JP2000089015A - Diffraction element - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide high diffraction efficiency, freely and stably set characteristics such as diffraction angle, good heat resistance, large area, light weight, low manufacturing cost, and handling. Is provided. A liquid crystal material exhibiting a smectic liquid crystal phase having a helical structure is formed at a temperature equal to or higher than the glass transition temperature, and then cooled to a glass state.
Or, after a liquid crystal material exhibiting a smectic liquid crystal phase having a helical structure is oriented at a temperature at which the liquid crystal material exhibits the liquid crystal phase, and then polymerized while maintaining the orientation, the smectic liquid crystal phase having a helical structure is obtained. A diffraction element comprising at least a film having a fixed orientation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diffractive element which is useful in the fields of optics, optoelectronics, liquid crystal display devices, etc., and which can be manufactured even in a large area and has good handleability.

[0002]

2. Description of the Related Art Diffraction is a phenomenon in which, when a wave represented by light is interrupted by an obstacle, the wave wraps around a shadowed portion of the background. Simply speaking, it is a phenomenon in which light bends, and an element utilizing this phenomenon is called a diffraction element. Diffraction elements are often used to split light of a certain wavelength into a plurality of lights, or as spectroscopes that use the property that the diffraction angle varies depending on the wavelength of light. Applications are being made in various fields such as optical pickups.

[0003] Diffraction elements are mainly classified into amplitude type diffraction elements and phase type diffraction elements. 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. However, there is a disadvantage that the amount of transmitted light is reduced due to the presence of a portion that does not transmit light, and diffraction efficiency is poor in principle. On the other hand, a phase type diffraction element is, for example, one in which a periodic groove is formed on a substrate having no light absorption, for example, one having a change in the film thickness of the substrate, or having a refractive index inside a layer having a uniform thickness. Those having a periodic distribution are exemplified. Unlike the amplitude type, there is no part that does not transmit light,
It is possible to increase the diffraction efficiency. As a phase type diffraction element having a groove, for example, an element which is periodically engraved on glass or metal can be cited, but it is difficult to obtain a large-area and lightweight object. A hologram is used as another phase type diffraction element. A hologram is useful in that a Lippmann hologram using dichromated gelatin or a photopolymer can provide high diffraction efficiency, but has a problem that the manufacturing process is complicated, the manufacturing cost is high, and it is difficult to increase the area.

[0004] By the way, the liquid crystal is composed of a liquid and a crystal (c
It is an intermediate phase (mesophase) having both properties of rystal, and is characterized by having both fluidity as a liquid and anisotropy as a crystal. Various substances such as so-called low-molecular liquid crystal substances and high-molecular liquid crystal substances are known as substances capable of exhibiting a liquid crystal state (hereinafter, referred to as “liquid crystal substance”). Since it has an orientational order, it can be applied to various uses by utilizing or controlling its molecular orientation, and has formed a large industrial field.

[0005] Liquid crystals are roughly classified into nematic liquid crystals, smectic liquid crystals, discotic liquid crystals, and the like, based on their molecular shapes and molecular arrangements. Among these, a smectic liquid crystal is a liquid crystal in which a liquid crystal substance such as a rod-like molecule has a layer structure that can be called a one-dimensional crystal or a two-dimensional liquid. The smectic liquid crystal has a smectic A phase (SmA phase), a smectic B phase (SmB phase), a smectic C phase (SmC phase),
Smectic E phase (SmE phase), Smectic F phase (Sm
mF phase), smectic G phase (SmG phase), smectic H phase (SmH phase), smectic I phase (SmI phase),
Smectic J phase (SmJ phase), Smectic K phase (S
mK phase), smectic L phase (SmL phase) and the like. In some of these smectic phases, the orientation vector of each layer in the phase is gradually twisted at a certain angle, and when viewed as a whole, the orientation vector exhibits a certain helical structure. When a film having such a spiral structure orientation is formed on a substrate such that the spiral axis is substantially parallel to the substrate surface, light incident on the substrate surface can be diffracted. For example, Jpn.J.Appl.Phys.21, 224
In (1982), a chiral smectic C liquid crystal was oriented in a liquid crystal cell having a gap of several hundred μm made of two glass substrates so that the helical axis was parallel to the substrate.
-Ne laser light is diffracted.

