JP3057298B2 - Image forming method and toner used therefor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of supplying a one-component developer to which an auxiliary agent is externally added as needed to a developer carrier which is driven to rotate, and developing the developer on the surface of the developer carrier. The electrostatic latent image formed on the latent image carrier is carried by the developer carrier in a developing area where the electrostatic latent image carrier and the developer carrier are opposed to each other. Further, the present invention relates to an image forming method for visualizing an image with the developer and a toner used therefor.

[0002]

2. Description of the Related Art In an image forming apparatus such as an electronic copier, a printer or a facsimile, which forms an electrostatic latent image on a latent image carrier and visualizes the latent image with a developer to obtain a recorded image, a powdery image is formed. Dry developing devices using a developer are widely used.

As such a powdery developer, a two-component developer having a toner and a carrier and a one-component developer not containing a carrier are known, and the former two-component developer is used. In the two-component developing method, a relatively stable and good recorded image can be obtained, but the deterioration of the carrier and the fluctuation of the mixing ratio of the toner and the carrier are apt to occur, the maintenance of the apparatus is complicated, and the structure of the entire apparatus is large. It has a disadvantage that it is easy to change.

[0004] From such a viewpoint, a one-component developing system using a one-component developer which does not have the above-mentioned disadvantages has attracted attention. One-component developer is composed of only toner,
In some cases, an auxiliary agent is externally added as necessary. As the toner, there are a magnetic toner in which magnetic powder is kneaded into each toner particle itself, and a non-magnetic toner containing no magnetic material. Here, since the magnetic material is generally opaque,
When a color image including a full-color image and a multi-color image is formed with a magnetic toner, a developed visible image becomes unclear and a vivid color image cannot be obtained. Therefore, it is desirable to adopt a one-component developing method using a non-magnetic toner especially for color development.

In a developing device employing a one-component developing system, a one-component developer is carried on a developer carrier and conveyed, and the developer carrier and the latent image carrier are opposed to each other. In the region, the electrostatic latent image formed on the latent image carrier is visualized with a developer, but in order to form a high-quality visible image of a predetermined density, a large amount of sufficiently charged toner is required. It is necessary to convey the latent image to a developing area and visualize the latent image with the toner.

In the case where a magnetic toner is used, the above-described requirement can be relatively easily satisfied because the one-component developer can be carried on the developer carrier by utilizing the magnetic force of a magnet provided in the developer carrier. It is possible to satisfy

However, when a non-magnetic one-component developer is used, it cannot be supported on a developer carrier by magnetic force, so that it is difficult to satisfy the above requirements. Various measures have been proposed for this,
For example, JP-A-61-42672 discloses that a layer of a dielectric (insulator) is formed on the surface of a developer carrying member (developing roller), and a developer supplying member comprising, for example, a sponge roller. Are pressed against each other to frictionally charge them with different polarities, and a non-magnetic toner charged with a polarity opposite to that of the dielectric is electrostatically attached to the dielectric, and the one-component developer is transported to the developing area. A way to do that has been proposed. However, even with this method, the strength of the electric field formed in the vicinity of the dielectric surface cannot be sufficiently increased, so that it is difficult to carry a large amount of toner on the surface of the developing roller, and the developing roller can be transported to the developing area. Insufficient amounts of the agent make it difficult to form a high-density visible image.

It is also known to apply an electric field between the developing roller and the developer supply member in such a direction that the non-magnetic toner electrostatically moves to the developing roller side. However, it is difficult to attach a sufficient amount of toner to the developing roller.

[0009] The toner supply member includes 10 ² to 10 ⁶
Ωcm conductive foam (JP-A-60-229057), elastic body with skin layer (JP-A-60-229060) and fur brush
(Japanese Patent Application Laid-Open No. 61-42672) and the like, and as a developing roller, a metal body having irregularities on its surface (Japanese Patent Application Laid-Open No. 60-53976), an insulating coated roller body ( JP-A-55-46768) Medium resistance coated roller (JP-A-58-132)
No. 768) and an electrode roller having an insulating surface and a conductive surface (JP-A-53-36245).

