JP2010085667A - Multicolor toner, image forming method, and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multicolor toner, an image forming method, and an image forming device capable of suppressing transfer failures such as a hollow defect of transfer, and reducing concentration failures resulting from deterioration of transfer efficiency. <P>SOLUTION: The multicolor toner includes four colors of monochromatic toners in which large silica with a primary particle size of 50 nm or more and small silica with a primary particle size of less than 50 nm are added to a toner mother particle externally, and is used for a device that forms a full-color image by transferring the toners in the order of A to D and overlaying toner images. The multicolor toner satisfies the formula 1: ä0.8≥K<SB>A</SB>/L<SB>A</SB>>K<SB>B</SB>/L<SB>B</SB>>K<SB>C</SB>/L<SB>C</SB>>K<SB>D</SB>/L<SB>D</SB>≥0.1} and the formula 2: ä0.5≤(K<SB>A</SB>/L<SB>A</SB>)-(K<SB>D</SB>/L<SB>D</SB>)} in which K represents the toner mother particle coverage by large silica, and L represents the coverage by small silica. The present technology includes the image forming method and the image forming device 10 using four colors of monochromatic toners satisfying the formulas 1 and 2. K<SB>A</SB>and L<SB>A</SB>, K<SB>B</SB>and L<SB>B</SB>, K<SB>C</SB>and L<SB>C</SB>, and K<SB>D</SB>and L<SB>D</SB>are the coverage in toners A, B, C, and D respectively, and toners A to D are selected from the combination of the four colors of the monochromatic toners. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a multicolor toner, an image forming method, and an image forming apparatus.

  In an image forming apparatus such as a laser printer, an electrostatic copying machine, a plain paper facsimile machine, and a composite machine of these using an electrophotographic method, an electrostatic recording method, an electrostatic printing method, etc., first, a latent image holder The surface of the (photosensitive member) is uniformly charged by a charging unit, and then the surface of the latent image holding member is exposed by an exposing unit such as a semiconductor laser or a light emitting diode to form an electrostatic latent image. The latent image is visualized into a toner image by developing means. Next, the toner image is directly transferred onto the surface of a printing material such as paper by a transfer unit, or transferred onto the surface of an intermediate transfer member (primary transfer), and then re-transferred onto the surface of a recording material such as paper. After the transfer (secondary transfer), a series of image forming steps is executed by fixing by a fixing unit.

Development methods for developing an electrostatic latent image into a toner image can be broadly classified into two types, dry and wet, and dry development methods are widely used.
Further, as a dry development method, based on the type of monochromatic toner to be used, a development method using a magnetic toner in which magnetic powder is encapsulated in toner base particles having a binder resin (magnetic one-component development method or magnetic 2). Component development methods) and development methods using non-magnetic toner that does not contain magnetic powder (non-magnetic one-component development method or non-magnetic two-component development method).

As an image forming apparatus, an image forming apparatus employing a rotary developing method (one-drum color superposition method) that sequentially forms a plurality of color images on a photoreceptor is known. The rotary development method is attracting attention as a technology that can form a color image with little color misregistration by accurately overlaying a single color toner on a photoconductor, and that can cope with high color image quality.
On the other hand, in recent years, a plurality of photoconductors corresponding to the color of the single color toner are used to form a color image in synchronization with the feeding of the intermediate transfer member, and after color superposition on the intermediate transfer member, An image forming apparatus that employs a tandem developing system that performs secondary transfer on the surface of a recording material has attracted attention. The tandem development system has the advantages of high image quality and excellent high speed.

  In the tandem development method, the transfer position is transferred on the downstream side of the upstream monochrome toner on the monochrome image formed by the monochrome toner having the most upstream transfer position (that is, the monochrome toner first transferred to the intermediate transfer member). A single color image formed by the single color toner is sequentially transferred and stacked to obtain a full color image. Therefore, the single color toner transferred on the upstream side passes through the subsequent transfer steps, and charge is injected every time, so that it is more susceptible to transfer than the single color toner transferred on the downstream side. The electrostatic adhesion force to the intermediate transfer member tends to increase. For this reason, there is a difference in the charge amount between the single color toner transferred on the upstream side and the single color toner transferred on the downstream side, and a part of the full color image (especially, transferred on the upstream side) is transferred to the recording material. A single-color toner) is not transferred from the intermediate transfer member to the recording material but remains on the intermediate transfer member, and a transfer drop-out phenomenon is likely to occur.

  When a transfer failure such as a transfer loss phenomenon occurs, a density failure is caused due to a decrease in transfer efficiency. Further, at the time of fixing by the fixing means, excessive charging leads to problems such as electrostatic scattering and electrostatic offset.

For example, Patent Documents 1 and 2 disclose image forming methods for suppressing transfer defects such as transfer omission phenomenon when S1, S2, S3, and S4 are set in order from a single-color toner that is located upstream and is developed quickly. The amount of silica (external additive) contained in the toner satisfies S1>S2>S3> S4, and the absolute value of the charge amount of the monochromatic toner at this time | Q _S1 / m |, | Q _S2 / m |, | Q _S2 / m |, | Q _S2 / m | uses a single color toner satisfying | Q _S1 / m |> | Q _S2 / m |> | Q _S2 / m |> | Q _S2 / m | It is disclosed.
JP 2002-278143 A JP 2002-278159 A

However, as described in Patent Documents 1 and 2, in the method of defining the additive amount and charge amount of the external additive of the single color toner to be used, the single color toner transferred on the upstream side where the charge amount is set large is downstream. Each time it passed through the transfer position on the side, it was charged up, and the electrostatic adhesion force to the intermediate transfer member was easy to increase. For this reason, there is a large difference between the electrostatic adhesion force of the monochromatic toner transferred on the upstream side and the electrostatic adhesion force of the monochromatic toner transferred on the downstream side, which may cause a transfer failure during the secondary transfer. there were.
In particular, as described in Patent Document 1, changing the addition amount of hydrophobized silica greatly affects the fluidity of a single-color toner, so that it is necessary to set conditions for each color even in the development process. was there.

  The present invention has been made in view of the above circumstances, and realizes a multicolor toner, an image forming method, and an image forming apparatus capable of suppressing transfer defects such as a transfer dropout phenomenon and reducing density defects due to a decrease in transfer efficiency. Objective.

In the multicolor toner of the present invention, large silica having a primary particle diameter of 50 nm or more and small silica having a primary particle diameter of less than 50 nm are externally added to toner base particles containing a binder resin and a colorant as external additives. It is a multi-color toner used in an apparatus that forms yellow toner, cyan toner, magenta toner, and black toner, and sequentially transfers toners A, B, C, and D and superimposes the toner images to form a full color image. When the coverage of the toner base particles with the large silica is K (%) and the coverage of the toner base particles with the small silica is L (%), the following formulas (1) and (2) are satisfied. It is characterized by that.
0.8 ≧ K _A / L _A > K _B / L _B > K _C / L _C > K _D / L _D ≧ 0.1 (1)
0.5 ≦ (K _A / L _A ) − (K _D / L _D ) (2)
In the formulas (1) and (2), K _A and L _A are coverage ratios in the toner A, K _B and L _B are coverage ratios in the toner B, and K _C and L _C are coverage ratios in the toner C. Yes, K _D and L _D are coverages in the toner D, and the toners A, B, C, and D are selected from a combination of the yellow toner, cyan toner, magenta toner, and black toner.