It is conceivable to use such a liquid crystal cell as a diffraction element. However, if a liquid crystal cell in which only such low-molecular liquid crystal is aligned in the cell is used as a diffraction element, it will be a grating of the diffraction element. Since the helical pitch (the period of the helical structure) changes depending on the temperature, it is difficult to set the diffraction angle to a desired value, and the diffraction angle changes, or the orientation is disturbed by heat, and the performance as a diffraction element increases. There are problems such as loss and difficulty in increasing the area.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a high diffraction efficiency, a characteristic such as a diffraction angle that can be freely and stably set, a good heat resistance, a large area, a light weight, An object of the present invention is to provide a diffraction element which is low in cost and easy to handle.

[0008]

According to the present invention, there is provided a diffraction element comprising at least a film in which the orientation of a smectic liquid crystal phase having a helical structure is fixed.

Further, according to the present invention, the film comprises:
After forming a liquid crystal material exhibiting a smectic liquid crystal phase having a helical structure at a temperature equal to or higher than the glass transition temperature, the liquid crystal material is cooled to a glass state, and the orientation of the liquid crystal phase is fixed. The diffraction element is provided.

Further, according to the present invention, the film comprises:
After aligning a liquid crystal material exhibiting a smectic liquid crystal phase having a helical structure at a temperature at which the liquid crystal material exhibits the liquid crystal phase, the film is polymerized while maintaining the orientation, and is a film formed by fixing the orientation of the liquid crystal phase. The diffraction element is provided.

Here, the film constituting the diffraction element of the present invention is one in which the orientation of the smectic liquid crystal phase having a helical structure is fixed. When the orientation of the liquid crystal phase is fixed, the liquid crystal material exhibiting a specific liquid crystal phase retains the phase and orientation exhibited by the liquid crystal material while the orientation is maintained under the condition that the diffraction element is used. It means that there is no disturbance and the performance as a diffraction element is not lost.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The diffraction element of the present invention comprises at least a film in which the orientation of a smectic liquid crystal phase having a helical structure is fixed.

The smectic liquid crystal phase is a liquid crystal phase in which the molecules constituting the liquid crystal phase have a layer structure that can be called a one-dimensional crystal or a two-dimensional liquid. Examples of the smectic liquid crystal phase include a smectic A phase and a smectic B phase.
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 or Smectic L phase. In particular, a phase in which rod-like molecules such as a smectic I phase, a smectic F phase, a smectic J phase, a smectic G phase, a smectic K phase, and a smectic H phase are inclined with respect to a layer normal direction of a liquid crystal phase is preferable.

In particular, among the smectic liquid crystal phases such as those described above, chiral smectic C phase (SmC
^* Phase), chiral smectic I phase (SmI ^* phase) or chiral smectic F phase (SmF ^* phase) indicates the a ferroelectric optical activity, such as, or chiral smectic C _A phase (SmC _A ^* phase) , chiral smectic I _A phase (SmI _A ^*
Phase), or chiral smectic F _A phase (SmF _A * phase) and various chiral smectic phase, such as those showing the antiferroelectric have optical activity is particularly preferred as smectic phase having a helical structure. However, being chiral is not a requirement, for example, J. Mater. Chem. 6, 1231
Page (1996) and J. Mater. Chem. 7, 1307 (1997) and the like, and may be an achiral smectic phase having a helical structure or the like.

Among the various smectic phases described above, the most preferred one is from the viewpoint of the stability of the helical structure, the easiness of changing the helical pitch, the ease of synthesis, and the ease of orientation due to low viscosity. Is chiral smectic C
Phase or a chiral smectic C _A phase.

The helical structure means that the arrangement of the molecules constituting the liquid crystal phase changes little by little for each layer, forming a structure in which the arrangement of the molecules is rotated as a whole. Examples of the change in the arrangement of the molecules include a structure in which the direction of inclination of the molecules in the major axis direction with respect to the normal direction of the layer of the smectic liquid crystal phase is slightly rotated in adjacent layers.

