JPH083682B2 - Development device - Google Patents

Description

Detailed Description of the Invention

The present invention relates to a developing device used in an image forming apparatus such as a copying machine. (Background of the Invention) Conventionally, as one mode of the phenomenon device, a developing sleeve including a plurality of magnets having magnetic poles extending in an axial direction and a toner supply roller adjacent to the developing sleeve are provided on the peripheral surface of the developing sleeve. At the same time, a two-component developer composed of a carrier and toner is adjusted, and the developer is conveyed to a portion facing the electrostatic latent image carrier while being held in a magnetic brush state by the magnetic force of the magnetic roller, It has been proposed to form a toner image corresponding to an electrostatic latent image on an electrostatic latent image carrier. In this type of developing device, it is necessary to supply toner to the developing sleeve in an amount commensurate with the amount of toner consumed and to keep the toner concentration in the developer constant. By scraping off the toner held on the developing sleeve, an amount of toner commensurate with the amount consumed in development is supplied to the developing sleeve,
A DC bias voltage is applied to each of the toner supply rollers, and the amount of toner supplied onto the developing sleeve is regulated based on the potential difference between the two.
Proposed in 1664 publication. However, with this one, for example, 0 per sheet.
When continuously copying a solid black solid image consuming 2 g of toner, the developer concentration on the developing sleeve was 8.0 wt% at the start of copying, as shown by the dotted line in FIG. When the copying was completed, it decreased to 2.0% by weight, and even after switching to the white solid copying, the recovery of the developer concentration was remarkably slow and the responsiveness was poor. Therefore, in order to eliminate the above-mentioned drawbacks, the present inventors have
First of all, many experiments were conducted to investigate the cause. As a result, when DC voltage is applied to the developing sleeve and the toner supply roller as in the conventional developing device, most of the toner adhering to the surface of the toner supply roller is loaded, and It has a strong electrostatic attraction with the supply roller and is hard to be scraped off by the magnetic brush on the sleeve. Therefore, the toner supplied onto the sleeve is only the toner having a small charge amount, and the supply efficiency is lowered. Furthermore, since most of the replenishment toner is toner with a poor load, fog is likely to occur. Therefore, if an AC voltage is superimposed on the toner supply roller in addition to a DC voltage, the toner vibrates in accordance with the periodic change of the voltage, and the electrostatic attraction between the toner and the toner supply roller is weakened. As described below, the toner supply amount from the toner supply roller to the developing sleeve and the toner recovery amount from the developing sleeve to the toner supply roller are changed in three cases by changing the combination of the voltages applied to the developing sleeve and the toner supply roller. A comparative experiment was performed.

[Experimental conditions]

As experimental conditions, the voltages shown in the following table were applied to the developing sleeve and the toner supply roller. In the table, DC indicates direct current and AC indicates alternating current. Especially, only in the toner supply roller of Experimental Example 3, direct current -400V, alternating current 700V.
Are superimposed, and the frequency of this alternating current is 200 Hz.

[Measurement Method] Under the above experimental conditions, the toner supply amount is measured in a non-developed state, that is, in a state where the toner on the developing sleeve is not consumed, for a predetermined time (1 second), the developing sleeve and the toner supply roller are After driving, the amount of toner supplied onto the developing sleeve was measured for each toner concentration. On the contrary, the amount of toner collected is the amount of the toner held on the developing sleeve collected by the toner supply roller, and is measured by the same method as described above.

