homogenizer (ULTRA-TURRAXT50, IKA), and then heat to 48 °C using a heating oil bath while stirring the inside of the flask. After maintaining the reaction system at 48 °C for 60 minutes, slowly add 70 parts of the resin particle dispersion (1). Next, adjust the pH to 8.0 using a 0.5 mol / L sodium hydroxide aqueous solution, seal the flask, magnetically seal the seal of the stirring shaft, continue stirring while heating to 90 °C, and maintain for 30 minutes. Next, cool at a cooling rate of 5 °C / minute, perform solid-liquid separation, and wash thoroughly with ion-exchanged water. Next, perform solid-liquid separation again, redisperse in ion-exchanged water at 30 °C, and stir at a rotation speed of 300 rpm for 15 minutes for washing. Repeat this washing operation 6 more times. When the pH of the filtrate is 7.54 and the conductivity is 6.5 μS / cm, perform solid-liquid separation and continue vacuum drying for 24 hours to obtain toner particles (1) with a volume average particle size of 5.7 μm.

[0227] Mix 100 parts of the above toner particles (1) with 0.7 parts of hydrophobic silica (RY50 manufactured by NIPPON AEROSIL Co., Ltd.) using a Henschel mixer to obtain toner (1).

[0228] [Preparation of Carrier]

[0229] [Preparation of Core Material]

[0230] - Ferrite Particles (1)-

[0231] Mix 74 parts of Fe2O3, 4 parts of Mg(OH)2, and 21 parts of MnO2, and pre-fire (the first time) in a rotary kiln at a temperature of 950 °C for 7 hours. Crush the obtained pre-fired product with a wet ball mill for 7 hours to make the average particle size 2.0 μm, and then granulate with a spray dryer. Use a rotary kiln to pre-fire (the second time) the obtained granulated product at a temperature of 950 °C for 6 hours. Crush the obtained pre-fired product with a wet ball mill for 3 hours to make the average particle size 5.6 μm, and then granulate with a spray dryer. Fire the obtained granulated product in an electric furnace at a temperature of 1300 °C for 5 hours. Crush and classify the obtained fired product to obtain ferrite particles (1) with a volume average particle size of 32 μm.

[0232] - Ferrite particles (2)-

[0233] Use a wet ball mill to crush the pre-fired product after the second pre-firing for 2 hours to make the average particle size 6.5 μm, and change the formal firing conditions to a temperature of 1200 °C for 4 hours. Except for this, make ferrite particles (2) in the same way as the production of ferrite particles (1).

[0234] - Ferrite particles (3)-

[0235] Use a wet ball mill to crush the pre-fired product after the second pre-firing for 5 hours to make the average particle size 4.7 μm, and change the formal firing conditions to a temperature of 1350 °C for 5.5 hours. Except for this, make ferrite particles (3) in the same way as the production of ferrite particles (1).

[0236] Show the types of each core material, the volume average particle size, and the surface roughness of the core material in Table 1. The volume average particle size and surface roughness Ra (μm) of the core material are obtained by the above measurement methods.

[0237] [Table 1]

[0238]

[0239] [Preparation of Inorganic Particles]

[0240] Silica particles, titanium dioxide particles, and alumina particles use the materials shown below.

[0241] · Silica particles

[0242] Hydrophobizing agent: hexamethyldisilazane,

[0243] Volume average particle size D: 12 nm

[0244] Manufactured by Tokuyama Corporation, product number HM20S

[0245] · Silica particles

[0246] Hydrophobizing agent: Decylsilane

[0247] Volume average particle size D: 40 nm

[0248] Using the product numbered OX50 manufactured by NIPPON AEROSIL Co., Ltd., decylsilane treatment was carried out to produce silica particles.

[0249] · Silica particles

[0250] Hydrophobizing agent: None

[0251] Volume average particle size D: 40 nm

[0252] Manufactured by NIPPON AEROSIL Co., Ltd., product number OX50

[0253] · Silica particles

[0254] Hydrophobizing agent: Polydimethylsiloxane

[0255] Volume average particle size D: 40 nm

[0256] Manufactured by NIPPON AEROSIL Co., Ltd., product number RY50

[0257] · Silica particles

[0258] Hydrophobizing agent: Hexamethyldisilazane

[0259] Volume average particle size D: 200 nm

[0260] Manufactured by CABOT Corporation, product number TG-6020N

[0261] · Silica particles (Synthetic product 1 synthesized by the following synthetic method)

[0262] Hydrophobizing agent: Hexamethyldisilazane

[0263] Volume average particle size D: 7 nm

[0264] (Adjustment of silica particle dispersion liquid (1))

[0265] 890 parts of methanol and 210 parts of 9.8% ammonia water were added to a 1.5 L glass reaction vessel equipped with a stirrer, a dropping nozzle, and a thermometer and mixed to obtain an alkali catalyst solution.

