WO2022264908A1 - 透過型液晶回折素子 - Google Patents
透過型液晶回折素子 Download PDFInfo
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- WO2022264908A1 WO2022264908A1 PCT/JP2022/023231 JP2022023231W WO2022264908A1 WO 2022264908 A1 WO2022264908 A1 WO 2022264908A1 JP 2022023231 W JP2022023231 W JP 2022023231W WO 2022264908 A1 WO2022264908 A1 WO 2022264908A1
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- Prior art keywords
- liquid crystal
- optically anisotropic
- anisotropic layer
- alignment pattern
- crystal alignment
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Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/30—Polarising elements
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/18—Diffraction gratings
- G02B5/1866—Transmission gratings characterised by their structure, e.g. step profile, contours of substrate or grooves, pitch variations, materials
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B7/00—Layered products characterised by the relation between layers; Layered products characterised by the relative orientation of features between layers, or by the relative values of a measurable parameter between layers, i.e. products comprising layers having different physical, chemical or physicochemical properties; Layered products characterised by the interconnection of layers
- B32B7/02—Physical, chemical or physicochemical properties
- B32B7/023—Optical properties
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/18—Diffraction gratings
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/30—Polarising elements
- G02B5/3016—Polarising elements involving passive liquid crystal elements
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
- G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
- G02F1/1333—Constructional arrangements; Manufacturing methods
- G02F1/1337—Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers
Definitions
- the present invention relates to a transmissive liquid crystal diffraction element that diffracts incident light.
- Diffraction elements are used in many optical devices or systems as an optical element that bends light to control the traveling direction of the light.
- a liquid crystal diffraction element using a liquid crystal compound has been proposed.
- US Pat. a first polarization grating layer containing molecular structures that are twisted according to a first twist property such that the magnetic orientation is rotated at the first twist angle;
- a second polarization grating layer wherein the relative orientation of each of the molecules of the second polarization grating layer over a second thickness defined between opposite surfaces of the second polarization grating layer is a second twist angle a second polarization grating layer comprising a molecular structure twisted according to a second torsion that is opposite to the first torsion so that it rotates at It is
- a polarizing diffraction element using a liquid crystal compound bends in different directions depending on the polarized light. Specifically, the right-handed circularly polarized light and the left-handed circularly polarized light incident on the polarization diffraction element are bent in opposite directions and separated. Therefore, the light could not be diffracted in a predetermined direction regardless of the polarization, and the efficiency of diffracted light in a desired direction was 50% at maximum for non-polarized light.
- An object of the present invention is to provide a transmissive liquid crystal diffraction element capable of diffracting different polarized light in the same direction and diffracting non-polarized light with high efficiency.
- the present invention has the following configurations.
- a liquid crystal diffraction element having a layer In the first optically anisotropic layer to the fourth optically anisotropic layer, the optical axis derived from the liquid crystal compound is twisted along the thickness direction, the direction of rotation of the optical axis in the liquid crystal alignment pattern of the first optically anisotropic layer is opposite to the direction of rotation of the optical axis in the liquid crystal alignment pattern of the second optically anisotropic layer; the direction of rotation of the optical axis in the liquid crystal alignment pattern of the third optically anisotropic layer is opposite to the direction of rotation of the optical axis in the liquid crystal alignment pattern of the fourth optically anisotropic layer;
- the twist direction of the optic axis derived from the liquid crystal compound in the thickness direction of the first optically anisotropic layer is opposite to the twist direction of the optic axis derived from the liquid crystal compound in the thickness direction of the second optically anisotropic layer,
- the transmission type liquid crystal diffraction element according to any one of [1] to [3], wherein one period of the liquid crystal alignment pattern gradually changes along one direction.
- [5] The reciprocal of one cycle of the liquid crystal alignment pattern of the first optically anisotropic layer and one cycle of the liquid crystal alignment pattern of the third optically anisotropic layer from the center to the outer side of the radial liquid crystal alignment pattern.
- liquid crystal compound in one optically anisotropic layer is a rod-like liquid crystal compound and the liquid crystal compound in the other optically anisotropic layer is a discotic liquid crystal compound.
- the present invention it is possible to provide a transmissive liquid crystal diffraction element that can diffract different polarized light in the same direction and has high diffraction efficiency even for non-polarized light.
- FIG. 1 is a diagram conceptually showing an example of a transmissive liquid crystal diffraction element of the present invention
- FIG. 2 is a diagram conceptually showing an optically anisotropic layer included in the transmissive liquid crystal diffraction element shown in FIG. 1.
- FIG. 3 is a plan view of the optically anisotropic layer shown in FIG. 2.
- FIG. 3 is a conceptual diagram of an example of an exposure apparatus for exposing an alignment film for forming the optically anisotropic layer shown in FIG. 2.
- FIG. It is a conceptual diagram for explaining the action of the optically anisotropic layer. It is a conceptual diagram for explaining the action of the optically anisotropic layer.
- FIG. 1 is a diagram conceptually showing an example of a transmissive liquid crystal diffraction element of the present invention
- FIG. 2 is a diagram conceptually showing an optically anisotropic layer included in the transmissive liquid crystal diffraction element shown in FIG. 1.
- FIG. 3 is a plan view of
- FIG. 2 is a conceptual diagram for explaining the operation of the transmissive liquid crystal diffraction element shown in FIG. 1;
- FIG. 4 is a diagram conceptually showing another example of the transmissive liquid crystal diffraction element of the present invention;
- FIG. 4 is a diagram conceptually showing another example of the transmissive liquid crystal diffraction element of the present invention;
- FIG. 4 is a plan view conceptually showing an optically anisotropic layer included in another example of the transmission type liquid crystal diffraction element of the present invention.
- 11 is a conceptual diagram of an example of an exposure apparatus for exposing an alignment film for forming the optically anisotropic layer shown in FIG. 10.
- FIG. 4 is a front view conceptually showing first and second optically anisotropic layers in another example of the transmission type liquid crystal diffraction element of the present invention.
- FIG. 4 is a front view conceptually showing third and fourth optically anisotropic layers in another example of the transmission type liquid crystal diffraction element of the present invention.
- 4 is a graph conceptually showing the relationship between one period of the first optically anisotropic layer and one period of the third optically anisotropic layer in another example of the transmission type liquid crystal diffraction element of the present invention.
- FIG. 4 is a conceptual diagram for explaining the action of another example of the transmissive liquid crystal diffraction element of the present invention;
- FIG. 4 is a conceptual diagram for explaining the action of another example of the transmissive liquid crystal diffraction element of the present invention;
- a numerical range represented by “to” means a range including the numerical values before and after “to” as lower and upper limits.
- (meth)acrylate means “either or both of acrylate and methacrylate”.
- the terms “same”, “equal”, etc. shall include the margin of error generally accepted in the technical field.
- the liquid crystal diffraction element of the present invention is It has a first optically anisotropic layer to a fourth optically anisotropic layer having 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 of the planes.
- a liquid crystal diffraction element In the first optically anisotropic layer to the fourth optically anisotropic layer, the optical axis derived from the liquid crystal compound is twisted along the thickness direction, the direction of rotation of the optical axis in the liquid crystal alignment pattern of the first optically anisotropic layer is opposite to the direction of rotation of the optical axis in the liquid crystal alignment pattern of the second optically anisotropic layer; the direction of rotation of the optical axis in the liquid crystal alignment pattern of the third optically anisotropic layer is opposite to the direction of rotation of the optical axis in the liquid crystal alignment pattern of the fourth optically anisotropic layer;
- the twist direction of the optic axis derived from the liquid crystal compound in the thickness direction of the first optically anisotropic layer is opposite to the twist direction of the optic axis derived from the liquid crystal compound in the thickness direction of the second optically anisotropic layer,
- FIG. 1 conceptually shows an example of the transmissive liquid crystal diffraction element of the present invention.
- the transmissive liquid crystal diffraction element 10 shown in FIG. 1 includes a first optically anisotropic layer 36a, a second optically anisotropic layer 36b, a third optically anisotropic layer 36c, and a third optically anisotropic layer 36c, which are arranged in this order in the thickness direction. It has 4 optically anisotropic layers 36d.
- FIG. 1 in order to simplify the drawing and clearly show the configuration of the transmissive liquid crystal diffraction element 10, in the first optically anisotropic layer 36a to the fourth optically anisotropic layer 36d, part of the liquid crystal Only compounds 40 (liquid crystal compound molecules) are shown conceptually. However, as conceptually shown in FIG.
- the first optically anisotropic layer 36a to the fourth optically anisotropic layer 36d have a structure in which liquid crystal compounds 40 are stacked in the thickness direction. It has a structure in which the optic axes of the stacked liquid crystal compounds 40 are twisted.
- Each of the first optically anisotropic layer 36a to the fourth optically anisotropic layer 36d is a liquid crystal in which the direction of the optical axis derived from the liquid crystal compound 40 changes while continuously rotating along at least one in-plane direction. It has an orientation pattern.
- Each of the first optically anisotropic layer 36a to the fourth optically anisotropic layer 36d can diffract transmitted light by having the liquid crystal alignment pattern.
- the angle of diffraction by each optically anisotropic layer at that time is the length of the 180° in-plane rotation of the optical axis derived from the liquid crystal compound 40 in the liquid crystal alignment pattern for one cycle (hereinafter referred to as one cycle of the liquid crystal alignment pattern). ), it depends on the length of this one cycle. Therefore, each optically anisotropic layer can adjust the diffraction angle by adjusting one period of the liquid crystal alignment pattern.
- the direction in which light is diffracted by the optically anisotropic layer having the liquid crystal alignment pattern differs depending on the polarized light. Specifically, right-handed circularly polarized light and left-handed circularly polarized light incident on the optically anisotropic layer are diffracted in opposite directions and separated. The direction of diffraction by the optically anisotropic layer depends on the direction of rotation of the optical axis in the liquid crystal alignment pattern.
- the optical axis derived from the liquid crystal compound is twisted along the thickness direction.
- an optically anisotropic layer having a liquid crystal alignment pattern diffracts in different directions depending on polarized light.
- the optic axis derived from the liquid crystal compound is twisted along the thickness direction, the equiphase plane becomes oblique to the main surface of the optically anisotropic layer. It is easily diffracted and the other polarized light is less diffracted. This point will be detailed later.
- the equiphase plane is a periodic plane in which liquid crystal compounds are aligned in the same direction.
- the direction of rotation of the optical axis in the liquid crystal alignment pattern of the first optically anisotropic layer 36a is opposite to the direction of rotation of the optical axis in the liquid crystal alignment pattern of the second optically anisotropic layer 36b.
- One cycle of the liquid crystal alignment pattern of the first optically anisotropic layer 36a is the same as one cycle of the liquid crystal alignment pattern of the second optically anisotropic layer 36b.
- the twist direction of the optic axis derived from the liquid crystal compound in the thickness direction of the first optically anisotropic layer 36a and the twist direction of the optic axis derived from the liquid crystal compound in the thickness direction of the second optically anisotropic layer 36b are different. On the contrary.
- the direction of rotation of the optical axis in the liquid crystal alignment pattern of the third optically anisotropic layer 36c is opposite to the direction of rotation of the optical axis in the liquid crystal alignment pattern of the fourth optically anisotropic layer 36d.
- One cycle of the liquid crystal alignment pattern of the third optically anisotropic layer 36c is the same as one cycle of the liquid crystal alignment pattern of the fourth optically anisotropic layer 36d.
- the twist direction of the optic axis derived from the liquid crystal compound in the thickness direction of the third optically anisotropic layer 36c and the twist direction of the optic axis derived from the liquid crystal compound in the thickness direction of the fourth optically anisotropic layer 36d are different. On the contrary.
- one period in the liquid crystal alignment pattern of the first optically anisotropic layer 36a (and the second optically anisotropic layer 36b) and one period of the third optically anisotropic layer 36c (and the fourth optically anisotropic layer 36d) It is different from one period in the liquid crystal alignment pattern.
- the rotation direction of the optical axis in the liquid crystal alignment pattern is clockwise (clockwise) from left to right when viewed from above in FIG. is rotating to
- the direction of rotation of the optical axis in the liquid crystal alignment pattern is rotated counterclockwise.
- the twist direction of the optic axis derived from the liquid crystal compound in the thickness direction is twisted rightward (clockwise) from top to bottom in FIG.
- the twist direction of the optic axis derived from the liquid crystal compound in the thickness direction is twisted counterclockwise.
- the third optically anisotropic layer 36c rotates the optical axis in the liquid crystal alignment pattern clockwise (clockwise) from left to right when viewed from above in FIG. rotation).
- the direction of rotation of the optical axis in the liquid crystal alignment pattern is rotated counterclockwise.
- the twist direction of the optical axis derived from the liquid crystal compound in the thickness direction is twisted clockwise (clockwise) from top to bottom in FIG.
- the twist direction of the optical axis derived from the liquid crystal compound in the thickness direction is twisted counterclockwise.
- one cycle of the liquid crystal alignment pattern of the first optically anisotropic layer 36a is the same as one cycle of the liquid crystal alignment pattern of the second optically anisotropic layer 36b, and the third optical anisotropic layer 36b has the same cycle.
- One period of the liquid crystal orientation pattern of the anisotropic layer 36c is the same as one period of the liquid crystal orientation pattern of the fourth optically anisotropic layer 36d, and one period of the liquid crystal orientation pattern of the first optically anisotropic layer 36a is the same. is different from one cycle of the liquid crystal alignment pattern of the third optically anisotropic layer 36c.
- the transmissive liquid crystal diffraction element 10 of the present invention having the above configuration diffracts incident light while transmitting it. At that time, right-handed circularly polarized light and left-handed circularly polarized light can be diffracted in the same direction. That is, the transmission type liquid crystal diffraction element 10 of the present invention can diffract different polarized light in the same direction, and can realize a transmission type liquid crystal diffraction element having high diffraction efficiency. Such action will be described in detail later.
- the rotation direction of the optic axis in the liquid crystal alignment pattern of each optically anisotropic layer and the twisting direction of the optic axis in the thickness direction are not limited to the example shown in FIG. 36a and the second optically anisotropic layer 36b, the rotation direction of the optic axis in the liquid crystal alignment pattern is opposite, the twist direction of the optic axis in the thickness direction is opposite, and the third optically anisotropic layer 36c and the fourth optically anisotropic layer 36d may be other combinations as long as the rotation direction of the optical axis in the liquid crystal alignment pattern is opposite and the twist direction of the optical axis in the thickness direction is opposite.
- the first optically anisotropic layer 36a and the third optically anisotropic layer 36c are arranged in the direction of rotation of the optical axis in the liquid crystal alignment pattern and the twisting of the optical axis in the thickness direction.
