JP2001083311A - Polarization diffraction element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarization diffraction element comprising a liquid crystal layer having polarization diffraction characteristics, high diffraction efficiency and easy setting of a diffraction angle.
Provided is a polarization diffraction element comprising a liquid crystal layer in which a helical structure is held in a smectic liquid crystal phase. SOLUTION: A liquid crystal layer formed of a liquid crystal material exhibiting a smectic liquid crystal phase expresses a smectic liquid crystal phase having a helical structure and is held in the liquid crystal layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention is applicable to various fields such as optics, optoelectronics, optical information recording, liquid crystal display devices, security applications, and design applications.
Further, the present invention relates to a polarization diffraction element which can be manufactured in a large area and has excellent handleability.

[0002]

2. Description of the Related Art A diffraction element utilizing a light diffraction phenomenon has functions such as a lens function, a spectral function, a branching / combining function, and a light intensity distribution conversion. Utilizing this function, it has been applied to various applications such as a hologram scanner for a barcode reader and an optical pickup for a CD (compact disk), and has been put to practical use. Diffraction elements are mainly classified into amplitude type diffraction elements and phase type diffraction elements according to their shapes. The amplitude type diffractive element is a device in which a uniform member that does not transmit light, such as a long and thin wire, is periodically arranged, and diffracted light is obtained by transmitting the light. On the other hand, phase-type diffraction elements are, for example, those having periodic irregularities formed on a substrate having no light absorption, and those having a refractive index modulation type in which a periodic distribution of the refractive index is formed inside a layer having a uniform thickness. is there. Further, unlike the amplitude type diffraction element, the phase type diffraction element has no portion that does not transmit light, so that the diffraction efficiency can be increased. Further, examples of the phase type diffraction element having irregularities include those in which irregularities are periodically provided on the surface of glass, metal, plastic, and the like, and examples of the refractive index modulation type phase type diffraction element include a hologram. . More recently,
A polarization diffraction element having diffracted light having polarization characteristics has been developed and applied to an optical head of a magneto-optical disk, an optical pickup of a DVD (digital video disk), and the like. As a structural concept of the polarization diffraction element, for example, as shown in FIG. 1 and FIG. 2, the refractive index is substantially equal to a certain polarized incident light (see FIG. 2 (b)) and orthogonal to it. It has a refractive index structure in which the refractive index is periodically modulated with respect to polarized incident light having a vibration direction (see FIG. 2A). Specific examples include a polarization diffraction element using a birefringent crystal such as LiNbO _3.
166237). However, birefringent crystals such as LiNbO ₃ are expensive and are not suitable for large area production.
As a polarization diffraction element, a polarization diffraction grating in which the orientation of a nematic liquid crystal is pattern-oriented has been developed (for example, Japanese Patent Application Laid-Open No. H10-265531). However, the patterning process of the liquid crystal alignment is complicated and manufacturing is not easy.

[0003]

SUMMARY OF THE INVENTION The object of the present invention is to
By maintaining the helical alignment state in the smectic liquid crystal phase having a helical structure, it has polarization diffraction characteristics, high diffraction efficiency, easy setting of diffraction angle, easy large-area production, and easy handling. It is an object of the present invention to provide a polarization diffraction element composed of a liquid crystal layer.

[0004]

