JP3020641B2 - 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 use in an image forming apparatus such as an electrophotographic copying machine, a printer or a facsimile. The present invention relates to a developing device that performs development by transporting the developing unit to a developing unit facing an image carrier.

[0002]

2. Description of the Related Art In a developing device of this type, a developer carrier having a thin layer of developer formed on a surface thereof and an electrostatic latent image carrier are opposed to each other in a developing section. 2. Description of the Related Art There is known an image forming apparatus which forms an electric field capable of transferring a developer on a body to an electrostatic latent image carrier and develops the electrostatic latent image on the electrostatic latent image carrier. In this developing device, there is a threshold value for transferring the developer from the developer carrier to the electrostatic latent image carrier, and the developer adheres to an image portion having a surface potential exceeding the threshold value. On the other hand, since the developer hardly adheres to an image portion having a surface potential equal to or lower than the threshold value, there is a problem that an image having a so-called γ and poor gradation is formed. However, it is known that this problem can be solved by forming an alternating electric field having a relatively low frequency in the developing section (for example, see Japanese Patent Publication No. 64-1013).

However, simply applying a low-frequency alternating electric field to the developing section lowers the image density if the condition of the alternating electric field is such that the gradation property can be improved. However, there is a problem that the line portion of the image becomes thicker when the value is increased. Further, in this type of developing device, particularly when a non-magnetic toner is used as a developer, when a reciprocating motion of the non-magnetic toner is caused, the toner is turned into a powder cloud and the image density is significantly reduced. (See, for example, Japanese Patent Publication No. 2-14706). In recent years, along with diversification of output information of an image created by an image forming apparatus, higher image quality than ever has been desired.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art. It is an object of the present invention to improve the image density while maintaining the gradation and improve the image density. An object of the present invention is to provide a developing device which can also prevent thickening of the line portion, and thereby can obtain a high quality image.

[0005]

In order to achieve the above object, the present invention is directed to an electrostatic latent image carrier for carrying an electrostatic latent image and a developer carrier for carrying a developer. In a developing device which is opposed to the developing unit and applies a bias in the developing unit to perform development, a plurality of portions having different resistances are regularly or irregularly mixedly exposed on the surface, and at least the portions are compared. a developer carrying member having high resistance is a large number of minute closed electric fields on the surface is frictionally charged to a predetermined polarity is formed, the friction strip the exposed portion to a predetermined polarity
An intensity of 1 V / μm or more in a direction for causing the developer to flow toward the electrostatic latent image carrier between the frictional charging means for charging and the relatively high resistance member and the image portion of the electrostatic latent image carrier. And a voltage applying means for applying a voltage capable of alternately forming an electric field having a strength of 1 V / μm or more in a direction in which the developer is directed to the surface, wherein the developer is charged in the charged state.
What is carried on the developer carrier by the minute closed electric field
The movement of the developer is controlled by an electric field determined by a correlation between an electric potential on the electrostatic latent image carrier , an electric field formed by the voltage applying means, and an electric field on the developer carrier. It is characterized by the following. The invention according to claim 2 is that, in place of the developer carrier, a conductive portion having a conductive substrate exposed on the surface and a dielectric portion having a dielectric fixed on the substrate exposed on the surface are regularly or irregularly formed on the surface. irregularly with mixed, using a number of the developer carrying member to minute closed electric field is formed on the surface dielectric portion is charged to a predetermined polarity, instead of the voltage applying means, said dielectric portion An electric field having an intensity of 1 V / μm or more for causing the developer to face the electrostatic latent image carrier, and an electric field for causing the developer to face the surface. It is characterized by using a voltage applying means for applying a voltage capable of alternately forming an electric field having an intensity of 1 V / μm or more. The invention of claim 3 is claim 1
In place of the voltage application means described in the above, between the above-mentioned portion and a relatively low resistance and the non-image portion of the electrostatic latent image carrier,
1 V / μ in a direction in which a developer is directed to the electrostatic latent image carrier
m, and a voltage applying means for applying a voltage capable of alternately forming an electric field having an intensity of 1 V / μm or more in a direction in which the developer is directed to the surface. . According to a fourth aspect of the present invention, instead of the voltage applying means according to the second aspect, a developer is supplied to the electrostatic latent image carrier between the conductive portion and the non-image portion of the electrostatic latent image carrier. Voltage applying means for applying a voltage capable of alternately forming an electric field having an intensity of 1 V / μm or more in a direction in which the developer is turned and an electric field having an intensity of 1 V / μm or more in a direction in which the developer is turned on the surface. It is assumed that. According to a fifth aspect of the present invention, in place of the voltage applying means according to the first aspect, a developer is provided between the relatively high resistance member and the image portion of the electrostatic latent image carrier. An electric field having an intensity of 1 V / μm or more directed toward the carrier, and 1 V / μ directed toward the surface of the developer;
m or more and an electric field having an intensity of at least m, and the developer is applied between the non-image portion of the electrostatic latent image carrier and the above-described portion having relatively low resistance. A voltage application for applying a voltage capable of alternately forming an electric field having an intensity of 1 V / μm or more directed toward the latent image carrier and an electric field having an intensity of 1 V / μm or more directed toward the surface of the developer. It is characterized by using means. According to a sixth aspect of the present invention, instead of the voltage applying means according to the second aspect, a developer is supplied between the dielectric portion and the image portion of the electrostatic latent image carrier toward the electrostatic latent image carrier. An electric field having an intensity of 1 V / μm or more in a direction of turning over and an electric field having an intensity of 1 V / μm or more in a direction of turning a developer toward the surface can be formed alternately. An electric field having an intensity of 1 V / μm or more between the non-image portion of the body and the developer for directing the developer toward the electrostatic latent image carrier, and an electric field of 1 V / μm or more for directing the developer toward the surface. It is characterized by using voltage applying means for applying a voltage capable of alternately forming a strong electric field. According to a seventh aspect of the present invention, in the developing device of the first, second, third, fourth, fifth, or sixth aspect, the developing device is supported on the developer carrier.
Means for regulating the layer thickness of the developer conveyed to the
Provided, the frictional charging means is more developed than the layer thickness regulating means.
On the upstream side in the developer transport direction, and
It is characterized by being located on the downstream side in the feeding direction .

