JPS5921035B2 - Electrostatic latent image developing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses a one-component magnetic toner to make an electrostatic latent image formed on an image carrier such as a photoreceptor, photosensitive paper, or recording paper visible through a predetermined process. This invention relates to a device for imaging.

First, an example of an electrophotographic copying machine equipped with such a developing device will be described with reference to FIG.

Around the photosensitive drum 1, there are a charging corona discharger 2, an exposure optical system 3, a developing device 4, a transfer corona discharger 5, a static elimination corona discharger 6, a static elimination lamp T, and a cleaning device 8. placed in a predetermined position. The surface of the photosensitive drum 1 rotating at a constant speed in the direction of the arrow is first uniformly charged by a charging corona discharger 2, and then an original image to be copied is projected onto this surface by an exposure optical system 3. An electrostatic latent image is formed.

This electrostatic latent image is visualized by applying developer from the next developing device 4. A transfer sheet s sent from a predetermined direction is superimposed on the toner image on the photoreceptor drum obtained by development, and the toner image is transferred to the transfer sheet by being acted on by a transfer corona discharger 5 from above. s is transcribed. The potential remaining on the photoreceptor drum and the residual toner held therein are removed by a static eliminating corona discharger 6.
, are removed from the photosensitive drum by the static eliminating lamp 7 and the cleaning device 8, respectively. The developer used in this developing device is a one-component magnetic toner.

Generally, there are two types of developer used in such a developing device: a two-component developer and a one-component developer. A two-component developer is used by mixing a toner and a carrier and frictionally charging each other, and a one-component developer is a toner alone or a mixture of magnetic powder and toner. The present invention particularly relates to a developing device using a one-component magnetic toner obtained by kneading the latter magnetic powder and toner. In order to obtain a good visible image using a one-component magnetic toner, it is necessary to charge the magnetic toner by some method to a polarity opposite to that which forms the electrostatic latent image. FIGS. 2 and 3 show a conventional magnetic toner charging method. In FIG. 2, magnetic toner 12 supplied from a hopper 11 is attracted onto the surface of a non-magnetic sleeve 13 by the magnetic attraction force of a magnet 14 housed inside the sleeve. As the sleeve 13 coaxially rotates around the stationary magnet 14, the magnetic toner on the sleeve is transported toward the development position where it contacts the photoreceptor drum 15. Before reaching the development position, a frictional charging member 16 is pressed against the magnetic toner on the sleeve to triboelectrically charge the magnetic toner to a predetermined polarity. For example, if the latent image has negative polarity, the magnetic toner is charged positively. Therefore, in this case, the material of the frictional charging member is selected from a material lower in the frictional charging series than the resin material constituting the toner. On the other hand, in the apparatus shown in FIG. 3, the magnetic toner is charged to a predetermined polarity by discharge from a corona discharger 17 instead of the frictional charging member.

Although corona dischargers have a better charging effect than triboelectric charging members, they are expensive and have drawbacks in terms of maintenance, such as toner adhesion to the discharge electrodes. However, in this method of charging magnetic toner, the behavior of the charged toner is unstable, especially between the charging position and the developing position, because there is no carrier to act as a carrier in the two-component developer. This resulted in instability, background smudges, and excessive toner adhesion, and was not practically satisfactory. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a developing device that uses an inexpensive triboelectric charging member, stabilizes the behavior of toner, and performs good development.

This invention will be explained below with reference to FIGS. 4 and 5.

