JP3021075B2 - 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 method for supplying a toner to a developer carrier which is driven to rotate, carrying the toner on the surface of the developer carrier, and transporting the toner. An electrostatic latent image formed on the latent image carrier, which moves in the forward direction with respect to the direction of movement of the surface of the developer carrier, is developed by the toner carried on the developer carrier in a developing region in which the carriers face each other. The present invention relates to a developing device for forming a visual image.

[0002]

2. Description of the Related Art In an image forming apparatus such as an electronic copying machine, a laser printer or a facsimile for obtaining a recorded image by visualizing an electrostatic latent image formed on a latent image carrier, an auxiliary agent is externally added as necessary. It is conventionally well known to employ a developing device of the above-mentioned type using a toner, that is, a one-component developer.

In a developing apparatus using a one-component developer, in order to form a high-quality visible image of a predetermined density, a large amount of sufficiently charged toner is conveyed to a developing area, and a latent image is formed by the toner. It needs to be visualized.

[0004] However, it is not easy to satisfy this demand with conventional developing devices of this type, and improvement has been desired in the past. That is, in a conventional developing device using a one-component developer, the amount of toner that can be deposited on the developer carrier is usually 0.1 to 0.1.
In contrast to black toner of about 3 mg / cm ² , in the case of black toner, it is necessary to attach about 0.4 to 0.5 mg / cm ² of toner on the transfer paper, so the amount of toner is insufficient. When a color toner is used, 0.6
It is necessary to attach a toner of about 1.2 mg / cm ^{2 to} about 1.2 mg / cm ^2, and the shortage of toner becomes more remarkable.

Therefore, conventionally, the speed of the developer carrier has been increased,
The linear velocity is set to be about three to four times the linear velocity of the latent image carrier to increase the amount of toner conveyed to the developing area, thereby preventing the density of the visible image from lowering.

However, according to this configuration, the linear velocity of the developer carrying member is increased, so that not only the toner is easily scattered, but also the stress acting on the toner is increased, which tends to cause fatigue. In addition, toner filming in which the toner adheres to the developer carrying member with the lapse of time in the form of a thin film tends to occur. In particular, when the contact development is performed, the horizontal line image of the latent image carrier becomes thinner than the vertical line image, and the image quality is inevitably reduced. Further, in a high-speed image forming apparatus, it is necessary to increase the speed of the latent image carrier. In such a case, the surface linear velocity of the developer carrier must be increased more and more. However, it was difficult to employ a conventional developing device.

When the linear velocity on the surface of the developer carrier is set to a large value of about three to four times the linear velocity on the surface of the latent image carrier, the carrier of the solid image formed on the latent image carrier is set. At the rear end only in the moving direction, a phenomenon called “rear end toner shift” occurs in which the density becomes abnormally high as compared with other portions, and the image quality deteriorates. This phenomenon of “toward the trailing edge of toner”
In the case of a color image, a portion where the image density is abnormally high and another portion appear as different colors, and this is a particularly serious problem in the case of color development. In order to prevent this phenomenon, if the linear velocity on the surface of the developer carrier approaches the linear velocity on the surface of the latent image carrier, the amount of toner becomes insufficient as described above, and a visible image having a predetermined density is obtained. Can not do. Further, if the rotation speed of the developer carrying member is reduced so that the linear velocities of the two become equal, there occurs a problem that the background portion of the latent image carrying member is stained and the image quality is deteriorated.

A developing device has been proposed in which irregularities are formed on the surface of a developer carrying member, and the irregularities are filled with toner and carried to increase the amount of toner conveyed to a developing area. According to the configuration, although the amount of toner that can be conveyed increases, a large amount of insufficiently charged toner is contained in the conveyed toner, so that the image quality of the visible image formed therefrom may be reduced.

[0009] The development which eliminates the above-mentioned disadvantages of the prior art, suppresses the occurrence of the trailing edge toner shift phenomenon, and conveys a large amount of sufficiently charged toner to the developing area to obtain a visible image of a predetermined density. As a device, the applicant of the present invention has not yet known the developer. However, as a developer carrier, a dielectric material and a conductive portion are mixed on the surface of the developer carrier so as to selectively hold electric charges, so that the developer can be finely closed in the vicinity of the surface of the developer carrier. An electric field is formed, and the charged toner is attracted by the closed electric field to use a developer carrying member that carries the toner on the surface. The linear velocity of the developer carrying member is V ₂ , and the linear velocity of the latent image carrying member is V _1. Where 1.0 ≦ V ₂ / V ₁ ≦
A developing device in which each linear velocity is set so as to satisfy 1.5 is proposed.

In a developer carrier in which a dielectric and a conductive part are mixed and selectively held on the surface, the adhesion state of the toner is not uniform, and a large amount of the toner adheres to the surface of the dielectric part, and The amount of toner attached to the surface is reduced. For this reason, when the photosensitive member as the latent image carrier and the developing roller as the developer carrier are driven so that the linear velocities of the surfaces are equal, the distribution of the dielectric and the conductive portion is formed on the surface of the latent image carrier. There is a problem that image unevenness occurs according to the pattern pattern.

Further, in the development in which the developing carrier is brought into contact with the latent image carrier, toner adheres to the non-image area, and the occurrence of background fogging cannot be avoided. However, the fogging is prevented by using a method as disclosed in Japanese Patent Publication No. 41-9475, in which the toner is caused to fly from the developer carrier toward the latent image carrier by the electric field of the electrostatic latent image. It is effective in that. However, in this developing method, when the toner overcomes the restraining force of the developer carrier due to the electric field of the electrostatic latent image, flight starts, and therefore, the developer is transferred from the developer carrier to the latent image carrier. There is a threshold value, and developer adheres to an image portion having a surface potential exceeding the threshold value, but on the contrary, almost no developer adheres to an image portion having a surface potential value equal to or less than the threshold value. There is a problem that an image with poor gradation is obtained.

[0012]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and enables development without unevenness of the image regardless of the pattern of the mixed conductive surface portions and the gradation characteristics and image quality. It is an object of the present invention to provide a developing device excellent in the reproducibility of the developing device.

