JP2017003659A - Multi-color toner, image forming apparatus, and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plurality of colors of toner capable of suppressing fixing defects caused by toner charge-up. A multi-color toner is used to form an image by sequentially superimposing a multi-color toner image on an intermediate transfer body. Each of the multicolored toners contains toner particles with a silica-containing external additive. The charge attenuation constant of the silica-containing external additive satisfies Equation 1 “αn-1> αn”. In Equation 1, n is an integer of 2 or more and equal to or less than the number of colors of the toners of a plurality of colors. αn-1 is a charge attenuation constant of the silica-containing external additive contained in the toner particles contained in the toner Tn-1. Toner Tn-1 is a toner that forms a toner image that is layered n-1st on an intermediate transfer body among toners of a plurality of colors. αn is a charge attenuation constant of the silica-containing external additive contained in the toner particles contained in the toner Tn. The toner Tn is a toner that forms a toner image that is superimposed on the intermediate transfer body at the nth position among the toners of a plurality of colors. αn-1 and αn are positive numbers. [Selection diagram] Fig. 1

Description

  The present invention relates to a multi-color toner (particularly, a multi-color electrostatic latent image developing toner), an image forming apparatus, and an image forming method.

  As an example of the image forming apparatus, a tandem image forming apparatus is known. A tandem image forming apparatus employs, for example, a direct transfer method or an intermediate transfer method. In an image forming apparatus that employs a tandem method and a direct transfer method, a toner image of each color is formed on each of a plurality of electrostatic latent image carriers. The formed toner images of the respective colors are sequentially transferred onto a recording medium conveyed by a conveyance belt. On the other hand, in an image forming apparatus that employs a tandem method and an intermediate transfer method, a toner image of each color is formed on each of a plurality of electrostatic latent image carriers. The formed toner images of respective colors are sequentially transferred to the intermediate transfer member and are superimposed on the intermediate transfer member. Subsequently, the superimposed toner images of each color are collectively transferred to the recording medium.

  In an image forming apparatus that employs an intermediate transfer method, various studies have been made to control the charge amount of toner on an intermediate transfer member. The image forming apparatus described in Patent Document 1 includes a pre-transfer charging control unit (pre-transfer charger) in the vicinity of the intermediate transfer member. The image forming apparatus described in Patent Document 2 includes a plurality of toner supply units (developers). The amount of the external additive contained in the toner differs for each toner stored in each of the plurality of toner supply units.

Japanese Patent Laid-Open No. 11-305566 JP 2002-23459 A

  However, in the image forming apparatus described in Patent Document 1, the provision of the pre-transfer charger increases the cost and complexity of the image forming apparatus. In addition, in the image forming apparatus described in Patent Document 2, the amount of external additive contained in each toner is different, which complicates setting of development conditions. Therefore, in the image forming apparatuses described in Patent Documents 1 and 2, it is difficult to suppress the occurrence of fixing failure (for example, electrostatic offset) due to toner charge-up.

  The present invention has been made in view of the above problems, and provides a multi-color toner, an image forming apparatus, and an image forming method capable of suppressing fixing failure (for example, electrostatic offset) caused by toner charge-up. .

The multi-color toner according to the present invention is used to form an image by sequentially superposing a plurality of color toner images on an intermediate transfer member. Each of the plurality of color toners includes toner particles including a silica-containing external additive. The charge decay constant of the silica-containing external additive satisfies the following formula 1.
α _n-1 > α _n (Formula 1)
(In Formula 1, n is an integer of 2 or more and is an integer equal to or less than the number of colors of the plurality of toners. Α _n-1 is the toner particle included in the toner T _n-1. The charge decay constant of the silica-containing external additive, wherein the toner T _n-1 is the toner that forms the n-1th superimposed toner image on the intermediate transfer member among the plurality of color toners. there .Arufa _n is the charge decay constant of the silica-containing external additive, wherein the toner particles contained in toner T _n is provided. the toner T _n is on the intermediate transfer member of toner of said plurality of colors (It is the toner that forms the n-th superimposed toner image. α _n-1 and α _n are positive numbers.)

The image forming apparatus according to the present invention uses a plurality of colors of toner. The image forming apparatus includes a plurality of electrostatic latent image carriers, a developing unit, a primary transfer unit, and a secondary transfer unit. The developing section develops the electrostatic latent image formed on each of the plurality of electrostatic latent image carriers using each of the plurality of color toners, thereby the plurality of electrostatic latent image carriers. Each color toner image is formed. The primary transfer unit sequentially superimposes the color toner images formed on each of the plurality of electrostatic latent image carriers on the intermediate transfer member. The secondary transfer unit collectively transfers the color toner images superimposed on the intermediate transfer member onto a recording medium. Each of the plurality of color toners includes toner particles including a silica-containing external additive. The charge decay constant of the silica-containing external additive satisfies the following formula 1.
α _n-1 > α _n (Formula 1)
(In Formula 1, n is an integer of 2 or more and is an integer equal to or less than the number of colors of the plurality of toners. Α _n-1 is the toner particle included in the toner T _n-1. The charge decay constant of the silica-containing external additive, wherein the toner T _n-1 is the toner that forms the n-1th superimposed toner image on the intermediate transfer member among the plurality of color toners. there .Arufa _n is the charge decay constant of the silica-containing external additive, wherein the toner particles contained in toner T _n is provided. the toner T _n is on the intermediate transfer member of toner of said plurality of colors (It is the toner that forms the n-th superimposed toner image. α _n-1 and α _n are positive numbers.)

The image forming method according to the present invention uses a plurality of color toners. The image forming method includes a development process, a primary transfer process, and a secondary transfer process. In the developing step, each of the plurality of electrostatic latent image carriers is developed by developing the electrostatic latent image formed on each of the plurality of electrostatic latent image carriers using each of the plurality of color toners. Each color toner image is formed. In the primary transfer step, the color toner images formed on each of the plurality of electrostatic latent image carriers are sequentially superimposed on the intermediate transfer member. In the secondary transfer step, the toner images of the respective colors superimposed on the intermediate transfer member are transferred collectively to a recording medium. Each of the plurality of color toners includes toner particles including a silica-containing external additive. The charge decay constant of the silica-containing external additive satisfies the following formula 1.
α _n-1 > α _n (Formula 1)
(In Formula 1, n is an integer of 2 or more and is an integer equal to or less than the number of colors of the plurality of toners. Α _n-1 is the toner particle included in the toner T _n-1. The charge decay constant of the silica-containing external additive, wherein the toner T _n-1 is the toner that forms the n-1th superimposed toner image on the intermediate transfer member among the plurality of color toners. there .Arufa _n is the charge decay constant of the silica-containing external additive, wherein the toner particles contained in toner T _n is provided. the toner T _n is on the intermediate transfer member of toner of said plurality of colors (It is the toner that forms the n-th superimposed toner image. α _n-1 and α _n are positive numbers.)

  According to the present invention, it is possible to provide a toner of a plurality of colors, an image forming apparatus, and an image forming method that can suppress fixing defects (for example, electrostatic offset) caused by toner charge-up.

1 is a diagram illustrating a schematic configuration of an image forming apparatus using a plurality of colors of toner according to the present invention.

  Embodiments of the present invention will be described below. However, the present invention is not limited to the following embodiments. The present invention can be implemented with appropriate modifications within the scope of the object of the present invention. In addition, about the location where description overlaps, although description may be abbreviate | omitted suitably, the summary of invention is not limited.

  Hereinafter, a compound and its derivatives may be generically named by adding “system” after the compound name. In addition, when “polymer” is added after the compound name to indicate the polymer name, it means that the repeating unit of the polymer is derived from the compound or a derivative thereof.

  Hereinafter, the average value means an arithmetic average value unless otherwise specified. In addition, evaluation values (values indicating shape, physical properties, etc.) regarding powders (for example, toner, toner particles, toner base particles, silica-containing external additives, or external additives other than silica-containing external additives, which will be described later), If nothing is specified, it means the arithmetic mean. The arithmetic average value is a value obtained by dividing the sum of values measured for a considerable number of measurement objects by the number of measurements. Furthermore, the particle diameter of the powder is the equivalent-circle diameter of the primary particles unless otherwise specified. The equivalent circle diameter is the diameter of a circle having the same area as the projected area of the particles.

  The present embodiment relates to a plurality of colors of toner (particularly, electrostatic latent image developing toner). Hereinafter, the toner of a plurality of colors will be described.

<1. Multi-color toner>
The multi-color toner is a toner set including a plurality of toners having different colors. Each of the multiple color toners includes a plurality of toner particles. The toner particles include a silica-containing external additive.

The silica-containing external additive has a charge decay constant that satisfies the formula 1 “α _n-1 > α _n ”. Thereby, fixing failure (for example, electrostatic offset) due to toner charge-up can be suppressed. The reason is presumed as follows.

  In the primary transfer step, the toner images of the respective colors formed on each of the plurality of electrostatic latent image carriers are sequentially superimposed on the intermediate transfer member. A primary transfer bias (bias having a polarity opposite to that of the toner) is applied to the toner image on the intermediate transfer member when the next color toner image is primarily transferred. When a primary transfer bias having a reverse polarity is applied to the toner image on the intermediate transfer member, the toner that forms the toner image is easily charged up by a mechanism similar to the repulsion caused by electrostatic friction. With reference to the primary transfer portion that performs the primary transfer earliest, the toner transferred on the upstream side in the rotation direction of the intermediate transfer member is considered to be easily charged up. This is because the number of times that the primary transfer bias is applied to the toner that forms the toner image on the intermediate transfer member is increased.

Here, the charge decay constant of the silica-containing external additive included in the toner particles included in each of the toners of the plurality of colors according to the present embodiment satisfies Formula 1 “α _n-1 > α _n ”. As the silica-containing external additive having a larger charge decay constant, the electric charge is more easily released, and as a result, the electric charge charged to the toner particles having the silica-containing external additive is also easily released. Therefore, by satisfying the expression 1 “α _n-1 > α _n ”, it becomes easy to suppress the charge-up of the toner that forms the toner images of the respective colors superimposed on the intermediate transfer member. In addition, it is easy to reduce the variation in the charge amount among the color toners. When toner charge-up is suppressed, the toner is less likely to electrostatically adhere to a fixing unit (for example, a fixing roller formed of a material having a polarity opposite to that of the toner). As a result, fixing failure (for example, electrostatic offset) is considered to be suppressed. The electrostatic offset is an image defect in which the toner attached to the fixing unit appears in the formed image every rotation period of the fixing unit.

