JP5081424B2 - Developing device and image forming apparatus - Google Patents

Description

  The present invention relates to a developing device and an image forming apparatus such as a copying machine, a printer, and a facsimile machine that forms an image using the developing device.

  Conventionally, as a developing device of this type, a toner that has been hopped on the surface of a toner carrier such as a toner carrying substrate is used for development instead of using toner adsorbed on a developing roller or a magnetic carrier for development. It has been.

  For example, the developing device described in Patent Document 1 includes a toner transport substrate including a plurality of electrodes arranged at a predetermined pitch on an insulating support plate. These electrodes are formed by repeatedly arranging electrode sets composed of three or more electrodes arranged continuously. A pulse voltage that is out of phase with each other is applied to each electrode in an electrode set including three or more electrodes. As a result, a traveling electric field is formed on the transport substrate, in which the toner is sequentially moved from one end side to the other end side while hopping the toner. The toner on the surface of the transport substrate is repeatedly hopped from above one electrode toward the adjacent electrode in a direction from one end side to the other end side of the substrate. And a latent image carrier such as a photosensitive member are conveyed to a developing region facing each other with a predetermined gap. Of the toner that hops in this development area, the toner that has floated to the vicinity of the latent image on the latent image carrier does not descend toward the transport substrate, but is attracted to the electric field by the latent image and adheres to the latent image. In such a configuration, not the toner adsorbed on the developing roller or the magnetic carrier but the toner that does not exhibit the adsorbing force by hopping is used for the development. As a result, it is possible to realize low-potential development that cannot be realized by the conventional one-component development method or two-component development method. For example, toner can be selectively attached to an electrostatic latent image having a potential difference of only a few tens [V] with respect to surrounding non-image portions.

  The developing device described in Patent Document 2 has a cylindrical toner carrier having a plurality of electrodes arranged at a predetermined pitch in the circumferential direction. These electrodes are formed by repeatedly arranging electrode pairs composed of two adjacent electrodes. An alternating electric field is formed between the two electrodes in each electrode pair. Then, the toner located on one electrode in the electrode pair floats and landes on the other electrode, or floats on the other electrode and landes on one electrode. Then, while repeating the hopping in this way, the cylindrical toner carrier is transported to the developing region by the surface movement accompanying the rotational driving. Even in such a configuration, by using the hopped toner for development, it is possible to realize low-potential development that cannot be realized by the conventional one-component development method or two-component development method.

JP 2002-341656 A JP-A-3-21967

  However, in these developing devices, the hopping amount of the toner is decreased with time, and eventually a development failure due to a hopping failure may occur. Therefore, the present inventors have conducted intensive research on the cause of such hopping failure, and have found the following. That is, in order to hop the toner satisfactorily on the surface of the toner carrier, the toner must be sufficiently charged. Therefore, the toner is sufficiently charged by being rubbed against a blade or a magnetic carrier before being supplied to the toner carrier. However, even if the sufficiently charged toner is supplied to the toner carrier, if the electrode provided on the toner carrier is exposed, the toner can easily be charged with the contact with the electrode. Will leak. In the developing device described in Patent Document 2, since a toner carrying member having a plurality of exposed electrodes is used, the charge of the toner supplied onto the surface of the toner carrying member can be easily supplied to the plurality of electrodes. Will leak. As a result, the charge of the toner is lost, causing hopping failure. On the other hand, in the developing device described in Patent Document 1, since a toner carrier (toner transport substrate) in which a surface protective layer made of an insulating material or the like is coated on a plurality of electrodes is used. Does not cause leaks. However, depending on the material of the surface protective layer, frictional charging to the side opposite to the normal polarity of the toner is promoted. Specifically, the toner supplied onto the surface of the toner carrier is rubbed with the surface of the toner carrier as the hopping occurs. There is no problem if this rubbing promotes frictional charging of the toner toward the normal charging polarity. However, depending on the material of the surface protective layer, the surface protective layer is frictionally charged to the same polarity side as the normal charging polarity of the toner as it rubs against the toner, whereas the toner has a polarity opposite to the normal charging polarity of the toner. It may promote frictional charging. It has been found that such a surface protective layer gradually reduces the amount of charge on the normal polarity side of the toner with hopping, and eventually causes toner charging failure.

  The present invention has been made in view of the above background, and an object of the present invention is to provide a developing device that can suppress development failure due to toner hopping failure, and an image forming device using dirt. It is to be.

In order to achieve the above object, the invention according to claim 1 is directed to a toner carried on the surface of a toner carrier comprising a plurality of electrodes arranged in a predetermined direction and a surface protective layer covering these electrodes. A developing device that develops the latent image by adhering to the latent image carried on the latent image carrier while hopping on the surface by an electric field formed by applying a voltage to the toner carrying The body is formed in the base, the plurality of electrodes formed in the plurality of recesses provided in the base, the non-recessed region on the surface of the base, and the plurality of recesses, respectively. It is intended to include a the above surface protective layer formed to cover the surface of the electrode, and, the surface protective layer, with the friction with the toner hopping on the surface of the toner carrying member Regular charging of the toner It is characterized in that is made of a material that promote the frictional charging of the sexual side.
The invention of claim 2 is the developing device of claim 1, wherein the main component of the toner is made of polyester or styrene acrylic, and the surface protective layer is made of a silicone resin, a nylon resin, a melamine resin, It is characterized by comprising a material selected from one or a combination of one or more selected from the group consisting of acrylic resins, polyvinyl alcohol (PVA), urethane, quaternary ammonium salts, and nigsylone dyes.
According to a third aspect of the present invention, there is provided an image forming apparatus having a latent image carrier that carries a latent image and a developing unit that develops the latent image on the latent image carrier. Alternatively, the second developing device is used.

