JPH061440Y2 - Magnetic blackboard - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic blackboard capable of high-resolution writing with a magnetic pen and capable of easy partial erasing and whole erasing.

[Prior art]

2. Description of the Related Art Conventionally, as a magnetic blackboard using magnetism, one in which ferromagnetic fine particles are confined in a solution and one in which a flat magnet is confined in a solution are known.

As shown in FIG. 2, the former structure of the magnetic blackboard in which the ferromagnetic fine particles are confined in the solution is such that the ferromagnetic fine particles 6'are dispersed together with the inclusion liquid 2 in the honeycomb core 1 divided into a large number, and the surface sheet 4 and the back sheet 5. In such a magnetic blackboard, magnetic fine particles 6 '
Does not move when no external force is applied, and when a magnetic pen is applied from above the surface sheet 4, it is attracted by the magnetic field generated from the magnetic pen and gathers on the surface. The inclusion liquid 2 has a milky white color, and when the magnetic fine particles 6'are on the back surface side, it appears white, and when the magnetic fine particles 6'is on the surface sheet side, the color of the fine particles (usually black) is visible. . The characters and figures are erased by sliding a magnet on the back surface of the back sheet and collecting the magnetic fine particles 6'on the back sheet side. In a magnetic blackboard using such ferromagnetic fine particles 6 ', in order to erase characters, figures, etc. written once, it is necessary to bring a magnet close to the back of the blackboard. Erase to
It is difficult to provide the function of making corrections, etc., and the applications used are limited.

On the other hand, in the latter magnetic blackboard using a flat magnet, characters can be erased and corrected from the surface by changing the polarity of the writing magnetic pen, but a flat magnet with different front and back colors in a transparent solution is used. Since they are placed, there is a problem in the contrast of characters and figures.

Both of these magnetic blackboards have a problem that it is difficult to obtain high resolution because writing is performed by using a leakage magnetic field generated from the tip of the magnetic pen.

〔Purpose〕

An object of the present invention is to provide a magnetic blackboard having excellent contrast and resolution and capable of erasing characters, figures and the like from the display surface.

〔Constitution〕

In order to achieve such a technical problem, the present inventor previously used magnetic particles having a phase transition point at a temperature exceeding room temperature as a partially erasable magnetic blackboard, and generates both heat and magnetic field during writing. A magnetic blackboard was devised and filed by contacting a magnetic sheet with a pen and heating and magnetizing the heat-induced magnetic particles by the heat of the pen, and at the same time moving the magnetic particles to the surface sheet side by the magnetic field of the pen ( 62
-82994). However, in this magnetic blackboard, it is necessary to heat the magnetic particles on the back sheet side from the front surface side through the encapsulating liquid before writing, and when the heat transfer speed is slow, in other words, the pen moving speed is too fast. In some cases, the pen moves before the magnetic particles are heated, and the magnetic particles may not move to the surface sheet side.

Subsequent studies by the present inventor show that ReRh and MnCr that cause an antiferromagnetic-ferromagnetic transition or an antiferromagnetic-ferrimagnetic transition
In the Sb alloy, we found a phenomenon that some magnetization exists even in the antiferromagnetic phase, and paid attention to this.

FIG. 3 shows a thermal magnetization curve of the MnCrSb alloy applied to the present invention. It can be seen from FIG. 3 that the saturation magnetization Ms rapidly increases with a temperature rise near 40 ° C. At the same time, some magnetization occurs even below 40 ° C. In fact, when a magnet is brought close to this alloy particle near room temperature, it does not show any reaction to a weak magnet such as a plastic magnet, but a magnet that generates a strong magnetic field such as a samarium-cobalt magnet. It is observed that it is sucked into. When the temperature is raised to about 50-70 ℃, it is naturally attracted to weak magnets.

The present inventor has developed a magnetic blackboard capable of partial erasing by applying the behavior of a magnetic alloy that causes such an antiferromagnetic-ferromagnetic transition or an antiferromagnetic-ferrimagnetic transition.

The structure of the present invention will be described below with reference to FIG. 1 showing an embodiment thereof.

In FIG. 1, the honeycomb core 1, the top sheet 4, the back sheet 5 and the inclusion liquid 2 which are divided into a large number are the same as those in the conventional example shown in FIG. The particles are formed of thermally induced magnetic particles 6 having ferromagnetism or ferrimagnetism at a temperature exceeding room temperature. Therefore, the thermally induced magnetic particles 6 have a ferromagnetism at a temperature exceeding room temperature, and at room temperature (40 ° C.) or lower, they cannot be attracted to a weak magnet but are attracted to a strong magnet. The magnet plate 7 is arranged on the entire back surface of the blackboard body configured as described above, and the magnet bar 8 movable from the end portion to the other end portion of the blackboard is arranged on the back surface.

To write characters, figures, etc. on such a magnetic blackboard, a magnetic pen 3 which generates a strong magnetic field is used as shown in FIG. 1. The magnetic pen 3 generates a strong magnetic field. Since the magnetic field of the magnet plate 7 arranged on the back surface is sufficiently strong, the heat-induced magnetic particles 6 are not shown in FIG.
Utilizing the slight magnetization at or below (room temperature), this is moved from the back surface to the front surface side in the core 1, and writing is performed there.

