JPH0713206A - Reloadable display medium - Google Patents

Abstract

PURPOSE:To provide the reloadable display medium which is short in the time required for writing and erasing, is high in contrast of images, is good in its stability and makes it possible to select the colors of the images from a wide range. CONSTITUTION:Flaky magnetic powder 411 in microcapsules 41 has a silicon dioxide film fixed with an org. coloring agent on its surface to enable a rapid orientation change by a magnetic field H. Light Ic returns to a medium surface side at the time of the state of (a) (unrecording region) and, therefore, the reflected light from the medium has the same color tone as the color tone of the org. coloring agent. On the other hand, the light does not substantially return to the medium surface side at the time of the state of (b) (recording region) and, therefore, the black visible image in a background exhibiting the color tone of the org. coloring agent is eventually displayed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a medium capable of displaying an image and rewriting the image.

[0002]

2. Description of the Related Art For prepaid cards and the like, it is required to visually display the balance and other information on the card every time it is used.

Examples of the medium capable of visible display include a thermal recording medium using a leuco dye. In this medium, a dye precursor and a color developer are dispersed in a binder and coated on the surface of a substrate to form a recording layer, and the recording layer is heated by a thermal head or the like, whereby the dye and the color developer are formed. And are reacted to develop color, which is then displayed visually. In addition to the thermal recording medium using the dye as described above, in recent years, JP-A-59-19
A low-melting-point metal thin film destruction type thermal recording medium as disclosed in Japanese Patent No. 9284 has been put into practical use. However, in these thermosensitive recording media, it is not possible to print again on the part that has been printed once. Therefore, from the viewpoint of securing a printable area and recycling of the card, a printing method that allows rewriting repeatedly is required.

Conventionally, rewritable heat-sensitive recording media have been proposed such as those using organic low molecular weight substances, those using leuco dyes, and those using polymer liquid crystals.
For example, Japanese Patent Laid-Open No. 63-39376 discloses a thermosensitive recording medium in which an organic low molecular weight substance is dispersed in a resin matrix and the transparency reversibly changes depending on temperature. However, this heat-sensitive recording medium has the disadvantages that heat must be applied for a long time when the recorded image is erased, and the contrast between the recorded image and the background is poor. Further, Japanese Patent Laid-Open No. 2-188293 proposes a reversible recording system using a leuco dye, which is originally a reversible reaction, but this system must also apply heat for a long time during erasing. Japanese Patent Application Laid-Open No. 2-16082 discloses that a side chain type polymer nematic liquid crystal is used to obtain an isotropic phase transition temperature (Tc).
A recording medium is disclosed in which the above-mentioned heat is applied to quench and record, and recorded information can be erased by heating and gradually cooling. Also, T. Ueno,
T. Nakamura, C. Tani, Japan Display '86, 290 (1986) and Japanese Patent Laid-Open No. 4-174415 realize reversible recording by using a polymer liquid crystal of a copolymer of a nematic monomer and a cholesteric monomer. In the case of a polymer liquid crystal, it is necessary to heat and gradually cool during erasing, and in the case of a polymer nematic liquid crystal, recording is carried out due to a change from white turbidity to transparency, so that the image contrast is poor.

On the other hand, there has also been proposed a medium capable of reversible recording by orienting or moving magnetic powder by an external magnetic field. For example, Japanese Patent Publication No. 53-44425,
JP-B-60-27003, JP-A-3-27352
Japanese Patent Publication No. 1 discloses a reversible recording method using magnetic powder. With this method, recording and erasing can be performed in a short time, but there is a disadvantage in that the contrast of the image is poor.

In Japanese Patent Publication No. 60-27003, a microcapsule layer is formed by adhering a microcapsule containing oil and magnetic flakes to a surface of a transparent substrate with a coloring material to form a microcapsule layer. When the is parallel to the surface of the transparent substrate, it reflects the visible incident light to display the color of the coloring material, and when the magnetic flakes are perpendicular to the surface of the transparent substrate, the visible incident light is reflected. A display article that displays the color of a magnetic sheet without reflection is disclosed. However, in this display article, high contrast cannot be obtained because the reflected light from the coloring material exists even when the magnetic flakes are perpendicular to the substrate surface.

JP-A-4-36997 discloses that white fine powder (alumina) is used on the surface of magnetic flakes without using a coloring material, as a solution to the drawbacks of the display article of JP-B-60-27003. It has been proposed to adopt an adsorbed structure, which is said to have the effect of improving the contrast and aesthetics of the visible display and simplifying the manufacturing process. However, in this proposal, since the white fine powder is mechanically adsorbed by the bead mill, the temporal stability tends to be insufficient due to the white fine powder falling off. Also, the displayable color is limited to white.

