Two-component developer

Abstract

To provide a two-component developer capable of forming an image of high image quality throughout its life by maintaining high electrostatic charge even in the latter half of its life.SOLUTION: The two-component developer of the present disclosure contains toner in which an external additive is attached to a surface of a toner particle, and a carrier in which a surface of a carrier core material is coated with a coating layer. The toner particles have a glass transition point of 50°C or more and 65°C or less, and a softening point of 100°C or more and 120°C or less. A coverage of the surface of the toner particle with silica particles contained as the external additive is 90% or more. The coating layer has an inner layer and an outer layer. When the carrier core material, inner layer particles composed of the carrier core material and the inner layer, and the carrier are charged under the same conditions, a charge amount ratio B / C is 1.05 or more and 1.35 or less, and a charge amount ratio A / B is 0.75 or more and 0.95 or less, where A is a charge amount of the carrier core material, B is a charge amount of the inner layer particles, and C is a charge amount of the carrier.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to two-component developers. [Background technology]

[0002] Two-component developers containing toner with external additives attached to the surface of toner particles (toner cores) and carrier with a coating layer on the surface of a carrier core (carrier core) are widely used as developers for image forming devices such as electrophotographic copiers, multifunction machines, printers, and facsimile machines.

[0003] For example, Patent Document 1 discloses a carrier for developing electrostatic latent images, in which a first coating layer and a second coating layer are laminated in this order from the surface of a carrier core material having recesses on its surface. In this carrier for developing electrostatic latent images, a conductive material is added to at least the second coating layer, and the second coating layer is configured to have lower electrical resistance than the first coating layer. In addition, the first coating layer covers the entire surface of the carrier core material, and the second coating layer selectively covers areas of the carrier core material that correspond to the recesses on its surface. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2017-223858 Summary of the Invention [Problem to be solved by the invention]

[0005] With conventional two-component developers, when the temperature inside the developer tank rises due to factors such as continuous printing, the load on the developer increases, causing external additives to become embedded in the toner particle surface. This can lead to spent toner on the carrier surface, external additive contamination, and reduced developer fluidity. These effects ultimately lead to a decrease in the charge level of the two-component developer in the latter half of its lifespan, resulting in image defects (fog, toner scattering, toner dropping, etc.). This problem is particularly pronounced when low-melting-point toner (toner that can be fixed at low temperatures) is used to save energy.

[0006] The contents of the present disclosure have been discovered in view of such circumstances, and the main object is to provide a two-component developer that can maintain high charge even in the latter half of its life, thereby forming high-quality images throughout its life. [Means for solving the problem]

[0007] In order to solve the above problems, the two-component developer of the present disclosure comprises: A two-component developer containing a toner having an external additive attached to the surface of the toner particles and a carrier having a carrier core material whose surface is covered with a coating layer, The toner particles have a glass transition point of 50°C or more and 65°C or less and a softening point of 100°C or more and 120°C or less, the external additive contains silica particles, and the coverage of the surfaces of the toner particles with the silica particles is 90% or more; the coating layer has an inner layer and an outer layer in this order from the carrier core material side, When the carrier core material, the inner layer particles composed of the carrier core material and the inner layer, and the carrier are charged under the same conditions, the charge amount of the carrier core material is A, the charge amount of the inner layer particles is B, and the charge amount of the carrier is C. The charge amount ratio B / C is 1.05 or more and 1.35 or less, and the charge amount ratio A / B is 0.75 or more and 0.95 or less.

[0008] In the two-component developer, it is preferable that the adhesion strength of the silica particles to the toner particles is 50% or more and 80% or less.

[0009] In the two-component developer, the charge amount ratio A / C is preferably 0.85 or more and 1.25 or less.

[0010] In the two-component developer, the external additive preferably contains titanium oxide particles.

[0011] In addition, in the above two-component developer, the average primary particle diameter of the silica particles is 5 nm or more and 20 nm or less, The titanium oxide particles are titanium oxide particles or strontium titanate particles, and the specific surface area thereof is 60 m 2 / g or more 150m 2 / g or less, The content of the titanium oxide particles is preferably 0.1 parts by mass or more and 0.5 parts by mass or less with respect to 100 parts by mass of the toner particles.

[0012] In addition, in the above two-component developer, the titanium oxide particle aggregate is present at one or more per 100 toner particles, The particle size of the aggregates is preferably 0.5 μm or more and 1.0 μm or less.

[0013] In addition, in the above two-component developer, the coating amount of the coating layer is 20 parts by mass or more with respect to 100 parts by mass of the carrier core material, the coating amount of the outer layer is 13 parts by mass or more and 17 parts by mass or less with respect to 100 parts by mass of the carrier core material, The carrier core preferably has a shape factor SF1 of 120 or less and a shape factor SF2 of 150 or more.

[0014] In the two-component developer, the coating layer preferably contains a crosslinkable silicone resin.

[0015] In the two-component developer, the coating layer preferably contains a conductive material and a charge adjusting agent. [Effects of the Invention]

[0016] The two-component developer of the present disclosure provides excellent effects such as the ability to form high-quality images throughout its life. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a cross-sectional view schematically illustrating a configuration of a two-component developer according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, an embodiment of the two-component developer of the present disclosure will be described in detail. First, the characteristics of the two-component developer as a whole will be described, and then the configurations of the toner and carrier contained in the two-component developer will be described.

[0019] 1. Two-component developer As shown in FIG. 1, the two-component developer according to this embodiment is a two-component developer containing toner and carrier. The two-component developer can be produced by mixing the toner and carrier using a known mixer. The blending ratio of the toner and carrier is not particularly limited and can be appropriately selected depending on the types of toner and carrier. For example, the ratio of the toner to the total amount of developer may be 2% by mass or more and 20% by mass or less. Furthermore, the coverage of the carrier by the toner is preferably 40% by mass or more and 80% or less.

[0020] The two-component developer according to this embodiment is a two-component developer containing a toner having an external additive attached to the surface of the toner particles and a carrier having a carrier core material whose surface is covered with a coating layer, and satisfies the following requirements (A) to (D). (A) The toner particles have a glass transition point of 50°C or more and 65°C or less, and a softening point of 100°C or more and 120°C or less. (B) The external additive contains silica particles, and the coverage of the surfaces of the toner particles with the silica particles is 90% or more. (C) The coating layer has an inner layer and an outer layer in this order from the carrier core material side. (D) When the carrier core material, the inner layer particles composed of the carrier core material and the inner layer, and the carrier are charged under the same conditions, the charge amount of the carrier core material is A, the charge amount of the inner layer particles is B, and the charge amount of the carrier is C, and the charge amount ratio B / C is 1.05 or more and 1.35 or less, and the charge amount ratio A / B is 0.75 or more and 0.95 or less.

[0021] The two-component developer of this embodiment has an external additive adhered to toner particles with a low melting point as specified by requirement (A) above, which satisfies requirement (B), and also has a carrier charge design that satisfies requirements (C) and (D) above. This allows the developer to maintain a high charge even in the latter half of its life, and ultimately makes it possible to form high-quality images throughout its life.

[0022] 2. Career As shown in FIG. 1, the carrier according to this embodiment has a carrier core (carrier core) whose surface is covered with a coating layer, and the coating layer has an inner layer and an outer layer in this order from the carrier core side.

[0023] The carrier according to this embodiment is designed so that the carrier core has a higher chargeability than the outer layer, and the inner layer has a higher chargeability than the carrier core. The reason for this charge design is as follows.

[0024] In conventional two-component developers, as the life of the developer progresses, carrier spent and external additive contamination progress, resulting in a decrease in the carrier charge amount. Peeling of the carrier coating layer also progresses. On the other hand, in the two-component developer according to the present embodiment, as the life of the developer progresses and the outer layer peels off, the inner layer, which has high chargeability, is exposed on the carrier surface, thereby increasing the carrier charge amount. Therefore, the combination of the decrease in carrier charge amount caused by the progression of carrier spent and external additive contamination and the increase in carrier charge amount caused by the exposure of the inner layer on the carrier surface makes it possible to maintain a constant carrier charge amount throughout the developer's life. In other words, a high charge can be maintained even in the latter half of the developer's life, and ultimately, high-quality images can be formed throughout the developer's life.

[0025] Furthermore, if the chargeability of the carrier core material is too high, there is a problem that carrier lift-up occurs significantly when the carrier core material is exposed. However, by controlling the chargeability of the carrier core material to a level lower than that of the outer layer, carrier lift-up can be suppressed.

