JP2008197482A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus which forms a plurality of toner images on one latent image carrier and can suppress unevenness in image density of second and subsequent toner images.
SOLUTION: A developing area on the downstream side in the surface movement direction of the surface of the photosensitive member 1 from a magenta developing region for forming a first toner image is a gap between the photosensitive member 1 and a toner conveying member 402 as a developer conveying member. It is set so that a certain developing gap is widened and a developing potential that is a potential difference between the surface of the photoreceptor 1 and the surface of the toner conveying member 402 in the developing region is increased.
[Selection] Figure 1

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, or a facsimile. Specifically, a plurality of developing units are opposed to the surface of one latent image carrier, and a plurality of toner images are superimposed on the latent image carrier. The present invention relates to an image forming apparatus for matching.

Conventionally, as a full-color image forming apparatus, a plurality of charging means and developing means are arranged to face one photosensitive member as a latent image carrier, and the photosensitive member is charged by each charging unit. Some have exposure means for exposing the surface. As the exposure means, a plurality of exposure apparatuses are arranged between each charging means and each developing means, or the light irradiated by one exposure apparatus is guided by a reflecting member, and each charging means, each developing means, In some cases, the surface of the photoreceptor is irradiated. In such an image forming apparatus, toner images of a plurality of colors are superposed on the surface of one photoconductor, and the superposed toner images are transferred onto a recording medium such as transfer paper or a toner image carrier such as an intermediate transfer belt by a transfer unit. Transfer at the transfer position to form a color image. With this type of image forming apparatus, the number of photoconductors can be reduced compared to a developing device having one photoconductor for each color, and the cost of the photoconductor can be reduced. The capacity can be reduced. In addition, the number of times of transfer can be reduced in order to form an image superimposed on the photoreceptor, so that deterioration in image quality can be suppressed.
As such an image forming apparatus, there are image forming apparatuses described in Patent Document 1, Patent Document 2, and the like.

Japanese Patent No. 3250851 Japanese Patent Publication No. 8-3673

However, when a plurality of color toner images are formed on one photoconductor, when developing the latent image for the second and subsequent colors, the latent image portion of the surface where the existing toner image is present on the surface of the photoconductor The surface potential is different. For example, a latent image is formed by exposing and neutralizing a negatively charged photoreceptor surface and developing the latent image with a negatively charged toner having the same polarity as the uniform charge. A phenomenon occurs. That is, the potential of the latent image portion on the surface of the toner layer, which is the outermost surface of the portion where the toner image is present, has a negative polarity potential that is larger in absolute value than the potential of the latent image portion on the surface of the photoreceptor where there is no toner image. . In addition, the absolute value of the negative polarity potential of the latent image portion was increased as the layer thickness was increased even at the location where the existing toner layer was formed.
As described above, when the surface potential of the latent image portion varies depending on the presence or absence of the existing toner layer and the difference in the thickness of the existing toner layer during development for the second and subsequent colors, the surface of the developer conveying member provided in the developing unit The development potential, which is a potential difference, becomes different. The difference in development potential causes a difference in the toner adhesion amount, and the image density varies depending on the presence or absence of the toner layer and the thickness of the toner layer.

  The present invention has been made in view of the above problems, and an object of the present invention is to form a plurality of toner images on one latent image carrier, and to adjust the image density of the second and subsequent toner images. An object of the present invention is to provide an image forming apparatus capable of suppressing unevenness.

In order to achieve the above object, the invention of claim 1 includes a latent image carrier that moves on the surface, a charging unit that uniformly charges the surface of the latent image carrier, and the latent image charged by the charging unit. A latent image forming means for forming a latent image on the surface of the image carrier, and a developer transport member that transports the developer on the surface of the latent image carrier facing the development region, are developed in the development region. A developing means for forming a toner image by supplying charged toner in the developer conveyed by the agent conveying member to the latent image on the latent image carrier; and a toner image formed on the latent image carrier. Transfer means for transferring to a recording medium or a toner image carrier at a transfer position, and a plurality of the developing means are opposed to the surface of one latent image carrier, and the latent image is formed by the plurality of development means. A plurality of toner images are superposed on the carrier, and the transfer means In the image forming apparatus that collectively transfers the image onto the recording medium or the toner image carrier at the transfer position, development is performed on the downstream side in the surface movement direction of the latent image carrier from the development region where the first toner image is formed. The latent image on the surface of the developer conveying member and the surface of the latent image carrier in the development region is such that the gap between the latent image bearing member and the developer conveying member becomes wider in the region. It is characterized in that it is set so that the potential difference with the formed latent image portion becomes large.
According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the two developing units are opposed to the one latent image carrier.
The invention according to claim 3 is the image forming apparatus according to claim 1 or 2, wherein the layer thickness of the toner image formed by one of the developing means is at least twice the average particle diameter of the toner used for development. The ratio of the toner adhesion amount to the image density ID is 1.4 / 0.4 [mg / cm ² ] ⁻¹ or more.
According to a fourth aspect of the present invention, in the image forming apparatus according to the first, second, or third aspect, the developer conveying member includes a plurality of electrodes for generating a traveling wave electric field for moving the toner, and the traveling wave The toner is conveyed to a position facing the latent image carrier by an electric field.
According to a fifth aspect of the present invention, in the image forming apparatus according to the first, second, or third aspect, the developer conveying member has a plurality of electrodes arranged in the surface moving direction via an insulating layer on a surface that moves endlessly. Characterized in that a potential difference is formed in a periodic manner between an assembly of odd-numbered electrodes starting from one of the plurality of electrodes and an assembly of even-numbered electrodes. It is.
According to a sixth aspect of the present invention, in the image forming apparatus of the first, second, third, fourth or fifth aspect, the average circularity of the toner supplied from the developing unit to the surface of the latent image carrier is 90% or more. It is characterized by being.

The amount of toner adhering to the latent image portion on the latent image carrier is affected by the magnitude of the development potential in the development area, but is also affected by the width of the development gap, which is the gap between the development areas. The larger the development potential, the more the toner adhesion amount, and the wider the development gap, the smaller the toner adhesion amount. That is, the amount of toner adhering to the latent image portion depends on the value of the electric field strength value obtained by dividing the development potential at the latent image portion by the development gap.
In a state where a toner image is formed on the surface of the latent image carrier, the potential difference between the latent image portion formed on the surface of the toner layer and the latent image portion formed on the surface of the latent image carrier is ΔV, and the latent image carrier the development potential of the latent image portion on the surface and V _P, the development gap and L. At this time, the development potential in the latent image portion on the surface of the toner layer is V _P −ΔV, and the electric field strength in the latent image portion on the surface of the latent image carrier is V _P / L. Then, the ratio of the layer thickness of the toner layer to the developing gap L is, if it is sufficiently smaller than the ratio of the potential difference ΔV with respect to the development potential V _P, electric field intensity in the latent image portion of the toner layer on the surface (V _P - ΔV) / L.
Since the amount of toner adhering to the latent image carrier due to the development potential depends on the electric field strength, ΔV / L, which is the difference in electric field strength between the latent image carrier surface and the toner layer surface, is small. As a result, unevenness in the toner adhesion amount can be reduced.
Also, ΔV increases as the toner layer thickness increases. Therefore, when three or more toner images are superimposed on a latent image carrier, the value of ΔV varies depending on how the toner images overlap. Since the value of ΔV increases as the layer thickness increases, the maximum value of ΔV increases in the developing region on the downstream side in the surface movement direction of the latent image carrier.
In the image forming apparatus according to any one of claims 1 to 6, since each member is arranged so that the developing gap L becomes wider in the developing region on the downstream side in the surface movement direction of the latent image carrier, the second and subsequent toners Even when the potential difference ΔV occurs in the latent image portion due to the presence or absence of an existing toner layer during image development, ΔV / L, which is a difference in electric field strength, can be reduced. In addition, when developing by superposing three or more toner images, the maximum value of the potential difference ΔV of the latent image portion increases as the toner images overlap and the layer thickness increases, but the latent image carrier that can increase the layer thickness Since the developing gap L becomes wider in the developing region on the downstream side in the surface movement direction, ΔV / L can be reduced even for the maximum value of the potential difference ΔV of the latent image portion.
Here, when the value of the development gap L is increased, the electric field strength _VP / L due to the development potential in the latent image portion on the surface of the latent image carrier is also decreased, which may lead to a decrease in the amount of toner adhesion. However, in the image forming apparatus according to the first to sixth aspects, since the developing potential V _P is set to be larger in the developing region on the downstream side in the surface movement direction of the latent image carrier, the electric field strength V _P / L Can be suppressed, and the amount of toner adhesion can be prevented from decreasing. Further, even if the development potential _VP is set to be large, ΔV / L that causes unevenness of the toner adhesion amount does not change, so that the electric field strength difference ΔV / L is maintained while maintaining the electric field strength V _P / L. L can be reduced.

  According to the first to sixth aspects of the present invention, the difference in the electric field strength of the latent image portion between the surface of the toner layer and the latent image carrier is reduced while maintaining the electric field strength during the development of the second and subsequent toner images. Therefore, there is an excellent effect that unevenness in image density of the second and subsequent toner images can be suppressed.

Embodiment 1
Hereinafter, a first embodiment (hereinafter referred to as Embodiment 1) in which the present invention is applied to an image forming apparatus will be described.
FIG. 1 is a schematic configuration diagram of an entire printer 100 as a full-color image forming apparatus according to the first embodiment.
The printer 100 shown in FIG. 1 superimposes four color toner images of magenta (M), yellow (Y), cyan (C), and black (K) on the photosensitive member 1 that is a latent image carrier. This is an image forming apparatus of a so-called photoconductor color superposition method for forming a color image. In the printer 100, a charging device 2 (M, Y) as charging means for four colors M, Y, C, and K is provided from the upstream portion to the downstream portion along the circumferential direction (arrow a direction) of the drum-shaped photosensitive member 1. , C, K) and a developing device 4 (M, Y, C, K) as developing means. In the charging device 2M, the photoreceptor 1 is uniformly charged, and the surface of the photoreceptor 1 is exposed by optical scanning of the photoreceptor 1 by the writing device 3 which is a latent image forming unit, and a magenta-colored static image is formed on the surface. An electrostatic latent image is formed, and the electrostatic latent image is developed by the developing device 4M to form a magenta toner image on the photoreceptor 1. For the YCK color, a toner image is formed on the photoreceptor 1 in the same manner as the magenta color.
The superposed toner images are collectively transferred from the photoreceptor 1 to the transfer paper P as a recording medium at a transfer position that is a facing portion between the transfer roller 61 and the photoreceptor 1 provided in the transfer device 6 that is a transfer means ( M, C, Y, and K toner images are all transferred simultaneously). The toner image transferred onto the transfer paper P is heat-fixed by a fixing device (not shown) to become an image on the transfer paper P.

The transfer device 6 includes a transfer roller 61 having conductivity and elasticity and a transfer conveyance belt 60 as a transfer paper conveyance member.
After the transfer paper P is transported by a transport means from a paper bank (not shown), the transfer paper P is transported to the transfer device 6 at a predetermined timing by a registration roller (not shown). At the transfer position where the transfer roller 61 and the photoconductor 1 of the transfer device 6 are opposed to each other, the toner images (the toner images for four colors) on the photoconductor 1 are at desired positions on the transfer paper P as described above. Transcribed. The fixing device heats and pressurizes the recording paper on which the toner image is transferred, whereby the toner image is fixed on the recording paper and is discharged outside the apparatus.
The writing device 3 shown in FIG. 1 has a surface of the photoreceptor 1 between the charging device 2 and the developing device 4 for each color through a mirror so that a laser beam emitted from one light source forms a latent image corresponding to each color. Irradiating. The writing device 3 is not limited to such a configuration. For example, the writing device 3 may have a configuration including four light sources in order to form an electrostatic latent image of each color.

Next, the developing device 4 (M, Y, C, K) will be described. The four developing devices 4 (M, Y, C, and K) are described as developing devices 4 because they have the same configuration and perform the same operation except for the color of the accommodated toner.
FIG. 2 is a schematic configuration diagram of the developing device 4.
As shown in FIG. 2, inside the casing 401 of the developing device 4, from the photosensitive member 1 side, a toner conveying member 402 as a developer conveying member, a magnetic brush roller 403 as a toner supply member, and a stirring / conveying member 404. 405 are disposed. A two-component developer (hereinafter referred to as “developer”) 12 containing the toner 10 and the magnetic particles 11 in the casing 401 is agitated by the agitating / conveying members 404 and 405, and a part thereof is the magnetic brush roller 403. Supported on. The developer 12 on the magnetic brush roller 403 comes into contact with the toner conveying member 402 in the toner supply region A2 after the layer thickness is regulated by a regulating blade 406 as a developer regulating member. In this toner supply area A2, only the toner 10 in the developer 12 on the magnetic brush roller 403 is separated and supplied to the toner conveying member 402.

