WO2001026906A1 - Image forming method and image forming apparatus - Google Patents

Abstract

By using a regulating blade (4), a charged toner particle layer is formed on a developing roller (2), and the charged toner particles (5) of the charged toner particle layer are densified so that they may not separate from the developing roller (2) and clog an opening (16) of a head member (7). An alternating electric field is generated in the space between the developing roller (2) and a conductive opposed member (30) which is opposed through a gap to the developing roller (2), to vibrate and rearrange the charged toner particles (5) on the developing roller (2). The highly dense charged toner particle layer is conveyed to the position confronting the opening (16) of the head member (7), and a voltage is applied to a control electrode around the opening in accordance with an image signal to fly highly dense charged toner particles (5) from the developing roller (2) through the opening (16) to a recording sheet (9) which is arranged on the side opposed to the developing roller (2) with respect to the head member (7).

Description

 Satsuki Itoda β Image forming method and image forming device

 The present invention is used in a printer such as a computer, a facsimile, a copying machine, and the like. Related to the device. Background art

 Generally, in this type of image forming apparatus, a head member having a plurality of openings for allowing the charged particles to pass therethrough is disposed between a conveying member that carries and conveys the charged particles, and a counter electrode. An image receiving body is arranged between the head member and the head member, and a control electrode is arranged around each opening of the head member. In forming an image, a potential difference for forming an electrostatic field for transferring charged particles from the transport member toward the counter electrode is provided between the transport member and the counter electrode, and a voltage applied to the control electrode is controlled. By doing so, the opening is electrostatically opened and closed, and the charged particles are separated from the conveying member and passed through the opening to adhere to the image receiving body according to the image signal.

 In the above-described image forming apparatus, there is a problem that the charged particles easily accumulate around the opening of the head member, and the opening is clogged by the charged particles. That is, when the charged particles are transported by the transport member, a charged particle layer composed of charged particles is usually formed on the transport member. If the adhesive force of the charged particles is weak, the charged particles separate from the transfer member during transfer due to van der Waals force generated between the charged particles and the head member and the image force generated between the charged particles and the control electrode. It is deposited especially near the control electrode. When used for a long period of time, the amount of accumulated charged particles increases, and eventually the openings are closed and clogging occurs.

In addition, the charged particle layer has a large number of voids, and charged particles having different particle sizes, Since the secondary particles formed by agglomeration of a number of charged particles are included, the surface of the charged particle layer is not smooth but has irregularities. As a result, even when the voltage applied to the control electrode is relatively low, if the vicinity of the opening of the head member that causes the charged particles to fly from the transport member is brought close to the transport member, the convex portion of the charged particle layer becomes a head. Charged particles are scraped off by contact with the member, causing uneven image density and increasing the amount of accumulated charged particles.

 Therefore, various methods have conventionally been proposed as measures against clogging of the openings. For example, Japanese Patent Application Laid-Open No. 58-128282 discloses that a high voltage is applied to a control electrode when it is detected that an image receiving member is not disposed, so that the control electrode and the counter electrode can be detected. It is described that a spark discharge is generated between the opening and the opening to repel toner clogged in the opening. Further, Japanese Patent Application Laid-Open No. 58-110469 discloses that by increasing the electric field between the control electrode and the image receiving member when image formation is not performed, toner staying in the opening can be reduced to the image receiving side. It is stated that it will be taken out.

 Further, Japanese Patent Application Laid-Open No. 58-107471 discloses that the electric field between the conveying member and the image receiving member and the electric field in the opening at the time of image recording are set so that the charged particles are directed to the image receiving member. At times, it is described that the direction of the electric field between the carrying member and the control member and the direction of the electric field between the control member and the image receiving member are reversed from those at the time of recording to prevent toner clogging of the opening. ing. However, in the above-described method of removing the charged particles in the opening by the spark discharge, if the head member having the opening is formed of synthetic resin, there is a concern that the head member may be broken by the spark discharge. In addition, a separate power supply for generating spark discharge is required, and the charged particles may be heated by the discharge and fused to the head member.

 In the method of removing the charged particles in the opening when an image is not formed (during non-recording), the charged particles are sequentially adhered according to an image signal during image formation, that is, for example, on one sheet of recording paper. In the meantime, even if the opening is clogged, the charged particles cannot be removed. In addition, any of the above methods requires the setting of a special voltage application mode for removing charged particles in the aperture, and also requires a special power supply (the charged particles cannot be removed without applying a considerably large voltage). Due to this, the cost tends to be high.

On the other hand, when forming the charged particle layer, the particles on the conveying member are pressed with a predetermined pressing force. Thus, it is easy to form a charged particle layer while applying a charge to the particles.However, if the pressing force of the particles during the formation of the charged particle layer is considerably increased, the adhesive force between the charged particles in the charged particle layer is increased. In addition, the adhesion between the charged particles and the transporting member increases, and the surface of the charged particle layer becomes smooth, so that the charged particles can be prevented from depositing on the head member, resulting in uneven image density and clogging of the openings. There are some students who can control the situation.

 However, if the particle pressing force at the time of forming the charged particle layer is increased, the thickness of the charged particle layer becomes too thin and the image density becomes low, and the adhesive force between the charged particles and the conveying member becomes too high, so that the control electrode becomes too high. Makes it difficult for charged particles to fly in response to the voltage applied to the charged particles.

 The present invention has been made in view of the above-described points, and an object of the present invention is to suppress the accumulation of charged particles on a head member without causing a decrease in image density, and to reduce unevenness in image density and clogging of openings. It is to try to control the outbreak. Disclosure of the invention

 In order to achieve the above object, in the present invention, the density of the charged particles is increased with respect to the charged particle layer formed on the transport member.

 Specifically, this is an image forming method for forming an image by attaching charged particles to an image receiving body, wherein a charge of the same polarity is applied to a large number of particles for forming an image, and the charged charge is applied. A charged particle layer forming step of forming a charged particle layer made of particles on a conveying member, a densifying step of densifying the charged particles with respect to the charged particle layer formed on the conveying member, A transport for transporting the densified charged particle layer to a position opposed to the opening in a head member having a plurality of openings and a control electrode disposed at least partially around each of the openings by the transport member. Applying a voltage to the control electrode around the opening in accordance with an image signal with the charged particles of the densified charged particle layer transported to a position facing the opening of the head member by the transporting member. From the transport member Through the mouth, and the head member in pairs to charged particles to fly to the image receptor disposed on the opposite side of the flight to the above conveying member step and Dressings containing.

Due to this, in the charged particle layer formed in the charged particle layer forming step, a large number of In addition to the presence of voids, the charged particles are non-uniform, and the charged particle layer surface has many irregularities.However, in the densification step, no extra voids in the charged particle layer are eliminated, and the charged particles are uniformly arranged. The adhesive force between the charged particles and the adhesive force between the charged particles and the transporting member are made uniform, so that a portion having a weak adhesive force is eliminated, and the surface of the charged particle layer is smoothed. As a result, the densely packed charged particle layer hardly comes into contact with the head member or the like in the transporting step, and even if it does, the charged particles hardly separate from the transport member. On the other hand, the densification step does not remove the charged particles, so that the amount of the charged particles adhered is maintained and the image density does not decrease. Accordingly, it is possible to prevent the charged particles from depositing on the head member while preventing the image density from lowering, and to suppress the occurrence of image density unevenness and clogging of the openings.

 The step of increasing the density may be specifically a step of pressing the charged particle layer. This makes it possible to easily increase the density of the charged particles in the charged particle layer.

