JP7341867B2 - White toner for electrophotography - Google Patents

Description

The present invention relates to an electrophotographic white toner used for developing latent images formed in electrophotography, electrostatic recording, electrostatic printing, etc., and an image forming method using the white toner.

2. Description of the Related Art When printing a color image on a recording medium such as colored paper or transparent film, it has been proposed to enhance the color development of the color toner image by layering the color toner image on top of the white toner image.

As an image forming method using a white toner and a colored toner (color toner), for example, Patent Document 1 describes a white toner image made of a white toner containing a first binder resin and a first colorant; The image forming method includes a heat fixing treatment step of laminating and heat fixing a colored toner image made of a colored toner other than white containing a second binder resin and a second colorant on a recording medium in this order. The second binder resin includes a vinyl resin and a hybrid crystalline polyester resin, and the storage elastic modulus G1' at 90°C of the white toner and the storage elastic modulus at 90°C of the colored toner other than white are the same. An image forming method is disclosed in which G2' satisfies a predetermined relational expression.

JP 2019-53219 Publication

However, if a white toner image and a color toner image are laminated in an unfixed state and then thermally fixed, the white toner and color toner will mix, resulting in a problem in that the color development of the color image will deteriorate.

The present invention provides a white toner for electrophotography that suppresses color mixing with color toners even when a white toner image and a color toner image are laminated in an unfixed state and thermally fixed to form an image, and the white toner. The present invention relates to the image forming method used.

The present invention
[1] A white toner for electrophotography containing a binder resin and titanium oxide particles, wherein the binder resin contains 25% by mass or more of a composite resin having a polyester resin and a styrene resin, and the titanium oxide particles [2] Using the white toner and color toner described in [1] above, the content of which is 50 parts by mass or more and 200 parts by mass or less based on 100 parts by mass of the binder resin. The present invention relates to an image forming method that includes a step of laminating a color toner image in an unfixed state on an unfixed white toner image on a recording medium and then thermally fixing the image.

By using the white toner for electrophotography of the present invention, even if a white toner image and a color toner image are laminated in an unfixed state and thermally fixed to form an image, color mixing between the white toner and the color toner is suppressed. can do.

The white toner for electrophotography of the present invention is characterized in that it contains a predetermined amount of titanium oxide particles, and the binder resin contains a composite resin containing a polyester resin and a styrene resin. Even if a white toner image and a color toner image are both stacked in an unfixed state and thermally fixed to form an image, color mixing between the white toner and the color toner can be suppressed.

The decrease in color development of a color toner image due to color mixing of white toner and color toner is due to the fact that the principle of color development of color toners such as cyan toner and yellow toner is different from that of white toner.
For example, the principle of color development of cyan toner is that a cyan pigment absorbs wavelengths other than the wavelength of light that is the source of the cyan color, and the color is developed by transmitting or reflecting light of the wavelength that is the source of the cyan color. Therefore, in the case of color toners, there is no problem even if the colors are mixed based on the above principle.
On the other hand, the principle behind white toner's color development is that white pigments refract, reflect, and scatter light of all wavelengths (visible light) to produce white color.
Therefore, when color toner and white toner are mixed, all wavelengths are refracted, reflected, and scattered in the white toner, reducing the color development properties of the color toner. decrease becomes noticeable.

Regarding this problem, although the details of the reason why color mixing is improved when the white toner contains a composite resin are not clear, it is presumed as follows.
When the white toner has non-uniform chargeability and fluidity, particles with high fluidity and particles with low chargeability are susceptible to external forces and are considered to be detached from the white toner image, causing color mixing. On the other hand, in a toner containing a composite resin, titanium oxide, which is a white pigment, is well dispersed, so that the uniformity of each toner is improved. As a result, the external additive adheres uniformly to the surface of the white toner, and the fluidity and chargeability of each toner become uniform. Due to this highly uniform toner, an unfixed image of white toner on a recording medium is formed by particles with uniform chargeability and fluidity. It is thought that this makes it difficult for the toner to scatter or separate, thereby suppressing color mixing between the color toner and the white toner.

As described above, the white toner of the present invention contains a composite resin containing a polyester resin and a styrene resin as a binder resin. The composite resin may be either an amorphous composite resin or a crystalline composite resin, and both may be used in combination. In the present invention, it is preferable to contain an amorphous composite resin from the viewpoint of low-temperature fixability and heat-resistant storage stability.

The crystallinity of the resin is expressed by a crystallinity index defined by the ratio of the softening point to the maximum endothermic peak temperature measured by a differential scanning calorimeter, that is, the value of [softening point/maximum endothermic peak temperature]. The crystalline resin has a crystallinity index of 0.6 or more, preferably 0.7 or more, more preferably 0.9 or more, and 1.4 or less, preferably 1.2 or less, more preferably 1.1 or less, while amorphous resin is a resin with a crystallinity index of more than 1.4, preferably more than 1.5, more preferably 1.6 or more, or less than 0.6, preferably 0.5 or less. The crystallinity of the resin can be adjusted by the types and ratios of raw material monomers, manufacturing conditions (for example, reaction temperature, reaction time, cooling rate), and the like. Note that the maximum endothermic peak temperature refers to the temperature of the peak with the largest peak area among the observed endothermic peaks. For crystalline resins, the maximum peak temperature of endotherm is defined as the melting point.

The polyester resin is preferably a polycondensate of an alcohol component containing a dihydric or higher alcohol and a carboxylic acid component containing a divalent or higher carboxylic acid compound.

Examples of the alcohol component include aliphatic diols, preferably carbon atoms of 2 to 20, more preferably carbon atoms of 2 to 15, and formula (I):

(In the formula, OR and RO are oxyalkylene groups, R is an ethylene group and/or a propylene group, x and y indicate the average number of added moles of alkylene oxide, and each is a positive number, x and y The sum value is 1 or more, preferably 1.5 or more, and 16 or less, preferably 8 or less, more preferably 6 or less, and even more preferably 4 or less)
Examples include alkylene oxide adducts of bisphenol A represented by the following, bisphenol A, hydrogenated bisphenol A, and glycerin.

