JPH04304481A - Developing device - Google Patents

Abstract

PURPOSE:To obtain a high quality image by improving an image density while maintaining the gradation. CONSTITUTION:A first dielectric 11 composed of polystyrene resin and a second dielectric 12 composed of silicone resin are provided so as to be mixed and exposed on the surface of a developing roller 5. A surface is friction-charged by a toner supplying roller 6 composed of polyurethane resin, so that the dielectric 11 holds the negative charge and the dielectric 12 holds the positive charge, to form a large number of fine closed electric fields. Then, negatively electrified toner is mainly carried on the dielectric 12 by the closed electric fields to be supplied to a developing part, and a bias by a pulse voltage is applied to the developing part, to carry out reverse development.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a developing device employed in an image forming apparatus such as an electrophotographic copying machine, a printer, or a facsimile machine, and more specifically, the present invention relates to a developing device that is employed in an image forming apparatus such as an electrophotographic copying machine, a printer, or a facsimile machine. The present invention relates to a developing device that carries an image carrier to a developing section opposite to it and performs development.

0002

[Prior Art] In this type of developing device, a developer carrier with a thin layer of developer formed on its surface and an electrostatic latent image carrier are arranged to face each other in a developing section, and the developer is carried in the developing section. It is known to develop an electrostatic latent image on an electrostatic latent image carrier by forming an electric field that can transfer the developer on the body to the electrostatic latent image carrier. In this developing device,
There is a threshold value for developer to transfer from the developer carrier to the electrostatic latent image carrier, and developer adhesion occurs in image areas with a surface potential exceeding this threshold value, but conversely, when the surface potential is below the threshold value, developer adhesion occurs. Since there is almost no developer adhesion in the image area having .gamma., there is a problem that the image has so-called γ and poor gradation. However, it is known that this problem can be solved by forming an alternating electric field of relatively low frequency in the developing section (see, for example, Japanese Patent Publication No. 1013/1983).

However, simply applying a low-frequency alternating electric field to the developing section results in a decrease in image density if the conditions of the alternating electric field are set to improve gradation; If the height was increased, there were problems such as the lines in the image becoming thicker. In recent years, as the output information of images created by image forming devices has become more diverse,
Even higher image quality than before is desired.

0004

SUMMARY OF THE INVENTION The present invention has been devised in view of the problems of the prior art, and its purpose is to improve image density while maintaining gradation. It is an object of the present invention to provide a developing device that enables high-quality images to be obtained.

[0005]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides an electrostatic latent image carrier carrying an electrostatic latent image and a developer carrying member carrying a developer in a developing section. In a developing device that performs development by facing each other and applying a bias in the developing section, a first substance and a second substance having different chargeability are regularly or irregularly mixed and exposed on the surface as the developer carrier. At the same time, an exposed portion of at least one of the first substance and the second substance on the surface is charged to a predetermined polarity to form a large number of minute electric fields on the surface, and the electrostatic latent image carrier is This is characterized in that the movement of the developer is controlled by an electric field determined by the mutual relationship between the potential above, the electric field due to the bias, and the electric field on the developer carrier. Here, chargeability is a property that determines the potential when transferred to the developing section after being charged by a predetermined charging means. For example, in a device that uses frictional charging means as the charging means, the chargeability The position on the triboelectric series that determines the polarity and amount of charge when applied;
This also corresponds to the resistivity which influences the potential attenuation during the period of movement to the developing section.

[0006]

[Function] In the present invention, the developer carrier carrying the developer is
An exposed portion of at least one of the first material and the second material on the surface is charged to a predetermined polarity to form a large number of minute electric fields on the surface, thereby forming a large number of electric field configurations on the surface. Then, an electric field is formed by a voltage applying means in a developing section where the developer carrier and the electrostatic latent image carrier face each other, and the electric potential on the electrostatic latent image carrier and the potential on the developer carrier are changed. controlling the movement of the developer by an electric field determined by the interaction between the potential and the electric field formed by the voltage applying means;
This acts to cause an appropriate amount of developer to adhere to the electrostatic latent image on the electrostatic latent image carrier.

[0007]