The center axis of rotation of the molecular arrangement is called a helical axis, and the distance in the helical axis direction for one rotation is called a helical pitch. When light enters the helical structure, the angle formed by the incident light and the molecule differs depending on the position in the helix, regardless of the incident angle, so that the refractive index felt by the incident light varies. As a result, the light feels a periodic distribution of the refractive index, and diffraction occurs.

The direction of diffraction when light passes through the helical structure is, for example, to form a film having a helical structure such that the helical axis is parallel to the film surface in the film, and to make the light perpendicular to the film surface. When incident, the light usually diffracts in the direction of the helical axis. The direction of the helical axis in the diffraction element of the present invention is not particularly limited, and may be a direction that can function as a desired diffraction element. For example, it may be perpendicular, parallel, or inclined with respect to the film surface, and the inclination may be discontinuous or continuous. The orientation of the helical axis is microscopically composed of an oriented region (domain) having orientation, and macroscopically, the helical axis may be a multi-domain phase with various orientations, or all are aligned in the same direction. It may be a monodomain phase.

The diffraction angle when light passes through the helical structure is determined by the distance of the periodic distribution of the refractive index corresponding to the grating interval, ie, the helical pitch. Therefore, the diffraction angle of the diffraction element of the present invention can be easily adjusted by adjusting the helical pitch.

The helical pitch of the helical structure in the diffraction element of the present invention is not particularly limited, but is preferably from 0.2 to 20 μm, more preferably from 0.3 to 10 μm. The helical pitch may be constant in the film, but may be different depending on the location in the film. The spiral pitch is
In the production of the diffraction element of the present invention, it can be easily adjusted by 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.

The liquid crystal material used as a raw material of the diffraction element of the present invention is not particularly limited as long as it has a smectic liquid crystal phase having the above-mentioned helical structure in a phase series and can fix its orientation. . For example, various low-molecular liquid crystal substances, high-molecular liquid crystal substances, or mixtures thereof can be used. The liquid crystal material referred to in the present invention is not particularly limited as long as the finally obtained composition exhibits desired liquid crystallinity, and is a composition comprising a low-molecular and / or high-molecular liquid crystal material and a non-liquid crystal material. It does not matter. Further, in the liquid crystal material, various additives such as a surfactant, a polymerization initiator, a polymerization inhibitor, a sensitizer, a stabilizer, a catalyst, and the like can be blended as long as the effects of the present invention are not impaired. . The content ratio of the liquid crystal material in the liquid crystal material is usually 30 to 100% by weight,
Preferably 50-100% by weight, more preferably 70%
It can be -100% by weight.

Examples of the low-molecular liquid crystal substance include Schiff base compounds, biphenyl compounds, terphenyl compounds, ester compounds, stilbene compounds, tolan compounds, azoxy compounds, azo compounds, phenylcyclohexane compounds, A pyrimidine compound, a cyclohexylcyclohexane compound, a composition thereof, or the like can be used.

As the polymer liquid crystal substance, various kinds of main-chain polymer liquid crystal substances, side-chain polymer liquid crystal substances, and compositions thereof can be used.

Examples of the main chain type polymer liquid crystal substance include polyester, polyamide, polycarbonate, polyimide, polyurethane, polybenzimidazole, polybenzoxazole, polybenzthiazole, polyazomethine, and polyesteramide. System, polyester carbonate system, polyester imide system, etc., or a composition thereof. As the main-chain type polymer liquid crystal material, a semi-aromatic polyester-based polymer liquid crystal material in which mesogenic groups providing liquid crystallinity and bent chains of polymethylene, polyethylene oxide, polysiloxane and the like are alternately bonded, in particular, Non-all aromatic polyester polymer liquid crystal materials are preferred.

