JP2003322996A - Developing method and image forming apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing method and an image forming apparatus by which image characteristics such as image density (ID) and fogging density (FD) are prevented from being deteriorated even by a use over a long term in a high speed machine. <P>SOLUTION: An electrostatic latent image formed on the surface of an image carrier is supplied with magnetic toner on a developing sleeve by applying DC bias voltage between the image carrier and the developing sleeve, and is developed. Then, a potential difference between the exposure part and the non-exposure part of the surface of the image carrier is set within the range of 200-230 V, and a potential difference between the DC bias voltage and the exposure part of the image carrier is set within the range of 120-140 V. Also, the magnetic toner whose volume averaged grain size is set within the range of 6-10 μm, and whose rate occupied by the grain size of ≤5 μm in toner grain size distribution is within the range of 6-10 vol.%, and whose electrification polarity is same as the non-exposure part of the image carrier and whose absolute value of the saturation electrification quantity is within the range of 10-14 μc/g is used. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing method and an image forming apparatus using the same, and more specifically, a so-called reversal developing method using a magnetic toner (hereinafter sometimes simply referred to as "toner") and the same. The present invention relates to an image forming apparatus using.

[0002]

2. Description of the Related Art In conventional image forming apparatuses, the photoconductor and the members arranged around the photoconductor are integrated as a developing unit, and after a predetermined number of images are formed, the development is performed by placing importance on the convenience of parts replacement. I was replacing the whole unit with a new one. However, as environmental awareness has increased in recent years, there has been a strong demand for reduction of disposable parts and extension of life of each part. In order to meet such a demand, even in an image forming apparatus such as a copying machine or a printer, instead of replacing the developing unit as a whole, it can be used for a long time without replenishing parts by simply replenishing the consumed toner. Various studies and developments of models were made. As a result, the so-called low image forming speed of 40 sheets / minute or less
As for the medium speed machine, the one that can achieve the above-mentioned effects has already been put on the market.

[0003]

However, in a so-called high-speed machine whose image forming speed exceeds 40 sheets / minute,
It was still difficult to use the toner for a long time (for example, 200,000 sheets) simply by replenishing the toner without replacing the parts.

The present invention has been made in view of such conventional problems, and an object thereof is to obtain image density (ID), fog density (FD), etc. even when used for a long time in a high speed machine. An object of the present invention is to provide a developing method and an image forming apparatus that do not deteriorate image characteristics.

[0005]

According to the present invention, a DC bias voltage is applied between the image carrier and the developing sleeve,
A developing method in which a magnetic toner on a developing sleeve is supplied to an electrostatic latent image formed on the surface of an image carrier to develop the electrostatic latent image, and a potential difference between an exposed portion and a non-exposed portion on the surface of the image bearing member is 200.
The potential difference between the DC bias and the exposed portion of the image carrier is in the range of 120 to 140V,
The volume average particle size of the magnetic toner is in the range of 6 to 10 μm, the ratio of the particle size of 5 μm or less in the toner particle size distribution is in the range of 6 to 10 vol%, and the charging polarity is the unexposed portion of the image carrier. With the same polarity, the saturation charge is 1 in absolute value
There is provided a developing method characterized by being in the range of 0 to 14 μc / g. In the present specification, the volume average particle diameter and the proportion occupied by the particle diameter of 5 μm or less are measured by “Coulter counter” (manufactured by Coulter Counter). The saturated charge amount is measured as follows. First, 3 g of toner is weighed and placed in a plastic cylindrical container. Then, it is mixed with a carrier so that the toner concentration becomes 3.0 wt%, and 100 rp is obtained by a ball mill.
Mix for 30 minutes at m. Next, about 500 mg of this two-component developer was sampled, and a suction type charge amount measuring device STC-1 (suction pressure -2.0 kP, suction time 60 sec, open mesh 37 μm stainless mesh made by Sankyo Piotech Co., Ltd. To measure the toner charge amount.