That is, the first aspect of the present invention is as follows.
The present invention relates to a polarization diffraction element comprising a liquid crystal layer that maintains a helical alignment state in a smectic liquid crystal phase having a helical structure. A second aspect of the present invention is that a liquid crystal material exhibiting a smectic liquid crystal phase having a helical structure is oriented in a helical structure at a temperature equal to or higher than a glass transition temperature, and then cooled to a glass state, and a helical alignment state in the liquid crystal phase is formed. The invention relates to the above-described polarization diffraction element, which is a liquid crystal layer in which is fixed. Further, a third aspect of the present invention is to align a liquid crystal material exhibiting a smectic liquid crystal phase having a helical structure in a helical structure at a temperature at which the liquid crystal phase is exhibited, and then polymerize the liquid crystal phase while maintaining the orientation. The present invention relates to the above-described polarization diffraction element, which is a liquid crystal layer in which a helical alignment state is fixed. A fourth aspect of the present invention relates to the above-described polarization diffraction element, wherein the smectic liquid crystal phase having a helical structure is a chiral smectic C phase. Further fifth aspect of the present invention, a smectic liquid crystal phase having a helical structure regarding polarization diffraction element of the claimed chiral smectic C _A phase.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The polarization diffraction element of the present invention comprises a liquid crystal layer having a spiral structure of a smectic liquid crystal phase having a spiral structure. When light is incident on this liquid crystal layer, the polarization dependence of the diffracted light can be recognized. Here, the polarization dependence of the diffracted light means that, for example, when natural light (non-polarized light) is perpendicularly incident on the liquid crystal layer, the diffracted light is polarized, and linearly polarized light is incident. At that time,
This means that a difference occurs in the diffracted light intensity depending on the vibration direction of the incident polarized light. In general, a smectic liquid crystal phase is a layer in which liquid crystal molecules are also referred to as a one-dimensional crystal or a two-dimensional liquid.
Defined as "smectic layer". ) Means the liquid crystal phase in the structure. The type of the smectic liquid crystal phase of the liquid crystal layer serving as the polarization diffraction element of the present invention is not limited. As the smectic liquid crystal phase, a smectic A phase, a smectic B phase,
Smectic C phase, Smectic E phase, Smectic F
Phase, smectic G phase, smectic H phase, smectic I phase, smectic J phase, smectic K phase, smectic L phase and the like are known. Among them, liquid crystal molecules are arranged obliquely with respect to the normal direction of the smectic layer, such as smectic C phase, smectic I phase, smectic F phase, smectic J phase, smectic G phase, smectic K phase, smectic H phase. The smectic phase is suitable in the present invention. In addition, as the smectic liquid crystal phase of the present invention, a chiral smectic C phase (SmC *
Phase), a chiral smectic I phase (SmI * phase), a chiral smectic F phase (SmF * phase), etc., a liquid crystal phase showing optical activity and ferroelectricity, a chiral smectic CA phase (SmCA ^* phase), Chiral smectic IA phase (Sm
IA ^* phase), chiral smectic FA phase (SmFA ^* phase), etc., liquid crystal phase showing optical activity and exhibiting antiferroelectricity, chiral smectic Cγ phase (SmCγ ^* phase), chiral smectic Iγ phase (SmIγ ^* phase) ), A liquid crystal phase exhibiting optical activity and exhibiting ferrielectricity, such as a chiral smectic Fγ phase (SmFγ ^* phase). Furthermore,
J. Mater. Chem. 6, 1231 (1
996) and J.M. Mater. Chem. Seven volumes,
Those which are achiral and have a smectic phase having a helical structure as described on page 1307 (1997) are also suitable as the smectic liquid crystal phase of the present invention.
However, the smectic liquid crystal in the liquid crystal layer of the present invention is not easy to synthesize the liquid crystal material, easily align the helical structure in the smectic liquid crystal phase, stabilize the helical structure, and easily change the helical pitch. The phase is chiral smectic C
The phase or chiral smectic CA phase is most preferred.

The helical structure in the smectic liquid crystal phase means that the major axis of the liquid crystal molecules is inclined at a fixed angle from the direction perpendicular to each smectic layer, and the liquid crystal molecules are twisted little by little from a layer having an inclined angle to the next layer. Say structure. The central axis of the spiral in this spiral structure is called a spiral axis, and the distance in the spiral axis direction for one rotation of the spiral is called the spiral pitch. In the polarization diffraction element of the present invention, the direction of the helical axis with respect to the liquid crystal layer surface is not particularly limited, and may be any direction in which desired characteristics can be exhibited. For example, it may be parallel or perpendicular to the liquid crystal layer surface, or may be inclined. Furthermore, the direction of the helical axis may or may not be the same in the entire liquid crystal layer constituting the polarization diffraction element. Also,
The helical axis need not be straight. There is no particular limitation on the rotation direction (twist direction) of the helical axis, and the liquid crystal layer constituting the polarization diffraction element may have the same twist direction as the whole layer, and a liquid crystal layer in which left twist and right twist are mixed. It may be. Furthermore, the above-mentioned helical structure does not need to be formed in the plane of the liquid crystal layer or in the entire thickness direction, and the liquid crystal layer in which the helical structure is formed only in the surface layer portion or the internal region also has the polarization property of the present invention. Included in diffraction elements. The helical pitch of the liquid crystal layer constituting the polarization diffraction element of the present invention is usually 0.1.
It is in the range of 1 to 20 μm, preferably 0.2 to 15 μm, more preferably 0.3 to 10 μm. However, this helical pitch is, in the entire liquid crystal layer constituting the polarization diffraction element,
It does not necessarily have to be constant, and may vary continuously or discontinuously in the liquid crystal layer. Incidentally, the helical pitch may be appropriately adjusted by a known method such as adjusting the alignment conditions such as temperature, adjusting the optical purity of the optically active site, the mixing ratio of the optically active substance, and the like in the process of manufacturing the liquid crystal layer. Can be. The helical pitch in the liquid crystal layer serving as the polarization diffraction element of the present invention is equivalent to the lattice spacing of the diffraction element. Therefore, when light is incident on the liquid crystal layer, the light is diffracted at an angle corresponding to the magnitude of the helical pitch. . Therefore, in order to obtain a liquid crystal layer having a desired diffractive power in the liquid crystal layer, the above-described measure for adjusting the helical pitch is adopted.