The magnetic particle 11 contains a magnetic material such as ferrite with a metal or resin as a core, and the surface layer is coated with a silicon resin or the like. The particle size of the magnetic particles 11 is preferably in the range of 20 to 50 [μm]. The resistance of the magnetic particles 11 is preferably in the range of 10 ⁴ to 10 ¹⁵ [Ω] in terms of dynamic resistance DR.
Here, the measurement of the dynamic resistance DR of the magnetic particles 11 was performed as follows using the measurement system shown in FIG. First, a rotatable sleeve 201 having a diameter of φ20 [mm] with a fixed magnet built in a predetermined position is set above the grounded base 200. A counter electrode (doctor) 202 having a facing area of width: 65 [mm] and length: 0.5 to 1 [mm] is opposed to the surface of the sleeve 201 with a gap of 0.9 [mm]. . Next, the sleeve 201 starts to be rotationally driven at a rotational speed of 600 [rpm] (linear speed of 628 [mm / sec]). Then, a predetermined amount (14 [g]) of the magnetic particles to be measured is supported on the rotating sleeve 201, and the magnetic particles 11 are stirred for 10 minutes by the rotation of the sleeve 201. Next, the current I _RII [A] flowing between the sleeve 201 and the counter electrode 202 is measured by the ammeter 203 without applying a voltage to the sleeve 201. Next, an applied voltage E [V] of a withstand voltage upper limit level (400 [V] for high-resistance silicon-coated carrier to several [V] for iron powder carrier) is applied from the DC power source 204 to the sleeve 201 for 5 minutes. In this embodiment, 200 [V] is applied. Then, the current I _RQ [A] flowing between the sleeve 201 and the counter electrode 202 with the voltage E applied is measured by the ammeter 203. From these measurement results, the dynamic resistance DR [Ω] is calculated using the following equation (1).
DR = E / (I _RQ −I _RII ) (1)

  The magnetic brush roller 403 includes a non-magnetic rotatable supply sleeve 408 having a built-in magnet member 407 having a plurality of magnetic poles. The magnet member 407 is fixedly arranged so that magnetic force acts when the developer 12 passes through a predetermined location on the supply sleeve 408. The supply sleeve 408 provided in the developing device 4 has a diameter of φ18 [mm] and is sandblasted so that the surface roughness Rz (ten-point average roughness) falls within the range of 10 to 20 [μm].

  The magnet member 407 built in the magnetic brush roller 403 is arranged in the direction of rotation of the supply sleeve 408 from the restriction portion by the restriction blade 406 in the N pole (N1), S pole (S1), N pole (N2), and S pole (S2). , S poles (S3). The arrangement of the magnetic poles of the magnet member 407 is not limited to the configuration shown in FIG. 2, and other arrangements may be set according to the arrangement of the regulating blade 406 around the magnetic brush roller 403. For example, as shown in FIG. 4, four magnetic poles of N pole (N1), S pole (S1), N pole (N2), and S pole (S2) are arranged in the rotation direction of the supply sleeve 408 from the restriction portion by the restriction blade 406. You may arrange.

  Due to the magnetic force of the magnet member 407, the developer 12 composed of the toner 10 and the magnetic particles 11 is carried on the supply sleeve 408 in a brush shape. The toner 10 in the magnetic brush on the magnetic brush roller 403 is mixed with the magnetic particles 11 to obtain a specified charge amount. The charge amount of the toner on the magnetic brush roller 403 is preferably in the range of −10 to −40 [μC / g].

The toner conveying member 402 is opposed to contact with the magnetic brush on the magnetic brush roller 403 in the toner supply region A2 adjacent to the magnetic pole N2 in the magnetic brush roller 403, and is opposed to the photoreceptor 1 in the developing region A1. It is arranged like this.
In the developing device 4, the distance at the closest portion between the regulating blade 406 and the magnetic brush roller 403 is set to 500 [μm]. Further, the magnetic pole N 1 of the magnet member 407 facing the regulation blade 406 is positioned at an angle of several degrees upstream of the position facing the regulation blade 406 in the rotation direction of the magnetic brush roller 403. Thereby, the circulation flow of the developer 12 in the casing 401 can be easily formed.

  The regulating blade 406 contacts the magnetic brush so as to regulate the amount of the developer 12 formed on the magnetic brush roller 403 at a portion facing the magnetic brush roller 403, and a predetermined amount of developer is conveyed to the toner supply region. In addition, frictional charging between the toner 10 and the magnetic particles 11 in the developer 12 is promoted.

  Further, the supply sleeve 408 of the magnetic brush roller 403 is rotationally driven in the direction of arrow c in FIG. 2 by a rotation driving device (not shown), and only the toner is supplied to the surface of the toner conveying member 402 in the toner supply region A2. In the developing device 4, the gap between the toner conveying member 402 and the supply sleeve 408 of the magnetic brush roller 403 in the toner supply region A2 is set to 0.1 [mm].

Further, a conveyance power source 409 is connected to a conveyance electrode of a toner conveyance member 402, which will be described in detail later, and voltages having a plurality of phases are applied. A transport power source 409 for applying a developing bias Vb for forming a developing electric field is connected to the developing region A1. A supply power source 410 for applying a toner supply bias for forming a toner supply electric field in the toner supply region A2 is connected to the supply sleeve 408 of the magnetic brush roller 403.
Further, a toner collecting roller as shown in FIG. 4 is used as a toner collecting means for collecting the toner 10 that is not supplied to the photosensitive member 1 in the developing area A1 out of the toner 10 carried on the toner conveying member 402 described later in detail. 411 may be provided. The toner collecting roller 411 collects the toner 10 from the toner conveying member 402 by applying a voltage from the toner collecting power source 412. The toner 10 collected by the toner collection roller 411 is removed from the toner collection roller 411 by a removing member (not shown) and taken into the developer 12.

Next, a toner supply operation to the toner conveying member 402 in the developing device 4 will be described.
The developer 12 accommodated in the casing 401 is a mixture of the toner 10 and the magnetic particles 11, and includes the rotational force of the stirring / conveying members 404 and 405 and the supply sleeve 408 of the magnetic brush roller 403, and the magnetic member 407. The toner is agitated by a magnetic force, and at that time, the toner 10 is given an electric charge by frictional charging with the magnetic particles 11.

  On the other hand, the developer 12 carried on the magnetic brush roller 403 is regulated by the regulating blade 406, and a certain amount of the developer 12 is transferred to the toner conveying member 402 by the electric field formed by the toner supply bias, and the rest is left. Returned into the casing 401.

  In the toner supply area A <b> 2, the toner in the magnetic brush is separated and transferred to the toner conveying member 402. Note that an AC bias voltage is applied to the magnetic brush roller 403.

Next, toner conveyance by the toner conveyance member 402 included in the developing device 4 will be described.
FIG. 5 is a schematic diagram of the vicinity of the developing area A1 that is a facing portion between the toner conveying member 402 and the photoreceptor 1, and is an explanatory diagram of the toner conveying member 402. FIG.

  The toner transport member 402 includes a transport substrate 110 having a plurality of electrodes 102 for generating an electric field for transporting, hopping, and collecting the toner 10 that is powder. Are applied with different drive waveforms Va1 to Vc1 and Va2 to Vc2 of n phases (here, three phases) for generating a required electric field from a carrier power supply 409 which is a carrier power supply circuit.

  Here, in the relationship between the photosensitive member 1 and the range of the electrodes 102 to which the drive waveforms Va1 to Vc1 and Va2 to Vc2 are applied, the transport substrate 110 transports the toner 10 to the vicinity of the photosensitive member 1 and the photosensitive member 1. A development area Ar2 (A1 in FIG. 2) for forming the toner image by attaching the toner 10 to the latent image, and an area after passing through the development area for collecting the toner 10 on the transport substrate 110 side (hereinafter referred to as “ It is referred to as “recovery area”.) Ar2.

  Then, the developing device 4 transfers the toner 10 to the vicinity of the photoreceptor 1 in the transport area Ar1 of the transport substrate 110, and the toner 10 is transferred to the image portion of the latent image on the photoreceptor 1 in the development area Ar2. The toner 10 is applied to the latent image by developing an electric field in the direction toward the side 1 and toward the non-image portion in a direction toward the opposite side (conveying substrate 110 side) of the photoreceptor 1. In the recovery area Ar3, the toner 10 forms an electric field in a direction toward the opposite side (conveying substrate 110 side) from the photoreceptor 1 for both the image portion and the non-image portion of the latent image.

  As a result, in the development area Ar2, the toner adheres to the latent image on the photoreceptor 1 to be visualized, and the toner that has not contributed to the development is collected in the collection area downstream in the rotation direction (movement direction) of the photoreceptor 1. Since the toner is collected on the transport substrate 110 side, generation of scattered toner is prevented. The collection area Ar3 is located downstream of the development area Ar2 in the surface movement direction of the photoreceptor 1, so that the floating toner can be reliably collected.

  Next, the transport substrate 110 of the toner transport member 402 will be described in more detail. FIG. 6 is a plan view of the transport substrate 110 on the surface of the toner transport member 402, and FIG. 7 is a cross-sectional view of the transport substrate 110 taken along the line AA ′ of FIG.

  In the transport substrate 110, three transport electrodes 102a, 102b, and 102c (these are also collectively referred to as “electrodes 102”) are arranged on a base substrate (support substrate) 101 as a set. Specifically, the transport electrodes 102 of each set are substantially perpendicular to the toner transport direction at predetermined intervals along the toner transport direction (the arrow X direction in FIGS. 6 and 7, also referred to as the toner traveling direction and the toner moving direction). It is repeatedly formed and arranged in an elongated shape whose direction is the longitudinal direction. The transport substrate 110 is an insulating transport surface forming member that forms a transport surface on the transport electrodes 102 that are repeatedly formed and arranged, and is an inorganic or organic insulating material that serves as a protective film that covers the surface of the transport electrode 102 The surface protective layer 103 formed in (1) is laminated. Here, the surface protective layer 103 forms the transport surface, but a surface layer having excellent compatibility with the powder (toner) can be additionally formed on the surface protective layer 103.

  Common electrodes 105a, 105b, and 105c interconnected with both ends of the transport electrodes 102 (a, b, c) on both sides of the transport electrodes 102 (a, b, c) (these are referred to as “common electrodes 105”). Are also provided along the toner transfer direction, that is, in a direction substantially orthogonal to the individual electrodes. In this case, the width of the common electrode 105 (this width is the width in the direction orthogonal to the toner transfer direction) is larger than the width of the electrode 102 (this width is the width along the toner transfer direction). In FIG. 6, the common electrode 105, the common electrode 105 (a1, b1, c1) in the transport area Ar1, the common electrode 105 (a2, b2, c2) in the development area Ar2, and the common electrode 105 (in the recovery area Ar3). a3, b3, and c3).

  Here, after the pattern of the common electrode 105 (a, b, c) is formed on the support substrate 101, the interlayer insulating film 107 (which may be the same material as or different from the surface protective layer 103) is formed. After a contact hole is formed in the interlayer insulating film 107, the transport electrode 102 (a, b, c) is formed. At this time, the transport electrodes 102 (a, b, c) and the common electrodes 105 (a, b, c) are interconnected through contact holes in the interlayer insulating film 107, respectively.

  Further, the method for forming the transfer substrate 110 is not limited to this. For example, there are the following methods. An interlayer insulating film is formed on a pattern in which the first transport electrode 102a and the first common electrode 105a are integrally formed, and a pattern in which the second transport electrode 102b and the second common electrode 105b are integrally formed on the interlayer insulating film. Form. Further, an interlayer insulating film is formed thereon, and a pattern in which the third transport electrode 102c and the third common electrode 105c are integrally formed is formed on the interlayer insulating film, that is, the electrode can have a three-layer structure. Alternatively, it is possible to mix the interconnection formed by integral formation and the interconnection formed by contact holes.

  Further, although not shown, these common electrodes 105 (a, b, c) are input for driving signal application for inputting driving signals (driving waveforms) Va, Vb, Vc from a transport power supply 409 as a transport power supply circuit. A terminal is provided. This drive signal input terminal may be provided on the back surface side of the support substrate 101 and connected to the common electrode 105 through a through hole, or may be provided on an interlayer insulating film 107 described later.

Here, as the support substrate 101, a substrate made of an insulating material such as a glass substrate, a resin substrate or a ceramic substrate, or a substrate made of a conductive material such as SUS, and an insulating film such as SiO ₂ is formed, A substrate made of a flexibly deformable material such as a polyimide film can be used.

