JP2003140382A - Electrophotographic developer and method for forming image by using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrophotographic developer which aims to obtain an image of high picture quality with high transfer efficiency and which can achieve improvement in cleaning property without decreasing the developing property of the toner, in reliability by reducing friction between a blade and a photoreceptor, or the like in good balance, and to provide a method for forming an image by using the developer. SOLUTION: The developer is a two-component developer consisting of a toner and a carrier and characterized in that the toner consists of toner mother particles and an external additive, and the external additive comprises at least two kinds or more of inorganic oxides including cerium oxide and lubricant particles, and the shape factor SF1 defined by SF1=L<2> /A×π/4×100 of the toner mother particles is 115 to 140 in average, wherein L is the maximum length of each toner mother particle and A is the projected area of each toner mother particle.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic developer and an image forming method used in electrophotography, electrostatic recording and the like.

[0002]

2. Description of the Related Art In electrophotography, an electrostatic latent image formed on the surface of a latent image carrier (photoreceptor) is developed with a toner containing a colorant, and the obtained toner image is transferred to the surface of a recording medium. Then, an image is obtained by fixing this with a hot roll or the like, while the latent image carrier is cleaned again to form an electrostatic latent image. Dry developers used in such electrophotographic methods include a one-component developer that uses a toner obtained by mixing a binder resin with a colorant and the like alone, and a two-component developer that mixes the toner with a carrier. Broadly divided. Further, the one-component developer is a magnetic one-component developer that is conveyed by a developer carrier by magnetic force using magnetic powder and is developed,
It can be classified as a non-magnetic one-component developer which is conveyed by a developer carrying member and developed by applying a charge such as a charging roll without using magnetic powder.

Since the latter half of the 1980s, there has been a strong demand for miniaturization and high functionality in the electrophotographic market with the keyword of digitalization, and in particular with respect to full-color image quality, high-quality printing and high image quality similar to silver halide photography are desired. ing. As a means of achieving high image quality, digitization processing is indispensable.
It is mentioned that complicated image processing can be performed at high speed.
This makes it possible to control the characters and the photographic image separately, and the reproducibility of both qualities is greatly improved compared to the analog technology. Especially for photographic images, there is a large point that gradation correction and color correction are possible.
It has advantages over analog in terms of definition, sharpness, color reproduction, and graininess. On the other hand, for image output, it is necessary to faithfully form an electrostatic latent image formed by an optical system, and as toner, the particle size is becoming smaller and smaller, and activities aiming for faithful reproduction are being accelerated. However, simply reducing the particle size of the toner
It is difficult to obtain high image quality in a stable manner.
Improving basic properties in fixing and cleaning is becoming more important.

Particularly in the transfer step, it is necessary to faithfully transfer the developed toner image in order to improve the image quality, but the transfer performance is deteriorated by reducing the diameter of the toner. Therefore, various techniques for making full use of small-diameter toner have been reported. For example, it has been reported that the transfer performance is improved by bringing the toner into a spherical shape (Japanese Patent Laid-Open No. 62-184469). In this case, transfer efficiency is improved by making the toner spherical, but
On the other hand, a small amount of transfer residual toner causes cleaning failure. On the contrary, a cleanerless system has been proposed in which the cleaning system is omitted and the toner remaining on the surface of the photoconductor after transfer is collected at the same time as development by the developing device (Japanese Patent Laid-Open Nos. Hei 2-302772 and Hei 5). -94113). However, generally, when the residual toner is collected at the same time as the development,
Since the collected toner and the other toners have different chargeability, the collected toner is not developed and accumulates in the developing unit, and as a result, the image quality deteriorates over time. Cleaning system required.

In response to the above, various means for cleaning the spherical toner have been proposed so far. For example, in the case of cleaning with a blade, the key is to suppress the frictional force of the blade nip portion on the surface of the photoconductor with the transfer residual toner interposed. It has been proposed (Japanese Patent Laid-Open No. 4-212190). According to this method, the cleaning property is certainly improved in the initial stage, but the lubricant particles on the surface of the blade may be depleted during long-term use, resulting in defective cleaning.
Further, it has been proposed to apply a DC and AC bias voltage to the cleaning blade (Japanese Patent Laid-Open No. 5-265).
360 gazette). However, since the charge amount of the transfer residual toner varies depending on the charge amount of the developing toner, the transfer conditions, the use environment or the type of the image, it is not possible to completely clean the toner by itself. Deterioration of the body surface may be promoted and the life of the photoreceptor may be shortened. Further, it has been proposed to increase the pressure contact force of the cleaning blade with respect to the photoconductor (Japanese Patent Laid-Open No. 4-001773), but although the initial cleaning performance is greatly improved by this, the blade material or physical properties are taken into consideration. If not done, on the contrary, a chipping of the blade will occur, resulting in defective cleaning. Further, as long as an organic photoconductor is used as the photoconductor, the amount of wear of the photoconductor may increase and the life of the photoconductor may be reduced.

On the other hand, as a study from the developer side, it has been proposed to add a fatty acid metal salt to the toner (Japanese Unexamined Patent Publication No. 2000-89502). However, in this method, the nip between the cleaning blade and the photoconductor is used. Although it is effective in reducing the frictional force of the area, the addition of fatty acid metal salt significantly reduces the charge amount of the toner, and as a result, fogging during development and toner scattering are likely to occur, resulting in poor image quality. It may decrease.

By the way, there is a method of using an intermediate transfer member as a method of transferring a full-color toner image.
In this case, the primary transfer from the latent image carrier to the intermediate transfer member, the secondary transfer from the intermediate transfer member to the recording material, and the two times of transfer are required, and the total transfer efficiency is reduced accordingly. Will end up. This method is also disadvantageous in terms of printing speed. On the other hand, a tandem system in which a latent image bearing member and a developer bearing member are placed in accordance with each of the four toner colors and the toner is directly transferred from the latent image bearing member to the recording medium is advantageous in terms of total transfer efficiency and printing speed. However, in this case,
Since the recording medium and the latent image carrier are in direct contact with each other, when the recording medium is paper, paper dust or the like may contaminate the latent image carrier and cause obstacles such as deletion. On the other hand, although it has been proposed to add an abrasive to the toner (Japanese Patent Laid-Open No. 2-257145), the abrasive conversely scratches the cleaning blade, resulting in a cleaning failure. is there.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems in the prior art and achieve the following problems. That is, the present invention aims to obtain a high quality image with high transfer efficiency, and also improves the cleaning property without reducing the developing property of the toner and the reliability by reducing the friction between the blade and the photoconductor. The present invention provides a developer for electrophotography that can achieve the above in a well-balanced manner and an image forming method using the same.

[0009]

As a result of intensive studies to achieve the above object, the present inventors have developed a developer for developing an electrostatic latent image formed on the surface of a latent image carrier, and further As an image forming method using a developer, it has been found that the above object can be achieved by using the following developer and image forming method, and the present invention has been completed.

