Silica powder used as external additive for toner

Abstract

To provide silica powder which is used as an external additive for a toner, reduces the influence of a temperature change and a humidity change on the electrostatic chargeability of the toner, and can improve the printing stability of the toner.SOLUTION: Provided is a silica powder having a hydroxyl group amount per unit weight of 1.25 * 1019 to 3.5 * 1019 groups / g and a methanol hydrophobicity of 68% or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a silica powder used as an external additive for a toner. [Background technology]

[0002] In image forming devices such as electrophotographic devices, electrostatic recording devices, and electrostatic printing devices, developers are used to visualize electrostatic latent images formed on photoconductors. Developers are primarily composed of colored particles (toner) in which colorants, charge control agents, release agents, etc. are dispersed in a binder resin. Due to their functionality, toners are called electrostatic image developing toners.

[0003] It is known that silica is externally added to toner particles in order to control the chargeability and fluidity of the toner and obtain good development characteristics. The silica used as an external toner additive is generally surface-treated with a silane compound, a silazane compound, silicone oil, or the like to hydrophobize it in order to control the chargeability. For example, Patent Document 1 discloses a method for producing surface-treated fumed silica, in which silica is surface-treated using organosilanes, silazanes, acyclic polysiloxanes, cyclic polysiloxanes, and mixtures thereof.

[0004] However, such conventional surface treatment methods have the problem that unreacted silanol remains on the silica after surface treatment, making it unable to be sufficiently hydrophobic, resulting in insufficient charge controllability when added to toner. Furthermore, although the fumed silica obtained by the method of Patent Document 1 is said to be able to reduce the effect of humidity on the charge characteristics of the toner composition when used as an external additive to toner, there is a need for silica external additives that can further reduce the effect of humidity. Furthermore, toners are sometimes used in high- or low-temperature environments, and there is a need for silica external additives that can reduce the effect of temperature and humidity changes on the charge characteristics of toners and improve the printing stability of toners. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-123868 Summary of the Invention [Problem to be solved by the invention]

[0006] The problem to be solved by the present invention is to provide a silica powder that can be used as an external additive for a toner, reduce the effects of temperature and humidity changes on the chargeability of the toner, and improve the printing stability of the toner. [Means for solving the problem]

[0007] According to the present invention, there is provided the following silica powder for use as an external additive for toner. [1] The amount of hydroxyl groups per unit weight is 1.25 × 10 19 ~3.5×10 19 Silica powder used as an external additive for toner, with a methanol hydrophobicity of 68% or more and a particle size of 1000p / g. [2] The silica powder used as an external additive for the toner according to [1], which has a primary particle diameter of 1 to 150 nm. [3] Specific surface area is 10 to 300 m 2 The silica powder used as an external additive for the toner according to [1] or [2], wherein the silica powder has a molecular weight of 1 / g. [4] Bulk density of 0.001 to 0.5 g / cm 3 The silica powder used as an external additive for the toner according to any one of [1] to [3], wherein: [5] The silica powder used as an external additive for a toner according to any one of [1] to [4], wherein the silica powder has been subjected to a treatment to reduce the number of hydroxyl groups on the surface. [6] The silica powder used as an external additive for a toner according to [5], wherein the silica powder has been subjected to a treatment to reduce surface hydroxyl groups by reacting a hydrosilane compound in a hydrocarbon solvent in the presence of a borane catalyst. [7] A silica powder used as an external additive for the toner according to any one of [1] to [6]. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a silica powder that can be used as an external additive for a toner, reduce the effects of temperature and humidity changes on the chargeability of the toner, and improve the printing stability of the toner. DETAILED DESCRIPTION OF THE INVENTION

[0009] The silica powder of the present invention has a hydroxyl group content of 1.25×10 19 ~3.5×10 19 The silica powder of the present invention has a methanol hydrophobicity of 68% or more and a molecular weight of 1000 or more particles / g. The silica powder of the present invention is used as an external additive for a toner for developing electrostatic images (hereinafter, sometimes simply referred to as "toner").

