JP2002127616A - Reversible recording material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reversible recording material capable of simply changing the temperature characteristics of a reflective wavelength. SOLUTION: A cholesteric liquid crystal base recording material is pinched between two sheets of substrates, at least one of them is transparent, and one part or the whole area of the same is heated to a temperature, showing an isotropic phase or a cholesteric liquid crystal phase, and, thereafter, the heated area is cooled suddenly to a temperature lower than a given value whereby a required cholesteric reflecting color can be fixed and recorded, further, the record can be eliminated by heating the same again.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a thermosensitive recording material capable of reversible recording.

[0002]

2. Description of the Related Art In a recording material comprising a cholesteric liquid crystal compound having a molecular weight of 2,000 or less and a glass transition temperature of 35.degree. C. or more or a mixture thereof, the fixed reflection color is prolonged at room temperature by rapidly cooling from the cholesteric liquid crystal state. Recording materials that can be stored for a period of time and that can be repeatedly written by returning to a liquid crystal state are known (N. Tamaoki, AV Parfenov,
A. Masaki, H .; Matsuda, Adv. Ma
ter. 1997, 9, 1102-1104;
1-24027). This recording material can be applied to rewritable full-color recording and multi-value recording media.

When this recording material is used as a rewritable full-color display material, as shown in FIG. 1, a light absorbing layer is provided on one of two substrates (a base film and a cover film), and A cholesteric liquid crystal-based recording material (Ch liquid crystal) is sandwiched between the cholesteric liquid crystal layers, the molecular orientation state of the cholesteric liquid crystal is changed, and the cholesteric liquid crystal is fixed by rapid cooling, whereby various colors can be stably recorded at room temperature. However, this recording material is characterized in that the reflection wavelength depends on temperature, and the dependence is compound-specific. Therefore, when it is desired to change the temperature characteristics of the reflection wavelength, it is necessary to design and synthesize a cholesteric liquid crystal that meets the newly required characteristics. In addition, the cholesteric liquid crystal obtained up to now has a reflection wavelength that changes almost monotonically with temperature.
Color bleeding due to heat diffusion, heating unevenness, etc. appears. In a reversible recording medium in which at least one cholesteric liquid crystal recording material is sandwiched between two transparent substrates,
Examples of the use of a mixture of two or more liquid crystal compounds as the recording material include polymer dispersion types (JP-A-6-258622, JP-A-8-1526).
No. 05), the effect of expanding the reflection wavelength range due to phase separation between the liquid crystal and the polymer cannot be obtained.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a reversible recording material capable of easily changing the temperature characteristic of the reflection wavelength. Reversible recording that is easy to rewrite, can fix the reflection color at room temperature, can set the selective reflection wavelength range to the visible light range, and can shift the temperature characteristics of the reflection wavelength to the shorter wavelength side. The purpose is to provide materials. It is another object of the present invention to provide a reversible recording material capable of eliminating color bleeding due to heat diffusion, heating unevenness, and the like at the time of heating printing and capable of performing beautiful printing.

[0005]