  As already mentioned, the toner particles comprise a silica-containing external additive. The toner particles may further include toner mother particles. When the toner particles include toner base particles, the silica-containing external additive is provided on the surface of the toner base particles. The toner particles may further include an external additive other than the silica-containing external additive on the surface of the toner base particles. Hereinafter, the toner base particles, the silica-containing external additive, and external additives other than the silica-containing external additive will be described.

<1-1. Toner mother particles>
The toner base particles may contain, for example, a binder resin, a colorant, a charge control agent, a release agent, and / or magnetic powder. Hereinafter, the binder resin, the colorant, the charge control agent, the release agent, and the magnetic powder will be described.

<1-1-1. Binder resin>
The binder resin is not particularly limited as long as it is a binder resin used for toner preparation. As the binder resin, a thermoplastic resin is preferable from the viewpoint of improving the fixing property of the toner. Examples of the thermoplastic resin include acrylic acid resin, styrene acrylic acid resin, polyester resin, polyamide resin, urethane resin, or vinyl alcohol resin. A polyester resin is particularly preferable as the binder resin in terms of improving the dispersibility of the colorant, the charging property of the toner, and the fixing property of the toner to the recording medium (for example, paper). Hereinafter, the polyester resin will be described.

  The polyester resin can be obtained by, for example, condensation polymerization or co-condensation polymerization of alcohol and carboxylic acid.

  Examples of the alcohol used when synthesizing the polyester resin include dihydric alcohols and trihydric or higher alcohols.

  Examples of the dihydric alcohol include diols or bisphenols. Examples of diols include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,4-butenediol, 1, Examples include 5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol, polypropylene glycol, or polytetramethylene glycol. Examples of bisphenols include bisphenol A, hydrogenated bisphenol A, polyoxyethylene bisphenol A ether, or polyoxypropylene bisphenol A ether. Specific examples of the polyoxyethylene bisphenol A ether include polyoxyethylene (2.2) -2,2-bis (4-hydroxyphenyl) propane.

  Examples of trihydric or higher alcohols include sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, diglycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, or 1,3,5-trihydroxy Mention may be made of methylbenzene.

  Examples of the carboxylic acid used when synthesizing the polyester resin include a divalent carboxylic acid or a trivalent or higher carboxylic acid.

  Examples of divalent carboxylic acids include maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, adipic acid, sebacic acid, azelaic acid, malonic acid, succinic acid. Examples include acids, alkyl succinic acids, or alkenyl succinic acids. Examples of alkyl succinic acids include n-butyl succinic acid, isobutyl succinic acid, n-octyl succinic acid, n-dodecyl succinic acid, or isododecyl succinic acid. Examples of alkenyl succinic acids include n-butenyl succinic acid, isobutenyl succinic acid, n-octenyl succinic acid, n-dodecenyl succinic acid, or isododecenyl succinic acid.

  Examples of trivalent or higher carboxylic acids include 1,2,4-benzenetricarboxylic acid (trimellitic acid), 2,5,7-naphthalene tricarboxylic acid, 1,2,4-naphthalene tricarboxylic acid, 4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane, 1,2,4-cyclohexanetricarboxylic acid, tetra (methylenecarboxyl) methane, 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, or empole trimer acid.

  Alcohol and carboxylic acid may be used individually by 1 type, respectively, and may be used in combination of 2 or more type. Furthermore, the carboxylic acid may be derivatized into an ester-forming derivative. Examples of ester-forming derivatives include acid halides, acid anhydrides, or lower alkyl esters. Here, “lower alkyl” means an alkyl group having 1 to 6 carbon atoms.

  The acid value of the polyester resin is preferably 5 mgKOH / g or more and 30 mgKOH / g or less. The hydroxyl value of the polyester resin is preferably 15 mgKOH / g or more and 80 mgKOH / g or less.

  The acid value and hydroxyl value of the polyester resin can be adjusted by changing the amount of alcohol used and the amount of carboxylic acid used when preparing the polyester resin. When the molecular weight of the polyester resin is increased, the acid value and hydroxyl value of the polyester resin tend to decrease. The acid value and hydroxyl value of the polyester resin can be measured according to a method based on JIS (Japanese Industrial Standard) K0070-1992.

  When a polyester resin is used as the binder resin, the content of the polyester resin in the binder resin is preferably 70% by mass or more, more preferably 80% by mass or more, and 90% by mass or more. Particularly preferred is 100% by mass.

  When a thermoplastic resin is used as the binder resin, one type of thermoplastic resin may be used alone, or two or more types may be used in combination. Moreover, you may add a crosslinking agent or a thermosetting resin to a thermoplastic resin. If a cross-linked structure is partially introduced into the binder resin, it is easy to improve the storage stability, form retention, and durability of the toner while ensuring the toner fixability.

  Thermosetting resins that can be used with thermoplastic resins include bisphenol A type epoxy resins, hydrogenated bisphenol A type epoxy resins, novolac type epoxy resins, polyalkylene ether type epoxy resins, cycloaliphatic type epoxy resins, or cyanate type resins. Is preferred. One kind of thermosetting resin may be used alone, or two or more kinds may be used in combination.

  The glass transition point (Tg) of the binder resin is preferably 30 ° C. or higher and 60 ° C. or lower. The glass transition point of the binder resin is measured, for example, according to the following method.

[Glass transition point measurement method]
The endothermic curve of the binder resin is measured using a differential scanning calorimeter (DSC) (for example, “DSC-6220” manufactured by Seiko Instruments Inc.). 10 mg of binder resin (measurement sample) is placed in an aluminum pan. Use an empty aluminum pan as a reference. The endothermic curve of the binder resin is measured under the conditions of a measurement temperature range of 25 ° C. to 200 ° C. and a temperature increase rate of 10 ° C./min. The glass transition point of the binder resin is determined from the obtained endothermic curve (specifically, the change point of the specific heat of the binder resin).

  The softening point (Tm) of the binder resin is preferably 60 ° C. or higher and 150 ° C. or lower. A plurality of types of resins having different softening points can be used in combination so that the softening point of the binder resin is within such a range. The softening point of the binder resin is measured, for example, according to the following method.

[Softening point measurement method]
The binder resin (sample) is set in a Koka flow tester (for example, “CFT-500D” manufactured by Shimadzu Corporation). A sample of 1 cm ³ is melted and discharged under the conditions of a die pore diameter of 1 mm, a plunger load of 20 kg / cm ² , and a heating rate of 6 ° C./min. Thereby, an S-shaped curve relating to temperature (° C.) / Stroke (mm) is obtained. The softening point of the sample is read from the obtained S-shaped curve. Specifically, with respect to the resulting S-shaped curve, the maximum value of the stroke and S _1, the stroke value of the low-temperature side of the base line and S _2. The temperature at which the stroke value is (S ₁ + S ₂ ) / 2 is taken as the softening point of the sample. Thereby, the softening point of the binder resin (sample) is obtained.

<1-1-2. Colorant>
As the colorant, a known pigment or dye can be used in accordance with each color of a plurality of colors of toner.

  When one of the toners of a plurality of colors is a black toner, a black colorant is used for the black toner. An example of a black colorant is carbon black. You may use the black colorant adjusted to black using the yellow colorant, magenta colorant, and cyan colorant which are mentioned later.

  When one of the toners of a plurality of colors is a yellow toner, a yellow colorant is used for the yellow toner. Examples of yellow colorants include condensed azo compounds, isoindolinone compounds, anthraquinone compounds, azo metal complexes, methine compounds, or arylamide compounds. More specifically, C.I. I. Pigment Yellow (3, 12, 13, 14, 15, 17, 62, 74, 83, 93, 94, 95, 97, 109, 110, 111, 120, 127, 128, 129, 147, 151, 154, 155 168, 174, 175, 176, 180, 181, 191, or 194), naphthol yellow S, Hansa yellow G, or C.I. I. Bat yellow is mentioned.

  When one of the toners of a plurality of colors is magenta toner, a magenta colorant is used for the magenta toner. Examples of magenta colorants include condensed azo compounds, diketopyrrolopyrrole compounds, anthraquinone compounds, quinacridone compounds, basic dye lake compounds, naphthol compounds, benzimidazolone compounds, thioindigo compounds, or perylene compounds. More specifically, C.I. I. Pigment Red (2, 3, 5, 6, 7, 19, 23, 48: 2, 48: 3, 48: 4, 57: 1, 81: 1, 122, 144, 146, 150, 166, 169, 177 184, 185, 202, 206, 220, 221 or 254).

  When one of the multiple color toners is a cyan toner, a cyan colorant is used for the cyan toner. Examples of cyan colorants include copper phthalocyanine, copper phthalocyanine derivatives, anthraquinone compounds, or basic dye lake compounds. More specifically, C.I. I. Pigment blue (1, 7, 15, 15: 1, 15: 2, 15: 3, 15: 4, 60, 62, or 66), phthalocyanine blue, C.I. I. Bat Blue, or C.I. I. Acid blue.

  One or more of the multiple color toners may be toners of other colors other than black, yellow, magenta, and cyan. The colorant used for another color toner is appropriately selected from known dyes or pigments.

  The amount of the colorant used is preferably 1 part by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the binder resin.

<1-1-3. Charge Control Agent>
The charge control agent is used for the purpose of improving the charge level and the charge rising property. Further, it is used for the purpose of obtaining a toner excellent in durability and stability. The charge rising characteristic is an index as to whether or not charging to a predetermined charge level is possible in a short time.

  When developing with positively charged toner, it is preferable to use a positively chargeable charge control agent. On the other hand, when developing using a negatively charged toner, it is preferable to use a negatively chargeable charge control agent. However, when sufficient chargeability is ensured in the toner, the charge control agent may not be used.

  Examples of positively chargeable charge control agents include azine compounds, direct dyes made from azine compounds, nigrosine compounds, acid dyes made from nigrosine compounds, metal salts of naphthenic acid or higher fatty acids, alkoxylated amines, alkylamides, or 4 A class ammonium salt is mentioned.

