JP2019159248A - Developing device and image forming apparatus including the same - Google Patents

Abstract

To provide a developing device in which charge relaxation of a recovered toner efficiently occurs and that can quickly start up charging when a new toner is supplied, and an image forming apparatus including the developing device.SOLUTION: A developing device 3a comprises: a developer container 20; a supply and conveying screw 23; a stirring and conveying screw 24; and a developing roller 25. The developer container 20 is partitioned with a partition part 20a into a supply and conveying chamber 21 and a stirring and conveying chamber 22. The supply and conveying screw 23 and the stirring and conveying screw 24 are provided in the supply and conveying chamber 21 and the stirring and conveying chamber 22, respectively. In the developing device 3a, the relationship of the electric characteristics between the supply and conveying screw 23 and the stirring and conveying screw 24 is regulated. When the time constant of a surface material of the supply and conveying screw 23 is τ1[s], the time constant of a surface material of the stirring and conveying screw 24 is τ2[s], and the dielectric constant is ε2[F/m], log(τ2/τ1)>5 and ε2>1.0E-5 are satisfied.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a developing device and an image forming apparatus including the same, and more particularly to a two-component developing type developing device using a two-component developer including a magnetic carrier and a toner and an image forming apparatus including the same. .

  In an image forming apparatus, a latent image formed on an image carrier made of a photoreceptor or the like is developed by a developing device and visualized as a toner image. As such a developing device, a two-component developing type developing device using a two-component developer containing a magnetic carrier and toner is used.

  As a two-component developing type developing device, a developer container containing a developer, a first agitating and conveying member for agitating and conveying the developer, a second agitating and conveying member, and a developer supplied from the second agitating and conveying member A developing device including a developing roller (developer carrier) to be carried is known. The first agitating and conveying member conveys the developer to one side in the axial direction of the developing roller, and the second agitating and conveying member supplies the developer to the developing roller while conveying the developer to the other side (the side opposite to the one side). To do. The developer is mixed and conveyed by a stirring unit in the developing container and is pumped up on the developing roller to form a magnetic brush. The layer thickness of the magnetic brush is regulated by a regulating member, and the toner in the magnetic brush develops an electrostatic latent image on the photoreceptor by a developing electric field. The toner that has not been used for development is collected from the developing roller, sent to the agitation unit, mixed with newly supplied toner, and used again for development.

  In the conventional developing device as described above, the toner carried on the carrier is subjected to a large force because it is restrained from moving in the magnetic brush on the developing roller, whereas the agitating unit is free to move and thus receives the force. Becomes smaller. As described above, when the developer circulates between the agitating unit and the developing roller in the developing container, the change in the contact distance between the toner carriers brings about the change in the capacitance of the contact surface, and the development in which the capacitance increases. The charge amount is increased by charging on the roller, and the charge amount is decreased by relaxing on the stirring screw whose electrostatic capacity is reduced. As a result, when the toner is replenished in the agitating portion where the relaxation of the staying toner in the developer is progressing, it becomes easier to receive electrons from the replenished toner, causing an electrostatic action between the toner particles. There was a risk of charging failure.

Patent Document 1 discloses a developer storage container of a process cartridge in which the chargeability of the developer is negative or a stationary developer supply container such as a copying machine, and has a dielectric tangent of 1 × 10 ⁻⁴ to 1 It is disclosed that a developer container is formed using a resin having a range of × 10 ⁻³ tan δ. According to this method, a required amount of developer can be discharged from a narrow developer opening of a process cartridge or the like in a certain time without increasing the size of the developer stirring member.

Japanese Patent Laid-Open No. 6-314020

  However, although the method of Patent Document 1 can suppress the adhesion of the developer to the developer storage container and improve the developer discharging property, it cannot suppress the charging failure of the toner.

