JP7200383B2 - optical element - Google Patents

Description

The present invention relates to optical elements.

Polarized light is used in many optical devices, optical systems, and the like. In response to this, development of optical elements for controlling the reflection, convergence, and divergence of polarized light is underway.
For example, U.S. Pat. No. 6,200,000 comprises a plurality of stacked birefringent sublayers configured to change the direction of propagation of light passing through them according to the Bragg condition, wherein the stacked birefringent sublayers are each grating Optical elements are described with local optic axes that vary along respective interfaces between adjacent ones of stacked birefringent sublayers to define a period.

The optical element described in Patent Document 1 has an optically anisotropic thin film (that is, a thin liquid crystal layer) containing a liquid crystal compound. Specifically, the optical element described in Patent Document 1 is a diffraction element having a liquid crystal layer that diffracts light by changing the orientation pattern of rod-like liquid crystal compounds in one direction in the plane.
A diffraction element using such a liquid crystal compound is expected to be used as an optical member such as an image projection device such as AR (Augmented Reality) glasses.

AR glasses, for example, allow the image displayed by the display to enter one end of the light guide plate, propagate, and exit from the other end, so that the virtual image is superimposed on the scene actually viewed by the user. indicate.
AR glasses use a diffraction element to diffract (refract) light (projection light) from a display and enter one end of a light guide plate. As a result, the light is introduced into the light guide plate at an angle, and the light is totally reflected and propagated within the light guide plate. The light propagating through the light guide plate is also diffracted by the diffraction element at the other end of the light guide plate and emitted from the light guide plate to the observation position of the user.

Japanese Patent Publication No. 2017-522601

An optical diffraction element that diffracts light by changing the orientation pattern of a liquid crystal compound, as described in Patent Document 1, has an orientation film for orienting the liquid crystal compound in the liquid crystal layer.
As described above, a photo-alignment film is used to form a liquid crystal layer having an alignment pattern in which the alignment pattern of the liquid crystal compound changes in one direction within the plane.

Here, in a conventional diffraction element using a liquid crystal compound, an azo-based material is used as a photo-alignment film. Therefore, a diffraction element using a conventional liquid crystal compound has absorption in a part of the visible light region and appears yellow. When such a diffraction element is used as an optical member of an image projection device such as AR glasses, there is a problem that the projected image and the actual scenery appear yellowish.
Therefore, there is a demand for an optical element in which no color is visible in the visible light range.

An object of the present invention is to solve the problems of the prior art, and to provide an optical element that diffracts reflected light or transmitted light by liquid crystal diffraction, and that has no visible color in the visible light range. That's what it is.

In order to solve this problem, the present invention has the following configurations.
(1) having an optically anisotropic layer formed using a composition containing a liquid crystal compound and a photo-alignment film;
The optically anisotropic layer has a liquid crystal alignment pattern in which the direction of the optic axis derived from the liquid crystal compound changes while continuously rotating along at least one in-plane direction,
An optical element, wherein the photo-alignment film has an average transmittance of 90% or more for light with a wavelength of 380 to 780 nm and an average transmittance for light with a wavelength of 380 to 480 nm.
(2) In the liquid crystal alignment pattern of the optically anisotropic layer, the length by which the direction of the optic axis derived from the liquid crystal compound rotates 180° in one direction in which the direction of the optic axis derived from the liquid crystal compound rotates continuously. is the length of one cycle,
The optical element according to (1), wherein the length of one period of the liquid crystal alignment pattern of the optically anisotropic layer is 2.00 μm or less.
(3) The optical element according to (2), wherein the length of one cycle of the liquid crystal alignment pattern of the optically anisotropic layer is 0.80 μm or less.
(4) The optical element according to any one of (1) to (3), wherein the photo-alignment film has an arithmetic mean height Sa of 2.0 nm or less.
(5) The optical element according to any one of (1) to (4), wherein the optically anisotropic layer is a layer having a fixed cholesteric liquid crystal phase.
(6) The optical element according to any one of (1) to (4), wherein the optically anisotropic layer has an optical axis derived from the liquid crystal compound aligned in the thickness direction.
(7) The optical element according to any one of (1) to (6), wherein the photo-alignment film contains a polymer having a cinnamate group.
(8) The optical element according to (7), wherein the polymer further has a side chain having a terminal carboxyl group.
(9) The optical element according to (7) or (8), wherein the polymer has a repeating unit represented by formula (A1) described later and a repeating unit represented by formula (B1) described later.
(10) The polymer according to any one of (7) to (9), wherein the polymer has a repeating unit represented by formula (A2) described later and a repeating unit represented by formula (B2) described later. optical element.
(11) The optical element according to (10), wherein L ³ in the repeating unit represented by formula (B2) is a group represented by formula (7).
(12) The optical element according to (10), wherein L ³ in the repeating unit represented by formula (B2) is a group represented by formula (6).

The optical element of the present invention is an optical element that diffracts reflected light or transmitted light by liquid crystal diffraction, and is an optical element in which no color is visually recognized in the visible light range.

It is a figure which shows notionally an example of the optical element of this invention. FIG. 2 is a conceptual diagram for explaining the optical element shown in FIG. 1; FIG. 2 is a plan view of the optical element shown in FIG. 1; FIG. 2 is a conceptual diagram for explaining the action of the optical element shown in FIG. 1; FIG. 4 is a diagram conceptually showing another example of the optical element of the present invention; FIG. 4 is a diagram conceptually showing another example of the optical element of the present invention; FIG. 7 is a plan view of the optical element shown in FIG. 6; FIG. 7 is a conceptual diagram for explaining the action of the optical element shown in FIG. 6; FIG. 7 is a conceptual diagram for explaining the action of the optical element shown in FIG. 6; FIG. 7 is a diagram conceptually showing an example of an exposure apparatus for producing an alignment film of the diffraction element shown in FIGS. 2 and 6. FIG. FIG. 4 is a diagram conceptually showing another example of the optically anisotropic layer of the optical element of the present invention. FIG. 12 is a diagram conceptually showing an example of an exposure apparatus for producing an alignment film forming the optically anisotropic layer shown in FIG. 11; It is a figure which shows conceptually the measuring method of a diffraction efficiency.

BEST MODE FOR CARRYING OUT THE INVENTION The optical element of the present invention will now be described in detail with reference to preferred embodiments shown in the accompanying drawings.

In this specification, a numerical range represented by "to" means a range including the numerical values before and after "to" as lower and upper limits.
As used herein, "(meth)acrylate" means "either or both of acrylate and methacrylate".

In this specification, visible light is light with a wavelength visible to the human eye among electromagnetic waves, and indicates light in the wavelength range of 380 to 780 nm. Invisible light is light in the wavelength range below 380 nm and the wavelength range above 780 nm.
In addition, although not limited to this, among visible light, light in the wavelength range of 420 to 490 nm is blue light, light in the wavelength range of 495 to 570 nm is green light, and wavelength range of 620 to 750 nm. is red light.

In this specification, the average transmittance of light can be measured by the following method.
A photo-alignment film is formed on the support, and the same support is used as a reference, and the transmittance in the wavelength range of 380 to 780 nm is measured using a spectrophotometer UV3150 (Shimadzu Corporation). Calculate the average transmittance of

FIG. 1 conceptually shows an example of the optical element of the present invention.
As shown in FIG. 1, the optical element 10 has a support 12, a photo-alignment film 14, and a cholesteric liquid crystal layer 16, which is an optically anisotropic layer. The cholesteric liquid crystal layer 16 is a layer having a fixed cholesteric liquid crystal phase.

Although the illustrated optical element 10 has a support 12, a photo-alignment film 14, and a cholesteric liquid crystal layer 16, the present invention is not limited to this.
That is, the optical element of the present invention is obtained by forming the photo-alignment film 14 and the cholesteric liquid crystal layer 16 on one surface of the support 12 and then peeling off the support 12. layer) only.

<Support>
In the optical element 10 , the support 12 supports the photo-alignment film 14 and the cholesteric liquid crystal layer 16 .

Various sheet-like materials (films, plate-like materials) can be used as the support 12 as long as it can support the photo-alignment film 14 and the cholesteric liquid crystal layer 16 .
The support 12 preferably has a transmittance of 50% or more, more preferably 70% or more, and even more preferably 85% or more for the corresponding light.

The thickness of the support 12 is not limited, and the thickness capable of holding the photo-alignment film 14 and the cholesteric liquid crystal layer can be appropriately set according to the use of the optical element 10, the material for forming the support 12, and the like. good.
The thickness of the support 12 is preferably 1 to 1000 μm, more preferably 3 to 250 μm, even more preferably 5 to 150 μm.

The support 12 may be a single layer or multiple layers.
Examples of the single layer support 12 include support 12 made of glass, triacetyl cellulose (TAC), polyethylene terephthalate (PET), polycarbonate, polyvinyl chloride, acrylic, polyolefin, and the like. Examples of the multi-layer support 12 include any one of the single-layer supports described above as a substrate, and another layer provided on the surface of this substrate.

<Photo-alignment film>
In the optical element 10 , a photo-alignment film 14 is arranged on the surface of the support 12 .
The photo-alignment film 14 is an alignment film for aligning the liquid crystal compound 20 in a predetermined liquid crystal alignment pattern when forming the cholesteric liquid crystal layer 16 of the optical element 10 .
As will be described later, in the optical element 10, the cholesteric liquid crystal layer 16, which is an optically anisotropic layer in the present invention, has an optical axis 20A (see FIG. 3) derived from the liquid crystal compound 20, which is oriented along one in-plane direction. It has a liquid crystal orientation pattern that changes while continuously rotating. Accordingly, the photo-alignment film 14 is formed such that the cholesteric liquid crystal layer 16 can form this liquid crystal alignment pattern.
In the following description, "rotation of the direction of the optical axis 20A" is also simply referred to as "rotation of the optical axis 20A".

In the optical element 10 of the present invention, the photo-alignment film 14 has an average transmittance of 90% or more for light with a wavelength of 380 to 780 nm and an average transmittance for light with a wavelength of 380 to 480 nm.
The average transmittance of light with a wavelength of 380 to 780 nm of the photo-alignment film 14 is preferably 91% or more, more preferably 92% or more. Although the upper limit is not particularly limited, it is often 95% or less.
The average transmittance of light with a wavelength of 380 to 480 nm of the photo-alignment film 14 is preferably 91% or more, more preferably 92% or more. Although the upper limit is not particularly limited, it is often 95% or less.
By using such a photo-alignment film 14, it is possible to prevent the optical element 10 from appearing yellow or the like. For example, when the optical element of the present invention is used as a diffraction element for propagating light incident on a light guide plate in AR glasses, it is possible to realize AR glasses in which colors are invisible.

In the optical element 10 of the present invention, the smoothness of the surface of the photo-alignment film 14 is preferably high.
Specifically, the arithmetic mean height Sa of the photo-alignment film 14 is not particularly limited, but is often 20 nm or less, and is preferably 4.0 nm or less, and 2.0 nm or less in terms of better diffraction efficiency of the optical element. is more preferable, 1.5 nm or less is more preferable, and 1.0 nm or less is particularly preferable. Although the lower limit is not particularly limited, it is often 0.1 nm or more.
Further, by setting the arithmetic mean height Sa of the photo-alignment film 14 to 4.0 nm or less, the length of one period of the liquid crystal alignment pattern described later is preferably 2.00 μm or less, more preferably 0.80 μm or less. can.
The method for measuring the arithmetic mean height Sa is as follows.
A photo-alignment film is formed on the support, and surface shape measurement is performed in wave mode using a non-contact surface/layer cross-sectional shape measurement system VertScan (registered trademark) 2.0 (Ryoka System). Calculate Sa.

The material constituting the photo-alignment film 14 is not particularly limited as long as it satisfies the above average transmittance. For example, a compound having a cinnamate group (low molecular weight compound, monomer or polymer) can be mentioned. In particular, the photo-alignment film 14 preferably contains a polymer having a cinnamate group in that coloration is further suppressed.
Main chains forming polymers having cinnamate groups include poly(meth)acrylates, polyimides, polyurethanes, polyamic acids, polymaleimides, polyethers, polyvinyl ethers, polyesters, polyvinyl esters, polystyrene derivatives, polysiloxanes, cycloolefins. base polymers, epoxy polymers, and copolymers thereof.
Further, examples of the monomer having a cinnamate group include monomers that provide repeating units that constitute the polymer described above.

