JP4815030B2 - Microcapsule type magnetic reversal display medium - Google Patents

Description

  The present invention relates to a microcapsule type magnetic reversal display medium.

  As a magnetic display medium, a fine magnetic material is dispersed in a dispersion liquid, a magnet is applied from one surface, and the magnetic material is migrated on the surface to form a display. Then, a so-called migration type magnetic display medium in which the display is erased by re-migrating the magnetic material is known. In this magnetic display medium, since a display is performed by moving a magnetic material on the surface of the display medium, it is difficult to erase only unnecessary display portions from the display surface side, and display / erasure is repeatedly performed. There was no suggestion of solving the above problem. In addition, since this magnetic display medium has to be erased from the back side of the panel, there is a drawback that the apparatus is complicated and large. (Patent Document 1 etc.)

  Further, Patent Document 2 proposes a magnetic reversal display medium that performs display by reversing a minute magnetic material colored with different colors by magnetic poles. This display medium uses a dispersion liquid having a specific yield value in which a fine magnetic material having a specific residual magnetic moment and coercive force is dispersed in a dispersion medium. However, this panel has a problem that the contrast is small and the image is not clear even when the display is performed by inverting the minute magnetic material with a magnet or when erasing is performed.

Therefore, the present applicant further retained a dispersion liquid having a yield value mainly composed of a fine magnetic material, a dispersion medium, and a thickening agent, each of which is color-coded by coloring the magnetic poles in different colors. A reversible magnetic display medium was proposed.
The magnetic reversal display medium according to the present invention is a disclosure in which one area of the display surface of the micromagnetic material occupying one honeycomb cell, that is, a so-called display area ratio, is in a specific range. The purpose of this was to provide a clear display, but a honeycomb cell was used as the container.
In the honeycomb type, since the honeycomb container is relatively large with respect to the particle diameter of the included fine magnetic body, the ratio of the container to the particle diameter of the fine magnetic body becomes large.
When such a magnetic reversal display medium is used, it is possible to prepare conditions for good display in the case of flat placement. However, if the medium is placed vertically and display and erasure are repeated, the magnetic material gradually becomes smaller. However, there is a problem that some particles are settled and agglomerated to cause inversion failure. Some attempts have been made to increase the viscosity of the dispersion and prevent sedimentation in order to eliminate this problem, but there is a tendency for thixotropic properties to increase when left for a long period of time. The problem of becoming higher than necessary remained.
Furthermore, the honeycomb type requires not only a large area of one honeycomb cell display surface but also a certain amount of cell thickness. Therefore, since the volume is increased, the particle-free region becomes wider as the fine magnetic material settles. Therefore, it is desired to reduce the cell thickness, but it is difficult due to the properties of the honeycomb type and the manufacturing process.

  On the other hand, although the microcapsule type magnetic display medium is disclosed in Patent Document 4 and the like, all of them are based on the correlation between the specific particle size of the microcapsule and the particle size of the minute magnetic material which is an inversion type magnetic material. There was no example of trying to improve the display, and it was insufficient as a more advanced display solution.

Further, Patent Document 5 proposes a microcapsule type magnetic display medium using a so-called twist ball, and is able to provide a display medium with a high contrast ratio.
However, this technique uses rotating spherical particles as a display element, and does not use minute magnetic materials obtained by coloring magnetic poles in different colors, that is, flat magnetic particles as display elements. The solution for increasing the contrast ratio is naturally different. In the proposal, in order to increase the contrast ratio, the solution means that two or more spherical particles are contained in the minimum region (in short, one cell). Furthermore, there is only a description of 70% or more of the minimum area, and there is no suggestion that the correlation between the particle diameter and the container is directly related to the contrast or the like.

