White toner, electrostatic image developer, toner cartridge, process cartridge, image forming apparatus and image forming method

Abstract

To provide a white toner which is less likely to cause the chalking phenomenon.SOLUTION: A white toner is provided, comprising toner particles containing a binder resin, a release agent, and titanium oxide, where at least a portion of the titanium oxide lies in release agent domains. In cross-sectional observation of the toner particles, an average major axis length Dt of the toner particles, an average major axis length Dw of the release agent domains, and an average major axis length Dp of the titanium oxide in the release agent domains satisfy the following expression (1) and (2): 2×Dp≤Dw≤10×Dp ...(1), 0.1×Dt≤Dw≤0.5×Dt ...(2).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a white toner, an electrostatic image developer, a toner cartridge, a process cartridge, an image forming apparatus, and an image forming method. [Background technology]

[0002] Patent Document 1 describes a coating composition containing a binder resin and at least two or more different white pigments, in which 10 to 30% by weight of the white pigments have a volume average particle diameter of 0.01 to 1 μm, a particle size distribution of 1.1 to 1.3, and a BET specific surface area of ​​250 to 500 m 2 / g porous titanium oxide toner is disclosed. Patent Document 2 discloses a white toner containing white toner particles and yellow toner particles containing an organic yellow pigment, in which the content of yellow toner particles in all toner particles is 0.01% by number or more and 3% by number or less. Patent Document 3 discloses a white toner having toner particles containing a binder resin, a release agent, and a white pigment, in which the content of the white pigment is 30% by mass or more relative to the entire toner particles, and in which, when the volume average particle diameter of the toner particles is d, the release agent is present in an amount of 50% by mass or more and 90% by mass or less relative to the total mass of the release agent in the toner particles at a distance of 0.075d or less from the toner particle surface, and the average maximum Feret diameter of the release agent domains in the toner particles is 0.05d or more and 0.15d or less. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-128008 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-146497 [Patent Document 3] Japanese Patent Publication No. 2018-018035 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present disclosure is to provide a white toner that forms images that are less susceptible to the chalking phenomenon than white toners in which the average major axis length of toner particles Dt, the average major axis length of release agent domains Dw, and the average major axis length of titanium oxide in the release agent domains Dp do not satisfy formula (1) or (2), where formula (1): 2×Dp≦Dw≦10×Dp, and formula (2): 0.1×Dt≦Dw≦0.5×Dt. [Means for solving the problem]

[0005] The means for solving the above problems include the following aspects.

[0006] <1> A white toner comprising toner particles containing a binder resin, a release agent, and titanium oxide, wherein at least a portion of the titanium oxide is in a release agent domain, and in cross-sectional observation of the toner particles, an average major axis length Dt of the toner particles, an average major axis length Dw of the release agent domains, and an average major axis length Dp of the titanium oxide in the release agent domains satisfy the following formulas (1) and (2): Formula (1): 2×Dp≦Dw≦10×Dp Formula (2): 0.1×Dt≦Dw≦0.5×Dt <2> In cross-sectional observation of the toner particles, an average major axis length Dt of the toner particles, an average major axis length Dw of the release agent domains, and an average major axis length Dp of the titanium oxide in the release agent domains satisfy the following formulas (1-1) and (2-1): <1> The white toner according to claim 1. Formula (1-1): 2.5×Dp≦Dw≦8×Dp Formula (2-1): 0.125×Dt≦Dw≦0.4×Dt <3> When a cross section of the toner particle is observed, the number ratio of the titanium oxide particles in the release agent domain is 50% or more of the total number of the titanium oxide particles contained in the toner particle. <1> or <2> The white toner according to claim 1. <4> When a cross section of the toner particle is observed, the number ratio of the titanium oxide particles in the release agent domain is 60% or more of the total number of the titanium oxide particles contained in the toner particle. <1> ~ <3> 10. The white toner according to claim 9, wherein the toner is a toner having a thickness of 100 nm or less. <5> a mass ratio of the release agent contained in the toner particles to the titanium oxide (release agent / titanium oxide) of 0.01 or more and 0.3 or less; <1> ~ <4> 10. The white toner according to claim 9, wherein the toner is a toner having a thickness of 100 nm or less. <6> the content of the titanium oxide contained in the toner particles is 30% by mass or more and 70% by mass or less of the total mass of the toner particles; <1> ~ <5> 10. The white toner according to claim 9, wherein the toner is a toner having a thickness of 100 nm or less. <7> In a cross-sectional observation of the toner particle, the average major axis length Dp of the titanium oxide in the release agent domain is 100 nm or more and 300 nm or less. <1> ~ <6> 10. The white toner according to claim 9, wherein the toner is a toner having a thickness of 100 nm or less. <8> The titanium oxide contained in the toner particles has a BET specific surface area of ​​4 m 2 / g or more 12m 2 / g or less, <1> ~ <7> 10. The white toner according to claim 9, wherein the toner is a toner having a thickness of 100 nm or less. <9> The release agent comprises an ester wax. <1> ~ <8> 10. The white toner according to claim 9, wherein the toner is a toner having a thickness of 100 nm or less. <10> <1> ~ <9> An electrostatic image developer comprising the white toner according to any one of claims 1 to 10. <11> <1> ~ <9> 10. A toner cartridge that contains the white toner according to any one of claims 1 to 9 and is detachably mounted on an image forming apparatus. <12> <10> and a developing means for developing an electrostatic image formed on the surface of an image carrier using the electrostatic image developer into a toner image, the process cartridge being detachably mountable to an image forming apparatus. <13> an image carrier; a charging means for charging the surface of the image carrier; an electrostatic image forming means for forming an electrostatic image on the charged surface of the image carrier; <10> a developing means for developing the electrostatic image formed on the surface of the image carrier into a toner image by using the electrostatic image developer; a transfer means for transferring the toner image formed on the surface of the image carrier to the surface of a recording medium; a fixing means for fixing the toner image transferred onto the surface of the recording medium; An image forming apparatus comprising: <14> a charging step of charging the surface of the image carrier; an electrostatic image forming step of forming an electrostatic image on the charged surface of the image carrier; <10> a developing step of developing the electrostatic image formed on the surface of the image carrier as a toner image using the electrostatic image developer according to claim 1; a transfer step of transferring the toner image formed on the surface of the image carrier to the surface of a recording medium; a fixing step of fixing the toner image transferred onto the surface of the recording medium; An image forming method comprising the steps of: [Effects of the Invention]

[0007] <1> , <6> , <7> , <8> or <9> According to the invention relating to (1), a white toner is provided that forms an image that is less susceptible to the chalking phenomenon than a white toner that does not satisfy formula (1) or does not satisfy formula (2). <2> According to the invention relating to (1), a white toner is provided that forms an image in which the chalking phenomenon is less likely to occur than a white toner that does not satisfy formula (1-1) or does not satisfy formula (2-1). <3> or <4> According to the invention, a white toner is provided that forms an image in which the chalking phenomenon is less likely to occur than in a white toner in which the number ratio of titanium oxide in the release agent domain is less than 50% by number. <5> According to the present invention, a white toner is provided that forms images that are less susceptible to the chalking phenomenon than white toners having a mass ratio of release agent to titanium oxide (release agent / titanium oxide) contained in toner particles of less than 0.01, and that forms images that are superior in whiteness and hiding power than white toners having a mass ratio of more than 0.3.

[0008] <10> According to the present invention, an electrostatic image developer is provided that forms images in which the choking phenomenon is less likely to occur than electrostatic image developers that use white toner that does not satisfy formula (1) or that does not satisfy formula (2). <11> According to the invention, a toner cartridge is provided that forms images that are less susceptible to the choking phenomenon than toner cartridges that use white toner that does not satisfy formula (1) or that does not satisfy formula (2). <12> According to the invention, a process cartridge is provided that forms images that are less susceptible to the choking phenomenon than a process cartridge that uses a white toner that does not satisfy formula (1) or that does not satisfy formula (2). <13> According to the invention, an image forming apparatus is provided that forms images in which the choking phenomenon is less likely to occur than an image forming apparatus that uses a white toner that does not satisfy formula (1) or does not satisfy formula (2). <14> According to the present invention, an image forming method is provided that forms an image in which the chalking phenomenon is less likely to occur than in an image forming method that uses a white toner that does not satisfy formula (1) or that does not satisfy formula (2). [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to an embodiment of the present invention. [Figure 2] 1 is a schematic diagram illustrating an example of a process cartridge that is detachably mounted to an image forming apparatus according to an exemplary embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010]

[0023] The following describes embodiments of the present disclosure. These descriptions and examples are intended to illustrate the embodiments and are not intended to limit the scope of the embodiments.

[0011] In the present disclosure, a numerical range indicated using "to" indicates a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in this disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in this disclosure, the upper or lower limit value of that numerical range may be replaced with a value shown in the examples.

[0012] In the present disclosure, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes as long as the intended purpose of the process is achieved.

[0013] When embodiments of the present disclosure are described with reference to the drawings, the configuration of the embodiment is not limited to the configuration shown in the drawings. Furthermore, the sizes of the components in each drawing are conceptual, and the relative size relationships between the components are not limited to these.

[0014] In the present disclosure, each component may contain multiple corresponding substances. When referring to the amount of each component in a composition in the present disclosure, if multiple substances corresponding to each component are present in the composition, the total amount of the multiple substances present in the composition is meant unless otherwise specified. In the present disclosure, the composition may contain multiple types of particles corresponding to each component. When multiple types of particles corresponding to each component are present in the composition, the particle size of each component means the value for a mixture of the multiple types of particles present in the composition, unless otherwise specified.

[0015] In the present disclosure, "(meth)acrylic" is an expression that includes both acrylic and methacrylic, and "(meth)acrylate" is an expression that includes both acrylate and methacrylate.

[0016] In this disclosure, "toner for developing electrostatic images" is also referred to as "toner," "electrostatic image developer" is also referred to as "developer," and "carrier for developing electrostatic images" is also referred to as "carrier."

[0017] <White toner> The white toner according to this exemplary embodiment includes toner particles containing a binder resin, a release agent, and titanium oxide, in which at least a portion of the titanium oxide is present in the release agent domain. In the white toner according to this embodiment, when a cross section of a toner particle is observed, the average major axis length Dt of the toner particle, the average major axis length Dw of the release agent domain, and the average major axis length Dp of the titanium oxide in the release agent domain satisfy the following formulas (1) and (2).

[0018] Formula (1): 2×Dp≦Dw≦10×Dp Formula (2): 0.1×Dt≦Dw≦0.5×Dt

[0019] The image formed using the white toner according to this embodiment is less likely to suffer from the chalking phenomenon. The mechanism behind this is presumed to be as follows.

[0020] Titanium oxide is widely used as a white pigment in toner. One way to improve the whiteness and hiding power of white images is to increase the amount of titanium oxide contained in the toner particles. However, because titanium oxide has photocatalytic activity, chalking (reduction in image strength, cracking, peeling, fading, etc.) occurs when a white image is exposed to light (especially ultraviolet light) for a long period of time. The chalking phenomenon becomes more pronounced as the amount of titanium oxide contained in the toner particles increases.

[0021] In response to the above phenomenon, the present inventors have discovered that by incorporating at least a portion of titanium oxide in a toner particle within a release agent domain and specifying the formulas (1) and (2) for the dimensions of the toner particle, the release agent domain, and the titanium oxide in the release agent domain, it is possible to suppress the chalking phenomenon while improving the releasability, whiteness, and hiding power of the white image.

[0022] Formula (1) specifies that Dw is 2 to 10 times the average major axis length Dp of the release agent domains, where Dw is the average major axis length Dp of the titanium oxide in the release agent domains. When Dw is at least twice as large as Dp, titanium oxide can exist in the white image in a state coated with the release agent, which is thought to suppress contact between titanium oxide and the binder resin, inhibit decomposition of the binder resin due to the photocatalytic activity of titanium oxide, and suppress the chalking phenomenon.When Dw is less than twice as large as Dp, the titanium oxide is not sufficiently coated with the release agent in the white image, and the chalking phenomenon is likely to occur. On the other hand, if Dw exceeds 10 times Dp, the whiteness and hiding power of the white image will be insufficient. From the above viewpoint, the formula (1) is preferably the following formula (1-1), and more preferably formula (1-2). Formula (1-1): 2.5×Dp≦Dw≦8×Dp Formula (1-2): 3×Dp≦Dw≦7×Dp

[0023] Equation (2) specifies that, with respect to the average major axis length Dt of the toner particles and the average major axis length Dw of the release agent domains, Dw is 0.1 to 0.5 times Dt, i.e., Dw is 1 / 10 to 1 / 2 of Dt. If Dw is less than 1 / 10 of Dt, the white image will have poor releasability from the fixing member when fixed to the recording medium, resulting in a rough surface of the white image and a tendency for chalking to occur. On the other hand, if Dw exceeds 1 / 2 of Dt, the intensity of the white image becomes insufficient, and the chalking phenomenon is likely to occur. From the above viewpoint, the formula (2) is preferably the following formula (2-1), and more preferably formula (2-2). Formula (2-1): 0.125×Dt≦Dw≦0.4×Dt Formula (2-2): 0.15×Dt≦Dw≦0.35×Dt

[0024] In the white toner according to the present embodiment, from the viewpoint of forming an image in which the chalking phenomenon is less likely to occur, when a cross section of a toner particle is observed, it is preferable that the average major axis length Dt of the toner particles, the average major axis length Dw of the release agent domains, and the average major axis length Dp of the titanium oxide particles in the release agent domains satisfy the formulas (1-1) and (2-1), and it is more preferable that the formulas (1-2) and (2-2) are satisfied.

[0025] In the white toner according to this embodiment, from the viewpoint of forming an image in which the chalking phenomenon is less likely to occur, when a cross section of a toner particle is observed, the number ratio of titanium oxide in the release agent domains to the total titanium oxide contained in the toner particle is preferably 50% by number or more, more preferably 60% by number or more, and even more preferably 80% by number or more. The upper limit of the number ratio (referred to in the present disclosure as the inclusion ratio of titanium oxide) is 100% by number.

[0026] In the white toner according to this embodiment, when a cross section of a toner particle is observed, the average major axis length Dp of titanium oxide in the release agent domains is preferably in the following range. From the viewpoint of suppressing aggregation of titanium oxide and increasing the number of titanium oxide particles included in the domain of the release agent, Dp is preferably 100 nm or more, more preferably 150 nm or more, and even more preferably 180 nm or more. From the viewpoint that titanium oxide is easily included in the domain of the release agent, Dp is preferably 300 nm or less, more preferably 250 nm or less, and even more preferably 220 nm or less.

[0027] In the white toner according to this exemplary embodiment, the average major axis length Dw of the release agent domains is preferably in the following range when observing a cross section of a toner particle. From the viewpoint of easily incorporating titanium oxide, Dw is preferably 600 nm or more, more preferably 800 nm or more, and even more preferably 1000 nm or more. From the viewpoint of ensuring the strength of a white image, Dw is preferably 3000 nm or less, more preferably 2500 nm or less, and even more preferably 2000 nm or less.

[0028] In the white toner according to this exemplary embodiment, the average major axis length Dt of the toner particles is preferably in the following range when observing a cross section of the toner particles. From the viewpoint of ease of toner particle granulation, Dt is preferably 3.5 μm or more, more preferably 4.0 μm or more, and even more preferably 4.5 μm or more. From the viewpoint of forming a fine white image, Dt is preferably 10 μm or less, more preferably 9.0 μm or less, and even more preferably 8.0 μm or less.

[0029] A method for observing the cross section of a toner particle and a method for measuring various geometrical quantities will be described below.

[0030] Toner particles (which may contain external additives) are embedded in bisphenol A liquid epoxy resin and a curing agent to prepare a cutting sample. The cutting sample is then cut at -100°C using a cutting machine equipped with a diamond knife (e.g., a LEICA Ultramicrotome, manufactured by Hitachi High-Technologies Corporation) to prepare a sample for observation. If necessary, the observation sample is left in a desiccator in an atmosphere of ruthenium tetroxide for staining. The sample is observed under a scanning transmission electron microscope (STEM), and a STEM image is recorded at a magnification that allows the cross section of a single toner particle to be viewed. The recorded STEM image is analyzed using image analysis software (e.g., WinROOF2015, Mitani Corporation) under conditions of 0.010 μm / pixel. The cross-sectional shape of a toner particle is determined by the difference in brightness (contrast) between the embedding epoxy resin and the binder resin of the toner particle. In a STEM image, titanium oxide appears black due to the difference in brightness (contrast) between the binder resin and the release agent and titanium oxide, so the black particles in the cross section of the toner particle are titanium oxide.

[0031] STEM images contain cross sections of toner particles of various sizes, and we select cross sections of toner particles whose major axis length is 80% or more of the volume average particle size of the toner particles, and then randomly select 200 cross sections of toner particles from these and observe them. The reason for selecting a cross section whose major axis length is 80% or more of the volume average particle diameter is that a cross section whose major axis length is less than 80% of the volume average particle diameter is predicted to be a cross section of the edge of a toner particle, and the cross section of the edge of a toner particle does not well reflect the state of the domains within the toner particle. In the present disclosure, the major axis length is the length of the longest straight line among all straight lines connecting two points on the contour line.

[0032] The average major axis length Dt of the toner particles is the arithmetic mean of the major axis lengths of 200 toner particles. The average major axis length Dw of the release agent domains is the arithmetic mean of the major axis lengths of all the release agent domains contained in 200 toner particles (i.e., the release agent domains are measured regardless of whether they contain titanium oxide inside). The average major axis length Dp of titanium oxide in the release agent domain is the arithmetic mean of the major axis lengths of titanium oxide particles when all titanium oxide particles included in the release agent domain (i.e., titanium oxide particles that are in the release agent domain but not in contact with the outline of the release agent domain) are measured in 200 toner particles. The inclusion ratio of titanium oxide is the percentage of titanium oxide that is included in the release agent domain (i.e., titanium oxide that is within the release agent domain but not in contact with the outline of the release agent domain), with all titanium oxide contained in 200 toner particles as the parent population.

[0033] In the white toner according to this embodiment, the mass ratio of the release agent to titanium oxide contained in the toner particles (release agent / titanium oxide) is preferably 0.01 or more and 0.3 or less, more preferably 0.015 or more and 0.25 or less, and even more preferably 0.02 or more and 0.2 or less, from the viewpoint of balancing the release property, whiteness, and hiding property of the white image and suppressing the chalking phenomenon.

[0034] The toner according to this embodiment will be described in detail below.

[0035] The toner according to this embodiment is configured to contain toner particles and, if necessary, external additives.

[0036] [Toner particles] The toner particles contain a binder resin, a release agent, and titanium oxide, and may also contain other additives as required.

[0037] -Binder resin- Examples of binder resins include homopolymers of monomers such as styrenes (e.g., styrene, parachlorostyrene, α-methylstyrene, etc.), (meth)acrylic acid esters (e.g., methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, lauryl methacrylate, 2-ethylhexyl methacrylate, etc.), ethylenically unsaturated nitriles (e.g., acrylonitrile, methacrylonitrile, etc.), vinyl ethers (e.g., vinyl methyl ether, vinyl isobutyl ether, etc.), vinyl ketones (e.g., vinyl methyl ketone, vinyl ethyl ketone, vinyl isopropenyl ketone, etc.), and olefins (e.g., ethylene, propylene, butadiene, etc.), and vinyl resins made of copolymers of two or more of these monomers. Examples of the binder resin include non-vinyl resins such as epoxy resins, polyester resins, polyurethane resins, polyamide resins, cellulose resins, polyether resins, and modified rosin, mixtures of these with the vinyl resins, and graft polymers obtained by polymerizing vinyl monomers in the presence of these. These binder resins may be used alone or in combination of two or more.

[0038] As the binder resin, a polyester resin is preferable. Examples of polyester resins include known amorphous polyester resins. The polyester resin may be used in combination with a crystalline polyester resin. The crystalline polyester resin is preferably used in an amount of 2% by mass to 40% by mass (preferably 2% by mass to 20% by mass) of the total binder resin.

[0039] The "crystalline" nature of a resin refers to the presence of a clear endothermic peak rather than a stepwise change in the amount of heat absorbed in differential scanning calorimetry (DSC). Specifically, this refers to the half-width of the endothermic peak being within 10°C when measured at a heating rate of 10°C / min. The term "amorphous" for a resin means that the half-width exceeds 10°C, that the endothermic amount exhibits a stepwise change, or that no clear endothermic peak is observed.

[0040] Amorphous polyester resin The amorphous polyester resin may be, for example, a condensation polymer of a polycarboxylic acid and a polyhydric alcohol. As the amorphous polyester resin, a commercially available product or a synthesized product may be used.

[0041] Examples of polycarboxylic acids include aliphatic dicarboxylic acids (such as oxalic acid, malonic acid, maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, succinic acid, alkenylsuccinic acid, adipic acid, and sebacic acid), alicyclic dicarboxylic acids (such as cyclohexanedicarboxylic acid), aromatic dicarboxylic acids (such as terephthalic acid, isophthalic acid, phthalic acid, and naphthalenedicarboxylic acid), anhydrides thereof, and lower alkyl esters thereof (e.g., having 1 to 5 carbon atoms). Among these, aromatic dicarboxylic acids are preferred as polycarboxylic acids. The polycarboxylic acid may be a trivalent or higher carboxylic acid having a crosslinked or branched structure in combination with a dicarboxylic acid. Examples of the trivalent or higher carboxylic acid include trimellitic acid, pyromellitic acid, anhydrides thereof, and lower alkyl esters thereof (e.g., having 1 to 5 carbon atoms). The polycarboxylic acids may be used alone or in combination of two or more.

[0042] Examples of polyhydric alcohols include aliphatic diols (e.g., ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, butanediol, hexanediol, neopentyl glycol, etc.), alicyclic diols (e.g., cyclohexanediol, cyclohexanedimethanol, hydrogenated bisphenol A, etc.), and aromatic diols (e.g., ethylene oxide adducts of bisphenol A, propylene oxide adducts of bisphenol A, etc.). Among these, preferred polyhydric alcohols are aromatic diols and alicyclic diols, and more preferred are aromatic diols. As the polyhydric alcohol, a trihydric or higher polyhydric alcohol having a crosslinked or branched structure may be used in combination with the diol. Examples of trihydric or higher polyhydric alcohols include glycerin, trimethylolpropane, and pentaerythritol. The polyhydric alcohols may be used alone or in combination of two or more.

[0043] The glass transition temperature (Tg) of the amorphous polyester resin is preferably from 50° C. to 80° C., more preferably from 50° C. to 65° C. The glass transition temperature is determined from a DSC curve obtained by differential scanning calorimetry (DSC), and more specifically, is determined from the “extrapolated glass transition onset temperature” described in the method for determining glass transition temperature in JIS K7121-1987 “Method for measuring transition temperature of plastics.”

[0044] The weight average molecular weight (Mw) of the amorphous polyester resin is preferably 5,000 or more and 1,000,000 or less, and more preferably 7,000 or more and 500,000 or less. The number average molecular weight (Mn) of the amorphous polyester resin is preferably 2,000 or more and 100,000 or less. The molecular weight distribution Mw / Mn of the amorphous polyester resin is preferably 1.5 or more and 100 or less, more preferably 2 or more and 60 or less. The weight-average molecular weight and number-average molecular weight are measured by gel permeation chromatography (GPC). Molecular weight measurement by GPC is performed using a Tosoh GPC HLC-8120GPC measuring device and a Tosoh TSKgel SuperHM-M (15 cm) column in THF solvent. The weight-average molecular weight and number-average molecular weight are calculated from the measurement results using a molecular weight calibration curve prepared with monodisperse polystyrene standard samples.

[0045] Crystalline polyester resin Examples of the crystalline polyester resin include a polycondensate of a polycarboxylic acid and a polyhydric alcohol. As the crystalline polyester resin, a commercially available product may be used, or a synthesized product may be used. Since the crystalline polyester resin easily forms a crystalline structure, a polycondensate using a linear aliphatic polymerizable monomer is preferred over a polymerizable monomer having an aromatic ring.

[0046] Examples of polycarboxylic acids include aliphatic dicarboxylic acids (e.g., oxalic acid, succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, 1,9-nonanedicarboxylic acid, 1,10-decanedicarboxylic acid, 1,12-dodecanedicarboxylic acid, 1,14-tetradecanedicarboxylic acid, 1,18-octadecanedicarboxylic acid, etc.), aromatic dicarboxylic acids (e.g., dibasic acids such as phthalic acid, isophthalic acid, terephthalic acid, and naphthalene-2,6-dicarboxylic acid), anhydrides thereof, and lower alkyl esters thereof (e.g., having 1 to 5 carbon atoms). The polycarboxylic acid may be a tricarboxylic or higher carboxylic acid having a crosslinked or branched structure in combination with a dicarboxylic acid. Examples of the tricarboxylic acid include aromatic carboxylic acids (e.g., 1,2,3-benzenetricarboxylic acid, 1,2,4-benzenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, etc.), anhydrides thereof, and lower alkyl esters thereof (e.g., having 1 to 5 carbon atoms). As the polycarboxylic acid, a dicarboxylic acid having a sulfonic acid group and a dicarboxylic acid having an ethylenic double bond may be used in combination with these dicarboxylic acids. The polycarboxylic acids may be used alone or in combination of two or more.

[0047] Examples of polyhydric alcohols include aliphatic diols (for example, straight-chain aliphatic diols having 7 to 20 carbon atoms in the main chain). Examples of aliphatic diols include ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol, 1,13-tridecanediol, 1,14-tetradecanediol, 1,18-octadecanediol, and 1,14-eicosanedecanediol. Among these, 1,8-octanediol, 1,9-nonanediol, and 1,10-decanediol are preferred as aliphatic diols. The polyhydric alcohol may be a trihydric or higher alcohol having a crosslinked or branched structure, such as glycerin, trimethylolethane, trimethylolpropane, or pentaerythritol, in combination with the diol. The polyhydric alcohols may be used alone or in combination of two or more.

[0048] Here, the polyhydric alcohol has an aliphatic diol content of 80 mol % or more, preferably 90 mol % or more.

[0049] The melting temperature of the crystalline polyester resin is preferably 50° C. or higher and 100° C. or lower, more preferably 55° C. or higher and 90° C. or lower, and even more preferably 60° C. or higher and 85° C. or lower. The melting temperature is determined from a DSC curve obtained by differential scanning calorimetry (DSC) as the "melting peak temperature" described in the method for determining the melting temperature in JIS K7121-1987 "Method for measuring transition temperatures of plastics."

[0050] The weight average molecular weight (Mw) of the crystalline polyester resin is preferably 6,000 or more and 35,000 or less.

[0051] The content of the binder resin is preferably 40% by mass to 70% by mass, more preferably 50% by mass to 65% by mass, and even more preferably 60% by mass to 60% by mass, based on the total mass of the toner particles.

[0052] -Mold release agent- Examples of release agents include hydrocarbon waxes, natural waxes such as carnauba wax, rice wax, and candelilla wax, synthetic or mineral / petroleum waxes such as montan wax, and ester waxes such as fatty acid esters and montanic acid esters, but are not limited thereto.

[0053] As the release agent, ester wax is preferred, and fatty acid ester wax is more preferred, from the viewpoint of having a high affinity with titanium oxide and easily incorporating titanium oxide.

[0054] The melting temperature of the release agent is preferably from 50° C. to 110° C., more preferably from 60° C. to 100° C. The melting temperature of the release agent is determined from a DSC curve obtained by differential scanning calorimetry in accordance with JIS K7121-1987 "Method for measuring transition temperature of plastics" and "Peak melting temperature".

[0055] The content of the release agent is preferably from 0.3 to 20% by mass, more preferably from 0.5 to 15% by mass, and even more preferably from 0.7 to 10% by mass, based on the total mass of the toner particles.

[0056] -Titanium oxide- Titanium oxide (TiO2) is a particulate pigment that imparts white color to toner. The crystalline structure of titanium oxide may be anatase, rutile, brookite, a mixed crystal structure of these, or an amorphous structure.

[0057] Examples of methods for producing titanium oxide include the chlorine method (gas phase method), the sulfuric acid method (liquid phase method), the sol-gel method using titanium alkoxide, and a method of baking metatitanic acid. An example of the chlorine process (gas phase process) is as follows: Rutile ore, the raw material, is reacted with coke and chlorine to form gaseous titanium tetrachloride, which is then cooled to obtain liquid titanium tetrachloride. Next, the gaseous or vaporous titanium tetrachloride is reacted with oxygen gas at high temperature, and the chlorine gas is separated to obtain titanium oxide.

[0058] From the viewpoints of dispersibility in binder resin and weather resistance of white images, titanium oxide is preferably titanium oxide whose surface has been treated with at least one of an inorganic compound and an organic compound. The surface treatment method and surface treatment agent for titanium oxide may be selected from known methods and treatment agents from the viewpoints of dispersibility in the binder resin, weather resistance of the white image, etc. Surface treatment methods for titanium oxide are roughly divided into wet treatments and dry treatments. The wet treatment is a treatment method in which a surface treatment agent is added to a slurry in which titanium oxide is dispersed in an aqueous solvent or an organic solvent, and the surface of the titanium oxide is coated with the slurry. Dry treatment is a treatment method in which the vapor or gas of a surface treatment agent is applied to flowing titanium oxide to coat the surface of the titanium oxide. Examples of surface treatment agents for titanium oxide include metal oxides containing Al, metal oxides containing Si, metal oxides containing Zr, fatty acids, silicones, and the like.

[0059] Titanium oxide is preferably titanium oxide coated with alumina (Al2O3) from the viewpoint of being easily included in the release agent domain. Titanium oxide coated with alumina may have other chemical substances (e.g., silica, zirconia, fatty acid, silicone) disposed between the alumina and titanium oxide, and it is preferable that the alumina is on the outermost surface. In the present disclosure, "coated" refers to adhesion to at least a portion of the surface of an object.

[0060] The average major axis length of titanium oxide is preferably 100 nm or more and 300 nm or less, more preferably 150 nm or more and 250 nm or less, and even more preferably 180 nm or more and 220 nm or less, from the viewpoint of being easily included in the domain of the release agent.

[0061] The BET specific surface area of ​​titanium oxide is set to 4m from the viewpoint of improving dispersibility in the release agent. 2 / g or more is preferable, and 6m 2 / g or more is more preferable. The BET specific surface area of ​​titanium oxide is 12m from the viewpoint of excellent whiteness. 2 / g or less is preferable, and 10m 2 / g or less is more preferable.

[0062] The BET specific surface area of ​​titanium oxide is determined by the following measurement method. If the white toner contains external additives, the white toner is placed in a 5% by weight aqueous solution of sodium alkylbenzene sulfonate and stirred. Next, ultrasonic waves are applied using a bath-type ultrasonic disperser to liberate the external additives from the surface of the toner particles. The toner particles are then settled by centrifugation, and the supernatant liquid containing the liberated and dispersed external additives is removed. The process from ultrasonic treatment to supernatant removal is repeated three times. The toner particles are then suspended in toluene to dissolve the binder resin and release agent, and the suspension is filtered for solid-liquid separation. The solid is thoroughly washed with water and then dried to obtain a powder. This powder is used as the sample for measuring the BET specific surface area. The BET specific surface area is a value measured by precisely weighing 1 g of a sample and measuring it with a BET specific surface area meter (for example, SA3100 manufactured by Beckman Coulter) by the BET multipoint method using nitrogen gas.

[0063] The toner particles may contain a white pigment other than titanium oxide. Examples of other white pigments include zinc oxide, silicon dioxide, alumina, calcium carbonate, aluminum hydroxide, satin white, talc, calcium sulfate, magnesium oxide, magnesium carbonate, white carbon, kaolin, aluminosilicate, sericite, bentonite, and smectite. These white pigments may be used alone or in combination of two or more. These white pigments may be added to the toner particles for purposes other than coloring (for example, toner charge control).

[0064] The content of titanium oxide contained in the toner particles is preferably 85% by mass or more and 100% by mass or less, more preferably 90% by mass or more and 100% by mass or less, and even more preferably 95% by mass or more and 100% by mass or less, based on the total amount of the white pigment contained in the toner particles.

[0065] From the viewpoint of whiteness and hiding power, the content of titanium oxide contained in the toner particles is preferably 30% by mass or more and 70% by mass or less, more preferably 40% by mass or more and 70% by mass or less, and even more preferably 50% by mass or more and 70% by mass or less, based on the total mass of the toner particles.

[0066] -Other additives- Examples of other additives include known additives such as magnetic materials, charge control agents, inorganic powders, etc. These additives are contained in the toner particles as internal additives.

[0067] -Characteristics of toner particles, etc.- The toner particles may be toner particles of a single layer structure, or may be toner particles of a so-called core-shell structure composed of a core (core particle) and a coating layer (shell layer) that covers the core. The toner particles of the core-shell structure may be composed of, for example, a core containing a binder resin, a release agent, and titanium oxide, and a coating layer containing a binder resin.

[0068] The volume average particle size (D50v) of the toner particles is preferably 2 μm or more and 10 μm or less, and more preferably 4 μm or more and 8 μm or less.

[0069] The various average particle sizes and particle size distribution indices of the toner particles are measured using a Coulter Multisizer II (manufactured by Beckman Coulter), and the electrolyte is measured using an ISOTON-II (manufactured by Beckman Coulter). For the measurement, 0.5 mg to 50 mg of the sample to be measured is added to 2 ml of a 5 mass % aqueous solution of a surfactant (preferably sodium alkylbenzene sulfonate) as a dispersant, and this is then added to 100 ml to 150 ml of the electrolyte. The electrolyte solution containing the suspended sample is dispersed in an ultrasonic disperser for 1 minute, and the particle size distribution of particles in the range of 2 μm to 60 μm is measured using a Coulter Multisizer II with an aperture diameter of 100 μm. The number of particles sampled is 50,000. Based on the particle size distribution measured, cumulative distributions of volume and number are drawn for each divided particle size range (channel) from the smallest diameter side, and the particle size at 16% of the cumulative total is defined as the volume particle size D16v, the number particle size D16p, the particle size at 50% of the cumulative total as the volume average particle size D50v, the cumulative number average particle size D50p, and the particle size at 84% of the cumulative total as the volume particle size D84v and the number particle size D84p. Using these, the volumetric particle size distribution index (GSDv) is (D84v / D16v) 1 / 2 , the number particle size distribution index (GSDp) is (D84p / D16p) 1 / 2 It is calculated as:

[0070] The average circularity of the toner particles is preferably 0.94 or more and 1.00 or less, and more preferably 0.95 or more and 0.98 or less.

[0071] The average circularity of toner particles is calculated by (circular equivalent perimeter) / (perimeter) [(perimeter of a circle having the same projected area as the particle image) / (perimeter of the particle projected image)]. Specifically, this value is measured by the following method. First, the toner particles to be measured are sucked and collected, forming a flat flow, and a still image of the particles is captured by instantaneously activating a strobe light, and the particle image is analyzed using a flow-type particle image analyzer (FPIA-3000 manufactured by Sysmex Corporation).The number of samples to be sampled when calculating the average circularity is 3,500. When the toner contains external additives, the toner (developer) to be measured is dispersed in water containing a surfactant, and then ultrasonic treatment is performed to obtain toner particles from which the external additives have been removed.

[0072] [External additives] Examples of external additives include inorganic particles, such as SiO2, TiO2, Al2O3, CuO, ZnO, SnO2, CeO2, Fe2O3, MgO, BaO, CaO, K2O, Na2O, ZrO2, CaO·SiO2, and K2O·(TiO2). n , Al2O3·2SiO2, CaCO3, MgCO3, BaSO4, MgSO4, etc.

[0073] The surfaces of inorganic particles as external additives are preferably subjected to a hydrophobic treatment. The hydrophobic treatment is carried out, for example, by immersing the inorganic particles in a hydrophobic treatment agent. The hydrophobic treatment agent is not particularly limited, and examples thereof include silane coupling agents, silicone oils, titanate coupling agents, and aluminum coupling agents. These may be used alone or in combination of two or more. The amount of the hydrophobic treatment agent is usually, for example, 1 part by mass or more and 10 parts by mass or less per 100 parts by mass of the inorganic particles.

[0074] Examples of external additives include resin particles (resin particles such as polystyrene, polymethyl methacrylate, and melamine resin), cleaning agents (for example, metal salts of higher fatty acids such as zinc stearate, and particles of fluorine-based polymers).

[0075] The amount of the external additive added is preferably 0.01% by mass or more and 5% by mass or less, and more preferably 0.01% by mass or more and 2.0% by mass or less, based on the toner particles.

[0076] [White toner manufacturing method] The white toner according to this embodiment is obtained by producing toner particles and then externally adding an external additive to the toner particles.

[0077] The toner particles may be produced by any of a dry production method (for example, a kneading and pulverization method) and a wet production method (for example, an aggregation and coalescence method, a suspension polymerization method, a dissolution and suspension method). There are no particular limitations on these production methods, and any known production method may be used. Among these, it is preferable to obtain toner particles by the aggregation and coalescence method.

[0078] When the toner particles are produced by the aggregation and coalescence method, the following production method is preferred from the viewpoint of including titanium oxide in the domains of the release agent. a step of preparing a resin particle dispersion in which resin particles to be a binder resin are dispersed (a resin particle dispersion preparation step); preparing a titanium oxide-containing release agent particle dispersion liquid in which particles containing a release agent and titanium oxide are dispersed; a step of aggregating the mixed particles in a mixed dispersion obtained by mixing a resin particle dispersion and a titanium oxide-containing release agent particle dispersion to form aggregated particles (aggregated particle forming step); a step of heating the aggregated particle dispersion in which the aggregated particles are dispersed to fuse and coalesce the aggregated particles to form toner particles (fusion and coalescence step).

[0079] -Resin particle dispersion preparation process- The resin particle dispersion is prepared, for example, by dispersing resin particles in a dispersion medium using a surfactant.

[0080] Examples of the dispersion medium used in the resin particle dispersion include aqueous media. Examples of aqueous media include water such as distilled water and ion-exchanged water, alcohols, etc. These may be used alone or in combination of two or more.

[0081] Examples of surfactants include anionic surfactants such as sulfate ester salts, sulfonate salts, phosphate esters, and soaps; cationic surfactants such as amine salts and quaternary ammonium salts; and nonionic surfactants such as polyethylene glycols, alkylphenol ethylene oxide adducts, and polyhydric alcohols. Among these, anionic surfactants and cationic surfactants are particularly preferred. Nonionic surfactants may be used in combination with anionic surfactants or cationic surfactants. The surfactants may be used alone or in combination of two or more.

[0082] In a resin particle dispersion, resin particles can be dispersed in a dispersion medium by common dispersion methods such as a rotary shear homogenizer, a ball mill with media, a sand mill, or a Dynomill. Depending on the type of resin particles, the resin particles may be dispersed in a dispersion medium by a phase inversion emulsification method. The phase inversion emulsification method involves dissolving the resin to be dispersed in a hydrophobic organic solvent in which the resin is soluble, neutralizing the organic continuous phase (O phase) by adding a base, and then introducing an aqueous medium (W phase) to invert the phase from W / O to O / W, thereby dispersing the resin in particulate form in the aqueous medium.

[0083] The volume average particle size of the resin particles dispersed in the resin particle dispersion is, for example, preferably 0.01 μm to 1 μm, more preferably 0.08 μm to 0.8 μm, and even more preferably 0.1 μm to 0.6 μm. The volume average particle size of the resin particles is measured using a particle size distribution obtained by measurement with a laser diffraction particle size distribution analyzer (e.g., HORIBA LA-700), and the cumulative distribution for the volume of the divided particle size range (channel) is calculated from the smallest particle size side, and the particle size at which the cumulative 50% of all particles is determined as the volume average particle size D50v. The volume average particle sizes of particles in other dispersions are also measured in the same way.

[0084] The content of resin particles contained in the resin particle dispersion is preferably 5% by mass or more and 50% by mass or less, and more preferably 10% by mass or more and 40% by mass or less.

[0085] -Step of preparing a titanium oxide-containing release agent particle dispersion- First, the release agent and titanium oxide are kneaded while being heated to obtain a kneaded product in which titanium oxide is mixed into the release agent. The kneaded product is cooled and solidified, and the solidified kneaded product is coarsely pulverized in a coarse pulverizer (e.g., a hammer mill or a cutter mill) to obtain a coarsely pulverized product. The coarsely pulverized product is then finely pulverized in a fine pulverizer (e.g., a jet mill) to obtain a finely pulverized product.

[0086] Next, the finely pulverized material, an aqueous medium, and a surfactant are mixed and dispersed in a disperser (e.g., a pressure discharge homogenizer or a rotary shear homogenizer). The aqueous medium and surfactant are the same as those described above for the resin particle dispersion.

[0087] The volume average particle size of the particles dispersed in the titanium oxide-containing release agent particle dispersion liquid is preferably 0.2 μm or more and 1 μm or less. The content of particles contained in the titanium oxide-containing release agent particle dispersion is preferably 5% by mass or more and 50% by mass or less, and more preferably 10% by mass or more and 40% by mass or less.

[0088] -Agglomerated particle formation process- Next, the resin particle dispersion liquid and the titanium oxide-containing release agent particle dispersion liquid are mixed together, and the resin particles and the titanium oxide-containing release agent particle dispersion liquid are hetero-aggregated in the mixed dispersion liquid to form aggregated particles containing the resin particles and the titanium oxide-containing release agent particles and having a diameter close to that of the target toner particles.

[0089] Specifically, for example, an aggregating agent is added to the mixed dispersion, and the pH of the mixed dispersion is adjusted to be acidic (for example, pH 2 or higher and 5 or lower), and a dispersion stabilizer is added as necessary.Then, the mixed dispersion is heated to a temperature close to the glass transition temperature of the resin particles (specifically, for example, the glass transition temperature of the resin particles minus 30°C or higher and the glass transition temperature minus 10°C or lower), causing the particles dispersed in the mixed dispersion to aggregate and form aggregated particles. In the aggregate particle formation step, for example, the mixed dispersion may be stirred with a rotary shear homogenizer, an aggregating agent may be added at room temperature (e.g., 25°C), the pH of the mixed dispersion may be adjusted to an acidic value (e.g., pH 2 or more and 5 or less), a dispersion stabilizer may be added as needed, and then the mixture may be heated.

[0090] Examples of the flocculant include a surfactant having a polarity opposite to that of the surfactant contained in the mixed dispersion, an inorganic metal salt, and a divalent or higher metal complex. When a metal complex is used as the flocculant, the amount of surfactant used can be reduced, and the charging characteristics can be improved. If necessary, an additive that forms a complex or a similar bond with the metal ions of the flocculant may be used together with the flocculant, and a chelating agent is preferably used as this additive.

[0091] Examples of inorganic metal salts include metal salts such as calcium chloride, calcium nitrate, barium chloride, magnesium chloride, zinc chloride, aluminum chloride, and aluminum sulfate; and inorganic metal salt polymers such as polyaluminum chloride, polyaluminum hydroxide, and calcium polysulfide. The chelating agent may be a water-soluble chelating agent, such as hydroxycarboxylic acid (e.g., tartaric acid, citric acid, gluconic acid), or aminocarboxylic acid (e.g., iminodiacetic acid (IDA), nitrilotriacetic acid (NTA), or ethylenediaminetetraacetic acid (EDTA). The amount of the chelating agent added is preferably 0.01 parts by mass or more and 5.0 parts by mass or less, and more preferably 0.1 parts by mass or more and less than 3.0 parts by mass, relative to 100 parts by mass of the resin particles.

[0092] -Fusion / coalescence process- Next, the aggregated particle dispersion liquid in which the aggregated particles are dispersed is heated, for example, to a temperature equal to or higher than the glass transition temperature of the resin particles (for example, a temperature 10°C to 30°C higher than the glass transition temperature of the resin particles) to fuse and coalesce the aggregated particles, thereby forming toner particles.

[0093] Through the above steps, toner particles are obtained. After obtaining the aggregated particle dispersion in which the aggregated particles are dispersed, the toner particles may be produced through the following steps: a step of further mixing the aggregated particle dispersion with a resin particle dispersion, and agglomerating the aggregated particles so that the resin particle dispersion adheres to the surfaces of the aggregated particles to form second aggregated particles; and a step of heating the second aggregated particle dispersion in which the second aggregated particles are dispersed to fuse and coalesce the second aggregated particles to form toner particles having a core-shell structure.

[0094] After the fusion and coalescence process is completed, the toner particles in the dispersion are subjected to a known washing process, solid-liquid separation process, and drying process to obtain dried toner particles. In the washing process, from the viewpoint of chargeability, it is preferable to perform sufficient substitution washing with ion-exchanged water. In the solid-liquid separation process, from the viewpoint of productivity, it is preferable to perform suction filtration, pressure filtration, etc. In the drying process, from the viewpoint of productivity, it is preferable to perform freeze drying, flash drying, fluidized drying, vibration-type fluidized drying, etc.

[0095] The toner according to this embodiment is produced by, for example, adding an external additive to the obtained dry toner particles and mixing them. The mixing can be carried out using, for example, a V blender, a Henschel mixer, a Loedige mixer, or the like. Furthermore, if necessary, coarse particles may be removed from the toner using a vibrating sieve, an air sieve, or the like.

[0096] <Electrostatic image developer> The electrostatic image developer according to this embodiment contains at least the white toner according to this embodiment. The electrostatic image developer according to this embodiment may be a one-component developer containing only the white toner according to this embodiment, or may be a two-component developer in which the white toner is mixed with a carrier.

[0097] The carrier is not particularly limited, and known carriers can be used. Examples of the carrier include a coated carrier in which the surface of a core material made of magnetic powder is coated with a resin; a magnetic powder dispersion carrier in which magnetic powder is dispersed in a matrix resin; and a resin-impregnated carrier in which porous magnetic powder is impregnated with a resin. The magnetic powder dispersion carrier or the resin-impregnated carrier may be a carrier in which the constituent particles of the carrier are used as a core material and the surface of the core material is coated with a resin.

[0098] Examples of magnetic powder include magnetic metals such as iron, nickel, and cobalt; and magnetic oxides such as ferrite and magnetite.

[0099] Examples of coating resins and matrix resins include polyethylene, polypropylene, polystyrene, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl ether, polyvinyl ketone, vinyl chloride-vinyl acetate copolymer, styrene-acrylic acid ester copolymer, straight silicone resins containing organosiloxane bonds or modified products thereof, fluororesin, polyester, polycarbonate, phenolic resin, and epoxy resin. The coating resin and matrix resin may contain additives such as conductive particles. Examples of conductive particles include particles of metals such as gold, silver, and copper, carbon black, titanium oxide, zinc oxide, tin oxide, barium sulfate, aluminum borate, and potassium titanate.

[0100] Examples of methods for coating the surface of a core material with a resin include a method of coating with a coating layer-forming solution prepared by dissolving the coating resin and various additives (used as needed) in an appropriate solvent. The solvent is not particularly limited and may be selected taking into consideration the type of resin used, its applicability, and the like. Specific resin coating methods include an immersion method in which the core material is immersed in the coating layer-forming solution; a spray method in which the coating layer-forming solution is sprayed onto the core material surface; a fluidized bed method in which the coating layer-forming solution is sprayed onto the core material while suspended in flowing air; and a kneader coater method in which the carrier core material and the coating layer-forming solution are mixed in a kneader coater and then the solvent is removed.

[0101] The mixing ratio (mass ratio) of the toner and the carrier in the two-component developer is preferably toner:carrier=1:100 to 30:100, and more preferably 3:100 to 20:100.

[0102] <Image forming device, image forming method> The image forming apparatus according to the present embodiment includes an image carrier, a charging unit that charges the surface of the image carrier, an electrostatic image forming unit that forms an electrostatic image on the surface of the charged image carrier, a developing unit that contains an electrostatic image developer and develops the electrostatic image formed on the surface of the image carrier as a toner image using the electrostatic image developer, a transfer unit that transfers the toner image formed on the surface of the image carrier to the surface of a recording medium, and a fixing unit that fixes the toner image transferred to the surface of the recording medium. The electrostatic image developer according to the present embodiment is used as the electrostatic image developer.

[0103] The image forming apparatus according to this embodiment carries out an image forming method (the image forming method according to this embodiment) that includes a charging step of charging the surface of an image carrier, an electrostatic image forming step of forming an electrostatic image on the surface of the charged image carrier, a developing step of developing the electrostatic image formed on the surface of the image carrier as a toner image using the electrostatic image developer according to this embodiment, a transfer step of transferring the toner image formed on the surface of the image carrier to the surface of a recording medium, and a fixing step of fixing the toner image transferred to the surface of the recording medium.

[0104] The image forming apparatus according to the present embodiment may be any of known image forming apparatuses, such as a direct transfer type apparatus that directly transfers a toner image formed on the surface of an image carrier to a recording medium; an intermediate transfer type apparatus that primarily transfers a toner image formed on the surface of an image carrier to the surface of an intermediate transfer medium, and then secondarily transfers the toner image transferred to the surface of the intermediate transfer medium to the surface of a recording medium; an apparatus equipped with a cleaning means that cleans the surface of the image carrier after the transfer of the toner image but before charging; and an apparatus equipped with a discharging means that irradiates the surface of the image carrier with discharging light to discharge it after the transfer of the toner image but before charging.

[0105] When the image forming apparatus according to the present embodiment is an apparatus of the intermediate transfer type, the transfer means is configured to have, for example, an intermediate transfer body onto whose surface a toner image is transferred, a primary transfer means for primarily transferring the toner image formed on the surface of the image carrier onto the surface of the intermediate transfer body, and a secondary transfer means for secondarily transferring the toner image transferred onto the surface of the intermediate transfer body onto the surface of the recording medium.

[0106] In the image forming apparatus according to the present embodiment, for example, the portion including the developing means may have a cartridge structure (process cartridge) that is detachably attached to the image forming apparatus. As the process cartridge, for example, a process cartridge that contains the electrostatic image developer according to the present embodiment and is equipped with the developing means is preferably used.

[0107] The image forming apparatus according to this embodiment may be an image forming apparatus that further uses at least one toner selected from yellow toner, magenta toner, cyan toner, and black toner in addition to the white toner according to this embodiment.

[0108] An example of an image forming apparatus according to the present embodiment will be described below, but the present invention is not limited to this. In the following description, the main parts shown in the drawings will be described, and the description of the rest will be omitted.

[0109] FIG. 1 is a schematic diagram showing the configuration of an image forming apparatus according to this embodiment, and is a diagram showing a five-tandem type and intermediate transfer type image forming apparatus. The image forming apparatus shown in Figure 1 includes first through fifth electrophotographic image forming units 10Y, 10M, 10C, 10K, and 10W (image forming means) that output images in the colors yellow (Y), magenta (M), cyan (C), black (K), and white (W) based on color-separated image data. These image forming units (hereinafter sometimes simply referred to as "units") 10Y, 10M, 10C, 10K, and 10W are arranged side by side horizontally spaced a predetermined distance apart from one another. These units 10Y, 10M, 10C, 10K, and 10W may be process cartridges that are detachably attached to the image forming apparatus.

[0110] An intermediate transfer belt (an example of an intermediate transfer body) 20 is provided below each of the units 10Y, 10M, 10C, 10K, and 10W and extends through each unit. The intermediate transfer belt 20 is provided wrapped around a drive roll 22, a support roll 23, and an opposing roll 24, which are in contact with the inner surface of the intermediate transfer belt 20, and runs in a direction from the first unit 10Y to the fifth unit 10W. An intermediate transfer body cleaning device (an example of an intermediate transfer body cleaning means) 21 is provided on the image bearing surface side of the intermediate transfer belt 20, facing the drive roll 22.

[0111] The intermediate transfer belt 20 is, for example, a laminate of a base layer and a surface layer disposed on the outer peripheral surface of the base layer. The base layer contains, for example, a resin such as polyimide resin, polyamide resin, polyamideimide resin, polyetherester resin, polyarylate resin, or polyester resin, and a conductive agent. The surface layer contains, for example, at least one of the above resins, a fluororesin, and a conductive agent. The thickness of the intermediate transfer belt 20 is, for example, 50 μm or more and 100 μm or less.

[0112] The developing devices (examples of developing means) 4Y, 4M, 4C, 4K, and 4W of each unit 10Y, 10M, 10C, 10K, and 10W are supplied with yellow, magenta, cyan, black, and white toner contained in toner cartridges 8Y, 8M, 8C, 8K, and 8W, respectively.

[0113] Since the first to fifth units 10Y, 10M, 10C, 10K, and 10W have the same configuration, operation, and function, we will explain here the first unit 10Y, which forms a yellow image and is arranged upstream in the direction of travel of the intermediate transfer belt.

[0114] The first unit 10Y has a photoconductor 1Y that acts as an image carrier. Around the photoconductor 1Y, there are arranged in this order: a charging roll (an example of a charging means) 2Y that charges the surface of the photoconductor 1Y to a predetermined potential; an exposure device (an example of an electrostatic image forming means) 3Y that exposes the charged surface to a laser beam based on a color-separated image signal to form an electrostatic image; a developing device (an example of a developing means) 4Y that supplies toner to the electrostatic image to develop it; a primary transfer roll (an example of a primary transfer means) 5Y that transfers the developed toner image onto the intermediate transfer belt 20; and a photoconductor cleaning device (an example of an image carrier cleaning means) 6Y that removes toner remaining on the surface of the photoconductor 1Y after the primary transfer.

[0115] The primary transfer roll 5Y is disposed inside the intermediate transfer belt 20 and is provided at a position facing the photoreceptor 1Y. A bias power supply (not shown) that applies a primary transfer bias is connected to the primary transfer rolls 5Y, 5M, 5C, 5K, and 5W of each unit. Each bias power supply changes the value of the transfer bias applied to each primary transfer roll under the control of a control unit (not shown).

[0116] The operation of forming a yellow image in first unit 10Y will be described below. First, prior to operation, the surface of the photosensitive member 1Y is charged to a potential of −600V to −800V by the charging roll 2Y. The photoconductor 1Y has conductivity (for example, a volume resistivity of 1×10 at 20°C). -6The photosensitive layer is formed by laminating a photosensitive layer on a substrate with a resistivity of Ωcm or less. This photosensitive layer is normally highly resistive (the resistance of ordinary resins), but when irradiated with a laser beam, the resistivity of the irradiated portion changes. Therefore, the charged surface of the photosensitive element 1Y is irradiated with a laser beam from the exposure device 3Y in accordance with image data for yellow sent from a control unit (not shown). This forms an electrostatic charge image of a yellow image pattern on the surface of the photosensitive element 1Y.

[0117] An electrostatic image is an image formed on the surface of the photosensitive element 1Y by charging it; it is a so-called negative latent image formed when the resistivity of the irradiated portion of the photosensitive layer is reduced by the laser beam from the exposure device 3Y, causing the charged charges on the surface of the photosensitive element 1Y to flow, while the charges remain in the portions not irradiated by the laser beam. The electrostatic image formed on the photoreceptor 1Y rotates to a predetermined development position as the photoreceptor 1Y moves, and at this development position, the electrostatic image on the photoreceptor 1Y is developed into a toner image by the developing device 4Y and made visible.

[0118] The developing device 4Y contains an electrostatic image developer containing, for example, at least yellow toner and a carrier. The yellow toner is frictionally charged by being stirred inside the developing device 4Y, and is held on a developer roll (an example of a developer holder) with a charge of the same polarity (negative polarity) as the charge on the photoreceptor 1Y. As the surface of the photoreceptor 1Y passes through the developing device 4Y, the yellow toner electrostatically adheres to the discharged latent image portion on the surface of the photoreceptor 1Y, and the latent image is developed with the yellow toner. The photoreceptor 1Y on which the yellow toner image has been formed continues to travel at a predetermined speed, and the toner image developed on the photoreceptor 1Y is transported to a predetermined primary transfer position.

[0119] When the yellow toner image on the photoreceptor 1Y is transported to the primary transfer position, a primary transfer bias is applied to the primary transfer roll 5Y, and an electrostatic force from the photoreceptor 1Y to the primary transfer roll 5Y acts on the toner image, causing the toner image on the photoreceptor 1Y to be transferred onto the intermediate transfer belt 20. The transfer bias applied at this time has a (+) polarity opposite to the (-) polarity of the toner, and is controlled to, for example, +10 μA by a control unit (not shown) in the first unit 10Y.

[0120] After the toner image is transferred to the intermediate transfer belt 20, the photoreceptor 1Y continues to rotate and comes into contact with a cleaning blade provided on the photoreceptor cleaning device 6Y. The toner remaining on the photoreceptor 1Y is removed and collected by the photoreceptor cleaning device 6Y.

[0121] The primary transfer bias applied to the primary transfer rolls 5M, 5C, 5K, and 5W of the second unit 10M and subsequent units is also controlled in accordance with that of the first unit. In this way, the intermediate transfer belt 20 onto which the yellow toner image has been transferred by the first unit 10Y is conveyed sequentially through the second to fifth units 10M, 10C, 10K, and 10W, and the toner images of each color are superimposed and transferred.

[0122] The intermediate transfer belt 20, onto which the five-color toner images have been multiplex-transferred through the first to fifth units, reaches a secondary transfer section composed of the intermediate transfer belt 20, an opposing roll 24 in contact with the inner surface of the intermediate transfer belt, and a secondary transfer roll (an example of a secondary transfer means) 26 arranged on the image bearing surface side of the intermediate transfer belt 20. Meanwhile, recording paper (an example of a recording medium) P is fed via a supply mechanism into the gap between the secondary transfer roll 26 and the intermediate transfer belt 20 at a predetermined timing, and a secondary transfer bias is applied to the opposing roll 24. The transfer bias applied at this time has a negative polarity, the same as the negative polarity of the toner. Electrostatic force from the intermediate transfer belt 20 toward the recording paper P acts on the toner image, transferring the toner image on the intermediate transfer belt 20 onto the recording paper P. The secondary transfer bias at this time is determined based on resistance detected by resistance detection means (not shown) that detects resistance in the secondary transfer section, and is voltage-controlled.

[0123] After transferring the toner image onto the recording paper P, the intermediate transfer belt 20 continues to run and comes into contact with a cleaning blade provided on the intermediate transfer body cleaning device 21. Toner remaining on the intermediate transfer belt 20 is removed and collected by the intermediate transfer body cleaning device 21.

[0124] The recording paper P onto which the toner image has been transferred is sent to the pressure contact portion (nip portion) of a pair of fixing rolls in a fixing device (an example of a fixing means) 28, where the toner image is fixed onto the recording paper P, forming a fixed image.

[0125] Examples of the recording paper P onto which the toner image is transferred include plain paper used in electrophotographic copiers, printers, etc. In addition to the recording paper P, examples of the recording medium include overhead projector sheets and the like. To further improve the smoothness of the image surface after fixing, it is preferable that the surface of the recording paper P is also smooth. For example, coated paper in which the surface of plain paper is coated with resin or the like, or art paper for printing, etc., is preferably used.

[0126] The recording paper P on which the color image has been fixed is conveyed toward the discharge section, and the series of color image forming operations is completed.

[0127] The image formation mode by the image forming apparatus shown in Fig. 1 is not limited to the above. A mode in which only the fifth unit 10W is operated to form a white image on one side of the recording paper P, and then the recording paper P is sent upstream in the direction of travel of the intermediate transfer belt, and the first unit 10Y to the fourth unit 10K are operated to form a color image on the white image on the recording paper P; A mode in which only the fifth unit 10W is operated to form a white image on one side of the recording paper P, and then the recording paper P is sent upstream in the direction of travel of the intermediate transfer belt, and the first unit 10Y to the fifth unit 10W are operated to form a white image and a color image on the white image on the recording paper P; An example of such a configuration is one in which only the fifth unit 10W is operated to form a white image on one side of the recording paper P, then the recording paper P is sent upstream in the direction of travel of the intermediate transfer belt, only the fifth unit 10W is operated again to overlay a white image on the white image on the recording paper P, the recording paper P is returned upstream in the direction of travel of the intermediate transfer belt, and the first unit 10Y to the fourth unit 10K are operated to form a color image on the multilayer white image on the recording paper P.

[0128] <Process cartridges, toner cartridges> The process cartridge according to this embodiment is a process cartridge that is detachably attached to an image forming apparatus and that contains the electrostatic image developer according to this embodiment and is equipped with a developing means that develops an electrostatic image formed on the surface of an image carrier using the electrostatic image developer into a toner image.

[0129] The process cartridge according to this embodiment is not limited to the above configuration, and may also be configured to include a developing means and, if necessary, at least one other means selected from an image carrier, a charging means, an electrostatic image forming means, and a transfer means.

[0130] An example of a process cartridge according to the present embodiment will be described below, but the present invention is not limited to this. In the following description, the main parts shown in the drawings will be described, and the description of the rest will be omitted.

[0131] FIG. 2 is a schematic diagram showing the configuration of the process cartridge according to the present embodiment. The process cartridge 200 shown in FIG. 2 is configured to integrally combine and hold a photosensitive member 107 (an example of an image carrier), a charging roll 108 (an example of a charging means) provided around the photosensitive member 107, a developing device 111 (an example of a developing means), and a photosensitive member cleaning device 113 (an example of an image carrier cleaning means), which are held by a housing 117 provided with, for example, mounting rails 116 and an opening 118 for exposure, and is formed into a cartridge. In FIG. 2, 109 denotes an exposure device (an example of an electrostatic image forming means), 112 denotes a transfer device (an example of a transfer means), 115 denotes a fixing device (an example of a fixing means), and 300 denotes recording paper (an example of a recording medium).

[0132] Next, the toner cartridge according to this embodiment will be described. The toner cartridge according to the present embodiment is a toner cartridge that contains the white toner according to the present embodiment and is detachably attached to an image forming apparatus. The toner cartridge contains replenishment toner to be supplied to a developing unit provided in the image forming apparatus.

[0133] The image forming apparatus shown in FIG. 1 has a configuration in which toner cartridges 8Y, 8M, 8C, 8K, and 8W are detachably mounted. The developing devices 4Y, 4M, 4C, 4K, and 4W are connected to toner cartridges corresponding to the respective colors via toner supply pipes (not shown). When the toner stored in a toner cartridge runs low, the toner cartridge is replaced. An example of a toner cartridge according to this embodiment is toner cartridge 8W, which contains white toner according to this embodiment. Toner cartridges 8Y, 8M, 8C, and 8K contain yellow, magenta, cyan, and black toner, respectively. [Example]

[0134] Hereinafter, the embodiments of the present invention will be described in detail with reference to examples, but the embodiments of the present invention are not limited to these examples. In the following description, unless otherwise specified, "parts" and "%" are by mass. All syntheses, processing, preparations, etc. were carried out at room temperature (25°C ± 3°C) unless otherwise noted.

[0135] <Preparation of Resin Particle Dispersion> [Amorphous polyester resin particle dispersion (A)] Terephthalic acid: 70 parts Fumaric acid: 30 parts Ethylene glycol: 41 parts 1,5-pentanediol: 48 parts The above materials were placed in a reactor equipped with a stirrer, nitrogen inlet tube, temperature sensor, and distillation column. The temperature was raised to 220°C over 1 hour under a nitrogen gas stream, and 1 part of titanium tetraethoxide was added for every 100 parts of the above materials. The temperature was raised to 240°C over 0.5 hours while distilling off the resulting water. The dehydration condensation reaction was continued at 240°C for 1 hour, and then the reaction mixture was cooled. Thus, an amorphous polyester resin (A) with a weight-average molecular weight of 96,000 and a glass transition temperature of 61°C was obtained.

[0136] A tank equipped with a temperature control device and nitrogen purge device was charged with 40 parts of ethyl acetate and 25 parts of 2-butanol to prepare a mixed solvent. Then, 100 parts of amorphous polyester resin (A) was gradually added and dissolved. A 10% aqueous ammonia solution (equivalent to three times the molar amount of the resin's acid value) was added and stirred for 30 minutes. The atmosphere inside the reaction vessel was then purged with dry nitrogen, the temperature was maintained at 40°C, and 400 parts of ion-exchanged water was added dropwise at a rate of 2 parts / min while stirring the mixed solution, resulting in emulsification. After the dropwise addition, the emulsion was returned to 25°C, and the solvent was removed under reduced pressure to obtain a resin particle dispersion containing resin particles with a volume average particle size of 160 nm. Ion-exchanged water was added to this resin particle dispersion to adjust the solids content to 20%, yielding amorphous polyester resin particle dispersion (A).

[0137] [Crystalline polyester resin particle dispersion (C)] 1,10-decanedicarboxylic acid: 265 parts 1,6-Hexanediol: 168 parts Dibutyltin oxide (catalyst): 0.3 parts The above materials were placed in a heated and dried reactor, the air in the reactor was replaced with nitrogen gas to create an inert atmosphere, and the mixture was stirred and refluxed at 180°C for 5 hours using mechanical stirring. The temperature was then gradually increased to 230°C under reduced pressure and stirred for 2 hours. When the mixture became viscous, it was air-cooled to stop the reaction. This yielded a crystalline polyester resin (C) with a weight-average molecular weight of 12,700 and a melting temperature of 73°C.

[0138] 90 parts of crystalline polyester resin (C), 1.8 parts of anionic surfactant (Dai-ichi Kogyo Seiyaku Co., Ltd., Neogen RK), and 210 parts of ion-exchanged water were mixed, heated to 120°C, and dispersed using a homogenizer (IKA Ultra-Turrax T50), followed by dispersion treatment using a pressure-discharge Gaulin homogenizer for 1 hour to obtain a resin particle dispersion containing resin particles with a volume average particle size of 160 nm. Ion-exchanged water was added to this resin particle dispersion to adjust the solid content to 20%, obtaining crystalline polyester resin particle dispersion (C).

[0139] <Preparation of titanium oxide-containing release agent particle dispersion> [Titanium oxide-containing release agent particle dispersion (1)] Ester wax (melting temperature 82°C, NOF Corporation): 16.0 parts Titanium oxide particles (surface-treated, commercially available, catalog value of particle size 200 nm): 84.0 parts The above materials were kneaded while being heated, and then cooled and solidified. The solidified kneaded material was coarsely pulverized with a cutter mill and then finely pulverized with a jet mill to obtain a titanium oxide-containing release agent powder.

[0140] Titanium oxide-containing release agent powder: 45 parts Ion-exchanged water: 200 parts Anionic surfactant (Dai-ichi Kogyo Seiyaku Co., Ltd., Neogen RK): 5 parts The above materials were mixed, heated to 120°C, and dispersed using a pressure discharge homogenizer (Gaulin Homogenizer manufactured by Gaulin Co., Ltd.) at a dispersion pressure of 5 MPa for 120 minutes, followed by 40 MPa for 360 minutes, and then cooled. Ion-exchanged water was added to adjust the solid content to 20%, yielding titanium oxide-containing release agent particle dispersion (1). The volume average particle size of the particles in the dispersion was 1800 nm.

[0141] [Titanium oxide-containing release agent particle dispersions (2) to (18)] Titanium oxide-containing release agent particle dispersions (2) to (18) were prepared in the same manner as in the preparation of titanium oxide-containing release agent particle dispersion (1), except that the type and amount of release agent, the particle size and amount of titanium oxide, and the volume average particle size of the particles in the dispersion were changed as shown in Table 1.

[0142] [Table 1]

[0143] <Preparation of Toner and Developer> [Example 1] - Toner particle production - Ion-exchanged water: 200 parts Amorphous polyester resin particle dispersion (A) (solid content 20%): 130 parts Crystalline polyester resin particle dispersion (C) (solid content 20%): 10 parts Titanium oxide-containing release agent particle dispersion (1) (solid content 20%): 200 parts Anionic surfactant (Dai-ichi Kogyo Seiyaku Co., Ltd., Neogen RK): 3.0 parts The above materials were placed in a stirring tank, and 0.1 N nitric acid was added to adjust the pH to 3.5. An aluminum sulfate aqueous solution was prepared by dissolving 2.5 parts of aluminum sulfate in 30 parts of ion-exchanged water, and this was added to the stirring tank. After dispersing at 30°C using a homogenizer (IKA Ultra Turrax T50), the mixture was heated to 45°C in a heating oil bath and maintained there until the volume average particle size of the aggregated particles reached 5.4 μm.

[0144] 15 parts of the amorphous polyester resin particle dispersion (A) (solid content 20%) was added to a stirring tank and held for 30 minutes. This was repeated a total of six times to obtain a dispersion containing second aggregated particles. 20 parts of a 10% by mass NTA (nitrilotriacetic acid) metal salt aqueous solution (Chilest 70, manufactured by Chelest Co., Ltd.) was added to the dispersion containing the second aggregated particles.

[0145] While continuing stirring in the stirring tank, 1.0 part of anionic surfactant (Dai-ichi Kogyo Seiyaku Co., Ltd., Neogen RK) was added, and the temperature was raised to 85°C and maintained for 5 hours. Next, the temperature was lowered to 30°C at a rate of 0.5°C / min. Next, the solid content was filtered, thoroughly washed with ion-exchanged water, and dried to obtain toner particles having a volume average particle size of 6.0 μm.

[0146] -External addition of hydrophobic silica particles- 1.5 parts of hydrophobic silica particles (RY50 manufactured by Nippon Aerosil Co., Ltd.) were added to 100 parts of the toner particles and mixed at 13,000 rpm for 30 seconds using a sample mill, and then sieved using a vibrating sieve with 45 μm openings to obtain an externally added toner.

[0147] -Mixed with Carrier- 10 parts of the toner with external additives and 100 parts of the carrier were placed in a V-blender and stirred for 20 minutes. After that, the mixture was sieved through a sieve with 212 μm openings to obtain a developer. The carrier was prepared as follows.

[0148] -Creating a carrier- Ferrite particles (volume average particle size 35 μm): 100 parts Toluene: 14 parts Styrene / methyl methacrylate copolymer (copolymerization ratio 15 / 85): 3 parts Carbon black (Cabot, Regal 330): 0.2 parts The above materials except for the ferrite particles were dispersed in a sand mill to prepare a dispersion liquid, which was then placed in a vacuum degassing kneader together with the ferrite particles, and dried under reduced pressure while stirring to obtain a resin-coated carrier.

[0149] [Examples 2 to 14, Comparative Examples 1 to 4] In the same manner as in Example 1, except that the type of titanium oxide-containing release agent particle dispersion was changed as shown in Table 2, toner particles, toner with external additives, and developer for each example were prepared.

[0150] <Performance evaluation> [White image formation] A white image with a density of 100% was formed on plain paper using an electrophotographic image forming apparatus. The toner amount per layer was 9.0 g / m. 2 A single-layer or double-layer white image was formed.

[0151] [UV exposure] Using an ultraviolet irradiation device (UV LED irradiator LX405S, manufactured by AS ONE Corporation), light source: 365 nm, irradiance: 9500 W / m 2 The ultraviolet irradiation was carried out for 72 hours under the conditions.

[0152] [Measurement of whiteness] Before and after UV exposure, the L of the white image was measured under a D50 light source using a spectrophotometer (X-Rite Ci62, manufactured by X-Rite). * The value (brightness) was measured. * The values ​​were classified into A to E as follows. The results are shown in Table 3. A:L * The value is 75 or more. B:L * The value is greater than or equal to 72 and less than 75. C:L * The value is greater than or equal to 69 and less than 72. D:L * The value is greater than or equal to 65 and less than 69. E:L * The value is less than 65.

[0153] [Evaluation of colorfastness] The degree of fading was calculated using the formula below and classified as A to E as follows. The results are shown in Table 3. Fading degree = (original L * Value - L after UV exposure * value) / original L * Value x 100 A: The degree of fading is less than 1. B: Degree of fading is 1 or more but less than 3. C: Degree of fading is 3 or more but less than 5. D: Degree of fading is 5 or more but less than 10. E: The degree of fading is 10 or more.

[0154] [Image intensity measurement] The strength of the white image was evaluated before and after UV exposure according to JIS K5600-5-4:1999 "Scratch Hardness (Pencil Method)." Mitsubishi High-Uni pencils (hardness: 10H, 9H, 8H, 7H, 6H, 5H, 4H, 3H, 2H, H, F, HB, B, 2B, 3B, 4B, 5B, 6B, 7B, 8B, 9B, 10B) were used. The hardest hardness that did not cause scratches on the white image is shown in Table 3.

[0155] [Table 2]

[0156] [Table 3] [Explanation of symbols]

[0157] 10Y, 10M, 10C, 10K, 10W Image forming units 1Y, 1M, 1C, 1K, 1W Photoconductor (an example of an image carrier) 2Y, 2M, 2C, 2K, 2W Charging roll (an example of charging means) 3Y, 3M, 3C, 3K, 3W exposure equipment (an example of electrostatic image forming means) 4Y, 4M, 4C, 4K, 4W developing device (an example of developing means) 5Y, 5M, 5C, 5K, 5W Primary transfer roll (an example of a primary transfer means) 6Y, 6M, 6C, 6K, 6W Photoconductor cleaning device 8Y, 8M, 8C, 8K, 8W toner cartridges 20 Intermediate transfer belt (an example of an intermediate transfer body) 21 Intermediate transfer body cleaning device 22 Drive Roll 23 Support Roll 24 opposing roll 26 Secondary transfer roll (an example of a secondary transfer means) 28 Fixing device (an example of fixing means) P Recording paper (an example of a recording medium) 107 Photoconductor (an example of an image carrier) 108 Charging roll (an example of charging means) 109 Exposure device (an example of electrostatic image forming means) 111 Developing device (an example of developing means) 112 Transfer device (an example of transfer means) 113 Photoconductor cleaning device 115 Fixing device (an example of fixing means) 116 Mounting Rail 117 Cabinet 118 Exposure opening 200 Process Cartridge 300 Recording paper (an example of a recording medium)

Claims

1. toner particles containing a binder resin, a release agent, and titanium oxide, at least a portion of the titanium oxide being in a release agent domain; when a cross section of the toner particle is observed, the number ratio of the titanium oxide particles in the release agent domain is 23% or more of the total number of the titanium oxide particles contained in the toner particle, In a cross-sectional observation of the toner particles, an average major axis length Dt of the toner particles, an average major axis length Dw of the release agent domains, and an average major axis length Dp of the titanium oxide in the release agent domains satisfy the following formulas (1) and (2): White toner. Formula (1): 2×Dp≦Dw≦10×Dp Formula (2): 0.1×Dt≦Dw≦0.5×Dt

2. 2. The white toner according to claim 1, wherein, in a cross-sectional observation of the toner particles, an average major axis length Dt of the toner particles, an average major axis length Dw of the release agent domains, and an average major axis length Dp of the titanium oxide in the release agent domains satisfy the following formulas (1-1) and (2-1): Formula (1-1): 2.5×Dp≦Dw≦8×Dp Formula (2-1): 0.125×Dt≦Dw≦0.4×Dt

3. 3. The white toner according to claim 1, wherein, upon cross-sectional observation of the toner particle, the number ratio of the titanium oxide particles in the release agent domain is 50% or more of the total number of the titanium oxide particles contained in the toner particle.

4. 4. The white toner according to claim 1, wherein, in a cross-sectional observation of the toner particle, a number ratio of the titanium oxide present in the release agent domain is 60% or more of the total number of the titanium oxide contained in the toner particle.

5. 5. The white toner according to claim 1, wherein a mass ratio of the release agent contained in the toner particles to the titanium oxide (release agent / titanium oxide) is 0.01 or more and 0.3 or less.

6. 6. The white toner according to claim 1, wherein the content of the titanium oxide contained in the toner particles is 30% by mass or more and 70% by mass or less of the total amount of the toner particles.

7. 7. The white toner according to claim 1, wherein, in cross-sectional observation of the toner particle, the average major axis length Dp of the titanium oxide in the release agent domain is 100 nm or more and 300 nm or less.

8. The titanium oxide contained in the toner particles has a BET specific surface area of ​​4 m ２ / g or more 12m ２ 8. The white toner according to claim 1, wherein the molecular weight of the white toner is 1 / g or less.

9. 9. The white toner according to claim 1, wherein the release agent comprises an ester wax.

10. An electrostatic image developer comprising the white toner according to any one of claims 1 to 9.

11. The white toner according to any one of claims 1 to 9 is contained therein, A toner cartridge that is detachably attached to an image forming device.

12. a developing unit containing the electrostatic image developer according to claim 10 and developing an electrostatic image formed on a surface of an image carrier into a toner image by using the electrostatic image developer, A process cartridge is detachably mounted in an image forming apparatus.

13. an image carrier; a charging means for charging the surface of the image carrier; an electrostatic image forming means for forming an electrostatic image on the charged surface of the image carrier; a developing unit containing the electrostatic image developer according to claim 10 and developing the electrostatic image formed on the surface of the image carrier into a toner image by using the electrostatic image developer; a transfer means for transferring the toner image formed on the surface of the image carrier to the surface of a recording medium; a fixing means for fixing the toner image transferred onto the surface of the recording medium; An image forming apparatus comprising:

14. a charging step of charging the surface of the image carrier; an electrostatic image forming step of forming an electrostatic image on the charged surface of the image carrier; a developing step of developing the electrostatic image formed on the surface of the image carrier into a toner image by using the electrostatic image developer according to claim 10; a transfer step of transferring the toner image formed on the surface of the image carrier to the surface of a recording medium; a fixing step of fixing the toner image transferred onto the surface of the recording medium; An image forming method comprising the steps of:

Images