 Further, the densification step includes a step of vibrating the charged particles of the charged particle layer between a transport member and an opposing member having a gap with respect to the transport member, and relocating the charged particles on the transport member. It may be about. With this configuration, the charged particles are loosened individually, and the charge amount of the charged particles is made uniform, so that the charged particles can be arranged more uniformly and densely. Even if the charged particles are aggregated to form secondary particles having a large particle diameter, the particles can be easily disintegrated into a single charged particle, thereby suppressing the clogging of the opening by the secondary particles. Can be

 When the charged particles are vibrated and rearranged as described above, it is desirable to include a step of removing particles attached to the facing member. In other words, charged particles with a very low charge amount or very few charged particles (poorly charged particles) charged to the opposite polarity tend to adhere to the opposing member, but if they remain attached, they adversely affect the vibration of the charged particles. In addition to the possibility, the defective charged particles once removed from the charged particle layer return to the transport member again. However, if the particles adhering to the opposing member are removed in this way, the charged particles can be satisfactorily vibrated and arranged densely, and the defective charged particles can be reliably removed from the charged particle layer.

In the image forming method, the vicinity of the opening of the head member is in contact with the densified charged particle layer. _r

 Five

Is desirable. With this configuration, the distance between the control electrode and the densely packed charged particle layer is always minimized, so that the charged particles can fly stably from the transport member. On the other hand, it is conceivable that the above-mentioned contact may remove the charged particles of the densely packed charged particle layer. However, since the charged particles of the densely packed charged particle layer have a high adhesive force as a whole as described above, It will not be done. Even if it is scraped off, it is deposited at a position almost in contact with the densified charged particle layer, so that it is collected on the conveying member side by a mirror image or van der Waals force. Further, the above-mentioned contact further increases the density of the charged particles and further smoothes the surface in the densely charged layer. In addition, when the charged particles are vibrated as described above, the vibrated charged particles may float on the opening of the head member. If the vicinity portion is in contact with the densely charged particles layer, the passage of the above-mentioned floating charged particles to the opening is blocked, and it is possible to prevent the floating charged particles from clogging the opening and adversely affecting the image.

 In the above-described image forming method, it is preferable that the filling rate of the particles before the charge is applied is 31 to 50%. This is because if the filling ratio is less than 31%, the cohesion between the particles is too large, and the density of the charged particles cannot be sufficiently increased with respect to the charged particle layer. If the particle size is large, the cohesive force between the particles is too small, and the particles are easily separated from the transport member during the transport process.

 In addition, the said filling rate is calculated | required by the following formula.

 Filling rate (%) = Static bulk density of particles / True density of particles X 100

 Here, the static bulk density in the above equation is determined using Powdertes Yu (registered trademark: manufactured by Hosokawa Miclon Co., Ltd. of Japan) at a temperature of 20 ° C. and a relative humidity of 50%. These values were measured with a mesh opening of 250 / m, a fall time of 3 minutes, and a Leos sunset level of 3 (the same applies hereinafter).

The image forming apparatus of the present invention for forming an image by adhering the charged particles to an image receiving body includes applying a charge of the same polarity to a large number of particles for forming an image, and charging the charged particles. A charged particle layer forming means for forming a charged particle layer composed of particles on a conveying member; and increasing the density of the charged particles with respect to the charged particle layer formed by the charged particle layer forming means. _

 D

A high-density means for performing, a counter electrode disposed so as to face a position at which the high-density charged particle layer is conveyed in the conveying member, and a counter electrode disposed between the conveying member and the counter electrode; A head member having a plurality of openings through which the charged particles of the densified charged particle layer pass, and a control electrode disposed at least partially around each of the openings; the transport member and the counter electrode; A transfer electrostatic field forming means for providing a potential difference for forming a transfer electrostatic field for transferring the charged particles of the densely packed charged particle layer toward the counter electrode; Voltage control means for applying a voltage to the control electrode of the head member to control the passage of the charged particles through the opening by the transfer electrostatic field, and disposing an image receptor between the head member and a counter electrode. And the opening is Is assumed to be configured so that by attaching the charged particles that have passed through. As a result, similarly to the above-described image forming method, it is possible to suppress the occurrence of image density unevenness and clogging of the openings.

 Specifically, the densification unit includes a pressing member that presses the charged particle layer, and the densification of the charged particles is performed on the charged particle layer by pressing the charged particle layer by the pressing member. What is necessary is just to be comprised. This makes it possible to increase the density of the charged particles in the charged particle layer with a simple configuration.

 In this case, the charged particle layer forming means is configured to apply a charge to the particles by pressing the particles on the conveying member with a predetermined pressing force and to form a charged particle layer. It is preferable that the pressing force of the charged particle layer by the member is set smaller than the particle pressing force of the charged particle layer forming means. That is, when the pressing force of the charged particle layer by the pressing member is equal to or higher than the particle pressing force of the charged particle layer forming means, the layer thickness of the densely packed charged particle layer becomes too thin, and the image density becomes low, and the charged particles are reduced. This is because the adhesive force between the charged particles and the transfer member becomes too high, and the flying response of the charged particles to the voltage applied to the control electrode is reduced.

The pressing member is preferably made of a grounded conductive material. In this way, the pressing member does not receive the charge from the charged particles and is not charged, and conversely, does not give the charged particles an electric charge, thereby preventing an unstable state from being electrostatically generated. . More preferably, the pressing member is made of a conductive material to which a voltage having the same polarity as that of the charged particles is applied. By doing so, the charge amount of the charged particles can be more stably maintained.

 Further, the high-density means has a vibration applying means for vibrating the charged particles of the charged particle layer and rearranging the charged particles on the conveying member. It may be configured to perform the conversion. Thereby, the charged particles can be arranged more uniformly and densely.

 Specifically, the vibration applying means may include an ultrasonic vibration source, and a vibration transmitting member that transmits ultrasonic vibration generated by the vibration source to the charged particles of the charged particle layer. A conductive opposing member disposed to face the conveying member with a gap, and an alternating electric field for generating an alternating electric field for vibrating the charged particles of the charged particle layer between the conveying member and the opposing member. And an electric field generating means. As a result, the charged particles in the charged particle layer can be locally vibrated, and the portion of the charged particle layer facing the opening of the head member can be prevented from vibrating. Can be prevented. When the vibration applying means has an alternating electric field generating means, the alternating electric field generating means is configured to generate an alternating electric field in which the charged particles of the charged particle layer reciprocate in the entire range between the conveying member and the opposing member. It is good to have. As a result, a high acceleration is applied to the charged particles, so that the aggregated charged particles collide with each other and are crushed well. Further, since the chance of the charged particles coming into contact with the opposing member, the developing roller, and other charged particles increases, the charge amount of the charged particles can be made more uniform.

 In this case, it is desirable to provide a particle removing unit for removing particles attached to the facing member. Thereby, the charged particles can be satisfactorily vibrated and arranged densely, and the defective charged particles can be reliably removed from the charged particle layer.

Further, when the vibration applying means has an alternating electric field generating means, a wiring portion for supplying a voltage to the control electrode of the head member is provided on the head member along a surface of the head member to the facing member along the surface of the head member. It is preferable that a conductive layer is provided so as to extend in the approaching direction, and a conductive layer covering at least the wiring portion is provided on a surface of the head member on the side of the transport member. With this, ₀

 o

It is possible to prevent a phenomenon (so-called crosstalk) in which the conductive layer performs the function of electrostatically shielding and the alternating electric field acts on the wiring portion to disturb the voltage supplied to the control electrode.