[0010] The amount of hydroxyl groups per unit weight of the silica powder of the present invention is 1.25×10 19 ~3.5×10 19 The lower limit is preferably 1.5 × 10 19 More preferably, 1.6 × 10 19 The upper limit is preferably 3.25×10 19 Less than or equal to 3.0 × 10 19 or less, more preferably 2.8 × 10 19 As a result of extensive research, the present inventors have found that by controlling the amount of hydroxyl groups per unit weight within the above range, the effects of temperature and humidity changes on the chargeability of a toner to which the silica powder of the present invention is added as an external additive can be reduced, and the toner can be made to have excellent print stability.

[0011] In the silica powder of the present invention, the amount of hydroxyl groups per unit weight is determined, for example, by the Sears method as the content of hydroxyl groups per unit surface area (number / nm 2 ) and the content of hydroxyl groups per unit surface area (number / nm2 ) and the specific surface area of ​​the silica powder (nm 2 This can be calculated by multiplying by 1 / g.

[0012] Measurement by the Sears method can be carried out with reference to GW Sears, Jr., Analytical Chemistry, Vol. 28, No. 12, pp. 1981-1983 (1956). Specifically, an aqueous solution of silica prepared at a concentration of 1 wt% is titrated with a 0.1 mol / L NaOH aqueous solution at a drop rate of 2 mL / min, and the hydroxyl group content per unit surface area of ​​the silica can be calculated based on the following formula: ρ=(a×b×N A )÷(c×d) ρ: Content of hydroxyl groups per unit surface area of ​​silica (number / nm 2 ) a: Concentration of the NaOH aqueous solution used in titration (mol / L) b: Amount of NaOH solution added (mL) at pH 4 to 9 N A :Avogadro's number c: weight of silica (g) d: specific surface area of ​​silica (nm 2 / g)

[0013] The content of hydroxyl groups per unit surface area of ​​the silica powder of the present invention is not particularly limited, but is preferably 0.01 to 2.0 groups / nm 2 The lower limit is more preferably 0.05 particles / nm 2 More preferably, 0.1 particles / nm 2 The upper limit is more preferably 1.5 particles / nm 2 or less, more preferably 1.25 particles / nm 2 or less, and even more preferably 0.6 particles / nm 2 Less than 0.15 particles / nm, particularly preferably 2 The content of hydroxyl groups per unit surface area of ​​the silica powder can be measured by the Sears method described above.

[0014] In the present invention, the method for adjusting the amount of hydroxyl groups per unit weight of silica powder to fall within the above-mentioned range is not particularly limited, and examples thereof include a method of subjecting raw material silica to a treatment to reduce the surface hydroxyl groups contained in the silica. The method for performing the treatment to reduce surface hydroxyl groups is not particularly limited as long as it is a method that can adjust the amount of hydroxyl groups per unit weight of the silica powder to fall within the above-mentioned range, and examples thereof include a method of performing a hydrosilanization treatment using a hydrosilane compound. According to the hydrosilanization treatment, the surface hydroxyl groups of the silica powder undergo a dehydrocondensation reaction with the hydrosilane compound, thereby capping the surface hydroxyl groups of the silica powder, and thereby appropriately reducing the surface hydroxyl groups of the silica powder.

[0015] The method for subjecting silica as a raw material to a hydrosilanization treatment is not particularly limited, but a suitable example is a method in which silica is reacted with a hydrosilane compound in a hydrocarbon solvent in the presence of a catalyst.

[0016] The hydrosilane compound is not particularly limited as long as it has a Si-H group in which a hydrogen atom is bonded to a silicon atom. Examples of the hydrosilane compound include hydrosilane compounds represented by the following general formula (1) or (2): R 1 R 2 R 3 SiH (1) R 4 [-SiH(R 5 )-O-] n R 6 (2) (In the above general formula (1) and general formula (2), R 1 ~R 6 represent, independently of each other, a monovalent hydrocarbon group having 1 to 10 carbon atoms which may have a substituent, and in the above general formula (2), n represents an integer of 10 to 50.