As the alcohol component of the amorphous composite resin, an alkylene oxide adduct of bisphenol A represented by formula (I) is preferable from the viewpoint of low-temperature fixability and heat-resistant storage stability. The content of the alkylene oxide adduct of bisphenol A represented by formula (I) is preferably 50 mol% or more, more preferably 70 mol% or more, and even more preferably 90 mol% in the alcohol component of the amorphous composite resin. % or more, more preferably 95 mol% or more, even more preferably 100 mol%.

As the alcohol component of the crystalline composite resin, aliphatic diols are preferred. As the aliphatic diol, α,ω-linear alkanediol is preferable from the viewpoint of increasing the crystallinity of the composite resin and improving the low-temperature fixability, and examples thereof include 1,4-butanediol, 1,6-hexanediol, 1, Examples include 9-nonanediol, 1,10-decanediol, 1,12-dodecanediol, 1,14-tetradecanediol, and the like. Among these, one or two selected from 1,10-decanediol and 1,12-dodecanediol are more preferred, and 1,10-decanediol is even more preferred.

The number of carbon atoms in the aliphatic diol contained in the alcohol component of the crystalline composite resin is preferably 4 or more, more preferably 9 or more, still more preferably 10 or more from the viewpoint of heat-resistant storage stability, and From the viewpoint of pigment dispersibility, it is preferably 14 or less, more preferably 12 or less.

The content of aliphatic diol in the alcohol component of the crystalline composite resin is preferably 70 mol% or more, more preferably 90 mol% or more, and even more preferably is 95 mol% or more, more preferably 100 mol%.

Among the carboxylic acid components, divalent carboxylic acid compounds include aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, and terephthalic acid, oxalic acid, malonic acid, maleic acid, fumaric acid, citraconic acid, itaconic acid, and glutaconic acid. , succinic acid, adipic acid, aliphatic dicarboxylic acids such as succinic acid, azelaic acid, sebacic acid, dodecanedioic acid, tetradecanedioic acid, etc. substituted with an aliphatic hydrocarbon group having 1 to 30 carbon atoms, cyclohexanedicarboxylic acid Examples include alicyclic dicarboxylic acids such as, their anhydrides, and derivatives such as alkyl esters in which the alkyl group has 1 to 3 carbon atoms. Note that the carboxylic acid compound refers to carboxylic acid, its anhydride, and its alkyl ester having 1 or more and 3 or less carbon atoms.

Examples of trivalent or higher carboxylic acid compounds include 1,2,4-benzenetricarboxylic acid (trimellitic acid), 2,5,7-naphthalenetricarboxylic acid, and 1,2,4,5-benzenetetracarboxylic acid (pyrotricarboxylic acid). mellitic acid), or their acid anhydrides.

The carboxylic acid component of the amorphous composite resin preferably contains an aromatic dicarboxylic acid compound from the viewpoint of charging stability. The content of the aromatic dicarboxylic acid compound in the carboxylic acid component of the amorphous composite resin is preferably 10 mol% or more, more preferably 25 mol% or more, even more preferably 40 mol% or more, and 100 mol% or more. It is mol% or less, preferably 90 mol% or less, more preferably 80 mol% or less.

The content of the trivalent or higher carboxylic acid compound in the carboxylic acid component of the amorphous composite resin is preferably 3 mol% or more, more preferably 5 mol% or more, from the viewpoint of low-temperature fixing properties and high-temperature offset resistance. , more preferably 8 mol% or more, and preferably 30 mol% or less, more preferably 25 mol% or less, even more preferably 20 mol% or less.

The carboxylic acid component of the crystalline composite resin preferably contains an aliphatic dicarboxylic acid compound.

The number of carbon atoms in the aliphatic dicarboxylic acid compound contained in the carboxylic acid component of the crystalline composite resin is preferably 4 or more, more preferably 6 or more, and still more preferably 10 or more from the viewpoint of low-temperature fixability, and From the viewpoint of durability, it is preferably 14 or less, more preferably 12 or less, and particularly preferably 10.

The content of the aliphatic dicarboxylic acid compound is preferably 70 mol% or more, more preferably 90 mol% in the carboxylic acid component of the crystalline composite resin, from the viewpoint of increasing the crystallinity of the resin and improving the low-temperature fixing properties. The content is more preferably 95 mol% or more, and even more preferably 100 mol%.

Note that the alcohol component may contain a monovalent alcohol, and the carboxylic acid component may contain a monovalent carboxylic acid compound as appropriate from the viewpoint of adjusting the molecular weight and softening point of the polyester resin.

From the viewpoint of adjusting the softening point of the polyester resin, the equivalent ratio of the carboxylic acid component to the alcohol component (COOH group/OH group) in the polyester resin is preferably 0.6 or more, more preferably 0.7 or more, and even more preferably 0.75 or more. Yes, and preferably 1.1 or less, more preferably 1.05 or less.

The polyester resin is prepared by, for example, combining an alcohol component and a carboxylic acid component in an inert gas atmosphere, preferably in the presence of an esterification catalyst, and if necessary, in the presence of an esterification co-catalyst, a polymerization inhibitor, etc. It can be produced by polycondensation at a temperature of 130°C or higher, more preferably 170°C or higher, and preferably 250°C or lower, more preferably 240°C or lower.

The styrenic resin is an addition polymer of a raw material monomer containing at least styrene or a styrene derivative such as α-methylstyrene or vinyltoluene (hereinafter, styrene and styrene derivatives are collectively referred to as "styrene compound").

In the amorphous composite resin, the content of the styrene compound, preferably styrene, is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more in the raw material monomer of the styrene resin. , and preferably 95% by mass or less, more preferably 93% by mass or less, even more preferably 90% by mass or less. In addition, in the crystalline composite resin, the content of the styrene compound, preferably styrene, is preferably 70% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, in the raw material monomer of the styrene resin. More preferably, it is 95% by mass or more, and even more preferably 100% by mass.

The styrene resin of the amorphous composite resin preferably contains (meth)acrylic acid alkyl ester in which the alkyl group has 7 or more carbon atoms as a raw material monomer. Examples of (meth)acrylic acid alkyl esters include 2-ethylhexyl (meth)acrylate, (iso)octyl (meth)acrylate, (iso)decyl (meth)acrylate, and (iso)stearyl (meth)acrylate. Can be mentioned. It is preferable to use one or more of these. In addition, in this specification, "(iso)" means both cases where this group exists and cases where it does not exist, and when these groups do not exist, it is normal. Show that. Moreover, "(meth)acrylic acid" refers to acrylic acid, methacrylic acid, or both.

