JP2009036981A - Toner and image forming apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a toner which avoids reduction of charge amount and causes neither fogging nor toner scattering, even when an image with low coverage is printed on many sheets. <P>SOLUTION: The toner includes colored resin particles, and silica particles and titanium oxide particles externally added to the surfaces of the colored resin particles, wherein the silica particles and titanium oxide particles have small particle diameter particles having a number average particle diameter of 5 to <25 nm and large particle diameter particles having a number average particle diameter of 25-120 nm, respectively, wherein the content SA (wt.%) of the small particle diameter silica particles, the content TA (wt.%) of the small particle diameter titanium oxide particles, the content SB (wt.%) of the large particle diameter silica particles, and the content TB (wt.%) of the large particle diameter titanium oxide particles satisfy expression: (SA/TA)×0.8≤SB/TB≤(SA/TA)×1.2. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a toner and an image forming apparatus. The toner of the present invention can be suitably used for an image forming apparatus having a printing function by an electrostatic electrophotographic method such as a copying machine, a printer, and a facsimile machine.

  An image forming apparatus using an electrophotographic method generally includes charging, exposure, development, transfer, peeling, cleaning, static elimination, and fixing processes. In the step of forming an image, for example, the surface of the photoconductor rotated by a charging device is uniformly charged, and the surface of the photoconductor charged by the exposure device is irradiated with laser light to form an electrostatic latent image. Subsequently, the electrostatic latent image on the photoconductor is developed by the developing device, and a toner image is formed on the surface of the photoconductor. The toner image on the photosensitive member is transferred onto the transfer material by the transfer device, and then heated by the fixing device, whereby the toner image is fixed on the transfer material.

  With the recent popularization of color in image forming apparatuses, development of color toners corresponding to oilless fixing and development of small particle size toners corresponding to high image quality are progressing. Such a toner has a problem that the toner particle size is small, and a toner having a low melting point is added to the toner, or a binder resin having a low softening temperature is used. Therefore, many external additives are added to the toner particle surface in order to improve fluidity.

  Silica particles are generally used as an external additive. Silica particles have a spherical shape and an excellent insulating property, and are highly effective in improving the toner fluidity and improving the chargeability of the toner. However, when a toner containing a large amount of silica particles having such characteristics is stirred in a developing tank, there is a drawback that the charge amount of the toner increases and the image density decreases.

As means for preventing an increase in charge amount, it is known to use titanium oxide particles having a resistance lower than that of silica particles as an external additive (Japanese Patent Laid-Open No. 2000-321812: Patent Document 1).
JP 2000-321812 A

  The toner to which titanium oxide particles are added does not increase the charge amount during continuous printing, and an image having a high image density can be obtained. However, when printing a large number of images with low coverage, that is, when the replenished toner is not consumed easily and is stirred in the developing tank for a long period of time, the charge amount decreases, and fogging and toner scattering occur. The inventor found a problem to do.

  Furthermore, the inventor has found that if the toner is continuously stirred in the developing tank for a long time, it tends to be buried in the surface of the toner particles from the external additive of the small particle size particles. At this time, if the amount of titanium oxide particles embedded (not in a fluidized state) increases relative to silica particles that are not embedded (in a fluidized state), the charge amount of the toner decreases, and fogging and toner scattering occur. Found to do.

As a result of intensive studies, the inventor of the present invention has found a toner that does not cause a decrease in charge amount and does not cause fogging or toner scattering even when a large number of low-coverage images are printed.
Thus, according to the present invention, it includes colored resin particles, silica particles and titanium oxide particles externally added to the surface of the colored resin particles, and each of the silica particles and the titanium oxide particles has a number average particle size of 5 nm. And having a small particle diameter of less than 25 nm and a large particle diameter having a number average particle diameter of 25 nm or more and 120 nm or less, the content of the silica particles having the small particle diameter being SA (% by weight), and the small particle diameter The content of the titanium oxide particles is TA (wt%), the content of the large silica particles is SB (wt%), and the content of the large titanium oxide particles is TB (wt%). The following formula (SA / TA) × 0.8 ≦ SB / TB ≦ (SA / TA) × 1.2
Toner satisfying the above is provided.

  Furthermore, according to the present invention, a photosensitive member on which an electrostatic latent image is formed, a charging device that charges the surface of the photosensitive member, an exposure device that forms an electrostatic latent image on the surface of the photosensitive member, A developing device that contains a two-component developer including the toner and a carrier and supplies the toner to an electrostatic latent image on the surface of the photoconductor to form a toner image; and a toner image on the surface of the photoconductor A transfer device that transfers the toner image to a recording medium, a cleaning device that cleans the surface of the photoreceptor, and a fixing device that fixes the toner image to the recording medium, and forms an image using an electrophotographic system An image forming apparatus is provided.

In the toner and the image forming apparatus of the present invention, even when the toner is continuously stirred in the developing tank for a long period of time, the charge amount hardly changes, and an image free from a decrease in image density or fog is obtained.
The toner of the present invention includes two types of silica particles having a small particle size and a large particle size, and two types of titanium oxide particles having a small particle size and a large particle size, and a combination of the small particle size silica particles and the titanium oxide particles. The ratio and the blending ratio of the large particle size silica particles and the titanium oxide particles are adjusted. In such a toner, even when silica particles and titanium oxide particles having a small particle diameter are embedded in the surface of the colored resin particles, the ratio of the titanium oxide particles and silica particles adhering to the colored resin particle surface in a fluid state does not change. . For this reason, even when the toner is continuously stirred in the developing tank for a long period of time, the change in the charge amount hardly occurs, and an image without a decrease in image density or fog is obtained.

Further, since the silica particles have a volume resistivity (measured by a compression method) of 1 × 10 ^{12 to} 5 × 10 ¹⁵ Ω · cm, more excellent electrical insulation can be obtained, and charging when the toner is left standing. The decrease in the amount is small and the occurrence of image fogging after being left can be suppressed.
Furthermore, since the titanium oxide particles have an appropriate electrical resistance with a volume resistivity (measured by a compression method) of 1 × 10 ⁸ Ω · cm to 1 × 10 ¹¹ Ω · cm, charge leakage is unlikely to occur. Generation of fog due to injection can be suppressed.

