White toner and method for producing white toner

Abstract

This white toner has excellent concealability and transferability. The white toner contains colored resin particles containing a binder resin, a colorant, and a charge control agent, wherein: the colorant contains titanium oxide particles surface-treated with two or more types of surface treatment agents, the surface treatment agents each containing an organosilicon compound and at least one type selected from the group consisting of aluminum hydroxide and aluminum oxide; and the charge control agent contains a quaternary ammonium salt-containing copolymer.

Description

White toner, and method for manufacturing white toner.

[0001] This disclosure relates to a white toner used for developing electrostatic latent images in electrophotography, electrostatic recording, and electrostatic printing, and to a method for manufacturing the white toner.

[0002] In image forming apparatuses such as electrophotographic devices, electrostatic recording devices, and electrostatic printing devices, an image forming method is widely implemented in which a desired image is formed by developing an electrostatic latent image formed on a photoreceptor with an electrostatic image developing toner (sometimes simply referred to as "toner" in this disclosure). This method is applied to photocopiers, printers, facsimile machines, and their multifunction devices. In recent years, the recording media used for printing have diversified, and there is a demand for support not only for white paper but also for colored paper, aluminum-metallized paper, transparent resin film, and textiles such as T-shirts. When printing on colored or transparent recording media other than white, white toner is used for the purpose of representing white or improving visibility.

[0003] Titanium dioxide, an inorganic pigment with high opacity, is commonly used as a colorant in white toner. While it is desirable for white toner to contain a large amount of titanium dioxide to achieve sufficient opacity, increasing the titanium dioxide content can lead to problems such as insufficient charge in the white toner or poor transferability due to titanium dioxide's low resistance. For example, Patent Document 1 discloses a technique for improving the opacity and chargeability of white toner by surface modification using mechanical shear force on a white toner containing a thermoplastic resin and white pigment, thereby coating the exposed white pigment microparticles on the surface of the white toner core particles, or the entire core particle of the white toner, with resin.

[0004] On the other hand, Patent Document 2 discloses the use of titanium dioxide with an inorganic compound surface treatment layer in a white toner in order to suppress the photocatalytic activity of titanium dioxide itself and suppress the degradation of the binder resin.

[0005] From the perspective of speeding up image formation and improving the image quality of the resulting images, further performance improvements are required for white toner.

[0006] Japanese Patent Publication No. 5-158283 Japanese Patent Publication No. 2018-77359

[0007] The object of this disclosure is to provide a white toner with excellent opacity and transferability, and to provide a method for manufacturing a white toner with excellent opacity and transferability.

[0008] In other words, the present disclosure provides the following white toner: [1] A white toner containing colored resin particles comprising a binder resin, a colorant and a charge control agent, wherein the colorant comprises titanium oxide particles surface-treated with two or more surface treatment agents, the surface treatment agent comprises at least one selected from the group consisting of aluminum hydroxide and aluminum oxide and an organosilicon compound, and the charge control agent comprises a quaternary ammonium salt-containing copolymer.

[0009] [2] The white toner according to [1], wherein the titanium dioxide particles are contained in an amount of 15 to 50 parts by mass per 100 parts by mass of the colored resin particles. [3] The white toner according to [1] or [2], wherein the binder resin is a styrene-acrylic resin. [4] The white toner according to any one of [1] to [3], wherein the colored resin particles further contain a polar resin. [5] The white toner according to any one of [1] to [4], wherein the colored resin particles further contain a styrene-based thermoplastic elastomer. [6] The white toner according to any one of [1] to [5], wherein the colored resin particles further contain a softener, and the softener contains a polyfunctional ester wax. [7] The white toner according to any one of [1] to [5], wherein the colored resin particles further contain a softener, and the softener contains a monoester wax. [8] The white toner according to any one of [1] to [7], wherein the average circularity of the white toner is 0.97 to 1.00.

[0010] The present disclosure also provides the following method for producing white toner: [9] A method for producing white toner comprising: preparing a polymerizable monomer composition containing at least a polymerizable monomer, a colorant, and a charge control agent; preparing a suspension in which droplets of the polymerizable monomer composition are dispersed in an aqueous medium containing a dispersion stabilizer; and subjecting the suspension to a polymerization reaction, wherein the colorant contains titanium dioxide particles surface-treated with two or more surface treatment agents, the surface treatment agent contains at least one selected from the group consisting of aluminum hydroxide and aluminum oxide, and an organosilicon compound, and the charge control agent contains a quaternary ammonium salt-containing copolymer.

[0011]

[10] The method for producing a white toner according to [9], wherein the content of the titanium dioxide particles is 15 to 50 parts by mass in 100 parts by mass of the polymerizable monomer composition.

[11] The method for producing a white toner according to [9] or

[10] , wherein the polymerizable monomer contains monovinyl monomer in a proportion of 95% by mass or more, and the monovinyl monomer comprises at least one selected from the group consisting of styrene and styrene derivatives, and at least one selected from the group consisting of acrylic acid esters and methacrylic acid esters.

[0012] According to this disclosure, it is possible to provide a white toner with excellent opacity and transferability.

[0013] In this disclosure, the "~" in numerical ranges means that the numbers before and after it are included as the lower and upper limits, respectively. Furthermore, among the numerical values ​​described in this disclosure that may include decimal places, unless otherwise specified, the numerical values ​​are obtained by rounding the digit that was one place smaller than the smallest digit included in the numerical value. Furthermore, in this disclosure, (meth)acrylate refers to acrylate and methacrylate respectively, and (meth)acrylic refers to acrylic and methacrylic respectively.

[0014] 1. White Toner The white toner of this disclosure is a white toner containing colored resin particles comprising a binder resin, a colorant, and a charge control agent, wherein the colorant comprises titanium oxide particles surface-treated with two or more surface treatment agents, the surface treatment agent comprises at least one selected from the group consisting of aluminum hydroxide and aluminum oxide, and an organosilicon compound, and the charge control agent comprises a quaternary ammonium salt-containing copolymer.

[0015] The reason why the white toner of this disclosure has excellent opacity and transferability is unknown, but it is presumed to be as follows. The surface-treated titanium dioxide particles contained in the white toner of this disclosure have negative charge properties in addition to being negatively charged themselves, and are further given negative charge properties by surface treatment with an organosilicon compound, and are also given hydrophobicity by surface treatment with an organosilicon compound. Furthermore, at least one selected from the group consisting of aluminum hydroxide and aluminum oxide, which is used as a surface treatment agent for the titanium dioxide particles, helps to adsorb the organosilicon compound to the titanium dioxide particles. On the other hand, the quaternary ammonium salt-containing copolymer has strong positive charge properties due to the presence of the quaternary ammonium salt, and the quaternary ammonium salt portion is hydrophilic. In the process of manufacturing colored resin particles, hydrophobically treated titanium dioxide particles are usually prone to aggregation, and aggregation of titanium dioxide particles causes deterioration of the opacity of the white toner. Furthermore, if titanium dioxide particles are included in the white toner in an amount sufficient to achieve adequate opacity, the titanium dioxide particles tend to be exposed on the surface of the toner particles, and these exposed titanium dioxide particles cause deterioration of the toner's transferability. In this disclosure, by using the above-mentioned titanium dioxide particles in combination with a quaternary ammonium salt-containing copolymer, the dispersibility of the titanium dioxide particles in the colored resin particles is improved, and the exposure of titanium dioxide particles to the surface of the colored resin particles is suppressed. This is presumed to be due to the fact that among the quaternary ammonium salt-containing copolymers contained in the colored resin particles, some are located on the surface of the colored resin particles and others interact with the titanium dioxide particles, and furthermore, steric repulsion occurs in the quaternary ammonium salt-containing copolymer. The quaternary ammonium salt-containing copolymer located on the surface of the colored resin particles suppresses the surface exposure of titanium dioxide particles. The quaternary ammonium salt-containing copolymer that interacts with the titanium dioxide particles improves the dispersibility of the titanium dioxide particles in the colored resin particles and also suppresses the surface exposure of the titanium dioxide particles by surrounding them. Furthermore, the steric repulsion of the quaternary ammonium salt-containing copolymer further improves the dispersibility of titanium dioxide particles.Thus, the white toner of this disclosure exhibits excellent opacity and transferability because the dispersibility of titanium dioxide particles is good and surface exposure of titanium dioxide particles is suppressed.

[0016] The following describes, in order, the colored resin particles contained in the white toner of this disclosure and their manufacturing method, the external additives that the white toner of this disclosure may further contain, and the physical properties of the white toner of this disclosure.

[0017] 1-1. Colored Resin Particles The colored resin particles contained in the white toner of this disclosure contain a binder resin, a colorant, and a charge control agent, and may further contain other additives such as a softener, a polar resin, and a styrene-based thermoplastic elastomer as needed. The colored resin particles may also be core-shell type colored resin particles having a core layer containing a binder resin and a shell layer containing a resin different from the binder resin.

[0018] [Binding Resin] As the binding resin, resins that have been widely used in toners in the past can be used, for example, styrene-acrylic resins, polystyrene, polyester resins, and epoxy resins. Among these, styrene-acrylic resins are preferably used because they improve the opacity and transferability of white toner, and provide a good balance between the low-temperature fixability and heat-resistant storage properties of white toner. The styrene-acrylic resin may be, for example, a copolymer of an aromatic vinyl monomer and a (meth)acrylate monomer. The copolymer may be further copolymerized with other monomers different from the aromatic vinyl monomer or the (meth)acrylate monomer, to the extent that it does not impair the purpose of this disclosure. The (meth)acrylate monomer is at least one selected from the group consisting of acrylic acid esters and methacrylic acid esters. In this disclosure, the styrene-acrylic resin used as the binding resin is distinguished from a static charge control resin in that the amount of functional groups is less than 0.1% by mass, and is distinguished from a polar resin in that the acid value is less than 0.5 mgKOH / g.

[0019] Furthermore, although not particularly limited, in order to improve the opacity and transferability of the white toner, and to achieve a good balance between the low-temperature fixability and heat-resistant storage properties of the white toner, the content of styrene-acrylic resin in 100 parts by mass of the total amount of binder resin may be, for example, 90 parts by mass or more, 95 parts by mass or more, or 99 parts by mass or more.

[0020] In the white toner of this disclosure, the styrene-acrylic resin used as the binder resin may be, for example, a polymer of the polymerizable monomers described below. Furthermore, although not particularly limited, in order to improve the opacity and transferability of the white toner and to achieve a good balance between the low-temperature fixability and heat-resistant storage of the white toner, the content of the polymer of the polymerizable monomers described below in 100 parts by mass of the total amount of binder resin may be, for example, 90 parts by mass or more, 95 parts by mass or more, or 99 parts by mass or more.

[0021] (Polymerizable Monomers) In this disclosure, a polymerizable monomer refers to a monomer having polymerizable functional groups. It is preferable to use a monovinyl monomer as the main component of the polymerizable monomer. That is, it is preferable that the binder resin contained in the colored resin particles is a polymer of a polymerizable monomer containing a monovinyl monomer. Examples of monovinyl monomers include aromatic monovinyl compounds such as styrene and styrene derivatives such as vinyltoluene and α-methylstyrene; acrylic acid and methacrylic acid; acrylic acid esters such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and dimethylaminoethyl acrylate; methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, and dimethylaminoethyl methacrylate; nitrile compounds such as acrylonitrile and methacrylonitrile; amide compounds such as acrylamide and methacrylamide; and olefins such as ethylene, propylene, and butylene. These monovinyl monomers can be used individually or in combination of two or more. Among these, styrene, styrene derivatives, acrylic acid esters, and methacrylic acid esters are preferably used as monovinyl monomers from the standpoint of improving the opacity and transferability of white toner, and balancing the low-temperature fixability and heat-resistant storage properties of white toner. Among acrylic acid esters, at least one selected from the group consisting of n-butyl acrylate, propyl acrylate, and 2-ethylhexyl acrylate is preferred, and among methacrylic acid esters, at least one selected from the group consisting of n-butyl methacrylate, propyl methacrylate, and 2-ethylhexyl methacrylate is preferred. Furthermore, from the same viewpoint as above, it is preferable that the monovinyl monomers include a combination of at least one selected from the group consisting of styrene and styrene derivatives and at least one selected from the group consisting of acrylic acid esters and methacrylic acid esters, and it is more preferable that they include a combination of styrene and at least one selected from the group consisting of acrylic acid esters and methacrylic acid esters.Furthermore, the styrene content in 100 parts by mass of the total monovinyl monomer is not particularly limited, but for the same reasons as above, it is preferably 60 parts by mass or more, more preferably 70 parts by mass or more, while preferably 90 parts by mass or less, more preferably 80 parts by mass or less. Also, for the same reasons as above, the total mass of monovinyl monomers, such as styrene, styrene derivatives, acrylic acid esters, and methacrylic acid esters, in 100 parts by mass of the total polymerizable monomer may be 90 parts by mass or more, 95 parts by mass or more, or 99 parts by mass or more. Furthermore, for the same reasons as above, the monovinyl monomer contains at least one selected from the group consisting of styrene and styrene derivatives, and at least one selected from the group consisting of acrylic acid esters and methacrylic acid esters, and the ratio (M1:M2) of the total mass of styrene and styrene derivatives (M1) to the total mass of acrylic acid esters and methacrylic acid esters (M2) is preferably in the range of 50:50 to 90:10, and more preferably in the range of 60:40 to 80:20.

[0022] The content of monovinyl monomer in 100% by mass of polymerizable monomer is not particularly limited, but in order to improve the opacity and transferability of the white toner, and to achieve a good balance between the low-temperature fixability and heat-resistant storage properties of the white toner, it may be, for example, 95% by mass or more, 98% by mass or more, or 99% by mass or more. The polymerizable monomer may consist of monovinyl monomer, but the content of monovinyl monomer in 100% by mass of polymerizable monomer may be 99.5% by mass or less.

