JP3159094B2 - Developing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device for visualizing a latent image caused by a difference in charged potential by attaching a developer, and more particularly to a developing device using a powdery one-component developer.

[0002]

2. Description of the Related Art As a developing device using a one-component developer, a developing device (developing roll) disposed opposite to a latent image carrier such as a photoconductive drum carrying an electrostatic latent image is used. It is known that a thin layer of a developer is formed on a developing area where the latent image carrier and the developer carrier are opposed to each other and the developer on the developer carrier is transferred to an electrostatic latent image to be visualized. I have. In such a developing device, the developer stored in the hopper is supplied to the surface of the developer carrier, and is conveyed by the orbiting movement of the surface of the developer carrier. Further, the developer carrier is exposed at a portion where the hopper opens toward the latent image carrier, and is opposed to the latent image carrier at this portion.

In this type of developing device, when the developer leaks from a portion outside the image area in the axial direction of the developer carrier or between the developer carrier and the hopper, the developer scatters outside the developing device and forms an image. Problems such as soiling other devices in the device occur. For this reason, there has been proposed a developing device provided with a side seal member for preventing the leakage of the developer near both ends in the axial direction of the developer carrying member (for example, Japanese Utility Model Laid-Open No. 1-1644).
No. 56, JP-A-5-289484). Each of these developing devices uses a porous elastic body or a felt-like material as a side seal member, and fills a space between the developer carrier and the hopper to prevent leakage of the developer.

[0004]

However, the following technical problems remain. It is essential to control the quality of the side seal members (plate thickness, fraying of end frays, etc.). The friction between the side seal member and the end of the developer carrier generates heat, which adversely affects the developer near the side seal member. In particular, it becomes worse with continuous copying. It is indispensable to manage the gap between the side seal member and the end of the developer regulating member, and the mounting work of the side seal member becomes troublesome.

In order to solve such a technical problem,
As another method that does not use a side seal member, a magnetic seal method in which a magnetic plate is made to closely approach a peripheral surface near an end of a developer carrier has been proposed (for example, Japanese Patent Application Laid-Open No. 54-10 / 1979).
No. 3043, Japanese Utility Model Application Laid-Open No. 60-74155, Japanese Patent Application Laid-Open No. 2-262171, Japanese Patent Application Laid-Open No. 4-34576). In this magnetic sealing method, a toner curtain (magnetic brush) is formed between a magnetic plate and a magnet roll disposed inside a developer carrier facing the magnetic plate, thereby sealing leakage of the developer to the outside. According to this magnetic sealing method, the above-mentioned problem can be solved. However, in this magnetic sealing method, the sealing performance level at a further increase in copy speed tends to be insufficient. When the outer diameter of the developer carrying member is increased, the centrifugal force acting on the toner curtain portion itself is increased, so that the sealing performance level tends to be insufficient.

In order to solve these problems, the present inventor has already proposed a technique in which the shape of the magnetic plate is devised, and the lines of magnetic force are concentrated on the magnetic plate to form a strong toner curtain. (See JP-A-8-137259). However, in this type, the length of the developer carrying member (for example, JIS standard A3 size → A2 size) / high speed rotation (for example, 22 → 32 CPM [Copy p
erminite]), there was a concern that toner would leak from both ends of the developer carrier, and there was a demand to form a more reliable toner curtain.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned technical problems, and has studied an optimum condition for effectively suppressing toner leakage due to a longer developer carrier and a higher rotation speed. Further, there is provided a developing device for improving the image fidelity of a line image, that is, the scattering of toner in a character portion (blurring) and the increase in the line width in repeated copying (copying of a copied document) as higher image quality. Things.

