JP7600766B2 - Toner set and image forming method using the same - Google Patents

Description

The present invention relates to a toner set and an image forming method using the same.

In an image forming method using electrophotography, the image forming body is uniformly charged by a charging means, and then exposed to light to form an electrostatic latent image. The latent image portion is then developed by a developing means to form a toner image. In recent years, in the field of electrostatic latent image toners used in electrophotographic image formation, developments have been made to meet various market demands. In particular, with the increasing number of types of recording media to be printed on, there is a high demand from the market for printers to be compatible with recording media.

For example, when printing on special recording media such as colored paper, black paper, aluminum-metallized paper, or transparent film, the color characteristics of the recording media affect the ability to obtain sufficient color development using only full-color toners such as yellow (Y), magenta (M), cyan (C), and black (K). Therefore, in order to increase the added value of images, various special color toners have been developed that are formed in lower or upper layers of images formed with combinations of the above-mentioned color toners, and market demand for such high-added-value images to increase the unit price per sheet is increasing year by year.

There are a wide variety of special toner types for creating high-value-added images, including white toner, transparent toner, silver toner using silver foil as a colorant, gold toner using gold foil as a colorant, and fluorescent toner.

When using these special color toners, one method is to add one cylinder to a normal four-cylinder machine, making it five cylinders, or two cylinders to make it six cylinders. With this method, an image consisting of many layers must be transferred and fixed simultaneously in all colors to a medium such as paper during the secondary transfer. For this reason, there is a demand for toners that have excellent fixing properties and are less likely to cause color mixing, even when images consisting of many layers are printed in multiple layers.

In particular, when performing high-value-added printing using special color toners, it is necessary to layer multiple layers of toner containing a high-density pigment (such as alumina or titanium oxide) as a colorant, so the amount of toner adherence tends to be significantly greater than in conventional printing using full-color toner of four colors (YMCK). This has created an urgent need to develop toners with better fixing properties.

To improve fixability, there is a method of fixing an image by applying stronger pressure or temperature to the fixing member than before. However, under such fixing conditions, a new problem arises in that the toner in the top layer in contact with the fixing member melts and dissolves with the toner in the adjacent layer, causing the color of layers other than the top layer to seep to the surface, decreasing the image density of the top layer (causing color turbidity). As a means of solving this problem, Patent Document 1 proposes a means of controlling the solubility parameter (SP value) of the resin that constitutes the toner.

JP 2016-048310 A

However, the technology described in Patent Document 1 was insufficient in terms of achieving both suppression of color turbidity and ensuring fixability.

Therefore, the present invention aims to provide a toner set that can suppress color turbidity during multi-layer printing while also achieving good fixability.

The inventors of the present invention have conducted extensive research in light of the above problems. As a result, they have discovered that the above problems can be solved by using a toner set having a specific molecular weight distribution, and have completed the present invention.

That is, the present invention provides a toner comprising a first toner containing at least a first binder resin;
a second toner containing at least a second binder resin,
The toner set is characterized by satisfying the following formulas (1) and (2):

In the formula, Mn(1) and Mn(2) represent the number average molecular weights of the tetrahydrofuran soluble fractions of the first toner and the second toner, respectively, and Mw(1) and Mw(2) represent the weight average molecular weights of the tetrahydrofuran soluble fractions of the first toner and the second toner, respectively.

The image forming method of the present invention makes it possible to suppress color turbidity during multi-layer printing while also achieving good fixability.

FIG. 1 is a schematic diagram illustrating an image forming apparatus that can be used for forming an image using a toner set according to an embodiment of the present invention.

One embodiment of the present invention will be described in detail below with reference to the attached drawings. Note that the present invention is not limited to the following embodiment. In this specification, the range "X to Y" means "X or more and Y or less." Unless otherwise specified, operations and measurements of physical properties are performed under the conditions of room temperature (range 20 to 25°C) and relative humidity 40 to 50% RH.

One embodiment of the present invention is a toner set including a first toner containing at least a first binder resin and a second toner containing at least a second binder resin, the toner set being characterized by satisfying the following formulas (1) and (2):

In the formula, Mn(1) and Mn(2) represent the number average molecular weights of the tetrahydrofuran soluble fractions of the first toner and the second toner, respectively, and Mw(1) and Mw(2) represent the weight average molecular weights of the tetrahydrofuran soluble fractions of the first toner and the second toner, respectively.

The toner set of this embodiment has the above-mentioned configuration, which allows for both suppression of color turbidity during multi-layer printing and good fixability.

The details of why the image forming method having the above-mentioned configuration produces the above-mentioned effects are unclear, but the following mechanism of action is thought to be the case. Note that the following mechanism of action is based on speculation, and the present invention is not limited to the following mechanism of action in any way.

The main component of the toner is a polymeric binder resin, and the low molecular weight components in the molecular weight distribution begin to melt at a temperature lower than the fixing temperature of the toner. Therefore, toner layer 1 formed by one toner (also called the first toner) is more likely to melt and adhere to toner layer 2 formed by another toner (also called the second toner) that is formed adjacent to the toner layer 1. As a result, it is expected that the fixing properties during multi-layer printing will be improved.

On the other hand, the presence of high molecular weight components in the toner's binder resin prevents the toner from melting too much due to the heat applied during fixing. Therefore, it is expected that the toner layer 1 will be less likely to mix with the adjacent toner layer 2, or to cause color mixing.

However, when the dispersity of the binder resin of the first toner and the dispersity of the second toner are both similarly large, the binder resin of the first toner or the binder resin of the second toner is likely to contain components with excessively large or small molecular weights. This makes it clear that problems such as poor fixing or color turbidity are likely to occur.

In contrast, in the toner set of this embodiment, as shown in the above formula (1), the ratio of the dispersity of the tetrahydrofuran (THF) soluble matter of the first toner (Mw(1)/Mn(1)) to the dispersity of the THF soluble matter of the second toner (Mw(2)/Mn(2)) is 3 or more. In this way, the molecular weight distribution of the THF soluble matter of one toner is broad, and the proportion of components with excessively large and small molecular weights is reduced, which is thought to make it possible to achieve both improved fixability and prevention of color turbidity during multilayer printing.

In addition, in the toner set of this embodiment, as shown in the above formula (2), the absolute value of the difference between the number average molecular weight Mn(1) of the THF-soluble portion of the first toner and the number average molecular weight Mn(2) of the THF-soluble portion of the second toner is 10,000 or less. If the absolute value of the difference in number average molecular weight exceeds 10,000, it is considered that the toner with the smaller number average molecular weight melts excessively and is likely to mix with the adjacent toner layer, which makes it more likely to cause color turbidity.

Note that the above mechanism of action is speculative, and the present invention is in no way limited to the above mechanism of action.

The toner set of this embodiment includes the first toner and the second toner, and the first toner and the second toner each include a binder resin (also referred to as the first binder resin and the second binder resin, respectively), and there are no particular limitations as long as the molecular weight distribution of the THF-soluble matter of these toners satisfies the specific relationship described above.

When performing multi-layer printing, the first toner and the second toner are transferred onto the recording medium in an overlapping state, but either toner may be the toner that forms the layer on the side that contacts the fixing member (upper layer), or it may be the toner that forms the layer on the recording medium side (lower layer).

The first toner and the second toner are preferably color toners or special color toners each containing a colorant of a different color, since this allows the effects of the present invention to be more pronounced, but either one may be a clear toner that does not contain a colorant. Specific forms of color toners and special color toners will be described later.

The toner set of this embodiment may also include toners other than the first toner and the second toner. For example, the toner set of this embodiment includes five or more types of toners, including the first toner and the second toner. Examples of toners other than the first toner and the second toner include color toners and special color toners containing colorants of different colors from these toners, and clear toners. It is preferable that the toners other than the first toner and the second toner include a binder resin, and the binder resin may be the same as or different from the first binder resin or the second binder resin. In order to obtain the effects of the present invention more significantly, it is preferable that the toner layer formed by the first toner and the toner layer formed by the second toner are arranged so as to be adjacent to each other and overlap each other when performing multi-layer printing, but this is not limited to this.

The molecular weight distribution of the THF-soluble portion of the first toner and the second toner is determined by the method described in the Examples below. The THF-soluble portion of the toner mainly contains binder resin, but does not contain colorants, external additives, etc. In addition, as described in the Examples below, the analysis is performed excluding components with molecular weights below a certain level, such as release agents and additives.

There are no particular limitations on the means for controlling the molecular weight distribution of the THF-soluble portion of the toner, and conventionally known knowledge may be referred to as appropriate. For example, the molecular weight distribution can be controlled by appropriately adjusting the types and compounding ratios of raw materials, the compounding ratios of polymerization initiators and chain transfer agents, etc., when synthesizing the binder resin, which is a polymer.

It is preferable that the toner set of this embodiment further satisfies the following formula (3).

The number average molecular weight Mn(2) of the second toner having a narrow molecular weight distribution is greater than the number average molecular weight Mn(1) of the first toner, which is more effective in reducing components with excessively large molecular weights, and therefore the fixability can be improved. Furthermore, when the difference between Mn(2) and Mn(1) is 2000 or more, the effect of preventing the first toner from excessively melting and easily mixing with adjacent toner layers, and thus preventing color turbidity, is greater. Furthermore, this is preferable because it is easy to achieve a good balance between excellent fixability and suppression of color turbidity.

In this case, it is preferable that Mn(1) and Mn(2) are both 4,000 or more and 11,000 or less. When Mn(1) and Mn(2) are both 4,000 or more, the amount of components with excessively small molecular weights is reduced, which is more effective in suppressing color turbidity. Also, when Mn(1) and Mn(2) are both 11,000 or less, the amount of components with excessively large molecular weights is reduced, which is more preferable, as this further improves fixability.

It is preferable that the toner set of this embodiment further satisfies the following formula (4).

The above-mentioned composition makes it more difficult for components with excessively small or large molecular weights to be generated, and the effect of achieving both excellent fixability and suppression of color turbidity can be more significantly achieved. It is also preferable because it is easy to achieve a good balance between excellent fixability and suppression of color turbidity.

It is preferable that the toner set of this embodiment further satisfies the following formula (5).

The above-mentioned configuration makes it more difficult for components with excessively small or large molecular weights to occur, and the effect of achieving both excellent fixability and suppression of color turbidity can be more significantly achieved. In addition, it is preferable because it is easy to achieve a good balance between excellent fixability and suppression of color turbidity. The smaller the value of Mw(2)/Mn(2), the more preferable, and although there is no particular lower limit, it is substantially 2 or more.

(toner)
Next, the toner will be described. The toner set of this embodiment includes a first toner and a second toner. In this specification, unless otherwise specified, matters common to the first toner and the second toner are referred to as "toner". In addition, the first toner includes a first binder resin, and the second toner includes a second binder resin, but unless otherwise specified, matters common to the first binder resin and the second binder resin are referred to as "binder resin".

The toner used in this embodiment is composed of toner base particles containing a binder resin. In addition, special color toners and color toners other than the transparent toner are composed of toner base particles further containing a colorant. The toner base particles to which an external additive has been added are called toner particles, and the toner base particles or an aggregate of toner particles are called toner. The toner base particles can generally be used as they are as toner particles, or toner base particles to which an external additive has been added can be used as toner particles. Examples of external additives include a fluidizing agent and a cleaning aid.

Color toners are based on yellow toner (Y) containing yellow colorants, which are the basic colors of the color materials used, magenta toner (M) containing magenta colorants, cyan toner (C) containing cyan colorants, and black toner (K) containing black colorants (hereinafter simply abbreviated as YMCK). Color toners may further contain toners of other chromatic colors than YMCK (e.g., orange toner, violet toner, etc.). By further including these other chromatic toners, it becomes possible to expand the color reproduction range. Such color toners based on YMCK can form images of various tones by overlapping each toner, and high-quality full-color images can be obtained.

On the other hand, special color toners are toners that do not contain colorants of basic colors. Examples include white toner (W) containing a white colorant such as titanium oxide, metallic toner (ME) containing a metallic colorant such as aluminum powder that exhibits metallic luster, gray toner containing a gray colorant, gold toner containing a gold colorant (gold foil), silver toner containing a silver colorant (silver foil), and fluorescent toners (fluorescent white toner, fluorescent yellow toner, fluorescent magenta toner, fluorescent cyan toner, etc.) containing fluorescent colorants, but are not limited to these. Special color toners are toners used in image formation as a single color other than the color toners YMCK, and are also called spot colors. These special color toners are used to improve the added value of images, and white toner, metallic toner, gray toner, gold toner, silver toner, and fluorescent toner are particularly high added value toner groups that can express colors that cannot be expressed by color toners as a single color, and can enhance the color development and luster of color toners by being present in the upper or lower layers of color toners. In particular, when a transparent film is used as the recording medium, forming an image with color toners on a white toner layer improves the visibility of the color toners, thereby increasing the added value of the image.

