JPH07106327B2 - Method for classifying magnetic carrier for electronic copying machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention classifies different types of ferromagnetic particles by utilizing the difference in Curie point, which is the temperature at which ferromagnetism is lost. The present invention relates to a method of selecting and separating magnetic particles as a magnetic carrier for an electronic copying machine without damaging the original shape.

[Prior Art] A magnetic sorting method is a typical method for sorting by utilizing the difference in physical properties of materials. However, the conventional magnetic sorting method is a method in which all the objects to be sorted are brought into contact with a magnet and the magnetic force thereof separates the adsorbed material from the non-adsorbed material.

For example, when separating magnetic particles by a dry process, all particles to be sorted are sprinkled on a magnetic roll and placed on the roll surface to rotate, and the magnetic particles rotate while being caught by the strong magnetic field of the roll surface, but non-magnetic. The particles are separated by utilizing the fact that the particles fall due to gravity and centrifugal force.

[Problems to be Solved by the Invention] Ferrite particles are often used as a carrier for a two-component developer for an electronic copying machine. In order to exhibit sufficiently good copying characteristics, it is important that the particle size of the carrier, its surface condition, magnetic properties, etc. are substantially uniform. However, in the case of ferrite carrier, the non-uniformity of the mixed state of the oxide raw materials, the micro-uniformity of oxygen supply during the sintering process, the correspondence between the raw material and the tool material during the sintering process, the composition segregation, the tool material It is unavoidable that not only non-magnetic particles / weak magnetic particles but also ferromagnetic particles with slightly different magnetic characteristics are mixed due to the mixing of fragments or the same kind of particles from other sources, resulting in a wide distribution of magnetic characteristics. . In addition, there is considerable variation in particle size.

Usually, in the manufacturing process of a ferrite carrier, it is possible to obtain a predetermined particle size by sieving classification, but it is not possible to classify even a magnetic characteristic difference by only that. Further, even if the magnetic sorting method as in the prior art is used, it is possible to separate magnetic particles and non-magnetic particles, but it is impossible to separate even particles whose magnetic properties are slightly deteriorated or weak magnetic particles. Is.

However, when the carrier containing the weak magnetic particles or the ferromagnetic particles having different characteristics as described above is used as a developer, there arises a problem that the original fidelity of a copied image is deteriorated.

The object of the present invention is to solve the above-mentioned drawbacks of the prior art and to further improve the fidelity of the original in the copied image by applying it to the classification of the carrier of the two-component developer for the electrostatic copying machine, for example. It is an object of the present invention to provide a method that can be achieved, that is, can classify ferromagnetic particles to be classified according to the difference in their magnetic properties.

[Means for Solving the Problems] The present invention that can achieve the above-mentioned object is to classify different types of ferromagnetic particles into ferromagnetic particles having uniform characteristics as a magnetic carrier for an electronic copying machine. This is a method of sorting and separating. Magnets placed in a position apart from the moving surface by heating and keeping the ferromagnetic particles to be classified at a temperature midway between the corresponding Curie points of different kinds of particles contained in it. Thereby magnetically adsorbing and separating ferromagnetic particles having a Curie point exceeding the above temperature.

The temperature for heating and retaining the particles to be classified is set to a temperature slightly higher than or slightly lower than the Curie point of the ferromagnetic particles to be selectively separated.

As a magnet for magnetically attracting and separating ferromagnetic particles, a magnetic roll in which the outer surface of a cylindrical permanent magnet whose surface is multi-pole magnetized for continuous treatment is covered with a (non-magnetic) stainless steel cover. And a scraper plate placed close to it. The ferromagnetic particles having a high Curie point are magnetically adsorbed on the outer peripheral surface of the magnetic roll so as to be arranged in a chain shape in the radial direction. With the scraper plate attached to the outer surface of the magnetic roll so that the tip has a distance of several times the diameter of the ferromagnetic particles, only the ferromagnetic particles adsorbed on the outer peripheral side of the magnetic roll are removed, The magnetic particles on the inner peripheral side are classified while being kept adsorbed on the magnetic roll while continuing to rotate.

[Operation] In the classified ferromagnetic particles, a group of particles exhibiting desired magnetic properties to be selectively separated and a group of particles exhibiting different magnetic properties are mixed. There is a difference in the Curie points of both particle groups.
Here, when heating and keeping at a temperature between the Curie point of one particle group and the Curie point of the other particle group, particles with a low Curie point lose ferromagnetism, whereas particles with a high Curie point exhibit ferromagnetism. Keep holding.

The particles to be classified in which such particles are mixed move in a state of being dispersed in a plane. Then, a magnetic field is generated around the magnet by a magnet provided at a position separated from the moving surface by a certain distance. Therefore, the particles to be classified move in the magnetic field, and are influenced by the correlation between the moving speed and the attracting magnetic force, only particles having a high Curie point are adsorbed by the magnet, and other particles continue to move.

By changing the temperature and repeating such a method, it is possible to sort and separate the classified ferromagnetic particles composed of several kinds of particle groups having different magnetic properties for each composition group.

[Examples] FIG. 1 is a conceptual diagram showing an example of a magnetic classifier suitable for carrying out the method of the present invention, and is particularly useful for classifying a ferrite carrier of a two-component developer for an electronic copying machine. .

This magnetic classifier is a hopper that holds particles to be classified.
10, an inclined guide plate 12 for particles located below it, and a magnetic roll 14 arranged at an interval above the center of the particle,
A scraper plate 16 attached to the magnetic roll 14 and receiving containers 18a and 18b located at the lower ends of the scraper plate 16 and the inclined guide plate 12 are provided, and the whole is housed in a constant temperature bath 20.

The hopper 10 has a structure in which the particles 22 to be classified are housed therein, and a vertical wall and an inclined wall are combined so as to face each other, and an elongated drop opening 24 is opened at the lower end. The falling port 24 is for uniformly dropping the particles 22 to be classified into a film shape, and the opening width thereof is set to about several times the diameter of the particles to be classified. When the wedge effect due to the weight of the particles impairs the fluidity and makes it difficult for the particles to fall smoothly, a ceramic plate with a small friction coefficient is attached to the inner surface of the vertical wall surface to create a difference in friction force between the opposing wall surfaces. By doing so, the fluidity of the particles is improved and the particles can be smoothly dropped.

The magnetic roll 14 is composed of a cylindrical permanent magnet 26 whose surface is multi-pole magnetized, and a stainless steel cover 28 which covers the outer peripheral surface thereof, and is supported substantially horizontally by a central shaft 30 such as a motor (not shown). ) To rotate in the direction of the arrow.

The scraper plate 16 is located on the lower side of the magnetic roll 14 and is attached to the outer surface of the scraper plate 16 so as to be separated from the outer surface of the scraper plate so that the tips have a distance of several times the diameter of the magnetic particles. Scraper plate 16
As a material of the above, it is desirable to use stainless steel or the like having a hardness higher than that of the magnetic particles so that fragments and abrasion debris are not mixed.

Now, the method of the present invention is carried out as follows. For example, the Curie point of the ferromagnetic particles 22a to be selectively separated in the classified particles 22 is T _c1 , and the Curie point of the other type of ferromagnetic particles 22b mixed is T _c2 , and T _c1 > T _c2 There is a relationship. In that case, the temperature is maintained so that the temperature T of the particles to be classified 22 becomes an intermediate value (T _c1 >T> T _c2 ) between the Curie points T _c1 and T _c2 .

The particles 22 to be classified contained in the hopper 10 fall into the drop port 24.
Free fall from. The particles 22 to be classified that have fallen in the form of a film are received by the upper part of the inclined guide plate 12 and roll down along the same. Since the magnetic roll 14 rotates in the direction of the arrow above the middle portion of the inclined guide plate 12, the particles 22 to be classified are affected by the magnetic field thereof.

The particles 22 to be classified are kept at the temperature T as described above,
For the ferromagnetic particles 22a to be separated and sorted, the temperature is lower than the Curie point T _{c1 and} therefore the ferromagnetism is not lost. On the other hand, the other particles 22b lose ferromagnetism due to the temperature higher than their Curie point T _c2 . In this way, the particles that exhibit the ferromagnetism to be selectively separated and the particles that have lost the ferromagnetism are mixed and fall down the inclined guide plate 12.

When these classified particles 22 reach the vicinity of the magnetic roll 14, not only the non-magnetic particles, but also the particles 22b that have lost the ferromagnetism at the temperature T are not magnetically attracted and remain on the inclined guide plate 12 as they are. It falls and collects in the receiving container 18b. On the other hand, the particles 22a, which remain ferromagnetic, are adsorbed so as to be arranged in a chain on the outer peripheral surface of the magnetic roll 14 and rotate as they are, as shown in FIG. This adhered ferromagnetic particle 22a
Only the magnetic particles on the outer peripheral side are gently removed by the scraper plate 16, and the magnetic particles on the inner peripheral side continue to rotate while being attracted to the magnetic roll 14. In this way, when the gap between the tip of the scraper plate 16 and the magnetic roll 14 is slightly opened,
When performing the scraper operation, the magnetic particles are not damaged by being applied with excessive stress, and the separation and removal efficiency is not lowered. The ferromagnetic particles 22a removed by the scraper plate 16 roll on the scraper plate 16 and collect in the receiving container 18a.

In this way, the particles 22 to be classified in the hopper 10 are separated into two types, that is, ferromagnetic particles 22a having a high Curie point accumulated in the receiving container 18a and non-magnetic or low magnetic particles 22b having a low Curie point accumulated in the receiving container 18b. Will be done.

By repeating such an operation several times while changing the temperature, it is possible to separate and extract several kinds of particles having different compositions even if they are the same ferromagnetic particles.

Although the preferred embodiment of the present invention has been described in detail above, various modifications can be made to the apparatus for carrying out the method of the present invention. In the above device, the particles to be classified are configured to roll down along the inclined guide plate, but may be configured to fall freely, or the particles to be classified are thinly and uniformly dispersed on a conveyor that moves at a constant speed. It may be configured to move particles by moving. As the magnet for selectively adsorbing the ferromagnetic particles, the combination of the magnetic roll and the scraper plate is most preferable as in the above embodiment, but a simple structure in which a permanent magnet or an electromagnet is simply arranged may be used.

What is important in the present invention is that the particles to be classified are kept at a constant temperature. For that purpose, even if the whole device is not housed in a thermostatic chamber, a heating and heat-retaining device is installed in the hopper and the inclined guide plate to keep the particles to be classified at a constant temperature, and the magnetic roll etc. is lower than that. You may make it hold | maintain at temperature.

EFFECTS OF THE INVENTION Since the present invention has a constitution in which the particles to be classified are heated and kept at a predetermined temperature and magnetically classified by utilizing the difference in Curie point as described above, even if the particles to be classified are the same ferromagnetic particles, Due to the difference in the magnetic properties, it becomes possible to carry out classification, and it has an excellent effect that only particles suitable for the intended purpose can be easily taken out.

Therefore, the apparatus of the present invention is particularly effective for classifying a ferrite carrier of a two-component developer for an electrostatic copying machine, whereby the mixed state of the oxide raw materials is non-uniform, and the oxygen supply in the sintering process is non-uniform. It is possible to eliminate non-magnetic / weakly magnetic particles and ferromagnetic particles with different magnetic properties caused by reaction with tool materials in the sintering process or mixing of tool material fragments, etc. It is possible to improve the fidelity of the original.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing an example of a magnetic classification apparatus suitable for carrying out the method of the present invention, and FIG. 2 is an operation explanatory diagram of the magnetic roll and scraper plate. 10 ... Hopper, 12 ... Inclined guide plate, 14 ... Magnetic roll, 16 ... Scraper plate, 18a, 18b ... Receiving container, 20 ...
… Constant bath, 22 …… Particles to be classified.

Claims (1)

[Claims] 1. A method for classifying different types of ferromagnetic particles to classify and separate ferromagnetic particles having uniform characteristics as a magnetic carrier for an electronic copying machine, which includes the above-mentioned ferromagnetic particles to be classified. The magnetic particles are heated and kept at a temperature midway between the corresponding Curie points of different types of ferromagnetic particles, and the ferromagnetic particles are moved in a plane to obtain a multi-pole magnetized cylindrical permanent magnet. A magnetic roll whose surface is covered with a stainless steel cover is installed at a position distant from the moving surface of the ferromagnetic particles and rotated, so that the ferromagnetic particles having a Curie point exceeding the above temperature are on the outer peripheral surface of the magnetic roll. With a scraper plate that is magnetically adsorbed so as to be arranged in a chain in the radial direction, and is attached to the outer surface of the magnetic roll so that the tip has a distance of several times the diameter of the ferromagnetic particles. Magnetic roll Classification of magnetic carriers for electronic copying machines, characterized in that only the ferromagnetic particles adsorbed on the outer circumference side are removed, and the ferromagnetic particles on the inner circumference side are adsorbed on the magnetic roll and continue to rotate while sorting. Method.