In other words, the solution to the problem of the contrast ratio in the present application is not only the overall solution such as the display area ratio, but also the ability of the fine magnetic particles themselves (the ability of one magnetic particle), that is, the minute The correlation between the particle size of the magnetic material, the particle size of the micromagnetic material, and the particle size of the microcapsule that is the container is the main part, and no proposal has been made that pays attention to such a point.
Incidentally, if the D ₅₀ of the micro magnetic material outside the particle size range of the present application is 30 μm or less, a good contrast cannot be obtained even if the display area ratio described in Patent Document 3 is 300%.

  In addition, Patent Document 6 and the like show examples of general magnetic display media, including a description of using a microcapsule for a container and examples of inversion type magnetic particles. Is 100 to 1000 μm, especially about 400 μm, and the magnetic particle diameter when used in a microcapsule type is preferably 0.2 to several μm. The result was insufficient.

  As described above, in the conventional technology, when an inversion type micro magnetic material (particularly, a flat micro magnetic material) is used as a display element and a microcapsule is used as a container, There was no disclosure that the correlation of particle diameters contributed to display performance such as contrast.

Japanese Patent Publication No.57-27463 Japanese Patent Publication No.59-32796 JP 2001-201772 A JP 60-107689 A JP 2002-350907 A JP-A-11-249594

  It is an object of the present invention to propose a microcapsule type magnetic reversal display medium having good display performance such as contrast when an inversion type micromagnetic material is used as a display element and a microcapsule is used as a container. It proposes a solution to this problem.

In order to solve the above-mentioned problems, the present invention has completed the microcapsule type magnetic reversal display medium of the present invention by combining a micro magnetic material having a specific particle size and particle size distribution and a microcapsule container.
That is, the present invention
“1. A magnetic reversal display medium including a microcapsule as a container, and including at least a flat micro magnetic body formed by cutting or crushing a layered body colored in different colors with magnetic poles as a display element, the particle size distribution of the fine magnetic material D ₁₀ = 30 [mu] m or more, D ₉₀ = 100 [mu] m or less, and D ₅₀ = 50~70μm der is, the outer diameter of the microcapsule is a 100 to 800, the particle size distribution of the microcapsules D ₁₀ = 100 μm or more, D ₉₀ = 700 μm or less, and D ₅₀ = 200 to 600 μm, and the particle diameter (D ₅₀ ) of the micromagnetic material as the display element and the inner diameter of the microcapsule as the container satisfy the following conditions: A microcapsule type magnetic reversal display medium characterized by satisfying the requirements .
(Particle size of D ₅₀ of fine magnetic) (microcapsules inner diameter) / = 1.5-15 about ".

  According to the said structure, there exists an outstanding effect which can obtain the microcapsule type | mold magnetic reversal display medium with favorable display performances, such as contrast. Furthermore, the localization of the micro magnetic material can be prevented, and even when the medium is placed in a vertical position, particle sedimentation can be suppressed. Display (so-called) suppression of line breaks, suppression (prevention) of poor appearance due to apparent display density reduction, and suppression (prevention) of contrast reduction due to resolution reduction, etc., to improve the uniformity of the display surface of the display medium be able to.

  The microcapsule type magnetic reversal display medium of the present invention is composed of at least a micro magnetic material in which magnetic poles used as display elements are colored by different colors and a microcapsule enclosing it.

  The minute magnetic material used in the present invention is a magnetic material obtained by coloring the two magnetic poles of the N pole and the S pole in different colors, and this magnetic material is reversed by magnetism to form a display. For example, when the display surface of the display medium is scanned with the south pole of the magnet, the N pole surface of the magnetic material is aligned with the surface of the display medium and becomes the color of the N pole surface. When this surface is written with the N pole of the magnetic pen, the magnetic body is inverted to display the S pole surface, and a display is formed in that color. When scanning with the south pole of the magnet again, it is reversed and the display disappears.

Various microcapsules can be used as long as the microcapsules enclosing the micro magnetic material act as a container.
For example, microcapsules produced by a known method such as an interfacial polymerization method, an in situ polymerization method, a submerged drying method, an orifice method, or a coacervation method can be used as appropriate.