Further, since the silica particles are silica particles surface-treated with hexamethyldisilazane, the humidity dependency is low, and stable charging characteristics can be obtained even in a high humidity environment.
Furthermore, the colored resin particles have a volume average particle diameter of 5 to 7 .mu.m, since it has a smooth surface represented by the BET specific surface area of 1.5m ² /g~1.9m ² / g, large It is possible to prevent a decrease in toner fluidity caused by the outer diameter additive entering the recess.

In addition, since the large particle diameters appropriately cover the surface of the colored resin particles at a coverage of 5 to 30%, the transfer efficiency can be improved without deteriorating the toner fixability.
Furthermore, by including the small particle diameter in an appropriate amount of 0.5 to 2% by weight, the fluidity of the toner can be improved without deteriorating the toner fixability.
Further, the image forming apparatus of the present invention is less likely to change the charge amount of the toner, so that an image free from a decrease in image density or fogging can be obtained throughout life.

(toner)
The toner of the present invention will be described.
The toner of the present invention includes colored resin particles (toner particles), silica particles externally added to the surface of the colored resin particles, and titanium oxide particles. Silica particles and titanium oxide particles are called external additives. Furthermore, the silica particles have small particle size silica particles having a number average particle size of 5 nm or more and less than 25 nm, and large particle size silica particles having a number average particle size of 25 nm or more and 120 nm or less. It has small particle size titanium oxide particles having a particle size of 5 nm or more and less than 25 nm, and large particle size titanium oxide particles having a number average particle size of 25 nm or more and 120 nm or less. The small particle size silica particles and the small particle size titanium oxide particles are collectively referred to as a small particle size external additive, and the large particle size silica particles and the large particle size titanium oxide particles are collectively referred to as a large particle size external additive. The definition of the number average particle diameter is described below.

In addition, the toner of the present invention has a small particle size silica particle content of SA (% by weight), a small particle size titanium oxide particle content of TA (% by weight), and a large particle size silica particle content of SB. (Wt%), when the content of the large-diameter titanium oxide particles is TB (wt%), the following formula (SA / TA) × 0.8 ≦ SB / TB ≦ (SA / TA) × 1.2
Satisfied.

When SB / TB <(SA / TA) × 0.8, as the small particle size external additive is buried, the charge amount of the toner decreases, and fogging and toner scattering may occur. Further, when SB / TB> (SA / TA) × 1.2, as the small particle size external additive is buried, the charge amount of the toner increases and the image density may decrease. More preferable SA, SB, TA and TB relationship is the following formula (SA / TA) × 0.9 ≦ SB / TB ≦ (SA / TA) × 1.1.
It is a relationship that satisfies

The effect of the toner of the present invention will be described with reference to FIGS.
FIG. 1 is a conceptual diagram showing the adhesion state of external additives at the initial stage of toner according to one embodiment of the present invention. In the initial toner, four types of external additives (that is, small particle size silica particles S1, small particle size titanium oxide particles T1, large particle size silica particles S2, and large particle size titanium oxide particles T2) are colored resin particles A. It adheres in a state where it can flow without being buried in the surface. The ratio (SA + SB) / (TA + TB) of effective silica particles and titanium oxide particles in this state is 2: 1.

  FIG. 2 is a conceptual diagram showing the adhesion state of the external additive after the toner of FIG. 1 is stirred for a long time in the developing tank. Two types of external additives (small particle size silica particles SA and small particle size titanium oxide particles TA) are embedded in the surface of the colored resin particles A, and two types of external additives (large particles) The diameter silica particles SB and the large particle size titanium oxide particles TB) are adhered in a state where they can flow without being buried in the surface of the colored resin particles A. The effective silica to titanium oxide ratio SB / TB in this state is 2: 1.

  As shown in FIG. 2, the toner is stirred for a long time in the developing tank, so that the small particle size external additives SA and TA are buried in the surface of the colored resin particles A. However, in the toner according to the present invention, the external particle additive in the state before the small particle size external additive is buried (the state shown in FIG. 1) and the state after the small particle size external additive is buried (the state shown in FIG. 2). The effective silica to titanium oxide ratio SB / TB that can function as an additive remains 2: 1. Therefore, the charge amount of the toner can be stabilized throughout the life without lowering or increasing the charge amount of the toner.

  Note that the ratio of 2: 1 (SA + SB) / (TA + TB) and SB / TB are examples, and are not limited to this ratio. These ratios can be appropriately set in the range of 1.5 to 3.5: 1. When the ratio of silica particles is less than 1.5: 1, sufficient chargeability or fluidity may not be obtained. On the other hand, when the ratio of silica particles is more than 3.5: 1, the image density may be lowered due to excessive charging. A more preferred ratio is 1.5 to 2.5: 1.

  The addition amount of the small particle size external additive is preferably 0.5 to 2% by weight. If it is less than 0.5% by weight, sufficient initial fluidity may not be imparted to the toner. In this case, it is difficult to obtain a sufficient toner charge amount, and toner aggregation may occur in the toner supply path. On the other hand, if it exceeds 2% by weight, the fixability may be lowered. A more preferable addition amount is 1.0 to 1.5% by weight.

  The addition amount of the large particle size external additive is preferably 0.8 to 3% by weight. If it is less than 0.8% by weight, sufficient fluidity may not be imparted to the toner after the small particle size external additive is buried. On the other hand, if it exceeds 3% by weight, the fixability may be lowered. A more preferable addition amount is 1.0 to 1.8% by weight.

  Even when the additive amount of the small particle size external additive is small (less than 0.5% by weight), the flowability can be improved by increasing the additive amount of the large particle size external additive. However, in this case, in order to give sufficient fluidity to the toner, it is necessary to add a large amount of external additive (greater than 3% by weight), which is not preferable from the viewpoint of fixability.

  As the silica particles and titanium oxide particles, silica particles and titanium oxide particles having the specific number average particle diameter can be used. Moreover, you may provide hydrophobicity by surface-treating the surface of a silica particle and a titanium oxide particle with a silane coupling agent, a titanium coupling agent, and silicone oil. In particular, silica particles using hexamethyldisilazane (hereinafter sometimes referred to as HMDS) as a silane coupling agent and having a trimethylsilyl group introduced on the surface are excellent in hydrophobicity and insulating properties. The toner to which the silica particles are externally added can provide excellent chargeability even in a high humidity environment.

