JPH0727298B2 - Development method with excellent character reproducibility - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a developing method with excellent reproducibility of characters, and more specifically, when reproducing multiple fine lines, the line width of each line is constant, The present invention relates to a developing method in which so-called leading edge chipping and trailing edge chipping are prevented.

(Prior Art) A two-component developer containing a magnetic carrier and a toner is widely used in a commercial electrophotographic copying machine, and a magnetic brush of this developer is used as a magnetic pole inside when a charge image is developed. The toner image is formed by rubbing this magnetic brush against a photoconductor having a charge image.

Many proposals have already been made regarding the setting of the developing conditions. For example, in JP-A-59-172660, a two-component developer composed of a ferrite carrier and an electrophotographic toner is used, and a toner is used. It is described that an image having high density and excellent gradation can be obtained by setting the density, the photosensitive drum / developing sleeve peripheral speed ratio, and the main pole angle in the developing sleeve within a certain range. Further, in JP-A-61-118767, the surface potential during development using a two-component developer,
It has been shown that by setting the DS distance (between the photosensitive drum and the developing sleeve) and the magnetic carrier resistance value within a certain range, a high quality image without image unevenness can be obtained.

(Problems to be Solved by the Invention) However, all of these proposals individually specify the characteristics of the developer and the developing conditions, and do not comprehensively capture the actual developing operation, and Since the characteristics of the developer and carrier are specified under static conditions and not under the dynamic conditions of the actual machine, they did not necessarily correspond well to the actual development method in the copying machine. .

The present inventors can understand that the development that occurs during actual development is dynamic electrical development that occurs in the electrical circuit that is composed of the developing sleeve, the surface of the photoconductor, and the developer layer interposed between the two. It was found that a high quality image can be obtained by comprehensively setting the development conditions so that the relaxation time measured under dynamic conditions falls within a certain range.

That is, an object of the present invention is to provide a developing method capable of forming a high-density and high-quality image in which the line width of each line is constant and chipping of the leading edge and trailing edge is prevented when reproducing multiple thin lines. .

Another object of the present invention is to provide a developing method which is excellent in reproducibility of Chinese characters and reproducibility when copying from one copy to another.

(Means for Solving the Problems) According to the present invention, a magnetic brush of a two-component developer containing a magnetic carrier and a toner is formed on a developing sleeve,
In a developing method of forming a toner image by rubbing the magnetic brush with a photoconductor having a charge image, a developing sleeve,
The relaxation time (τ) of the circuit of the developer and the surface of the photoconductor is set to be 8 to 40 milliseconds when the photoconductor surface is changed to a conductive surface of the same size and measured under a dynamic condition at a frequency of 50 Hz. There is provided a developing method having excellent reproducibility of characters.

According to the present invention, a two-component developer magnetic brush containing a magnetic carrier and toner is formed on a developing sleeve,
In the developing method of forming a toner image by rubbing this magnetic brush against a photoconductor having a charge image, the developing sleeve and the photoconductor surface are driven in the same direction at the nip position, and In the formula, Nip is the nip width of the developer on the surface of the photoconductor (m
m), V _S is the moving speed of the developing sleeve (mm / sec), V _D is the moving speed of the photoconductor surface (mm / sec), and τ
Changes the surface of the photoconductor to a conductive surface of the same size and frequency
Characterized by setting the development conditions so that the time difference (ΔT) defined by, which represents the relaxation time (msec) measured under dynamic conditions at 50 Hz, is 0 to 130 msec. A development method is provided.

(Operation) In FIG. 1 showing a relaxation time measuring device, a magnetic field is provided between a developing sleeve 1 having a magnetic pole (not shown) inside and a body drum 2 having the same shape and size as the photosensitive drum. A two-component developer layer 3 containing a carrier and a toner is interposed. The drum 2 and the developer sleeve 1 are rotated so as to move in the same direction at their nip positions (the rotation directions are opposite directions). The sleeve 1 and the drum 2 are connected 4 respectively.
And 5 are connected to the measuring digital oscillograph 6, and the sleeve 1 is connected to the measuring AC power supply 7.
The sleeve 1 and the drum 2 are rotated, an AC voltage of 50 Hz is applied between them by the AC power supply 7, the voltage and the current are measured by the oscillograph 6, and the relaxation time (τ) is obtained from the phase difference between them.