  Examples of azine compounds include pyridazine, pyrimidine, pyrazine, 1,2-oxazine, 1,3-oxazine, 1,4-oxazine, 1,2-thiazine, 1,3-thiazine, 1,4-thiazine, 1 , 2,3-triazine, 1,2,4-triazine, 1,3,5-triazine, 1,2,4-oxadiazine, 1,3,4-oxadiazine, 1,2,6-oxadiazine, 1,3 , 4-thiadiazine, 1,3,5-thiadiazine, 1,2,3,4-tetrazine, 1,2,4,5-tetrazine, 1,2,3,5-tetrazine, 1,2,4,6 -Oxatriazine, 1,3,4,5-oxatriazine, phthalazine, quinazoline or quinoxaline.

  Examples of direct dyes composed of azine compounds include azine fast red FC, azine fast red 12BK, azine violet BO, azine brown 3G, azine light brown GR, azine dark green BH / C, azine deep black EW, or Azin Deep Black 3RL is mentioned. Examples of nigrosine compounds include nigrosine, nigrosine salts, or nigrosine derivatives.

  Examples of acidic dyes composed of a nigrosine compound include nigrosine BK, nigrosine NB, or nigrosine Z. Examples of quaternary ammonium salts include benzyldecylhexylmethylammonium chloride or decyltrimethylammonium chloride.

  Further, a resin having a quaternary ammonium salt, a carboxylate, or a carboxyl group can also be used as a positively chargeable charge control agent. A nigrosine compound is particularly preferred in order to obtain a rapid start-up property. One type of charge control agent may be used alone, or a plurality of types of charge control agents may be used in combination.

<1-1-4. Release agent>
The release agent is used, for example, for the purpose of improving the toner fixing property and offset resistance. In order to improve the fixing property and offset resistance of the toner, the content of the release agent is preferably 1 part by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the binder resin. More preferably, it is 20 parts by mass or less.

  Examples of release agents include aliphatic hydrocarbon waxes, oxides of aliphatic hydrocarbon waxes, plant-derived waxes, animal-derived waxes, mineral-derived waxes, waxes based on fatty acid esters, or fatty acid esters. And a wax in which a part or all of the above is deoxidized. Examples of aliphatic hydrocarbon waxes include ester wax, polyethylene wax (eg, low molecular weight polyethylene), polypropylene wax (eg, low molecular weight polypropylene), polyolefin copolymer, polyolefin wax, microcrystalline wax, paraffin wax, or fisher Tropsch wax is mentioned. Examples of the oxide of the aliphatic hydrocarbon wax include an oxidized polyethylene wax or a block copolymer of oxidized polyethylene. Examples of plant-derived waxes include candelilla wax, carnauba wax, wood wax, jojoba wax, or rice wax. Examples of animal-derived waxes include beeswax, lanolin, or whale wax. Examples of mineral-derived waxes include ozokerite, ceresin, or petrolatum. Examples of the wax mainly composed of a fatty acid ester include montanic acid ester wax and caster wax. Deoxidized carnauba wax is an example of a wax in which a part or all of the fatty acid ester has been deoxidized.

  A mold release agent may be used individually by 1 type, and may be used in combination of 2 or more type.

  The melting point of the release agent is preferably 50 ° C. or higher and 100 ° C. or lower. When the melting point of the release agent is within such a range, the low-temperature fixability of the toner containing the release agent is improved, and the occurrence of offset at a high temperature of the toner tends to be suppressed. The melting point of the release agent can be measured using, for example, a differential scanning calorimeter (DSC) (for example, “DSC-6220” manufactured by Seiko Instruments Inc.).

<1-1-5. Magnetic powder>
Examples of magnetic powders include iron, ferromagnetic metals, alloys containing iron and / or ferromagnetic metals, compounds containing iron and / or ferromagnetic metals, ferromagnetic alloys subjected to ferromagnetization, or chromium dioxide Is mentioned. Examples of iron include ferrite or magnetite. Examples of the ferromagnetic metal include cobalt or nickel. An example of the ferromagnetization treatment is heat treatment.

  The particle size of the magnetic powder is preferably 0.1 μm or more and 1.0 μm or less. When magnetic powder having a particle size in such a range is used, it is easy to uniformly disperse the magnetic powder in the binder resin.

<1-2. Silica-containing external additive>
The charge decay constant of the silica-containing external additive provided in the toner particles contained in the toner differs among toners of a plurality of colors. The charge decay constant of the silica-containing external additive satisfies the formula 1 “α _n-1 > α _n ”. In Formula 1, n is an integer equal to or larger than 2, and is an integer equal to or smaller than the number of colors of a plurality of toners. α _n-1 is a charge decay constant of the silica-containing external additive provided in the toner particles contained in the toner T _n-1 . The toner T _n-1 forms a toner image superimposed on the intermediate transfer member n−1th among the toners of a plurality of colors. α _n is a charge decay constant of the silica-containing external additive provided in the toner particles contained in the toner T _n . The toner T _n forms a toner image that is nth superimposed on the intermediate transfer member among the toners of a plurality of colors. α _n-1 and α _n are positive numbers.

For convenience of explanation, a case where the toner of a plurality of colors is a four-color toner will be described as an example. In this case, in Formula 1, n is an integer of 2 or more and 4 or less. Toners T ₁ , T ₂ , T ₃ , and T ₄ are the toners that form the first, second, third, and fourth superimposed toner images on the intermediate transfer member among the four color toners, respectively. . The charge decay constants of the silica-containing external additive provided in the toner particles contained in the toners T ₁ , T ₂ , T ₃ , and T ₄ are charge decay constants α ₁ , α ₂ , α ₃ , and α ₄ , respectively. At this time, the charge decay constant of each silica-containing external additive satisfies the relationship of “α ₁ > α ₂ > α ₃ > α ₄ ”. The multi-color toners are not limited to four-color toners. The number of colors that can be used in an image forming apparatus using a plurality of colors of toner can be selected as appropriate. For example, n may be an integer of 2 to 10, an integer of 2 to 7, or an integer of 2 to 6.

As the silica-containing external additive having a larger charge decay constant, the electric charge is more easily released, and as a result, the electric charge charged to the toner particles having the silica-containing external additive is also easily released. Therefore, by satisfying the formula 1 “α _n-1 > α _n ”, it is possible to suppress the charge-up of the toner that forms the toner images of the respective colors superimposed on the intermediate transfer member, and the charge amount between the respective color toners It is thought that the variation of the can be reduced. As a result, it is considered that fixing failure (for example, electrostatic offset) due to toner charge-up is suppressed.

  Further, since the silica-containing external additive is located on the surface of the toner base particles, the silica-containing external additive is in direct contact with the electrostatic latent image carrier and the intermediate transfer member. Therefore, the charge decay constant of the silica-containing external additive tends to greatly affect the charge decay constant of the entire toner particles. It is considered that by controlling the charge decay constant of the silica-containing external additive, the charge decay constant of the entire toner particles can be controlled more efficiently than controlling the charge decay constant of the toner base particles. As a result, fixing failure (for example, electrostatic offset) due to toner charge-up is suppressed, and a good image tends to be stably obtained.

The charge decay constant (α) of the toner is determined using an electrostatic diffusivity measuring device (for example, “NS-D100” manufactured by Nano Seeds Co., Ltd.) based on the equation 2 “V = V ₀ exp (−α√t)”. Measured. In Equation 2, V represents the surface potential, V ₀ represents the initial surface potential, and t represents the decay time. Α is a positive number.

In the toner T ₁ that forms the first superimposed toner image on the intermediate transfer body among the toners of a plurality of colors, the charge decay constant α ₁ of the silica-containing external additive provided in the toner particles contained in the toner T ₁ It is preferably 0.020 or more and 0.200 or less in an environment of 32.5 ° C. and humidity 80% RH. When the charge attenuation constant α ₁ is 0.020 or more, it is possible to suppress the charge-up of the toner on the intermediate transfer member and to easily suppress the variation in the charge amount among the color toners. As a result, it becomes easier to suppress the occurrence of fixing failure (for example, electrostatic offset). Moreover, it becomes easy to suppress the occurrence of voids in the formed image. Here, if the charge amount of the toner at the time of secondary transfer is insufficient, when a secondary transfer bias having a polarity opposite to the charge polarity of the toner is applied, the toner is not easily attracted to the recording medium, and the toner is placed at a desired position on the recording medium. Toner may not adhere. However, when the charge attenuation constant α ₁ is 0.200 or less, it becomes easy to secure the toner charge amount necessary for the secondary transfer. As a result, it is easy to suppress the occurrence of secondary transfer failure (for example, transfer scattering) due to insufficient charge amount of toner during secondary transfer. The transfer scattering is an image defect in which fine dots due to toner appear around the character portion of the formed image.

Further, in addition to the charge attenuation constant α ₁ being 0.020 or more and 0.200 or less, toner particles contained in the toner that forms the toner image that is finally superimposed on the intermediate transfer member among a plurality of color toners. The charge decay constant of the silica-containing external additive provided is more preferably 0.020 or more. The charge decay constant is a value measured in an environment of a temperature of 32.5 ° C. and a humidity of 80% RH.

  The silica-containing external additive contains silica. Silica is not particularly limited as long as it can be used as an external additive. As silica, hydrophilic silica is preferable, and hydrophilic fumed silica is more preferable.

  The silica-containing external additive preferably has a predetermined structure. Specifically, the silica-containing external additive preferably includes an external additive core and a coating layer. The coating layer covers the external additive core. The toner particles including the silica-containing external additive having such a structure may be contained in at least one of the toners of a plurality of colors. When the mass of the coating layer increases with respect to the mass of the external additive core, the charge decay constant of the silica-containing external additive tends to increase. Therefore, toner particles including the silica-containing external additive having such a structure are included in all toners other than the toner that forms the toner image that is finally superimposed on the intermediate transfer member among the plurality of color toners. Is more preferable. Furthermore, it is particularly preferable that toner particles including a silica-containing external additive having such a structure are included in all of the toners of a plurality of colors. By adjusting the mass of the coating layer with respect to the mass of the external additive core, a silica-containing external additive having a charge decay constant that satisfies Equation 1 can be easily obtained.

  The external additive core preferably contains silica. The silica contained in the external additive core is not particularly limited as long as it can be used for the external additive. As silica, hydrophilic silica is preferable, and hydrophilic fumed silica is more preferable.

  The coating layer preferably contains a metal hydroxide. The hydroxyl group of the metal hydroxide tends to release the positive charge of the toner. Therefore, when the toners of a plurality of colors are positively chargeable toners, the coating layer contains a metal hydroxide, so that the positive charge of the toner on the intermediate transfer member can be easily attenuated. As a result, it becomes easy to suppress the toner charge-up due to the application of the primary transfer bias, and it becomes easy to suppress fixing defects (for example, electrostatic offset). In addition, it becomes easy to suppress the occurrence of uneven transfer and voids in the formed image.