Further, the side chain type polymer liquid crystal material includes:
Polyacrylate-based, polymethacrylate-based, polyvinyl-based, polysiloxane-based, polyether-based, polymalonate-based, polyester-based substances having a skeleton chain of a linear or cyclic structure, such as a mesogen group bonded as a side chain, Or these compositions are mentioned. As the side-chain type polymer liquid crystal substance, a substance in which a mesogen group providing liquid crystallinity is bonded to a skeleton chain via a spacer formed of a bent chain is preferable. Further, those having a molecular structure having a mesogen in both the main chain and the side chain are also preferable.

As the liquid crystal material, a mixture of a low-molecular liquid crystal material and / or a high-molecular liquid crystal material as described above mixed with a chiral agent or introduced with an optically active unit exhibits a smectic liquid crystal phase having a desired helical structure. Is preferred. For example, a chiral agent is added to a liquid crystal material exhibiting a smectic C phase, a smectic I phase, a smectic F phase, or the like, or an optically active unit is introduced into the liquid crystal material to obtain a chiral smectic C phase, a chiral smectic I phase, a chiral smectic phase. A liquid crystal substance which can exhibit a chiral smectic phase which easily exhibits a helical structure such as a smectic F phase can be obtained. By appropriately adjusting the compounding amount of such a chiral agent, the introduced amount / optical purity of the optically active unit, the temperature condition at the time of orientation, etc., the characteristics of the film constituting the diffraction element of the present invention such as the helical pitch are adjusted. can do.

As the film constituting the diffraction element of the present invention, (A) a liquid crystal material exhibiting a smectic liquid crystal phase having a helical structure is formed at a temperature equal to or higher than the glass transition temperature and then cooled. A film in which the liquid crystal phase is fixed in the glassy state; or (B) a liquid crystal material exhibiting a smectic liquid crystal phase having a helical structure is oriented at a temperature at which the liquid crystal material exhibits the liquid crystal phase. Examples thereof include a film obtained by polymerizing while maintaining the orientation and fixing the orientation of the liquid crystal phase.

As the film (A), a film formed by using a liquid crystal material which can form a smectic liquid crystal phase having a desired helical structure in a liquid crystal state and which can be brought into a glass state by cooling is used. Can be used. Usually, a material formed using a liquid crystal material mainly composed of a polymer liquid crystal substance having the above properties is suitably used.

The film (B) may be a group which can be polymerized by a thermal reaction or a photoreaction, for example, a vinyl group, an acryl group, a methacryl group, a vinyl ether group, an allyl group, an epoxy group, an isocyanate group, an amino group, A material formed from a liquid crystal material containing at least a substance having a reactive functional group such as a hydroxyl group, a carboxylic acid group, an aldehyde group, a sulfonic acid group, or a silanol group can be used.
Usually, a material formed from a liquid crystal material containing a low-molecular liquid crystal substance as a main component is suitably used. Note that the low-molecular liquid crystal substance itself does not need to have the reactive functional group. For example, a composition with a non-liquid crystalline substance having the reactive functional group can be used in the present invention as a liquid crystal material.

As described above, the liquid crystal material may be a composition comprising a low molecular weight and / or high molecular weight liquid crystal substance alone or a plurality of types of liquid crystal substances, and exhibit a desired liquid crystal phase as the composition. As long as the composition is a low-molecular-weight and / or high-molecular-weight non-liquid crystalline material, the composition may be used.

The method for manufacturing the diffraction element of the present invention is not particularly limited, and a liquid crystal material containing a liquid crystal material is developed between two interfaces to orient the liquid crystal material into a smectic liquid crystal phase having a desired helical structure. After that, a film is formed by fixing the orientation of the liquid crystal phase, and the film may be used alone or appropriately processed as necessary to form a diffraction element. Here, as a method of fixing the orientation, (A) a liquid crystal material exhibiting a smectic liquid crystal phase having a helical structure is formed at a temperature equal to or higher than the glass transition temperature, and then cooled to a glass state. And (B) a method in which a liquid crystal material exhibiting a smectic liquid crystal phase having a helical structure is oriented at a temperature at which the liquid crystal material exhibits the liquid crystal phase, and then polymerized while maintaining the orientation.