Specifically, means for solving the above problems are as follows. That is, <1> A two-component developer comprising a toner and a carrier, wherein the toner comprises toner mother particles and an external additive, and the external additive contains at least cerium oxide.
A developer for electrophotography, comprising at least one kind of inorganic oxide and lubricant particles, wherein the toner mother particles have an average shape factor SF1 represented by the following formula (1) of 115 to 140. is there.

[0011]

[Equation 2]

In the above equation, L represents the maximum length of each toner base particle, and A represents the projected area of each toner.

<2> When the addition amount of cerium oxide is A parts by mass and the addition amount of lubricant particles is B parts by mass relative to 100 parts by mass of the toner mother particles, A and B are A> B and A + B ≧ 0. <1> which satisfies the relationship of
The electrophotographic developer described in 1.

<3> A latent image forming step of forming an electrostatic latent image on the surface of the latent image carrier, and a developer carried on the developer carrier are used to form the electrostatic image formed on the surface of the latent image carrier. A developing step of developing the latent image to form a toner image, a transfer step of directly transferring the toner image formed on the surface of the latent image carrier to the surface of the recording medium, and a toner transferred to the surface of the recording medium. In an image forming method including a fixing step of thermally fixing an image and a cleaning step of cleaning the toner remaining on the surface of the latent image carrier, the developer is <1> or <1>.
2> is an electrophotographic developer described in 2>.

<4> Each of the plurality of latent image carriers has a developer carrier, and the latent image forming step, the developing step, the transfer step, and the latent image carrier by the plurality of latent image carriers and the developer carrier, respectively. By the series of steps including the cleaning step, the toner images of each of the series of steps are sequentially formed on the surface of one recording medium, and the stacked toner images are heated on the recording medium in the fixing step. The image forming method according to <3> is characterized in that the image is fixed.

The operation and effect of the above means will be briefly described as follows. In order to achieve high transfer efficiency, it is necessary to bring the toner close to a spherical shape, but considering the cleaning mechanism, the following problems are likely to occur. For example, when cleaning is performed using a blade, the transfer residual toner is dammed at the blade nip portion to form a dam, and the dam is cleaned. , The particle size has become finer. Regardless of the shape of the toner, the particle size is separable in the blade nip part, but as the toner approaches a spherical shape, the shape is more likely to be uniform in the blade nip part, so it is easier to arrange the most densely and the minute Since the number of toner contact points per unit surface of the photoconductor is increased and the toner frictional force of each grain is directed in the same direction, the total amount of force received by the blade during cleaning is considerably large. As a result, the blade is pushed up, or the blade edge is chipped and the toner slips through the blade, resulting in poor cleaning. Even with cleaning methods other than the blade, the same state is exhibited when the surface contaminants are removed by rubbing the surface of the photoconductor.

Therefore, in order to clean near-spherical toner, the key is to reduce the frictional force between the toner and the photosensitive member at the blade nip portion. Generally, in order to supply the lubricant particles to the surface of the cleaning blade, it is general to externally add the lubricant particles to the toner mother particles, but in the case of an irregular toner having a shape factor (SF1) of more than 140 In order to exert the effect of reducing the frictional force in the blade nip portion, it is necessary to add a large amount of the lubricant particles to the toner mother particles, and as a result, the chargeability of the toner is greatly reduced. .

However, the inventors of the present invention have a large effect of reducing the frictional force at the blade nip portion when the shape of the toner base particles is approximated to a sphere, even if the amount of the lubricant particles added to the toner base particles is small. I found that. Although the details of this reason are unknown, when the toner mother particles are blended with the lubricant particles, as the toner mother particles become round, the area in which the toner mother particles can come into contact with each other expands, and as a result, the lubricant particles become the toner mother particles. It is considered that not only the particles easily spread on the surface of the particles, but also the particles are uniformly dispersed in the entire toner. Since the lubricant particles have high cohesiveness among themselves,
The effect seems to be more prominent.

On the other hand, when the toner image is directly transferred from the photoconductor to the recording medium, not only the toner but also the cleaning function of paper dust is important for cleaning the surface of the photoconductor. When acidic paper is used as the recording medium, the lubricant particles cannot completely clean the photoreceptor due to talc component contamination, and the lubricant particles tend to reduce the refreshing function of the photoreceptor surface. ,
Removal of ozone products (discharge products) is also an issue.

The influence of the discharge products is remarkable in the image system having the high image quality and the process speed switching which is adopted for the thick paper in recent years. In such an image system, for example,
When switching from the high speed mode to the normal mode, if the friction coefficient between the blade and the latent image carrier increases due to the discharge products formed on the surface of the latent image carrier, the blade will be distorted as the process speed changes. Occurs, which causes squeal, poor cleaning, and the like, which is a new problem.
In this case, in order to reduce the interaction between the latent image bearing member and the blade, a means for supplying an abrasive to the blade nip portion via the toner and cleaning the discharge product may be adopted, but a normal abrasive is used. If it is simply added to the toner mother particles, the abrasive agent detached from the toner will continue to accumulate in the blade nip portion, and on the contrary, the blade will be damaged.

In order to solve these problems, the addition of cerium oxide to the toner exerted a great effect. It seems that cerium oxide has an effect as a polishing agent, but with other polishing agents such as strontium titanate and magnetite, the charge amount of the toner is reduced and the image quality is deteriorated. On the other hand, also in the case of this cerium oxide, similar to the case of the lubricant particles, it is effective for a toner having a nearly spherical shape by adding a small amount, and it is possible to achieve high image quality without significantly reducing the charge amount of the toner. I was able to. Further, by controlling the amount ratio of cerium oxide and lubricant particles and the total amount of external additives, the balance of lubricity and abrasivity was optimized, and it became possible to deal with the problem in the cleaning.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. —Electrophotographic Developer— The electrophotographic developer of the present invention is a two-component developer including a toner and a carrier.

<Toner> The toner used in the present invention is
It is composed of toner mother particles and an external additive, and the external additive is composed of at least two kinds of inorganic oxides containing cerium oxide and lubricant particles.

(Toner Base Particles) The toner base particles of the toner used in the present invention are composed of a binder resin and a colorant, and if necessary, a release agent, silica and a charge control agent.

As the binder resin, styrenes such as styrene and chlorostyrene; monoolefins such as ethylene, propylene, butylene and isoprene; vinyl esters such as vinyl acetate, vinyl propionate, vinyl benzoate and vinyl butyrate; Α-methylene aliphatic monocarboxylic acid esters such as methyl acrylate, ethyl acrylate, butyl acrylate, dodecyl acrylate, octyl acrylate, phenyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, dodecyl methacrylate, etc. Examples: vinyl ethers such as vinyl methyl ether, vinyl ethyl ether and vinyl butyl ether; vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone and vinyl isopropenyl ketone; homopolymers and copolymers thereof Bets can be, typical binder resins include polystyrene, styrene - alkyl acrylate copolymer, styrene - alkyl methacrylate copolymer, styrene - acrylonitrile copolymer, styrene -
Examples thereof include butadiene copolymer, styrene-maleic anhydride copolymer, polyethylene and polypropylene. Further, polyester, polyurethane, epoxy resin, silicone resin, polyamide, modified rosin, paraffin wax and the like can be mentioned. Of these, styrene-alkyl acrylate copolymers and styrene-alkyl methacrylate copolymers are particularly preferable.