[0006]

According to the present invention, a large number of electric fields are formed on the surface of a developer carrying member for carrying a developer, and a voltage is applied to a developing section in which the developer carrying member and the electrostatic latent image carrying member are opposed to each other. Means for forming an electric field, and developing by an electric field determined by a correlation between the electric potential on the electrostatic latent image carrier, the electric potential on the developer carrier, and the electric field formed by the voltage applying means. The movement of the developer is controlled, so that an appropriate amount of the developer is attached to the electrostatic latent image on the electrostatic latent image carrier. Then, by forming a predetermined electric field in the developing section by the above-described voltage applying means, an image having high density, excellent gradation, and no thick line portion can be formed particularly favorably.

[0007]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a diagram showing an entire configuration of a developing device according to an embodiment of the present invention. The casing of the developing device 2 is provided with an opening for development at a portion opposed to the photosensitive drum 3, and the developing roller 1 is held in the casing with a predetermined gap between the photosensitive drum 3 through this opening. It is provided rotatably. Around the developing roller 1, a blade member 4 for regulating the thickness of the toner layer carried and conveyed by the roller 1 is provided so as to resiliently press the roller 1 above the roller 1. The thickness of the toner 7 supplied from the toner tank 5 formed in accordance with the rotation of the agitator 6 and the toner supply roller 8 is regulated. Instead of the blade member 4, a regulating roller or a regulating belt may be used. The agitator 6 rotates clockwise as indicated by the arrow, and agitates the toner 7 with the resistance of the tip thereof and moves the toner 7 to the left in the figure. The toner supply roller 8 is made of a sponge material made by foaming urethane rubber, or a brush made of polyester, tetrafluoroethylene resin or the like as a fiber. The toner supply roller 8 includes an agitator 6
Rubbing the surface of the developing roller 1 in the forward or reverse direction with the toner 7 conveyed by
This function scrapes the toner 7 remaining on the developing roller 1 without being used for development and returning. The toner 7 supplied to the surface of the developing roller 1 by the toner supply roller 8 is also charged by the frictional charging action generated by mutual friction with the toner supply roller 8 or the developing roller 1, and the toner 7 itself is charged on the surface of the developing roller 1. It is carried electrostatically. Thus, the thickness of the toner 7 carried and transported by the developing roller 1 is regulated by the blade member 4 which resiliently presses above the developing roller 1, and is transported to the developing section where the photosensitive drum 3 and the developing roller 1 are opposed to each other. Is done. The blade member 4 may be manufactured by attaching a material having a toner charging property such as urethane rubber to an elastic leaf spring, or may use an elastic member as it is. The blade member 4 may be provided in the trailing direction as shown in the drawing with respect to the rotation direction of the developing roller 1, or may be provided in the leading direction opposite to the rotating direction. A developing bias applying unit 9 is connected to the developing roller 1 and the toner supply roller 8. Further, the voltage applying means 9 may be connected to the blade member 4. In developing the electrostatic latent image formed on the photosensitive drum 3, a required amount of toner 7 is transferred from the developing roller 1 to the electrostatic latent image according to the electrostatic latent image while applying a bias voltage to the developing roller 1. This is done by letting The developing roller 1 has a positional relationship of 30 to 500 μm which does not substantially contact the photosensitive drum 3,
Preferably, they are arranged with a gap of 50 to 250 μm. As a result, an excessive load such as when the developing roller 1 is brought into contact with the photosensitive drum 3 to develop an electrostatic latent image is not required, and the drive motor can be made smaller. If the peripheral speed of the photosensitive drum 3 is substantially equal to the peripheral speed of the developing roller 1, the driving torque can be further reduced. As a developing bias by the developing bias applying means 9, an AC electric field can be used in combination with a DC electric field. As an alternating electric field,
The square-wave pulse electric field is applied to a low frequency of 300-2.
000 Hz, preferably in the range of 500 to 1500 Hz, and using a waveform having a different ratio of the time of the high voltage portion and the time of the low voltage portion to the time of one cycle, the low voltage portion can be sharpened. Good nature,
It is possible to obtain an excellent developed image having a high image density in a high voltage portion and a less background stain. The ratio (duty ratio) between the time of the high voltage portion and the time of the low voltage portion varies depending on the polarity of the electrostatic latent image and the polarity of the toner 7. Is developed with the negative polarity toner 7, the high voltage portion (−100V
Above) and the time of the low-voltage section (-800 V or less) may be 5-18: 2-8. In the case of normal development, if this ratio is generally reversed, an excellent developed image can be obtained in which similar low-potential portions have good sharpness, high-potential portions have high image density, and less background smear.

In this embodiment, the surface of the developing roller 1 is constituted by a finely divided conductive region surface and an insulating region surface. FIG. 2A shows the appearance of an example of such a developing roller 1. FIG. 2B is an enlarged sectional view of the surface portion. The developing roller 1 is made of a plurality of materials having different resistances or dielectric constants. FIG. 2 (a),
In the example shown in (b), a conductive material, for example, a metal material such as aluminum, a conductive rubber or a conductive plastic 2 is used.
1 Roller surface knurled on the surface of the roller, polycarbonate, acrylic, polyester,
A dielectric resin such as ethylene tetrafluoride is rubbed in and filled.
A fine mesh-shaped insulating region surface 22 is formed, and a fine conductive region surface 21 is formed in contact with the fine mesh-shaped insulating region surface 22. The method for forming the fine conductive region surface 21 and the insulating region surface 22 is not limited to the above example, and various methods can be adopted. The size of the insulating region is 3 as an average diameter.
It is 0 to 2000 μm, preferably 50 to 1000 μm. When the shape of the insulating region surface 22 is, for example, circular, the diameter D1 (see FIG. 3) is 30 to 2000 μm,
Preferably, it is set to about 100 to 400 μm, and the center distance P1 is appropriately set in a well-balanced manner. When the shape of the insulating region surface 22 is rectangular, the length of the shortest side is about 30 to 2000 μm. Similarly, when the shape of the insulating region surface 22 is an ellipse or an ellipse, the width on the minor axis side is about 30 to 2000 μm. Even when the shape of the insulating region surface 22 is another shape, the width is set to about 30 to 2000 μm according to these. The occupied area ratio may be 50 to 80%, preferably 65 to 75% of the surface area of the developing roller 1. With the structure of the developing roller 1, a sufficient amount of toner is charged on the surface of the developing roller 1 by charging the toner 7 by a frictional charging effect generated when the toner 7 is rubbed against the developing roller 1 by the toner supply roller 8. 7 can be carried.