[0023] As polymerizable monomers, it is preferable to use any crosslinkable polymerizable monomer together with a monovinyl monomer to improve the hot offset and shelf life of white toner. A crosslinkable polymerizable monomer is a monomer having two or more polymerizable functional groups. Examples of crosslinkable polymerizable monomers include aromatic divinyl compounds such as divinylbenzene, divinylnaphthalene, and their derivatives; ester compounds in which two or more carboxylic acids having carbon-carbon double bonds are ester-bonded to an alcohol having two or more hydroxyl groups, such as ethylene glycol dimethacrylate and diethylene glycol dimethacrylate; other divinyl compounds such as N,N-divinylaniline and divinyl ether; compounds having three or more vinyl groups; and so on. These crosslinkable polymerizable monomers can be used individually or in combination of two or more. Of these, aromatic divinyl compounds are preferably used as crosslinkable polymerizable monomers, and divinylbenzene is particularly preferably used. When the polymerizable monomer contains the crosslinkable polymerizable monomer, the content of the crosslinkable polymerizable monomer is not particularly limited, but is usually 0.1 to 5 parts by mass, preferably 0.3 to 2 parts by mass, and more preferably 0.5 to 1 part by mass, per 100 parts by mass of monovinyl monomer.

[0024] Furthermore, using macromonomers as part of the polymerizable monomer is preferable because it provides a good balance between the storage properties and low-temperature fixability of the white toner. Macromonomers are oligomers or polymers with a number average molecular weight of typically 1,000 to 30,000 and a high reactivity, having polymerizable carbon-carbon unsaturated double bonds at the ends of their molecular chains. Examples of the above macromonomers include styrene macromonomers, styrene-acrylonitrile macromonomers, polyacrylic acid ester macromonomers, and polymethacrylic acid ester macromonomers. Among these, at least one selected from the group consisting of polyacrylic acid ester macromonomers and polymethacrylic acid ester macromonomers is preferably used. Examples of acrylic acid esters used in polyacrylic acid ester macromonomers include those similar to those usable as monovinyl monomers, and examples of methacrylic acid esters used in polymethacrylic acid ester macromonomers include those similar to those usable as monovinyl monomers. Among the macromonomers mentioned above, it is preferable to appropriately select and use those that, when included in the polymerizable monomer, result in a higher glass transition temperature (Tg) of the resulting binder resin compared to when they are not included. Commercially available macromonomers may also be used. Examples of commercially available macromonomers include the macromonomer series AA-6, AS-6, AN-6S, AB-6, AW-6S, etc., manufactured by Toagosei Co., Ltd. Each of the macromonomers can be used individually or in combination of two or more. When the polymerizable monomer contains the macromonomer, the content of the macromonomer is not particularly limited, but is preferably 0.03 to 5 parts by mass, more preferably 0.05 to 2 parts by mass, even more preferably 0.1 to 1.5 parts by mass, even more preferably 0.2 to 1 part by mass, and even more preferably 0.3 to 1 part by mass per 100 parts by mass of the monovinyl monomer. Furthermore, the upper limit of the content of the macromonomer per 100 parts by mass of the monovinyl monomer may be 0.5 parts by mass or less.

[0025] In the white toner of this disclosure, the content of the binder resin is not particularly limited, but in order to improve the opacity and transferability of the white toner, and to achieve a good balance between the low-temperature fixability and heat-resistant storage of the white toner, it may be, for example, 60 to 95 parts by mass, 65 to 90 parts by mass, or 70 to 85 parts by mass per 100 parts by mass of colored resin particles.

[0026] [Coloring agent] The coloring agent includes titanium dioxide particles that have been surface-treated with two or more surface treatment agents, wherein the surface treatment agent comprises at least one selected from the group consisting of aluminum hydroxide and aluminum oxide, and an organosilicon compound. In this disclosure, the titanium dioxide particles that have been surface-treated with the above surface treatment agents may be simply referred to as "titanium dioxide particles," and the titanium dioxide particles before surface treatment may be referred to as "raw material titanium dioxide particles" to distinguish them from the surface-treated titanium dioxide particles. Furthermore, in this disclosure, the titanium dioxide particles that have been surface-treated with a surface treatment agent may be titanium dioxide particles that have been surface-treated with a surface treatment agent by a general method, for example, titanium dioxide particles on which the surface treatment agent is chemically bonded or physically attached to the surface of the titanium dioxide particles.

[0027] The surface treatment agent used for the titanium oxide particles comprises at least one selected from the group consisting of aluminum hydroxide and aluminum oxide, and an organosilicon compound, and may further contain another compound. As the at least one selected from the group consisting of aluminum hydroxide and aluminum oxide, aluminum hydroxide is preferably used from the viewpoint of improving the opacity and transferability of the white toner.

[0028] As organosilicon compounds, for example, compounds containing siloxane bonds, such as silicone oils and siloxane compounds, are preferably used from the viewpoint of improving the opacity and transferability of white toner, and among these, silicone oil is preferably used. Examples of silicone oils include straight silicone oils such as dimethylpolysiloxane (dimethicone), methylphenylpolysiloxane (phenyl trimethicone), and methylhydrogenpolysiloxane (hydrogen dimethicone); and various modified silicone oils such as amino-modified, epoxy-modified, carboxy-modified, methacrylic-modified, phenol-modified, alkyl-modified, or fluorine-modified. Among these, straight silicone oil is preferred from the viewpoint of improving the opacity and transferability of white toner, at least one selected from the group consisting of dimethylpolysiloxane (dimethicone) and methylhydrogenpolysiloxane (hydrogen dimethicone) is more preferred, and methylhydrogenpolysiloxane (hydrogen dimethicone) is particularly preferred.

[0029] The surface treatment agent used for the titanium oxide particles described above may further contain other compounds different from the aluminum hydroxide, aluminum oxide, or organosilicon compounds described above, as necessary, to the extent that it does not impair the purpose of this disclosure. Other compounds that are commonly used as surface treatment agents for titanium oxide particles can be used without particular limitation, and examples include oxides of inorganic metals such as zirconium, titanium, zinc, tin, and silicon; polyols such as pentaerythritol and trimethylolpropane; alkanolamines such as triethanolamine and trimethylolamine and their organic acid salts; higher fatty acids such as stearic acid and their metal salts.

[0030] Any crystalline form of titanium dioxide particles can be used as the raw material: anatase, rutile, or brookite. Among these, rutile-type titanium dioxide particles, which have a high refractive index, are preferred for improving the opacity of the white toner. Furthermore, titanium dioxide particles obtained by general titanium dioxide particle manufacturing methods such as the sulfuric acid method or the chlorine method can be used as the raw material.

[0031] The volume-average primary particle size of the titanium dioxide particles is not particularly limited, but is preferably 100 to 500 nm, more preferably 150 to 350 nm, and even more preferably 200 to 300 nm. When the volume-average primary particle size of the titanium dioxide particles is above the lower limit, the white toner of this disclosure can exhibit improved opacity and high whiteness. Furthermore, although titanium dioxide itself has high photocatalytic activity and may degrade the binder resin, when the volume-average primary particle size of the titanium dioxide particles is below the upper limit, the surface area in contact with the binder resin by the titanium dioxide particles is not too large, thereby suppressing the degradation of the binder resin. The primary particle size of the titanium dioxide particles is measured by acquiring particle images using a transmission electron microscope and performing image analysis. The volume-average primary particle size is the 50% cumulative diameter in the particle size distribution of primary particles determined by volume.

[0032] The content of the titanium dioxide particles is not particularly limited, but is preferably 15 to 50 parts by mass, more preferably 20 to 40 parts by mass, per 100 parts by mass of colored resin particles. When the content of the titanium dioxide particles is above the lower limit, it has an excellent effect in improving the opacity of the white toner of this disclosure, and when it is below the upper limit, it can suppress deterioration of the transferability of the white toner of this disclosure. The titanium dioxide particles can be used individually or in combination of two or more types.

[0033] The white toner of this disclosure may further contain colorants different from the titanium dioxide particles, to the extent that they do not impair the purpose of this disclosure. Examples of colorants different from the titanium dioxide particles include known white pigments, specifically zinc oxide, silicon dioxide, alumina, calcium carbonate, aluminum hydroxide, satin white, talc, calcium sulfate, magnesium oxide, magnesium carbonate, white carbon, kaolin, aluminosilicate, sericite, bentonite, smectite, etc. On the other hand, if the white toner of this disclosure further contains colorants different from the titanium dioxide particles, the content of the titanium dioxide particles in 100% by mass of the total amount of colorants contained in the white toner of this disclosure may be, for example, 90% by mass or more, 95% by mass or more, or 99% by mass or more, in order to improve the opacity and transferability of the white toner.

[0034] In the white toner of this disclosure, the content of the colorant is not particularly limited, but in order to improve the opacity and transferability of the white toner, the content of the colorant per 100 parts by mass of the binder resin may be, for example, 30 to 90 parts by mass or 40 to 70 parts by mass. Also, the content of the colorant per 100 parts by mass of the polymerizable monomer may be, for example, 30 to 90 parts by mass or 40 to 70 parts by mass. Also, the content of the colorant per 100 parts by mass of the monovinyl monomer may be, for example, 30 to 90 parts by mass or 40 to 70 parts by mass.

[0035] [Charge Control Agent] The charge control agent includes a quaternary ammonium salt-containing copolymer. Here, the quaternary ammonium salt-containing copolymer is a copolymer containing monomer units containing a quaternary ammonium salt (quaternary ammonium salt-containing monomer), and may be, for example, a copolymer of a quaternary ammonium salt-containing monomer and another monomer copolymerizable with said monomer. The quaternary ammonium salt-containing copolymer is a positively charged polymeric charge control agent (charge control resin), and the white toner of this disclosure is a positively charged toner because it contains the quaternary ammonium salt-containing copolymer. As described above, the white toner of this disclosure has excellent opacity and transferability because it contains the quaternary ammonium salt-containing copolymer as a charge control agent. Furthermore, since the quaternary ammonium salt-containing copolymer is colorless, it is also preferable in that it suppresses changes in the color of the white toner.

[0036] In the above-mentioned quaternary ammonium salt-containing copolymer, it is preferable that the content ratio of quaternary ammonium salt-containing monomer units in 100% by mass of total monomer units, i.e., the copolymerization ratio of quaternary ammonium salt-containing monomers, is 1 to 8% by mass. As a result, the above-mentioned quaternary ammonium salt-containing copolymer is excellent in the effect of imparting the desired electrostatic properties to white toner, as well as improving the opacity and transferability of white toner. In this disclosure, for polymer-type electrostatic control agents (electrostatic control resins), the content ratio of monomer units containing electrostatic-imparting functional groups in 100% by mass of total monomer units, i.e., the copolymerization ratio of monomers containing electrostatic-imparting functional groups, may be referred to as the "amount of functional groups." In the above-mentioned quaternary ammonium salt-containing copolymer, the group containing the quaternary ammonium salt is a functional group that imparts positive charge to the toner. Therefore, the proportion of quaternary ammonium salt-containing monomer units in 100% by mass of total monomer units, i.e., the copolymerization ratio of quaternary ammonium salt-containing monomers, may be simply referred to as the "amount of functional groups." The reason why quaternary ammonium salt-containing copolymers with a functional group amount within the above range are excellent in improving the opacity and transferability of the white toner of this disclosure is presumed to be that, when the amount of functional groups of the quaternary ammonium salt-containing copolymer is within the above range, the amount of quaternary ammonium salt-containing copolymer used to appropriately adjust the charge amount of the white toner of this disclosure is appropriate from the viewpoint of suppressing surface exposure of the titanium oxide particles while maintaining good dispersibility of the titanium oxide particles.

[0037] The quaternary ammonium salt contained in the above quaternary ammonium salt-containing copolymer is -NR ３ ＋ ・X － It is contained as a group having an ionic structure represented by . In this ionic structure, each of the three Rs is independently a hydrogen atom or a substituent such as an alkyl group. From the viewpoint of excellent effect in imparting positive charge to the toner, it is preferable that the three Rs are hydrogen atoms or linear, branched, or cyclic alkyl groups having 1 to 6 carbon atoms. X － -SO4 is a halogen ion, an alkyl group in which one hydrogen atom is substituted with a halogen ion, or a group in which at least one hydrogen atom may be substituted with a halogen atom.３ － , -PO ３ － or -BO ３ － is a hydrocarbon group having. Examples of the hydrocarbon group include an alkyl group, an aromatic hydrocarbon group, a substituted aromatic hydrocarbon group, and the like. X － , among others, in the white toner of the present disclosure, from the viewpoints of facilitating maintaining the charge amount during continuous printing to suppress printing defects, and improving hiding property and transferability, at least one hydrogen atom may be substituted with a halogen atom, -SO ３ － is preferably a hydrocarbon group having, more preferably an aromatic sulfonate anion which may have at least one substituent selected from the group consisting of a linear, branched or cyclic alkyl group having 1 to 6 carbon atoms and a halogen atom, and still more preferably a benzenesulfonate anion or a para-toluenesulfonate anion.

[0038] As a quaternary ammonium salt-containing copolymer, for example, a quaternary ammonium salt-containing styrene-acrylic resin can be preferably used. Examples of quaternary ammonium salt-containing styrene-acrylic resins include copolymers containing quaternary ammonium salt-containing monomer units, aromatic vinyl monomer units, and (meth)acrylate monomer units. Here, the aromatic vinyl monomer units and (meth)acrylate monomer units do not contain functional groups that impart electrostatic properties. The quaternary ammonium salt-containing styrene-acrylic resin may be further copolymerized with other monomers different from the quaternary ammonium salt-containing monomer, aromatic vinyl monomer, or (meth)acrylate monomer, to the extent that it does not impair the purpose of this disclosure. The content of the other monomer units is not particularly limited, but is usually 10% by mass or less, may be 5% by mass or less, or may be 1% by mass or less. The above-mentioned quaternary ammonium salt-containing styrene-acrylic resin is preferred in the white toner of this disclosure from the viewpoint of uniformizing the charge amount, and also from the viewpoint of improving opacity and transferability, due to its high compatibility with the binder resin. From this viewpoint, among the quaternary ammonium salt-containing styrene-acrylic resins, it is preferable that the quaternary ammonium salt-containing monomer units are quaternary ammonium salt-containing (meth)acrylate monomer units. Furthermore, from the viewpoint of dispersibility in polymerizable monomer compositions, the above-mentioned quaternary ammonium salt-containing copolymer is preferably soluble in aromatic vinyl monomers.

[0039] Examples of quaternary ammonium salt-containing (meth)acrylate monomer units that are preferably contained in the above-mentioned quaternary ammonium salt-containing copolymer include structural units represented by the following formula [I].