The two interfaces for developing the liquid crystal material are not particularly limited, and any of a gas phase interface, a liquid phase interface and a solid phase interface can be used. Also the same 2
One interface may be used, or different interfaces may be used in combination. However, it is preferable to use two solid-phase interfaces or a combination of a solid-phase interface and a gas-phase interface from the viewpoint of practicality of the obtained product and easiness of production.

Examples of the gaseous phase interface include an air interface and a nitrogen interface. As the liquid phase interface,
Examples thereof include water, organic solvents, liquid metals, and polymer compounds in a molten state. 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-
Cellulose plastics such as methylpentene-1 resin and triacetyl cellulose; plastic film substrates such as epoxy resin and phenolic resin; metal substrates such as aluminum, iron and copper; blue plate glass, alkali glass, alkali-free glass, borosilicate glass Glass substrates such as glass, flint glass and quartz glass; various substrates such as ceramic substrates;
Alternatively, a substrate provided with an organic film such as a polyimide film, a polyamide film, or a polyvinyl alcohol film on these substrates, or a substrate provided with an oblique deposition film of silicon oxide or the like can be given.

These substrates can be used after being subjected to an orientation treatment as required. When using a substrate that has been subjected to an orientation treatment, the direction of the helical axis in the obtained diffraction element can be a fixed direction defined by the direction of the orientation treatment of the substrate, but the direction of the helical axis is not necessarily the orientation of the substrate. It does not always coincide with the direction of the alignment treatment, and may slightly deviate. When a substrate that is not subjected to an alignment treatment is used, the obtained diffraction element can exhibit a multi-domain phase in which the direction of the helical axis of each domain is random, but even in that case, the effect as a diffraction element can be obtained. Obtainable.

The orientation treatment of the substrate is not particularly limited, but includes a rubbing method, an oblique deposition method, a microgroove method, a stretched polymer film method, an LB (Langmuir-Blodgett) film method, a transfer method, and a light irradiation method. (Photoisomerization, photopolymerization, photodecomposition, etc.), peeling method and the like. In particular, a rubbing method and a light irradiation method are preferred from the viewpoint of ease of the manufacturing process.

The method for developing the liquid crystal material between the interfaces is not particularly limited, and various known methods can be used. For example, if the two substrates are used as interfaces and the liquid crystal material is added between them,
A cell can be created using two substrates, and the cell can be developed by injecting the molten liquid crystal material into the cell or by laminating the liquid crystal material on the two substrates.

In the case where one substrate and the gas phase are used as an interface, the development can be carried out by applying the liquid crystal material which has been melted or dissolved in an appropriate solvent to form a solution. preferable. In particular, from the viewpoint of the easiness of the manufacturing process, it is preferable to develop by applying a solution. As the solvent, an appropriate solvent can be appropriately selected depending on the type, composition, and the like of the liquid crystal material, but usually, chloroform, dichloromethane, carbon tetrachloride, dichloroethane, tetrachloroethane, trichloroethylene, tetrachloroethylene, chlorobenzene, orthodiethylene Halogenated hydrocarbons such as chlorobenzene, phenols such as phenol and parachlorophenol, benzene, toluene,
Aromatic hydrocarbons such as xylene, methoxybenzene, 1,2-dimethoxybenzene, acetone, methyl ethyl ketone, ethyl acetate, isopropyl alcohol, tert-butyl alcohol, glycerin, ethylene glycol, triethylene glycol, ethylene glycol monomethyl ether, diethylene glycol dimethyl ether , Ethyl cellosolve, butyl cellosolve, 2-pyrrolidone,
N-methyl-2-pyrrolidone, pyridine, triethylamine, tetrahydrofuran, dimethylformamide, dimethylacetamide, dimethylsulfoxide, acetonitrile, butyronitrile, carbon disulfide, a mixed solvent thereof and the like are used. Further, a surfactant may be added to the solution, if necessary, in order to adjust the surface tension of the solution and improve coatability.

The concentration of the liquid crystal material in the solution can be appropriately adjusted depending on the type and solubility of the liquid crystal material to be used, the thickness of the diffraction element to be manufactured, and the like, but is usually 3 to 50% by weight, preferably 3 to 50% by weight. Can range from 5 to 30% by weight.