[0017] In the above general formula (1) and general formula (2), R 1 ~R 6are each independently a monovalent hydrocarbon group having 1 to 10 carbon atoms which may have a substituent, and specific examples thereof include linear or branched alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, t-butyl, pentyl, hexyl, and octyl; cycloalkyl groups such as cyclopentyl and cyclohexyl; aryl groups such as phenyl and tolyl; and aralkyl groups such as benzyl, phenylethyl, and phenylpropyl.

[0018] Specific examples of the hydrosilane compound represented by the general formula (1) include trialkylhydrosilanes such as trimethylsilane, triethylsilane, tripropylsilane, tributylsilane, trioctylsilane, and t-butyldimethylsilane; dialkylarylhydrosilanes such as phenyldimethylsilane, phenyldiethylsilane, phenyldipropylsilane, phenyldioctylsilane, o-chlorophenyldimethylsilane, m-chlorophenyldimethylsilane, p-chlorophenyldimethylsilane, p-fluorophenyldimethylsilane, p-bromophenyldimethylsilane, p-methylphenyldimethylsilane, p-butylphenyldimethylsilane, p-octylphenyldimethylsilane, p-methoxyphenyldimethylsilane, and p-butoxyphenyldimethylsilane; and methyldiphenylsilane. Examples of suitable alkyldiarylhydrosilanes include alkyldiphenylsilane, ethyldiphenylsilane, propyldiphenylsilane, octyldiphenylsilane, methyldi(p-chlorophenyl)silane, methyldi(p-bromophenyl)silane, methyldi(p-fluorophenyl)silane, methyldi(p-methylphenyl)silane, methyldi(p-butylphenyl)silane, methyldi(p-octylphenyl)silane, methyldi(p-methoxyphenyl)silane, and methyldi(p-butoxyphenyl)silane; and triarylhydrosilanes such as triphenylsilane, tri(p-chlorophenyl)silane, tri(p-bromophenyl)silane, tri(p-fluorophenyl)silane, tri(p-methylphenyl)silane, tri(p-butylphenyl)silane, and tri(p-octylphenyl)silane. These may be used alone or in combination of two or more.

[0019] Examples of the hydrosilane compound represented by the general formula (2) include hydrogen-modified compounds of oligodimethylsiloxanes such as pentamethyldisiloxane and heptamethyldisiloxane; terminally hydrogen-modified polydimethylsiloxanes, polymethylhydrosiloxanes, and the like.

[0020] In the above general formulas (1) and (2), R 1 ~R 6 As for the silica powder, from the viewpoint that the content of hydroxyl groups per unit surface area of ​​the silica powder can be suitably controlled within the above range, R 1 ~R 6 In addition, from the viewpoint of suitably controlling the content of hydroxyl groups per unit surface area of ​​the silica powder within the above range, it is preferable that R 1 ~R 3 are preferably all the same group (i.e., R 1 =R 2 =R 3 is preferred).

[0021] The hydrosilane compound represented by the general formula (1) is preferably trimethylsilane, triethylsilane, tripropylsilane, tributylsilane, trioctylsilane, or t-butyldimethylsilane, more preferably trimethylsilane, triethylsilane, tripropylsilane, or tributylsilane, still more preferably trimethylsilane or triethylsilane, and particularly preferably triethylsilane.

[0022] As the hydrosilane compound, the compound represented by the above general formula (2) is preferred from the viewpoint that the content of hydroxyl groups per unit surface area of ​​the silica powder can be suitably controlled within the above range.

[0023] The amount of the hydrosilane compound used is preferably 0.001 to 3 parts by weight, more preferably 0.01 to 2 parts by weight, and even more preferably 0.02 to 1.5 parts by weight, based on 100 parts by weight of silica used in the reaction.

