JP2010122306A - Positively charged toner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a positively charged toner which permits a wide transferrable area even in an environment of high temperature and high humidity. <P>SOLUTION: The positively charged toner is composed of: a base toner particle comprising at least a colorant and polyester as a binder resin; and an external additive externally added to the base toner particle, wherein the base toner particle comprises silica (A) which is surface-treated with fluorine type silane coupling agent as the external additive and has a BET relative surface area of 50 to 200 m<SP>2</SP>/g and silica (B) which is surface-treated with amino-modified silicone and has a BET relative surface area of 50 to 200 m<SP>2</SP>/g, an addition amount of the silica (B) is 0.7 to 2.3 pts.wt. based on 100 pts.wt. of the base toner particle and a resistivity of the toner is 1.10×10<SP>11</SP>to 3.0×10<SP>11</SP>Ωcm. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a positively chargeable toner used for developing a latent image formed in an electrophotographic method, an electrostatic recording method, an electrostatic printing method or the like.

  For the purpose of preventing fogging and uniform image density under low and high humidity, Patent Document 1 discloses that in a toner containing toner particles and fine particle aggregate, the fine particle aggregate contains silicone oil or silicone varnish. The fine particles forming the fine particle aggregate are treated with a silane coupling agent and a hydrophobizing agent having nitrogen atoms at least in the side chains, or treated with a silicone oil or silicone varnish having at least nitrogen atoms in the side chains. Disclosed toners are disclosed. In order to improve transferability in a high-temperature and high-humidity environment, Patent Document 2 discloses a hydrophobic rutile type titanium oxide, hexamethyl, whose average particle size of primary particles hydrophobized with a silane coupling agent is 5 to 30 nm. Hydrophobic silica with an average primary particle size of 6 to 14 nm hydrophobized with disilazane and hydrophobic silica with an average primary particle size of 20 to 100 nm hydrophobized with silicone oil are externally added. Toner is disclosed.

Further, in order to improve cleaning properties and transfer properties, Patent Document 3 discloses that toner particles have a circularity of 0.95 or more, a shape factor SF-2 of 120 to 150, and a toner resistance of 5 × 10 ^{7 to} 3. A toner having × 10 ¹¹ Ω · cm is disclosed.
JP-A-10-142833 JP 2004-258265 A JP 2005-257976 A

  However, in an electrophotographic apparatus that applies a certain voltage to the transfer roll and transfers the toner image on the photoreceptor onto the paper, a transfer failure occurs when printing on a narrow paper such as a postcard in a high-temperature and high-humidity environment. In the prior art, the shape of the toner is increased and the amount of silica added as an external additive is increased for the purpose of reducing the adhesion of the toner to the photoreceptor in order to improve the transfer from the photoreceptor to the paper. However, sufficient effect is not obtained. In Patent Document 3, although the problem is solved by adjusting the sphericity and resistance value of the polymerized toner, for example, a spheroidizing step is required to adjust the sphericity in the production of toner by a pulverization method. .

  An object of the present invention is to provide a positively chargeable toner capable of obtaining a wide transferable region even under high temperature and high humidity.

The present invention relates to a positively chargeable toner comprising toner base particles containing at least a colorant and polyester as a binder resin, and an external additive externally added to the toner base particles. , the silica a of the external additive is a BET specific surface area surface-treated with a fluorine silane coupling agent is 50 to 200 m ² / g, a BET specific surface area surface-treated with an amino-modified silicone is 50 to 200 m ² / g The amount of silica B added is 0.7 to 2.3 parts by weight with respect to 100 parts by weight of toner base particles, and the toner resistivity is 1.10 × 10 ^{11 to} 3.0 × 10 ¹¹ Ωcm. The present invention relates to a certain positively chargeable toner.

  The positively chargeable toner of the present invention has an excellent effect that a wide transferable region can be obtained even under high temperature and high humidity.

