HK1050928A - Composite diffraction device - Google Patents

Description

Composite diffraction device

[ field of the invention ]

The present invention relates to a composite diffraction device suitable for use in various fields, such as optics, optoelectronics, optical information recording, liquid crystal display devices, and various uses such as security devices and design devices, which can be prepared to have a large area and easy handling.

[ background of the invention ]

A diffraction device utilizing the light diffraction phenomenon or a type of hologram device as it has various functions such as a lens function, a spectrum function, a branching/multiplexing function and an optical intensity distribution conversion. Based on these functions, they are widely used in spectroscopic devices, holographic scanners of bar-code readers, and optical readers of compact disks. In addition, they are also used to prevent forgery of credit cards or various bills, taking advantage of the difficulty of holographic forgery and design.

The diffraction devices are classified into an amplitude type diffraction device and a phase type diffraction device according to their shapes. The amplitude type diffraction device obtains diffracted light for light that is allowed to pass through a non-light transmitting portion of uniform thickness such as a periodically arranged elongated line. The phase type diffraction apparatus is further classified into an apparatus in which periodic grooves are formed on the surface of a substrate that does not absorb light, and a refractive index modulation type apparatus in which the refractive index is periodically changed is formed in a uniform thickness. Unlike the amplitude type diffraction device, the diffraction efficiency of the phase type diffraction device can be improved because there is no region that does not transmit light. Examples of the phase type refraction device having grooves on the surface thereof are those formed by forming grooves on the surface of glass, metal, or plastic. Examples of refractive index type diffraction devices are holographic devices made using gel dichromate or optical polymers.

The helical structure of smectic liquid crystals is also known to be used as a refractive index type device as described in journal of applied physics of japan, volume 21, page 224 (1982).

In the aforementioned use for preventing forgery of credit cards or bills, a hologram image is prepared by embossing a thermoplastic film to form grooves. However, such holographic images are limited in the case of enhancing designability and anti-counterfeiting properties. If light incident on a diffractive device can be diffracted from multiple directions or angles thereof, the device can be expected to have a wider range of uses.

An object of the present invention is to provide a composite diffraction device having a refractive index modulation type diffraction function using a liquid crystal phase helical structure, combined with a diffraction function using grooves formed on the surface thereof, resulting in an improvement in design, and easy to set a diffraction angle and processing, adapted to an increase in size.

[ summary of the invention ]

The diffraction device according to the present invention is characterized in that a diffraction function derived from an uneven pattern is used for a diffraction device including a liquid crystal layer in which a spiral direction of a smectic liquid crystal phase having a spiral structure is maintained.

The diffraction device according to the invention has two diffraction functions, one obtained from a fixed helical direction of the smectic liquid crystal phase and the other from a non-uniform pattern forming its surface.

The smectic liquid crystal phase of the liquid crystal layer used in the present invention refers to a liquid crystal phase in which liquid crystal molecules form a smectic layer structure of one-dimensional and two-dimensional liquids.

Examples of smectic liquid crystal phases are smectic A phase, smectic B phase, smectic C phase, smectic E phase, smectic F phase, smectic G phase, smectic H phase, smectic I phase, smectic J phase, smectic K phase, smectic L phase. Among them, preferred are liquid crystal molecular phases aligned in an oblique manner with respect to the general direction of the smectic liquid crystal layer, such as smectic C phase, smectic I phase, smectic F phase, smectic J phase, smectic G phase, smectic K phase, smectic H phase.

Alternatively, the inventionAmong them, those exhibiting optical activity and exhibiting, for example, chiral smectic C phase (SmC) can be suitably used^*) Chiral smectic I phase (Smi)^*) And chiral smectic F phase (SmF)^*) Exhibit optical activity and are as chiral smectic C_APhoto (SmC)_A ^*) Chiral smectic I_APhoto (SmI)_A ^*) Chiral smectic F_APhoto (SmF)_A ^*) And exhibit optical activity and are as chiral smectic C_γPhoto (SmC)_γ ^*) Chiral smectic I_γPhoto (SmI)_γ ^*) Chiral smectic F_γPhoto (SmF)_γ ^*) A ferroelectric liquid crystal phase of (1).

Further alternatively, those smectic phases which are chiral and exhibit a helical structure as described in J.Matter, chem.Vol.6, pages 1231 or J.Matter.chem.Vol.7, pages 1307, published in 1996, may be suitably used.

However, the chiral smectic C phase or chiral smectic C is most preferable for the purpose of easy synthesis of liquid crystal material, easy orientation of helical structure in smectic liquid crystal phase, easy change of helical pitch, and stability of helical structure_AAnd (4) phase(s).

The term "helical structure in a smectic liquid crystal phase" is used herein to refer to a structure in which the meridional axes of liquid crystal molecules are tilted at an angle from the vertical direction of the smectic layers, and the tilt direction is twisted little by little between the layers. The central axis of such a helical structure is called a helical axis, and the length in the helical axis direction of one turn of the helix is called "helical pitch".

