JP7512604B2 - Toner set and image forming apparatus using said toner set - Google Patents

Description

The present invention relates to a toner set and an image forming device that uses the toner set.

In recent years, in the field of toners for developing electrostatic images used in electrophotographic image formation, development has been carried out to meet various market demands. In particular, market demand for high-value-added images is increasing year by year, and a wide variety of special color toners, such as white, transparent, silver foil, gold foil, and fluorescent, are being used to form high-value-added images.

For example, Patent Document 1 describes a colored toner and a white toner that contain a hydrocarbon wax and a crystalline resin with different heat absorption amounts. Patent Document 1 claims that it is possible to reduce the difference in gloss between the white image area and the colored image area formed with the toner, thereby obtaining an image with high color development.

For example, Patent Document 2 describes a toner containing toner particles that include a hydrocarbon wax, a crystalline resin, and at least one of an inorganic pigment and a metallic pigment. Patent Document 2 describes the toner as having excellent low-temperature fixing properties by containing a crystalline resin whose endothermic temperature Tm (°C) and heat generating temperature Tc (°C) are such that Tm>Tc.

JP 2012-177763 A JP 2018-084607 A

The inventors of the present application have found that when the white toner and color toner described in Patent Document 1 or Patent Document 2 are used to print by overlaying the color toner on the white toner, the white toner and the color toner are fused and mixed together due to the pressure during fixing, resulting in color turbidity and white streaks on the image. In addition to paper media, there is also a demand for image formation on film substrates made of, for example, polyethylene terephthalate or polypropylene, which are used as labels.

The present invention was made in consideration of these points, and aims to provide a toner set that does not cause color turbidity and has excellent fixing separation properties, and an image forming device that uses the toner set.

In order to solve the above problem, a toner set according to one embodiment of the present invention includes a first toner containing a white pigment and a first hydrocarbon wax, and a second toner containing a second hydrocarbon wax, and when the branching degree of the first hydrocarbon wax is B1 and the branching degree of the second hydrocarbon wax is B2, B1 and B2 satisfy the condition of the following formula (1).

In order to solve the above problem, an image forming apparatus according to one embodiment of the present invention includes a toner image forming unit that develops an electrostatic latent image with multiple types of toner to form a toner image, a transfer unit that transfers the toner image to a surface of a recording medium, and a fixing unit that fixes the toner image to the surface of the recording medium, and the multiple types of toner include a first toner containing a white pigment and a first hydrocarbon wax, and a second toner containing a second hydrocarbon wax, and when the branching degree of the first hydrocarbon wax is B1 and the branching degree of the second hydrocarbon wax is B2, B1 and B2 satisfy the condition of the following formula (1).

The present invention provides a toner set that does not cause color turbidity and has excellent fixing and separation properties, and an image forming device that uses the toner set.

FIG. 1 is a schematic diagram showing the configuration of an image forming apparatus according to an embodiment of the present invention.

The following describes in detail the embodiments of the present invention.

[Toner Set]
The toner set includes a white toner and at least one color toner. The term "toner set" refers to a combination of toners that are used or should be used in an image forming method. The toner set may be, for example, a state in which all of the toners of each color are contained in a developing container in a developing device of each color of a full-color image forming apparatus, or a set of toner bottles of all colors or a set of process cartridges containing the toners of each color.

The toner set according to an embodiment of the present invention includes a first toner containing a white pigment and a first hydrocarbon wax, and a second toner containing a second hydrocarbon wax.

(First Toner and Second Toner)
The first toner according to the embodiment of the present invention is preferably a white toner containing a white pigment and a first hydrocarbon wax, and the second toner according to the embodiment of the present invention is preferably a colored toner or a transparent toner containing a second hydrocarbon wax. In particular, the second toner preferably contains a pigment other than the white pigment.

As described above, the first toner contains a white pigment. Examples of the white pigment include inorganic pigments such as heavy calcium carbonate, light calcium carbonate, titanium oxide, aluminum hydroxide, titanium white, talc, calcium sulfate, barium sulfate, zinc oxide, magnesium oxide, magnesium carbonate, amorphous silica, colloidal silica, white carbon, kaolin, calcined kaolin, delaminated kaolin, aluminosilicate, sericite, bentonite, and smexite; and organic pigments such as polystyrene resin particles and urea formalin resin particles. In addition, pigments having a hollow structure such as hollow resin particles and hollow silica are also included. Among the above white pigments, titanium oxide is preferable from the viewpoint of charging property and hiding property. Titanium oxide can have any crystal structure such as anatase type, rutile type, or brookite type.

In the first toner, the content of the white pigment is preferably 10% by mass or more and 40% by mass or less, and more preferably 20% by mass or more and 30% by mass or less, relative to the total mass of the first toner. By making the content of the white pigment 10% by mass or more, the surface of the recording medium can be concealed, so that the color image formed thereon can be obtained with high color development without being affected by the color tone of the recording medium. In addition, by making the content of the white pigment 40% by mass or less, the fixing property is improved.

As mentioned above, it is preferable that the second toner contains a pigment other than a white pigment. Examples of the pigment other than the white pigment include a black pigment and a chromatic pigment.

Examples of the black pigments include carbon blacks such as furnace black, channel black, acetylene black, thermal black, and lamp black, as well as magnetic powders such as magnetite and ferrite.

Examples of the above chromatic pigments include C.I. Pigment Red 2, 3, 5, 7, 15, 16, 48:1, 48:3, 53:1, 57:1, 81:4, 122, 123, 139, 144, 149, 166, 177, 178, 208, 209, 222, 238, 269, C.I. Pigment Orange 31, 43, C.I. C.I. Pigment Yellow 3, 9, 14, 17, 35, 36, 65, 74, 83, 93, 94, 98, 110, 111, 138, 139, 153, 155, 180, 181, 185, C.I. Pigment Green 7, C.I. Pigment Blue 15:3, 15:4, 60, and phthalocyanine pigments whose central metal is zinc, titanium, magnesium, etc. These pigments may be used alone or in combination of two or more types.

The second toner may be a chromatic dye. Examples of the chromatic dye include C.I. Solvent Red 1, 3, 14, 17, 18, 22, 23, 49, 51, 52, 58, 63, 87, 111, 122, 127, 128, 131, 145, 146, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 176, 179, pyrazolotriazole azo dye, pyrazolotriazole azomethine dye, pyrazolone azo dye, pyrazolone azomethine dye, C.I. Solvent Yellow 19, 44, 77, 79, 81, 82, 93, 98, 103, 104, 112, 162, C.I. Solvent Blue 25, 36, 60, 70, 93 and 95. These dyes may be used alone or in combination of two or more.

In the second toner, the content of the black or chromatic colorant is preferably 2% by mass or more and 25% by mass or less, and more preferably 5% by mass or more and 15% by mass or less, relative to the total mass of the second toner. By making the content of the colorant 2% by mass or more, the color development of the obtained image is sufficient. In addition, by making the content of the colorant 25% by mass or less, the fixability is good.

(First Hydrocarbon Wax and Second Hydrocarbon Wax)
In the first hydrocarbon wax contained in the first toner and the second hydrocarbon wax contained in the second toner according to this embodiment, when the branching degree of the first hydrocarbon wax is B1 and the branching degree of the second hydrocarbon wax is B2, it is preferable that the difference in branching degree between B1 and B2 satisfies the condition of the following formula (1), and it is more preferable that the difference in branching degree between B1 and B2 satisfies the condition of the following formula (2).

The first and second hydrocarbon waxes are not particularly limited as long as they are hydrocarbon waxes with a branching degree (B1, B2) of 1% or more and 60% or less. For example, polyolefin waxes such as polyethylene wax and polypropylene wax, branched hydrocarbon waxes such as microcrystalline wax, and linear hydrocarbon waxes such as paraffin wax and Fischer-Tropsch wax can be used. Among the above-mentioned hydrocarbon waxes, paraffin wax, Fischer-Tropsch wax, and microcrystalline wax are preferable. The combination of the first hydrocarbon wax contained in the first toner and the second hydrocarbon wax contained in the second toner is not particularly limited as long as the difference in branching degree satisfies the above formula (1) or (2).

In this embodiment, the branching degree (B1) of the first hydrocarbon wax is preferably 0% or more and 80% or less, and more preferably 1% or more and 20% or less. The branching degree (B2) of the second hydrocarbon wax is preferably 10% or more and 80% or less, and more preferably 20% or more and 60% or less.

In addition, by containing a hydrocarbon wax with a lower acid value than the ester wax in the first toner and the second toner, the difference in acid value between the hydrocarbon wax and the binder resin (e.g., styrene-acrylic resin) contained in the first toner and the second toner can be increased. This makes it difficult for the hydrocarbon wax and the binder resin to be compatible with each other when thermally melted, so that the hydrocarbon wax is more likely to seep out onto the surface of the formed image, making it easier to separate the recording medium (e.g., a film) from the heating roller (described later) in the image forming device.

