JPH10123827A - Developing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize the density of developed image without making a developing device large in size for a high speed printing by specifying absolute value of difference between bias to the developer feeding rotary body and the bias to the developer carrying rotary body and circumferential speed of the developer feeding rotary body/the developer carrier rotary body by a specified condition. SOLUTION: This developing device is provided with a developing roller 31 being the developer carry rotary body and coming into counter contact with a photosensitive drum 21, in a developing device 26 disposed on the periphery of the photosensitive drum 21 being a electrostatic latent image carrier, and a toner feeding roller 32 being the developer carrying rotary body and coming into counter contact with the developing roller 31 behind the developing roller 31. In this case, when the absolute value of difference between the bias to the toner feeding roller 32 being the developer feeding rotary body and the bias to the developing roller 31 being the developer carrying rotary body is defined as X, and the circumferential speed of the toner feeding roller 32/the peripheral speed of the developing roller 31 is defined as Y, the following inequality is satisfied, 700>=X and Y>=350 (wherein, X>0 and Y>0), and X is defined as discharge start voltage or below.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device used in an image forming apparatus such as a laser printer or a copying machine for forming an image according to an electrophotographic process.

[0002]

2. Description of the Related Art As an image forming apparatus for forming an image according to an electrophotographic process, for example, an image forming apparatus described in Japanese Patent Publication No. 6-16210 is known. As shown in FIG. 6, a charger 2 for uniformly charging the surface of the photosensitive drum 1 around a photosensitive drum 1 which is a rotating body for holding an electrostatic latent image, and a photosensitive member charged by the charger 2 A laser scanning unit (not shown) for irradiating the body drum 1 with the laser beam 3 to form an electrostatic latent image, and attaching the toner 5 in the toner container 4 to the electrostatic latent image formed by the laser beam 3 A developing device 6 for developing to form a toner image; a transfer device 8 for transferring the toner image formed by the developing device 6 onto a recording paper 7 conveyed and supplied; and a toner 5 ′ remaining after being transferred to the photosensitive drum 1
A cleaning device 9 for scraping off the photosensitive drum 1 and a neutralizing lamp 10 for neutralizing the surface of the photosensitive drum 1 are provided.

A developing device 6 used in such an image forming apparatus is provided with a developing roller 11 which is a rotating developer holding member in contact with the photosensitive drum 1 and has the same structure as the developing roller 11.
Behind the developing roller 11, a toner supply roller 12 which is a developer supply rotating body is provided in contact with the developing roller 11, and a toner for uniformly thinning the toner layer on the developing roller 11 is provided above the developing roller 11. A layer thickness regulating member 13 is provided in elastic contact with a spring 14 and a toner 5
Is provided with a toner stirring bar 15 for stirring the toner.

The developing device 6 performs development by rotating the developing roller 11 and the toner supply roller 12 in the directions indicated by arrows in the drawing. That is, the developing roller 11 rotates so as to move in the same direction with respect to the photosensitive drum 1 at the contact portion with the photosensitive drum 1, and the toner supply roller 12 rotates at the contact portion with the developing roller 11. Rotate to move in the opposite direction to. Then, by the rotation of the developing roller 11 and the toner supply roller 12, the toner 5 in the toner container 4 adheres to the toner supply roller 12, is conveyed to the developing roller 11, and adheres to the developing roller 11. After the toner 5 attached to the developing roller 11 is thinned by the toner layer thickness regulating member 13, the toner 5 is attached to the electrostatic latent image forming portion of the photosensitive drum 1.

[0005] Such a developing device has a printing speed of 100.
It is used at about mm / sec or less. For example, as the developing roller 11, a hardness of 30 degrees (JI
A conductive urethane rubber layer of SA) is provided, and a conductive urethane paint is applied to the surface of the urethane rubber layer, and the resistance between the metal shaft and the surface of the conductive urethane coating is 10 ⁸ Ω.
· Cm was adjusted to become less using a conductive elastic roller of 18 mm, also, as a toner supply roller 12, a conductive urethane farm resistance around the metal Shaft is 10 ⁷ to 10 ⁹ Omega · cm When the provided φ12 roller is used, the peripheral speed of the toner supply roller / the peripheral speed of the developing roller =
0.5, and set the absolute value of the difference between the bias to the toner supply roller and the bias to the developing roller to 100 to 15
By setting the voltage to about 0 V, good printing can be performed.

