Magnetic sheet, magnetic writing system, drawing method and erasing method

Abstract

A magnetic sheet capable of color display is provided. The magnetic sheet of the present invention uses the effect of magnetic lines of force from a magnetic pen to display, and forms a microcapsule layer between upper and lower transparent sheets. The microcapsule layer includes a first microcapsule (140A) and a second microcapsule (140B), wherein the first microcapsule (140A) includes black magnetic particles (142A) with a lower magnetic susceptibility, and the second microcapsule (140B) includes red magnetic particles (142B) with a higher magnetic susceptibility. When weaker magnetic lines of force are applied, the red magnetic particles (142B) react, and when stronger magnetic lines of force are applied, the black magnetic particles (142A) and the red magnetic particles (142B) react.

Description

Technical Field

[0001] The present invention relates to a magnetic sheet or a magnetic panel for drawing arbitrary characters, figures, symbols, etc. by causing a magnetic field to act, and more particularly to a structure of a magnetic sheet having a plurality of microcapsules. Background Art

[0002] Disclosed are a magnetic pen (Patent Document 1) that moves on a magnetic sheet and is used to cause a magnetic field to act on the magnetic sheet to draw text, graphics, symbols, etc. corresponding to the movement trajectory, or a demagnetization tool (Patent Document 2) that is used to erase the drawn text, graphics, symbols by moving on a magnetic sheet.

[0003] Regarding magnetic sheets, Patent Document 3 discloses a magnetic display obtained by arranging a microcapsule layer between a non-magnetic substrate and a protective layer, and arranging large-particle microcapsules containing magnetic powder and non-magnetic powder and small-particle microcapsules containing neither magnetic powder nor non-magnetic powder in the microcapsule layer. The voids generated between the particles of the large-particle microcapsule group are filled with the small-particle microcapsule group, so the filling of the microcapsules becomes high-density and the generation of pores is suppressed. In addition, Patent Document 4 discloses a microcapsule magnetophoresis display sheet that can be eliminated from the surface. The microcapsule contains a dispersion, a white pigment, an additive, and magnetic particles. The average particle size of the microcapsule is 50μm to 650μm, and it has two or more magnetic particles with different magnetic particles, thereby being able to completely or partially eliminate from the recording surface side.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent No. 6179788

[0007] Patent Document 2: Japanese Patent No. 6213886

[0008] Patent Document 3: Japanese Patent No. 2850056

[0009] Patent Document 4: Japanese Patent No. 4089808 Summary of the invention

[0010] Problems to be solved by the invention

[0011] The magnetic sheets disclosed in Patent Documents 3 and 4 increase the packing density of microcapsules or adjust the diameter of microcapsules to enable erasure from the recording surface side, etc. Such magnetic sheets require further improvement in the drawing speed during drawing or display characteristics of suppressing residual images during erasure. Moreover, in the magnetic writing system using such magnetic sheets, there is a problem that it cannot correspond to two-color display of white and black.

[0012] The present invention solves such conventional problems, and an object of the present invention is to provide a magnetic sheet having improved display properties during drawing or erasing.

[0013] Furthermore, an object of the present invention is to provide a magnetic sheet capable of displaying in at least three colors.

[0014] Means for solving problems

[0015] The magnetic sheet of the present invention utilizes the effect of magnetic lines of force from a magnetic pen for display, wherein the magnetic sheet comprises: a first sheet; a second sheet, which is opposite to the first sheet; and a microcapsule layer, which is formed between the first sheet and the second sheet, the microcapsule layer comprises a plurality of microcapsules filled with at least a magnetic body, a non-magnetic body, an anti-precipitation agent and a solvent, and the plurality of microcapsules at least comprise: a first microcapsule, which comprises a magnetic body with a first magnetic susceptibility; and a second microcapsule, which comprises a magnetic body with a second magnetic susceptibility greater than the first magnetic susceptibility.

[0016] The magnetic writing system of the present invention comprises: the magnetic sheet described above; and a magnetic pen that applies magnetic lines of force to the magnetic sheet, wherein the magnetic pen applies magnetic lines of force of different strengths to the magnetic sheet.

[0017] Furthermore, the magnetic sheet of the present invention has a plurality of microcapsules arranged between the first sheet and the second sheet, each microcapsule comprising at least a magnetic body, a non-magnetic body, an anti-precipitation agent and a solvent, wherein the magnetic body in response to the magnetic lines of force applied from the first sheet side moves to the inner wall surface of the microcapsule on the first sheet side and remains stationary.

[0018] Furthermore, the magnetic sheet of the present invention has a plurality of microcapsules arranged between the first sheet and the second sheet, each microcapsule comprising at least a magnetic body, a non-magnetic body, an anti-precipitation agent and a solvent, wherein the magnetic body in response to the rotating magnetic lines of force applied from the first sheet side rotates and moves in a direction opposite to the rotation direction of the magnetic lines of force, and gathers and stops near the center of the microcapsule.

[0019] The drawing method of the present invention is a drawing method for a magnetic sheet, wherein a plurality of microcapsules are arranged between a first sheet and a second sheet, each microcapsule containing at least a magnetic body, a non-magnetic body, an anti-precipitation agent and a solvent, wherein the magnetic body in response to the magnetic lines of force applied from the first sheet side is moved toward the inner wall surface of the microcapsule on the first sheet side and becomes stationary.

[0020] The elimination method of the present invention is an elimination method for a magnetic sheet, wherein a plurality of microcapsules are arranged between a first sheet and a second sheet, each microcapsule containing at least a magnetic body, a non-magnetic body, an anti-precipitation agent and a solvent, wherein the magnetic body in response to the rotating magnetic lines of force applied from the first sheet side is caused to rotate and move in a direction opposite to the rotation direction of the magnetic lines of force, gather near the center of the microcapsule and remain stationary.