The coating method is not particularly limited.
Spin coating, roll coating, printing, immersion pulling, curtain coating, Meyer bar coating,
Doctor blade method, knife coat method, die coat 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 if necessary, and the liquid crystal material can be developed on the substrate as a layer having a uniform thickness.

The method of orienting the developed liquid crystal material into a smectic liquid crystal phase having a helical structure is not particularly limited. However, when the liquid crystal material is developed at a temperature at which the liquid crystal material can take a smectic liquid crystal phase having a helical structure,
In some cases, a smectic liquid crystal phase having a helical structure is obtained simultaneously with the development. Further, if necessary, the developed liquid crystal material is heated to a temperature at which a smectic liquid crystal phase having a helical structure is developed, or is developed at a temperature at which a smectic liquid crystal phase having a helical structure or a temperature at which a smectic liquid crystal phase having a helical structure is developed. When there is another liquid crystal phase, the alignment can be performed by heating once to a temperature at which the phase develops and then cooling to a temperature at which a smectic liquid crystal phase having a helical structure develops. However, in any case, when the subsequent fixing step is performed by the method (A), the liquid crystal material is oriented at a temperature equal to or higher than the glass transition point.

At this time, if necessary, the orientation direction of the liquid crystal material can be controlled to a specific direction. This control can be performed, for example, by using, as the interface, one or more substrates that have been subjected to the alignment treatment. If two substrates are used as the interface, one of them
Only one of the sheets may be subjected to the orientation treatment, or both of the sheets may be subjected to the orientation treatment.

Specifically, for example, as the above-mentioned cell for injecting the molten liquid crystal material, a rubbing polyimide glass or the like is used to form a thick film cell in which the liquid crystal material is not spiraled by using two sheets. In addition, the orientation of the liquid crystal material can be set to a specific direction. Alternatively, the orientation can be set to a specific direction by laminating the liquid crystal material with two plastic films that have been subjected to an orientation treatment. In these cases, when the direction of the alignment process of the two substrates is made antiparallel (the direction of the alignment process is reversed. For example, in the case of rubbing, the rubbing direction is reversed), the helical axis is parallel to the substrate or uniformly. An inclined structure is obtained, and when the structure is made parallel (the orientation processing direction is the same), a structure in which the helical axis is parallel to the substrate, a structure in which the helical axis changes in the middle of the film thickness direction, and the like can be obtained.

Also, without using an alignment-treated substrate, a diffraction element can be obtained by applying a magnetic field, an electric field, shear stress, flow, stretching, temperature gradient, etc. to a liquid crystal material developed on an interface. The direction of the helical axis can be fixed.

The alignment of the liquid crystal material can be fixed by the method (A) or the method (B).

In the above method (A), the liquid crystal material having formed a smectic liquid crystal phase having a helical structure by the above method or the like is cooled at a temperature equal to or higher than the glass transition temperature until the liquid crystal material becomes a glass state. By lowering the temperature, the liquid crystal material is not brought into a crystalline state,
The orientation can be fixed in a glassy state. The cooling means is not particularly limited, and it is possible to perform desired cooling sufficient for immobilization simply by taking out from the heating atmosphere in the development or orientation step to an atmosphere below the glass transition point, for example, at room temperature. In order to increase the production efficiency and the like, forced cooling such as air cooling or water cooling may be performed.

In the method (B), the liquid crystal material oriented in a smectic liquid crystal phase having a helical structure is polymerized while maintaining the orientation. Although there is no particular limitation on the polymerization method, thermal polymerization, photopolymerization, radiation polymerization such as γ-ray, electron beam polymerization, polycondensation, polyaddition and the like can be used. Above all, photopolymerization using visible light or ultraviolet light which is easy to control the reaction and is advantageous in production is preferable.