Embodiments Hereinafter, embodiments in which the present invention is applied to a developing device of an electronic copying machine will be described in detail with reference to the drawings. In FIG. 1, a belt-shaped photoreceptor 1, which is an example of an electrostatic latent image holder, is driven in the direction of arrow A, and a developing device 2 is provided opposite to it. In the developing container 3 of the developing device 2, a one-component developer consisting of a non-magnetic toner 4 to which an auxiliary agent is externally added as required is accommodated. The volume resistivity value of the toner is, for example, about 10 7 to 10 12 Ωcm. A developing roller 5, which is a developer carrying member, is supported on the front and rear side plates of the developing container 3 with a portion exposed from the opening of the developing container. Driven to rotate clockwise. The developing roller 5 is an example of a structure of a developer holder, and a belt-shaped developer holder may be used instead of the developing roller 5. A toner supply roller 6, which is an example of a charging member, is supported on the front and rear side plates of the developer container 3, and the roller 6 is rotated counterclockwise while being in contact with the developer roller 5. The toner in the developer container 3 is conveyed to a toner supply roller 6 while being agitated by an agitator 7 that rotates clockwise, and then supplied to the developer roller 5 by this roller 6. During this supply, the toner is frictionally charged to a predetermined polarity, in this example, the same polarity as the uniform charging polarity of the photoreceptor 1, electrostatically adheres to the circumferential surface of the developing roller 5, and is held by the developing roller 5. The configuration and operation related to this will be explained in detail later. The toner supplied and supported on the circumferential surface of the developing roller 5 is conveyed by the rotation of the roller 5, and is leveled by a doctor blade 8, which is an example of a layer thickness regulating member, to regulate it to a uniform predetermined thickness. This predetermined thickness may be made to match the development gap between the surface of the photoreceptor 1 and the surface of the developing roller 5, or may be made thinner than this to provide a space between the developer layer and the surface of the developing roller 5. You can also do it. In the latter case, so-called non-contact development will be performed. Next, this toner is transferred to the photoreceptor 1 and the developing roller 5.
The electrostatic latent image is transferred to the developing section 9 opposite to the photoreceptor 1, where it is electrostatically transferred to the electrostatic latent image formed on the photoreceptor 1, and the electrostatic latent image is visualized. As a layer regulating member, a doctor blade 8 is used.
In addition to this, a regulating roller, a regulating belt, etc. can also be used. The toner that has passed through the developing section 9 without being subjected to development is returned to the toner supply roller 6 while being supported on the developing roller 5. Further, the visible image formed on the photoreceptor 1 is transferred to a transfer paper (not shown), and fixed onto the transfer paper by a fixing device.

In the developing roller 5 shown in FIG. 3, a first dielectric material 11 is formed in a layered manner with a constant thickness on the surface of a conductive substrate 10 such as aluminum, iron, or copper. A second dielectric material 12 is embedded in the first dielectric material 11, and this second dielectric material is distributed and exposed regularly or irregularly over a small area over a large number of areas on the surface of the first dielectric material 11. ing. The first dielectric 11 and the second dielectric 12 have different charging properties from each other, and are sufficiently far apart in the triboelectrification series. For example, the first dielectric 11 is made of polystyrene resin, and this is used as the conductive substrate 10.
The second dielectric material 12 made of silicone resin, which is far away from the polystyrene resin in terms of triboelectrification, is coated on the surface to a thickness of about 500 μm, for example, with a thickness of about 200 μm.
The developing roller 5 is fabricated by heat-sealing the sheets into square pieces of μm square and about 50 μm thick. Incidentally, instead of burying one dielectric body in the other dielectric body, the first dielectric body 11 and the second dielectric body 12 made of the same material as those exemplified above may be regularly or irregularly conductive. They may be arranged and fixed on the sexual substrate 10, and the surface thereof may be exposed in a minute area. FIG. 2 is an enlarged view of the surface of the developing roller 5 viewed from the outside. In this example, the second dielectrics 12 have a square shape, and are regularly arranged at a predetermined pitch. . Each dielectric 1 exposed on the surface
The surface shapes and sizes of the developing rollers 1 and 12 can be appropriately set in consideration of the electric field strength of the minute closed electric field, which will be described later. It is desirable to set it to 5 to 40% of the surface area. On the other hand, the toner supply roller 6 in contact with the developing roller 5 contacts the surface of the developing roller 5 and charges the first and second dielectrics 11 and 12 with opposite polarities, so that the toner supply roller 6 is positively or negatively charged. Toner (in this example, negatively charged toner) is attached to these. For this purpose, the surface of the developing roller 5 is made of a material between the materials constituting the first and second dielectric bodies 11 and 12 in terms of frictional charging. In this example, as shown in FIG. 3, the toner supply roller 6 is made up of a conductive core member 14 and a cylindrical foam 15 laminated around the core member 14, and this foam 15 is pressed against the developing roller 5 while being elastically deformed. are doing. When such a toner supply roller 6 is used, the foam 15 is made of a material between the materials constituting the first and second dielectric bodies 11 and 12 in terms of frictional charging as described above. For example, in terms of triboelectrification, the first and second dielectrics 11 and 12 are made of polyurethane resin between polystyrene resin and silicone resin. In this case, the polystyrene resin is negatively charged compared to the polyurethane resin, and the silicon resin is positively charged, so the first dielectric 11 on the surface of the developing roller is made negative by the toner supply roller 6, and the second The dielectric 12 is triboelectrically charged to a positive polarity. Further, instead of the foam 15, a known material such as a fur brush made of polyurethane fibers may be used.