The positively chargeable toner of the present invention comprises toner base particles containing at least a colorant and polyester as a binder resin, and an external additive externally added to the toner base particle, and the external additive is a fluorine-based silane. A toner containing silica A having a BET specific surface area of 50 to 200 m ² / g surface-treated with a coupling agent and silica B having a BET specific surface area of 50 to 200 m ² / g surface-treated with an amino-modified silicone, and a toner It has a great feature in that the resistivity is 1.10 × 10 ^{11 to} 3.0 × 10 ¹¹ Ωcm. As a result of examination by the inventors of the transfer failure under high temperature and high humidity, the cause of the transfer failure is the charge injection of the reverse polarity to the toner to the toner on the photoconductor in the transfer portion (contact portion between the paper and the toner). It was estimated that there was an outbreak. In a high-temperature and high-humidity environment (for example, 35 ° C. and relative humidity 85%), the electrical resistance of the paper is smaller than that in a normal temperature and normal humidity environment, and current flows easily through the paper. That is, in a high temperature and high humidity environment, the electrical resistance value of the transfer roll decreases and the electrical resistance value of the paper also decreases. In particular, when printing is performed on a narrow paper such as a postcard, the area where the transfer roll and the paper are in contact with each other is small, so that the current per unit area flowing through the paper in the transfer unit is large. However, in the present invention, by controlling the resistivity of the toner to 1.10 × 10 ^{11 to} 3.0 × 10 ¹¹ Ωcm, it becomes difficult for current to flow from the paper to the toner on the photoconductor, and the toner on the photoconductor in the transfer portion It is presumed that charge injection into the is suppressed. Since the fluorine-based silane coupling agent has high negative chargeability, the toner adheres to the surface of the positively charged photoreceptor through silica A surface-treated with the fluorine-based silane coupling agent. It is considered that there is an effect of reducing the adhesive force and an effect of making it difficult for the current to flow from the paper to the toner on the photoconductor. Furthermore, by using silica B surface-treated with amino-modified silicone in combination, the positive chargeability of the toner and the water repellency of the toner surface are improved, the chargeability of the toner in a high-temperature and high-humidity environment is reduced, and the moisture on the toner surface is reduced. By suppressing the adhesion, it is considered that the toner particles are prevented from aggregating due to a decrease in the cross-linking force between water and the electrical resistance value is suppressed, and the effect of suppressing the charge injection to the toner on the photoreceptor is exhibited. From the above, the effect of suppressing the charge injection to the toner on the photoreceptor at the transfer portion, the effect of reducing the adhesion between the photoreceptor and the toner, and the effect of reducing the cohesive force of the toner due to the liquid crosslinking force are produced. Even when printing on narrow paper, for example, paper having a width of 150 mm or less, preferably 50 to 150 mm, more preferably 70 to 110 mm, it is estimated that a wide transferable area can be obtained.

As the fluorine-based silane coupling agent, a known fluorine-containing silane coupling agent can be used. For example, a fluorine-based silane compound having a hydrolyzable silyl group, a hydroxysilyl group, an epoxy group, or the like as a functional group. Can be mentioned. Examples of the fluorine silane compound include fluorine-containing chlorosilane, fluorine-containing alkoxysilane, fluorine-containing epoxy silane, and the like. Specifically, as fluorine-containing chlorosilane, CF ₃ CH ₂ CH ₂ SiCl ₃ , CF ₃ CH ₂ CH ₂ Si (CH ₃ ) Cl ₂ , CF ₃ (CF ₂ ) ₃ CH ₂ CH ₂ SiCl ₃ , CF ₃ C (= O) OCH ₂ CH ₂ Si (OCH ₃ ) ₃ , nC ₈ F ₁₇ CH ₂ CH ₂ Si (CH ₃ ) (OCH ₃ ) ₂ , nC ₄ F ₉ CH ₂ CH ₂ Si (OCH ₃ ) ₃ , C ₇ F ₁₅ CONHCH ₂ CH ₂ Si (OC ₂ H ₅ ) ₃ , CF ₃ CH ₂ CH ₂ Si (CH ₃ ) (OCH ₃ ) ₂ , C ₈ F ₁₇ SO ₂ NHCH ₂ CH ₂ CH ₂ Si (OC ₂ H ₅ ) ₃ , CF ₃ CH ₂ CH ₂ Si ( OCH ₃ ) ₃ , C ₇ H ₁₅ COOCH ₂ CH ₂ Si (OCH ₃ ) ₃ , C ₉ F ₁₉ SO ₂ CH ₂ CH ₂ Si (OCH ₃ ) ₃ , CF ₃ C (= O) OSi (CH ₃ ) ₃ , CF ₃ SO ₂ Si (CH ₃ ) _{3 and the} like. These can be used alone or in combination of two or more. Among these, from the viewpoint of imparting charging performance and water repellency, a fluorine-based silane compound having a hydrolyzable silyl group, for example, chlorosilane having fluorine is preferable. Specifically, CF ₃ CH ₂ CH ₂ Si (OCH ₃ ) ₃ is preferred.

