JP2007171668A - Developing device with toner charging control mechanism - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device in which a current discharge is actively generated to positively give electric charges to toner not only by friction between a sleeve and a restricting member, but also by another means. <P>SOLUTION: The developing device 20, equipped with a toner-agitating and conveying means having an agitating member that includes at least a spiral 1 or a paddle, is equipped with a voltage-applying means which uses a shaft 3 of the agitating member as one electrode and has the other electrode 7 arranged on the side of an opposite developing device housing 6 for applying a bias voltage between both the electrodes. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a developing device used for an image forming apparatus such as a copying machine or a printer using an electrophotographic method or an electrostatic recording method.

  In an electrophotographic apparatus, as a developer, a two-component developer composed of a magnetic one-component developer that contains a magnetic substance in the toner without using a carrier, a toner, and a magnetic carrier is widely used. In recent years, a one-component developing system is often used preferably for the purpose of reducing the weight and size of an image forming apparatus. In the one-component development method, conductive magnetic toner is held on a cylindrical conductive developer carrier (development roll) having magnetism inside, and is developed by bringing it into contact with an electrostatic latent image. At this time, a conductive path is formed by the toner particles between the surface of the electrostatic latent image holding member, which is the developing unit, and the sleeve surface of the developing roll, and the charge is guided from the sleeve to the toner particles through this conductive path, The toner particles adhere to the image portion and are developed by the electrostatic force between the electrostatic latent image and the image portion.

  As a means for attaching toner particles to the electrostatic latent image, a method of forming a properly charged toner layer on the developing roller and applying a bias to the developing roller is generally employed. 2. Description of the Related Art Conventionally, in a one-component developing device, as a method for imparting charge to toner, a method of friction charging between a sleeve and a regulating member (contact blade or non-contact blade) is generally used.

  However, with the conventional method alone, once it is set in the system, there is always only a constant triboelectric charge imparting ability, so in order to obtain a certain level of toner charge, it is necessary to rely on the design of the toner itself. Further, when the ease of frictional charging of the toner fluctuates due to environmental fluctuations (temperature, humidity) or the like, there is a problem that problems such as density reduction and tailing occur. Regarding the decrease in density, Patent Document 1 discloses a method of applying a voltage to a spiral shaft. However, this method is intended to stabilize the inside of the developing device (for example, toner supply) by providing a potential difference in the longitudinal direction of the spiral to improve the transportability of charged toner, and to positively charge the toner. is not. That is, there is a limit to the chargeability of the toner as in the conventional method.

Japanese Patent Application Laid-Open No. 07-5760

  SUMMARY OF THE INVENTION An object of the present invention is to provide a developing device that can positively discharge toner in a developing device, and can positively charge the toner not only by frictional charging of the sleeve and the regulating member but also by another means. That is.

  As a result of intensive research to solve the above problems, the inventors of the present invention arranged one electrode using a conductive member on the shaft of the toner stirring member, and arranged the other electrode facing the inside of the developing device housing. Thus, the inventors have newly found that by applying a bias voltage to the metal shaft of the stirring member, a discharge occurs between the counter electrode and the toner can be charged, and the present invention has been completed.

That is, the developing device of the present invention has the following configuration.
(1) A developing device including a toner stirring and conveying unit having a stirring member including at least a spiral or a paddle, wherein the shaft of the stirring member is one electrode, and the other electrode is disposed on the opposite developing device housing side. A developing device, comprising: a voltage applying means for applying a bias voltage between the electrodes.
(2) The developing device according to (1), wherein the bias voltage is a DC voltage.
(3) The developing device according to (1), wherein the bias voltage is an AC voltage.
(4) The developing device according to (1), wherein the bias voltage superimposes an AC voltage on a DC voltage.
(5) The developing device according to any one of (1) to (4), wherein the bias voltage is controlled according to an environment.
(6) The developing device according to any one of (1) to (5), which is a one-component developing device.

  According to the developing device of the present invention, it is possible to maintain toner charging properly even when the environment changes, and it is possible to obtain a developing device free from image defects such as image density reduction and tailing.

  The developing device according to the present invention will be described below with reference to the drawings. A developing device according to an embodiment of the present invention is a developing device using a magnetic one-component developing system, FIG. 1 is a longitudinal sectional view of the developing device according to an embodiment of the present invention, and FIG. 2 is a plan view of FIG. Indicates.