When light is allowed to transmit through a liquid crystal layer composed of a smectic liquid crystal phase of a helical structure, the diffraction direction of the light depends on the helical axis direction of the liquid crystal phase. For example, in the case where the helical axis is parallel to the liquid crystal layer, the light incident perpendicularly is diffracted to the helical axis direction. There is no particular limitation imposed on the helical axis direction of the liquid crystal layer forming the composite diffraction device of the present invention. Therefore, the screw axis direction can be appropriately selected so as to exhibit desired characteristics. For example, the helical axis direction may be parallel to or inclined with respect to the liquid crystal layer surface. In addition, the tilt angle may vary discretely or continuously. In addition, the helical axis direction may be microscopically determined by the crystal domains, and may be macroscopically directed in various directions or the same direction. The helical structure need not be formed entirely on the liquid crystal layer and may be formed on a surface area or inside the liquid crystal layer, or a portion thereof.

The helical pitch of the liquid crystal layer is usually 0.1 to 20 μm, preferably 0.2 to 15 μm, more preferably 0.3 to 10 μm. In the liquid crystal layer, the pitch of the helices may be constant, but may vary depending on the position thereof. The variation may be continuous or discrete. The pitch of the helices can be suitably adjusted in a conventional manner, for example, to adjust the orientation conditions such as temperature, the optical purity of the optically active portion, and the mixing ratio of the optically active materials. The spiral pitch corresponds to the grid pitch. When light is incident on the helical structure, diffraction occurs at an angle corresponding to the pitch of the helix. Therefore, the pitch of the spirals must be properly adjusted to obtain the desired diffraction angle.

In the complex diffraction device according to the present invention, the liquid crystal layer having the diffractivity derived from the spiral structure thereof is provided on the surface thereof in a non-uniform pattern. May be of any shape as long as it exhibits diffraction caused by it. For example, it may be a rectangular groove, a corrugation, a serration or a step shape formed on a flat surface with the same gap. Alternatively, the graphics may be of a combination of two or more of these types of unevenness. The pattern may also be designed to be revealed by diffraction by mixing a portion having an uneven pattern and a portion having no unevenness, or forming areas where light is diffracted in different directions so as to be marked.

Since the period or interval of the uneven pattern corresponds to the grid pitch, a desired diffraction angle can be obtained by appropriately adjusting the period or interval.

The complex diffraction device may be obtained by forming a layer having an uneven pattern and then laminating it onto a liquid crystal layer, or by directly forming an uneven pattern thereon. In the latter case, the uneven pattern may be formed on one or both sides of the surface of the liquid crystal layer.

In the present invention, the direction and/or angle of diffraction of the liquid crystal layer may be the same as or different from those caused by the non-uniform pattern. However, when considering the effect or designability of the complex diffraction device, it is preferable that the direction and/or angle of diffraction caused by the spiral structure is partially different from the direction and/or angle caused by the uneven pattern.

In the liquid crystal layer forming the composite diffraction device of the present invention, the helical structure of the smectic liquid crystal phase must be maintained. By "maintaining the helical structure" is meant that the change of the helical structure over time does not occur in the case where the liquid crystal layer is used in a compound diffraction device. One of the methods for maintaining the spiral structure is to sandwich a liquid crystal layer between a pair of alignment substrates. In this way, if one of the substrates is removed, the spiral structure may not be maintained in a stable state.

Another approach is to fix the helical structure of the liquid crystal phase. This method is superior to the above method in terms of easy production, heat resistance, and practicality of the liquid crystal layer.

Methods of fixing the helical structure of the liquid crystal phase are roughly classified into a glass fixing method and a polymerization fixing method. In the glass fixing method, the helical structure is fixed by converting the smectic liquid crystal phase into a glassy state. The liquid crystal material that can be selected for this method is a material that is hereinafter referred to as "liquid crystal material a" and that is capable of forming a smectic liquid crystal phase having a helical structure and is capable of being cooled to a glassy state. In the coacervation immobilization method, a smectic liquid crystal phase having a helical structure is immobilized by coacervating or crosslinking liquid crystal molecules. Liquid crystal materials which are an alternative to this method are those hereinafter referred to as "liquid crystal materials B" which are capable of forming a smectic liquid crystal phase having a helical structure and which are capable of being condensed or crosslinked by light, electron beam, or heat.

More specific examples of liquid crystal materials that may be selected for the liquid crystal layer are low molecular weight liquid crystals and liquid crystal polymers capable of forming smectic liquid crystal phases of helical structures. The liquid crystals need only be those exhibiting the desired liquid crystalline state and orientation and may be a mixture of single or multiple low molecular weight-and/or liquid crystalline polymer materials and single or multiple low molecular weight-and/or non-liquid crystalline polymer materials.

Optional low molecular weight liquid crystals are schiff base compounds, biphenyl compounds, terphenyl compounds, ester compounds, thioester compounds, stillbene compounds, tolyne compounds, azoxy compounds, phenylcyclohexylamine compounds, pyrimidine compounds, cyclohexylcyclohexylcyclohexane compounds, and mixtures thereof.

