JPH04251881A - Developing method - Google Patents

Abstract

PURPOSE:To provide a two-component magnetic developing method for reducing an effective potential in a developing area so that the occurrence of tailing and density spot can be reduced even in the case of using a photosensitive body in which the electrostatically charged quantity of toner to be used is comparatively made small, and also the method provided with excellent reproducibility of a fine line and capable of forming a toner image provided with high image density and good image quality. CONSTITUTION:As to the two-component magnetic developing method for supporting developer constituted of the toner and carrier on a developing sleeve, for carrying it on a drum provided with an electrostatic image and for developing the electrostatic image, the resistivity of the toner in the developer is made 3X10<9> or 1X10<11>OMEGA.cm, and the electrostatically charged quantity of the toner is made 5 or 15muC/g as an absolute value, and also as to the density distribution of the carrier coming into contact with the drum within the extent of a developing nip width, a developing condition is set so that the maximum value may lie on nearly the most adjacent position of the nip width, and also a single peak distribution can be substantially obtained near the most adjacent position of the nip width.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a developing method in electrophotography, and more specifically, the present invention relates to a developing method in electrophotography. The present invention relates to a developing method that makes it possible to form high-quality images in which leading edge chipping and trailing edge chipping are prevented.

0002

[Prior Art] A two-component developer containing a carrier and a toner is widely used in commercial electrophotographic copying machines, and when developing a charged image, the magnetic brush of this developer is A toner image is formed on a developing sleeve provided with the toner image, and this magnetic brush is rubbed against a photoreceptor having a charged image to form a toner image.

Many proposals have already been made regarding the setting of development conditions, for example, Japanese Patent Laid-Open No. 59-1726.
No. 60 discloses that a two-component developer consisting of a ferrite carrier and electrostatic toner is used, and the toner concentration, photosensitive drum/developing sleeve peripheral speed ratio, and main pole angle in the developing sleeve are kept within a certain range. It is described that by setting this value, an image with high density and excellent gradation can be obtained. In addition, JP-A-61-118767 discloses that when developing using a two-component developer, the surface potential, the distance between D and S (between the photoreceptor drum and the developing sleeve), and the magnetic carrier resistance value are selected within a certain range. It has been shown that by doing so, a high quality image without image unevenness can be obtained.

[0004] The present applicant previously filed Japanese Patent Application No. 1-107331.
In this issue, the state of contact between the developer magnetic brush and the photosensitive surface during actual development can be easily determined by pouring collodion onto the magnetic brush to fix it, and then taking a scanning electron micrograph of the brush. What can be known; and the frequency (k) defined as the product of the number of carrier contacts per photoreceptor area (n, pieces/mm^2) measured in this way and the development length (L), It is proposed that by setting a range within this range, it is possible to prevent leading edge chipping and trailing edge chipping and obtain high-quality images.

[0005]

[Problems to be Solved by the Invention] However, when using a photoreceptor such as an amorphous silicon photoreceptor or an organic photoreceptor (OPC), which has a low effective potential in the development area, under conventional development conditions, the formation of However, it was found that there were still some shortcomings in terms of image density and quality. That is, when a normal developing material (with a charge amount of 20 to 40 .mu.C/g) is used for a photoreceptor having a small effective potential in the developing area, the image density inevitably decreases significantly. On the other hand, if a developer with a low charge amount is used to maintain a predetermined image density,
There is a significant tendency for image quality to deteriorate, such as trailing and reduced fine line reproducibility.

Therefore, an object of the present invention is to provide a two-component magnetic development method capable of forming a toner image having high image density and excellent image quality even on a photoreceptor having a small effective potential in the development area. It's about doing. Another object of the present invention is to provide a developing method that has a small effective potential in the development area, and therefore produces less trailing and uneven density even when the amount of charge of the toner used is relatively low, and has excellent fine line reproducibility. is to provide.

[0007]

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention supports a developer consisting of toner and a carrier on a developing sleeve, conveys it onto a drum having an electrostatic image, and In a two-component magnetic development method for developing
The resistivity of the toner in the developer is 3×10^9 to 1×10
^11 Ω・cm, the absolute value of the toner charge amount is 5 to 15 μC/g, and the density distribution of the carrier that contacts the drum within the developing nip width has a maximum value at the position almost closest to the nip width, In addition, the development conditions are set so that the distribution is substantially one peak near the position closest to the nip width.