[0266] After adjusting the alkali catalyst solution to 45°C, while stirring, 550 parts of tetramethoxysilane and 140 parts of 7.6% ammonia water were simultaneously added dropwise over 450 minutes to obtain a hydrophilic silica particle dispersion (1) with a particle size of 7 nm and a particle size distribution of 1.2.

[0267] (Production of surface-treated silica particles (S1))

[0268] Using the silica particle dispersion (1), the silica particles were surface-treated with a siloxane compound under a supercritical carbon dioxide atmosphere as follows. It should be noted that the surface treatment used a device equipped with a carbon dioxide cylinder, a carbon dioxide pump, an entrainer pump, a high-pressure autoclave (capacity 500 ml) with a stirrer, and a pressure valve.

[0269] First, 300 parts of the silica particle dispersion (1) were put into a high-pressure autoclave (capacity 500 ml) with a stirrer, and the stirrer was rotated at 100 rpm. Then, liquefied carbon dioxide was injected into the autoclave, and while heating with a heater and boosting the pressure with a carbon dioxide pump, the inside of the autoclave was brought to a supercritical state of 150°C and 15 MPa. The pressure inside the autoclave was maintained at 15 MPa using a pressure valve, and at the same time, supercritical carbon dioxide was circulated using a carbon dioxide pump to remove methanol and water from the silica particle dispersion (1) (solvent removal process) to obtain silica particles (untreated silica particles).

[0270] Next, at the moment when the flow rate of the circulated supercritical carbon dioxide (cumulative amount: measured as the flow rate of carbon dioxide in the standard state) reached 900 parts, the circulation of supercritical carbon dioxide was stopped.

[0271] After that, the temperature was maintained at 150°C using a heater, and the pressure was maintained at 15 MPa using a carbon dioxide pump. While maintaining the supercritical state of carbon dioxide inside the autoclave, 50 parts of hexamethyldisilazane (HMDS: manufactured by Organic Synthesis Chemical Industry Co., Ltd.), which is a hydrophobization treatment agent, were previously injected into the autoclave relative to 100 parts of the above silica particles (untreated silica particles) using an entrainer pump, and then the reaction was carried out at 180°C for 20 minutes while stirring. After that, supercritical carbon dioxide was circulated again to remove the remaining treatment agent solution. Then, the stirring was stopped, the pressure valve was opened, the pressure inside the autoclave was released to atmospheric pressure, and the temperature was lowered to room temperature (25°C).

[0272] In this way, the solvent removal process and the surface treatment with a siloxane compound were carried out in sequence to obtain surface-treated silica particles (S1) with a volume particle size of 7 nm.

[0273] · Silica particles (Synthetic product 2 synthesized by the synthesis method shown below)

[0274] Hydrophobizing agent: hexamethyldisilazane

[0275] Volume average particle size D: 1 nm

[0276] (Adjustment of silica particle dispersion (2))

[0277] Add 890 parts of methanol and 210 parts of 9.8% ammonia water to a 1.5 L glass reaction vessel equipped with a stirrer, a dropping nozzle, and a thermometer, and mix them to obtain an alkali catalyst solution.

[0278] After adjusting the alkali catalyst solution to 47°C, while stirring, simultaneously add dropwise 550 parts of tetramethoxysilane and 140 parts of 7.6% ammonia water over 450 minutes to obtain a hydrophilic silica particle dispersion (2) with a particle size of 1 nm and a particle size distribution of 1.25.

[0279] (Production of surface-treated silica particles (S2))

[0280] Using the silica particle dispersion (2), the silica particles are surface-treated with a siloxane compound in a supercritical carbon dioxide atmosphere as follows. It should be noted that the surface treatment uses a device equipped with a carbon dioxide cylinder, a carbon dioxide pump, an entrainer pump, a high-pressure autoclave (capacity 500 ml) with a stirrer, and a pressure valve.

[0281] First, put 300 parts of the silica particle dispersion (2) into a high-pressure autoclave (capacity 500 ml) with a stirrer, and rotate the stirrer at 100 rpm. Then, inject liquefied carbon dioxide into the high-pressure autoclave, heat it with a heater and increase the pressure with a carbon dioxide pump to make the inside of the high-pressure autoclave in a supercritical state of 150°C and 15 MPa. Keep the inside of the high-pressure autoclave at 15 MPa with a pressure valve, and at the same time circulate supercritical carbon dioxide with a carbon dioxide pump to remove methanol and water from the silica particle dispersion (2) (solvent removal process) to obtain silica particles (untreated silica particles).

