JP2011043759A - Toner for electrostatic charge image development, and image forming apparatus and image forming method using the toner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a toner for electrostatic charge image development in which an external additive is suppressed from embedding in the surfaces of toner base particles and from separating from the surfaces of toner base particles and secondary aggregation of the external additive on the surfaces of toner base particles is eliminated. <P>SOLUTION: The toner for electrostatic charge image development includes an external additive added to toner base particles, wherein the external additive comprises particles having a number average primary particle diameter of 20 nm or more and less than 80 nm, a ratio of the minimum particle diameter to the number average primary particle diameter (minimum particle diameter/number average primary particle diameter) of not less than 0.5 and a ratio of the maximum particle diameter to the number average primary particle diameter (maximum particle diameter/number average primary particle diameter) of not more than 1.7, and the external additive particles are present in a monodispersion state in the surfaces of toner base particles. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electrostatic image developing toner used in an electrophotographic system, an image forming apparatus using the toner, and an image forming method.

  In general, in an image forming apparatus such as a copying machine, a printer, or a digital multifunction machine that forms an image on a sheet by electrophotography, an electrostatic charge image (electrostatic latent image) formed on the peripheral surface of a photosensitive drum as an image carrier. Image) is developed with toner by a developing device, and visualized as a toner image. The toner image on the photosensitive drum is transferred onto a sheet by a transfer device, and then heated and pressed by a fixing device to be fixed on the sheet. The sheet on which the toner image is fixed is finally discharged out of the image forming apparatus.

  The electrostatic image developing toner used in such an electrophotographic system may be used alone as a one-component developer or may be used as a two-component developer mixed with a magnetic carrier. In the case of a two-component developer, for example, a magnetic roller as a two-component developer carrying member is disposed in the vicinity of the developing roller in the developing device of the image forming apparatus, and a magnetic brush is provided on the peripheral surface of the magnetic roller. Thus, only the two-component developer toner carried thereon moves onto the developing roller, whereby a thin toner layer is formed on the developing roller. The developing roller as the toner carrying member is disposed to face the photosensitive drum, and the toner carried as a thin toner layer on the peripheral surface of the developing roller moves on the photosensitive drum (this “movement”). The peripheral surface of the developing roller and the peripheral surface of the photosensitive drum are separated from each other, and the toner flies from the peripheral surface of the developing roller to the peripheral surface of the photosensitive drum (including a touch-down method). The electrostatic charge image on the drum is visualized.

  On the other hand, in the case of a one-component developer or a two-component developer, an external additive is usually added to toner base particles (bulk toner) in which a colorant or the like is mixed in a binder resin. is there. The external additive, for example, improves toner fluidity, stabilizes charging properties, stabilizes adhesion to a toner carrier such as a developing roller or a photosensitive drum, and suppresses direct contact between toner mother particles (spacer function). Therefore, it is added to the toner base particles. Conventionally known as such external additives are silica fine particles, titanium oxide fine particles, aluminum oxide fine particles, silicon carbide fine particles, metal soap fine particles, and the like. In particular, fumed particles having a primary particle diameter of about 7 to 20 nm. Silica, sulfuric acid titania and the like are widely used because of relatively good effects.

  However, with the recent increase in the speed of image forming apparatuses, mechanical stress acting on the toner tends to increase. As a result, when the primary particle diameter of the external additive becomes fine to about 7 to 20 nm, There is a problem that the additive is easily embedded in the surface of the toner base particles, and various effects such as improvement of the fluidity of the toner and stabilization of the adhesion to the carrier are not sufficiently exhibited.

  Therefore, as described in Patent Document 1, as an external additive, in addition to an inorganic compound having an average primary particle size of 10 nm to less than 30 nm and an inorganic compound having an average primary particle size of 30 nm to 100 nm, an average of 1 It is proposed to use a mixture of silica having a secondary particle size of 80 nm to 300 nm and a relatively large particle size. According to this, silica having a relatively large particle diameter exhibits a spacer function, and embedding of an inorganic compound having a relatively small particle diameter on the surface of the toner base particles is avoided.

Japanese Patent Laying-Open No. 2005-3726 (paragraphs 0020 and 0064)

  However, the relatively large external additive having an average primary particle size of 80 nm or more is likely to be detached from the surface of the toner base particle, so that the detached external additive is applied to the surface of a toner carrier such as a developing roller or a photosensitive drum. In the case of a two-component developer, the surface of the magnetic carrier is also contaminated. In the case of a tandem color image forming apparatus, the toner images of each color are combined into one before the color image is transferred to the paper. There is a problem that the surface of the intermediate transfer belt to be superposed is also contaminated (contamination problem in the image forming apparatus).

  Also, since the conventional external additive has a relatively wide particle size distribution, for example, when the minimum particle size of the external additive is too small away from the average primary particle size, or when the maximum particle size of the external additive is When the average primary particle size is too far away from the average primary particle size, there is a problem that the expected effects of the external additive (improved fluidity, spacer function, etc.) cannot be obtained satisfactorily.

