JPS5852587B2 - Electrostatic image developing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrostatic image developing device using magnetic toner.

In a method of developing an electrostatic image using magnetic toner, permanent magnets arranged in reverse polarity and a sleeve containing the permanent magnets are moved relative to each other, and the toner particles held on the sleeve are rolled to form a static image. A method has been proposed in which the charge is brought to the image plane and developed.

In this method, toner particles are fluffed on the magnetic poles of a magnet, and these fluffs (magnetic brushes), which are spaced at regular intervals, rub the electrostatic image surface one after another, turning it into a visible image.

In the above method, the permanent magnet may be fixed and the sleeve may be moved, the sleeve may be fixed and the permanent magnet may be moved, or both may be moved.

In any of these embodiments, the toner particles move relative to the sleeve and create friction at their contact points.

The commonly used magnetic brush method uses a cylindrical permanent magnet whose magnetic poles are magnetized parallel to or inclined to the axial direction.
A developing device is used that includes a cylindrical nonmagnetic sleeve installed coaxially with the developing device and a magnetic toner supply device that supplies magnetic toner to the sleeve.

Generally, a doctor member for regulating the height of the magnetic brush is arranged parallel to the sleeve at a predetermined distance, forming a slit-like space there.

The height of the magnetic brush is averaged by this slit, and the development density is kept constant.

In the above-mentioned commonly used magnetic brush method (hereinafter referred to as the "rotating magnetic brush method"), the area from the point where magnetic toner is supplied to the sleeve to the point where it is closest to the electrostatic image surface is This is a feeding section for magnetic toner.

The magnetic toner rolls around the cylindrical sleeve while being held by the magnetic force of the permanent magnet inside the sleeve.

Therefore, centrifugal force acts on the magnetic toner together with the magnetic force of the permanent magnet.

Many of the effects described above for the rotating magnetic brush method are
When applied to high-speed development, these are harmful and cannot be ignored.

This will become clear from the explanation below.

That is, in the rotating magnetic brush method, the magnetic toner consumed for development is only a part of the sleeve, and most of it remains on the sleeve and is used again.

Therefore, most of the magnetic toner on the sleeve is used repeatedly, causing many inconveniences.

One of the reasons is that the friction between the magnetic toner and the sleeve melts the thermoplastic resin, which is a component of the magnetic toner, and forms a film of the thermoplastic resin on the sleeve.

This is detrimental to the electrical properties of the sleeve, which acts as a counterelectrode, and the magnetic toner is also worn away as a result.

Next, the doctor for regulating the height of the magnetic brush blocks the magnetic toner rolling on the sleeve or the magnetic toner supplied from the supply device, and the width of the slit formed between the doctor and the sleeve is The amount of magnetic toner determined by can pass through here.

However, this slit is usually extremely narrow, around 1 mm, so if the sleeve is rolled at a speed higher than that at which the magnetic toner can pass through without getting caught, a magnetic toner blocking phenomenon will occur, resulting in an insufficient supply of magnetic toner to the sleeve. This causes uneven development, resulting in a lot of wasted copies.

Furthermore, since the magnetic toner is forced to pass through this portion, the magnetic toner is worn out and its deterioration is accelerated.

This results in a magnetic toner that cannot withstand long-term use.

In the rotating magnetic brush method, since centrifugal force acts on the magnetic toner in addition to the magnetic force of the permanent magnet, it is not possible to roll the magnetic toner around the sleeve at high speed.

This is because the magnetic toner is moved at high speed on the outer periphery of the cylindrical sleeve, and due to the centrifugal force acting on the magnetic toner, the magnetic force of the permanent magnet is no longer able to hold the magnetic toner on the sleeve, and the magnetic toner is eventually released from there. This is because they will separate and contaminate the surrounding area significantly.

However, in high-speed development, the rotation speed of the magnetic brush cannot be slowed down.

This is because the electrostatic charge image surface requires constant contact with the magnetic brush, and if the supply of the magnetic brush is cut off or delayed, it will cause turbulence (stripes with regular intervals that appear perpendicular to the direction of development of the electrostatic charge image). This is because it causes phenomenon called unevenness.

