JP2007093698A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain and provide a developing device using two-component system for maintaining an initial image quality for over a long term with simple structure. <P>SOLUTION: The developing device includes: a developing container which develops an electrostatic latent image formed on an image carrier, stores developer containing toner and a magnetic carrier and is comprised of a development chamber and a stirring chamber; a developer carrier installed in the development chamber and rorating opposite to the image carrier; a first stirring member provided inside the development chamber; and a second stirring member provided inside the stirring chamber in order to stir/convey the developer. Further, a ventilation member comprised of a member which prevents leak of the developer while permitting passage of the air between the inside and the outside of the developing device is provided at a part of a member forming a stirring chamber which contacts the developer stored in the stirring chamber. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using an electrophotographic method employed in a copying machine, a printer, a fax machine, and the like, and more particularly to a two-component developing apparatus that uses a mixture of nonmagnetic toner and magnetic carrier. is there.

  In a conventional electrophotographic image forming apparatus, particularly an image forming apparatus that forms a chromatic image, a friction between a magnetic carrier and a magnetic carrier is required to visualize an electrostatic latent image on an image carrier. A two-component development system using a developer obtained by mixing a nonmagnetic toner adhering to a charge in a certain ratio is widely used.

  In the two-component development system, the developer in the developing device is carried by a developing sleeve as a developer carrying member including a magnet, conveyed to a position facing the image carrying body, and magnetic at a position opposed to the image carrying body. A brush is formed to visualize (develop) the electrostatic latent image on the image carrier. By using such a two-component development method, it is possible to make a visible image faithfully (high image quality) with respect to the electrostatic latent image, and there are advantages such as excellent stability.

  In the above two-component development method, development is performed and the toner density of the developer injection in the developing device is lowered. For this purpose, the same amount of toner as that used for development is supplied to the developing device by the replenishing means, and is controlled so as to have a charge amount suitable for development by frictional charging by mixing and stirring with the magnetic carrier.

  Here, the toner concentration in the developing device is accurately detected in a timely manner using a developer concentration control device (ATR), and is controlled so that the toner concentration in the developing device is always constant. Various types of developer concentration control devices (ATR) have been put to practical use.

  For example, it is installed at a position close to the developer transport path in the developing sleeve or the developing device, and applies light to the developer transported on the developing sleeve or the developer in the developing device, and the reflection at that time There is a system (optical ATR system) that controls the toner density by utilizing the fact that the rate varies depending on the toner density.

  In addition, an inductance head is used that is disposed on the wall surface in the developing device in contact with the developer, detects an apparent magnetic permeability due to the mixing ratio of the magnetic carrier and the non-magnetic toner in the developing device, and converts this into an electric signal. There is a method (inductance ATR method) for controlling the toner concentration by utilizing the fact that the apparent permeability varies depending on the toner concentration.

  The patch image density formed on the image carrier is read by a light source provided at a position facing the surface and a sensor that receives the reflected light, and the read image density is converted into a digital signal by an analog-digital converter. When the image density is higher than the initial setting value, the toner supply is stopped until it returns to the initial setting value. When the image density is lower than the initial setting value, the toner is supplied until it returns to the initial setting value. As a result, there is a method in which the toner density is indirectly maintained at a desired value.

  Here, a general two-component developing device will be described with reference to FIG.

  In FIG. 1, a developing device 1 includes a developing container 2 that contains a developer, a developing sleeve 3 as a developer carrying member that is a rotating hollow cylinder, and a fixed arrangement in the developing sleeve 3 with respect to its rotation. The magnetic roller 4 serving as the magnetic field generating means, the agitating screws 2a and 2b as the agitating and conveying means for the developer installed in the developing container 2, and the developer sleeve 1 are disposed to form a thin layer on the surface of the developing sleeve 1. It comprises a regulating blade 7 as a developer layer thickness regulating member. A toner container 5 containing toner for replenishment is provided separately from the developing device 1, and the replenished toner is supplied from the toner container 5 to the developing device 1 through a toner replenishing port 6 provided above the developing device 1. To be replenished.

  A DC bias and an AC bias are applied to the developing sleeve 1 from a power source (not shown). In general, application of an AC bias increases development efficiency and develops the toner faithfully with respect to the electrostatic latent image on the image carrier, so that the image becomes high quality.

  Here, a developing process for developing the electrostatic latent image formed on the image carrier by the two-component developing method using the developing device 2 shown in FIGS. 1 and 2 and a developer circulation system. explain.

  First, the developer pumped up onto the developing sleeve 3 by the magnetic pole N1 with the rotation of the developing sleeve 3 is carried by the regulating blade 7 in an amount carried by the developing sleeve 3 in the process of being conveyed from the magnetic pole N1 to the magnetic pole S1. It is regulated and a thin layer is formed on the developing sleeve 3. Here, when the developer formed in a thin layer is transported to the magnetic pole S1, which is the main development pole, a spike is formed by the magnetic force. The electrostatic latent image is developed by the spike-shaped developer, and then the developer on the developing sleeve 3 is repelled by the repulsive magnetic field generated by the magnetic pole N1 and the magnetic pole N2 installed inside the developing container 2 of the magnet roller 4. And returned to the developing container 2.

  As described above, in the developing device based on the two-component developing method, by arranging the magnetic poles of the same polarity in the magnet 4 inside the developing sleeve 3 on the inner side of the developing container 2, the developer after development is temporarily removed from the developing sleeve. 3 is peeled off 3 and the previous image history is not left.