[0013]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problem by providing a developing carrier which is arranged opposite to a latent image carrier carrying an electrostatic latent image in a developing section and carries a developer. In a developing device in which a developer carrier develops under a bias applied by a bias applying unit, two types of surface portions different in either resistance or permittivity are regularly mixed on the surface of the developer carrier. Exposed on the surface, or two types of surface portions different in either the resistance or the dielectric constant are regularly mixed and exposed on the surface in the form of a grid inclined at 30 to 60 ° with respect to the moving direction. When a minute electric field is formed between the surface portions, a large number of minute electric fields are formed on the surface of the developer carrying member, and a linear velocity ratio of the developer carrying member to the latent image carrying member is determined by the following equation. (Pitch + low resistance part width) /
(Pattern pitch) or (pattern pitch + development nip width) / (development nip width) or a value larger than (low resistance portion width + development nip width) / (development nip width) or 1.2 or more and 1.5 or less And the bias applying means forms one cycle with the transition polarity region and the reverse transition polarity region, wherein the reverse transition polarity region includes the first region and the second region following the first region. In the first region having the reverse transition polarity, the developer having released an electric field having a strength enough to release the developer attached on the latent image carrier arrives at the developer carrier. The second region has a potential intermediate between the latent image potential of the latent image carrier and the background potential in the second region, and is strong enough to allow the developer adhered to the background region to reach the developer carrier. Electric field for a sufficient time to reach The problem is solved by a developing device, wherein the movement of the developer is controlled by an electric field determined by a correlation between an electric field due to astigmatism and an electric field on the developer carrier and a potential on the latent image carrier. .

[0014]

According to the present invention, two types of surface portions having different resistances or dielectric constants are mixed on the surface of the developer carrying member, or two different types of surface portions are inclined by 30 to 60 ° with respect to the moving direction. The surface of the developer carrier is formed with a large number of minute electric fields by forming a regular pattern by mixing regularly and forming a minute electric field between both surface members, and the charged toner is attracted by the minute electric field. And transport. Therefore, the toner is surely sucked and conveyed to the developer carrier even at a high speed, so that the trailing edge of the toner is eliminated and a sufficiently large amount of toner can be conveyed to the developing area. The linear velocity ratio of the developer carrier to the latent image carrier is 1.2 or more and 1.5 or less, or (pattern pitch + low resistance portion width) / (pattern pitch), or (pattern pitch + developing nip width) / ( By setting the value to be larger than (development nip width) or (low resistance portion width + development nip width) / (development nip width), the influence of toner unevenness on the developer carrier is avoided, and transfer is performed by bias applying means. When the polarity and the reverse transition polarity are defined as one cycle, the reverse transition polarity region has a strength to release the developer adhered on the latent image carrier, and is used for a short time when the released toner does not reach the developer carrier. A first region having a potential intermediate between the latent image potential of the latent image carrier and the background region potential following the first region, and having sufficient strength and time to allow the toner adhered to the background region to reach the developer carrier. With a second region having By applying the toner, the toner once adhered is not substantially peeled off from the part where the image is formed, regardless of the application of the alternating bias, and the toner adhered to the background area is peeled off. An image with excellent image reproducibility and rich in gradation has been obtained.

[0015]

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

FIG. 1 is a schematic view showing an example of a developing device according to the present invention. First, the overall structure and operation will be clarified.

In FIG. 1, a belt-shaped photosensitive member 1 as an example of a latent image carrier is driven in the direction of an arrow A, and a developing device 2 is provided to face the photosensitive member. In the toner container 3 of the developing device 2, a non-magnetic toner 4 mixed with an auxiliary agent as necessary, that is, a non-magnetic one-component developer is stored. The specific volume resistivity of the toner is, for example, 10 ⁷ to 10
It is about ¹² Ωcm. On the front and rear side plates of the toner container 3, a developer carrier, for example, a developing roller 5 is supported in a state where a part thereof is exposed from the opening of the container. It is driven to rotate counterclockwise. Although the developing roller 5 is an example of a configuration of a developer carrier or a toner carrier, a belt-shaped developer carrier may be used instead of the developing roller 5. A toner supply roller 6 as an example of a toner supply member is supported on the front and rear side plates of the toner container 3, and the toner supply roller 6 maintains a developing gap with the developing roller 5 and is in a non-contact state with a line of, for example, about 100 mm / sec. It is rotated counterclockwise at a high speed (moving speed on the surface of the toner supply roller).

The toner 4 in the toner container 3 is conveyed to the toner supply roller 6 while being stirred by the agitator 7 rotating clockwise, and then supplied to the developing roller 5 by the toner supply roller 6. At the time of this supply, the toner is frictionally charged to a predetermined polarity, in this example, a polarity opposite to that of the electrostatic latent image on the photoconductor 1, adheres electrostatically to the peripheral surface of the developing roller 5, and is carried by the developing roller 5. The configuration and operation related to this will be described later in detail.

As described above, the toner supplied and carried on the peripheral surface of the developing roller 5 is conveyed by the rotation of the developing roller 5 and is leveled by the doctor blade 8, which is an example of a layer thickness regulating member, to have a uniform thickness. Is regulated. Next, the toner is applied to a developing area 9 where the photosensitive member 1 and the developing roller 5 are opposed to each other.
And electrostatically transfers to the electrostatic latent image formed on the photoreceptor 1 to visualize the latent image.

The toner that has not passed through the developing area 9 and is not subjected to development is returned to the toner supply roller 6 while being carried on the developing roller 5. Further, the visible image formed on the photoreceptor 1 is transferred to a transfer sheet (not shown) and fixed on the transfer sheet by a fixing device.

The moving direction of the surface of the developing roller 5 in the developing area 9 and the moving direction of the surface of the photosensitive member 1 are forward directions. The forward direction means that the moving directions of the photosensitive member 1 and the developing roller 5 in the developing area 9 are the same in the closest part as shown in FIG. When the developing roller rotates in the counterclockwise direction and the photoconductor 1 moves in the direction opposite to the arrow A, or when the developing roller 5 moves in the clockwise direction and the photoconductor moves in the direction of the arrow A, the two moving directions are "Reverse direction". Such a relationship is the same when the photosensitive member is a drum or when the developer carrying member is a belt.