[0040] [In the above formula [I], R １ R is a hydrogen atom or a methyl group, ２ R is a linear or branched alkylene group having 1 to 3 carbon atoms, in which at least one hydrogen atom may be substituted with a halogen atom. ３ ~R ５ Each is independently a hydrogen atom or a linear, branched, or cyclic alkyl group having 1 to 6 carbon atoms, and X－ It may have a halogen ion, or at least one substituent selected from the group consisting of a linear, branched, or cyclic alkyl group having 1 to 6 carbon atoms, and a halogen atom, -SO ３ － , -PO ３ － Or -BO ３ － It is a benzene or naphthalene having either of the following properties.

[0041] X － -SO ３ － , -PO ３ － Or -BO ３ － It is a benzene or naphthalene having either of the following properties. － For example, the toner charge is easily maintained during continuous printing, making printing defects less likely, and improving the opacity and transferability of the white toner of this disclosure. Therefore, the atom may be an aromatic sulfonate anion which may have the above substituents. Examples of the above aromatic sulfonate anion include benzenesulfonate anion and p-toluenesulfonate anion.

[0042] Specific examples of structural units represented by the above formula [I] include structural units corresponding to quaternary ammonium salt-containing monomers such as N,N-diethyl-N-methyl-2-(methacryloyloxy)ethylammonium chloride, 2-(methacryloyloxy)ethyltrimethylammonium chloride (DMC; dimethylaminoethylmethyl chloride methacrylate), 2-(methacryloyloxy)-N-benzyl-N,N-dimethylethaneammonium chloride (DML; dimethylaminoethylbenzyl chloride methacrylate), and N,N-diethyl-N-methyl-2-(methacryloyloxy)ethylammonium p-toluenesulfonate, 2-(methacryloyloxy)ethyltrimethylammonium p-toluenesulfonate, and 2-(methacryloyloxy)-N-benzyl-N,N-dimethylethaneammonium p-toluenesulfonate. Among these, the structural unit corresponding to N,N-diethyl-N-methyl-2-(methacryloyloxy)ethylammonium p-toluenesulfonate is preferred.

[0043] In the above-mentioned quaternary ammonium salt-containing styrene-acrylic resin, the copolymerization ratio of aromatic vinyl monomer and (meth)acrylate monomer is not particularly limited, but from the viewpoint of solubility in polymerizable monomers and dispersibility in binder resins, the mass ratio of (meth)acrylate monomer units to aromatic vinyl monomer units ((meth)acrylate monomer units / aromatic vinyl monomer units) is preferably 0.05 to 0.35, more preferably 0.10 to 0.30, and even more preferably 0.15 to 0.25.

[0044] The glass transition temperature (Tg) of the above-mentioned quaternary ammonium salt-containing copolymer is not particularly limited, but is preferably in the range of 50°C to 110°C, and more preferably in the range of 60°C to 100°C. When the glass transition temperature (Tg) of the above-mentioned quaternary ammonium salt-containing copolymer is within the above range, the shelf life of the white toner of this disclosure can be improved. The above-mentioned quaternary ammonium salt-containing copolymer tends to localize near the surface of the colored resin particles and can function like a shell, so when the Tg of the above-mentioned quaternary ammonium salt-containing copolymer is within the above range, it is presumed that the shelf life of the toner will be improved because the Tg is sufficiently high. In this disclosure, the glass transition temperature (Tg) can be determined, for example, in accordance with ASTM D3418-82. Specifically, the sample is heated at a heating rate of 10°C / min using a differential scanning calorimeter (e.g., Seiko Electronics Industries Ltd.: SSC5200), and the temperature at which the maximum endothermic peak of the DSC curve obtained in that process is shown can be taken as the glass transition temperature.

[0045] The weight-average molecular weight (Mw) of the above-mentioned quaternary ammonium salt-containing copolymer is not particularly limited, but is preferably in the range of 5,000 to 30,000, and more preferably in the range of 10,000 to 25,000. If the weight-average molecular weight (Mw) is above the lower limit, a decrease in the toner's storage life and print durability can be suppressed, and if it is below the upper limit, a decrease in the toner's fixation can be suppressed. Furthermore, if the weight-average molecular weight (Mw) is within the above range, the above-mentioned quaternary ammonium salt-containing copolymer can be suitably dispersed in the colored resin particles, making it easier to obtain toner with a stable charge over time. In this disclosure, the weight-average molecular weight (Mw) is a polystyrene-equivalent value measured by gel permeation chromatography (GPC) using tetrahydrofuran (THF).

[0046] The content of the above quaternary ammonium salt-containing copolymer is not particularly limited, but in order to improve the opacity and transferability of the white toner of this disclosure, the content of the above quaternary ammonium salt-containing copolymer per 100 parts by mass of titanium oxide particles may be, for example, 1 to 50 parts by mass, 3 to 40 parts by mass, or 5 to 30 parts by mass. Also, although not particularly limited, in order to improve the opacity and transferability of the white toner of this disclosure, the content of the above quaternary ammonium salt-containing copolymer per 100 parts by mass of the binder resin may be, for example, 1 to 30 parts by mass, 2 to 20 parts by mass, or 5 to 15 parts by mass. The content of the above quaternary ammonium salt-containing copolymer per 100 parts by mass of the polymerizable monomer may be, for example, 1 to 30 parts by mass, 2 to 20 parts by mass, or 5 to 15 parts by mass. The content of the quaternary ammonium salt-containing copolymer per 100 parts by mass of the monovinyl monomer may be, for example, 1 to 30 parts by mass, 2 to 20 parts by mass, or 5 to 15 parts by mass. The quaternary ammonium salt-containing copolymer can be used alone or in combination of two or more types.

[0047] The white toner of this disclosure may further contain other charge control agents different from the above-mentioned quaternary ammonium salt-containing copolymer as charge control agents. Examples of other charge control agents include charge control resins different from the above-mentioned quaternary ammonium salt-containing copolymer, and charge control compounds with relatively low molecular weight. Examples of positively charged charge control compounds include nigrosine dyes, quaternary ammonium salts, triaminotriphenylmethane compounds, and imidazole compounds. On the other hand, from the viewpoint of improving the opacity and transferability of the white toner of this disclosure, it is preferable that the content of the above-mentioned quaternary ammonium salt-containing copolymer in 100% by mass of the charge control agent contained in the white toner of this disclosure is 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more.

[0048] In the white toner of this disclosure, the content of the charge control agent is not particularly limited, but the content of the charge control agent per 100 parts by mass of binder resin may be, for example, 1 to 30 parts by mass, 3 to 20 parts by mass, or 5 to 15 parts by mass. Also, the content of the charge control agent per 100 parts by mass of polymerizable monomer may be, for example, 1 to 30 parts by mass, 3 to 20 parts by mass, or 5 to 15 parts by mass. Also, the content of the charge control agent per 100 parts by mass of monovinyl monomer may be, for example, 1 to 30 parts by mass, 3 to 20 parts by mass, or 5 to 15 parts by mass. When the content of the charge control agent is within the above range, it is excellent in improving the opacity and transferability of the white toner of this disclosure. Furthermore, when the content of the charge control agent is above the lower limit, the occurrence of fogging can be suppressed, while when it is below the upper limit, printing smudges can be suppressed.

[0049] [Softener] The colored resin particles may contain a softener. By including a softener, the release properties of the toner from the fixing roll during fixing can be improved. As a softener, any softener commonly used as a softener or release agent for toner can be used without particular limitations. Examples include low molecular weight polyolefin waxes and their modified waxes; petroleum waxes such as paraffin; mineral waxes such as ozokerite; synthetic waxes such as Fischer-Tropsch wax; ester waxes such as dipentaerythritol ester and carnauba wax; and so on. Among these, ester waxes are preferred in terms of improving the balance between the storage properties and low-temperature fixing properties of the toner, and synthetic ester waxes obtained by esterifying an alcohol and a carboxylic acid can be preferably used. The alcohol used in the ester wax may be a saturated aliphatic alcohol, an unsaturated aliphatic alcohol, or an aromatic alcohol, and may be a monohydric alcohol or a polyhydric alcohol. The carboxylic acid used in the ester wax may be a monocarboxylic acid or a polyhydric carboxylic acid, and a fatty acid that is a monocarboxylic acid is preferably used. The fatty acid may be a saturated fatty acid, an unsaturated fatty acid, or an aromatic carboxylic acid. Among ester waxes, monoester waxes are preferred because they are excellent at improving the low-temperature fixation of toners, while polyfunctional ester waxes are preferred because they are less prone to bleed-out. Examples of monoester waxes include behenyl palmitate (C １５ H ３１ -COO-C ２２ H ４５ ), behenyl stearate (C １７ H ３５ -COO-C ２２ H ４５ ), behenyl eicosanoate (C １９ H ３９ -COO-C ２２ H ４５ ), behenyl behenate (C ２１ H ４３ -COO-C ２２ H ４５ ), eicosyl palmitate (C １５ H３１ -COO-C ２０ H ４１ ), eicosyl stearate (C １７ H ３５ -COO-C ２０ H ４１ ), eicosyl eicosanoate (C １９ H ３９ -COO-C ２０ H ４１ ), eicosyl behenate (C ２１ H ４３ -COO-C ２０ H ４１ ), stearyl stearate (C １７ H ３５ -COO-C １８ H ３７ ), stearyl eicosanoate (C １９ H ３９ -COO-C １８ H ３７ ), stearyl behenate (C ２１ H ４３ -COO-C １８ H ３７ ), hexadecyl eicosanoate (C １９ H ３９ -COO-C １６ H ３３ ), hexadecyl behenate (C ２１ H ４３ -COO-C １６ H ３３Examples include the following. Among these, behenyl stearate, behenyl palmitate, behenyl behenate, and stearyl behenate are particularly preferred. As the polyfunctional ester wax, for example, at least one selected from the group consisting of pentaerythritol ester compounds, glycerin ester compounds, and dipentaerythritol ester compounds can be preferably used. Examples of such preferred polyfunctional ester waxes include pentaerythritol ester compounds such as pentaerythritol tetrapalmitate, pentaerythritol tetrabehenate, and pentaerythritol tetrastearate; glycerin ester compounds such as hexaglycerin tetrabehenate tetrapalmitate, hexaglycerin octabehenate, pentaglycerin heptabehenate, tetraglycerin hexabehenate, triglycerin pentabehenate, diglycerin tetrabehenate, and glycerin tripehenate; and dipentaerythritol ester compounds such as dipentaerythritol hexamiristate and dipentaerythritol hexapalmitate.

[0050] From the viewpoint of improving the balance between the storage properties and low-temperature fixing properties of the toner, the melting point of the softener is preferably in the range of 50 to 90°C, more preferably in the range of 60 to 85°C, and even more preferably in the range of 70 to 80°C. In this disclosure, the melting point of the softener is the transparent melting point.

[0051] In the white toner of this disclosure, the content of the softener is not particularly limited, but in order to improve the balance between the storage properties and low-temperature fixing properties of the toner, the content of the softener per 100 parts by mass of the binder resin may be, for example, 1 to 30 parts by mass, 5 to 25 parts by mass, or 8 to 20 parts by mass. Also, the content of the softener per 100 parts by mass of the polymerizable monomer may be, for example, 1 to 30 parts by mass, 5 to 25 parts by mass, or 8 to 20 parts by mass. Also, the content of the softener per 100 parts by mass of the monovinyl monomer may be, for example, 1 to 30 parts by mass, 5 to 25 parts by mass, or 8 to 20 parts by mass. The softener can be used alone or in combination of two or more types.

[0052] [Polar Resin] The colored resin particles may contain polar resin. By including polar resin in the colored resin particles, the heat resistance and print durability of the toner can be improved. The polar resin tends to be unevenly distributed on the surface side of the colored resin particles. The polar resin, unevenly distributed on the surface side of the colored resin particles, reinforces the particle surface and acts as a shell. As a result, even when using binder resins and release agents with high low-temperature fixation properties, the toner can have excellent heat resistance. In addition, the print durability of the toner is improved because the surface of the colored resin particles becomes less prone to deterioration.

[0053] As the polar resin, an acidic group-containing copolymer is preferably used, and among these, an acrylate copolymer containing an acidic group is preferred. As an acrylate copolymer containing an acidic group, for example, a copolymer of (meth)acrylic acid ester and (meth)acrylic acid is preferably used. The copolymer of (meth)acrylic acid ester and (meth)acrylic acid is a copolymer of at least one selected from the group consisting of acrylic acid ester and methacrylic acid ester and at least one selected from the group consisting of acrylic acid and methacrylic acid. Examples of such copolymers include a copolymer of acrylic acid ester and acrylic acid, a copolymer of acrylic acid ester and methacrylic acid, a copolymer of methacrylic acid ester and methacrylic acid, a copolymer of acrylic acid ester, methacrylic acid ester and acrylic acid, and a copolymer of acrylic acid ester, methacrylic acid ester and methacrylic acid. Of these, the copolymer of acrylic acid ester, methacrylic acid ester and acrylic acid is preferred.

[0054] Examples of the (meth)acrylic acid esters include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, tert-butyl (meth)acrylate, n-pentyl (meth)acrylate, sec-pentyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, n-hexyl (meth)acrylate, isohexyl (meth)acrylate, neohexyl (meth)acrylate, sec-hexyl (meth)acrylate, and tert-hexyl (meth)acrylate. Among the acrylic acid esters, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, and n-butyl acrylate are preferred, and ethyl acrylate and n-butyl acrylate are more preferred. Among the methacrylate esters, methyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, and n-butyl methacrylate are preferred, with methyl methacrylate being more preferred.

[0055] The mass ratio of each monomer unit in the acrylate copolymer is preferably adjusted to satisfy the acid value, weight-average molecular weight Mw, and glass transition temperature Tg described later. The content of (meth)acrylic acid units in 100% by mass of all monomer units constituting the acrylate copolymer is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.3% by mass or more as a lower limit, and preferably 1.0% by mass or less, more preferably 0.6% by mass or less, and even more preferably 0.5% by mass or less as an upper limit. The content of (meth)acrylic acid ester units in 100% by mass of all monomer units constituting the acrylate copolymer is preferably 99.0% by mass or more, more preferably 99.4% by mass or more, and even more preferably 99.5% by mass or more as a lower limit, and preferably 99.95% by mass or less, more preferably 99.9% by mass or less, and even more preferably 99.7% by mass or less as an upper limit.