[0026] Specifically, when the carrier core material, inner layer particles composed of the carrier core material and inner layer, and carrier are charged under the same conditions, the charge amount of the carrier core material is A, the charge amount of the inner layer particles is B, and the charge amount of the carrier is C. The charge amount ratio B / C is 1.05 to 1.35, and A / B is 0.75 to 0.95. Having the charge amount ratio within the above ranges allows high charge to be maintained even in the latter half of the product's life, and ultimately enables the formation of high-quality images throughout the product's life. It is more preferable that the charge amount ratio B / C is 1.1 to 1.3, and it is more preferable that A / B is 0.8 to 0.9.

[0027] In the carrier according to the present embodiment, the charge ratio A / C is preferably 0.9 to 1.2, more preferably 0.95 to 1.1. By keeping the charge ratio A / C within the above range, it is possible to suppress carrier lift and maintain a high charge even in the latter half of the carrier life.

[0028] The coating amount of the coating layer is preferably 20 parts by mass or more, more preferably 20 to 25 parts by mass, per 100 parts by mass of the carrier core material. If the coating amount of the coating layer is less than the above lower limit, the carrier may not have a sufficiently long life. The coating amount of the outer layer is preferably 13 to 17 parts by mass, more preferably 14 to 16 parts by mass, per 100 parts by mass of the carrier core material. When the coating amount of the outer layer is within the above range, it becomes easier to maintain a constant charge amount throughout the carrier's life. If the coating amount of the outer layer is outside the above range, the charge amount may decrease compared to the initial stage of use due to the influence of spent toner, or the charge amount may increase compared to the initial stage of use due to peeling of the coating layer.

[0029] The shape factor SF1 of the carrier core material is preferably 120 or less, and more preferably 115 or less. Furthermore, the shape factor SF2 of the carrier core material is preferably 150 or more, and more preferably 155 or more. The shape factor SF1 indicates the degree of roundness of the particle, and the shape factor SF2 indicates the degree of irregularity of the particle. As the particle becomes less spherical, the value of SF1 increases. As the irregularity of the particle surface becomes more pronounced, the value of SF2 increases. Therefore, carrier core materials with shape factors SF1 and SF2 within the above ranges have a shape that has irregularities on the surface but high sphericity. Carrier core materials with such shapes allow for uniform peeling of the coating layer and improve the fluidity of the developer, thereby extending the carrier's lifespan.

[0030] The volume average particle diameter of the carrier is not particularly limited, but from the viewpoint of achieving high image quality, it is preferably 20 μm or more and 100 μm or less, and more preferably 30 μm or more and 60 μm or less. If the volume average particle diameter of the carrier is too small, the carrier may move from the developing roller to the photosensitive drum during development, causing white spots in the resulting image. If the volume average particle diameter of the carrier is too large, dot reproducibility may deteriorate, resulting in a coarse image.

[0031] The carrier's magnetization strength (maximum magnetization) is preferably 10 emu / g or more and 60 emu / g or less, more preferably 15 emu / g or more and 40 emu / g or less. Under the magnetic flux density conditions of a typical developing roller, if the magnetization strength is less than 10 emu / g, the magnetic binding force will not work, which may cause carrier scattering. Furthermore, if the magnetization strength exceeds 60 emu / g, in non-contact development, the carrier will become too stiff, making it difficult to maintain a non-contact state between the image carrier and the toner, and in contact development, sweeping marks may easily appear in the toner image.

[0032] As the carrier core material, those commonly used in the art can be used, such as simple or composite ferrite particles made of iron, copper, zinc, nickel, cobalt, manganese, chromium, etc.

[0033] The coating layer may be made of any material commonly used in the art, such as polytetrafluoroethylene, monochlorotrifluoroethylene polymer, polyvinylidene fluoride, silicone resin, polyester resin, metal compound of di-tert-butyl salicylic acid, styrene resin, acrylic resin, polyamide, polyvinyl butyral, nigrosine, aminoacrylate resin, basic dye, lake of basic dye, silica fine powder, alumina fine powder, etc. Among these, silicone resin is preferred. The use of silicone resin improves the releasability of the toner from the carrier during development, resulting in good developability. In addition, the coating layer can be made to have the desired hardness and can further improve adhesion to the carrier core material.

[0034] Among silicone resins, crosslinkable silicone resins are more preferred as the resin constituting the coating layer. The inclusion of a crosslinkable silicone resin further improves the releasability of the toner from the carrier during development, resulting in better developability. Furthermore, the coating layer can be given a desired hardness, and adhesion to the carrier core material can be further improved. Crosslinkable silicone resins are silicone resins cured by crosslinking between hydroxyl groups bonded to Si atoms, or between hydroxyl groups and -OX groups, via a thermal dehydration reaction, room temperature curing reaction, or the like, as shown in the following formula. In the following formula, R represents a monovalent organic group, and multiple Rs may be the same or different. The -OX group is an acetoxy group, an aminoxy group, an alkoxy group, an oxime group, or the like.

[0035] [ka]

[0036] The crosslinkable silicone resin is not particularly limited, and either a heat-curable silicone resin or a room-temperature-curable silicone resin can be used. To crosslink a heat-curable silicone resin, the resin must be heated to about 200°C to 250°C. To cure a room-temperature-curable silicone resin, heating is not required, but heating to 150°C to 280°C is preferred to shorten the curing time.

[0037] The inner layer and the outer layer of the coating layer according to the present embodiment preferably contain the same resin. By containing the same resin, the interface between the inner layer and the outer layer is less likely to peel off, and the adhesion between the two layers is improved.

[0038] A conductive material can be added to the coating layer. Examples of conductive materials include silicon oxide, alumina, carbon black, graphite, zinc oxide, titanium black, iron oxide, titanium oxide, tin oxide, potassium titanate, calcium titanate, aluminum borate, magnesium oxide, barium sulfate, and calcium carbonate. These conductive materials may be used alone or in combination. Among these conductive materials, carbon black is preferred from the viewpoints of production stability, cost, and low electrical resistance. The type of carbon black is not particularly limited, but carbon black having a DBP (dibutyl phthalate) oil absorption of 90 ml / 100 g or more and 170 ml / 100 g or less is preferred from the viewpoint of excellent production stability. Carbon black having an average primary particle diameter of 50 nm or less is also preferred from the viewpoint of excellent dispersibility.

[0039] Furthermore, the coating layer may contain a charge adjusting agent such as a silane coupling agent for the purpose of adjusting the charge amount. Among silane coupling agents, silane coupling agents having an electron-donating functional group are preferred, and examples thereof include amino group-containing silane coupling agents represented by the following formula (1): (Y) n Si(R) m ···(1) (In the formula, R may be the same or different and represent an alkyl group, an alkoxy group, or a chlorine atom; Y may be the same or different and represent a saturated hydrocarbon and / or aromatic hydrocarbon group containing an amino group; m and n each represent an integer of 1 to 3, and m+n=4.)

[0040] In the above formula (1), examples of the alkyl group represented by R include linear or branched alkyl groups having 1 to 4 carbon atoms, such as a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, and a tert-butyl group, and among these, a methyl group is preferred.

[0041] In the above formula (1), examples of the alkoxy group represented by R include linear or branched alkoxy groups having 1 to 4 carbon atoms, such as methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, and tert-butoxy groups, and among these, methoxy and ethoxy groups are preferred.

[0042] In the above formula (1), examples of the saturated hydrocarbon and / or aromatic hydrocarbon group containing an amino group represented by Y include -(CH2) a -X (wherein X represents an amino group, an aminocarbonylamino group, an aminoalkylamino group, a phenylamino group, or a dialkylamino group, and a represents an integer of 1 to 4), -Ph-X (wherein X is the same as above, and -Ph- represents a phenylene group), and the like.

[0043] Specific examples of the amino group-containing silane coupling agent include the following: H2N(H2C)3Si(OCH3)3 H2N(H2C)3Si(OC2H5)3 H2N(H3C)3Si(CH3)(OCH3)2 H2N(H2C)2HN(H2C)3Si(CH3)(OCH3)2 H2NOCHN(H2C)3Si(OC2H5)3 H2N(H2C)2HN(H2C)3Si(OCH3)3 H2N-Ph-Si(OCH3)3 (wherein -Ph- represents a p-phenylene group) Ph-HN(H2C)3Si(OCH3)3 (where Ph- represents a phenyl group) (H9C4)3N(H2C)3Si(OCH3)3

[0044] The coupling agent may be used alone or in combination of two or more. The amount of the coupling agent is appropriately selected from a range that provides a sufficient charge to the toner and does not significantly reduce the mechanical strength of the coating layer, and is, for example, preferably 10 parts by mass or less, more preferably 0.01 to 10 parts by mass, per 100 parts by mass of the resin used to form the coating layer.