Liquid crystal polymers can be classified into main chain-type and side chain-type liquid crystal polymers. Both of which may be selected to form the liquid crystal material of the liquid crystal layer of the present invention.

Examples of main chain type liquid crystalline polymers are polyester-, polyamide-, polycarbonate-, polyimide-, polyurethane-, polybenzimidazole-, polybenzoxazole-, polybenzothiazole-, polyimide-, polyesteramide-, polycarbonate-, polyesterimide-liquid crystalline polymers. Of these, particularly preferred are semi-aromatic polyester-based liquid crystalline polymers in which mesogen (mesogen) providing liquid crystallinity is alternately bonded to flexible chains such as polymethylene, polyethylene oxide, and polysiloxane and wholly aromatic polyester-based liquid crystals having no flexible chain.

Examples of side-chain liquid crystalline polymers are those having a straight-or ring-main chain with a mesogen on each side, such as polyacrylic, polyisobutylene, polyethylene, polysiloxane, polyether, polypropylenic, polyester-based liquid crystals. Of these, particularly preferred are those in which a mesogen providing liquid crystallinity is linked to the main chain via a spacer group composed of a flexible chain, and those having a molecular structure in which both the main chain and the side chain have a mesogen.

The liquid crystal materials referred to herein include those obtained by mixing a chiral dopant or introducing an optically active unit into the above-mentioned low molecular weight and/or liquid crystal polymer. Such liquid crystals can be obtained, for example, by mixing chiral dopants or introducing optically active units into liquid crystal materials exhibiting smectic C, smectic I or smectic F phases. The resulting liquid crystal material exhibits a chiral smectic liquid crystal phase, such as a chiral smectic C phase, a chiral smectic I phase, or a chiral smectic F phase, which is easily aligned in a helical structure.

As described above, the spiral pitch and the diffraction angle of the complex diffraction device of the present invention can be adjusted by appropriately adjusting the chiral doping amount, the introduction ratio of the optically active unit, the optical purity, and the temperature condition for the formation of the smectic liquid crystal phase. The helical structure is either a right-handed helix or a left-handed helix depending on the chirality of the chiral dopant or the optically active group used. Therefore, a helical structure having a right-handed helix or a left-handed helix can be obtained by selecting chirality.

Among the above liquid crystal materials, suitable for the liquid crystal material a are liquid crystal polymers. Suitable liquid crystal materials B are those having functional groups responsive to light, electron beam, or heat. Examples of such functional groups are vinyl, acrylic, methacrylic, vinyl ether, cinnamyl, aryl, ethynyl, crotonyl, aziridinyl, epoxy, isocyanate, sulfur-containing isocyanate, amino, hydroxyl, mercapto, carboxyl, acyl, halocarbonyl, aldehyde, sulfonic acid, and silanol groups. Of these, preferred are acrylic, methacrylic, vinyl ether, cinnamyl, epoxy, and aziridyl groups.

These functional groups need only be contained in the liquid crystal material, and thus may be contained in the liquid crystal material, the non-liquid crystal material, or one or more additives described later. In the case where functional groups are included in each of two or more types of materials, the functional groups may be the same or different. In addition, in the case where two or more functional groups are contained in one material, they may be the same or different.

When producing the liquid crystal layer of the composite device of the present invention, additives such as surfactants, polymerization activators, polymerization inhibitors, photosensitizers, stabilizers, catalysts, dyes, pigments, ultraviolet absorbers, adhesion improvers may be mixed in an amount of 50% by mass or less, preferably 30% by mass or less, more preferably 10% by mass or less, based on the total mass, if necessary.

The liquid crystal layer of the composite device of the present invention can be prepared by processing the liquid crystal material, if necessary, along with additives and maintaining the helical structure.

At the time of processing, no particular limitation is imposed on both side interfaces of the liquid crystal material, and therefore the interfaces may be gas phase-, liquid phase-or solid phase-interfaces, and need not be the same. However, for the purpose of easy processing of the liquid crystal layer, it is recommended to use an interface in which both are solid phase or one solid phase and the other gas phase.

Examples of gas phase interfaces are air and nitrogen interfaces. Examples of liquid phase interfaces are water, organic solvents, liquefied metals, other liquid crystals, melted polymeric compounds. Examples of the solid phase interface are plastic film substrates whose composition comprises polyimide, polyamideimide, polyamide, polyetherimide, polyetheretherketone, polyetherketone, polysulphide ketone, polysulfonic ether, polysulfonic group, polysulphide phenylene, polyoxyphenylene, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyvinyl acetal, polycarbonate, polyallyl, acrylic resin, methacrylic resin, polyethylene glycollate, polyethylene, polypropylene, poly-4-methylpentene-1 resin, and cellulose-based plastics such as triacetyl cellulose, epoxy resin, polyphenol resin, and liquid crystal polymer; metal substrates such as aluminum, iron, and copper; a glass substrate such as a blue glass plate, an alkali glass, a non-alkali glass, a borosilicate glass, a lead-containing glass, and a quartz glass; a ceramic substrate; various semiconductor substrates such as silicon wafers. The solid phase interface may also be obtained by forming an organic film comprising polyimide, polyamide, or polyvinyl alcohol, obliquely depositing a thin film of silicon dioxide or the like, or a transparent ITO (indium tin oxide) electrode, or by depositing or sputtering a metal film of gold, aluminum, copper on the film of the above-mentioned substrate. In addition, another option for the solid phase interface is a Thin Film Transistor (TFT) of amorphous silicon.