  The developing device 20 according to this embodiment has a developer carrier 8 (development roller or the like) disposed to face an electrostatic latent image carrier (not shown), and behind the development roller 8. Are provided with spirals 1 and 2 for conveying the first and second toners. These are accommodated in the developing housing 6.

  The first and second spirals 1 and 2 are a rotating shaft 3 (hereinafter also referred to as a metal shaft 3), a rotating shaft 4, and a toner stirring blade 33 formed in a spiral shape on the outer peripheral surface of the rotating shafts 3 and 4, 44, and are installed substantially in parallel via the partition wall 15.

  Then, the first spiral 1 conveys the magnetic one-component toner 10 from the right side to the left side in FIG. The toner 10 conveyed to the left side of the developing device in FIG. 2 passes through an opening (not shown) formed at one end of a partition wall 15 that partitions the first and second spirals 1 and 2, and then passes through the second. It is conveyed to the spiral 2 chamber. Next, the toner 10 is conveyed from the left side to the right side by the second spiral 2 and a part of the toner 10 is sent to the developing roller 8. The toner 10 conveyed to the right side in FIG. 2 repeats a cycle of being conveyed to the chamber of the first spiral 1 through an opening (not shown) formed at one end of the partition wall 15.

  Seal members 24 and 24 are attached to both ends of the developing roller 8, and the toner 10 forms a thin toner layer on the developing roller 8 by the magnetic force and the restriction of the restriction member 5. Further, on the inner surface of the developing housing 6, a sealing material that also serves as the regulating member 5 is attached so that the toner 10 does not scatter over the developing roller 8. In FIG. 2, reference numeral 14 denotes a drive box of the developing device.

  In the first and second spirals 1 and 2, the rotary shafts 3 and 4 and the toner stirring blades 33 and 44 may be integrally formed, or may be separate members. Each of the toner stirring blades 33 is made of a conductive member, and the rotating shaft 3 is supported on the developing housing 6 by an insulating bearing member.

  Normally, the toner 10 is charged only by frictional charging between the sleeve of the developing roller 8 and the regulating member 5. However, when the ease of frictional charging of the toner 10 varies due to environmental fluctuations such as temperature and humidity, the image density is increased. There is a problem that problems such as lowering and tailing occur.

Therefore, in the developing device 20 of the present invention, not only frictional charging of the sleeve of the developing roller 8 and the regulating member 5 but also another charging means is provided by positively discharging current in the developing device 20 to provide toner. 10 can be charged.
That is, as shown in FIG. 1, a power source of electromotive force E (positive polarity) is attached to the metal shaft 3 of the spiral 1 of the present invention, and the voltage of the electromotive force E (positive polarity) is set by a switch (Sw). Can be applied. More specifically, a direct current bias and an alternating current bias are connected to the metal shaft 3 of the spiral 1 and a bias in which alternating current is superimposed on the direct current between the opposing electrode 7 connected to the GND of the developing device 20 main body. To work. The AC component supplied by this AC bias is composed of a rectangular wave with a duty ratio of 50% or less. The switch is electrically connected to a control circuit (not shown) that controls ON / OFF of voltage application. The opposed electrodes 7 are preferably provided inside the developing housing 6 and preferably as far away from the developing roller 8 as possible. As a result, a stably charged toner 10 is obtained.

  When the temperature and humidity inside the developing device 20 exceed predetermined values, the control circuit applies a positive voltage to the spiral 1 when the toner 10 has the same polarity, that is, when the toner 10 is positively charged. The same voltage is also applied when the number of printed sheets exceeds a predetermined value. By applying a voltage having the same polarity as that of the conveying toner 10 to the spiral 1, an effect of maintaining the charge amount of the magnetic toner 10 appropriately appears. Specifically, the spiral 1 (the rotating shaft 3 and the toner stirring blade 33) is made of a conductive member such as SUS (stainless steel) or aluminum, and the toner with respect to the potential of the developing device 20 and the toner 10 in the developing device 20 is expressed. Preferably, a voltage having the same polarity as 10 is applied at a DC bias of 100 to 150 V or an AC bias of about 0.5 to 3 KV. The DC bias and AC bias can be applied simultaneously.

