JP2001091719A - Optical device and security device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new optical device using a liquid crystal film holding a smectic liquid crystal phase. SOLUTION: The device consists of a film having a smectic liquid crystal phase holding a helical alignment structure. The device is produced by adding a diffraction function caused by a rugged pattern to the liquid crystal film that the axial direction of the helix in the aforementioned helical structure is almost in the normal direction of the film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a new optical element having a diffraction function, a security element provided with the element, and a security system using the security element.

[0002]

2. Description of the Related Art Diffraction grating films have been applied not only to conventional spectroscopic applications but also to 3-D display devices such as holographic stereoscopy in recent years, and their demand has been increasing, and their optical properties and physical properties have also been attracting attention. I have. In recent years, diffractive films using holograms have also been used for anti-counterfeiting (security) purposes such as cash vouchers and cards, and the diffusion rate from beer vouchers to computer software packages is expanding. However, the amount of information is small in the security using only the diffracted light by the hologram, and there is a limit in advanced security applications. Further, there has been a problem that a security element using a hologram is forged in recent years, and development of a new security element that is difficult to forge has been required.

[0003]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and provides a new optical element using a liquid crystal film holding a smectic liquid crystal phase and a security system using the element as a security element. The purpose is to provide.

[0004]

That is, an optical element according to the present invention comprises a film of a smectic liquid crystal phase retaining a helical alignment structure, wherein the helical axis direction of the helical structure is substantially in the normal direction of the film. It is characterized by having a film. The security element of the present invention is obtained by further imparting a diffraction function derived from the uneven shape to one or both surfaces of the above-mentioned liquid crystal film, whereby more advanced security information can be held.
The security system according to the present invention includes the above-described security element and a reader that optically recognizes the element, and selectively reflects the smectic helical pitch of the security element and 1/1 / sm of the smectic helical pitch. It is characterized in that the authenticity of the security element is determined by optically recognizing one or both of the selective reflections derived from the two pitches and the diffracted light derived from the diffraction function.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. The optical diffraction element of the present invention includes a liquid crystal film formed of a smectic liquid crystal phase having a helical alignment structure. The smectic liquid crystal phase refers to a liquid crystal phase in which molecules constituting the liquid crystal phase have a layer structure that can be called a one-dimensional crystal or a two-dimensional liquid (hereinafter, referred to as a “smectic layer”), which includes a smectic A phase and a smectic phase. 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. Among these, a smectic liquid crystal phase in which rod-like molecules are inclined with respect to the normal direction of the smectic layer, such as a smectic C phase, 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. It is preferred in the present invention. In addition, chiral smectic C phase (Sm
C * phase), a chiral smectic I phase (SmI * phase), a chiral smectic F phase (SmF * phase), etc., a smectic liquid crystal phase showing optical activity and ferroelectricity, a chiral smectic CA phase (SmCA ^*). Phase), chiral smectic IA phase (SmIA ^* phase), chiral smectic FA phase (SmFA ^* phase), etc., a smectic liquid crystal phase showing optical activity and antiferroelectricity, a chiral smectic Cγ phase (SmCγ ^* phase) , Chiral smectic Iγ phase (SmI
A smectic liquid crystal phase exhibiting optical activity and exhibiting ferrielectricity, such as a γ ^* phase) and a chiral smectic Fγ phase (SmFγ ^* phase), is also suitable for the present invention. Furthermore,
J. Mater. Chem. 6, 1231 (1
996) and J.M. Mater. Chem. Seven volumes,
A smectic liquid crystal phase which is achiral and exhibits a smectic phase having a helical alignment structure as described in page 1307 (1997) can also be suitably used in the present invention. In the present invention, among the various smectic liquid crystal phases described above, chiral from the viewpoint of stability of the helical alignment structure, easiness of variable helical pitch, ease of synthesis, and ease of alignment due to low viscosity. The smectic C phase is most preferred.