[0021] Effects of the Invention

[0022] According to the present invention, by using magnetic bodies with different magnetic susceptibilities, it is possible to realize display of multiple colors when drawing on a magnetic sheet. Furthermore, according to the present invention, it is possible to control the movement of magnetic particles or magnetic bodies of microcapsules with high precision by using magnetic lines of force applied from the outside, thereby improving the display characteristics of the magnetic sheet when drawing or erasing compared to the past. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a diagram for explaining the outline of a magnetic sheet according to an example of the present invention.

[0024] Figure 2 This is a diagram schematically showing the state of magnetic particles of the microcapsule during drawing in this example.

[0025] Figure 3 This is a schematic cross-sectional view of a microcapsule when depicting this example.

[0026] Figure 4 This is a schematic cross-sectional view of the microcapsule during elimination in this example.

[0027] Figure 5 This is a diagram for explaining the change in the intensity of the magnetic field lines acting on the microcapsules during the erasure in this example.

[0028] Figure 6 This is a diagram for explaining the eddy current and the backflow generated in the microcapsule during the elimination in this example.

[0029] Figure 7 This is a diagram for explaining the behavior of microcapsules in a range A where magnetic lines of force strongly act.

[0030] Figure 8 This is a diagram for explaining the behavior of microcapsules in a range B where magnetic lines of force act moderately.

[0031] Fig. 9 This is a diagram for explaining the behavior of microcapsules in a range C where magnetic lines of force act weakly.

[0032] Fig.10 This is a diagram for explaining the behavior of the microcapsules in a range D where the magnetic force lines do not act.

[0033] Fig.11A This is a photograph showing an example of characters drawn on a magnetic sheet.

[0034] Fig. 11B It is shown Fig.11A This is an enlarged photograph of the state of the magnetic body after the circle range is drawn.

[0035] Fig. 12A It shows the magnetic sheet in the process of elimination Fig.11A The enlarged photo of the magnetic body in the circle is Figure 5 and Figure 7 The photo corresponding to the eliminated state of range A.

[0036] Fig. 12B It shows the magnetic sheet in the process of elimination Fig.11A The enlarged photo of the magnetic body in the circle is Figure 5 and Figure 8 The photograph corresponding to the eliminated state of range B.

[0037] Fig. 12C It shows the magnetic sheet in the process of elimination Fig.11A The enlarged photo of the magnetic body in the circle is Figure 5 and Fig. 9 The photograph corresponding to the eliminated state of range C.

[0038] Fig.12D It shows the magnetic sheet in the process of elimination Fig.11A The enlarged photo of the magnetic body in the circle is Figure 5 and Fig.10 The photograph corresponding to the eliminated state of range D.

[0039] Fig.13 is a diagram for explaining the second embodiment of the present invention. Fig.13 (A) is a diagram for explaining the action state of the microcapsule when the rotating magnetic lines of force are applied and eliminated, Fig.13 (B) is a diagram illustrating the action state of the microcapsule when a weak magnetic field line is applied. Fig.13 (C) is a diagram for explaining the action state of the microcapsule when a strong magnetic field line is applied and drawn. Fig.13 (D) is a diagram for explaining a preferred operating state of the microcapsule when drawing is performed with weak magnetic lines of force applied.

[0040] Fig.14 is a diagram for explaining the third embodiment of the present invention. Fig.14(A) is a diagram for explaining the operation state of the microcapsule in the elimination state. Fig.14 (B) and Fig.14 (C) is a diagram illustrating the action state of the microcapsule when a weak magnetic field line is applied. Fig.14 (D) is a diagram for explaining the action state of the microcapsules when drawing is performed with strong magnetic lines of force applied. DETAILED DESCRIPTION

[0041] Next, regarding the magnetic sheet of the present invention, when the magnetic writing tool moves on the drawing surface of the magnetic sheet, the magnetic lines of force or magnetic field from the magnetic writing tool are used to display text, graphics, pictures, etc. corresponding to the moving track, and when the rotating magnetic lines of force or magnetic field from the demagnetizing tool is applied to the drawing surface or back of the magnetic sheet, the drawn text, etc. are eliminated. The drawings referred to in the embodiments of the present invention emphasize various parts for easy understanding of the invention, and it should be noted that the size or shape of the actual product is not necessarily the same.

[0042] Example

[0043] Next, an embodiment of the present invention will be described with reference to the accompanying drawings. The plane shape of the magnetic sheet of the embodiment of the present invention is not particularly limited, for example, it has a rectangular shape. The size of the rectangular shape can be more than 50 inches, and it can be used as a magnetic display system or a magnetic writing system for wall-mounted use in an office or home. In such a magnetic writing system, the characteristic point is that there is actually no need for electricity to draw text on the magnetic sheet or to maintain the drawn text. Moreover, in the case of erasing the drawn text, etc., electricity is not necessarily required. Even if electricity is required, it is a very small amount of electricity used to change the magnetic lines of force. Furthermore, impurities or garbage will not be eliminated when erasing. Therefore, compared with a writing system using a liquid crystal panel that requires electricity or an electronic blackboard that is drawn using a marker, the magnetic writing system is a very economical and environmentally friendly device.

[0044] Figure 1 (A) and (B) show a schematic cross-section of a magnetic writing system 10 of an embodiment of the present invention. The magnetic writing system 10 has a magnetic sheet 100, a magnetic pen 200, and a demagnetizing tool 300. When drawing text, etc., the magnetic pen 200 is moved on the magnetic sheet 100, so that the magnetic lines of force from the magnet 202 included in the magnetic pen 200 are applied to the magnetic sheet 100. When the magnetic pen 200 is moved in the Y direction, a line corresponding to the direction of its movement is drawn. Moreover, when erasing the drawn text, etc., the demagnetizing tool 300 is moved on the magnetic sheet 100, and the rotating magnetic lines of force from the demagnetizing tool 300 are applied to the magnetic sheet 100. The demagnetizing tool 300, for example, rotates the magnet 302, and applies the rotating magnetic lines of force to the magnetic sheet 100 while moving in the Y direction.