This point will be described in more detail. The insulating region surface 22 of the developing roller 1 is charged to a positive polarity opposite to the charging polarity of the toner 7 by friction with the toner supply roller 6. On the other hand, the toner 7 conveyed to the developing roller 1 while being in contact with the peripheral surface of the toner supply roller 8 is
Is negatively charged by friction with the developing roller 1
At this time, the toner is further frictionally charged to the negative polarity by friction with the developing roller 1, particularly its insulating region surface 22, and is electrostatically attached to the peripheral surface of the developing roller 1. At this time, each insulating region surface 22 of the developing roller 1 is frictionally charged to a positive polarity, and the conductive region surface 21 is in contact with each insulating region surface 22. The positive charge is selectively applied only to the insulating region surface 22 of FIG. As a result, as shown in FIG. 3, a closed electric field is formed between each positively charged insulating region surface 22 and the conductive region surface 21 in contact therewith, and countless minute electric fields are formed near the surface of the developing roller 1. A closed electric field (microfield) is formed. That is, when considering the lines of electric force indicating the state of the electric field, the space near the surface of the developing roller 1 exits from the developing roller 1 as shown by a number of arc-shaped lines in FIG. 1 is formed, and a closed electric field is formed between each insulating region surface 22 and the conductive region surface 21. Since the area of each insulating region surface 22 is minute as described above, the intensity of each closed electric field is greatly increased by the fringing effect (peripheral electric field effect). Due to such a closed electric field, the negatively charged toner 7 is strongly attracted to the insulating area surface 22 and is held on the roller 1 in a state where it is hard to separate. Further, when the layer thickness of the toner 7 held on the developing roller 1 is regulated by the blade member 4, the toner 7 having a sufficient charge is strongly held on the surface of the developing roller 1 by the minute closed electric field. The small toner 7 is removed by the contact pressure with the blade member 4, so that only the toner 7 having a large charge amount, for example, the toner 7 charged to about 5 to 20 (preferably 10 to 15) μC / g, is developed. It is carried to the gap 9.

In the developing device 2, since the conductive area surface 21 and the insulating area surface 22 are mixed on the surface of the developing roller 1, charge-up of the developing roller 1 and the toner supply roller 8 is prevented. Is done. The reason is that
The toner is charged on the insulating region surface 22 and the conductive region surface 2
In No. 1, it is considered that the charge of the toner supply roller is removed, and a well-balanced charged state is maintained as a whole. Here, a rectangular wave pulse electric field applied as a developing bias acts on a minute electric field between the conductive area surface 21 and the insulating area surface 22 existing on the surface of the developing roller 1 and the charged toner to act on the electrostatic latent image. It is believed that this provides suitable mechanical energy for development.

Hereinafter, more specific embodiments of the present invention will be described. 4A, 4B, and 4C show examples in which the conductive region surface 21 and the insulating region surface 22 are formed on the surface of the developing roller 1 by knurling, respectively. In these examples, the pitch P of the knurl is 0.3 mm
And the width W of the insulating region surface 22 is W1 = 0.07, respectively.
5 mm, W2 = 0.15 mm, and W3 = 0.225 mm, and the surface of the developing roller 1 is configured so that the insulating region surface 22 and the conductive region surface 21 coexist. These developing rollers 1 were used in Examples described later.

First, a first embodiment will be described. In this embodiment, an OPC is used as the photosensitive drum 3, the surface potential of the background portion is -900V, the potential of the exposed portion is -100V, and the developing roller 1 having the surface shape shown in FIG.
Are arranged opposite to the surface of the photosensitive drum 3 with a gap of 100 μm and reverse development is performed. The insulating region surface 22 on the surface of the developing roller 1 is
, So that about 1.0 to 1.2 mg / cm ² of the negatively charged toner 7 was carried. Then, a peak-to-peak 1000 V, a maximum potential 0 V, and a frequency 5
A pulse voltage of 00 Hz and a duty ratio of 30% (T ₂ / T ₁ ) was applied.

FIGS. 5A and 5B show the change over time of the surface potential of the developing roller 1 with respect to the ground. FIG. 5A shows the surface potential of the insulating region surface 22, and FIG. 5B shows the conductive region surface. 21 shows the surface potential. In these figures, the surface potential level (−900 V) of the background portion of the photosensitive drum 3 and the surface potential level (−10 V) of the exposed portion are shown.
0V) are shown as horizontal lines. As can be seen from the continuous rectangular line showing the change over time in the surface potential of the insulating region surface 22 in FIG.
The potential applied by the developing bias applying means 9 becomes a potential deviated by +200 V with the retained charge. On the other hand, the surface potential of the conductive region surface 21 is equal to that of the region surface 2 in FIG.
As can be seen from the continuous rectangular line showing the temporal change of the surface potential of No. 1, the applied voltage itself by the developing bias applying means 9 is obtained.

Next, an electric field between the surface of the developing roller 1 and the photosensitive drum 3 when the potential of the surface of the developing roller 1 changes as described above will be described. This electric field is applied to the developing roller 1
Depending on whether the surface is on the insulating region surface 22 or the conductive region surface 21, the respective region surfaces 22, 22 are further opposed to either the image portion or the background portion of the photosensitive drum 3. It depends on what

FIG. 6 is a view for explaining an electric field on the conductive region surface 21 which causes a temporal change in the surface potential as shown in FIG. 5 (b), and FIG. FIG. 6 shows a temporal change of a potential difference between the area surface 21 and the image portion (exposure portion) of the photosensitive drum 3 when the region surface 21 faces the image portion.
(B) shows a temporal change of a potential difference between the area surface 21 and the non-image portion (unexposed portion) of the photosensitive drum 3 when the surface 21 faces the non-image portion. FIG. 7 is a view for explaining an electric field on the insulating region surface 22 which causes a temporal change in the surface potential as shown in FIG. 5A. FIG.
7 shows a temporal change of the potential difference between the photosensitive drum 3 and the image portion (exposure portion) of the photosensitive drum 3, and FIG. 5 shows a temporal change in a potential difference between the two when the light-receiving portion is opposed to an unexposed portion).