The number of carbon atoms in the alkyl group in the (meth)acrylic acid alkyl ester as a raw material monomer for the styrene resin is preferably 7 or more, more preferably 8 or more, from the viewpoint of improving the low-temperature fixing properties of the toner. is 12 or less, more preferably 10 or less. Note that the number of carbon atoms in the alkyl ester refers to the number of carbon atoms derived from the alcohol component constituting the ester.

The content of the (meth)acrylic acid alkyl ester whose alkyl group has 7 or more carbon atoms is preferably 5% by mass or more, more preferably 7% by mass or more, in the raw material monomer of the styrene resin of the amorphous composite resin. More preferably, it is 10% by mass or more, and preferably 30% by mass or less, and more preferably 20% by mass or less.

Raw material monomers for styrenic resins include raw material monomers other than styrene compounds and (meth)acrylic acid alkyl esters, such as ethylenically unsaturated monoolefins such as ethylene and propylene; diolefins such as butadiene; and vinyl chloride. Halobinyls; vinyl esters such as vinyl acetate and vinyl propionate; ethylenic monocarboxylic acid esters such as dimethylaminoethyl (meth)acrylate; vinyl ethers such as methyl vinyl ether; vinylidene halides such as vinylidene chloride; N-vinyl N-vinyl compounds such as pyrrolidone may also be included.

The addition polymerization reaction of raw material monomers for styrenic resin can be carried out, for example, in the presence of a polymerization initiator such as dicumyl peroxide, a polymerization inhibitor, a crosslinking agent, etc., in the presence of an organic solvent, or in the absence of a solvent. The temperature conditions are preferably 110°C or higher, more preferably 140°C or higher, and preferably 200°C or lower, more preferably 170°C or lower.

When using an organic solvent during the addition polymerization reaction, xylene, toluene, methyl ethyl ketone, acetone, etc. can be used. The amount of the organic solvent used is preferably 10 parts by mass or more and 50 parts by mass or less based on 100 parts by mass of the raw material monomer of the styrene resin.

In the present invention, from the viewpoint of low-temperature fixability and pigment dispersibility, the composite resin is made to react with the polyester resin and the styrene-based resin via a dual-reactive monomer that can react with either the raw material monomer of the polyester resin or the raw material monomer of the styrene-based resin. Preferably, the resin is chemically bonded.

The bireactive monomer has at least one functional group selected from the group consisting of a hydroxyl group, a carboxy group, an epoxy group, a primary amino group, and a secondary amino group, preferably a hydroxyl group and/or a carboxy group, in the molecule. A compound having a group, more preferably a carboxyl group, and an ethylenically unsaturated bond is preferable, and at least one selected from the group consisting of acrylic acid, methacrylic acid, fumaric acid, maleic acid and maleic anhydride is more preferable. From the viewpoint of reactivity in polycondensation reactions and addition polymerization reactions, at least one selected from the group consisting of acrylic acid, methacrylic acid, and fumaric acid is more preferable. However, when used together with a polymerization inhibitor, a polyhydric carboxylic acid compound having an ethylenically unsaturated bond, such as fumaric acid, functions as a raw material monomer for the polyester resin. In this case, fumaric acid and the like are not bireactive monomers but are raw material monomers for the polyester resin.

The amount of the bireactive monomer used is preferably 1 mol or more per 100 mol in total of the alcohol component of the polyester resin, from the viewpoint of increasing the dispersibility of the styrene resin and polyester resin and improving the durability of the toner. , more preferably 2 mol or more, and, from the viewpoint of low-temperature fixability, preferably 30 mol or less, more preferably 20 mol or less, even more preferably 10 mol or less.
In addition, the amount of the bireactive monomer to be used is preferably based on a total of 100 parts by mass of the raw material monomers for the styrene resin, from the viewpoint of increasing the dispersibility of the styrene resin and the polyester resin and improving the durability of the toner. is 1 part by mass or more, more preferably 2 parts by mass or more, and from the viewpoint of low-temperature fixability, is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 15 parts by mass or less. Here, the polymerization initiator is included in the total of raw material monomers for the styrene resin.

Specifically, the composite resin obtained using the bireactive monomer is preferably manufactured by the following method. The bireactive monomer is preferably used in the addition polymerization reaction together with the raw material monomer of the styrene resin from the viewpoint of improving the durability of the toner, the low-temperature fixing property, and the heat-resistant storage stability of the toner.

(i) A method in which step (A) of polycondensation reaction using raw material monomers of polyester resin is followed by step (B) of addition polymerization reaction using raw material monomers of styrenic resin and bireactive monomers. After step (B), The reaction temperature is raised again, and if necessary, raw material monomers for trivalent or higher polyester resins that will serve as crosslinking agents are added to the reaction system to further carry out the polycondensation reaction in step (A) and the reaction with bireactive monomers. You may proceed.

(ii) A method in which step (A) of a polycondensation reaction using a raw material monomer of a polyester resin is performed after step (B) of an addition polymerization reaction using a raw material monomer of a styrene resin and a bireactive monomer.

(iii) The step (A) of the polycondensation reaction using the raw material monomer of the polyester resin and the step (B) of the addition polymerization reaction using the raw material monomer of the styrene resin and the bireactive monomer are carried out in parallel. how to do it

In the method (i) above, a prepolymerized polycondensation resin may be used instead of the step (A) of performing a polycondensation reaction. In the method (iii) above, when performing step (A) and step (B) in parallel, a mixture containing raw material monomers for styrenic resin is added to the mixture containing raw material monomers for polyester resin. The reaction can also be carried out by dropping.

The above methods (i) to (iii) are preferably carried out in the same container.

The mass ratio of styrene resin and polyester resin in the composite resin (styrene resin/polyester resin) is preferably 3/97 or more, more preferably 5/95 or more, from the viewpoint of pigment dispersibility and heat-resistant storage stability. From the viewpoint of low-temperature fixability and heat-resistant storage stability, it is preferably 45/55 or less, more preferably 40/60 or less, even more preferably 35/65 or less, even more preferably 30/70 or less, and even more preferably 25/75. It is as follows. In addition, in the above calculation, the mass of the polyester resin is the total amount of the raw material monomer and bireactive monomer of the polyester resin used. Further, the amount of styrene resin is the total amount of the raw material monomer of the styrene resin and the polymerization initiator.