  In a developing device using a two-component system, it is desirable that the toner and the magnetic carrier are transported with good stirring. Accordingly, the developing chamber 3 is divided by a partition wall into a developing chamber for supplying the developer to the developing sleeve 3 and a stirring chamber for receiving the supply of replenished toner from the toner container 5, and screw-like stirring means 2a, It is common to use a biaxial stirring system in which 2b are arranged parallel to each other.

  As shown in FIG. 2, the toner density of the developer stored in the developing container 2 is detected by the toner density sensor 9, and as a result, necessary toner is supplied into the developing container 2 from the toner supply port 6. The replenished toner is agitated with the developer by the agitating means 2b in the agitating chamber and is conveyed in the direction of the arrow in the figure. Then, the developer is sent to the end of the agitating chamber and sent from the developer delivery portion provided between the agitating chamber and the developing chamber to the developing chamber. The developer sent to the developing chamber supplies a developer having an appropriate toner concentration, which has been replenished with toner, onto the developing sleeve 3 and returns the toner after image formation returned from the developing sleeve 3 to the developing container 2. The developer whose density has decreased is transported in the direction of the arrow in the figure, sent from the developer delivery section provided between the developing chamber and the stirring chamber to the stirring chamber, and transported to the toner concentration sensor 9 and the toner supply port 6. Then, the replenishment toner is supplied from the toner container 5.

  By configuring the circulation path as described above, the developer in the developing container 2 is repeatedly used for the developing action and maintains high quality and high stability.

  However, with the recent miniaturization of the image forming apparatus, the development apparatus 1 itself is required to be miniaturized, and it may be difficult to maintain the basic performance with the small development apparatus 1. Specifically, since the developing container 2 is downsized and the amount of developer stored in the developing container 2 is reduced, the replenished toner is not sufficiently stirred with the developer by the stirring members 2a and 2b. In some cases, the toner is conveyed as it is and supplied to the developing sleeve 3. At this time, since the replenishment toner is not sufficiently frictionally charged with the magnetic carrier in the developer, there is a possibility that the charge amount suitable for development has not been reached. In such a case, image problems such as image fog, density unevenness, and toner scattering may occur.

  As a method of solving this problem, there is a method of providing a large number of ribs on the rotating shaft core of the stirring member 2 as described in Patent Document 1, for example. The replenishment toner replenished into the agitation chamber from the toner replenishing port 6 is forcibly mixed and agitated with the developer by the rib provided on the rotating shaft core of the agitating member 2 to increase the number of times of contact with the magnetic carrier. Therefore, the charge amount suitable for development can be obtained. Thus, by changing the shape of the stirring member 2 and improving the mechanical stirring ability of the developer, the above-mentioned problems such as image fogging, density unevenness, and toner scattering can be solved.

However, in such a method for improving the mechanical stirring ability, an excessive load is applied to the developer, which may promote deterioration of the developer (particularly magnetic carrier). Examples of the deterioration of the magnetic carrier include adhesion of a toner resin and a toner external additive to the surface of the magnetic carrier and peeling of a coating material provided for charging the toner on the surface of the magnetic carrier. When such magnetic carrier deterioration progresses, the charge imparting ability of the magnetic carrier to the toner decreases, so it becomes difficult to load the replenishment toner with a charge amount suitable for development, and the number of images formed increases. As a result, image problems such as the above-mentioned image fogging, density unevenness, and toner scattering may occur.
JP 2004-272017 A

  While various market needs have been demanded due to the recent expansion of the full-color copying machine / printer market, many image forming apparatuses that pursue particularly high image quality and high stability have been commercialized. As the need for color imaging continues to expand, high image quality and high stability will be essential not only in the printing market but also in the general office market, and it is expected that the size of image forming apparatuses will be further reduced. Therefore, even in an image forming apparatus using the two-component developing system, even if the developing apparatus is downsized, the image has no sufficient image agitation, density unevenness, toner scattering, etc. It is necessary to maintain the level over a long period of time.

  Accordingly, an object of the present invention is to prevent image problems caused by insufficient toner charge amount by having a sufficient agitating ability of replenishment toner and developer even when the developing device is miniaturized, and developing agent It is to realize and provide a developing device using a two-component system with a simple configuration that prevents deterioration of the developer by not applying an excessive load to the image and maintains the initial image quality over a long period of time.

  In order to achieve the above object, the present invention develops an electrostatic latent image formed on an image carrier, contains a developer containing toner and a magnetic carrier, and comprises a developing chamber and a stirring chamber. A container, a developer carrier installed in the developing chamber and rotating to face the image carrier, and a first agitating member provided in the developing chamber for agitating / conveying the developer; And a second agitation member provided in the agitation chamber, wherein the developing device is formed on a part of the member that forms the agitation chamber in contact with the developer stored in the agitation chamber. A ventilation member comprising a member that prevents the developer from leaking while allowing air to pass between the inside and the outside of the apparatus is provided.

  According to the present invention, it is possible to maintain a sufficient stirring ability of the replenishment toner and the developer, and it is possible to prevent an image problem caused by insufficient toner charge amount and maintain an initial image quality over a long period of time. Can do.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

<Embodiment 1>
FIG. 7 shows a schematic configuration of the image forming apparatus according to the first embodiment of the present invention. The image forming apparatus 100 according to the first embodiment is an electrophotographic laser beam printer (printer) that employs a two-component contact development method. FIG. 5 is a diagram for explaining a developing device adopting the two-component developing system of the first embodiment.
(Entire printer configuration)
First, the overall configuration of the printer 100 according to the first embodiment will be described with reference to FIG.