Further, in a developing apparatus using a non-magnetic one-component developer, a sponge roller is disclosed in JP-A-60-229057, an elastic roller is disclosed in JP-A-62-229060,
In 52663, using a fur brush or the like, a charge is applied to the toner by frictional charging between the toner and the replenishing member, and further, by friction in contact with the developing roller, the toner is electrostatically attached to the developing roller, Further, the latent image on the photoreceptor is developed by controlling the toner layer using a layer thickness regulating member such as a blade. As the material of the developing roller, various materials such as an insulating material, a medium-resistance material, and a laminated material are used.

According to the methods shown in these references, toner is adhered to the developing roller by friction between the toner replenishing member and the developing roller. Is difficult to obtain, resulting in insufficient toner adhesion. The need for a large amount of this adhesion also makes one-component development difficult.

Japanese Patent Application Laid-Open No. 63-261284 discloses a method of forming a color image by over-development. However, in order to obtain a required density, it is specified that one toner layer has the highest density. I have. However, if a toner that reaches the highest density in such a single layer is used, gradation and reproducibility are poor,
There is a problem that it is difficult to obtain a fine-grained image.

Further, as shown in Japanese Patent Application Laid-Open No. 54-51841, the one-component developer on the developing roller after passing through the developing area is scraped off, and the surface layer of the developing roller is removed. On the other hand, there has been proposed a technique in which a corona discharge is performed to apply a charge, and then a non-magnetic toner is positively electrostatically adhered to a developing roller by a developer supply member. Also, the amount of developer carried on the surface of the developing roller cannot be increased, and a large amount of developer cannot be transported to the developing area.

[0014]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances of the prior art, and is intended to form a fine color image with good gradation and reproducibility in superposition development. It is an object of the present invention to provide an image forming method that can be used, and to provide a toner that can be suitably used in the image forming method.

As a method for transferring a large amount of sufficiently charged toner to the developing area and obtaining a high-density, high-quality image, the present inventors have previously described "rotating and driving developer loading." A one-component developer composed of a non-magnetic toner to which an auxiliary agent is externally added as necessary is supplied to the body, and the developer is carried on the surface of the carrier and transported. In a developing method in which an electrostatic latent image formed on the latent image carrier is visualized by the developer carried on the developer carrier in a development region in which the developer carriers are opposed to each other, the developer A plurality of minute closed electric fields are formed near the surface of the carrier by selectively holding electric charges on the surface of the carrier, and the charged electric toner is sucked by the closed electric field, and the developer adheres to the surface of the developer carrier. The electrostatic latent image is visualized by the loaded developer. Was proposed that an image forming method ". In such a method, a large number of minute closed electric fields (microfields) are formed in the vicinity of the surface of the developer carrier, so that the electric field strength can be significantly increased as compared with the conventional method, and a large amount of sufficiently charged toner can be obtained. It has many advantages that it can be carried on the developer carrier and transported to the development area,
It has many more advantages for a color image that requires a gradation, reproducibility and fine-grained image.

[0016]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that an image forming method for superimposing an image by using the above-mentioned image forming method for forming a large number of minute closed electric fields on the surface of a developer carrying member. The inventors have found that the method is suitable for the above-mentioned purpose, and have found that a toner having a specific coloring power and transmittance is suitable for the image forming method, thereby completing the present invention.

That is, according to the present invention, by holding electric charges selectively on the surface of the developer carrying member, a large number of minute closed electric fields are formed near the surface of the developer carrying member. A one-component developer composed of a toner to which an auxiliary agent is externally added as necessary is supplied onto the body, and the developer is carried on the surface of the developer carrier by the minute closed electric field. In an image forming method of transporting an electrostatic latent image to a developing gap facing a surface of an electrostatic latent image carrier to visualize the electrostatic latent image, an electric field is formed in the developing gap to transport the developer to the electrostatic latent image carrier. The toner image is developed by flying on the surface, and the electrostatic latent image carrier carrying the toner image is charged and charged via the toner image.
An image forming method is provided in which image exposure is performed and development is performed by superimposing the toner image on the toner image with a toner different in color from the toner image.

According to the present invention, there is provided a toner for use in the above-mentioned image forming method, wherein the toner comprises at least a binder resin and a colorant.
Tinting strength at 5 mg / cm ² is not less than 75% of the coloring power in the 1.0 mg / cm ^2, and the transmittance at 1.0 mg / cm ² is the toner which is characterized in that 50% or more Further, according to the present invention, there is provided a toner used in the above-mentioned image forming method, wherein the toner comprises at least a binder resin and a colorant, and the dispersion diameter of the colorant is 4.5 μm or less. A toner is provided.