However, if the printing speed is set to 150 mm / sec or more under the same condition as the developing device, a defect in density follow-up occurs particularly in solid printing. 7 to 9
And the peripheral speed of the developing roller: the peripheral speed of the toner supply roller = 1: 0.
5 shows a density gamma curve at each printing speed when printing is performed with the bias Vb applied to the developing roller−the bias Vs applied to the toner supply roller = 100 V. FIG. 7 shows the relationship between the developing roller bias Vb and the potential difference between the photosensitive member residual potential Vr and the density when the printing speed is 8 ppm (58 mm / sec). FIG. 8 shows the development when the printing speed is 16 ppm (116 mm / sec). FIG. 9 shows the relationship between the roller bias Vb and the potential difference between the photosensitive member residual potential Vr and the density.
(174 mm / sec) shows the relationship between the potential difference between the developing roller bias Vb and the photosensitive member residual potential Vr and the density. In the figure, x indicates the average value, ◇ indicates the value at the leading edge of the recording sheet, □ indicates the value at the center of the recording sheet, and △ indicates the value at the trailing edge of the recording sheet.

At each printing speed, the potential difference between the developing roller bias Vb and the photosensitive member residual potential Vr is 20 at the leading end.
A good concentration is obtained at about 0 V or more. However, when the printing speed is 8 ppm, the density, which was uniform from the leading end to the trailing end, becomes larger as the printing speed increases. In other words, it indicates that a problem that the followability of the density deteriorates with the increase in the printing speed occurs.

A peripheral speed ratio between the toner supply roller and the developing roller,
Means for solving the following of the density without changing the condition of the potential difference between the developing roller and the toner supply roller include: a. Increasing the size of the developing device, increasing the diameter of the developing roller, and reducing the number of rotations of the developing roller required to print one sheet of recording paper; b. Increasing the number of toner supply rollers to increase the amount of toner supply, and the like. However, this requires not only a drastic change in the developing device, but also a problem that the developing device becomes large, and as a result, the whole device becomes large.

Further, Japanese Patent Application Laid-Open No. 4-281479 discloses that by setting the peripheral speed of a toner supply roller, an optimal amount of toner is supplied to perform good printing. That is, as shown in FIG. 10, the toner 17 in the toner container 16 is supplied to the developing roller 19 by the rotation of the toner supply roller 18, and the toner is supplied from the developing roller 19 to the photosensitive drum.
Is set to be 1.4 to 1.7 times the circumferential speed of the developing roller 19. Further, it is disclosed that the bias to the developing roller 19 is set to -300 V, and the bias to the toner supply roller 18 is set to -400 to -500 V. That is, the toner supply roller 1
8 and the developing roller 19 have a potential difference of 100V to 200V.
Is disclosed.

[0010]

Problems to be Solved by the Invention
In Japanese Patent Application Laid-Open No. 9-204, it is possible to optimize the amount of toner used for development without increasing the size of the developing device. However, this is also a case where the printing speed is relatively low, and
When the speed is 0 mm / sec or more, there is a problem that the followability of the toner supply is deteriorated, and the density is reduced. In particular, the decrease in the density is increased toward the rear end of the recording paper, and the followability of the density is also deteriorated. .

Therefore, according to the first and second aspects of the present invention, high-speed printing at a printing speed of 150 mm / sec or more can improve the stability of density and the followability of density without increasing the size of the apparatus. Provided is a developing device capable of holding development.