The above-described structure itself is the same as that of the conventional developing device. In such a conventional developing device, it is difficult to transport a large amount of sufficiently charged toner to the developing area. Is set to be three to four times the linear velocity of the surface of the photoreceptor, and the above-described various problems have occurred.

In the illustrated developing device, the developing roller 5 includes, as schematically shown in FIG. 2 to FIG. 4, a conductive base made of a conductive roller portion 10 made of, for example, aluminum or the like. A dielectric 11 is embedded and fixed in a groove 20 formed on the surface of the conductive roller portion 10, and a conductive surface portion 12 made of the conductive roller surface itself is embedded on the surface of the developing roller 5. Dielectric 11
As shown in FIG. 3, the dielectric surface portion 11a composed of the surface is regularly exposed, and the surface is formed smooth. Groove 2
0, that is, the exposed dielectric surface portion 11
The shape of “a” can be set as appropriate, but in the examples of FIGS. 3 and 4, the dielectric surface portion 11 a extends in a lattice shape on the surface of the developing roller 5. The pitch P of the dielectric surface portion 11a, that is, the groove 20 is set to, for example, about 0.1 to 1.0 mm, preferably about 0.2 to 0.4 mm. The ratio of the total area of 12 is, for example, about 20 to 80%, preferably about 30 to 60%. As described above, the dielectric surface portion 1 is provided on the surface of the developing roller 5.
1a and the conductive surface portion 12 are mixed in a very small area.

Each of the numerical values exemplified above is appropriately selected each time so that the electric field strength of a closed electric field described later can be increased and an optimum amount of toner can be attached to the developing roller 5.

The conductive roller portion 1 of the developing roller 5
For 0, an alternate bias voltage is applied by the bias power supply 16 so as to enhance the quality of a visible image. The same applies to the toner supply roller 6.

In this embodiment, a material that is frictionally charged to the opposite polarity to the charged polarity of the toner, for example, negatively, is selected for the dielectric 11.

On the other hand, the toner supply roller 6 in contact with the developing roller 5 comes into contact with the dielectric 11 of the developing roller 5 to frictionally charge the dielectric surface portion 11a to a polarity (negative polarity) opposite to the polarity of the toner. Further, it is made of a material that frictionally charges the toner to a positive polarity. In the example shown in FIGS. 1 and 2, the toner supply roller 6 is made up of a conductor core member 14 and a cylindrical foam 15 laminated therearound. Is pressed against. When such a toner supply roller 6 is used, the foam 15 may be made of a material that frictionally charges the dielectric 11 to a negative polarity as described above. Instead of the foam 15, a known material such as a fur brush may be used.

The more detailed operation of the above configuration will be described below.

As described above with reference to FIG. 1, the portion of the developing roller 5 that has passed through the developing area 9 moves toward the toner supply roller 6 and comes into contact with the toner supply roller 6. Here, the toner carried on the developing roller 5 and not subjected to the development is mechanically and electrically scraped off by the toner supply roller 6. At the same time, the dielectric surface portion 11a of the developing roller 5 comes into contact with the toner supply roller 6, and is charged to a negative polarity opposite to the charging polarity of the toner by the friction. At this time, even if an electrostatic afterimage due to the influence of the electrostatic latent image of the photoconductor 1 remains on the dielectric surface portion 11a of the developing roller 5 that has passed through the developing area 9, friction with the toner supply roller 6 causes Since the dielectric surface portion 11a is charged to a substantially saturated state and the charge amount becomes uniform, the afterimage is eliminated and the developing roller 5 is initialized.

On the other hand, the toner 4 carried to the developing roller 5 while being in contact with the peripheral surface of the toner supply roller 6 is frictionally charged to a positive polarity by friction with the toner supply roller 6 as schematically shown in FIG. Is supplied to the developing roller 5,
At this time, the friction with the dielectric surface portion 11a of the developing roller 5 further strongly positively charges the friction with the positive polarity.
Electrostatically adheres to the peripheral surface of

At this time, the dielectric surface portion 11 of the developing roller 5
a is negatively charged by friction with the toner supply roller 6, and a large number of conductive surface portions 12 having a small area are present adjacent to the dielectric surface portion 11a, and the conductive surface portion 12 and the dielectric surface portion 11a Are mixed. In this state, a negative charge is selectively held on the dielectric surface portion 11a on the surface of the developing roller 5.

For this reason, as shown in FIG. 5, a large potential difference is generated between each conductive surface portion 12 and the dielectric surface portion 11a, and a closed electric field is formed between both surface portions. That is, innumerable minute closed electric fields (microfields) are formed near the surface of the developing roller 5. To elaborate,
When considering the lines of electric force representing the state of the electric field, the developing roller 5
In the space in the vicinity of the surface, electric lines of electric force E are formed as shown by a large number of arc-shaped lines in FIG. 5, and the electric lines of electric force exit from the developing roller 5 and return to the same developing roller 5, A closed electric field is formed near the surface of the roller 5. Thus, an electric field having a large electric field gradient is formed near the surface of the developing roller.

Since the dielectric surface portion 11a and the conductive surface portion 12 are adjacent to each other with a very small area, the intensity of each minute closed electric field becomes very strong due to the so-called edge effect or fringing effect (peripheral electric field effect). The toner positively charged by the closed electric field is applied to the surface of the dielectric 11 (dielectric surface portion 11a).
, And is held on the developing roller 5 in such a state that it is hard to separate a large amount. At this time, the toner is strongly frictionally charged due to the friction between the toner supply roller 6 and the developing roller 5 and is held on the surface of the developing roller 5 by the action of a strong micro electric field. A large amount of toner having Moreover, when the layer thickness of the toner carried on the developing roller 5 is regulated by a doctor blade 8 made of, for example, urethane, a sufficiently charged toner is strongly held on the surface of the developing roller 5 by a minute closed electric field. Even if the toner having a small charge amount is mixed with the toner, this is removed by the contact pressure with the doctor blade 8, so that only the toner having a large charge amount is conveyed to the developing area 9 in a larger amount than before. Then, the electrostatic latent image is visualized as described above. The electric field between the developing roller 5 and the photoconductor 1 in the developing area 9 has a large electrode effect, and the toner on the developing roller 5 is easily attached to the photoconductor 1,
The developing operation is performed efficiently.