Further, the image forming method of the present invention is a method in which toner A, B, C, and D are sequentially transferred in this order to superimpose toner images to form a full color image, and a toner base containing a binder resin and a colorant. The particles are externally added with large silica having a primary particle diameter of 50 nm or more as external additives and small silica having a primary particle diameter of less than 50 nm, and the coverage of the toner base particles by the large silica is K (%), Four color monochromatic toners satisfying the following formulas (1) and (2) are used when the coverage of the toner base particles with the small silica is L (%).
0.8 ≧ K _A / L _A > K _B / L _B > K _C / L _C > K _D / L _D ≧ 0.1 (1)
0.5 ≦ (K _A / L _A ) − (K _D / L _D ) (2)
In the formulas (1) and (2), K _A and L _A are coverage ratios in the toner A, K _B and L _B are coverage ratios in the toner B, and K _C and L _C are coverage ratios in the toner C. Yes, K _D and L _D are the coverages of the toner D, and the toners A, B, C, and D are selected from a combination of the above-mentioned four color single color toners.

The image forming apparatus of the present invention is a toner base containing a binder resin and a colorant in an apparatus for forming a full color image by sequentially transferring toners A, B, C, and D in order and superimposing the toner images. The particles are externally added with large silica having a primary particle diameter of 50 nm or more as external additives and small silica having a primary particle diameter of less than 50 nm, and the coverage of the toner base particles by the large silica is K (%), Four color monochromatic toners satisfying the following formulas (1) and (2) are used when the coverage of the toner base particles with the small silica is L (%).
0.8 ≧ K _A / L _A > K _B / L _B > K _C / L _C > K _D / L _D ≧ 0.1 (1)
0.5 ≦ (K _A / L _A ) − (K _D / L _D ) (2)
In the formulas (1) and (2), K _A and L _A are coverage ratios in the toner A, K _B and L _B are coverage ratios in the toner B, and K _C and L _C are coverage ratios in the toner C. Yes, K _D and L _D are the coverages of the toner D, and the toners A, B, C, and D are selected from a combination of the above-mentioned four color single color toners.

According to the multicolor toner of the present invention, it is possible to suppress transfer defects such as a transfer dropout phenomenon and reduce density defects due to a decrease in transfer efficiency. The multicolor toner of the present invention is suitable for a full-color image forming apparatus employing a tandem development system, a rotary development system, or the like.
According to the image forming method and the image forming apparatus of the present invention, it is possible to suppress transfer defects such as a transfer dropout phenomenon and reduce density defects due to a decrease in transfer efficiency.

Hereinafter, the present invention will be described in detail.
[Multicolor toner]
The multicolor toner of the present invention comprises a yellow toner, a cyan toner, a magenta toner, and a black toner (hereinafter, these may be referred to as “monochromatic toner”). Each of these monochromatic toners is obtained by externally adding an external additive to the toner base particles, and the coverage of the toner base particles by the external additive is in a specific range. The external additive externally added to the toner base particles adheres to the surface of the toner base particles. A part of the externally added additive may not be attached to the toner base particles but may be included in the monochromatic toner in a free state.

<Toner base particles>
The toner base particles contain a binder resin and a colorant.
(Binder resin)
The binder resin is not particularly limited, but polystyrene resin, acrylic resin, styrene-acrylic copolymer, polyethylene resin, polypropylene resin, vinyl chloride resin, polyester resin, polyamide resin, polyurethane resin. It is preferable to use thermoplastic resins such as polyvinyl alcohol resins, vinyl ether resins, N-vinyl resins, and styrene-butadiene resins. Of these, polystyrene resins and polyester resins are preferable.

Examples of the polystyrene resin include a homopolymer of a styrene monomer and a copolymer of a styrene monomer with another monomer copolymerizable with styrene.
Examples of other monomers copolymerizable with styrene include p-chlorostyrene; vinyl naphthalene; ethylene unsaturated monoolefins such as ethylene, propylene, butylene, and isobutylene; vinyl chloride, vinyl bromide, vinyl fluoride, and the like. Vinyl esters of vinyl acetate, vinyl acetate, vinyl propionate, vinyl benzoate, vinyl butyrate, etc .; methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, dodecyl acrylate, n-acrylate (Meth) acrylates such as octyl, 2-chloroethyl acrylate, phenyl acrylate, methyl α-chloroacrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate; acrylonitrile, methacrylonitrile, acrylamide, etc. Other acrylic acid derivatives; vinyl ethers such as vinyl methyl ether and vinyl isobutyl ether; vinyl ketones such as vinyl methyl ketone, vinyl ethyl ketone and methyl isopropenyl ketone; N-vinyl pyrrole, N-vinyl carbazole, N-vinyl indole, N-vinyl compounds, such as N-vinyl pyrrolidene, etc. are mentioned. These may be used alone or in combination of two or more with a styrene monomer.

The polystyrene resin preferably has two mass average molecular weight (Mw) peaks (referred to as a low molecular weight peak and a high molecular weight peak) in its molecular weight. Specifically, the low molecular weight peak is preferably in the range of 3000 to 20,000, and the high molecular weight peak is preferably in the range of 300,000 to 1,500,000. Moreover, the ratio (Mw / Mn) to the number average molecular weight (Mn) is preferably 10 or more. If the mass average molecular weight peak is within such a range, the monochromatic toner can be easily fixed, and offset resistance can be improved.
The Mw and Mn of the binder resin are measured by measuring the elution time from the column using a molecular weight measuring device (GPC) and comparing with a calibration curve prepared in advance using a standard polystyrene resin. Can be sought.

  As the polyester resin, those obtained by condensation polymerization or co-condensation polymerization of an alcohol component and a carboxylic acid component can be used. The following are mentioned as a component used when synthesize | combining a polyester-type resin.

  Examples of the alcohol component include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1,4-butenediol, 1,5- Diols such as pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol; bisphenol A, hydrogenated bisphenol A, polyoxyethylenated bisphenol A, bisphenols such as polyoxypropylenated bisphenol A; sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipe Taerythritol, tripentaerythritol, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, diglycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, tri Examples thereof include divalent or trivalent or higher alcohols such as methylolethane, trimethylolpropane, 1,3,5, -trihydroxymethylbenzene.

  As the carboxylic acid component, a divalent or trivalent carboxylic acid, an acid anhydride or a lower alkyl ester thereof is used. Maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid , Cyclohexanedicarboxylic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, malonic acid, or n-butyl succinic acid, n-butenyl succinic acid, isobutyl succinic acid, isobutenyl succinic acid, n-octyl succinic acid, n-octenyl succinic acid Divalent carboxylic acids such as alkyl, alkenyl succinic acid such as acid, n-dodecyl succinic acid, n-dodecenyl succinic acid, isododecyl succinic acid, isododecenyl succinic acid; 1,2,4-benzenetricarboxylic acid (trimerit Acid), 1,2,5-benzenetricarboxylic acid, , 5,7-Naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl- Trivalent or higher such as 2-methylenecarboxypropane, 1,2,4-cyclohexanetricarboxylic acid, tetra (methylenecarboxyl) methane, 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, emporic trimer acid, etc. The carboxylic acid of is illustrated.

  It is preferable that the softening point of a polyester-type resin is 110-150 degreeC, More preferably, it is 120-140 degreeC. If the softening point is within the above range, the monochromatic toner can be easily fixed, and offset resistance can be improved.