The helical alignment 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 one inclined angle to the next. Means the structure. And
The central axis of the helix in this helical orientation structure is called the helix axis, the direction of the helix axis is called the helix axis direction, and the distance in the helix axis direction for one rotation of the helix is called the smectic helix pitch. In the liquid crystal film provided in the optical element of the present invention, the helical axis direction of the smectic liquid crystal phase is substantially in the normal direction of the film. Here, the substantially normal direction of the film means that the angle formed between the spiral axis of the smectic liquid crystal phase and the normal of the film is usually 30 ° or less as an absolute value, preferably 20 ° or less,
It is more preferably 10 ° or less, most preferably 5 ° or less. Spiral axis rotation direction (twist direction)
Has no special restrictions. The entire liquid crystal layer constituting the liquid crystal film may have the same twist direction, or a mixture of left and right twists may be used. However, it is particularly desirable in the present invention that the entire liquid crystal layer has the same twist direction. Further, the helical alignment structure of the liquid crystal phase does not need to be formed over the entire surface area or the entire thickness direction of the liquid crystal film, and may be formed on a part or a plurality of parts such as the surface area or the internal area of the film. . Although the smectic spiral pitch is not particularly limited, it is usually 0.1 to 30 μm.
m, preferably in the range of 0.2 to 20 μm, more preferably 0.3 to 10 μm. The helical pitch may be constant in the liquid crystal film (liquid crystal layer) or may be partially changed, and the change may be continuous or discontinuous. In the process of manufacturing a liquid crystal film, the smectic helical pitch adjusts alignment conditions such as temperature, and adjusts the optical purity of the optically active site of the liquid crystal material used as a raw material of the liquid crystal film, the compounding ratio of the optically active substance, and the like. Can be appropriately adjusted by a known method.

In the liquid crystal film provided in the optical element of the present invention, the helical axis direction of the smectic liquid crystal phase having the helical alignment structure is substantially in the normal direction of the film. It has similar selective reflection characteristics. The center wavelength of this selective reflection can be obtained from the following relational expression (1) by using １ ／ of the smectic spiral pitch (hereinafter, referred to as “half pitch”). Center wavelength λ ^h _normal = 2 × in-plane average refractive index (N) × spiral pitch (p) / 2 (1) Further, the circularly polarized light selection characteristic of the selectively reflected light (direction of circularly polarized light)
Is determined by the twist direction of the helical orientation structure. The selective reflection obtained by the half pitch is defined as "half pitch reflection" in the present invention. In the half pitch reflection, a blue shift phenomenon similar to the cholesteric alignment structure can be observed when obliquely observed. The liquid crystal film included in the optical element of the present invention has a selective reflection (hereinafter, referred to as “full pitch”) itself caused by a smectic spiral pitch (hereinafter, referred to as “full pitch”), separately from the above half-pitch reflection.
This is called "full pitch reflection." ) With characteristics. The selective reflection center wavelength of this full-pitch reflection can be obtained by the following relational expression (2) according to the helical pitch. Center wavelength λ ^f _normal = 2 × in-plane average refractive index (N) × helical pitch (p) (2) This full pitch reflection cannot be observed from the helical axis direction, but is observed when obliquely observed. be able to.
However, when observed from an oblique direction, a so-called blue shift phenomenon appears. Therefore, the center wavelength is actually observed as a value smaller than the center wavelength λ ^f _normal determined by the relational expression (2) according to the observation angle. Note that the circularly polarized light selection characteristic in full pitch reflection does not show a remarkable circularly polarized light selection characteristic as seen in a half pitch. Λ ^h _normal and λ ^f _normal of the liquid crystal film used in the present invention are not particularly limited, and are appropriately selected according to various uses. For example, in a liquid crystal film in which λ ^h _normal is in the visible light region and λ ^f _normal is in the infrared region, reflected light with the color of λ ^h _normal is observed. The color based on the phenomenon can be observed.
Further, depending on λ ^h _normal , it shifts to the ultraviolet region and cannot be observed with the naked eye. On the other hand, λ ^f _normal has a center wavelength in the infrared region even when observed from the front and tilted slightly from the front, so it cannot be observed visually. Light can be observed. These center wavelengths can be observed by a machine or system using a spectroscope or the like irrespective of the infrared, visible, and ultraviolet regions. In addition, the specificity of the liquid crystal film can be confirmed visually. Furthermore, by utilizing the circularly polarized light selection characteristic at λ ^h _normal and adding a diffraction function derived from the concavo-convex shape described later, the specialty of the liquid crystal film can be further improved, which is very effective for security use. is there.

