Electrostatic charge image developing toner

Abstract

To provide an electrostatic charge image developing toner which suppresses fogging in a low-temperature, low-humidity environment.SOLUTION: An electrostatic charge image developing toner is provided, comprising toner base particles containing a binder resin and colorant, and an external additive containing silica particles A charged with a polarity opposite that of the toner base particles, the silica particles A having a shape index of 2.0 or greater as expressed as a ratio of a number average particle diameter to a BET equivalent particle diameter.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a toner for developing electrostatic images used for developing latent images formed in electrophotography, electrostatic recording, electrostatic printing and the like. [Background technology]

[0002] Conventionally, external additives have been used in toners for developing electrostatic images from the viewpoint of chargeability and fluidity. Generally, negatively charged external additives are used for negatively charged toners, and positively charged external additives are used for positively charged toners, but the addition of external additives with opposite polarity to the toner base particles and the combined use of positively charged and negatively charged external additives have been considered.

[0003] Patent Document 1 discloses a positively charged toner for developing electrostatic images, which contains colored resin particles including a binder resin and a colorant, and an external additive, characterized in that the external additive is surface-treated negatively charged silicone resin particles, the negatively charged silicone resin particles have a number average particle size of 0.3 to 3 μm and an adsorbed moisture content of 0.20 mass % or less, and the content of the negatively charged silicone resin particles is 0.05 to 2.0 mass parts per 100 mass parts of the colored resin particles.

[0004] Patent Document 2 discloses an invention relating to a toner for developing electrostatic images, the toner comprising toner base particles containing a binder resin, a colorant and a wax, and an external additive, the external additive comprising composite oxide particles (a) and silica particles (b), and satisfying predetermined conditions (A) to (C). It also discloses that the toner may contain, together with the silica particles (b), particles (c) that are charged with an opposite polarity to the silica particles (b). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2016-126140 A [Patent Document 2] JP 2014-142605 A Summary of the Invention [Problem to be solved by the invention]

[0006] Although an external additive having an opposite polarity to the toner base particles has a stronger adhesive force due to electrostatic forces compared to a combination of additives having the same polarity, the external additive is easily detached under low temperature and low humidity conditions, which reduces the chargeability and causes fogging.

[0007] The present invention relates to a toner for developing electrostatic images, which is suppressed from causing fogging under low temperature and low humidity conditions. [Means for solving the problem]

[0008] The present invention relates to a toner for developing electrostatic images, which contains toner base particles containing a binder resin and a colorant, and an external additive, wherein the external additive contains silica particles A having a charge polarity opposite to that of the toner base particles and a shape index, expressed as the ratio of the number average particle diameter to the BET converted particle diameter, of 2.0 or more. Effect of the Invention

[0009] The toner for developing electrostatic images of the present invention exerts an excellent effect of suppressing fogging under low temperature and low humidity conditions. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic cross-sectional view of a conventional silica particle. [Diagram 2] FIG. 2 is an example of a schematic cross-sectional view of a bonded silica particle. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The toner for developing electrostatic images of the present invention is characterized in the shape of the silica particles (silica particles A) contained as an external additive and having a charge polarity opposite to that of the toner base particles. Usually, the particle size and the BET specific surface area are negatively correlated. That is, the larger the number average particle size, the smaller the BET specific surface area. In contrast, the silica particles A in the present invention have a large number average particle size compared to silica particles of the same number average particle size, but have a large BET specific surface area and a small BET converted particle size (particle size) converted from the BET specific surface area, so that the ratio of the number average particle size to the BET converted particle size (shape index) is also large. Such characteristics are due to the shape of the silica particles A, and usually, silica particles exist in a partially aggregated state. Generally, silica particle aggregates are densely aggregated as shown in FIG. 1, whereas the aggregates contained in the silica particles A have gaps between the silica particles as shown in FIG. 2, and have multiple clear convexities on the surface like tetrapods. Silica particles of such a shape (hereinafter also referred to as "bonded silica particles") can adhere to the surface of the toner base particle at multiple points, so they are difficult to detach. On the other hand, under low temperature and low humidity conditions, the liquid bridging force acting between the toner base particles and the external additives is weakened, and the adhesive force of the external additives is likely to decrease. However, in the present invention, since the silica particles A having the above-mentioned shape have the opposite polarity to the toner base particles, they are more firmly attached to the toner base particles by electrostatic force. Therefore, the silica particles are less likely to roll on the toner surface during frictional charging between toner particles, and large aggregation of silica particles is less likely to occur. Therefore, it is presumed that, even though silica particles having the opposite polarity to the toner base particles are added, the charging ability is less likely to decrease, and the occurrence of fogging can be suppressed.