 And it is desirable that the charged particles are configured so as to generate an electrostatic field between the conductive layer and the transport member, the electrostatic field moving to the transport member side. This can prevent the floating charged particles from adhering and accumulating on the surface of the head member.

 On the other hand, a wiring portion for supplying a voltage to the control electrode is provided on the head member, and the wiring portion extends in a direction away from the opposing member along the surface of the head member from the control electrode. Is also good. By doing so, it is possible to prevent the occurrence of crosstalk without providing the conductive layer as described above.

 In the above-described image forming apparatus, it is preferable that the vicinity of the opening of the head member is in contact with the densified charged particle layer, as in the above-described image forming method. It is desirable to set it to ~ 50%. BRIEF DESCRIPTION OF THE FIGURES

 FIG. 1 is a cross-sectional view illustrating an image forming apparatus according to Embodiment 1 of the present invention.

 FIG. 2 is an enlarged cross-sectional view showing a part of the device.

 FIG. 3 is a plan view showing a part of a head member of the apparatus.

 FIG. 4 is an enlarged cross-sectional view showing the vicinity of the opening of the head member of the device.

 FIG. 5 is a bottom view of a part of a head member showing the arrangement of deflection electrodes of the device.

 FIG. 6 is a plan view showing another example of the shape of the control electrode in the device.

 FIG. 7 is a cross-sectional view showing an enlarged part of the same device.

 FIG. 8 is a time chart of the voltage applied to the control electrode of the device.

 FIG. 9 is an explanatory diagram showing an example of voltage control of the deflection electrode of the same device.

Fig. 10 is a plan view showing the arrangement of dots formed using the deflection electrode of the same device. C Fig. 11 shows the case where ultrasonic vibration is applied to the charged toner particles of the charged toner particle layer. FIG. 2 is a diagram corresponding to FIG. y

 FIG. 12 is a diagram corresponding to FIG. 2 showing the second embodiment of the present invention.

 FIG. 13 is a diagram corresponding to FIG. 2 showing the third embodiment of the present invention. BEST MODE FOR CARRYING OUT THE INVENTION

 Embodiment 1

 FIG. 1 shows an image forming apparatus according to Embodiment 1 of the present invention. The image forming apparatus has a housing 1, and a developing roller 2, a supply roller 3, and a regulating blade 4 are provided in the housing 1. Is housed.

 The developing roller 2 carries toner particles 5 (particles for image formation) as a developer, and is rotated counterclockwise in FIG. 1 at a peripheral speed of, for example, 20 to 40 O mm / sec. It is a transport member that transports to a position facing a counter electrode 6 (opening 16 of the head member 7) described later. The developing roller 2 is formed of a metal or alloy such as aluminum or iron in a cylindrical shape, has a diameter of, for example, about 16 to 18111111, and a thickness of, for example, about 1 mm. In the illustrated example, the developing roller 2 is grounded, but a DC or AC voltage may be applied. Further, the developing roller 2 may be made of synthetic rubber such as urethane and silicon. In this case, the outer diameter of the whole is covered with synthetic rubber over a metal shaft of about 6 to 8 mm so that the outer diameter is 16 to 1. It may be about 8 mm. Further, a belt or the like may be used instead of the roller.

The supply roller 3 is brought into contact with the outer peripheral surface of the developing roller 2 and rotates in a direction opposite to the developing roller 2 to supply the toner particles 5 to the developing roller 2 and to remove excess toner particles 5 from the developing roller 2. Drop from two. The supply roller 3 is formed by winding a synthetic rubber (for example, about 2 to 6 mm in thickness) such as urethane foam or silicon around a metal shaft (for example, about 8 mm in diameter) such as iron. It is designed to bite in the range of 0.1 to 2 mm. The supply roller 3 is also grounded, or a DC or AC voltage is applied, similarly to the developing roller 2. The supply roller 3 not only controls the supply amount of the toner particles 5 to the developing roller 2 but also assists the charging of the toner particles 5 due to frictional contact with the developing roller 2 with a peripheral speed difference. Also has a function (toner particles 5 Is mainly performed by a regulating blade 4 described later).

The regulating blade 4 presses the toner particles 5 supplied onto the developing roller 2 by the supply roller 5 with a predetermined pressing force, so that many toner particles 5 have the same polarity (either positive or negative). In this embodiment, a negative (−) charge is applied, and a charged toner particle layer having a thickness of about 10 to 20 μm made of the charged toner particles 5 to which the charge is applied is placed on the developing port 2. To form. The regulating blade 4 has one end fixed to a support member of the housing 1. For example, an elastic member 4 made of urethane rubber or the like having a thickness of about 1 mm is attached to the other end of a phosphor bronze plate 4 a having a thickness of about 0.5 mm. The elastic member 4b is applied to the toner particles 5 on the developing roller 2 (see FIG. 2). The pressing force of the regulating blade 4 against the toner particles 5 is preferably 3.5 to 17 g per 1 mm in the longitudinal direction of the developing roller 2. If the pressing force is smaller than 3.5 g / mm, the toner particles 5 are agglomerated and blown out from between the regulating blade 4 and the developing roller 2 to improve the charged toner particle layer. On the other hand, if it is larger than 17 g / mm, the charge amount of the toner particles 5 becomes too high, so that it becomes difficult for the toner particles 5 to fly even when a flying voltage is applied to the control electrode 19 as described later. This is because the flight response is lowered and the thickness of the charged toner particle layer is too thin, which is insufficient for printing a high-density image. In the above-mentioned charged toner particle layer, most of the toner particles are occupied by negatively charged toner particles 5 (normally charged toner particles 5), while slightly slightly positively charged toner particles. 5 (charged toner particles 5 of opposite polarity) is present, but if it is simply referred to as charged toner particles 5, it is usually charged toner particles 5 of forward polarity. As shown in FIG. 2, on the side of the developing roller 2 where the vicinity of the regulating blade 4 moves by rotation with respect to the regulating blade 4, as shown in FIG. A conductive plate-shaped opposing member 30 is provided along the circumferential direction of the developing roller 2. The opposing member 30 includes the regulating blade 4 between the developing roller 2 and the opposing member 30. Thus, an AC power source 32 as an alternating electric field generating means for generating an alternating electric field for oscillating the charged toner particles 5 of the charged toner particle layer formed on the developing roller 2 is connected. That is, the facing member 30 and the AC power source 32 are charged toner particles of the charged toner particle layer. Vibration means for vibrating 5 and re-arrangement on the developing roller 2 constitute a means for increasing the density of the charged toner particles 5 with respect to the charged toner particle layer by the rearrangement. . This densely packed charged toner particle layer is conveyed to a position facing an opening 16 of a head member 7 described later by the rotation of the developing roller 2. The layer thickness of the densified charged toner particle layer is almost the same as the charged toner particle layer formed by the regulating blade 4 (it tends to be slightly smaller).

 The opposing member 30 is disposed so as to oppose the developing roller 2 over the entire range in the length direction thereof, and a preferable interval with the developing roller 2 is about 50 to 500 / m. . If the diameter is smaller than 500 μm, the charged toner particle layer may come into contact with the charged toner particle layer.If the diameter is larger than 500 μm, it is necessary to apply a high voltage to vibrate the charged toner particles 5. Because there is. The appropriate width of the facing member 30 (length along the circumferential direction of the developing roller 2) is determined by the diameter of the developing roller 2 and the like, but the diameter of the developing roller 2 is 16 to 20 mm. In this case, the diameter is preferably 1 to 10 mm.