The particle size distribution of the micromagnetic material of the present invention is optimally D ₁₀ = 30 μm or more, D ₉₀ = 100 μm or less, and D ₅₀ = _{50 to} 70 μm.

At that time, the particle size of the microcapsules preferably satisfies the following conditions.
(Inner diameter of the microcapsules) / (particle size of D ₅₀ of fine magnetic) = 1.5 to 15

Various methods have been proposed to show the particle size distribution of particles (micro magnetic material or microcapsule). In the present invention, a general cumulative particle size distribution is employed. D ₅₀ is the median value of the particle size distribution (median diameter) and refers to the particle size corresponding to 50% of the cumulative particle size distribution. The particle diameter corresponding to 10% of the cumulative particle size distribution is indicated by D ₁₀ , and the particle diameter corresponding to 90% is indicated by D ₉₀ . The larger the value of D ₁₀ / D ₉₀ is, the narrower the distribution width is, and the distribution diagram has a sharp shape, and a smaller value indicates a broad shape.

If the particle size distribution of the fine magnetic substance is out of the above range, the contrast and resolution are lowered, and as a result, the display itself cannot be performed. In addition, problems such as that the obtained microcapsules do not reach the desired performance tend to occur. Specifically, it is as follows.
When D ₅₀ is less than ₅₀ μm, the inversion of the minute magnetic material is possible, but the contrast tends to be remarkably lowered.
If D ₅₀ = 50 μm or more, good contrast and resolution can be obtained.
When D ₅₀ exceeds 70 μm, the resolution tends to decrease.
When D ₅₀ exceeds 75 μm, the content of the micromagnetic material contained in the prepared microcapsule tends to be non-uniform, and the magnetic particles contained in each microcapsule tend to be coarse and dense.
When D ₅₀ = _{50 to} 70 μm, it is possible to obtain a microcapsule-type magnetic reversal display medium in which both contrast and resolution can be achieved and the micromagnetic material is uniformly included.
When D ₉₀ = 100 μm is exceeded, the amount of fine magnetic material that leaks from the droplets during emulsification during the production of the microcapsules tends to increase, making it difficult to obtain the desired microcapsules.
When D ₉₀ exceeds 120 μm, the tendency becomes stronger,
When D ₉₀ = 150 μm is exceeded, the target microcapsules can hardly be obtained.
If D _{10 is} smaller than 30 μm, the magnetic poles having a flat structure are hardly colored as different magnetic colors, and the ability to form contrast as a display element is reduced. For this reason, it is desirable that the particle size distribution of the fine magnetic material to be used is substantially free of particles smaller than 30 μm.
Further, if D _{10 is} smaller than 20 μm, the number of elements that cannot be reversed increases and does not function as a display element. Moreover, the probability that the shape is not appropriate or does not contain magnetic powder increases. As a result, the existence probability of those that cannot function as a minute magnetic substance increases, and cannot be used .
This tendency appears more prominently when the particle size of the microcapsules used as the container is 100 to 800 μm.

Since the volume of the microcapsule-type container can be made smaller than that of the honeycomb cell type, it is easy to design a large particle size ratio of the micromagnetic material to the container.
As described above, there is Patent Document 4 as a microcapsule type magnetic display medium, but there is no disclosure of a specific microcapsule particle size, and a display medium that sufficiently satisfies the performance can be obtained as it is. is not.
Furthermore, the display performance of the microcapsule type magnetic reversal display medium depends not only on the performance of the micromagnetic material but also on the correlation with the particle size of the microcapsule that is the container.