In addition, the binder resin is preferably a thermoplastic resin from the viewpoint of good fixability, but the amount of cross-linked portion (gel amount) measured using a Soxhlet extractor is 10% by mass or less, more preferably 0. A thermosetting resin may be used as long as the value is within a range of 1 to 10% by mass. By introducing a partially crosslinked structure in this way, the storage stability, shape retention, or durability of the monochromatic toner can be further improved without deteriorating the fixability.
Therefore, it is not necessary to use 100% by mass of the thermoplastic resin as the binder resin, and a crosslinking agent can be added or a part of the thermosetting resin can be used.

  As the thermosetting resin, an epoxy resin, a cyanate resin, or the like can also be used. More specifically, one or more of bisphenol A type epoxy resin, hydrogenated bisphenol A type epoxy resin, novolac type epoxy resin, polyalkylene ether type epoxy resin, cycloaliphatic type epoxy resin, cyanate resin, etc. Combinations are listed.

Further, as the binder resin, in order to improve the dispersibility of the magnetic powder, which will be described later, at least one functional group selected from the group consisting of hydroxy (hydroxy) group, carboxyl group, amino group, and glycidoxy (epoxy) group. It is preferable to use a resin having a group in the molecule.
In addition, it can be confirmed using an FT-IR apparatus whether it has these functional groups, and also can be quantified using a titration method.

The binder resin used in the present invention preferably has a glass transition point (Tg) in the range of 55 to 70 ° C. When the glass transition point of the binder resin is less than 55 ° C., the obtained monochromatic toners are fused with each other and the storage stability tends to be lowered. On the other hand, when the glass transition point of the binder resin exceeds 70 ° C., the fixability of the monochromatic toner tends to be poor.
In addition, the glass transition point of binder resin can be calculated | required from the change point of specific heat using a differential scanning calorimeter (DSC).

(Coloring agent)
As the colorant, it is possible to use colorants of various colors that match the colors of yellow toner, cyan toner, magenta toner, and black toner. Suitable examples are as follows.
Black pigment;
Carbon black such as acetylene black, run black and aniline black.
Yellow pigment;
Yellow lead, yellow lead, zinc yellow, cadmium yellow, yellow iron oxide, mineral fast yellow, nickel titanium yellow, navel yellow, naphthol yellow S, Hansa yellow G, Hansa yellow 10G, benzidine yellow G, benzidine yellow GR, quinoline yellow Rake, Permanent Yellow NCG, Tartrazine Rake etc.
Orange pigment;
Red lead yellow lead, molybdenum orange, permanent orange GTR, pyrazolone orange, vulcan orange, indanthrene brilliant orange RK, benzidine orange G, indanthrene brilliant orange GK, etc.

Red pigment;
Bengala, Cadmium Red, Lead Red, Mercury Cadmium, Permanent Red 4R, Risor Red, Pyrazolone Red, Watching Red Calcium Salt, Lake Red D, Brilliant Carmine 6B, Eosin Lake, Rhodamine Lake B, Alizarin Lake, Brilliant Carmine 3B, etc. .
Purple pigment;
Manganese purple, fast violet B, methyl violet lake, etc.
Blue pigment;
Bitumen, cobalt blue, alkali blue lake, Victoria blue lake, phthalocyanine blue, metal-free phthalocyanine blue, phthalocyanine blue partially chlorinated, fast sky blue, indanthrene blue BC, etc.
Green pigment;
Chrome green, chromium oxide, pigment green B, malachite green lake, final yellow green G, etc.
White pigment;
Zinc white, titanium oxide, antimony white, zinc sulfide, barite powder, barium carbonate, clay, silica, white carbon, talc, alumina white, etc.

  In addition, when using a monochromatic toner as a magnetic toner, you may use a magnetic powder as a coloring agent. Examples of the magnetic powder include metals or alloys exhibiting ferromagnetism, such as magnetite and ferrite powder, or compounds containing these elements.

In the case other than the magnetic toner, the content of the colorant is preferably 2 to 20 parts by mass, more preferably 5 to 15 parts by mass with respect to 100 parts by mass of the binder resin.
In the case of magnetic toner, the content of the magnetic powder is preferably 50 to 200 parts by mass with respect to 100 parts by mass of the binder resin.

(Other)
The toner base particles may further contain a charge control agent (charge control agent) or a wax (release agent).
The charge control agent is for controlling the triboelectric charging characteristics of the single color toner, and a charge control agent for positive charge control and / or negative charge control is used according to the charge polarity of the single color toner.
The type of charge control agent is not particularly limited. For example, in the case of a charge control agent exhibiting positive chargeability, a resin type in which an amine compound is bound to nigrosine, a quaternary ammonium salt compound, or a resin. Examples thereof include a charge control agent. When used for a color toner, a colorless or white one is preferable.
The content of the charge control agent is preferably 0.5 to 10 parts by mass and more preferably 1 to 5 parts by mass with respect to 100 parts by mass of the binder resin.

  The wax is not particularly limited, but for example, plant wax such as carnauba wax, sugar wax, and wood wax; animal wax such as beeswax, insect wax, whale wax, wool wax; Examples thereof include Fischer-Tropsch (hereinafter sometimes referred to as “FT”) wax, synthetic hydrocarbon wax such as polyethylene wax and polypropylene wax. Among these, from the viewpoint of dispersibility, FT wax or polyethylene wax having an ester in the side chain is preferable.

  The wax preferably has an endothermic main peak in a range of 70 to 120 ° C. in an endothermic curve obtained by a differential scanning calorimeter. When the endothermic main peak is less than 70 ° C., toner blocking and hot offset may occur. On the other hand, when the endothermic main peak exceeds 120 ° C., low-temperature fixability tends to be difficult to obtain.

  The content of the wax is preferably 0.1 to 20 parts by mass with respect to 100 parts by mass of the binder resin. When the wax content is less than 0.1 parts by mass, it is difficult to obtain a sufficient wax effect. On the other hand, when the content of the wax exceeds 20 parts by mass, the blocking resistance of the monochromatic toner is lowered, and the detachment from the monochromatic toner may occur.

(Method for producing toner mother particles)
The toner base particles can be produced by a known kneading and pulverizing method, polymerization method, spinning method or the like. For example, in the case of a kneading and pulverizing method, it is manufactured by the following procedure. After mixing the necessary materials such as the binder resin, colorant, charge control agent, wax, etc. for each color monochromatic toner with a mixer such as a Henschel mixer, and melt-mixing with a twin-screw extruder or the like (melt-mixing step) ), Coarsely pulverized by a pulverizer such as a hammer mill, and further finely pulverized by an airflow pulverizer such as a jet mill or a mechanical pulverizer such as a turbo mill. Thereafter, the particles are classified by a classifier such as an airflow classifier (particle forming step) to obtain toner base particles corresponding to the single color toner of each color.

The toner base particles thus obtained preferably have a volume-based center particle size of 5 to 9 μm.
The volume-based center particle size of the toner base particles is, for example, a particle size distribution measuring device “Multimizer III” manufactured by Beckman Coulter, Inc. And a solution obtained by ultrasonically dispersing for 1 minute is represented by a value calculated from the measured value of the particle size distribution measured under the condition of an aperture diameter of 100 μm.

<External additive>
In the present invention, large silica having a primary particle diameter of 50 nm or more and small silica having a primary particle diameter of less than 50 nm are used in combination as external additives. In the present invention, each of the small silica and the large silica may use one type of silica or two or more types of silica.
The primary particle size of the external additive is, for example, an enlarged photograph of the external additive taken by a scanning electron microscope (SEM, manufactured by JEOL Ltd., “JSM-880”) at a magnification of 30,000 times, and image analysis. It can be determined by measuring the diameter or maximum diameter of the particles as the primary particle diameter using an apparatus. Note that it is sufficient to take 50 enlarged externally selected additives for taking a magnified picture by SEM.