Therefore, if you try to prevent this problem without changing the rotational speed of the magnetic brush, you have no choice but to increase the magnetic poles of the permanent magnet and arrange many magnetic brushes in the sleeve. Must be.

As described above, as long as the rotating magnetic brush method is used, the magnetic toner is abraded by the sleeve and abraded by the slit.

Furthermore, the rotating magnetic brush method limits the development speed and cannot be freely controlled.

In order to use the magnetic toner in its desired form in high-speed development, the distance of the magnetic toner from the storage container to the electrostatic image surface is the shortest, and the distance of the magnetic toner that accompanies its feeding, such as in the rotating magnetic brush method, must be minimized. The method must not cause wear and tear.

As a result of intensive research in order to meet these demands, the inventor of the present invention has found that the amount of magnetic toner discharged is controlled by a magnet installed near the discharge section of the storage container, and the discharged magnetic toner that is attracted and formed by this magnet is It has now been discovered that all of the above-mentioned disadvantages can be obviated by using brush-like toner aggregates for developing electrostatic images.

According to this invention, the magnetic toner comes into contact with the electrostatic charge image at the same time as it is discharged from the storage container, so unlike the rotating magnetic brush method in which the magnetic toner must be forcibly moved on the sleeve, the magnetic toner is abraded. I have nothing to do.

Further, the height of the magnetic brush depends on the magnetic force of the magnet when the magnetic toner is discharged or the width of the opening of the discharge section.

Therefore, a doctor member for regulating the height of the magnetic brush is unnecessary, and the magnetic toner is not worn out due to resistance due to regulating the height of the magnetic brush.

In addition to these features, a special feature of the present invention is that the magnetic brush is replenished with the same amount of characteristic toner as is consumed in developing the electrostatic charge image. To explain this in more detail, the magnetic toner that is consumed during development and becomes insufficient in the brush-like aggregate (magnetic brush) of magnetic toner that is attracted and formed by the magnet is replenished by the magnetic brush. Immediately from the discharge section of the adjacent magnetic toner storage container.

This effect is caused by the magnetic force working to attract the magnetic toner to a certain distance from the center of the magnetic pole of the magnet, so in areas where magnetic toner is insufficient, the magnetic flux is disturbed, and a force is applied in the direction to correct this. .

Since the magnetic toner moves to that part, it is thought that a certain amount of magnetic toner is retained.

In connection with this action, the pressure exerted by the magnetic brush on the electrostatic image surface becomes constant.

Moreover, since the consumed amount of magnetic toner is immediately replenished, the developed density is faithful to the potential of the electrostatic image and is extremely stable.

This method is much simpler and superior to the rotating magnetic brush method, which stabilizes the developer density by supplying a new magnetic brush whose height is regulated at a constant level by the rotation of a magnet.

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

FIG. 1 is a diagram showing the principle of the present invention. In FIG. 1, a permanent magnet 11 attracts magnetic toner 12 at a certain distance from the center of its magnetic pole to form a magnetic brush.

The photoreceptor 14 has an electrostatic charge image 13 electrophotographically formed on its surface.

As shown in the figure, when the photoreceptor 14 crosses the magnetic brush, the electrostatic charge image 13 becomes a visible image due to the magnetic toner 12.

The magnetic brush is displaced in the direction of movement and slightly deformed due to friction with the photoreceptor 14.

Along with this, the direction of the magnetic flux 15 also changes.

However, as shown in Figure C, when the cause of the deformation of the magnetic brush disappears, the magnetic flux 15 attempts to return to its original position.

Therefore, when the magnetic toner 12 is replenished from the magnetic toner replenishing device 16 as shown in FIG. d, the replenishment is completed at the same time as the magnetic flux 15 returns to its original state.

FIG. 2 is a side view of a developing device showing an embodiment of the present invention, in which a permanent magnet 21 is fixed to a magnetic toner storage container 23. As shown in FIG.

The lower part of this storage container 23 is open, and the magnetic toner 22 is discharged from there by its own weight.