Here, from the viewpoint of suppressing the increase of fog density and improving the image quality, the saturation magnetization of the magnetic toner is 1
The range of 6 to 27 Am ² / kg is preferable, and the gap between the image carrier and the developing sleeve is preferably larger than the thickness of the toner layer formed on the developing sleeve. In the present specification, the saturation magnetization is 79.6 kA / m (1 magnetic field) using "VSM-P7" manufactured by TOEI.
kOe).

From the viewpoint of further improving durability, it is preferable to use an amorphous silicon photoconductor as the image carrier.

Further, according to the present invention, there is provided an image forming apparatus using the developing method described in any one of the above.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The inventors of the present invention have earnestly studied to establish a developing method in which image characteristics such as image density (ID) and fog density (FD) do not deteriorate even after long-term use in a high-speed machine. As a result, they have found that the above object can be achieved by using the reversal developing method and optimizing the combination of the magnetic toner to be used and the developing conditions, and completed the present invention. Hereinafter, each configuration of the developing method according to the present invention will be described in order.

First, in the developing method of the present invention, a so-called reversal developing method is used in which toner having the same polarity as that of the non-exposed portion is attached to the exposed portion (electrostatic latent image portion) of the image carrier by a DC bias voltage. Here, it is important to set the potential difference between the exposed portion and the non-exposed portion on the surface of the image carrier within the range of 200 to 230V. If the potential difference between the exposed portion and the non-exposed portion is smaller than 200 V, the toner easily moves not only to the exposed portion but also to the unexposed portion, and the fog density increases, while the potential difference between the exposed portion and the non-exposed portion is 230 V. This is because the reproducibility of one dot is reduced when the value is larger than this. A more preferable potential difference is 210
The range is 220V.

It is also important to set the potential difference between the DC bias and the exposed portion of the image carrier within the range of 120 to 140V. If the potential difference is smaller than 120 V, the toner cannot be sufficiently moved to the exposed portion of the image carrier, that is, the electrostatic latent image portion, and the ID decreases. On the other hand, if the potential difference is 14
This is because if it is higher than 0 V, toner adhesion to the non-image portion increases. More preferable potential difference is 125 to 135
It is in the range of V.

Next, the magnetic toner used in the present invention will be described. First, the volume average particle diameter of the magnetic toner is 6.0 to 1.
It is 0.0 μm. Volume average particle diameter of toner is 6.0 μm
If it is smaller, the fog density will be higher, while if the volume average particle size is larger than 10.0 μm, the image density will be low. A more preferable range of the volume average particle diameter is 7.0 to 9.
It is in the range of 0 μm.

The ratio of toner particles having a particle size of 5 μm or less is 6.0.
It is important to be ˜10.0 vol%. Particle size 5μ
This is because when the ratio of m or less is less than 6.0 vol%, the image density tends to decrease as the image is formed. On the other hand, if it is more than 10.0 vol%, the fog density becomes high. A more preferable ratio of the particle size of 5 μm or less is in the range of 7.0 to 9.0 vol%.

Further, the saturated charge amount of the toner has the same polarity as that of the non-exposed portion of the image bearing member and an absolute value of 10 to 14 μc / g.
The range is important. Since the developing method of the present invention is the reversal development as described above, if the toner saturation charge amount is lower than 10 μc / g in absolute value, the toner is applied to the toner other than the image portion.
Fouling easily occurs, so-called fog is likely to occur, or the developing roller is separated from the developing roller as the developing roller rotates, causing so-called in-machine contamination. On the other hand,
This is because when the toner saturated charge amount is higher than 14 μc / g in absolute value, the electrostatic adhesion force to the developer carrying member becomes strong and the image density becomes low. A more preferable range of the toner saturated charge amount is a range of 11 to 13 μc / g in absolute value.

The saturation magnetization of the toner is 16 to 27 Am ² / k
A range of g is preferred. Toner saturation magnetization is 16 Am ² / k
If it is less than g, the fog density may be high, while if it is more than 27 Am ² / kg, the image density may be insufficient from the beginning. More preferable saturation magnetization is 2
It is in the range of 0 to 24 Am ² / kg.