A color image forming method by superposition development, that is, a cycle of charging, exposure and development is repeated a plurality of times to form a plurality of toner images of different colors on an electrostatic latent image carrier (photoreceptor). In the batch transfer method, it is difficult to obtain a high-density subtractive color mixture in which the amount of adhered toner is large, and it is difficult to develop the toner layer at a constant thickness. It was difficult to obtain a perfect color image. However, the present invention uses an image forming method in which a number of minute closed electric fields are formed in the vicinity of the surface of the developer carrying member, and the toner carried on the developer carrying member flies onto the photoreceptor. By performing the over-development, the above-mentioned drawbacks are solved, and a fine-grained image having good gradation and reproducibility can be obtained. In particular, by using a toner having a specific transmittance and a coloring power or a toner containing a colorant having a specific dispersion diameter, it is easily and stably provided, and gradation, good reproducibility and fine-grained fineness can be obtained. Images can be obtained.

Hereinafter, the image forming method of the present invention will be described. FIG. 1 shows an outline of a typical developing device useful for carrying out this image forming method, focusing on a developer carrier. In FIG. 1, a toner supply member (a sponge roller, a fur brush, or the like) is supplied to a toner 60 contained in a toner tank 70 by a stirring blade (toner supply auxiliary member) 50.
The toner 60 is forcibly moved to the toner supply member 40. On the other hand, the developer carrier (developing roller) 20 that has completed the development rotates in the direction of the arrow (for example, 40
0 rpm) to reach a contact portion with the toner supply member 40.
The toner supply member 40 rotates in a direction opposite to that of the developer carrier 20, charges the developer carrier 20 and the toner 60, and causes the toner 60 to adhere to the developer carrier 20. Further, the developer carrier 20 rotates, and the toner adhered on the developer carrier 20 is moved by a toner layer thickness regulating member (elastic blade) 30.
The charging is stabilized while the thickness is controlled, and the developing gap 80
Reach When a bias voltage is applied to the developer carrier 20 and the toner supply member 40, the toner flies on the surface of the electrostatic latent image carrier (photoconductor) 10 in the developing gap 80 by the electric field formed, and , The latent image is developed.

Next, the mechanism of toner adhesion to the developer carrier 20 of this type (electrode type) will be described. As an example of the developer carrying member 20, as shown in FIG. 2, for example, a dielectric portion and a conductive portion are mixed on a surface thereof with a small area. The size of the area is
When the shape is circular, the diameter is 30 to 2000 μ
m, preferably small areas with a size of 100 to 400 μm are dispersed randomly or according to a certain rule.
As the area ratio, the area of the dielectric portion is preferably in the range of 50 to 80%.

The toner adhesion is as follows. First, the developer carrier 20 that has completed the development rotates in the direction of the arrow and comes into contact with the toner supply member 40. Here, the remaining toner in the non-image portion that has not been developed is mechanically and electrically scraped off by the toner supply member 40, and the dielectric portion is charged by friction. At this time, the charges of the developer carrier 20 and the toner by the previous development are fixed and initialized by friction. Next, the toner carried by the supply member 40 is charged by friction and adheres to the dielectric portion of the developer carrier 20 electrostatically. At this time, the polarity of the toner is opposite to the charge of the photosensitive member, and the dielectric portion of the developer carrier 20 has the same polarity. The electric field on the developer carrier 20 at this time becomes a microfield (closed electric field) as shown in FIG.
The electric field has a large electric field gradient, so that the toner can be attached in multiple layers. Further, since the attached toner has a closed electric field, it is strongly pulled toward the developer carrier 20 side,
It is difficult to leave.

The thickness of the toner layer is further controlled by the toner layer thickness regulating member 30, and reaches the developing gap 80. By the electric field between the developer carrier 20 and the electrostatic latent image carrier 10 in the developing gap 80, the toner on the developer carrier 20 flies to the surface of the electrostatic latent image carrier 10 to perform development.
The developer carrier 20 and the electrostatic latent image carrier 10 have a positional relationship of 30 to 500 μm,
Preferably, they are arranged with a gap of 50 to 250 μm.