As the toner colorant, magnetic powder such as magnetite and ferrite, carbon black, aniline blue, calcyl blue, chrome yellow, ultramarine blue, DuPont oil red, quinoline yellow, methylene blue chloride, phthalocyanine blue, Malachite Green Oxalate, Lamp Black, Rose Bengal, C.I. I. Pigment Red 4
8: 1, C.I. I. Pigment Red 122, C.I. I.
Pigment Red 57: 1, C.I. I. Pigment Yellow 97, C.I. I. Pigment Yellow 17, C.I.
I. Pigment Blue 15: 1, C.I. I. Pigment Blue 15: 3 and the like can be illustrated as a typical example.

If desired, a release agent or a charge control agent may be added to the toner used in the present invention. Representative examples of the release agent include low molecular weight polyethylene, low molecular weight polypropylene, Fischer-Tropsch wax, montan wax, carnauba wax, rice wax, candelilla wax and the like.

As the charge control agent, known ones can be used, and an azo type metal complex compound, a metal complex compound of salicylic acid, and a resin type charge control agent containing a polar group can be used. When manufacturing toner by a wet method, in terms of ionic strength control and reduction of wastewater pollution,
It is preferable to use a material that is difficult to dissolve in water. In addition,
The toner in the invention may be either a magnetic toner containing a magnetic material or a non-magnetic toner containing no magnetic material.

The toner mother particles are produced by, for example, a kneading and pulverizing method of kneading, pulverizing, and classifying a binder resin, a colorant, and if necessary, a release agent, a charge control agent, etc .; a kneading and pulverizing method. A method of changing the shape of the formed particles by mechanical impact force or heat energy; emulsion polymerization of a polymerizable monomer of a binder resin, a dispersion formed, a colorant, and if necessary, release Emulsion polymerization agglomeration method in which toner particles are mixed with a dispersion liquid such as an agent and a charge control agent and agglomerated and heat-fused to obtain toner particles; a polymerizable monomer for obtaining a binder resin, a colorant, and if necessary A suspension polymerization method in which a solution of a release agent, a charge control agent, etc. is suspended in an aqueous solvent and polymerized; a binder resin and a colorant, and if necessary, a solution of a release agent, a charge control agent, etc. And the like can be used. Further, the toner obtained by the above method may be used as a core, and agglomerated particles may be further adhered and heat-fused to provide a core-shell structure.

The particle diameter of the toner mother particles produced as described above is preferably in the range of 2 to 12 μm in volume average particle diameter, and more preferably in the range of 3 to 9 μm.

As described above, it is essential that the toner mother particles used in the present invention have a pseudo-spherical shape from the viewpoints of improving the developability / transfer efficiency and improving the image quality. The sphericity of the toner base particles can be expressed by using the shape factor SF1 of the following formula (1), and the average value of the coefficient factor SF1 of the toner base particles used in the present invention is in the range of 115 to 140. It is indispensable to be present, and the range of 120 to 140 is preferable.

[0032]

[Equation 3]

In the above formula, L represents the maximum length of each toner base particle, and A represents the projected area of each toner base particle.

When the average value of the shape factor SF1 is smaller than 115, the state becomes close to a true sphere, and the cleaning latitude is greatly reduced, so that cleaning failure easily occurs. Shape factor SF1
When the average value of is larger than 140, the transfer efficiency is lowered, and the deterioration of the image quality of the print sample can be visually confirmed.

The average value of the shape factor SF1 is 2
From the optical microscope, 1000 toner images magnified 50 times were taken into an image analyzer (LUZEX III, manufactured by Nireco), and the value of SF1 was calculated for each particle from the maximum length and projected area and averaged. is there.

The toner mother particles used in the present invention are not particularly limited by the manufacturing method as long as they are in the range satisfying the above-mentioned shape factor SF1 and particle diameter, and known methods can be used. it can.

(Lubricant Particles) Lubricant particles added to the above toner include graphite, molybdenum disulfide, talc,
Solid lubricants such as fatty acids, aliphatic alcohols and fatty acid metal salts, low molecular weight polyolefins such as polypropylene, polyethylene and polybutene; silicones having a softening point by heating; oleic acid amide, erucic acid amide, ricinoleic acid amide, stearin Aliphatic amides such as acid amides; plant waxes such as carnauba wax, rice wax, candelilla wax, wax, jojoba oil, etc .; animal waxes such as beeswax; montan wax, ozokerite, ceresin, paraffin Minerals such as wax, microcrystalline wax, Fischer-Tropsch wax and the like; petroleum waxes; and their modified products can be used, and these may be used alone or in combination.

Among these, fatty acid metal salts and aliphatic alcohols are particularly preferable, and as the fatty acid metal salt, metal salts of fatty acids having 10 to 50 carbon atoms and zinc, aluminum, magnesium, calcium, etc. are preferably used. . The aliphatic alcohol has 16 to 1 carbon atoms.
50 higher aliphatic alcohols and the like are preferably used.

The volume average particle size of the lubricant particles is 0.1 to 1
The particle size is preferably in the range of 0 μm, and the particles having the above-mentioned chemical structure may be pulverized to have the same particle size. Further, the addition amount to the toner base particles is preferably in the range of 0.05 to 2.0 parts by mass with respect to 100 parts by mass of the toner base particles,
The range of 0.1 to 1.5 parts by mass is more preferable.

As described above, when the toner base particles have a quasi-spherical shape like those used in the present invention, it is considered that the lubricant particles are uniformly diffused / dispersed between the surface of the toner base particles and the toner base particles. Perhaps due to this, in order to obtain sufficient lubricity, the amount of lubricant particles added is smaller than in the case of irregularly shaped toner mother particles, and even when used for a long time in the developing device. A stable friction reducing effect with the photoreceptor can be obtained.

(Inorganic oxide containing cerium oxide) The volume average particle diameter of cerium oxide added to toner mother particles is
It is preferably in the range of 0.1 to 3.0 μm,
More preferably, it is in the range of 5 to 2.0 μm. The amount of cerium oxide added to the toner base particles is 1
It is preferably in the range of 0.3 to 2.0 parts by mass with respect to 00 parts by mass.

In this case, the addition amount of cerium oxide is preferably larger than the addition amount of the lubricant particles, and the sum of the addition amount of the lubricant particles and the addition amount of the lubricant particles is 100 parts by mass of the toner mother particles.
It is preferably 0.6 parts by mass or more. The reason why the above range is preferable is that in order to achieve both the cleaning property of the discharge product from the surface of the photoconductor and the cleaning property of the pseudo-spherical toner, the balance between the polishing property of cerium oxide and the lubricity of lubricant particles is required. This is because the addition amount of cerium oxide is less than or equal to the addition amount of lubricant particles, and the polishing property may not be sufficiently exhibited, and the sum of the addition amounts of cerium oxide and lubricant particles is less than 0.6 parts by mass. In some cases, sufficient lubricity may not be expressed. These results are also influenced by the high specific gravity of cerium oxide.