 The AC power supply 32 preferably has a peak amplitude voltage of 1 to 2 kV and a frequency of 1 to 4 kHz. In other words, if the frequency is lower than 1 kHz, the charged toner particles 5 cannot reciprocate over the entire range between the developing roller 2 and the opposing member 30, while the frequency is higher than 4 kHz. However, since the charged toner particles 5 only slightly vibrate on the developing roller 2, the range is 1 to 4 kHz. Thus, the AC power supply 32 generates an alternating electric field in which the charged toner particles 5 of the charged toner particle layer reciprocate in the entire range between the developing roller 2 and the facing member 30. The peak amplitude voltage of the AC power supply 32 needs to be adjusted according to the distance between the developing roller 2 and the facing member 30.

In FIG. 1, reference numeral 6 denotes a counter electrode disposed so as to face a position on the developing roller 2 where the above-described densely charged toner particle layer is conveyed. A head member 7 composed of a flexible print circuit is disposed between the developing roller 2 and the counter electrode 6, and an image receiving member is provided between the head member 7 and the counter electrode 6. The recording paper 9 is transported by the transport belt 10 and passes therethrough. Further, a fixing device 11 for fixing the toner particles 5 attached to the recording paper 9 is provided at a destination of the recording paper 9. Soshi 丄 L

In addition, a transfer power source 12 for applying a voltage for transferring the toner particles 5 to the counter electrode 6 is connected to the counter electrode 6. By this voltage application, a transfer electrostatic field for transferring the charged toner particles 5 toward the counter electrode 6 is formed between the developing roller 2 and the counter electrode 6. It constitutes forming means. The voltage for this transfer is, for example, 400 to: L500V.

 Although only one housing accommodating the developing roller 2 and the like is shown in FIG. 1, for example, when forming a full-color image, four types of toner, yellow, magenta, cyan, and black, are used. The same thing is configured for the particles 5, and they are provided so as to be arranged in a line in the conveying direction of the recording paper 9.

 As shown in FIGS. 3 and 4, the head member 7 includes a base plate 17 having a plurality of openings 16 arranged in the length direction of the developing roller 2, and a base plate 17 side of the developing roller 2. A control electrode 19 provided for each opening 16 on the surface of the base plate 17 and a pair of deflection electrodes 2 provided for each opening 16 on the surface on the opposite side of the base plate 17 (the surface on the side of the counter electrode 6). 0a, 2Ob and a cover coat 2 of an electrically insulating polymer provided to cover the control electrode 19 and the deflection electrodes 20a, 20b from the inner surface of the opening 16 of the base plate 17. With one. Further, each control electrode 19 is connected to a power supply 23 via a voltage control means 22 such as a dry IC. The base plate 17 is formed of, for example, polyimide or the like, has electrical insulation properties, and has a thickness of 25 to 40 μm. The plurality of openings 16 are for allowing the toner particles 5 to pass through. In this embodiment, the openings 16 are arranged in two rows in the length direction of the developing roller 2, and the openings 16 of both rows are aligned with each other in the row direction. It is formed so as to have a positional relationship shifted by half a pitch at a time. The plurality of openings 16 may be arranged in one row, but the arrangement density (dot density) is increased by arranging them in the above-described positional relationship.

The control electrode 19 opens and closes the opening 16 electrostatically when an appropriate voltage described later is selectively applied by the voltage control means 22, that is, the charged toner particles 5 are The developing device exposes a transfer electrostatic field passing through the opening 16 between the developing roller 2 and the counter electrode 6 so as to fly away from the developing roller 2 and the counter electrode 6 through the opening 16. Restrict. This control electrode 19 is connected to each opening 16 in the example of FIG. 丄

It is provided on the entire circumference and is formed in a ring shape. The thickness of the control electrode 19 is set to 5 to 20 m, for example, about 10 zm.

 On the surface of the base member 17 of the head member 7 on the side of the developing roller 2, wiring portions 18 for supplying a voltage to each control electrode 19 are provided, and each of the wiring portions 18 It extends in the direction away from the opposing member 30 along the surface of the head member 7 from the electrode 19 (the side where the portion near the head member 7 of the developing roller 2 from the control electrode 19 moves by rotation). The leading end is connected to the voltage control means 22. The reason for moving the wiring portion 18 away from the opposing member 30 is that an alternating electric field generated between the developing roller 2 and the opposing member 30 acts on the wiring portion 18 to control the control electrode. This is to prevent the phenomenon that the voltage supplied to 19 is disturbed (so-called crosstalk) from occurring. In other words, when this crosstalk occurs, a normal voltage is not supplied to the control electrode 19 and a disturbed image is printed, but the image is disturbed by moving the wiring portion 18 away from the opposing member 30. Can be prevented.

 Note that each wiring section 18 is moved from the control electrode 19 along the surface of the head member 7 to approach the opposing member 30 (from the control electrode 19 to the vicinity of the head member 7 of the developing roller 2 being rotated). (The side opposite to the side to move). In this case, in order to prevent the crosstalk, a conductive layer covering at least the wiring portion 18 may be provided on the surface of the head member 7 on the side of the developing roller 2 (the upper surface of the cover coat 21). By doing so, the conductive layer functions to shield electrostatically, and crosstalk can be prevented from occurring even when the wiring portion 18 is close to the opposing member 30. It is desirable that the charged toner particles 5 generate an electrostatic field between the conductive layer and the developing roller 2 so as to move toward the developing roller 2. That is, it is desirable to apply the same polarity (negative) voltage as that of the charged toner particles 5 to the conductive layer while grounding the developing roller 2. As a result, even if the charged toner particles 5 oscillating between the developing roller 2 and the facing member 30 float, the floating charged toner particles 5 adhere and accumulate on the surface of the head member 7. Can be prevented.

The deflection electrodes 20a and 2Ob deflect the charged toner particles 5 passing through the openings 16 As shown in FIG. 5, they are arranged obliquely to the conveying direction of the recording paper 9 (the direction orthogonal to the 16 rows of the openings), and are provided with the wiring portions 24 and 24, respectively. It is connected to a power supply 26 for deflection via deflection voltage control means 25. The thickness of the deflection electrodes 20a and 20b is set to 5 to 20 m, for example, about 10 m. The manner of deflection will be described later. The force bar coat 21 can be formed by coating an insulating polymer or attaching or depositing an insulating polymer thin film, and has a thickness of, for example, 5 to 2 jum. The total thickness of the head member 7 including the base plate 17, the control electrode 19, the deflection electrode 20, and the force bar coat 21 is preferably, for example, about 80 to 200 im. The opening 16 of the head member 7 is preferably a circle having a diameter of 50 to 200 zm, and more preferably a circle having a diameter of 60 / m or more. In this case, the opening area is 30 × 30 07Γ (rn ² ) or more. However, the shape may be an ellipse or a polygon having the same opening area. When the opening 16 is elliptical, the major axis / minor axis ratio is preferably 1-2, and when it is polygonal, the number of corners is preferably 4 or more, and the major axis / minor axis ratio is 1-2. Is preferred.