[0007] In the liquid crystal layer constituting the polarization diffraction element of the present invention, the spiral structure of the smectic liquid crystal phase must be maintained. Here, maintaining the helical structure means that the helical structure does not change with time in a situation where the liquid crystal layer functions as a polarization diffraction element. One method of retaining the helical structure in the smectic liquid crystal phase is, for example,
In this method, a liquid crystal layer is sandwiched between two alignment substrates to maintain a helical structure of a smectic liquid crystal phase formed by the liquid crystal layer. In this method, if one of the two alignment substrates is removed, the spiral structure may not be able to be maintained in a stable state. Another method of keeping the helical structure in the smectic liquid crystal phase is a method of fixing the helical structure of the smectic liquid crystal phase. This method is superior to the above-mentioned method in which the liquid crystal layer is not fixed, in terms of ease of manufacturing the liquid crystal layer, heat resistance, and practicality. The method for fixing the helical structure in the smectic liquid crystal phase is roughly classified into glass fixing and polymerization fixing. Glass fixing is a method of fixing a smectic liquid crystal phase having a helical structure by transferring it to a glass state.When this method is adopted, a helical structure in a liquid crystal state is used as a liquid crystal material for providing a liquid crystal layer. The liquid crystal material (A), which can form a smectic liquid crystal phase and has a glassy state when cooled, is used. On the other hand, polymerization fixation is a method of fixing a smectic liquid crystal phase having a helical structure by polymerizing or cross-linking liquid crystal molecules. The liquid crystal material (B) which can form a smectic liquid crystal phase having a helical structure and is polymerized or cross-linked by light, electron beam, heat or the like is used.

The liquid crystal material for providing the liquid crystal layer of the present invention includes a low molecular liquid crystal capable of forming a smectic liquid crystal phase having a helical structure,
Polymer liquid crystals are all possible. The liquid crystal material may be any material as long as the material finally exhibits desired liquid crystallinity and orientation. For example, a single or plural kinds of low-molecular and / or high-molecular liquid crystal substances may be used alone or plural kinds of low-molecular substances. A mixture with a molecule and / or a polymer non-liquid crystalline substance may be used. Low-molecular liquid crystals that can be used in the present invention include Schiff base compounds, biphenyl compounds, terphenyl compounds, ester compounds, thioester compounds, stilbene compounds, tolan compounds, azoxy compounds, azo compounds, There are phenylcyclohexane compounds, pyrimidine compounds, cyclohexylcyclohexane compounds and mixtures thereof. Polymer liquid crystals can be classified into main-chain polymer liquid crystals and side-chain polymer liquid crystals, and any of these can be used as a liquid crystal material for obtaining the liquid crystal layer of the present invention. As the main-chain type polymer liquid crystal, polyester-based, polyamide-based, polycarbonate-based, polyimide-based, polyurethane-based, polybenzimidazole-based, polybenzoxazole-based, polybenzthiazole-based, polyazomethine-based, polyesteramide-based, and polyestercarbonate-based Or polyesterimide-based polymer liquid crystals. Among them, semi-aromatic polyester polymer liquid crystals in which mesogenic groups that provide liquid crystal properties and bent chains such as polymethylene, polyethylene oxide, and polysiloxane are alternately bonded, and wholly aromatic polyester polymer liquid crystals without bent chains Is particularly preferable as a main chain type polymer liquid crystal that provides the liquid crystal layer of the present invention. As side-chain type polymer liquid crystals, polyacrylates,
Polymer liquid crystals having a skeleton chain of a linear or cyclic structure, such as polymethacrylate, polyvinyl, polysiloxane, polyether, polymalonate, and polyester, and having a mesogen group in a side chain are exemplified. Above all,
A side-chain type polymer liquid crystal in which a mesogen group that provides liquid crystallinity is bonded to the skeletal chain via a bent chain spacer, and a side-chain type polymer liquid crystal having a molecular structure having a mesogen in both the main chain and the side chain Is particularly preferred as a side-chain polymer liquid crystal that provides the liquid crystal layer of the present invention. The liquid crystal material referred to in the present invention includes a material obtained by blending a chiral agent or introducing an optically active unit into the above-mentioned low-molecular liquid crystal and / or high-molecular liquid crystal. Liquid crystal materials containing a chiral agent or incorporating an optically active unit include, for example, smectic C phase, smectic I
Liquid crystal material having a chiral agent or a chiral smectic C phase, a chiral smectic I phase or a chiral smectic F phase are mixed with a chiral agent.
Phase, a chiral smectic liquid crystal phase that is easily oriented in a helical structure, such as a chiral smectic F phase. As described above, the blending amount of the chiral agent, the introduced amount of the optically active unit,
By appropriately adjusting the optical purity, the temperature conditions for forming a smectic liquid crystal phase, and the like, the helical pitch can be adjusted, and the diffraction angle as a polarization diffraction element can be adjusted. Further, whether the helical structure becomes a right helical or a left helical depends on the chirality of the chiral agent or the optically active unit used, and therefore the right helical or the left helical depends on which chirality is selected. Can also be manufactured. As the liquid crystal material (A) used for fixing glass having a helical structure in the smectic liquid crystal phase, a polymer liquid crystal is suitable among the above liquid crystal materials. Also, as the liquid crystal material (B) used for the polymerization and immobilization, a liquid crystal material having a functional group sensitive to light, electron beam or heat is suitable. Such functional groups include vinyl, acrylic,
Methacryl group, vinyl ether group, cinnamoyl group, allyl group, acetylenyl group, crotonyl group, aziridinyl group, epoxy group, isocyanate group, thioisocyanate group, amino group, hydroxyl group, mercapto group, carboxylic acid group, acyl group, halocarbonyl group, Examples thereof include an aldehyde group, a sulfonic acid group, and a silanol group. Among them, an acryl group, a methacryl group, a vinyl group, a vinyl ether group, a cinnamoyl group, an epoxy group, an aziridinyl group and the like are preferable, and in particular, an acryl group, a methacryl group,
Vinyl, vinyl ether, cinnamoyl and epoxy groups are preferred. These functional groups need only be contained in the liquid crystal material, and may be contained in at least one of the liquid crystal substance and the non-liquid crystal substance constituting the material, and additives described later. When two or more kinds of substances each include the above functional groups, the functional groups may be the same and / or different functional groups. Further, even when one kind of substance has two or more functional groups, it may have the same kind and / or different kind of functional groups.

When preparing a liquid crystal layer to be a polarization diffraction element of the present invention, a surfactant, a polymerization initiator, a polymerization inhibitor, a sensitizer, a stabilizer, a catalyst, Additives such as dyes, pigments, ultraviolet absorbers, and adhesion improvers can be appropriately compounded in an amount of 50% by weight or less, preferably 30% by weight or less, more preferably 10% by weight or less. The liquid crystal layer to be the polarization diffraction element of the present invention, between the appropriate two interfaces, the above liquid crystal material, if necessary, and the above-mentioned additives are spread, to form a smectic liquid crystal phase having a helical structure, It can be obtained by holding this spiral structure. There is no particular limitation on the two interfaces for spreading the liquid crystal material, and any of a gas phase interface, a liquid phase interface, and a solid phase interface can be adopted, and the two interfaces need not be the same. However, it is recommended that two interfaces be a solid phase interface, one be a solid phase interface, and the other be a gas phase interface because of ease of manufacturing the liquid crystal layer. Examples of the gas phase interface include an air interface and a nitrogen interface, and the liquid phase interface includes water, an organic solvent, a liquid metal,
Other liquid crystals, polymer compounds in a molten state, and the like can be given. As the solid phase interface, polyimide, polyamide imide, polyamide, polyether imide, polyether ether ketone, polyether ketone, polyketone sulfide, polyether sulfone, polysulfone, polyphenylene sulfide, polyphenylene oxide, polyethylene terephthalate, polybutylene terephthalate , Polyethylene naphthalate, polyacetal, polycarbonate, polyarylate, acrylic resin, methacrylic resin, polyvinyl alcohol, polyethylene, polypropylene, poly-4-methylpentene-1 resin, cellulosic plastics such as triacetyl cellulose, epoxy resin, phenolic resin , Plastic film substrate made of polymer liquid crystal, etc .; aluminum, iron,
Metal substrates such as copper; glass substrates such as blue plate glass, alkali glass, alkali-free glass, borosilicate glass, flint glass, and quartz glass; various substrates such as ceramic substrates;
Examples include various semiconductor substrates such as a silicon wafer. Further, another film such as a film provided with an organic film such as a polyimide film, a polyamide film, or a polyvinyl alcohol film, a film provided with an obliquely deposited film such as silicon oxide, or a film such as ITO (indium-tin oxide) is provided on the substrate. Those having a transparent electrode, those having a metal film of gold, aluminum, copper or the like formed by vapor deposition or sputtering, and various semiconductor elements such as amorphous silicon thin film transistors (TFTs) can also be used as the solid phase interface. . The surface of various substrates that can be used as a solid phase interface may be subjected to an alignment treatment as needed. When a substrate that has been subjected to an alignment process is used, the direction of the helical axis in the obtained liquid crystal layer can be a fixed direction defined by the direction of the alignment process of the substrate. Further, depending on the type of the liquid crystal material, the type of the solid phase interface, and the method of the alignment treatment, the direction of the helical axis does not always match the direction of the alignment treatment of the substrate used as the solid phase interface, and may be slightly shifted. . The polarization diffraction element of the present invention can exhibit the effect as a polarization diffraction element even with such a liquid crystal layer. Further, in the present invention, a polarization diffraction element in which the direction of the helical axis is patterned can be obtained by changing the direction of the alignment treatment in a part. In the case of using such a method, for example, by setting a pattern of a region having a different direction of the helical axis to a period at which light interference occurs, in addition to a polarization diffraction effect caused by a smectic liquid crystal phase having a helical structure, alignment In the present invention, a polarization diffraction element that can also exhibit a diffraction effect by a pattern can be obtained. If the substrate used as the solid phase interface is not subjected to an alignment treatment, the resulting liquid crystal layer may be a multi-domain phase in which the direction of the helical axis of each domain is random, but even in such a liquid crystal layer. The effect as a polarization diffraction element can be exhibited. The orientation treatment applied to various substrates is not particularly limited,
For example, rubbing method, oblique evaporation method, micro groove method,
Stretched polymer membrane method, LB (Langmuir Blodgett)
Examples include a film method, a transfer method, a light irradiation method (photoisomerization, photopolymerization, photodecomposition, and the like), a peeling method, and the like. In particular, a rubbing method and a light irradiation method are desirable in the present invention from the viewpoint of ease of the manufacturing process. Furthermore, in the present invention, even when using various substrates that have not been subjected to an alignment treatment as a solid phase interface, a magnetic field, an electric field, shear stress, flow,
By applying stretching, temperature gradient, and the like, a liquid crystal layer in which the direction of the helical axis is defined in a fixed direction can be obtained.

The method of spreading the liquid crystal material between the interfaces is not particularly limited, and a method known in the art can be appropriately employed. For example, if a liquid crystal material is to be spread between two substrates, create a cell using the two substrates and inject the liquid crystal material into the cell, or laminate the liquid crystal material on the two substrates. Can be adopted. In the case where one substrate and the gas phase are used as an interface, the liquid crystal material is directly applied to the substrate, or after dissolving in a suitable solvent to form a liquid crystal material solution, the solution is applied to the substrate. Can be spread by such a method. In the present invention, from the viewpoint of the easiness of the manufacturing process, a method of spreading by applying a solution is particularly desirable. As the solvent when applying the solution, the type of liquid crystal material,
Appropriate ones can be selected according to the composition and the like, but usually, halogenated hydrocarbons such as chloroform, dichloromethane, carbon tetrachloride, dichloroethane, tetrachloroethane, trichloroethylene, tetrachloroethylene, chlorobenzene, orthodichlorobenzene, phenol, Phenols such as parachlorophenol,
Benzene, toluene, xylene, methoxybenzene,
Aromatic hydrocarbons such as 1,2-dimethoxybenzene, alcohols such as isopropyl alcohol and tert-butyl alcohol, glycols such as glycerin, ethylene glycol and triethylene glycol, ethylene glycol monomethyl ether, diethylene glycol dimethyl ether and ethyl cell Glycol ethers such as Solve, butyl cellosolve, acetone, methyl ethyl ketone, ethyl acetate, 2-pyrrolidone, N-methyl-2-pyrrolidone, pyridine, triethylamine, tetrahydrofuran, dimethylformamide, dimethylacetamide, dimethylsulfoxide, acetonitrile, butyronitrile, Carbon sulfide, a mixed solvent thereof and the like are used. To these solvents, a surfactant or the like may be added as necessary to adjust the surface tension of the solution and improve coatability. The concentration of the liquid crystal material in the solution needs to be appropriately adjusted according to the type and solubility of the liquid crystal material to be used, the final thickness of the target liquid crystal layer, and the like, but is usually 3 to 50% by weight, and preferably 3 to 50% by weight. It is in the range of 5 to 30% by weight. The coating method is not particularly limited, but a spin coating method, a roll coating method, a printing method, a dipping and pulling method, a curtain coating method, a Meyer bar coating method, a doctor blade method, a knife coating method, a die coating method, a gravure coating method, A microgravure coating method, an offset gravure coating method, a lip coating method, a spray coating method, or the like can be used. After the application, the solvent is removed by drying if necessary. After spreading the liquid crystal material as a uniform layer between various interfaces by the method described above, the liquid crystal material forms a helical alignment state in a smectic liquid crystal phase having a desired helical structure, and by maintaining the state, The polarization diffraction element of the present invention can be obtained. The method for forming the helical alignment state in the smectic liquid crystal phase having a helical structure is not particularly limited, and a method according to the type of the liquid crystal material and the like can be appropriately employed. For example, when a liquid crystal material is spread at a temperature at which a smectic liquid crystal phase having a helical structure can be formed, a smectic liquid crystal phase having a helical structure may be obtained simultaneously with the spreading. Further, the spread liquid crystal material is once heated to a temperature higher than a temperature at which a smectic liquid crystal phase having a helical structure is developed, for example, to develop a smectic A phase, a chiral nematic phase or an isotropic phase, and thereafter, Alternatively, it can be cooled to a temperature at which a smectic liquid crystal phase develops and can be oriented in a helical structure.

After a smectic liquid crystal phase having a helical structure is developed in the liquid crystal layer by any of the above methods, the helical structure of the smectic liquid crystal phase is determined according to the type and composition of the liquid crystal material forming the liquid crystal layer. Is held by an appropriate means. As a means for holding the spiral structure, it is preferable to employ the glass fixing or the polymerization fixing described above. When the glass fixing method is employed, the liquid crystal material (A) constituting the liquid crystal layer has a smectic liquid crystal phase having a helical structure developed at a temperature equal to or higher than the glass transition temperature, and the liquid crystal material (A) has a glassy state. The liquid crystal layer is fixed by cooling to a temperature. The cooling may be natural cooling, or may be forced cooling such as air cooling or water cooling. When the polymerization fixing method is adopted, a smectic liquid crystal phase having a helical structure in which the liquid crystal material (B) constituting the liquid crystal layer is expressed in a liquid crystal state is fixed by polymerizing or crosslinking the liquid crystal material (B). As the polymerization or crosslinking method, reactions such as thermal polymerization, photopolymerization, radiation polymerization such as γ-ray, electron beam polymerization, polycondensation, and polyaddition can be used. Among them, it is desirable to use photopolymerization or electron beam polymerization, which facilitates reaction control.

The thickness of the liquid crystal layer holding the smectic liquid crystal phase having a helical structure is usually 0.1 to 100 μm, preferably 0.2 to 50 μm, and more preferably 0.3 to 20 μm.
In the range. The liquid crystal layer obtained by fixing the smectic liquid crystal phase having a helical structure obtained on the substrate does not disturb the helical structure of the smectic liquid crystal phase even when the substrate is removed. Can be used. Further, the substrate can be used as a polarization diffraction element without removing the substrate, and the liquid crystal layer on the substrate can be transferred to another substrate to form a polarization diffraction element. Furthermore, a plurality of liquid crystal layers having the same or different polarization diffraction characteristics can be laminated to form a polarization diffraction element.
As another substrate on which the liquid crystal layer is transferred, for example, polyimide, polyamide imide, polyamide, polyether imide, polyether ether ketone, polyether ketone, polyketone sulfide, polyether sulfone, polysulfone, polyphenylene sulfide, polyphenylene oxide, Polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyacetal, polycarbonate, polyarylate, acrylic resin, methacrylic resin, polyvinyl alcohol, polyethylene, polypropylene, poly-4-
Examples include a plastic substrate formed from cellulose-based plastics such as methylpentene-1 resin and triacetyl cellulose, an epoxy resin, a phenol resin, and the like, a glass substrate, a ceramic substrate, paper, and a metal plate. Further, as the above another substrate, a polarizing plate, a retardation plate, a reflection plate, an optical element such as a diffusion plate, a nematic alignment film,
Various liquid crystal films such as a cholesteric alignment film can also be used. The polarizing diffraction element of the present invention may be provided with a protective layer such as a transparent plastic film or a hard coat layer on the surface of the liquid crystal layer in order to protect the surface, increase the strength, and improve environmental reliability. The polarization diffraction element of the present invention is an optical element for improving the viewing angle and improving the luminance of an optical pickup or a liquid crystal display device such as a CD, a DVD, a magneto-optical disk or the like, and a design utilizing iridescence of diffraction. It can be used for various applications such as films, optical information recording elements, security films, and combiners for head-up displays.