[0012]

According to the first aspect of the present invention,
The electrostatic latent image holding rotator is arranged so as to face and contact with the electrostatic latent image holding rotator. A developer holding rotator that supplies a one-component non-magnetic developer to the electrostatic latent image holding rotator; and a developer holding rotator that is disposed in opposing contact with the developer holding rotator. A developer supply rotator that rotates so as to move in the opposite direction with respect to the developer holding rotator and supplies the developer to the developer holding rotator. When the absolute value of the difference from the bias to the developer holding rotator is X and the peripheral speed of the developer supply rotator / the peripheral speed of the developer holding rotator is Y, 700 ≧ X · Y ≧ 350 (where, X> 0, Y> 0) and X is equal to or lower than the discharge starting voltage. That.

According to a second aspect of the present invention, the electrostatic latent image holding rotating body is disposed so as to face and contact with the electrostatic latent image holding rotating body. A developer holding rotator that rotates so as to move in the same direction and supplies a one-component non-magnetic developer to the electrostatic latent image holding rotator; A developer supply rotator that rotates so as to move in a direction opposite to the developer holding rotator at a contact portion with the developer holding rotator and supplies the developer to the developer holding rotator; When the peripheral speed of the electrostatic latent image holding rotator is 150 mm / sec or more, the developer holding rotator has a peripheral speed of the electrostatic latent image holding rotator: the peripheral speed of the developer holding rotator of 1: 1.5 to 2 In the developing device which rotates so as to achieve a bias of 0.5, the bias to the developer supply rotating body and the bias to the developer holding rotating body are changed. When the absolute value of the difference from the bias is X and the peripheral speed of the developer supply rotary member / the peripheral speed of the developer holding rotary member is Y, 700 ≧ XY · 350 (where X> 0, Y> 0 ) Is satisfied and X is equal to or lower than the discharge starting voltage.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, a charger 22 for uniformly charging the surface of the photosensitive drum 21 is provided around the photosensitive drum 21 which is a rotating body for holding an electrostatic latent image. A laser scanning unit (not shown) for irradiating the photosensitive drum 21 with a laser beam 23 to form an electrostatic latent image;
A developing device 26 for attaching and developing a toner 25 as a developer contained in a toner container 24 to the electrostatic latent image formed by the laser beam 23 to form a toner image is formed by the developing device 26. A transfer device 28 for transferring the toner image onto a recording paper 27 fed and supplied; a cleaning device 29 for scraping off the toner 25 ′ remaining after transfer on the photosensitive drum 21; and the photosensitive drum 21
Are disposed respectively.

The developing device 26 is provided with a developing roller 31 which is a rotating developer holding member in contact with the photosensitive drum 21 and at the rear of the developing roller 31 is in contact with the developing roller 31 to supply the developer. A toner supply roller 32 as a rotating body is provided. Further, the developing roller 31
A toner layer thickness regulating member 33 for uniformly thinning the toner layer on the developing roller 31 is provided in elastic contact with a spring 34 on the upper portion of the developing roller 31. A toner stirrer 35 that stirs the toner 25 is provided.

The developing roller 31 is provided with a conductive urethane rubber layer having a hardness of 30 degrees (JIS-A) around a metal shaft, and a conductive urethane paint is applied to the surface of the urethane rubber layer to form a metal shaft and a conductive shaft. Φ adjusted so that the resistance between the conductive urethane coating surfaces is 10 ⁸ Ω · cm or less.
And 18 conductive elastic rollers. The toner supply roller 32 has a resistance value of 10 around the metal shaft.
Φ with conductive urethane firm of ⁷ to 10 ⁹ Ωcm
It consists of 12 rollers. A bias Vb is applied to the developing roller 31, and a bias Vs is applied to the toner supply roller 32. The toner layer thickness regulating member 33 is made of an elastic material of silicon rubber, and has a cross-sectional shape of R.
A 1.5 curved surface comes into contact with the peripheral surface of the developing roller 31, has a semicircle hardness of 70 degrees (JIS-A) and a load of 1.33 kg.
(5.94 g / mm). The toner 25
Is a one-component non-magnetic toner and uses a styrene acrylic pulverized toner material. The developing roller 31 and the toner supply roller 32 are in contact with each other with a nip of about 1 to 2 mm.

