JP2009229533A - Toner for electrophotography and image-forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a toner for electrophotography which forms images which are stable and good for a long period of time, realizes the long life of a machine, prevents the occurrence of a dark spot due to dielectric breakdown on an amorphous silicone photosensitive material, and firmly polishes a discharge product adhering to the amorphous silicone photosensitive material, and to provide an image-forming device using the toner. <P>SOLUTION: The toner has toner particles on the surfaces of which agglutinative titanium oxide is externally added, the oxide being at least 500 kg/mm<SP>2</SP>in Vickers hardness, at least 200 nm in secondary particle size and at most 1.0<SP>-5</SP>Ω in resistance. The image-forming device using the toner uses an amorphous photosensitive material as a latent image carrier and is provided with a charging roller. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrophotographic toner and an image forming apparatus that are preferably used in a copying machine, a printer, a facsimile machine, and the like.

  It is well known that the color ratio of office documents has increased in recent years, and there is an increasing demand for speeding up color printing. Conventionally, a one-drum type color copier and its multifunction peripheral (MFP) have been the mainstream, but the one-drum type has a problem that color printing is slower than monochrome printing. Therefore, there is a demand for speeding up color printing with a 4-drum tandem color machine.

On the other hand, in order to reduce the running cost and extend the life of the machine, a photoconductor (amorphous silicon photoconductor is often used as an electrostatic latent image carrier. The amorphous silicon photoconductor has a surface hardness. For example, even if the photosensitive member is polished by inorganic fine particles on the surface of the toner, there is almost no film scraping of the photoreceptor, so that a long life of the machine is achieved without deterioration in performance.
However, amorphous silicon photoconductors tend to have a high dielectric constant and tend to hold charges, so they are charged by friction with the cleaning blade, causing discharge and causing a so-called “drum black spot” dielectric breakdown. There is.
Therefore, conventionally, an attempt has been made to suppress charge-up on the surface of the photoreceptor and prevent dielectric breakdown by externally adding low resistance titanium oxide to the toner and interposing it between the amorphous silicon photoreceptor and the cleaning blade. ing.

  In recent years, many charging rollers have been used for the purpose of reducing the amount of ozone generated. However, the photosensitive member is charged by the contact between the charging roller and the photosensitive member, and discharge occurs near the contact point to generate a large amount of discharge products. This discharge product generates a phenomenon called “image flow” in a high temperature and high humidity environment, and raises the cleaning blade by raising the friction coefficient of the photosensitive member.

Therefore, it has been proposed to use a toner externally added with titanium oxide and to polish the surface of the photoreceptor by pressing the toner against the surface of the photoreceptor with a cleaning blade (see Patent Document 1).
JP 2007-272204 A

  However, when the toner disclosed in Patent Document 1 is used, it is sufficiently satisfactory to prevent the generation of black spots due to dielectric breakdown on the amorphous silicon photoconductor and to scrape off the discharge products adhering to the amorphous silicon photoconductor. It was not a thing.

  The present invention has been made in view of the above problems, and can obtain a stable and stable image for a long period of time, achieve a long life of the machine, and also provide a black spot due to dielectric breakdown on the amorphous silicon photoconductor. It is an object of the present invention to provide a toner capable of suppressing generation and firmly polishing a discharge product adhering to an amorphous silicon photoreceptor, and an image forming apparatus using the toner.

The toner for electrophotography according to the present invention is characterized in that cohesive titanium oxide having a Vickers hardness of 500 kg / mm ² or more and a secondary particle diameter of 200 nm or more is externally added.

  Further, the toner of the present invention preferably contains 0.1 to 5.0 parts by weight of titanium oxide with respect to 100 parts by weight of the toner.

  An image forming apparatus according to the present invention is an image forming apparatus using an amorphous silicon photoconductor as a latent image carrier and provided with a charging roller, wherein the toner is used.

In the electrophotographic toner according to the present invention, the agglomerated titanium oxide having a Vickers hardness of 500 kg / mm ² or more and a secondary particle diameter of 200 nm or more is externally added. The discharge product adhering to the photoconductor can be scraped off without damage, and the photoconductor surface without image flow can be maintained, and the dielectric breakdown of the amorphous silicon photoconductor is interposed between the amorphous silicon photoconductor and the cleaning blade. By preventing this, a good image can be obtained stably for a long period of time, and a long machine life can be achieved.

  Hereinafter, the toner and the image forming apparatus according to the present invention will be described in detail. The toner of the present invention is used in an image forming apparatus using an amorphous silicon photoconductor as a latent image carrier and having a cleaning blade for removing the toner remaining on the photoconductor after the transfer process. In the toner, specific cohesive titanium oxide is externally added to the surface of the toner particles.

(External additive)
The cohesive titanium oxide externally added to the surface of the toner particles has a Vickers hardness of 500 kg / mm ² or more and a secondary particle diameter on the toner surface and in the toner of 200 nm or more. Thus, when the toner polishes the photoconductor, the discharge product adhering to the photoconductor can be scraped off without the external additive being loosened. Moreover, it is preferable that the primary particle diameter of this titanium oxide is 100 nm or less. The resistance of the titanium oxide is preferably 1 × 1.0 ⁻⁵ Ω or less.

  The amount of cohesive titanium oxide added to the surface of the toner particles is preferably 0.1 to 5.0 parts by weight with respect to 100 parts by weight of the toner particles.

The cohesive titanium oxide is prepared, for example, as follows. First, titanium oxide having a primary particle size of 100 nm or less is dispersed in a solvent such as an organic solvent, and after adding and adding a conductivity-imparting agent such as tin oxide and antimony to this, a solid is separated by filtration, This is added to water and at least one selected from inorganic flocculants such as magnesium sulfate and aluminum sulfate, nonionic or anionic polymer flocculants of polyacrylamide or copolymers thereof (acrylamide-acrylic acid copolymer, etc.). Add seed and mix well. Subsequently, the aggregated titanium oxide fine particles having high hardness and low resistance (conductivity) can be obtained by sintering the aggregated particles obtained by filtration and washing at 500 to 1200 ° C. for 1 to 8 hours. That is, the primary particles of titanium oxide are strongly aggregated with the above-described inorganic or organic aggregating agent, and further, the aggregates are sintered, whereby strong aggregated fine particles with clogged particles are obtained.
The agglomerated titanium oxide fine particles may be further surface-treated with a silane coupling agent, a titanium coupling agent, aminosilane, silicone oil or the like for the purpose of hydrophobization and charge control, if necessary.
In order to externally add the cohesive titanium oxide fine particles to the toner particles, for example, both components may be mixed using a Henschel mixer, a V-type mixer, a turbula mixer, a hybridizer, or the like. At that time, other external additives may be used in combination with the cohesive titanium oxide. Examples of other external additives include inorganic fine powders such as silica, alumina, zinc oxide, magnesium oxide and calcium carbonate, organic fine powders such as polymethyl methacrylate, fatty acid metal salts such as zinc stearate, and the like, Two or more types can be mentioned.

(Toner particles)
The toner particles used in the present invention are not particularly limited, and either a magnetic one-component toner or a non-magnetic two-component toner may be used.
As the toner particles, various toner compounding agents such as a colorant can be dispersed in the binder resin by, for example, a pulverization method to obtain toner particles.
That is, the toner particles used in the present invention are obtained by adding a predetermined amount of a colorant and, if necessary, an additive such as a wax and a charge suppressant to a predetermined amount of a binder resin, and then adding it to a Henschel mixer or the like. It can be obtained by stirring and mixing with a mixing device. The mixture obtained by stirring and mixing is melt-kneaded with a twin screw extruder or the like, cooled, and then pulverized with a pulverizer such as a hammer mill or a jet mill. Next, after classification using a classifier such as an air classifier, toner particles having a predetermined particle size and shape factor can be obtained. The toner particles are preferably adjusted to a particle size of about 5 to 8 μm.

  Also, a polymerization method can be used to obtain toner particles. In the polymerization method, a suspension polymerization method and an emulsion polymerization method are mainly used. In the polymerization method, wax, colorant, and if necessary, charge control agent, polymerization initiator, and crosslinking agent are used for the binder resin, and the mixture or dispersion obtained by adding other additives to the binder resin in the aqueous phase. The toner particles having a desired particle size can be obtained by granulation and polymerization while stirring.

(Binder resin)
The binder resin is not particularly limited. For example, styrene-acrylic resin, polyester resin, polyacrylic resin, polyethylene resin, polypropylene resin, vinyl chloride resin, polyamide resin, polyurethane resin, polyvinyl alcohol resin. Examples thereof include thermoplastic resins such as resins, vinyl ether resins, N-vinyl resins, and styrene-butadiene resins. Of course, if necessary, other resins may be used in combination with these resins, or two or more of these resins may be used.

  The polyester resin is mainly obtained by polycondensation of polyvalent carboxylic acids and polyhydric alcohols. Examples of the polyvalent carboxylic acids include phthalic acid, isophthalic acid, terephthalic acid, succinic acid, 1, 2 Aromatic polycarboxylic acids such as 1,4-benzenetricarboxylic acid, 2,5,7-naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, pyromellitic acid; maleic acid, fumaric acid, succinic acid, adipic acid Aliphatic dicarboxylic acids such as sebacic acid, malonic acid, azelaic acid, mesaconic acid, citraconic acid and glutaconic acid; cycloaliphatic dicarboxylic acids such as cyclohexanedicarboxylic acid and methylmedicic acid; anhydrides and lower alkyl esters of these carboxylic acids 1 type or 2 types or more of these are used.

  Examples of the polyhydric alcohol used in the polyester resin include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,4-butenediol, neopentyl glycol, 1 Alkylene glycols such as 1,5-pentane glycol and 1,6-hexane glycol; alkylene ether glycols such as diethylene glycol, triethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol and polytetramethylene glycol; 1,4-cyclohexane Aliphatic polyhydric alcohols such as dimethanol and hydrogenated bisphenol A; bisphenols such as bisphenol A, bisphenol F, and bisphenol S, and bisphenols It can be mentioned alkylene oxide adducts can be used in combination of two or more thereof.

The glass transition temperature (Tg) of the binder resin is preferably in the range of 54 to 70 ° C. When the glass transition temperature is less than 54 ° C., there is a risk of solidifying in the developing device or the toner cartridge. On the other hand, when the glass transition temperature exceeds 70 ° C., the toner may not be sufficiently fixed on the transfer object such as paper.
In order to measure the glass transition temperature, for example, DSC6200 manufactured by SII (SII) Technology Co., Ltd. is used. About 10 mg of a sample is placed in an aluminum sample container, placed on a holder unit, and set in an electric furnace. And after heating from 30 degreeC to 1700 degreeC with the temperature increase rate of 10 degreeC / min, the sample was cooled to 30 degreeC, and it heated at the temperature increase rate of 10 degreeC / min again to 170 degreeC, and performed DSC measurement. The glass transition temperature is determined by calculating from the contact point between the tangent line of the endothermic curve near the glass transition temperature and the base line using the analysis system in the DSC 6200.

(Release agent)
As the mold release agent, for example, various waxes, low molecular weight olefin resins, and the like can be used. Examples of waxes include polyhydric alcohol esters of fatty acids, higher alcohol esters of fatty acids, alkylene bis fatty acid amide compounds, natural waxes, and the like. Examples of the low molecular weight olefin-based resin include polypropylene, polyethylene, propylene-ethylene copolymer having a number average molecular weight in the range of 1,000 to 10,000, particularly 2,000 to 6,000. The content of the release agent is preferably 0.1 to 20 parts by weight with respect to 100 parts by weight of the binder resin.

(Coloring agent)
The colorant that can be used for the production of the toner particles is not particularly limited, and examples thereof include magenta, cyan, yellow, and black colorants.

  As the magenta colorant, for example, C.I. I. Pigment red 81, C.I. I. Pigment red 122, C.I. I. Pigment red 57, C.I. Pigment Red 49, C.I. I. Solvent Red 49, C.I. I. Solvent Red 19, C.I. I. Solvent Red 52, C.I. I. Basic Red 10, C.I. I. Disperse Red 15 etc. are mentioned.

  As the cyan colorant, for example, C.I. I. Pigment blue 15, C.I. I. Pigment blue 15-1, C.I. Pigment blue 16, C.I. I. Solvent Blue 55, C.I. I. Solvent Blue 70, C.I. I. Direct Blue 86, C.I. I. Direct Blue 25 etc. are mentioned.

  Examples of the yellow colorant include nitro pigments such as naphthol yellow S, azo pigments such as Hansa Yellow 5G, Hansa Yellow 3G, Hansa Yellow G, Benzidine Yellow G, and Vulcan Fast Yellow 5G, or yellow iron oxide and ocher. And inorganic pigments. In addition, C.C. I. Pigment yellow 12, C.I. I. Pigment yellow 180, C.I. I. Solvent Yellow 2, C.I. I. Solvent Yellow 6, C.I. I. Solvent Yellow 14, C.I. I. Solvent Yellow 15, C.I. I. Solvent Yellow 16, C.I. I. Solvent Yellow 19, C.I. I. Solvent yellow 21 etc. are mentioned.

  Examples of the black colorant include carbon black such as furnace black, channel black, acetylene black, run black, and aniline black. Moreover, you may add the metal (magnetic powder) which shows ferromagnetism, such as iron, cobalt, nickel, such as ferrite and magnetite, as a black type | system | group coloring agent.

  In the case of a magnetic toner, magnetic powder is used for the toner, and this magnetic powder also serves as a colorant. Magnetic powders known per se, for example, iron, cobalt, nickel and other ferromagnetic metals such as ferrite, magnetite, alloys, compounds containing these elements, or ferromagnetic elements are included. An alloy that exhibits ferromagnetism by applying an appropriate heat treatment, chromium dioxide, or the like can be given. These magnetic powders are uniformly dispersed in the above-described binder resin in the form of fine powder having an average particle diameter of 0.1 to 1 μm, particularly 0.1 to 0.5 μm. The magnetic powder can also be used after being subjected to a surface treatment with a surface treatment agent such as a titanium coupling agent or a silane coupling agent. The average particle diameter of the magnetic powder is a Martin diameter (equivalent circle diameter) measured for 300 magnetic powders photographed by magnifying a photograph taken with a transmission electron microscope (magnification 10,000 times) four times. Is the average value.

(Charge control agent)
In the toner of the present invention, the charge level and charge rising characteristics (indicator of whether to charge to a constant charge level in a short time) are remarkably improved, and from the viewpoint of obtaining excellent durability and stability characteristics, etc. It is preferable to add a control agent. Here, the kind of the charge control agent to be added is not particularly limited, but examples thereof include nigrosine, quaternary ammonium salt compounds, and resin-type charge control agents in which an amine compound is bonded to the resin. It is preferable to use a charge control agent exhibiting positive chargeability. Further, these charge control agents may be used in combination. The content of the charge control agent is preferably 0.1 to 10 parts by weight with respect to 100 parts by weight of the binder resin.

(Career)
As the carrier used for the two-component developer containing the toner according to the present invention, a carrier core material whose surface is coated with a resin can be used. Although it does not specifically limit as a carrier core material, For example, magnetic body metals, such as iron, nickel, cobalt, and those alloys, or alloys containing rare earth, hematite, magnetite, manganese-zinc ferrite, nickel-zinc ferrite Magnetic particles produced by sintering and atomizing magnetic materials such as soft ferrites such as manganese-magnesium ferrite and lithium ferrite, iron-based oxides such as copper-zinc ferrite and mixtures thereof Can be used. Examples of the surface coating agent for the carrier core material include fluorine-based binder resins (polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, etc.). The particle diameter of the carrier is generally 20 to 200 · m, particularly 30 to 150 · m in terms of particle diameter by electron microscopy. In addition, 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, etc. when the magnetic material is mainly used. The toner concentration in the two-component developer comprising the toner and carrier is 1 to 20% by weight, preferably 3 to 15% by weight. When the toner concentration is less than 1% by weight, the image density becomes too thin, while when the toner concentration exceeds 20% by weight, toner scattering occurs in the developing device, and the toner adheres to the background portion such as the machine dirt or transfer paper. There is a risk of malfunction.

(Image forming device)
As an embodiment of the image forming apparatus of the present invention, for example, as shown in FIG. 1, four image forming units 101, 102, 103, 104 are arranged in a tandem type (transfer body) arranged on a transfer belt 11 (transfer body). Direct transfer tandem system) full-color image forming apparatus.

  As shown in FIG. 1, a transfer belt 11 is provided in a housing 10 of the image forming apparatus so as to run while being stretched between a pair of rollers 12 and 12 ′. A toner image is placed on the transfer belt 11. Cyan, magenta, yellow, and black image forming units 101, 102, 103, and 104 are arranged in the order of transfer.

  Each of the image forming units 101, 102, 103, and 104 is provided around the photosensitive drums 61, 62, 63, and 64, and the surface of the photosensitive drums 61,. The charging device 1 for charging, the exposure device 2 for forming an electrostatic latent image on the surface of the charged photosensitive drums 61,. The developing device 3 for forming a toner image and the cleaning means 5 for removing untransferred toner from the surfaces of the photosensitive drums 61,.

In the image forming units 102, 103, and 104, magenta toner, yellow toner, and black toner are accommodated, respectively. The charging device 1 preferably uses a charging roller in order to reduce the generation of ozone.

(Image formation process)
Next, an image forming process of the image forming apparatus will be described. Taking the image forming unit 101 as an example, first, the surface of the photosensitive drum 61 is uniformly charged positively by the charging device 1 (charging process). Next, an electrostatic latent image is formed on the surface of the photosensitive drum 61 by the exposure device 2 (exposure process).

  In the developing device 3, the toner T <b> 1 supplied from the toner hopper is agitated and mixed with the carrier and sequentially supplied to the developing sleeve 31 to form a developer layer on the developing sleeve 31. The developer in the developing sleeve 31 is sent to a position facing the photosensitive drum 61 (developing portion) by the rotation of the developing sleeve 31. At this time, the amount of developer sent to the developing unit is controlled by a blade (not shown) and frictional charge is applied to the toner T1. The charged toner T1 adheres to the electrostatic latent image on the photosensitive drum 61, and the electrostatic latent image is visualized (developed) to form a toner image. In the other image forming units 102, 103, and 104, the electrostatic latent images on the photosensitive drums 62, 63, and 64 are visualized and toner images are formed in the same flow as described above (development process).

  On the other hand, the transfer paper 81 conveyed from the paper feed cassette 13 provided in the lower part of the housing 10 moves from the right to the left on the transfer conveyance belt 11 as indicated by an arrow in FIG. At this time, a bias charge having a polarity opposite to the charging polarity of the toner is applied to the transfer roller 4 provided to face the photosensitive drums 61,. The toner images of the respective colors formed on the photosensitive drums 61,..., 64 are sequentially transferred from the upstream photosensitive drum 61 to the transfer paper 81 conveyed above (transfer process).

  The toner that has not been transferred onto the photosensitive drums 61,..., 64 is removed by the cleaning means 5 having a cleaning blade. The full color image transferred onto the transfer paper 81 is melted and fixed on the transfer paper 81 by applying heat and pressure in the fixing means 7 having the fixing roller 71 and the lower fixing roller 72, and then the transfer paper 81. Is discharged above the housing 10.

(Photoconductor)
As the photoreceptor constituting the photoreceptor drums 61,..., 64, an organic photoreceptor provided with an organic photosensitive layer containing at least a charge generator and a charge transport agent on a conductive substrate, or an amorphous silicon layer, Se. An inorganic photosensitive member provided with a photosensitive layer, a ZnO photosensitive layer, a CdS photosensitive layer, or the like can be used, but it is particularly preferable to use an amorphous silicon photosensitive member. Amorphous silicon photoreceptors usually include an amorphous silicon-based photosensitive layer on the surface of a conductive substrate formed in a predetermined shape such as a drum shape. The amorphous silicon-based photosensitive layer can be formed, for example, by a vapor phase growth method such as a glow discharge decomposition method, a sputtering method, an ECR method, or a vapor deposition method. In forming the photosensitive layer, H or a halogen element may be included. it can. In order to adjust the characteristics of the photoreceptor, an element such as C, N, or O may be included, or a group 13 element or a group 15 element in the periodic table (long period type) may be included.

Specifically, the photosensitive layer is preferably formed from various photoconductive materials such as a-SiC, amorphous silicon-based materials such as a-SiC, a-SiO, and a-SiON. In particular, a-SiC is preferably used. In that case, the value of x in Si _1-x C _x should be set to 0 <x ≦ 0.5, preferably 0.05 ≦ x ≦ 0.45. Within this range, the a-SiC layer can have a higher resistance than the a-Si layer while maintaining good carrier transport, and the photosensitivity characteristics of the photoreceptor can be improved.

  In the image forming method described above, the cohesive titanium oxide is developed on the photosensitive drum together with the toner particles and conveyed to the transfer region, but a part thereof is detached from the toner particles in the transfer process and remains on the drum surface. , Many stay on the cleaning blade. As a result, the surface of the photosensitive member can be firmly polished by the high-hardness cohesive titanium oxide retained between the drum surface and the cleaning blade, and discharge products generated when the charging roller comes into contact with the drum surface and discharges are generated. Since it is removed, the frictional resistance of the drum surface is reduced, the cleaning blade is prevented from being rolled up, and the occurrence of image flow in a high temperature and high humidity environment can be suppressed. Moreover, since the cohesive titanium oxide has a relatively low resistance, it is possible to suppress the occurrence of black spots due to dielectric breakdown on the drum.

EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further in detail, this invention is not limited to a following example. The characteristic value of titanium oxide was measured as follows.
(1) Secondary particle diameter The secondary particle diameter was measured by observation with an electron microscope.
(2) Vickers hardness Using a Vickers hardness tester (Shimadzu Corporation dynamic ultra micro hardness tester DUH-W201), the Vickers hardness tester was molded to a thickness of 5 mm in a 20 mm diameter mold, and the Vickers indenter was 15 under a 10 g load. The Vickers hardness was determined from the indentation on the sample.

(Production of titanium oxide a)
70 g of titanium oxide “PT-401M” (manufactured by Ishihara Sangyo Co., Ltd.) having a primary particle diameter of 70 nm was dispersed in 500 g of toluene, and 10 g of tin oxide and 1 g of antimony were added thereto and mixed. The solid substance obtained by filtering and washing this was put into 1000 g of water, and 1 g of a 1% by mass aqueous solution of polyacrylamide (manufactured by Arakawa Chemical Co., Ltd.) was further added. And after mixing for 3 minutes with a homomixer, it filtered and wash | cleaned again, and the obtained aggregated particle was sintered at 800 degreeC for 2 hours, and the aggregated titanium oxide of electroconductive fine particles was obtained. To 100 g of this titanium oxide, 3 g of a titanium coupling agent was added and mixed at 150 ° C. for 30 minutes to obtain titanium oxide a. This titanium oxide a had a Vickers hardness of 700 kg / mm ² and a secondary particle size of 280 nm.

(Production of titanium oxide b)
Titanium oxide b was prepared in the same manner as titanium oxide a except that 10 g of a 1% aqueous solution of acrylamide / sodium acrylate copolymer was added in place of the polyacrylamide aqueous solution. Titanium oxide b had a Vickers hardness of 680 kg / mm ² and a secondary particle size of 220 nm.

(Production of titanium oxide c)
Titanium oxide c was prepared in the same manner as titanium oxide a except that 10 g of 1% aluminum sulfate aqueous solution was added instead of polyacrylamide aqueous solution in the preparation of titanium oxide a. Titanium oxide c had a Vickers hardness of 710 kg / mm ² and a secondary particle size of 300 nm.

(Production of titanium oxide d)
Titanium oxide d was prepared in the same manner as titanium oxide a except that in the preparation of titanium oxide a, 10 g of a 1% aqueous solution of polyaluminum chloride was added instead of the polyacrylamide aqueous solution. Titanium oxide d had a Vickers hardness of 720 kg / mm ² and a secondary particle size of 350 nm.

(Production of titanium oxide e)
Titanium oxide e was prepared in the same manner as titanium oxide a, except that 10 g of a 1% polyacrylamide aqueous solution was added instead of the polyacrylamide aqueous solution in the preparation of titanium oxide a. Titanium oxide e had a Vickers hardness of 800 kg / mm ² and a secondary particle size of 410 nm.

(Production of titanium oxide f)
In the production of the titanium oxide a, except that 60 g of titanium oxide “PT-501A” (manufactured by Ishihara Sangyo Co., Ltd.) having a primary particle diameter of 100 nm was added instead of titanium oxide “PT-401M” having a primary particle diameter of 70 nm, Titanium oxide f was produced in the same manner as titanium oxide a. Titanium oxide f had a Vickers hardness of 600 kg / mm ² and a secondary particle size of 240 nm.

(Production of titanium oxide g)
Titanium oxide g was prepared in the same manner as titanium oxide a except that in the preparation of titanium oxide a, the amount of polyacrylamide aqueous solution added was 0.6 g instead of 1 g. Titanium oxide g had a Vickers hardness of 580 kg / mm ² and a secondary particle size of 220 nm.