A more detailed explanation of the operation of the above configuration is as follows. As explained earlier with reference to Figure 1,
The developing roller portion that has passed through the developing section 9 moves to the toner supply roller 6 and comes into contact with the member 6. Here, it is supported on the developing roller 5. The toner that has not been subjected to development is scraped off by the scavenging force received from the toner supply roller 6. At the same time, the first
The dielectric 11 and the second dielectric 12 are charged to opposite polarities by friction with the toner supply roller 6. on the other hand,
The developing roller 5 is in contact with the circumferential surface of the toner supply roller 6.
The toner conveyed to the developing roller 5 is frictionally charged to a negative polarity by friction with the toner supply roller 6, and then supplied to the developing roller 5. At this time, the toner is further frictionally charged to a negative polarity by the friction with the developing roller 5. Here, the first
Since the second dielectrics 11 and 12 are triboelectrically charged with opposite polarities, a potential difference is generated between the first and second dielectrics 11 and 12, and this potential difference is generated in countless small areas. According to this potential difference, the first and second dielectrics 11, 12
During this time, a closed electric field as shown by symbol E in FIG. 4 is formed. That is, on the surface of the developing roller 5, an infinite number of minute closed electric fields (micro fields) are formed.
Since the surfaces of the first dielectric 11 and the second dielectric 12 are adjacent to each other in a small area, the strength of each small closed electric field becomes very strong due to the edge effect or peripheral electric field effect. The toner charged to a predetermined polarity is attracted to the surface of the developing roller 5 by the closed electric field, and as shown in FIG. It is strongly attracted by the second dielectric 12) and held on the roller 5 in a state where it is difficult to separate (
In the figure, a first dielectric 11 and a second dielectric 12 are shown.
are regularly or irregularly arranged and fixed on the conductive substrate 10, and the surface thereof is exposed in a minute area to constitute the developing roller 5). At this time, the toner is strongly triboelectrically charged due to the friction between the toner supply roller 6 and the developing roller 5, and is held by the action of a strong minute closed electric field on the surface of the developing roller 5. A large amount of charged toner is supported. In this embodiment, the exposed portion of the second dielectric 11 becomes the part that attracts the toner, and the exposed part of the first dielectric 11 becomes the part that repels the toner. Figure 6 (
As shown in a), toner may adhere to the central portion. The toner supply roller 6 charges the dielectric 12 of the developing roller 5 and the toner, and also serves to supply the toner onto the developing roller 5 . At this time, the toner is strongly held on the developing roller 5 by the closed electric field formed between the first and second dielectrics 11 and 12. Note that when the layer thickness of the toner carried on the developing roller 5 is regulated by a doctor blade 8 made of polyurethane resin, for example, the sufficiently charged toner is strongly held on the surface of the developing roller 5 by a minute closed electric field. The toner with a small amount of charge is removed by the contact pressure with the doctor blade 8, and in the end, only the toner with a large amount of charge is removed.
A larger amount than before is conveyed to the developing section 9, and the electrostatic latent image is visualized as described above. For example, in order to suppress staining of the visible image and increase its sharpness, -5 to 2
A large amount of toner (for example, 0.8 to 1.2 mg/cm 2 or more) charged to about 0 (preferably 8 to 15) μc/g can be conveyed to the developing section 9. Therefore, even if the surface linear velocity of the developing roller 5 is made close to the surface linear velocity of the photoreceptor 1, or even if they are set to be equal, it is possible to prevent the image density of the visible image from decreasing. This is the same when the toner is black or when it is a chromatic color toner. Furthermore, the toner supply roller 6
Conductive treatment is applied to the parts of the foam 15 and the fur brush that are in contact with the surface of the developing roller, and a bias voltage is applied to the toner supply roller 6 by the power source 50 as shown in FIG. If the surface of the developing roller 5 is configured to be charged by charge injection or discharge, the electric field strength of the minute closed electric field formed on the developing roller 5 as described above can be controlled. As a result, the developing roller 5
It is possible to freely control the amount of toner that can be carried on the toner and transported to the developing section 9, making it possible to form a visible image of desired image quality. For example, if the fur brush of the toner supply roller 6 in contact with the developing roller 5 is made of polyurethane fibers as in the above-mentioned example, the fibers are subjected to conductive treatment in advance to reduce the specific volume resistivity to 1, for example.
This is made conductive by setting it to about 04 to 105 Ωcm, and a bias voltage is applied to it by the power supply 50. 1 is a power supply that applies a bias voltage to the conductive substrate 10 of the developing roller 5, and this bias is a direct current or A method in which alternating current is superimposed on this is adopted.

An example of bias application to the developing roller 50 by the power source 51 will be described below with reference to FIGS. 7 to 9. In this example, an OPC is used as the photoreceptor 1, the surface potential of the background part is -900V, and the potential of the exposed part is -900V.
At 100 V, reversal development is performed using negative polarity toner. The developing roller 5 is constructed by using a polystyrene resin as the first dielectric 11, a silicone resin as the second dielectric, and a polyurethane resin on the surface of the toner supply roller 5. As shown in FIG. 6(a), the first dielectric 11 holds an amount of charge that is rubbed by the toner supply roller 8 and has a potential of -80V with respect to the ground, while the second dielectric The body 12 is rubbed by the toner supply roller 8, and the potential with respect to the ground becomes plus 20.
Holds enough charge to reach 0V. Then, a power source 51 is applied to the developing roller 5 to generate peak-to-peak (hereinafter referred to as P-P) power.
) 1000V, maximum potential 0V, frequency 500Hz
, a pulse voltage with a duty ratio of 30% (T2/T1) was applied.

FIG. 7 shows temporal changes in the surface potential of the developing roller 5 with respect to grounding, and (a) shows the change in the surface potential of the developing roller 5 with respect to the ground.
(b) shows the surface potential of the first dielectric 11. In these figures, the surface potential level (-90
0V) and the surface potential level (-100V) of the exposed portion are shown as horizontal lines, respectively. As can be seen from the continuous rectangular line showing temporal changes in the surface potential of the second dielectric 12 in FIG. 7(a), the surface potential of the second dielectric 12 is
The applied voltage becomes a potential biased by +200V due to the retained charge. On the other hand, the surface potential of the first dielectric 11 is determined by the charge held by the voltage applied by the power source 51, as seen from the continuous rectangular line showing the temporal change in the surface potential of the dielectric 11 in FIG. 7(b). The potential is biased by -80V.

