JPS6318375A - Developing device - Google Patents

Abstract

PURPOSE:To remove a sleeve ghost phenomenon and to obtain an excellent developing picture quality by sticking toner adhering to the surface of a developer carrier to the scraper side and scraping the adhering toner by a developer. CONSTITUTION:A gap G1 between the tip part of the scraper 30 and the developer carrier (developing sleeve) 21 is narrowed as compared to a gap G2 between the tip part of an ear cutting blade 22 and the sleeve 21 and DC voltage is impressed to the scraper 30. A part of the developer adhering to the sleeve 21 is scraped by the scraper 30 and carried to a stirring blade 23 through the upper part 40 of the scraper 30. The developer passing under the scraper 30 and toner on the surface of the sleeve 21 are stuck to the scraper 30 at the time of passing the gap G1 and scraped by the developer entering the gap G1 and sufficiently stirred with the preceding developer 41. Consequently, the toner adhering to the surface of the sleeve 21 is recovered and removed, so that the sleeve ghost phenomenon can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Object of the Invention [Field of Industrial Application] The present invention relates to a developing device that performs development using a 2J&min. developer. More specifically, the present invention relates to a device for removing toner adhered to a developer carrier such as a developing sleeve or a developing belt (hereinafter referred to as a developing sleeve).

[Conventional technology]

Generally, in the reversal development method, development is performed using toner with a charged polarity that is the same as the photoreceptor surface potential polarity, so in background areas where toner does not adhere, the toner is subjected to a repulsive force in the direction of the developing sleeve due to the photoreceptor surface potential. A part of it adheres to the sleeve surface. After one rotation of the developing sleeve, when the developing sleeve faces the surface of the photoreceptor again for development, the adhered toner has an electrostatic charge, which causes a change in the effective bias voltage.

This situation will be further explained using FIG. 4.

FIG. 4 shows the exposure amount-surface potential characteristics of a commonly used photoreceptor. In this example, an OPC photoreceptor is used as the photoreceptor, which is negatively charged and has a surface potential of about -350V just before development.

In order to perform reversal development with this surface potential, a DC bias voltage of approximately -300V, indicated by 45 in the figure, is applied to the developing sleeve.As is clear from Figure 6, under this development condition, the contrast potential is approximately 250V. Become.

Next, considering the state in which toner adheres to the developing sleeve for the reasons mentioned above, the effective DC bias value seen from the photoreceptor side due to this toner adhesion is due to the charge of this adhered toner.
The same effect as apparently rising to the level of FIG. 446 is generated. This is the same as increasing the DC bias voltage.

The contrast potential increases, and an increase in image density appears in that area. Also, this part is the developing sleeve 1
This corresponds to the image pattern before rotation, and unevenness in image density occurs that matches the image pattern (hereinafter this phenomenon will be referred to as sleeve ghost).

Of course, this phenomenon is not limited to reversal development, but can also be observed in normal development methods, but it goes without saying that they are essentially the same phenomenon, with the only difference being the degree of development. This seems to be because the effect of the photoreceptor surface potential is added during reversal development, whereas this effect is less in the latter case.

On the other hand, conventionally, it has been common to apply a direct current voltage as the bias voltage applied during development, but as a means of improving development performance, an alternating current bias voltage is applied at the same time as the direct current bias voltage h pressure, and a type of bias voltage is applied to the toner. A method of improving developing performance by applying vibration has also been proposed. This method certainly improves development performance and increases image density, but at the same time, it essentially has the effect of increasing the amount of toner that moves toward the development sleeve during reverse development. . Therefore, the sleeve ghost phenomenon becomes more noticeable when a DC bias voltage and an AC bias voltage are applied, and it becomes necessary to take countermeasures against this phenomenon.

The easiest way to counter these problems is to press a scraper onto the developing sleeve to scrape off the toner on the sleeve. However, experimental results show that almost no toner can be removed from the developing sleeve, and since it is customary to treat the sleeve surface with a rough surface to increase the amount of developer conveyed, this method is completely useless as a countermeasure for sleeve ghosting. has no effect.