It is also preferable to select a combination that satisfies the above condition of formula (1) |B1-B2|>10% or formula (2) |B1-B2|>40% using a first hydrocarbon wax with a branching degree (B1) of 0% or more and a second hydrocarbon wax with a branching degree (B2) of 10% or more and 80% or less, a combination in which 10%<|B1-B2|<80% is more preferable, and a combination in which 40%<|B1-B2|<60% or less is even more preferable. Unlike conventional toners that use waxes with the same branching degree, by combining waxes in which the difference in branching degree between the first and second hydrocarbon waxes is 10%<|B1-B2|, the first toner and the second toner are less likely to be compatible with each other, so that fusion and compatibility during fixing are suppressed, and color turbidity can be suppressed. In addition, by combining a first hydrocarbon wax and a second hydrocarbon wax such that the difference in branching degree between them is |B1-B2|<80%, the first toner and the second toner are less likely to be compatible with each other, which suppresses fusion and compatibility during fixing, and more significantly suppresses color turbidity.

This is believed to be because, during fixing and melting, the hydrocarbon waxes contained in the first toner and the second toner seep out onto the toner surface, forming a pseudo core-shell structure. In other words, the first wax constituting the pseudo shell layer of the first toner and the second wax constituting the pseudo shell layer of the second toner have different degrees of branching and different structures, making it difficult for the molecules contained in the wax to approach each other. This reduces the interaction between the molecules contained in the wax, which is believed to suppress color turbidity in the formed image.

The "paraffin" in the paraffin wax refers to an alkane having 20 or more carbon atoms (a linear saturated hydrocarbon having the general formula _{CnH2n +2} ). Paraffin wax is a hydrocarbon wax whose main component is a linear hydrocarbon (normal paraffin).

The paraffin wax preferably has a weight average molecular weight (Mw) of 400 to 1000 and a melting point of 60 to 90°C, and more preferably has a weight average molecular weight (Mw) of 500 to 800 and a melting point of 65 to 80°C. The paraffin wax may be synthesized using known techniques with a branching degree (B1, B2) of 5% to 60%, or a commercially available product with a branching degree (B1, B2) of 5% to 60% may be used.

Examples of commercially available paraffin waxes include Paraffin Wax-155, Paraffin Wax-135, Paraffin Wax-115, HNP-3, HNP-9, HNP-11, SP-0165, SP-1039, and SP-3040 (all manufactured by Nippon Seiro Co., Ltd.).

The Fischer-Tropsch wax is a synthetic hydrocarbon wax obtained by the Fischer-Tropsch process. The Fischer-Tropsch process is a process in which a synthetic gas of carbon monoxide and hydrogen is generated from natural gas and air using steam reforming or partial oxidation, and then the resulting hydrocarbon wax is synthesized by a catalytic reaction using a catalyst such as iron, cobalt, or nickel under high temperature and pressure conditions, and then refined and reformed (molded) after fractional distillation.

The Fischer-Tropsch wax preferably has a weight average molecular weight (Mw) of 400 to 1000 and a melting point of 60 to 90°C, and more preferably has a weight average molecular weight (Mw) of 500 to 800 and a melting point of 65 to 80°C. The paraffin wax may be synthesized using known techniques with a branching degree (B1, B2) of 1% to 20%, or a commercially available product with a branching degree (B1, B2) of 1% to 20% may be used.

Examples of commercially available Fischer-Tropsch waxes include Paraflint C77, Paraflint C80, Paraflint H1 (all manufactured by Sasol Waxes), FT100, FT-0070 (manufactured by Nippon Seiro Co., Ltd.), CIREBELLE 108, CIREBELLE 109L, CIREBELLE 303 (all manufactured by CIREBELLE), etc.

The microcrystalline wax is a petroleum wax that, unlike the Fischer-Tropsch wax described above, contains a large amount of branched-chain hydrocarbons (isoparaffins) and cyclic hydrocarbons (cycloparaffins). In general, microcrystalline wax contains a large amount of low-crystalline isoparaffins and cycloparaffins, and therefore has smaller crystals and a larger molecular weight than the paraffin wax described above.

The microcrystalline wax preferably has a carbon number of 30 to 60, a weight average molecular weight (Mw) of 500 to 800, and a melting point of 60 to 90°C, and more preferably has a weight average molecular weight (Mw) of 600 to 800 and a melting point of 60 to 85°C. In addition, for low molecular weight waxes, the number average molecular weight (Mn) is preferably 300 to 1000, and more preferably 400 to 800. The ratio of the weight average molecular weight to the number average molecular weight (Mw/Mn) is preferably 1.01 to 1.20.

The above microcrystalline wax may be synthesized using known techniques to have a branching degree (B1, B2) of 30% or more and 80% or less, or a commercially available product with a branching degree (B1, B2) of 5% or more and 60% or less may be used.

Examples of commercially available microcrystalline waxes include HNP-0190, Hi-MiC-1045, Hi-MiC-1070, Hi-MiC-1080, Hi-MiC-1090, Hi-MiC-2045, Hi-MiC-2065, Hi-MiC-2095, EMW-0001, EMW-0003, etc. (all manufactured by Nippon Seiro Co., Ltd.).

The first toner and the second toner may contain an ester wax in addition to the hydrocarbon wax, within the range that satisfies the above-mentioned condition of formula (1) |B1-B2|>10% or formula (2) |B1-B2|>40%. Examples of ester waxes include carnauba wax, pentaerythritol behenate, behenyl behenate, and behenyl citrate.

The weight average molecular weight (Mw) of the above paraffin wax, Fischer-Tropsch wax, and microcrystalline wax can be measured using a GPC device "HLC-8120GPC" (manufactured by Tosoh Corporation) and a column "TSKguard column + TSKgel Super HZM-M triple column" (manufactured by Tosoh Corporation).

The branching degree of the paraffin wax, Fischer-Tropsch wax and microcrystalline wax can be calculated from the area ratio (%) of branched hydrocarbons in the area of the obtained chromatogram by measuring a xylene solution having a sample concentration of 1% using a GC-2010Plus (manufactured by Shimadzu Corporation).
(Analysis conditions)
Column: UA-SIMDIS (HT) 5m*0.53mm i.d.*0.1um
Inlet: 350°C
Detection: FID 430°C

In this embodiment, the first hydrocarbon wax contained in the first toner is preferably a paraffin wax or a Fischer-Tropsch wax. The second hydrocarbon wax contained in the second toner is preferably a microcrystalline wax.

By using paraffin wax or Fischer-Tropsch wax as the first hydrocarbon wax contained in the first toner, heat-resistant storage stability can be ensured. By using microcrystalline wax as the second hydrocarbon wax contained in the second toner, heat-resistant storage stability can be ensured.

In addition, in the first toner, the content of the first hydrocarbon wax is preferably 3% by mass or more and 15% by mass or less, and more preferably 5% by mass or more and 10% by mass or less, relative to the total mass of the first toner. By setting the content of the first hydrocarbon wax to 3% by mass or more and 15% by mass or less in the first toner, it is possible to achieve both fixability and heat-resistant storage stability.

In addition, in the second toner, the content of the second hydrocarbon wax is preferably 3% by mass or more and 15% by mass or less, and more preferably 5% by mass or more and 10% by mass or less, relative to the total mass of the second toner. By setting the content of the second hydrocarbon wax to 3% by mass or more and 15% by mass or less in the second toner, it is possible to achieve both fixability and heat-resistant storage stability.

In this embodiment, the first hydrocarbon wax and the second hydrocarbon wax can be used as a release agent.

(Binder resin)
The first toner and the second toner according to the present embodiment preferably contain a binder resin. Examples of the binder resin include an amorphous resin and a crystalline resin.

(Amorphous Resin)
The term "amorphous resin" refers to a resin that has a glass transition temperature (Tg) but has no melting point, i.e., no clear endothermic peak upon heating, in an endothermic curve obtained by differential scanning calorimetry (DSC).

Examples of the above-mentioned amorphous resins include vinyl resins, urethane resins, urea resins, and amorphous polyester resins such as styrene-acrylic modified polyester resins. Among the above-mentioned amorphous resins, vinyl resins are preferred from the viewpoint of ease of controlling thermoplasticity.

The vinyl resin is a resin produced by polymerization of a monomer containing a compound having a vinyl group or a derivative thereof. Examples of vinyl resins include acrylate resin, styrene-acrylic resin, and ethylene-vinyl acetate resin. Of the vinyl resins, styrene-acrylic resin is preferred. By using styrene-acrylic resin as the binder resin, excessive seepage of the release agent during fixing can be suppressed, and wax adhesion can be suppressed.