Means for Solving the Problems The above problems are as follows:
The invention 16) (hereinafter referred to as Inventions 1 to 16) is solved. 1) A cholesteric liquid crystal-based recording material is sandwiched between two substrates, at least one of which is transparent, and the recording material is
After heating a part or all of the region to a temperature showing an isotropic phase or a cholesteric liquid crystal phase, by rapidly cooling the heated region to a predetermined temperature or lower, or After heating a part or all of the region to a temperature showing an isotropic phase or a cholesteric liquid crystal phase, the heated region is determined by selecting an appropriate cooling rate according to a selected wavelength for which immobilization is desired. By cooling to a temperature below, the desired cholesteric reflection color can be fixed and recording can be performed.
In the reversible recording material characterized in that the recording can be erased by heating again, the recording material contains two or more kinds of compounds, and the reflection color can be fixed in a glass state as the first compound. A reversible recording material comprising a cholesteric liquid crystal compound and an optically active compound as a second compound. 2) The reversible recording material according to 1), wherein the second compound is a liquid crystal compound. 3) The reversible recording material according to 1) or 2), wherein the cholesteric liquid crystal compound as the first compound and / or the second compound has a glass transition point of 30 ° C or higher. 4) The reversible recording material according to any one of claims 1 to 3, wherein the cholesteric liquid crystal compound as the first compound and / or the second compound has a molecular weight of 10,000 or less. 5) The reversible recording material according to 4), wherein the cholesteric liquid crystal compound as the first compound and / or the second compound has a molecular weight of 900 to 2,000. 6) The reversible recording material according to any one of 1) to 5), wherein the reflection color can be fixed at room temperature. 7) The selective reflection wavelength range is within the visible light range 1) to
The reversible recording material according to any one of 6). 8) The cholesteric liquid crystal compound constituting the recording layer is
The reversible recording material according to any one of 1) to 7), which is at least one compound represented by the following formula (a) or (b):

Embedded image Z—O—CO— (CH ₂ ) m—C≡C—C≡C— (CH ₂ ) n——CO—O—Y (a)

Embedded image Z—O—CO— (CH ₂ ) p—CO—O—Y (b) (wherein Z and Y each independently represent a cholesteryl group, a stigmasteryl group, a dehydroisoandrosteryl group) ,
R represents a hydrogen atom or an alkyl group, wherein m and n are each independently an integer of 1 to 10, p is an integer of 1 to 20, and at least one of Z and Y is a cholesteryl group or a stigmaster; Represents a ril group or a dehydroisoandrosteryl group. 9) The two types of cholesteric liquid crystal compounds constituting the recording layer may be any one of 1) to 8) in which in formula (a), both Z and Y are compounds having a cholesteryl group and both are compounds having a stigmasteryl group. A reversible recording material according to any one of the above. 10) The two types of cholesteric liquid crystal compounds constituting the recording layer are, in the formula (a), both Z and Y compounds of a cholesteryl group and both compounds of a dehydroisoandrosteryl group 1) to 8) The reversible recording material according to any one of the above. 11) The reversible recording material according to any one of 1) to 7), wherein the two kinds of cholesteric liquid crystal compounds constituting the recording layer are a compound represented by the formula (a) and a compound represented by the formula (b). 12) The reversible recording material according to any one of 1) to 11), which has a region in which the reflection wavelength does not change even when the temperature changes. 13) One of the two types of cholesteric liquid crystal compounds constituting the recording layer is a compound in which both Z and Y are cholesteryl groups in the formula (a), and the other is a compound having n = m = 8 in the formula (a). There is a compound in which both Z and Y are stigmasteryl groups, and the mixing ratio of the latter compound is
The reversible recording material according to 12), which is less than 10% by weight of the whole. 14) Two types of cholesteric liquid crystal compounds constituting the recording layer are a compound in which both Z and Y are cholesteryl groups in the formula (a) and n = m = 8, and a compound in the formula (b) where both are cholesteryl. And n = 18, wherein the mixing ratio of the compound of the formula (b) is 20
12) The reversible recording material according to 12), wherein the content is more than 40% by weight and less than 40% by weight. 15) A rewritable card having a thermosensitive recording layer using the reversible recording material according to any one of 1) to 14). 16) Digital paper having a thermosensitive recording layer using the reversible recording material according to any one of 1) to 14).

Hereinafter, the present invention will be described in detail. FIG.
It is a phase change model of a cholesteric liquid crystal compound,
As the crystal phase is heated, it becomes an isotropic phase at or above the melting point. When it is cooled down to a temperature range showing a cholesteric liquid crystal phase, a selective reflection color according to the temperature is obtained. In general, many materials exhibit short-wavelength colors on the high-temperature side and long-wavelength colors on the low-temperature side, but materials exhibiting a cholesteric liquid crystal phase in a relatively high-temperature region of about 80 ° C. to 150 ° C. are preferable. When the cholesteric liquid crystal phase is gradually cooled to about room temperature, it is crystallized and becomes cloudy due to light scattering. At this time, the number of recording layers is +
When it is thinner than μm, it may be observed as almost transparent.