  Examples of metal oxides include aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or zinc hydroxide. The metal hydroxide is preferably aluminum hydroxide or magnesium hydroxide.

The silica-containing external additive having a charge decay constant α _n-1 preferably has a higher metal hydroxide content relative to the mass of silica than the silica-containing external additive having a charge decay constant α _n . For example, the silica-containing external additive having a charge decay constant α ₁ preferably has a higher metal hydroxide content relative to the mass of silica than the silica-containing external additive having a charge decay constant α ₂ . By adjusting the content of the metal hydroxide, the charge decay constant of the silica-containing external additive tends to be adjusted. Therefore, the content rate of the silica-containing external additive with respect to the mass of the toner base particles can be set to the same value among the toners of a plurality of colors.

  As already described, the hydroxyl group of the metal hydroxide tends to release the positive charge charged in the toner. When the plurality of toners are positively chargeable toners, the positive potential of the toner on the intermediate transfer member is easily attenuated when the content of the metal hydroxide with respect to the mass of silica increases. Therefore, the toner that forms a toner image with a faster primary transfer timing increases the metal hydroxide content of the silica-containing external additive contained in the toner, thereby charging the toner by applying the primary transfer bias. It becomes easy to suppress. As a result, it becomes easy to suppress toner fixing failure (for example, electrostatic offset). Further, by adjusting the content of the metal hydroxide with respect to the mass of silica, it becomes easy to adjust the charge amount of the toner while keeping the content of the silica-containing external additive contained in each color toner constant. As a result, it becomes easy to maintain the fluidity of the toner, and it becomes easy to avoid the complicated setting of the development conditions.

  It is more preferable that the surface of the silica-containing external additive is subjected to a hydrophobic treatment. In other words, the silica-containing external additive may have a hydrophobic layer. When the silica-containing external additive is provided with a coating layer, the hydrophobic layer is provided so as to further coat the external additive core provided with the coating layer. If the silica-containing external additive does not have a coating layer, the hydrophobic layer is provided to cover the external additive core. For the hydrophobic treatment, for example, a silane coupling agent (for example, an aminosilane compound or an alkylsilane compound) is used.

  Even when a toner is stored in a normal temperature / humidity environment or a high temperature / high humidity environment to form an image after the toner has been stored for a long period of time by hydrophobizing the silica-containing external additive, It is considered that the charging property is stabilized. Further, it is considered that good fluidity of the toner is maintained.

The toner forming the toner image is superimposed on the first of the plurality of color toners on the intermediate transfer member and the toner T _1. In this case, the content of the metal hydroxide of the silica-containing external additive included in the toner particles included in the toner T ₁ is 5.0% by mass or more and 50.0% by mass or less with respect to the mass of silica. Is preferred. When the content of the metal hydroxide is 5.0% by mass or more, it is possible to suppress the charge-up of the toner on the intermediate transfer body and to further suppress the occurrence of fixing failure (for example, electrostatic offset). Further, it tends to be possible to suppress the occurrence of voids in the formed image. On the other hand, when the content of the metal hydroxide is 50.0% by mass or less, the charge decay constant does not become too large. For this reason, it is easy to secure a charge amount necessary for the toner during the secondary transfer, and it is easy to suppress the occurrence of a secondary transfer failure (for example, transfer scattering).

  Hereinafter, an example of a method for producing the silica-containing external additive will be described. Depending on the purpose, unnecessary operations may be omitted as appropriate. First, an aqueous medium and silica are stirred using a mixing apparatus to obtain an aqueous medium dispersion of silica. A metal hydroxide and a base are added dropwise to the aqueous medium dispersion. After completion of dropping, an acid is added to the aqueous medium dispersion to neutralize it. Thereby, the coating layer containing a metal hydroxide is formed on the surface of the silica (external additive core).

  Subsequently, the surface portion of the coating layer formed on the silica surface is subjected to a hydrophobic treatment. First, a silane coupling agent (for example, a silane coupling agent having an amino group) is added to the aqueous medium dispersion and stirred. Subsequently, the aqueous medium dispersion is subjected to solid-liquid separation to obtain a wet cake. The obtained wet cake is washed with water and then dried. The obtained dried product is pulverized using a pulverizer to obtain a pulverized product. The ground product is added to the amino-modified silicone oil and heated with stirring. The resulting product is further heated at a high temperature (eg, at 200 ° C.) under a nitrogen stream. As a result, the surface portion of the coating layer covering the silica (external additive core) is hydrophobized. Specifically, the hydroxyl group of the metal hydroxide contained in the surface portion of the coating layer is substituted with a silanol group having an amino group. Furthermore, an ether bond is formed between silicon atoms (Si) in the silanol group having an amino group. Thereby, a silica-containing external additive is obtained.

<1-3. External additives other than silica-containing external additives>
Another external additive other than the silica-containing external additive is appropriately selected from known external additives. Examples of another external additive include silica or metal oxide (more specifically, alumina, titanium oxide, magnesium oxide, zinc oxide, strontium titanate, or barium titanate). Another external additive may be used alone or in combination of two or more. The number average particle diameter of another external additive is preferably 1 nm or more and 1 μm or less, and more preferably 1 nm or more and 50 nm or less. The amount of the external additive used is preferably 0.5 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the toner base particles.

<2. Career>
Each of the toners of a plurality of colors may be mixed with a desired carrier and used as a two-component developer. When preparing a two-component developer, it is preferable to use a magnetic carrier.

  A carrier core coated with a resin may be used as the carrier. Further, as the carrier, a resin carrier in which a carrier core is dispersed in a resin may be used.

  Examples of carrier cores include iron, oxidized iron, reduced iron, magnetite, copper, silicon steel, ferrite, nickel, or cobalt particles; these materials and metals (eg, manganese, magnesium, zinc, and / or aluminum) ) Particles of iron-nickel alloy; particles of iron-cobalt alloy; particles of ceramics; or particles of a high dielectric constant material. Examples of ceramics include titanium oxide, aluminum oxide, copper oxide, magnesium oxide, lead oxide, zirconium oxide, silicon carbide, magnesium titanate, barium titanate, lithium titanate, lead titanate, lead zirconate, or niobic acid Lithium is mentioned. Examples of the high dielectric constant material include ammonium dihydrogen phosphate, potassium dihydrogen phosphate, or Rochelle salt. These carrier cores can be used singly or in combination of two or more.

  Examples of the resin covering the carrier core include acrylic acid polymer, styrene polymer, styrene-acrylic acid copolymer, olefin polymer, polyvinyl chloride, polyvinyl acetate, polycarbonate, cellulose resin, and polyester resin. , Unsaturated polyester resin, polyamide resin, urethane resin, epoxy resin, silicone resin, fluorine resin, phenol resin, xylene resin, diallyl phthalate resin, polyacetal resin, or amino resin. Examples of olefin polymers include polyethylene, chlorinated polyethylene, or polypropylene. Examples of the fluororesin include polytetrafluoroethylene, polychlorotrifluoroethylene, or polyvinylidene fluoride. These resins can be used alone or in combination of two or more.

  The particle diameter of the carrier is preferably 20 μm or more and 120 μm or less, and more preferably 25 μm or more and 80 μm or less. The particle diameter of the carrier can be measured with an electron microscope.

  When the toner is used in the two-component developer, the toner content is preferably 3% by mass or more and 20% by mass or less, and more preferably 5% by mass or more and 15% by mass or less with respect to the mass of the two-component developer. It is more preferable.

<3. Manufacturing method of multi-color toner>
Hereinafter, an example of a method for producing a multi-color toner will be described.

<3-1. Step of forming toner base particles>
Examples of the method for producing toner base particles include an agglomeration method or a pulverization method. The agglomeration method is easier to produce toner mother particles having a higher degree of circularity than the pulverization method. Further, the aggregation method is easy to produce toner base particles having a uniform shape and particle size. On the other hand, the pulverization method can produce toner mother particles more easily than the aggregation method.

(Crushing method)
Hereinafter, an example of the pulverization method will be described. First, a binder resin, a colorant, a charge control agent, a release agent, and / or magnetic powder are mixed. Subsequently, the obtained mixture is melted and kneaded. Subsequently, the obtained melt-kneaded product is pulverized and classified. As a result, toner base particles having a desired particle diameter are obtained.

(Aggregation method)
Next, an example of the aggregation method will be described. First, fine particles containing a binder resin, a colorant, a charge control agent, a release agent, and / or magnetic powder are aggregated in an aqueous medium to obtain aggregated particles. Subsequently, the obtained aggregated particles are heated to unite the components contained in the aggregated particles. As a result, an aqueous dispersion containing toner base particles is obtained.

  Subsequently, toner base particles are obtained by removing components (for example, a dispersant) other than the toner base particles from the aqueous dispersion. Specifically, wet cake-like toner mother particles are recovered from the dispersion containing the toner mother particles by solid-liquid separation. The obtained wet cake-like toner base particles are washed with water. The conductivity of the filtrate separated by solid-liquid separation is preferably 10 μS / cm or less. For example, an electrical conductivity meter “Horiba COND METER ES-51” manufactured by Horiba, Ltd. can be used for the measurement of the electrical conductivity. Instead of solid-liquid separation, the following method may be used. The toner mother particles in the aqueous dispersion are settled, and the supernatant is replaced with water. After the replacement, the toner base particles are redispersed in water.

  Subsequently, the toner base particles are dried. Examples of the method for drying the toner base particles include a method using a dryer (for example, a spray dryer, a fluidized bed dryer, a vacuum freeze dryer, or a vacuum dryer). Among these methods, a method using a spray dryer is preferable in order to suppress aggregation of toner base particles during drying. When a spray dryer is used, drying and an external addition process described later can be performed simultaneously. Specifically, a dispersion of a silica-containing external additive is sprayed together with a dispersion of toner base particles. Thereby, the silica-containing external additive can be attached to the surface of the toner base particles.

<3-2. External process>
In the external addition step, a silica-containing external additive is attached to the surface of the toner base particles. As an example of the method for attaching the silica-containing external additive, a mixer (for example, FM mixer or Nauter mixer (registered trademark)) is used under such a condition that the silica-containing external additive is not buried in the surface of the toner base particles. Is used to mix the toner base particles and the silica-containing external additive.