[0282] Next, at the moment when the flow rate of the circulated supercritical carbon dioxide (cumulative amount: measured as the flow rate of carbon dioxide in the standard state) reaches 900 parts, stop the circulation of the supercritical carbon dioxide.

[0283] Thereafter, the temperature was maintained at 150 °C using a heater, and the pressure was maintained at 15 MPa using a carbon dioxide pump. While maintaining the supercritical state of carbon dioxide in the autoclave, 100 parts of hexamethyldisilazane (HMDS: manufactured by Organic Synthesis Chemical Industry Co., Ltd.), which is a hydrophobization treatment agent, was injected into the autoclave in advance relative to 100 parts of the above-mentioned silica particles (untreated silica particles). Thereafter, the reaction was carried out at 180 °C for 20 minutes while stirring. Thereafter, supercritical carbon dioxide was circulated again to remove the remaining treatment agent solution. Thereafter, the stirring was stopped, the pressure valve was opened, the pressure in the autoclave was released to atmospheric pressure, and the temperature was lowered to room temperature (25 °C).

[0284] In this way, the solvent removal process and the surface treatment using a siloxane compound were sequentially carried out to obtain surface-treated silica particles (S2) having a volume particle diameter of 1 nm.

[0285] · Titanium dioxide particles, hydrophobization treatment agent: isobutylsilane, volume average particle diameter D: 20 nm

[0286] Manufactured by Titan Kogyo, Ltd., product number STT100H

[0287] · Alumina particles, hydrophobization treatment agent: decylsilane, volume average particle diameter D: 13 nm

[0288] Manufactured by NIPPON AEROSIL Co., Ltd., product number C805

[0289] [Example 1]

[0290]

[0291]

[0292] In the above material, silica particles, cyclohexyl methacrylate / methyl methacrylate copolymer, toluene, and glass beads (diameter 1 mm, the same amount as toluene) were put into a sand mill (Kansai Paint Co., Ltd.) and stirred at a rotational speed of 1200 rpm for 30 minutes to prepare a solution (1) for forming a resin layer. Ferrite particles (1) were put into a vacuum degassing type kneader, and then the solution (1) for forming a resin layer was put in. While stirring, the temperature was raised and the pressure was reduced to distill off toluene, and the ferrite particles (1) were coated with resin. Next, fine powder and coarse powder were removed using an Elbow-Jet to obtain a carrier (1). The properties of the carrier (1) are shown in Table 2.

[0293] [Examples 2 to 25, Comparative Examples 1 to 6]

[0294] Change the types and amounts of the core material, inorganic particles, and resin; the thickness of the coating resin layer, D / T, D / Ra, the free rate, or the surface roughness of the carrier, and produce the carriers of each example in the same manner as the production of the carrier (1) except for these. The abbreviations in the table are as follows.

[0295] CHMA: Cyclohexyl methacrylate

[0296] MMA: Methyl methacrylate

[0297] DMAEMA: 2-(Dimethylamino)ethyl methacrylate

[0298] HMDS: Hexamethyldisilazane

[0299] PDMS: Polydimethylsiloxane (silicone oil)

[0300] [Table 2]

[0301]

[0302] <Initial concentration unevenness and blur evaluation>

[0303] Under the environment of 22.5°C and 50% RH, using a modified machine of DocuCentre Color 400 (manufactured by Fuji Xerox Co., Ltd.), and using A4-sized plain paper (manufactured by Fuji Xerox Co., Ltd., C2 paper), after conducting a test of continuously outputting 500 images with rectangular patches at an image density of 1%, change to the environment of 28°C and 90% RH, and then when running in the morning of the next day, output the Japan Society for Imaging Science and Technology Test Chart No. 5-1 to evaluate the image quality.

[0304] - Blur evaluation -

[0305] After continuous printing, in the morning of the day after changing to the environment of 28°C and 90% RH, output 5 sheets of the Japan Society for Imaging Science and Technology Test Chart No. 5-1, and conduct a visual sensory evaluation on the non-image part and the in-machine contamination after printing. A to C are acceptable.

[0306] A: No contamination of the non-image part is observed on the image, and the image quality is okay.

[0307] B: Toner scattering occurred in the machine, but the image quality is okay.

[0308] C: Slight contamination of the non-image part is observed on the image.

[0309] D: Clear contamination of the non-image part is observed on the image.