[0045] The magnetic sheet 100 is composed of an upper support (sheet) 110, a lower support (sheet) 120, and a microcapsule layer 130 formed between the two supports. The upper support 110 and the lower support 120 are composed of, for example, transparent resin sheets. The upper support 110 provides a drawing surface of the magnetic sheet, and the lower support 120 holds microcapsules and an adhesive and provides a non-drawing surface of the magnetic sheet. The upper support 110 and the lower support 120 have a thickness of 50 μm to 150 μm.

[0046] The microcapsule layer 130 has a plurality of microcapsules 140 arranged therein, and the thickness of the microcapsule layer 130 is adjusted so that the interval between the upper support 110 and the lower support 120 is approximately 300 to 500 μm. The microcapsule 140 is substantially spherical, and its outer diameter is 50 to 500 μm, preferably 200 to 300 μm.

[0047] Microcapsule 140 contains a magnetic substance (e.g., black ferroferric oxide (Fe3O4) particles), a non-magnetic substance (e.g., white titanium oxide particles), a high boiling point solvent, a low boiling point solvent, a defoaming agent, an anti-precipitation agent (e.g., micro-powdered silica gel (aerosil) having thixotropic properties), and a dispersant. The thixotropic property has the property that the viscosity increases once it is still.

[0048] In order to accurately control the movement of the magnetic body in the microcapsule in response to the magnetic lines of force from the magnetic pen or the demagnetizing tool, the mixing ratio of the above-mentioned contents contained in the microcapsule 140 is determined to satisfy the following characteristics.

[0049] A. When drawing

[0050] (1) The line (black magnetic substance) drawn with a magnetic pen remains still at that position even after being drawn, and the black magnetic substance needs to be separated from the non-magnetic substance (white titanium oxide particles) as much as possible. Figure 2 This is a schematic diagram of microcapsule 140 viewed from the drawing surface side of magnetic sheet 100. When drawing with magnetic pen 200, magnetic particles 142 are attracted and stationary along the magnetic force lines from magnetic pen 200. The stationary position of magnetic particles 142 in the height direction is the upper part of microcapsule 140.

[0051] (2) When drawing with the magnetic pen 200, it is necessary to be able to use weak magnetic lines of force to attract the magnetic particles 142 to the inner wall surface of the microcapsule 140. By attracting the magnetic particles 142 to the inner wall surface, a clear drawing line can be formed. Figure 32 is a schematic cross-sectional view showing a state when the magnetic lines of force of the magnetic pen 200 are applied to the microcapsule 140. The magnetic pen 200 accommodates the magnet 202 at the end of the housing 204 made of magnetic material, and a circular opening 206 is formed at the end of the housing 204. The controlled magnetic lines of force from the magnet 202 act on the microcapsule 140 through the opening 206. As a result, the magnetic particles 142 are separated from the non-magnetic particles (e.g., TiO2) 144, and are attracted to the inner wall surface above the microcapsule 140 and remain stationary.

[0052] (3) The magnetic particles 142 in the microcapsule 140 need to be sensitive to weaker magnetic lines of force from the outside (be movable). The magnetic particles 142 attracted to the inner wall surface of the microcapsule 140 move toward the center of the microcapsule 140 and exist in a clustered manner when the elimination is completed, so they are easy to respond to weaker magnetic lines of force and move.

[0053] B. Elimination

[0054] (1) When degaussing the drawn characters and the like using the degaussing tool 300, the magnetic particles 142 need to respond to the rotating magnetic lines of force from the outside and apply magnetic lines of force that rotate the magnetic particles 142 in the microcapsule 140 in the direction opposite to the rotation direction of the magnetic lines of force. Figure 4 1 is a schematic cross-sectional view when rotating magnetic lines of force are applied to the microcapsule. When the magnet 302 of the demagnetizing tool 300 is rotated in the clockwise direction Ra around the rotation axis C and horizontally moved on the magnetic sheet 100, the magnetic particles 142 in the microcapsule 140 respond to the rotating magnetic lines of force and rotate in the counterclockwise direction Rb. Through this rotation, eddy currents are generated in the fluid in the microcapsule 140, and a backflow toward the center of the microcapsule 140 is generated by the internal pressure difference caused by the centrifugal force.

[0055] (2) The strength of the eddy current generated by the rotating magnetic lines of force from the outside needs to be proportional to the magnetic lines of force. By moving the demagnetizing tool 300 parallel to the drawing surface of the magnetic sheet 100, the rotating magnetic lines of force from the outside act on the microcapsules. In this case, the strength of the magnetic lines of force from the demagnetizing tool 300 changes continuously in a "strong", "medium" and "weak" manner. Figure 5This situation is schematically shown. As shown in the figure, the magnet 302 of the demagnetization tool 300 rotates at a certain rotation speed and moves on the magnetic sheet 100 at a speed V. Moreover, the magnet 302 is separated from the depicted surface of the magnetic sheet 100 by a distance H. The distance H is a size at which the magnetic lines of force from the magnet 302 act appropriately on the magnetic sheet 100. When the demagnetization tool 300 is moved in the horizontal direction, the range A close to the magnet 302 is a range where the magnetic lines of force act strongly, the range B farther away from the above situation is a range where the magnetic lines of force act moderately, the range C farther away from the above situation is a range where the magnetic lines of force act weakly, and the range D farther away from the above situation is a range where the magnetic lines of force hardly act or the magnetic particles are stationary near the center of the microcapsule 140.