The permanent magnet 21 captures the magnetic toner 22 discharged from the discharge section 24 with its magnetic flux 25 to form a magnetic brush.

Then, the magnetic brush prevents the magnetic toner 22 from being discharged from the discharge section 24 due to gravity.

In this figure, the photosensitive plate 27 having the electrostatic charge image 26 moves from right to left, but it may move from left to right.

In this case, the magnetic toner 22 is replenished to the magnetic brush with a magnetic flux of 2
This is done at the same time as the transformation in step 5.

The developing device shown in FIG. 3 uses a magnetic brush to apply magnetic toner 2.
2 represents another method of controlling emissions of 2.

The permanent magnets 21 are fixed to the magnetic toner storage container 23 so that their magnetic poles are opposite to each other.

The polarity of the magnet is not necessarily important in this case.

Since the entire weight of the magnetic toner 22 in the storage container 23 is applied to the discharge section 24, a buffer member 28 can be provided to keep the weight constant regardless of the amount stored.

Since the magnetic flux 25 is closed, it is very stable, and the magnetic toner 22 is quickly replenished regardless of the direction of development.

FIG. 4 shows the arrangement of the permanent magnets 21 fixed near the discharge portion 24 of the magnetic toner storage container 23. As shown in FIG.

These may be arranged with opposite polarities in order, or may be arranged with the same polarity.

The storage container 23 can be connected to a vibration generator 29 and made to swing.

Further, as shown in FIG. 5, it can also be connected to a permanent magnet 21 and made to swing.

These means have the effect of making the flow of the magnetic toner 22 very smooth.

FIG. 6 shows a case in which the present invention is applied to an automatic copying machine. Here, instead of swinging the developing device, an electromagnet 30 is connected to an AC power source 31 to generate an alternating magnetic field at a predetermined time. The magnetic toner 22 near the discharge section 24 is vibrated.

The developed electrostatic charge image on the photosensitive drum 37 is transferred to the transfer device 32 by a feeding roller 33 for a transfer material 38 which also serves as a preliminary charge.
is sent to and transcribed.

The photoconductive insulating layer of the photosensitive drum 31 may be a resin binding layer mainly composed of lead oxide, or a vapor deposition layer mainly composed of amorphous selenium.

The remaining magnetic toner 22 that has not been transferred is cleaned by a cleaning device 36.

Then the electrophotographic cycle is repeated.

Examples of magnetic toners that can be used in the present invention include those obtained by hot-melting and pulverizing triiron tetroxide and thermoplastic resin, and powder obtained by spray-drying the above two substances dissolved in a solvent and mixed. .

Generally, these powders have an average particle size of 10 to 30 microns.

The electric resistance of the magnetic toner may be low, but when copying on plain paper, it is preferable that the magnetic toner has the property of exhibiting high resistance during electric field transfer.

As mentioned above, the present invention makes it possible to provide a developing device that is much simpler and more advantageous than known developing devices.

[Brief explanation of the drawing]

FIG. 1 is a diagram explaining the principle of this invention. FIGS. 2 to 6 are diagrams showing embodiments of the present invention. 34...DC power supply, 35...Corona charger.

Claims (1)

[Scope of Claims] 1. A container for storing magnetic toner for developing an electrostatic latent image, a discharge section for the magnetic toner provided below the container, and a discharge section disposed near the discharge section for discharging the magnetic toner. an electrostatic image developing device comprising: a magnet for forming a brush-like aggregate of the magnetic toner that rubs the electrostatic latent image on the outside of the part, and for preventing the magnetic toner from flowing out from the discharge part; 2. A storage container for magnetic toner that develops an electrostatic latent image, a discharge section for the magnetic toner provided below the container, and a discharge section for the magnetic toner disposed near the discharge section and outside the discharge section for storing the magnetic toner. An electrostatic image developing device comprising: a magnet that forms a brush-like aggregate of the magnetic toner that rubs the electrolatent image and prevents the magnetic toner from flowing out from the discharge section; and means for vibrating the magnet.