In the vicinity of the surface of the developing roller 5 having passed through the toner supply roller 6, only a small closed electric field is formed over the entire surface as schematically shown in FIG. Although it is considered that it is mixed in a closed electric field,
In any case, since the closed electric field exists, its intensity is increased. In this way, a large amount of toner can be carried, and in order to prevent background smearing of a visible image and to enhance its sharpness, for example, 0.6 to 2.0 mg / cm charged to about 8 to 15 μc / g. ² , preferably 0.8-1.2 mg
/ Cm ² can be conveyed to the developing area 9.

In the above-described example, the dielectric 11 is charged to the opposite polarity to the toner. However, the dielectric surface portion 11a is charged to the same polarity as the charged polarity of the toner. It can also be done.

As described above, since a large amount of toner can be carried on the developing roller 5 and conveyed to the developing area 9, it is not necessary to increase the linear speed of the developing roller 5 as in the related art. That is, assuming that the linear speed of the developing roller 5 (peripheral speed on the roller surface) is V ₂ and the linear speed of the photoconductor 1 (speed of the photoconductor surface) is V ₁ , the ratio V ₂ / V ₁ is 1. Even if it is set to 0 or more and 1.5 or less, a large amount of sufficiently charged toner can be conveyed to the developing area 9 as exemplified above, so that the amount of toner does not become insufficient and the density of the visible image becomes insufficient. Can be prevented. For example, in the apparatus shown in FIG.
20 mm / sec, the linear velocity of the developing roller 5 is about 170 mm / sec.
Can be set to Thus, conventionally, V ₂ / V
_{Although 1} has to be set to about 3 to 4, the value of this ratio can be suppressed to 1.5 or less in the configuration according to the present invention.

As a result, it is possible to prevent various disadvantages which have conventionally occurred, such as scattering of toner, premature fatigue of toner, toner filming on a developing roller, and thinning of a horizontal line image. The developing device according to the present invention can be adopted without any trouble in the forming device.

Further, by setting V ₂ / V ₁ to 1.5 or less, it is possible to substantially prevent the occurrence of the above-described trailing end toner shift phenomenon. Incidentally, according to an experiment, the V ₂ / V ₁ regardless lowered to 1.5, by setting it to a level lower than 2.5, but has been found to be able to prevent problems such as the above-described toner scattering, the present invention V ₂ / V like
_{When 1} is set to 1.5 or less, the occurrence of the above-described trailing edge toner shift phenomenon can be substantially prevented as described below.

FIG. 8 shows the toner shift formed at the rear end of the visible image I with a width a, and the image density of this portion is higher than that of the other image portions. FIG. 9 is a graph showing an example of a relationship between the width a of the trailing end toner on the slave axis and V ₂ / V ₁ on the horizontal axis. If the width a of the trailing end toner is generally 0.5 mm or less, the width a is inconspicuous when observed at a visual distance, and the viewer is not conscious of the trailing end toner. Then, as can be seen from FIG. 9, V ₂ / V
₁ is greater than 1.5, the width a is greater than 0.5 mm, and the trailing edge of the toner is conspicuous, but if V ₂ / V ₁ is 1.5 or less, the width a is 0.1 mm. It is 5 mm or less, and the trailing edge of the toner is not a problem. To completely prevent the trailing edge toner shift phenomenon, as can be seen from FIG. 9, V ₂ / V ₁ =
1.0, but even if the value of the ratio between V ₂ and V ₁ is set in this way, a large amount of sufficiently charged toner is carried on the developing roller 5 as described above, Since the toner can be conveyed to the developing region 9, whether the toner is black toner or color toner, the amount of toner in the developing area 9 does not become insufficient, and a high-quality visible image can be formed.

As described above, V ₂ / V ₁ can be set to 1.5 or less. Even if this value is set to 1, for example, V ₂ = V ₁ , it is possible to prevent toner shortage in the development area, and to obtain a visible image. Can be prevented from lowering.

However, if the _two linear velocities V ₂ and V ₁ are equal, the following problem occurs.

In the illustrated embodiment, a large amount of toner adheres to the dielectric surface portion 11a of the developing roller 5 as described above.
When the dielectric surface portion 11a and the toner 4 are charged to the same polarity, a large amount of toner adheres to the conductive surface portion 12. That is, it is difficult to completely and uniformly adhere the toner on the developing roller 5. For this reason, when the developing operation is performed while rotating the developing roller 5 at the same linear speed as the photosensitive member 1, the visible image formed on the photosensitive member 1 corresponds to the unevenness of the adhesion state of the toner on the developing roller 5. There is a risk that extremely small "after", that is, uneven development may occur.

If the dielectric surface portion 11a and the conductive surface portion 12 exposed on the surface of the developing roller 5 are arranged irregularly, such a problem hardly occurs. However, the manufacturing cost of the developing roller 5 is reduced, and the precision of the parts is reduced. In order to raise the height, it is desirable to form a groove 20 on the surface of the conductive roller portion 10 by, for example, knurling, and bury the dielectric 11 in the groove 20. However, when the developing roller is manufactured by such a method, since the groove 20, that is, the dielectric material 11 appears regularly on the surface of the developing roller 5, the linear velocity ratio V ₂ / V ₁ between the developing roller 5 and the photosensitive member 1 is reduced. If it is set to 1, a very small but knurled pattern will appear as "uneven" on the image plane of the visible image.

As described above, when the surface of the dielectric 11 and the conductive surface portion 12 regularly appear, it is particularly easy to appear later in a visible image.

If V ₂ and V ₁ are equal, the photosensitive member 1
Background dirt is likely to occur on the upper ground. That is, when the linear velocity V ₂ of the developing roller 5 to be larger than the linear velocity V ₁ of the photosensitive member 1, the toner on the developing roller 5 exerts a scavenging effect on the background portion of the photosensitive member 1, thereby the land dirt is reduced, but when an equal V ₂ and V _1, can not be expected to scavenging effect, scumming tends to occur.

[0046] Therefore, in the present invention, the developing roller 5 and the linear velocity V ₂ of the surface of the photosensitive member 1, V ₁ ratio V ₂ / V ₁ of 1.2 or more, preferably set to 1.3 or more.