  In these inventions, the surface protective layer of the toner carrier promotes frictional charging toward the normal charge polarity side of the toner in accordance with the friction with the toner to be hopped, so that the toner accompanying the friction with the surface protective layer is urged. Avoid frictional charging to the side opposite to the normal charging polarity. Thereby, by suppressing the decrease in the toner charge amount (regular charge polarity) due to hopping, it is possible to suppress the development failure due to the toner hopping failure.

First, an experiment related to the present invention will be described. As shown in FIG. 1, by depositing aluminum on a glass substrate 1, an electrode pattern 2 composed of a plurality of electrodes 21, 22, 23,... Arranged in the moving direction at a pitch of p [μm] is formed. A substrate 4 as a toner carrier is formed by forming a protective layer 3 on which a resin coat having a thickness of about 3 [μm] and a volume resistivity of about 10 ¹⁰ [Ω · cm] is formed. A charged toner layer 5 is formed on the substrate 4.

  The toner layer 5 was formed by developing a solid image into a thin layer on the substrate 4 by a two-component developing device (not shown). As the toner, a polyester-based particle size of about 6 [μm] was used, and the charge amount of the toner formed in a thin layer on the substrate 4 was about −22 [μC / g]. For the toner layer 5 in this state, as shown in FIG. 2, while applying an AC voltage from the AC power source 6 to the odd-numbered electrode group which is an assembly of the odd-numbered electrodes 21, 23. When an AC voltage having a phase opposite to that of the AC voltage is applied to the even-numbered electrode group, which is an aggregate of the th-th electrodes 22..., The toner 5 has the odd-numbered electrode groups 21, 23. Perform a reciprocating motion. This phenomenon is hereinafter referred to as flare (or flare phenomenon). The state causing the flare phenomenon is called flare state.

  Applied between the electrodes 21, 22, 23... From the AC power source 6 using four types of substrates 4 with the pitches of the electrodes 21, 22, 23. The flare activity was observed with a high-speed camera while changing (changing) Vmax [V], which is the absolute value of the difference between the positive peak value and negative peak value of the alternating current voltage, to several points. Results as shown in FIG. 3 were obtained. Incidentally, the width of the electrodes 21, 22, 23... And the distance between the electrodes 21, 22, 23... Are 1/2 of the pitch of the electrodes 21, 22, 23. did.

  Here, the activity of flare is obtained by sensory evaluation of about five stages by observing the state of toner that sticks to the surface of the substrate 4 and does not move. From FIG. 3, it can be confirmed that the flare activity can be obtained almost uniquely by Vmax [V] / p [μm] regardless of the values of Vmax and p. It can be seen that the flare starts to be activated when Vmax [V] / p [μm]> 1, and the flare is completely activated when Vmax [V] / p [μm]> 3.

In addition, in order to investigate the influence of the electrical characteristics of the surface of the substrate 4, the flare activity was confirmed in the same manner by changing (changing) the volume resistivity of the surface layer 3 of the substrate 4 at several points. The material used for the surface layer 3 is a silicone-based resin, and by changing the amount of carbon fine particles dispersed therein, a protective layer having a volume resistivity of 10 ⁷ to 10 ¹⁴ [Ω · cm] (thickness is about 5 [μm]) 3 was formed. As a representative example, the same experiment as described above was performed using the electrodes 21, 22, 23... Having a pitch of 50 [μm], and the result shown in FIG. 4 was obtained.

From this result, it can be confirmed that the volume resistivity of the surface layer 3 is in the range of 10 ⁹ to 10 ¹² [Ω · cm]. This is because if the surface layer 3 having a very high volume resistivity is used, the surface of the substrate 4 remains charged due to friction between the toner that repeatedly flies and the surface layer 3. This charging causes the surface potential of the substrate to fluctuate, making the bias contributing to development unstable. On the other hand, if the conductivity of the surface layer 3 is too high, charge leakage (short circuit) occurs between the electrodes 21, 22, 23..., And an efficient bias effect cannot be obtained. is there. The surface layer 3 has an appropriate resistivity (volume resistivity of 10 ⁹ to 10 ¹² [Ω · cm]) so that charges accumulated on the surface of the substrate 4 can be easily escaped to the electrode groups 21, 22, 23. It is necessary to become. The optimum range of the volume resistivity is obtained by an experiment using an experimental facility equipped with the apparatus shown in FIG. In the case of a developing device provided with a developing roller (details will be described later) shown in FIG. 11 instead of the device shown in FIG. 2, the optimum range may be different from that described above. In such a case, it is desirable to adjust the volume resistivity to an appropriate one after examining the optimum range of the volume resistivity in the developing device by experiments.

In order to examine the influence of the triboelectric charging characteristics of the surface of the substrate 4, the inventors performed flare activity observations similar to the above with the surface layer 3 being two types of silicone resin and fluorine resin. The surface layer 3 has a volume resistivity of 10 ¹¹ to 10 ¹² [Ω · cm] as a coating layer of either a silicone resin or a fluorine resin by finely dispersing carbon fine particles. When an alternating bias is applied from the AC power source 6 to the electrodes 21, 22, 23... And the flare activity is observed, the flare state is maintained for a long time when the surface layer 3 is a silicone resin. In the case of the fluorine-based resin, the flare disappeared immediately and the toner remained stuck to the substrate 4.

