JP2742924B2 - Magnet roller - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnet roller for development of a plain paper copying machine, and more particularly, to a method for providing a good image and providing toner and a carrier from a development device. The present invention relates to a magnet roller which is effective for preventing falling and scattering of the magnet. 2. Description of the Related Art Magnet rollers are frequently used in developing plain paper copiers to transport toner and carriers.
One of the disadvantages unique to such a magnetic developing method is that a magnetic toner caused by a magnetic field generated around a magnet roller,
In addition to the problem that the carrier catching power is insufficient and these fall and scatter around the developing device and cause the copier to become dirty, the toner and the carrier adhered to the photoreceptor reduce the gradation of the image. There is a problem that the image quality deteriorates such as white spots and black spots. Conventionally, as a method for preventing the toner and the carrier from falling and scattering, a method is employed in which the HR is maximized by focusing on the magnetic field component HR in the developing magnetic pole on the sleeve surface of the magnet roller. In general, a method of increasing the capturing power of toner and carrier is adopted. For this purpose, a method is used in which a magnet having high magnetic properties (for example, an anisotropic sintered ferrite magnet) is finished with high dimensional accuracy and used. However, there is a regret that this method increases the cost. FIG. 3 of Japanese Utility Model Laid-Open Publication No. 51-8745 shows that the width of the developing magnetic pole 21 is made sufficient by using a cylindrical magnet and is separated from the developing magnetic pole 21 so as to be close to the conveying magnetic pole 22 having a narrow width.
By providing the magnet 23, the problem in the case of using a conventional magnet having a rectangular cross section, that is, the magnetic flux density A 'in the vertical direction is large, the magnetic flux density B' in the tangential direction contributing to the transport of the developing pole is small, and the transport capacity is small. It is disclosed that this problem has been solved. FIG. 3 shows the magnetic flux density A ′ in the vertical direction and the magnetic flux density B ′ in the tangential direction.
Distribution is two peaks, so that the so-called “spike” of the developer is disturbed, and tailing (tailing) at copying, carrier adhesion to paper and toner adhesion are likely to occur, and good image quality is obtained. There is a problem that it is difficult. Although the magnet material is not specified, it is determined from the filing date that it is a sintered magnet.However, the sintered magnet has restrictions on the formability, the degree of freedom in the orientation and magnetization direction, and the degree of freedom in the cross-sectional shape. Yes, and therefore the design of the magnet roller is also constrained. SUMMARY OF THE INVENTION The present invention solves the above-mentioned drawbacks of the prior art, and the use of an inexpensive magnet having moderate magnetic properties results in a strong catching force. It is an object of the present invention to provide a magnet roller in which the carrier is effectively prevented from dropping and scattering, the resolution is enhanced, and the gradation and fine line properties are improved. That is, the present invention provides a plain paper copy comprising a magnet group in which a plurality of bond magnets are joined and arranged around a support shaft and a non-magnetic sleeve covering the outer circumference of the magnet group. In the machine magnet roller, a magnetic field component in the radial direction on the sleeve of the developing magnetic pole has a single peak near the developing magnetic pole and is larger than the peak value and is tangential to the magnetic field component in the radial direction. A magnetic field vector having a combined magnetic field vector with the directional magnetic field component, and a range of the composite magnetic field vector being closer to the center of the developing magnetic pole than the position of the toner and the carrier measuring blade and within 45 ° from the center of the developing magnetic pole. Includes net rollers. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The magnetic field strength of a developing magnet roller is generally evaluated by measuring only the radial magnetic field component HR at the sleeve surface, because of its ease of measurement. It is. However, since the magnetic field is a vector quantity, a tangential magnetic field component HT is inevitably present, and it is considered that this naturally contributes to the developing mechanism. The inventors of the present invention focused on a “synthetic magnetic field HA” that combines a radial magnetic field component and a tangential magnetic field component, and as a result, the trapping force of toner and a carrier is generally measured in the radial magnetic field. It has been found that it is more strongly associated with the absolute value of the resultant magnetic field than with the component value. Further, the present inventors, in addition to the HR magnetic field distribution on the surface of the sleeve of the magnet roller,