[0056] (3) In the range A where the magnetic lines of force exert a strong effect, the magnetic particles are drawn to be attracted to the inner wall surface of the microcapsule 140 and are in a stationary state. When the magnetic particles stop, the viscosity increases due to the thixotropic properties of the anti-precipitation agent, and the mobility of the magnetic particles decreases due to the residual magnetism of the magnetic particles, thereby maintaining the stationary position. In order to eliminate this, a larger force needs to be applied, and this larger force releases the force that maintains the stationary state of the magnetic particles. In other words, it is necessary to apply a stronger magnetic line of force to the magnetic particles in the stationary state so that the magnetic particles begin to rotate.

[0057] When strong magnetic lines of force act, strong eddy currents are generated by the rotation of magnetic particles, so that the stationary magnetic particles after drawing are decomposed and start to rotate as aggregates of several to several dozen magnetic particles in the microcapsule 140. The magnetic particles are aggregated by strong magnetic lines of force, but are decomposed into multiple aggregates by the eddy currents generated in the microcapsule. Figure 6 The eddy currents P1 , P2 , P3 , and P4 in the microcapsule 140 when rotating magnetic lines of force are applied are illustrated. Figure 6 (A) is a diagram schematically showing an eddy current when a cross section of a microcapsule 140 is observed from a lateral direction or a horizontal direction, Figure 6 (B) is a schematic diagram showing Figure 6 (A) is a cross-sectional view of the backflow generated. Figure 6 (C) is a schematic diagram showing the Figure 6 (A) is a diagram of eddy current when the microcapsule 140 is observed in directions different by 90 degrees.

[0058] like Figure 6As shown in (A), the magnetic particles rotate and move in the direction opposite to the rotating magnetic lines of force, which becomes the motive force, thereby generating vortices P1, P2, P3, and P4 of the fluid in the microcapsule 140. When the magnetic particles rotate around the horizontal axis HC passing through the center of the microcapsule 140, the centrifugal force caused by the vortex generated in the microcapsule is very weak or has no effect on the center side, and becomes larger on the end side. That is, the centrifugal forces F1, F2, F3, and F4 caused by the vortexes P1, P2, P3, and P4 satisfy the relationship of F1>F2>F3>F4. The internal pressure difference caused by the centrifugal forces F1, F2, F3, and F4 of the vortexes P1, P2, P3, and P4 is as shown in FIG. Figure 6 As shown in (B), reflux Q1, Q2, Q3, and Q4 are generated from the periphery toward the center. Therefore, the aggregates of magnetic particles tend to gather toward the center, and when appropriate magnetic field strength and rotation speed are applied, the phenomenon of magnetic particles gathering toward the center through reflux is significant.

[0059] The range of the static state after drawing A( Figure 5 ) are aggregated by the action of the rotating strong magnetic lines of force, but the force brought by the eddy current is strong, so the magnetic particles are decomposed into dozens of aggregates by the reaction force or friction of the viscosity of the solvent, and the decomposed multiple aggregates rotate violently along the eddy current and backflow of the microcapsule. In addition, the non-magnetic body that is not affected by the magnetic lines of force is dispersed on the inner wall surface of the microcapsule 140 by the centrifugal force of the eddy current. Figure 7 This situation is shown schematically.

[0060] The range B ( Figure 5 ), the eddy current slows down, so the aggregates that are decomposed into dozens of pieces in range A become larger under the action of magnetic lines of force, and their number decreases. Such aggregates rotate in the microcapsule under the action of eddy currents and backflow toward the center, thereby easily separating from the non-magnetic particles contained in the solvent and making them easy to move. Figure 8 This situation is shown schematically.

[0061] In the range where the magnetic field lines have a weaker effect, C( Figure 5 ), the aggregated mass begins to aggregate toward the center by the backflow toward the center of the microcapsule 140. In the center of the microcapsule, the eddy current and the backflow become weak, and the viscosity increases due to the thixotropic property, so when the magnetic particles aggregate and stop in the center, they are easily retained in the center. Fig. 9 This situation is shown schematically.

[0062] In the range A to range C, the non-magnetic body (titanium oxide particles) rotates with the eddy current and the backflow, thereby separating from the magnetic particles, being evenly distributed on the inner wall of the microcapsule 140 and resting on the inner wall. In the range D where the magnetic lines of force do not act, the magnetic particles 142 rest near the center of the microcapsule 140. In addition, the magnetic particles 142 have residual magnetism, so the magnetic particles attract each other, thereby promoting the magnetic particles 142 to rest near the center. Fig.10 This situation is shown. This completes the elimination.

[0063] The magnetic writing system using the magnetic sheet of this embodiment has the following features.

[0064] The magnetic sheet 100 includes upper and lower transparent films 110 and 120 and a microcapsule layer 130 sandwiched between the upper and lower transparent films. The microcapsule layer 130 includes a plurality of microcapsules 140 and an adhesive that combines the plurality of microcapsules 140. Each microcapsule 140 is filled with a magnetic body or magnetic particles that respond to magnetic lines of force from the outside. The movement of the magnetic particles in the microcapsule is controlled with high precision in response to the magnetic lines of force that act during drawing and erasing.

[0065] When using such a magnetic sheet, drawing can be performed from either side of the magnetic sheet, and erasure can also be performed from either side of the magnetic sheet. Moreover, by using an appropriate amount of an anti-precipitation agent and residual magnetic effect, the black color (contrast) after drawing can be maintained, and the characteristics of the magnetic particles in the microcapsule that react continuously / stage by stage according to the strength of the magnetic lines of force change less over time. Furthermore, by improving the mobility of the components in the microcapsule, a magnetic pen with clear magnetic lines of force obtained by controlling the magnetic lines of force can be used to obtain clear drawing lines. After erasure, the aggregated mass of the magnetic body exists near the center of the microcapsule, so that it can respond to weak magnetic lines of force from either side of the upper or lower side of the magnetic sheet.

[0066] Titanium oxide particles (white), which are non-magnetic, rotate by eddy current until they are close to a stationary state, and are thus evenly distributed on the inner wall of the microcapsule. As a result, as a characteristic of having a large refractive index (larger than diamond), they reflect external light well, so the whiteness of the magnetic sheet is improved compared to the conventional elimination method of eliminating by contacting a strip (N / S) magnet from the back of the sheet.