[0012] The shape index of the silica particles A is 2.0 or more, preferably 2.5 or more, more preferably 2.7 or more, and even more preferably 2.9 or more, and from the viewpoint of the durability of the toner, is preferably 10 or less, more preferably 7.0 or less, and even more preferably 5.0 or less. In the present invention, the shape index of the silica particles is a value calculated from the ratio of the number average particle size to the BET converted particle size (number average particle size / BET converted particle size).

[0013] The BET specific surface area of ​​the silica particles A is preferably 70 m from the viewpoint of suppressing detachment from the surface of the toner base particles. 2 / g or more, more preferably 80m 2 / g or more, more preferably 85m 2 / g or more, and preferably 150m 2 / g or less, more preferably 130m 2 / g or less, more preferably 100m 2 / g or less.

[0014] From the viewpoint of suppressing detachment from the surface of the toner base particle, the number average particle size of the silica particles A is preferably 80 nm or more, more preferably 90 nm or more, even more preferably 100 nm or more, and is preferably 130 nm or less, more preferably 120 nm or less, even more preferably 110 nm or less. In this specification, the number average particle size of the silica particles is measured by counting not only primary particles but also aggregates of silica particles as one particle. Generally, external additives with large particle diameters have low van der Waals forces. However, even though the silica particles A have a large particle diameter, they can adhere firmly to the toner base particles due to the electrostatic force and adhesion at multiple points to the toner base particle surface, as described above.

[0015] The silica particles A can be produced by reacting water glass with sulfuric acid in warm water, filtering the resulting silica precipitate, washing with water, and drying, preferably by a precipitation method. The number-average particle size and BET specific surface area of ​​the resulting silica particles can be adjusted by adjusting the reaction conditions (temperature, drop speed of water glass and sulfuric acid into water, precipitation time of silica, etc.).

[0016] The silica particles A and / or the silica particles B described below are preferably subjected to a hydrophobic treatment on the surface. Examples of hydrophobic treatment agents include hexamethyldisilazane (HMDS), dimethyldichlorosilane (DMDS), polydimethylsiloxane, coupling agents having amino groups or quaternary ammonium bases, silicone oil, modified silicone oil, cyclic silazane, etc. Commercially available products may be used, but for example, in the case of silica particles A, the bonded silica particles obtained by the above method may be surface-treated with one of these hydrophobic treatment agents alone, or in the case of two or more types, may be mixed, or may be surface-treated stepwise to impart surface treatment characteristics required according to the application.

[0017] As described above, the silica particles A have a polarity opposite to that of the toner base particles. Therefore, negatively charged silica particles A are used for positively charged toner base particles, and positively charged silica particles A are used for negatively charged toner base particles. The chargeability of the toner base particles and silica particles can be confirmed by the sign of the charge amount measured by frictional charging with iron powder, but in the case of the toner base particles, it can also be determined by the charge control agent contained therein or the type of resin used, and in the case of the silica particles, it can also be determined by the surface treatment agent or functional group. In the present invention, the charge polarity of the toner base particles may be selected according to the characteristics of the printer used, but it is preferable that the toner base particles are positively charged because the effect of the present invention is more significantly exhibited.

[0018] From the viewpoint of controlling the charge polarity, the silica particles are preferably treated with a surface treatment agent, and the surface treatment agent can impart a charge polarity opposite to the charge polarity that the silica particles themselves have. Although the silica particles are negatively chargeable, they can also be used as positively chargeable silica particles by introducing a positive charge imparting group into the surface treatment agent.

[0019] Examples of general-purpose surface treatment agents include hydrophobic treatment agents such as hexamethyldisilazane (HMDS), polydimethylsiloxane (PDMS), and silicone oil.

[0020] Hydrophobic treatment agents such as hexamethyldisilazane (HMDS), polydimethylsiloxane (PDMS), and silicone oil do not themselves affect the chargeability of silica particles. However, by introducing a positive chargeability-imparting group into the hydrophobic treatment agent, it is possible to impart a positive chargeability to negatively charged silica particles.

[0021] Examples of the positive charge imparting group include an amino group.

[0022] The content of silica particles A is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 1.5 parts by mass or more, relative to 100 parts by mass of the toner base particles, and is preferably 6 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 4 parts by mass or less.

[0023] From the viewpoint of the chargeability of the toner, the external additive preferably further contains silica particles B having the same charge polarity as the toner base particles.

[0024] Commercially available positively charged silica products include "RA 50 H", "NA 50 Y", "NA 50 H", "REA 90", "RA 200H", "RA 200 HS", "REA 200", and "NA 300 H" (all from Nippon Aerosil Co., Ltd.), "TG-828F", "TG-820F", "TG-7120", and "TG-6120F" (all from Cabot Specialty Chemicals, Inc.).

