JPH041909B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a method for developing an electrostatic latent image, and more particularly, to a method for developing an electrostatic latent image using a magnetic brush developing device equipped with a developing sleeve having a magnet inside, and comprising a mixture of a magnetic carrier and a toner. By using two-component magnetic developer,
The present invention relates to an electrostatic latent image developing method in which an electrostatic latent image carried on the surface of an electrostatic latent image carrier is developed.

Prior Art As mentioned above, the magnetic brush developing device used in the electrostatic latent image developing method has the advantage that it can be designed to be extremely compact, so it is currently widely used in developing devices such as electrophotographic copying machines. has been done.

On the other hand, in recent years, there has been a demand for higher copying speeds in electrophotographic copying machines, and along with this, high-speed development of electrostatic latent images (e.g., 400 mm/sec) has become necessary.
It has also come to be required to efficiently develop an electrostatic latent image carried on the surface of an electrostatic latent image carrier that moves at a speed such as 100 mm or more.

By the way, in order to meet such demands regarding the development method, in other words, to increase the development efficiency, it is necessary to increase the number of development sleeves in the magnetic brush development device used during development. As a result, in order to meet such demands, there is a problem that the developing device itself has to be enlarged. For this reason, with regard to the development method, the advantages mentioned above are sacrificed in order to increase the development efficiency.In order to avoid such sacrifices, another effective measure to increase the development efficiency is taken. The current situation is that it is desired that such measures be taken.

Purpose of the Invention An object of the present invention is to improve the developing efficiency without substantially increasing the size of the developing device used during development.
An object of the present invention is to provide an improved electrostatic latent image developing method.

Summary of the Invention The summary of the present invention is that in the electrostatic latent image developing method according to the present invention,
There are two points: AC developing bias is applied, and the filling rate of the developer is set to a value within the range of approximately 0.05 to 0.15. As a result of the interaction between the two, development efficiency can be effectively increased.

In addition, in the above-mentioned developing method, the toner in the developer can be easily moved by setting the filling rate of the developer to a value within the range of approximately 0.05 to 0.15. By applying a developing bias, movement of the toner toward the surface of the electrostatic latent image carrier is promoted. As a result, the development efficiency can be effectively increased.

Embodiment FIG. 1 shows a magnetic brush developing device MD used in developing experiments by the present inventor.
MD can be used to carry out the electrostatic latent image development method according to the present invention. The developing device MD is incorporated in a powder image transfer type electrophotographic copying machine, and in the copying machine, the electrophotographic photosensitive drum 1 is driven to rotate at a circumferential speed of 400 mm/sec in the direction of arrow a. be done. Here, an electrostatic latent image is formed on the surface of the photoreceptor drum 1 with a maximum potential (+) of 400 V in the image area and a potential of approximately (+) 30 V in the non-image area, and the electrostatic latent image as described above carried on the surface The electro-latent image is developed by a developing device MD.

The developing device MD includes a rotatably provided developing sleeve 2 made of a non-magnetic stainless steel material, and a magnetic roller 3 fixed stationary therein. The magnetic force of the four magnet pieces 3a is applied to the developing sleeve 2.
The setting is such that a magnetic field of 1000 Gauss is generated on the circumferential surface of the During development, the developing sleeve 2 is rotated at 150 rpm in the direction of arrow b, and the two-component magnetic developer De is conveyed in the same direction on the circumferential surface of the developing sleeve 2. Further, the outer diameter of the developing sleeve 2 is 31 mm, and in order to form a developing area between the developing sleeve 2 and the photosensitive drum 1, the developing sleeve 2 is placed facing the photosensitive drum 1 while maintaining a developing gap of d ₂ =0.8 mm.

