JPH11277914A - Reversible thermal recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a reversible thermal recording medium by which full color displaying can be performed at a high speed and written informations can be easily erased. SOLUTION: This recording medium consists of a sheet-like base layer 2, an intermediate layer 3, a reversible heat-sensitive recording layer 4 and a protective layer 5. The recording layer 4 has a low mol.wt. cholesteric liq. crystal compd. which exhibits cholesteric phase at a higher temp. than room temp. and reflects a light in a wave region corresponding to the temp. and is solidified under the reflecting condition by quenching from the temp. and exhibits scattering condition by cooling slowly from the temp. or at least the temp. as a main ingredient.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reversible thermosensitive recording medium, and more particularly, to a two-dimensional recording medium on which information can be written and erased under a specific heating condition.

[0002]

2. Description of the Related Art Heretofore, as reversible thermosensitive recording materials, leuco dyes / color-reducing agents, organic low molecular weight / polymer resin matrices, and polymer cholesteric liquid crystals have been known.

[0003] Leuco dyes / decolorizers develop color by opening a lactone ring contained in leuco dye molecules, and decolor by closing the ring. The lactone ring opens by rapid cooling after the temperature rise, and closes by slow cooling. Such a leuco dye / developing colorant is applied on a sheet material, and information is written using a thermal head, and erased by passing between heat rollers.

As the organic low molecular weight / polymer resin matrix, those using BA (behenic acid) as the organic low molecular weight compound and PVCA (vinyl chloride-vinyl acetate copolymer) as the high molecular weight compound are known. . This material can be switched between transparent and scattering depending on the heating temperature, and that state is maintained after cooling. Information is written on this material using a thermal head.

[0005] A polymer cholesteric liquid crystal has been known in which a vinyl compound having a cholesteric liquid crystal compound in a side chain is polymerized. This material can be heated to a temperature higher than the crystallization temperature and then rapidly cooled from a certain temperature to change the display color.

[0006]

With the above-mentioned leuco dye / color reducing agent, the color that can be displayed is determined by the leuco dye, and a full-color display of an arbitrary image cannot be made. In the case of an organic low molecular weight / polymer resin matrix, display is performed by transmission / scattering, so that full-color display cannot be performed. In the polymer cholesteric liquid crystal, in principle, the display color can be changed according to the heating temperature, but the color change requires a time on the order of minutes, which has been a major obstacle to practical use. As described above, at present, a reversible thermosensitive recording medium capable of writing and erasing a full-color image at a speed that can withstand practical use has not yet been obtained.

An object of the present invention is to provide a novel reversible thermosensitive recording medium capable of performing full-color display at a high speed and easily erasing written information.

[0008]

In order to achieve the above objects, the reversible thermosensitive recording medium according to the present invention comprises a sheet-like base layer and a recording layer, and the recording layer is cholesteric at a temperature higher than room temperature. A low-molecular-weight cholesteric that reflects a phase and reflects light in a wavelength range according to temperature, solidifies in a reflective state by rapidly cooling from that temperature, and gradually diffuses from that temperature or higher to show a scattering state. Contains liquid crystal compounds.

In the present invention, a sheet-like base layer is used, and a low-molecular-weight cholesteric liquid crystal compound is used as a reversible thermosensitive recording material used for a recording layer. By quenching, it is possible to display a desired color at high speed,
Full color display can be performed. The recording material becomes transparent when rapidly cooled from a state of reflecting light outside the visible wavelength range such as an infrared region or an ultraviolet region or an isotropic phase state. Further, by heating to an isotropic phase state or a cholesteric selective reflection state and gradually cooling the liquid crystal compound, the liquid crystal compound enters a light scattering state, and information already written is erased.