The styrene-acrylic resin has a molecular structure of a radical polymer of a compound having a radically polymerizable unsaturated bond, and can be synthesized, for example, by radical polymerization of the compound. Examples of the compound include styrene monomer and its derivatives, and (meth)acrylic acid monomer and its derivatives. The compound may be used alone or in combination of two or more types. Note that "(meth)acrylic acid" is a general term for acrylic acid and methacrylic acid, and means either or both of them.

Examples of the styrene monomer and its derivatives include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-methoxystyrene, p-phenylstyrene, p-chlorostyrene, p-ethylstyrene, p-n-butylstyrene, p-tert-butylstyrene, p-n-hexylstyrene, p-n-octylstyrene, p-n-nonylstyrene, p-n-decylstyrene, p-n-dodecylstyrene, 2,4-dimethylstyrene, and 3,4-dichlorostyrene.

Examples of the (meth)acrylic acid and its derivatives include methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, phenyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, β-ethyl hydroxyacrylate, γ-propyl aminoacrylate, stearyl methacrylate, dimethylaminoethyl methacrylate, and diethylaminoethyl methacrylate.

From the viewpoint of controlling the plasticity of the styrene-acrylic resin, the content of structural units derived from styrene monomer in the styrene-acrylic resin is preferably 40 to 90% by mass. In addition, the content of structural units derived from (meth)acrylic acid in the styrene-acrylic resin is preferably 10 to 60% by mass.

The styrene-acrylic resin may further contain structural units derived from other monomers than the styrene monomer and (meth)acrylic ester monomer. The other monomer is preferably a compound that forms an ester bond with a hydroxy group (-OH) derived from a polyhydric alcohol or a carboxy group (-COOH) derived from a polycarboxylic acid. In other words, the styrene-acrylic resin is preferably a polymer that is capable of addition polymerization with the styrene monomer and (meth)acrylic ester monomer, and is further polymerized with a compound (amphoteric compound) having a carboxy group or a hydroxy group.

Examples of the amphoteric compounds include compounds having a carboxy group, such as acrylic acid, methacrylic acid, maleic acid, itaconic acid, cinnamic acid, fumaric acid, maleic acid monoalkyl esters, and itaconic acid monoalkyl esters, and compounds having a hydroxy group, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and polyethylene glycol mono(meth)acrylate.

The content of the structural units derived from the amphoteric compound in the styrene-acrylic resin is preferably 0.5 to 20% by mass.

The styrene-acrylic resin can be obtained by adding any commonly used polymerization initiator, such as a peroxide, persulfide, or azo compound, to the polymerization of the styrene monomer, and polymerizing the monomer by a known polymerization method, such as bulk polymerization, solution polymerization, emulsion polymerization, mini-emulsion, suspension polymerization, or dispersion polymerization. During polymerization, commonly used chain transfer agents, such as alkyl mercaptans and mercapto fatty acid esters, can be used to adjust the molecular weight.

In the first toner according to the present embodiment, the content of the styrene-acrylic resin is preferably 60% by mass or more and 90% by mass or less, and more preferably 70% by mass or more and 80% by mass or less, relative to the total mass of the first toner. By making the content of the styrene-acrylic resin in the first toner 60% by mass or more and 90% by mass or less, it is possible to achieve both fixability and heat-resistant storage stability.

In addition, in the second toner according to the present embodiment, the content of the styrene-acrylic resin is preferably 60% by mass or more and 90% by mass or less, and more preferably 70% by mass or more and 80% by mass or less, relative to the total mass of the second toner. By making the content of the styrene-acrylic resin in the second toner 60% by mass or more and 90% by mass or less, it becomes possible to achieve both fixing performance and heat-resistant storage stability.

(Crystalline Resin)
The crystalline resin is a resin that has a clear endothermic peak rather than a stepwise endothermic change in differential scanning calorimetry (DSC). The clear endothermic peak means a peak whose half-width is within 15° C. when measured at a heating rate of 10° C./min in differential scanning calorimetry (DSC).

Examples of the above crystalline resins include crystalline polyester resins and crystalline acrylic resins. Among the above crystalline resins, crystalline polyester resins are preferred because their melting points are easy to adjust.

Crystalline polyester resin is a polyester resin obtained by a polycondensation reaction between a divalent or higher carboxylic acid (polycarboxylic acid) and a divalent or higher alcohol (polyhydric alcohol).

The polycarboxylic acid compound is a compound having two or more carboxy groups in one molecule, and alkyl esters, acid anhydrides, and acid chlorides of the polycarboxylic acid compound can be used.

Examples of the polyvalent carboxylic acid compounds include divalent aliphatic carboxylic acids such as oxalic acid, succinic acid, malonic acid, adipic acid, β-methyladipic acid, pimelic acid, azelaic acid, sebacic acid, nonanedicarboxylic acid, decanedicarboxylic acid, undecanedicarboxylic acid, dodecanedicarboxylic acid, maleic acid, fumaric acid, citraconic acid, diglycolic acid, cyclohexane-3,5-diene-1,2-dicarboxylic acid, malic acid, citric acid, hexahydroterephthalic acid, tartaric acid, and mucic acid; phthalic acid, isophthalic acid, terephthalic acid, tetrachlorophthalic acid, chlorophthalic acid, nitrophthalic acid, p-carboxylate, phthalic acid ... These include divalent aromatic carboxylic acids such as diphenylacetic acid, p-phenylene diacetic acid, m-phenylenediglycolic acid, p-phenylenediglycolic acid, o-phenylenediglycolic acid, diphenyl-p,p'-dicarboxylic acid, naphthalene-1,4-dicarboxylic acid, naphthalene-1,5-dicarboxylic acid, naphthalene-2,6-dicarboxylic acid, anthracene dicarboxylic acid, and dodecenylsuccinic acid; and trivalent or higher aromatic carboxylic acids such as trimellitic acid, pyromellitic acid, naphthalene tricarboxylic acid, naphthalene tetracarboxylic acid, pyrene tricarboxylic acid, and pyrene tetracarboxylic acid.

From the viewpoint of increasing the crystallinity of the crystalline polyester resin, among the polycarboxylic acid compounds, a divalent aliphatic carboxylic acid is preferable. Note that the polycarboxylic acid compounds may be used alone or in combination of two or more kinds.

The above polyhydric alcohol compound is a compound that has two or more hydroxyl groups in one molecule.

Examples of the polyhydric alcohol compounds include dihydric straight-chain aliphatic alcohols such as ethylene glycol, propylene glycol, butanediol, diethylene glycol, hexanediol, octanediol, decanediol, and dodecanediol; dihydric alicyclic alcohols such as cyclohexanediol; dihydric aromatic alcohols such as ethylene oxide adducts of bisphenol A and propylene oxide adducts of bisphenol A; trihydric or higher aliphatic alcohols such as glycerin and pentaerythritol; and alcohols having a trihydric or higher guanidine skeleton such as hexamethylol melamine, tetramethylol benzoguanamine, and tetraethylol benzoguanamine.

From the viewpoint of increasing the crystallinity of the crystalline polyester resin, among the above polyhydric alcohol compounds, dihydric aliphatic alcohols are preferred, and dihydric linear aliphatic alcohols are more preferred. The above polyhydric alcohol compounds may be used alone or in combination of two or more types.

The ratio of the polyhydric alcohol compound to the polycarboxylic acid compound in the monomers for synthesizing the crystalline polyester resin is preferably 2.0/1.0 to 1.0/2.0, more preferably 1.5/1.0 to 1.0/1.5, in terms of the equivalent ratio [OH]/[COOH] of the hydroxyl group [OH] of the polyhydric alcohol compound to the carboxyl group [COOH] of the polycarboxylic acid compound.

The melting point (Tm) of the crystalline polyester resin is preferably 50 to 90°C, and more preferably 60 to 80°C, from the viewpoint of obtaining sufficient low-temperature fixability and high-temperature storage stability.

The melting point of the crystalline polyester resin can be measured by differential scanning calorimetry (DSC). Specifically, 5 mg of the sample is sealed in an aluminum pan KIT NO. B0143013 and set in the sample holder of a thermal analysis device Diamond DSC (manufactured by PerkinElmer), and the temperature is changed in the order of heating, cooling, and heating again. During the first and second heating, the temperature is raised from 0°C to 100°C at a heating rate of 10°C/min and held at 100°C for 1 minute. During cooling, the temperature is lowered from 100°C to 0°C at a cooling rate of 10°C/min and held at 0°C for 1 minute. The temperature at the top of the endothermic peak in the endothermic curve obtained during the second heating is measured as the melting point (Tm).

The weight average molecular weight (Mw) of the crystalline polyester resin is preferably 5,000 to 50,000, and the number average molecular weight (Mn) is preferably 2,000 to 10,000. By setting the weight average molecular weight (Mw) of the crystalline polyester resin to 5,000 to 50,000, low temperature fixability can be improved.