[0025] Commercially available negatively charged silica products include "RY 50", "RY 50 L", "RX 50", "NY 50", "NY 50 L", "R 972", "RY 200 S", "NX 130", "R 974", "RY 200 L", "RX 200", "R 805", "NK 200", "R 976", "R 976 S", "RY 300", and "RX 300" (all from Nippon Aerosil Co., Ltd.), "TG-811F", "TG-810G", "TG-815F", "TG-3110", "TG-3155F", "TG-308F", "TG-3130", "TG-7180", "TG-7110", "TG-6110G", "TG-709G", "TG-5110", "TG-5150", "TG-5180", "TG-C413", "TG-C390", "TG-C243", "TG-C110", "TG-C191", and "TG-C6020" (all from Cabot Specialty Chemicals, Inc.).

[0026] The number average particle size of the silica particles B is preferably 4 nm or more, more preferably 6 nm or more, and even more preferably 7 nm or more, and from the viewpoint of toner charge rise property, is preferably 40 nm or less, more preferably 30 nm or less, and even more preferably 20 nm or less.

[0027] From the viewpoint of durability, the number average particle size of silica particles B is preferably smaller than that of silica particles A, and the difference in number average particle size between silica particles A and silica particles B is preferably 60 nm or more, more preferably 70 nm or more, even more preferably 80 nm or more, and is preferably 130 nm or less, more preferably 110 nm or less, even more preferably 100 nm or less.

[0028] The shape index of the silica particles B is preferably less than 2.0, more preferably 1.7 or less, and even more preferably 1.4 or less, and from the viewpoint of toner fluidity, is preferably 0.8 or more, more preferably 0.9 or more, and even more preferably 1.0 or more. The shape index of commercially available silica particles that do not have any particular shape characteristics is usually less than 2.0.

[0029] The content of silica particles B is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, even more preferably 0.4 parts by mass or more, and is preferably 2 parts by mass or less, more preferably 1.5 parts by mass or less, and even more preferably 1 part by mass or less, relative to 100 parts by mass of the toner base particles.

[0030] The mass ratio of silica particles A to silica particles B is preferably 1 / 5 or more, more preferably 1 / 2 or more, and even more preferably 1 / 1 or more from the viewpoint of suppressing embedding of silica particles B, and is preferably 6 / 1, more preferably 5 / 1 or less, and even more preferably 4.5 / 1 or less from the viewpoint of toner fluidity.

[0031] The content of silica particles A, or, when silica particles B are used in combination, the total content of silica particles A and silica particles B in the external additive is preferably 80 mass % or more, more preferably 90 mass % or more, even more preferably 95 mass % or more, and even more preferably 100 mass %.

[0032] The content of the external additive is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 2 parts by mass or more, relative to 100 parts by mass of the toner base particles, and is preferably 6 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 4 parts by mass or less.

[0033] The toner base particles contain a binder resin and a colorant.

[0034] Examples of the binder resin include polyester resin, vinyl resin such as styrene-acrylic resin, epoxy resin, polycarbonate, polyurethane, and composite resin containing two or more of these resins. In the present invention, it is preferable that the binder resin contains a polyester resin from the viewpoint of low-temperature fixing property and production stability.

[0035] The polyester resin is preferably a polycondensation product of an alcohol component, including an alkylene oxide adduct of bisphenol A, and a carboxylic acid component.

[0036] Examples of the alkylene oxide adduct of bisphenol A include those represented by the formula (I):

[0037] [ka]

[0038] (In the formula, OR and RO are oxyalkylene groups, R is an ethylene group and / or a propylene group, x and y are the average number of moles of alkylene oxide added, each of which is a positive number, and the sum of x and y is 1 or more, preferably 1.5 or more, and 16 or less, preferably 8 or less, more preferably 6 or less, and even more preferably 4 or less.) Preferred is a compound represented by the following formula:

[0039] From the viewpoint of low-temperature fixing ability, the content of the alkylene oxide adduct of bisphenol A in the alcohol component is preferably 70 mol % or more, more preferably 80 mol % or more, even more preferably 90 mol % or more, even more preferably 95 mol % or more, and even more preferably 100 mol %.

[0040] Examples of other alcohol components include aliphatic diols, bisphenol A, hydrogenated bisphenol A, sorbitol, pentaerythritol, glycerin, trimethylolpropane and other trihydric or higher alcohols.

[0041] Examples of the carboxylic acid component include aromatic dicarboxylic acid compounds, aliphatic dicarboxylic acid compounds, and trivalent or higher carboxylic acid compounds.