If V ₂ is made larger than V _{1 in} this manner, the dielectric surface portion 11a and the conductive surface portion 12 of the developing roller surface in the developing area 9 will not face the photosensitive member 1 at a constant speed. , Since there is a relative speed between the two,
The problem that the pattern of the dielectric surface portion 11a or the conductive surface portion 12 appears as "uneven" or "after" in the visible image can be prevented.

By setting V ₂ / V ₁ ≧ 1.2, a scavenging effect on the background portion of the photoreceptor 1 is exhibited, and background contamination can be suppressed. FIG. 10 is a graph showing the background dirt rank on the vertical axis and the value of V ₂ / V _{1 on} the horizontal axis. Is inconspicuous and has no practical problem. As can be seen from this graph, if V ₂ / V ₁ is set to 1.2 or more, especially 1.3 or more, the problem of background contamination does not occur.

[0049] Finally, in the developing device according to the present invention shown in FIG. 1, developed in the area 9 of the surface of the developing roller 5 to move forward the linear velocity V ₂ and the linear velocity V ₁ of the surface of the photoreceptor 1 The ratio is 1.2 ≦ V ₂ / V ₁ ≦ 1.5, preferably 1.3 ≦
V ₂ / V ₁ ≦ 1.5 is set, so that when the toner is a black toner or a color toner, the occurrence of toner scattering, toner filming, or trailing toner deviation is suppressed. In addition, it is possible to obtain a high-quality visible image of a predetermined density without background contamination. Photoconductor is formed in a drum shape, and also when the developer carrying member is constituted by a belt, the linear velocity ratio V ₂ / V ₁ is also set as was described above.

The shape of the dielectric surface portion or the conductive surface portion appearing on the surface of the developing roller can be appropriately set as described above. However, as shown in FIG. When the surface of the roller 5 is formed in a grid shape extending at an angle θ of 30 ° to 60 °, preferably 45 ° with respect to the moving direction Y), the toner adhered to the surface of the dielectric surface portion 11a 5, the unevenness corresponding to the pattern of the dielectric surface portion 11a and the conductive surface portion 12 appears on the image plane of the visible image. Failures can be more reliably prevented.

The conductive surface portion 12 appears to extend in a grid pattern on the surface of the developing roller 5, that is, the conductive surface portion 12 and the dielectric surface portion 11a in FIG. When the angle θ between the direction in which the grid-like conductive surface portion extends and the direction in which the developing roller 5 moves is set to 30 ° to 60 °, the same advantages as described above can be obtained. Can be

A more specific example of a developing device including the above-described developing roller 5 will be described below.

(1) Developing Roller The diameter D1 of the developing roller 5 shown in FIG. 6 is 25.4 mm, a groove 20 is formed on the surface by knurling, the pitch of the groove 20 is 0.4 mm, and the depth D2. (FIG. 4) is 0.1 mm, the groove width W1 (FIG. 3) is 0.15 mm, and the angle θ of the grooves 20 extending in a lattice pattern or the dielectric 11 with respect to the developing roller moving direction Y is 45 °. 3 and 5 indicates the axial direction of the developing roller 5. The area ratio of the dielectric surface portion 11a exposed on the surface of the developing roller 5 is 61%, the conductive surface portion is 39%, and the width of the conductive surface portion 12 is 0.15 mm.

(2) The foam material of the toner supply roller is a foamed polyurethane carbon-treated material.
Its outer diameter is 14mm and the amount of bite into the photoreceptor 1 is 1m
m, the surface resistance of the foam 15 is 10 ⁷ Ω.

(3) Doctor blade A fluororesin PTFE sheet (PTFE resin tape 200μ: manufactured by Nichiya Corporation) is fixed to an elastic member made of phosphor bronze having a thickness of 0.1 mm.

(4) AC 500 V (P /
P), a voltage of 250 Hz and DC-250V is applied, and a voltage of DC-250V is applied to the toner supply member.

(5) Photoconductor OPC photoconductor.

(6) Toner A non-magnetic styrene acrylic-based positively charged toner. Polarity control agent Nigrosine, external additive SiO ₂ fine powder 0.5wt
%.

Next, a method of manufacturing the developing roller 5 will be briefly described.

(1) First, as shown in FIG. 7A, a metal roller (conductive roller portion 10) having a surface subjected to square groove processing is formed.

The lattice-shaped square groove 20 is formed by knurling a square groove, for example, with a pitch of 0.2 to 1.0 mm and a depth D.
Is set to 0.1 to 0.5 mm, and is extended at an angle of 30 ° to 60 °, particularly 45 ° with respect to the axis X of the developing roller 5.

(2) Next, as shown in FIG. 7B, the surface of the roller 10 in which each groove 20 is formed is coated with a dielectric material 11 made of, for example, a fluorine-based resin (Lumiflon LF200 manufactured by Asahi Glass Co., Ltd.). Allow to dry. The coating thickness is set so that the groove 20 is completely filled.

(3) Further, as shown in FIG. 7C, the surface of the roller is cut or polished to expose the surfaces of the conductive surface portion 12 and the dielectric surface portion 11a in a mixed state.
Is set to, for example, 20 to 80%. Thus, the developing roller 5 having a substantially smooth surface is completed.

In the case of a belt-shaped developer carrier, a conductive sheet is used in place of the conductive roller portion 10 shown in FIGS. 7A, 7B and 7C, and grooves are formed on the surface thereof. Then, a dielectric may be embedded and fixed here, and the manufacturing method is not substantially different from the method shown in FIG.

It is obvious that various other methods can be used to form the developer carrier in various forms in which the dielectric and the conductive surface are exposed on the surface.

Incidentally, a dielectric layer having a predetermined thickness may be further laminated on the surface of the developing roller 5 manufactured as shown in FIG. 7C. When such a developing roller is used, the dielectric 11
And the thickness of the dielectric layer thereover differs according to the groove 20 of the developing roller, and the capacitance thereof differs. Therefore, when the surface of the dielectric layer is charged by the toner supply roller 6, a potential difference is generated on the surface of the developing roller in accordance with the difference in the capacitance, and a large number of minute closed electric fields can be formed near the surface. According to this configuration, even when an AC voltage or a bias voltage in which AC is superimposed on DC is applied to the developing roller, it is possible to prevent the electric charge from leaking between the developing roller 5 and the photoconductor 1, and to disturb the electrostatic latent image due to the leak. Can be prevented. A belt-shaped developer carrier can be similarly configured.

