JP2006259633A - Electrophotographic toner and method for manufacturing same, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrophotographic toner in which toner and carrier deterioration is reduced and image density can be stabilized in spite of printing of a number of sheets of low-density manuscripts by maintaining high fluidity in a hybrid development apparatus. <P>SOLUTION: The toner is used for image formation to be performed on a paper sheet by using a developing roller 20 formed with a thin layer of the toner on its surface and a magnetic roller 21 for supplying the toner by a magnetic carrier to the developing roller 20 and developing an electrostatic latent image by the developing roller 20, in which the circularity for the toner is ≥0.97 and ≤0.99 and an inorganic fine powder is externally added at ≥0.1 wt% and ≤5.0 wt% onto the surface of the toner. A DC voltage is applied to the magnetic roller 21 and an AC voltage is applied to the developing roller 20. The inorganic fine powder is silica and titanium oxide. The toner is manufactured by polymerizing at least a colorant and a thermoplastic resin by a polymerization initiator. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrophotographic toner, a manufacturing method thereof, and an image forming apparatus, and more particularly to a developing method used in an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multifunction machine using an electrophotographic system. Using a two-component developer that charges a non-magnetic toner using a magnetic carrier, holding only the charged toner on the developing roller, and developing the latent image by flying the toner onto the electrostatic latent image The present invention relates to a toner for electrophotography to be used in a non-contact hybrid development system, a method for producing the same, and an image forming apparatus.

  In recent years, attention has been paid to a tandem method in which a plurality of photoconductors corresponding to toner colors are used to form a color image in synchronization with feeding of a transfer member and color is superimposed on the transfer member. Although this method has the advantage of being excellent in high-speed performance, it has the disadvantage of increasing the size because the electrophotographic process members of each color must be arranged side by side. As a countermeasure, there has been proposed a small tandem image forming apparatus in which a compact image forming unit is arranged by narrowing the interval between the photosensitive members. In a miniaturized tandem image forming apparatus, it is advantageous to use a vertical developing device in order to minimize the size of the image forming unit in the width direction. That is, it is desirable in terms of layout that the developing device is arranged in the upper direction of the photosensitive member. Also, in the conventional two-component development system, in such a vertical system, the reflux of the developer, that is, the supply from the developer stirring unit to the developing member close to the photosensitive member becomes complicated, and there is a limit to the miniaturization of the apparatus. There is a problem that carrier adhesion to the photosensitive member and toner scattering cannot be avoided. As another method, a one-component developing method that does not use a carrier has been proposed, but the method in which the developing roller is in contact with the photosensitive member causes torque fluctuation of the photosensitive member and promotes color misregistration, which is a weak point of tandem. There were drawbacks. In the non-contact method with the photoconductor, the toner is charged by a charge roller, and the layer thickness on the developing roller is regulated by an elastic ear cutting blade. In this method, the toner additive adheres to the charge roller and the charging ability is lowered, or the toner adheres to the ear cutting blade, resulting in non-uniform layer formation, which may cause image defects. As one means for solving these problems, there has been proposed a hybrid developing system in which toner is once charged using a carrier and then the toner is ejected in a non-contact manner with respect to the photoreceptor.

  As a prior art of this hybrid development system, Patent Document 1 discloses that a thin layer is formed with a non-magnetic toner on a donor roller (developing roller) installed in a non-contact manner with respect to the photoreceptor, and a latent image on the photoreceptor is formed by an AC electric field. Proposals for flying the toner have been made.

  As a conventional technology of the hybrid development system, Patent Document 2 discloses a developing device that forms a toner layer by transferring a developer to a donor roller using a magnetic roller and transferring the toner onto the donor roller. ing. In this proposal, it is possible to form a thin layer on the donor roller by using a two-component developer. However, when the charge of the toner becomes high, it becomes difficult to separate the toner on the donor roller, and a strong AC electric field is generated. Needed. Since this electric field disturbs the toner layer on the photoreceptor, there is a problem with color superposition and the like.

  On the other hand, as a toner, in Patent Document 3, an ultrafine powder is contained in the two-component development system by setting the average circularity of the toner to 0.93 to 0.99 and the fine powder content of 2 μm or less to 20% by number or less. There has been proposed a toner that hardly adheres to carriers and machine parts. However, although fluidity can be stabilized by spheroidization, problems such as cost in production also occur in order to suppress ultrafine powder.

Patent Document 4 proposes a toner that maintains a high level of transferability by using a non-magnetic one-component developing method with a volume average particle size of 4 to 10 μm and an average circularity of 0.950 to 0.990. ing. However, if the fluidity is too good, charging is insufficient, while if the fluidity is lowered, the layer formation becomes unstable.
U.S. Pat. No. 3,866,574 U.S. Pat. No. 3,929,098 JP 2003-177568 A JP 2004-126005 A

  In this specification, hybrid development uses a developing roller that forms a thin layer of toner on the surface, and a magnetic roller that supplies the toner to the developing roller by a magnetic carrier, and converts the electrostatic latent image into the developing roller. Is developed to form an image on a sheet, and a DC voltage is applied to the magnetic roller and an AC voltage is applied to the developing roller. Here, the electrostatic latent image carrier (photoconductor) and the developing roller are not in contact with each other, and the DC voltage applied to the magnetic roller is changed to supply toner to the developing roller, or image-like after one copy. It is determined whether the toner layer whose thickness has changed is cleaned from the developing roller and collected on the magnetic roller. In the hybrid development, when the two-component developer is held and mixed on the magnetic roller, the toner is likely to deteriorate due to adhesion of the toner to the carrier. Therefore, the fluidity in the developing machine is lowered and the stirring in the developing machine is performed. This increases the load and further promotes deterioration.

  Patent Document 3 discloses a two-component developing system in which the toner has an average circularity of 0.93 to 0.99 and a fine powder content of 2 μm or less is 20% by number or less so that no super fine powder is contained. A toner having a low adhesion to the toner has been proposed, but at this level, the fine powder content is still high, and the toner adhesion to the carrier in the hybrid development is not solved. In addition, when only the toner is uniformly formed into a thin layer on the developing roller and a DC or AC electric field is applied to the latent electrostatic image bearing member for development, the toner in the developing machine includes a magnetic roller and a developing roller. Because of the AC bias, the external additive on the toner surface is easily buried in the toner or deteriorated from the toner, and the fluidity in the developing machine is lowered and the flow in the developing machine is reduced. The agitation load increases and further deterioration is promoted. In particular, toner and carrier deterioration is promoted at the time of printing a low-printing document, and the image density is lowered.

