JPS6331780B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a copying process in which an electrostatic latent image formed on the surface of a photoreceptor or dielectric layer is developed, and a final image is formed through a transfer process and a fixing process. In particular, the present invention relates to a magnetic brush development and cleaning method in which development and cleaning are performed using a single magnetic brush.

[Prior art]

An electrostatic latent image is formed on the surface of the photoreceptor layer or dielectric layer, this electrostatic latent image is developed by a magnetic brush method, the obtained toner image is transferred onto a transfer sheet such as plain paper, and then pressure is applied. Copying methods in which the toner is fixed by heating to obtain a hard copy, the toner remaining on the surface of the image holding member is removed, and the above cycle is repeated again are well known.

In this copying process, the apparatus described in US Pat. No. 3,455,276 or US Pat. No. 4,081,571 is known as an apparatus for performing magnetic brush development.

In the above-mentioned copying process, one image-bearing member, usually an endless belt or drum, is used.
One copy is made by rotating, but a method has also been proposed in which the toner remaining on the belt or drum after transfer is cleaned using a magnetic brush used for development, and this method has already been put into practical use in a few copying machines. has been done. In this method, an electrostatic latent image is formed and developed during one rotation of the image holding member, and transfer, charge removal, and cleaning are performed during the next rotation. In other words, the image holding member rotates twice. One copy is performed in between. According to this method, since there is no need to provide a separate cleaning device, there is an advantage that a copying machine having a simple structure, small size, light weight, and low cost can be obtained. However, during development, it is necessary to bring the magnetic brush into soft contact with the latent image surface, while during cleaning, it is necessary to strongly rub the latent image surface with the magnetic brush, so it is necessary to satisfy both conditions with a single magnetic brush. It is difficult. In particular, compared to using a two-component developer that is a mixed powder of carrier and toner as a magnetic developer, when using a single-component magnetic toner, development and cleaning are performed with a single magnetic brush. That is extremely unreasonable.

For example, it has been proposed in US Pat. No. 3,918,808 to use a blade in combination with cleaning, and a fur brush has also been used in combination, but this increases the size of the device or easily damages the surface of the image holding member. It has the disadvantage of becoming. It has also been proposed to use a regulating member to narrow the contact width of the magnetic toner with the photoreceptor during development, and to change the position of the magnetic brush to change the state of the magnetic brush between development and cleaning. have also been proposed, but both have problems such as complicated mechanisms and low reliability.

〔the purpose〕

It is an object of the present invention to provide a magnetic brush development and cleaning method that overcomes the drawbacks of the prior art.

Another object of the present invention is to provide a magnetic brush development and cleaning method that has a simple structure and can form a magnetic brush suitable for development and a magnetic brush suitable for cleaning using the same magnetic brush.

〔composition〕

The magnetic brush development and cleaning method of the present invention comprises: facing a carrier having an electrostatic latent image on its surface;
A magnetic brush comprising a cylindrical non-magnetic sleeve and a permanent magnet roll provided within the sleeve and having a plurality of magnetic poles, and configured such that the sleeve and the permanent magnet roll can rotate relative to each other. A forming roller is arranged, a magnetic developer is supplied onto the magnetic brush forming roller to form a magnetic brush, the magnetic brush rubs the surface of the carrier to form a toner image thereon, and the toner image is In a magnetic brush development and cleaning method in which the toner remaining on the carrier is removed by sliding the toner on the carrier again with the magnetic brush after being transferred onto a transfer sheet, a permanent magnet roll is rotated at high speed during development and The non-magnetic sleeve is stopped or rotated in the same direction as the permanent magnet roll but slower than the permanent magnet roll, so that the developer is transported mainly by rotational force, and the magnetic brush is brought into soft contact with the surface of the carrier;
During cleaning, the non-magnetic sleeve is rotated in the opposite direction to the permanent magnet roll at a slower speed than the permanent magnet roll, so that the developer conveying force is made stronger than during development, and the magnetic brush is brought into strong contact with the carrier surface.