Such a toner can be manufactured by a method known per se, such as a pulverizing and classifying method, a melt granulating method, a spray granulating method, and a suspension / emulsion polymerization method. Therefore, the pulverizing and classifying method can be preferably used. In such a pulverizing and classifying method, a binder resin, magnetic particles, and if necessary, a colorant,
A toner composition such as a charge control agent and a release agent is premixed with a Henschel mixer, a V-type mixer or the like, and then melt-kneaded using a melt-kneading device such as a twin-screw extruder. After this melt-kneaded product is cooled, it is roughly pulverized and finely pulverized, and if necessary, then classified to obtain toner particles having a predetermined particle size distribution.
Then, if necessary, the surface of the toner particles is treated with a surface treating agent to obtain a toner. It should be noted that in order to bring the particle size distribution of the toner into the above-mentioned range, various conditions such as the air volume and the air speed of the classifier in the classifying step may be adjusted, or the toner fine powder prepared separately may be mixed. . Also,
The saturation magnetization of the toner can be controlled within the above-specified range by adjusting the type and content of the magnetic substance contained in the toner.

The binder resin used for the toner is not particularly limited, and examples thereof include styrene-acrylic resin and polyester resin. Of course, if necessary, other resins may be used in combination with these resins.

Examples of the styrene-acrylic resin base monomer include styrene, α-methylstyrene, p
-Styrene derivatives such as methylstyrene, pt-butylstyrene, p-chlorostyrene and hydroxystyrene;
Methacrylic acid, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, glycidyl (meth)
Acrylate, methoxyethyl (meth) acrylate,
Propoxyethyl (meth) acrylate, methoxydiethylene glycol (meth) acrylate, ethoxydiethylene glycol (meth) acrylate, benzyl (meth) acrylate, cyclohexyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate,
(Meth) acrylonitrile, (meth) acrylamide,
N-methylol (meth) acrylamide, ethylene glycol di (meth) acrylate, 1,3-butylene glycol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, trimethylolethane tri (meth) acrylate, etc. (Meth) acrylic acid ester can be mentioned.

The mixture of various monomers described above can be polymerized by any method such as solution polymerization, bulk polymerization, emulsion polymerization, suspension polymerization, etc., to obtain the binder resin used in the present invention. Polymerization initiators that can be used in such polymerization include acetyl peroxide, decanoyl peroxide, lauroyl peroxide, benzoyl peroxide, azobisisobutyronitrile, 2,2′-azobis-2,4-dimethylvaleronitrile, and 2 A known polymerization initiator such as 2,2'-azobis-4-methoxy-2,4-dimethylvaleronitrile can be used. These polymerization initiators are preferably used in the range of 0.1 to 15% by weight based on the total weight of the monomers.

The polyester resin is obtained mainly by polycondensation of polyhydric carboxylic acids and polyhydric alcohols, and examples of the polyhydric carboxylic acids include phthalic acid, isophthalic acid, terephthalic acid, succinic acid, 1,
Aromatic polycarboxylic acids such as 2,4-benzenetricarboxylic acid, 2,5,7-naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid and pyromellitic acid; maleic acid, fumaric acid, succinic acid, adipine Acids, sebacic acid, malonic acid, azelaic acid, mesaconic acid, citraconic acid, glutaconic acid and other aliphatic dicarboxylic acids; cyclohexanedicarboxylic acid, cyclohexenedicarboxylic acid and other alicyclic dicarboxylic acids; anhydrides and lower alkyls of these carboxylic acids Esters may be mentioned, and one or more of these may be used.

The content of the trivalent or higher valent component depends on the degree of crosslinking, and the amount of addition may be adjusted to obtain the desired degree of crosslinking. Generally, the content of trivalent or higher components is 1
It is preferably 5 mol% or less.