[0056] The acrylate copolymer may contain other monomer units different from (meth)acrylic acid ester units or (meth)acrylic acid units, to the extent that it does not impair the purpose of this disclosure. Examples of such other monomers include aromatic vinyl compounds, nitrile compounds, and amide compounds, which are exemplified in the monovinyl monomers constituting the binder resin. In the acrylate copolymer, the content of the other monomer units is preferably 10 parts by mass or less, more preferably 2 parts by mass or less, and most preferably 0 parts by mass, per 100 parts by mass of (meth)acrylic acid ester units.

[0057] The acid value of the polar resin is not particularly limited, but is preferably 0.5 mg KOH / g or more, more preferably 1.0 mg KOH / g or more, and even more preferably 2.0 mg KOH / g or more. On the other hand, it is preferably 5.0 mg KOH / g or less, more preferably 4.0 mg KOH / g or less, and even more preferably 3.0 mg KOH / g or less. When the acid value of the polar resin is within the above range, it is easy to obtain a toner with excellent low-temperature fixability, heat resistance, and print durability. In this disclosure, the acid value of the resin is measured in accordance with JIS K 0070.

[0058] The weight-average molecular weight (Mw) of the polar resin is not particularly limited, but is preferably 6,000 or more, more preferably 7,000 or more, and even more preferably 9,000 or more, while preferably 50,000 or less, more preferably 45,000 or less, and even more preferably 40,000 or less. When the weight-average molecular weight (Mw) of the polar resin is within the above range, the low-temperature fixability, heat resistance, and print durability of the white toner of this disclosure can be improved.

[0059] The glass transition temperature Tg of the polar resin is not particularly limited, but is preferably 60°C or higher, more preferably 65°C or higher, and even more preferably 70°C or higher, while preferably 85°C or lower, more preferably 80°C or lower, and even more preferably 77°C or lower. When the glass transition temperature Tg of the polar resin is within the above range, the low-temperature fixability, heat resistance, and print durability of the white toner of this disclosure can be improved.

[0060] In the white toner of this disclosure, the content of the polar resin is not particularly limited, but the content of the polar resin per 100 parts by mass of the binder resin may be, for example, 0.2 to 5 parts by mass, 0.5 to 3 parts by mass, or 0.7 to 2 parts by mass. Also, the content of the polar resin per 100 parts by mass of the polymerizable monomer may be, for example, 0.2 to 5 parts by mass, 0.5 to 3 parts by mass, or 0.7 to 2 parts by mass. Also, the content of the polar resin per 100 parts by mass of the monovinyl monomer may be, for example, 0.2 to 5 parts by mass, 0.5 to 3 parts by mass, or 0.7 to 2 parts by mass. When the content of the polar resin is above the lower limit, the decrease in print durability is suppressed, and when it is below the upper limit, the charge amount of the toner tends to be appropriate, in particular, the decrease in the charge amount of the toner is suppressed, and the decrease in production stability and the decrease in low-temperature fixability are suppressed.

[0061] The polar resin can be a commercially available product, but it can also be produced by known polymerization methods such as solution polymerization, aqueous solution polymerization, ionic polymerization, high-temperature high-pressure polymerization, and suspension polymerization. A typical example of a method for producing the polar resin is as follows. Note that the method for producing the polar resin is not limited to the following typical example. First, a solvent is appropriately added to the reaction vessel, the inside of the reaction vessel is replaced with an inert atmosphere, the temperature is raised, and the raw material monomer is added to the reaction vessel. At this time, it is preferable to add a polymerization initiator at the same time. It is also preferable to gradually add a mixture of the raw material monomer and polymerization initiator dropwise into the reaction vessel. Next, the temperature is raised to a temperature at which polymerization proceeds, and polymerization is started. After polymerization is complete, the solvent is appropriately removed by distillation to obtain the desired polar resin.

[0062] (Styrene-based thermoplastic elastomer) The colored resin particles may contain a styrene-based thermoplastic elastomer. The styrene-based thermoplastic elastomer can improve the toner's fixation while maintaining the toner's heat resistance temperature. Here, styrene-based thermoplastic elastomer refers to a copolymer of a styrene-based monomer and at least one other monomer selected from the group consisting of monoolefins and diolefins that can copolymerize with the styrene-based monomer, such as a random, block, or graft copolymer, and hydrogenated products of these copolymers.

[0063] Examples of styrene-based thermoplastic elastomers include styrene-butadiene-styrene type block copolymers, styrene-butadiene type block copolymers, styrene-isoprene-styrene type block copolymers, styrene-isoprene type block copolymers, styrene-butadiene-isoprene-styrene type block copolymers and their hydrogenated derivatives; styrene-ethylene-butylene-styrene type block copolymers, styrene-ethylene-propylene-styrene type block copolymers, and styrene-ethylene-ethylene-propylene-styrene type block copolymers. Among these styrene-based thermoplastic elastomers, styrene-isoprene-styrene type block copolymers are preferred from the viewpoint of optimizing the balance between toner storage and low-temperature fixing properties.

[0064] The styrene content in the above-mentioned styrene-based thermoplastic elastomer is preferably 15 to 70% by mass, more preferably 15 to 60% by mass, and even more preferably 20 to 40% by mass. When the styrene content is above the lower limit, the decrease in toner fixability is suppressed. On the other hand, when the styrene content is below the upper limit, the decrease in toner storage life is suppressed.

[0065] The weight-average molecular weight Mw of the above-mentioned styrene-based thermoplastic elastomer is not particularly limited, but is preferably 50,000 to 350,000, and more preferably 80,000 to 250,000, from the standpoint of being excellent in improving the fixability of the toner while maintaining the heat resistance temperature of the toner.

[0066] Commercially available styrene-based thermoplastic elastomers can be used. Examples of commercially available styrene-based thermoplastic elastomers include the Quintac® series manufactured by Nippon Zeon Co., Ltd. and the Septon® series manufactured by Kuraray Co., Ltd.

[0067] In the white toner of this disclosure, the content of the styrene-based thermoplastic elastomer is preferably adjusted to achieve a good balance between the low-temperature fixability and storage properties of the toner. While not particularly limited, the content of the styrene-based thermoplastic elastomer per 100 parts by mass of the binder resin may be, for example, 0.5 to 10 parts by mass, 1 to 8 parts by mass, or 2 to 6 parts by mass. Furthermore, the content of the styrene-based thermoplastic elastomer per 100 parts by mass of the polymerizable monomer may be, for example, 0.5 to 10 parts by mass, 1 to 8 parts by mass, or 2 to 6 parts by mass. Furthermore, the content of the styrene-based thermoplastic elastomer per 100 parts by mass of the monovinyl monomer may be, for example, 0.5 to 10 parts by mass, 1 to 8 parts by mass, or 2 to 6 parts by mass. Note that the styrene-based thermoplastic elastomer can be used alone or in combination of two or more types.

[0068] 1-2. Methods for Manufacturing Colored Resin Particles Generally, methods for manufacturing colored resin particles are broadly classified into dry methods such as pulverization methods, and wet methods such as emulsion polymerization agglutination methods, suspension polymerization methods, and dissolution suspension methods. Wet methods are preferred because they make it easier to obtain toner with excellent printing characteristics such as image reproducibility. Among wet methods, polymerization methods such as emulsion polymerization agglutination methods and suspension polymerization methods are preferred because they make it easier to obtain toner with a relatively small particle size distribution on the order of microns, and among polymerization methods, suspension polymerization methods are more preferred.

[0069] The emulsion polymerization agglutination method involves polymerizing an emulsified polymerizable monomer to obtain a resin fine particle emulsion, which is then agglutinated with a colorant dispersion or the like to produce colored resin particles. The dissolution suspension method involves dissolving or dispersing toner components such as binder resin and colorant in an organic solvent, forming droplets in an aqueous medium, and then removing the organic solvent to produce colored resin particles. Known methods can be used for both of these methods.

[0070] The colored resin particles used in this disclosure can be manufactured by a wet or dry method, and are not particularly limited, but among wet methods, the manufacturing method using suspension polymerization is preferred because it can produce colored resin particles with high average circularity, and consequently, it is preferred because it can produce a white toner with high average circularity and excellent transferability. The colored resin particles used in this disclosure can be manufactured, for example, by employing the preferred suspension polymerization method among wet methods, through the following process.

[0071] (A) Suspension polymerization As one embodiment of a method for producing colored resin particles using suspension polymerization, the following method can be cited: Prepare a polymerizable monomer composition containing at least a polymerizable monomer, a colorant, and a charge control agent (preparation step of polymerizable monomer composition); prepare a suspension in which droplets of the polymerizable monomer composition are dispersed in an aqueous medium containing a dispersion stabilizer (suspension step); and subject the suspension to a polymerization reaction (polymerization step), wherein the colorant contains titanium dioxide particles surface-treated with two or more surface treatment agents, the surface treatment agent contains at least one selected from the group consisting of aluminum hydroxide and aluminum oxide, and an organosilicon compound, and the charge control agent contains a quaternary ammonium salt-containing copolymer. In the above manufacturing method, the quaternary ammonium salt-containing copolymer and the titanium oxide particles interact in the suspension, and furthermore, steric repulsion of the quaternary ammonium salt-containing copolymer results in good dispersibility of the titanium oxide particles. Additionally, the quaternary ammonium salt-containing copolymer is located on the surface of the colored resin particles, or the quaternary ammonium salt-containing copolymer surrounds the titanium oxide particles, making it difficult for the titanium oxide particles to be exposed on the surface of the colored resin particles. As a result, a white toner with excellent opacity and transferability can be obtained.

[0072] The following describes each step of the above manufacturing method. In the manufacturing method described herein, two or more of the steps may be performed simultaneously as a single step, or they may be performed in a different order, as long as it is technically possible.

[0073] (A-1) Preparation process for polymerizable monomer composition First, a polymerizable monomer composition is prepared by mixing a polymerizable monomer, a colorant, a charge control agent, and, if necessary, other additives such as a softener, polar resin, styrene-based thermoplastic elastomer, and molecular weight adjuster. The material contained in the polymerizable monomer composition is the material of the core layer of the colored resin particles if it is a core-shell type colored resin particle, and the material of the colored resin particles if it is not a core-shell type colored resin particle. The polymerizable monomer, colorant, charge control agent, softener, polar resin, and styrene-based thermoplastic elastomer are as described above. The polymerizable monomer, which is the raw material for the binder resin, is used as the polymerizable monomer contained in the polymerizable monomer composition. For mixing when preparing the polymerizable monomer composition, for example, a media-type disperser is used.

[0074] The content of polymerizable monomers is not particularly limited, but may be, for example, 60 to 95 parts by mass, 65 to 90 parts by mass, or 70 to 85 parts by mass per 100 parts by mass of polymerizable monomer composition. The content of titanium dioxide particles is not particularly limited, but is preferably 15 to 50 parts by mass, more preferably 20 to 40 parts by mass per 100 parts by mass of polymerizable monomer composition. When the content of titanium dioxide particles is above the lower limit, it has an excellent effect of improving the opacity of the white toner of this disclosure, and when it is below the upper limit, it can suppress deterioration of the transferability of the white toner of this disclosure.

[0075] [Molecular Weight Adjuster] As other additives, it is preferable to use a molecular weight adjuster when polymerizing the polymerizable monomer that forms the binder resin. The molecular weight adjuster is not particularly limited as long as it is one that is generally used as a molecular weight adjuster for toner, and examples include mercaptans such as t-dodecyl mercaptan, n-dodecyl mercaptan, n-octyl mercaptan, and 2,2,4,6,6-pentamethylheptan-4-thiol; thiuram disulfides such as tetramethyl thiuram disulfide, tetraethyl thiuram disulfide, tetrabutyl thiuram disulfide, N,N'-dimethyl-N,N'-diphenyl thiuram disulfide, and N,N'-dioctadecyl-N,N'-diisopropyl thiuram disulfide; and so on. These molecular weight adjusters may be used individually or in combination of two or more. In this disclosure, the molecular weight adjusting agent is used in a ratio of typically 0.01 to 10 parts by mass, preferably 0.1 to 5 parts by mass, and more preferably 0.3 to 3 parts by mass, per 100 parts by mass of polymerizable monomer (preferably monovinyl monomer).

[0076] (A-2) Suspension process (droplet formation process) Next, a suspension is prepared in which droplets of the polymerizable monomer composition are dispersed in an aqueous medium containing a dispersion stabilizer. For example, the suspension can be prepared by dispersing the polymerizable monomer composition in an aqueous medium containing a dispersion stabilizer, adding a polymerization initiator, and then forming droplets of the polymerizable monomer composition. The method of droplet formation is not particularly limited, but for example, it can be carried out using a device capable of strong stirring, such as an (in-line type) emulsifier / disperser (manufactured by Taiheiyo Kiko Co., Ltd., product name: Milder) or a high-speed emulsifier / disperser (manufactured by Primix Corporation, product name: T.K. Homomixer MARK II). In this disclosure, the aqueous medium containing the dispersion stabilizer may be referred to as the "aqueous dispersion medium".

[0077] Examples of polymerization initiators include persulfates such as potassium persulfate and ammonium persulfate; azo compounds such as 4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis(2-methyl-N-(2-hydroxyethyl)propionamide), 2,2'-azobis(2-amidinopropane)dihydrochloride, 2,2'-azobis(2,4-dimethylvaleronitrile), and 2,2'-azobisisobutyronitrile; and organic peroxides such as di-t-butyl peroxide, benzoyl peroxide, t-butyl peroxy-2-ethylhexanoate, t-butyl peroxydiethyl acetate, t-hexyl peroxy-2-ethylbutanoate, diisopropyl peroxydicarbonate, di-t-butyl peroxyisophthalate, and t-butyl peroxyisobutyrate. These can be used individually or in combination of two or more. Among these options, using organic peroxides is preferable because it reduces the amount of residual polymerizable monomers and the resulting white toner exhibits excellent print durability.

[0078] Among organic peroxides, peroxyesters are preferred because they have good initiator efficiency and can reduce the amount of residual polymerizable monomers, and non-aromatic peroxyesters, i.e., peroxyesters without aromatic rings, are more preferred.

[0079] The polymerization initiator may be added after the polymerizable monomer composition has been dispersed in an aqueous medium and before droplet formation, as described above, or it may be added to the polymerizable monomer composition before it is dispersed in the aqueous medium.

