JP3078337B2 - Developing method and apparatus - 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 method and an apparatus used in an image forming apparatus such as an electrophotographic copying machine, a printer or a facsimile, and more particularly to a developing method in which a developer is carried on a developer carrier. The present invention relates to a developing method and an apparatus for performing development by transporting the developer to a developing unit facing an electrostatic latent image carrier.

[0002]

2. Description of the Related Art In this type of developing method, a developer carrying member having a thin layer of developer formed on its surface and an electrostatic latent image carrying member 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 method, there is a threshold for transferring the developer from the developer carrier to the electrostatic latent image carrier, and the developer may adhere to an image portion having a surface potential exceeding this threshold. 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 method, particularly when a non-magnetic toner is used as a developer, when the 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. It is an object of the present invention to provide a developing method and an apparatus capable of preventing thickening of the line portion, thereby obtaining a high-quality image.

[0005]

[0006]

According to the present invention, a developer carrying member having a large number of electric fields disposed on its surface is used as a developer carrying member for carrying a developer, and the developer carrying member and the developer carrying member are electrically connected to each other. The latent image carrier forms an electric field in a developing unit opposed to each other by a voltage applying unit, and is formed by the potential on the electrostatic latent image carrier, the potential on the developer carrier, and the voltage applying unit. controls the movement of the developer by the electric field is determined by the interactions with that field, thereby, it is to shall to deposit an appropriate amount of the developer to the electrostatic latent image on the electrostatic latent image bearing member .

[0007]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a diagram showing the overall configuration of an embodiment of a developing device according to the present invention suitable for carrying out the developing method according to 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 supplies the toner 7 conveyed by the agitator 6 by rubbing the surface of the developing roller 1 in the forward or reverse direction, and also returns to the developing roller 1 without being used for development. It has the function of scraping off the toner 7 that has fallen. 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 bias 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, preferably 50 to 500 μm, which does not substantially contact the photosensitive drum 3.
They are arranged with a gap of 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 reduced in size.
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 the AC electric field, a rectangular wave pulse electric field is set in a low frequency range of 300 to 2000 Hz, preferably in a range of 500 to 1500 Hz, and one cycle of the time of the high voltage part and the time of the low voltage part. When used in a waveform having different ratios with respect to time, sharpness in a low voltage portion is good, an image density in a high voltage portion is high, and an excellent developed image with less background smear can be obtained. The ratio of the time of the high-voltage part to the time of the low-voltage part (duty ratio) is as follows:
The optimum ratio differs depending on the polarity of the electrostatic latent image and the polarity of the toner 7. For example, when reversal development is performed on a negative electrostatic latent image with the negative toner 7, the time of the high voltage portion (−100 V or more) and the low voltage Part (-800 V or less) to the time of 5-1
8: 2 to 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, OPC is used as the photosensitive drum 3, the surface potential of the background portion is -900V, and the potential of the exposed portion is -100V.
V indicates that the developing roller 1 having the surface shape shown in FIG. 4B is opposed to the surface of the photosensitive drum 3 with a gap of 100 μm, and reverse development is performed. The insulative area surface 22 on the surface of the developing roller 1 holds an amount of electric charge that is rubbed by the toner supply roller 8 so that the electric potential with respect to the ground becomes +200 V, whereby the negatively charged toner 7 is removed. 1.0 to 1.2 mg / cm ^{2 was} supported. Then, a peak-to-peak (hereinafter referred to as PP) 1000 is applied to the developing roller 1 by the developing bias applying means 9.
V, a maximum potential of 0 V, a frequency of 500 Hz, and a duty ratio of 30% (T ₂ / T ₁ ) were 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 photoconductor drum 3. -900V as shown by the shaded portion in (b)
It is considered that when the developing electric field is reached, the image is transferred in the direction of the developing roller 1.

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 faces the background of the photosensitive drum 3, as shown by the hatched portion in FIG.
Is transferred to the developing roller 1, and it is considered that the transfer does not occur alternately.

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 thus obtained was compared with an image developed using only the developing electric field as shown in FIGS. 6A and 6B using the developing roller 1 whose surface is all aluminum. However, a high-density image was obtained without background contamination, and the reproducibility of the diagram was excellent. 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.

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.

Next, a second embodiment will be described. In this example, an OPC is used as the photosensitive drum 3, the surface potential of the background portion is -10V, and the surface potential of the image portion is -850V.
4B, the developing roller 1 having the surface shape shown in FIG. 4B is arranged to face the surface of the photosensitive drum 3 with a gap of 100 μm, and normal development is performed. The insulative area surface 22 on the surface of the developing roller 1 holds an amount of charge that is rubbed by the toner supply roller 8 and has an electric potential of -200 V with respect to the ground, thereby carrying the positively charged toner 7. did. The charge amount of this toner was about 10 μC / g. Then, PP-P750 whose maximum potential is biased to +200 V by the developing bias applying means 9 is applied to the developing roller 1.
V, a sine wave alternating current with a frequency of 500 Hz was applied.