The electrical circuit of FIG. 1 is represented as the equivalent circuit of FIG. That is, the two-component developer layer 3 is interposed between the sleeve 1 and the drum 2 at the nip position, and the developer layer 3 has a constant capacitance C and a constant electric resistance R connected in parallel. It can be approximated as an item. When an AC voltage V is applied to this circuit, the current I becomes as shown in FIG. That is, the current i _R flowing through the resistor R has the same phase as the voltage V, but the current i _C flowing through the capacitor C leads the voltage V by 90 ° in phase. Therefore, the overall current I is φ
Only the phase is ahead of the voltage. Thus, the relaxation time (τ) in this circuit is given by the equation, where φ is the phase difference between voltage and current and ω (= 2πf, f: frequency) is the angular frequency of the measurement power source. Required by.

According to the present invention, when the development conditions are comprehensively set so that the relaxation time (τ) under the dynamic conditions thus obtained is 8 to 40 milliseconds, particularly 10 to 30 milliseconds, This is based on the knowledge that the line width of each line can be made constant during development to prevent chipping at the leading end and chipping at the trailing end, and a high quality copy image can be formed.

In FIG. 4 for explaining the leading edge chipping and trailing edge chipping that occur during the development of dense fine lines, this graph shows the distance in the feeding direction on the horizontal axis and the reflection image density of the dense fine line copied image by the microdensitometer on the vertical axis. This is a plot of the relationship between the two. The curve (i) in FIG. 4 has a constant line width for each line, and no tip or rear end chipping is observed. The curve (ii) has significant tip chipping and the curve (iii) shows The one with a marked edge is shown. Regarding the reproduction of each line width, the deviation (δ) in the feed direction is calculated by the formula when the image density of each mountain in the feed direction is A, B, C in order. Given in. When the value of δ is 100 or its vicinity, each line width is constant and there is no deviation, when it is larger than 100, there is a chip at the tip, and when it is smaller than 100, there is a chip at the rear end. It shows that each.

FIG. 5 is a plot of the relaxation time (.tau.) And the relationship between the relaxation time and the line width deviation (.delta.) By changing the development conditions using developers having different characteristics. Fifth
From the results shown in the figure, the deviation of the line width can be maintained close to 100% by selecting the combination in which the relaxation time (τ) falls within the above-mentioned constant range from among the combinations of various developers and various development conditions. The surprising fact becomes clear.

In the present invention, the fact that the deviation of the line width of each line can be reduced by selecting the relaxation time (τ) of the dynamic developing circuit within a certain range has been revealed as a phenomenon from the results of many experiments. However, its theoretical elucidation has not yet been fully clarified. However, as a general tendency, when the relaxation time (τ) decreases, the trailing edge chipping (δ <10
0) tends to occur, and tip relaxation (δ> 100) tends to occur as the relaxation time (τ) increases. Therefore, when the relaxation time (τ) is larger than the range of the present invention, the initial stage The carrier residual charge image is likely to be recombined with the toner, resulting in a decrease in density. On the other hand, when the relaxation time (τ) is smaller than the range of the present invention, the toner charge is also lost at the final stage, and the carrier charge is lost. This is probably because the toner is scraped off due to the decrease in image density.

In the present invention, the developing sleeve and the photosensitive member surface are driven in the same direction at the nip position, and In the formula, Nip · V _S , V _D and τ have the above-mentioned meanings.

The time difference (ΔT) defined by is 0 to 130 msec, especially 40
Setting to 100 msec is effective for reducing the deviation of the line width while maintaining the high image density. In the formula (1), the first term (Nip · V _S ) / V _D
² is a characteristic value expressed in the dimension of time, which corresponds to the time when one point of the electrostatic latent image passes through the developing nip. On the other hand, since the relaxation time (τ) is considered to be the time when the carrier charge disappears, it is considered that the time difference (ΔT) in the above equation (1) indicates matching between both times.

FIG. 6 of the accompanying drawings plots the relationship between the two with the time difference (ΔT) as the horizontal axis and the line width deviation (δ) as the vertical axis, while FIG. 7 shows this time difference (ΔT) as the horizontal axis. axis,
The density (I ₁ D) of the formed toner image is plotted on the vertical axis, and the relationship between the two is plotted. By selecting ΔT in the above range, the image density can be increased and the deviation of the line width can be reduced. It is understood that it is possible to obtain (δ approaches 100%).