  Patent Document 4 proposes a toner that maintains the transferability at a high level by using a non-magnetic one-component developing method with a volume average particle size of 4 to 10 μm and an average circularity of 0.950 to 0.990. However, this is not necessarily suitable for hybrid development using a two-component developer.

  Therefore, an object of the present invention is to provide an electrophotographic toner that is optimal for a hybrid developing device. Specifically, according to the present invention, in the hybrid developing device, toner and carrier deterioration is reduced, and by maintaining high fluidity, the image density can be stabilized even when a large number of low density originals are printed. It is an object to provide a toner for electrophotography that can be produced. Further, the present invention particularly relates to a small tandem type color image forming apparatus (a belt for conveying paper, a photoconductor for forming an electrostatic latent image for each color sequentially arranged in the conveying direction on the upper side of the belt, An object of the present invention is to provide an electrophotographic toner that is optimal for an image forming apparatus that includes a developing roller for each color that develops a photoreceptor and a magnetic roller for each color that supplies the toner for each color to each developing roller. Yes.

A first means for solving the above-described problems uses a developing roller that forms a thin layer of toner on the surface, and a magnetic roller that supplies the toner to the developing roller by a magnetic carrier,
In the toner for developing an electrostatic latent image with the developing roller to form an image on a sheet, the circularity of the toner is 0.97 or more and 0.99 or less, and an inorganic surface is formed on the surface of the toner. The external addition of the fine powder is 0.1% by weight or more and 5.0% by weight or less.

  The second means is that in the first means, a DC voltage is applied to the magnetic roller and an AC voltage is applied to the developing roller.

  A third means is that, in the first means, the inorganic fine powder is silica and titanium oxide.

  A fourth means is a method for producing an electrophotographic toner according to the first means, wherein the toner is produced by polymerizing at least a colorant and a thermoplastic resin with a polymerization initiator.

  A fifth means is an image forming apparatus using the electrophotographic toner of the first means, and a belt for transporting the paper, and an electrostatic for each color sequentially disposed in the transport direction above the belt. A photosensitive member that forms a latent image; a developing roller that develops each of the photosensitive members; and a magnetic roller that supplies the toner to each developing roller.

  According to the present invention, in the hybrid developing device, the toner and carrier deterioration is reduced, and the high density is maintained, so that the image density can be stabilized even when a large number of low density originals are printed. Toner can be provided. Furthermore, according to the present invention, toner and carrier deterioration can be reduced and high fluidity can be maintained even in a small tandem color image forming apparatus in which toner and carrier deterioration is extremely difficult to maintain high fluidity. An electrophotographic toner can be provided. Accordingly, it is possible to provide an electrophotographic toner capable of stabilizing the image density even when a large number of low density originals are printed.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, but are merely illustrative examples. Not too much.

[Developer]
FIG. 1 is a cross-sectional view of a hybrid developing apparatus using the electrophotographic toner of this embodiment, and FIG. 2 is a plan view thereof.

  In this specification, the hybrid development uses a developing roller that forms a thin layer of toner on the surface and a magnetic roller that supplies the toner to the developing roller by a magnetic carrier, and the electrostatic latent image is converted into the above-mentioned electrostatic latent image. In this method, an image is formed on a sheet by developing with a developing roller. A DC voltage is applied to the magnetic roller and an AC voltage is applied to the developing roller. Here, the electrostatic latent image carrier (photoconductor) and the developing roller are not in contact with each other, and the DC voltage applied to the magnetic roller is changed to supply toner to the developing roller, or image-like after one copy. It is determined whether the toner layer whose thickness has changed is cleaned from the developing roller and collected on the magnetic roller.

Hereinafter, the configuration of the hybrid developing device will be described with reference to FIGS. 1 and 2.
1 and 2, reference numeral 3 denotes a photoreceptor electrostatic latent image carrier, 4 denotes imagewise exposure light, 22 denotes a paddle mixer, 20 denotes a developing roller, and 21 denotes a magnetic roller. Reference numeral 24 denotes a spike cutting blade for controlling the thickness of the magnetic brush. A voltage (Vac + Vdc1) in which a DC bias voltage Vdc1 and an AC voltage Vac are superimposed is applied to the developing roller 20, and a DC voltage Vdc2 is applied to the magnetic roller 21.

Next, the operation of the developing device will be described with reference to FIGS.
The developer composed of toner and carrier held on the surface of the magnetic roller 21 is held, and the developer is stirred and charged by the stirring mixer 23 and the paddle mixer 22 partitioned by the partition plate 26, and the toner is charged to an appropriate level. Let The developer passes through the pan blade 24 and contacts the developing roller 20 with a constant layer thickness. The gap between the ear cutting blade 24 and the magnetic roller 21 is about 0.3 to 1.5 mm, and the gap between the magnetic roller 21 and the developing roller 20 is about 0.3 to 1.5 mm. The thin layer of toner on the developing roller is set to a thickness of 6 to 50 μm, preferably 30 to 70 μm. This thickness is a value corresponding to about 5 to 10 layers of toner when the average particle size of the toner is 7 μm. The gap between the developing roller 20 and the photoreceptor 3 is 150 to 400 μm, preferably 200 to 300 μm. If it is smaller than 150 μm, it causes fogging. If it is larger than 400 μm, it becomes difficult to cause the toner to fly to the photoreceptor 3, and a sufficient image density cannot be obtained. Further, it becomes a factor that causes selective development.

[toner]
The toner of the present invention is characterized by using a toner having a circularity of 0.97 or more and 0.99 or less. The toner can be obtained, for example, by containing a colorant, a wax, and a charge control agent in a binder resin that is a polymer produced in an aqueous medium by a suspension polymerization method or an emulsion polymerization aggregation method.

(Binder resin for toner)
The binder resin may be any resin that is usually used in the production of toner. For example, a styrene resin, an acrylic resin, a polyethylene resin, a polypropylene resin, a vinyl chloride resin, a polyester resin, Examples include polyamide resins, polyurethane resins, polyvinyl alcohol resins, vinyl ether resins, N-vinyl resins, styrene-butadiene resins, etc., preferably styrene resins, particularly styrene copolymer resins are used. It is good to do.

