1. Field of the Invention
The present invention relates to a method of multipolar-magnetization of a rollable long magnetic sticking sheet so as to enable it to be stuck to a ferrous metal surface or other soft magnetic material by magnetic force and to a simple magnetization apparatus for the same.
2. Description of the Related Art
As a conventional magnetic sticking sheet, one comprised of a flexible hard magnetic sheet formed by extrusion or calendaring and then multipolar-magnetized can be mentioned. In the extrusion or calendaring, a mixture of particles of a hard magnetic material such as barium ferrite or strontium ferrite and a binder such as rubber or plastic is compressed to form a flexible hard magnetic sheet having a thickness of for example 0.05 to 0.5 mm (see Japanese Unexamined Patent Publication (Kokai) No. 10-24534). As another conventional magnetic sticking sheet, one comprised of a substrate coated with a magnetic coating, dried, then multipolar-magnetized can be mentioned (see Japanese Unexamined Patent Publication (Kokai) No. 58-178508, Japanese Unexamined Patent Publication (Kokai) No. 2001-76920, Japanese Patent Application No. 2001-231833 (Japanese Patent No. 3297807), and Japanese Patent Application No. 2001-228542 (Japanese Patent No. 3309854)).
On the other hand, as a method of multipolar-magnetization of a magnetic sticking sheet, a method using a capacitor type power supply for magnetization can be mentioned. In this method, a plate-shaped multipolar magnetization yoke is placed closely against the sheet to be magnetized and a large current is supplied to the yoke using a capacitor type power supply for magnetization to create N-poles and S-poles periodically on one side or both sides of the sheet (see Japanese Unexamined Patent Publication (Kokai) No. 2001-76920 and Japanese Unexamined Patent Publication (Kokai) No. 61-7609).
As another method of magnetization, a method of arranging plate-type permanent magnets in a line to create a combined permanent magnet and moving it relative to the sheet to be magnetized is also disclosed (see Japanese Patent Application No. 2001-231833 (Japanese Patent No. 3297807), Japanese Patent Application No. 2001-228542 (Japanese Patent No. 3309854), Japanese Unexamined Patent Publication (Kokai) No. 2001-68337, Japanese Unexamined Patent Publication (Kokai) No. 2001-230118, Japanese Unexamined Patent Publication (Kokai) No. 2001-297911, and Japanese Patent Application No. 2001-256774 (Japanese Patent No. 3309855). In the combined permanent magnets described in Japanese Patent No. 3297807, No. 3309854, and No. 3309855, the plate type permanent magnets are arranged so that different poles face each other. As opposed to this, in the combined permanent magnets described in Japanese Unexamined Patent Publication (Kokai) Nos. 2001-68337, 2001-230118, and 2001-297911, the plate type permanent magnets are arranged so that the same poles face each other.
As described in Japanese Patent No. 3297807, No. 3309854, and No. 3309855, when forming a magnetic layer by coating a magnetic coating on a substrate and multipolar-magnetizing it by a combined permanent magnet, it is also possible to produce a long magnetic sticking sheet reel to reel, that is, in-line.
As described in the Japanese Unexamined Patent Publications (Kokai) No. 2001-76920 and No. 61-7609, when multipolar-magnetizing by a capacitor type magnetization apparatus, the larger the area of the magnetic sticking sheet, the larger the scale of the magnetization system required and the more expensive the equipment cost. Further, since a large current is supplied during magnetization, there is the danger of electric leakage, shock, etc.
Further, charging is necessary before discharge, so the magnetization is conducted intermittently. In other words, continuous magnetization is not possible. Therefore, particularly when producing a long sheet roll, the productivity falls. For these reasons, the running cost of the capacitor type magnetization apparatus becomes higher.
As a method of increasing the magnetic sticking force of a magnetic sticking sheet, there is the method of making the magnetization pitch narrower. However, in the case of a capacitor type magnetization apparatus, a large current is supplied instantaneously, so discharge ends up occurring between electrodes if the magnetization pitch is made narrower to for example 2 mm or less. Therefore, there is a limit to narrowing the magnetization pitch and therefore a limit to the magnetization strength.