[0024] Although not particularly limited, silica having a BET specific surface area of ​​50 m 2 When silica having a BET specific surface area of ​​more than 50 m / g is used, the amount of the hydrosilane compound used is preferably 0.05 to 0.3 parts by weight based on 100 parts by weight of the silica used in the reaction. 2 When silica having a solubility of 0.03 to 0.6 parts by weight is used, the amount of the hydrosilane compound used is preferably 0.03 to 0.6 parts by weight per 100 parts by weight of the silica used in the reaction.

[0025] Examples of catalysts include platinum catalysts such as Kastredt's catalyst (platinum(0)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex), Speier's catalyst, Wilkinson's catalyst, and Trost's catalyst, as well as borane catalysts such as tris(pentafluorophenyl)borane (B(CF)). These may be used alone or in combination of two or more. Among these, borane catalysts are preferred, with tris(pentafluorophenyl)borane being more preferred, from the standpoint of economy and the ability to suitably control the hydroxyl group content per unit surface area of ​​silica within the above-mentioned range.

[0026] The amount of the catalyst used is preferably 0.0003 to 0.1 part by weight, more preferably 0.001 to 0.05 part by weight, and even more preferably 0.01 to 0.05 part by weight, based on 100 parts by weight of the hydrosilane compound used in the reaction.

[0027] The hydrocarbon solvent is not particularly limited as long as it does not inhibit the dehydrogenation condensation reaction between the surface hydroxyl groups of silica and the hydrosilane compound. Examples of the hydrocarbon solvent include alkanes such as hexane, octane, decane, and dodecane; cycloalkanes such as cyclohexane; halogenated solvents such as dichloromethane and dichloroethane; aromatic hydrocarbons such as toluene, xylene, and benzene; alkyl and aryl ether solvents such as diethyl ether, tetrahydrofuran (THF), dioxane, cyclopentyl methyl ether, and diphenyl ether; aprotic polar solvents such as N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and acetonitrile; mineral oil; and linear and cyclic silicone oils. These solvents can be used alone or in combination. Aromatic hydrocarbons are preferred as the hydrocarbon solvent, and toluene is more preferred.

[0028] The amount of the hydrocarbon solvent used is preferably 1.0 to 33 parts by weight, more preferably 1.2 to 15 parts by weight, and even more preferably 1.5 to 13.5 parts by weight, relative to 100 parts by weight of silica used in the reaction.

[0029] In the present invention, the silica used as the raw material for the hydrosilanization treatment is not particularly limited, and may be silica obtained by any of the sol-gel method, deflagration method, wet method, and melting method. Furthermore, the silica used as the raw material for the hydrosilanization treatment may be untreated silica, which has not been subjected to a surface treatment, or surface-treated silica, which has been subjected to a surface treatment. Examples of surface treatment methods include surface treatment with hexamethyldisilazane (HMDS), dimethyldichlorosilane (DDS), octylsilane (OTAS), polydimethylsiloxane (PDMS), and the like.

[0030] The hydrosilanization treatment can be carried out, for example, by adding a borane catalyst to a dispersion or solution obtained by dispersing or dissolving silica and a hydrosilane compound in a hydrocarbon solvent. The reaction may be carried out under stirring using a stirrer or the like. The reaction temperature is preferably 0 to 130°C, more preferably 5 to 90°C, and the reaction time is preferably 10 to 600 minutes, more preferably 30 to 180 minutes. Since hydrogen gas is generated as the hydrosilanization reaction proceeds, the reaction time may be adjusted appropriately by checking whether or not hydrogen gas is generated.

[0031] Silica can be subjected to a hydrosilanization treatment according to the above method. The obtained hydrosilanized silica may be washed with a hydrocarbon solvent and dried, as necessary. In this case, the hydrocarbon solvent may be any of those described above.