The photosensitive drum 21, the developing roller 31, and the toner supply roller 32 rotate in the directions shown by the arrows in FIG. That is, the developing roller 31 is
The toner supply roller 32 rotates so as to move in the same direction with respect to the photosensitive drum 21 at a contact portion with the toner supply roller 32.
Is the developing roller 3 at the contact portion with the developing roller 31.
1 to rotate in the opposite direction. The developing roller 31 rotates at a speed such that the peripheral speed of the photosensitive drum 21: the peripheral speed of the developing roller 31 is 1: 1.5 to 2.5.

The rotation of the developing roller 31 and the toner supply roller 32 causes the toner 25 in the toner container 24 to adhere to the toner supply roller 32 and to be conveyed to the developing roller 31, where it is adhered to the developing roller 31. After the toner 25 attached to the developing roller 31 is thinned by the toner layer thickness regulating member 33, the toner 25 is attached to the electrostatic latent image forming portion of the photosensitive drum 21.

In such a configuration, for example, the printing speed (that is, the peripheral speed of the photosensitive drum 21) is 173.9 mm.
/ Sec (corresponding to 24 ppm in A4 vertical printing), the potential difference between the bias Vs of the toner supply roller 32 and the bias Vb of the developing roller 31 and the toner supply roller 3
The density characteristic on the recording paper 27 when the peripheral speed of No. 2 is changed is
The leading end is as shown in FIG. 2 and the trailing end is as shown in FIG. In the figure, fine cross lines indicate a Macbeth density range of 1.4 to 1.5, fine diagonal lines indicate a Macbeth density range of 1.3 to 1.4, and coarse cross lines. Indicates a Macbeth concentration in the range of 1.2 to 1.3,
The coarse oblique lines indicate the Macbeth density range of 1.1 to 1.2, and the dotted portions indicate the Macbeth density range of 1.0 to 1.1.

That is, a good density can be obtained at the tip portion under each condition. Further, the rear end portion makes the bias Vs of the toner supply roller 32 deep, and
When the peripheral speed is increased, the density increases, and the followability of the density is improved. Further, the bias V of the toner supply roller 32 is
The relationship between the potential difference between s and the bias Vb of the developing roller 31 and the density indicated on the coordinate axis of (peripheral speed of the toner supply roller 32) / (peripheral speed of the developing roller 31) is a Macbeth density of 1.3 to 1. Judging from the region of .4 and the region of the Macbeth density of 1.4 to 1.5, it can be seen that the relationship is inversely proportional or close to a quadratic curve.

Further, from FIG. 3, in order to increase the concentration at the rear end, a. Increasing the potential difference between the bias Vs of the toner supply roller 32 and the bias Vb of the development roller 31 to increase the amount of toner supplied from the toner supply roller 32 to the development roller 31 by the force of the electric field generated by the potential difference; b. Increasing the peripheral speed ratio between the toner supply roller 32 and the development roller 31 to mechanically increase the amount of toner supplied from the toner supply roller 32 to the development roller 31;
Is necessary.

When these conditions are independently changed, the concentration behavior at that time is similar, and in both cases, the conditions should be changed (increase the potential difference, increase the peripheral speed ratio). As a result, the amount of adhesion of the toner 25 to the developing roller 31 increases, and as a result, the density is improved. That is, if one of the potential difference and the peripheral speed ratio is increased, the other may select the condition so as to complement it, and a good black density can be obtained by the balance between the two.

If the Macbeth density is 1.4 or more, it can be said that the black density is good. Therefore, from FIG. 2 and FIG. 3, the points satisfying the Macbeth density of 1.4 or more are plotted. Become like That is, the bias Vs of the toner supply roller 32 and the bias V
b, the toner supply roller 32 and the developing roller 3
It is determined from the relationship with the peripheral speed ratio of 1 that the relationship is close to the inverse proportional relationship, and | toner supply roller bias Vs−developing roller bias Vb | = X (V) toner supply roller peripheral speed / developing roller peripheral speed = Y, XY can be approximated to 350.