Furthermore, in the present invention, an intermediate layer having a smooth surface in contact with the recording layer may be provided between the base layer and the recording layer. In order to direct the helical axis in a direction perpendicular to the base layer when the liquid crystal exhibits a cholesteric phase, the surface of the base layer is preferably substantially flat. By interposing the intermediate layer, a material having a rough surface such as plain paper can be used as the base layer. In addition, the direction of the helical axis of the liquid crystal is well aligned in the direction perpendicular to the base layer, and a display with high reflectance can be performed. Furthermore, if the function of absorbing visible light is imparted to the intermediate layer, there is no restriction on the color, reflectance, etc. of the surface of the base layer, so that the range of available base layers can be widened. Also, if the function of reflecting light of a specific wavelength is imparted to the intermediate layer, a display in which the reflected light from the intermediate layer is a display color, or the reflected light from the intermediate layer and the reflected light from the recording layer are superimposed. Display can be performed. Even if the function of totally reflecting incident light is given to the intermediate layer, if the recording medium is tilted so that the reflected light of light incident from a specific light source does not directly enter the eyes, color display with a white background Can be confirmed. If the function of absorbing infrared rays is given to the intermediate layer, it is effective for writing with a laser printer.

Further, in the present invention, the recording layer may include a spacer. The thickness of the recording layer can be made uniform, and the thickness of the recording layer can be kept constant when display information is erased with a heat roller. Further, in the present invention, a protective layer may be provided on the recording layer. With this protective layer, the recording layer is mechanically or chemically protected from the outside.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a reversible thermosensitive recording medium according to the present invention will be described with reference to the accompanying drawings. In each of the embodiments described below, specific substance names are described. However, this is only one example, and the present invention is not limited to these substances. It is possible to use the following materials.

(First Embodiment, see FIG. 1) In FIG. 1, a reversible thermosensitive recording medium 1 comprises a base layer 2, an intermediate layer 3, a recording layer 4, and a protective layer 5 from below. The base layer 2 is made of paper or a flexible sheet material such as polycarbonate and PET (polyethylene terephthalate). By using a flexible sheet material, paper-like handling, such as bending or binding a plurality of sheets, becomes possible. The intermediate layer 3 includes a component having a function of absorbing visible light, and a surface in contact with the recording layer 4 is formed smoothly.

When the intermediate layer 3 is colored and translucent, the base layer 2 may become light-absorbing or light-absorbing in combination with the intermediate layer 3 in order to reproduce a good full-color image. desirable. It is also possible to use a transparent material as the intermediate layer 3, but in that case, the base layer 2
It is desirable that the material has a light absorbing property.

The recording layer 4 contains an organic low-molecular cholesteric liquid crystal compound. This liquid crystalline compound exhibits a cholesteric phase at a temperature higher than room temperature, reflects light in a wavelength range corresponding to the temperature, and is rapidly cooled from that temperature to be solidified in a reflection state. Further, this liquid crystalline compound shows an isotropic phase when heated to a temperature higher than that, but shows a scattering state when gradually cooled from a temperature showing a cholesteric phase or a temperature showing an isotropic phase. As such a low-molecular-weight cholesteric liquid crystal compound, dicholesteryl 10,12-docosadiindionate represented by the following chemical structural formula (A) is most suitable. Regarding the thickness of the recording layer 4, 3 to 50 μm
m is preferable, and more preferably, 6 to 20 μm.

[0016]

Embedded image

In the recording medium 1 having the recording layer 4 containing the liquid crystal compound represented by the chemical structural formula (A) as in Experimental Example 1 described below, when heated to 87 to 115 ° C., the cholesteric liquid crystal compound has a helical axis. Indicates a cholesteric phase oriented in a direction perpendicular to the intermediate layer 3, and reflects light having a specific wavelength according to the temperature. It shows a red color at about 87 ° C., a green color at about 95 ° C., and a blue color at about 115 ° C., and solidifies in its reflection state by quenching from those temperatures.

When heated to a temperature of about 119 ° C. or more, the phase changes to an isotropic phase, rapidly cools to a transparent state, and gradually cools to a scattering state and becomes cloudy. That is, when the recording medium 1 is heated to 119 ° C. or more by a heat roller or the like and then gradually cooled, the entire recording layer 4 is in a scattering state. At this time, a white display is provided to the observer viewing from the direction of arrow A.