  Specific external additives include RY50 (number average particle size: about 40 nm), Aerosil 50 (number average particle size: about 30 nm), Aerosil 90 (number average particle size: about 30 nm), Aerosil manufactured by Nippon Aerosil Co., Ltd. 130 (number average particle size: about 16 nm), Aerosil 200 (number average particle size: about 12 nm), Aerosil 300 (number average particle size: about 7 nm), Aerosil 380 (Number average particle size: about 7 nm), Titanium oxide P -25 (number average particle size: about 21 nm), MOX170 (number average particle size: about 15 nm), TTO-51 (number average particle size: about 20 nm) manufactured by Ishihara Sangyo Co., Ltd., TTO-55 (number average particle size: about 40 nm).

The silica particles that can be used as an external additive in the present invention are preferably silica particles having a volume resistivity in the range of 1 × 10 ^{8 to} 5 × 10 ¹⁵ Ω · cm as measured by the compression method. When the volume resistivity is less than 1 × 10 ⁸ Ω · cm, the charge amount tends to decrease when the toner is left, and image fogging may occur after the toner is left. Further, silica particles exceeding 5 × 10 ¹⁵ Ω · cm are difficult to produce and costly to produce. The definition of volume resistivity is described below.

The titanium oxide particles that can be used as an external additive in the present invention are preferably titanium oxide particles having a volume resistivity in the range of 1 × 10 ⁵ to 1 × 10 ¹⁵ Ω · cm or less as measured by a compression method. When the volume resistivity is less than 1 × 10 ⁵ Ω · cm, charge leakage of the charged toner may occur, which is not desirable. On the other hand, when it exceeds 1 × 10 ¹⁵ Ω · cm, it is not desirable because it is easily affected by a low humidity environment.

  The volume resistivity of the external additive can be adjusted by changing the type of surface treatment agent used and the amount of treatment. An external additive obtained by treating silica particles with hexamethyldisilazane as a silane coupling agent is preferable because of high resistance, excellent hydrophobicity, and stable toner charge amount even in a high humidity environment.

  The coverage of the colored resin particle surface with the large particle size external additive is preferably 5 to 30%. If the coverage is less than 5%, it is difficult to obtain the effect of improving the fluidity of the toner due to the large particle size external additive. Conversely, if it exceeds 30%, the fixability may be lowered. A more preferable coverage is 10 to 20%. The definition of coverage is described below.

Next, materials other than the external additive that can be used in the toner of the present invention will be described.
The toner of the present invention can be produced, for example, by mixing the external additive with the colored resin particles using an airflow mixer such as a Henschel mixer (that is, external addition treatment). The volume average particle diameter of the colored resin particles is preferably in the range of 3 to 15 μm. Within this range, a high-quality image with excellent dot reproducibility and less fog and toner scattering can be obtained. The definition of the volume average particle diameter is described below.

The BET specific surface area of the colored resin particles is preferably 1.5 to 1.9 m ² / g. When the BET specific surface area exceeds 1.9 m ² / g, unevenness is increased on the surface of the colored resin particles, and the external additive may enter the concave portion, and the external additive may not be uniformly adhered to the surface. In this case, the roller effect (effect of improving fluidity) and the spacer effect (preventing charge leakage) of the external additive cannot be obtained sufficiently, and fog and toner scattering are likely to occur. Moreover, if it is less than 1.5 m < ² > / g, the colored resin particle surface may become too smooth, and fogging may generate | occur | produce when cleaning defect generate | occur | produces.

  A known method can be used as a method for controlling the BET specific surface area. For example, there are a method of rotating colored resin particles in a cylindrical pipe at high speed to take a corner, and a method of a sfusion system that instantaneously melts toner in a hot air stream. The definition of the BET specific surface area is described below.

  The colored resin particles can be produced by a known method such as a kneading and pulverizing method or a polymerization method. Specifically, when the kneading and pulverization method is adopted, the binder resin, the colorant, the charge control agent, the release agent, and other additives are mixed with a mixer such as a Henschel mixer, a super mixer, a mechano mill, or a Q type mixer. Mix. The obtained raw material mixture is melt-kneaded at a temperature of about 100 to 180 ° C. by a kneader such as a twin-screw kneader or a single-screw kneader. The obtained kneaded product is cooled and solidified, and the solidified product is pulverized by an air pulverizer such as a jet mill. Colored resin particles can be produced by adjusting the particle size such as classification of the obtained pulverized product as necessary.

  As the binder resin that can be used in the toner of the present invention, various known styrene resins, acrylic resins, polyester resins, and the like can be used. A linear or non-linear polyester resin is particularly preferable. The polyester resin is excellent in achieving both mechanical strength (difficult to generate fine powder), fixability (hard to peel off from paper after fixing), and hot offset resistance.

  The polyester resin can be obtained by polymerizing a monomer composition composed of a polyhydric alcohol having two or more valences and a polybasic acid. Examples of the divalent alcohol used for polymerization of the polyester resin include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1 Diols such as 1,4-butenediol, 1,5-pentanediol, 1,6-hexanediol, bisphenol A alkylene such as bisphenol A, hydrogenated bisphenol A, polyoxyethylenated bisphenol A, polyoxypropylenated bisphenol A Examples thereof include oxide adducts and the like.

  Examples of the divalent polybasic acid include maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, Examples include malonic acid, anhydrides and lower alkyl esters of these acids, or alkenyl succinic acids or alkyl succinic acids such as n-dodecenyl succinic acid and n-dodecyl succinic acid.

  If necessary, a trihydric or higher polyhydric alcohol or a polybasic acid may be added to the monomer composition. Examples of the trihydric or higher polyhydric alcohol include sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, sucrose, 1,2,4- Butanetriol, 1,2,5-pentanetriol, glycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, 1,3,5-trihydroxymethyl Benzene and others can be mentioned.

  Examples of the tribasic or higher polybasic acid include 1,2,4-benzenetricarboxylic acid, 1,2,5-benzenetricarboxylic acid, 1,2,4-cyclohexanetricarboxylic acid, and 2,5,7-naphthalenetricarboxylic acid. 1,2,4-naphthalenetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane, tetra (methylenecarboxyl) methane, 1,2,7 , 8-octanetetracarboxylic acid, and anhydrides thereof.