[0008]

[Operation] In the present invention, first, in order to maintain a predetermined image density even when the effective potential in the development area is small, the toner charge amount is set to 5 to 15 μC/g in absolute value. If the toner charge amount of the developer is less than 5 μC/g in absolute value, toner scattering occurs and image quality deteriorates even if the toner resistivity and carrier density distribution described below are maintained within the range of the present invention. On the other hand, when the toner charge amount exceeds 15 μC/g in absolute value, the image density decreases.

Next, in order to improve fine line reproducibility, the resistivity of the toner is set to 3×10^9 to 1×10^11 Ω・
cm. If the resistivity of the toner is less than 3 x 10^9 Ω/cm, the image will have poor fine line reproducibility, and if the resistivity of the toner exceeds 1 x 10^11 Ω/cm, the edge effect will be strong and the image density will decrease. .

Further, in the present invention, in order to prevent trailing (front-drawing) and density unevenness from occurring, the density distribution of the carrier that contacts the drum within the developing nip width has a maximum value at a position almost closest to the nip width; In addition, the development conditions are set so that the distribution is substantially one peak near the position closest to the nip width. In this specification, the density distribution of the carrier in contact with the drum within the width of the development nip is measured in the following manner.

(Measurement of density distribution) After the photosensitive drum, developing sleeve, and developer are all set to the developing conditions used in the actual machine, a slight acclimatization operation (aging) is performed. To prevent the developer from moving after the machine is stopped, a collodion solution or the like is poured between D and S to fix the developer between D and S. After it hardens, the developer from the entire width of the nip is taken out, photographed using a scanning electron microscope, and the density distribution is calculated by counting the number of carriers in contact with the drum. The density distribution is calculated by dividing the fixed developer strip into 1 mm width sections in the drum axis direction, and then centering on the nearest position,
The drum is sequentially divided into sections at intervals of 1 mm on the upstream and downstream sides, and the density of the carrier in each section with an area of 1 mm^2 is calculated. The classification is +1, +2, ... on the upstream side, -1, on the downstream side.
Indicated by -2,...

FIG. 1 is a diagram showing the carrier density distribution within the development conditions of the present invention, and A and B are distribution curves measured at different measurement points. From these distribution curves,
Under the development conditions of the present invention, the density distribution of the carrier in contact with the drum within the development nip width always has a maximum value at the position almost closest to the nip width, and has a substantially single peak distribution near the position closest to the nip width. Moreover, it is clear from the examples described later that under these development conditions, trailing and development density unevenness are effectively prevented. On the other hand, FIG. 2 is a diagram showing the carrier density distribution under development conditions outside the range of the present invention, and A and B are distribution curves measured at different measurement points. From these distribution curves, it can be seen that under development conditions other than those of the present invention, the density distribution of the carrier that contacts the drum within the development nip width is always
There is a maximum value at a position other than the position closest to the nip width, and there is essentially a two-peak distribution near the position closest to the nip width.Furthermore, under this development condition, trailing and development density unevenness occur, as shown in the comparison described later. This is clear from the example.

It is recognized that the following mechanism is responsible for the occurrence of trailing (front-drawing) under developing conditions outside the range of the present invention. a. Under these development conditions, the panicle stands at its maximum on the upstream side of the position closest to the nip width. This is related to the fact that the size of the spike is large, the amount of developer conveyed is excessive, and the main pole angle is large on the upstream side. b. If maximum peaking occurs on the upstream side of the closest position, it becomes difficult for the developer to pass through the gap between D and S, where the gap becomes even narrower. c. The ears that cannot fit between D and S will accumulate above the developing area. Therefore, the developer density (pressure) in this portion increases. d. When the developer accumulates to a certain extent and the pressure increases, the developer passes through the D-S all at once. e. The above process is repeated, and the strength of the developing pressure is repeatedly increased. f. Due to this variation in the strength of the developing pressure, the toner once placed on the electrostatic latent image is blown away forward, resulting in front trailing (tailing in terms of copies). g. In addition, since the strength of development pressure fluctuates repeatedly,
Horizontal striped density spots occur in the solid image.

On the other hand, under the development conditions of the present invention, the distribution of the developer density indicated by the carrier density is a single peak distribution, and the maximum value of this distribution is located almost at the position closest to the nip width. , the developer passes smoothly between D and S without accumulating above the developing area, and there is no fluctuation in the strength of the developing pressure, effectively preventing the occurrence of trailing (tailing) and density unevenness. will be done.

[0015]

Preferred Embodiment of the Invention In FIG. 3 for explaining the magnetic brush developing method used in the present invention, a large number of polar magnets 10 (N
, S) is housed in a developing sleeve 12 made of a non-magnetic material such as aluminum. A photosensitive drum 15 consisting of a base 13 and an electrophotographic photosensitive layer 14 provided thereon is provided at a minute gap, ie, a distance dD-S, from the developing sleeve 12. The developing sleeve 12 and the photosensitive drum 15 are mounted on the machine frame (
(not shown), and are driven so that the moving directions (arrows) at the nip position are the same (the rotating directions are opposite to each other).

The developing sleeve 12 is located at the opening of the developing device 16, and inside the developing device 16 is a mixing agitator 17 for a two-component developer (ie, a mixture of toner and magnetic carrier) 18. A toner supply mechanism 20 for supplying the toner 19 is provided above the toner supply mechanism 20 . The two-component developer 18 is mixed by the stirrer 17 to give the toner a triboelectric charge, and then supplied to the developing sleeve 12 to form a magnetic brush 21 on its surface. This magnetic brush 21
The standing length of the panicle is adjusted by the panicle cutting mechanism 22, and it is conveyed to the nip position with the electrophotographic photosensitive layer 14, that is, to the development area, and an electrostatic latent image is developed on the photosensitive layer 14 with toner 19 to form a visible image. Form.

(Developer) In the present invention, the toner has a resistivity of 3 x 10^9 to 1 x 10^11 Ωcm, particularly 5 x 10^9 to 5 x 10^10 Ωcm, and an electrostatic charge. The amount is 5 to 15μC/g in absolute value, especially 8 to 13μ
Use one within the range of C/g. The resistivity of the toner is
It depends on the resistivity of the fixing resin medium used, the type and amount of the conductive agent to be blended, and the dispersion structure on the surface. That is, as the resistivity of the fixing resin medium used increases, the resistivity of the toner also increases. In addition, the better the conductivity of the conductive agent to be mixed, the lower the resistivity of the toner will be, and as the amount of the conductive agent increases, the resistivity of the toner will be lower, and the conductive agent will be distributed more on the surface of the toner. In this case, the resistivity of the toner also becomes low. On the other hand, the amount of charge of the toner depends on the particle size and specific surface area of the toner, the resistivity of the toner, the type and concentration of polar groups in the fixing medium, and the like. That is, the amount of charge increases as the particle size of the toner becomes finer or as its specific surface area increases. Furthermore, when the resistivity of the toner decreases, charge leakage occurs, resulting in a decrease in the amount of charge. The type of polar group in the fixing medium not only controls the charge polarity caused by charging, but also has a significant effect on the amount of charge.
On the other hand, its concentration is related to both the amount of charge trapped and the amount of charge leaked during charging.

The toner used in the present invention can be said to have a higher resistance and a lower charge amount than ordinary toners, and the types and amounts of the materials constituting the toner are selected based on the above-mentioned criteria. An example of such criteria is as follows. a. As the fixing resin medium, one with relatively high resistivity is used. b. Reduce the amount of conductive agent. c. The combination of the conductive agent and resin is selected (for example, by using bleed-out) and the kneading conditions are selected so that the conductive agent is sufficiently dispersed in the toner. d. Although the particle size of the toner is increased or its specific surface area is decreased, there is a certain limit in relation to the resolution. e. The concentration of polar groups (both in the resin and in the added charge control agent) in the fixing medium is selected within a certain range in relation to the amount of charge trapped and the amount of charge leaked during charging.

As the fixing resin medium, styrene resin, acrylic resin or styrene-acrylic copolymer resin is generally used. The styrenic monomers used in these resins include styrene, vinyltoluene, α
Examples include -methylstyrene, α-chlorostyrene, vinylxylene, and vinylnaphthalene. Among these, styrene is preferred. On the other hand, examples of acrylic monomers include ethyl acrylate, methyl methacrylate, butyl acrylate, butyl methacrylate, 2-
Ethylhexyl acrylate, 2-ethylhexyl methacrylate, 2-hydroxyethyl acrylate, 3-
These include hydroxypropyl methacrylate, 2-aminoethyl acrylate, N-aminoethylaminoethyl methacrylate, acrylic acid, methacrylic acid, and the like. In addition to the above-mentioned acrylic monomers, other ethylenically unsaturated carboxylic acids or their anhydrides, such as maleic anhydride, fumaric acid, maleic acid, crotonic acid, and itaconic acid, can also be used.

[0020] Styrene-acrylic copolymer resin is one of the suitable resin media, and the styrene monomer (A) and the acrylic monomer (B) are A:B=
50:50 to 90:10, especially 60:40 to 85:
It is preferable to set it in the range of 15. Further, it is preferable that the resin used generally has an acid value of 0 to 25. In addition, from the viewpoint of fixing properties, the glass transition temperature (Tg) is 50 to 65°C.
It is good to have

As the charge control agent, any charge control agent known per se may be used, for example nigrosine base (CI504
15), oil-soluble dyes such as oil black (CI26150) and spirone black, 1:1 type or 2:1 type metal complex dyes, naphthenic acid metal salts, fatty acids, soaps, resin acid soaps, etc. are used.

The polar groups in the resin and/or the polar groups in the charge control agent are of a type that provides the desired charge polarity to the toner.

As the coloring agent contained in the resin, the following inorganic or organic pigments and dyes may be used alone or in combination of two or more. Carbon black such as furnace black and channel black; iron black such as triiron tetroxide; titanium dioxide such as rutile type or anatase type; phthalocyanine blue; phthalocyanine green; cadmium yellow; molybdenum orange; pyrazolone red;
Fast Violet B etc. can be exemplified.

[0024] The particle size of the toner particles is 8 to 16 μm based on volume as measured by a Coulter counter.
m, particularly preferably in the range of 10 to 14 μm,
The particle size may be amorphous produced by melt-kneading and pulverization, or spherical produced by dispersion or suspension polymerization.

As the magnetic carrier, any one such as a ferrite carrier or an iron powder carrier can be used, but in order to form the carrier distribution structure of the present invention and make it easier for the developer to pass between D and S, saturation magnetization is required. But within a certain range, 40 to 7
It is desirable that it be in the range of 0 emu/g, especially in the range of 45 to 65 emu/g. As the magnetic carrier, ferrite carriers satisfying the above conditions, especially spherical ferrite carriers are suitable, and the particle size thereof is 20 to 14
The thickness is preferably in the range of 0 μm, particularly 50 to 100 μm.

Conventionally, ferrite has been used, for example, iron zinc oxide (ZnFe2O4), iron yttrium oxide (Y3F
e5O12), iron cadmium oxide (CdFe2O4)
, iron gadolinium oxide (Gd3Fe2O12), iron copper oxide (CuFe2O4), iron lead oxide (PbFe12O
19), iron nickel oxide (NiFe2O4), iron neodymium oxide (NdFeO3), iron oxide barium (BaF
e12O19), magnesium iron oxide (MgFe2O4
), iron manganese oxide (MnFe2O4), lanthanum iron oxide (LaFeO3), etc. Sintered ferrite particles are used, with a composition consisting of one or more of iron oxide (LaFeO3), etc.
Soft ferrite containing at least one metal component, preferably two or more metal components selected from the group consisting of Cu, Zn, Mg, Mn and Ni, such as copper-zinc-magnesium ferrite, is used. Among ferrites, one that satisfies the above conditions is used. The electrical resistance of a ferrite carrier varies not only depending on its chemical composition, but also on its particle structure, manufacturing method, and coating type and thickness. Generally, its volume resistivity is 1×1010 to 5×1011Ω
・cm, particularly preferably in the range of 4×10 10 to 1×10 10 Ω·cm.

The mixing ratio of the toner and the magnetic carrier varies depending on the physical properties of the toner and the magnetic carrier, but the weight ratio is generally 1:99 to 10:90, particularly 2:98.
It is desirable that the ratio be within the range of 5:95 to 5:95. In addition, the electrical resistivity of the developer as a whole is 5×10^9 to 5×
10^10 Ω・cm, especially 1×10^10 to 4×
A range of 10^10 Ω·cm is preferred for the purposes of the present invention.

(Development conditions) In order to satisfy the development conditions of the present invention, a. The best ear standing is achieved near the position closest to the nip width where the distance between D and S is the narrowest. b. To eliminate or reduce the accumulation of developer on the upstream side of a development area by setting the amount of developer supplied in proportion to the distance between D and S. Ensure that one or both of the following are satisfied. In order to satisfy the above condition a, it is effective to lower (smallen) the magnetic angle α, that is, the angle from the position closest to the nip width to the axis of the main pole, and this magnetic angle α is generally 0 to 12 degrees. It is particularly preferable that the angle is in the range of 3 to 8 degrees.

On the other hand, in order to satisfy the above condition b, it is better to increase the distance between D and S or reduce the size of the ear cut, but of course, it is better to increase the distance between D and S too much. If the size of the ear cut is made too small, the developed density will be lowered, so there is an optimum range. Generally, the D-S distance, dD-S, is 0.5 to 3.0 mm, especially 0.7 to 1.7 mm, and the ear cutting dimension dB is 0.5 to 3 mm, especially 0.6 to 1.7 mm. Then, the value of dD-S/dB is 0
．． It is preferable to set the value to be between 5 and 1.2, particularly between 0.7 and 1.

In the formula, Nip is the nip width (mm) of the developer on the surface of the photoreceptor, VS is the moving speed of the developing sleeve (mm/sec), and Vd is the moving speed of the photoreceptor surface (mm/sec). The development length L, defined as (mm/sec), is related to the carrier density distribution and also to the image density. In the present invention, the nip width (Nip), the peripheral speed of the developing sleeve (VS), and the peripheral speed of the drum (Vd) are preferably determined so that the developing length L is 4 to 35 mm, particularly 4 to 20 mm. Among these, the developing nip width (Nip) is generally 1 to 15 mm, especially 2 to 8 mm.
It is preferable to set it in the range of mm.

Further, in the present invention, the following formula:
f represents the number of rotations of the developing sleeve (times/second), m represents the saturation magnetization of the magnetic carrier (e.m.u/g), and H
It is preferable to set the developing conditions so as to satisfy the following equation, which represents the magnetic flux density (Gauss) of the magnetic pole in the developing sleeve. The magnetic pole in the developing sleeve should preferably have a relatively low magnetic flux density within a range that does not cause carrier attraction, generally 400 to 1500 Gauss, particularly 550 to 100 Gauss.
It is better to use one with 0 Gauss. It is also effective to make the rotation speed of the developing sleeve relatively high, and generally a range of 1.50 to 5.00 rotations/second is appropriate, although it depends on the sleeve diameter.

As the photoreceptor, photoreceptors conventionally used in electrophotography, such as selenium photoreceptors, amorphous silicon photoreceptors, zinc oxide photoreceptors, cadmium selenide photoreceptors,
Cadmium sulfide photoreceptors, various organic photoreceptors, and the like can all be used, but the present invention is particularly effective for photoreceptors with a small effective potential difference.

As another development condition, the bias voltage applied between the developing sleeve and the photoreceptor conductive substrate is such that the average electric field strength is in the range of 100 to 1000 V/mm, particularly 125 to 500 V/mm. is preferred.

[0034]

EXAMPLES The present invention will be explained below based on examples. Developer A Styrene acrylic resin
10
0 parts by weight Carbon black (manufactured by Mitsubishi Kasei Co., Ltd., trade name MA-100) 6 parts by weight Low molecular weight polypropylene (manufactured by Sanyo Kasei Co., Ltd., trade name Viscole 550P) 1 part by weight Metal complex salt compound of an azo compound
1 part by weight The components according to the above formulation were mixed, melted and kneaded, then pulverized with a jet mill and classified to obtain powder with an average size of 12 μm. 100 parts by weight of the above powder was subjected to surface treatment using a Henschel mixer using 0.8 parts by weight of hydrophobic silica (manufactured by Nippon Aerosil Co., Ltd., trade name R972) to obtain a toner. A developer was prepared by mixing 5 parts by weight of the above toner and 95 parts by weight of a silicone resin-coated ferrite carrier (manufactured by Powder Tech Co., Ltd., trade name F97).

Developer B In the preparation of the powder, carbon black was changed to 3 parts by weight instead of 6 parts by weight, and in the preparation of the toner, the hydrophobic silica was changed to 0.3 parts by weight instead of 0.8 parts by weight. A developer was prepared in the same manner as developer A except for that.

Developer C In the preparation of the powder, carbon black was changed to 5 parts by weight instead of 6 parts by weight, and in the preparation of the toner, the hydrophobic silica was changed to 1.0 parts by weight instead of 0.8 parts by weight. A developer was prepared in the same manner as developer A except for that.

Developer D Developer except that 6 parts by weight of carbon black was replaced with 10 parts by weight of a phthalocyanine pigment (blue pigment), and a metal salicylate compound was used in place of the metal complex salt compound of the azo compound. A developer was prepared in the same manner as A.

Developer E A developer was prepared in the same manner as Developer A except that 95 parts by weight of ferrite carrier coated with acrylic resin was used instead of 95 parts by weight of ferrite carrier coated with silicone resin. .

Developer F A developer was prepared in the same manner as Developer B except that 95 parts by weight of ferrite carrier coated with acrylic resin was used instead of 95 parts by weight of ferrite carrier coated with silicone resin. .

Developer G A developer was prepared in the same manner as Developer A except that 10 parts by weight of carbon black was used instead of 6 parts by weight.

Developer H In the preparation of the powder, the same as Developer A was used, except that the carbon black was changed to 2 parts by weight instead of 6 parts by weight, and the metal complex salt compound of the azo compound was changed to 3 parts by weight instead of 1 part by weight. A developer was prepared in the same manner.

[Evaluation of physical properties] Toner charge amount: Measured by blow-off method. Toner resistivity: Using a parallel plate electrode type measuring device with an electrode area of 2.27cm^2 and a distance between electrodes of 0.5mm, the porosity is 25% filled with toner, and the peak to peak is from +1V. Measured by applying an AC voltage of -1V. The above results are shown in Table 1.

[0043]

[Table 1]

Examples 1 to 4, Comparative Examples 1 to 5 (Number of peaks in carrier density distribution) Electrophotographic copying machine DC
-1657 (manufactured by Sanda Kogyo Co., Ltd.), using each of the developers A to H shown in Table 1, the type of photoreceptor and development conditions (distance between photoreceptor drum and developing sleeve dD-S,
Main pole angle α, ear cutting size dB, bias potential) were set as shown in Table 2, and after obtaining a copy image, the machine was stopped,
A collodion solution is poured between the photoreceptor drum and the developing sleeve to fix the developer between the photoreceptor drum and the developing sleeve so that the developer does not move. After it had solidified, the developer from the entire nip width was taken out and photographed using a scanning electron microscope, the number of carriers in contact with the drum was counted to calculate the density distribution, and the number of peaks was counted. (Measurement of effective potential difference) Electrophotographic copying machine DC-1657 (manufactured by Sanda Kogyo Co., Ltd.) set to each condition as above.
After measuring the surface potential of the photoreceptor after charging, the effective potential difference was calculated. Effective potential difference = surface potential of photoreceptor - bias potential (image density: ID) Using the obtained copy image, T
Measured with a C-6D model. (Image quality) Visually judge using the obtained copy image. The above measurement results are shown in Table 3.

[0045]

[Table 2]

[0046]

[Table 3]

[0047]

According to the present invention, there is provided a two-component magnetic developing method in which a developer consisting of toner and carrier is supported on a developing sleeve, conveyed onto a drum having an electrostatic image, and the electrostatic image is developed. , the resistivity of the toner in the developer is 3×10
^9 to 1 x 10^11 Ω・cm, the toner charge amount is 5 to 15 μC/g in absolute value, and the density distribution of the carrier that contacts the drum within the developing nip width is approximately at the closest position to the nip width. By setting the development conditions so that there is a local maximum value and a substantially single peak distribution near the position closest to the nip width, high image density can be achieved even for a photoreceptor with a small effective potential in the development area. It is possible to form toner images with excellent image quality, and the effective potential in the development area is small, so even when the amount of charge of the toner used is relatively low, there is little trailing or density unevenness. , we were able to provide a developing method with excellent fine line reproducibility.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the carrier density distribution within the development conditions of the present invention.

FIG. 2 is a diagram showing carrier density distribution under development conditions outside the scope of the present invention.

FIG. 3 is a side layout diagram for explaining a magnetic brush developing method.

Claims (1)

[Claims] 1. A method in which a developer consisting of toner and a carrier is supported on a developing sleeve and conveyed onto a drum having an electrostatic image to develop the electrostatic image, in which the resistivity of the toner in the developer is 3 x 10^9 to 1 x 10^11 Ωcm, the toner charge amount is 5 to 15 μC/g in absolute value, and the density distribution of the carrier that contacts the drum within the developing nip width is approximately near the nip width. A developing method characterized in that developing conditions are set so that the maximum value is at the nip width position, and the nip width is substantially distributed in the vicinity of the nip width closest position.