[0042] Examples of the aromatic dicarboxylic acid compound include phthalic acid, isophthalic acid, terephthalic acid, anhydrides of these acids, and alkyl esters of these acids having 1 to 3 carbon atoms.

[0043] From the viewpoint of image density, the carboxylic acid component preferably contains an aromatic dicarboxylic acid compound. The content of the aromatic dicarboxylic acid compound in the carboxylic acid component is preferably 50 mol % or more, more preferably 70 mol % or more, and is 100 mol % or less, preferably 90 mol % or less.

[0044] Examples of the aliphatic dicarboxylic acid compound include fumaric acid, maleic acid, succinic acid, succinic acid derivatives substituted with a hydrocarbon group, glutaric acid, adipic acid, sebacic acid, anhydrides of these acids, and alkyl esters of these acids having 1 to 3 carbon atoms.

[0045] Examples of the trivalent or higher carboxylic acid compound include trimellitic acid, pyromellitic acid, anhydrides of these acids, and alkyl esters of these acids having 1 to 3 carbon atoms.

[0046] The alcohol component may appropriately contain a monohydric alcohol, and the carboxylic acid component may appropriately contain a monovalent carboxylic acid compound.

[0047] From the viewpoint of adjusting the softening point of the polyester resin, the equivalent ratio of the carboxy group of the carboxylic acid component to the hydroxyl group of the alcohol component (COOH group / OH group) is preferably 0.6 or more, more preferably 0.7 or more, even more preferably 0.75 or more, and is preferably 1.2 or less, more preferably 1.15 or less.

[0048] The polyester resin can be produced, for example, by polycondensing the raw material monomers, that is, an alcohol component and a carboxylic acid component, in an inert gas atmosphere, preferably in the presence of an esterification catalyst, and further, if necessary, in the presence of an esterification promoter, a polymerization inhibitor, etc., at a temperature of preferably 130°C or higher, more preferably 170°C or higher, and preferably 250°C or lower, more preferably 240°C or lower.

[0049] Examples of the esterification catalyst include tin compounds such as dibutyltin oxide and tin(II) 2-ethylhexanoate, and titanium compounds such as titanium diisopropylate bistriethanolamine, and tin compounds are preferred. The amount of the esterification catalyst used is preferably 0.01 parts by mass or more, more preferably 0.1 parts by mass or more, and preferably 1.5 parts by mass or less, more preferably 1 part by mass or less, relative to 100 parts by mass of the raw material monomer. Examples of the esterification promoter include gallic acid, etc. The amount of the esterification promoter used is preferably 0.001 parts by mass or more, more preferably 0.01 parts by mass or more, and preferably 0.5 parts by mass or less, more preferably 0.1 parts by mass or less, relative to 100 parts by mass of the raw material monomer. Examples of the polymerization inhibitor include tert-butylcatechol, etc. The amount of the polymerization inhibitor used is preferably 0.001 parts by mass or more, more preferably 0.01 parts by mass or more, and preferably 0.5 parts by mass or less, more preferably 0.1 parts by mass or less, relative to 100 parts by mass of the raw material monomer.

[0050] In the present invention, the polyester resin may be modified to such an extent that its properties are not substantially impaired. Examples of modified polyester resins include polyester resins grafted or blocked with phenol, urethane, epoxy, or the like by the methods described in JP-A-11-133668, JP-A-10-239903, JP-A-8-20636, etc., and among the modified polyester resins, urethane-modified polyester resins in which polyester resins are urethane-extended with a polyisocyanate compound are preferred.

[0051] From the viewpoint of hot offset resistance, the softening point of the polyester resin is preferably 90° C. or higher, more preferably 100° C. or higher, and even more preferably 110° C. or higher, and from the viewpoint of low-temperature fixability, it is preferably 160° C. or lower, more preferably 150° C. or lower, and even more preferably 140° C. or lower.

[0052] From the viewpoint of heat-resistant storage stability, the glass transition temperature of the polyester resin is preferably 40° C. or higher, more preferably 45° C. or higher, and even more preferably 50° C. or higher, and from the viewpoint of low-temperature fixability, it is preferably 75° C. or lower, more preferably 70° C. or lower, and even more preferably 65° C. or lower.

[0053] The content of the polyester resin in the binder resin is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and still more preferably 100% by mass.

[0054] The content of the binder resin in the toner base particles is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 75% by mass or more, and is preferably less than 100% by mass, more preferably 98% by mass or less, even more preferably 95% by mass or less.