[0008]

SUMMARY OF THE INVENTION The present invention has been made under these circumstances, and the time required for writing and erasing is short, the contrast of the image is high, the stability thereof is good, and the color of the image is improved. An object is to provide a rewritable display medium that can be selected from a wide range.

[0009]

These objects are achieved by the present invention described in (1) to (8) below. (1) A microcapsule layer is provided on the surface side of the substrate, the microcapsule layer contains a microcapsule and a binder, and the flaky magnetic powder is dispersed in a liquid in the microcapsule. The rewritable type display characterized in that the orientation of the flaky magnetic powder can be changed by an applied magnetic field, and that the surface of the flaky magnetic powder is formed with a silicon dioxide film containing an organic colorant. Medium. (2) The rewritable display medium according to (1), wherein a polymer liquid crystal layer is provided on the surface side of the microcapsule layer, and the polymer liquid crystal layer contains a polymer liquid crystal exhibiting selective reflection. (3) The rewritable display medium according to (2), in which the microcapsule layer and the polymer liquid crystal layer are separated by a barrier layer. (4) The rewritable display medium according to the above (2) or (3), wherein the polymer liquid crystal exhibiting the selective reflection is a side chain polymer cholesteric liquid crystal of a copolymer of a cholesteric monomer and a nematic monomer. (5) The side chain type polymer cholesteric liquid crystal has the following chemical formula 3.
The rewritable display medium of the above (4) represented by:

[0010]

[Chemical 3]

[In Chemical Formula 3, R ₁ represents a cholesterol group represented by Chemical Formula 4, and R ₂ represents a biphenyl group, a cyanophenyl group or a methoxyphenyl group.

[0012]

[Chemical 4]

A and d each represent an integer of 2 to 4, b and e each represent 0 or 1, and c
And f each represent 1. x is 0.1 to 0.7
And n is 2.5-10. (6) The rewritable display medium according to any one of (1) to (5), which has a magnetic layer between the substrate and the microcapsule layer. (7) The above (1) to (5), wherein the substrate has magnetism
One of the rewritable display media. (8) The rewritable display medium according to any one of the above (1) to (7), wherein a protective layer is provided as the uppermost layer on the front surface side.

[0014]

FUNCTION AND EFFECT FIG. 1 is a schematic cross-sectional view of a constitutional example of the rewritable display medium of the present invention. FIG. 1 (a) shows
Magnetic field H applied from the magnetic layer 3 to the microcapsules 41
Indicates that the direction of is almost parallel to the main surface of the medium, (b)
Indicates that the direction of the magnetic field H applied from the magnetic layer 3 to the microcapsules 41 is substantially perpendicular to the medium main surface. The microcapsules 41 contained in the microcapsule layer 4 contain scale-like magnetic powder 411 dispersed in a liquid 412. Due to the magnetic anisotropy caused by the flat shape, the flaky magnetic powder 411 is oriented so that the main surface is substantially parallel to the direction of the magnetic field H. On the surface of the flaky magnetic powder 411,
A silicon dioxide coating containing an organic colorant has been formed.

Light I incident on the medium in the state (a)
Most of ₀ is reflected by the main surface of the flaky magnetic powder 411.
Since this reflected light I _C returns to the medium surface side, the color of the silicon dioxide film containing the organic colorant is observed from the medium surface side.

Light I incident on the medium in the state of (b)
₀ reflects on the main surface of the flaky magnetic powder 411, but since the main surface of the flaky magnetic powder 411 is perpendicular to the medium surface, the reflected light I _C does not return to the medium surface side and is directed to the magnetic layer 3. Proceed to.
If the light absorption rate below the microcapsule layer 4 is high,
Since light does not substantially return to the medium surface side, black is observed from the medium surface side.

In the display medium of the present invention, the unrecorded area is normally in the state of (a), and the scale-like magnetic powder 411 in the area corresponding to the image (including characters) pattern to be displayed is in this unrecorded area. If the orientation is changed to the state of (b), a black visible image is displayed in the background having the color tone of the organic colorant.

The rewritable display medium shown in FIG.
It has the same structure as the medium shown in FIG. 1 except that it does not have the magnetic layer 3. In the configuration shown in FIG. 2, instead of the magnetic field from the magnetic layer 3, a magnetic field from the outside is applied to the microcapsule 4
1 to change the orientation of the flat magnetic powder 411 from (a) to (b) or from (b) to (a).

