JP2001059954A - Method for recording picture on thermally reversible recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a method for recording pictures on a thermally reversible recording medium having a high utilization factor of the applied energy, multicolor displaying and having high precision. SOLUTION: In this method, a picture is formed on a thermosensitive recording layer 4 with the heat generated by the near infrared laser irradiation on a thermally reversible recording medium 1 provided with the thermosensitive recording layer 4 containing a cholesteric liquid crystal material of which the selective reflection wavelength varies depending on the temperature. The thermosensitive recording layer 4 is laminated on a substrate 2 via a photothermic converter 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recording an image on a thermoreversible recording medium, and more particularly to a method for recording an image on a thermoreversible recording medium with high utilization efficiency of applied energy and high resolution.

[0002]

2. Description of the Related Art In recent years, reversible thermosensitive recording media capable of repeatedly recording and erasing an image have been attracting attention from the viewpoint of visualizing electronic information and saving resources, and some of them have been put to practical use.
As typical examples thereof, a high molecular weight / low molecular weight mixed type, a leuco dye / long chain alkyl type mixed colorant mixed type are known.

[0003] In the future, since recording of a larger amount of information is required, a reversible thermosensitive recording medium capable of full-color and high-definition recording is required. However, in principle, the display color is limited to white turbidity and transparent in the polymer / low molecular mixture system. In the leuco dye / long-chain alkyl developer mixture system, only one color or two colors is developed. is there.

Many of the conventional heating methods for a reversible thermosensitive recording medium involve bringing a heating element such as a thermal head into contact with the surface of the medium. In this case, since the surface is rubbed with the heating element during heating, a problem such as scratching of the surface may occur. Furthermore, when the reversible thermosensitive layer is heated via a support or the like, a part of the applied thermal energy is consumed for heating the support, and the heat is diffused, making it difficult to record a high-definition image.

An object of the present invention is to solve the above-mentioned problems and to provide a multicolor display and high-definition image recording method with high utilization efficiency of applied energy.

[0006]

In order to achieve the above objects, the present inventor has conducted various studies and obtained the following findings.

(1) By including a specific cholesteric liquid crystal material in the heat-sensitive recording layer, multicolor display can be achieved with a relatively simple structure.

(2) If a photothermal converter is provided in contact with a cholesteric liquid crystal material and a specific laser beam is focused on a portion where an image is to be formed and / or erased, high-definition recording can be performed efficiently.

The present invention has been made based on the above-mentioned knowledge. The present invention provides a thermoreversible recording layer provided with a cholesteric liquid crystal material containing a cholesteric liquid crystal material which exhibits a selective reflection wavelength corresponding to a heating temperature and which is solidified in a selective reflection state by cooling. An image is formed on the heat-sensitive recording layer by heat generated by irradiating a near-infrared laser beam to the recording medium.

The cholesteric liquid crystal material exhibits at least one type of cholesteric liquid crystal which reflects a cholesteric phase at a temperature higher than room temperature, reflects light in a visible wavelength range according to the temperature, and rapidly cools from that temperature to fix it in a reflection state. It is composed of a liquid crystal compound. Such materials include, for example,
Adv. Mater. 1997, 9, No. 14, p. Materials such as those described in 1102-1104 can be mentioned, but liquid crystal materials having other chemical structures having similar properties may be used. Other liquid crystal compounds and non-liquid crystal compounds may be further added to the liquid crystal material.

It is preferable that a photothermal converter having a photothermal conversion function is arranged on the thermoreversible recording medium so as to be in contact with the cholesteric liquid crystal material. The light-to-heat converter only needs to be in contact with the cholesteric liquid crystal material, and can be formed into a shape such as a layer, a particle, a polygon, a lattice, or a stripe. Further, a cholesteric liquid crystal material may be dispersed in a polymer matrix having a light-to-heat conversion function to form a heat-sensitive recording layer. In the case of a configuration in which liquid crystal and a photothermal converter are simultaneously present in the recording layer, such as a shape such as a particle shape, a polygonal shape, a lattice shape, and a stripe shape, and a form in which a liquid crystal material is dispersed in a polymer matrix, It is preferable that the continuous portion where the photothermal converter does not exist is smaller than the minimum line width of the image even if it has a shape.