As the colorant that can be used in the toner of the present invention, known pigments and dyes generally used in toners can be used.
Specific examples of the black toner include carbon black and magnetite.
For yellow toner, C.I. I. Pigment Yellow 1, 3, 74, 97, 98, etc. acetoacetic acid arylamide monoazo yellow pigments, C.I. I. Pigment Yellow 12, 13, 13, 14, etc., acetoacetic acid arylamide disazo yellow pigments, C.I. I. Condensed monoazo yellow pigments such as CI Pigment Yellow 93 and 155; I. Other yellow pigments such as C.I. Pigment Yellow 180, 150 and 185, C.I. I. Solvent Yellow 19, 77, 79, C.I. I. Examples include yellow dyes such as Disperse Yellow 164.

For magenta toner, C.I. I. Pigment Red 48, 49: 1, 53: 1, 57, 57: 1, 81, 122, 5, 146, 184, 238; I. Red or red pigments such as CI Pigment Violet 19; I. Examples thereof include red dyes such as Solvent Red 49, 52, 58 and 8.
For cyan toner, C.I. I. Pigment Blue 15: 3, 15: 4, and the like, and blue dyes and pigments of copper phthalocyanine and derivatives thereof; I. Examples thereof include green pigments such as CI Pigment Green 7 and 36 (phthalocyanine green).
The addition amount of the colorant is preferably about 1 to 15 parts by weight, more preferably 2 to 10 parts by weight with respect to 100 parts by weight of the binder resin.

As the charge control agent that can be used in the toner of the present invention, known charge control agents can be used.
Specifically, as a charge control agent imparting negative chargeability, chromium azo complex dye, iron azo complex dye, cobalt azo complex dye, salicylic acid or its derivative chromium / zinc / aluminum / boron complex or salt compound, naphtholic acid or Chromium / zinc / aluminum / boron complex or salt compound of its derivative, chrome / zinc / aluminum / boron complex or salt compound of benzylic acid or its derivative, long chain alkyl / carboxylate, long chain alkyl / sulfonate, etc. Can be mentioned.

Examples of the charge control agent that imparts positive chargeability include nigrosine dyes and derivatives thereof, triphenylmethane derivatives, quaternary ammonium salts, quaternary phosphonium salts, quaternary pyridinium salts, guanidine salts, amidine salts, and the like. be able to.
The addition amount of these charge control agents is preferably in the range of 0.1 to 20 parts by weight, more preferably in the range of 0.5 to 10 parts by weight with respect to 100 parts by weight of the binder resin. .

  Examples of the release agent that can be used in the toner of the present invention include synthetic waxes such as polypropylene and polyethylene, paraffin wax and derivatives thereof, petroleum waxes such as microcrystalline wax and derivatives thereof, and modified waxes thereof, carnauba wax, rice wax, Plant waxes such as candelilla wax can be mentioned. By including these release agents in the toner, the releasability of the toner with respect to the fixing roller or the fixing belt can be improved, and high temperature / low temperature offset during fixing can be prevented. The amount of the release agent added is not particularly limited, but is generally 1 to 5 parts by weight with respect to 100 parts by weight of the binder resin.

(Developer)
The toner of the present invention can be used as a one-component developer, or mixed with a carrier and used as a two-component developer. Among these, a two-component developer is advantageous and preferable from the viewpoint of charging uniformity and toner transportability.
The mixing ratio of carrier and toner is generally 3 to 15 parts by weight of toner with respect to 100 parts by weight of carrier.
Examples of the method for mixing the carrier and the toner include a method of stirring with a mixer such as a Nauta mixer.

  The carrier that can be used in the present invention is not particularly limited, but a magnetic material having a volume average particle diameter of 20 to 100 μm can be used. If the volume average particle diameter is too small, white spots may occur in the resulting image due to the carrier moving from the developing roller to the photosensitive drum during development. On the other hand, if it is too large, the dot reproducibility may deteriorate and the image may become rough. The volume average particle size of the carrier is more preferably 30 to 60 μm. The definition of the volume average particle diameter is described below.

  The lower the saturation magnetization of the carrier, the softer the magnetic brush in contact with the photosensitive drum, so that an image faithful to the electrostatic latent image can be obtained. However, if the saturation magnetization is too low, carriers adhere to the surface of the photosensitive drum and white spots are likely to occur. On the other hand, if the saturation magnetization is too high, it becomes difficult to obtain an image faithful to the electrostatic latent image due to the stiffening of the magnetic brush. Therefore, the saturation magnetization of the carrier is preferably in the range of 30 to 100 emu / g. The definition of saturation magnetization is described below.

As such a carrier, a coated carrier in which a coating layer is provided on the surface of magnetic core particles is generally used.
As the core particles, known magnetic particles can be used, but ferrite particles are preferable from the viewpoint of chargeability and durability. Known ferrite particles can be used, such as zinc ferrite, nickel ferrite, copper ferrite, nickel-zinc ferrite, manganese-magnesium ferrite, copper-magnesium ferrite, manganese-zinc ferrite, Examples of the particles include manganese-copper-zinc ferrite.

These ferrite particles can be produced by a known method. For example, ferrite raw materials such as Fe ₂ O ₃ and Mg (OH) ₂ are mixed, and this mixed powder is heated in a heating furnace and calcined. After cooling the obtained calcined product, it is pulverized by a vibration mill so as to become particles of about 1 μm, and a dispersant and water are added to the pulverized powder to prepare a slurry. This slurry is wet pulverized with a wet ball mill, and the resulting suspension is granulated and dried with a spray dryer to obtain ferrite-based particles.

  As the material for the coating layer (coating material), a known resin material can be used, for example, an acrylic resin, a silicone resin, or the like. In particular, a coated carrier having a silicone resin as a coating layer is preferable because the boron compound is less likely to be spent (adhered) on the surface, and the toner can be charged for a long period of time.