- the direction is the same, and the second optically anisotropic layer 36b and the fourth optically anisotropic layer 36d have the same rotation direction of the optic axis in the liquid crystal alignment pattern and the same twist direction of the optic axis in the thickness direction.
- the first optically anisotropic layer 36a and the fourth optically anisotropic layer 36d have the same rotation direction of the optic axis in the liquid crystal alignment pattern and the same twist direction of the optic axis in the thickness direction
- the second optical The anisotropic layer 36b and the third optically anisotropic layer 36c may have the same structure in the rotation direction of the optic axis in the liquid crystal alignment pattern and the twist direction of the optic axis in the thickness direction.
- one of the first optically anisotropic layer 36a and the second optically anisotropic layer 36b and one of the third optically anisotropic layer 36c and the fourth optically anisotropic layer 36d are liquid crystal aligned.
- the rotation direction of the optical axis in the pattern and the twist direction of the optical axis in the thickness direction are the same, and the other of the first optically anisotropic layer 36a and the second optically anisotropic layer 36b and the third optically anisotropic layer
- the other of the layer 36c and the fourth optically anisotropic layer 36d preferably has the same rotation direction of the optic axis in the liquid crystal alignment pattern and the same twist direction of the optic axis in the thickness direction.
- the average tilt direction of the equiphase plane (tilt to the right or tilt to the left) is the same for each optically anisotropic layer.
- the average inclination angle of the equiphase plane is preferably 5 degrees to 35 degrees when the normal direction of the substrate surface is 0 degrees.
- the average tilt angle is an angle obtained by averaging the tilt angles in the thickness direction when the optically anisotropic layer has a tilt angle distribution in the thickness direction.
- each optically anisotropic layer is configured to be spaced apart from each other, but the configuration is not limited to this, and the optically anisotropic layers are configured to be in contact with each other.
- the first optically anisotropic layer 36a and the second optically anisotropic layer 36b are arranged in contact with each other, and the second optically anisotropic layer 36b and the third optically anisotropic layer 36c are arranged separately.
- the third optically anisotropic layer 36c and the fourth optically anisotropic layer 36d may be arranged in contact with each other.
- the first optically anisotropic layer 36a to the fourth optically anisotropic layer 36d will be described with reference to FIGS. 2 and 3.
- FIG. The first optically anisotropic layer 36a to the fourth optically anisotropic layer 36d differ from each other except for the rotation direction of the optic axis in the liquid crystal alignment pattern, one cycle of the liquid crystal alignment pattern, and the twist direction of the optic axis in the thickness direction.
- the first optically anisotropic layer 36a to the fourth optically anisotropic layer 36d will be collectively described as the optically anisotropic layer 36 when there is no need to distinguish between them.
- the liquid crystal phase in which the liquid crystal compound is oriented is fixed, and the direction of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane.
- the optically anisotropic layer 36 is laminated on the alignment film 32 laminated on the support 30 .
- the first optically anisotropic layer 36a to the fourth optically anisotropic layer 36d are used as a transmissive liquid crystal diffraction element, as in the example shown in FIG. It may be used in a state of being laminated on the support 30 and the alignment film 32 .
- the optically anisotropic layer 36 may be used, for example, in a state in which only the alignment film 32 and the optically anisotropic layer 36 are laminated with the support 30 removed.
- the optically anisotropic layer 36 may be used in the state of only the optically anisotropic layer 36, for example, with the support 30 and the alignment film 32 removed.
- the support 30 supports the alignment film 32 and the optically anisotropic layer 36 .
- Various sheet-like materials can be used as the support 30 as long as they can support the alignment film 32 and the optically anisotropic layer 36 .
- the support 30 preferably has a transmittance of 50% or more, more preferably 70% or more, and even more preferably 85% or more with respect to the diffracted light.
- the thickness of the support 30 is not limited, and the thickness capable of holding the alignment film 32 and the optically anisotropic layer 36 can be appropriately adjusted depending on the use of the transmissive liquid crystal diffraction element, the material for forming the support 30, and the like. , should be set.
- the thickness of the support 30 is preferably 1 to 1000 ⁇ m, more preferably 3 to 250 ⁇ m, even more preferably 5 to 150 ⁇ m.
- the support 30 may be a single layer or multiple layers.
- the single layer support 30 include supports 30 made of glass, triacetyl cellulose (TAC), polyethylene terephthalate (PET), polycarbonate, polyvinyl chloride, acrylic, polyolefin, and the like.
- the multi-layer support 30 include any one of the single-layer supports described above as a substrate, and another layer provided on the surface of this substrate.
- the alignment film 32 is an alignment film for aligning the liquid crystal compound 40 in a predetermined liquid crystal alignment pattern when forming the optically anisotropic layer 36 .
- the direction of the optical axis 40A (see FIG. 3) derived from the liquid crystal compound 40 changes while continuously rotating along one in-plane direction. has a liquid crystal alignment pattern.
- the alignment film 32 is formed such that the optically anisotropic layer 36 can form this liquid crystal alignment pattern.
- “rotation of the direction of the optical axis 40A” is also simply referred to as "rotation of the optical axis 40A”.
- rubbed films made of organic compounds such as polymers, oblique deposition films of inorganic compounds, films with microgrooves, and Langmuir films of organic compounds such as ⁇ -tricosanoic acid, dioctadecylmethylammonium chloride and methyl stearate.
- LB Liquinuir-Blodgett
- the alignment film 32 by rubbing treatment can be formed by rubbing the surface of the polymer layer with paper or cloth several times in one direction.
- Materials used for the alignment film 32 include polyimide, polyvinyl alcohol, a polymer having a polymerizable group described in JP-A-9-152509, JP-A-2005-97377, JP-A-2005-99228, and , a material used for forming the alignment film 32 and the like described in Japanese Patent Application Laid-Open No. 2005-128503 is preferable.
- a so-called photo-alignment film obtained by irradiating a photo-alignment material with polarized or non-polarized light to form the alignment film 32 is preferably used. That is, a photo-alignment film formed by coating a photo-alignment material on the support 30 is preferably used as the alignment film 32 . Irradiation with polarized light can be performed in a direction perpendicular to or oblique to the photo-alignment film, and irradiation with non-polarized light can be performed in a direction oblique to the photo-alignment film.
- photo-alignment materials used in the alignment film include, for example, JP-A-2006-285197, JP-A-2007-76839, JP-A-2007-138138, and JP-A-2007-94071.
- Preferable examples include photodimerizable compounds described in JP-A-177561 and JP-A-2014-12823, particularly cinnamate compounds, chalcone compounds and coumarin compounds.
- azo compounds, photocrosslinkable polyimides, photocrosslinkable polyamides, photocrosslinkable polyesters, cinnamate compounds, and chalcone compounds are preferably used.
- the thickness of the alignment film 32 is not limited, and the thickness may be appropriately set according to the material forming the alignment film 32 so that the required alignment function can be obtained.
- the thickness of the alignment film 32 is preferably 0.01-5 ⁇ m, more preferably 0.05-2 ⁇ m.
- the method for forming the alignment film 32 is not limited, and various known methods can be used depending on the material for forming the alignment film 32 .
- a method of coating the alignment film 32 on the surface of the support 30 and drying it, exposing the alignment film 32 with a laser beam to form an alignment pattern is exemplified.
- FIG. 4 conceptually shows an example of an exposure apparatus that exposes the alignment film 32 to form an alignment pattern.
- the exposure device 60 shown in FIG. 4 includes a light source 64 having a laser 62, a ⁇ /2 plate 65 for changing the polarization direction of the laser beam M emitted by the laser 62, and a beam MA and a beam MA of the laser beam M emitted by the laser 62. It comprises a beam splitter 68 that splits the MB into two, mirrors 70A and 70B placed on the optical paths of the two split beams MA and MB, respectively, and ⁇ /4 plates 72A and 72B.
- the light source 64 emits linearly polarized light P 0 .
- the ⁇ /4 plate 72A converts the linearly polarized light P 0 (light ray MA) into right circularly polarized light PR
- the ⁇ /4 plate 72B converts the linearly polarized light P 0 (light ray MB) into left circularly polarized light P L .
- a support 30 having an alignment film 32 before the alignment pattern is formed is placed in an exposure area, and two light beams MA and MB cross each other on the alignment film 32 to interfere with each other. exposed to light. Due to the interference at this time, the polarization state of the light with which the alignment film 32 is irradiated periodically changes in the form of interference fringes. As a result, an alignment film having an alignment pattern in which the alignment state changes periodically (hereinafter also referred to as a patterned alignment film) is obtained.
- the period of the alignment pattern can be adjusted by changing the crossing angle ⁇ of the two light beams MA and MB.
- the length of one cycle in which the optical axis 40A rotates 180° can be adjusted.
- an optically anisotropic layer on the alignment film 32 having such an alignment pattern in which the alignment state is periodically changed, as described later, the optical axis 40A derived from the liquid crystal compound 40 is aligned in one direction.
- An optically anisotropic layer 36 can be formed having a liquid crystal alignment pattern that continuously rotates along. Further, by rotating the optical axes of the ⁇ /4 plates 72A and 72B by 90°, the direction of rotation of the optical axis 40A can be reversed.
- the orientation of the optical axis of the liquid crystal compound in the optically anisotropic layer formed on the patterned alignment film changes while continuously rotating along at least one in-plane direction. It has an alignment pattern for aligning the liquid crystal compound so that a liquid crystal alignment pattern is obtained. Assuming that the orientation axis of the patterned orientation film is along the direction in which the liquid crystal compound is oriented, the direction of the orientation axis of the patterned orientation film changes while continuously rotating along at least one in-plane direction. It can be said that it has an orientation pattern.
- the orientation axis of the patterned orientation film can be detected by measuring the absorption anisotropy.
- the patterned alignment film is irradiated with linearly polarized light while being rotated and the amount of light transmitted through the patterned alignment film is measured, the direction in which the light amount becomes maximum or minimum gradually changes along one direction in the plane. Observed to change.
- the alignment film 32 is provided as a preferred embodiment and is not an essential component.
- the optically anisotropic layer is derived from the liquid crystal compound 40 by forming an alignment pattern on the support 30 by a method of rubbing the support 30, a method of processing the support 30 with a laser beam, or the like.
- a configuration having a liquid crystal orientation pattern in which the direction of the optical axis 40A changes while continuously rotating along at least one in-plane direction is also possible. That is, in the present invention, the support 30 may act as an alignment film.
- optically anisotropic layer 36 is formed on the surface of the alignment film 32 .
- the optically anisotropic layer 36 is an optically anisotropic layer formed by fixing the liquid crystal phase in which the liquid crystal compound is oriented, and the direction of the optical axis derived from the liquid crystal compound is in at least one in-plane direction. It is an optically anisotropic layer having a liquid crystal orientation pattern that changes while continuously rotating along.
- the optically anisotropic layer 36 has a twisted structure in which the liquid crystal compound 40 is stacked while rotating in the thickness direction.
- the total twist angle from the liquid crystal compound 40 present on one main surface side of the optically anisotropic layer 36 to the liquid crystal compound 40 present on the other main surface side is less than 360°.
- the optically anisotropic layer 36 has a liquid crystal alignment pattern in which the direction of the optical axis 40A changes while continuously rotating along the alignment axis D in the plane, and the liquid crystal compound 40
- the equiphase plane connecting the liquid crystal compounds 40 facing the same direction in the thickness direction is aligned with the main surface of the optically anisotropic layer 36. It has a slanted configuration. Since the equiphase plane is tilted in this way, the diffraction efficiency may be reduced depending on the angle of the incident light and the direction of rotation of the circularly polarized light. .
- each of the first optically anisotropic layer 36a to the fourth optically anisotropic layer 36d utilizes the case where the 0th-order light is transmitted, whereby the transmission type liquid crystal diffraction
- the element is configured to diffract right-handed circularly polarized light and left-handed circularly polarized light in the same direction. This point will be described in detail later.
- 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. It is possible to fix and form a liquid crystal phase aligned in a twisted structure stacked in a direction rotating in a layer.
- the structure in which the liquid crystal phase is fixed may be a structure in which the alignment of the liquid crystal compound that is the liquid crystal phase is maintained.
- the polymerizable liquid crystal compound is aligned along the liquid crystal alignment pattern.
- the structure is polymerized and cured by UV irradiation, heating, or the like to form a layer having no fluidity, and at the same time, the structure is changed to a state in which the orientation is not changed by an external field or external force.
- the liquid crystal phase is fixed, it is sufficient if the optical properties of the liquid crystal phase are maintained, and the liquid crystal compound 40 does not have to exhibit liquid crystallinity in the optically anisotropic layer.
- the polymerizable liquid crystal compound may be polymerized by a curing reaction and lose liquid crystallinity.
- Examples of materials used for forming the optically anisotropic layer having a fixed liquid crystal phase include liquid crystal compositions containing liquid crystal compounds.
- the liquid crystal compound is preferably a polymerizable liquid crystal compound.
- the liquid crystal composition may contain a chiral agent.
- the liquid crystal composition used for forming the optically anisotropic layer may further contain a surfactant, a polymerization initiator, and the like.
- the polymerizable liquid crystal compound may be a rod-like liquid crystal compound or a discotic liquid crystal compound.
- rod-like polymerizable liquid crystal compounds forming the optically anisotropic layer 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.
- phenyldioxane, tolan, and alkenylcyclohexylbenzonitriles are preferably used. 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.
- 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.
- a cyclic organopolysiloxane compound having a cholesteric phase as disclosed in JP-A-57-165480 can be used as polymerizable liquid crystal compounds other than the above.
- 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 JP-A-9-133810, and liquid-crystalline polymers as disclosed in JP-A-11-293252 and the like can be used.
- discotic Liquid Crystal Compound 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 amount of the polymerizable liquid crystal compound added in the liquid crystal composition is preferably 75 to 99.9% by mass, and preferably 80 to 99%, based on the solid content mass (mass excluding the solvent) of the liquid crystal composition. % by mass is more preferred, and 85 to 90% by mass is even more preferred.
- a chiral agent has a function of inducing a twisted structure of a liquid crystal phase.
- the chiral agent may be selected depending on the purpose, since the helical twisting direction and helical twisting power (HTP) induced by the compound differ.
- 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.
- 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.
- the chiral agent has a photoisomerizable group
- a desired twisted orientation corresponding to the emission wavelength can be formed by irradiation with a photomask such as actinic rays after application and orientation.
- 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-2002-80478, JP-A-2002-80851, 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 content molar amount of the liquid crystal compound.
- the liquid crystal composition used for forming the optically anisotropic 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 liquid crystal compound.
- Examples of surfactants include silicone-based surfactants and fluorine-based surfactants, with fluorine-based surfactants being preferred examples.
- 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.