FIG. 3 shows an example of a flowchart for controlling the ON / OFF timing of the voltage application. As shown in FIG. 3, at the start of the image forming operation, voltage application to the spiral 1 is turned off, and the temperature and humidity in the developing device 20 are measured by a temperature / humidity sensor or the like. When the temperature Tm is 30 to 40 ° C. or higher and the humidity Hm is 75 to 85% or higher, a control circuit that receives a signal from a temperature / humidity sensor (not shown) applies voltage to the spiral 1 for T ₁ (min). Thereafter, the voltage application is turned off. If the voltage is continuously applied, the charge amount becomes excessive. Therefore, the voltage is not applied for T0 minutes after the previous voltage application.

Further, in addition to the measurement of the temperature Tm and the humidity Hm, the number of printed sheets A (sheets) may be measured, and the voltage may be applied when the number of sheets is equal to or greater than a predetermined range. That is, as shown in FIG. 3, when the number of printed sheets is A or more, the control circuit that receives a signal from the number-of-sheets measuring means (not shown) applies voltage to the spiral 1 for T ₁ time, and then the voltage Turn off the application. The voltage application may be controlled by replacing the number A of printed sheets with the printing time Tp (minutes). That is, when the predetermined printing time Tp is exceeded, the voltage may be applied. After the voltage application, when the application is turned off, the number A of prints or the print time Tp is reset and measured again, and the control is performed by repeating the operation.

The voltage application time T ₁ is 0.1 to 5 minutes, preferably 0.5 to 3 minutes. The elapsed time T0 after voltage application is preferably 5 to 30 minutes. The temperature Tm and the humidity Hm are preferably set such that Tm is 30 to 40 ° C. and Hm is 75 to 90%. The number of prints A is preferably set to 500 to 2000, and the printing time Tp is preferably set to 1 to 10 minutes.

(Developer)
As the developer according to the present invention, both a magnetic one-component developer and a two-component developer can be used. A magnetic one-component developer is preferred. The magnetic one-component toner 10 can be obtained by adding magnetic powder, a release agent, a colorant, and a charge control agent to a predetermined amount of a binder resin, and stirring and mixing them with a mixing device such as a Henschel mixer. The mixture obtained by stirring and mixing is melt-kneaded with a twin screw extruder or the like, cooled, and then pulverized with a pulverizer such as a hammer mill or a jet mill. Next, after classification using a classifier such as an air classifier, toner particles having a predetermined particle diameter are obtained. Next, the obtained toner particles can be manufactured by adding a predetermined amount of the external additive and stirring and mixing with a mixing device such as a Henschel mixer.
The binder resin, magnetic powder, release agent, colorant, and charge control agent are not particularly limited, and those conventionally used can be used.

  Further, in the magnetic one-component toner 10, 0.5 wt% or more, preferably 0.5 to 2.0 wt% of silica as an external additive is added to the toner particles, or 1.0 to 1.0 wt% of metal oxide. It is preferable to add at least wt%, preferably 1.0 to 3.0 wt%. Thereby, the charge-up of the toner can be alleviated, and the adhesion of the toner 10 to the spirals 1 and 2 is reduced.

(External additive)
Examples of the external additive include silica described above. Along with silica, for example, titanium oxide, alumina or the like may be used as the metal oxide. Examples of the silica powder include Aerosil RA200H, NAY200, NA50H, R972, R974, 90, Silica D-17, T-805, R-812, RA200, HRX-C manufactured by Nippon Aerosil Co., Ltd .; TG820F, TG824F manufactured by Cabot Corporation Cab-o-SilM-5, MS-7, MS-75, HS-5, EH-5, S-17, TS-72; KE-E30 and KE-E40 manufactured by Nippon Shokubai Co., Ltd.
Among the silicas, hydrophobic silica is preferable, and the hydrophobic silica is mixed with silica in a solvent such as toluene, and a silane coupling agent and / or silicone oil for hydrophobizing is added thereto. Stirring while irradiating with ultrasonic waves, and then distilling off the solvent, the solid material obtained is dried and heat-treated to form a powder, which is pulverized with a pulverizer such as a jet mill to obtain a desired volume standard. It can be obtained as a powder having a particle size distribution.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further in detail, this invention is not limited only to a following example.