[0067] Due to the unique response characteristics of the microcapsules, the conditions for generating the rotating magnetic field lines acting from the outside are determined by the following factors.

[0068] 1. Strength of magnetic lines of force: When the magnetic lines of force are too strong, the eddy currents and backflows become larger, and the magnetic particles continue to rotate and cannot gather near the center of the microcapsule, thus eliminating incompletely.

[0069] 2. Rotational speed of magnetic lines of force: When the rotational speed of magnetic lines of force becomes too fast, the magnetic particles cannot respond to the rotating magnetic lines of force, cannot rotate and move appropriately, and cannot gather near the center of the microcapsule, resulting in incomplete elimination.

[0070] 3. Distance from the surface of the magnetic sheet: The strength of the magnetic lines of force is a function of the distance from the surface of the magnetic sheet.

[0071] 4. The speed of magnetic force lines: When the speed of magnetic force lines is too fast, magnetic particles cannot respond to the speed of movement and cannot Figure 5 The behavior of the range A to D shown here eliminates the incompleteness.

[0072] The microcapsule is spherical, and the range (vector) of the microcapsule in response to the magnetic field lines is 360 degrees. The centrifugal force generated by the eddy current generates a flow that flows back toward the center, so that the ferrosoferric oxide gathers toward the center while gathering.

[0073] The magnetic body in the microcapsule has the characteristics of being magnetized in a magnetic field and gathering along the magnetic lines of force. The magnetic body used in this example is ferroferric oxide. If there is no magnetic field, the gathering force will not work. Therefore, in order to assist the gathering force, it is preferred to add an appropriate amount of ferrite that has a magnetic conductivity and residual magnetic properties than ferroferric oxide, so as to supplement the gathering force of ferroferric oxide. After the magnetic lines of force disappear, the ferrite retains residual magnetism for a short time, so that the ferroferric oxide is easy to gather.

[0074] The volume ratio of the magnetic body to the non-magnetic body and the solvent in the microcapsule needs to be fully considered. When there are more magnetic bodies (black), they move to the center of the microcapsule when eliminated, but they can be seen through the surface of the microcapsule, so the brightness of white decreases and appears gray. In addition, when there are fewer magnetic bodies, the black color during drawing becomes less, the drawing line becomes lighter, and the contrast decreases. When the volume ratio of the magnetic body to the non-magnetic body is larger than that of the solvent, the mobility decreases.

[0075] An example of the compounding of materials contained in the microcapsules of this example is shown.

[0076] Magnetic material: Ferroferric oxide particles (black) are composed of a combination of small particles of 0.1 μm to 0.3 μm (1.0 wt% to 1.5 wt%) and medium particles of 2 μm to 3 μm (1.0 wt% to 1.5 wt%). Alternatively, they are composed of magnetic particles clustered to a size of about 1 μm to 3 μm (1.0 wt% to 1.5 wt%). Clustered magnetic particles are obtained by solidifying particles of 0.1 μm to 0.3 μm, for example.

[0077] Non-magnetic material: Titanium oxide (white) powder in the form of particles of 0.2 μm to 0.3 μm (11.0 wt% to 13.0 wt%), or non-magnetic particles clustered in the form of particles of about 0.8 μm to 1.0 μm (11.0 wt% to 13.0 wt%).

[0078] High boiling point solvent: dibutyl phthalate (38.0 wt% to 41.0 wt%)

[0079] Low boiling point solvent: triene (40.0 wt% to 44.0 wt%)

[0080] Defoaming agent (appropriate amount)

[0081] Anti-precipitation agent: micro powder silica gel (0.3 wt% to 0.5 wt%)

[0082] Dispersant (appropriate amount)

[0083] Considering the resolution of the magnetic sheet, the difficulty of the manufacturing process, and the cost, the outer diameter of the microcapsule is 30 μm to 1,100 μm. In addition, an adhesive is included to support the microcapsule between the upper and lower transparent films 110 and 120 as necessary.

[0084] The mobility and separability of magnetic and non-magnetic materials are important characteristics for improving contrast or performance during erasing and drawing. By mixing particles of different sizes in a magnetic material, the mobility of the magnetic material is improved, and the contrast is also improved.

[0085] In order to improve mobility, it is preferred that magnetic particles are clustered. Cluster processing is a process of spheroidizing multiple magnetic particles into a certain size. Magnetic particles and particles using the magnetic particles are clustered, and these blocks are appropriately mixed, thereby using magnetic particles with improved mobility as (black). Blocks are spherical blocks obtained by gathering dozens of magnetic particles, so mobility is improved. Non-magnetic particles and particles using the non-magnetic particles are clustered, and these blocks are appropriately mixed, thereby using non-magnetic particles with improved mobility as (white). The cluster is spherical and its size can be controlled. Moreover, non-magnetic particles are clustered, and these blocks are appropriately mixed, thereby using non-magnetic particles with improved mobility. By clustering non-magnetic particles, it is difficult for non-magnetic particles to be attracted to the inner wall of the microcapsule along the magnetic field lines during drawing and enter the gap of the stationary magnetic body, which prevents the reduction of the contrast of the magnetic particles and easily responds to the rotating magnetic field lines.

[0086] FIG. 11A to FIG. 12D A photograph showing actual magnetic particles in microcapsules is shown. Fig.11A An example of characters drawn on a magnetic sheet is shown, and magnetic particles in a range indicated by a circle are observed. Fig. 11BIt shows the drawn Fig.11A The enlarged photograph of the magnetic body in the circled area shows that the magnetic particles are attracted to the upper side of the microcapsule and remain stationary there.