The rewritable display medium shown in FIGS. 3 and 4, respectively, is the rewritable display medium shown in FIGS. 1 and 2 in which the polymer liquid crystal layer 5 is provided on the microcapsule layer 4. is there. The polymer liquid crystal layer 5 contains a polymer liquid crystal exhibiting selective reflection.

Part of the light I ₀ incident on the medium in the state (a) of FIG. 3 and FIG. 4 is reflected by the polymer liquid crystal layer 5, and is selectively reflected light I _S to the medium surface side. Return. On the other hand, most of the light transmitted through the polymer liquid crystal layer 5 and incident on the microcapsule layer 4 is reflected by the main surface of the flaky magnetic powder 411, and the reflected light I _C returns to the medium surface side. Therefore, in addition to the light I _C reflected by the silicon dioxide film containing the organic colorant, the selective reflection light I _S reflected by the polymer liquid crystal layer 5 returns to the medium surface side.

In the state (b) of FIG. 3 and FIG. 4, the microcapsule layer 4 is transmitted through the polymer liquid crystal layer 5.
The light incident on is reflected on the main surface of the flaky magnetic powder 411, but since the main surface of the flaky magnetic powder 411 is perpendicular to the medium surface, the reflected light I _C does not return to the medium surface side and is magnetic. Go in the direction of layer 3. If the light absorption rate below the microcapsule layer 4 is high, substantially only the selectively reflected light I _S returns to the medium surface side.

In the media shown in FIGS. 3 and 4, respectively, the reflected light I of a silicon dioxide coating containing an organic colorant is shown.
A visible image of the color tone of the selective reflection light (bright cholesteric color) is displayed with the color tone of the combined light of _C and the selective reflection light I _S of the polymer liquid crystal as the background.

In the present invention, the image pattern can be written and erased only by changing the direction of the magnetic field applied to the microcapsules, so that rapid writing and erasing can be performed unlike thermal recording. Further, since the flaky magnetic powder itself is colored, high contrast display is possible. Furthermore, since the organic colorant is used, the display color of the image can be selected from a wide range. Further, since the organic colorant is fixed in the silicon dioxide film, there is little change in color over time, and stable display is possible for a long period of time.

[0024]

Specific Structure The specific structure of the present invention will be described in detail below.

An example of the structure of the rewritable display medium of the present invention is shown in FIGS. The rewritable display medium shown in FIG. 1 has a magnetic layer 3 and a microcapsule layer 4 on a substrate 2 in this order. The rewritable display medium shown in FIG. 2 has the same configuration as that of FIG. 1 except that the magnetic layer 3 is not provided. The rewritable display medium shown in FIG.
The polymer liquid crystal layer 5 is formed on the microcapsule layer 4 of the medium of FIG.
The rewritable display medium shown in FIG. 4 has the polymer liquid crystal layer 5 provided on the microcapsule layer 4 of the medium shown in FIG.

<Substrate 2> The material, shape and dimensions of the substrate 2 are
It may be appropriately determined according to the field to which the present invention is applied, such as a magnetic card. For example, when applied to a magnetic card,
The thickness of the substrate is usually 50 to 500 μm, preferably 10
It is about 0 to 300 μm.

In order to obtain a high-contrast display image in the structure shown in FIGS. 2 and 4 in which the magnetic layer 3 is not provided, it is preferable to use a substrate having a low light reflectance and a high light absorption rate. Examples of such a substrate include paper and a plastic film provided with a light absorption layer on the surface thereof, or a plastic film having a high light absorption rate. The light absorption layer may be a resin layer containing a pigment having a high light absorption rate such as carbon black. Examples of the plastic film having a high light absorption rate include a polyethylene terephthalate (PET) film in which carbon black is kneaded.

<Magnetic Layer 3> The magnetic layer 3 is for applying a magnetic field to the microcapsules 41, but when the present invention is applied to a magnetic card, ordinary magnetic recording, that is, visible display is not performed. It can also be used to record information.

The magnetic layer 3 may be a coating type magnetic layer in which magnetic powders are bound with a binder, or a continuous thin film type magnetic layer formed by sputtering or vapor deposition. Further, the magnetic material used for the magnetic layer is not particularly limited. However, in order to obtain a high-contrast display image, a magnetic layer having a low light reflectance and a high light absorptivity is preferable, so that a coating type magnetic layer using a dark iron oxide magnetic powder may be used. It is preferable to add carbon black.

By using a plate-shaped or film-shaped magnetic material as the substrate, the magnetic layer 3 as shown in the drawing can be omitted. Examples of the plate-shaped or film-shaped magnetic material include those obtained by binding magnetic powder with a binder such as resin or rubber.