In the embodiment shown in FIGS. 1 and 2, by charging the dielectric 11 or the dielectric layer laminated thereon to a predetermined polarity, a minute closed electric field is generated near the surface of the developer carrying member. The toner supply roller 6 is used as a charging unit for forming and adhering the toner used for visualizing the latent image to the developer carrier by a closed electric field, but other independent frictional charging members and a corona discharger are used. Appropriate charging means known per se, such as an electric device or a member for injecting electric charge in contact with the developer carrying member, may be used.

Next, the materials of the non-magnetic toner and the main members of the developing device will be further illustrated for reference.

As the toner, generally, polyester, B
Basically, resins such as MA, polystyrene, epoxy, and phenol are used, and the charge polarity and charge amount thereof can be controlled by a polarity control agent internally or externally added to the toner. The external addition is to mix an auxiliary agent such as a polarity control agent with the toner, and the internal addition is to knead the toner particles and integrate them.

As the members of the developing device, those shown in Table 1 are appropriately used in consideration of the charging polarity of the toner, the releasability from the toner, the durability, and the like.

[0071]

[Table 1]

Although the developing apparatus using a one-component developer of a non-magnetic toner, which is particularly suitable for color development, has been described above, the present invention relates to a one-component system comprising a magnetic toner to which an auxiliary agent is added as necessary. The present invention can also be applied to a developing device using a developer.

In the example in which the developing roller 5 has the dielectric surface portion 11a and the conductive surface portion 12 formed in a grid pattern as shown in FIG. 11, as shown in FIG. The amount of toner adhered on the surface of the developing roller 5 is not uniform,
The amount of toner attached to the dielectric surface portion 11a is larger than the amount of toner attached to the conductive surface portion 12.

[0074] Thus the peripheral speed V ₂ of the developing roller 5 and the circumferential speed V ₁ of the photosensitive member 1 are equivalent, it occurs uneven development pattern conforming to the pattern of the dielectric surface portion 11a and the conductive surface portion 12. This finally appears as uneven density of the copied image.

To prevent this phenomenon, the peripheral speed V ₁ of the photosensitive member ₁
It is effective to greater than 1.0 the ratio of the circumferential speed V ₂ of the developing roller 5 against. That is, as shown in FIG. 12, the adhesion of the toner to the photoconductor 1 after the development is substantially uniform.

The circumferential length of the dielectric surface portion 11a on the surface of the developing roller 5 is L ₁ , the circumferential length of the conductive surface portion 12 is L ₂ , one dielectric surface portion 11a and one conductive surface portion 12 , Ie, the pattern pitch is L _0, and the developing roller 5 is moved along the circumferential length L by a distance corresponding to the pattern pitch L ₀ during the time when the photoconductor ₁ moves at the speed V _1.
It is preferable to rotate the circumference at a speed V ₂ by ₀ and at least a width L ₂ of the conductive surface portion 12. As a result, the developing roller 5 slides relatively with respect to the photosensitive member 1, and the conductive surface portion with a small amount of toner adhered is filled with the toner in the portion having a large valley with respect to the surface of the photosensitive member 1 so that development is performed. No unevenness occurs.

From this, V ₂ / V ₁ ≧ (L ₀ + L ₂ )
By setting / L ₀ , the occurrence of pattern-like image density unevenness can be prevented.

As one example, L ₀ = 0.35 mm, L ₂
= 0.07 mm, using a developing roller 5 having a grid-like dielectric and a conductive surface pattern, and a linear velocity V ₁ of the photoconductor ₁ = 120 mm / sec.
, Linear velocity of developing roller V ₂ = 120 × (0.35 + 0.07) /
When a development experiment was performed at 0.35 = 120 × 1.2 = 145 mm / sec, a uniform and uniform image was obtained.

When the developing roller 5 was rotated at the same speed as the photosensitive member 1 at 120 mm / sec, slight image unevenness was observed.

The pattern of the dielectric surface portion 11a of the developing roller 5 may be a lattice pattern, a twill pattern, a horizontal stripe pattern, or any other regular pattern.

Further, taking into account that the amount of toner adhered to the conductive surface 12 is smaller than that of the dielectric surface portion 11a, the photosensitive member 1 and the developing roller 5 are separated in consideration of the fact that the conductive surface region is in a concave state as a toner layer. In the case of relative movement, image unevenness can be greatly reduced by filling the concave state. That is, FIG.
As shown in FIG. 2, the latent image carrier 1 is a photoreceptor belt, and the nip width between the photoreceptor 1 and the developing roller 5 in the developing area 9 is L
₃ , when L ₀ <L ₃ , the developing roller 5 is moved to the nip width L ₃ and at least the circumferential length L ₂ of the conductive surface portion 12 during the time when the photosensitive member 1 moves the distance L ₃ at the speed V _1. if moved by a length obtained by adding a length corresponding to or (rotation) to set the speed V ₂ of the developing roller 5 as, i.e. V ₂ / V ₁
If ≧ (L ₃ + L ₂ ) / L ₃ , the surface of the photoconductor 1 can be filled with the toner of the dielectric surface portion 11 a in the concave portion of the surface of the photoconductor 1, even in the region where the toner adheres little. As a result, it is possible to prevent pattern-like image density unevenness.

As shown in FIG. 12, even when L ₀ ≧ L ₃ , the recess as a toner layer in the conductive surface portion 12 can be filled with toner in the same manner as described above.

Also in this case, the pattern of the developing roller is not limited to the lattice, as described above.