In the liquid crystal layer forming the liquid crystal film of the present invention, the helical alignment structure of the smectic liquid crystal phase must be maintained. Here, maintaining the helical alignment structure means that the helical alignment structure does not change with time in a situation where the liquid crystal film is used as an optical element or a security element. One method of maintaining the helical alignment structure in the smectic liquid crystal phase is, for example, a method of maintaining the helical alignment structure of the smectic liquid crystal phase formed by the liquid crystal layer by sandwiching a liquid crystal layer between two alignment substrates. It is. In this method, the presence of an alignment substrate is indispensable for maintaining the helical alignment structure. Another method of keeping the helical alignment structure in the smectic liquid crystal phase is a method of fixing the smectic liquid crystal phase having the helical alignment structure.
This method is preferable to the method of sandwiching the liquid crystal layer between two alignment substrates in terms of ease of manufacturing the liquid crystal layer, heat resistance, and practicality. Methods for fixing the helical alignment structure of the smectic liquid crystal phase are 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. Liquid crystal material (A) capable of forming a smectic liquid crystal phase and having a glassy state by cooling
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 composite 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 forming the liquid crystal layer of the present invention, if necessary, a surfactant,
Additives such as a polymerization initiator, a polymerization inhibitor, a sensitizer, a stabilizer, a catalyst, a dye, a pigment, an ultraviolet absorber, an adhesion improver,
It can be appropriately compounded in an amount of 70% by weight or less, preferably 50% by weight or less, more preferably 30% by weight or less of the whole.

The liquid crystal layer to be a composite diffraction element of the present invention is formed by spreading the above-mentioned liquid crystal material together with the above-mentioned additives, if necessary, between two suitable interfaces to form a smectic liquid crystal phase having a helical structure. It can be obtained by forming and retaining this helical 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.
Examples of the liquid phase interface include water, organic solvents, liquid metals, other liquid crystals, 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-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 compound diffraction element of the present invention can exhibit the effect as a compound diffraction element even with such a liquid crystal layer. Further, in the present invention, by changing the orientation processing direction in the partial portion, a composite diffraction element in which the helical axis direction is patterned can be obtained. In the case of using such a method, for example, in addition to the compound diffraction effect caused by the smectic liquid crystal phase having a helical structure, by setting the pattern of the region having a different helical axis direction to a period that causes light interference, the alignment In the present invention, a composite 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 composite 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.
In the present invention, any of the above-described gas-phase interface, liquid-phase interface, and solid-phase interface can be used, but among them, an interface having such a property that the liquid crystal molecule director rises with respect to the interface is used. Is very desirable from the viewpoint of orientation control. As such an interface, a combination of a solid phase interface using a glass substrate or a substrate having a hard coat layer such as silicon or polysiloxane and a gas phase interface is desirable.
As a substrate having a hard coat layer, a triacetyl cellulose film is most desirable.

The method for 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 composite 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 alignment structure is developed in the liquid crystal layer by any of the above methods,
The helical alignment structure of the smectic liquid crystal phase is maintained by appropriate means according to the type, composition, and the like of the liquid crystal material forming the liquid crystal layer. As means for maintaining the helical orientation, it is desirable to employ the glass fixing or the polymerization fixing described above. In the case of employing glass fixing, 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 a temperature at which the liquid crystal material (A) changes to a glassy state. It is fixed by cooling the liquid crystal layer until it. The cooling may be natural cooling, or may be forced cooling such as air cooling or water cooling. The cooling rate is usually 5 ° C./sec or more, preferably 10 ° C./sec or more, and more preferably 20 ° C./sec or more.
C / sec or more can be adopted. When the polymerization fixing method is employed, the 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 converted into the liquid crystal material (B).
Is immobilized by polymerizing or crosslinking. 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 liquid crystal layer of the present invention fixed by the above method can be used as a compound diffraction element in which the orientation of the helical axis remains defined without disturbing the orientation even when the substrate used for the preparation is removed. can do. The thickness of the liquid crystal layer in which the helical alignment state is fixed is usually 0.1 to 100 μm from the viewpoint of alignment and productivity.
m, preferably 0.2 to 50 μm, more preferably 0.3 to 20 μm.