The film obtained by fixing the orientation by these methods can be used as a diffraction element of the present invention as it is or by processing it as needed. For example, when a film is formed on a substrate, the film can be peeled off to form a diffraction element, the diffraction element can be formed as it is formed on the substrate, or a different element from the substrate can be used. A film can be laminated on the above substrate to form a diffraction element. The another substrate,
It is not particularly limited as long as it is transparent, for example, polyimide, polyamideimide, polyamide, polyetherimide, polyetheretherketone, polyetherketone, polyketonesulfide, polyethersulfone, polysulfone, polyphenylenesulfide, polyphenylene oxide, polyethylene terephthalate, poly Butylene terephthalate, polyethylene naphthalate, polyacetal, polycarbonate, polyarylate, acrylic resin, methacrylic resin, polyvinyl alcohol, polyethylene, polypropylene, poly-4-methylpentene-1 resin, cellulose-based plastics such as triacetyl cellulose, epoxy resin, A plastic substrate such as phenolic resin or a glass substrate can be used. It may be those that are not. Diffraction element of the present invention, even if the orientation-treated substrate is removed after obtaining a film in which the direction of the helical axis is defined in a fixed direction using the orientation-treated substrate, the orientation disorder is caused. Instead, it can be used as an element in which the direction of the helical axis is defined.

For the purpose of protecting the surface, increasing the strength and improving the environmental reliability, the above-mentioned protective layer such as a transparent plastic film may be provided on a film having the above-mentioned orientation fixed as necessary. .

The diffractive element of the present invention includes various optical films utilizing diffraction, such as an optical film for improving visibility, for enhancing the viewing angle and the luminance of a liquid crystal display device, and a design film utilizing iridescent diffraction. And optical recording films.

[0050]

As described above, the diffraction element of the present invention includes a film in which a specific orientation is fixed, so that the diffraction efficiency is high, the characteristics such as the diffraction angle can be freely and stably set, and the heat resistance is good. Because of its large area, light weight, low manufacturing cost, easy handling, and extremely easy integration into other optical systems, its industrial value is high in the optical field, optoelectronics field, liquid crystal display field, etc. high.

[0051]

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, measurement of intrinsic viscosity,
Determination of liquid crystal phase series, measurement of refractive index, measurement of film thickness, and 1
Observation of the next diffraction light and measurement of the diffraction angle 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) Measurement of Refractive Index The refractive index was measured with an Abbe refractometer (Type-4, manufactured by Atago Co., Ltd.). (4) Film thickness measurement Surface profile measuring device Dektak 3030ST manufactured by Japan Vacuum Engineering Co., Ltd.
A mold was used. In addition, a method of measuring the thickness from the data of the refractive index and the interference wave measurement (UV-visible / near-infrared spectrophotometer V-570 manufactured by JASCO Corporation) was also used. (5) Observation of first-order diffracted light and measurement of diffraction angle He-Ne laser light (wavelength λ = 632.8 nm) was irradiated to the sample, first-order diffracted light was observed, and the diffraction angle was determined. When the helical axis was tilted in the plane or in the film thickness direction, the diffraction angle was determined by rotating the sample so that the ± first-order diffraction angles became equal.

[0053]

Example 1 200 mmol of dimethyl 4,4'-biphenyldicarboxylate, 120 of (R) -2-methyl-1,4-butanediol (enantiomeric excess, ee = 60.0%)
A liquid crystalline polyester was synthesized by melt polymerization at 220 ° C. for 2 hours using 80 mmol of 1,6-hexanediol, and 1,2-hexanediol as a catalyst at 220 ° C. (intrinsic viscosity: 0.18 dL / g).

A 10% by weight solution of the liquid crystalline polyester in tetrachloroethane was prepared, applied to a glass substrate having a rubbed polyimide film by a spin coating method, and the solvent was removed at 60 ° C. on a hot plate. . Then, after heat-treating at 180 ° C. for 10 minutes in a thermostat to orientate in the smectic A phase, chiral smectic C
The temperature was lowered at a rate of 4 ° C./min to 120 ° C., which is the temperature at which the liquid crystal polyester was oriented to the phase, taken out of the thermostat, cooled to room temperature, and the orientation of the liquid crystalline polyester was fixed. The thus obtained film of the liquid crystalline polyester on the glass substrate was glass-fixed with a chiral smectic C phase having a helical structure, and had a uniform thickness (1.1 μm). Observation with a polarizing microscope and observation with an electron microscope of the cross section of the film revealed that the helical pitch of the helical structure formed on the film was about 1.0 μm. The helical axis was inclined about 15 degrees in the film thickness direction with respect to the substrate surface, and the direction of the inclination was the same as the direction in which the normal nematic liquid crystal tilted with respect to the rubbing direction. 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 this film is irradiated with a He-Ne laser, a primary diffraction spot is observed on the screen,
The diffraction angle was 48 degrees.