  Known silicone resins can be used, such as silicone varnishes (trade names: TSR115, TSR114, TSR102, TSR103, YR3061, TSR110, TSR116, TSR117, TSR108, TSR109, TSR180, TSR181, TSR187, TSR144, TSR165, etc. Shin-Etsu Chemical Co., Ltd., KR271, KR272, KR275, KR280, KR282, KR267, KR269, KR211, KR212, etc., manufactured by Toshiba), alkyd-modified silicone varnish (trade name: TSR184, TSR185, etc., manufactured by Toshiba), epoxy-modified silicone Varnish (trade name: TSR194, YS54, etc., manufactured by Toshiba), polyester-modified silicone varnish (trade name: TSR187, manufactured by Toshiba), acrylic modified Ricone varnish (trade name: TSR170, TSR171, etc., manufactured by Toshiba), urethane-modified silicone varnish (trade name: TSR175, manufactured by Toshiba), reactive silicone resin (trade names: KA1008, KBE1003, KBC1003, KBM303, KBM403, KBM503, KBM602, KBM603, etc., manufactured by Shin-Etsu Chemical Co., Ltd.).

  In order to control the volume resistivity value of the carrier, a conductive material is preferably added to the coating material. Examples of the conductive material include silicon oxide, alumina, carbon black, graphite, zinc oxide, titanium black, iron oxide, titanium oxide, tin oxide, potassium titanate, calcium titanate, aluminum borate, magnesium oxide, barium sulfate, Examples thereof include calcium carbonate. A conductive material can be used individually by 1 type, or can use 2 or more types together.

  Among these conductive materials, carbon black is preferable from the viewpoint of production stability, cost, and low electrical resistance. The type of carbon black is not particularly limited, but those having a DBP (dibutyl phthalate) oil absorption in the range of 90 to 170 ml / 100 g are preferred from the viewpoint of excellent production stability. Carbon black having a primary particle size of 50 nm or less is particularly preferable because of excellent dispersibility. The amount of the conductive material used can be 0.1 to 20 parts by weight with respect to 100 parts by weight of the covering material.

  As a method for coating the carrier with the coating material, a known method can be employed. For example, an immersion method in which the carrier is immersed in an organic solvent solution of the coating material, a spray method in which the organic solvent solution of the coating material is sprayed on the carrier, or an organic solvent solution of the coating material is sprayed in a state where the carrier is suspended by flowing air Examples thereof include a fluidized bed method and a kneader coater method in which a carrier and an organic solvent solution of a coating material are mixed in a kneader coater to remove the solvent. At this time, a conductive material for resistance value control can be added to the organic solvent solution of the coating material together with the coating material.

(Image forming device)
Next, the image forming apparatus of the present invention will be described.
FIG. 3 is an explanatory view showing an embodiment of the image forming apparatus according to the present invention. The image forming apparatus of the present invention is not limited to the configuration shown in FIG. As shown in FIG. 3, the image forming apparatus is a tandem color image forming apparatus including four image forming units 1 to 4.

  Among these, reference numeral 1 indicates a first image forming unit for forming a black toner image, and reference numeral 2 indicates a second image forming unit for forming a cyan toner image. Reference numeral 3 indicates a third image forming unit for forming a magenta toner image, and reference numeral 4 indicates a fourth image forming unit for forming a yellow toner image.

  Above these four image forming units 1 to 4, an intermediate transfer belt (endless belt) 5 is disposed. The intermediate transfer belt 5 is stretched over two support rolls 6 and rotates in the direction indicated by the arrow R. Hereinafter, upstream and downstream are expressed with respect to the rotation direction of the intermediate transfer belt 5 on the basis of the secondary transfer position where the secondary transfer roller indicated by reference numeral 8 is arranged. As a material for the intermediate transfer belt 5, a material in which an appropriate amount of an electronic conductive material is contained in a resin such as polyimide or polyamide can be used.

  The four image forming units 1 to 4 are, from the upstream side in the rotation direction R of the intermediate transfer belt 5, the first image forming unit 1 (black), the second image forming unit 2 (cyan), and the third image forming unit 3 ( Magenta) and the fourth image forming unit 4 (yellow).

Inside the intermediate transfer belt 5, a primary transfer roller 7 that transfers the single-color toner image formed by the image forming units 1 to 4 onto the intermediate transfer belt 5 faces the image forming units 1 to 4. Are provided respectively. The single-color toner images formed by the image forming units 1 to 4 are transferred so as to be superimposed on the intermediate transfer belt 5 to form one color image.
A secondary transfer roller 8 for transferring a color image formed on the intermediate transfer belt 5 to a sheet (recording medium) downstream of the fourth image forming unit 4 (yellow) in the rotation direction R of the intermediate transfer belt 5. Is arranged.

  Further, a belt cleaning unit 10 for cleaning the surface of the intermediate transfer belt 5 is provided downstream of the secondary transfer roller 8 in the rotation direction R of the intermediate transfer belt 5. The belt cleaning unit 10 includes a belt cleaning brush 11 disposed in contact with the intermediate transfer belt 5 and a belt cleaning blade 12. The belt cleaning blade 12 is disposed downstream of the belt cleaning brush 11 in the rotation direction R of the intermediate transfer belt 5.

  Further, below the four image forming units 1 to 4, a tray 14 for storing paper is disposed. The paper in the toner 14 is conveyed by a plurality of paper feed rollers 13 to a secondary transfer position where the secondary transfer roller 8 faces the intermediate transfer belt 5. An arrow P indicates the sheet conveyance direction.

  A fixing unit 15 for fixing the color image transferred onto the paper on the paper is provided downstream of the secondary transfer roller 8 in the paper conveyance direction P. Further, a discharge roller 13 a that discharges the sheet on which the color image is fixed from the image forming apparatus is provided further downstream of the fixing unit 15 in the sheet conveyance direction P.

  In such a configuration, the single color toner images formed by the image forming units 1 to 4 are sequentially transferred onto the intermediate transfer belt 5 to form a color image on the intermediate transfer belt 5. The color image on the intermediate transfer belt 5 is secondarily transferred to the paper conveyed by the paper feed roller 13 at the secondary transfer position, and then fixed on the paper by the fixing unit 15. The sheet on which the color image is fixed is discharged from the image forming apparatus by the discharge roller 13a. On the other hand, after the secondary transfer, the toner remaining on the intermediate transfer belt 5 without being transferred to the paper is removed by the belt cleaning unit 10.