[0008]

That is, the present invention relates to a developer carrying member which is arranged to face a latent image carrying member on which an electrostatic latent image is carried, and which adheres and transports a developer to a surface thereof; A developer regulating member that regulates the amount of developer on the developer carrier and forms a thin layer of developer, and a magnetic plate that is disposed so as to face the peripheral surfaces near both ends of the developer carrier. In the developing device, the developer carrier includes a cylindrical developing sleeve having a rotatable periphery, and a magnet roll fixedly installed in the developing sleeve and having magnetic poles formed and arranged at predetermined intervals. S, the gap between the magnetic plate and the developer regulating member is T, the gap between the magnetic plate and the surface of the developing sleeve is T, the overlap area between the magnetic plate and the magnetic pole forming portion of the magnet roll is X, the surface of the magnetic plate and the magnet roll S <T
<X <L is satisfied.

In such technical means, the configuration of the developing sleeve of the developer carrier, the arrangement of the magnetic poles of the magnet roll, the method of forming the magnetic poles, and the like may be appropriately selected.
Further, the developer regulating member is not limited to a member arranged to be in contact with the developer carrier, but also includes a member arranged in non-contact with the developer carrier. Furthermore, the magnetic plate may be appropriately selected as long as it has magnetism, and the fixing method may be such that the magnetic plate is attached with a double-sided tape or the like, or a predetermined stopper is used. It may be.

In the present invention, from the viewpoint of more reliably forming a strong toner curtain, 0 <
It is preferable to satisfy S <T ≦ 1 and 0 <T / X <1.

Further, as a specific means for reliably forming a strong toner curtain, a thin developing sleeve having high rigidity is manufactured, the magnetizing force of the magnet roll is improved, and the magnetic roll is fixed to the magnetic plate. It is preferable to make the distance relatively close. As the developing sleeve in this case, for example, a developing sleeve in which a semiconductive layer is formed on the surface of a cylindrical metal pipe is preferable. In this type, the electric resistance value R of the semiconductive layer of the developing sleeve is 10 ⁴ ≦ R ≦ 10
It is preferably ⁶ (Ω · cm). Here, the upper limit of the electric resistance value of the developing sleeve indicates a limit for avoiding a situation where the electrostatic latent image reaches a saturation density even when the potential is relatively low and the gradation property is deteriorated. The lower limit of the electric resistance value indicates a limit for avoiding a situation where the saturation density of the image is low and the developing bias voltage is likely to leak.

Further, a one-component developer is carried on the developer carrier, and the one-component magnetic developer on the developer carrier is caused by an alternating electric field applied between the developer carrier and the latent image carrier. Is developed to develop a latent image on the latent image carrier by flying the image to the latent image carrier side (to prevent leakage of a developing bias, to prevent fogging of a developed image, and to prevent a decrease in image density). From the viewpoint, the peak-to-peak voltage (VP-P) of the alternating electric field and the dark development potential VD in the development area
And the distance G between the latent image carrier and the developer carrier: 11.02 × 10 ⁵ /VP-P≦VD≦11.78×10 ⁵ /
VP-P (unit V) and 2.85 × 10 ⁵ /VP-P≦G≦4.75×10 ⁵
/ VP-P (unit: μm).

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the accompanying drawings. FIG. 1 is an explanatory diagram showing an embodiment of a developing device to which the present invention is applied. In FIG. 1, the developing device employs a non-contact developing method using, for example, a magnetic one-component toner (developer). For example, a photoconductive drum (for example, a photoconductive drum having a surface made of a negatively charged organic photoreceptor) is used. (Latent image carrier) 10 to visualize the electrostatic latent image. In this embodiment, the photoconductive drum 10 is uniformly charged over the entire surface by a charging device (not shown), and then is exposed to an electrostatic latent image (having a surface potential of −580 to −620 V, preferably −60 V) by an exposure device (not shown).
0 V and the potential of the background portion is -120 V).