Another possible method is to scrape off the toner by adhering it to an elastic body such as urethane rubber at the tip of the scraper. However, in experiments, the adhesion to the surface of the developing sleeve increased and the effect was certainly observed, but the friction between the developing sleeve and the scraper caused the temperature of the developing sleeve φ scraper to rise, and during long-term copying, the toner fused. Phenomena such as this occur.

[Problem that the invention seeks to solve]

SUMMARY OF THE INVENTION An object of the present invention is to propose a new developing device that eliminates the above-mentioned sleeve ghost phenomenon by only partially improving a conventionally used device.

Summary: Structure of the Invention [Means for Solving Problems] The present invention provides a two-component developing device in which a developer carrier 21
r4AG1 between the tip of the scraper 30 that scrapes off the upper developer from the surface of the developer carrier 21 and the developer carrier 21;
By applying a DC voltage to the scraper 30, the gap is narrower than the distance G2 between the tip of the ear cutting blade 22 and the developer carrier 21, which regulates the amount of developer conveyed on the developer carrier 21.
This developing device is characterized in that it removes toner adhering to the surface of a developer carrier.

[For production]

When the developing sleeve 21 rotates, the ear cutting blade 22 first
A certain amount of developer is transported by the photosensitive drum 2.
0 and development is performed.

At this time, the toner in the non-developing area moves toward the developing sleeve 21 in accordance with the image pattern, and some of the toner adheres to the developing sleeve 21. This is thought to be because in the reversal development system, the surface charge of the photosensitive drum in the non-developing area remains without being busy charging and discharging, and the toner charged with the same polarity is repelled by this charge and moves toward the developing sleeve.

When the above-mentioned adhered developer is conveyed to the scraper 30 position, a part of it is scraped off by the scraper 30,
It passes through the upper part of the scraper 40 and is sent to the stirring blade 23.

On the other hand, when the developer and the toner on the surface of the developing sleeve passing through the lower part of the scraper 30 pass through the gap G1, the toner on the developing sleeve can move in the direction of the scraper, which is the opposite of when passing through the photosensitive drum/developing sleeve gap 03. Since an electric field is formed, the toner adhering to the developing sleeve 21 moves toward the scraper. It goes without saying that when an AC bias voltage is applied, the amount of moving toner increases for the reasons mentioned above, and the toner adhering to the scraper 30 is subsequently scraped by the developer that enters this interval G1. The developer that has finally passed through this position is separated from the developing sleeve 21 by the repulsion magnetic field, and is separated from the previous developer 41 by the stirring blade 23 to a sufficient extent. Stirring is performed. Thereafter, it is sent to the developing sleeve again and the same process is repeated.

Due to the above-described behavior, the toner adhering to the developing sleeve 21 is collected and removed, thereby preventing the sleeve ghost phenomenon described above.

〔Example〕

FIG. 1 is a longitudinal sectional view of an embodiment of the developing device of the present invention.

FIG. 2 is an enlarged vertical cross-sectional view of a portion thereof.

In the figure, 20 is a photosensitive drum, 21 is a developing sleeve, 2
2 is an ear cutting blade, and 23 is a stirring blade. The photosensitive drum 20, the developing sleeve 21, and the stirring blade 23 are rotating in the illustrated direction. Further, inside the developing sleeve 21, as a magnetic field generating means, for example, magnets are arranged and fixed at the positions shown and with the polarities shown, and one of the magnets 33
is installed to match the position of the tip of the scraper 30. The magnetic flux density on the developing sleeve is approximately 700 Gauss.

As shown in the figure, the tip of the scraper 30 does not completely contact the developing sleeve 21, and is set at an interval Gl of about 150 pm in the embodiment. Further, the leading end thereof is arranged so that the same interval extends over a width of approximately 3H toward the developing sleeve side. A DC voltage of, for example, -50V is applied to the scraper 30 from a power source 42. On the other hand, the distance G2 between the developing sleeve 21 and the cutting blade 22 is set to approximately 300 ILm, and the distance G3 between the developing sleeve 21 and the photosensitive drum 20 is set to approximately 500 #Lm.