When the recording medium 1 is partially heated and quenched using a thermal head that generates heat in accordance with image information, the heated portion shows a reflection color corresponding to the heating temperature. In FIG. 1, reference numeral 4a indicates a heat reflection portion.
Therefore, when writing is performed at 95 ° C. by the thermal head, when viewed from the direction of arrow A, a green display can be observed on a white background.

The portion indicated by the reference numeral 4b indicates that the portion is heated to a temperature of 119 ° C. or higher, rapidly cooled, and is in a transparent state. This part appears to be the color of the intermediate layer 3, that is, black when viewed from the observation side (the direction of arrow A). Therefore, 119 ° C
When writing is performed as described above, black display can be performed on a white background. The portion indicated by reference numeral 4c is a portion that is gradually cooled after being heated by the heat roller and is in a scattered state, and is a margin region where writing is not performed by the thermal head. Also,
When writing is performed at 87 ° C., 95 ° C., 115 ° C., or 119 ° C. or higher, full-color display can be performed. In the first embodiment, in a portion where low reflectance is desired to be displayed, the reflectance can be reduced as a result by mixing black display portions.

In the first embodiment, the melting point of the base layer 2 is 200 ° C. or higher, and the melting point of the intermediate layer 3 is 200 ° C.
The protective layer 5 has a melting point of 200 ° C. or more, and the temperature at which the liquid crystal component of the recording layer 4 changes from a liquid crystal phase to an isotropic phase (phase transition temperature) is 119 ° C. Therefore, even if the recording layer 4 is liquefied by being heated to 119 ° C. or more during writing and erasing,
If the base layer 2, the intermediate layer 3, and the protective layer 5 are maintained at a temperature lower than their melting point, their mechanical strength does not decrease, and the recording layer 4 does not resist the pressure applied from the thermal head. The thickness can be maintained. If a spherical spacer is mixed in the recording layer 4, the thickness can be more reliably maintained.

Here, various compositions and manufacturing methods of the reversible thermosensitive recording medium of the first embodiment will be described.

(Experimental Example 1) Carbon black was dispersed in a silicone resin (YR3370, manufactured by Toshiba Silicone Co., Ltd.) as a light absorbing material, and an isopropyl alcohol solution mixed with a catalyst (CR15, manufactured by Toshiba Silicone Co., Ltd.) was mixed on synthetic paper. It was applied, dried and cured to form a black intermediate layer 3 having a light absorbing function and a thickness of 5 μm.

Next, 10 parts by weight of the liquid crystal compound represented by the chemical structural formula (A) is mixed and dissolved in 100 parts by weight of toluene, and the mixture is coated on the intermediate layer 3 with a blade, and dried by heating to a thickness of 10 μm. The reversible thermosensitive recording layer 4 was obtained.
Further, a 3 μm-thick polyester film as a protective layer 5 is superimposed on the film, and the polyester film is heated and bonded at 100 ° C., and the edge is adhesive (Toa Gosei: Aron Alpha).
And sealed.

In the recording medium of this experimental example 1, the portion where writing was performed at 120 ° C. using a thermal head was the recording layer 4.
Became transparent, and a black image with good contrast with a white background was obtained. When writing was performed at 87 ° C., 95 ° C., and 115 ° C., respectively, using a thermal head, clear, high-contrast images of red, green, and blue were obtained on a white background, respectively. 120 ℃ of recording medium
After passing through a heat roller and gradually cooling, the entire surface was turned into a cloudy scattering state.

(Experimental Example 2) An isopropyl alcohol solution obtained by dispersing a phthalocyanine pigment in a silicone resin (YR3370, manufactured by Toshiba Silicone Co., Ltd.) as a light absorbing material and further mixing a catalyst (CR15, manufactured by Toshiba Silicone Co., Ltd.) on woodfree paper was used. It was applied, dried and thermally cured to obtain a blue intermediate layer 3 having a thickness of 5 μm. On this intermediate layer 3, an average particle size of 15
A μm silica spacer was dispersed in ethanol and spray applied.