[0084] Matazu 12, as shown in FIG. 13, to the time the distance of the nip width L ₃ in the developing region of the photosensitive member 1 move at the speed V _1, further 1 pattern than the developing roller 5 nip width L ₃ When the speed V ₂ of the developing roller 5 is set so as to move by an amount equivalent to the pitch L ₀ , that is, by the sum of the circumferential length of one dielectric surface portion 11 a and one conductive surface portion 12, a photosensitive member linear speed V ratio V ₂ / V ₁ with respect to the _first linear velocity _{V 2 V 2 / V 1 ≧} (L 3 +
When L ₀ ) / L ₃ is set, all portions of the photoconductor 1 are developed at the average level of the developing ability distribution in the area of each pattern pitch L ₀ as shown in FIG. Does not occur. As one example, a photoreceptor 1 is formed such that L ₃ ≒ 3 mm using a grid-like developing roller of L ₁ = 0.35 mm, V ₁ = 120 mm / sec, V ₂ = 120 ×
When developed at (3 + 0.35) /3≒120×1.12 × 135 mm / sec, an extremely uniform and good image was obtained.

A bias power supply 16 for applying a bias voltage between the developer carrier 5 and the latent image carrier 1 is formed so that an alternating bias can be applied.
As shown in FIG. 5, a transfer polarity region R ₁ having a polarity that generates a force for causing a developer, for example, a toner, to fly from a developing roller 5 serving as a developer carrier to a photosensitive member 1 serving as a latent image carrier, and the transfer polarity region R _1. And the reverse transition polarity region, which is the opposite polarity
Form a cycle. The reverse transition polarity region is applied for a short time t _1, for example, 0.1 to ₁ msec, when the electric field having a strength enough to cause the developed toner attached to the photoreceptor 1 to separate from the latent image surface does not reach the developing roller 5. The first region R
₂ has the first region more becomes the second region R ₃ followed by R _2, an intermediate potential between the second region R ₃ with the electrostatic latent image potential of the photosensitive member 1 ground potential of the photosensitive member 1, a photosensitive the previously developed toner adhered to the body 1 is detached from the latent image surface toner an electric field strong enough to reach the developing roller only enough time t ₂ for example 0.15~10msec to reach the developing roller 5 Apply.

In the transition polarity region R ₁ of the alternating bias, the toner jumps from the developing roller 5 toward the photosensitive member 1, and the toner adheres to both the image region and the background region. Subsequently biased polarity is reversed, at the reverse transition polarity region, the force to leave toward the developing roller from the photosensitive member 1 in the first region R ₂ acts on the toner, the second region R ₃ in the course of time t ₁ change. In the image area changes to the second region R ₃ while the toner removed from the photosensitive member 1 is not separated from the electric field effect of the electrostatic latent image,
Since the electric field due to the electrostatic latent image is stronger than the bias electric field, the toner again moves to and adheres to the photoconductor 1 under the attractive force of the electric field of the electrostatic latent image. Since there is no electrostatic latent image is background area not an image area, the bias of the first region R _2, toner is detached toward the developing roller 5 from the photosensitive member 1 with a strong force, the bias is changed in the second region R ₃ Then, the toner is pulled back to the developing roller 5 by the bias electric field attraction and reversely transferred. Thus, the movement of the toner is transferred to the transition polarity region R.
₁ for each period of the alternating bias having three regions of the first region R ₂ and the second region R ₃ of the reverse transition polarity region,
Development is performed by repetition.

The toner once adhered to the image area of the photoreceptor 1 is not substantially peeled off by such toner control, and the toner adhered to the background area is strongly peeled off. The reproducibility is excellent, and the image is rich in gradation.

When the development process is completed in the transition polarity region of the bias, dirt is left on the background. Therefore, the development is terminated after the reverse transition polarity is completed, or the strength of the electric field in the transition polarity region is reduced. And stop.

[0089]

According to the present invention, a large amount of sufficiently charged toner can be conveyed to the developing area without rotating the developer carrier at a high speed as in the prior art, and a visible image having a desired density can be formed. In addition to this, it is possible to prevent the conventional drawbacks associated with rotating the toner carrier at a high speed, such as toner scattering, and to prevent or substantially prevent the development of the rear end toner near the visible image.

According to the present invention, by applying an alternating electric field as a bias, sharp gradation, smooth gradation and uniform image density were obtained.

According to the present invention, the bias applying means forms one cycle with the transition polarity region and the reverse transition polarity region, wherein the reverse transition polarity region has a first region and a second region following the first region. In the first region having the reverse transition polarity, the developer that has released an electric field having a strength enough to release the developer adhered on the latent image carrier reaches the developer carrier. The second region has a potential intermediate between the latent image potential of the latent image carrier and the background potential in the second region, and has sufficient strength to allow the developer attached to the background region to reach the developer carrier. The electric field was applied for a sufficient time to reach the electric field, and good image reproducibility and excellent gradation were obtained.

According to the present invention, development is performed by an alternating bias and an alternating electric field deflected by a minute closed electric field, so that powder cloud formation is prevented, gradation is obtained, and the developer carrying member is moved relative to the latent image carrying member. By selecting the above linear velocity ratio, the density of the solid portion can be made uniform. Further, the toner adhered to the non-image area is peeled off with a strong force by the above-mentioned bias waveform, thereby preventing background contamination.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view illustrating an example of a developing device.

FIG. 2 is an explanatory diagram schematically showing an enlarged view of a dielectric material and toner particles of a developing roller.

FIG. 3 is an enlarged plan view of a developing roller surface.

FIG. 4 is an enlarged sectional view taken along the line IV-IV in FIG. 3;

FIG. 5 is an explanatory diagram showing lines of electric force of a minute closed electric field formed near the surface of a developing roller.

FIG. 6 is a perspective view of a developing roller.

FIG. 7 is a schematic view showing a process of manufacturing the developing roller.
A, B, and C respectively show changes in the order of the manufacturing process.

FIG. 8 is an explanatory diagram of the trailing edge of the toner.

FIG. 9 is a graph showing the relationship between the amount of toner near the trailing end and the linear velocity ratio between the developing roller and the photosensitive member.

FIG. 10 is a graph showing a relationship between background contamination and a linear velocity ratio between a developing roller and a photosensitive member.

FIG. 11 is a perspective view of another example of the developing roller.

FIG. 12 is an enlarged view illustrating a state of toner adhesion near a developing unit.

FIG. 13 is an explanatory diagram of another example of FIG.

FIG. 14 is a development capacity distribution diagram of the developing roller when the latent image carrier and the developer carrier are at the same linear speed.