[0080] In this disclosure, an aqueous medium refers to a medium whose main component is water. It is preferable to include a dispersion stabilizer in the aqueous medium. Examples of dispersion stabilizers include inorganic compounds such as sulfates such as barium sulfate and calcium sulfate; carbonates such as barium carbonate, calcium carbonate, and magnesium carbonate; phosphates such as calcium phosphate; metal oxides such as aluminum oxide and titanium oxide; metal hydroxides such as aluminum hydroxide, magnesium hydroxide, and ferric hydroxide; and organic compounds such as water-soluble polymers such as polyvinyl alcohol, methylcellulose, and gelatin; anionic surfactants; nonionic surfactants; and amphoteric surfactants. One or more of the above dispersion stabilizers can be used in combination.

[0081] Among the above-mentioned dispersion stabilizers, inorganic compounds, particularly colloids of poorly water-soluble metal hydroxides, are preferred. By using inorganic compounds, especially colloids of poorly water-soluble metal hydroxides, the particle size distribution of the colored resin particles can be narrowed, and the amount of residual dispersion stabilizer after washing can be reduced. As a result, the resulting white toner can reproduce images clearly and has excellent environmental stability.

[0082] (A-3) Polymerization process After preparing a suspension by forming droplets of the polymerizable monomer composition in an aqueous medium as described in (A-2) above, the obtained suspension is subjected to a polymerization reaction. For example, the obtained suspension is heated to polymerize the polymerizable monomers in the suspension. This yields an aqueous dispersion of colored resin particles. The polymerizable monomers polymerize to form a binder resin. The polymerization temperature is preferably 50°C or higher, and more preferably 60 to 95°C. The polymerization reaction time is preferably 1 to 20 hours, and more preferably 2 to 15 hours.

[0083] The colored resin particles obtained by the polymerization process described above may be used as is as the colored resin particles contained in the white toner of this disclosure. Alternatively, the colored resin particles obtained by the polymerization process described above may be used as a core layer, and a shell layer made of a different material on the outside thereof may be formed to obtain so-called core-shell type (or "capsule type") colored resin particles, which may then be used as the colored resin particles contained in the white toner of this disclosure. The core-shell type colored resin particles can be made by coating a core layer made of a material with a low softening point with a material with a higher softening point, thereby achieving a balance between lowering the fixing temperature and preventing aggregation during storage.

[0084] There are no particular restrictions on the method for producing core-shell type colored resin particles using the colored resin particles described above, and they can be produced by conventionally known methods. In situ polymerization and phase separation methods are preferred from the viewpoint of production efficiency.

[0085] The following describes a method for producing core-shell type colored resin particles by in situ polymerization. Core-shell type colored resin particles can be obtained by adding a polymerizable monomer for forming the shell layer (polymerizable monomer for the shell) and a polymerization initiator to an aqueous medium in which colored resin particles are dispersed, and then polymerizing them. In this case, the shell layer of the core-shell type colored resin particles consists of a polymer of the polymerizable monomer for the shell.

[0086] As the polymerizable monomer for the shell, the same polymerizable monomers as those described above can be used. Among these, monomers that yield polymers with a Tg of over 80°C, such as styrene, acrylonitrile, and methyl methacrylate, are preferably used individually or in combination of two or more. The amount of polymerizable monomer for the shell used is not particularly limited, but for example, it may be 0.1 to 10 parts by mass, 0.5 to 7 parts by mass, or 1 to 5 parts by mass per 100 parts by mass of the total amount of polymerizable monomer used to form the core layer. Furthermore, the content of polymerized polymerizable monomers for the shell in 100% by mass of the shell layer may be, for example, 90% by mass or more, 95% by mass or more, or 99% by mass or more, and the shell layer may consist only of polymerized polymerized monomers for the shell.

[0087] Examples of polymerization initiators used for polymerizing polymerizable monomers for shells include metal persulfate salts such as potassium persulfate and ammonium persulfate; azo-based initiators such as 2,2'-azobis(2-methyl-N-(2-hydroxyethyl)propionamide) and 2,2'-azobis-(2-methyl-N-(1,1-bis(hydroxymethyl)2-hydroxyethyl)propionamide); and other water-soluble polymerization initiators. These can be used individually or in combination of two or more. The amount of polymerization initiator is preferably 0.1 to 30 parts by mass, more preferably 1 to 20 parts by mass, per 100 parts by mass of polymerizable monomer for shells.

[0088] The polymerization temperature of the shell layer is preferably 50°C or higher, and more preferably 60 to 95°C. The polymerization reaction time is preferably 1 to 20 hours, and more preferably 2 to 15 hours.

[0089] (A-4) Washing, filtration, dehydration, and drying process In the above manufacturing method, after polymerization is complete, the aqueous dispersion of colored resin particles is preferably washed, filtered, dehydrated, and dried several times as needed, in accordance with conventional methods to remove the dispersion stabilizer.

[0090] Regarding the above cleaning method, when an inorganic compound is used as a dispersion stabilizer, it is preferable to dissolve and remove the dispersion stabilizer in water by adding an acid or alkali to the aqueous dispersion of colored resin particles. When a colloid of a poorly water-soluble metal hydroxide is used as a dispersion stabilizer, it is preferable to add an acid to adjust the pH of the aqueous dispersion of colored resin particles to 6.5 or less. As the acid to be added, inorganic acids such as sulfuric acid, hydrochloric acid, and nitric acid, as well as organic acids such as formic acid and acetic acid, can be used, but sulfuric acid is particularly preferred due to its high removal efficiency and low burden on manufacturing equipment.

[0091] The dehydration and filtration methods are not particularly limited and can be any of the known methods. For example, centrifugal filtration, vacuum filtration, and pressure filtration can be used. Similarly, the drying method is not particularly limited and can be any of the various methods used.

[0092] (B) Grinding Method An embodiment of a method for producing colored resin particles using a grinding method is as follows: A method comprising: kneading at least a binder resin, a colorant, and a charge control agent, grinding the resulting kneaded material to obtain colored resin pulverized material (step for obtaining colored resin pulverized material); dispersing the colored resin pulverized material in an aqueous medium containing a dispersion stabilizer to obtain a dispersion of colored resin pulverized material (dispersion step); and heating the dispersion of colored resin pulverized material to form colored resin particles (heating step). The method comprises: the colorant includes titanium oxide particles surface-treated with two or more surface treatment agents, the surface treatment agent includes at least one selected from the group consisting of aluminum hydroxide and aluminum oxide, and an organosilicon compound; and the charge control agent includes a quaternary ammonium salt-containing copolymer. The above method is preferred among grinding methods because it increases the sphericity of the colored resin pulverized material by heating the dispersion of colored resin pulverized material to obtain colored resin particles, and thus yields colored resin particles with a high average circularity. Furthermore, in the above manufacturing method, when the dispersion of the colored resin pulverized material is heated, the quaternary ammonium salt-containing copolymer and the titanium oxide particles interact, and steric repulsion occurs due to the quaternary ammonium salt-containing copolymer, resulting in good dispersibility of the titanium oxide particles. Additionally, because the quaternary ammonium salt-containing copolymer is located on the surface of the colored resin particles or surrounds the titanium oxide particles, the titanium oxide particles are less likely to be exposed on the surface of the colored resin particles, thus enabling the production of the white toner of this disclosure with excellent opacity and transferability. The steps of the above manufacturing method will now be described.

[0093] (B-1) Process for obtaining colored resin pulverized material First, a mixture is obtained by mixing a binder resin, a colorant and an antistatic agent, and, if necessary, other additives such as a softener, polar resin and styrene-based thermoplastic elastomer. The material contained in the mixture is the material of the core layer of the colored resin particles if the colored resin particles are of the core-shell type, and the material of the colored resin particles if the colored resin particles are not of the core-shell type. The binder resin, colorant, antistatic agent, softener, polar resin and styrene-based thermoplastic elastomer are as described above. The above mixing can be done using a mixer, for example, a ball mill, a V-type mixer, an FM mixer (product name, manufactured by Nippon Coke Industries Co., Ltd.), a high-speed dissolver, an internal mixer, etc. Next, the mixture obtained above is kneaded while heating using a pressure kneader, a twin-screw extruder, or a roller. The resulting kneaded material is coarsely pulverized using a pulverizer such as a hammer mill, a cutter mill, or a roller mill. Furthermore, after fine grinding using a pulverizer such as a jet mill or a high-speed rotary pulverizer, the colored resin pulverized material is obtained by classifying it to the desired particle size using a classifier such as an air-powered classifier or an airflow classifier.

[0094] (B-2) Dispersion step Next, the colored resin pulverized material obtained above is dispersed in an aqueous medium containing a dispersion stabilizer to obtain a dispersion of the colored resin pulverized material. As the dispersion stabilizer and aqueous medium, those that can be used in the suspension polymerization method described above can be used. The amount of dispersion stabilizer used is preferably 1 part by mass or more, more preferably 10 to 500 parts by mass, and even more preferably 20 to 300 parts by mass, per 100 parts by mass of the colored resin pulverized material, from the viewpoint of good dispersion of the colored resin pulverized material. The amount of aqueous medium used is not particularly limited, but from the viewpoint of good dispersion of the colored resin pulverized material, the ratio of the mass of the aqueous medium to the mass of the colored resin pulverized material (mass of aqueous medium / mass of colored resin pulverized material) may be, for example, 10 to 100 or 20 to 60.

[0095] The method for dispersing the colored resin pulverized material in an aqueous medium containing a dispersion stabilizer is not particularly limited, but one example is to add the colored resin pulverized material to an aqueous medium containing a dispersion stabilizer and stir it with a stirring device. Alternatively, after adding the colored resin pulverized material to an aqueous medium containing a dispersion stabilizer, a dispersion treatment such as ultrasonic dispersion, dispersion using a high-shear stirring device such as an in-line emulsifying disperser, or dispersion using a jet mill may be performed to obtain a dispersion of the colored resin pulverized material.

[0096] (B-3) Heating step Next, the dispersion of the colored resin pulverized material is heated. The heating temperature is preferably above the glass transition temperature Tg of the colored resin pulverized material and below 95°C. The specific heating temperature in the heating step is not particularly limited, but may be, for example, 40 to 95°C or 50 to 90°C. The heating time may be, for example, 5 minutes or more and 10 hours or less, 10 minutes or more and 5 hours or less, or 20 minutes or more and 2 hours or less. By heating the dispersion of the colored resin pulverized material, the sphericity of the colored resin pulverized material can be improved to form colored resin particles with a high average circularity.

[0097] (B-4) Preheating step In the above manufacturing method, it is preferable to preheat the dispersion of colored resin pulverized material before the heating step. The temperature of the preheating is not particularly limited, but for example it can be 10 to 1°C lower than the glass transition temperature Tg of the colored resin particles (Tg-10 to Tg-1°C). The specific heating temperature in the preheating step is not particularly limited, but for example it may be 30 to 60°C or 40 to 55°C. The preheating time may be, for example, 30 minutes or more and 10 hours or less, or 60 minutes or more and 5 hours or less.

[0098] (B-5) Washing, filtration, dehydration, and drying process The dispersion of colored resin particles obtained by the heat treatment is preferably subjected to a series of operations of washing, filtration, dehydration, and drying, repeated several times as needed, according to a conventional method. The washing, dehydration, and filtration methods can be similar to those used in the suspension polymerization method described above.

[0099] The colored resin particles obtained by the pulverization method can also be converted into core-shell type colored resin particles by methods such as in situ polymerization, similar to the colored resin particles obtained by the suspension polymerization method (A) described above.

[0100] 1-3. External Additives The white toner of this disclosure may contain external additives. By mixing and stirring colored resin particles together with external additives, and uniformly adhering the external additive to the surface of the colored resin particles (external addition), a toner containing colored resin particles and external additives can be obtained. Alternatively, the external additive may be attached to the surface of the colored resin particles to form a one-component toner (developer), or the one-component toner may be further mixed and stirred together with carrier particles to form a two-component developer.

[0101] Examples of external additives include inorganic fine particles such as silica, titanium dioxide, aluminum oxide, zinc oxide, tin oxide, strontium titanate, calcium carbonate, calcium phosphate, or cerium oxide; organic fine particles such as polymethyl methacrylate resin, silicone resin, or melamine resin; and metal soap fine particles such as zinc stearate or magnesium stearate. While each of these external additives can be used individually, it is preferable to use two or more in combination.

[0102] As an external additive, it is preferable to include at least inorganic fine particles in order to improve the fluidity of the toner. The inorganic fine particles are preferably at least one selected from the group consisting of silica fine particles and titanium dioxide fine particles, with silica fine particles being more preferable.

[0103] Furthermore, it is preferable that the inorganic fine particles are hydrophobized. Examples of hydrophobizing agents used to hydrophobize the inorganic fine particles include silane coupling agents, silicone oils, fatty acids, and fatty acid metal salts. Among these, silane coupling agents and silicone oils are preferred.

[0104] The number-average primary particle size of the above inorganic fine particles is not particularly limited, but from the viewpoint of ensuring proper toner fluidity, it may be, for example, 5 to 300 nm, 10 to 200 nm, or 20 to 100 nm.

[0105] The content of the inorganic fine particles is not particularly limited, but the content of the inorganic fine particles per 100 parts by mass of colored resin particles may be, for example, 0.1 to 5.0 parts by mass, or 0.3 to 3.0 parts by mass. If the content of the inorganic fine particles is above the lower limit, the decrease in toner fluidity can be suppressed, thereby suppressing deterioration of the toner's printing performance, shelf life, or durability. On the other hand, if the content of the inorganic fine particles is below the upper limit, the release of inorganic fine particles from the surface of the toner particles is suppressed, thereby suppressing deterioration of the electrostatic properties and suppressing the occurrence of fogging. Furthermore, if the content of the inorganic fine particles is within the above range, it is easier to obtain toner with the desired fluidity.

[0106] Furthermore, the inorganic fine particles may include multiple types of inorganic fine particles with different number-average primary particle sizes. For example, it is preferable to include at least one selected from the group consisting of inorganic fine particles A having a number-average primary particle size of 36 to 100 nm and inorganic fine particles B having a number-average primary particle size of 6 to 35 nm, and it is more preferable to include both inorganic fine particles A and inorganic fine particles B. The fluidity of the toner can be adjusted by adjusting the particle size and amount of inorganic fine particles A and B.

[0107] The number-average primary particle size of the inorganic fine particles A may be 40 to 80 nm or 45 to 70 nm, from the viewpoint of ensuring proper toner fluidity. The number-average primary particle size of the inorganic fine particles B may be 10 to 30 nm or 15 to 25 nm, from the viewpoint of ensuring proper toner fluidity.