  The printer 100 includes a rotating drum type electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”) as an image carrier. In the first embodiment, the photosensitive drum 27 is an organic photoconductor (OPC) having a negative charging property, and has a process speed (peripheral speed) of 100 mm / sec with an outer diameter of 30 mm and a center spindle. It is rotated in the counterclockwise direction indicated by the arrow.

  The surface of the photosensitive drum 27 is uniformly charged by the charging device 21. In the first embodiment, the charging device 21 employs a corona charging method. The corona charger 21 is mainly composed of a shield, a discharge wire, and a grid. As the discharge wire, a tungsten wire having a diameter of about 40 to 100 μm is used. A voltage (charging bias) applied to the discharge wire is 10 kV at the maximum and a current amount of about 1400 μA is applied to perform the discharge operation. As the grid, a conductive member (SUS304, 430) having a diameter of 50 to 200 μm is used. However, a metal conductive material having a specific pattern shape such as a mesh by edging may be used. By such a corona charger 21, the surface of the photoreceptor 27 is charged in a range of about 200 to 800V.

  On the photosensitive drum 27 whose surface is uniformly charged by the corona charging 21, an electrostatic latent image is formed by the exposure device 22 as information writing means in the next process. In the first embodiment, the exposure device 22 is a laser beam scanner using a semiconductor laser. The laser beam scanner 22 outputs a laser beam modulated in response to an image signal sent from a host processing device such as an image reading device (not shown) to the printer side, and is uniformly charged and rotated. The surface of the photosensitive drum 27 is subjected to laser scanning exposure (image exposure) at an exposure position (exposure portion). By this laser scanning exposure, the potential of the surface of the photosensitive drum 27 irradiated with the laser light is lowered, and electrostatic latent images corresponding to image information are sequentially formed on the surface of the rotating photosensitive drum 27. Go.

  The electrostatic latent image formed on the surface of the photosensitive drum 27 by the laser beam scanner 22 is visualized as a toner image by the developing device 1 in the next process. In the case of the first embodiment, toner adheres to the exposed bright portion of the surface of the photosensitive drum 1 and the electrostatic latent image is reversely developed. A detailed description of the two-component developing device used in the developing device 1 will be described later.

  The toner image on the surface of the photosensitive drum 27 visualized by the developing device 1 is transferred onto the recording material 30 by the transfer device 23 in the next step. In the first embodiment, the transfer device 23 is a transfer roller. The transfer roller 23 is pressed against the photosensitive drum 27 with a predetermined pressing force, and the press nip portion is a transfer portion. The recording material 30 is conveyed to the transfer portion by the recording material conveyance belt 24 at a predetermined control timing. The recording material 30 fed to the transfer unit is sandwiched between the rotating photosensitive drum 27 and the transfer roller 23, and the transfer roller 23 has a polarity opposite to the negative polarity that is the normal charging polarity of the toner. A positive transfer bias, +2 kV is applied in the first embodiment. As a result, the toner image on the surface of the photosensitive drum 27 is sequentially electrostatically transferred onto the surface of the recording material 30 that is conveyed by the recording material conveying belt 24 through the transfer portion.

  The recording material 30 that has received the transfer of the toner image through the transfer portion is conveyed to the fixing device 25 in the next process. In the first embodiment, the fixing device 25 is a heat roller fixing device, and the recording material 30 is subjected to toner image fixing processing by the fixing device 25 and is output as an image formed product (print, copy).

On the other hand, a toner image (so-called transfer residual toner) that is not transferred to the recording material 30 by the transfer device 23 and remains on the photosensitive drum 27 is a cleaning device that is disposed on the downstream side of the transfer device 23 in the rotational direction of the photosensitive drum 27. 26 is removed from the surface of the photosensitive drum 27. The first embodiment is a blade cleaning method in which a rubber blade made of plate-like urethane rubber is pressed against the photosensitive drum 27 with a predetermined pressing force. The photosensitive drum 27 from which the transfer residual toner has been completely removed from the surface by the cleaning device 26 is prepared for the next image formation starting from the charging device 21 described above.

(Developer)
Next, the developing device 1 will be described in detail with reference to FIG.

  The developing device 1 contains a two-component developer composed of a non-magnetic toner and a magnetic carrier, and the mixing ratio thereof is about 1: 9 by weight. This ratio should be appropriately adjusted according to the toner charge amount, the carrier particle size, the configuration of the printer 100, and the like, and does not necessarily follow this value.

  In the developing device 1, a developing area facing the photosensitive drum 27 is opened, and the developing sleeve 3 is rotatably arranged so as to be partially exposed to the opening. The developing sleeve 3 containing a fixed magnet 4 that is a magnetic field generating means is made of a non-magnetic material, and rotates during the developing operation, holds the developer in the developing container 2 in a layered form, and carries and transports it to the developing area. A developer is supplied to the developing area facing the drum 27, and the electrostatic latent image formed on the photosensitive drum 27 is developed with toner.