A polymer having a cinnamate group preferably exhibits liquid crystallinity. By exhibiting liquid crystallinity, the degree of orientation of cinnamate groups is improved, so that the cholesteric liquid crystal layer is easily oriented. Moreover, the diffraction efficiency of the optical element is further improved.
Examples of polymers exhibiting liquid crystallinity include biphenyl groups, terphenyl groups, naphthalene groups, phenylbenzoate groups, and azobenzene groups, which are often used as mesogenic components of liquid crystalline polymers, or substituents of these derivatives (mesogenic group) as a side chain and a polymer having a structure such as acrylate, methacrylate, maleimide, N-phenylmaleimide, or siloxane in the main chain.
The side chain containing the mesogenic component and the cinnamate group may be independent side chains or may be contained within the same side chain.
Examples of polymers exhibiting liquid crystallinity without containing a mesogenic component include polymers having carboxyl groups at the ends of side chains. This polymer is a material that develops a liquid crystal phase through dimer formation due to hydrogen bonding of carboxyl groups at the ends of side chains.
The side chain having a carboxyl group at the end and the cinnamate group may be independent side chains, or may be included in the same side chain, but are preferably independent side chains.

A polymer having a cinnamate group may optionally have a side chain containing a polymerizable group or a crosslinkable group. That is, a polymer having a cinnamate group may have repeating units having a polymerizable group or a crosslinkable group.
The polymerizable group is preferably a radically polymerizable group or a cationic polymerizable group, more preferably a (meth)acrylate group, an epoxy group, or an oxetanyl group.
A crosslinkable group is a site that bonds with a crosslinker described later by light or heat. Specific functional groups depend on the type of crosslinker, but for example, epoxy compounds, methylol compounds, and isocyanate compounds are used as crosslinkers. is used, it includes hydroxy, carboxy, phenolic hydroxy, mercapto, glycidyl, and amide groups. Among them, from the viewpoint of reactivity, an aliphatic hydroxy group is preferable, and a primary hydroxy group is more preferable.

Low-molecular-weight compounds having a cinnamate group include the compounds described in paragraphs [0042] to [0053] of WO 2016/002722 and paragraphs [0030] to [0051] of WO 2015/056741. , and those having a cinnamate group are exemplified.
Polymers having functional groups capable of forming covalent bonds by reacting with these low-molecular-weight compounds include polymers described in paragraphs [0091] to [0134] of WO 2016/002722, WO 2015/ 129890, paragraphs [0045] to [0092], WO 2015/030000, paragraphs [0057] to [0087], WO 2014/171376, paragraph [0051 ] to [0086], the polymers described in paragraphs [0042] to [0058] of WO 2014/104320 are exemplified.

In addition, the polymer preferably has a side chain having a carboxyl group at its terminal and exhibits liquid crystallinity in that the length of one cycle of the liquid crystal alignment pattern, which will be described later, can be made shorter. Since this polymer exhibits liquid crystallinity, the alignment property is improved and the alignment control force is increased. Therefore, even if the length of one cycle of the liquid crystal alignment pattern is short, the liquid crystal compound can be aligned according to the pattern.

Among them, as the polymer, a polymer having a repeating unit represented by formula (A1) and a repeating unit represented by formula (B1) is preferable.

In the formula, R ¹ is a hydrogen atom or a methyl group, preferably a methyl group.
R ² is an alkyl group or a phenyl group substituted with a group selected from an alkyl group, an alkoxy group, a cyano group and a halogen atom, and is selected from an alkyl group, an alkyl group, an alkoxy group, a cyano group and a halogen atom; Phenyl groups substituted with one group are preferred. A preferred example of R ² is a cyano-substituted phenyl group or an alkyl group, more preferably an alkyl group. Another preferred example of R ² is an alkyl group, or a phenyl group substituted with an alkoxy group or a cyano group, preferably a phenyl group substituted with an alkoxy group, or an alkyl group. Another preferred example of R ² is a phenyl group substituted with an alkoxy group or a cyano group, more preferably a phenyl group substituted with an alkoxy group. Another preferred example of R ² is an alkyl group.
The alkyl group for R ² or the alkyl group for the substituent of the phenyl group for R ² is preferably an alkyl group having 1 to 12 carbon atoms, more preferably an alkyl group having 1 to 6 carbon atoms, and more preferably an alkyl group having 1 to 4 carbon atoms. is more preferred, and a methyl group is particularly preferred.
The alkoxy group as a substituent of the phenyl group of R ² is preferably an alkoxy group having 1 to 12 carbon atoms, more preferably an alkoxy group having 1 to 6 carbon atoms, still more preferably an alkoxy group having 1 to 4 carbon atoms, and methoxy. groups are particularly preferred.
The halogen atom of the substituent of the phenyl group of R ² includes a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, with a fluorine atom being preferred.

L ¹ and L ² are each independently any of the groups represented by formulas (1) to (5). * represents a binding position.

X ¹ to X ³⁸ are each independently a hydrogen atom, an alkyl group, an alkoxy group, a halogen atom or a cyano group, preferably a hydrogen atom or a halogen atom.
Among X ¹ to X ³⁸ , the alkyl group is preferably an alkyl group having 1 to 4 carbon atoms, more preferably a methyl group. As the alkoxy group, an alkoxy group having 1 to 4 carbon atoms is preferable, and a methoxy group is more preferable. A halogen atom includes a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom, with a fluorine atom being preferred.

In formula (B), the portion represented by -CH=CHCOO- represents a trans form. The trans form represents a group in which two hydrogen atoms are located on opposite sides of the double bond, as represented by the above formula.

Each of p and q is independently an integer of 1 to 12, preferably an integer of 3 to 9, more preferably an integer of 5 to 7, and even more preferably 6.

The content of the repeating unit represented by formula (A1) in the polymer is not particularly limited, but is preferably 65 to 95 mol%, more preferably 75 to 85 mol%, based on the total repeating units in the polymer. .
The content of the repeating unit represented by formula (B1) in the polymer is not particularly limited, but is preferably 5 to 35 mol%, more preferably 15 to 25 mol%, based on the total repeating units in the polymer. .
The total content of the repeating units represented by formula (A1) and the repeating units represented by formula (B1) in the polymer is preferably 90 mol% or more, preferably 100 mol%, based on all repeating units in the polymer. Mole % is more preferred.

As the polymer, a polymer having a repeating unit represented by formula (A2) and a repeating unit represented by formula (B2) is more preferable.

The definitions of R ¹ and p in formula (A2) are the same as the definitions of R ¹ and p in formula (A1).
X ^1A to X ^4A are each independently a hydrogen atom, an alkyl group, an alkoxy group, a halogen atom or a cyano group, preferably a hydrogen atom or a halogen atom. A preferred embodiment of X ^1A to X ^4A is an embodiment in which any one of X ^1A to X ^4A is a halogen atom and the others are hydrogen atoms. Another preferred embodiment of X ^1A to X ^4A is an embodiment in which all of X ^1A to X ^4A are hydrogen atoms.

R ^{1 , R 2 and q in formula (B2) have the same definitions as R 1 , R 2} and q in formula (A1).
L ³ is any one of groups represented by formulas (6) to (7). * represents a binding position.

X ^1B to X ^4B and X ^31B to X ^38B are each independently a hydrogen atom, an alkyl group, an alkoxy group, a halogen atom or a cyano group, preferably a hydrogen atom or a halogen atom, more preferably a hydrogen atom.

A polymer having a repeating unit represented by formula (A1) and a repeating unit represented by formula (B1) is a monomer represented by formula (X) and a polymer represented by formula (Y). It can be produced by polymerizing the following monomers in the absence of solvent or in a solvent.

The definition of each group in the monomer represented by formula (X) and the monomer represented by formula (Y) is as described above.

Polymerization can be carried out using light or heat.
In the polymerization, the method of charging the materials, solvent, etc. is not particularly limited, and the polymerization may be started after all the materials are charged into the reaction vessel before the polymerization, or the monomer represented by the formula (X), And, after mixing the monomer represented by the formula (Y), a part of the mixture, solvent, etc. may be polymerized, and then the remainder may be added stepwise by a method such as dropwise addition or divided addition. .

In addition to the monomer represented by formula (X) and the monomer represented by formula (Y), other monomers may be used in combination for polymerization.
Other monomers include methyl (meth)acrylate, t-butyl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, ethoxyethyl (meth)acrylate, hydroxyethyl (meth)acrylate, phenyl ( meth)acrylates and (meth)acrylic monomers such as N,N-dimethylacrylamide, styrene, α-methylstyrene, p-styrenesulfonic acid, ethyl vinyl ether, N-vinylimidazole, vinyl acetate, vinylpyridine, 2-vinyl Naphthalene, vinyl chloride, vinyl fluoride, N-vinylcarbazole, vinylamine, vinylphenol, and vinyl monomers such as N-vinyl-2-pyrrolidone, 4-allyl-1,2-dimethoxybenzene, 4-allylphenol, and allyl monomers such as 4-methoxyallylbenzene, and maleimides such as phenylmaleimide and cyclohexylmaleimide.

When polymerizing in a solution, a general-purpose organic solvent can be used. Specific examples of solvents include alcohol solvents, ketone solvents, ester solvents, ether solvents, hydrocarbon solvents, nitrile solvents, and amide solvents.
Any of these solvents may be used alone, or two or more thereof may be used in combination.

A polymerization initiator may be used in the above polymerization.
Examples of the polymerization initiator include known polymerization initiators such as azobisisobutyronitrile (AIBN), diethyl-2,2'-azobisisobutyrate (V-601), 2,2'-azobis ( 2,4-dimethylvaleronitrile), and azo polymerization initiators such as dimethylazobismethylpropionate, benzoyl peroxide, hydrogen peroxide, and peroxide polymerization initiators such as lauroyl peroxide, and Persulfate-based polymerization initiators such as potassium persulfate and ammonium persulfate are included.
Any of the polymerization initiators may be used alone, or two or more thereof may be used in combination.

Although the temperature during polymerization is not particularly limited, it is preferably 40 to 150°C.

The photo-alignment film 14 is preferably formed using a composition for forming a photo-alignment film containing the above materials (for example, a polymer having a cinnamate group).
The composition for forming a photo-alignment film may contain other components such as a cross-linking agent, a photoinitiator, a surfactant, a solvent, a rheology modifier, a pigment, a dye, a storage stabilizer, an antifoaming agent, and an antioxidant. may be included.

The cross-linking agent may form a cross-linked structure by reacting with a compound having a cinnamate group, or a polymer having a functional group capable of forming a covalent bond by reacting with the above compound, or may not react with these. It may form a separate crosslinked structure.
Cross-linking agents include (meth)acrylate compounds, epoxy compounds, methylol compounds, and isocyanate compounds.
A radical initiator, an acid generator, or a base generator may be used as necessary to trigger or promote the reaction of these cross-linking agents.

As the photopolymerization initiator, any general-purpose photopolymerization initiator generally known for forming a uniform film with a small amount of light irradiation can be used. Specific examples include azonitrile-based photopolymerization initiators, α-aminoketone-based photopolymerization initiators, acetophenone-based photopolymerization initiators, benzoin-based photopolymerization initiators, benzophenone-based photopolymerization initiators, thioxanthone-based photopolymerization initiators, and triazines. photopolymerization initiators, carbazole photopolymerization initiators, and imidazole photopolymerization initiators.
Any of the photopolymerization initiators may be used alone, or two or more thereof may be used in combination.

As the surfactant, any surfactant generally used for forming a uniform film can be used. Surfactants include anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants.

The solvent is not particularly limited as long as it can dissolve each of the above components. Examples include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, methyl cellosolve acetate, ethyl cellosolve acetate, diethylene glycol monomethyl ether, diethylene glycol mono Ethyl ether, propylene glycol, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, propylene glycol propyl ether acetate, ethylene glycol dimethyl ether, propylene glycol dimethyl ether, toluene, xylene, methyl ethyl ketone, cyclopentanone, cyclohexanone, 2-butanone, 3-methyl -2-pentanone, 2-pentanone, 2-heptanone, γ-butyrolactone, ethyl 2-hydroxypropionate, ethyl 2-hydroxy-2-methylpropionate, ethyl ethoxyacetate, ethyl hydroxyacetate, 2-hydroxy-3-methylbutane methyl acid, methyl 3-methoxypropionate, ethyl 3-methoxypropionate, ethyl 3-ethoxypropionate, methyl 3-ethoxypropionate, methyl pyruvate, ethyl pyruvate, ethyl acetate, butyl acetate, ethyl lactate, butyl lactate , N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone.

As a method for producing the photo-alignment film 14, for example, the composition for forming a photo-alignment film is applied to a substrate, the solvent is distilled off to form a film (photo-alignment precursor film), and then the anisotropic a method of producing a photo-alignment film by irradiating the film with light having a property and then heating it to produce a liquid crystal alignment ability.
Examples of the method of applying the composition for forming a photo-alignment film include a spin coat method, a bar coat method, a die coater method, a screen printing method, and a spray coater method.
In addition, the light to be irradiated is not particularly limited as long as it is irradiation such as infrared rays, visible rays, ultraviolet rays, X-rays, and charged particle beams that can cause a chemical reaction. It often has a wavelength of 200-500 nm.
It is preferable to apply heat after the light irradiation, because heat polymerization proceeds and a photo-alignment film having higher durability against light, heat, and the like can be obtained.