Transparent toner (CL), which does not contain colorants, is also used as a single-color toner for image formation and is used to improve the added value of images. Its presence in an upper or lower layer of color toners can enhance the color development and gloss of the color toners.

In a preferred embodiment of the present invention, the first toner contains a colorant. This configuration makes it possible to obtain the effects of the present invention more significantly.

According to a preferred embodiment of the present invention, the first toner contains a colorant, which is a white colorant or a metallic colorant. According to a further preferred embodiment, the first toner contains a white colorant as a colorant. When printing using a toner using such a high specific gravity colorant, the amount of toner adhesion increases, making it particularly difficult to achieve both fixability and prevention of color bleeding, but by using the first toner, these can be achieved in a well-balanced manner. In addition, images with high added value can be formed.

(Binder resin)
The binder resin is not limited to any of the components contained in known toners. The binder resin can be either an amorphous resin or a crystalline resin. For example, an amorphous vinyl resin, an amorphous polyester resin, or a crystalline polyester resin can be used. The amorphous vinyl resin, the amorphous polyester resin, and the crystalline polyester resin can be used in any one of these, or in combination. In particular, by including a crystalline polyester resin as the binder resin, the fixing energy can be further reduced.

(Amorphous Resin)
The amorphous resin is not particularly limited, and examples thereof include amorphous vinyl resins and amorphous polyester resins.

A non-crystalline resin is defined as a resin that does not have a clear endothermic peak when heated in an endothermic curve obtained by differential scanning calorimetry (DSC). That is, an amorphous resin is a resin that does not have a melting point (i.e., does not have the above-mentioned clear endothermic peak when heated) and has a relatively high glass transition temperature (Tg) in the endothermic curve obtained when differential scanning calorimetry (DSC) of toner particles or an amorphous resin is performed. Here, a "clear endothermic peak" means a peak whose half-width of the endothermic peak is within 15°C when measured at a heating rate of 10°C/min in differential scanning calorimetry (DSC). The endothermic curve can be measured, for example, using a differential scanning calorimeter "Diamond DSC" (manufactured by PerkinElmer).

In addition, the glass transition temperature (Tg) of the above-mentioned amorphous resin is preferably 35°C or higher and 80°C or lower, and more preferably 45°C or higher and 65°C or lower, from the viewpoint of maintaining a better balance between low-temperature fixability and fixation separation property.

The glass transition temperature can be measured according to the above-mentioned DSC method. For the measurement, a differential scanning calorimeter "Diamond DSC" (manufactured by PerkinElmer), a DSC-7 differential scanning calorimeter (manufactured by PerkinElmer), a TAC7/DX thermal analysis device controller (manufactured by PerkinElmer), etc. can be used.

From the viewpoint of easy control of the plasticity of the amorphous resin, the weight average molecular weight (Mw) of the amorphous resin is preferably 20,000 or more and 150,000 or less, and more preferably 25,000 or more and 130,000 or less. From the viewpoint of easy control of the plasticity of the amorphous resin, the number average molecular weight (Mn) of the amorphous resin is preferably 5,000 or more and 150,000 or less, and more preferably 8,000 or more and 70,000 or less. The molecular weight of the amorphous resin can be measured in the same manner as the molecular weight of the crystalline resin described above.

(Amorphous vinyl resin)
The amorphous vinyl resin is formed using a monomer having a vinyl group (hereinafter referred to as a "vinyl monomer"). Examples of the amorphous vinyl resin include a styrene-acrylic resin, a styrene resin, and an acrylic resin. Among them, a styrene-acrylic resin is preferable.

Examples of vinyl monomers include:

(1) Styrene-Based Monomers Examples of styrene-based monomers include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-phenylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, p-tert-butylstyrene, p-n-hexylstyrene, p-n-octylstyrene, p-n-nonylstyrene, p-n-decylstyrene, p-n-dodecylstyrene, and derivatives thereof.

(2) (Meth)acrylic acid ester monomers Examples of the (meth)acrylic acid ester monomers include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isopropyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, phenyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, and derivatives thereof.

(3) Vinyl Esters Examples of vinyl esters include vinyl propionate, vinyl acetate, and vinyl benzoate.

(4) Vinyl Ethers Examples of vinyl ethers include vinyl methyl ether and vinyl ethyl ether.

(5) Vinyl Ketones Examples of vinyl ketones include vinyl methyl ketone, vinyl ethyl ketone, and vinyl hexyl ketone.

(6) N-Vinyl Compounds Examples of N-vinyl compounds include N-vinylcarbazole, N-vinylindole, and N-vinylpyrrolidone.

(7) Others Examples of vinyl monomers other than the above (1) to (6) include vinyl compounds such as vinylnaphthalene and vinylpyridine, and acrylic acid or methacrylic acid derivatives such as acrylonitrile, methacrylonitrile, and acrylamide.

The above vinyl monomers can be used alone or in combination of two or more.

As the vinyl monomer, it is preferable to use a monomer having an ionic dissociable group such as a carboxy group, a sulfonic acid group, or a phosphoric acid group. Specific examples include the following:

Examples of monomers having a carboxy group include acrylic acid, methacrylic acid, maleic acid, itaconic acid, cinnamic acid, fumaric acid, maleic acid monoalkyl esters, and itaconic acid monoalkyl esters.

Examples of monomers having a sulfonic acid group include styrene sulfonic acid, allyl sulfosuccinic acid, and 2-acrylamido-2-methylpropanesulfonic acid.

Examples of monomers having a phosphate group include acidophosphooxyethyl methacrylate.

Furthermore, polyfunctional vinyls may be used as vinyl monomers to give a vinyl polymer with a crosslinked structure.

Examples of polyfunctional vinyls include divinylbenzene, ethylene glycol dimethacrylate, ethylene glycol diacrylate, diethylene glycol dimethacrylate, diethylene glycol diacrylate, triethylene glycol dimethacrylate, triethylene glycol diacrylate, neopentyl glycol dimethacrylate, and neopentyl glycol diacrylate.

(styrene acrylic resin)
From the viewpoint of plasticity during thermal fixing, it is preferable that each toner contains a styrene-(meth)acrylic acid ester resin (hereinafter, simply referred to as a styrene-acrylic resin) as a binder resin among the above vinyl resins. By using a styrene-acrylic resin, the amount of exudation of the release agent during fixing can be controlled, and tacking can be prevented and adhesion of the release agent can be suppressed.

In particular, it is preferable that the second toner contains 50% by mass or more of styrene acrylic resin relative to the total amount of the toner. By doing so, the effects of the present invention can be obtained more significantly. In addition, the heat resistance and storage stability of the toner can be improved.

Styrene-acrylic resin is formed by addition polymerization of at least a styrene monomer and a (meth)acrylic acid ester monomer. The styrene monomer includes, in addition to styrene represented by the structural formula CH ₂ ═CH-C ₆ H ₅ , those having a structure having a known side chain or functional group in the styrene structure. The (meth)acrylic acid ester monomer here includes, in addition to acrylic acid ester compounds and methacrylic acid ester compounds represented by CH(Ra)═CHCOORb (Ra represents a hydrogen atom or a methyl group, and Rb represents an alkyl group, preferably an alkyl group having 1 to 24 carbon atoms), ester compounds having a known side chain or functional group in the structure of an acrylic acid ester derivative or a methacrylic acid ester derivative. In this specification, the term "(meth)acrylic acid ester monomer" collectively refers to "acrylic acid ester monomer" and "methacrylic acid ester monomer".

Specific examples of styrene monomers and (meth)acrylic acid ester monomers capable of forming styrene-acrylic resins include those mentioned above.

The content of structural units derived from styrene monomers in the styrene-acrylic resin is preferably in the range of 40% by mass or more and 90% by mass or less, based on the total amount of the resin. Also, the content of structural units derived from (meth)acrylic acid ester monomers in the resin is preferably in the range of 10% by mass or more and 60% by mass or less, based on the total amount of the resin.

Furthermore, the styrene-acrylic resin is preferably a polymer obtained by further polymerizing a monomer compound (amphoteric compound) that is capable of addition polymerization with the styrene monomer and (meth)acrylic acid ester monomer and has a carboxyl group or a hydroxyl group. In other words, in addition to the above-mentioned styrene monomer and (meth)acrylic acid ester monomer, the styrene-acrylic resin may contain the following monomer compound (amphoteric compound):

Examples of such monomer compounds (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. These monomer compounds can be used alone or in combination of two or more.

The content of the constituent units derived from the above monomer compound (amphoteric compound) in the styrene-acrylic resin is preferably in the range of 0.5% by mass or more and 20% by mass or less based on the total amount of the resin.

The number average molecular weight (Mn) and weight average molecular weight (Mw) of the vinyl resin are not particularly limited as long as the toners constituting the toner set satisfy the above formulas (1) and (2).

The method for producing the vinyl resin is not particularly limited, and examples thereof include a method of carrying out polymerization by a known polymerization method such as bulk polymerization, solution polymerization, emulsion polymerization, miniemulsion, or dispersion polymerization using any polymerization initiator such as peroxide-based polymerization initiators such as benzoyl peroxide, methyl ethyl ketone peroxide, diisopropyl peroxycarbonate, cumene hydroperoxide, t-butyl hydroperoxide, di-t-butyl peroxide, dicumyl peroxide, 2,4-dichlorobenzoyl peroxide, lauroyl peroxide, 2,2-bis-(4,4-t-butylperoxycyclohexyl)propane, and tris-(t-butylperoxy)triazine, which are commonly used in the polymerization of the above monomers; water-soluble radical polymerization initiators such as persulfides, potassium persulfate, and ammonium persulfate; or azo compound-based polymerization initiators. In addition, a commonly used chain transfer agent can be used for the purpose of adjusting the molecular weight. There are no particular limitations on the chain transfer agent, but examples include alkyl mercaptans such as n-octyl mercaptan, n-octyl-3-mercaptopropionate, and mercapto fatty acid esters.

The content of the amorphous vinyl resin in the binder resin is not particularly limited, but is preferably 50% by mass or more, and more preferably 70% by mass or more.

(Amorphous polyester resin)
From the viewpoint of further improving the low-temperature fixing property, each toner may contain an amorphous polyester resin as a binder resin.

Amorphous polyester resin is a known polyester resin obtained by a polycondensation reaction between a divalent or higher carboxylic acid component (polycarboxylic acid component) and a divalent or higher alcohol component (polyhydric alcohol component), which does not have a clear melting point and has a relatively high glass transition point (Tg). This can be confirmed by performing differential scanning calorimetry (DSC) on the amorphous polyester resin. In addition, since it is different from the monomers that make up crystalline polyester resin, it can also be distinguished from crystalline polyester resin by analysis such as NMR.

There are no particular limitations on the amorphous polyester resin, and any amorphous polyester resin known in the art may be used.

<Components of amorphous polyester resin>
(Polycarboxylic Acid Component)
As the polycarboxylic acid component constituting the amorphous polyester resin, it is preferable to use an unsaturated aliphatic polycarboxylic acid, an aromatic polycarboxylic acid, or a derivative thereof, and it is more preferable to use an unsaturated aliphatic polycarboxylic acid, since it promotes compatibility with the crystalline polyester resin and improves low-temperature fixability. A saturated aliphatic polycarboxylic acid may be used in combination as long as it can form an amorphous resin.

Examples of the unsaturated aliphatic polycarboxylic acids include unsaturated aliphatic dicarboxylic acids such as methylene succinic acid, fumaric acid, maleic acid, 3-hexenedioic acid, 3-octenedioic acid, and succinic acid substituted with an alkyl group having 1 to 20 carbon atoms or an alkenyl group having 2 to 20 carbon atoms; unsaturated aliphatic tricarboxylic acids such as 3-butene-1,2,3-tricarboxylic acid, 4-pentene-1,2,4-tricarboxylic acid, and aconitic acid; and unsaturated aliphatic tetracarboxylic acids such as 4-pentene-1,2,3,4-tetracarboxylic acid. Lower alkyl esters and acid anhydrides of these can also be used.

Specific examples of succinic acid substituted with an alkyl group having 1 to 20 carbon atoms or an alkenyl group having 2 to 20 carbon atoms include dodecylsuccinic acid, dodecenylsuccinic acid, octenylsuccinic acid, and decenylsuccinic acid. Lower alkyl esters and acid anhydrides of these acids can also be used.