  The developer after developing the electrostatic latent image is conveyed according to the rotation of the developing sleeve 3 and collected in the developing container 2. The developing container 2 is divided into two chambers, a developing chamber having a developing sleeve 3 and an agitating chamber that receives toner supply from the toner replenishing port 6, both of which are spirals for agitating and conveying the developer. A stirring screw 2a and a stirring screw 2b. The developer collected by the stirring screws 2a and 2b circulates in the developing container 2 and is mixed and stirred again. In this embodiment, the developer circulation direction is the direction from the back side of FIG. 5 toward the near side on the stirring screw 2a side, and the direction from the near side to the far side of FIG. 5 on the stirring screw 2b side. Further, both the stirring screw 2a and the stirring screw 2b were those having a central axis diameter of 7 mm and an outer diameter of 14 mm.

  Next, the two-component developer used in this embodiment will be described.

The toner is composed of colored resin particles containing additives such as a binder resin, a colorant, other charge control agents, and wax. Then, as necessary for improving fluidity, adjusting the charge amount, etc., inorganic oxide fine particles such as colloidal silica and titania are externally added to the surface of the colored resin fine particles. In the toner according to the first exemplary embodiment, the binder resin is made of a polyester resin, the resistance value is about 10 ¹⁴ Ωcm, and the volume average particle diameter D ₄ is about 7.0 μm.

For the volume average particle diameter D ₄ of the toner, Coulter Counter TA-II type (manufactured by Coulter Inc.) is used. As a measuring method, 0.1 to 5 ml of a surfactant (preferably alkylbenzene sulfonate) is added as a dispersant to 100 to 150 ml of an electrolytic solution composed of 1% NaCl aqueous solution prepared using primary sodium chloride, and further measured. Add 2-20 mg of sample. The electrolyte solution in which the sample is suspended is dispersed for about 1 to 3 minutes with an ultrasonic disperser, and the volume distribution is measured by measuring the volume of toner of 2 μm or more using the Coulter Counter TA-II with a 100 μm aperture. And the median diameter of 50% volume is taken as the volume average particle diameter from the measurement results.

As the magnetic carrier, for example, metal such as surface oxidized or unoxidized iron, nickel, cobalt, manganese, chromium, rare earth and alloys thereof, or oxide ferrite can be preferably used. The production method is not particularly limited. The resistance value of the magnetic carrier in the first embodiment is 10 ¹⁰ Ωcm (10 ⁸ Ωcm to 10 ¹² Ωcm), the amount of magnetization is 200 emu / cc (100 emu / cc to 300 emu / cc), and the volume average particle diameter is About 30 μm.

  The volume average particle diameter of the magnetic carrier is measured by dividing the range of 0.5 to 350 μm on the basis of volume by 32 logarithm using a laser diffraction particle size distribution measuring device HEROS (manufactured by JEOL Ltd.). The number of particles is measured, and the median diameter of 50% volume is taken as the volume average particle diameter from the measurement results.

The resistance of the magnetic carrier is determined by using a sandwich type cell with a measuring electrode area of 10 cm ² and an inter-electrode spacing of 0.4 cm, applying a load of 1 kg to one electrode and applying an applied voltage E (V / cm between both electrodes). ) Was used to measure the resistance value of the magnetic carrier.

  Next, characteristic parts of the first embodiment will be described in detail.

  In order to improve the mixing / stirring property of powders such as replenishing toner and developer, there is a method of improving the mechanical stirring ability by providing ribs or the like on the stirring screw 2b as described above (see FIG. 9). . However, in this case, an excessive load may be applied to the developer, which causes deterioration of the developer, particularly the magnetic carrier.

  As another method for improving the mixing and stirring properties of the powder, there is a method in which an air flow such as air is poured into the powder. In general, it is known that, under the situation where an air flow exists in a powder, the adhesion force (cohesive force) between particles decreases due to the presence of air between the powders, and the powder behaves like a fluid. That is, when there is no airflow, the powder is in a solid state and aggregated due to the adhesion force (cohesive force) acting between the particles.

  Next, as the velocity of the airflow passing through the powder (so-called gas flow velocity) is increased, the adhesion force acting between the particles is reduced, and the powder becomes a fluid state. Furthermore, when the speed of the airflow passing through the powder (gas flow rate) is increased, a boiling state occurs in which large bubbles are generated in the powder, and the powder becomes non-uniform.

  From the above, it is considered that the fluidity of the powder, that is, the mixing / stirring property can be improved by creating a constant air flow so as to obtain an optimum gas flow rate in the powder.

  The above phenomenon is applied to the developing device 1 and considered.

  In the conventional developing device 1, the developer is stirred and conveyed by the stirring screw 2 b in the stirring chamber in which the developer supplied with toner is present. At this time, the developer is mechanically stirred and conveyed by the stirring screw 2b, and the developer surface moves up and down by the stirring screw 2b. Therefore, a part of the air in contact with the developer surface is brought into the developer. It is considered that an air flow having a weak gas flow rate is generated in the developer by taking in a little.

  Therefore, in the first embodiment, by controlling the airflow in the developing container 2, an airflow having a larger gas flow rate is generated in the developer than in the conventional developing device 1, and the developer agitation / mixing property is generated. Improved. Specifically, as shown in FIG. 5, a ventilation member 8 made of a porous material filter that does not allow toner particles to pass is provided on the side wall surface of the stirring chamber of the developing container 2 in contact with the developer.

  FIG. 6 shows the arrangement of the ventilation member 8 in the longitudinal direction in the developing container 2.