(Large silica)
Large silica plays a role of a spacer, and can adjust the adhesion of monochromatic toner. As more large silica is externally added, a space (space) tends to exist between the intermediate transfer member and the adhesion tends to be weakened.
The primary particle diameter of large silica is 50 nm or more. From the viewpoint of suppressing development defects such as toner scattering and fogging due to image defects due to a decrease in fluidity of the single color toner, and a decrease in charge imparting ability due to desorption from the single color toner and adhering to the carrier described later (spent). The upper limit of the primary particle diameter is preferably 100 nm or less.
The large silica is not particularly limited as long as it has a primary particle diameter of 50 nm or more, and known silica used as an external additive can be used.
The external addition amount of large silica is preferably 0.5 to 4.0 parts by mass, and more preferably 0.7 to 3.0 parts by mass with respect to 100 parts by mass of the toner base particles.

(Small silica)
Small silica imparts fluidity to a single color toner.
The primary particle size of the small silica is less than 50 nm. From the viewpoint of suppressing a decrease in the life of the toner due to embedding in the surface of the toner base particles, the lower limit of the primary particle diameter is preferably 25 nm or more.
The small silica is not particularly limited as long as the primary particle diameter is less than 50 nm, and known silica used as an external additive can be used.
The external addition amount of the small silica is preferably 1.0 to 3.0 parts by mass and more preferably 1.6 to 2.8 parts by mass with respect to 100 parts by mass of the toner base particles.

(Other external additives)
In the present invention, as long as the effects of the present invention are not impaired, other external additives other than the small silica and the large silica described above may be used in combination.
Examples of other external additives include alumina, magnetite, tin oxide, titanium oxide, strontium oxide, and various resin powders.
The external addition amount of other external additives is set in an appropriate range depending on the type, specific gravity, particle diameter, etc. of the external additive to be used.

<Method for producing monochromatic toner>
The monochromatic toner is obtained by adding an external additive to the toner base particles corresponding to each color described above (external addition) and mixing with a mixer such as a Henschel mixer.
The monochromatic toner thus obtained may be used as it is as a one-component developer to constitute a multicolor toner, or may be used as a two-component developer in combination with a carrier to constitute a multicolor toner.
When combined with the carrier, the addition amount of the monochromatic toner is preferably 6 to 15 parts by mass and more preferably 8 to 12 parts by mass with respect to 100 parts by mass of the carrier.

  Carriers include particles of iron, oxidized iron, reduced iron, magnetite, copper, silicon steel, ferrite, nickel, cobalt, etc., particles of alloys of these materials with manganese, zinc, aluminum, etc., iron-nickel alloys , Particles such as iron-cobalt alloy, titanium oxide, aluminum oxide, copper oxide, magnesium oxide, lead oxide, zirconium oxide, silicon carbide, magnesium titanate, barium titanate, lithium titanate, lead titanate, lead zirconate, Examples include magnetic materials such as ceramic particles such as lithium niobate, and particles of a high dielectric constant material such as ammonium dihydrogen phosphate, potassium dihydrogen phosphate, and Rochelle salt. In addition, a resin carrier in which the magnetic material is dispersed in a resin can be used.

Further, as the carrier, a so-called resin coat type carrier in which the above-described magnetic body is used as a carrier core material and the surface thereof is coated with a resin coating layer can also be used.
Examples of resins include (meth) acrylic polymers, styrene polymers, styrene- (meth) acrylic copolymers, olefin polymers (polyethylene, chlorinated polyethylene, polypropylene, etc.), polyvinyl chloride, polyvinyl acetate. , Polycarbonate, cellulose resin, polyester resin, unsaturated polyester resin, polyamide resin, polyurethane resin, epoxy resin, silicone resin, fluorine resin (polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, etc.), phenol resin, xylene Various conventionally known resins can be used for coating carriers such as resins, diallyl phthalate resins, polyacetal resins and amino resins. These are used alone or in admixture of two or more.

10-200 micrometers is preferable and, as for the mass average particle diameter of a carrier, 30-150 micrometers is more preferable.
The coating layer may contain additives for adjusting the properties of the coating layer such as silica, alumina, carbon black, fatty acid metal salt, silane coupling agent, titanate coupling agent, etc. it can.
Although it does not restrict | limit especially as a film thickness of a coating layer, Specifically, it represents with the coating amount to a carrier core material, It is preferable to coat 0.01-10 mass parts with respect to 100 mass parts of carrier core materials, More preferably, it is 0.05-5 mass parts.

The multicolor toner of the present invention is composed of the above-described four single color toners (yellow toner, cyan toner, magenta toner, and black toner), and sequentially transfers the toner images in the order of toners A, B, C, and D. Used in an apparatus that forms a full color image by superimposing.
Each single color toner constituting the multicolor toner of the present invention has the following formula when the coverage of the toner base particles with large silica is K (%) and the coverage of the toner base particles with small silica is L (%). Satisfy (1) and (2).
0.8 ≧ K _A / L _A > K _B / L _B > K _C / L _C > K _D / L _D ≧ 0.1 (1)
0.5 ≦ (K _A / L _A ) − (K _D / L _D ) (2)

In the formulas (1) and (2), K _A and L _A are coverage ratios in the toner A, K _B and L _B are coverage ratios in the toner B, and K _C and L _C are coverage ratios in the toner C. Yes, K _D and L _D are the coverages of the toner D, and the toners A, B, C, and D are selected from a combination of yellow toner, cyan toner, magenta toner, and black toner.

If four-color single-color toners satisfying the expressions (1) and (2) are used, a multi-color toner in which the adhesion force F of each single-color toner satisfies the following expression (3) can be obtained. In the formula (3), F _A is the force of adhesion of toner A, F _B is the adhesion of the toner B, F _C is the adhesion of the toner C, F _D is the adhesion of the toner D Yes, toners A, B, C, and D are selected from a combination of yellow toner, cyan toner, magenta toner, and black toner.
F _A <F _B <F _C <F _D (3)

  Normally, the single color toner (toner A) having the most upstream transfer position is first transferred to the intermediate transfer member, and therefore, the subsequent transfer process is also passed, and the remaining three color single color toners are transferred. Charges are injected every time, and the electrostatic adhesion force to the intermediate transfer member tends to increase. For this reason, a difference in charge amount between toner A and toner D is likely to occur, and a transfer skip phenomenon is likely to occur during secondary transfer onto a recording material such as paper.

  However, in the case of the multicolor toner of the present invention, the adhesion of the monochromatic toner is set so that the adhesion of the monochromatic toner becomes stronger as the transfer order is later. The weakest of the four color single color toners. Therefore, even if the monochromatic toner transferred on the upstream side passes through the transfer process on the downstream side and the electrostatic adhesion force increases, it is possible to control the physical adhesion force in advance. Secondary transfer is possible, and as a result, the image can be transferred without omission and the transfer omission phenomenon can be suppressed.

In the above formula (1), the value of K A _/ L _A is greater than 0.8, the spacer effect, adhesion of the single-color toner (physical adhesion force) can be reduced, a small silica Since the ratio is reduced, the fluidity and developability of the toner A are likely to be lowered. On the other hand, if the value of K _D / L _D is less than 0.1, the fluidity of the toner D is good, but the ratio of large silica is reduced, so that the spacer effect cannot be obtained sufficiently and the adhesive force is reduced. As the strength increases, the small silica is buried in the toner base particles, and the developability tends to decrease.
In the above formula (2), when the value of {(K _A / L _A ) − (K _D / L _D )} is smaller than 0.5, each single color toner (particularly, toner A and toner D) is attached. A sufficient difference in adhesion cannot be obtained, and it becomes difficult to suppress transfer defects such as a transfer dropout phenomenon and a decrease in density.