The heat-sensitive recording layer and the light-to-heat converter are provided on a suitable support, for example, a thin support such as glass or a polymer film. In particular, when a flexible polymer film is used for the support, paper-like handling such as bending or binding a plurality of sheets becomes possible.

When a polymer film containing a material having a high light absorption intensity such as carbon black is used as the support, the support can also serve as a photothermal converter.

As the photothermal converter, it is preferable to use a material having a sufficiently large absorption coefficient at the laser wavelength in order to increase the photothermal conversion efficiency.

The oscillation wavelength of the laser is preferably a wavelength absorbed by the photothermal converter, and a near infrared laser such as a YAG laser or a semiconductor laser can be used. When a near-infrared laser is used, the irradiation spot can be made smaller than that of a mid-infrared light laser such as a carbon dioxide laser, and the material is less likely to be chemically decomposed than an ultraviolet light laser such as an excimer laser.

The "near-infrared laser" in the present invention refers to a laser having an oscillation wavelength from 780 nm to 2500 nm, and includes a solid-state laser such as a YAG laser and a glass laser, and a semiconductor laser.

When a near-infrared laser is used, since the oscillation wavelength of the laser beam is out of the visible region, the laser beam is reflected by the liquid crystal regardless of the position of the selective reflection wavelength included in the recording layer in the visible region. Thus, writing is not hindered, and the energy use efficiency is high and constant.

The laser beam used in the present invention has an intensity per pulse of the laser beam of 0.1 W / cm ^2.
To 1600 W / cm ² . By setting the intensity range as described above, it is possible to perform good image recording without writing failure and without destroying the recording layer.

If a protective film made of glass or a polymer material is provided on the heat-sensitive recording layer, the mechanical strength of the surface of the thermoreversible recording medium is improved. At least one of the support and the protective film is transparent or translucent with respect to the irradiated light.

The laser beam may be irradiated from either the heat-sensitive recording layer side or the support side, or from both sides. In any case, the portion where the near-infrared laser beam passes before reaching the photothermal converter is transparent or translucent to the near-infrared laser beam.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for recording an image on a thermoreversible recording medium according to the present invention will be described below with reference to the accompanying drawings. In each of the embodiments described below, specific substance names are described.However, this is merely an example, and the present invention is not intended only for these substances. It is possible to use various materials.

FIG. 1 shows an example of an image recording / erasing method according to the present invention. A laser light 7 is emitted from a laser light source 6, condensed by a lens 8 on a photothermal converter 3 on a support 2 of the thermoreversible recording medium 1, and heat is generated. Record the image.

In FIG. 1, a laser beam 7 is applied from the heat-sensitive recording layer 4 side.
Is irradiated, but it may be irradiated from the support 2 side, or may be irradiated from both sides. In any case, the layer through which the laser light 7 passes before reaching the light-to-heat converter 3 or the support 2 also serving as the light-to-heat converter is transparent or translucent to the laser light 7.

As the material of the support 2, glass or a polymer material is used. As the polymer material, for example, polyethylene terephthalate, polycarbonate, polyether sulfone, polyphenyl sulfide, or the like is used. Further, a protective layer may be provided on the heat-sensitive recording layer 4. As the material of the protective layer, the above-mentioned various materials listed as the material of the support 2 can be used.

As the material of the light-to-heat converter 3, a material having a relatively strong absorption intensity at the laser oscillation wavelength is used. In particular,
Carbon black, Ge, Bi, I as inorganic material
Metals or metalloids such as n, Te, Se, and Cr and alloys containing the same are included. Various dyes can be appropriately used as the organic material depending on the wavelength of light to be absorbed. When a near-infrared laser is used, a cyanine dye, a quinone dye, a quinoline derivative of indnaphthol, a phenylenediamine nickel complex, a phthalocyanine dye, and the like can be used.

The light-to-heat converter is shown in FIG. 1 as a layered body sandwiched between the support 2 and the heat-sensitive recording layer 4, but may be in contact with the cholesteric liquid crystal material. That is, as shown in FIGS. 2 to 5, a light-to-heat converter 3 having a shape such as a circle, a polygon, a lattice, or a stripe may be provided in the thermosensitive recording layer 4.

As shown in FIG. 6, a composite film of a polymer matrix 9 and a cholesteric liquid crystal material 10 made of a polymer having a light-to-heat conversion function or mixed with a light-to-heat conversion material may be used as the heat-sensitive recording layer 4.