  The ventilation member 8 is located at a position upstream of the toner supply port 6 and upstream of the developer delivery portion in the agitation chamber and the development chamber with respect to the developer conveyance direction by the agitation screw 2b in the agitation chamber. It is arranged. The reason for the arrangement within this longitudinal range is to prevent the airflow from affecting the replenished toner replenished from the toner replenishing port 6 and the developer in the developing chamber (especially the developer carried on the developing sleeve 3) as much as possible. At the same time, it is for improving the mixing / stirring ability of the developer immediately after the replenished toner is replenished (the role required for the stirring screw 2b in the stirring chamber). Of course, as long as it is within this longitudinal range, the size and arrangement position of the ventilation member 8 in the longitudinal direction can be arbitrarily set.

  In the first embodiment, in order to further improve the mixing and stirring properties of the developer by the stirring screw 2b, the entire region 10 mm upstream of the developer delivery portion from the stirring chamber 10 to the developing chamber from the downstream 10 mm of the toner supply port 6 ( The ventilation member 8 was disposed at 160 mm).

  FIG. 8 shows the vertical arrangement of the ventilation member 8 in the developing container 2.

  The ventilation member 8 is disposed between a position below the upper end in the vertical direction of the blade of the stirring screw 2b and a position above the center of the rotation axis of the stirring screw 2b. The reason for the arrangement within this vertical range is as follows.

  That is, in FIG. 8, the developer surface moves up and down between the arrows due to the effect of the stirring screw 2b with respect to the developer surface when the stirring screw 2b is stationary. The role of the ventilation member 8 is to create an air flow in the developer stirred by the stirring screw 2b to take air into the developer and improve the fluidity of the developer, that is, the mixing / stirring property. This effect can be achieved by providing the ventilation member 8 in a place where the air gap moves greatly.

  In the first embodiment, the upper end of the ventilation member 8 is at the same vertical position as the upper end in the vertical direction of the stirring screw 2b blade, and the lower end of the ventilation member 8 is higher in the same vertical direction as the rotation shaft center of the stirring screw 2b. 7 mm in length was used.

  Next, the effect of the airflow in the developing container 2 and the airflow of the ventilation member 8 will be described.

  FIG. 3 shows the state of airflow in the conventional developing container 2.

  As the developing sleeve 3 rotates, air currents (F1 and F2) are generated around the developing sleeve 3. As the developing sleeve 3 rotates, an air flow F <b> 1 from the outside of the developing container 2 to the inside of the developing container 2 is formed, and air is taken into the developing container 2. A part of the air is exhausted to the outside of the developing container 2 by the air flow F <b> 2 from the inside of the developing container 2 that is formed along with the rotation of the developing sleeve 3 to the outside of the developing container 2.

  However, a part of the air taken in by the airflow F1 forms an airflow such as F3 and F4 in the cavity A in the developing container 2, and also increases the air pressure in the cavity A of the developing container 2. When the air pressure in the cavity A rises above a certain level, an air flow F2 having a larger gas flow rate than usual is formed to reduce the air pressure in the cavity A, and the air in the cavity A is exhausted to the outside of the developing container 2. Is done. Since the airflow formed at this time is very large, particularly when the speed of the image forming apparatus 100 is high, the toner in the developing container 2 may also be discharged out of the developing container 2 and the toner may be scattered. However, the air pressure in the cavity A increases slightly, so that the penetration of air into the developer slightly increases and the fluidity of the developer, that is, the mixing / stirring property is slightly improved, but the air pressure in the cavity A is unstable. In addition, problems such as toner scattering are significant.

  In order to solve the above problem, there is a method of providing a ventilation member 8 on a part of the upper surface of the developing container 2 as shown in FIG. By adopting such a method, when the air pressure in the cavity A increases due to the air taken into the cavity A of the developing container 2 by the airflow F1, the airflow F4 formed through the ventilation member 8 Since the developing container 2 can be evacuated from the inside to the outside, problems such as toner scattering that may occur in the developing device 1 of FIG. 3 described above can be prevented.

  From the state of the air flow inside the developing container 2 shown in FIGS. 3 and 4 described above, the air flow inside the developing container 2 is effectively used to improve the fluidity of the developer, that is, the mixing / stirring property. This is the developing device 1 shown in FIG. 5 which is the first embodiment described above. That is, by arranging the ventilation member 8 used in FIG. 4 on the side wall surface of the agitation chamber of the developing container 2 so as to be in contact with the developer, the air taken into the cavity A of the developing container 2 by the air flow F1 is ventilated. The air flow F4 formed through the member 8 allows the developer whose bulk density has become sparse by the stirring action of the stirring screw 2b to pass through and is discharged from the inside of the developing container 2 to the outside. As air passes through the developer in this manner, the air can be taken into the developer, and the fluidity of the developer, that is, the mixing / stirring property can be improved. It is possible to solve problems such as toner scattering that occur when the air pressure increases.

  Here, although there is a concern that the toner adheres to the filter surface forming the ventilation member 8 to cause clogging, as described above, the ventilation member 8 comes into contact with the developer stirred by the stirring screw 2b. Since the magnetic carrier in the developer attracts and collects the toner adhering to the filter surface by the electrostatic force, the ventilation member 8 can always maintain good air permeability.

  Further, when the gas flow rate of the airflow passing through the developer is too large, there is a concern that the toner carried on the surface of the magnetic carrier may be peeled off due to electrostatic force due to frictional charging with the magnetic carrier. As a result of measuring the adhesion force between the magnetic carrier and the toner used in the first embodiment by a centrifugal separation method, the adhesion force between the magnetic carriers is sub nN, and the adhesion force between the toners is several nN. The electrostatic adhesive force was several tens of nN, which is sufficiently larger than the former. For this reason, the gas flow velocity of the airflow passing through the developer generated in the first embodiment is sufficient to reduce the adhesion between the magnetic carriers and between the toners. It is thought that the power could not be weakened. Further, it is possible to achieve an optimum gas flow rate by adjusting the air permeability of the filter used for the ventilation member 8, that is, the pore diameter of the porous material.