FIG. 10 conceptually shows an example of an exposure apparatus that exposes the photo-alignment precursor film 140 to form an alignment pattern.
The exposure device 60 shown in FIG. 10 includes a light source 64 having a laser 62 and a λ/2 plate (not shown) that changes the polarization direction of the laser light M emitted by the laser 62 (arranged between the light source 64 and the polarizing beam splitter 68). ), a polarizing beam splitter 68 that splits the laser beam M emitted by the laser 62 into two beams MA and MB, a mirror 70A and 70B, and λ/4 plates 72A and 72B.
The light emitted from the light source 64 and passed through the λ/2 plate (not shown) becomes linearly polarized light P ₀ . The λ/4 plate 72A converts the linearly polarized light P ₀ (light ray MA) into right circularly polarized light _PR , and the λ/4 plate 72B converts the linearly polarized light P ₀ (light ray MB) into left circularly polarized light P _L .

The support 12 having the photo-alignment precursor film 140 before the alignment pattern is formed is placed in the exposure area, and the two light beams MA and MB are crossed and interfered on the photo-alignment precursor film 140, The photo-alignment precursor film 140 is irradiated with interference light to be exposed.
Due to the interference at this time, the polarization state of the light with which the photo-alignment precursor film 140 is irradiated changes periodically in the form of interference fringes. As a result, an alignment pattern in which the alignment state changes periodically is obtained in the photo-alignment film 14 .
In the exposure device 60, the period of the alignment pattern can be adjusted by changing the crossing angle α of the two light beams MA and MB. That is, in the exposure device 60, by adjusting the crossing angle α, in the orientation pattern in which the optical axis 20A derived from the liquid crystal compound 20 rotates continuously along one direction, , the length of one cycle in which the optical axis 20A rotates 180° can be adjusted.
By forming a cholesteric liquid crystal layer on the photo-alignment film 14 having such an alignment pattern in which the alignment state is periodically changed, as will be described later, the optical axis 20A derived from the liquid crystal compound 20 is aligned along one direction. A cholesteric liquid crystal layer can be formed having a liquid crystal alignment pattern that continuously rotates with the
Further, by rotating the optical axes of the λ/4 plates 72A and 72B by 90°, the direction of rotation of the optical axis 20A can be reversed.

<Cholesteric liquid crystal layer>
In the optical element 10 , a cholesteric liquid crystal layer 16 is formed on the surface of the photo-alignment film 14 .
As described above, the cholesteric liquid crystal layer 16 is a layer in which the cholesteric liquid crystal phase is fixed.

In FIG. 1 , in order to simplify the drawing and clearly show the configuration of the optical element 10 , the cholesteric liquid crystal layer 16 is the liquid crystal compound 20 (liquid crystal compound) on the surface of the photo-alignment film 14 and the surface of the cholesteric liquid crystal layer 16 molecules) are shown conceptually. However, as conceptually shown in FIG. 2, the cholesteric liquid crystal layer 16 has a helical structure in which liquid crystal compounds 20 are helically rotated and stacked, similar to a cholesteric liquid crystal layer in which a normal cholesteric liquid crystal phase is fixed. The structure in which the liquid crystal compounds 20 are stacked one helically (rotated by 360°) is one helical pitch, and the helically swirling liquid crystal compounds 20 have a structure in which a plurality of pitches are stacked.

As is well known, a cholesteric liquid crystal layer in which a cholesteric liquid crystal phase is fixed has wavelength-selective reflectivity.
As will be described in detail later, the selective reflection wavelength range of the cholesteric liquid crystal layer depends on the thickness direction length of the above-mentioned helical one pitch (pitch P shown in FIG. 2).

As described above, the cholesteric liquid crystal layer 16 is a cholesteric liquid crystal layer having a fixed cholesteric liquid crystal phase. That is, the cholesteric liquid crystal layer 16 is a layer made of a liquid crystal compound 20 (liquid crystal material) having a cholesteric structure.

(cholesteric liquid crystal phase)
Cholesteric liquid crystal phases are known to exhibit selective reflectivity at specific wavelengths.
In a general cholesteric liquid crystal phase, the central wavelength of selective reflection (selective reflection central wavelength) λ depends on the helical pitch P in the cholesteric liquid crystal phase, and the relationship between the average refractive index n of the cholesteric liquid crystal phase and λ = n × P obey. Therefore, by adjusting this helical pitch, the selective reflection central wavelength can be adjusted.
The central wavelength of selective reflection of the cholesteric liquid crystal phase becomes longer as the pitch P becomes longer.
The pitch P of the spiral is, as described above, one pitch of the helical structure of the cholesteric liquid crystal phase (the period of the spiral), in other words, it is one turn of the spiral, which constitutes the cholesteric liquid crystal phase. It is the length of the helical axis direction in which the director of the liquid crystal compound (long axis direction in the case of rod-like liquid crystal) rotates 360°.

The helical pitch of the cholesteric liquid crystal phase depends on the type of chiral agent used together with the liquid crystal compound and the concentration of the chiral agent added when forming the cholesteric liquid crystal layer. Therefore, a desired helical pitch can be obtained by adjusting these.
As for the adjustment of the pitch, refer to Fuji Film Research Report No. 50 (2005) p. 60-63 for a detailed description. As for the method for measuring the sense and pitch of the helix, the method described in "Introduction to Liquid Crystal Chemistry Experiments" edited by the Japan Liquid Crystal Society, published by Sigma Publishing, 2007, page 46, and "Liquid Crystal Handbook" Liquid Crystal Handbook Editing Committee, Maruzen, page 196 is used. be able to.

A cholesteric liquid crystal phase exhibits selective reflectivity for either left or right circularly polarized light at a specific wavelength. Whether the reflected light is right-handed circularly polarized light or left-handed circularly polarized light depends on the twist direction (sense) of the spiral of the cholesteric liquid crystal phase. The selective reflection of circularly polarized light by the cholesteric liquid crystal phase reflects right-handed circularly polarized light when the helical twist direction of the cholesteric liquid crystal layer is rightward, and reflects left-handed circularly polarized light when the helical twist direction is leftward.
The direction of rotation of the cholesteric liquid crystal phase can be adjusted by the type of liquid crystal compound forming the cholesteric liquid crystal layer and/or the type of chiral agent added.

Further, the half width Δλ (nm) of the selective reflection wavelength region (circularly polarized light reflection wavelength region) indicating selective reflection depends on Δn of the cholesteric liquid crystal phase and the spiral pitch P, and follows the relationship Δλ=Δn×P. Therefore, the width of the selective reflection wavelength band (selective reflection wavelength band) can be controlled by adjusting Δn. Δn can be adjusted by the type and mixing ratio of the liquid crystal compounds forming the cholesteric liquid crystal layer, and the temperature during orientation fixation.
The half width of the reflection wavelength range is adjusted according to the use of the diffraction element, and may be, for example, 10 to 500 nm, preferably 20 to 300 nm, more preferably 30 to 100 nm.

(Method for Forming Cholesteric Liquid Crystal Layer)
The cholesteric liquid crystal layer 16 can be formed by fixing a cholesteric liquid crystal phase in layers.
The structure in which the cholesteric liquid crystal phase is fixed may be any structure as long as the alignment of the liquid crystal compound in the cholesteric liquid crystal phase is maintained. It is preferable that the structure is polymerized and cured by UV irradiation, heating, or the like to form a non-fluid layer and, at the same time, changed to a state in which the orientation is not changed by an external field or external force.
In the structure in which the cholesteric liquid crystal phase is fixed, it is sufficient if the optical properties of the cholesteric liquid crystal phase are maintained, and the liquid crystal compound 20 does not have to exhibit liquid crystallinity in the cholesteric liquid crystal layer. For example, the polymerizable liquid crystal compound may lose liquid crystallinity due to a high molecular weight due to a curing reaction.

Examples of materials used for forming a cholesteric liquid crystal layer in which a cholesteric liquid crystal phase is fixed include a liquid crystal composition containing a liquid crystal compound. The liquid crystal compound is preferably a polymerizable liquid crystal compound.
Moreover, the liquid crystal composition used for forming the cholesteric liquid crystal layer may further contain a surfactant and a chiral agent.

--Polymerizable Liquid Crystal Compound--
The polymerizable liquid crystal compound may be a rod-like liquid crystal compound or a discotic liquid crystal compound.
Examples of rod-like polymerizable liquid crystal compounds that form a cholesteric liquid crystal phase include rod-like nematic liquid crystal compounds. Rod-shaped nematic liquid crystal compounds include azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, and alkoxy-substituted phenylpyrimidines. , phenyldioxanes, tolanes, or alkenylcyclohexylbenzonitriles are preferred. Not only low-molecular-weight liquid crystal compounds but also high-molecular liquid-crystal compounds can be used.

A polymerizable liquid crystal compound is obtained by introducing a polymerizable group into a liquid crystal compound. Examples of polymerizable groups include unsaturated polymerizable groups, epoxy groups, and aziridinyl groups, with unsaturated polymerizable groups being preferred, and ethylenically unsaturated polymerizable groups being more preferred. Polymerizable groups can be introduced into molecules of liquid crystal compounds by various methods. The number of polymerizable groups possessed by the polymerizable liquid crystal compound is preferably 1 to 6, more preferably 1 to 3.
Examples of polymerizable liquid crystal compounds are described in Makromol. Chem. , 190, 2255 (1989), Advanced Materials 5, 107 (1993), U.S. Pat. No. 4,683,327, U.S. Pat. No. 5,622,648, U.S. Pat. 95/022586, International Publication No. 95/024455, International Publication No. 97/000600, International Publication No. 98/023580, International Publication No. 98/052905, JP-A-1-272551, JP-A-6-016616 JP-A-7-110469, JP-A-11-080081, and JP-A-2001-328973. Two or more types of polymerizable liquid crystal compounds may be used in combination. When two or more kinds of polymerizable liquid crystal compounds are used together, the alignment temperature can be lowered.

As other polymerizable liquid crystal compounds, cyclic organopolysiloxane compounds having a cholesteric phase as disclosed in JP-A-57-165480 can be used. Further, as the polymer liquid crystal compounds described above, there are polymers in which mesogenic groups exhibiting liquid crystal are introduced into the main chain, side chains, or both of the main chain and side chains, and polymer cholesteric compounds in which cholesteryl groups are introduced into the side chains. Liquid crystals, liquid crystalline polymers as disclosed in Japanese Patent Application Laid-Open No. 9-133810, and liquid crystalline polymers as disclosed in Japanese Patent Application Laid-Open No. 11-293252 can be mentioned.

As the discotic liquid crystal compound, for example, those described in JP-A-2007-108732 and JP-A-2010-244038 can be preferably used.

The addition amount of the polymerizable liquid crystal compound in the liquid crystal composition is preferably 75 to 99.9% by mass, more preferably 80 to 99% by mass, based on the solid content mass (mass excluding the solvent) of the liquid crystal composition. More preferably, 85 to 90% by mass is even more preferable.

--Surfactant--
The liquid crystal composition used for forming the cholesteric liquid crystal layer may contain a surfactant.
The surfactant is preferably a compound that can stably or quickly function as an alignment control agent that contributes to the alignment of the cholesteric liquid crystal phase. Examples of surfactants include silicone-based surfactants and fluorine-based surfactants, with fluorine-based surfactants being preferred examples.

Specific examples of the surfactant include compounds described in paragraphs [0082] to [0090] of JP-A-2014-119605, and compounds described in paragraphs [0031] to [0034] of JP-A-2012-203237. , Compounds exemplified in paragraphs [0092] and [0093] of JP-A-2005-099248, paragraphs [0076] to [0078] and paragraphs [0082] to [0085] of JP-A-2002-129162 compounds exemplified therein, and fluorine (meth)acrylate polymers described in paragraphs [0018] to [0043] of JP-A-2007-272185.
In addition, surfactant may be used individually by 1 type, and may use 2 or more types together.
As the fluorosurfactant, compounds described in paragraphs [0082] to [0090] of JP-A-2014-119605 are preferable.

The amount of the surfactant added in the liquid crystal composition is preferably 0.01 to 10% by mass, more preferably 0.01 to 5% by mass, and 0.02 to 1% by mass with respect to the total mass of the liquid crystal compound. is more preferred.