The external additive of the toner in the present invention is composed of at least two kinds of inorganic oxides containing cerium oxide and lubricant particles. At least one kind of inorganic oxides other than cerium oxide is powder. It is preferable to use a small-diameter inorganic oxide having a primary particle diameter of 7 to 40 nm as an average particle diameter, which has functions such as body fluidity and charge control. Examples of small-diameter inorganic oxides include silica, alumina, titanium oxides (titanium oxide, metatitanic acid, etc.), calcium carbonate, magnesium carbonate, calcium phosphate and the like.

In particular, the use of titanium oxide having a volume average particle size of 15 to 40 nm does not affect the transparency, and has good chargeability, environmental stability, fluidity, caking resistance, and stable negative chargeability. -It is preferable in that the image quality can be maintained.

Further, the surface treatment of the small-diameter inorganic fine particles enhances the dispersibility and the effect of improving the powder fluidity. As the surface treatment, specifically,
Hydrophobic treatment with dimethyldimethoxysilane, hexamethyldisilazane (HMDS), methyltrimethoxysilane, isobutyltrimethoxysilane, decyltrimethoxysilane or the like is preferably used.

Further, in addition to the small-diameter inorganic oxide and the cerium oxide, it is preferable to add a large-diameter inorganic oxide having a volume average particle diameter of 20 to 300 nm in order to reduce the adhesive force and control the charging. Examples of these large-diameter inorganic oxide fine particles include silica, titanium oxide, metatitanic acid, aluminum oxide, magnesium oxide, alumina, barium titanate, magnesium titanate, calcium titanate, strontium titanate, zinc oxide, chromium oxide, and trioxide. Examples thereof include fine particles of antimony oxide, magnesium oxide, zirconium oxide and the like. Among these, it is desirable to use one selected from silica, titanium oxide, and metatitanic acid from the viewpoint of precisely controlling the charging of the toner to which the lubricant particles and cerium oxide are added.

The true specific gravity of the silica is 1.3 to
It is preferably 1.9, and the monodisperse spherical silica having a volume average particle diameter of 80 to 300 nm is preferable. True specific gravity is 1.
By controlling to 9 or less, peeling from the toner mother particles can be suppressed. Further, by controlling the true specific gravity to be 1.3 or more, aggregation and dispersion can be suppressed. The true specific gravity of the monodisperse spherical silica is 1.4 to 1.8.
The range is more preferably.

The average particle size of the monodisperse spherical silica is 80 n.
When it is less than m, the non-electrostatic adhesion between the toner and the photoconductor tends to be effectively reduced. In particular, due to the stress in the developing device, the monodisperse spherical silica is likely to be embedded in the toner mother particles, and the effect of improving the developability and transferability is significantly reduced. On the other hand, when it exceeds 300 nm, it becomes easy to be separated from the toner mother particles, which does not work effectively to reduce the non-electrostatic adhesion force, and at the same time, it easily migrates to the contact member, and secondary obstacles such as charge inhibition and image quality defect. It is easy to cause. The average particle size of the monodisperse spherical silica is 100 to 200 nm.
Is more preferable.

Since the monodisperse spherical silica is monodisperse and spherical, it can be uniformly dispersed on the surface of the toner mother particles and a stable spacer effect can be obtained. The definition of monodisperse can be discussed by the standard deviation with respect to the average particle diameter including aggregates, and the standard deviation is the volume average particle diameter D _50.
It is preferably × 0.22 or less. Further, as a definition of a sphere, it can be discussed by Wadell's sphericity, and it is preferable that the sphericity is 0.6 or more,
It is more preferably 0.8 or more.

The sphericity of Wadell was calculated from the following equation.

[0051]

[Equation 4]

In the above formula, the molecule was calculated from the average particle size. As the denominator, a Shimadzu powder specific surface area measuring device SS-100 type was used, and the BET specific surface area was substituted.

The reason why silica is preferable is that the refractive index is around 1.5, and the transparency is lowered due to light scattering even if the particle size is increased. Particularly, the PE value (the light transmission It does not affect the index).

The amount of the small-diameter inorganic oxide added is preferably in the range of 0.5 to 2.0 parts by mass with respect to 100 parts by mass of the toner mother particles. Further, when the large-diameter inorganic oxide is added other than cerium oxide, the addition amount of the large-diameter inorganic oxide is 1.0 to 100 parts by mass of the toner mother particles.
It is preferably 5.0 parts by mass.

Since the toner base particles used in the present invention are quasi-spherical, the effect of adding the above-mentioned inorganic oxide is also superior to the case of the amorphous toner base particles. That is, when the same amount of the inorganic oxide is added to the toner base particles, the powder flowability of the pseudo spherical toner base particles becomes considerably higher than that of the irregular base toner base particles. Even if the charge amount is about the same, the toner of the pseudo spherical toner mother particles exhibits high developability and transferability.

The toner used in the present invention can be produced by mixing the toner mother particles and the external additives with a Henschel mixer or a V blender. When the toner base particles are manufactured by a wet method, it is possible to add them externally by a wet method.

<Carrier> The carrier that can be used in the two-component developer of the present invention is not particularly limited, and known carriers can be used. For example, a resin-coated carrier having a resin coating layer on the surface of the core material can be mentioned.
Further, it may be a resin dispersion type carrier in which magnetic powder or the like is dispersed in a matrix resin.

The coating resin / matrix resin used for the carrier includes polyethylene, polypropylene, polystyrene, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl ether, polyvinyl ketone, vinyl chloride-vinyl acetate copolymer, Examples thereof include styrene-acrylic acid copolymer, straight silicone resin composed of an organosiloxane bond or a modified product thereof, fluororesin, polyester, polycarbonate, phenol resin, epoxy resin, urea resin, urethane resin, melamine resin and the like. However, the present invention is not limited to these.

Generally, the carrier preferably has an appropriate electric resistance value, and in order to adjust the resistance, it is preferable to disperse the conductive fine powder in the resin. Examples of the conductive fine powder include metals such as gold, silver and copper and carbon black, as well as titanium oxide, zinc oxide, barium sulfate, aluminum borate, potassium titanate, tin oxide and carbon black. However, the present invention is not limited to these.

Examples of the core material of the carrier include magnetic metals such as iron, nickel and cobalt, magnetic oxides such as ferrite and magnetite, and glass beads. To use the carrier for the magnetic brush method, It is preferably a magnetic material. The volume average particle diameter of the core material of the carrier is preferably in the range of 10 to 100 μm,
The range of 25 to 50 μm is more preferable.

To coat the surface of the core material of the carrier with a resin, a method of coating the coating resin and, if necessary, various additives with a coating layer forming solution dissolved in a suitable solvent is employed. The solvent is not particularly limited and may be appropriately selected in consideration of the coating resin used, coating suitability and the like.

As a concrete resin coating method, a dipping method in which powder of a core material of a carrier is dipped in a coating layer forming solution,
Spray method of spraying the coating layer forming solution on the surface of the core material of the carrier, fluidized bed method of spraying the coating layer forming solution while the core material of the carrier is suspended by fluidized air, core material of the carrier in a kneader coater And a kneader coater method in which the solvent is removed by mixing the coating solution with the coating layer forming solution.