The polystyrene copolymer resin is a copolymer having a styrene monomer as a main component. Examples of the styrene monomer include styrene, o-methyl styrene, p-methyl styrene and the like, and styrene is particularly preferable.
Examples of other copolymerizable monomers that can be copolymerized 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) acrylic acid such as octyl, 2-chloroethyl acrylate, phenyl acrylate, methyl α-chloroacrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, n-octyl methacrylate Beauty treatment Other acrylic acid derivatives such as acrylonitrile, methacrylonitrile and acrylamide; 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 compounds such as N-vinylcarbazole, N-vinylindole, N-vinylpyrrolidene and the like can be mentioned. These may be used alone or in combination of two or more with a styrene monomer. Preferably, the aliphatic alcohol (meth) acrylic acid ester having 1 to 12 carbon atoms, more preferably 3 to 8 carbon atoms is used alone or in combination of two or more.

(Coloring agent)
Examples of the colorant include inorganic pigments, organic pigments, synthetic dyes, and the like, and one or more kinds of pigments and / or one or more kinds of dyes may be used in combination. Examples of the inorganic pigment include metal powder pigments, metal oxide pigments, and carbon pigments. The colorant is usually blended at a ratio of 1 to 10 parts by mass with respect to 100 parts by mass of the binder resin.

  Examples of metal powder pigments include iron powder and copper powder. Examples of the metal oxide pigment include magnetite, ferrite, and bengara. Examples of the carbon pigment include carbon black and furnace black. Examples of the organic pigment include azo pigments, acidic dye pigments and basic dye pigments, mordant dye pigments, phthalocyanine pigments, quinacdrine pigments, and dioxane pigments.

  Examples of the azo pigments include benzidine yellow and benzidine orange. Examples of the acidic dye-based pigment and basic dye-based pigment include quinoline yellow, acid green, alkali blue, and other dyes precipitated with a precipitating agent, or rhodamine, magenta, and macalite green dyes such as tannic acid, phosphomolybdenum. Examples thereof include those precipitated with an acid. Examples of the mordant dye-based pigments include metal salts of hydroxyanthraquinones. Examples of the phthalocyanine pigment include phthalocyanine blue and sulfonated copper phthalocyanine. Examples of the quinacridone pigment and dioxane pigment include quinacridone red and quinacridone violet.

  Examples of the synthetic dye include aniline black, azo dye, naphthoquinone dye, indigo dye, nigrosine dye, phthalocyanine dye, polymethine dye, tri- and diallylmethane dye, and the like.

(Charge control agent)
The charge control agent is added to improve the charge level and charge rising characteristics (indicator of whether to charge to a constant charge level in a short time), and to obtain characteristics such as excellent durability and stability. is there. That is, when the toner is positively charged for development, a positively chargeable charge control agent is added. When the toner is negatively charged for development, a negatively chargeable charge control agent can be added. .

  Such a charge control agent is not particularly limited. For example, specific examples of the positively chargeable charge control agent include quaternary ammonium compounds, pyridazines, pyrimidines, pyrazines, orthooxazines, and metaoxazines. , Paraoxazine, orthothiazine, metathiazine, parathiazine, 1,2,3-triazine, 1,2,4-triazine, 1,3,5-triazine, 1,2,4-oxadiazine, 1,3,4-oxadiazine, 1,2,6-oxadiazine, 1,3,4-thiadiazine, 1,3,5-thiadiazine, 1,2,3,4-tetrazine, 1,2,4,5-tetrazine, 1,2,3 Azides such as 5-tetrazine, 1,2,4,6-oxatriazine, 1,3,4,5-oxatriazine, phthalazine, quinazoline and quinoxaline Compounds; direct dyes comprising azine compounds such as azine fast red FC, azine fast red 12BK, azine violet BO, azine brown 3G, azine light brown GR, azine dark green BH / C, azine deep black EW and azine black 3RL; Nigrosine compounds such as nigrosine, nigrosine salts and nigrosine derivatives; acid dyes comprising nigrosine compounds such as nigrosine BK, nigrosine NB and nigrosine Z; metal salts of naphthennaphthenic acid or higher fatty acids; alkoxylated amines; alkylamides; benzylmethylhexyl decyl Quaternary ammonium salts such as ammonium and decyltrimethylammonium chloride can be exemplified, and these may be used alone or in combination of two or more. In combination it can also be used. In particular, the nigrosine compound is optimal for use as a positively chargeable toner from the viewpoint of obtaining a quicker start-up property.

  Also, a quaternary ammonium salt, a carboxylate, or a resin or oligomer having a carboxyl group as a functional group can be used as the positively chargeable charge control agent. More specifically, a styrene resin having a quaternary ammonium salt, an acrylic resin having a quaternary ammonium salt, a styrene-acrylic resin having a quaternary ammonium salt, a polyester resin having a quaternary ammonium salt, a carboxylic acid Styrene resin with salt, acrylic resin with carboxylate, styrene-acrylic resin with carboxylate, polyester resin with carboxylate, polystyrene resin with carboxyl group, acrylic with carboxyl group 1 type, or 2 or more types, such as resin, the styrene-acrylic resin which has a carboxyl group, and the polyester-type resin which has a carboxyl group, are mentioned. In particular, a styrene-acrylic copolymer resin having a quaternary ammonium salt as a functional group is optimal from the viewpoint that the charge amount can be easily adjusted to a value within a desired range.

  In this case, preferred acrylic comonomers to be copolymerized with the styrene units include methyl acrylate, ethyl acrylate, n-propyl acrylate, iso-propyl acrylate, n-butyl acrylate, iso-butyl acrylate, Examples include (meth) acrylic acid alkyl esters such as 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, and iso-butyl methacrylate. As the quaternary ammonium salt, a unit derived from a dialkylaminoalkyl (meth) acrylate through a quaternization step is used. Examples of the derived dialkylaminoalkyl (meth) acrylate include di (amino) ethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, dipropylaminoethyl (meth) acrylate, dibutylaminoethyl (meth) acrylate and the like ( Lower alkyl) aminoethyl (meth) acrylate; dimethylmethacrylamide, dimethylaminopropylmethacrylamide are preferred. Further, hydroxy group-containing polymerizable monomers such as hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, and N-methylol (meth) acrylamide can be used in combination during polymerization.

  As the charge control agent exhibiting negative chargeability, for example, organometallic complexes and chelate compounds are effective, and examples thereof include aluminum acetylacetonate, iron (II) acetylacetonate, chromium 3,5-di-tert-butylsalicylate. In particular, acetylacetone metal complexes, salicylic acid metal complexes or salts are preferable, and salicylic acid metal complexes or salicylic acid metal salts are particularly preferable.