In FIG. 4, magnetic toner 21 having a specific resistance value of about 108 to 101゛4Ωα is accommodated in a hopper 22, and is supplied from the lower opening of the hopper 22 to the surface of a sleeve 23 rotating in the direction of the arrow. Ru. A magnet 24 having a plurality of magnetic poles is mounted in the sleeve 23 so as not to rotate, and the magnetic toner is attracted onto the sleeve surface by the magnetic attraction force of the magnet 24. The attracted magnetic toner is conveyed to the development position as the sleeve rotates. The development position refers to an area where the toner on the sleeve comes into contact with the surface of the photoreceptor drum 25, centered on a line passing through the center of the sleeve and perpendicular to the surface of the photoreceptor drum 25. The tip of the triboelectric charging member 26 is located at a part of this development position and between the toner on the sleeve and the surface of the photoreceptor drum. As shown in the partially enlarged view of FIG.
is composed of a frictional charging plate 26a and a support member 26b, and the tip of the charging plate 26a is 0.0 mm from the surface of the photoreceptor drum.
They are separated by about 1 to IllL, and their tips extend to the center of the development position. The frictional charging plate 26a is preferably made of a non-magnetic conductor such as aluminum or phosphor bronze and has a certain degree of hardness, and is grounded via a support member 26b. The triboelectric charging plate 26a is also selected in consideration of the triboelectrification series so that the magnetic toner can be charged to a predetermined polarity. The magnetic toner 21 in the soil of the sleeve 23 that has been conveyed to the development position is charged to a predetermined polarity, for example, positive, by frictional contact with a frictional charging plate 26a provided extending over a part of the development position, and at the same time Charge plate 26
a is charged with the opposite polarity, that is, negatively charged.

Therefore, since the negatively charged triboelectric plate 26a is present at the development position, this plays the role of a carrier in the two-component developer, stabilizing the behavior of the positively charged toner, and causing this toner to be negatively charged. When contacted with the formed electrostatic latent image, the charged toner is ensured to adhere to the latent image. The force relationship at this time is such that the magnetic attraction force of the magnet 24 to the magnetic toner 21 is greater than the electrostatic attraction force between the magnetic toner 21 and the frictional charging plate 26a, and the latent image charge is greater than this magnetic attraction force. It is most preferable to increase the electrostatic attraction force toward the magnetic toner. The conductive triboelectric charging plate 26a may not be grounded. However, if frictional charging is repeated, electric charge will accumulate on the frictional charging plate, and it may eventually reach a saturated state and no longer function as a frictional charging member, so it must be grounded to prevent electric charge from accumulating. By letting it escape, a good charged state can be maintained at all times. Furthermore, the frictional charging plate 26a can be made insulative rather than conductive.

For example, a plastic plate is suitable, and one that can charge the toner to a predetermined polarity is selected. Also at this time, the frictional charging plate 26a is charged to the opposite polarity to the magnetic toner 21,
It serves as a carrier for two-component developer. When the triboelectric charging plate is conductive, it corresponds to a carrier of the two-component developer, for example, iron powder, and when it is insulative, it corresponds to a carrier, for example, glass beads. Furthermore, the frictional charging plate 26a may be provided in contact with the surface of the photoreceptor drum 25.

However, in this case, care must be taken not to damage the surface of the photoreceptor drum, and it is more convenient to provide it close to the surface of the photoreceptor since it also functions as a counter electrode. As described above, according to the present invention, the triboelectric charging member is a part of the development position where the magnetic toner on the sleeve comes into contact with the electrostatic latent image on the image carrier, and the frictional charging member is connected to the surface of the image carrier. The frictional charging member charges the magnetic toner to a predetermined polarity at the development position and also serves as a carrier for the two-component developer.
As a result, the behavior of the charged magnetic toner is stable, reliable development is possible, high quality images are obtained, and the structure is simple.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing an example of an electrophotographic copying machine to which a developing device of the present invention is applied, and FIGS. 2 and 3 are
FIG. 4 is a schematic sectional view showing a conventional method of charging magnetic toner, FIG. 4 is a schematic sectional view showing an example of a developing device according to the present invention, and FIG. 5 is a partially enlarged view of FIG. 4. 21...-One-component magnetic toner, 22...-Hopper 23...Non-magnetic sleeve, 24...
...Magnet, 25...Photosensitive drum, 26...
-...Frictional charging member.

Claims (1)

[Claims] 1 By relatively moving a non-magnetic sleeve and a magnet housed therein, one-component magnetic toner supplied onto the sleeve is held and conveyed, and this magnetic toner is transferred to an electrostatic latent image on an image carrier. In an electrostatic latent image developing device that visualizes the electrostatic latent image by bringing it into contact with the sleeve, a grounded triboelectric charging member is placed at one of the development positions where the magnetic toner on the sleeve comes into contact with the electrostatic latent image on the image carrier. An electrostatic latent image developing device, characterized in that the electrostatic latent image developing device is provided between the magnetic toner and the surface of the image carrier.