【Experimental result】

The amount of toner supplied and the amount of toner collected in each experimental example are shown in FIGS. 4 to 6. In the figure, the solid line indicates the toner supply amount and the dotted line indicates the toner recovery amount. As a result, as is clear from FIGS. 4 and 5 showing the results of Experimental Examples 1 and 2, if the voltage applied to the toner supply roller is simply changed from −400V to −300V, the toner supply amount , But the recovery amount decreases, the curve showing the supply amount and the recovery amount only shifts, and
/ s) is about 6wt% (= 8wt% -2wt)
%) To about 5 wt% (= 13 wt% -8 wt%), and it is apparent that the width is large and the responsiveness is poor. Also,
In the case of the experimental example 2 shown in FIG. 5, the toner concentration (about 13 wt%) in which the toner supply amount and the recovery amount are balanced is larger than that in the experimental example 1 shown in FIG. 1 (about 8 wt%). Therefore, there was a phenomenon that the quality of the copy deteriorated due to fogging of the copied image. On the other hand, according to FIG. 6 showing the result of Experimental Example 3 in which the AC voltage is superposed on the toner supply roller, the control width for the predetermined consumption amount (0.2 g / s) is about 2 wt% and The concentration that balances the amount with the recovered amount is about 8w
Since it could be maintained at t%, it was possible to obtain a good-quality copy without fog. That is, from the above experimental results, a bias voltage in which an AC voltage is superimposed on a DC voltage applied to the toner supply roller is applied, and a DC component and an AC component are superimposed between the developing sleeve and the toner supply roller. If an alternating electric field is formed, the toner concentration will not decrease much even if images with large toner consumption are copied continuously, and the recovery will be quick.
Moreover, they have found that it is possible to obtain a good quality copy without fog. (Means for Solving Problems) The present invention has been made on the basis of the above-mentioned findings. A developing sleeve having a plurality of magnets and a toner supply roller are provided in a developing tank, and a magnetic field is formed on the developing sleeve. By supplying toner to the adsorbed magnetic carrier with the toner supply roller, a developer consisting of a mixture of carrier and toner is adjusted around the developing sleeve, and this developer is used for electrostatic discharge. In a developing device for developing an electrostatic latent image on a latent image carrier, a bias voltage in which an alternating current is superimposed on a direct current is applied to the toner supply roller, and a direct current is applied between the developing sleeve and the toner supply roller. An alternating electric field in which the component and the AC component are superposed is formed. (Operation) In the developing device having the above-described configuration, since the alternating electric field in which the direct current component and the alternating current component are superposed is formed between the developing sleeve and the toner supply roller, the toner is changed according to the time-varying electric field. The weighted toner held on the surface of the supply roller vibrates between the toner supply roller and the developing sleeve, comes into contact with the magnetic brush of the developing sleeve, and is more likely to be scraped by the magnetic brush. On the other hand, since the electrostatic attraction of the toner electrostatically attracted to the carrier of the magnetic brush is weakened, the efficiency of collecting the toner to the toner supply roller is increased. (Example) Hereinafter, the present invention will be described with reference to the drawings as an example. FIG. 1 shows a developing section of a copying machine equipped with a developing device (1) according to the present invention. The developing device (1) is a photosensitive drum (10).
0), which supplies toner to the electrostatic latent image of the copy image formed by charging and exposing the surface of the photoconductor drum (100) and visualizes it. Is what you do. The developing device (1) generally includes a developing sleeve (4) in a developing tank (2) composed of a casing (3) and a cover (3a) from the photosensitive drum (100) side to the right in order. ), A toner supply roller (12) is arranged, and a toner storage tank (22) is formed behind the toner supply roller (12). The developing sleeve (4) is a cylindrical body made of a conductive non-magnetic material such as aluminum. The surface of the developing sleeve (4) has minute recesses formed by blasting. The photosensitive drum (4) is driven to rotate in the direction of arrow (a). 