Examples of the aromatic polycarboxylic acids include aromatic dicarboxylic acids such as phthalic acid, terephthalic acid, isophthalic acid, t-butylisophthalic acid, tetrachlorophthalic acid, chlorophthalic acid, nitrophthalic acid, p-phenylenediacetic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, and anthracenedicarboxylic acid; aromatic tricarboxylic acids such as 1,2,4-benzenetricarboxylic acid (trimellitic acid), 1,2,5-benzenetricarboxylic acid (trimesic acid), 1,2,4-naphthalenetricarboxylic acid, and hemimellitic acid; aromatic tetracarboxylic acids such as pyromellitic acid and 1,2,3,4-butanetetracarboxylic acid; and aromatic hexacarboxylic acids such as mellitic acid. Lower alkyl esters and acid anhydrides of these may also be used.

Examples of saturated aliphatic polycarboxylic acids include saturated aliphatic dicarboxylic acids among the polycarboxylic acid components listed in the section on crystalline polyester resins below.

(Polyhydric alcohol component)
As the polyhydric alcohol component constituting the amorphous polyester resin, from the viewpoint of electrostatic chargeability and toner strength, it is preferable to use unsaturated aliphatic polyhydric alcohols, aromatic polyhydric alcohols, and derivatives thereof, and saturated aliphatic polyhydric alcohols may be used in combination as long as an amorphous polyester resin can be formed.

Examples of the unsaturated aliphatic polyhydric alcohols include unsaturated aliphatic diols such as 2-butene-1,4-diol, 3-butene-1,4-diol, 2-butyne-1,4-diol, 3-butyne-1,4-diol, and 9-octadecene-7,12-diol. Examples of the saturated aliphatic polyhydric alcohols include glycerin, trimethylolpropane, pentaerythritol, and sorbitol. Furthermore, derivatives of these can also be used.

Examples of the aromatic polyhydric alcohol include bisphenols such as bisphenol A and bisphenol F, and alkylene oxide adducts of bisphenols such as their ethylene oxide adducts and propylene oxide adducts, 1,3,5-benzenetriol, 1,2,4-benzenetriol, 1,3,5-trihydroxymethylbenzene, and the like. Derivatives of these can also be used. Among these, it is preferable to use bisphenol A-based compounds such as ethylene oxide adducts and propylene oxide adducts of bisphenol A, particularly from the viewpoint of improving the charging uniformity of the toner and making it easier to optimize the thermal properties.

The polyhydric alcohol component is not limited to one type, and two or more types may be mixed together.

The method for producing the amorphous polyester resin is not particularly limited, and the resin can be produced by polycondensing (esterifying) the polyvalent carboxylic acid component and the polyhydric alcohol component using a known esterification catalyst.

Examples of catalysts that can be used in the production include alkali metal compounds such as sodium and lithium; compounds containing Group 2 elements such as magnesium and calcium; metal compounds such as aluminum, zinc, manganese, antimony, titanium, tin, zirconium, and germanium; phosphorous compounds; phosphoric acid compounds; and amine compounds. Considering availability, it is preferable to use dibutyltin oxide, tin octylate, tin dioctylate, salts thereof, tetra-normal-butyl titanate (tetrabutyl orthotitanate, Ti(O-n-Bu) ₄ ), tetraisopropyl titanate (titanium tetraisopropoxide), tetramethyl titanate, tetrabutoxytitanium (titanium tetrabutoxide), and the like. These may be used alone or in combination of two or more.

The polycondensation (esterification) temperature is not particularly limited, but is preferably in the range of 150°C to 250°C. The polycondensation (esterification) time is not particularly limited, but is preferably in the range of 0.5 hours to 15 hours. During polycondensation, the reaction system may be decompressed as necessary.

The amorphous polyester resin may also be a vinyl-modified amorphous polyester resin having a block copolymer structure in which a vinyl polymerization segment (vinyl resin segment) is chemically bonded to an amorphous polyester polymerization segment consisting of the above-mentioned polyvalent carboxylic acid component and polyhydric alcohol component. A preferred example of such a vinyl-modified amorphous polyester resin is a styrene-acrylic-modified amorphous polyester resin. The following describes a preferred form of the vinyl-modified amorphous polyester resin, styrene-acrylic-modified amorphous polyester resin.

<Styrene acrylic modified amorphous polyester resin>
The styrene acrylic modified amorphous polyester resin is a resin composed of polyester molecules having a block copolymer or graft copolymer structure in which an amorphous polyester polymerized segment (amorphous polyester resin segment) and a styrene acrylic polymerized segment (styrene acrylic copolymer segment) are chemically bonded to each other. The styrene acrylic modified amorphous polyester resin may be used alone or in combination of two or more kinds.

The method for forming the amorphous polyester polymerized segment is not particularly limited. The specific types of polyvalent carboxylic acid component and polyhydric alcohol component used in forming the polymerized segment and the polycondensation conditions of these monomers are the same as those described above, so the explanation is omitted here.

On the other hand, the styrene acrylic polymerized segment constituting the styrene acrylic modified amorphous polyester resin is formed by addition polymerization of at least (1) a styrene monomer and (2) a (meth)acrylic acid ester monomer. As the styrene monomer and the (meth)acrylic acid ester monomer, those listed in the above [Styrene acrylic resin] section can be used. Among them, as the styrene monomer, styrene is preferred. As the (meth)acrylic acid ester monomer, n-butyl acrylate is preferred.

The styrene acrylic polymerized segment may be formed using the following monomers in addition to the above monomers. That is, (3) vinyl esters, (4) vinyl ethers, (5) vinyl ketones, (6) N-vinyl compounds, (7) other monomers, etc. Specific examples of the monomers (3) to (7) above can be those listed in the vinyl resin section above.

The method for forming the styrene-acrylic polymerized segment is not particularly limited, and examples of the method include a method in which any polymerization initiator used in the polymerization of the above-mentioned monomers is used to carry out polymerization by a known polymerization method such as bulk polymerization, solution polymerization, emulsion polymerization (emulsion association method), mini-emulsion method, or dispersion polymerization method. Specific examples of the polymerization initiator are as described above.

The content of the amorphous polyester polymerized segment in the styrene acrylic modified amorphous polyester resin is not particularly limited, but is preferably 60 to 95% by mass, and more preferably 70 to 85% by mass.

The content of styrene acrylic polymerized segments in the styrene acrylic modified amorphous polyester resin (hereinafter also referred to as the "styrene acrylic modification amount") is preferably 5 to 40% by mass, and more preferably 15 to 30% by mass.

The amount of styrene acrylic modification specifically refers to the ratio of the total mass of the styrene monomer and (meth)acrylic acid ester monomer to the total mass of the resin raw material used to synthesize the styrene acrylic modified amorphous polyester resin, that is, the total mass of the monomers (excluding bireactive monomers) that become the amorphous polyester polymerization segment, the styrene monomer and (meth)acrylic acid ester monomer that become the styrene acrylic polymerization segment, and the bireactive monomers that bond them.

Here, the "bireactive monomer" is a monomer that bonds a styrene-acrylic polymerization segment and an amorphous polyester polymerization segment, and has in its molecule both a group selected from a hydroxy group, a carboxy group, an epoxy group, a primary amino group, and a secondary amino group that forms an amorphous polyester polymerization segment, and an ethylenically unsaturated group that forms a styrene-acrylic polymerization segment.

Specific examples of bireactive monomers include acrylic acid, methacrylic acid, fumaric acid, maleic acid, etc., and may further be esters of these hydroxyalkyls (having 1 to 3 carbon atoms), but from the viewpoint of reactivity, acrylic acid, methacrylic acid, or fumaric acid is preferred. The styrene-acrylic polymerized segment and the amorphous polyester polymerized segment are bonded via this bireactive monomer.

From the viewpoint of improving low-temperature fixability, the amount of the bireactive monomer used is preferably 1 to 20% by mass, and more preferably 5 to 15% by mass, based on the total amount of monomers constituting the styrene-acrylic polymerized segment.

There are no particular limitations on the method for producing the styrene acrylic modified amorphous polyester resin, so long as it is a method capable of forming a polymer having a structure in which an amorphous polyester polymerized segment and a styrene acrylic polymerized segment are chemically bonded. Specific examples of the method for producing the styrene acrylic modified amorphous polyester resin include the methods shown below.

(A) a method of forming a styrene-acrylic polymerization segment by polymerizing an amorphous polyester polymerization segment in advance, reacting the amorphous polyester polymerization segment with a bireactive monomer, and further reacting the same with a styrene monomer and a (meth)acrylic acid ester monomer for forming a styrene-acrylic polymerization segment;
(B) A method of forming an amorphous polyester segment by polymerizing a styrene-acrylic polymerization segment in advance, reacting the styrene-acrylic polymerization segment with a bireactive monomer, and further reacting a polyvalent carboxylic acid component and a polyhydric alcohol component for forming an amorphous polyester polymerization segment;
(C) A method in which an amorphous polyester polymer segment and a styrene-acrylic polymer segment are polymerized in advance, and then reacted with a bireactive monomer to bond the two together.

The number average molecular weight (Mn) and weight average molecular weight (Mw) of the amorphous polyester resin (including styrene acrylic modified amorphous polyester resin) are not particularly limited as long as the molecular weight distribution of the THF soluble content of the toner constituting the toner set satisfies the above formulas (1) and (2). The number average molecular weight (Mn) and weight average molecular weight (Mw) can be measured by gel permeation chromatography (GPC) using polystyrene as a standard substance.

The content of the amorphous polyester resin in the binder resin is preferably in the range of 5% by mass to 30% by mass, and more preferably in the range of 10% by mass to 20% by mass.

(Crystalline Resin)
The binder resin (the first binder resin and/or the second binder resin) preferably contains a crystalline resin.

The crystalline resin is not particularly limited, but examples thereof include polyolefin resins, polydiene resins, and polyester resins. Among these, crystalline polyester resins are preferred in terms of improving low-temperature fixability and ease of use. The crystalline polyester resin may be a hybrid crystalline polyester resin.

A crystalline resin is defined as a resin that has a clear endothermic peak when heated in an endothermic curve obtained by differential scanning calorimetry (DSC). Here, a "clear endothermic peak" means a peak whose half-width is within 15°C when measured by differential scanning calorimetry (DSC) at a heating rate of 10°C/min.

The content of the crystalline resin in the toner is preferably in the range of 5% by mass to 20% by mass, and more preferably in the range of 7% by mass to 15% by mass. If the content of the crystalline resin is 5% by mass or more, a sufficient plasticizing effect is obtained, and low-temperature fixing properties are improved. If the content of the crystalline resin is 20% by mass or less, the thermal stability of the toner and stability against physical stress are improved. If the content is in the range of 7% by mass to 15% by mass, in addition to the above effects being more pronounced, it is preferable because it is easier to select the composition of the amorphous resin and an appropriate manufacturing method to control the viscoelasticity to a desired value.

The melting point of the crystalline resin (e.g., crystalline polyester resin) is preferably in the range of 55°C or higher and 80°C or lower from the viewpoint of achieving both fixability and thermal stability.

The molecular weight of the crystalline resin (e.g., crystalline polyester resin) is not particularly limited as long as the number average molecular weight and weight average molecular weight of the THF-soluble portion of the toner constituting the toner set satisfy the above formulas (1) and (2), but it is preferable that the number average molecular weight is in the range of 4,500 or more and 12,500 or less.

(Crystalline polyester resin)
The crystalline polyester resin can be obtained by a polycondensation reaction between a divalent or higher alcohol (a polyhydric alcohol component) and a divalent or higher carboxylic acid (a polycarboxylic acid component).

The crystalline polyester resin is not particularly limited, and may be a homopolymer synthesized by a polycondensation reaction between a polyhydric alcohol component and a polycarboxylic acid component, or a hybrid crystalline polyester resin in which a crystalline polyester polymer segment synthesized by a polycondensation reaction between a polyhydric alcohol component and a polycarboxylic acid component is copolymerized with an amorphous polymer segment other than the polyester resin.

A hybrid crystalline polyester resin is a resin in which a crystalline polyester polymerized segment and an amorphous polymerized segment other than polyester resin are chemically bonded. The crystalline polyester polymerized segment refers to a portion derived from a crystalline polyester resin, and the amorphous polymerized segment other than polyester resin refers to a portion derived from an amorphous resin other than polyester resin. Examples of amorphous resins other than polyester resin include vinyl resins such as styrene acrylic resin, urethane resins, and urea resins. The amorphous polymerized segments other than polyester resins may be used alone or in combination of two or more types.