[Example 1]
A magnetic one-component toner 10 as a developer was produced by the following method. First, polyester resin X (glass transition point: 60 ° C., softening point: 150 ° C., acid value: 7.0, gel fraction: 30%) 30 parts by weight, polyester resin Y (glass transition point: 50 ° C., softening point) : 100 ° C., acid value: 4.0, gel fraction: none) 70 parts by weight, magnetic powder 75 parts by weight, charge control component 3 parts by weight, charge control resin 8 parts by weight, and wax component 3 parts by weight Mix with a mixer. This was kneaded with a twin screw extruder and then coarsely pulverized with a feather mill. Thereafter, the mixture was finely pulverized with a turbo mill and classified with an airflow classifier to obtain toner particles having an average particle size of 8.0 μm. To 100 parts by weight of the obtained toner particles, 0.4% by weight of silica and 0.8% by weight of titanium oxide were mixed with a Henschel mixer to obtain a magnetic one-component toner. The initial toner amount was 180 g.
Using the toner 10 thus obtained, the developing device 20 having the structure shown in FIGS. 1 and 2 was set in an electrophotographic tester, and a voltage test was performed on the spiral 1 using the control shown in FIG. The voltage application conditions and the print test pattern are as follows.
(1) Voltage application condition Vdc = 150V
Vpp = 1.5KV
Duty ratio = 40%
Frequency = 5kHz
T0 = 5 minutes T1 = 1 minute where Vdc is a DC bias and Vpp is a peak AC bias.
(2) Print test pattern 0 to 50,000 sheets; A4 6% original document 80 sheets / minute (continuous printing)

[Comparative Example 1]
A printing experiment was performed under the same conditions as in Example 1 except that the voltage was not applied to the spiral 1.

表１に示すように、実施例１については、良好な画像濃度が得られたが、比較例１については、電圧印加がなかったためトナーは適正な帯電量を保つことができず、画像濃度の低下がみられた。 (Evaluation test)
Using the electrophotographic tester, the image density was evaluated under the conditions of either Example 1 or Comparative Example 1. First, 1000 sheets were printed under the above-mentioned printing test pattern conditions in a temperature of 35 ° C. and a humidity of 60%. Thereafter, after passing for 12 hours in an environment of temperature 35 ° C. and humidity 85%, the first sheet was output. Then, the image density was evaluated by comparing the 1000th image after printing 1000 sheets with the first image after 12 hours.
Evaluation was performed based on the following measurement methods and evaluation criteria, and the results are shown in Table 1.
The image density was measured using a spectroeye reflection densitometer manufactured by Gretag Macbeth. The determination criteria were ◯ when the image density was maintained at the same density as compared to an image at a temperature of 35 ° C. and a humidity of 60%, and x when the density was lowered.

As shown in Table 1, a good image density was obtained for Example 1, but in Comparative Example 1, the toner could not maintain an appropriate charge amount because no voltage was applied, and the image density A decrease was observed.

  As described above, by applying a predetermined voltage to the spiral for stirring the toner under a predetermined condition, the toner can maintain a sufficient charge amount even when the environment changes, and image defects such as a decrease in image density and tailing can be prevented. I understand.

1 is a schematic longitudinal sectional view of a developing device according to an embodiment of the present invention. FIG. 2 is a schematic plan view of FIG. 1. It is a flowchart which shows an example of the voltage application control concerning this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Spiral 2 Spiral 3 Metal shaft 5 Regulating member 6 Developing device housing 7 Counter electrode 8 Developing roller 10 Toner 20 Developing device

Claims (6)

  A developing device including a toner stirring and conveying unit having a stirring member including at least a spiral or a paddle, wherein the shaft of the stirring member is one electrode, and the other electrode is disposed on the opposite developing device housing side, A developing device comprising voltage applying means for applying a bias voltage between the electrodes.   The developing device according to claim 1, wherein the bias voltage is a DC voltage.   The developing device according to claim 1, wherein the bias voltage is an AC voltage.   The developing device according to claim 1, wherein the bias voltage superimposes an AC voltage on a DC voltage.   The developing device according to claim 1, wherein the bias voltage is controlled according to an environment. 6. The developing device according to claim 1, wherein the developing device is a one-component developing device.

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