The developing device includes a hopper 12 containing a one-component magnetic toner 13 (for example, containing 48% by weight of magnetic powder).
And an opening 14 is formed in a portion of the hopper 12 facing the photoconductive drum 10. The developing roll 20 is located at a position facing the opening 14 of the hopper 12.
Are arranged. The developing roll 20 is spaced from the photoconductive drum 10 by a predetermined distance (for example, 150 to 250 μm).
m, preferably 200 μm), a rotatable non-magnetic developing sleeve 21,
1 and a magnet roll 22 having a plurality of magnetic poles (for example, five magnetic poles) arranged therearound, and a portion facing the photoconductive drum 10 functions as an effective developing area. Further, the developing sleeve 21 has a developing bias power source 23 including an AC power source 24 and a DC power source 25.
Are connected, and a predetermined DC superimposed AC voltage is applied.

A toner regulating blade 30 is provided in front of the effective developing area of the developing roll 20. In the present embodiment, for example, a 0.1 mm thick non-magnetic stainless steel (SUS304CS) is attached to the support bracket 15 fixed to a part of the hopper 12.
A base end of a metal blade 31 made of P3 / 4H material) is fixed, and a free end of the metal blade 31 is arranged so as to protrude so as to face the rotation direction of the developing sleeve 21.
At the free end of the metal blade 31, an elastic friction member 32, for example, a silicone rubber having a rubber hardness of 50 ° and a thickness of 1 mm is fixed by vulcanization, and the elastic friction member 3 is attached to the surface of the developing sleeve 21.
2 is disposed under pressure at a predetermined pressure.

Further, the developing roll 2 in the hopper 12
An agitator 41 that supplies the magnetic toner 13 in the hopper 12 to the developing roll 20 side is disposed behind the agitator 41, and supplies the supplied magnetic toner 13 to the agitator 41 side behind the agitator 41. Transport Auger 4
2 are provided. In FIG. 1, reference numeral 43 denotes a toner empty detection sensor that detects the empty state of the magnetic toner 13 accommodated in the hopper 12.

Further, in this embodiment, FIG.
3, a substantially C-shaped magnetic plate 50 is disposed in the vicinity of both ends of the developing roll 20 so as to face the peripheral surfaces near the both ends of the developing roll 20. The regulating blade 30 is disposed close to both ends. The magnetic plate 50 has a shape that opens substantially corresponding to the opening 14 of the hopper 12, and is fixed to the inner wall surface of the hopper 12 by, for example, a double-sided tape (not shown).
The magnetic toner 13 carried on the peripheral surface of the developing roller 20 is prevented from leaking from both ends of the developing roller 20. In FIG. 1, reference numeral 51 denotes an elastic spacer that fills a gap formed between the toner regulating blade 30 and the inner wall of the hopper 12.

In particular, in the present embodiment, the magnetic plate 5
0, developing roll 20 (developing sleeve 21, magnet roll 2)
2) and optimization of the relative positional relationship of the toner regulating blade 30 was studied. Here, as shown in FIG.
And the gap between the toner regulating blade 30 and the magnetic plate 5
The gap between the magnetic plate 50 and the surface of the magnet roll 22 is X, the gap between the magnetic plate 50 and the surface of the magnet roll 22 in the axial direction of the magnet roll 22 is X, and the gap between the magnetic plate 50 and the surface of the magnet roll 22 is L. As shown below, these specific desirable numerical values are as follows: S = 0.2 to 0.5 (mm) T = 0.5 to 1 (mm) X ≦ 1 (mm) L ≦ 2 (Mm), and satisfies the relationship of S <T <X <L.
It was confirmed that it was necessary to satisfy the relationships of 0 <S <T ≦ 1 and 0 <T / X <1. In FIG. 4,
Reference numeral 211 denotes a flange that rotatably supports the developing sleeve 21.