Examples of hybrid crystalline polyester resins include resins having a structure in which other components are copolymerized into a main chain made of crystalline polyester polymerized segments, and resins having a structure in which crystalline polyester polymerized segments are copolymerized into a main chain made of other components.

Examples of polyhydric alcohol components include dihydric alcohols such as ethylene glycol, propylene glycol, butanediol, diethylene glycol, hexanediol, cyclohexanediol, octanediol, decanediol, dodecanediol, ethylene oxide adduct of bisphenol A, and propylene oxide adduct of bisphenol A; trihydric or higher polyols such as glycerin, pentaerythritol, hexamethylolmelamine, hexaethylolmelamine, tetramethylolbenzoguanamine, and tetraethylolbenzoguanamine; and ester compounds and hydroxycarboxylic acid derivatives thereof.

Examples of polyvalent carboxylic acid components include oxalic acid, succinic acid, maleic acid, mesaconic acid, adipic acid, β-methyladipic acid, azelaic acid, sebacic acid, nonanedicarboxylic acid, decanedicarboxylic acid, undecanedicarboxylic acid, dodecanedicarboxylic acid, fumaric acid, citraconic acid, diglycolic acid, cyclohexane-3,5-diene-1,2-dicarboxylic acid, malic acid, citric acid, hexahydroterephthalic acid, malonic acid, pimelic acid, tartaric acid, mucic acid, phthalic acid, isophthalic acid, terephthalic acid, tetrachlorophthalic acid, chlorophthalic acid, nitrophthalic acid, p-carboxyphenylacetic acid, p-phenylenediacetic acid, Examples of such carboxylic acids include divalent carboxylic acids such as m-phenylenediglycolic acid, p-phenylenediglycolic acid, o-phenylenediglycolic acid, diphenylacetic 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 carboxylic acids such as trimellitic acid, pyromellitic acid, naphthalene tricarboxylic acid, naphthalene tetracarboxylic acid, pyrene tricarboxylic acid, and pyrene tetracarboxylic acid, as well as their alkyl esters, acid anhydrides, and acid chlorides.

The monomers (polyhydric alcohol component and polyvalent carboxylic acid component) constituting the crystalline polyester resin preferably contain 50% by mass or more of linear aliphatic monomers, and more preferably 80% by mass or more. When aromatic monomers are used, the melting point of the crystalline polyester resin is often high, and when branched aliphatic monomers are used, the crystallinity is often low, so it is preferable to use linear aliphatic monomers. Furthermore, by making the linear aliphatic monomer 50% by mass or more, it is possible to maintain crystallinity in the toner. By making it 80% by mass or more, it is possible to maintain sufficient crystallinity.

The ratio of the polyhydric alcohol component to the polycarboxylic acid component used is preferably in the range of 1.5/1 to 1/1.5, more preferably 1.2/1 to 1/1.2, in terms of the equivalent ratio of the hydroxyl groups of the polyhydric alcohol component to the carboxyl groups of the polycarboxylic acid component.

The method for producing the crystalline polyester resin is not particularly limited, and the resin can be formed by polycondensing (esterifying) the polyhydric alcohol component and the polycarboxylic acid component using a known esterification catalyst.

Catalysts that can be used in the production of crystalline polyester resins are the same as those used in the production method of amorphous polyester resins described above.

The polymerization temperature is not particularly limited, but is preferably in the range of 150°C to 250°C. The polymerization time is not particularly limited, but is preferably in the range of 0.5 hours to 10 hours. During polymerization, the reaction system may be depressurized as necessary.

(Coloring Agent)
The special color toners and color toners (YMCK, etc.) other than the transparent toner (CL) further contain a colorant. Generally known dyes and pigments can also be used as the colorant. That is, the colorant used in each toner (excluding CL) can be any of carbon black, magnetic materials, dyes, pigments, etc. As carbon black, channel black, furnace black, acetylene black, thermal black, lamp black, etc. can be used. As magnetic materials, ferromagnetic metals such as iron, nickel, and cobalt, alloys containing these metals, compounds of ferromagnetic metals such as ferrite and magnetite, alloys that do not contain ferromagnetic metals but exhibit ferromagnetism when heat-treated, for example, alloys of the type called Heusler alloys such as manganese-copper-aluminum and manganese-copper-tin, and chromium dioxide can be used.

(Colorants for special color toners)
As the white colorant used in the white toner (W), both inorganic and organic pigments can be used. Specifically, examples of the white inorganic pigment include heavy calcium carbonate, light calcium carbonate, titanium oxide (titanium dioxide), 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, smexite, and the like. Examples of the white organic pigment include polystyrene resin particles, urea formalin resin particles, and the like. In addition, examples of the white pigment having a hollow structure include hollow resin particles, hollow silica, and the like. From the viewpoint of charging property and hiding property, the white colorant (pigment) is preferably titanium oxide. Any crystal structure such as anatase type, rutile type, or brookite type can be used for the titanium oxide.

The metallic colorant used in metallic toner (ME) refers to a material that can produce a metallic color tone, and includes not only conductive metal materials, but also non-metallic materials and non-conductive materials. Examples of such metallic colorants include aluminum pigments (aluminum powder; aluminum or its alloy powder), bronze powder, and pearl pigments.

The gray colorant used in gray toner does not require any special preparation; instead, existing black colorant can be used and the amount used reduced to produce gray toner.

Examples of gold colorants used in gold toner include gold powder and gold leaf.

Examples of silver colorants used in silver toner include silver powder and silver foil.

Examples of fluorescent colorants used in fluorescent toners include Solvent Yellow 98 and Solvent Orange 63.

(Coloring agents for color toners)
As the black colorant used in the black toner (K), any of various known black colorants can be used, for example, carbon black such as furnace black, channel black, acetylene black, thermal black, and lamp black, magnetic powder such as magnetite and ferrite, dyes, and inorganic pigments including non-magnetic iron oxide.

Examples of orange or yellow colorants used in the yellow toner (Y) include C.I. Pigment Orange 31, C.I. Pigment Orange 43, C.I. Pigment Yellow 12, C.I. Pigment Yellow 13, C.I. Pigment Yellow 14, C.I. Pigment Yellow 15, C.I. Pigment Yellow 17, C.I. Pigment Yellow 74, C.I. Pigment Yellow 93, C.I. Pigment Yellow 94, C.I. Pigment Yellow 138, C.I. Pigment Yellow 155, C.I. Pigment Yellow 180, and C.I. Pigment Yellow 185.

The magenta or red colorants used in the magenta toner (M) include C.I. Pigment Red 2, C.I. Pigment Red 3, C.I. Pigment Red 5, C.I. Pigment Red 6, C.I. Pigment Red 7, C.I. Pigment Red 15, C.I. Pigment Red 16, C.I. Pigment Red 48;1, C.I. Pigment Red 53;1, C.I. Pigment Red 57;1, C.I. Pigment Red 122, C.I. Pigment Red 123, C.I. Pigment Red 139, C.I. Pigment Red 144, C.I. Pigment Red 149, C.I. Pigment Red 150, C.I. Pigment Red 166, C.I. Pigment Red 177, C.I. Pigment Red 178, Pigment Red 184, C.I. Pigment Red 222, C.I. Pigment Red 238, etc.

Furthermore, examples of the green or cyan colorant used in the cyan toner (C) include C.I. Pigment Blue 15, C.I. Pigment Blue 15:2, C.I. Pigment Blue 15:3, C.I. Pigment Blue 15:4, C.I. Pigment Blue 16, C.I. Pigment Blue 18:3, C.I. Pigment Blue 60, C.I. Pigment Blue 62, C.I. Pigment Blue 66, and C.I. Pigment Green 7.

Colorants used in color toners other than the basic colors YMCK, such as orange toners, include pigments such as C.I. Pigment Orange 1 and 11. Colorants used in violet toners include pigments such as C.I. Pigment Violet 19, 23, and 29.

The colorants used in each color toner (excluding CL) can be used alone or in combination of two or more for each color.

The average particle size (volume-based median diameter) of the colorant (excluding ME) is preferably 10 to 1,000 nm, and more preferably 50 to 500 nm.

The shape of the metallic colorant (pigment) can be, for example, spherical or flat (scale-like). When the metallic colorant is spherical, its average particle size is preferably 1 μm or more and 30 μm or less, more preferably 3 μm or more and 20 μm or less, and even more preferably 5 μm or more and 15 μm or less. When the metallic colorant is flat, its average length in the major axis direction is preferably 1 μm or more and 30 μm or less, more preferably 3 μm or more and 20 μm or less, and even more preferably 5 μm or more and 15 μm or less. The ratio (aspect ratio) of the average length in the major axis direction to the average length in the thickness direction of the flat metallic colorant (lustrous pigment) is preferably 5 to 200, more preferably 10 to 100, and even more preferably 30 to 70.

The average particle size, or average length and aspect ratio of a metallic colorant (pigment) is measured by the following method. A scanning electron microscope (S-4800, manufactured by Hitachi High-Technologies Corporation) is used to take photographs of pigment particles at a measurable magnification (300 to 100,000 times), and the resulting image of the pigment particles is converted into a two-dimensional image, after which the particle size, or the length in the major axis direction and the length in the thickness direction of each particle can be measured and calculated.

The content of the colorant in the toner is preferably in the range of 2% by mass to 50% by mass, more preferably in the range of 5% by mass to 45% by mass, and even more preferably in the range of 10% by mass to 40% by mass. If the content of the colorant is 2% by mass or more, sufficient coloring power can be obtained, and if it is 50% by mass or less, the colorant does not separate from the toner and adhere to the carrier, and the charging property is stable, so that a high-quality image can be obtained.

(Release Agent)
The toner base particles constituting each toner may contain a release agent. The release agent is not particularly limited and may be any known agent. For example, an ester wax or a hydrocarbon wax may be used alone or in combination. Specific examples of the wax include polyolefin waxes such as polyethylene wax and polypropylene wax, branched chain hydrocarbon waxes such as microcrystalline wax, paraffin wax, long chain hydrocarbon waxes such as Sasol wax and Fischer-Tropsch wax, and other hydrocarbon waxes; dialkyl ketone waxes such as distearyl ketone, carnauba wax, montan wax, behenyl behenate (behenyl behenate), trimethylolpropane tribehenate, pentaerythritol tetrabehenate, pentaerythritol diacetate dibehenate, glycerin tribehenate, 1,18-octadecanediol distearate, tristearyl trimellitate, distearyl maleate, fatty acid polyglycerin ester waxes, and amide waxes such as ethylenediamine behenylamide and tristearyl trimellitate. Hydrocarbon waxes are preferred from the viewpoints of high melting point, easy crystallization after seeping out onto the toner image surface, and reduced adhesion of the release agent to the member.

The melting point of the release agent is preferably in the range of 40°C to 160°C, more preferably in the range of 50°C to 120°C. By setting the melting point of the release agent within the above range, tacking and release agent adhesion can be improved, and stable toner image formation can be achieved without cold offset, even when fixing is performed at low temperatures.

The content of the release agent in the toner is preferably in the range of 1% by mass to 30% by mass, more preferably in the range of 3% by mass to 20% by mass, and even more preferably in the range of 5% by mass to 15% by mass. By keeping the content of the release agent within the above range, tacking and release agent adhesion can be improved, and stable toner image formation can be achieved without causing cold offset, even when fixing is performed at low temperatures.

(Other ingredients)
The toner base particles constituting each toner may contain a charge control agent and may also contain other components that are generally used in toner base particles or toner particles.

The charge control agent is a substance that can be given a positive or negative charge by frictional charging, and is not particularly limited as long as it is colorless, and various known positively charged charge control agents and negatively charged charge control agents can be used.

The content of the charge control agent in the toner is preferably in the range of 0.01% by mass to 30% by mass, and more preferably in the range of 0.1% by mass to 10% by mass.

The toner containing the binder resin may have a single-layer structure or a core-shell structure. There are no particular limitations on the type of binder resin used in the core particles and shell layer of the core-shell structure.

(External additives)
In order to improve the fluidity, chargeability, cleaning properties, etc. of the toner, external additives such as a fluidizing agent, a cleaning aid, etc., which are so-called post-treatment agents, may be added to the surface of the toner base particles.

Examples of external additives include inorganic oxide particles such as silica particles, hydrophobic silica particles (e.g., hydrophobic sol-gel silica particles, hydrophobic fumed silica particles, etc.), alumina particles, titanium oxide particles, hydrophobic titanium oxide (hydrophobic titania) particles, inorganic particles such as inorganic stearic acid compound particles such as aluminum stearate particles and zinc stearate particles, and inorganic titanic acid compound particles such as strontium titanate particles and zinc titanate particles. The size of the inorganic particles is preferably 2 nm or more and 200 nm or less, and more preferably 7 nm or more and 150 nm or less, in terms of average particle size.