 The shape of the control electrode 19 can be a circular, oval, or polygonal ring surrounding the opening 16 (a ring shape corresponding to the peripheral shape of each opening 16). However, the ring may be partially missing instead of a complete ring. FIG. 6 shows another example of the shape of the control electrode 19. In this example, both sides of the circular ring (both sides in the arrangement direction of the openings 16) are oriented in the direction of the wiring section 18. It is shaped like a linear cut, that is, narrow. This is advantageous in that a large number of openings 16 (or control electrodes 19) are densely arranged while securing the distance between adjacent control electrodes 19 so as to obtain insulating properties. Dot density increases. '

On the side of the head member 7 on the side of the developing roller 2 opposite to the side on which the portion near the head member 7 of the developing roller 2 rotates with respect to the opening 16 as shown in FIG. A spacer 13 of 10 to 20 μm is provided over the entire range in the longitudinal direction of the developing roller 2, and the end of the spacer 13 on the opening 16 side is as described above. It is in contact with the densified charged toner particle layer on the developing roller 2. In other words, the vicinity of the opening 16 of the head member 7 and the high-density zone This means that the toner layer is in contact with the toner layer via the spacer 13. If the shape of the head member 7 is made the same as the shape provided with the spacer 13, the portion near the opening 16 of the head member 7 and the high-density charged toner can be provided without the spacer 13. It can be brought into direct contact with the particle layer.

 When the thickness of the densely packed charged toner particle layer is 10 to 20 ^ m and the thickness of the cover coat 21 on the control electrode 19 is 10 to 25 m by the spacer 13, The distance from the surface of the densified charged toner particle layer to the control electrode 19 is maintained at 30 to 65 m. Although not limited to this distance, if it is smaller than 30 μm, the charged toner particles 5 in the densely packed charged toner particle layer are scraped off at the edge of the opening 16, and the removed toner is removed. The particles 5 may leak out of the openings 16, and if the thickness of the cover coat 21 is reduced and brought close to the cover 5, the possibility of an electrical short circuit between the developing roller 2 and the control electrode 19 increases. On the other hand, if it is larger than 65 μm, the flying responsiveness of the charged toner particles 5 is reduced. Therefore, it is desirable to set it to 30 to 65 μm. However, if a voltage higher than the voltage value described later can be applied to the control electrode 19 as a flying voltage, there is no problem even if the voltage is set to be larger than 65 / m.

 The distance between the end of the spacer 13 on the opening 16 side and the opening 16 is preferably 100 m or less, and more preferably 100 m to 400 m. The distance between the opening 16 of the head member 7 and the counter electrode 6 is preferably 50 to 500 m, and more preferably 50 to 30 Om.

The end of the above-mentioned head member 7 where the portion near the head member 7 of the developing roller 2 with respect to the opening 16 is moved by rotation is connected to the housing 1 via a tension panel 15. On the other hand, the opposite end is fixed to the housing 1. As a result, contact between the vicinity of the opening 16 of the head member 7 and the densely packed charged toner particle layer via the spacer 13 is always maintained regardless of the rotation position of the developing roller 2. The contact force is desirably 0.3 to lg per 1 mm in the length direction of the developing roller 2. This is because if the contact force is smaller than 0.3 g / mm, the head member 7 and the densely packed charged toner particle layer do not come into uniform contact with each other in the length direction of the developing roller 2. Opening 16 and denser electrification 1

If the distance from the toner particle layer, that is, the electric field strength is not uniform and the image density unevenness occurs, while if it is larger than 1 g / mm, the charged toner particles 5 in the densely charged toner particle layer are scraped off, If the size of the toner particles becomes excessively large, the densely packed charged toner particle layer directly contacts the opening 16, and the charged toner particles 5 are scraped off at the edge of the opening 16, and the cut toner particles 5 are removed from the opening 16. Because it will pass through.

 Next, the control of the exposure of the transfer electrostatic field by the control electrode 19 will be described. FIG. 8 is a time chart of the voltage applied to the control electrode 19 by the voltage control means 22 when an image signal is externally applied to the voltage control means 22 of the control electrode 19. When the image forming apparatus is used, a transfer voltage Vbe for forming a transfer electrostatic field is applied to the counter electrode 6. The control electrode 19 is supplied with a reference potential Vw. When an image signal is input, the control voltage Vc of the pulse waveform is applied to the control electrode 19 at time Tb, and the superimposed voltage Vk of the pulse waveform is generated at the same time as the rise of the control voltage Vc. Is applied to the control electrode 19. As a result, Vw + Vc (or Vw + Vc + Vk) is moved to the opening 16 to expose the electrostatic field, and the charged toner particles 5 (the opening 1 of the head member 7) of the densified charged toner particle layer are exposed. The flying voltage is such that all the charged toner particles 5) located in the portion corresponding to 6 pass through the opening 16 from the developing roller 2 and fly to adhere to the recording paper 9.

 The reference potential Vw is a voltage having the same polarity as the charged toner particles 5, and may be, for example, about 150 to 0 V, and particularly preferably about −50 V. The control voltage Vc is a voltage having a polarity opposite to that of the charged toner particles 5 and may be, for example, 100 to 400 V, and particularly preferably around 320 V. The superimposed voltage Vk is a voltage having a polarity opposite to that of the charged toner particles 5, and may be, for example, 20 to 150 V, and particularly preferably around 50 V. The time Tb can be set to, for example, 80 s, and the time Tk can be set to, for example, 25〃s. The application of the superimposed voltage Vk is performed to make it easier to separate the charged toner particles 5 from the developing roller 2.

Therefore, an intermediate voltage between the voltage difference (transfer voltage Vbe) between the developing roller 2 and the counter electrode 6 is given to the control electrode 19 as a flying voltage, so that the opening between the developing roller 2 and the counter electrode 6 is opened. A potential gradient passing through 16, that is, a transfer electrostatic field is formed (exposed), and the charged toner particles 5 of the densely charged toner particle layer are separated from the developing roller 2 and pass through the opening 16. To reach recording paper 9.

 When the above time Tb elapses, the time Tw until the next pulse of the control voltage Vc for flight enters is a state where only the reference potential Vw is given to the control electrode 19. This reference potential Vw can be the same potential as the developing roller 2, 0 V or a potential higher than that (but lower than Vc), but if it is a negative potential having the same polarity as the charged toner particles 5, Since the developing potential of the developing roller 2 is lower than the ground potential 0 V, a limiting static electric field is generated between the developing roller 2 and the control electrode 19 in a direction opposite to the above-described transfer electrostatic field, and a new charging is performed from the developing roller 2. The flying of the toner particles 5 toward the opening 16 is reliably prevented. However, since the gradient of the electric potential of the limited electrostatic field is relatively gentle, the charged toner particles 5 already flying toward the opening 16 when the limited voltage (reference potential Vw) is applied are directly fly. And the recording paper 9 is reached through the opening 16. This prevents the dot density from becoming lower than expected.

 In the first half of the time Tw, only the reference potential Vw is applied to the control electrode 19, and in the second half, as shown by a two-dot chain line in FIG. A return voltage Vr of 50 V may be applied to the control electrode 19. In that case, the reference potential Vw and the return voltage Vr are applied to the control electrode 19. As a result, it is possible to form a limited electrostatic field between the developing roller 2 and the control electrode 19 in a direction opposite to the above-mentioned transfer electrostatic field and with a relatively steep potential gradient. The charged toner particles 5 remaining around the control electrode 19 without passing through 6 can be reliably returned to the developing roller 2.

 A desirable value or a desirable range of each voltage applied to the control electrode 19 described above is when the developing roller 2 is grounded, but when the developing roller 2 is set to a potential other than 0 V. In this case, a voltage is applied to the control electrode 19 so that the voltage difference described above or a voltage difference corresponding to the voltage range is obtained with reference to the potential of the developing roller 2. .