When the cholesteric liquid crystal phase showing various selective reflection colors depending on the temperature is rapidly cooled to about room temperature at once,
It becomes a glassy solid (cholesteric glass phase) substantially retaining the helical molecular arrangement of the cholesteric liquid crystal phase, and the selective reflection color depending on the helical pitch is fixed. At this time, by providing a light absorbing layer for absorbing the light of the wavelength transmitted without being selectively reflected among the light incident on the choleslitech glass phase, only the light of the selectively reflected wavelength is observed, and the contrast is increased. Is improved. Also, by changing the quenching rate when cooling from the isotropic phase to about room temperature, the selective reflection color of the cholesteric glass phase can be changed. When the quenching speed is high, the selective reflection color of short wavelength appearing at high temperature can be fixed, and when the quenching speed is low, the selective reflection color of long wavelength appearing at low temperature can be fixed.

By heating the once recorded cholesteric glass phase again to a high temperature and changing it to an isotropic phase or a liquid crystal phase, the recording is erased, and new information is recorded under another cooling condition, whereby any arbitrary information is recorded. A recording section showing a selective reflection color can reversibly record. Choles Retech glass phase 1
Even when reheated to a temperature of about 00 ° C., a crystallized cloudy state can be recorded. However, depending on the material, the cholesteric glass phase may directly transition to the liquid crystal phase. Here, the molecular weight of the cholesteric liquid crystalline compound having a medium molecular weight is 900.
If it is smaller than that, crystallization occurs even under rapidly cooling conditions, and the cholesteric glass phase may not be fixed. This is considered to be due to the rapid reorientation of the molecules due to the rapid cooling.
On the other hand, if the molecular weight is larger than 10,000, it may be difficult to perform practical recording or erasing in one pixel in about several hundred milliseconds or less.

The present invention is characterized in that a mixture containing at least a cholesteric liquid crystal compound and an optically active compound is used as a recording material. Here, "optically active compound"
Is a compound that has a molecular structure without a plane of symmetry.A plane of symmetry is the cutting of a molecule when it is cut on one side and one part is a reflection image of the other part. It is a face. Examples of such optically active compounds include cholesterol, dihydrocholesterol, stigasterol, dehydroisoandrosterol, sasasapogenin, mannitol, epiandrosterone, campesterol, 1,3-butanediol, 1,1 ′ -Bi-2-naphthol and the like. In general, it is known that a cholesteric liquid crystal can be obtained by mixing an optically active compound with a nematic liquid crystal that is not optically active, but in the present invention, a cholesteric liquid crystal that can fix a reflection color in a glass state is further provided with an optically active compound. Is mixed, the strength of intermolecular interaction changes compared to when each is used alone, and the temperature range of the liquid crystal phase, the refractive index, and the width of the helical pitch of the cholesteric liquid crystal change accordingly. The temperature characteristic of the reflection wavelength can be changed (the present inventions 1 and 2).

When the cholesteric liquid crystal compound used in the present invention has a glass transition point of less than 30 ° C., it is not possible to stably maintain a reflected color at room temperature, and therefore, the compound must have a glass transition point of 30 ° C. or more. , And polymers are difficult to reversibly record by reheating, so that the molecular weight is 10,000.
Or less, and preferably contains at least one having a molecular weight of 2000 or less (the present invention 3 to 3).
5). When a cholesteric liquid crystal compound having a molecular weight of 2,000 or less is used as the second optically active compound constituting the recording layer, the cholesteric liquid crystal compound having a molecular structure close to that of the cholesteric liquid crystal compound as the first compound has a cholesteric glass phase. Thermal stability is high, which is preferable (Invention 5).