  FIG. 4 shows the first image forming unit 1 shown in FIG. The configurations of the second image forming unit 2, the third image forming unit 3, and the fourth image forming unit 4 are substantially the same. Therefore, a detailed description of the configuration of the second image forming unit 2, the third image forming unit 3, and the fourth image forming unit 4 is omitted.

  Around the photosensitive drum 16, a charger 17 that charges the photosensitive drum 16, an exposure unit 18 that writes an electrostatic latent image on the photosensitive drum 16, and a development that visualizes the electrostatic latent image on the photosensitive drum 16 An apparatus 19 is provided with a photosensitive drum cleaner 20 that removes a residue including toner remaining on the photosensitive drum 16 after the primary transfer.

  The charger 17 is composed of, for example, a scorotron charger, and performs corona discharge on the photosensitive drum 16 to charge the photosensitive drum 16 to a predetermined potential. In addition, it can also be comprised from a contact-type charger using a corotron charger, a charging roller, or a charging brush.

  The exposure device 18 is composed of, for example, a laser exposure device, performs exposure by laser scanning according to an image signal, and changes the surface potential of the photosensitive drum 16 charged by the charger 17, thereby changing the static potential according to the image information. An electrostatic latent image is formed. An LED array device or the like can also be used as the exposure device.

  The developing device 19 accommodates a developer containing the toner of the present invention in the developing tank, and develops the electrostatic latent image on the surface of the photosensitive drum 16 with the toner contained in the developer. As the developer, there are a two-component developer including a toner and a carrier, a one-component developer including only a toner not including a carrier, and the like. As the developer, the developer of the present invention can be used.

The photosensitive drum cleaner 20 includes a cleaning blade 21, a cleaner housing 22, and a seal 23.
The cleaning blade 21 is disposed in pressure contact with the rotation direction Rd of the photosensitive drum 16 in the counter direction, and scrapes off the residue on the surface of the photosensitive drum 16. The cleaner housing 22 stores the scraped residue, and the cleaning blade 21 is attached to the cleaner housing 22. The seal 23 seals the inside of the cleaner housing 22. One end of the seal 23 is fixed to the cleaner housing 22 and the other end is connected to the photosensitive drum 16 on the upstream side in the rotational direction Rd of the photosensitive drum 16 with respect to the cleaning blade 21. Arranged in contact.

  FIG. 5 is an explanatory diagram showing a configuration around the developing device 19 in FIG. The developing device 19 includes a developing tank 27 in which a two-component developer 32 (hereinafter also simply referred to as a developer) is accommodated, and the developing tank 27 faces the outer peripheral surface of the photosensitive drum 16. An opening 30 is provided at the position.

  In the developing tank 27, at a position facing the open portion 30, the developer is carried on the outer peripheral surface and conveyed to supply the developer to the photosensitive drum 16, thereby developing the electrostatic latent image. A developing roller 24 is provided. The developing roller 24 is disposed with a gap from the outer peripheral surface of the photosensitive drum 16.

  The developing roller 24 is a multi-pole magnetized multi-pole magnetized in which magnetic poles N1, N2, and N3 and magnetic poles SI and SII made of a bar magnet 31 having a rectangular cross-sectional shape are radially spaced apart at a plurality of circumferential positions. A member 25 and a nonmagnetic sleeve 26 that is rotatably fitted to the multipolar magnetized member 25 are provided.

  Both ends of the multipolar magnetized member 25 are supported non-rotatingly on both side walls of the developing tank 27, and the magnetic pole N1 (peak value 110 mT) is positioned at the position toward the rotation center of the photosensitive drum 16 and the magnetic pole SI (peak value). = −78 mT) is upstream from the magnetic pole N1, for example, at a position of 59 °, the magnetic pole N2 (peak value = 56 mT) is upstream from the magnetic pole N1, for example, at a position of 117 °, and the magnetic pole N3 (peak value = 42 mT) is The magnetic pole SII (peak value = −80 mT) is arranged upstream from the magnetic pole N1, for example, at a position of 282 °, for example.

In the vicinity of the opening 30 in the developing tank 27 and on the upstream side in the developer transport direction of the developing roller 24, the thickness of the developer layer carried on the outer peripheral surface of the developing roller 24 is regulated, A regulating member 28 that regulates the amount of conveyance to the electrostatic latent image is provided. The regulating member 28 is arranged at a predetermined interval with respect to the outer peripheral surface of the developing roller 24.
A stirring member 29 that stirs the developer in the developing tank 27 and supplies the developer to the developing roller 24 is rotatably provided in the developing tank 27 at a position facing the developing roller 24.

(Various definitions)
The definitions of number average particle diameter, volume average particle diameter, volume resistivity, coverage, BET specific surface area, and saturation magnetization in this specification are described below.

"Number average particle size"
In this specification, the number average particle diameter of the external additive is measured by measuring the particle diameter of 100 external additives from the obtained image by photographing the external additive using a scanning electron microscope (SEM). And the average value of the obtained particle diameters.

"Volume average particle diameter of colored resin particles"
In the present specification, the volume average particle diameter of the colored resin particles means a value measured by Coulter Multisizer II (manufactured by Beckman Coulter, Inc.). As a specific measuring method, first, about 1% NaCl aqueous solution is prepared using first grade sodium chloride. For example, Isoton II (manufactured by Coulter Scientific Japan) can be used. Next, 0.1 to 3 ml of a surfactant (preferably alkyl ether sulfate ester salt) as a dispersant is added to 50 to 80 ml of the electrolytic aqueous solution, and 2 to 20 mg of a sample is further added. The electrolytic solution in which the sample is dispersed is treated with an ultrasonic disperser for about 3 to 8 minutes, and the volume and number distribution of toner particles are calculated by the measuring apparatus using a 100 μm aperture. The volume average particle size is determined from the measured particle size distribution.

"Volume average particle diameter of carrier"
In this specification, the volume average particle diameter of the carrier is measured under the condition of a dispersion pressure of 3.0 bar using a dry dispersion apparatus RODOS (manufactured by SYMPATEC) in a laser diffraction particle size distribution measuring apparatus HELOS (manufactured by SYMPATEC). Means the value.