On the other hand, the polyhydric alcohols used for the polyester resin include, for example, ethylene glycol,
Alkylene glycols such as 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,4-butenediol, neopentyl glycol, 1,5-pentane glycol and 1,6-hexane glycol Alkylene ether glycols such as diethylene glycol, triethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol;
Alicyclic polyhydric alcohols such as 1,4-cyclohexanedimethanol and hydrogenated bisphenol A; bisphenols such as bisphenol A, bisphenol F and bisphenol S, and alkylene oxides of bisphenols, and one of these Alternatively, two or more kinds can be used in combination.

If necessary, monocarboxylic acid or monoalcohol may be used for the purpose of adjusting the molecular weight or controlling the reaction. Examples of the monocarboxylic acid include benzoic acid, parahydroxybenzoic acid, toluenecarboxylic acid, salicylic acid, acetic acid, propionic acid and stearic acid. Examples of the monoalcohol include benzyl alcohol, toluene-4-methanol and cyclohexanemethanol.

The binder resin used has a glass transition temperature of 45.
Those in the range of to 90 ° C are preferable. Glass transition temperature is 4
If the temperature is lower than 5 ° C., the toner may be solidified in the toner cartridge or the developing device. On the other hand, if the temperature is higher than 90 ° C., the toner may not be sufficiently fixed on the transferred material such as paper.

In the case of a magnetic toner, since the toner color is black due to the magnetic particles, it is generally unnecessary to use a colorant when used as a black toner, but acetylene black, run black, aniline black or the like is used as a color reinforcement. Carbon black may be dispersed and mixed in the toner particles. In this case, the content of the coloring agent is 10
It is about 0.1 to 10 parts by weight with respect to 0 parts by weight.

The magnetic particles added to the binder resin include, for example, iron trioxide (Fe ₃ O ₄ ) and iron sesquioxide (γ-Fe).
₂ O ₃ ), zinc iron oxide (ZnFe ₃ O ₄ ), yttrium iron oxide (Y ₃ Fe ₅ O ₁₂ ), cadmium iron oxide (CdFe _2).
O ₄ ), gadolinium iron oxide (Gd ₃ Fe ₅ O ₁₂ ), copper iron oxide (CuFe ₂ O ₄ ), lead iron oxide (PbFe ₁₂ O ₁₉ ), nickel iron oxide (NiFe ₂ O ₄ ), iron neodymium oxide ( N
dFeO ₃ ), iron oxide barium (BaFe ₁₂ O ₁₉ ), iron oxide magnesium (MgFe ₂ O ₄ ), iron manganese oxide (MnFe ₂ O ₄ ), lanthanum iron oxide (LaFeO ₃ ),
Iron powder (Fe), cobalt powder (Co), nickel powder (N
i) etc. are mentioned. A particularly suitable magnetic particle is finely particulate iron trioxide (magnetite). The preferred magnetite has a regular octahedral shape and a particle size of 0.05 to 1.0 μm. The magnetite particles may be surface-treated with a silane coupling agent, a titanium coupling agent, or the like. The content of the magnetic particles is preferably 50 to 30 parts by weight, and particularly preferably 70 to 150 parts by weight, per 100 parts by weight of the binder resin.

As the charge control agent, conventionally known charge control agents can be used. For example, as the positively chargeable charge control agent, nigrosine dye, fatty acid-modified nigrosine dye, carboxyl group-containing fatty acid-modified nigrosine dye, quaternary ammonium salt can be used. , Amine compounds, organometallic compounds and the like can be used, and as the negatively chargeable charge control agent, metal complexes of oxycarboxylic acid, metal complexes of azo compounds, metal complex salt dyes, salicylic acid derivatives and the like can be used.

As the release agent, various waxes and low molecular weight olefin resins can be used. Examples of waxes include polyhydric alcohol esters of fatty acids,
Higher alcohol esters of fatty acids, alkylene bis fatty acid amide compounds and natural waxes can be used. The low molecular weight olefin resin has a number average molecular weight of 1,000 to 10,000, particularly 2,000 to 6,0.
In the range of 00, polypropylene, polyethylene, propylene-ethylene copolymer and the like can be used, and polypropylene can be particularly preferably used.

