JPH0693153B2 - Magnet controller - Google Patents

Description

The present invention relates to a developing magnet roller for a plain paper copying machine, and more specifically, it provides a good image and, at the same time, drops toner or carrier from the developing device. The present invention relates to a magnet roller that is effective in preventing scattering.

"Prior Art and Problems" In developing a plain paper copying machine, a magnet roller is often used for carrying toner and carrier. One of the drawbacks peculiar to such a magnetic developing system is that the magnetic toner generated by the magnetic field generated around the magnet roller and the carrier cannot be sufficiently captured by the carrier, and they fall and scatter around the developing device, resulting in Not only is there a problem of causing stains, but there is also a problem that the toner and carrier attached to the photoconductor lowers the gradation of the image, and the image quality such as white spots and black spots deteriorates.

Heretofore, as a method of preventing the toner and carrier from falling and scattering, attention has been paid to the radial magnetic field component HR at the developing magnetic pole on the sleeve surface of the magnet roller, and by making HR as large as possible, the toner and carrier The method of increasing the capturing power of is generally adopted. For this purpose, a means of using a magnet having a high magnetic property (for example, an anisotropic sintered ferrite magnet) after finishing with high dimensional accuracy is used.
However, this method has a drawback that the cost is high.

"Means for Solving Problems" The inventors of the present invention have solved the above drawbacks, and have diligently studied a magnet roller that does not drop or scatter toner or carrier even if an inexpensive magnet having a medium magnetic property is used. As a result, the present invention has been completed.

That is, the present invention relates to a magnet roller for a plain paper copying machine, which comprises a magnet group in which a plurality of magnets are joined and arranged around a support shaft and a non-magnetic sleeve covering the outer circumference of the magnet group, in the vicinity of the developing magnetic pole. , There is a combined magnetic field vector of the radial magnetic field component and the tangential magnetic field component that has a radial magnetic field component on the sleeve of the developing magnetic pole larger than the peak value, and its range is 45 from the developing magnetic pole center. The content is a magnet roller characterized by being within °.

Conventionally, the magnetic field strength distribution of the developing magnet roller has been focused only on the radial magnetic field component on the sleeve surface. The inventors of the present invention have conducted extensive studies on the trapping force of toner and carrier, and as a result, the trapping force of toner and carrier is not regulated by the magnetic field component in a specific direction on the sleeve of the magnet roller, but by It was found that it is defined by the absolute value of the composite magnetic field vector obtained as the vector sum. That is, in FIG. 1, HR is a radial magnetic field component, HT is a tangential magnetic field component, and HA.
Represents the composite magnetic field vector, but the trapping force of toner and carrier is defined by HA instead of HR. Therefore, the present inventors examined various magnetic field distributions of HA in addition to the magnetic field distribution of HR on the surface of the sleeve of the magnet roller, and found that HA near the developing magnetic pole was larger than the peak value PG of HR. When there are two magnetic field vectors with the absolute value of, the range of HA ≧ PG is within 45 ° from the center of the developing magnetic pole, the peak value of HR is relatively small. It has been found that even a roller has a high toner and carrier trapping force, and these particles do not fall or scatter.

The magnetic pole center referred to here is the distribution center of two points on the left and right that cut this pattern at the half-height of the PG value in one magnetic HR distribution pattern. An example of the magnetic field distribution on the sleeve surface of the magnet roller, which is effective for preventing the toner and carrier from falling as described above, is shown in FIG. Although it is not clear why such surface magnetic field distribution is effective, regions where HA ≧ PG appear on the left and right sides of the developing magnetic pole, and the HA distribution is a double-headed distribution with two peaks.
It is considered that the toner and carrier existing between the two peaks are stably captured.

The area where HA ≧ PG is preferably within 45 ° from the magnetic pole center of the developing magnetic pole, more preferably within 30 ° C., 15
It is more preferable if it is within the range of °. If such a region is too wide, various inconveniences occur. In other words, the amount of toner and carrier held in the area becomes excessive, and the weight effect causes the toner and carrier to drop violently.
The direction of the magnetic field vector at the peak of HA opens too outward,
For example, the trapping action of toner and carrier is reduced. Therefore, it is preferable that the area where HA ≧ PG is within the above-mentioned angle range, but if the angle range is too narrow, the area for trapping toner and carrier becomes small and the effect becomes insufficient. Although it cannot be unconditionally specified because it fluctuates depending on the peak value level, it is preferable that the range be approximately 5 ° or more. Furthermore, it has been described that it is inconvenient if the vector direction at the peak of the magnetic field vector HA is too wide, but it is also possible to define this opening as the angle formed by the vector HA with respect to the radial direction and suppress it within a certain angle. It is valid.