<Microcapsule Layer 4> In the microcapsule layer 4, the microcapsules 41 are dispersed in the binder 42, and the scale-like magnetic powder 411 is enclosed in the microcapsules 41 together with the liquid 412.

The scale-like magnetic powder 411 is made of, for example, Fe, Ni, a Fe-Ni alloy, or a Fe-Ni alloy.
-Cr alloy, Al-Co alloy, Fe-Al-Si alloy,
Flat powder such as Sm-Co alloy is suitable. The average diameter of the main surface of the flaky magnetic powder 411 is preferably 1 μm or more. If the average diameter is too small with respect to the wavelength of visible light, the reflectance becomes low and the reflectance change due to the orientation change becomes small, so that the contrast of display information becomes low. The specific value of the average diameter of the main surface, the diameter of the microcapsules, depending on the number of magnetic powder contained in the microcapsules, it is appropriately determined within the range where the orientation can be changed in the microcapsules, usually, The thickness is preferably 5 to 15 μm.

A silicon dioxide film containing an organic colorant is formed on the surface of the flaky magnetic powder 411. The method for forming the silicon dioxide film is not particularly limited, but for example, the method described in “Industrial materials, 38 , 69 (1990)” can be used.

In this method, first, an aqueous solution of hydrosilicofluoric acid (H ₂ SiF ₆ ) in which silicon dioxide is dissolved in saturation is prepared. When boric acid (H ₃ BO ₃ ) is added to this aqueous solution, the following changes in the equilibrium state occur in the solution.

[0035]

[Chemical 5]

That is, as shown in equation (2), H ₃
The addition of BO ₃ causes a decrease in the HF concentration in the solution, changing the equilibrium reaction of equation (1) to the SiO ₂ precipitation side. It is considered that the precipitated SiO ₂ exists as a hydrate (silicic acid sol) in the solution, and the film is formed in the solution or through the gelation process on the substrate (scaly magnetic powder in the present invention). And so on. In addition, since SiO ₂ is precipitated when the HF concentration in the solution is reduced to change the equilibrium state in the above formula (1), an ammonia solution or a metal halide may be used in addition to boric acid. Alternatively, a method of raising the temperature of the solution to move the equilibrium of the formula (1) to the right side may be used.

In order to fix the organic colorant in the silicon dioxide film using this method, the organic colorant may be added before or at the same time as the addition of the flaky magnetic powder. When the organic colorant is not water-soluble, the organic colorant may be dissolved in an amphipathic solvent such as alcohol and added.

The organic colorant used in the present invention is not particularly limited, and those which can be fixed in the silicon dioxide film and have a desired color tone may be appropriately selected. Examples of such an organic colorant include rhodamine 6
G, rhodamine B, malachite green, fluorescein, crystal violet, acridine red, Victoria blue, basic yellow and the like.

When the flaky magnetic powder is brought into contact with the supersaturated solution containing the organic colorant, a silicon dioxide film containing the organic colorant is formed on the surface of the flaky magnetic powder. The contact between the solution and the magnetic powder may be carried out by adding the flaky magnetic powder into the solution and stirring. In order to enhance the adhesiveness of the silicon dioxide coating, the surface of the flaky magnetic powder may be pretreated with a silane coupling agent or the like. After the silicon dioxide film is formed, it is washed with water and dried.

Although the thickness of the silicon dioxide coating is not particularly limited, it is usually preferably about 0.2 to 1.0 μm. If the coating is too thin, the amount of the organic coloring agent taken in will be small, and as a result, the degree of coloring of the flaky magnetic powder will be low. If the coating is too thick, the flatness of the flat magnetic powder will be low, and the volume of the magnetic powder will increase, reducing the number of magnetic powders contained in the microcapsules, resulting in insufficient color change. Tends to become.

The microcapsules 41 are composed of the scale-like magnetic powder 4
The average diameter is preferably 20 μm or more because it is necessary to have a diameter that allows the orientation change of No. 11. Further, if the microcapsules are too large, the surface roughness of the microcapsule layer becomes large and the recorded image becomes uneven,
Further, since the resolution also deteriorates, it is usually preferable to set it to 200 μm or less.

The liquid 412 may be any liquid that can stably disperse and retain the flaky magnetic powder 411 in the microcapsules 41. For example, liquid paraffin or the like can be preferably used, but the composition and the like are not particularly limited. . When the magnetic layer 3 is provided, the magnetic field is always applied to the flaky magnetic powder 411, so that the orientation is stable. However, when the magnetic layer 3 is not provided, the orientation magnetic field is applied only during recording. Since the applied voltage is easily affected by a disturbance magnetic field from the outside, it is preferable to use a liquid 412 having a high viscosity to improve the stability of orientation. The microcapsules may contain a dispersant for preventing agglomeration of the flaky magnetic powder.