  After the above observation, the charge amount of the toner on the substrate 4 was measured. When the surface layer 3 was a silicone resin, the charge amount of the toner on the substrate 4 was only slightly reduced compared to the initial value. However, when the surface layer 3 is made of a fluororesin, the toner charge on the substrate 4 is almost free of toner charge. As a test, when an uncharged toner was rubbed against the surface of each surface layer 3, when the surface layer 3 was a silicone resin, the toner obtained a triboelectric charge of normal polarity, whereas the surface layer 3 In the case of fluororesins, the frictional charge was hardly obtained, and the polarity was slightly reversed. In other words, the flare phenomenon is a process in which the toner and the surface of the substrate 4 collide with each other innumerably, so the material of the surface layer 3 does not take away the charge of the toner but is a material that can give the toner a regular charge. It can be understood that this is preferable. This is learned from the triboelectric series of materials, and as the material of the surface layer 3, for example, a glass-based material or a material used for a carrier coat of a two-component developer is preferably used.

Next, experimental results in the system as shown in FIG. 5 will be described. The substrate A is configured by forming a resin layer (this is assumed to be a photoreceptor) 8 having a thickness of about 20 [μm] on a substrate 7 made of aluminum. The substrate 7 is grounded, and a 0.4 [mg / cm ² ] toner layer 9 corresponding to a solid image is formed on the resin layer 8. The toner layer 9 is formed by performing solid development on the resin layer 8 with a two-component developing device (not shown).

  The substrate B is placed so as to face the substrate A with a distance d [μm]. The substrate B is configured in the same manner as the substrate 4, and the surface layer 3 is a white coat layer so that the amount of toner transferred here can be easily measured by an optical measuring device (reflected light density measuring device) in the following operations. And From FIG. 3, if Vmax [V] / p [μm] = 4, a stable flare can be formed under any conditions. Therefore, four types of conditions where Vmax [V] / p [μm] = 4 are used. When the dependence of the toner transfer amount on the substrate B on the development gap (d [μm]) was examined, the results shown in FIG. 6 were obtained. The vertical axis of the graph in FIG. 6 indicates the amount of increase in the optical density of the surface layer 3 on the substrate B, and the amount of increase in the optical density is 0 when no toner adheres to the surface layer 3. The graph includes the result that the optical density increase amount is larger than 0. This is because a part of the toner in the toner layer 9 adhered to the resin layer 8 of the substrate A is on the substrate B. This is because the toner layer 9 is transferred to the surface layer 3 of the substrate B under the influence of the electric field formed. When such a transition occurs, in the overlay development, the toner in the toner layer formed on the latent image carrier (for example, the photoreceptor) during the previous development is transferred into the subsequent color developing device during the subsequent development. Cause color mixing. In addition, the image on the latent image carrier obtained by the preceding development is disturbed. Such color mixing and image disturbance can be avoided under the condition that the optical density increase is zero in the graph. From the graph, it can be seen that such a condition is that the pitch distance p is smaller than the development gap d, that is, p <d.

  This is considered to be a condition that the influence of the electric field curtain formed on the toner carrier (substrate B) does not reach the electrostatic latent image electric field or toner image on the latent image carrier (substrate A). Can do. Under such conditions, for example, 1200 dpi or 2400 dpi isolated dots can be accurately developed without scavenging, and as described above, the toner image is superimposed on the latent image carrier (substrate A). Even when using the image forming process, the toner image previously formed on the latent image carrier is not disturbed, and the toner in the developing device is not mixed. Image superposition can be realized.

  Conventionally, developing devices used in image forming apparatuses such as copying machines, printers, and facsimiles include a two-component developing method and a one-component developing method. The two-component development method is very suitable for high-speed development, and is the mainstream method for current medium-speed and high-speed image forming apparatuses. In this two-component development method, in order to aim for high image quality, it is necessary to make the state of the developer very dense in the contact portion with the electrostatic latent image on the latent image carrier. For this reason, the carrier particles are now being reduced in diameter, and carriers of about 30 μm are beginning to be used on a commercial level.

  The one-component developing method is the mainstream method of current low-speed image forming apparatuses because the mechanism is small and light. In this one-component development system, toner carried on the surface of a developer carrying member such as a developing roller is used for development without hopping. Specifically, in order to form a toner thin layer on the developing roller, a toner regulating member such as a blade or a roller is brought into contact with the toner on the developing roller, and at that time, the developing roller or the toner regulating member and the toner are The toner is charged by friction. The charged toner layer formed as a thin layer on the developing roller is carried to the developing unit and develops the electrostatic latent image on the latent image carrier. The one-component development method here is roughly divided into a contact type and a non-contact type. The former is a type in which the developing roller and the latent image carrier are in contact, and the latter is a type in which the developing roller and the latent image carrier are non-contact. It is a contact.

  In order to compensate for the disadvantages of the two-component development method and the one-component development method, there is also a hybrid method in which the two-component development method and the one-component development method are hybridized, as described in Japanese Patent Laid-Open No. 3-100575. Several proposals have been made.

  As a method for developing high-resolution minute uniform dots, for example, there is a method described in Japanese Patent Laid-Open No. 3-113474. In this method, a high-resolution dot developability is realized by installing a wire to which a high-frequency bias is applied to the developing unit, to form a toner cloud in the developing unit, as compared to the hybrid method.

  Japanese Patent Laid-Open No. 3-21967 (Patent Document 2) proposes a method of forming an electric field curtain on a rotating roller in order to form the most efficient and stable toner cloud.

  Japanese Patent Laid-Open No. 2003-15419 discloses a developing device that transports a developer by an electric field curtain using a traveling wave electric field. Japanese Patent Application Laid-Open No. 9-269661 discloses a developing device having a plurality of magnetic poles that attract substantially one layer of carriers almost uniformly on the peripheral surface of the developing roller. Japanese Patent Laid-Open No. 2003-84560 discloses that a periodic conductive electrode pattern is provided on the surface of a developer carrying member carrying non-magnetic toner via an insulating portion, and a predetermined bias potential is applied to the electrode. Describes a developing device that generates an electric field gradient in the vicinity of the surface of the developer carrying member and adheres and conveys the non-magnetic toner onto the developer carrying member.