  As a filter used for the ventilation member 8 used in the first embodiment, the base material is made of a woven fabric of polyester. A two-layer filter in which a porous film having a pore diameter of 0.1 to 1.0 μm was laminated on a substrate was used. As the base material, in addition to polyester, a woven fabric or a nonwoven fabric made of polypropylene or polyethylene terephthalate resin may be used.

  Next, the effect of the developer on the fluidity, that is, the mixing / stirring property when the developing device 1 of Embodiment 1 is used will be described.

  FIG. 10 shows a method for comparing the fluidity of the developer when the conventional developing device 1 is used and when the developing device according to the first embodiment is used, and the result. FIG. 10A is an explanatory diagram of a measurement method for repose angle, which is a general method for measuring the fluidity of powder.

  A funnel with a conical interior is installed above. This funnel used was used when measuring the fluidity of the powder from the flow speed (time) determined by JIS Z 2502. The opening diameter of this funnel is 2.63 mmφ, and the opening is temporarily closed with a finger to fill the developer to be measured so that it reaches the top of the funnel. A cylinder with a diameter of 16 mmφ is disposed 30 mm below the opening of the funnel so that the center of the opening of the funnel and the center thereof overlap. After the funnel is filled with the developer, the developer drops from the opening onto the upper surface of the lower cylinder by releasing the finger that closed the opening.

  The dropped developer forms a developer crest on the upper surface of the cylinder, and after the developer crest is formed over the upper surface of the cylinder, the developer crest becomes a steady state. At this time, the angle formed by the ridgeline of the developer peak and the upper surface of the cylinder (the bottom face of the developer peak) is the angle of repose, and a value with good reproducibility and accuracy is derived by measuring the angle after taking a picture from the side. it can. The angle of repose indicates that the smaller the angle, the better the fluidity of the powder. Further, as the developer for measuring the angle of repose, the developer sampled from the region B in FIG. 6 after stirring the developing device 1 (the developer immediately after passing through the transfer portion from the stirring chamber to the developing chamber) was used. . Incidentally, in the fluidity measurement obtained from the flow velocity defined in JIS Z 2502, the developer used in the first embodiment could not be measured with good reproducibility, so the method for measuring the angle of repose was selected. did.

  FIG. 10B shows the developer obtained by the above measurement method when using the conventional developing device 1 and the developer when using the developing device 1 according to the first embodiment, and the angle of repose of each. The measurement results are shown. The angle of repose of the developer when the conventional developing device 1 is used is about 50 °, whereas the angle of repose of the developer when the developing device 1 of the first embodiment is used is about 38 °. It can be seen that by using the developing device 1 used in the present embodiment, the fluidity of the developer, that is, the mixing / stirring property is improved.

  In FIG. 11, about 0.5 g of toner is replenished from the toner replenishing port 6, stirred and conveyed by the agitating screw 2 b in the agitating chamber in the developing device 1, and then passes through the developer delivery section and reaches the developing chamber. 7 is a measurement result obtained by measuring a toner charge amount distribution of the developed developer (B area in FIG. 6 where the developer was sampled at the time of repose angle measurement).

  The toner charge amount distribution was measured by using a Hosokawa Micron E-Spart Analyzer and measuring the toner charge amount and its frequency of 3000 toners. FIG. 11A shows the toner charge amount distribution result of the developer when the conventional developing device 1 is used, and FIG. 11B shows the developer when the developing device 1 of the first embodiment is used. It is a toner charge amount distribution result. The toner used in Embodiment 1 is negatively charged by being mixed with a magnetic carrier. When the conventional developing device 1 is used, since the replenishment toner is not sufficiently mixed and stirred with the magnetic carrier in the developer, there is a large amount of toner that is hardly charged (peak near 0 in the figure).

  On the other hand, when the developing device 1 of the present embodiment is used, there is a positively charged toner that is slightly opposite to the normal polarity, but it is charged as compared with the case where the conventional developing device 1 is used. The amount of toner is not significantly reduced. From this result, it can be seen that by using the developing device 1 used in the present embodiment, the fluidity of the developer, that is, the mixing / stirring property is improved.

  FIG. 12 shows the result of measurement of the number of toners charged to the reverse polarity that is considered to be the cause of image fog (positively charged toner in the case of the first embodiment). This result was obtained by data processing of the number of positively charged toners with a charge amount of 0 μC / g from the toner charge amount distribution data of FIG. When the conventional developing device 1 is used, the number of reversely charged toners is about 230, whereas when the developing device 1 of the present embodiment is used, the number of reversely charged toners is about 30. It is greatly reduced. From this result, it can be seen that by using the developing device 1 used in the present embodiment, the fluidity of the developer, that is, the mixing / stirring property is improved.

  FIG. 13 shows measurement results obtained by printing an entire white background image using the image forming apparatus 100 employing the conventional developing device 1 and the developing device 1 of Embodiment 1, and measuring the fog density.

  The fog density measurement results include two results when the initial developer is used and when the developer after printing 50k sheets is used. For the fog density measurement, REFLECTMETER MODEL TC-6DS manufactured by Tokyo Denshoku was used, and the fog density (%) was calculated from the difference between the whiteness of the printed white background image and the whiteness of the transfer paper. The fog density indicates that the smaller the value, the less the fog.