--Chiral agent (optically active compound)--
The liquid crystal composition used for forming the cholesteric liquid crystal layer may contain a chiral agent.
A chiral agent (chiral agent) has a function of inducing a helical structure of a cholesteric liquid crystal phase. The chiral agent may be selected depending on the purpose, since the helical twist direction or helical pitch induced by the compound differs.
The chiral agent is not particularly limited, and known compounds (for example, liquid crystal device handbook, Chapter 3, Section 4-3, chiral agent for TN (twisted nematic), STN (Super Twisted Nematic), page 199, Japan Society for the Promotion of Science 142nd Committee, ed., 1989), isosorbide, isomannide derivatives, and the like can be used.
Chiral agents generally contain an asymmetric carbon atom, but axially chiral compounds or planar chiral compounds that do not contain an asymmetric carbon atom can also be used as chiral agents. Examples of axially or planarly chiral compounds include binaphthyl, helicene, paracyclophane, and derivatives thereof. The chiral agent may have a polymerizable group. When both the chiral agent and the liquid crystal compound have a polymerizable group, a repeating unit derived from the polymerizable liquid crystal compound and a repeating unit derived from the chiral agent are formed by the polymerization reaction of the polymerizable chiral agent and the polymerizable liquid crystal compound. A polymer having repeating units can be formed. In this aspect, the polymerizable group possessed by the polymerizable chiral agent is preferably the same type of group as the polymerizable group possessed by the polymerizable liquid crystal compound. Therefore, the polymerizable group of the chiral agent is also preferably an unsaturated polymerizable group, an epoxy group or an aziridinyl group, more preferably an unsaturated polymerizable group, and an ethylenically unsaturated polymerizable group. More preferred.
Also, the chiral agent may be a liquid crystal compound.

In the case where the chiral agent has a photoisomerizable group, it is possible to form a desired reflection wavelength pattern corresponding to the emission wavelength by photomask irradiation with actinic rays or the like after coating and alignment, which is preferable. The photoisomerizable group is preferably an isomerization site of a compound exhibiting photochromic properties, an azo group, an azoxy group, or a cinnamoyl group. Specific compounds include JP-A-2002-080478, JP-A-2002-080851, JP-A-2002-179668, JP-A-2002-179669, JP-A-2002-179670, JP-A-2002- 179681, JP-A-2002-179682, JP-A-2002-338575, JP-A-2002-338668, JP-A-2003-313189, and compounds described in JP-A-2003-313292, etc. can be used.

The content of the chiral agent in the liquid crystal composition is preferably 0.01 to 200 mol %, more preferably 1 to 30 mol %, relative to the molar amount of the liquid crystal compound.

--Polymerization initiator--
When the liquid crystal composition contains a polymerizable compound, the liquid phase composition preferably contains a polymerization initiator. In the embodiment in which the polymerization reaction is advanced by ultraviolet irradiation, the polymerization initiator used is preferably a photopolymerization initiator capable of initiating the polymerization reaction by ultraviolet irradiation.
Examples of photoinitiators include α-carbonyl compounds (described in US Pat. Nos. 2,367,661 and 2,367,670), acyloin ethers (described in US Pat. No. 2,448,828), α-hydrocarbons substituted aromatic acyloin compounds (described in US Pat. No. 2,722,512), polynuclear quinone compounds (described in US Pat. Nos. 3,046,127 and 2,951,758), triarylimidazole dimers and p-aminophenyl ketone Combinations (described in US Pat. No. 3,549,367), acridine and phenazine compounds (described in JP-A-60-105667, US Pat. No. 4,239,850), and oxadiazole compounds (described in US Pat. No. 4,212,970) described) and the like.
The content of the photopolymerization initiator in the liquid crystal composition is preferably 0.1 to 20% by mass, more preferably 0.5 to 12% by mass, relative to the liquid crystal compound.

--crosslinking agent--
The liquid crystal composition may optionally contain a cross-linking agent in order to improve film strength and durability after curing. As the cross-linking agent, one that is cured by ultraviolet rays, heat, humidity, and the like can be preferably used.
The cross-linking agent is not particularly limited and can be appropriately selected depending on the purpose. Examples include polyfunctional acrylate compounds such as trimethylolpropane tri(meth)acrylate and pentaerythritol tri(meth)acrylate; Epoxy compounds such as ethylene glycol diglycidyl ether; aziridine compounds such as 2,2-bishydroxymethylbutanol-tris[3-(1-aziridinyl)propionate] and 4,4-bis(ethyleneiminocarbonylamino)diphenylmethane; hexamethylene Isocyanate compounds such as diisocyanate and biuret isocyanate; polyoxazoline compounds having oxazoline groups in side chains; and alkoxysilane compounds such as vinyltrimethoxysilane and N-(2-aminoethyl)3-aminopropyltrimethoxysilane. be done. Also, a known catalyst can be used depending on the reactivity of the cross-linking agent, and productivity can be improved in addition to the enhancement of membrane strength and durability. These may be used individually by 1 type, and may use 2 or more types together.
The content of the cross-linking agent is preferably 3 to 20% by mass, more preferably 5 to 15% by mass, based on the solid mass of the liquid crystal composition. When the content of the cross-linking agent is within the above range, the effect of improving the cross-linking density is likely to be obtained, and the stability of the cholesteric liquid crystal phase is further improved.

--Other Additives--
If necessary, the liquid crystal composition may further contain polymerization inhibitors, antioxidants, ultraviolet absorbers, light stabilizers, colorants, metal oxide fine particles, etc., within a range that does not reduce optical performance. can be added with

The liquid crystal composition is preferably used as a liquid when forming the cholesteric liquid crystal layer 16 .
The liquid crystal composition may contain a solvent. The solvent is not particularly limited and can be appropriately selected depending on the purpose, but organic solvents are preferred.
Examples of organic solvents include ketones, alkyl halides, amides, sulfoxides, heterocyclic compounds, hydrocarbons, esters, and ethers. These may be used individually by 1 type, and may use 2 or more types together. Among these, ketones are preferred in consideration of the load on the environment.

When forming the cholesteric liquid crystal layer, a liquid crystal composition is applied to the surface on which the cholesteric liquid crystal layer is to be formed, the liquid crystal compound is aligned in the cholesteric liquid crystal phase state, and then the liquid crystal compound is cured to form the cholesteric liquid crystal layer. is preferred.
That is, when a cholesteric liquid crystal layer is formed on the photo-alignment film 14, a liquid crystal composition is applied on the photo-alignment film 14, the liquid crystal compound is aligned in a cholesteric liquid crystal phase state, and then the liquid crystal compound is cured. It is preferable to form a cholesteric liquid crystal layer in which the cholesteric liquid crystal phase is fixed.
The liquid crystal composition can be applied by printing methods such as inkjet and scroll printing, and known methods such as spin coating, bar coating and spray coating, which can uniformly apply the liquid to the sheet.

The applied liquid crystal composition is optionally dried and/or heated and then cured to form a cholesteric liquid crystal layer. In this drying and/or heating step, the liquid crystal compound in the liquid crystal composition may be oriented in the cholesteric liquid crystal phase. When heating is performed, the heating temperature is preferably 200° C. or lower, more preferably 130° C. or lower.

The aligned liquid crystal compound is further polymerized as necessary. Polymerization may be either thermal polymerization or photopolymerization by light irradiation, but photopolymerization is preferred. It is preferable to use ultraviolet rays for light irradiation. The irradiation energy is preferably 20 mJ/cm ² to 50 J/cm ² , more preferably 50 to 1500 mJ/cm ² . In order to accelerate the photopolymerization reaction, light irradiation may be performed under heating conditions or under a nitrogen atmosphere. The wavelength of the ultraviolet rays to be irradiated is preferably 250 to 430 nm.

The thickness of the cholesteric liquid crystal layer is not limited, and the required light reflectance is determined according to the application of the optical element 10, the light reflectance required for the cholesteric liquid crystal layer, the material for forming the cholesteric liquid crystal layer, and the like. The thickness at which is obtained can be set as appropriate.

(Liquid crystal alignment pattern of cholesteric liquid crystal layer)
In the optical element 10 of the present invention, the cholesteric liquid crystal layer 16, which is an optically anisotropic layer, has an optical axis 20A derived from a liquid crystal compound 20 forming a cholesteric liquid crystal phase. It has a liquid crystal orientation pattern that changes while rotating continuously.
Note that the optical axis 20A derived from the liquid crystal compound 20 is the axis in which the liquid crystal compound 20 has the highest refractive index. For example, when the liquid crystal compound 20 is a rod-like liquid crystal compound, the optic axis 20A is along the long axis direction of the rod shape. In the following description, the optic axis 20A derived from the liquid crystal compound 20 is also referred to as "the optic axis 20A of the liquid crystal compound 20" or "the optic axis 20A".

FIG. 3 conceptually shows a plan view of the cholesteric liquid crystal layer 16 .
The plan view is a view of the cholesteric liquid crystal layer 16 and the optical element 10 in FIG. It is a diagram.
3 shows only the liquid crystal compound 20 on the surface of the photo-alignment film 14, as in FIG. 1, in order to clearly show the structure of the optical element 10 of the present invention.

As shown in FIG. 3, the liquid crystal compound 20 forming the cholesteric liquid crystal layer 16 is distributed in the plane of the cholesteric liquid crystal layer 16 on the surface of the photo-alignment film 14 according to the alignment pattern formed on the lower photo-alignment film 14 . , has a liquid crystal alignment pattern in which the direction of the optical axis 20A changes while rotating continuously along a predetermined direction indicated by an arrow X. FIG. In the illustrated example, the optic axis 20A of the liquid crystal compound 20 has a liquid crystal orientation pattern that changes while continuously rotating clockwise along the arrow X direction.
The liquid crystal compounds 20 forming the cholesteric liquid crystal layer 16 are arranged two-dimensionally in the direction of the arrow X and the direction orthogonal to this one direction (the direction of the arrow X).
In the following description, the direction orthogonal to the arrow X direction is referred to as the Y direction for convenience. That is, the arrow Y direction is a direction orthogonal to one direction in which the orientation of the optical axis 20A of the liquid crystal compound 20 changes while continuously rotating within the plane of the cholesteric liquid crystal layer. Therefore, in FIGS. 1, 2, and FIG. 4, which will be described later, the Y direction is a direction perpendicular to the plane of the paper.

That the direction of the optical axis 20A of the liquid crystal compound 20 changes while continuously rotating in the direction of the arrow X (predetermined one direction) specifically means that the liquid crystal compounds arranged along the direction of the arrow X The angle between the optical axis 20A of 20 and the arrow X direction varies depending on the position in the arrow X direction. This means that the angle changes sequentially up to θ−180°.
The difference in angle between the optical axes 20A of the liquid crystal compounds 20 adjacent to each other in the direction of the arrow X is preferably 45° or less, more preferably 15° or less, and even more preferably a smaller angle. .

On the other hand, the liquid crystal compound 20 forming the cholesteric liquid crystal layer 16 has the same optic axis 20A in the Y direction orthogonal to the arrow X direction, that is, the Y direction orthogonal to one direction in which the optic axis 20A rotates continuously. .
In other words, the liquid crystal compound 20 forming the cholesteric liquid crystal layer 16 has an equal angle between the optic axis 20A of the liquid crystal compound 20 and the arrow X direction in the Y direction.

In the cholesteric liquid crystal layer 16, in the liquid crystal orientation pattern of the liquid crystal compound 20, the optical axis 20A of the liquid crystal compound 20 rotates 180° in the direction of the arrow X in which the optical axis 20A continuously rotates and changes in the plane. The length (distance) of the liquid crystal alignment pattern is defined as the length Λ of one period of the liquid crystal alignment pattern.
That is, the distance between the centers in the direction of arrow X of two liquid crystal compounds 20 having the same angle with respect to the direction of arrow X is defined as the length of one cycle Λ. Specifically, as shown in FIG. 3 (FIG. 4), the distance between the centers of the two liquid crystal compounds 20 in the direction of the arrow X and the direction of the optical axis 20A is equal to the length of one cycle. Let be Λ. In the following description, the length Λ of one period is also referred to as "one period Λ".
In the cholesteric liquid crystal layer 16, the liquid crystal alignment pattern of the cholesteric liquid crystal layer repeats this one cycle Λ in the direction of the arrow X, that is, in one direction in which the direction of the optical axis 20A rotates continuously.

A cholesteric liquid crystal layer in which a cholesteric liquid crystal phase is fixed normally mirror-reflects incident light (circularly polarized light).
On the other hand, the cholesteric liquid crystal layer 16 reflects the incident light by tilting it in the direction of the arrow X with respect to the specular reflection. The cholesteric liquid crystal layer 16 has a liquid crystal orientation pattern that changes while the optical axis 20A continuously rotates along the arrow X direction (predetermined one direction) in the plane. Description will be made below with reference to FIG.

As an example, assume that the cholesteric liquid crystal layer 16 is a cholesteric liquid crystal layer that selectively reflects left-handed circularly polarized red light R _L . Therefore, when light is incident on the cholesteric liquid crystal layer 16, the cholesteric liquid crystal layer 16 reflects only left-handed circularly polarized red light R _L and transmits other light.