  The above-described positively or negatively chargeable charge control agent is generally in a ratio of 1.5 to 15 parts by mass, preferably 2.0 to 8.0 parts by mass, more preferably 3.0 to 7.0 parts by mass. Therefore, the toner is preferably contained in the toner (the total amount of the toner is 100 parts by mass). If the addition amount of the charge control agent is smaller than the above range, it tends to be difficult to stably charge the toner to a predetermined polarity, and the electrostatic latent image is developed using this toner to develop an image. When forming, there is a tendency that the image density is lowered and the durability of the image density is lowered. In addition, the charge control agent tends to be poorly dispersed, causing so-called fogging, and the contamination of the photoreceptor is apt to occur. On the other hand, when the charge control agent is used in a larger amount than the above range, it tends to cause defects such as environmental resistance, particularly poor charging under high temperature and high humidity and defective images, and contamination of the photoreceptor.

(wax)
The waxes used for improving the fixing property and offset property are not particularly limited. For example, polyethylene wax, polypropylene wax, Teflon (registered trademark) wax, Fischer-Tropsch wax, paraffin wax, It is preferable to use carnauba wax, ester wax, montan wax, rice wax or the like. Two or more of these waxes may be used in combination. By adding such wax, offset property and image smearing can be more efficiently prevented.

  The above-described waxes are not particularly limited, but generally, the wax is preferably blended in the toner in an amount of 1 to 10 parts by weight (the total amount of the toner is 100 parts by mass). If the addition amount of the wax is less than 1 part by mass, there is a tendency that offset property and image smearing cannot be effectively prevented. On the other hand, if it exceeds 10 parts by weight, the toners are fused together. Storage stability tends to decrease.

(Suspension polymerization method)
In the suspension polymerization method, a colorant, a wax, a charge control agent, a crosslinking agent, etc. are dispersed in a polymerizable monomer, and the monomer composition after the dispersion treatment is dispersed in an aqueous medium (for example, water or water miscible with water). The mixture is stirred in a solvent mixture with a solvent to obtain an appropriate particle size, and then a polymerization initiator is added and heated to polymerize the polymerizable monomer.

  Examples of the crosslinking agent that can be used in the present invention include aromatic divinyl compounds such as divinylbenzene and divinylnaphthalene, carboxylic acid esters such as ethylene glycol diacrylate, ethylene glycol dimethacrylate, and 1,3-butanediol dimethacrylate, and divinyl. And divinyl compounds such as aniline, divinyl ether, divinyl sulfide, and divinyl sulfone. These can be used alone or in combination of two or more. The addition amount of the crosslinking agent is preferably 0.1 to 10 parts by weight with respect to 100 parts by weight of the monomer.

  Examples of the polymerization initiator used in the suspension polymerization method include 2,2-azobis (2,4-dimethylvaleronitrile), 2,2′-azobis- (2,4-dimethylvaleronitrile), and 2,2 ′. -Azobisisobutyronitrile, 1,1'-azobis (cyclohexane-1-carbonitrile), 2,2'-azobis-4-methoxy-2,4-dimethylvaleronitrile, azobisisobutyronitrile, etc. Examples include azo- and diazo-based polymerization initiators, benzoyl peroxide, methyl ethyl ketone peroxide, diisopropyl peroxycarbonate, cumene hydroperoxide, 2,4-dichlorobenzoyl peroxide, and lauroyl peroxide. Two or more types can be used in combination. The addition amount of the polymerization initiator is preferably 0.5 to 20 parts by weight with respect to 100 parts by weight of the monomer.

  When a suspension stabilizer is used, it is preferable to select a suspension stabilizer that is neutral or alkaline in water and can be easily removed by acid washing. Such suspension stabilizers include inorganic compounds such as tricalcium phosphate, magnesium phosphate, aluminum phosphate, zinc phosphate, calcium carbonate, magnesium carbonate, polyvinyl alcohol, gelatin, methyl cellulose, methyl hydroxypropyl cellulose, An organic compound such as ethyl cellulose, or a sodium salt thereof. The addition amount of the suspension stabilizer is preferably 0.2 to 2.0 parts by weight with respect to 100 parts by weight of the monomer. Moreover, in order to refine | miniaturize these suspension stabilizers, you may add 0.001-0.5 weight part of surfactant with respect to 100 weight part of monomers. Examples of the surfactant herein include sodium dodecylbenzenesulfonate, sodium oleate, sodium laurate, potassium stearate, calcium oleate and the like.

  The suspension polymerization is carried out with stirring in an aqueous medium in which a polymerizable monomer, a colorant, a wax, a charge control agent, a crosslinking agent, a polymerization initiator, and the like are dispersed and a suspension stabilizer is contained. The amount of the aqueous medium is preferably 300 to 1000 parts by weight with respect to 100 parts by weight of the monomer. In this stirring, the stirring speed and the stirring time may be adjusted so that the toner particles have a desired size. For example, the stirring speed is set to 2000 to 10,000 rpm for 5 minutes to 1 hour. Thereafter, polymerization may be carried out at 50 to 90 ° C. for 2 to 20 hours while maintaining the particle state and stirring to such an extent that the particles can be prevented from settling. A dispersion is obtained.

  The obtained toner base particles have a circularity of 0.97 or more and a Tg of 50 to 75 ° C., preferably 60 to 70 ° C. In order to make the circularity 0.97 or more, the stirring speed may be adjusted within the above range.

(Emulsion polymerization aggregation method)
In the emulsion polymerization aggregation method, a resin dispersion is generally prepared by emulsion polymerization, while an additive dispersion in which a colorant, wax, charge control agent and the like are dispersed in a solvent is prepared and mixed to form toner particles. In this method, aggregated particles corresponding to the diameter are formed and then fused to form toner particles. According to this method, toner particles having a high degree of spheroidization can be produced.