Next, the electric field between the surface of the developing roller 5 and the photoreceptor 1 will be explained when the potential of the surface of the developing roller 5 changes as described above. Depending on whether the electric field is on the second dielectric 12 or the first dielectric 11 on the surface of the developing roller 5, the electric field may be applied to the image area and the background area of the photoreceptor 1 for each of the dielectrics 11 and 12. It depends on which side you are facing. FIG. 8 shows a first dielectric material 11 which causes a temporal change in surface potential as shown in FIG. 7(b).
This is for explaining the above electric field, and FIG. 8(a) shows a temporal change in the potential difference between the dielectric 11 and the image area (exposed area) of the photoreceptor 1 when the dielectric body 11 faces the image area (exposed area) of the photoreceptor 1. Figure 8(b)
) shows a temporal change in the potential difference between the dielectric 11 and the background portion (unexposed portion) of the photoreceptor 1 when the two are opposed to each other. Further, FIG. 9 is for explaining the electric field on the second dielectric 12 that causes a temporal change in surface potential as shown in FIG. 7(a). 9(b) shows a temporal change in the potential difference between the two when the dielectric body 22 faces the image area (exposed area) of the photoreceptor 1, and FIG. It shows the temporal change in the potential difference between the two when they are facing each other. In FIGS. 8 and 9, since the electric field exerts an electrostatic force on the toner carried on the surface of the developing roller 5 or the toner carried on the surface of the photoreceptor 1, the direction of this electrostatic force cannot be distinguished. In order to do this, the potential difference corresponding to the electric field in the direction in which the toner is directed toward the photoreceptor 1 is expressed as positive, and the potential difference corresponding to the electric field in the direction in which the toner is directed toward the developing roller 5 is expressed as negative. In addition, the threshold value of the potential difference +100V at which the toner on the developing roller 5 is transferred to the photoreceptor 1 and the threshold value of the electric field at which the toner on the photoreceptor 1 is transferred toward the developing roller 5 -100V were confirmed through experiments. The level of , respectively, is shown by a horizontal line, and the portion corresponding to an electric field that exceeds this threshold and contributes to the transfer of toner is shown by a diagonal line. In the above experiment, the gap between the developing roller 5 and the photoreceptor 1 was set to 100 μm, a DC voltage was applied to the developing roller 5, and the transfer of toner was observed while changing the value of this DC voltage. In this example, the threshold value of the developing electric field was found to be 1 V/μm. Further, the charge amount of the toner used at this time was investigated and found to be approximately 10 μC/g.

When the toner existing on the first dielectric 11 of the developing roller 5 faces the image area of the photoreceptor 1,
As shown by the hatched area in FIG. 8(a), it is thought that the transfer occurs in the direction of the photoreceptor 1 when the developing electric field (hereinafter referred to as the developing electric field) corresponding to a potential difference of +980V is reached. When facing the background area, a negative electric field of -820V and a positive electric field of +180V appear alternately as electric fields contributing to toner transfer, as shown by the hatched area in FIG. 8(b). is transferred from the developing roller 5 to the photoreceptor 1, and from the photoreceptor 1 to the developing roller 5 when there is a negative electric field,
The period during which toner is transferred from the photoreceptor drum 1 to the developing roller 5 due to the negative electric field is sufficiently long and the transfer force is also large, so even if toner is transferred to the photoreceptor 1 due to the positive electric field, this It is considered that the toner is transferred to the developing roller 5 again. Similarly, the second developing roller 5
Since this second dielectric 12 is originally charged to +200V, the toner existing on the second dielectric 12 is generated in the shaded area in FIG. As shown, a negative electric field of -300V and a positive electric field of +700V appear alternately, and the positive electric field is transferred from the developing roller 5 to the photoreceptor 1, and the negative electric field is transferred from the photoreceptor 1 to the developing roller 5. considered to be a thing. In addition, when facing the background part of the photoreceptor 1, as shown by the diagonal line in FIG. 9(b), -
It is considered that the negative electric field of 1100 V causes the transfer from the photoreceptor 1 to the developing roller 5, and that the transfer does not occur alternately.

According to this embodiment, areas holding different charges coexist on the surface of the developing roller 5, and locally different developing biases are applied in the developing section, so that the photoreceptor 1 having an electrostatic latent image and When developing is performed by applying a bias between the toner and the developing roller 5 carrying toner on its surface, the toner transfer can be selectively controlled by the developing roller 5. For example, in the above example, as shown in FIG. 9(a), positive and negative electric fields exceeding the threshold are acting on the toner present on the second dielectric 12, and excessive toner While adhesion is suppressed, the toner existing on the first dielectric 11 has a higher electric field than the second dielectric 12, as shown in FIG. 8(a). Can be done. By changing the materials of the first and second dielectrics, such bias can be set to a condition that allows a desired image to be obtained by changing the charge held by each dielectric.