The left-handed circularly polarized red light R _L incident on the cholesteric liquid crystal layer 16 changes its absolute phase according to the orientation of the optical axis 20 A of each liquid crystal compound 20 when reflected by the cholesteric liquid crystal layer.
Here, in the cholesteric liquid crystal layer 16, the optical axis 20A of the liquid crystal compound 20 changes while rotating along the arrow X direction (one direction). Therefore, the amount of change in the absolute phase of the left-handed circularly polarized light _RL of the incident red light differs depending on the direction of the optical axis 20A.
Furthermore, the liquid crystal alignment pattern formed in the cholesteric liquid crystal layer 16 is a periodic pattern in the arrow X direction. Therefore, as conceptually shown in FIG. 4, the left-handed circularly polarized red light R _L incident on the cholesteric liquid crystal layer 16 has a periodic absolute phase Q in the direction of the arrow X corresponding to the direction of each optical axis 20A. is given.
Also, the orientation of the optical axis 20A of the liquid crystal compound 20 with respect to the arrow X direction is uniform in the alignment of the liquid crystal compound 20 in the Y direction orthogonal to the arrow X direction.
As a result, in the cholesteric liquid crystal layer 16, an _equiphase plane E inclined in the direction of the arrow X with respect to the XY plane is formed with respect to the left-handed circularly polarized red light RL.
Therefore, the left-handed circularly polarized red light R _L is reflected in the normal direction of the equal phase plane E, and the reflected left-handed circularly polarized light R _L is reflected with respect to the XY plane (principal surface of the cholesteric liquid crystal layer). It is reflected in a direction tilted in the arrow X direction.

Therefore, by appropriately setting the arrow X direction, which is one direction in which the optical axis 20A rotates, the reflection direction of the left circularly polarized red light _RL can be adjusted.
For example, if the direction of arrow X is reversed and the direction of rotation of the optical axis 20A is clockwise toward the left in the figure, the direction of reflection of the left-handed circularly polarized light _RL of red light will also be the opposite direction to that in FIG. .

Further, by reversing the rotation direction of the optical axis 20A of the liquid crystal compound 20 in the direction of the arrow X, the reflection direction of the left circularly polarized red light _RL can be reversed.
That is, in FIGS. 1 to 4, the rotation direction of the optical axis 20A in the direction of the arrow X is clockwise, and the left-handed circularly polarized light _RL of the red light is reflected in the direction of the arrow X with an inclination. By rotating, the left-handed circularly polarized light _RL of the red light is tilted in the direction opposite to the arrow X direction and reflected.

Furthermore, in the cholesteric liquid crystal layer having the same liquid crystal alignment pattern, the reflection direction is reversed depending on the spiraling direction of the liquid crystal compound 20, that is, the rotating direction of the reflected circularly polarized light.
The cholesteric liquid crystal layer 16 shown in FIG. 4 is a liquid crystal orientation pattern in which the helical turning direction is right-handed and selectively reflects right-handed circularly polarized light, and the optical axis 20A rotates clockwise along the arrow X direction. , the right-handed circularly polarized light is tilted in the arrow X direction and reflected.
Therefore, a cholesteric liquid crystal layer having a liquid crystal orientation pattern in which the direction of spiral rotation is left-handed, selectively reflects left-handed circularly polarized light, and the optical axis 20A rotates clockwise along the direction of the arrow X is left-handed. Circularly polarized light is tilted in the direction opposite to the arrow X direction and reflected.

As described above, the cholesteric liquid crystal layer 16 of the optical element 10 has a liquid crystal alignment pattern in which the optic axis 20A of the liquid crystal compound 20 rotates along one direction in an in-plane manner. In this liquid crystal alignment pattern, the length of 180° rotation of the optical axis 20A is defined as one cycle Λ (see FIGS. 1, 3 and 4).
In the cholesteric liquid crystal layer 16 having this liquid crystal alignment pattern, the shorter the period Λ, the greater the angle of the reflected light with respect to the incident light. That is, the shorter the period Λ, the greater the inclination of the reflected light with respect to the incident light.

One period Λ is not limited, and may be appropriately set according to the use of the optical element.
One period Λ of the cholesteric liquid crystal layer 16 is preferably 2.00 μm or less, more preferably 1.60 μm or less, even more preferably 0.80 μm or less, and further preferably less than the wavelength λ of incident light. Although the lower limit is not particularly limited, it is often 0.20 μm or more.
By setting one period .LAMBDA. Therefore, for example, when the optical element of the present invention is used as a diffraction element for making light incident on the above-described AR glass light guide plate, the light can be incident on the light guide plate at an angle sufficient for propagation by total reflection. .

The same applies to the patterned liquid crystal layer 32 in the optical element 30 of another aspect of the present invention, which will be described later, with respect to one period Λ of the liquid crystal alignment pattern.

The optical element of the present invention may be used by laminating a plurality of layers.
An example is shown in FIG.
The conceptually laminated optical element 24 shown in FIG. 5 has three diffractive elements of the present invention, an R optical element 10R, a G optical element 10G, and a B optical element 10B.
The R optical element 10R corresponds to red light, and has a support 12, a photo-alignment film 14R, and a cholesteric liquid crystal layer 16R that reflects red left-handed circularly polarized light _RL .
The G optical element 10G corresponds to green light, and has a support 12, a photo-alignment film 14G, and a cholesteric liquid crystal layer 16G that reflects green left-handed circularly polarized light G _L .
The B optical element 10B corresponds to blue light, and has a support 12, a photo-alignment film 14B, and a cholesteric liquid crystal layer 16B that reflects blue left-handed circularly polarized light B _L .
In the R optical element 10R, the G optical element 10G, and the B optical element 10B, the support, the alignment film, and the cholesteric liquid crystal layer are all the same as the support 12, the photo-alignment film 14, and the cholesteric liquid crystal layer 16 in the optical element 10 described above. are similar. However, each cholesteric liquid crystal layer (diffraction element) has a spiral pitch P according to the wavelength range of light to be selectively reflected.

Here, in the R optical element 10R, the G optical element 10G, and the B optical element 10B, the permutation of the length of the selective reflection center wavelength of the cholesteric liquid crystal layer is equal to the permutation of one period Λ in the liquid crystal orientation pattern of the cholesteric liquid crystal layer. .
That is, in the laminated optical element 24, the selective reflection center wavelength of the R optical element 10R corresponding to reflection of red light is the longest, and the selective reflection center wavelength of the G optical element 10G corresponding to reflection of green light is second longest. The selective reflection center wavelength of the B optical element 10B corresponding to the reflection of light is the shortest.
Accordingly, in the R optical element 10R, the G optical element 10G, and the B optical element 10B, the cholesteric liquid crystal layer of the R optical element 10R has the longest period Λ R , and the cholesteric liquid crystal layer of the G optical element 10G has the longest period Λ _R . The period Λ _G is the second longest, and one period Λ _B of the cholesteric liquid crystal layer of the B optical element 10B is the shortest.

The angle of reflection of light by the cholesteric liquid crystal layer in which the optical axis 20A of the liquid crystal compound 20 rotates continuously along one direction (direction of arrow X) varies depending on the wavelength of the reflected light. Specifically, the longer the wavelength of the light, the larger the angle of the reflected light with respect to the incident light. Therefore, the red light reflected by the R optical element 10R has the largest angle of reflected light with respect to the incident light, the green light reflected by the G optical element 10G has the second largest angle of reflected light with respect to the incident light, and the angle of the reflected light with respect to the incident light is large. The angle of the reflected light with respect to the incident light is the smallest for blue light.
On the other hand, as described above, a cholesteric liquid crystal layer having a liquid crystal alignment pattern in which the optical axis 20A of the liquid crystal compound 20 rotates along one direction has one period Λ in which the optical axis 20A rotates 180° in the liquid crystal alignment pattern. The shorter, the greater the angle of the reflected light relative to the incident light.

Therefore, in the R optical element 10R, the G optical element 10G, and the B optical element 10B, the permutation of the length of the selective reflection center wavelength in the diffraction element (cholesteric liquid crystal layer) and the one period Λ (Λ _R , _{Λ G} and _{Λ B} ), the _stacking is shown in FIG. The wavelength dependency of the angle of reflection of the light reflected by the optical element 24 can be greatly reduced, and light with different wavelengths can be reflected in substantially the same direction.

When the optical elements of the present invention that selectively reflect different wavelength ranges are laminated, the order of lamination is not limited.

When a plurality of optical elements of the present invention are laminated, the configuration having the R optical element 10R, G optical element 10G, and B optical element 10B shown in FIG. 5 is not limited.
For example, it may have two layers appropriately selected from the R optical element 10R, the G optical element 10G, and the B optical element 10B. Further, one or more of the R optical element 10R, the G optical element 10G and the B optical element 10B, or in addition to the R optical element 10R, the G optical element 10G and the B optical element 10B, selectively reflects ultraviolet light. It may have optical elements and/or optical elements that selectively reflect infrared light.

When a plurality of optical elements of the present invention are laminated, the structure is not limited to the structure in which optical elements having different selective reflection center wavelengths are laminated as shown in FIG.
For example, two cholesteric liquid crystal layers having the same selective reflection center wavelength and different rotating directions of reflected circularly polarized light, that is, different spiral rotating directions (senses) in the cholesteric liquid crystal phase may be used.
With such a configuration, both the right-handed circularly polarized light and the left-handed circularly polarized light included in the incident light can be reflected, and the amount of reflected light with respect to the incident light can be increased.

Although the optical element 10 of the above example uses a cholesteric liquid crystal layer as an optically anisotropic layer, the present invention is not limited to this. That is, in the optical element of the present invention, the optically anisotropic layer is formed using a composition containing a liquid crystal compound, and the optical axis 20A derived from the liquid crystal compound 20 is less than in-plane. Various optically anisotropic layers are available as long as they have a liquid crystal orientation pattern that is continuously rotated along one direction.
As an example, the optical element of the present invention has a liquid crystal alignment pattern continuously rotating along at least one in-plane direction, and the liquid crystal compound is helically twisted and rotated in the thickness direction. Non-optically anisotropic layers are also available.

FIG. 6 conceptually shows an example thereof.
The optical element 30 shown in FIG. 6 has a support 12 , a photo-alignment film 14 and a patterned liquid crystal layer 32 .
In the optical element 30, the patterned liquid crystal layer 32 is an optically anisotropic layer in the present invention and has the same liquid crystal alignment pattern as the cholesteric liquid crystal layer 16 described above. Therefore, as conceptually shown in FIG. 7, the patterned liquid crystal layer 32, like the cholesteric liquid crystal layer 16, has a liquid crystal orientation in which the optical axis 20A of the liquid crystal compound 20 continuously rotates clockwise along the arrow X direction. have a pattern. 7 also shows only the liquid crystal compound on the surface of the photo-alignment film 14, like FIG. 3 described above.
In the pattern liquid crystal layer 32, the liquid crystal compound 20 forming the diffraction element (liquid crystal layer) is not helically twisted and rotated in the thickness direction, and the optical axis 20A faces the same direction in the thickness direction. That is, the direction of the optical axis 20A derived from the liquid crystal compound 20 is aligned with the thickness direction. Such a liquid crystal layer can be formed by not adding a chiral agent to the liquid crystal composition in forming the cholesteric liquid crystal layer described above.

In the optical element 30, the support 12 and the photo-alignment film 14 are the same as those of the optical element 10 shown in FIG.

As described above, the patterned liquid crystal layer 32 is a liquid crystal in which the direction of the optical axis 20A derived from the liquid crystal compound 20 changes while continuously rotating in the direction of the arrow X, that is, along one direction indicated by the arrow X. It has an orientation pattern.
On the other hand, in the liquid crystal compound 20 forming the patterned liquid crystal layer 32, the direction of the optic axis 20A is the same in the Y direction perpendicular to the arrow X direction, that is, the Y direction perpendicular to the one direction in which the optic axis 20A rotates continuously. Compounds 20 are arranged at regular intervals. In other words, in the liquid crystal compounds 20 forming the patterned liquid crystal layer 32, the liquid crystal compounds 20 aligned in the Y direction have the same angle between the direction of the optical axis 20A and the arrow X direction.

In the pattern liquid crystal layer 32, the liquid crystal compounds arranged in the Y direction have an equal angle between the optic axis 20A and the arrow X direction (one direction in which the optic axis of the liquid crystal compound 20 rotates). A region R is defined as a region in which the liquid crystal compound 20 having the same angle formed by the optical axis 20A and the arrow X direction is arranged in the Y direction.
In this case, the value of the in-plane retardation (Re) in each region R is preferably half the wavelength, ie, λ/2. These in-plane retardations are calculated from the product of the refractive index difference Δn associated with the refractive index anisotropy of the region R and the thickness of the optically anisotropic layer. Here, the refractive index difference associated with the refractive index anisotropy of the region R in the optically anisotropic layer is the refractive index in the direction of the slow axis in the plane of the region R and the direction orthogonal to the direction of the slow axis is the refractive index difference defined by the difference from the refractive index of That is, the refractive index difference Δn associated with the refractive index anisotropy of the region R is the refractive index of the liquid crystal compound 20 in the direction of the optical axis 20A and the refractive index of the liquid crystal compound 20 in the direction perpendicular to the optical axis 20A in the plane of the region R. Equal to the difference in refractive index. That is, the refractive index difference Δn is equal to the refractive index difference of the liquid crystal compound 20 .

When circularly polarized light is incident on the patterned liquid crystal layer 32, the light is refracted and the direction of the circularly polarized light is changed.
This action is conceptually shown in FIGS. 8 and 9. FIG. In the pattern liquid crystal layer 32, the product of the refractive index difference of the liquid crystal compound and the thickness of the optically anisotropic layer is assumed to be λ/2.
As shown in FIG. 8, when the product of the refractive index difference of the liquid crystal compound of the patterned liquid crystal layer 32 and the thickness of the optically anisotropic layer is λ/2, left-handed circularly polarized light incident on the patterned liquid crystal layer 32 When the light L ₁ is incident, the incident light L ₁ is given a 180° phase difference by passing through the patterned liquid crystal layer 32, and the transmitted light L ₂ is converted into right-handed circularly polarized light.
In addition, when the incident light L ₁ passes through the patterned liquid crystal layer 32 , the absolute phase changes according to the direction of the optical axis 20 A of each liquid crystal compound 20 . At this time, since the direction of the optical axis 20A changes while rotating along the direction of the arrow X, the amount of change in the absolute _phase of the incident light L1 differs according to the direction of the optical axis 20A. Furthermore, since the liquid crystal alignment pattern formed on the patterned liquid crystal layer 32 is a periodic pattern in the direction of the arrow X, the incident light L ₁ passing through the patterned liquid crystal layer 32 has, as shown in FIG. A periodic absolute phase Q1 is given in the direction of the arrow X corresponding to the direction of the optical axis 20A. As a result, an equiphase surface E1 inclined in the direction opposite to the direction of the arrow X is formed.
Therefore, the transmitted light _L2 is refracted so as to be inclined in a direction perpendicular to the equal phase plane E1, and travels in _a direction different from the traveling direction of the incident light L1. In this manner, the left-handed circularly polarized incident light L ₁ is converted into right-handed circularly polarized transmitted light L ₂ , which is inclined in the direction of the arrow X by a certain angle with respect to the incident direction.

On the other hand, when the product of the refractive index difference of the liquid crystal compound of the patterned liquid crystal layer 32 and the thickness of the optically anisotropic layer is λ/2, as shown in FIG. When the light L ₄ is incident, the incident light L ₄ passes through the patterned liquid crystal layer 32, is given a phase difference of 180°, and is converted into a left circularly polarized transmitted light L ₅ .
In addition, when the incident light L ₄ passes through the patterned liquid crystal layer 32 , the absolute phase changes according to the direction of the optical axis 20 A of each liquid crystal compound 20 . At this time, since the direction of the optical axis 20A changes while rotating along the direction of the arrow X, the amount of change in the absolute phase of the incident light _L4 differs according to the direction of the optical axis 20A. Furthermore, since the liquid crystal alignment pattern formed on the patterned liquid crystal layer 32 is a periodic pattern in the direction of the arrow X, the incident light L ₄ that has passed through the patterned liquid crystal layer 32 is divided into the respective optical patterns as shown in FIG. A periodic absolute phase Q2 is given in the direction of the arrow X corresponding to the orientation of the axis 20A.
Here, since the incident light L ₄ is right-handed circularly polarized light, the periodic absolute phase Q2 in the direction of the arrow X corresponding to the direction of the optical axis 20A is opposite to that of the incident light L ₁ which is left-handed circularly polarized light. . As a result, the incident light L4 forms _{an equiphase} surface E2 inclined in the direction of the arrow X opposite to the incident light L1.
Therefore, the incident light _L4 is refracted so as to be inclined in a direction perpendicular to the equal phase plane E2, and travels in a direction different from the traveling direction of the incident light _L4 . _In this way, the incident light L4 is converted into left _- handed circularly polarized transmitted light L5 which is inclined by a certain angle in the direction opposite to the direction of the arrow X with respect to the incident direction.

Similar to the cholesteric liquid crystal layer 16 and the like, the patterned liquid crystal layer 32 can also adjust the angles of refraction of the transmitted lights L ₂ and L ₅ by changing one period Λ of the formed liquid crystal alignment pattern. Specifically, in the patterned liquid crystal layer 32, the shorter one period Λ of the liquid crystal alignment pattern is, the stronger the light passing through the adjacent liquid crystal compounds 20 interferes with each other, so that the transmitted lights L2 and _{L5 are} greatly refracted. be able to. As described above, one circumference Λ is preferably 1.6 μm or less, more preferably 0.8 μm or less, and further preferably less than the wavelength λ of incident light.
Also in the patterned liquid crystal layer 32, as in the cholesteric liquid crystal layer 16 and the like, the longer the wavelengths of the incident lights L1 and _L4 , the _more the transmitted lights L2 and _{L5 are} refracted.
Furthermore, by reversing the rotation direction of the optical axis 20A of the liquid crystal compound 20 rotating along the arrow X direction, the direction of refraction of the transmitted light can be reversed. That is, in the examples shown in FIGS. 6 to 9, the rotation direction of the optical axis 20A in the direction of the arrow X is clockwise. You can do it in the opposite direction.

In the above examples, in the optically anisotropic layer of the optical element, the direction of the optical axis 20A derived from the liquid crystal compound 20 continuously changes only in the arrow X direction.
However, the optically anisotropic layer of the optical element of the present invention is not limited to this, and is formed using a composition containing a liquid crystal compound, and the optical axis 20A of the liquid crystal compound 20 is in one direction. Various configurations are available as long as they rotate continuously along the .

As an example, as conceptually shown in the plan view of FIG. 11, the liquid crystal alignment pattern is concentrically directed from the inside to the outside in one direction in which the direction of the optic axis of the liquid crystal compound 20 changes while continuously rotating. An optically anisotropic layer 34 is exemplified, which has a concentric pattern.
Alternatively, instead of concentric circles, a liquid crystal alignment pattern in which one direction in which the direction of the optic axis of the liquid crystal compound 20 changes while continuously rotating is provided radially from the center of the optically anisotropic layer 34 can also be used. be.

11 also shows only the liquid crystal compound 20 on the surface of the alignment film as in FIGS. 3 and 7, but in the optically anisotropic layer 34, this alignment As described above, the liquid crystal compound 20 on the surface of the film has a helical structure in which the liquid crystal compound 20 spirally turns and is stacked.

In the optically anisotropic layer 34 shown in FIG. 11 , the optic axis (not shown) of the liquid crystal compound 20 is the longitudinal direction of the liquid crystal compound 20 .
In the optically anisotropic layer 34, the orientation of the optic axis of the liquid crystal compound ₂₀ is oriented in _a number of directions outward from the center of the optically anisotropic layer 34, such as the direction indicated by arrow X1, the direction indicated by arrow X2, It changes while continuously rotating along the direction indicated by the arrow _X3 .
In addition, as a preferred embodiment, as shown in FIG. 11, there is one that changes radially from the center of the optically anisotropic layer 34 while rotating in the same direction. The embodiment shown in FIG. 11 is a counterclockwise orientation. In each of the arrows X ₁ , X ₂ and X ₃ in FIG. 11, the direction of rotation of the optical axis is counterclockwise from the center toward the outside.
Circularly polarized light incident on the optically anisotropic layer 34 having this liquid crystal orientation pattern changes its absolute phase in individual local regions where the directions of the optical axes of the liquid crystal compound 20 are different. At this time, the amount of change in each absolute phase differs according to the direction of the optical axis of the liquid crystal compound 20 on which the circularly polarized light is incident.

The optically anisotropic layer 34 having such a concentric liquid crystal orientation pattern, that is, a liquid crystal orientation pattern in which the optic axis rotates continuously and changes radially, is the rotation direction of the optic axis of the liquid crystal compound 20 and the reflection direction. Incident light can be reflected or transmitted as divergent or converging light, depending on the direction of circular polarization applied.
That is, when the optically anisotropic layer 34 is a cholesteric liquid crystal layer, the optical element of the present invention functions as, for example, a concave mirror or a convex mirror by making the liquid crystal alignment pattern concentric. When the optically anisotropic layer 34 is a patterned liquid crystal layer, the optical element of the present invention functions as a concave lens or a convex lens by making the liquid crystal alignment pattern concentric.

Here, when the liquid crystal alignment pattern of the optically anisotropic layer is concentric and the optical element acts as a concave mirror or a convex lens, one period .LAMBDA. From the center of layer 34, it preferably tapers progressively outward in one direction in which the optic axis rotates continuously.
As described above, the reflection angle of light with respect to the direction of incidence increases as one period Λ in the liquid crystal alignment pattern is shorter. Therefore, by gradually shortening one period Λ in the liquid crystal alignment pattern from the center of the optically anisotropic layer 34 toward the outer direction in which the optical axis rotates continuously, the light can be more focused. It is possible to improve the performance as a concave mirror and a convex lens.

In the present invention, when the optical element acts as a convex mirror or a concave lens, it is preferable that the continuous rotation of the optical axis in the liquid crystal orientation pattern is reversed from the center of the optically anisotropic layer 34 . When the optically anisotropic layer is a cholesteric liquid crystal layer, the direction of rotation of the reflected circularly polarized light, ie, the sense of helix, may be reversed.
In addition, by gradually shortening one period Λ in which the optical axis rotates 180° from the center of the optically anisotropic layer 34 outward in one direction in which the optical axis rotates continuously, the optical The anisotropic layer 34 can make the light more divergent and improve its performance as a convex mirror and a concave lens.

In the present invention, when the optical element acts as a convex mirror and a concave lens, or as a concave mirror and a convex lens, it is preferable to satisfy the following formula (1).
Φ(r)=(π/λ)[(r ² +f ² ) ^1/2 -f] Equation (1)
Here, r is the distance from the center of the concentric circle and is represented by the formula "r=(x ² +y ² ) ^1/2 ". x and y represent in-plane positions, and (x, y)=(0, 0) represents the center of the concentric circles. Φ(r) is the angle of the optical axis at the distance r from the center, λ is the central wavelength of selective reflection of the cholesteric liquid crystal layer, and f is the target focal length.

In the present invention, depending on the application of the optical element, conversely, one period Λ in the concentric liquid crystal orientation pattern is set to one direction in which the optical axis continuously rotates from the center of the optically anisotropic layer 34. It may be gradually lengthened in an outward direction.
Furthermore, depending on the application of the optical element, for example, when it is desired to provide a light amount distribution to the reflected light, instead of gradually changing one period Λ in one direction in which the optical axis rotates continuously, the optical axis It is also possible to use a configuration having regions with partially different periods Λ in one continuously rotating direction.
Furthermore, the optical element of the present invention may have a cholesteric liquid crystal layer having a uniform period Λ over the entire surface and a cholesteric liquid crystal layer having regions with different periods Λ. In this regard, the same applies to a configuration in which the optical axis rotates continuously only in one direction, as shown in FIG. 1, which will be described later.

FIG. 12 conceptually shows an example of an exposure apparatus for forming such a concentric alignment pattern on the photo-alignment film 14 corresponding to the optically anisotropic layer 34 .
The exposure device 80 includes a light source 84 having a laser 82, a polarizing beam splitter 86 that splits the laser beam M from the laser 82 into S-polarized light MS and P-polarized light MP, and a mirror 90A arranged in the optical path of the P-polarized light MP. and a mirror 90B arranged in the optical path of the S-polarized MS, a lens 92 arranged in the optical path of the S-polarized MS, a polarizing beam splitter 94, and a λ/4 plate 96.

The P-polarized light MP split by the polarizing beam splitter 86 is reflected by the mirror 90A and enters the polarizing beam splitter 94 . On the other hand, the S-polarized light MS split by the polarizing beam splitter 86 is reflected by the mirror 90B, condensed by the lens 92, and enters the polarizing beam splitter 94. FIG.
The P-polarized MP and S-polarized light MS are combined by a polarizing beam splitter 94 into right-handed circularly polarized light and left-handed circularly polarized light according to the polarization direction by a λ/4 plate 96 to form a photo-alignment precursor on the support 12 . It is incident on the body membrane 140 .
Here, due to the interference between the right-handed circularly polarized light and the left-handed circularly polarized light, the polarization state of the light with which the photo-alignment precursor film 140 is irradiated changes periodically in the form of interference fringes. Since the crossing angle of the left-handed circularly polarized light and the right-handed circularly polarized light changes from the inside to the outside of the concentric circle, an exposure pattern is obtained in which the pitch changes from the inside to the outside. As a result, a concentric alignment pattern in which the alignment state changes periodically is obtained in the photo-alignment film 14 .

In this exposure apparatus 80, the length Λ of one period of the liquid crystal orientation pattern in which the optical axis of the liquid crystal compound 20 is continuously rotated by 180° is the refractive power of the lens 92 (F number of the lens 92), the focal length of the lens 92 , and by changing the distance between the lens 92 and the photo-alignment film 14 .
Also, by adjusting the refractive power of the lens 92 (the F-number of the lens 92), the length Λ of one cycle of the liquid crystal alignment pattern can be changed in one direction in which the optical axis rotates continuously. Specifically, the length Λ of one period of the liquid crystal alignment pattern can be changed in one direction in which the optical axis continuously rotates, depending on the spread angle of the light spread by the lens 92 that interferes with the parallel light. More specifically, when the refractive power of the lens 92 is weakened, the light becomes closer to parallel light, so the length Λ of one period of the liquid crystal orientation pattern gradually decreases from the inside to the outside, and the F-number increases. Conversely, when the refractive power of the lens 92 is strengthened, the length Λ of one period of the liquid crystal alignment pattern suddenly shortens from the inside to the outside, and the F-number becomes smaller.

In this way, in one direction in which the optic axis rotates continuously, the configuration for changing one period Λ in which the optic axis rotates 180° is achieved by changing the liquid crystal compound 20 only in one direction in the arrow X direction shown in FIGS. It is also possible to use a configuration in which the optical axis 20A of is continuously rotated and changed.
For example, by gradually shortening one period Λ of the liquid crystal alignment pattern in the direction of the arrow X, it is possible to obtain an optical element that reflects or transmits light so as to converge.
Furthermore, depending on the application of the optical element, for example, when it is desired to provide a light amount distribution for reflected light and transmitted light, instead of gradually changing one period Λ in the direction of arrow X, partially Configurations having regions with different periods Λ are also available. For example, as a method of partially changing one period Λ, a method of patterning the photo-alignment film by scanning exposure while arbitrarily changing the polarization direction of condensed laser light can be used.

Although the optical element of the present invention has been described in detail above, the present invention is not limited to the above examples, and various improvements and modifications may be made without departing from the gist of the present invention. is.

The features of the present invention will be described more specifically with reference to examples below. The materials, reagents, amounts used, amounts of substances, ratios, treatment details, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the gist of the present invention. Therefore, the scope of the present invention should not be construed to be limited by the specific examples shown below.

<Example 1>
(Synthesis of photo-alignment agent 1)
Polymer 1 (corresponding to photo-alignment agent 1) having the following repeating unit was synthesized according to the description in paragraph [0066] of International Publication No. 2012/014915. The polymer had a weight average molecular weight of 31,700, an acid value of 130 mgKOH/g, and a phase transition temperature of 148-173°C.
Incidentally, R ¹ is a methyl group, the content of the repeating unit represented by the formula (A3) is 80 mol% with respect to the total repeating units of the polymer 1, represented by the formula (B3) The content of repeating units was 20 mol % with respect to the total repeating units of polymer 1 .
Polymer 1 exhibited liquid crystallinity.

(Formation of photo-alignment film P-1)
A glass substrate was prepared as a support.
The photo-alignment film-forming composition 1 was applied onto the support by a spin coater (coating step). After that, the support coated with the photo-alignment film-forming composition 1 was dried on a hot plate at 80° C. for 2 minutes to remove the solvent (drying step), and the photo-alignment precursor film 1 having a thickness of 0.02 μm was obtained. formed.

Photo-alignment film-forming composition 1
――――――――――――――――――――――――――――――――――
Photo-alignment agent 1 1.00 parts by mass Cyclohexanone 99.00 parts by mass ――――――――――――――――――――――――――――――――――

The photo-alignment precursor film 1 was exposed using the exposure apparatus shown in FIG. 10 to form a photo-alignment film P-1 having an alignment pattern.
In the exposure apparatus, a laser that emits laser light with a wavelength (325 nm) was used. The amount of exposure by interference light was set to 300 mJ/cm ² . The crossing angle (crossing angle α) of the two lights is such that one period Λ (the length of the 180° rotation of the optical axis) of the alignment pattern formed by the interference of the two laser beams is 1.90 μm. was adjusted.
Then, a heat treatment was performed at 140° C. for 10 minutes (heat treatment step) to induce orientation and prepare a photo-alignment film P-1.
The photo-alignment film P-1 exhibited liquid crystallinity.

(Formation of cholesteric liquid crystal layer)
As a liquid crystal composition for forming a cholesteric liquid crystal layer, the following liquid crystal composition LC-1 was prepared.
Liquid crystal composition LC-1
――――――――――――――――――――――――――――――――――
Liquid crystal compound L-1 100 parts by mass Initiator I-2 3 parts by mass Leveling agent T-1 0.08 parts by mass Chiral agent Ch-1 4.5 parts by mass Methyl ethyl ketone 199.64 parts by mass ――――――――――――――――――――――――――

Liquid crystal compound L-1 (hereinafter referred to as a mixture of compounds)

Initiator I-2

Leveling agent T-1

Chiral agent Ch-1

The phase transition temperature of the liquid crystal compound L-1 was determined by heating the liquid crystal compound on a hot stage and observing the texture with a polarizing microscope. As a result, the crystal phase-nematic phase transition temperature was 79.degree. C., and the nematic phase-isotropic phase transition temperature was 144.degree.
The Δn of the liquid crystal compound L-1 was measured by injecting the liquid crystal compound into a wedge-shaped cell, irradiating the cell with a laser beam having a wavelength of 550 nm, and measuring the refraction angle of the transmitted light. The measurement temperature was 60°C. Δn of the liquid crystal compound L-1 was 0.16.

The above liquid crystal composition LC-1 was applied onto the photo-alignment film P-1 using a spin coater at 1000 rpm for 10 seconds (coating step).
The coating film of liquid crystal composition LC-1 was heated on a hot plate at 80° C. for 3 minutes (180 sec) (heating step).
Thereafter, the liquid crystal composition LC-1 was cured by irradiating the coating film with ultraviolet light having a wavelength of 365 nm at a dose of 300 mJ/cm ² at 80° C. in a nitrogen atmosphere using a high-pressure mercury lamp (exposure step). to fix the orientation of the liquid crystal compound, forming a cholesteric liquid crystal layer.
Thus, an optical element having a support, a photo-alignment film and a cholesteric liquid crystal layer was produced.

It was confirmed with a polarizing microscope that the cholesteric liquid crystal layer had a periodically oriented surface as shown in FIG.
The optical element was cut along the direction of rotation of the optical axis, and the cross section was observed with an SEM (scanning electron microscope). By analyzing the SEM image, the film thickness d of the cholesteric liquid crystal layer, one period Λ in the liquid crystal alignment pattern, and the length pitch P of one spiral pitch were measured.

<Example 2>
(Synthesis of photo-alignment agent 2)
4-Aminocyclohexanol (50.0 g), triethylamine (48.3 g), and N,N-dimethylacetamide (800 g) were weighed into a 2 L three-necked flask equipped with a stirring blade, thermometer, dropping funnel and reflux tube. It was taken out and stirred under ice-cooling.
Next, methacrylic acid chloride (47.5 g) was added dropwise into the flask over 40 minutes using a dropping funnel, and after the dropping was completed, the reaction solution was stirred at 40°C for 2 hours.
After cooling the reaction solution to room temperature (23° C.), the reaction solution was subjected to suction filtration to remove precipitated salts. The obtained organic phase was transferred to a 2 L three-necked flask equipped with a stirring blade, a thermometer, a dropping funnel and a reflux tube, and stirred under water cooling.
Next, N,N-dimethylaminopyridine (10.6 g) and triethylamine (65.9 g) were added to the flask, and 4-n-octyloxy dissolved in tetrahydrofuran (125 g) in advance was added using a dropping funnel. Cinnamic acid chloride (127.9 g) was added dropwise into the flask over 30 minutes, and after completion of the dropwise addition, the reaction solution was stirred at 50°C for 6 hours. After the reaction solution was cooled to room temperature, it was separated and washed with water, the resulting organic phase was dried over anhydrous magnesium sulfate, and the resulting solution was concentrated to obtain a yellowish white solid.
The resulting yellowish white solid was dissolved in methyl ethyl ketone (400 g) by heating and recrystallized to obtain 76 g of monomer mA-1 shown below as a white solid (yield 40%).

As the monomer mB-1 below, Cychromer M-100 (manufactured by Daicel Corporation) was used.

A flask equipped with a condenser, a thermometer, and a stirrer was charged with 2-butanone (5 parts by mass) as a solvent, and refluxed by heating in a water bath while flowing nitrogen into the flask at 5 mL/min. Here, monomer mA-1 (1.2 parts by mass), monomer mB-1 (8.8 parts by mass), 2,2'-azobis(isobutyronitrile) (1 part by mass) as a polymerization initiator, and , and 2-butanone (5 parts by mass) as a solvent was added dropwise over 3 hours, and the resulting reaction solution was stirred while maintaining the reflux state for 3 hours. After completion of the reaction, the reaction solution was allowed to cool to room temperature, and diluted by adding 2-butanone (30 parts by mass) to obtain a polymer solution having a polymer concentration of about 20% by mass. The resulting polymer solution is poured into a large excess of methanol to precipitate the polymer, the precipitate is filtered off, the resulting solid content is washed with a large amount of methanol, and dried with air at 50° C. for 12 hours. By doing so, a polymer (corresponding to the photo-alignment agent 2) having a photo-alignment group (cinnamate group) was obtained.

(Formation of photo-alignment film P-2)
A glass substrate was prepared as a support.
The photo-alignment film-forming composition 2 was applied onto the support by a spin coater. After that, the substrate coated with the photo-alignment film-forming composition 2 was dried on a hot plate at 125° C. for 2 minutes to remove the solvent and form a photo-alignment precursor film 2 having a thickness of 0.3 μm.

──────────────────────────────────
Photo-alignment film-forming composition 2
──────────────────────────────────
Photo-alignment agent 2 100.00 parts by mass Thermal acid generator D-1 described below 3.00 parts by mass Diisopropylethylamine 0.60 parts by mass Butyl acetate 4061.12 parts by mass Methyl ethyl ketone 1015.28 parts by mass ──────────────────────────

Thermal acid generator D-1

The photo-alignment precursor film 2 was exposed using the exposure apparatus shown in FIG. 10 to form a photo-alignment film P-2 having an alignment pattern.
In the exposure apparatus, a laser that emits laser light with a wavelength (325 nm) was used. The amount of exposure by interference light was set to 300 mJ/cm ² . The crossing angle of the two lights (crossing angle α) is such that one period Λ (the length of the 180° rotation of the optical axis) of the alignment pattern formed by the interference of the two laser beams is 1.90 μm. was adjusted.

An optical element was produced according to the same procedure as in Example 1, except that the photo-alignment film P-2 was used, and the same measurements were performed.

<Example 3>
(Synthesis of photo-alignment agent 3)
A polymer (PA-4) described in JP-A-2014-026261 was synthesized as a photo-alignment agent 3 according to the following procedure.

2-(3,4-Epoxycyclohexyl)ethyltrimethoxysilane (100.0 g), methyl isobutyl ketone (500 g) and triethylamine (10.0 g) were added to a reaction vessel equipped with a stirrer, thermometer, addition funnel and reflux condenser. 0 g) were charged and mixed at room temperature. Then, deionized water (100 g) was added dropwise from the dropping funnel over 30 minutes, and the reaction was allowed to proceed at 80° C. for 6 hours while stirring under reflux. After completion of the reaction, the organic phase was taken out and washed with a 0.2% by mass aqueous solution of ammonium nitrate until the water after washing became neutral. 1) was obtained as a viscous transparent liquid.
When this polyorganosiloxane (POS-1) was subjected to ¹ H-NMR (nuclear magnetic resonance) analysis, a peak based on the oxiranyl group was obtained at a chemical shift (δ) of around 3.2 ppm, with theoretical intensity. It was confirmed that no side reaction of the epoxy group occurred during the reaction.
This polyorganosiloxane (POS-1) had an Mw of 2,200 and an epoxy equivalent of 186.

In a 100 mL three-necked flask, polyorganosiloxane (POS-1) (9.3 g), methyl isobutyl ketone (26 g), cinnamic acid derivative (C-2) (3 g), Aronix M-5300 (manufactured by Toa Gosei) (1 g ), and tetrabutylammonium bromide (0.93 g) were added and stirred at 80° C. for 12 hours. After completion of the reaction, it was diluted with butyl acetate (100 g) and washed with water three times. The operation of concentrating this solution and diluting it with butyl acetate was repeated twice to finally obtain a solution containing polyorganosiloxane having a photo-alignment group (corresponding to photo-alignment agent 3).

A polymer (PB-5) described in JP-A-2014-026261 was synthesized according to the following procedure.