These various substrates may be subjected to an alignment process if necessary. In the case of using such a substrate, the helical axis direction of the resulting liquid crystal layer may be located in a direction determined by the substrate alignment direction. Depending on the type of liquid crystal material, the solid phase interface and the alignment method, the helical axis direction does not always coincide with the alignment direction of the substrate, shifting it. Even if such a liquid crystal layer is contained, the composite diffraction device of the present invention can achieve the effect of the composite diffraction device. In addition, in the present invention, a complex diffraction device can be obtained in which the screw axis direction is fixed in one mode by changing the partial alignment direction. In the case of using this method, a complex diffraction device can be obtained which can exhibit a complex diffraction effect of a complex caused by a smectic liquid crystal having a helical structure and a diffraction effect caused by a diffraction pattern, for example, by arranging a region pattern in which the helical axis direction is periodically different to such an extent that light interference occurs.

In the case where the alignment treatment is not performed on the substrate, the resulting liquid crystal layer may contain a multi-domain layer in which the direction of the helical axis in each domain is random. However, even such a liquid crystal phase can provide the resulting device with an effect as a complex diffraction device.

No particular limitation is imposed on the alignment process performed on the various substrates. Examples of alignment processes are rubbing, oblique deposition, micro-grooves, polymer film scribing, LB (langmuir-blodgett) films, transfer, photo irradiation (photo-isomerisation, photo-polymerization, photo-deposition), and lift-off methods. Particularly for the purpose of simplifying the processing, rubbing and light irradiation methods are preferable.

In addition, even in the case where various substrates which are not subjected to alignment treatment are used as solid phase interfaces, by applying a magnetic or electric field or shear stress to a liquid crystal material processed between the interfaces; liquefying or drawing the liquid crystal material; or a temperature gradient process is performed, it is possible to obtain a liquid crystal layer in which the direction of the helical axis is adjusted in a certain direction.

The method of processing the liquid crystal material to be applied to the interface is not particularly limited. Thus, any suitable method known in the art can be employed. For example, in the case of processing a liquid crystal material between two substrates, the liquid crystal material is injected into a cell formed by these substrates. A method of laminating a liquid crystal material with a substrate may be alternatively employed.

In the case of using one substrate and a gas phase interface, the liquid crystal material is processed by coating the liquid crystal material directly on the substrate or dissolving it in a suitable solvent before coating. In the present invention, for the purpose of simplifying the processing, it is preferable to cover the liquid crystal after dissolving in a solvent.

Suitable solvents for this process may be selected depending on the type of liquid crystal material and its composition. In general, examples of the solvent are halogenated hydrocarbons such as chloroform, dichloromethane, carbon tetrachloride, dichloroethane, tetrachloroethane, trichloroethylene, tetrachloroethylene, chlorobenzene, n-dichlorobenzene, phenols such as phenol and isochlorophenol, aromatic hydrocarbons such as benzene, toluene, xylene, methoxybenzene, 1, 2-dimethoxybenzene, alcohols such as isopropyl alcohol and t-butyl alcohol, glycols such as glycerol, ethylene glycol, and triethylene glycol, such as ethylene glycol monomethyl ether, diethylene glycol dimethyl ether, glycol ethers of ethyl cellulose solvents and butyl cellulose solvents, acetone, methyl ethylene ketone, ethyl acetate, 2-pyrrolidine, N-methyl-2-pyrrolidine, pyrimidine, triethylamine, tetrahydrofuran, diemthylformamide, dimethyllacenamide, dimethyl sulfoxide, acetonitrile, butyronitrile, carbon disulfide, and mixtures thereof. If necessary, a surfactant or the like may be added to the solvent to adjust the surface tension and improve the coverage.

The concentration of the liquid crystal material in the solution must be adjusted according to the type of the liquid crystal material, its solubility, and the film thickness of the final liquid crystal layer. However, it is usually in the range of 3 to 50% by mass, preferably 5 to 30% by mass.

There is no particular limitation imposed on the method of coating the solution. Spin coating, roll coating, printing, dip coating, roller coating, line coating, doctor blade, knife coating, die coating, gravure coating, microgravure coating, offset gravure coating, edge-press coating, and spray coating methods may be used. After coating, the solvent may be dried, if desired.