When the liquid crystal film of the present invention obtained as described above is visually observed from the normal direction of the film, reflected light (half-pitch reflection) derived from selective reflection is observed. In the case where the transmittance is measured by wavelength using, for example, the transmittance decreases due to reflection only in the wavelength region where selective reflection can occur (a well-shaped transmittance curve is obtained). When polarization analysis is performed by a method such as ellipsometry, right circularly polarized light or left circularly polarized light is observed (circular polarization selectivity by half pitch). When obliquely observed from the front of the film, the wavelength of half pitch reflection Full-pitch reflection is observed on the wavelength side that is twice or slightly lower than twice (a well-type transmittance curve is obtained when measured with a spectroscope or the like, or depending on the wavelength, Can be confirmed I) has optical characteristics and the like.

The optical element of the present invention comprises a liquid crystal film as described above. The liquid crystal film may have an alignment substrate used at the time of film preparation, or may be a single liquid crystal film from which the alignment substrate has been peeled off. Further, a liquid crystal film prepared on an alignment substrate can be transferred to another substrate and used in an optical element in the form of a liquid crystal film with another substrate. Furthermore, a plurality of liquid crystal films having the same or different optical characteristics can be laminated, and this laminated body can be incorporated into an optical element. As another substrate used for transferring a liquid crystal film, 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-methylpentene-1
A plastic substrate formed of resin, cellulosic plastics such as triacetyl cellulose, epoxy resin, phenol resin, or the like, a glass substrate, a ceramic substrate, paper, a metal plate, or the like can be used. In addition, optical elements such as a polarizing plate, a retardation plate, a reflection plate, and a diffusion plate, and various liquid crystal films such as a nematic alignment film and a cholesteric alignment film can also be used as the above-mentioned another substrate. In addition, it is also possible to employ a diffraction film as another substrate and transfer a liquid crystal film to the diffraction film. However, in the present invention, it is desirable to impart diffractive power to the liquid crystal film itself. This is because when the optical element of the present invention is used as a security element, it is not only possible to make it thinner, but also it is more excellent in the specialty of the element, so that forgery becomes difficult. Any method can be used as a method for imparting a diffraction function to the liquid crystal film itself. For example, a method of laminating a substrate having a diffraction pattern (hereinafter, referred to as an “emboss plate”) on a liquid crystal film using a press or a laminating machine and transferring the pattern to the liquid crystal film (hereinafter, “embossing”) is known. This is one example. The embossing plate is not particularly limited, and is made of metal, resin, or the like, and has a diffraction grating shape (diffraction pattern) on its surface, but any of them can be used. The embossing plate may be obtained by laminating an inorganic or organic thin film formed into a desired diffraction pattern on a film surface having self-supporting properties.

The shape of the diffraction pattern may be any shape as long as diffracted light can be obtained. For example, various stripe patterns can be adopted, and any desired pattern or logo can be adopted for the diffraction pattern. The embossing conditions are selected so that the optical characteristics of the liquid crystal film, specifically, the conditions under which the helical alignment structure is not disturbed or destroyed. Incidentally, the embossing temperature varies depending on the thermal characteristics (glass transition temperature, degree of cross-linking, etc.) of the liquid crystal material forming the liquid crystal film, the support of the liquid crystal film, the type of embossing plate, the transfer method, etc., so it is generally specified. Although not possible, usually from room temperature to 200 ° C, preferably from room temperature to 150 ° C
Range. Also, the embossing time, usually 0.01
Seconds or more, preferably 0.05 seconds to 1 minute, more preferably 0.1 seconds to 15 seconds. When embossing is performed, it is desirable that the liquid crystal film itself has a certain degree of fluidity. Since this fluidity varies depending on the type of liquid crystal material constituting the liquid crystal material, it is extremely difficult to quantitatively describe the fluidity, and it cannot be defined by a single physical quantity. As one index for determining such embossing conditions, the glass transition temperature (T
g). In general, when the fluidity is measured while increasing the temperature of a liquid crystal material having Tg, the temperature is Tg.
It is known that when it reaches the vicinity, the fluidity gradually increases from a state of being vitrified and having extremely poor fluidity. Therefore, when a liquid crystal material having a desired helical alignment structure is obtained by using a liquid crystal material having Tg as a liquid crystal material, it is preferable to determine embossing conditions using the Tg as an index. If Tg is out of the above-described temperature range, embossing may be difficult. After the embossing is performed, the embossing plate used for the processing may be left attached to the liquid crystal film, or the embossing plate may be removed from the liquid crystal film. Embossing can also be applied to one film surface or both film surfaces of the liquid crystal film. The optical diffraction element of the present invention can be obtained by embossing a liquid crystal film by the above method.
The embossed liquid crystal film has half pitch reflection derived from the smectic liquid crystal phase unique to the film itself, circular polarization selection characteristics based on half pitch reflection, and optical characteristics such as full pitch reflection, and a diffraction function by embossing. The optical characteristic effect described above is exhibited. This liquid crystal film can be used as it is as an optical diffraction element, but if it is desired to increase the reliability against temperature, humidity, solvents, etc., mechanical strength, etc., the liquid crystal film (liquid crystal layer) after embossing is used. Curing can also be performed using a technique such as light irradiation or thermal crosslinking. For example, when a liquid crystal film is manufactured using the liquid crystal material (B) described above, when the helical alignment state is formed in the smectic liquid crystal phase, the liquid crystal material is cured to some extent to fix the helical alignment state. Thereafter, a method of performing embossing, and thereafter, fully curing the liquid crystal material can be adopted. The embossed liquid crystal film (liquid crystal layer) may be provided with a protective layer such as a transparent plastic film, a hard coat layer, and the like, as necessary, for the purpose of protecting the surface, increasing the strength, and improving environmental reliability.