In such a numerical limitation, for example, 0 <
If the condition of T / X <1 is satisfied, it is certain that the developing roll 2
At the toner curtain 60 between the zero and the magnetic plate 50, toner leakage from the both is effectively avoided. However, when the developing sleeve 21 rotates at a higher speed, the toner sealability (airtightness) of the current toner curtain 60 tends to be insufficient, and the dimensional tolerance of S in particular becomes more severe. That is,
If S is too large, the toner sealing property is deteriorated and the adverse effect of toner leak is caused. If the S is small (contact), the toner control blade 30 or the dimension control of the developing device mounting portion or the toner control blade 3
Local transport failure occurs due to deformation of the zero end.

Focusing on the toner curtain 60, under the condition that the developing sleeve 21 is not rotating at such a high speed, for example, the degree indicated by 60 'in FIG. As the rotation speed increases, a stronger toner curtain 60 is required.
As shown in FIG. 5, for example, as shown in FIG. 5, the absolute value of the magnetic force lines forming the toner curtain 60 is larger (proportional to the thickness of the line). It is also preferable that the magnetic plate 50 is extended from the developing sleeve 21 to the toner regulating blade 30 around the magnetic plate 50.

In order to realize such a strong toner curtain 60, the magnet roll 22 in the developing sleeve 21 is required.
It is only necessary to improve the magnetizing force and make the distance to the magnetic plate 50 relatively closer. Under such a request, in the present embodiment, a study was made to further reduce the thickness of the developing sleeve 21 used. That is, in the comparative embodiment of FIG. 6, since phenol resin (thickness Y2 = 2.0 mm) was used as the developing sleeve 21 ', L (gap between the magnetic plate 50 and the surface of the magnet roll 22) was L2. On the other hand, in the present embodiment, the thickness is 1 mm.
Coat sleeve (0.1 mm thick semiconductive layer) coated on the surface of an inner pipe made of SUS (thickness Y1 =
1.1 mm).
L was narrowed to L1 (L1 <L2). The method of manufacturing the coat sleeve is described in, for example, Japanese Patent Application Laid-Open No. Hei 2-222978.
It is sufficient to use the manufacturing method disclosed in Japanese Patent Application Laid-Open Publication No. H10-26095.

At this time, as shown in FIG. 5, the inner diameter of the developing sleeve 21 made of a coat sleeve can be increased by changing the material while maintaining the outer diameter R. Since the diameter is set to be large, the magnetic pole volume formed on the magnet roll 22 increases, and the magnetizing force of the magnet roll 22 improves. As a result,
In the present embodiment, the strong toner curtain 60 is generated, and the dimensional tolerance of S (gap between the magnetic plate 50 and the toner regulating blade 30) is reduced accordingly (S2 →
S1 (S1 <S2) is performed.

As a secondary effect due to the use of the developing sleeve 21 formed of a coat sleeve, in the comparative form (phenol resin type), for example, the developing sleeve 21 'is made longer (JIS standard A3). Size correspondence →
In the case of (A2 size), the central portion is bent by its own weight. However, in the present embodiment, even if the developing sleeve 21 is lengthened (JIS standard A3 size compatible → A2 size compatible), it is sufficient. High rigidity is ensured, and there is no concern that the central portion may be bent.

Next, there is another problem to be solved by the present embodiment, namely, the fidelity of the original of the line image at high image quality, that is, the toner scattering (blurring) at the character portion and the line width at copy-to-copy. The improvement in fatness will be described.

The developing sleeve (coat sleeve: Coat Sleeve) according to the present embodiment and the developing sleeve (phenol resin sleeve: Phenol Sleeve) according to the comparative embodiment are compared in each item, and the results are shown in Table 1 below. Show.

[0026]

[Table 1]

As can be seen from Table 1, the advantage of the developing sleeve (coating sleeve) according to the present embodiment is that the toner charging property is stabilized (the density fluctuation is small) because the surface roughness has little change with time. ) Point, in a developing device of a long specification capable of copying JIS A2 size drawings,
The point is that the line density uniformity at 0.2GL reproducibility (corresponding to the reproducibility of a thin line with a pencil) in a two-copy plane is high, and the line density variation is smaller than that of a phenol resin.