"Volume resistivity"
In this specification, the measurement of the volume resistivity of the external additive means a value obtained by the following procedure. First, an external additive after being left for 24 hours in an environment of an air temperature of 20 ° C. and a humidity of 65% is sandwiched between two copper plate electrodes, the pressing pressure is 10 kg / cm ² , and the distance between the copper plate electrodes is 8 A compact that has a thickness of 10 mm is prepared. Next, a voltage of 500 V / cm is applied, the resistance 15 seconds after the voltage application is measured, and the value is taken as the volume resistivity of the external additive.

"Coverage"
In this specification, the coverage (surface coverage of colored resin particles) Cg (%) means a value calculated by the following method.
Cg = Sg ÷ St × 100
Sg: Projected area of large particle size external additive (m ² / g)
St: Total surface area of the colored resin particles (m ² / g)
That is,
Cg = 150 × Wg ÷ (Bt × Dg × Rg)
Wg: Addition amount of external additive (parts by weight: addition amount per 100 parts by weight of colored resin particles)
Bt: BET specific surface area per 1 g of colored resin particles (m ² / g)
Dg: primary particle size of external additive (nm)
Rg: Specific gravity of external additive (g / cm ² )

"BET specific surface area"
In this specification, the BET specific surface area means a value measured using a BET specific surface area measuring device Gemini 2360 (manufactured by Shimadzu Corporation). Specifically, nitrogen gas was adsorbed on the sample surface, and the value was calculated by the BET multipoint method.

"Saturation magnetization"
In this specification, the measurement of saturation magnetization was performed using a vibration type magnetometer VSMP-1S manufactured by Toei Kogyo Co., Ltd. The sample is filled in a measurement capsule (0.0565 cc) and measured with a magnetic field of 1.1 (MA / m). The volume-based particle size distribution in the present invention is measured using a laser diffraction particle size distribution measuring device manufactured by SYMPATEC. The volume-based particle size distribution 1% particle size and the volume-based particle size distribution 50% particle size are calculated by integrating the obtained volume-based particle size distribution from the smaller particle size.

(Example)
<Toner>
The toners of Examples and Comparative Examples were prepared by the following method.
The toner material is described below.
Binder resin (polyester resin obtained by polycondensation using bisphenol A propylene oxide, terephthalic acid or trimellitic anhydride as a monomer: glass transition temperature 60 ° C., softening temperature 115 ° C .: manufactured by Kao Corporation)
100 parts by weight Colorant (CI Pigment Blue 15: 3) 5 parts by weight Charge control agent (boron compound: LR-147 manufactured by Nippon Carlit)
2 parts by weight Release agent (microcrystalline wax: HNP-9 manufactured by Nippon Seiki Co., Ltd.)
3 parts by weight The above toner material was mixed for 10 minutes with a Henschel mixer, and then melt-kneaded and dispersed with a kneading and dispersing apparatus (Mitsui Mining Co., Ltd .: Needix MOS140-800). The kneaded product was coarsely pulverized with a cutting mill and then finely pulverized with a jet pulverizer (manufactured by Nippon Pneumatic Kogyo Co., Ltd .: IDS-2 type). By classifying the finely pulverized product using an air classifier (manufactured by Nippon Pneumatic Industry Co., Ltd .: MP-250 type), the volume average particle size is 6.5 ± 0.1 μm and the BET specific surface area is 1.8 ±. Colored resin particles of 0.1 m ² / g were obtained.

100 parts by weight of the colored resin particles obtained were each of the amounts shown in Table 1 and small particle size silica particles having a number average particle size of 16 nm (volume resistivity 5 × 10 ¹³ Ω · cm: manufactured by Nippon Aerosil Co., Ltd.) Small particle size titanium oxide particles having a number average particle size of 20 nm (volume resistivity 3 × 10 ⁹ Ω · cm: manufactured by Titanium Industry Co., Ltd.) and large particle size silica particles having a number average particle size of 40 nm (volume resistivity) 2 × 10 ¹³ Ω · cm: manufactured by Nippon Aerosil Co., Ltd.) and large particle size titanium oxide particles having a number average particle size of 40 nm (volume resistivity is 1 × 10 ⁹ Ω · cm: manufactured by Titanium Industry Co., Ltd.). Then, negatively chargeable toners (T1 to T20) were prepared by stirring for 2 minutes with an airflow mixer (manufactured by Mitsui Mining Co., Ltd .: Henschel mixer) in which the tip speed of the stirring blade was set to 15 m / second. Table 1 also shows the ratio SA / TA, the ratio SB / TB, and the ratio (SB / TB) / (SA / TA).

<Career>
The carriers of Examples and Comparative Examples were produced by the following method.
After mixing the ferrite raw material (manufactured by Kanto Denka Kogyo Co., Ltd.) with a ball mill, calcining at 900 ° C. with a rotary kiln, the obtained calcined powder is average particle size by a wet pulverizer (using steel balls as the pulverizing medium) Finely pulverized to 2 μm or less. The obtained ferrite powder was granulated by a spray drying method, and the granulated product was fired at 1300 ° C. After firing, pulverization was performed using a crusher to obtain core particles composed of a ferrite component having a volume average particle diameter of about 50 μm and a volume low efficiency of 1 × 10 ⁹ Ω · cm.

Next, the coating layer coating solution for forming the coating layer for coating the core particles is composed of 100 parts by weight of a silicone resin (trade name: TSR115, manufactured by Shin-Etsu Chemical Co., Ltd.) and carbon black (primary particle size 25 nm, oil absorption 150 ml). / 100 g: manufactured by Cabot Corporation) and 3 parts by weight were prepared by dissolving and dispersing in toluene.
The prepared coating liquid for coating layer was coated on the core particles composed of the ferrite component by a spray coating apparatus. Thereafter, toluene was completely removed by evaporation to prepare a carrier having a volume average particle diameter of 50 μm, a coating layer thickness of 1 μm, a volume resistivity of 2 × 10 ¹⁰ Ω · cm, and a saturation magnetization of 65 emu / g. .

<Two-component developer>
The two-component developers of Examples and Comparative Examples were prepared by mixing toners (T1 to T16) with the carrier. The two-component developer was prepared by charging 6 parts by weight of toner and 94 parts by weight of a carrier into a Nauter mixer (trade name: VL-0, manufactured by Hosokawa Micron Corporation) and stirring and mixing for 20 minutes.