FIG. 15 is a waveform diagram of an alternating bias.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 latent image carrier 5 developer carrier 9 developing section 11 dielectric 11 a dielectric surface portion 12 conductive surface portion 16 bias power supply L ₀ pattern pitch L ₁ dielectric material L ₂ conductive surface width L ₃ nip width R ₁ development polarity region R ₂ separation polarity first area R ₃ separation polarity second area

Continued on the front page (72) Inventor Shigekazu Enoki 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company (72) Inventor Junko Tomita 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Company (56) References JP-A-2-214874 (JP, A) JP-A-60-134262 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 15/08 G03G 15/00 303

Claims (4)

(57) [Claims] An image forming apparatus includes: a developing unit that is opposed to a latent image carrier that carries an electrostatic latent image in a developing unit and carries a developer; In the developing device, two types of surface portions having different resistance or permittivity are regularly mixed and exposed on the surface of the developer carrier, and between the two surface portions. When a minute electric field is formed, a large number of minute electric fields are formed on the surface of the developer carrier, and the linear velocity ratio of the developer carrier to the latent image carrier is:
A value obtained from the pattern pitch of the surface portion and the width of the low-resistance surface portion (pattern pitch + low-resistance portion width) / (pattern pitch); And the reverse transition polarity region constitutes one cycle, in which case the reverse transition polarity region is the first period.
An alternating bias having an area and a second area subsequent to the first area is applied, and in the first area having the reverse transition polarity, an electric field strong enough to release the developer adhered on the latent image carrier. Is applied for a short period of time so that the developer that has separated from the developer carrier does not reach the developer carrier, and the second region has a potential intermediate between the latent image potential of the latent image carrier and the background potential, and the developer attached to the background region An electric field of sufficient strength to cause the developer to reach the developer carrier for a time sufficient to reach the developer carrier; and an electric field determined by a correlation between the bias electric field and the electric field on the developer carrier and the latent image. A developing device, wherein the movement of the developer is controlled by a potential on a carrier. 2. A developing unit, which is disposed opposite to a latent image carrier for carrying an electrostatic latent image in a developing unit and carries a developer, wherein the developer carrier is under a bias applied by a bias applying unit. In the developing device, two types of surface portions having different resistance or permittivity are regularly mixed and exposed on the surface of the developer carrier, and between the two surface portions. When a minute electric field is formed, a large number of minute electric fields are formed on the surface of the developer carrier, and the linear velocity ratio of the developer carrier to the latent image carrier is:
Value obtained from the pattern pitch of the surface portion and the nip width of the latent image carrier with respect to the developer carrier in the developing section (pattern pitch + developing nip width) / (developing nip width)
Being set to a larger value, the bias applying means forms one cycle with the transition polarity region and the reverse transition polarity region, and in this case, the reverse transition polarity region is the first period.
An alternating bias having an area and a second area subsequent to the first area is applied, and in the first area having the reverse transition polarity, an electric field strong enough to release the developer adhered on the latent image carrier. Is applied for a short period of time so that the developer that has separated from the developer carrier does not reach the developer carrier, and the second region has a potential intermediate between the latent image potential of the latent image carrier and the background potential, and the developer attached to the background region An electric field of sufficient strength to cause the developer to reach the developer carrier for a time sufficient to reach the developer carrier; and an electric field determined by a correlation between the bias electric field and the electric field on the developer carrier and the latent image. A developing device, wherein the movement of the developer is controlled by a potential on a carrier. 3. A developing unit, which is opposed to a latent image carrier for carrying an electrostatic latent image in a developing unit and carries a developer, wherein the developer carrier is under a bias applied by a bias applying unit. In the developing device, two types of surface portions having different resistance or permittivity are regularly mixed and exposed on the surface of the developer carrier, and between the two surface portions. When a minute electric field is formed, a large number of minute electric fields are formed on the surface of the developer carrier, and the linear velocity ratio of the developer carrier to the latent image carrier is:
Set to a value larger than the value obtained from the low resistance portion width of the surface portion and the nip width of the latent image carrier with respect to the developer carrier in the developing section (low resistance portion width + development nip width) / (development nip width). And the bias applying means forms one cycle with the transition polarity region and the reverse transition polarity region, wherein the reverse transition polarity region is the first period.
An alternating bias having an area and a second area subsequent to the first area is applied, and in the first area having the reverse transition polarity, an electric field strong enough to release the developer adhered on the latent image carrier. Is applied for a short period of time so that the developer that has separated from the developer carrier does not reach the developer carrier, and the second region has a potential intermediate between the latent image potential of the latent image carrier and the background potential, and the developer attached to the background region An electric field of sufficient strength to cause the developer to reach the developer carrier for a time sufficient to reach the developer carrier; and an electric field determined by a correlation between the bias electric field and the electric field on the developer carrier and the latent image. A developing device, wherein the movement of the developer is controlled by a potential on a carrier. 4. A developing device, which is disposed opposite to a latent image carrier for carrying an electrostatic latent image in a developing section and carries a developer, wherein the developer carrier is under a bias applied by a bias applying means. In the developing device, the surface of the developer carrier is provided with two types of surface portions having different resistances and dielectric constants at an angle of 30 to 60 degrees with respect to the moving direction.
It is regularly mixed in an inclined grid and exposed on the surface,
By forming a minute electric field between the two surface portions, a large number of minute electric fields are formed on the surface of the developer carrying member, and the linear velocity ratio of the developer carrying member to the latent image carrying member is 1 The bias application means forms one cycle with the transition polarity region and the reverse transition polarity region, and in this case, the reverse transition polarity region is the first period.
An alternating bias having an area and a second area subsequent to the first area is applied, and in the first area having the reverse transition polarity, an electric field strong enough to release the developer adhered on the latent image carrier. Is applied for a short period of time so that the developer that has separated from the developer carrier does not reach the developer carrier, and the second region has a potential intermediate between the latent image potential of the latent image carrier and the background potential, and the developer attached to the background region An electric field of sufficient intensity to cause the developer to reach the developer carrier for a sufficient time to reach the developer carrier; and an electric field determined by a correlation between the bias electric field and the electric field on the developer carrier and the latent image. A developing device, wherein the movement of the developer is controlled by a potential on a carrier.