〔Example〕

The details of the present invention will be explained below with reference to the drawings.

FIG. 1 is a schematic sectional view of a copying system in which a photosensitive drum rotates twice to make one copy.

In FIG. 1, a photosensitive drum 1 having a photoconductive layer 1a formed on its surface is rotating in the direction of an arrow z in the figure, and a corona is provided around it to uniformly charge the surface of the photoconductive layer 1a. Charger 2, photoconductive 1a
An optical system 3, a magnetic brush forming device 4, and a corona transfer device 5 are arranged for exposing the surface of. In this copying system, the surface of the photoconductive layer 1a is first uniformly charged by a corona charger 2 and then exposed to light by an optical system 3 to form an electrostatic latent image (not shown). The electrostatic latent image is then developed by magnetic brush device 4 to form a toner image 7' on the surface of photoconductive layer 1a. Next, a transfer sheet 6 such as plain paper is placed on top of the toner image 7', and a transfer electric field is applied from the back side of the transfer sheet 6 by a corona transfer device 5 to transfer the toner image 7 onto the transfer sheet 6. Note that the transfer means is not limited to this, and a charging roller or the like may be used. Toner image 7' on transfer sheet 6
is fixed by pressure and/or heat to obtain a hard copy. However, the amount of toner transferred onto the transfer sheet during transfer is not 100%,
Usually about 20% remains on the photoconductive layer 1a. The photosensitive drum 1 that has undergone one rotation after the transfer process is then rotated a second time, and its surface is cleaned by the magnetic brush device 4 again. That is, in the copying system shown in FIG. 1, one hard copy is obtained by two rotations of the photosensitive drum. Note that in a typical copying machine, a static eliminating means such as an AC corona charger and/or a lamp is provided between the transfer device 6 and the corona charger 2 in order to improve cleaning performance.

The magnetic brush forming apparatus shown in FIG. 1 is constructed as follows. Magnetic brush forming roller 4
2 has a non-magnetic sleeve 43 and a permanent magnet roll 44. A cylindrical non-magnetic sleeve 43 is rotatably arranged opposite to the photosensitive drum 1, and inside the sleeve 43 is a permanent magnet roll 44 in which a cylindrical magnet 46 having a plurality of magnetic poles on its surface is supported by a shaft 45. It is arranged so that it can rotate freely. A hopper-shaped toner tank 41 having a toner supply port 41a at its lower part is provided outside the sleeve 43, and a magnetic toner 7, for example, as a magnetic developer is stored inside the hopper-shaped toner tank 41.

According to such a configuration, the toner supply port 41a
Magnetic toner 7 supplied onto sleeve 43 from
is conveyed on the sleeve by the relative rotation between the permanent magnet roll 44 and the sleeve 43, thereby forming the magnetic brush 7a. Development and cleaning are performed by rubbing the photoconductive layer 1a with the magnetic brush 7a.

As a result of examining the conditions for performing good development and cleaning using the above magnetic brush forming device 4, the following conditions were obtained.

First, regarding the conveying direction of the magnetic toner, when the magnetic toner is conveyed in the same direction as the drum 1, that is, in the direction of the arrow y in the figure, at the closest position between the photoreceptor drum 1 and the sleeve 43, both development and cleaning are performed satisfactorily. It is necessary to This is because, at the closest position, when the toner transport direction is opposite to the moving direction of the photoreceptor drum, a toner reservoir 7b is formed on the downstream side of the toner transport direction, and a portion of this toner reservoir that is away from the permanent magnet roll is This is because the toner becomes unstable and adheres to non-image areas, making fogging and the like more likely to occur.