From the viewpoint of durability, the softening point of the amorphous composite resin is preferably 80°C or higher, more preferably 90°C or higher, even more preferably 100°C or higher, and from the viewpoint of low-temperature fixability, preferably 160°C or higher. The temperature is preferably 155°C or lower, more preferably 150°C or lower.

From the viewpoint of durability, the glass transition temperature of the amorphous composite resin is preferably 40°C or higher, more preferably 45°C or higher, even more preferably 50°C or higher, and from the viewpoint of low-temperature fixability, preferably The temperature is 75°C or lower, more preferably 70°C or lower, even more preferably 65°C or lower.

The acid value of the amorphous composite resin is preferably 1 mgKOH/g or more, more preferably 5 mgKOH/g or more, even more preferably 10 mgKOH/g or more from the viewpoint of charging property, and preferably from the viewpoint of environmental stability. is 50 mgKOH/g or less, more preferably 40 mgKOH/g or less, even more preferably 30 mgKOH/g or less.

The softening point of the crystalline composite resin is preferably 60°C or higher, more preferably 70°C or higher, even more preferably 75°C or higher from the viewpoint of durability, and preferably 100°C or higher from the viewpoint of low-temperature fixability. The temperature is more preferably 90°C or lower, and even more preferably 85°C or lower.

The melting point of the crystalline composite resin is preferably 60°C or higher, more preferably 70°C or higher, even more preferably 75°C or higher from the viewpoint of durability, and preferably 100°C or lower from the viewpoint of low-temperature fixability. , more preferably 90°C or lower, still more preferably 85°C or lower.

The acid value of the crystalline composite resin is preferably 1 mgKOH/g or more, more preferably 3 mgKOH/g or more, even more preferably 5 mgKOH/g or more from the viewpoint of charging property, and preferably from the viewpoint of environmental stability. is 30 mgKOH/g or less, more preferably 20 mgKOH/g or less, even more preferably 10 mgKOH/g or less.

When an amorphous composite resin and a crystalline composite resin are included, the mass ratio of the amorphous composite resin to the crystalline composite resin (amorphous composite resin/crystalline composite resin) is preferably from the viewpoint of durability. 50/50 or more, more preferably 60/40 or more, even more preferably 70/30 or more, and from the viewpoint of low-temperature fixability, preferably 99/1 or less, more preferably 95/5 or less, even more preferably 90/10 or less.

The content of the composite resin in the binder resin is 25% by mass or more, preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, More preferably, it is 95% by mass or more, and even more preferably 100% by mass.

The binder resin may contain resins other than the amorphous composite resin and the crystalline composite resin within a range that does not impair the effects of the present invention. Examples include polyester resin, vinyl resin, epoxy resin, polycarbonate, polyurethane, and the like.

Note that when the binder resin contains a crystalline resin, from the viewpoint of pigment dispersibility, the content of the crystalline resin is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass. % or less. Here, examples of the crystalline resin include those that are crystalline among the above composite resins (crystalline composite resin), crystalline polyester resin, and the like.

The content of the binder resin in the toner is preferably 25% by mass or more, more preferably 30% by mass or more, even more preferably 35% by mass or more, and preferably 65% by mass or less, more preferably 55% by mass. % or less, more preferably 50% by mass or less.

The white toner of the present invention contains titanium oxide particles as a colorant from the viewpoint of improving the white density of the white toner. The content of titanium oxide in the coloring agent is preferably 90% by mass or more, and it is more preferable to use only titanium oxide particles as the coloring agent, but other than titanium oxide particles may be used as long as the white coloring effect is not impaired. Other colorants may also be included. Other colorants include zinc oxide, aluminum oxide, hollow resin particles, and the like.

The titanium oxide particles may be of anatase type, rutile type, or brookite type.

The number average primary particle diameter of the titanium oxide particles is preferably 150 nm or more, more preferably 200 nm or more, and even more preferably 230 nm or more, from the viewpoint of improving the white density of the white toner and improving the hiding property. Further, from the viewpoint of improving toner productivity and high temperature offset resistance, the particle diameter is preferably 350 nm or less, more preferably 300 nm or less, and even more preferably 270 nm or less.

Commercially available titanium oxide particles include "CR-50-2" and "CR-58" (both manufactured by Ishihara Sangyo Co., Ltd.).

The content of titanium oxide particles is 50 parts by mass or more, preferably 75 parts by mass or more, more preferably 100 parts by mass or more, based on 100 parts by mass of the binder resin, and from the viewpoint of pigment dispersibility. , 200 parts by mass or less, preferably 175 parts by mass or less, more preferably 150 parts by mass or less, still more preferably 125 parts by mass or less.

The white toner of the present invention contains additives such as a release agent, a charge control agent, a magnetic powder, a fluidity improver, a conductivity adjuster, a reinforcing filler such as a fibrous substance, an antioxidant, and a cleaning property improver. may be contained.

As mold release agents, hydrocarbon waxes such as polypropylene wax, polyethylene wax, polypropylene polyethylene copolymer wax, microcrystalline wax, paraffin wax, Fischer-Tropsch wax, Sasol wax, and their oxides; carnauba wax, montan Waxes and their deoxidized waxes, ester waxes such as fatty acid ester waxes; fatty acid amides, fatty acids, higher alcohols, fatty acid metal salts, etc., can be mentioned, and these can be used alone or in combination of two or more.

The melting point of the release agent is preferably 60°C or higher, more preferably 70°C or higher, from the viewpoint of toner transferability, and preferably 160°C or lower, more preferably 140°C from the viewpoint of low-temperature fixability. The temperature is more preferably 120°C or lower, and even more preferably 110°C or lower.

The content of the release agent is preferably 0.5 parts by mass or more, and more preferably 0.5 parts by mass or more based on 100 parts by mass of the binder resin, from the viewpoints of low-temperature fixability and offset resistance of the toner and dispersibility in the binder resin. The amount is preferably 1 part by weight or more, more preferably 1.5 parts by weight or more, and preferably 10 parts by weight or less, more preferably 8 parts by weight or less, and even more preferably 7 parts by weight or less.