[0032] The primary particle diameter of the silica powder of the present invention is not particularly limited, but is preferably 1 to 150 nm, more preferably 5 to 120 nm, and even more preferably 10 to 100 nm. When the primary particle diameter of the silica powder is within the above range, the effect of temperature and humidity changes on the chargeability of the toner when the silica powder is used as an external additive to the toner can be further reduced. The primary particle diameter of the silica powder is the arithmetic mean particle diameter of the primary particles of the silica powder. The primary particle diameter of the silica powder can be determined by observing the primary particles of the silica powder with an electron microscope.

[0033] The specific surface area of ​​the silica powder of the present invention is not particularly limited, but is preferably 10 to 300 m 2 / g, more preferably 20 to 250m 2 / g, more preferably 25 to 220 m 2 / g. When the silica powder is used as an external additive to a toner, the specific surface area of ​​the silica powder can be further reduced in influence of temperature and humidity changes on the chargeability of the toner. The specific surface area of ​​the silica powder can be measured, for example, by the BET method in accordance with ASTM D3037-81.

[0034] The bulk density of the silica powder of the present invention is not particularly limited, but is preferably 0.001 to 0.5 g / cm 3 and more preferably 0.05 to 0.4 g / cm 3 , and more preferably 0.02 to 0.3 g / cm 3 is.

[0035] The silica powder of the present invention has a methanol hydrophobicity of 68% or more, preferably 68.5% or more, and more preferably 69.0% or more. The upper limit of the methanol hydrophobicity is not particularly limited, but is usually 80% or less. By having the methanol hydrophobicity within the above range, when the silica powder is used as an external additive to a toner, the effects of temperature and humidity changes on the toner's chargeability can be reduced. The methanol hydrophobicity can be calculated by adding 0.2 g of silica powder to 50 g of distilled water, stirring with a stirrer, dropping methanol into the liquid with the silica powder floating on the surface, and calculating the amount of methanol (g) dropped when all the silica has settled, using the following formula: Methanol hydrophobicity (%) = methanol weight (g) / (methanol weight (g) + water weight (g))

[0036] The silica powder of the present invention has a hydroxyl group content of 1.5×10 19 ~3.0×10 19 Since the particle size is 1 / g and the degree of methanol hydrophobicity is 68% or more, the particle can be suitably used as an external additive for toner.

[0037] When the silica powder of the present invention is used as an external additive for a toner, the silica powder is added to colored resin particles containing a binder resin and a colorant, and the mixture is mixed using a stirrer to prepare a toner.

[0038] The binder resin contained in the colored resin particles is not particularly limited, but can be a polymerized resin obtained by polymerizing a polymerizable monomer mainly composed of a monovinyl monomer. Examples of monovinyl monomers include styrene-based monomers such as styrene, vinyltoluene, α-methylstyrene, and ethylstyrene; (meth)acrylate-based monomers such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, dimethylaminoethyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, and dimethylaminoethyl methacrylate; acrylic acid and methacrylic acid; nitrile compounds such as acrylonitrile and methacrylonitrile; amide compounds such as acrylamide and methacrylamide; and olefins such as ethylene, propylene, and butylene. These monovinyl monomers can be used alone or in combination of two or more.

[0039] When producing a color toner (usually, four types of toner are used: black toner, cyan toner, yellow toner, and magenta toner), the colorants contained in the colored resin particles can be black colorants, cyan colorants, yellow colorants, and magenta colorants. The colorants can be used alone or in combination of two or more.

[0040] The amount of silica powder added is preferably an amount that gives a ratio of silica powder of 0.5 to 5% by weight, more preferably 1 to 3% by weight, based on the total weight of the colored resin particles and silica powder.

[0041] The toner containing the silica powder of the present invention as an external additive has excellent charging characteristics, and the effects of temperature and humidity changes on the charging characteristics are reduced, resulting in excellent printing stability. [Example]

[0042] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. Note that "parts" are by mass unless otherwise specified.