<Developer> The two-component developer of the present invention is produced by mixing the toner and the carrier described above. The mixing ratio (mass ratio) of the toner and the carrier in the developer is toner: carrier = 1: 100 to.
It is preferably in the range of about 20: 100, and 3: 1.
The range of 00 to 12: 100 is more preferable.

-Image Forming Method- The image forming method of the present invention will be described in detail below. The image forming method of the present invention uses a latent image forming step of forming an electrostatic latent image on the surface of a latent image carrier and a developer carried on the developer carrier, and is formed on the surface of the latent image carrier. A development step of developing the electrostatic latent image to form a toner image, a transfer step of directly transferring the toner image formed on the surface of the latent image carrier to the surface of the recording medium, and a transfer step of transferring the toner image to the surface of the recording medium. And a cleaning step for cleaning the toner remaining on the surface of the latent image bearing member, wherein the electrophotographic developer of the present invention is used as the developer. It is characterized by.

In the latent image forming step, the surface of the latent image carrier is uniformly charged by the charging means, and then the latent image carrier is exposed by a laser optical system or LED array to form an electrostatic latent image. It is a process of forming. As the charging means, a non-contact type charger such as a corotron or a scorotron, and a contact type in which a latent image carrier surface is charged by applying a voltage to a conductive member in contact with the latent image carrier surface. Charging device of any type may be used. However, a contact charging type charger is preferable from the viewpoint of producing less ozone, being environmentally friendly, and exhibiting excellent printing durability. In the contact charging type charger, the conductive member may have any of a brush shape, a blade shape, a pin electrode shape, a roller shape and the like, but a roller shape member is preferable. The image forming method of the present invention is not particularly limited in the latent image forming step.

In the developing step, the electrostatic latent image on the surface of the latent image bearing member is brought into contact with or brought close to the surface of the latent image bearing member with a developer bearing member having a developer layer containing at least toner. In this step, toner particles are attached to the image to form a toner image on the surface of the latent image carrier. The developing method can be carried out by using a known method, but the developing method using the two-component developer used in the present invention includes a cascade method and a magnetic brush method. The image forming method of the present invention is not particularly limited regarding the developing method.

The transfer step is a step of forming a transfer image by transferring the toner image formed on the surface of the latent image carrier to the recording medium. The transfer step in the present invention directly transfers the toner image onto a recording medium such as paper.

A corotron can be used as a transfer device for transferring the toner image from the latent image carrier onto paper or the like. Corotron is effective as a means for uniformly charging the paper, but in order to give a predetermined charge to the paper, which is the recording medium,
A high voltage of several kV must be applied, which requires a high voltage power supply. Moreover, since ozone is generated by corona discharge, which causes deterioration of the rubber parts and the latent image carrier, a conductive transfer roll made of an elastic material is pressed against the latent image carrier to transfer the toner image to the paper. The contact transfer method is preferred. In the image forming method of the present invention, the transfer device is not particularly limited.

The cleaning step is a step in which a blade, a brush, a roll or the like is brought into direct contact with the surface of the latent image carrier to remove toner, paper dust, dust and the like adhering to the surface of the latent image carrier.

As the most commonly adopted method,
This is a blade cleaning method in which a blade made of rubber such as polyurethane is brought into pressure contact with the latent image carrier. In contrast,
A magnet is fixedly arranged inside, a rotatable cylindrical non-magnetic sleeve is provided on the outer periphery, and a magnetic brush method in which a magnetic carrier is supported on the sleeve surface to collect toner, or a semi-conductive resin fiber Alternatively, the hair of an animal may be rotated in a roll shape, and a bias having a polarity opposite to that of the toner may be applied to the roll to remove the toner. In the former magnetic brush method, a corotron for cleaning pretreatment may be installed. In the image forming method of the present invention, the cleaning method is not particularly limited.

The fixing step is a step of fixing the toner image transferred on the surface of the recording medium by a fixing device. As the fixing device, a heat fixing device using a heat roll is preferably used. The heating and fixing device is provided with a heater lamp for heating inside a cylindrical cored bar, and a fixing roller having a so-called release layer formed on its outer peripheral surface by a heat resistant resin coating layer or a heat resistant rubber coating layer, and the fixing roller. A pressure roller or a pressure belt, which is arranged in pressure contact with the roller and has a heat resistant elastic layer formed on the outer peripheral surface of the cylindrical core metal or the surface of the belt-shaped substrate. In the fixing process of the unfixed toner image, the recording medium on which the unfixed toner image is formed is inserted between the fixing roller and the pressure roller or the pressure belt, and the binder resin, the additive, etc. in the toner are removed. Fixing is performed by heat melting. In the image forming method of the present invention, the fixing method is not particularly limited.

In the image forming method of the present invention, in the case of producing a full-color image, each of a plurality of latent image bearing members has a developer bearing member of each color. By a series of steps including a latent image forming step, a developing step, a transfer step, and a cleaning step with each developer carrier, toner images of respective colors are sequentially formed on the same recording medium surface, and the toner images are laminated. An image forming method in which a full-color toner image is thermally fixed in the fixing step is preferably used. By using the electrophotographic developer in the image forming method, stable development, transfer, and fixing performance can be obtained even in a tandem system suitable for miniaturization and speeding up of color.

As the recording medium on which the toner image is transferred,
Examples thereof include plain paper and OHP sheets used in electrophotographic copying machines and printers. In order to further improve the smoothness of the image surface after fixing, it is preferable that the surface of the transferred material be as smooth as possible,
For example, coated paper in which the surface of plain paper is coated with resin or the like, art paper for printing, and the like can be preferably used.

According to the image forming method using the electrophotographic developer of the present invention, it is possible to obtain a high quality image due to high transfer efficiency, and to improve the cleaning property without lowering the developing property of the toner. It is possible to achieve a well-balanced improvement in reliability and the like by reducing wear between the blade and the photoconductor.

[0075]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. In the following description, all "parts" mean "parts by mass" unless otherwise specified.

-Measurement Method of Physical Properties- <Particle Size Distribution of Toner Base Particles and External Additives> A particle size distribution measuring device (Multisizer: manufactured by Nikkaki Co., Ltd.) was used to measure with an aperture diameter of 100 μm.

<Measurement of toner charge amount> About 0.3 to 0.7 g of the developer on the surface of the sleeve (developer carrier) of the developing device is sampled and blown off using a charge amount measuring device (TB200: manufactured by Toshiba Corporation). It was measured by the method.

<Image Density> Image Density Meter (X-Rite4
04A: manufactured by X-Rite).

<Carrier volume specific resistance> A sample of the carrier is filled in the lower electrode of the cell (100 mmφ, thickness 1.0 mm), the upper electrode is set, and 3.43 k from above is set.
A load of g was applied and the thickness was measured with a dial gauge. Next, a voltage was applied and the current value was read to determine the volume resistivity.