  First, when the initial developer is used, the fog density is about 0.75% when the conventional developing device 1 is used, whereas when the developing device 1 of the first embodiment is used. It can be seen that the fog density is reduced to about 0.4%. Next, when the developer after printing 50k sheets is used, the fog density is about 1.8% and the fog on the image is conspicuous when the conventional developing device 1 is used. When the developing device 1 was used, the fog density was about 0.8%, which was not a problem on the image at all. As can be seen from the results of FIGS. 10 to 12, the measurement result of the fog density is provided with the ventilation member 8 on the side wall surface of the stirring chamber of the first embodiment, and the air flow is supplied to the developer in the developing container 2. By passing the toner to improve the fluidity of the developer, the toner supplied from the toner supply port 6 is sufficiently mixed and stirred with the developer by the stirring screw 2b in the stirring chamber, and almost all the supplied toner is developed. It is shown that the toner is sufficiently charged up to a toner charge amount suitable for the above.

  As described above, even when the developing device is downsized by the image forming apparatus according to the first embodiment of the present invention, it is generated due to insufficient toner charge amount due to sufficient stirring ability of the replenishment toner and developer. A simple developing device using a two-component system that prevents image problems and prevents deterioration of the developer by not adding an extra load to the developer and maintains the initial image quality over a long period of time. It can be realized and provided with a configuration.

<Embodiment 2>
Next, a second embodiment of the present invention will be described.

  The basic configuration of the printer 100 of the second embodiment is the same as that of the first embodiment, and a detailed description thereof will be omitted. Characteristic portions of the present embodiment will be described below.

  In the second embodiment, a stirring screw 2b having a vent hole as shown in FIG. 14 is used instead of the vent member 8 used in the developing device 1 of the first embodiment. As shown in FIG. 14 (a), the stirring screw 2b has a hollow inside of the rotating shaft, and ensures air permeability between the hollow portion and the surface in contact with the developer in the stirring chamber. Therefore, a large number of ventilation holes of about 2 mmφ are provided. 14B is a cross-sectional view of the rotating shaft of the stirring screw 2b. The mold member 12a is provided with a vent hole in order from the outside, the filter 12b similar to that used in Embodiment 1, and the hollow portion. The configuration of 12c is adopted.

  The arrangement of the ventilation holes in the stirring screw 2b in the longitudinal direction is the same as the arrangement condition of the ventilation member 8 of the first embodiment, and from the position downstream of the toner replenishing port 6, the stirring chamber and the developing chamber are arranged. It is preferably provided at a position upstream of the developer delivery section. In the second embodiment, the rotating shaft of the stirring screw 2b corresponding to the same condition as in the first embodiment, that is, the region 10 mm upstream of the developer delivery portion from the stirring chamber 10 to the developing chamber from 10 mm downstream of the toner supply port 6. Vent holes were provided on the surface.

  The both ends of the agitating screw 2b are configured such that only the end on the side that receives rotational driving by a drive motor via a gear or the like is opened, and the airflow from the developing container 2 is the hollow portion 12c of the agitating screw 2b. And is exhausted to the outside of the developing device 1 from the end on the driving side.

  FIG. 15 shows the state of airflow in the developing container 2 used in the second embodiment.

  The air taken into the cavity A in the developing container 2 by the air flow F1 generated by the rotation of the developing sleeve 3 passes through the developer stirred by the stirring screw 2b, and is vented on the surface of the stirring screw 2b. An air flow F4 sent into the hole and the hollow portion 12c of the rotating shaft is formed, and is exhausted out of the developing device 1. Here, when compared with the developing device 1 of the first embodiment, in the first embodiment, the developer that receives the passage of air is limited to a region in contact with the side wall surface of the stirring chamber, whereas the second embodiment. Then, it is possible to pass through the entire developer stirred by the stirring screw 2b in the stirring chamber, and it is possible to further improve the fluidity of the developer, that is, the stirring / mixing property, as compared with the first embodiment.

  In order to confirm the effect of the second embodiment, the same measurement as that performed in the first embodiment is performed, and the results are shown in FIG. 10 (developer angle of repose), FIG. 13 (fogging density). It can be seen that a significant improvement can be seen in comparison with the conventional developing device 1 in each case, as well as a slight improvement in comparison with the case where the developing device 1 of the first embodiment is used.

  As described above, the image forming apparatus according to the second embodiment of the present invention provides a developing device using a two-component system that maintains the initial image quality over a long period of time with stability higher than that of the first embodiment. It becomes possible.

<Embodiment 3>
Next, a third embodiment of the present invention will be described.

  The basic configuration of the printer 100 according to the third embodiment is the same as that of the first and second embodiments, and a detailed description thereof will be omitted. Characteristic portions of the present embodiment will be described below.

  The image forming apparatus 100 and the developing apparatus 1 used in the third embodiment are shown in FIGS. 16 and 17, respectively.

  The third embodiment is characterized in that a stirring screw 2b having a cavity 12c similar to that in the second embodiment is used, and a ventilation member 8 is provided on the upper surface of the developing container 2. Here, a vent pipe 14 is attached to the drive side end of the agitating screw 2b, and is connected to the air supply device 13 (so-called compressor) via the vent pipe. That is, a configuration is adopted in which air is supplied from the air generator 13 to the stirring screw 2b through the vent pipe 14. The air supplied to the stirring screw 2b passes through the developer in the developing container 2 through a vent hole provided on the surface thereof, reaches the cavity A in the developing container 2, and then passes through the vent member 8 to the developing container 2. Exhausted to the outside. By adopting such a configuration, it becomes possible to generate an airflow passing through the developer more stably than in the first and second embodiments. The fluidity, that is, the stirring / mixing property can be further improved.