When the display capability of the micro magnetic material itself is sufficient, the contrast itself is greatly affected by the area occupied by the micro magnetic material relative to the container. To increase the occupancy rate for the container,
(1) Use a small number of large magnetic bodies contained in a container. (2) Either a large number of small magnetic bodies included in a container can be used.
However,
In the case of (1), if the particle size of the fine magnetic material is too large, there arises a problem that gaps between particles are generated. In order to solve this problem, if a large amount of minute magnetic material is added, mutual interference occurs and reversal inhibition occurs. Furthermore, there is an unfavorable tendency that the resolution of display decreases when a large magnetic material as a display element is used. To solve this problem, a method of using a honeycomb cell as a container having a sufficiently large space is used. It was not possible to reduce the size and thickness. (Conventional technology)
In the case of (2), there is a minute magnetic substance without a gap, and even if a certain amount is added, inversion inhibition hardly occurs, and the resolution is good because the display element is fine. However, if it becomes too small, the display capability of the micro magnetic material itself, that is, the light reflection performance of the surface of the display color is lowered, and the contrast tends not to be secured. In addition, if the particle size difference between the cell container and the micro magnetic material becomes too large, it is not preferable because localization proceeds as the micro magnetic material settles and shifts.
Therefore, it has been found that in order to solve these problems, the particle size of the micromagnetic material, the particle size of the microcapsule as the container, and the ratio thereof are important in obtaining the display medium of the present invention.

Therefore, in the present invention, a microcapsule having a specific correlation as described below is used as a container while using a micromagnetic material in a specific range as described above.
By making the particle size ratio between the micromagnetic body and the container appropriate, the localization of the micromagnetic body in the container is prevented, or even if localization occurs, it is virtually impossible to visually recognize it. It becomes possible to keep to the extent. For this reason, even if writing and erasing are repeated on the display surface, defects such as sedimentation and aggregation of the fine magnetic material are not observed, and a uniform display surface can be maintained. Further, since a flat or foil piece of magnetic material as a minute magnetic material is reversed while being displaced, good display can be achieved by securing a necessary minimum space.
(Inner diameter of the microcapsules) / (particle size of D ₅₀ of fine magnetic) = 20
Can be displayed sufficiently even after writing and erasing,
further,
(Inner diameter of the microcapsules) / (particle size of D ₅₀ of fine magnetic) = 1.5 to 15
Within this range, display deterioration is hardly observed, and thus it is more preferable.

Moreover, it is preferable that the particle size of the microcapsule satisfies the above correlation, and the outer diameter of the microcapsule is 50 to 3000 μm.
If the outer diameter of the microcapsule is less than 50 μm, it is possible to produce the microcapsule itself, but there is an unfavorable tendency that it becomes difficult to encapsulate the micromagnetic material or a reversal failure occurs.
When it exceeds 3000 μm, it tends to be difficult to form a stable emulsion during the production of microcapsules, and as a result, stable production of microcapsules tends to be difficult.

The outer diameter of the microcapsule is further preferably 100 to 1100 μm, and more preferably 100 to 800 μm.
When the outer diameter of the microcapsule exceeds 1100 μm, it is difficult to produce a stable microcapsule. In addition, the strength of the microcapsule itself is reduced, and a thin film is formed when a layer structure is formed when the microcapsules are arranged. Inconveniences such as difficulty.
If the outer diameter of the microcapsule is in the range of 100 μm to 800 μm, good reversal of the fine magnetic material is maintained, there is no sedimentation or misalignment of the particles even when used repeatedly, and the microcapsules are stably manufactured. It is optimal because it can.

The particle size distribution of the microcapsules is more preferably D ₁₀ = 100 μm or more, D ₉₀ = 700 μm or less, and D ₅₀ = 200 to 600 μm.

  As described above, various microcapsules can be used as long as the microcapsules enclosing the fine magnetic material usable in the present invention function as a container.

  For example, microcapsules having a gelatin film such as acid-treated gelatin or alkali-treated gelatin, microcapsules having an alginate film, melamine-formaldehyde resin film, and microcapsules having a resin film such as urea-formaldehyde resin can be used.