[0108] The content of the inorganic fine particles A is not particularly limited, but from the viewpoint of improving printing performance or shelf life, it is preferably 0.30 parts by mass or more, more preferably 0.50 parts by mass or more, per 100 parts by mass of colored resin particles. On the other hand, from the viewpoint of suppressing deterioration of printing performance by suppressing the release of inorganic fine particles A from the surface of toner particles, the content of the inorganic fine particles A per 100 parts by mass of colored resin particles is preferably 2.50 parts by mass or less, more preferably 2.00 parts by mass or less, and even more preferably 1.50 parts by mass or less. Furthermore, when the content of inorganic fine particles A is within the above range, it is easier to obtain toner with the desired fluidity.

[0109] The content of the inorganic fine particles B is not particularly limited, but in order to suppress the decrease in toner fluidity and prevent deterioration of the toner's shelf life or durability, it is preferably 0.10 parts by mass or more, more preferably 0.30 parts by mass or more, and even more preferably 0.50 parts by mass or more, per 100 parts by mass of colored resin particles. On the other hand, in order to suppress the release of inorganic fine particles B from the surface of toner particles, prevent deterioration of charging characteristics, and prevent fogging, the content of the inorganic fine particles B per 100 parts by mass of colored resin particles is preferably 2.00 parts by mass or less, more preferably 1.50 parts by mass or less, and even more preferably 1.00 part by mass or less. Furthermore, when the content of the inorganic fine particles B is within the above range, it is easier to obtain toner with the desired fluidity.

[0110] The inorganic fine particles A and B described above may have different materials, but it is preferable that they be at least one selected from the group consisting of silica fine particles and titanium oxide fine particles, and it is more preferable that both be silica fine particles.

[0111] Various commercially available silica nanoparticles can be used as inorganic nanoparticles A, for example, VPNA50H (product name, number mean primary particle size: 40 nm) manufactured by Nippon Aerosil Co., Ltd.; H05TA (product name, number mean primary particle size: 50 nm) manufactured by Wacker Corporation; and so on. Various commercially available silica nanoparticles can be used as inorganic nanoparticles B, for example, NA50Y (product name, average primary particle size: 35 nm) from Nippon Aerosil Co., Ltd.; MSP-012 (product name, average primary particle size: 16 nm) from Teika Corporation; TG-7120 (product name, average primary particle size: 20 nm) from Cabot Corporation; HDK2150 (product name, average primary particle size: 12 nm) from Clariant Corporation; R504 (product name, average primary particle size: 12 nm) and RA200HS (product name, average primary particle size: 12 nm) from Nippon Aerosil Co., Ltd.; MSP-013 (product name, average primary particle size: 12 nm) from Teika Corporation; and TG-820F (product name, average primary particle size: 7 nm) from Cabot Corporation.

[0112] The white toner of this disclosure may contain silicone resin particles C as an external additive. This improves the fluidity of the toner, reduces the likelihood of filming onto the photoreceptor, imparts stable charge to the toner particles over time, and reduces image quality degradation due to fogging, etc., even when printing many pages continuously. The silicone resin particles C are organopolysiloxane particles having a three-dimensional network structure, for example, polymethylsilsesquioxane particles can be used. Furthermore, it is preferable that the silicone resin particles C are hydrophobized silicone resin particles. Examples of hydrophobizing agents used for the silicone resin particles C include those similar to those that can be used for the inorganic fine particles.

[0113] The number-average primary particle size of the silicone resin particles C is not particularly limited, but is preferably 0.05 to 1.00 μm, more preferably 0.07 to 0.50 μm, and even more preferably 0.08 to 0.30 μm. When the number-average primary particle size of the silicone resin particles C is within the above range, the toner can have appropriate charging characteristics under a wide range of temperature and humidity conditions.

[0114] The above-mentioned silicone resin particles C have a ratio (BS / TS) of the BET specific surface area (BS) measured by gas adsorption method to the theoretical specific surface area (TS), which is preferably 3.0 to 30.0, more preferably 3.5 to 25.0, and even more preferably 4.0 to 20.0. The above ratio (BS / TS) can be used as an indicator of the porosity of the silicone resin particles C. The higher the BS / TS, the more porous the particles, and the closer it is to 1, the less porous the particles. When the above ratio (BS / TS) is within the above range, the particles are light and flexible, which suppresses crushing of the silicone resin particles C during continuous printing. The theoretical specific surface area (TS) is the theoretical specific surface area per unit mass calculated using a theoretical calculation formula from the number-average particle size measured by scanning electron microscopy (SEM) observation. In other words, in this disclosure, assuming that the silicone resin particles C are spherical regardless of their shape, the theoretical specific surface area (TS) per unit mass is calculated using the following theoretical calculation formula (1) for calculating the specific surface area per unit mass of a sphere. Theoretical calculation formula (1): Theoretical specific surface area TS (unit: m ２ / g) = 6 / (average density (g / cm ３ ) x number average particle diameter (nm) x 10 ３ There are no particular restrictions on how the average density used in the above calculation formula is determined, and known methods can be used. BET specific surface area (BS) per unit mass measured by gas adsorption method (unit: m ２ The specific surface area (BS) of silicone resin particles can be determined by applying the BET formula to measure the amount of monolayer nitrogen gas adsorbed onto the surface of the silicone resin particles. Known methods can be used to measure the BET specific surface area (BS) of silicone resin particles C. An example of measuring the BET specific surface area (BS) of silicone resin particles C is to measure it using the nitrogen adsorption method (BET method) with a BET specific surface area measuring device (product name: Macsorb HM model-1208, manufactured by Mountec Co., Ltd.).

[0115] The silicone resin particles C preferably have an adsorbed moisture content of 1.0% by mass or less, and more preferably 0.35% by mass or less. When the adsorbed moisture content of the silicone resin particles C is below the above upper limit, fogging under high temperature and high humidity conditions can be suppressed.

[0116] There are no particular restrictions on the shape of the silicone resin particles C, and they may be irregular in shape, but they are preferably spherical. The sphericity (Sc / Sr) of the silicone resin particles C is not particularly limited, but from the viewpoint of fine line reproducibility of the toner, it may be, for example, 0.930 to 1.000, preferably 0.970 to 1.000, and more preferably 0.985 to 1.000. In this disclosure, sphericity is defined as the value obtained by dividing the area of ​​a circle (Sc) whose diameter is the absolute maximum length of the particle by the effective projected area (Sr) of the particle. The sphericity (Sc / Sr) of the silicone resin particles C is obtained by analyzing Sc and Sr from a photograph of the silicone resin particles taken with an electron microscope using an image processing analyzer, calculating the sphericity (Sc / Sr), and taking the arithmetic mean. Known methods can be used to measure sphericity. For example, the sphericity can be measured by taking electron microscope images of silicone resin particles and then analyzing those images using an image processing and analysis device (product name: Luzex IID, manufactured by Nireco Corporation).

[0117] The content of the silicone resin particles C is not particularly limited, but is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, and even more preferably 0.1 parts by mass or more, per 100 parts by mass of colored resin particles, while preferably 2 parts by mass or less, more preferably 1 part by mass or less, and even more preferably 0.5 parts by mass or less. If the content of the silicone resin particles C is above the lower limit, the fluidity of the toner tends to improve, so toner ejection is easily suppressed, and the occurrence of filming or fogging is suppressed. If the content of the silicone resin particles C is below the upper limit, the release of the silicone resin particles C from the surface of the toner particles is suppressed, thereby suppressing deterioration of printing performance or the occurrence of fogging. The silicone resin particles C can be used alone or in combination of two or more types.

[0118] The white toner of the present disclosure may contain metal soap fine particles D as an external additive. This makes it easy to obtain a toner having desired fluidity. Further, when the metal soap fine particles D are contained as an external additive, filming on a photoreceptor is less likely to occur, stable chargeability over time is imparted to the toner particles, and even when continuous printing is performed on a large number of sheets, deterioration of image quality due to fog or the like is less likely to occur, and a toner that is less prone to image quality deterioration particularly even under high-temperature and high-humidity environments can be obtained. From the viewpoint that the effect of such metal soap fine particles D is easily exhibited, the number-average primary particle diameter of the metal soap fine particles D preferably has a lower limit of 0.3 µm or more, more preferably 0.4 µm or more, still more preferably 0.5 µm or more, and an upper limit of preferably 1.0 µm or less, more preferably 0.9 µm or less, still more preferably 0.8 µm or less.

[0119] As the metal soap fine particles D, it is preferable to use fatty acid metal salt particles. The fatty acid moiety (R-COO － ) derived from the fatty acid (R-COOH) in the fatty acid metal salt particles may be a monocarboxylic acid containing only one carboxyl group (-COOH), is preferably a monocarboxylic acid having a chain structure, more preferably a saturated monocarboxylic acid having a chain structure, and still more preferably a linear saturated monocarboxylic acid.

[0120] Further, the fatty acid moiety (R-COO － ) contained in the fatty acid metal salt particles is preferably one derived from a higher fatty acid having a large number of carbon atoms in the alkyl group (R-). The number of carbon atoms in the alkyl group of the fatty acid moiety is not particularly limited, but is preferably 12 to 24, more preferably 14 to 22, and still more preferably 16 to 20. Preferred higher fatty acids used as raw materials for the fatty acid metal salt particles include, for example, lauric acid (CH ３ (CH ２ ) １０ COOH), tridecanoic acid (CH ３ (CH ２ ) １１ COOH), myristic acid (CH ３ (CH ２ ) １２COOH), pentadecanoic acid (CH ３ (CH ２ ) １３ COOH), palmitic acid (CH ３ (CH ２ ) １４ COOH), heptadecanoic acid (CH ３ (CH ２ ) １５ COOH), stearic acid (CH ３ (CH ２ ) １６ COOH), arachidic acid (CH ３ (CH ２ ) １８ COOH), behenic acid (CH ３ (CH ２ ) ２０ COOH), lignoceric acid (CH ３ (CH ２ ) ２２ Examples include COOH. Among these, stearic acid and behenic acid are preferred, with stearic acid being more preferred. These fatty acids used as raw materials for fatty acid metal salt particles can be used individually or in combination of two or more, but it is preferable to use them individually in order to obtain uniform properties.

[0121] The metal contained in the fatty acid metal salt particles may be an alkali metal, an alkaline earth metal, or a metal element of Group 12 of the periodic table, such as Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba, Zn, etc. Among these, alkaline earth metals or metal elements of Group 12 of the periodic table are preferred, at least one selected from the group consisting of Mg and Zn is more preferred, and Zn is even more preferred.

[0122] Various commercially available fatty acid metal salt particles can be used, for example, SPZ-100F (product name, zinc stearate particles, number average primary particle size: 0.5 μm) and SPX-100F (product name, magnesium stearate particles, number average primary particle size: 0.72 μm) manufactured by Sakai Chemical Industry Co., Ltd.

[0123] The content of metal soap fine particles D is not particularly limited, but in order to suppress toner aggregation and prevent toner ejection, and to suppress the decrease in electrostatic charge in high temperature and high humidity environments and prevent fogging, it is preferably 0.01 parts by mass or more, more preferably 0.02 parts by mass or more, even more preferably 0.03 parts by mass or more, and even more preferably 0.04 parts by mass or more, per 100 parts by mass of colored resin particles. On the other hand, in order to suppress deterioration of toner fixation due to an excessive amount of external additive, and to suppress the release of metal soap fine particles D from the surface of toner particles and prevent a decrease in toner fluidity, the content of metal soap fine particles D per 100 parts by mass of colored resin particles is preferably 0.30 parts by mass or less, more preferably 0.25 parts by mass or less, and even more preferably 0.20 parts by mass or less. Furthermore, when the content of metal soap fine particles D is within the above range, it is easier to obtain toner with the desired fluidity. Note that metal soap fine particles D can be used alone or in combination of two or more types.

[0124] External additive treatment, which involves attaching an external additive to the surface of colored resin particles, can be carried out by known methods and is not particularly limited. External additive treatment can be carried out using a mixer capable of mixing and stirring, such as a Henschel mixer (trade name, manufactured by Mitsui Mining Co., Ltd.), an FM mixer (trade name, manufactured by Nippon Coke Industries Co., Ltd.), a Super mixer (trade name, manufactured by Kawada Manufacturing Co., Ltd.), a Q mixer (trade name, manufactured by Nippon Coke Industries Co., Ltd.), a Mechanofusion System (trade name, manufactured by Hosokawa Micron Corporation), and a Mechano Mill (trade name, manufactured by Okada Seikou Co., Ltd.).

[0125] In this disclosure, the number-average primary particle size is determined by first measuring the particle size of each individual particle using a transmission electron microscope (TEM) or scanning electron microscope (SEM). The particle sizes of 30 or more particles are measured, and the average value is taken as the number-average primary particle size of that particle. If the particle shape is non-spherical and the major and minor axes can be determined by observation using a TEM or SEM, the major and minor axes are first measured for each individual particle. The major and minor axes of 30 or more particles are measured in this manner, and the average value of each is taken as the average major or average minor axis of that particle. The sum of the calculated average major and average minor axes is divided by 2 to obtain the number-average primary particle size of that particle.

[0126] In the white toner of this disclosure, the total content of the external additives per 100 parts by mass of colored resin particles is not particularly limited, but is preferably 2.0 parts by mass or more and 6.0 parts by mass or less. If the total content of the external additives is above the lower limit, the fluidity of the toner is improved, and if it is below the upper limit, deterioration of the toner's transferability is suppressed.

[0127] 1-4. Toner Physical Properties The white toner disclosed herein is an aggregate of toner particles. These toner particles may be the colored resin particles themselves, or they may be particles formed by adding the external additive to the surface of the colored resin particles.

[0128] The blow-off charge amount of the white toner in this disclosure is not particularly limited, but in order to suppress toner spillage from the positive charge cartridge, it may be, for example, 2 to 40 μC / g or 4 to 20 μC / g. The blow-off charge amount of the toner is measured by the blow-off charge amount measurement method described in the embodiments below.

[0129] The volume-average particle size (Dv) of the white toner in this disclosure is not particularly limited, but is preferably 3 to 15 μm, and more preferably 7 to 12 μm. When Dv is above the lower limit, the fluidity of the toner can be improved, and deterioration of transferability and a decrease in image density can be suppressed. When Dv is below the upper limit, deterioration of toner fixation can be suppressed, and a decrease in image resolution can be suppressed.