The weight average molecular weight (Mw) and number average molecular weight (Mn) of the crystalline polyester resin can be determined from the molecular weight distribution measured by gel permeation chromatography (GPC) as follows. The sample is added to tetrahydrofuran (THF) to a concentration of 1 mg/mL, and dispersed for 5 minutes at room temperature using an ultrasonic disperser, and then treated with a membrane filter with a pore size of 0.2 μm to prepare a sample solution. A GPC device "HLC-8120GPC" and a column "TSKguard column + TSKgel Super HZM-M triple column" (both manufactured by Tosoh Corporation) are used, and THF is passed as a carrier solvent at a flow rate of 0.2 mL/min while maintaining the column temperature at 40°C. 10 μL of the prepared sample solution is injected into the GPC device together with the carrier solvent, and the sample is detected using a refractive index detector (RI detector). The molecular weight distribution of the sample is then calculated using a calibration curve measured using 10 points of monodispersed polystyrene standard particles.

The first toner according to the present embodiment may contain the crystalline polyester resin. The content of the crystalline polyester resin is preferably 0% by mass or more and 10% by mass or less, and more preferably 0% by mass or more and 5% by mass or less, relative to the total mass of the first toner. By making the content of the crystalline polyester resin in the first toner 10% by mass or less, it is possible to suppress color turbidity even when the first toner (white toner) and the second toner (color toner) are printed on top of each other.

In addition, in the second toner according to the present embodiment, the content of the crystalline polyester resin is preferably 5% by mass or more and 20% by mass or less, and more preferably 7% by mass or more and 15% by mass or less, relative to the total mass of the second toner. By making the content of the crystalline polyester resin 5% by mass or more in the second toner, sufficient plasticity can be obtained, and low-temperature fixability is also good. In addition, by making the content 20% by mass or less, excellent thermal stability and physical stability are achieved.

In addition, in this embodiment, the crystalline polyester resin may contain a hybrid crystalline polyester resin.

A hybrid crystalline polyester resin is a crystalline polyester resin modified with a styrene-acrylic resin. "Crystalline polyester resin modified with a styrene-acrylic resin" means that a crystalline polyester resin segment and a styrene-acrylic resin segment are chemically bonded. A crystalline polyester resin segment refers to the resin portion of a hybrid crystalline polyester resin that is derived from a crystalline polyester resin, i.e., a molecular chain that has the same chemical structure as a crystalline polyester resin. A styrene-acrylic resin segment refers to the resin portion of a hybrid crystalline polyester resin that is derived from a styrene-acrylic resin, i.e., a molecular chain that has the same chemical structure as a styrene-acrylic resin.

The above hybrid crystalline polyester resin can also be obtained by carrying out a polymerization reaction to produce a styrene-acrylic resin in the presence of a crystalline polyester resin, or by carrying out a polymerization reaction to produce a crystalline polyester resin in the presence of a styrene-acrylic resin that has been prepared in advance.

The first toner and second toner according to this embodiment may contain charge control agents, external additives, etc., as necessary.

Examples of charge control agents include known compounds such as nigrosine dyes, metal salts of naphthenic acid or higher fatty acids, alkoxylated amines, quaternary ammonium salts, azo metal complexes, and metal salts of salicylic acid. The charge control agent can provide a toner with excellent charging properties. The content of the charge control agent can usually be within the range of 0.1 to 5 parts by weight per 100 parts by weight of the binder resin.

Examples of external additives include inorganic oxide fine particles such as silica fine particles, alumina fine particles, and titanium oxide fine particles; inorganic stearic acid compound fine particles such as aluminum stearate fine particles and zinc stearate fine particles; and inorganic titanic acid compound fine particles such as strontium titanate and zinc titanate. The above external additives may be used alone or in combination of two or more types. The amount of the above external additives (the total amount when multiple external additives are used) is preferably 0.05 to 5 parts by mass, and more preferably 0.1 to 3 parts by mass, per 100 parts by mass of toner.

[Method of Manufacturing First Toner and Second Toner]
The first toner and the second toner according to the present embodiment can be manufactured by a known method. Examples of the method for manufacturing the first toner and the second toner include a kneading and pulverizing method, a suspension polymerization method, an emulsion aggregation method, a dissolution suspension method, a polyester elongation method, and a dispersion polymerization method. Among these, the emulsion aggregation method is preferable from the viewpoints of uniformity of particle size, controllability of shape, and ease of forming a core-shell structure. Here, a method for manufacturing a toner using the emulsion aggregation method will be described.

The emulsion aggregation method is a method in which a dispersion of fine resin particles (hereafter referred to as "resin particles") dispersed with a surfactant or dispersion stabilizer is mixed with a dispersion of toner components such as fine colorant particles, and an aggregating agent is added to aggregate the particles to the desired toner particle size, and then, either after or simultaneously with the aggregation, the resin particles are fused together and the shape is controlled to form a toner.

According to the emulsion aggregation method, a dispersion of binder resin particles obtained by emulsion polymerization is mixed with particles of optional colorants, release agents, charge control agents, external additives, etc., and these are aggregated, associated, or fused until particles of the desired particle size are obtained, and then external additives are added as required to obtain toner particles.

According to the emulsion aggregation method, a dispersion of binder resin particles is obtained by dropping a solution in which a binder resin is dissolved into a poor solvent, and the resulting dispersion is mixed with particles of colorants, release agents, charge control agents, external additives, and other optional additives, and these are aggregated, associated, or fused together until particles of the desired particle size are obtained, and then external additives are added as required to obtain toner particles.

When mixing as described above, a dispersion of colorant particles is mixed at the same time, thereby producing toner particles that constitute a colored toner. On the other hand, when mixing as described above, a dispersion of colorant particles is not mixed at the same time, thereby producing toner particles that constitute a colored toner.

It is also possible to obtain toner particles having a structure of two or more layers by further adding a polymerization initiator and a polymerizable monomer to the dispersion liquid of the binder resin particles and carrying out a polymerization process. Alternatively, binder resin particles having a structure of two or more layers may be produced by an emulsion polymerization method, and the toner may be produced using these.

(Career)
The carrier is mixed with the toner particles to form a two-component magnetic toner. The carrier may be any known magnetic particle that can be contained in a toner.

Examples of the magnetic particles include particles containing magnetic materials such as iron, steel, nickel, cobalt, ferrite, and magnetite, as well as alloys of these with aluminum and lead. The carrier may be a coated carrier in which the surface of particles made of the magnetic material is coated with a resin or the like, or a resin-dispersed carrier in which the magnetic material is dispersed in a binder resin. Examples of the resin for coating include olefin resin, styrene resin, styrene-acrylic resin, silicone resin, polyester resin, and fluororesin. Examples of the binder resin include acrylic resin, styrene-acrylic resin, polyester resin, fluororesin, and phenol resin.

The average particle size of the carrier is preferably a volume-based median diameter (D50) of 20 μm or more and 100 μm or less, and more preferably 25 μm or more and 80 μm or less. The average particle size of the carrier can be measured using a laser diffraction particle size distribution measuring device equipped with a wet disperser, such as HELOS manufactured by SYMPATEC.

The carrier content is preferably 2% by mass or more and 10% by mass or less based on the total mass of the toner particles and carrier.

[Image forming apparatus]
An image forming apparatus according to an embodiment of the present invention includes a toner image forming unit that develops an electrostatic latent image with multiple types of toner to form a toner image, a transfer unit that transfers the toner image to a surface of a recording medium, and a fixing unit that fixes the toner image to the surface of the recording medium, and the toner set includes a first toner containing a white pigment and a first hydrocarbon wax, and a second toner containing a second hydrocarbon wax, and when the branching degree of the first hydrocarbon wax is B1 and the branching degree of the second hydrocarbon wax is B2, B1 and B2 satisfy the condition of the following formula (1).

The image forming apparatus may be a five-cycle type image forming apparatus consisting of five types of color developing devices (white, yellow, magenta, cyan, and black) and one electrophotographic photoreceptor, or a tandem type image forming apparatus consisting of five types of color developing devices (white, yellow, magenta, cyan, and black) and five electrophotographic photoreceptors, one for each color.

Figure 1 is a schematic diagram showing an example of an image forming apparatus 10 according to this embodiment. The image forming apparatus 10 has an image reading unit 20, a toner image forming unit 30, an intermediate transfer unit 40 and a fixing unit 60 that constitute a fixing device, and a recording medium conveying unit 80.

Although not shown, the image forming device 10 includes a calculation device such as a CPU unit including a central processing unit (CPU) and random access memory (RAM) that also function as a control unit, and a read only memory (ROM) that also functions as a storage unit, as well as a communication circuit.

The image reading unit 20 reads an image from the original D and obtains image data for forming an electrostatic latent image. The image reading unit 20 has a paper feeder 21, a scanner 22, a CCD sensor 23, and an image processing unit 24.