As the surface treatment agent, an inorganic material such as (hydrophobic) silica, alumina, titanium oxide, zinc oxide, magnesium oxide, calcium carbonate, etc. is used in order to adjust the charge controllability and bulk density (fluidity) of the toner. Fine powders; organic fine powders such as polymethylmethacrylate; fatty acid metal salts such as zinc stearate; and the like, and one or more of these may be used in combination. The amount of surface treatment agent added is
The range of 0.1 to 2.0 wt% per toner is preferable.
The surface treatment agent and the toner particles can be mixed using, for example, a Henschel mixer, a V-type mixer, a Turbula mixer, a hybridizer, or the like.

The developing method used in the developing method of the present invention may be either a contact developing method in which the thin toner layer and the photoreceptor are in contact with each other or a jumping developing method in which both are not in contact, but from the viewpoint of obtaining a high quality image, jumping is performed. The developing method is preferred. In this case, the gap between the image carrier and the developing sleeve is larger than the toner thin layer on the developing sleeve, and it is desirable to apply an alternating voltage in which alternating current is superimposed on direct current as the developing bias.

The material of the image carrier that can be used here is not limited, and conventionally known materials can be used. For example, an amorphous silicon-based photoconductor, an organic-based photoconductor, a Se-based photoconductor, a ZnO photoconductor, a CdS-based photoconductor, and the like can be mentioned. Among them, the amorphous silicon photoconductor is preferable from the viewpoint of durability. The shape of the photosensitive member is not limited, and a conventionally known shape can be used. For example, drum shape, sheet shape,
Examples thereof include a belt shape and a web shape. Of these, the drum shape is preferable.

Next, the image forming apparatus of the present invention will be described. FIG. 1 is a sectional view showing an example of the image forming apparatus of the present invention. The surface of the photoconductor (image carrier) 1 is uniformly charged with positive polarity by the charging means 2. Next, an electrostatic latent image (exposed portion) is formed on the surface of the photoconductor 1 by the exposure means 3. And
Using the developing device 4 using the above-described developing method, toner is attached to the electrostatic latent image by a thin toner layer (not shown) formed on the developing sleeve 41 having a magnet inside, and visible. Image. The transfer unit 5 transfers the toner image on the photoconductor 1 to the transfer target member 7. The toner image on the transferred member 7 is then fused and fixed on the transferred member 7 by applying heat and pressure in a fixing unit (not shown). On the other hand, the untransferred toner remaining on the photoconductor 1 is previously cleaned by the cleaning brush 61 in the cleaning unit 6, and then completely cleaned by the cleaning blade 62.

[0033]

Example (Preparation of Toner) Styrene as a binder resin
Example 1 in which 100 parts by weight of an acrylic resin and a charge control agent (a Nigsilon dye, N-01, manufactured by Orient Chemical Co., Ltd.) were used.
Comparative Examples 1-8, 5 parts by weight for Comparative Examples 11 and 12, 7 parts by weight for Example 2, 3 parts by weight for Example 3, 9 parts by weight for Comparative Example 9, and 10 for Comparative Example 10. 1.5 parts by weight of magnetic powder (EPT-1000, manufactured by Toda Kogyo Co., Ltd.) is 70 for Example 1 and Comparative Examples 1-10.
Parts by weight, 80 parts by weight for Example 2, 60 parts by weight for Example 3, 90 parts by weight for Comparative Example 11,
As for Comparative Example 12, 50 parts by weight of wax (PP wax, Yumex 100TS, manufactured by Sanyo Kasei Kogyo Co., Ltd.) was used.
Each part by weight was put into a Henschel mixer and mixed, then melt-kneaded with a twin-screw extruder, cooled with a drum flaker, and coarsely crushed with a hammer mill. Next, it was finely pulverized with a mechanical mill and classified with an air classifier to prepare toner particles having a predetermined volume average particle size and particle size distribution. Then, with respect to the toner particles, hydrophobic silica (particle size: 0.
012 μm) and titanium oxide (particle size 0.2
5 μm) was added thereto, and the mixture was stirred and mixed with a Henschel mixer with high stirring to prepare positively chargeable one-component magnetic toners used in Examples 1 to 3 and Comparative Examples 1 to 12. In addition,
A Coulter Multisizer (manufactured by Coulter) was used for the volume average particle diameter and the weight average particle diameter of the produced toner.
It was measured with a 0 μm aperture tube.