(Preferred Embodiment of the Invention) In FIG. 8 for explaining the magnetic brush developing method used in the present invention, a magnet roll 11 provided with a large number of magnetic poles N and S is placed in a developing sleeve 12 made of a non-magnetic material such as aluminum. It is housed. A photosensitive drum 15 including a substrate 13 and an electrophotographic photosensitive layer 14 provided thereon is provided at a minute gap, that is, a distance d _DS , from the developing sleeve 12. The developing sleeve 12 and the photosensitive drum 15 are rotatably supported by a machine frame (not shown), and are driven so that the moving directions (arrows) at the nip position are the same direction (rotational 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, a mixing and stirring device 17 for a two-component developer (that is, a mixture of toner and magnetic carrier) 18 is provided. A toner supply mechanism 20 for supplying the toner 19 is provided above it. The two-component developer 18 is mixed by the stirrer 17 and the toner obtains a triboelectric charge, and then is supplied to the developing sleeve 12 to form the magnetic brush 21 on the surface thereof. The magnetic brush 21 has its spike length adjusted by a spike cutting mechanism 22, is conveyed to a nip position with the electrophotographic photosensitive layer 14, and develops an electrostatic latent image on the photosensitive layer 14 with toner 19 to form a visible image. Form.

According to the present invention, the relaxation time (τ) of the developing circuit including the developing sleeve 12, the two-component developer 18 and the photosensitive layer 14 is set within the range described above. The relaxation time (τ) of the developing circuit is set by the apparatus shown in FIG. 1 and the principle described above, and the setting is performed as follows.

In the present invention, the developing conditions including the developer characteristics are
It is comprehensively defined by the relaxation time (τ) of the developing circuit,
The relaxation time (τ) is adjusted by changing the combination of the capacitance component (C) and the resistance component (R) of the circuit. That is, the relaxation time (τ) is increased by increasing the capacitance component or the resistance component, while the relaxation time (τ) is reduced by decreasing the capacitance component (C) or the resistance component. Decreases.

On the other hand, factors affecting the capacitance component (C) and the resistance component (R) of the circuit include the shape of the magnetic carrier, the particle size, the specific resistance, the dielectric constant, the shape of the toner, the particle size, the specific resistance and the dielectric constant; The mixing ratio of the magnetic carrier and the toner; the distance between the developing sleeve and the surface of the photoconductor d _DS ; the nip width of the developer on the surface of the photoconductor; the filling rate of the two-component developer at the nip position. For example, if the distance between the developing sleeve and the surface of the photoconductor is increased, R is increased and C is decreased. Conversely, if the distance is decreased, R is decreased and C is increased. When the nip width increases, R decreases, C increases, and conversely, when the nip width decreases, R increases and C decreases. If the developer filling rate increases, R decreases, C increases, and if it decreases, R increases and C decreases.

On the other hand, the dielectric constant ε _C of the magnetic carrier and the dielectric constant ε of the toner
_{When T} increases (decreases), the capacitance component (C) of the circuit increases (decreases), but the capacitance of the circuit is considered to be a series combination of both, and is generally ε _T + ε _C , so the capacitance of the circuit ( The influence on C) is greater with the dielectric constant ε _C of the magnetic carrier. Further, when the mixing ratio of the magnetic carrier is increased or the particle size is made fine, the capacitance component of the circuit generally tends to increase.

According to the present invention, the relaxation time (τ) of the developing circuit is adjusted to the above-mentioned range by selecting these various conditions based on the above-mentioned criteria and combining them, and the formula (1) The time difference (ΔT) at can be adjusted in the range of 0 to 130.

The detailed conditions will be described below.

Toner The toner used in the present invention comprises a colorant and a charge control agent or a compounding agent for toner known per se in a fixing resin medium. The toner used in the present invention preferably has a resistivity of 1 × 10 ^{8 to} 3 × 10 ⁹ Ω · cm, particularly 2 × 10 ^{8 to} 8 × 10 ⁸ Ω · cm as measured by the method described in detail later. , And its dielectric constant is 2.5 to 4.5, especially 3.0 to 4.0
It is desirable to be in the range of.