Further, in order to adjust the supply amount of toner and carrier to the developing magnetic pole, it is common to provide a blade for measuring toner and carrier scraping in front of the developing magnetic pole, for example, in the vicinity of about 45 to 50 ° from the center of the developing magnetic pole. Is. If the magnetic field HA at the position of this blade is too strong, in addition to the above-mentioned weighing being difficult, there is also the drawback that the magnet roller drive torque will be high, so the range HA ≥ PG is higher than the position of this blade. It is necessary to be on the center side of the developing magnetic pole. Therefore, HA ≧ PG
It is necessary that the position of is within the above range.

Since the developing sleeve and the photoconductor are used by rotating in a fixed direction, the peak position of the magnetic field vector HA does not necessarily have to be on both sides of the peak of HR, but may be on at least one effective side.

As described above, the magnet roller according to the present invention is effective in preventing the toner and the carrier from falling as a result of the strong capturing force even when the value of the magnetic field component in the radial direction is relatively low. By pulling back the toner and carrier attached to the extra portion (white portion in the image) to the magnet roller side, the resolving power is enhanced and the gradation and fine line property are improved. Therefore, it is not necessary to use a magnet having particularly high magnetic characteristics.

In order to realize such a magnet roller, the orientation and magnetization direction and sectional shape of the magnet to be used and the combination method with the adjacent magnet are adjusted. For example, the width of the permanent magnet corresponding to the developing magnetic pole in the rotation angle direction is widened, both ends in the rotation direction of the permanent magnet are magnetized more strongly than the center part, and the cross-sectional shape of the permanent magnet in the rotation direction is Means such as a shape closer to the sleeve surface (double-headed shape),
Alternatively, there is means such as arranging a magnet having the same characteristics as the permanent magnet adjacent to the developing magnetic pole and having the same magnetic field effect to increase the HA at both ends of the developing magnetic pole. Used in combination. Therefore, although a general-purpose magnet material generally used can be used for each magnetic pole magnet used in the present invention, it is desirable that the magnetic material has a degree of freedom in the orientation and magnetization direction and a degree of freedom in the cross-sectional shape. Therefore,
So-called plastics and bonded magnets using rubber as a binder are preferred.

"Examples" Hereinafter, the present invention will be described with reference to Examples, but the present invention is not limited thereto.

Example 1 and Comparative Example 1 As shown in the cross section of the scale diagram in FIG. 3, the maximum energy product of each shape was 1.
5MGOe plastic anisotropic magnet (2) (2 ')
Each of (2 ') and (2') molded and magnetized into the illustrated shape was joined to an iron shaft (1), and the outer diameter of rotation was finished to 27.5 mm for assembly. The pattern diagram of HR and HA at the position 0.5 mm from the sleeve surface was as shown in FIG. HA
The range of ≧ PG was ± 37 °. I did a copy test by incorporating this magnet roller into a plain paper copier.
Almost no drop of toner or carrier was seen.

On the other hand, for comparison, the magnet roller with the aluminum shaft (1) and the magnets (2) (2 ') (2') (2 ') of maximum energy product 3.5MGOe joined in a scaled shape as shown in FIG. 5 is removed. It was assembled using an aluminum sleeve (3) with a diameter of 31 mm. In the copy test using this magnet roller, toner and carrier were found to have fallen and stains were observed on the paper. H at 0.5 mm from the sleeve surface
A pattern diagram of R and HA is shown in FIG. 6. The above-mentioned inconvenience occurs even though the PG of this magnet roller is larger than that of the magnet roller according to the present invention. This is because there is no region where ≧ PG.

[Operation / Effect] As described above, the magnet roller according to the present invention does not drop or scatter toner or carrier, and provides good copy quality.

[Brief description of drawings]

FIG. 1 is a vector diagram of the magnetic field on the sleeve surface of the magnet roller, FIG. 2 is a conceptual diagram of the magnetic field distribution of the magnet roller of the present invention, FIG. 3 is a schematic sectional view showing an embodiment of the present invention, and FIG. FIG. 3 is a magnetic field distribution diagram of the magnet roller of FIG. 3, FIG. 5 is a schematic sectional view of the magnet roller for comparison, and FIG. 6 is a magnetic roller magnetic field distribution diagram of FIG. 1 ... Shaft 2 ... Development magnetic pole magnet 2 '... Magnet 3 ... Sleeve

Continuation of the front page (56) References JP-A-54-95243 (JP, A) JP-A-57-114164 (JP, A) JP-A-59-57265 (JP, A) Actual development-Sho 51-8745 (JP , U)

Claims (1)

[Claims] 1. A magnet roller for a plain paper copying machine comprising a magnet group in which a plurality of magnets are joined and arranged around a support shaft, and a non-magnetic sleeve covering the outer circumference of the magnet group, in the vicinity of a developing magnetic pole. , There is a combined magnetic field vector of the radial magnetic field component and the tangential magnetic field component that has a radial magnetic field component on the sleeve of the developing magnetic pole larger than the peak value, and its range is 45 from the developing magnetic pole center. A magnet roller characterized by being within °.