  In the emulsion polymerization for preparing the resin dispersion, for example, the same monomer, cross-linking agent, ion-exchanged water, and water-soluble polymerization initiator as exemplified in the suspension polymerization are mixed in a predetermined amount, and 10 to 90 What is necessary is just to carry out for about 1 to 24 hours at 10 degreeC and stirring speed 10-1000 rpm. Examples of the water-soluble polymerization initiator include persulfates such as potassium persulfate and ammonium persulfate, water-soluble azo polymerization initiators such as 2,2′-azobis (2-amidinopropane) dihydrochloride, hydrogen peroxide And water-soluble radical polymerization initiators such as redox polymerization initiators in which the persulfate is combined with a reducing agent such as sodium bisulfite or sodium thiosulfate. In addition, it is preferable to perform superposition | polymerization in inert gas (for example, nitrogen gas etc.) atmosphere. The average particle diameter of the resin particles in the resin dispersion is preferably 0.01 to 1 μm.

  On the other hand, the additive dispersion is prepared by, for example, adding a predetermined amount of the above-described colorant, wax, charge control agent, etc. into an aqueous medium, and further adding a dispersant as necessary, using a dispersing means such as a ball mill. Obtained by dispersive mixing. Examples of the aqueous medium include water such as distilled water and ion exchange water, and alcohols. These may be used individually by 1 type and may use 2 or more types together.

  Examples of the dispersant include anionic surfactants such as sulfate ester, sulfonate, phosphate, and soap; cationic surfactants such as amine salt type and quaternary ammonium salt type; polyethylene glycol And nonionic surfactants such as polyphenols, alkylphenol ethylene oxide adducts, and polyhydric alcohols. Among these, anionic surfactants and cationic surfactants are preferable. The nonionic surfactant is preferably used in combination with the anionic surfactant or the cationic surfactant. The said surfactant can use 1 type (s) or 2 or more types.

  Specific examples of the anionic surfactant include sodium dodecylbenzenesulfonate, sodium dodecylsulfate, sodium alkylnaphthalenesulfonate, sodium dialkylsulfosuccinate and the like. Specific examples of the cationic surfactant include alkylbenzene dimethyl ammonium chloride, alkyl trimethyl ammonium chloride, distearyl ammonium chloride and the like.

  In order to form aggregated particles, for example, a salt such as sodium chloride is added as an aggregating agent. As a method for adding the flocculant, an aqueous solution of the dispersant may be added dropwise to the mixed dispersion obtained by mixing the resin dispersion and the additive dispersion with stirring for about 10 minutes to 24 hours. At this time, the temperature of the mixed dispersion is preferably less than the Tg of the resin in the resin dispersion.

  After the aggregated particles are grown, the temperature is raised to Tg of the resin in the resin dispersion to fuse the aggregated particles. The aggregation of the agglomerated particles is carried out with stirring for about 10 minutes to 24 hours to obtain a dispersion of toner base particles. The obtained toner base particles have a circularity of 0.97 or more and a Tg of 50 to 75 ° C., preferably 60 to 70 ° C. In order to achieve a circularity of 0.97 or more, the stirring conditions in each step of agglomerated particle growth and agglomerated particle fusion may be adjusted within the above ranges.

(External additive)
As the external additive material, fine metal oxide particles (usually having an average particle size of 1.0 μm or less) such as silica, titanium oxide, and alumina can be used. Silica is necessary to maintain the fluidity of the toner, and it is preferable to use titanium oxide in combination for polishing the surface of the photoreceptor. Further, third metal oxide fine particles may be used in combination.

The metal oxide fine particles are preferably surface-treated with a hydrophobizing agent.
Examples of the hydrophobizing agent generally include silane coupling agents, silicone oils, titanate coupling agents, and modified substances thereof, and may be used in combination.
The metal oxide fine particles are used in an amount of 0.1 to 10.0 parts by mass per 100 parts by mass of the toner.

[Career]
There is no particular limitation on the carrier of the present invention, for example, as a core agent, magnetic metal such as iron, nickel, cobalt and alloys thereof, alloys containing rare earth, hematite, magnetite, manganese-zinc ferrite, By sintering and atomizing magnetic materials such as nickel-zinc ferrites, manganese-magnesium ferrites, soft ferrites such as lithium ferrites, iron-based oxides such as copper-zinc ferrites, and mixtures thereof The surface of the produced magnetic particles can be used as a resin coating.
For the carrier core material obtained above, examples of the surface coating agent fluorine-based binder resin include polytetrafluoroethylene, polychlorotrifluoroethylene, and polyvinylidene fluoride.
The particle diameter of the carrier is generally 20 to 200 [mu] m, particularly preferably 30 to 150 [mu] m, expressed in terms of particle diameter by electron microscopy. Further, the apparent density of the carrier is preferably in the range of 2.4 to 3.0 g / cm ³ , although it varies depending on the composition of the magnetic material, the surface structure and the like when the magnetic material is mainly used.
Among these carriers, a ferrite carrier having a volume resistivity of 10 ⁷ Ωcm, a saturation magnetization of 70 emu / g, and an average particle size of 35 μm is particularly effective, and particularly a magnetite carrier, a Mn ferrite, Mn—Mg based ferrite is particularly effective.

  The mixing ratio of the toner and the carrier is 2 to 40% by weight, preferably 3 to 30% by weight, and more preferably 4 to 25% by weight with respect to the total amount of the carrier and the toner. When the mixing ratio of the toner is less than 2% by weight, the toner charge amount becomes high and a sufficient image density cannot be obtained, and when it exceeds 40% by weight, a sufficient charge amount cannot be obtained. The toner is scattered from the inside and contaminates the inside of the image forming apparatus, or toner fog occurs on the image. The two-component developer composed of toner and carrier forms a magnetic brush composed of toner and carrier on the magnetic roller 21, and the toner is stirred and charged by the stirring mixer 23 and the paddle mixer 22. The developer is layer-limited by the ear cutting blade 24, and a thin layer of only toner is formed on the developing roller 20 by the potential difference between the magnetic roller 20 and the developing roller 21. The thin toner layer on the developing roller 20 varies depending on the resistance of the developer and the rotational speed difference between the developing roller 20 and the magnetic roller 21, but can also be controlled by the above potential difference. When the potential difference is increased, the toner layer on the developing roller 20 is thickened, and when the potential difference is decreased, the toner layer is thinned. The range of potential difference is generally about 100 to 250 v.