[0087] Fig. 12A This is a diagram showing the aggregation of rotating magnetic particles in the process of elimination when a rotating magnetic field is applied to a magnetic sheet. Fig.11A The enlarged photo of the magnetic body in the circle is Figure 5 and Figure 7 Corresponding to the elimination state of range A. Fig. 12B is with Figure 5 and Figure 8 The enlarged photo corresponding to the eliminated state of range B, Fig. 12C is with Figure 5 and Fig. 9 The enlarged photo corresponding to the eliminated state of range C, Fig.12D is with Figure 5 and Fig.10 The enlarged photo corresponding to the eliminated state of range D. FIG. 12A to FIG. 12D It can be seen that as the elimination progresses, the magnetic body enters the vicinity of the center of the microcapsule, and finally the microcapsule turns into a clean white color, indicating that the elimination is completed.

[0088] Next, the second embodiment of the present invention is described. In the second embodiment, it relates to a colored magnetic sheet that can depict more than three colors or colors. In the second embodiment, in order to correspond to the color depiction, there are multiple microcapsules obtained by filling colored magnetic bodies with different magnetic susceptibilities. As an example, an example of depicting three colors of white, black or brown, and red on a magnetic sheet is described. In this case, two types of microcapsules are prepared. The first microcapsule 140A is filled with black magnetic particles having a first magnetic susceptibility, and the second microcapsule 140B is filled with red magnetic particles having a second magnetic susceptibility greater than the first magnetic susceptibility. Magnetic susceptibility is a physical property value that indicates the ease of causing magnetization of a substance. The magnetic susceptibility of the second magnetic particle is greater than that of the first magnetic particle, so the second magnetic particle is easier to be magnetized than the first magnetic particle. That is, the second magnetic particle will be magnetized by a weaker magnetic field or magnetic field line than the first magnetic particle and react.

[0089] The first microcapsules 140A are adjusted so that the average outer diameter is larger than the average outer diameter of the second microcapsules 140B, and the number of the first microcapsules 140A is larger than the number of the second microcapsules 140B. In addition, as in the first embodiment, the first and second microcapsules 140A and 140B are filled with a non-magnetic body (e.g., white titanium oxide particles), a high boiling point solvent, a low boiling point solvent, a defoaming agent, an anti-precipitation agent, and a dispersant.

[0090] Colored magnetic bodies are, for example, black magnetite (Fe3O4: ferroferric oxide), brown hematite (γ-Fe2O3: hematite), etc. Moreover, regarding colored magnetic bodies, there are methods of coating colored magnetic glass and magnetic bodies with polymers, etc., and the magnetic susceptibility can be changed according to the film thickness of the coating of the magnetic body or the size of the particles. Generally, the smaller the particles become, the lower the magnetic susceptibility. Moreover, even for the same magnetic body, the magnetic susceptibility can be changed. For example, by making the size of the particles of ferroferric oxide different, or changing the film thickness of the silicon coating, the magnetic susceptibility can be changed. The larger particles can be clustered particles. Moreover, non-magnetic bodies can use colored polystyrene, polyethylene, etc.

[0091] In addition, the magnetic pen has the function of selectively causing weaker magnetic lines of force or stronger magnetic lines of force to act on the magnetic sheet. The strength of the magnetic lines of force can vary depending on the distance from the magnet in the magnetic pen to the magnetic sheet and the size of the magnet. For example, the magnetic pen can be a structure that generates weaker magnetic lines of force from one end and stronger magnetic lines of force from the other end, or it can be a structure that can selectively switch the generation of weaker magnetic lines of force and stronger magnetic lines of force by making the position of the magnet installed at one end variable. Alternatively, two magnetic pens can be prepared, one magnetic pen generates weaker magnetic lines of force and the other magnetic pen generates stronger magnetic lines of force. For example, Patent Document 1 discloses a magnetic pen that can change the strength of the magnetic lines of force by making the distance from the magnetic sheet to the magnet variable.

[0092] Next, refer to Fig.13 The drawing action of the magnetic writing system of the second embodiment is described. In addition, for ease of description, the magnetic particles responding to the magnetic lines of force and resting on the inner wall surface of the microcapsule are called reaction (ON), and the magnetic particles responding to the magnetic lines of force and resting in the center are called non-reaction (OFF).

[0093] Fig.13 (A) is a schematic side view of the first and second microcapsules 140A and 140B when being erased. When erasing drawn text, etc., the rotating magnetic lines of force from the demagnetizing tool are applied to the magnetic sheet. As described in the first embodiment, the first and second magnetic particles 142A and 142B in the first and second microcapsules are separated from the non-magnetic particles 144A and 144B in response to the magnetic lines of force, so that the first and second magnetic particles 142A and 142B eventually gather near the center of the first and second microcapsules 140A and 140B and remain stationary there. The black first magnetic particles 142A and the red second magnetic particles 142B are surrounded by the white non-magnetic particles 144A and 144B, so that the drawn surface of the magnetic sheet is white.

[0094] Fig.13(B) shows the situation when weaker magnetic lines of force are applied from the magnetic pen to the magnetic sheet to draw. When weaker magnetic lines of force are applied to the first and second microcapsules 140A and 140B in the eliminated state, the red second magnetic particles 142B of the second microcapsule 140B respond to the weaker magnetic lines of force, and the second magnetic particles 142B are attracted from the vicinity of the center of the second microcapsule 140B to the upper inner wall surface and remain stationary there. On the other hand, the first magnetic particle 142A has a smaller magnetic susceptibility and therefore does not respond to the weaker magnetic lines of force, thereby remaining near the center of the first microcapsule 140A. Therefore, red is drawn on the magnetic sheet using weaker magnetic lines of force. At this time, as Fig.13 As shown in (D), the average outer diameter of the second microcapsules 140B is smaller than that of the first microcapsules 140A, and the number of the second microcapsules 140B is less than that of the first microcapsules 140A. However, since the background is white, the contrast of red is sufficient.