  In addition, when the conventional external additive has a primary particle size as small as about 7 to 20 nm, the external additive tends to agglomerate on the surface of the toner base particles. There is also a problem that the coating amount is reduced, and various effects such as improvement of toner fluidity and stabilization of adhesion to the carrier are not so much increased with respect to the addition amount of the external additive.

  The present invention addresses the above-described problems in toners for developing electrostatic images used in electrophotography. Both the embedding of external additives on the surface of toner base particles and the separation from the surface of toner base particles are both performed. Further, it is possible to provide a toner for developing an electrostatic image in which the expected effect of the external additive is satisfactorily obtained and secondary aggregation on the surface of the toner base particles of the external additive is eliminated, and the toner It is an object of the present invention to provide an image forming apparatus and an image forming method using the image forming apparatus.

  That is, one aspect of the present invention is an electrostatic charge image developing toner in which an external additive is added to toner base particles, and the external additive has a number average primary particle size of 20 nm or more and less than 80 nm, The ratio between the minimum particle diameter and the number average primary particle diameter (minimum particle diameter / number average primary particle diameter) is 0.5 or more, and the ratio between the maximum particle diameter and the number average primary particle diameter (maximum particle diameter). The electrostatic charge image developing toner is characterized in that the toner has a number average primary particle diameter) of 1.7 or less and is monodispersed on the surface of the toner base particles (claim 1).

  According to this configuration, in the electrostatic charge image developing toner in which the external additive is added to the toner base particles, the external additive is a particle having a number average primary particle size of 20 nm or more, and therefore the particle size is excessive. Even if the mechanical stress acting on the toner tends to increase with the recent increase in the speed of the image forming apparatus, the embedding of the external additive on the surface of the toner base particles is suppressed. As a result, various effects such as improvement of toner fluidity and stabilization of adhesion to the carrier are sufficiently exhibited, and image quality (image quality) such as image density, fog (non-image area density), and charge amount is long. It will be secured stably over the period.

  Further, since the external additive is a particle having a number average primary particle diameter of less than 80 nm, the particle diameter is not excessively large, and separation of the external additive from the surface of the toner base particle is suppressed. As a result, the problem of contamination in the image forming apparatus due to the detached external additive is avoided.

  The external additive has a ratio of the minimum particle size to the number average primary particle size (minimum particle size / number average primary particle size) of 0.5 or more, and the maximum particle size and number average primary particle. Since the ratio to the diameter (maximum particle diameter / number average primary particle diameter) is 1.7 or less, both the minimum particle diameter and the maximum particle diameter of the external additive are too far from the number average primary particle diameter. The particle size distribution is relatively narrow. As a result, the expected effects of external additives such as fluidity improvement and spacer function can be obtained satisfactorily.

  Further, since the external additive is particles that are monodispersed on the surface of the toner base particles, secondary aggregation on the surface of the toner base particles is eliminated. As a result, the surface of the toner base particles is satisfactorily and uniformly coated with the external additive, and the toner fluidity is improved and the adhesion to the carrier is stabilized in a smaller amount than when the external additive is secondary agglomerated. Various effects such as conversion will be obtained.

  In that case, in the above configuration, silica particles produced by a sol-gel method can be employed as the external additive (claim 2).

  According to this configuration, the external additive is reliably monodispersed on the surface of the toner base particles, and secondary aggregation is reliably eliminated. That is, the silica particles produced by the sol-gel method are silica particles that are less likely to agglomerate and are excellent in monodispersity than, for example, fumed silica particles produced by a dry high-temperature hydrolysis method.

In that case, in the above configuration, the silica particles having a true specific gravity of 1.4 to 1.9 g / cm ³ can be employed.

According to this configuration, since the silica particles have a relatively low specific gravity, the separation of the silica particles from the surface of the toner base particles and the embedding in the surface of the toner base particles are further suppressed. That is, the silica particles produced by the sol-gel method are silica particles having a smaller true specific gravity than, for example, fumed silica particles produced by the dry high-temperature hydrolysis method (the true specific gravity of fumed silica is about 2). 2 g / cm ³ ).

  Another aspect of the present invention is an image forming apparatus using the toner for developing an electrostatic charge image having the above-described configuration (claim 4). Here, the image forming apparatus generally includes an image carrier on which an electrostatic charge image is formed on a peripheral surface, and a developing device that develops the electrostatic charge image of the image carrier using toner. The toner for developing an electrostatic charge image having the above configuration is used as the toner.

  According to still another aspect of the present invention, there is provided an image forming method using the toner for developing an electrostatic charge image having the above structure. Here, the image forming method generally includes a step of forming an electrostatic charge image on the peripheral surface of the image carrier and a step of developing the electrostatic image of the image carrier using toner. Therefore, the toner for developing an electrostatic charge image having the above-described configuration is used as the toner.

  According to these configurations, in the image forming apparatus or the image forming method, the embedding of the external additive on the surface of the toner base particle and the separation from the surface of the toner base particle are suppressed, and the expected effect of the external additive is satisfied. The secondary aggregation on the surface of the toner base particles of the external additive is eliminated.