As a developer, a coated carrier in which the surface of spherical iron powder is coated with resin is used as a carrier, and as a toner, a polyester resin is used as a main ingredient, to which pigments of the desired colors are added.

In this embodiment, the photosensitive drum 20 is set to negative polarity "F, (
-350V), the image area is exposed with a laser beam, and the image area is developed with toner of negative polarity. To this developing sleeve 21, only a DC bias voltage (-300V) and an AC bias voltage (eg, tip-to-tip voltage 800V, IKHz) are simultaneously applied from a power source (not shown).

FIG. 3 shows an example in which the developing device of the present invention is applied to four sets of electrophotographic laser beam printer mechanisms as a plurality of sets of image forming apparatuses.However, in this embodiment, a digital color copying machine was taken as an example. The present invention is not limited to this device.

It goes without saying that it is perfectly possible to implement the invention in conventional analog monochrome copying machines.

In the figure, 10 indicates the main unit box of the apparatus, PaaPb-PC/Pd indicates four sets of image forming apparatuses arranged sequentially from the right side to the left side in the figure, and 11 indicates a conveyor belt drive roller. Rotationally driven by a drive source that is not A conveyor belt 8 is suspended around the conveyor belt drive roller 11 . This conveyor belt 8 is made of a mesh of Tetoron fibers, and is moved by a drive roller 11 in the direction of the arrow shown in the figure. Reference numeral 13 indicates a paper feeding mechanism disposed on the right side of the machine frame, numeral 7 indicates an image fixing device disposed on the left end side, and numeral 14 indicates an outlet for discharging the transfer member to the outside of the machine.

The mechanical configurations of the image forming apparatuses Pa to Pd are substantially the same. That is, each image forming apparatus has a shaft 8a.
Photosensitive drums 1a to 1d as image carriers which are rotationally driven in the direction of the arrow about ~8d, and chargers 15a to 15d that are disposed around the drums in order in the direction of drum rotation, chargers 15a to 15d, phenomenon devices 3a to 3d, It consists of transfer scanners 4a to 4d, cleaning devices 5a to 5d, and laser beam scanners 16a to 16d arranged above the photosensitive drum. The laser beam scanner is composed of a semiconductor laser, a polygon mirror, an fO lens, etc., and upon receiving an input of an electric digital pixel signal, sends a laser beam modulated in accordance with the signal to chargers 15a-15d and developers 3a-3d. The drum surface is exposed by scanning in the direction of the drum generatrix between the two.

Furthermore, the developing device 3a of the first image forming bag 21Pa is filled with yellow toner, the second developing device 3a is filled with magenta toner, the third developing device 3a is filled with cyan toner, and the fourth developing device is filled with black toner. It is to be accommodated. The laser beam scanner 16a of the first image forming apparatus Pa receives a pixel signal corresponding to the yellow component image of the color image, and the second image forming apparatus Pb receives a signal corresponding to the magenta component image.
A signal corresponding to the cyan component image is input to the third device Pc, and a signal corresponding to the black component image is input to the fourth device Pd.

Now, when a cut sheet-like transfer paper 6 is inserted as a transfer member onto the paper feed guide 51 of the paper feed mechanism 13, its leading edge is detected by the sensor 52, and this start signal causes each image forming apparatus Pa to Pd to be exposed to light. The drums 1a to 1d start rotating. The drive roller 11 is also driven at the same time, and the conveyor belt 8 also begins to run in the direction of the arrow. The transfer paper 6 passes through a paper feed guide 57 and is fed onto the conveyor belt 8 . Thereupon, the transfer paper 6 receives corona radiation π from the attraction charger 59 and is reliably attracted to the conveyor belt 8.