[0310] - Concentration unevenness evaluation -

[0311] Output five Japan Society of Radiological Technology test charts No. 5-1, and measure the density of the solid image patches. ΔE is calculated as follows. A to C are acceptable.

[0312] ΔE = (the maximum image density among the five images) - (the minimum image density among the five images)

[0313] It should be noted that the image density (=(L *2 +a *2 +b *2 ) 0.5 ) is measured using an image densitometer X-RITE938 (manufactured by X-RITE).

[0314] A: The density deviation ΔE on the image is less than 0.3, which cannot be visually judged, and the image quality is okay.

[0315] B: The density deviation ΔE on the image is 0.3 or more and 0.5 or less. There is a slight unevenness, but the image quality is at an acceptable level.

[0316] C: The density deviation ΔE on the image is 0.5 or more and 1.0 or less. Slight unevenness is observed.

[0317] D: The density deviation ΔE on the image is a value exceeding 1.0, and distinct density unevenness is observed on the image.

[0318] <Evaluation of density unevenness over time>

[0319] In an environment of 22.5°C and 50% RH, using a modified DocuCentreColor400 (manufactured by Fuji Xerox Co., Ltd.), and using A4-sized plain paper (manufactured by Fuji Xerox Co., Ltd., C2 paper), conduct a test of outputting 100,000 images with rectangular patches at an image density of 1% over a period of 10 days. After a total of 100,000 images are output, change to an environment of 28°C and 90% RH, and then when running in the morning of the next day, output the Japan Society of Radiological Technology test chart No. 5-1 and evaluate the image quality.

[0320] As shown in Table 2, it can be seen that compared with the carrier for electrostatic image development of the comparative example, the carrier for electrostatic image development of the example can suppress density unevenness of the image.

Claims

1. A carrier for electrostatic image development, comprising: A core material; and A coating resin layer containing inorganic particles and coating the core material, The content of the inorganic particles is 10% by mass or more and 60% by mass or less based on the total mass of the coating resin layer, The volume average particle diameter D of the inorganic particles and the thickness T of the coating resin layer satisfy the following relational expression (1), where The unit of the volume average particle diameter D is μm, and the unit of the thickness T is μm, Relationship (1) ··· 0.007 ≤ D / T ≤ 0.24, Using a drum mixer, 100 parts by mass of the carrier separated from an electrostatic image developer containing silica particles as an external additive and 10 parts by mass of a model toner are stirred at a temperature of 20°C for a stirring time of 2 minutes. When the obtained mixture is separated again into the carrier and the model toner through a wire gauge, the free rate of the silica particles from the surface of the carrier, that is, (S1 - S2) / S1 × 100 obtained from the coating rate S1 of the silica particles coating the surface of the carrier after being separated from the electrostatic image developer and before being mixed with the model toner and the coating rate S2 of the silica particles coating the surface of the carrier after being separated from the model toner, is 50% or more and 85% or less, The surface roughness Ra of the carrier exceeds 0.1 μm and is less than 0.9 μm, The volume average particle diameter D of the inorganic particles and the surface roughness Ra of the carrier satisfy the following relationship (2), where the unit of the volume average particle diameter D is μm and the unit of the surface roughness Ra is μm, Relationship (2) ··· 0.003 < D / Ra < 0.

50.

2. The carrier for electrostatic image development according to claim 1, wherein The volume average particle diameter D of the inorganic particles exceeds 1 nm and is 80 nm or less.

3. The carrier for electrostatic image development according to claim 1 or 2, wherein, The inorganic particles contain silica particles.

4. The carrier for electrostatic image development according to claim 3, wherein, The silica particles contain hydrophobized silica particles.

5. The carrier for electrostatic image development according to claim 4, wherein, The treatment agent for the hydrophobization treatment is at least one of hexamethyldisilazane HMDS and dimethylpolysiloxane PDMS.

6. The carrier for electrostatic image development according to claim 1 or 2, wherein, The coating resin layer contains an alicyclic (meth)acrylic resin.

7. The carrier for electrostatic image development according to claim 6, wherein, The alicyclic (meth)acrylic resin contains cyclohexyl (meth)acrylate as a polymerization component.

8. The carrier for electrostatic image development according to claim 1 or 2, wherein, The surface roughness Ra of the core material is 0.5 μm or more and 1.5 μm or less.

9. An electrostatic image developer, comprising an electrostatic image developing toner and the electrostatic image developing carrier according to any one of claims 1 to 8.

10. A processing cartridge that is a processing cartridge detachably installed in an image forming apparatus, the processing cartridge comprising: A developing unit that accommodates the electrostatic image developer according to claim 9 and develops an electrostatic image formed on the surface of an image holding body into a toner image.

Images