  According to the present invention, both the embedding of the external additive on the surface of the toner base particle and the separation from the surface of the toner base particle are suppressed, and the expected effect of the external additive can be obtained satisfactorily. Since secondary aggregation on the surface of the mother particle is eliminated, image quality (image quality) such as image density, fog (non-image area density), charge amount, etc. is secured over a long period of time, and image formation Contamination problems within the device are avoided.

It is a particle size distribution (particle size distribution) figure of silica A, B, C, D, and E used as an external additive in the Example. FIG. 2 is a schematic diagram showing an enlarged dispersion state of an external additive on the surface of a toner base particle, in which (a) is manufactured by a sol-gel method and has a number average primary particle diameter of 32 nm. A plan view of the toner A showing that the silica C used as the toner is monodispersed without secondary aggregation on the surface of the toner base particles, (b) is a cross-sectional view thereof, and (c) is a dry high-temperature hydrolysis. Of toner E having a number average primary particle diameter of 20 nm, which is produced by the method, and indicates that the silica (fumed silica) A used as an external additive in the examples is secondarily aggregated on the surface of the toner base particles. A plan view, (d) is a cross-sectional view thereof.

[Toner for electrostatic image development]
The toner for developing an electrostatic charge image according to the present invention has a configuration in which an external additive is added to toner base particles (bulk toner).

<Toner base particles>
The toner base particles are obtained by blending a binder resin with a colorant, a release agent, a charge control agent, or the like. The toner base particles are prepared by mixing these raw materials with a mixer or the like, melt-kneading with an extruder or the like, cooling, pulverizing, and classifying. The volume average particle diameter of the toner base particles is 2 to 12 μm, more preferably 4 to 10 μm, and still more preferably 6 to 8 μm. In the present invention, the toner base particles are preferably spherical with a high degree of circularity (close to 1), but may be, for example, a cylindrical shape depending on the situation.

(Binder resin)
In the present invention, as the binder resin, those conventionally used as the binder resin for toner base particles can be used without particular limitation. Specific examples thereof include, for example, styrene resins, acrylic resins, styrene-acrylic resins, polyethylene resins, polypropylene resins, vinyl chloride resins, polyester resins, polyamide resins, polyurethane resins, polyvinyl alcohol resins. Examples thereof include thermoplastic resins such as resins, vinyl ether resins, N-vinyl resins, and styrene-butadiene resins. These may be used alone or in combination of two or more.

  In the present invention, as the binder resin, it is preferable to use the thermoplastic resin as described above from the viewpoint of good fixability, but it is not necessary to use only the thermoplastic resin. A part of the functional resin may be used. Thus, by introducing a partially crosslinked structure into the binder resin, it is possible to improve the storage stability, form retention or durability of the toner without deteriorating the fixability.

  Examples of the thermosetting resin that can be used in the present invention include bisphenol A type epoxy resins, hydrogenated bisphenol A type epoxy resins, novolac type epoxy resins, polyalkylene ether type epoxy resins, cyclic aliphatic type epoxy resins, and cyanates. Examples thereof include resins. These may be used alone or in combination of two or more.

  The glass transition point (Tg) of the binder resin is preferably, for example, 50 to 65 ° C, and more preferably 50 to 60 ° C. When the glass transition point of the binder resin is less than 50 ° C., the toners are fused in the developing device during operation of the image forming apparatus, or the toners are fused in the container during storage or transportation of the toner. In addition, the storage stability of the toner tends to decrease. On the other hand, when the glass transition point of the binder resin exceeds 65 ° C., the low-temperature fixability of the toner tends to decrease.

(Coloring agent)
In the present invention, as the colorant, those conventionally used as a colorant for monochrome toners or color toners can be used without particular limitation. Specific examples thereof include pigments such as carbon black and dyes such as acid violet.

  In this invention, the compounding quantity of a coloring agent is 1-15 mass parts with respect to 100 mass parts of binder resin, for example.

(Release agent)
In the present invention, the release agent is blended for the purpose of improving the fixing property of the toner and preventing the deterioration of the offset property. In the present invention, as a release agent, those conventionally used as a release agent for toner base particles can be used without particular limitation. Specific examples thereof include polyethylene wax, polypropylene wax, Teflon (registered trademark) wax, Fischer-Tropsch wax, paraffin wax, ester wax, carbana wax, montan wax, rice wax, and the like. These may be used alone or in combination of two or more.

  In this invention, the compounding quantity of a mold release agent is 1-5 mass parts with respect to 100 mass parts of binder resin, for example. When the blending amount of the release agent is less than 1 part by mass, there is a tendency that improvement in toner fixing property and prevention of deterioration in offset property are not satisfactorily achieved. On the other hand, when the compounding amount of the release agent exceeds 5 parts by mass, the toners are fused, and the storage stability of the toner tends to be lowered.

(Charge control agent)
In the present invention, the charge control agent is blended for the purpose of maintaining the charge amount of the toner and improving the charge rising characteristic (characteristic of charging to a predetermined charge amount in a short time). When the toner is positively charged and used for development, a positively chargeable charge control agent is used. When the toner is negatively charged and used for development, a negatively chargeable charge control agent is used.

  In the present invention, as a positively chargeable charge control agent, those conventionally used as a positively chargeable charge control agent for toner base particles can be used without any particular limitation. Specific examples thereof include azine compounds such as pyridazine, pyrimidine, pyrazine, orthooxazine, metaoxazine, paraoxazine, orthothiazine, metathiazine, parathiazine, and 1,2,3-triazine. These may be used alone or in combination of two or more.

  In the present invention, as the negatively chargeable charge control agent, those conventionally used as a negatively chargeable charge control agent for toner base particles can be used without any particular limitation. Specific examples thereof include organometallic complexes such as acetylacetone metal complexes and salicylic acid metal complexes, and chelate compounds such as aluminum acetylacetonate and iron (II) acetylacetonate. These may be used alone or in combination of two or more.

  In this invention, the compounding quantity of an electric charge control agent is 0.5-15 mass parts with respect to 100 mass parts of binder resin, for example. When the amount of the charge control agent is less than 0.5 parts by mass, the image density decreases, it becomes difficult to maintain the image density, the fog (density in the non-image area) increases, or the photosensitive drum is contaminated. Tend to increase. On the other hand, when the blending amount of the charge control agent exceeds 15 parts by mass, there is a tendency that charging failure / image failure under high temperature and high humidity increases and contamination of the photosensitive drum increases.

<External additive>
The external additive is the center of the feature of the present invention, and first, it is required that the number average primary particle diameter is 20 nm or more and less than 80 nm (condition a). When the number average primary particle diameter of the external additive is less than 20 nm, the external additive is easily embedded in the surface of the toner base particles, and image quality such as image density, fog (non-image area density), charge amount, and the like. (Image quality) tends to decrease. On the other hand, when the number average primary particle diameter of the external additive is 80 nm or more, the external additive tends to be detached from the surface of the toner base particles, and the fluidity of the toner tends to be lowered and the developability tends to be insufficient. At the same time, there is a tendency for contamination in the image forming apparatus such as the toner carrier, the magnetic carrier, and the intermediate transfer belt to increase.

  In the present invention, the number average primary particle diameter of the external additive is more preferably 30 to 70 nm, and further preferably 40 to 60 nm.

  Next, in the present invention, the external additive has a ratio of the minimum particle size to the number average primary particle size (minimum particle size / number average primary particle size) of 0.5 or more, and the maximum particle size and number The ratio with respect to the average primary particle size (maximum particle size / number average primary particle size) is required to be 1.7 or less (condition b). As a result, both the minimum particle size and the maximum particle size of the external additive are not excessively separated from the number average primary particle size, and the particle size distribution is relatively narrow, so that the flowability is improved and the spacer function is not affected. The expected effect of the additive can be obtained satisfactorily. Conversely, when the ratio between the minimum particle size and the number average primary particle size of the external additive (minimum particle size / number average primary particle size) is less than 0.5, the maximum particle size and the number average primary particle When the ratio to the diameter (maximum particle diameter / number average primary particle diameter) exceeds 1.7, the minimum particle diameter and maximum particle diameter of the external additive are excessively separated from the number average primary particle diameter, and the particles The diameter distribution becomes relatively wide, and the expected effects of external additives such as fluidity improvement and spacer function cannot be obtained satisfactorily.

  In the present invention, the particle size distribution (particle size distribution), number average primary particle size, minimum particle size, and maximum particle size of the external additive are, for example, a flow type particle image analyzer (“FPIA-3000” manufactured by Sysmex Corporation). ) Etc., image analysis and statistical processing can be performed for measurement.

  Next, in the present invention, the external additive is required to be particles that are monodispersed on the surface of the toner base particles (condition c). As a result, the secondary additive is eliminated from the secondary aggregation on the surface of the toner base particles, and the surface of the toner base particles is satisfactorily coated with the external additive in comparison with the case where the external additive is secondary aggregated. Thus, various effects such as improvement of toner fluidity and stabilization of adhesion to the carrier can be obtained with a small amount.

  In the present invention, as long as the above conditions a, b, and c are satisfied, as the external additive, those conventionally used as the external additive added to the toner base particles can be used without particular limitation. Specific examples thereof include, for example, a dry high-temperature hydrolysis method (a dry method in which silicon chloride such as silicon tetrachloride is vaporized and a silica fine particle is synthesized by a gas phase reaction in a high-temperature hydrogen flame). Silica produced by fumed silica, deflagration method (dry method of synthesizing silica fine particles by oxidizing silicon in a stream of oxygen and cooling it to vapor with its reaction heat), sol-gel method (hydration of alkoxysilane) Silica produced by a wet method for synthesizing silica fine particles by decomposition), silica produced by a colloidal method (wet method for synthesizing silica fine particles by hydrolysis of water glass), sulfuric acid method, chlorine method or dry high-temperature water addition Examples thereof include titanium oxide, alumina, silicon carbide, and metal soap synthesized by a decomposition method. These may be used alone or in combination of two or more.

In the present invention, the external additive is preferably silica particles, and more preferably silica particles produced by a sol-gel method. This is because the silica particles produced by the sol-gel method are more easily monodispersed than the fumed silica particles produced by the dry high-temperature hydrolysis method, for example, and are less likely to aggregate secondarily. Further, silica particles produced by the sol-gel method have a smaller true specific gravity than, for example, fumed silica particles produced by a dry high-temperature hydrolysis method (the true specific gravity of silica produced by the sol-gel method is about 1). 4 to 1.9 g / cm ³ , and the true specific gravity of fumed silica is approximately 2.2 g / cm ³ ). Therefore, since the specific gravity is relatively low, the external additive is detached from the surface of the toner base particles. This is because it is further suppressed and is difficult to be buried.

  In the present invention, the surface of the external additive may be hydrophobized using silicone oil, aminosilane, hexamethyldisilazane, titanate coupling agent, silane coupling agent, or the like depending on the situation. .

  In the present invention, the external additive is more preferably a true sphere having a high degree of circularity (close to 1).

  The external addition process for producing the toner by adding the external additive to the toner base particles is carried out by stirring and mixing the toner base particles and the external additive in a dry manner. In that case, the stirring and mixing is preferably performed using a Henschel mixer, a Nauter mixer, or the like so that the external additive as fine particles is not buried in the surface of the toner base particles.

  In the present invention, the additive amount of the external additive that has been conventionally used can be employed without particular limitation as the additive amount of the toner base particles. For example, the external additive is 0.5 to 5.0 parts by mass, and more preferably 1.5 to 3.0 parts by mass with respect to 100 parts by mass of the toner base particles.

[Developer]
The toner for developing an electrostatic charge image according to the present invention can be used alone as a one-component developer or can be used as a two-component developer by mixing with a magnetic carrier.

<Magnetic carrier>
In the present invention, as the magnetic carrier, those conventionally used as a magnetic carrier for a two-component developer can be used without any particular limitation. As a specific example, for example, a carrier core material whose surface is coated with a resin can be used.

  Examples of the carrier core material include magnetic metals such as iron, nickel, and cobalt, alloys thereof, alloys containing rare earths, hematite, magnetite, manganese-zinc ferrite, nickel-zinc ferrite, manganese-magnesium. Magnetic particles produced by sintering and atomizing magnetic materials such as soft ferrites such as ferrite and lithium ferrite, iron oxides such as copper-zinc ferrite, and mixtures thereof. .

  Examples of the resin that covers the surface of the carrier core material include fluorine resins such as polytetrafluoroethylene, polychlorotrifluoroethylene, and polyvinylidene fluoride.

The particle diameter of the carrier is 20 to 200 μm, more preferably 30 to 150 μm, still more preferably 50 to 100 μm, as measured by electron microscopy. The apparent density of the carrier varies depending on the composition of the magnetic material, the surface structure, and the like, but generally it is preferably in the range of 3000 to 8000 kg / m ³ .

  The two-component developer can be prepared by stirring and mixing the toner and the magnetic carrier in a dry manner using, for example, a ball mill. The toner concentration in the two-component developer is 3 to 20% by mass, more preferably 5 to 16% by mass, and still more preferably 8 to 13% by mass. When the toner density is less than 3% by mass, the image density tends to be excessively thin. On the other hand, when the toner concentration exceeds 20% by mass, toner scattering occurs in the developing device during operation of the image forming apparatus, and fog (non-image area density) and contamination in the image forming apparatus tend to increase. .

[Image forming apparatus]
The image forming apparatus according to the present invention is configured to use the electrostatic charge image developing toner having the above-described configuration. An image forming apparatus generally includes a photosensitive drum (image carrier) on which an electrostatic charge image (electrostatic latent image) is formed on a peripheral surface, and a developing device that develops the electrostatic charge image on the photosensitive drum using toner. The electrostatic charge image developing toner having the above structure is used as the toner.

  A charging device, an exposure device, a developing device, a transfer device, and a cleaning device are disposed around the photosensitive drum.

  As the photosensitive drum, an organic photosensitive member (OPC) or an amorphous silicon photosensitive member is used. The charging device applies a predetermined potential to the peripheral surface of the photosensitive drum by generating corona discharge. The exposure apparatus selectively attenuates the potential of the peripheral surface of the photosensitive drum by irradiating light based on the image data to form an electrostatic charge image. The developing device forms a toner image by developing the electrostatic image formed on the peripheral surface of the photosensitive drum with toner. The transfer device transfers the toner image formed on the photosensitive drum onto the paper. The cleaning device removes the toner remaining on the peripheral surface of the photosensitive drum after the toner image is transferred onto the paper.

  The image forming apparatus further includes a fixing device having a heating roller and a pressure roller. The fixing device fixes the toner image on the paper by heating and pressurizing the paper on which the toner image is transferred.

  The developing device includes a housing that contains a two-component developer including toner and a magnetic carrier, a stirring roller that is rotatably provided in the housing, a magnetic roller (two-component developer carrier), and a developing roller (toner carrier). Body).

  The stirring roller is for charging newly supplied toner by stirring and for uniformly dispersing the toner in the two-component developer. The magnetic roller carries the two-component developer supplied from the stirring roller as a magnetic brush on the peripheral surface. A control blade for controlling the thickness of the magnetic brush on the magnetic roller is disposed around the magnetic roller. The developing roller is disposed in the vicinity of the magnetic roller, and only the toner moves from the magnetic brush on the magnetic roller to the peripheral surface, so that a thin toner layer is formed on the peripheral surface. The developing roller is disposed opposite to the photosensitive drum by a predetermined distance, and the toner moves from the toner thin layer on the peripheral surface onto the photosensitive drum (this “movement” is performed between the peripheral surface of the developing roller and the photosensitive drum). The electrostatic charge image on the photosensitive drum is visualized by separating the peripheral surface and causing the toner to fly from the peripheral surface of the developing roller to the peripheral surface of the photosensitive drum (including a touch-down method).

  The image forming apparatus may be for a one-component developer. Further, a tandem color image forming apparatus having an intermediate transfer belt on which toner images of respective colors are superimposed on each other before the color image is transferred onto the paper may be used.

[Image forming method]
The image forming method according to the present invention is configured to use the electrostatic charge image developing toner having the above-described configuration. The image forming method generally includes a step of forming an electrostatic charge image on the peripheral surface of a photosensitive drum (image carrier) and a step of developing the electrostatic charge image of the photosensitive drum with toner. The toner for developing an electrostatic charge image having the above structure is used as the toner.

  Hereinafter, the present invention will be described in more detail through examples. In addition, this invention is not limited at all by this Example.

<Preparation of silica particles>
(Silica A)
100 g of dimethylpolysiloxane and 100 g of 3-aminopropyltrimethoxysilane (both manufactured by Shin-Etsu Chemical Co., Ltd.) were dissolved in 200 g of toluene, and further diluted 10-fold with toluene. While the mechanically stirred 200 g of hydrophilic fumed silica particles (“Aerosil (registered trademark) 90” manufactured by Nippon Aerosil Co., Ltd.) produced by dry high temperature hydrolysis method, the above diluted solution was gradually added dropwise thereto. Thereafter, the mixture was further stirred for 30 minutes by applying ultrasonic vibration. The obtained mixture was heated in a high-temperature bath at 150 ° C., and then toluene was distilled off using a rotary evaporator, and the obtained solid was dried with a vacuum dryer at a set temperature of 50 ° C. until it was not reduced. Furthermore, heat treatment was performed at 200 ° C. for 3 hours in a nitrogen stream in an electric furnace. The obtained powder was pulverized by a jet mill and collected by a bag filter to obtain hydrophobized silica A used as an external additive.
(Silica B)
60 g of dimethylpolysiloxane, 60 g of 3-aminopropyltrimethoxysilane, 100 g of toluene, and hydrophilic fumed silica particles produced by dry high temperature hydrolysis (“Aerosil (registered trademark)” manufactured by Aerosil Japan) Except for the change to 50)), a hydrophobized silica B used as an external additive was obtained in the same manner as silica A.
(Silica C)
Silica particles produced by a commercially available sol-gel method were used as silica C (hydrophobized) as an external additive.
(Silica D)
Silica particles produced by a colloidal method that can be obtained on the market were used as silica D (hydrophobized) as an external additive.
(Silica E)
Another silica particle produced by a colloidal method available on the market was used as silica E (hydrophobized) as an external additive.

<Measurement of particle size distribution and particle size>
The obtained silica A to E were subjected to image analysis and statistical processing of 5000 particles using a flow type particle image analyzer (“FPIA-3000” manufactured by Sysmex Corporation) to obtain a particle size distribution (particle size distribution). The number average primary particle size, the minimum particle size, and the maximum particle size are measured, and the ratio of the minimum particle size to the number average primary particle size (minimum particle size / number average primary particle size), maximum particle size and number The ratio to the average primary particle size (maximum particle size / number average primary particle size) was determined. The results are shown in Table 1 and FIG.

The number average primary particle diameter of silica A was 20 nm, the minimum particle diameter was 5.8 nm, and the maximum particle diameter was 38.2 nm.
Silica B had a number average primary particle size of 30 nm, a minimum particle size of 3.3 nm, and a maximum particle size of 72.9 nm.
The number average primary particle size of silica C was 32 nm, the minimum particle size was 20.8 nm, and the maximum particle size was 43.8 nm.
The number average primary particle size of silica D was 65 nm, the minimum particle size was 14.9 nm, and the maximum particle size was 109.9 nm.
The number average primary particle diameter of silica E was 110 nm, the minimum particle diameter was 39.6 nm, and the maximum particle diameter was 170.5 nm.
As is clear from FIG. 1, the particle size distribution of silica C was narrower than that of other silicas, and silica C was in a state where grains were aligned.

<Preparation of toner base particles>
100 parts by mass of a styrene-acrylic resin (“ESREC PP-170W” manufactured by Sekisui Chemical Co., Ltd.) as a binder resin, 12 parts by mass of carbon black “MA-100” manufactured by Mitsubishi Chemical as a colorant, and a release agent 4 parts by weight of “Carbana Wax No. 1” manufactured by Kato Yoko Co., Ltd. and 1 part by weight of “P-51” manufactured by Orient Chemical Co., Ltd. as a charge control agent were put into a Henschel mixer, mixed, and then twin screw extruder And kneaded and cooled with a drum flaker. The obtained solid material is coarsely pulverized with a hammer mill, then finely pulverized with a turbo mill, and classified using an air classifier. The toner base particles have a volume average particle size of 6.81 μm and an average circularity of 0.951. Was prepared.

<Preparation of toner for developing electrostatic image>
(Toner A)
By adding 40 g of silica C as an external additive to 2 kg of the prepared toner base particles, and stirring and mixing for 5 minutes at a rotational peripheral speed of 40 m / s using a Henschel mixer (manufactured by Mitsui Mining Co., Ltd.), an electrostatic charge image is obtained. Developing toner A was prepared.
(Toner B)
An electrostatic charge image developing toner B was prepared in the same manner as in the toner A except that 20 g of silica C and 20 g of silica A were added instead of adding 40 g of silica C.
(Toner C)
An electrostatic charge image developing toner C was prepared in the same manner as in the toner A except that 20 g of silica C and 30 g of silica B were added instead of adding 40 g of silica C.
(Toner D)
An electrostatic charge image developing toner D was prepared in the same manner as in the toner A except that 30 g of silica C and 10 g of silica E were added instead of adding 40 g of silica C.
(Toner E)
An electrostatic charge image developing toner E was prepared in the same manner as in the toner A except that 30 g of silica A was added instead of 40 g of silica C.
(Toner F)
An electrostatic charge image developing toner F was prepared in the same manner as in the toner A except that 40 g of silica B was added instead of 40 g of silica C.
(Toner G)
An electrostatic image developing toner G was prepared in the same manner as in the toner A except that 50 g of silica D was added instead of adding 40 g of silica C.
(Toner H)
An electrostatic charge image developing toner H was prepared in the same manner as in the toner A except that 80 g of silica E was added instead of adding 40 g of silica C.

  Table 2 shows combinations and blending ratios of silicas A to E in these toners A to H.

<Observation of dispersion state of silica>
When the surface of the toner A was observed with a scanning electron microscope, as shown in FIGS. 2A and 2B, silica C produced by the sol-gel method and having a number average primary particle size of 32 nm is the toner base. It was monodispersed without secondary aggregation on the surface of the particles. As a result, the surface of the toner base particles was satisfactorily and uniformly coated with silica C. On the other hand, when the surface of the toner E was observed with a scanning electron microscope, as shown in FIGS. 2 (c) and 2 (d), it was produced by a dry high-temperature hydrolysis method, and the number average primary particle diameter was 20 nm. The silica A was secondary agglomerated on the surface of the toner base particles. As a result, the coating amount of the surface of the toner base particles with silica A was smaller than that of toner A with respect to the amount of silica A added.

  The silicas D and E produced by the colloidal method are considered to be monodispersed without secondary aggregation on the surface of the toner base particles, like the silica C produced by the sol-gel method. On the other hand, it is considered that the silica B produced by the dry high temperature hydrolysis method is secondarily aggregated on the surface of the toner base particles, like the silica A.

<Preparation of magnetic carrier>
As a carrier core material, a ferrite carrier “F51-50” (particle size 50 μm) manufactured by Powdertech Co., Ltd. is used for 10 kg, and a fluidized bed coating apparatus (“SFC-5” manufactured by Freund Sangyo Co., Ltd.) is used. 2.4 kg of “Epicoat 1004” manufactured by Japan Epoxy Resin Co., Ltd. was dissolved in 40 kg of toluene, and the surface of the carrier core material was coated while feeding hot air at 80 ° C. This was heated and baked at 230 ° C. for 1 hour in a dryer, then cooled and crushed to prepare a magnetic carrier having a particle diameter of 30 to 80 μm by electron microscopy.

<Preparation of two-component developer>
(Developer A)
Toner A 30 g and magnetic carrier 300 g were stirred and mixed uniformly with a ball mill for 10 minutes to prepare a two-component developer A.
(Developer B)
A two-component developer B was produced in the same manner as in the case of the developer A except that the toner B was used instead of the toner A.
(Developer C)
A two-component developer C was produced in the same manner as in the case of the developer A except that the toner C was used instead of the toner A.
(Developer D)
A two-component developer D was prepared in the same manner as in developer A except that toner D was used instead of toner A.
(Developer E)
A two-component developer E was prepared in the same manner as in the case of the developer A except that the toner E was used instead of the toner A.
(Developer F)
A two-component developer F was prepared in the same manner as in the case of the developer A except that the toner F was used instead of the toner A.
(Developer G)
A two-component developer G was prepared in the same manner as in the case of the developer A except that the toner G was used instead of the toner A.
(Developer H)
A two-component developer H was produced in the same manner as in the case of the developer A except that the toner H was used instead of the toner A.