[0013]

The present invention will be described in more detail with reference to the following examples.
The present invention is not limited to these. In the examples, the measurement of the intrinsic viscosity, the determination of the liquid crystal phase series, and the measurement of the film thickness were performed according to the following methods. (1) Measurement of Intrinsic Viscosity Using an Ubbelohde viscometer, it was measured in a phenol / tetrachloroethane (60/40 weight ratio) mixed solvent at 30 ° C. (0.5 g / dL). (2) Determination of liquid crystal phase series Determined by DSC (Perkin Elmer DSC-7) measurement and observation with an optical microscope (BH2 polarizing microscope manufactured by Olympus Optical Co., Ltd.). (3) Film thickness measurement Dektak, a surface profile measuring device manufactured by Japan Vacuum Engineering Co., Ltd.
Model 3030ST was used. Also, interference wave measurement (UV-visible / near-infrared spectrophotometer V-570 manufactured by JASCO Corporation)
And a method of obtaining the film thickness from the data of the refractive index was also used. Example 1 Dimethyl 4,4'-biphenyldicarboxylate 200 m
mol, (S) -2-methyl-1,4-butanediol (enantiomeric access, ee.
= 50.0%) Using 120 mmol, 1,6-hexanediol 80 mmol, and tetra-n-butyl orthotitanate as a catalyst, a liquid crystalline polyester was synthesized by melt polymerization at 220 ° C. for 2 hours (intrinsic viscosity). 0.18 dL / g). A 10 wt% tetrachloroethane solution of this liquid crystalline polyester was prepared, applied to a polyphenylene sulfide film substrate having a rubbed polyimide film by spin coating, and the solvent was removed at 60 ° C. on a hot plate. Next, after heat-treating at 180 ° C. for 10 minutes in a thermostat to orientate in the smectic A phase, the temperature is lowered at a rate of 4 ° C./min to 120 ° C., which is the temperature for orienting to the chiral smectic C phase, taken out of the thermostat and cooled to room temperature. Then, the orientation of the liquid crystalline polyester was fixed in a glass state. The liquid crystal film thus obtained on the polyphenylene sulfide substrate was transferred onto a triacetyl cellulose film using an adhesive, and an overcoat layer was further provided as a protective layer, thereby producing Sample 1. The liquid crystal film in Sample 1 was glass-fixed with a chiral smectic C phase having a helical structure, and had a uniform film thickness (1.1 μm). Observation with a polarizing microscope and observation of the cross section of the film with an electron microscope showed that Sample 1
The helical pitch of the helical structure in the middle liquid crystal film was found to be about 1.0 μm. The direction of the helical axis in the film plane did not coincide with the rubbing direction and was shifted about 10 degrees counterclockwise. When linearly polarized light was incident on Sample 1 perpendicular to the surface, diffraction occurred in the direction of the helical axis. When linearly polarized light oscillating parallel and perpendicular to the helical axis was incident and the diffracted light was observed, there was a large difference in the intensity of the diffracted light depending on the oscillation direction of the incident polarized light. It turned out that there was also a difference. From the above, it was found that Sample 1 functions as a polarization diffraction element that exhibits a polarization diffraction effect. Example 2

Embedded image A bifunctional low-molecular liquid crystal represented by the above chemical formula (1),
A monofunctional chiral liquid crystal represented by the chemical formula (2) and a racemic monofunctional liquid crystal represented by the chemical formula (3) are mixed at 10: 8.
The mixture mixed at 0:10 (weight ratio) was 15% by weight, 0.2% by weight of Irgacure 907 (trade name, manufactured by Ciba Specialty Chemicals) as a photopolymerization initiator, and Kayacure DETX (trade name) as a sensitizer. A γ-butyrolactone solution containing 0.02% by weight of Nippon Kayaku Co., Ltd. and 0.05% by weight of Megafac F-144D (trade name, manufactured by Dainippon Ink) as a surfactant was prepared. A rubbed polyethylene terephthalate (PE)
T) The composition was applied on a substrate by spin coating, and the solvent was removed at 60 ° C. Next, heat treatment is performed at 100 ° C. for 3 minutes in a thermostatic oven, and after orientation in the smectic A phase, the temperature is lowered at a rate of 5 ° C./min to 60 ° C., which is a temperature for orientation in the chiral smectic C phase, and further heat treatment at 60 ° C. for 3 minutes. did. At that time, the oxygen concentration was reduced to 3% or less by purging with nitrogen. Then 60 ° C
The orientation of the liquid crystal material was fixed by performing photopolymerization with an irradiation energy of 800 mJ / cm 2 using an ultraviolet irradiation apparatus having a high-pressure mercury lamp of 120 W / cm as it was. The liquid crystal film on the PET substrate thus obtained is
It was fixed with a chiral smectic C phase having a helical structure, and had a uniform film thickness (1.2 μm). The direction of the helical axis in the film plane did not coincide with the rubbing axis, and was shifted about 13 degrees counterclockwise. When linearly polarized light was incident on this liquid crystal film perpendicularly to the film surface, diffraction occurred in the direction of the helical axis. When linearly polarized light oscillating parallel and perpendicular to the helical axis was incident and the diffracted light was observed, there was a large difference in the intensity of the diffracted light depending on the oscillation direction of the incident polarized light.
It was found that there was also a difference between the first order and the minus first order diffracted light intensities.
From the above, it has been found that the liquid crystal film can function as a polarization diffraction element exhibiting a polarization diffraction effect. Example 3 dimethyl 4,4'-biphenyldicarboxylate 200 m
mol, (R) -1,3-butanediol (enant)
iomeric excess, e. e. = 95.0
%) 80 mmol, 1,5-pentanediol 12
0 mmol, and tetra-ortho titanate as a catalyst
Liquid crystalline polyester was synthesized by melt polymerization at 220 ° C. for 2 hours using n-butyl (intrinsic viscosity:
0.20 dL / g). 10w of this liquid crystalline polyester
A t-% N-methyl-2-pyrrolidone solution was prepared, applied to a rubbed PET film substrate by a spin coating method, and the solvent was removed at 60 ° C. on a hot plate. Next, after heat-treating at 120 ° C. for 10 minutes in a thermostatic oven, it was taken out of the thermostatic oven, cooled to room temperature, and the orientation of the liquid crystalline polyester was fixed in a glassy state. Sample 2 was prepared by further providing an overcoat layer as a protective layer on the liquid crystal film of liquid crystalline polyester on the substrate thus obtained. The liquid crystal film in Sample 2 was glass-fixed with a chiral smectic CA phase having a helical structure, and had a uniform film thickness (1.2 μm). From observation with a polarizing microscope and electron microscopy of the film cross section,
The spiral pitch of the spiral structure in the liquid crystal film is about 0.8
μm. The direction of the helical axis in the film plane did not match the rubbing direction and was shifted clockwise by about 10 degrees. When linearly polarized light was incident on this sample 2 perpendicularly to the film surface, diffraction occurred in the helical axis direction. When linearly polarized light oscillating parallel and perpendicular to the helical axis was incident and the diffracted light was observed, there was a large difference in the intensity of the diffracted light depending on the oscillation direction of the incident polarized light. It turned out that there was also a difference. From the above, it was found that Sample 2 functions as a polarization diffraction element that exhibits a polarization diffraction effect.