[0056]

[Example 2] ◎

Embedded image 20% by weight of a 15:85 (weight ratio) mixture of the bifunctional low molecular liquid crystal (1) and the monofunctional chiral liquid crystal (2), Irgacure 907 (trade name, Ciba Specialty Chemicals) as a photopolymerization initiator 0.2% by weight, Kayacure DETX (trade name, manufactured by Nippon Kayaku) as a sensitizer
0.02% by weight, and Megafac F as a surfactant
-144D (trade name, manufactured by Dainippon Ink) 0.05% by weight
-Xylene-acetone mixed solution containing (8: 2, volume ratio)
A solution was prepared. The solution was applied on a 75 μm polyarylate substrate having a rubbed polyimide film by a doctor blade method, and the solvent was removed at 50 ° C. Next, heat treatment is performed at 100 ° C. for 3 minutes in a constant temperature bath, and after orientation in the smectic A phase, the temperature is lowered at a rate of 5 ° C./min to 60 ° C., which is the temperature for orientation in the chiral smectic C phase. did. Thereafter, the mixture comprising the bifunctional low molecular liquid crystal and the monofunctional chiral liquid crystal is subjected to photopolymerization at an irradiation energy of 1200 mJ / cm ² using an ultraviolet irradiation apparatus having a high pressure mercury lamp of 120 W / cm at 60 ° C. Was fixed. The film thus obtained on the polyarylate substrate was fixed with a chiral smectic C phase having a helical structure, and had a uniform film thickness (1.5 μm). The helical axis was inclined about 20 degrees in the film thickness direction with respect to the substrate surface, and the direction of the inclination was the same as the direction in which the normal nematic liquid crystal tilted with respect to rubbing. The direction of the helical axis in the film plane does not coincide with the rubbing direction, and is approximately 1 counterclockwise.
It was off by four degrees. Observation with a polarizing microscope and observation with an electron microscope of the cross section of the film revealed that the helical pitch of the helical structure formed on the film was about 1.5 μm.

When this film is irradiated with a He—Ne laser, a primary diffraction spot is observed on the screen,
The diffraction angle was 25 degrees.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takehiro Toyooka 8 Chidori-cho, Naka-ku, Yokohama-shi, Kanagawa Nippon Petroleum Oil Co., Ltd. (72) Inventor Akira Takagi 8 Chidori-cho, Naka-ku, Yokohama-shi, Kanagawa N-Sekiyu Co., Ltd. Central Research Laboratory F-term (reference) 2H049 AA02 AA51 2H088 EA48 GA04 GA06 HA03 HA10 MA20 2H090 HB08Y HB13Y HC01 HC02 HC05 KA12 KA14 LA19 MB01

Claims (3)

[Claims] 1. A diffraction element comprising at least a film in which the orientation of a smectic liquid crystal phase having a helical structure is fixed. 2. The method according to claim 1, wherein the film is formed by forming a liquid crystal material exhibiting a smectic liquid crystal phase having a helical structure at a temperature equal to or higher than the glass transition temperature and then cooling the glass to a glassy state. The diffraction element according to claim 1, wherein the diffraction element is a film fixed. 3. The film is arranged such that a liquid crystal material exhibiting a smectic liquid crystal phase having a helical structure is oriented at a temperature at which the liquid crystal material exhibits the liquid crystal phase, and then polymerized while maintaining the orientation. The diffraction element according to claim 1, wherein the diffraction element is a film having a fixed orientation.