  In view of the above problems, the present invention efficiently reduces the charge of the toner in the developer collected from the developer carrier, and quickly raises the charge amount when new toner is replenished. It is an object of the present invention to provide a developing device that can perform the above and an image forming apparatus including the developing device.

In order to achieve the above object, a first configuration of the present invention includes a developing container, a first agitating / conveying member, a second agitating / conveying member, a developer carrier, and a toner supply port. It is. The developing container includes a first transport chamber and a second transport chamber disposed in parallel with the first transport chamber with the partition portion interposed therebetween, and accommodates a two-component developer including a carrier and toner. The first agitating and conveying member is rotatably supported in the first conveying chamber, and agitates and conveys the developer in the first conveying chamber in the first direction. The second agitating and conveying member is rotatably supported in the second conveying chamber in parallel with the first agitating and conveying member, and the developer in the second conveying chamber is agitated and conveyed in the second direction which is opposite to the first direction. To do. The developer carrying member is rotatably supported by the developing container and carries the developer in the first transport chamber on the surface. The toner replenishing port is provided upstream of the central portion in the longitudinal direction of the second transport chamber with respect to the transport direction of the developer in the developer container. When the time constant of the surface material of the first stirring and conveying member is τ1 [s], the time constant of the surface material of the second stirring and conveying member is τ2 [s], and the dielectric constant is ε2 [F / m], (1), (2)
log (τ2 / τ1)> 5 (1)
ε2> 1.0E-5 (2)
Meet.
However, τ1, τ2; those calculated by the equation τ = 1 / (2π · f) from the frequency f [Hz] at which the reactance is maximized.
A Cole-Cole plot is created under the condition of ε2; 1 Vpp — 1 MHz—10 mHz, the capacitance C is calculated as an RC parallel circuit model, and the result calculated from the result is shown.

  According to the first configuration of the present invention, when the time constants of the surface materials of the first agitation transport member and the second agitation transport member satisfy the formula (1), the first agitation transport member is placed on the developer carrier. Operation in which the developer is supplied and separated from the developer carrier after passing through the opposing area (development area) between the developer carrier and the image carrier and transported back to the first agitation transport member The charging of the developer at the first agitating / conveying member is efficiently reduced and the replenishment toner is quickly charged at the second agitating / conveying member after the toner is replenished. Therefore, it is possible to suppress toner scattering due to insufficiently charged toner and occurrence of background fogging due to reversely charged toner. Further, when the dielectric constant of the surface material of the second agitating / conveying member satisfies the formula (2), the dielectric property of the second agitating / conveying member for quickly raising the charge of the replenishing toner at the time of toner replenishment can be ensured. It is possible to effectively suppress the occurrence of insufficiently charged toner and reversely charged toner.

Schematic sectional view showing the overall configuration of a color printer 100 including the developing devices 3a to 3d of the present invention. Side surface sectional drawing which shows the structure of the developing device 3a which concerns on one Embodiment of this invention. Plan sectional drawing which shows the structure of the stirring part of the developing device 3a of this embodiment A graph showing the Q / S relationship when the horizontal axis represents the cumulative value of the surface area S per toner particle and the vertical axis represents the cumulative value of the charge amount Q per toner particle.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of a color printer 100 provided with developing devices 3a to 3d of the present invention, and here, a tandem color printer is shown. In the main body of the color printer 100, four image forming portions Pa, Pb, Pc, and Pd are sequentially arranged from the upstream side in the transport direction (right side in FIG. 1) in the order of Pd to Pa. These image forming portions Pa to Pd are provided corresponding to images of four different colors (black, yellow, magenta, and cyan), and cyan, magenta, and yellow are respectively performed by charging, exposure, development, and transfer processes. And a black image are sequentially formed.

  These image forming portions Pa to Pd are provided with photosensitive drums 1a, 1b, 1c and 1d for carrying visible images (toner images) of the respective colors, and further rotate clockwise in FIG. An intermediate transfer belt 8 is provided adjacent to each of the image forming portions Pa to Pd.