(Development conditions) An amorphous silicon photoconductor is used as a photoconductor, and a frequency of 2.5 kH is used as a bias power source.
z, peak-to-peak voltage of 1.9kV AC voltage 140
-180V direct current is superposed, the surface potential of the exposed part on the photoconductor is 25-35V, the surface potential of the non-exposed part is 220-270V, and the gap between the developing sleeve and the photoconductor is 320μm. And jumping development was performed. In Table 1, V0 is the surface potential of the non-exposed portion, VL is the surface potential of the exposed portion, and VDC is the DC bias potential.

(Evaluation of Image) Using the prepared one-component magnetic toner under the developing conditions shown in Table 1 at room temperature and normal humidity, FIG.
A printing durability test was performed with a high-speed printer of 50 sheets / min having the configuration described above, and the image density (ID) and the fog density (FD) were measured after the initial printing of 50,000 sheets, 100,000 sheets, and 200,000 sheets. The specific measuring method is as follows. The results are shown in Table 2.
Using the above-prepared one-component magnetic toner, a high-speed printer of 50 sheets / minute (Kysera LS-9500 development modified machine) having the configuration of FIG. 2 was used at room temperature and normal humidity (23 ± 3).
The image density (ID), fog density (FD), and 1-dot reproducibility were measured at 50 ° C. and 55 ± 10% RH at the initial stage and after printing for 50,000 sheets, 100,000 sheets, and 200,000 sheets. The specific measuring method is as follows. The results are shown in Table 1. The printing durability test is
An A4 size paper (64 g paper) was used, and an image with a printing rate of 5% per sheet was output with the short side direction of the paper being the paper transport direction.

(Measurement of Image Density and Fog Density) For measurement of image density and fog density, the same A4 size paper (64 g paper) as in the durability test was used, and the short side direction of the paper was used as the paper conveyance direction, and the measurement image was used. For the paper, three solid image areas of 3 × 3 cm are arranged on the paper, and the solid image areas are arranged vertically at 10 cm intervals in the central portion in the paper transport direction.
Five solid image portions were measured at five locations, and the average value of the five sheets was obtained. For fogging, the non-printed portion of the paper on which the above-mentioned image for measurement was printed was measured at 5 locations per sheet, and the average value of the 5 sheets was obtained. A reflection densitometer (Model No. TC-6D manufactured by Tokyo Denshoku Co., Ltd.) was used for measuring the image density and the fog density. The evaluation criteria are image density of 1.300 or more and fog density of 0.008.
It is the following.

(Evaluation of 1-dot reproducibility) For evaluation of 1-dot reproducibility, the same A4 size paper (64 g paper) as in the durability test was used.
Using the short side direction of the paper as the paper transport direction, the measurement image has a resolution of 3 × 3 cm (600 DPI) on the paper.
Visual evaluation using a binocular microscope with a magnification of 20 using an image in which three dots for evaluation are arranged, which are arranged vertically at 10 cm intervals in the center of the paper conveyance direction with respect to the paper conveyance direction. did. As an evaluation criterion, dot dropout is 5% or less in the initial and durability evaluations.

[0038]

[Table 1]

[0039]

[Table 2]

As is clear from Table 2, in the developing methods of Examples 1 to 3, both the initial image density, the image density after printing, and the fog density satisfied the evaluation criteria. Moreover, the dot reproducibility was also satisfactory. On the other hand, in the developing method of Comparative Example 1 in which the potential difference between the exposed portion and the non-exposed portion was large, dot reproducibility was difficult, and in the developing method of Comparative Example 2 in which the potential difference was small, the fog density was high from the initial stage. Further, the fog density was high from the initial stage even in the developing method of Comparative Example 3 in which the potential difference between the DC bias and the exposed portion was large. On the other hand, in the developing method of Comparative Example 4 in which the potential difference between the DC bias and the exposed portion was small, the image density was low from the initial stage.