In these figures, since the electric field exerts an electrostatic force on the toner 7 carried on the surface of the developing roller 1 or the toner 7 carried on the surface of the photosensitive drum 3, the direction of the electrostatic force is The potential difference corresponding to the electric field in the direction of the toner 7 toward the photosensitive drum 3 is expressed as positive, and the electric potential difference corresponding to the electric field in the direction toward the developing roller 1 is expressed as negative. Also, the level of the above-mentioned potential difference threshold +100 V at which the toner 7 on the developing roller 1 transfers to the photosensitive drum 3 and the electric field at which the toner 7 on the photosensitive drum 3 transfers to the developing roller 1 have been confirmed by experiments. And the level of −100 V are indicated by horizontal lines, and portions corresponding to electric fields exceeding the threshold and contributing to the transfer of the toner 7 are indicated by oblique lines.

In the above experiment, a DC voltage was applied to the developing roller 1 with the gap between the developing roller 1 and the photosensitive drum 3 being 100 μm, and the transfer of toner was observed while changing the value of the DC voltage. It is. In this example, it was found that the threshold value of the developing electric field was 1 V / μm. The charge amount of the toner 7 used at this time was examined to be about 10 μC /
g.

When the toner 7 present on the conductive area surface 21 of the developing roller 1 is opposed to the image portion of the photosensitive drum 3, the toner 7 is +900 as shown by the hatched portion in FIG.
It is considered that when a developing electric field corresponding to a potential difference of V (hereinafter, referred to as a developing electric field) is applied, the transfer is made in the direction of the photosensitive drum 3. -900 as indicated by the hatched portion in FIG.
It is considered that the transition to the direction of the developing roller 1 occurs when the developing electric field reaches V.

Similarly, the insulating region surface 22 of the developing roller 1
Since the insulating region surface 22 of the toner 7 existing above is charged to +200 V from the beginning, when the toner 7 is opposed to the image portion of the photosensitive drum 3, as shown by the hatched portion in FIG. A negative electric field of -300 V and a positive electric field of +700 V appear alternately. When the electric field is positive, the toner is transferred from the developing roller 1 to the photosensitive drum 3, and when the electric field is negative, the toner is transferred from the photosensitive drum 3 to the developing roller 1. it is conceivable that. When the photosensitive drum 3 is opposed to the non-image portion, as shown by a hatched portion in FIG. 7B, the photosensitive drum 3 is transferred from the photosensitive drum 3 to the developing roller 1 by a negative electric field of -1100 V, and alternately. It is not considered to transfer to.

As described above, the transfer of the toner 7 carried on the developing roller 1 is selectively controlled by the electric field formed on the surface of the developing roller 1. The image obtained in this manner is applied to a developing roller 1 whose surface is all aluminum.
As a result, when compared with an image developed only with a developing electric field as shown in FIGS. 6A and 6B, an image having a high density without background contamination was obtained, and the reproducibility of the diagram was excellent. I was Further, an attempt was made to obtain the same reproducibility of the diagram as in this embodiment using a developing roller whose surface is entirely made of aluminum, but the image density was reduced.

According to the present embodiment, a region where a different developing bias acts locally is provided on the surface of the developing roller 1, and therefore, the photosensitive drum 3 having an electrostatic latent image and the toner are carried on the surface. When the developing is performed by applying a bias between the developing roller 1 and the developing roller 1, the transfer of the toner can be selectively controlled by the developing roller 1 having the electric charges selectively held on the surface. Is considered to be possible. That is, as shown in FIG. 7A, a positive and negative electric field exceeding the threshold acts on the toner 7 existing on the insulating region surface 22 as shown in FIG. 7A, and excessive toner adhesion is suppressed. On the other hand, the electric field of the toner existing on the conductive area surface 21 is changed as shown in FIG.
Has a higher developing capability than the insulating region surface 22. Further, since this portion is conductive, it acts to suppress the edge effect and make the image density uniform.

More specifically, although the image density is low, the reproducibility and gradation of the diagram are excellent, but if the density is increased as it is, the reproducibility and gradation of the diagram are impaired. The characteristics of the developing roller, whose surface is insulated, and its electrode effect make it possible to obtain a high density image with excellent uniformity of the solid part, but the surface is poor in the reproducibility of the diagram and the gradation. The developing roller 3 according to this embodiment has the features of the conductive developing roller at the same time. According to the applied bias, the toner on the insulating area surface 22 of the developing roller 1 is transferred from the developing roller 1 to the photosensitive member 1 and the toner is transferred from the photosensitive member 3 to the developing roller with respect to the image area on the photosensitive member. It is considered that since the transition to 1 (reverse transition) is performed, the image density can be improved while the gradation is maintained, and the thickening of the line portion of the image can be prevented, so that a high-quality image can be obtained. Can be

Next, the developing roller 1 and the photosensitive drum 3
The transfer of the toner 7 was examined by setting the gap to 200 μm, and it was found that the transfer of the toner 7 occurred when the developing electric field exceeded 200 V. That is, it was found that the threshold value of the developing electric field was constant at 1 V / μm. When the test was conducted with the developing gap further widened, it was possible to produce an image up to about 500 μm while changing the bias voltage together. However, it is preferable that the thickness be within 300 μm in order to withstand practical use. In addition, at 300 μm, when a PP pulse voltage exceeding 4500 V was applied as a developing bias, leakage occurred between the developing roller 1 and the photosensitive drum 3. That is, it is necessary to set the electric field to 15 V / μm or less.

The width W of the insulating region surface 22 on the surface of the developing roller 1 is small. For example, the developing roller 1 shown in FIG.
Can be prevented from appearing in the image. When the width of the insulating region surface 22 is equal to or larger than the width of the conductive region surface 21, the photosensitive drum 3 may be moved at substantially the same speed or at a slightly higher speed. In any case, good results could be obtained in the range of 1.0 to 2.0 times, preferably 1.0 to 1.2 times.