Although the polarity of the charged toner particles 5 is negative, if the polarity is positive, the developing roller 2, the counter electrode 6 and the And the voltage of the control electrode 19 is set.

 The central part in FIG. 9 shows a case where the same voltage is applied to both the deflection electrodes 20a and 20b, and the charged toner particles 5 pass straight through the opening 16 as shown by the arrow. The recording paper 9 reaches a position corresponding to the position of the opening 16 (no deflection). On the other hand, the left part of the figure shows the right side of the deflection electrodes 20a and 2Ob on the deflection electrode 20a arranged on the left side of the opening 16 with respect to the conveyance direction of the recording paper 9 as a reference. This shows a case in which a voltage higher than the voltage applied to the deflection electrode 2 Ob arranged at the negative electrode is applied, and the negatively charged toner particles 5 are caused by the electrostatic field generated between the deflection electrodes 20a and 2 Ob. Deflected to the left. The right part of the figure shows the case where a relatively higher voltage is applied to the right deflection electrode 20b than to the left deflection electrode 20a. Since the voltage is generated between the deflection electrodes 20a and 2Ob, the negatively charged toner particles 5 are deflected to the right.

 However, since the deflecting electrodes 20a and 2Ob face obliquely to the transport direction of the recording paper 9 as described above, there are three modes, namely, no deflection, left deflection and right deflection as shown in FIG. As shown in FIG. 0, when the recording paper 9 is stopped, three dots 27 that are linearly arranged obliquely to the traveling direction of the recording paper 9 are formed. In this case, by determining the transport speed so that the recording paper 9 is transported by the shift amount (distance) between the adjacent dots 27 and 27 in the cycle (time) at which the recording paper 9 hits the dot 27, the three dots 27 can be linearly arranged in a direction perpendicular to the transport direction A of the recording paper 9. Therefore, three dots 27 can be covered by one opening 16, and the density of dots can be increased.

 The deflection is performed by controlling the voltage applied to the left and right deflection electrodes 20a and 20b by the voltage control means 25. For example, when the vehicle is going straight, both electrodes 20a and 2Ob Apply a voltage of 50 V to both, and when deflecting to the left, apply a voltage of 120 V to the left electrode 20 a, apply a voltage of −50 V to the right electrode 20 b, and apply a voltage of 50 V to the right. To deflect, a voltage of −50 V is applied to the left electrode 20 a and a voltage of 120 V is applied to the right electrode 20 b.

Here, the toner particles 5 will be described in detail. The binder resin used in the production of the toner particles 5 is a polyester resin, a styrene-acrylic copolymer, and a styrene resin. Gen-based copolymers and epoxy resins and their mixed resins are suitable. When magnetic properties are imparted, magnetic powder is further contained. As the magnetic powder, alloys and compounds containing ferromagnetic elements, such as ferrite, magnetite, iron, conoreto, and nickel, are effective. It is appropriate that the coercive force of the magnetic powder is 7958 to 39789 A / m, and the content of the magnetic powder is 20 to 40% by mass ratio to the toner particles 5. Appropriate. However, if the magnetic powder is exposed on the surface of the toner particles 5, the magnetic toner particles 5 may polish a member that comes into contact with the toner particles 5. Non-magnetic is better as it will be rough. When a magnetic material is used, if the toner particles 5 are subjected to a heat treatment during the manufacturing process of the toner particles 5, the magnetic powder exposed on the toner particles 5 is coated with the binder resin, and the polishing action is performed. Can be reduced. Also, the magnetic powder is coated even if the particle surface after granulation is used.

Moreover, silica (S i O ²⁾ to control the flow of the charge control agent and toner particles 5, titanium oxide (T i 0 ^2), adding a metal salt of stearic acid from 0.1 to 5% Is preferred. In particular, silica greatly affects fluidity, and clogging of the opening 16 of the head member 7 by the toner particles 5 hardly occurs. Moreover, since silica has a small diameter and high chargeability, it easily adheres to the inner wall surface of the opening 16. However, since the attached toner particles 5 play a role as a hole for other toner particles 5, It facilitates the passage of toner particles 5 through openings 16. The specific surface area (by BET method) of such silica for nitrogen adsorption is suitably in the range of 100 to 300 m ² / g. If silica having a small diameter of less than 100 m ² / g is used, the resin is mixed so as to be shredded, so that sufficient fixability cannot be obtained. In addition, carbon black or the like is added as a coloring agent in an amount of 5 to 15%.

It is desirable that the filling rate of the toner particles 5 before the charge is applied is 31 to 50%. This is because if the filling ratio is less than 31%, the cohesive force between the toner particles 5 is too large, and the density of the charged toner particles 5 cannot be sufficiently increased with respect to the charged toner particle layer. If it is larger than 50%, the cohesive force between the toner particles 5 is too small, and the toner particles 5 are easily separated from the developing roller 2 during transportation. The operation of the image forming apparatus having the above configuration will be described.

 First, toner particles 5 are supplied to the developing roller 2 by the supply roller 3, and the supplied toner particles 5 are conveyed to the regulating blade 4 by the developing roller 2, and then pressed by the regulating blade 4 to become negative. While being charged, a charged toner particle layer is formed on the developing roller 2. In this charged toner particle layer, many voids are present, and the charged toner particles 5 are non-uniformly present. In addition, there are also secondary particles having a large particle diameter formed by agglomeration of the charged toner particles 5.

 Next, when the charged toner particle layer is conveyed to a position facing the opposing member 30, the charged toner particles of the charged toner particle layer are charged by an alternating electric field generated between the developing roller 2 and the opposing member 30. Particle 5 vibrates. At this time, the charged toner particles 5 vibrate so as to reciprocate in the entire range between the developing roller 2 and the opposing member 30, whereby the charged toner particles are moved to the opposing member 30, the developing roller 2, and other components. The charged toner particles 5 come into contact with each other, and the charged amount of the charged toner particles 5 becomes uniform. Also, the secondary particles collide with each other and are broken into one toner particle 5. Then, after the toner particles 5 vibrate, they are rearranged on the developing roller 2 to form a high-density charged toner particle layer. In other words, due to this rearrangement, extra voids in the charged toner particle layer are eliminated, and the charged toner particles are arranged in a uniform and dense state, and the surface of the densely charged toner particle layer is smooth. . As a result, the adhesive force between the charged toner particles 5 and the adhesive force between the charged toner particles 5 and the developing roller 2 are made uniform, and a portion having a weak adhesive force is eliminated.

Subsequently, the densely packed charged toner particle layer comes into contact with the head member 7 via the spacer 13 just before the opening 16. This contact further increases the density of the charged toner particles 5 in the densely charged charged toner particle layer, and further smoothes the surface. On the other hand, it is conceivable that the charged toner particles 5 in the densely charged toner particle layer are scraped off by this contact, but the charged toner particles 5 in the densely charged toner particle layer are generally high as described above. Since it has an adhesive force, it will not be removed if the contact force is set appropriately as described above. Even if it is scraped off, it is deposited at a position where it comes into substantial contact with the densely packed charged toner particle layer, and is collected on the developing roller 2 side by a mirror image force or a van der Waals force. Sa ₂ j Even if the charged toner particles 5 oscillating due to the alternating electric field float, the floating charged toner particles 5 do not reach the opening 16 due to the above-mentioned contact. Clogging of the opening 16 and adverse effects on the image can be prevented.