-Production of Toner Base Particles- <Preparation of Resin Fine Particle Dispersion> 370 g of styrene, 30 g of n-butyl acrylate, 8 g of acrylic acid, 24 g of dodecanethiol, and 4 g of carbon tetrabromide were mixed and dissolved, Nonionic surfactant (Nonipol 400: manufactured by Sanyo Kasei Co., Ltd.) 6 g and anionic surfactant (Neogen SC: manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 10 g were added to ion-exchanged water 550.
emulsified and dispersed in a flask, and slowly mixed for 10 minutes with ammonium persulfate 4
50 g of ion-exchanged water having g dissolved therein was added. After purging with nitrogen, the content in the flask was heated with an oil bath until the temperature reached 70 ° C. while stirring the inside of the flask, and emulsion polymerization was continued for 5 hours. As a result, the average particle size is 150 nm
Thus, a resin fine particle dispersion liquid was prepared in which resin particles having a glass transition temperature Tg of 58 ° C. and a mass average molecular weight Mw of 11,500 were dispersed. The solid content concentration of this dispersion was 40% by mass.

<Preparation of Colorant Dispersion Liquid (1)> 60 g of carbon black (Mogal L: Cabot Co.), nonionic surfactant (Nonipol 400: Sanyo Kasei Co., Ltd.) 6
g, and 240 g of deionized water mixed and dissolved, and a homogenizer (Ultra Turrax T50: IK
Stirring is carried out for 10 minutes using A), and then dispersion treatment is carried out by an ultimizer to prepare a colorant dispersant (1) in which colorant (carbon black) particles having an average particle diameter of 250 nm are dispersed. .

<Preparation of Colorant Dispersion Liquid (2)> 60 g of Cyan pigment (B15: 3), 5 g of a nonionic surfactant (Nonipol 400: manufactured by Sanyo Kasei Co., Ltd.), and 240 g of ion-exchanged water were mixed and dissolved. 1 using a homogenizer (Ultra Turrax T50: manufactured by IKA)
The mixture was stirred for 0 minutes, and then dispersed by an optimizer to prepare a colorant dispersant (2) in which colorant (Cyan pigment) particles having an average particle diameter of 250 nm were dispersed.

<Preparation of Colorant Dispersion Liquid (3)> Magen
Using a homogenizer (Ultra Turrax T50: manufactured by IKA Co.), 60 g of ta pigment (R122), 5 g of nonionic surfactant (Nonipol 400: manufactured by Sanyo Kasei Co., Ltd.), and 240 g of ion-exchanged water were mixed and dissolved. For 10 minutes, and then the dispersion treatment is carried out with an ultimizer to obtain a colorant having an average particle size of 250 nm (Mag.
A colorant dispersant (3) having enta pigment particles dispersed therein was prepared.

<Preparation of Colored Dispersion Liquid (4)> Yellow
A pigment (Y180) 90 g, a nonionic surfactant (Nonipol 400: manufactured by Sanyo Kasei Co., Ltd.) 5 g, and ion-exchanged water 240 g were mixed and dissolved, and a homogenizer (Ultra Turrax T50: manufactured by IKA) was used. 1
Stir for 0 minutes, then disperse with an optimizer to give a colorant having an average particle size of 250 nm (Yellow
A colorant dispersant (4) in which pigment particles were dispersed was prepared.

<Preparation of Release Agent Dispersion Liquid> Paraffin wax (HNP0190: manufactured by Nippon Seiro Co., Ltd., melting point 85 ° C.) 10
0 g, 5 g of a cationic surfactant (Sanisol B50: manufactured by Kao Corporation), and 240 g of ion-exchanged water are mixed to obtain 95
After heating to 0 ° C. and dispersing for 10 minutes using a homogenizer (Ultra Turrax T50: manufactured by IKA Co.) in a round stainless steel flask, dispersion treatment was performed with a pressure discharge type homogenizer, and the average particle diameter was 550 nm. A release agent dispersion liquid in which release agent particles were dispersed was prepared.

<Preparation of Toner Base Particles K1> 234 parts of the resin fine particle dispersion, 30 parts of the colorant dispersion (1), 40 parts of the releasing agent dispersion, polyaluminum hydroxide (made by Asada Chemical Co., P
aho2S) 0.5 part, and ion exchange water 600 parts,
Mix in a round stainless steel flask using a homogenizer (Ultra Turrax T50: IKA),
After dispersion, the flask was heated to 40 ° C. in an oil bath for heating while stirring. After holding at 40 ° C. for 30 minutes, it was confirmed that aggregated particles having a volume average particle diameter D ₅₀ of 4.5 μm were generated. When the temperature of the heating oil bath was further raised and kept at 56 ° C. for 1 hour, the volume average particle diameter D ₅₀ of the agglomerated particles was 5.3 μm. Then, 26 parts of the resin fine particle dispersion was added to the dispersion containing the aggregated particles, and then the temperature of the heating oil bath was adjusted to 50 ° C. and kept for 30 minutes. The pH of the system was adjusted to 7.0 by adding a 1N sodium hydroxide solution to the dispersion liquid containing the agglomerated particles, then the stainless steel flask was closed, and the mixture was stirred up to 80 ° C. using a magnetic seal. Heated and held for 4 hours. After cooling, the reaction product was filtered off, washed with ion-exchanged water 4 times, and then freeze-dried to prepare toner mother particles K1. The volume average particle diameter D ₅₀ of the toner mother particles K1 is 5.9.
The average value of μm and shape factor SF1 was 132.

<Preparation of Toner Base Particles C1> Toner base particles C1 are prepared in the same manner as the toner base particles K1 except that the colored particle dispersion liquid (2) is used instead of the colored particle dispersion liquid (1). did. The volume average particle diameter D ₅₀ of the toner mother particles C1 was 5.8 μm, and the average value of the shape factor SF1 was 131.

<Preparation of Toner Base Particles M1> Toner base particles M1 are prepared in the same manner as the toner base particles K1 except that the colored particle dispersion liquid (3) is used instead of the colored particle dispersion liquid (1). did. The volume average particle diameter D ₅₀ of the toner mother particles M1 was 5.5 μm, and the average value of the shape factor SF1 was 135.

<Preparation of Toner Base Particles Y1> Toner base particles Y1 are prepared in the same manner as the toner base particles K1 except that the colored particle dispersion liquid (4) is used instead of the colored particle dispersion liquid (1). did. The volume average particle diameter D ₅₀ of the toner mother particles Y1 was 5.9 μm, and the average value of the shape factor SF1 was 130.