These can be used alone or in combination of two or more.

These inorganic particles may be surface-modified with silane coupling agents, titanium coupling agents, higher fatty acids, silicone oils, etc. to improve heat resistance and environmental stability.

The content of the external additive in the toner is preferably in the range of 0.05% by mass to 5% by mass, and more preferably in the range of 0.1% by mass to 3% by mass.

(Average particle size of toner particles)
The average particle size of the toner particles is preferably in the range of 4 μm to 10 μm, more preferably in the range of 4 μm to 7 μm, in terms of the volume-based median diameter (D50). By having the volume-based median diameter (D50) within the above range, the transfer efficiency is increased, the image quality of halftones is improved, and the image quality of thin lines, dots, etc. is improved.

The volume-based median diameter (D50) of the toner particles is measured and calculated using a measuring device consisting of a "Coulter Counter 3" (manufactured by Beckman Coulter, Inc.) connected to a computer system (manufactured by Beckman Coulter, Inc.) equipped with data processing software "Software V3.51."

Specifically, 0.02 g of the measurement sample (toner) is added to 20 mL of surfactant solution (for example, a surfactant solution prepared by diluting a neutral detergent containing a surfactant component 10 times with pure water in order to disperse the toner particles) and allowed to mix, after which ultrasonic dispersion is performed for 1 minute to prepare a toner particle dispersion. This toner particle dispersion is then pipetted into a beaker containing an "ISOTON II" (manufactured by Beckman Coulter, Inc.) in the sample stand until the concentration indicated on the measuring device reaches 8%.

By setting this concentration range, it is possible to obtain reproducible measurement values. In the measurement device, the measurement particle count is set to 25,000 particles, the aperture diameter is set to 50 μm, the measurement range from 1 μm to 30 μm is divided into 256 parts, and frequency values are calculated. The particle diameter of 50% of the particles with the largest volume cumulative fraction is determined to be the volume-based median diameter (D50).

(Toner Manufacturing Method)
The method for producing the toner is not limited as long as it is a known method, for example, a kneading and pulverizing method, a suspension polymerization method, an emulsion association method, or other known methods.

The kneading and grinding method involves dry mixing a binder resin and, if necessary, additives such as a colorant, a release agent, a charge control agent, and a dispersant in a mixer, then melting and kneading the mixture in a kneader to disperse it uniformly, and then grinding and classifying it.

As a mixer, for example, a Henschel type mixer such as a Henschel Mixer (registered trademark, the same applies below, manufactured by Mitsui Mining Co., Ltd.) can be used. As a kneader, for example, a single screw extruder or a twin screw extruder can be used. For pulverization, a collision type airflow pulverizer using a jet stream, a mechanical pulverizer, etc. can be used, and it is preferable to adjust the particle size to a predetermined size by classification using wind force, etc.

The method for producing toner base particles using the emulsion association method is a method in which an aqueous dispersion liquid (amorphous resin dispersion liquid) in which amorphous resin particles containing a release agent are dispersed in an aqueous medium, an aqueous dispersion liquid (colorant dispersion liquid) of colorant particles (excluding CL), and, if necessary, an aqueous dispersion liquid (crystalline resin dispersion liquid) in which crystalline resin particles are dispersed are mixed, and the amorphous resin particles, colorant particles, and, if necessary, crystalline resin particles are aggregated, and further association (fusion) between binder resin particles is performed, and shape control is performed to form toner particles (toner base particles).

The average particle size of the amorphous resin particles (oil droplets) or crystalline resin particles (oil droplets) in such an amorphous resin particle dispersion (amorphous resin dispersion) or crystalline resin particle dispersion (crystalline resin dispersion) is preferably 60 to 1000 nm, and more preferably 80 to 500 nm. The average particle size of the amorphous resin particles, crystalline resin particles, colorant particles, release agent (particles), etc. can be measured using a laser diffraction/scattering particle size distribution measuring device (Microtrack particle size distribution measuring device "UPA-150" (manufactured by Nikkiso Co., Ltd.)). The average particle size of these resin particles (oil droplets) can be controlled by the magnitude of the mechanical energy during emulsification and dispersion.

Here, the aqueous dispersion is a dispersion (particles) dispersed in an aqueous medium, and the aqueous medium is one whose main component (50% by mass or more) is water. Components other than water include organic solvents that dissolve in water, such as methanol, ethanol, isopropanol, butanol, acetone, methyl ethyl ketone, tetrahydrofuran, and ethyl acetate. Among these, alcohol-based organic solvents such as methanol, ethanol, isopropanol, and butanol, which do not dissolve resins, are particularly preferred.

A dispersion stabilizer may be dissolved in the aqueous medium, and surfactants or resin particles may be added to improve the dispersion stability of the oil droplets.

Examples of dispersion stabilizers include inorganic compounds such as tricalcium phosphate, calcium carbonate, colloidal silica, and hydroxyapatite. However, since it is necessary to remove the dispersion stabilizer from the toner base particles obtained, it is preferable to use one that is soluble in acid or alkali, such as tricalcium phosphate, or from an environmental standpoint, it is preferable to use one that is decomposable by enzymes.

Examples of surfactants include anionic surfactants such as alkylbenzene sulfonates, α-olefin sulfonates, phosphate esters, sodium alkyldiphenylether disulfonates, and sodium polyoxyethylene lauryl ether sulfate; amine salt-type surfactants such as alkylamine salts, aminoalcohol fatty acid derivatives, polyamine fatty acid derivatives, and imidazolines; cationic surfactants of quaternary ammonium salt-type surfactants such as alkyltrimethylammonium salts, dialkyldimethylammonium salts, alkyldimethylbenzylammonium salts, pyridinium salts, alkylisoquinolinium salts, and benzethonium chloride; nonionic surfactants such as fatty acid amide derivatives and polyhydric alcohol derivatives; amphoteric surfactants such as alanine, dodecyldi(aminoethyl)glycine, di(octylaminoethyl)glycine, and N-alkyl-N,N-dimethylammonium betaine; and anionic surfactants and cationic surfactants having a fluoroalkyl group can also be used.

In addition, resin particles for improving dispersion stability are preferably those with a particle size of 0.5 to 3 μm. Specific examples include polymethyl methacrylate resin particles with particle sizes of 1 μm and 3 μm, polystyrene resin particles with particle sizes of 0.5 μm and 2 μm, and polystyrene-acrylonitrile resin particles with a particle size of 1 μm.

Such emulsification and dispersion of the oil phase liquid can be carried out using mechanical energy, and the dispersing machine used for emulsification and dispersion is not particularly limited, and examples include low-speed shear dispersing machines, high-speed shear dispersing machines, friction dispersing machines, high-pressure jet dispersing machines, ultrasonic dispersing machines such as ultrasonic homogenizers, and high-pressure impact dispersing machines such as ultimaizers.

Next, for example, the prepared amorphous resin dispersion and, if necessary, a colorant dispersion are mixed, and the amorphous resin particles and colorant particles are aggregated in an aqueous medium. Furthermore, a crystalline resin dispersion may be added to fuse the particles together to form a core particle (core portion). During aggregation and fusion, an aggregating agent is added at or above the critical aggregation concentration, and the mixture is heated to or above the glass transition temperature (Tg) of the amorphous resin to promote aggregation and fusion.

For example, it is preferable to add a base such as an aqueous sodium hydroxide solution to the solution containing the amorphous resin dispersion in advance to adjust the pH to 9 to 12. Next, it is preferable to add a colorant dispersion as necessary, and then add the coagulant while stirring at 25 to 35°C for 5 to 15 minutes. Examples of coagulants that can be used include, but are not limited to, inorganic metal salts such as alkali metal salts and Group 2 metal salts.

Examples of inorganic metal salts include metal salts such as sodium chloride, potassium chloride, lithium chloride, calcium chloride, barium chloride, magnesium chloride, zinc chloride, aluminum chloride, copper sulfate, magnesium sulfate, aluminum sulfate, manganese sulfate, and calcium nitrate, as well as inorganic metal salt polymers such as polyaluminum chloride, polyaluminum hydroxide, polyiron silica, and calcium polysulfide. Among these, aluminum salts and polyaluminum chloride are particularly suitable. To obtain a sharper particle size distribution, inorganic metal salts with a valence of 2 are more suitable than 1, 3 than 2, and 4 than 3.

The amorphous resin particles may have a multi-layer structure of two or more layers made of resins with different compositions. For example, amorphous resin particles having such a two-layer structure can be obtained by preparing a dispersion of resin particles by a conventional polymerization process (first-stage polymerization), adding a polymerization initiator and a polymerizable monomer to this dispersion, and polymerizing the system (second-stage polymerization, third-stage polymerization).

In the aggregating step, it is preferable to add the aggregating agent and then heat the mixture to increase the temperature. Furthermore, if necessary, it is preferable to continue the fusion by maintaining the temperature for a certain period of time after adding the crystalline resin dispersion, preferably until the volume-based median diameter reaches 4.5 to 7.0 μm.

When preparing toner base particles having a core-shell structure, for example, an aqueous dispersion of resin particles that form the shell portion is further added, and the resin that forms the shell portion is aggregated and fused to the surface of the binder resin particles (core particles) obtained above. Then, when the size of the aggregated particles reaches the target size, a salt such as an aqueous sodium chloride solution is added to stop the aggregation. Thereafter, the reaction system may be further heated (second maturation process) until the aggregation and fusion of the shell portion to the core particle surface is further strengthened and the particle shape is the desired shape. This second maturation process may be performed until the average circularity of the toner base particles having a core-shell structure falls within the desired average circularity range.

Then, the obtained dispersion liquid containing the toner base particles is cooled by a known method, the toner base particles are separated from the cooled dispersion liquid of the toner base particles into solid-liquid separation, and the toner cake (a cake-like aggregate of the toner base particles in a wet state) obtained by the solid-liquid separation is washed and dried. Toner can be obtained by adding an external additive to the obtained toner base particles.

(Developer)
The toner for developing electrostatic images can be used as a magnetic or non-magnetic one-component developer. It may also be mixed with a carrier to be used as a two-component developer. When the toner is used as a two-component developer, the carrier may be magnetic particles made of a conventionally known material such as a metal such as iron, ferrite, or magnetite, or an alloy of such a metal with a metal such as aluminum or lead, and ferrite particles are particularly preferred.

As the carrier, a coated carrier in which the surface of magnetic particles is coated with a coating agent such as resin, or a dispersion type carrier in which magnetic fine powder is dispersed in a binder resin may be used.

The volume-based median diameter (volume average particle size) (d50) of the carrier is preferably in the range of 20 μm to 100 μm, and more preferably in the range of 25 μm to 80 μm.

The volume-based median diameter (volume average particle size) (d50) of the carrier can be measured typically using a laser diffraction particle size distribution analyzer "HELOS" (manufactured by SYMPATEC) equipped with a wet disperser.

The amount of toner mixed with the carrier is preferably in the range of 2% by mass to 10% by mass, with the total mass of the toner and carrier being 100% by mass.

(Image forming method)
According to one embodiment of the present invention, there is provided an image forming method using the toner set according to the present embodiment. The toner set according to the present embodiment is applied to, for example, an image forming method using an image forming apparatus that forms a color toner image by a plurality of developing machines.

In the image forming method of this embodiment, an image is formed by fixing an image forming layer A obtained by using a first toner, which is preferably a color toner or a special color toner, and an image forming layer B adjacent to the image forming layer A and obtained by using a second toner, which is preferably a clear toner or a color toner or a special color toner different from the first toner, on a recording medium. It is more preferable that the second toner is a color toner or a special color toner different from the first toner. In this case, the following methods can be used: after fixing the image forming layer A obtained by transferring the first toner onto the recording medium, the image forming layer B obtained by transferring the second toner onto the recording medium is fixed (a form in which a toner layer is formed by the first toner on the lower layer of a full-color image); after fixing the image forming layer B obtained by transferring the second toner onto the recording medium, the image forming layer A obtained by transferring the first toner onto the recording medium is fixed (a form in which a toner layer is formed by the first toner on the upper layer of a full-color image); and a method in which the image forming layer A obtained by transferring the first toner onto the recording medium and the image forming layer B obtained by transferring the second toner onto the recording medium are fixed together (a form in which a toner layer is formed by the first toner on the upper layer or lower layer of a full-color image). Since the effect of the present invention is further improved and image formation is fast, it is preferable to form an image by fixing the image forming layer A and the image forming layer B together. That is, a preferred embodiment of the present invention is an image forming method using the toner set of this embodiment, which includes transferring five or more types of toners, including the first toner and the second toner, onto a recording medium and fixing the resulting image forming layer all at once.