[0043] <Hydroxyl group content per unit surface area of ​​silica> The hydroxyl group content per unit surface area of ​​silica was measured by the Sears method. Measurements using the Sears method were performed with reference to "GW Sears, Jr., Analytical Chemistry, Vol. 28, No. 12, pp. 1981-1983 (1956)." Specifically, 2.50 g of silica was mixed with 120 mL of methanol, 100 mL of distilled water, and 25 g of sodium chloride, and then dispersed using an ultrasonic bath, a homomixer, or a disperser to prepare a slurry. An additional 25 g of sodium chloride was then added to prepare a slurry. This silica slurry was titrated with a 0.1 mol / L or 0.01 mol / L NaOH aqueous solution, and the hydroxyl group content per unit surface area of ​​silica was calculated using the following formula: ρ=(a×b×N A )÷(c×d) ρ: Content of hydroxyl groups per unit surface area of ​​silica (number / nm 2 ) a: Concentration of the NaOH aqueous solution used in titration (mol / L) b: Amount of NaOH solution added (mL) at pH 4 to 9 N A :Avogadro's number c: weight of silica (g) d: BET specific surface area of ​​silica (nm 2 / g)

[0044] <Hydroxyl group content per unit weight of silica> The content of hydroxyl groups per unit weight of silica (particles / g) is the content of hydroxyl groups per unit surface area of ​​silica (particles / nm²) determined by the Sears method. 2 ) and the specific surface area of ​​silica (nm 2 / g).

[0045] <Methanol hydrophobicity of silica> 0.2 g of silica and 50 g of distilled water were weighed and added to a 300 mL beaker. A stirrer was placed in the beaker, and the total weight A (g) of these was measured. Next, while stirring the liquid, methanol was added to the liquid, and the addition of methanol was stopped when all of the silica powder floating on the liquid surface had settled. The total weight B (g) of the beaker at this time was weighed, and the amount of methanol added C (g) (= BA) was calculated. The amount of methanol added C (g) was used to calculate the degree of methanol hydrophobicity using the following formula. Methanol hydrophobicity (%) = methanol added amount C (g) / (methanol added amount C (g) + water weight (g))

[0046] <Toner charge amount> After storing the toner for 24 hours at room temperature and humidity (NN) conditions of 23°C and 30-50% RH, the toner was filled into a cartridge and installed in a commercially available non-magnetic single-component development printer (print speed 20 ppm). Two solid white prints were performed at room temperature and humidity (NN). The charge amount (μC / g) of the toner adhering to the developing roll was measured using a suction-type charge amount measuring device (Trek Japan, product name: 210HS-2A).

[0047] The charge amount of the toner was measured in the same way when printing was performed under low temperature, low humidity conditions (LL) using toner that had been stored for 24 hours under low temperature, low humidity conditions (LL) at 10°C and 15% RH. The charge amount of the toner was also measured in the same way when printing was performed under high temperature, high humidity conditions (HH) using toner that had been stored for 24 hours under high temperature, high humidity conditions (HH) at 30°C and 80% RH.

[0048] The change in toner charge amount when the environment was changed from low temperature, low humidity conditions (LL) to high temperature, high humidity conditions (HH) was calculated as the difference between the charge amount under high temperature, high humidity conditions (HH) and the charge amount under low temperature, low humidity conditions (LL). The change in toner charge amount when the environment was changed from low temperature, low humidity conditions (LL) to normal temperature, normal humidity conditions (NN) was calculated as the difference between the charge amount under normal temperature, normal humidity conditions (NN) and the charge amount under low temperature, low humidity conditions (LL). The charge amount was evaluated for Example 1-2 and Comparative Example 1-2.