  In the conventional two-component development method, the demand for higher image quality is increasing, and the dot size of the required pixel itself needs to be equal to or smaller than the current carrier particle size, so that it is isolated. In terms of dot reproducibility, carrier particles must be further reduced. However, as the carrier diameter is reduced, the permeability of the carrier particles decreases, so that carrier detachment from the developing roller tends to occur, and when the detached carrier particles adhere to the latent image carrier, the carrier In addition to image defects due to the attachment itself, various side effects such as scratching the latent image carrier from the origin are caused.

  In order to prevent this carrier detachment, attempts have been made to increase the magnetic permeability of carrier particles from the material surface and to increase the magnetic force of the magnet included in the developing roller. Development is extremely difficult due to this balance. In addition, due to the downsizing of the developing roller, the developing roller is becoming smaller in diameter, and it becomes difficult to design a developing roller having a strong magnetic field configuration that can completely prevent carrier detachment. Yes.

  In the first place, the two-component development method is a process of forming a toner image by rubbing the ears of a two-component developer called a magnetic brush against the electrostatic latent image. Unevenness tends to occur in the developability. Although an image quality can be improved by forming an alternating electric field between the developing roller and the latent image carrier, it is difficult to completely eliminate the fundamental image unevenness such as the unevenness of the ears of the developer.

  In order to improve transfer efficiency and cleaning efficiency in the step of transferring the developed toner image on the latent image carrier and the step of cleaning the toner remaining on the latent image carrier after the transfer, It is necessary to reduce the non-electrostatic adhesion between the carrier and the toner as much as possible. As a method for reducing the non-electrostatic adhesion force between the latent image carrier and the toner, it is known that reducing the friction coefficient on the surface of the latent image carrier is effective. Since the spikes of the agent smoothly pass through the developing portion, the development efficiency and the dot reproducibility become very poor.

  In the one-component development method, the toner layer on the developing roller thinned by the toner regulating member is sufficiently pressed on the developing roller, so that the toner responsiveness to the electric field in the developing unit is very high. bad. Therefore, in general, in order to obtain high image quality, it is mainstream to form a strong alternating electric field between the developing roller and the latent image carrier. However, even if this alternating electric field is formed, an electrostatic latent image is formed. On the other hand, it is difficult to stably develop a certain amount of toner, and it is difficult to uniformly develop high resolution minute dots. In addition, this one-component development system applies a very large stress to the toner when the toner thin layer is formed on the developing roller, so that the toner circulating in the developing device deteriorates very quickly. As the toner deteriorates, unevenness and the like easily occur in the process of forming a toner thin layer on the developing roller, and the one-component developing method is generally not suitable as a high-speed and highly durable image forming apparatus.

  In the hybrid system (Japanese Patent Laid-Open No. 3-110355), although the size of the developing device itself and the number of parts increase, some problems are overcome. However, the developing unit still has the same problem as the one-component developing method, that is, it is difficult to develop a high-resolution minute uniform dot.

  The method described in Japanese Patent Laid-Open No. 3-113474 can be considered to realize highly stable and high-quality development, but the configuration of the developing device is complicated.

  Moreover, although the method described in JP-A-3-21967 (Patent Document 2) can be interpreted as being extremely excellent for obtaining a small-sized and high-quality development, as a result of intensive studies by the present inventors, In order to obtain an ideal high image quality, it was discovered that the conditions such as the electric field curtain and development to be formed must be limited. In other words, if image formation is performed under conditions that deviate from the appropriate conditions, not only the effect is not obtained, but also poor image quality is provided. In this method, the toner to be hopped on the toner carrier is transported to the development area by moving the surface of the toner carrier. However, the toner is only moved by hopping without moving the surface of the toner carrier. The same can be said for the method described in Japanese Patent Laid-Open No. 2002-341656 (Patent Document 1).

  In the image forming process in which the first toner image is formed on the latent image carrier and the second toner image and the third toner image are sequentially formed thereon, the latent image carrier is first formed. The developing method must not disturb the toner image formed on the body. By using the non-contact one-component developing method or the toner cloud developing method described in Japanese Patent Application Laid-Open No. 3-11474, it is possible to sequentially form each color toner on the latent image carrier. However, since an alternating electric field is formed between the latent image carrier and the developing roller, a part of the toner is peeled off from the toner image previously formed on the latent image carrier to the developing device. Get in. This not only disturbs the image on the latent image carrier, but also causes a problem that the toner in the developing device is mixed. These are fatal for obtaining high-quality images, and as a method for solving this problem, it is necessary to realize cloud development by a method in which an alternating electric field is not formed between the latent image carrier and the developing roller. .

  As methods for realizing such cloud development, the methods described in JP-A-3-21967 (Patent Document 2) and JP-A-2002-341656 (Patent Document 1) are considered effective. However, as described above, there is no effect if these are not used under appropriate conditions. Specifically, if the conditions are inappropriate, the toner cannot be clouded. Furthermore, even if the toner is made cloudy, in the overlay development, the toner in the toner layer on the latent image carrier obtained in the preceding development is transferred into the developing device of the subsequent color, and the image is distorted. And cause color mixing.

  Therefore, the image forming apparatus according to the present embodiment has a condition of Vmax [V] / p [μm]> 1 in view of the results of the above-described experiment. With such a configuration, the toner can be reliably clouded. Therefore, according to the present embodiment, it is possible to achieve higher image quality and to be smaller than the prior art.