The binder 42 is not particularly limited in its composition and the like as long as it can stably disperse and bond the microcapsules 41 made of gelatin or the like and has good adhesiveness to the substrate and is transparent. For example, polyvinyl alcohol can be preferably used.

The thickness of the microcapsule layer 4 needs to be larger than the average diameter of the microcapsules 41, and the specific thickness may be appropriately determined so that an image can be displayed with high contrast. In the illustrated example, only one microcapsule 41 is arranged in the thickness direction of the microcapsule layer 4, but in order to obtain a high-contrast image, a plurality of microcapsules are arranged in the thickness direction of the layer or It is preferable to have a structure in which they are overlapped. Normally,
The thickness of the microcapsule layer 4 is preferably about 20 to 200 μm.

The method of forming the microcapsule layer 4 is not particularly limited, and it can be formed, for example, by the method disclosed in Japanese Patent Application Laid-Open Nos. 3-273521 and 4-3699597. Any method may be used as long as a fine microcapsule layer can be formed.

<Polymer Liquid Crystal Layer 5> The polymer liquid crystal layer 5 includes
A polymer liquid crystal exhibiting selective reflection is contained. As such a polymer liquid crystal, a side chain polymer cholesteric liquid crystal is preferable, and a copolymer of a nematic monomer and a cholesteric monomer is particularly preferable. However, other than this, any polymer liquid crystal exhibiting selective reflection, such as various polymer liquid crystals described as polymer liquid crystal having selective reflection in JP-A-4-174415, can be used.

The selective reflection wavelength is usually 400 to 700 nm.
It preferably exists in a visible light region of a certain degree, and in this case, it can be visually recognized by humans. However, in the case of mechanical reading, the selective reflection wavelength may exist in the ultraviolet region or the infrared region.

The polymer cholesteric liquid crystal exhibits a cholesteric liquid crystal phase at a temperature not lower than the glass transition temperature (Tg) and lower than the isotropic phase transition temperature (Tc), and at this time, it exhibits selective reflection. Then, by cooling the liquid crystal exhibiting the cholesteric alignment liquid crystal phase below Tg, the cholesteric alignment liquid crystal state can be fixed.

The glass transition temperature (Tg) of the side chain type polymer cholesteric liquid crystal is preferably 40 ° C. or higher in order to enhance the stability at room temperature. Although there is no particular upper limit to Tg, Tg is usually about 100 ° C. or lower. There is no particular limitation on the isotropic phase transition temperature (Tc),
Preferably 160 ° C or higher, more preferably 180 ° C to 2
It is 00 ° C.

As the side chain type polymer cholesteric liquid crystal, for example, the one represented by the above chemical formula 3 can be used.

In Chemical Formula 3, R ₁ represents the cholesterol group of Chemical Formula 4, and R ₂ represents a biphenyl group, a cyanophenyl group or a methoxyphenyl group. The substitution position of the phenyl group in the biphenyl group represented by R ₂ is not particularly limited, but preferably 4-biphenyl group and the like can be mentioned. Further, biphenyl groups having different phenyl group substitution positions may be mixed. Also, when R ₂ is a cyanophenyl group, the substitution position of the cyano group is not particularly limited, but preferably 4-cyanophenyl group and the like can be mentioned, and cyanophenyl groups having different substitution positions of the cyano group May be mixed. Further, when R ₂ is a methoxyphenyl group, the substitution position of the methoxy group is not particularly limited, but preferably 4-methoxyphenyl group and the like can be mentioned. May be mixed.

In the chemical formula 3, a and d are respectively 2
It represents an integer of 4 and particularly preferably 3. a
Usually, it is preferable that d and d are the same, but in some cases, they may be different. Also, b and d are
Each represents 0 or 1, and c and f each represent 1. x is 0.1 to 0.7. n represents an average degree of polymerization and is preferably 2.5 to 10, and more preferably 3 to 7.

Table 1 shows specific examples of the polymer cholesteric liquid crystal of Chemical formula 3. In Table 1, R ₁ , R ₂ , and
Specific examples are shown by combinations of a, d, b, e, c, f, x and n.

[0054]

[Table 1]

The polymer cholesteric liquid crystal of Chemical formula 3 is a known compound, and its synthesis method is FHKreuzer, et al., Mo.
l. Electron., 3, 1 , 9 (1987), FHKreuzer, et al.,
Mol.Cryst.Liq.Cryst., 199 , 345 (1991).