  The transport electrode 102 is formed by forming a conductive material such as Al or Ni—Cr on the support substrate 101 in a thickness of 0.1 to 10 [μm], preferably 0.5 to 2.0 [μm]. It is formed by patterning into a required electrode shape using a photolithographic technique or the like. The width W1 in the powder traveling direction of the plurality of transport electrodes 102 is set to 1 to 20 times the average particle diameter of the powder to be moved, and the distance W2 in the powder traveling direction between the transport electrodes 102 is also moved. The average particle diameter of the powder is 1 to 20 times.

As the surface protective layer 103, for example, SiO ₂ , TiO ₂ , TiO ₄ , SiON, BN, TiN, Ta ₂ O _{5, and the} like have a thickness of 0.5 to 10 [μm], preferably 0.5 to 3 [ [mu] m]. In addition, inorganic nitride compounds such as SiN, Bn, and W can be used. In particular, since the charge amount of the charged toner tends to decrease in the middle of conveyance when the surface hydroxyl groups increase, inorganic nitride compounds with few surface hydroxyl groups (SiOH, silatol groups) are preferable.

Next, the principle of electrostatic transport of toner on the transport substrate 110 configured as described above will be described.
By applying an n-phase driving waveform to the plurality of transport electrodes 102 of the transport substrate 110, a phase shift electric field (traveling wave electric field) is generated by the plurality of transport electrodes 102. The charged toner on the transport substrate 110 receives a repulsive force and / or suction force and moves in the transport direction including hopping and transport.

  For example, as shown in FIG. 8, with respect to the plurality of transport electrodes 102 of the transport substrate 110, a three-phase pulse-shaped drive waveform (drive signal) A (A) that changes between the ground G (0 V) and the positive voltage +. Phase), B (B phase), and C (C phase) are applied at different timings.

  At this time, as shown in FIG. 9, the negatively charged toner 10 is present on the transport substrate 110, and each of the plurality of transport electrodes 102 on the transport substrate 110 is “G” as indicated by the first timing T <b> 1 in FIG. 9. ”,“ G ”,“ + ”,“ G ”, and“ G ”are applied, the negatively charged toner 10 is positioned on the“ + ”transport electrode 102.

  At the next timing, “+”, “G”, “G”, “+”, and “G” are respectively applied to the plurality of transport electrodes 102 as shown in the second timing T2, and the negatively charged toner 10 In FIG. 3, a repulsive force acts between the left “G” transport electrode 102 and a suction force acts between the right “+” transport electrode 102. It moves to the “+” side of the transport electrode 102. Further, at the next timing, “G”, “+”, “G”, “G”, and “+” are respectively applied to the plurality of transport electrodes 102 as shown in the third timing T3, and negatively charged. Similarly, since repulsive force and suction force act on the toner 10 respectively, the negatively charged toner 10 further moves toward the “+” transport electrode 102 side.

  In this way, by applying a plurality of phases of drive waveforms whose voltages change to the plurality of transport electrodes 102, a traveling wave electric field is generated on the transport substrate 110, and the negatively charged toner 10 is generated in the traveling direction of the traveling wave electric field. Moves while carrying and hopping. In the case of positively charged toner, the movement pattern is similarly reversed by reversing the drive waveform change pattern.

  The electrostatic transfer of toner will be described more specifically with reference to FIG. In FIG. 10, the plurality of transport electrodes 102 are described as electrodes A to F. As shown in FIG. 10A, the electrodes A to F of the transport substrate 110 are all 0 [V] (G), and the negatively charged toner 10 is placed on the transport substrate 110. ), When the voltage “+” is applied to the electrodes A and D, the toner 10 is attracted by the electrodes A and D and moves onto the electrodes A and D. At the next timing, as shown in FIG. 10C, when the electrodes A and D become “0” and a voltage “+” is applied to the electrodes B and E, The toner 10 receives a repulsive force and receives the suction force of the electrodes B and E, so that the toner 10 is transferred to the electrodes B and E. Furthermore, at the next timing, as shown in FIG. 10D, when the electrodes B and E are both “0” and a voltage of “+” is applied to the electrodes C and F, the electrodes B and E The upper toner 10 receives a repulsive force and receives the suction force of the electrodes C and F, so that the toner 10 is transferred to the electrodes C and F. Thus, the negatively charged toner 10 is sequentially transferred to the right in FIG. 10 by the traveling wave electric field.

Next, the overall configuration of the transport power supply 409 that is a transport power supply circuit will be described. FIG. 11 is a block diagram of the transport power source 409.
The carrier power supply 409 generates a pulse signal from a pulse signal generation circuit 121 that generates and outputs a pulse signal, and waveform amplifiers 122a, 122b, and 122c that generate and output drive waveforms Va1, Vb1, and Vc1 by inputting the pulse signal from the pulse signal generation circuit 121. And waveform amplifiers 123a, 123b, and 123c that receive the pulse signals from the pulse signal generation circuit 121 and generate and output the drive waveforms Va2, Vb2, and Vc2.

  The pulse signal generation circuit 121 receives, for example, a logic level input pulse, and includes two sets of pulses that are phase-shifted to 120 [°], and switching means included in the next stage waveform amplifiers 122a to 122c and 123a to 123c, for example, The transistor is driven to generate and output a pulse signal having an output voltage of 10 to 15 [V] that can perform switching of 100 [V].

  For example, as shown in FIG. 12, the waveform amplifiers 122a, 122b, and 122c apply +100 [V] applied time ta to each transport electrode 102 in the transport region Ar1 and each transport electrode 102 in the recovery region Ar3. Is set to about 33 [%] which is 1/3 of the repetition period tf (this is referred to as “carrier voltage pattern” or “collected carrier voltage pattern”). Three-phase drive waveforms (drive pulses) Va1, Vb1, Vc1 Apply.

  For example, as shown in FIG. 13 or FIG. 14, the waveform amplifiers 123a, 123b, and 123c apply +100 [V] or 0 [V] for each phase to the respective transport electrodes 102 in the development area Ar2. Is set to approximately 67% which is 2/3 of the repetition period tf (this is referred to as “hopping voltage pattern”). Three-phase drive waveforms (drive pulses) Va2, Vb2, and Vc2 are applied.

  As described above, the developing device 4 according to the first embodiment is a so-called EH developing device that reversely develops the electrostatic latent image on the photoreceptor 1 by the one-component developing method by hopping the toner 10. In other words, in the development area Ar2, the toner 10 forms an electric field in the direction toward the photoreceptor 1 with respect to the image portion of the latent image, and toward the opposite side of the photoreceptor 1 with respect to the non-image portion. By providing the means, development can be performed.

For example, in the case of a pulsed voltage waveform transitioning from 0 to −100 [V] as in the driving waveform of the hopping voltage pattern shown in FIG. 14, the non-image portion potential on the photoreceptor 1 is from −100 [V]. When the temperature is low, the toner 10 is directed to the photoreceptor 1 for the image portion, and the toner 10 is directed to the opposite side to the photoreceptor 1 for the non-image portion. In this case, it was confirmed that when the potential of the non-image portion of the latent image is −150 [V] or −170 [V] which will be described later, the toner 10 moves toward the photoreceptor 1 side.
Further, when the driving waveform of the hopping voltage pattern is a pulsed voltage waveform transitioning from 20 [V] to −80 [V], the potential of the image portion is about 0 [V] and the potential of the non-image portion is −110 [V]. V], the low-level potential of the pulse-like drive waveform is between the latent image portion potential and the non-image portion potential. For this reason, similarly, the toner 10 is directed to the photoreceptor 1 for the image portion, and the toner is directed to the opposite side to the photoreceptor 1 for the non-image portion.
In short, by setting the low-level potential of the pulse-like driving waveform to a potential between the potential of the image portion of the latent image and the potential of the non-image portion, adhesion of the toner 10 to the non-image portion can be prevented, and Quality development can be performed.

  As described above, in the EH development, since the toner 10 is hopped, the toner 10 is attracted and adhered to the image portion of the latent image, and the toner is repelled and not adhered to the non-image portion. At this time, since the toner that has already been hopped does not generate an adsorbing force with the transport substrate 110, it can be easily transferred to the photoreceptor 1 side, and high image quality can be obtained. Development can be performed at a low voltage.

  That is, in the conventional so-called jumping development method, in order to peel off the charged toner from the developing roller and transfer it to the photosensitive member, an applied voltage higher than the adhesion force of the toner to the developing roller is required. V] bias voltage must be applied. On the other hand, in the case of the EH development method, the adhesion force of the toner is usually 50 to 200 [nN], but since the hopping is performed on the conveyance substrate 110, the adhesion force to the conveyance substrate 110 becomes substantially zero. Therefore, the force for peeling the toner from the transport substrate 110 becomes unnecessary. As a result, the toner 10 can be sufficiently transferred to the photoreceptor 1 side with a low voltage.

  Moreover, the absolute value of the voltage applied between the transport electrodes 102 is 150 to 100 [V], or even if the voltage is lower than this value, the generated electric field has a very large value and adheres to the surface of the transport electrode 102. It is possible to easily peel off the toner, and to fly and hop. Further, ozone and NOx generated when the photosensitive member 1 such as OPC is charged can be very little or not at all, which is very advantageous for environmental problems and durability of the photosensitive member.

  Therefore, a high voltage bias of 500 [V] to several K [V] applied between the developing roller and the photoconductor for peeling off toner adhering to the surface of the conventional developing roller or the carrier surface is applied. The latent image can be formed and developed with the charging potential of the photoconductor set to a very low value without the necessity.

For example, using the photosensitive member 1 OPC, thickness of 15 [[mu] m] of CTL (Charge Transport Layer) of the surface, the dielectric constant ε is 3, the charge density of the charged toner (-3 × 10 ^{- In the case of 4} [C / m ² ], the OPC surface potential is about −170 [V]. In this case, the applied voltage to the transport electrode 102 of the transport substrate 110 is 0 to −100 [V], and the duty is 50. When the pulse drive voltage of [%] is applied, the average is −50 [V], and if the toner is negatively charged, the electric field between the transport electrode 102 of the transport substrate 110 and the OPC photoreceptor 1 is the relationship described above. become.

  At this time, if the gap (interval) between the transport substrate 110 and the OPC photoreceptor 1 is 0.3 [mm] or less, the development can be sufficiently performed. Depending on the Q / M of the toner, the voltage applied to the transport electrode 102 of the transport substrate 110, and the printing speed, that is, the rotational speed of the photosensitive member 1, in the case of negatively charged toner, at least the potential for charging the photosensitive member 1 is -300 [ V] or less, or in the case of a configuration in which development efficiency is prioritized, development can be sufficiently performed even at −100 [V] or less. Note that the charging potential in the case of positive charging is a positive potential.

Development will be described with reference to FIG.
If the development gap, which is the gap between the photoconductor and the developer transport member in the development area, is very narrow,
An amount of toner corresponding to the development potential given by development potential = post-exposure potential-DC development bias is developed. Specifically, as shown in FIG. 15A, toner corresponding to the development potential adheres to the latent image portion, and development stops. In the development shown in FIG. 15A, the surface potential of the developer carrier is −160 [V] and the potential of the latent image portion on the photosensitive member is −40 [V], and the non-latent image portion on the photosensitive member. Is -200 [V]. At this time, the toner of the developing potential of 120 [V] adheres to the latent image portion and is developed until the surface potential of the toner layer becomes −160 [V] which is the same as the surface potential of the developing carrier.
In such a development method, the larger the value of the development potential, the larger the amount of toner attached, so that more toner than necessary may adhere to the latent image portion.

FIG. 15B is a graph showing the development characteristics of the first color development (development by the magenta development device 4M in FIG. 1) of the printer 100 of the first embodiment.
As shown in FIG. 15B, in the development by the developing device 4M of the printer 100, the development potential is 100 [V], the toner adhesion amount is 0.5 [mg / cm ² ], and the development potential is 100 [V]. ], The toner adhesion amount does not change. In other words, in the printer 100, an upper limit is set for the toner adhesion amount per unit area in the development region. In this development method, even if the development potential is larger than the development potential reaching the upper limit of the toner adhesion amount, the toner adhesion amount does not change from the upper limit.
As a method of setting the upper limit of the toner adhesion amount, the toner amount to be conveyed per unit area of the developer conveying member is set in advance, and all the toner on the developer conveying member facing the latent image portion is moved to the latent image portion. This state can be set as the upper limit of the toner adhesion amount. The development in which the toner adhering to the latent image portion becomes the upper limit so that the toner adhesion amount in FIG. 15B is 0.5 [mg / cm ² ] is called saturation development, and the development potential for performing the saturation development is The minimum value (100 [V] in FIG. 15B) is called a saturated development potential.

In the developing method as shown in FIG. 15B, the toner adhesion amount does not change even when the development potential is equal to or higher than the saturation development potential. However, in the development potential less than the saturation development potential, the toner adhesion amount depends on the value. Change. In this development method, the toner adhesion amount becomes sensitive to the development potential, and the adhesion amount is affected by a slight fluctuation. Specifically, as shown in FIG. 15 (b), the inclination is about 5 [mg / cm ² / kV], so that the fluctuation range is 0.1 [mg / cm ² ] with a fluctuation of ± 10 [V]. Will have.