The toner image forming section 30 includes five image forming units 31W, 31Y, 31M, 31C, and 31K, which correspond to the colors W (white), Y (yellow), M (magenta), C (cyan), and K (black). Each image forming unit 31 has a photoconductor (electrophotographic photoconductor) 32, a charging device 33, an exposure device 34, a developing device 35, and a cleaning device 36.

The photoconductor 32 is a negatively charged organic photoconductor having photoconductivity. The photoconductor 32 is charged by the charging device 33. The charging device 33 is a contact-type charging device that charges the photoconductor 32 by contacting a contact charging member such as a charging roller or a charging brush with the photoconductor 32, for example, a contact-type charging device that charges the photoconductor 32 by contact with a charging roller.

The exposure device 34 irradiates the charged photoconductor 32 with light to form an electrostatic latent image. The exposure device 34 is, for example, a semiconductor laser. The development device 35 supplies toner to the photoconductor 32 on which the electrostatic latent image has been formed, and causes the toner to adhere to a shape corresponding to the electrostatic latent image. The development device 35 is, for example, a known development device used in electrophotographic image forming devices. The cleaning device 36 removes residual toner from the photoconductor 32. In this manner, a toner image corresponding to each toner is formed.

The toner image includes a first toner (white toner) and a second toner (color toner), and the second toner is disposed closer to the surface of the intermediate transfer body (described later) than the first toner. That is, first, the toner images of the colors Y (yellow), M (magenta), C (cyan), and K (black) contained in the second toner are transferred from the image forming unit 31 to the intermediate transfer belt (described later), and then the first toner (white toner) is transferred onto the surface of the toner image formed by the second toner previously transferred to the intermediate transfer belt, thereby forming a toner image. Then, when the toner image is transferred to the recording medium S, the first toner (white toner) is disposed closer to the surface of the recording medium S than the second toner (color toner).

The intermediate transfer section 40 includes a primary transfer unit 41 and a secondary transfer unit 42.

The primary transfer unit 41 has an intermediate transfer belt 43, a primary transfer roller 44 arranged according to each image forming unit 31, a backup roller 45, a plurality of first support rollers 46, and a cleaning device 47. The intermediate transfer belt 43 is an endless belt. The intermediate transfer belt 43 is stretched by the backup roller 45 and the first support roller 46. The intermediate transfer belt 43 runs in one direction at a constant speed on an endless track by at least one of the backup roller 45 and the first support roller 46 being driven to rotate.

The secondary transfer unit 42 has a secondary transfer belt 48, a secondary transfer roller 49, and a plurality of second support rollers 50. The secondary transfer belt 48 is an endless belt. The secondary transfer belt 48 is stretched by the secondary transfer roller 49 and the second support rollers 50.

The toner images of each color (white, yellow, magenta, cyan, and black) are primarily transferred from each image forming unit 31 to the intermediate transfer belt 43, and the toner images are merged. The merged toner images are then secondarily transferred from the intermediate transfer belt 43 to the recording medium S traveling on the secondary transfer belt 48. The secondarily transferred toner image is made up of multiple types of toner, including a second toner (colored toner) and a first toner (white toner), attached to the same area of the recording medium S.

The fixing device 60 includes a fixing belt 61, a heating roller 62, a first pressure roller 63, a second pressure roller 64, a heater, a temperature sensor, an airflow separation device, a guide plate, and a guide roller.

The fixing belt 61 is made up of a base layer, an elastic layer, and a release layer laminated in that order. The fixing belt 61 is supported by a heating roller 62 and a first pressure roller 63 with the base layer on the inside and the release layer on the outside.

The heating roller 62 has a rotatable aluminum sleeve and a heater disposed inside it. The first pressure roller 63 has, for example, a rotatable core metal and an elastic layer disposed on its outer circumferential surface.

The second pressure roller 64 is disposed opposite the first pressure roller 63 via the fixing belt 61. The second pressure roller 64 is disposed so as to be able to approach and move away from the first pressure roller 63. When the second pressure roller 64 approaches the first pressure roller 63, it presses the elastic layer of the first pressure roller 63 via the fixing belt 61, forming a fixing nip portion which is the contact portion with the fixing belt 61.

The first pressure roller 63 and the second pressure roller 64, heated by the heating roller 62, press the toner image, in which the toner has been softened by irradiation with active light from the light irradiation section 65, against the recording medium, thereby further improving the fixability of the toner image.

The airflow separation device is a device that generates an airflow from the downstream side of the movement direction of the fixing belt 61 toward the fixing nip portion to promote separation of the recording medium S from the fixing belt 61.

The guide plate is a member for guiding the recording medium S having an unfixed toner image to the fixing nip. The guide roller is a member for guiding the recording medium having the fixed toner image from the fixing nip to the outside of the image forming device 10.

The recording medium transport section 80 has three recording medium tray units 81 and multiple registration roller pairs 82. The recording medium tray units 81 store recording media (film substrates in this embodiment) S, identified based on basis weight, size, etc., in a preset type. The registration roller pairs 82 are arranged to form a desired transport path.

In such an image forming device 10, first, a charged photoconductor 32 is irradiated with light to form an electrostatic latent image, and then toner is supplied to the photoconductor 32 to form a toner image corresponding to the electrostatic latent image. The toner image is transferred to the recording medium S sent by the recording medium conveying unit 80 by the intermediate transfer unit 40. The recording medium S to which the toner image has been transferred by the intermediate transfer unit 40 is fixed to the recording medium S by the fixing device 60. As a result, multiple types of toner including the first toner (white toner) and the second toner (colored toner) are fixed to the same area included in the recording medium S. The recording medium to which the toner image has been fixed is guided by a guide roller toward the outside of the image forming device 10.

In this embodiment, in addition to paper such as plain paper, a film substrate can be used as the recording medium onto which the toner image formed by the image forming device is transferred.

The above-mentioned films include known plastic films. Examples of the above-mentioned plastic films include polyester (PET) films, polyethylene (PE) films, polypropylene (PP) films, nylon (NY) films, polystyrene (PS) films, ethylene-vinyl acetate copolymer (EVA) films, polyvinyl chloride (PVC) films, polyvinyl alcohol (PVA) films, polyacrylic acid (PAA) films, polycarbonate films, polyacrylonitrile films, and biodegradable films such as polylactic acid films.

To impart gas barrier properties, moisture resistance, and aroma retention, one or both sides of the film may be coated with polyvinylidene chloride or a metal oxide may be vapor-deposited. The film may also be anti-fogging. The film may also be corona discharged, ozone treated, etc.

The film may be an unstretched film or a stretched film, or it may be a multi-layered substrate in which a layer such as a PVA coating is provided on the surface of an absorbent substrate such as paper, making the area to be recorded non-absorbent.

The image forming device according to this embodiment is capable of printing A4 sheets at an output speed of 100 sheets per minute or more.

The present invention will be described in more detail below using examples and comparative examples, but the present invention is not limited to the following examples. In addition, unless otherwise specified, each operation was performed at room temperature (25°C).

[Preparation of amorphous resin particle dispersion]
(First stage polymerization)
A 5L reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube and a nitrogen introduction device was charged with 8 parts by mass of sodium dodecyl sulfate and 3000 parts by mass of ion-exchanged water, and the internal temperature of the reaction vessel was raised to 80° C. while stirring at a stirring speed of 230 rpm under a nitrogen stream. After the temperature was raised, an aqueous solution in which 10 parts by mass of potassium persulfate was dissolved in 200 parts by mass of ion-exchanged water was added to the resulting mixture, and the temperature of the resulting mixture was again raised to 80° C. A monomer mixture 1 having the following composition was added dropwise to the mixture over 1 hour, and the mixture was heated and stirred at 80° C. for 2 hours to polymerize, thereby preparing a dispersion a1 of resin fine particles.
(Monomer Mixture 1)
Styrene 480 parts by weight n-Butyl acrylate 250 parts by weight Methacrylic acid 68 parts by weight

(Second stage polymerization)
A 5L reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube, and a nitrogen introduction device was charged with a solution of 7 parts by weight of sodium polyoxyethylene (2) dodecyl ether sulfate dissolved in 3000 parts by weight of ion-exchanged water, and the solution was heated to 80°C, after which 80 parts by weight of dispersion a1 of resin microparticles (solid content equivalent) and monomer mixture 2 having the following composition were added, and the mixture was mixed and dispersed for 1 hour using a mechanical disperser "CLEARMIX" (manufactured by M Technique Co., Ltd., "CLEARMIX" is a registered trademark of the company) having a circulation path to prepare a dispersion containing emulsified particles (oil droplets). The following hydrocarbon wax 1 is a Fischer-Tropsch wax with a branching degree of 2% (branching degree: 2%, melting point: 80°C).
(Monomer Mixture 2)
Styrene 285 parts by weight n-Butyl acrylate 95 parts by weight Methacrylic acid 20 parts by weight n-Octyl-3-mercaptopropionate 8 parts by weight Hydrocarbon wax 1 190 parts by weight

Next, an initiator solution in which 6 parts by weight of potassium persulfate was dissolved in 200 parts by weight of ion-exchanged water was added to the above dispersion, and the resulting dispersion was heated and stirred at 84°C for 1 hour to polymerize, thereby preparing dispersion a2 of resin microparticles.