- surfactant may be used individually by 1 type, and may use 2 or more types together.
- 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.
- the liquid crystal composition contains a polymerizable compound, it preferably contains a polymerization initiator.
- the polymerization initiator used is preferably a photopolymerization initiator capable of initiating the polymerization reaction by ultraviolet irradiation.
- photoinitiators include ⁇ -carbonyl compounds (described in US Pat. Nos. 2,367,661 and 2,367,670), acyloin ethers (described in US Pat. No. 2,448,828), ⁇ -hydrocarbons substituted aromatic acyloin compounds (described in US Pat. No.
- 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, based on the content of the liquid crystal compound.
- the liquid crystal composition may optionally contain a cross-linking agent in order to improve film strength and durability after curing.
- a cross-linking agent those that are cured by ultraviolet rays, heat, moisture, etc. can be preferably used.
- the cross-linking agent is not particularly limited and can be appropriately selected depending on the intended purpose.
- 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
- hexa isocyanate compounds such as methylene diisocyanate and biuret-type isocyanate
- alkoxysilane compounds such as vinyltrimethoxysilane and N-(2-aminoethyl)3-aminopropyltrimethoxysilane, etc.
- 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 liquid crystal phase is further improved.
- 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 at
- the liquid crystal composition is preferably used as a liquid when forming the optically anisotropic layer.
- the liquid crystal composition may contain a solvent.
- the solvent is not limited and can be appropriately selected according to the purpose, but organic solvents are preferred.
- the organic solvent is not limited and can be appropriately selected depending on the purpose. Examples include ketones, alkyl halides, amides, sulfoxides, heterocyclic compounds, hydrocarbons, esters, and ethers. etc. 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.
- a liquid crystal composition is applied to the surface on which the optically anisotropic layer is to be formed, and the liquid crystal compound is aligned in a predetermined liquid crystal alignment pattern in a liquid crystal phase.
- the liquid crystal compound is cured to form an optically anisotropic layer. That is, when an optically anisotropic layer is formed on the alignment film 32, the liquid crystal composition is applied to the alignment film 32, the liquid crystal compound is aligned in a predetermined liquid crystal alignment pattern, and then the liquid crystal compound is cured. It is preferable to form an optically anisotropic layer having a fixed liquid crystal phase.
- 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 dried and/or heated as necessary, and then cured to form an optically anisotropic layer.
- the liquid crystal compound in the liquid crystal composition may be aligned in a predetermined liquid crystal alignment pattern and twisted structure.
- 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.
- the irradiation energy is preferably 20 mJ/cm 2 to 50 J/cm 2 , more preferably 50 to 1500 mJ/cm 2 .
- 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 optically anisotropic layer is not limited, and may vary depending on the application of the optically anisotropic layer, the light reflectance required for the optically anisotropic layer, the material for forming the optically anisotropic layer, and the like. In this way, the thickness with which the required light reflectance can be obtained can be set as appropriate.
- the direction of the optical axis 40A derived from the liquid crystal compound 40 continuously rotates in one direction in the plane of the optically anisotropic layer. It has a liquid crystal alignment pattern that changes while Note that the optical axis 40A derived from the liquid crystal compound 40 is an axis with the highest refractive index in the liquid crystal compound 40, a so-called slow axis.
- the optic axis 40A is along the long axis direction of the rod shape.
- the optic axis 40A derived from the liquid crystal compound 40 is also referred to as "the optic axis 40A of the liquid crystal compound 40" or "the optic axis 40A".
- FIG. 3 conceptually shows a plan view of the optically anisotropic layer 36 .
- FIG. 3 shows only the liquid crystal compound 40 on the surface of the alignment film 32 in order to clearly show the structure of the optically anisotropic layer 36 .
- the liquid crystal compound 40 that constitutes the optically anisotropic layer 36 is distributed on the surface of the optically anisotropic layer according to the alignment pattern formed on the underlying alignment film 32 .
- it has a liquid crystal alignment pattern in which the orientation of the optical axis 40A changes while continuously rotating along a predetermined direction indicated by an arrow D (hereinafter referred to as an alignment axis D).
- the optic axis 40A of the liquid crystal compound 40 has a liquid crystal alignment pattern that changes while continuously rotating clockwise along the alignment axis D direction.
- the liquid crystal compounds 40 forming the optically anisotropic layer 36 are two-dimensionally aligned along the alignment axis D and a direction orthogonal to this one direction (the alignment axis D direction).
- the direction orthogonal to the array axis D 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 40A of the liquid crystal compound 40 changes while continuously rotating within the plane of the optically anisotropic layer. Therefore, in FIGS. 1 and 2 and FIGS. 5 and 6, which will be described later, the Y direction is a direction perpendicular to the plane of the paper.
- That the direction of the optic axis 40A of the liquid crystal compound 40 changes while continuously rotating in the direction of the alignment axis D specifically means that the liquid crystal compound 40 is aligned along the direction of the alignment axis D.
- the angle formed by the optic axis 40A of the liquid crystal compound 40 and the direction of the alignment axis D varies depending on the position in the direction of the alignment axis D, and the angle formed by the optic axis 40A and the direction of the alignment axis D along the direction of the alignment axis D. changes sequentially from ⁇ to ⁇ +180° or ⁇ 180°.
- the difference between the angles of the optical axes 40A of the liquid crystal compounds 40 adjacent to each other in the direction of the alignment axis D is preferably 45° or less, more preferably 15° or less, and further preferably a smaller angle. preferable.
- the liquid crystal compound 40 forming the optically anisotropic layer 36 has a Y direction orthogonal to the alignment axis D direction, that is, a Y direction orthogonal to one direction in which the optical axis 40A continuously rotates. equal orientation.
- the angle between the optical axis 40A of the liquid crystal compound 40 and the direction of the alignment axis D is equal in the Y direction.
- the liquid crystal compounds aligned in the Y direction have an equal angle between the optic axis 40A and the alignment axis D direction (one direction in which the optic axis of the liquid crystal compound 40 rotates).
- a region R is defined as a region where the liquid crystal compound 40 having the same angle formed by the optical axis 40A and the direction of the alignment axis D is arranged in the Y direction.
- the value of the in-plane retardation (Re) in each region R is preferably half the wavelength, ie, ⁇ /2.
- 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 ⁇ n accompanying the refractive index anisotropy of the region R is the difference between the refractive index of the liquid crystal compound 40 in the direction of the optical axis 40A and the refractive index of the liquid crystal compound 40 in the direction perpendicular to the optical axis 40A within the plane of the region R. Equal to the difference in refractive index. That is, the refractive index difference ⁇ n is equal to the refractive index
- the optic axis 40A of the liquid crystal compound 40 is aligned in the direction of the alignment axis D in which the optic axis 40A continuously rotates and changes in the plane.
- the length (distance) of 180° rotation is defined as the length ⁇ of one cycle in the liquid crystal alignment pattern. That is, the distance between the centers in the direction of the alignment axis D of two liquid crystal compounds 40 having the same angle with respect to the direction of the alignment axis D is defined as the length of one period ⁇ .
- the distance between the centers of the two liquid crystal compounds 40 in the direction of the alignment axis D and the direction of the optical axis 40A is equal to the length of one period ⁇ and In the following description, the length ⁇ of one period is also referred to as "one period ⁇ ".
- the liquid crystal alignment pattern of the optically anisotropic layer 36 repeats this one period ⁇ in one direction in which the direction of the alignment axis D, that is, the direction of the optical axis 40A rotates continuously and changes.
- FIGS. 5 and 6 When circularly polarized light is incident on such an optically anisotropic layer 36, the light is refracted and the direction of the circularly polarized light is changed. This action is conceptually illustrated in FIGS. 5 and 6.
- FIG. in the optically anisotropic layer 36 the product of the refractive index difference of the liquid crystal compound and the thickness of the optically anisotropic layer is assumed to be ⁇ /2.
- the explanation using FIGS. 5 and 6 is for explaining the action of the liquid crystal alignment pattern of the optically anisotropic layer 36, and the explanation is given assuming that the optical axis does not have a twisted structure in the thickness direction. conduct.
- the optically anisotropic layer 36 has a left circular shape.
- the incident light L 1 passes through the optically anisotropic layer 36 and is given a phase difference of 180°, and the transmitted light L 2 is converted into right-handed circularly polarized light.
- the liquid crystal alignment pattern formed on the optically anisotropic layer 36 is a periodic pattern in the direction of the alignment axis D, the transmitted light L2 travels in a direction different from the traveling direction of the incident light L1. .
- the left-handed circularly polarized incident light L1 is converted into right - handed circularly polarized transmitted light L2, which is tilted by a certain angle in the direction of the array axis D with respect to the incident direction.
- the transmitted light L2 is diffracted so as to travel downward and to the right.
- the optically anisotropic layer 36 when the product of the refractive index difference of the liquid crystal compound of the optically anisotropic layer 36 and the thickness of the optically anisotropic layer is ⁇ /2, the optically anisotropic layer 36 When circularly polarized incident light L 4 is incident, the incident light L 4 passes through the optically anisotropic layer 36, is given a phase difference of 180°, and is converted into left circularly polarized transmitted light L 5 . be. Further, since the liquid crystal alignment pattern formed on the optically anisotropic layer 36 is a periodic pattern in the direction of the alignment axis D, the transmitted light L5 travels in a direction different from the traveling direction of the incident light L4 . .
- the transmitted light L5 travels in a direction different from that of the transmitted light L2, that is, in a direction opposite to the arrow direction of the array axis D with respect to the incident direction.
- 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 array axis D with respect to the incident direction.
- the transmitted light L5 is diffracted to travel in the lower left direction.
- the optically anisotropic layer 36 can adjust the angles of refraction of the transmitted lights L 2 and L 5 according to the length of one cycle ⁇ of the formed liquid crystal alignment pattern. Specifically, in the optically anisotropic layer 36, the shorter the period ⁇ of the liquid crystal alignment pattern, the stronger the interference between the lights passing through the liquid crystal compounds 40 adjacent to each other. can be refracted.
- the direction of refraction of transmitted light can be reversed. That is, in the examples shown in FIGS. 5 and 6, the rotation direction of the optical axis 40A toward the direction of the array axis D is clockwise. , can be done in the opposite direction. Specifically, in FIGS.
- the first optically anisotropic layer 36a to the fourth optically anisotropic layer 36d each having a liquid crystal orientation pattern are arranged in this order.
- the optical layer 36a and the second optically anisotropic layer 36b have opposite directions of rotation of the optical axis in the liquid crystal alignment pattern, opposite directions of twist of the optical axis in the thickness direction, and the third optically anisotropic layer 36a.
- the layer 36c and the fourth optically anisotropic layer 36d have opposite directions of rotation of the optical axis in the liquid crystal alignment pattern, and opposite directions of twist of the optical axis in the thickness direction.
- first optically anisotropic layer 36a and the second optically anisotropic layer 36b have the same liquid crystal alignment pattern cycle
- the third optically anisotropic layer 36c and the fourth optically anisotropic layer 36d have the same period. has the same liquid crystal alignment pattern for one cycle
- the first optically anisotropic layer 36a and the third optically anisotropic layer 36c have different liquid crystal alignment patterns for one cycle.
- one cycle of the liquid crystal alignment pattern is the same as that of the first optically anisotropic layer 36a.
- one cycle of the liquid crystal alignment pattern of the second optically anisotropic layer 36b has a difference of about 0.8 to 1.2, the light is emitted from the second optically anisotropic layer 36b. The influence on the diffraction angle of light is small.
- one cycle of the liquid crystal alignment pattern is the same as one cycle of the liquid crystal alignment pattern of the third optically anisotropic layer 36c.
- one cycle of the liquid crystal alignment pattern of the fourth optically anisotropic layer 36d can be emitted from the fourth optically anisotropic layer 36d if the difference is about 0.8 to 1.2.
- the influence on the diffraction angle of light is small.
- the third optically anisotropic layer 36c and the fourth optically anisotropic layer 36c are different.
- the one-period difference in the liquid crystal orientation pattern of the anisotropic layer 36d is offset by the one-period difference in the liquid crystal orientation patterns of the first optically anisotropic layer 36a and the second optically anisotropic layer 36b, resulting in a fourth optical difference.
- the diffraction angles of the right-handed circularly polarized light and the left-handed circularly polarized light emitted from the anisotropic layer 36d are appropriate angles.
- the direction of the alignment axis D of the liquid crystal alignment pattern in the first optically anisotropic layer 36a matches the direction of the alignment axis D of the liquid crystal alignment pattern in the second optically anisotropic layer 36b.
- the direction of the alignment axis D of the liquid crystal alignment pattern in the third optically anisotropic layer 36c matches the direction of the alignment axis D of the liquid crystal alignment pattern in the fourth optically anisotropic layer 36d.
- the direction of the alignment axis D of the liquid crystal alignment pattern in the first optically anisotropic layer 36a matches the direction of the alignment axis D of the liquid crystal alignment pattern in the third optically anisotropic layer 36c.
- the direction of the alignment axis D of each optically anisotropic layer is the left direction in the drawing.
- the optically anisotropic layer diffracts right-handed circularly polarized light I R and left-handed circularly polarized light I L along the alignment axis D in opposite directions.
- the first optically anisotropic layer 36a directs the incident right-handed circularly polarized light I R to the left in FIG. Diffract in the direction
- the diffracted light is converted into left-handed circularly polarized light I L1 .
- the first optically anisotropic layer 36a scatters the incident left-handed circularly polarized light I L along the alignment axis D with respect to the traveling direction of the incident left-handed circularly polarized light I L . to diffract in the right direction in FIG.
- the optically anisotropic layer has a twisted structure and the equiphase plane is tilted with respect to the main surface of the optically anisotropic layer.
- the left-handed circularly polarized light I L is hardly diffracted, and passes through the first optically anisotropic layer 36a downward in FIG. 7 as left-handed circularly polarized light I L (zero-order light).
- the direction of rotation of the optical axis in the liquid crystal alignment pattern is opposite to that of the first optically anisotropic layer 36a. Therefore, the second optically anisotropic layer 36b diffracts incident circularly polarized light in a direction opposite to that of the first optically anisotropic layer 36a. That is, left circularly polarized light is diffracted leftward along the array axis D.
- the left-handed circularly polarized light IL1 is incident on the second optically anisotropic layer 36b so as to travel from the upper right direction to the lower left direction.
- the second optically anisotropic layer 36b aligns the incident left-handed circularly polarized light I L1 along the alignment axis D with respect to the traveling direction of the incident left-handed circularly polarized light I L1 . It tries to diffract in the left direction in FIG. However, since it is incident on the optically anisotropic layer obliquely in the lower left direction, it cannot be bent further to the left.