[0045] Known methods can be used to form the coating layer. Examples include an immersion method in which the raw materials for the coating layer are dissolved in a solvent (e.g., an organic solvent such as toluene or acetone) and the carrier core material is immersed in the resulting solution; a spray method in which the raw material solution for the coating layer is sprayed onto the carrier core material; a fluidized bed method in which the raw material solution for the coating layer is sprayed onto the carrier core material while suspended in flowing air; and a kneader coater method in which the raw material solution for the carrier core material and the raw material solution for the coating layer are mixed in a kneader coater and the solvent is removed. When the coating layer contains a conductive material, it can be formed by adding the conductive material together with the resin to the raw material solution for the coating layer.

[0046] By forming an inner layer using the above method and then forming an outer layer using the same method, it is possible to form an inner layer and an outer layer (two-layer coating). By allowing the curing reaction to proceed during the coating process, independent coating layers can be formed, and by suppressing the progress of the curing reaction, the change between layers can be made continuous. The curing reaction can be controlled by the temperature during the coating process; for example, the coating process can be performed at about 50°C to 250°C.

[0047] 3. Toner The toner contained in the two-component developer according to the present embodiment has an external additive attached to the surface of the toner particle (toner core), as shown in FIG. 1 . The toner particles according to the present embodiment are composed of a binder resin and an internal additive, and the internal additive is dispersed in the binder resin. Examples of the internal additive include a colorant, a release agent, and a charge control agent. If necessary, optional components may also be contained within a range that does not impair the effects of the present disclosure. The volume average particle diameter of the toner particles can be appropriately selected depending on the purpose, and examples include small particle diameter toners of 5.0 μm to 8.0 μm. With such small particle diameter toners, the problems of "spent on the carrier surface, external additive contamination, and reduced developer fluidity" and the resulting "decrease in charge amount at the end of the life of the two-component developer" become more pronounced. However, the two-component developer according to the present embodiment can maintain a high charge even in the latter half of its life, thereby enabling the formation of high-quality images throughout its life.

[0048] The toner particles according to this embodiment have a glass transition point of 50°C or higher and 65°C or lower, and a softening temperature of 100°C or higher and 120°C or lower. When the glass transition point and softening point of the toner particles are within the above ranges, both low-temperature fixability and heat-resistant storage stability can be achieved. The toner particles according to this embodiment more preferably have a glass transition point of 55°C or higher and 60°C or lower, and a softening point of 105°C or higher and 115°C or lower.

[0049] <Binder resin> The binder resin contained in the toner particles according to this embodiment is not particularly limited, and resins used in the field of electrophotography can be used, such as polyester resins, polystyrene resins such as styrene-acrylic resins, (meth)acrylic acid ester resins, polyolefin resins, polyurethane resins, and epoxy resins. These resins may be used alone or in combination of two or more. Among these, polystyrene resins and polyester resins are preferred, and polyester resins are particularly preferred.

[0050] The polystyrene resin is preferably a styrene-acrylic resin (styrene-acrylic copolymer resin), and examples of styrene monomers that can be used as resin raw materials include styrene derivatives such as styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-ethylstyrene, and 2,4-dimethylstyrene. Examples of acrylic monomers include acrylic acid derivatives and methacrylic acid derivatives such as acrylic acid, methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, propyl acrylate, octyl acrylate, 2-chloroethyl acrylate, phenyl acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, phenyl methacrylate, and dimethylamino methacrylate.

[0051] Furthermore, vinyl monomers such as maleic anhydride, maleic acid monomethyl ester, maleic acid monoethyl ester, maleic acid monophenyl ester, maleic acid monoallyl ester, and divinylbenzene may be used as resin raw materials.

[0052] The polyester resin used in the binder resin is usually obtained by polycondensation reaction of one or more selected from dihydric alcohol components and trihydric or higher polyhydric alcohol components with one or more selected from dicarboxylic acids and trihydric or higher polycarboxylic acids via an esterification reaction or an ester exchange reaction by a known method.

[0053] The conditions for the polycondensation reaction may be appropriately set depending on the reactivity of the monomer components, and the reaction may be terminated when the polymer has reached the desired physical properties. For example, the reaction temperature is about 170°C to 250°C, and the reaction pressure is about 5 mmHg to atmospheric pressure.

[0054] Examples of the dihydric alcohol component include alkylene oxide adducts of bisphenol A such as polyoxypropylene(2.2)-2,2-bis(4-hydroxyphenyl)propane, polyoxypropylene(3.3)-2,2-bis(4-hydroxyphenyl)propane, polyoxypropylene(2.0)-2,2-bis(4-hydroxyphenyl)propane, polyoxypropylene(2.0)-polyoxyethylene(2.0)-2,2-bis(4-hydroxyphenyl)propane, and polyoxypropylene(6)-2,2-bis(4-hydroxyphenyl)propane; ethylene glycol Examples of suitable bisphenol A include diols such as glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1,4-butenediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol; bisphenol A; propylene adducts of bisphenol A; ethylene adducts of bisphenol A; and hydrogenated bisphenol A.

[0055] Examples of trihydric or higher polyhydric alcohol components include sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, sucrose (cane sugar), 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, and 1,3,5-trihydroxymethylbenzene.

[0056] In the toner particles according to this embodiment, one of the dihydric alcohol components and trihydric or higher polyhydric alcohol components may be used alone, or two or more of them may be used in combination.

[0057] Examples of divalent carboxylic acids include maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, malonic acid, n-dodecenylsuccinic acid, n-dodecylsuccinic acid, n-octylsuccinic acid, isooctenylsuccinic acid, isooctylsuccinic acid, and acid anhydrides and lower alkyl esters thereof.

[0058] Examples of trivalent or higher polyvalent carboxylic acids include 1,2,4-benzenetricarboxylic acid, 1,2,5-benzenetricarboxylic acid, 2,5,7-naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane, 1,2,4-cyclohexanetricarboxylic acid, tetra(methylenecarboxyl)methane, 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, empol trimer acid, and acid anhydrides and lower alkyl esters thereof.

[0059] In the toner particles according to this exemplary embodiment, one of the dicarboxylic acids and tricarboxylic or higher polycarboxylic acids may be used alone, or two or more of them may be used in combination.

[0060] The weight-average molecular weight of the polyester resin is preferably 3,000 or more and 50,000 or less. If the weight-average molecular weight is less than the lower limit, the peelability may be poor on the high-temperature side of the fixable region (non-offset region). On the other hand, if the weight-average molecular weight exceeds the upper limit, the low-temperature fixability may be poor.

[0061] The polyester resin preferably has an acid value of 5 mgKOH / g or more and 30 mgKOH / g or less. If the acid value is less than the lower limit, the chargeability of the polyester resin decreases, and the charge control agent becomes difficult to disperse in the polyester resin, which may adversely affect the charge buildup and charge stability during continuous printing. On the other hand, if the acid value exceeds the upper limit, the hygroscopicity increases, which may cause the chargeability to become unstable.

[0062] <Coloring agent> The toner particles according to this embodiment may contain a colorant, which may be any of various types and colors of organic or inorganic pigments and dyes commonly used in the field of electrophotography, such as black, white, yellow, orange, red, purple, blue, and green colorants.

[0063] Examples of black colorants include carbon black, copper oxide, manganese dioxide, aniline black, activated carbon, non-magnetic ferrite, magnetic ferrite, and magnetite.

[0064] Examples of white colorants include zinc oxide, titanium oxide, antimony white, and zinc sulfide.

[0065] Examples of yellow colorants include yellow lead, zinc yellow, cadmium yellow, yellow iron oxide, mineral fast yellow, nickel titanium yellow, navel yellow, naphthol yellow S, Hansa yellow G, Hansa yellow 10G, benzidine yellow G, benzidine yellow GR, quinoline yellow lake, permanent yellow NCG, tartrazine lake, CI pigment yellow 12, CI pigment yellow 13, CI pigment yellow 14, CI pigment yellow 15, CI pigment yellow 17, CI pigment yellow 93, CI pigment yellow 94, and CI pigment yellow 138.