[0049] Example 1 (1) Preparation of hydrosilanized silica Silica (product name "TG-308F", manufactured by Cabot Corporation, primary particle diameter: 12 nm, BET specific surface area: 200 m) was placed in a reaction vessel equipped with a stirrer and filled with nitrogen. 2 100 parts of HCl (H2SO4 / g), 21 parts of cyclohexane, and 0.053 parts of polymethylhydrosiloxane (PMHS) were added, and stirring was initiated. A solution of 0.004 parts of tris(pentafluorophenyl)borane (B(CF)) in 0.032 parts of toluene was then added. Upon addition of tris(pentafluorophenyl)borane (B(CF)), hydrogen was generated, confirming the initiation of the reaction. Stirring was continued for 60 minutes after the start of the reaction. After hydrogen generation ceased and the reaction was confirmed to be complete, the reacted silica was thoroughly washed with toluene and then dried under reduced pressure at room temperature for 2 hours to obtain hydrosilanized silica in which the surface hydroxyl groups had been reduced with polymethylhydrosiloxane (PMHS). The resulting hydrosilanized silica was subjected to measurements of the hydroxyl group content per unit weight and the degree of methanol hydrophobicity according to the methods described above. The results are shown in Table 1.

[0050] (2) Preparation of colored resin particles A polymerizable monomer mixture was prepared by dispersing 75 parts of styrene and 25 parts of n-butyl acrylate as polymerizable monomers, 0.25 parts of a polymethacrylate macromonomer (manufactured by Toa Gosei Chemical Industry Co., Ltd., trade name: AA6, Tg = 94°C) as a macromonomer, 0.9 parts of divinylbenzene as a crosslinkable polymerizable monomer, and 12 parts of carbon black as a black colorant using a media-type emulsifier / disperser. To the wet-milled mixture, 4.3 parts of a charge control resin (manufactured by Fujikura Chemical Co., Ltd., trade name: Acribase FCA-676P) as a charge control agent, 6 parts of Wax A (pentaerythritol tetrastearate, acid value: 0.1 mg KOH / g, hydroxyl value: 3 mg KOH / g) as a mold release agent, and 1.0 part of tetraethyl thiuram disulfide as a molecular weight modifier. The mixture was then mixed and dissolved to prepare a polymerizable monomer composition.

[0051] A magnesium hydroxide colloidal dispersion was prepared by gradually adding, with stirring, an aqueous solution of 7.3 parts of sodium hydroxide in 50 parts of ion-exchanged water to an aqueous solution of 10.4 parts of magnesium chloride in 280 parts of ion-exchanged water.

[0052] The polymerizable monomer composition was added to the magnesium hydroxide colloidal dispersion (amount of magnesium hydroxide colloid: 5.3 parts), and the mixture was further stirred, followed by the addition of 6 parts of t-butylperoxy-2-ethylhexanoate as a polymerization initiator. The dispersion containing the polymerization initiator was dispersed at a rotation speed of 15,000 rpm using an in-line emulsifying disperser (manufactured by Pacific Machinery Works, Ltd., trade name: Milder) to form droplets of the polymerizable monomer composition.

[0053] The dispersion containing droplets of the polymerizable monomer composition was placed in a reactor and heated to 90°C to carry out the polymerization reaction. After the polymerization conversion rate reached nearly 100%, 0.1 parts of 2,2'-azobis(2-methyl-N-(2-hydroxyethyl)-propionamide) (manufactured by Wako Pure Chemical Industries, Ltd., trade name: VA-086, water-soluble initiator) as a shell polymerization initiator was dissolved in the aqueous dispersion of the shell polymerizable monomer and added to the reactor. The temperature was then maintained at 95°C for 4 hours to further continue the polymerization, after which the reaction was stopped by water cooling to obtain an aqueous dispersion of core-shell type colored resin particles. While stirring the aqueous dispersion of colored resin particles, sulfuric acid was added to the mixture until the pH reached 4.5 or less, followed by acid washing (25°C, 10 minutes). The colored resin particles were filtered out, washed with water, and the wash water was then filtered. The electrical conductivity of the filtrate was 20 μS / cm. Furthermore, the colored resin particles after the washing and filtering steps were dehydrated and dried to obtain dried colored resin particles.

[0054] (3) Toner Preparation Next, hydrosilanized silica was added to the obtained colored resin particles in an amount of 1% by weight based on the total weight of the colored resin particles and silica, and the mixture was mixed and stirred using a high-speed mixer (manufactured by Nippon Coke & Engineering Co., Ltd., product name: FM Mixer) to perform external addition treatment, thereby preparing a toner. The charge amount of the obtained toner was measured according to the method described above. The results are shown in Table 1.