  The toner manufacturing method can be arbitrarily changed according to the required configuration or characteristics of the toner. Further, unnecessary operations and processes may be omitted. In order to produce the toner efficiently, it is preferable to form a large number of toner particles simultaneously.

<4. Image Forming Apparatus and Image Forming Method>
Hereinafter, an image forming apparatus and an image forming method using a plurality of colors of toner according to the present embodiment will be described. Hereinafter, an example of a tandem image forming apparatus will be described with reference to FIG.

  FIG. 1 shows an image forming apparatus 100. The image forming apparatus 100 includes a plurality of developing units 11a to 11d, a plurality of electrostatic latent image carriers 12a to 12d, an intermediate transfer member 13, a plurality of primary transfer units 15a to 15d, and a secondary transfer unit 16. The fixing unit 17 and the cleaning roller 18. Specific examples of the developing units 11a to 11d, the electrostatic latent image carriers 12a to 12d, the intermediate transfer member 13, the primary transfer units 15a to 15d, the secondary transfer unit 16, and the fixing unit 17 include a developing device and a photosensitive unit, respectively. Examples thereof include a body drum, a transfer belt, a primary transfer roller, a secondary transfer roller, and a fixing device.

  The intermediate transfer member 13 is stretched around a driving roller 14a, a driven roller 14b, and a tension roller 14c. The intermediate transfer member 13 is driven by a driving roller 14a and rotates in a direction indicated by an arrow in FIG. The cleaning roller 18 removes the toner remaining on the intermediate transfer member 13.

When an image is formed by the image forming apparatus 100 using a plurality of toners T ₁ , T ₂ , T ₃ , and T ₄ , a developer including toner T ₁ , a developer including toner T ₂ , and toner T ₃ are included. The developer and the developer including the toner T ₄ are set in each of the developing units 11a, 11b, 11c, and 11d.

The development process is performed as follows. Developing units 11a, 11b, 11c, and 11d each of which an electrostatic latent image bearing member 12a, 12b, 12c, and an electrostatic latent image formed on the 12d, the toner _{T 1, T 2, T 3} , and T ₄ Develop using. As a result, toner images (color toner images) of colors corresponding to the toners T ₁ , T ₂ , T ₃ , and T ₄ are formed on the electrostatic latent image carriers 12a, 12b, 12c, and 12d, respectively. .

The primary transfer process is performed as follows. The primary transfer portions 15a, 15b, 15c, and 15d pass through the intermediate transfer member 13 and the toners T ₁ , T ₂ , T ₃ , and T ₄ on the electrostatic latent image carriers 12a, 12b, 12c, and 12d. First, a primary transfer bias is applied. The primary transfer bias is, for example, a bias having a polarity opposite to the charging polarity of the toners T ₁ , T ₂ , T ₃ , and T ₄ . As a result, the toner images of the respective colors formed on the electrostatic latent image carriers 12a, 12b, 12c, and 12d are transferred to the intermediate transfer member 13.

The primary transfer portions 15a, 15b, 15c, and 15d are arranged in this order from the upstream side in the rotation direction of the intermediate transfer body 13 with respect to the primary transfer portion 15a. That is, the primary transfer portion 15a is disposed at the position where primary transfer is performed earliest. The primary transfer portion 15d is arranged at the position where the primary transfer is performed the latest. The toner images of the respective colors formed on the electrostatic latent image carriers 12a, 12b, 12c, and 12d corresponding to the primary transfer portions 15a, 15b, 15c, and 15d are sequentially superimposed on the intermediate transfer member 13. Specifically, first, a toner image formed by the toner T ₁ is disposed on the intermediate transfer member 13. The toner image formed by the toner T ₂ is superimposed on the toner image formed by the toner T ₁ . The toner image formed by the toner T ₃ is superimposed on the toner image formed by the toner T ₂ . On the toner image formed by toner T _3, a toner image formed by the toner T ₄ are superposed.

Toner T ₁ of the on the intermediate transfer body 13, T _2, T _3, and T _4, the primary transfer bias of the opposite polarity is applied by the same mechanism and repulsion due to electrostatic friction, the toner T _1, T ₂ , T ₃ and T ₄ are easy to charge up. Among them, the toner T ₁ is considered to be most easily charged up. This is because the primary transfer bias is applied to the toner T ₁ on the intermediate transfer body 13 a total of four times by the primary transfer portions 15a, 15b, 15c, and 15d.

However, the charge decay constant of the silica-containing external additive provided in the toner particles contained in each of the toners T ₁ , T ₂ , T ₃ , and T ₄ satisfies the formula 1 “α _n-1 > α _n ”. Specifically, when the charge decay constants of the silica-containing external additives provided in the toner particles contained in the toners T ₁ , T ₂ , T ₃ , and T ₄ are α ₁ , α ₂ , α ₃ , and α _4. The relationship “α ₁ > α ₂ > α ₃ > α ₄ ” is satisfied. The toners T ₁ , T ₂ , T ₃ , and T ₄ form the first, second, third, and fourth superimposed toner images on the intermediate transfer member 13, respectively.

As the silica-containing external additive having a larger charge decay constant, the electric charge is more easily released, and as a result, the electric charge charged to the toner particles having the silica-containing external additive is also easily released. For this reason, when the relationship of “α ₁ > α ₂ > α ₃ > α ₄ ” is satisfied, the toners T ₁ , T ₂ , T ₃ , and the like that form toner images of the respective colors superimposed on the intermediate transfer member 13. It is considered that the charge-up of T ₄ and T ₄ can be suppressed, and the variation in the charge amount can be reduced. As a result, it is considered that fixing failure (for example, electrostatic offset) due to toner charge-up is suppressed.

Next, the secondary transfer process is performed as follows. The secondary transfer unit 16 applies a secondary transfer bias (toner T ₁ , T ₂ , T ₃ , and T ₄ charging polarities) to each color toner image superimposed on the intermediate transfer member 13 via the recording medium P. Reverse polarity bias). As a result, the toner images of the respective colors superimposed on the intermediate transfer member 13 are collectively transferred to the recording medium P. For example, paper can be used as the recording medium P.

  The fixing unit 17 heats and / or pressurizes the recording medium P to which each color toner image is transferred. As a result, each color toner image is fixed on the recording medium P. As a result, an image is formed on the recording medium P. As described above, the image forming apparatus and the image forming method using the toners of a plurality of colors according to the present embodiment have been described with reference to FIG.

  As described above, according to the multi-color toner, the image forming apparatus, and the image forming method according to the present embodiment, it is possible to suppress fixing defects (for example, electrostatic offset) due to toner charge-up.

  Hereinafter, the present invention will be described more specifically with reference to examples. The present invention is not limited to the scope of the examples.

<1. Measuring method>
First, a method for measuring physical properties will be described.

(Measurement of softening point)
The softening point of the binder resin was measured using a Koka flow tester (“CFT-500D” manufactured by Shimadzu Corporation). Specifically, the binder resin (sample) was set in a Koka flow tester. A sample of 1 cm ³ was melted and discharged under the conditions of a die pore diameter of 1 mm, a plunger load of 20 kg / cm ² , and a temperature rising rate of 6 ° C./min. Thereby, an S-shaped curve related to temperature (° C.) / Stroke (mm) was obtained. The softening point of the sample was read from the obtained S-shaped curve. Specifically, with respect to the resulting S-shaped curve, the maximum value of the stroke and S _1, the stroke value of the low-temperature side of the base line was S _2. The temperature at which the stroke value was (S ₁ + S ₂ ) / 2 was taken as the softening point of the sample.

(Measurement of volume median diameter of toner base particles)
The volume median diameter (D ₅₀ ) of the toner base particles was measured using a precision particle size distribution measuring device (“Coulter Counter Multisizer 3” manufactured by Beckman Coulter Inc.).

(Measurement of volume median diameter of silica-containing external additives)
The volume median diameter (D ₅₀ ) of the silica-containing external additive is 100 or more at a magnification of 1,000,000 using a transmission electron microscope (H-7100FA (manufactured by Hitachi, Ltd.), TEM). A TEM photograph of the silica particles was taken. About 100 silica particles arbitrarily selected in the obtained TEM photograph, the equivalent circle diameter was measured using image analysis software (Mitani Corporation WinROOF), and the average value was calculated.

(Measurement of charge decay constant)
The charge decay constant of the silica-containing external additive was measured by a method based on JIS C 61340-2-1 using an electrostatic diffusivity measuring device (“NS-D100” manufactured by Nano Seeds Co., Ltd.). The method for measuring the charge decay constant of the silica-containing external additive will be described in detail below.

  A sample (silica-containing external additive) was placed in the measurement cell. The measurement cell was a metal cell in which a recess having an inner diameter of 10 mm and a depth of 1 mm was formed. The sample was pushed in from above using a slide glass, and the concave portion of the cell was filled with the sample. The sample overflowed from the cell was removed by reciprocating the slide glass on the surface of the cell. The filling amount of the sample was 0.04 g or more and 0.06 g or less.

Subsequently, the measurement cell filled with the sample was left in an environment of a temperature of 32.5 ° C. and a humidity of 80% RH for 12 hours. Subsequently, the grounded measurement cell was placed in an electrostatic diffusivity measuring apparatus, and ions were supplied to the sample by corona discharge to charge the sample. And the surface potential of the sample was continuously measured from the time when 0.7 seconds passed after the end of corona discharge. A charge decay constant (charge decay rate) was calculated based on the measured surface potential and the expression 2 “V = V ₀ exp (−α√t)”. In Equation 2, V represents the surface potential [V], V ₀ represents the initial surface potential [V], and t represents the decay time [second]. Α is a positive number indicating a charge decay constant.

<2. Preparation of toner>
Next, a toner preparation method will be described. In preparing the toner, first, a binder resin was prepared. Toner mother particles were prepared using the obtained binder resin. Next, a silica-containing external additive was prepared. The obtained silica-containing external additive was externally added to the toner base particles. Thus, a toner containing toner particles was prepared. In the following description, room temperature means 25 ° C.

<2-1. Preparation of binder resin>
A binder resin was prepared as follows. 1.0 mol of polyoxyethylene (2.2) -2,2-bis (4-hydroxyphenyl) propane, 4.5 mol of terephthalic acid, 0.5 mol of trimellitic anhydride, 4 g of dibutyltin oxide, Was placed in a reaction vessel. The contents of the reaction vessel were reacted at 230 ° C. for 8 hours under a nitrogen atmosphere. Subsequently, the unreacted raw material was removed by distilling off the content of the reaction vessel under reduced pressure under the condition of 8.3 kPa. The obtained reaction product was washed and dried. This obtained the polyester resin whose softening point is 120 degreeC.