[0015] In the above embodiment, the first dielectric material was replaced with polystyrene resin and Teflon (trade name, hereinafter the same) was used.
It may also be constructed using resin. In this case as well, the first dielectric made of Teflon resin is turned to negative polarity, which is the opposite polarity to the friction charging polarity of the second dielectric made of silicone resin, by the toner supply roller 6 made of polyurethane resin. Triboelectrically charged, negatively polarized toner is attracted onto the second dielectric, which is primarily made of silicone resin. Further, in the same manner as in the above embodiment, the toner was negatively charged, polycarbonate resin was used as the first dielectric material, and polycarbonate resin was used as the second dielectric material 1.
It is also possible to use Teflon resin as the toner supply roller 2, and to use polyurethane resin or polystyrene resin as the foam or the like of the toner supply roller 6. In this example, a dielectric made of polycarbonate resin is positively charged, a dielectric made of Teflon resin is negatively charged,
A closed electric field is formed between both dielectrics, and the negative polarity toner is mainly attracted onto the first dielectric 11 made of polycarbonate resin which is triboelectrically charged to a positive polarity. Contrary to this example, Teflon resin is used as the first dielectric, polycarbonate resin is used as the second dielectric (the toner supply roller 6 uses polyurethane resin or polystyrene resin as in the above example), and positive polarity is used. It is also possible to use toner that is charged to . FIG. 6(b) shows the state of toner carried on the surface of the developing roller 5, in which positive polarity toner is mainly deposited on the first dielectric material made of Teflon resin that is frictionally charged to negative polarity. Attracted.

In the above embodiment, the first dielectric 1
The first dielectric body 12 and the second dielectric body 12 are frictionally charged to opposite polarities, thereby forming an infinite number of minute closed electric fields (microfields) on the surface of the developing roller 5. It is also possible to form an infinite number of minute closed electric fields (microfields) on the surface of the developing roller 5 by frictionally charging only one of the dielectric body 11 and the second dielectric body 12 positively or negatively. . For example, the second dielectric 12
When triboelectrically charging only the first dielectric 11 and the second
The second dielectric body 12 is composed of dielectric bodies that have different charging properties and are sufficiently far apart in the triboelectric charging series, and the toner supply roller 6 in contact with the developing roller 5 is configured to be far away from the second dielectric body 12 in the triboelectric charging series. , and are made of the same or substantially the same material as the first dielectric 11 in terms of charging series. According to this, the second dielectric body 12, which has a different charging series from the toner supply roller 6, is strongly frictionally charged to a predetermined polarity determined by the frictional charging series, while the second dielectric body 12, which has a different charging series from the toner supply roller 6, is frictionally charged to a predetermined polarity determined by the frictional charging series, while the second dielectric body 12 has a charging series that is the same or approximately the same as the toner supply roller 6. A potential difference is generated between the first and second dielectric bodies 11 and 12 without any or almost no triboelectric charging of the first dielectric body 11, which is the same material, and this potential difference is generated in infinitely small areas. Therefore, a closed electric field as shown by the symbol E in FIG. 4 is formed between the first and second dielectrics 11 and 12, as in the above embodiment, and on the surface of the developing roller 5 there are so many minute particles that it can be said to be innumerable. A closed electric field (micro field) is formed, and since the surfaces of the first dielectric 11 and the second dielectric 12 are adjacent to each other in a small area, the strength of each micro closed electric field increases due to the edge effect or peripheral electric field effect. becomes very strong. For example, the first dielectric 11 is made of polystyrene resin, the second dielectric 12 is made of polycarbonate resin, and the foam 15 of the toner supply roller 6 is made of foamable polyurethane resin or polystyrene resin. Instead of the foam 15, for example, a fur brush made of urethane fibers or the like may be used. In this example, only the second dielectric 12 is frictionally charged to a positive polarity, and as a result, as shown in FIG. 6(c), the negatively charged toner is strongly attracted to the dielectric 12 by the closed electric field. A large amount can be held on the roller 5 in a state where it is difficult to separate. Note that the first dielectric 1 in FIG.
1, the "-" shown near the boundary with the second dielectric 12 indicates that the second dielectric 12 is triboelectrically charged.
This shows a small amount of negative charge induced on the interface portion of the dielectric 11, and a closed electric field is formed between this charge and the triboelectric charge of the second dielectric 12. Further, the toner is also attracted to the center of the first dielectric 11, and the toner strongly adsorbed on the second dielectric 12 and the relatively attracted toner on the first dielectric 11 are placed on the developing roller 5. weakly adsorbed toner is supported.

In the above embodiment, the toner may be positively charged, and the toner may be mainly attracted to the surface of the first dielectric 11 and carried on the developing roller 5. or,
In the above embodiment, regarding the toner supply roller 6,
This is made of a material on substantially the same charging series as the first dielectric 11, and a different material from the second dielectric 12, but by reversing this, the toner supply roller 6 may be made of a substance on substantially the same charge series as the second dielectric 12, and the first dielectric 11 may be made of a different material. For example, if the toner is positively charged, a brush made of polyurethane fiber or a roller made of the same material is used as the toner supply roller 6, a Teflon resin is used as the first dielectric 11, and a second dielectric As the body 12, polystyrene resin, which is close to polyurethane in terms of charging series, is used. According to this,
The exposed portion of the first dielectric material 12 made of Teflon resin on the outer surface is negatively charged, while the exposed portion of the second dielectric material 12 made of polystyrene resin has a charging series close to the toner supply roller 6. Therefore, the first and second dielectric bodies 1 on the surface of the developing roller 5 are not substantially charged.
A minute closed electric field will be formed between 1 and 12,
Functions similar to those of the embodiments described above can be achieved. In this example, a roller made of polystyrene resin or the like may be used as the toner supply roller 6. Further, as a device to which the toner is negatively charged, for example, a fur brush roller made of Teflon resin is used as the toner supply roller 6, silicon resin is used as one dielectric material, and Teflon resin is used as the other dielectric material. As a result, a minute electric field is formed between the dielectric material made of silicone resin that is tribo-charged to a positive polarity by the toner supply roller 6 made of Teflon resin, and the dielectric material made of Teflon resin that is not substantially tribo-charged. Toner can be attracted to and carried on the exposed portion of the dielectric made of silicone resin. The point is that at least one of two types of dielectric materials having different charging properties may be charged by a charging member.