In the above embodiment, the insulating area surface 22 is charged to the opposite polarity to the toner, but the material of the surface of the toner supply roller 8 and the material of the insulating area surface 21 are selected in consideration of the charging sequence. Then, the insulating region surface 22 may be charged to the same polarity as the toner. Also in this case, a minute electric field is formed by a potential difference between the conductive region surface 21 and the insulating region surface 22, and the toner can be attracted and carried by an edge effect or a peripheral electric field effect due to the minute electric field. Also in this case, the toner on the insulating region surface 22 is transferred from the developing roller 1 to the photosensitive member 1 and from the photosensitive member 3 to the developing roller 1 in consideration of the potential due to the charging of the insulating region surface 22. The applied bias is set so as to perform (reverse transition).

Next, a second embodiment will be described. In this embodiment, instead of the applied bias in the first embodiment,
900V peak-to-peak, maximum potential minus 20
0 V, frequency 500 Hz, duty ratio 30% (T ₂
/ T ₁ ). The other points are the same as in the first embodiment.

FIGS. 8A and 8B show the change over time of the surface potential of the developing roller 1 with respect to the ground, similarly to FIG. 5 for the first embodiment. FIG. (B) shows the surface potential of the conductive region surface 21. In these figures, the surface potential level (-900 V) of the non-image portion on the surface of the photosensitive drum 3 is shown.
And the level (-100 V) of the surface potential of the image portion is shown as a horizontal line. Insulating region surface 2 in FIG.
As can be seen from the continuous rectangular line showing the temporal change of the surface potential of No. 2, the surface potential of the insulating region surface 22 is a potential deviated by +200 V with the charge held by the voltage applied by the developing bias applying means 9. On the other hand, the surface potential of the conductive region surface 21 is, as can be seen from the sine wave continuous line indicating the temporal change of the surface potential of this region surface 21 in FIG. become.

Next, the electric field between the surface of the developing roller 1 and the photosensitive drum 3 when the potential of the surface of the developing roller 1 changes as described above will be described. As in the first embodiment, the electric field further depends on whether the surface of the developing roller 1 is on the insulating region surface 22 or on the conductive region surface 21, and furthermore, the photosensitive member for each of the region surfaces 22 and 21. It differs depending on which of the image section and the non-image section of the drum 3 faces.
FIG. 9 is a view for explaining an electric field on the conductive region surface 21 which causes a temporal change of the surface potential as shown in FIG. 8B, and FIG. FIG. 9B shows a temporal change of a potential difference between the photosensitive drum 3 and the non-image part (see FIG. 9B). 5 shows a temporal change in a potential difference between the two when the light-receiving portion is opposed to an unexposed portion).
10A and 10B are diagrams for explaining an electric field on the insulating region surface 22 that causes a temporal change in the surface potential as shown in FIG. 8A. FIG. FIG. 10B shows a temporal change in the potential difference between the photosensitive drum 3 and the image portion (exposed portion) when the photosensitive drum 3 faces the image portion (exposed portion). 2 shows a temporal change in the potential difference between the two when the electric field is opposed to the part (2).

In these figures, since the electric field exerts an electrostatic force on the toner 7 carried on the surface of the developing roller 1 or the toner 7 carried on the surface of the photosensitive drum 3, the first embodiment is described. 6 and 7, the potential difference corresponding to the electric field in the direction in which the toner 7 moves toward the photosensitive drum 3 is changed to a positive electric field in the direction toward the developing roller 1 in order to distinguish the direction of the electrostatic force. The corresponding potential difference is represented as negative. Further, the threshold value of the potential difference at which the toner 7 on the developing roller 1 is transferred to the photosensitive drum 3 was confirmed by an experiment similar to that of the first embodiment.
The level of 100 V and the threshold value of the electric field at which the toner 7 on the photosensitive drum 3 is transferred to the developing roller 1 minus 100 V are indicated by horizontal lines.
The portion corresponding to the electric field contributing to the transition of the is represented by hatching. Also in this example, the threshold value of the developing electric field was 1 V / μm.

When the toner 7 present on the conductive area surface 21 of the developing roller 1 is opposed to the image area of the photosensitive drum 3, as shown by a hatched portion in FIG.
When a positive electric field of 0 V is applied, it is considered that the transfer is made in the direction of the photosensitive drum 3. When the electric field is opposed to the non-image portion of the photosensitive drum 3, as shown by a hatched portion in FIG. A negative electric field of -700 V and a positive electric field of +200 V appear alternately as electric fields contributing to toner transfer. When the electric field is positive, the developing roller 1 moves to the photosensitive drum 3. Although the transfer to the roller 1 occurs, the period during which the transfer from the photosensitive drum 3 to the developing roller 1 occurs due to the negative electric field is sufficiently longer and the transfer force is large.
It is considered that even if the toner 7 transferred to the photosensitive drum by the positive electric field occurs, the toner 7 is transferred to the developing roller 1 again.

Similarly, the insulating region surface 22 of the developing roller 1
When the toner 7 present above faces the image portion of the photosensitive drum 3, when the positive electric field of +800 V is applied as shown by the hatched portion in FIG. The transfer to the body drum 3 is made,
Is originally charged to +200 V, the transfer force is considered to be smaller than that of the toner 7 existing on the conductive positive area surface 21 described above. When the photoconductive drum 3 is opposed to the non-image portion, as shown by the hatched portion in FIG. 10B, only a negative electric field of -900 V appears as an electric field contributing to toner transfer. It is not considered to transfer to.

As described above, the transfer of the toner 7 carried on the developing roller 1 is selectively controlled by the electric field formed on the surface of the developing roller 1. Also in this example, compared to the case where the same sine wave voltage is applied to the developing roller 1,
An image with high density was obtained without background contamination, and the reproducibility of the diagram was excellent. Also in this example, since the conductive region surface 21 and the insulating region surface 22 are mixed on the surface of the developing roller, the above-described effect is obtained. Since the toner on the conductive area surface 21 transfers from the developing roller 5 to the photoreceptor 1 and from the photoreceptor 1 to the developing roller 5, it is possible to improve the image density while maintaining the gradation and improve the image density. It is considered that thickening of the part can be prevented and a high quality image can be obtained. In this embodiment, the insulating region surface 2
2 may be charged to the same polarity as the toner.

