JP6935665B2 - Toner set for static charge image development, toner cartridge, electrostatic charge image developer set, image forming apparatus and image forming method - Google Patents

Description

The present invention relates to an electrostatic charge image developing toner set, a toner cartridge, an electrostatic charge image developing agent set, an image forming apparatus, and an image forming method.

Patent Document 1 describes silica / silica in a four-color toner set in which each toner contains silica and titanium oxide as an external additive, and the amount of charge before the addition of the external additive is lower than that of other toners. A toner set in which the titanium oxide ratio is larger than the silica / titanium oxide ratio in other toners is disclosed.

Patent Document 2 describes, as an external additive, hydrophobic silica particles having a number average particle size of 5 to 20 nm, particles selected from hydrophobic titania and silica having a number average particle size of 20 to 100 nm, and silica and magnesia. A toner containing composite oxide particles having an average primary particle size of 0.01 to 0.5 μm is disclosed.

Patent Document 3 describes silica particles as an external additive and surface-modified silica particles whose surface is modified with an oxide or hydroxide of at least one metal selected from titanium, tin, zirconium and aluminum. Is disclosed, and a toner containing surface-modified silica particles in a weight ratio of 1.5 times or less with respect to the silica particles is disclosed.

Japanese Unexamined Patent Publication No. 2006-0392229 Japanese Unexamined Patent Publication No. 2007-218941 Japanese Unexamined Patent Publication No. 2004-093335

An image forming apparatus including four image holders, two primary intermediate transfer bodies, and one secondary intermediate transfer body.
From the upstream side in the rotation direction of the first intermediate transfer body to the first intermediate transfer body, which is the primary intermediate transfer body to which the toner image is transferred from the first image holder and the second image holder, the second image holder, These two image holders are in contact with each other in the order of the first image holder.
From the upstream side in the rotation direction of the second intermediate transfer body to the second intermediate transfer body, which is the primary intermediate transfer body to which the toner image is transferred from the third image holder and the fourth image holder, the fourth image holder, These two image holders are in contact with each other in the order of the third image holder.
From the upstream side in the rotation direction of the third intermediate transfer body, the first intermediate transfer body is transferred to the third intermediate transfer body, which is the secondary intermediate transfer body to which the toner image is transferred from the first intermediate transfer body and the second intermediate transfer body. In the image forming apparatus in which these two primary intermediate transfer bodies are in contact with each other in the order of the second intermediate transfer body.
Streaky density unevenness may occur in the image formed by the third image holder.

In the present invention, the third image is retained in the image forming apparatus having the above configuration, as compared with the case where the titanium concentration ratio of the first to fourth toners is 1.0: 1.0: 1.0: 1.0. An object of the present invention is to provide a toner set for static charge image development that suppresses the occurrence of streaky density unevenness in an image formed by a body.

Specific means for solving the above problems include the following aspects.

The invention according to <1 > is
It has a first toner, a second toner, a third toner, and a fourth toner containing toner particles and titanium oxide particles externally attached to the toner particles.
The titanium concentration ratio of the first to fourth toners is: first toner: second toner: third toner: fourth toner = 1.6 to 1.9: 2.0 to 2.4: 1.2 to 1. .5: Toner set for static charge image development of 0.5 to 1.1.

The invention according to <2 > is
The toner set for developing an electrostatic charge image according to < 1 > , wherein the titanium oxide particles are particles containing at least one of titanium oxide and metatitanic acid.

The invention according to <3 > is
The toner set for static charge image development according to <1 > or < 2 > is housed, and the toner set is accommodated.
A toner cartridge that is attached to and detached from the image forming device.

The invention according to <4 > is
It has a first developer, a second developer, a third developer, and a fourth developer, which contain a toner containing toner particles and titanium oxide particles externally attached to the toner particles.
The titanium concentration ratio of the toner contained in the first to fourth developing agents is as follows: first developing agent: second developing agent: third developing agent: fourth developing agent = 1.6 to 1.9: 2.0 to A static charge image developer set of 2.4: 1.2 to 1.5: 0.5 to 1.1.

The invention according to <5 > is
The electrostatic charge image developer set according to < 4 > , wherein the titanium oxide particles are particles containing at least one of titanium oxide and metatitanic acid.

The invention according to <6 > is
The first image holder, the second image holder, the third image holder, the fourth image holder,
A first charging means for charging the surface of the first image holder, a second charging means for charging the surface of the second image holder, and a third charging means for charging the surface of the third image holder. , The fourth charging means for charging the surface of the fourth image holder, and
Electrostatic image forming means for forming an electrostatic charge image on the surfaces of the charged first image holder, the charged second image holder, the charged third image holder, and the charged fourth image holder. When,
A first developing means that accommodates a first developing agent and uses the first developing agent to develop an electrostatic charge image formed on the surface of the first image holder as a toner image.
A second developing means that accommodates a second developing agent and uses the second developing agent to develop an electrostatic charge image formed on the surface of the second image holder as a toner image.
A third developing means that accommodates a third developing agent and develops an electrostatic charge image formed on the surface of the third image holder as a toner image by the third developing agent.
A fourth developing means that accommodates a fourth developing agent and uses the fourth developing agent to develop an electrostatic charge image formed on the surface of the fourth image holder as a toner image.
A primary intermediate transfer body to which a toner image is transferred from the first image holder and the second image holder, and the second image holder from the upstream side in the rotation direction of the primary intermediate transfer body, the first image holder. The first intermediate transfer body, which these image holders are in contact with in the order of the image holders,
A primary intermediate transfer body to which a toner image is transferred from the third image holder and the fourth image holder, and the fourth image holder and the third image holder from the upstream side in the rotation direction of the primary intermediate transfer body. The second intermediate transfer body, which these image holders are in contact with in the order of the image holders,
A secondary intermediate transfer body to which a toner image is transferred from the first intermediate transfer body and the second intermediate transfer body, and the first intermediate transfer body from the upstream side in the rotation direction of the secondary intermediate transfer body. The third intermediate transcript, to which these primary intermediate transcripts are in contact, in the order of the second intermediate transcript,
A transfer means for transferring the toner image transferred to the surface of the third intermediate transfer body to the surface of the recording medium, and
A fixing means for fixing the toner image transferred to the surface of the recording medium, and
A first cleaning means for cleaning the toner remaining on the surface of the first image holder after the toner image is transferred, and
A second cleaning means for cleaning the toner remaining on the surface of the second image holder after the toner image is transferred, and
A third cleaning means for cleaning the toner remaining on the surface of the third image holder after the toner image is transferred, and
A fourth cleaning means for cleaning the toner remaining on the surface of the fourth image holder after the toner image is transferred, and
With
The first developing agent, the second developing agent, the third developing agent, and the fourth developing agent each contain a toner containing toner particles and titanium oxide particles externally attached to the toner particles. The titanium concentration ratio of the toner contained in the first to fourth developing agents is: first developing agent: second developing agent: third developing agent: fourth developing agent = 1.6 to 1.9: 2.0 to 2. .4: 1.2 to 1.5: 0.5 to 1.1,
Image forming device.

The invention according to <7 > is
An image forming method for forming an image on a recording medium using the image forming apparatus according to < 6 >.

According to the inventions of < 1 > and < 2 > , the above configuration is as compared with the case where the titanium concentration ratio of the first to fourth toners is 1.0: 1.0: 1.0: 1.0. In the image forming apparatus, the toner set for static charge image development that suppresses the occurrence of streak-like density unevenness in the image formed by the third image holder is provided.

According to the invention according to < 3 > , an image forming apparatus having the above configuration as compared with the case where the titanium concentration ratio of the first to fourth toners is 1.0: 1.0: 1.0: 1.0. A toner cartridge that suppresses the occurrence of streak-like density unevenness in an image formed by a third image holder is provided.

According to the inventions of < 4 > and < 5 > , compared with the case where the titanium concentration ratio of the toner contained in the first to fourth developing agents is 1.0: 1.0: 1.0: 1.0. In the image forming apparatus having the above-described configuration, a static charge image developing agent set that suppresses the occurrence of streak-like density unevenness in the image formed by the third image holder is provided.

According to the inventions of < 6 > and < 7 > , as compared with the case where the titanium concentration ratio of the toner contained in the first to fourth developing agents is 1.0: 1.0: 1.0: 1.0. , An image forming apparatus and an image forming method for suppressing the occurrence of streak-like density unevenness in an image formed by a third image holder are provided.

It is a schematic block diagram which shows an example of the image forming apparatus which concerns on this embodiment.

Hereinafter, embodiments of the invention will be described. These explanations and examples exemplify embodiments and do not limit the scope of the invention.

When referring to the amount of each component in the composition in the present disclosure, if a plurality of substances corresponding to each component are present in the composition, unless otherwise specified, the plurality of types present in the composition. It means the total amount of substances.

In the present disclosure, "(meth) acrylic" means that it may be either "acrylic" or "methacryl".

In the present disclosure, the "electrostatic image developer" is also simply referred to as a "developer".

<Toner set for static charge image development>
The toner set for static charge image development according to the present embodiment (hereinafter, also referred to as “toner set”) is a first toner or a second toner containing toner particles and titanium oxide particles externally attached to the toner particles. It has a toner, a third toner, and a fourth toner, and the titanium concentration ratio of the first to fourth toners is 1st toner: 2nd toner: 3rd toner: 4th toner = 1.6 to 1.9: 2. It is 0.0 to 2.4: 1.2 to 1.5: 0.5 to 1.1.

In the present embodiment, the titanium concentration ratio of the first to fourth toners is determined by fluorescent X-ray analysis. Specifically, it is obtained by the following method using a fluorescent X-ray analyzer (for example, XRF-1500 manufactured by Shimadzu Corporation).
_{Standard toner in which titanium oxide particles (TiO 2} , for example, volume average particle size of 50 nm) are externally added by varying the amount of external addition to resin particles (for example, volume average particle size of 6.0 μm) consisting only of resin (for example, polyester resin). A sample is prepared, the X-ray intensity of Ti is measured, and a calibration curve of titanium element concentration (mass%) is prepared. The X-ray intensity of Ti is measured for the first to fourth toners to be tested, and the X-ray intensity of Ti is converted to the titanium element concentration by applying it to the calibration curve. Is calculated. Instead of creating a calibration curve for the standard toner sample, the X-ray intensity of Ti may be measured for the first to fourth toners, and the X-ray intensity ratio between the toners may be used as the titanium concentration ratio.
Regarding the toner contained in the developing agent, the toner and the carrier are separated by blow-off, and the separated toner is used as a test sample.

The toner set according to this embodiment is
An image forming apparatus including four image holders, two primary intermediate transfer bodies, and one secondary intermediate transfer body.
From the upstream side in the rotation direction of the first intermediate transfer body to the first intermediate transfer body, which is the primary intermediate transfer body to which the toner image is transferred from the first image holder and the second image holder, the second image holder, These two image holders are in contact with each other in the order of the first image holder.
From the upstream side in the rotation direction of the second intermediate transfer body to the second intermediate transfer body, which is the primary intermediate transfer body to which the toner image is transferred from the third image holder and the fourth image holder, the fourth image holder, These two image holders are in contact with each other in the order of the third image holder.
From the upstream side in the rotation direction of the third intermediate transfer body, the first intermediate transfer body is transferred to the third intermediate transfer body, which is the secondary intermediate transfer body to which the toner image is transferred from the first intermediate transfer body and the second intermediate transfer body. In the image forming apparatus in which these two primary intermediate transfer bodies are in contact with each other in the order of the second intermediate transfer body.
It suppresses the occurrence of streaky density unevenness in the image formed by the third image holder.

In the image forming apparatus having the above configuration, when the surfaces of the four image holders are cleaned by the respective cleaning means, the image holder has a first image holder, a second image holder, and a fourth image holder. In the three-image holder, the phenomenon of toner sticking and forming a film (filming) is likely to occur. As a result, the surface potential of the third image holder is lowered, and the amount of toner adhered to the electrostatic charge image is reduced. Therefore, streaky density unevenness may occur in the image formed by the third image holder. The following is presumed as the mechanism by which filming is likely to occur in the third image holder.

In the image forming apparatus having the above configuration, when the image holder, the primary intermediate transfer body, and the secondary intermediate transfer body continue to rotate, at least the toner remaining on the secondary intermediate transfer body without being transferred to the recording medium is transferred. A part of the toner was transferred to the primary intermediate transfer body, and at least a part of the toner transferred from the secondary intermediate transfer body to the primary intermediate transfer body and remained in the primary intermediate transfer body without being transferred to the secondary intermediate transfer body. At least a portion of the toner is transferred to the image retainer. At this time, the transition to four image holders is performed according to the contact order between the one secondary intermediate transfer body and the two primary intermediate transfer bodies and the contact order between the one primary intermediate transfer body and the two image holders. It is estimated that the amount of toner is different.
That is, more toner is transferred to the first intermediate transfer body that comes into contact with the secondary intermediate transfer body first among the two primary intermediate transfer bodies, and the primary intermediate transfer body comes into contact with the primary intermediate transfer body first among the two image holders. As a result, more toner is transferred to the image holder (the second image holder for the first intermediate transfer body and the fourth image holder for the second intermediate transfer body), and as a result, the intermediate transfer body It is estimated that the amount of toner transferred from the first to the fourth image holders is in the order of 2> 1 ≧ 4> 3.
When the amount of toner transferred from the intermediate transfer body to the image holder is relatively small, the pressure applied to one toner when the cleaning means cleans the image holder becomes relatively high, so that the toner is filmed. It is presumed that filming is likely to occur on the surface of the third image holder, which has a smaller amount of toner transferred from the intermediate transfer body than the first image holder, the second image holder, and the fourth image holder. .. In the first image holder, the second image holder, and the fourth image holder, the amount of toner transferred from the intermediate transfer body is secured to some extent, and the pressure of the cleaning means applied to one toner is dispersed, so that filming can be performed. It is presumed that filming is unlikely to occur because it is unlikely to occur or because the amount of toner transferred from the intermediate transfer body is large, the toners aggregate to form a toner mass and come into contact with the cleaning means as a toner mass. Toner filming is likely to occur when continuous image formation is performed in an environment of low temperature and low humidity (for example, temperature 10 ° C. and relative humidity 10%).

In response to the above event, the toner set according to the present embodiment sets the titanium concentration ratio of the first to fourth toners to that of the first toner: the second toner: the third toner: the fourth toner = 1.6 to 1.9. : 2.0 to 2.4: 1.2 to 1.5: 0.5 to 1.1, and when applied to an image forming apparatus having the above configuration, the first toner is used as the first image holder. By using the second toner for the second image holder, the third toner for the third image holder, and the fourth toner for the fourth image holder, the third image holder It suppresses the occurrence of toner filming, and as a result, suppresses the occurrence of streak-like density unevenness in the image formed by the third image holder. The reason why the toner set according to this embodiment adopts the above configuration is as follows.

Since the titanium oxide has a low electric resistance, it has an effect of attenuating the charge of the toner. Therefore, the larger the content of the titanium oxide, the smaller the charge amount of the toner. On the other hand, the larger the amount of charge, the more difficult the toner is to be transferred and the more easily it remains on the image holder, and the more difficult it is to be removed by the cleaning means. Therefore, it can be said that the lower the titanium oxide content, the easier it is for the toner to remain on the image holder (in other words, the higher the titanium oxide content, the less likely it is to remain on the image holder).
Therefore, first, the amount of toner transferred from the intermediate transfer body to the first, second, and fourth image holders is matched in descending order, and the amount of toner remaining in the image holder without being transferred to the primary intermediate transfer body is ordered. In order to control, the titanium concentrations of the first, second, and fourth toners are set in the order of the second toner, the first toner, and the fourth toner from the highest to the highest.
Next, regarding the third toner, since the amount of toner transferred from the intermediate transfer body is the smallest in the third image holder, the titanium concentration of the third toner is increased in order to maximize the amount of toner remaining in the image holder. It is also considered that should be the lowest. However, considering that the toner remaining in the 4th image holder is placed on the primary intermediate transfer body and transferred to the 3rd image holder, the titanium concentration of the 3rd toner is set to the lowest, and the 1st to 4th toners are used. When the titanium concentration of is set in the order of 2nd>1st>4th> 3rd, the amount of toner existing in the 3rd image holder (the amount of toner remaining in the 3rd image holder and the amount of toner transferred from the intermediate transfer body). And the total amount of toner transferred from the 4th image holder to the primary intermediate transfer body) becomes excessive, and the 3rd image holder covers the image recording surface forming the image (static charge of the image holder). A phenomenon in which toner adheres to a portion without an image and an image appears) may occur. The titanium concentration of the third toner is set higher than the titanium concentration of the fourth toner from the viewpoint of suppressing fog while suppressing image density unevenness caused by toner filming.
Therefore, the titanium concentration of the first to fourth toners is set in the order of 2nd>1st>3rd> 4th.
Further, if there is too much difference in the titanium concentration of each toner, the density of the image formed by the toner having a relatively low titanium concentration may decrease. Therefore, the titanium concentration ratio is set to 1st toner: 2nd toner: Third toner: Fourth toner = 1.6 to 1.9: 2.0 to 2.4: 1.2 to 1.5: 0.5 to 1.1.

In the toner set according to the present embodiment, the titanium concentration ratio of each toner is 1st toner: 2nd toner: 3rd toner: 4th toner = 1.6 to 1.9: 2.0 to 2.4: 1. It is .2 to 1.5: 0.5 to 1.1, more preferably 1.7 to 1.8: 2.1 to 2.2: 1.3 to 1.4: 0.7 to 0. It is 9.9.

The titanium concentration ratio between the first to fourth toners can be controlled by the amount of titanium oxide particles externally added to the toner particles constituting each of the four toners.

Each toner in the toner set according to the present embodiment may contain an external additive other than titanium oxide particles.

In the toner set according to this embodiment, the color of each toner is not limited. In one embodiment of the toner set according to the present embodiment, the first toner is yellow, the second toner is magenta, the third toner is cyan, and the fourth toner is black.

Hereinafter, the toner material, composition, and manufacturing method in this embodiment will be described in detail.

[Toner particles]
The toner particles include, for example, a binder resin, a colorant, a mold release agent, and other additives.

The toner particles may be toner particles having a single layer structure, or may be toner particles having a so-called core-shell structure having a core portion (core particles) and a coating layer (shell layer) covering the core portion. good. The toner particles having a core-shell structure are composed of, for example, a core portion containing a binder resin, a colorant, and a mold release agent, and a coating layer containing the binder resin.

-Bound resin-
Examples of the binder resin include styrenes (for example, styrene, parachlorostyrene, α-methylstyrene, etc.) and (meth) acrylic acid esters (for example, methyl acrylate, ethyl acrylate, n-propyl acrylate, acrylic acid). n-butyl, lauryl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, lauryl methacrylate, 2-ethylhexyl methacrylate, etc.), ethylenically unsaturated nitriles (eg, acrylonitrile, Methacronitrile, etc.), vinyl ethers (eg, vinyl methyl ether, vinyl isobutyl ether, etc.), vinyl ketones (eg, vinyl methyl ketone, vinyl ethyl ketone, vinyl isopropenyl ketone, etc.), olefins (eg, ethylene, propylene, butadiene, etc.) Examples thereof include homopolymers of the above-mentioned monomers, and vinyl-based resins composed of copolymers in which two or more kinds of these monomers are combined.
Examples of the binder resin include non-vinyl resins such as epoxy resins, polyester resins, polyurethane resins, polyamide resins, cellulose resins, polyether resins, and modified rosins, mixtures of these with the vinyl resins, or these. Examples thereof include a graft polymer obtained by polymerizing a vinyl-based monomer in the coexistence.
These binder resins may be used alone or in combination of two or more.

As the binder resin, a polyester resin is preferable from the viewpoint of image fixability, and a styrene- (meth) acrylic acid ester copolymer is preferable from the viewpoint of maintaining the charge of the toner and the weather resistance of the image.

Examples of the binder resin include a modified polyester resin. The modified polyester resin is a polyester resin having a bonding group other than an ester bond, and a polyester resin in which a resin different from the polyester resin is bonded by a covalent bond or an ionic bond. Examples of the modified polyester resin include a polyester resin in which a functional group such as an isocyanate group that reacts with an acid group or a hydroxyl group is introduced at the terminal and a compound having an active hydrogen group is reacted to modify the terminal. Be done.

As the modified polyester resin, a urea-modified polyester resin is preferable. The content of the urea-modified polyester resin is preferably 5% by mass or more and 40% by mass or less, and more preferably 10% by mass or more and 20% by mass or less with respect to the total binder resin.

The urea-modified polyester resin is preferably a urea-modified polyester resin obtained by reacting a polyester resin having an isocyanate group (hereinafter referred to as "polyester prepolymer") with an amine compound (at least one reaction of a cross-linking reaction and an extension reaction). .. Urethane bonds may be present in the urea-modified polyester together with the urea bonds.

Examples of the polyester prepolymer include a reaction product of a polyester having a group having active hydrogen and a polyisocyanate compound. Examples of the group having active hydrogen include hydroxyl groups (alcoholic hydroxyl groups and phenolic hydroxyl groups), amino groups, carboxyl groups, mercapto groups and the like, and alcoholic hydroxyl groups are preferable. Polyisocyanate compounds include aliphatic polyisocyanates (tetramethylene diisocyanate, hexamethylene diisocyanate, 2,6-diisocyanatomethylcaproate, etc.); alicyclic polyisocyanates (isophorone diisocyanate, cyclohexylmethane diisocyanate, etc.); aromatics. Diisocyanates (tolylene diisocyanates, diphenylmethane diisocyanates, etc.); aromatic aliphatic diisocyanates (α, α, α', α'-tetramethylxylylene diisocyanates, etc.); isocyanurates; polyisocyanates blocked from phenol derivatives, oximes, caprolactams, etc. Compounds blocked with the agent: include. One type of polyisocyanate compound may be used alone, or two or more types may be used in combination.

The content of the portion derived from the polyvalent isocyanate compound in the polyester prepolymer is preferably 0.5% by mass or more and 40% by mass or less, more preferably 1% by mass or more and 30% by mass or less, based on the entire polyester prepolymer. More preferably, it is 2% by mass or more and 20% by mass or less. The average number of isocyanate groups per molecule of the polyester prepolymer is preferably 1 or more, more preferably 1.5 or more and 3 or less, and further preferably 1.8 or more and 2.5 or less.

Examples of the amine compound that reacts with the polyester prepolymer include diamine, trivalent or higher polyamine, amino alcohol, amino mercaptan, amino acid, and a compound in which the amino group of these amine compounds is blocked.

Examples of the diamine include aromatic diamines (phenylenediamine, diethyltoluenediamine, 4,4'diaminodiphenylmethane, etc.); alicyclic diamines (4,4'-diamino-3,3'dimethyldicyclohexylmethane, diaminecyclohexane, isophoronediamine, etc.) ); aliphatic diamines (ethylenediamine, tetramethylenediamine, hexamethylenediamine, etc.); and the like. Examples of the triamine or higher polyamine include diethylenetriamine and triethylenetetramine. Examples of the amino alcohol include ethanolamine, hydroxyethylaniline and the like. Examples of the amino mercaptan include aminoethyl mercaptan and aminopropyl mercaptan. Examples of amino acids include aminopropionic acid and aminocaproic acid.
Examples of the compound in which the amino group of the amine compound is blocked include a ketimine compound and an oxazoline compound derived from the amine compound and a ketone compound (acetone, methyl ethyl ketone, methyl isobutyl ketone, etc.).
As the amine compound, a ketimine compound is preferable. One type of amine compound may be used alone, or two or more types may be used in combination.

The urea-modified polyester resin is a resin whose molecular weight after the reaction is adjusted by adjusting the reaction between the polyester prepolymer and the amine compound with a terminator that stops at least one of the cross-linking reaction and the extension reaction. good. Examples of the terminator include monoamines (diethylamine, dibutylamine, butylamine, laurylamine, etc.), compounds in which the amino group of monoamine is blocked (ketimine compound), and the like.

The glass transition temperature (Tg) of the binder resin is preferably 50 ° C. or higher and 80 ° C. or lower, and more preferably 50 ° C. or higher and 65 ° C. or lower.
The glass transition temperature is obtained from the DSC curve obtained by differential scanning calorimetry (DSC), and more specifically, it is described in "Supplementary" described in JIS K7121-1987 "Method for measuring transition temperature of plastics". It is obtained by "outer glass transition start temperature".

The weight average molecular weight (Mw) of the binder resin is preferably 5000 or more and 1,000,000 or less, and more preferably 7,000 or more and 500,000 or less. The number average molecular weight (Mn) of the binder resin is preferably 2000 or more and 100,000 or less. The molecular weight distribution Mw / Mn of the binder resin is preferably 1.5 or more and 100 or less, and more preferably 2 or more and 60 or less.
The weight average molecular weight and the number average molecular weight of the binder resin are measured by gel permeation chromatography (GPC). The molecular weight measurement by GPC is carried out using a Tosoh GPC / HLC-8120 GPC as a measuring device, a Tosoh column / TSKgel SuperHM-M (15 cm), and a tetrahydrofuran solvent. The weight average molecular weight and the number average molecular weight are calculated from the measurement results using a molecular weight calibration curve prepared from a monodisperse polystyrene standard sample.

The content of the binder resin is preferably 40% by mass or more and 95% by mass or less, more preferably 50% by mass or more and 90% by mass or less, and further preferably 60% by mass or more and 85% by mass or less with respect to the entire toner particles.

-Colorant-
Examples of colorants include carbon black, chrome yellow, Hansa yellow, benzine yellow, slene yellow, quinoline yellow, pigment yellow, permanent orange GTR, pyrazolone orange, vulcan orange, watch young red, permanent red, brilliant carmine 3B, and brilliant. Carmin 6B, Dupont Oil Red, Pyrazolon Red, Resole Red, Rhodamine B Lake, Lake Red C, Pigment Red, Rose Bengal, Aniline Blue, Ultra Marine Blue, Calco Oil Blue, Methylene Blue Chloride, Phthalocyanine Blue, Pigment Blue, Phthalocyanine Green, Pigments such as malachite green oxalate; aclysin, xanthene, azo, benzoquinone, azine, anthraquinone, thioindico, dioxazine, thiazine, azomethine, indico, phthalocyanine, aniline black, polymethine , Triphenylmethane-based, diphenylmethane-based, thiazole-based dyes;
As the colorant, one type may be used alone, or two or more types may be used in combination.

As the colorant, a surface-treated colorant may be used if necessary, or may be used in combination with a dispersant. Further, a plurality of kinds of colorants may be used in combination.

The content of the colorant is preferably 1% by mass or more and 30% by mass or less, and more preferably 3% by mass or more and 15% by mass or less with respect to the entire toner particles.

-Release agent-
Examples of the release agent include hydrocarbon waxes; natural waxes such as carnauba wax, rice wax and candelilla wax; synthetic or mineral / petroleum waxes such as montan wax; ester-based waxes such as fatty acid ester and montanic acid ester. Wax; etc. The release agent is not limited to this.

As the release agent, paraffin wax and olefin wax are preferable from the viewpoint of stabilizing toner charging because the content of impurities is small.

The melting temperature of the release agent is preferably 50 ° C. or higher and 110 ° C. or lower, and more preferably 60 ° C. or higher and 100 ° C. or lower.
The melting temperature is determined from the DSC curve obtained by differential scanning calorimetry (DSC) by the "melting peak temperature" described in the method for determining the melting temperature in JIS K7121: 1987 "Method for measuring transition temperature of plastics".

The content of the release agent is preferably 1% by mass or more and 20% by mass or less, and more preferably 5% by mass or more and 15% by mass or less with respect to the entire toner particles.

-Other additives-
Examples of other additives include known additives such as magnetic materials, charge control agents, and inorganic powders. These additives are contained in the toner particles as an internal additive.

-Characteristics of toner particles-
The volume average particle size D50v of the toner particles is preferably 3 μm or more and 15 μm or less, more preferably 5 μm or more and 10 μm or less, and further preferably 5 μm or more and 8 μm or less.

The volume particle size distribution index GSDv of the toner particles is preferably 1.00 or more and 1.50 or less, more preferably 1.00 or more and 1.40 or less, and further preferably 1.00 or more and 1.30 or less.

The volume average particle size D50v and the volume particle size distribution index GSDv of the toner particles are obtained by measuring the particle size distribution with a Coulter type particle size distribution measuring device (for example, Beckman Coulter Coulter Multisizer II). Specifically, the particle size distribution is measured according to the following procedure.
Toner of 0.5 mg or more and 50 mg or less is mixed with 2 ml of a 5 mass% aqueous solution of a surfactant (for example, sodium alkylbenzene sulfonate), and further, an electrolytic solution of 100 ml or more and 150 ml or less (for example, ISOTON-II manufactured by Beckman Coulter) is used. And disperse with an ultrasonic disperser for 1 minute to prepare a dispersion. Using this dispersion as a measurement sample, the particle size of 50,000 particles in the range of 2 μm or more and 60 μm or less is measured using a Coulter-type particle size distribution measuring device and an aperture with a diameter of 100 μm. The particle size distribution of 50,000 particles is drawn from the small diameter side on a volume basis, and the cumulative 16% particle size is D16v, the cumulative 50% particle size is the volume average particle size D50v, and the cumulative 84% particle size is D84v. The volume particle size distribution index GSDv is (D84v ÷ D16v).

[External agent]
In the toner set according to the present embodiment, each toner contains titanium oxide particles as an external additive. Examples of the titanium oxide include titanium oxide (TIO ₂ ) and metatitanic acid (TIO (OH) ₂ ). Metatitanic acid is preferable because it efficiently attenuates the charge of the toner because electrons move easily.

The volume average particle diameter of the titanium oxide particles is preferably 10 nm or more and 60 nm or less, more preferably 15 nm or more and 50 nm or less, still more preferably 20 nm or more and 35 nm or less, from the viewpoint of being difficult to be embedded in the toner particles and not easily separated from the toner particles.
The volume average particle size of the titanium oxide particles is measured using a laser diffraction type particle size distribution measuring device (for example, HORIBA, Ltd. LA-700).

In the toner set according to the present embodiment, each toner may contain other external additives other than titanium oxide particles. Other external additives include SiO ₂ , Al ₂ O ₃ , CuO, ZnO, SnO ₂ , CeO ₂ , Fe ₂ O ₃ , MgO, BaO, CaO, K ₂ O, Na ₂ O, ZrO ₂ , CaO. _{SiO 2, K 2 O · (} TiO 2) n, Al 2 O 3 · 2SiO 2, CaCO 3, MgCO 3, BaSO 4, MgSO 4 , etc. particles. Of these, silica particles (SiO ₂ ) and alumina particles (Al ₂ O ₃ ) are preferable.

The surface of the inorganic particles as an external additive should be hydrophobized. The hydrophobizing treatment is performed, for example, by immersing the inorganic particles in a hydrophobizing agent. The hydrophobizing agent is not particularly limited, and examples thereof include a silane-based coupling agent, a silicone oil, a titanate-based coupling agent, and an aluminum-based coupling agent. These may be used alone or in combination of two or more.
The amount of the hydrophobizing agent is, for example, 1 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the inorganic particles.

Examples of the external additive include resin particles (resin particles such as polystyrene, polymethylmethacrylate, and melamine resin), cleaning activators (for example, metal salts of higher fatty acids typified by zinc stearate, particles of fluoropolymer). And so on.

The amount of the external additive added is preferably 0.01% by mass or more and 5% by mass or less, and more preferably 0.01% by mass or more and 2.0% by mass or less with respect to the toner particles.

The external addition amount ratio (mass standard) of titanium oxide particles to the toner particles constituting each of the four toners in the toner set is as follows: 1st toner: 2nd toner: 3rd toner: 4th toner = 1.6 to 1. 9: 2.0 to 2.4: 1.2 to 1.5: 0.5 to 1.1 is preferable, and 1.7 to 1.8: 2.1 to 2.2: 1.3 to 1. 4: 0.7 to 0.9 is more preferable.

[Toner manufacturing method]
The toner according to the present embodiment can be obtained by externally adding an external additive to the toner particles after producing the toner particles.

The toner particles may be produced by any of a dry production method (for example, kneading and pulverization method, etc.) and a wet production method (for example, coagulation coalescence method, suspension polymerization method, dissolution suspension method, ester extension method, etc.). These manufacturing methods are not particularly limited, and known manufacturing methods are adopted. Among these, it is preferable to obtain toner particles by the aggregation and coalescence method.

-Aggregation and coalescence method When the toner particles are produced by the aggregation and coalescence method, for example.
A step of preparing a resin particle dispersion liquid in which resin particles to be a binder resin are dispersed (resin particle dispersion liquid preparation step) and a step of preparing the resin particle dispersion liquid (after mixing other particle dispersion liquids as necessary). (In the dispersion), resin particles (other particles if necessary) are agglomerated to form agglomerated particles (aggregated particle forming step), and the agglomerated particle dispersion in which the agglomerated particles are dispersed is heated and agglomerated. Toner particles are manufactured through a step of fusing and coalescing the particles to form toner particles (fusing and coalescing step).

Hereinafter, details of each step of the aggregation and coalescence method will be described.
In the following description, a method of obtaining toner particles containing a colorant and a release agent will be described, but the colorant and the release agent are used as needed. Of course, other additives other than colorants and mold release agents may be used.

-Resin particle dispersion liquid preparation process-
Along with the resin particle dispersion liquid in which the resin particles to be the binder resin are dispersed, for example, a colorant particle dispersion liquid in which the colorant particles are dispersed and a release agent particle dispersion liquid in which the release agent particles are dispersed are prepared.

The resin particle dispersion liquid is prepared, for example, by dispersing the resin particles in a dispersion medium with a surfactant.

Examples of the dispersion medium used in the resin particle dispersion liquid include an aqueous medium.
Examples of the aqueous medium include distilled water, water such as ion-exchanged water, alcohols, and the like. These may be used alone or in combination of two or more.

Examples of the surfactant include anionic surfactants such as sulfate ester type, sulfonate type, phosphoric acid ester type and soap type; cationic surfactants such as amine salt type and quaternary ammonium salt type; Examples thereof include nonionic surfactants such as polyethylene glycol-based, alkylphenol ethylene oxide adduct-based, and polyhydric alcohol-based. Among these, anionic surfactants and cationic surfactants are particularly mentioned. The nonionic surfactant may be used in combination with an anionic surfactant or a cationic surfactant.
The surfactant may be used alone or in combination of two or more.

Examples of the method for dispersing the resin particles in the dispersion medium in the resin particle dispersion liquid include general dispersion methods such as a rotary shear homogenizer, a ball mill having a medium, a sand mill, and a dyno mill. Further, depending on the type of resin particles, the resin particles may be dispersed in a dispersion medium by a phase inversion emulsification method. In the phase inversion emulsification method, a resin to be dispersed is dissolved in a hydrophobic organic solvent in which the resin is soluble, and a base is added to an organic continuous phase (O phase) to neutralize the resin, and then an aqueous medium (W phase) is used. ) Is added to perform phase inversion from W / O to O / W, and the resin is dispersed in an aqueous medium in the form of particles.

The volume average particle diameter of the resin particles dispersed in the resin particle dispersion is, for example, preferably 0.01 μm or more and 1 μm or less, more preferably 0.08 μm or more and 0.8 μm or less, and further preferably 0.1 μm or more and 0.6 μm or less. preferable.
The volume average particle size of the resin particles is determined by using the particle size distribution obtained by the measurement of a laser diffraction type particle size distribution measuring device (for example, LA-700 manufactured by Horiba Seisakusho) with respect to the divided particle size range (channel). The cumulative distribution is subtracted from the small particle size side, and the particle size that is cumulatively 50% of all particles is measured as the volume average particle size D50v. The volume average particle size of the particles in the other dispersions is measured in the same manner.

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

Similar to the resin particle dispersion, a colorant particle dispersion and a release agent particle dispersion are also prepared. That is, the dispersion medium, the dispersion method, the volume average particle diameter of the particles, and the content of the particles in the resin particle dispersion are the same in the colorant particle dispersion and the release agent particle dispersion.

-Agglomerated particle formation process-
Next, the resin particle dispersion liquid, the colorant particle dispersion liquid, and the release agent particle dispersion liquid are mixed.
Then, in the mixed dispersion, the resin particles, the colorant particles, and the release agent particles are heteroaggregated to form the resin particles, the colorant particles, and the release agent particles having a diameter close to the diameter of the target toner particles. Form agglomerated particles containing.

Specifically, for example, a flocculant is added to the mixed dispersion, the pH of the mixed dispersion is adjusted to acidic (for example, pH 2 or more and 5 or less), a dispersion stabilizer is added as necessary, and then the resin particles. (Specifically, for example, the glass transition temperature of the resin particles is -30 ° C or higher and the glass transition temperature is -10 ° C or lower), and the particles dispersed in the mixed dispersion are aggregated. Form agglomerated particles.
In the agglomerated particle forming step, for example, the mixed dispersion is stirred with a rotary shear homogenizer, and an aggregating agent is added at room temperature (for example, 25 ° C.) to adjust the pH of the mixed dispersion to acidic (for example, pH 2 or more and 5 or less). Then, if necessary, the dispersion stabilizer may be added and then heating may be performed.

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

Examples of the inorganic metal salt include metal salts such as calcium chloride, calcium nitrate, barium chloride, magnesium chloride, zinc chloride, aluminum chloride and aluminum sulfate; and inorganic metal salts such as polyaluminum chloride, polyaluminum hydroxide and calcium polysulfide. Polymer; and the like.
As the chelating agent, a water-soluble chelating agent may be used. Examples of the chelating agent include oxycarboxylic acids such as tartrate acid, citric acid and gluconic acid; aminocarboxylic acids such as iminodic acid vinegar (IDA), nitrilotriacetic acid (NTA) and ethylenediaminetetraacetic acid (EDTA); Be done.
The amount of the chelating agent added is preferably 0.01 parts by mass or more and 5.0 parts by mass or less, and more preferably 0.1 parts by mass or more and less than 3.0 parts by mass with respect to 100 parts by mass of the resin particles.

-Fusion union process-
Next, the agglomerated particle dispersion liquid in which the agglomerated particles are dispersed is heated until, for example, the liquid temperature reaches the glass transition temperature of the resin particles or higher, and the agglomerated particles are fused and united.

Toner particles are obtained through the above steps.
After obtaining the agglomerated particle dispersion liquid in which the agglomerated particles are dispersed, the agglomerated particle dispersion liquid and the resin particle dispersion liquid in which the resin particles are dispersed are further mixed, and the resin particles are further adhered to the surface of the agglomerated particles. The step of forming the second agglomerated particles and the second agglomerated particle dispersion liquid in which the second agglomerated particles are dispersed are heated, and the second agglomerated particles are fused and united to form a core. The toner particles may be produced through the steps of forming the toner particles having a shell structure.

After the fusion and coalescence step is completed, the toner particles formed in the solution are subjected to a known washing step, solid-liquid separation step, and drying step to obtain dried toner particles. In the cleaning step, from the viewpoint of chargeability, it is preferable to sufficiently perform replacement cleaning with ion-exchanged water. In the solid-liquid separation step, suction filtration, pressure filtration and the like may be performed from the viewpoint of productivity. From the viewpoint of productivity, the drying step may be freeze-dried, air-flow-dried, fluid-dried, vibrating fluid-dried or the like.

-Ester extension method In the ester extension method, at least a polyester resin, a polymer having a site capable of reacting with a compound having an active hydrogen group, a colorant and a mold release agent are dissolved or dispersed in an organic solvent, and then the solution is dissolved. Alternatively, it is a production method in which a dispersion is dispersed in an aqueous medium and granulated.

Examples of the method for producing the toner particles containing the urea-modified polyester resin as the binder resin include the ester extension method described below. In the following description, the ester extension method will be described by taking toner particles containing an unmodified polyester resin and a urea-modified polyester resin as the binder resin and also containing a colorant and a mold release agent as an example.

-Oil phase liquid preparation process-
An oil phase liquid is prepared by dissolving or dispersing an unmodified polyester resin, a polyester resin having an isocyanate group (referred to as "polyester prepolymer"), an amine compound, a colorant and a mold release agent in an organic solvent (oil phase liquid preparation step). ).

In the oil phase liquid preparation step, for example, any of the following operations is performed.
(I) All the toner materials are collectively dissolved or dispersed in an organic solvent.
(Ii) After kneading all the toner materials in advance, the kneaded product is dissolved or dispersed in an organic solvent.
(Iii) An unmodified polyester resin, a polyester prepolymer, and an amine compound are dissolved in an organic solvent, and then a colorant and a release agent are dispersed.
(Iv) Disperse the colorant and mold release agent in an organic solvent, and then dissolve the unmodified polyester resin, polyester prepolymer and amine compound.
(V) An unmodified polyester resin, a colorant and a mold release agent are dissolved or dispersed in an organic solvent, and then a polyester prepolymer and an amine compound are dissolved.

As the organic solvent of the oil phase liquid, an organic solvent in which the binder resin is dissolved, the amount dissolved in water is 0% by mass or more and 30% by mass or less, and the boiling point is 100 ° C. or less is preferable. Examples of the organic solvent of the oil phase liquid include ester solvents such as methyl acetate and ethyl acetate; ketone solvents such as methyl ethyl ketone and methyl isopropyl ketone; aliphatic hydrocarbon solvents such as hexane and cyclohexane; dichloromethane, chloroform, trichloroethylene and the like. Halogenated hydrocarbon solvents; and the like. Among these organic solvents, ethyl acetate is preferable.

-Dispersion preparation process-
The oil phase liquid is dispersed in the aqueous phase liquid to prepare a dispersion liquid (dispersion liquid preparation step).

The aqueous phase liquid is an aqueous medium containing a dispersant. The aqueous medium contains water as a main component and may contain an organic solvent such as alcohol, dimethylformamide, tetrahydrofuran, cellsolves, and lower ketones. Dispersants include resin particles such as poly (meth) acrylic acid alkyl ester resin, polystyrene resin, poly (styrene-acrylonitrile) resin, and polystyrene acrylic resin; silica, alumina, titania, calcium carbonate, magnesium carbonate, tricalcium phosphate. , Clay, styrene soil, inorganic particles such as bentonite; The surface of these particle dispersants may be surface-treated with a polymer having a carboxyl group. Other examples of the dispersant include polymer dispersants such as carboxymethyl cellulose and carboxyethyl cellulose.

After preparing the dispersion, the reaction between the polyester prepolymer and the amine compound is carried out. This reaction produces a urea-modified polyester resin. This reaction involves at least one of a molecular chain cross-linking reaction and an extension reaction. The reaction between the polyester prepolymer and the amine compound may be carried out in the organic solvent removing step described later.

If necessary, a catalyst (dibutyltin laurate, dioctyltin laurate, etc.) may be used for the reaction between the polyester prepolymer and the amine compound. That is, the catalyst may be added to the oil phase liquid or the dispersion liquid. The reaction time between the polyester prepolymer and the amine compound is preferably 10 minutes or more and 40 hours or less, and more preferably 2 hours or more and 24 hours or less. The reaction temperature is preferably 0 ° C. or higher and 150 ° C. or lower, more preferably 40 ° C. or higher and 98 ° C. or lower.

-Solvent removal process-
The organic solvent is removed from the dispersion liquid to form toner particles to obtain a toner particle dispersion liquid (solvent removal step). In the solvent removing step, the organic solvent is removed from the dispersion liquid by, for example, cooling or heating the dispersion liquid in the range of 0 ° C. or higher and 100 ° C. or lower.

In the solvent removing step, for example, any of the following operations is performed.
(I) An air flow is blown onto the dispersion liquid to forcibly update the gas phase on the dispersion liquid surface. When performing this operation, gas may be blown into the dispersion liquid.
(Ii) Reduce the pressure around the dispersion. When performing this operation, the gas phase on the dispersion liquid surface may be forcibly updated by filling with gas, or gas may be blown into the dispersion liquid.

Toner particles are obtained through the above steps. After the solvent removal step is completed, the toner particles formed in the solution are subjected to a known washing step, solid-liquid separation step, and drying step to obtain dried toner particles. In the cleaning step, from the viewpoint of chargeability, it is preferable to sufficiently perform replacement cleaning with ion-exchanged water. In the solid-liquid separation step, suction filtration, pressure filtration and the like may be performed from the viewpoint of productivity. From the viewpoint of productivity, the drying step may be freeze-dried, air-flow-dried, fluid-dried, vibrating fluid-dried or the like.

The toner according to the present embodiment is produced, for example, by adding an external additive to the obtained dry toner particles and mixing them. The mixing may be carried out by, for example, a V blender, a Henschel mixer, a Ladyge mixer or the like. Further, if necessary, coarse particles of toner may be removed by using a vibration sieving machine, a wind sieving machine, or the like.

<Toner cartridge>
The toner cartridge accommodates replenishing toner for supplying to the developing means provided in the image forming apparatus, and is attached to and detached from the image forming apparatus.

The toner cartridge according to the present embodiment is a toner cartridge that houses the toner set according to the present embodiment and is attached to and detached from the image forming apparatus. That is, the toner cartridge according to the present embodiment contains the first toner, the second toner, the third toner, and the fourth toner, which contain the toner particles and the titanium oxide particles externally attached to the toner particles, as a set. The titanium concentration ratio of the first to fourth toners is 1st toner: 2nd toner: 3rd toner: 4th toner = 1.6 to 1.9: 2.0 to 2.4: 1.2 to 1.5: 0.5 to 1.1.

In the toner cartridge according to the present embodiment, the preferred embodiments of the first to fourth toners are as described above.

<Static charge image developer set>
The electrostatic charge image developer set (hereinafter, also referred to as “developer set”) according to the present embodiment is the first development including a toner containing toner particles and titanium oxide particles externally attached to the toner particles. It has an agent, a second developer, a third developer, and a fourth developer, and the titanium concentration ratio of the toner contained in the first to fourth developers is the first developer: the second developer: the third developer. Agent: Fourth developer = 1.6 to 1.9: 2.0 to 2.4: 1.2 to 1.5: 0.5 to 1.1.

In the developer set according to the present embodiment, the toners contained in each of the first developer, the second developer, the third developer, and the fourth developer are the above-mentioned first toner, second toner, and third toner. And the fourth toner, the preferred form thereof is also as described above.

In the developer set according to this embodiment, the color of each developer is not limited. In one embodiment of the developer set according to the present embodiment, the first developer is yellow, the second developer is magenta, the third developer is cyan, and the fourth developer is black.

In the developer set according to the present embodiment, each developer may be a one-component developer containing only toner or a two-component developer in which toner and a carrier are mixed.

The carrier is not particularly limited, and examples thereof include known carriers. As the carrier, for example, a coating carrier in which the surface of a core material made of magnetic powder is coated with a resin; a magnetic powder dispersion type carrier in which magnetic powder is dispersed in a matrix resin; and a porous magnetic powder is impregnated with resin. Resin-impregnated carrier; etc. The magnetic powder dispersion type carrier and the resin impregnation type carrier may be carriers in which the constituent particles of the carrier are used as a core material and the surface thereof is coated with a resin.

Examples of the magnetic powder include magnetic metals such as iron, nickel and cobalt; magnetic oxides such as ferrite and magnetite; and the like.

Examples of the coating resin and matrix resin include polyethylene, polypropylene, polystyrene, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl ether, polyvinyl ketone, vinyl chloride-vinyl acetate copolymer, and styrene- (meth). ) Acrylic acid ester copolymers, straight silicone resins or modified products thereof containing organosiloxane bonds, fluororesins, polyesters, polycarbonates, phenolic resins, epoxy resins and the like can be mentioned. The coating resin and the matrix resin may contain other additives such as conductive particles. Examples of the conductive particles include metals such as gold, silver and copper, and particles such as carbon black, titanium oxide, zinc oxide, tin oxide, barium sulfate, aluminum borate and potassium titanate.

Examples of coating the surface of the core material with a resin include a method of coating with a coating resin and a coating layer forming solution in which various additives (used if necessary) are dissolved in an appropriate solvent. The solvent is not particularly limited, and may be selected in consideration of the type of resin to be used, coating suitability, and the like.
Specific resin coating methods include a dipping method in which the core material is immersed in a coating layer forming solution; a spray method in which the coating layer forming solution is sprayed onto the core material surface; and the core material is suspended by flowing air. Examples thereof include a fluidized bed method in which a coating layer forming solution is sprayed; a kneader coater method in which a carrier core material and a coating layer forming solution are mixed in a kneader coater, and then the solvent is removed.

One embodiment of the carrier includes a carrier in which magnetic particles having a volume average particle diameter of 10 μm or more and 60 μm or less (preferably 20 μm or more and 40 μm or less) are coated with a resin. Ferrite particles are preferable as the magnetic particles.

From the viewpoint of suppressing image density unevenness, the magnetic particles have a surface unevenness average interval Sm of 1.0 μm ≦ Sm ≦ 3.5 μm and a surface arithmetic average roughness Ra of 0.2 μm ≦ Ra ≦ 0.7 μm. It is preferable to have. When Sm and Ra are in this range, the contact frequency between the carrier and the toner is stabilized, so that the charge distribution of the toner is narrowed and unevenness in image density is suppressed. From this point of view, it is more preferable that the surface unevenness average spacing Sm of the magnetic particles is 2.0 μm ≦ Sm ≦ 3.0 μm and the surface arithmetic average roughness Ra is 0.4 μm ≦ Ra ≦ 0.5 μm. ..

The volume average particle size of the magnetic particles is measured using a laser diffraction type particle size distribution measuring device (for example, HORIBA, Ltd. LA-700).

The unevenness average interval Sm and the arithmetic mean roughness Ra on the surface of the magnetic particles are determined by observing the surface of 50 magnetic particles at a magnification of 3000 times using an ultra-depth color 3D shape measuring microscope (Keyence VK-9500).
The unevenness average interval Sm is an average value of the intervals of one cycle of peaks and valleys obtained by obtaining the roughness curve from the three-dimensional shape of the magnetic particle surface and obtaining from the intersection where the roughness curve intersects the average line. The reference length for determining the Sm value is 10 μm, and the cutoff value is 0.08 mm.
The arithmetic average roughness Ra is a value obtained by obtaining a roughness curve from the three-dimensional shape of the surface of a magnetic particle, and summing and averaging the measured value of the roughness curve and the absolute value of the deviation to the average value. The reference length for obtaining the Ra value is 10 μm, and the cutoff value is 0.08 mm.
The Sm value and Ra value are measured according to JIS B0601: 1994.

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

<Image forming device, image forming method>
The image forming apparatus according to the present embodiment includes four image holders, two primary intermediate transfer bodies, and one secondary intermediate transfer body, and the electrostatic charge image developer set according to the present embodiment is applied. NS.

That is, the image forming apparatus according to this embodiment is
The first image holder, the second image holder, the third image holder, the fourth image holder,
A first charging means for charging the surface of the first image holder, a second charging means for charging the surface of the second image holder, a third charging means for charging the surface of the third image holder, and a fourth. A fourth charging means that charges the surface of the image holder,
A static charge image forming means for forming a static charge image on the surfaces of a charged first image holder, a charged second image holder, a charged third image holder, and a charged fourth image holder.
A first developing means that accommodates a first developing agent and develops a static charge image formed on the surface of the first image holder as a toner image by the first developing agent.
A second developing means that accommodates the second developing agent and develops the electrostatic charge image formed on the surface of the second image holder as a toner image by the second developing agent.
A third developing means that accommodates a third developer and develops a static charge image formed on the surface of the third image holder as a toner image by the third developer.
A fourth developing means that accommodates the fourth developing agent and develops the electrostatic charge image formed on the surface of the fourth image holder as a toner image by the fourth developing agent.
A primary intermediate transfer body to which a toner image is transferred from the first image holder and the second image holder, and the second image holder and the first image holder from the upstream side in the rotation direction of the primary intermediate transfer body. The first intermediate transfer member, which these image holders are in contact with in order,
A primary intermediate transfer body to which a toner image is transferred from the third image holder and the fourth image holder, and the fourth image holder and the third image holder from the upstream side in the rotation direction of the primary intermediate transfer body. The second intermediate transfer body, which these image carriers are in contact with in order,
A secondary intermediate transfer body to which a toner image is transferred from the first intermediate transfer body and the second intermediate transfer body, and the first intermediate transfer body and the second intermediate transfer body are transferred from the upstream side in the rotation direction of the secondary intermediate transfer body. The third intermediate transcript, which these primary intermediate transcripts are in contact with in the order of the body,
A transfer means for transferring the toner image transferred to the surface of the third intermediate transfer body to the surface of the recording medium, and
A fixing means for fixing the toner image transferred to the surface of the recording medium, and
A first cleaning means for cleaning the toner remaining on the surface of the first image holder after the toner image is transferred, and
A second cleaning means for cleaning the toner remaining on the surface of the second image holder after the toner image is transferred, and
A third cleaning means for cleaning the toner remaining on the surface of the third image holder after the toner image is transferred, and
A fourth cleaning means for cleaning the toner remaining on the surface of the fourth image holder after the toner image is transferred, and
To be equipped.

Then, the electrostatic charge image developer set according to the present embodiment is applied to the image forming apparatus according to the present embodiment.

An example of the image forming apparatus according to the present embodiment will be described with reference to the drawings. In the following description, the first developing means forms a yellow (Y) toner image, the second developing means forms a magenta (M) toner image, and the third developing means is a cyan (C). An embodiment in which the fourth developing means forms a black (K) toner image is illustrated, but the color of the toner image formed by each developing means is not limited to this.

FIG. 1 is a schematic view showing a configuration of an image forming apparatus 10 which is an example of the image forming apparatus according to the present embodiment. The image forming apparatus 10 includes an image forming unit 20 in the central portion inside the housing 12, an optical scanning device 50 on the right side in the drawing of the image forming unit 20, and a recording medium before image recording below the image forming unit 20. An accommodating portion 14 accommodating P is provided, and a transport path for the recording medium P is provided on the left side of the drawing of the image forming unit 20.

Above the accommodating portion 14, a take-out roll 16 for taking out the recording medium P from the accommodating portion 14 one by one, and an alignment roll 18 for adjusting the position of the tip of the recording medium P taken out from the accommodating portion 14 by the take-out roll 16. Is provided.

The optical scanning device 50 (an example of an electrostatic charge image forming means) scans a light beam emitted from a light source with a rotating multifaceted mirror (polygon mirror), reflects it with a plurality of optical components such as a reflecting mirror, and emits light. The beams 52Y, 52M, 52C or 52K are emitted. The light beams 52Y, 52M, 52C, and 52K irradiate the surfaces of the corresponding photoconductors 22Y, 22M, 22C, and 22K, respectively, and form an electrostatic charge image on the surfaces.

The image forming unit 20 includes a photoconductor 22Y (an example of a first image holder), a photoconductor 22M (an example of a second image holder), a photoconductor 22C (an example of a third image holder), and a photoconductor 22K (an example of a third image holder). An example of a four-image holder) is provided, and these four photoconductors are arranged in an upper and lower row at intervals.

Around the photoconductor 22Y, a charging roll 24Y (an example of the first charging means) that charges the surface of the photoconductor 22Y, and a developing device that develops a static charge image formed on the surface of the photoconductor 22Y with yellow toner. 26Y (an example of the first developing means) and a photoconductor cleaning device 28Y (an example of the first cleaning means) for cleaning the surface of the photoconductor 22Y after the transfer of the toner image and before charging are arranged.

Around the photoconductor 22M, a charging roll 24M (an example of a second charging means) that charges the surface of the photoconductor 22M, and a developing device that develops a static charge image formed on the surface of the photoconductor 22M with magenta toner. 26M (an example of the second developing means) and 28M (an example of the second cleaning means) for cleaning the surface of the photoconductor 22M after the transfer of the toner image and before charging are arranged.

Around the photoconductor 22C, a charging roll 24C (an example of a third charging means) that charges the surface of the photoconductor 22C, and a developing device that develops a static charge image formed on the surface of the photoconductor 22C with cyan toner. 26C (an example of a third developing means) and a photoconductor cleaning device 28C (an example of a third cleaning means) that cleans the surface of the photoconductor 22C after the transfer of the toner image and before charging are arranged.

Around the photoconductor 22K, a charging roll 24K (an example of a fourth charging means) that charges the surface of the photoconductor 22K, and a developing device that develops an electrostatic charge image formed on the surface of the photoconductor 22K with black toner. A 26K (an example of a fourth developing means) and a photoconductor cleaning device 28K (an example of a fourth cleaning means) that cleans the surface of the photoconductor 22K after the transfer of the toner image and before charging are arranged.

In the present embodiment, the titanium concentration ratio of the toner contained in each developer contained in the developing devices 26Y, 26M, 26C, and 26K is 26Y: 26M: 26C: 26K = 1.6 to 1.9: 2.0. To 2.4: 1.2 to 1.5: 0.5 to 1.1.

An intermediate transfer body 32 (an example of a first intermediate transfer body) is in contact with the photoconductor 22Y and the photoconductor 22M. The intermediate transfer body 32 is a primary intermediate transfer body to which the yellow toner image formed on the photoconductor 22Y and the magenta toner image formed on the photoconductor 22M are transferred. The intermediate transfer member 32 is in contact with these two photoconductors in the order of the photoconductor 22M and the photoconductor 22Y from the upstream side in the rotation direction (the direction of the arrow shown in the drawing).

An intermediate transfer body 34 (an example of a second intermediate transfer body) is in contact with the photoconductor 22C and the photoconductor 22K. The intermediate transfer body 34 is a primary intermediate transfer body to which the cyan toner image formed on the photoconductor 22C and the black toner image formed on the photoconductor 22K are transferred. The intermediate transfer member 34 is in contact with these two photoconductors in the order of the photoconductor 22K and the photoconductor 22C from the upstream side in the rotation direction (the direction of the arrow shown in the drawing).

The intermediate transfer body 36 (an example of the third intermediate transfer body) is in contact with the intermediate transfer body 32 and the intermediate transfer body 34. The intermediate transfer body 36 is a secondary intermediate transfer body to which the toner image transferred to the intermediate transfer body 32 and the toner image transferred to the intermediate transfer body 34 are transferred. The intermediate transfer body 36 is in contact with these two primary intermediate transfer bodies in the order of the intermediate transfer body 32 and the intermediate transfer body 34 from the upstream side in the rotation direction (arrow direction shown in the drawing).

A transfer roll 38 (an example of transfer means) for transferring the toner image transferred to the intermediate transfer body 36 to the recording medium P is provided at a position facing the intermediate transfer body 36. The recording medium P is conveyed between the intermediate transfer body 36 and the transfer roll 38, and the toner image on the intermediate transfer body 36 is transferred to the recording medium P.

A fixing device 60 (an example of fixing means) is provided on the downstream side of the transfer roll 38 in the transport direction of the recording medium P. The fixing device 60 has a heating belt 62 and a pressure roll 64, and heats and pressurizes the recording medium P to fix the toner image on the recording medium P.

A transport roll 66 is provided on the downstream side of the recording medium P in the transport direction with respect to the fixing device 60, and the recording medium P is discharged to the outside of the machine by the transport roll 66 and loaded on the discharge unit 68.

Next, the image forming operation of the image forming apparatus 10 will be described by taking the case of forming a full-color image as an example. In the following description, when it is necessary to distinguish YMCK, any one of Y, M, C, and K is added after the reference numeral, and when it is not necessary to distinguish YMCK, YMCK is omitted.

When the image forming apparatus 10 is operated, the surface of the photoconductor 22 rotating in the direction of the arrow shown in the drawing is charged by the charging roll 24.

Light beams 52 of each color corresponding to the output image are irradiated from the optical scanning device 50 to the surface of the photoconductor 22 after charging, and a static charge image is formed on the surface of the photoconductor 22.

The developing device 26 applies toner to the electrostatic charge image on the surface of the photoconductor 22, and a toner image is formed on the surface of the photoconductor 22.

The magenta toner image is primary transferred from the photoconductor 22M to the intermediate transfer body 32, and then the yellow toner image is primary transfer from the photoconductor 22Y to the intermediate transfer body 32.
Similarly, the black toner image is primary transferred from the photoconductor 22K to the intermediate transfer body 34, and then the cyan toner image is primary transfer from the photoconductor 22C to the intermediate transfer body 34.

After transferring the toner image, the photoconductor 22 continues to rotate and comes into contact with the cleaning brush or cleaning blade included in the photoconductor cleaning device 28. The toner remaining on the photoconductor 22 is removed from the photoconductor 22 by the photoconductor cleaning device 28 and recovered.

The magenta toner image and the yellow toner image on the intermediate transfer body 32 are secondarily transferred to the intermediate transfer body 36. Next, the black toner image and the cyan toner image on the intermediate transfer body 34 are also secondarily transferred to the intermediate transfer body 36.

The four-color toner image on the intermediate transfer body 36 reaches the contact portion between the intermediate transfer body 36 and the transfer roll 38. At the same time, the recording medium P taken out from the accommodating portion 14 by the take-out roll 16 is conveyed to the contact portion under the control of the alignment roll 18, and the four-color toner image is transferred onto the recording medium P (final). Is transcribed).

The recording medium P that has passed through the contact portion between the intermediate transfer body 36 and the transfer roll 38 is conveyed to the fixing device 60 and passes through the contact portion between the heating belt 62 and the pressure roll 64. At that time, the four-color toner image is fixed on the recording medium P by the action of the heat and pressure given from the heating belt 62 and the pressure roll 64. After fixing, the recording medium P is discharged to the discharge unit 68 by the transport roll 66, and the image formation on the recording medium P is completed.

The image forming apparatus according to the present embodiment is a static elimination means for irradiating the surface of the image holder with static elimination light after the transfer of the toner image and before charging; a cleaning means for cleaning the surface of the primary intermediate transfer body; Cleaning means for cleaning the surface of the intermediate transfer member; etc. may be provided.

In the image forming apparatus according to the present embodiment, for example, the portion including the developing means may have a cartridge structure (process cartridge) attached to and detached from the image forming apparatus.

Hereinafter, embodiments of the invention will be described in detail with reference to Examples, but the embodiments of the invention are not limited to these Examples. In the following description, all "parts" are based on mass unless otherwise specified.

[Preparation of carrier (1)]
・ Fe ₂ O ₃ : 1318 parts ・ Mn (OH) ₂ : 586 parts ・ Mg (OH) ₂ : 96 parts Mix the above materials, add water and zirconia beads with a diameter of 1 mm, and mix while crushing with a sand mill. bottom. Then, the zirconia beads were removed by filtration, dried, and then mixed in a rotary kiln at a rotation speed of 20 rpm and a temperature of 900 ° C. for 60 minutes. Then, polyvinyl alcohol and water were added, and the mixture was pulverized with a wet ball mill until the volume average particle size became 1.4 μm. Then, using a spray dryer, granulation and drying were performed so that the dry particle size was 40 μm. Next, firing was carried out in an electric furnace for 5 hours in an oxygen-nitrogen mixed atmosphere at a temperature of 1100 ° C. and an oxygen concentration of 1% by volume. The particles after firing were crushed and classified, mixed in a rotary kiln at a rotation speed of 15 rpm and a temperature of 900 ° C. for 2 hours, and classified after cooling to obtain magnetic particles (1). The magnetic particles (1) had a volume average particle size of 35 μm, a surface unevenness average interval Sm of 2.5 μm, and an arithmetic mean roughness Ra of the surface of 0.4 μm.

-Cyclohexyl methacrylate-monoethylaminoethyl methacrylate copolymer (mass ratio 95: 5, weight average molecular weight 60,000): 36 parts-Carbon black (Cabot, VXC72): 4 parts-Toluene (Wako Pure Chemical Industries, Ltd.): 500 Part ・ Isopropyl alcohol (Wako Pure Chemical Industries, Ltd.): 50 parts The above material and glass beads (particle size 1 mm) in the same amount as toluene are put into a sand mill and stirred at a rotation speed of 1200 rpm for 30 minutes to form a coating layer. The solution (1) was prepared.

200 parts of the magnetic particles (1) and 34 parts of the coating layer forming solution (1) were placed in a vacuum degassing type kneader, and the pressure was reduced to −200 mmHg at a temperature of 60 ° C. with stirring and mixed for 20 minutes. Then, the temperature was raised and the pressure was reduced, and the mixture was stirred and dried at 94 ° C. and −720 mmHg for 30 minutes to obtain resin-coated magnetic particles. The resin-coated magnetic particles were sieved with a sieving network of a 75 μm mesh to obtain a carrier (1).

[Preparation of colorant dispersion liquid (Y)]
-Pigment: Pigment Yellow 74 (Dainichiseika Kogyo): 50 parts-Anionic surfactant: Neogen SC (Daiichi Kogyo Seiyaku): 5 parts-Ion exchange water: 200 parts Mix the above materials and homogenizer (IKA) A colorant dispersion liquid (Y) having a solid content of 21% by mass was obtained by dispersion treatment with Ultratarax T50) manufactured by the same company for 5 minutes and further dispersion treatment with an ultrasonic bath for 10 minutes. The volume average particle size was measured with a particle size distribution measuring device (LA-700 manufactured by HORIBA, Ltd.) and found to be 160 nm.

[Preparation of colorant dispersion liquid (M)]
-Pigment: Pigment Red 122 (DIC): 50 parts-Anionic surfactant: Neogen SC (Daiichi Kogyo Seiyaku): 5 parts-Ion exchange water: 200 parts Same as the preparation of the colorant dispersion liquid (Y). A colorant dispersion liquid (M) having a solid content of 21% by mass and a volume average particle size of 160 nm was obtained.

[Preparation of colorant dispersion liquid (C)]
-Pigment: Pigment Blue 15: 3 (Dainichiseika Kogyo): 50 parts-Anionic surfactant: Neogen SC (Daiichi Kogyo Seiyaku): 5 parts-Ion exchange water: 200 parts Colorant dispersion liquid (Y) In the same manner as in the preparation, a colorant dispersion liquid (C) having a solid content of 21% by mass and a volume average particle size of 160 nm was obtained.

[Preparation of colorant dispersion liquid (K)]
-Pigment: Carbon black (Cabot, Legal 330): 50 parts-Anionic surfactant: Neogen SC (Daiichi Kogyo Seiyaku): 5 parts-Ion exchange water: 200 parts Preparation of colorant dispersion (Y) Similarly, a colorant dispersion liquid (K) having a solid content of 21% by mass and a volume average particle size of 160 nm was obtained.

[Preparation of release agent dispersion liquid (1)]
・ Paraffin wax: HNP-9 (Nippon Seiwa): 19 parts ・ Anionic surfactant: Neogen SC (Daiichi Kogyo Seiyaku): 1 part ・ Ion exchange water: 80 parts Mix the above materials in a heat-resistant container. , The temperature was raised to 90 ° C., and stirring was performed for 30 minutes. Next, the melt was circulated from the bottom of the container to the Gorin homogenizer, and a circulation operation equivalent to 3 passes was performed under a pressure of 5 MPa, then the pressure was increased to 35 MPa, and a circulation operation equivalent to 3 passes was further performed. The emulsion thus formed was cooled in a heat-resistant solution until the temperature became 40 ° C. or lower to obtain a release agent dispersion liquid (1) having a solid content of 20% by mass. The volume average particle size was measured with a particle size distribution measuring device (LA-700 manufactured by HORIBA, Ltd.) and found to be 240 nm.

[Preparation of resin particle dispersion liquid (1)]
-Oil phase material-
・ Styrene (Wako Pure Chemical Industries): 30 parts ・ n-Butyl acrylate (Wako Pure Chemical Industries): 10 parts ・ β-carboxyethyl acrylate (Rhodia Nikka): 1.3 parts ・ Dodecane thiol (Wako Pure Chemical Industries) ): 0.4 copies

-Material of aqueous phase 1-
・ Ion-exchanged water: 17 parts ・ Anionic surfactant: Dowfax (Dow Chemical): 0.4 parts

-Material for aqueous phase 2-
・ Ion-exchanged water: 40 parts ・ Anionic surfactant: Dowfax (Dow Chemical): 0.05 parts ・ Ammonium peroxodisulfate (manufactured by Wako Pure Chemical Industries, Ltd.): 0.4 parts

The oil phase material and the aqueous phase 1 material were each stirred and mixed, and both were stirred and mixed to obtain a monomeric emulsion dispersion. Separately, the material of the aqueous phase 2 was put into the reaction vessel, the inside of the reaction vessel was sufficiently replaced with nitrogen, and the inside of the reaction system was heated to 75 ° C. with an oil bath while stirring. A monomer emulsified dispersion was gradually added dropwise to the reaction vessel over 3 hours to carry out emulsion polymerization. After completion of the dropping, the polymerization was further continued at 75 ° C., and the polymerization was terminated after 3 hours to obtain a resin particle dispersion liquid (1) having a solid content of 42% by mass.
The volume average particle size was measured with a particle size distribution measuring device (LA-700 manufactured by HORIBA, Ltd.) and found to be 250 nm. The glass transition temperature of the resin was measured at a heating rate of 10 ° C./min with a differential scanning calorimeter (DSC-50 manufactured by Shimadzu Corporation) and found to be 52 ° C. The number average molecular weight (in terms of polystyrene) was measured by GPC and found to be 13000.

[Preparation of toner particles (Y1)]
・ Resin particle dispersion (1): 150 parts ・ Colorant dispersion (Y): 25 parts ・ Release agent dispersion (1): 35 parts ・ Polyaluminum chloride: 0.4 parts Round stainless steel After mixing and dispersing in the flask using a homogenizer (Ultratarax T50 manufactured by IKA), the inside of the flask was heated to 48 ° C. in a heating oil bath while stirring. After holding at 48 ° C. for 60 minutes with stirring, 70 parts of the resin particle dispersion liquid (1) was slowly added. Next, after adjusting the pH in the system to 8.0 using an aqueous sodium hydroxide solution having a concentration of 0.5 mol / L, the stainless flask was sealed, the stirring shaft was magnetically sealed, and stirring was continued. It was heated to 90 ° C. and held at that temperature for 30 minutes. Then, the mixture was cooled at a temperature lowering rate of 5 ° C./min, filtered, and the solid content was sufficiently washed with ion-exchanged water, and then solid-liquid separation was performed by Nucci-type suction filtration. The solid content was redistributed in 3 L of ion-exchanged water at 30 ° C., and the mixture was stirred and washed at a rotation speed of 300 rpm for 15 minutes. This washing operation was repeated 6 more times, and when the pH of the filtrate became 7.54 and the electrical conductivity was 6.5 μS / cm, No. Solid-liquid separation was performed using 5A filter paper. Vacuum drying of the solid content was continued for 24 hours to obtain toner particles (Y1). The volume average particle size was measured and found to be 5.7 μm.

[Preparation of toner particles (M1)]
Toner particles (M1) were produced in the same manner as in the production of toner particles (Y1) except that the colorant dispersion liquid (Y) was changed to the colorant dispersion liquid (M). The volume average particle size was measured and found to be 5.7 μm.

[Preparation of toner particles (C1)]
Toner particles (C1) were produced in the same manner as in the production of toner particles (Y1) except that the colorant dispersion liquid (Y) was changed to the colorant dispersion liquid (C). The volume average particle size was measured and found to be 5.7 μm.

[Preparation of toner particles (K1)]
Toner particles (K1) were produced in the same manner as in the production of toner particles (Y1) except that the colorant dispersion liquid (Y) was changed to the colorant dispersion liquid (K). The volume average particle size was measured and found to be 5.7 μm.

[Preparation of Hydrophobic Titanium Oxide Particles (1)]
Ilmenite ore (FeTIO ₃ ) was heated and dissolved in concentrated sulfuric acid to separate iron powder to obtain _{titanium oxysulfate (TIOSO 4).} Next, titanium oxysulfate is hydrolyzed by heating _{to form a precipitate of metatitanic acid (TiO (OH) 2} ), the precipitate is filtered, and after repeated washing with water, 10 ppm (mass basis) with respect to metatitanic acid. The polycarboxylic acid of No. 1 and 100 times the amount (mass basis) of water were added, and the mixture was sufficiently stirred and then dried at 150 ° C. Then, it was heated and calcined at 500 ° C. for 100 minutes to obtain a titanium oxide (1) containing titanium oxide _{(TiO 2} ) and metatitanium acid (TiO (OH) _2). Next, the titanium oxide (1) was dispersed in water, and 5% by mass of isobutylmethoxysilane was added dropwise to the titanium oxide (1) at a liquid temperature of 25 ° C. while stirring the dispersion. Then, solid-liquid separation was performed by filtration, and after repeated washing of the solid content with water, the solid content was dried at 150 ° C. Then, the dried product was redispersed in 100 times the amount (mass basis) of methanol, separated into solid and liquid by filtration, and dried at 100 ° C. In this way, hydrophobic titanium oxide particles (1) obtained by surface-treating the titanium oxide (1) with isobutylmethoxysilane were obtained. When the volume average particle size was measured with a particle size distribution measuring device (LA-700 manufactured by HORIBA, Ltd.), the volume average particle size of the hydrophobic titanium oxide particles (1) was 50 nm.

<Example 1>
[Preparation of external toner]
To 500 parts of toner particles (Y1), 10 parts of silica particles (Aerosil Japan, RY50, volume average particle size 40 nm) and 8.5 parts of titanium oxide particles (Taika, JMT2000, volume average particle size 20 nm) are added. , Mixed with a Henschel mixer to obtain an external toner (Y1).
To 500 parts of toner particles (M1), 10 parts of silica particles (RY50, Nippon Aerosil) and 11 parts of titanium oxide particles (Tayca, JMT2000) are added, mixed with a Henshell mixer, and the external toner (M1) is added. Obtained.
To 500 parts of toner particles (C1), 10 parts of silica particles (RY50, Nippon Aerosil) and 7 parts of titanium oxide particles (Tayca, JMT2000) are added, mixed with a Henshell mixer, and the external toner (C1) is added. Obtained.
To 500 parts of toner particles (K1), 10 parts of silica particles (RY50, Nippon Aerosil) and 4 parts of titanium oxide particles (Tayca, JMT2000) are added, mixed with a Henshell mixer, and the external toner (K1) is added. Obtained.

[Preparation of developer]
10 parts of each external toner and 100 parts of the carrier (1) are placed in a V-blender, stirred for 20 minutes, mixed, and then sieved with a sieve having a mesh size of 212 μm to develop agents (Y1), (M1), ( A set of C1) and (K1) was obtained.
The toner was separated from each developer, and the titanium concentration ratio between the toners was calculated according to the measurement method described above. The titanium concentration ratio is shown in Table 2.

[Evaluation of uneven density]
As an image forming apparatus having the configuration illustrated in FIG. 1, a DocuPrint C3200A manufactured by Fuji Xerox was prepared. Developers (Y1), (M1), (C1) and (K1) are added to each of the four developing devices of this image forming device, and the concentration is added to A4 plain paper in an environment of a temperature of 10 ° C. and a relative humidity of 10%. A 30% full-scale halftone image was repeated in the order of yellow single color, magenta single color, cyan single color, and black single color, and a total of 10,000 images were continuously output. (1) The 4999th cyan monochromatic full-face halftone image and (2) the 9999th cyan monochromatic full-face halftone image were visually observed and classified as follows. The results are shown in Table 2.

No uneven density is observed in either G1: (1) or (2).
G2: No uneven density is observed in (1), but a slight streak-like density unevenness is observed in (2).
G3: No uneven density is observed in (1), but a wide band-like portion with low concentration is observed in (2).
G4: Streaky density unevenness is observed in (1).
G5: In (1), white streaks are observed and image omissions are observed.

After a total of 10,000 sheets were continuously output, the surface of the third photoconductor, which was a photoconductor using a cyan developer, was visually observed, and the presence or absence of toner filming was classified as follows. The results are shown in Table 2.

A: Toner filming is not allowed.
B: Fine toner filming is observed.
C: Toner filming occurs frequently or over a wide area.

[Evaluation of concentration decrease]
A reference patch with a density of 100% was formed on A4 plain paper using an external toner (C1), and the L ^* value, a ^* value, and b ^{* value in the CIE1976L *} a ^* b ^* color system were set by X-Light Co., Ltd. The measurement was performed using X-Rite 939 manufactured by X-Rite 939 (aperture diameter 4 mm).
After the continuous output of 10,000 images performed for the above [evaluation of density unevenness], one image having a cyan color density of 100% is output, and the L ^* value, a ^* value, and b ^* value are calculated in the same manner as above. It was measured.
Based on the following formula, the color difference ΔE between the reference patch and the image formed by the actual machine was calculated between the cyan colors.

Ｌ_１、ａ_１、ｂ_１は、基準パッチのＬ^＊値、ａ^＊値、ｂ^＊値であり、Ｌ_２、ａ_２、ｂ_２は、実機で形成した画像のＬ^＊値、ａ^＊値、ｂ^＊値である。

L ₁ , a ₁ , b ₁ are the L ^* value, a ^* value, and b ^* value of the reference patch, and L ₂ , a ₂ , and b ₂ ^{are the L *} value and a ^* value of the image formed by the actual machine. , B ^* value.

The values of the color difference ΔE between the reference patch and the image formed by the actual machine were classified as follows. The results are shown in Table 2.

G1: ΔE is 1.0 or less.
G2: ΔE is more than 1.0 and 2.0 or less.
G3: ΔE is more than 2.0 and 3.0 or less.
G4: ΔE is more than 3.0 and 4.0 or less.
G5: ΔE is over 4.0.

[Evaluation of fog]
The developers (Y1), (M1), (C1) and (K1) are put into each of the four developing devices of Fuji Xerox's DocuPrint C3200A, and the temperature is 25 ° C. and the relative humidity is 80%. The test charts of 50,000 sheets were continuously output, and the last 10 sheets were visually observed and classified as follows. The results are shown in Table 2.

No fog is observed on all G1:10 sheets.
G2: A slight fog is observed on one sheet, but it is within a practically acceptable range.
G3: A slight fog is observed on a plurality of sheets, which is within a practically acceptable range.
G4: Clear fog is observed on multiple sheets, which is not suitable for practical use.
Fogging is observed on all G5: 10 sheets.

<Examples 2 to 12, Comparative Examples 1 to 10>
A toner set and a developer set were prepared in the same manner as in Example 1 except that the amount of titanium oxide particles (TAYCA, JMT2000) added was changed as shown in Table 1. The toner was separated from each developer, and the titanium concentration ratio between the toners was calculated according to the measurement method described above. The titanium concentration ratio is shown in Table 2.
Then, using each developer set, an image was formed and evaluated in the same manner as in Example 1. The results are shown in Table 2.
The tin oxide particles used in Comparative Example 9 are SnO ₂ (Ishihara Sangyo Co., Ltd., SN-100P, volume average particle size 20 nm).

<Example 13>
[Preparation of polyester particle dispersion liquid (1)]
・ Telephthalic acid: 30 mol parts ・ Fumaric acid: 70 mol parts ・ Bisphenol A ethylene oxide adduct: 5 mol parts ・ Bisphenol A propylene oxide adduct: 95 mol parts Stirrer, nitrogen introduction tube, temperature sensor and rectification tower The above-mentioned material was charged into the provided flask, the temperature was raised to 220 ° C. over 1 hour, and 1 part of titanium tetraethoxydo was added to 100 parts of the above-mentioned material. The temperature was raised to 230 ° C. over 0.5 hours while distilling off the generated water, and the dehydration condensation reaction was continued at that temperature for 1 hour, and then the reaction product was cooled. In this way, a polyester resin having a weight average molecular weight of 18,000, an acid value of 15 mgKOH / g, and a glass transition temperature of 60 ° C. was obtained.

40 parts of ethyl acetate and 25 parts of 2-butanol were added to a container equipped with a temperature control means and a nitrogen substitution means to prepare a mixed solvent, and then 100 parts of a polyester resin was gradually added to dissolve the mixture. A% aqueous ammonia solution (equivalent to 3 times the molar ratio of the acid value of the resin) was added and stirred for 30 minutes.
Next, the inside of the container was replaced with dry nitrogen, the temperature was maintained at 40 ° C., and 400 parts of ion-exchanged water was added dropwise at a rate of 2 parts / minute while stirring the mixture to emulsify. After completion of the dropping, the emulsion was returned to room temperature (20 ° C. to 25 ° C.) and bubbling with dry nitrogen for 48 hours with stirring to reduce ethyl acetate and 2-butanol to 0.1% by mass or less. Then, ion-exchanged water was added to adjust the solid content to 20% by mass to prepare a polyester particle dispersion liquid (1). The volume average particle diameter of the resin particles in the dispersion was 200 nm.

[Preparation of toner particles (YP1)]
-Polyester particle dispersion (1): 150 parts-Colorant dispersion (Y): 30 parts-Release release agent dispersion (1): 40 parts-Anionic surfactant: Neogen SC (Daiichi Kogyo Seiyaku): Part 1 The above material was placed in a reaction vessel equipped with a thermometer, a pH meter and a stirrer, heated to a temperature of 30 ° C. from the outside with a mantle heater, and held for 30 minutes while stirring at a rotation speed of 150 rpm. Next, a 0.3N nitric acid aqueous solution was added to adjust the pH to 3.0, and then a 3% by mass polyaluminum chloride aqueous solution was added while dispersing with a homogenizer (Ultratarax T50 manufactured by IKA). Then, the temperature was raised to 50 ° C. with stirring and held for 30 minutes. Next, 100 parts of the polyester particle dispersion (1) was added and held for 1 hour, and a 0.1N sodium hydroxide aqueous solution was added to adjust the pH to 8.5, and then the mixture was heated to 85 ° C. while continuing stirring. , The temperature was maintained for 5 hours. Next, cooling, solid-liquid separation, washing of solid matter, and drying were sequentially performed to obtain toner particles (YP1). The volume average particle size of the toner particles (YP1) was 6.2 μm.

[Preparation of toner particles (MP1)]
Toner particles (MP1) were produced in the same manner as in the production of toner particles (YP1) except that the colorant dispersion liquid (Y) was changed to the colorant dispersion liquid (M). The volume average particle size of the toner particles (MP1) was 6.2 μm.

[Preparation of toner particles (CP1)]
Toner particles (CP1) were produced in the same manner as in the production of toner particles (YP1) except that the colorant dispersion liquid (Y) was changed to the colorant dispersion liquid (C). The volume average particle size of the toner particles (CP1) was 6.2 μm.

[Preparation of toner particles (KP1)]
Toner particles (KP1) were produced in the same manner as in the production of toner particles (YP1) except that the colorant dispersion liquid (Y) was changed to the colorant dispersion liquid (K). The volume average particle size of the toner particles (KP1) was 6.2 μm.

[Preparation of external toner]
To 500 parts of toner particles (YP1), 10 parts of silica particles (Aerosil Japan, RY50) and 8.5 parts of titanium oxide particles (Taika, JMT2000) are added, mixed with a Henschel mixer, and external toner (YP1) is added. ) Was obtained.
To 500 parts of toner particles (MP1), 10 parts of silica particles (RY50, Nippon Aerosil) and 11 parts of titanium oxide particles (Taika, JMT2000) are added, mixed with a Henshell mixer, and the external toner (MP1) is added. Obtained.
To 500 parts of toner particles (CP1), 10 parts of silica particles (RY50, Nippon Aerosil) and 7 parts of titanium oxide particles (Taika, JMT2000) are added, mixed with a Henshell mixer, and the external toner (CP1) is added. Obtained.
To 500 parts of toner particles (KP1), 10 parts of silica particles (RY50, Nippon Aerosil) and 4 parts of titanium oxide particles (Tayca, JMT2000) are added, mixed with a Henschel mixer, and an external toner (KP1) is added. Obtained.

[Preparation of developer]
10 parts of each external toner and 100 parts of the carrier (1) are placed in a V-blender, stirred for 20 minutes, mixed, and then sieved with a sieve having a mesh size of 212 μm to develop agents (YP1), (MP1), ( A set of CP1) and (KP1) was obtained.
When the toner was separated from each developer and the titanium concentration ratio between the toners was calculated according to the measurement method described above, the toner (YP1): toner (MP1): toner (CP1): toner (KP1) = 1.7: It was 2.2: 1.4: 0.8.

[Image formation and image evaluation]
The set of the developer was placed in each of the four developing devices of Fuji Xerox's DocuPrint C3200A, and an image was formed in the same manner as in Example 1 to evaluate density unevenness, density decrease and fog. The density unevenness was G1, the density decrease was G1, and the fog was G1.

<Example 14>
[Preparation of unmodified polyester resin (A)]
-Terephthalic acid: 1243 parts-Bisphenol A ethylene oxide adduct: 1830 parts-Bisphenol A propylene oxide adduct: 840 parts After mixing the above materials while heating at 180 ° C, add 3 parts of dibutyltin oxide and at 220 ° C. Water was distilled off while heating to obtain an unmodified polyester resin (A). The glass transition temperature Tg of the unmodified polyester resin (A) was 60 ° C.

[Preparation of polyester prepolymer (A)]
-Terephthalic acid: 1243 parts-Bisphenol A ethylene oxide adduct: 1830 parts-Bisphenol A propylene oxide adduct: 840 parts After mixing the above materials while heating at 180 ° C, add 3 parts of dibutyltin oxide and at 220 ° C. Water was distilled off while heating to obtain a polyester resin. 350 parts of the polyester resin, 50 parts of tolylene diisocyanate, and 450 parts of ethyl acetate were placed in a container, mixed, and heated at 130 ° C. for 3 hours to obtain a polyester prepolymer (A) having an isocyanate group.

[Preparation of ketimine compound (A)]
50 parts of methyl ethyl ketone and 150 parts of hexamethylenediamine were placed in a container and stirred at 60 ° C. to obtain ketimine compound (A).

[Preparation of colorant dispersion liquid (YA)]
-Pigment: Pigment Yellow 74 (Dainichiseika Kogyo): 30 parts-Ethyl acetate: 270 parts The above material is wet-ground with a microbead type disperser (DCP mill), and a colorant dispersion liquid (YA) having a solid content of 10% by mass is used. ) Was obtained.

[Preparation of colorant dispersion liquid (MA)]
-Pigment: Pigment Red 122 (DIC Corporation): 30 parts-Ethyl acetate: 270 parts Wet pulverize the above material with a microbead type disperser (DCP mill) to obtain a colorant dispersion liquid (MA) having a solid content of 10% by mass. Obtained.

[Preparation of colorant dispersion liquid (CA)]
-Pigment: Pigment Blue 15: 3 (Dainichiseika Kogyo): 30 parts-Ethyl acetate: 270 parts Wet pulverize the above material with a microbead type disperser (DCP mill), and a colorant dispersion liquid with a solid content of 10% by mass. (CA) was obtained.

[Preparation of colorant dispersion liquid (KA)]
-Pigment: Carbon black (Cabot, Regal 330): 30 parts-Ethyl acetate: 270 parts The above material is wet-ground with a microbead type disperser (DCP mill), and a colorant dispersion liquid (KA) having a solid content of 10% by mass is used. ) Was obtained.

[Preparation of release agent dispersion liquid (A)]
-Paraffin wax: HNP-9 (Nippon Seiwa): 30 parts-Ethyl acetate: 270 parts With the above material cooled to 10 ° C, it is wet-ground with a microbead type disperser (DCP mill) and has a solid content of 10 mass. %% Release agent dispersion (A) was obtained.

[Preparation of Styrene Acrylic Resin Particle Dispersion Liquid (A)]
・ Styrene: 332 parts ・ n-butyl acrylate: 68 parts ・ Acrylic acid: 4 parts ・ Dodecanthiolu: 8 parts ・ Carbon tetrabromide: 4 parts Nonionic surfactant (Nonipol 400, Sanyo Kasei Kogyo) ) 6 parts and 10 parts of anionic surfactant (Neogen SC, Daiichi Kogyo Seiyaku) were dissolved in 560 parts of ion-exchanged water, and the mixture of the above materials was dispersed and emulsified in the solution in the flask. bottom. Next, while stirring the inside of the flask, a solution prepared by dissolving 4 parts of ammonium persulfate in 50 parts of ion-exchanged water was added to carry out nitrogen substitution. Next, while stirring the inside of the flask, the contents were heated in an oil bath until the contents reached 70 ° C., and emulsion polymerization was continued for 5 hours. Styrene acrylic resin particle dispersion liquid (A) (volume average particle diameter of resin particles 180 nm, solid Amount of 40% by mass) was obtained. The styrene acrylic resin had a glass transition temperature of 59 ° C. and a weight average molecular weight of 15500.

[Preparation of oil phase liquid (A)]
-Unmodified polyester resin (A): 60 parts-Colorant dispersion (YA): 50 parts-Release release agent dispersion (A): 70 parts-Ethyl acetate: 30 parts Ethyl acetate, unmodified polyester resin (A) After stirring and mixing the colorant dispersion liquid (YA), the release agent dispersion liquid (A) was added to the mixture, and the mixture was further stirred to obtain an oil phase liquid (A).

[Preparation of aqueous phase liquid (A)]
・ Styrene acrylic resin particle dispersion (A): 50 parts ・ Polymer dispersant (2% by mass aqueous solution of cellogen BS-H (Daiichi Kogyo Seiyaku)): 200 parts ・ Ion exchange water: 200 parts Stir the above materials. And mixed to obtain an aqueous phase liquid (A).

[Preparation of toner particles (YA1)]
・ Oil phase liquid (A): 1200 parts ・ Polyester prepolymer (A): 150 parts ・ Ketimine compound (A): 10 parts Put the above materials in a container and disperse with a homogenizer (Ultra Tarax T50 manufactured by IKA) for 2 minutes. The treatment was carried out to obtain an oil phase liquid (AP). 1000 parts of the aqueous phase liquid (A) was added to the oil phase liquid (AP), and dispersion treatment was carried out with a homogenizer for 20 minutes to obtain a dispersion liquid. Next, the dispersion is stirred with a propeller-type stirrer at room temperature (25 ° C.) and normal pressure (1 atm) for 48 hours to react the polyester prepolymer (A) with the ketimine compound (A) to cause a urea-modified polyester resin. The organic solvent was removed to form granules. Then, the granules were washed with water, dried and classified to obtain toner particles (YA1). The volume average particle size of the toner particles (YA1) was 6.0 μm.

[Preparation of toner particles (MA1)]
Toner particles (MA1) were produced in the same manner as in the production of toner particles (YA1) except that the colorant dispersion liquid (YA) was changed to the colorant dispersion liquid (MA). The volume average particle size of the toner particles (MA1) was 6.0 μm.

[Preparation of toner particles (CA1)]
Toner particles (CA1) were produced in the same manner as in the production of toner particles (YA1) except that the colorant dispersion liquid (YA) was changed to the colorant dispersion liquid (CA). The volume average particle size of the toner particles (CA1) was 6.0 μm.

[Preparation of toner particles (KA1)]
Toner particles (KA1) were produced in the same manner as in the production of toner particles (YA1) except that the colorant dispersion liquid (YA) was changed to the colorant dispersion liquid (KA). The volume average particle size of the toner particles (KA1) was 6.0 μm.

[Preparation of external toner]
To 500 parts of toner particles (YA1), 10 parts of silica particles (Aerosil Japan, RY50) and 8.5 parts of titanium oxide particles (TAYCA, JMT2000) are added, mixed with a Henshell mixer, and the external toner (YA1) is added. ) Was obtained.
To 500 parts of toner particles (MA1), 10 parts of silica particles (RY50, Nippon Aerosil) and 11 parts of titanium oxide particles (Tayca, JMT2000) are added, mixed with a Henshell mixer, and the external toner (MA1) is added. Obtained.
To 500 parts of toner particles (CA1), 10 parts of silica particles (RY50, Nippon Aerosil) and 7 parts of titanium oxide particles (Taika, JMT2000) are added, mixed with a Henshell mixer, and the external toner (CA1) is added. Obtained.
To 500 parts of toner particles (KA1), 10 parts of silica particles (RY50, Nippon Aerosil) and 4 parts of titanium oxide particles (TAYCA, JMT2000) are added, mixed with a Henschel mixer, and an external toner (KA1) is added. Obtained.

[Preparation of developer]
10 parts of each external toner and 100 parts of the carrier (1) are placed in a V-blender, stirred for 20 minutes, mixed, and then sieved with a sieve having a mesh size of 212 μm to develop agents (YA1), (MA1), ( A set of CA1) and (KA1) was obtained.
When the toner was separated from each developer and the titanium concentration ratio between the toners was calculated according to the measurement method described above, the toner (YA1): toner (MA1): toner (CA1): toner (KA1) = 1.7: It was 2.2: 1.4: 0.8.

[Image formation and image evaluation]
The set of the developer was placed in each of the four developing devices of Fuji Xerox's DocuPrint C3200A, and an image was formed in the same manner as in Example 1 to evaluate density unevenness, density decrease and fog. The density unevenness was G1, the density decrease was G1, and the fog was G1.

10 Image forming apparatus 12 Housing 14 Accommodating part 16 Extracting roll 18 Aligning roll 20 Image forming unit 22Y Photoreceptor (example of first image holder)
22M Photoreceptor (Example of 2nd image retainer)
22C Photoreceptor (Example of 3rd image holder)
22K Photoreceptor (Example of 4th image retainer)
24Y charging roll (an example of the first charging means)
24M charging roll (an example of the second charging means)
24C charging roll (an example of a third charging means)
24K charging roll (an example of the fourth charging means)
26Y developing device (an example of the first developing means)
26M developing device (example of second developing means)
26C developing device (example of third developing means)
26K developing device (example of 4th developing means)
28Y Photoreceptor Cleaning Device (Example of First Cleaning Means)
28M Photoreceptor Cleaning Device (Example of Second Cleaning Means)
28C Photoreceptor Cleaning Device (Example of Third Cleaning Means)
28K Photoreceptor Cleaning Device (Example of Fourth Cleaning Means)
32 Intermediate transcript (an example of the first intermediate transcript)
34 Intermediate transcript (an example of the second intermediate transcript)
36 Intermediate Transcript (Example of Third Intermediate Transcript)
38 Transfer roll (an example of transfer means)
50 Optical scanning device (an example of electrostatic charge image forming means)
52Y, 52M, 52C, 52K Optical beam 60 fixing device (example of fixing means)
62 Heating belt 64 Pressurized roll 66 Conveying roll 68 Discharge section P Recording medium

Claims (9)

It has a first toner, a second toner, a third toner, and a fourth toner containing toner particles and titanium oxide particles externally attached to the toner particles.
The first toner is yellow, the second toner is magenta, the third toner is cyan, and the fourth toner is black.
The titanium concentration ratio of the first to fourth toners is: first toner: second toner: third toner: fourth toner = 1.6 to 1.9: 2.0 to 2.2: 1.2 to 1. .5: Toner set for static charge image development of 0.5 to 1.1. The toner set for developing an electrostatic charge image according to claim 1, wherein the titanium oxide particles are particles containing at least one of titanium oxide and metatitanic acid. Accommodating the toner set for developing an electrostatic charge image according to claim 1 or 2,
A toner cartridge that is attached to and detached from the image forming device. It has a first developer, a second developer, a third developer, and a fourth developer, which contain a toner containing toner particles and titanium oxide particles externally attached to the toner particles.
The first developer is yellow, the second developer is magenta, the third developer is cyan, and the fourth developer is black.
The titanium concentration ratio of the toner contained in the first to fourth developing agents is as follows: first developing agent: second developing agent: third developing agent: fourth developing agent = 1.6 to 1.9: 2.0 to An electrostatic charge image developer set of 2.2: 1.2 to 1.5: 0.5 to 1.1. The electrostatic charge image developer set according to claim 4 , wherein the titanium oxide particles are particles containing at least one of titanium oxide and metatitanic acid. The first image holder, the second image holder, the third image holder, the fourth image holder,
A first charging means for charging the surface of the first image holder, a second charging means for charging the surface of the second image holder, and a third charging means for charging the surface of the third image holder. , The fourth charging means for charging the surface of the fourth image holder, and
Electrostatic image forming means for forming an electrostatic charge image on the surfaces of the charged first image holder, the charged second image holder, the charged third image holder, and the charged fourth image holder. When,
A first developing means that accommodates a first developing agent and uses the first developing agent to develop an electrostatic charge image formed on the surface of the first image holder as a toner image.
A second developing means that accommodates a second developing agent and uses the second developing agent to develop an electrostatic charge image formed on the surface of the second image holder as a toner image.
A third developing means that accommodates a third developing agent and develops an electrostatic charge image formed on the surface of the third image holder as a toner image by the third developing agent.
A fourth developing means that accommodates a fourth developing agent and uses the fourth developing agent to develop an electrostatic charge image formed on the surface of the fourth image holder as a toner image.
A primary intermediate transfer body to which a toner image is transferred from the first image holder and the second image holder, and the second image holder from the upstream side in the rotation direction of the primary intermediate transfer body, the first image holder. The first intermediate transfer body, which these image holders are in contact with in the order of the image holders,
A primary intermediate transfer body to which a toner image is transferred from the third image holder and the fourth image holder, and the fourth image holder and the third image holder from the upstream side in the rotation direction of the primary intermediate transfer body. The second intermediate transfer body, which these image holders are in contact with in the order of the image holders,
A secondary intermediate transfer body to which a toner image is transferred from the first intermediate transfer body and the second intermediate transfer body, and the first intermediate transfer body from the upstream side in the rotation direction of the secondary intermediate transfer body. The third intermediate transcript, to which these primary intermediate transcripts are in contact, in the order of the second intermediate transcript,
A transfer means for transferring the toner image transferred to the surface of the third intermediate transfer body to the surface of the recording medium, and
A fixing means for fixing the toner image transferred to the surface of the recording medium, and
A first cleaning means for cleaning the toner remaining on the surface of the first image holder after the toner image is transferred, and
A second cleaning means for cleaning the toner remaining on the surface of the second image holder after the toner image is transferred, and
A third cleaning means for cleaning the toner remaining on the surface of the third image holder after the toner image is transferred, and
A fourth cleaning means for cleaning the toner remaining on the surface of the fourth image holder after the toner image is transferred, and
With
The first developing agent, the second developing agent, the third developing agent, and the fourth developing agent each contain a toner containing toner particles and titanium oxide particles externally attached to the toner particles. The titanium concentration ratio of the toner contained in the first to fourth developing agents is: first developing agent: second developing agent: third developing agent: fourth developing agent = 1.6 to 1.9: 2.0 to 2. .4: 1.2 to 1.5: 0.5 to 1.1,
Image forming device. The sixth aspect of claim 6, wherein the first developer is yellow, the second developer is magenta, the third developer is cyan, and the fourth developer is black. Image forming device. The image forming apparatus according to claim 6 or 7 , wherein the titanium oxide particles are particles containing at least one of titanium oxide and metatitanic acid. An image forming method for forming an image on a recording medium using the image forming apparatus according to any one of claims 6 to 8.

Images