The thickness of the polymer liquid crystal layer is preferably 0.5.
It may be appropriately selected from the range of 10 to 10 μm, more preferably 1 to 5 μm. If the polymer liquid crystal layer is too thin, the reflectance of the wavelength at which maximum reflection is obtained will be low, and the contrast of the displayed image will be reduced. To do.

The polymer liquid crystal layer is preferably composed only of polymer liquid crystals exhibiting selective reflection, but may contain a binder resin. Examples of the binder resin include polyvinyl chloride, polyvinyl acetate, epoxy resin, phenoxy resin, acrylic resin, polyurethane,
Examples include polyester.

The polymer liquid crystal layer may be formed by using a coating liquid of polymer cholesteric liquid crystal (also referred to as "paint") by a coating method such as a bar coating method, a gravure coating method, a roll coating method or an air knife coating method. Good. The coating liquid is prepared by containing a polymer cholesteric liquid crystal in an organic solvent [for example, toluene, tetrahydrofuran (THF), isophorone or a mixed solvent thereof]. The content of the polymer cholesteric liquid crystal is set to about 10 to 80 wt%.

After coating, it is dried. Usually Tg or more and T
When dried by heating at a temperature lower than c, a cholesteric color corresponding to the selective reflection wavelength is exhibited, and the cholesteric color is maintained even after cooling. Since the selective reflection wavelength also depends on the holding temperature during heat treatment, the color tone can be controlled by appropriately setting the holding temperature during drying. Further, it is possible to change the color tone by further performing a heat treatment at a holding temperature different from that during heating and drying.

Some liquid crystals do not exhibit cholesteric alignment only by such heating, but in that case, Tg
Using a heat roller set to a temperature above and below Tc,
It is also possible to cause the color to be changed by the displacement force.

<Barrier Layer> In the case where the adhesion between the microcapsule layer 4 and the polymer liquid crystal layer 5 is poor, between them,
It is preferable to provide a barrier layer for separating these.

The thickness of the barrier layer is preferably 0.5 to 10 μm. If the barrier layer is too thin, the effect is insufficient, and if it is too thick, the displayed image becomes unclear.

The material of the barrier layer is not particularly limited as long as it does not impair the functions of the microcapsule layer and the polymer liquid crystal layer, but is preferably one that is immiscible with the polymer liquid crystal of the polymer liquid crystal layer. Specifically, water-soluble resins are preferable, and examples thereof include polyvinyl alcohol, polyvinyl chloride, polyvinyl acetate, polyvinyl butyral, epoxy resin, phenoxy resin, acrylic resin, polyurethane and polyester.

The barrier layer may be formed according to the polymer liquid crystal layer using a coating liquid containing a predetermined resin.

<Protective Layer> It is preferable to provide a protective layer on the microcapsule layer 4 in the examples of FIGS. 1 and 2, and on the polymer liquid crystal layer 5 in the examples of FIGS. 3 and 4. The durability of the medium is improved by providing the protective layer as the uppermost layer on the medium surface side. The material of the protective layer is not particularly limited as long as it does not adversely affect the contacting microcapsule layer or the polymer liquid crystal layer, and may be appropriately selected from thermoplastic resin, thermosetting resin, ultraviolet curable resin, and the like. Good. Specifically, it is possible to use polyvinyl chloride, polyvinyl acetate, polyvinyl butyral, polystyrene, polyurethane, polyvinyl alcohol, cellulose or the like alone or a copolymer thereof.

The thickness of the protective layer is usually 0.5 to 30 μm.
, Preferably 1 to 10 μm.

The protective layer may be formed according to the polymer liquid crystal layer by using a coating liquid containing a predetermined resin.

In addition to these layers, the rewritable display medium of the present invention may optionally include a magnetic recording layer other than the above magnetic layer, a reversible or irreversible thermosensitive recording layer, a fixed information recording layer, and the like. It may be provided.

<Recording / Deletion of Display Information> In the present invention, the unrecorded area (background area) is usually in the state of (a) in FIGS. 1 to 4, and the recording area (image display area) is shown in FIGS. Four
It is preferable to perform recording so that each state (b) is achieved.

A method of recording an image to be displayed, that is, (a)
The method of changing from the state of (b) to the state of (b) and the method of deleting the displayed image, that is, the method of changing from the state of (b) to the state of (a) are not particularly limited. Can be used.