The cholesteric liquid crystal compound includes:
Those having a temperature characteristic such that the reflection color can be fixed at room temperature are preferable. Further, it is preferable that the selective reflection wavelength exists in a visible light region of about 400 to 700 nm in a normal state, and in this case, it can be visually recognized by a human. However, in the case of reading by a machine or the like, the selective reflection wavelength may exist in the ultraviolet region or the infrared region (the present inventions 6 and 7).

Preferred examples of the liquid crystal compound used in the present invention include compounds represented by the above formula (a) or (b) (Invention 8). A specific example of such a cholesteric liquid crystal compound having a medium molecular weight is shown in FIG.
-8, III-6, II-18, I-8-DHIA, I-8
-Stig and I-8-DiHC (III-
6 is a compound other than the above (a) and (b)), and these compounds are preferable because a visible wavelength is obtained and a glass state is stable at room temperature. However, the compounds are not limited to these compounds as long as they exhibit the recording characteristics of the cholesteric glass phase described above.

Further, by mixing and mixing two or more of these compounds, the temperature characteristic of the reflection wavelength, which is a characteristic of the reversible recording material, can be easily changed, and the reflection color can be fixed at room temperature. A reversible recording material which is easy to rewrite and has a selective reflection wavelength range within a visible light region can be obtained (the present inventions 8, 9, and 11). In the present invention 10, the temperature characteristics of the reflection wavelength can be shifted to the shorter wavelength side by mixing and mixing two or more of these compounds. Furthermore, in the present inventions 12 to 14, for the first time, it was found that by changing the mixing ratio, it was possible to have a region where the reflection wavelength did not change even when the temperature changed, and the problem of color bleeding during heating printing was found. Was solved. The cholesteric liquid crystal compound as the first or second compound used in the present invention may be used by mixing a plurality of kinds.

The thickness of the heat-sensitive recording layer is 0.5 to 50 μm,
Preferably, it may be appropriately selected from the range of 1 to 20 μm. If the heat-sensitive recording layer is too thin, the reflectance of the display image at a wavelength at which the maximum reflection is obtained becomes low, so that the contrast of the displayed image decreases. If the heat-sensitive recording layer is too thick, the light absorption in the heat-sensitive recording layer increases and the contrast of the displayed image decreases. The heat-sensitive recording layer is preferably composed of only a liquid crystal compound exhibiting selective reflection, but may contain a binder resin or spacer particles. Examples of the binder resin include polyvinyl chloride, polyvinyl acetate, epoxy resin, phenoxy resin, acrylic resin, polyurethane, polyester, and the like. As the spacer particles, those used for general liquid crystal displays can be used.

Next, an embodiment of the present invention will be described. A cholesteric liquid crystal compound having a molecular weight of 2000 or less and an optically active compound are dissolved in an appropriate ratio in an organic solvent,
After stirring and drying, a cholesteric liquid crystal mixture is obtained. At this time, other liquid crystal compounds, polymer compounds, and the like may be appropriately mixed according to the desired characteristics. The mixture is sandwiched between two substrates and heated by a heating means to a temperature at which the cholesteric liquid crystal mixture becomes a transparent state, and then cooled by a cooling means at a certain cooling rate, and the cholesteric reflection wavelength at each temperature is changed to a UV-visible wavelength. Measure with a spectrometer.

Referring to FIGS.
The temperature dependence of the reflection wavelength of the cholesteric liquid crystal mixture when the mixture ratio was changed was shown. From each figure, it can be seen that the temperature dependence of the reflection wavelength can be freely changed only by changing the mixture ratio. In addition, these cholesteric liquid crystal mixtures can be easily changed to a cholesteric glass state by rapidly cooling from a temperature at which a reflected color is obtained to room temperature using water or the like, and the reflected color can be fixed. Further, when the recording material in the cholesteric liquid crystal state is heated to a temperature at which the recording material becomes an isotropic phase, the recording is erased, and recording can be performed again by the same procedure (the present inventions 9 to 11).