<Preparation of Toner Mother Particles K2> 234 parts of resin fine particle dispersion, 30 parts of colorant dispersion (1), 40 parts of release agent dispersion, polyaluminum hydroxide (P. made by Asada Chemical Co., Ltd.
0.5 parts and 600 parts of ion-exchanged water,
Mix in a round stainless steel flask using a homogenizer (Ultra Turrax T50: IKA),
After dispersion, the flask was heated to 40 ° C. in an oil bath for heating while stirring. After holding at 40 ° C. for 30 minutes, it was confirmed that aggregated particles having a volume average particle diameter D ₅₀ of 4.5 μm were generated. Furthermore, when the temperature of the heating oil bath was raised and kept at 56 ° C. for 1 hour, the volume average particle diameter D ₅₀ of the agglomerated particles was 5.3 μm. Then, 26 parts of the resin fine particle dispersion was added to the dispersion containing the aggregated particles, and the temperature of the heating oil bath was adjusted to 50 ° C.
Hold for minutes. The pH of the system was adjusted to 5.0 by adding 1N sodium hydroxide solution to the dispersion liquid containing the aggregated particles.
After adjusting to, the stainless steel flask was sealed and heated to 95 ° C. while continuing stirring with a magnetic seal.
Held for hours. After cooling, the reaction product was separated by filtration, washed with ion-exchanged water four times, and then freeze-dried to obtain toner mother particles K2.
Was produced. The volume average particle diameter D ₅₀ of the toner mother particles K2 was 5.8 μm, and the average value of the shape factor SF1 was 109.

<Preparation of Toner Base Particles C2> Toner base particles C2 are prepared in the same manner as the toner base particles K2 except that the colored particle dispersion liquid (2) is used instead of the colored particle dispersion liquid (1). did. The volume average particle diameter D ₅₀ of the toner mother particles C2 was 5.7 μm, and the average value of the shape factor SF1 was 110.

<Preparation of Toner Base Particles M2> Toner base particles M2 are prepared in the same manner as the toner base particles K2 except that the colored particle dispersion liquid (3) is used instead of the colored particle dispersion liquid (1). did. The volume average particle diameter D ₅₀ of the toner mother particles M2 was 5.6 μm, and the average value of the shape factor SF1 was 114.

<Preparation of Toner Base Particles Y2> Toner base particles Y2 are prepared in the same manner as the toner base particles K2, except that the colored particle dispersion liquid (4) is used instead of the colored particle dispersion liquid (1). did. The volume average particle diameter D ₅₀ of the toner mother particles Y2 was 5.8 μm, and the average value of the shape factor SF1 was 108.

<Production of toner mother particles K3> Polyester resin (linear polyester obtained from terephthalic acid, bisphenol A ethylene oxide adduct and cyclohexanedimethanol, glass transition temperature Tg: 62 ° C., number average molecular weight Mn: 12000 , Mass average molecular weight Mw: 3
2000) 100 parts, carbon black (Mogar L:
A mixture of 4 parts by Cabot Corporation and 5 parts by carnauba wax is kneaded by an extruder, pulverized by a jet mill, and then classified by a wind classifier, and a volume average particle diameter D ₅₀ is 5.9 μm and a shape factor SF1. To produce toner mother particles K3 having an average value of 145.

<Preparation of Toner Base Particles C3> The toner base particles K3 described above are used except that a cyan colorant (CI Pigment Blue 15: 3) is used instead of carbon black.
In the same manner as described above, toner mother particles C3 having a volume average particle diameter D ₅₀ of 5.6 μm and an average value of the shape factor SF1 of 141 were produced.

<Preparation of Toner Base Particles M3> The volume average particle size D ₅₀ is 5.9 μm and the shape is the same as that of the toner base particles K3 except that the magenta colorant (R122) is used in place of carbon black. The average value of the coefficient SF1 is 14
Toner mother particles M3 of No. 9 were prepared.

<Preparation of Toner Base Particle Y3> The volume average particle diameter D ₅₀ is 5.8 μm and the shape is the same as the toner base particle K3 except that the yellow colorant (Y180) is used in place of carbon black. The average value of the coefficient SF1 is 144
Toner mother particles Y3 of

-Preparation of Carrier- 14 parts of toluene, 2 parts of styrene-methacrylate copolymer (component ratio: 90/10), and 0.2 parts of carbon black (R330: manufactured by Cabot Co.) were mixed to obtain 10 parts.
The mixture was stirred for 1 minute with a stirrer to prepare a coating layer forming solution in which carbon black was dispersed. Next, this coating solution and 100 parts of ferrite particles (volume average particle size: 50 μm) were placed in a vacuum degassing kneader, stirred at 60 ° C. for 30 minutes, and then degassed by further heating while reducing the pressure. A carrier was prepared by drying. This carrier had a volume resistivity value of 10 ¹¹ Ωcm when an electric field of 1000 V / cm was applied.

(Example 1) The toner mother particles K1 and C
1, 100 parts of each of M1, and Y1, 1 part of rutile type titanium oxide (average particle size 20 nm, treated with n-decyltrimethoxysilane), silica (prepared by gas phase oxidation method, volume average particle size 40 nm, silicone oil) Processing) 2.0
Part, cerium oxide (volume average particle size 0.7 μm), and higher aliphatic alcohol (higher aliphatic alcohol having a molecular weight of 700) were pulverized with a jet mill to obtain a volume average particle size of 8.
0.3 μm) was added and blended for 15 minutes at a peripheral speed of 30 m / s using a 5 liter Henschel mixer, and then coarse particles were removed using a sieve with an opening of 45 μm to remove the toner. It was made. Further, 100 parts of the carrier and 5 parts of the toner were stirred with a V-blender at 40 rpm for 20 minutes, and sieved with a sieve having an opening of 212 μm to prepare an electrophotographic developer.

Using each of the above developers, Docu
Print C2221 (manufactured by Fuji Xerox Co., Ltd.) was used to evaluate the developability and transferability by the following methods.

<Evaluation of initial developability and transferability> 5c for each color under high temperature and high humidity (30 ° C., 80% RH) environment
A solid patch of m × 2 cm was developed, the developed toner image on the surface of the photoconductor was transferred using the adhesiveness of the tape surface, and the mass (W1) was measured. Next, the same developed toner image was transferred onto the surface of paper (J paper: manufactured by Fuji Xerox Office Supply Co., Ltd.), and the weight (W2) of the transferred image was measured. From these, the transfer efficiency was determined by the following formula and the transferability was evaluated. Transfer efficiency (%) = (W2 / W1) × 100 The developability was evaluated by the mass of W1 at this time.

The judgment criteria for the above evaluation are as follows.
In addition, each evaluation was performed by averaging the evaluations of four colors except for Example 5 and Comparative Example 6. [Developmentability Evaluation Criteria] ○: W1 is 4.0 g / m ² or more. Δ: W1 is 3.5 or more and less than 4.0 g / m ² ×: W1 is less than 3.5 g / m ^2.

[Evaluation Criteria for Fogging on Paper] ∘: Visual confirmation is not possible, but there are less than 30 toner particles in the visual field range of 50 times the magnifier. Δ: Visual inspection range is 50 times in the magnifying field, which cannot be visually confirmed. And toner particles are 30 or more. ×: Visually observable level

[Transferability Evaluation Criteria] -○: Transfer efficiency is 90% or more -: Transfer efficiency is 85% or more and less than 90% *: Transfer efficiency is less than 85% The results are shown in Table 1.