As the developer, a carrier having a resistance of 10 ⁶ Ωcm to 10 ⁹ Ωcm, which has a role of collecting and supplying the toner, is used, and the toner that adheres strongly and electrostatically at the nip between the developing roller 20 and the magnetic roller 21 is used. It is to peel off with a magnetic brush and to supply toner necessary for development. At this time, in order to increase the contact point with the toner, it is preferable to use a carrier having a small diameter of 40 μm or less and to increase the surface area of the carrier. At 10 ⁶ Ωcm or less, a low-resistance carrier that emphasizes recovery is effective as a countermeasure against development ghosts, but it is difficult to maintain accurate development without causing fogging by applying accurate charging to the toner, and operation for a longer period of time. toner scattered from the developing roller surface when, will thereby generating a problem of contaminating the charger and the exposure unit (not shown), in 10 ⁹ [Omega] cm or more resistors, it is possible to impart charging performance charging There was a problem that was likely to rise. By making the resistance value of the carrier appropriate, the toner on the developing roller 20 can be collected and the charged toner can be recharged to the developing roller 20. The toner is controlled to 5 to 20 μC / g, prevents toner scattering and fogging, and does not leave a development history phenomenon on the developing roller 20 by developing with a low electric field, and is excellent in toner recoverability. An image forming method was devised.

  The charged toner is held in a thin layer on the developing roller 20 due to a potential difference between the magnetic roller 20 and the developing roller 21, and is developed by applying a bias in which direct current and alternating current are superimposed on the photosensitive member 3. . In order to prevent toner scattering, alternating current is applied immediately before development.

  The toner remaining on the development is not provided with a special device such as a scraping blade, and the magnetic brush on the magnetic roller 21 contacts the toner layer on the developing roller 20. By changing the developer by stirring the developer with a mixer, the toner can be easily collected and replaced. At this time, since the width of the magnetic brush is a width for collecting the toner on the developing roller 20, the uncollected area can be surely eliminated by making the width of the developing roller 20 shorter than the magnetic brush width 27. By doing so, there is no toner adhering to the developing roller 20 outside the magnetic brush width 27, and toner scattering at both ends can be eliminated. As a method for promoting the replacement of the developer, the rotational speed of the magnetic roller 21 is set to 1.0 to 2.0 times the speed of the developing roller 20, and the toner on the developing roller is collected and an appropriate toner is collected. A uniform toner layer can be formed by supplying the developer set to the density to the developing roller.

  Further, in order to maintain a uniform image density, the toner on the developing roller 20 is not subjected to a burden on the toner by applying the same potential between the developing roller 20 and the magnetic roller 21 at a time other than the development timing. Recovery to the magnetic roller 21 is effective.

  When an a-Si photosensitive member is used as the photosensitive material for the photosensitive member 3, the post-exposure potential on the surface has a very low characteristic of 10v or less, but the saturation charging potential decreases when the film thickness is reduced. In addition, the withstand voltage leading to dielectric breakdown is reduced. On the other hand, the charge density on the surface of the photoreceptor 3 when a latent image is formed tends to be improved, and the development performance tends to be improved. This characteristic is particularly remarkable when the dielectric constant is about 10 or less for an a-Si photoreceptor having a dielectric constant of about 10 or less, more preferably 20 μm or less. The constant DC bias voltage Vdc1 can be developed with 150V or less, more preferably 100V or less, VP-P500 to 2000V as an AC component, and a frequency of 1 to 3 kHz. When a positively charged organic photoconductor (OPC) is used as the photoconductor 3, the thickness of the photosensitive layer is set to 25 μm or more to increase the amount of charge generation material added in order to make the residual potential 100 V or less. It is particularly important. In particular, OPC having a single layer structure is advantageous in that a charge generating material is added to the photosensitive layer, and therefore sensitivity and change are small even when the photosensitive layer is reduced. Even in this case, setting the developing bias Vdc1 to 400 V or less, more preferably 300 V or less is also preferable in terms of preventing a strong electric field from being applied to the toner. Setting the developing bias to be low in this way is effective for suppressing the dielectric breakdown of the thin film a-Si photosensitive member, preventing excessive charging of the toner, and suppressing the development history phenomenon. Further, a toner layer of 10 to 100 μm, preferably 30 to 70 μm, is formed on the developing roller 20, and the gap between the developing roller 20 and the photosensitive member 3 is 150 to 400 μm, preferably 200 to 300 μm. A sharp image can be obtained by causing the toner to fly on the photoreceptor 3 by an AC electric field. Conventionally, an OPC photoconductor is known as the photoconductor 3 used in the image apparatus. However, the OPC photosensitive member has a problem that the surface of the photosensitive layer is soft and the photosensitive layer is easily scraped by rubbing with a cleaning blade. Therefore, an a-Si photosensitive member having a photosensitive layer thickness of 25 μm or more has been used in recent years because it has a hard surface compared to an OPC photosensitive member and is excellent in durability and function retention (maintenance-free). ing.

FIG. 3 is a conceptual diagram of an example of an image forming apparatus using the electrophotographic toner of the present embodiment.
First, the configuration of the image forming apparatus will be described.
In this image forming apparatus 20, an endless belt 54 is disposed so that the recording paper from the paper feed cassette 53 can be conveyed toward the fixing device 59, and the black belt is disposed above the belt 54 that conveys the recording paper. A developing device 50A for yellow, a developing device 50B for yellow, a developing device 50C for cyan, and a developing device 50D for magenta are provided. These developing devices 50 (A, B, C, D) are developed in close proximity to the magnetic roller 1 (A, B, C, D) and the magnetic roller 1 (A, B, C, D), respectively. A roller 2 (A, B, C, D) is disposed, and a photosensitive member 3 (A, B, C, D) faces the developing roller 2, and a charging device is disposed around the photosensitive member 3. 56 (A, B, C, D) and exposure device 57 (A, B, C, D) are arranged.