The reason is that the material is used. That is, the developing sleeve 21 (coat sleeve) according to the present embodiment uses, for example, a polyester resin as a binder on a SUS inner pipe, and a paint (compound) of carbon or metal powder and an inorganic compound (hard). . Then, this is coated by, for example, electrostatic coating (electrostatic spray coating) to expose the inorganic compound (hard) to the surface. Since the inorganic compound does not change with time, the change in the surface roughness of the coat sleeve is small. Also,
The thickness of the coat sleeve is a semiconductive layer of 0.1 mm,
By taking an approach from conductivity (metal) to semi-conductivity, a resistance value of 10 ⁴ to 10 ⁶ Ω · cm can be obtained, and particularly, 10 ⁵ Ω · cm has high production stability.

Here, the reason why the electric resistance value of the developing sleeve 21 (coat sleeve) is preferably 10 ⁴ to 10 ⁶ Ω · cm is as follows. That is, when the electric resistance value of the developing sleeve 21 exceeds 10 ⁶ Ω · cm, even when the electrostatic latent image has a relatively low potential, it reaches the saturated density. For this reason, the gradation is deteriorated, and a halftone image cannot be obtained. FIG. 7 is a diagram for explaining this phenomenon. As can be seen from FIG. 7, when the electric resistance value of the developing sleeve 21 is 10 ⁹ Ω · cm, the image density sharply increases as the potential of the electrostatic latent image increases. Development characteristics γ). That is, when the electrical resistance value of the developing sleeve 21 increases, the contrast of the density of the image increases, but in the experiment of the present inventor, the upper limit is 10 ⁶ Ω · cm in order to obtain a desired gradation. It turns out. On the other hand, it was found that when the electric resistance value of the developing sleeve 21 was less than 10 ⁴ Ω · cm, the saturation density of the formed image was low, and the leakage of the developing bias voltage was easily caused.

The phenol resin is employed from the viewpoints of hardness, abrasion resistance, etc., and includes various resistance controls (carbon black, etc.), fillers (glass fibers, etc.), and other materials (resin binder, conductive metal oxide, etc.). Powder). This makes it possible to change from insulating to semiconductive,
0 ⁷ to 10 ⁵ Ω · cm is obtained, and 10 ⁶ Ω · cm has high production stability.

The reason for this is that the developing device is made longer (J
When the IS standard A3 → A2 size is applied), a gap difference (about 20 to 40 μm) between the photoconductive drum 10 occurs at both ends and the center of the developing sleeve (phenol resin sleeve) 21 ′ according to the comparative embodiment. This is because, in addition to the weight of the phenol resin itself at a thickness of 2.0 mm, an external pressure is applied in such a manner that the toner regulating blade applied to the developing sleeve pushes out toward the photoconductive drum 10. Here, if the developing sleeve (coat sleeve) according to the present embodiment is used, this problem is eliminated. This is because the SUS inner pipe significantly increases rigidity and eliminates the gap between the photoconductive drum at both ends and the center. Therefore, JIS
The line density uniformity (variation) at 0.2GL reproducibility (pencil) in the standard A2 copy plane was much better than the phenolic resin.

Further, in the present embodiment, by appropriately balancing the surface roughness of the developing sleeve 21 and the pressing force of the toner regulating blade 30, the toner adhesion amount regulated by the toner regulating blade 30 is appropriately adjusted. More specifically, for example, the surface roughness of the developing sleeve 21 is set at about Rz = 4 to 6 μm in terms of JIS 10-point average roughness, and the toner regulating blade 30 is attached to the developing sleeve 21 by, for example, about 90 g / cm. , The toner adhesion amount regulated by the toner regulation blade 30 is 1.0 m per unit area of the developing sleeve 21.
g / cm ² are provided.

