JP3559721B2 - Method for producing colored magnetic particles for magnetophoretic display - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a method for producing colored magnetic particles to be used in a magnetophoretic display panel that displays images using magnetophoresis.
[0002]
[Prior art]
Generally, as a drawing board for infants, a honeycomb core having a large number of hexagonal cells is sealed between a transparent or translucent drawing surface plate (substrate) and a surface material facing the drawing surface plate (substrate). 2. Description of the Related Art A magnetic plate enclosing a plastic dispersion liquid containing magnetic particles is known.
[0003]
This is because a magnetic field is applied to the dispersion liquid by bringing the tip of a pen magnet into contact with the drawing surface, and the magnetic particles float on the drawing surface, and the difference in contrast between the dispersion medium and the magnetic particles causes the picture or text to be drawn on the drawing surface. Is displayed, and by moving the eraser bar below the substrate, the floating magnetic particles are settled again to erase pictures and characters.
[0004]
As the plastic dispersion liquid, a liquid in which magnetic particles, a fine particle thickener, and a colorant are mixed in a dispersion medium is known. Examples of the dispersion medium include polar dispersion media such as water and glycols, and non-polar dispersion media such as organic solvents and oils. As the magnetic particles, particles of an oxide magnetic material such as black magnetite, γ-hematite, chromium dioxide, and ferrite, and particles of an alloy-based metallic magnetic material such as iron, cobalt, and nickel may be used. Examples of the fine particle thickener include silicic anhydride, hydrous calcium silicate, hydrous aluminum silicate, silica powder, diatomaceous earth, kaolin, clay, benite, etc. There are ultra-fine calcium carbonate, ultra-fine activated calcium carbonate, heavy calcium carbonate, hydrated basic magnesium carbonate, barium sulfate, and the like. Further, as a coloring agent, there are white colored pigments and dyes. As magnetic particles, particles of oxide magnetic materials such as black magnetite, γ-hematite, chromium dioxide, and ferrite, and particles of alloy-based metallic magnetic materials such as iron, cobalt, and nickel have been used. In this manner, figures, characters, and the like are displayed on the drawing surface due to the contrast between the ground color of the white or milky dispersion medium and the lines drawn by the black magnetic particles.
[0005]
[Problems to be solved by the invention]
However, colorization is desired as a display panel at the next stage of display with a black line on such a white background, and the present inventors have repeatedly studied for the realization thereof. There were the following problems.
(A) When displayed by chroma colored particles, the color "red" should appear in "brown" or "vermilion", and the color "blue" should appear in "black". Could not be satisfied.
(B) The white color of the dispersion medium is mainly used as a colored white dispersion medium. The colored magnetic particles are caused to migrate into the dispersion medium. In addition, a part of the paint may become a lump (paint lump) of the same size as the colored magnetic particles and may be mixed into the cell. Further, when the colored magnetic particles in the same cell repeatedly float and settle, they may collide with each other and a part of the paint may be separated from the magnetic particles. Such a paint alone mixed with the dispersion medium and changed color, resulting in incomplete contrast with the colored magnetic particles, and the display was also unclear in this respect.
(C) Realization of a plurality of colors It is meaningless if a plurality of colors cannot be displayed. The problem was how to display this.
[0006]
SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and provides a coating of a coating agent around the magnetic particles evenly and neatly.Also, it is possible to develop a beautiful color with a small amount of the coating agent and to improve a chromatophoretic display. It is an object of the present invention to provide a method for producing colored magnetic particles for use.
[0007]
[Means for Solving the Problems]
In order to solve the above problems, a method for producing colored magnetic particles for magnetophoretic display according to the present invention comprises coating a coating agent composed of a colored pigment and a synthetic resin on the surface of the magnetic particles by tumbling fluidized granulation coating. In addition, the coating amount of the coating agent is set to 10 to 35 Wt% of the particles after coloring, and after performing the colored coating, only the synthetic resin is overcoated, and the amount of the overcoat is set to 3 to 6 Wt%. Features.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is an enlarged cross-sectional view of colored magnetic particles provided for a magnetophoretic display panel. The colored magnetic particles 1 for magnetophoretic display are provided with a colored layer of a coating agent 3 composed of a colored pigment and a synthetic resin on the surface of the magnetic particles 2.