  Examples of the production method include complex coacervation method, simple coacervation method, orifice method, in situ polymerization method and the like. In particular, as an example using the complex coacervation method, a dispersion composed of at least a fine magnetic substance and a dispersion medium is charged into an aqueous solution containing gelatin as a coating substance to form an O / W emulsion. And a microcapsule produced by forming a film substance by a complex coacervation method and then curing the film with a curing agent such as transglutaminase.

The particle size distribution of the fine magnetic material is measured by a laser diffraction / scattering particle size distribution measurement method, and a value obtained as an area reference distribution is used. The micro magnetic material is indefinite, preferably flat. Therefore, in the laser diffraction / scattering type particle size distribution measurement, the particle diameter of the micromagnetic material is a value converted as a sphere equivalent diameter due to its properties.
Moreover, the particle diameter measurement of a microcapsule measures the internal diameter by visual measurement with a microscope (175 times). This is because the correlation with the encapsulated micromagnetic material cannot be derived by measuring the outer diameter. In the present invention, the particle size of the microcapsule means the inner diameter of the partition wall of the microcapsule. The objects to be measured were those sampled at n = 10 except for the large and small microcapsules with remarkably different sizes, and the average value of the measured values was used.
For the particle size distribution (outer diameter) measurement of the microcapsules, the value obtained as a volume reference distribution is measured by laser diffraction / scattering particle size distribution measurement in the same manner as the fine magnetic material. In this case, the outer diameter is measured, but it is not practical to measure the particle size distribution by visual measurement. It is sufficient to grasp the uneven distribution of the particle size (inner diameter) of the microcapsules, and the above values are used approximately. .

  The microcapsule-type magnetic reversal display medium of the present invention is mainly composed of the above-mentioned micromagnetic material and microcapsules, but if desired, a dispersion medium, a thickener, a colorant, a surfactant, a viscosity modifier, an antistatic agent. An agent or the like can be used.

  An example of the configuration of the microcapsule-type magnetic reversal display medium of the present invention is as follows. A microcapsule is encapsulated with a dispersion liquid in which a micromagnetic material is dispersed in a dispersion medium, and a plurality of the microcapsules are arranged and fixed. A magnetic reversal display medium having the display surface can be obtained.

The dispersion liquid in which the fine magnetic material is dispersed preferably has a specific yield value and viscosity. The yield value works to prevent the sedimentation because the fine magnetic material in the dispersion liquid is properly dispersed and needs to be held near the surface. This is important for reversing only the magnetized part. Since the yield value and the viscosity are greatly related to the material, shape, size, and the like of the fine magnetic material, they can be appropriately designed as long as they satisfy the above-described effects. If the yield value and viscosity are outside the design philosophy, the stability of the formed display deteriorates, and when writing with a magnetic pen, the surrounding magnetic material gathers, so the distribution of the magnetic material becomes uneven and inverts. Since the background color of the display formed by a magnetic material that is not reversed at the vicinity of the display and the periphery thereof changes, the display becomes blurred as a whole, and the sharpness tends to deteriorate.
However, if a combination of the micro magnetic material of the present invention having a specific particle size and a microcapsule is used, there is a specific effect that the degree of freedom in design increases.

  In order to give the dispersion a specific yield value and viscosity, a thickener may be added. There are broadly divided into inorganic thickeners and organic thickeners, but organic thickeners are relatively stable. For example, a yield value can be imparted even with an inorganic material such as silica, but the inorganic thickener has a drawback that the viscosity and yield value change greatly with the passage of time. However, organic thickeners selected from fatty acid bisamide, hydrogenated castor oil, N-acylamino acid amide and the like are preferred because they have the advantage that their viscosity and yield value are unlikely to change over time.