[0014]

The polarization diffraction element of the present invention is composed of a liquid crystal layer which maintains an alignment state in a smectic liquid crystal phase having a helical structure, and is controlled by controlling the alignment in the liquid crystal phase. A polarization diffraction effect can be obtained. In addition, since it is possible to increase the area, it is lightweight, the manufacturing cost is low, and the handleability is good, so that it can be easily incorporated into another optical system. Therefore, the polarization diffraction element of the present invention is extremely industrially useful, such as being useful in optics, optoelectronics, optical information recording, liquid crystal display devices, security, design applications, and the like.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating the concept of a polarization diffraction element.

[Figure 2] A schematic diagram showing the refractive index of the polarization diffraction element shown in FIG. 1, (a) shows the refractive indices n _x in the x-axis direction, (b) the refractive index n _z in the z-axis direction Show.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Ryo Nishimura 8 Chidori-cho, Naka-ku, Yokohama-shi, Kanagawa Prefecture Inside the Central Research Laboratory, Nisseki Mitsubishi Co., Ltd. (72) Inventor Takehiro Toyooka 8, Chidori-cho, Naka-ku, Yokohama-shi, Kanagawa Prefecture Address F-term in Nisseki Mitsui Co., Ltd. Central Research Laboratory (reference) 2H049 AA43 AA57 AA60 BA02 BA46 BB42 BC04 BC21 BC22

Claims (5)

[Claims] 1. A polarization diffraction element comprising a liquid crystal layer holding a spiral structure of a smectic liquid crystal phase having a spiral structure. 2. A layer of a liquid crystal material exhibiting a smectic liquid crystal phase having a helical structure is heated to orient the smectic liquid crystal phase formed by the liquid crystal material into a helical structure at a temperature equal to or higher than its glass transition temperature. 2. The polarization diffraction element according to claim 1, comprising a liquid crystal layer obtained by fixing the helical structure by cooling the layer of the liquid crystal material to a glass state. 3. A layer of a liquid crystal material exhibiting a smectic liquid crystal phase having a helical structure, orienting the smectic liquid crystal phase into a helical structure at a temperature at which the liquid crystal material exhibits a smectic liquid crystal phase, and then polymerizing the liquid crystal material. 2. The polarization diffraction element according to claim 1, comprising a liquid crystal layer in which the helical structure of the smectic liquid crystal phase is fixed. 4. The polarization diffraction element according to claim 1, wherein the smectic liquid crystal phase having a helical structure is a chiral smectic C phase. 5. The polarization diffraction element according to claim 1, wherein the smectic liquid crystal phase having a helical structure is a chiral smectic C _A phase.