[0009]
The coating agent 3 is composed of a colored pigment and a synthetic resin. The reason why the synthetic resin is mixed is that the colored pigment alone is not adhered and fixed to the magnetic particles, so that the synthetic resin is mixed with the colored pigment and adhered securely to the surface of the magnetic particles. In addition, the strength of the colored layer against peeling can be improved by overcoating the colored layer only with the resin after performing the colored coating.
[0010]
For example, as a red colored pigment, there are permanent red, fast red, pigment red, brilliant carmine, chinching red, red iron, etc., and as a yellow colored pigment, first yellow, pigment yellow, pigment orange, acid yellow, anza There are yellow, yellow iron oxide and the like, and the blue colored pigments include cyanine blue, cobalt blue, dark blue, ultramarine blue, and the like, and further, as the green colored pigments, phthalocyanine green, pigment green, cobalt green and the above. There is a mixture of blue and yellow.
[0011]
In addition to the above-mentioned organic colored pigments and inorganic colored pigments, resin colors obtained by pulverizing colored resins can also be used.
[0012]
Next, as a synthetic resin, when a solvent is used as a dispersion medium, a butyral resin, an acrylic resin, an epoxy resin, a cellulose resin, or the like can be used. When water is used, an acrylic ester emulsion resin, an acrylic copolymer emulsion, an acrylic styrene copolymer emulsion, a vinyl acetate emulsion, or the like can be used as the emulsion. Further, as the water-soluble resin, HPC (hydroxypropylcellulose), HPMC (hydroxypropylmethylcellulose), CMC (carboxymethylcellulose), methylcellulose and the like can be used.
[0013]
As the magnetic particles 2, silicon steel or stainless steel can be used. SUS405, SUS410L, SUS430, SUS434, SUS329JI and the like are suitable. The apparent density before coloring is 2.3 to 3.0 g / cm ³ , and preferably 130 to 200 emu / g, and the optimal value is 130 to 160 emu / g. As in the conventional case, particles of an oxide magnetic material such as black magnetite, γ-hematite, chromium dioxide, or ferrite, or particles of an alloy-based metallic magnetic material such as iron, cobalt, or nickel may be used.
[0014]
If the saturation magnetization is too small or too large, the thickness of the colored layer formed by the coating agent 3 is too small or too large to obtain proper magnetization after coloring. If the colored layer is thin, the ground color of the magnetic particles is transparent, and if it is too thick, a part of the coating agent is peeled off and the dispersion medium is easily contaminated.
[0015]
The saturation magnetization in a state colored by the coating agent 3 is preferably 80 to 150 emu / g, and the magnetization in an applied magnetic field of 1 Koe close to the magnetic field strength when used with a pen magnet is 35 to 65 emu / g (an applied magnetic field of 1 Koe). A vibrating sample magnetometer VSM2 manufactured by Toei Kogyo). This is to make the colored magnetic particles 2 float or settle well with the pen magnet. If the magnetization is smaller than 35 emu / g, the response of the floating or the sedimentation is slow, so that the display color becomes light. If it is larger than 65 emu / g, colored magnetic particles in nearby cells that are not in contact with the pen magnet will also float, causing sharpness of the drawn line, and so-called fine whisker-like projections at the side edges of the actually drawn line. And broken lines occur. The optimal value is between 40 and 55 emu / g.
[0016]
The colored magnetic particles 1 in a colored state preferably have a particle diameter of 50 to 130 μm of 90 Wt% or more. This is because when the diameter of the colored magnetic particles 1 is 50 to 130 μm, the coating operation of the coating agent can be performed most efficiently and a beautiful drawing line can be obtained. If it is smaller than 50 μm, the number of colored magnetic particles in one cell is too large, and it is difficult for all of them to instantaneously react to the magnetic pen. On the other hand, if it is larger than 130 μm, the number of colored magnetic particles in one cell is small, and the drawing line becomes rough even if it floats due to the attractive force of the magnetic pen depending on the size of the particles.
[0017]
When the content of the colored magnetic particles 1 having the above particle diameter is less than 90 Wt%, the particles are not uniform, and it is difficult to obtain a clear drawing line.