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 (−10 V) of the background portion on the surface of the photosensitive drum 3 and the surface potential level (−850 V) of the image portion are shown as horizontal lines, respectively. 8A, 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 sine wave continuous line indicating the temporal change of the surface potential of the insulating region surface 22 in FIG. It becomes a potential deviated by -200 V due to the electric charge. 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 portion and the background portion of the drum 3 faces.

FIG. 9 is a diagram for explaining an electric field on the conductive region surface 21 which causes a temporal change in the surface potential as shown in FIG. 8B, and FIG. FIG. 9B shows a temporal change in the potential difference between the area surface 21 and the image portion (unexposed portion) of the photosensitive drum 3 when the area surface 21 faces the image portion (unexposed portion). 5 shows a temporal change of a potential difference between the non-image portion (exposure portion) and the non-image portion (exposure 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. 10 shows a temporal change in the potential difference between the photosensitive drum 3 and the image portion (exposure portion) when the photosensitive drum 3 faces 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, since the electric field exerts an electrostatic force on the toner 7 carried on the surface of the developing roller 1 or on 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, the toner 7 is always +10 as shown by the hatched area in FIG.
A positive electric field of 0 to +1050 V is considered, and it is considered that the electric field shifts in the direction of the photoconductor drum 3. When the electric field is opposed to the background of the photoconductor drum 3, it is indicated by a hatched portion in FIG. As described above, the electric field contributing to the toner transfer is −10.
A negative electric field of 0 to -540 V and a positive electric field of +100 to +210 V alternately appear. In the case of a positive electric field, the transfer from the developing roller 1 to the photosensitive drum 3 is performed, and in the case of a negative electric field, the transfer from the photosensitive drum 3 to the developing roller 1 is performed. Is a photosensitive drum 3 caused by a negative electric field.
Since the period during which the transfer from the toner to the developing roller 1 occurs is sufficiently longer and the transfer force is large, even if the toner 7 that transfers to the photosensitive drum by the positive electric field occurs, the toner 7 transfers to the developing roller 1 again. it is conceivable that.

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, the positive electric field of + 100V to + 850V is always present as shown by the hatched portion in FIG.
The transfer from the developing roller 1 to the photosensitive drum 3 is performed. However, since the insulating region surface 22 is originally charged to −200 V,
It is considered that the transfer force is smaller than the toner 7 existing on the conductive positive area surface 21. When the photoconductor drum 3 is opposed to the background portion, as shown by the hatched portion in FIG.
Since only a negative electric field of 0 to -740 V appears, it is considered that the transition does not occur alternately.

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 a similar sine wave voltage is applied to the developing roller 1, an image having a high density without a background stain can be obtained. Moreover, the reproducibility of the diagram was excellent.

In the first and second embodiments, the developing roller 1 having the surface shape shown in FIG. 4B is used, but the surface shape shown in FIGS. 4A and 4C is used. The experiment was conducted using the developing roller 1 provided with the pulse voltage of the first embodiment and the sine-wave AC voltage of the second embodiment. As a result, similarly, a high-density image without background contamination was obtained. An image with excellent reproducibility of the diagram could be obtained.

Further, in each of the above-described 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.

[0037]

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.

[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 background 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 background 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 background 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 background portion.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Developing 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 Company, Ltd. (72) Inventor Junko Tomita 1-3-6 Nakamagome, Ota-ku, Tokyo In Ricoh Co., Ltd. (56) References JP-A-61-273563 (JP, A) JP-A-2-61652 (JP, A) JP-A-1-267566 (JP, A) Jpn. JP, U) Shokai Sho 62-79257 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) G03G 15/06 G03G 15/08

Claims (17)