[0095] Fig.13 (C) shows the situation when stronger magnetic lines of force are applied from the magnetic pen to the magnetic sheet. When stronger magnetic lines of force are applied, the black first magnetic particles 142A of the first microcapsule 140A react, and the first magnetic particles 142A are attracted to the upper inner wall surface from near the center of the first microcapsule 140A, and remain stationary along the magnetic lines of force. The red second magnetic particles 142B of the second microcapsule 140B also react in the same way, and the second magnetic particles 142B are also attracted to the upper inner wall surface and remain stationary there. In this case, the state is achieved in which black and red are simultaneously depicted using the black magnetic particles 142A and the red magnetic particles 142B, but the average outer diameter and number of the first microcapsule 140A are larger than the average outer diameter and number of the second microcapsule 140B, so black becomes the dominant color, resulting in an actual depiction of black.

[0096] Thus, according to this embodiment, microcapsules of colored magnetic bodies (magnetic particles) with different magnetic susceptibilities are mixed, thereby enabling display of at least three colors. In addition, in the above-mentioned embodiment, black and red are exemplified as colored magnetic bodies, but this is only an example, and other color combinations are also possible. For example, a combination of black and green, or a combination of green and yellow is also possible.

[0097] Furthermore, in the above-mentioned embodiment, an example is shown in which two kinds of colored magnetic microcapsules with different magnetic susceptibilities are mixed, but this is only an example, and three or more kinds of colored magnetic microcapsules may be mixed. In this case, magnetic lines of force of different strengths corresponding to the number of colored magnetic bodies are applied to the magnetic sheet, but different colored magnetic bodies react at the same time, so it is preferable to adjust the color mixing by appropriately selecting the average outer diameter or number of different kinds of microcapsules.

[0098] Next, the third embodiment of the present invention is described. In the third embodiment, three kinds of microcapsules are prepared, and the magnetic particles are colored into the three primary colors of cyan (C), magenta (M), and yellow (Y), respectively, and the non-magnetic particles are made white. The first microcapsule 140A contains cyan magnetic particles 142A with a higher magnetic susceptibility and white non-magnetic particles 144A, the second microcapsule 140B contains magenta magnetic particles 142B with a lower magnetic susceptibility and white non-magnetic particles 144B, and the third microcapsule 140C contains yellow magnetic particles 142C with a lower magnetic susceptibility and white non-magnetic particles 144C.

[0099] Fig.14 (A) shows the situation of the elimination state. In the first to third microcapsules 140A, 140B, 140C, the magnetic particles 142A, 142B, 142C all respond to the rotating magnetic lines of force and gather near the center of the microcapsule and remain still. The magnetic particles 142A, 142B, 142C are surrounded by white non-magnetic particles 144A, 144B, 144C, so the depicted surface of the magnetic sheet is white.

[0100] When a weak magnetic field line is applied to the magnetic sheet during drawing, such as Fig.14 As shown in (B), the magnetic particle 142A with a higher magnetic susceptibility reacts, while the magnetic particles 142B and 142C with a lower magnetic susceptibility do not react. Therefore, the magnetic particle 142A is attracted to the inner wall surface above the first microcapsule 140A and remains stationary there. As a result, the depicted area where weak magnetic lines of force are applied becomes the cyan color of the magnetic particle 142A.

[0101] Assuming that the second and third microcapsules 140B and 140C contain magnetic particles 142B and 142C with relatively high magnetic susceptibility, and the first microcapsule 140A contains magnetic particles 142A with relatively low magnetic susceptibility, Fig.14 As shown in (C), the magnetic particles 142B and 142C of the second and third microcapsules 140B and 140C are attracted to the upper inner wall surface, so the drawing area becomes red, which is a mixed color of magenta and yellow.

[0102] When strong magnetic lines of force are applied to the magnetic sheet, Fig.14 As shown in (D), all magnetic particles 140A, 140B, 140C of the first to third microcapsules 140A, 140B, 140C are attracted to the upper inner wall surface and remain stationary there. Therefore, the drawing area to which strong magnetic lines of force are applied becomes a mixed color of cyan, magenta and yellow, that is, black.

[0103] Thus, according to the present embodiment, the depiction of the magnetic sheet can be displayed in multiple colors by assigning the three primary colors of color to the magnetic particles. However, the above-mentioned combination of colors is an example, and other combinations are also possible. Moreover, between microcapsules of different types, the size or number of the outer diameter can be appropriately selected according to the color displayed. Furthermore, in the above-mentioned embodiment, the three primary colors of color are assigned to the magnetic particles, but for example, non-magnetic particles can also be composed of fluorescent materials, and the three primary colors of light are assigned to these non-magnetic particles. For example, the three primary colors of light (R, G, B) can also be assigned to the non-magnetic particles respectively, and the magnetic particles can be made black (iron tetroxide), so that they are white (R+G+B) when the rotation is eliminated, and black when a stronger magnetic line of force is applied to depict (all magnetic particles are attracted to the inner wall surface on the upper side of the microcapsule), and when a weaker magnetic line of force is applied to depict, the microcapsules of R react to become a mixed color of G+B, or the microcapsules of G react to become a mixed color of R+B, or the microcapsules of B react to become a mixed color of R+G. In this case, it is preferred that the number or size of the microcapsules to be reacted be relatively small so that the mixed color display becomes the dominant color.

[0104] Furthermore, in the above-mentioned embodiment, the magnetic susceptibility of the magnetic body is set to two stages, strong and weak, but it is not limited to this. The magnetic body can also be made different in three or more stages, so that the magnetic lines of force applied from the magnetic pen are different in three stages. As a result, the magnetic body in the microcapsule can be attracted to the inner wall surface of the microcapsule and remain still according to the strength of the magnetic lines of force in multiple stages, so that the display color during drawing can be obtained by utilizing this phenomenon.