The fixing resin medium for the toner, the colorant, the charge control agent, and the other compounding agents for the toner are preferably selected and combined so as to obtain the above characteristics. First, as the fixing resin medium,
A styrene resin, an acrylic resin or a styrene-acrylic copolymer resin is generally used. The styrenic monomer used for these resins has the following formula In the formula, R ₁ is a hydrogen atom, a lower (C4 or less) alkyl group, or a halogen atom, and R ₂ is a lower alkyl group,
A monomer such as a halogen atom and n is an integer of 2 or less including zero, such as styrene, vinyltoluene, α-methylstyrene, α-chlorostyrene, vinylxylene and vinylnaphthalene. Etc. can be mentioned. Among these, styrene is preferable.

On the other hand, as the acrylic monomer, In the formula, R ₃ is a hydrogen atom or a lower alkyl group, and R ₄ is a hydrogen atom or an alkyl group having up to 18 carbon atoms.

And a monomer represented by, for example, ethylene acrylate, methyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, acrylic acid, methacrylic acid and the like. As the acrylic monomer, other than the above-mentioned ones, other ethylenically unsaturated carboxylic acids or anhydrides thereof, for example, maleic anhydride, crotonic acid, itaconic acid or the like can be used.

Styrene-acrylic copolymer resin is one suitable as a resin medium, and the styrene monomer (A) and the acrylic monomer (B) are A: B = 50: 50 to 90: 10, especially 6
It is recommended that the range is 0:40 to 85:15. In addition, the resin used generally preferably has an acid value of 0 to 25. From the standpoint of fixability, the glass transition temperature (T
g).

As the colorant to be contained in the resin, the following inorganic or organic pigments and dyes are used alone or in combination of two or more kinds. Carbon black such as furnace black and channel black; iron black such as ferric tetroxide; titanium dioxide such as rutile type or anatase type; phthalocyanine blue; phthalocyanine green; cadmium yellow; molybdenum orange; pyrazolone red; fast violet B and the like.

As the charge control agent, any charge control agent known per se, for example, an oil-soluble dye such as nigrosine base (CI 50415), oil black (CI 26150) and spirone black, or a 1: 1 type or a 2: 1 type Metal complex salt dye, naphthenic acid metal salt, fatty acid soap, resin acid soap and the like are used.

The toner particles have a volume-based median diameter measured by a Coulter counter of 8 to 14 μm, particularly 10 to
The particle size may be in the range of 12 μm, and the particle size may be an irregular shape produced by the melt kneading / pulverization method or a spherical shape produced by the dispersion or suspension polymerization method.

Magnetic Carrier The magnetic carrier used in the present invention has a dielectric constant of 4 to 1
It is preferably in the range of 5, especially 5 to 9. Also, its volume resistivity is 1 × 10 ^{10 to} 5 × 10 ¹¹ Ω · c
m, especially in the range of 4 × 10 ^{10 to} 1 × 10 ¹¹ Ω · cm. The magnetic carrier is preferably a ferrite carrier satisfying the above conditions, particularly a spherical ferrite carrier, and the particle size thereof is 20 to 140 μm, particularly 50 to 100 μm.
It is desirable to be in the range of.

Conventionally as a ferrite, for example, iron zinc oxide (ZnFe ₂ O ₄ ),
Yttrium iron oxide (Y ₃ Fe ₅ O ₁₂ ), cadmium iron oxide (CdFe ₂ O ₄ ), gadolinium iron oxide (CdFe ₅ O ₁₂ ), lead iron oxide (PbFe ₁₂ O ₁₉ ), nickel iron oxide (NiFe ₂ O _4). ), Iron neodymium oxide (NdFeO ₃ ), iron oxide barium (BaFe
₁₂ O ₁₉ ), magnesium iron oxide (MgFe ₂ O ₄ ), manganese iron oxide (MnFe ₂ O ₄ ), lanthanum iron oxide (LaFeO ₃ ), etc. Sintered ferrite particles having a composition of one kind or two or more kinds are used. In particular, a soft ferrite containing at least one metal component selected from the group consisting of Cu, Zn, Mg, Mn and Ni, preferably two or more, such as copper-zinc-magnesium ferrite, is used. However, among these ferrites, those satisfying the above conditions are used.

The permittivity and electric resistance of the ferrite carrier will of course vary depending on its chemical composition, but will also vary depending on its particle structure, manufacturing method, surface coating and the like. For example, as the coating resin for surface coating, one kind of silicone resin, fluororesin, acrylic resin, styrene resin, styrene-acrylic resin, olefin resin, ketone resin, phenol resin, xylene resin, sialyl phthalate resin, etc. Alternatively, two or more kinds can be used.