(Experimental Example 1) A silica spacer having an average particle diameter of 20 μm was dispersed in ethanol and spray-coated on a well-cleaned black polyethylene terephthalate (PET) (Lumirror X30 manufactured by Toray Industries, Inc.) film. Next, a cholesteric liquid crystalline compound represented by the following chemical structural formula (A) is placed on black PET provided with spacers, and 1
Melted on a hot plate at 30 ° C. After a glass plate was put on the molten compound and cooled to room temperature, the glass plate was removed to obtain a thermoreversible recording medium having a thermosensitive recording layer.

[0029]

Embedded image

The thermoreversible recording medium was heated to 130 ° C. on a hot plate to convert the cholesteric liquid crystal into an isotropic phase, and then gradually cooled to 100 ° C. to obtain a state of blue selective reflection. After that, it was immersed in ice water and rapidly cooled, and fixed in a blue selective reflection state. Light is irradiated in the vertical direction of the thermoreversible recording medium, and reflected light is detected from an angle of 20 degrees to obtain a spectrophotometer (instantaneous multi-photometry system: MCPD-
2000, manufactured by Otsuka Electronics Co., Ltd.), and the reflection peak wavelength was 420 nm.

Next, from the heat-sensitive recording layer side of the thermoreversible recording medium, a pulse light (1) of a YAG laser (laser processing apparatus: LAY-603A, manufactured by Toshiba Corporation) having an oscillation wavelength of 1064 nm.
50 J / cm ² · pulse, 0.8 ms / pulse, 18
(8 kW / cm ² · pulse), the reflected light at the irradiated portion turned blue-green, and the state was maintained for a long time. When the reflection peak wavelength of the discolored portion was measured, it was 480.
nm.

As described above, in a thermoreversible recording medium using a cholesteric liquid crystal material, blue-green could be written by irradiating near-infrared light of a YAG laser on a blue portion.

(Experimental Example 2) The thermoreversible recording medium obtained in the same manner as in Experimental Example 1 was heated to 130 ° C. on a hot plate to convert the cholesteric liquid crystal into an isotropic phase.
The mixture was gradually cooled to a state where green selective reflection was exhibited. Then, when immersed in ice water and cooled rapidly, it was fixed in a green selective reflection state. When the reflection spectrum was measured, the reflection peak wavelength was 525 nm.

From the thermosensitive recording layer side of this thermoreversible recording medium, using the apparatus used in Experimental Example 1, pulse light of a YAG laser (314 J / cm ² · pulse, 0.2 ms / pulse, 1570 kW / cm ²⁾ (Pulse), the reflected light of the irradiated part turned red, and this state was maintained for a long time. It was 600 nm when the reflection peak wavelength of the discolored part was measured.

The thermoreversible recording medium showing selective reflection of green color obtained in Experimental Example 2 was irradiated with YAG laser pulse light (400 J / cm ² · pulse, 0.2 millisecond /
(A pulse, 2000 kW / cm ² · pulse), the liquid crystal film of the irradiated portion was peeled off. Thus, if the energy of the laser beam is too strong, the thermosensitive recording layer will be destroyed.

(Experimental Example 3) The thermoreversible recording medium obtained in the same manner as in Experimental Example 1 was heated to 130 ° C. on a hot plate to convert the cholesteric liquid crystal into an isotropic phase.
The temperature was gradually cooled to ° C. to give a state of blue selective reflection. After that, it was immersed in ice water and rapidly cooled, and fixed in a blue selective reflection state. When the reflection spectrum was measured, the reflection peak wavelength was 410 nm.

From the thermosensitive recording layer side of this thermoreversible recording medium, using the apparatus used in Experimental Example 1, pulse light of a YAG laser (126 J / cm ² · pulse, 0.4 ms / pulse, 314 kW / cm ²⁾ (Pulse), the reflected light at the irradiated part turned red, and the state was maintained for a long time. When the reflection peak wavelength of the discolored portion was measured, it was 605.
nm.

(Experimental Example 4) The particle size of the spacer was 1 μm.
Other than the above, a thermoreversible recording medium was obtained in the same manner as in Experimental Example 1. This thermoreversible recording medium is placed on a hot plate for 1 hour.
After heating the cholesteric liquid crystal to an isotropic phase by heating to 30 ° C., it was gradually cooled to 80 ° C. to obtain a state showing selective reflection of green. Then, when immersed in ice water and cooled rapidly, it was fixed in a green selective reflection state. When the reflection spectrum was measured, the reflection peak wavelength was 530 nm.