In the developing device MD, the developer De is housed in the developer tank 4 and is mixed and agitated by the developer stirring blade 5 which is rotated in the direction of the arrow c. During development, the developer De is rotated in the direction of the arrow d. The developing sleeve 2 is supplied onto the circumferential surface by a plurality of bucket buckets 6a attached to the circumferential surface of the driven bucket troller 6. Note that the developing device MD is provided with a toner replenishing device (not shown), which supplies the developer contained in the developing tank 4.
Toner is replenished to the developer De at appropriate times so that the toner concentration of De is always maintained at a constant value. The developer De supplied onto the circumferential surface of the developing sleeve 2 is magnetically attracted onto the circumferential surface, and
The sheet is conveyed in the direction of arrow b while the conveyance amount is regulated by the height regulating plate 7, and is used for development in a developing area where the photosensitive drum 1 and the developing sleeve 2 are closely opposed to each other. Here, the tip of the regulating plate 7 is provided facing the magnetic pole of the magnet piece 3a, and maintains a height regulating gap of _d1 with respect to the circumferential surface of the developing sleeve 2. And the regulation plate 7
can be moved and adjusted to change the value of _d1 . Note that the developer De used for development is further conveyed in the direction of arrow c, returned to the bottom of the developer tank 4, and moved by the stirring blade 5 to be used again for development.
The mixture is mixed and stirred by

By the way, regarding the developing sleeve 2,
A DC development bias power supply 21 and an AC development bias power supply 22 are connected to each other, and during development, a power source of the same polarity as the electrostatic latent image is applied to the development sleeve 2.
A DC developing bias and a high frequency AC developing bias of 1200 Hz are applied in a superimposed manner. The voltage values of these power supplies 21 and 22 can be changed arbitrarily.

The electrostatic latent image developing method according to the present invention uses a developing device as described above, that is, a magnetic brush developing device equipped with a developing sleeve having a magnet inside, and a two-component system consisting of a mixture of a magnetic carrier and a toner. An electrostatic latent image developing method for developing an electrostatic latent image carried on the surface of an electrostatic latent image carrier using a magnetic developer, in which an AC developing bias is applied to the developer in a developing area. The developer is characterized in that the filling rate of the developer is within the range of approximately 0.05 to 0.15. As a result, development efficiency can be effectively increased without substantially forcing the development device itself to become larger.

Here, the filling rate of the developer is expressed by the following formula: α=ρs/ _ρp ... However, α: Filling rate _ρp : True specific gravity of the developer _ρs : Apparent specific gravity of the developer at the center of the development area This is the value expressed as . Note that the apparent specific gravity ρs of the developer at the center of the developing area refers to the space volume at the center of the developing area surrounded by the surface of the photoreceptor drum 1 and the circumferential surface of the developing sleeve 2, and the volume of space actually existing within that space. It is derived from the weight of the developer De. In addition, the true specific gravity ρp of the developer De means an appropriate toner concentration. Specifically, regarding the developing device MD, it corresponds to the value of the toner concentration of the developer De that should be kept constant by the action of the toner replenishing device. true specific gravity of the developer De with the toner concentration (developer
It means the specific gravity when De exists without any gap in the space at the center of the developing area.

Here, the technical meaning of the developer filling rate will be explained in more detail. The developer filling rate is a numerical value indicating the proportion of the developer occupying the space at the center of the development area. In this space, developer can exist in various states. For example, when a large amount of developer is supplied to the developing area, or when the distance between the developing sleeve 2 and the photoreceptor drum 1 is narrow and the space at the center of the developing area is small, the proportion of the developer occupying this space is It gets expensive. When it is highest, the developer is present in the space at the center of the developing area without any gaps, and at this time, in the equation, ρ _p =ρ _s and the developer filling rate α=1. On the other hand, when the amount of developer supplied to the developing area is small, or when the gap between the developing sleeve 2 and the photoreceptor drum 1 is wide and the space at the center of the developing area is large, the proportion of developer occupying this space is low. Become. When it is at its lowest, there is no developer at all in the space at the center of the developing area.
At this time, the filling rate α=0.

That is, the filling rate α of the developer is a value in the range of 0 to 1, and the ratio of the developer existing in the space at the center of the development area increases as α increases, and decreases as α decreases.