Preferably, the electrostatic latent image formed electrostatically on the image carrier is visualized by charging the developer with a frictional charging member in a developing machine (developing device) to obtain a toner image (image forming layer), and this toner image is transferred onto a recording medium. Thereafter, the toner image transferred onto the recording medium is fixed to the recording material by a fixing process using a contact heating method, thereby obtaining a visible image.

A suitable fixing method is the so-called contact heating method. Examples of the contact heating method include the heat and pressure fixing method, the heat roll fixing method, and the pressure contact heat fixing method in which fixing is performed by a rotating pressure member containing a fixedly arranged heating body.

In the hot roll fixing method, a fixing device is used that is usually made up of an upper roller with a heat source inside a metal cylinder made of iron or aluminum with a fluororesin or similar coating on the surface, and a lower roller made of silicone rubber or similar.

A linear heater is used as the heat source, and this heater heats the surface temperature of the upper roller to about 120 to 200°C. Pressure is applied between the upper and lower rollers, and this pressure causes the lower roller to deform, forming a so-called nip at this deformation point. The width of the nip is 1 to 10 mm, preferably 1.5 to 7 mm. The fixing linear speed is preferably 40 mm/sec to 600 mm/sec.

(Recording medium)
The recording medium (also referred to as media, recording material, recording paper, recording paper, etc.) may be any commonly used one, and is not particularly limited as long as it holds a toner image formed by a known image forming method using an image forming apparatus or the like. Examples of usable image supports include plain paper ranging from thin paper to thick paper, wood-free paper, art paper, or coated printing paper such as coated paper, commercially available Japanese paper and postcard paper, plastic films for soft packaging and OHP, cloth, soft transparent films, synthetic paper such as Yupo paper, etc. Examples of the plastic films include PP film, PET film, OPS film, OPP film, ONy film, PVC film, PE film, and TAC film. The image forming method of the present invention is excellent in that it can form a high-quality image with improved visibility of special color toners and color toners, good reproducibility of secondary colors of a color image, and no color bleeding or image peeling, and can increase the added value of the image, particularly when outputting onto a special recording medium such as colored paper, black paper, aluminum-deposited paper, or transparent film. Moreover, by outputting onto a plastic film such as a PP film or a PET film, it can be used as a label.

(Image forming apparatus)
There are no particular limitations on the image forming apparatus capable of forming a color toner image using the toner set of this embodiment by a plurality of developing units, and examples thereof include the apparatus disclosed in JP-A-2006-220694 and the like.

The image forming method using the toner set of this embodiment is described below.

Figure 1 is a schematic cross-sectional view showing an example of an image forming apparatus that can be used to form an image using the toner set of the present invention. In Figure 1, four types of YMCK are used as color toners, and a white toner (W) is used as a special color toner. However, in addition to the white toner, special color toners such as metallic toner (ME) or transparent toner (CL) can be used alone or in combination depending on the purpose. That is, in Figure 1, an example is shown in which a special color toner (one type) is used on five cylinders, with one cylinder added to a normal four-cylinder machine (YMCK), but depending on the purpose, special color toners (two types) can be used on six cylinders, with two cylinders added to a normal four-cylinder machine (YMCK).

First, we will provide an overview of a color electrophotographic image forming apparatus equipped with a detection sensor and a secondary transfer device.

The image forming apparatus GS is known as a tandem type color image forming apparatus, and has image forming units arranged along the direction of movement of the intermediate transfer body 36 to form yellow, magenta, cyan and black color toner images and a white toner image, which is a type of special color toner. The color toner images and white toner images formed on the image carriers of each image forming unit are multiple-transferred and superimposed onto the intermediate transfer body, and then transferred together onto the image support.

In FIG. 1, an original image placed on the image reading device SC, which is disposed at a position occupying the upper part of the image forming device GS, is scanned and exposed by the optical system and read into the line image sensor CCD. The analog signal photoelectrically converted by the line image sensor CCD undergoes analog processing, A/D conversion, shading correction, image compression processing, etc. in the image processing section, and then sends the image data signal to the exposure optical system 33, which serves as an image writing means.

Intermediate transfer body 36 can be a drum type or an endless belt type, both of which have similar functions, but in the following explanation, the intermediate transfer body refers to the endless belt type intermediate transfer body 36.

In addition, in FIG. 1, five process units 100 are provided around the periphery of the intermediate transfer body 36 for forming images of each color, yellow (Y), magenta (M), cyan (C), black (K) and white (W). The process units 100 are arranged as means for forming color toner images and white toner images, in a vertical line along the intermediate transfer body 36 with respect to the rotation direction of the intermediate transfer body 36, which is the vertical direction indicated by the arrow in the figure, in the order of Y, M, C, K and W.

All five process units 100 have a common structure, and each is made up of a photoconductor drum 31, a charger 32 as a charging means, an exposure optical system 33 as an image writing means, a developing device (developing machine) 34, and a photoconductor cleaning device 190 as an image carrier cleaning means.

The photoconductor drum 31 is, for example, a cylindrical substrate made of a metallic member such as aluminum with an outer diameter of about 40 to 100 mm, on which a photoconductor layer with a thickness (film thickness) of about 20 to 40 μm is formed. The photoconductor drum 31 is rotated in the direction of the arrow with the substrate grounded by power from a driving source (not shown), for example at a linear speed of about 80 to 280 mm/s, preferably 220 mm/s.

Around the photoconductor drum 31, an image forming unit consisting of a charger 32 as a charging means, an exposure optical system 33 as an image writing means, and a developing device (developing machine) 34 is arranged in the direction of rotation of the photoconductor drum 31 as indicated by the arrow in the figure.

The charger 32, which serves as a charging means, is attached in close proximity to and faces the photosensitive drum 31 in a direction parallel to the rotation axis of the photosensitive drum 31. The charger 32 is equipped with a discharge wire as a corona discharge electrode that applies a predetermined potential to the photosensitive layer of the photosensitive drum 31, and performs charging (negative charging in this embodiment) by corona discharge of the same polarity as the toner, thereby applying a uniform potential to the photosensitive drum 31.

The exposure optical system 33, which is an image writing means, rotates and scans the laser light emitted from a semiconductor laser (LD) light source (not shown) in the main scanning direction using a rotating polygon mirror (no symbol), and exposes (writes an image) the photosensitive drum 31 using an electrical signal corresponding to the image signal via an fθ lens (no symbol), a reflecting mirror (no symbol), etc., forming an electrostatic latent image corresponding to the original image on the photosensitive layer of the photosensitive drum 31.

The developing device 34 as a developing means contains two-component developers of each color, yellow (Y), magenta (M), cyan (C), black (K) and white (W), charged to the same polarity as the charging polarity of the photosensitive drum 31, and is equipped with a developing roller 34a, which is a cylindrical developer carrier formed of non-magnetic stainless steel or aluminum material, for example, with a thickness of 0.5 to 1 mm and an outer diameter of 15 to 25 mm. The developing roller 34a is kept in non-contact with the photosensitive drum 31 by abutting rollers (not shown) with a predetermined gap, for example, 100 to 1000 μm, and rotates in the same direction as the rotation direction of the photosensitive drum 31. During development, a DC voltage of the same polarity as the toner (negative polarity in this embodiment) or a developing bias voltage in which an AC voltage is superimposed on a DC voltage is applied to the developing roller 34a, thereby performing reverse development on the exposed portion on the photosensitive drum 31.

The intermediate transfer body 36 is a semiconductive endless (seamless) resin belt having a volume resistivity of about 1.0×10 ⁷ to 1.0×10 ⁹ Ω·cm and a surface resistivity of about 1.0×10 ¹⁰ to 1.0×10 ¹² Ω/□. The resin belt may be a semiconductive resin film having a thickness of 0.05 to 0.5 mm, which is made of engineering plastics such as modified polyimide, thermosetting polyimide, ethylene tetrafluoroethylene copolymer, polyvinylidene fluoride, nylon alloy, etc., in which a conductive material is dispersed. The intermediate transfer body 36 may also be a semiconductive rubber belt having a thickness of 0.5 to 2.0 mm, which is made of silicone rubber, urethane rubber, etc., in which a conductive material is dispersed. The intermediate transfer body 36 is wound around a plurality of roller members including a tension roller 36a and a backup roller 36B facing the secondary transfer member, and is supported so as to be rotatable in the vertical direction.

The primary transfer roller 37, which serves as the first transfer means for each color, is made of a roller-shaped conductive member using foamed rubber such as silicone or urethane, and is disposed opposite the photoconductor drum 31 for each color, sandwiching the intermediate transfer body 36 between them, and presses the back surface of the intermediate transfer body 36 to form a transfer area between the photoconductor drum 31 and the roller. A constant DC current of the opposite polarity to the toner (positive polarity in this embodiment) is applied to the primary transfer roller 37 by constant current control, and the toner image on the photoconductor drum 31 is transferred onto the intermediate transfer body 36 by the transfer electric field formed in the transfer area.

The toner image transferred onto the intermediate transfer body 36 is then transferred to a recording medium (image support) P. A detection sensor 38 that measures the density of the patch image toner is installed on the circumference of the intermediate transfer body 36.

The fixing device 47 that fixes the transferred recording medium P is provided with a heating roller 47a and a pressure belt 47b, which form a nip. Therefore, in FIG. 1, the fixing member that comes into contact with the upper layer (toner layer) of the multiple toner layers transferred onto the recording medium P is the heating roller 47a.

In addition, a conventional fixing device (not shown) that uses a fixing belt for fixing may be used to accommodate high-speed printing. In a fixing method using such a fixing belt, the recording medium P carrying an unfixed toner image is sent to the fixing device and guided by a guide plate to the nip section. The unfixed toner image is then quickly fixed to the recording medium P by the fixing belt (the "upper fixing belt" in the embodiment) coming into close contact with the recording medium P. In addition, the recording medium P receives an airflow from the airflow separating device at the downstream end of the fixing nip section. This promotes the separation of the recording medium P from the fixing belt. The recording medium P that has been separated from the fixing belt is guided by a guide roller toward the outside of the image forming apparatus.

Downstream of the fixing device 47, there are provided paper discharge rollers 54 for clamping and discharging the fixed recording medium P, and a paper discharge tray 55 for placing the recording medium P discharged outside the machine.

On the other hand, a cleaning device 190A is provided to clean residual toner on the intermediate transfer body 36.

Furthermore, a secondary transfer device 70 is provided to clean the patch image toner on the secondary transfer member 37A.

Next, we will explain the image formation method.

When image recording starts, the photoconductor drive motor (not shown) starts, rotating the yellow (Y) photoconductor drum 31 in the direction indicated by the arrow in the figure, and the Y charger 32 applies a potential to the Y photoconductor drum 31. After the Y photoconductor drum 31 is applied with a potential, the Y exposure optical system 33 exposes (writes an image) the Y photoconductor drum 31 with an electrical signal corresponding to the first color signal, i.e., the Y image data, and an electrostatic latent image corresponding to the yellow (Y) image is formed on the Y photoconductor drum 31. This latent image is reverse-developed by the Y developing device 34, and a toner image made of yellow (Y) toner is formed on the Y photoconductor drum 31. The Y toner image formed on the Y photoconductor drum 31 is transferred onto the intermediate transfer body 36 by the primary transfer roller 7 as a primary transfer means.

Next, a potential is applied to the M photoconductor drum 31 by the magenta (M) charger 32. After the M photoconductor drum 31 is applied with a potential, the M exposure optical system 33 exposes (writes an image) the M photoconductor drum 31 with an electrical signal corresponding to the first color signal, i.e., the M image data, and an electrostatic latent image corresponding to the magenta (M) image is formed on the M photoconductor drum 31. This latent image is reverse-developed by the M developing device 34, and a toner image made of magenta (M) toner is formed on the M photoconductor drum 31. The M toner image formed on the M photoconductor drum 31 is transferred onto the intermediate transfer body 36 by the primary transfer roller 37 as a primary transfer means, superimposed on the Y toner image.

By a similar process, a toner image made of cyan (C) toner formed on the cyan (C) photoconductor drum 31 and a toner image made of black (K) toner formed on the black (K) photoconductor drum 31 are sequentially superimposed on the intermediate transfer body 36, and a superimposed color toner image made of Y, M, C and K toners is formed on the peripheral surface of the intermediate transfer body 36.