Next, the operation of the image forming apparatus 20 will be described.
In the tandem type image forming apparatus having the hybrid type developing apparatus configured as described above, the two-component developer composed of toner and carrier corresponding to each color such as yellow, cyan, magenta and black is supplied to the developer container 51 ( A, B, C, D) are supplied to the respective developing devices 50, a magnetic brush is formed on the magnetic roller 1, and the toner is charged by stirring. The magnetic brush on the magnetic roller 1 is layer-regulated by a cutting blade, and is developed by the potential difference between the DC voltage Vdc2 applied to the magnetic roller 1 and the constant DC bias voltage Vdc1 applied to the developing roller 2 and the AC voltage Vac. A thin layer of toner only is formed on the roller 2. Then, when a print start signal is received from a control circuit (not shown), first, the photosensitive member 3 composed of a positively charged organic photosensitive member (positive OPC) is charged to, for example, 400 V by the charger 56, and then, for example, 770 nm. By the exposure by the exposure device 57 using the LED having the wavelength, the post-exposure potential of the photosensitive member 3 becomes about 70 V, and a latent image is formed. The latent image is developed with the toner that has jumped from the toner layer on the developing roller 2 to the photosensitive member 3 by a constant DC bias voltage Vdc1 and an AC voltage Vac applied to the developing roller 2 to form a toner image. Then, the recording paper is fed from the paper feed cassette 53 and sent by the belt 54. When the recording paper reaches the photosensitive member 3, a transfer bias by the transfer device 58 (A, B, C, D) is applied. Then, the toner image is transferred to the recording paper, fixed by the fixing device 59, and discharged. After that, as described above, the DC voltage Vdc2 is changed to the magnetic roller 1 (A, B, C, D) while applying the AC voltage Vac periodically according to the print data, and the toner layer on the developing roller is magnetized. A toner stripping process collected on the brush and a subsequent toner layer re-forming process are performed.

  The exposure device 57 can use a semiconductor laser or an LED. When a positively charged organic photoconductor is used, a wavelength around 770 nm is effective, and when an amorphous silicon photoconductor is used, a wavelength around 685 nm is effective. When a positively charged organic photoconductor (positive OPC) is used, there is little generation of ozone, etc., and charging is stable. Especially, when a positive OPC with a single layer structure is used over a long period of time and the film thickness changes, the photosensitive characteristics. The image quality is stable and the image quality is stable. In addition, it is also possible to use an a-Si photoconductor. When used in a long-life system, the film thickness of the positive OPC is set to about 20 μm to 40 μm. In the case of 20 μm or less, when the film decreases and reaches 10 μm, black spots are noticeably generated due to dielectric breakdown. On the other hand, if the film thickness is thicker than 40 μm, the sensitivity is lowered and the image is lowered. The exposure apparatus 11 may be a system using a semiconductor laser or LED. A wavelength near 770 nm is effective for positive OPC, and a wavelength near 685 nm is effective for an a-Si photoreceptor.

  The charger 56 charges the photosensitive member 3 as an electrostatic latent image carrier to 400V. Thereafter, when exposure is performed with an LED having a wavelength of 770 nm, the post-exposure potential is set to 70V. The photoreceptor 3 is arranged with a space of about 250 μm with respect to the developing roller 2. No wire electrode or the like is used in this space. The surface of the developing roller 2 is a rotating body made of conductive aluminum. The material of the rotator may be a uniform conductor, and SUS, conductive resin coating, etc. can be applied. A DC voltage Vdc1 and an AC voltage Vac are superimposed and applied to this conductive rotor. Vdc1 is, for example, 100 v, and Vac is, for example, Vpp is 1.5 kv, frequency is 3.0 KHz, and Duty is 30%. The AC component waveform is preferably a rectangular wave. By applying these superimposed biases to the conductive rotator, the latent image on the photoreceptor 3 has good developability, and the toner layer is more easily recovered from the magnetic roller 1, so that continuous printing is stable. Improved. In order to stabilize the image density in continuous printing, it is necessary to periodically remove the toner from the developing roller and refresh.

  In order to supply sufficient toner to the latent image on the photosensitive member 3 without increasing the sheet interval, if the peripheral speed of the developing roller 1 is set to 1.5 times or more with respect to the photosensitive member 3, the toner can be removed in a short time. It can be put in and out. Further, when the magnetic roller 1 is set at a speed of 1 to 2 times that of the developing roller 2, the toner replacement is promoted. At this time, it is preferable that the rotating direction of the magnetic roller 1 is opposite to the developing roller 2.

  To replace the toner layer on the developing roller 2, the alternating current (Vac + Vdc 1) is applied at the end of development, and the DC voltage Vdc 2 of the magnetic roller 1 is changed to change the toner layer of the developing roller 2 to the magnetic layer on the magnetic roller 1. Collect on brush.

The amount of saturated toner in the toner layer is determined by the difference between Vdc2 and Vdc1. When Vdc1 is set to 150 V and the value of Vdc2 is set to 400 V, a toner layer of about 1.0 mg / cm ² is obtained on the second round of the developing roller. Adjustment of the toner layer is basically obtained by (Vdc2−Vdc1), but factors such as the charge amount of the toner and the magnetic pole strength of the magnetic roller may also contribute. The toner layer is varied by changing the value of Vdc2 according to the image data, whereby an image with a uniform density can be obtained. When performing high density printing continuously, it is advantageous to set the value of (Vdc2-Vdc1) slightly higher. If the toner layer is too thin at 0.5 mg / cm ² or less, the followability of the density when a high density image is continuous is lowered and image unevenness is likely to occur. On the other hand, if the toner layer exceeds 1.5 mg / cm ² and is too thick, the development ghost tends to be noticeable and the toner scattering tends to be noticeable. The toner layer thickness also depends on the charge amount of the toner. When the toner charge amount is as low as 10 μC / g or less, particularly 5 μC / g or less, the toner layer thickness increases and scattering increases. On the other hand, when the toner charge amount is 20 μC / g or more, the toner layer thickness becomes thin, the charge increases, and the developability of the toner decreases.

  The toner layer of the developing roller 2 is collected by the magnetic brush held by the magnetic roller 1, and new developer is carried to the developing roller 2 through the spike cutting blade.