  Table 3 shows the correspondence between these developers A to H and Examples 1 to 4 and Comparative Examples 1 to 4. As is clear, the examples include silica C as an external additive, and the comparative examples do not. That is, as shown in Table 1, only silica C has a ratio of the minimum particle size to the number average primary particle size (minimum particle size / number average primary particle size) of 0.5 or more and the maximum particle size. The ratio of the number average primary particle size (maximum particle size / number average primary particle size) is 1.7 or less (that is, the particle size distribution is relatively narrow), whereas silica A, B, D , E are the ratio between the minimum particle diameter and the number average primary particle diameter (minimum particle diameter / number average primary particle diameter) and the ratio between the maximum particle diameter and the number average primary particle diameter (maximum particle diameter / number average). At least one of the primary particle diameters is out of the above range (that is, the particle diameter distribution is relatively wide). In particular, the number average primary particle diameter of silica E is outside the range of 20 nm or more and less than 80 nm.

<Real machine test>
The two-component developer produced as described above is mounted on a digital color composite machine “KM-C4035E” manufactured by Kyocera Mita Co., Ltd. at a temperature of 20 to 23 ° C. and a relative humidity of 50 to 65% RH at normal temperature and normal humidity. The following evaluations were performed in the initial stage (within 5 sheets after the start of image formation) and the stage after continuous formation of 200,000 sheets on the PPC paper. . Similarly, in the initial stage (within 5 sheets after the start of image formation) and after the 50,000-sheet intermittent formation after changing the developer and starting to form an image with a printing rate of 2%, the following Was evaluated.

(Image density)
The image density of the solid portion (solid portion) of the sample image formed on the paper was measured using a spectroeye reflection densitometer manufactured by Gretag Macbeth. An acceptable value is that the image density is 1.2 or more.

(Cover)
The image density of the portion where the sample image was not formed on the paper (white paper portion) was measured using a spectroeye reflection densitometer manufactured by Gretag Macbeth. An acceptable value is that the fog (the density of the non-image area) is 0.008 or less.

(Charge amount)
The charge amount of the toner was measured with a q / m meter (charge amount meter) “MODEL210HS” manufactured by Trek.

  The results are shown in Table 3. In Table 3, the reject values are marked with “*”. As is clear, the number average primary particle size is 20 nm or more and less than 80 nm, and the ratio of the minimum particle size to the number average primary particle size (minimum particle size / number average primary particle size) is 0.5 or more. Yes, the ratio of the maximum particle size to the number average primary particle size (maximum particle size / number average primary particle size) is 1.7 or less, and silica C monodispersed on the surface of the toner base particles is excluded. In Examples 1 to 4, which are included as additives, the image density and fogging are stable over a long period of time regardless of the difference in printing pattern (printing rate) and usage environment (continuous printing, intermittent printing, number of printed sheets). The image quality (image quality) such as the density of the non-image area) and the charge amount was excellent.

  On the other hand, Comparative Example 1 using silica A having a relatively wide particle size distribution and secondary aggregation on the surface of the toner base particles is inferior in image density after intermittent printing of 50,000 sheets, and the particle size distribution. Comparative example 2 using silica B which is relatively wide and secondary aggregated on the surface of the toner base particles is inferior to the image density after continuous printing of 200,000 sheets and the image density after intermittent printing of 50,000 sheets, In Comparative Example 3 using silica D having a relatively wide particle size distribution, silica E having inferior image density after intermittent printing of 50,000 sheets, a relatively wide particle size distribution, and an excessively large number average primary particle size is used. Comparative Example 4 used was inferior to the initial image density, the image density after continuous printing of 200,000 sheets, the image density after intermittent printing of 50,000 sheets, and the fog after continuous printing of 200,000 sheets.

Claims (5)

An electrostatic charge image developing toner in which an external additive is added to toner base particles,
The external additive has a number average primary particle size of 20 nm or more and less than 80 nm, and the ratio of the minimum particle size to the number average primary particle size (minimum particle size / number average primary particle size) is 0.5 or more. The ratio of the maximum particle size to the number average primary particle size (maximum particle size / number average primary particle size) is 1.7 or less, and the particles are monodispersed on the surface of the toner base particles. A toner for developing an electrostatic charge image.   2. The electrostatic image developing toner according to claim 1, wherein the external additive is silica particles produced by a sol-gel method. The electrostatic image developing toner according to claim 2, wherein the silica particles have a true specific gravity of 1.4 to 1.9 g / cm ³ .   An image forming apparatus comprising: an image carrier on which an electrostatic charge image is formed on a peripheral surface; and a developing device that develops the electrostatic image on the image carrier using toner. An image forming apparatus using the electrostatic image developing toner according to any one of items 1 to 3.   An image forming method comprising: forming an electrostatic charge image on a peripheral surface of an image carrier; and developing the electrostatic image on the image carrier with toner, wherein the toner is used as the toner. An image forming method using the electrostatic image developing toner according to any one of items 1 to 3.

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