[0018]
Further, the apparent density in the colored state is preferably 1.6 to 2.0 g / cm ³ as described above, because the colored magnetic particles are attracted to the display surface side by a magnet pen and floated. When displaying characters, pictures, or the like, or moving the erase magnet along the opposite surface to completely settle the floating colored magnetic particles and erase the display, the apparent density is 1.6 g / cm. ^If it is smaller than ^{3, the} floating colored magnetic particles cannot be sedimented unless the erasing magnet is reciprocated repeatedly, and if it is larger than 2.0 g / cm ³ , the colored magnetic particles are dispersed liquid. This is because the colored magnetic particles do not float as expected even if the magnet pen is moved, so that the drawn line becomes thin or faint. In particular, it is possible to efficiently erase drawing lines.
[0019]
According to the colored magnetic particles 1 having the above configuration, it is possible to realize a clear color and a display with clear lines without causing contamination of the dispersion medium.
[0020]
Incidentally, when the colored magnetic particles are produced by coating the magnetic particles with the coating agent as described above, it may be performed by tumbling fluidized granulation coating. In this coating method, the material is tumbled and flown by a blade rotor while flowing, and a binder is sprayed to granulate and dry. As shown in FIGS. Is provided, and flowing air (warm air) 7 is supplied from a gap between the outer peripheral portion of the blade rotor 6 and the side wall of the apparatus. As a result, the magnetic particles supplied onto the blade rotor 6 are strongly subjected to the rolling consolidation effect of the blade 5 and the rotor 6, roll on the outer periphery, and are sprayed from the nozzle 8 when sprayed from the nozzle 8 by the blade 5. It is blown up to the upper center on the coating agent and circulates along the taper of the central cone portion 6a. The process is repeated in the order that after the magnetic particles have undergone wetting, the coating agent is adsorbed, compacted spheroidized and dried and solidified.
[0021]
According to the above-mentioned tumbling fluidized granulation coating, since the granulation can be advanced in a high moisture state, colored magnetic particles can be obtained in a relatively short time. Since the magnetic particles are entrained in the whirlpool and the granulation proceeds in a dry state, the fine powder adheres to the surface in the dry state.Therefore, there is very little residual fine powder, and the particle size distribution becomes sharp. The density can be controlled by controlling the balance between wet and dry. In addition, overcoating can be easily performed.
[0022]
By the way, in this case, the coating amount of the coating agent is set to 10 to 35 Wt% of the colored particles. When the amount of the coating agent exceeds 35 Wt%, the colored layer on the magnetic particles is thick, so that the color is good, but on the other hand, the magnetic particles collide with each other while the magnetic particles repeatedly float and settle during use. In addition, a part of the coating agent is peeled off and the dispersion medium is easily contaminated. On the other hand, if the amount of the coating agent is too large, the magnetization after coloring decreases, and the responsiveness to the pen magnet deteriorates. On the other hand, when the amount of the coating agent is less than 10 Wt%, there is a problem that the saturation is insufficient. Furthermore, if the coating amount is large, the diameter of the particles including the colored layer becomes too large and the apparent density is low, so that it is difficult to settle after floating, and if the coating amount is small, the apparent density becomes high, and the settling becomes easy after floating. There is also a problem. Therefore, the optimum value is 20 to 30 Wt%. Further, the amount of the overcoat is desirably 10 Wt% or less. When the content is more than 10 Wt%, the strength of the coloring layer against peeling increases, but the coloring layer becomes relatively thin, the overcoat layer becomes thick, and the saturation decreases. The optimum value is 3 to 6 Wt% based on the relationship between the intensity and the saturation.
[0023]
In order to increase the saturation, a certain amount of coating must be secured. Also, not all color coatings need to be the same thickness. To achieve the same saturation, the amount of coating must be greater or smaller for some colors than for others. At that time, there arises a problem that magnetization and apparent density are different from those of other colored particles.
[0024]
Therefore, to the above-mentioned coating agent, one selected from constitutional colored pigments such as silicon dioxide, calcium carbonate, barium sulfate, clay and talc may be added. Since these additives do not have magnetization and are large in particle size, they can be mixed with the coating agent to adjust the apparent density and magnetization of the colored particles, or to improve the fluidity and shorten the labor and coating time. be able to.