[0130] The ratio of the volume-average particle size (Dv) to the number-average particle size (Dp) of the white toner of this disclosure (Dv / Dp) is not particularly limited, but is preferably 1.0 to 1.3, and more preferably 1.0 to 1.2. By having a Dv / Dp of 1.3 or less, a decrease in transferability, image density, and resolution can be suppressed.

[0131] In this disclosure, the volume-average particle size and number-average particle size of the particles can be measured, for example, using a particle size distribution analyzer that uses the Coulter counter method (e.g., Beckman Coulter, product name: Multisizer). A dispersion of the particles to be measured is used as the sample for measurement. The sample for measurement can be prepared, for example, by the same method as when measuring the particle size of toner in the examples described later. The volume-average particle size is the 50% cumulative diameter in the particle size distribution determined by volume, and the number-average particle size is the 50% cumulative diameter in the particle size distribution determined by number.

[0132] The average circularity of the white toner in this disclosure is not particularly limited, but from the viewpoint of image reproducibility, it is preferably 0.95 to 1.00, more preferably 0.97 to 1.00, and even more preferably 0.98 to 1.00. Circularity is defined as the value obtained by dividing the perimeter of a circle having the same projection area as the particle image by the perimeter of the projection image of the particle. In this disclosure, average circularity is used as a simple method to quantitatively express the shape of the particle and is an index that indicates the degree of unevenness of the toner particle. Average circularity is 1 when the toner particle is a perfect sphere, and becomes smaller as the surface shape of the toner particle becomes more complex. Average circularity (Ca) is a value obtained by the following formula for calculating average circularity.

[0133]

[0134] In the above formula, n is the number of particles for which the circularity Ci was determined. In the above formula, Ci is the circularity of each particle calculated using the following circularity calculation formula based on the circumference measured for each particle in a group of particles with equivalent circle diameters of 0.6 to 400 μm. Circularity calculation formula: Circularity (Ci) = Perimeter of a circle equal to the projected area of ​​the particle / Perimeter of the particle projection image In the above formula, fi is the frequency of particles with circularity Ci. The above circularity and average circularity can be measured using the Sysmex Corporation flow-type particle image analyzer "FPIA-3000".

[0135] The present disclosure will be further described below with reference to examples and comparative examples, but the present disclosure is not limited to these examples. Parts and percentages are by mass unless otherwise specified.

[0136] The weight-average molecular weight (Mw) of the polymer was measured by GPC and determined in polystyrene equivalent. For the measurement sample, the polymer was dissolved in tetrahydrofuran (THF) to a concentration of 2 mg / mL, sonicated for 10 minutes, and then passed through a 0.45 μm membrane filter. The measurement conditions were: temperature: 40°C, solvent: tetrahydrofuran, flow rate: 1.0 mL / min, concentration: 0.2 wt%, sample injection volume: 100 μL. The column used was a GPC TSKgel MultiporeHXL-M (30 cm x 2) manufactured by Tosoh Corporation. Furthermore, measurements were performed under conditions where the linear correlation equation between Log(Mw) and elution time for weight-average molecular weights (Mw) between 1,000 and 300,000 was 0.98 or higher.

[0137] [Preparation of Titanium Oxide A-G] Titanium oxide (TiO ２ Titanium oxide particles were obtained by surface-treating the particles with the surface treatment agents shown in Table 1, and these were designated as titanium oxide A to G. The volume-average primary particle sizes of titanium oxide A to G are also shown in Table 1.

[0138]

[0139] [Production Example 1: Production of Polar Resin P1] 200 parts of toluene were added to the reaction vessel, and the reaction vessel was thoroughly replaced with nitrogen while stirring the toluene, and then the temperature was raised to 90°C. Subsequently, a mixed solution of 97.0 parts of methyl methacrylate, 2.6 parts of ethyl acrylate, 0.4 parts of acrylic acid, and 3 parts of t-butyl peroxy-2-ethylhexanoate (manufactured by Nippon Oil & Fats Co., Ltd., trade name: Perbutyl O) was added dropwise to the reaction vessel over 2 hours. Furthermore, polymerization was completed by holding under reflux of toluene for 10 hours, and then the solvent was removed by distillation under reduced pressure. Polar resin P1 (MMA / EA / AA) was obtained in this manner. The obtained polar resin P1 had an acid value of 2.5 mg KOH / g, a Tg of 74°C, and a Mw of 12600.

[0140] [Production Example 2: Synthesis of SIS Composition] 23.2 kg of cyclohexane, 1.5 mmol of N,N,N',N'-tetramethylethylenediamine, and 1.70 kg of styrene were added to a pressure reactor and stirred at 40°C. 99.1 mmol of n-butyllithium was then added, and the resulting mixture was polymerized for 1 hour while increasing the temperature to 50°C. The polymerization conversion rate of styrene was 100% by weight. Subsequently, 6.03 kg of isoprene was continuously added to the reactor over 1 hour while maintaining a temperature of 50-60°C. After the addition of isoprene was completed, polymerization was carried out for another hour to obtain styrene-isoprene triblock copolymer (a). The polymerization conversion rate of isoprene was 100%. Next, 15.0 mmol of dimethyldichlorosilane was added as a coupling agent, and a coupling reaction was carried out for 2 hours to obtain styrene-isoprene-styrene triblock copolymer (b). Subsequently, 198 mmol of methanol was added as a polymerization inhibitor and thoroughly mixed to stop the reaction, thereby obtaining a reaction solution containing a styrene-isoprene-styrene triblock copolymer (SIS) composition containing the block copolymers (a) and (b). Then, 0.3 parts of 2,6-di-tert-butyl-p-cresol was added to 100 parts of the reaction solution thus obtained (containing 30 parts of the polymer component) as an antioxidant and mixed. The mixed solution was then added dropwise in small amounts to warm water heated to 85-95°C to evaporate the solvent and obtain a precipitate. This precipitate was pulverized and dried with hot air at 85°C to recover the SIS composition.

[0141] [Production Example 3: Production of Styrene-Butyl Acrylate Copolymer (α-1)] 200 parts of deionized water were mixed with 0.2 parts of a nonionic dispersant (Kuraray Co., Ltd., "PVA235"), then 70 parts of styrene, 30 parts of butyl acrylate, and a polymerization initiator (benzoyl peroxide) were added. The mixture was kept at 130°C for 2 hours with stirring to carry out suspension polymerization and obtain a copolymer suspension. The obtained suspension was cooled to 30°C, dehydrated using a centrifugal dehydrator, and dried at 50°C for 24 hours to obtain styrene-butyl acrylate copolymer (α-1). The obtained styrene-butyl acrylate copolymer (α-1) consisted of 70% styrene units and 30% butyl acrylate units.

[0142] [Production Example 4: Production of Silicone Resin Particles 1] 60.0 g of water and 0.01 g of acetic acid as a catalyst were placed in a 200 mL round-bottom flask and stirred at 30°C. 70.0 g of methyltrimethoxysilane was added and stirred for 1 hour to obtain a raw material solution. 3.0 g of 25% aqueous ammonia solution, 128.0 g of water, and 390.0 g of methanol were placed in a 1000 mL round-bottom flask and stirred at 30°C to prepare an alkaline aqueous medium. The raw material solution was added dropwise to this alkaline aqueous medium over 1 minute. The mixture after the addition of the raw material solution was stirred for 25 minutes to allow the polycondensation reaction of the fine particle precursor to proceed and obtain a polycondensation reaction solution. 3000 g of water was placed in a 5000 mL round-bottom flask as an aqueous solution, and the polycondensation reaction solution was added dropwise over 1 minute while stirring at 25°C. As soon as the polycondensation reaction solution mixed with water, it became cloudy, and a dispersion containing silicone particles was obtained. To the obtained silicone particle dispersion, 30.5 g of hexamethyldisilazane was added as a hydrophobic agent, and the mixture was stirred at 25°C for 48 hours. As a result, hydrophobic spherical polymethylsilsesquioxane fine particles floated in the upper layer of the liquid, and a powder suspension liquid was obtained. The powder suspension liquid was allowed to stand for 5 minutes, and the floating powder was collected by suction filtration. The mixture was then dried under reduced pressure at 100°C for 24 hours to obtain 32 g of dried silicone resin particle 1 powder. The obtained silicone resin particle 1 had a number-average primary particle size of 0.09 μm and a theoretical specific surface area (TS) of 50 m². ２ / g, BET specific surface area (BS) is 230m² ２ The particles were spherical silicone resin particles with a saturation ratio of 4.6, adsorbed water content of 0.35%, and sphericity (Sc / Sr) of 0.933.

[0143] [Example 1] 1. Production of colored resin particles 1-1. Preparation of polymerizable monomer composition for core: 70 parts styrene, 30 parts n-butyl acrylate, 0.25 parts polymethacrylate macromonomer (manufactured by Toa Synthetic Chemical Industry Co., Ltd., trade name: AA-6, Tg = 94°C), and 60 parts of the above titanium dioxide A as a coloring agent were wet-milled using a media-type disperser (manufactured by Asada Iron Works Co., Ltd., trade name: Picomil).

[0144] To the mixture obtained by the wet grinding described above, 0.3 parts of divinylbenzene, 0.5 parts of tetraethyl thiuram disulfide as a molecular weight modifier, 12 parts of quaternary ammonium salt-containing styrene acrylic resin (manufactured by Fujikura Chemical Co., Ltd., trade name: Acrybase® FCA-676P, functional group content 1% by mass) as a charge control agent, and 20 parts of synthetic ester wax (pentaerythritol tetrabehenate, melting point 76°C) were added, mixed, and dissolved to prepare a polymerizable monomer composition for cores.

[0145] 1-2. Preparation of aqueous dispersion medium: On the other hand, magnesium hydroxide colloid (magnesium hydroxide content 5.3 parts) was prepared by gradually adding an aqueous solution prepared by dissolving 10.4 parts magnesium chloride in 280 parts deionized water under stirring.

[0146] 1-3. Preparation of aqueous dispersion of polymerizable monomer for shells: On the other hand, 3 parts methyl methacrylate and 130 parts water were finely dispersed using an ultrasonic emulsifier to prepare an aqueous dispersion of polymerizable monomer for shells.

[0147] 1-4. Droplet Formation Process: The polymerizable monomer composition for the core was added to the magnesium hydroxide colloid and stirred further. Then, 4 parts of t-butyl peroxy-2-ethyl butyrate were added as a polymerization initiator. The dispersion with the polymerization initiator added was dispersed using an in-line emulsifier / disperser (manufactured by Taiheiyo Kiko Co., Ltd., product name: Milder) at a rotation speed of 15,000 rpm to form droplets of the polymerizable monomer composition for the core.

[0148] 1-5. Polymerization process: A dispersion containing droplets of the polymerizable monomer composition for the core was placed in a reactor and heated to 90°C to carry out the polymerization reaction. After the polymerization conversion rate reached approximately 100%, 0.1 parts of 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)-propionamide] (manufactured by Wako Pure Chemical Industries, Ltd., trade name: VA-086, water-soluble initiator) dissolved in the aqueous dispersion of the polymerizable monomer for the shell was added to the reactor as a polymerization initiator for the shell. The polymerization was then continued by maintaining the temperature at 95°C for 4 hours, after which the reaction was stopped by water cooling to obtain an aqueous dispersion of core-shell type colored resin particles.

[0149] 1-6. Washing, Filtration, Dehydration, and Drying Process: An aqueous dispersion of colored resin particles was stirred and sulfuric acid was added until the pH was 4.5 or lower. Acid washing was then performed at 25°C for 10 minutes. The filtered colored resin particles were then washed with water, and the washing water was filtered. The electrical conductivity of the filtrate at this stage was 20 μS / cm. Furthermore, the washed and filtered colored resin particles were dehydrated and dried to obtain dried colored resin particles.

[0150] 2. External Addition Treatment: To 100 parts by mass of the above-mentioned dried colored resin particles, 0.72 parts of hydrophobized silica fine particles (manufactured by Wacker, product name: H05TA) with a number average primary particle size of 50 nm as inorganic fine particles A, 0.6 parts of hydrophobized silica fine particles (manufactured by Cabot, product name: TG-7120) with a number average primary particle size of 20 nm as inorganic fine particles B, 0.1 parts of silicone resin particles 1 obtained in the above-mentioned Production Example 4 as silicone resin particles C, and 0.17 parts of fatty acid metal salt particles (zinc stearate particles, manufactured by Sakai Chemical Industry Co., Ltd., product name: SPZ-100F) with a number average primary particle size of 0.5 μm as metal soap fine particles D were added and mixed and stirred using a high-speed stirrer (manufactured by Nippon Coke Industries Co., Ltd., product name: FM Mixer) under the conditions of a blade peripheral speed of 46.6 m / s and an external addition treatment time of 8 minutes to prepare the white toner of Example 1.

[0151] [Examples 2-7 and Comparative Examples 1-7] White toners for Examples 2-7 and Comparative Examples 1-7 were obtained in the same manner as in Example 1, except that at least one of the following was changed according to Table 2 or Table 3: the type and amount of colorant, the type and amount of charge control agent, and the type and amount of softener.

[0152] [Examples 8-10] White toners for Examples 8-10 were obtained in the same manner as in Example 1, except that at least one of the following was changed according to Table 2: the type and amount of colorant, the type and amount of charge control agent, and the type and amount of softener; and when preparing the polymerizable monomer composition for the core, instead of adding polymethacrylate macromonomer (manufactured by Toa Synthetic Chemical Industry Co., Ltd., trade name: AA-6), one part of the polar resin P1 obtained in Production Example 1 was added; and in Examples 8 and 9, five parts of the SIS composition obtained in Production Example 2 were further added to the mixture obtained by wet grinding together with ester wax, etc.