(Third stage polymerization)
400 parts by mass of ion-exchanged water was added to the dispersion a2 of resin fine particles obtained by the second-stage polymerization and mixed thoroughly, and then a solution in which 11 parts by mass of potassium persulfate was dissolved in 400 parts by mass of ion-exchanged water was added to the resulting dispersion, and a monomer mixture 3 having the following composition was added dropwise over 1 hour at a temperature condition of 82° C. After completion of the dropwise addition, the dispersion was heated and stirred for 2 hours to polymerize, and then cooled to 28° C. to prepare amorphous resin fine particle dispersion X1 (hereinafter also referred to as "amorphous dispersion X1") made of vinyl resin (styrene-acrylic resin).
(Monomer Mixture 3)
Styrene 307 parts by weight n-Butyl acrylate 147 parts by weight Methacrylic acid 52 parts by weight n-Octyl-3-mercaptopropionate 8 parts by weight

The physical properties of the obtained amorphous dispersion X1 were measured, and the volume-based median diameter (d50) of the amorphous resin microparticles was 220 nm, the glass transition temperature (Tg) was 46°C, and the weight average molecular weight (Mw) was 32,000.

The median diameter (d50) was measured using a Microtrac particle size distribution analyzer "UPA-150" (manufactured by Nikkiso Co., Ltd.), the glass transition temperature (Tg) was measured using a thermal analyzer "Diamond DSC" (manufactured by PerkinElmer), and the weight average molecular weight (Mw) was measured using a GPC device "HLC-8120GPC" (manufactured by Tosoh Corporation).

[Preparation of amorphous dispersions X2 to X7]
Amorphous dispersions X2 to X7 were obtained in the same manner as in the preparation of amorphous dispersion X1, except that the hydrocarbon wax 1 in the second-stage polymerization was changed to the wax shown in Table 1.

[Synthesis of crystalline polyester resin P]
281 parts by mass of sebacic acid and 283 parts by mass of 1,10-decanediol were placed in a reaction vessel equipped with a stirrer, a thermometer, a cooling tube, and a nitrogen gas inlet tube. After replacing the inside of the reaction vessel with dry nitrogen gas, 0.1 parts by mass of Ti(OBu) ₄ was added, and the resulting mixture was stirred under a nitrogen gas flow at about 180°C for 8 hours to carry out a reaction. Furthermore, 0.2 parts by mass of Ti(OBu) ₄ was added to the mixture, the temperature of the mixture was raised to about 220°C, and the mixture was stirred for 6 hours to carry out a reaction. Thereafter, the pressure in the reaction vessel was reduced to 1333.2 Pa, and the reaction was carried out under reduced pressure to obtain a crystalline polyester resin P. The number average molecular weight (Mn) of the crystalline polyester resin P was 5500, the weight average molecular weight (Mw) was 18000, and the melting point (Tm) was 70°C. The number average molecular weight (Mn) and weight average molecular weight (Mw) of the crystalline polyester resin P were measured using a GPC apparatus "HLC-8120GPC", and the melting point (Tm) was measured using a thermal analysis apparatus "Diamond DSC".

[Preparation of Crystalline Resin Particle Dispersion Y]
30 parts by mass of crystalline polyester resin P was transferred to an emulsifier/disperser "Cavitron CD1010" (manufactured by Eurotech Co., Ltd.) at a transfer rate of 100 parts by mass per minute in a melted state. At the same time, dilute ammonia water with a concentration of 0.37% by mass was transferred to the emulsifier/disperser at a transfer rate of 0.1 liters per minute while being heated to 100°C by a heat exchanger. The dilute ammonia water was prepared by diluting 70 parts by mass of reagent ammonia water with ion-exchanged water in an aqueous solvent tank. Then, the emulsifier/disperser was operated under conditions of a rotor rotation speed of 60 Hz and a pressure of 5 kg/cm ² (490 kPa) to prepare a crystalline resin microparticle dispersion Y of crystalline polyester resin P with a solid content of 30 parts by mass (hereinafter also referred to as "crystalline dispersion Y"). The volume-based median diameter (d50) of the particles of crystalline polyester resin P contained in crystalline dispersion Y was 200 nm. The above median diameter (d50) was measured using a Microtrack particle size distribution measuring device "UPA-150" (manufactured by Nikkiso Co., Ltd.).

[Preparation of White Dispersion W]
90 parts by mass of sodium dodecyl sulfate was dissolved in 1600 parts by mass of ion-exchanged water by stirring, and 420 parts by mass of titania pigment was gradually added while stirring the solution. The obtained dispersion was then subjected to a dispersion treatment using a stirring device "CLEARMIX" to prepare titania pigment fine particle dispersion W (hereinafter also referred to as "white dispersion W") in which titania pigment fine particles were dispersed. The volume-based median diameter (d50) of the white dispersion W1 was 150 nm. The above median diameter (d50) was measured using a Microtrack particle size distribution measuring device "UPA-150".

[Preparation of Colorant Dispersion C]
90 parts by mass of sodium dodecyl sulfate was dissolved in 1600 parts by mass of ion-exchanged water by stirring, and 420 parts by mass of C.I. Pigment Blue 18:3 was gradually added while stirring the solution. Next, the obtained dispersion was dispersed using a stirring device "CLEARMIX" to prepare a colorant particle dispersion C (hereinafter also referred to as "colorant dispersion C") in which colorant particles were dispersed. The volume-based median diameter (d50) of the colorant dispersion C was 150 nm. The above median diameter (d50) was measured using a Microtrack particle size distribution measuring device "UPA-150".

[Synthesis of amorphous polyester resin S]
Monomer mixture 4 having the following composition including an amphoteric compound (acrylic acid) was placed in the dropping funnel. Di-t-butyl peroxide was used as a polymerization initiator.
(Monomer Mixture 4)
Styrene 80 parts by weight n-Butyl acrylate 20 parts by weight Acrylic acid 10 parts by weight Di-t-butyl peroxide 16 parts by weight

Furthermore, the raw material monomers for the polycondensation segment (amorphous polyester segment) described below were placed in a four-neck flask equipped with a nitrogen inlet tube, a dehydration tube, a stirrer and a thermocouple, and were heated to 170° C. to dissolve.
(Amorphous polyester segment)
Bisphenol A propylene oxide 2 mole adduct 285.7 parts by mass Terephthalic acid 66.9 parts by mass Fumaric acid 47.4 parts by mass

Next, the monomer mixture 4 was added dropwise to the resulting solution under stirring over a period of 90 minutes, and the mixture was aged for 60 minutes, after which unreacted monomers among the components of the monomer mixture 4 were removed from the four-neck flask under reduced pressure (8 kPa). Then, 0.4 parts by mass of Ti(OBu) ₄ was added as an esterification catalyst to the four-neck flask, and the mixture in the four-neck flask was heated to 235° C. and reacted under normal pressure (101.3 kPa) for 5 hours and further under reduced pressure (8 kPa) for 1 hour to obtain an amorphous polyester resin S.

[Preparation of Amorphous Polyester Fine Particle Dispersion S]
100 parts by mass of amorphous polyester resin S was dissolved in 400 parts by mass of ethyl acetate (manufactured by Kanto Chemical Co., Ltd.) and mixed with 638 parts by mass of a 0.26% by mass sodium lauryl sulfate solution prepared in advance. The resulting mixture was ultrasonically dispersed for 30 minutes with stirring using an ultrasonic homogenizer "US-150T" (manufactured by Nippon Seiki Seisakusho Co., Ltd.) under a condition of V-LEVEL of 300 μA. Thereafter, the mixture was heated to 40° C. and stirred under reduced pressure for 3 hours using a diaphragm vacuum pump "V-700" (manufactured by BUCHI Co., Ltd.) to completely remove ethyl acetate, thereby obtaining an amorphous polyester resin fine particle dispersion S (hereinafter also referred to as "shell dispersion S") having a solid content of 13.5% by mass. The volume-based median diameter (d50) of the shell resin particles in the shell dispersion S was 160 nm. The above median diameter (d50) was measured using a Microtrac particle size distribution measuring device "UPA-150."