Furthermore, when the leading edge of the transfer paper 6 interrupts each of the processors 60a to 60d, image formation is sequentially started on each of the pre-rotating photosensitive drums 1a to ld of each of the lfj image forming apparatuses Pa to Pd based on the signal. 1!1st image form r&
A yellow image is formed on the photosensitive drum 1a of the device FaPa, a magenta image is formed on the second device Pb, a cyan image is formed on the third device Pc, and a black image is formed on the fourth device 1lPd. be done.

The image forming principle in each image forming apparatus is already well known as the Carlson process, so its explanation will be omitted. Then, the transfer paper 6 is conveyed toward the fixing device 7yJ by the rotation of the conveyance belt 8, sequentially passing through the lower part of the first to fourth image forming apparatuses Pa to Pd, and transferred to the transfer discharger 4a of each apparatus.
- Each color is sequentially superimposed and transferred onto the surface of the transfer paper 6 by 4b, 4c, and 4d, and a color image is synthesized. When the transfer paper 6 passes through the fourth image forming device Pd, the static electricity is removed by a static eliminator 61 applied with an AC voltage, and the transfer paper 6 is separated from the conveyor belt 8.Next, the transfer paper 6 enters a fixing device to fix one image. After that, it is discharged from the outlet 14 to the outside of the machine, and one print cycle is completed.

The configuration shown in FIG. 5 is exactly the same as the embodiment shown in FIG. 3, and is an embodiment in which the DC voltage applied to the scraper 30 is changed at a fixed timing to increase the effect of scraping off the toner on the scraper (7) by the developer. 3 shows a timing chart of the direct 1iL voltage applied to the scraper 30 of FIG.

The figure shows the timing of changes in the DC voltage applied to the scraper 30 in accordance with the timing of the image area and non-image area at the development position. In the figure, 47 represents the delay time between the development position and the tip of the scraper.

As is clear from the figure, the same DC voltage as in the previous embodiment in which the image area is developed is applied, but when entering the non-image area after one image area has been developed, the DC voltage is changed. It is at the same level as the developing sleeve voltage (-300V).

In this state, the adhesion force of the toner on the scraper 30 to the scraper is weakened, and the scraping effect of the developer is increased.

Such a timing program can be changed by replacing the ROM installed in the copying machine as necessary using a known method. Further, each timing condition may be selected using a DIP switch provided on a control board or the like.

C. Effects of the Invention As described above, the present invention moves toner adhering to a developer carrier such as a sleeve or belt to the scraper passing surface or adheres to the scraper side, and also allows the adhering toner to pass through there. By scraping off the toner with the developer, a good developed image quality could be obtained without causing a phenomenon of toner adhering to the developer carrier, such as a sleeve ghost phenomenon.

Particularly, this becomes a more effective measure against sleeve ghost when both a DC bias voltage and an AC bias voltage are applied during development to improve development performance.

In addition, the present invention allows the conventional configuration to be used as is without providing a new mechanism to prevent sleeve ghosts, which is advantageous in reducing cost and reliability as developing devices tend to be smaller in recent years. This is an effective method from the viewpoint of gender and other factors.

[Brief explanation of drawings]

FIG. 1 is a vertical sectional view of the developing device of the present invention, FIG. 2 is an enlarged vertical sectional view of a part thereof, FIG. 3 is an explanatory diagram of the present invention applied to a digital color copying device, and FIG. 4 is a photosensitive drum. E-V
FIG. 5 is a timing chart of the DC voltage applied to the scraper of another embodiment of the present invention. 20... Electrostatic latent image carrier (photosensitive drum), 21...
Developer carrier (developing sleeve), 22... ear cutting blade, 23... t-1 stirring blade, 30... scraper,
Gl・620G3...interval.

Claims (1)

[Claims] (1) In a two-component developing device, the distance between the tip of the scraper that scrapes the developer on the developer carrier from the surface of the developer carrier and the developer carrier is defined as the amount of developer conveyed on the developer carrier. The spacing is narrower than the gap between the tip of the cutting blade that regulates the developer carrier and the developer carrier, and a DC voltage is applied to the scraper to remove toner adhering to the developer carrier surface. developing device.