The liquid crystal film of the present invention, which is composed of a film of a smectic liquid crystal phase retaining a helical alignment structure, and has a helical axis of the helical alignment structure substantially in the normal direction of the film, has the following optical characteristics in addition to By embossing the film surface, the incident light is diffracted at an angle specific to its wavelength and the shape of the diffraction grating, and also has a diffraction function (optical feature) that allows diffracted light of color to be visually recognized. From this, it can be said that the above liquid crystal film is very suitable for a security element. In the case where the liquid crystal film of the present invention is used as a security element as a detection target in a forgery prevention determination, one or two or more of the above-described optical characteristics can be used as determination criteria. Examples of the actual detection means include, for example, a method in which detection light is incident from the front or oblique direction, and the intensity of transmitted light or reflected light at a specific wavelength is measured.
In addition, regarding the transmitted light or reflected light, the polarization state of the detected transmitted light or reflected light is analyzed by ellipsometry or the like, or the light passes through the filter using a filter such as a circularly polarizing plate combining a polarizing plate and a quarter-wave plate. A method of detecting from the intensity of the emitted light can also be adopted. In this method, for example, for a liquid crystal film (diffraction element) that reflects right-handed circularly polarized light, a circularly-polarized filter that transmits right-handed circularly polarized light and a circularly-polarized light filter that transmits left-handed circularly polarized light are prepared. After that, the light intensity hardly decreases, and after passing through the latter, it can be determined by an extremely simple method, for example, by confirming that almost no light is transmitted. Regarding further, a method of detecting diffracted light at an angle at which diffracted light appears with respect to incident light of a certain wavelength, and confirming the diffraction function visually using a film provided with a diffraction grating pattern having designability It can be determined by a method or the like. Of the four glossy features, the presence of reflected light, especially due to full pitch reflection, is extremely difficult to manufacture except for liquid crystal films using smectic liquid crystals,
The present invention is intended to exert a tremendous effect as a security application intended. In other words, it is a security method that is already in use,
In addition to the optical characteristics described above, it is possible to detect optical characteristics that cannot be imitated at all except for the liquid crystal film of the present invention, whereby the authenticity of the subject can be confirmed. The security element of the present invention has a possibility of extracting more information by the development of the detection method, and can be said to greatly contribute to the future development of the security field.

[0017]