Two-component developer The mixing ratio of the toner and the magnetic carrier varies depending on the physical properties of the toner and the magnetic carrier, but is generally within the range of 1:99 to 10:90, particularly 2:98 to 5:95 by weight. Is desirable. The electric resistance of the developer as a whole is
5 × 10 ^{9 to} 5 × 10 ¹⁰ Ω · cm, especially 1 × 10 ^{10 to} 4 × 10
The range of ¹⁰ Ω · cm is preferable for the purpose of the present invention.

Developing Conditions The developing conditions that affect the relaxation time (τ) of the developing circuit and the time difference (ΔT) of the formula (1) include the physical properties of the developer described above, various dimensions in the developing circuit, and the moving speed of each member. Etc.

First, since the change in the nip width (Nip) in the developing region has a reverse effect on the change in the relaxation time (τ) by the capacitance component (C) and the resistance component (R), the relaxation time (τ) There is an optimal range for
It is preferably in the range of 15 mm, especially 2 to 8 mm. Similarly, for the distance d _DS between the developing sleeve and the photosensitive layer,
Regarding the change of relaxation time (τ), there is an adverse effect due to C and R, and generally, the optimum range is 0.5 to 3.0 mm, and especially 0.
7 to 1.7 mm can be mentioned.

It is important for the developing sleeve and the photoconductor to be in the same direction at their rubbing positions in order to suppress the generation of brush marks, but at the same time, in relation to the nip width (Nip),
The above formula (1) should be satisfied.

Further, the filling rate of the developer in the developing area of the developer is determined by the distance d _DS between the developing sleeve and the photosensitive layer, the nip width (Nip), the peripheral speed of the developing sleeve (Vs) and the cutting edge length (d) on the developing sleeve. It also relates to _B ).

As another developing condition, the bias voltage applied between the developing sleeve and the photoconductor conductive substrate has an average electric field strength of 100.
To 1000 V / mm, particularly preferably 125 to 500 V / mm.

The resistivity and the dielectric constant of the toner used in the present invention are measured by using a parallel plate electrode type measuring device having an electrode area of 2.27 cm ² and a distance between electrodes of 0.5 mm, and filling the toner with a porosity of 25%. , Peak-to-peak is measured by applying an AC voltage of + 1V to -1V.

The electric resistance of the carrier used in the present invention is measured by the following method using the measuring device shown in FIG. That is, as shown in FIG. 9, the carrier 93 is introduced into the developing device 92 equipped with the stirring roller 91, the carrier 93 is carried on the sleeve 94, and the carrier 93 layer is made to have a predetermined thickness by the spike control member 95. Carrier adjusted to
Transport 93. Further, along the imaginary line 96 on the surface of the photoconductor facing the sleeve 94 with a predetermined gap therebetween, a detection unit 98 having a predetermined surface area is arranged by a micrometer 97 as an inter-electrode distance adjusting means, While carrying the carrier 93 together with the sleeve 94, an AC voltage having a predetermined frequency is applied to the sleeve 94 to supply the detection signal y from the detection unit 98 to the parallel circuit of the dummy and the oscilloscope 99 and on the oscilloscope 99. The waveform data is read by the reading means 80, and the electrical resistivity is calculated by the computing unit 81.

In the figure, reference numeral 82 indicates a carrier remaining on the sleeve 94.
A cleaning blade as a cleaning means for removing 93.

And, in the measurement of the dielectric constant by the above measuring device,
The distance between the sleeve 94 and the detection unit 98, that is, the inter-electrode distance d = 1.2 mm, the surface area of the detection unit 98, that is, the electrode area S
= 0.785 cm ^2, and an alternating voltage with a frequency of 50 Hz was applied.

Further, the layer thickness of the carrier 93 carried on the sleeve 94 is adjusted by the spike-up regulating member 95 so that the carrier filling rate is about 15%.
It can be set to ~ 50%.