That is, the condition satisfying the Macbeth density of 1.4 or more is as follows: XY ≧ 350 (where X> 0, Y> 0).

On the other hand, if the values of X and Y are too large, the transport of the toller onto the developing roller 31 becomes excessive, and the toner that is not sufficiently charged is also transported. Become. The fog value is determined by measuring the difference in reflectance between unprinted paper and paper on which solid white printing has been performed, using a colorimeter. The fog on the recording paper 27 can be considered to be good if the color difference by the colorimeter is 1% or less. Therefore, the potential difference between the bias Vs of the toner supply roller 32 and the bias Vb of the developing roller 31 and the toner supply roller 3
The fog when the peripheral speed ratio of the developing roller 31 and the peripheral speed of the developing roller 31 are changed is measured by a colorimeter and the points under the condition showing the value of 1% of the color difference are plotted as a dotted line graph g2 in FIG.
The relationship between these conditions can be approximated as XY = 700. Therefore, the condition for satisfying the fog (color difference) of 1% or less is XY 700 (where X> 0, Y> 0).

Therefore, at a print speed of 173.9 mm / sec, 700 ≧ XY ≧ 350 (where X> 0, Y> 0)
That is, the graphs g1 and g1 in FIG.
In the shaded area surrounded by 2, the density from the leading edge to the trailing edge of the recording paper 27 is good, and printing without fog can be performed. This condition, for example, 150mm printing speed
When applied at less than / sec, good results can be obtained with respect to the density, but fogging occurs on printing, which is not preferable. Therefore, this condition is suitable when the printing speed is 150 mm / sec or more.

Also, the photosensitive drum 21 and the developing roller 31
Rotate so as to move in opposite directions, that is, in the same direction at the contact portions with each other. This peripheral speed ratio is
1 is determined. When the peripheral speed ratio between the developing roller 31 and the photosensitive drum 21 is small, the layer thickness of the toner adhering to the photosensitive drum 21 becomes thin, and the print density becomes low. Further, the developing roller 31 and the photosensitive drum 21
When the peripheral speed ratio is large, the layer thickness of the toner adhering to the photosensitive drum 21 becomes thick and the density on printing becomes good, but when the peripheral speed ratio is too large, the toner layer thickness becomes unnecessarily thick. Not only fogging occurs, but also friction due to rubbing between the photosensitive drum 21 and the developing roller 31 is promoted, which adversely affects the life. Therefore, it is necessary to select an optimum value for the peripheral speed ratio between the photosensitive drum 21 and the developing roller. That is, by rotating the developing roller 31 at a speed such that the peripheral speed of the photosensitive drum 21: the peripheral speed of the developing roller 31 is 1: 1.5 to 2.5, better printing is possible.

Table 1 shows the density and fog quality at a printing speed of 100 mm / sec and at a printing speed of 150 mm / sec or more. In this table, ○ is good, the density is 1.4 or more from the leading edge to the trailing edge of the recording paper, and the fog is the reflection between unprinted paper and solid white paper as measured by a colorimeter. This is the case when the difference between the rates is 1% or less. In addition, x is bad, and there is a portion where the density is lower than the Macbeth density 1.4 on the print, and a portion where the difference in the reflectance is greater than 1% as measured by a colorimeter with respect to fog.

[0030]

[Table 1]

However, even if the condition of 700 ≧ XY ≧ 350 is satisfied, the bias Vs
If the potential difference between the bias and the bias Vb of the developing roller 31 is too large, good printing cannot be performed. FIG. 4 shows the bias Vs of the toner supply roller 32 and the bias V of the developing roller 31.
b from the toner supply roller 32 to the developing roller 3
The relationship between the current values flowing into 1 is shown in a graph.