From the thermosensitive recording layer side of this thermoreversible recording medium, a semiconductor laser (FD-25, SD
L) (0.04 J / cm ² · pulse, 2
(00 ms / pulse, 0.2 W / cm ² · pulse), the reflected light at the irradiated portion turned red, and this state was maintained for a long time. When the reflection peak wavelength of the discolored portion was measured, it was 610 nm.

(Experimental Example 5) The particle size of the spacer was 5 μm.
Other than the above, a thermoreversible recording medium was obtained in the same manner as in Experimental Example 1. This thermoreversible recording medium is placed on a hot plate for 1 hour.
After heating to 30 ° C. to make the cholesteric liquid crystal into an isotropic phase, the liquid crystal was gradually cooled to 100 ° C. to give a state of blue selective reflection. After that, it was immersed in ice water and rapidly cooled, and fixed in a blue selective reflection state. When the reflection spectrum was measured, the reflection peak wavelength was 420 nm.

From the thermosensitive recording layer side of this thermoreversible recording medium, using the apparatus used in Experimental Example 4, pulse light of a semiconductor laser (0.15 J / cm ² · pulse, 30 ms / pulse, 5 W / cm ²⁾ (Pulse), the reflected light at the irradiated part turned green, and this state was maintained for a long time. When the reflection peak wavelength of the discolored portion was measured, it was 530.
nm.

(Experimental Example 6) The thermoreversible recording medium obtained in the same manner as in Experimental Example 1 was heated to 130 ° C. on a hot plate to convert the cholesteric liquid crystal into an isotropic phase.
The mixture was gradually cooled to a state where blue-green selective reflection was exhibited. Then, when immersed in ice water and cooled rapidly, it was fixed in a blue-green selective reflection state. When the reflection spectrum was measured,
The reflection peak wavelength was 490 nm.

From the thermosensitive recording layer side of this thermoreversible recording medium, using the apparatus used in Experimental Example 4, pulsed light of a semiconductor laser (0.48 J / cm ² · pulse, 30 ms / pulse, 16 W / cm ²⁾ (Pulse), the reflected light of the irradiated part changed to blue, and that state was maintained for a long time. When the reflection peak wavelength of the discolored portion was measured, it was 430.
nm.

(Experimental Example 7) In Experimental Example 1, the cholesteric liquid crystal material was mixed with a compound represented by the chemical structural formula (A) and a compound represented by the following chemical structural formula (B) (weight ratio 1: 1) and the average particle size of the spacer is 1 μm
Other than the above, a thermoreversible recording medium was obtained in the same manner as in Example 1. This thermoreversible recording medium is placed on a hot plate for 1 hour.
After heating the cholesteric liquid crystal to an isotropic phase by heating to 30 ° C., it was gradually cooled to 50 ° C. to give a state of showing green selective reflection. Then, when immersed in ice water and cooled rapidly, it was fixed in a green selective reflection state. When the reflection spectrum was measured, the reflection peak wavelength was 530 nm. The compound represented by the structural formula (B) can be obtained, for example, by reacting cholesterol with a dicarboxylic acid halide or a dicarboxylic acid derivative in the presence of a suitable catalyst.

[0045]

Embedded image

From the thermosensitive recording layer side of this thermoreversible recording medium, the pulse light of the YAG laser (1 J / cm ² · pulse, 1 millisecond / pulse, 1 kW) was applied using the apparatus used in Experimental Example 1.
/ Cm ² · pulse), the reflected light at the irradiated portion turned blue, and this state was maintained for a long time. When the reflection peak wavelength of the discolored portion was measured, it was 430 nm.

The YAG laser pulse light (0.01 J / cm ² · pulse, 500 ms / pulse, 0 ms) was applied from the thermosensitive recording layer side of the thermoreversible recording medium exhibiting green selective reflection obtained in Experimental Example 7. (0.22 W / cm ² · pulse), no color change was observed. When the energy of the laser beam is small as described above, the temperature of the heat-sensitive recording layer is incomplete and writing cannot be performed.