Next, when developing and cleaning are performed using the same magnetic brush, a magnetic brush with low bristles is formed during development and this magnetic brush gently rubs the surface of the photoreceptor, while a hard magnetic brush is formed during cleaning. It is necessary to strongly rub the surface of the photoreceptor with this magnetic brush. Therefore, the inventor of the present invention has proposed a toner regulation thickness d in various toner conveyance methods.
When the dimensions of the magnetic brush were measured while changing the doctor gap (hereinafter referred to as doctor gap), the results shown in FIG. 2 were obtained. In addition, Fig. 2 shows an outer diameter of 32 mm.
φ sleeve, outer diameter 29.3 mmφ, permanent magnet roll with 8-pole symmetrical magnetization and magnetic flux density of 570G on the sleeve, and 50 wt% magnetic powder.
The resistance under a DC electric field of 4000V/cm is 10 ¹² Ω・
This is the result when using cm magnetic toner.

From Figure 2, in the method in which only the permanent magnet roll is rotated (hereinafter referred to as the magnet rotation method), the conveyance force is the weakest, so the amount of toner that passes through the doctor gap is also small, so the magnetic brush is small,
The height ^h2 of the valley of the magnetic brush is smaller than d.
In addition, in the method in which only the sleeve is rotated (hereinafter referred to as the sleeve rotation method), the conveying force is strong and _a large amount of toner passes through the doctor gap. A large magnetic brush is formed where both h _{and 2} are larger than d. Furthermore, a method in which both the sleeve and the permanent magnet roll were rotated in the same direction (hereinafter referred to as a "both rotation method") gave almost the same results as the sleeve rotation method.

Therefore, it is conceivable to adopt a magnetic rotation type as a toner conveyance method during development, and on the other hand, to use a sleeve rotation type during cleaning. However, in order to carry out this method, it is necessary for the permanent magnet roll to repeatedly rotate and stop, but the permanent magnet roll has a large moment of inertia due to its weight and cannot rotate at high speed. It is mechanically and mechanically difficult to stop a permanent magnet roll that is currently in use, and furthermore, it is extremely difficult in practice because a permanent magnet roll cannot be stopped suddenly.

Therefore, as a result of various studies, the inventor of the present invention found that at least the permanent magnet roll is rotated in the direction of the arrow x' in Fig. 1 during development and cleaning, while the sleeve is stopped during development or rotated in the same direction as the permanent magnet roll, that is, in the first direction. It has been found that good results can be obtained by rotating the roller relatively slowly in the direction of the arrow x in the figure, and during cleaning by rotating it in the opposite direction to the permanent magnet roll, that is, in the direction of the arrow y in FIG. The details will be described below.

First, in the magnetic rotation method, the toner on the sleeve rotates in the opposite direction due to the rotation of the magnet, so the toner conveying force is extremely weak.In the sleeve rotation method, the toner on the sleeve rotates in the opposite direction. It is well known that rotation causes the toner to be conveyed in the same direction mainly due to the frictional force with the sleeve, so that the toner conveying force becomes strong. Therefore, the present inventor proposed the fourth
The toner conveyance forces of various toner conveyance methods were compared using the apparatus shown in the figure. i.e. outer diameter 31.4
Magnetic toner 7 is uniformly adhered to a thickness of 0.4 mm on a magnetic brush forming roll 44 having a sleeve 43 of mmφ and an outer diameter of 29.3 mmφ, 8-pole symmetrical magnetization, and a permanent magnet roll 46 with a magnetic flux density of 850G on the sleeve. Seshime,
A cover glass 8 supported by a fulcrum 9 is installed above this toner layer, and a weight 10 is attached to one end of the glass 8.
The weight value when the flow of the toner was blocked was determined, and this value was taken as the conveyance force.

As a result, the toner conveyance force when the sleeve rotates is approximately 10 times that when the magnet rotates, and the toner conveyance force is unrelated to the rotation speed of the magnet or sleeve, that is, the toner movement speed. It was discovered that

Next, during development, a small magnetic brush with low bristles is formed by employing a magnetic rotation system, but in order to perform good development, it is necessary to bring this magnetic brush into soft contact with the drum. Therefore, the relationship between the toner thickness when the gap D between the photosensitive drum and the sleeve (hereinafter referred to as the developing gap) and the doctor gap d was changed was determined. The results are shown in FIG. In this case, the experimental conditions are the same as in FIG.