(Production of titanium oxide h)
Titanium oxide h was produced in the same manner as titanium oxide a except that tin oxide and antimony were not added in the production of titanium oxide a. The titanium oxide h had a Vickers hardness of 700 kg / mm ² and a secondary particle size of 300 nm.

(Production of titanium oxide i)
In the production of the titanium oxide a, except that 50 g of titanium oxide “PT-501R” (manufactured by Ishihara Sangyo Co., Ltd.) having a primary particle diameter of 180 nm was added instead of titanium oxide “PT-401M” having a primary particle diameter of 70 nm. Titanium oxide i was produced in the same manner as titanium oxide a. The titanium oxide i had a Vickers hardness of 480 kg / mm ² and a secondary particle size of 170 nm.

(Production of titanium oxide j)
Titanium oxide j was prepared in the same manner as titanium oxide a except that in the preparation of titanium oxide a, the amount of polyacrylamide aqueous solution added was changed to 0.2 g instead of 1 g. Titanium oxide j had a Vickers hardness of 440 kg / mm ² and a secondary particle size of 140 nm.

Example 1
(Production of black toner)
The following toner components were mixed for 2 minutes with a Henschel mixer (Mitsui Mining Co., Ltd.) and melt-kneaded with a twin screw extruder to prepare a toner mixture.
-100 parts by weight of polyester resin obtained by condensing bisphenol A and fumaric acid-4 parts by weight of carbon black "MA-100" (manufactured by Mitsubishi Chemical Corporation)-Fischer-Tropsch wax "FT-100" (manufactured by Nippon Seiki Co., Ltd.) 3 parts by weight / quaternary ammonium salt compound “P-51” (manufactured by Orient Chemical Co., Ltd.) 2 parts by weight Next, the toner mixture was finely pulverized with an airflow pulverizer, classified with an air classifier, and the volume average diameter 8 μm toner particles were obtained. 1 part by weight of silica particles “TG-820” (manufactured by Cabot) and 1.5 parts by weight of titanium oxide a are added to 100 parts by weight of the toner particles, and 10 minutes at 3000 rpm using a Henschel mixer. A black toner was prepared by mixing.

(Production of yellow toner)
In place of carbon black “MA-100”, C.I. I. Except for adding 2 parts by weight of Pigment Yellow 180, the same procedure as in the black toner preparation method was performed.

(Production of cyan toner)
In place of carbon black “MA-100”, C.I. I. Except that 3 parts by weight of Pigment Blue 15: 3 was added, the same procedure as in the above black toner preparation method was performed.

(Production of magenta toner)
In place of carbon black “MA-100”, C.I. I. Except that 3 parts by weight of Pigment Red 238 was added, the same procedure as in the black toner preparation method was performed.

(Creation of carrier)
Trimellitic anhydride (TMA) and 4,4′-diphenylmethane diisocyanate (MDI) were mixed in ion-exchanged water and copolymerized to prepare a polyamideimide solution. Next, 100 parts by weight of “MP-102” (manufactured by DuPont) as a tetrafluoroethylene-hexafluoropropylene copolymer (4.6 fluoride) (FEP) is dispersed in 100 parts by weight of this solution, and coating is performed. A resin solution was prepared. 5 parts by weight of the coating resin solution was spray-coated with 100 parts by weight of a ferrite carrier having a center particle diameter of 40 μm using a fluid coating apparatus. Thereafter, heat treatment was performed at 280 ° C. for 1 hour in the fluidized bed to cure the resin, and a coating carrier was produced.

(Development of developer)
A two-component developer in which the toner and the carrier were blended so that the toner concentration was 10% by weight and uniformly stirred and mixed was prepared for each toner of black toner, yellow toner, cyan toner, and magenta toner.

(Example 2)
A toner and a two-component developer were prepared in the same manner as in Example 1 except that titanium oxide b was used instead of titanium oxide a in the production of the toner and the two-component developer of Example 1.

(Example 3)
A toner and a two-component developer were prepared in the same manner as in Example 1 except that in the preparation of the toner and the two-component developer of Example 1, titanium oxide c was used instead of titanium oxide a.

Example 4
A toner and a two-component developer were prepared in the same manner as in Example 1 except that titanium oxide d was used instead of titanium oxide a in the preparation of the toner and the two-component developer of Example 1.