  FIG. 7 shows a representative example of the toner carrier in the image forming apparatus according to the embodiment of the present invention. This toner carrier 31 is formed in the shape of a rotating roller, and is composed of a plurality of electrodes 41, 42, 43... Arranged in a spatial direction and arranged at a pitch of p [μm] in the moving direction. It is possible to rotate about the axis 40A of the odd-numbered electrode group that is an aggregate of the odd-numbered electrodes in the pattern and the electrode axis 40B of the even-numbered electrode group that is the aggregate of the even-numbered electrodes. it can. An AC voltage is applied to each of the electrode shafts 40A and 40B as a bias potential from an AC power source by an electrode brush (not shown) or the like. As shown in FIG. 15, the AC voltage includes a rectangular wave-shaped A-phase pulse voltage applied to the electrode shaft (40A) in which the odd-numbered electrode groups are bundled and an electrode shaft (in which even-numbered electrode groups are bundled). 40B) and a rectangular wave B-phase pulse voltage applied. These A-phase pulse voltage and B-phase pulse voltage are in opposite phases as shown in the figure, and the average potentials per unit time are the same. As shown in FIG. 16, a rectangular wave pulse voltage having a frequency f is applied to one electrode axis, while a DC voltage that is an average potential of the pulse voltage is applied to the other electrode axis. However, it is possible to cause a flare phenomenon as in the case of employing a pulse voltage having an opposite phase.

As shown in FIG. 8 (a), the toner carrier 31 is provided with a shaft hole 52 in an acrylic resin cylinder 51 as an insulator, and as shown in FIG. 8 (b), stainless steel electrode shafts 40A and 40B. Are pressed into the shaft hole 52 of the cylinder 51 to connect the electrode shafts 40A, 40B to the odd-numbered electrode groups 41, 43. Next, a pattern electrode is formed in each step shown in FIGS. FIG. 9 is a view of the surface of the toner carrying roller 31 as viewed in the direction along the rotation axis. In the process shown in FIG. 9A, the surface of the roller 51 obtained by the process shown in FIG. In the step shown in FIG. 9B, the groove 53 is cut so that the groove pitch is 100 [μm] and the groove width is 50 [μm]. In the step shown in FIG. 9C, the electroless nickel 54 is plated on the roller 51 that has been groove-cut, and in the step shown in FIG. 9D, the outer periphery of the roller 31 that has been electroless nickel 54 plated. To remove unnecessary conductive film. At this time, the electrodes 41, 42, 43,... Thereafter, the surface of the roller 51 is smoothed by coating the roller 51 with silicone resin, and at the same time, a surface protective layer (thickness of about 5 [μm], volume resistivity of about 10 ¹⁰ [Ω · cm]) 55 is formed. A toner carrying roller 31 was manufactured. FIG. 10 shows a state in which the toner carrying roller 31 is developed in a planar shape.

In the toner carrying roller 31, a thin toner layer is formed on the protective layer 55 in the same manner as the substrate 4. When the AC voltage shown in FIG. 15 is applied to the electrode shafts 40A and 40B as a bias potential from an AC power source (not shown) via an electrode brush or the like, the toner is odd-numbered electrode groups 41, 43. A movement (flare) is performed so as to reciprocate the second electrode group 42. The absolute value of the difference between the positive peak value and the negative peak value of the AC voltage applied between the electrodes 41, 42, 43... From the AC power source is Vmax [V], and Vmax [V] / p [μm]. The flare starts to be activated when> 1, and the flare is completely activated when Vmax [V] / p [μm]> 3. In the toner carrier 31, as with the substrate 4, it is appropriate that the volume resistivity of the surface layer 55 is in the range of 10 ⁹ to 10 ¹² [Ω · cm], and the surface layer 55 is a silicone resin. . As described above, the material of the surface layer 55 is preferably a material that can impart a regular charge to the toner by friction with the toner. For example, it is used for a glass-based material or a carrier coat of a two-component developer. It is preferable to use a material. p is set to be smaller than the development gap d, that is, p <d.

  FIG. 11 is a schematic configuration diagram illustrating an image forming apparatus according to the present embodiment. This image forming apparatus has a developing device using the toner carrying roller 31. The toner carrying roller 31 is in contact with the spikes of the two-component developer by a normal two-component developer 56. Specifically, a two-component developer in which a magnetic carrier powder having a particle size of 50 [μm] and a polyester toner having a particle size of about 6 [μm] are mixed in a weight ratio of 7 to 8 [wt%] A magnetic sleeve 57 containing 56 permanent magnets is conveyed to the toner carrying roller 31, where a part of the toner is transferred to the toner carrying roller 31 by a DC bias potential applied between the magnet sleeve 57 and the toner carrying roller 31. To do. The toner transferred to the toner carrying roller 31 is conveyed to a portion facing the latent image carrier 58 when the toner carrier 31 is rotationally driven by a driving unit (not shown) while forming a flare on the toner carrier 31. A toner image is formed by developing the electrostatic latent image by adhering to the electrostatic latent image on the latent image carrier 58 by the difference between the average potential on the surface of the toner carrying roller 31 and the potential of the latent image carrier 58. . An AC voltage is applied as a bias potential from an AC power source 59 by an electrode brush or the like between the electrode shafts 40A and 40B, and between the odd-numbered electrode groups 41, 43... And the even-numbered electrode groups 42. A time-periodic potential difference is formed.