Furthermore, the first dielectric 11 and the second dielectric 1
2 are frictionally charged to have the same polarity, thereby forming an infinite number of minute closed electric fields (microfields) on the surface of the developing roller 5. 1st and 2nd
For example, when triboelectrically charging the dielectric material to positive polarity, the first
The dielectric material 11 and the second dielectric material 12 are made of dielectric materials that have different charging properties and are sufficiently separated from each other in the triboelectric charging series, and the toner supply roller 6 in contact with the developing roller 5 is made of
and a material located on the negative polarity side in the charging series with respect to the second dielectric. According to this, even if the polarities of the charges due to frictional electrification on both dielectrics are the same, there is a difference in the amount of charge, and a potential difference is generated between the two dielectrics. A closed electric field can be formed between both dielectrics. For example, a positively charged toner is used as the toner, a polystyrene resin is used as the first dielectric 11, a polypropylene resin is used as the second dielectric 12, and a foamed polyurethane resin is used as the toner supply roller 6. According to this, as shown in FIG. 6(d), although both dielectric materials are triboelectrically charged to a negative polarity by the toner supply roller 6 made of polyurethane resin, polypropylene resin is relatively far away from polyurethane resin in the charging series. The second dielectric 12 made of resin holds more triboelectric charges than the first dielectric, and as a result, a closed electric field is formed between the two dielectrics, and the positive toner is mainly strongly attracted onto the second dielectric.

Next, referring to FIGS. 4 and 5, a developing device using a modified example of the developing roller 5 in which dielectric materials having different charging properties are regularly or irregularly exposed on the surface in a minute area will be explained. explain. FIG. 4 shows a developing roller 5 according to a modified example.
(a) is an explanatory diagram showing each dielectric of the developing roller 5 and toner particles enlarged in a schematic manner, and (b) is an explanatory diagram showing each dielectric in a schematic enlargement. (c) is a cross-sectional view taken along the line IV-IV of (a), and (d) shows the lines of electric force of the minute closed electric field formed near the surface of the developing roller. It is an explanatory diagram. Figure 4(a)
As shown schematically and enlarged in FIG.
A roller is used which includes a base made of zero and a medium resistance element 12 and a high resistance element 11 fixed to the peripheral surface thereof. The medium resistance element and the high resistance element are composed of dielectric materials having at least different resistivities, and have different charging properties. The resistivity of the medium resistor 12 is higher than the resistivity of the conductive base surface (in this example, the conductive roller 10), and the resistivity of the high resistor 11 is set even higher than that of the medium resistor 12. Ru. For example, the resistivity of both resistors is 1
It is set to 0.08 Ωcm or more, preferably 1010 Ωcm or more. In FIG. 4(b), the high-resistance element 11 is shown with a horizontal line in order to make it easier to distinguish between the two resistors 11 and 12 (the same applies to FIGS. 5(a) to 5(d)). Figures and Figure 4 (
As can be seen from a) and FIG. 4(c), the high resistance elements 11 and the medium resistance elements 12 are arranged regularly (or irregularly) and are exposed on the surface of the developing roller 5. are doing. The shape of each medium resistance element 12 and high resistance element 11 can be set appropriately, but if the surface shape is a rectangle as illustrated in FIG. 4(b), the lengths of one side D1 and D2 are, for example,
It can be set to an appropriate value of about 0 to 500 μm. The values related to the size of the resistors 11 and 12 and their resistivities can increase the strength of the closed electric field and carry an optimal amount of toner on the developing roller 5, as in the above-described embodiment. In addition, it is appropriately selected so as to form a desired electric field in the developing section. In this example, the toner that is positively charged is used, and the high-resistance element 11 and the medium-resistance element 12 are made of materials that are triboelectrically charged to have a polarity opposite to that of the toner, that is, to have a negative polarity. is selected. Furthermore, if necessary, a bias voltage such as direct current, alternating current, superimposed direct current alternating current, or pulse voltage can be applied to the conductive roller 10 of the developing roller 5 to improve the quality of the visible image, or the roller 10 can be grounded. It is also possible to configure it so that the The same applies to the toner supply roller 6. When the toner carrier comprises a belt, a medium resistance element and a high resistance element are laminated and fixed in the above-mentioned state on the surface of the conductive base of the belt. On the other hand, a toner supply roller 6 in contact with the developing roller 5
The foam 15 is made of polyurethane foam, for example.