When the magnetic field distribution was varied and examined, it was found that a magnetic field vector having an HR consisting of a single peak near the developing magnetic pole and having an absolute value of HA larger than the peak value PG, HA ≧ When the two conditions that the PG range is on the center of the developing magnetic pole from the position of the toner and the carrier and the blade for metering and is within 45 ° from the center of the developing magnetic pole are satisfied, the peak value of HR becomes relative. Even a small magnet roller has a high toner and carrier capture power,
It has been found that these drops and scatters do not substantially occur and that good copy quality can be obtained. The magnetic pole center referred to here is one magnetic H
In the distribution pattern of R, it refers to the distribution center of two points on the left and right that cut this pattern at the half value height of the PG value. FIG. 2 shows an example of the magnetic field distribution on the surface of the sleeve of the magnet roller which is effective in preventing the toner and the carrier from dropping as described above. It is not clear why such a surface magnetic field distribution is effective, but regions where HA ≧ PG appear on the left and right sides of the developing magnetic pole, respectively, and the distribution of HA becomes a double-headed distribution having two peaks. It is considered that the toner and carrier present between the peaks are stably captured. In the present invention, HR needs to be a single peak. When the HR has a plurality of peaks, the HA distribution also has a plurality of (values exceeding 2) peaks,
Disorder occurs in the so-called "spring" of the developer, so that tailing and carrier adhesion are likely to occur, and good image quality cannot be obtained. The area where HA ≧ PG is preferably within 45 ° from the center of the magnetic pole of the developing magnetic pole, more preferably within 30 ° C., even more preferably within 15 °. If the area is too large, various disadvantages occur. That is, the amount of the toner and the carrier held in the area becomes excessive and the weight effect causes the toner and the carrier to drop sharply. The direction of the magnetic field vector at the peak of the magnetic field vector HA is excessively opened outward, and the toner and the carrier are removed. For example, the capturing effect is reduced. Therefore, the region where HA ≧ PG is preferably within the above-mentioned angle range, but if the angle range is too narrow, the region for capturing toner and carrier becomes small and the effect becomes insufficient. Since it varies depending on the level of the peak value, it cannot be unconditionally specified, but it is preferable that the range covers a range of about 5 ° or more. Further, as described above, it is inconvenient if the vector direction at the peak of the magnetic field vector HA is too open, but it is also possible to restrict this opening to an angle formed by the vector HA with respect to the radiation direction and suppress the opening within a certain angle. It is valid. Further, in order to adjust the amount of toner and carrier supplied to the developing magnetic pole, a blade for measuring the amount of toner and carrier cut off is provided before the developing magnetic pole, for example, in the vicinity of about 45 to 50 ° from the center of the developing magnetic pole. Is common.
If the magnetic field HA at the position of this blade is too strong, in addition to the difficulty of the above-mentioned measurement, there is also a drawback that the driving torque of the magnet roller increases, so that the range of HA ≧ PG is smaller than the position of this blade. Must be on the center side of the magnetic pole. Therefore, the position where HA ≧ PG needs to be within the above range. In the present invention, the "magnetic field component on the sleeve" will be described. Since the magnetic brush development performed by the magnet roller appears on the "sleeve surface", the magnetic field of the magnet roller has been developed in the industry. The measurement position is usually “on the sleeve surface” or “on the sleeve”. However, actually, due to the structure of the “hole probe” used for measurement, the magnetic field measurement has been performed at a position slightly away from the position in contact with the sleeve surface. That is, the Hall element, which is a sensor for measuring the magnetic field, is embedded at a position separated by a certain depth d from the surface of the probe. Although it is possible to expose this element to the probe surface, it is well known that the element is worn by contact with the object to be measured and its operation is not stable due to the influence of temperature fluctuation. Therefore, as described above, the Hall element is usually commercially available in an embedded state. Thus, strictly speaking, "measurement on the sleeve surface" means that the measurement is performed at a position distant from the position in contact with the sleeve surface by d. Calling "magnetic field above" is an industry practice. For example, in Japanese Patent Publication No. 60-37607,
In this case, it is described that "the magnetic flux distribution on the surface of the sleeve 20 was measured. (Col. 4, lines 12 to 14)." According to Japanese Utility Model Publication No. 57-9798, "the roll surface magnetic flux density can be increased to 1000G. (Second column 19-
21)), and the measurement position is not described. In the embodiment described later, the measurement position is
The value of the used hole probe, d = 0.5 mm, is described. In the first place, the characteristics (maximum or minimum) of the magnetic field pattern become clearer as they are closer to the magnet.