  Unnecessary toner that has not contributed to the development returns to the magnetic sleeve 57 from the developing portion again. Since the flare is formed, the adhesion force of the toner to the toner carrying roller 31 is very low, and the toner returned from the developing portion by the toner carrying roller 31 is the ear of the two-component developer following the rotation of the magnet sleeve 57. Is easily scraped or habituated. By repeating this, a substantially constant amount of toner flare is always formed on the toner carrying roller 31. The two-component developer 56 conveys and circulates the two-component developer 63 in the container 60 while stirring, and the magnet sleeve 57 conveys a part of the two-component developer to the toner carrying roller 31 and from the developing unit. Unnecessary toner that did not contribute to development is returned.

  As the latent image carrier 58, a case where an organic photoreceptor having a thickness of 13 [μm] is used and a latent image is formed using a 1200 dpi laser writing system will be described below. The photosensitive member 58 is rotationally driven by a driving unit (not shown), is uniformly charged by a charging device, and is exposed by a laser writing system as an exposure unit to form an electrostatic latent image. In this case, the electrostatic potential image is formed under the condition that the charging potential of the photoconductor 58 is −300 to −500 [V] and the writing potential at the solid portion is 0 to −50 [V].

  The electrostatic latent image is developed with toner that forms flare on the toner carrier 31 to become a toner image. At this time, using toner having a charge amount of about −22 [μC / g] and a particle diameter of 6 [μm], there is no background stain, the solid portion is well filled, and one dot of 1200 dpi can be reproduced. As a result, the gap between the toner carrier 31 and the photoconductor 58 is about 500 [μm], and the odd-numbered electrode group and the even-numbered electrode group of the toner carrier 31 are −400 [V] and 0 [0]. V] is realized by applying an AC bias with an average potential of −200 [V] from each AC power source 59 at a frequency of 5 [kHz] at each instantaneous moment having a peak of each of V] (an odd-numbered electrode group and an even-numbered electrode group). The AC bias phases of the electrode groups were opposite to each other).

The toner image on the toner carrier 31 is transferred to a recording medium such as recording paper fed from a paper feeding device by a transfer means, and the toner image is fixed to the recording medium by a fixing device and discharged to the outside.
If excessive toner is placed on the toner carrying roller 31, the electric field curtain is shielded by the charge of the toner and flare cannot be formed, so the amount of toner on the toner carrying roller 31 per unit area is 0. A DC bias of about 200 [V] is applied between the magnet sleeve 57 and the toner carrying roller 31 from the power source so as to be 2 [mg / cm ² ]. Incidentally, since there is a toner diffusion effect due to flare, there is no problem even if there is some unevenness in toner transfer from the magnet sleeve 57 to the toner carrying roller 31, and there is no problem between the magnet sleeve 57 and the toner carrying roller 31. There is no particular need to devise superimposing the AC bias on the direct current bias, and no particular contrivance to make the spikes of the two-component developer strictly uniform.

On the other hand, since the amount of toner required as a solid image on the photoreceptor 58 is 0.4 [mg / cm ² ], the moving speed of the toner carrying roller 31 is prevented so that the toner does not run out in the developing unit. Needs to be at least twice as fast as the moving speed of the photosensitive member 58, and here, it is set to 2.5 times the moving speed of the photosensitive member 58. The moving direction of the toner carrying roller 31 and the moving direction of the photosensitive member 58 may be the same as shown in FIG. The moving direction of the magnet sleeve 57 and the toner carrying roller 31 is preferably reverse as shown in FIG. 11 in order to obtain a return toner scraping effect.
With the above system, it was confirmed that high-quality development without smearing excellent in solid portion filling property and 1200 dpi dot reproducibility can be realized under the linear velocity of 300 [mm / s] of the photoconductor 58.

  Next, a characteristic configuration of the image forming apparatus according to the present embodiment will be described. In this image forming apparatus, a toner having a base material resin (main component of toner) made of polyester or styrene acrylic and having a normal charging polarity of negative polarity (negative polarity) is used. Then, both the uniformly charged portion (background portion) and the latent image portion of the latent image carrier 58 have the same polarity as the normal charging polarity of the toner (negative polarity in this example), and the potential is attenuated more than the background portion. So-called reversal development in which toner is selectively attached to the latent image portion is performed.

  As shown in FIG. 1, the cylindrical toner carrying roller 31 in FIG. 11 includes a glass substrate 1, a plurality of electrodes (21, 22...), And a protective layer that is a surface protective layer covering these electrodes. 3. The protective layer 3 is made of a material that promotes frictional charging to the normal charging polarity side (minus side in this example) of the toner in accordance with the rubbing with the toner hopping on the surface of the toner carrying roller 31 as a toner carrying body. Is used. That is, the toner is positioned on the minus side in the triboelectric charging series rather than the protective layer 3. Examples of the material of the protective layer 3 that can realize such a relationship include organic materials such as silicone, nylon, melamine resin, acrylic resin, PVA, and urethane. Moreover, a quaternary ammonium salt, a nigusilon type dye, etc. may be sufficient. Furthermore, the material which mixed 2 or more of the material illustrated so far may be used. In addition to promoting frictional charging of the toner toward the normal charging polarity side of the toner, these materials can avoid leakage of toner charge to the electrodes due to its insulating properties.

  In this image forming apparatus having such a protective layer 3, the protective layer 3 (surface protective layer) of the toner carrying roller 31 serving as a toner carrying member is rubbed with the toner to be hopped, and the toner is charged at the normal charging polarity side. Promotes frictional charging. Then, frictional charging to the side opposite to the normal charging polarity of the toner due to rubbing with the protective layer 3 is avoided. Thereby, by suppressing the decrease in the toner charge amount (regular charge polarity) due to hopping, it is possible to suppress the development failure due to the toner hopping failure.

  As the toner, a toner whose normal charging polarity is positive polarity (positive polarity) may be used. In this case, the protective layer 3 may be made of a material that promotes frictional charging of the toner toward the positive polarity side as the toner rubs.