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

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

In addition, as the negatively chargeable charge control agent, polymer type, such as "FCA-2521NJ" (manufactured by Fujikura Kasei Co., Ltd.); metal-containing azo dye, such as "Varifast Black 3804", "Bontron S-31", etc. , "Bontron S-32", "Bontron S-34", "Bontron S-36" (manufactured by Orient Chemical Co., Ltd.), "Eisenspiron Black TRH", "T-77" (manufactured by Hodogaya Chemical Co., Ltd.) Metal compounds of benzylic acid compounds, such as "LR-147" and "LR-297" (manufactured by Nippon Carlit Co., Ltd.), etc.; Metal compounds of salicylic acid compounds, such as "Bontron" "E-81", "Bontron E-84", "Bontron E-88", "Bontron E-304" (manufactured by Orient Chemical Co., Ltd.), "TN-105" (manufactured by Hodogaya Chemical Co., Ltd.) Copper phthalocyanine dyes; quaternary ammonium salts such as "COPY CHARGE NX VP434" (manufactured by Clariant), nitroimidazole derivatives, and organometallic compounds.

From the viewpoint of charging stability of the toner, the content of the charge control agent is preferably 0.01 parts by mass or more, more preferably 0.2 parts by mass or more, and preferably 10 parts by mass, based on 100 parts by mass of the binder resin. parts by weight or less, more preferably 5 parts by weight or less, still more preferably 3 parts by weight or less, still more preferably 2 parts by weight or less. However, if the charge control agent is a polymer type, it is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and preferably 15 parts by mass or less, based on 100 parts by mass of the binder resin. The amount is more preferably 10 parts by mass or less, and even more preferably 7.5 parts by mass or less.

The white toner of the present invention may be a toner obtained by any conventionally known method such as melt-kneading method, emulsion phase inversion method, polymerization method, etc., but from the viewpoint of productivity and colorant dispersibility, , a pulverized toner produced by a melt-kneading method is preferred. In the case of pulverized toner produced by the melt-kneading method, for example, raw materials such as a binder resin, titanium oxide particles, a mold release agent, and a charge control agent are mixed uniformly in a mixer such as a Henschel mixer, and then mixed in a closed kneader, single screw or It can be produced by melt-kneading using a twin-screw extruder, open roll kneader, etc., followed by cooling, pulverization, and classification.

In the present invention, from the viewpoint of pigment dispersibility, it is preferable to mix silica particles with the binder resin and titanium oxide particles. Therefore, the white toner of the present invention is
Step 1: a step of mixing components including a binder resin, titanium oxide particles, and silica particles to obtain a mixture;
It is preferable to manufacture by a method including step 2: melt-kneading the obtained mixture to obtain a kneaded product, and step 3: pulverizing and classifying the obtained kneaded product.

The silica particles used in step 1 are preferably hydrophobic silica particles that have been subjected to a hydrophobic treatment from the viewpoint of improving the productivity of white toner.

Examples of hydrophobizing agents for silica particles include organochlorosilane, organoalkoxysilane, organodisilazane, cyclic organopolysilazane, linear organopolysiloxane, etc. Specifically, hexamethyldisilazane (HMDS), dimethyldisilazane, etc. Examples include chlorosilane (DMDS), silicone oil, octyltriethoxysilane (OTES), methyltriethoxysilane, and the like.

The number average primary particle diameter of the silica particles used in step 1 is preferably 5 nm or more, more preferably 8 nm or more, and even more preferably 12 nm or more, from the viewpoint of improving the productivity of the white toner. From the viewpoint of improving the high-temperature offset resistance of the toner, and suppressing the occurrence of transfer omission, the particle diameter is preferably 20 nm or less, more preferably 18 nm or less, and even more preferably 16 nm or less.

The amount of silica particles used in step 1, preferably the content in the toner, is determined from the viewpoint of improving the productivity of white toner, from the viewpoint of improving the high temperature offset resistance of the toner with respect to 100 parts by mass of the binder resin, And from the viewpoint of suppressing the occurrence of transfer omissions, the content is preferably 0.25 parts by mass or more, more preferably 0.3 parts by mass or more, even more preferably 0.5 parts by mass or more, still more preferably 0.6 parts by mass or more, and even more preferably 0.8 parts by mass or more. And, from the viewpoint of improving the high temperature offset resistance of the toner and suppressing the occurrence of transfer omission, preferably 4.5 parts by mass or less, more preferably 4 parts by mass or less, still more preferably 3 parts by mass or less, and Preferably it is 2 parts by mass or less.

Step 1 is a step of mixing components including a binder resin, titanium oxide particles, and silica particles to obtain a mixture. In step 1, examples of the mixer used for mixing (pre-mixing) the binder resin, titanium oxide particles, and silica particles include a Henschel mixer, a super mixer, and a ball mill. is preferred.

The toner raw materials are mixed in the Henschel mixer by adjusting the circumferential stirring speed and mixing time. The peripheral speed of stirring is preferably 10 to 30 m/s from the viewpoint of improving the dispersibility of the colorant and charge control agent in the binder resin. Further, the stirring time is preferably 1 to 10 minutes from the viewpoint of improving the dispersibility of the colorant and charge control agent in the binder resin.

Step 2 is a step of melt-kneading the mixture obtained in Step 1. Melt-kneading can be carried out using a known kneader such as a closed kneader, a single- or twin-screw kneader, or a continuous open-roll kneader, but it is preferably carried out with a twin-screw kneader. A twin-screw kneading machine is a closed-type kneading machine in which two kneading shafts are covered by a barrel. A type that can rotate in the same direction is preferable. As a commercially available product, the twin screw extruder PCM series manufactured by Ikegai Tekko Co., Ltd. is preferred because it has good twin screw engagement at high speeds from the viewpoint of improving productivity.

Melt-kneading in the twin-screw kneader is performed by adjusting the barrel setting temperature (temperature of the inner wall surface of the extruder), the circumferential speed of rotation of the shaft, and the feeding rate of the toner raw material mixture. The barrel temperature setting is preferably 80 to 140°C, more preferably 90 to 120°C, from the viewpoint of improving the dispersibility of the colorant and charge control agent in the binder resin.