Micro magnetic material used in the present invention, S pole face and is colored the N pole surface in different colors, from clearness such as a display formed of the formed display when writing with a magnetic pen, in flat Preferably there is. According to the research of the present inventors, the minute magnetic material is reversed when a magnetic force of the opposite polarity is applied, but the flat or foil piece-shaped magnetic material is reversed while being overlapped, so that the display formation speed is high. In addition, there are few cases where non-inverted and incompletely inverted ones are mixed, and a clear display is formed.
Further, the color-coded fine particle-like fine magnetic material is a layered material obtained by applying a colored composition of another color on one side of a layer in which magnetic particles are dispersed in a specific color synthetic resin and / or synthetic rubber composition. A fine magnetic body obtained by cutting or pulverizing, or a layered body obtained by laminating a colored sheet of another color on one side of a layer in which a basic magnetic particle is dispersed in a synthetic resin and / or synthetic rubber composition of a specific color. A fine magnetic material obtained by cutting or pulverizing is preferable.

  Micro magnetic materials tend to rub against each other during reversal, and static electricity tends to be charged. In particular, in the case of a flat or foil-shaped micro magnetic material, the micro magnetic materials are reversed and overlapped so that they are easily charged. When the minute magnetic body is charged, the minute magnetic body aggregates and becomes unevenly distributed (localized), and even if magnetism is applied with a magnetic pen, it may not be reversed smoothly or may not be reversed. Because of this, it may not be possible to obtain a clear display of color-coded fine magnetic materials, which is not preferable. When an antistatic agent is added to the dispersion of the fine magnetic material, a good display can be obtained.

  Antistatic agents include polybutene sulfate, aliphatic alkyl quaternary ammonium salts, aminoethanol / epichlorohydrin polycondensate, alkylbenzene sulfonic acid, alkyl salicylic acid metal salt, sulfosuccinate, dialkyl sulfosuccinate, dodecylbenzene sulfonate metal 1 type or 2 types or more are selected from the salts, but in particular, polybutene sulfate, aliphatic alkyl quaternary ammonium salts, aminoethanol / epichlorohydrin polycondensate, alkylbenzene sulfonic acid mixture, alkyl salicylic acid chromium salt, sulfosuccinic acid. A mixture of calcium acid salt and polymer is preferred.

  In the present invention, the dispersion medium for dispersing the fine magnetic material may be either aqueous or oily. In the case of oil, nonpolar solvents such as oils and aliphatic hydrocarbons, glycols and alcohols are used. -One type or two or more types of polar solvents such as thiols can be selected and used alone or in combination. Specifically, isoparaffin, spindle oil, ethylene glycol, or the like is used, and isoparaffin is preferable from the viewpoint of components to be blended.

  Hereinafter, examples of the present invention will be described with reference to the drawings, but the present invention is not limited thereto.