[0105] As mentioned above, although the preferred embodiment of the present invention was described in detail, the present invention is not limited to the specific embodiment, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims.

[0106] Description of symbols

[0107] 100: magnetic sheet; 110: upper support (sheet); 120: lower support (sheet); 130: microcapsule layer; 140, 140A, 140B, 140C: microcapsules; 142, 142A, 142B, 142C: magnetic particles; 144, 144A, 144B, 144C: ​​non-magnetic particles; 200: magnetic pen; 202: magnet; 300: demagnetization tool; 302: magnet.

Claims

1. A magnetic sheet, wherein a plurality of microcapsules are arranged between a first sheet and a second sheet, each microcapsule comprising at least magnetic particles, clustered magnetic particles, non-magnetic particles, clustered non-magnetic particles, an anti-precipitation agent, and a solvent, wherein a portion of the magnetic particles comprises a material having residual magnetic properties, wherein: In response to the rotating magnetic lines of force applied from the first sheet side, the magnetic particles rotate and move in a direction opposite to the rotation direction of the magnetic lines of force, gather near the center of the microcapsule, and then come to rest.

2. The magnetic sheet according to claim 1, wherein The magnetic particles are kept stationary by utilizing the thixotropic property of the anti-settling agent.

3. The magnetic sheet according to claim 1 or 2, wherein: The magnetic particles are attracted to each other and remain stationary due to residual magnetism.

4. The magnetic sheet according to claim 1 or 2, wherein The rotational movement of the magnetic particles generates an eddy current in the fluid in the microcapsule, and the backflow generated by the eddy current moves the magnetic particles toward the center of the microcapsule, so that the non-magnetic particles are dispersed around the entire inner wall surface of the microcapsule.

5. The magnetic sheet according to claim 1, wherein The plurality of microcapsules respectively contain magnetic particles with different magnetic susceptibility, The magnetic particles with different magnetic susceptibilities have different colors, respectively, and the colors are different from the colors of the non-magnetic particles.

6. The magnetic sheet according to claim 1 or 2, wherein: The magnetic particles include ferroferric oxide and ferrite having higher magnetic conductivity and residual magnetism than the ferroferric oxide.

7. The magnetic sheet according to claim 1, wherein The non-magnetic particles include titanium oxide.

8. A magnetic sheet that uses magnetic lines of force from a magnetic pen to display, wherein: The magnetic sheet comprises: 1st piece; a second sheet, which is opposite to the first sheet; and a microcapsule layer formed between the first sheet and the second sheet, The microcapsule layer comprises a plurality of microcapsules filled with at least magnetic particles, clustered magnetic particles, non-magnetic particles, clustered non-magnetic particles, an anti-precipitation agent and a solvent. The plurality of microcapsules at least comprises: a first microcapsule comprising magnetic particles having a first magnetic susceptibility; and a second microcapsule comprising magnetic particles having a second magnetic susceptibility greater than the first magnetic susceptibility, A portion of the magnetic particles comprises a material having residual magnetic properties, The magnetic particles of the first magnetic susceptibility and the magnetic particles of the second magnetic susceptibility rotate and move toward the vicinity of the center of the microcapsule in response to the rotating magnetic lines of force from the outside, gather near the center, and then come to rest.

9. A magnetic sheet that uses magnetic lines of force from a magnetic pen to display, wherein: The magnetic sheet comprises: 1st piece; a second sheet, which is opposite to the first sheet; and a microcapsule layer formed between the first sheet and the second sheet, The microcapsule layer comprises a plurality of microcapsules filled with at least magnetic particles, clustered magnetic particles, non-magnetic particles, clustered non-magnetic particles, an anti-precipitation agent and a solvent. The plurality of microcapsules at least comprises: a first microcapsule comprising magnetic particles having a first magnetic susceptibility; and a second microcapsule comprising magnetic particles having a second magnetic susceptibility greater than the first magnetic susceptibility, The magnetic particles include magnetic particles of ferroferric oxide and magnetic particles of ferrite having a longer residual magnetism time than the magnetic particles of ferroferric oxide. The magnetic particles rotate and move toward the vicinity of the center of the microcapsule in response to the rotating magnetic lines of force from the outside, gather near the center, and then come to rest.

10. The magnetic sheet according to claim 8 or 9, wherein The magnetic particles of the first magnetic susceptibility and the magnetic particles of the second magnetic susceptibility have any color of cyan, magenta, and yellow.

11. A magnetic writing system comprising: The magnetic sheet according to any one of claims 1 to 9; and Degaussing tools, The demagnetizing tool applies rotating magnetic lines of force to the magnetic pieces.

12. The magnetic writing system according to claim 11, wherein: The magnetic writing system also includes a magnetic pen. The magnetic pen applies magnetic lines of force to the magnetic sheet.

13. A method for eliminating magnetic sheets, wherein a plurality of microcapsules are arranged between a first sheet and a second sheet, each microcapsule comprising at least magnetic particles, clustered magnetic particles, non-magnetic particles, clustered non-magnetic particles, an anti-precipitation agent, and a solvent, wherein a portion of the magnetic particles comprises a material having residual magnetic properties, wherein: The magnetic particles, in response to the rotating magnetic lines of force applied from the first sheet side, are caused to rotate and move in a direction opposite to the rotation direction of the magnetic lines of force, gather near the center of the microcapsule, and then come to rest.

14. The elimination method according to claim 13, wherein: The magnetic particles, in response to the rotating magnetic lines of force applied from the second sheet side, are caused to rotate and move in a direction opposite to the rotation direction of the magnetic lines of force, gather near the center of the microcapsule, and then come to rest.

15. The elimination method according to claim 13 or 14, wherein: The rotational movement of the magnetic particles generates an eddy current in the fluid in the microcapsule, and the backflow generated by the eddy current moves the magnetic particles toward the center of the microcapsule, so that the non-magnetic particles are dispersed around the entire inner wall surface of the microcapsule.

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