- the light zero-order light
- the second optically anisotropic layer 36b directs the left-handed circularly polarized light I L incident perpendicularly to the main surface to the left-hand side in FIG. Diffract in the direction of travel. Also, as described above, the diffracted light is converted to right circularly polarized light I R1 .
- the diffraction angle of the left-handed circularly polarized light I L1 in the first optically anisotropic layer 36a is is substantially the same as the diffraction angle of the right-handed circularly polarized light I R1 in the second optically anisotropic layer 36b. Therefore, the right-handed circularly polarized light I R1 and the left-handed circularly polarized light I L1 transmitted through the first optically anisotropic layer 36a and the second optically anisotropic layer 36b travel in the same direction (substantially parallel).
- the right circularly polarized light I R1 and the left circularly polarized light I L1 are diffracted by the first optically anisotropic layer 36a and the second optically anisotropic layer 36b, so that the right circularly polarized light I R1 and the left circularly polarized light I L1 is incident on the third optically anisotropic layer 36c from a direction oblique to the main surface of the third optically anisotropic layer 36c.
- the third optically anisotropic layer 36c diffracts the incident left-handed circularly polarized light I L1 rightward in FIG. 7 along the array axis D with respect to the traveling direction of the incident left-handed circularly polarized light I L1 . Also, as described above, the diffracted light is converted to right-handed circularly polarized light I R2 .
- the left-handed circularly polarized light I L1 incident on the third optically anisotropic layer 36c is diffracted leftward in FIG. 7 by the first optically anisotropic layer 36a. , diffracts this left-handed circularly polarized light I L1 in the opposite direction (rightward direction) to the first optically anisotropic layer 36a.
- the diffraction angle of the right-handed circularly polarized light I R2 after passing through the first optically anisotropic layer 36a to the third optically anisotropic layer 36c with respect to the right-handed circularly polarized light I R incident on the transmissive liquid crystal diffraction element 10 is is the difference between the diffraction angle by the first optically anisotropic layer 36a and the diffraction angle by the third optically anisotropic layer 36c.
- one cycle of the liquid crystal alignment pattern of the third optically anisotropic layer 36c is different from one cycle of the liquid crystal alignment pattern of the first optically anisotropic layer 36a. Therefore, the diffraction angle by the first optically anisotropic layer 36a is different from the diffraction angle by the third optically anisotropic layer 36c.
- one cycle of the liquid crystal alignment pattern of the third optically anisotropic layer 36c is larger than one cycle of the liquid crystal alignment pattern of the first optically anisotropic layer 36a.
- the diffraction angle by the layer 36c is smaller than the diffraction angle by the first optically anisotropic layer 36a.
- the right-handed circularly polarized light I R2 after passing through the first optically anisotropic layer 36a to the third optically anisotropic layer 36c travels in the lower left direction in a state nearly perpendicular to the main surface in FIG. Become.
- the third optically anisotropic layer 36c converts the incident right-handed circularly polarized light I R1 along the alignment axis D to the traveling direction of the incident right-handed circularly polarized light I R1 . 7, it tries to diffract to the left.
- the optically anisotropic layer has a twisted structure and the equiphase plane is tilted with respect to the main surface of the optically anisotropic layer.
- the right-handed circularly polarized light I R1 is hardly diffracted, and passes through the third optically anisotropic layer 36c in the lower left direction in FIG. 7 as it is (0-order light).
- the rotation direction of the optical axis in the liquid crystal orientation pattern is opposite to that of the third optically anisotropic layer 36c. Therefore, the fourth optically anisotropic layer 36d diffracts the incident circularly polarized light in a direction opposite to that of the third optically anisotropic layer 36c. That is, right-handed circularly polarized light is diffracted rightward along the array axis D.
- the right-handed circularly polarized light I R2 travels from the upper right direction to the lower left direction with respect to the fourth optically anisotropic layer 36d at an angle nearly perpendicular to the main surface of the fourth optically anisotropic layer 36d. to be incident.
- the fourth optically anisotropic layer 36d aligns the incident right-handed circularly polarized light I R2 along the alignment axis D with respect to the traveling direction of the incident right-handed circularly polarized light I R2 . It tries to diffract in the right direction in FIG.
- the equiphase plane is tilted with respect to the main plane of the optically anisotropic layer, the diffraction action in this direction does not work, and the incident right-handed circularly polarized light I R2 is hardly diffracted, and the right-handed circularly polarized light I R2 (zero-order light) is transmitted through the fourth optically anisotropic layer 36d from the upper right direction to the lower left direction in FIG. 7 at an angle nearly perpendicular to the main surface.
- the fourth optically anisotropic layer 36d directs the incident right-handed circularly polarized light I R1 with a large inclination from the upper right direction to the lower left direction, along the alignment axis D with respect to the traveling direction of the incident right-handed circularly polarized light I R1 . 7 along the right direction in FIG. Also, as described above, the diffracted light is converted into left-handed circularly polarized light I L2 .
- the right-handed circularly polarized light I R1 incident on the fourth optically anisotropic layer 36d is diffracted leftward in FIG. 7 by the second optically anisotropic layer 36b.
- the right-handed circularly polarized light I R1 is diffracted in the opposite direction (to the right) of the second optically anisotropic layer 36b.
- the diffraction angle of the left-handed circularly polarized light I L2 after passing through the first optically anisotropic layer 36a to the fourth optically anisotropic layer 36d with respect to the left-handed circularly polarized light I L incident on the transmissive liquid crystal diffraction element 10 is is the difference between the diffraction angle by the second optically anisotropic layer 36b and the diffraction angle by the fourth optically anisotropic layer 36d.
- One cycle of the liquid crystal alignment pattern of the fourth optically anisotropic layer 36d is different from one cycle of the liquid crystal alignment pattern of the second optically anisotropic layer 36b. Therefore, the diffraction angle by the second optically anisotropic layer 36b and the diffraction angle by the fourth optically anisotropic layer 36d are different.
- one cycle of the liquid crystal alignment pattern of the fourth optically anisotropic layer 36d is larger than one cycle of the liquid crystal alignment pattern of the second optically anisotropic layer 36b.
- the diffraction angle by the layer 36d is smaller than the diffraction angle by the second optically anisotropic layer 36b.
- the left-handed circularly polarized light I L2 after passing through the first optically anisotropic layer 36a to the fourth optically anisotropic layer 36d travels in the lower left direction in a state nearly perpendicular to the main surface in FIG. Become.
- the first optically anisotropic layer 36a and the second optically anisotropic layer 36b have the same one period of the liquid crystal alignment pattern, and the third optically anisotropic layer 36c and the fourth optically anisotropic layer 36d. 1 period of the liquid crystal alignment pattern is the same. Therefore, the right-handed circularly polarized light I R2 and the left-handed circularly polarized light I L2 that have passed through the first optically anisotropic layer 36a to the fourth optically anisotropic layer 36d are diffracted at approximately the same angle and diffracted in the same direction (substantially parallel). proceed.
- the transmissive liquid crystal diffraction element of the present invention can diffract different polarized light (right-handed circularly polarized light and left-handed circularly polarized light) in the same direction, and can diffract non-polarized light with high efficiency.
- the incident right-handed circularly polarized light I R and left-handed circularly polarized light IL are directed in the same direction. can be diffracted.
- an optically anisotropic layer having a structure in which the equiphase plane is tilted with respect to the main surface there are cases where diffraction does not occur depending on the angle of incident light and the direction of rotation of circularly polarized light, as described above. For this to occur, it is necessary to increase the diffraction angle in the optically anisotropic layer.
- the transmission type liquid crystal diffraction element of the present invention has four optically anisotropic layers, that is, the first optically anisotropic layer 36a to the fourth optically anisotropic layer 36d.
- the combination of the layer 36a and the second optically anisotropic layer 36b diffracts the incident right-handed circularly polarized light and left-handed circularly polarized light in the same direction at a large diffraction angle to form the third optically anisotropic layer 36b.
- the combination of the layer 36c and the fourth optically anisotropic layer 36d diffracts the right-handed circularly polarized light and the left-handed circularly polarized light diffracted by the combination 1 in a direction opposite to the direction of diffraction by the combination 1.
- the transmissive liquid crystal diffraction element can diffract right-handed circularly polarized light and left-handed circularly polarized light in the same direction at a diffraction angle with a small difference between the diffraction angles of combination 1 and combination 2. can.
- one period of the liquid crystal alignment patterns of the first optically anisotropic layer 36a and the second optically anisotropic layer 36b is ⁇ 1
- the liquid crystal of the third optically anisotropic layer 36c and the fourth optically anisotropic layer 36d is Assuming that one period of the alignment pattern is ⁇ 2
- the final diffraction angle of the transmissive liquid crystal diffraction element 10 is determined by the absolute value of ⁇ 1 ⁇ 2 /( ⁇ 1 - ⁇ 2 ).
- the diffraction angle of each of the optically anisotropic layers of the first optically anisotropic layer 36a to the fourth optically anisotropic layer 36d is preferably 50° to 130°, more preferably 60° to 120°. , 70° to 110° are more preferred.
- the transmissive liquid crystal diffraction element of the present invention is not limited to the configuration having only the first optically anisotropic layer 36a to the fourth optically anisotropic layer 36d.
- each optically anisotropic layer 36 of the transmissive liquid crystal diffraction element may be laminated with the support 30 and the alignment film 32, or may be laminated with the alignment film 32. good.
- the transmission type liquid crystal diffraction element of the present invention may have other layers.
- it may have a C plate between the optically anisotropic layers.
- a transmissive liquid crystal diffraction element 10b shown in FIG. 8 has a C plate 38 between a second optically anisotropic layer 36b and a third optically anisotropic layer 36c.
- the optically anisotropic layer 36 converts incident circularly polarized light into circularly polarized light with the opposite direction of rotation.
- the light is not completely converted into circularly polarized light in the opposite direction and becomes elliptically polarized light.
- a transmissive liquid crystal diffraction element if the light converted by one optically anisotropic layer becomes elliptically polarized light, the effect of the next optically anisotropic layer may not be obtained properly, resulting in a decrease in diffraction efficiency.
- the C plate 38 is provided between the optically anisotropic layers, it is possible to impart a phase difference to the elliptically polarized light emitted from a certain optically anisotropic layer and convert it into circularly polarized light. , the effect of the following optically anisotropic layer can be properly obtained, and the diffraction efficiency can be increased. Even when a C plate is provided between the optically anisotropic layers, the C plate does not affect diffraction. Obtainable.
- a C plate and an A plate can be used as the retardation layer as long as it can give a retardation to the elliptically polarized light emitted from the first optically anisotropic layer 36a.
- the retardation in the thickness direction of the retardation layer can convert elliptically polarized light emitted from the first optically anisotropic layer 36a into circularly polarized light depending on the incident angle of light, the structure of the first optically anisotropic layer 36a, and the like. can be set as appropriate.
- Rth is the retardation in the thickness direction
- Re is the retardation in the in-plane direction.
- Nz is preferably 0.1 to 1.1, more preferably 0.8 to 0.2, even more preferably 0.7 to 0.3.
- combination 1 of the first optically anisotropic layer 36a and the second optically anisotropic layer 36b, and combination 1 of the third optically anisotropic layer 36c and the fourth optically anisotropic layer 36d In at least one of the combinations 2, it is preferable that the liquid crystal compound in one optically anisotropic layer is a rod-like liquid crystal compound and the liquid crystal compound in the other optically anisotropic layer is a discotic liquid crystal compound.
- FIG. 9 shows a diagram conceptually showing another example of the transmissive liquid crystal diffraction element of the present invention.
- a transmission type liquid crystal diffraction element 10c shown in FIG. have in this order.
- 9 conceptually shows only the liquid crystal compound 40 on the surface of each optically anisotropic layer in order to simplify the drawing and clearly show the configuration of the transmissive liquid crystal diffraction element 10c.
- each optically anisotropic layer has a structure in which the liquid crystal compounds 40 are stacked in the thickness direction similarly to the example shown in FIG. structure.
- the liquid crystal compound of the first optically anisotropic layer 36e is the discotic liquid crystal compound 40b.
- the liquid crystal compound of the second optically anisotropic layer 36b is the rod-like liquid crystal compound 40.
- the liquid crystal compound of the third optically anisotropic layer 36f is the discotic liquid crystal compound 40b, and the fourth optically anisotropic layer 36f
- the liquid crystal compound of the liquid layer 36d is the rod-like liquid crystal compound 40.
- the second optically anisotropic layer 36b and the fourth optically anisotropic layer 36d respectively have the same structures as the second optically anisotropic layer 36b and the fourth optically anisotropic layer 36d shown in FIG. are omitted.
- the first optically anisotropic layer 36e has the same configuration as the first optically anisotropic layer 36a shown in FIG. 1 except that it is formed using the discotic liquid crystal compound 40b.
- the direction of the optical axis of the discotic liquid crystal compound 40b is along the direction perpendicular to the disc surface. Therefore, in the first optically anisotropic layer 36e, the discotic liquid crystal compound 40b is oriented such that the discotic surface is perpendicular to the interface of the first optically anisotropic layer 36e.
- the first optically anisotropic layer 36e 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 plane, and the rotation direction of the optic axis is , the direction of rotation of the optical axis in the liquid crystal alignment pattern of the second optically anisotropic layer 36b.
- the optic axis derived from the liquid crystal compound is twisted in the thickness direction, and the twisting direction is the twisting direction of the optic axis in the thickness direction of the second optically anisotropic layer 36b. is the opposite.
- One cycle of the liquid crystal alignment pattern of the first optically anisotropic layer 36e is the same as one cycle of the liquid crystal alignment pattern of the second optically anisotropic layer 36b.
- the third optically anisotropic layer 36f has the same configuration as the third optically anisotropic layer 36c shown in FIG. 1 except that it is formed using the discotic liquid crystal compound 40b.
- the direction of the optical axis of the discotic liquid crystal compound 40b is along the direction perpendicular to the disc surface. Therefore, in the third optically anisotropic layer 36f, the discotic liquid crystal compound 40b is oriented such that the discotic surface is perpendicular to the interface of the third optically anisotropic layer 36f.
- the third optically anisotropic layer 36f 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 plane, and the rotation direction of the optic axis is , the direction of rotation of the optical axis in the liquid crystal alignment pattern of the fourth optically anisotropic layer 36d.
- the optic axis derived from the liquid crystal compound is twisted in the thickness direction. is the opposite.
- One period of the liquid crystal orientation pattern of the third optically anisotropic layer 36f is the same as one period of the liquid crystal orientation pattern of the fourth optically anisotropic layer 36d, and the liquid crystal orientation of the first optically anisotropic layer 36e is the same. It is different from one period in the pattern.
- the liquid crystal compound in one optically anisotropic layer is a rod-like liquid crystal compound and the liquid crystal compound in the other optically anisotropic layer is a discotic liquid crystal compound.