Next, a cholesteric liquid crystalline compound represented by the chemical structural formula (A) and a photopolymerization initiator DAROCU
A liquid crystal composition was prepared by mixing a bifunctional acrylate R712 (manufactured by Nippon Kayaku Co., Ltd.) having an aromatic ring to which R1173 (manufactured by Ciba Geigy) at 3 wt% was added in a weight ratio of 8: 2 to prepare a liquid crystal composition. This liquid crystal composition was applied on the intermediate layer 3, and a 2 μm thick transparent polyethersulfone film was laminated thereon as a protective layer 5. Next, the protective layer 5
While pressing, a UV ray of 0.02 mW / cm ² was irradiated for 1 hour, and then a UV ray of 0.25 mW / cm ² was irradiated for 1 hour to form a color reversible thermosensitive recording layer 4 having a thickness of 15 μm.

In the recording medium of Experimental Example 2, the portion where writing was performed at 120 ° C. using a thermal head became transparent. In this recording medium, the portion in the cloudy scattering state became white, and a clear blue image with a good contrast against a white background was obtained. Further, the recording medium was passed through a heat roller at 120 ° C., and gradually cooled, whereby the entire surface became cloudy and scattered.

(Experimental Example 3) An isopropyl alcohol solution in which carbon black was dispersed in copolymerized nylon (manufactured by Toray Industries, Inc .: CM8000) was applied as a light absorbing material on a synthetic paper and dried to form an intermediate layer 3 having a thickness of 5 μm. did. Next, a silica spacer having an average particle diameter of 15 μm, the liquid crystal compound represented by the chemical structural formula (A), and a photopolymerization initiator DAROC
A liquid crystal composition was prepared by mixing UR1173 (manufactured by Ciba Geigy) and bifunctional acrylate R712 (manufactured by Nippon Kayaku Co., Ltd.) having an aromatic ring to which 3 wt% was added at a weight ratio of 8: 2. This liquid crystal composition is applied on the intermediate layer 3, and a 2 μm thick transparent PET
(Polyethylene terephthalate) films were overlaid. Next, while pressing the protective layer 5, 15 mW / cm ²
For 5 minutes to form a color reversible thermosensitive recording layer 4 having a thickness of 15 μm.

In the recording medium of Experimental Example 3, the portion where writing was performed at 120 ° C. using a thermal head became transparent. In this recording medium, the portion in the cloudy scattering state became white, and a clear black image with good contrast against a white background was obtained. When writing is performed at 87 ° C., 95 ° C., and 115 ° C. using a thermal head, respectively,
On each white background, clear images of red, green, and blue with good contrast were obtained. The recording medium was passed through a heat roller at 120 ° C., and gradually cooled, whereby the entire surface was turned into a cloudy scattering state.

(Experimental Example 4) A perylene pigment was dispersed in a silicone resin (YR3370, manufactured by Toray Industries, Inc.) as a light absorbing material on a high-quality paper, and a catalyst (CR, manufactured by Toshiba Silicone Co., Ltd.) was used.
Apply isopropyl alcohol solution mixed with 15),
After drying, a red intermediate layer 3 having a thickness of 3 μm was obtained. Next, the liquid crystalline compound represented by the chemical structural formula (A) and a photopolymerization initiator DAROCUR 1173 (manufactured by Ciba-Geigy) were added in 3w.
Bifunctional acrylate R712 having an aromatic ring added by t%
(Manufactured by Nippon Kayaku) in a weight ratio of 8: 2,
A liquid crystal composition was prepared. This liquid crystal composition was mixed with the intermediate layer 3
After application on the upper surface, the substrate was irradiated with ultraviolet rays of 0.02 mW / cm ² for 1 hour, and further irradiated with ultraviolet rays of 0.25 mW / cm ² for 1 hour to form a color composite film (reversible thermosensitive recording layer 4) having a thickness of 20 μm. ) Formed.

In the recording medium of Experimental Example 4, the portion where writing was performed at 120 ° C. using a thermal head became transparent. In this recording medium, the portion in the cloudy scattering state became white, and a clear image of good red contrast with a white background was obtained. Further, the recording medium was passed through a heat roller at 120 ° C., and gradually cooled, whereby the entire surface became cloudy and scattered.