100) and a developing gap (Ds), and can be rotated in the counterclockwise direction [arrow (b) direction]. A DC developing bias power source (5) (developing bias voltage: Vb) is connected between the developing sleeve (4) and the ground, and the negative side of the developing bias power source (5) is connected to the developing sleeve (4). As a result, a negative charge is stored on the surface of the developing sleeve (4). The magnetic roller (6) housed inside the developing sleeve (4) has a plurality of magnets whose magnetic poles are extended in the axial direction, and the magnetic poles are arranged so that the magnetic poles are alternately located at the S pole and the N pole at the outer peripheral portion. It is fixed in the state shown in FIG. A main developer stirring plate (7) attached to the cover (3a) faces the developing sleeve (4) above the photosensitive drum (100) side with a spike height regulating gap (Db). Also,
The auxiliary developer stirring plate (9) attached to the support portion (8) of the cover (3a) faces the diagonally upper right of the developing sleeve (4), and together with the main developer stirring plate (7), An empty chamber (11) is formed above the developing sleeve (4). A slit (10) is formed on the auxiliary developer stirring plate (9) in the axial direction of the developing sleeve (4). The toner supply roller (12) is made of a conductive non-magnetic material such as aluminum, has a minute recess formed on the surface thereof, and has a supply gap (Ds) on the back side of the developing sleeve (4).
s) are arranged in parallel and can be driven to rotate in the direction of arrow (c). In addition, this toner supply roller (12) is
3) It is grounded via a DC power source (14), and as a result, a pulsating recovery bias voltage in which AC is superimposed on DC is applied to the toner supply roller (12). That is, an alternating electric field in which a DC component and an AC component are superposed is formed between the developing sleeve (4) and the toner supply roller (12). Above the rear side of the toner supply roller (12), a partition (1
5) is mounted so that it can rotate around the support shaft (16),
The other end of a pressure contact spring (17) having one end attached to the upper rear end of the developing tank (3) is locked to its upper end, and the partition wall (15) is constantly urged in the direction of arrow (e). ing. As a result, the metal blade (18) attached to the lower part of the partition wall (15) is in light contact. In addition, the metal blade (18) and the auxiliary developer stirring plate (9) are connected by a sheet (19).
An empty chamber (20) is formed above the toner supply roller (12). Below the toner supply roller (12), a toner return prevention film (21) attached to the casing (3) is provided.
Are pressed along the rotation direction of the toner supply roller (12). The toner storage tank (22) is formed by partitioning the rear part of the developing tank (3) by the partition wall (15), the metal blade (18), the toner supply roller (12), and the toner return prevention film (21). A stirring rod (23) is attached to the inside of the toner storage tank (22) so as to be rotatable in the direction of the arrow (d). The operation of the developing device having the above configuration will be described. First, a starter made of a mixture of a negatively chargeable magnetic carrier and a positively chargeable insulating toner is loaded in the chamber (11) above the developing sleeve (4) and the toner supply roller (12), and the toner storage tank ( 22) Insulate the above-mentioned insulating toner. At this time, only the magnetic carrier may be loaded in the vacant chamber (11) instead of the starter. This enables the developing device (1) to develop the electrostatic latent image. When a print switch (not shown) is turned on in this state, the developing sleeve (4), the toner supply roller (12) and the stirring rod (23) rotate in the directions of arrows (b), (c) and (d), respectively. As the developing device (1) operates as described above, the toner flows toward the toner supply roller (12) by the stirring action of the stirring rod (23) at the bottom portion of the toner storage tank (22), and the toner supply roller (12). It is taken in and filled in the minute recesses on the surface of (12). The toner supplied to the toner supply roller (12) is transported in the direction of the arrow (c) and scraped off by the metal blade (18) to remove excess toner, and the toner is precharged due to the contact with the developing sleeve (4). It reaches the facing portion [toner supply area (Y)]. In the toner supply area (Y), the developing sleeve (4)
Toner is supplied to the developer held on the top,