- thickness direction retardation Rth can be brought close to zero. This reduces the change in the in-plane retardation Re when light is obliquely incident on the transmissive liquid crystal diffraction element. Therefore, the incident angle dependency of diffraction performance such as diffraction efficiency can be improved. Thereby, the diffraction efficiency of the transmissive liquid crystal diffraction element can be increased.
- the present invention is not limited to this, and various configurations can be used as long as the optical axis 40A of the liquid crystal compound 40 rotates continuously along one direction in the optically anisotropic layer. be.
- the optically anisotropic layer 36 may have a liquid crystal orientation pattern radially.
- the orientation of the optic axis of the liquid crystal compound 40 is in a number of directions outward from the center of the optically anisotropic layer 36, for example, the direction indicated by arrow A 1 and the direction indicated by arrow A 2 . , the direction indicated by arrow A 3 . . . , while continuously rotating. That is, arrows A 1 , A 2 and A 3 are array axes.
- the optic axis of the liquid crystal compound 40 changes from the center of the optically anisotropic layer 36 outward while rotating in the same direction.
- the embodiment shown in FIG. 10 is a counterclockwise orientation.
- the direction of rotation of the optical axis rotating along the arrows A 1 , A 2 and A 3 in FIG. 10 is counterclockwise from the center toward the outside.
- the lines connecting the liquid crystal compounds whose optical axes are directed in the same direction are circular, and the circular line segments form a concentric pattern.
- the optically anisotropic layer 36 having such a radial liquid crystal alignment pattern diffracts the incident light along each alignment axis (A 1 to A 3 etc.) so that the azimuth direction is directed toward the center, can collect transmitted light.
- the incident light is diffracted along each of the array axes (A 1 to A 3 ) so that the azimuth direction is directed outward, the transmitted light can be diffused. Whether the transmitted light is diffracted toward the center or toward the outside depends on the polarization state of incident light and the rotation direction of the optical axis in the liquid crystal orientation pattern.
- the liquid crystal alignment patterns of the first to fourth optically anisotropic layers are made into such a radial pattern, so that the right-handed circularly polarized light and the left-handed circularly polarized light are obtained. Since the light can be condensed or diverged in the same direction, a lens that can converge or diverge even non-polarized light with high efficiency can be obtained.
- the transmissive liquid crystal diffraction element of the present invention when the liquid crystal orientation patterns of the first optically anisotropic layer to the fourth optically anisotropic layer are the radial patterns described above, the first optically anisotropic layer and the In at least one of combination 1 with two optically anisotropic layers and combination 2 with a third optically anisotropic layer and a fourth optically anisotropic layer, one cycle of the liquid crystal alignment pattern is in one direction. is preferably changed gradually along
- one period of the liquid crystal alignment pattern of combination 1 when one period of the liquid crystal alignment pattern of combination 1 is smaller than one period of the liquid crystal alignment pattern of combination 2, that is, when the diffraction angle by combination 1 is larger than the diffraction angle by combination 2
- one cycle of the liquid crystal alignment pattern of combination 1 gradually decreases from the center of the radial pattern toward the outside.
- one period of the liquid crystal alignment pattern of combination 2 gradually increases from the center of the radial pattern toward the outside.
- one cycle of the liquid crystal alignment pattern of combination 1 gradually decreases outward from the center of the radial pattern
- one cycle of the liquid crystal alignment pattern of combination 2 gradually decreases outward from the center of the radial pattern. , can be large.
- the diffraction angle by combination 1 is larger and/or the diffraction angle by combination 2 is smaller outward from the center of the radial pattern, the diffraction angle by combination 1 and the diffraction by combination 2 are The absolute value of the difference from the angle increases outward from the center of the radial pattern. Therefore, the light incident near the outside of the transmissive liquid crystal diffraction element is diffracted more than the light incident near the center, so that it can function more preferably as a condensing lens or a diverging lens.
- one cycle of the liquid crystal alignment pattern of combination 1 When one cycle of the liquid crystal alignment pattern of combination 1 is longer than one cycle of the liquid crystal alignment pattern of combination 2, one cycle of the liquid crystal alignment pattern of combination 1 gradually increases from the center of the radial pattern toward the outside. and/or it is preferable that one period of the liquid crystal alignment pattern of combination 2 gradually decreases from the center of the radial pattern toward the outside.
- the relationship between one period ⁇ 1 of the liquid crystal alignment pattern of combination 1 (first optically anisotropic layer) and one period ⁇ 2 of the liquid crystal alignment pattern of combination 2 (third optically anisotropic layer) can be represented by the difference of their reciprocals, and the reciprocal of one cycle of the liquid crystal alignment pattern of combination 1 (first optically anisotropic layer) (1/ ⁇ 1 ) and combination 2 (third optically anisotropic layer ) and the reciprocal of one period of the liquid crystal orientation pattern (1/ ⁇ 2 ) is the reciprocal of the period ⁇ of the combined element of combination 1 and combination 2.
- the synthetic element can be used as a condensing or diverging element such as a lens.
- FIG. 14 shows a graph representing the relationship between ⁇ and the position (x) from the center of the optically anisotropic layer.
- FIG. 12 shows a conceptual diagram for explaining the liquid crystal alignment pattern of the first optically anisotropic layer 36a and the second optically anisotropic layer 36b (combination 1).
- FIG. 13 shows a conceptual diagram for explaining the liquid crystal alignment patterns of the third optically anisotropic layer 36c and the fourth optically anisotropic layer 36d (combination 2).
- the interval of one cycle of the liquid crystal alignment pattern of the optically anisotropic layer is indicated by a dashed line.
- one cycle of the liquid crystal alignment patterns of the first optically anisotropic layer 36a and the second optically anisotropic layer 36b (combination 1) is constant. Further, as shown in FIG. 13, one cycle of the liquid crystal alignment patterns of the third optically anisotropic layer 36c and the fourth optically anisotropic layer 36d (combination 2) gradually decreases from the center of the radial pattern toward the outside. It's becoming 12 and 13 are examples in which one cycle of the liquid crystal alignment pattern of combination 2 is smaller than one cycle of the liquid crystal alignment pattern of combination 1. FIG.
- the light diffracted by combination 1 enters combination 2, and is diffracted by combination 2 at a predetermined angle toward the center. At this time, since one period of the liquid crystal alignment pattern of combination 2 gradually decreases from the center toward the outside, the diffraction angle becomes larger toward the outside from the center side in the plane of the optically anisotropic layer. Thereby, as shown in FIG. 15, the diffracted light is collected.
- the combination 1 diffracts light outward and the combination 2 diffracts light toward the center.
- combination 1 may diffract light toward the center
- combination 2 may diffract light toward the outside.
- the combination 1 diffracts the light toward the center and the combination 2 diffracts the light toward the outside, and a condensing lens for condensing the light is used, the diffraction angle of the combination 1 is changed to that of the combination 2. It should be larger than the diffraction angle.
- the optically anisotropic layer 36 shown in FIG. 2 has a configuration in which the optical axis of the liquid crystal compound is parallel to the main surface of the optically anisotropic layer, but it is not limited to this.
- the optical axis of the liquid crystal compound may be inclined with respect to the main surface of the optically anisotropic layer.
- At least one of the optically anisotropic layers has a configuration in which a rod-like liquid crystal layer in which a rod-like liquid crystal compound is aligned in a liquid crystal alignment pattern and a discotic liquid crystal layer in which a discotic liquid crystal compound is aligned in a liquid crystal alignment pattern are alternately laminated. It may be a configuration having. It is more preferable that all optically anisotropic layers have a structure in which rod-like liquid crystal layers and discotic liquid crystal layers are alternately laminated.
- the thickness direction retardation Rth of the optically anisotropic layer can be brought close to zero by forming the optically anisotropic layer in such a manner that the rod-like liquid crystal layer and the discotic liquid crystal layer are alternately laminated. This reduces the change in the in-plane retardation Re when light is obliquely incident on the optically anisotropic layer. Therefore, the incident angle dependency of diffraction performance such as diffraction efficiency can be improved.
- Rth is preferably close to zero at any location in the thickness direction of the layer that causes diffraction. It is preferred that the Rth be canceled at each location of .
- the rod-shaped liquid crystal layers and the disk-shaped liquid crystal layers that are alternately laminated have a positive and negative Rth relationship between the adjacent layers, and that the absolute value of the Rth of each layer is about 10 to 200 nm.
- each rod-shaped liquid crystal layer and the discotic liquid crystal layer is preferably not too large relative to the wavelength of incident light, and is preferably from 0.1 ⁇ m. 5 ⁇ m is preferred, 0.1 ⁇ m to 2 ⁇ m is more preferred, and 0.1 ⁇ m to 0.5 ⁇ m is even more preferred.
- the optically anisotropic layer 36 has a twisted structure in which the optic axis derived from the liquid crystal compound in the thickness direction has a constant twist angle per unit length.
- the optically anisotropic layer 36 may have a twisted structure of the optic axis derived from the liquid crystal compound in the thickness direction, and the twist angle per unit length may gradually change.
- Alignment film forming coating solution ⁇ ⁇
- the following optical alignment material 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 ⁇ ⁇
- the alignment film P-2 thus obtained was irradiated with polarized ultraviolet rays (50 mJ/cm 2 , using an ultra-high pressure mercury lamp) to expose the alignment film P-2.
- the alignment film was exposed using the exposure apparatus shown in FIG. 4 to form an alignment film P-2 having an alignment pattern.
- 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 ⁇ ) of the two laser beams is adjusted so that one period ⁇ (length of rotation of the optical axis by 180°) of the alignment pattern formed by the interference of the two laser beams is 10 ⁇ m. did.
- Composition B-1 below was prepared as a liquid crystal composition for forming an optically anisotropic layer.
- Rod-shaped liquid crystal compound L-1 100.00 parts by mass ⁇
- Polymerization initiator manufactured by BASF, Irgacure (registered trademark) 907
- 3.00 parts by mass Photosensitizer manufactured by Nippon Kayaku, KAYACURE DETX-S
- 1.00 parts by mass Leveling agent T-1 0.08 parts by mass Methyl ethyl ketone 2000.00 parts by mass ⁇ ⁇
- Rod-shaped liquid crystal compound L-1 (including the following structure in the mass ratio shown on the right)
- the optically anisotropic layer was formed by coating the composition B-1 on the alignment film P-2 in multiple layers. First, the composition B-1 for the first layer was applied on the alignment film, heated, cooled, and then cured with ultraviolet light to prepare a liquid crystal fixing layer. Then, the coating was applied, followed by heating, cooling, and UV curing.
- the following composition B-1 was applied on the alignment film P-2, the coating film was heated on a hot plate to 80 ° C., and then at 80 ° C. under a nitrogen atmosphere with a high-pressure mercury lamp. was used to irradiate the coating film with ultraviolet rays having a wavelength of 365 nm at an irradiation amount of 300 mJ/cm 2 to fix the orientation of the liquid crystal compound.
- the second and subsequent layers were overcoated on this liquid crystal fixing layer, heated under the same conditions as above, cooled, and then UV-cured to produce a liquid crystal fixing layer. In this manner, multiple coatings were repeated until the total thickness reached a desired thickness to form an optically anisotropic layer.
- the refractive index difference ⁇ n of the cured layer of the composition B-1 was obtained by coating the composition B-1 on a separately prepared support with an alignment film for retardation measurement, and making the director of the liquid crystal compound parallel to the substrate.
- the retardation Re( ⁇ ) and film thickness of the liquid crystal fixed layer obtained by fixing the liquid crystal fixed layer by irradiating with ultraviolet rays after being oriented so as to be were measured and obtained.
- ⁇ n ⁇ can be calculated by dividing the retardation Re( ⁇ ) by the film thickness.
- Retardation Re( ⁇ ) was measured at a target wavelength using Axoscan manufactured by Axometrix, and film thickness was measured using SEM.
- ⁇ is the wavelength of incident light. In the following, the wavelength ⁇ of incident light is set to 600 nm.
- the twist angle in the thickness direction of the optically anisotropic layer was 0°.
- bright and dark lines were observed perpendicular to the lower interface of the optically anisotropic layer (interface with the glass substrate). These bright and dark lines are observed due to the structure in which the liquid crystal compounds oriented in the same direction are stacked in the thickness direction.
- This one optically anisotropic layer was used as a transmissive liquid crystal diffraction element of Comparative Example 1.
- Comparative Example 2 An optically anisotropic layer was prepared in the same manner as in Comparative Example 1, and the direction of rotation of the optic axis derived from the liquid crystal compound that changed while continuously rotating along one in-plane direction was opposite to that of the optically anisotropic layer.
- the optically anisotropic layer of Comparative Example 2 was obtained by rotating the layer by 180 degrees.
- the configurations of Comparative Examples 1 and 2 are shown in Table 1 below.
- the number of lines is the number of cycles per mm, which is obtained by dividing 1000 ( ⁇ m) by one cycle ( ⁇ m).
- the angle of inclination is the angle formed by the line of brightness and darkness observed in the SEM cross section and the perpendicular to the main surface.
- Example 1 (Formation of first optically anisotropic layer) An alignment film of Comparative Example 1 was formed in the same manner as in Comparative Example 1, except that one period ⁇ of the alignment pattern was set to 1 ⁇ m.
- a first optically anisotropic layer was formed in the same manner as in Comparative Example 1, except that in the formation of the optically anisotropic layer of Comparative Example 1, the following composition B-2 was used instead of the composition B-1. formed.
- composition B-2 was used as the liquid crystal composition forming the first optically anisotropic layer.
- Composition B-2 ⁇ ⁇ Rod-shaped liquid crystal compound L-1 100.00 parts by mass ⁇ Chiral agent Ch-A 0.24 parts by mass ⁇ Polymerization initiator (manufactured by BASF, Irgacure (registered trademark) 907) 3.00 parts by mass Photosensitizer (manufactured by Nippon Kayaku, KAYACURE DETX-S) 1.00 parts by mass Leveling agent T-1 0.08 parts by mass Methyl ethyl ketone 2000.00 parts by mass ⁇ ⁇
- the orientation film is the same as in the case of the first optically anisotropic layer. It was rotated 180 degrees so that it would rotate in the opposite direction.
- a second optically anisotropic layer was formed in the same manner as in Comparative Example 1 except that in the formation of the optically anisotropic layer of Comparative Example 1, the following composition B-3 was used instead of the composition B-1. did.
- composition B-3 was used as the liquid crystal composition forming the second optically anisotropic layer.
- a third optically anisotropic layer was formed in the same manner as the first optically anisotropic layer except that one period ⁇ of the orientation pattern of the orientation film was set to 1.111 ⁇ m in the formation of the first optically anisotropic layer. formed.
- a fourth optically anisotropic layer was formed in the same manner as the second optically anisotropic layer, except that one period ⁇ of the orientation pattern of the orientation film was 1.111 ⁇ m in the formation of the second optically anisotropic layer. formed.
- the twist angle in the thickness direction of the first optically anisotropic layer was 80° (right twist).
- oblique bright and dark lines were observed with respect to the lower interface (interface with the glass substrate) of the first optically anisotropic layer.
- the twist angle in the thickness direction of the second optically anisotropic layer was ⁇ 80° (left twist).
- oblique bright and dark lines were observed with respect to the lower interface of the second optically anisotropic layer. The oblique angle at this time was the same as that of the first optically anisotropic layer, and the inclination direction was the same.
- the twist angle in the thickness direction of the third optically anisotropic layer was 80° (right twist).
- oblique bright and dark lines were observed with respect to the lower interface (interface with the glass substrate) of the third optically anisotropic layer. The oblique angle at this time was different from that of the first optically anisotropic layer, but the inclination direction was the same.
- the twist angle in the thickness direction of the fourth optically anisotropic layer was ⁇ 80° (left twist).
- oblique bright and dark lines were observed with respect to the lower interface of the fourth optically anisotropic layer.
- the oblique angle at this time was the same as that of the third optically anisotropic layer, and the inclination direction was the same.
- the first optically anisotropic layer to the fourth optically anisotropic layer were laminated in this order to prepare a transmission type liquid crystal diffraction element of Example 1.
- the size of the diffraction element is 20 mm square.
- Table 2 below shows the configuration of the transmissive liquid crystal diffraction element of Example 1.
- Example 2 A transmissive liquid crystal diffraction element was produced in the same manner as in Example 1, except that one period of the third optically anisotropic layer and the fourth optically anisotropic layer was 0.909 ⁇ m. Table 3 below shows the configuration of the transmissive liquid crystal diffraction element of Example 2.
- ⁇ A The intensity (diffraction efficiency) is 90% or more
- ⁇ B The intensity (diffraction efficiency) is 80% or more
- ⁇ C The intensity (diffraction efficiency) is 70% or more
- ⁇ D The intensity (diffraction efficiency) is 60% or more
- ⁇ E Intensity (diffraction efficiency) of 50% or more
- F Intensity (diffraction efficiency) of less than 50%
- Example 11 The first optical anisotropy was formed in the same manner as in Example 1, except that an exposure apparatus as shown in FIG. An optical layer to a fourth optically anisotropic layer were formed to prepare a transmission type liquid crystal diffraction element. The size was 40 mm in diameter. This transmissive liquid crystal diffraction element acts as a condenser lens. Table 6 below shows the configuration of the transmissive liquid crystal diffraction element of Example 11.
- Example 12 Using an exposure apparatus as shown in FIG. 11 as an exposure apparatus for the alignment film, the exposure method described in WO2019/189818 was used to form a radial alignment pattern, and the in-plane rotation direction of each optically anisotropic layer was the same as in Example 11.
- the first optically anisotropic layer to the fourth optically anisotropic layer were formed in the same manner as in Example 2, except that the layers were formed in the reverse order of the above, and a transmissive liquid crystal diffraction element was produced.
- the size was 40 mm in diameter. This transmissive liquid crystal diffraction element acts as a condenser lens. Table 7 below shows the configuration of the transmissive liquid crystal diffraction element of Example 12.
- Unpolarized straight light (40 mm diameter) with a wavelength of 600 nm was applied to the prepared transmission type liquid crystal diffraction element from the normal direction of the main surface of the transmission type liquid crystal diffraction element (the main surface on the side of the first optically anisotropic layer in the example). was incident, and the diffraction intensity (diffraction efficiency) of condensed light (first-order diffracted light) by the lens was measured with a power meter.
- the criteria for intensity (diffraction efficiency) are as follows.
- ⁇ A The intensity (diffraction efficiency) is 90% or more
- ⁇ B The intensity (diffraction efficiency) is 80% or more
- ⁇ C The intensity (diffraction efficiency) is 70% or more
- ⁇ D The intensity (diffraction efficiency) is 60% or more
- ⁇ E Intensity (diffraction efficiency) of 50% or more
- F Intensity (diffraction efficiency) of less than 50%
- the comparative examples have a diffraction efficiency of less than half for non-polarized light due to the polarization dependence, while the examples of the present invention exhibit a large diffraction efficiency regardless of the non-polarized light. I know you can get it.
- the lens is visually observed, in the comparative example, an unnecessary image due to the divergent light of the -1st order light is observed, but in the example, it is hardly observed, indicating that the lens is good for non-polarized light. has been realized. From the above results, the effect of the present invention is clear.
- 10b transmission type liquid crystal diffraction element 30 support 32 alignment film 36 optically anisotropic layer 36a, 36e first optically anisotropic layer 36b second optically anisotropic layer 36c, 36f third optically anisotropic layer 36d 4 optically anisotropic layer 38 C plate 40 liquid crystal compound (rod-like liquid crystal compound) 40b discotic liquid crystal compound 40A optical axis 60, 80 exposure device 62, 82 laser 64, 84 light source 65 ⁇ /2 plate 68 beam splitter 70A, 70B, 90A, 90B mirror 72A, 72B, 96 ⁇ /4 plate 86, 94 polarization Beam splitter 92 Lens I R , I R1 , I R2 Right-handed circularly polarized light I L , I L1 , IL2 Left-handed circularly polarized light D, A 1 , A 2 , A 3 Arrangement axis R Region ⁇ 1 period MA, MB Light beam P O straight line Polarization P R right circular polarization P L left circular polar
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Abstract
Description
このような回折素子として、液晶化合物を用いた液晶回折素子が提案されている。
[1] 液晶化合物由来の光学軸の向きが面内の少なくとも一方に沿って連続的に回転しながら変化している液晶配向パターンを有する、第1光学異方性層~第4光学異方性層を有する液晶回折素子であって、
第1光学異方性層~第4光学異方性層において、液晶化合物由来の光学軸が厚み方向に沿って捩じれており、
第1光学異方性層の液晶配向パターンにおける光学軸の回転方向と、第2光学異方性層の液晶配向パターンにおける光学軸の回転方向とが逆であり、
第3光学異方性層の液晶配向パターンにおける光学軸の回転方向と、第4光学異方性層の液晶配向パターンにおける光学軸の回転方向とが逆であり、
第1光学異方性層の厚み方向での液晶化合物由来の光学軸の捩じれ方向と、第2光学異方性層の厚み方向での液晶化合物由来の光学軸の捩じれ方向とが逆であり、
第3光学異方性層の厚み方向での液晶化合物由来の光学軸の捩じれ方向と、第4光学異方性層の厚み方向での液晶化合物由来の光学軸の捩じれ方向とが逆であり、
液晶配向パターンにおける液晶化合物由来の光学軸の向きが面内で180°回転する長さを1周期とすると、第1光学異方性層の液晶配向パターンにおける1周期と、第2光学異方性層の液晶配向パターンにおける1周期とが同じであり、
第3光学異方性層の液晶配向パターンにおける1周期と、第4光学異方性層の液晶配向パターンにおける1周期とが同じであり、
第1光学異方性層の液晶配向パターンにおける1周期と、第3光学異方性層の液晶配向パターンにおける1周期とが異なる、透過型液晶回折素子。
[2] 第1光学異方性層~第4光学異方性層の厚み方向での液晶化合物由来の光学軸の捩じれ角が360°未満である、[1]に記載の透過型液晶回折素子。
[3] 第1光学異方性層~第4光学異方性層は、液晶配向パターンを放射状に有する、[1]または[2]に記載の透過型液晶回折素子。
[4] 第1光学異方性層と第2光学異方性層との組み合わせ、および、第3光学異方性層と第4光学異方性層との組み合わせのうち、少なくとも一方の組み合わせにおいて、液晶配向パターンの1周期が一方向に沿って漸次変化している、[1]~[3]のいずれかに記載の透過型液晶回折素子。
[5] 放射状の液晶配向パターンの中央部から外側部に向かって、第1光学異方性層の液晶配向パターンの1周期の逆数と、第3光学異方性層の液晶配向パターンの1周期の逆数との差分が漸次大きくなる、[3]または[4]に記載の透過型液晶回折素子。
[6] 第1光学異方性層~第4光学異方性層のいずれかの間にCプレートをさらに有する、[1]~[5]のいずれかに記載の透過型液晶回折素子。
[7] 第1光学異方性層と第2光学異方性層との組み合わせ、および、第3光学異方性層と第4光学異方性層との組み合わせのうち、少なくとも一方の組み合わせにおいて、一方の光学異方性層の液晶化合物が棒状液晶化合物で、他方の光学異方性層の液晶化合物が円盤状液晶化合物である、[1]~[6]のいずれかに記載の透過型液晶回折素子。
本明細書において、「(メタ)アクリレート」は、「アクリレートおよびメタクリレートのいずれか一方または双方」の意味で使用される。
本明細書において、「同じ」、「等しい」等は、技術分野で一般的に許容される誤差範囲を含むものとする。
本発明の液晶回折素子は、
液晶化合物由来の光学軸の向きが面内の少なくとも一方に沿って連続的に回転しながら変化している液晶配向パターンを有する、第1光学異方性層~第4光学異方性層を有する液晶回折素子であって、
第1光学異方性層~第4光学異方性層において、液晶化合物由来の光学軸が厚み方向に沿って捩じれており、
第1光学異方性層の液晶配向パターンにおける光学軸の回転方向と、第2光学異方性層の液晶配向パターンにおける光学軸の回転方向とが逆であり、
第3光学異方性層の液晶配向パターンにおける光学軸の回転方向と、第4光学異方性層の液晶配向パターンにおける光学軸の回転方向とが逆であり、
第1光学異方性層の厚み方向での液晶化合物由来の光学軸の捩じれ方向と、第2光学異方性層の厚み方向での液晶化合物由来の光学軸の捩じれ方向とが逆であり、
第3光学異方性層の厚み方向での液晶化合物由来の光学軸の捩じれ方向と、第4光学異方性層の厚み方向での液晶化合物由来の光学軸の捩じれ方向とが逆であり、
液晶配向パターンにおける液晶化合物由来の光学軸の向きが面内で180°回転する長さを1周期とすると、第1光学異方性層の液晶配向パターンにおける1周期と、第2光学異方性層の液晶配向パターンにおける1周期とが同じであり、
第3光学異方性層の液晶配向パターンにおける1周期と、第4光学異方性層の液晶配向パターンにおける1周期とが同じであり、
第1光学異方性層の液晶配向パターンにおける1周期と、第3光学異方性層の液晶配向パターンにおける1周期とが異なる、透過型液晶回折素子である。
また、等位相面の平均的な傾きの向き(右に倒れるように傾く、あるいは左に傾くように傾く)は、各光学異方性層同士で同じであることが好ましい。光学異方性層の等位相面の傾きが逆のときには、回折する光の強度(回折効率)が小さくなる。また、等位相面の平均的な傾きの角度は、基板面の法線方向を0度としたときに、5度~35度が好ましい。ここで、平均的な傾きの角度とは、光学異方性層が厚さ方向で傾き角の分布を持った時には傾き角を厚さ方向で平均化した角度のことである。
第1光学異方性層36a~第4光学異方性層36dについて図2および図3を用いて説明する。なお、第1光学異方性層36a~第4光学異方性層36dは、液晶配向パターンにおける光学軸の回転方向、液晶配向パターンの1周期、厚み方向での光学軸の捩じれ方向が異なる以外は同様の構成を有するので、第1光学異方性層36a~第4光学異方性層36dを区別する必要がない場合にはまとめて光学異方性層36として説明を行う。
なお、第1光学異方性層36a~第4光学異方性層36dが透過型液晶回折素子として、用いられる際には、図2に示す例のように、光学異方性層36は、支持体30および配向膜32の上に積層された状態で用いられてもよい。あるいは、光学異方性層36は、例えば、支持体30を剥離した、配向膜32および光学異方性層36のみが積層された状態で用いられてもよい。または、光学異方性層36は、例えば、支持体30および配向膜32を剥離した、光学異方性層36のみの状態で用いられてもよい。
支持体30は、配向膜32、および、光学異方性層36を支持するものである。
支持体30は、配向膜32、光学異方性層36を支持できるものであれば、各種のシート状物(フィルム、板状物)が利用可能である。
なお、支持体30は、回折する光に対する透過率が50%以上であるのが好ましく、70%以上であるのがより好ましく、85%以上であるのがさらに好ましい。
支持体30の厚さは、1~1000μmが好ましく、3~250μmがより好ましく、5~150μmがさらに好ましい。
単層である場合の支持体30としては、ガラス、トリアセチルセルロース(TAC)、ポリエチレンテレフタレート(PET)、ポリカーボネート、ポリ塩化ビニル、アクリル、および、ポリオレフィン等からなる支持体30が例示される。多層である場合の支持体30の例としては、前述の単層の支持体のいずれかなどを基板として含み、この基板の表面に他の層を設けたもの等が例示される。
支持体30の表面には配向膜32が形成される。
配向膜32は、光学異方性層36を形成する際に、液晶化合物40を所定の液晶配向パターンに配向するための配向膜である。
前述のとおり、本発明において、光学異方性層36は、液晶化合物40に由来する光学軸40A(図3参照)の向きが、面内の一方向に沿って連続的に回転しながら変化している液晶配向パターンを有する。従って、配向膜32は、光学異方性層36が、この液晶配向パターンを形成できるように、形成される。
以下の説明では、『光学軸40Aの向きが回転』を単に『光学軸40Aが回転』とも言う。
例えば、ポリマーなどの有機化合物からなるラビング処理膜、無機化合物の斜方蒸着膜、マイクログルーブを有する膜、ならびに、ω-トリコサン酸、ジオクタデシルメチルアンモニウムクロライドおよびステアリル酸メチルなどの有機化合物のラングミュア・ブロジェット法によるLB(Langmuir-Blodgett:ラングミュア・ブロジェット)膜を累積させた膜、等が例示される。
配向膜32に使用する材料としては、ポリイミド、ポリビニルアルコール、特開平9-152509号公報に記載された重合性基を有するポリマー、特開2005-97377号公報、特開2005-99228号公報、および、特開2005-128503号公報記載の配向膜32等の形成に用いられる材料が好ましい。
偏光の照射は、光配向膜に対して、垂直方向または斜め方向から行うことができ、非偏光の照射は、光配向膜に対して、斜め方向から行うことができる。
中でも、アゾ化合物、光架橋性ポリイミド、光架橋性ポリアミド、光架橋性ポリエステル、シンナメート化合物、および、カルコン化合物は、好適に利用される。
配向膜32の厚さは、0.01~5μmが好ましく、0.05~2μmがより好ましい。
図4に示す露光装置60は、レーザ62を備えた光源64と、レーザ62が出射したレーザ光Mの偏光方向を変えるλ/2板65と、レーザ62が出射したレーザ光Mを光線MAおよびMBの2つに分離するビームスプリッター68と、分離された2つの光線MAおよびMBの光路上にそれぞれ配置されたミラー70Aおよび70Bと、λ/4板72Aおよび72Bと、を備える。
なお、光源64は直線偏光P0を出射する。λ/4板72Aは、直線偏光P0(光線MA)を右円偏光PRに、λ/4板72Bは直線偏光P0(光線MB)を左円偏光PLに、それぞれ変換する。
この際の干渉により、配向膜32に照射される光の偏光状態が干渉縞状に周期的に変化するものとなる。これにより、配向状態が周期的に変化する配向パターンを有する配向膜(以下、パターン配向膜ともいう)が得られる。
露光装置60においては、2つの光線MAおよびMBの交差角αを変化させることにより、配向パターンの周期を調節できる。すなわち、露光装置60においては、交差角αを調節することにより、液晶化合物40に由来する光学軸40Aが一方向に沿って連続的に回転する配向パターンにおいて、光学軸40Aが回転する1方向における、光学軸40Aが180°回転する1周期の長さを調節できる。
このような配向状態が周期的に変化した配向パターンを有する配向膜32上に、光学異方性層を形成することにより、後述するように、液晶化合物40に由来する光学軸40Aが一方向に沿って連続的に回転する液晶配向パターンを有する、光学異方性層36を形成できる。
また、λ/4板72Aおよび72Bの光学軸を、それぞれ、90°回転することにより、光学軸40Aの回転方向を逆にすることができる。
例えば、支持体30をラビング処理する方法、支持体30をレーザ光などで加工する方法等によって、支持体30に配向パターンを形成することにより、光学異方性層が、液晶化合物40に由来する光学軸40Aの向きが面内の少なくとも一方向に沿って連続的に回転しながら変化している液晶配向パターンを有する構成とすることも、可能である。すなわち、本発明においては、支持体30を配向膜として作用させてもよい。
光学異方性層36は、配向膜32の表面に形成される。
上述したように、光学異方性層36は、液晶化合物を配向した液晶相を固定してなる、光学異方性層であり、液晶化合物由来の光学軸の向きが面内の少なくとも一方向に沿って連続的に回転しながら変化している液晶配向パターンを有する光学異方性層である。
光学異方性層は、液晶化合物由来の光学軸の向きが面内の少なくとも一方向に沿って連続的に回転しながら変化している液晶配向パターンを有し、液晶化合物(光学軸)が厚み方向に旋回して積み重ねられた捩じれ構造に配向した液晶相を層状に固定して形成できる。
液晶相を固定した構造は、液晶相となっている液晶化合物の配向が保持されている構造であればよく、典型的には、重合性液晶化合物を液晶配向パターンに沿った配向状態としたうえで、紫外線照射、加熱等によって重合、硬化し、流動性が無い層を形成して、同時に、外場または外力によって配向形態に変化を生じさせることない状態に変化した構造が好ましい。
なお、液晶相を固定した構造においては、液晶相の光学的性質が保持されていれば十分であり、光学異方性層において、液晶化合物40は液晶性を示さなくてもよい。例えば、重合性液晶化合物は、硬化反応により高分子量化して、液晶性を失っていてもよい。
また、光学異方性層を、厚み方向において液晶化合物が捩じれ配向している構成とするために、液晶組成物にキラル剤を含有させればよい。
また、光学異方性層の形成に用いる液晶組成物は、さらに界面活性剤、重合開始剤等を含んでいてもよい。
重合性液晶化合物は、棒状液晶化合物であっても、円盤状液晶化合物であってもよい。
光学異方性層を形成する棒状の重合性液晶化合物の例としては、棒状ネマチック液晶化合物が挙げられる。棒状ネマチック液晶化合物としては、アゾメチン類、アゾキシ類、シアノビフェニル類、シアノフェニルエステル類、安息香酸エステル類、シクロヘキサンカルボン酸フェニルエステル類、シアノフェニルシクロヘキサン類、シアノ置換フェニルピリミジン類、アルコキシ置換フェニルピリミジン類、フェニルジオキサン類、トラン類、および、アルケニルシクロヘキシルベンゾニトリル類等が好ましく用いられる。低分子液晶化合物だけではなく、高分子液晶化合物も用いることができる。
重合性液晶化合物の例は、Makromol.Chem.,190巻、2255頁(1989年)、Advanced Materials 5巻、107頁(1993年)、米国特許第4683327号明細書、米国特許第5622648号明細書、米国特許第5770107号明細書、国際公開第95/22586号、国際公開第95/24455号、国際公開第97/00600号、国際公開第98/23580号、国際公開第98/52905号、特開平1-272551号公報、特開平6-016616号公報、特開平7-110469号公報、特開平11-080081号公報、および、特開2001-328973号公報等に記載の化合物が含まれる。2種類以上の重合性液晶化合物を併用してもよい。2種類以上の重合性液晶化合物を併用すると、配向温度を低下させることができる。
円盤状液晶化合物としては、例えば、特開2007-108732号公報や特開2010-244038号公報に記載のものを好ましく用いることができる。
キラル剤(カイラル剤)は液晶相の捩じれ構造を誘起する機能を有する。キラル剤は、化合物によって誘起する螺旋の捩れ方向および螺旋誘起力(Helical twisting power:HTP)が異なるため、目的に応じて選択すればよい。
キラル剤としては、特に制限はなく、公知の化合物(例えば、液晶デバイスハンドブック、第3章4-3項、TN(twisted nematic)、STN(Super Twisted Nematic)用キラル剤、199頁、日本学術振興会第142委員会編、1989に記載)、イソソルビド、および、イソマンニド誘導体等を用いることができる。
キラル剤は、一般に不斉炭素原子を含むが、不斉炭素原子を含まない軸性不斉化合物または面性不斉化合物もキラル剤として用いることができる。軸性不斉化合物または面性不斉化合物の例には、ビナフチル、ヘリセン、パラシクロファン、および、これらの誘導体が含まれる。キラル剤は、重合性基を有していてもよい。キラル剤と液晶化合物とがいずれも重合性基を有する場合は、重合性キラル剤と重合性液晶化合物との重合反応により、重合性液晶化合物から誘導される繰り返し単位と、キラル剤から誘導される繰り返し単位とを有するポリマーを形成することができる。この態様では、重合性キラル剤が有する重合性基は、重合性液晶化合物が有する重合性基と、同種の基であるのが好ましい。従って、キラル剤の重合性基も、不飽和重合性基、エポキシ基またはアジリジニル基であるのが好ましく、不飽和重合性基であるのがより好ましく、エチレン性不飽和重合性基であるのがさらに好ましい。
また、キラル剤は、液晶化合物であってもよい。
光学異方性層を形成する際に用いる液晶組成物は、界面活性剤を含有してもよい。
界面活性剤は、安定的に、または迅速に、液晶化合物の配向に寄与する配向制御剤として機能できる化合物が好ましい。界面活性剤としては、例えば、シリコ-ン系界面活性剤およびフッ素系界面活性剤が挙げられ、フッ素系界面活性剤が好ましく例示される。
なお、界面活性剤は、1種を単独で用いてもよいし、2種以上を併用してもよい。
フッ素系界面活性剤として、特開2014-119605号公報の段落[0082]~[0090]に記載の化合物が好ましい。
液晶組成物が重合性化合物を含む場合は、重合開始剤を含有しているのが好ましい。紫外線照射により重合反応を進行させる態様では、使用する重合開始剤は、紫外線照射によって重合反応を開始可能な光重合開始剤であるのが好ましい。
光重合開始剤の例には、α-カルボニル化合物(米国特許第2367661号、米国特許第2367670号の各明細書記載)、アシロインエーテル(米国特許第2448828号明細書記載)、α-炭化水素置換芳香族アシロイン化合物(米国特許第2722512号明細書記載)、多核キノン化合物(米国特許第3046127号、米国特許第2951758号の各明細書記載)、トリアリールイミダゾールダイマーとp-アミノフェニルケトンとの組み合わせ(米国特許第3549367号明細書記載)、アクリジンおよびフェナジン化合物(特開昭60-105667号公報、米国特許第4239850号明細書記載)、ならびに、オキサジアゾール化合物(米国特許第4212970号明細書記載)等が挙げられる。
液晶組成物中の光重合開始剤の含有量は、液晶化合物の含有量に対して0.1~20質量%であるのが好ましく、0.5~12質量%であるのがさらに好ましい。
液晶組成物は、硬化後の膜強度向上、耐久性向上のため、任意に架橋剤を含有していてもよい。架橋剤としては、紫外線、熱、および、湿気等で硬化するものが好適に使用できる。
架橋剤としては、特に制限はなく、目的に応じて適宜選択することができ、例えばトリメチロールプロパントリ(メタ)アクリレートおよびペンタエリスリトールトリ(メタ)アクリレート等の多官能アクリレート化合物;グリシジル(メタ)アクリレートおよびエチレングリコールジグリシジルエーテル等のエポキシ化合物;2,2-ビスヒドロキシメチルブタノール-トリス[3-(1-アジリジニル)プロピオネート]および4,4-ビス(エチレンイミノカルボニルアミノ)ジフェニルメタン等のアジリジン化合物;ヘキサメチレンジイソシアネートおよびビウレット型イソシアネート等のイソシアネート化合物;オキサゾリン基を側鎖に有するポリオキサゾリン化合物;ならびに、ビニルトリメトキシシラン、N-(2-アミノエチル)3-アミノプロピルトリメトキシシラン等のアルコキシシラン化合物などが挙げられる。また、架橋剤の反応性に応じて公知の触媒を用いることができ、膜強度および耐久性向上に加えて生産性を向上させることができる。これらは、1種単独で使用してもよいし、2種以上を併用してもよい。
架橋剤の含有量は、液晶組成物の固形分質量に対して、3~20質量%が好ましく、5~15質量%がより好ましい。架橋剤の含有量が上記範囲内であれば、架橋密度向上の効果が得られやすく、液晶相の安定性がより向上する。
液晶組成物中には、必要に応じて、さらに重合禁止剤、酸化防止剤、紫外線吸収剤、光安定化剤、色材、および、金属酸化物微粒子等を、光学的性能等を低下させない範囲で添加することができる。
液晶組成物は溶媒を含んでいてもよい。溶媒には、制限はなく、目的に応じて適宜選択することができるが、有機溶媒が好ましい。
有機溶媒には、制限はなく、目的に応じて適宜選択することができ、例えば、ケトン類、アルキルハライド類、アミド類、スルホキシド類、ヘテロ環化合物、炭化水素類、エステル類、および、エーテル類などが挙げられる。これらは、1種単独で使用してもよいし、2種以上を併用してもよい。これらの中でも、環境への負荷を考慮した場合にはケトン類が好ましい。
すなわち、配向膜32上に光学異方性層を形成する場合には、配向膜32に液晶組成物を塗布して、液晶化合物を所定の液晶配向パターンに配向した後、液晶化合物を硬化して、液晶相を固定してなる光学異方性層を形成するのが好ましい。
液晶組成物の塗布は、インクジェットおよびスクロール印刷等の印刷法、ならびに、スピンコート、バーコートおよびスプレー塗布等のシート状物に液体を一様に塗布できる公知の方法が全て利用可能である。
前述のように、光学異方性層において、光学異方性層は、液晶化合物40に由来する光学軸40Aの向きが、光学異方性層の面内において、一方向に連続的に回転しながら変化する液晶配向パターンを有する。