Regarding FIG. 3, in the area below the straight line a, the toner pool formed on the upstream side of the developing gap grows, but in the area above the straight line b, the toner pool can be prevented from growing. As this toner pool grows, the contact width between the photosensitive drum and the toner changes, making it impossible to perform stable development.
For this purpose, it is preferable to set D to be approximately 0.05 mm larger than d. In addition, in order to obtain a practical copy with a copy density of 1.0 or higher, sufficient contact between the magnetic brush and the drum is required, so it is necessary to set D to be approximately 0.20 mm larger than d. be. In other words, it eliminates toner accumulation and
To obtain a copy density of 1.0 or higher, D=d+
It is preferable to set it to 0.02 to d+0.20 mm, that is, the area indicated by the broken line in the figure. in short,
In the magnetic rotation system, as mentioned above, the toner conveying force is small, so if the developing gap is too narrow, toner pools tend to grow, so it is necessary to set the developing gap to a certain extent. However, if D is too wide, the toner will not be able to make sufficient contact with the drum, and a sufficient copy density will not be obtained.

As the rotation speed of the permanent magnet roll increases, the toner velocity also increases, and therefore the magnetic brush also increases in size. If the magnetic brush is too small, sufficient contact cannot be made, while if it is too large, the cleaning effect will become stronger. Therefore, it is preferable that the rotational speed of the permanent magnet roll is set in a range of 5 to 20 times the circumferential speed of the photoreceptor drum.

Furthermore, during development, the development is not limited to the above-mentioned rotation of the magnet, but also good development can be achieved by rotating the sleeve in the same direction as the magnet at a relatively low speed. In this case, the toner conveying force is naturally stronger than in the case of magnetic rotation, but it is considerably weaker than in the case of sleeve rotation. Further, the toner conveyance speed is a value obtained by subtracting the revolution speed of the sleeve from the rotation speed due to the rotation of the magnet, and is relatively slow. Therefore, in this dual-rotation method, the toner conveying force is strong but the toner conveying speed is slow, so a relatively large magnetic brush is formed, but since the magnetic brush comes into soft contact with the drum, the developing efficiency is reduced. becomes higher. In this case, the peripheral speed of the sleeve is preferably 0.1 to 0.2 times the peripheral speed of the permanent magnet roll.

Next, during cleaning, it is conceivable to form a large magnetic brush and rotate the sleeve at a relatively high speed in the opposite direction to the permanent magnet roll during cleaning in order to strongly rub the surface of the drum with this magnetic brush. According to such a toner conveying method, the rotational force based on the alternating magnetic field caused by the rotation of the permanent magnet roll and the frictional force due to the rotation of the sleeve act together on the toner on the sleeve.
The toner conveying force becomes extremely strong, and since the toner conveying force becomes even stronger, the thickness of the toner layer becomes larger than in the case of the magnetic rotation method, and a large magnetic brush is formed. Furthermore, since the toner on the sleeve is conveyed at a speed equal to the rotation speed plus the revolution speed of the sleeve, this magnetic brush comes into strong contact with the drum. Therefore, according to the above-mentioned toner conveying method, the toner remaining on the drum is misaligned with the drum, weakening its adhesion to the drum, and is easily collected into the magnetic brush, making it possible to perform good cleaning. can. However, if the toner transport force is too strong, the force with which the magnetic brush rubs the surface of the photoconductor becomes strong, making it easy to damage the photoconductor and cause filming.
In addition, toner blocking tends to occur. Therefore, the circumferential speed of the sleeve is 1/ of the rotation speed of the permanent magnet roll.
It is preferable to set it to about 7 to 1/10.

FIG. 5 shows a time chart of toner layer thickness and toner accumulation in the development and cleaning process of the present invention.