Excess toner on the developing sleeve (4) is collected by the toner supply roller (12). The operation of supplying and collecting the toner will be described later in detail. The toner supplied to the developing sleeve (4) is carried in the direction of arrow (b) based on the rotation of the toner, together with the carrier held on the peripheral surface of the developing sleeve (4), and the auxiliary developer stirring plate (9). ) Blocks most of the developer. Then, the developer is pushed by the developer which will be conveyed later, warps up along the auxiliary developer stirring plate (9), passes through the slit (10), and is sent to the vacant chamber (11) on the downstream side. . The remaining developer passes through the gap between the auxiliary developer stirring plate (9) and the developing sleeve (4) and reaches the empty chamber (11) on the downstream side. The developer reaching the empty room (11) is stored in the main developer stirring plate (7).
It is blocked by, and along it, it rises while rotating counterclockwise in the vacant chamber (11), backflows and falls, and merges with the developer passing through the slit (10) and is mixed. . In this way, a part of the developer that has been sufficiently mixed and stirred passes through the spike height regulating gap (Db) between the main developer stirring plate (7) and the developing sleeve (4) to form a magnetic brush. The magnetic brush has a photosensitive drum (10
The surface of (0) is rubbed, and the electrostatic latent image on the surface is developed and visualized. After passing through the developing area (X), the developer remaining on the peripheral surface of the developing sleeve (4) continues to be the developing sleeve (4).
Is conveyed in the direction of the arrow (b) based on the rotation of the toner supply area (Y), which is a portion facing the toner supply roller (12).
The developing sleeve (4) and the toner supply roller (1
Toner supply and recovery operations are performed between 2). Then, when the toner supplied to the developing sleeve (4) reaches the empty chambers (20) and (11) again, the sufficiently mixed and stirred developer is uniformly replenished on the surface of the developing sleeve (4), The consumption pattern of the toner consumed in the previous development is erased. On the other hand, the toner collected by the toner supply roller (12) enters the minute concave portion, passes between the toner return prevention film (21) and the toner storage tank (2), and the toner is replenished in the minute concave portion again. To be done. Hereinafter, the operation of supplying and collecting the toner in the toner supply area (Y) will be described. In the toner supply area (Y), the developing sleeve (4)
In the above, the developer is connected in series along the magnetic field formed in the radial direction from the magnetic pole (N) of the magnetic roller (6) to form a magnetic brush. On the other hand, the surface minute recesses of the toner supply roller (12) are filled with toner, and in particular, the charged toner contained therein has a large electrostatic attraction with the toner supply roller due to its electrostatic force. . However, since an alternating electrolysis in which a DC component and an AC component are superposed is formed between the developing sleeve (4) and the toner supply roller (12), the charged toner is
The toner supply roller (12) vibrates on the surface of the toner supply roller (12) toward the developing sleeve (4) in accordance with the periodic change of the AC voltage (Vrms). For this reason, the toner and the magnetic brush frequently come into contact with each other, and not only the toner located on the surface of the minute concave portion but also the toner located on the bottom of the minute concave portion also comes into contact with the magnetic brush and the toner is removed by the magnetic brush. Can be scraped efficiently. On the other hand, on the developer sleeve (4), the excess toner that is in contact with the carrier and is positively charged is based on the bias voltage difference applied to the developing sleeve (4) and the toner supply roller (12). And is attracted electrically to the toner supply roller (12), and the attraction force acting there is also changed periodically under the influence of the AC power source (13), so excess toner weakens the electrostatic attraction with the carrier. The excess toner is easily peeled off, and excess toner is efficiently collected by the toner supply roller (12). As described above, between the developing sleeve (4) and the toner supply roller (12), the toner supply amount and the recovery amount are remarkably increased and the toner fluctuation width is reduced. The amount of toner conveyed is stable, and a copy image without density unevenness can be obtained. Then, the toner collected by the toner supply roller (12) enters the minute concave portion, and the toner return prevention film (21)
When it reaches the toner storage tank (2) through the space between and, the minute recesses are filled with the toner again. Experiment 1 Next, the developing device (1) having the above-mentioned configuration was set under the following conditions, and the developing sleeve (12) was obtained when 100 solid black copies and 100 continuous solid copies were copied.
The developer concentration above was measured.