 Next, the densified charged toner particle layer is conveyed by the developing roller 2 to a position facing the opening 16 of the head member 7, and when a flying voltage is applied to the control electrode 19, the densified charged toner particle layer The charged toner particles 5 are separated from the developing roller 2 and fly to the recording paper 9 through the opening 16.

 Therefore, in the first embodiment, the density of the charged toner particles 5 is increased with respect to the charged toner particle layer formed on the developing roller 2 by the regulating blade 4, so that the densified charged toner particle layer is formed. In this densely packed charged toner particle layer, the charged toner particles 5 are arranged in a uniform and densely packed state, and the surface of the layer becomes smooth. As a result, the charged toner particles 5 are less likely to be separated from the developing roller 2 during transportation, and it is possible to suppress the charged toner particles 5 from being deposited on the head member 7. On the other hand, the amount of the charged toner particles 5 attached to the densified charged toner particle layer is almost the same as the charged toner particle layer formed by the regulating blade 4, so that the image density does not decrease. Accordingly, it is possible to prevent the image density from decreasing and to prevent the image density from being uneven and the opening 16 from being clogged. Here, a line image is formed on the recording paper 9 by using two kinds of toner particles 5 a and 5 b (both having a filling ratio of 31 to 50%) having substantially the same configuration as the first embodiment. (Equivalent to 600 dots along the transport direction in one sheet of recording paper). When printing continuously, the number of apertures varies depending on whether vibration is applied or not. 6 was clogged. At this time, the particle size (volume average particle size, number average particle size) of each toner particle 5 a, 5 b, the adhesion amount and charge amount of each toner particle 5 a, 5 b on the developing roller 2, and the maximum fluctuation of the line The amount (the amount of movement in the direction perpendicular to the line) was also examined. Table 1 shows the results.

As a result, the amount of charge slightly increases when vibration is applied, and the amount of adhesion tends to slightly decrease. This decrease in the amount of adhesion is caused by attachment or floating on the facing member 30 and has little effect on the image density. The maximum fluctuation of the line is reduced by applying vibration, and the clogging of the opening 16 is greatly improved. Two

I understand. Further, when the charged toner particle layer was visually observed, it was confirmed that the area of the exposed portion of the metal surface of the developing roller 2 was reduced by the application of vibration, and the density and homogeneity were increased. Therefore, it can be said that the densification and homogenization of the toner particle layer by the application of vibration improved the clogging of the opening 16 and the image quality.

 table 1

尚、 上記実施形態 1では、 現像ローラ 2と対向部材 3 0との間に交番電界を発生さ せて、 この交番電界により帯電トナー粒子 5を振動させたが、 超音波振動 （約 2 O k H z ) を帯電トナー粒子層の帯電トナー粒子 5に付与するようにしてもよい。 すなわ ち、 図 1 1に示すように、 対向部材 3 0に対して超音波振動源 3 9を当接させ、 この 振動源 3 9により発生した超音波振動を帯電トナー粒子層の帯電トナ一粒子 5に伝達 するようにすればよい。 この場合、 対向部材 3 0は、 超音波振動を帯電トナー粒子 5 に伝達する振動伝達部材としての役割を有しており、 例えば約 1 0 0 zm厚の樹脂フ イルム等が適している。 また、 対向部材 3 0は、 現像ローラ 2に対して 2 0 3 0〃 mの間隙を有するように配置すればよいが、 帯電トナー粒子層に軽く接触する位置に 配置するのが望ましい。

In the first embodiment, an alternating electric field is generated between the developing roller 2 and the opposing member 30 and the charged toner particles 5 are vibrated by the alternating electric field. H z) may be applied to the charged toner particles 5 of the charged toner particle layer. That is, as shown in FIG. 11, the ultrasonic vibration source 39 is brought into contact with the facing member 30 and the ultrasonic vibration generated by the vibration source 39 is used to charge the toner of the charged toner particle layer. It may be transmitted to the particles 5. In this case, the facing member 30 has a role as a vibration transmitting member for transmitting the ultrasonic vibration to the charged toner particles 5, and for example, a resin film having a thickness of about 100 zm is suitable. Further, the opposing member 30 may be arranged so as to have a gap of 230 μm with respect to the developing roller 2, but is desirably arranged at a position where the opposing member 30 comes into light contact with the charged toner particle layer.

 Embodiment 2

FIG. 12 shows Embodiment 2 of the present invention (in the following embodiments, the same parts as those in FIG. 2 are shown). L

The same reference numerals are used and the detailed description is omitted), and the charged toner particles 5 attached to the facing member 30 are removed.

 That is, in the second embodiment, as in the first embodiment, an alternating electric field is generated between the developing roller 2 and the facing member 30 to vibrate the charged toner particles 5 of the charged toner particle layer. The opposing member 30 is formed in a rotatable roller shape (the charged toner particles 5 can be sufficiently vibrated even if it is not plate-shaped), and the opposing member 30 and the developing roller 2 oppose each other. Rotate so that the moving part moves in the same direction. A scraper 36 is in contact with a portion of the opposing member 30 opposite to the developing roller 2 over the entire range in the length direction of the opposing member 30, and is opposed by the scraper 36. The opposite polarity toner particles 5 attached to the surface of the member 30 are removed. That is, the scraper 36 constitutes a toner particle removing means for removing the toner particles 5 attached to the facing member 30.

 In addition to the AC power supply 32 having the same peak amplitude voltage and frequency as in the first embodiment, a DC power supply 33 is connected to the facing member 30 in series to apply a voltage having the same polarity as the charged toner particles 5. Have been. This makes it easier for the charged toner particles 5 of the opposite polarity to adhere to the facing member 30, so that such defective charged toner particles 5 can be removed. In addition, since the toner particles 5 having a large particle diameter usually have a low charge amount or are charged to the opposite polarity, it is possible to effectively remove such a material that disturbs the uniformity of the charged toner particle layer. it can.

 Therefore, in the second embodiment, even if the charged toner particles 5 adhere to the surface of the facing member 30, the charged toner particles 5 are conveyed to the scraper 36 and removed by the scraper 36. Is always kept in a clean state, and even when printing is performed for a long time, the operation and effect of the first embodiment can be stably obtained. (When clogging evaluation similar to that of the first embodiment is performed, almost the same effect is obtained.) confirmed) .

In the second embodiment, the opposing member 30 is formed in a rotatable roller shape. However, when the opposing member 30 is formed in a plate shape as in the first embodiment, the scraper 36 is attached to the opposing member 30 during non-recording. Reciprocating to remove the toner particles 5 attached to the facing member 30. You may.

 Further, as described above, even in a configuration in which ultrasonic vibration is applied to the charged toner particles 5 of the charged toner particle layer, the toner particles 5 adhered to the opposing member 30 as the vibration transmitting member are removed by the scraper 36. To remove it.

 Embodiment 3

 FIG. 13 shows Embodiment 3 of the present invention, and the method of increasing the density of the charged toner particle layer is different from those of Embodiments 1 and 2. That is, in the third embodiment, instead of the facing member 30 in the first and second embodiments, a pressing member 37 for pressing the charged toner particle layer is provided, and the charged toner particle layer is pressed by the pressing member 37. It is configured to increase the density of the charged toner particles 5 with respect to the charged toner particle layer by pressing. As the pressing member 37, a resin sheet such as PET film, polycarbonate, polyimide, or PTFE, a metal film such as aluminum or iron, or a rubber sheet such as urethane rubber or silicon rubber can be used. It is good to be made of a material and grounded. In this case, the pressing member 37 does not receive the charge from the charged toner particles 5 and is not charged, and conversely, does not give the charged toner particles 5 a charge, so that an electrostatically unstable state is obtained. Can be prevented. Further, it is more preferable to apply a voltage (−200 to −50 V) of the same polarity (negative) as that of the charged toner particles 5 by using a conductive material. In this way, the charge amount of the charged toner particles 5 can be more stably maintained.