The circumferential speed of rotation of the shaft is preferably 0.1 to 1 m/s from the viewpoint of improving the dispersibility of the colorant and charge control agent in the binder resin.

The feeding rate of the toner raw material mixture to the twin-screw kneader is appropriately adjusted depending on the permissible capacity of the kneader used, the barrel temperature setting, and the shaft rotation speed. For example, when using a twin-screw extruder PCM-87 manufactured by Ikegai Tekko Co., Ltd., the feed rate of the toner raw material mixture to the twin-screw kneader is preferably 100 to 200 kg/h.

Step 3 is a step of pulverizing and classifying the melt-kneaded material obtained in Step 2.

The pulverization process may be performed in multiple stages. For example, the melt-kneaded product may be coarsely ground to about 0.1 to 5 mm and then further finely ground.

The pulverizer used in the pulverization process is not particularly limited, and examples of pulverizers suitable for coarse pulverization include an atomizer, a rotoplex, and the like, but a hammer mill and the like may also be used. Further, examples of the crusher suitably used for fine pulverization include a fluidized bed counter jet mill, a collision plate jet mill, and a mechanical mill.

Examples of the classifier used in the classification process include an air classifier, an inertial classifier, and a sieve classifier. During the classification step, the pulverized material that is removed due to insufficient pulverization may be subjected to the pulverization step again, and the pulverization step and the classification step may be repeated as necessary.

The volume median particle diameter (D ₅₀ ) of the toner obtained in step 3 is preferably 3 μm or more, more preferably 4 μm or more, and more preferably 15 μm or less, more preferably from the viewpoint of improving the image quality of the toner. is 12 μm or less. In this specification, the volume median particle size (D ₅₀ ) means a particle size at which the cumulative volume frequency calculated from the volume fraction is 50% from the smallest particle size.

From the viewpoint of improving transferability, the toner of the present invention is preferably obtained by a method including a step of mixing the toner particles obtained in step 3 as base particles with an external additive. In the present invention, the content in the toner means the content in the toner base particles.

Examples of external additives include inorganic fine particles such as silica, alumina, titania, zirconia, tin oxide, and zinc oxide, and organic fine particles such as melamine resin fine particles and polytetrafluoroethylene resin fine particles. Among these, silica is preferred.

The silica used as an external additive is preferably hydrophobic silica that has been subjected to a hydrophobic treatment from the viewpoint of improving toner transferability.

The number average primary particle diameter of the external additive is preferably 10 nm or more, more preferably 15 nm or more, and preferably 250 nm or less, more preferably is 200 nm or less, more preferably 90 nm or less.

The content of the external additive is preferably 0.05 parts by mass or more, based on 100 parts by mass of the toner base particles before being treated with the external additive, from the viewpoint of improving the chargeability, fluidity, and transferability of the toner. It is more preferably 0.1 parts by mass or more, still more preferably 0.3 parts by mass or more, and preferably 5 parts by mass or less, more preferably 4 parts by mass or less, and even more preferably 3 parts by mass or less.

For mixing the toner base particles and the external additive, it is preferable to use a mixer equipped with a stirring tool such as a rotary blade, a high-speed mixer such as a Henschel mixer or a super mixer is preferable, and a Henschel mixer is more preferable.

The white toner of the present invention can be used as a one-component developing toner as it is, or as a two-component developing toner mixed with a carrier, in a one-component developing system or a two-component developing system, respectively, in an image forming apparatus.

The present invention further provides an image forming method using the white toner and color toner of the present invention. Specifically, this is an image forming method that includes a step of laminating a color toner image in an unfixed state on an unfixed white toner image on a recording medium, and then thermally fixing the image.

The recording medium is not particularly limited, and may include plain paper from thin paper to thick paper, high-quality paper, coated printing paper such as art paper and coated paper, commercially available Japanese paper, postcard paper, synthetic paper, film, Examples include cloth.

The color of the recording medium is preferably a color that requires a white background (base layer) from the viewpoint of visibility, specifically a color other than colorless and transparent or white.

The image forming method is not particularly limited as long as it includes a heat fixing step and forms an image by electrophotography, but specifically, for example, a charging step of charging a photoreceptor, an exposure step of exposing the photoreceptor to light. , a developing process in which toner particles are attached to the electrostatic latent image formed on the photoconductor to form a toner image, a transfer process in which the formed toner image is transferred to a recording medium, and the transferred toner image is recorded. Examples include a method including a fixing step of thermally fixing the image onto the medium.

In the heat fixing step, a contact heating method is preferable. Examples of the contact heating method include, in particular, a heat-pressure fixing method, a heat roller fixing method, and a pressure-contact heat fixing method in which fixing is performed using a rotating pressure member containing a fixedly arranged heating body.

In the heat roll fixing method, an upper roller is usually equipped with a heat source inside a metal cylinder made of iron or aluminum whose surface is coated with fluororesin, etc., and a lower roller is made of silicone rubber or the like. A fixing device or the like composed of the following is used. Pressure is applied between the upper roller and the lower roller, and when the lower roller is deformed by this pressure, a so-called nip is formed at this deformed portion.

[Softening point of resin]
Using a flow tester "CFT-500D" (manufactured by Shimadzu Corporation), a 1.5 g sample was heated at a heating rate of 6°C/min while a plunger applied a load of 1.96 MPa, and the diameter was 1 mm and the length was 1 mm. Extrude through a 1mm nozzle. Plot the fall of the plunger of the flow tester against the temperature, and take the temperature at which half of the sample flows out as the softening point.

[Maximum peak temperature of endothermic resin]
Using a differential scanning calorimeter "Q-100" (manufactured by TA Instruments Japan Co., Ltd.), 0.01 to 0.02 g of the sample was weighed into an aluminum pan, and the temperature was lowered from room temperature (25°C) at a rate of 10°C. Cool to 0°C at /min and maintain at 0°C for 1 minute. Then, measure at a heating rate of 10°C/min. Among the observed endothermic peaks, the temperature of the peak with the largest peak area is defined as the maximum endothermic peak temperature.