If the developer filling rate α is too large, the toner separated from the carrier by the AC bias will collide with nearby developer and be captured again before contributing to development, resulting in a decrease in development efficiency. On the other hand, the filling factor α
If is too small, the amount of toner itself that can contribute to development will decrease, making it impossible to obtain sufficient image density. Therefore, in order to improve development efficiency,
It is necessary to set the developer filling rate α to an appropriate value.

Below, among the many development experiments conducted by the present inventor, representative ones are shown as experimental examples.
A specific embodiment of the electrostatic latent image developing method according to the present invention will be explained.

[Experiment Example 1] The height regulating gap in the developing device MD shown in Fig. 1 was set to d ₁ = 0.25 mm, and the voltage values of the DC developing bias power supply 21 and AC developing bias power supply 22 were set to 150 V and 500 V (peak-to -peak), and the developer De is a toner with a toner concentration of 8.0ωt% consisting of a mixture of a high-resistance magnetic carrier with an average particle size of 40 μm and a resistance value of 10 ¹⁴ Ωcm or more, and an insulating toner with an average particle size of 13 μm. Using the developer, the developing device
When the electrostatic latent image carried on the surface of the photoreceptor drum 1 was developed by MD, a developed image of good quality was obtained.

Here, in order to know the density of the developed image, we investigated the relationship between the density of the copied image obtained by a copying machine incorporating the developing device MD and the potential of the electrostatic latent image, and the results are as follows. is the third
This was as shown by the solid line A in the graph of the figure.
In the graph shown in FIG. 3, the vertical axis indicates the density of the copied image, and the horizontal axis indicates the potential of the electrostatic latent image corresponding to the copied image. As is clear from this result, even though the surface of the photoreceptor drum 1 is moved at a high speed of 400 mm/sec during the development, the electrostatic latent image carried on the surface is efficiently If so, it can be seen that the toner image is developed as a high-density toner image. This means that
This becomes even clearer when compared with the dashed-dotted line B showing the results of Comparative Example 1, which will be described later.

By the way, according to the inventor's analysis regarding the development, the developer during the development
The behavior of De is considered to be as schematically shown in Figure 2. That is, on the entrance side of the developing area, indicated by A in FIG. drum 1
gradually approached the surface of the At this time, since the toner To in the developer De has a (-) polar charge, the toner To near the tip of the magnetic brush is is separated from the carrier Ca and deposited on the surface of the photoreceptor 1 carrying a high potential electrostatic latent image. In addition, during the development, the development gap is d ₂ =
0.8mm, while the height regulation gap is d ₁ =
Since the value is set to a sufficiently small value of 0.25 mm, the ears of the magnetic brush are kept in a non-contact state with the surface of the photoreceptor drum 1 in the developing area. Therefore, the toner To does not adhere to the surface of the photoreceptor drum 1 as described above from the tip of the magnetic brush.
This occurs as a result of the particles flying toward the surface of the photoreceptor drum 1.

Subsequently, the magnetic brush is brought closest to the surface of the photosensitive drum 1 at the center of the developing area, indicated by B in FIG. In this state, the ears of the magnetic brush are kept in a non-contact state with the surface of the photoreceptor drum 1 as described above, and the ears of the magnetic brush are erected. The brush tips are separated from each other. Therefore, the toner To in the developer De is easily moved (flying) in the direction of the arrow e, and the developing sleeve 2
Since an AC developing bias is applied to the developing sleeve 2 and the photosensitive drum 1, the movement (flying) is promoted by the action of the AC electric field formed between the developing sleeve 2 and the photosensitive drum 1. Therefore, at the center of the development area, the toner To in the developer De efficiently adheres to the surface of the photoreceptor drum 1 based on the electric field formed according to the potential of the electrostatic latent image, and as a result, The electrostatic latent image will be efficiently developed. In particular, here, the entire developer De present in the development area is effectively used for developing the electrostatic latent image.
This is because the toner To in the developer De located near the base of the ear of the magnetic brush is also reliably moved (flying) toward the surface of the photosensitive drum 1.