Next, a third embodiment will be described. In this embodiment, instead of the applied bias in the first embodiment,
Peak-to-peak 1000V, maximum potential minus 1
00V, frequency 500Hz, duty ratio 30% (T
₂ / T ₁ ). The other points are the same as in the first embodiment.

FIG. 11 shows the change over time of the surface potential of the developing roller 1 with respect to the ground, similarly to FIG. 5 for the first embodiment.
(B) shows the surface potential of the conductive region surface 21. In these figures, the surface potential level (−900) of the non-image portion on the surface of the photosensitive drum 3 is shown.
V) and the level of the surface potential of the image portion (−100 V) are shown as horizontal lines, respectively. 11A, the surface potential of the insulating region surface 22 is maintained by the voltage applied by the developing bias applying unit 9, as can be seen from the continuous rectangular line showing the temporal change of the surface potential of the insulating region surface 22 in FIG. +20 in charge
The potential is shifted by 0V. On the other hand, the conductive region surface 2
The surface potential 1 is the voltage applied by the developing bias applying means 9 itself, as can be seen from the continuous sinusoidal line showing the temporal change of the surface potential of the area surface 21 in FIG.

Next, an electric field between the surface of the developing roller 1 and the photosensitive drum 3 when the potential of the surface of the developing roller 1 changes as described above will be described. As in the first embodiment, the electric field further depends on whether the surface of the developing roller 1 is on the insulating region surface 22 or on the conductive region surface 21, and furthermore, the photosensitive member for each of the region surfaces 22 and 21. It differs depending on which of the image section and the non-image section of the drum 3 faces.
FIG. 12 is a view for explaining an electric field on the conductive region surface 21 which causes a temporal change of the surface potential as shown in FIG. 11B, and FIG. 12A shows this region surface. FIG. 12 shows a temporal change of the potential difference between the photosensitive drum 3 and the photosensitive drum 3 when the photosensitive drum 21 faces the image portion (exposed portion) of the photosensitive drum 3.
(B) shows a temporal change of a potential difference between the area surface 21 and the non-image portion (unexposed portion) of the photosensitive drum 3 when the surface 21 faces the non-image portion. 13A and 13B are diagrams for explaining an electric field on the insulating region surface 22 that causes a temporal change in the surface potential as shown in FIG. 11A, and FIG. FIG. 13 shows a temporal change of the potential difference between the photosensitive drum 3 and the image portion (exposure portion) when the photosensitive drum 3 is opposed to the image portion (exposure portion).
(B) shows a temporal change in the potential difference between the region surface 22 and the non-image portion (unexposed portion) of the photosensitive drum 3 when the region surface 22 faces the non-image portion.

In these figures, similarly to FIGS. 6 and 7 according to the first embodiment, the potential difference corresponding to the electric field in the direction in which the toner 7 moves toward the photosensitive drum 3 is positive, and the potential difference is moving toward the developing roller 1. The potential difference corresponding to the electric field in the direction is expressed as negative. Also, the level of the above-mentioned potential difference + 100V at which the toner 7 on the developing roller 1 transfers to the photosensitive drum 3 and the toner 7 on the photosensitive drum 3 were developed by the same experiment as in the first embodiment. The threshold value of the electric field transferred to the roller 1 and the level of −100 V are indicated by a horizontal line, and a portion corresponding to the electric field exceeding the threshold value and contributing to the transfer of the toner 7 is indicated by oblique lines. Also in this example, the threshold value of the developing electric field was 1 V / μm.

When the toner 7 present on the conductive area 21 of the developing roller 1 is opposed to the image area of the photosensitive drum 3, as shown by the hatched portion in FIG.
When a positive electric field of 00 V is applied, the transfer is considered to be in the direction of the photosensitive drum 3, and when the electric field is opposed to the non-image portion of the photosensitive drum 3, as shown by the hatched portion in FIG. As an electric field contributing to toner transfer, a negative electric field of -800 V and a positive electric field of +200 V appear alternately. When the electric field is positive, the developing roller 1 moves to the photosensitive drum 3. Although the toner is transferred to the roller 1, the period during which the transfer from the photosensitive drum 3 to the developing roller 1 is caused by the negative electric field is sufficiently longer and the transfer force is large. It is considered that the transfer to the developing roller 1 occurs again even if the image occurs.

Similarly, the insulating region surface 22 of the developing roller 1
When the toner 7 present above faces the image portion of the photosensitive drum 3, as shown by the hatched portion in FIG. 13A, the positive electric field of +800 V and the negative electric field contribute to the toner transfer. A negative electric field of 200 V appears alternately. When the electric field is positive, the transfer from the developing roller 1 to the photosensitive drum 3 is performed, and when the electric field is negative, the transfer from the photosensitive drum 3 to the developing roller 1 is performed. Since the period during which the transfer to the body drum 3 occurs is sufficiently longer and the transfer force is large, it is considered that sufficient toner is transferred from the developing roller 1 to the photosensitive drum 3 by the positive electric field. When the photoconductive drum 3 is opposed to the non-image area, as shown by the hatched area in FIG. 13B, only a negative electric field of -1000 V appears as an electric field contributing to toner transfer. It is not considered to transfer to.

As described above, the transfer of the toner 7 carried on the developing roller 1 is selectively controlled by the electric field formed on the surface of the developing roller 1. Also in this example, compared to the case where the developing roller 1 whose surface is entirely made of aluminum and the same pulse voltage is applied to the developing roller 1, a high-density image without background contamination is obtained, and the diagram is reproduced. The nature was also excellent. Further, in this example, more excellent results were obtained than in the above-described first and second embodiments.
Also in this example, since the conductive region surface 21 and the insulating region surface 22 are mixed on the surface of the developing roller, the above effect can be obtained.
2 transfer from the developing roller 1 to the photoconductor 1 and from the photoconductor 3 to the developing roller 1, and the toner on the conductive area surface 21 with respect to the non-image area on the photoconductor Performs the transfer from the developing roller 5 to the photoconductor 1 and the transfer from the photoconductor 1 to the developing roller 5, so that it is possible to improve the image density while maintaining the gradation and prevent the line portion of the image from being thickened. It is considered that a high quality image can be obtained. In this embodiment and in this embodiment, the insulating region surface 22 may be charged to the same polarity as the toner. Also in this case, the toner on the insulating region surface 22 is transferred from the developing roller 1 to the photosensitive member 1 and from the photosensitive member 3 to the developing roller 1 in consideration of the potential due to the charging of the insulating region surface 22. The applied bias is set so as to perform (reverse transition).