In this example as well, as in the example shown in FIG.
The high-resistance element 11 and the medium-resistance element 12 are negatively charged by friction, but since their resistivities are different from each other, as shown in FIG. 4(d)
As schematically shown in , the amount of charge on the high resistance element 11 is greater than the amount of charge on the medium resistance element 11, resulting in a difference in surface potential between the two. Therefore, a closed electric field is formed between both resistors 11 and 12. On the surface of the conductive roller 10, an infinite number of high-resistance elements 11 and medium-resistance elements 12 are alternately positioned, so that countless minute closed electric fields (microfields) are generated on the surface of the developing roller 5. It is formed uniformly distributed on the roller surface. That is, when considering the lines of electric force representing the state of the electric field, a positive electric force E is formed in the space near the surface of the developing roller 5, as shown by many arcuate lines in FIG. 4(d). , the lines of electric force exit from the developing roller 5 and return to the same developing roller 5, forming a large number of closed electric fields near the surface of the roller 5. In this way, an electric field with a large electric field gradient is formed near the surface of the developing roller. Since the surface size of the high-resistance element 11 and the medium-resistance element 12 is extremely small as described above, each closed electric field is also very small, and as a result, the strength of each closed electric field becomes very large due to the so-called edge effect or peripheral electric field effect. Become stronger. Due to such a high-intensity closed electric field, the positively charged toner is
As schematically shown in FIG. 1A, it is strongly attracted to the surface of the high-resistance element 11 and is held on the developing roller 5 in a large amount in a state where it is difficult to separate. That is, the charged toner is given a strong binding force inside the closed electric field and is held on the developing roller 5 along the lines of electric force. At this time, the toner is strongly triboelectrically charged due to the friction between the toner supply roller 6 and the developing roller 5, and is held by the action of a strong minute electric field on the surface of the developing roller 5, so that the toner is carried on the developing roller 5. When the layer thickness of the toner is regulated by a doctor blade 8 made of urethane, for example, the sufficiently charged toner is strongly held on the surface of the developing roller 5 by a minute closed electric field, but the toner with a small amount of charge is held by this. Even if the toners are mixed together, such toners are removed by the contact pressure with the doctor blade 8, and in the end, only toners with a large amount of charge are transported to the developing area 9 in a larger amount than conventionally, and as described above, the electrostatic latent image is formed. Visualize. The electric field between the developing roller 5 and the photoreceptor 1 in the developing area 9 has a large electrode effect, and the toner on the developing roller 5 tends to adhere to the photoreceptor 1 . In this way, the image density of the visible image can be increased and background smearing can be prevented.

[0021] In the vicinity of the surface of the developing roller 5, as shown in Fig. 4 (
As shown schematically in d), there are cases where only a small closed electric field is formed over the entire field, and cases where electric fields that are not closed electric fields are mixed in the closed electric field, but in either case, the closed electric field , its strength is increased and a large amount of toner can be supported. Further, the medium resistance element 12 is not substantially charged, and only the high resistance element 11 is charged to a predetermined polarity,
It is also possible to form a closed electric field between these elements to support the toner.The key is to charge at least the high resistance element among the high resistance element and the medium resistance element, and use the difference in surface potential to create a closed electric field. All that is required is to form a layer to support the toner. Furthermore, as explained earlier, the surface shape and size of the medium resistance element and the high resistance element can be selected as appropriate, and the arrangement state thereof can also be set as appropriate. For example, as shown in FIGS. 5(a) and 5(b), , the high-resistance element 11 with an appropriate surface shape is present in the medium-resistance element 12, or vice versa, as shown in FIG.
), a medium-resistance element 12 of an appropriate shape may be present within the high-resistance element 11. Or Figure 5(c)
As shown in FIG. 2, long elongated medium resistance elements 12 and high resistance elements 11 may be alternately arranged. When the surface shape of each high resistance element 11 (or medium resistance element) is made circular as shown in FIG.
When each high-resistance element 11 is formed into a minute width shape as shown in FIG. 9, the respective widths and intervals are set to about 10 to 500 μm, for example. Also, as a base for laminating and fixing a high resistance element and a medium resistance element, a substrate is used in which only the surface on which these resistors are laminated is made conductive, and this conductive layer is grounded or a predetermined bias voltage is applied to it. You may also do so.

In any of the above-described embodiments, a developing roller on which two types of dielectric materials with different charging series are exposed in a mixed manner is used, and the above-mentioned charging member is rotated in contact with the developing roller, thereby creating a minute closure. An electric field can be formed on the surface of the developer roller. Even when the toner carrier is a belt, the same effects can be obtained by using a sheet-like base material laminated with dielectric materials having different charging series. Further, according to each of the above embodiments, the dielectric materials 11 and 12 are laminated on the surface of the developing roller 5, and the conductive substrate 10 is not exposed on the surface of the developing roller 5.
Even if an alternating current bias voltage or a superimposed alternating current and direct current bias voltage is applied between the developing roller 5 and the photoreceptor 5, charge leakage between the photoreceptor 1 and the developing roller 5 can be prevented. This makes it possible to suppress the occurrence of speckled image white spots, etc., and to greatly control the developing bias voltage. Note that the dielectrics 11 and 12 have a resistance of 108 Ωcm or more, preferably 1010 Ωcm or more, in order to prevent the above-mentioned charge from leaking and to ensure the ability to retain the charge in the dielectrics 11 and 12.
More preferably, it is a substance having a specific volume resistivity of 1012 Ωcm or more, and an appropriate material is selected in consideration of its durability. Further, in the illustrated embodiment, the charging member and the toner supplying member are used together, which has the advantage of simplifying the configuration, but the charging member may be a separate member from the member that supplies toner to the developing roller. In addition, in image forming apparatuses that use a latent image carrier such as a drum-shaped photoconductor instead of a belt-shaped photoconductor, and in a contact development method in which a latent image carrier and a toner carrier are brought into contact with each other via toner, Needless to say, the present invention can also be applied to an image forming apparatus that employs a non-contact developing method in which these components are separated from each other. Furthermore, in each of the above-described embodiments, a developing device using a single-component non-magnetic toner developer particularly suitable for color development has been exemplified. It can also be applied to a developing device using a one-component developer consisting of:

[0023]

According to the present invention, the developer carrier carrying the developer is charged with a predetermined polarity on the surface where at least one of the first substance and the second substance, which have different chargeability, is exposed. A large number of minute electric fields are formed on the surface, thereby forming a large number of electric field arrangements on the surface, and a voltage applying means is used to apply a voltage to a developing section where the developer carrier and the electrostatic latent image carrier face each other. An electric field is formed, and the developer is moved by an electric field determined by the mutual relationship between the potential on the electrostatic latent image carrier, the potential on the developer carrier, and the electric field formed by the voltage application means. As a result, an appropriate amount of developer can be applied to the electrostatic latent image on the electrostatic latent image carrier, and the image density can be improved while maintaining the gradation, thereby producing high-quality images. There are excellent effects that can be obtained. Furthermore, if the developer is carried on the developer carrier by the minute electric field, a larger amount of developer will be carried than in the past due to the edge effect or peripheral electric field effect due to the minute electric field, thereby further increasing the image density. You can improve your performance. Furthermore, if materials having sufficiently low efficiency are used as the first and second materials, leakage of charge between the electrostatic latent image carrier and the developer carrier can be prevented.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing an example of a developing device.

FIG. 2 is a schematic enlarged plan view of each dielectric of the developing roller according to one embodiment.

3(a) is an explanatory diagram schematically showing each dielectric material and toner particles of the developing roller shown in FIG. 2 enlarged; FIG. 3(b) is a micro closed electric field formed near the surface of the developing roller; An explanatory diagram showing the electric force of.

FIG. 4(a) is an explanatory diagram schematically showing each dielectric material and toner particles of a developing roller according to another embodiment;
b) is a schematic enlarged plan view of each dielectric of the developing roller, (c) is a sectional view taken along the line IV-IV of (a), and (d)
) is an explanatory diagram showing the electric force of a minute closed electric field formed near the surface of the developing roller.

FIGS. 5A to 5D are enlarged views showing other arrangement examples of each dielectric.

FIGS. 6(a) to 6(d) are schematic representations of the electric force of a minute closed electric field and toner particles formed near the surface of a developing roller constructed by changing the materials of each dielectric and the toner supply roller. Explanatory diagram enlarged and shown.

FIG. 7 is an explanatory diagram showing an example of the bias applied to the developing roller, in which (a) is an explanatory diagram of a change in the potential of the second dielectric, and (b) is an explanatory diagram of the change in the potential of the first dielectric. An explanatory diagram of changes.

FIG. 8 is an explanatory diagram of the developing electric field on the first dielectric in the same example, in which (a) is an explanatory diagram of the temporal change when facing the image area on the photosensitive drum, and (b) is an explanatory diagram of the developing electric field on the first dielectric. An explanatory diagram of temporal changes when facing the skin part on the body drum.

FIG. 9 is an explanatory diagram of the developing electric field on the second dielectric in the same example, in which (a) is an explanatory diagram of the temporal change when facing the image area on the photoconductor, and (b) is an explanatory diagram of the developing electric field on the second dielectric. An explanatory diagram of temporal changes when facing the upper skin part.

[Explanation of symbols]

1 Photoreceptor
, 2 developing device 5 developing roller
, 6 toner supply roller 9 developing section
, 10 conductive substrate 11 first dielectric
, 12 second dielectric 15 foam
, 51 Bias power supply

Claims (6)

[Claims] Claims: 1. An electrostatic latent image bearing member carrying an electrostatic latent image and a developer carrying member carrying a developer are opposed in a developing section, and a bias is applied to the developing section by a voltage applying means to perform development. In the developing device, a first substance and a second substance having different chargeability are regularly or irregularly mixed and exposed on the surface of the developer carrier, and the first substance and the second substance on the surface are mixed and exposed regularly or irregularly. The exposed portion of at least one of the substances in No. 2 is charged to a predetermined polarity to form a large number of minute electric fields on the surface, and the potential on the electrostatic latent image carrier, the electric field due to the bias, and the developer support are used. A developing device characterized in that the movement of developer is controlled by an electric field determined by a mutual relationship with an electric field on the body. 2. The developing device according to claim 1, wherein the developer is supported on the developer carrier by the minute electric field. 3. The developing device according to claim 1, wherein said bias forms an alternating electric field. 4. The developing device according to claim 1, wherein the exposed portions of the first substance and the second substance are charged with opposite polarities to form a large number of minute electric fields on the surface. . 5. The exposed portion of one of the first substance and the second substance is charged to a predetermined polarity to form a large number of minute electric fields on the surface. Developing device. 6. The exposed portions of the first substance and the second substance are charged to different potentials of the same polarity to form a large number of minute electric fields on the surface. developing device.