  Here, the gas flow rate of the air supplied by the air supply device 13 was about 0.2 cm / sec. The relationship between the gas flow rate and the flowability of the developer differs depending on, for example, the particle sizes of the toner and magnetic carrier constituting the developer, the diameter of the capillary formed when they contact each other, and the adhesion force acting between them. Depending on the type of developer, it is preferable to select a range in which the fluidity is most stably improved without any adverse effects (a range in which the above-described flow state can be stably realized).

  In order to confirm the effect of the third embodiment, the same measurement as that performed in the first and second embodiments is performed, and the results are shown in FIG. 10 (developer angle of repose) and FIG. FIG. 13 (fogging density) shows. It can be seen that, as compared with the conventional developing device 1, a significant improvement can be seen in each case, as well as a slight improvement as compared with the case where the developing devices 1 of the first and second embodiments are used.

  As described above, the image forming apparatus according to the third embodiment of the present invention uses the two-component developing device that maintains the initial image quality for a long time with the stability of the first and second embodiments. It becomes possible to provide.

It is a model figure which shows schematic structure of the conventional image development apparatus. It is an upper surface model figure which shows schematic structure of the conventional image development apparatus. It is a model figure which shows the flow of the airflow in the conventional developing device. It is a model diagram showing the flow of airflow in a conventional developing device in which a ventilation member is provided on the upper surface of the developing device. 1 is a model diagram illustrating a schematic configuration of a developing device according to a first embodiment of the present invention. FIG. 2 is a top model diagram illustrating a schematic configuration of the developing device according to the first embodiment of the present invention. 1 is a model diagram showing a schematic configuration of Embodiment 1 of an image forming apparatus according to the present invention. In the developing device of Embodiment 1 which concerns on this invention, it is a model figure which shows the height relationship of the stirring direction of a stirring screw, a developer surface, and a ventilation member in the perpendicular direction. It is a model figure which shows the rib provided on the stirring screw used in the conventional image development apparatus. The model of angle of repose measurement used for evaluating the fluidity of the developer, and the relationship diagram of the fluidity of each developing device and developer when using the conventional developing device and the developing device according to the embodiment of the present invention, respectively. is there. FIG. 6 is a relationship diagram of toner charge amount distribution in each developing device according to the conventional and the first embodiment of the present invention. FIG. 6 is a relationship diagram of the number of reversely charged toners in each developing device according to the related art and an embodiment of the present invention. It is a relational diagram of the fog density of the image output in the image forming apparatus using each developing device of the conventional and the embodiment according to the present invention. It is a model diagram which shows schematic structure of the stirring screw used with the image development apparatus of Embodiment 2 and 3 which concerns on this invention. It is a model figure which shows schematic structure of Embodiment 2 of the developing device which concerns on this invention. It is a model figure which shows schematic structure of Embodiment 3 of the image forming apparatus which concerns on this invention. It is a model figure which shows schematic structure of Embodiment 3 of the developing device which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Developing device 2 Developing container 2a Stirring screw 2b Stirring screw 3 Developing sleeve 4 Developing magnet 5 Replenishing toner container 6 Toner replenishing port 7 Development regulating blade 8 Venting member 9 Toner concentration sensor 10 Stirring blade 11 Rib 12 Stirring screw rotating shaft 13 Air supply Device 14 Vent pipe

Claims (7)

A developing container that is composed of a developing chamber and a stirring chamber that develops an electrostatic latent image formed on the image carrier, contains a developer containing toner and a magnetic carrier, and is installed in the developing chamber. A developer carrier that rotates opposite to the image carrier, a first stirring member provided in the developing chamber for stirring / conveying the developer, and a first stirring member provided in the stirring chamber. A developing device having two stirring members,
Prevent leakage of the developer while allowing passage of air between the inside and the outside of the developing device in a part of the member forming the stirring chamber that comes into contact with the developer stored in the stirring chamber An image forming apparatus comprising a ventilation member made of a member.   The image forming apparatus according to claim 1, wherein a part of a side wall surface of the stirring chamber that comes into contact with the developer is formed of the ventilation member.   The vertical upper end of the ventilation member provided on the side wall surface of the stirring chamber is equal to or lower than the height of the vertical upper end of the stirring blade provided in the second stirring member. The image forming apparatus according to 1 or 2.   The vertical lower end portion of the ventilation member provided on the side wall surface of the stirring chamber is not less than the vertical height of the center of the rotation axis of the second stirring member. The image forming apparatus described in 1.   The longitudinal arrangement of the ventilation member provided on the side wall surface of the stirring chamber is downstream of the toner replenishment site provided in the stirring chamber in the transport direction of the developer by the second stirring member, The image forming apparatus according to claim 1, wherein the image forming apparatus is upstream of a portion where the developer is transferred from the stirring chamber to the developing chamber.   The rotating shaft of the second stirring member provided in the stirring chamber is formed of a hollow member, and a part of the rotating shaft that is in contact with the developer is formed of a member that can vent the hollow portion of the rotating shaft. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 6, wherein air having a constant gas flow rate is supplied by an air supply device to the second agitating member formed of a member having a hollow rotating shaft and capable of passing air.

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