The first, second, and third embodiments described above use the developing roller 1 having the surface shape shown in FIG. 4B, and FIG. 4A and FIG. The developing roller 1 having the surface shape shown in FIG.
When an experiment was performed by applying the sine wave AC voltage of the example, an image having a high density without background contamination was obtained, and an image having excellent line diagram reproducibility was obtained.

Further, in each of the above embodiments, it was found that the contamination by the toner 7 around the developing portion was smaller than that of the conventional developing roller 1. That is, in addition to improving the image quality, it is possible to obtain an effect that contamination by the toner 7 around the apparatus can be reduced.

[0042]

According to the present invention, the electric field is determined by the electric field determined by the correlation between the electric potential on the electrostatic latent image carrier, the electric potential on the developer carrier, and the electric field formed by the voltage applying means. The transfer of the developer is controlled, and this allows an appropriate amount of developer to adhere to the electrostatic latent image on the electrostatic latent image carrier, resulting in a high image density and excellent line diagram reproducibility and gradation. There is an excellent effect that a developed image can be obtained. Further, if the developer is carried on the developer carrying member by the minute electric field, a larger amount of the developer is carried by the edge effect or the peripheral electric field effect due to the minute electric field as compared with the related art, thereby further increasing the image density. Can be improved.

[Brief description of the drawings]

FIG. 1 is a side sectional view schematically showing an entire developing device according to an embodiment of the present invention.

FIG. 2A is a perspective view showing an appearance of an example of the developing roller, and FIG. 2B is an enlarged sectional view of an outer layer portion thereof.

FIG. 3 is an explanatory diagram showing electric lines of force of a minute closed electric field formed near the surface of an insulating region.

FIGS. 4A to 4C are diagrams illustrating an enlarged view of the surfaces of three developing rollers having insulating region surfaces having different widths from each other.

FIGS. 5A and 5B show a change over time in the surface potential of the developing roller in the first embodiment, where FIG. 5A shows a change in potential on an insulating region surface, and FIG. It shows a change in potential.

6A and 6B are explanatory diagrams of a developing electric field on a conductive region surface in the embodiment, where FIG. 6A shows a temporal change when facing an image portion on a photosensitive drum, and FIG. 6B shows a photosensitive drum. It shows a temporal change when facing the upper non-image portion.

FIGS. 7A and 7B are explanatory diagrams of a developing electric field on an insulating region surface in the embodiment, where FIG. 7A shows a temporal change when facing an image portion on a photoconductor, and FIG. It shows a temporal change when facing a non-image portion.

FIGS. 8A and 8B show the change over time in the surface potential of the developing roller in the second embodiment, where FIG. 8A shows the change in potential on the insulating region surface and FIG. It shows a change in potential.

9A and 9B are explanatory diagrams of a developing electric field on a conductive region surface in the embodiment, where FIG. 9A shows a temporal change when facing an image area on a photosensitive drum, and FIG. 9B shows a photosensitive drum. It shows a temporal change when facing the upper non-image portion.

FIGS. 10A and 10B are explanatory diagrams of a developing electric field on an insulating region surface in the same example, where FIG. 10A shows a temporal change when facing an image portion on a photoconductor, and FIG. It shows a temporal change when facing a non-image portion.

FIGS. 11A and 11B show a change over time in a surface potential of a developing roller in a third embodiment, where FIG. 11A shows a change in potential on an insulating region surface and FIG. It shows a change in potential.

12A and 12B are explanatory diagrams of a developing electric field on a conductive region surface in the embodiment, where FIG. 12A shows a temporal change when facing an image portion on a photosensitive drum, and FIG. 12B shows a photosensitive drum. It shows a temporal change when facing the upper non-image portion.

13A and 13B are explanatory diagrams of a developing electric field on an insulating region surface in the same example, where FIG. 13A shows a temporal change when facing an image area on a photoconductor, and FIG. It shows a temporal change when facing a non-image portion.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Development roller, 2 Developing device 3 Photoconductor drum, 4 Blade member 5 Toner tank, 6 Agitator 7 Toner, 8 Toner supply roller 9 Developing bias applying means, 21 Conductive area surface 22 Insulating area surface

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yuichi Ueno 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (72) Inventor Junko Tomita 1-3-6 Nakamagome, Ota-ku, Tokyo (56) References JP-A-2-214874 (JP, A) JP-A-60-61774 (JP, A) JP-A 1-267566 (JP, A) (58) Fields investigated ( Int.Cl. ⁷ , DB name) G03G 15/08

Claims (7)