When the potential difference between the bias Vs of the toner supply roller 32 and the bias Vb of the development roller 31 exceeds AV, an excessive current accompanied by local discharge between the toner supply roller 32 and the development roller 31 is generated. Flowing and stripe-like shading occur in the print density. Therefore, the potential difference between the bias Vs of the toner supply roller 32 and the bias Vb of the developing roller 31 needs to be equal to or less than the discharge start voltage AV. In this embodiment, A = 500 V because discharge occurred when Vs-Vb was 500 V or more.

The range in which abnormal discharge starts varies depending on the developing device, especially the material of the developing roller, the material of the toner supply roller, the environment such as humidity, the condition of contact between the development roller and the toner supply roller, and the like. Actually, it must be determined by experiment. As described above, when the peripheral speed of the photosensitive drum 21, that is, the printing speed is 150 mm / sec or more, the developing roller 31 is moved to the peripheral speed of the photosensitive drum 21: the developing roller 3.
In the developing device that rotates so that the peripheral speed of 1 = 1: 1.5 to 2.5, the bias Vs of the toner supply roller 32 is
When the absolute value of the potential difference between the bias voltage Vb and the bias Vb of the developing roller 31 is X, and the peripheral speed of the toner supply roller 32 / the peripheral speed of the developing roller 31 is Y, 700 ≧ XY · 350, and the potential difference X Is not more than the discharge starting voltage, it is possible to print in a stable density state from the leading edge to the trailing edge of the recording paper 27, and it is possible to perform high-quality printing with good follow-up of density, no fogging on printing. Become. Also, there is no need to increase the size of the developing device.

The peripheral speed ratio between the toner supply roller 32 and the developing roller 31 also has an upper limit. If the peripheral speed ratio between the toner supply roller 32 and the developing roller 31 is too high, the developing roller 3
1 is increased, but at the same time, there are many chances of applying a charge by rubbing between the developing roller 31 and the toner supply roller 32, so that the specific charge (μC /
g) becomes abnormally high, and there is a possibility that a development history, fogging, etc. may occur on printing. The development history refers to a density difference caused by a difference in layer thickness on the development roller caused by printing, and is caused by the level of specific charge of the toner, and is particularly conspicuous in a halftone portion.

If the peripheral speed of the toner supply roller 32 is excessively increased, the developing roller 31 or the toner supply roller 32 is seriously damaged due to the rotation, and one or both of the two are worn, and in some cases, the damage is caused. Will cause. Considering these, the peripheral speed of the developing roller 31:
It is optimal that the peripheral speed of the toner supply roller 32 is about 1: 0.5 to 1.2. This value differs depending on the selection of the material of the developing roller 31 and the toner supply roller 32 and the contact condition between them. Also, since there is a difference in the allowance of the development history depending on the resolution and use of the device to be used, it is necessary to determine the tolerance by an experiment.

In the above-mentioned embodiment, the conductive urethane rubber is used for the developing roller. However, the present invention is not limited to this. A material having a resistance value of 10 ¹⁰ Ω · cm or less by dispersing conductive carbon particles, metal particles, metal fibers, or the like may be used. Further, the surface of these rubbers may be coated with a silicon resin, a urethane resin, a fluorine resin, or the like, or the surface of a semiconductor rubber roller may be provided with minute electrodes electrically insulated from each other.

Although a conductive urethane firm was used for the toner supply roller, the present invention is not limited to this. A silicone-based, NBR-based, ethylene-propylene-based or CR-based foamed elastic body may be used. Preferably, the foamed elastic body is impregnated with or mixed with conductive fine particles such as carbon to impart a conductivity in the range of 10 ⁷ to 10 ⁹ Ω · cm. Further, the toner layer thickness regulating member 33
Although an elastic body made of silicon rubber was used for the above, the present invention is not limited to this, and EPDM, urethane rubber, or the like may be used. Further, a styrene acrylic toner is used as the toner, but the present invention is not limited to this, and a polyester toner may be used. Further, although the pulverized toner is used, a spherical toner may be used.

In the above-described embodiment, the developing roller is set so that the peripheral speed of the photosensitive drum is equal to the peripheral speed of the developing roller.
The rotation is performed at a speed of 1.5 to 2.5, but is not necessarily limited to this.