<2-2. Preparation of toner base particles>
Using the obtained polyester resin as a binder resin, yellow toner base particles, cyan toner base particles, magenta toner base particles, and black toner base particles were prepared as follows.

(Yellow toner mother particles)
100 parts by mass of a polyester resin, 4 parts by mass of a phthalocyanine pigment as a colorant (“CI Pigment Yellow 180” manufactured by Sanyo Dyeing Co., Ltd.), 10 carnauba wax (“Carnauba No. 1” manufactured by Hiroyuki Kato) 10 3 parts by mass of a quaternary ammonium salt compound (“FCA201PS” manufactured by Fujikura Kasei Co., Ltd.) as a charge control agent was mixed using an FM mixer (“FM20B” manufactured by Nippon Coke Industries, Ltd.). The obtained mixture was melted and kneaded at 150 ° C. using a twin screw extruder (“TEM45” manufactured by Toshiba Machine Co., Ltd.). The resulting kneaded product was cooled. The cooled kneaded product was coarsely pulverized using an impact type screen type pulverizer (“Fezamill (FM-2S) 350 × 600 type” manufactured by Hosokawa Micron Corporation). The obtained coarsely pulverized product was finely pulverized using a supersonic jet pulverizer (“Jet Mill IDS-2” manufactured by Nippon Pneumatic Industry Co., Ltd.). The obtained finely pulverized product was classified using a classifier (“Elbow Jet EJ-LABO type” manufactured by Nippon Steel Mining Co., Ltd.). As a result, yellow toner base particles were obtained. The volume median diameter (D ₅₀ ) of the yellow toner base particles was 7 μm.

(Cyan toner base particles)
Instead of 4 parts by mass of a phthalocyanine pigment (“CI Pigment Yellow 180” manufactured by Sanyo Dye Co., Ltd.), 3 parts by mass of a phthalocyanine pigment (“CI Pigment Blue 15: 1” manufactured by Sanyo Dye Co., Ltd.) is used. Except for the above, cyan toner mother particles were prepared in the same manner as the yellow toner mother particles.

(Magenta toner base particles)
Instead of 4 parts by mass of a phthalocyanine pigment (Sanyo Dye Co., Ltd. “CI Pigment Yellow 180”), 3 parts by mass of a quinacridone pigment (Sanyo Dye Co., Ltd. “CI Pigment Red 122”) was used. Except for the above, magenta toner mother particles were prepared in the same manner as the yellow toner mother particles.

(Black toner mother particles)
Preparation of yellow toner base particles, except that carbon black (“REGAL (registered trademark) 330R” manufactured by Cabot) was used in place of the phthalocyanine pigment (“CI Pigment Yellow 180” manufactured by Sanyo Dye Co., Ltd.) Black toner base particles were prepared in the same manner as described above.

<2-3. Preparation of silica-containing external additive>
Silica-containing external additives A to J were prepared as follows.

(Silica-containing external additive A)
500 mL of ion-exchanged water and 50 g of silica (hydrophilic fumed silica, “Aerosil (registered trademark) 200” manufactured by Nippon Aerosil Co., Ltd.) are mixed with a mixing device (“TK Hibis Dispermix HM-3D manufactured by PRIMIX Co., Ltd.). -5 type "), and stirred at room temperature for 30 minutes at a stirring speed of 30 rpm. Thereby, an aqueous medium dispersion of silica was prepared. The resulting silica aqueous medium dispersion was heated until the temperature of the dispersion reached 45 ° C. While maintaining the temperature of the dispersion at 45 ° C., 500 mL of a sodium aluminate solution (concentration: 50 g / L as Al (OH) ₃ ) and a 5N sodium hydroxide aqueous solution are brought to a pH of 6.0 of the dispersion. Were simultaneously added dropwise. After completion of dropping, the dispersion was cooled to 30 ° C. 0.5N dilute hydrochloric acid was added to the obtained silica aqueous medium dispersion to adjust the pH of the dispersion to 3 or more and 4 or less. As a result, a coating layer containing aluminum hydroxide (Al (OH) ₃ ) was formed on the surface of the silica (external additive core).

  Subsequently, the surface portion of the coating layer formed on the surface of silica was subjected to a hydrophobic treatment as follows. First, 25 g of γ-aminopropyltriethoxysilane was added to the dispersion. After the dispersion was stirred for 4 hours, 2N sodium hydroxide aqueous solution was added to the dispersion to adjust the pH of the dispersion to 6.5. The dispersion was stirred for an additional 2 hours. Subsequently, the dispersion was filtered to obtain a wet cake. The obtained wet cake was washed with water. The washed wet cake was dried at 130 ° C. Subsequently, the obtained dried product was pulverized using a collision plate jet pulverizer (“IJT-2” manufactured by Nippon Pneumatic Industry Co., Ltd.) to obtain a pulverized product. In the pulverization, a ceramic flat plate was used as the collision plate. The crushing pressure was set to 0.6 MPa.

  Next, 500 mL of n-hexane (“n-hexane first grade” manufactured by Wako Pure Chemical Industries, Ltd.) 500 mL and amino is added to a mixing device (“TK Hibis Disper Mix HM-3D-5 type” manufactured by PRIMIX Corporation). 0.2 g of modified silicone oil (“KF857” manufactured by Shin-Etsu Chemical Co., Ltd.) was added. As a result, the amino-modified silicone oil was dissolved in n-hexane. 50 g of the obtained pulverized product was added to an n-hexane solution of amino-modified silicone oil in the mixing apparatus. Thereafter, the contents of the mixing apparatus were stirred at room temperature for 30 minutes at a stirring speed of 30 rpm. After stirring, the contents of the mixing apparatus were transferred to a 1 liter separable flask equipped with a thermometer and stirring blades.

While stirring the contents of the flask using a stirrer, the temperature was increased from 35 ° C. to 70 ° C. at a rate of 5 ° C./15 minutes. As an agitator, an agitator equipped with an agitating blade (as one agitating blade R-1345 type sold by As One Co., Ltd.) on a motor (as one tornado motor 1-5472-04 sold by As One Corporation) was used. Thereafter, the contents of the flask at 70 ° C. were dried using a vacuum dryer at a set temperature of 70 ° C. until the mass of the contents was not reduced. The obtained dried product was further heated at 200 ° C. for 3 hours under a nitrogen stream using an electric furnace. Thus, the surface portion of the coating layer covering silica (external additive core) was subjected to a hydrophobic treatment. Specifically, the hydroxyl group of aluminum hydroxide (Al (OH) ₃ ) contained in the surface portion of the coating layer was substituted with an aminopropylsilanol group. Furthermore, an ether bond was formed between silicon atoms (Si) in the aminopropylsilanol group. As a result, a coarse powder of silica-containing external additive A was obtained.

  The obtained coarse powder of silica-containing external additive A was pulverized using a collision plate jet pulverizer (“IJT-2” manufactured by Nippon Pneumatic Industry Co., Ltd.). In the pulverization, a ceramic flat plate was used as the collision plate. The crushing pressure was set to 0.6 MPa. Thereby, silica-containing external additive A was obtained.

In the obtained silica-containing external additive A, the silica (external additive core) was coated with a coating layer containing aluminum hydroxide. The coating layer was further coated with a hydrophobic layer. The volume median diameter (D ₅₀ ) of the silica-containing external additive A was 20 nm. The charge decay constant of the silica-containing external additive A was 0.200.

(Silica-containing external additive B)
A silica-containing external additive B was obtained in the same manner as the preparation of the silica-containing external additive A, except that the amount of sodium aluminate solution added was changed from 500 mL to 400 mL. The charge decay constant of the silica-containing external additive B was 0.161.

(Silica-containing external additive C)
A silica-containing external additive C was obtained in the same manner as in the preparation of the silica-containing external additive A, except that the amount of sodium aluminate solution added was changed from 500 mL to 200 mL. The charge decay constant of silica-containing external additive C was 0.082.

(Silica-containing external additive D)
A silica-containing external additive D was obtained in the same manner as the preparation of the silica-containing external additive A, except that the amount of sodium aluminate solution added was changed from 500 mL to 50 mL. The charge decay constant of silica-containing external additive D was 0.020.

(Silica-containing external additive E)
500 mL of ion-exchanged water and 50 g of silica (hydrophilic fumed silica, “Aerosil (registered trademark) 200” manufactured by Nippon Aerosil Co., Ltd.) are mixed with a mixing device (“TK Hibis Dispermix HM-3D manufactured by PRIMIX Co., Ltd.). -5 type ") and stirred at room temperature for 30 minutes at a stirring speed of 30 rpm. Thereby, an aqueous medium dispersion of silica was prepared. 500 mL of magnesium hydroxide slurry (concentration: 50 g / L) was added to the obtained silica aqueous medium dispersion. Subsequently, sulfuric acid was added dropwise over 1 hour until the pH of the aqueous medium dispersion containing the slurry was 9. After the dropwise addition, the aqueous medium dispersion was heated at 80 ° C. for 1 hour. Thereafter, the aqueous medium dispersion was cooled to 30 ° C. 0.5N diluted hydrochloric acid was added to the cooled aqueous medium dispersion to adjust the pH of the aqueous medium dispersion to 3 or more and 4 or less. As a result, a coating layer containing magnesium hydroxide (Mg (OH) ₂ ) was formed on the surface of the silica (external additive core).

  Subsequently, the surface portion of the coating layer formed on the surface of silica was subjected to a hydrophobic treatment as follows. First, 25 g of γ-aminopropyltriethoxysilane was added to the dispersion. The dispersion was stirred for 4 hours. After stirring, 2N aqueous sodium hydroxide solution was added to the dispersion to adjust the pH of the dispersion to 6.5. The dispersion was stirred for an additional 2 hours. Subsequently, the dispersion was filtered to obtain a wet cake. The obtained wet cake was washed with water. The washed wet cake was dried at 130 ° C. Then, it grind | pulverized using the collision board type jet mill ("IJT-2" by Nippon Pneumatic Industry Co., Ltd.), and obtained the ground material. In the pulverization, a ceramic flat plate was used as the collision plate. The crushing pressure was set to 0.6 MPa.