As shown in FIG. 5, the thickness of the toner layer conveyed on the sleeve becomes thinner during development, while it becomes thicker during cleaning. Next, the amount of toner pool formed on the upstream side of the development gap exhibits a certain peak value during development, but is completely eliminated during cleaning.

In the present invention, the permanent magnet roll is constantly rotated as described above, but by making the rotation speed and rotation direction of the sleeve variable, the size and size of the magnetic brush can be changed during development and cleaning. Adjusting contact status. In this case, since the weight of the sleeve is small, the moment of inertia is small, and the number of revolutions does not have to be so high, so the above-mentioned adjustment can be easily carried out and is sufficiently practical.

〔effect〕

The effects of the present invention are as follows.

(1) Developing and cleaning can be performed efficiently with the same magnetic brush.

(2) Good results can be obtained without complicating the structure of the magnetic brush device.

〔Concrete example〕

In Figure 1, the diameter of the photoreceptor drum is 120 mm.
A Se drum of mmφ was used and rotated at 150 mm/sec. The permanent magnet roll has an outer diameter of 29.3mmφ, 10 poles symmetrical magnetization, and a sleeve top of 700G.
Rotated at 1200rpm. The sleeve used was a stainless steel cylinder with a diameter of 32 mm. The magnetic toner used had a specific resistance of 10 ¹⁴ Ω·cm and a particle size of 10 to 20 μm. During development, the sleeve is rotated at 30 rpm, and during cleaning, the sleeve is rotated at 30 rpm.
When rotated at 150 rpm, up to 55 consecutive copies were obtained with no problem in practical use.

Next, when cleaning was performed under the same conditions as during development, only a copy with a thin double image was obtained.

However, in the above example, cleaning was performed after the surface of the drum after transfer was neutralized at 5.5 KV using an AC corona charger.

[Brief explanation of the drawing]

Figure 1 is a sectional view showing a two-rotation, one-copy copying system, Figure 2 is a diagram showing the heights of the doctor gap and magnetic brush in various toner conveyance systems, and Figure 3 is a diagram showing the heights of the doctor gap and magnetic brush in the magnetic rotation system. FIG. 4 is a cross-sectional view showing a device for measuring the toner conveyance force, and FIG. 5 is a view showing the height of the magnetic brush and the state of the toner reservoir. 1: Photosensitive drum, 4: Magnetic brush forming device,
7: Magnetic toner, 43: Sleeve, 44: Permanent magnet roll.

Claims (1)

[Claims] 1. A cylindrical non-magnetic sleeve facing a carrier having an electrostatic latent image on its surface and a permanent magnet roll having a plurality of magnetic poles on its surface provided inside the sleeve. and a magnetic brush forming roller configured such that the sleeve and the permanent magnet roll can rotate relative to each other, a magnetic developer is supplied onto the magnetic brush forming roller to form a magnetic brush, and the magnetic brush forming roller is configured to rotate relative to the sleeve and the permanent magnet roll. A toner image is formed by rubbing the surface of the carrier with a brush, and after the toner image is transferred onto a transfer sheet, the surface of the carrier is rubbed again with the magnetic brush to remove the toner remaining on the surface of the carrier. In the magnetic brush development and cleaning method, during development, the permanent magnet roll is rotated at a relatively high speed, and the sleeve is stopped or rotated in the same direction as the permanent magnet roll at a slower speed, so that the magnetic development is carried out mainly by rotational force. The magnetic brush is brought into soft contact with the surface of the carrier to transport the developer, and during cleaning, the sleeve is rotated in the opposite direction to the permanent magnet roll at a slower speed than the permanent magnet roll, thereby increasing the transporting force of the magnetic developer compared to that during development. A magnetic brush developing and cleaning method characterized by strongly bringing the magnetic brush into contact with the surface of the carrier. 2. The magnetic brush development and cleaning method according to claim 1, wherein a magnetic toner containing at least a resin and magnetic powder is used as the magnetic developer.