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

[Acid value of resin]
Measured based on the method of JIS K 0070:1992. However, the measurement solvent should be changed from the JIS K 0070 specified mixed solvent of ethanol and ether to a mixed solvent of acetone and toluene (acetone:toluene = 1:1 (volume ratio)).

[Melting point of mold release agent]
Using a differential scanning calorimeter (manufactured by T.A. Instruments Japan Co., Ltd., DSC Q20), the temperature was raised to 200°C at a heating rate of 10°C/min, and then from that temperature at a cooling rate of 5°C/min. The sample cooled to -10°C is heated to 180°C at a heating rate of 10°C/min, and the maximum peak temperature of the endotherm observed from the melting endothermic curve obtained there is taken as the melting point of the mold release agent.

[Number average primary particle diameter of titanium oxide particles, silica particles, and external additives]
The number average primary particle diameter is determined by measuring the particle diameter (average value of major axis and minor axis) of 100 particles using a scanning electron microscope (SEM) at an appropriate magnification of 5,000 to 50,000 times. The average value is taken as the number average primary particle diameter of titanium oxide particles, silica particles, and external additives.

[Toner volume median particle size]
Measuring device: Coulter Multisizer II (manufactured by Beckman Coulter, Inc.)
Aperture diameter: 100μm
Analysis software: Coulter Multisizer AccuComp version 1.19 (manufactured by Beckman Coulter, Inc.)
Electrolyte: Isoton II (manufactured by Beckman Coulter, Inc.)
Dispersion liquid: Emulgen 109P (manufactured by Kao Corporation, polyoxyethylene lauryl ether, HLB (Griffin): 13.6) was dissolved in an electrolytic solution and adjusted to 5% by mass Dispersion conditions: 10 mg of measurement sample in 5 mL of the above dispersion liquid was added and dispersed for 1 minute using an ultrasonic dispersion machine (machine name: US-1 manufactured by SND Co., Ltd., output: 80W), then 25mL of the electrolyte was added, and further dispersed using an ultrasonic dispersion machine. Disperse for 1 minute to prepare a sample dispersion.
Measurement conditions: Add the sample dispersion to 100 mL of the electrolyte to a concentration that allows the particle size of 30,000 particles to be measured in 20 seconds, measure 30,000 particles, and calculate the volume from the particle size distribution. Determine the median particle size (D ₅₀ ).

Resin production example 1
The raw material monomers for polyester resin other than fumaric acid and trimellitic anhydride shown in Table 1, 40 g of tin(II) 2-ethylhexanoate, and 1 g of gallic acid were placed in a 10L unit equipped with a nitrogen introduction tube, a dehydration tube, a stirrer, and a thermocouple. The mixture was placed in a 4-necked flask, and reacted at 230°C for 8 hours, and then at 8.3 kPa for 1 hour. The temperature was lowered to 170°C, and a raw material monomer for a styrenic resin, a bireactive monomer, and a polymerization initiator were added dropwise through a dropping funnel over a period of 1 hour. After aging the addition polymerization reaction for 1 hour while maintaining the temperature at 170°C, the temperature was raised to 210°C and at 8.3 kPa, the raw material monomer of the styrenic resin was removed and the polyester moiety was reacted with the bireactive monomer for 1 hour. Ta. Further, at 210°C, trimellitic anhydride, fumaric acid, and 5 g of tert-butylcatechol were added, and the reaction was carried out until a desired softening point was reached, to obtain an amorphous composite resin (resin A).

Resin production example 2
The raw material monomers for polyester resin other than fumaric acid and trimellitic anhydride shown in Table 1, 40 g of tin(II) 2-ethylhexanoate, and 1 g of gallic acid were placed in a 10L unit equipped with a nitrogen introduction tube, a dehydration tube, a stirrer, and a thermocouple. The mixture was placed in a four-necked flask, and the reaction was carried out at 230°C for 8 hours. After the reaction, the reaction was carried out at 8.3 kPa for 1 hour. Furthermore, the temperature was lowered to 210° C., trimellitic anhydride, fumaric acid, and 5 g of tert-butylcatechol were added, and the reaction was carried out until a desired softening point was reached to obtain an amorphous polyester resin (resin B).

Resin production example 3
The raw material monomers for polyester resins other than sebacic acid shown in Table 2 were placed in a 10 L four-necked flask equipped with a nitrogen inlet tube, a dehydration tube, a stirrer, and a thermocouple, and heated to 120°C. At 120°C, 1500g of sebacic acid shown in Table 2 was added, and the mixture was further heated to 160°C and reacted for 6 hours. Thereafter, raw material monomers, polymerization initiators, and bireactive monomers for styrenic resin shown in Table 2 were added dropwise through a dropping funnel over a period of 1 hour. After aging the addition polymerization reaction for 1 hour while maintaining the temperature at 160°C, the raw material monomer of the styrenic resin was removed for 1 hour at 8.3 kPa. Furthermore, the remaining sebacic acid was added, the temperature was raised to 200°C over 8 hours, and the reaction was carried out at 8.3 kPa for 30 minutes. Furthermore, 20 g of tin(II) 2-ethylhexanoate and 2 g of gallic acid were added and reacted at 200°C for 1 hour, and then at 8.3 kPa for 1 hour to form a crystalline composite resin (resin C). Obtained.

Resin production example 4
The raw material monomers for the polyester resin shown in Table 2 were placed in a 10L four-necked flask equipped with a nitrogen inlet tube, a dehydration tube, a stirrer, and a thermocouple, and heated to 140°C. After further heating to 200°C and reacting for 10 hours, the mixture was reacted at 8.3 kPa for 30 minutes. Furthermore, 20 g of tin(II) 2-ethylhexanoate and 2 g of gallic acid were added and reacted at 200°C for 1 hour, and then at 8.3 kPa for 1 hour to form a crystalline polyester resin (resin D). Obtained