(Example 5)
A toner and a two-component developer were prepared in the same manner as in Example 1 except that in the preparation of the toner and the two-component developer of Example 1, titanium oxide e was used instead of titanium oxide a.

(Example 6)
A toner and a two-component developer were prepared in the same manner as in Example 1 except that in the preparation of the toner and the two-component developer of Example 1, titanium oxide f was used instead of titanium oxide a.

(Example 7)
A toner and a two-component developer were prepared in the same manner as in Example 1 except that in the preparation of the toner and the two-component developer of Example 1, titanium oxide g was used instead of titanium oxide a.

(Example 8)
A toner and a two-component developer were prepared in the same manner as in Example 1 except that in the preparation of the toner and the two-component developer of Example 1, titanium oxide h was used instead of titanium oxide a.

Example 9
In the production of the toner and the two-component developer of Example 1, the toner and the two-component developer were the same as in Example 1 except that the amount of titanium oxide a added was changed to 3 parts by weight instead of 1.5 parts by weight. Was made.

(Example 10)
In the production of the toner and the two-component developer of Example 1, the toner and the two-component developer are the same as in Example 1 except that the amount of titanium oxide a added is 6 parts by weight instead of 1.5 parts by weight. Was made.

(Comparative Example 1)
A toner and a two-component developer were prepared in the same manner as in Example 1 except that in the preparation of the toner and the two-component developer of Example 1, titanium oxide i was used instead of titanium oxide a.

(Comparative Example 2)
A toner and a two-component developer were prepared in the same manner as in Example 1 except that in the preparation of the toner and the two-component developer of Example 1, titanium oxide j was used instead of titanium oxide a.

(Evaluation test and evaluation method)
For the developers prepared in Examples 1 to 12 and Comparative Examples 1 and 2, a color MFP “KM-C3232” (manufactured by Kyocera Mita Co., Ltd.) equipped with an amorphous silicon photoreceptor was used. An image characteristic evaluation test was conducted.
The initial image is an image output immediately after stabilization after the developer is set and the machine power is turned on. The image is a solid image of 2 × 2 cm provided at three places on the left side, the central part, and the right side of the printed document (printing ratio 5%). The image density was determined from the average value of the reflection densities of the three images. Thereafter, the developer was taken out from the developing machine, and the initial charge amount of the toner was measured.
Next, the image density and charge amount after printing 300,000 sheets continuously at the same printing ratio of 5% were measured in the same manner as the initial image.
The image density was measured with a Macbeth reflection densitometer “RD-19I” (manufactured by Gretag Macbeth), and the charge amount was measured with a suction-type charge amount measuring device (manufactured by Trek). The image density was 1.30 or higher and judged to be acceptable. These results are shown in Table 1.

  In Comparative Example 1, the evaluation was stopped because the color was fogged at the stage of confirming the performance of the initial image. In Comparative Example 2, a cleaning failure occurred due to the winding of the cleaning blade after 10,000 sheets, and the image density of black toner and magenta toner after 300,000 sheets was less than 1.30. In contrast, the image density and the charge amount at the initial stage and after 300,000 sheets in Examples 1 to 10 all reached the acceptance criteria.

1 is a schematic diagram of an image forming apparatus according to an embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Charging device 2 Exposure device 3 Developing device 4 Transfer roller 5 Cleaning means 7, 7 ′ / Fixing means 10 Housing 11 Transfer conveyance belt (transfer body)
12, 12 ′, roller 13 paper feed cassette 31 developing sleeves 61, 62, 63, 64 photosensitive drum 71 upper fixing roller 72 lower fixing rollers 101, 102, 103, 104 image forming unit

Claims (4)

An electrophotographic toner, characterized in that a coherent titanium oxide having a Vickers hardness of 500 kg / mm ² or more and a secondary particle diameter of 200 nm or more is externally added.   The electrophotographic toner according to claim 1, wherein the addition amount of the titanium oxide is 0.1 to 5.0 parts by weight with respect to 100 parts by weight of the toner particles.   An image forming apparatus comprising an amorphous silicon photoconductor and a charging roller, wherein the toner according to claim 1 is used.   The image forming apparatus according to claim 4, which is a tandem type full-color image forming apparatus.

Images