(57) [Claims] A developing device for carrying out development by applying a bias in the developing unit such that an electrostatic latent image carrier for carrying an electrostatic latent image and a developer carrier for carrying a developer are opposed to each other in a developing unit; In the method, a plurality of portions having different resistances are regularly or irregularly mixedly exposed on the surface, and at least the portions having relatively high resistance are triboelectrically charged to a predetermined polarity and a large number of minute a developer carrying member closed electric field is formed, the frictional charging means for frictionally charging the exposed portion to a predetermined polarity
And between the relatively high resistance member and the image portion of the electrostatic latent image carrier, one direction in which the developer is directed to the electrostatic latent image carrier.
And the electric field V / [mu] m or more strength, developer is provided and a voltage application means for applying voltage capable of forming the electric field alternating 1V / [mu] m or more of the intensity of the direction directing to the surface, as the developer , In the charged state
Determined by a correlation between an electric potential on the electrostatic latent image carrier , an electric field formed by the voltage applying means, and an electric field on the developer carrier using a developer carried on the developer carrier. A developing device that controls the movement of the developer by the applied electric field. 2. A developing device in which an electrostatic latent image carrier carrying an electrostatic latent image and a developer carrier carrying a developer are opposed to each other in a developing section, and a bias is applied to the developing section to perform development. In the above, a conductive part having a conductive substrate exposed on the surface and a dielectric part having a dielectric fixed on the substrate exposed on the surface are regularly or irregularly mixed on the surface, and the dielectric part is a developer carrying member a large number of minute closed electric field is formed on the surface is frictionally charged to a predetermined polarity, the frictional charging means for frictionally charging the dielectric portion to a predetermined polarity
And an electric field having an intensity of 1 V / μm or more between the dielectric portion and the image portion of the electrostatic latent image carrier for causing the developer to face the electrostatic latent image carrier; Direction 1 to face the surface
Provided a voltage applying means for applying a voltage capable of forming the electric field V / [mu] m or more intensity alternately above as the developer, by the minute閉電field in a charged state
Determined by a correlation between an electric potential on the electrostatic latent image carrier , an electric field formed by the voltage applying means, and an electric field on the developer carrier using a developer carried on the developer carrier. A developing device that controls the movement of the developer by the applied electric field. 3. A developing device in which an electrostatic latent image carrier for carrying an electrostatic latent image and a developer carrier for carrying a developer are opposed to each other in a developing section, and a bias is applied in the developing section to perform development. In the method, a plurality of portions having different resistances are regularly or irregularly mixedly exposed on the surface, and at least the portions having relatively high resistance are triboelectrically charged to a predetermined polarity and a large number of minute a developer carrying member closed electric field is formed, thereby frictionally charge the higher of the above relatively resistant to a predetermined polarity
1 V / μm between the triboelectric charging means and the non-image portion of the electrostatic latent image carrier between the portion having a relatively low resistance and the non-image portion of the electrostatic latent image carrier. and electric field intensity or more, and a voltage applying means for applying a voltage capable of forming alternately a field of 1V / [mu] m or more of the intensity of orientation to direct the developer to the surface provided, as the developer, the charged state Above due to the above minute closed electric field
Determined by a correlation between an electric potential on the electrostatic latent image carrier , an electric field formed by the voltage applying means, and an electric field on the developer carrier using a developer carried on the developer carrier. A developing device that controls the movement of the developer by the applied electric field. 4. A developing device in which an electrostatic latent image carrier for carrying an electrostatic latent image and a developer carrier for carrying a developer are opposed in a developing section, and a bias is applied in the developing section to perform development. In the above, a conductive part having a conductive substrate exposed on the surface and a dielectric part having a dielectric fixed on the substrate exposed on the surface are regularly or irregularly mixed on the surface, and the dielectric part is a developer carrying member a large number of minute closed electric field is formed on the surface is frictionally charged to a predetermined polarity, the frictional charging means for frictionally charging the dielectric portion to a predetermined polarity
And an electric field having an intensity of 1 V / μm or more in a direction for causing the developer to face the electrostatic latent image carrier between the conductive portion and the non-image portion of the electrostatic latent image carrier. Direction 1 to face the surface
Provided a voltage applying means for applying a voltage capable of forming the electric field V / [mu] m or more intensity alternately above as the developer, by the minute閉電field in a charged state
Determined by a correlation between an electric potential on the electrostatic latent image carrier , an electric field formed by the voltage applying means, and an electric field on the developer carrier using a developer carried on the developer carrier. A developing device that controls the movement of the developer by the applied electric field. 5. A developing device in which an electrostatic latent image carrier for carrying an electrostatic latent image and a developer carrier for carrying a developer are opposed in a developing section, and a bias is applied in the developing section to perform development. In the method, a plurality of portions having different resistances are regularly or irregularly mixedly exposed on the surface, and at least the portions having relatively high resistance are triboelectrically charged to a predetermined polarity and a large number of minute a developer carrying member closed electric field is formed, thereby frictionally charge the higher of the above relatively resistant to a predetermined polarity
One of the directions in which the developer is directed to the electrostatic latent image carrier between the triboelectric charging means and the relatively high resistance member and the image portion of the electrostatic latent image carrier.
An electric field having an intensity of not less than V / μm and an electric field having an intensity of not less than 1 V / μm for directing the developer toward the surface can be alternately formed. An electric field having an intensity of 1 V / μm or more for directing the developer toward the electrostatic latent image carrier between the non-image portion of the electrostatic latent image carrier and a direction for directing the developer toward the surface; And a voltage applying means for applying a voltage capable of alternately forming an electric field having an intensity of 1 V / μm or more as described above.
Using what is carried on serial developer carrying member, determined by the mutual relationship between the potential on the latent electrostatic image bearing member, and the electric field formed by the voltage applying means, the electric field on the developer carrying member A developing device that controls the movement of the developer by the applied electric field. 6. A developing device in which an electrostatic latent image carrier for carrying an electrostatic latent image and a developer carrier for carrying a developer are opposed to each other in a developing section, and a bias is applied to the developing section to perform development. In the above, a conductive part having a conductive substrate exposed on the surface and a dielectric part having a dielectric fixed on the substrate exposed on the surface are regularly or irregularly mixed on the surface, and the dielectric part is a developer carrying member a large number of minute closed electric field is formed on the surface is frictionally charged to a predetermined polarity, the frictional charging means for frictionally charging the dielectric portion to a predetermined polarity
And an electric field having an intensity of 1 V / μm or more between the dielectric portion and the image portion of the electrostatic latent image carrier for causing the developer to face the electrostatic latent image carrier; Direction 1 to face the surface
And an electric field having an intensity of V / μm or more can be alternately formed, and
An electric field having an intensity of 1 V / μm or more in a direction in which the developer is directed to the electrostatic latent image carrier between the conductive portion and the non-image portion of the electrostatic latent image carrier, and a developer applied to the surface. 1 of the direction to turn
And voltage applying means for applying a voltage capable of forming the electric field V / [mu] m or more intensity alternately provided, as the developer, the band
Carried on the developer carrier by the minute electric field in the charged state
Using what is, the potential on the latent electrostatic image bearing member, and the electric field formed by the voltage applying means, by an electric field is determined by the interaction of the electric field on the developer carrying member of the developer A developing device for controlling movement. 7. The developing unit supported by the developer carrier
Is provided to regulate the layer thickness of the developer conveyed to the
In addition, the frictional charging means is more conveyed with the developer than the layer thickness regulating means.
Direction upstream side and the developer transport direction relative to the developing section.
The method according to claim 1, 2, 3, or 3,
4, 5, or 6 developing devices.