In FIGS. 1 and 3 having the magnetic layer 3, the magnetic layer 3 is magnetized so as to generate a magnetic field perpendicular to the main surface of the medium, so that the flaky magnetic powder 411 is oriented perpendicular to the main surface of the medium. , Images can be recorded. Alternatively, the magnetic layer 3 may be magnetized in the in-plane direction by transfer or the like, and the flaky magnetic powder 411 may be oriented by a substantially perpendicular magnetic field leaking from the magnetization reversal portion to the microcapsule layer 4 to record an image. In this case, the magnetization reversal interval may be appropriately set according to the image pattern and the like. And the magnetic layer 3
By applying a DC magnetic field in the in-plane direction to DC-magnetize the magnetic layer 3, the flaky magnetic powder 411 can be oriented parallel to the medium and the displayed image can be erased.

2 and 4 in which the magnetic layer 3 is not provided,
A magnetic field is applied to the microcapsule layer 4 while scanning the medium with a magnetic head for in-plane recording. At this time, the magnetic head is energized in the area where the image is recorded and is not energized in the background area. In this method, a DC magnetic field or an AC magnetic field may be applied in the area where an image is recorded.
Then, by applying a DC magnetic field in the in-plane direction of the microcapsule layer 4, the displayed image can be erased.

[0073]

EXAMPLES The present invention will be specifically described below with reference to examples.

<Example 1> A display medium having a magnetic layer, a microcapsule layer and a protective layer in this order on a substrate was prepared.
It was produced as shown below.

A polyethylene terephthalate film having a substrate thickness of 188 μm was used.

Magnetic layer Magnetic powder (barium ferrite powder 1 with coercive force of 1000 Oe
00 parts by weight), a dispersant (3 parts by weight of oleic acid), a binder resin (15 parts by weight of vinyl chloride and vinyl chloride resin and a urethane resin 15).
Parts by weight) and a solvent (100 parts by weight of methyl ethyl ketone and 100 parts by weight of toluene), and a magnetic coating material prepared by kneading was used to form a film having a thickness of 10 μm by gravure coating.

Microcapsule layer 2 mol / l hydrosilicofluoric acid (H ₂ SiF ₆ ) aqueous solution 1
30 g of silica gel was added to 1 liter and reacted at 35 ° C. for 5 hours to prepare an aqueous solution of hydrosilicofluoric acid in which silicon dioxide was dissolved in saturation. The supernatant of this aqueous solution 500
An aqueous solution of 250 ml in which 0.05 g of an organic colorant (Rhodamine 6G) was dissolved in 1.5 ml of boric acid (H ₃ BO ₃ )
5g and scale-like magnetic powder (Fe- with an average diameter of the main surface of 10 μm-
Ni alloy) 0.5 g was added, and the mixture was stirred at 35 ° C. for 2 hours to deposit a silicon dioxide film containing an organic coloring agent on the surface of the flaky magnetic powder to obtain a colored powder. The colored powder was washed with water and dried. The thickness of the silicon dioxide film is about 0.5 μm
Met.

Next, using the complex coacervation method,
A microcapsule dispersion was prepared by the procedure shown in FIG.
The microcapsules had an average diameter of 50 μm, and coloring powder was dispersed in liquid paraffin inside the microcapsules.

This microcapsule dispersion was applied onto the magnetic layer and dried to form a microcapsule layer. The thickness after drying was 100 μm.

Protective Layer A 20 wt% aqueous solution of an aqueous urethane resin was applied onto the microcapsule layer and dried to form a protective layer. The thickness after drying was 2 μm.

A direct-current magnetic field was applied in the in-plane direction of the magnetic layer of the display medium manufactured as described above to apply a magnetic field almost parallel to the main surface of the medium to the microcapsule layer, and observation from the protective layer side was performed. It was magenta. Next, a magnetization reversal pattern was recorded in the in-plane direction of the magnetic layer, a magnetic field almost perpendicular to the main surface of the medium was applied to the microcapsule layer, and when observed from the protective layer side, it was black.

When a medium having the structure shown in FIG. 2 was produced according to the above method and an image was recorded by a magnetic head, it was confirmed that a black image could be displayed on a magenta background.

Example 2 A display medium having a magnetic layer, a microcapsule layer, a barrier layer, a polymer liquid crystal layer and a protective layer on a substrate in this order was prepared. The magnetic layer, the microcapsule layer and the protective layer were formed in the same manner as in Example 1. The barrier layer and the polymer liquid crystal layer were formed as follows.

Barrier Layer A 25 wt% aqueous solution of an aqueous urethane resin was applied onto the microcapsule layer and dried to form a barrier layer. The thickness after drying was 3 μm.