  The toner charging series means a charging series of the whole toner in which an external additive such as silica or titanium oxide is added to the toner base resin (particles). The order in the charging series can be examined as follows. That is, after the toner is rubbed against the surface protective layer for a predetermined time on the surface protective layer, the toner is sucked and collected. Then, the charge amount of the collected toner is measured with an electrometer. If this measurement result indicates an increase in the charge amount of the toner to the negative polarity, the toner becomes a negative charge series with respect to the surface protective layer. Further, if the measurement result indicates an increase in the charge amount of the toner to the positive polarity, the toner becomes a positive charge series with respect to the surface protective layer.

An intermediate layer may be provided between the protective layer 3 and the electrode. In this case, as the intermediate _{layer, Ti, Sn, Fe, Cu} , Cr, Ni, Zn, Mg, Al, T i O 2, SnO 2, Fe 2 O 3, Fe 3 O 4, CuO, Cr 2 O 3, It is possible to use a conductive material such as NiO, ZnO, MgO, Al ₂ O ₃ or the like.

  FIG. 12 shows another embodiment of the present invention. In this embodiment, in the embodiment shown in FIG. 11, the developing device 56 has a simplified configuration in which the magnet sleeve 57 is omitted, and the toner supply to the toner carrying roller 31 is performed by the cascade development phenomenon of the two-component developer. Since the developing device 56 forms a thin toner layer on the toner carrying roller 31 using a simple cascade, the toner transfer rate to the toner carrying roller 31 is lower than that in the embodiment shown in FIG. By increasing the rotation speed of the carrying roller 31, it is possible to cope with the developing speed on the photoconductor 58. The developing device including the two-component developing device 56 and the toner carrying roller 31 in which the magnet sleeve 57 of the embodiment shown in FIG. 12 is omitted is substantially the same size as the conventional two-component developing device. It is possible to configure a compact and high-quality image forming engine.

  Therefore, according to the present embodiment, it is possible to achieve higher image quality and to be smaller than the prior art.

  FIG. 13 shows another embodiment of the present invention. In this embodiment, in the embodiment shown in FIG. 12, a one-component developing device 64 having only toner is used instead of the two-component developing device 56, and this one-component developing device 64 supplies toner to the toner carrying roller 31. A thin toner layer is formed on the toner carrying roller 31 by shifting. In this case, the one-component developing device 64 supplies the toner 66 in the container 65 to the toner carrying roller 31 while being stirred and circulated by the circulation paddle 67, and the toner on the toner carrying roller 31 is metered as a toner regulating member. The blade 68 regulates the thickness to a constant value to form a thin toner layer.

  In terms of the stability of toner supply to the toner carrying roller 31, there are some inferior parts to the embodiment shown in FIG. 11 and the embodiment shown in FIG. 12, but this is a problem that can be solved if conditions are narrowed down. A small, light and high-quality developing device can be provided.

  Therefore, according to the present embodiment, it is possible to achieve higher image quality and to be smaller than the prior art.

  FIG. 14 shows yet another embodiment of the present invention. In this embodiment, the same developing device as the developing device including the two-component developing device 56 and the toner carrying roller 31 in the embodiment shown in FIG. 11 is used, and the toner images of the respective colors are formed on the photoreceptor. 1 is an example of an image forming apparatus. In this embodiment, the belt-shaped organic photoconductor 69 as a photoconductor is wound around two rollers (not shown) and is rotationally driven by a drive unit (not shown).

  On the left side of the photoreceptor 69, image forming devices 70K, 70Y, 70C, and 70M are arranged as a plurality of image forming units that respectively form images of a plurality of colors, for example, black, yellow, cyan, and magenta. First, the photosensitive member 69 is uniformly charged by the charging device 71K in the image forming device 70K, and is exposed by the light beam 72K modulated by the black image data by a writing device as an exposure unit (not shown). An electrostatic latent image is formed, and this electrostatic latent image is developed by a developing device 73K having the same configuration as the developing device comprising the two-component developing device 56 and the toner carrying roller 31 in the embodiment shown in FIG. It becomes a toner image. Thereafter, the photoreceptor 69 is neutralized by the static eliminator 74K to prepare for the next image formation.

  Next, the photosensitive member 69 is uniformly charged by the charging device 71Y in the image forming device 70Y, and exposed by a light beam 72Y modulated by yellow image data by a writing device as an exposure unit (not shown). An electrostatic latent image is formed, and this electrostatic latent image is developed by the developing device 73Y having the same configuration as the developing device comprising the two-component developing device 56 and the toner carrying roller 31 in the embodiment shown in FIG. The yellow toner image overlaps with the toner image. Thereafter, the photoreceptor 69 is neutralized by the static eliminator 74Y to prepare for the next image formation.

  Next, the photoreceptor 69 is uniformly charged by the charging device 71C in the image forming device 70C, and exposed by a light beam 72C modulated by cyan image data by a writing device as an exposure unit (not shown). Thus, an electrostatic latent image is formed, and the electrostatic latent image is developed by the developing device 73C having the same configuration as the developing device including the two-component developing device 56 and the toner carrying roller 31 in the embodiment shown in FIG. A black toner image and a cyan toner image overlapping the yellow toner image are obtained. Thereafter, the photoreceptor 69 is neutralized by the static eliminator 74C to prepare for the next image formation.

  Next, the photosensitive member 69 is uniformly charged by the charging device 71M in the image forming device 70M, and exposed by a light beam 72M modulated by magenta image data by a writing device as an exposure unit (not shown). Thus, an electrostatic latent image is formed, and this electrostatic latent image is developed by the developing device 73M having the same configuration as the developing device including the two-component developing device 56 and the toner carrying roller 31 in the embodiment shown in FIG. A full-color image is formed by forming a black toner image, a yellow toner image, and a magenta toner image overlapping the cyan toner image.