Examples 1 to 5, Comparative Example 1 and Reference Example 1
Binder resin shown in Table 3 (100 parts by mass in total), titanium oxide particles "CR-50-2" (manufactured by Ishihara Sangyo Co., Ltd., number average primary particle diameter: 250 nm), and charge control agent "FCA-2521NJ" (Fujikura 5 parts by mass of mold release agent "HNP-9" (manufactured by Nippon Seiro Co., Ltd., paraffin wax, melting point: 79°C), and 1.5 parts by mass of hydrophobic silica "R972" (manufactured by Nippon Aerosil Co., Ltd., number average) 2 parts by mass (primary particle diameter: 16 nm) were premixed for 1 minute using a Henschel mixer, and then melt-kneaded using a twin-screw extruder "PCM-87" (manufactured by Ikegai Iron Works). The melt-kneading conditions were: feed rate of raw materials 2.5 kg/min (150 kg/h), barrel temperature set at 100°C, screw kneading section shaft rotation speed 180 r/min (circumferential speed of shaft rotation 0.30 m/sec). . The obtained kneaded product was cooled to 20° C. or lower while being rolled with a cooling roll, and the cooled molten kneaded product was coarsely ground to 3 mm using a Rotoplex (manufactured by Toa Kikai Co., Ltd.). The obtained coarsely crushed material was coarsely crushed using a cutter mill (manufactured by Nara Kikai Seisakusho Co., Ltd.) to a volume median particle diameter (D ₅₀ ) of 1.5 to 2.5 mm, and then crushed using a collision plate jet mill “I-20 type” ( (manufactured by Nippon Pneumatic Kogyo Co., Ltd.).
Furthermore, the obtained pulverized product was classified using an air classifier "DSF type" (manufactured by Nippon Pneumatic Industries Co., Ltd.) to obtain toner base particles having a volume median particle diameter (D ₅₀ ) of 7.0 μm.
100 parts by mass of the obtained toner base particles, 1.0 parts by mass of hydrophobic silica "R972" (manufactured by Nippon Aerosil Co., Ltd., hydrophobic treatment agent: DMDS, number average primary particle diameter: 16 nm) as an external additive, and hydrophobic silica "R972" as an external additive. RY50'' (manufactured by Nippon Aerosil Co., Ltd., hydrophobic treatment agent: silicone oil, number average primary particle diameter: 40 nm) was added and mixed for 3 minutes using a Henschel mixer to obtain a white toner.

Furthermore, a cyan toner was obtained in the same manner as in Example 1, except that 5 parts by mass of the cyan pigment "ECB-301" (manufactured by Dainichiseika Chemical Co., Ltd., Phthalocyan Blue) was used instead of the titanium oxide particles. The obtained cyan toner was used in the test examples described below in combination with the white toner of each Example and Comparative Example.

Test example [Color mixing resistance under HH environment]
A non-magnetic single-component developing device "COREFIDO C712dnw" (manufactured by Oki Data Co., Ltd.) was equipped with white toner, and after being left in an HH environment (temperature 30°C/humidity 80%) for 24 hours, 1000 sheets were printed at 5% printing rate. I did it. Thereafter, an unfixed image having a solid image area of 2 cm x 3 cm (toner adhesion amount: 1.5 mg/cm ² ) was obtained on 90 kg paper (Kishu color wood-free paper, thick, black). Furthermore, the fixing device of "COREFIDO C712dnw" (manufactured by Oki Data Co., Ltd.) was modified to an external fixing device with a fixing speed of 100 mm/sec, and the unfixed image was fixed by setting the fixing temperature to 170°C.
On the fixed image, a solid image area of 2 cm x 3 cm (toner adhesion A cyan toner image having an amount of 1.0 mg/cm ² ) was laminated onto the white toner fixed image. Furthermore, the fixing temperature was set at 170° C. using the modified fixing device, and the unfixed cyan toner image was fixed. This sample, in which a cyan toner image was printed on a white toner image, had the cyan toner fixed thereon after the white toner image was fixed, and there was no color mixture, so it was set as standard A.

Next, white toner was mounted on the non-magnetic single-component developing device "COREFIDO C712dnw" (manufactured by Oki Data Co., Ltd.), and after being left in an HH environment (temperature 30 degrees Celsius/humidity 80%) for 24 hours, a printing rate of 5% was achieved. 1000 sheets were printed. Thereafter, an unfixed image having a solid image area of 2 cm x 3 cm (toner adhesion amount: 1.5 mg/cm ² ) was obtained on 90 kg paper (Kishu color wood-free paper, thick, black). On top of this white toner unfixed image, a 2cm x 3cm solid image was created using cyan toner that had been left in an HH environment (temperature 30°C/humidity 80%) for 24 hours and then printed on 1000 sheets at a 5% print rate. cyan toner images having a total of 1.0 mg/cm ² (toner adhesion amount: 1.0 mg/cm 2 ) were laminated. Further, the fixing temperature was set at 170° C. using the modified fixing device, and an image in which a cyan toner image was laminated in an unfixed state on an unfixed white toner image was fixed.
The color difference (ΔE) between a sample in which a cyan toner image was printed on this white toner and Standard A was measured to evaluate color mixing resistance. The smaller the color difference, the better the color mixing resistance. The results are shown in Table 3.

From the above results, in contrast to the white toner of Comparative Example 1, in which the content of composite resin is too low, the white toners of Examples 1 to 5 are obtained by laminating color toner images in an unfixed state and thermally fixing them. It can also be seen that color mixture is suppressed. In particular, from the comparison of Examples 1, 4, and 5, it can be seen that color mixing resistance is significantly improved by reducing the content of crystalline resin.
In addition, from the results of Reference Example 1, color mixing between white color toner and color toner is not recognized when the content of titanium oxide particles is small, but is uniquely recognized when the content of titanium oxide particles is large. I understand that this is an issue.

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

Claims (3)

A white toner for electrophotography containing a binder resin and titanium oxide particles, wherein the binder resin is composed of an amorphous resin and a crystalline resin, and the binder resin is a composite comprising a polyester resin and a styrene resin. Contains 25% by mass or more of a resin, the composite resin contains an amorphous composite resin, and the content of the titanium oxide particles is 50 parts by mass or more and 200 parts by mass or less with respect to 100 parts by mass of the binder resin. A white toner for electrophotography. The white toner for electrophotography according to claim 1, wherein the content of the crystalline resin in the binder resin is 25% by mass or less. 3. An image forming method using the white toner and color toner according to claim 1 or 2, wherein a color toner image is laminated in an unfixed state on an unfixed white toner image on a recording medium, and then thermally fixed. An image forming method including a step.