By the above method, after the liquid crystal material exhibiting a smectic liquid crystal phase of a helical structure between the interfaces is processed to form a uniform layer, the composite diffraction device of the present invention can be obtained by forming the liquid crystal material to form a helical orientation on the smectic liquid crystal phase of an ideal helical structure. The method to form the liquid crystal material to achieve the rotational orientation in the smectic liquid crystal phase is not particularly limited. Depending on the type of liquid crystal material, an appropriate method may be employed. For example, in the case of processing a liquid crystal material at a temperature at which the forming material exhibits a helical smectic liquid crystal phase, the helical smectic liquid crystal phase can be obtained simultaneously. The liquid-crystalline material being processed, once heated at a temperature higher than the temperature at which the smectic liquid-crystalline phase of the helical structure appears, exhibits a smectic A phase, a chiral nematic phase or an isotropic phase, which is oriented to assume the helical structure after a certain time by cooling at the temperature at which the smectic liquid-crystalline phase appears.

By any of the above methods, after the smectic liquid crystal phase of the helical structure appears in the liquid crystal layer, the helical structure of the smectic liquid crystal phase is fixed by selecting an appropriate method according to the type and composition of the liquid crystal material. For fixing the helical structure, the above-described glass fixing method or polymerization fixing method is preferably used.

In the case of using the glass fixing method, by cooling the liquid crystal layer to a temperature at which the liquid crystal material a is in a glass state, a smectic liquid crystal phase occurring in a helical structure higher than the glass transition temperature of the liquid crystal material a is fixed. The cooling may be natural cooling or forced cooling.

In the case of using the polymerization fixing method, the smectic liquid crystal phase of the helical structure occurring when the liquid crystal material B is in a liquid crystal state is fixed by polymerizing or crosslinking the liquid crystal material B. The method of polymerization or crosslinking may be thermal polymerization, photopolymerization, radiation polymerization by gamma rays or the like, electron beam polymerization, polycondensation, or polyaddition. Of these, photopolymerization and electron beam polymerization are preferable because they are easy to control.

The liquid crystal layer fixed by the foregoing method has no disorder of crystal orientation even after the substrate is removed, and can be used as a complex diffraction device in which the spiral direction is fixed. The film thickness of the resulting liquid crystal layer is usually in the range of 0.1 to 100. mu.m, preferably 0.2 to 50 μm, more preferably 0.3 to 20 μm for the purpose of orientability and yield.

In the present invention, the above-mentioned liquid crystal layer is provided with a diffraction function derived from the uneven pattern and the depressions formed thereon. The diffractive function may be provided on the liquid crystal with the substrate or after removal of the substrate. Alternatively, the resulting liquid crystal layer may be transferred onto another substrate, and the uneven pattern is formed on the layer with the substrate. Still alternatively, a plurality of liquid crystal layers having the same or different diffraction properties are laminated, and a diffraction function derived from the uneven pattern is provided thereon.

Examples of the substrate are plastic substrates formed of polyimide, polyamideimide, polyamide, polyetherimide, polyetheretherketone, polyetherketone, polysulphide ketone, polysulphide ether, polysulfonic acid, polysulphide phenylene, polyoxyphenylene, polyethyleneterephthalic acid, polybutyleneterephthalic acid, polyethylenenaphthalene, polyacetal, polycarbonate, polyallylene, acrylic resin, methacrylic resin, polyvinylalcohol, polyethylene, polypropylene, poly-4-methylpentene-1 resin, and cellulose-based plastics such as triacetylcellulose, epoxy resin, polyphenolic resin; a glass substrate; a ceramic substrate; paper; a metal substrate. In addition, optional substrates are optical elements such as polarizing plates, retardation plates, reflection plates, scattering films, and various liquid crystal films such as nematic films and cholesteric films.

No particular limitation is imposed on the method of providing the uneven pattern. A method in which another layer having a diffraction function derived from an uneven pattern is laminated on the liquid crystal layer of the present invention or a method in which a diffraction pattern is provided by forming an uneven pattern directly on the surface of the liquid crystal layer may be employed. Examples of the plastic film or the glass substrate having the diffraction function are those having a diffraction function.

The method of forming the uneven pattern can be simplified by a method of forming protrusions and depressions on the surface of the liquid crystal by an etching technique, or by a method of forming a mold having a diffraction grating form therein, hereinafter referred to as "embossed plate", which is pressed against the liquid crystal layer by a pressing machine, or a method of transferring a diffraction grating to an embossing process on the liquid crystal layer by a film having a diffraction grating form therein, hereinafter referred to as "embossed film", which is laminated onto the liquid crystal layer by a laminating machine or the like. In the present invention, it is preferable to provide a diffraction function derived from an uneven pattern by embossing the surface of the liquid crystal layer.

There is no particular limitation imposed on the embossed plate and the film. Most embossed plates are formed of metal or resin, having a structure of diffraction grating. The embossed film may be a thin film obtained by forming a diffraction grating on the surface of a free-standing film or on a self-supporting film and a laminated layer with a diffraction grating layer. After the embossing process, the embossed plate or film is mostly peeled off from the liquid crystal layer-containing film and the substrate. However, in the case of using the embossed film, a liquid crystal layer laminated with a thin film can be used.