[0055] <Example 2, Comparative Example 1> Hydrosilanized silica and toner were obtained and evaluated in the same manner as in Example 1, except that the amount of polymethylhydrosiloxane used was changed to the amount shown in Table 1. The results are shown in Table 1.

[0056] <Comparative Example 2> A toner was obtained and evaluated in the same manner as in Example 1, except that silica was used as is without being subjected to hydrosilanization treatment with polymethylhydrosiloxane. The results are shown in Table 1.

[0057] Example 3 Silica (product name "Aerosil 50", manufactured by Aerosil Co., Ltd., primary particle diameter: 30 nm, BET specific surface area: 50 m 2 Hydrosilanized silica was obtained in the same manner as in Example 1, except that a hydroxyl group content per unit weight and a degree of methanol hydrophobicity were measured. The results are shown in Table 2.

[0058] <Example 4, Comparative Examples 3-4> Hydrosilanized silica was obtained and evaluated in the same manner as in Example 3, except that the amount of polymethylhydrosiloxane used was changed to the amount shown in Table 2. The results are shown in Table 1.

[0059] <Comparative Example 5> The silica used in Example 3 was not subjected to hydrosilanization treatment, and the hydroxyl group content per unit weight and the degree of methanol hydrophobicity were measured. The results are shown in Table 2.

[0060] [Table 1]

[0061] [Table 2]

[0062] As shown in Table 1, the amount of hydroxyl groups per unit weight is 1.25 × 10 19 ~3.5×10 19 The toners of Examples 1 and 2, which contain silica powder with a methanol hydrophobicity of 68% or more and a particle density of 100 / g, exhibited reduced charge under normal temperature and humidity conditions, high temperature and humidity conditions, and low temperature and humidity conditions, and also exhibited reduced absolute values ​​of charge change due to temperature and humidity changes. In other words, the toners of Examples 1 and 2 exhibited reduced effects of temperature and humidity changes on chargeability and exhibited excellent print stability.

[0063] On the other hand, the amount of hydroxyl groups per unit weight is 1.25 × 10 19Less than 3.5 x 10 particles / g 19 The toners of Comparative Examples 1 and 2, which contain silica powder with a methanol hydrophobicity of less than 68% and a particle density of more than 100 / g, exhibited a large amount of charge under normal temperature and humidity conditions and low temperature and low humidity conditions, and also exhibited a large amount of change in charge amount due to changes in temperature and humidity. In other words, the toners of Comparative Examples 1 and 2 were significantly affected by changes in temperature and humidity on chargeability, and were inferior in print stability.

Claims

1. The amount of hydroxyl groups per unit weight is 1.25 x 10 １９ ~3.5 x 10 １９ The silica powder used as an external additive for a toner has a methanol hydrophobicity of 68% or more and a particle size of 1000 / g.

2. 2. The silica powder used as an external additive for a toner according to claim 1, wherein the primary particle diameter is 1 to 150 nm.

3. Specific surface area is 10 to 300 m ２ 3. The silica powder used as an external additive for the toner according to claim 1, wherein the silica powder has a molecular weight of 1 / g.

4. Bulk density of 0.001 to 0.5 g / cm ３ 3. The silica powder used as an external additive for the toner according to claim 1, wherein

5. 3. The silica powder used as an external additive for a toner according to claim 1, wherein the silica powder has been subjected to a treatment to reduce the number of hydroxyl groups on the surface.

6. 6. The silica powder used as an external additive for a toner according to claim 5, wherein the silica powder has been subjected to a treatment to reduce surface hydroxyl groups by reacting a hydrosilane compound in a hydrocarbon solvent in the presence of a borane catalyst.

7. 3. The silica powder used as an external additive for a toner according to claim 1 or 2.

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