[Experimental conditions]

 a.Development sleeve (4) ・ Diameter …… 24.5mm ・ Rotational speed …… 200rpm ・ Development bias voltage (Vb) …… DC-200V b. Toner supply roller (12) ・ Diameter …… 20mm ・ Rotational speed …… 200rpm・ Recovery bias voltage (Vss) …… DC-400V, AC700V ・ AC frequency …… 300Hz ・ Surface roughness …… 40μm ・ Small concave surface area …… 80% c. Gap ・ Development gap (Ds) …… 0.6mm ・Hot height control gap (Db) …… 0.45mm ・ Supply gap (Dss) …… 0.8mm d. Metal blade (12a) ・ Thickness …… t = 150μm ・ Pressing force …… 0.1g / mm

【Experimental result】

The result obtained from the above experiment is shown by the solid line in FIG. As is clear from this figure, the developer concentration on the developing sleeve (12) gradually decreased after the solid black copy was started, but the amount of the decrease was 8.0 wt% at 6.0% initially.
The difference is only 2.0 wt%, only decreasing to wt%. Then, when the white solid copy is switched to, the developer concentration relatively quickly recovers to the initial state (8.0 wt%). Comparing the above experimental results with the conventional one shown by the dotted line in FIG. 2, it can be seen that the amount of decrease in the developer concentration is very small, and the developer concentration recovery speed and recoverability are remarkably improved. Recognize. Experiment 2 Next, the correlation between the frequency of the AC power supply (13) and the toner concentration control width was determined by the voltage (Vrms) of the AC power supply (13).
Fig. 3 shows the experimental results of investigations with different values. As is clear from the figure, the voltage of the AC power supply (13) (Vrm
The higher s) is, the smaller the toner control width can be, and the minimum value of the toner control width is in the low frequency region. However, in the low frequency band below 20 Hz, the toner density control width sharply decreases. Therefore, it is understood that the present invention can be effectively implemented when the AC voltage (Vrms) is in a frequency band of 300 V or more and a frequency of 2 KHz to 20 Hz, that is, a range surrounded by a dotted line in the figure. Experiment 3 Next, the results of experiments on the method of applying the AC power source (13) are shown below. In the experiment, as shown in FIGS. 7 to 9, the AC power supply (13) was connected to the developing sleeve (4) and the toner supply roller (1).
Cases 2), 2), only the developing sleeve (4), and only the toner supply roller (12) according to the present invention. As a result, a good copy could be obtained in the case shown in FIG. 9, but when an AC power source (13) was applied to the developing sleeve (4) as shown in FIGS. The AC power supply (13) also acts between the sleeve (4) and the photoconductor drum (100), which causes fog on the copy image, uneven pitches corresponding to the frequency, and development of toner scattering, etc., resulting in copy quality. Has dropped. From the above, it is understood that the method of applying the AC power source (13) is best according to the present invention (FIG. 9). The AC power supply (13) may be a so-called sinusoidal AC power supply, or a non-sinusoidal AC power supply such as a pulse wave or a triangular wave, as long as it forms an alternating electric field. (Effects of the Invention) As is clear from the above description, the developing device according to the present invention includes the developing sleeve and the toner supply roller, and supplies the toner onto the developing sleeve by the toner supply roller and also the developing sleeve. A developer consisting of a carrier and toner is adjusted on the peripheral surface of the magnetic brush to form a magnetic brush, and the magnetic brush develops the electrostatic latent image formed on the surface of the electrostatic latent image carrier into a visible form. In the apparatus, a bias voltage in which alternating current is superimposed on direct current is applied to the toner supply roller,
An alternating electric field in which a DC component and an AC component are superposed is formed between the developing sleeve and the toner supply roller. Therefore, as a result of the attraction force for the toner varying as the temporal voltage of the AC power source varies, the probability of contact between the toner and the magnetic brush on the developing sleeve increases,
The efficiency of toner supply to the developing sleeve is improved, and the coupling force between the excess toner on the developing sleeve and the carrier is weakened, and the efficiency of toner recovery to the toner supply roller is improved. Therefore, the toner commensurate with the toner consumption amount can be immediately supplied to the developing sleeve, and the toner density reduction amount on the developing sleeve can be minimized even if the black solid copy with a large toner consumption amount is continuously performed. Can be suppressed. In addition, after the solid black copy is completed, even if you make a normal copy that consumes less toner, the toner density will recover faster,
It is possible to obtain a clear copy without uneven density fog.

[Brief description of drawings]

FIG. 1 is a sectional view of the developing device, FIG. 2 is a diagram showing a change in developer concentration on a developing sleeve when black solid and white solid copying are continuously performed, and FIG. FIG. 4 to FIG. 6 are diagrams showing the correlation with the toner concentration control width, FIG. 4 to FIG. 6 are diagrams showing the relation between the toner concentration and the toner replenishment / collection amount, and FIG. 7 to FIG. FIG. 1 ... Developing device, 2 ... Developing tank, 3 ... Casing, 4 ... Developing sleeve, 5 ... Developing bias power source, 6 ... Magnetic roller, 7 ... Main developer stirring plate, 8 ... Sub-developing Agent stirring plate, 12 ... Toner supply roller, 13 ... AC power supply, 14 ... DC power supply.

Front Page Continuation (72) Inventor Koichi Eto 2-30 Azuchi-cho, Higashi-ku, Osaka City, Osaka Prefecture Osaka Osaka Building Minolta Camera Co., Ltd. (56) Reference JP-A-60-140277 (JP, A) JP-A-SHO 58-2853 (JP, A)

Claims (1)

[Claims] 1. A developing sleeve containing a plurality of magnets and a toner supply roller are provided in a developing tank, and toner is supplied by the toner supply roller to a magnetic carrier magnetically attracted onto the developing sleeve. By adjusting a developer composed of a mixture of carrier and toner on the periphery of the developing sleeve, and developing the electrostatic latent image on the electrostatic latent image carrier by using the developer, the toner A bias voltage having a direct current and an alternating current superposed thereon is applied to the supply roller, and an alternating electric field in which a direct current component and an alternating current component are superposed is formed between the developing sleeve and the toner supply roller. apparatus.