The liquid crystal layer must have fluidity in a suitable range at the temperature at which the embossing process is performed. The temperature used for the embossing process cannot be freely determined because it depends on the thermal characteristics of the liquid crystal layer, such as the glass transition temperature (Tg) and the degree of crosslinking, the liquid crystal layer substrate, the type of embossing plate or film, or the embossing transfer method. However, the embossing process is carried out at room temperature to 300 ℃, preferably room temperature to 200 ℃. That is, it is necessary that the disorder of the helical state of the liquid crystal layer hardly occurs at the relief transfer temperature therebetween, and the effect achieved by the present invention is not lost after the relief transfer is completed. It is also required to effectively influence the embossing process and obtain the embossed liquid crystal layer having the effect of the present invention if the embossing transfer conditions are appropriately selected.

Although it is extremely difficult to quantitatively describe such a temperature range, it is impossible to specify it by a single physical quantity, and the glass transition temperature (Tg) of the liquid crystal layer after alignment can be used as an index. In the case of using a liquid crystal polymer or oligomer as the liquid crystal material used in the present invention, the glass transition temperature is present in most polymers or oligomers. When the fluidity of such a polymer or oligomer is measured while increasing its temperature, the fluidity is known to gradually increase from a poor state due to glassy fixation once the temperature reaches around the glass transition temperature. Therefore, in the case of using a polymer or oligomer in which a glass transition temperature exists, the embossing process can be applied to the liquid crystal layer whose glass transition temperature after alignment is in the range from room temperature to 200 ℃. If the glass transition temperature is room temperature or lower, the fluidity at the time of the embossing process becomes too high, so that the alignment disorder tends to occur. If the glass transition temperature exceeds 200 c, it is difficult to sufficiently affect the embossing process in the usual manner to provide the effect achieved by the present invention.

The resulting embossed liquid crystal layer may be used as it is, but may be further cured by light irradiation or thermal crosslinking for the purpose of reliability according to temperature, humidity, solvent, and mechanical strength. In the case of using a photo-crosslinkable liquid crystal cell and fixing it by a method for the liquid crystal material B, a method may be used in which once an orientation is formed, the orientation is fixed to a certain extent by light irradiation after the orientation, a diffraction grating is formed, and then another light irradiation is performed to cure the liquid crystal layer.

The complex diffraction device of the present invention can be provided on the surface thereof with a protective layer formed of the above-mentioned transparent plastic film of the hard coat layer for protecting the surface, enhancing the strength, increasing the environmental reliability.

The composite diffraction device can be used for various purposes, for example, as an optical pickup for a CD, DVD, or magneto-optical disk, or an optical element for improving the viewing angle or brightness of a liquid crystal display; programmable films that utilize diffraction-induced iris toning; an optical information recording apparatus; security films for credit cards or tickets; a head-up display combination.

[ Industrial applicability ]

The composite diffraction device of the present invention includes a liquid crystal layer maintaining a spiral direction of a smectic liquid crystal phase of a spiral structure, and also provides a diffraction function caused by an uneven pattern formed thereon. Thus, the inventive device has diffractive effects in multiple directions or angles. In addition, the inventive apparatus can be constructed in another optical system because it is suitable for large-sized, light, low in manufacturing cost, and easy to handle. Therefore, the device of the present invention is suitable for various uses of optical, optoelectronic, optical information recording, liquid crystal display devices, such as security applications and design applications, and is industrially highly valuable.

[ best mode for carrying out the invention ]

The invention will be further described with reference to the following examples, but not limited thereto.

In the following examples, the intrinsic viscosity measurement, the determination of the liquid crystal series, and the film thickness measurement were carried out according to the following methods.

(1) Intrinsic viscosity measurement

Measured at a temperature of 30 ℃ in a mixed solvent of phenol and tetrachloroethane at a weight ratio of 60/40 using an Erblonde viscometer.

(2) Determination of liquid crystal phase

DSC (differential scanning calorimeter) analysis was performed using berkins elmer DSC-7 and Optical microscopy was performed using a BH2 polarization microscope manufactured by Olympus Optical co.

(3) Film thickness measurement

Measured using the surface texture analysis system Dektak 3030ST manufactured by ULVAC inc. A method for obtaining the film thickness from the interference wave measurement and refractive index data was also carried out using an ultraviolet, visible light, near infrared spectrophotometer V-570 manufactured by JASCO Corporation.

Example 1

200 mmol of dimethylbiphenyl-4, 4' -dicarboxy, 120 mmol of (S) -2-methyl-1, 4-butanediol (optical isomerization excess, e.e.. gtoreq.50.0%) and 80 mmol of 1, 6-hexanediol were melt-polymerized at 220 ℃ using tetra-n-butyl n-titanate, and a liquid crystalline polyester was prepared for 2 hours. The intrinsic viscosity of the resulting polyester was 0.18 dL/g.

A10 wt% solution of the resulting polyester in tetrachloroethane was prepared, spin coated onto a vulcanized polyphenylene substrate with a rubbed polyimide film, followed by removal of the solvent on a hot plate at a temperature of 60 ℃. After the substrate was heated in an oven at a temperature of 180 ℃ for 10 minutes to orient into the smectic A phase, it was oriented into the smectic C phase when it was cooled to a temperature of 120 ℃ at a rate of 4 ℃/minute. The substrate was removed from the oven and cooled to room temperature, thereby fixing the liquid crystal polymer crystal orientation in the glassy state (sample 1). With adhesion, the resulting liquid crystal layer was transferred to a triacetyl cellulose film, thereby obtaining sample 2.