  Next, 500 mL of n-hexane (“n-hexane first grade” manufactured by Wako Pure Chemical Industries, Ltd.) 500 mL and amino is added to a mixing device (“TK Hibis Disper Mix HM-3D-5 type” manufactured by PRIMIX Corporation). 0.2 g of modified silicone oil (“KF857” manufactured by Shin-Etsu Chemical Co., Ltd.) was added. As a result, the amino-modified silicone oil was dissolved in n-hexane. 50 g of the obtained pulverized product was added to an n-hexane solution of amino-modified silicone oil in the mixing apparatus. Thereafter, the contents of the mixing apparatus were stirred at room temperature for 30 minutes at a stirring speed of 30 rpm. After stirring, the contents of the mixing apparatus were transferred to a 1 liter separable flask equipped with a thermometer and stirring blades.

The contents of the flask were heated from 35 ° C. to 70 ° C. at a rate of 5 ° C./15 minutes while stirring using a stirrer. As a stirrer, a stirrer in which a stirrer blade (As One Stirrer Blade R-1345 type sold by As One Corporation) was attached to a motor (As One Tornado Motor 1-5472-04 sold by As One Corporation) was used. Thereafter, the contents of the flask at 70 ° C. were dried using a vacuum dryer at a set temperature of 70 ° C. until the mass of the contents was not reduced. The obtained dried product was further heated at 200 ° C. for 3 hours under a nitrogen stream using an electric furnace. Thus, the surface portion of the coating layer covering silica (external additive core) was subjected to a hydrophobic treatment. Specifically, the hydroxyl group of magnesium hydroxide (Mg (OH) ₂ ) contained in the surface portion of the coating layer was substituted with an aminopropylsilanol group. Furthermore, an ether bond was formed between silicon atoms (Si) in the aminopropylsilanol group. As a result, a coarse powder of silica-containing external additive E was obtained.

  The obtained coarse powder of silica-containing external additive E was pulverized using a collision plate jet pulverizer (“IJT-2” manufactured by Nippon Pneumatic Industry Co., Ltd.). In the pulverization, a ceramic flat plate was used as the collision plate. The crushing pressure was set to 0.6 MPa. Thereby, a silica-containing external additive E was obtained.

In the obtained silica-containing external additive E, the silica (external additive core) was coated with a coating layer containing magnesium hydroxide. The coating layer was further coated with a hydrophobic layer. The volume median diameter (D ₅₀ ) of the silica-containing external additive E was 20 nm. The charge decay constant of silica-containing external additive E was 0.200.

(Silica-containing external additive F)
A silica-containing external additive F was obtained in the same manner as in the preparation of the silica-containing external additive E, except that the addition amount of the magnesium hydroxide slurry was changed from 500 m to 400 mL. The charge decay constant of the silica-containing external additive F was 0.160.

(Silica-containing external additive G)
A silica-containing external additive G was obtained in the same manner as the preparation of the silica-containing external additive E, except that the amount of the magnesium hydroxide slurry added was changed from 500 m to 200 mL. The charge decay constant of the silica-containing external additive G was 0.080.

(Silica-containing external additive H)
A silica-containing external additive H was obtained in the same manner as in the preparation of the silica-containing external additive E, except that the addition amount of the magnesium hydroxide slurry was changed from 500 m to 50 mL. The charge decay constant of the silica-containing external additive H was 0.020.

(Silica-containing external additive I)
500 mL of ion-exchanged water and 50 g of silica (hydrophilic fumed silica, “Aerosil (registered trademark) 200” manufactured by Nippon Aerosil Co., Ltd.) are mixed with a mixing device (“TK Hibis Dispermix HM-3D manufactured by PRIMIX Co., Ltd.). -5 type "), and stirred at room temperature for 30 minutes at a stirring speed of 30 rpm. Thereby, an aqueous medium dispersion of silica was prepared. 25 g of γ-aminopropyltriethoxysilane was added to the obtained silica aqueous medium dispersion. After the dispersion was stirred for 4 hours, a 2N aqueous sodium hydroxide solution was added to the dispersion to adjust the pH of the dispersion to 6.5. After pH adjustment, the dispersion was further stirred for 2 hours. Subsequently, the dispersion was filtered to obtain a wet cake. The obtained wet cake was washed with water. The washed wet cake was dried at 130 ° C. Subsequently, the obtained dried product was pulverized using a collision plate jet pulverizer (“IJT-2” manufactured by Nippon Pneumatic Industry Co., Ltd.) to obtain a pulverized product. In the pulverization, a ceramic flat plate was used as the collision plate. The crushing pressure was set to 0.6 MPa.

  Next, 500 mL of n-hexane (“n-hexane first grade” manufactured by Wako Pure Chemical Industries, Ltd.) 500 mL and amino is added to a mixing device (“TK Hibis Disper Mix HM-3D-5 type” manufactured by PRIMIX Corporation). 0.2 g of modified silicone oil (“KF857” manufactured by Shin-Etsu Chemical Co., Ltd.) was added. As a result, the amino-modified silicone oil was dissolved in n-hexane. 50 g of the obtained pulverized product was added to an n-hexane solution of amino-modified silicone oil in the mixing apparatus. Thereafter, the contents of the mixing apparatus were stirred at room temperature for 30 minutes at a stirring speed of 30 rpm. After stirring, the contents of the mixing apparatus were transferred to a 1 liter separable flask equipped with a thermometer and stirring blades.

  While stirring the contents of the flask using a stirrer, the temperature was increased from 35 ° C. to 70 ° C. at a rate of 5 ° C./15 minutes. As an agitator, an agitator equipped with an agitating blade (as one agitating blade R-1345 type sold by AS ONE Corporation) on a motor (as one tornado motor 1-5472-04 sold by AS ONE Corporation) was used. Thereafter, the contents of the flask at 70 ° C. were dried using a vacuum dryer at a set temperature of 70 ° C. until the mass of the contents was not reduced. The obtained dried product was further heated at 200 ° C. for 3 hours under a nitrogen stream using an electric furnace. As a result, the surface portion of silica (external additive core) was hydrophobized. Specifically, the hydroxyl group present on the surface of the silica was substituted with an aminopropylsilanol group. Furthermore, an ether bond was formed between silicon atoms (Si) in the aminopropylsilanol group. As a result, a coarse powder of silica-containing external additive I was obtained.

  The obtained coarse powder of silica-containing external additive I was pulverized using a collision plate jet pulverizer (“IJT-2” manufactured by Nippon Pneumatic Industry Co., Ltd.). In the pulverization, a ceramic flat plate was used as the collision plate. The crushing pressure was set to 0.6 MPa. Thereby, silica-containing external additive I was obtained.

In the obtained silica-containing external additive I, silica (external additive core) was coated with a hydrophobic layer. The volume median diameter (D ₅₀ ) of the silica-containing external additive I was 20 nm. The charge decay constant of silica-containing external additive I was 0.005.

(Silica-containing external additive J)
A silica-containing external additive J was obtained in the same manner as the preparation of the silica-containing external additive A, except that the amount of sodium aluminate solution added was changed from 500 mL to 600 mL. The charge decay constant of the silica-containing external additive J was 0.241.

  Regarding the silica-containing external additives A to J, Table 1 shows the charge decay constant of the silica-containing external additive, the content of silica (external additive core), and the type and content of the metal hydroxide (coating layer). Shown in In Table 1, “α” represents the charge decay constant of the silica-containing external additive. “Content” indicates the ratio of the content of the metal hydroxide to the mass (content) of silica.

<2-4. External processing>
The resulting silica-containing external additive was externally added to toner base particles (magenta, cyan, yellow, and black toner base particles) as follows. Thus, magenta toner, cyan toner, yellow toner, and black toner were prepared.

(Magenta toner)
100 parts by mass of magenta toner base particles, 1.5 parts by mass of silica-containing external additive, and 1.0 parts by mass of titanium oxide (“MT-500B” manufactured by Teika Co., Ltd., untreated titanium oxide fine particles) were charged into a container. . The contents of the container were mixed for 5 minutes at a rotational speed of 3500 rpm using an FM mixer ("FM-10B" manufactured by Nippon Coke Industries, Ltd.). As a result, a magenta toner was obtained. Thereafter, the obtained toner was sieved using a sieve of 200 mesh (aperture 75 μm). As a result, a toner containing a large number of toner particles was produced. The magenta toner used in each example and each comparative example used the types of silica-containing external additives shown in Table 2 as silica-containing external additives.

(Cyan toner)
A cyan toner was prepared in the same manner as the magenta toner except that the magenta toner mother particles were changed to cyan toner mother particles. In the cyan toners used in the examples and comparative examples, the types of silica-containing external additives shown in Table 2 were used as silica-containing external additives.

(Yellow toner)
A yellow toner was prepared in the same manner as the magenta toner except that the magenta toner mother particles were changed to yellow toner mother particles. The yellow toner used in each example and each comparative example used the types of silica-containing external additives shown in Table 2 as silica-containing external additives.

(Black toner)
A black toner was prepared in the same manner as in the preparation of the magenta toner except that the magenta toner base particles were changed to black toner base particles. The black toner used in each Example and each Comparative Example used the types of silica-containing external additives shown in Table 2 as silica-containing external additives.

<3. Preparation of two-component developer>
Any of the obtained magenta toner, cyan toner, yellow toner, and black toner was mixed with a carrier to prepare a two-component developer.

  First, a carrier was prepared as follows. 2 kg of an epoxy resin (“jER (registered trademark) 1004” manufactured by Mitsubishi Chemical Corporation) was dissolved in 20 liters of acetone. To the obtained solution, 100 g of diethylenetriamine and 150 g of phthalic anhydride were added and mixed. The obtained mixed liquid was sprayed onto 10 kg of the carrier core while feeding hot air at 80 ° C. using a fluidized bed coating apparatus (“Spiraflow (registered trademark) SFC-5” manufactured by Freund Sangyo Co., Ltd.). As the carrier core, a Mn—Mg—Sr ferrite core (“EF-35” manufactured by Powder Tech Co., Ltd., particle diameter: 35 μm) was used. As a result, the carrier core was coated with an uncured organic layer (fluidized bed). The carrier core coated with the uncured organic layer (fluidized bed) was heated at 180 ° C. for 1 hour using a dryer. Thereby, the fluidized bed was hardened. As a result, a carrier having a carrier core and a resin layer (coat layer) covering the carrier core was obtained.