[0066] Examples of orange colorants include red lead yellow, molybdenum orange, permanent orange GTR, pyrazolone orange, vulcan orange, induthrene brilliant orange RK, benzidine orange G, induthrene brilliant orange GK, CI pigment orange 31, and CI pigment orange 43.

[0067] Examples of red colorants include red iron oxide, cadmium red, red lead, mercury sulfide, cadmium, permanent red 4R, lithol red, pyrazolone red, watching red, calcium salt, lake red C, lake red D, brilliant carmine 6B, eosin lake, rhodamine lake B, alizarin lake, brilliant carmine 3B, CI pigment red 2, CI pigment red 3, CI pigment red 5, CI pigment red 6, CI pigment red 7, CI pigment red 8, CI pigment red 9, CI pigment red 10, CI pigment red 11, CI pigment red 12, CI pigment red 13, CI pigment red 14, CI pigment red 15, CI pigment red 16, CI pigment red 17, CI pigment red 18, CI pigment red 19, CI pigment red 20, CI pigment red 21, CI pigment red 22, CI pigment red 23, CI pigment red 24, CI pigment red 25, CI pigment red 26, CI pigment red 27, CI pigment red 28, CI pigment red 29 ... Examples of pigments that can be used include CI Pigment Red 7, CI Pigment Red 15, CI Pigment Red 16, CI Pigment Red 48:1, CI Pigment Red 53:1, CI Pigment Red 57:1, CI Pigment Red 122, CI Pigment Red 123, CI Pigment Red 139, CI Pigment Red 144, CI Pigment Red 149, CI Pigment Red 166, CI Pigment Red 177, CI Pigment Red 178, and CI Pigment Red 222.

[0068] Examples of purple colorants include manganese violet, fast violet B, and methyl violet lake.

[0069] Examples of blue colorants include Prussian blue, cobalt blue, alkali blue lake, Victoria blue lake, phthalocyanine blue, metal-free phthalocyanine blue, partially chlorinated phthalocyanine blue, fast sky blue, indanthrene blue BC, CI pigment blue 15, CI pigment blue 15:2, CI pigment blue 15:3, CI pigment blue 16, and CI pigment blue 60.

[0070] Examples of green colorants include chrome green, chromium oxide, pigment green B, micalite green lake, final yellow green G, and CI pigment green 7.

[0071] In the toner according to the present embodiment, the above colorants may be used alone or in combination of two or more, and the combination may be of different colors or the same color. The content of the colorant in the toner particles is preferably 0.1% by mass or more and 20% by mass or less, and more preferably 3% by mass or more and 15% by mass or less.

[0072] <Release agent> The toner particles according to this embodiment may contain a release agent. Examples of the release agent include waxes commonly used in the electrophotography field. Examples include petroleum-based waxes such as paraffin wax and its derivatives, microcrystalline wax and its derivatives; hydrocarbon-based synthetic waxes such as Fischer-Tropsch wax and its derivatives, polyolefin wax and its derivatives, polypropylene wax and its derivatives, polyolefin polymer wax (e.g., low-molecular-weight polyethylene wax) and its derivatives; plant-based waxes such as carnauba wax and its derivatives, rice wax and its derivatives, candelilla wax and its derivatives, and Japan wax; animal-based waxes such as beeswax and spermaceti; oil-based synthetic waxes such as fatty acid amides, phenol fatty acid esters, and their derivatives; silicone polymers, higher fatty acids, and the like. These may be used alone or in combination. Derivatives include oxides, block copolymers of vinyl monomers and waxes, and graft-modified products of vinyl monomers and waxes.

[0073] The content of the release agent in the toner particles according to this exemplary embodiment is preferably 0.5% by mass or more and 10% by mass or less.

[0074] <Other internal additives> The toner according to this embodiment may contain internal additives other than those described above, if necessary. Examples of internal additives other than those described above include charge control agents. Charge control agents are added to impart desirable chargeability to the toner.

[0075] The charge control agent is added to impart a desirable chargeability to the toner. There are no particular limitations on the charge control agent, and charge control agents for positive charge control and negative charge control used in the electrophotography field can be used.

[0076] Examples of charge control agents for controlling positive charges include quaternary ammonium salts, pyrimidine compounds, triphenylmethane derivatives, guanidine salts, and amidine salts.

[0077] Charge control agents for negative charge control include metal-containing azo compounds, azo complex dyes, metal complexes and metal salts of salicylic acid and its derivatives (metals include chromium, zinc, zirconium, etc.), organic bentonite compounds, and boron compounds.

[0078] <External additives> -Silica particles- The external additive in the toner according to this embodiment contains silica particles, and the silica particles provide a surface coverage of 90% or more of the toner particles. That is, in the production of the toner according to this embodiment, silica particles are added as an external additive in an amount that provides a surface coverage of 90% or more of the toner particles. Low-melting point toners have the problem of blocking when the temperature inside the developer tank rises. This problem becomes more pronounced when continuous printing or double-sided printing is performed due to the increased load inside the developer tank and the increased temperature inside the machine. However, by providing a surface coverage of silica particles within the above range, the toner can maintain its fluidity even when subjected to a load. In the toner according to this embodiment, the surface coverage of silica particles as an external additive is more preferably 95% or more.

[0079] In this embodiment, the adhesion strength of silica particles to toner particles is preferably 50% or more and 80% or less, and more preferably 65% ​​or more and 75% or less. A high coverage of the toner particle surface with silica particles can lead to the problem of external additive contamination of the carrier. However, by keeping the adhesion strength within the above range, external additive contamination of the carrier can be suppressed. If the adhesion strength exceeds the above upper limit, the silica particles are likely to be embedded in the toner particles, which can reduce the fluidity of the toner and make blocking more likely to occur. If the adhesion strength is below the above lower limit, the toner fluidity is high, but the silica particles are likely to detach, making external additive contamination more likely to occur.

[0080] In this embodiment, the average primary particle diameter of the silica particles as an external additive is preferably 5 nm or more and 20 nm or less, and more preferably 7 nm or more and 15 nm or less. If the average primary particle diameter of the silica particles exceeds the above upper limit, the silica particles are likely to detach from the toner particle surface, which may cause external additive contamination of the carrier. If the average primary particle diameter of the silica particles is less than the above lower limit, the silica particles may become embedded in the toner particles as the life progresses, which may reduce the fluidity of the toner and ultimately reduce the chargeability of the developer.

[0081] Examples of silica particles used as external additives include silica particles commonly used in the art, such as fumed silica obtained by burning silicon tetrachloride and dry-process silica particles such as arc-process silica, in which silica is atomized in the gas phase using high energy such as plasma; wet-process silica particles such as precipitation-process silica synthesized under alkaline conditions using an aqueous sodium silicate solution as a raw material and gel-process silica synthesized under acidic conditions; colloidal silica particles obtained by polymerizing acidic silicic acid in an alkaline state; and sol-gel-process silica particles obtained by hydrolysis of an organic silane compound. To improve the electrical properties of the photoreceptor, the surface may be hydrophobized with a hydrophobizing agent such as a silane coupling agent. Examples of silane coupling agents used for hydrophobizing the silica particle surface include hexamethyldisilazane (HMDS), dimethyldichlorosilane (DDS), octylsilane (OTAS), and polydimethylsiloxane (PDMS).

[0082] As the silica particles used as the external additive, commercially available hydrophobized silica particles may be used, or silica particles that have not been hydrophobized may be used after being subjected to a treatment.

[0083] -Titanium oxide particles- The external additive of the toner according to this embodiment preferably contains titanium oxide particles. This can improve the charge buildup of the toner and provide a leak effect. Titanium oxide particles or strontium titanate particles are preferred as the titanium oxide particles used as the external additive.

[0084] The titanium oxide particles may be anatase-type titanium oxide particles or rutile-type titanium oxide particles. Rutile-type titanium oxide particles can be produced, for example, by the method described in JP 2001-26423 A, i.e., by hydrolyzing an aqueous titanium tetrachloride solution to prepare a fine titania sol having rutile nuclei, separating the sol, and then heat-treating it to obtain titanium oxide particles. An anatase-type titanium oxide particle can be produced, for example, by the method described in JP 2000-10335 A, i.e., by hydrolyzing and granulating a solution obtained by dissolving raw materials such as ilmenite ore in sulfuric acid, followed by drying and high-temperature calcination to obtain titanium oxide particles.