As the heating means, appropriate heating means and heating conditions may be selected according to the required heating rate and the like, and specifically, a hot plate, a laser beam, a thermal head and the like can be used. However, the present invention is not limited to these. As the cooling means, appropriate cooling means and cooling conditions may be selected according to the required cooling rate and the like, and specifically, water cooling, air cooling, a metal plate, a glass plate, or the like can be used. However, the present invention is not limited to these. As the substrate, a plastic film such as glass, polyethersulfone (PES), or polyethylene terephthalate (PET) can be used, but is not limited thereto.

A substrate having an alignment film formed on the surface in contact with the recording layer can also be used. For example, the substrate can be manufactured by the following method. First, a soluble polyimide solution (JSR Optmer AL3046, manufactured by Nippon Synthetic Rubber Co., Ltd.) was used, and a coating solution in which this was dissolved to a concentration of 1% by weight was spin-coated on a washed glass substrate and dried. To form a resin thin film. Next, the general L
A rubbing cloth for a CD alignment film is stuck and placed so as to be able to contact and separate from the polyimide surface. Here, the glass substrate or the plane member is reciprocated, and the rubbing cloth and the polyimide surface are rubbed in one direction by making uniform contact with the rubbing cloth only when moving in one direction. The substrate is used as a reversible recording medium substrate such that the rubbed polyimide film surface faces inside.

[0019]

EXAMPLES The present invention will be described below in more detail with reference to examples, but the present invention is not limited to these examples.

Example 1 I-8 [in the formula (a), Z and Y are cholesteryl groups,
compound in which m = n = 8], I-8-Stig [in the formula (a), Z and Y are stigmasteryl groups, and m =
n = 8] were mixed in the proportions of 5, 10 and 30% by weight, both were dissolved in dichloromethane, stirred and dried to prepare three types of liquid crystal mixtures. About 10 mg of this mixture is 1.8 cm × 2.5 cm × 0.12 m
m on a hot plate
When the liquid crystal mixture was heated to ° C. to obtain an isotropic phase and the temperature was lowered, the reflection color was visually confirmed. As a result, the reflection wavelength shifted to a longer wavelength as the temperature was lowered. On the other hand, when the reflection wavelength at 100 ° C. was measured with a microscope ultraviolet-visible spectrometer, the results were as shown in Table 1. Even at the same temperature, the wavelength could be shifted to a longer wavelength by changing the mixing ratio. That is, it was found that the temperature dependence of the reflection wavelength could be easily changed by changing the mixture ratio of the liquid crystal mixture.

[0021]

[Table 1]

Example 2 I-8 [in the formula (a), Z and Y are cholesteryl groups,
Compound with m = n = 8] and 10-20% by weight of I-8-DHIA [compound of formula (a) wherein Z and Y are dehydroisoandrosteryl groups and m = n = 8]
, And the two were dissolved in dichloromethane, stirred and dried to prepare two types of liquid crystal mixtures.
About 10 mg of this mixture is 1.8 cm × 2.5 cm ×
When sandwiched between glass plates of 0.12 mm, heated to 130 ° C. on a hot plate to make an isotropic phase, and the reflection color when the temperature was lowered was visually confirmed, the liquid crystal mixture of any mixing ratio was
As the temperature decreased, the reflection wavelength shifted to a longer wavelength. on the other hand,
When the reflection wavelength at 80 ° C. was measured with a microscope ultraviolet-visible spectrometer, the results were as shown in Table 2. Even at the same temperature, the wavelength could be shifted to a shorter wavelength by changing the mixing ratio. That is, it was found that the temperature dependence of the reflection wavelength could be easily changed by changing the mixture ratio of the liquid crystal mixture.