(Synthesis of poly(meth)acrylate (PB-2))
A flask equipped with a condenser and a stirrer was charged with 2,2′-azobis(isobutyronitrile) (1 part by mass) as a polymerization initiator and diethylene glycol methyl ethyl ether (180 parts by mass) as a solvent. Subsequently, 3,4-epoxycyclohexylmethyl methacrylate (70 parts by mass) and 3-methyl-3-oxetanylmethyl methacrylate (30 parts by mass) were further added to the flask, the inside of the flask was replaced with nitrogen, and then gentle stirring was started. rice field. The solution temperature was raised to 80° C. and maintained at this temperature for 5 hours to obtain a polymer solution containing poly(meth)acrylate (PB-2). The solid content concentration of the obtained polymer solution was 32.8% by mass. The Mn of the resulting polymer was 16,000.

(Synthesis of poly(meth)acrylate (PB-5))
Poly (meth) acrylate obtained above (PB-2) (100 parts by mass), acryloyl group-containing carboxylic acid (Aronix M-5300, manufactured by Toagosei) (20 parts by mass), tetrabutylammonium bromide as a catalyst (10 parts by mass) and propylene glycol monomethyl ether acetate (150 parts by mass) as a solvent were charged, and stirred at 90° C. for 12 hours in a nitrogen atmosphere. After completion of the reaction, the resulting reaction solution was diluted with propylene glycol monomethyl ether acetate (100 parts by mass) and washed with water three times. The operation of concentrating this solution and diluting it with butyl acetate was repeated twice to finally obtain a polymer solution containing poly(meth)acrylate (PB-5).

(Preparation of composition 3 for forming a photo-alignment film)
An amount equivalent to 30 parts by mass of the solution containing the photo-alignment agent 3 converted to the photo-alignment agent 3 and a solution containing poly (meth) acrylate (PB-5) converted to poly (meth) acrylate (PB-5) 70 parts by mass, 10 parts by mass of the following (B-1) as a metal chelate compound, and 40 parts by mass of the following (K-1) as a curing accelerator. As n-butyl acetate, methyl ethyl ketone and propylene glycol monomethyl ether acetate (mass ratio of each solvent 65: 25: 10) are added to obtain a solution with a solid content concentration of 2.5% by mass, and a composition for forming a photo-alignment film Item 3.

[Metal chelate compound]
(B-1): Tris(acetylacetonate) aluminum (aluminum chelate A (W), manufactured by Kawaken Fine Chemicals)

[Curing accelerator]
(K-1): tri(p-tolyl)silanol

(Formation of photo-alignment film P-3)
A glass substrate was prepared as a support.
The photo-alignment film-forming composition 3 was applied onto the support by a spin coater. After that, the substrate coated with the photo-alignment film-forming composition 3 was dried on a hot plate at 125° C. for 2 minutes to remove the solvent, thereby forming a photo-alignment precursor film 3 having a thickness of 0.3 μm.

The photo-alignment precursor film 3 was exposed using the exposure apparatus shown in FIG. 10 to form a photo-alignment film P-3 having an alignment pattern.
In the exposure apparatus, a laser that emits laser light with a wavelength (325 nm) was used. The amount of exposure by interference light was set to 300 mJ/cm ² . The crossing angle (crossing angle α) of the two lights is such that one period Λ (the length of the 180° rotation of the optical axis) of the alignment pattern formed by the interference of the two laser beams is 1.90 μm. was adjusted.

An optical element was produced according to the same procedure as in Example 1 except that the photo-alignment film P-3 was used, and the same measurements were performed.

<Example 4>
An optical element was produced according to the same procedure as in Example 1 except that the photo-alignment precursor film 1 of Example 1 was used and various manufacturing conditions as shown in Table 1 were changed, and the same measurements were performed.

<Example 5>
An optical element was produced according to the same procedure as in Example 2, except that the photo-alignment precursor film 2 of Example 2 was used and various manufacturing conditions as shown in Table 1 were changed, and the same measurements were performed.

<Example 6>
An optical element was produced according to the same procedure as in Example 3 except that the photo-alignment precursor film 3 of Example 3 was used and various manufacturing conditions as shown in Table 1 were changed, and the same measurements were performed.

<Example 7>
The same procedure as in Example 1 except that the photo-alignment film-forming composition 1 of Example 1 was changed to the following photo-alignment film-forming composition 1-2, and various production conditions as shown in Table 1 were changed. An optical element was produced according to the method, and the same measurement was performed.

Photo-alignment film-forming composition 1-2
―――――――――――――――――――――――――――――――――
Photo-alignment agent 1 5.00 parts by mass Cyclohexanone 95.00 parts by mass ――――――――――――――――――――――――――――――――――

<Example 8>
The same procedure as in Example 1 except that the photo-alignment film-forming composition 1 of Example 1 was changed to the following photo-alignment film-forming composition 1-3, and various production conditions as shown in Table 1 were changed. An optical element was produced according to the method, and the same measurement was performed.

Photo-alignment film-forming composition 1-3
―――――――――――――――――――――――――――――――――
Photo-alignment agent 1 20.00 parts by mass Cyclohexanone 80.00 parts by mass ――――――――――――――――――――――――――――――――――

<Comparative Example 1>
(Formation of photo-alignment film P-4)
A glass substrate was prepared as a support.
The photo-alignment film-forming composition 4 was applied onto the support by a spin coater. Thereafter, the substrate coated with the photo-alignment film-forming composition 4 was dried on a hot plate at 60° C. for 1 minute to remove the solvent and form a photo-alignment precursor film 4 having a thickness of 0.02 μm.

Photo-alignment film-forming composition 4
―――――――――――――――――――――――――――――――――
Photo-alignment agent 4 1.00 parts by mass Water 16.00 parts by mass Butoxyethanol 42.00 parts by mass Propylene glycol monomethyl ether 42.00 parts by mass―――――――――――――――――――― ――――――――――――――
In addition, as the photo-alignment agent 4, the following was used.

The photo-alignment precursor film 4 was exposed using the exposure apparatus shown in FIG. 10 to form a photo-alignment film P-4 having an alignment pattern.
In the exposure apparatus, a laser that emits laser light with a wavelength (325 nm) was used. The amount of exposure by interference light was set to 300 mJ/cm ² . The crossing angle (crossing angle α) of the two lights is such that one period Λ (the length of the 180° rotation of the optical axis) of the alignment pattern formed by the interference of the two laser beams is 1.90 μm. was adjusted.

An optical element was produced according to the same procedure as in Example 1, except that the photo-alignment film P-4 was used, and the same measurements were performed.

<Comparative Example 2>
An optical element was produced according to the same procedure as in Comparative Example 1 except that the photo-alignment precursor film 4 of Comparative Example 1 was used and various manufacturing conditions as shown in Table 1 were changed, and the same measurements were performed.

In addition, in Example 9, liquid crystal layers were overcoated to form 10 layers of liquid crystal layers.

<Measurement of diffraction efficiency>
The diffraction efficiency of the produced optical element was measured by the following method.
As shown in FIG. 13, the manufactured optical element D was placed on the Dove prism 100. As shown in FIG. The Dove prism 100 used has a refractive index of 1.517 and a slope angle of 45°.
A laser L having a measurement wavelength shown in Table 1 was passed through the Dove prism 100 through a linear polarizer 102 and a λ/4 plate 104 to be right-handed circularly polarized light, and the angle was set so that the diffracted light was emitted vertically from the oblique surface. was made incident on the surface of the optical element D.
The intensity of the emitted light Lr was measured using a measuring device 106 (manufactured by Newport, power meter 1918-C), and the ratio (Lr/Li×100[%]) to the incident light intensity Li was defined as the diffraction efficiency.
Table 1 shows the results.

<Arithmetic mean height Sa>
The photo-alignment films formed in the same manner as in Examples 1 to 8 and Comparative Examples 1 and 2 were measured using a non-contact surface/layer cross-sectional shape measurement system VertScan (registered trademark) 2.0 (Ryoka System). The surface shape measurement was performed in the mode, and the arithmetic mean height Sa was calculated.

<Transmittance>
The photo-alignment films formed in the same manner as in Examples 1 to 8 and Comparative Examples 1 and 2 were measured at 380 to 780 nm using a spectrophotometer UV3150 (Shimadzu Corporation) using the same support (glass substrate) as a reference. The transmittance in the wavelength range of 380 to 780 nm and 380 to 480 nm were averaged to calculate the transmittance.

As shown in Table 1 above, it was confirmed that the optical element of the present invention provided the desired effects.
Among them, it was confirmed from the comparison of Examples 1 to 3 that the diffraction efficiency was further improved when the photo-alignment agent 1 exhibiting liquid crystallinity was used.
Moreover, it was confirmed from the comparison of Examples 4, 7 and 8 that the diffraction efficiency was further improved when the arithmetic mean height Sa was 4.0 nm or less.

The optical element of the present invention can be suitably used for various optical devices such as AR glasses.

Reference Signs List 10, 30 optical element 12 support 14, 14R, 14G, 14B alignment film 16 cholesteric liquid crystal layer 20 liquid crystal compound 20A optical axis 32 pattern liquid crystal layer 34 optically anisotropic layer 60, 80 exposure device 62, 82 laser 64, 84 light source 68, 86, 94 polarizing beam splitter 70A, 70B, 90A, 90B mirror 72A, 72B, 96 λ/4 plate 92 lens 100 Dove prism 102 linear polarizer 104 λ/4 plate 106 measuring device 140 photo-alignment precursor film _BR Right-hand circularly polarized light of blue G _R Right-handed circularly polarized light of green R _R Right-handed circularly polarized light of red M Laser light MA, MB Ray MP P-polarized light MS S-polarized light P _O Linearly polarized light P _R Right-handed circularly polarized light P _L Left-handed circularly polarized light Q, Q1, Q2 Absolute phase E, E1, E2 Equal phase surface L1, L4 Incident light L2, L5 Transmitted light

Claims (9)

having an optically anisotropic layer formed using a composition containing a liquid crystal compound and a photo-alignment film,
The optically anisotropic layer has a liquid crystal alignment pattern in which the orientation of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one in-plane direction,
The photo-alignment film has an average transmittance of 90% or more for light with a wavelength of 380 to 780 nm and an average transmittance for light with a wavelength of 380 to 480 nm ,
The photo-alignment film contains a polymer having a cinnamate group,
An optical element, wherein the polymer has a repeating unit represented by formula (A1) and a repeating unit represented by formula (B1) .

In the formula, R ¹ is a hydrogen atom or a methyl group, R ² is an alkyl group or a phenyl group substituted with a group selected from an alkyl group, an alkoxy group, a cyano group and a halogen atom, and L ¹ and L ² is each independently any of the groups represented by formulas (1) to (5), and p and q are each independently any integer of 1-12.

X ¹ to X ³⁸ are each independently a hydrogen atom, an alkyl group, an alkoxy group, a halogen atom or a cyano group. * represents a binding position. In the liquid crystal alignment pattern of the optically anisotropic layer, the direction of the optic axis derived from the liquid crystal compound rotates 180° in the one direction in which the direction of the optic axis derived from the liquid crystal compound changes while rotating continuously. When the length is the length of one cycle,
2. The optical element according to claim 1, wherein the length of one cycle of the liquid crystal alignment pattern of the optically anisotropic layer is 2.00 [mu]m or less. 3. The optical element according to claim 2, wherein the length of one period of the liquid crystal alignment pattern of the optically anisotropic layer is 0.80 [mu]m or less. The optical element according to any one of claims 1 to 3, wherein the photo-alignment film has an arithmetic mean height Sa of 4.0 nm or less. 5. The optical element according to claim 1, wherein the optically anisotropic layer is a layer having a fixed cholesteric liquid crystal phase. 5. The optical element according to any one of claims 1 to 4, wherein the optical anisotropic layer has an optical axis derived from the liquid crystal compound aligned in the thickness direction. 7. The optical element according to any one of claims 1 to 6 , wherein the polymer has a repeating unit represented by formula (A2) and a repeating unit represented by formula (B2).

R ¹ is a hydrogen atom or a methyl group, R ² is an alkyl group or a phenyl group substituted with a group selected from an alkyl group, an alkoxy group, a cyano group and a halogen atom, and X ^1A to X ^4A are Each independently represents a hydrogen atom, an alkyl group, an alkoxy group, a halogen atom or a cyano group, L ³ is any of the groups represented by formulas (6) to (7), and p and q are Each is independently an integer from 1 to 12.

X ^1B to X ^4B and X ^31B to X ^38B are each independently a hydrogen atom, an alkyl group, an alkoxy group, a halogen atom or a cyano group. * represents a binding position. 8. The optical element according to claim ⁷ , wherein L3 in the repeating unit represented by formula (B2) is a group represented by formula ( 7 ). 8. The optical element according to claim ⁷ , wherein L3 in the repeating unit represented by formula (B2) is a group represented by formula ( 6 ).

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