[0085] The surfaces of titanium oxide particles may be hydrophobized. For example, a method of hydrophobizing the titanium oxide particles by reacting a hydrophobizing agent with the surface of the titanium oxide particles can be used. Specifically, titanium oxide particles are placed in a four-neck flask equipped with a stirrer and a thermometer and fitted with inlet tubes for introducing the hydrophobizing agent and an inert gas such as nitrogen gas. While stirring to maintain the temperature at 120°C to 350°C, the hydrophobizing agent and the inert gas are introduced, and the reaction is allowed to proceed for a predetermined period of time (e.g., 2 to 8 hours). Examples of hydrophobizing agents that can be used include silane coupling agents such as hexamethyldisilazane, methyltrimethoxysilane, dimethyldimethoxysilane, and trimethylchlorosilane, as well as silicone oil and silicone varnish. Hexamethyldisilazane is preferred. Furthermore, the hydrophobized titanium oxide particles preferably have a hydrophobicity of 95% or more and 100% or less. Titanium oxide particles that have been hydrophobized with hexamethyldisilazane and have a hydrophobicity of 95% or more and 100% or less are less likely to be fixed to the surface of the developing roller.Furthermore, it is preferable that the hydrophobized titanium oxide particles have a loss on drying of 0.8% by mass or less.

[0086] Strontium titanate particles can be produced, for example, by a normal pressure heating reaction method. When producing by the normal pressure heating reaction method, a mineral acid peptized product of a titanium compound hydrolyzate is used as the titanium oxide source, and a water-soluble acidic metal compound is used as the metal source other than titanium. For example, strontium nitrate or hydrochloride can be used as the strontium source. The nitrate salt includes strontium nitrate, and the hydrochloride salt includes strontium chloride. Strontium titanate particles can be produced by adding an aqueous alkaline solution to a mixture of these raw materials at 60°C or higher, reacting them, and then treating them with an acid. The strontium titanate particles obtained in this manner have a perovskite crystal structure, which is advantageous in that they have increased stability of charge to environmental changes.

[0087] The surfaces of the strontium titanate particles may be subjected to a hydrophobic treatment, and the hydrophobic treatment method can be a method of reacting a hydrophobic agent with the surface of the strontium titanate, similar to the method for the titanium oxide particles described above.

[0088] Titanium oxide particles as an external additive have a specific surface area of ​​60m 2 / g or more 150m 2 / g or less, and 2 / g or more 120m 2 / g or less is more preferable. When the specific surface area of ​​the titanium oxide particles is within the above range, the charge build-up of the toner is further improved. If the specific surface area of ​​the titanium oxide particles is below the above lower limit, the titanium oxide particles are large and may not adhere well to the toner particles. If the specific surface area of ​​the titanium oxide particles is above the above upper limit, the titanium oxide particles are small and may reduce the dispersibility of the toner.

[0089] The content of titanium oxide particles as an external additive is preferably 0.1 to 0.5 parts by mass, more preferably 0.2 to 0.4 parts by mass, per 100 parts by mass of toner particles. If the content of titanium oxide particles exceeds the upper limit, the leakage effect may become too large, resulting in a lower than appropriate charge amount. If the content of titanium oxide particles is less than the lower limit, the leakage effect may become insufficient, resulting in a higher than appropriate charge amount.

[0090] Preferably, titanium oxide particle aggregates are present on the surface of the toner particles according to this embodiment, and more preferably, one or more titanium oxide particle aggregates are present per 100 toner particles. The presence of titanium oxide particle aggregates on the surface of the toner particles allows for an appropriate leakage of carrier charge when a large number of sheets are continuously printed. Preferably, several titanium oxide particle aggregates are present per 100 toner particles, and specifically, one to five aggregates per 100 toner particles.

[0091] The particle size of the titanium oxide particle aggregates is preferably 0.5 μm to 1.0 μm, more preferably 0.6 μm to 0.9 μm. If the titanium oxide particle aggregates are not present on the toner particle surface or if the particle size of the aggregates is below the lower limit, the leak effect is insufficient, and developability may not be maintained. If the particle size of the aggregates exceeds the upper limit, the photosensitive drum may be damaged, resulting in poor images.

[0092] <Toner manufacturing method> Methods for producing toner particles include dry methods and wet methods. Dry methods include a kneading and pulverizing method, and wet methods include a suspension polymerization method, an emulsion aggregation method, a dispersion polymerization method, a solution suspension method, a melt emulsification method, etc. A method for producing toner particles by a kneading and pulverizing method will be described below.

[0093] In the production of toner particles by the pulverization method, raw materials for toner particles, including a binder resin and an internal additive, are dry-mixed in a mixer, and then melt-kneaded in a kneader to obtain a molten mixture. The molten mixture is then cooled and solidified to obtain a solid, which is then pulverized in a pulverizer to obtain a finely pulverized product. The pulverized product is then subjected to particle size adjustment, such as classification, as necessary, to obtain toner particles.

[0094] Known mixers, kneaders, pulverizers, and classifiers can be used. Examples of mixers include a Henschel Mixer (trade name, manufactured by Nippon Coke and Engineering Co., Ltd.) and a Super Mixer (trade name, manufactured by Kawata Corporation). Examples of kneaders include single- or twin-screw extruders such as PCM-65 / 87 and PCM-30 (both trade names, manufactured by Ikegai Corporation), and open-roll kneaders such as Kneadex (trade name, manufactured by Nippon Coke and Engineering Co., Ltd.). Examples of pulverizers include pulverizers that utilize a supersonic jet stream, such as Counter Jet Mill AFG (trade name, manufactured by Hosokawa Micron Corporation). Examples of classifiers include rotary classifiers such as TSP Separator (trade name, manufactured by Hosokawa Micron Corporation). [Example]

[0095] The two-component developer of the present disclosure will be specifically described below based on examples and comparative examples. First, various measurement methods and evaluation methods will be described.

[0096] 1. Measurement and evaluation methods <Method for measuring the glass transition temperature of toner particles> A DSC curve was measured by heating 1 g of the sample to be measured at a heating rate of 10°C / min using a differential scanning calorimeter (Seiko Instruments Inc., Model: DSC220) in accordance with JIS (Japanese Industrial Standards) K7121-1987. In the obtained DSC curve, the glass transition point (Tg, unit: °C) was determined as the temperature at the intersection of a straight line extending the high-temperature side baseline of the endothermic peak corresponding to the glass transition toward the low-temperature side and a tangent drawn from the rising part of the peak to the apex of the curve at the point where the gradient is maximum.

[0097] <Method for measuring the softening point of toner particles> Using a flow property evaluation device (Shimadzu Corporation, Model: Flow Tester CFT-100C), 1 g of the sample to be measured was heated at a temperature increase rate of 6°C / min while applying a load of 20 kgf / cm 2 (9.8×10 5 A pressure of 1 Pa was applied, and the sample was allowed to flow out of the die (nozzle diameter 1 mm, length 1 mm). The temperature at which the sample started to flow out was taken as the flow-out initiation temperature (Tfb, unit: °C), and the temperature at which half of the sample had flowed out was taken as the softening point (Tm, unit: °C).

[0098] <Method for measuring the volume average particle size of toner particles> 20 mg of the sample to be measured and 1 mL of sodium alkyl ether sulfate were added to 50 mL of electrolyte (manufactured by Beckman Coulter, Inc., product name: ISOTON-II), and the mixture was dispersed for 3 minutes at a frequency of 20 kHz using an ultrasonic disperser (manufactured by AS ONE Corporation, model: tabletop dual-frequency ultrasonic cleaner VS-D100) to prepare a dispersion for measurement.

[0099] The volumetric particle size distribution of the sample particles was measured using a particle size distribution analyzer (Beckman Coulter, Inc., Model: Multisizer 3) under the conditions of an aperture diameter of 100 μm and a particle count of 50,000. The volume average particle diameter [μm] was calculated from this volumetric particle size distribution.

[0100] <Method for measuring the average primary particle size of external additives> Using a scanning transmission electron microscope (Hitachi High-Technologies Corporation, model: S-4800), 100 external additive particles were photographed at a magnification of 50,000 times while changing the field of view, and the particle size of each primary particle was measured by image analysis. The average primary particle size of the external additive was calculated based on the measured values ​​of the 100 particles obtained.