[0025]
The colored pigment preferably has a particle size of 0.01 to 6 μm. If the particle size is too small, fine powder contaminating the dispersion medium is likely to be generated in the production process. If the particle size is too large, it is difficult to obtain sufficient saturation after coloring. In order to realize vivid saturation, 0 to 1 to 4 μm is optimal.
[0026]
The coating agent preferably has a weight ratio of the colored pigment to the synthetic resin of 9: 1 to 5: 5. If the proportion of the colored pigment is too large, the adhesion to the magnetic particles is poor, and if the proportion of the synthetic resin is too large, the amount of the coating agent must be increased in order to obtain a satisfactory color, so that coating takes time. is there.
[0027]
As described above, according to the tumbling fluidized granulation coating method, the coating agent can be coated evenly and neatly around the magnetic particles. Since the particle diameter of each particle becomes uniform and the magnetization is averaged, a beautiful color can be developed with a small amount of the coating agent, and the saturation is improved.
[0028]
Further, according to the coating method, since the magnetic particles are caught in the spiral by the rolling and the granulation proceeds, the residual of the fine powder is extremely small, so that the contamination of the dispersion medium can be effectively prevented.
[ 0029 ]
Next, the colored magnetic particles having the above-described structure are formed into a predetermined shape together with a plastic dispersion liquid in which a fine particle thickener or a coloring agent is blended with a polar dispersion medium such as water, a glycol, or a non-polar dispersion medium such as an organic solvent or oil. By filling the inside of the honeycomb core and bonding the panel to the front and back surfaces of the honeycomb core, a panel for magnetophoretic display as shown in FIG. 3 is completed. Colored magnetic particles of different colors may be enclosed in each cell or in a group a, b, c,...
[ 0030 ]
As shown in FIG. 4 , the tip of the pen magnet 14 is brought into contact with the drawing surface of the magnetophoretic display panel, or the eraser 16 slidably arranged on the back side of the panel 15 is moved to the left and right, so that plasticity is reduced. By applying a magnetic field to the dispersion liquid 17, the colored magnetic particles 1 can be floated on the drawing surface or settled away from the drawing surface to display or erase pictures and characters on the drawing surface. As described above, the colored magnetic particles 1 prevent the dispersion medium 18 from being contaminated, and exhibit a high-saturation, vivid color at the time of floating, so that multicolor display of the magnetophoretic display panel can be realized.
[ 0031 ]
【The invention's effect】
According to the first aspect of the present invention, since the colored magnetic particles are obtained by the tumbling fluidized-granulation coating method, the coating agent is uniformly and finely coated around the magnetic particles. In addition, since the particle diameter of each particle becomes uniform and the magnetization is averaged, a beautiful color can be developed with a small amount of coating agent, and the saturation is improved.
[ 0032 ]
Further, according to the coating method, since the magnetic particles are caught in the spiral by the rolling and the granulation proceeds, the residual of the fine powder is extremely small, so that the contamination of the dispersion medium can be effectively prevented.
[ 0033 ]
Furthermore, the adhesiveness to magnetic particles is good, and coating can be performed with high efficiency in a short time. Further, since the colored layer is overcoated with 3 to 6 Wt%, the strength against peeling of the colored layer is increased, and the decrease in chroma is not impaired.
[Brief description of the drawings]
Figure 1 is an enlarged cross-sectional view of the colored magnetic particles [2] (a) (b) is a perspective view, and partial cross-sectional view [FIG 3] magnetic migration display panel in each rotary fluidized granulation coating apparatus FIG . 4 is a sectional view showing an embodiment of a magnetophoretic display panel.
1 colored magnetic particles 2 magnetic particles 3 coating agent

Claims (1)

A coating agent composed of a colored pigment and a synthetic resin is coated on the surfaces of the magnetic particles by tumbling fluidized-granulation coating, and the coating amount of the coating agent is set to 10 to 35 Wt% of the colored particles, and coloring is performed. A method for producing colored magnetic particles for magnetophoretic display , wherein after coating, only the above synthetic resin is overcoated, and the amount of overcoat is 3 to 6 Wt% .

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