The semiconductive layer of the developing sleeve 21 is adjusted to have a specific resistance of, for example, 3.5 × 10 ⁵ Ω · cm, and the gap between the semiconductive layer and the photoconductive drum 10 is set to 150 to 250.
.mu.m, preferably 200 .mu.m, and under the condition that the dark developing potential VD is 580 V.ltoreq. | VD.vertline.
When various parameters of the developing bias were examined, it was found that it was preferable to apply a DC superimposed AC voltage having a frequency of 2.4 kHz, a peak-to-peak voltage of 1,900 V, and a DC component of -250 V, for example.

Here, how the respective parameters of the developing bias are determined will be described. First, the peak-to-peak voltage V
When the PP was examined, in the present embodiment, as shown in FIG. 8, the gap G between the photoconductive drum and the developing roll was 2.5 G + 0.75 (kV) to 5.0.
G + 2.00 (kV) is sufficient, and 2.5G +
When it is less than 0.75 (kV), ground fogging of the developed image occurs, and when it exceeds 5.0 G + 2.00 (kV),
It was found that the developing bias voltage leaked. Therefore, in the present embodiment, for example, 1,900 V is selected as the peak-to-peak voltage VP-P. Further, when the relationship between the frequency of the developing bias voltage and the image density was examined under the conditions of the peak-to-peak voltage VP-P of the developing bias, as shown in FIG. The frequency (in the present embodiment, the image density was 1.3) was found to be 1.0 to 6.2 kHz.
Therefore, in the present embodiment, 2.4 kHz is selected as the frequency of the developing bias.

Further, various experiments were conducted on the basis of the above conditions to determine conditions for satisfying the dark developing potential VD and the gap G between the photoconductive drum and the developing roll. The results shown in FIG. 10 were obtained. Was done. According to the figure, when the dark developing potential | VD | (unit: V) exceeds 11.78 × 10 ⁵ / VP-P, the ground fog of the developed image occurs, and 11.02 ×
It has been found that if it is lower than 10 ⁵ / VP-P, the image density decreases. Further, the photoconductive drum 10 and the developing roll 2
A gap G (unit: μm) between 0 and 2.85 × 10 ⁵ /
If it is smaller than VP-P, a developing bias leak will occur,
On the other hand, when it exceeds 4.75 × 10 ⁵ / VP-P, it has been found that the toner chain is too wide to form a toner chain and development becomes impossible. Therefore, 11.02 × 10 ⁵ / VP
-P ≦ | VD | ≦ 11.78 × 10 ⁵ / VP-P and 2.8
It has been found necessary that 5 × 10 ⁵ /VP-P≦G≦4.75×10 ⁵ / VP-P. As described above, the original image fidelity of the line image in high image quality, that is, the scattering of the toner in the character portion (blurring) and the increase in the line width in the repeated copying (copying of the copied original) are improved.

[0036]

As described above, according to the first aspect of the present invention, the magnetic plate and the developer carrying member (developing sleeve, magnet roll) are provided on the peripheral surfaces near both ends of the developer carrying member.
In addition, since the relative positional relationship between the developer regulating members is optimized, it is possible to effectively prevent toner leakage by a stable toner curtain even when the developer carrier is made longer or rotates at a higher speed. it can. In particular, if the conditions described in claim 2 are adopted, a stable toner curtain can be more reliably generated, and toner leakage can be more reliably avoided.
Further, if the developing sleeve according to the third aspect is adopted, the magnetizing force of the magnet roll is increased and the relative distance between the magnet roll and the magnetic plate is easily narrowed by forming a thin and highly rigid developing sleeve. Therefore, a stable toner curtain can be easily formed. Further, according to the developing sleeve of the third aspect, it is possible to stably obtain a resistance value in a predetermined range where the surface roughness does not change with time, so that the toner charging property is stabilized and the density is improved. Since fluctuations can be suppressed and a highly rigid developing sleeve can be obtained, bending deformation of the developer carrier can be effectively suppressed even in a long-sized developing device, and line density uniformity can be improved. And the variation in line density can be reduced.