According to the multipolar-magnetization method using a permanent magnet, the above problems found in the capacitor type magnetization apparatus are solved. However, as shown in FIG. 1, in the cylindrical combined permanent magnet described in Japanese Unexamined Patent Publications (Kokai) No. 2001-68337, No. 2001-230118, and No. 2001-297911, the plate type permanent magnets are stacked so that the same poles face each other. Further, as shown in FIG. 2, in the cylindrical combined permanent magnet described in Japanese Unexamined Patent Publication (Kokai) No. 2001-230118, thin plate type permanent magnets are arranged so that the same poles face each other.
Due to this, a repulsive force acts between the stacked plate type permanent magnets. Therefore, unless an external force of a magnitude canceling out the repulsive force is continuously supplied, the configuration as a combined permanent magnet cannot be maintained. Further, in the combined permanent magnets described in Japanese Unexamined Patent Publication (Kokai) No. 2001-68337, No. 2001-230118, and No. 2001-297911, if the magnetization pitch is made narrower for the purpose of increasing the magnetic sticking force of the magnetic sticking sheet to be magnetized, the plate type permanent magnets inevitably become thinner. Due to this, the distance between magnetic poles becomes shorter and the leakage magnetic flux density decreases, so the magnetization force is weakened.
When rotating a combined permanent magnet having N-poles and S-poles arranged along a shaft of a cylinder as shown in FIG. 1 on a sheet, the sheet is multipolar-magnetized so that N-poles and S-poles are arranged alternately in the axial direction of the cylinder. On the other hand, when multipolar-magnetizing a long sheet by using a cylindrical combined permanent magnet, unless the axial direction of the combined permanent magnet is orthogonal to the sheet longitudinal direction, the sheet cannot be processed continuously.
When rotating a combined permanent magnet in the state where the axial direction of the cylindrical combined permanent magnet is orthogonal to the sheet longitudinal direction and the combined permanent magnet contacts the sheet to be magnetized, the sheet is magnetized proceeding along the longitudinal direction. However, according to the configuration of the combined permanent magnet shown in FIG. 1, the N-poles and S-poles are arranged along the shaft of the cylinder, so this is not suitable for continuous multipolar-magnetization of a long sheet having an axis of easy magnetization oriented in the sheet longitudinal direction.
Japanese Patent No. 3309854 and No. 3309855 disclose methods of magnetization wherein a square columnar combined permanent magnet is moved relative to the sheet to be magnetized are disclosed, but have no specific description about a cylindrical combined permanent magnet.
Japanese Patent No. 3297807 discloses a cylindrical combined permanent magnet composed of permanent magnets arranged so that the different pole surfaces face each other as shown in FIG. 3. According to this combined permanent magnet, the N-poles and S-poles are arranged alternately on the circumference, so by rotating the combined magnet on a long sheet, it is possible to continuously multipolar-magnetize a long sheet having an axis of easy magnetization oriented in the sheet longitudinal direction. Further, since the permanent magnets composing the combined permanent magnet are arranged cylindrically so that the different pole surfaces face each other, no repulsive force acts between permanent magnets.
As described above, according to the cylindrical combined permanent magnet for magnetization described in Japanese Patent No. 3297807, it is possible to magnetize a long sheet conveniently at a high speed. However, in the method of magnetization described in Japanese Patent No. 3297807, when the angle of contact of the sheet fed to the cylindrical combined permanent magnet is not suitable, problems specific to the magnetic sticking sheet not found in usual roll paper arise.
When printing or coating a coating material on roll paper, wrinkling of the paper being rolled, slack, uneven rolled end surfaces, etc. are prevented by adjusting the angle of contact and tension of the paper. However, when magnetizing a roll type magnetic sticking sheet by a cylindrical magnet, since the magnetic sticking force acts between the sheet being magnetized and the magnet, if the angle of contact is larger than necessary, the sheet sticks to the magnet more than the angle of contact.
Due to this, the sheet traveling over the cylindrical magnet flaps around and obstructs the feed of the sheet. If the sheet does not travel smoothly, the entire surface of the sheet may not be magnetized uniformly or slack may occur when rolling up the magnetized sheet. Further, even if adjusting the tension of the sheet fed to the magnet, since the effect of the magnetic sticking force acting between the sheet and the cylindrical magnet is large, it is difficult to improve the running condition of the sheet by adjusting the tension.
In recent years, demand for printers able to print on large size paper such as A0 size paper has increased. At present, roll paper is used for all of commercially available printers for large size paper. Therefore, when desiring to produce a large size printed object from a magnetic sticking sheet, it is necessary to feed the sheet to the printer from a roll.