Example 1
<Preparation of microcapsule encapsulation solution>
A magnetic ink colored green was applied onto a PET film having a thickness of 25 μm and dried to obtain a green magnetic layer. At this time, the thickness of the green magnetic layer was 7 μm. Next, a white ink was applied and dried on the green magnetic layer and laminated on the green magnetic layer. The white layer had a thickness of 10 μm. In this way, a two-color coating layer having a thickness of 17 μm was formed on the base film together with the previously coated green magnetic layer. Subsequently, this two-color coating sheet is magnetized, the green side is made the N pole, the white side is made the S pole, the two-color coating layer is peeled off from the base film, pulverized, and then classified by an air classifier. A desired micromagnetic material was obtained. The particle size distribution of the obtained micromagnetic material was measured using a laser diffraction particle size distribution measuring device (manufactured by Shimadzu Corporation: SALD3000S). For the measurement, isoparaffin (ExxonMobil Chemical Co., Ltd .: Isopar M) was used as the circulating solvent, and the particle size distribution was made using the refractive index of 1.70-0.20i and the area-based distribution as analysis conditions. The obtained micromagnetic material had a particle size distribution of D ₁₀ = 33.7 μm, D ₅₀ = 53.3 μm, and D ₉₀ = 74.6 μm.
Next, an antistatic agent and a thickener are added to isoparaffin having a viscosity of 3.2 mPa · s at 20 ° C. (product name: ISOPAR M) as a dispersion medium, and plastic dispersion having a viscosity and a yield value is obtained. A liquid was prepared.
While stirring 100 parts by mass of this plastic dispersion with a propeller, 0.18 part by mass of a fine magnetic material was added and stirred until uniform to prepare a microcapsule inclusion liquid.
<Preparation of microcapsules>
While maintaining the temperature of the system at 40 ° C. and stirring 90 parts by mass of a 10% by mass acid-treated gelatin aqueous solution (AP200 manufactured by Nippi Co., Ltd.), 120 parts by mass of warm water (ion-exchanged water) at 40 ° C. was added, and further as a polyanion 90 mass parts of 1.25 mass% sodium carboxymethylcellulose aqueous solution (Daiichi Kogyo Seiyaku Co., Ltd. cellogen F-7A) was mixed and made uniform. Next, 132 parts by mass of the prepared microcapsule inclusion liquid was added and emulsified and dispersed to form an S / O / W emulsion. Then, acetic acid (a reagent manufactured by Wako Pure Chemical Industries, Ltd.) was added to adjust the pH to 4.6, thereby forming a coacervate film. The emulsion was gradually cooled to 5 ° C. while stirring to gel the film and kept at 5 ° C. for 30 minutes for stabilization. Thereafter, the temperature of the system was raised again to 20 ° C., and 12 parts by mass of sulfonic acid-modified polyvinyl alcohol (Goseiran L3266 manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) was added. Next, 10 mass% sodium hydroxide aqueous solution was added, pH was adjusted to 7.0, and 0.90 mass part of transglutaminase (Ajinomoto Co., Ltd. Activa TG-S) was added. Finally, stirring was continued for 16 hours while maintaining the temperature of the system at 20 ° C. to obtain a microcapsule dispersion liquid in which the film was cured.
The inner diameter of the obtained microcapsule was 463 μm as measured with a microscope (175 times).
Moreover, when the particle size distribution of the obtained microcapsule was measured using a laser diffraction type particle size distribution measuring apparatus (manufactured by Shimadzu Corporation: SALD3000S), D ₁₀ = 382.0 μm, D ₅₀ = 504.6 μm, D It had a particle size distribution of ₉₀ = 643.2 μm. . In the measurement, water was used as a circulating solvent, and the particle size distribution was obtained using a refractive index of 1.70-0.20i and a volume-based distribution as analysis conditions.
<Preparation of display medium>
A water-based binder was mixed with the obtained microcapsules, applied to a 125 μm-thick PET film, and dried to obtain a magnetic reversal display medium in which the microcapsules were arranged.
After the multi-pole rubber magnet is brought into contact with the PET film side of this display medium and moved to the left and right so as to be perpendicular to the magnetization pitch, the micro magnetic materials separately coated in two colors in the microcapsule are individually dispersed. The green display surface was formed while the S poles of the magnets were brought into contact with each other so that the minute magnetic bodies were aligned while partially overlapping each other. Next, a writing operation is performed on the display surface with the N pole of the magnet from the top of the PET film on the surface, and a clear white display can be obtained only on the portion where the N pole of the magnet has passed through the green display surface. It was.
Next, when the white display portion was rubbed from above again using the south pole of the magnet, the magnetic display body with the white surface facing the surface was inverted and returned to the green display surface again. . The evaluation at that time is shown in Table 1.

Examples 2 to 4, Reference Examples 1 to 5, Comparative Examples 1 to 5
A micropsel and a display medium were obtained in the same manner as in Example 1 except that the micromagnetic material and the microcapsule were those shown in Table 1.

Examples 10 to 14, Reference Examples 6 to 16, Comparative Examples 6 to 9
A micropsel and a display medium were obtained in the same manner as in Example 1 except that the micromagnetic material shown in Example 1 and Reference Example 2 was used, and the microcapsule as the container had a particle size shown in Table 2. It was.

Tables 1 and 2 show the particle sizes, particle size distributions, particle size ratios, evaluation results, and the like of the micromagnetic material and the microcapsules in each example.