  When image data is input from a host device such as a personal computer, first, the surfaces of the photosensitive drums 1a to 1d are uniformly charged by the chargers 2a to 2d. Next, light is irradiated by the exposure device 5 according to the image data, and electrostatic latent images corresponding to the image data are formed on the respective photosensitive drums 1a to 1d. The developing devices 3a to 3d are filled with a predetermined amount of a two-component developer (hereinafter, also simply referred to as a developer) containing toners of black, yellow, magenta, and cyan by toner containers 4a to 4d. The toner in the developer is supplied onto the photosensitive drums 1a to 1d by 3a to 3d and electrostatically adheres. Thereby, a toner image corresponding to the electrostatic latent image formed by exposure from the exposure device 5 is formed.

  Then, the primary transfer rollers 6a to 6d apply an electric field at a predetermined transfer voltage between the primary transfer rollers 6a to 6d and the photosensitive drums 1a to 1d, and black, yellow, magenta and the like on the photosensitive drums 1a to 1d are applied. A cyan toner image is primarily transferred onto the intermediate transfer belt 8. Toner remaining on the surfaces of the photosensitive drums 1a to 1d after the primary transfer is removed by the cleaning devices 7a to 7d.

  The transfer paper P onto which the toner image is transferred is housed in a paper cassette 16 disposed in the lower part of the color printer 100, and the transfer paper P passes through a paper feed roller 12a and a registration roller pair 12b at a predetermined timing. Then, the sheet is conveyed to the nip portion (secondary transfer nip portion) between the secondary transfer roller 9 provided adjacent to the intermediate transfer belt 8 and the intermediate transfer belt 8. The transfer sheet P on which the toner image is secondarily transferred is conveyed to the fixing unit 13.

  The transfer paper P conveyed to the fixing unit 13 is heated and pressed by the fixing roller pair 13a to fix the toner image on the surface of the transfer paper P, thereby forming a predetermined full color image. The transfer paper P on which the full-color image is formed is discharged to the discharge tray 17 by the discharge roller pair 15 as it is (or after being distributed to the reverse conveyance path 18 by the branching unit 14 and the image is formed on both sides).

  FIG. 2 is a side cross-sectional view showing the configuration of the developing device 3a according to the embodiment of the present invention mounted on the color printer 100. FIG. 3 is a plan sectional view (cross-sectional view taken along the line XX ′ in FIG. 2) showing the structure of the stirring unit of the developing device 3a. Here, the developing device 3a disposed in the image forming unit Pa of FIG. 1 will be described, but the configuration of the developing devices 3b to 3d disposed in the image forming units Pb to Pd is basically the same, and thus described. Is omitted. Further, FIG. 2 shows a state in which the developing device 3a is viewed from the back side in FIG. 1, and the arrangement of each member in the developing device 3a is opposite to that in FIG.

  As shown in FIG. 2, the developing device 3 a includes a developing container 20, a stirring and conveying screw 23, a supply and conveying screw 24, a developing roller (developer carrying member) 25, and a regulating blade 29. The developing container 20 constitutes an outline of the developing device 3a, and the inside thereof is partitioned into a supply transfer chamber 21 and an agitation transfer chamber 22 by a partition portion 20a. A two-component developer containing a magnetic carrier and toner is accommodated in the developing container 20. Further, the developing container 20 rotatably holds the supply conveyance screw 23, the agitation conveyance screw 24, and the development roller 25.

  The developing roller 25 includes a fixed shaft (not shown) and a developing sleeve. A magnet having a plurality of magnetic poles is fixed to the fixed shaft, and the developing sleeve is rotatably held. In the vicinity of the developing roller 25, there is provided a regulating blade 29 that is disposed at a predetermined distance from the developing roller 25 and regulates the layer thickness of the developer (magnetic brush) carried on the surface of the developing roller 25. The developing roller 25 is rotated in the direction of the arrow in FIG. 2 (counterclockwise direction) by a driving mechanism including a motor and a gear (not shown). The developing roller 25 is applied with a developing voltage obtained by superimposing an AC voltage on a DC voltage.