[0023]

[Table 2]

Example 3 I-8 [in the formula (a), Z and Y are cholesteryl groups,
II-18 [compound of formula (b), wherein Z and Y are cholesteryl groups and n = 18] are mixed with 20, 30 and 40% by weight of a compound having m = n = 8 and dichloromethane. Are dissolved in water, stirred and dried.
Different kinds of liquid crystal mixtures were prepared. About 10mg of this mixture
Was sandwiched between glass plates of 1.8 cm × 2.5 cm × 0.12 mm, heated to 130 ° C. on a hot plate to form an isotropic phase, and the reflection color when the temperature was lowered was visually confirmed. The reflection wavelength of the liquid crystal mixture shifted to a longer wavelength as the temperature decreased. On the other hand, when the reflection wavelength at 90 ° C. was measured by a microscopic ultraviolet-visible spectrometer, Table 3 was obtained.
Thus, even at the same temperature, it was possible to rapidly shift to a longer wavelength by changing the mixing ratio. That is, it was found that the temperature dependence of the reflection wavelength could be easily changed by changing the mixture ratio of the liquid crystal mixture.

[0025]

[Table 3]

Example 4 I-8 [in the formula (a), Z and Y are cholesteryl groups,
compound in which m = n = 8], I-8-Stig [in the formula (a), Z and Y are stigmasteryl groups, and m =
n = 8] were mixed in the proportions of 5, 10 and 30% by weight, both were dissolved in dichloromethane, stirred and dried to prepare three types of liquid crystal mixtures. About 10 mg of this mixture is 1.8 cm × 2.5 cm × 0.12 m
m on a hot plate
C. to obtain an isotropic phase, and the reflection wavelength when the temperature was lowered was measured by a microscopic UV-visible spectrometer. From the measurement results shown in FIG. 4, it can be seen that the temperature dependence of the reflection wavelength can be changed by changing the mixture ratio of the liquid crystal mixture. Further, at a mixing ratio of 5% by weight, a region where the reflection wavelength was unchanged at about 630 nm was formed over a temperature range of 70 to 80 ° C. When this area was formed, a reflected color was produced on a hot plate at 75 ° C., and when rapidly cooled with water at room temperature, an orange color recording without blurring due to uneven heating, thermal diffusion, etc. was obtained.

Example 5 I-8 [in the formula (a), Z and Y are cholesteryl groups,
II-18 [compound of formula (b), wherein Z and Y are cholesteryl groups and n = 18] are mixed with 20, 30 and 40% by weight of a compound having m = n = 8 and dichloromethane. Are dissolved in water, stirred and dried.
Different kinds of liquid crystal mixtures were prepared. About 10mg of this mixture
Was sandwiched between 1.8 cm × 2.5 cm × 0.12 mm glass plates, heated to 130 ° C. on a hot plate to form an isotropic phase, and the reflection wavelength when the temperature was lowered was measured by a micro-ultraviolet-visible spectrometer. From the measurement results shown in FIG. 6, it is understood that the temperature dependence of the reflection wavelength can be changed by changing the mixture ratio of the liquid crystal mixture. Further, at a mixing ratio of 30%, a region where the reflection wavelength was not changed at about 560 nm was formed over a temperature range of 70 to 80 ° C. When this area was formed, a reflected color was produced on a hot plate at 80 ° C. and rapidly cooled with water at room temperature. As a result, green recording was obtained without bleeding due to uneven heating and heat diffusion.

Example 6 I-8 [in the formula (a), Z and Y are cholesteryl groups,
Compound with m = n = 8], 10-20% by weight of I-8-DHIA [compound of formula (a) wherein Z and Y are dehydroisoandrosteryl groups and m = n = 8] , And the two were dissolved in dichloromethane, stirred and dried to prepare two types of liquid crystal mixtures. About 10 mg of this mixture is 1.8 cm × 2.5 cm
It was sandwiched between glass plates of × 0.12 mm, heated to 130 ° C. on a hot plate to form an isotropic phase, and the reflection wavelength when the temperature was lowered was measured by a micro-ultraviolet-visible spectrometer. From the measurement results shown in FIG. 6, it is understood that the temperature dependence of the reflection wavelength can be shifted to the shorter wavelength side by changing the mixture ratio of the liquid crystal mixture.