<Image evaluation>
A continuous print test was performed using the produced two-component developer and the test image forming apparatus shown in FIG. In the continuous print test, the toners T1 to T12 were tested using only the image forming unit 1 among the four image forming units. As the development conditions of the image forming apparatus, the peripheral speed of the photosensitive member is 400 mm / second, the peripheral speed of the developing roller is 560 mm / second, the gap between the photosensitive member and the developing roller is 0.42 mm, and the gap between the developing roller and the regulating blade is 0.5 mm. The surface potential of the photosensitive member and the development bias are set so that the toner adhesion amount on paper in a solid image (100% density) is 0.5 mg / cm ² and the toner adhesion amount in the non-image area is the smallest. Was adjusted respectively. A4 size electrophotographic paper (multi receiver: manufactured by Sharp Document System) was used as a test paper.
10K (10000) print tests were performed on text images that would provide 6% coverage of the print images recorded on the paper.

Image evaluation was performed by measuring the toner charge amount, image density, and fog density. The measurement method for each of these values is described below.
The toner charge amount is measured using a suction type small charge amount measuring device (manufactured by Trek Japan Co., Ltd .: 210HS-2A).
The image density is evaluated as follows. That is, a solid image (100% density) with a side of 3 cm is printed. The image density of the printed part is measured using a reflection densitometer (Macbeth: RD918). The image density is 1.3 or more (paper fiber is completely covered with toner), and 1.2 or more and less than 1.3 is slightly poor, and less than 1.2 (paper fiber is incomplete with toner) The state covered with is considered defective.

As for the fog density, the density of the non-image area (0% density) is calculated by the following procedure.
Using a whiteness meter (Nippon Denshoku Industries Co., Ltd .: Z-Σ90 COLOR MEASURING SYSTEM), the whiteness of the paper before printing is measured in advance. Next, the whiteness in the non-image area of the paper after printing is measured using a whiteness meter, and the difference from the whiteness before printing is obtained. This difference is the fog density.
The fog density is less than 0.6 (a state in which fog is hardly visible to the naked eye), 0.6 to less than 1.0 is slightly poor, and 1.0 or more (a state in which fog is clearly visible to the naked eye) is poor. .

<Result>
Table 2 shows the results of the continuous print test. As shown in Examples 1 to 10, in the continuous print test of toners of T1 to T10, the toner charge amount was stable, and the image density was high and an image without fog was obtained.
On the other hand, as shown in Comparative Examples 11 to 13, in the 10K continuous print test using the toners T11 to T13, the toner charge amount was reduced, and fogging and toner scattering were observed.
Further, as shown in Comparative Examples 14 to 16, in the 10K continuous print test using the toners T14 to T16, the toner charge amount increased and the image density decreased.

2 is a schematic view of a toner of the present invention. FIG. FIG. 3 is a schematic view of the toner of the present invention at the time of life. 2 is a schematic enlarged view of a process unit of the image forming apparatus. FIG. FIG. 2 is a schematic enlarged view of a developing unit of the image forming apparatus. 1 is a schematic diagram of an image forming apparatus.

Explanation of symbols

A colored resin particles, N1, N2, N3, SI, SII magnetic pole, P transport direction R, Rd rotation direction, S1 small particle size silica particles, S2 large particle size silica particles T1, small particle size titanium oxide particles, T2 large particle size Titanium oxide particles 1 to 4 Image forming unit, 5 Intermediate transfer belt, 6 Support roll 7 Primary transfer roller, 8 Secondary transfer roller 10 Belt cleaning unit, 11 Belt cleaning brush 12, Belt cleaning blade, 13 Paper feed roller 13a Paper discharge Roller, 14 toner, 15 fixing unit, 17 charger 18 exposure device, 19 developing device, 20 photosensitive drum cleaner 21 cleaning blade, 22 cleaner housing, 23 seal 24 developing roller, 25 multipolar magnetized member, 26 sleeve, 27 Developing tank 28 Restricting member, 29 Stirring member, 30 Opening part, 31 Bar magnet 3 Two-component developer

Claims (8)

A colored resin particle; and a silica particle and a titanium oxide particle externally added to the surface of the colored resin particle, wherein the silica particle and the titanium oxide particle each have a number average particle size of 5 nm or more and less than 25 nm. Particles having a number average particle size of 25 nm or more and 120 nm or less, the content of the silica particles having a small particle size being SA (% by weight), and the content of the titanium oxide particles having a small particle size Is TA (% by weight), the content of the large particle size silica particles is SB (% by weight), and the content of the large particle size titanium oxide particles is TB (% by weight), the following formula (SA / TA) × 0.8 ≦ SB / TB ≦ (SA / TA) × 1.2
Satisfy the toner. The toner according to claim 1, wherein the silica particles have a volume resistivity (measured by a compression method) of 1 × 10 ^{12 to} 5 × 10 ¹⁵ Ω · cm. The toner according to claim 1, wherein the titanium oxide particles have a volume resistivity (measured by a compression method) of 1 × 10 ⁸ Ω · cm to 1 × 10 ¹¹ Ω · cm.   The toner according to claim 1, wherein the silica particles are silica particles surface-treated with hexamethyldisilazane. Said colored resin particles have a volume average particle diameter of 5 to 7 .mu.m, any one of the preceding claims, characterized in that it has a BET specific surface area of 1.5m ² /g~1.9m ² / g The toner according to one.   The toner according to claim 1, wherein the large particle diameter particles cover the surface of the colored resin particles at a coverage of 5 to 30%.   The toner according to claim 1, wherein the small particle size particles are included in an addition amount of 0.5 to 2% by weight.   The photosensitive member on which an electrostatic latent image is formed on the surface, a charging device that charges the surface of the photosensitive member, an exposure device that forms an electrostatic latent image on the surface of the photosensitive member, and any one of claims 1 to 7. A developing device that contains a two-component developer including one toner and a carrier and supplies the toner to an electrostatic latent image on the surface of the photoreceptor to form a toner image; and toner on the surface of the photoreceptor An image is formed using an electrophotographic method, including a transfer device that transfers an image to a recording medium, a cleaning device that cleans the surface of the photoreceptor, and a fixing device that fixes the toner image to the recording medium. An image forming apparatus.

Images