In the present invention, the one-component developer is carried on the surface of the developer carrier 20 by the minute closed electric field,
Most of the one-component developer to be conveyed to the developing gap 80 is supported by the portion mainly holding the electric charge, and the amount of the one-component developer supported in the other portions is reduced to 0 to a small amount.
The one-component developer jumps from the entire surface of the surface 0 at the same time and does not cause a sudden increase in air pressure in the developing gap 80.

Although many types of developing device parts can be used, as shown in Table 1, when only materials that are preferable in terms of releasability from toner and durability are used.

[0026]

Next, a method for producing the developer carrier used in the present invention will be described. For example, the following method is employed. (i) First, a metal roller whose surface is grooved is manufactured. The groove is formed by a method such as iris knurling. The grooves have a pitch of 0.1 to 0.5 mm and are processed at an angle of about 45 degrees with respect to the longitudinal direction of the roller. [See FIG. 3 (a)] (ii) Next, the grooved metal surface is coated with, for example, a fluororesin (Lumiflon LF200; manufactured by Asahi Glass Co., Ltd.) and cured and dried at 100 ° C. for about 30 minutes. The coating thickness is set so that the grooves are completely filled. [See; FIG. 3 (b)] (iii) Subsequently, the surface of the roller is cut or polished so that the conductive surface is mixed in a small area, and the conductive area is reduced to 2
Grind to 0-50%. [See; FIG. 3 (c)]

Further, in addition to the above-mentioned methods, various conductive materials may be formed by using various materials, such as forming a conductive rubber material having a concave portion on the surface by molding, filling the concave portion with an insulating substance, and polishing. be able to.

The toner used in the method of the present invention comprises at least a binder resin and a colorant, and when the toner is formed into a thin film, the coloring power at 0.5 mg / cm ² is 1.0 mg / cm 2. ² , which have a transmittance of not less than 75% of the coloring power of No. ² and a transmittance of not less than 50% at 1.0 mg / cm ² , or comprise at least a binder resin and a coloring agent, and have a dispersed diameter of the coloring agent. Is preferably 4.5 μm or less. By using a toner having such characteristics, no problem occurs in the charging / image exposure process from the toner, and the gradation and reproducibility are good, and a fine-grained image can be easily and stably formed. Obtainable.

When the toner is formed into a thin film, 0.5 mg
/ Coloring power in cm ² of coloring power in 1.0 mg / cm ² 7
If the ratio exceeds 5% or the transmittance at 1.0 mg / cm ² is less than 50%, an image having poor gradation reproducibility and poor sharpness is obtained. Also,
Even when a toner containing a colorant, particularly a pigment having a dispersion diameter of more than 4.5 μm, is used, an image having poor gradation reproducibility and poor sharpness is similarly obtained.

As the binder resin used in the toner of the present invention, all of those conventionally used as binder resins for toner are applied. Specifically, polystyrene,
Homopolymers of styrene such as polychlorostyrene and polyvinyltoluene and substituted products thereof; styrene / p-chlorostyrene copolymer, styrene / propylene copolymer, styrene / vinyltoluene copolymer, styrene / vinylnaphthalene copolymer , Styrene / methyl acrylate copolymer, styrene / ethyl acrylate copolymer, styrene /
Butyl acrylate copolymer, styrene / octyl acrylate copolymer, styrene / methyl methacrylate copolymer, styrene / ethyl methacrylate copolymer, styrene / butyl methacrylate copolymer, styrene / α-chloromethacrylic acid Methyl copolymer, styrene / acrylonitrile copolymer, styrene / vinyl methyl ether copolymer, styrene / vinyl ethyl ether copolymer, styrene / vinyl methyl ketone copolymer, styrene / butadiene copolymer, styrene / isoprene copolymer Styrene copolymers such as polymers, styrene / acrylonitrile / indene copolymers, styrene / maleic acid copolymers, styrene / maleic acid ester copolymers; polymethyl methacrylate, polybutyl methacrylate, polyvinyl chloride, polyvinyl acetate Vinyl, poly Tylene, polypropylene, polyester, polyvinyl butyl butyral, polyacrylic acid resin, rosin, modified rosin, terpene resin, phenolic resin, aliphatic or alicyclic hydrocarbon resin, aromatic petroleum resin, chlorinated paraffin, paraffin wax, etc. These may be used alone or in combination of two or more.