[0029]

According to the present invention, a reversible recording material capable of easily changing the temperature characteristic of the reflection wavelength can be obtained. According to the fifth aspect, a reversible recording material that can be easily rewritten is obtained. According to the sixth to ninth and eleventh aspects of the invention, it is possible to obtain a reversible recording material that can fix a reflection color at room temperature and has a selective reflection wavelength range in a visible light region. According to the tenth aspect, a reversible recording material in which the temperature characteristic of the reflection wavelength shifts to the shorter wavelength side can be obtained. According to the present inventions 12 to 14, further, as a temperature characteristic of the reflection wavelength, even if the temperature changes, there is a region where the wavelength does not change at the red or green reflection wavelength, by having such a region,
At the time of printing by heating, color bleeding due to heat diffusion, uneven heating and the like is eliminated, and a reversible recording material capable of performing clear printing can be obtained. According to the inventions 15 and 16, it is possible to provide a rewritable card or digital paper utilizing the excellent physical properties of the reversible recording materials of the inventions 1 to 14.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a rewritable full-color display device using cholesteric liquid crystal.

FIG. 2 is a diagram showing a phase change model of a cholesteric liquid crystal compound.

FIG. 3 is a view showing an example of a cholesteric liquid crystal compound having a medium molecular weight used in the present invention. (A) is a diagram showing I-8. (B) is a diagram showing III-6. (C) II-
FIG. (D) is a diagram showing I-8-DHIA.
(E) is a diagram showing I-8-Stig. (F) is I-
The figure which shows 8-DiHC.

FIG. 4 is a diagram showing the temperature dependence of the reflection wavelength of the mixed cholesteric liquid crystal compound of Example 4 when the mixing ratio is changed.

FIG. 5 is a graph showing the temperature dependence of the reflection wavelength of the mixed cholesteric liquid crystal compound of Example 5 when the mixing ratio is changed.

FIG. 6 is a graph showing the temperature dependence of the reflection wavelength of the mixed cholesteric liquid crystal compound of Example 6 when the mixing ratio is changed.

 ──────────────────────────────────────────────────続 き Continued on front page (74) The above four agents 100094466 Patent Attorney Eiji Tomomatsu (71) Applicant 301021533 National Institute of Advanced Industrial Science and Technology 1-3-1 Kasumigaseki, Chiyoda-ku, Tokyo (74) One sub-agent 100094466 Patent Attorney Eiji Tomomatsu (72) Inventor Ero 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (72) Inventor Hiroyuki Sugimoto 1-chome, Nakamagome, Ota-ku, Tokyo No.3-6 Ricoh Co., Ltd. (72) Inventor Shigenobu Hirano 1-3-6 Nakamagome, Ota-ku, Tokyo No.3 Ricoh Co., Ltd. (72) Nobuyuki Tamaki 1-1, Higashi 1-1, Tsukuba, Ibaraki, Japan Within the Institute of Technology, Engineering and Technology (72) Inventor Hiroo Matsuda 1-1, Higashi 1-1, Tsukuba, Ibaraki Prefecture Within the Institute of Materials Science and Technology, Institute of Industrial Science and Technology (72) Inventor Yoshiyoshi Kida Shige 4-5 Kawaramachi, Kashiwara-shi, Osaka F-term in Okamura Oil Co., Ltd. (Reference) 2H026 AA09 BB48 2H088 EA62 GA03 JA21 MA20 2H111 HA07 HA12

Claims (16)