The coverage of toner base particles with large silica (hereinafter referred to as “large silica coverage K”) is obtained as follows.
First, 10 toner particles to which an external additive has been added (monochromatic toner particles having an external additive attached to the surface of the toner base particle) are analyzed by SEM (manufactured by JEOL Ltd., “JSM-880”). Take an image by observing at a magnification of 30,000 times or more. At this time, it is preferable to image the surface of the toner base particles as flat as possible. Next, for the obtained image, as image analysis, for example, image analysis software (“Win ROOF” manufactured by Mitani Corporation) is used to determine the area of the toner base particles and the projected area of the large silica in one toner particle. (The toner particle and the outline portion of the large silica are selected in a freehand range, and the number of dots in the range is defined as the area.) The coverage of one toner particle is calculated by the following equation (4).
Coverage (%) per toner particle = (total projected area of large silica / area of toner base particle) × 100 (4)
Then, for each of the 10 toner particles, the coverage of one toner particle is obtained, and the average of these values is defined as “large silica coverage (unit:%)”.

Further, the coverage of the toner base particles with small silica (hereinafter referred to as “small silica coverage L”) is obtained as follows.
First, in the same manner as the method for obtaining the coverage of the entire external additive, an image of 10 toner particles is taken by SEM (manufactured by JEOL Ltd., “JSM-880”). At this time, it is preferable to image the surface of the toner base particles as flat as possible. Next, with respect to the obtained image, as image analysis, for example, image analysis software (“Win ROOF” manufactured by Mitani Corporation) is used to determine the area of toner base particles and the projected area of small silica in one toner particle. (A free particle is used to select a range of toner particle and small silica outlines, and the number of dots within the range is defined as an area.) The coverage of each toner particle is calculated by the following equation (5).
Coverage (%) per toner particle = (total projected area of small silica / area of toner base particle) × 100 (5)
Then, for each of the 10 toner particles, the coverage of one toner particle is obtained, and the average of these values is defined as “small silica coverage (unit:%)”.

The covering ratio K of large silica and the covering ratio L of small silica can be controlled by adjusting the additive amount (external additive amount) of the external additive according to the particle size of the toner base particles, for example. The coverage tends to increase as the amount of external additive increases, and the coverage tends to decrease as the amount of external additive decreases.
In the present invention, the external addition amount of large silica and small silica may be adjusted so that the coverage of each single color toner satisfies the above formulas (1) and (2).
As the particle diameter of the external additive increases, the external additive amount tends to increase in order to adjust the coverage.

  The multicolor toner of the present invention is used in an apparatus for forming a full color image by sequentially transferring toners A, B, C, and D in order and superimposing the toner images. Examples of such an image forming apparatus include an image forming apparatus that employs a tandem developing system, an image forming apparatus that employs a rotary developing system, and the like.

  The multi-color toner of the present invention described above is a four-color single color toner (yellow toner, cyan toner, magenta) in which the ratio of the coverage ratio K to the coverage ratio L of each single color toner satisfies the above (1) and (2). Toner, and black toner), the adhesion force (physical adhesion force) of the monochromatic toner can be set smaller as it goes to the transfer position on the upstream side. Therefore, even if the upstream monochromatic toner passes through the downstream transfer process and the electrostatic adhesion increases, good secondary transfer is possible. As a result, transfer defects such as transfer dropout phenomenon and density reduction occur. And density defects due to a decrease in transfer efficiency can be reduced.

[Image forming method]
The image forming method of the present invention is a method for forming a full-color image by using toners of four colors and transferring them sequentially in the order of toners A, B, C, and D and superimposing the toner images.
The four-color single-color toner is obtained by externally adding large silica having a primary particle diameter of 50 nm or more and small silica having a primary particle diameter of less than 50 nm as external additives to toner base particles containing a binder resin and a colorant. When the coverage of the toner base particles with large silica is K (%) and the coverage of the toner base particles with small silica is L (%), the following formulas (1) and (2) are satisfied. .
0.8 ≧ K _A / L _A > K _B / L _B > K _C / L _C > K _D / L _D ≧ 0.1 (1)
0.5 ≦ (K _A / L _A ) − (K _D / L _D ) (2)

In the formulas (1) and (2), K _A and L _A are coverage ratios in the toner A, K _B and L _B are coverage ratios in the toner B, and K _C and L _C are coverage ratios in the toner C. Yes, K _D and L _D are the coverages of the toner D, and the toners A, B, C, and D are selected from a combination of four single color toners.

By using four color monochromatic toners that satisfy the equations (1) and (2), the adhesion force F of each monochromatic toner can satisfy the following equation (3). In the formula (3), F _A is the force of adhesion of toner A, F _B is the adhesion of the toner B, F _C is the adhesion of the toner C, F _D is the adhesion of the toner D Yes, toners A, B, C, and D are selected from a combination of four single color toners.
F _A <F _B <F _C <F _D (3)

  Therefore, according to the image forming method of the present invention, the adhesive force of the single color toner is set to become stronger as the transfer order is later, and therefore the adhesive force of the single color toner (toner A) whose transfer position is the most upstream (toner A) (Physical adhesion force) is the weakest among the four color monochromatic toners. Therefore, even if charges are injected during the transfer of the toners B to D, an increase in adhesion to the intermediate transfer member can be reduced, and the single color toner transferred on the upstream side and the single color toner transferred on the downstream side (particularly the toner A). And toner D) are less likely to have a difference in adhesion. As a result, it is possible to suppress a transfer dropout phenomenon in the secondary transfer, and to reduce a density decrease due to the transfer.

The four color monochromatic toners satisfying the above formulas (1) and (2) may be selected from a combination of yellow toner, cyan toner, magenta toner, and black toner. The yellow toner, cyan toner, magenta toner, and black toner are not particularly limited as long as the ratio of the coverage ratio K and the coverage ratio L of each single color toner satisfies the above formulas (1) and (2). It is preferable to use a yellow toner, a cyan toner, a magenta toner, and a black toner constituting the multicolor toner.
As described above, the coverage can be controlled by adjusting the external addition amount of the external additive.

  The image forming method according to the present invention described above uses four color single color toners in which the ratio of the coverage ratio K and the coverage ratio L of each single color toner satisfies the above formulas (1) and (2). As the transfer position is reached, the adhesion (physical adhesion) of the monochromatic toner can be set smaller. Therefore, even if the upstream monochromatic toner passes through the downstream transfer process and the electrostatic adhesion increases, good secondary transfer is possible. As a result, transfer defects such as transfer dropout phenomenon and density reduction occur. And density defects due to a decrease in transfer efficiency can be reduced.

[Image forming apparatus]
The image forming apparatus of the present invention is an apparatus for forming a full-color image by using toners of four colors and transferring them sequentially in the order of toners A, B, C, and D and superimposing the toner images.
Here, an example of the image forming apparatus of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic configuration diagram showing a main part of a tandem type full-color image forming apparatus (hereinafter simply referred to as “image forming apparatus”) 10. The image forming apparatus 10 includes image forming units 11 (11A, 11B, 11C, and 11D) that respectively correspond to four single color toners. These image forming units 11 are arranged in order of image forming units 11A, 11B, 11C, and 11D from the upstream side, and are filled with toners A, B, C, and D, respectively.

The image forming unit 11 includes a photoconductor 12 on which a toner image is formed, a charging member 13, an exposure member 14, and a developing device 15. The developing device 15 contains a single color toner. Yes. Examples of the photoreceptor 12 include an amorphous silicon photoreceptor and an organic photoreceptor.
In each image forming unit 11, the surface of the photoreceptor 12 charged by the charging member 13 is exposed by the exposure member 14 to form an electrostatic latent image, and the electrostatic latent image is developed by the developing device 15. As a result, a toner image is formed on the photoreceptor 12.

Further, the image forming apparatus 10 includes an intermediate transfer body 16 to which the toner image formed on the photoconductor 12 is transferred, and the toner image formed on the photoconductor 12 is used for each image formation. The primary transfer roll 17 disposed opposite the unit 11 is primarily transferred to the surface of the intermediate transfer body 16, that is, the transfer surface 16a. At this time, the toner images on the photoconductors 12 are primarily transferred to the intermediate transfer body 16 in the order of the image forming units 11A, 11B, 11C, and 11D, and the toner images are superposed in the order of the toners A, B, C, and D. At the same time, a full-color toner image is formed on the transfer surface 16 a of the intermediate transfer body 16.
The full-color toner image transferred onto the transfer surface 16a of the intermediate transfer member 16 in this manner is further transferred to a recording material 19 such as paper by the action of the secondary transfer roll 18.

  In the figure, reference numeral 20 denotes a drive roll for the intermediate transfer member 16, reference numeral 21 denotes a backup roll for the secondary transfer roll 18, reference numeral 22 denotes a tension roll, reference numeral 23 denotes a cleaning blade, and reference numeral 24 denotes a fixing device.

The four color monochromatic toners accommodated in the developing device 15 of each image forming unit 11 include toner base particles containing a binder resin and a colorant, large silica having a primary particle diameter of 50 nm or more as an external additive, Small silica having a primary particle diameter of less than 50 nm is externally added, the coverage of the toner base particles with large silica is K (%), and the coverage of the toner base particles with the small silica is L (%). Sometimes, the following expressions (1) and (2) are satisfied.
0.8 ≧ K _A / L _A > K _B / L _B > K _C / L _C > K _D / L _D ≧ 0.1 (1)
0.5 ≦ (K _A / L _A ) − (K _D / L _D ) (2)

In the formulas (1) and (2), K _A and L _A are coverage ratios in the toner A, K _B and L _B are coverage ratios in the toner B, and K _C and L _C are coverage ratios in the toner C. Yes, K _D and L _D are the coverages of the toner D, and the toners A, B, C, and D are selected from a combination of four single color toners.

By using four color monochromatic toners that satisfy the equations (1) and (2), the adhesion force F of each monochromatic toner can satisfy the following equation (3). In the formula (3), F _A is the force of adhesion of toner A, F _B is the adhesion of the toner B, F _C is the adhesion of the toner C, F _D is the adhesion of the toner D Yes, toners A, B, C, and D are selected from a combination of four single color toners.
F _A <F _B <F _C <F _D (3)

  Normally, the monochromatic toner (toner A) accommodated in the developing device 15 of the image forming unit 11A having the most upstream transfer position is first primarily transferred to the intermediate transfer body 16, and therefore the subsequent transfer positions (that is, The image forming units 11B, 11C, and 11D and the primary transfer rolls 17 disposed so as to pass through the image forming units 11B, 11C, and 11D also pass therethrough, and the remaining three color toners (toners B, C, and D) are transferred to the primary transfer. Each time the charge is injected, the electrostatic adhesion to the intermediate transfer member 16 is likely to increase. For this reason, good secondary transfer is not performed, and a transfer dropout phenomenon and density unevenness are liable to occur during secondary transfer onto a recording material 19 such as paper.

  However, with the image forming apparatus 10 of the present invention, the adhesion force (physical adhesion force) of the single color toner (toner A) having the most upstream transfer position is the weakest among the four color single color toners. Therefore, even if charges are injected during the transfer of the toners B to D, an increase in adhesion to the intermediate transfer member can be reduced, and the single color toner transferred on the upstream side and the single color toner transferred on the downstream side (particularly the toner A). And toner D) are less likely to have a difference in adhesion. As a result, it is possible to suppress a transfer dropout phenomenon in the secondary transfer, and to reduce a density decrease due to the transfer.

The four color monochromatic toners satisfying the above formulas (1) and (2) may be selected from a combination of yellow toner, cyan toner, magenta toner, and black toner. The yellow toner, cyan toner, magenta toner, and black toner are not particularly limited as long as the ratio of the coverage ratio K and the coverage ratio L of each single color toner satisfies the above formulas (1) and (2). It is preferable to use a yellow toner, a cyan toner, a magenta toner, and a black toner constituting the multicolor toner.
As described above, the coverage can be controlled by adjusting the external addition amount of the external additive.

  The image forming apparatus according to the present invention described above uses four color single color toners in which the ratio of the coverage ratio K to the coverage ratio L of each single color toner satisfies the above formulas (1) and (2). As the transfer position is reached, the adhesion (physical adhesion) of the monochromatic toner can be set smaller. Therefore, even if the upstream monochromatic toner passes through the downstream transfer process and the electrostatic adhesion increases, good secondary transfer is possible. As a result, transfer defects such as transfer dropout phenomenon and density reduction occur. And density defects due to a decrease in transfer efficiency can be reduced.

  Note that the image forming apparatus of the present invention is not limited to the apparatus adopting the above-described tandem developing method, and may be an apparatus adopting a rotary developing method, for example.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to a following example.
Various measurements and evaluations in Examples and Comparative Examples were performed as follows.

(1) Measurement of coverage of toner base particles with large silica For 10 toner particles to which an external additive was added, the surface of the toner base particles as flat as possible was made into SEM (manufactured by JEOL Ltd., “JSM-880”). The images were observed at a magnification of 30,000. Next, the obtained image is subjected to image analysis software (“Win ROOF”, manufactured by Mitani Corporation), and one toner particle (a toner particle having an external additive attached to the surface of the toner base particle). The area of the toner base particles and the projected area of the large silica were determined (the toner particles and the outline of the large silica were selected by freehand, and the number of dots within the range was defined as the area), and the following formula (4) Thus, the coverage of one toner particle was calculated.
Coverage (%) per toner particle = (total projected area of large silica / area of toner base particle) × 100 (4)
Then, for each of the 10 toner particles, the coverage of one toner particle was obtained, and the average of these values was defined as “large silica coverage (K)”.

(2) Measurement of coverage of toner base particles with small silica In the same manner as in (1), for as many as 10 toner particles to which an external additive has been added, the surface of the toner base particles as flat as possible is measured with an SEM at a magnification of 30,000. The image is photographed by observing the image at a magnification, and the area of the toner base particle and the projected area of the small silica in one toner particle are obtained by using image analysis software. The coverage was calculated.
Coverage (%) per toner particle = (total projected area of small silica / area of toner base particle) × 100 (5)
Then, for each of the 10 toner particles, the coverage of one toner particle is obtained, and the average of these values is defined as “small silica coverage (L)”.