On the other hand, a recording medium such as recording paper is fed from a sheet feeding device (not shown), and a full color image on the photosensitive member 69 is transferred to the recording medium by a transfer roller 75 as a transfer unit to which a transfer bias is applied from a power source. . The recording medium on which the full color image is transferred is fixed by the fixing device 76 and discharged to the outside. Residual toner and the like are removed from the photoconductor 69 by a cleaner 77 as a cleaning unit after the transfer of a full-color image.
The developing devices 73K, 73Y, 73C, and 73M use the developing device that includes the two-component developing device 56 and the toner carrying roller 31 shown in FIG. 12, or the developing device that includes the one-component developing device 64 and the toner carrying roller 31 shown in FIG. May be.

  In this embodiment, four colors are written on the same photoconductor 69, and therefore, in principle, there is almost no positional deviation compared to the normal quadruple tandem system, and colors can be superimposed on the photoconductor. Therefore, it is possible to obtain a high-quality full-color image with no positional deviation.

  In the image forming apparatus shown in FIG. 14, in view of the result of the above-described experiment, in addition to the condition of Vmax [V] / p [μm]> 1, the condition of p [μm] <d [μm]. Is also provided. In this configuration, as described above, the toner image once formed on the photoconductor 69 is not affected at all, and the preceding color toner layer formed on the photoconductor 69 is replaced with the subsequent color. It is not transferred into the developing device. Therefore, there are no problems such as scavenging and color mixing, and a high-quality image forming process can be performed stably over a long period of time.

  So far, an embodiment of an image forming apparatus that conveys toner to a developing region by moving the surface of a toner carrier while hopping so as to reciprocate the toner between two adjacent electrodes and obtaining a flare phenomenon will be described. However, the present invention can also be applied to the following image forming apparatus. That is, as in the method described in Japanese Patent Application Laid-Open No. 2002-341656, in the toner carrier, hopping from above one electrode toward the adjacent electrode is performed from one end of the toner carrier to the other end. The image forming apparatus conveys the toner toward the developing region by repeatedly performing in the direction toward the side. The present invention can also be applied to an image forming apparatus that conveys toner toward the developing region by both the movement of toner by such hopping and the surface movement of the toner carrier.

It is sectional drawing which shows the system used for the experiment regarding this invention. It is sectional drawing which shows the flare state of the same system. It is a characteristic view which shows the relationship between Vmax [V] / p [micrometer] which is an experimental result of the same system, and flare activity. It is a characteristic view which shows the relationship between the volume resistivity and flare activity of the surface layer 3 which are the experimental results of the same system. It is sectional drawing which shows the system used for the experiment regarding this invention. FIG. 6 is a characteristic diagram showing the relationship between the development gap and the increase in optical density on the substrate A, which is the same experimental result. FIG. 3 is a perspective view illustrating a representative example of a toner carrier in an embodiment of the present invention. FIG. 6 is a cross-sectional view showing a part of the manufacturing process of the toner carrier. FIG. 10 is a cross-sectional view showing another part of the manufacturing process of the toner carrier. FIG. 4 is a development view showing a state where the toner carrier is developed in a planar shape. It is sectional drawing which shows one Embodiment of this invention. It is sectional drawing which shows other embodiment of this invention. It is sectional drawing which shows another embodiment of this invention. It is sectional drawing which shows another embodiment of this invention. FIG. 6 is a waveform diagram showing characteristics of an A-phase pulse voltage and a B-phase pulse voltage applied to the electrode of the toner carrier. FIG. 6 is a waveform diagram showing characteristics of a pulse voltage and an average voltage applied to the electrode of the toner carrier.

Explanation of symbols

1: Glass substrate 2: Electrode pattern 21, 22, 23: Electrode 3: Protective layer 4: Substrate 5, 9: Toner layer 6: AC power supply 7: Substrate 8: Resin layer A, B: Substrate 31: Toner carrier 40 : Electrode pattern 40A, 40B: Electrode shaft 41, 42, 43: Electrode 51: Cylinder 55: Surface layer 56: Two-component developer 58: Photoconductor 59: AC power source 64: One-component developer 69: Photoconductor 70K, 70Y, 70C, 70M: Image forming device 73K, 73Y, 73C, 73M: Developing device

Claims (3)

A toner carried on the surface of a toner carrier comprising a plurality of electrodes arranged in a predetermined direction and a surface protective layer covering these electrodes is applied to the surface by an electric field formed by applying a voltage to the plurality of electrodes. A developing device that develops the latent image by adhering to the latent image carried on the latent image carrier while hopping above .
The toner carrier includes a substrate, a plurality of electrodes formed in a plurality of recesses provided on the substrate, a region on the surface of the substrate that is not the recess, and a plurality of the recesses, respectively. The surface protective layer formed to cover the surface of the formed electrode, and
And, wherein the surface protective layer, characterized in that it is made of a material encouraging frictional charge to the normal charging polarity of the toner with the friction with the toner hopping on the surface of the toner carrying member Development device. The developing device according to claim 1,
The main component of the toner is made of polyester or styrene acrylic, and the surface protective layer is made of silicone resin, nylon resin, melamine resin, acrylic resin, polyvinyl alcohol (PVA), urethane, quaternary ammonium salt, and nigusilon. A developing device comprising one or a combination of one or more selected from the group consisting of dyes. In an image forming apparatus having a latent image carrier that carries a latent image, and a developing unit that develops the latent image on the latent image carrier.
An image forming apparatus using the developing device according to claim 1 or 2 as the developing means.

Images