なお、液晶化合物40に由来する光学軸40Aとは、液晶化合物40において屈折率が最も高くなる軸、いわゆる遅相軸である。例えば、液晶化合物40が棒状液晶化合物である場合には、光学軸40Aは、棒形状の長軸方向に沿っている。以下の説明では、液晶化合物40に由来する光学軸40Aを、『液晶化合物40の光学軸40A』または『光学軸40A』ともいう。
なお、平面図とは、図2において光学異方性層36を上方から見た図であり、すなわち、光学異方性層36を厚み方向(=各層(膜)の積層方向)から見た図である。
また、図3では、光学異方性層36の構成を明確に示すために、液晶化合物40は配向膜32の表面の液晶化合物40のみを示している。
光学異方性層36を構成する液晶化合物40は、配列軸D、および、この一方向(配列軸D方向)と直交する方向に、二次元的に配列された状態になっている。
以下の説明では、配列軸D方向と直交する方向を、便宜的にY方向とする。すなわち、矢印Y方向とは、液晶化合物40の光学軸40Aの向きが、光学異方性層の面内において、連続的に回転しながら変化する一方向と直交する方向である。従って、図1、図2および後述する図5、図6では、Y方向は、紙面に直交する方向となる。
なお、配列軸D方向に互いに隣接する液晶化合物40の光学軸40Aの角度の差は、45°以下であるのが好ましく、15°以下であるのがより好ましく、より小さい角度であるのがさらに好ましい。
言い換えれば、光学異方性層36を形成する液晶化合物40は、Y方向では、液晶化合物40の光学軸40Aと配列軸D方向とが成す角度が等しい。
この場合に、それぞれの領域Rにおける面内レタデーション(Re)の値は、半波長すなわちλ/2であるのが好ましい。これらの面内レタデーションは、領域Rの屈折率異方性に伴う屈折率差Δnと光学異方性層の厚さとの積により算出される。ここで、光学異方性層における領域Rの屈折率異方性に伴う屈折率差とは、領域Rの面内における遅相軸の方向の屈折率と、遅相軸の方向に直交する方向の屈折率との差により定義される屈折率差である。すなわち、領域Rの屈折率異方性に伴う屈折率差Δnは、光学軸40Aの方向の液晶化合物40の屈折率と、領域Rの面内において光学軸40Aに垂直な方向の液晶化合物40の屈折率との差に等しい。つまり、屈折率差Δnは、液晶化合物40の屈折率差に等しい。
すなわち、配列軸D方向に対する角度が等しい2つの液晶化合物40の、配列軸D方向の中心間の距離を、1周期の長さΛとする。具体的には、図3に示すように、配列軸D方向と光学軸40Aの方向とが一致する2つの液晶化合物40の、配列軸D方向の中心間の距離を、1周期の長さΛとする。以下の説明では、この1周期の長さΛを『1周期Λ』とも言う。
光学異方性層36の液晶配向パターンは、この1周期Λを、配列軸D方向すなわち光学軸40Aの向きが連続的に回転して変化する一方向に繰り返す。
この作用を、図5および図6に概念的に示す。なお、光学異方性層36は、液晶化合物の屈折率差と光学異方性層の厚さとの積の値がλ/2であるとする。また、図5および図6を用いた説明は、光学異方性層36の液晶配向パターンによる作用を説明するためのもので、厚み方向での光学軸の捩じれ構造を有さないものとして説明を行う。
また、光学異方性層36に形成された液晶配向パターンは、配列軸D方向に周期的なパターンであるため、透過光L2は、入射光L1の進行方向とは異なる方向に進行する。このように、左円偏光の入射光L1は、入射方向に対して配列軸D方向に一定の角度だけ傾いた、右円偏光の透過光L2に変換される。図5に示す例では、透過光L2は、右下方向に進行するように回折されている。
また、光学異方性層36に形成された液晶配向パターンは、配列軸D方向に周期的なパターンであるため、透過光L5は、入射光L4の進行方向とは異なる方向に進行する。このとき、透過光L5は透過光L2と異なる方向、つまり、入射方向に対して配列軸Dの矢印方向とは逆の方向に進行する。このように、入射光L4は、入射方向に対して配列軸D方向とは逆の方向に一定の角度だけ傾いた左円偏光の透過光L5に変換される。図6に示す例では、透過光L5は、左下方向に進行するように回折されている。
次に、このような液晶配向パターンを有する光学異方性層を4層積層した構成を有する本発明の透過型液晶回折素子の作用について、図7を用いて説明する。
同様に、第3光学異方性層36cと第4光学異方性層36dについて、液晶配向パターンの1周期が同じとは、第3光学異方性層36cの液晶配向パターンの1周期を基準にした場合、第4光学異方性層36dの液晶配向パターンの1周期は、0.8~1.2程度の大きさの差であれば、第4光学異方性層36dから出射される光の回折角への影響は少ない。
一例として、図7に示すように、右円偏光IRおよび左円偏光ILは、第1光学異方性層36aの主面に対して垂直に入射する。
なお、光学異方性層同士の間にCプレートを設けた場合でも、Cプレートは回折に影響は与えないため、透過型液晶回折素子としては、図7に示す例と同様の回折の作用を得ることができる。
図9に示す透過型液晶回折素子10cは、第1光学異方性層36e、第2光学異方性層36b、第3光学異方性層36f、および、第4光学異方性層36dをこの順に有する。なお、図9においては、図面を簡略化して透過型液晶回折素子10cの構成を明確に示すために、各光学異方性層は、表面の液晶化合物40のみを概念的に示している。しかしながら、各光学異方性層は、図1等に示す例と同様に、厚み方向において、液晶化合物40が積み重ねられた構造を有し、厚み方向に積み重ねられた液晶化合物40の光学軸が捩じれた構造を有する。
しかしながら、本発明は、これに制限はされず、光学異方性層において、液晶化合物40の光学軸40Aが一方向に沿って連続して回転するものであれば、各種の構成が利用可能である。
図14に、Λと、光学異方性層の中心からの位置(x)との関係を表すグラフを示す。
図15に示す透過型液晶回折素子10の第1光学異方性層36a側から平行光が入射する。入射した平行光は、組み合わせ1によって所定の角度、外側に向かって回折される。その際、組み合わせ1の液晶配向パターンの1周期は一定であるため、光学異方性層の面内のどの位置においても回折角度は一定である。
また、回折光は回折を生じさせる層の厚み方向の様々な場所で生じるため、回折を生じさせる層の厚み方向のどの場所でもRthがゼロに近いことが好ましく、回折を生じさせる層の厚み方向のそれぞれの場所でRthが相殺されることが好ましい。よって、交互に積層した棒状液晶層および円盤状液晶層は隣り合う層のRthが正負の関係であり、かつそれぞれの層のRthの絶対値が10~200nm程度であることが好ましい。
このような光学異方性層を有することで、透過型液晶回折素子の回折効率をより高くすることができる。
<透過型液晶回折素子の作製>
(配向膜の形成)
支持体としてガラス基板を用意した。支持体上に、下記の配向膜形成用塗布液をスピンコートで塗布した。この配向膜形成用塗布液の塗膜が形成された支持体を60℃のホットプレート上で60秒間乾燥し、配向膜P-2を形成した。
―――――――――――――――――――――――――――――――――
・下記光配向用素材 1.00質量部
・水 16.00質量部
・ブトキシエタノール 42.00質量部
・プロピレングリコールモノメチルエーテル 42.00質量部
―――――――――――――――――――――――――――――――――
得られた配向膜P-2に偏光紫外線を照射(50mJ/cm2、超高圧水銀ランプ使用)することで、配向膜P-2の露光を行った。
図4に示す露光装置を用いて配向膜を露光して、配向パターンを有する配向膜P-2を形成した。露光装置において、レーザとして波長(325nm)のレーザ光を出射するものを用いた。干渉光による露光量を300mJ/cm2とした。なお、2つのレーザー光の干渉により形成される配向パターンの1周期Λ(光学軸が180°回転する長さ)が、10μmになるように、2つの光の交差角(交差角α)を調節した。
光学異方性層を形成する液晶組成物として、下記の組成物B-1を調製した。
――――――――――――――――――――――――――――――――――
・棒状液晶化合物L-1 100.00質量部
・重合開始剤(BASF製、Irgacure(登録商標)907)
3.00質量部
・光増感剤(日本化薬製、KAYACURE DETX-S)
1.00質量部
・レベリング剤T-1 0.08質量部
・メチルエチルケトン 2000.00質量部
――――――――――――――――――――――――――――――――――
この光学異方性層1層を比較例1の透過型液晶回折素子とした。
比較例1と同じように光学異方性層を作製し、面内一方向に沿って連続的に回転しながら変化している液晶化合物由来の光学軸の回転方向が光学異方性層と逆回転になるよう、180度回転させて、これを比較例2の光学異方性層とした。
下記表1に比較例1および比較例2の構成を示す。なお、表1中、ライン数とは、1mmあたりの周期の数であり、1000(μm)を1周期(μm)で割った数である。また、傾き角とはSEM断面で観察される明暗線が主面の垂線となす角である。
(第1光学異方性層の形成)
比較例1の配向膜の形成において、配向パターンの1周期Λが1μmになるようする以外は比較例1と同様に、配向膜を形成した。
――――――――――――――――――――――――――――――――――
・棒状液晶化合物L-1 100.00質量部
・キラル剤Ch-A 0.24質量部
・重合開始剤(BASF製、Irgacure(登録商標)907)
3.00質量部
・光増感剤(日本化薬製、KAYACURE DETX-S)
1.00質量部
・レベリング剤T-1 0.08質量部
・メチルエチルケトン 2000.00質量部
――――――――――――――――――――――――――――――――――
配向膜は第1光学異方性層の場合と同じで、面内一方向に沿って連続的に回転しながら変化している液晶化合物由来の光学軸の回転方向が第1光学異方性層と逆回転になるよう、180度回転させた。
――――――――――――――――――――――――――――――――――
・棒状液晶化合物L-1 100.00質量部
・キラル剤Ch-B 0.41質量部
・重合開始剤(BASF製、Irgacure(登録商標)907)
3.00質量部
・光増感剤(日本化薬製、KAYACURE DETX-S)
1.00質量部
・レベリング剤T-1 0.08質量部
・メチルエチルケトン 2000.00質量部
――――――――――――――――――――――――――――――――――
第1光学異方性層の形成において、配向膜の配向パターンの1周期Λが1.111μmになるようした以外は、第1光学異方性層と同様にして、第3光学異方性層を形成した。
第2光学異方性層の形成において、配向膜の配向パターンの1周期Λが1.111μmになるようした以外は第2光学異方性層と同様にして、第4光学異方性層を形成した。
下記表2に実施例1の透過型液晶回折素子の構成を示す。
実施例1において、第3光学異方性層および第4光学異方性層の1周期を0.909μmとした以外は、実施例1と同様にして透過型液晶回折素子を作製した。
下記表3に実施例2の透過型液晶回折素子の構成を示す。
作製した透過型液晶回折素子に、透過型液晶回折素子の主面(実施例は第1光学異方性層側の主面)の法線方向から波長600nmの無偏光の直進光(1mm径)を入射し、1次の回折光の回折強度(回折効率)をパワーメーターで測定した。強度(回折効率)の基準は以下の通りである。
・A:強度(回折効率)が90%以上
・B:強度(回折効率)が80%以上
・C:強度(回折効率)が70%以上
・D:強度(回折効率)が60%以上
・E:強度(回折効率)が50%以上
・F:強度(回折効率)が50%未満
結果を下記の表4に示す。
配向膜の露光装置として図11に示すような露光装置を用いて、WO2019/189818に記載の露光方法で、放射状の配向パターンを形成した以外はそれぞれ比較例1、2と同様にして透過型液晶回折素子を作製した。大きさは直径40mmとした。この透過型液晶回折素子は集光レンズとして作用する。
下記表5に比較例1および比較例2の構成を示す。
配向膜の露光装置として図11に示すような露光装置を用いて、WO2019/189818に記載の露光方法で、放射状の配向パターンを形成した以外は実施例1と同様にして、第1光学異方性層~第4光学異方性層を形成し、透過型液晶回折素子を作製した。大きさは直径40mmとした。この透過型液晶回折素子は集光レンズとして作用する。
下記表6に実施例11の透過型液晶回折素子の構成を示す。
配向膜の露光装置として図11に示すような露光装置を用いて、WO2019/189818に記載の露光方法で、放射状の配向パターンで、光学異方性層のそれぞれの面内回転方向が実施例11のそれぞれとは逆になるようにして形成した以外は実施例2と同様にして、第1光学異方性層~第4光学異方性層を形成し、透過型液晶回折素子を作製した。大きさは直径40mmとした。この透過型液晶回折素子は集光レンズとして作用する。
下記表7に実施例12の透過型液晶回折素子の構成を示す。
作製した透過型液晶回折素子に、透過型液晶回折素子の主面(実施例は第1光学異方性層側の主面)の法線方向から波長600nmの無偏光の直進光(40mm径)を入射し、レンズによる集光(1次回折光)の回折強度(回折効率)をパワーメーターで測定した。強度(回折効率)の基準は以下の通りである。
・A:強度(回折効率)が90%以上
・B:強度(回折効率)が80%以上
・C:強度(回折効率)が70%以上
・D:強度(回折効率)が60%以上
・E:強度(回折効率)が50%以上
・F:強度(回折効率)が50%未満
結果を下記の表8に示す。
以上の結果から本発明の効果は明らかである。
30 支持体
32 配向膜
36 光学異方性層
36a、36e 第1光学異方性層
36b 第2光学異方性層
36c、36f 第3光学異方性層
36d 第4光学異方性層
38 Cプレート
40 液晶化合物(棒状液晶化合物)
40b 円盤状液晶化合物
40A 光学軸
60、80 露光装置
62、82 レーザ
64、84 光源
65 λ/2板
68 ビームスプリッター
70A,70B、90A、90B ミラー
72A,72B、96 λ/4板
86、94 偏光ビームスプリッター
92 レンズ
IR、IR1、IR2 右円偏光
IL、IL1、IL2 左円偏光
D、A1、A2、A3 配列軸
R 領域
Λ 1周期
MA,MB 光線
PO 直線偏光
PR 右円偏光
PL 左円偏光
M レーザ光
MP P偏光
MS S偏光
α 角度
L1,L2,L4,L5 光
Claims (7)
- 液晶化合物由来の光学軸の向きが面内の少なくとも一方に沿って連続的に回転しながら変化している液晶配向パターンを有する、第1光学異方性層~第4光学異方性層を有する液晶回折素子であって、
前記第1光学異方性層~前記第4光学異方性層において、前記液晶化合物由来の光学軸が厚み方向に沿って捩じれており、
前記第1光学異方性層の前記液晶配向パターンにおける光学軸の回転方向と、第2光学異方性層の前記液晶配向パターンにおける光学軸の回転方向とが逆であり、
第3光学異方性層の前記液晶配向パターンにおける光学軸の回転方向と、前記第4光学異方性層の前記液晶配向パターンにおける光学軸の回転方向とが逆であり、
前記第1光学異方性層の厚み方向での前記液晶化合物由来の光学軸の捩じれ方向と、前記第2光学異方性層の厚み方向での前記液晶化合物由来の光学軸の捩じれ方向とが逆であり、
前記第3光学異方性層の厚み方向での前記液晶化合物由来の光学軸の捩じれ方向と、前記第4光学異方性層の厚み方向での前記液晶化合物由来の光学軸の捩じれ方向とが逆であり、
前記液晶配向パターンにおける前記液晶化合物由来の光学軸の向きが面内で180°回転する長さを1周期とすると、前記第1光学異方性層の前記液晶配向パターンにおける1周期と、前記第2光学異方性層の前記液晶配向パターンにおける1周期とが同じであり、
前記第3光学異方性層の前記液晶配向パターンにおける1周期と、前記第4光学異方性層の前記液晶配向パターンにおける1周期とが同じであり、
前記第1光学異方性層の前記液晶配向パターンにおける1周期と、前記第3光学異方性層の前記液晶配向パターンにおける1周期とが異なる、透過型液晶回折素子。 - 前記第1光学異方性層~前記第4光学異方性層の厚み方向での前記液晶化合物由来の光学軸の捩じれ角が360°未満である、請求項1に記載の透過型液晶回折素子。
- 前記第1光学異方性層~前記第4光学異方性層は、前記液晶配向パターンを放射状に有する、請求項1または2に記載の透過型液晶回折素子。
- 前記第1光学異方性層と前記第2光学異方性層との組み合わせ、および、前記第3光学異方性層と前記第4光学異方性層との組み合わせのうち、少なくとも一方の組み合わせにおいて、前記液晶配向パターンの1周期が一方向に沿って漸次変化している、請求項1~3のいずれか一項に記載の透過型液晶回折素子。
- 放射状の前記液晶配向パターンの中央部から外側部に向かって、前記第1光学異方性層の前記液晶配向パターンの1周期の逆数と、前記第3光学異方性層の前記液晶配向パターンの1周期の逆数との差分が漸次大きくなる、請求項3または4に記載の透過型液晶回折素子。
- 前記第1光学異方性層~前記第4光学異方性層のいずれかの間にCプレートをさらに有する、請求項1~5のいずれか一項に記載の透過型液晶回折素子。
- 前記第1光学異方性層と前記第2光学異方性層との組み合わせ、および、前記第3光学異方性層と前記第4光学異方性層との組み合わせのうち、少なくとも一方の組み合わせにおいて、一方の光学異方性層の前記液晶化合物が棒状液晶化合物で、他方の光学異方性層の前記液晶化合物が円盤状液晶化合物である、請求項1~6のいずれか一項に記載の透過型液晶回折素子。
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