(3) Measurement of adhesion of monochromatic toner Place monochromatic toner on a grounded glass substrate and set the surface on which monochromatic toner is placed so that it faces the outside of the rotating surface of the centrifuge (manufactured by KUBOTA). The change in the remaining amount of monochromatic toner with respect to the rotational speed of the stage is confirmed by microscopic observation, and the adhesive force is calculated from the rate of change, and the weakest adhesive force is “1” and the strongest adhesive force is “11”. As the numerical value increased from 1 to 11, the adhesion strength increased, and the evaluation was made in 11 stages.

(4) Evaluation of transfer dropout 10 parts by mass of each monochromatic toner were mixed with 100 parts by mass of a magnetic carrier (Cu-Zn ferrite particles having a mass average particle diameter of 35 μm coated with silicone resin; manufactured by Powdertech). As a two-component developer, set in a quadruple tandem full-color page printer (manufactured by Kyocera Mita, “FS-C5016”) and image evaluation pattern (normal temperature and humidity environment (temperature: 23 ° C., relative humidity 60% RH)) Characters, dot images, and line images) were printed (single print), and the obtained images were visually evaluated. Judgment is `` O '' when no transfer omission occurs, `` △ '' when a slight transfer omission occurs, and `` X '' when an apparent transfer omission occurs, “○” was accepted.

(5) Measurement of image density In the same manner as in (4), a monochromatic toner and a magnetic carrier are mixed to form a two-component developer, set on a four-tandem full-color page printer, and an image evaluation pattern (100% solid band image) Was printed continuously 100,000 sheets. For the solid image (initial image) printed on the first sheet and the solid image (post-printing image) printed on the 100,000th sheet, a Macbeth reflection densitometer (“RD914” manufactured by Gretag Macbeth Co., Ltd.) was used. The image density (ID) was measured. In the judgment, an initial image having an image density of 1.20 or higher and an after-printing image having an image density of 1.10 or higher were accepted.

(6) Evaluation of image unevenness In the same manner as in (4), a single-color toner and a magnetic carrier are mixed to form a two-component developer, which is set on a quadruple tandem full-color page printer, and an image evaluation pattern (A4 size entire surface 100% solid image) ) Was printed, and the obtained images were visually evaluated. The determination is “◯” when the image density unevenness is not generated, “△” when the image density unevenness is slightly generated, and “X” when the image density unevenness is clearly generated, “○” was accepted.

(7) Evaluation of transfer efficiency In the same manner as in (4), a single-color toner and a magnetic carrier are mixed to form a two-component developer, set on a quadruple tandem full-color page printer, and an image evaluation pattern (100% solid strip image) Is printed. In one sheet of printing, the toner amount per unit area of the toner image on the intermediate transfer body immediately before secondary transfer (toner amount before transfer) and the unit of toner image remaining on the intermediate transfer body immediately after secondary transfer The toner amount per area (toner amount after transfer) was measured, and the transfer efficiency was calculated from the following equation (6). The determination was made that the transfer efficiency was 95% or more. The toner amount was measured by directly sucking the toner image using a Q / M meter (manufactured by TREC, “210HS-2A”).
Transfer efficiency (%) = {(toner amount before transfer−toner amount after transfer) / toner amount before transfer} × 100 (6)

[Example 1]
<Preparation of binder resin>
Put 300 parts by mass of xylene in a reaction vessel connected with a thermometer, a stirrer, a nitrogen introduction tube, and a reflux tube. While continuously introducing nitrogen from the nitrogen introduction tube, heat the reaction vessel to adjust the liquid temperature. While maintaining the temperature at 170 ° C., a solution obtained by dissolving 845 parts by mass of styrene, 155 parts by mass of n-butyl acrylate, and 8.5 parts by mass of di-tert-butyl peroxide in 125 parts by mass of xylene was added to the above reaction vessel. The solution was added dropwise over a period of time. After completion of the addition, the mixture was further stirred at 170 ° C. for 1 hour, and then the solvent was removed to prepare a styrene-n-butyl acrylate copolymer as a binder resin.

<Manufacture of yellow toner>
To 92 parts by mass of the previously produced binder resin (styrene-n-butyl acrylate copolymer), 4 parts by mass of a yellow pigment (manufactured by Sanyo Color Co., Ltd., “Fast Yellow FG”) as a colorant, and as a charge control agent After mixing 1 part by mass of a quaternary ammonium salt (Orient Chemical Industries, "Bontron P-51") and 3 parts by mass of a wax (Sazol, "Sazol Wax H1") with a Henschel mixer for 3 minutes The mixture was melt kneaded with a twin screw extruder, cooled, and coarsely pulverized with a hammer mill. Further finely pulverized by a mechanical pulverizer was classified by an airflow classifier to obtain toner base particles having a volume-based center particle diameter of 7 μm.
The volume-based center particle size of the toner base particles is determined by using a particle size distribution measuring device (“Multimizer III”, manufactured by Beckman Coulter, Inc.) and using the Isoton II diluent as a dispersion medium. A solution in which particles were added and ultrasonically dispersed for 1 minute was calculated from the measured value of the particle size distribution measured under the condition of an aperture diameter of 100 μm.

With respect to 100 parts by mass of the obtained toner base particles, 3.0 parts by mass of large silica (manufactured by CABOT, primary particle diameter: 70 ± 15 nm) as an external additive, and small silica (manufactured by Nippon Aerosil Co., Ltd., primary particle diameter: 1.7 parts by mass of 20 ± 5 nm) and 0.9 parts by mass of titanium oxide (“EC-100T1J” manufactured by Titanium Industry Co., Ltd.) were added and mixed for 5 minutes with a Henschel mixer to obtain a yellow toner. With respect to the obtained yellow toner, the coverage of the toner base particles with the large silica and the small silica and the adhesion of the monochromatic toner were measured. The results are shown in Table 1.
The primary particle size of the large silica used as the external additive was obtained by taking an enlarged photograph of 50 randomly selected large silicas at a magnification of 30,000 with an SEM, and using the image analysis software, The maximum diameter was determined by measuring as the primary particle diameter. The primary particle diameter of small silica was also measured in the same manner as for large silica.

<Manufacture of cyan toner>
Instead of the yellow pigment, a cyan pigment (“Cyanine Blue KRO” manufactured by Sanyo Dye Co., Ltd.) was used, and each external additive was added so that the coverage of the toner base particles with the large silica and the small silica became the values shown in Table 1. Except for the above, a cyan toner was produced in the same manner as the yellow toner.
With respect to the obtained cyan toner, the adhesion of the monochromatic toner was measured. The results are shown in Table 1.

<Manufacture of magenta toner>
Instead of the yellow pigment, a magenta pigment (manufactured by Sanyo Dye Co., “Pigment Red 8301”) is used, and each external additive is adjusted so that the coverage of the toner base particles with the large silica and the small silica becomes the value shown in Table 1. A magenta toner was produced in the same manner as the yellow toner except that it was added.
With respect to the obtained magenta toner, the adhesion force of the monochromatic toner was measured. The results are shown in Table 1.

<Manufacture of black toner>
Instead of yellow pigment, carbon black (manufactured by Mitsubishi Kasei Co., Ltd., “MA100”) was used, and each external additive was added so that the coverage of the toner base particles with large silica and small silica would be the values shown in Table 1. Except for the above, a black toner was produced in the same manner as the yellow toner.
With respect to the obtained black toner, the adhesion of the monochromatic toner was measured. The results are shown in Table 1.

<Evaluation>
Using the obtained single color toners of four colors, evaluation of transfer dropout, image density, image unevenness, and transfer efficiency was performed based on the evaluation method described above. The results are shown in Table 2.
Each single color toner was set in a quadruple tandem full color page printer so that the order of transfer was yellow toner, cyan toner, magenta toner, and black toner.