FIG. 4 shows the case of partial erasing. The thermal block 9 is brought into contact with the surface sheet 4 side of the portion to be erased. As a result, the heat-induced magnetic particles 6 are usually heated up to the strong magnetization range shown in FIG. Therefore, it is easily attracted by the magnetic field of the magnet plate 7 having a weak magnetic field arranged on the back surface side of the blackboard body, moves from the front surface side to the back surface side, and the desired portion is partially erased.

Further, FIG. 5 shows the case of erasing the entire body. In this case, the magnet rod 8 arranged on the back side of the magnet plate 7 for generating a strong magnetic field is moved from the end portion to the other end portion of the entire blackboard. By doing so, due to the action of the strong magnetic field of the magnet rod 8, all the magnetic particles 6 that have moved to the front surface side can be moved to the back surface side, whereby the entire erasure is performed.

As described above, in the magnetic blackboard of the present invention, the heat-induced magnetic particles that become ferromagnetic or ferrimagnetic at a temperature exceeding room temperature are used as the magnetic particles 6, and moreover, generated from the magnetic pen 3 and the magnet rod 8 for total erasure. The magnetic field strength to be generated is stronger than the magnetic field strength generated from the magnet plate 7, and partial erasing is carried out by heating the magnetic particles 6 as described above and erasing by the magnet plate 7 which generates a weak magnetic field. To do.

The thermally induced magnetic particles 6 used in the present invention are Fe-Rh alloy particles or the like having an antiferromagnetic property at a temperature exceeding room temperature-particles having a ferromagnetic transition point, MnCrSb alloy particles or the like having an antiferromagnetic property at a temperature exceeding room temperature- Examples thereof include particles having a ferrimagnetic transition point.

As one specific example below, MnCrSb is used as the thermally induced magnetic particles.
The case where an alloy is used is shown.

The composition of MnCrSb alloy is _{Mn 62 · 9 Cr 3 · 8} Sb 33 · 3. The thermal magnetization curve for this composition is as shown in FIG.

The procedure for producing particles is such that first, the raw material of MnCrSb is arc-melted in the above composition ratio, and then it is heated to 1500 ° C. or higher in a high temperature furnace in an Angon atmosphere and gradually cooled. By this operation, a polycrystal having a crystal grain size of about 2 to 3 mm can be formed. Next, this polycrystal is cleaved along the cleavage plane of the crystal. The width of cleavage at this time is about 50 μm to 100 μm. Further, the cleaved thin plate is finely crushed to a size of about 50 μm to 100 μm / piece and colored black.

The fine particles are distributed in a honeycomb core made of polyester or the like shown in FIG. 1 at a rate of 10 mg to 100 mg per cm ² , and a sodium hexametaphosphate solution in which white fibers are mixed together with the fine particles is added. Seal as a dispersion.
The honeycomb core is partitioned into an area of about 0.1 to 10 mm ^{2 as} needed. The honeycomb core has a thickness of 0.1 to 1 mm, and the inner walls on the front surface side and the back surface side of the core are coated with a fluorine-based resin so that MnCrSb fine particles are easily adsorbed.

On the back surface of the magnetic blackboard body having the above structure, a plastic magnet having a surface magnetic field strength of about 200 to 1000 Oe is placed over the entire back surface of the blackboard body.

From the tip of the magnetic pen 3 shown in FIG.
A magnetic field of a certain degree is generated. A similar magnetic field is also generated from the magnet rod 8 shown in FIG. The surface of the erasing thermal block 9 shown in FIG. 4 is heated to 50 to 70 ° C., but no magnetic field is generated.

〔effect〕

According to the present invention as described above, there is an effect that it is possible to realize a magnetic blackboard having excellent resolution and fast erasing speed and capable of partial erasing and whole erasing.

[Brief description of drawings]

FIG. 1 shows an embodiment of a magnetic blackboard according to the present invention.
It is explanatory drawing which shows the state at the time of writing. FIG. 2 is an explanatory view showing a conventional magnetic blackboard. FIG. 3 is a thermal magnetization curve diagram of magnetic particles of the MnCrSb alloy used in the present invention. FIG. 4 is an explanatory diagram showing a state when the magnetic blackboard shown in FIG. 1 is partially erased. FIG. 5 is an explanatory diagram showing a state when the magnetic blackboard shown in FIG. 1 is entirely erased. DESCRIPTION OF SYMBOLS 1 ... Honeycomb core 2 ... Encapsulating liquid 3 ... Magnetic pen 4 ... Top sheet 5 ... Back sheet 6 ... Thermally induced magnetic particles 7 ... Magnet plate 8 ... Magnet rod 9 ... Erase thermal block

Claims (1)

[Scope of utility model registration request] 1. A blackboard main body divided into a large number of cores, in which magnetic particles are dispersed together with an inclusion liquid in each core, a magnet plate over the entire back surface of the blackboard main body, and a magnet rod under the blackboard main body. In a magnetic blackboard for writing by moving the magnetic particles to the front side with a pen and erasing by moving the magnet rod to the back side, the magnetic particles become ferromagnetic or ferrimagnetic at a temperature exceeding room temperature. It is a heat-induced magnetic particle and has a heat block to be placed on the surface at the time of partial erasing, and the magnetic field strength generated from the magnetic pen and the magnet rod is set to be larger than the magnetic field strength generated from the magnet plate. When the magnetic particles are ferromagnetic or ferrimagnetic, the magnetic blackboard has a strength that attracts them.