Next, the white (W) photoconductor drum 31 is rotated in the direction indicated by the arrow in the figure, and a potential is applied to the W photoconductor drum 31 by the W charger 32. After the W photoconductor drum 31 is applied with a potential, the W exposure optical system 33 performs exposure (image writing) by an electrical signal corresponding to the first color signal, i.e., the W image data, and an electrostatic latent image corresponding to the white (W) image is formed on the W photoconductor drum 31. This latent image is reverse developed by the W developing device 34, and a toner image made of white (W) toner is formed on the W photoconductor drum 31. The W toner image formed on the W photoconductor drum 31 is transferred onto the intermediate transfer body 36 by the primary transfer roller 7 as a primary transfer means. As a result, a superimposed color toner image made of Y, M, C, and K toners is formed on the peripheral surface of the intermediate transfer body 36, and a white (special color) toner image made of W toner is formed on the color toner image. In the example of FIG. 1, the toner image made of white (W) toner is formed on the lower layer of the color image (color toner layer) formed by a combination of color toners, and is formed on the entire image forming area of the recording medium P so that the visibility of the color toners can be improved by forming an image on the white toner layer with color toners, and the added value of the image can be increased. In the example of FIG. 1, an example is shown in which a white toner layer is formed on the entire image forming area of the recording medium P in order to form a white toner layer (a solid white base layer) on the lower layer of the color image, but in this embodiment, the special color toner such as white toner may be included in any of the multiple toner layers depending on the purpose of use, or may be included in the layer (upper layer) that contacts the fixing member.

Any toner remaining on the surface of each photoconductor drum 31 after transfer is cleaned by the photoconductor cleaning device 190.

Meanwhile, the recording medium P as recording paper stored in the paper feed cassettes 50A, 50B, and 50C is fed by the feed roller 51 and the paper feed roller 52A provided in each of the paper feed cassettes 50A, 50B, and 50C, and is transported on the transport path 52 by the transport rollers 52B, 52C, and 52D, and is transported through the resist roller 53 to the secondary transfer member 37A as a secondary transfer means to which a voltage of the opposite polarity to the toner (positive polarity in this embodiment) is applied. In the transfer area of the secondary transfer member 37A, the superimposed color toner image (color image) formed on the intermediate transfer body 36 and the white (special color) toner image on the color toner image (color image) are transferred together onto the recording medium (image support) P. As a result, an image is formed with color toner on the white toner layer.

The recording medium P, on which the color image has been transferred onto the white toner layer (solid white base layer), is heated and pressurized in the nip formed by the heating roller 47a and pressure belt 47b of the fixing device 47, where the image is fixed, then sandwiched between the paper discharge rollers 54 and placed on the paper discharge tray 55 outside the machine.

After the white toner layer (solid white base layer) and color image are transferred onto the recording medium P by the secondary transfer member 37A as the secondary transfer means, the residual toner on the intermediate transfer body 36 that separated the recording medium P by curvature is removed by the intermediate transfer body cleaning device 190A.

Furthermore, the patch image toner on the secondary transfer member 37A is cleaned by the cleaning blade 71 of the secondary transfer device 70.

The effects of the present invention will be explained using the following examples and comparative examples. However, the technical scope of the present invention is not limited to the following examples.

[Preparation of amorphous resin dispersion X2]
(1) First-stage polymerization 8 parts by mass of sodium dodecyl sulfate and 3,000 parts by mass of ion-exchanged water were charged into a 5 L reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube, and a nitrogen introduction device, 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 particles.

(Monomer Mixture 1)
Styrene 480 parts by weight, n-butyl acrylate 250 parts by weight, methacrylic acid 68 parts by weight.

(2) Second-stage polymerization A solution of 7 parts by mass of sodium polyoxyethylene (2) dodecyl ether sulfate dissolved in 3,000 parts by mass of ion-exchanged water was charged into a 5 L reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube, and a nitrogen introducing device, and the solution was heated to 80°C, after which 80 parts by mass of resin particle dispersion a1 (solid content equivalent) and monomer mixture 2 in which monomers and a release agent having the following composition were dissolved at 90°C 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 release agent and has a melting point of 80°C.

(Monomer Mixture 2)
Styrene 285 parts by mass n-Butyl acrylate 95 parts by mass Methacrylic acid 20 parts by mass n-Octyl-3-mercaptopropionate 8 parts by mass Hydrocarbon wax 1 (C80 (manufactured by Sasol)) 190 parts by mass.

Next, an initiator solution in which 6 parts by mass of potassium persulfate was dissolved in 200 parts by mass of ion-exchanged water was added to the dispersion, and the resulting dispersion was polymerized by heating and stirring at 84°C for 1 hour to prepare a resin particle dispersion a2.

(3) Third-stage polymerization: Further, 400 parts by mass of ion-exchanged water was added to the dispersion a2 of resin particles and thoroughly mixed, 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 dispersion X2 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 X2 were measured, and the volume-based median diameter (d50) of the amorphous resin particles was 220 nm, the glass transition temperature (Tg) was 46°C, and the weight average molecular weight (Mw) was 32,000.

[Preparation of amorphous resin dispersions X1, X3 to X11]
Amorphous resin dispersions X1, X3 to X11 were obtained in the same manner as in the preparation of amorphous resin dispersion X2, except that the amount of n-octyl-3-mercaptopropionate (NOM) in the second and third polymerization stages and the amount of dispersion a1 (converted into solid content) were changed as shown in Table 1 below.

[Synthesis of crystalline polyester resin P1]
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(O-n-Bu) ₄ was added, and the resulting mixed liquid was stirred at about 180 ° C. for 8 hours under a nitrogen gas flow to carry out a reaction. Furthermore, 0.2 parts by mass of Ti(O-n-Bu) ₄ was added to the mixed liquid, the temperature of the mixed liquid was raised to about 220 ° C., and the mixed liquid 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 P1. The number average molecular weight (Mn) of the crystalline polyester resin P1 was 5500, the weight average molecular weight (Mw) was 18000, and the melting point (Tm) was 70 ° C.

[Preparation of Crystalline Resin Dispersion Y1]
The crystalline polyester resin P1 prepared above was transferred to an emulsifying and dispersing machine "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 having a concentration of 0.37% by mass was transferred to the emulsifying and dispersing machine 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 emulsifying and dispersing machine 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 dispersion Y1 of the crystalline polyester resin P1 having a solid content of 30% by mass. The volume-based median diameter (d50) of the particles of the crystalline polyester resin P1 contained in the crystalline resin dispersion Y1 was 200 nm.

(Preparation of Cyan Colorant Dispersion)
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, a cyan colorant (pigment), was gradually added while stirring the solution. The resulting dispersion was then subjected to a dispersion treatment using a stirring device "Clearmix" (manufactured by M Technique Co., Ltd.) to prepare a cyan colorant dispersion (colorant dispersion C) in which particles of the cyan colorant were dispersed. The volume-based median diameter d50 of the cyan colorant in colorant dispersion C was measured using a microtrack particle size distribution measuring device "UPA-150" (manufactured by Nikkiso Co., Ltd.) and found to be 150 nm.

(Preparation of Magenta Colorant Dispersion)
As a magenta colorant (pigment), 50 parts by mass of C.I. Pigment Red 238 was added to a surfactant aqueous solution in which 1% by mass of sodium alkyl diphenyl ether disulfonate was dissolved in 200 parts by mass of ion-exchanged water, and then dispersed using an ultrasonic homogenizer to prepare a magenta colorant dispersion (colorant dispersion M). The solid content concentration (content of magenta colorant) in the colorant dispersion M was adjusted to 20% by mass. The volume-based median diameter of the magenta colorant in the colorant dispersion M was 150 nm.

(Preparation of Yellow Colorant Dispersion)
As a yellow colorant (pigment), 50 parts by mass of C.I. Pigment Yellow 74 was added to a surfactant aqueous solution in which 1% by mass of sodium alkyl diphenyl ether disulfonate was dissolved in 200 parts by mass of ion-exchanged water, and then dispersed using an ultrasonic homogenizer to prepare a yellow colorant dispersion (colorant dispersion Y). The solid content concentration (yellow colorant content) in the colorant dispersion Y was adjusted to 20% by mass. The volume-based median diameter of the yellow colorant in the colorant dispersion Y was 153 nm.

(Preparation of Metallic Colorant Dispersion)
As a metallic colorant (pigment), 210 parts by mass of aluminum pigment (260EA, manufactured by Showa Aluminum Powder Co., Ltd., average particle size 10 μm) in which the solvent was removed from a paste was added to a surfactant aqueous solution in which 1% by mass of sodium alkyl diphenyl ether disulfonate was dissolved in 480 parts by mass of ion-exchanged water, and then dispersed using an ultrasonic homogenizer to prepare a metallic colorant dispersion (colorant dispersion ME). The solid content concentration (content of metallic colorant) in the colorant dispersion ME was adjusted to 30% by mass. The average particle size of the metallic colorant in the colorant dispersion ME was 4 μm.

[Synthesis of amorphous polyester resin s1]
A monomer mixture 4 having the following composition and containing 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.

The raw material monomers for the polycondensation segment (amorphous polyester polymerized segment) shown 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:
Bisphenol A propylene oxide 2-mol adduct 285.7 parts by mass Terephthalic acid 66.9 parts by mass Fumaric acid 47.4 parts by mass.

Next, the above-mentioned monomer mixture 4 was added dropwise to the resulting solution over a period of 90 minutes while stirring, and after aging for 60 minutes, the unreacted monomers from the monomer mixture 4 were removed from the four-neck flask under reduced pressure (8 kPa).

Then, 0.4 parts by mass of Ti(O-n-Bu) 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 amorphous polyester resin s1. The number average molecular weight (Mn) of amorphous polyester resin s1 was 10,500 and the weight average molecular weight (Mw) was 29,500.

[Preparation of amorphous polyester particle dispersion S1]
100 parts by mass of the amorphous polyester resin s1 prepared above was dissolved in 400 parts by mass of ethyl acetate (Kanto Chemical Co., Ltd.), and mixed with 638 parts by mass of a previously prepared aqueous solution of sodium dodecyl sulfate having a concentration of 0.26% by mass.

The resulting mixture was ultrasonically dispersed for 30 minutes with stirring using an ultrasonic homogenizer "US-150T" (manufactured by Nippon Seiki Seisakusho Co., Ltd.) at a V-LEVEL of 300 μA.

Then, 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) to completely remove the ethyl acetate. In this way, an amorphous polyester resin dispersion (shell dispersion) S1 with a solid content of 13.5% by mass was prepared. The volume-based median diameter (d50) of the resin particles in the amorphous polyester resin dispersion S1 was 160 nm.

[Synthesis of amorphous polyester resin s2]
Terephthalic acid (TPA) 80 parts by mass, trimellitic acid (TMA) 6 parts by mass, fumaric acid (FA) 19 parts by mass, dodecenylsuccinic anhydride (DDSA) 85 parts by mass, bisphenol A propylene oxide adduct (BPA.PO) 351 parts by mass, bisphenol A ethylene oxide adduct (BPA.EO) 58 parts by mass, a stirrer, a thermometer, a cooling tube, a reaction vessel equipped with a nitrogen gas inlet tube, and after replacing the inside of the reaction vessel with dry nitrogen gas, 0.3 parts by mass of titanium tetrabutoxide (Ti(O-n-Bu) ₄ ) was added, and a polymerization reaction was carried out for 5 hours while stirring at 100 ° C. under a nitrogen gas stream. Further, 0.2 parts by mass of titanium tetrabutoxide was added, and the temperature was raised to 220 ° C. and the polymerization reaction was carried out for 6 hours while stirring, and the pressure in the reaction vessel was reduced to 10 mmHg, and the reaction was carried out under reduced pressure to obtain amorphous polyester resin s2. The amorphous polyester resin s2 had a number average molecular weight (Mn) of 4,100 and a weight average molecular weight (Mw) of 24,000.

[Synthesis of amorphous polyester resin s3]
Terephthalic acid (TPA) 80 parts by mass, fumaric acid (FA) 19 parts by mass, dodecenylsuccinic anhydride (DDSA) 85 parts by mass, bisphenol A propylene oxide adduct (BPA.PO) 351 parts by mass, bisphenol A ethylene oxide adduct (BPA.EO) 58 parts by mass, a stirrer, a thermometer, a cooling tube, a reaction vessel equipped with a nitrogen gas inlet tube, the inside of the reaction vessel was replaced with dry nitrogen gas, and then 0.1 parts by mass of titanium tetrabutoxide (Ti(O-n-Bu) ₄ ) was added, and a polymerization reaction was carried out for 10 hours while stirring at 100 ° C. under a nitrogen gas stream. Further, 0.1 parts by mass of titanium tetrabutoxide was added, the temperature was raised to 220 ° C., and a polymerization reaction was carried out for 8 hours while stirring, and then the pressure in the reaction vessel was reduced to 10 mmHg, and the reaction was carried out under reduced pressure to obtain a pale yellow transparent amorphous polyester resin s3. The amorphous polyester resin s3 had a number average molecular weight (Mn) of 10,100 and a weight average molecular weight (Mw) of 83,000.