[Claims] A temperature at which a cholesteric liquid crystal-based recording material is sandwiched between two substrates, at least one of which is transparent, and the recording material exhibits an isotropic phase or a cholesteric liquid crystal phase in a part or all of the recording material. After heating to
By rapidly cooling the heated region to a certain temperature or lower, or after the recording material is heated to a temperature at which a part or all of the region exhibits an isotropic phase or a cholesteric liquid crystal phase, By cooling the selected area to a predetermined temperature or less by selecting an appropriate cooling rate according to the selected wavelength for which immobilization is desired, it is possible to fix and record a desired cholesteric reflection color,
Further, by reheating, in a reversible recording material characterized in that recording can be erased, the recording material contains two or more compounds, and the first compound has a reflection color in a glassy state. A reversible recording material comprising a fixable cholesteric liquid crystal compound and an optically active compound as a second compound. 2. The reversible recording material according to claim 1, wherein the second compound is a liquid crystal compound. 3. The cholesteric liquid crystal compound as the first compound and / or the second compound has a glass transition point of 30 ° C.
The reversible recording material according to claim 1 or 2, wherein: 4. The reversible recording material according to claim 1, wherein the cholesteric liquid crystal compound as the first compound and / or the second compound has a molecular weight of 10,000 or less. 5. The cholesteric liquid crystal compound as the first compound and / or the second compound has a molecular weight of 900 to 20.
5. The reversible recording material according to claim 4, wherein the number is 00. 6. The method according to claim 1, wherein the reflection color can be fixed at room temperature.
A reversible recording material according to any one of the above. 7. The reversible recording material according to claim 1, wherein a selective reflection wavelength range is within a visible light region. 8. The reversible recording material according to claim 1, wherein the cholesteric liquid crystal compound constituting the recording layer is at least one compound represented by the following formula (a) or (b). Embedded image Z—O—CO— (CH ₂ ) m—C≡C—C≡C— (CH ₂ ) n——CO—O—Y (a) CH ₂ ) p-CO-OY (b) (wherein Z and Y each independently represent a cholesteryl group, a stigmasteryl group, a dehydroisoandrosteryl group,
R represents a hydrogen atom or an alkyl group, wherein m and n are each independently an integer of 1 to 10, p is an integer of 1 to 20, and at least one of Z and Y is a cholesteryl group or a stigmaster; Represents a ril group or a dehydroisoandrosteryl group. ) 9. The two types of cholesteric liquid crystal compounds constituting the recording layer are, in the formula (a), a compound having both cholesteryl groups Z and Y and a compound having both stigmasteryl groups. A reversible recording material according to any one of the above. 10. The two kinds of cholesteric liquid crystal compounds constituting the recording layer are, in the formula (a), a compound in which both Z and Y are cholesteryl groups and a compound in which both are dehydroisoandrosteryl groups. 9. The reversible recording material according to any one of items 1 to 8. 11. The reversible recording material according to claim 1, wherein the two kinds of cholesteric liquid crystal compounds constituting the recording layer are a compound represented by the formula (a) and a compound represented by the formula (b). 12. The reversible recording material according to claim 1, which has a region in which the reflection wavelength does not change even if the temperature changes. 13. One of two types of cholesteric liquid crystal compounds constituting a recording layer is a compound of formula (a) in which both Z and Y are cholesteryl groups, and the other is a compound of formula (a)
13. The reversible recording material according to claim 12, wherein n = m = 8, wherein Z and Y are both stigmasteryl groups, and the mixing ratio of the latter compound is less than 10% by weight of the whole. . 14. The two types of cholesteric liquid crystal compounds constituting the recording layer include a compound in which both Z and Y are cholesteryl groups in the formula (a) and n = m = 8, and a compound in the formula (b) Both are cholesteryl groups and n = 1
13. The reversible recording material according to claim 12, wherein the mixing ratio of the compound of formula (b) is more than 20% by weight and less than 40% by weight. 15. A rewritable card having a thermosensitive recording layer using the reversible recording material according to claim 1. 16. A digital paper having a heat-sensitive recording layer using the reversible recording material according to claim 1. Description: