KR19990017317A - Reversible and optical information storage materials, information storage devices and information storage methods using the same - Google Patents

Abstract

New liquid crystal monomers of the following structural formula (I) in which azobenzene groups sensitive to light are bonded to the side chains are provided as reversible and optical information recording materials.

Where R is

X is H, OCH ₃ , CN or an alkyl group, and n is 1, 2 or 3

In addition, reversible and optical information recording is composed of a laser light source, a reflection medium for reflecting all or part of the light irradiated from the laser light source, and a recording thin film coated with a liquid crystal polymer positioned on a path of light reflected from the reflection medium. An apparatus is provided, and a reversible and optical information storage method for recording, reading, erasing, and rewriting information using such a reversible and optical information recording apparatus is disclosed.

Description

Reversible and optical information storage materials, information storage devices and information storage methods using the same

The present invention relates to a novel liquid crystal polymer used as an optical information storage material, and a reversible and optical information storage device and information storage method using the same, more specifically, azobenzene group of a photodichroic dye is repeated polymer The present invention relates to a new liquid crystal polymer coupled to side chains of two per unit structure, and an information storage device and an information storage method for storing and reading information reversibly and optically.

In contrast to the magnetic recording method using an inorganic metal magnetic medium as an information storage medium, the optical information storage method uses an organic material having excellent processability, and employs a non-contact method using a laser beam for recording and reading information. Therefore, the information storage density is much higher (about 10 ⁸ -10 ⁹ bit / in ² ) and the information storage stability is excellent. In addition, there is an advantage that a large amount of information of high resolution can be produced (Polymer News, 1987, vol. 13, pp. 6-10).

Recently, a reversible (record-read-erase-rewrite) information storage method capable of recording, storing, and reading a large amount of information as well as erasing and rewriting stored information has been developed. That is, U.S. Patent Nos. 4,551,819, 5,319,481, 5,384,221, 5,589237, Japanese Patent Laid-Open Nos. 62-246963 and (H) 1-294791, or British Patent GB2. According to 146787A et al., Optical energy is used to change the birefringence of a recording medium, to cause a difference in spectroscopic absorbance, or to cause a liquid crystal phase transition from an liquid crystal phase to an isotropic phase (or crystal to amorphous). A method of erasing and rewriting recorded information by causing a change in the optical properties of a recording material, such as causing, has been developed.

As a recording material causing such optical property change, a low liquid crystal liquid having simple liquid crystallinity is mixed with a matrix such as PMMA, polycarbonate, or polyvinyl alcohol (PVA) having excellent optical properties. Materials, materials in which low-molecular liquid crystal materials are encapsulated in PVA, side-chain liquid crystal polymers in which liquid crystal groups are bonded to side chains, or photochromic groups and photoisomerization which show differences in absorbance by absorbing light of a specific wavelength The side chain type liquid crystal polymer material in which the azo group which produces | generates) is couple | bonded is mainly used.

However, according to the known technique, when the photofunctional organic dye or the low molecular liquid crystal materials are mixed with the polymer material, (1) the melting temperature (T _m ) and the glass transition of the polymer material itself. The temperature (T _g ) is lowered, and ② the photofunctional material and the polymer material have low compatibility, and 30% of the concentration of the photofunctional material to the used matrix material is sufficient to cause optical property change. It is very difficult to uniformly mix in the polymer matrix material. In addition, the recording medium may be partially disassembled by repeating the process of erasing and re-recording the recorded information. Recently, polymer materials combined with low molecular liquid crystal groups and organic dyes have been reported as optical functional materials to overcome such problems .- (US Pat. No. 4,513,075 and Polymer News. 13. pp. 6-10 (1987))- However, the above problems are still not solved.

In order to solve this problem, liquid crystal polymer materials have been reported that combine the unique properties of liquid crystal materials with the advantages of polymers.

Low molecular liquid crystal materials, which are organic materials currently used as display devices, exhibit a liquid crystalline phase spontaneously oriented by the dipole moments of axial molecules of the molecular chain at temperatures between the solid and liquid phases. Have The orientation axis of the molecular chains of these materials can be changed by externally applied electric fields, magnetic fields or surface treatment of the substrates used, and these materials are characterized by optical anisotropy. have.

The liquid crystal polymer material combining the unique characteristics of the liquid crystal material and the advantages of the polymer has excellent mechanical properties as well as excellent processability compared to the low molecular liquid crystal material, and can be manufactured as a thin and stable thin film. In addition, since the liquid crystal solidifies to a glassy state at or below the glass transition temperature (T _g ) of the liquid crystal polymer, it also has the advantage of freezing-in the molecular structure oriented in the liquid crystal phase.

(Prior Art 1)

In 1983, the research of applied liquid crystal polymers as optical reversible information storage materials was carried out by the Soviet Union. blood. One example is the thermo-recording method performed by the V.P. Shibaev group.

According to this, a nematic acrylate-based side chain type liquid crystal polymer having the following structural formula is inserted between an ITO electro-optical cell specially made to conduct electricity, and then an electric field is applied to the polymer chain. A thin film of a liquid crystal phase which is completely oriented in one direction (order parameter = 1) is prepared in advance (pre-alignment step).

When irradiated with high-power laser light, the lighted portion is locally heated above the melting temperature of the liquid crystal polymer so that the oriented molecular chains undergo phase transition to an isotropic state (order parameter = 0). Save it. The information thus stored is fixed by cooling the information below the glass transition temperature (T _g ) of the liquid crystal polymer using the recording thin film (information recording step).

As such, when the recorded information is irradiated with a low power laser, the isotropically arranged liquid crystal polymers disperse all the light and appear as a black image, whereas the area oriented in the liquid crystal phase is transparent by transmitting all the light. Seems to be. The recorded information is read out by this difference in contrast ratio (information reading step).

The recorded information can be erased by heating the recording thin film again above the melting temperature of the liquid crystal polymer (information erasing step). If the information recording step is repeatedly performed on the erased recording layer, information is reversibly rewritten (information rewriting step) (Polym. Commun. 24. 346 (1983)).

However, the above-described thermal recording method has a very high intensity of the laser light source used in the information recording step as about 100 W / cm 2, which causes a phenomenon in which liquid crystal polymers of unintended portions are arranged in an isotropic phase due to thermal diffusion. Since the resolution of the information is reduced, storage of high density and high density information requiring high resolution is difficult to expect.

(Prior Art 2)

On the other hand, organic dye groups sensitive to low power light sources such as azobenzene and spiropyran have been reported using liquid crystal polymers bonded to polymer side chains as information recording media to cause phase transition by optical property change. As an example of this research, M. in Germany. M. Eich and Jay. H. JH Wendorff et al. Reported a new holographic reversible information storage method using an acrylate-based side chain type liquid crystal polymer on a smectic with azobenzene group as a recording medium (German Patent No. 3,623,395, UK). Patent GB2.193338. U.S. Patent Nos. 4,837,745, 4,896,292, 5,024,784, Japanese Patent Laid-Open Nos. 62-191826, 62-283433, and 63-87626.

According to this, the side chain type liquid crystal polymer containing azobenzene group is placed in the above-described ITO electro-optical cell, and the electric field is applied and arranged in a uniform liquid crystal phase (pre-orientation process), and then a beam splitter (beam) When two laser polarizations whose angle difference between the reference light source and the incident light source separated by the splitter are crossed are irradiated, information such as phase grating is recorded by the interference pattern of these light sources (Die Makromol. Chem., Vol. 186, No. 12, 2639 (1985); Makromol. Chem., Rapid Commun. 10, 477-483 (1989)). At this time, the azobenzene group undergoes a photoisomerization in which a configuration is converted from a trans form that is stable at room temperature to a cis form. As a result, the liquid crystal polymer axes uniformly arranged are reorientated and information is stored by the difference in optical birefringence caused thereby (information storage step).

The information thus stored is erased by heating above the temperature at which the liquid crystal phase is phase shifted into an isotropic phase (information erasing step). Subsequently, the information can be reversibly rewritten by repeating the above information recording process again.

This hologram method has a much lower output intensity (about 2 to 10 mW / cm 2) than the thermal recording method mentioned above, and because information is recorded by a light source rather than heat, the resolution is improved. There is an advantage that digital information can be stored excellently high density.

However, the hologram method also has a fundamental disadvantage of requiring an ITO electro-optical cell for uniform orientation of the liquid crystal polymer before recording the information. Since a strong electric field is required in this pre-orientation process, energy loss is increased, and reversibly recording information several times affects the stability of the photofunctional pigment introduced into the recording medium.

(Prior Art 3)

A new reversible optical information recording method for overcoming this problem was invented by the inventor and registered in Korean Patent No. 077801 (filed date: December 27, 1991).

According to this, low-power ultraviolet polarization is irradiated to an information recording layer coated with an isotropic side chain type liquid crystal polymer bonded to an azobenzene group sensitive to a light source, thereby inducing the photoisomerization reaction of azobenzene described above to obtain high-density information having high resolution. The recorded information can be recorded, erased, and then rewritten.

More specifically, a glass plate of a liquid crystal polymer solution (J. Polym. Sci., Polym. Chem. Vol. 30, 1177-1185 (1992)) in which azobenzene groups are bonded to two side chains per polymer repeating structure is used. A thin and uniform recording thin film is applied on the film, and the recording thin film is heated to a melting temperature higher than the melting temperature inherent to the liquid crystal polymer (T _m ), and then quenched below the glass temperature (T _g ) to fix the liquid crystal polymer in an isotropic state. Get the film.

After placing a photo-mask including a fine pattern on the film and irradiating ultraviolet polarization with a maximum absorption wavelength of 365 nm passing through the optical filter and the polarizing plate, cooling to room temperature is recorded and stored.

Such a recording method, first, does not require a pre-orientation process that must be preceded by information logging in the thermal recording method and the hologram information storage method. Second, the liquid crystal phase isotropically compared to the phase transition from the liquid crystal phase to the isotropic phase. The phase transition to is very fast, and a relatively high information recording speed of about several tens of seconds can be obtained because liquid crystal polymers in which two azobenzene groups are bonded to side chains per polymer repeat structure are used. Third, photoisomerization of liquid crystals By storing the information, the contrast ratio due to thermal diffusion can be prevented, so that a higher resolution can be obtained than the thermal recording method.

However, the minimum information storage speed is still unsatisfactory as tens of seconds, the storage period is only about one month, there is a problem in storage stability, and the resolution is also not satisfactory.

(Prior Art 4)

Meanwhile, a. L. Al Natansohn et al. Reported a reversible information storage method using an acrylate-based polymer containing an azobenzene group at about the same time as the application of Korean Patent No. 077801 (US Pat. No. 5,173,381; date of application: 1991 15 August).

According to this, argon laser polarization having an intensity of 5 GHz is irradiated to the isotropic polymer thin film for 1 to 2 seconds to store information having excellent resolution with a line width of 1 μm. On the other hand, the stored information is erased by heating above the melting temperature of the polymer used. This principle is similar to the method disclosed in Korean Patent No. 077801, except that an acrylate homopolymer or copolymer containing one light-sensitive azobenzene group per repeating unit structure of the polymer as an information recording medium ( copolymer) is different.

According to this information recording method, (1) a pre-orientation step of arranging the polymer liquid crystals in a liquid crystal phase is unnecessary, and (2) a minimum information recording speed of about 1 to 2 seconds can be secured.

However, as in the above-mentioned Korean Patent No. 078081, the information storage speed is still not satisfactory, and there is a problem in storage stability.

The first technical problem of the present invention for solving the problems of the prior art is to provide a novel liquid crystal polymer material for the reversible, optical information storage.

In addition, a second technical problem of the present invention is to provide a novel information recording apparatus for reversible and optical information recording,

A third technical problem of the present invention is to provide a method for storing reversible and optical information using the above information storage device.

1 is an analog information recording apparatus according to an embodiment of the present invention.

2 is an analog information recording apparatus according to another embodiment of the present invention.

3 is a digital information recording apparatus according to an embodiment of the present invention.

4 is a digital information reading apparatus according to an embodiment of the present invention.

FIG. 5 shows an image with a magnification of 100 times obtained by reading information recorded by the information recording apparatus shown in FIG. 1 with an optical polarizing microscope.

FIG. 6 shows an image of 25 times magnification in which information recorded by the information recording apparatus shown in FIG. 2 is read by an optical polarizing microscope.

In order to achieve the above first technical problem, the present invention provides novel liquid crystal monomers having the following structural formula in which two light-sensitive azobenzene groups are bonded to the side chain, i.e., itaconate-based (I), fumarate ( homopolymers derived from fumarate (II) or maleic ester (III) liquid crystal monomers or copolymers derived from these liquid crystal monomers with methylmethacrylate and styrene monomers. It serves as an optical information recording material.

Where R is

X is H, OCH ₃ , CN or an alkyl group, and n is 1, 2 or 3

In order to achieve the second technical object of the present invention, a laser light source, a reflection medium for reflecting all or part of the light irradiated from the laser light source, and a liquid crystal polymer located on the path of the light reflected from the reflection medium is applied A novel reversible and optical information storage device composed of a recording thin film is provided.

In addition, the second technical problem is an ultraviolet light filter for filtering the ultraviolet light located on the path of light passing through the ultraviolet (UV) light source, the first ultraviolet (UV) polarizing plate irradiated with the ultraviolet light, and the first ultraviolet polarizing plate. And a second ultraviolet polarizing plate positioned on a path of light passing through the ultraviolet filter, the second ultraviolet polarizing plate having a polarization axis direction perpendicular to the polarization axis of the first ultraviolet polarizing plate, and a liquid crystal polymer positioned on a path of light passing through the second ultraviolet polarizing plate. It can also be achieved by a novel reversible and optical information recording apparatus composed of a recording thin film coated with.

In order to achieve the third technical problem of the present invention, a step of preparing a recording thin film coated with a liquid crystal polymer made of a polymer of a liquid crystal monomer in which azobenzene groups are bonded to two side chains;

Heating the recording thin film above the melting temperature of the liquid crystal polymer to align the liquid crystal polymers in an isotropic phase, and then quenching the liquid crystal polymer below the glass transition temperature (T _g );

Recording predetermined information onto the recording thin film using the novel information recording apparatus disclosed in the present invention;

Reading the information recorded on the recording thin film by using the information reading apparatus disclosed in the present invention;

Erasing the recorded information by heating the recording thin film on which the information is recorded to a melting temperature (T _m ) or higher of the liquid crystal polymer;

Disclosed is a reversible and optical information storage method comprising rewriting information by repeatedly performing the information recording step on the recording thin film from which information has been erased.

Hereinafter, a novel liquid crystal polymer material according to the present invention will be described in more detail.

The present inventors further synthesized a novel liquid crystal polymer material for reversible and optical information recording in addition to the polymalonic acid ester disclosed in Korean Patent No. 077801. These are novel liquid crystal monomers each having the following structural formulas (I, II, III), i.e., itacate (I), fumarate (II), or maleic esters. Homopolymers derived from system (III) monomers or copolymers derived from these novel liquid crystal monomers and methylmethacrylate and styrene monomers.

Where R is

X is H, OCH ₃ , CN or an alkyl group, and n is 1, 2 or 3

The recording thin film coated with the liquid crystal polymer obtained from the novel liquid crystal monomer can secure an information recording speed of several hundred nanoseconds, which is the minimum information recording speed disclosed in the Republic of Korea Patent No. 077801, or the conventional US patent. It is much faster than 1 to 2 seconds, which is the minimum information recording speed disclosed in No. 5,173,381.

This is because the weight percentage of the R group included in the novel liquid crystal monomers has a value ranging from 48 to 68% of the molecular weight of the liquid crystal monomer. This value is much higher than 20 to 45%, which is the weight ratio of the group of optical properties included in the liquid crystal polymer used as the information storage medium in the aforementioned known technology. This inherent property of liquid crystal monomers is one reason for the rapid information recording speeds of tens to hundreds of nanoseconds, which could not be reached in the existing technologies. In addition, such a high-speed information recording is possible because a new recording apparatus is employed as described later.

In addition, when information is recorded by using the novel monomer disclosed in the present invention, a high resolution of 2 m or less can be obtained. This is because the new liquid crystal polymers are arranged in an isotropic phase and then remain stable in the subsequent heating and quenching process.

In more detail, the manufacturing conditions of the isotropic thin film manufacturing process of the recording thin film vary depending on the chemical structure of the material used. In particular, in order to maintain the information recording speed below the hundreds of nanoseconds, which is a characteristic of the present study, heating after the thin film manufacturing is performed. The conditions (heating temperature and heating time) and the quenching conditions (quenching temperature and quenching time) are very important. That is, in order for the resolution (S / N ratio) of the recorded information to be excellent up to 2 µm or less, it is essential that the recording thin film maintains a complete isotropic phase after the heating and quenching steps are completed. If the liquid crystal polymer chains used as the recording thin film are oriented at least in part during the heating and quenching processes, this causes noise during information reading, thereby reducing the signal / noise ratio, thereby causing a decrease in resolution. However, the novel recording materials are stable to heating conditions and quenching conditions for isotropic thin film production, thereby ensuring a better resolution when reading information.

Hereinafter, a novel method for producing a liquid crystal monomer according to the present invention will be described.

Synthesis of Itaconate-based Liquid Crystal Monomer

First, the novel itaconate-based liquid crystal monomer (I) according to the present invention was synthesized by the following method.

First, 5.8 g (0.0183 mol) of mesogenic alcohol of the following structural formula (IV) with n = 2 in a 3-necked round flask at room temperature, 1.26 g (0.00968 mol) of itaconic acid, and triphenylphosphine 7.213 g (0.0275 mol) and 125 ml of tetra hydrofuran (hereinafter abbreviated as THF) were added thereto, followed by stirring under a nitrogen atmosphere. A solution of 12.473 ml (0.0275 mol) of diethyl azodicarboxy-late and 15 ml of THF was added to the mixed solution over a dropping funnel over 2 hours, and then reacted with stirring for 20 hours.

Subsequently, THF was removed from the mixed solution with a rotary evaporator, and the resultant was dissolved in 400 ml of dichloromethane, and then neutralized with the remaining itaconic acid as a 5% sodium bicarbonate solution. After washing with distilled water (200 mL × 4 times), dichloromethane was distilled off using a rotary evaporator.

The resultant was dried in a vacuum dryer at 40 ° C. for 24 hours, and then the obtained solid was extracted with ethyl ether for 24 hours using a Soxhlet's extractor. The precipitate formed while cooling the solid and ethyl ether in the thimble at room temperature was filtered, and the resultant solid was dried in a vacuum dryer at 40 ° C. for 24 hours. The resultant solid was dissolved in a small amount of chloroform, and then purified by column chromatography using a solution of chloroform and ethyl acetate in a ratio of 3: 1, thereby pure itaconate. ) Liquid crystal monomer (I) was obtained.

The yield of the obtained itaconate-based liquid crystal monomer (I) was 60% (3.4 g), the melting point was 114 ° C, and the liquid crystal structure was a relatively stable smectic structure.

Synthesis of Liquid Crystal Polymer from Itaconate Liquid Crystal Monomer (I)

The copolymerization reaction of the itaconate-based liquid crystal monomer and methacrylate (MMA) obtained as described above is as follows.

First, 2.8 g (0.004 mol) of itaconate monomer, 0.18 ml (0.0016 mol) of methacrylate (MMA), 0.016 g of Azo Iso Butyro Nitrile (hereinafter abbreviated as AIBN) 0.0001 mol) and 20 ml of dimethyl formamide (hereinafter abbreviated as DMF) are placed in ampoules and frozen in a freeze-thawing method, that is, liquid nitrogen, and decompressed with a vacuum pump to extract gas. The oxygen solution in the solution was removed and the ampoule was sealed. The solution was subjected to radical polymerization over a period of 12 hours in a 70 ° C. oven. Subsequently, the dark orange solution obtained after the polymerization was precipitated in 500 ml of methanol, filtered and dried to obtain a novel orange itaconate-MMA side chain type liquid crystal copolymer.

The polymerization conversion rate was 47%, and the intrinsic viscosity (η _ihn ) measured at 25 ° C. using a chloroform solvent was 0.1, and a relatively low molecular weight polymer (copolymer composition ratio: itaconate / MMA = 7/3) was obtained. The liquid crystal structure of the synthesized copolymer was also a smectic structure, and the glass transition temperature (T _g ) and the melting temperature (T _m ) were 66 ° C. and 100 ° C., respectively. Differential Scanning Calorimetry; Was confirmed).

Synthesis of Fumarate Liquid Crystal Monomer (II)

The novel fumarate-based liquid crystal monomer (II) was also prepared in the same manner as the above-described itacate-based liquid crystal monomer (I). At this time, the solvent of the column chromatography was separated using ethyl acetate / chloroform in a ratio of 1/3 each.

The yield and melting point of the pure fumarate liquid crystal monomer were 45% and 197 ° C when n was 1, 50% and 140 ° C respectively when n was 2, and n was 3, respectively. 50% and 145 ° C, respectively.

As mentioned above, these novel liquid crystal monomers are capable of recording information at high speed because the photosensitive azobenzene groups are bonded to two side chains per liquid crystal monomer, and are stable under heating and quenching conditions in the manufacturing process of the recording thin film. By maintaining the isotropic phase, high resolution can be obtained.

On the other hand, as described above, another reason why the high speed information recording speed can be secured in the present invention is that a new information recording apparatus is employed. Therefore, hereinafter, an information recording method according to the present invention and an information recording apparatus according to an embodiment of the present invention will be described in detail.

Analog information storage

The principle of information storage according to the present invention is to heat the liquid crystal polymers used above the intrinsic melting temperature and then quench them to room temperature to arrange the liquid crystal polymers in an isotropic state, and then irradiate the ultraviolet polarized light through the photomast to the light. The exposed part is used by the phenomenon which is uniformly oriented in an isotropic state by the photoisomerization reaction of azobene. That is, a photoisomerization reaction in which the azo group contained in the liquid crystal polymer is transformed into a cis form in a stable trans conformation by an information polarization irradiated ultraviolet polarized light causes the polymer chain to be irradiated with respect to the planar light direction. Are arranged in the vertical direction (Nature 1991, 351, 49; Makromol. Chem. Rapid Commum., 8, 477 (1987); Applied optics, 23, 4309 (1984)).

This phenomenon is a technology that applies the principle opposite to the existing method of causing the liquid crystal polymer phase change from the liquid crystal phase to the isotropic phase by ultraviolet light or laser light, there are various advantages as follows. First, there is no need for a uniform pre-orientation process of liquid crystal polymers, which must be preceded by information logging in the conventional thermal recording method and hologram information storage method. Therefore, there is no possibility of decomposition of organic materials, such as azobenzene group which induces energy loss or optical property change by the high voltage applied at full orientation, and can record high-resolution information. Second, the difference in contrast ratio between the information storage portion induced by ultraviolet polarization and the isotropic portion not exposed to ultraviolet polarization is very large, so the signal / noise ratio (S / N) representing the resolution of the information is very high. . Third, since there is no decrease in the contrast ratio due to thermal diffusion (Macromolecules, 24, 42 (1990)) generated in the conventional thermal recording method, there is an advantage that can prevent the degradation of the resulting resolution.

This information storage method is the same as the method disclosed in the Republic of Korea Patent No. 077801 and the United States Patent No. 5,173,381, but in the present invention to store the information at a higher speed, and to ensure that the stored information has a higher resolution and storage stability Adopt one information storage device.

1 shows a novel information recording apparatus according to the present invention, wherein reference numeral 10 denotes a neodymium-yag pulse laser, and reference numerals 12 and 14 denote reflection media having predetermined reflectivity, respectively. 16 and 18 show recording thin films coated with photo-masks and liquid crystal polymers, respectively.

On the recording thin film 18, a port mask 16 on which a fine pattern having a line width of 2 to 50 µm is recorded is placed, and the Nd-YAG pulse laser 10 shown in the device diagram of FIG. 1 is reflected. Reflected by (12, 14), ultraviolet polarized light having a desired intensity is selected and irradiated to the recording thin film 18. In this case, in order for the reflective medium to be irradiated with ultraviolet rays having a desired intensity to the recording thin film 18, one or more reflecting plates having a specific reflectivity may be employed. At this time, the intensity and irradiation time of ultraviolet rays depend on the thickness and structure of the polymer used as the information recording medium. The recording thin film 18 is then cooled to below the glass transition temperature T _g of the used liquid crystal polymer to store the information.

By employing such a novel information recording apparatus, as shown in Experimental Examples 1 and 2 described later, a recording speed of several hundred nanoseconds, which was unreachable in the prior art, can be obtained, and high resolution and excellent storage stability can be secured.

2 shows an information recording apparatus according to another embodiment of the present invention, which stores information in an analog manner using a xenon (Xe) arc lamp as a UV light source. In this case, reference numeral 20 denotes an UV enhanced Xe lamp, 22a and 22b denote first and second UV polarizing plates, respectively, and reference numerals 24 and 26 denote recordings coated with a UV filter and a polymer liquid crystal, respectively. A thin film is shown. In this case, the first polarizing plate 22a and the second polarizing plate 22b may be disposed such that the polarization axes are perpendicular to each other, and a mercury (Hg) lamp or the like may be used instead of the xenon (Xe) lamp as a UV light source.

As will be described later, such information recording apparatus can also store information at high speed, and the storage stability of the obtained information is also very high.

Reading of stored information

The recorded information is read by a low power optical polarizing microscope that does not destroy the stored information. The information reading process is performed by using the difference between the IR transmittance at the portion where the birefringence is induced and the IR transmittance at the portion not exposed to the ultraviolet ray due to the photoisomerization reaction caused by the ultraviolet ray. At this time, when the ultraviolet polarization axis incident upon the information recording is 45 ° with respect to the crossed polarization direction of the optical polarization microscope, information of excellent resolution with maximum contrast is obtained. Therefore, by changing the angle of ultraviolet polarization incident upon the information recording, it is also possible to store different information superimposed on the same recording layer several times.

Digital information storage

The optical axis of the polymer chain exposed to ultraviolet polarization is arranged in a direction perpendicular to the irradiated ultraviolet polarization direction to cause birefrengence, while birefringence is not induced in an isotropic portion not exposed to ultraviolet polarization. Therefore, when the information signal of the information storage portion where the birefringence is induced is set to the maximum value 1, the information signal value of the isotropic portion not exposed to ultraviolet polarization becomes zero. Eventually, digital information is stored from the difference of these values.

3 shows a novel information recording apparatus for digital information storage. In this case, except that the photomask is the same as the analog data storage device, the same reference numerals as in FIG. 1 denote the same device. Even when information is recorded by using the information recording apparatus shown in FIG. 3, as in the information recording process by the analog method, excellent information recording speed of several hundred nanoseconds, high resolution and excellent storage stability can be secured.

Reading of digital information

The stored information can be read using the novel digital information reading apparatus shown in FIG. In this case, reference numerals 100 and 102 denote IR laser drives and IR lasers, respectively, and reference numerals 110a, 110b and 110c denote first, second and third refractive lenses, respectively, and 120a and 120b denote first and second, respectively. An IR polarizing plate is shown. Reference numeral 130 denotes a recording thin film coated with liquid crystal polymer, and 140, 150 and 160 denote a photodiode, a digital voltmeter and a computer, respectively.

Between the two orthogonal IR polarizers 120a and 120b, a recording thin film 130 having information stored therein is irradiated with the IR laser 102. In this case, a gallium-arsenic (Ga / As) laser having a wavelength of 84 nm or a helium-neon (He-Ne) laser having a wavelength of 633 nm may be used as the IR laser 102.

The IR transmittance of the birefringence-induced information storage portion is maximum when the information polarization incident ultraviolet polarization axis is 45 ° with respect to the polarization direction where the two IR polarizing plates 120a and 120b provided in the information reading device cross each other. Light is blocked by two vertical IR polarizers 120a and 120b of the information reading apparatus, which are not exposed to ultraviolet polarization. Accordingly, the transmittance difference of the IR laser resulting from these differences is sensed by the photodiode 140. At this time, the photodiode 140 represents the intensity of the incident light as a voltage change, which is displayed numerically on the digital voltmeter 150, which is read back through the computer 160.

Like the analog information reading, the information is read by the difference between the IR transmittances of the exposed and unexposed portions of the ultraviolet rays. Therefore, different information is transferred to the same recording layer by changing the angle of the ultraviolet polarization incident upon the information recording. You can save multiple nests. That is, when ultraviolet polarized light is irradiated to an isotropic polymer thin film used as an information recording medium, the optical axes of the polymer chains exposed to the polarized light are arranged in a direction perpendicular to the irradiated polarization direction. Therefore, a thin film in which birefringence (Δn) is induced when reading information is placed between the polarizing plates perpendicular to each other, and the intensity of IR light used for reading information is given by the following equation.

Is the birefringence of the information recording thin film,

λ: wavelength of IR light used for reading information,

I _o : intensity of light before passing through the sample,

I is the intensity of light passing through the sample,

d: thickness of the sample,

θ: The angle between the axis of the polarizing plate and the optical axis of the polymer chain oriented by ultraviolet polarization.

In other words, when the angle between the axis of the polarizing plate and the optical axis of the information recording medium is 45 °, 135 °, 225 °, or 315 °, the intensity of IR transmitted light at the portion not irradiated with the ultraviolet ray and at the portion irradiated is 0 and sin ^2. It is represented by two values of (πdΔn / λ). By using this, digital information of on-state, that is, sin ² (πdΔn / λ) and off-state, that is, zero, can be spatially recorded and detected in a medium.

Therefore, if the angle of ultraviolet polarization incident on the recording thin film is arbitrarily changed, different information can be superimposed and stored in the same recording layer. For example, if the angle of incident ultraviolet polarization is changed by 1 ° with respect to the original angle, θ is changed to (θ + 1) ° in the above equation, and the angles of the polarizing plates perpendicular to each other when reading information are (θ + 1) °. At 45 °, 135 °, 225 °, and 315 ° with respect to, the S / N ratio is maximized.

Erase and rewrite stored information

When the recording thin film on which information is recorded is heated above the melting temperature (T _m ) of the used liquid crystal polymer, the liquid crystal polymer is uniformly oriented in an isotropic phase, so that the recorded information can be erased. Subsequently, after the information thin film is cooled to room temperature, new information can be rewritten again by repeatedly performing the above-described information recording process.

In the following, the characteristics obtained when using the information recording apparatus disclosed in the present invention will be described through several experimental examples.

Experimental Example 1

The information was recorded by the novel information recording apparatus shown in FIG. 1 using the side chain type liquid crystal polymer manufactured by the present inventors and disclosed in Korean Patent No. 077801.

First, the polymalonic acid ester obtained from the side chain type liquid crystal polymer monomer of Structural Formula (V) disclosed in Korean Patent No. 077801 was dissolved in 1,4-dioxane (1,4-dioxane) solvent at a concentration of about 4%. The solution was dropped on a glass plate (2 cm x 2 cm) by 3-4 drops, spin-coated to produce a recording thin film (about 0.5 mu m), and then depressurized to remove the solvent. This was placed on a heating plate and heated to 102 DEG C, the melting temperature (T _m ) of the used liquid crystal polymer, and then cooled to below the glass transition temperature (T _g ) to obtain a recording thin film in which the liquid crystal polymer was fixed in an isotropic state.

Using the information recording apparatus shown in FIG. 1, a photomask 16 (line width 2 to 50 µm) in which a fine pattern is drawn is placed on the recording thin film 18, and the Nd-YAG pulse laser 10 is reflected. Was reflected on the first reflecting plate 12 and the second reflecting plate 14 at 30% and 4%, respectively, and ultraviolet polarized light having a specific intensity was irradiated on the recording thin film 18. At this time, the Nd-YAG pulsed laser 10 had a maximum absorption wavelength of 365 nm, a maximum output intensity of 7.37 mW / cm 2, a pulse time of 6 mW, a beam diameter of 1.2 mm, and a repetition speed of 10 mW. In addition, the intensity | strength and irradiation time of an ultraviolet-ray were 80-500 mW / cm <2> and 1-100 times, respectively in the case of the polymalonic acid ester of the said Formula (V). The intensity and the number of irradiation of ultraviolet rays can be adjusted according to the thickness and structure of the polymer used as the information recording medium.

As a result, analog information can be recorded at very high speeds, ranging from hundreds to tens of nanoseconds. This is much faster than tens of seconds, which is the minimum information recording rate that can be obtained by the conventional Korean Patent No. 077801 using the same liquid crystal polymer, and 1, which is the minimum information recording rate that can be obtained by the conventional US Patent No. 5,173,381. It is faster than 2 seconds.

In addition, the analog information stored in this manner has maintained a very stable state at room temperature for more than one year, showing high storage stability.

On the other hand, Fig. 5 shows the information obtained by irradiating the information recording layer of polymalonic acid ester (m = 6, n = 2) with 70 times of pulsed laser ultraviolet polarization having an intensity of 295 KW / cm 2 and recording information obtained by an optical polarization microscope. It is understood that the image recorded by the information recording apparatus according to the present invention is also excellent in resolution.

Experimental Example 2

This Experimental Example is the same as Experimental Example 3 except for using the information storage device shown in FIG.

That is, after manufacturing the recording film 26 coated with polymalonic acid ester disclosed in Korean Patent No. 077801 as a recording thin film, using a Xe arc lamp 20 having an output intensity of 150 W as a UV light source, the first UV polarizing plate Ultraviolet polarized light which was sequentially passed through (22a), the UV filter 24 and the second UV polarizing plate 22b was irradiated onto the recording thin film 26 through a photomask (not shown). At this time, the maximum absorption wavelength of the ultraviolet rays irradiated on the recording thin film 26 was 365 nm, and the intensity was 1-20 mW / cm 2. After irradiating ultraviolet rays, the recording thin film 26 was cooled to room temperature to obtain a film in which the information of the fine pattern was stored.

At this time, the information storage speed was excellent as hundreds of nanoseconds, and the stored information was very stable at room temperature.

FIG. 6 is irradiated with ultraviolet polarized light for 22 minutes with an Xe lamp having an intensity of 3.7 mW / cm 2 on an information recording layer of polymalonic acid ester (m = 6, n = 2) using the information recording apparatus shown in FIG. The recorded information was obtained by an optical polarization microscope at 25 times magnification.

As a result, it can be seen from Experimental Examples 1 and 2 that the novel analog information recording apparatus according to the present invention can record information at a higher speed, and can secure high resolution and excellent storage stability. In addition, even when digital information was recorded using the digital information recording apparatus shown in FIG. 3, the same result was obtained as in the analog information storage.

(Comparative Example 1)

As a comparative experiment, a polymer thin film coated with an acrylate polymer, which is a conventional liquid crystal polymer, was prepared, and analog information was recorded using the information recording apparatus shown in FIG. 1, and storage stability was measured.

The acrylate-based liquid crystal monomer has the following structural formula (VI),

CH ₂ -CR-CO (OCH ₂ CH ₂ ) ₂ -R '(Ⅵ)

Where R is CH ₃ and R 'is

to be. The synthesis method of such an acrylate-based liquid crystal monomer (VI) is as follows.

First, a three-necked round flask was placed in an ice bath at 0 ° C to 5 ° C, and 0.40 g (0.0038 mol) of methacryloyl chloride and 5 ml of methylene chloride were added and stirred under a nitrogen atmosphere. The 3-spheres were dissolved in a solution of 1.0 g (0.00316 mol) of n = 2 mesogen alcohol having the above-described formula (IV) and 0.215 g (0.00316 mol) of imidazole in 20 ml of methylene chloride. To the round flask was added at a rate of 0.5 mL / min and stirred for 2 hours, refluxed for 6 hours, and reacted with stirring. After extracting this with distilled water four times, methylene chloride was distilled off by the rotary evaporator. The resulting solid was dissolved in a small amount of methylene chloride and column chromatography was performed using a solution of a ratio of n-hexane and ethyl acetate 5: 1 to obtain pure monomers. At this time, the yield was 53%, the melting temperature (T _m ) was 101 ℃.

On the other hand, the method of obtaining an acrylate polymer from the said acrylate liquid-crystal monomer (VI) is as follows.

2.0 g (0.0052 mol) of said monomers and 0.025 g (0.00016 mol, 3 mol% of monomer concentrations) of AIBN were put into a glass ampoule, and 13 mL of purified THF was put into the ampoule. After confirming that the solid sample was completely dissolved, the mixture was frozen in liquid nitrogen and decompressed with a vacuum pump to remove oxygen in the solution (Freeze-Thawing method). After dissolving the resultant, it was put in liquid nitrogen again, frozen, decompressed with a vacuum pump, and the ampoule was sealed. The solution was subjected to radical polymerization for 12 hours in an oven preheated to 70 ° C. The dark yellow solution obtained by superposition | polymerization was precipitated in 150 ml of methanol, and it filtered and obtained the yellow azobenzene acrylate type side chain type liquid crystal polymer. The polymerization conversion rate was 76%, and the polymer viscosity was 0.12. The melting temperature (T _m ) and glass transition temperature (T _g ) measured by DSC thermal analyzer were 76 ° C and 56 ° C, respectively.

The acrylate polymer synthesized as described above was coated on a substrate to prepare a recording thin film, and the analog information was stored in the same manner as in Example 1 using the apparatus shown in FIG.

As a result, it was confirmed that the stored information was spontaneously deleted within one hour, and the storage stability of the information was very poor. This phenomenon is the same in the case of digital information storage.

This is very poor considering that the storage stability obtained from the liquid crystal polymer used in the present invention is 1 year or more. Therefore, it can be seen that the novel liquid crystal polymers disclosed by the present invention have superior storage stability and the like than conventional liquid crystal polymers, for example, the liquid crystal polymers disclosed in US Pat. No. 5,173,381.

As mentioned above, when the novel liquid crystal polymer according to the present invention is used, not only can information be recorded at high speed, but also high resolution and excellent storage stability can be ensured.

In addition, even when optical information is recorded and read using the information recording apparatus according to the present invention, information can be stored at a higher speed, and high resolution and excellent storage stability can be ensured.

Claims (43)

A novel thermotropic liquid crystal polymer, comprising a polymer of a novel liquid crystal monomer having the following structural formula (I). Where R is X is H, OCH ₃ , CN or an alkyl group, and n is 1, 2 or 3 The thermotropic liquid crystal polymer according to claim 1, wherein the weight percentage of the R group is 48 to 68% of the molecular weight of the liquid crystal monomer. A novel thermotropic liquid crystal polymer comprising a polymer of a novel liquid crystal monomer having the following structural formula (II). Where R is X is H, OCH ₃ , CN or an alkyl group, and n is 1, 2 or 3 The thermotropic liquid crystal polymer according to claim 2, wherein the weight percentage of the R group is 48 to 68% of the molecular weight of the liquid crystal monomer. A novel thermotropic liquid crystal polymer comprising a polymer of a novel liquid crystal monomer having the following structural formula (III). Where R is X is H, OCH ₃ , CN or an alkyl group, and n is 1, 2 or 3 The thermotropic liquid crystal polymer according to claim 5, wherein the weight percentage of the R group is 48 to 68% of the molecular weight of the liquid crystal monomer. Laser light source, A reflection medium reflecting all or part of the light irradiated from the laser light source; And a recording thin film coated with a liquid crystal polymer positioned on a path of light passing through the reflection medium. 8. The reversible and optical information recording apparatus according to claim 7, further comprising a photomask positioned on an optical path between the reflective medium and the recording thin film. The reversible and optical information recording apparatus according to claim 7 or 8, wherein the reflection medium is composed of one or two or more reflection plates. The reversible and optical information recording apparatus according to claim 7 or 8, wherein the reflecting medium comprises a first reflecting plate having a reflectivity of 30% and a second reflecting medium having a reflectance of 4%. The reversible and optical information recording apparatus according to claim 7, wherein the liquid crystal polymer is a polymer of side chain type liquid crystal monomers in which azobenzene groups are bonded to two side chains. 12. The reversible and optical information recording apparatus according to claim 11, wherein the weight percentage of the azobenzene group is 48 to 68% of the molecular weight of the liquid crystal monomer. 12. The reversible and optical information recording apparatus according to claim 11, wherein the side chain type liquid crystal monomer is selected from the group consisting of materials having structural formulas (I), (II), (III) and (V). Where R is X is H, OCH ₃ , CN or an alkyl group, and n is 1, 2 or 3 At this time, m is 4 to 12, n is 1 to 3. An ultraviolet (UV) light source, A first ultraviolet (UV) polarizing plate irradiated with the ultraviolet rays, An ultraviolet filter positioned on a path of light passing through the first ultraviolet polarizer and filtering the ultraviolet light; A second ultraviolet polarizer disposed on a path of light passing through the ultraviolet filter and having a polarization axis direction perpendicular to the polarization axis of the first ultraviolet polarizer; And a recording thin film coated with a liquid crystal polymer positioned on a path of the light passing through the second ultraviolet polarizing plate. 15. The reversible and optical information recording apparatus according to claim 14, further comprising a photomask positioned on an optical path between the second ultraviolet polarizer and the recording thin film. 16. The reversible and optical information recording apparatus according to claim 14 or 15, wherein the ultraviolet (UV) light source is a UV enhanced Xe lamp. 16. The reversible and optical information recording apparatus according to claim 14 or 15, wherein the ultraviolet light source is a mercury (Hg) lamp. 16. The reversible and optical information recording apparatus according to claim 14 or 15, wherein the liquid crystal polymer is a polymer of side chain type liquid crystal monomers in which azobenzene groups are bonded to two side chains. 19. The reversible and optical digital information reading device according to claim 18, wherein the weight percentage of the azobenzene group is 48 to 68% of the molecular weight of the liquid crystal monomer. 19. The reversible and optical information recording apparatus according to claim 18, wherein the side chain type liquid crystal monomer is selected from the group consisting of materials having structural formulas (I), (II), (III) and (V). Where R is X is H, OCH ₃ , CN or an alkyl group, and n is 1, 2 or 3 At this time, m is 4 to 12, n is 1 to 3. Laser light source, A first IR polarizing plate to which light irradiated from the light source is incident; A recording thin film coated with a liquid crystal polymer positioned on a path of light passing through the IR polarizing plate; A second IR polarizing plate positioned on a path of light passing through the recording thin film and having a polarization axis perpendicular to the polarization axis of the first IR polarizing plate; And an output device for inputting the light passing through the second IR polarizing plate to output the information recorded on the recording thin film. 22. The method of claim 21, further comprising a first refractive lens positioned on an optical path between the laser light source and the first IR polarizer such that light irradiated from the laser light source is incident in parallel to the first IR polarizer. Reversible, optical digital information reading device characterized in that. 22. The device of claim 21, wherein the output device comprises: a photodiode positioned on a path of light passing through the second IR polarizer; And a display device for displaying the recorded information by receiving the output of the photodiode. 24. The display device of claim 23, wherein the display device includes a voltmeter indicating the output of the photodiode as a voltage change, and a computer for storing and processing the output of the voltmeter and displaying the image as an image. Device. 22. The method of claim 21, further comprising a second refractive lens positioned on an optical path between the second IR polarizing plate and the photodiode so that light passing through the second IR polarizing plate can be detected by the photodiode. Reversible, optical digital information reading device comprising a. 22. The reversible and optical digital information reading device of claim 21, wherein the laser light source is an IR laser. 22. The reversible and optical digital information reading device of claim 21, wherein the liquid crystal polymer is a polymer of side chain type liquid crystal monomers in which azobenzene groups are bonded to two side chains. 28. The reversible and optical digital information reading device according to claim 27, wherein the weight percentage of the azobenzene group is 48 to 68% of the molecular weight of the liquid crystal monomer. 28. The reversible and optical information recording apparatus according to claim 27, wherein the side chain type liquid crystal monomer is selected from the group consisting of materials having structural formulas (I), (II), (III) and (V). Where R is X is H, OCH ₃ , CN or an alkyl group, and n is 1, 2 or 3 At this time, m is 4 to 12, n is 1 to 3. (a) manufacturing a recording thin film coated with liquid crystal polymer; (b) heating the recording thin film above the melting temperature of the liquid crystal polymer to align the liquid crystal polymers in an isotropic phase, and then quenching the liquid crystal polymer below the glass transition temperature (T _g ); (c) recording analog information on the recording thin film using the information recording apparatus of claim 8; (d) reading analog information recorded on the recording thin film using an optical polarizing microscope; (e) erasing recorded information by heating the recording thin film to a melting temperature (T _m ) or higher of the liquid crystal polymer; And and (f) rewriting the information by repeating steps (b) to (c) with respect to the recording thin film from which the information has been erased. 31. The reversible and optical information storage method according to claim 30, wherein the liquid crystal polymer in the recording film manufacturing step (a) is a polymer of a side chain type liquid crystal monomer in which azobenzene groups are bonded to two side chains. 32. The reversible and optical digital information reading device of claim 31, wherein the weight percentage of the azobenzene group is 48 to 68% of the molecular weight of the liquid crystal monomer. 32. The reversible and optical information recording apparatus according to claim 31, wherein the side chain type liquid crystal monomer is selected from the group consisting of materials having structural formulas (I), (II), (III) and (V). Where R is X is H, OCH ₃ , CN or an alkyl group, and n is 1, 2 or 3 At this time, m is 4 to 12, n is 1 to 3. 31. The reversible and optical method according to claim 30, wherein the polarization axes of the ultraviolet polarization axis incident to the recording thin film in the (c) information recording step and the optical polarization microscope used in the (d) information reading step are 45 ° to each other. Information storage method. 31. The reversible and optical information storing method according to claim 30, wherein in the (c) information recording step, different information is overwritten on the same recording layer by changing the polarization axis of the ultraviolet light irradiated on the recording thin film. (a) manufacturing a recording thin film coated with liquid crystal polymer; (b) heating the recording thin film above the melting temperature of the liquid crystal polymer to align the liquid crystal polymers in an isotropic phase, and then quenching the liquid crystal polymer below the glass transition temperature (T _g ); (c) recording analog information on the recording thin film using the information recording apparatus of claim 15; (d) reading analog information recorded on the recording thin film using an optical polarizing microscope; (e) erasing recorded information by heating the recording thin film to a melting temperature (T _m ) or higher of the liquid crystal polymer; And and (f) rewriting the information by repeating steps (b) to (c) with respect to the recording thin film from which the information has been erased. (a) manufacturing a recording thin film coated with liquid crystal polymer; (b) heating the recording thin film above the melting temperature of the liquid crystal polymer to align the liquid crystal polymers in an isotropic phase, and then quenching the liquid crystal polymer below the glass transition temperature (T _g ); (c) recording digital information on the recording thin film using the information recording apparatus of claim 7; (d) reading the information recorded on the recording thin film by using the digital information reading apparatus of claim 21; (e) erasing recorded information by heating the recording thin film to a melting temperature (T _m ) or higher of the liquid crystal polymer; And and (f) rewriting the information by repeating steps (b) to (c) with respect to the recording thin film from which the information has been erased. 38. The reversible and optical information storage method according to claim 37, wherein the liquid crystal polymer in the recording film manufacturing step (a) is a polymer of a side chain type liquid crystal monomer in which azobenzene groups are bonded to two side chains. 39. The reversible and optical digital information reading device of claim 38, wherein the weight percentage of the azobenzene group is 48 to 68% of the molecular weight of the liquid crystal monomer. The reversible and optical information recording apparatus according to claim 38, wherein the side chain type liquid crystal monomer is selected from the group consisting of materials having structural formulas (I), (II), (III) and (V). Where R is X is H, OCH ₃ , CN or an alkyl group, and n is 1, 2 or 3 At this time, m is 4 to 12, n is 1 to 3. 38. The method of claim 37, further comprising a 45 ° angle with the crossed polarization directions of the ultraviolet polarization axis incident on the recording thin film in the (c) information recording step and the two IR polarizing plates used in the (d) information reading step. Reversible and optical information storage method. 38. The reversible and optical information storing method according to claim 37, wherein in the (c) information recording step, different information is overwritten on the same recording layer by changing the polarization axis of ultraviolet light irradiated on the recording thin film. (a) manufacturing a recording thin film coated with liquid crystal polymer; (b) heating the recording thin film above the melting temperature of the liquid crystal polymer to align the liquid crystal polymers in an isotropic phase, and then quenching the liquid crystal polymer below the glass transition temperature (T _g ); (c) recording digital information on the recording thin film using the information recording apparatus of claim 14; (d) reading the information recorded on the recording thin film by using the digital information reading apparatus of claim 21; (e) erasing recorded information by heating the recording thin film to a melting temperature (T _m ) or higher of the liquid crystal polymer; And and (f) rewriting the information by repeating steps (b) to (c) with respect to the recording thin film from which the information has been erased.