[0101] <Method for measuring the coverage rate of external additives on the toner particle surface> The coverage rate of the toner particle surface with the external additive represents the ratio of the area of ​​the external additive present on the toner particle surface to the surface area of ​​the toner particle, and was calculated using the following formula. f[%]=(√3·D·ρt·C) / (2π·d·ρi)×100

[0102] In the formula, f is the coverage rate by the external additive, D is the average particle diameter of the toner particles [μm], d is the average particle diameter of the external additive [μm], ρt is the true specific gravity of the toner particles, ρi is the true specific gravity of the external additive, and C is (mass of the external additive) / (mass of the toner particles).

[0103] <Measurement of adhesion strength of external additives> The adhesion strength of the external additive to the toner particles was measured by the following procedure.

[0104] First, a toner sample obtained by carrying out the external additive removal treatments shown in (1) to (6) below was designated as "Sample 1," and a toner sample before carrying out the external additive removal treatments described below was designated as "Sample 0." (1) 2.0 g of toner is added to 40 mL of a 0.2% by mass Triton (polyoxyethylene octylphenyl ether) aqueous solution, and the mixture is stirred for 1 minute. (2) The aqueous solution is irradiated with ultrasonic waves (output: 40 μA, 4 minutes) using an ultrasonic homogenizer (manufactured by Nippon Seiki Seisakusho Co., Ltd., model: US-300T). (3) After the ultrasonic irradiation, the aqueous solution is left to stand for 3 hours, and the toner and the liberated external additives are separated. (4) After removing the supernatant, add approximately 50 mL of pure water to the precipitate and stir for 5 minutes. (5) The solution is subjected to suction filtration using a membrane filter (manufactured by Advantec) with a pore size of 1 μm. (6) The toner remaining on the filter is vacuum dried overnight.

[0105] Next, an X-ray fluorescence analyzer (Rigaku Corporation, model: ZSX Primus II) was used to analyze the intensity of Si in the external additive for 1 g of each of "Sample 0" and "Sample 1," and the adhesion strength [%] of the silica particles as an external additive was calculated using the following formula. Adhesion strength = (Si strength in sample 1) / (Si strength in sample 0) × 100

[0106] <Method for measuring the number of agglomerates and particle size of titanium oxide particles> Using a scanning transmission electron microscope (Hitachi High-Technologies Corporation, model: S-4800), 100 toner particles were photographed at a magnification of 10,000x while changing the field of view, and the number of titanium oxide particle aggregates present on the surface of or near the toner particles was confirmed. In addition, the particle diameter of the titanium oxide particle aggregates was determined by measuring the particle diameter through image analysis, and when multiple aggregates were present, the average value was used.

[0107] <Method for measuring the specific surface area of ​​titanium oxide particles> Using a specific surface area measuring device (Mountec, model: Macsorb model-1280), nitrogen gas is adsorbed onto the sample surface, and the BET multipoint method is used to measure the BET specific surface area [m 2 / g] was calculated. Specifically, the measurement was carried out according to the following procedure.

[0108] First, the mass of an empty sample cell was measured, and then 0.1 g of the sample to be measured was filled into the sample cell. Next, the sample cell filled with the sample was placed in a degassing device and subjected to dry degassing at 150°C for 30 minutes under a nitrogen atmosphere, after which it was cooled to room temperature. The mass of the entire sample cell was measured, and the exact mass of the sample was calculated from the difference with the empty sample cell. Next, while the sample cell was cooled with liquid nitrogen, a measurement gas was passed through the sample cell, and the amount of measurement gas adsorbed onto the sample was measured to calculate the BET specific surface area.

[0109] <Method for measuring the volume average particle size of carrier> The particle size distribution was measured using a particle size measuring instrument (manufactured by Nikkiso Co., Ltd., model: Microtrac MT3000). In this particle size distribution, the value D50, which is the cumulative particle size up to a volume ratio of 50%, was taken as the volume average particle size of the carrier.

[0110] <Method for measuring carrier shape factor> Using a scanning transmission electron microscope (Hitachi High-Technologies Corporation, model: S-4800), 50 carrier particle images magnified 300 times were randomly sampled, and image analysis was performed. The values ​​obtained by calculating using the following formulas (2) and (3) were defined as shape factors SF1 and SF2. SF1=(L 2 / A)×(π / 4)×100 (2) SF2=(P 2 / A)×(1 / 4π)×100 (3)

[0111] In the formula, L is the absolute maximum length of the particle (the length of the circumscribed circle), P is the perimeter of the particle, and A is the projected area of ​​the particle. The shape factor SF1 indicates the degree of roundness of the particle, and the shape factor SF2 indicates the degree of irregularity of the particle. As the particle deviates from a spherical shape (the particle image deviates from a circle), the value of SF1 increases. As the irregularity of the particle surface becomes more pronounced, the value of SF2 increases.

[0112] <Method for measuring charge amount> The charge amount A of the carrier core material, the charge amount B of the inner layer particle composed of the carrier core material and the inner layer, and the charge amount C of the carrier were measured using the following procedure, and the charge amount ratios B / C, A / B, and A / C were calculated.

[0113] The sample to be measured was sucked through a mesh using a small suction-type charge measurement device (TREK Corporation, model: 210HS-2A), and the charge of the sample separated by suction was measured. The charge of the sample [-μc / g] was calculated from the measured charge and the mass of the sample separated by suction.

[0114] <Evaluation method for image density (ID) transition> The two-component developer was filled into the developing unit of a copier, and the amount of toner adhered to the photoreceptor was 0.45 mg / cm 2 The image was formed on an A4 size recording paper (manufactured by Sharp Corporation, product name: PPC paper SF-4AM3) with the image adjusted to the following. After the image was formed on the recording paper, the image density (ID) of the solid image area was measured using a reflection densitometer (manufactured by X-Rite, model: RD914). Based on this measurement value, the image was evaluated according to the following criteria.

[0115] ◎ (Excellent): ID is 1.4 or higher throughout life. ○ (Good): The minimum ID value throughout life is between 1.3 and 1.4. △ (No practical problems): The minimum ID value throughout life is between 1.2 and 1.3. × (Poor): There will be a period during its life when its ID will be less than 1.2.

[0116] <Method for evaluating fog (BG) transition> The two-component developer was filled into the developing unit of a copier, and the amount of toner adhered to the photoreceptor was 0.45 mg / cm 2 The image was formed on A4-size recording paper (manufactured by Sharp Corporation, product name: PPC paper SF-4AM3). After image formation, the whiteness of the non-image area of ​​the recording paper was measured using a whiteness meter (manufactured by Nippon Denshoku Industries Co., Ltd., model: Z-Σ90 COLOR MEASURING SYSTEM). The difference between this whiteness and the whiteness of the recording paper before image formation, which had been measured using the whiteness meter, was determined, and this difference was taken as fog (BG). Based on this measurement, evaluation was performed according to the following criteria.

[0117] ◎ (Excellent): BG is less than 1.0 throughout life. ○ (Good): The maximum BG value throughout life is 1.0 or more and less than 1.2. △ (No practical problems): The maximum BG value throughout life is 1.2 or more and less than 1.5. × (Poor): There will be a period during the product's life when BG will be 1.5 or more.

[0118] <Evaluation method for carrier adhesion> The two-component developer was loaded into the development unit of a copier, and a white solid image was formed on an A4-size recording paper (manufactured by Sharp Corporation, product name: PPC Paper SF-4AM3). After the white solid image was formed, the number of carrier particles adhering to the photoreceptor was visually confirmed. Based on this number, evaluation was made according to the following criteria.

[0119] ◎ (Excellent): The number of carriers is less than 10. ◯ (Good): The number of carriers is 10 or more and less than 20. △ (no problem in practical use): The number of carriers is 20 or more and less than 30. × (bad): The number of carriers is 30 or more.

[0120] <How to check for scratches on the drum> The two-component developer was filled into the developing unit of a copier, and a text document with 6% coverage was continuously printed on 100,000 sheets of A4-sized recording paper (manufactured by Sharp Corporation, product name: PPC paper SF-4AM3) with an intermittent print of 6 sheets. After this continuous printing, the photosensitive drum was visually inspected for scratches.

[0121] <Method for Evaluating Toner Blocking Resistance> The two-component developer was filled into the developing unit of a copier, and a text document with 6% coverage was continuously printed on 100,000 sheets of A4-size recording paper (manufactured by Sharp Corporation, product name: PPC paper SF-4AM3) with six intermittent prints, and then the presence or absence of toner aggregates and the state of the developer transported by the developing roller were visually confirmed. Based on this confirmation, the "toner blocking resistance" was evaluated according to the following criteria.

[0122] ⊚ (Excellent): No toner agglomerates are observed, and the developer is transported uniformly by the developing roller. ◯ (Good): Although minute toner aggregates are present, the developer is transported uniformly on the developing roller. Δ (no problem in practical use): Toner agglomerates are observed, but the developer is transported uniformly on the developing roller. × (bad): Toner agglomerates were observed, and the developer was not transported uniformly on the developing roller.

[0123] <Method for Evaluating Toner Fixability> The two-component developer was filled into the developing unit of a copier, and a sample image including a rectangular solid image measuring 20 mm in length and 50 mm in width was prepared as an unfixed image on an A4-size recording paper (manufactured by Sharp Corporation, product name: PPC Paper SF-4AM3). At this time, the amount of toner adhesion in the solid image area was 0.5 mg / cm. 2 was adjusted as follows.

[0124] Next, a fixed image was produced using an external fixing device utilizing the fixing section of a multifunction printer. The fixing process speed was set to 250 mm / sec, and the temperature of the fixing belt was increased in 10°C increments from 150°C to 220°C. The temperature range in which neither low-temperature offset nor high-temperature offset occurred was measured, and this temperature range was designated the non-offset range. Note that high-temperature offset and low-temperature offset refer to the occurrence of toner not being fixed to the recording paper during fixing, remaining attached to the fixing belt, and then re-adhering to the recording paper after the fixing belt has completed one revolution.

[0125] Furthermore, on the fixed image sample with the fixing belt temperature at 150°C, the surface of the image was rubbed three times back and forth with a sand eraser with a load of 1 kg on a Gakushin fastness tester. The optical reflection density (image density) before and after this rubbing was measured with a reflection densitometer (manufactured by Macbeth), and the fixing rate [%] was calculated using the following formula. Fixation rate [%] = [(image density after rubbing) / (image density before rubbing)] x 100

[0126] Based on the results of the non-offset area and the fixing rate, the fixing property was evaluated according to the following criteria. ◎ (Excellent): There is no offset on the image sample heated to 150℃~180℃, and the fixing rate is 80% or more. ◯ (Good): There is no offset on the image sample at 150°C to 180°C, and the fixing rate is 60% or more and less than 80%. △ (no problem in practical use): There is no offset on the image sample at 150°C to 180°C, and the fixing rate is less than 60%. × (bad): Offset occurs on the image sample at 150°C to 180°C.

[0127] <Method of overall evaluation> Based on the results of the six evaluation items (ID transition, BG transition, carrier adhesion, drum scratches, blocking resistance, and fixability), an overall evaluation was made according to the following criteria. For the item of drum scratches, "absent" was rated as "○" and "present" was rated as "△." ○ (Good): All items are rated as "◎" or "○". △ (no practical problems): There are no "×" ratings, and even one item has a "△" rating. × (bad): There is an "×" rating for even one item.

[0128] 2. Example of manufacturing two-component developer <Preparation of strontium titanate particles A as an external additive> Metatitanic acid obtained by the sulfuric acid method was desulfurized and bleached, and then a sodium hydroxide solution was added to adjust the pH to 9.0, followed by desulfurization. After desulfurization, the mixture was neutralized to pH 5.8 with hydrochloric acid, filtered, and washed with water to obtain a washed cake. Water was added to the washed cake to form a slurry, and then hydrochloric acid was added to adjust the pH to 1.4, followed by peptization. This metatitanic acid was placed in a reaction vessel, and a strontium chloride solution was added. Next, the mixture was heated to 90°C with stirring, and then a 10N sodium hydroxide solution was added over 2 hours. The reaction was then completed by continuing stirring at 95°C for 1 hour.

[0129] The reaction-completed slurry was cooled to 50°C, and hydrochloric acid was added until the pH reached 5.0, followed by stirring for 1 hour. The resulting precipitate was decanted and washed, then adjusted to 50°C, and hydrochloric acid was added to adjust the pH to 2.5, followed by hydrophobic treatment. Sodium hydroxide solution was then added to adjust the pH to 6.5, and the mixture was stirred for 1 hour. The resulting cake was then filtered and washed, and dried in air at 120°C for 10 hours to obtain strontium titanate particles A. The average primary particle diameter of strontium titanate particles A was 40 nm.

[0130] <Preparation of Toner T1> Toner particles (toner cores) were prepared by a melt-pulverization method using the following raw materials. Binder resin 5000g of polyester resin that satisfies the glass transition temperature and softening point shown in Table 1 Coloring agents Carbon black (Mitsubishi Chemical Corporation, product name: #44) 500g ·Mold release agent Release agent A: Fischer-Tropsch wax (melting point 90°C, manufactured by Nippon Seiro Co., Ltd., product name: FNP0090) 86 g Release agent B: Polypropylene wax (melting point 140°C, manufactured by Mitsui Chemicals, Inc., product name: NP-505) 57g Charge control agent Potassium salt, bis[benzilate(2-)-k(2)O,O]borate(1-) potassium, solubility in water 4.382 g / L (20 °C), manufactured by Nippon Carlit Co., Ltd., product name: Ion Conductor LR-147, 50 g

[0131] The above raw materials for the toner particles were pre-mixed for 5 minutes at a rotation speed of 1500 rpm using a high-performance fluid mixer (Henschel mixer, total capacity: 20 L, manufactured by Nippon Coke & Engineering Co., Ltd., model: FM20C).

[0132] The obtained mixture was melt-kneaded using a twin-screw extruder (manufactured by Ikegai Corporation, model: PCM-30) under conditions of a cylinder set temperature of 100°C, a barrel rotation speed of 250 rpm, and a raw material supply rate of 10 kg / hour to obtain a melt-kneaded product.

[0133] The obtained molten kneaded material was cooled and solidified on a cooling belt, and then the solidified material was finely pulverized using a fluidized bed opposed jet mill (manufactured by Hosokawa Micron Corporation, model: Counter Jet Mill AFG) and classified using a rotary (centrifugal airflow) classifier (manufactured by Hosokawa Micron Corporation, model: TSP Separator) to produce toner particles with a volume average particle diameter of 6.3 μm.

[0134] For 100 parts by mass of the produced toner particles, silica particles (average primary particle diameter: 10 μm) in an amount such that the coverage rate of the toner particle surface was 100% and 0.3 parts by mass of strontium titanate particles A as titanium oxide particles were added to a Henschel mixer and stirred and mixed to obtain toner T1 after external addition.

[0135] <Preparation of Toners T2 to T26> Toners T2 to T26 were prepared in the same manner as in "Preparation of Toner T1" above, except that the physical properties and amounts of the polyester resin, silica particles, and titanium oxide particles used were changed as shown in Table 1 below.

[0136] [Table 1]

[0137] <Preparation of carrier C1> A crosslinkable silicone resin solution (manufactured by Shin-Etsu Chemical Co., Ltd., product name: KR251) was diluted with toluene to prepare a solution with a solids concentration of 10% by mass, and a curing catalyst (manufactured by Shin-Etsu Chemical Co., Ltd., product name: D-20) was added thereto so that the concentration was 0.5% by mass relative to the silicone resin to prepare coating liquid 1. In addition, a conductive material (carbon black, manufactured by Mitsubishi Chemical Corporation, product name: MA100) was dispersed in toluene to prepare coating liquid 2 (carbon dispersion with a solids concentration of 2% by mass).

[0138] Next, a first coating layer (inner layer) and a second coating layer (outer layer) were formed around the carrier core material using a mixture of Coating Liquid 1 and Coating Liquid 2. The number of coated parts of the inner layer and outer layer per 100 parts by mass of the carrier core material was as shown in Table 2 below.

[0139] Specifically, the carrier core material (MnMg ferrite, volume average particle size: 41 μm, SF1: 115, SF2: 155) was weighed into the container of a mixer / stirrer, and the coating liquid was added to the mixer while stirring at room temperature. Once homogenized, the temperature was raised to 80°C. Stirring was continued while degassing, and the solvent was removed from the coating liquid, forming an inner layer around the carrier core material. After about 10 minutes had passed since the solvent had run out, the outer layer coating liquid was added, and the same procedure as for forming the inner layer was repeated to obtain a multi-layer coated carrier.

[0140] In order to harden and stabilize the coating layer of the obtained carrier, it was cured in an oven at 180° C. for 1 hour. After being taken out and cooled to room temperature, the coated carrier was sieved to remove coarse particles, thereby obtaining carrier C1.