As the colorant used in the toner of the present invention, all pigments and dyes conventionally used as colorants for toner are applied. Specifically, carbon black, lamp black, iron black, ultramarine, nigrosine dye, aniline blue, calco oil blue, Dupont oil red, quinoline yellow, methylene blue chloride, phthalocyanine blue, phthalocyanine green, hansa yellow G, rhodamine 6C lake, Examples thereof include chrome yellow, quinacridone, benzidine yellow, malachite green, malachite green hexalate, oil black, azo oil black, rose bengal, monoazo dyes, disazo dyes, and trisazo dyes. However, in the toner of the present invention, it is required to use a colorant, particularly a pigment, having a dispersion diameter of 4.5 μm or less.

In the toner of the present invention, it is effective to add a polarity controlling agent to control the polarity. Examples of the polarity controlling agent in this case include a nigrosine dye, a quaternary ammonium salt, a basic dye, a polymer having an amino group, a chromium-containing azo dye, and a metal salt of a salicylic acid derivative.

Further, in the toner of the present invention, in order to impart releasability, in addition to synthetic waxes such as low molecular weight polyethylene and polypropylene, candelilla wax, carnauba wax, rice wax, wood wax, jojoba oil Vegetable waxes such as beeswax, lanolin,
Animal waxes such as whale wax; mineral waxes such as montan wax and ozokerite; and oil waxes such as hardened castor oil, hydroxystearic acid, fatty acid amide, and phenol fatty acid ester can be contained.

In the toner used in the present invention, in addition to the polarity control agent and the release agent, various plasticizers (for the purpose of adjusting the thermal properties, electrical properties, physical properties, etc. of the toner, if necessary). It is also possible to add auxiliary agents such as dibutyl phthalate and dioctyl phthalate, and a resistance adjusting agent (such as tin oxide, lead oxide, and antimony oxide). Further, the toner of the present invention may contain additives other than the above-mentioned polarity controlling agent, release agent, auxiliary agent, and the like, if necessary. Examples of the additive include fluidity imparting agents such as colloidal silica, titanium oxide, and aluminum oxide.

[0036]

The present invention will be described in more detail with reference to the following examples. Parts represent parts by weight.

Example A toner was prepared according to the following formulation. (Cyan) Binder resin Polyester polymer 97 parts Release agent Low molecular weight polypropylene 3 parts Colorant Phthalocyanine blue 2 parts Charge control agent Salicylate zinc salt 2 parts (Magenta) Binder resin Polyester polymer 97 parts Release agent Low Molecular weight polypropylene 3 parts Colorant thioindigo pigment 3 parts Charge control agent Salicylic acid zinc salt 2 parts (yellow) Binder resin Polyester polymer 97 parts Release agent Low molecular weight polypropylene 3 parts Colorant monoazo yellow 5 parts Charge control agent Zinc salicylate 2 parts salt

Each mixture having the above composition was melt-kneaded using three rolls, cooled, coarsely crushed using a hammer mill, and then finely crushed with an air jet-type fine crusher. Each of the obtained finely pulverized products was classified to have an average particle size of 11 μm. Colloidal silica 0.2
Were added and mixed to obtain a toner. The coloring degree and transmittance of each of the obtained toners were as shown in Table 2. Further, when each toner was dissolved in THF and filtered with a syringe filter having a pore size of 4.5 μm, permeation of the pigment was observed.

[0039] Note-1) Coloring degree of toner: A specified amount of toner is adhered and fixed on plain paper and measured with a Macbeth densitometer. Note-2) Transmittance: A specified amount of toner is adhered and fixed on a transparent film, and the surface of the toner layer is smoothed, and then measured with a haze meter.

FIG. 4 shows a color useful for carrying out the method of the present invention.
1 shows an example of an overall configuration diagram of an image forming apparatus. Here, each developing unit has a developing roller having a cross section as shown in FIG. 3 (c) [FIG. 3 (a)] (a dielectric part and a conductive part are mixed in a small area, and the area of the dielectric part is small). 61%). In FIG. 4, 11 is an electrostatic latent image carrier (organic photoreceptor), 12 is a charging member (corona charger), 13 is a laser optical system, and 14, 15, and 16 contain yellow, magenta, and cyan toners, respectively. Developing device, 17 is a transfer member, and 18 is a cleaning member.