(57) [Claims] A developing device that carries a developer on a developer carrying member and performs development in a developing section where the developer carrying member and the electrostatic latent image carrying member are opposed to each other; A developer carrier having a large number of electric field arrangements formed on the surface thereof; and a voltage applying means for forming an electric field in the developing section, wherein the large number of electric field arrangements are adjacent to the surface of the developer carrier.
It consists of a number of fine regions with different potentials
閉電field is formed between the thin region is <br/> determined by the potential on the latent electrostatic image bearing member, a potential on the developer carrying member, and the electric field formed by the voltage applying means A developing device wherein the movement of the developer is controlled by an electric field. 2. The developing device according to claim 1, wherein the developer is carried by the plurality of electric field arrangements. 3. The developing device according to claim 1, wherein the electric field formed by said voltage applying means is an alternating electric field. 4. The developing unit according to claim 1, wherein the movement of the developer is controlled so as to transfer and reversely transfer between the developer carrier and the electrostatic latent image carrier. 4. The developing device according to 2 or 3. 5. The image forming apparatus according to claim 1, wherein said developer carrier and said electrostatic latent image carrier are moved relative to each other.
5. The developing device according to 2, 3, or 4. 6. The method according to claim 1, wherein a gap between the surface of the developer carrier and the surface of the electrostatic latent image carrier is equal to or less than a layer thickness of the developer carried on the developer carrier. 1, 2,
6. The developing device according to 3, 4, or 5. 7. The image forming apparatus according to claim 1, wherein a gap between the surface of the developer carrier and the surface of the electrostatic latent image carrier is larger than a layer thickness of the developer carried on the developer carrier. 1,
6. The developing device according to 2, 3, 4, or 5. 8. A developing method in which a developer is carried on a developer carrying member, and is transported to a developing section facing the electrostatic latent image carrier to perform development. A large number of first regions that hold electric charge and are charged to a predetermined potential and a second region having a lower potential than the first region are mixed, and both adjacent regions
A large number of closed electric fields are formed, and an electric field is formed in the developing section by voltage applying means. The electric charge held in the first area and the charge of the electrostatic latent image are formed on the first area. A developing method, wherein a developing electric field different from that on the second region is formed by a potential on the body and an electric field by the voltage applying means. 9. The developing method according to claim 8 , wherein the developer is carried on the developer carrier by an electric field formed between the first area and the second area. 10. A developing method according to claim 8 or 9, wherein the electric field by the voltage applying means is an alternating electric field. 11. The apparatus according to claim 1, wherein a gap between the surface of the developer carrier and the surface of the electrostatic latent image carrier is larger than a layer thickness of the developer carried on the developer carrier. 8 ,
9 or 1 0 developing method according. 12. A method according to claim 1, wherein the surface of the developer carrying member comprises an insulating region and a conductive region, the insulating region being used as the first region, and the conductive region being used as the second region. claim 8, wherein, 9, 1 0 or 1 1 developing method according. 13. The developing method according to claim 1 2, wherein the allowed to hold a charge by triboelectric charging on the insulating region of the surface of the developer carrying member. 14. The image forming apparatus according to claim 8, wherein said developer carrier and said electrostatic latent image carrier are moved relative to each other .
9, 10, 11, 12 or 1 3 Symbol placement methods development. 15. A developer carrying member for carrying and transporting a developer on a surface thereof, and a layer thickness regulating means for regulating a layer thickness of the developer carried and transported by the developer carrying member. In a developing device that visualizes an electrostatic latent image formed on an electrostatic latent image carrier by a developer whose layer thickness is regulated by the layer thickness regulating unit, the developer carrier includes a conductive part, Using a developer carrier in which a dielectric portion is mixedly exposed, with respect to the moving direction of the developer carrier, upstream of the developer layer thickness regulating section by the layer thickness regulating means, and than developing area visible image is performed positioned downstream and in contact with the surface of the developer carrying member is charged to said dielectric portion to a predetermined polarity, the developer carrying member surface, charged the
A large number of minute gaps between the dielectric part and the conductive part adjacent thereto
A bearing member charging means for forming a closed field, a developer charging means for charging the developer to be supplied to said developer carrying member to a predetermined polarity, relates to a mobile direction of the developer carrying member, the layer thickness regulating means Is located on the upstream side of the developer layer thickness regulating section, and on the downstream side of the developing area where the electrostatic latent image is visualized, and is charged by the carrier charging means, and is a small closed electric field. A toner supply unit for continuously supplying charged toner to the surface of the developer carrier on which the developer is formed, and an alternating electric field is formed in a developing unit in which the developer carrier and the electrostatic latent image carrier oppose each other. And a voltage applying means for applying a voltage to the developing device. 16. carries a developer on the developer carrying member, the developing device for performing development in a developing unit and the developer carrying member and an electrostatic latent image bearing member are opposed to each other, the developer carrying member , Next to the surface of the developer carrier on the surface
Region and the potential to meet consists a number of different micro-regions to form a plurality of <br/> electric field arrangement, using <br/> developer carrier 閉電boundary is made form between the fine regions, the developing A gap between the surface of the developer carrier and the surface of the electrostatic latent image carrier is larger than the layer thickness of the developer carried on the developer carrier. 17. A developer carrying member for carrying and transporting a developer on a surface thereof, and a layer thickness regulating means for regulating a layer thickness of the developer carried and transported by the developer carrying member, In a developing device that visualizes an electrostatic latent image formed on an electrostatic latent image carrier by a developer whose layer thickness is regulated by the layer thickness regulating unit, the developer carrier includes a conductive part, Using a developer carrier in which a dielectric portion is mixedly exposed, with respect to the moving direction of the developer carrier, upstream of the developer layer thickness regulating section by the layer thickness regulating means, and than developing area visible image is performed positioned downstream and in contact with the surface of the developer carrying member is charged to said dielectric portion to a predetermined polarity, the developer carrying member surface, charged the
A bearing member charging means for multiple forming a minute closed electric field between the dielectric portion and the conductive portion adjacent thereto, the developer charging means for charging the developer to be supplied to said developer carrying member to a predetermined polarity With respect to the moving direction of the developer carrying member, on the upstream side of the developer layer thickness regulating unit by the layer thickness regulating unit, and on the downstream side of the developing region where the visualization of the electrostatic latent image is performed. And a toner supply unit for continuously supplying charged toner to the surface of the developer carrier on which a minute closed electric field is formed by being charged by the carrier charging unit. A gap between the developer and the surface of the electrostatic latent image carrier is larger than a layer thickness of the developer carried on the developer carrier.