<Evaluation of Cleaning Property> The cleaning property was evaluated with Docu print C2221 (manufactured by Fuji Xerox Co., Ltd.) using the developers of the four colors. At this time, the distance from the tip of the sheet metal of the cleaning blade to the tip of the rubber (rubber protrusion amount) was set to 10 mm to 7.5 mm in the above apparatus, and the length of the sheet metal was increased accordingly. High temperature and high humidity (30 ℃, 80% R
Take 30000 prints with acid paper in H),
Image distortion due to deletion, dirt on the charger due to poor cleaning and image quality deterioration were evaluated, and then J paper (manufactured by Fuji Xerox Office Supply Co., Ltd.) was used under low temperature and low humidity (10 ° C, 20% RH). 30,000 prints were taken, and stains on the charger due to poor cleaning and image quality deterioration were evaluated.

The judgment criteria for the above evaluation are as follows. [Evaluation Criteria for Cleaning]-○: No deterioration in image quality and no problem other than image quality. -: There was no deterioration in image quality, but some problem other than image quality occurred. *: The image quality deteriorated. The results are shown in Table 2.

(Example 2) The toner mother particles K1 and C
1, 100 parts of each of M1 and Y1, 1 part of anatase type titanium oxide (average particle size 20 nm, i-butyltrimethoxysilane treatment), silica (prepared by sol-gel method, volume average particle size 140 nm, HMDS treatment) 2 Part, cerium oxide (volume average particle size 0.7 μm) 0.8 part, and zinc stearate (ZNS-S: manufactured by Asahi Denka Kogyo Co., Ltd.) 0.3 part were added, and the peripheral speed was 3 using a 5 liter Henschel mixer.
After blending at 0 m / s for 15 minutes, coarse particles were removed using a sieve having an opening of 45 μm to prepare a toner. Further, 100 parts of the carrier and 5 parts of the toner were stirred by a V-blender at 40 rpm for 20 minutes, and sieved with a sieve having an opening of 212 μm to prepare a developer. The same evaluations as in Example 1 were performed using these four color developers. The results are shown in Tables 1 and 2.

(Example 3) In Example 1, the addition amount of cerium oxide was 0.4 with respect to 100 parts of the toner mother particles.
And a higher aliphatic alcohol were added in an amount of 0.2 part to prepare a toner and a developer in the same manner as in Example 1. The same evaluations as in Example 1 were performed using these four color developers. The results are shown in Tables 1 and 2.

Example 4 In Example 2, the addition amount of cerium oxide was 0.5 with respect to 100 parts of the toner mother particles.
Parts and a toner and a developer were prepared in the same manner as in Example 2 except that the amount of zinc stearate added was 0.5 part. The same evaluations as in Example 1 were performed using these four color developers. The results are shown in Tables 1 and 2.

(Example 5) Docu print C2
No. 221, evaluation was performed in the same manner as in Example 1 except that only the black developing cartridge (photoconductor and developing device) was set to be drivable, and only the developer using K1 as the toner mother particles was evaluated. I went. The results are shown in Table 1,
It shows in Table 2.

(Comparative Example 1) K2 and C as toner mother particles
A toner and a developer were prepared in the same manner as in Example 1 except that 2, M2, and Y2 were used. The same evaluations as in Example 1 were performed using these four color developers. The results are shown in Tables 1 and 2.

(Comparative Example 2) K3 and C as toner mother particles
A toner and a developer were obtained in exactly the same manner as in Example 2 except that 3, 3, and Y3 were used. The same evaluations as in Example 1 were performed using these four color developers. The results are shown in Tables 1 and 2.

Comparative Example 3 Example 1 was repeated except that the higher aliphatic alcohol was not used as an additive.
A toner and a developer were prepared in the same manner as in. These four
The same evaluation as in Example 1 was performed using the color developers.
The results are shown in Tables 1 and 2.

Comparative Example 4 A toner and a developer were prepared in the same manner as in Example 1 except that cerium oxide was not used as an additive. The same evaluations as in Example 1 were performed using these four color developers. The results are shown in Tables 1 and 2.

Comparative Example 5 A toner and a developer were prepared in the same manner as in Example 1 except that strontium titanate (volume average particle size 0.3 μm) was used instead of cerium oxide. The same evaluations as in Example 1 were performed using these four color developers. The results are shown in Tables 1 and 2.
Shown in.

(Comparative Example 6) Docu print C2
No. 221, evaluation was performed in the same manner as in Example 1 except that only the black developing cartridge (photoconductor and developing device) was set to be drivable, and only the developer using K2 as the toner mother particles was evaluated. I went. The results are shown in Table 1,
It shows in Table 2.

[0117]

[Table 1]

[0118]

[Table 2]

[0119]

According to the present invention, it is possible to obtain a high quality image due to the high transfer efficiency as described above, and to stabilize the image quality over time by improving the cleaning property without deteriorating the developing property of the toner. Can be achieved.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Sakon Takahashi             Fuji Zero, 1600 Takematsu, Minamiashigara City, Kanagawa Prefecture             X Co., Ltd. (72) Inventor Masahiro Uchida             Fuji Zero, 1600 Takematsu, Minamiashigara City, Kanagawa Prefecture             X Co., Ltd. (72) Inventor Rieko Kataoka             Fuji Zero, 1600 Takematsu, Minamiashigara City, Kanagawa Prefecture             X Co., Ltd. (72) Inventor Eiko Seino             Fuji Zero, 1600 Takematsu, Minamiashigara City, Kanagawa Prefecture             X Co., Ltd. F-term (reference) 2H005 AA08 CA14 CB07 CB13 EA07                       EA10 FA01

Claims (4)

[Claims] 1. A two-component developer comprising a toner and a carrier, the toner comprising toner mother particles and an external additive, wherein the external additive is at least two kinds of inorganic oxides containing cerium oxide. Shape factor SF represented by the following formula (1) of the toner mother particles
The average value of 1 is 115-140, The electrophotographic developer characterized by the above-mentioned. [Equation 1] (In the above formula, L represents the maximum length of each toner base particle, and A represents the projected area of each toner base particle.) 2. When the addition amount of cerium oxide is A parts by mass and the addition amount of lubricant particles is B parts by mass relative to 100 parts by mass of the toner mother particles, A and B are A> B and A +.
The electrophotographic developer according to claim 1, wherein the relationship of B ≧ 0.6 is satisfied. 3. A latent image forming step of forming an electrostatic latent image on the surface of a latent image carrier, and an electrostatic latent image formed on the surface of the latent image carrier using a developer carried on the developer carrier. A developing step of developing an image to form a toner image, a transfer step of directly transferring the toner image formed on the surface of the latent image carrier to the surface of the recording medium, and a toner image transferred to the surface of the recording medium. An image forming method including a fixing step of thermally fixing the toner and a cleaning step of cleaning the toner remaining on the surface of the latent image carrier, wherein the developer is the electrophotographic developer according to claim 1 or 2. An image forming method characterized by the following. 4. A plurality of latent image carriers each have a developer carrier, and the latent image forming process, the developing process, the transfer process and the cleaning by the plurality of latent image carriers and the developer carrier respectively. By a series of steps, a toner image for each of the series of steps is sequentially laminated and formed on one recording medium surface, and in the fixing step, the laminated toner images are thermally fixed on the recording medium. The image forming method according to claim 3, wherein the image forming method is performed.