  Silica A may be used in combination with a treatment agent other than the fluorine-based silane coupling agent as long as the effects of the present invention are not impaired.

BET specific surface area of the silica A, from the viewpoint of adhesion to the photosensitive member in the toner is 50 to 200 m ² / g, preferably from 50 to 150 m ² / g, more preferably 75~125m ² / g. If the BET specific surface area of silica A is less than 50 m ² / g, adhesion to the photoreceptor will not occur, and if it is greater than 200 m ² / g, adhesion to the photoreceptor will occur excessively to contaminate the photoreceptor.

  The amount of silica A added is preferably 0.1 parts by weight or more with respect to 100 parts by weight of toner base particles from the viewpoint of adhesion of the toner to the photoreceptor, and 3 parts by weight or less from the viewpoint of preventing contamination of the photoreceptor. preferable. Therefore, from these viewpoints, the addition amount of silica A is preferably 0.1 to 3 parts by weight and more preferably 0.3 to 1.5 parts by weight with respect to 100 parts by weight of the toner base particles.

  Examples of the amino-modified silicone include an organopolysiloxane having an amino group, and the amino equivalent of the organopolysiloxane having an amino group is preferably 250 or more from the viewpoint of imparting positive chargeability to the toner.

  Silica B may be used in combination with a treatment agent other than amino-modified silicone as long as the effects of the present invention are not impaired. However, when a fluorine-based silane coupling agent is used in combination, it is classified as silica A.

BET specific surface area of the silica B from the viewpoint of fluidity of toner and positively chargeable, is 50 to 200 m ² / g, preferably from 50 to 150 m ² / g, more preferably 75~125m ² / g.

  The addition amount of silica B is 0.7 to 2.3 parts by weight, preferably 0.4 to 2.0 parts by weight, and more preferably 0.5 to 1.7 parts by weight with respect to 100 parts by weight of the toner base particles from the viewpoint of positive chargeability of the toner. It is.

  The weight ratio of silica A and silica B is preferably 1/9 to 4/6, more preferably 1/9 to 3/7, and more preferably 2/8 to 3/7, from the viewpoint of positive chargeability and transferability of the toner. Is more preferable.

  In the toner of the present invention, it is preferable that silica C having a BET specific surface area larger than any of BET specific surface areas of silica A and silica B is externally added as an external additive. Silica C can reduce toner aggregation due to the pressure of the transfer roll and the photoreceptor in the transfer portion, and can maintain good fluidity of the toner, thereby further improving transferability and image density.

  Silica C may be treated with a surface treatment agent. Examples of the surface treatment agent include hexamethyldisilazane (HMDS), dimethyldichlorosilane (DMDS), aminosilane, silicone oil, amino-modified silicone, cyclic silazane, silicone oil such as methyltriethoxysilane, and the like. Or in combination of two or more. Among these, cyclic silazane is preferable from the viewpoint of positive chargeability, and more preferably used in combination with HMDS from the viewpoint of fluidity. The weight ratio of cyclic silazane to HMDS treatment (cyclic silazane / HMDS) is preferably 1/9 to 9/1.

The difference of the silica C a BET specific surface area and silica A, and BET specific surface area of the larger one of the silica B is preferably from 50 m ² / g or more, more preferably 50~300m ² / g, 50~200m ² / More preferred is g.

The BET specific surface area of silica C is preferably 210 to 400 m ² / g, more preferably 210 to 350 m ² / g, from the viewpoint of improving the fluidity of the toner.

  The addition amount of silica C is preferably from 0.1 to 3 parts by weight, more preferably from 0.1 to 2 parts by weight, based on 100 parts by weight of the toner base particles, from the viewpoints of toner fluidity and fixability.

  Further, it is preferable that polytetrafluoroethylene (PTFE) particles having an average particle diameter of 100 to 1000 nm are further externally added as an external additive. PTFE particles have the effect of increasing the positive chargeability of the toner by frictional charging with the toner particles, and the effect of increasing the positive chargeability by PTFE adhering to the regulating blade, etc. and frictionally charging the toner. Further improvement.

  PTFE particles are classified into a polymerization type / decomposition type and a regeneration type obtained by pulverizing cutting scraps, etc., depending on the manufacturing method. In the present invention, any type may be used, but from the viewpoint of ensuring the charging stability of the toner, a polymerization type is preferable, and an emulsion polymerization type is more preferable. Commercially available emulsion polymerization types include `` Lublon L2 '' (Daikin Industries, average particle size 300 nm), `` Lublon L5 '' (Daikin Industries, average particle size 200 nm), `` Lublon L-5F '' (Daikin Industries) And an average particle size of 300 nm), “Lublon L7” (manufactured by Daikin Industries, Ltd., average particle size of 400 nm), and the like. Examples of the reproduction type commercial product include “KTL-500F” (manufactured by Kitamura Co., Ltd., average particle size: 500 nm).

  The average particle diameter of the PTFE particles is preferably 100 to 1000 nm, more preferably 100 to 700 nm, from the viewpoint of stabilizing the chargeability of the toner.

  The amount of PTFE particles added is preferably 0.1 to 2 parts by weight and more preferably 0.1 to 1 part by weight with respect to 100 parts by weight of the toner base particles from the viewpoint of stabilizing the chargeability of the toner.

  The toner of the present invention may contain external additives other than the silicas A to C and PTFE particles as long as the effects of the present invention are not impaired. The total content of PTFE particles in the external additive is preferably 50% by weight or more, more preferably 80% by weight or more, further preferably 90% by weight or more, and substantially more preferably 100% by weight.

  Silica A and B, as well as silica C and PTFE particles can be added to the toner base particles by adding silica A, B, C and PTFE particles to the toner base particles all at once. From the viewpoint of suppressing the aggregation of the external additive due to the charging property, it is preferable that silica B and C are mixed with the toner base particles in the first mixing step, and then silica A and PTFE particles are added in the second mixing step.

  In the toner of the present invention, the toner base particles contain a binder resin and a colorant, and contain polyester as the binder resin from the viewpoint of optimizing the low-temperature fixability, durability and toner resistivity of the toner. To do.

  The polyester is not particularly limited, and can be obtained by polycondensing a raw material monomer containing an alcohol component composed of a divalent or higher alcohol and a carboxylic acid component composed of a divalent or higher carboxylic acid compound.

  As the dihydric or higher alcohol, from the viewpoint of the storage stability of the toner, the formula (I):

(In the formula, RO and OR are oxyalkylene groups, R is an ethylene and / or propylene group, x and y represent the number of added moles of alkylene oxide, each being a positive number, and the sum of x and y. 1 to 16 is preferable, 1 to 8 is more preferable, and 1.5 to 4 is more preferable)
An alkylene oxide adduct of bisphenol A represented by The content of the alkylene oxide adduct of bisphenol A is preferably 50 mol% or more, more preferably 60 mol% or more, and further preferably 80 mol% or more in the alcohol component.

  Examples of the alkylene oxide adduct of bisphenol A represented by the formula (I) include polyoxyethylene-2,2-bis (4-hydroxyphenyl) propane and other ethylene oxide adducts having 2 carbon atoms, such as polyoxypropylene. Examples thereof include propylene oxide adducts having 3 carbon atoms such as -2,2-bis (4-hydroxyphenyl) propane.

  As alcohol components other than the alkylene oxide adduct of bisphenol A, ethylene glycol, 1,2-propylene glycol, 1,4-butanediol, neopentyl glycol, polyethylene glycol, polypropylene glycol, bisphenol A, hydrogenated bisphenol A, sorbitol , Pentaerythritol, glycerol, trimethylolpropane and the like.

  Examples of the divalent or higher carboxylic acid compound include adipic acid, fumaric acid, maleic acid, succinic acid (for example, n-dodecenyl succinic acid, isododecenyl succinic acid, n-dodecyl succinic acid, isooctenyl succinic acid, Aliphatic carboxylic acids such as succinic acid substituted with alkyl groups having 1 to 20 carbon atoms or alkenyl groups having 2 to 20 carbon atoms such as isooctyl succinic acid, phthalic acid, isophthalic acid, terephthalic acid, 1,2, 4-Benzenetricarboxylic acid (trimellitic acid), 2,5,7-naphthalenetricarboxylic acid, aromatic carboxylic acids such as pyromellitic acid, anhydrides of these acids and lower alkyl (C1-3) esters, etc. Is mentioned. In addition, the acids as described above, anhydrides of these acids, and alkyl esters of the acids are collectively referred to as carboxylic acid compounds in this specification.

  The alcohol component may contain a monovalent alcohol and the carboxylic acid component may contain a monovalent carboxylic acid compound as appropriate from the viewpoint of adjusting the molecular weight of the resin and improving the offset resistance of the toner.

  The condensation polymerization of the alcohol component and the carboxylic acid component can be performed, for example, in an inert gas atmosphere at a temperature of 180 to 250 ° C., but may be performed in the presence of an esterification catalyst, a polymerization inhibitor, or the like. preferable. Examples of the esterification catalyst include dibutyltin oxide, titanium compounds, tin (II) compounds having no Sn—C bond, and the like. These may be used alone or in combination.

  In the present invention, the polyester may be a polyester modified to such an extent that the characteristics are not substantially impaired. Examples of the modified polyester include grafting and blocking with phenol, urethane, epoxy and the like by the methods described in JP-A-11-133668, JP-A-10-239903, JP-A-8-20636, and the like. Polyester.

  The binder resin may contain a polycondensation resin other than polyester, a vinyl resin such as styrene-acrylic resin, an epoxy resin, a polycarbonate, a polyurethane, etc., as long as the effects of the present invention are not impaired. The polyester content in the binder resin is preferably 90% by weight or more, and more preferably 95% by weight or more.

  The softening point of the polyester is preferably 120 to 160 ° C, more preferably 130 to 155 ° C, from the viewpoint of toner durability. When the polyester is composed of two or more kinds, it is preferable that the weighted average value is within the above range.

  The glass transition point of the polyester is preferably from 50 to 85 ° C, more preferably from 55 to 80 ° C, from the viewpoint of toner storage stability. The acid value is preferably 0.5 to 40 mg KOH / g from the viewpoint of environmental stability of the toner.

  As the colorant, all of dyes and pigments used as toner colorants can be used. Carbon black, black pigment, phthalocyanine blue, permanent brown FG, brilliant first scarlet, pigment green B, rhodamine- B base, Solvent Red 49, Solvent Red 146, Solvent Blue 35, Quinacridone, Carmine 6B, Isoindoline, Disazo yellow and the like can be used alone or in combination of two or more of the present invention. The toner may be either black toner or color toner. The content of the colorant is preferably 1 to 40 parts by weight and more preferably 1 to 10 parts by weight with respect to 100 parts by weight of the binder resin.

  Examples of toner raw materials other than the binder resin and the colorant include charge control agents, release agents, magnetic powders, conductivity modifiers, extender pigments, reinforcing fillers such as fibrous substances, antioxidants, and anti-aging agents. An additive is mentioned.

  As the charge control agent, either a negative charge property or a positive charge property can be used, but a positive charge property charge agent is preferable. Examples of the positively chargeable charge control agent include nigrosine dyes, triphenylmethane dyes, quaternary ammonium salt compounds, polyamine resins, and imidazole derivatives. The content of the positively chargeable charge control agent is preferably 0.1 to 8 parts by weight and more preferably 0.2 to 5 parts by weight with respect to 100 parts by weight of the binder resin. In addition, a polymer-type positively chargeable charge control resin such as a resin can be used. In the case of a positively chargeable charge control resin, the content is 1 to 20 weights with respect to 100 parts by weight of the binder resin. Part is preferable, and 2 to 15 parts by weight is more preferable. Further, a negatively chargeable charge control agent may be used in combination as long as the positive chargeability of the toner is not impaired. Examples of the negatively chargeable charge control agent include metal-containing azo dyes, copper phthalocyanine dyes, metal complexes of salicylic acid alkyl derivatives, polymers of phenols and aldehydes such as nitroimidazole derivatives and calixarene, and the like.

  As the release agent, low molecular weight polypropylene, low molecular weight polyethylene, low molecular weight polypropylene polyethylene copolymer, aliphatic hydrocarbon waxes such as microcrystalline wax, paraffin wax, Fischer-Tropsch wax and their oxides, carnauba wax, Examples include ester waxes such as montan wax, sasol wax and their deoxidized wax, fatty acid amides, fatty acids, higher alcohols, fatty acid metal salts and the like. Among these, aliphatic hydrocarbon waxes and ester waxes are preferable from the viewpoint of releasability and stability, and these may be contained alone or in admixture of two or more. The content of the release agent is preferably 1 to 20 parts by weight and more preferably 1 to 10 parts by weight with respect to 100 parts by weight of the binder resin.

As described above, the toner of the present invention has a resistivity of 1.10 × 10 ^{11 to} 3.0 × 10 ¹¹ Ωcm, preferably 1.20 × 10 ^{11 to} 2.0 × 10 ¹¹ Ωcm, more preferably 1.30 × 10 ^{11 to} 1.50 × 10. ¹¹ Ωcm. The resistivity of the toner can be adjusted by, for example, addition of a material having high or low conductivity or surface treatment of the toner. Specifically, when carbon black is used as the colorant, the toner resistivity decreases as the carbon black increases, and the efficiency decreases as the carbon black decreases. When the colorant is not carbon black, for example, the resistivity of the toner can be adjusted by adding indium oxide, tin oxide, antimony oxide powder, metal powder, copper iodide, or the like as conductive metal fine particles.

  In the present invention, the method for producing toner base particles is not particularly limited, and for example, toner base particles obtained by any of a polymerization method and a pulverization method may be used. In the present invention, the raw material containing the binder resin and the colorant is kneaded in that the toner base particles are produced by a pulverization method and the resistance can be controlled to be lower than that obtained by the polymerization method. Toner base particles obtained by a pulverization method, including a step of pulverizing the obtained kneaded product with a pulverizer, are preferred.

  When toner base particles are produced by a pulverization method, for example, a raw material such as a binder resin, a charge control agent, and a colorant are mixed uniformly with a mixer such as a Henschel mixer, and then a sealed kneader or a uniaxial or biaxial It can be manufactured by kneading using a kneader such as an extruder or an open roll kneader, cooling to an extent capable of pulverization, pulverizing, and classifying appropriately.

  Examples of the pulverizer used for pulverization of the melt-kneaded product include jet pulverizers such as an atomizer, a rotoplex, a fluidized bed jet mill, and an airflow jet mill, a turbo mill, a collision plate mill, and a rotary mechanical mill.

  As the mixer used for mixing the toner base particles and the external additive, a high-speed stirrer such as a Henschel mixer or a super mixer, or a stirrer used for dry mixing such as a V-type blender is preferable. The external additives may be mixed in advance and added to a high-speed stirrer or a V-type blender, or may be added separately.

The volume median particle diameter (D ₅₀ ) of the toner is preferably 3 to 15 μm, more preferably 4 to 10 μm. In the present specification, the volume-median particle size (D ₅₀ ) means a particle size at which the cumulative volume frequency calculated by the volume fraction is 50% when calculated from the smaller particle size.

  The positively chargeable toner of the present invention can be used as a one-component developing toner or as a two-component developer mixed with a carrier.

[Softening point of resin]
Using a flow tester (Shimadzu Corporation, CFT-500D), a 1 g sample is heated at a heating rate of 6 ° C / min. While applying a load of 1.96 MPa with a plunger and extruded from a nozzle with a diameter of 1 mm and a length of 1 mm. . Plot the plunger drop amount of the flow tester against the temperature, and let the softening point be the temperature at which half of the sample flows out.

[Glass transition point of resin]
Using a differential scanning calorimeter (Seiko Denshi Kogyo Co., Ltd., DSC210), the temperature was raised to 200 ° C, and the sample was cooled to 0 ° C at a temperature drop rate of 10 ° C / min. The temperature at the intersection of the extended line of the baseline below the maximum peak temperature of endotherm and the tangent line indicating the maximum slope from the peak rising portion to the peak apex.

[Acid value of the resin]
Measured by the method of JIS K0070. However, only the measurement solvent was changed from the mixed solvent of ethanol and ether specified in JIS K0070 to the mixed solvent of acetone and toluene (acetone: toluene = 1: 1 (volume ratio)).

[BET specific surface area of silica]
Measured by nitrogen adsorption method.

[Average particle diameter of silica]
Number average particle diameter (nm) = 6 / (ρ × specific surface area (m ² / g)) × 1000
In the formula, ρ is the specific gravity of silica (2.2). The specific surface area is a BET specific surface area determined by a nitrogen adsorption method. In the case of silica containing a metal or metal oxide, the specific surface area of the raw material before containing the metal or metal oxide is used. In the case of a hydrophobized external additive, Specific surface area.
Note that the above equation assumes a sphere with a particle size R,
BET specific surface area = S x (1 / m)
m (weight of particle) = 4/3 x π x (R / 2) ³ x specific gravity
S (surface area) = 4π (R / 2) ²
Is an expression obtained from

[Average particle size of PTFE particles]
The average particle diameter is the number average particle diameter.
The number average particle size is measured with a scanning electron microscope at an appropriate magnification of 5000 to 50000 times, and the particle size (average value of major axis and minor axis) is measured for 100 particles, and the average value is averaged. The particle size.

[Toner resistivity]
A pressure of 1.2 tons is applied to 5 g of toner for 10 seconds to prepare pellets with a smooth surface having a diameter of 60.0 mm and a thickness of 1.8 mm. When the obtained pellet was measured at 1 kHz in an environment with a temperature of 25 ° C. and a humidity of 50% using a region LCR meter “HP4284A” and a dielectric measurement electrode “HP16451B” (both manufactured by Yokogawa Hewlett Packard). Adopt resistivity.

[Volume-median particle size of toner (D ₅₀ )]
In this specification, the volume-median particle size (D ₅₀ ) of the toner means the particle size of the toner in which the cumulative volume frequency calculated by the volume fraction is 50% calculated from the smaller particle size.
Measuring instrument: Coulter Multisizer II (Beckman Coulter, Inc.)
Aperture diameter: 50μm
Analysis software: Coulter Multisizer AccuComp version 1.19 (Beckman Coulter)
Electrolyte: Isoton II (Beckman Coulter)
Dispersion: Emulgen 109P (manufactured by Kao Corporation, polyoxyethylene lauryl ether, HLB: 13.6) 5% by weight Electrolyte dispersion condition: 10 mg of measurement sample was added to 5 mL of dispersion, and dispersed for 1 minute with an ultrasonic disperser. Thereafter, 25 mL of an electrolytic solution is added, and further dispersed with an ultrasonic disperser for 1 minute.
Measurement conditions: The dispersion is added to 100 mL of the electrolytic solution so that the particle size of 30,000 toner particles can be measured in 20 seconds, and 30,000 particles are measured. Determine the median particle size (D ₅₀ ).

Example of resin production The alcohol component and carboxylic acid component shown in Table 1 and 20 g of tin (II) 2-ethylhexanoate as an esterification catalyst were added in a 5-liter volume equipped with a nitrogen introduction tube, a dehydration tube, a stirrer and a thermocouple. Place in a four-necked flask and react in a nitrogen atmosphere at 230 ° C until the reaction rate reaches 90%, then react at 8.3 kPa until the desired softening point is reached, and polyester (resins A and B). Obtained. The reaction rate means a value of the amount of generated reaction water (mol) / theoretical generated water amount (mol) × 100.

Examples 1-8 and Comparative Examples 1-7
Resin A 50 parts by weight, Resin B 50 parts by weight, colorant “Regal 330R” (carbon black, manufactured by Cabot) shown in Table 2, positive charge control agent “Bontron N-04” (manufactured by Orient Chemical Co., Ltd.) Using Henschel mixer, 3 parts by weight, 7 parts by weight of positively chargeable charge control resin “FCA-F201-PS” (Fujikura Kasei) and 2.0 parts by weight of polypropylene wax “NP-055” (Mitsui Chemicals) And mixed. The obtained mixture was melt-kneaded by a twin screw extruder, cooled, and then roughly pulverized to about 1 mm using a hammer mill. The obtained coarsely pulverized product was finely pulverized by an air jet type pulverizer and classified to obtain toner mother particles having a volume median particle size (D ₅₀ ) of 7.5 μm.

  An external additive (commercially available product) shown in Table 2 was added to 100 parts by weight of the toner base particles, and externally added using a Henschel mixer to obtain a toner. As an addition method, silica B and C were mixed with toner base particles for 180 seconds (first mixing step), and then silica A and PTFE particles were added and mixed for 180 seconds (second mixing step). “Parts by weight” in Table 2 is parts by weight with respect to 100 parts by weight of the binder resin of the toner base particles.

<Transferable area>
Toner is mounted on a positively chargeable non-magnetic one-component developing device “HL-2040” (Brother Kogyo Co., Ltd.) equipped with an organic photoconductor (OPC) in an environment (HH environment) at a temperature of 35 ° C and a relative humidity of 85%. After leaving for 24 hours, change the applied current to the transfer roll from 2μA to 20μA with an external power supply, and print 4on4off images (4 dot line / 4 dot blank images) at the beginning of postcard paper (vertical feed) went. The presence or absence of retransfer of the transfer residual toner that occurred in the circumferential long period of the photoconductor (transfer defect occurrence) was visually confirmed, and the area of the applied current where no retransfer occurred was used as the transfer window. The results are shown in Table 2.

<Image density>
Toner is mounted on a positively chargeable non-magnetic one-component developing device “HL-2040” (Brother Kogyo Co., Ltd.) equipped with an organic photoconductor (OPC) in an environment (HH environment) at a temperature of 35 ° C and a relative humidity of 85%. Then, the current applied to the transfer roll was set to -8 μA, and the developing bias was set so that the toner adhesion amount on the photoreceptor was 0.42 to 0.45 mg / cm ² . Thereafter, a 1-inch square image was printed on postcard paper (vertical feed). The image density of the solid image was measured by “X-Rite” (manufactured by X-Rite), and the image density was evaluated according to the following evaluation criteria. The results are shown in Table 2.

〔Evaluation criteria〕
A: Image density is 1.40 or more B: Image density is 1.35 or more and less than 1.40 C: Image density is 1.30 or more and less than 1.35 D: Image density is less than 1.30

  From the above results, it can be seen that the toners of Examples 1 to 8 have a wide transferable area and a good image density as compared with Comparative Examples 1 to 7.

  The positively chargeable toner of the present invention is suitably used for developing latent images formed in electrophotography, electrostatic recording, electrostatic printing, and the like.

Claims (5)

A positively chargeable toner comprising toner base particles containing at least a colorant and polyester as a binder resin and an external additive externally added to the toner base particles, wherein the toner base particles are the external additive. Silica A having a BET specific surface area of 50 to 200 m ² / g surface-treated with a fluorine-based silane coupling agent and Silica B having a BET specific surface area of 50 to 200 m ² / g surface-treated with amino-modified silicone And the addition amount of the silica B is 0.7 to 2.3 parts by weight with respect to 100 parts by weight of the toner base particles, and the toner has a resistivity of 1.10 × 10 ^{11 to} 3.0 × 10 ¹¹ Ωcm. toner.   The positively chargeable toner according to claim 1, wherein the weight ratio of silica A and silica B (silica A / silica B) is 1/9 to 4/6.   The positively chargeable toner according to claim 1 or 2, wherein the addition amount of silica A is 0.1 to 3 parts by weight with respect to 100 parts by weight of the toner base particles.   The positively chargeable toner according to claim 1, further comprising silica C having a BET specific surface area larger than either silica A or silica B as an external additive.   The positively chargeable toner according to claim 1, further comprising polytetrafluoroethylene particles having an average particle diameter of 100 to 1000 nm as an external additive.