Polymer liquid crystal layer Polymer liquid crystal No. 4 shown in Table 1 (Tg = 47 ° C., Tc = 1
96 ° C.) 1 part by weight of the polymer liquid crystal layer coating solution prepared by dissolving 2 parts by weight of toluene is applied on the barrier layer and dried,
The polymer liquid crystal layer was used. Drying was performed at 150 ° C. for 2 minutes. The thickness after drying was 2 μm.

A direct current magnetic field was applied in the in-plane direction of the magnetic layer of the display medium manufactured as described above to apply a magnetic field almost parallel to the main surface of the medium to the microcapsule layer, and when observed from the protective layer side, It was magenta. Next, a magnetization reversal pattern was recorded in the in-plane direction of the magnetic layer, a magnetic field almost perpendicular to the main surface of the medium was applied to the microcapsule layer, and when observed from the protective layer side, it showed blue.

When a medium having the structure shown in FIG. 4 was produced according to the above method and an image was recorded by a magnetic head, it was confirmed that a blue image could be displayed on a magenta background.

When the colored powder used in the above examples was stored in water, no elution of the organic coloring agent was observed despite being water-soluble. From this result, it was confirmed that the organic colorant was firmly fixed in the silicon dioxide film.

The effects of the present invention are apparent from the above examples.

[Brief description of drawings]

1A and 1B are schematic cross-sectional views of a constitutional example of a rewritable display medium of the present invention, in which the direction of a magnetic field H applied to a microcapsule 41 and the scale-like magnetic powder 41 are shown.
The relationship with the orientation of 1 is shown.

2A and 2B are schematic cross-sectional views of a configuration example of the rewritable display medium of the present invention, in which the direction of the magnetic field H applied to the microcapsules 41 and the scale-like magnetic powder 41 are shown.
The relationship with the orientation of 1 is shown.

3A and 3B are schematic cross-sectional views of a configuration example of a rewritable display medium of the present invention, in which the direction of a magnetic field H applied to a microcapsule 41 and the flaky magnetic powder 41 are shown.
The relationship with the orientation of 1 is shown.

4A and 4B are schematic cross-sectional views of a configuration example of the rewritable display medium of the present invention, in which the direction of the magnetic field H applied to the microcapsules 41 and the scale-like magnetic powder 41 are shown.
The relationship with the orientation of 1 is shown.

FIG. 5 is a flowchart showing a method for preparing a microcapsule dispersion liquid.

[Explanation of symbols]

2 Substrate 3 Magnetic Layer 4 Microcapsule Layer 41 Microcapsule 411 Scale-like Magnetic Powder 412 Liquid 42 Binder 5 Polymer Liquid Crystal Layer I ₀ Incident Light I _C Light Reflected by Silicon Dioxide Film Containing Organic Colorant I _S Polymer Light reflected by the liquid crystal layer (selective reflected light)

Claims (8)

[Claims] 1. A microcapsule layer is provided on the surface side of a substrate, the microcapsule layer contains a microcapsule and a binder, and flaky magnetic powder is dispersed in a liquid in the microcapsule. The orientation of the scale-like magnetic powder can be changed by the magnetic field applied to the capsule, and the surface of the scale-like magnetic powder has a silicon dioxide coating containing an organic colorant, which is rewritable. Type display medium. 2. The rewritable display medium according to claim 1, wherein a polymer liquid crystal layer is provided on the surface side of the microcapsule layer, and the polymer liquid crystal layer contains a polymer liquid crystal exhibiting selective reflection. 3. The rewritable display medium according to claim 2, wherein the microcapsule layer and the polymer liquid crystal layer are separated by a barrier layer. 4. The rewritable display medium according to claim 2, wherein the polymer liquid crystal exhibiting the selective reflection is a side chain polymer cholesteric liquid crystal of a copolymer of a cholesteric monomer and a nematic monomer. 5. The rewritable display medium according to claim 4, wherein the side chain type polymer cholesteric liquid crystal is represented by the following chemical formula 1. [Chemical 1] [In Chemical Formula 1, R ₁ represents a cholesterol group represented by Chemical Formula 2, and R ₂ represents a biphenyl group, a cyanophenyl group or a methoxyphenyl group. [Chemical 2] a and d each represent an integer of 2 to 4, b and e each represent 0 or 1, and c and f each represent
Each represents 1. x is 0.1 to 0.7 and n is 2.5 to 10. ] 6. The rewritable display medium according to claim 1, further comprising a magnetic layer between the substrate and the microcapsule layer. 7. The rewritable display medium according to claim 1, wherein the substrate has magnetism. 8. The rewritable display medium according to claim 1, wherein a protective layer is provided as the uppermost layer on the front surface side.