[0141] <Preparation of carriers C2 to C15> Carriers C2 to C15 were produced in the same manner as in "Preparation of Carrier C1," except that the curing temperature was adjusted within the range of 150°C to 200°C to achieve the charge amount ratios shown in Table 2 below, and the coating amount of the coating layer and the shape factor of the carrier core material were changed as shown in Table 2 below. Note that the coating amount of the coating layer in Table 2 represents the number of parts by mass per 100 parts by mass of the carrier core material.

[0142] [Table 2]

[0143] <Preparation of two-component developer> The toner and carrier prepared as described above were weighed out so that the toner concentration (T / D where D is the mass of the developer and T is the mass of the toner) was 7%, and then placed in a cylindrical resin container. After that, they were mixed and stirred on a double-axis driven plastic bottle rotating stand at 200 rpm for 1 hour to prepare two-component developers for the Examples and Comparative Examples. The combinations of toner and carrier in each Example and Comparative Example are as shown in Table 3 below.

[0144] [Table 3]

[0145] The evaluation results of the Examples and Comparative Examples are shown in Table 3. As is clear from these evaluation results, the two-component developers of Examples 1 to 33, which contain a toner having an external additive attached to the surface of the toner particles and a carrier having a carrier core material whose surface is covered with a coating layer and which satisfy the following requirements (A) to (D), were capable of forming images with good quality throughout their life. (A) The toner particles have a glass transition point of 50°C or more and 65°C or less, and a softening point of 100°C or more and 120°C or less. (B) The external additive contains silica particles, and the coverage of the surfaces of the toner particles with the silica particles is 90% or more. (C) The coating layer has an inner layer and an outer layer in this order from the carrier core material side. (D) When the carrier core material, the inner layer particles composed of the carrier core material and the inner layer, and the carrier are charged under the same conditions, the charge amount of the carrier core material is A, the charge amount of the inner layer particles is B, and the charge amount of the carrier is C, and the charge amount ratio B / C is 1.05 or more and 1.35 or less, and the charge amount ratio A / B is 0.75 or more and 0.95 or less.

[0146] In contrast, Comparative Examples 1 to 7, which did not satisfy these requirements, were inferior to the Examples in evaluation of at least one of the six evaluation items (ID transition, BG transition, carrier adhesion, drum scratches, blocking resistance, and fixability).

[0147] It can be seen that Examples 1, 12, 13, etc., in which the adhesion strength of silica particles to toner particles is 50% or more and 80% or less, are particularly superior in the evaluation of BG transition than Example 25, in which the adhesion strength is below the above lower limit, and are particularly superior in the evaluation of blocking resistance than Example 26, in which the adhesion strength exceeds the above upper limit.

[0148] It can be seen that Examples 1 to 3, in which the charge amount ratio A / C is 0.9 or more and 1.2 or less, are particularly superior in the evaluation of BG transition than Comparative Example 1, in which A / C is less than the above lower limit, and are particularly superior in the evaluation of ID transition than Comparative Example 2, in which A / C exceeds the above upper limit.

[0149] It can be seen that Examples 1, 9, 10, etc., in which the average primary particle diameter of the silica particles is 5 nm or more and 20 nm or less, are particularly superior in the evaluation of BG transition compared to Example 29, in which the average primary particle diameter of the silica particles exceeds the upper limit.

[0150] The specific surface area of ​​titanium oxide particles is 60m 2 / g or more 150m 2 / g are particularly superior in the evaluation of ID transition than Example 30, whose specific surface area is less than the above lower limit, and are particularly superior in the evaluation of BG transition than Example 31, whose specific surface area exceeds the above upper limit.

[0151] It can be seen that Examples 1, 16, 17, etc., in which the content of titanium oxide particles is 0.1 parts by mass or more and 0.5 parts by mass or less per 100 parts by mass of toner particles, are particularly superior in the evaluation of ID transition and carrier adhesion than Example 32, which does not contain titanium oxide particles, and are particularly superior in the evaluation of BG transition than Example 33, in which the content of titanium oxide particles exceeds the above upper limit.

[0152] It can be seen that Examples 1, 18, 19, etc., in which there is one or more titanium oxide particle aggregates per 100 toner particles and the particle diameter of the aggregates is 0.5 μm or more and 1.0 μm or less, are particularly superior in the evaluation of ID transition than Example 27, in which the particle diameter is below the above lower limit, and are particularly superior in terms of the presence or absence of drum scratches than Example 28, in which the particle diameter exceeds the above upper limit.

[0153] It can be seen that Example 1 and the like, in which the coating amount of the coating layer is 20 parts by mass or more per 100 parts by mass of the carrier core material, are particularly superior in the evaluation of BG transition and carrier adhesion compared to Example 20, in which the coating amount is less than the lower limit.

[0154] It can be seen that Examples 1, 5, 6, etc., in which the coating amount of the outer layer is 13 to 17 parts by mass per 100 parts by mass of the carrier core material, are particularly superior in the evaluation of ID transition than Example 21, in which the coating amount is below the above lower limit, and are particularly superior in the evaluation of BG transition than Example 22, in which the coating amount exceeds the above upper limit.

[0155] It can be seen that Example 1 and the like, in which the carrier core material has a shape factor SF1 of 120 or less and a shape factor SF2 of 150 or more, are superior in the evaluation of ID transition, BG transition and blocking resistance to Example 23, in which the shape factor SF1 exceeds the above upper limit, and Example 24, in which the shape factor SF2 is less than the above lower limit.

[0156] The embodiments disclosed herein are illustrative in all respects and are not intended to be limiting. Therefore, the technical scope of the present disclosure should not be interpreted solely by the above-described embodiments, but should be defined based on the claims. Furthermore, all modifications within the scope and meaning equivalent to the claims are included. [Explanation of symbols]

[0157] 1. Career 11 Carrier core material 12 Inner layer of coating layer 13 Outer layer of coating layer 2 Toner 21 Toner particles (toner cores) 22 Silica particles 23 Titanium oxide particles

Claims

1. A two-component developer containing a toner having an external additive attached to the surface of the toner particles and a carrier having a carrier core material whose surface is covered with a coating layer, The toner particles have a glass transition point of 50° C. or more and 65° C. or less and a softening point of 100° C. or more and 120° C. or less, the external additive contains silica particles, and the coverage of the surfaces of the toner particles with the silica particles is 90% or more; the coating layer has an inner layer and an outer layer in this order from the carrier core material side, a charge amount ratio B / C of 1.05 or more and 1.35 or less, and a charge amount ratio A / B of 0.75 or more and 0.95 or less, when the carrier core material, inner layer particles composed of the carrier core material and the inner layer, and the carrier are charged under the same conditions, where A is the charge amount of the carrier core material, B is the charge amount of the inner layer particles, and C is the charge amount of the carrier.

2. The two-component developer according to claim 1 , A two-component developer, wherein the adhesion strength of the silica particles to the toner particles is 50% or more and 80% or less.

3. 3. The two-component developer according to claim 1, A two-component developer, wherein the charge amount ratio A / C is 0.9 or more and 1.2 or less.

4. 3. The two-component developer according to claim 1, The two-component developer is characterized in that the external additive contains titanium oxide particles.

5. The two-component developer according to claim 4, the average primary particle diameter of the silica particles is 5 nm or more and 20 nm or less; The titanium oxide particles are titanium oxide particles or strontium titanate particles, and the specific surface area thereof is 60 m ２ / g or more 150m ２ / g or less, The two-component developer is characterized in that the content of the titanium oxide particles is 0.1 parts by mass or more and 0.5 parts by mass or less with respect to 100 parts by mass of the toner particles.

6. The two-component developer according to claim 4, the titanium oxide particle aggregate is present at one or more per 100 toner particles, The two-component developer is characterized in that the particle diameter of the aggregates is 0.5 μm or more and 1.0 μm or less.

7. 3. The two-component developer according to claim 1, the coating amount of the coating layer is 20 parts by mass or more with respect to 100 parts by mass of the carrier core material, the coating amount of the outer layer is 13 parts by mass or more and 17 parts by mass or less with respect to 100 parts by mass of the carrier core material, The two-component developer is characterized in that the carrier core material has a shape factor SF1 of 120 or less and a shape factor SF2 of 150 or more.

8. 3. The two-component developer according to claim 1, The two-component developer is characterized in that the coating layer contains a crosslinkable silicone resin.

9. 3. The two-component developer according to claim 1, The two-component developer, wherein the coating layer contains a conductive material and a charge control agent.

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