The liquid crystal layer in sample 2 was fixed in a glassy state, in a chiral smectic C phase, with a helical structure and a uniform film thickness (1.1 μm). The polarization microscope observation and the cross-sectional electron microscope observation confirmed that the helical pitch of the helical structure of the liquid crystal layer in sample 2 was about 1.0 μm. The helical axis direction was also found to be not coincident with the rubbing direction but offset by about 10 ° from it in the counterclockwise direction.

A commercial embossed film J52, 989 produced by Edmond Scientific Japan Co, ltd. was cut into a rectangular piece of 20cm × 15cm with the diffraction direction of the diffraction grating being the direction of the long side, and then placed on sample 2 so that the liquid crystal layer thereof was in contact with the surface of the diffraction grating. The helical axis direction of sample 2 was approximately perpendicular to the grating direction of the diffraction grating. The short side of the embossed film was then fixed to sample 2 using cellophane tape and inserted into a thermal lamination apparatus DX-350 produced by toram co. The thermal lamination was carried out at a laminating roller temperature of 75 ℃ and the moving speed of the sample was 25mm per second. Sample 2 and the embossed film were brought into intimate contact with each other after thermal lamination. The resulting sheet was cooled to room temperature and the film was gently removed from sample 2. It was found that the liquid crystal layer remaining on the tetraacetyl cellulose substrate was fixed in the helical crystal orientation state of the smectic liquid crystal with an uneven pattern transferred from the relief film, thereby obtaining sample 3.

When light is perpendicularly incident on the surface of the sample 3, a diffraction angle of about 40 ° is generated in the spiral direction, and diffraction caused by the uneven pattern of the relief film generates a diffraction angle of 35 ° perpendicular to the spiral axis. Thus, sample 3 proved to function as the complex diffraction device of the present invention.

Example 2

The same procedure as in example 1 was followed except that the spiral axis was approximately parallel to the gate direction of the embossed film, thereby obtaining sample 4.

When light was perpendicularly incident on the surface of the sample 4, diffraction occurred at about 40 ° diffraction angle in the spiral direction, and diffraction occurred by the uneven pattern of the relief film at 35 ° diffraction angle parallel to the spiral axis. Thus, sample 4 was demonstrated to function identically to the complex diffraction device of the present invention.

Example 3

Sample 1 was subjected to the same embossing process as in example 1. Thus, sample 1 was laminated on the embossed film so that the helical axis direction was offset from the gate direction of the embossed film by an angle of about 30 °. The resulting liquid crystal layer with the uneven pattern formed on the vulcanized polyphenylene substrate was transferred onto a tetraacetyl cellulose film with adhesion, thereby obtaining sample 5. The liquid crystal surface of sample 5 was again subjected to the same embossing treatment. Thus, the embossed film was arranged such that the reverse of the gate direction at the first embossment was offset from the spiral axis of sample 5 by about 30 °, thereby obtaining sample 6.

When light is perpendicularly incident on the surface of the sample 6, diffraction occurs at 40 ° in the spiral direction, and diffraction due to the uneven pattern of the relief film occurs at 35 ° diffraction angles in the directions of about ± 30 ° with respect to the spiral axis direction. Thus, it was confirmed that sample 6 functioned identically to the complex diffraction apparatus of the present invention.

Example 4

A gamma-butyrolactone solution comprising 15% by mass of a mixture of a bifunctional low molecular weight liquid crystal represented by the above formula (1), a monofunctional chiral liquid crystal represented by the above formula (2), and a racemic monofunctional liquid crystal represented by the formula (3) mixed in a weight ratio of 10: 80: 10, 0.2% by mass of Irugacure907 manufactured by Ciba specialty Chemical Co. as a photopolymerization activator, 0.02% by mass of Nippon Kayaku Co. as a photosensitizer, KAYACURE DETX manufactured by Ltd, and 0.05% by mass of Megaface F-144D manufactured by Dai Nippon ink and Chemicals Inc. as a surfactant was prepared.

The resulting solution was spin coated on a rubbed polyethylene terephthalate (PET) substrate, and then the solvent was removed at a temperature of 60 ℃. Then, after the substrate was heated in a 100 ℃ temperature oven for 3 minutes to orient in the smectic A phase, it was cooled at a rate of 5 ℃ per minute to a temperature of 60 ℃ to orient in the smectic C phase and maintained at the temperature of 60 ℃ for 3 minutes. Thus, nitrogen substitution is performed so that the oxygen concentration is 3% by volume or less. Thereafter, by photopolymerization, an ultraviolet irradiation apparatus having a high-pressure mercury lamp of 120W/cm was used at 200mJ/cm²The radiation energy of (a) fixes the crystal orientation of the liquid crystal material while maintaining a temperature of 60 ℃. The resulting liquid crystal layer on PET was fixed, exhibiting a chiral smectic C phase with a helical structure and a uniform film thickness (1.2 μm). The polarization microscope observation and the cross-sectional electron microscope observation confirmed that the helical pitch of the helical structure of the liquid crystal layer was about 1.3 μm. It was also found that the screw axis direction was not coincident with the rubbing direction, and shifted by an angle of about 13 ° in the counterclockwise direction, thereby obtaining sample 7.