[Preparation of Cyan Toner 1]
Into a reaction vessel equipped with a stirrer, a temperature sensor, and a cooling tube, 288 parts by mass of the amorphous resin dispersion X1 (converted into solid content) and 2,000 parts by mass of ion-exchanged water were charged, and then a 5 mol/L aqueous sodium hydroxide 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 of 30 parts by mass of magnesium chloride dissolved in 60 parts by mass of ion-exchanged water as a flocculant was added to the dispersion over 10 minutes at 30°C while stirring. The resulting mixture was heated to 80°C, and 40 parts by mass of crystalline polyester resin dispersion Y1 (solid content equivalent) was added to the mixture over 10 minutes to promote flocculation.

The particle size of the particles associated in the 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 amorphous polyester resin dispersion (shell dispersion) S1 (solid content equivalent) was added to the 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 solution was then heated to 80°C and stirred to promote fusion of the particles, and the particles in the reaction solution were measured (HPF detection count: 4,000 particles) using a measuring device "FPIA-2100" (Sysmex Corporation). When the average circularity of the particles reached 0.945, the reaction solution was cooled to 30°C at a cooling rate of 2.5°C/min.

Next, the particles were separated from the cooled reaction liquid, dehydrated, and the resulting cake was washed by repeating redispersion in ion-exchanged water and solid-liquid separation three times, and then dried at 40°C for 24 hours to obtain toner base particles B1.

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 toner base particles B1, and these were mixed in a "Henschel Mixer" (manufactured by Nippon Coke & Engineering Co., Ltd.) at a rotor peripheral 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, cyan toner 1, which is an aggregate of toner particles 1 for electrostatic latent image development, was produced as the evaluation toner.

[Preparation of Cyan Toners 2, 4 to 9, and 11]
Cyan toners 2, 4 to 9, and 11 were produced by changing the amorphous resin dispersion X1 in the production of cyan toner 1 to the corresponding amorphous resin dispersions X2 to X6, and X8 to X10 in accordance with Tables 2 and 3 below.

[Preparation of Metallic Toner 1, Yellow Toner 1, Magenta Toners 1, 2, 4, and 6]
Metallic toner 1, yellow toner 1, magenta toners 1, 2, 4, and 6 were produced by changing the amorphous resin dispersion X1 to a corresponding amorphous resin dispersion in accordance with Tables 2 and 3 below, and by changing the colorant dispersion C to a corresponding colorant dispersion in accordance with Tables 2 and 3 below, in the production of cyan toner 1.

[Preparation of White Toner 1]
For the white toner (white toner) 1, 90 parts by mass of amorphous polyester resin s2, 10 parts by mass of amorphous polyester resin s3, 1.0 part by mass of BONTRON E-84 (trade name) (manufactured by Orient Chemical Industry Co., Ltd.) as a charge control agent for the toner, 95 parts by mass of titanium oxide as a white colorant (pigment), and 4.0 parts by mass of "CARNAUBA WAX (trade name)" (Carnauba wax No. 1 powder, manufactured by Kato Yoko Co., Ltd.) as a release agent were mixed in a Henschel mixer, melt-kneaded in a twin-screw extruder, cooled, and then roughly crushed in a cutter mill having a screen with a diameter of 2 mm, pulverized using a collision plate type crusher, and further classified using an air classifier to obtain toner base particles.

Next, 3.0 parts by mass of hydrophobic silica R972 (product name) (manufactured by Nippon Aerosil Co., Ltd., average particle size 16 [nm]) was added to 100 parts by mass of the obtained toner base particles as an external addition process, and the mixture was stirred for 3 minutes using a Henschel mixer to obtain white toner 1 with an average particle size of 7.0 [μm] as the toner for evaluation.

For this white toner 1, the average particle size of the toner can be measured using a particle size distribution measuring device (Coulter Multisizer 3, manufactured by Beckman Coulter, Inc., aperture diameter 100 [μm]).

[Preparation of Cyan Toner 10, Magenta Toner 3, and Magenta Toner 5]
In the preparation of the above-mentioned white toner 1, the titanium oxide used as the colorant was changed to a cyan pigment (C.I. Pigment Blue) or a magenta pigment (C.I. Pigment Red), and the type and amount of the amorphous polyester resin added was changed as shown in Tables 2 and 3 below, to prepare cyan toner 10, magenta toner 3, and magenta toner 5.

The obtained evaluation toner was used as a developer prepared according to the "Developer Preparation" below, and an evaluation toner set was formed by combining these developers as shown in Table 4 below. In Tables 2 to 4 below, StAc represents styrene acrylic resin, and PES represents polyester resin.

(Preparation of Developer)
A ferrite carrier having a volume average particle size of 32 μm coated with an acrylic resin was mixed with each toner so that the toner concentration was 6% by mass, to prepare a developer.

[Evaluation method]
<Weight average molecular weight (Mw) and number average molecular weight (Mn)>
Preparation of liquid: 5 mg of a toner sample (toner to be evaluated) was added to a sample bottle, 10 mL of tetrahydrofuran was added, and the mixture was stirred at room temperature for 30 minutes. The mixture was filtered through a 45 μm filter manufactured by ADVANTEC Co., Ltd. The obtained solution was used as a sample for GPC (gel permeation chromatography) measurement as a tetrahydrofuran soluble matter.

The GPC device used is "HLC-8320GPC (manufactured by Tosoh Corporation)," the column is "TSKgel SuperHZ (manufactured by Tosoh Corporation)," and THF is used as the eluent. The analysis is performed with a sample injection volume of 50 μL, a measurement temperature of 25°C, and an RI detector. The molecular weight distribution of the measurement sample is calculated using a calibration curve measured using monodisperse polystyrene standard particles.

Analysis: The maximum and maximum values before 15 minutes of retention time were taken as the peak top molecular weight. The minimum and minimum values after 15 minutes of retention time were cut off. The side with shorter retention times was analyzed.

<Low temperature fixability: Under offset>
The evaluation of low-temperature fixability was carried out by sequentially loading each developer (evaluation toner set) in which the above-prepared toners were combined as shown in Tables 2 and 3 into an image forming apparatus shown in FIG. 1 (however, the fixing apparatus used was an apparatus that fixes with a fixing belt; not shown), and forming an unfixed solid image on a plywood sheet of 152 g/m ² (manufactured by Nippon Paper Industries Co., Ltd.) with the image forming apparatus under an environment of normal temperature and normal humidity (20° C. and 50% RH). The adhesion amount of each toner was 4 g/m ^2. At this time, the toner layer of the first toner was formed as the lower layer, and the toner layer of the second toner was formed as the upper layer. Next, the surface temperature of the pressure roller of the fixing apparatus was set to 140° C., and the surface temperature of the heating roller was changed in 2° C. increments within the range of 140 to 180° C. to perform fixing. At this time, the lower limit fixing temperature of the fixing upper belt at which under-offset did not occur was measured. The evaluation of low-temperature fixability was carried out according to the following evaluation criteria, and a lower limit fixing temperature of 151° C. or less (◎ and ○) was deemed to be acceptable. The obtained evaluation results are shown in Table 4.

*Evaluation criteria for low temperature fixing performance: ⊚: The minimum fixing temperature is 148°C or lower; ◯: The minimum fixing temperature is 149°C or higher and 151°C or lower; △: The minimum fixing temperature is 152°C or higher and 155°C or lower; ×: The minimum fixing temperature is 156°C or higher.

＜Muddy color＞
Five developing machines, each containing a developer (toner set for evaluation) in which the toners prepared above were combined as shown in Tables 2 and 3, were placed in a modified bizhub PRO C6500 image forming apparatus (four units of YMCK were modified to five units of YMCK + special color toner; see FIG. 1), and a transparent OHP sheet was used to create an image of the alphabet "A" (20 pt) 5 x 5 cm square on the OHP sheet. In this case, the toner layer of the first toner was the lower layer, and the toner layer of the second toner was the upper layer. The edges of the "A" image in each of the first and 10,000th formed images were visually observed and observed with a 2000x optical microscope (Keyence: VHX-2000) to see whether the color of the color toner or special color toner in the lower layer could be identified. In addition, ○ and ⊚ were considered to be acceptable. The obtained evaluation results are shown in Table 4.

*Evaluation criteria for reduction in image density (color bleeding) ◎: Cannot be identified with the naked eye or with an optical microscope ○: Cannot be identified with the naked eye, but the toner color underneath can be identified with an optical microscope △: Can be slightly identified with the naked eye, but the toner color underneath can be clearly identified with an optical microscope ×: Can be clearly identified with the naked eye, and dot collapse is obvious even with an optical microscope.

The results in Table 4 confirm that the toner sets of Examples 1 to 12, in which the molecular weight distribution of the binder resin of the toner constituting the toner set satisfies formulas (1) and (2), have excellent low-temperature fixing properties and suppress color turbidity.

On the other hand, in Comparative Examples 1, 2, and 4, which do not satisfy formula (1), and Comparative Example 3, which does not satisfy formula (2), it was not possible to achieve both low-temperature fixability and suppression of color turbidity. When the Mw/Mn ratios of the toner binder resins are the same and are both relatively large values, as in Comparative Examples 1 and 4, color turbidity is likely to occur, and when they are relatively small values, as in Comparative Example 2, fixability is insufficient. It was also found that, even if the Mw/Mn ratio of the toner binder resin is 3 or more, color turbidity is likely to occur when the difference in Mn is 10,000 or more, as in Comparative Example 3.

31 photosensitive drum,
32 charger,
33 Exposure optical system as image writing means,
34 developing device,
34a developing roller,
36 intermediate transfer member,
36a tension roller,
36B Backup roller,
37 Primary transfer roller,
37A secondary transfer member,
38 detection sensor,
47 Fixing device,
47a heating roller,
47b pressure belt,
50A, 50B, 50C paper feed cassette,
51 Feed roller,
52 conveying path,
52A paper feed roller,
52B, 52C, 52D transport rollers,
53 registration roller,
54 paper discharge roller,
55 paper output tray,
70 Secondary transfer device,
71 cleaning blade,
100 Yellow (Y), Magenta (M), Cyan (C), Black (K) and White (W) process units;
190 Photoconductor cleaning device as image carrier cleaning means,
190A intermediate transfer body cleaning device,
GS image forming device,
SC Image reader,
CCD line image sensor,
P recording medium.

Claims (10)

a first toner containing at least a first binder resin as a main component ;
a second toner containing at least a second binder resin as a main component ,
A toner set, characterized in that the following formulas (1) , (2) and (3) are satisfied:


In the formula, Mn(1) and Mn(2) represent the number average molecular weights of the tetrahydrofuran soluble fractions of the first toner and the second toner, respectively, and Mw(1) and Mw(2) represent the weight average molecular weights of the tetrahydrofuran soluble fractions of the first toner and the second toner, respectively. a first toner containing at least a first binder resin as a main component;
a second toner containing at least a second binder resin as a main component,
A toner set, characterized in that the following formulas (1), (2) and (5) are satisfied:


In the formula, Mn(1) and Mn(2) represent the number average molecular weights of the tetrahydrofuran soluble fractions of the first toner and the second toner, respectively, and Mw(1) and Mw(2) represent the weight average molecular weights of the tetrahydrofuran soluble fractions of the first toner and the second toner, respectively. The toner set according to claim 1 or 2 , wherein the first toner comprises a colorant. The toner set according to claim 3 , wherein the first toner contains a white colorant as the colorant. The toner set according to claim 1 , wherein the first toner and the second toner each contain a colorant of a different color. The toner set according to any one of claims 1 to 5, wherein Mn(1) and Mn(2) are both 4,000 or more and 11,000 or less. The toner set according to any one of claims 1 to 6, further satisfying the following formula (4):
The toner set according to claim 1 , further satisfying the following formula (5):
The toner set according to any one of claims 1 to 8, wherein the second toner contains 50% by mass or more of styrene acrylic resin relative to the total amount of the toner. An image forming method using the toner set according to any one of claims 1 to 9, comprising transferring five or more types of toners, including the first toner and the second toner, onto a recording medium and fixing the resulting image forming layer all at once.