Further, in the developing method of Comparative Example 5 using a toner having a small volume average particle diameter, the fog density is high from the initial stage, and conversely, in the developing method of Comparative Example 6 using a toner having a large volume average particle diameter, the fog density is Although the evaluation criteria were satisfied, the initial image density was low. In the developing method of Comparative Example 7 using a toner having a small ratio of particle size of 5 μm or less, the image density
Both fog densities satisfied the evaluation criteria, but the image densities decreased after printing 50,000 sheets. On the other hand, in the developing method of Comparative Example 8 in which a toner having a large proportion of particle diameters of 5 μm or less was used, the initial image density satisfied the evaluation criteria, but the initial fog density was high.
Further, in the developing method of Comparative Example 9 using the toner having a high saturated charge amount, the initial image density did not satisfy the evaluation standard.
On the other hand, in the developing method of Comparative Example 10 using the toner having a low saturated charge amount, the fog density did not satisfy the evaluation standard at the initial stage. Comparative Example 11 using a toner having a high saturation magnetization
In the developing method of No. 1, the initial image density did not satisfy the evaluation standard. On the other hand, in the developing method of Comparative Example 12 using the toner having low saturation magnetization, the initial fog density did not satisfy the evaluation standard.

[0042]

In the developing method and the image forming apparatus of the present invention, the reversal developing method is used and the combination of the magnetic toner to be used and the developing conditions is optimized, so that the developing method and the image forming apparatus can be used in a high-speed machine for a long period of time. Image density (ID)
The image characteristics such as the fog density and the fog density (FD) do not deteriorate.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example of an image forming apparatus of the present invention.

[Explanation of symbols]

1 photoconductor (image carrier) 2 charging means 3 exposure means 4 developing means 5 Transfer means 6 Cleaning means 7 Transferred member 41 Development sleeve

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI Theme Coat (reference) G03G 15/08 506 G03G 15/08 506A 507 507L (72) Inventor Hiroko Sugimoto 1-chome Tamakuzo, Chuo-ku, Osaka No. 28 Kyocera Mita Stock Company In-house F-term (reference) 2H005 AA02 AB04 EA01 EA02 EA05 EA07 FA06 2H068 DA23 DA80 2H073 AA03 BA04 BA13 BA43 CA02 CA14 2H077 AD06 AD36 DB08 EA13 EA16 GA03 GA17 2H200 FA02 GA18 GA28 GA28 GA28 GA18 GA28 GA28 GA28 GA02 GA18 GA28 GA52 HB48 NA06 NA09

Claims (5)

[Claims] 1. A developing method in which a DC bias voltage is applied between an image carrier and a developing sleeve to supply the magnetic toner on the developing sleeve to an electrostatic latent image formed on the surface of the image carrier to develop the toner. The potential difference between the exposed portion and the non-exposed portion on the surface of the image carrier is 20
In the range of 0 to 230 V, the potential difference between the DC bias and the exposed portion of the image carrier is in the range of 120 to 140 V, and the magnetic toner has a volume average particle size of 6 to 10 μm and a toner particle size. The particle size of 5 μm or less in the distribution is in the range of 6 to 10 vol%, the charging polarity is the same as the unexposed portion of the image carrier, and the saturated charge amount is 1 in absolute value.
A developing method, which is in the range of 0 to 14 μc / g. 2. The saturation magnetization of the magnetic toner is 16 to 27.
The developing method according to claim 1, wherein the range is Am ² / kg. 3. The developing method according to claim 1, wherein the gap between the image bearing member and the developing sleeve is larger than the thickness of the toner layer formed on the developing sleeve. 4. The developing method according to claim 1, wherein the image carrier is an amorphous silicon photoconductor. 5. An image forming apparatus using the developing method according to claim 1.