Using this apparatus, an image was formed by the method described below. While rotating the photoconductor 11 (diameter 150 mm) in the direction of the arrow at a peripheral speed of 94 mm / sec,
The charging member 12 charges the photoconductor 11 to −850V. Next, the non-image portion -850 V was applied by the laser optical system 13.
The image portion forms an electrostatic latent image of -100V. In forming the electrostatic latent image, an image whose laser beam spot diameter was controlled in eight steps by a pulse width modulation method was used.

This electrostatic latent image was developed with a developing gap of 100 μm.
The image was developed by a yellow developing device with a developing bias of -750 V. Yellow adhesion amount to the photosensitive member of the toner, from the maximum 0.8 mg / cm ² according to the pulse width modulation level to obtain a minimum 0.2 mg / cm ^2. No toner adhered to the non-image area. The charge amount of this toner is about 10
μC / g. Next, in order to develop a magenta color on the photoreceptor 11, the charging member 12 continues to apply -8 again.
It was charged to 50 V and an electrostatic latent image was formed by the laser optical system 13. The potential of the image portion was −130 V in the portion where the yellow toner adhered most, and was −100 V in the portion where the toner did not adhere. This electrostatic latent image was developed by a magenta developing device with a developing gap of 100 μm and a developing bias of −750 V. Similarly it was examined adhesion amount to the photoconductor for magenta toner, a minimum 0.2 mg / c from the maximum 0.8 mg / cm ² according to the pulse width modulation level
It was obtained m ^2. The area where the maximum amount of yellow toner adheres is
The combined amount is 1.6 mg / cm ² .
Finally, cyan development was performed as described above. However,
Optical writing to the portion where the magenta toner overlaps the yellow toner portion has been avoided in advance by image processing. The potential of the image portion is -140 V in a portion where magenta toner is most attached, and -100 in a portion where toner is not attached.
V. 0.8mg / cm of cyan toner
^{2 ~0.2mg} / cm ^2, together with by yellow or magenta toner developing earlier, maximum 1.6 mg / cm ²
Was obtained. The charge amount of each of the magenta toner and the cyan toner was about 10 μC / g.

As described above, at least two
When the toner image in which the colors are superimposed is transferred to transfer paper by the transfer member 17 and fixed, not only each of the single-color portions of yellow, magenta, and cyan, but also each of the mixed-color portions of red, green, and blue mixed with each other, A fine-grained image with good tone reproducibility according to the toner adhesion amount could be obtained.

In addition to the above-described yellow, magenta, and cyan (YMC), a fourth color black toner developing device 1
If the so-called inking is applied to the portion where the three colors YMC are originally overlapped, a practical full-color image can be obtained.

Comparative Example 1 Each mixture having the same composition as in Example 1 was melt-kneaded using two rolls, cooled, coarsely pulverized using a hammer mill, and then finely pulverized by an air jet type pulverizer. Each of the obtained finely pulverized products was classified to have an average particle size of 11 μm. Colloidal silica 0.2
Parts were added and mixed to obtain a toner. The coloring degree and transmittance of each of the obtained toners were as shown in Table 3. Also,
When each toner was dissolved in THF and filtered with a syringe filter having a pore size of 4.5 μm, no permeation of the pigment was observed.

[0046]

When the toner images were superimposed by the same operation as in the above embodiment, none of the colors responded well to the pulse width modulation level. Looking at the image after the transfer and fixing, the image was inferior in gradation reproducibility and blurred without sharpness.

COMPARATIVE EXAMPLE 2 The photoreceptor 11 was replaced with an organic photoreceptor by using a selenium photoreceptor, and the charging potential was set to +850 V and the latent image potential was set to +100 V.
Yellow, cyan, and magenta toners positively charged to about 5 μC / g were prepared. The average particle size is 11 μm.