  Next, the obtained carrier and 10% by mass of toner (magenta toner, cyan toner, yellow toner, or black toner) with respect to the mass of the carrier were mixed for 30 minutes using a ball mill. Thereby, a two-component developer (magenta, cyan, yellow, or black two-component developer) was prepared.

<4. Evaluation of electrostatic offset and transfer scattering>
An image was formed using the prepared two-component developer, and transfer scattering and electrostatic offset were evaluated. As an evaluation machine, a color multifunction machine (“Taskafa 5551ci” manufactured by Kyocera Document Solutions Inc.) was used. The two-component developer was put into the developing device of the evaluation machine. The toner corresponding to the charged two-component developer was charged into the toner container of the evaluation machine.

  Specifically, the evaluator had four developing units (first to fourth developing units). The first developing device was located at the uppermost stream of primary transfer (it was the position where primary transfer was earliest). The first to fourth developing units have a first developing unit, a second developing unit, and a third developing unit in a direction toward the downstream of the primary transfer (the side where the timing of the primary transfer is delayed) with respect to the first developing unit. , And the fourth developing device in this order. The first developer was charged with a two-component developer for magenta. The second developer was charged with a two-component developer for cyan. The third developer was charged with a yellow two-component developer. A black two-component developer was charged into the fourth developer.

In the evaluation of electrostatic offset and transfer scattering, evaluation images were continuously formed on 100 evaluation sheets using the evaluation machine. As an evaluation image, an image including a solid part with a printing rate of 100%, a halftone part with a printing rate of 50%, and a character part was used. “ColorCopy (registered trademark)” (A4 size, 90 g / m ² ) manufactured by Mondi was used as the evaluation paper.

Evaluation of electrostatic offset of the toner was evaluated as follows. Specifically, the presence or absence of the occurrence of electrostatic offset was observed for the 100th image formed as described above (mainly a solid portion with a printing rate of 100%). From the observation results, electrostatic offset was evaluated according to the following evaluation criteria. When an electrostatic offset occurs, an image corresponding to a solid portion with a printing rate of 100% appears in the image every rotation cycle of the fixing roller.
(Evaluation criteria for electrostatic offset)
A: No electrostatic offset is observed, and the image quality is very good.
B: Electrostatic offset is observed and image quality is poor.

Toner transfer scattering was evaluated as follows. Specifically, for the 100th image (mainly the character portion) formed as described above, the presence or absence of transfer scattering was observed using an optical microscope at a magnification of 50 times. From the observation results, the transfer scattering was evaluated according to the following evaluation criteria. When transfer scattering occurs, fine dots due to toner appear around the character portion of the formed image.
(Evaluation criteria for transfer scattering)
A: No transfer scattering is observed, and the image quality is very good.
B: Transfer scattering is observed and the image quality is poor.

From the evaluation results of electrostatic offset and transfer scattering, comprehensive evaluation was performed according to the following evaluation criteria.
(Comprehensive evaluation criteria)
A (very good): Evaluation of electrostatic offset was A. Furthermore, the evaluation of transfer scattering was A.
○ (good): Evaluation of electrostatic offset was A. The evaluation of transfer scattering was B.
X (defect): Evaluation of electrostatic offset was B.

  Table 2 shows the evaluation results of the electrostatic offset of the toner, the toner transfer scattering, and the comprehensive evaluation for each of the examples and the comparative examples.

Each of the multi-color toners (magenta, cyan, yellow, and black four-color toners) according to Examples 1 to 4 contained toner particles including a silica-containing external additive. Furthermore, the charge decay constant of the silica-containing external additive had a relationship of “α ₁ > α ₂ > α ₃ > α ₄ ”. Therefore, as shown in Table 2, no electrostatic offset was observed in images formed using these multiple color toners. From this, it is considered that these multi-color toners can suppress fixing defects caused by toner charge-up.

The multi-color toners (four-color toners of magenta, cyan, yellow, and black) according to Examples 1 to 3 are each included in the magenta toner that forms a magenta toner image that is superimposed first on the intermediate transfer member. The charge decay constant α ₁ of the silica-containing external additive provided in the toner particles was 0.020 or more and 0.200 or less in an environment of a temperature of 32.5 ° C. and a humidity of 80% RH. Therefore, as shown in Table 2, not only electrostatic offset but also transfer scattering was not observed in an image formed using these multiple color toners. From these facts, it is considered that these multi-color toners can suppress not only fixing defects but also secondary transfer defects due to insufficient charge amount of toner during secondary transfer.

In the multi-color toners (magenta, cyan, yellow, and black four-color toners) according to Comparative Examples 1 and 2, the charge decay constant of the silica-containing external additive satisfies α ₁ > α ₂ > α ₃ > α ₄ . Did not have a relationship. Therefore, it is considered that at least one of the toners of a plurality of colors has been charged up. As a result, as shown in Table 2, an electrostatic offset was observed in an image formed using these multiple color toners.

  The multi-color toner, the image forming apparatus, and the image forming method according to the present invention are used to form an image in an image forming apparatus that employs, for example, an electrophotographic method, an electrostatic recording method, or an electrostatic printing method. Can do.

DESCRIPTION OF SYMBOLS 100 Image forming apparatus 11a-11d Developing part 12a-12d Electrostatic latent image carrier 13 Intermediate transfer body 14a Drive roller 14b Driven roller 14c Tension roller 15a-15d Primary transfer part 16 Secondary transfer part 17 Fixing part 18 Cleaning roller P Recording Medium

Claims (8)

A plurality of color toners for forming an image by sequentially superimposing a plurality of color toner images on an intermediate transfer member,
Each of the plurality of color toners includes toner particles including a silica-containing external additive,
The toner containing a plurality of colors satisfying the following formula 1 in the charge decay constant of the silica-containing external additive.
α _n-1 > α _n (Formula 1)
(In Formula 1, n is an integer of 2 or more, and is an integer equal to or less than the number of colors of the plurality of color toners,
α _n-1 is the charge decay constant of the silica-containing external additive provided in the toner particles contained in the toner T _n-1 .
The toner T _n-1 is the toner that forms the toner image superimposed on the intermediate transfer member n−1 times among the toners of the plurality of colors.
α _n is the charge decay constant of the silica-containing external additive provided in the toner particles contained in the toner T _n ,
The toner T _n is the toner that forms the n-th toner image superimposed on the intermediate transfer body among the plurality of color toners,
α _n-1 and α _n are positive numbers. ) In the toner T ₁ that forms the toner image that is superimposed first on the intermediate transfer member among the toners of the plurality of colors,
The charge decay constant α ₁ of the silica-containing external additive included in the toner particles included in the toner T ₁ is 0.020 or more and 0.200 or less in an environment of a temperature of 32.5 ° C. and a humidity of 80% RH. The multi-color toner according to claim 1, wherein In at least one of the toners of the plurality of colors,
The silica-containing external additive provided in the toner particles contained in the at least one toner includes an external additive core and a coating layer that covers the external additive core,
The external additive core contains silica,
The multi-color toner according to claim 1, wherein the coating layer contains a metal hydroxide. The silica-containing external additive having the charge decay constant α _n-1 has a higher content of the metal hydroxide with respect to the mass of the silica than the silica-containing external additive having the charge decay constant α _n. The multi-color toner according to claim 3. In the toner T ₁ that forms the toner image that is superimposed first on the intermediate transfer member among the toners of the plurality of colors,
The metal hydroxide content of the silica-containing external additive included in the toner particles included in the toner T ₁ is 5.0% by mass or more and 50.0% by mass or less based on the mass of the silica. The multi-color toner according to claim 3 or 4, wherein   The multi-color toner according to claim 3, wherein the metal hydroxide is aluminum hydroxide or magnesium hydroxide. An image forming apparatus using a plurality of color toners,
A plurality of electrostatic latent image carriers;
The electrostatic latent image formed on each of the plurality of electrostatic latent image carriers is developed using each of the plurality of colors of toner, so that each of the plurality of electrostatic latent image carriers has each color. A developing unit for forming a toner image;
A primary transfer unit that sequentially superimposes the toner images of the respective colors formed on each of the plurality of electrostatic latent image carriers on an intermediate transfer member;
A secondary transfer unit that collectively transfers the toner images of the respective colors superimposed on the intermediate transfer member to a recording medium;
Each of the plurality of color toners includes toner particles including a silica-containing external additive,
An image forming apparatus in which a charge decay constant of the silica-containing external additive satisfies the following formula 1.
α _n-1 > α _n (Formula 1)
(In Formula 1, n is an integer of 2 or more, and is an integer equal to or less than the number of colors of the plurality of color toners,
α _n-1 is the charge decay constant of the silica-containing external additive provided in the toner particles contained in the toner T _n-1 .
The toner T _n-1 is the toner that forms the toner image superimposed on the intermediate transfer member n−1 times among the toners of the plurality of colors.
α _n is the charge decay constant of the silica-containing external additive provided in the toner particles contained in the toner T _n ,
The toner T _n is the toner that forms the n-th toner image superimposed on the intermediate transfer body among the plurality of color toners,
α _n-1 and α _n are positive numbers. ) An image forming method using a plurality of color toners,
By developing the electrostatic latent image formed on each of the plurality of electrostatic latent image carriers using each of the plurality of color toners, each color toner is applied to each of the plurality of electrostatic latent image carriers. A development process for forming an image;
A primary transfer step of sequentially superimposing the respective color toner images formed on each of the plurality of electrostatic latent image carriers on an intermediate transfer member;
A secondary transfer step of collectively transferring the toner images of the respective colors superimposed on the intermediate transfer body onto a recording medium,
Each of the plurality of color toners includes toner particles including a silica-containing external additive,
The image forming method, wherein the charge decay constant of the silica-containing external additive satisfies the following formula 1.
α _n-1 > α _n (Formula 1)
(In Formula 1, n is an integer of 2 or more, and is an integer equal to or less than the number of colors of the plurality of color toners,
α _n-1 is the charge decay constant of the silica-containing external additive provided in the toner particles contained in the toner T _n-1 .
The toner T _n-1 is the toner that forms the toner image superimposed on the intermediate transfer member n−1 times among the toners of the plurality of colors.
α _n is the charge decay constant of the silica-containing external additive provided in the toner particles contained in the toner T _n ,
The toner T _n is the toner that forms the n-th toner image superimposed on the intermediate transfer body among the plurality of color toners,
α _n-1 and α _n are positive numbers. )

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