= 0.5 mm also holds true on the literal “on the sleeve”. Therefore, the embodiment is represented by d =
Even if it is performed at the position of 0.5 mm, a result different from the gist of the present invention is not obtained. As described above, the magnet roller according to the present invention is effective in preventing the toner and the carrier from dropping because the trapping force is increased even if the value of the radial magnetic field component (HR) is relatively low. In addition, the toner and the carrier adhered to an extra portion (white portion in the image) on the photoreceptor are pulled back to the magnet roller, so that the resolving power is enhanced, and the gradation and fine line are improved. Therefore, it is not necessary to use a magnet having a particularly high magnetic property. In order to realize such a magnet roller, the magnet is used by adjusting the orientation and magnetizing direction and sectional shape of the magnet to be used and the method of combining the magnet with an adjacent magnet. For example, the width in the rotation angle direction of the permanent magnet corresponding to the developing magnetic pole 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 in the rotation direction of the permanent magnet is both ends. Means such as a shape closer to the sleeve surface (double-headed shape), or a magnet having the same magnetism as the permanent magnet corresponding to the developing magnetic pole is arranged, and the developing magnetic pole There are means such as increasing the HA at both ends, and these are used in combination. Therefore, it is desirable that each magnetic pole for use in the present invention has a degree of freedom in the orientation and magnetization direction and a degree of freedom in the cross-sectional shape. Therefore, a bonded magnet using a so-called plastic or rubber as a binder is used. In the present invention, the term “joining arrangement” means that a plurality of bonded magnets are arranged by joining their circumferential end faces on a support shaft. Hereinafter, the present invention will be described with reference to examples.
The present invention is not limited by these. Example 1 and Comparative Example 1 As shown in the cross-sectional view of the scale shown in FIG. 3, a plastic anisotropic magnet (2) having a maximum energy product of 1.5 MGOe of each shape was placed in an aluminum sleeve (3) having an outer diameter of 31 mm. )
(2 ') (2') (2 ') molded and magnetized into the respective shapes shown in the figure were joined to an iron shaft (1), and the outer diameter of rotation was finished to 27.5 mm and assembled. FIG. 4 shows a pattern diagram of HR and HA at a position of 0.5 mm from the surface of the sleeve. The range where HA ≧ PG was ± 37 °. This magnet roller was assembled in a plain paper copying machine and a copying test was carried out. As a result, toner and carrier were hardly dropped. On the other hand, for comparison, the aluminum shaft (1) and the maximum energy product 3.
A magnet roller to which 5MGOe magnets (2), (2 ′), (2 ′), and (2 ′) were joined was assembled using an aluminum sleeve (3) having an outer diameter of 31 mm. In a copy test using this magnet roller, toner and carrier dropped, and stains were observed on the paper. FIG. 6 shows a pattern diagram of HR and HA at a position of 0.5 mm from the surface of the sleeve. However, although the PG of the magnet roller is larger than the magnet roller according to the present invention, the disadvantages described above are obtained. And HA ≧ PG
Is not present. As described above, the magnet roller according to the present invention can effectively prevent the toner and the carrier from dropping and scattering, and provide good copy quality. According to the present invention, a high quality magnet roller can be efficiently designed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a magnetic field vector diagram of a sleeve surface of a magnet roller. FIG. 2 is a conceptual diagram of a 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. FIG. 4 is a magnetic field distribution diagram of the magnet roller of FIG. 3; FIG. 5 is a schematic sectional view of a magnet roller for comparison. 6 is a magnetic roller magnetic field distribution diagram of FIG. [Description of Signs] 1 shaft 2 developing magnetic pole magnet 2 'magnet 3 sleeve

Claims (1)

(57) [Claims] In a magnet roller for a plain paper copying machine comprising a magnet group in which a plurality of bond magnets are joined and arranged around the support shaft and a non-magnetic sleeve covering the outer circumference of the magnet group, the developing roller is disposed near the developing magnetic pole. There is a combined magnetic field vector of the radial magnetic field component and the tangential magnetic field component whose radial magnetic field component on the sleeve of the magnetic pole has a single peak and is larger than the peak value, and the range is the toner. A magnet roller which is closer to the center of the developing magnetic pole than the position of the carrier wear measuring blade and is within 45 ° from the center of the developing magnetic pole.