[Example 2, Comparative Examples 1 to 6]
<Manufacture of single color toner for each color>
A yellow toner, a cyan toner, a magenta toner, a black toner are the same as in Example 1 except that each external additive is added so that the coverage of the toner base particles with the large silica and the small silica becomes the value shown in Table 1. Each toner was manufactured and the adhesion was measured. The results are shown in Table 1.
In addition, each evaluation was performed in the same manner as in Example 1 using each obtained single color toner. The results are shown in Table 2.

As is apparent from Table 2, in each of the examples using the four-color single-color toner satisfying the above formulas (1) and (2), the transfer dropout phenomenon can be suppressed, the transfer efficiency can be maintained well, and the high The image density was obtained, and the occurrence of image unevenness could be suppressed.
On the other hand, in each of the comparative examples, it was difficult to suppress the occurrence of a transfer dropout phenomenon and the occurrence of image unevenness, and the transfer efficiency and the image density were lower than in each example.
Specifically, in Comparative Example 1, the coverage ratio (K / L) of the four-color single-color toners used increased as the transfer order was later. As a result, as the transfer order was later, the adhesion of the monochromatic toner was weak, and the results of all the evaluation items were inferior to those of the examples. This is because the adhesion force of the first-color toner (yellow toner) transferred first is larger than that of the other single-color toner, and further, the charge is injected into the yellow toner every time the other single-color toner is primarily transferred. Thus, it is considered that the electrostatic adhesion force to the intermediate transfer member is increased, and transfer failure such as a transfer dropout phenomenon occurs during the secondary transfer, resulting in a decrease in transfer efficiency.

  In Comparative Example 2, the coverage ratio (K / L) of the monochrome toner (yellow toner) transferred first is equal to the coverage ratio (K / L) of the monochrome toner (black toner) transferred last. It was the same. As a result, the adhesion strength of the yellow toner and the black toner was almost the same, and the results of all the evaluation items were inferior to the respective examples. This is because the monochromatic toner in the second and subsequent transfer orders was favorably secondary transferred, but the monochromatic toner transferred first has a large adhesive force, and the charge is charged each time another monochromatic toner is primary transferred. It is considered that the transfer efficiency is lowered due to an increase in electrostatic adhesion force to the intermediate transfer member and a transfer failure such as a transfer dropout phenomenon during the secondary transfer.

  In Comparative Example 3, four-color single-color toners were used such that the ratio (K / L) of the coverage of single-color toners decreased as the transfer order was later, but these single-color toners satisfy the above formula (1). As a result, the coverage ratio (K / L) of the first-color toner (yellow toner) transferred first was as large as 1.3. As a result, the proportion of large silica in the yellow toner was increased and the fluidity was lowered, resulting in development failure and transfer failure. In particular, the image density of the image after printing 100,000 sheets (image after printing) was remarkably lowered.

  In Comparative Example 4, four single color toners satisfying the above formula (1) were used, but these single color toners did not satisfy the above formula (2). As a result, a sufficient difference was not obtained in the adhesion of each single color toner (particularly yellow toner and black toner), and the effects of the present invention were not fully exhibited, resulting in transfer failure.

  In Comparative Example 5, four single color toners satisfying the above formula (2) were used. However, these single color toners did not satisfy the above formula (1), and large silica was added to the single color toner (black toner) to be transferred last. Since no external addition was performed, the value of the coverage ratio (K / L) was 0.0. As a result, although the flowability of the black toner was good, the spacer effect due to the large silica was not obtained, the adhesion was remarkably increased, and transfer failure occurred. In particular, the image density of the image after printing 100,000 sheets (image after printing) was remarkably lowered. This is presumably because the developability deteriorated because the small silica was buried in the toner base particles due to the printing durability.

  In Comparative Example 6, since the coverage ratios (K / L) of the four-color single color toners were all the same, the adhesion was all the same. As a result, the results of all evaluation items were inferior to those of the examples. This is because the electrostatic adhesion force to the intermediate transfer member is increased by injecting electric charge into the first-color toner (yellow toner) transferred first, when the other single-color toner is primarily transferred. It is thought that transfer efficiency such as transfer dropout occurred during transfer and transfer efficiency was lowered.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus of the present invention.

Explanation of symbols

  10: Image forming apparatus, 12: Photoconductor, 16: Intermediate transfer member.

Claims (3)

Toner base particles containing a binder resin and a colorant are externally added with large silica having a primary particle diameter of 50 nm or more and small silica having a primary particle diameter of less than 50 nm as external additives, yellow toner, cyan toner, A multicolor toner comprising a combination of magenta toner and black toner, used in an apparatus for sequentially transferring toners A, B, C, and D and superimposing the toner images to form a full color image,
The following formulas (1) and (2) are satisfied when the coverage of the toner base particles with the large silica is K (%) and the coverage of the toner base particles with the small silica is L (%). Multicolor toner.
0.8 ≧ K _A / L _A > K _B / L _B > K _C / L _C > K _D / L _D ≧ 0.1 (1)
0.5 ≦ (K _A / L _A ) − (K _D / L _D ) (2)
In the formulas (1) and (2), K _A and L _A are coverage ratios in the toner A, K _B and L _B are coverage ratios in the toner B, and K _C and L _C are coverage ratios in the toner C. Yes, K _D and L _D are coverages in the toner D, and the toners A, B, C, and D are selected from a combination of the yellow toner, cyan toner, magenta toner, and black toner. In a method of forming a full-color image by sequentially transferring toners A, B, C, and D in order and superimposing toner images,
Toner base particles containing a binder resin and a colorant are externally added with large silica having a primary particle diameter of 50 nm or more and small silica having a primary particle diameter of less than 50 nm as external additives, and the toner made of the large silica Use four-color single-color toners that satisfy the following formulas (1) and (2), where the coverage of the mother particles is K (%) and the coverage of the toner mother particles with the small silica is L (%). An image forming method.
0.8 ≧ K _A / L _A > K _B / L _B > K _C / L _C > K _D / L _D ≧ 0.1 (1)
0.5 ≦ (K _A / L _A ) − (K _D / L _D ) (2)
In the formulas (1) and (2), K _A and L _A are coverage ratios in the toner A, K _B and L _B are coverage ratios in the toner B, and K _C and L _C are coverage ratios in the toner C. Yes, K _D and L _D are the coverages of the toner D, and the toners A, B, C, and D are selected from a combination of the above-mentioned four color single color toners. In an apparatus for sequentially transferring toners A, B, C, and D in order and superimposing toner images to form a full color image,
Toner base particles containing a binder resin and a colorant are externally added with large silica having a primary particle diameter of 50 nm or more and small silica having a primary particle diameter of less than 50 nm as external additives, and the toner made of the large silica Use four-color single-color toners that satisfy the following formulas (1) and (2), where the coverage of the mother particles is K (%) and the coverage of the toner mother particles with the small silica is L (%). An image forming apparatus.
0.8 ≧ K _A / L _A > K _B / L _B > K _C / L _C > K _D / L _D ≧ 0.1 (1)
0.5 ≦ (K _A / L _A ) − (K _D / L _D ) (2)
In the formulas (1) and (2), K _A and L _A are coverage ratios in the toner A, K _B and L _B are coverage ratios in the toner B, and K _C and L _C are coverage ratios in the toner C. Yes, K _D and L _D are the coverages of the toner D, and the toners A, B, C, and D are selected from a combination of the above-mentioned four color single color toners.

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