(Effect of the Invention) According to the present invention, the relaxation time in the dynamic developing circuit consisting of the developing sleeve, the surface of the photoconductor and the developer layer interposed therebetween is set within a certain range, and more preferably, By setting the time difference between the time required for one point of the electrostatic latent image to pass through the developing nip and the relaxation time to be within a certain range, the line width of each line is made constant when reproducing multiple thin lines, leading to chipping of the leading edge or trailing edge. It has become possible to prevent chipping and form high-density and high-quality images. Further, it has become possible to provide a copying method with excellent reproducibility of kanji.

Hereinafter, the present invention will be described with reference to experimental examples.

(Experimental Example 1) In a modified electrophotographic copying machine DC-2555 (manufactured by Mita Kogyo Co., Ltd., trade name), three kinds of developers having physical properties shown in Table 1 were used, and developing conditions (drum between the drum and the sleeve DS) , Drum-sleeve peripheral speed ratio S / D) was changed, and relaxation time was measured by the method shown in FIG. Then, the image quality (image density
ID and bias) were measured at the same time. The developing brush cutting gap was 1.0 [mm], and the surface potential of the main charging photosensitive member was 700 [V]. The results are shown in Table-2.

As can be seen from Table-2, if the relaxation time becomes too short, even if the image density is high, the deviation of the line image is severe and the image is not good. Further, if the relaxation time becomes too long, the image density will be low, and the deviation of the line image will be severe, and a good image will not be obtained. When the relaxation time (τ) is 8 to 40 msec, the image density is high and a satisfactory image can be obtained with less deviation of the line image.

(Experimental Example 2) Using the copying machine and the developer used in Experimental Example 1, the actual image quality when ΔT described above was changed was measured. The results are shown in Table-3.

As is clear from Table 3, when the time difference (ΔT) is too small or too large, it is impossible to obtain a good image because the image density is lowered and the deviation of the line image becomes severe.

Needless to say, the present invention is not limited to the experimental examples described above.

[Brief description of drawings]

1 is a diagram showing an apparatus for measuring relaxation time, FIG. 2 is a diagram showing the electric circuit of FIG. 1 as an equivalent circuit, and FIG. 3 is an electric circuit of FIG. FIG. 4 is a diagram showing a current when an AC voltage is applied, FIG. 4 is a diagram showing a relationship between a distance in a feeding direction and an image density of a dense thin line, and FIG. 5 is a relaxation time (τ) and a line width. FIG. 6 is a diagram showing the relationship between the time difference (ΔT) and the line width deviation (δ), and FIG. 7 is a graph showing the relationship between the time difference (ΔT). FIG. 9 is a diagram showing a relationship with image density (ID), FIG. 8 is a diagram for explaining a magnetic brush developing method, and FIG. 9 is a diagram for measuring electric resistivity of a carrier used in the present invention. It is a device.

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Toshio Nishino 1-2-2 Tamatsukuri, Chuo-ku, Osaka City, Osaka Prefecture Mita Industry Co., Ltd. (72) Shoji Tomita 1-2-2 Tamatsukuri, Chuo-ku, Osaka City, Osaka Prefecture No. 28 in Mita Industry Co., Ltd. (56) Reference JP-A-60-53968 (JP, A) JP-A-60-134262 (JP, A)

Claims (2)

[Claims] 1. A developing method in which a magnetic brush of a two-component developer containing a magnetic carrier and toner is formed on a developing sleeve, and the magnetic brush is rubbed against a photoconductor having a charge image to form a toner image. In the method, the relaxation time (τ) of the developing sleeve, the developer and the circuit on the surface of the photoconductor is 8 to 40 mm when the photoconductor surface is changed to a conductive surface of the same size and measured at a frequency of 50 Hz under dynamic conditions. A development method with excellent reproducibility of characters, which is set so that it becomes a second. 2. A developing method in which a magnetic brush of a two-component developer containing a magnetic carrier and toner is formed on a developing sleeve, and the magnetic brush is rubbed against a photoconductor having a charge image to form a toner image. In the method, the developing sleeve and the photosensitive member surface are driven in the same direction at the nip position, and In the formula, Nip is the nip width of the developer on the surface of the photoconductor (m
m), V _S is the moving speed of the developing sleeve (mm / sec), V _D is the moving speed of the photoconductor surface (mm / sec), and τ
Changes the surface of the photoconductor to a conductive surface of the same size and frequency
Characterized by setting the development conditions so that the time difference (ΔT) defined by, which represents the relaxation time (msec) measured under dynamic conditions at 50 Hz, is 0 to 130 msec. Development method.