Note that on the exit side of the developing area, indicated by C in FIG. 2, the magnetic brush gradually moves away from the surface of the photoreceptor drum 1, making it difficult for the toner To to move (fly) as described above. Development of the electrostatic latent image is now complete.

In addition, in the developing device MD shown in FIG. 1, the present inventor confirmed that by changing the head height regulation gap in the range of d ₁ =0.1 to 0.6 mm (the developing gap was fixed at d ₂ =0.8 mm). according to,
There is a relationship shown in FIG. 4 between the value of "d ₁ /d ₂ ", that is, the gap ratio, and the filling rate of developer in the developing area, and in the development, d ₁ =0.25 mm,
Since d ₂ is set to 0.8 mm, it is known that the filling rate of the developer in the development area at that time is approximately 0.10. Additionally, within the range of d ₁ = 0.1 to 0.6 mm, that is, within the range of the gap ratio of 0.125 to 0.75, the ears of the magnetic brush of the developer formed on the circumferential surface of the developing sleeve are exposed to light in the developing area. It has also been found that the surface of the body drum 1 is maintained in a non-contact state. In addition, in the graph shown in Fig. 4,
The vertical axis shows the filling rate, while the horizontal axis shows the gap ratio. It changes depending on the state etc.

[Comparative Experiment Example 1] The brush height regulation gap in the developing device MD shown in FIG. 1 was set to d ₁ =0.8 mm, and the voltage values of the DC developing bias power supply 21 and AC developing bias power supply 22 were set to 100 V and 0 V, respectively. When the electrostatic latent image was developed under the same conditions as in Experimental Example 1, it was found that there were scratches on the leading edge and trailing edge (edges based on the moving direction of the photoreceptor drum), and a low density image was developed. Only developed images could be obtained.

In order to find out the density of the developed image obtained, we investigated the relationship between the density of the copied image and the potential of the electrostatic latent image in the same manner as in Experimental Example 1, and the results are shown in the graph of Figure 3. It was as shown by the dashed line B. That is, it was found that the maximum density of the copied image was only 0.95 at most, and the efficiency of developing the electrostatic latent image was insufficient. In addition, during the development,
In the developing area, the surface of the photosensitive drum 1 was in a state of being rubbed by the ears of the magnetic brush of the developer De formed on the circumferential surface of the developing sleeve 2 .

[Comparative Experiment Example 2] DC developing bias power supply 2 in Comparative Experiment Example 1
1. The voltage value of the AC developing bias power supply 22 was reset to 150V and 500V (peak-to-peak) as in Experimental Example 1, and the electrostatic latent image was developed under the same conditions as in Comparative Experimental Example 1. As a result, although a slight increase in image density was observed, only the same developed image as in Comparative Experiment Example 1 was obtained.

[Experimental example 2] While changing the gap ratio by changing the value of the ear height regulation gap _d1 within the range of 0.1 to 0.5 mm,
That is, as a result, when the electrostatic latent image was developed under the same conditions as in Experimental Example 1 while changing the filling rate of the developer in the development area, a developed image of good quality was obtained. However, the density of the obtained developed image varied greatly depending on the filling rate.

In order to know the density of the obtained developed image, we investigated the relationship between the maximum density of the copied image obtained by a copying machine incorporating the developing device MD and the filling rate, and the results were as follows. It was as shown in the figure. In the graph shown in FIG. 5, the vertical axis represents the maximum density of the copied image, while the horizontal axis represents the filling rate. As is clear from FIG. 5, even though the image quality of the developed image is good, if the filling factor is less than 0.05 or more than 0.15, the maximum density of the copied image will be less than 1.2, and the electrostatic latent image It can be seen that the efficiency of development is not necessarily sufficient, and from the point of view of development efficiency, it is desirable that the filling rate is within the range of about 0.05 to 0.15. Incidentally, as is clear from the graph shown in Figure 4, when the filling rate is 0.05 to 0.15, the gap ratio is 0.16 (d ₁ =
0.13 mm) and 0.5 (d ₁ =0.4 mm).