Test and Evaluation In the microcapsule type magnetic reversal display medium in each of the above examples and comparative examples, the following items were tested and evaluated. The description of the writing and erasing operations in the evaluation of the display medium is as follows.
a) Formation of green display surface The S pole of the erasing tool is brought into contact with the display surface side of the display medium to perform an erasing operation, and the N pole surface (green) of the minute magnetic material in the display medium is displayed on the display surface. The entire display surface of the display medium is formed as an N-polar surface (green) while being aligned so that the particles are aligned side by side and partially overlap each other.
b) Display (writing) operation The N pole of a magnetic pen, which is a writing instrument, is brought into contact with the display surface side of the display medium to perform a writing operation, the N pole surface (green) of the minute magnetic body in the display medium is reversed, and S A writing line is formed by displaying the polar surface (white).
c) Erasing operation The writing line displayed on the display medium is erased with the south pole of the erasing tool, and the writing line formed on the south pole surface of the minute magnetic material is reversed to the north pole surface (green) to erase. To do.
(1) Contrast Using a spectrocolorimeter (CM-512 m2 manufactured by Konica Minolta Holdings, Inc.), measure the L ^* (45 °) value on the N-polar surface (green) and S-polar surface (white) of the display medium. The contrast was evaluated from the difference (ΔL ^* _{45 °} ).
(2) Resolution The state of the writing line when writing was visually observed.
◎ ・ ・ ・ The width of the writing part is constant and displayed very clearly.
○ The width of the writing part is constant and displayed clearly.
Δ: There is a part where the width of the writing part is not constant, and the whole part is slightly blurred
It is displayed.
X: The width of the writing part is not constant and is displayed in a blurred state.
Or if it is not reversed.
(3) Microencapsulation ○: Microcapsules were successfully produced.
X: Microcapsules could not be produced well.
(4) Amount of particles encapsulated:... An equal amount of fine magnetic material is contained in the microcapsule.
X: The content of the contained micromagnetic material is different for each microcapsule.
(5) Sedimentation / offset evaluation ○ ・ ・ ・ Even if a multipolar magnet is applied only in one direction,
The localization of the minute magnetic material is not visually recognized, and a good display is maintained.
△ ・ ・ ・ When a multi-pole magnet is applied only in one direction,
The localization of the minute magnetic material is slightly visible, and the display is slightly unclear.
× ・ ・ ・ When a multipolar magnet is applied only in one direction,
The localization of the minute magnetic material is visually recognized, and the display becomes unclear.
(6) Initial evaluation In performing the above tests and evaluations, after the display medium is manufactured, first, evaluation is made as to whether each operation of a) green display surface formation, b) display (writing) operation, and c) erasing operation can be performed without any problems. Went.
(7) Comprehensive evaluation Through the above tests and evaluations, it was judged whether or not the display medium was comprehensively good.

As described above, the present invention can be used as a microcapsule type magnetic reversal display medium having good display performance such as contrast when a reversal type micro magnetic material is used as a display element and a microcapsule is used as a container. .

Claims (1)

A magnetic reversal display medium containing a microcapsule as a display element and including at least a flat micromagnetic body obtained by cutting or crushing a layered body colored with different colors by coloring magnetic poles as a display element. particle size distribution D ₁₀ = 30 [mu] m or more, D ₉₀ = 100 [mu] m or less, and D ₅₀ = 50~70μm der is, a outer diameter of the microcapsule is 100 to 800, the particle size distribution of the microcapsules is D ₁₀ = 100 μm or more, D ₉₀ = 700 μm or less, and D ₅₀ = 200 to 600 μm, and the particle diameter (D ₅₀ ) of the micromagnetic material as the display element and the inner diameter of the microcapsule as the container satisfy the following conditions. There is provided a microcapsule type magnetic reversal display medium.
(Inner diameter of the microcapsules) / (particle size of D ₅₀ of fine magnetic) = 1.5 to 15