(Thermal Printer, see FIGS. 3 and 4) FIG. 3 shows a thermal printer for writing information on the recording medium 1. The printer includes transport rollers 11, 1 in a housing 10 along a traveling direction B of the recording medium 1.
2. A heating / slow cooling plate 13, a thermal head 16, and a platen 17 are provided. The heating / slow cooling plate 13 is a recording medium 1
For heating and gradually cooling the transfer rollers 11, 1
The recording medium 1 is gradually cooled as the distance from the rollers 11 and 12 increases.

The recording medium 1 enters the printer from the entrance 10a and is sent from the conveying rollers 11 and 12 to the heating / cooling plate 13, where it is heated to an erasing temperature of 119 ° C. or higher.
It is further cooled slowly. Thus, the recording on the recording medium 1 is erased. Next, the recording medium 1 is conveyed between the platen 17 and the thermal head 16, where necessary information is written. The recording medium 1 heated by the thermal head 16 to be in the display state is naturally cooled rapidly after the heating from the thermal head 16 is stopped, and the writing is fixed.
It is discharged from the outlet 10b.

After the heating element provided on the thermal head 16 has passed, the recording medium is rapidly cooled by natural cooling. Therefore, the cooling means for the recording medium is not necessary, but the operation can be performed more reliably. For this purpose, a cooler may be provided downstream of the thermal head 16.

The width of the heating / cooling plate 13 is preferably set to be larger than the writing area width of the thermal head 16. This is to ensure that already written information can be erased even if the conveyance of the recording medium 1 is slightly shifted in the width direction. Further, in order to perform uniform erasure over the entire surface of the recording medium 1, it is desirable that the width of the heating / cooling plate 13 be larger than the width of the recording medium 1.

As shown in FIG. 4, the thermal head 16 has four heating elements 16t, 16r, 16g, 16b arranged side by side in a direction perpendicular to the traveling direction B of the recording medium 1. The heating element 16t is for writing red, the heating element 16r is for writing red, the heating element 16g is for writing green, and the heating element 16b is for writing blue. Many pixel components are arranged along the traveling direction B.

The thermal head 16 is moved in a direction C perpendicular to the feeding direction B of the recording medium 1 (a direction perpendicular to the plane of FIG. 3).
In addition, the recording medium 1 is configured to be driven back and forth in synchronization with the progress of the recording medium 1. Each heating element 16t, 16b, 16g, 1
6r is turned on and off based on image information for each color while moving in the C direction, and by repeating heating and non-heating, an image is written to the recording medium 1 by the number of lines equal to the number of pixels. First, a full-color image is reproduced on the recording medium 1. The writing by the heating element is performed in the order of the temperature, that is, the heating element for transparent 16t, the heating element for blue 1
6b, the heating element for green 16g, and the heating element for red 16r are preferably performed in this order. Note that it is possible to write the transparent and three colors with one heating element, but it is preferable to write in four parts because the temperature control becomes complicated.

(Second Embodiment, see FIG. 2) The second embodiment has a configuration in which the intermediate layer 3 is omitted from the recording medium of the first embodiment, as shown in FIG. The configurations of the base layer 2, the recording layer 4, and the protective layer 5 can be the same as those described in the first embodiment. The first
As described for the intermediate layer in the embodiment, if a light-absorbing material is used as the base layer 2, if the recording medium is made opaque and scattered over the entire surface, and writing is performed with a thermal head for each color, a white background is obtained. Any full-color image can be expressed well. Further, if a material that reflects a part of visible light is used as the base layer 2, if the recording medium is made to be in a cloudy scattering state over the entire surface and writing is performed with a transparent thermal head, the reflection color of the base layer 2 on a white background Images can be reproduced well. In this case, it is desirable that the base layer 2 is opaque.

(Third Embodiment) On the other hand, the first embodiment shown in FIG.
In the embodiment, a near-infrared absorbing agent may be dispersed in the intermediate layer 3 and / or the protective layer 5 to have a function of converting infrared light into heat. The intermediate layer 3 and / or the protective layer 5 itself may be formed from an infrared absorbing material. Although not particularly shown, the third embodiment of the present invention is provided with an infrared absorbing function in the vicinity of the recording layer 4 as described above, so that information can be effectively written by a laser printer.

