JP2003268374A - Liquid crystal composition and recording display medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal composition which can form a liquid crystal layer that does not impair metallic gloss of a cholesteric reflection color even when the amount used of the liquid crystal compound is reduced, that has sufficient strength, and that excels in adhesion to a protective layer, and which can achieve a cost reduction. <P>SOLUTION: The composition contains a cholesteric liquid crystal compound and a gelling agent. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rewritable liquid crystal composition which constitutes a liquid crystal layer capable of recording display with a heat-sensitive specific color or full color, and a recording display medium using the liquid crystal composition.

[0002]

2. Description of the Related Art Color photographs and color copies are known as recording materials capable of recording full color and non-rewritable. Rewritable and not full-color recording materials include thermal recording materials containing long-chain alkylcarboxylic acid derivatives such as behenic acid, optical recording materials using photochromic compounds such as spiropyran derivatives, and other memory such as magnetic and magneto-optical. The material is known.

Conventional recording materials have not been compatible with both full color and rewritable characteristics. Certainly, there are some display materials such as TV and liquid crystal display that change the display and there are full-color display materials, but it is used as a thin card that fits in a wallet and displays images stably without power. It could not be used as a recording material because it could not be stored.

In recent years, rewritable full-color recording has been achieved by a new method using a liquid crystalline compound (Japanese Patent Laid-Open No. HEI 1).
1-224027, Japanese Patent No. 2946042,
JP-A-2000-7613).

The recording and displaying medium described in the above publication has a liquid crystal compound sandwiched between substrates. However, since the liquid crystal layer sandwiched between the substrates is composed only of the liquid crystal compound, the strength of the liquid crystal layer is high. Insufficiently, when providing a protective layer made of a resin on the liquid crystal layer, there was a problem that the adhesion with the protective layer was insufficient. Further, since the liquid crystal compound is generally expensive, there is also a problem that the recording display medium in which the liquid crystal layer is formed of only the liquid crystal compound is expensive.

[0006]

In view of the above-mentioned problems of the prior art, the present invention does not impair the metallic luster characteristic of the cholesteric reflection color even if the amount of the liquid crystal compound used is reduced, and is sufficient. An object of the present invention is to provide a liquid crystal composition which has a strength and can form a liquid crystal layer having excellent adhesion to a protective layer and which can reduce the cost, and a recording display medium using the liquid crystal composition.

[0007]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that the gelling agent functions as a binder for liquid crystal compounds even when used in a small amount and does not develop color. Without changing the characteristics of the liquid crystal compound such as not being able to fix the state even if the color is developed, the color changing, the relationship between the temperature and the color shifting, and taking advantage of the metallic luster characteristic of the cholesteric reflection color. The present invention has been completed based on the finding that a liquid crystal layer having high strength and adhesiveness with a protective layer can be produced, and cost can be reduced because the amount of a liquid crystal compound used can be reduced.

That is, the liquid crystal composition of the present invention is characterized by containing a cholesteric liquid crystal compound and a gelling agent.

The recording and displaying medium of the present invention is characterized by having a liquid crystal layer made of the above liquid crystal composition on a substrate.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.

The cholesteric liquid crystal compound is not particularly limited, but a compound that develops a color depending on the heating temperature in a liquid crystal state and retains the colored state by rapidly cooling from the temperature (a compound capable of fixing the color) is preferable. .

Examples of the cholesteric liquid crystal compound which develops a color in a liquid crystal state depending on the heating temperature and retains the colored state by quenching from the temperature include the following compounds.
Examples of such compounds include

Dibasic acid dicholesteryl ester Specifically, dibasic acid dicholesteryl ester represented by the following general formula (I) can be mentioned. _{YO-CO (CH 2) o} -R- (CH 2) p CO-OY ··· (I) ( wherein, Y represents a cholesterol residue obtained by removing a hydroxyl group bonded thereto cholesterol, R represents Are any of the groups shown in the following (a) to (k), wherein o and p are
They are the same or different and each represents an integer of 1 to 20.
In addition, in the following (f), l represents an integer of 2 to 20. )

[0014]

[Chemical 1]

A cholesteric liquid crystal compound having a molecular weight of 2000 or less and a glass transition temperature of 35 ° C. or more.

The molecular weight of this compound is preferably 500.
~ 1500, more preferably 700-1200,
The glass transition temperature is preferably 50 ° C or higher, more preferably 70 to 110 ° C.

Particularly preferred cholesteric liquid crystal compounds include compounds represented by the following general formula (II). Z-O-CO-Q-CO-O-Z '... (II) (In formula, Z and Z'are each independently a cholesteryl group, a hydrogen atom or an alkyl group, and Q is a C2-C20. Represents a divalent hydrocarbon group, and at least one of Z and Z ′ represents a cholesteryl group)

Examples of the divalent hydrocarbon group include groups represented by the following general formula (III). _{- (CH 2) q -C≡C-} C≡C- (CH 2) r - ··· (III) ( wherein q and r are each independently an integer of 1 or more, provided that the q and r Of total shall not exceed 30)

As preferred examples, 10,12-docosadiyne dicarboxylic acid dicholesteryl ester, eicosane dicarboxylic acid dicholesteryl ester, 10,12-pentacosadiyne dicarboxylic acid cholesteryl ester, dodecadicarboxylic acid dicholesteryl ester, 12,14
-Hexacosadiyne dicarboxylic acid dicholesteryl ester and the like.

A mixture comprising at least two cholesteryl ester compounds and having a cholesteryl ester compound which has a reflection peak in the liquid crystal state outside the visible region or does not take the liquid crystal state.

Such a mixture exhibits a temperature range different from the liquid crystal temperature range exhibited by the cholesteryl ester compound alone, and also has a fixed reflection wavelength region. Therefore, by appropriately setting the compounds to be mixed and the mixing ratio, the liquid crystal The temperature range and the fixed reflection wavelength region can be controlled arbitrarily. As a result, it becomes possible to fix the color at a temperature lower than that of the compound alone. Also, in the case of a mixture of compounds that cannot fix colors, a temperature range different from the liquid crystal temperature range shown by a single substance is shown, and the range of fixed reflection wavelength is also different, so that the colors can be fixed. Become.

Examples of the mixture include a mixture of dicholesteryl ester compounds, a mixture of a dicholesteryl ester compound and a monocholesteryl ester compound, and the like. A mixture of a compound capable of fixing color and a compound not capable of fixing color, a compound not capable of fixing color. It may be any mixture of the compounds, but at least one of the compounds other than the compound that cannot fix the color is in a liquid crystal state, which develops color depending on the heating temperature, and maintains the developed state by quenching from the temperature, That is, a compound that fixes the color is preferable.

As the dicholesteryl ester compound,
Although not particularly limited, examples thereof include dibasic acid dicholesteryl ester, and specifically include dibasic acid dicholesteryl ester represented by the following general formula (IV):
When s is odd, it is a compound that can fix the color, and when s is even, it is a compound that cannot fix the color. _{YO-CO (CH 2) s} -O-R'-O- (CH 2) s CO-OY ··· (IV) ( wherein, Y represents a cholesteryl group, R 'is p- phenylene or 4, 4'-biphenylene, s is 1 to 20
The number of)

Further, examples of the monocholesteryl ester compound include compounds represented by the following general formula (V). This is a compound that cannot fix color or can hardly fix it. During _{YO-CO (CH 2) t} -O-R'-OH ··· (V) ( wherein, Y represents a cholesteryl group, R 'represents a p- phenylene or 4,4'-biphenylene, t is 1-20
The number of)

Among these, a mixture of dibasic acid dicholesteryl esters represented by the general formula (IV), that is, a mixture of a compound capable of fixing a color and a compound not capable of fixing a color, represented by the general formula (IV) Of the dibasic acid dicholesteryl ester that can fix the color and the general formula (V)
A mixture with a monocholesteryl ester represented by

The mixing ratio is not particularly limited, but is 2
When mixing two types of compounds, the weight ratio of the two is 1 :.
It is preferably 0.8 to 1.2. Further, it is preferable to contain a compound capable of fixing a color in an amount of 20% by weight or more, more preferably 40% by weight to 60% by weight. With such a mixing ratio, the liquid crystal temperature range and the reflection wavelength range can be widened.

As a mixing method, a conventionally known method can be used. For example, the compound to be mixed is dissolved in a solvent such as methylene chloride which dissolves these, and the solvent is distilled off, followed by vacuum drying. By doing so, a powdery mixture can be obtained.

A group having at least one group capable of intermolecular hydrogen bonding, having a steroid skeleton, and having 3 to 20 carbon atoms.
A cholesteric liquid crystal containing a superstructured substance having an alkylene group.

Here, the superstructured substance is a compound of a type having a supramolecular structure, that is, a structure having a geometrical order due to the interaction of weak forces acting between molecules, specifically hydrogen bonding. It is a substance that forms a self-assembly (self-organization, self-assembly).

The group capable of intermolecular hydrogen bonding is not particularly limited, and examples thereof include a carboxyl group, a hydroxyl group, an amide group, an amino group, an imino group, a nitrilo group, and a nitrogen-containing heterocyclic group such as a pyridyl group. , An imidazolyl group, an aminopyridyl group, and a uracil group.

The intermolecular hydrogen bond to be formed is not particularly limited, but is preferably a carboxyl group, a hydroxyl group, an amide group, a heterocyclic group having nitrogen such as a carboxyl group and a pyridyl group, a hydroxyl group and a pyridyl group. And an intermolecular hydrogen bond formed by a heterocyclic group having nitrogen such as a group, a carboxyl group and a nitrilo group, or a diaminopyridyl group and a uracil group.

The group having a steroid skeleton is not particularly limited, but a cholesterol residue obtained by removing the hydroxyl group bonded to it from cholesterol, a dihydrocholesterol residue obtained by removing the hydroxyl group bonded to it from dihydrocholesterol, Cholic acid residue obtained by removing the hydroxyl group bonded to it from cholic acid,
β-sitosterol residue obtained by removing the hydroxyl group bound to it from β-sitosterol, α-spinasterol residue obtained by removing the hydroxyl group bonded to it from α-spinasterol, and the like, among which various Cholesterol residues and dihydrocholesterol residues are preferable because they can exhibit a color.

The alkylene group has 3 to 20 carbon atoms,
It is preferably 3 to 11. If the carbon number exceeds 20,
The viscosity in the liquid crystal state of the superstructure may increase and the response to temperature change may be delayed, and if the carbon number is less than 3, it is difficult to fix the cholesteric reflection color by the quenching operation from the liquid crystal state of the superstructure, which is preferable. Absent.

The molecular weight of the superstructured material is preferably 385.
To 900, more preferably 500 to 800. If the molecular weight exceeds 900, the viscosity in the liquid crystal state of the superstructure may increase and the response to temperature change may be delayed. If the molecular weight is less than 385, the cholesteric reflection color is fixed by the quenching operation from the liquid crystal state of the superstructure. May be difficult to convert.

Specific examples of the superstructured substance include the cholesteryl ester compounds shown below.

[0036]

[Chemical 2]

[0037]

[Chemical 3]

(In the formula, Y represents a cholesterol residue obtained by removing a hydroxyl group bonded to cholesterol from n, n represents an integer of 3 to 20, and X represents —OH,
_{-Me, -OMe, -NO 2, -Cl} , -Br, -I,
Represents —CN, m represents an integer of 0 to 2, and when m = 2, the same or different substituents may be used. )

Specific examples of the cholesteric liquid crystal include compounds represented by the general formulas (1) to (1 ″), compounds represented by the general formulas (2) to (2 ″), and the general formula (3). ) And compounds in which n is an even number or n
A supramolecular compound formed by a combination of an even number and an odd number may be mentioned, and those having the same carbon number n may be used alone, or those having a different carbon number n may be combined. In the latter case, by appropriately setting the carbon number n and the mixing ratio,
The liquid crystal temperature and the wavelength range that can be fixed can be adjusted.

A combination of the compound represented by any one of the above general formulas (1) to (4) and the compound represented by any one of the above general formulas (5) to (5 ″), the above general formula (1) )
To (4) in combination with 4,4′-bipyridyl, and a compound represented by any of the general formulas (5) to (5 ″) in combination with terephthalic acid. In these cases, the liquid crystal temperature and the wavelength range that can be fixed can be adjusted by appropriately setting the mixing ratio of both, and the mixing ratio of the two is not particularly limited. It is preferable that the parts and the hydrogen acceptor are mixed in a molar ratio of 1: 2 to 2: 1.

The gelling agent is not particularly limited,
Those having good compatibility with the cholesteric liquid crystal compound are preferable. Specifically, for example, oligomeric ester made from polyhydric alcohol and fatty acid such as behenic acid, oligomeric ester composed of eicosanedioic acid and glycerin (for example, Nomcoat HK-G (manufactured by Nisshin Oil Co., Ltd.)), 12-
Hydroxystearic acid, for example (palmitic acid / 2-
Ethylhexanoic acid) dextrin fatty acid ester such as dextrin, sugar derivative such as sugar benzylidene derivative, for example, β-estradiol, steroidal compound having a group capable of hydrogen bonding such as methylandrostenediol (in the case of having an alkylene group, Alkylene groups having 2 or less carbon atoms), N-lauroyl-n-butylamide, linear and / or cyclic polyorganosiloxane having a group capable of hydrogen bonding, superstructure substances such as amino acid derivatives, and polyisobutylene. .

The content of the gelling agent is preferably 1 part by weight to 2 parts by weight with respect to 100 parts by weight of the cholesteric liquid crystal compound.
00 parts by weight, more preferably 1 part by weight to 10 parts by weight in the case of a superstructure substance, and 10 parts by weight to 150 parts by weight in the case of polyisobutylene. If it is less than 1 part by weight, the effect of the present invention may not be sufficiently obtained. If it exceeds 200 parts by weight, it will not develop color, the state cannot be fixed even if it develops color, the color will change, the relationship between temperature and color will shift, etc.
The characteristics of the cholesteric liquid crystal compound may change.

By the way, the cholesteric liquid crystal compound used in the present invention is in a crystalline state and has no fluidity near room temperature,
Although the state in which the reflection color is fixed is not glass because it is in a glass state, it is assumed in the present invention that the gelling agent has a three-dimensional network structure and is entangled with the liquid crystal compound near room temperature. It was As described above, the superstructured substance forms an aggregate. Since this aggregate can form a fibrous aggregate, it is known to gelate a liquid with a small amount of addition. The gelling agent, which has become a fibrous aggregate, is entangled in the interstices of the liquid crystal compound in a mesh shape, which was confirmed by observation with a scanning electron microscope (SEM).

Further, when the DSC of the composition of the present invention was measured, a change in peak was observed near the transition temperature peculiar to each component. That is, the melting point of the gelling agent and the phase transition point of the liquid crystal compound could be confirmed. It is considered that the liquid crystal substance and the gelling agent can retain their unique thermal properties in the state where the coexisting gelling agent forms a three-dimensional network structure around the liquid crystal molecules.

The composition of the present invention may contain additives such as dyes and antioxidants, and by using a dichroic dye, a cholesteric liquid crystal compound which does not show a reflection color in the visible portion is also used. You can The content of these additives is
It is preferably 10% by weight or less with respect to the cholesteric liquid crystal compound.

The recording and displaying medium of the present invention has a liquid crystal layer comprising the above composition on a substrate. The method for forming the liquid crystal layer is not particularly limited, and examples thereof include a method in which the composition is heated to a molten state and cast on a substrate. Further, as a method which does not require heating to a molten state, a method of forming a liquid crystal layer by dissolving the composition in an organic solvent and coating the solution on a substrate and then drying the composition to remove the organic solvent can be mentioned. To be

The coating method is not particularly limited, and a general method such as a spin coating method, a bar coating method, a reverse roll coating method or a gravure coating method can be used.
The organic solvent is not particularly limited as long as it can dissolve the composition of the present invention, and examples thereof include toluene, xylene, tetrahydrofuran and methylene chloride.

The organic solvent may be used at least in an amount capable of dissolving the composition of the present invention. In order to obtain a liquid crystal layer utilizing the metallic luster characteristic of the cholesteric reflection color, a cholesteric liquid crystal compound is used. It is preferable that the concentration of is as high as possible. Specifically, it varies depending on the combination of the composition used and the organic solvent, but in general, it is preferably used in the range of 100 parts by weight to 1500 parts by weight with respect to 100 parts by weight of the cholesteric liquid crystal compound.

As the base material, a polymer film, a thin glass plate, a metal plate or the like is used. When the recording layer is sandwiched by two base materials, one of the two base materials is at least a part of the base material. Transparency that allows light to pass through is required. Further, as will be described later, when light is used for writing or erasing a record, it is desirable that one substrate absorb the light.

As the material of the protective layer provided on the liquid crystal layer, acrylic resin, polyamide resin, polyimide resin, polyether sulfone resin, polyether ether imide resin, acrylic urethane resin, polyester resin, Polyolefin resin, synthetic resin such as UV-curable resin, inorganic material such as siloxane compound, organic / inorganic hybrid material such as organosiloxane, glass plate, etc. can be used, heat resistance, flexibility, adhesion to liquid crystal layer A material having excellent properties is appropriately selected, and for example, the above material is applied by a spin coating method, a reverse roll coating method, a gravure coating method, or in the case of a resin film or a glass plate, it is formed by laminating.

The recording / display medium of the present invention can record (write) or display a record by heating partially or entirely. A thermal head,
Any method such as a heating roll or a laser beam is possible. For heating that requires temperature control within the liquid crystal temperature range, either control the temperature of the thermal head or heating roll, adjust the laser beam intensity or spot diameter, or image after heating the whole to a certain temperature. It is possible to lower the temperature to the required temperature with a flat metal plate or rubber plate.

On the other hand, in order to fix the color of the cholesteric liquid crystal compound, it is necessary to rapidly cool the liquid crystal to a temperature below its glass transition temperature. For this purpose, the entire liquid crystal is cooled in a refrigerant or a cooled atmosphere. A method of immersing in a head, a method of contacting a part with a cooled head, or the like is adopted.

The recording / display medium of the present invention is, for example, a card, a sheet for overhead project, a label,
It can be used as a ticket or the like, and a back surface layer or the like may be further provided if necessary. For example, in the case of a label, a backing sheet is provided on the back surface of the recording / display medium via an adhesive layer.
In the case of a magnetic ticket, a magnetic recording layer made of a binder and a ferromagnetic powder is provided instead of the mount.

[0054]

EXAMPLES Example 1 A coating liquid prepared by dissolving 10 g of the following liquid crystal compound (Y represents a cholesterol residue) and 0.5 g of Nomcoat HK-G (manufactured by Nisshin Oil Co., Ltd.) in 100 g of toluene to give a thickness of 188 μm. Was coated on the black PET film of No. 1 by spin coating to form a liquid crystal layer having a thickness of 7 μm. Also,
For comparison, a liquid crystal layer was prepared using a coating liquid containing no gelling agent.

[0055] _{Y-O-CO- (CH 2} ) 8 -C≡C-C≡
_{C- (CH 2) 8 -CO-} O-Y

After heating the liquid crystal layer to a liquid crystal state to increase the smoothness of the surface, an ultraviolet curable resin was applied on the liquid crystal layer by spin coating and irradiated with ultraviolet rays to form a transparent protective layer. .

An adhesion test of the protective layer was carried out by peeling off the cellophane tape. As a result, the recording / display medium of the present invention was improved in adhesion as compared with the recording / display medium prepared by using the coating liquid containing no gelling agent. Was.

Example 2 1.0 g of the following liquid crystal compound (Y represents a cholesterol residue) and 0.01 g of 12-hydroxystearic acid were dissolved by heating to a thickness of 0.
Cast onto a 18 mm glass substrate. A glass substrate having the same thickness was covered thereon to produce a recording / display medium. The two pieces of glass were kept spaced by a spacer having a particle size of 10 μm.

When this recording / display medium is heated to 180 ° C., it becomes a blue cholesteric reflection color, and from this state, 0
When it was rapidly cooled to ℃, the blue color was fixed. When the transmission spectrum of the sample with the fixed reflection color was measured, the peak wavelength was 450 nm and the transmittance was 55%. This was the same value as that of the recording and display medium produced in the same manner except that the gelling agent was not added.

[0060]

[Chemical 4]

[0061]

As described above, according to the present invention, it has a metallic luster characteristic of the cholesteric reflection color,
It is possible to form a liquid crystal layer capable of clear display, having sufficient strength, and having excellent adhesion to the protective layer. Further, the amount of the liquid crystal compound used can be reduced without impairing the recording / displaying ability, and the cost can be reduced. Further, a thick liquid crystal layer can be formed. Also,
The fluidity in the liquid crystal state is suppressed, and the liquid crystal layer is well retained.

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2H088 EA22 GA03 GA11 JA23 MA01                       MA20                 4H027 BA02 BB07 BC08 BE05 DM01

Claims (5)

[Claims] 1. A liquid crystal composition comprising a cholesteric liquid crystal compound and a gelling agent. 2. The cholesteric liquid crystal compound is a cholesteric liquid crystal compound which, in a liquid crystal state, develops a color depending on a heating temperature, and is rapidly cooled from the temperature to maintain the colored state. The liquid crystal composition according to item 1. 3. The liquid crystal composition according to claim 1, wherein the content of the gelling agent is 1 part by weight to 200 parts by weight with respect to 100 parts by weight of the cholesteric liquid crystal compound. 4. A recording / display medium having a liquid crystal layer comprising the liquid crystal composition according to claim 1 on a substrate. 5. The recording / display medium according to claim 4, further comprising a protective layer on the liquid crystal layer.