JPH0486868A - High-density developing method - Google Patents

Abstract

PURPOSE:To obtain a high-density image while preventing carriers from tailing by satisfying the specific condition of the composition and concentration of a developer, a developer coating amount, and the distance between a drum and a sleeve. CONSTITUTION:An inequality is satisfied and simultaneously the magnetic force X of the sleeve surface in the tangent direction and the magnetic force Y in the normal direction at the position where a developer layer on the sleeve 12 finishes rubbing against the surface of the photosensitive drum 15 are so related that Y >= 0 when X >= 430 (gauss) and Y >= -X+800 (gauss) when X < 430 (gauss). Then the flow state of the two-component developer 18 in a development area is remarkably improved and a defect at the rear end part of a solid image part due to carrier tailing can be prevented.

Description

Detailed Description of the Invention (Field of Application of the Invention) The present invention relates to a developing method used in a developing device such as a copying machine or a printer, and more specifically to a two-component developer consisting of a toner and a carrier. This invention relates to a developing method for obtaining high-density image quality using.

(Prior Art) In the field of electrophotography, two-component magnetic developers are widely used as a means for developing electrostatic latent images. Two-component developers usually consist of toner particles containing a colorant and magnetic carrier particles.

Stirred during development. The toner and carrier are triboelectrically charged by stirring, and the toner is attracted to the surface of the carrier due to the electrostatic charge. The developer in this state is supplied onto a developing sleeve that has a magnet inside, and is formed into a magnetic brush shape by the attraction of the internal magnet. The developer is conveyed in this state by the sleeve and sent to the photoreceptor having the electrostatic latent image.

The developer is rubbed onto the photoreceptor surface using a magnetic brush. 1F1
The toner that has fallen out is transferred to the electrostatic latent image surface to form a toner image by Coulomb force based on the potential difference with the electrostatic latent image surface. On the other hand, the magnetic carrier is attracted by the magnet in the sleeve and remains on the sleeve. The toner image on the electrostatic latent image surface is transferred and fixed onto a subsequent transfer paper or the like, and development is performed.

In a two-component developer, the necessary conditions for obtaining sufficient image density, preventing toner scattering, and maintaining these characteristics over a long period of time are determined by the compatibility between the toner and the carrier. -As for boat fishing trends,
When the toner concentration increases, a high image density can be obtained, but the frictional charging force of the toner tends to be insufficient, its ability to combine with the carrier decreases, and moreover, the toner movement in and out of the developing device increases, resulting in toner scattering. Increase l,
X (a tendency is observed.For this reason, in conventional two-component developing methods, the toner concentration is suppressed to a low level, resulting in low development efficiency and low density in solid areas). Tend.

To prevent this drawback, Japanese Patent Application Laid-Open No. 62-6397
In Publication No. 0, it is proposed to form an alternating electric field between the drum and the sleeve, and to set the volume occupied by the magnetic carrier per volume between the drum and the sleeve in the range of 1.5 to 30%. , Nru.

(Problem to be solved by the invention) If the charging characteristics of the toner and carrier in the two-component developer are sufficient, the toner density will be high (even in the case of X, the image density will be high and toner scattering will be low). However, this is almost impossible to achieve with commercial toners and development methods.In other words, in toner manufacturing, it is necessary to produce defective toner particles that do not contain or contain a small amount of charge control agent. In addition, the charge control agent is often lost due to mechanical forces inside and outside the developing device, or toner particles with a reduced content are formed in the image.Also, when the area ratio of the original is This includes uncharged toner particles that have temporarily failed to obtain the necessary charge due to changes in the environment or other factors, so toner scattering will inevitably occur, causing contamination and damage inside the copying machine. This may lead to contamination of copies.

In another invention, the present inventors have discovered that in a developer using a two-component developer consisting of a magnetic carrier and a toner, there is a key point in the flow state of the developer passing through the development area, and that there is a key point in relation to this flow state. It has been found that by setting development conditions within a certain range, toner scattering can be effectively prevented even when toner having a relatively high toner concentration and containing defective charged particles is used. However, although the above proposal is optimal as a countermeasure against such defective charged particles, since the degree of freedom of the developer in the development area, that is, the development nip is small, the developer hits the photoreceptor strongly, causing the image to deteriorate. Sweeping marks are more likely to occur, which may deteriorate the image quality. For this reason, there are methods of lowering the saturation magnetization of the carrier or lowering the magnetic strength of the magnet roll in the developing sleeve, but such simple methods cannot prevent carrier pull.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a high-density developing method that enables a high-density image without any traces while preventing carrier attraction.

In addition, in recent years, there has been a desire for miniaturization in the development of full-color developing systems, and there is an urgent need to develop a developing device that uses a sleeve with a diameter of 20 mm or less and does not cause carrier drag.

Therefore, another object of the present invention is to provide a developing method in which a sleeve is made into a 7Jl type and a high-density image can be obtained.

(Means for Solving the Problems) According to the present invention, a two-component developer consisting of a magnetic carrier and toner is conveyed to a developing area by a developing sleeve, and
? In a developing method in which an electrostatic latent image on a photoreceptor drum is developed in the area, the image conditions are expressed as %, where M is the amount of developer applied per unit area of the sleeve (
z/crrf), H is the distance (cm) on the line connecting the centers of the photoreceptor drum and the sleeve, and T/D
is the toner concentration weight fraction in the developer, C/D is the carrier concentration weight fraction in the developer, ρL is the true density of the toner (g/cm'), and ρC is the true density of the carrier. (
g/cm'), and the relationship between the magnetic force X in the tangential direction of the sleeve surface and the magnetic force Y in the normal direction at the position where the developer layer on the sleeve finishes rubbing against the photoreceptor drum surface is: When ≧430 (Gauss), Y≧0, or X<430
(Gauss) when Y≧−x+so.

To provide a high density development method characterized by satisfying (Gauss).

The present invention also provides a maximum magnetic force on the sleeve surface of 1000
It can be characterized by making it less than Gaussian.

The present invention may further be characterized in that the developing sleeve is used with a diameter of 20 m or less.

Note that the normal direction is the radial direction of the sleeve, and the magnetic force in the normal direction refers to the value in the normal direction when magnetic force is vectorized. Furthermore, the tangential direction refers to the direction of the tangential line when drawn on the circumferential surface of the sleeve at the position where the developer finishes sliding, and the tangential magnetic force is the tangential direction when the magnetic force is vectorized. I say direct.

(Function) The present invention provides development conditions such that the above formula (1) is satisfied.
That is, developer application per unit area of sleeve t (M;
g/am? ), the distance H on the line connecting the centers of both the photoreceptor drum and the sleeve (Hic, also referred to as the distance between D and 3), the toner weight fraction in the developer (T/D), and the true value of the toner. Density (ρt; g/c+n'), carrier weight fraction in developer (C/D), and true density of carrier (
By setting ρc;g/c++'), the flow state of the two-component developer in the development area is significantly improved, and toner scattering is effectively suppressed even under development conditions where the image density is high. By setting the magnetic force and the direction of the magnetic force within a specific range at the position on the developing sleeve surface where the developer finishes sliding against the photoreceptor, it is possible to sufficiently prevent carrier pull during development. This is based on the knowledge that defects such as defects at the rear end of solid image areas due to pulling are prevented.

That is, the mixed state of toner and carrier in the development area is defined by the following formula (%). R is a dimensionless number and indicates the volume ratio occupied by the two-component developer in the volume of the development area. can be,
By maintaining the value of R at a value greater than 30% but less than 40%, toner scattering can be effectively prevented.

First, this developer occupancy (R) is 30%9. At the bottom, the volume occupied by the developer in the development area between D-5 decreases, and the magnetic brush in this area draws in air from above the valley between D-5 and carries it to the bottom of the valley between D-8. There is a tendency to generate airflow and scatter toner with the airflow outside the developing device and into the inside of the machine. On the other hand, when this developer occupancy rate (R) exceeds 40%, the developer is too clogged in the valley between D-3, and the developer does not flow smoothly, resulting in a considerable load on the developer sleeve. , the sleeve does not rotate smoothly and the developer is disturbed, making toner scattering more likely to occur above the valley. On the other hand, within the range defined by the present invention, while the developer flows smoothly through the valley between D-3 in the developing area, the above-mentioned air current is also prevented from occurring, and the toner scattering is reduced to reduce the toner concentration. It is effectively prevented even when the

In the present invention, the relationship between the developer occupancy (R) and various factors of development conditions is clear from the above formula (la). In other words, the larger the developer application AM to the sleeve, the more R
increases, and the larger the distance RH between D-8, the more R
becomes smaller. In addition, since ρ is generally expressed as <ρ C... (3), as the toner concentration (V amount fraction) in the two-component developer increases, the developer occupancy increases.

More specifically, M is generally between 0.06 and 0.25 g/
cm', especially 0.1 to 0.2 g/cr! From the range of 19, H is generally 0.04 to 0.16 cm, especially 0.16 cm.
R from the range of 0.06 to 0.14 cm, and the toner weight fraction in the developer from 0.03 to 0.08, especially from the range of 0.035 to 0.075, when these are combined.
is determined so that it satisfies equation (1).

Further, in the present invention, as is clear from FIG. 5 obtained from the experimental example described later, the magnetic state that appears on the surface of the developing sleeve when the developing layer is rubbed is important, and the developer is Magnetic force X in the tangential direction at the end position of sliding with
It is important to set the value to 430 Gauss or more. As mentioned above, the tangential direction means that the direction of the magnetic lines of force is parallel or oblique to the sleeve surface.

This can be set by the overall relationship between the strength and distance of the X and S magnetic poles alternately provided in the developing sleeve, and the sleeve diameter. If the magnetic force X in the tangential direction satisfies the above range, the magnetic brush will be in a cradled state with respect to the photoreceptor surface at a position away from the photoreceptor. This type of brush condition has a large effect on the rubbing area, which is the developing area. An image without chipping at the rear end of the image can be obtained.

In addition, in such a state, it is possible to use a carrier with low saturation magnetization by lowering the strength of the main pole, and it is possible to form a soft magnetic brush of developer to achieve clear development. Furthermore, the magnetic brush of the developer is bound to stick to the sleeve surface at the f′g rubbing part, which prevents the carrier from scattering at this part, and unlike the conventional case, the magnetic brush of the developer is bound so as to stick to the sleeve surface. Carrier scattering is also prevented. In addition, when the magnetic force X in the tangential direction is less than 430 Gauss, it is important to regulate the magnetic force Y in the normal direction at the end position of rubbing, and the magnetic force Y in the normal direction should be set to Y≧−X+800 (Gauss). is important. The normal direction is a direction extending perpendicularly to the sleeve surface, and means a state in which the magnetic brush of the developer stands up. As is clear from Table 1 of the examples described later, in a device that satisfies the above relationship, carrier pull does not occur, and the carrier remains stuck on the sleeve surface at the sliding portion, as in the case of X≧430 Gauss. The above effects are fully exhibited.

It is also important for the present invention that the maximum magnetic force appearing on the main pole or alternately placed poles in the sleeve, ie on the sleeve surface, is less than 1000 Gauss, especially less than 9° Gauss. If the magnetic force of the main pole is too strong, a soft magnetic brush cannot be formed, depending on the diameter of the sleeve, and a clear image cannot be obtained. The details will be explained according to the attached drawings. 1 to 3 are explanatory diagrams of main parts of a developing device according to the present invention.

In FIG. 1 for explaining the magnetic brush developing method used in the present invention, a magnet roll 11 having a large number of magnetic poles N and S is housed in a developing sleeve 12 made of a non-magnetic material such as aluminum. This developing sleeve 1
A photosensitive drum 15 consisting of a substrate 3 and an electrophotographic photosensitive layer 14 provided thereon is provided with a minute gap between the two. The developing sleeve 12 and the photosensitive drum 15 are rotatably supported by a machine frame (not shown), and are immediately moved so that the moving directions (arrows) at the nip position are the same (the rotating directions are opposite to each other). be done.

The developing sleeve 12 is located at the mouth of the upper IFi imager 16, and inside the developing device 16 is provided a mixing agitator 17 for a two-component developer (i.e., a mixture of toner and magnetic carrier) 18. A toner supply mechanism 20 for supplying toner is provided above it. The two-component developer 18 is mixed by the stirrer 17 to give the toner an e-friction charge, and then supplied to the developing sleeve 12 to form a magnetic brush 21 on its surface. This magnetic brush 21 is adjusted to the length of the ears by the ear cutting mechanism 22, and is exposed to electrophotography W114.
The photosensitive layer 14 is conveyed to a nip position to form a visible latent image with toner on the photosensitive layer 14.

The developing sleeve 12 as a whole is located at the opening of the developing device indicated by 23, and the above-mentioned panicle cutting mechanism 22 is arranged on the supply side to the developing sleeve, and the above-mentioned panicle cutting mechanism 22 is arranged on the circulation side from the sleeve to the developing device. , a developer side receiver 25 having an opening edge 24 is disposed.

The developer application amount M can be set to a predetermined value by changing the circumferential speed of the sleeve 12 and by adjusting the distance between the sleeve 12 and the ear cutting mechanism 22.

As shown in FIG. 2, the sleeve 12 is provided so as to be driven and rotated in the direction of the arrow, that is, in the counterclockwise direction. A magnetic brush, which is a two-component developer 1121, is formed on the outer peripheral surface of the sleeve 12.
2, it moves in the same direction as the sleeve rotation direction.

The electrostatic latent image formed on the photoreceptor surface of the opposing photoreceptor layer 14 has a development area, that is, a sliding contact g (A in FIG. 2) with the magnetic brush.
Only the toner is transferred in the area), and the latent image area is thereby developed. Further, a point P shown in FIG. 2 on the surface of the sleeve 12 corresponds to the position where the rubbing of the developer ends, and the point P shown in FIG.
This is the intersection of the straight line connecting the upper friction end position and the center of the magnet roll and the surface of the developing sleeve.

In the present invention, as shown in FIG. 3, a predetermined magnetic force is applied from the internal magnet roll 11 at point P, and the magnetic force is directed into a vector in the normal direction Y (perpendicular to the sleeve surface) and the tangential direction X. Decompose it and add the scalar quantity,
The value is set within a certain range. FIG. 4(A) shows a chart of the magnetic force acting in the normal direction on the sleeve surface. Further, FIG. 4(B) shows a chart of the magnetic force generated on the sleeve surface and acting in the tangential direction. The equidistant reference circles of the sleeve 12 indicate a scalar amount (Gauss) of magnetic force, and indicate the strength of the magnetic field in the normal and tangential directions on the sleeve surface.

In the present invention, the sleeve surface point P where the sliding ends
The magnetic force in the tangential direction X is X≧430 Gauss,
The formation of such a magnetic force is performed by adjusting the positional relationship and distance between X and Sa of the magnet roll 4 in the sleeve 6 according to the radius of the sleeve. Further, when the magnetic force in the tangential direction X is less than 430 Gauss, the value in the normal direction Y is limited and set so that Y≧−X+800 Gauss.

Furthermore, in the present invention, it is desirable that the maximum magnetic force of the N and S poles be 1°O○ Gauss or less, particularly 900 Gauss or less.

On a sleeve set within such a range, the ears of the magnetic brush tend to remain soft.

Further, the diameter of the developing sleeve 12 in the present invention can be used in the range of 15 to 50 mm, and especially when used with a diameter of 20 mm or less, the developing sleeve 12 at the developing ES bridge portion can be used.
occupies a smaller area.

In addition, the above formula (
1).

The developer magnetic carrier generally has a density ρC of 3.50 to 6.501/mo, although it depends on the carrier concentration C/D.
, particularly preferably 4.00 to 5.50 g/mm 2 , and ferrite-based magnetic carriers are particularly used.

Conventionally, ferrite has been used, for example, iron zinc oxide (ZnFe2
0. ), yttrium iron oxide (ysFeso+=),
Iron cadmium oxide (CdFe20□), iron gadolinium oxide CGd5Fe, O+2> - iron copper oxide (CuFe2
0. l), iron oxide complex (PbFe+20+,), iron nickel oxide (\1Fe20.), iron neodymium oxide dF
eO), barium iron oxide (BaFe+20+e),
Magnesium iron oxide (MzFe20-), iron mankane oxide (MnFe2OA) - lanthanum iron oxide (LaFe
Sintered ferrite particles having a composition consisting of one or more types such as Cu, Zn, 'Ag
Soft ferrites containing at least one, preferably two or more metal components selected from the group consisting of , Mn and λi, such as copper-zinc-magnesium ferrite, are used; among these ferrites, Use one that satisfies the above conditions.

The saturation magnetization of the carrier is 40 to 65 eIIu/g r
In particular, a range of 45 to 56 emu/g is desirable. The magnetic carrier is preferably a ferrite carrier that satisfies the above conditions, particularly a spherical ferrite carrier, and its particle size is 20 to 140 μn.

In particular, it is desirable that it be in the range of 50 to 100 μD.

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 between 5X10' and 5X1
0'-Ω・0 mouth, especially 1×109 to l×10′lΩ・
It is better to be within the crl range.

The toner generally has a density ρL of 1.00 to 1.40 g, although it depends on the density of the magnetic carrier and toner concentration.
/mm', especially 1.10 to 1.20 g/nm'.

The toner used in the present invention is one in which a colorant and a charge control agent, or further toner ingredients known per se, are blended in a fixing resin medium. The toner used in the present invention is also l
XlO7 to 3 XIO=Ω'cm, especially 2X1
It preferably has a volume resistivity of 0' to 8×10 10 Ω'em, and its dielectric constant preferably lies in the range 2.5 to 4.5, particularly 2.5 to 4.2.

The fixing resin medium, colorant, charge control agent, and other toner compounding agents for the toner are preferably selected and combined so as to obtain the above characteristics. First, as the fixing resin medium, styrene resin, acrylic resin, styrene-acrylic resin, polyester, epoxy resin, rosin-modified maleic acid resin, silicone resin, polyvinyl butyral resin, etc. are used.

Further, it is preferable that the resin used generally has an acid value of 0 to 25. Also, from the viewpoint of fixing properties, the temperature should be 50 to 65°C.
It is preferable that the glass transition temperature (Tg) is as follows.

As the colorant contained in the resin, any known inorganic or organic pigments, dyes, etc. may be used alone or in combination of two or more. For example, carbon black such as furnace blank and channel black; iron black such as triiron tetroxide; titanium dioxide such as rutile type or anatase type; phthalocyanine blue; phthalocyanine green; cadmium yellow; molybrene orange; pyrazolone red; fast violet B can be mentioned.

As the charge control agent, any charge control agent known per se may be used, such as oil-soluble dyes such as Nigrosine Base (CI50415), Oil Black (CI20150), and Subiron Blank, and 1:1 type or 2:1 type metals. Complex dyes, metal complexes of (alkyl)salicylic acid and naphthoic acid
Salt etc. are used.

The particle size of the toner particles is 8 to 14 μm on a volume basis, especially 10 μm as measured by a Coulter counter.
The particle size is preferably in the range of 12 μm to 12 μm, and the particle shape may be amorphous particles produced by a melt mixing/pulverization method, or spherical particles produced by a dispersion or suspension polymerization method.

The toner weight fraction T/D in the developer is generally in the range of 0.03 to 0.10, particularly 0.035 to 0.07+.

Also, the electrical resistance of the developer as a whole is 5 x 106
~5 X 10'2Ω・cII+, especially lX109
For the purposes of the present invention, it is preferable that the resistance is in the range of 5×10 11 Ω·cm to 5×10 11 Ω·cm.

Other development conditions The application amount M of the developer is preferably within the range mentioned above, and this depends on both the circumferential speed of the developing sleeve and the magnetic flux density and length of the developing sleeve. The circumferential speed of the sleeve is 60 to 800 cm/sec, especially 9 to 4
50 am/see, and the panicle length depends on the magnetic flux density, but it is 0.6 to 1.6 mm, especially 0.8 to 1.4 mm.
A range of mm is appropriate.

Further, the distance between D and 5 (H) is preferably selected from the range of 0.4 to 1.6 mm, particularly 0.6 to 1.4 mm.

Examples of the photoreceptor include photoreceptors conventionally used in electrophotography, such as selenium photoreceptors, amorphous silicon photoreceptors, zinc oxide photoreceptors, cadmium selenide photoreceptors, cadmium sulfide photoreceptors, and various organic photoreceptors. etc. are all used.

As another development condition, the bias voltage applied between the developing sleeve and the photoreceptor conductive substrate has an average electric field strength of 10
0 to 1000 V/no, especially 125 to 800
It is preferable to use one in the range of V/am.

(Experiment example) Based on the development conditions below, LP manufactured by Sanda Kogyo Co., Ltd.
Using the X-1 modified machine, developer application amount M, toner weight $T/D, carrier weight fraction C/D, and drum-to-sleeve distance g! 4 Images were taken with various changes in the panicle cutting gap.

Development conditions Development sleeve diameter: 20m, development sleeve peripheral speed: 210m
m/SEC, photoreceptor drum: negatively charged organic photoreceptor, photoreceptor surface potential knee 700V, development bias potential knee 5
00V, development magnetic pole: normal magnetic force at point P 330 gauss, tangential magnetic force at point P 440 gauss, toner: carbon blank dispersed in polyester, true density 1.11 with a volume-based median diameter of 11 μm. g/crn' toner, carrier: Ferrite core coated with resin, saturation magnetization is 55 emu/g, electrical resistance is 5X109Ω・
The true density of crv is 5g/CIN! It is.