  In the printer 100, a latent image is formed on the photosensitive member on which the toner image is formed, and the latent image is developed to superimpose the toner image on the photosensitive member 1. In such a configuration, the potential of the latent image portion to be developed differs depending on whether the latent image of the second color or later is formed on the surface of the existing toner layer or the surface of the photoreceptor 1. Further, the potential of the latent image portion to be developed varies depending on the thickness of the portion where the toner layer is present.

Here, when a plurality of color toner images are overlaid on the photosensitive member 1, when the second color toner image is formed, whether the position where the second color latent image is formed is on the surface of the first color toner layer, or is photosensitive. An example will be described in which the potential of the latent image portion of the second color varies depending on whether the surface of the body 1 is on the surface.
FIG. 16 is an explanatory diagram of a process of developing a magenta toner image of the first color on the surface of the photoreceptor 1, FIG. 16A is when charging the first color, and FIG. FIG. 16C is an explanatory diagram for the development of one color plane when the latent image is formed. FIG. 17 is an explanatory diagram of a process of developing a yellow toner image of the second color on the surface of the photosensitive member 1 on the surface of the photosensitive member 1 on which a magenta toner image is formed. FIG. 17A is an explanatory diagram when charging the second color, FIG. 17B is an explanatory diagram when forming a latent image of the second color, and FIG. 17C is an explanatory diagram when developing the two-color surface.

Development of magenta, which is the first color, is performed as follows. First, as shown in FIG. 16A, the surface of the photoreceptor 1 is uniformly charged to −200 [V] by the charging device 2M for the first color.
Next, as shown in FIG. 16 (b), the laser beam L _M for magenta generated based on the image information corresponding to the first color magenta is irradiated on the surface of the photosensitive member 1, the surface of the photoreceptor 1 A magenta latent image _IM is formed. At this time, the potential on the surface of the photoreceptor 1 where the magenta latent image _IM is formed is −50 [V], and the potential on the surface of the photoreceptor 1 where no latent image is formed is −200 [V]. is there.
The next, as shown in FIG. 16 (c), in the developing area of the first color is a portion facing the toner conveying member 402M for magenta and the photosensitive member 1, the latent image I _M of magenta on the photosensitive member 1 surface Developed. At this time, as shown in FIG. 16 (c), the developing bias of the toner conveying member 402M for magenta is -150 [V], a latent image _{I M} for magenta surface potential is -50 [V] is formed The developing potential on the surface of the photoreceptor 1 is 100 [V]. Note that the latent image I _M is formed photoreceptor 1 surface of magenta, the potential of the developing potential 100 [V] min toner adhering magenta toner layer T _M surface is -150 [V] Instead, in this example, toner of the degree that the surface of the toner layer becomes −75 [V] adheres. That is, the increase in the uppermost surface potential with respect to the lowermost surface potential of the toner layer at this time (hereinafter referred to as toner layer potential) is about −25 [V].

Development of the second color, yellow, is performed as follows. First, as shown in FIG. 17A, the surface of the photoreceptor 1 is uniformly charged to −250 [V] by the charging device 2Y of the second color. Here, as shown in FIG. 16 (c), the surface of the photosensitive member 1 after the development of the magenta, the surface of the toner layer _{T M} of magenta surface potential -85 [V], the surface potential is -200 V] has a potential difference from the surface of the photoreceptor 1 on which the toner layer is not formed. However, as shown in FIG. 17A, by charging the second color, the surface of the photosensitive member 1 is uniformly charged so that the absolute value is −250 [V], which is larger than that of the first color. , the potential of the photosensitive member 1 surface is also the potential of the magenta toner layer T _M surface does not toner layer is formed becomes -250 [V]. At this time, -25 [V] of the toner layer potential of the toner layer T _M of magenta remains maintained, the potential of the photosensitive member 1 surface location where the toner layer T _M of magenta is formed -225 [V ]become.

Next, as shown in FIG. 17 (b), 2 color yellow laser beam L _Y generated based on the image information corresponding to yellow is irradiated on the surface of the photosensitive member 1, on the surface of the photoreceptor 1 A yellow latent image _IY is formed. Here, the first latent image and the latent image portion on the photosensitive member 1 surface of the latent image I _Y of yellow I _{Y a,} a latent image formed on the portion where there is the toner layer T _M of the magenta second latent image I _Y b. At this time, the surface of the latent image I _Y of yellow is not formed, a toner layer of magenta T _M and the photosensitive member 1 together -250 [V].

In the portion where the second latent image I _{Y b} are formed, rather than the toner layer T _M of magenta is neutralization, the photoreceptor underlying the toner layer T _M of magenta toner layer T _M of magenta is formed The surface of 1 is neutralized.
Here, since the laser beam at the time of forming the latent image is strong light, the potential of the latent image portion after the exposure becomes substantially uniform even if there is a certain potential difference on the surface of the photoreceptor 1 before the latent image is formed. Further, the charge removal by exposure is less affected by the presence or absence of the toner layer. In the explanation of this example, even if there is a certain potential difference on the surface of the photoconductor before exposure, the potential of the latent image portion after exposure becomes uniform, and there is toner on the surface of the photoconductor. This will be described without considering the attenuation of the exposure amount.
Therefore, the toner layer T _M is formed surface of the photosensitive member 1 of magenta potential has a potential difference of -225 [V] with the photosensitive member 1 surface on which the toner layer is not formed 25 [V], the even toner layer T _M of magenta is formed on the surface, when it is discharged by the yellow laser beam L _Y, becomes similar to -100 [V] and the surface potential of the first latent image I _{Y a.} That is, the potential of the photosensitive member 1 surface at the bottom of the toner layer T _M of magenta places the second latent image I _{Y b} is formed, as shown in FIG. 17 (b), a -100 [V] .
Even after the neutralization of the yellow laser beam L _Y is made, the toner layer potential is maintained, the surface potential of the toner layer T _M of the magenta second latent image I _{Y b} are formed is -125 [V] It becomes. Thus, the surface potential of the second latent image I _{Y b} is a latent image portion of the toner layer T _M of magenta, the first latent image I _Y a a latent image portion of the photosensitive member 1 part no toner layer The absolute value of the toner layer potential is -25 [V] higher than the surface potential of -100 [V].

After neutralization by the yellow laser beam L _Y it is made, as shown in FIG. 17 (c), in the developing area of the second color is a facing portion of the yellow toner conveying member 402Y and the photosensitive member 1, the photosensitive member 1 surface latent image I _Y of the yellow upper is developed, the toner layer T _Y of yellow is formed. Here, what is formed on the first latent image I _{Y a} first toner layer of yellow toner layer T _Y T _{Y a,} what is formed on the second latent image I _{Y b} second toner Let it be layer T _Y b. At this time, as shown in FIG. 17C, the development bias of the yellow toner conveying member 402Y is −200 [V], and the development of the first latent image I _Y a having the surface potential of −100 [V]. The potential is 100 [V]. On the other hand, the development potential of the second latent image I _Y b having a surface potential of −125 [V] is 75 [V]. Thus, the first latent image I _Y a and the second latent image I _Y b have different development potentials in the development area. When the development potential of the second latent image I _Y b having a small value is smaller than the saturation development potential, the second latent image I _Y b is more per unit area than the first latent image I _Y a. The amount of yellow toner attached is reduced. That is, the second toner layer T _Y b is thinner than the first toner layer T _Y a, and the image density and color tone of the second color yellow image change.
Thus, there is a difference in potential between the first latent image I _Y a and the second latent image I _Y b. Hereinafter, the potential difference of the latent image portion is referred to as a latent image portion potential difference ΔV. In the example using FIGS. 16 and 17, the absolute value of the toner layer potential is the latent image portion potential difference ΔV. In the example using FIGS. 16 and 17, it has been described that the latent image portion potential difference ΔV is caused by the presence or absence of the toner layer of the previous color. However, a plurality of toner layers are formed by the previous color. In some cases, the latent image portion potential difference ΔV also occurs due to the difference in the layer thickness of the portion where the latent image is formed.

As described above, development is a potential difference between the toner conveying member 402 as the developer conveying member and the latent image portion on the photosensitive member 1 due to the difference in the presence or absence of the toner layer on the photosensitive member 1 or the difference in layer thickness. The potential fluctuates. When the development potential changes, as described with reference to FIG. 15B, the toner adhesion amount also changes, and the image density and color tone change.
Further, the toner adhesion amount to the latent image portion on the photoreceptor 1 is affected by the magnitude of the development potential in the development area A1, but is also affected by the width of the development gap in the development area A1. The larger the development potential, the more the toner adhesion amount, and the wider the development gap, the smaller the toner adhesion amount. That is, the amount of toner attached to the latent image portion depends on the magnitude of the electric field strength value obtained by dividing the development potential by the development gap.

Here, a method for calculating the toner layer potential will be described.
FIG. 18 is a schematic view showing a state where a toner layer is formed on the surface of the photoreceptor.
A description of each parameter in FIG. 18 is given below.
M: Toner adhesion amount (per unit area) [g / m ² ]
Q: Charge amount of toner (per unit mass) [C / g]
Vt: potential on the surface of the toner layer Vk: potential on the surface of the photoreceptor h: height of the toner layer d: thickness of the photoreceptor εt: dielectric constant of the toner layer εk: dielectric constant of the photoreceptor C ₀ : unit area of the photoreceptor At this time, the potential Vt of the toner layer surface can be obtained by the following equation (2).
Vt = Vk + (Q · M ² ) / (2 · g · f · εt)
= Q · M / C ₀ + (Q · M ² ) / (2 · g · f · εt) (2)
Here, description of each parameter of Formula (2) is shown below.
C ₀ = εk / d
εt = ε0 (1−f + κt · f)
εk = κk · ε0
g: specific gravity of toner f: toner filling rate κt: relative dielectric constant of toner κk: relative dielectric constant of photoconductor ε0: dielectric constant of vacuum

Here, since the toner layer potential is Vt−Vk, when the toner layer potential is V (t−k), the toner layer potential V (t−k) can be obtained by the following equation (3). .
V (t−k) = (Q · M ² ) / (2 · g · f · εt)
= (Q · M ² ) / {2 · g · f · ε0 · (1−f + κt · f)} (3)

Here, FIG. 19 shows a graph showing the relationship between the toner adhesion amount and the toner layer potential when the parameter of the expression (3) is set to the toner used in the printer 100. The values of the parameters for calculating the graph of FIG. 19 are as follows: toner particle size: 6 [μm], toner charge amount: −30 [μC / g], toner filling rate: 30 [%], toner relative dielectric constant : 1.05.
Further, after developing with the toner used in the printer 100 to form a toner layer, the entire surface was exposed to reduce the potential of the photoreceptor, and the surface potential of the toner layer was measured by the surface potential. Specifically, after developing that the toner adhesion amount forming the toner layer is 0.9 [mg / cm ² ] and performing recharging (VDC = −700 [V]) with an AC charger (Corotron). The entire surface was exposed and the surface potential of the toner layer was measured. At this time, the surface potential of the toner layer was about -70 [V]. Since the surface potential of the photoreceptor is approximately 0 [V] due to the entire surface exposure, the measured value of the toner layer potential when the toner adhesion amount is 0.9 [mg / cm ² ] is −70 [ V]. Here, in the graph of calculated values shown in FIG. 19, the toner layer potential when the toner adhesion amount is 0.9 [mg / cm ² ] may substantially coincide with the measured value of about −70 [V]. I can confirm.

Next, the characteristic part of Embodiment 1 is demonstrated.
FIG. 20 is a diagram for explaining the characteristic part of the first embodiment. The latent image of the second color on the surface of the photosensitive member 1 and the surface of the toner layer T of the photosensitive member 1 on which the toner layer T of the first color is formed. It is a schematic diagram of the state in which was formed. Each code | symbol of FIG. 20 shows the following.
T: toner layer of the first color Ea: development bias Eb: surface potential of the latent image portion on the photoreceptor Ec: surface potential of the latent image portion on the surface of the toner layer V _P : development potential ΔV: latent image portion potential difference V _T : toner Development potential at the latent image portion on the surface of the layer (= V _P −ΔV)
L: development gap α: first latent image portion formed on the surface of the photoreceptor to which toner is not attached β: second latent image portion formed on the surface of the toner layer In FIG. 20, the second latent image portion β is the toner Although described as a latent image portion formed on the surface of the layer, as described with reference to FIGS. 16 and 17, the surface of the toner layer is removed by removing the surface of the photoreceptor 1 below the toner layer. As a result, a latent image is formed.

Amount of toner adhering to the first latent image portion α in the developing area of the second color shown in FIG. 20 is affected by the size of the development potential V _P, the distance of a gap between the developing area developing gap L Is also affected. The adhesion amount of the toner as the development potential V _P is high increases, the amount of toner adhering as developing gap L is wide decreases. That is, the amount of toner adhering to the latent image portion, the development potential V _P at the latent image portion obtained by dividing the developing gap L, depends on the magnitude of the value of the electric field strength (V P _{/ L).} If there is no upper limit on the toner adhesion amount, the greater the electric field strength (V _P / L), the greater the toner adhesion amount.

  In the development area for the second color, the toner image is superimposed on the photoconductor 1, so that the toner layer T for forming the second color image is formed in a state where the toner layer T for the first color is formed on the photoconductor 1. In this state, the film is uniformly charged and a latent image is formed by exposure. When the latent image of the second color is formed, the potential of the first latent image portion α on the surface of the photoreceptor 1 without the toner layer T is different from the potential of the second latent image portion β on the surface of the toner layer T. Then, a latent image portion potential difference ΔV is generated.

At this time, the development potential V _T at the second latent image portion β on the surface of the toner layer T is (V _P −ΔV), and the electric field strength at the first latent image portion α on the surface of the photoreceptor 1 is (V _P / L ) Then, the ratio of the layer thickness of the toner layer T to the developing gap L is, if it is sufficiently smaller than the ratio of the latent image portion potential difference ΔV for the development potential V _P, the second latent image portion on the toner layer T surface β The electric field strength at is V _T / L = (V _P −ΔV) / L.
Since the adhesion amount of the toner to the latent image carrier due to the development potential depends on the electric field strength, the difference in the toner adhesion amount is caused by the difference in the electric field strength.
Here, when the difference in electric field strength between the first latent image portion α on the surface of the photoreceptor 1 and the second latent image portion β on the surface of the toner layer T is obtained,
V _P / L−VT / L = V _P / L− (V _P −ΔV) / L = ΔV / L
It becomes.
The smaller the electric field intensity difference (ΔV / L) between the first latent image portion α and the second latent image portion β, the smaller the latent image portion α on the surface of the photoreceptor 1 and the latent image portion on the surface of the toner layer T. The difference in the toner adhesion amount from β is reduced, and unevenness in the adhesion amount of the second color toner can be reduced.

  In addition, as the toner layer thickness increases, the latent image portion potential difference ΔV increases. Therefore, when three or more toner images are stacked on the latent image carrier, the latent image portion potential difference ΔV is determined depending on the overlapping state of the toner images. The value of is different. Since the latent image portion potential difference ΔV increases as the thickness of the toner layer increases, the maximum value of the latent image portion potential difference ΔV increases in the developing region downstream of the surface movement direction of the latent image carrier.

  In the printer 100 according to the first embodiment, each member is arranged so that the developing gap L becomes wider in the developing region on the downstream side in the surface movement direction of the photoreceptor 1. For this reason, even when a latent image portion layer potential difference ΔV is generated between the first latent image portion α and the second latent image portion β due to the presence or absence of the existing toner layer T during development of the second color toner image, the electric field strength is increased. (ΔV / L), which is the difference between the two, can be reduced. Further, in the developing areas of the cyan developing device 4C and the black developing device 4K that develop by superimposing three or more toner images, the toner images overlap and the maximum value of the latent image portion potential difference ΔV increases as the layer thickness increases. Will grow. In the printer 100, the development gap L becomes wider in the development area on the downstream side in the surface movement direction of the latent image carrier where the layer thickness of the toner layer can be increased. Therefore, the maximum potential difference ΔV in the development area of the third and subsequent colors. As for the value, ΔV / L can be reduced.

Here, when the value of the development gap L is increased, the electric field strength (V _P / L) in the first latent image portion α on the surface of the photoreceptor 1 and the electric field strength in the second latent image portion β on the surface of the toner layer T. [(V _P −ΔV) / L] also becomes small, which may lead to a decrease in the total toner adhesion amount during the development of the second color. However, since the printer 100 is set such that the development potential V _P becomes larger in the development area downstream of the surface movement direction of the photoreceptor 1, the electric field strength (V _P / L) in the latent image portion α, and It is possible to suppress a decrease in the electric field strength [(V _P −ΔV) / L] in the latent image portion β and to prevent a decrease in the toner adhesion amount during the development of the second color.
Here, even if the developing potential _VP is set to be large, the value of (ΔV / L) that causes unevenness of the toner adhesion amount does not change, so the electric field strength (V _P / L) and [(V _P The difference in electric field strength (ΔV / L) can be reduced while maintaining the value of −ΔV) / L]. In this way, the difference in electric field strength between the first latent image portion α on the surface of the photoreceptor 1 and the second latent image portion β on the surface of the toner layer T while maintaining the electric field strength during development of the second color toner image ( (ΔV / L) can be reduced, so that unevenness in the image density of the second color toner image can be suppressed.

The development potential _VP is set to be larger in the development area downstream of the surface movement direction of the photoreceptor 1 and the development gap L is set to be wider in the development area downstream of the surface movement direction of the photoreceptor 1. Table 1 shows numerical values of the development conditions of the examples.

As a comparative example, Table 2 shows numerical values of development conditions when the development potential _VP and the development gap L are constant in the four development regions.

Regarding Tables 1 and 2, the latent image portion potential difference ΔV for the third and fourth colors in Table 1 varies depending on the overlapping state of the toner images. The values of the latent image portion potential difference ΔV shown in Tables 1 and 2 are the latent image portion formed on the surface of the portion where the toner layer is thickest (the portion where the toner images overlap most), and the surface of the photoreceptor 1. The potential difference from the latent image portion formed in Specifically, in the development of the third color, the potential difference between the latent image portion on the surface of the toner layer where the toner images of two colors overlap and the latent image portion on the surface of the photoreceptor 1, the three color toner images are developed in the development of the fourth color. This is a potential difference between the latent image portion on the surface of the overlapping toner layer and the latent image portion on the surface of the photoreceptor 1.
Further, in the example shown in Table 1, the absolute value of the potential of the toner conveying member 402 as a developer conveying member is increased, that is, the absolute value of the developing bias Ea is increased as compared with the comparative example of Table 2. The development potential _VP is set to be large.

Under the development conditions shown in Tables 1 and 2, the electric field strength (hereinafter referred to as saturation electric field strength) due to the saturation development potential in the latent image portion formed on the surface of the photoreceptor 1 is set to 2.0 [V / μm]. To do. That is, even when the electric field strength is 2.0 [V / μm] or more, the toner adhesion amount hardly changes from the toner adhesion amount when the electric field strength is 2.0 [V / μm]. In addition, when developing using any of the four color toners, the toner of each color is used such that the toner adhesion amount is 0.45 [mg / cm ² ] when the electric field strength is 2 [V / μm]. Shall.

In the examples shown in Table 1, development is performed with the development gap L during development of the first color (magenta) being 50 [μm] and the development potential _VP being 100 [V]. The second color (yellow) is developed with a development gap L of 75 [μm] and a development potential _VP of 150 [V]. Here, since the electric field strength in the latent image portion on the surface of the photoreceptor 1 is the same at 2 [V / μm] for both the first color and the second color, the toner moves in the same manner during development, and the toner adhesion amount is the same. .
Incidentally, when the saturation field strength of the development of the first color developing and the second color are the same, increases the development potential V _P at the same rate or greater than the proportion of the increased proportion of the developing gap L. In the printer 100, as shown in Table 1, the development gap L is 50 [μm] for the first color, whereas it is 75 [μm] for the second color, so the development gap L increases 1.5 times. ing. The development potential _{V P} is that the first color is 100 [V], the second color as 0.99 [V], has increased to be 1.5 times the development potential _{V P.} As a result, when developing the second color, the electric field strength at the first latent image portion α on the surface of the photoreceptor to which the toner is not attached is set to 2.0 [V / μm] similarly to the first color. it can.

In the comparative example shown in Table 2, the development condition for the second color is the same as that for the first color, the development gap L is 50 [μm], and the development potential _VP is 100 [V]. At this time, the electric field strength of the first latent image portion α on the surface of the photoconductor on which the toner is not attached becomes 2 [V / μm] similarly to the first color, and it adheres to the first latent image portion α by the development of the second color. The amount of toner to be applied is 0.45 [mg / cm ² ].
On the other hand, since the toner adhesion amount of the toner layer T on which the second latent image portion β is formed is 0.45 [mg / cm ² ], the toner layer potential at this time is about −25 [V] from FIG. It is. In this embodiment, since the absolute value of the toner layer potential is the latent image portion potential difference ΔV, the latent image portion potential difference ΔV is 25 [V] as shown in Table 2. The development potential _{V T} in the toner layer surface is _V P - [Delta] V, a 75 [V]. In the comparative example shown in Table 2, since the development gap L for the second color is also 50 [μm], the electric field strength at the second latent image portion β of the comparative example is 1.5 [V / μm]. At this time, the difference ΔV / L in the electric field strength between the first latent image portion α and the second latent image portion β is 0.5 [V / μm]. Further, as described with reference to FIG. 15B, since the toner adhesion amount until the saturation electric field intensity is reached is proportional to the electric field intensity, the second electric field intensity of 1.5 [V] is developed in the second color development. The amount of toner adhering to the latent image portion β is 0.34 [mg / cm ² ].

Meanwhile, in the embodiment shown in Table 1, the developing conditions of the second color, the developing gap L and 75 [[mu] m], have set development potential _{V P} to 0.99 [V]. Under such development conditions, the development potential on the surface of the toner layer T is 125 [V], and the electric field strength of the second latent image portion β is 1.66 [V / μm]. At this time, the difference ΔV / L in the electric field strength between the first latent image portion α and the second latent image portion β is 0.34 [V / μm]. Further, the amount of toner attached to the second latent image portion β in which the electric field strength is 1.66 [V / μm] by the development of the second color is 0.38 [mg / cm ² ]. On the other hand, the amount of toner adhering to the first latent image portion α with the electric field strength of 2.0 [V / μm] in the development of the second color is 0.45 [mg / cm ² ].
As in the comparative example shown in Table 2, when the development gap and the development potential are the same as those in the first color, the value of ΔV / L is 0.5 [V / μm]. By increasing, the difference in electric field intensity due to the latent image portion potential difference can be reduced. In the development conditions of the examples shown in Table 1, the electric field strength of the first latent image portion α is 2 [V / μm] and the same electric field strength as that of the first color latent image portion when developing the second color toner image. While maintaining, the difference in electric field strength between the first latent image portion α and the second latent image portion β can be reduced. By maintaining the electric field strength, the amount of toner adhering to the photoconductor by the development of the second color is 0.45 [mg / cm ² ] as in the first color. Further, by reducing the difference in electric field strength between the first latent image portion α and the second latent image portion β, the amount of toner adhering to the first latent image portion α in the second color development and the second latent image portion The difference from the amount of toner adhering to β can be reduced. For this reason, unevenness in the image density of the toner image of the second color can be suppressed.

In the comparative example shown in Table 2, the development gap and the development potential of the third color are the same as the development gap and the development potential of the first color as in the second color.
In the comparative example, where the two color toner layers before development of the third color overlap, the second color is formed on the toner layer to which 0.45 [mg / cm ² ] of magenta toner has adhered in the development of the first color. In this development, 0.34 [mg / cm ² ] yellow toner is adhered. For this reason, in the portion where the toner adhesion amount before development of the third color is the largest, 0.79 [mg / cm ² ] of toner is adhered. Since the toner layer potential when the toner adhesion amount is 0.79 [mg / cm ² ] is about −55 [V] from FIG. 19, the latent image portion potential difference ΔV is considered as 55 [V].
Since the latent image portion potential difference ΔV during development of the third color is 55 [V] and the development potential _VP is 100 [V], the development potential VT on the surface of the toner layer is 45 [V]. Since the development gap L is 50 [μm], the electric field strength of the second latent image portion β formed where the two color toner layers overlap is 0.90 [V / μm]. At this time, the difference in electric field strength between the first latent image portion α and the second latent image portion β is 1.1 [V / μm], and it adheres to the second latent image portion β by the development of the third color. The amount of toner is 0.2 [mg / cm ² ].
Further, in the portion where the three color toner layers overlap before the development of the fourth color, the third color is formed on the toner layer to which 0.79 [mg / cm ² ] of toner has adhered by the development of the second color. In the development, 0.2 [mg / cm ² ] cyan toner is adhered. For this reason, in the portion where the toner adhesion amount before the development of the third color is the largest, 0.99 [mg / cm ² ] of toner is adhered. Since the toner layer potential when the toner adhesion amount is 0.99 [mg / cm ² ] is about −75 [V] from FIG. 19, the latent image portion potential difference ΔV is considered as 75 [V].
Since the latent image portion potential difference ΔV during development of the fourth color is 75 [V] and the development potential _VP is 100 [V], the development potential VT on the toner layer surface is 25 [V]. Further, since the development gap L is 50 [μm], the electric field strength of the second latent image portion β formed where the two color toner layers are overlapped is 0.50 [V / μm]. At this time, the difference in electric field strength between the first latent image portion α and the second latent image portion β is 1.5 [V / μm], and it adheres to the second latent image portion β in the development of the fourth color. The amount of toner is 0.11 [mg / cm ² ].

On the other hand, in the embodiment shown in Table 1, the development condition for the third color is set such that the development gap is 125 [μm] and the development potential is 250 [V].
In the embodiment, at the portion where the toner adhesion amount before development of the third color is the largest, 0.83 [mg / cm ² ] of toner is adhered. Since the toner layer potential when the toner adhesion amount is 0.83 [mg / cm ² ] is about −60 [V] from FIG. 19, the latent image portion potential difference ΔV is considered as 60 [V].
For the third color latent image portion potential difference ΔV at the time of development of a 60 [V] in the development potential _{V P} is 250 [V], the development potential _{V T} of the toner layer surface 190 [V], and the two-color toner layer The electric field strength of the second latent image portion β formed at the overlap is 1.52 [V / μm]. At this time, the amount of toner attached to the second latent image portion β by the development of the third color is 0.34 [mg / cm ² ].
In the embodiment, the development condition for the fourth color is set such that the development gap is 180 [μm] and the development potential is 360 [V].
In the embodiment, at the portion where the toner adhesion amount before the development of the fourth color is the largest, 1.17 [mg / cm ² ] of toner is adhered. Since the toner layer potential when the toner adhesion amount is 1.17 [mg / cm ² ] is about −95 [V] from FIG. 19, the latent image portion potential difference ΔV is considered as 95 [V].
4 for developing potential _{V P} at the latent image portion potential difference ΔV is 95 [V] at the time of development of the color is 360 [V], the development potential _{V T} of the toner layer surface 265 [V], and the three color toner layer The electric field strength of the second latent image portion β formed at the overlap is 1.47 [V / μm]. At this time, the amount of toner attached to the second latent image portion β by the development of the fourth color is 0.33 [mg / cm ² ].
As described above, in the development conditions of the examples shown in Table 1, the electric field strength of the latent image portion on the surface of the toner layer and on the surface of the photosensitive member is maintained while maintaining the electric field strength in the third and fourth colors. The difference can be reduced. In addition, since the difference in the amount of toner adhered to the first latent image portion α and the toner adhered to the second latent image portion β can be reduced in each developing region, unevenness in the image density of the toner image is suppressed. can do.

As described above, when the second color image is formed, the surface of the toner layer and the surface of the photoconductor are charged in the same manner and exposed to form a latent image. A latent image portion potential difference ΔV occurs with the latent image portion on the body surface. The latent image portion potential difference ΔV is reflected in the toner adhesion amount, resulting in uneven image density. In order to reduce such image density unevenness, writing control is generally performed when the second color exposure is performed. Specifically, based on the image information of the first color, the intensity of light at the time of exposure of the second color can be changed, and when a latent image is formed in the region where the toner layer of the first color is formed, A stronger light is irradiated than when a latent image is formed in an area. Even when such writing control is performed, the difference in electric field strength between the latent image on the surface of the toner layer and the latent image on the surface of the photosensitive member is reduced by widening the development gap and increasing the development potential as in the printer 100. By doing so, the accuracy of adjustment by write control is improved.
In the printer 100, when the toner images for the second and subsequent colors are formed, even if the difference in electric field strength due to the presence or absence of the toner layer exists, image processing is performed, and a latent image is formed so as to further reduce the difference. Change. Specifically, it adjusts the writing level at the time of dither formation. Based on the image information up to the previous color, the part where the toner layer exists is irradiated with stronger light than the other part at the time of exposure, and deeper It forms a latent image. Thereby, the latent image portion potential difference can be reduced, and by combining with a configuration in which the development gap is widened and the development potential is increased, the difference in electric field strength due to the presence or absence of the toner layer can be further reduced. For the third and fourth colors, the writing device 3 irradiates the toner image so that the thicker the toner layer, the deeper the latent image is formed in accordance with the overlapping state of the toner images, that is, the thickness of the toner layer. The amount of light to be controlled may be controlled.

FIG. 21 is a graph comparing the toner adhesion amounts of the respective colors when full-color image formation is performed by the image forming apparatus of the example shown in Table 1 and the image forming apparatus of the comparative example shown in Table 2.
In the graph shown in FIG. 21, the thicker the toner layer, the deeper the toner layer on the surface of the photoreceptor 1 when the latent image corresponding to the image information of each color is formed. The amount of light irradiated by the writing device 3 is controlled so as to form a latent image.
As shown in FIG. 21, it can be seen that the difference in the toner adhesion amount between the example and the comparative example becomes larger in the development region on the downstream side in the surface movement direction.

  As shown in Table 1, in the printer 100, the combination of the development gap and the development potential is set as follows. 50 [μm], 100 [V] for the first color, 75 [μm], 150 [V] for the second color, 125 [μm], 250 [V] for the third color, 180 [μm], 360 [V] for the fourth color ]. With this setting, four color toner images are formed on the surface of the photoconductor 1 and the color toner images are collectively transferred onto the transfer paper P conveyed in contact with the photoconductor 1 at the transfer position. Then, a full color image is formed on the transfer paper P.

  In the printer 100, when a toner image for the second color or later is formed, a potential difference is generated between the latent image portion on the surface of the toner layer and the latent image portion on the surface of the photoreceptor due to the toner layer potential of the toner layer formed by the charged toner. I explained that. However, the mechanism of occurrence of the latent image portion potential difference between the toner layer surface and the photoreceptor surface is not limited thereto. When the exposure is performed after charging when forming a toner image for the second and subsequent colors, the presence of the toner layer makes the exposure amount attenuated and the portion where the toner layer is formed is less likely to be neutralized, It is also conceivable that a potential difference occurs between the latent image portion on the surface of the toner layer and the latent image portion on the surface of the photoreceptor. Further, the toner layer is formed even after the charging due to the difference in charging property between the surface on which the toner layer is formed and the surface of the photoreceptor, or the difference in potential before charging, and even before the exposure. There may be a potential difference between the surface of the photosensitive member and the surface of the photoreceptor. As described above, there is a potential difference between the surface of the toner layer and the surface of the photoconductor before forming the latent image. Even when there is a potential difference between the latent image portion and the latent image portion, the characteristic portion of the first embodiment can be applied. That is, in an image forming apparatus that superimposes a plurality of toner images on a single photoreceptor surface, a potential difference is generated between the latent image portion on the toner layer surface and the latent image portion on the photoreceptor surface in the development area for the second and subsequent colors. If this is the case, the development area on the downstream side in the surface movement direction of the photoconductor is increased by increasing the development gap and increasing the development potential, thereby increasing the electric field strength of the latent image portion due to the latent image portion potential difference due to the presence or absence of the toner layer. The difference can be suppressed. By suppressing the difference in the electric field strength of the latent image portion, it is possible to suppress the unevenness of the toner adhesion amount and to suppress the image density unevenness.

Further, in the examples of Table 1, the latent image portion potential difference ΔV in the development regions of the second to fourth colors is the absolute value of the toner layer potential of the portion where the overlapping toner layers are the most, and is 25 [V], 60 [ V] and 95 [V]. The latent image portion potential difference ΔV is not only the amount of toner deposited on the photoreceptor, but also the chargeability of the surface on which the toner layer is formed, the charging conditions of the charging device 2, the exposure conditions when forming the latent image, and the photosensitivity. It may be affected by various conditions such as chargeability of the body surface. However, regardless of the value of the latent image portion potential difference ΔV, the latent image portion on the surface of the toner layer is increased by widening the development gap in the development region and increasing the value of the development potential as in the embodiment. It is possible to reduce the difference in electric field strength from the latent image portion on the surface of the photoreceptor.
Further, the thicker the toner layer, the larger the latent image portion potential difference ΔV. Therefore, as in the printer 100, as a developing region of the surface moving direction downstream side of the photosensitive member 1, the toner layer may become thicker, so that a wide development gap L, and the value of the development potential V _P is increased With this setting, the difference in electric field strength between the latent image portion on the surface of the toner layer and the latent image portion on the surface of the photoreceptor can be reduced while maintaining the electric field strength in the development area for the second and subsequent colors.

[Modification 1]
Note that the thicker the toner layer on the photoreceptor 1, the larger the potential difference between the latent image portion on the surface of the toner layer and the latent image portion on the surface of the photoreceptor 1. Therefore, in order to obtain a desired image density with a thinner toner layer thickness, a highly colored toner may be used.
As the toner having a high degree of coloring, a toner in which the content of the colorant is increased from 1.5 times to 2 times that of a commonly used toner is used. As the toner of Modification Example 1, a toner having a colorant content approximately twice that of the entire toner is used.
FIG. 22 shows the values of the image density ID with respect to the toner adhesion amount [mg / cm ² ] between the toner having the normal colorant content and the toner having the double colorant content. As shown in FIG. 22, the use of highly colored toner increases the slope of the graph indicating the relationship between the image density ID and the toner adhesion amount. As the colorant, carbon materials, quinacridone materials, carmine materials and the like are usually used.
By using such a highly colored toner, the necessary amount of adhesion can be reduced, and the thickness of the toner layer can be reduced.

Further, by reducing the particle size of the toner, the total surface area of the entire toner may be increased to increase the coloring degree. Further, the reduction of the toner particles may be combined with the increase of the colorant content. For example, in the case of a normal spherical toner having a particle size of 5.8 [μm], a toner particle size of 0.45 [mg / cm ² ] is adhered to make the ID 1.4. By setting the colorant content 1.2 times as 1 / 1.5, the toner adhesion amount of about 0.3 [mg / cm ² ] can be set to ID: 1.4. Become.

The image density ID becomes a saturation value when ID = 1.4. In other words, the value of the image density ID does not change even if a larger amount of toner is attached than the amount of toner that has reached ID = 1.4. In the case of the highly colored toner shown in FIG. 22, since the toner adhesion amount is 0.3 [mg / cm ² ] and the value of the image density ID is 1.4, which is a saturation value, the toner adhesion at the time of saturation development is achieved. The amount can be set to 0.3 [mg / cm ² ]. On the other hand, the toner of Embodiment 1 is a normal toner, and the image density ID reaches ID = 1.4 when the toner adhesion amount is 0.45 [mg / cm ² ].
Thereby, the toner layer can be made thinner than the printer 100 of the first embodiment in which the toner adhesion amount at the time of the saturation development is 0.5 [mg / cm ² ]. By using such toner for the first color, the existing toner layer when forming the second color toner image can be thinned, so the surface of the toner layer and the surface of the photoreceptor when the latent image of the second color is formed And the potential difference of the latent image portion can be reduced as compared with the first embodiment.

When the development condition for the second color of Modification 1 is 150 [V] and the development gap is 75 [V] as in the embodiment shown in Table 1, the electric field strength of the latent image portion on the surface of the photoreceptor is as follows. Is 2.0 [V / μm]. The second color development in the first embodiment is a saturated development with an electric field strength of 2.0 [V / μm] and a toner adhesion amount of 0.5 [mg / cm ² ]. If a highly colored toner is used for the second color toner, the toner adhesion amount becomes 0.3 [mg / cm ² ] in the state of the electric field strength of 2.0 [V / μm] in the development of Modification Example 1, and the electric field strength is increased. Saturated development with sufficient margin. Further, since the first color toner is also a highly colored toner and the toner layer thickness is made thinner than that of the first embodiment, the latent image portion potential difference during the development of the second color is the example described with reference to Table 1. Less than 25 [V]. For this reason, the electric field strength on the surface of the toner layer during the development of the second color in Modification 1 is 1.67 [V / μm, which is the electric field strength of the latent image portion on the surface of the toner layer during the development of the second color in Embodiment 1. ].
As described above, in Modification 1, the electric field strength of the latent image portion on the surface of the toner layer is larger than 1.67 [V / μm], and the electric field strength of the latent image portion on the surface of the photoreceptor is 2.0 [V. / Μm], and the saturation electric field strength becomes smaller than 2.0 [V / μm]. For this reason, the electric field strength at the latent image portion on the surface of the toner layer reaches or is close to the saturation electric field strength. Similarly, for the third and fourth colors, the electric field strength of the latent image portion on the surface of the toner layer can be made closer to the saturation electric field strength than in the first embodiment.
As in Modification 1, by using a highly colored toner, the electric field strength of the latent image portion on the surface of the photoreceptor exceeds the saturation electric field strength, and the electric field strength of the latent image portion on the toner layer surface approaches the saturation electric field strength. Therefore, the difference in toner adhesion amount between the latent image portion on the surface of the photoreceptor and the latent image portion on the surface of the toner layer can be further reduced.

FIG. 23 is a graph illustrating the toner adhesion amount with respect to the gradation level of the development area of the second color of the printer 100 according to the first modification.
Here, the gradation level is an image density level. The higher the gradation level, the stronger the light to be exposed when forming a latent image.
As in the printer 100, by setting the development gap to be wider and the development potential to be larger in the development area on the downstream side in the surface movement direction of the photoreceptor 1, development is performed using toner having a high degree of coloration. Even when the first color toner layer is present, the adhesion amount becomes 0.3 [mg / cm ² ] or a value close thereto, and when there is no toner layer, a toner adhesion amount that is almost the same as that of the portion is obtained. Yes.

[Embodiment 2]
Next, a second embodiment (hereinafter, referred to as “embodiment 2”) in which the present invention is applied to a full-color electrophotographic copying machine as an image forming apparatus will be described with reference to FIG.
FIG. 24 is a schematic configuration diagram of an entire printer 100 as a full-color image forming apparatus according to the second embodiment. The printer 100 of the second embodiment is different from the printer 100 of the first embodiment in that the two photoconductors 1 are provided and two developing devices 4 face each of the two photoconductors. The image forming operation of the printer 100 according to the second embodiment is basically the same as that according to the first embodiment, and thus the configuration is the same as that of the first embodiment, and the description of the operating part is omitted.
In addition, the structure of each developing device 4 can use the thing of the structure similar to the developing device 4 of Embodiment 1 demonstrated using FIG. 2, FIG.
The toner in the second embodiment is the same as that in the first embodiment. The toner adhesion amount is 0.45 [mg / cm ² ] and the image density ID is 1.4.
In the printer 100 according to the second embodiment, the number of developing devices 4 facing one photoconductor 1 is two, so that the image formation is more stabilized than the configuration of the first embodiment. That is, by reducing the number of times of superposition on the photosensitive member 1, the thickness of the existing toner layer is prevented from increasing and the influence thereof is increased.

In the first embodiment, four color toner images are superimposed on one photoconductor 1 to form a full color image, but the printer 100 of the second embodiment includes two photoconductors 1. Two developing devices 4 are arranged to face each photoconductor 1. A black developing device 4K and a yellow developing device 4Y are opposed to the first photosensitive member 1a, and a magenta developing device 4M and a cyan developing device 4C are opposed to the second photosensitive member 1b, respectively. Has been placed. Note that the arrangement of the color arrangement for each photoconductor 1 can be changed as appropriate.
With the configuration of the printer 100 according to the second embodiment, the number of toners to be overlapped is limited to two, so that the increase in the toner layer thickness is small and the increase in the latent image portion potential difference can be suppressed. As in the first embodiment, the toner adhesion amount is 0.45 [mg / cm ² ] at an electric field strength of 2 [V / μm].

Next, the supply limit for saturated development will be described.
Similar to that described with reference to FIG. 15B of the first embodiment, the printer 100 of the second embodiment also has a saturation electric field strength even if the electric field strength of the latent image portion exceeds a predetermined electric field strength (saturation electric field strength). In this configuration, toner exceeding the toner adhesion amount at this time does not adhere to the latent image portion.
In the second embodiment, the toner supply amount to the toner conveying member 402 included in the developing device 4 is limited in order to limit the toner adhesion amount of the latent image portion on the photosensitive member. Specifically, in the developer 12 forming the magnetic brush, the DC component of the applied voltage of the supply power supply 410 that applies the toner supply bias to the supply sleeve 408 that supplies toner to the toner conveying member 402 in the toner supply region A2 is lowered. The toner supply capacity in the toner supply area A2 is reduced by reducing the toner density of the toner. Thereby, the amount of toner conveyed on the toner conveying member 402 can be limited, and even when the developing potential is increased and the electric field strength is increased, a certain amount or more of toner is transferred to the latent image portion on the photoreceptor 1. Can be prevented from adhering to the surface.

The toner supply of the second embodiment uses a two-component magnetic brush, and the supply gap that is the width of the gap between the toner conveying member 402 and the supply sleeve 408 in the toner supply region A2 and the toner in the toner supply region A2 at the time of supply. The toner supply amount depends on the potential difference between the conveying member 402 and the supply sleeve 408 (hereinafter referred to as supply potential difference).
FIG. 25A is a graph showing the relationship between the toner conveyance amount and the supply potential difference, and FIG. 25B shows the relationship between the upper limit value of the toner adhesion amount of the latent image portion on the photoreceptor and the supply potential difference. It is a graph to show. Note that the toner transport amount [mg / cm · s] in FIG. 25A is the total transport amount [mg / s] per unit time of the toner transport member 402 in the width direction (sleeve axis direction) [cm]. ] Divided by].

In the configuration described with reference to FIG. 15B of the first embodiment, the toner adhesion amount in the saturated development state is 0.5 [mg / cm ² ], so that the supply potential difference is set to −1. As 2 [kV], the toner conveyance amount by the toner conveyance member 402 is 13 [mg / cm · s]. The toner used in the first and second embodiments has a toner adhesion amount of 0.45 [mg / cm ² ] and an image density ID of ID = 1.4, which is a saturation value. [Mg / cm ² ] is a state where excessive toner is adhered. Therefore, in the second embodiment, the supply potential difference is set to −1.1 [kV], which is lower than that in the first embodiment. Accordingly, the toner conveyance amount conveyed by the toner conveyance member 402 is 12 [mg / cm · s], which is smaller than 13 [mg / cm · s] in the first embodiment. Therefore, the toner adhesion amount in the saturated development state is 0.46 [mg / cm ² ], and the toner adhesion amount can be reduced as compared with the first embodiment while satisfying the image density ID = 1.4. In this way, by limiting the amount of toner supplied to the toner conveying member 402, the amount of toner attached to the latent image portion of the photoreceptor 1 can be set in a state that does not exceed a predetermined amount.
In addition, when using the toner with high coloring degree demonstrated in the modification 1, it is possible to further reduce the toner adhesion amount. For example, by setting the supply potential difference to −0.9 [kV], the toner conveyance amount becomes 9.9 [mg / cm · s], and the toner adhesion amount in the saturation development is 0.38 [mg / cm ^2]. ] Can be set. In the toner of Modification Example 1, since the toner adhesion amount is 0.3 [mg / cm ² ] and the image density ID is a saturation value ID = 1.4, even if the value of the supply potential difference is set lower. good.

When forming a latent image in the second color image formation, the area where the first color toner layer is formed is controlled so as to emit light stronger than the other areas, but the toner layer is formed. If the latent image portions in the existing area have the same amount of writing light, the portion with a small amount of toner of the first color has a higher light transmittance during exposure, and therefore the potential after exposure decreases more than necessary. In this state, when a uniform developing bias is applied, the toner adhesion amount becomes excessive in a portion where the toner adhesion amount of the first color is small, and there is a possibility that sufficient image quality cannot be ensured. On the other hand, by controlling the supply amount, the maximum value of the toner adhesion amount can be set even if the development potential becomes larger, so that the toner adhesion amount can be regulated.
The area where the toner layer is formed is not exposed with the same amount of light, but the portion where the image density of the first color is low, that is, the amount of toner attached to the first color is small, based on the image information of the first color The portion is set so that the average post-exposure potential is increased by adjusting the light amount, and is controlled so that the second color toner has a necessary adhesion amount according to the toner adhesion amount of the first color toner layer. Also good.

In the second embodiment, the number of toner overlaps is defined by using two developing devices 4 corresponding to one photoconductor 1. In order to obtain a prescribed image density ID, the toner developed for the first color is assumed to have an average particle diameter of 6 [μm] and a toner adhesion amount of about 0.45 [mg / cm ² ]. Yes. When the toner charge amount at that time is −30 [μC / g] and the filling rate is about 30 [%], the thickness of the toner layer is 1 to 1.5 times the toner particle diameter. At this time, the toner layer potential difference which is the potential difference between the lowermost surface and the uppermost surface of the toner layer is about 35 [V]. Although recharging, exposure, and development are repeated in the presence of the existing toner layer, the configuration of Embodiment 2 is a configuration in which the number of repetitions is limited to two. Since four colors of yellow, magenta, cyan, and black are required, it is possible to consider a configuration in which there are two photoconductors and the image on the photoconductor is directly transferred to transfer paper or an intermediate transfer body. As shown in FIG. 24, in the second embodiment, the image is directly transferred onto a transfer sheet and an image is formed through a fixing process.

After the first color image formation is completed, the entire image including the toner layer is uniformly recharged with a higher absolute value than the first color. It is -250 [V] with respect to -200 [V] of the first color. At this time, the toner layer potential difference of about 35 [V] is maintained. Here, exposure is performed, but the printer 100 according to the second embodiment superimposes only two colors, and the toner adhesion amount is 0.45 [mg / cm ² ] at the maximum. Further, since the toner is negatively charged and has the same polarity, the toner is easily repelled and spaced apart, and the light transmittance is very good. FIG. 26 shows the post-exposure potential for the second color, which is sufficiently lower than that with a large amount of adhesion. The potential changes due to the potential of the toner layer at the part where the toner layer is present and the part where the toner layer is not at the time of development, but development is performed using development that has a depletion characteristic according to the part where the toner layer is present. Uniform image characteristics can be obtained regardless of the presence or absence. As described with reference to FIG. 15B, the depletion characteristic is a characteristic in which no further development is performed when there is no toner on the developer conveying member.

As the toner, it is desirable to use a spherical toner.
By using the spherical toner, the necessary toner can be adhered without depending on the first-color toner adhesion amount. The spherical toner can have the smallest surface area. In order to obtain an appropriate post-exposure potential by performing exposure in the presence of the toner layer, it is necessary for light to pass through the toner layer and reach the surface of the photoreceptor. However, since the toner itself is negatively (minus) charged in this embodiment and repels, it does not exist in a completely finely packed form. However, the conventional amorphous toner has a large surface area when it is exposed in a state where the thickness of the toner layer is 2 to 3 times as large as the toner particle diameter. In the case of a spherical toner, since the surface area is small and an additive is externally added around the toner (the external additive is the same as that of an irregular toner), the distance between the toners is secured, so that light is transmitted. It becomes easy. FIG. 27 shows a general tendency of the relationship between the first color adhesion amount and the required writing amount. FIG. 28 shows the difference depending on the toner shape when the horizontal axis is the first color toner adhesion amount and the vertical axis is the average potential after exposure. It can be seen that the spherical toner has a margin for light transmission even when the number of toner layers increases.

[Modification 2]
In the developing device 4 included in the printer 100 according to the first embodiment, a traveling wave electric field is generated by a plurality of transport electrodes on the transport substrate 110 provided in the toner transport member 402 to transport the toner on the transport substrate 110.
The toner conveying member 402 is not limited to such a configuration. Hereinafter, as a second modification, the developing device 4 that reciprocates between adjacent electrodes on the surface of the toner conveying member 402 and conveys the toner to the developing region A1 by moving the surface of the toner conveying member 402 will be described. .

FIG. 29 is a schematic explanatory diagram of the surface substrate 210 and the conveyance power supply circuit of the toner conveyance member 402 provided in the developing device 4 of Modification 2. FIG. 29 (a) is an explanatory diagram of a state before applying an AC voltage to the surface electrodes (21, 22, 23... 2n), and FIG. 29 (b) applies an AC voltage to the surface electrodes. It is explanatory drawing of a state. FIG. 30 is a schematic configuration diagram of the developing device 4 including the toner conveying member 402 shown in FIG.
The developing device of Modification 2 develops the toner by transporting the toner to a developing area A1 that is a portion facing the photoreceptor 1 in order to develop the electrostatic latent image formed on the photoreceptor 1 that is a latent image carrier. A toner conveying member 402 as an agent conveying member is provided. Also, a supply sleeve 408 that carries the developer 12 composed of toner and carrier and supplies the toner to the toner conveying member 402 in the toner supply region A2, and a casing 401 that contains the developer 12 carried by the supply sleeve 408, Is provided. Further, the toner conveying member 402 contacts or approaches the surface of the toner conveying member 402 on the downstream side in the surface movement direction of the toner conveying member 402 with respect to the toner supply region A2 and on the upstream side of the developing region A1 in the surface moving direction of the toner conveying member 402. And a toner regulating member 69 for regulating the thickness of the toner layer. The toner conveying member 402 includes a surface substrate 210 on the surface thereof.

The surface substrate 210 is provided with a spatially periodic electrode pattern 20 with a pitch width of W3 [μm] through a surface protective layer 103 which is an insulating layer. An assembly of odd-numbered electrodes (first electrode 21, third electrode 23,...) Starting from an electrode (not shown) on the left side of the first electrode 21 in FIG. And an even-numbered electrode (second electrode 22, fourth electrode 24,...) (Hereinafter, even-numbered electrode group) are formed with a time-periodic potential difference.
FIG. 29A shows an AC power supply 66 that applies a bias voltage. From the state where the toner layer of FIG. 29A is formed by applying an AC voltage, FIG. Thus, the toner moves along the electric field formed by the potential difference between the electrodes.
In the developing device 4 shown in FIG. 30, since an AC voltage is applied to the electrodes, the two electrodes basically reciprocate. In the developing device 4, surface electrodes (21, 22, 23... 2n) The surface substrate 210 containing the toner is formed endlessly on the surface of the toner conveying member 402. Then, development is performed by hopping while transporting toner by mechanically rotating the toner transport member 402.
In the second modification, the toner transport member 402 can be rotated to improve the problems related to transport, and the reliability including transport quality can be improved. In addition, since the distance between the conveying members can be shortened as compared with the configuration of the first embodiment, it is possible to realize development with higher image quality and to realize downsizing.

In any of the developing devices 4 of the first embodiment, the second embodiment, the first modification, and the second modification, the toner transport member 402 includes an electrode on the surface, and transports the toner to the development area A1 while hopping the toner. The toner conveying member 402 is not limited to a configuration that conveys toner while hopping.
If the developing device 4 for the second and subsequent colors is a non-contact developing system in a configuration in which a plurality of developing devices 4 face one photoconductor 1, the surface movement direction of the photoconductor 1, which is a feature of the present invention. A configuration in which the development gap is widened and the development potential is increased in the downstream development region is applicable.

As described above, according to the first embodiment, in the printer 100 as the image forming apparatus in which the developing device 4 as the four developing units faces the photosensitive member 1 as the latent image carrier, the photosensitive member 1 faces the transfer roller 61. From the transfer position to the development area on the downstream side in the surface movement direction of the photoconductor 1, that is, from the magenta development area for forming the first toner image to the development area on the downstream side in the surface movement direction of the photoconductor 1. Development by increasing the absolute value of the potential of the toner conveying member 402 having the same polarity as the charging polarity of the toner so that the developing gap L, which is the gap between the toner conveying member 402 and the developer conveying member, becomes wide. is set to the development potential V _P is the potential difference between the surface of the photosensitive member 1 surface and the toner conveying member 402 in the area increases, the surface movement direction downstream side of the photosensitive member 1 developing region Since each member is arranged so that the development gap L becomes wider, the latent image portion on the surface of the toner layer and the latent image on the surface of the photoreceptor 1 are determined depending on the presence or absence of the existing toner layer when developing the second and subsequent toner images. Even if a potential difference ΔV occurs with the image portion, ΔV / L, which is a difference in electric field strength, can be reduced. Furthermore, since the development potential _VP is set to be larger in the development area downstream of the surface movement direction of the photoreceptor 1, the electric field strength V _P / L of the latent image portion on the surface of the photoreceptor 1 and the toner layer surface are set. It is possible to suppress a decrease in the electric field strength (V _P −ΔV) / L of the latent image portion and to prevent the toner adhesion amount from decreasing. Further, even if the development potential _VP is set to be large, ΔV / L that causes unevenness of the toner adhesion amount does not change, so that the electric field strength difference ΔV / L is maintained while maintaining the electric field strength V _P / L. L can be reduced. In this way, the difference in electric field strength between the latent image portion on the surface of the toner layer and the photosensitive member 1 can be reduced while maintaining the electric field strength during the development of the second and subsequent toner images. It is possible to suppress unevenness in the image density of the toner images after the eyes.
Further, as in the second embodiment, by providing two developing devices 4 facing one photoconductor 1, since the toner layer has a small thickness, an increase in potential due to the toner layer can be suppressed, and the toner layer having a developing potential can be suppressed. Since the difference due to the presence / absence can be reduced, the difference in the electric field strength between the latent image portion on the surface of the toner layer and on the photosensitive member 1 can be reduced, thereby suppressing unevenness in the image density of the second color toner image. can do.
Further, the layer thickness of the toner image formed by one developing device 4 is set to be not less than one time and less than twice the average particle diameter of the toner used for development, and the ratio of the toner adhesion amount to the image density ID is 1.4 /. By setting it to 0.4 [mg / cm ² ] ⁻¹ or more, since the overall toner layer thickness is small, an increase in the latent image portion potential difference can be suppressed, and the difference in development potential due to the presence or absence of the toner layer can be reduced. Can do. For this reason, the difference in the electric field strength of the latent image portion on the surface of the toner layer and on the photoreceptor 1 can be reduced, and unevenness in the image density of the second and subsequent toner images can be suppressed.
Further, like the developing device 4 of the first embodiment, the toner conveying member 402 is a conveying member having a plurality of electrodes for generating a traveling wave electric field for moving the powder, so that non-contact overlapping development is performed. Can be achieved efficiently. This is due to the following reason. That is, in contact development, non-contact development is advantageous for overlay because contact may occur in the existing toner layer up to the previous color formed on the photoreceptor due to contact at the time of overlay. Even in the case of non-contact development, there is a possibility that the toner reciprocates between the photosensitive member and the developer carrying member in the conventional AC bias application development, and there is a possibility of interference. On the other hand, by using a transport system using a traveling wave electric field, overlay development can be performed without affecting the existing toner layer. Therefore, non-contact overlay development can be achieved efficiently.
Further, like the developing device 4 of Modification 2, the toner conveying member 402 moves on the surface, and the surface substrate 210 is provided on the surface, and the surface substrate 210 is interposed through the surface protective layer 103 that is an insulating layer. A spatially periodic electrode pattern 20 is provided, and by forming a time-periodic potential difference between an assembly of odd-numbered electrodes starting from an electrode and an assembly of even-numbered electrodes, The conveying member moves to the surface while reciprocating the toner between the two kinds of electrodes on the surface, thereby conveying the toner to the developing region. By using such a toner conveying member, it is possible to reduce the toner adhesion amount, and even if the ratio of the toners that receive the repulsive force between the toners is the same, the absolute amount decreases, so image degradation due to scattering Can be suppressed.
In addition, since spherical toner having an average circularity of 90% or more is used as the toner, the charging characteristics of the supplied toner are more stable than those using an indeterminate toner. Adhesive properties can be obtained, and desired image formation can be performed.

1 is a schematic configuration diagram of a printer according to Embodiment 1. FIG. 1 is a schematic configuration diagram of a developing device according to Embodiment 1. FIG. Explanatory drawing of the dynamic resistance measurement system of the magnetic particle of a developing agent. FIG. 3 is a schematic configuration diagram of a developing device according to Embodiment 1 of an example different from FIG. 2. FIG. 3 is a configuration diagram illustrating a transport substrate and a transport power supply circuit of a toner transport member included in the developing device, together with a photoreceptor. The top view which shows a conveyance board | substrate from the front surface side. The longitudinal cross-sectional view which shows the A-A 'cross section in FIG. 6 of the same conveyance board | substrate. The wave form diagram which shows the A phase pulse voltage Va, the B phase pulse voltage Vb, and the C phase pulse voltage Vc which are applied to each conveyance electrode of the conveyance board | substrate. The schematic diagram which shows the state of the voltage applied to the same conveyance board | substrate and each conveyance electrode. (A), (b), (c), (d) is a schematic diagram for demonstrating the behavior of the toner on the conveyance board, respectively. The block diagram which shows the conveyance power supply which is a conveyance power supply circuit. The wave form diagram which shows the repetitive pulse voltage of 3 phases applied to each conveyance electrode in the conveyance area | region and collection | recovery area | region of the same conveyance board | substrate. The wave form diagram which shows the repetitive pulse voltage of 3 phases applied to each conveyance electrode in the image development area | region of the conveyance board | substrate. FIG. 14 is a waveform diagram showing a repetitive pulse voltage at a timing different from that in FIG. 13. Explanatory diagram of development characteristics, (a) is an explanatory diagram of development in which the development potential and the amount of change in surface potential due to the toner layer coincide, and (b) is an explanatory diagram of development in which an upper limit is set for the toner adhesion amount. FIG. 4 is an explanatory diagram of a process of developing a magenta toner image of the first color on the surface of the photoreceptor. (A) is an explanatory view when charging the first color, (b) is an explanatory view when forming a latent image of the first color, and (c) is an explanatory view when developing the first color surface. FIG. 5 is an explanatory diagram of a process of developing a yellow toner image of the second color on the surface of the photoreceptor. (A) is an explanatory diagram when charging the second color, (b) is an explanatory diagram when forming a latent image of the second color, and (c) is an explanatory diagram when developing a two-color surface. FIG. 3 is a schematic diagram illustrating a state in which a toner layer is formed on the surface of a photoreceptor. 6 is a graph showing the relationship between the toner adhesion amount and the toner layer potential. FIG. 3 is a schematic diagram showing a state where a second color latent image is formed on the surface of the photoreceptor and the surface of the toner layer of the photoreceptor on which the toner layer of the first color is formed. 4 is a graph comparing toner adhesion amounts of a printer having four development areas of “same gap + same development potential” and a printer having “gap spread + development potential increase”. 6 is a graph showing the value of the image density ID with respect to the toner adhesion amount when a normal toner is used and when a highly colored toner is used. 10 is a graph showing the toner adhesion amount with respect to the gradation level of the development area of the second color of the printer of Modification 1. FIG. 3 is a schematic configuration diagram of a printer according to a second embodiment. A graph showing the relationship between the toner conveyance amount or toner adhesion amount and the supply potential difference, (a) is a graph showing the relationship between the toner conveyance amount and the supply potential difference, and (b) is an upper limit value of the toner adhesion amount and the supply potential difference. The graph which shows the relationship. 9 is a graph showing the second color post-exposure potential with respect to the first color toner adhesion amount according to the second embodiment. The graph which shows the tendency of the relationship between the general 1st color adhesion amount and the required writing amount. 6 is a graph showing a difference in toner shape when the horizontal axis is the first color toner adhesion amount and the vertical axis is the average potential after exposure. Schematic explanatory diagram of the surface substrate 210 and the conveyance power supply circuit of the toner conveyance member 402 provided in the developing device 4 of Modification 2, (a) is an explanatory diagram of a state before an AC voltage is applied to the surface electrode, and (b) is The explanatory view of the state where the AC voltage was impressed to the surface electrode. FIG. 10 is a schematic configuration diagram of a developing device 4 according to Modification 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Charging device 3 Writing device 4 Developing device 6 Transfer device 10 Toner 11 Magnetic particle 12 Developer 100 Printer 402 Toner conveying member

Claims (6)

A latent image carrier that moves on the surface;
Charging means for uniformly charging the surface of the latent image carrier;
Latent image forming means for forming a latent image on the surface of the latent image carrier charged by the charging means;
A developer conveying member that conveys the developer on the surface thereof facing the latent image carrier in the developing region is provided, and charged toner in the developer conveyed by the developer conveying member in the developing region is transferred to the latent image. Developing means for supplying the latent image on the carrier to form a toner image;
Transfer means for transferring the toner image formed on the latent image carrier to a recording medium or toner image carrier at a transfer position;
A plurality of the developing means are opposed to the surface of one latent image carrier, and a plurality of toner images are formed on the latent image carrier by the plurality of developing means. In the image forming apparatus for collectively transferring the combined toner images to the recording medium or the toner image carrier at the transfer position,
The gap between the latent image carrier and the developer transport member is increased from the development region where the first toner image is formed to the development region downstream of the latent image carrier in the surface movement direction, and Image formation characterized in that the potential difference between the surface of the developer conveying member in the development region and the latent image portion on the surface of the latent image carrier on which the latent image is formed is increased. apparatus. The image forming apparatus according to claim 1.
An image forming apparatus, wherein two developing means are opposed to one latent image carrier. The image forming apparatus according to claim 1 or 2,
The layer thickness of the toner image formed by one of the developing means is one or more times and less than twice the average particle diameter of the toner used for development, and the ratio of the toner adhesion amount to the image density ID is 1.4 / 0. 4 [mg / cm ² ] ⁻¹ or more. The image forming apparatus according to claim 1, 2 or 3.
The developer conveying member includes a plurality of electrodes for generating a traveling wave electric field for moving the toner, and conveys the toner to a position facing the latent image carrier by the traveling wave electric field. apparatus. The image forming apparatus according to claim 1, 2 or 3.
The developer transport member includes a plurality of electrodes arranged in the surface moving direction on an endless surface moving surface via an insulating layer, and a set of odd-numbered electrodes starting from one of the plurality of electrodes. An image forming apparatus characterized in that a potential difference is formed periodically between a body and an assembly of even-numbered electrodes. The image forming apparatus according to claim 1, 2, 3, 4, or 5.
An image forming apparatus, wherein an average circularity of toner supplied to the surface of the latent image carrier by the developing unit is 90% or more.

Images