[Preparation of release agent dispersion]
As a release agent, 200 parts by mass of the hydrocarbon wax 6 was heated to 95°C and melted. Further, the wax was added to a surfactant aqueous solution in which 800 parts by mass of alkyl diphenyl ether disulfonate sodium was dissolved in ion-exchanged water to give a concentration of 3% by mass, and then dispersed with an ultrasonic homogenizer to prepare a release agent dispersion. The solid content (content of the release agent) in the release agent dispersion was adjusted to 20% by mass. The average particle size of the release agent in the release agent dispersion was 190 nm. The above-mentioned hydrocarbon wax 6 was a microcrystalline wax (branching degree: 53%).

[Production of White Toner 1]
Into a reaction vessel equipped with a stirrer, a temperature sensor, and a cooling tube, 288 parts by mass of amorphous dispersion X1 (solid content equivalent) and 2000 parts by mass of ion-exchanged water were added, and then 5 mol/L of sodium hydroxide aqueous solution was further added to adjust the pH of the dispersion in the reaction vessel to 10 (measurement temperature 25 ° C.). 30 parts by mass of white dispersion W (solid content equivalent) was added to the dispersion. Next, an aqueous solution in which 30 parts by mass of magnesium chloride was dissolved in 60 parts by mass of ion-exchanged water as a flocculant was added to the reaction vessel over 10 minutes at 30 ° C. under stirring. The particle size of the particles associated in the mixture was measured with a "Coulter Multisizer 3" (manufactured by Beckman Coulter, Inc.), and when the volume-based median diameter (d50) of the particles became 6.0 μm, 37 parts by mass of shell dispersion S (solid content equivalent) was added to the mixture over 30 minutes. When the supernatant of the resulting reaction solution became transparent, an aqueous solution of 190 parts by mass of sodium chloride dissolved in 760 parts by mass of ion-exchanged water was added to the reaction solution to stop particle growth.

The reaction liquid was further heated to 80°C and stirred to promote fusion of the particles, and the particles in the reaction liquid were measured (HPF detection number: 4,000) using a measuring device "FPIA-2100" (Sysmex Corporation). When the average circularity of the particles reached 0.945, the reaction liquid was cooled to 30°C at a cooling rate of 2.5°C/min. Next, the particles were separated from the cooled reaction liquid and dehydrated, and the resulting cake was washed by redispersing in ion-exchanged water and separating the solid from the liquid three times, and then dried at 40°C for 24 hours to obtain white toner base particles 1.

0.6 parts by mass of hydrophobic silica (number average primary particle diameter = 12 nm, hydrophobicity = 68) and 1.0 parts by mass of hydrophobic titanium oxide (number average primary particle diameter = 20 nm, hydrophobicity = 63) were added to 100 parts by mass of white toner base particles, and these were mixed in a "Henschel Mixer" (manufactured by Nippon Coke & Engineering Co., Ltd.) at a rotor circumferential speed of 35 mm/sec and 32°C for 20 minutes, after which coarse particles were removed using a sieve with 45 μm openings. By carrying out this external additive treatment, white toner particles 1, which are aggregates of white toner base particles B, were produced.

The above white toner particles 1 and a ferrite carrier with a volume average particle size of 32 μm coated with an acrylic resin were added and mixed so that the toner particle concentration was 6 mass %. In this way, white developer 1, which is a two-component developer containing white toner particles 1, was produced.

[Production of White Toner 3]
Into a reaction vessel equipped with a stirrer, a temperature sensor, and a cooling tube, 288 parts by mass of amorphous dispersion X1 (solid content equivalent) and 2000 parts by mass of ion-exchanged water were added, and then 5 mol/L of sodium hydroxide aqueous solution was further added to adjust the pH of the dispersion in the reaction vessel to 10 (measurement temperature 25 ° C.). 30 parts by mass of white dispersion W (solid content equivalent) was added to the dispersion. Next, an aqueous solution in which 30 parts by mass of magnesium chloride was dissolved in 60 parts by mass of ion-exchanged water as a flocculant was added to the reaction vessel at 30 ° C. over 10 minutes under stirring. The resulting mixture was heated to 80 ° C., and 40 parts by mass of crystalline dispersion Y (solid content equivalent) was added to the mixture over 10 minutes to flocculate. The particle size of the particles associated in the above mixture was measured using a "Coulter Multisizer 3" (manufactured by Beckman Coulter, Inc.), and when the volume-based median diameter (d50) of the particles reached 6.0 μm, 37 parts by mass of shell dispersion S (solid content equivalent) was added to the above mixture over 30 minutes. When the supernatant of the resulting reaction solution became transparent, an aqueous solution in which 190 parts by mass of sodium chloride was dissolved in 760 parts by mass of ion-exchanged water was added to the reaction solution to stop particle growth.

The reaction liquid was further heated to 80°C and stirred to promote fusion of the particles, and the particles in the reaction liquid were measured (HPF detection number: 4,000) using a measuring device "FPIA-2100" (manufactured by Sysmex Corporation). When the average circularity of the particles reached 0.945, the reaction liquid was cooled to 30°C at a cooling rate of 2.5°C/min. Next, the particles were separated from the cooled reaction liquid and dehydrated, and the resulting cake was washed by redispersing in ion-exchanged water and separating the solid from the liquid three times, and then dried at 40°C for 24 hours to obtain white toner base particles 3.

The white toner particles and white developer were produced in the same manner as for white toner 1.

[Production of White Toners 2, 4 to 6]
White toners 2, 4 to 6 were produced in the same manner as white toner 1, except that amorphous dispersion X1 was changed to the amorphous dispersion shown in Table 2. White developers 2, 4 to 6 were produced in the same manner as white developer 1. Table 2 shows the content (unit: parts by mass) of each component of white toners 2, 4 to 6. The contents of the amorphous dispersion and crystalline dispersion are values calculated as solid contents.

[Production of Cyan Toner 1]
Into a reaction vessel equipped with a stirring device, a temperature sensor, and a cooling tube, 288 parts by mass of amorphous dispersion X6 (solid content equivalent) and 2000 parts by mass of ion-exchanged water were added, and then 5 mol/L of sodium hydroxide aqueous solution was further added to adjust the pH of the dispersion in the reaction vessel to 10 (measurement temperature 25 ° C.). 30 parts by mass of colorant dispersion C (solid content equivalent) was added to the dispersion. Next, an aqueous solution in which 30 parts by mass of magnesium chloride was dissolved in 60 parts by mass of ion-exchanged water as a flocculant was added to the reaction vessel at 30 ° C. over 10 minutes under stirring. The resulting mixture was heated to 80 ° C., and 40 parts by mass of crystalline dispersion Y (solid content equivalent) was added to the mixture over 10 minutes to flocculate. The particle size of the particles associated in the above mixture was measured using a "Coulter Multisizer 3" (manufactured by Beckman Coulter, Inc.), and when the volume-based median diameter (d50) of the particles reached 6.0 μm, 37 parts by mass of shell dispersion S (solid content equivalent) was added to the above mixture over 30 minutes. When the supernatant of the resulting reaction solution became transparent, an aqueous solution in which 190 parts by mass of sodium chloride was dissolved in 760 parts by mass of ion-exchanged water was added to the reaction solution to stop particle growth.

The reaction liquid was further heated to 80°C and stirred to promote fusion of the particles, and the particles in the reaction liquid were measured using a measuring device "FPIA-2100" (HPF detection number: 4,000 particles). When the average circularity of the particles reached 0.945, the reaction liquid was cooled to 30°C at a cooling rate of 2.5°C/min. Next, the particles were separated from the cooled reaction liquid and dehydrated, and the resulting cake was washed by redispersing in ion-exchanged water and separating the solid from the liquid three times, and then dried at 40°C for 24 hours to obtain cyan toner base particles.

0.6 parts by mass of hydrophobic silica (number average primary particle diameter = 12 nm, hydrophobicity = 68) and 1.0 parts by mass of hydrophobic titanium oxide (number average primary particle diameter = 20 nm, hydrophobicity = 63) were added to 100 parts by mass of cyan toner base particles, and these were mixed in a "Henschel Mixer" (manufactured by Nippon Coke & Engineering Co., Ltd.) at a rotor circumferential speed of 35 mm/sec and 32°C for 20 minutes, after which coarse particles were removed using a sieve with 45 μm openings. This external additive treatment was carried out to produce cyan toner 1, which is an aggregate of cyan toner base particles.

The above cyan toner particles 1 and a ferrite carrier with a volume average particle size of 32 μm coated with an acrylic resin were added and mixed so that the toner particle concentration was 6 mass %. In this way, cyan developer 1, which is a two-component developer containing cyan toner 1, was produced.