(A) Production of toner having a circularity of 0.97 to 0.99 (a-1)
A round bottom flask was charged with 20 parts by weight of styrene, 3.5 parts by weight of butyl acrylate, 0.2 parts by weight of divinylbenzene, 0.7 parts by weight of potassium persulfate as a water-soluble polymerization initiator, and 200 parts by weight of ion-exchanged water. The emulsion polymerization was carried out at 70 ° C. for 8 hours while stirring at 100 rpm with an anchor type stirring blade to obtain a styrene acrylic resin dispersion having an average particle size of 0.3 μm.
(A-2) Preparation of additive dispersion Carnauba wax No. 1 (manufactured by Kato Hiroyuki) 5 parts by weight, Bontron P-51 (manufactured by Orient Chemical) 2 parts by weight, carbon black 7 parts by weight, sodium dodecylbenzenesulfonate 0.1 part by weight was put into 200 parts by weight of ion-exchanged water and dispersed and mixed for 3 hours with a ball mill to obtain an additive dispersion having an average particle size of 0.3 μm.
(A-3) Formation of core particles The above resin dispersion and additive dispersion were mixed, and agglomerates were grown for 1 hour at 40 ° C while stirring at 100 rpm with an anchor-type stirring blade in a round bottom flask. . During this 1 hour, 50 parts by weight of ion-exchanged water in which 0.5 part by weight of NaCl was dissolved as a flocculant was continuously added for 50 minutes at a rate of 1 part by weight per minute. After the coagulation growth, the temperature was raised to 70 ° C., fusion was performed at 100 rpm, and the fusion time was changed to obtain a toner particle dispersion having a volume average particle diameter of 8.0 μm.
The toner particle dispersion thus obtained was filtered, washed and dried to obtain toner particles having a Tg of 63 ° C. and a circularity of 0.97 to 0.99 as shown in Table 1.
Subsequently, silica RA200HS (manufactured by Nippon Aerosil Co., Ltd.) and titanium oxide fine particle Aerosil 50 (manufactured by Nippon Aerosil Co., Ltd.) were mixed for 2 minutes using a Henschel mixer at a blending ratio shown in Table 1 with respect to 100 parts by weight of toner particles. In addition, toners of Comparative Examples 2 and 3 were obtained.
(B) Production of toner having a circularity of 0.93 to 0.95 100 parts by mass of styrene acrylic copolymer, 7 parts by mass of carbon black, 5 parts by mass of wax as a release agent, and nigrosine dye as a positive charge control agent After mixing 2 parts by mass with a Henschel mixer (FM-20B manufactured by Mitsui Mining), the mixture was melt-kneaded using a twin screw extruder (PCM-30 manufactured by Ikegai), cooled, and coarsely pulverized using a hammer mill. Further finely pulverized by a mechanical pulverizer was classified by an airflow classifier to obtain a magnetic toner having a volume average particle size of 8.0 μm.
By changing the fine powder time, toners with circularity of 0.93 and 0.95 were obtained.
Next, silica RA200HS (manufactured by Nippon Aerosil Co., Ltd.) and titanium oxide fine particle Aerosil 50 (manufactured by Nippon Aerosil Co., Ltd.) were mixed with 100 parts by weight of toner particles for 2 minutes using a Henschel mixer in the mixing ratio shown in Table 1, and Comparative Examples 1 and 4 No toner was obtained.
The circularity of the toners of Examples 1 to 4 and Comparative Examples 1 to 4 was measured by Sysmex: FPIA.
The toners of Examples 1 to 4 and Comparative Examples 1 to 4 thus obtained were mixed with a carrier (ferrite carrier 50 μm manufactured by Powder Tech Co., Ltd.) and a toner concentration 8% ball mill for 30 minutes to obtain a developer. Using this developer, 50,000 prints were evaluated by low density (initial optical density 1.28 to 1.50) optical printing using a Kyocera Mita page printer (FS-5016N).
The results are shown in Table 1.

  According to Table 1, in Examples 1 to 4, toners having a circularity of 0.97 to 0.99 and a surface treatment agent wt% of 0.50 wt% to 5.00 wt% were used. It is. In this case, the initial optical density was 1.38 to 1.49, but the durable density after completion of continuous copying of 50,000 sheets was 1.36 to 1.42, and even with continuous copying of many sheets. The toner chargeability was not deteriorated, the developer fluidity was not deteriorated, and the optical density of the copy was not significantly reduced.

  On the other hand, according to Table 1, in Comparative Examples 1 to 4, a toner having a circularity of 0.93 to 0.99 or a surface treatment agent wt% of 0.08 wt% to 6.00 wt% is used. It is a thing. In this case, the initial optical density was 1.28 to 1.50, but the endurance density after completion of continuous copying of 50,000 sheets was 1.10 to 1.20. The toner chargeability and / or developer fluidity deteriorated, and the optical density of the copy was significantly reduced.

  Thus, when the condition that the circularity is 0.97 to 0.99 is satisfied and the condition that the surface treatment agent wt% is 0.50 wt% to 5.00 wt% is satisfied, It has been proved that the use of such a toner does not cause a decrease in the optical density of the copy even when a large number of continuous copies are made.

  The present invention can be used for an image forming apparatus such as a copying machine, a printer, a facsimile, or a complex machine using an electrophotographic system.

FIG. 2 is a cross-sectional view of a hybrid developing device using the electrophotographic toner of the present embodiment. FIG. 2 is a plan view of a hybrid developing device using the electrophotographic toner of the present embodiment. 1 is a conceptual diagram illustrating an example of an image forming apparatus using an electrophotographic toner according to an exemplary embodiment.

Explanation of symbols

3 Photoreceptor 4 Imagewise exposure light 20 Developing roller 21 Magnetic roller 22 Paddle mixer 23 Stirring mixer 24 Ear cutting blade 26 Partition plate 27 Magnetic brush width 50 (A, B, C, D) Developing device (for black 50A, for yellow) 50B, 50C for cyan and 50D for magenta)
53 Paper feeding cassette 54 Endless belt 56 (A, B, C, D) Charger 57 (A, B, C, D) Exposure device 59 Fixing device 1 (A, B, C, D) Magnetic roller 2 (A , B, C, D) Developing roller 3 (A, B, C, D) Photoconductor

Claims (5)

A developing roller for forming a thin layer of toner on the surface;
Using a magnetic roller for supplying the toner to the developing roller by a magnetic carrier,
In the toner for developing an electrostatic latent image by the developing roller to form an image on paper,
The circularity of the toner is 0.97 or more and 0.99 or less,
An electrophotographic toner, wherein an inorganic fine powder is externally added to the toner surface in an amount of 0.1% by weight to 5.0% by weight.   2. The electrophotographic toner according to claim 1, wherein a DC voltage is applied to the magnetic roller and an AC voltage is applied to the developing roller.   2. The electrophotographic toner according to claim 1, wherein the inorganic fine powder is silica and titanium oxide. A method for producing an electrophotographic toner according to claim 1,
A method for producing an electrophotographic toner, wherein the toner is produced by polymerizing at least a colorant and a thermoplastic resin with a polymerization initiator. An image forming apparatus using the electrophotographic toner according to claim 1,
A belt for conveying the paper;
A photoreceptor for forming an electrostatic latent image for each color sequentially disposed on the upper side of the belt in the conveying direction;
The developing roller for each color for developing each of the photoreceptors;
An image forming apparatus comprising: the magnetic roller for each color that supplies the toner for each color to each developing roller.

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