(Laser Printer, See FIG. 5) FIG. 5 shows a schematic configuration of a laser printer for writing information on the recording medium of the third embodiment. This printer is
Semiconductor lasers 31t, 31b, 31g, and 31r for writing transparent, blue, green, and red light are modulated by a drive circuit 33, and laser beams radiated from the semiconductor lasers are polygon mirrors via collimator lenses 32t, 32b, 32g, and 32r. 34. Polygon mirror 34
Is driven to rotate in the direction of arrow c, the laser beam is deflected based on this rotation, and scans the recording medium 1 linearly,
By transporting the recording medium 1 in the direction of arrow B, two-dimensional full-color information is written. Although not shown, the laser printer is also provided with an optical element such as an fθ lens.

The colors to be written are the semiconductor lasers 31t and 31t.
The correspondence is made by controlling the radiant energies of b, 31g and 31r. Therefore, it is also possible to write by controlling the energy of the laser beam for each color by using one semiconductor laser. However, it is easier to control the energy when writing is performed for each color using four semiconductor lasers.

(Other Embodiments) The reversible thermosensitive recording medium according to the present invention is not limited to the above embodiment, but can be variously modified within the scope of the invention.
In particular, as the low-molecular-weight cholesteric liquid crystal compound constituting the recording layer, various compounds other than those represented by the chemical structural formula (A) can be used. Further, it goes without saying that a thermal printer or a laser printer for writing information other than those shown in FIGS. 3 and 5 can be used.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a recording medium according to a first embodiment of the present invention.

FIG. 2 is a sectional view showing a recording medium according to a second embodiment of the present invention.

FIG. 3 is a schematic configuration diagram illustrating a thermal printer.

FIG. 4 is a plan view showing a thermal head of the thermal printer.

FIG. 5 is a schematic perspective view showing a laser printer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Recording medium 2 ... Base layer 3 ... Intermediate layer 4 ... Recording layer 5 ... Protective layer

Claims (11)

[Claims] 1. A sheet-like base layer, which shows a cholesteric phase at a temperature higher than room temperature, reflects light in a wavelength range corresponding to a temperature, and solidifies in a reflection state by quenching from that temperature, Or a recording layer containing a low-molecular-weight cholesteric liquid crystalline compound that exhibits a scattering state by being gradually cooled from a temperature higher than the above. 2. The reversible thermosensitive recording medium according to claim 1, wherein the recording layer contains a polymer material in addition to the liquid crystal compound. 3. The reversible thermosensitive recording medium according to claim 1, wherein the recording layer includes a spacer. 4. The liquid crystal display device according to claim 1, wherein the melting point of the base layer is higher than the melting point of the liquid crystal compound.
Or the reversible thermosensitive recording medium according to claim 3. 5. The recording medium according to claim 1, wherein an intermediate layer having a smooth surface in contact with the recording layer is provided between the base layer and the recording layer. Item 6. A reversible thermosensitive recording medium according to Item 4. 6. The reversible thermosensitive recording medium according to claim 5, wherein the intermediate layer contains a component that absorbs visible light. 7. The reversible thermosensitive recording medium according to claim 5, wherein said intermediate layer contains a component reflecting light of a specific wavelength. 8. The reversible thermosensitive recording medium according to claim 5, wherein the intermediate layer contains a component that absorbs infrared rays. 9. The method according to claim 5, wherein the melting point of the intermediate layer is higher than the melting point of the liquid crystalline compound.
The reversible thermosensitive recording medium according to claim 7. 10. The recording medium according to claim 1, wherein a protective layer is provided on the recording layer.
Claim 5, Claim 6, Claim 7, Claim 8, or Claim 9
The reversible thermosensitive recording medium according to the above. 11. The reversible thermosensitive recording medium according to claim 10, wherein a melting point of said protective layer is higher than a melting point of said liquid crystalline compound.