Sample 7 was laminated to the embossed film at a temperature of 55 c, similar to example 1. Thereafter, the sample 7 laminated with the embossed film was further subjected to light irradiation of 800mJ, thereby completely curing the liquid crystal layer. The embossed film was removed from the liquid crystal layer, thereby obtaining sample 8.

When light was perpendicularly incident on the surface of the sample 8, diffraction occurred at a diffraction angle of about 29 ° in the spiral direction, and diffraction occurred by the uneven pattern of the relief film at a diffraction angle of 35 ° perpendicular to the spiral axis. Thus, sample 8 proved to function as the complex diffraction device of the present invention.

Example 5

Liquid crystalline polyesters were prepared by melt polymerization of 200 mmol of dimethylbiphenyl-4, 4' -dicarboxy, 80 mmol of (R) -1, 3-butanediol (optical isomeric excess, e.e. ═ 95.0%), and 120 mmol of 1, 5-pentanediol using tetra-n-butyl n-titanate at a temperature of 220 ℃ for 2 hours. The intrinsic viscosity of the resulting polyester was 0.20 dL/g.

An N-methyl-2-pyrrolidine solution of the resultant polyester at 10% by mass was prepared and spin-coated on a rubbed PET film substrate, followed by removal of the solvent on a hot plate at a temperature of 60 ℃. The substrate was heated in an oven at a temperature of 120 ℃ for 10 minutes, taken out therefrom, and cooled to room temperature to fix the crystal orientation of the liquid-crystalline polyester in the glassy state, thereby obtaining sample 9.

The liquid crystal layer in sample 9 was fixed in a glassy state and was chiral smectic C having a helical structure and a uniform film thickness (1.2 μm)_AAnd (4) phase(s). Polarization microscope observation and cross-sectional electron microscope observation confirmed that the helical pitch of the helical structure of the liquid crystal layer in sample 9 was about 0.8 μm.

Sample 9 was laminated on the embossed film at a temperature of 75 deg.c, similarly to example 1, to thereby obtain sample 10.

When light is perpendicularly incident on the surface of the sample 10, diffraction occurs at about 52 ° diffraction angle in the spiral direction, and diffraction occurs at 35 ° diffraction angle perpendicular to the spiral axis due to the uneven pattern of the relief film. Thus, it was confirmed that the sample 10 and the complex diffraction apparatus of the present invention functioned identically.

Claims (8)

1. A composite diffraction device in which a diffraction function due to an uneven pattern is added to a diffraction device including a liquid crystal layer in which a helical crystal orientation of a smectic liquid crystal phase having a helical structure is maintained.

2. A composite diffraction device in which a diffraction function due to an uneven pattern is added to one surface or both surfaces of a diffraction device including a liquid crystal layer in which a helical crystal orientation of a smectic liquid crystal phase having a helical structure is maintained.

3. A composite diffraction device according to claim 1 or 2, wherein the direction and/or angle of diffraction of the diffraction element comprising the liquid crystal layer is different from the direction and/or angle of diffraction caused by the uneven pattern at least in a part of the device, the helical crystal orientation of the smectic liquid crystal phase having a helical structure in the liquid crystal layer being maintained.

4. The composite diffraction device according to claim 1, 2 or 3, wherein the liquid crystal layer is formed by fixing the helical structure of the smectic liquid crystal phase formed in the thin film layer by orienting a thin film of a liquid crystal material capable of exhibiting a smectic liquid crystal phase of a helical structure at a temperature of glass transition temperature or higher and cooling it to a glassy state.

5. The composite diffraction device according to claim 1, 2 or 3, wherein the liquid crystal layer is formed by fixing the helical structure of the smectic liquid crystal phase formed in the film layer by aligning a film of the liquid crystal material capable of exhibiting a helical smectic liquid crystal phase at a temperature at which the liquid crystal material exhibits the liquid crystal phase and polymerizing the liquid crystal material while maintaining the crystal orientation.

6. The complex diffraction device according to claim 1, 2 or 3, wherein the smectic liquid crystal phase of the helical structure formed in the liquid crystal layer is a chiral smectic C phase.

7. The complex diffraction device according to claim 1, 2 or 3, wherein the smectic liquid crystal phase of the helical structure formed in the liquid crystal layer is chiral smectic C_AAnd (4) phase(s).

8. A method of manufacturing a composite diffraction device, in which a helical structure of a smectic liquid crystal phase in a liquid crystal layer is prepared from a liquid crystal material exhibiting a smectic liquid crystal phase containing the helical structure, and then, the surface of the liquid crystal layer is subjected to relief processing to provide a diffraction function caused by an uneven pattern.