[0055] As the colorant, dyes, pigments, magnetic materials, etc. used as colorants for toners can be used. For example, carbon black, phthalocyanine blue, permanent brown FG, brilliant fast scarlet, pigment red 122, pigment green B, rhodamine-B base, solvent red 49, solvent red 146, solvent blue 35, quinacridone, carmine 6B, isoindoline, disazo yellow, etc. can be mentioned. In the present invention, the toner may be either a black toner or a color toner.

[0056] From the viewpoint of improving the image density and low-temperature fixability of the toner, the content of the colorant is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and preferably 40 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 10 parts by mass or less, relative to 100 parts by mass of the binder resin.

[0057] The toner base particles may contain additives such as a release agent, a charge control agent, a magnetic powder, a flowability improver, a conductivity adjuster, a reinforcing filler such as a fibrous substance, an antioxidant, and a cleaning property improver, in addition to the binder resin and the colorant. It is preferable that the toner base particles contain a release agent and a charge control agent.

[0058] Examples of the release agent include hydrocarbon waxes such as polypropylene wax, polyethylene wax, polypropylene-polyethylene copolymer wax, microcrystalline wax, paraffin wax, and Fischer-Tropsch wax, and oxides thereof; ester waxes such as carnauba wax, montan wax, and deacidified waxes thereof, and fatty acid ester wax; fatty acid amides, fatty acids, higher alcohols, and fatty acid metal salts. These may be used alone or in combination of two or more.

[0059] The melting point of the release agent is preferably 60° C. or higher, more preferably 70° C. or higher, from the viewpoint of toner transferability, and is preferably 160° C. or lower, more preferably 150° C. or lower, from the viewpoint of low-temperature fixability.

[0060] The content of the release agent is, from the viewpoint of the low-temperature fixing property and offset resistance of the toner and the viewpoint of dispersibility in the binder resin, preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and even more preferably 7 parts by mass or less, relative to 100 parts by mass of the binder resin.

[0061] The charge control agent is not particularly limited, and may contain either a positively chargeable charge control agent or a negatively chargeable charge control agent.

[0062] Examples of the positively charged charge control agent include nigrosine dyes such as "Nigrosine Base EX", "Oil Black BS", "Oil Black SO", "Bontron N-01", "Bontron N-04", "Bontron N-07", "Bontron N-09", and "Bontron N-11" (all manufactured by Orient Chemical Industries Co., Ltd.); triphenylmethane dyes containing a tertiary amine as a side chain; quaternary ammonium salt compounds such as "Bontron P-51" (manufactured by Orient Chemical Industries Co., Ltd.), cetyltrimethylammonium bromide, and "COPY CHARGE PX Examples of such resins include "VP435" (manufactured by Clariant), etc.; polyamine resins, such as "AFP-B" (manufactured by Orient Chemical Industry Co., Ltd.); imidazole derivatives, such as "PLZ-2001" and "PLZ-8001" (both manufactured by Shikoku Kasei Corporation); and styrene-acrylic resins, such as "FCA-701PT" and "FCA-201-PS" (manufactured by Fujikura Kasei Co., Ltd.).

[0063] Examples of the negatively chargeable charge control agent include metal-containing azo dyes such as "Varifast Black 3804", "Bontron S-31", "Bontron S-32", "Bontron S-34", and "Bontron S-36" (all manufactured by Orient Chemical Industry Co., Ltd.), "Aizenspiron Black TRH", and "T-77" (manufactured by Hodogaya Chemical Industry Co., Ltd.); metal compounds of benzilic acid compounds such as "LR-147" and "LR-297" (all manufactured by Nippon Carlit Co., Ltd.); metal compounds of salicylic acid compounds such as "Bontron E-81", "Bontron E-84", "Bontron E-88", and "Bontron E-304" (all manufactured by Orient Chemical Industry Co., Ltd.), and "TN-105" (manufactured by Hodogaya Chemical Industry Co., Ltd.); copper phthalocyanine dyes; and quaternary ammonium salts such as "COPY CHARGE NX VP434 (Clariant), nitroimidazole derivatives, and organometallic compounds.

[0064] From the viewpoint of the charging stability of the toner, the content of the charge control agent is preferably 0.01 parts by mass or more, more preferably 0.2 parts by mass or more, and preferably 10 parts by mass or less, more preferably 5 parts by mass or less, even more preferably 3 parts by mass or less, and even more preferably 2 parts by mass or less, relative to 100 parts by mass of the binder resin.

[0065] The method for producing the toner base particles may be any of the conventionally known methods such as a melt kneading method, an emulsion phase inversion method, a polymerization method, etc., but from the viewpoint of productivity, the melt kneading method is preferred. When producing the toner base particles by the melt kneading method, for example, raw materials such as a binder resin, a colorant, a release agent, a charge control agent, etc. are uniformly mixed in a mixer such as a Henschel mixer, and then melt kneaded in an internal kneader, a single-screw or twin-screw extruder, an open roll type kneader, etc., and then cooled, pulverized, and classified to produce the toner base particles.

[0066] The volume median particle size of the toner base particles (D 50 ) is preferably 3 μm or more, more preferably 4 μm or more, and is preferably 15 μm or less, more preferably 10 μm or less. 50 ) means the particle size at which the cumulative volume frequency calculated by volume fraction is 50% calculated from the smallest particle size.

[0067] The external addition treatment by mixing the toner base particles with the external additives can be carried out according to a conventional method, and a mixer such as a Henschel mixer can be used.

[0068] The toner of the present invention can be used as a toner for one-component development or as a two-component developer mixed with a carrier in an image forming apparatus of a one-component development system or a two-component development system, respectively. EXAMPLES

[0069] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Physical properties of resins and the like can be measured by the following methods.

[0070] [Softening point of resin] Using a flow tester "CFT-500D" (Shimadzu Corporation), 1g of sample is heated at a temperature increase rate of 6℃ / min while applying a load of 1.96MPa with the plunger, and extruding the sample from a nozzle with a diameter of 1mm and a length of 1mm. The amount of plunger descent of the flow tester is plotted against the temperature, and the temperature at which half of the sample has flowed out is taken as the softening point.

[0071] [Glass transition temperature of resin] Using a differential scanning calorimeter "Q-100" (manufactured by TA Instruments Japan Co., Ltd.), 0.01 to 0.02 g of sample is weighed into an aluminum pan, heated to 200°C, and cooled from that temperature at a rate of 10°C / min to 0°C. Next, measure while heating to 150°C at a rate of 10°C / min. The glass transition temperature is the temperature at the intersection of the extension of the baseline below the maximum endothermic peak temperature and the tangent line showing the maximum slope from the rising part of the peak to the top of the peak.

[0072] [Melting point of release agent] Using a differential scanning calorimeter "Q-100" (manufactured by TA Instruments Japan Co., Ltd.), 0.02 g of the sample is weighed into an aluminum pan and heated to 200°C, then cooled from 200°C to 0°C at a rate of 10°C / min. The sample is then heated at a rate of 10°C / min, the amount of heat is measured, and the maximum endothermic peak temperature is taken as the melting point.

[0073] [Volume median particle size of toner base particles (D 50 )〕 Measuring instrument: Coulter Multisizer III (manufactured by Beckman Coulter, Inc.) Aperture diameter: 100μm Analysis software: Multisizer III version 3.51 (Beckman Coulter, Inc.) Electrolyte: "Isoton (registered trademark) II" (manufactured by Beckman Coulter, Inc.) Dispersion liquid: Polyoxyethylene lauryl ether "Emulgen (registered trademark) 109P" (manufactured by Kao Corporation, HLB (Griffin) = 13.6) was dissolved in the electrolyte to adjust the concentration to 5% by mass. Dispersion conditions: 10 mg of the measurement sample is added to 5 mL of the dispersion liquid, and dispersed for 1 minute using an ultrasonic disperser (machine name: US-1, manufactured by SND Co., Ltd., output: 80 W). Then, 25 mL of electrolyte is added, and the mixture is further dispersed for 1 minute using the ultrasonic disperser to prepare a sample dispersion liquid. Measurement conditions: The sample dispersion was added to 100 mL of the electrolyte to adjust the concentration so that the particle size of 30,000 particles could be measured in 20 seconds. Then, 30,000 particles were measured, and the volume median particle size (D 50 ) is required.

[0074] [Number average particle size of external additives] The particle size (average of the long and short diameters) of 500 particles is measured from a scanning electron microscope (SEM) photograph, and the number average value of these is taken as the number average particle size. Here, among the particles observed in the SEM photograph, aggregates are also counted as one particle.

[0075] [BET specific surface area of ​​external additives] Measured by nitrogen adsorption method under the following conditions. Measurement device: Specific surface area measurement device "Micromeritics FlowSorbIII" (manufactured by Shimadzu Corporation) Sample size: 0.04~0.08g Degassing conditions: 40℃, 10 minutes Adsorption gas: Nitrogen gas

[0076] [BET equivalent particle size of external additives] Calculate based on the following formula. BET equivalent particle size=6000 / ([BET specific surface area]×ρ(density))

[0077] [Shape index of external additives] Calculate based on the following formula. Shape index = [number average particle size] / [BET equivalent particle size]

[0078] Resin manufacturing example 1 The alcohol component, carboxylic acid component other than trimellitic anhydride, esterification catalyst and esterification promoter shown in Table 1 were placed in a 5-liter four-neck flask equipped with a nitrogen inlet tube, a stirrer and a thermocouple, and the mixture was heated to 200°C under a nitrogen atmosphere and reacted for 6 hours. After further heating to 210°C, trimellitic anhydride was added and reacted for 1 hour at normal pressure (101.3 kPa), and further reacted at 40 kPa until the desired softening point was reached, to obtain resin A. The physical properties of the obtained resin are shown in Table 1.

[0079] [Table 1]

[0080] Resin manufacturing example 2 2 L of xylene was placed in a 10-liter four-neck flask equipped with a thermometer, a stainless steel stirring rod, a flow-down condenser, a dropping funnel, and a nitrogen inlet tube, and 880 g of styrene, 220 g of n-butyl acrylate, and 100 g of dibutyl peroxide as a radical polymerization initiator were placed in the dropping funnel. Under a nitrogen atmosphere, the xylene was heated to 135°C while stirring, and the mixture in the dropping funnel was dropped over 1 hour. After that, the temperature was raised to 200°C and held at 200°C for 2 hours, and then the pressure in the flask was further reduced and held at 8 kPa for 1 hour, and xylene was removed to obtain a styrene-acrylic resin (resin B). The softening point of the obtained resin was 115°C, and the glass transition temperature was 54°C.

[0081] Example 1 of the production of bonded silica particles Grafted silica particles were prepared by precipitation according to the following method. A 3-liter glass flask equipped with a metal stirring rod, a dropping nozzle, a heating device, and a thermometer was charged with 1000 mL of water and heated to 80°C. Next, while maintaining the pH value at 9 under stirring, 184 mL of water glass and 818 mL of sulfuric acid were dropped over 1 hour to allow silica to settle for 20 minutes. After that, sulfuric acid was continuously dropped to adjust the pH value to 3.5. The precipitated silica was separated from the suspension, washed with water, and then dried to obtain silica fine powder. 100 parts by mass of the obtained silica fine powder was placed in a reaction vessel, and 5 parts by mass of water and 10 parts by mass of hexamethyldisilazane were added under a nitrogen atmosphere. The reaction mixture was stirred at 150°C for 2 hours, and then stirred and dried under a nitrogen stream at 220°C for 2 hours. The mixture was cooled to obtain hydrophobic silica particles A1.

[0082] Example 2 of the production of bonded silica particles Hydrophobic silica particles A2 having a number average particle size and a BET specific surface area different from those of silica particles A1 were obtained in the same manner as in Production Example 1, except that the drop time of the water glass and sulfuric acid was adjusted to 70 minutes and the settling time of the silica was adjusted to 10 minutes.

[0083] Manufacturing Example 3 of Bonded Silica Particles Hydrophobic silica particles A3 having a number average particle size and a BET specific surface area different from those of silica particles A1 were obtained in the same manner as in Production Example 1, except that the drop time of the water glass and sulfuric acid was adjusted to 50 minutes and the settling time of the silica was adjusted to 30 minutes.

[0084] Production Example 4 of Bonded Silica Particles Hydrophobic silica particles A4 were obtained in the same manner as silica particles A1, except that amino-modified silicone oil was used instead of hexamethyldisilazane in Production Example 1.

[0085] Table 2 shows the physical properties of the silica particles A1 to A4 and the silica particles A5 used in the examples and comparative examples.

[0086] [Table 2]

[0087] Examples 1 to 3, 5 and Comparative Examples 2 and 3 100 parts by mass of the binder resin shown in Table 3, 1.0 part by mass of release agent "NP-055" (manufactured by Mitsui Chemicals, Inc., polypropylene wax, melting point: 145°C), 1.0 part by mass of positively charged charge control agent "Bontron N-04" (manufactured by Orient Chemical Industries, Ltd.), and 5.0 parts by mass of colorant "REGAL 330R" (manufactured by Cabot Specialty Chemicals, Inc.) were mixed for 1 minute using a Henschel mixer, and then melt-kneaded under the conditions shown below.

[0088] Co-rotating twin screw extruder "PCM-30" (manufactured by Ikegai Co., Ltd., shaft diameter 2.9 cm, shaft cross-sectional area 7.06 cm 2 The operating conditions were: barrel temperature 100°C, shaft rotation speed 200 r / min (shaft rotation peripheral speed 0.30 m / sec), mixture supply speed 10 kg / h (mixture supply amount per unit cross-sectional area of ​​the shaft 1.42 kg / h cm 2 ) was.

[0089] The kneaded product obtained was cooled and coarsely pulverized using a pulverizer "Rotoplex" (manufactured by Hosokawa Micron Co., Ltd.), and a coarsely pulverized product having a volume median particle size of 2 mm or less was obtained using a sieve with a mesh size of 2 mm. The coarsely pulverized product obtained was finely pulverized using a DS2 type air classifier (impingement plate type, manufactured by Nippon Pneumatic Co., Ltd.) by adjusting the pulverization pressure so that the volume median particle size became 8.0 μm. The finely pulverized product obtained was classified using a DSX2 type air classifier (manufactured by Nippon Pneumatic Co., Ltd.) by adjusting the static pressure (internal pressure) so that the volume median particle size became 8.5 μm, and toner base particles were obtained.

[0090] 100 parts by mass of the obtained toner base particles, 2 parts by mass of silica particles A shown in Table 3, and 0.5 parts by mass of positively charged hydrophobic silica "TG-820F" (manufactured by Cabot Specialty Chemicals, Inc., number average particle size: 8 nm, shape index: 1.0, hydrophobic treatment agent: HMDS and cyclic silazane) as silica particles B were mixed in a Henschel mixer (manufactured by Nippon Coke and Engineering Co., Ltd.) at 2100 r / min (circumferential speed: 29 m / sec) for 3 minutes to obtain a toner.

[0091] Example 4 and Comparative Example 1 Toner base particles were obtained in the same manner as in Example 1, except that 1.0 part by mass of a negatively chargeable charge control agent "Bontron E-304" (manufactured by Orient Chemical Industry Co., Ltd.) was used instead of the positively chargeable charge control agent.

[0092] 100 parts by mass of the obtained toner base particles, 2 parts by mass of silica particles A shown in Table 3, and 1.0 part by mass of negatively charged hydrophobic silica "R 972" (manufactured by Nippon Aerosil Co., Ltd., number average particle size: 16 nm, shape index: 1.0, hydrophobizing agent: DMDS) as silica particles B were mixed using a Henschel mixer (manufactured by Nippon Coke and Engineering Co., Ltd.) at 2100 r / min (circumferential speed: 29 m / sec) for 3 minutes to obtain a toner.

[0093] Test Example [Fogging under low temperature and low humidity conditions] When the charge polarity of the toner base particles is positive, the toner is filled in a printer "HL-2040" (manufactured by Brother Industries, Ltd.) equipped with a cleanerless development system, and when the charge polarity of the toner base particles is negative, the toner is filled in a non-magnetic one-component developing device "OKI MICROLINE 5400" (manufactured by Oki Data Corporation), and 5,000 images with a print rate of 1% are printed under conditions of a temperature of 10°C, humidity of 20%, and 20 seconds per page. Next, a solid white image is printed, and the power is turned off during the printing. Thereafter, the toner on the surface of the photoconductor is attached with "Scotch (registered trademark) Mending Tape 810" (manufactured by Sumitomo 3M Co., Ltd., width: 18 mm), and the color density is measured at five equally spaced points with an image density meter "GRETAG SPM50" (manufactured by GRETAG Co., Ltd.), and the difference from the color density of the tape itself before the toner is attached is obtained, and the average of the measured values ​​is obtained. The results are shown in Table 3. The smaller the value, the more the fogging is suppressed.

[0094] [Table 3]

[0095] From the above results, it is seen that fogging under low temperature and low humidity conditions is suppressed in Examples 1 to 5, in comparison with Comparative Examples 1 to 3. In Comparative Examples 1 and 2, in which silica particles of the same polarity as the toner mother particles were added externally, the silica particles were easily detached, and in Comparative Example 3, in which normal large-diameter silica particles were added externally, the adhesion of the silica particles was weak, and large aggregation occurred on the silica particles due to movement on the toner surface, leading to detachment. [Industrial Applicability]

[0096] The toner for developing electrostatic images of the present invention is suitably used for developing latent images formed in electrophotography, electrostatic recording, electrostatic printing and the like.

Claims

1. An electrostatic charge image developing toner containing toner mother particles containing a binder resin and a colorant and an external additive, wherein the external additive contains silica particles A having a charging polarity opposite to that of the toner mother particles and a shape index represented by a ratio of the number average particle diameter to the BET equivalent particle diameter of 2.0 or more.

2. The electrostatic charge image developing toner according to claim 1, wherein the number average particle diameter of the silica particles A is 80 nm or more.

3. The electrostatic charge image developing toner according to claim 1, wherein the shape index of the silica particles A is 2.5 or more and 10 or less.

4. The electrostatic charge image developing toner according to claim 1, wherein the external additive further contains silica particles B having a charging polarity the same as that of the toner mother particles.

5. The electrostatic charge image developing toner according to claim 4, wherein the number average particle diameter of the silica particles B is smaller than that of the silica particles A.