(Cyanide) Binder resin Styrene / acrylic copolymer 95 parts Release agent Low molecular weight polypropylene 5 parts Colorant phthalocyanine blue 5 parts Charge control agent Molybdate quaternary ammonium salt 2 parts (Magenta) Binder resin styrene / Acrylic copolymer 95 parts Release agent Low molecular weight polypropylene 5 parts Coloring agent Quinacridone pigment 10 parts Charge control agent Morridebnic acid quaternary ammonium salt 2 parts (yellow) Binder resin Styrene / acrylic copolymer 95 parts Release Molding agent Low molecular weight polypropylene 5 parts Coloring agent Disazo Yellow 10 parts Charge control agent Molybdate quaternary ammonium salt 2 parts

Each mixture having the above composition was melt-kneaded using two rolls, cooled, coarsely pulverized using a hammer mill, and then finely pulverized using an air jet type pulverizer. Each of the obtained finely pulverized products was classified to have an average particle size of 11 μm. Colloidal silica 0.2
Parts were added and mixed to obtain a toner. The coloring degree and transmittance of each of the obtained toners were as shown in Table 4. Also,
Each toner was dissolved in THF and filtered with a syringe filter having a pore size of 4.5 μm. As a result, the pigment did not pass through.

[0051]

[0052] While obtained superimposed toner image by the above embodiment the same operation, each color without successfully respond to the pulse width modulation level, the toner adhesion amount of 0.8mg / cm ² ~0.6mg / cm ² I was nothing. Looking at the image after the transfer and fixing, the image was inferior in gradation reproducibility and blurred without sharpness.

[0053]

According to the image forming method of the present invention, a large number of minute closed electric fields are formed in the vicinity of the surface of the developer carrier, and the toner carried on the developer carrier is transferred to the electrostatic latent image carrier. Since the image forming system is used to perform development by superimposing the image, the image can be obtained with good gradation and reproducibility and fine-grained images.

The toner of the present invention has a specific transmittance and coloring power, or contains a colorant having a specific dispersion diameter. Therefore, the toner is used in the above-described image forming method. Then, there is no problem in the charging / image exposure process from above the toner, and a fine-grained image having good gradation and reproducibility can be stably obtained.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of an example of a developing device that forms a microfield electric field on a developer carrier useful for carrying out the present invention, focusing on a developer carrier portion.

FIG. 2 is a schematic cross-sectional view for explaining a state in which a closed electric field is generated by a microfield on a developer carrier in the apparatus shown in FIG.

3 (a) to 3 (c) are schematic cross-sectional views showing surface states in a process of manufacturing a developer carrier used in a developing device of the type shown in FIG.

FIG. 4 is a cross-sectional view illustrating an example of an overall configuration diagram of an image forming apparatus useful for implementing the present invention.

[Explanation of symbols]

 10, 11 electrostatic latent image carrier 12 charging member 13 laser optical system 14 to 16, 19 developing device 17 transfer member 18 cleaning member 20 toner transport member 30 toner layer thickness regulating member 40 toner supply member 50 stirring blade 60 toner 70 toner Tank 80 Development gap

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shigekazu Enomoto 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company, Limited (56) References JP-A-62-30261 (JP, A) Hei 2-87160 (JP, A) JP-A-63-261284 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 9/09 G03G 13/08 G03G 15/08 501

Claims (3)

(57) [Claims] An electric charge is selectively retained on a surface of a developer carrier to form a large number of minute closed electric fields near the surface of the developer carrier. In response, a one-component developer composed of a toner externally added with an auxiliary agent is supplied, and the developer is carried on the surface of the developer carrier by the minute closed electric field. In the image forming method of conveying the electrostatic latent image into a visible image by transporting the developer to the developing gap opposite to the developing gap, an electric field is formed in the developing gap, and the transported developer is caused to fly to the surface of the electrostatic latent image carrier to develop the image. And carrying out charging and image exposure on the electrostatic latent image carrier carrying the toner image via the toner image, and performing development by superimposing the toner image on the toner image with a toner different in color from the toner image. Characteristic image forming method. 2. A toner for use in the image forming method according to claim 1, comprising at least a binder resin and a colorant, and when the toner is formed into a thin film, has a coloring power of 0.5 mg / cm ^2. A toner characterized by having a coloring power at 1.0 mg / cm ² of 75% or less and a transmittance at 1.0 mg / cm ² of 50% or more. 3. The toner for use in the image forming method according to claim 1, wherein the toner comprises at least a binder resin and a colorant, and the dispersion diameter of the colorant is 4.5 μm or less.