  When the developing roller 25 to which the developing voltage is applied rotates counterclockwise in FIG. 2, the development carried on the surface of the developing roller 25 by the potential difference between the potential of the developing roller 25 and the potential of the exposed portion of the photosensitive drum 1a. The toner in the agent is supplied to the photosensitive drum 1a. The toner sequentially adheres to the exposed portion on the photosensitive drum 1a that rotates in the clockwise direction, and the electrostatic latent image on the photosensitive drum 1a is developed.

  The supply conveyance screw 23 and the agitation conveyance screw 24 are provided in the supply conveyance chamber 21 and the agitation conveyance chamber 22, respectively. The supply / conveying screw 23 disposed in the supply / conveying chamber 21 is provided integrally with the rotation shaft 23a and the rotation shaft 23a, and is formed in a spiral shape at a constant pitch in the axial direction of the rotation shaft 23a. And have. The agitating / conveying screw 24 disposed in the agitating / conveying chamber 22 is provided integrally with the rotating shaft 24a and the rotating shaft 24a, and is formed in a spiral shape with a constant pitch in the axial direction of the rotating shaft 24a. And have. The supply conveyance screw 23 and the agitation conveyance screw 24 convey the developer while stirring, and charge the toner in the developer to a predetermined level. As a result, the toner is held on the carrier.

  As shown in FIG. 3, communication portions 20 b and 20 c are provided at both ends in the longitudinal direction (left and right ends in FIG. 3) of the partition portion 20 a that partitions the supply transfer chamber 21 and the stirring transfer chamber 22. A toner replenishing port 20 d for replenishing toner into the developing container 20 is provided at one end (right end in FIG. 3) of the agitation transport chamber 22. A toner supply path (not shown) connected to the toner container 4a (see FIG. 1) is connected to the toner supply port 20d.

  The toner replenished from the toner replenishing port 20d is mixed with the developer in the agitating and conveying chamber 22 by the agitating and conveying screw 24 and conveyed in one direction (in the direction of arrow P in FIG. 3) while being agitated, and is provided in the partition portion 20a. It passes through the communication part 20 b and joins to one end of the supply transfer chamber 21. Then, the developer is supplied to the developing roller 25 from the supply / conveying screw 23 disposed in the supply / conveying chamber 21, and a magnetic brush is formed on the developing roller 25.

  On the other hand, the developer on the developing roller 25 that has not been used for development is peeled off from the developing roller 25 and collected in the supply conveyance chamber 21. When the supply / conveyance screw 23 rotates, the developer in the supply / conveyance chamber 21 is conveyed in one direction (in the direction of arrow Q in FIG. 3), passes through the communication portion 20c provided in the partition portion 20a, and passes through the toner supply port. It joins to one end of the agitating and conveying chamber 22 where 20d is formed. As described above, the developer passes through the agitating and conveying chamber 22, the communicating portion 20b, the supply and conveying chamber 21, and the communicating portion 20c in order and circulates in the developing container 20.

  A toner concentration detection sensor 30 is disposed on the side surface of the agitation transport chamber 22. The toner concentration detection sensor 30 detects the ratio (T / C) of the toner with respect to the carrier of the developer conveyed in the developer container 20, and detects, for example, the magnetic permeability of the developer in the developer container 20. A magnetic permeability sensor is used. As shown in FIG. 3, the toner concentration detection sensor 30 is disposed upstream of the communicating portion 20 b with respect to the developer transport direction (the arrow Q direction in FIG. 3) in the stirring transport chamber 22. A predetermined amount of toner is supplied from the toner container 4a to the developing container 20 through the toner supply port 20d according to the detection result of the toner concentration detection sensor 30.

  As described above, since the toner carried on the carrier is restricted in movement in the magnetic brush on the developing roller 25 (subject to magnetic restraining force), the toner does not pass through the regulating blade 29 (regulating portion). The physical stress that is received increases. On the other hand, since the toner can move freely in the supply transfer chamber 21 and the stirring transfer chamber 22 (stirring section), the physical stress that the toner receives is reduced. Therefore, the contact distance between the toner particles and the carrier particles is different between the regulating unit and the stirring unit, and the electrostatic capacity of the toner and the carrier is increased in the regulating unit. Further, in the restricting portion, deterioration and alteration of the toner external additive present on the toner surface also occur. As a result, the ionization potential of the toner itself is reduced in the regulation unit as compared with the stirring unit.

  That is, when toner (hereinafter referred to as staying toner) existing in the developing container 20 circulates between the regulating portion and the agitating portion, the change in the contact distance between the toner particles and the carrier particles causes the static contact surface between the carrier and the toner. The regulation portion that brings about a change in the capacitance and the charge increases at the regulating portion where the capacitance increases, the charge amount increases, and the charge is reduced at the stirring portion where the capacitance decreases, and the charge amount decreases.

  Accordingly, toner newly supplied from the toner container 4a (hereinafter referred to as “replenished toner”) exchanges electrons with the carrier, and reduces the ionization potential and makes it easy to receive electrons. Send and receive electronic data between them.

  Specifically, when the toner is replenished from the toner replenishing port 20d in the agitating and conveying chamber 22 in which the charge of the staying toner in the developer is being moderated, the replenished toner is charged by applying electrons to the carrier ( Although positively charged), electrons are also given from the replenishment toner to the staying toner. As a result, the positive charge amount of the staying toner decreases, and toner scattering due to insufficiently charged toner and background fogging due to reversely charged (negatively charged) toner occur.

Therefore, in the developing device 3a of the present embodiment, the relationship between the electrical characteristics of the supply conveyance screw 23 and the agitation conveyance screw 24 is defined. Specifically, when the time constant of the surface material of the supply conveyance screw 23 is τ1 [s] and the time constant of the surface material of the stirring conveyance screw 24 is τ2 [s], the following equation (1)
log (τ2 / τ1)> 5 (1)
The surface materials of the supply conveyance screw 23 and the agitation conveyance screw 24 are determined so as to satisfy the above conditions. However, the time constants τ1 and τ2 represent those calculated by the equation τ = 1 / (2π · f) from the frequency f [Hz] at which the reactance is maximized.

  According to this configuration, the developer is supplied onto the developing roller 25 from the supply / conveying screw 23, and the developer is separated from the developing roller 25 after passing through the opposed region (developing region) between the developing roller 25 and the photosensitive drum 1 a. The developer whose charge amount has increased on the developing roller 25 can be efficiently relieved on the supply and conveyance screw 23 while repeating the operation of returning to the supply and conveyance screw 23 and being conveyed. Further, the charge of the replenishing toner can be quickly raised by the stirring and conveying screw 24 after the toner is replenished. That is, it is possible to achieve both charge relaxation on the supply and conveyance screw 23 and start-up of charge on the agitation and conveyance screw 24, and toner scattering due to insufficiently charged toner and background fogging caused by reversely charged (negatively charged) toner can be achieved. Occurrence can be suppressed.

When the dielectric constant of the surface material of the agitating and conveying screw 24 is ε2 [F / m],
ε2> 1.0E-5 (2)
The surface material of the stirring and conveying screw 24 is determined so as to satisfy the above. However, the dielectric constant ε represents a value calculated from a result of creating a Cole-Cole plot under the condition of 1 Vpp_1 MHz-10 mHz and calculating the capacitance C as an RC parallel circuit model.

  According to this configuration, since the agitating / conveying screw 24 having a high dielectric constant is present in the agitating / conveying chamber 22 where the toner is replenished, the replenishing toner and the agitation are compared with the transfer of electrons between the replenishing toner and the staying toner. The exchange of electrons with the conveying screw 24 has priority, and the exchange of electrons between the replenishing toner and the staying toner is suppressed. As a result, it is possible to suppress the decrease in the charge amount due to the staying toner receiving electrons from the replenishment toner, and to ensure the dielectric property of the agitating and conveying screw 24 for quickly raising the charge of the replenishment toner when the toner is replenished. In addition, generation of insufficiently charged toner and reversely charged (negatively charged) toner can be effectively suppressed.

  The supply / conveying screw 23 used in the developing devices 3a to 3d of the present invention can be formed of, for example, a synthetic resin in which a conductive material is dispersed. Examples of the synthetic resin include polystyrene (PS), ABS resin, polymethyl methacrylate (PMMA), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (FPA), nylon 6, and the like. As the conductive material, carbon particles having an average particle diameter of 50 to 100 nm can be used.

  The stirring and conveying screw 24 used in the developing devices 3a to 3d of the present invention can be molded from a synthetic resin in which a dielectric material is dispersed, for example. As the synthetic resin, the same resin as the supply conveyance screw 23 can be used. Examples of the dielectric material include barium titanate (relative dielectric constant: about 1400), strontium titanate (relative dielectric constant: about 300), and the like. In particular, it is preferable to use barium titanate having a relative dielectric constant of 1000 or more.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, in the above-described embodiment, the example in which the developer is supplied from the supply and conveyance screw 23 to the developing roller 25 has been described, but the present invention is not limited to this. A developer carrier such as a magnetic roller is further provided between the agitating / conveying screw 23 and the developing roller 25, and after supplying the developer from the agitating / conveying screw 23 to the magnetic roller or the like, the toner is transferred from the magnetic roller or the like to the developing roller 25. You may supply.

  In the above embodiment, the developing device using the two-component developer containing the positively charged toner has been described as an example. However, the present invention can be applied to a developing device using the two-component developer containing the negatively charged toner.

Further, the present invention is not limited to the tandem color printer 100 shown in FIG. 1, but a supply / conveying chamber 21 for supplying a developer to the developing roller 25 such as a digital or analog monochrome copying machine, a color copying machine, or a facsimile. In addition, the present invention can be applied to various image forming apparatuses including a developing device including a stirring / conveying chamber 22 that mixes and stirs toner collected from the developing roller 25 with replenishing toner. Hereinafter, the effects of the present invention will be described more specifically with reference to examples.
(Example of producing a supply and conveyance screw)

  80 parts by weight of ABS resin was charged into a twin screw extruder (PCM45, manufactured by Ikegai Iron Works Co., Ltd.), melted at a cylinder temperature of 210 ° C., and then 20 parts by weight of carbon black (average particle diameter 60 nm) was added and kneaded. After mixing, strand cutting was performed to obtain ABS resin pellets in which carbon black was dispersed. This was molded into a screw shape to obtain a supply / conveying screw 23.

A supply / conveying screw 23 was obtained in the same manner as in Example 1 except that 70 parts by weight of ABS resin and 30 parts by weight of carbon black were used.
[Reference Example 1]

A supply / conveying screw 23 was obtained in the same manner as in Example 1 except that 90 parts by weight of ABS resin and 10 parts by weight of carbon black were used.
[Reference Example 2]

A supply conveyance screw 23 was obtained by the same method as in Example 1 except that 100 parts by weight of ABS resin was used and carbon black was not added.
(Example of production of stirring and conveying screw)

60 parts by weight of ABS resin is charged into a twin screw extruder (PCM45, manufactured by Ikekai Tekko Co., Ltd.), melted at a cylinder temperature of 210 ° C., and then 40 parts by weight of barium titanate particles (average particle size 150 nm, relative dielectric constant 1400). Was added and kneaded. After mixing, strand cutting was performed to obtain ABS resin pellets in which barium titanate was dispersed. This was molded into a screw shape to obtain a stirring and conveying screw 24.
[Reference Example 3]

A stirring and conveying screw 24 was obtained in the same manner as in Example 3 except that 80 parts by weight of ABS resin and 20 parts by weight of barium titanate particles were used.
[Reference Example 4]

A stirring and conveying screw 24 was obtained by the same method as in Example 3 except that 100 parts by weight of ABS resin was used and no barium titanate particles were added.
[Test example]

  The relationship between the surface material of the supply conveyance screw 23 and the stirring conveyance screw 24 and the toner charge amount was investigated. As a testing machine, a color multifunction machine (TASKalfa 2552ci, manufactured by Kyocera Document Solutions) equipped with the developing devices 3a to 3d shown in FIG. 2 was used. And when the surface material of the supply conveyance screw 23 and the stirring conveyance screw 24 satisfy | fills the relationship of Formula (1), (2) (this invention 1,2), the surface material of the supply conveyance screw 23 and the stirring conveyance screw 24 is The charge amount distributions of the toners were compared in the case where the relationship of the expressions (1) and (2) was not satisfied (Comparative Examples 1 to 4).

  As the developer, a two-component developer comprising a positively charged toner having an average particle diameter of 6.5 μm and a ferrite carrier having an average particle diameter of 35 μm is used, and the ratio of carrier to toner (weight ratio, T / C) is 8 %. Further, tan δ (measured values at 1 V and 100 kHz) of the toner and the carrier were 0.01 and 0.15, respectively. The amount of developer charged into the developing device 3a was 450 g.

  As a test method, a pattern of three character images with a printing rate of 1% was continuously printed 500 times in an environment of a developing device of 20 ° C. and 65% RH. Thereafter, 100 originals with a printing rate of 50% are continuously printed, and the background fog of the output image during continuous printing and the spread of the developer charge distribution after continuous printing (Q / S deviation; relative average deviation) are simulated. I did.

  The toner charge amount was measured by fixing 5 mg of developer on a neodymium magnet and measuring under the following conditions. The Q / S for each particle is calculated using the obtained charge amount Q per particle and the particle diameter D, and sorted in order from the smallest Q / S. As shown in FIG. The cumulative value of the surface area S per particle was taken, and the cumulative value of the charge amount Q per particle was plotted on the vertical axis (curve R1 in FIG. 4). A straight line representing an ideal state where the Q / S for each particle is constant is R2, the area of the region surrounded by R1 and R2 is A, and the area of the region surrounded by R1 and the X axis is B. The deviation from R2 (Q / S deviation) is shown as the ratio of A to A + B. This Q / S deviation was calculated as an index representing the degree of background fog and toner scattering.

Measurement of the electrical characteristics of the supply conveyance screw 23 and the stirring conveying screw 24, finely pulverized product of a screw surface material (particle diameter 100 [mu] m), by applying a load of 40 kgf / cm ² between material electrode (area 1.327cm ²⁾ The pellet was about 3 mm thick. An AC voltage of 1 Vpp was applied to the electrodes sandwiching the pellets using FRA (Frequency Response Analyzer, frequency characteristic analyzer), and the frequency was changed from 1 MHz to 10 mHz at 5 points / decade to create a Cole-Cole plot. . Using this plot, the time constants τ1 and τ2 were calculated from the frequency f at which the reactance was maximum, and the dielectric constant ε2 was calculated by fitting as a RC parallel circuit model.

The evaluation criteria were ◯ when the Q / S deviation was less than 25%, Δ when it was 25% or more and less than 30%, and × when it was 30% or more. The evaluation results are shown in Table 1 together with the combination of the feed conveyance screw 23 and the agitation conveyance screw 24 used, log (τ ₂ / τ ₁ ), ε2, and Q / S deviation.

  As is apparent from Table 1, the developing device 3a, log (log (τ2 / τ1) = 5.08 (> 5), ε2 = 2.23E-5 (> 1.0E-5). In the developing device 3a of the present invention 2 in which τ2 / τ1) = 5.33 (> 5) and ε2 = 2.23E-5 (> 1.0E-5), the Q / S deviation is 20.5%, respectively. 21.1 and it was confirmed that background fogging and toner scattering were suppressed.

  On the other hand, development of Comparative Examples 1 and 2 where ε2 = 2.23E-5 (> 1.0E-5) but log (τ2 / τ1) = 4.64, 2.69 (<5). Development apparatus 3a, log (τ2 / τ1) of Comparative Example 3 in which apparatus 3a, log (τ2 / τ1) = 5.05 (> 5) but ε2 = 8.47E-6 (<1.0E-5) ) = 1.00 (<5), and in the developing device 3a of Comparative Example 4 where ε2 = 1.97E-11 (<1.0E-5), the Q / S deviations are 29.7% and 32, respectively. .6%, 30.1%, and 38.9%, and it was confirmed that background fogging and toner scattering occurred.

  The present invention can be applied to a two-component developing type developing device using a two-component developer containing a magnetic carrier and a toner. By utilizing the present invention, development in which the toner in the developer recovered from the developer carrying member is efficiently relieved and the amount of charge when a new toner is replenished can be quickly started up. An apparatus and an image forming apparatus including the apparatus can be provided.

3a to 3d Developing device 20 Developing container 20a Partition unit 20b, 20c Communication unit 20d Toner supply port 21 Supply conveyance chamber (first conveyance chamber)
22 Stirring transfer chamber (second transfer chamber)
23 Supply conveyance screw (first stirring conveyance member)
24 Agitating and conveying screw (second agitating and conveying member)
25 Development roller (developer carrier)
29 Regulating blade 100 Color printer (image forming device)

Claims (5)

A developing container for containing a two-component developer including a carrier and toner, the first conveying chamber, and a second conveying chamber disposed in parallel with the first conveying chamber across the partition portion;
A first agitating and conveying member that is rotatably supported in the first conveying chamber and agitates and conveys the developer in the first conveying chamber in a first direction;
The second conveying chamber is parallel to the first agitating / conveying member and is rotatably supported, and secondly agitates and conveys the developer in the second conveying chamber in a second direction opposite to the first direction. An agitating and conveying member;
A developer carrying member rotatably supported by the developing container and carrying a developer in the first transport chamber on the surface;
A toner replenishing port provided on the upstream side of the central portion in the longitudinal direction of the second transport chamber with respect to the transport direction of the developer in the developer container;
In a developing device comprising:
When the time constant of the surface material of the first stirring and conveying member is τ1 [s], the time constant of the surface material of the second stirring and conveying member is τ2 [s], and the dielectric constant is ε2 [F / m], Equations (1) and (2)
log (τ2 / τ1)> 5 (1)
ε2> 1.0E-5 (2)
A developing device characterized by satisfying the above.
However,
τ1, τ2: those calculated by the equation τ = 1 / (2π · f) from the frequency f [Hz] at which the reactance is maximized.
A Cole-Cole plot is created under the condition of ε2; 1 Vpp — 1 MHz—10 mHz, the capacitance C is calculated as an RC parallel circuit model, and the result calculated from the result is shown.   2. The developing device according to claim 1, wherein the surface material of the first agitating and conveying member is obtained by dispersing carbon particles having an average particle diameter of 50 to 100 nm in a synthetic resin.   3. The developing device according to claim 1, wherein a surface material of the second agitating and conveying member is obtained by dispersing a dielectric material having a relative dielectric constant of 1000 or more in a synthetic resin.   The developing device according to claim 3, wherein the dielectric material is barium titanate.   An image forming apparatus comprising the developing device according to claim 1.

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