According to the first aspect of the present invention, further, the dark developing potential, the peak-to-peak voltage as a developing bias, and the gap between the latent image carrier and the developer carrier are optimized. Original fidelity of a line image, that is, scattering of toner in a character portion (blurring) and thickening of a line width in repeated copying (copying of a copied original) can be improved, and high image quality can be achieved.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating an outline of a developing device according to an embodiment.

FIG. 2 is an explanatory diagram schematically showing a configuration around a developing roll according to the embodiment.

FIG. 3 is a view as viewed from an arrow III in FIG. 2;

FIG. 4 is an explanatory diagram showing a relative positional relationship among a magnetic plate, a developing roll (developing sleeve, magnet roll), and a toner regulating blade of the developing device according to the embodiment.

FIG. 5 is an explanatory diagram illustrating a state of a toner curtain formed by the developing device according to the embodiment;

FIG. 6 is an explanatory diagram illustrating a state of a toner curtain formed by a developing device according to a comparative embodiment.

FIG. 7 is a graph showing a relationship between an electrostatic latent image potential and an image density depending on a difference in electric resistance value of the developing sleeve according to the embodiment.

FIG. 8 is a graph showing a relationship between a gap G between a photoconductive drum and a developing roll and a peak-to-peak voltage (VP-P) of a developing bias in the embodiment.

9 is a graph showing the relationship between the developing bias frequency and the image density within the range of the peak-to-peak voltage VP-P in FIG.

FIG. 10 is a graph showing the influence on the developed image of the dark developing potential and the distance G between the photoconductive drum and the developing roll.

[Explanation of symbols]

Reference Signs List 10 photoconductive drum (latent image carrier), 20 developing roller (developer carrier), 21 developing sleeve, 22 magnet roll, 30 toner regulating blade (developer regulating member), 50 magnetic plate

Claims (4)

(57) [Claims] 1. A developer carrying member which is arranged opposite to a latent image carrying member on which an electrostatic latent image is carried and which conveys a developer adhered to a surface thereof, and a developer amount on the developer carrying member. A developer regulating member that regulates and forms a thin layer of developer, and a magnetic plate that is disposed so as to face the peripheral surfaces near both ends of the developer carrier, wherein the developer The carrier includes a cylindrical developing sleeve whose periphery is rotatable, and a magnet roll fixedly installed in the developing sleeve and having magnetic poles formed and arranged at predetermined intervals, and a magnetic plate and a developer regulating member. When the gap is S, the gap between the magnetic plate and the surface of the developing sleeve is T, the overlap region between the magnetic plate and the magnetic pole forming portion of the magnet roll is X, and the gap between the magnetic plate and the surface of the magnet roll is L, S < A developing device characterized by satisfying a relationship of T <X <L. 2. The developing device according to claim 1, wherein 0 <S <T ≦ 1 and 0 <T / X <1 are satisfied. 3. The developing device according to claim 1, wherein the developing sleeve has a semiconductive layer formed on a surface of a cylindrical metal pipe, and the semiconductive layer has an electric resistance R of 10 ⁴ ≦ R ≦
A developing device characterized by 10 ⁶ (unit: Ω · cm). 4. The developing device according to claim 1, wherein the one-component developer is carried on the developer carrier, and the one-component developer is carried by an alternating electric field applied between the developer carrier and the latent image carrier. A developing device for flying a one-component magnetic developer on the developer carrier toward the latent image carrier and developing the latent image on the latent image carrier, wherein a peak-to-peak voltage (VP-P) of the alternating electric field; Regarding the dark development potential VD in the development area and the distance G between the latent image carrier and the developer carrier, 11.02 × 10 ⁵ /VP-P≦VD≦11.78×10 ⁵ /
VP-P (unit V) and 2.85 × 10 ⁵ /VP-P≦G≦4.75×10 ⁵ / VP-P
(Unit: μm).