[0153] [Example 11] 1. Production of colored resin particles 1-1. Step to obtain colored resin pulverized material: 100 parts of styrene-butyl acrylate copolymer (α-1) obtained in Production Example 3 as a binder resin, 60 parts of titanium dioxide B as a coloring agent, 20 parts of pentaerythritol tetrabehenate as a softening agent, and 12 parts of a static charge control resin (styrene acrylic resin containing quaternary ammonium salt, manufactured by Fujikura Chemical Co., Ltd., trade name: Acrybase (registered trademark) FCA-676P, functional group content 1% by mass) as a static charge control agent were mixed in a Henschel mixer (manufactured by Nippon Coke Industries Co., Ltd., trade name: FM20B). The resulting mixture was then melt-kneaded at 145°C for 10 minutes using a twin-screw extruder, and cooled after kneading. The cooled kneaded mixture was crushed using a mechanical pulverizer (manufactured by Turbo Industries Co., Ltd., product name: Turbo Mill) and then classified using an elbow jet classifier (manufactured by Nippon Steel Mining Co., Ltd., product name: EJ-LABO) to obtain an amorphous colored resin pulverized material with a volume-average particle size of 9.5 μm.

[0154] 1-2. Dispersion process: On the other hand, magnesium hydroxide colloid (5.3 parts magnesium hydroxide) was prepared by gradually adding an aqueous solution prepared by dissolving 7.3 parts sodium hydroxide in 50 parts deionized water to an aqueous solution prepared by dissolving 10.4 parts magnesium chloride in 280 parts deionized water, while stirring for 10 minutes. Next, a mixed solution of 4.0 parts of the magnesium hydroxide colloid and 400.0 parts of deionized water was added to 10 parts of the colored resin pulverized material obtained above, and the mixture was stirred to obtain a dispersion of the colored resin pulverized material.

[0155] 1-3. Preheating process: Next, a sample tube containing a stirring bar was placed in a constant temperature water bath set to 50°C. The dispersion of the colored resin pulverized material obtained above was placed in the sample tube and allowed to stand for 120 minutes while slowly stirring to perform preheating and obtain the dispersion of colored resin pulverized material after preheating.

[0156] 1-4. Heating process: Next, a sample tube containing a stirring bar was placed in a constant temperature water bath set to 80°C. The dispersion of preheated colored resin pulverized material obtained above was placed in the sample tube and allowed to stand for 30 minutes while slowly stirring. This heat treatment of the dispersion of preheated colored resin pulverized material caused the colored resin pulverized material to become spherical, and a dispersion of colored resin particles was obtained.

[0157] 1-5. Core-Shell Structure Formation Process: On the other hand, 3 parts of methyl methacrylate and 130 parts of water were finely dispersed using an ultrasonic emulsifier to prepare an aqueous dispersion of polymerizable monomers for the shell. In the reactor, a solution of 0.1 parts of 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)-propionamide] (manufactured by Wako Pure Chemical Industries, Ltd., trade name: VA-086, water-soluble initiator) dissolved in the aqueous dispersion of polymerizable monomers for the shell, and the dispersion of colored resin particles obtained above were added. Next, the polymerization of the polymerizable monomers for the shell was carried out by maintaining the temperature at 95°C for 4 hours, and then the reaction was stopped by water cooling to obtain an aqueous dispersion of core-shell type colored resin particles.

[0158] 1-6. Washing, Filtration, Dehydration, and Drying Process: The aqueous dispersion of core-shell type colored resin particles obtained above was stirred and sulfuric acid was added until the pH reached 4.5. Acid washing was performed at a temperature of 25°C for 10 minutes. The filtered colored resin particles were then washed with water, and the washing water was filtered. The electrical conductivity of the filtrate at this stage was 11 μS / cm. The colored resin particles after washing and filtration were further dehydrated and dried to obtain dried colored resin particles.

[0159] 2. External additive treatment process: The same external additive treatment as performed in Example 1 was applied to the dried colored resin particles to obtain the white toner of Example 11.

[0160] The details of the electrostatic control agents listed in Tables 2 and 3 are as follows: "FCA676P" Manufactured by Fujikura Chemical Co., Ltd., product name: Acrybase (registered trademark) FCA676P, a styrene-acrylic resin in which the copolymerization ratio of the quaternary ammonium salt-containing (meth)acrylate monomer (N,N-diethyl-N-methyl-2-(methacryloyloxy)ethylammonium p-toluenesulfonate) is 1% by mass. "FCA592P" Manufactured by Fujikura Chemical Co., Ltd., product name: Acrybase (registered trademark) FCA592P, a styrene-acrylic resin in which the copolymerization ratio of the quaternary ammonium salt-containing (meth)acrylate monomer (N,N-diethyl-N-methyl-2-(methacryloyloxy)ethylammonium p-toluenesulfonate) is 2% by mass. "FCA161P" Fujikura Chemical Co., Ltd., Product name: Acrybase (registered trademark) FCA161P, Styrene acrylic resin "Bontron P-51" containing a quaternary ammonium salt-containing (meth)acrylate monomer (N,N-diethyl-N-methyl-2-(methacryloyloxy)ethylammonium p-toluenesulfonate) with a copolymerization ratio of 8% by mass. Orient Chemical Industry Co., Ltd., Product name: BONTRON (registered trademark) P-51, Quaternary ammonium salt. Bontron N-71, Orient Chemical Industry Co., Ltd., Product name: BONTRON (registered trademark) N-71, Adin compound. Styrene acrylic resin containing a tertiary amine, with a copolymerization ratio of dimethylaminoethyl acrylate of 2% by mass.

[0161] Furthermore, the melting points of the softening agents (ester waxes) used are as follows: Pentaerythritol tetrabehenate: 78.7°C Behenyl stearate: 67.1°C Behenyl behenate: 73.8°C Pentaerythritol tetrastearate: 76.0°C

[0162] [Evaluation] 1. Amount of toner blow-off charge 0.25 g of toner and 9.75 g of a standard carrier, ferrite carrier (product name: EF-60, manufactured by Powdertec, Mn-Mg-Sr-Fe system, spherical, no resin coating, average particle size 60 μm), were placed in a glass container with a volume of 30 cc (internal dimensions: bottom diameter 30 mm, height 50 mm), and triboelectric charging treatment was performed using a roller-type agitator, rotating at 160 revolutions / minute for 30 minutes in an environment of 23°C and relative humidity 50%. 1.2 g of the mixture of toner and ferrite carrier after the triboelectric treatment was placed in a Faraday cage. Using a blow-off powder charge measuring device (product name: Q / M meter, manufactured by Epping), a mesh with a mesh opening of 16 μm was attached to the cell, and the mixture was blown off for 90 seconds under conditions of a suction pressure of 1.05 mbar and a nitrogen gas flow rate of 2.0 L / min to measure the blow-off charge amount (μC) of the mixture. The blow-off charge amount (μC / g) of the toner was calculated using the following formula (1): Formula (1) Blow-off charge amount of toner (μC / g) = Blow-off charge amount of mixture (μC) / Amount of toner blown off during measurement (g)

[0163] 2. Toner Particle Size Measurement (Multisizer) The volume-average particle size Dv of the toner was measured using a particle size distribution analyzer (Beckman Coulter, Ltd., product name: Multisizer). This measurement using the Multisizer was performed under the following conditions: aperture diameter: 100 μm, dispersion medium: Isoton II (product name), concentration: 10%, number of particles measured: 100,000. Specifically, 0.2 g of toner sample was placed in a beaker, and an aqueous surfactant solution (Fujifilm Corporation, product name: Drywell) was added as a dispersant. Then, 2 ml of dispersion medium was added to wet the toner, and after that, 10 ml of dispersion medium was added, and the toner was dispersed in an ultrasonic disperser for 1 minute before measurement using the above particle size distribution analyzer.

[0164] 3. Average Circularity: 10 mL of deionized water was pre-filled into a container, 0.02 g of surfactant as a dispersant was added, and then 0.02 g of toner was added. Dispersion treatment was performed using an ultrasonic disperser at 60 W for 3 minutes. The toner particle concentration at the time of measurement was adjusted to 3,000 to 10,000 particles / μL, and 5,000 to 10,000 toner particles with a circle equivalent diameter of 0.4 μm or larger were measured using a flow-type particle image analyzer (Simex Corporation, product name: FPIA-3000). The average circularity was calculated from the measured values. The circularity is shown in Formula 1 below, and the average circularity was taken as the number average. Formula 1: (Circularity) = (Perimeter of a circle equal to the projected area of ​​the particle) / (Perimeter of the particle projection image)

[0165] 4. Lightness L ＊ Measurement and Evaluation of Opacity: A modified non-magnetic one-component developing printer (Brother Industries, Ltd., HL-L9310CDW, print speed: 31 pages / minute) was used to measure and evaluate opacity. Black printing paper was loaded into the printer, toner was placed in the developing unit, and the printer was left for 24 hours in an environment of 23°C and 50% RH. After that, the developing bias was set to 400V, and a solid patch measuring 5 cm square was printed on the top of the paper. The brightness L was measured at a total of five points in the solid area of ​​the printed material (top left, top right, center, bottom left, and bottom right) using a reflectivity densitometer (product name: eXact, X-Rite). ＊ Measure the L of the five points mentioned above. ＊ The average value of white toner L ＊ This was used as the evaluation value. L ＊ The lower the value, the lower the toner's opacity and the inferior its whiteness. ＊ If the evaluation value is 70 or higher, it can be evaluated as being sufficiently usable as a white image, L ＊ A higher evaluation value indicates a higher whiteness in the image, and therefore, it can be evaluated as having superior opacity. ＊ Based on the evaluation values, the opacity of the white toner was evaluated according to the following evaluation criteria. L ＊ The evaluation values ​​and the results of the concealment evaluation are shown in Tables 2 and 3. <Concealment Evaluation Criteria> A: L ＊ Rating score of 70 or higher: B:L ＊ Evaluation score between 60 and 70: C:L ＊ Rating score between 50 and 60: D:L ＊Rating less than 50

[0166] 5. A transferable, non-magnetic, one-component developing printer (Brother Industries, Ltd., HL-L9310CDW, print speed: 31 pages / minute) was loaded with black printing paper, toner was placed in the developing unit, and the printer was left for 24 hours at a temperature of 23°C and a humidity of 50% RH. Afterward, 1.5 cm square solid patches were printed on the left, center, and right sides of the top of the paper, so that the yellow toner and then the white toner were transferred in that order. A commercially available yellow toner included with the above printer was used. Immediately after the white toner was transferred from the photoreceptor, the printer was stopped, and the toner remaining on the developed photoreceptor was attached to adhesive tape (Sumitomo 3M, product name: Scotch Mending Tape 810-3-18). This adhesive tape was then attached to the black printing paper. The five colors on the black printing paper with the adhesive tape attached were measured using a reflective densitometer (product name: eXact, X-Rite). ＊ a ＊ b ＊ Measured in color space, 5 points L ＊ a ＊ and b ＊ The average value of each is measured L ＊ Measurement a ＊ and measurement b ＊ Similarly, the five colors of the black printing paper with unused adhesive tape attached were also L ＊ a ＊ b ＊ Measured in color space, 5 points L ＊ a ＊ and b ＊ The average values ​​of each are set to the standard L ＊ , criterion a ＊ and criterion b ＊ The color difference ΔE was calculated using the following formula: <Formula for calculating color difference ΔE> ΔE = √((reference L ＊ -Measurement L ＊ ) ２ +(criteria a ＊ - Measurement a ＊ ) ２ +(criteria b ＊ - Measurement b ＊ ) ２A smaller ΔE value indicates less toner residue and superior transfer performance. The transfer performance of white toner was evaluated according to the following criteria. The evaluation results are shown in Tables 2 and 3. <Transfer Performance Evaluation Criteria> A: ΔE less than 5 B: ΔE 5 or more and less than 10 C: ΔE 10 or more and less than 15 D: ΔE 15 or more

[0167]

[0168]

[0169] The white toners of Comparative Examples 1 to 4 had poor opacity and transferability because the surface treatment agent used on the titanium oxide particles did not contain at least one selected from the group consisting of aluminum hydroxide and aluminum oxide, and either or both of the organosilicon compounds. The white toners of Comparative Examples 5 to 7 also had poor opacity and transferability because they did not contain a quaternary ammonium salt-containing copolymer. In contrast, the white toners of Examples 1 to 11 had excellent opacity and transferability because they contained titanium oxide particles surface-treated with a surface treatment agent containing at least one selected from the group consisting of aluminum hydroxide and aluminum oxide, and an organosilicon compound, in combination with a quaternary ammonium salt-containing copolymer.

Claims

A white toner containing colored resin particles comprising a binder resin, a colorant, and a charge control agent, The coloring agent comprises titanium dioxide particles surface-treated with two or more surface treatment agents, and the surface treatment agent comprises at least one selected from the group consisting of aluminum hydroxide and aluminum oxide, and an organosilicon compound. A white toner wherein the charge control agent contains a quaternary ammonium salt-containing copolymer. 　 The white toner according to claim 1, wherein the content of the titanium oxide particles is 15 to 50 parts by mass per 100 parts by mass of the colored resin particles. 　 The white toner according to claim 1 or 2, wherein the binder resin is a styrene-acrylic resin. 　 The white toner according to claim 1 or 2, wherein the colored resin particles further contain a polar resin. 　 The white toner according to claim 1 or 2, wherein the colored resin particles further contain a styrene-based thermoplastic elastomer. 　 The white toner according to claim 1 or 2, wherein the colored resin particles further contain a softening agent, and the softening agent contains a polyfunctional ester wax. 　 The white toner according to claim 1 or 2, wherein the colored resin particles further contain a softening agent, and the softening agent contains a monoester wax. 　 The white toner according to claim 1 or 2, wherein the average circularity of the white toner is 0.97 to 1.

00. Prepare a polymerizable monomer composition containing at least a polymerizable monomer, a colorant, and a charge control agent. A suspension is prepared in which droplets of the polymerizable monomer composition are dispersed in an aqueous medium containing a dispersion stabilizer. The suspension is subjected to a polymerization reaction, The coloring agent comprises titanium dioxide particles surface-treated with two or more surface treatment agents, and the surface treatment agent comprises at least one selected from the group consisting of aluminum hydroxide and aluminum oxide, and an organosilicon compound. A method for producing white toner, wherein the charge control agent includes a quaternary ammonium salt-containing copolymer. 　 The method for producing white toner according to claim 9, wherein the content of the titanium oxide particles is 15 to 50 parts by mass per 100 parts by mass of the polymerizable monomer composition. 　 The polymerizable monomer contains monovinyl monomer in a proportion of 95% by mass or more. The method for producing white toner according to claim 9 or 10, wherein the monovinyl monomer comprises at least one selected from the group consisting of styrene and styrene derivatives, and at least one selected from the group consisting of acrylic acid esters and methacrylic acid esters.

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