The pressing force of the pressing toner particle layer by the pressing member 37 is smaller than the pressing force of the regulating blade against the toner particles 5, and the pressure member near the opening 16 of the head member 7 and the densely charged toner particle layer It is better to set the contact force to be larger than the contact force via the spacer 13. Specifically, the amount is preferably 0.7 to 3.3 g per 1 mm in the length direction of the developing roller 2. This is because if it is less than 0.7 g / mm, the density of the charged toner particles 5 cannot be sufficiently increased with respect to the charged toner particle layer, while if it is more than 3.3 g / mm, the charged toner particles 5 This is because the charged toner particles 5 in the particle layer are scraped off and the charged amount of the charged toner particles 5 becomes too high, so that the flying responsiveness of the charged toner particles 5 by the control electrode 19 decreases. By pressing the charged toner particle layer with the pressing member 37, as in the case where vibration is applied, the charged toner particles 5 are uniformly and densely arranged by eliminating extra voids in the charged toner particle layer. With the simple configuration, the same operation and effect as those of the first and second embodiments can be obtained (when the same clogging evaluation as that of the first embodiment is performed, substantially the same effect is confirmed).

 In the first to third embodiments, the vicinity of the opening 16 of the head member 7 is brought into contact with the high-density charged toner particle layer via the spacer 13. The head may not be in contact with the head member 7 itself or the constituent members on the head member 7. However, if the contact is made as described above, the head member 7 follows the surface position of the developing roller 2 (densified charged toner particle layer) even if the developing roller 2 has a large tolerance such as roundness and runout. Is very preferable because the distance from the surface of the densely charged toner particle layer to the control electrode 19 can be kept constant and various effects can be obtained as described above. Industrial applicability

 INDUSTRIAL APPLICABILITY The image forming method and the image forming apparatus of the present invention are useful when used in a printing machine such as a computer, a facsimile machine, a copying machine, and the like. Availability is high.

Claims

Speculation of Word 1. An image forming method for forming an image by attaching charged particles to an image receiving body,  A charged particle layer forming step of applying a charge of the same polarity to a large number of particles for forming an image and forming a charged particle layer composed of the charged particles to which the charge is applied on a transport member; A densification step of densifying the charged particles with respect to the charged particle layer formed in  The above-described densely packed charged particle layer is opposed to the above-mentioned opening in the head member having a plurality of openings and control electrodes disposed at least partially around each of the openings by the above-mentioned conveying member. A transfer process of transferring to a position,  The charged particles of the densified charged particle layer conveyed to a position facing the opening of the head member by the conveying member are applied from a conveying member by applying a voltage to a control electrode around the opening according to an image signal. Flying a charged particle through an opening to an image receiving body disposed on the side opposite to the transport member with respect to the head member.  2. The image forming method according to claim 1, wherein the densification step is a step of pressing the charged particle layer. 3. The densification step is a step in which the charged particles of the charged particle layer are vibrated between the transporting member and an opposing member disposed to face the transporting member with a gap therebetween, and are rearranged on the transporting member. The image forming method according to claim 1.  4. The image forming method according to claim 3, further comprising a step of removing particles attached to the facing member. 5. The image forming method according to claim 1, wherein the vicinity of the opening of the head member is in contact with the densified charged particle layer.  6. The image forming method according to claim 1, wherein the filling rate of the particles before applying the electric charge is 31 to 50%.  7. An image forming apparatus for forming an image by attaching charged particles to an image receiving body, Charged particle layer forming means for providing a charge of the same polarity to a large number of particles for forming an image, and forming a charged particle layer composed of charged particles to which the charge has been applied on a transport member; The density of the charged particles is increased for the charged particle layer formed by the forming means. High density means,  A counter electrode disposed to face a position where the densely packed charged particle layer is transported in the transporting member;  A plurality of openings through which the charged particles of the densely packed charged particle layer pass and a control electrode provided at least partially around each of the openings; A head member having  A transfer electrostatic field forming means for providing a potential difference between the transport member and the counter electrode for forming a transfer electrostatic field for transferring the charged particles of the densely packed charged particle layer toward the counter electrode;  Voltage control means for applying a voltage to a control electrode of the head member in accordance with an image signal and controlling passage of the charged particles through the opening by the transfer electrostatic field,  An image forming apparatus, wherein an image receiving member is arranged between the head member and the counter electrode, and the charged particles passing through the opening are attached to the image receiving member.  8. The densification means has a pressing member for pressing the charged particle layer, and is configured to increase the density of the charged particles on the charged particle layer by pressing the charged particle layer by the pressing member. The image forming apparatus according to claim 7, wherein  9. The charged particle layer forming means is configured to apply a charge to the particles by pressing the particles on the conveying member with a predetermined pressing force and form a charged particle layer,  9. The image forming apparatus according to claim 8, wherein the pressing force of the charged particle layer by the pressing member is set smaller than the particle pressing force of the charged particle layer forming unit.  10. The image forming apparatus according to claim 8, wherein the pressing member is made of a grounded conductive material. 11. The image forming apparatus according to claim 8, wherein the pressing member is made of a conductive material to which a voltage having the same polarity as the charged particles is applied.  12. The densification means has a vibration imparting means for vibrating the charged particles of the charged particle layer and relocating them on the conveying member. The rearrangement increases the density of the charged particles with respect to the charged particle layer. The image forming apparatus according to claim 7, wherein the image forming apparatus is configured to perform the operation. 13. The vibration applying means includes an ultrasonic vibration source and an ultrasonic vibration generated by the vibration source. 13. The image form according to claim 12, further comprising a vibration transmitting member that transmits the charged particles of the charged particle layer. 14. The vibration imparting means vibrates the charged particles of the charged particle layer between the conductive opposing member disposed opposite to the conveying member with a gap therebetween, and the conveying member and the opposing member. 13. The image forming apparatus according to claim 12, further comprising an alternating electric field generating means for generating an alternating electric field. 15. The image according to claim 14, wherein the alternating electric field generating means is configured to generate an alternating electric field in which the charged particles of the charged particle layer reciprocate in the entire range between the conveying member and the opposing member. Forming equipment.  16. The image forming apparatus according to claim 15, further comprising a particle removing means for removing particles attached to the facing member.  17. The head member is provided with a wiring portion for supplying a voltage to the control electrode of the head member so as to extend from the control electrode along the surface of the head member in a direction approaching the opposing member, 15. The image forming apparatus according to claim 14, wherein a conductive layer that covers at least the wiring portion is provided on a surface of the head member on the side of the transport member.  18. The image forming apparatus according to claim 17, wherein the image forming apparatus is configured to generate an electrostatic field between the conductive layer and the transport member, in which the charged particles move toward the transport member.  19. A wiring section for supplying voltage to the control electrode is provided on the head member,  15. The image forming apparatus according to claim 14, wherein the wiring portion extends in a direction away from the opposing member along the surface of the head member from the control electrode.  20. The image forming apparatus according to claim 7, wherein a portion near the opening of the head member is in contact with the densified charged particle layer.  21. The image forming apparatus according to claim 7, wherein the filling rate of the particles before applying the electric charge is set to 31 to 50%.