[Experiment Example 3] Set the voltage value of AC developing bias 22 to 250 to 700V.
When the electrostatic latent image was developed under the same conditions as in Experimental Example 1 while changing the value within the range of (peak-to-peak), a developed image of good quality was obtained. The density of the obtained images was sufficient in all cases, but the density varied approximately proportionally to the voltage value.

As is clear from this experimental example and the aforementioned experimental example 1, the developing efficiency can be arbitrarily changed by adjusting either the voltage value of the AC developing bias 22 or the filling rate of the developer De, or both. It can also be seen that the developed image density can be changed by these adjustments.

[Experimental Example 4] When the electrostatic latent image was developed under the same conditions as in Experimental Example 1 when the moving speed of the photoreceptor drum 1 was 150 mm/sec, good image quality and high density development was obtained. Image obtained. In this case, it was also found that even if the potential of the electrostatic latent image is low and its maximum potential is about 250V, a developed image with a high density, for example, a density of 1.2 or higher in terms of the maximum density of the copied image, can be obtained. .

[Experiment Example 5] As developer De, average particle size 20 μm, resistance value 10 ¹³
High resistance magnetic carrier of Ωcm or more and average particle size
When an electrostatic latent image was developed under the same conditions as in Experimental Examples 1 to 4 using a developer with a toner concentration of 10.0 ωt% consisting of a mixture with a 12 μm insulating toner, the results were almost the same as those described above. The results were confirmed.

Effects of the Invention In the electrostatic latent image developing method according to the present invention, when developing an electrostatic latent image, an AC development bias is applied to the developer in the development area, and the filling rate of the developer is approximately Since the value is within the range of 0.05 to 0.15, the electrostatic latent image is efficiently developed due to the interaction between the two. Therefore, it is possible to develop an electrostatic latent image at high speed without forcing the size of the developing device itself used during development.

In addition, in the above development method, the development efficiency
Since the up is effectively measured, the above-mentioned developing method is not only capable of high-speed development of electrostatic latent images, but also can satisfactorily develop electrostatic latent images having an overall low potential.
In addition, the developing efficiency can be arbitrarily changed by adjusting either the voltage value of the AC developing bias, the filling rate of the developer, or both.
Therefore, the developed image density can also be changed by these adjustments.

[Brief explanation of drawings]

FIG. 1 is a drawing showing an example of a magnetic brush developing device used to carry out the electrostatic latent image developing method according to the present invention, and FIG. 2 is an enlarged view of the vicinity of the developing area of the magnetic brush developing device. The drawings schematically showing the situation, and FIGS. 3 to 5 are drawings showing the results of experiments conducted by the present inventor. MD...magnetic brush developing device, De...two-component magnetic developer, Ca...magnetic carrier, To...toner, _d1 ...brush height regulation gap, _d2 ...developing gap, 1...electrophotographic exposure Body drum, 2...Developing sleeve, 3...Magnetic roller, 7...Hot height regulation plate,
22...AC developing bias power supply.

Claims (1)

[Claims] 1. A magnetic brush developing device equipped with a developing sleeve having a magnet inside is used, and a two-component magnetic developer consisting of a mixture of a magnetic carrier and a toner is used to develop an electrostatic latent image carrier. An electrostatic latent image developing method for developing an electrostatic latent image carried on a surface, in which an AC development bias is applied to a developer in a development area, and the developer is expressed by the following formula: An electrostatic latent image developing method characterized in that the filling rate is set to a value within a range of 0.05 to 0.15. α=ρ _s /ρ _p However, α: Filling rate ρ _p : True specific gravity of the developer ρ _s : Apparent specific gravity of the developer at the center of the developing area 2 In the magnetic brush developing device, while the magnet is kept stationary; 2. The electrostatic latent image developing method according to claim 1, wherein the developing sleeve is rotationally driven in a fixed direction. 3. Claim No. 3, characterized in that in the developing region, the ears of the magnetic brush of the developer formed on the peripheral surface of the developing sleeve are kept in a non-contact state with the surface of the electrostatic latent image carrier. The electrostatic latent image developing method according to item 1 or 2.