(Experimental Example 8) A thermoreversible recording medium was obtained in the same manner as in Experimental Example 4 except that the average particle size of the spacer was changed to 20 μm. The thermoreversible recording medium was heated to 130 ° C. on a hot plate to convert the cholesteric liquid crystal into an isotropic phase, and then gradually cooled to 90 ° C. so as to exhibit a blue selective reflection. After that, it was immersed in ice water and rapidly cooled, and fixed in a blue selective reflection state. When the reflection spectrum was measured, the reflection peak wavelength was 46.
It was 0 nm.

The YAG laser pulse light (6.4 J / cm ² · pulse, 0.4 ms / pulse, 16 kW / pulse) was applied from the thermosensitive recording layer side of this thermoreversible recording medium using the apparatus used in Experimental Example 1. (cm ² · pulse), the reflected light at the irradiated portion turned blue-green, and this state was maintained for a long time. When the reflection peak wavelength of the discolored portion was measured, it was 4
It was 98 nm.

(Experimental Example 9) The thermoreversible recording medium obtained in the same manner as in Experimental Example 1 was heated to 130 ° C. on a hot plate to convert the cholesteric liquid crystal into an isotropic phase.
The temperature was gradually cooled to ° C. to give a state of blue selective reflection. After that, it was immersed in ice water and rapidly cooled, and fixed in a blue selective reflection state. When the reflection spectrum was measured, the reflection peak wavelength was 420 nm.

From the PET film side of this thermoreversible recording medium, using the apparatus used in Experimental Example 1, pulse light of a YAG laser (450 J / cm ² · pulse, 0.8 ms / pulse, 560 kW / cm ² · pulse) (Pulse), the reflected light at the irradiated portion turned green, and this state was maintained for a long time. When the reflection peak wavelength of the discolored portion was measured, it was 520 nm. As described above, an image could be written even when laser light was irradiated from the substrate side.

(Other Embodiments) The image recording method 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, various cholesteric liquid crystal materials can be used in addition to those shown in the chemical formulas (A) and (B). The structure of the thermoreversible recording medium and the structure of the laser drawing apparatus are also arbitrary.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an embodiment of an image recording method according to the present invention and a cross-sectional structure of a thermoreversible recording medium to be recorded.

FIG. 2 is a plan view showing an arrangement (first example) of a photothermal converter in a thermoreversible recording medium.

FIG. 3 is a plan view showing an arrangement (second example) of a photothermal converter in a thermoreversible recording medium.

FIG. 4 is a plan view showing an arrangement (third example) of a photothermal converter in a thermoreversible recording medium.

FIG. 5 is a plan view showing an arrangement (fourth example) of a photothermal converter in a thermoreversible recording medium.

FIG. 6 is a sectional view showing another structure of the thermoreversible recording medium.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Thermoreversible recording medium 2 ... Support 3 ... Light-to-heat converter 4 ... Thermal recording layer 6 ... Laser light source 7 ... Laser light 8 ... Condensing lens 9 ... Polymer matrix 10 ... Cholesteric liquid crystal material

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H088 EA62 FA02 GA03 HA01 MA20 2H111 HA07 HA14 HA23 HA35 5C094 AA05 AA60 BA43 CA24 FB20 GA01 HA10

Claims (6)

[Claims] 1. A selective reflection wavelength according to a heating temperature,
An image is formed on the thermosensitive recording layer by heat generated by irradiating a near-infrared laser beam to a thermoreversible recording medium provided with a thermosensitive recording layer containing a cholesteric liquid crystal material that solidifies while being selectively reflected by cooling. Forming an image. 2. The image recording method according to claim 1, wherein the thermoreversible recording medium is provided such that a photothermal converter having a photothermal conversion function is in contact with the cholesteric liquid crystal material. 3. The image recording method according to claim 1, wherein the laser light source for irradiating the thermoreversible recording medium is a YAG laser. 4. The image recording method according to claim 1, wherein the laser light source for irradiating the thermoreversible recording medium is a semiconductor laser. 5. The laser beam according to claim 1, wherein an intensity per pulse of the laser beam is from 0.1 W / cm ² to 1600 kW / cm ^2.
The image recording method described in the above. 6. The method according to claim 1, wherein the laser light is emitted from an image observation side and / or a back side of the thermoreversible recording medium. 5. The image recording method according to 5.