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, the measurement of the refractive index, the measurement of the film thickness, the measurement of the total light transmittance, the observation of the first-order diffracted light, and the 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 using an Abbe refractometer (Type-4, manufactured by Atago Co., Ltd.). (4) 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. (5) Measurement of transmittance The transmittance was measured using a spectrometer (UV-visible / near-infrared spectrophotometer V-570 manufactured by JASCO Corporation). (6) Observation of first-order diffracted light and measurement of diffraction angle He-Ne laser light (wavelength λ = 632.8 nm) was irradiated perpendicularly to the sample, the first-order diffracted light was observed, and the diffraction angle was determined. Example 1 Dimethyl 4,4'-biphenyldicarboxylate 200 m
mol, (S) -2-methyl-1,4-butanediol (enantiomeric excess, ee).
= 95.0%) A liquid crystalline polyester was synthesized by melt polymerization at 220 ° C for 2 hours using 120 mmol, 80 mmol of 1,6-hexanediol, and tetra-n-butyl orthotitanate as a catalyst (intrinsic viscosity). 0.18 dL / g). A 15 wt% tetrachloroethane solution of this liquid crystalline polyester was prepared, applied to a well-washed 12.5 cm square blue plate glass substrate with a bar coater, and dried on a hot plate at 60 ° C. for 2 hours to remove the solvent. Removed. On this liquid crystal layer surface, a polyethylene terephthalate (PET) film whose surface was silicon-treated (A-43 manufactured by Teijin) was laminated so that the silicon-treated surface was in contact with the liquid crystal layer. After heat-treating for a minute to orient in the smectic A phase, the temperature is lowered at a rate of 4 ° C./min to 120 ° C., which is the temperature at which the liquid crystal polyester is oriented to the chiral smectic C phase, taken out of the thermostat and cooled to room temperature. The glass was immobilized. Next, the siliconized PET film was peeled off from the laminate. The thus obtained liquid crystal film on the glass substrate is glass-fixed with a spiral chiral smectic C phase in which the spiral direction is in the normal direction of the film, and has a uniform film thickness (2.1
μm). Observation with a polarizing microscope revealed that the liquid crystal layer had a substantially uniform smectic spiral structure, and electron microscopic observation of the film cross section revealed that the liquid crystal layer had a layer structure laminated in the film thickness direction. (Sample 1). A commercially available embossed film J52,989 (manufactured by Edmund Scientific Japan) is cut out into a rectangle of 20 cm x 15 cm such that the grating direction of the diffraction grating is long, and the sample is covered so as to cover the liquid crystal surface of sample 1. 1 and the diffraction grating surface of the embossed plate film are in contact with each other, and one short side is fixed to the glass with cellophane tape. (Made by the company). The heat lamination was performed at a temperature of the laminating roll of 75 ° C., and the moving speed of the sample was 25 mm / sec. After the heat lamination, Sample 1 and the embossed plate film were integrally adhered. The laminate was cooled to room temperature, and the embossed plate film was gently peeled off from the laminate along the longitudinal direction of the film. The liquid crystal layer left on the glass substrate was again fixed in the smectic liquid crystal phase (Sample 2).
Sample 2 has a blue selective reflection light in a homeotropic helical orientation visually when viewed from the front, and the spectrometer V-5
Sample 2 in the sample folder of 00 (manufactured by JASCO)
Was set in front (the measurement light axis and the film normal of sample 2 were parallel) and the transmission spectrum was evaluated. As a result, a reduced area of transmitted light due to selective reflection was observed in the vicinity of 485 nm of the visible light region, and 460 to 460 nm. A "well-type" spectrum having a low transmittance only at around 510 nm was obtained. In order to examine the circular polarization selectivity of this selective reflection, a linear polarizing plate (LLC-5618 manufactured by Sanritz Co.) and a substantially 波長 wavelength plate (a retardation of 120 nm and a wavelength of 800 when measuring a wavelength band of 400 to 550 nm) are used. When measuring a band of ~ 1200 nm, a 250 nm uniaxial wave plate) is set to 45
A right circularly polarizing plate which is bonded at a right angle to allow right circularly polarized light to pass therethrough, and a left circularly polarizing plate obtained by bonding a polarizing plate and an approximately 波長 wavelength plate to each other at 45 ° are prepared. When the transmittance measurement was performed with the right circularly polarizing plate overlaid, a well-type selective reflection region similar to that when the circularly polarizing plate was not used was observed. No region where the transmittance was significantly reduced was observed. Therefore, it was confirmed that the selectively reflected light was half-pitch reflection having circular polarization, and the spiral direction of sample 2 was confirmed to be a right-handed spiral from the circular polarization of the selectively reflected light. Furthermore, sample 2 was placed on the sample holder of the spectrometer at an angle of about 30 degrees from the front, and the same measurement was performed. When the right circularly polarizing plate was superimposed, a reduced area of transmitted light was observed at around 465 nm. Further, another reduced region of transmitted light was observed around 995 nm. In the measurement with the left circularly polarizing plate superimposed, a very weak transmitted light reduction region around 465 nm and 995 nm as in the case with the right circularly polarizing plate superimposed.
A reduced area of transmitted light was observed in the vicinity. From these facts, the transmittance reduction region around 465 nm is a region in which the circularly polarized light selective reflection derived from half pitch reflection is shifted to the lower wavelength side by blue shift, and the 975 nm transmission light reduction region is a circle derived from full pitch reflection. It is considered to be a polarization-nonselective blue shift of the reflected light. In addition, in the sample 2, apart from the selective reflection derived from the homeotropic helical structure, the direction in which the longitudinal direction of the embossed film was in contact was 1
When viewed obliquely from the 3 o'clock and 9 o'clock directions when viewed in the 2 o'clock direction, iridescent light characteristic of the diffraction grating was observed. From the glass substrate side of sample 2, He /
When collimated light from a Ne laser was incident, diffracted light was observed in the short side direction of the film, and the diffraction angle of the first-order diffracted light (the angle of the diffracted light with respect to the film normal) was 23 degrees. Example 2

Embedded image A bifunctional low-molecular liquid crystal represented by the above chemical formula (1),
The monofunctional chiral liquid crystal represented by the chemical formula (2) and the racemic monofunctional liquid crystal represented by the chemical formula (3) were mixed in a ratio of 3: 8
15% by weight of a mixture mixed at a ratio of 0:17 (weight ratio), 0.2% by weight of Irgacure 907 (trade name, manufactured by Ciba Specialty Chemicals) as a photopolymerization initiator, and Kayacure DETX as a sensitizer A γ-butyrolactone solution containing 0.02% by weight (trade name, manufactured by Nippon Kayaku) and 0.05% by weight of Megafac F-144D (trade name, manufactured by Dainippon Ink) as a surfactant was prepared. The solution was applied onto a commercially available triacetyl cellulose film-coated triacetyl cellulose film (KC80-HC manufactured by Konica) substrate by a spin coating method, and the solvent was removed at 60 ° C. Then, heat treatment was performed at 100 ° C. for 3 minutes in a thermostatic oven, and after orientation in the smectic A phase, chiral smectic C was obtained.
The temperature is lowered at a rate of 5 ° C./min to 60 ° C., which is a temperature at which the phase is oriented,
Further, heat treatment was performed at 60 ° C. for 3 minutes. At that time, nitrogen substitution was performed to reduce the oxygen concentration to 3% or less. After that, leave it at 60 ° C for 1
The alignment of the liquid crystal material was fixed by photopolymerization using an ultraviolet irradiation device having a high-pressure mercury lamp of 20 W / cm and irradiation energy of 200 mJ / cm 2. The film on the triacetylcellulose film substrate thus obtained was fixed with a chiral smectic C phase having a homeotropic helical structure, and had a uniform film thickness (2.2 μm) (Sample 3). A diffraction grating was formed on Sample 3 by laminating an embossed plate film at 55 ° C. in the same manner as in Example 1.
Thereafter, with the embossed plate film laminated, light irradiation of 800 mJ was further performed to completely cure the liquid crystal layer. Sample 4 was obtained by removing the embossed plate film from the film laminate. When the same optical measurement as in Example 1 was performed on Sample 4, a center wavelength of 505 nm and right-circular polarization selective half-pitch reflection were observed at an angle from the front, and a wavelength of 480 nm and a pseudo-right circle were observed at an angle of 30 degrees. A blue shift of half pitch reflection with polarization selectivity and a blue shift of full pitch reflection with non-circular polarization selectivity at a wavelength of 995 nm were observed. In sample 4, iridescent light diffracted by the same diffraction grating as in sample 2 was observed. Example 3 The sample 4 prepared in Example 2 was evaluated using the optical system shown in FIGS. As the observation light source 1, a commercially available tungsten-iodine lamp RJ-2012 (manufactured by JASCO Corporation) is used, and a monochromator is used to change the wavelength. A collimated light source is used, and the measurement light from the light source is reflected by the sample surface. The sample 2 is irradiated with light through a half-mirror for separating the observation light, a circular polarizing plate composed of a laminate of a polarizing plate and a substantially quarter-wave plate (each used in Example 1), The light reflected on the four surfaces again passes through the circularly polarizing plate and is reflected on the half mirror,
It is extracted as observation light 1. The observation light is converted into an electric signal by a photodiode, and when light is detected based on a dark state where no film is installed, “o” is detected.
If there is no change from the dark state to the dark state, the presence or absence of the observation light is determined based on the binary value of “off”. The axial arrangement of the polarizing plate included in the circular polarizing plate is as shown in FIG.
The four-wavelength plate switches between the two arrangements shown in FIG. 2 and transmits right-handed circularly polarized light in a relative relationship between the transmission axis of the polarizing plate and the slow axis of the quarter-wave plate as shown in the figure. "Right circularly polarizing plate", "Left circularly polarizing plate" that transmits left circularly polarized light
Used in one of the two states. As the measurement light source 2, a light source combining a tungsten-iodine lamp / monochrome meter is used similarly to the measurement light source 1, and is irradiated from the angle of elevation φ = 59 degrees to the surface of the sample 2, and φ = 5
From the angle of 9 degrees, the presence or absence of reflected light is determined by the above-mentioned "on" and "off". Table 1 shows the measurement conditions and the results of discriminating the observation light.

[0018]

[Table 1]

From the results shown in Table 1, the observation light was detected at the specific wavelength and the specific circularly polarized light of the measurement light 1, and the sample 4
Was confirmed to be a smectic liquid crystal film having a homeotropic helical structure. Comparative Example 1 Example 3 was the same as in Examples 1 and 2, except that the embossed plate film used for forming the diffraction grating was used instead of Sample 4.
The same operation as described above was performed. Table 2 shows the measurement conditions and the results of discriminating the observation light.

[0020]

[Table 2]

The embossed plate film was visually observed as sample 4.
However, the measurement result of Example 3 and the result of this comparative example were different, and it was confirmed that the film was a different kind of film from the smectic liquid crystal film. Example 4 The sample 4 prepared in Example 2 was evaluated using the optical system shown in FIG. As the observation light sources 1 and 2, as in the third embodiment, a collimated light source having a wavelength variable by combining a tungsten-iodine lamp with a monochromator was used.
It is assumed that the presence or absence of observation light is determined based on binary values of “n” / “off”. Also in the third embodiment, the elevation angle φ is 59 degrees. Further, a He / Ne laser (wavelength 63) is used as the measurement light source 3.
3 nm) is vertically incident from the lower side of the film surface, and at the position of the elevation angle ψ on the front side in the figure, the presence or absence of the diffracted light is similarly determined as “on” /
The determination is made based on the binary value “off”. Table 3 shows each measurement condition and the result of discriminating the observation light.

[0022]

[Table 3]

Comparative Example 2 Example 4 was repeated except that the embossed plate film used for forming the diffraction grating in Example 1 and 2 was used instead of Sample 4.
The same operation as described above was performed. Table 4 shows the measurement conditions and the results of discriminating the observation light.

[0024]

[Table 4]

The measurement results of Example 4 were different from the results of this comparative example, and it was confirmed that the embossed plate film was a different type of film from the smectic liquid crystal film.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an optical system adopted when a sample created in Example 2 is evaluated in Example 3.

FIG. 2 is an explanatory diagram showing the axial arrangement of a sample created in Example 2.

FIG. 3 is a schematic diagram of an optical system adopted when a sample created in Example 2 is evaluated in Example 4.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Takehiro Toyooka 8 Chidori-cho, Naka-ku, Yokohama-shi, Kanagawa Nishiishi Central Research Laboratory Co., Ltd. F-term (reference) 2H049 AA03 AA31 AA37 AA40 AA43 AA55 AA65 BA05 BA07 BA43 BB03 BC23

Claims (6)

[Claims] 1. An optical element comprising a liquid crystal film made of a film of a smectic liquid crystal phase having a helical alignment structure, wherein the helical axis direction of the helical alignment is substantially normal to the film. 2. The optical element according to claim 1, wherein the liquid crystal film itself has a diffraction function. 3. The optical element according to claim 1, wherein one or both sides of the liquid crystal film are provided with a diffraction function derived from an uneven shape. 4. The optical element according to claim 1, wherein the smectic liquid crystal phase held by the liquid crystal film is a chiral smectic C phase. 5. A security element comprising the optical element according to claim 1. 6. A security system comprising the security element according to claim 5 and a reader for optically recognizing the element, wherein the security element has a selective reflection derived from a smectic spiral pitch and a smectic spiral. A security system that optically recognizes one or both of the selective reflections derived from a half of the pitch and the diffracted light derived from the diffraction function to determine whether the security element is authentic.