[Production of Cyan Toner 8]
313.4 parts by mass of amorphous polyester resin dispersion S (solid content), 11.6 parts by mass of release agent dispersion (solid content), 30 parts by mass of colorant dispersion C (solid content), 40 parts by mass of crystalline dispersion Y (solid content), and 0.5 parts by mass of sodium polyoxyethylene lauryl ether sulfate were charged into a reaction vessel equipped with a stirrer, a cooling tube, and a thermometer, and 0.1N hydrochloric acid was added while stirring to adjust the pH to 2.5. Next, 0.4 parts by mass of an aqueous polyaluminum chloride solution (10% by mass aqueous solution in terms of AlCl ₃ ) was dropped over 10 minutes, and the temperature was raised at a rate of 0.05 ° C. / min while stirring, and the particle size of the aggregated particles was appropriately measured using "Multisizer 3" (manufactured by Beckman Coulter, Inc.). When the median diameter based on the volume of the aggregated particles reached 5.6 μm, the temperature was stopped. Then, the pH in the system was adjusted to 8.5 with a 0.5N aqueous sodium hydroxide solution to stop the particle size growth. Furthermore, the internal temperature was raised to 85°C, and when the average circularity (shape factor) reached 0.960 using "FPIA-2000" (manufactured by Sysmex), the mixture was cooled to room temperature at a rate of 10°C/min. The reaction liquid was repeatedly filtered and washed, and then dried to obtain cyan toner 8.

Cyan developer 8 was also produced in the same manner as cyan developer 1.

[Production of Cyan Toners 2 to 7]
Cyan toners 2 to 7 were produced in the same manner as for cyan toner 1, except that amorphous dispersion X1 was changed to the amorphous dispersion shown in Table 3. Cyan developers 2 to 7 were produced in the same manner as for cyan developer 1. Table 3 shows the content (unit: parts by mass) of each component in cyan toners 1 to 8. The contents of the amorphous dispersion and crystalline dispersion are values calculated as solid contents.

4. Evaluation The prepared white toners 1 to 6 and cyan toners 1 to 8 were combined as shown in Table 4 to form toner sets, which were then evaluated for color turbidity and fixing separation properties.

[Color turbidity evaluation]
(Evaluation method)
Five developing machines, each loaded with the toner set shown in Table 4, were placed in a modified image forming apparatus "bizhub PRO C6500," and an A4-sized recording medium "Tencolor (152 g/ ^cm2 per square meter, manufactured by Oji F-Tex Co., Ltd.)" was used to create an image depicting the alphabet "A" (20 pt) measuring 5 x 5 cm. The edges of the "A" image in the first formed image and the 10,000th formed image were visually inspected and observed with a 2000x optical microscope "VHX-2000" (manufactured by Keyence Corporation) to see whether the color of the color toner underneath could be identified. ◯ and ◎ were deemed to be acceptable.

(Evaluation criteria)
◎: Cannot be distinguished by visual inspection or optical microscope ○: Cannot be distinguished by visual inspection, but the toner color of the lower layer can be distinguished by optical microscope △: Can be slightly distinguished by visual inspection, but the toner color of the lower layer can be clearly distinguished by optical microscope ×: Can be clearly distinguished by visual inspection

[Evaluation of Fixing Separation]
(Evaluation method)
In a copying machine "bizhub PRO C6501" (manufactured by Konica Minolta, Inc.), a fixing device was modified so that the surface temperature of the fixing heat roller could be changed within the range of 100 to 210°C, and toner sets 1 to 12 shown in Table 4 were loaded into the fixing device. The surface temperature of the heating roller of the fixing device was set to 190°C, and a 10 cm wide solid band image extending in the axial direction of the heating roller was fixed on an A4 size recording medium "Tencolor (152 g/ ^cm2 per unit area)" conveyed vertically at room temperature and normal pressure (temperature 20°C, relative humidity 55%), and the separation property was evaluated according to the following evaluation criteria. ◎ and ◯ were deemed to be acceptable.

(Evaluation criteria)
⊚: The recording medium can be separated from the heating roller without curling, and there is no degradation of the image. ◯: The recording medium is separated from the heating roller, but white streaks are observed on the image. ×: The recording medium wraps around the heating roller, and cannot be separated from the heating roller.

The evaluation results are shown in Table 5.

It was found that by making the difference (|B1-B2|) between the branching degree of the first hydrocarbon wax (B1) and the branching degree of the second hydrocarbon wax (B2) 10% or more, and by making the branching degree of the second hydrocarbon wax (B2) 10% or more, color turbidity does not occur even when the first toner (white toner) and the second toner (colored toner) are printed on top of each other.

This is believed to be because, during fixing and melting, the hydrocarbon waxes contained in the first toner and the second toner seep out onto the toner surface, forming a pseudo core-shell structure. In other words, the first wax constituting the pseudo shell layer of the first toner and the second wax constituting the pseudo shell layer of the second toner have different degrees of branching and different structures, making it difficult for the molecules contained in the wax to approach each other. This reduces the interaction between the molecules contained in the wax, which is believed to suppress color turbidity in the formed image.

In addition, by using the toner of the present invention, it is possible to suppress deterioration of the formed image. This is thought to be because the binder resin and the hydrocarbon wax contained in the first toner and the second toner are poorly compatible with each other, which makes it easier for the hydrocarbon wax to seep out onto the surface of the formed image, improving separation properties.

According to the present invention, it is possible to provide a toner set that has excellent fixability to a substrate and excellent separability from a fixing member, and that can suppress a decrease in image density, and an image forming apparatus that uses the toner set. Therefore, according to the present invention, it is expected that the performance of electrophotographic image forming apparatuses will be improved, and further spread of image forming apparatuses is expected.

10 Image forming apparatus 20 Image reading section 21 Paper feeding device 22 Scanner 23 CCD sensor 24 Image processing section 30 Toner image forming section 31 Image forming unit 32 Photoconductor 33 Charging device 34 Exposure device 35 Developing device 36 Cleaning device 40 Intermediate transfer section 41 Primary transfer unit 42 Secondary transfer unit 43 Intermediate transfer belt 44 Primary transfer roller 45 Backup roller 46 First support roller 47 Cleaning device 48 Secondary transfer belt 49 Secondary transfer roller 50 Second support roller 60 Fixing device 61 Fixing belt 62 Heating roller 63 First pressure roller 64 Second pressure roller 80 Recording medium transport section 81 Recording medium tray unit 82 Registration roller pair D Document S Recording medium

Claims (10)

a first toner containing a white pigment and a first hydrocarbon wax;
a second toner containing a second hydrocarbon wax;
Including,
the first hydrocarbon wax is a paraffin wax, a Fischer-Tropsch wax or a microcrystalline wax;
the second hydrocarbon wax is a paraffin wax, a Fischer-Tropsch wax or a microcrystalline wax;
When the area ratio (%) of branched hydrocarbons in the area of a chromatogram obtained by measuring a xylene solution of a hydrocarbon wax having a sample concentration of 1%, is defined as the branching degree of the hydrocarbon wax,
A toner set, in which when the degree of branching of the first hydrocarbon wax is B1 and the degree of branching of the second hydrocarbon wax is B2, B1 and B2 satisfy the condition of the following formula (1).

The toner set according to claim 1 , wherein B1 and B2 satisfy the condition of the following formula (2).

The toner set according to claim 1 or 2, wherein the branching degree (B2) of the second hydrocarbon wax is 10% or more. The toner set according to any one of claims 1 to 3, wherein the content of the second hydrocarbon wax in the second toner is 3 mass% or more with respect to the total mass of the second toner. The toner set according to any one of claims 1 to 4, wherein the second toner contains a crystalline polyester resin. The toner set according to any one of claims 1 to 5, wherein the content of the crystalline polyester resin in the first toner is 10% by mass or less with respect to the total mass of the first toner. The toner set according to any one of claims 1 to 6, wherein the second toner contains a styrene-acrylic resin, and the content of the styrene-acrylic resin in the second toner is 60% by mass or more relative to the total mass of the second toner. a toner image forming unit that develops the electrostatic latent image with a plurality of types of toner to form a toner image;
a transfer section for transferring the toner image onto a surface of a recording medium;
a fixing section for fixing the toner image onto a surface of the recording medium;
Equipped with
The plurality of toners include a first toner containing a white pigment and a first hydrocarbon wax;
a second toner containing a second hydrocarbon wax;
Including,
the first hydrocarbon wax is a paraffin wax, a Fischer-Tropsch wax or a microcrystalline wax;
the second hydrocarbon wax is a paraffin wax, a Fischer-Tropsch wax or a microcrystalline wax;
When the area ratio (%) of branched hydrocarbons in the area of a chromatogram obtained by measuring a xylene solution of a hydrocarbon wax having a sample concentration of 1%, is defined as the branching degree of the hydrocarbon wax,
An image forming apparatus, wherein when the degree of branching of the first hydrocarbon wax is B1 and the degree of branching of the second hydrocarbon wax is B2, B1 and B2 satisfy the condition of the following formula (1):

The image forming device according to claim 8, wherein the toner image forming unit forms the toner image so that the second toner is disposed closer to the surface of the intermediate transfer body than the first toner. The image forming apparatus according to claim 8 or claim 9, wherein the recording medium is a film substrate.

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