Table 1 From the results in Table 1, it was found that when the developer occupancy was in the range of 30 to 40%, toner scattering was prevented and high density could be obtained. Furthermore, for Nα1 (comparative example), the ear cutting gap was widened to increase the coating amount to 0.111 g/c.
When an image was produced with m2 and a development occupancy of 37.3% (Nα1' present example), toner scattering was prevented and image density was improved. In addition, for the Nα4 (comparative example), the drum-sleeve distance was narrowed to 0.07
cm and the development occupancy rate was 40.2%, density unevenness occurred in the image and toner scattering occurred. As a result, the effectiveness of setting the developer occupancy to 30 to 40% was confirmed. On the other hand, these images had good image density and toner scattering, but when the magnetic force in the tangential direction of the developing magnetic pole was lower than 430 Gauss, the trailing edge of the solid area image was chipped and the image area was scratched by the carrier. In addition, the carrier is developed in some places in the non-image area.

(Experimental Example 2) The excellent Nα2, Nα3, and Nα1′ of Example 1 above! When images were produced using developing magnet rolls with various magnetic strengths under various conditions, the fifth
As shown in the figure, the magnetic force in the tangential direction on the surface of the developing sleeve corresponding to the end of development in the developing area is 430 Gauss or more, or in the figure, Y=-X+800 (7) Setting the magnetic force relationship as follows (FIGS. 4A and CB) is a magnetic force distribution chart at point P in the experimental example showing Pl in FIG. ), it was confirmed that one image area could be maintained at a satisfactory level, and that the sweep marks caused by the magnetic carrier and the carrier adhesion were eliminated from the image. Note that in Figure 1, the symbol "." indicates that the carrier was pulled or a sweep mark by the carrier was generated on the image, and the symbol "O" indicates that the above-mentioned problem did not occur.

(Effects of the Invention) As explained above, according to the present invention, the composition and density of the developer, the amount of developer applied, and the distance between the drum and sleeve satisfy the above (1) in the development area during development. This selection allows the developer to flow through the development area with good fluidity, forming a high-density image without toner scattering. By setting the magnetic force in the tangential direction at the point where the process ends, or by setting the magnetic force in the tangential and normal directions within a certain range, it is possible to prevent carrier attraction during development. . Moreover, it is possible to lower the magnetic force within the developing sleeve and use a carrier with low saturation magnetization to form a soft developer layer, and by reducing the diameter of the developing sleeve, the entire developing device can be downsized. Is possible.

[Brief explanation of drawings]

1, 2, and 3 are explanatory diagrams of the main parts of the developing method and apparatus according to the present invention, and FIGS. 4(A) and 4(B) are magnetic force distribution charts at point P, and FIG. FIG. 5 is a diagram showing the relationship between the magnitude of magnetic force in the normal direction and the tangential direction.

Claims (3)

[Claims] (1) In a developing method in which a two-component developer consisting of a magnetic carrier and toner is conveyed to a developing area by a developing sleeve, and an electrostatic latent image on a photoreceptor drum is developed in the developing area, the developing conditions are expressed as follows: 30<M×[(T/D)×(1/ρt)+(C/D)×
(1/ρc)]÷H<40 In the formula, M is the amount of developer applied per unit area of the sleeve (g/cm^2), and H is on the line connecting the centers of the photoreceptor drum and sleeve. is the distance (cm), T/D is the toner concentration weight fraction in the developer, C/D is the carrier concentration weight fraction in the developer, and ρt is the toner true density (g/cm ^3), where ρc is the true density of the carrier (g/cm^3) and the magnetic force in the tangential direction of the sleeve surface at the position where the developer layer on the sleeve finishes rubbing against the photoreceptor drum surface. The relationship between X and the magnetic force Y in the normal direction is: When X≧430 (Gauss), Y≧0, or X<430
A high-density development method characterized in that when (Gauss), Y≧−X+800 (Gauss) is satisfied. (2) The developing method according to claim 1, characterized in that the maximum magnetic force on the sleeve surface is 1000 Gauss or less. (3) The developing method according to claim 1, wherein the developing sleeve is used with a diameter of 20 mm or less.