[0039]

As described above, according to the first and second aspects of the present invention, for high-speed printing at a printing speed of 150 mm / sec or more, the density stability and the density tracking can be achieved without increasing the size of the apparatus. Development that maintains good properties.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an embodiment of the present invention.

FIG. 2 is a graph showing a relationship among a Macbeth density, a potential difference between a toner supply roller bias Vs and a development roller bias Vb, and a peripheral speed ratio between the toner supply roller and the development roller in the embodiment.

FIG. 3 is a graph showing a relationship among a Macbeth density, a potential difference between a toner supply roller bias Vs and a developing roller bias Vb, and a peripheral speed ratio between the toner supply roller and the developing roller in the embodiment.

FIG. 4 is a graph showing a relationship between a potential difference between a toner supply roller bias Vs and a development roller bias Vb and a current value flowing from the toner supply roller to the development roller in the embodiment.

FIG. 5 is a graph showing an optimum region in a relationship between a peripheral speed ratio between a toner supply roller and a developing roller and a potential difference between a toner supply roller bias Vs and a developing roller bias Vb in the embodiment.

FIG. 6 is a cross-sectional view illustrating an example of a conventional image forming apparatus.

FIG. 7 is a graph showing the relationship between the density and the potential difference between the developing roller bias Vb and the photosensitive member residual potential Vr when the printing speed is 8 ppm.

FIG. 8 is a graph showing the relationship between the density and the potential difference between the developing roller bias Vb and the photosensitive member residual potential Vr when the printing speed is 16 ppm.

FIG. 9 is a graph showing the relationship between the density and the density difference between the developing roller bias Vb and the photosensitive member residual potential Vr when the printing speed is 24 ppm.

FIG. 10 is a sectional view showing an example of a conventional developing device.

[Explanation of symbols]

 21: Photoconductor drum (electrostatic latent image holding rotating body) 25: Toner 26: Developing device 31: Developing roller (developer holding rotating body) 32: Toner supply roller (developer feeding rotating body)

Claims (2)

[Claims] 1. An electrostatic latent image holding rotating body is disposed so as to face and contact an electrostatic latent image holding rotating body, and moves in the same direction with respect to the electrostatic latent image holding rotating body at a contact portion with the electrostatic latent image holding rotating body. A developer holding rotator that rotates and rotates to supply a one-component non-magnetic developer to the electrostatic latent image holding rotator. A developer supply rotator that rotates at a contact portion so as to move in a direction opposite to the developer holding rotator and supplies the developer to the developer holding rotator. When the absolute value of the difference between the bias to the rotating body and the bias to the developer holding rotating body is X, and the peripheral speed of the developer supply rotating body / the peripheral speed of the developer holding rotating body is Y, 700 ≧ X · Y ≧ 350 (where X> 0, Y> 0) and X is A developing device having a discharge starting voltage or lower. 2. An electrostatic latent image holding rotating body is disposed so as to face and contact with the electrostatic latent image holding rotating body, and moves in the same direction with respect to the electrostatic latent image holding rotating body at a contact portion with the electrostatic latent image holding rotating body. A developer holding rotator that rotates and rotates to supply a one-component non-magnetic developer to the electrostatic latent image holding rotator. A developer supply rotator that rotates in a contact portion to move in a direction opposite to the developer holding rotator and supplies the developer to the developer holding rotator; When the peripheral speed of the rotator is 150 mm / sec or more, the developer holding rotator has a peripheral speed of the electrostatic latent image holding rotator: a peripheral speed of the developer holding rotator of 1: 1.5 to 2. 5, a bias to the developer supply rotating body and the developer holding rotation speed. When the absolute value of the difference from the bias to the body is X, and the peripheral speed of the developer supply rotating body / the peripheral speed of the developer holding rotating body is Y, 700 ≧ X · Y ≧ 350 (where X> 0, Y> 0), and X is equal to or lower than a discharge starting voltage.